The anxiety for long driving range and for reducing the cost of lithium-ion cells is pushing to increase the nickel content in layered oxide cathodes. This is because Ni is less expensive and more abundant than Co. As the Ni^3+/4+: 3d band barely touches the top of the O^2-: 2p band, Ni³⁺ can be oxidized all the way close to Ni⁴⁺ without much oxygen loss from the layered lattice, resulting in capacities of as high as 240 mAh/g. In contrast, the overlap of Co^3+/4+: 3d band with the top of the O^2-: 2p band leads to an oxidation of O^2- ions to oxygen beyond about 50% charge, resulting in a limited capacity of < 150 mAh/g. However, increasing the Ni contents above about 70% is met with a few hurdles: (i) The tendency of Ni³⁺ to get reduced to Ni²⁺ at the synthesis temperatures of about 700 ^oC necessitates a high stream of oxygen gas flow, introducing scale-up challenges for obtaining high quality materials with consistency. (ii) The instability of Ni⁴⁺ in contact with the liquid electrolyte in the charged state introduces aggressive surface reactivity, which results in rapid capacity fade and thermal runway. The surface reactivity is accompanied by loss of oxygen from the surface, reduction of Ni⁴⁺ to Ni²⁺ on the surface and formation of resistive rock-salt phases, formation of cracks, loss of active lithium in cathode-electrolyte interphase formation, Ni dissolution and migration to the anode due to the electronically driven lattice instability associated with the Jahn-Teller active Ni³⁺, and consequent capacity fade during extended cycling [1]. The reactivity also leads to thermal instability, oxygen loss, gas evolution, and safety concerns [2]. These challenges become exponentially aggravated with Ni contents > 80% and even much more for > 90%.

To overcome the challenges, generally doping of high-Ni cathodes with various dopants is pursued. However, no clear understanding is available in the literature on which dopant does what. Doping is generally carried out randomly in the literature by a trial and error process. This presentation will provide a systematic investigation of doping LiNiO₂ with 5% or 10% of various common dopants like Co, Mn, Al, and Mg. The effect of dopants on capacity, cycle life, thermal stability, and gas evolution will be presented. The surface reactivity depends both on the surface characteristics of the high-Ni cathodes and the electrolyte. This presentation will then focus on the development of cathodes with a robust surface as well as more stable electrolytes to overcome the challenges. The ability to achieve long cycle life, while reducing the amount of gas evolution, by tuning the cathode and electrolyte compositions will be presented. Also, the fundamental understanding developed with the use of advanced analytical techniques, such as in-situ XRD, SEM, XPS, and TOF-SIMS will be discussed.