Electrochemical insertion of lithium into the ramsdellite-type oxide Li_2Ti_3O_7: influence of the Li_2Ti_3O_7 particle size

摘要

The effect of a milling process on the electrochemical performance of Li_2Ti_3O_7 electrodes has been investigated by the galvanostatic intermittent titration technique (GITT) and AC impedance spectroscopy. The insertion ratio is slightly increased by the milling treatment and a values of x_(Li) = 1.25 per mol Li_2Ti_3O_7 has been determined. The average potential during insertion is close to 1.5 V/Li. The analysis of impedance data obtained at equilibrium during insertion and reinsertion shows two relaxation processes and a diffusion phenomenon at low frequency according to the Frumkin-Melik-Gayakazian model. Cycling experiments of batteries using this material were performed with unfilled and milled particles. Composite electrodes containing different amounts of electroactive material added to a binder and a conductive additive have also been prepared in order to check the effect of grinding on the cyclability of the compound. Interesting electrochemical performances have been determined with such electrodes: lithium uptake up to 1.25 Li per Li_2Ti_3O_7, low irreversible capacity loss between the first and the following cycles, good stability upon cycling even after 50 cycles. However, the milled process has not improved significantly the electrochemical performance of the Li_2Ti_3O_7 electrodes.