采用固相法、溶胶-凝胶法合成LiMn1.5Ni0.5O4.其中固相法前驱体采用高能球磨机细化颗粒,并采用整体升温和阶梯升温两种方式制备LiMn1.5Ni0.5O4,通过XRD表征发现合成的样品均不含有杂质.SEM表征显示通过高能球磨处理后的固相法制备的材料颗粒比溶胶-凝胶法小.其中阶梯升温固相法合成的LiMn1.5Ni0.5O4循环稳定性较好,可能是因为退火过程中使得Fd3m结构中的少量Mn3+变成Mn4+转变成P4332结构,Mn3+的量减少使得容量衰减减慢.整体升温固相法(G-LMNO)合成的样品首周放电比容量可达114.5 mAh g-1,只比溶胶-溶胶法合成的LiMn1.5Ni0.5O4(S-LMNO)的放电比容量低1.3 mAhg-1.但是其循环性能得到提升,经过50th循环充放电,整体升温固相法(G-LMNO)合成的样品容量保持率高达98.43％,原因可能是溶胶-凝胶法合成的LiMn1.5Ni0.5O4的粒子尺寸大,使得Li+的扩散路径变长,极化变大而导致循环性变差.
Effects of Different Synthesis Methods on the Properties of LiMn1.5Ni0.5O4 Cathode Materials
Solid method and sol-gel method are used to synthesize LiMn1.5Ni0.5O4 material.The precursor synthesized by solid method refines the particles by high-energy ball mill,and two heating ways,i.e.,o-verall heating and step heating,are uised to prepare LiMn1.5Ni0.5O4.All the synthesized samples have no impurity as being determined by XRD.Comparison of the SEM images indicted that the solid-state sample had smaller particle than sol-gel sample,and electrochemical test further showed that it has better cycling stability than the latter phase,possibly because during the cooling,a small amount of Mn3+in the Fd3m structure is converted to Mn4+,thus changing into P4332 structure,and the reduction of the amount of Mn3+slows down the capacity fading.The sample synthesized by overall heating solid method(G-LMNO)discharges specific capacity reaches 114.5 mAhg-1 in the initial cycle,while it was 1.3 mAhg -1 lower than the capacity discharged by LiMn1.5Ni0.5O4(S-LMNO).However,it has better cycling stability,and after 50th cycle charging and discharging,the retention rate of the capacity of the samples synthesized by G-LM-NO reach 98.43％.The reason may be that the particle size of LiMn1.5Ni0.5O4 synthesized by sol-gel method is larger,which makes the diffusion path of Li+longer,polarization larger and cyclic property worse.
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