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Abstract Li-rich (LR) layered oxide cathode for high-energy-density Li-ion batteries are receiving considerable attention. However, their intrinsic issues hinder the implementation of LR in simultaneously achieving higher energy and power densities. Herein, a dual-conductive surface control strategy is proposed. This surface layer contains an electronic conductive carbon nanotube (CNT) skeleton and an ionic conductive heteroepitaxial spinel structure, which endows the LR with the light-weight and self-standing characteristic. As evidenced by prolonged electrochemical and structural evolution, this surface layer can reduce polarization, restrain structural distortion and facilitate fast electronic/ionic diffusion. Density functional theory (DFT) calculations demonstrate a higher electron conductivity with a narrower band gap across the CNT/LR interface than that of pure LR, and reveal a highly connective Li+ percolation network and reduced Li+ migration energies for the layered-spinel heterogeneous interface. The designed LR cathode presents a high energy density (1077 Wh kg−1 at 0.1 C), excellent rate capability (195 mAh g−1 at 10 C) and superior cycle stability. When utilized as an additive-free cathode for high-voltage full-battery, impressive energy density (645 Wh kg−1 based on the cathode and anode) and ultra-long cycle life (maintaining 87% capacity after 400 cycles) can be achieved. These results and this dual-conductive surface control strategy provide an exciting perspective and avenue for the further development of high-performance electrode material. Graphical abstract We propose a novel dual-conductive surface control strategy and new insight into the correlation between the surface structure and electrochemical reactivity to ameliorate the LR cathode's inherent issues. The specially designed surface layer endows the LR cathode with the light-weight and self-standing characteristic. The prolonged electrochemical/structural evolution analysis and theoretical study indicate that the designed surface layer can reduce polarization caused by the side reaction, stabilize LR to restrain the structural distortion, and facilitate the fast electronic/ionic diffusion. Image 1 Highlights • Propose a dual-conductive surface control strategy to construct light-weight, self-standing, CNT/spinel coated LR cathode. • DFT calculations reveal the electron distribution and narrowed the band gap of the CNT/LR interface model. • The layered-spinel hetero-interface equips highly connective Li+ percolation networks and reduced Li+ migration energies. • The designed LR cathode exhibits impressive energy density, excellent rate capability and superior cycle stability. [ABSTRACT FROM AUTHOR]

Abstract Ti-based compounds are considered as attractive anode materials for sodium-ion capacitors (SICs) due to their favorable safety and stability. However, achieving more Na+ intercalated sites and fast sodiation kinetics in Ti-based anodes is still challenging. Herein, a facile strategy to promote the electrochemical properties of H-titanates by regulating their electronic structure and Na+ diffusion kinetics through thermal-induced interlayer defect engineering is developed. The targeted distorted quasi-layered H-titanate (Q-LT) with abundant interlayer defects exhibits superfast and stable cycle performance (97% capacity retention after 10,000 cycles at 25 C) in Na-ion half-cells. Applied in the high-working voltage (1.5–4.5 V) SICs as additive anodes, high energy density (124 Wh kg−1) and competitive cycle stability (88% capacity retained after 5000 fast cycles) are achieved. The thermal-induced structure evolution in layered H-titanate has been probed by in-situ X-ray diffraction. First-principles density functional theory calculations demonstrate that the Q-LT is equipped with lower coordinate Ti-O polyhedral, higher delocalized Ti-O environment, narrowed band gap and reduced Na+ migration energies; bond valence sum maps expose the continuous Na+ diffusion pathways within the interlayer of Q-LT. This work may offer a conceptual advance in the understanding of the structure-function-performance relationship of titanates for energy storage. Graphical abstract A new thermal-induced interlayer defect engineering (IDE) has been proposed to target a novel distorted quasi-layered H-titanate (Q-LT), exhibiting superfast and stable cycle performance in SICs. Based on the first-principles calculations and bond valence sum (BVS) mismatch mapping, the quasi-layered configuration is equipped with lower coordinate Ti-O polyhedral, higher delocalized Ti-O environment, narrowed band gap, reduced Na+ migration energies and interconnected pathways, which endows Q-LT with unique crystallographic flexibility and fast electron/ion transportation. fx1 Highlights • Quasi-layered H-titanate (Q-LT) was tailored by the thermal-induced IDE strategy. • The structural evolution in layered H-titanate has been probed by the in-situ XRD. • BVS maps expose interconnected Na+ diffusion pathways within the interlayer of Q-LT. • DFT calculations reveal narrowed bandgap and reduced Na+ migration energies in Q-LT. [ABSTRACT FROM AUTHOR]

Well-aligned hierarchical heterostructures composed of hydrogen titanate (H 2 Ti 2 O 5 ·H 2 O, labeled as HTO) nanowire stems and anatase TiO 2 nanoparticle branches (HTO/TiO 2 NWAs) have been synthesized successfully on Ti-foil substrate as additive-free electrodes for hybrid Li-ion capacitors (LICs). The inner 3D HTO conductive scaffold consisted of vertically aligned nanowires and porous rooftop network is beneficial to large capacitance. Moreover, the countless anatase TiO 2 particles on the surface of HTO nanowires can enrich electro-active sites, reduce the ion and electron resistance, shorten Li-ion transport pathways and enhance structural stability. Owning to the synergistic effects of HTO and anatase TiO 2 , the electrodes deliver large capacitance, superior rate capability and excellent cycle stability. The HTO/TiO 2 //AC (activated carbon) hybrid system presents fascinating energy density (84.7 Wh kg −1 at 0.5 A g 1 ) and ultralong lifespan (78.5% capacity retention after 10000 cycles at 10.0 A g −1 within 0.0-4.0 V). Even at high power density of 20 kW kg −1 , an excellent energy density of 44.4 Wh kg −1 can be retained. Thus, the LIC assembled with HTO/TiO 2 NWAs anode and AC cathode can be a potential candidate as high-performance energy storage application. [ABSTRACT FROM AUTHOR]

The commercialization of sodium-ion batteries (SIBs) is tremendously limited as performance decline in extreme environments (such as below 0 ℃). This work proposes remarkable low-temperature (low-T) SIBs based on 0.5 M NaPF 6 diglyme electrolyte. By a series of in-depth analysis, including XPS, temperature-dependent EIS, in- and ex-situ XRD, etc., finding that the weakly solvated structure of Na+-diglyme is beneficial to accelerating diffusivity of Na+ and reducing charge transfer energy (from 461.9 to 158.6 meV), which is effectively to ameliorate the low-T sodium storage mechanism. Moreover, The NaF-rich cathode electrolyte interphase (CEI) formed in diglyme is conducive to stabilize the interfacial structure and accelerate transport of Na+. All these merits collectively lead to high adaptability of low-concentration diglyme-based electrolyte to low-T. It has been verified that this system delivers 95.6% of room-temperature (RT) capacity, and full-cell delivers huge superiority in lifespan (working stably for 10,000 cycles) at − 20 ℃. Even at − 60 ℃, the battery still attains high capacity density (79.2 mAh g−1). These results provide new research ideas for improving the low-T performance of energy storage equipment. A low-concentration electrolyte system of 0.5 M NaPF 6 in diglyme is developed to improve the low-temperature property of Na-ion batteries substantially. The assembled Na 3 V 2 (PO 4) 2 F 3 //Na 2 Ti 2 O 5 full cell delivers remarkable low-T performance including ultra-low operating-temperature (− 60 ℃) and superior rate capability (94 mAh g−1) especially the long cycle performance (cycling over 10,000 cycles) at 5 C at − 20 ℃. [Display omitted] • Diglyme electrolyte impacts the interfacial kinetics and electrode stability. • Weakly-solvated effect contributes to excellent adaptability at − 60 ℃. • A Na 3 V 2 (PO 4) 2 F 3 //Na 2 Ti 2 O 5 full cell with a long lifespan of 10,000 cycles. [ABSTRACT FROM AUTHOR]

Spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) is widely utilized because of its high-energy-density and high-voltage. Unfortunately, there is still much research to be done for LNMO due to its poor structural stability. Here, a strategy is confirmed to stabilize LNMO via modulating interstitial sites. The interstitial 16c sites of the octahedron are partially occupied by Ni2+ to suppress the migration and dissolution of manganese ions upon electrochemical cycling and stabilize lithium-ion vacancies in the state of charge. Unexpectedly, this protocol not only suppresses the phase separation restraining the phase boundary dislocations and stress but also decreases the magnitude of cell volume change during cycling, which originates from the change in Ni redox couple energy states. This two-pronged modification strategy endows the cathode material with a lower charge transfer barrier and faster Li+ transfer kinetics, revealing superior electrochemical performance. The regulated cathode material remains robust after 900 cycles at 1C and its capacity retention rate is 29% higher than that of the original sample. Our research is useful for providing a concrete example of how the electrochemical performance of spinel LNMO and other high voltage cathode materials can be enhanced. [Display omitted] • The interstitial 16c sites of the octahedron is partially occupied by Ni2+ to suppress the dissolution of manganese ions. • The change in Ni redox couple energy states restrains phase separation and decreases cell volume change during cycles. • The capacity retention rate of optimal LNMO is 29% higher than that of the original sample after 900 cycles at 1C. [ABSTRACT FROM AUTHOR]

Compared with Li-ions, it is difficult to achieve fast dynamics for Na/K-ion storage. H-titanates as potential candidates suffer from low theoretical capacity, limiting the energy density of full cells. Herein, we report an Sn(Ⅱ)/Sn(Ⅳ) gradient doping strategy to simultaneously realizes the construction of a disordered interface with abundant defects and well-organized interlayered structure with larger interlayer spacing in H-titanate. The interfacial-located Sn2+ with a larger ionic radius triggers surface structural distortion to realize a favorable electronic structure with a narrower bandgap. Meanwhile, the interlayer-located Sn4+ plays a pillar effect to enhance the structural stability and modify the interlayer ion transport channel. Based on the analysis of ex-situ XRD, time of flight secondary ion mass spectrometry and temperature-dependent EIS, it is found that Sn(Ⅱ)/Sn(Ⅳ) gradient doping can effectively enhance structural stability, lower charge transfers barrier and boost ion diffusion kinetics, then resulting in 2.4- and 1.5-fold improvement for Li-ion and Na-ion storage, high capacity of 223 mAh g−1 and long cycle stability over 1800 cycles for K-ion storage. When used as additive-free anodes for hybrid capacitors, impressive energy densities in Li/Na-ion systems and superior cycle stability in Na/K-ion configurations have been achieved. These findings indicating that Sn(Ⅱ)/Sn(Ⅳ) gradient doping strategy has significant advantages for fast and durable alkali-ion storage. A Sn(Ⅱ)/Sn(Ⅳ) gradient doping strategy is proposed to promote Li/Na/K-ion storage performance by facilitating ion diffusion kinetics and lowering charge transfer barrier, which is conducive to deeply understand the complex ion storage dynamics and charge transfer kinetics and provide new ideas for designing advanced energy storage materials. [Display omitted] • A Sn(Ⅱ)/Sn(Ⅳ) gradient doping is proposed to construct disordered interface and expand interlayer structure of HTO. • Sn(Ⅱ)/Sn(Ⅳ) gradient doping can effectively lower charge transfers barrier and boost ion diffusion kinetics. • 2.4- and 1.5-fold improvement in LIBs and SIBs, capacity of 223 mAh g-1 and long cycle stability in KIBs are achieved. • When used as additive-free anodes for hybrid capacitors, high energy densities and long cycle stability are obtained. [ABSTRACT FROM AUTHOR]

Na 3 V 2 (PO 4) 2 F 3 is a promising cathode candidate for sodium ion batteries due to its high working voltage. However, an "unknown" low-voltage plateau around ~3.3 V lowers its operating voltage and puzzles researchers. Herein, the reasons for its appearance are explored. It is found that the formation of the low-voltage plateau originates from the extra-generated [VO 6 ] induced by the fluorine loss during the synthesis. To enable better performance, a feasible strategy of stabilizing fluorine is proposed to eliminate the low-voltage plateau. It is demonstrated that this strategy can effectively guarantee the existence of fluorine and modulate the local electronic structure of V to maintain [VO 4 F 2 ] in Na 3 V 2 (PO 4) 2 F 3 phase, thus eliminating the undesirable plateau and achieving an operating-voltage increase of ~100 mV. Moreover, the enhanced structural stability and kinetics of the optimized Na 3 V 2 (PO 4) 2 F 3 cathode are confirmed by in-situ XRD. As expected, the Na 3 V 2 (PO 4) 2 F 3 cathode delivers higher energy density (446.4 Wh kg−1), better rate capability and longer cycling performance (89.2%@30 C after 1000 cycles). Furthermore, its excellent adaptability to wide temperature range (−25 °C–55 °C) and strong competence in Na 3 V 2 (PO 4) 2 F 3 ||hard carbon full-cell are verified. These excellent properties further qualify Na 3 V 2 (PO 4) 2 F 3 as a competitive cathode for sodium ion batteries. The strategy of stabilizing fluorine guarantees fluorine to maintain [VO 4 F 2 ] in Na 3 V 2 (PO 4) 2 F 3 cathode and suppress the formation of [VO 6 ], thus modulating the local electronic structure of V and eliminating the undesirable low-voltage plateaus (circled in purple dashed lines). [Display omitted] • Stabilizing fluorine to regulate local electronic structure around vanadium. • Eliminating low-voltage plateau to increase operating voltage of ~100 mV. • Optimizing structure to improve long-term durability and cyclic stability. [ABSTRACT FROM AUTHOR]

Lithium-rich materials, which exhibit high capacity due to the existence of anionic redox, are in highly demanded for high energy density Li ion batteries. Nevertheless, the low operating voltage and rapid voltage drop of Li-Rich cathodes are seen as the fatal issues, which result in reduced energy density and degraded energy quality of the batteries, limiting their further commercial application. Herein, we focus on the local electronic structure controlled by chemical composition (to prepared high Ni content Li-rich cathode) to improve the operating voltage and suppress voltage decay. Through detailed physical characterization, electrochemical analysis and theoretical calculations, we summarize three main factors for improving the voltage of lithium-rich materials: 1) Increasing the O-Ni2+/3+/Li+ content effectively regulates the coordination environment of oxygen in Li-rich materials, realizes the regulation of local electronic structure; 2) the substitution of Ni increases the oxidation state of TM ions, especially for Mn, to keep charge balance, so as to improve the operating voltage and suppress voltage decay; 3) adjusting local electronic structure shifts the TM 3d-O 2p bands and the non-bonding O 2p band to lower energy, leading to an increase in the redox reaction potential. This strategy provides a method to regulate the coupling reaction of cation and anion redox in Li-rich cathodes by compositional design, so as to realize the regulation of voltage. Furthermore, when the as-prepared high Ni content electrode assembled with Si/C anode into a full-cell, impressive operating voltage (~3.70 V) and long cycle life (72.29% capacity retention after 200 cycles at 1C) can be achieved. Our work provides an efficient and up-scalable strategy for the preparation of electrodes with high voltage and high useful energy density, and making them a rather promising cathode candidate for Li ion batteries. Location electronic structure tuned by chemical composition to greatly improve operating voltage of Li-rich cathode for Li-ion battery. Image 1 • Increasing O-Ni2+/3+/Li+ regulates coordination environment of oxygen, realizes regulation of local electronic structure. • The substitution of Ni increases the oxidation state of TM ions, improves the operating voltage and suppress voltage decay. • Adjusting local electronic structure shifts TM 3d-O 2p band and non-bonding O 2p band to lower energy. • High Ni electrode assembled with Si/C anode into a full-cell, impressive operating voltage and long cycle life achieved. [ABSTRACT FROM AUTHOR]