Mn掺杂LiFePO4的结构及电化学性能研究

Effects on the structure and electrochemical performance of LiFePO_4 by Mn^(2+) doping

利用高温固相反应法在惰性气氛下合成了掺Mn的LiFePO4正极材料。考察了Mn2+的掺杂浓度对于目标化合物结构及其电化学性能的影响。应用XRD、循环伏安和恒流充放电等方法对产物进行了结构表征和性能测试。结果表明,产物具有单一的橄榄石型结构,Mn2+掺杂并未影响目标产物的结构,而是与LiFePO4形成了LiFe1-yMnyPO4(y为Mn的掺杂浓度)固溶体。目标产物具有优良的电化学性能。充放电测试表明,在0.1C倍率下放电,LiFe0.5Mn0.5PO4材料的首次放电比容量达129.1mAh/g,在4.1及3.5V处各存在一个放电平台。充放电循环20次循环后,容量仍保持在120.9mAh/g。利用循环伏安测试分析了Mn的改性效果及锂离子在目标化合物中脱嵌的过程。

Stoichiometric Mn-doped lithium iron phosphate （LiFePO4） cathode material was synthesized by a solid-state reaction in an inert atmosphere. The effects of doping content on the physical and electrochemical properties of as-synthesized cathode materials were investigated. The samples were characterized by powder X-ray diffraction （XRD）, and their electrochemical performance was systematically measured by Cycle Voltammetry and constant current charge/discharge cycling tests. The results indicate that Mn^2＋ doping does not affect the structure of the material but considerably form solid solution LiFe1-yMnyPO4 （y is the doping content of Mn^2＋） with a single crystal olivine structure. The title compound showed excellently in terms of capacity delivery and cycle performance compared with pure LiFePO4. At 0.1C discharging rate,the results showed that the LiFe0.5 Mn0.5PO4 cathode material reversible has a specific capacities of 129. 1mAh/g,and exhibits 3.5 and 4.1V discharge voltage plateau respectively. After 20 cycles, the specific capacity was 120. 9mAh/g. The doping effect and the insertion-deinsertion of lithium ions were analyzed by cycle voltammetry.