Thermal relaxation of lithium dendrites

Abstract

The average lengths λ^- of lithium dendrites produced by charging symmetric Li^0 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 λ^-(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 Li^0(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 T_MB (T_MB = 453 K: the melting point of bulk Li^0).

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