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Captured by the remarkable environmental/economic value, recycling spent LiFePO4 has attracted numerous attention. However, restricted by diverse failure mechanisms and different particle‐sizes/active‐sites, recycling strategies still suffer from uneven repairing results and poor accessibility. For promoting their application in commercial systems, the uniform physical‐chemical properties are urgent for regenerated samples. Herein, by tailoring oxidation‐reduction manners, the homogeneous cathode materials can be prepared, displaying uniform particle size and restored lattice. The capacity of as‐optimized samples can be kept ≈141.5 mAh g−1 at 1.0 C, and 137 mAh g−1 with a retention of 92% after 300 cycles at 2.0 C. After Kg‐scale experiments, the pouch full‐cell (LFP‐500 vs recovered graphite) delivers ≈4200 mAh capacity, with considerable cycling stability (retention 96.83%, after 500 loops). Importantly, the detailed mechanism of oxidation/reduction‐conditions is investigated, especially their lattice reconstitution and ions‐ diffusion behaviors. Supported by kinetic analysis and DFT calculations, the fascinating stability of LFP‐500 is further proved, mainly derived from the accelerated Li‐diffusion behaviors. Compared to traditional recovering manners, oxidation/reduction process displays low cost, energy‐consumption, and pollution, accompanied with considerable large‐scale application potential. Given this, this work is anticipated to illustrate the in‐depth mechanism of lattice‐reconstruction, while offering significant strategies for large‐scale and homogenized regeneration. [ABSTRACT FROM AUTHOR]

Further commercialization of Ni‐rich layered cathodes is hindered by severe structure/interface degradation and kinetic hindrance that occur during electrochemical operation, which leads to safety risks and reduced range in electric vehicles (EVs). Herein, by selecting elements with different solubility properties, a multifunctional strategy that synchronously fabricates perovskite‐type SrZrO3 coating and Sr/Zr co‐doping is employed to strengthen the structure/interface stability and the Li+ transport mobility of LiNi0.85Co0.10Mn0.05O2 (NCM). Perovskite‐type SrZrO3 protective layers formed on the particle surface can substantially mitigate the unexpected interfacial side reactions and surface phase transitions. In addition, a robust crystal framework is constructed by optimizing local O coordination through the introduction of strong Zr−O bonds. Notably, Li+ diffusion kinetics is effectively improved due to expanded cell parameters and O‐Li‐O slab spacing with the incorporation of large‐diameter Sr pillar ions, as revealed by X‐ray diffraction. As a result, the Sr/Zr‐modified NCM achieves a remarkable capacity retention of 99.4% after 200 cycles at 1 C, and a high rate capacity of 168.9 mAh g−1 at 10 C. This work opens new avenues to develop high‐performance NCM cathodes with high energy and high power for EVs with long calendar life. [ABSTRACT FROM AUTHOR]

Sodium layered oxides feature in high capacity and diverse composition, however, are plagued by various issues including limited kinetics and interfacial instability with residual alkali. Conventional substitution/doping and heterogeneous coating are promising to tackle the problems of bulk and surface, respectively, but normally insufficient to address both. Herein, a post‐substitution strategy is proposed to modify primary sodium‐layered‐oxide particles that can simultaneously deal with bulk and surficial issues. As a typical example, post Ti‐substitution for O3‐NaNi1/3Fe1/3Mn1/3O2 is successfully performed by adjusting thermodynamic driving force, resulting in depth‐controllable Ti infusion from surface to bulk, as proved by energy dispersive spectroscopy maps collected at the cross‐section. Residual alkali species are efficiently diminished and benefited from the surface‐to‐bulk osmotic reaction, significantly improving Coulombic efficiency. Moreover, remarkable enhancements in reversible capacity (135 mAh g−1 at C/10), rate capability (74% retention at 5 C), and long‐term cycling stability (80% retention after 300 cycles at 2 C) are achieved by manipulating gradient‐like Ti distribution in a primary particle that brings with increased kinetics and strengthened interfacial stability, surpassing those given by rough heterotic coating and homogeneous Ti‐substitution. Such post‐substitution is expected to provide a universal strategy to modify primary layered‐oxide particles for developing advanced cathode materials of SIBs. [ABSTRACT FROM AUTHOR]

Hybrid supercapacitors (HSCs) comprising a battery‐type cathode and capacitive anode have recently become a research hotspot. Nevertheless, the low capacity utilization, poor kinetic behavior, and unstable structure of a single battery‐type oxide cathode restrict the overall performance of the device. Herein, the carbon quantum dots (CQDs) modified NiO/Co3O4 heterostructured flower‐like microspheres are constructed, and enhanced specific capacity, rate capability, and cycling performance are achieved when used as the cathode for HSCs. This is attributed to the fact that the modification of bifunctional CQDs as size regulators and conductive agents and the construction of heterostructure can not only improve the specific surface area and provide more electroactive sites, thereby enhancing the charge storage performance but also regulate the electronic structure and boost the interface charge transfer capability and electronic conductivity, thereby boosting the reaction kinetics and cycle stability. The enhanced electrochemical kinetic behavior is revealed by electrochemical kinetic analyses based on cyclic voltammetry, electrochemical impedance spectroscopy tests and density functional theory calculations. Meanwhile, the electrochemical reaction process and energy storage mechanism are illustrated by ex‐situ X‐ray diffraction and X‐ray photoelectron spectroscopy characterizations. Furthermore, an HSC is further constructed using the CQDs/NiO/Co3O4 heterostructured flower‐like microspheres as the cathode, simultaneously achieving high energy density (40.9 Wh kg−1), high power density (24 kW kg−1), and splendid cyclic stability (94.2% capacity retention after 5000 cycles at 10 A g−1). These synergistic modification strategies of bifunctional CQDs modification and heterostructure design provide a valuable direction for the design and development of HSCs with both high energy density and high power density. [ABSTRACT FROM AUTHOR]

Highlights: The robust organic/inorganic hybrid interlayer derived from in situ formed tribofilms were fabricated by using a scalable rolling method. The interlayer facilitates dendrite-free lithium metal anodes by building local de-solvation environments near the interface and inhibiting both dendrite growth and electrolytes corrosion. The symmetrical cell exhibits a remarkable lifespan of 5,600 h (1.0 mA cm-2 and 1.0 mAh cm-2) and 1,350 cycles even at a harsh condition (18.0 mA cm-2 and 3.0 mAh cm-2). The practical application of Li metal anodes (LMAs) is limited by uncontrolled dendrite growth and side reactions. Herein, we propose a new friction-induced strategy to produce high-performance thin Li anode (Li@CFO). By virtue of the in situ friction reaction between fluoropolymer grease and Li strips during rolling, a robust organic/inorganic hybrid interlayer (lithiophilic LiF/LiC6 framework hybridized -CF2-O-CF2- chains) was formed atop Li metal. The derived interface contributes to reversible Li plating/stripping behaviors by mitigating side reactions and decreasing the solvation degree at the interface. The Li@CFO||Li@CFO symmetrical cell exhibits a remarkable lifespan for 5,600 h (1.0 mA cm−2 and 1.0 mAh cm−2) and 1,350 cycles even at a harsh condition (18.0 mA cm−2 and 3.0 mAh cm−2). When paired with high-loading LiFePO4 cathodes, the full cell lasts over 450 cycles at 1C with a high-capacity retention of 99.9%. This work provides a new friction-induced strategy for producing high-performance thin LMAs. [ABSTRACT FROM AUTHOR]

Although lithium-sulfur (Li-S) batteries with high specific energy exhibit great potential for next-generation energy-storage systems, their practical applications are limited by the growth of Li dendrites and lithium polysulfides (LiPSs) shuttling. Herein, a highly porous red phosphorus sponge (HPPS) with well distributed pore structure was efficiently prepared via a facile and large-scale hydrothermal process for polysulfides adsorption and dendrite suppression. As experimental demonstrated, the porous red phosphorus modified separator with increased active site greatly promotes the chemisorption of LiPSs to efficiently immobilize the active sulfur within the cathode section, while Li metal anode activated by Li3P interlayer with abundant ionically conductive channels significantly eliminates the barrier for uniform Li+ permeation across the interlayer, contributing to the enhanced stability for both S cathode and Li anode. Mediated by the HPPS, long-term stability of 1,200 h with minor voltage hysteresis is achieved in symmetric cells with Li3P@Li electrode while Li-S half-cell based on HPPS modified separator delivers an outperformed reversibility of 783.0 mAh·g−1 after 300 cycles as well as high-rate performance of 694.5 mAh·g−1 at 3 C, which further boosts the HPPS tuned full cells in practical S loading (3 mg·cm−2) and thin Li3P@Li electrode (100 µm) with a capacity retention of 71.8% after 200 cycles at 0.5 C. This work provides a cost-effective and metal free mediator for simultaneously alleviating the fundamental issues of both S cathode and Li anode towards high energy density and long cycle life Li-S full batteries. [ABSTRACT FROM AUTHOR]

Fe‐Mn based layered oxides are recognized as promising cathode materials for sodium‐ion batteries (SIBs) with high capacities and earth‐abundant ingredients. However, their real‐world applications are still constrained by fast capacity decay accompanied with the requirements of deeper insights into the principles behind. Herein, taking O3‐NaxFe1/2Mn1/2O2 as a classic sample, the capacity fading mechanism of Fe‐Mn based layered oxides is comprehensively investigated through combined techniques. For the first time, it is revealed that Fe migration is merely triggered after the oxidation of ≈0.3 mol Fe3+ based on solid proofs from ex situ X‐ray absorption spectroscopy and Mössbauer spectroscopy, which implies the crucial role of the accumulated structural distortion induced by Jahn–Teller active Fe4+. O3‐P3 phase transition during cycling is obviously constrained along with Fe migration as evidenced by in situ/ex situ X‐ray diffraction, well interpreting the intensified polarization and the resulting large capacity loss. More importantly, within the desodiation depth (≈80% of sodium extraction) where Fe migration is almost absent, the capacity fading is dominantly rooted in the Fe4+ activated and Mn‐dissolution aggravated surface passivation as confirmed by mass/X‐ray spectroscopies and electrochemical analysis. These renewed understandings of the fast capacity decay in Fe‐Mn based layered oxides offer clearer clues for designing desirable cathodes for SIBs. [ABSTRACT FROM AUTHOR]

The extensive applications of spinel LiMn2O4 (LMO) are severely plagued by grievous capacity degradation and structural collapse, mainly ascribed to deleterious Jahn−Teller distortion and subsequent dissolution of Mn2+. Herein, highly stable LMO with atomic interlocking effect is rationally designed via engineering Al into the unoccupied 16c sites. The local coordination environment of the surficial MnO6 octahedron is reconstructed by robust Al−O band coherency, giving strengthened lattice oxygen skeleton and constraining heterophase evolution with the suppression of Jahn−Teller distortion, validated by theoretical calculations coupled with synchrotron X‐ray absorption spectrum. Concomitantly, with the occupation of Al in interstitial site, the migration of Mn is effectively restrained, directly observed by scanning transmission electron microscopy, leading to the inhibition of inactivation as well as dissolution loss of Mn. Resultantly, splendid long cycling stability of Al‐LMO after 1000 loops with only 0.019% capacity fading per cycle is presented. Given this, this elaborate study can provide an ingenious avenue for regulating the structure/interface chemistry architecture in electrode materials. [ABSTRACT FROM AUTHOR]

With the large-scale application of lithium-ion batteries, the recycling of retired LIBs has been a crucial problem to address. Among the spent LIBs, LiFePO4 (LFP) recycling is urgently needed as it is one of the most extensively utilized cathodes in the sustainable development of LIBs. However, traditional pyro-/hydro-metallurgical recycling methods are normally complicated and uneconomical. Here, we exhibit an efficient and green method with a simple route to regenerate a degraded LiFePO4 cathode, through which the cathode sheets are directly broken down into aluminum foil, high-purity FePO4 and lithium-containing solution by the introduction of hydrogen peroxide as a leaching reagent. The leaching efficiency of Li exceeds 96.3% with scarce Al and Fe, and the regenerated LiFePO4 from recovered FePO4 displays excellent rate capability and long-term cycling stability. This research greatly reduces the processing steps and chemical consumption, which is conducive to the sustainable industrial development of spent lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The ever‐increasing energy density requirements in electric vehicles (EVs) have boosted the development of Ni‐rich layered oxide cathodes for state‐of‐the‐art lithium‐ion batteries. Nevertheless, the commercialization of polycrystalline Ni‐rich cathodes (PCNCs) is hindered by the severe performance degradation and safety concerns that are tightly related to its particle cracking during cycling. Single‐crystalline Ni‐rich cathodes (SCNCs) with eliminated grain boundaries and high mechanical strength have recently attracted extensive attention owing to their superior structural and cycling stability, which present high crack resistance during electrochemical operation. Various articles have focused on the trial‐and‐error synthesis and modifications of SCNCs, as well as the comparison of performances and mechanisms with PCNCs. However, there has been much less effort in systematic analysis and summary to reveal their key challenges, controversies, and the corresponding primary causes. In this review, the advantages and debates in structural and electrochemical properties of SCNCs over PCNCs are summarized to provide fundamental understanding of SCNCs. Then the current practical issues and challenges are comprehensively discussed from the viewpoints of both academia and industry, as well as the proposed modification strategies and underlying mechanisms for SCNCs. The outlook and perspectives are further given to facilitate the commercial applications of SCNCs in high‐performance EVs. [ABSTRACT FROM AUTHOR]

Capacity fading and safety concerns accompanied other deep‐rooted challenges have severely hindered commercial development of Ni‐rich layered cathodes. Herein, a robust Sr‐doped Ni‐rich cathode is structurally designed by the reconstruction of the crystal lattice and electronic distribution. Notably, the orbital hybridization between Ni 3d (t2g) and O 2p is remarkably reinforced owing to the shortened NiO bond enabled by the electrostatic interaction between Ni and Sr atoms, giving rise to the enhanced crystal structure. Theoretically, the formation energy of oxygen vacancies is greatly increased due to the intensified electronic polarization between Ni and O states evoked by the weak electronegativity of Sr, resulting in the alleviation of lattice oxygen loss. More impressively, the distances of LiO bonds and the OLiO slab are also extended on account of the electrochemically inactive Sr ion functioning as a pillar, further promoting the transmission of lithium ions. Therefore, the as‐designed Sr‐modified NCM delivers an ultrahigh capacity retention of 98.5% after 150 cycles. This work provides a powerful mechanistic incentive to increase the stability of the crystal phase and electrochemical performance for Ni‐rich layered cathodes through appropriate chemical and mechanical engineering, facilitating the practical applications of Ni‐rich cathodes in high‐performance electric vehicles. [ABSTRACT FROM AUTHOR]

As a high-capacity cathode material with a considerable cycle life, lithium metal orthosilicates have attracted much attention. In this paper, Li2FeSiO4, Li2FeSiO4−xClx and Li2FeSiO4−xFx are successfully synthesized via solid-state method. Li2FeSiO4−xFx is also composited with reduced graphene oxide (rGO). The X-ray diffraction patterns show 0.2% expansion in the lattice volume of Li2FeSiO4−xFx and 0.7% shrinkage for Li2FeSiO4−xClx due to the doping effect. Fourier-transform infrared spectroscopy also indicates a frequency shift for [SiO4]4− and [LiO4] functional groups due to ion doping. The SEM images confirm that rGO surrounded Li2FeSiO4−xFx microparticles. The electrochemical performance illustrates a reversible ox/red reaction of Fe2+/Fe3+ couple at the potential of 3/2.6 V for Li2FeSiO4, 3.5/2.9 V for Li2FeSiO4−xFx, and 3.3/2.3 V for Li2FeSiO4−xClx. Lithiation curves at 0.05C rate show the first specific capacity of 168 mAh g−1 for Li2FeSiO4 with 84% retention after 25th cycles, 190 mAh g−1 for Li2FeSiO4−xFx with 100% retention, and 120 mAh g−1 for Li2FeSiO4−xClx with 73% retention. Li2FeSiO4−xFx/rGO cathode delivers 265 mAh g−1 with 88% retention after 25th cycles. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) have grasped renewed attentions in recent years owing to the blooming growth of clean energy and corresponding demands of grid‐scale energy storage. Note that, the properties of cathode materials are quite important to the development of SIBs as they largely determine the energy density, cycle life, and cost of a battery. Direct inheriting those Co/Ni based layered cathodes that are successfully utilized in lithium‐ion batteries seems to be impracticable for SIBs in view of the high materials costs. Fortunately, the discovery of the electrochemical activity of Fe3+/Fe4+ redox couple in sodium layered materials has opened a new way to design high capacity/voltage and low‐cost cathodes for SIBs. To date, various Fe‐based layered oxides have been explored, showing encouraging electrochemical performances in SIBs. However, issues and challenges still remain upon the practical utilization of Fe‐based layered cathodes, calling for further targeted and in‐depth investigations. In this review, the developing history, key problems, and current progress of Fe‐based layered cathodes on electrochemical performances and working mechanism are summarized and discussed. In addition, possible research trends and perspectives are proposed. It is believed that Fe‐based layered oxides will be one of the most attractive cathodes for SIBs. [ABSTRACT FROM AUTHOR]

In the past 10 years, preeminent achievements and outstanding progress have been achieved on sodium‐ion capacitors (SICs). Early work on SICs focussed more on the electrochemical performance. While it is easy to confirm which specific electrodes exhibit excellent properties, it is difficult to understand the mechanisms which are most promising for the next generation of SICs. From the early research in supercapacitors iterations to the present well‐developed Na‐ion batteries, the evolution of the controversial pseudocapacitive mechanism for SICs has been full of breakthroughs and back tracing steps. Moreover, as the research has progressed and the interests have changed, different emphases on the different subdisciplines (cell configurations, flexible devices, and presodiation technologies) have increased. In this review, first, the electric double layer mechanism, battery‐type mechanism, and the controversial pseudocapacitance mechanism are systematically analyzed and compared. Subsequently, mechanism‐oriented SICs cell configurations with different cathode and anode mechanisms are discussed. Moreover, the characteristics and features of electrode materials in different SICs cell configurations are summarized. Finally, key technologies and possible future developments are discussed. This review summarizes SICs from a broad and macro perspective from mechanisms to cell configurations, from cathodes to anodes, and from history to future, and offers a deep understanding of SICs devices. [ABSTRACT FROM AUTHOR]

The practical application of Li‐rich Mn‐based oxide cathode is predominately retarded by the capacity decline and voltage fading, associated with the structure distortion and anionic redox reactions. Here, a linkage‐functionalized modification approach to tackle these challenges via a synchronous lithium oxidation strategy is reported. The doping of Ce in the bulk phase activates the pseudo‐bonding effect, effectively stabilizing the lattice oxygen evolution and suppressing the structure distortion. Interestingly, it also induces the formation of spinel phase Li4Mn5O12 in the subsurface, which in turn constructs the phase boundaries, thereby arousing the interior self‐built‐in electric field to prevent the outward migration of bulk oxygen anions and boost the charge transfer. Moreover, the formed coating layer Li2CeO3 with oxygen vacancies accelerates Li+ diffusion and mitigates electrolyte cauterization. The corresponding cathode exhibits superior long‐cycle stability after 300 cycles with only a 0.013% capacity drop and 1.76 mV voltage decay per cycle. This work sheds new light on the development of Li‐rich Mn‐based oxide cathodes toward high energy density applications. [ABSTRACT FROM AUTHOR]

High‐working potential layered oxides as cathode materials have been considered as an effective way to improve the energy density of Na‐ion batteries (NIBs) to enhance their competitiveness as a promising alternative for lithium ion batteries in large‐scale energy storage applications. However, they generally suffer irreversible phase transition, large volume change and electrolyte corrosion when charged to high voltage (>4.2 V), resulting in poor cyclic stability. In this work, a P2@tunnel heterostructure cathode material is designed and obtained by wet chemistry combined with solid‐state reaction method. Moreover, partly of the Ti4+ ions which are designed for the tunnel structure is also doped into the P2 phase under high temperature annealing process, resulting in expanded crystal parameters and smooth charge‐discharge profiles. The stable tunnel structure layer can effectively protect the layered P2 type cathode material from corrosion by electrolyte upon high voltage and alleviate the crack propagated from the particle surface. Therefore, the P2@tunnel heterostructure cathode can still maintain a discharge capacity of 146.3 mAh g−1 while the discharge capacity of pristine P2 type cathode is only 114.4 mAh g−1 after 100 cycles at 0.25 C, it also reveals superior cyclic stability and rate performance compared to the pristine P2 type cathode. [ABSTRACT FROM AUTHOR]

Nonoxidative cathodically induced graphene (CIG) here incorporates conductive agents for Li4Ti5O12 (LTO) anode materials. The tailored LTO/CIG composite is fabricated by controlled hydrolysis of tetrabutyl titanate in the presence of nonoxidative defect-free cathodically induced graphene (CIG) and oxalic acid in a mixed solvent of ethanol and water, followed by hydrothermal reaction and a calcination treatment. Due to the introduction of defect-free graphene, the resulting LTO/CIG composite shows an excellent electrical conductivity (1.2 × 10−4 S cm−1) and Li+ diffusion coefficient (1.61 × 10−12 cm2 s−1). As a result, the tuned LTO/CIG composite exhibits outstanding electrochemical performance, including excellent cycling stability (the capacity retention ratios after 500 cycles at 0.5 C is 96.2%) and a remarkable rate capability (162 mAh g−1 at 10C, 126 mAh g−1 at 100 C). A specific energy of 272 Wh kg−1 at power of 136 W kg−1 is observed when cycling against Li-foil. Even during 36 s of charge/discharge, the specific energy of LTO/CIG composite remains at 166 Wh kg−1. [ABSTRACT FROM AUTHOR]

Na4Mn1.5Fe1.5(PO4)2P2O7 (NMFPP), with its low cost and high energy density, is essential for accelerating the commercialization of sodium‐ion batteries. However, its practical application is limited by serious voltage hysteresis and detrimental Jahn‐Teller distortions. Herein, a high operating voltage and superior stable Nb‐doped NMFPP with fewer intrinsic anti‐site defects are elaborately designed by the reconstruction of the crystal lattice and electronic distribution. By introducing higher charge density Nb─O bonds, the lengths of Mn‐O bonds are shortened, enhancing lattice stability. As a result, the lattice volume contracted during Na+ extraction/insertion is decreased with niobium‐modified Na4(Mn0.5Fe0.5)2.94Nb0.06(PO4)2P2O7, mitigating lattice distortion from the Jahn‐Teller effect and increasing the capacity retention after 1000 cycles from 57.5% to 82.3%. More importantly, the delayed effect of Mn2+ involvement in redox reactions is significantly reduced, raising the average operating voltage from 3.32 to 3.64 V and increasing the overall energy density by 13%. This study opens new avenues to develop advanced sodium‐ion battery cathode materials with high energy density and long calendar life for energy storage. [ABSTRACT FROM AUTHOR]

Highlights: Pore size and graphitization engineering of carbon cathode were orientated-designed by regulating the molar ratios of Zn/Co ions. Zn90Co10-APC and its assembled PLG//Zn90Co10-APC LIC both deliver the excellent electrochemical performances. The lack of methods to modulate intrinsic textures of carbon cathode has seriously hindered the revelation of in-depth relationship between inherent natures and capacitive behaviors, limiting the advancement of lithium ion capacitors (LICs). Here, an orientated-designed pore size distribution (range from 0.5 to 200 nm) and graphitization engineering strategy of carbon materials through regulating molar ratios of Zn/Co ions has been proposed, which provides an effective platform to deeply evaluate the capacitive behaviors of carbon cathode. Significantly, after the systematical analysis cooperating with experimental result and density functional theory calculation, it is uncovered that the size of solvated PF6− ion is about 1.5 nm. Moreover, the capacitive behaviors of carbon cathode could be enhanced attributed to the controlled pore size of 1.5–3 nm. Triggered with synergistic effect of graphitization and appropriate pore size distribution, optimized carbon cathode (Zn90Co10-APC) displays excellent capacitive performances with a reversible specific capacity of ~ 50 mAh g−1 at a current density of 5 A g−1. Furthermore, the assembly pre-lithiated graphite (PLG)//Zn90Co10-APC LIC could deliver a large energy density of 108 Wh kg−1 and a high power density of 150,000 W kg−1 as well as excellent long-term ability with 10,000 cycles. This elaborate work might shed light on the intensive understanding of the improved capacitive behavior in LiPF6 electrolyte and provide a feasible principle for elaborate fabrication of carbon cathodes for LIC systems. [ABSTRACT FROM AUTHOR]

Here we show that P2/O3 biphasic layered structure is originated from internal heterogeneity of "cationic potential" induced by locally compositional non-uniformity, which largely depends on the temperature-driven reaction thermodynamics and kinetics. The clarified material-formation mechanism enables facile design and preparation of P2/O3 biphasic materials with much-improved sodium-storage performances than single-phase one, promoting the exploration of advanced cathodes for sodium-ion batteries. [Display omitted] Sodium layered oxides generally suffer from deep-desodiation instability in P2 structure and sluggish kinetics in O3 structure. It will be great to design P2/O3 biphasic materials that bring the complementary merits of both structures. However, such exploration is hindered by the ambiguous mechanism of material formation. Herein, supported by theoretical simulations and various spectroscopies, we prove that P2/O3 biphasic structures essentially originate from the internal heterogeneity of cationic potential, which can be realized by constraining the temperature-driven ion diffusion during solid-state reactions. Consequently, P2/O3 biphasic Na 0.7 Ni 0.2 Cu 0.1 Fe 0.2 Mn 0.5 O 2– δ with well-designed quaternary composition is successfully obtained, exhibiting much-improved rate capabilities (62 mAh g−1 at 2.4 A g−1) and cycling stabilities (84% capacity retention after 500 cycles) than its single-phase analogues. Furthermore, synchrotron-based diffraction and X-ray absorption spectroscopy are employed to unravel the underlying sodium-storage mechanism of the P2/O3 biphasic structure. This work presents new insights toward the rational design of advanced layered cathodes for sodium-ion batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-performance cathode materials for all-organic proton full-battery are synthesized. • Organic copolymers of tertiary amines exhibit nanorod-like morphology. • The device delivers energy densities of 33.9 & 9.6 Wh kg−1 at 423 & 1880 W kg−1. • The assembled proton battery can operate even at −25 °C with > 93% of capacity retention. High-performance aqueous all-organic rechargeable batteries are promising candidates for cost-effective, safe, and environment-friendly next-generation energy storage devices. Herein, two organic copolymers with nanorod-like morphology (AN-TA, and AN-PA), composed of different tertiary amines, are synthesized as the cathode material for an aqueous proton battery. The individual copolymer electrodes possess the dominated diffusion-controlled electrode kinetics resulting from the proton insertion/de-insertion along with the surface-controlled processes in 2 M HCl and 2 M H 2 SO 4. Among the two copolymers, AN-PA exhibits the maximum specific capacity of 145 mAh g−1 at 1 A g−1 and then, even at the higher current density of 10 A g−1, it possesses the capacity as 110 mAh g−1 in 2 M HCl. The assembled aqueous proton battery comprising of AN-PA as a cathode delivers the capacity of 80 mAh g−1 at 1 A g−1 in 2 M HCl. The maximum deliverable energy density of 33.9 Wh kg−1 is achieved at the power density of 423 W kg−1. Notably, our proton battery can well operate at the sub-zero temperature of −25 °C with a cell voltage of 1.1 V. More importantly, the device retains 84 % of the initial capacity after 1000 cycles at 2 A g−1 and exhibits the retention of specific capacity of about > 93% when compared to that of room temperature. [ABSTRACT FROM AUTHOR]

The electrochemical performance of the cathode material is influenced by its structure, including morphology, pore size, specific surface area, layer spacing, impurity content, and species. Each of these factors plays a distinct role in the energy storage process of the electrode. The purpose of this review is not only to provide the relationship between the structure and mechanism of cathode materials, but also to provide directional guidance for optimizing electrochemical performance of the materials. [Display omitted] • Critically reviewing the applications of various cathode materials in MIHCs (Li, Na, K and Zn). • Discussing the relationship between material structure and energy storage mechanism. • Summarizing the methods of optimizing electrochemical properties of cathode materials. Metal ion hybrid capacitors (MIHCs) consist of both capacitance-type electrodes and battery-type electrodes, thereby combining the advantages of metal ion batteries and supercapacitors. Nevertheless, the disparity between the specific capacity and rate performance of the cathode and anode materials suggests that the current performance of MIHCs does not meet practical requirements. The performance of MIHCs is affected by the type, composition, and morphology of the cathode material, affirming their essential role as critical components. Therefore, there is a need to concentrate on and discuss the electrochemical properties of electrode materials, as well as strategies aimed at enhancing their electrochemical performance. This article introduces the composition, types, and energy storage mechanisms of MIHCs. Subsequently, a review is conducted on the cathode materials used in lithium, sodium, potassium, and zinc ion capacitors, with emphasis on their physical and chemical properties and the resulting electrochemical performance. Moreover, a comprehensive investigation is conducted to explore effective strategies for enhancing the electrochemical properties of materials, incorporating a substantial number of theoretical calculations and experimental results. Finally, this review provides valuable suggestions for the development and large-scale production of cathode electrode materials for MIHCs (Li+, Na+, K+, and Zn2+), addressing current issues and proposing potential research directions. [ABSTRACT FROM AUTHOR]

Recycling of spent lithium-ion batteries (LIBs) has emerged as an inevitable trend in promoting environmental sustainability and resource conservation. Lithium iron phosphate (LiFePO 4 or LFP) battery, renowned for its unique stability and favorable price, has been the predominant focus for lithium-ion battery manufacturers, consequently resulting in a surge in the number of spent LIBs. In view of the failure mechanism, the direct regeneration technology presents a potential strategy for the closed-loop recycling of LFP. The aim is to retain the high added value and revitalize optimal state of the spent cathode materials through a non-destructive process that maximizes efficiency and ensures desirable profits. Hence, the existing technical challenges and recent progress in the separation pretreatment are reviewed and summarized. Subsequently, the current direct regeneration methods and advanced upcycling techniques for spent LFP cathode are outlined, along with an appraisal of their respective advantages and disadvantage. Specifically, a comprehensive analysis of environmental and economic benefits derived from three presentative examples is highlighted compared to traditional metallurgy process. The review also aims to provide an overview on direct regeneration of spent LFP cathode, making it favorable for further industry adoption. • Potential strategy for low-value LFP via direct regeneration is presented. • Challenges and recent progress in separation pretreatment are discussed. • Recent advancements and advanced upcycling for spent LFP cathode are summarized. • The merits and drawbacks of each approach are assessed. • The comprehensive analysis of environmental and economic benefits is emphasized. [ABSTRACT FROM AUTHOR]

In this study, we unravel the effect of Ni doping on the half-cell and full-cell performances of the Na 0.67 Mn 0.5-x Ni x Fe 0.43 Ti 0.07 O 2 cathode materials where x varies between 0.02 and 0.1. The cyclic voltammetry (CV) analysis of the half-cells is performed at 10 °C, room temperature (RT), and 50 °C to elucidate the redox reaction mechanisms at different temperatures. Among the studied cathodes, the highest specific capacity is obtained fox = 0.06 which delivered a specific capacity of 186 mAh g−1 at C/3-rate. The full cell of Na 0.67 Mn 0.44 Ni 0.06 Fe 0.43 Ti 0.07 O 2 /hard carbon couple is assembled in coin cell format and the specific capacity of the cell at C/2, 1C, and 2C rates are found as 153 mAh g−1, 125 mAh g−1 and 120 mAh g−1, respectively. At the C/2-rate, the excellent capacity retention of the full cell is around 70% after 500 cycles delivering a specific capacity of 103 mAh g−1. Along with the conventional physicochemical characterization methods such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman and Fourier-transform Infrared Spectroscopies (FTIR), we also utilize X-ray photoelectron spectroscopy (XPS) to bridge the nexus between the performance and the structure properties of the studied materials. Furthermore, we also employ synchrotron-based X-ray Absorption (XAS) to understand the local geometry of the optimized cathode materials in operando. • Ni doping on P2 type Na 0.67 Mn 0.5-x Ni x Fe 0.43 Ti 0.07 O 2 cathode active material was studied. • Na 0.67 Mn 0.44 Ni 0.06 Fe 0.43 Ti 0.07 O 2 cathode material delivered a specific capacity of 186 mAh g-1 at C/3-rate. • Full-cell containing Na 0.67 Mn 0.44 Ni 0.06 Fe 0.43 Ti 0.07 O 2 /Hard Carbon couple revealed 70% capacity retention after 500 cycles. [ABSTRACT FROM AUTHOR]

The transformation of energy structure is deemed as a paramount strategy in accomplishing the ambition of carbon neutrality. Lithium-ion batteries (LIBs), as one of the most exceptional energy storage and conversion devices available, play a pivotal role in this energy revolution. However, due to the extensive production and limited lifespan of LIBs, the retirements of LIBs are set to boom in the coming years. The proper and timely recycling of these batteries are of paramount importance, from both environmental and economic perspectives. Direct cathode regeneration technology is the most promising solution for the treatment of these waste cathodes, as it enables the healing of spent cathodes with minimal energy and chemical consumption, without compromising the original structure of the cathode. Herein, we analyzed the degraded mechanisms of spent LIBs and found that relithiation and defect reparation are crucial steps for the regeneration of spent cathode materials. Various direct regeneration methods previously reported have been summarized, and their respective advantages and limitations as well as technical challenges when implemented into practical industrial applications are discussed. In addition, possible solutions to these problems are proposed, which guide the future direction for the sustainable development of the battery recycling industry. • The degraded mechanisms of spent lithium-ion batteries are summarized. • Current status on direct regeneration of spent cathodes is presented. • The advantages and limitations of direct regeneration approaches are identified. • The future directions of direct regeneration strategies were proposed. [ABSTRACT FROM AUTHOR]

The booming development of the lithium-ion battery market has aroused the transformation of people's consumption and life style. As a significant branch of lithium-ion batteries, LiFePO 4 (LFP)-type batteries has been widely employed in electric vehicles and energy storage devices due to its high safety and decent charge-discharge stability. Nevertheless, the resulted massive scrap of LFP batteries will greatly pose environmental threats and waste of resources if appropriate technical means are not adopted. The advanced recycling methods of spent LFP cathode have long been constantly explored in recent years but have not been systematically discussed. Hence, this review comprehensively summarizes the recovery technologies of spent LiFePO 4 cathode in the current status, including traditional pyro-/hydro-metallurgical processes, direct regeneration and other innovative methods, etc. Furthermore, the pretreatment process is also covered to promote all-sided understanding of the development of LFP cathode recovery approaches. Based on the systematic analysis of spent LFP cathode recycling, the future outlook of efficient recycling methods is proposed to promote the sustainable development of spent lithium-ion batteries. Schematic illustration of strategies and characteristics towards spent LFP cathode recycling. [Display omitted] • A comprehensive summary and prospect of spent LFP cathode recycling. • Pretreatment is introduced to ensure deep understanding of recycling implication. • Mainstream recycling technologies of spent LFP battery are reviewed. • Up-to-date novel recycling methods for spent LFP cathode are summarized. • Future challenges and perspectives are proposed to promote efficient recycling. [ABSTRACT FROM AUTHOR]

Schematic of direct recovery via mild chemical relithiation strategy. [Display omitted] • Reductive H 2 O 2 results in LiFePO 4 regeneration without high temperature/pressure. • The Gibbs free energy of chemical relithiation process is precisely calculated. • Lithium loss and structure defects are resolved through direct regeneration. • Excellent properties of restored LFP reach the standards of secondary utilization. • Moderate regeneration strategy guarantees profit and application potential. With the rapid popularization of LiFePO 4 (LFP) based lithium-ion batteries, the rational recycle of spent LFP has become focus in recent years. Direct regeneration of spent LFP has received continuous attention as it can effectively eliminate the capacity attenuation caused by lithium loss and Fe (Ⅲ) phase and maintain the original LFP structure. Here, we propose an efficient approach on basis of mild chemical relithiation combining with appropriate thermal annealing to realize the direct regeneration of spent LFP without high temperature/pressure or extra hazardous chemical. Specifically, subtle reductive hydrogen peroxide in LiOH solution is utilized to remove the structural defects of a degraded LFP cathode, and the restored LFP shows excellent cycling stability and rate capability (a capacity retention of 84.9% after 1000 cycles at 5C). Moderate regeneration conditions guarantee high security and profit of this strategy compared with other regeneration technologies, which reveals a favourable potential of practical application and is expected to the sustainable development of spent lithium-ion batteries. [ABSTRACT FROM AUTHOR]

• Propose a strategy of synergetic modulation on electrolyte and electrode interface. • Synergistically accelerate the interfacial reaction kinetics at low temperature. • Niobium oxide with high intercalation potential inhibit the generation of Li plating at low temperature. • Promising rate and cycle performance of T-Nb 2 O 5 @C||LFP at ultra-low temperature. The performance of rechargeable lithium-ion batteries (LIBs) in cold environments remains a challenge due to the insufficient ionic conductivity of electrolyte and lithium plating at graphite anodes. Herein, we demonstrate that the synergistic effect of ether-based electrolyte and niobium oxide with high intercalation potential can significantly improve the low-temperature charging/discharging performance of LIBs. Theoretical calculations and in-situ characterizations prove that the weak desolvation energy of electrolyte and the strong binding energy Li+-O bridging coordination synergistically accelerate the interfacial reaction kinetics. The full cells by coupling the niobium oxide anode with LiFePO 4 cathode show 95.6% of the initial capacity after 500 cycles at −30 °C, and exhibit excellent rechargeability at −50 °C. This work verifies that the synergism of solvating power of solvent and Li+ intercalation behavior is crucial in low-temperature LIBs. [ABSTRACT FROM AUTHOR]

3D interconnected ultrathin CoSe nanosheets are prepared via a hydrothermal synthesis method and utilized as superior battery-like electrode material for the first time. Due to the features of the unique 3D interconnected ultrathin nanosheets with a large BET specific surface area, superior mesoporous structure and good electrical conductivity, the as-resulted 3D interconnected ultrathin CoSe nanosheets manifests a high specific capacity of 70.6 mAh g −1  at 1 A g −1 and remarkable rate performance with 52.8% of capacity retention rate at 100 A g −1 compared with 1 A g −1 . Furthermore, a novel aqueous hybrid supercapacitor is assembled by employing 3D interconnected ultrathin CoSe nanosheets and activated carbon as the cathode and anode, respectively. The assembled hybrid device displays a specific energy of 18.6 Wh kg −1  at a specific power of 750 W kg −1 and outstanding cycling life with 95.4% of the initial capacity retention for 20000 cycles at 5 A g −1 . These results imply that the unique 3D interconnected ultrathin CoSe nanosheets can be considered as highly potential candidate electrode materials for hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Na storage mechanism of Cu-substitution P′2-Na x MnO 2 cathodes are systematically studied. • The Mn–O bond anisotropy in transition metal layer is decreased by the modulation of the CuO 6 octahedron. • The P′2-OP4-(P′2 + P′2-I) phase evolution of P′2-Na x MnO 2 is suppressed duo to the introduction of Cu. • P′2-Na 2/3 Cu 0.1 Mn 0.9 O 2 exhibits outstanding rate capabilities and enhanced cycle performances. Orthorhombic Mn-based layered oxides (P′2) have drawn much attention as promising cathode materials for sodium ion batteries (SIBs) with high specific capacities and rich resources. However, P′2-Na x MnO 2 cathode suffers from inferior rate capability and poor cycling performances, owing to the complicated phase transition during de-/sodiation process. Herein, Cu-substitution P′2-Na 2/3 Cu 0.1 Mn 0.9 O 2 is successfully prepared to mitigate the multiple phase transition by reducing the distortion of the MnO 6 octahedron. Mn–O bond anisotropy is decreased and the spacing distance of Na layer is constricted by the modulation of the CuO 6 octahedron, giving enhanced electronic conduction, validated by theoretical calculations and X-ray diffraction refinement. P′2-OP4 phase transition is replaced by reversible P′2-Z phase transition with slighter volume change, leading to the lower lattice strain in both c -axis direction and a-b plane, as probed by Operando/ ex situ X-ray diffraction and synchrotron X-ray absorption spectra, which strengthens the stability of lattice skeleton. Consequently, P′2-Na 2/3 Cu 0.1 Mn 0.9 O 2 exhibits outstanding rate capabilities (102 mAh/g at 750 mA g−1) and enhanced cycle performances (91 % at 150 mA g−1 after 100 cycles). This Cu-substitution strategy provides an effective method to design the structure-stable layered oxide cathodes for SIBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • C 6 H 12 O 6 as a reagent resulted in LiCoO 2 reduction at low temperature (<550 °C). • LiCoO 2 reduction mechanisms have been determined by thermodynamic calculations. • 97% of Li can be selective leached out by using water as the only leaching reagent. • The recovered Li 2 CO 3 and Co 3 O 4 could be directly used for cathode regeneration. • The proposed closed-loop process mitigates energy consumption, pollution and costs. Due to the mounting pressure to mitigate environmental pollution and guarantee the sustainability of the battery metals, the recycling of spent lithium-ion batteries (LIBs) has become a crucial issue in recent years. Numerous studies have focused on utilizing high temperatures or strong acid/alkali to reduce the spent active cathode material to a low valence state, which exacerbates recycling and post-treatment costs. Herein, a low-temperature roasting process followed by a water leaching strategy is developed to recycle and regenerate LiCoO 2 cathode material from spent LiCoO 2 batteries. The spent LiCoO 2 is roasted with glucose (C 6 H 12 O 6) as a reagent to attain reduction of the cathode material into water-soluble Li salt (Li 2 O and Li 2 CO 3) and water-insoluble (Co and CoO). The proposed method utilizes moderate roasting temperature and water as the only leaching reagent, which effectively reduces energy and chemical consumption. Li and Co recovery rates are 97 % and 99 %, respectively, under the optimal conditions of 1 h roasting at 550 °C followed by 30 min water leaching using a solid–liquid ratio of 50 g/L. The recovered Li-rich solution and Co-rich residue can be easily converted to Li 2 CO 3 and Co 3 O 4 , respectively, which are the precursors for regenerating the LiCoO 2 cathode material. The regenerated LiCoO 2 exhibits superior cycling stability with 87 % capacity retention after 800 cycles at 4.4 V. This developed closed-loop recycling process has lower recycling costs, is eco-friendly and efficient, and thus could potentially promote the sustainable long-run development of the LIBs industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrochemical performances of LiMn 2−x Ru x O 4 (x = 0, 0.01, 0.03, 0.05) cathodes are systematically studied. • The Ru-LMO cathode presents superior structural stability and cycling durability. • The robust crystal structure framework is effectively reconstructed based on d-p orbital hybridization design. • It inaugurates an explicit direction for rationally tuning the orbital hybridization for alkali metal batteries. Spinel LiMn 2 O 4 is a prevalent cathode material due to its environmental benignities and high operating voltage. Nevertheless, capacity attenuation and structural collapse are still inevitable, caused by the native Jahn–Teller distortion and spontaneous disproportionation of Mn3+. Hereby, LiMn 2 O 4 cathode with stable crystallographic structure is rationally designed based on valence-bond theory with introduction of Ru dopant. The enhanced orbital hybridization between Mn 3d and O 2p is successfully achieved owing to the reinforcing band coherency of Mn–O aroused from the electrostatic interaction between Mn and Ru atoms. Notably, the robust crystal structure framework is effectively reconstructed, which is beneficial for ameliorating phase evolution and inhibiting structural degradation substantiated by the state-of-the-art synchrotron X-ray absorption spectroscopy and in-situ X-ray diffraction. Concomitantly, LiO 4 tetrahedron is effectively weakened, further facilitating the rapid Li+ diffusion kinetics intensively confirmed by theoretical calculations and electrochemical tests. Remarkably, the as-designed Ru-doped LiMn 2 O 4 manifests splendid long cycling stability, affording a respectable capacity retention of 88.2 % after 200 loops. Given this, the intriguing work might inaugurate an explicit direction for rationally tuning the orbital hybridization towards advanced electrodes in alkali metal batteries. [ABSTRACT FROM AUTHOR]

• Anchor-oxygen interface layer is rationally designed. • Interfacial quasicrystal bonding effects are ingeniously aroused. • Formation energy of oxygen vacancy is effectively elevated. • Capacity/voltage fading is significantly mitigated. Sacrificial additive as an electrolyte engineering could regulate the electrode/electrolyte interface for advanced energy storage devices. In particular, the evolution of cathode electrolyte interface (CEI) is closely related with the epitaxial coordination environment of cathode materials. Herein, polarly modulated solvent strategy is successfully achieved, in which the electrochemical oxidation potential of perfluorinated electrolyte with tris(trimethylsilyl)borate additive is manipulated by the polarity of solvent structure. By taking Li-rich Mn-based oxide (LRM) as a model cathode, the interfacial quasicrystal bonding effects are ingeniously aroused between the interfacial lattice oxygen of LRM cathode and anchor oxygen CEI layer. More greatly, the formation energy of oxygen vacancy is effectively elevated by constructing the epitaxially strong covalent B/Si-O bonding, thereby considerably mitigating the lattice oxygen escaping and inhibiting the irreversible phase transformation. Consequently, LRM cathode with robust anchor oxygen CEI renders improved cycling stability after 200 loops with 87.5% capacity retention at 1C as compared to anchor oxygen-free LRM with only 61.9%. Given this, these findings inform new chemical and interface strategies to facilitate the application of high voltage cathodes. [ABSTRACT FROM AUTHOR]

The transition towards a new energy system has proliferated demand for lithium-ion batteries (LIBs) cathode materials with stable performance. To enhance the performance of the cathode materials, here-in, flexible LiMn 0.8 Fe 0.2 PO 4 /C (LMFP) dense microspheres with primary nanocrystalline are prepared by spray drying and solid state sintering. Coating the LiMn 0.8 Fe 0.2 PO 4 primary nanocrystalline with a conformal carbon nanolayer (∼3 nm) significantly improves the electronic conductivity of the active cathode material. The prepared LMFP cathode exhibited excellent rate performance with a discharge capacity of 129.1 mAh g−1 at 10C. Furthermore, the LMFP cathode depicted excellent cyclic stability, maintained a capacity retention of 95% after 1000 cycles at 1C and only 0.0073 mAh g−1 loss per cycle. Thermodynamics, surface morphology, phase structure, and electrochemical performance were used to investigate the effect of blending flexible LMFP and Ni-rich LiNi 0.85 Co 0.10 Al 0.05 O 2 (NCA) electrodes. The results depict that the thermal stability and cyclic reversibility of blending electrodes are significantly improved compared with the pristine NCA, and the blended electrodes display superior comprehensive properties. [Display omitted] • Flexible LMFP nanocrystalline microspheres was prepared by a scalable route. • An e−/Li+ 3D transport network was successfully constructed for LMFP microspheres. • The LMFP exhibits an excellent rate performance and long cycling durability. • The blended cathode shows a satisfactory energy density and thermal stability. • Synergies between stability of LMFP and energy density of Ni-rich NCA are realized. [ABSTRACT FROM AUTHOR]

Co 2 MnO 4 /Co hydroxide chloride (CMO/CHC) nanocomposite is firstly obtained through an electrochemically alternating voltage methodology for supercapacitor applications. The CMO/CHC electrode materials display a high specific capacitance of 779 F g −1 at 1 A g −1 and an excellent rate behavior (77.5% and 63.6% at 20 and 40 A g −1 compared with 1 A g −1 , respectively). An asymmetric supercapacitor based on CMO/CHC as cathode and activated carbon (AC) as anode presents a maximum energy density of 27.8 Wh kg −1 at power density of 570.9 W kg −1 . [ABSTRACT FROM AUTHOR]

Cathodic corrosion, a green electrochemical method, has been employed to obtain Sb nanomaterials utilized as anode material for lithium-ion batteries and sodium-ion batteries. Interestingly, two different corrosion mechanisms are found, coming from the impact of electrolyte, resulting in the formation of hexagonal and amorphous Sb in aqueous and organic solution, respectively. With the help of water-soluble carboxymethyl cellulose binder and the electrolyte additive fluoroethylene carbonate, both hexagonal and amorphous Sb electrodes exhibit good cycling stability when utilized as anode materials for lithium-ion batteries and sodium-ion batteries. Additionally, both the hexagonal and amorphous Sb electrodes show very good rate capability in lithium-ion batteries. Even at high current density (2000 mA g −1 ), the hexagonal and amorphous Sb give reversible capacities of 422 and 379 mA h g −1 , respectively. Surprisingly, when used as anode materials for sodium-ion batteries, the hexagonal Sb electrode exhibits a good rate performance of 632, 625, 569, 515 and 426 mA h g −1 at a current density of 100, 200, 500, 1000, and 2000 mA g −1 , respectively. However, limited rate performance is observed from the amorphous Sb electrode in case of sodium-ion battery due to the large impedance. [ABSTRACT FROM AUTHOR]

Robust single-crystalline Ni-rich cathodes with increasing Ni proportion, LiNi 0.83 Co 0.11 Mn 0.06 O 2 (SC83), LiNi 0.88 Co 0.06 Mn 0.06 O 2 (SC88), and LiNi 0.95 Co 0.03 Mn 0.02 O 2 (SC95) were successfully designed with molten salt-assisted method, and the correlation between the Li+ storage properties, particle microcracking, surface phase transitions, and Ni fraction in the single-crystalline Ni-rich cathodes have been profoundly investigated. [Display omitted] • -crystalline Ni-rich cathodes with increasing Ni proportion were designed with molten salt-assisted method. • The single-crystalline LiNi 0.83 Co 0.11 Mn 0.06 O 2 cathode presents superior structural stability and cycling durability. • Performance degradations were attributed to the aggravated Li/Ni mixing and H2 ↔ H3 phase transition. • It provides approach for designing high-energy density and stable single-crystalline Ni-rich cathodes. Further commercial development of polycrystalline Ni-rich layered cathode is severely hindered by the deep-rooted particle microcracking, mainly initiated among the randomly orientated grain boundaries of the primary particles. Herein, robust single-crystalline Ni-rich LiNi 0.83 Co 0.11 Mn 0.06 O 2 (SC83) prepared by molten salt-assisted method shows the enhanced structure stability and cycling durability. It's found that the particle microcracking is effectively removed for SC83 cathode during prolonged cycling helped with its eliminated grain boundaries and slight crystal shrinkage, leading to superior capacity retention of 92.8% after 100 cycles. Notably, the discharge capacity and energy density are effectively boosted with increasing Ni fraction majorly based on the more available Ni2+/Ni3+ redox, giving rise to high capacities of 211.2 and 219.4 mAh g−1 for LiNi 0.88 Co 0.06 Mn 0.06 O 2 (SC88) and LiNi 0.95 Co 0.03 Mn 0.02 O 2 (SC95) cathodes, respectively. However, the particle microcracking is progressively exacerbated owing to the aggravated Li/Ni mixing and H2 ↔ H3 phase transition with Ni proportion higher than or equal to 88% in SC cathodes, resulting in severe structure collapse and capacity fading during high-rate cycling, in which a poor capacity retention of 51.8% after 250 cycles at 5C is observed for single-crystalline SC95cathode. This work sheds light on the rational design of single-crystalline Ni-rich cathodes, and highlighted the trade-off between the energy density and cycling durability, facilitating the extensive applications of single-crystalline Ni-rich cathodes in high-performance electric vehicles (EVs). [ABSTRACT FROM AUTHOR]

P2–Na 2/3 Ni 1/3 Mn 2/3 O 2 as a promising cathode material for sodium ion batteries (SIBs) has attracted much attention owing to high capacity and wide operation voltage. However, it suffers from inferior rate and cycling performances due to P2–O2 phase transition and Na+/vacancy ordering during charge/discharge process. Herein, a Fe/Ti co-substitution strategy is successfully utilized to mitigate these issues. Notably, as probed by In-situ X-ray diffraction, the substitution of Ni with Fe significantly stabilizes the interlayer framework by impeding slab glide during deep Na+ extraction, resulting in reversible P2-OP4 phase transition with smaller volume change of host structure compared to P2–O2 transition. Meanwhile, synchrotron X-ray diffraction shows that, the Na+/vacancy ordering is greatly suppressed by further replacing Mn with Ti, which breaks down the long-range ordering of Ni/Mn distribution, promoting Na ion transport. In addition, the charge compensation mechanism of Fe/Ti co-substituted P2–Na 0.67 Ni 0.23 Fe 0.1 Mn 0.57 Ti 0.1 O 2 (NFMT) revealed by Ex-situ X-ray absorption spectroscopy demonstrates that the incorporation of Fe3+/4+ redox couple largely improve the working voltage. Consequently, the obtained NFMT cathode delivers a high energy density over 420 Wh/kg within 4.3–2.6 V, accompanied with remarkably enhanced kinetics and capacity retention. Such co-substitution strategy provides a promising approach to develop high-voltage and cycle-stable cathode materials for SIBs. [Display omitted] • Fe/Ti co-substitution is proposed to modify the P2–Na 2/3 Ni 1/3 Mn 2/3 O 2 cathode. • Fe substitution can prevent the P2–O2 phase transition. • Ti substitution disrupts cation ordering and Na+/vacancy ordering. • Fe/Ti co-substitution can stabilize the reversible OP4 phase. [ABSTRACT FROM AUTHOR]

The explosively growing demand for electrical energy is generating a great deal of spent lithium-ion batteries (LIBs). Therefore, a simple and effective strategy for the sustainable recycling of used batteries is urgently needed to minimize chemical consumption and to reduce the associated environmental pollution. In this work, 2-naphthalenesulfonic acid is innovatively proposed for the highly-selective recovery of valuable metals. Impressively, lithium and cobalt are simultaneously separated through a single-step process, in which 99.3% of lithium is leached out as Li+ enriched solutions while 99% of cobalt is precipitated as cobalt-naphthalenesulfonate. The obtained lithium enriched solutions are recovered as Li 2 CO 3. The cobalt-naphthalenesulfonate with high purity (99%) is ready to be transformed into Co 3 O 4 , and then generated into LiCoO 2 by reacting with the above-obtained Li 2 CO 3. The cathode material LiCoO 2 with micro/nanostructures exhibits excellent electrochemical properties. Characterization results confirm the coordination structure of the extracted cobalt complex (Co(NS)2•6H 2 O). Finally, compared to other selective metal extraction techniques, this strategy avoids additional separation and purification processes, thus improving the recycling efficiency. Overall, this route can be extended to selectively extract valuable metals from other types of cathode materials in spent LIBs as a sustainable approach. [Display omitted] • HNS is effective for highly-selective recovery of valuable metals from LiCoO 2. • Lithium and cobalt are leached and separated in one single step. • Over 99% Li and Co can be recovered and regenerated. • LiCoO 2 cathode is regenerated via cobalt-naphthalenesulfonate precipitates. [ABSTRACT FROM AUTHOR]

The impacts of Cu substitution upon the cycling stability of Na x MO 2 (M = Fe, Mn) cathodes are systematically studied. Evidenced by CuO segregation and XPS analysis, the average valence of Mn can hardly reach +4, possibly owing to the production of Mn(II). It is proposed that, Cu substitution can efficiently enhance the cycling stability by reducing the content of Mn(III) and suppressing the electrochemical activities of Mn4+/3+ redox couple. • Cycling stability of Na x MO 2 (M = Cu, Fe, Mn) cathodes are systematically studied. • CuO segregation is evidenced to be associated with the limited valent state of Mn. • Adding Cu2+ actually lower Mn valence by decreasing Mn(III) and generating Mn(II). • Cu2+-substitution may enhance the cycling stability mainly by suppressing Mn(III). Adding Cu2+ has substantially boosted the practical potentiality of Fe/Mn-based layered cathodes for sodium ion batteries (SIBs) owing to the enhanced stabilities, which were previously ascribed to the raised valence of Mn. Herein, the roles of Cu2+ are verified by investigating Cu2+-substituted materials with the stoichiometry of Na 0.5+x Cu x Fe 0.5-x Mn(IV) 0.5 O 2. Surprisingly, it is found that Mn valence can hardly reach the expected value (IV) even by adjusting Cu2+ content. For the first time, the separation of CuO, which has been previously detected but rarely explained, is ascribed to the restrained chemical states of Mn. Detailed analyses show that, Mn(II) is generated while Mn(III) is decreased in pace of Cu2+ substitution, actually lowering down the oxidation states of Mn. Moreover, Mn4+/3+ redox can be efficiently restricted by importing Cu2+. Albeit the loss of capacity, the cycling stability is greatly enhanced, achieving a high capacity retention of 92.3% after 200 cycles within 4.2–2.5 V. Therefore, the suppression of Jahn-Teller Mn(III) should be intrinsically responsible for the superior cycling stability after Cu2+ substitution. These findings may present a new sight to probe the roles of Cu in layered Na x MO 2 system for the design of advanced cathodes for SIBs. [ABSTRACT FROM AUTHOR]

• Mn2+ dissolution enabled MnO to be an active cathode for aqueous Zn-ion battery. • A H+/Zn2+ co-insertion mechanism of the as-activated Mn 1-x O cathode was proposed. • A MnO nanochain@Graphene scroll configuration was obtained by hydrothermal method. • Cycling stability of MnO electrode was greatly enhanced by graphene wrapping. Aqueous Zn-ion batteries (ZIBs) attract ever-growing attention due to low cost, high safety, and environmental friendliness. Among the limited cathode candidates, manganese-based oxides stand out owing to large ion channels and multiple valence of Mn. Notably, MnO, thought to be inactive before, actually exhibits high energy densities in AZIBs, thus arousing wide interests. Herein, the electrochemical behavior of MnO electrode is extensively investigated in ZnSO 4 electrolytes with different concentration of MnSO 4. It is confirmed that the inactive MnO is electrochemically activated during the initial charge process. Greatly, the initial capacity and the following cycling stability of MnO electrode strongly depends on the concentration of MnSO 4 , indicating that the activation of MnO could be attributed to Mn dissolution, leading to the higher valence of Mn as evidenced by ex-situ XPS analysis. Greatly, a H+/Zn2+ co-insertion mechanism is suggested for the as-activated Mn 1-x O electrode according to the ex-situ XRD results. In addition, by constructing a core-sheath MnO@N-doped graphene scrolls (MnO@NGS) configuration through a modified hydrothermal process, the reversible capacity of MnO has been successfully improved to 288 mAh g−1 (0.1 A g−1), leading to high energy density of 367 mWh g−1. More importantly, benefiting from the graphene wrapping and sufficient internal voids, 98% of the initial capacity can be retained after 300 cycles (0.5 A g−1), much better than the unmodified MnO and MnO 2 electrodes. This work is expected to deepen the understanding of the charge-storage mechanism of MnO and help to design durable manganese-based cathodes for ZIBs. [ABSTRACT FROM AUTHOR]