中文摘要：

采用水热法,通过Fe、Mg共掺杂制备了一系列锂二次电池正极材料LiMn（0.7）Fe（0.3-x）MgxPO4/C（x=0,0.02,0.05,0.07）。通过X射线衍射、扫描电子显微镜对材料结构、形貌进行表征。采用所得正极材料组装电池,并利用恒流充放电和循环伏安对其电化学性能进行测试。结果表明：Fe、Mg元素完全进入材料晶格,并占据Mn位,适量的Mg掺杂能够增大（101）的晶面间距,使得Li~＋扩散通道变宽。所制得的电池倍率性能曲线在1C前后发生反转：当充放电倍率小于1C时,LiMn（0.7）Fe（0.28）Mg（0.02）PO4/C的放电比容量最高,在0.1C时为150.3 mA·h/g;当倍率大于1C时,LiMn（0.7）Fe（0.23）Mg（0.07）PO4/C放电比容量最高,5C时为94.5 mA·h/g。

英文摘要：

A series of LiMn0.7Fe0.3.xMgxPO4/C（x=0, 0.02, 0.05, 0.07） composite materials as a cathode for lithium secondary batteries were synthesized by a hydrothermal method with Fe and Mg as co-substituted materials. The crystal structure and morphology of the products were investigated by X-ray diffraction and scanning electron microscopy. The coin-type cells were assembled and its electrochemical properties were evaluated via galvanostatic charge/discharge tests and cyclic voltammetry. The results show that Fe and Mg enter the lattice fully, which can occupy Mn position, and the interplanar distance of （101） plane of LiMnPO4 can be enlarged by Mg doping, thus increasing the diffusion channels of Li＋. The rate performance of the materials reverses at 1C. The obtained LiMno.TFe0.2sMg0.02PO4/C can deliver the highest discharge capacity when the charge/discharge rate is 〈 1C and it has a capacity of 150.3 mA.h/g at 0.1C. However, LiMno.7Feo.z3Mgo.o7PO4/C can deliver the highest capacity at 〉 1C and it even delivers the capacity of 94.5 mA.h/g at 5C.