  When State of Charge, State of Health, and parameters of the Lithium-ion
battery are estimated simultaneously, the estimation accuracy is hard to be
ensured due to uncertainties in the estimation process. To improve the
estimation performance a sequential algorithm, which uses frequency scale
separation and estimates parameters/states sequentially by injecting currents
with different frequencies, is proposed in this paper. Specifically, by
incorporating a high-pass filter, the parameters can be independently
characterized by injecting high-frequency and medium-frequency currents,
respectively. Using the estimated parameters, battery capacity and State of
Charge can then be estimated concurrently. Experimental results show that the
estimation accuracy of the proposed sequential algorithm is much better than
the concurrent algorithm where all parameters/states are estimated
simultaneously, and the computational cost can also be reduced. Finally,
experiments are conducted under different temperatures to verify the
effectiveness of the proposed algorithm for various battery capacities.
