The handling of positive electrode active materials must be done carefully due to their propensity to degrade when exposed to ambient atmosphere. The growth of impurities on Ni-rich layered lithium transition metal oxides (LTMOs) is particularly concerning as these materials readily react with H₂O and CO₂in atmosphere. The resulting surface impurity species have detrimental effects on the performance of the Li-ion cell and are commonly removed by washing the positive electrode active materials. However, little is understood about the reaction between these materials and aqueous solutions. In this study, LTMOs samples were exposed to acidic and neutral aqueous solutions for various periods of time. The resulting material samples were analysed by X-ray powder diffraction (XRD), thermogravimetric analysis coupled with mass spectrometry (TGA-MS), and by scanning electron microscopy (SEM). The solutions collected after washing were analysed by pH titration and inductively coupled plasma optical emission spectrometry (ICP-OES). From this, we propose two pH-dependent regimes that define the reaction between the positive electrode material and the aqueous solution used for washing. Possible consequences of these reactions on cell performance and lifetime are discussed.

One way to lower the cost of lithium ion batteries using LiNi_xMn_yCo_zO₂ (NMC) or LiNi_0.80Co_0.15Al_0.05O₂ is to lower the Co content in the positive electrode materials. This work systematically studied the impact of the synthesis conditions on the performance of LiNi_xCo_yAl_zO₂ (x ≥ 0.8, z ≤ 0.05 and x + y + z = 1) (NCA) with high Ni and low Co content. The impacts of oxygen flow rate, sintering temperature, initial Li/TM ratio and sintering time on the structural and electrochemical properties of NCA were systematically studied. The conditions when impurity phases such as Li₂CO₃ and Li₅AlO₄ appear were carefully examined. The impact of residual lithium compounds on the electrochemical performance was also discussed. It was found that the synthesis conditions, which affect the a-axis, c-axis and Ni_Li content of the NCA samples, have strong impacts on the lithium diffusion at low and high states of charge based on differential capacity vs. voltage (dQ/dV vs. V) measurements at various rates and temperatures. Additionally, the reversible capacity and cycling stability correlated strongly with the intensity of the dQ/dV vs V peak at 3.5 V (discharge) measured with a C/20 rate at 30°C.

This work studies the effect of Mg doping in LiMO₂ (M = Ni, Ni+Al, Ni+Co+Al, Ni content >0.8) at a dopant level of less than 5%. Synthesized materials were all single phase and contained no appreciable amount of surface or bulk impurities. Structural and electrochemical characterization of the materials was carried out to understand how Mg affects the materials and whether the presence of Al or Co influences the dopant effects of Mg. All synthesized materials, even those without Co, were found to contain a small amount of Ni in the Li layer. Increases in the Mg content of the material reduced the initial capacity of the materials but improved the capacity retention. The capacity reduction was related to the amount of Li trapped by electrochemically inactive Al and Mg. The capacity retention was related either to the number of Ni ions substituted by electrochemically inactive dopants or to the amount of Li trapped by those dopants. Mg helped improve capacity retention by reducing the growth of polarization during cycling. No synergistic effects were found to exist from co-doping materials containing Co and/or Al with Mg.