Hydroxyapatite functionalization of solid polymer electrolytes for high-conductivity solid-state lithium ion batteries

Abstract As a key component of next-generation high-safety lithium batteries, solid-state electrolytes have attracted extensive attention. Polyethylene oxide (PEO)-based solid polymer electrolytes exhibit outstanding flexibility and excellent electrode-electrolyte interfaces in comparison with that of inorganic solid electrolytes. Unfortunately, the practical applications of PEO-based solid polymer electrolytes are severely limited by the low ionic conductivity arising from the sluggish segment movement of PEO crystal phase. Herein, a solid-state electrolyte (SSE) design is presented which leverages the good flexibility of PEO and enhances its ionic conductivity by directly introducing hydroxyapatite (HAP) as filler into solid polymer electrolyte. With negative potential vacancies of surface, HAP filler can facilitate lithium salt dissociation with a minor dissociation energy of -0.76 eV by attracting Li+. A remarkable ionic conductivity of 0.064 mS cm-1 and a Li+ transference number of 0.366 at 30 °C are achieved. In addition, LiFePO4 (LFP)-Li cell with HAP-modified polymer SSE also delivers a capacity of 118 mAh g-1 after 500 cycles at 1 C at 30 °C, which confirms the practical operability of novel SSE and the validity of HAP filler for SSE enhancement.