First-Principles Study of Microscopic Electrochemistry at the LiCoO₂ Cathode/LiNbO₃ Coating/β-Li₃PS₄ Solid...

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⁺, η_Li, and demonstrated that the interfacial η_Li 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 η_Li 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 η_Li 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.