Thermal relaxation of lithium dendrites

The average lengths of lithium dendrites produced by charging symmetric Li0 batteries at various temperatures are matched by Monte Carlo computations dealing both with Li+ transport in the electrolyte and thermal relaxation of Li0 electrodeposits. We found that experimental (T) variations cannot be solely accounted by the temperature dependence of Li+ mobility in the solvent but require the involvement of competitive Li-atom transport from metastable dendrite tips to smoother domains over ΔE‡R ∼ 20 kJ mol−1 barriers. A transition state theory analysis of Li-atom diffusion in solids yields a negative entropy of activation for the relaxation process: ΔS‡R ≈ −46 J mol−1 K−1 that is consistent with the transformation of amorphous into crystalline Li0 electrodeposits. Significantly, our ΔE‡R ∼ 20 kJ mol−1 value compares favorably with the activation barriers recently derived from DFT calculations for self-diffusion on Li0(001) and (111) crystal surfaces. Our findings suggest a key role for the mobility of interfacial Li-atoms in determining the morphology of dendrites at temperatures above the onset of surface reconstruction: TSR ≈ 0.65 TMB (TMB = 453 K: the melting point of bulk Li0).