Mechanochemical reactions between polyanionic borate and residue Li2CO3 on LiCoO2 to stabilize cathode/electrolyte interface in sulfide-based all-solid-state batteries

Sulfide-based all-solid-state Li-ion batteries (ASSLIBs) are recognized as promising next-generation batteries, due to its advantage of high energy density, high safety and high Li+ diffusivity in sulfide solid electrolytes (SEs). However, interfacial instability between cathode (like LiCoO2) and sulfide SEs hinders its commercial applications. Herein, a simple mechanochemical strategy, which mechanically mixed polyanionic borate precursor and Li2CO3 residue on LiCoO2 (LCO) cathode with subsequent thermochemical reactions, was proposed to achieve analogous “solid electrolyte interphase (SEI)” to address such issues. The artificial SEI consists of crystalline LiBa(B3O5)3 (LBBO), Li3BO3 (LBO) and amorphous lithium boron oxide (Li-B-O). Therein, the former two endow high interfacial stability with SEs and ionic conductivity respectively, while the latter presented in the former interspace isolated the LCO cathode from Li10GeP2S12 (LGPS) solid electrolyte and constructed a continuous interlayer with LBBO and LBO. According to the phase diagram and direct observation through TEM, it is confirmed that a suitable ratio of raw LBBO precursor and Li2CO3 residue can realize an appropriate proportion of LBO to balance the interfacial stability and the diffusion of Li+ in obtained artificial interlayer, which enables high cyclability and rate performance in LCO/LGPS/Li-In ASSLIBs. Specifically, SEI with 9.4 mol.% LBO boosts an initial discharge capacity of 153.8 mAh g−1 (2.6–4.3 V (vs. Li/Li+), 0.1 C) with 74.4 % retention (150 cycles) and an excellent rate capability of 92.9 and 56.1 mAh g−1 at 1 C and 2 C respectively. Upon increased cut-off voltage of 4.5 V, an initial 167.3 mAh g−1 capacity (0.2 C) and 64.7 % retention (150 cycles) can also be achieved. The present strategy utilizing mechanochemical reactions between polyanionic borate and Li2CO3 residue to construct analogous SEI will offer fresh insights to stabilize the electrode/electrolyte interface of ASSLIBs derived from diverse polyanionic-type borates or phosphates, which can be widely used in other all-solid-state batteries with various cathodes and electrolytes.