Influence of synergistic effect of LiNi0.8Co0.15Al0.05O2@Cr2O5 composite on the electrochemical properties

LiNi_0.8Co_0.15Al_0.05O₂ (NCA)@Cr₂O₅ composite electrode combines the high rate-capability characteristics of NCA with the stability of Cr₂O₅, playing a synergistic role in improving the cyclic stability, initial discharge capacity and the security of low cut-off voltage (2.0 V). When the mass ratio of Cr₂O₅ in NCA is 45% (mass), the capacity retention rate increases from 58.5% without Cr₂O₅ to 69.3% in the range of 2.0-4.3 V. The initial discharge capacity of NCA@Cr₂O₅ composite material is 211.4 mA·h·g^-1, its first coulombic efficiency is 94.2%, and the charging capacity remains approximately constant when mixed with 15% (mass) Cr₂O₅. The reason for the improvement of the initial charge-discharge efficiency (ICDE) was explained. Impedance and cyclic voltammetry analysis reveal more detailed reasons of the observed improvements. Compared with NCA cathode material, the NCA@Cr₂O₅ composite material can provide not only additional stable sites and channels for Li⁺ insertion/extraction to make up for the loss of active Li⁺ sites and prevent the accumulation of Li⁺ in the circulation process, but also protect the NCA electrode from the corrosion of the electrolyte decomposition by the Cr₂O₅ nanoparticles adhering to NCA interface.