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Halide solid electrolytes have been considered as the most promising candidates for practical high-voltage all-solid-state lithium-ion batteries (ASSLIBs) due to their moderate ionic conductivity and good interfacial compatibility with oxide cathode materials. Aliovalent ion doping is an effective strategy to increase the ionic conductivity of halide electrolytes. However, the effects of ion doping on the electrochemical stability window of halide electrolytes and carbon additive on electrochemical performance are still unclear by far. Herein, a series of Zr-doped Li3–xEr1–xZrxCl6halide solid electrolytes (SEs) are synthesized through a mechanochemical method and the effects of Zr substitution on the ionic conductivity and electrochemical stability window are systematically investigated. Zr doping can increase the ionic conductivity, whereas it narrows the electrochemical stability window of the Li3ErCl6electrolyte simultaneously. The optimized Li2.6Er0.6Zr0.4Cl6electrolyte exhibits both a high ionic conductivity of 1.13 mS cm–1and a high oxidation voltage of 4.21 V. Furthermore, carbon additives are demonstrated to be beneficial for achieving high discharge capacity and better cycling stability and rate performance for halide-based ASSLIBs, which are completely different from the case of sulfide electrolytes. ASSLIBs with uncoated LiCoO2cathode and carbon additives exhibit a high discharge capacity of 147.5 mAh g–1and superior cycling stability with a capacity retention of 77% after 500 cycles. This work provides an in-depth understanding of the influence of ion doping and carbon additives on halide solid electrolytes and feasible strategies to realize high-energy-density ASSLIBs.

Li-rich Mn-based layered oxide (LMLO) cathode materials have high-capacity and high-energy density, which are highly potential for next generation Li-ion batteries; however, their disadvantages of low initial coulombic efficiency, poor cyclic stability, large voltage fading during cycling and poor rate capability hinder their practical applications. In this work, a novel surface modification strategy to improve the electrochemical properties of LMLO cathodes is developed, where a highly reductive compound of LiBH4is adopted as an additive to a conventional electrolyte. Examined by a conventional LMLO material of Li1.2Ni0.13Co0.13Mn0.54O2- (L1.2M0.54LO), the cyclic stability and rate capability of the cathode are significantly improved when 0.3 wt.% LiBH4is added. The cathode has an initial reversible discharge capacity of 280 mAh g−1at 20 mA g−1, showing the capacity retention of 94.3% after 100 cycles. A capacity of 193 mAh g−1maintains after 300 cycles at 200 mA g−1, corresponding to the capacity retention of 86.2%, and the capacity reaches as high as 138 mAh g−1at 2000 mA g−1. It is found that partial transition metals (TMs) at the surface of the L1.2M0.54LO particles are reduced by LiBH4during the initial several cycles of activation, resulting in an in situformation of a stable and lithium-diffusion feasible spinel structure surface coating in thickness of several nanometers with atomic match to the bulk particle. The surface coating not only retards the dissolution of the TMs from L1.2M0.54LO to the electrolyte, stabilizing the crystal structure during cycling, but also facilitates the lithium diffusion. As a result, the cyclic stability and rate capability of the cathode are evidently improved. The method is facile, scalable, and low cost, which has potential for commercial utilization.