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Increased demand for hybrid and electric vehicles has motivated research to improve onboard state of charge (SOC) and state of health estimation (SOH). In particular, batteries with composite electrodes have become popular for automotive applications due to their ability to balance energy density, power density, and cost by adjusting the amount of each material within the electrode. SOH algorithms that do not use electrochemical-based models may have more difficulty maintaining an accurate battery model as the cell ages under varying degradation modes, such as lithium consumption at the solid-electrolyte interface or active material dissolution. Furthermore, efforts to validate electrochemical model-based state estimation algorithms with experimental aging data are limited, particularly for composite electrode cells. In this paper, we first present a reduced-order electrochemical model for a composite LiMn2O4-LiNi1/3Mn1/3Co1/3O2 electrode battery that predicts the surface and bulk lithium concentration of each material in the composite electrode, as well as the current split between each material. The model is then used in dual-nonlinear observers to estimate the cell SOC and loss of cyclable lithium over time. Three different observer types are compared: 1) the extended Kalman filter; 2) fixed interval Kalman smoother; and 3) particle filter. Finally, an experimental aging campaign is used to compare the estimated capacities for five different cells with the measured capacities over time. [ABSTRACT FROM PUBLISHER]

Abstract: This paper examines the effect of the electrical double layer on the performance of a lithium ion battery electrochemical cell. We begin by introducing the Poisson Nernst–Planck equations of electrochemistry to describe ion transport within a representative liquid solvent and derive an expression for the current–voltage relationship in the electroneutral liquid within the separator pores. Different assumptions about the electrical double layer lead to variation of the lithium ion concentration profiles in the liquid electrolyte, which alter the cell voltage during discharge. The contribution of the electrical double layer to the cell overpotential is combined with the bulk liquid potential difference and a simplified treatment of the electrode solid phase to obtain an expression for the time-varying cell terminal voltage. We conclude by presenting experimental data for a cell using a graphite anode and lithium iron phosphate cathode to validate the new model, which includes electrical double layer effects, and construct modifications to the model to compensate for resistive effects that are associated with the cathode solid phase. [Copyright &y& Elsevier]