To compare the effects of aluminum and manganese elements on the cycle performance of high-nickel cathode materials and further determine the differences in cycling stability and degradation mechanisms of nickel-cobalt-aluminum (NCA), nickel-cobalt-manganese (NCM), and nickel-cobalt-manganese-aluminum (NCMA), three common NCA, NCM, and NCMA high-nickel cathode materials with the same nickel content were chosen to study their similarities and differences of the cycle performance and the structural changes. The outcomes show that the three high-nickel cathode materials' cycle performance under room temperature is in the order of NCA>NCMA>NCM. Additionally, discovered by differential capacity (dQ/dV) curve and scanning electron microscopy, the degree of structural damages of the three materials at the same stage is in the order of NCM>NCMA>NCA, and the capacity decay of the battery during cycling is primarily caused the structural damages of the cathode materials. More study was performed on the cathode materials by electrochemical impedance spectroscopy at various cycle stages. It was discovered that the impedance of the cathodes continued to increase during cycling, and the impedance increase was influenced by the modifications in the crystal and the secondary particle structures. The discrepancies in the cycle performance of the three high-nickel cathode materials would ultimately be caused because the cycle stability of the cells is directly tied to the structural stability of the cathode materials. Systematic comparison and analysis of the cycle performance of NCA, NCMA, and NCM are helpful to deepen the understanding of the composition-structure-performance relationship of high-nickel content cathode materials, and it is of great significance for improving their cycle stabilities.
Fig. 1
Capacity retention rate curves of the three batteries during cycling (the capacity retention rate curves fluctuate due to factors such as the power outage of the incubator during the test)
Fig. 2
Ratio of recoverable capacity and non-recoverable capacity at small rate, as well as total loss of (a) NCA, (b) NCMA and (c) NCM battery during cycle process
图9
NCA正极循环首次循环与循环28次后充电过程与放电过程中 c 轴长度(原位XRD精修计算结果)对比
Fig. 9
The c-axis lengths (in-situ XRD refinement calculation results) during (a) charging process and (b) discharging process of NCA cathode before cycling and after cycling 28 times
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