Composite electrodes of disordered carbon and graphite for improved battery state estimation with minimal performance penalty

Voltage based state of charge (SOC) estimation is challenging for lithium ion batteries that exhibit little open circuit voltage (OCV) change over a large SOC range. We demonstrate that by using a composite negative electrode composed of disordered carbon and graphite, we were able to introduce additional features to the OCV–SOC relationship that facilitate voltage-based SOC estimation. In contrast to graphite, the potential of disordered carbon is sensitive to the state of charge; this behavior, when manifested in a lithium ion battery, gives rise to additional beneficial features of the cell OCV–SOC relationship in terms of state estimation. We have demonstrated the effectiveness of the approach by comparing model simulations and corresponding experimental data of a cell composed of LiFePO4 positives and graphite + disordered carbon composite negative electrodes. Last, we find that although the graphite material has a higher coulombic capacity, very little (dynamic) performance loss is manifest with the mixed graphite + disordered carbon composite is employed.

► We have constructed and analyzed a Graphite (SG)/disorder carbon (MCMB) composite electrode.
► The composite electrode has been shown to exhibit good rate capability and cycling stability.
► The sloping voltage towards the end of discharge improves enhances voltage-based SOC estimation.
► We show a straightforward application of OCV relations to formulate the composite equilibrium potential.
► Demonstrated that composite electrode provides an early warning and facilitates voltage-based SOC estimation.