Pushing the Energy-Lifetime Frontier of Li-Ion Batteries with Optimized Ni-Rich, Co-Free NMA-W Cathodes

Especially in the electric vehicle industry where both high energy density and long lifetime batteries are sought, Ni-based cathode materials such as LiNi1−x−yMnxCoyO2 (NMC) and LiNi1−x−yCoxAlyO2 (NCA) provide a fitting compromise in capacity and cyclability. In recent years, the high cost of cobalt in addition to the problematic geopolitics surrounding cobalt mining have motivated research efforts toward cobalt-free cathode materials.1 However, Ni-rich materials are subject to inevitable failure mechanisms such as microcracking and parasitic reactions with the electrolyte which are further aggravated with an increase in Ni-content and in the absence of Co.2 Many strategies have been proposed to overcome these challenges such as doping and/or coating the cathode particles,3 but there remains a need to further increase energy density with minimal compromise to lifetime. In this work we present a cathode active material system designed to push Ni-rich and Co-free materials to the limit of their performance. This is done by choosing optimal polycrystalline particle size, a balance of Mn and Al content, and a sufficient amount of high-valence doping. Additionally, appropriate synthesis conditions are needed to obtain the desired morphology and infuse the intergranular boundaries with the W dopant. It is then important to choose an appropriate upper cutoff voltage during cycling to maximize energy while avoiding drastic crystal changes.4 This optimized NMA-W material system delivers specific capacity above 200 mAh/g while retaining 95% of its capacity without relying on any amount of Co. The series of NMA-W materials presented in this work were characterized and tested. Scanning electron microscopy (SEM) images were used to observe morphology and crystallite growth after synthesis. X-ray diffraction (XRD) analysis was conducted to monitor the crystal parameters and accelerated rate calorimetry (ARC) was used to assess the thermal stability and safety of the material. Compression tests were also conducted to study the strength of the particles and their propensity to crack under stress. Choi, J. U., Voronina, N., Sun, Y. K. & Myung, S. T. Recent Progress and Perspective of Advanced High-Energy Co-Less Ni-Rich Cathodes for Li-Ion Batteries: Yesterday, Today, and Tomorrow. Adv. Energy Mater. 10, 1–31 (2020). Li, H. et al. An Unavoidable Challenge for Ni-Rich Positive Electrode Materials for Lithium-Ion Batteries. (2019) doi:10.1021/acs.chemmater.9b02372. Yan, W., Yang, S., Huang, Y., Yang, Y. & Guohui Yuan. A review on doping/coating of nickel-rich cathode materials for lithium-ion batteries. J. Alloys Compd. 819, 153048 (2020). Nam, G. W. et al. Capacity Fading of Ni-Rich NCA Cathodes: Effect of Microcracking Extent. ACS Energy Lett. 4, 2995–3001 (2019).

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