Electrochemical performance evaluation of a Ni/Fe mixed oxide natural clay composite as anode material for Li-ion batteries

Abstract

A Ni/Fe mixed oxide natural clay composite was obtained by simple addition of bentonite natural clay sample after coprecipitation of layered double hydroxide (Ni0.75Fe0.25(OH)2(CO3)0.125) precursor; later this composite was sintered at 400 °C. The natural clay was collected from La Plata city (Argentina), and this has been used without further purification treatment. The electrochemical characterization allowed to identify stability improvement of the charge-discharge capacity values for the materials with calcination (35 % capacity retention after 60 cycles) against an anode prepared without clay (only 8 % retention). However, the anodic material without clay delivered a higher discharge capacity than the anode material with clay, as expected, due to the lacking the non-electroactive clay quantity. Physical characterization of the materials, such as nitrogen physisorption, showed a smaller particle diameter (37 nm against 54 nm) for the mixed oxides with and without natural clay, respectively. Despite this, by scanning electron microscopy a greater size difference was observed in the morphology for the oxide- natural clay composites. This could be because the smaller particle size along the interstitial space of the consecutive clay flakes and the pore volume of the material could be produced a synergistic effect between them; and thus promote a buffered volumetric expansion. This is generally reported to be responsible for the low charge- discharge cyclic performance observed in the conversion anodes. Also, the process of re-dissolution of the hydroxide precursor in the basic media, followed by the double hydroxide re-precipitation from Ni+2 and Fe+3 which are adsorbed in negative sites of the clay could be responsible for the achievement of the smaller size particles.