Preparation And Performance Investigation Of Transition-metal Borates As Lithium-ion Rechargeable Battery Materials

Lithium-ion rechargeable battery has drawn much attention for its multiple merits:such as long cycle service life, high safty, non-memory, little volumn, high energy density, and so on. Since1997, Goodenough et al. have investigated the performance of LiFePO4with polyanionic structure as canthode material for lithium-ion battery, increasing research efforts have been carried out by more and more scientists. The polyanionic structure has open three-dimensional frame network. The structure has little rearrangement and keeps good stability when the lithium ions de-intercalate in the cathode material. Meanwhile, the anion with larger volumn can provide greater three-dimensional space for the migration of lithium ions; Secondly, such kind of material has a flexible and controllable charge-discharge potential. Compared with P element. B has a lower electronegativity, lower atomic weight, abundant advantages. LiMBO3material has a high energy density, little volume change. Therefore, this paper is focused on the preparation and electrochemical properties of LiMnBO3material. Besides LiMBO3material, the preparation and electrochemical properties of Fe3BO6material has also been explored. The main results and progresses are summarized as follows:1. LiMnBO3/C composites have been prepared via a solid state reaction process on the basis of investigation of structure, synthesis methods and applications of borate materials. In addition, phase controllable synthesis was achieved by adjusting the reaction temperature. The reaction temperature has been optimized. The initial reaction mechanism of LiMnBO3/C composite cathode materials in lithium-ion battery has been discussed and studied. The h-LiMnBO3/C particles were obtained at750℃, which keep high cycle stability and retain86.5%of the initial discharge capacity (90.7mAh g-1) after40cycles at11mA g-1within1.25-4.80V under constant current charge-discharge mode. While the m-LiMnBO3/C particles could be obtained at500-600℃. The m-LiMnBO3/C particles prepared at600℃have an initial discharge capacity of up to107mAh g-1. It is notable that even if the current density is increased to22mA g-1, the specific discharge capacity of74.4mAh g-1still can be obtained. The above results indicate that the LiMnBO3/C materials with controllable phases obtained via the convenient in-situ carbothermal solid state synthesis method are promising cathode materials for lithium-ion rechargeable batteries.2. Fe3BO6nanocrystals were obtained via a solvothermal process in autoclave at700℃following a subsequent calcination treatment. In the absence of the subsequent calcination process, Fe3BO6nanorods encapsulated in graphite core-shell like powders were obtained. The rate performances at varied current densities (100,200,500,1000mA g-1) and long cycle stability (at100mA g-1within0.01-3.0V) of the Fe3BO6powders were systematically investigated for the first time. The Fe3BO6nanocrystals composed of nanoscale nanorods and particles obtained here have enhanced cycling stability and high improved specific capacity. The discharge capacity of Li/Fe3BO6battery can maintain at873mAh g-1after100cycles at the current density of100mA g-1, and the discharge specific capacity is up to550mAh g"1at high current density of1000mA g-1, indicating its excellent cycle stability and good rate performances as anode material at high power field. Besides, the present synthesis strategy is believed to be helpful to fabricate series of many other target materials that are sensitive to air or undertake large volume changes in the charge-discharge process.