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采用碳热还原法以磷铁和碳酸锂为原料合成了LiFePO4,用XRD、恒流充放电法和EIS对其进行表征,用TG-DTA分析了反应过程。预焙烧过程中磷铁中的磷与碳酸锂反应形成Li4P2O7和LiFeP2O7,再与中间产物Fe2O3、Fe3O4和补充磷源NH4H2PO4进一步反应生成LiFePO4。产物具有良好的电化学性能,在0.1C时放电容量可以达到151.68mAh/g,0.2和0.5C分别循环10和20次后放电容量仍有125.94和103.51mAh/g,衰减率分别为4.23%和7.24%。不同荷电状态的EIS结果表明:放电至2.4V具有最小的溶液阻抗;界面阻抗由于充放电至3.4V时包括一部分不稳定的SEI膜,因此比充放电至2.4V时大;随着充放电过程的继续,反应过程由反应控制逐渐变为扩散控制。
LiFePO4 was synthesized from the ferrochromium and lithium carbonate by carbothermic reduction method, characterized by XRD, constant current charge-discharge method and EIS. The reaction process was analyzed by TG-DTA. During the pre-calcination, phosphorus in the iron phosphate reacts with lithium carbonate to form Li4P2O7 and LiFeP2O7, and further reacts with the intermediate products Fe2O3, Fe3O4 and the additional phosphorus source NH4H2PO4 to generate LiFePO4. The product has good electrochemical properties. The discharge capacity can reach 151.68mAh / g at 0.1C and 125.94 and 103.51mAh / g after 0.2 and 0.5C cycles respectively. The decay rates are 4.23% and 7.24%. The EIS results at different states of charge show that the discharge impedance to 2.4V has the lowest solution impedance. The interface impedance is larger than the charge-discharge to 2.4V due to the inclusion of some unstable SEI films due to charge-discharge to 3.4V. The continuation of the process, the reaction process gradually changed from reaction control to diffusion control.