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We have revisited the study of the nanostructured lithium iron silicate-based cathode for a safe lithium-ion battery and to understand the reaction mechanism from the first cycle to the second cycle. Ex situ Mössbauer and X-ray absorption near edge structure spectroscopy (XANES) measurements have been carried out on electrodes charged at various voltages to investigate the electrochemical activity of the Fe3+/Fe4+ redox couple to confirm the existence of Fe4+ and its role in defining the structural and electrochemical properties. The first charge and discharge lead to a structural change, which results in a potential plateau shift after the first charge. To validate this understanding, ex situ synchrotron X-ray diffraction (SXRD) along with Rietveld refinement results and first-principles density functional theory-based analysis have been performed, which also support the change in the crystal structure of the material with cycling. The in situ electrochemical impedance spectroscopy demonstrates phase transformation in delithiated iron silicate as lithium concentration changes during the charging process, which has been correlated with change in the density of states calculated by density functional theory. Finally, a full-cell prototype has been demonstrated for the first time using a lithium iron silicate cathode as the cathode and graphite as the anode, and this full cell showed a capacity retention of 92% after 50 cycles at a 1 C rate.

Safe and high-capacity cathode materials are a long quest for commercial lithium-ion battery development. Among various searched cathode materials, LiFeSiO has taken the attention due to optimal working voltage, high elemental abundance, and low toxicity. However, as per our understanding and observation, the electrochemical performance of this material is significantly limited by the intrinsic low electronic conductivity and slow lithium-ion diffusion, which limits the practical capacity (a theoretical value of ∼330 mAh g). In this report, using first-principles density functional theory based approach, we demonstrate that chlorine doping on oxygen site can enhance the electronic conductivity of the electrode and concurrently improve the electrochemical performance. Experimentally, X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission gun scanning electron microscopy elemental mapping confirms Cl doping in LiFeSiOCl/C (x ≤ 0.1), while electrochemical cycling performance demonstrated improved performance. The theoretical and experimental studies collectively predict that, via Cl doping, the lithium deinsertion voltage associated with the Fe/Fe and Fe/Fe redox couples can be reduced and electronic conductivity can be enhanced, which opens up the possibility of utilization of silicate-based cathode with carbonate-based commercial electrolyte. In view of potential and electronic conductivity benefits, our results indicate that Cl doping can be a promising low-cost method to improve the electrochemical performance of silicate-based cathode materials.

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