关键词: 锂离子电池, 正极补锂添加剂, Li₅FeO₄, 等离子增强型化学气相沉积法, 碳包覆改性

Abstract:

Li₅FeO₄ (LFO) is a promising prelithium cathode additive owing to its high theoretical specific capacity, low cost, and non-toxic nature. However, practical applications of LFO are hindered by its high residual alkali content and low electrical conductivity, which significantly reduce its delithiation capacity. To address these challenges, this study employed a high-temperature solid-phase method to prepare pure LFO material and used plasma-enhanced chemical vapor deposition (PECVD) to produce LFO@C material. The physicochemical and electrochemical properties of LFO@C were investigated under varying carbon-coating times and temperatures. Characterizations using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dissipative spectroscopy (EDS) showed that different PECVD carbon-coating parameters deposited different carbon layer structures on the LFO@C surface. A uniform and dense carbon layer was achieved when the material was carbon-coated at 500 ℃ for 2 h. X-ray diffraction (XRD) analysis confirmed that no irreversible phase transition occurred in LFO@C under these conditions, provided the carbon-coating temperature did not exceed 500 ℃ and the duration was limited to 2 h.The carbon content and electrical conductivity of LFO@C initially increased and then declined with extended carbon-coating time, while both properties increased steadily as the coating temperature rose. Residual alkali analysis demonstrated a significant reduction in the residual alkali content after PECVD carbon-coating. The surface of the carbon layer played a key role in the residual alkali value of LFO@C material. 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 756.4 mAh/g at 2.0—4.2 V, and an irreversible capacity of 623.51 mAh/g, exceeding the uncoated LFO material by over 200 mAh/g. The results showed that PECVD could be used to coat the surface of LFO particles with a uniform and dense carbon layer. This process significantly reduced the residual alkali of the carbon-coated materials, while greatly enhancing electrical conductivity and capacity, and the prelithiation performance. In this work, the irreversible capacity of cathode prelithiation material LFO was significantly improved by carbon-coating modification, which provided technical guidance for the design of high capacity cathode prelithiation materials.

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