engleski

Effect of structural and microstructural features on the performance of CoMn2O4 as anode material in lithium ion batteries

Cobalt-dimanganate samples were prepared by the precipitation route at RT. Additionally, samples were thermally treated at T=300-500 °C. Structural investigation using XRPD and Raman spectroscopy have been carried out in order to correlate specific structural features with preparation conditions and furthermore with electrochemical properties. Changes in unit-cell as function of temperature were calculated ; observed decrease is inconsistent with simple spinel-type exchange of Co2+ by Mn3+ on the tetrahedral site, and vice versa on the octahedral site. Based on the Raman spectroscopy an alternative structural model: IV[Co2+1- xMn2+x]VI[Co3+xMn3+2-x]O4 has been proposed. Rietveld refinement showed increase of M-O distances within tetrahedra, caused by thermally enhanced substitution of Co2+ by larger Mn2+ cations at A-site. Consequently, octahedral B-site becomes partially occupied by Co3+ on the account of the transferred Mn cations. In all samples, initial capacity drops as commonly observed in high capacity metal oxide materials. However, after a certain number of cycles specific capacity increases again. Among all samples, thermally treated from 100-500 oC, highest specific capacities are observed for sample thermally treated at highest temperature (500 oC) despite its large particle size. Thus, contrary to the common assumption that nanostructuring of the anode material improves the battery performance, samples with the largest particle sizes exhibit excellent performance with a capacity retention of 104% after 1000 cycles (compared to the 2nd cycle)

li-ion battery

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