Synthesis of LiNi_0.8Mn_0.1Co_0.1O₂ by an Oxalate Precipitation

Abstract

Batteries with high energy densities and long cycle lives are important for enabling the transition from fossil fuels to electrical vehicles. Lithium ion batteries are the most popular batteries for use in electrical vehicles, but there is still a need to increase the gravimetric and volumetric energy densities from state-of-the-art batteries without increasing the costs. Since cobalt is one of the most costly and also toxic elements used in the cathode, developing low cobalt chemistries is highly desirable. LiNixMnyCozO2 (x+y+z = 1; NMC) with high Ni content is one of the cathode materials which has received attention because its high capacity and energy density. The capacity of NMC increases with increasing Ni content because Ni is the main electrochemically active transition metal in NMC. However, the capacity retention and thermal stability decreases with increasing Ni content as well [1]. Still, there is research on stabilising NMC with high Ni content, such as LiNi0.8Mn0.1Co0.1O2 (NMC 811), both with respect to performance and safety. An example of such an effort is to coat NMC 811 with AlPO4 [2]. NMC has a layered structure with lithium ions and transition metal ions in separate layers. One of several reasons for the capacity fade of NMC during cycling is cation mixing, where some Ni2+ and Li+ switch positions in the structure because of their similar ionic radii, blocking pathways for Li+ during lithiation and delithiation [3, 4, 5]. Work performed by Huaquan Lu et al. (2013) on NMC 811 indicates that the synthesis method may affect both morphology and degree of cation mixing [6]. In this work, the effect of different experimental parameters on quality of the synthesised material is studied. NMC 811 was synthesised by an oxalate precipitation from transition metal acetates and lithium nitrate precursors, adapted from a method described by Zhen Chen et al. [7]. Initial results show a phase pure layered structure with low cation mixing. Further work will include adjusting different experimental parameters, such as precursor mixing sequences, precursor mixing rates, annealing temperatures and atmosphere, in an effort to optimise the synthesis. The success of the synthesis will be evaluated based on factors such as phase purity, cation mixing, and electrochemical performance. References [1] Noh, Hyung-Joo, et al. "Comparison of the structural and electrochemical properties of layered Li[NixCoyMnz]O2 (x= 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) cathode material for lithium-ion batteries." Journal of power sources 233 (2013): 121-130. [2] Cho, Jaephil, Hyemin Kim, and Byungwoo Park. "Comparison of Overcharge Behavior of AlPO4-Coated LiCoO2 and LiNi0.8Co0.1Mn0.1O2 Cathode Materials in Li-Ion Cells." Journal of The Electrochemical Society 151.10 (2004): A1707-A1711. [3] Yu, Haijun, et al. "Study of the lithium/nickel ions exchange in the layered LiNi0.42Mn0.42Co0.16O2 cathode material for lithium ion batteries: experimental and first-principles calculations." Energy & Environmental Science 7.3 (2014): 1068-1078. [4] Wu, Feng, et al. "Effect of Ni2+ content on lithium/nickel disorder for Ni-rich cathode materials." ACS applied materials & interfaces 7.14 (2015): 7702-7708. [5] MacNeil, D. D., Z. Lu, and Jeff R. Dahn. "Structure and Electrochemistry of Li[NixCo1−2xMnx]O2 (0⩽ x⩽ 1/2)." Journal of The Electrochemical Society 149.10 (2002): A1332-A1336. [6] Lu, Huaquan, et al. "High capacity Li [Ni0.8Co0.1Mn0.1] O2 synthesized by sol–gel and co-precipitation methods as cathode materials for lithium-ion batteries." Solid State Ionics 249 (2013): 105-111. [7] Chen, Zhen, et al. "Manganese phosphate coated Li [Ni0.6Co0.2Mn0.2]O2 cathode material: Towards superior cycling stability at elevated temperature and high voltage." Journal of Power Sources 402 (2018): 263-271.