but the voltage response is different. The voltage difference in the nondegraded cell is ϕ s,c -ϕ s,a . For the degraded cell, it contains an additional term from the voltage shift for degradation, resulting in ∆ϕ s,c -∆ϕ s,a +(ϕ s,c -ϕ s,a ). The two current hold equations (Eqs. 5, 6) can be solved for the exact solution of the voltage difference. Though an approximate linear solution of this model can be derived for the half cell, there is no absolute fitness for the full cell since the reference potentials between electrodes are arbitrary (the half cell linearizations are shown in Appendix D). The only viable solution is an implicit solution for the current pulses.