First steps towards reproducing chemical shifts spectra of c-LiSi alloys using a semi-empirical force field

F. FERNANDEZ; M. OTERO; S.A. PAZ; D. BARRACO; E. LEIVA

Belgrado

Congreso; 71st Annual Meeting of the International Society of Electrochemistry; 2020

International Society of Electrochemistry

Silicon has been proposed as a promising anode for rechargeable lithium-ion batteries because of the low cost, low discharge voltage and high theoretical capacity of 3579 mA h g−1.This capacity is 10 times higher than the presented by current graphite anodes (372 mA hg−1). However, they exhibit a large volume expansion upon cycling ( 300%) and structuralchanges that lead to capacity degradation and short cycle life.Nuclear magnetic resonance (NMR) has proven to be a useful tool for investigating thestructural changes that occur in electrode materials in electrochemistry and semi-empiricalforce field are useful for study process that involve the charge of each atom.In a previous work of Key et al. [1], 7Li chemical shift spectra for different c-LiSi alloys have been correlated with the local chemical environment. The authors observed inthe spectrums a shift of the center of the peak to lower frequencies when the ratio Li/Si increases. They concluded that among the Si neighbors of Li ions, those that are also bondedto other Si shift the signal to a higher frequency in comparison to those that are isolated, i.e.only bonded to other Li ions.In this work we hypothesize that each lithium ion in the c-LiSi alloy has a contribution tothe total chemical shift spectra that depends only on the charge associated to this particularlithium. We use this framework to predict the c-LiSi NMR spectra.