Conditioning Safety Index of Ni-Rich Cathode Oxides for Lithium Ion Batteries

Ni-rich cathode materials with high energy density has degradation issue of electrochemical performance due to the significant side reaction between electrolyte and cathode. To solve this, a Full Concentration Gradient (FCG) materials consisting of a high-Ni core and a relatively high-Mn outer layer was designed to provide improved stability as well as cycle life characteristic. However, a Ni-rich core still has some possibilities to be contact with electrolyte, especially if the particle in the core part is unexpectedly porous. We found the strategy to tune the particle porosity by controlling a feed rate of transition metal sulfate solutions and ammonium hydroxide solution during co-precipitation synthesis using Continuous Stirred Tank Reactor (CSTR). Additionally, the effect of surfactant was studied in the standpoint of the electrode stability. The structural characteristics was compared for the materials obtained by different feed rate with analysis of by X-ray diffraction, electron microscopy and dynamic light scattering. The interfacial kinetic reaction between the delithiated Ni-rich cathode and a nonaqueous electrolyte was investigated by our home-built high-precision leakage current measurement system. The result of this study indicated a different reaction phenomenon and further implies that the safety of Ni-rich cathode by co-precipitation could be controlled.