Comparison of the Reactions Between Li[sub x]Si or Li[sub 0.81]C[sub 6] and Nonaqueous Solvent or Electrolytes at Elevated Temperature

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Abstract
The reaction of lithiated silicon (LixSi)(LixSi) with ethylene carbonate∕diethyl carbonate (EC∕DEC) solvent, LiPF6LiPF6 - or lithium bisoxalatoborate (LiBOB)-based electrolyte at elevated temperature was compared with that of Li0.81C6Li0.81C6 and the same solvent or electrolyte using accelerating rate calorimetry. The self-heating rate of LixSiLixSi reacting with all solvent or electrolyte samples was less than that of Li0.81C6Li0.81C6 reacting with the same liquids, even though the specific surface area of LixSiLixSi was larger. Additions of the salts, LiPF6LiPF6 or lithium bisoxalatoborate (LiBOB), to EC∕DEC suppresses the self-heating rate dramatically for both LixSiLixSi and Li0.81C6Li0.81C6 samples. This work suggests that composite electrodes using powdered Si-based electrode materials should be safer than corresponding graphite electrodes in Li-ion cells at least during initial cycling. An equal capacity (mAh) of LixSiLixSi is safer than Li0.81C6Li0.81C6 because silicon can store more Li per unit volume than graphite, leading to thicker films of reaction products that slow the further strong reaction with solvent or electrolyte.