通过微波诱导液相无焰燃烧法一步合成了一系列的尖晶石型LiMn2O4正极材料。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学测试等分析方法系统地探究了柠檬酸作为燃料和还原剂时对尖晶石型LiMn2O4晶体结构、微观形貌和电化学性能的影响。结果表明:柠檬酸添加剂不会改变合成材料的初始物相组成,所有合成的产物均可被索引为尖晶石型LiMn2O4的立方晶系结构和Fd3m空间群。随着柠檬酸加入量的增加,LiMn2O4的颗粒尺寸趋于减小,结晶性增强。对合成样品进行室温下1C恒电流充放电测试时,发现样品的初始放电比容量随着柠檬酸含量的增加而增大,在0.8%时达到最大值,为125.2mAh/g,远高于未添加样品的92.1mAh/g。经过300次循环后,容量保持率达53.4%。循环伏安(CV)测试结果证实了在柠檬酸加入量为0.8%时具有最佳的电化学可逆性,电化学阻抗(EIS)测试显示最低的电荷转移电阻(Rct)值为95.2Ω。
A series of spinel LiMn2O4 cathode materials were synthesized in one step by a microwave-induced solution flameless combustion method.The crystal structure,microscopic morphology and electrochemical performance of spinel LiMn2O4 were characterized by X-ray diffraction (XRD),scanning electron microscope (SEM) and electrochemical testing when citric acid was used as fuel and reducing agent.The results shown that the citric acid additive did not change the initial phase composition of the synthetic materials,and all the as-prepared samples can be indexed into the cubic crystal structure and the Fd3m space group of the spinel LiMn2O4.In addition,the particle size of LiMn2O4 tended to decrease with the increase of citric acid,resulting in enhanced crystallinity.The initial discharge specific capacities of the samples were increased with the increase of citric acid content at 1 C and room temperature.When x=0.8%,the maximum discharge specific capacity of 125.2mAh/g was reached,which was much higher than the unoptimized sample of the 92.1mAh/g.And the capacity retention rate reached 53.4% after 300 cycles.Cyclic voltammetry (CV) and electrochemical impedance (EIS) test results confirmed the best electrochemical reversibility and the lowest charge transfer resistance (Rct) value of 95.21Ω when citric acid was added at 0.8%.
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