Study of the Effect of Lithium Precursor Choice on Performance of Nickel-Rich NMC

摘要

According to market research, use of NMC cathode materials for electric vehicle applications will increase dramatically over the next decade. Specifically, migration toward nickel rich NMC532, NMC622 and NMC811 appears likely in all major xEV markets (1). Nickel-rich layered cathode materials such as LiNi0.8Co0.15A10.05O2 (NCA) and nickel-rich LiNil-x-yCoxMny02 (NMC), where Ni content is >0.6 moles can deliver high specific capacities of over 200 mAh g-1. However, the challenges surrounding synthesis of these materials are well documented (2), (3), (4). As nickel content increases the choice of lithium precursor, LiOH.H20 or Li2C03, can have a dramatic effect on the performance of these cathode materials. Here we report the advantages of using lithium hydroxide as the lithium precursor on the performance of nickel-rich NMC cathode materials. Specifically we will show that using lithium hydroxide as the lithium precursor results in: 1. Superior physical properties, such as higher tap and packing density, can be achieved at lower synthesis temperatures for nickel-rich NMC materials. 2. Improved material crystallinity as observed by x-ray diffraction, greater structural purity and less mixing of Ni2+ in the lithium layer determined by Rietveld refinement, leading to improved power performance. 3. Significant cost reduction due to increased process through-put. 4. Higher energy density materials at lower production energy consumption. Also in this study statistical design of experiments has been used to evaluate the effect of temperature, nickel content and synthesis temperature on NMC discharge rate capability and lithium content in the lithium layer. The results show statistically significant interaction between temperature, nickel content and lithium precursor. Linear regression modeling of the DOE data predicts as nickel content in NMC increases, synthesis temperature has a dramatic effect on high rate discharge capacity. The model predicts that the optimum synthesis temperature for NMC622 is 850oC. At this temperature material synthesized using LiOH.H20 as the lithium precursor performs significantly better under high rate discharge conditions compared to material synthesized using Li2C03.