LiCo 1Ày Fe y PO 4 solid solutions (0 # y # 1) were prepared by the mechanochemically assisted carbothermal reduction of Co 3 O 4 and Fe 2 O 3 . Mechanical activation was performed using a high-energy planetary mill AGO-2. The samples were characterized in detail by X-ray powder diffraction (XRD) using a Rietveld refinement, Fourier transform infrared spectroscopy (FTIR), M össbauer spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), galvanostatic cycling, and galvanostatic intermittent titration technique (GITT). According to XRD, all the samples are single-phase solid solutions, crystallized in an orthorhombic structure (S.G. Pnma). The cell volume of LiCo 1Ày Fe y PO 4 linearly increases vs. the Fe content. All the Fe ions are in the 2+ oxidation state and are octahedrally coordinated. The LiCo 1Ày Fe y PO 4 solid solutions show improved electrochemical performance, compared with LiCoPO 4 . Based on the data from XRD and GITT, the improvement is attributed to the enhanced Li + diffusion, due to the enlargement of the 1D diffusion channels in the polyanion structure of LiCoPO 4 and the reduced cell volume change in the material during the Li extraction/insertion process. Moreover, a systematic decrease in the average potential of the Co 2+ /Co 3+ redox pair is observed with the increased Fe content, leading to the reaction termination in the electrochemical window of conventionally available electrolytes. In situ synchrotron diffraction shows that upon charging LiCo 0.5 Fe 0.5 PO 4 , the twophase mechanism of Li (de)intercalation at the Fe 2+ /Fe 3+ and Co 2+ /Co 3+ redox stages changes to a solid solution-like mechanism, contrary to the pristine LiFePO 4 and LiCoPO 4 materials.
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