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Rechargeable lithium-ion batteries with high energy density that can be safely charged and discharged at high rates are desirable for electrified transportation and other applications 1-3. However, the sub-optimal intercalation potentials of current anodes result in a trade-off between energy density, power and safety. Here we report that disordered rock salt 4,5 Li3+xV2O5 can be used as a fast-charging anode that can reversibly cycle two lithium ions at an average voltage of about 0.6 volts versus a Li/Li + reference electrode. The increased potential compared to graphite 6,7 reduces the likelihood of lithium metal plating if proper charging controls are used, alleviating a major safety concern (short-circuiting related to Li dendrite growth). In addition, a lithium-ion battery with a disordered rock salt Li3V2O5 anode yields a cell voltage much higher than does a battery using a commercial fastcharging lithium titanate anode or other intercalation anode candidates (Li3VO4 and LiV0.5Ti0.5S2) 8,9. Further, disordered rock salt Li3V2O5 can perform over 1,000 charge-discharge cycles with negligible capacity decay and exhibits exceptional rate capability, delivering over 40 per cent of its capacity in 20 seconds. We attribute the low voltage and high rate capability of disordered rock salt Li3V2O5 to a redistributive lithium intercalation mechanism with low energy barriers revealed via ab initio calculations. This low-potential, high-rate intercalation reaction can be used to identify other metal oxide anodes for fast-charging, long-life lithium-ion batteries.

CONSPECTUS: Lithium ion batteries (LIBs) not only power most of today's hybrid electric vehicles (HEV) and electric vehicles (EV) but also are considered as a promising system for grid-level storage. Large-scale applications for LIBs require substantial improvement in energy density, cost, and lifetime. Layered lithium transition metal (TM) oxides, in particular, Li(Ni x Mn y Co z )O 2 (NMC, x + y + z = 1) are the most promising candidates as cathode materials with the potential to increase energy densities and lifetime, reduce costs, and improve safety. In order to further boost Li storage capacity, a great deal of attention has been directed toward developing Ni-rich layered TM oxides. However, structural disorder as a result of Ni/Li exchange in octahedral sites becomes a critical issue when Ni content increases to high values, as it leads to a detrimental effect on Li diffusivity, cycling stability, first-cycle efficiency, and overall electrode performance. Increasing effort has been dedicated to improving the electrochemical performance of layered TM oxides via reduction of cationic mixing. Therefore, it is important to summarize this research field and provide in-depth insight into the impact of Ni/Li disordering on electrochemical characteristics in layered TM oxides and its origin to accelerate the future development of layered TM oxides with high performance. In this Account, we start by introducing the Ni/Li disordering in LiNiO 2 , the experimental characterization of Ni/Li disordering, and analyzing the impact of Ni/Li disordering on electrochemical characteristics of layered TM oxides. The antisite Ni in the Li layer can limit the rate performance by impeding the Li ion transport. It will also degrade the cycling stability by inducing anisotropic stress in the bulk structure. Nevertheless, the antisite Ni ions do not always bring drawbacks to the electrochemical performance; some studies including our works found that it can improve the thermal stability and the cycling structure stability of Ni-rich NMC materials. We next discuss the driving forces and the kinetic advantages accounting for the Ni/Li exchange and conclude that the steric effect of cation size and the magnetic interactions between TM cations are the two main driving forces to promote the Ni/Li exchange during synthesis and the electrochemical cycling, and the low energy barrier of Ni 2+ migration from the 3a site in the TM layer to the 3b site in the Li layer further provides a kinetic advantage. Based on this understanding, we then review the progress made to control the Ni/Li disordering through three main ways: (i) suppressing the driving force from the steric effect by ion exchange; (ii) tuning the magnetic interaction by cationic substitution; (iii) kinetically controlling Ni migration. Finally, our brief outlook on the future development of layered TM oxides with controlled Ni/Li disordering is provided. It is believed that this Account will provide significant understanding and inspirations toward developing high-performance la...

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Aqueous electrolytes come with an intrinsic narrow electrochemical stability window (1.23 V). Expanding this window represents significant benefits in both fundamental science and practical battery applications. Recent breakthroughs made via super-concentration have resulted in >3.0 V windows, but fundamental understanding of the related mechanism is still absent. In the present work, we examined the widened window (2.55 V) of a super-concentrated (unsaturated) aqueous solution of LiNO 3 through both theoretical and spectral analyses and discovered that a local structure of intimate Li + -water interaction arises at super-concentration, generating (Li + (H 2 O) 2 ) n polymer-like chains to replace the ubiquitous hydrogen bonding between water molecules. Such structure is mainly responsible for the expanded electrochemical stability window. Further theoretical and experimental analyses quantitatively differentiate the contributions to this window, identifying the kinetic factor (desolvation) as the main contributor. Such molecular-level and quantitative understanding will further assist in tailor designing more effective approaches to stabilizing water electrochemically.

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Historically long accepted to be the singular root cause of capacity fading, transition metal dissolution has been reported to severely degrade the anode. However, its impact on the cathode behavior remains poorly understood. Here we show the correlation between capacity fading and phase/surface stability of an LiMn2O4 cathode. It is revealed that a combination of structural transformation and transition metal dissolution dominates the cathode capacity fading. LiMn2O4 exhibits irreversible phase transitions driven by manganese(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks results in serious manganese dissolution. Meanwhile, fast manganese dissolution in turn triggers irreversible structural evolution, and as such, forms a detrimental cycle constantly consuming active cathode components. Furthermore, lithium-rich LiMn2O4 with lithium/manganese disorder and surface reconstruction could effectively suppress the irreversible phase transition and manganese dissolution. These findings close the loop of understanding capacity fading mechanisms and allow for development of longer life batteries.