(601a) The Effect of Al2O3 Atomic Layer Deposition Parameters on LiNi0.8Mn0.1Co0.1O2 Powder Properties and Electrochemical Performance

Inorganic surface coatings such as alumina are applied to layered transition metal oxides like LiNi_xMn_yCo_1-x-yO₂ (NMC) to improve their electrochemical performance when manufactured into Li-ion batteries. In particular, atomic layer deposition (ALD) is a surface coating technique that deposits conformal, pin-hole free films with Angstrom-level precision. Moreover, alumina ALD has been shown to provide electrochemical improvements like increased cycling stability and reduced capacity fade for NMC materials. However, there are many ALD process parameters that can be adjusted to achieve the desired electrochemical performance. Furthermore, different ALD reactor systems deposit different amounts of film per ALD cycle, which makes comparison of ALD-on-LiMO₂ papers difficult. Here we present a systemic correlation between the trimethylaluminum (TMA)/water ALD parameters and their effects on NMC811 powders using a 2³ full factorial design of experiments. We investigated the effect of ALD temperature (120°C, 180°C), number of ALD cycles (1 cycle, 10 cycles), and termination chemistry (H₂O, TMA) on powder and electrochemical properties using a variety of techniques including ICP-OES, Brunauer-Emmett-Teller (BET) analysis, SEM, low energy ion scattering (LEIS), and galvanostatic cycling. Generally, the particle specific surface area increased after ALD. The number of ALD cycles had the most significant effect on electrochemical performance compared to ALD temperature or termination step. Most interestingly, 1 cycle of ALD had a preservative effect on NMC811 handled in air. The 1 cycle samples possessed capacity retentions similar to that of the pristine powder, while the uncoated NMC811 control that was handled in air retained significantly less capacity. The extent of film coverage was analyzed using LEIS and compared to LiAlO₂ and Al₂O₃ references. Our study summarizes the interaction of ALD process parameters that leads to an electrochemically beneficial (or not) coating on NMC811 active material and provides further evidence of a beneficial Li-Al-O layer that forms during the initial ALD cycles.