Abstract:

Li₅FeO₄(LFO) prelithium cathode additive has the advantages of high theoretical specific capacity, low cost and non-toxicity, and is one of the most promising prelithiation technologies. However, its high residual alkali and low electrical conductivity lead to its greatly reduced delithium capacity in practical use, which limits its further application. To solve this problem, this study employed a high temperature solid phase method to prepare pure LFO material, and used plasma enhanced chemical vapor deposition (PECVD) to obtain LFO@C material and investigated the physicochemical and electrochemical properties of LFO@C material at different carbon-coating time and temperature. Scanning electron microscopy (SEM), transmission electron microscope (TEM) and energy analysis spectroscopy (EDS) showed that different PECVD carbon-coating paramaters deposited different carbon layer structures on the surface of LFO@C. A uniform and dense carbon layer was deposited on the surface of the LFO@C material when the carbon-coating was perfoermed at 500℃ for 2h. X-ray diffraction (XRD) analysis showed that there was no irreversible phase transition of LFO@C when the carbon-coating temperature was 500℃ and the carbon-coating time was less than 2h.The carbon content and electrical conductivity of LFO@C increased and then decreased with the increase of carbon-coating time, and increased with the increase of carbon-coating temperature. The residual alkali analysis showed that the residual alkali value of LFO material decreased obviously after PECVD carbon-coating, and the residual alkali value of LFO@C material was related to the surface carbon layer structure. The electrochemical properties of the carbon-coated LFO@C materials have been greatly improved. Among the carbon-coated materials, the LFO-5002 material exhibited the highest initial charge specific capacity of 756.4mAh/g at 2.0~4.2V, and an irreversible capacity reaches 623.51mAh/g, which exceeded that of the uncoated LFO material by more than 200mAh/g. The results showed that PECVD could be used to coat the surface of LFO particles with a uniform and dense carbon layer, and the residual alkali of the carbon-coated materials was greatly reduced, the electrical conductivity and capacity were greatly improved, and the prelithium effect was greatly improved. In this work, the irreversible capacity of cathode prelithium material LFO was significantly improved by carbon-coating modification, which provided technical guidance for the design of high capacity cathode prelithium materials.

Key words: lithium-ion battery, cathode prelithium additive, Li₅FeO₄, plasma enhanced chemical vapor deposition(PECVD), carbon-coating modification