Optimal charging method for lithium ion batteries using a universal voltage protocol accommodating aging

An effective optimum charging technique for lithium ion batteries using a universal voltage protocol (UVP) that can accommodate cell aging is presented here. This charging method demands less learning to varying state-of-health (SOH) conditions with potential to improve charging efficiency and cycle life. The simplicity of UVP makes the implementation easier than the conventional constant current-constant voltage (CC-CV)-based methods. Here, the mathematical formulation, optimization targets (e.g. minimal time) and constraints (terminal voltages and other instrumental and cell electrochemistry-limited ones) are explained from the protocol design considerations. An equivalent circuit model was used and its parameters derived from the analysis of test data, which could yield a nonlinear varying current profile (VCP) by simulation and a genetic algorithm-based optimization. Both UVP and VCP were used in the validation to illustrate better charging efficiency and capacity retention, which showed a much improved cycle life.