Well-ordered spherical LiNixCo(1―2x)MnxO2 cathode materials synthesized from cobolt concentration-gradient precursors

Spherical NixCo(1-2x)Mnx(OH)2 (x = 0.333, 0.4, 0.416, 0.45) precursors with Co concentration-gradient were prepared by co-precipitation from sulfate solutions using NaOH and NH4OH as precipitation and complexing agents. Then, well-ordered spherical LiNixCo(1-2x)MnxO2 was synthesized by sintering the mixture of as-prepared precursor and Li2CO3 at 950 degree C for 16 h in air. EDXS results indicated that the concentration of cobalt decreased gradually inside out of the spherical precursor particle, and it was uniform in spherical LiNixCo(1-2x)MnxO2 particle obtained by sintering with Li2CO3. According to Rietveld refinement of XRD patterns, the LiNixCo(1-2x)MnxO2 synthesized from Co gradient precursor showed lower degree of cation disorder than that prepared from conventional precursor. The well-ordered LiNixCo(1-2x)MnxO2 from Co gradient precursor delivered much better high-rate capability than conventional one. The decrease of cation disorder of LiNixCo(1-2x)MnxO2 is attributed to the cobalt-rich in core of the precursor particles. Both abundant Co3+ and Li+ can restrain cation mixing effectively. Since Li+ needs long time to reach core during calcining, cobalt-rich in core of the precursor particle is very important for restraining cation mixing. Concentration-gradient precursor is helpful to prepare well-ordered LiNixCo(1-2x)MnxO2 with good high-rate capability, and the total content of expensive and toxic cobalt does not need to be increased.