The effects of Co doping on the crystal structure and electrochemical performance of Mg(Mn2 − xCox)O4 negative materials for lithium ion battery

• Pure and Co doped MgMn2O4 are studied as negative materials for lithium ion battery for the first time.
• Co doping induces a phase transition of MgMn2O4 from a tetragonal to a cubic spinel-structure.
• Co content has a significant effect on the electrochemical performance.
• The anti-sites defects resulting from the Co substitution for Mn is discovered by neutron diffraction.

MgMn2O4 and Co doped Mg(Mn2 − xCox)O4 (x = 0.5, 1.0 and 2.0) compounds have been successfully synthesized and studied as negative materials for lithium ion battery for the first time. Co doping induced a phase transition of MgMn2O4 from a tetragonal spinel-structure with a space group of I41/amd to a cubic spinel structure with a space group of Fd-3m. Electrochemical measurements indicate that the reversible capacity and cyclability of Mg(Mn2 − xCox)O4 first increases and then decreases with increasing Co content indicating that Co content has a significant effect on the electrochemical performance. MgMn1.5Co0.5O4 shows the best electrochemical performance compared to the other three samples. This might be largely attributed to the phase transition and anti-sites defects of spinel crystal cell resulting from the Co substitution for Mn, which was further confirmed by Rietveld refinement of neutron diffraction.

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