Modulating electrostatic barriers at <i>β</i> -Li3PS4/Li <i>x</i> CoO2 interfaces through LiAlO2 interlayer in an all-solid-state battery

The high interfacial resistance between an electrode and a solid electrolyte remains a critical problem needed to be addressed for the practical application of all-solid-state batteries (ASSBs). While introducing an interlayer is a promising strategy to mitigate this resistance, the unclear action mechanism of the interlayer on the interfacial Li+ transport impedes further development. Herein, employing a first-principles-informed thermodynamic model, we demonstrate an effective approach for modulating the space–charge layers and electrostatic barriers for Li+ transport at the β-Li3PS4/LixCoO2 interfaces by incorporating a LiAlO2 interlayer in Li/β-Li3PS4/LixCoO2 ASSBs. The potential profile calculations reveal a high discharge barrier for Li-ion migration at the β-Li3PS4/LiCoO2 cathode interface, hindering the discharge process. By contrast, at the β-Li3PS4/LiAlO2/LiCoO2 interface, a lower interface potential drop is achieved to assist Li+ transport for fast discharging. Further analysis of the charge transfer and the band alignment reveals that the reduced interface potential drop stems from the synergistic effects of LiAlO2's Fermi level, chemical potential, and ionization potential. This work enhances the understanding of the interlayer's impact on interfacial Li+ transport and provides design principles for interlayer materials in ASSBs.