(Invited) Calendar Life Prognosis in Si-Containing Li-Ion Batteries

Abstract

Because of their high-gravimetric capacities, use of Si-containing anodes in Li-ion batteries can lead to a big jump in energy densities. The calendar life of Si in these batteries however is difficult to prognose and try to extend because of the highly chemical reactivity of lithium silicides at high states of charge (SOC). The control of lithium consumption and loss of inventory to solid electrolyte interphase (SEI) growth (and re-growth), and potential impedance growth contributes greatly to the shortened calendar life of, perhaps, one year to 80% energy retention. There is a US Department of Energy DOE program (Silicon Consortium Project or SCP) that currently is confronting the basic and applied science problems of Si with the hopes of developing > 10 year calendar life for Si-containing cells. We have been developing a constant voltage testing protocol using LFP/Si cells in order to ascertain the irreversible capacity amount associated with the chemical and electrochemical side reactions on the Si side of this system. However, due to the slow Li-Si electrochemical equilibrium kinetics, continuing reversible lithiation results for 100s of hours, and thus a semi-quantitative estimate of the calendar life is not feasible. Reference performance tests (RPT) with capacity checks every month at some fixed SOC and temperature continue to provide the most reliable indicator of calendar life. We believe that the voltage hold tests do provide a qualitative solution or stage-gate to continuation of pursuit of solutions to calendar life limitations. In this presentation, I will discuss these issues and provide some solutions to partly solve the short calendar life of Si together with models to estimate the future life.