Enhanced electrochemical stability of high-voltage LiNi_0.5Mn_1.5O₄ cathode by surface modification using atomic layer deposition

We report improved cycling performance of high-voltage LiNi_0.5Mn_1.5O₄ cathode for lithium-ion batteries by modifying its surface with ultrathin layer coating of Al₂O₃ (<1 nm) using atomic layer deposition (ALD) technique. Four and six layers of ALD Al₂O₃ were coated directly on the porous LiNi_0.5Mn_1.5O₄ nanoparticle (~200 nm) slurry composite. Electrochemical characterization results show that LiNi_0.5Mn_1.5O₄ electrode with four and six layers of ALD Al₂O₃ maintained 92 and 98 % of their initial capacity after 200 cycles, respectively, in comparison to bare LiNi_0.5Mn_1.5O₄ electrode which showed 84 % capacity retention. We show that the ALD Al₂O₃ coated cathode surface is protected from undesired side reactions occurring at the electrode/electrolyte interface. For the first time, we used XPS studies to investigate the surface chemistry of ultrathin ALD Al₂O₃ coated LiNi_0.5Mn_1.5O₄ and confirmed that the ultrathin ALD Al₂O₃ layer reduces side reactions involving organic components of the electrolyte decomposition product in high-voltage cathodes.