In-situ Hybridization Of Lithium Iron Silicates With Lithium Iron Borates (Phosphates) As Cathode Materials For Lithium Ion Batteries

With the development of science and technology, the traditional electrode materials of lithium ion battery is more and more difficult to meet modern electronic equipments demand. Silicate represented by Li₂FeSiO₄ as lithium ion battery cathode material with high theoretical capacity?332 mAh/g?, abundant raw materials, low price, non-pollution and good structure stability and safety, etc, is the new potential cathode material of lithium-ion battery. But Li₂FeSiO₄ has common defects of the most polyanionic materials that lower intrinsic electronic conductivity and lithium ion diffusion rate as the cathode material. This kind of defects of Li₂FeSiO₄ can lead to the poor cycle performance and power charge and discharge performance as lithium ion battery cathode material, so its application was limited.In order to relieve these problems of Li₂FeSiO₄ in this paper, Li₂FeSiO₄ is prepared via suitable synthesis method, and modified: carbon coated on surface and heterophase structure hybridization, improving the electrochemical properties of Li₂FeSiO₄. This study mainly includes two mainly aspect as follow:?1??1-x?Li₂FeSiO₄·xLiFeBO₃/C?x = 0, 0.02, 0.05, 0.08 and 0.12? heterogeneous grain nanocomposites are obtained by in situ citric acid assisted-sol-gel method, and their electrochemical performance are investigated. The results show that 0.92Li₂FeSiO₄·0.08LiFeBO₃/C sample has the best cycle performance and rate performance as the cathode material. The discharge specific capacity of 0.92Li₂FeSiO₄·0.08LiFeBO₃/C sample reach 251 mAh/g after five cycles at the rate of 0.1 C and compare to the first cycle, the capacity retention rate is 104.5%, and discharge specific capacity of Li₂FeSiO₄/C electrode is only 192.7 mAh/g after five cycles, 93.0% of capacity retention rate. 0.92Li₂FeSiO₄·0.08LiFeBO₃/C display a good cycle stability at the rate of 1 C, after one hundred cycles, the capacity still has 102.9% of the tenth cycle, and even the capacity still has 115 mAh/g at the rate of 10 C, far above 84 mAh/g of Li₂FeSiO₄/C sample, and the capacity?175.1 mAh/g? of 0.92Li₂FeSiO₄·0.08LiFeBO₃/C sample after 40 higher rate cycles back to 1 C rate is slightly higher than that?171.1 mAh/g? of 1 C rate before higher rate cycles. In addition, the electrochemical performance of 0.92Li₂FeSiO₄·0.08LiFeBO₃/C is very excellent as the anode material, and promising in the potential application of high-energy lithium-ion battery anode materials.?2? The same above-mentioned method is used to synthesize?1-x-y?Li₂FeSiO₄·xLiFeBO₃·yLiFePO₄/C heterogeneous nanometer grain composites. The results show that the 0.92Li₂FeSiO₄·0.04LiFeBO₃·0.04LiFePO₄/C sample has the best charge and discharge performance. The discharge specific capacity of 0.92Li₂FeSiO₄·0.04LiFeBO₃·0.04LiFePO₄/C cathode material still has 168.6, 115.9 and 108.3 mAh/g after 30, 200, 500 cycles at the rate of 0.1 C, 1 C, 5 C, respectively, far higher than that of Li₂FeSiO₄/C?134.5, 134.5 and 134.5 mAh/g? and 0.8Li₂FeSiO₄·0.1LiFeBO₃·0.1LiFePO₄/C?134.5, 134.5 and 134.5 mAh/g?. And at the rate performance test, the capacity 0.92Li₂FeSiO₄·0.04LiFeBO₃·0.04LiFePO₄/C cathode material still has 133.4 mAh/g after 40 cycles at different rate back to 1 C rate, showing more excellent cycle stability.Proper LiFe BO₃ or LiFeBO₃ and LiFePO₄ hybridized with Li₂FeSiO₄ can generate fast electrons and ions conduction network structure within the grain, thus the composite can more rapidly conduct electronic and lithium ion in grain internal, and reduce the interface dynamics of material, greatly improving the electrochemical performance of such materials.