Lithiophilic composite solid electrolyte interphase layer modified Li foils: Li metal battery failure analysis

Abstract

Li metal battery with higher energy density becomes increasing important to reach a carbon neutrality society. However, the usage of Li metal is usually failed due to the side-reactions, dendrite formations, and volume expansion. To tackle these difficulties, artificial solid electrolyte interphase with multiple functions is proposed. In our work, a magnesium-based inorganic-organic film is coated on Li metal with tape-casting. LixMg alloy and nano-LiF particles produced after activation process can lower the nucleation energy barriers and increase the Li ion transportation. Polymer layers with high flexibility are adopted to control the volume change caused by repeatly lithium plating/stripping. As a result, the Li symmetrical cell runs stable for 1300 h with a lower over-potential of 3 mV under limited carbonate electrolyte. Li metal batteries degradation mechanism with different N/P ratio and C rates are discussed in details. The full cell with LiFePO4 and 30 μm Li foil delivers a capacity of 132 mA h g−1 after 300 cycles, the bare Li is dead after 75 cycles due to the loss of active lithium. LiNi0.6Co0.2Mn0.2O2 coupled with modified Li foil with mass loading of 1.44 mA h cm−2 is superior than bare Li at 1 C, the latter quickly die due to the dry-out of electrolyte.