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 LiNi_0.8Co_0.15Al_0.05O₂ (NCA) and nickel-rich LiNi_1-x-yCo_xMn_yO₂ (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^.H₂O or Li₂CO₃, 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 850^oC. At this temperature material synthesized using LiOH^.H₂O as the lithium precursor performs significantly better under high rate discharge conditions compared to material synthesized using Li₂CO₃.

References

1. Avicenne Energy, International Battery Seminar and Exhibit, March 20^th, 2017.

2. B. H. Kim, et al., The effect of oxygen pressure on the synthesis of LiNiO₂. Solid State Phenomena, Vols. 124-126, (2007), p. 1043-1046

3. P. Kalyani, N. Kalaiselvi, Various aspects of LiNiO₂ chemistry: A Review. Science and Technology of Advanced Materials, 6, (2005), p. 689–703

4. Kim, M.-H., Shin, H.-S., Shin, D. & Sun, Y.-K., Synthesis and electrochemical properties of Li[Ni_0.8Co_0.1Mn_0.1]O₂ and Li[Ni_0.8Co_0.2]O₂ via co-precipitation. Journal of Power Sources, (2006), 159, p. 1328-1333