Clean Solid-Electrolyte/Electrode Interfaces Double the Capacity of Solid-State Lithium Batteries

Solid-state lithium (Li) batteries using spinel-oxide electrode materials such as LiNi_0.5Mn_1.5O₄ are promising power supplies for mobile devices and electric vehicles. Here, we demonstrate stable battery cycling between the Li₀Ni_0.5Mn_1.5O₄ and Li₂Ni_0.5Mn_1.5O₄ phases with working voltages of approximately 2.9 and 4.7 V versus Li/Li⁺ in solid-state Li batteries with contamination-free clean Li₃PO₄/LiNi_0.5Mn_1.5O₄ interfaces. This clean interface has the effect of doubling the capacity of conventional battery cycling between the Li₀Ni_0.5Mn_1.5O₄ and Li₁Ni_0.5Mn_1.5O₄ phases. We also investigated the structural changes between the Li₀Ni_0.5Mn_1.5O₄ and Li₂Ni_0.5Mn_1.5O₄ phases during battery cycling. Furthermore, we found an inhomogeneous distribution of the Li₂Ni_0.5Mn_1.5O₄ phase in the LiNi_0.5Mn_1.5O₄ electrode, induced by spontaneous Li migration after the formation of the Li₃PO₄/LiNi_0.5Mn_1.5O₄ interface. These results indicate that the formation of a contamination-free clean Li₃PO₄/LiNi_0.5Mn_1.5O₄ interface is key to increase the battery capacity.