磷酸钒锂微纳结构的可控制备及其用作高能量锂电池正极材料的研究

Because of their high energy density, good cycling performance and charge retention capability, lithium-ion batteries (LIBs) have been widely used in portable electronic devices. To date, the performance of the lithium ion batteries still cannot totally fullfill the requirement of high energy density and power capability for electric vehicles. Currently the commercial and most studied cathode materials are lithium transition metal oxides, which suffer from their low capcity and inferior safety. Monoclinic Li3V2(PO4)3 heritates the safety feature of phosphates, and has high operating voltage pleatues,high specific discharge capacity and better rate capability. However, the electronic conductivity of Li3V2(PO4)3 needs improvement and the capacity fades fast operated in high voltage. Taking the advantages of making Li3V2(PO4)3/carbon composites, metal oxide coating and cations doping, the electrochemical performance of the Li3V2(PO4)3 cathodes can be improved by fabricating optimized structures, which ensure the high quality of Li3V2(PO4)3/carbon composites, and the homogeneity of metal oxide coating and cations doping.It will be a new alternative cathode material for energy conversion and storage with high efficiency.

锂离子电池因为其高能量密度、良好的循环性能及荷电保持能力被广泛地应用在便捷式的电子器件中。但是目前锂离子电池还不能完全满足电动汽车高能量密度，大功率的要求。其原因主要是商品化的和即将进入开发性研究的正极材料大多是嵌锂过渡族金属氧化物，其主要原因是这些正极材料的容量偏低，安全性能较差。单斜结构的Li3V2(PO4)3不仅继承了磷酸盐安全性能好的特点，而且工作电压平台高，容量大，能量密度高和倍率性能好，作为锂离子电池的正极材料被广泛研究。但Li3V2(PO4)3自身导电性能仍需改进，且高电压充电时容量衰减明显。本项目拟通过优化材料的微纳结构，实现可控制备，集合炭复合、氧化物包覆和阳离子掺杂的优势，提高Li3V2(PO4)3纳米颗粒与炭的复合效率，优化氧化物包覆和离子掺杂的均匀性，获得电化学性能优异的Li3V2(PO4)3正极材料。成为能源高效存储和释放的新一代正极材料。

锂离子电池因为其高能量密度、长寿命等特点在便携式的电子器件中得到了广泛的引用。磷酸盐电极材料相比于其他正极材料具有更好的安全性能和循环稳定性，在电动汽车等领域中具有独特的优势。磷酸钒锂正极材料相比于商业化的LiFePO4具有更高的工作电压和更高的容量，而且还具有更大的锂离子扩散系数。但是Li3V2(PO4)3正极材料也存在容量衰减和导电性差等问题，如何构筑低尺度的电极材料、提高活性物质与导电材料的复合效率是提升其电池性能的关键。 本项目通过材料结构优化、炭包覆和离子参杂等技术，构筑Li3V2(PO4)3/C复合材料，提升综合电化学性能。具体开展的工作包括硬模板法制备Li3V2(PO4)3/C多孔微纳米球，Li3V2(PO4)3/石墨烯等；软模板法制备炭包覆的纳米片密堆积的Li3V2(PO4)3微米球；表面活性剂辅助高温一步法制备Li3V2(PO4)3/C纳米带等；溶胶-凝胶法制备KB炭/Li3V2(PO4)3/C复合材料和MOF衍生炭/ Li3V2(PO4)3复合材料；阳离子共掺杂的x Li3V2(PO4)3．yLiFePO4、Li3V2(PO4)3．LiMnPO4等复相磷酸盐。通过上述材料的优化，提升了整个电极材料的倍率性能和循环性能。