Suppression of thermal runaway by continuous heat generation using porous silicon covered with a thin oxide layer

The safety of the negative electrode was improved by a thin oxide covered porous silicon, which was synthesized by the thermal oxidation of Mg2Si. The reaction of lithiated porous Si with a 1 M LiPF6 ethylene carbonate-diethyl carbonate electrolyte was compared with that of lithiated bulk Si in the same electrolyte by differential scanning calorimetry at temperatures from room temperature to 450 degrees C. The total heat value of bulk Si was 4444 J g(-1), whereas that of porous Si was 3121 J g(-1). This difference was comparable to the heat value caused by reaction between fully Li intercalated graphite (C6Li) and the electrolyte. In situ heating X-ray diffraction showed that a reaction between Li in the porous Si electrode and the electrolyte progressed from 200 degrees C or lower, and Li was consumed to form Li2CO3 and LiOH with a mildly exothermic reaction. Above 200 degrees C, LiF with high formation entropy was formed by a reaction of PF5 derived from LiPF6 and Li in the electrode. In the case of porous Si, it was revealed that the small amount of LiF formation and its low crystallinity suppressed the exothermic reaction in the high temperature range.

Automated summary

The study found that the reaction between lithium in porous silicon and the electrolyte progressed from 200 degrees C or lower, consuming lithium to form Li2CO3 and LiOH with a mildly exothermic reaction, enhancing electrode safety. At temperatures above 200 degrees C, the formation of high entropy LiF by a reaction of PF5 derived from LiPF6 and lithium in the electrode suppressed the exothermic reaction in the high temperature range due to the small amount of LiF formation and its low crystallinity.