Preventing lithium dendrite-related electrical shorting in rechargeable batteries by coating separator with a Li-killing additive

Abstract

Dendritic electrodeposition is an intrinsic feature of Li metal, and Li dendrite-related electrical shorting is a major cause of thermal runaway in Li metal batteries. In order to prevent such electrical shorting, a Li-killing layer consisting of TiO₂ nanoparticles embedded in a porous Kynar polymer matrix is coated onto one side of a conventional Celgard separator and faced to the cathode. After filling with liquid electrolyte, the Kynar polymer swells to a gel while TiO₂ serves as a Li-killer by reacting with the Li dendrites that penetrate through the separator. Additionally, the Li-killing layer increases the thermal dimensional stability of the separator, and the wettability, uptake and uphold of the liquid electrolyte. It is shown that a Li/Cu cell with the Li-killing layer does not undergo electrical shorting even if the Li metal is entirely plated onto the counter electrode, whereas an identical cell using a pristine separator rapidly experiences shorting. Moreover, the Li-killing layer increases the rate capability and capacity retention of a Li/LiNi_0.80Mn_0.10Co_0.10O₂ cell. Impedance analysis reveals that such improvements are attributed to increased electrolyte uptake and uphold, which consequently reduces the solid electrolyte interphase resistance and charger-transfer resistance.