Constructing ultrathin TiO2 protection layers via atomic layer deposition for stable lithium metal anode cycling

Highlights: • The TiO₂ layer deposited by ALD was proven to be an effective protective film for lithium anode. • The TiO₂ layer promoted uniform deposition of Li⁺ and effectively inhibited the growth of lithium dendrites. • Optimized thickness of TiO₂ with ~5 nm was obtained (ALD 50 cycles). • Battery cycling performance was effectively enhanced with TiO₂ layer assistance. -- Abstract: Uncontrollable dendrite growth during the repeated plating/stripping of Li ions induces short cycle life and safety issues, which has severely impeded the practical application of lithium metal battery. It is acknowledged that the solid electrolyte interphase (SEI) is pivotal for Li metal anode stabilization. Here, a lithium metal anode coated with an artificial SEI film as the working electrode is applied. The TiO₂ coating layer is firstly demonstrated for the lithium metal anode protection via atomic layer deposition (ALD) method. Thanks to the ultrathin TiO₂ layer, dendritic growth is suppressed and the cycling lifetime is significantly improved. Additionally, the thickness of TiO₂ protective layer has been further optimized. Comparing with other different thickness TiO₂ layer, 5 nm TiO₂ layer is found to be the optimized parameter toward capacity, cycling stability and rate capability in both symmetric battery system and full-cell system. The TiO₂ layer promoted uniform deposition of Li⁺ and effectively inhibited the growth of lithium dendrites. Symmetric Li/50TiO₂ Li/50TiO₂ battery could cycle stably for more than 1600 h at 1 mA cm⁻², and more than 500 h at 3 mA cm⁻² and 10 mA cm⁻² current density. The Li/50TiO₂ NCM622 full-cell exhibited better rate performance and long-cycle performance, which capacity retention was increased by 23.3% compared to bare electrode after 100 cycles at 0.5 C charge-discharge current density. Furthermore, the inherent working mechanism of TiO₂ artificial SEI film has been proposed. This work provides an effective and new alternative method for lithium metal anodes protection, which is critical for the future design of next-generation Li metal batteries under safe operation.