Capacity Fading Mechanism of Ni-Rich Layered Li[Ni_xCo_yMn_1-x-Y]O₂ Cathode with x ≥ 0.9

Abstract

Electric vehicles (EVs) require rechargeable batteries with high energy density and excellent capacity retention to meet the target driving range and ensure sufficient vehicle service life. However, the specific energy density and lifetime of EVs are largely limited by the performance of the cathode. For this reason, research on EV batteries primarily concentrated on characterizing and developing optimal cathode materials. Among the numerous proposed cathodes, Ni-rich Li[NixCoyMn1-x-y]O2 (NCM) and Li[NixCoyAl1-x-y]O2 (NCA) cathodes are the main candidates for high performance EVs because of their high reversible capacity and operating potential. However, due to structural instability, parasitic surface reactions arising from accumulation of a NiO-like phase on the surface, it is difficult to satisfy the recommended driving range and battery lifetime at the same time.1-3 Many researches have revealed the degradation mechanism of Ni < 90%, however, there are few experimental reports on the NCM cathodes with x ≥ 0.9. Because there is a lack of comprehensive data explicitly showing the capacity fading trend of NCM cathodes (x ≥ 0.9), the current technology shows the ultimate limitation in safely utilizing the energy storage capabilities of the Ni-rich NCM cathode. In the studies presented here, Ni-rich NCM cathodes with precisely controlled compositions, LNO (x = 1.00), NCM98 (x = 0.98), NCM96 (x = 0.96), NCM94 (x = 0.94), NCM92 (x = 0.92) and NCM90 (x = 0.90) were synthesized and compared to obtain a comprehensive mechanism of the capacity fading of highly Ni-rich NCM cathodes. In situ-XRD, scanning spreading resistance microscopy (SSRM) and electrochemical analysis became the main experiment and revealed the mechanism. Reference s Yoon, C. S.; Choi, M. H.; Lim, B.-B.; Lee, E.-J.; Sun, Y.-K, Electrochem. Soc. 2015, 162, A2483-A2489. Ryu, H.-H.; Park, K.-J.; Yoon, C. S.; Sun, Y.-K, Mater. 2018, 30, 1155-1163. Yoon, C. S.; Ryu, H.-H.; Park, G.-T.; Kim, J.-H.; Kim, K.-H.; Sun, Y.-K, Mater. Chem. A, 2018, 6, 4126-4132.