B) Assume that the cell was discharged till 2.5 V at a moderate C-rate (i.e., C-rate is slow enough to allow the Single Particle approximation but high enough to lead to considerable concentration gradients in active material particle). For such a situation, variation along the cell thickness direction can be neglected. Dominant gradients are present in active material particles. The cell is then allowed to rest till it reaches the OCV value. Sketch the concentration evolution in a spherical active material particle and corresponding voltage evolution in time as it approaches the rest phase. Obtain an expression for the Li conservation in a spherical active material particle during discharge and at rest.