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

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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.