Thermal relaxation of lithium dendrites

Abstract

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: T_SR ≈ 0.65 T_MB (T_MB = 453 K: the melting point of bulk Li⁰).