A kinetic descriptor to optimize Co-precipitation of Nickel-rich cathode precursors for Lithium-ion batteries

Abstract

This work proposes a kinetic descriptor, reaction quotient to equilibrium constant ratio ( Q / K ), to optimize co-precipitation of nickel-rich hydroxides. Ammonia concentration of 1.0 M rendered the Q / K close to 1, where the crystals can grow efficiently by Ostwald ripening. The enhanced morphological uniformity and performances of the nickel-rich cathode validate the effectiveness of this methodology. • A descriptor to optimize co-precipitation of precursors for nickel-rich cathodes. • Well-ordered hydroxide particles can grow by Ostwald ripening if Q / K approaches 1. • The enhanced morphology and performances validate the suggested descriptor. Nickel-rich cathodes are advantageous for lithium-ion batteries (LIBs) due to their exceptional energy densities at lower cost. In general, particles' shape and crystal structure greatly influence the electrochemical performances of cathode active materials. In this regard, co-precipitation can afford secondary particles made of highly crystalline primary particles with uniform composition. Auxiliary complexing agent such as ammonia provides sufficient time for the well-ordered nucleation and growth of primary and secondary particles by retarding the hydroxide formation. Herein we suggest the reaction quotient ( Q ) to equilibrium constant ( K ) ratio, as a kinetic descriptor for the effective nucleation and crystal growth of metal hydroxide. Based on the cumulative formation constant and the solubility product values of each metal ion, about 1.0 M NH 3 concentration rendered the Q / K ratio close to 1, which implies balanced precipitation and dissolution of metal hydroxide that provides sufficient time for the crystal growth. In accordance with the theoretical expectation, co-precipitation at 1 M NH 3 rendered particles with uniform shape and size. And the resultant nickel-rich cathode outperformed other samples co-precipitated at different NH 3 concentrations, in terms of significantly higher discharge capacity, cycle stability, and rate capability.