Effects of residual stress on overpotentials and mechanical integrity during electrochemical Li-alloying of Al film electrodes

The possibilities of achieving reductions in overpotentials and improvements in mechanical integrity, upon electrochemical Li-alloying/dealloying, by inducing pre-cycling tensile residual stress via facile annealing treatment have been demonstrated in this work. Monitoring of the stress developments in-situ during galvanostatic lithiation/delithiation of Al film electrodes indicated that the mechanical degradations occurred primarily during potential plateaus corresponding to the Al a dagger AlLi first-order phase transformations. Such degradations tended to get suppressed, as did the overpotentials needed to drive the electrochemical Li-alloying/dealloying (including initiation of the phase transformation), in the presence of the tensile residual stress. The improved mechanical integrity agreed with features observed in the stress profiles recorded in real-time during galvanostatic cycling. The magnitudes for the reductions in the overpotentials agreed with theoretical estimation based on the incremental residual stress. This exploratory idea related to engineering of residual stress to improve various electrochemical performances may be applicable also to other 'alloying reaction' based electrode materials.