In/ex-situ Raman spectra combined with EIS for observing interface reactions between Ni-rich layered oxide cathode and sulfide electrolyte

The interfacial instability between Ni-rich layered oxide cathodes and sulfide electrolytes is a serious problem, leading to poor electrochemical properties of all-solid-state lithium batteries (ASSLB). The chemical/electrochemical side reactions are considered to be the origin of the interfacial deterioration. However, the influence of chemical and electrochemical side reactions on the interfacial deterioration is rarely studied specifically. In this work, the deterioration mechanism of the interface between LiNi0.85-xCo0.15AlxO2 and Li10GeP2S12 is investigated in detail by combining in/ex-situ Raman spectra and Electrochemical Impedance Spectroscopy (EIS). It can be determined that chemical side reaction between LiNi0.8Co0.15Al0.05O2 and Li10GeP2S12 will occur immediately once contacted, and the interfacial deterioration becomes more serious after charge-discharge process under the dual effects of chemical and electrochemical side reactions. Moreover, our research reveals that the interfacial stability and the cycle performance of ASSLB can be greatly enhanced by increasing Al-substitution for Ni in LiNi0.85-xCo0.15AlxO2. In particular, the capacity retention of LiNi0.6Co0.15Al0.25O2 cathode after 200 cycles can reach 81.9%, much higher than that of LiNi0.8Co0.15Al0.05O2 cathode (12.5%@200 cycles). This work gives an insight to study the interfacial issues between Ni-rich layered oxide cathode and sulfide electrolyte for ASSLBs.