(Invited) In-Situ Nanoscale Coatings on Silicon Anodes

Abstract

One of the directions being pursued for next generation electrochemical cells is the incorporation of elemental silicon into a lithium-ion battery anode. Silicon's high storage capacity and abundance make it an appealing material for lithium-ion cells. While many studies revolve around its mechanical issues (high volume expansion) and coulombic efficiency on cycling, a major roadblock to its use is its poor calendar life. On standing while charged, silicon based electrodes are observed to lose capacity (active lithium). Since this type of test does not involve particle breakdown, losses due to issues associated with parasitic currents are in part derived from the high reactivity of charged silicon anodes with the surrounding electrolyte and electrode binder. In this talk we will be discussing a new concept that deactivates the redox activity of the silicon surface while maintaining the high lithium-ion conductivity of the highly charged surface phases. We have found that by selectively adding alkaline earth cations to the surface, a more electron precise phase (i.e. Li14MgSi4 vs Li15Si4) forms that acts to change the phase evolution moving away from phases formed by gradual one-electron oxidation in the binary lithium-silicon system. Various studies show that the parasitic currents are seen to drop with addition and cycling with extended calendar life observed. Mechanistic studies will be presented that highlight magnesium addition to the electrolyte and electrode and the role of time on the surface phases.