Fabrication and Characterization of Lithium-Silicon Thick-Film Electrodes for High-Energy-Density Batteries

Abstract

We have developed a method to operate lithium-silicon (Li-Si) thick-film electrodes in a manner consistent with traction applications. Key to the operating strategy is the voltage control of the electrode. It is expected that strong reducing environments, created by operating the electrode at low potentials (near that of Li), reduce battery life. We show that operating Li-Si at higher potentials is also damaging, and this is counterintuitive in that common negative electrodes (e.g., graphites and titanates) do not suffer from this limitation. Arguments based on measured Coulombic efficiencies, cycle life tests, in-situ stress measurements, and high-resolution microscopy resolve the otherwise anomalous findings. We show that promising half-cell (cells constructed with a lithium counter electrode) cycling data are reflected in full cells that employ a 622-NMC positive electrode (Ni0.6Mn0.2Co0.2O2). Last, a modified hysteresis model, based in part on our earlier approach to treat NiMH (nickel metal hydride) cells, is shown to represent well the constant-current cycling data, and open questions associated with needed improvements in modeling Li-Si hysteresis and related low-current phenomena are highlighted.