Low resistance at LiNi1/3Mn1/3Co1/3O2 and Li3PO4 interfaces

We report the low resistance observed at the interface of LiNi1/3Mn1/3Co1/3O2 (NMC) and Li3PO4. First, we show the deposition of high-quality single-phase NMC (001) epitaxial thin films on Al2O3 (0001) substrates using pulsed laser deposition. Controlling the oxidation states of the three transition metals in NMC films is crucial for stable battery operation. However, in general, it is very difficult to simultaneously control the oxidation states of three elements in vacuum deposition processes. Tuning the oxygen partial pressure and temperature during deposition led to the growth of NMC thin films with ideal oxidation states (Ni2+, Mn4+, and Co3+), as confirmed using bulk-sensitive x-ray excited optical luminescence. Next, using the NMC epitaxial thin films, we prepared solid-state batteries that demonstrated stable operation and very low resistance at the solid electrolyte/electrode interfaces. These results provide insight into the fabrication of multi-transition-metal electrode thin film materials, which are important for investigating the mechanisms of lithium battery operation. Furthermore, the low interface resistance indicates that Li3PO4 and oxide electrode materials form very stable low-resistance interfaces.