草酸亚铁法水热合成磷酸铁锂的晶化条件研究

Crystallization Conditions for Hydrothermal Synthesis of LiFePO_4 via A Ferrous Oxalate Route

以草酸亚铁为原料,通过水热晶化法制备了锂电池正极材料磷酸铁锂(LiFePO_4)S1~S6、S8和S10,进一步以葡萄糖为碳源,w(C)=6%时,制得Li Fe PO4/C复合正极材料S7和S9。采用XRD和FE-SEM对产物的结构进行了表征,对水热晶化条件进行了优化,利用扣式电池充放电方法考察了S7的电化学性能。结果表明:水热晶化的最佳反应时间为10 h,最低晶化温度为190℃。当水热晶化温度达到280℃时,无碳产物(S10)中的部分Fe(Ⅱ)会被氧化为Fe(Ⅲ),生成FePO_4·2H_2O杂质相,而葡萄糖的添加则可以抑制Fe(Ⅱ)向Fe(Ⅲ)的转化。以草酸亚铁为铁源,当晶化温度为240~260℃、晶化时间为10 h时,可以通过水热法制备出颗粒团聚程度轻微的磷酸铁锂正极材料。S7的0.1 C放电比容量达到154 m Ah/g,经过42个循环测试,其0.1 C放电比容量仍可达到149 m Ah/g。与硫酸亚铁为铁源的传统水热法相比,每制备1 t纯相LiFePO_4,锂源(氢氧化锂)的使用量从190 16 mol降低到6 339 mol。

Ferrous oxalate was employed as iron source to synthesize LiFePO4（ denoted as S1 ~ S6,S8 and S10）,a cathode material for Li-ion batteries,via hydrothermal crystallization method. Subsequently,glucose[w（ C） =6%]was used as carbon source to prepare LiFePO4/C composite materials（ S7 and S9）. XRD and FESEM were used to characterize the structure and texture of samples. Additively,the hydrothermal crystallization conditions for synthesis of LiFePO4 were optimized. The electrochemical performance of sample S7 was also evaluated by coin-cell charge/discharge tests. The results demonstrated that the best reaction time for hydrothermal crystallization process was 10 hours,and 190 ℃ was the minimum feasible crystallization temperature. When the crystallization temperature was 280 ℃,part of the Fe（Ⅱ） in carbonfree product（ S10） could be oxidized into Fe（ Ⅲ） and generated Fe PO4·2H2O impurity phase. However,the introduction of glucose could prevent Fe（Ⅱ） converting into Fe（ Ⅲ）. The LiFePO4 cathode material with slight reunion were obtained when the reaction was carried out at 240 - 260 ℃ for 10 hours with ferrous oxalate as iron source. Sample S7 exhibited excellent electrochemical performances. The initial discharge capacity reached 154 m Ah/g at 0. 1 C. Even after 42 cycles,the capacity still reached 149 m Ah/g at 0. 1 C.This hydrothermal crystallization method was better than traditional hydrothermal process by using ferrous sulfate as iron source,which could reduce amount of lithium source（ lithium hydroxide）. For the preparation of one ton pure LiFePO4,the amount of lithium source dropped from 19016 to 6339 mol.