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

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 Mn versus Ni versus Co on silicon anode remains to be delineated. Since all three TM ions can dissolve from LiNiMnCoO (NMC) cathodes and migrate to the anode, here a LiFePO cathode is paired with SiO anode and assess the impact by introducing a specific amount of Mn or Ni or Co ions into the electrolyte. It is found that Mn ions cause a much larger increase in SiO electrode thickness during cycling due to increased electrolyte decomposition and solid-electrolyte interphase (SEI) formation compared to Ni and Co ions, similar to previous findings with graphite anode. However, with a lower impedance, the SEI formed with Mn protects the Si anode from excessive degradation compared to that with Co or Ni ions. Thus, Mn ions have a less detrimental effect on Si anodes than Co or Ni ions, which is the opposite of that seen with graphite anodes.