Optimization of 10-μm, sputtered, LiCoO2 cathodes to enable higher energy density solid state batteries

An investigation of the morphology of lithium-cobalt-oxide (LCO) films for the production of energy dense, solid-state, thin-film batteries with cathodes in the 10 μm thickness range is described. It was found that, in order to achieve devices with over 80% charge utilization, capable of extended cycling, with cathodes greater than 5 μm, LCO film texture must be actively controlled to maintain orientations preferential to Li diffusion. It was found that the oxygen: argon ratio during sputtering of the cathode plays a critical role in determining the crystallographic texture of LCO films thicker than 5 μm. Specifically, LCO films deposited with an oxygen presence of as little as 4% in Ar showed no detectable (003) peak following anneal. Working cells were fabricated using texture-controlled 10 μm cathodes, exhibiting discharge capacities of 60 μAh/cm2-μm (600 μAh/cm2) at C/10, with greater than 95% capacity retention after 100 cycles at a C/5 discharge rate. Cells with 10 μm cathodes and un-controlled (predominantly (003)) texture were capable of achieving similar capacities, however their rate and cycling performance were severely diminished.