Delineating the Effects of Transition-Metal-Ion Dissolution on Silicon Anodes in Lithium-Ion Batteries.

Abstract

Silicon anode is an appealing alternative to enhance the energy density of lithium-ion batteries due to its high capacity, but it suffers from severe capacity fade caused by its fast degradation. The crossover of dissolved transition-metal (TM) ions from the cathode to the anode is known to catalyze the decomposition of electrolyte on the graphite anode surface, but the relative impact of dissolved Mn2+ versus Ni2+ versus Co2+ on silicon anode remains to be delineated. Since all three TM ions can dissolve from LiNi1-x-y Mnx Coy O2 (NMC) cathodes and migrate to the anode, here a LiFePO4 cathode is paired with SiOx anode and assess the impact by introducing a specific amount of Mn2+ or Ni2+ or Co2+ ions into the electrolyte. It is found that Mn2+ ions cause a much larger increase in SiOx electrode thickness during cycling due to increased electrolyte decomposition and solid-electrolyte interphase (SEI) formation compared to Ni2+ and Co2+ ions, similar to previous findings with graphite anode. However, with a lower impedance, the SEI formed with Mn2+ protects the Si anode from excessive degradation compared to that with Co2+ or Ni2+ ions. Thus, Mn2+ ions have a less detrimental effect on Si anodes than Co2+ or Ni2+ ions, which is the opposite of that seen with graphite anodes.