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Sodium-ion batteries (SIBs) have attracted more and more attention for scalable electrical energy storage due to the abundance and wide distribution of Na resources. However, the anode still remains a great challenge for the application of SIBs. Here the production of uniform hard carbon microtubes (HCTs) made from natural cotton through one simple carbonization process and their application as an anode are reported. The study shows that the electrochemical performance of the HCTs is seriously affected by the carbonization temperature due to the difference in their microstructure and heteroatomic content. The HCTs carbonized at 1300 °C deliver the highest reversible capacity of 315 mAh g−1 and good rate capability due to their unique tubular structure. This contribution not only provides a new approach for the preparation of hard carbon materials with unique tubular microstructure using natural inspiration, but it also deepens the fundamental understanding of the sodium storage mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Nickel iron binary oxide electrocatalysts prepared from different precursors were evaluated to facilitate the oxygen evolution reaction (OER) on semiconducting metal-oxide photoelectrodes. The electrocatalysts deposited from Ni(II) and Ni(II)Fe(II) precursors had the highest activity for OER, however, their presence on the surface of the Ti doped hematite photoelectrode decreased the incident photon-to-current efficiency (IPCE) of the photoelectrode for water splitting in an alkaline electrolyte. In contrast, the NiFe-oxide deposited from the Ni(II)–Fe(III) precursor which had a lower OER activity was found to increase the IPCE of the photoelectrode by as much as a factor of 5. [Copyright &y& Elsevier]

Nanoporous materials have attracted great technological interest during the past two decades, essentially due to their wide range of applications: they are used as catalysts, molecular sieves, separators and gas sensors as well as for electronic and electrochemical devices. Most syntheses of nanoporous materials reported so far have focused on template-assisted bottom-up processes, including soft templating (chelating agents, surfactants, block copolymers and so on) and hard templating (porous alumina, carbon nanotubes and nanoporous materials) methods. Here, we exploit a mechanism implicitly occurring in lithium batteries at deep discharge to develop it into a room-temperature template-free method of wide applicability in the synthesis of not only transition metals but also metal oxides with large surface area and pronounced nanoporosity associated with unprecedented properties. The power of this top-down method is demonstrated by the synthesis of nanoporous Pt and RuO2, both exhibiting superior performance: the Pt prepared shows outstanding properties when used as an electrocatalyst for methanol oxidation, and the RuO2, when used as a supercapacitor electrode material, exhibits a distinctly better performance than that previously reported for non-hydrated RuO2 (refs 19,20). [ABSTRACT FROM AUTHOR]

Abstract: This work studies a novel rechargeable all-solid-state Ag battery by using AgI nanoplates in unusual polytype phases as solid Ag electrolytes, Ag as anode and TiTe2 as cathode. Sufficiently high conductivity at room temperature (ca. 2.2×10−3 Scm−1) of the polytype AgI nanoplates leads to a successful battery operation even at room temperature, which is not at all possible in the case of commercial AgI. The working temperature of the batteries with a high current density (up to 2500μAcm−2) using high-temperature modification of AgI (α-AgI) with conductivity >10−1 Scm−1 can be lowered as much as by ∼50°C (from 150°C to 100°C) due to the anomalous phase transition to α-phase (a large hysteresis) of the polytype nanoplates. Not only are the cycling and rate performance of the Ag batteries remarkable, but also the novel electrolyte (AgI nanoplates) promises the miniaturization into nanoscaled batteries (nano-batteries). [Copyright &y& Elsevier]

CoF3 aqueous solution was used to modify the surface of Ti-doped iron oxide thin film photoanodes to negatively shift the flat-band potential and allow photogenerated electrons to directly reduce water to hydrogen without an external bias; the zero bias performance was further improved by the use of glucose (a biomass analog) to bypass the relatively slow oxygen evolution reaction to provide a source of electrons to rapidly consume photogenerated holes. [ABSTRACT FROM AUTHOR]

CoF3aqueous solution was used to modify the surface of Ti-doped iron oxide thin film photoanodes to negatively shift the flat-band potential and allow photogenerated electrons to directly reduce water to hydrogen without an external bias; the zero bias performance was further improved by the use of glucose (a biomass analog) to bypass the relatively slow oxygen evolution reaction to provide a source of electrons to rapidly consume photogenerated holes. [ABSTRACT FROM AUTHOR]

Anode‐free designs can obtain the ultimate energy density of lithium metal batteries. However, without a continuous Li supply from the anode side, it is much more challenging to achieve high capacity retention with a competitive energy density. Here, the lifespan of an anode‐free Li metal battery is prolonged by applying an epitaxial induced plating current‐collector (E‐Cu). The functional layer on E‐Cu initiates Li storage by an alloying approach, forming an epitaxial induce layer, which exhibits speedy surface diffusion for of Li‐ions, resulting in the block like epitaxial growth of Li. Moreover, this alloying process also promotes the formation of a LiF‐rich solid electrolyte interphase (SEI), which is very useful for uniform Li plating. Due to the benefits of epitaxial Li plating and LiF‐rich SEI, the initial coulombic efficiency of the E‐Cu/Li asymmetric cell increases from 93.24 to 98.24%, and the capacity retention of anode‐free NCM811/E‐Cu pouch cell increases from 66 to 84% with a remarkable energy density of 420 Wh kg−1 in the condition of limited electrolyte addition (E/C ratio of 2 g Ah−1). This strategy is promising in the development of high energy batteries in extending their lifespans. [ABSTRACT FROM AUTHOR]

High‐performance layered oxide cathode materials are vital to the industrialization of Na‐ion batteries (NIBs) due to their high theoretical capacity and facile production. These materials, however, suffer from complicated phase transitions and poor capacity retention cycling. The modifying impacts of classic strategies, such as doping and coating, are generally restricted. Herein, a rational four‐in‐one strategy to boost the overall performance of Nax[Ni,Mn]O2 materials by innovative composition design and elegant synthesis management is provided. After modification, the half‐cell capacity retention rate increases from 45% to 77% after 250 cycles at 1 C rate. The capacity of the full cells is maintained at 83% after 300 cycles at 0.5 C rate. This four‐in‐one strategy, which encompasses optimization of the energy band structure, ion diffusion, crystal structure, and particle morphology, sheds new insight into the overall optimization of cathode materials for NIBs. [ABSTRACT FROM AUTHOR]

Na superionic conductor of Na3MnTi(PO4)3 only containing high earth‐abundance elements is regarded as one of the most promising cathodes for the applicable Na‐ion batteries due to its desirable cycling stability and high safety. However, the voltage hysteresis caused by Mn2+ ions resided in Na+ vacancies has led to significant capacity loss associated with Mn reaction centers between 2.5–4.2 V. Herein, the sodium excess strategy based on charge compensation is applied to suppress the undesirable voltage hysteresis, thereby achieving sufficient utilization of the Mn2+/Mn3+ and Mn3+/Mn4+ redox couples. These findings indicate that the sodium excess Na3.5MnTi0.5Ti0.5(PO4)3 cathode with Ti4+ reduction has a lowest Mn2+ occupation on the Na+ vacancies in its initial composition, which can improve the kinetics properties, finally contributing to a suppressed voltage hysteresis. Based on these findings, it is further applied the sodium excess route on a Mn‐richer phosphate cathode, which enables the suppressed voltage hysteresis and more reversible capacity. Consequently, this developed Na3.6Mn1.15Ti0.85(PO4)3 cathode achieved a high energy density over 380 Wh kg−1 (based on active substance mass of cathode) in full‐cell configurations, which is not only superior to most of the phosphate cathodes, but also delivers more application potential than the typical oxides cathodes for Na‐ion batteries. [ABSTRACT FROM AUTHOR]

Na‐ion batteries (NIBs) are promising for grid‐scale energy storage applications. However, the lack of Co, Ni‐free cathode materials has made them less cost‐effective. In this work, Mg2+ is successfully utilized to activate the oxygen redox reaction in earth‐abundant Fe/Mn‐based layered cathodes to achieve reversible hybrid anionic and cationic redox capacities. A high first charge capacity of ≈210 mAh g−1 with balanced charge–discharge efficiency is achieved without O‐loss, showing a promising energy cost of $2.02 kWh−1. Full cell against hard carbon anode without pre‐sodiation shows energy density exceeding ≈280 Wh kg−1 with a decent capacity retention of 85.6% after 100 cycles. A comprehensive analysis of the charge compensation mechanisms and structural evolution is conducted. Voltage and capacity loss resulting from partially reversible Fe3+ migration to the Na layer is confirmed, shedding light on further improvements for low‐cost NIB cathodes in application scenarios. [ABSTRACT FROM AUTHOR]

The rhombohedral sodium manganese hexacyanoferrate (MnHCF) only containing cheap Fe and Mn metals was regarded as a scalable, low‐cost, and high‐energy cathode material for Na‐ion batteries. However, the unexpected Jahn‐teller effect and significant phase transformation would cause Mn dissolution and anisotropic volume change, thus leading to capacity loss and structural instability. Here we report a simple room‐temperature route to construct a magical CoxB skin on the surface of MnHCF. Benefited from the complete coverage and the buffer effect of CoxB layer, the modified MnHCF cathode exhibits suppressed Mn dissolution and reduced intergranular cracks inside particles, thereby demonstrating thousands‐cycle level cycling lifespan. By comparing two key parameters in the real energy world, i.e. cost per kilowatt‐hours and cost per cycle‐life, our developed CoxB coated MnHCF cathode demonstrates more competitive application potential than the benchmarking LiFePO4 for Li‐ion batteries. [ABSTRACT FROM AUTHOR]

The rhombohedral sodium manganese hexacyanoferrate (MnHCF) only containing cheap Fe and Mn metals was regarded as a scalable, low‐cost, and high‐energy cathode material for Na‐ion batteries. However, the unexpected Jahn‐teller effect and significant phase transformation would cause Mn dissolution and anisotropic volume change, thus leading to capacity loss and structural instability. Here we report a simple room‐temperature route to construct a magical CoxB skin on the surface of MnHCF. Benefited from the complete coverage and the buffer effect of CoxB layer, the modified MnHCF cathode exhibits suppressed Mn dissolution and reduced intergranular cracks inside particles, thereby demonstrating thousands‐cycle level cycling lifespan. By comparing two key parameters in the real energy world, i.e. cost per kilowatt‐hours and cost per cycle‐life, our developed CoxB coated MnHCF cathode demonstrates more competitive application potential than the benchmarking LiFePO4 for Li‐ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: Sodium (Na) metal, which possesses a high theoretical capacity and the lowest electrochemical potential, is regarded as a promising anode material for Na–metal batteries. However, both Na dendrite growth and large volume change in cycling have severely impeded its practical applications. This study demonstrates that a 3D flexible carbon (C) felt which is already commercialized in large‐scale can be employed as a host for prestoring Na via a melt infusion strategy, through which a Na/C composite anode is obtained. The resulting anode exhibits a stable voltage profile and a small hysteresis over 120 cycles in carbonate‐based electrolytes in symmetrical cells owing to the fact that the metallic Na is confined in a conductive carbon felt host, which increases the Na+ deposition sites to lower the effective current density and render a uniform Na nucleation, restricting the dimension change in electrochemical cycling. More importantly, effective inhibition of Na dendrite growth and large volume change is achieved. When coupled with a Na0.67Ni0.33Mn0.67O2 cathode, the Na/C composite demonstrates a good suitability in full cells. This work provides an alternative option for the fabrication of stable Na metal anodes, which is of great significance for the practical applications of Na metal anodes in high‐energy‐density batteries. [ABSTRACT FROM AUTHOR]

Li ion batteries are important components of portable devices, electric vehicles, and smart grids owing to their high energy density, excellent cyclic performance, and safe operation. However, further development of electrode materials for these batteries is needed to satisfy continually increasing performance demands. Typically, both the charge/discharge kinetics and structural stability of these electrode materials depend on the transport and storage properties of the Li ions. High-spatial-resolution information on structural changes and on the strong interaction between electrons and ions is essential for a better understanding of the electrochemical performance of rechargeable batteries. In this article, we review the known atomic-scale structural changes of these electrode materials during the charge/discharge process, with special emphasis on ion/electron interactions. [ABSTRACT FROM AUTHOR]

Na-ion batteries (NIBs), as one of the next-generation rechargeable battery systems, hold great potential in large-scale energy storage applications owing to the abundance and costeffectiveness of sodium resources. Despite the extensive exploration of electrode materials, the relatively low attainable capacity of NIBs hinders their practical application. In recent years, the anionic redox reaction (ARR) in NIBs has been emerging as a new paradigm to deliver extra capacity and thus offers an opportunity to break through the intrinsic energy density limit. In this review, the fundamental investigation of the ARR mechanism and the latest exploration of cathode materials are summarized, in order to highlight the significance of reversible anionic redox and suggest prospective developing directions. [ABSTRACT FROM AUTHOR]

Na superionic conductor structured Na3V2(PO4)3 cathodes have attracted great interest due to their long cycling lifespan and high thermal stability rendered by the robust 3D framework. However, their practical application is still hindered by the high cost of raw materials and limited energy density. Herein, a doping strategy with low‐cost Fe2+ is developed to activate V4+/V5+ redox, in an attempt to increase the energy density of phosphate cathodes. It is also revealed that reversible activation of V4+/V5+ redox is related to the Na positions (Na1, 6b; Na2, 18e). Only the V‐based compounds with enough Na2 content can activate the V4+/V5+ reversibly. More importantly, without presodiation treatment and addition of any sodiation agent, Na3.4V1.6Fe0.4(PO4)3 is delicately designed as both cathode and the Na self‐compensation agent in full cells, allowing a promising energy density of ≈260 Wh kg−1. This work sheds light on enhancing the energy density, and designing Na self‐compensation for practical Na‐ions batteries. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries as a prospective alternative to lithium‐ion batteries are facing the challenge of developing high‐performance, low‐cost and sustainable anode materials. Hard carbons are appropriate to store sodium ions, but major energy and environmental concerns during their fabrication process (i.e., high‐temperature carbonization) have not been properly assessed. Furthermore, the rational design of high‐performing hard carbon anodes is usually limited by the conventional direct carbonization of organic precursors. Here, the hydrothermal carbonization process is employed as a versatile pre‐treatment method of renewable precursors, followed by high‐temperature carbonization, for producing advanced hard carbon anodes. The critical role of hydrothermal pre‐treatment in regulating the structure for an optimized performance of hard carbon anodes is elucidated, while revealing the sodium‐ion storage mechanism using electrochemical kinetic calculations, advanced characterization and multi‐scale modeling. Furthermore, the environmental impacts of hydrothermal pre‐treatment and subsequent carbonization are evaluated using life cycle assessment compared to direct carbonization. By comparing hard carbon anodes with and without the hydrothermal pre‐treatment, it is verified that the additional hydrothermal process is responsible for enhanced electrochemical performance, increased carbon yields and reduced carbon emissions. The work provides a systematic understanding of functions and energy consumptions of hydrothermal systems to achieve next‐generation sustainable sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Heteroatom doping has been proved to effectively enhance the sloping capacity, nevertheless, the high sloping capacity almost encounters a conflict with the disappointing initial Coulombic efficiency (ICE). Herein, we propose a heteroatom configuration screening strategy by introducing a secondary carbonization process for the phosphate‐treated carbons to remove the irreversible heteroatom configurations but with the reversible ones and free radicals remaining, achieving a simultaneity between the high sloping capacity and ICE (≈250 mAh g−1 and 80 %). The Na storage mechanism was also studied based on this "slope‐dominated" carbon to reveal the reason for the absence of the plateau. This work could inspire to distinguish and filter the irreversible heteroatom configurations and facilitate the future design of practical "slope‐dominated" carbon anodes towards high‐power Na‐ion batteries. [ABSTRACT FROM AUTHOR]

Heteroatom doping has been proved to effectively enhance the sloping capacity, nevertheless, the high sloping capacity almost encounters a conflict with the disappointing initial Coulombic efficiency (ICE). Herein, we propose a heteroatom configuration screening strategy by introducing a secondary carbonization process for the phosphate‐treated carbons to remove the irreversible heteroatom configurations but with the reversible ones and free radicals remaining, achieving a simultaneity between the high sloping capacity and ICE (≈250 mAh g−1 and 80 %). The Na storage mechanism was also studied based on this "slope‐dominated" carbon to reveal the reason for the absence of the plateau. This work could inspire to distinguish and filter the irreversible heteroatom configurations and facilitate the future design of practical "slope‐dominated" carbon anodes towards high‐power Na‐ion batteries. [ABSTRACT FROM AUTHOR]

Na-ion batteries (NIBs) have been attracting growing interests in recent years with the increasing demand of energy storage owing to their dependence on more abundant Na than Li. The exploration of the industrialization of NIBs is also on the march, where some challenges are still limiting its step. For instance, the relatively low initial Coulombic efficiency (ICE) of anode can cause undesired energy density loss in the full cell. In addition to the strategies from the sight of materials design that to improve the capacity and ICE of electrodes, presodiation technique is another important method to efficiently offset the irreversible capacity and enhance the energy density. Meanwhile, the slow release of the extra Na during the cycling is able to improve the cycling stability. In this review, we would like to provide a general insight of presodiation technique for high-performance NIBs. The recent research progress including the principles and strategies of presodiation will be introduced, and some remaining challenges as well as our perspectives will be discussed. This review aims to exhibit the basic knowledge of presodiation to inspire the researchers for future studies. [ABSTRACT FROM AUTHOR]

The high weight fraction of the electrolyte in lithium–sulfur (Li–S) full cell is the primary reason its specific energy is much below expectations. Thus far, it is still a challenge to reduce the electrolyte volume of Li–S batteries owing to their high cathode porosity and electrolyte depletion from the Li metal anode. Herein, we propose an ultralight electrolyte (0.83 g mL−1) by introducing a weakly‐coordinating and Li‐compatible monoether, which greatly reduces the weight fraction of electrolyte within the whole cell and also enables Li–S pouch cell functionality under lean‐electrolyte conditions. Compared to Li–S batteries using conventional counterparts (≈1.2 g mL−1), the Li–S pouch cells equipped with our ultralight electrolyte could achieve an ultralow electrolyte weight/capacity ratio (E/C) of 2.2 g Ah−1 and realize a 19.2 % improvement in specific energy (from 329.9 to 393.4 Wh kg−1) under E/S=3.0 μL mg−1. Moreover, more than 20 % improvement in specific energy could be achieved using our ultralight electrolyte at various E/S ratios. [ABSTRACT FROM AUTHOR]

The high weight fraction of the electrolyte in lithium–sulfur (Li–S) full cell is the primary reason its specific energy is much below expectations. Thus far, it is still a challenge to reduce the electrolyte volume of Li–S batteries owing to their high cathode porosity and electrolyte depletion from the Li metal anode. Herein, we propose an ultralight electrolyte (0.83 g mL−1) by introducing a weakly‐coordinating and Li‐compatible monoether, which greatly reduces the weight fraction of electrolyte within the whole cell and also enables Li–S pouch cell functionality under lean‐electrolyte conditions. Compared to Li–S batteries using conventional counterparts (≈1.2 g mL−1), the Li–S pouch cells equipped with our ultralight electrolyte could achieve an ultralow electrolyte weight/capacity ratio (E/C) of 2.2 g Ah−1 and realize a 19.2 % improvement in specific energy (from 329.9 to 393.4 Wh kg−1) under E/S=3.0 μL mg−1. Moreover, more than 20 % improvement in specific energy could be achieved using our ultralight electrolyte at various E/S ratios. [ABSTRACT FROM AUTHOR]

This is the first time that a novel anode material, spinel Li4Ti5O12which is well known as a "zero-strain" anode material for lithium storage, has been introduced for sodium-ion battery. The Li4Ti5O12 shows an average Na storage voltage of about 1.0 V and a reversible capacity of about 145 mAh/g, thereby making it a promising anode for sodiumion battery. Ex-situ X-ray diffraction (XRD) is used to investigate the structure change in the Na insertion/deinsertion process. Based on this, a possible Na storage mechanism is proposed. [ABSTRACT FROM AUTHOR]

As a new electrochemical power system, safety (especially thermal safety) of Na-ion batteries (NIBs) is the key towards large-scale industrialization and market application. Thus, research on the thermal stability of NIBs is helpful to evaluate the safety properties and to provide effective strategies to prevent the occurrence of battery safety failure. Thermal stability of the high-power 26650 cylindrical NIBs using Cu-based layered oxide cathode and hard carbon anode is studied. The high power NIBs can achieve fast charge and discharge at 5–10 C rate and maintain 80% capacity after 4729 cycles at 2 C/2C rate, where the unit C denotes a measure of the rate at which a battery is charge-discharged relative to its maximum capacity. The results of accelerating rate calorimeter and differential scanning calorimetry (ARC-DSC) test results show that NIBs have a higher initial decomposition temperature (≥110 °C) and a lower maximum thermal runaway temperature (≤350 °C) than those of Li-ion batteries (LIBs), exhibiting a favorable thermal stability. It should be noted that the heat generation of cathode accounts for a large proportion of the total heat generation while the thermal stability of the anode determines the initial thermal runaway temperature, which is similar to LIBs. Finally, the whole temperature characteristics of the NIBs in the range of –60 °C–1000 °C are summarized, which provide guidance for the safety design and applications of NIBs. [ABSTRACT FROM AUTHOR]

The irreversible consumption of sodium at the anode side during the first cycle prominently reduces the energy density of Na‐ion batteries. Different sacrificial cathode additives have been recently reported to address this problem; however, critical issues such as by‐products (e.g., CO2) release during cycling and incompatibility with current battery fabrication procedures potentially deteriorate the full‐cell performance and prevent the practical application. Herein, an additive‐free self‐presodiation strategy is proposed to create lattice‐coherent but component‐dependent O3‐NaxTMMnO2 (TM = transition metal ion(s)) cathodes by a quenching treatment rather than the general natural cooling. The quenching material preserves higher Mn3+ and Na+ content, which is able to release Na+ via Mn3+ oxidation to compensate for sodium consumption during the initial charge while adopting other TM to provide the capacity in the following cycles. Full cells fabricated with hard carbon anode and this material as both cathode and sodium supplement reagent have a nearly 9.4% cathode mass reduction, around 9.9% energy density improvement (from 233 to 256 Wh kg−1), and 8% capacity retention enhancement (from 76% to 84%) after 300 cycles. This study presents the route to rational design cathode materials with sodium reservoir property to simplify the presodiation process as well as improve the full‐cell performance. [ABSTRACT FROM AUTHOR]

Engineering the structure and chemistry of solid electrolyte interface (SEI) on electrode materials is crucial for rechargeable batteries. Using hard carbon (HC) as a platform material, a correlation between Na+ storage performance, and the properties of SEI is comprehensively explored. It is found that a "good" SEI layer on HC may not be directly associated with certain kinds of SEI components, such as NaF and Na2O. Whereas, arranging nano SEI components with refined structures constructs the foundation of "good" SEI that enables fast Na+ storage and interface stability of HC in Na‐ion batteries. A layer‐by‐layer SEI on HC with inorganic‐rich inner layer and tolerant organic‐rich outer flexible layer can facilitate excellent rate and cycling life. Besides, SEI layer as the gate for Na+ from electrolyte to HC electrode can modulate interfacial crystallographic structures of HC with pillar‐solvent that function as "pseudo‐SEI" for fast and stable Na+ storage in optimal 1 m NaPF6‐TEGDME electrolytes. Such a layer‐by‐layer SEI combined with a "pseudo‐SEI" layer for HC enables an outstanding rate of 192 mAh g−1 at 2 C and stable cycling over 1100 cycles at 0.5 C. This study provides valuable guidance to improve the electrochemical performance of electrode materials through regulation of SEI in optimal electrolytes. [ABSTRACT FROM AUTHOR]

The Na+ superionic conductor (NASICON)‐type Na3V2(PO4)3 cathodes have attracted extensive interest due to their high structural stability and fast Na+ mobility. However, the substitution of vanadium with low‐cost active elements remains imperative due to high cost of vanadium, to further boost its application feasibility. Herein, a novel ternary NASICON‐type Na4VMn0.5Fe0.5(PO4)3/C cathode is designed, which integrates the advantages of large reversible capacity, high voltage, and good stability. The as‐obtained Na4VMn0.5Fe0.5(PO4)3/C composite can deliver an excellent rate capacity of 96 m Ah g‐1 at 20 C and decent cycling durability of 94% after 3000 cycles at 20 C, which is superior to that of Na4VFe(PO4)3/C and Na4VMn(PO4)3/C. The synergetic contributions of multimetal ions and facilitated Na+ migration of the Na4VMn0.5Fe0.5(PO4)3/C cathode are confirmed by the first‐principles calculations. The processive reduction/oxidation involved in Fe2+/Fe3+, Mn2+/Mn3+, V3+/V4+/V5+ redox couples are also revealed upon the charging/discharging process by ex situ soft X‐ray absorption spectroscopy. The reversible structure evolution and small volume change during the electrochemical reaction is demonstrated by in situ X‐ray diffraction characterization. The rational design of NASICON‐type cathodes by regulating composition with substitution of multimetal ions can provide new perspectives for high‐performance Na‐ion batteries. [ABSTRACT FROM AUTHOR]

Anode‐free lithium metal batteries can maximize the energy density at the cell level. However, without the Li compensation from the anode side, it faces much more challenging to achieve a long cycling life with a competitive energy density than Li metal‐based batteries. Here, we prolong the lifespan of an anode‐free Li metal battery by introducing Li‐rich Li2[Ni0.8Co0.1Mn0.1]O2 into the cathode as a Li‐ions extender. The Li2[Ni0.8Co0.1Mn0.1]O2 can release a large amount of Li‐ions during the first charging process to supplement the Li loss in the anode, then convert into NCM811, thus extending the lifespan of the battery without the introduction of inactive elements. By the benefit of Li‐rich cathode and high reversibility of Li metal on Cu foil, the anode‐free pouch cells enable to achieve 447 Wh kg−1 energy density and 84 % capacity retention after 100 cycles in the condition of limited electrolyte addition (E/C ratio of 2 g Ah−1). [ABSTRACT FROM AUTHOR]

Anode‐free lithium metal batteries can maximize the energy density at the cell level. However, without the Li compensation from the anode side, it faces much more challenging to achieve a long cycling life with a competitive energy density than Li metal‐based batteries. Here, we prolong the lifespan of an anode‐free Li metal battery by introducing Li‐rich Li2[Ni0.8Co0.1Mn0.1]O2 into the cathode as a Li‐ions extender. The Li2[Ni0.8Co0.1Mn0.1]O2 can release a large amount of Li‐ions during the first charging process to supplement the Li loss in the anode, then convert into NCM811, thus extending the lifespan of the battery without the introduction of inactive elements. By the benefit of Li‐rich cathode and high reversibility of Li metal on Cu foil, the anode‐free pouch cells enable to achieve 447 Wh kg−1 energy density and 84 % capacity retention after 100 cycles in the condition of limited electrolyte addition (E/C ratio of 2 g Ah−1). [ABSTRACT FROM AUTHOR]

The commercialization of rechargeable Li metal batteries is hindered by dendrite growth and volumetric variation. Herein, we report a Li-rich dual-phase Li-Cu alloy with built-in 3D conductive skeleton to replace conventional planar Li anode. The Li-Cu alloy is simply prepared by fusion of Li and Cu metals at a relatively low-temperature of 500 °C, followed by a cooling process where phase-segregation leads to metallic Li phase distributed in the network of LiCu x solid solution phase. Different from the common Li alloy, the electrochemical alloying reaction between Li and Cu metals is not observed. Therefore, the lithiophilic LiCu x nanowires guides conformal plating of Li and the porous framework provides superior dimensional stability for the anode. This unique ferroconcrete-like structure of Li-Cu alloy enables dendrite-free Li plating for an expanded cycling lifetime. Constructing a new type of Li alloy with in situ formed electrochemically inactive framework is a promising and easily scaled-up strategy toward practical application of Li metal anodes. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries have captured widespread attention for grid-scale energy storage owing to the natural abundance of sodium. The performance of such batteries is limited by available electrode materials, especially for sodium-ion layered oxides, motivating the exploration of high compositional diversity. How the composition determines the structural chemistry is decisive for the electrochemical performance but very challenging to predict, especially for complex compositions. We introduce the “cationic potential” that captures the key interactions of layered materials and makes it possible to predict the stacking structures. This is demonstrated through the rational design and preparation of layered electrode materials with improved performance. As the stacking structure determines the functional properties, this methodology offers a solution toward the design of alkali metal layered oxides. [ABSTRACT FROM AUTHOR]

Mass dissolution is one main problems for cathodes in aqueous electrolytes due to the strong polarity of water molecules. In principle, mass dissolution is a thermodynamically favorable process as determined by the Gibbs free energy. However, in real situations, dissolution kinetics, which include viscosity, dissolving mass mobility, and interface properties, are also a critical factor influencing the dissolution rate. Both thermodynamic and kinetic dissolving factors can be regulated by the ratio of salt to solvent in the electrolyte. In this study, concentration‐controlled cathode dissolution is investigated in a susceptible Na3V2(PO4)3 cathode whose time‐, cycle‐, and state‐of‐charge‐dependent dissolubility are evaluated by multiple electrochemical and chemical methods. It is verified that the super‐highly concentrated water‐in‐salt electrolyte has a high viscosity, low vanadium ion diffusion, low polarity of solvated water, and scarce solute−water dissolving surfaces. These factors significantly lower the thermodynamic‐controlled solubility and the dissolving kinetics via time and physical space local mass interfacial confinement, thereby inducing a new mechanism of interface concentrated‐confinement which improves the cycling stability in real aqueous rechargeable sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Na‐ion batteries have experienced rapid development over the past decade and received significant attention from the academic and industrial communities. Although a large amount of effort has been made on material innovations, accessible design strategies on peculiar structural chemistry remain elusive. An approach to in situ construction of new Na‐based cathode materials by substitution in alkali sites is proposed to realize long‐term cycling stability and high‐energy density in low‐cost Na‐ion cathodes. A new compound, [K0.444(1)Na1.414(1)][Mn3/4Fe5/4](CN)6, is obtained through a rational control of K+ content from electrochemical reaction. Results demonstrate that the remaining K+ (≈0.444 mol per unit) in the host matrix can stabilize the intrinsic K‐based structure during reversible Na+ extraction/insertion process without the structural evolution to the Na‐based structure after cycles. Thereby, the as‐prepared cathode shows the remarkably enhanced structural stability with the capacity retention of >78% after 1800 cycles, and a higher average operation voltage of ≈3.65 V versus Na+/Na, directly contrasting the non‐alkali‐site‐substitution cathode materials. This provides new insights into alkali‐site‐substitution constructing advanced Na‐ion cathode materials. [ABSTRACT FROM AUTHOR]

Safety requirements stimulate Na-based batteries to evolve from high-temperature Na–S batteries to room-temperature Na-ion batteries (NIBs). Even so, NIBs may still cause thermal runaway due to the external unexpected accidents and internal high activity of electrodes or electrolytes, which has not been comprehensively summarized yet. In this review, we summarize the significant advances about the failure mechanisms and related strategies to build safer NIBs from the selection of electrodes, electrolytes and the construction of electrode/electrolyte interfaces. Considering the safety risk, the thermal behaviors are emphasized which will deepen the understanding of thermal stability of different NIBs and accelerate the exploitation of safe NIBs. [ABSTRACT FROM AUTHOR]

Material innovation on high‐performance Na‐ion cathodes and the corresponding understanding of structural chemistry still remain a challenge. Herein, we report a new concept of high‐entropy strategy to design layered oxide cathodes for Na‐ion batteries. An example of layered O3‐type NaNi0.12Cu0.12Mg0.12Fe0.15Co0.15Mn0.1Ti0.1Sn0.1Sb0.04O2 has been demonstrated, which exhibits the longer cycling stability (ca. 83 % of capacity retention after 500 cycles) and the outstanding rate capability (ca. 80 % of capacity retention at the rate of 5.0 C). A highly reversible phase‐transition behavior between O3 and P3 structures occurs during the charge‐discharge process, and importantly, this behavior is delayed with more than 60 % of the total capacity being stored in O3‐type region. Possible mechanism can be attributed to the multiple transition‐metal components in this high‐entropy material which can accommodate the changes of local interactions during Na+ (de)intercalation. This strategy opens new insights into the development of advanced cathode materials. [ABSTRACT FROM AUTHOR]

Material innovation on high‐performance Na‐ion cathodes and the corresponding understanding of structural chemistry still remain a challenge. Herein, we report a new concept of high‐entropy strategy to design layered oxide cathodes for Na‐ion batteries. An example of layered O3‐type NaNi0.12Cu0.12Mg0.12Fe0.15Co0.15Mn0.1Ti0.1Sn0.1Sb0.04O2 has been demonstrated, which exhibits the longer cycling stability (ca. 83 % of capacity retention after 500 cycles) and the outstanding rate capability (ca. 80 % of capacity retention at the rate of 5.0 C). A highly reversible phase‐transition behavior between O3 and P3 structures occurs during the charge‐discharge process, and importantly, this behavior is delayed with more than 60 % of the total capacity being stored in O3‐type region. Possible mechanism can be attributed to the multiple transition‐metal components in this high‐entropy material which can accommodate the changes of local interactions during Na+ (de)intercalation. This strategy opens new insights into the development of advanced cathode materials. [ABSTRACT FROM AUTHOR]

Replacing the commonly used nonaqueous liquid electrolytes in rechargeable sodium batteries with polymer solid electrolytes is expected to provide new opportunities to develop safer batteries with higher energy densities. However, this poses challenges related to the interface between the Na‐metal anode and polymer electrolytes. Driven by systematically investigating the interface properties, an improved interface is established between a composite Na/C metal anode and electrolyte. The observed chemical bonding between carbon matrix of anode with solid polymer electrolyte, prevents delamination, and leads to more homogeneous plating and stripping, which reduces/suppresses dendrite formation. Full solid‐state polymer Na‐metal batteries, using a high mass loaded Na3V2(PO4)3 cathode, exhibit ultrahigh capacity retention of more than 92 % after 2 000 cycles and over 80 % after 5 000 cycles, as well as the outstanding rate capability. [ABSTRACT FROM AUTHOR]

Replacing the commonly used nonaqueous liquid electrolytes in rechargeable sodium batteries with polymer solid electrolytes is expected to provide new opportunities to develop safer batteries with higher energy densities. However, this poses challenges related to the interface between the Na‐metal anode and polymer electrolytes. Driven by systematically investigating the interface properties, an improved interface is established between a composite Na/C metal anode and electrolyte. The observed chemical bonding between carbon matrix of anode with solid polymer electrolyte, prevents delamination, and leads to more homogeneous plating and stripping, which reduces/suppresses dendrite formation. Full solid‐state polymer Na‐metal batteries, using a high mass loaded Na3V2(PO4)3 cathode, exhibit ultrahigh capacity retention of more than 92 % after 2 000 cycles and over 80 % after 5 000 cycles, as well as the outstanding rate capability. [ABSTRACT FROM AUTHOR]

Reversibly intercalating ions into host materials for electrochemical energy storage is the essence of the working principle of rocking-chair type batteries. The most relevant example is the graphite anode for rechargeable Li-ion batteries which has been commercialized in 1991 and still represents the benchmark anode in Li-ion batteries 30 years later. Learning from past lessons on alkali metal intercalation in graphite, recent breakthroughs in sodium and potassium intercalation in graphite have been demonstrated for Na-ion batteries and K-ion batteries. Interestingly, some significant differences proved to exist for the intercalation of Na+ and K+ into graphite compared with the Li+ case. Such different host–guest interactions are unique depending on the host materials and electrolytes, which greatly contribute to a deeper understanding of intercalation-type electrode materials for next generation alkali metal ion batteries. This review summarizes significant advances from both experimental and theoretical calculations with a focus on comparing the intercalation of three alkali metal ions (Li+, Na+, K+) into graphite and aims to clarify the intimate host–guest relationships and the underlying mechanisms. New approaches developed to achieve favorable intercalation coupled with the challenges in this field are also discussed. We also extrapolate alkali metal ion intercalation in graphite to mono-/multi-valent ions in layered electrode materials, which will deepen the understanding of intercalation chemistry and provide guidance to explore new guests and hosts. [ABSTRACT FROM AUTHOR]

The comprehensive performance of carbon anodes for Na‐ion batteries (NIBs) is largely restricted by their inferior rate capability and safety issues. Herein, a slope‐dominated carbon anode is achieved at a low temperature of 800 °C, which delivers a high reversible capacity of 263 mA h g−1 at 0.15C with an impressive initial Coulombic efficiency (ICE) of 80 %. When paired with the NaNi1/3Fe1/3Mn1/3O2 cathode, the reversible capacity at 6C is still 75 % of that at 0.15C, and 73 % of the capacity is retained after 1000 cycles at 3C. The enhanced Na storage performance could be attributed to the unique microstructure with randomly oriented short carbon layers and the relatively higher defect concentration. Given its robustness, such a low‐temperature carbonization strategy could also be applicable to other precursors and provide a new opportunity to design slope‐dominated carbon anodes for high safety, low‐cost NIBs with excellent ICE and superior rate capability. Positive energy: The slope‐dominated carbon anode produced by the inverse low‐temperature strategy shows great potential for low‐cost and high‐safety Na‐ion batteries in terms of high specific capacity, impressive ICE, superior rate capability, and long cycle stability, without any doping, nano‐sizing, or pore‐creating procedures. [ABSTRACT FROM AUTHOR]

The comprehensive performance of carbon anodes for Na‐ion batteries (NIBs) is largely restricted by their inferior rate capability and safety issues. Herein, a slope‐dominated carbon anode is achieved at a low temperature of 800 °C, which delivers a high reversible capacity of 263 mA h g−1 at 0.15C with an impressive initial Coulombic efficiency (ICE) of 80 %. When paired with the NaNi1/3Fe1/3Mn1/3O2 cathode, the reversible capacity at 6C is still 75 % of that at 0.15C, and 73 % of the capacity is retained after 1000 cycles at 3C. The enhanced Na storage performance could be attributed to the unique microstructure with randomly oriented short carbon layers and the relatively higher defect concentration. Given its robustness, such a low‐temperature carbonization strategy could also be applicable to other precursors and provide a new opportunity to design slope‐dominated carbon anodes for high safety, low‐cost NIBs with excellent ICE and superior rate capability. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Sodium-based rechargeable batteries are very promising energy storage and conversion systems owing to their wide availability and the low cost of Na resources, which is beneficial to large-scale electric energy storage applications in future. In the context of attempting to achieve high-energy densities and low cost, multi-electron reaction materials for both cathodes and anodes are attracting significant attention due to high specific capacities involved. Here, we present a brief review on recently reported multi-electron reaction materials for sodium-based batteries. We mostly concentrate on true multi-electron reactions that involve individually valence changes greater than one per redox center, but in addition include materials in the discussion, which undergo multi-electron processes per formula unit. The theoretical gravimetric and volumetric (expanded state) capacities are studied for a broad range of examples. Then, the practically achievable volumetric energy density and specific energy of Na cells with hard carbon, sodium (Na), and phosphorus (P) anodes are compared. For this purpose, various data are recalculated and referred to the same basis cell. The results show the potential superiority of the cells using multi-electron reaction materials and provide an intuitive understanding of the practically achievable energy densities in future Na-based rechargeable batteries. However, these multi-electron reaction materials are facing several key challenges, which are preventing their high-performance in current cells. In order to overcome them, general strategies from particle design to electrolyte modification are reviewed and several examples in both cathode and anode materials using such strategies are studied. Finally, future trends and perspectives for achieving promising Na-based batteries with better performance are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Disordered carbons have captured extensive interest as anode materials for Na‐ion batteries (NIBs) due to the abundant resources, competitive specific capacity, and low cost. Here, a facile strategy of pre‐oxidation is successfully adopted to tune the microstructure of carbon anode to facilitate sodium storage. Pitch is selected as the low‐cost and high carbon yield precursor. An easy pre‐oxidation treatment in air can enable pitch to realize an effective structural conversion from ordered to disordered at further carbonization processes. Compared with the carbonized pristine pitch, the carbonized pre‐oxidation pitch increases the carbon yield from 54 to 67%, the sodium storage capacity from 94.0 to 300.6 mAh g−1, and the initial Coulombic efficiency from 64.2 to 88.6%. Experiment results reveal that the introduction of oxygen based functional groups is the key to achieve the highly disordered structure, not only ensuring the cross‐linkage during low‐temperature pre‐oxidation process but also suppressing the carbon structure from melting and rearranging in the high‐temperature carbonization process. Most importantly, this facile pre‐oxidation strategy can also be extended to other carbon precursors to facilitate the low‐cost and high‐performance disordered carbon anodes for NIBs and beyond. [ABSTRACT FROM AUTHOR]

Abstract: Due to their numerous advantages, such as high specific capacity, lithium–sulfur batteries (Li–S batteries) have attracted much attention as next‐generation energy storage systems. To meet future needs for commercial application, Li–S batteries will require both improved cycle life and high energy density. It is of critical importance to understand the fundamental mechanisms in Li–S systems to further improve the overall battery performance. Various advanced characterization techniques, over the past few years, have proven their important role in promoting the mechanism understanding for Li–S batteries. Here, the recent progress of mechanism understanding, including redox reactions, Li polysulfides dissolution, etc., in Li–S systems based on the advanced characterization techniques is reviewed. Special focus is placed on how these advanced characterization techniques are being employed and what characteristic or capability they possess. The importance of the combination of multiple characterization techniques, differences between ex situ and in situ experimental methods, as well as effects of characterization conditions in Li–S batteries are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Hard carbon has long been considered the leading candidate for anode materials of Na‐ion batteries. Intensive research efforts have been carried out in the search of suitable carbon structure for an improved storage capability. Herein, an anode based on multishelled hollow carbon nanospheres, which are able to deliver an outstanding electrochemical performance with an extraordinary reversible capacity of 360 mAh g−1 at 30 mA g−1, is designed. An interesting dependence of the electrochemical properties on the multishelled structural features is identified: with an increase in the shell number of the model carbon materials, the sloping capacity in the charge/discharge curve remains almost unchanged while the plateau capacity continuously increases, suggesting an adsorption‐filling Na‐storage mechanism for the multishelled hollow hard carbon materials. The findings not only provide new perspective in the structural design of high‐performance anode materials, but also shed light on the complicated mechanism behind Na‐storage by hard carbon. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Sodium-ion batteries (NIBs) show great prospect on the energy storage applications benefiting from their low cost and the abundant Na resources despite the expected lower energy density compared with lithium-ion batteries (LIBs). To further enhance the competitive advantage, especially in energy density, developing the high-capacity carbon anode materials can be one of the effective approaches to realize this goal. Herein, we report a novel carbon anode made from charcoal with a high capacity of ∼400 mAh g−1, wherein about 85% (>330 mAh g−1) of its total capacity is derived from the long plateau region below ∼0.1 V, which differs from those of typical hard carbon materials (∼300 mAh g−1) in NIBs but is similar to the graphite anode in LIBs. When coupled with air-stable Na 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O 2 oxide cathode, a high-energy density of ∼240 Wh kg−1 is achieved with good rate capability and cycling stability. The discovery of this promising carbon anode is expected to further improve the energy density of NIBs towards large-scale electrical energy storage. [ABSTRACT FROM AUTHOR]