Structure and electrochemical characteristics of LiFePO$_4$ cathode materials for rechargeable Li-Ion batteries

Complex investigations of cathode materials for rechargeable lithium-ion batteries have been carried out using the following techniques: scanning electron microscopy, microanalysis, extended X-ray absorption fine structure (EXAFS) spectroscopy, Mössbauer spectroscopy, and porosimetry. Investigations have been performed on samples prepared according to the original technology at the St. Petersburg State Institute of Technology (Technical University) (SPbSTI (TU)) and on four commercial cathode materials. It has been established that there is a correlation between the nanostructured morphology of the cathode materials, their chemical composition, and electrochemical capacity. It has been found that the internal resistance of the LiFePO$_4$ cathode material is linearly dependent on the diffusion coefficient of lithium ions. The valence state and local coordination of Fe ions have been studied using the $^{57}$Fe Mössbauer effect. It has been shown that more than 90% of the iron ions are in the valence state Fe$^{2+}$. Based on the data available in the literature on the methods of synthesizing LiFePO$_4$ and data on the diagnosis of the studied samples, conclusions have been drawn about a modification of the synthesis for producing high-quality cathode materials for Li-ion batteries.