ІMPACT OF THE NATURE OF ELECTRICALLY CONDUCTIVE IMPURITY ON CAPACITIVE PROPER­TIES AND RESISTANCE TO CURRENT LOADS OF CATHODE MATERIALS BASED ON LiMn2O4

Abstract

The impact of the nature of electrically conductive graphite and graphene admixtures in spinel LiMn2O4 with different degrees of dispersion, composition and morphology on the surface element distribution and the  cycling ability under current loads  from 0.5 to 8 C of composite cathode materials based on such spinels have been studied by the methods of electron microscopy, X-ray spectrometry, the BET method and galvanostatic-potentiostatic cycling. The specific surface of graphene structures was studied, which was 23 m2/g for G-N and 27.7 m2/g for G-H2O, and the porosity was about 100 nm for the above samples. It was established that the degree of dispersion of spinel affects not only the morphology of the surface of the electrodes, but also the distribution of elements, primarily manganese and oxygen, which take part in electrode redox reactions, as well as the content of the carbon component. Using the elemental analysis of the component composition of the surface, the ratio of manganese to oxygen was calculated, and it was shown that in samples with graphite, manganese is in a more reduced state, and the maximum oxidized state of manganese is observed in samples with graphene, which was synthesized from an aqueous medium. In the case of finely dispersed spinel, the dependence of the carbon content and the ratio of manganese to oxygen on the surface has an antibate character relative to samples with coarsely dispersed spinel and correlates with the number of meso­pores on the surface. The dependence of the degree of dispersion and the oxidation state of manganese is in good agreement with the dependence of specific capacity on the discharge current density for composite electrodes. In XDM spinel with graphene synthesized from an aqueous medium, the obtained capacitive characteristics exceed the other characteristics of the materials by 20%. It has been experimentally proven that by changing the nature of the impurity and the degree of dispersion of the spinel, it is possible to adjust the capacitive properties and resistance to current loads of composite electrodes.