In this work, magnesium borate fiber (MBO) is used as a functional ceramic to coat onto a polypropylene (PP) separator (MBO@PP). This MBO coating layer increases the lithium‐ion transference number (tLi+) from 0.24 to 0.57 in the LiPF6‐based electrolyte due to the MBO acting as Lewis acid sites interacts with Lewis base PFbold6-
. The increase in the tLi+ reduces the concentration polarization and promotes the migration of lithium ions. Besides, the prepared MBO@PP separator has better wettability with liquid electrolyte, the electrolyte uptake as well as thermal stability. The LiFePO4 half‐coin with MBO@PP separator not only had better cycle stability, but also had a higher capacity retention rate at high current.