Search

Disordered rocksalt cathodes have shown attractive electrochemical performance via oxygen redox, but are limited by a necessary Li‐excess level above the percolation threshold (x > 1.09 in LixTM2‐xO2, TM = transition metals) to obtain electrochemical activity. However, a relatively low‐Li content is essential to alleviate excessive oxygen charge compensation in rocksalt oxides. Herein, taking the homogeneous Li2MnO3 and LiMn2O4 as the starting point, disordered rocksalt‐like cathodes are prepared with initial Li‐deficient nanostructures, cation vacancies, and partial spinel‐type structures that provide a solution for the acquisition of fast Li+ percolation channels under Li‐deficient condition. As a result, the prepared sample exhibits high initial discharge capacity (363 mAh g−1) and energy density (1081 Wh kg−1). Advanced spectroscopy and in situ measurements observe highly reversible charge compensation during electrochemical process and assign coupled Mn‐ and O‐related redox contribution. Theoretical calculations also suggest the novel and chemical reversible trapped molecular O2 model in the rocksalt structure with vacancies, demonstrating a dual role of Li‐deficient structure in promoting cationic oxidation and extending reversible oxygen redox boundary. This work is expected to breakthrough the existing ideas of oxygen oxidation and opens up a higher degree of freedom in the design of disordered rocksalt structures. [ABSTRACT FROM AUTHOR]

Constructing stable electrode/electrolyte interphase with fast interfacial kinetics is vital for fast‐charging batteries. Herein, we investigate the interphase that forms between a high‐voltage Na3V2(PO4)2F3 cathode and the electrolytes consisting of 3.0, 1.0, or 0.3 M NaClO4 in an organic carbonate solvent (47.5 : 47.5 : 5 mixture of EC: PC: FEC) during charging up to 4.5 V at 55 °C. It is found that a higher anion/solvent ratio in electrolyte solvation structure induces anion‐dominated interphase containing more inorganic species and more anion derivatives (CxClOy), which leads to a larger interfacial Na+ transport resistance and more unfavorable gas evolution. In comparison, a low anion/solvent ratio derives stable anion‐tuned interphase that enables better interfacial kinetics and cycle ability. Importantly, the performance of a failed cathode is restored by triggering the decomposition of CxClOy species. This work elucidates the role of tuning interphase in fast‐charging batteries. [ABSTRACT FROM AUTHOR]

Spinel LiNi0.5Mn1.5O4 (LNMO), high‐voltage and high‐power density, is a very promising cathode candidate. Nevertheless, its lack of cycling stability has historically been long accepted as an inherent issue. Based on the above problem, a strategy is initiated to directly address Mn dissolution and unstable interface structure. A beneficial solid‐phase reaction occurs at the LNMO interface, transforming the spinel phase into two functional phases. One is the layered phase that provides electrochemical activity and supports charge transport. The other is the rock‐salt like phase induced by Li/Mn exchange that can inhibit the dissolution of Mn and provide inert protection. The Li/Mn exchange structure increases the diffusion energy barriers of Mn, which restrains the loss of Mn, proven by the bond valence sum calculation. The two phases are modulated successfully at the LNMO interface to balance the stable material structure and excellent charge transfer, obtaining a sample with excellent electrochemical performance. The capacity retention rate of modified LNMO is 15% higher than that of the pristine sample after 500 cycles. The preparation method does not utilize any dopants or coatings and can play a guiding role in addressing issues regarding structural stability and electrochemical performance for cathode materials. [ABSTRACT FROM AUTHOR]

Achieving fast‐charging capabilities in Li‐ion batteries (LIBs)—charging 80% of the battery capacity within 15 minutes—while maintaining an acceptable cycle life remains challenging due to various polarizations occurring at elevated charge rates. Such a goal is more tough at subzero, as temperature reduction slows the kinetics process including electrolyte mass transport and electrode charge transfer, substantially increasing the risk of lithium plating. Herein, it is found that adding LiFSI to a LiPF6 carbonate‐based electrolyte alters the Li+ solvation structure, endowing the dual‐salt electrolyte with a higher Li+ diffusion coefficient and lower desolvation energy. Benefit from the smaller structural change and the formation of a robust, conductive solid electrolyte interphase, the 12Ah‐pouch cells based on LiNi0.52Co0.2Mn0.28O2 cathodes and graphite anodes demonstrate fast‐charging capabilities and stable cycling performance across a wide temperature range of −20 to 50 ℃: charging 89% and 93% of pouch cell capacity within 4 minutes at 25 and 50 ℃ and 82% within 15 minutes at −20 ℃, maintaining capacity retention of 94% after 2000 cycles at 8C at 0 ℃ and 89% after 350 cycles at −20 ℃ at 4C. This work might offer new insights into enhancing the fast‐charging capabilities of LIBs under extreme conditions. [ABSTRACT FROM AUTHOR]