Pressure-Driven Contact Mechanics Evolution of Cathode Interfaces in Lithium Batteries

The interfacial instability due to periodic volume expansion of electrodes in the charging and discharging process directly affects the contact performance and interface impedance between the electrodes and the solid-state electrolyte(SSE).The existing work has studied the local stress state behavior on a single spatial scale or only focused on the interfacial influence of electrochemical characteristics at a specific time.In this paper,a semi-analytical method-based chemoelastic contact model was developed to study the evolution behavior of the cathode/SSE interface,and the stress and displacement fields subjected to contact forces were calculated by means of the discrete convolution-fast Fourier transform algorithm.The interface evolution subjected to mechanical pressure was analyzed for the local influence of the stress at one position at a specified time on the contact behavior at the present time and position,and the global influence of those at other positions at a later time.Based on this model,the mechanical-chemical coupling effect of lithium intercalation on interface stability was quantitatively studied,and the mechanism of enhancing interfacial contact stability by mechanical load was further explored.The results show that a larger current causes the contact toward the center,while a larger mechanical force leads to a smaller pressure peak.With the increase in mechanical force,the compressive stress in the contact area decreases significantly,while the tensile stress outside the contact area increases slightly.Based on the model results,a transition map was constructed with bonder equation(P/I=25MPa·cm^(2)/mA)to define whether an interfacial contact is stable or not.Quantitatively,applying a mechanical pressure P/I>25MPa·cm^(2)/mA can maintain a stable interfacial contact between the SSE and the cathode.The proposed model provides a theoretical basis in the chemomechanics view for the understanding of using pressure to suppress diffusion-induced contact instability in lithium batteries.