An improved coulomb counting method based on non-destructive charge and discharge differentiation for the SOC estimation of NCM lithium-ion battery

Accurate state of charge (SOC) estimation plays a crucial role in the safe and efficient operation of batteries. The coulomb counting (CC) approach has been used extensively in industrial production as a relatively easy-to-use and reliable algorithm for estimating battery SOC. However, the accuracy of standard CC method is constrained and it cannot satisfy some complex operating environment requirements. In this paper, a CC approach based on non-destructive charge and discharge differentiation is proposed on NCM battery. This method corrects the battery's initial SOC value using the open-circuit voltage method. It also corrects the actual capacity of the battery based on temperature, discharge rate and aging. Finally, it corrects the CC method's cumulative error using non-destructive capacity differentiation (dQ/dV) and voltage differentiation (dV/dQ). Experimental results show the maximum estimation error of the proposed approach is 3.33 % in the temperature range of -10 degrees C to 45 degrees C which is 15.57 % lower than the traditional OCV - CC method at -10 degrees C.