Eu3+ doped hydroxyapatite nanowires enabling solid-state electrolytes with enhanced ion transport

The polymer-based solid-state electrolytes (PSEs) are promising for solid-state batteries but they have deficiencies such as low ionic conductivity, low lithium-ion transference number, and unstable electrode/electrolyte interface. Herein, we designed a hydroxyapatite nanowire doped with high-valence cations in anticipation of the formation of positively charged active sites on the nanowire surface. The higher surface activity can reduce the reaction activation energy on the nanowire surface and adsorb the anions in the PSEs as a way to improve the ionic conductivity and Li+ transference number of the PSEs. The active sites on the surface of the nanowires anchor the anions, thus increasing the Li+ transference number to 0.38, which effectively improves the ionic conductivity of the PSE to 1.58 × 10−4 S cm−1 at room temperature. At the same time, the composite polymer electrolyte has a wide electrochemical window. The lithium symmetric cell stably cycles for 800 h at a current density of 0.1 mA cm−2, and the LiFePO4||Li full cell steadily cycles for 180 cycles at a rate of 0.5 C with a capacity retention of 94.2%. The ion doping strategy to change the surface electrical behavior of nanowires provides an idea to improve the ionic conductivity of solid-state electrolytes.