Identifying the Role of the TMA/H2O Atomic Layer Deposition Process on NMC811 Electrochemical Performance

Abstract

The widely used trimethylaluminum (TMA)/water atomic layer deposition (ALD) chemistry has been shown to improve the electrochemical cycling stability of LiMO₂ materials, including nickel-rich LiNi_xMn_yCo_1-x-yO₂ (x > 0.5). However, there are many process options users must select when choosing to perform ALD, which makes comparison of ALD-on-LiMO₂ papers difficult. This work studies the significance of three ALD process parameters (temperature, number of ALD cycles, and termination step) on the polycrystalline LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) electrochemical performance using a 2³ full factorial design. We observe that termination on a half-step (TMA) leads to inferior electrochemical performance. This work also evaluates the role of the TMA/water ALD process on doped NMC811 powder. When fabricated into full cells and assessed for discharge capacity and energy, overall cell resistances at low and high states of delithiation, and pulse power, the ALD-coated sample did not perform significantly better or worse compared to the uncoated, doped NMC811. Our findings suggest that rather than serving as a barrier film from the electrolyte, low cycle counts of TMA/H₂O ALD fulfill a role similar to that of the dopants added during the NMC synthesis steps.