Coating Solution for High-Voltage Cathode: AlF₃ Atomic Layer Deposition for Freestanding LiCoO₂ Electrodes with High Energy Density and Excellent Flexibility

Freestanding LiCoO₂/multiwall carbon nanotube/nanocellulose fibril (LCO-MWCNT-NCF) electrodes are fabricated by a vacuum filtration technique. The electrode has a high LCO loading of 20 mg/cm² with excellent flexibility, uniform material distribution, and low surface resistivity. When coated with 2 ALD cycles of AlF₃, LCO-MWCNT-NCF has a high specific capacity of 216 mAh/g at 4.7 V. The freestanding AlF₃-coated electrode preserves 75.7% of its initial capacity after 100 cycles and 70% after 160 cycles of charge discharge. In contrast, electrodes coated with 2 ALD cycles of Al₂O₃ cannot be cycled above 4.5 V. By elimination of the unnecessary weight of current collector, and increasing in the working voltage simultaneously, this freestanding LCO-MWCNT-NCF electrode can significantly improve the gravimetric and volumetric energy density of lithium ion batteries.