Unveiling the influence of electrode/electrolyte interface on the capacity fading for typical graphite-based potassium-ion batteries

Potassium-ion battery (KIBs) as an economical and high energy candidate for grid-scale applications has drawn significant attention recently. Given the reversible formation of K-graphite intercalation compound, mass production and low price, the graphite is one of the most promising anode materials for KIBs. However, the issue on the fast capacity fading seriously limits the real application of graphite. The formation and stability of solid electrolyte interphase (SEI) at electrode/electrolyte interfaces during the potassiation/depotassiation or plating/striping processes is closely correlated to the above issue. Herein, by employing typical K/graphite batteries the effect of SEI on the capacity fading were systematically investigated in two electrolyte systems (i.e., ester (EC/DEC) and ether (DEGDME) based electrolytes). The decomposition of EC/DEC electrolyte led to the continuous thickening of SEI on K anode, which should be mainly responsible for the fast capacity decay of K/graphite batteries in EC/DEC electrolyte. The gradual distortion of graphite structure is the secondary cause. By comparison, the more stable DEGDME electrolyte and slight graphitic structure degradation lead to better cyclic stability. Additionally, the components of SEI on graphite anodes in full-cells are basically consistent with those in half-cells. In a word, our work provides a guidance for understanding the scientific issues on how the formation and the stability of SEI influences on the capacity decay in KIBs with graphite anodes.