Development of new polyanionic cathode/anode active materials for post Li-ion batteries

本课题为实现电动汽车用低成本、高能量密度锂离子电池的研究主要包括以下几个方面：1）磷酸铁合成新工艺：a）高温熔融合成LiFePO_4：以活性较低的氧化铁为原料，将FeO与P_2O_5和LiOH-H_2 O在1500 ℃下熔融几分钟，在Ar气氛中冷却。慢冷样品的放电容量为140 mAh/g，与固相合成的橄榄石型LiFePO_4的放电容量曲线相似，而急冷非晶态样品的放电容量曲线单调下降，容量较低。B）低温软化学法制备FePO_4：以廉价铁粉为原料，在室温下，将金属铁粉与P_2O_5在水中反应。在500 ℃退火时，最大比容量可达153 mAh/g。2）焦磷酸盐体系我们可以得到LiVP_2O_7和TiP_2O_7等新化合物。它们在充/放电循环中显示了M^<2+>/M^<3 +>和M^<3+>/M^<4+>氧化还原反应。（MoO_2）_2P_2O_7作为钠离子电池的正极材料，其可逆容量最大（150 mAh/g）。3）硼酸盐体系合成了方解石型硼酸铁（FeBO_3）作为聚阴离子负极材料，其容量高于石墨。为了降低电压，可以成功地将Fe置换为V或Ti。4）硅酸盐体系合成了单相Li_2CoSiO_4。橄榄石型硅酸盐的理论容量比橄榄石型磷酸盐如LiFePO_4的理论容量大两倍。（5）氟磷酸盐体系作为一种新的氟磷酸盐体系，采用固相法合成了单相Li_2CoPO_4F，并通过中子衍射对其结构进行了鉴定。理论容量是LiFePO_4的两倍，电池电压为4.8V。

Our research of realize low-cost and high-energy density post Li-ion batteries for EV use can be summarized as follows;1)New synthesis process for iron phosphate :a)High temperature melting synthesis for LiFePO_4 :In order to use low reactive iron oxide as starting material, FeO was melted with P_2O_5 and LiOH-H_2O at 1500 ℃ for a few minutes and cooled in an Ar atmosphere. The slow-cooled sample with 140 mAh/g shows a similar profile to solid-state synthesized olivine LiFePO_4, though the quenched amorphous sample shows a monotonically decreasing discharge profile with poor capacity.b)Low temperature soft chemistry method for FePO_4 :In the use of low cost iron powder as a starting material, metallic iron powder and P_2O_5 were reacted in water at room temperature. The highest capacity obtained by annealing at 500 ℃ was 153 mAh/g.2)Pyrophosphate systemWe could obtained LiVP_2O_7 andTiP_2O_7 as new compounds. They show both M^<2+>/M^<3+> and M^<3+>/M^<4+> redox reactions on charge/discharge cycle. Moreover, (MoO_2)_2P_2O_7 shows the largest reversible capacity (150 mAh/g) as a cathode fur Na battery.3)Borate systemWe synthesized the calcite-type iron borate (FeBO_3) as polyanionic anode with higher capacity than that of graphite. In order to reduce the voltage, the redox couple replacement from Fe to V or Ti could be done successfully.4)Silicate systemWe could synthesized the single-phase Li_2CoSiO_4. The theoretical capacity of the olivine-type silicate is two times larger than that of the olivine-type phosphate such as LiFePO_4.5)Fluoro-phosphate systemAs a new fluorophosphate system, single phase Li_2CoPO_4F could be obtained by solid-state synthesis method and the structure was identified by neutron diffraction. The theoretical capacity is two times larger than that of LiFePO_4 and the cell voltage is 4.8 V.versus Li.