Model-based state of charge estimation and observability analysis of a composite electrode lithium-ion battery

Composite electrode lithium-ion batteries can offer improved energy and power density, as well as increased cycle life compared to batteries with a single active material electrode. Both available power and cell life are functions of the local current allocated to each composite material, however there are no examples in literature of electrochemical-based models of composite electrode cells that are suitable for estimation and control. We present a reduced order, electrochemical model of a composite LiMn₂O₄ - LiNi_1/3Mn_1/3Co_1/3O₂ cell that predicts bulk and surface concentrations of each composite material, as well as the local current allocated to each material. Observability properties are analyzed by approximating the system as linear over certain operating conditions. A solution method is developed to use the model in an extended Kalman filter for online state of charge estimation, which is validated with experimental data.