Gel electrolyte modification enables planar Li deposition and fast kinetics toward high energy Li metal batteries

Abstract

Owing to the low redox potential (−3.040 V vs. SHE) and high theoretical specific capacity (3860 mA h g⁻¹), lithium metal is regarded as the ‘holy grail” anode for energy storage systems. However, traditional porous polypropylene (PP) separators cause inhomogeneous flux of lithium ions, leading to lithium dendrites and unstable byproducts (known as “dead lithium”). In the work, a composite coating consisting of lithium ion conductor Li_1+xAl_xTi_2−x(PO₄)₃ (LATP) and polymer polyvinylidene fluoride–hexafluoropropylene (PVDF–HFP) is proposed. The conductive LATP nanoparticles regulate the lithium ion flux and induce homogeneous lithium metal deposition. The flexible PVDF–HFP/LATP coating layer reduces the energy barrier for Li deposition and enables fast kinetics at the interface. As a result, stable and high rate performance lithium metal batteries are achieved. With an areal capacity of 1 mA h cm⁻², Li||Li symmetric batteries cycled steadily with very low overpotentials for over 850 h at a current density of 1 mA cm⁻², and at the 520th cycle, the battery with a modified separator exhibited a capacity of 156 mA h g⁻¹ (capacity retention of 88.6%). In the rate test, the modified batteries exhibited a capacity of 145.9 mA h g⁻¹ at a high rate of 4C, which suggests that the modified separator results in uniform and dendrite-free Li deposition and stripping as well as fast kinetics.