Insights into the effects of multi-layered graphene as buffer/interlayer for a-Si during lithiation/delithiation

With the usage of well-ordered multi-layered graphene film (MLG; ∼9/10 layers) as interlayer between continuous films of a-Si (active electrode material) and Ni (current collector), the present work (involving in-situ experiments) aims at assessing/understanding various scientific aspects related to the influence of graphenic carbon based 'buffer' interlayer on the stress developments, integrity and electrochemical behavior of a-Si upon repeated lithiation/delithiation. The presence of MLG interlayer significantly improved the Li-capacity and coulombic efficiency in each cycle, even though the improvement in capacity retention was modest. More importantly, as recorded in real-time, the magnitudes of overall in-plane stresses per degree of Li-insertion/removal were significantly lower in presence of MLG (lowering >100%). Interestingly, presence of MLG interlayer resulted in predominantly elastic response (as opposed to predominant flow, sans MLG) during lithiation from 2nd cycle onwards. Despite a-Si films fracturing into 'islands' during the first delithiation half cycles in both cases, presence of MLG helped maintain integrity of the 'islands' during further cycling. Scratch tests indicated weaker adhesion of a-Si on graphene. Suppression of flow has been partly explained in the contexts of observed 'island' sizes and adhesion strengths; which in turn has been partly accounted for the improved integrity in presence of MLG.

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