Synthesis and Characterization of a Multication Doped Mn Spinel, LiNi$_{0.3}$Cu$_{0.1}$Fe$_{0.2}$Mn$_{1.4}$O$_{4}$, as 5 V Positive Electrode Material

The suitability of multication doping to stabilize the disordered Fd3̅m structure in a spinel is reported here. In this work, LiNi$_{0.3}$Cu$_{0.1}$Fe$_{0.2}$Mn$_{1.4}$O$_{4}$ was synthesized via a sol–gel route at a calcination temperature of 850 °C. LiNi$_{0.3}$Cu$_{0.1}$Fe$_{0.2}$Mn$_{1.4}$O$_{4}$ is evaluated as positive electrode material in a voltage range between 3.5 and 5.3 V (vs Li$^{+}$/Li) with an initial specific discharge capacity of 126 mAh g$^{-1}$ at a rate of C/2. This material shows good cycling stability with a capacity retention of 89% after 200 cycles and an excellent rate capability with the discharge capacity reaching 78 mAh g$^{-1}$ at a rate of 20C. In operando X-ray diffraction (XRD) measurements with a laboratory X-ray source between 3.5 and 5.3 V at a rate of C/10 reveal that the (de)lithiation occurs via a solid-solution mechanism where a local variation of lithium content is observed. A simplified estimation based on the in operando XRD analysis suggests that around 17–31 mAh g$^{-1}$ of discharge capacity in the first cycle is used for a reductive parasitic reaction, hindering a full lithiation of the positive electrode at the end of the first discharge.