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 Mn²⁺ versus Ni²⁺ versus Co²⁺ on silicon anode remains to be delineated. Since all three TM ions can dissolve from LiNi_1-x-yMn_xCo_yO₂ (NMC) cathodes and migrate to the anode, here a LiFePO₄ cathode is paired with SiO_x 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 SiO_x 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.