First-Principles Study of Microscopic Electrochemistry at the LiCoO₂ Cathode/LiNbO₃ Coating/β-Li₃PS₄ Solid Electrolyte Interfaces in an All-Solid-State Battery

High interfacial resistance between electrode and solid electrolyte (SE) is one of the major challenges for the commercial application of all-solid-state batteries (ASSBs), and coating at the interface is an effective way for decreasing the resistance. However, microscopic electrochemistry especially for the electrochemical potential and the distribution of Li+ at the interface has not been well established yet, impeding the in-depth understanding of interfacial Li+ transport. Herein, we have introduced a potential energy profile for Li+, ηLi+, and demonstrated that the interfacial ηLi+ can be evaluated from the calculated interfacial Li vacancy formation energy or the bulk vacancy formation energy and the interface band alignment. Through computational analysis of the representative LiCoO2 cathode/LiNbO3 coating/β-Li3PS4 SE interfaces using the novel interface structure prediction scheme based on the CALYPSO method, we found that ηLi+ at the LiCoO2/β-Li3PS4 interface is highly disordered under the influence of the interface reconstruction and is rather electronic conductive. Insertion of LiNbO3 coating can effectively decrease the preference of ion mixing. Besides, the appropriate changes in band alignments lead to a decrease of difference in the interfacial ηLi+ and lower resistances at the interfaces. The results provide a reliable explanation for the effectiveness of the coating layer observed experimentally. Furthermore, our study provides a guidance for the future simulation of the microscopic electrochemistry at the electrode/SE interfaces in ASSBs.