The Effect of Stress on Battery-Electrode Capacity

Constraint-induced stresses develop during Li-ion battery cycling, because anode and cathode materials expand and contract as they intercalate or de-intercalate Li. We show in this manuscript that these stresses, in turn, can significantly modify the maximum capacity of the device at a given cell voltage. All-solid-state batteries impose an external elastic constraint on electrode particles, promoting the development of large stresses during cycling. We employ an analytic and a finite element model to study this problem, and we predict that the electrode's capacity decreases with increasing matrix stiffness. In the case of lithiation of a silicon composite electrode, we calculate 64% of capacity loss for stresses up to 2 GPa. According to our analysis, increasing the volume ratio of Si beyond 25-30% has the effect of decreasing the total capacity, because of the interaction between neighboring particles. The stress-induced voltage shift depends on the chemical expansion of the active material and on the constraint-induced stress. However, even small voltage changes may result in very large capacity shift if the material is characterized by a nearly flat open-circuit potential curve.