水合肼对锂离子正极材料LiNi_(0.5)Mn_(1.5)O_4性能的影响

以NiSO4和MnSO4为原料,在用共沉淀法经二次干燥制备锂离子电池正极材料LiNi0.5Mn1.5O4的前驱体时,加入水合肼进行还原处理.实验结果发现:经还原处理的前驱体制备正极材料LiNi0.5Mn1.5O4的充放电比容量远远高于同样条件下不经水合肼还原处理的前驱体制备的正极材料的充放电比容量,而且处理前驱体制备的正极材料在高倍率放电条件下电化学行为更好.粉末X射线衍射(XRD)和扫描电镜(SEM)测试结果表明,用还原剂水合肼处理的前驱体合成的样品为单一的尖晶石结构,晶粒呈规则的八面体形貌,没有杂质相,而未处理前驱体合成的样品则含有少量的杂质相.这种杂质相是在前驱体的制备过程中由于Mn(OH)2被O2氧化而形成难溶Na0.55Mn2O4.1.5H2O化合物,最终转变为Na0.7MnO2.05.

Effect of Hydrazine on the Performance of LiNi0.5Mn1.5O4 Cathode Materials

Reduction pretreatment of the precursor of LiNi_0.5Mn_1.5O₄ was carried out by adding hydrazine to a solution of NaOH during precursor synthesis. Accordingly, the effect of hydrazine on the performance of LiNi_0.5Mn_1.5O₄ was studied by comparing the electrochemical properties of this sample with those of pristine samples (LiNi_0.5Mn_1.5O₄ without hydrazine pretreatment). We synthesized LiNi_0.5Mn_1.5O₄ by co-precipitation using a two-step drying method with NiSO₄ and MnSO₄ as raw materials. The results of electrochemical experiments show that the LiNi_0.5Mn_1.5O₄ from the hydrazine pretreated precursor has a much higher special capacity than the pristine sample at the same charge/ discharge current density. Moreover, the former shows much better electrochemical performance at a high discharge current density. Results of powder X-ray diffraction (XRD) reveal that the LiNi_0.5Mn_1.5O₄ from the hydrazine pretreated precursor shows a pure spinel phase (no impurity phase detected) while the pristine sample containsa minor impurity phase. Results of scanning electron microscopy (SEM) show that the crystal impurities have a layered structure and are mixed with octahedral crystals of LiNi_0.5Mn_1.5O₄. We show that the impurity in the precursor is insoluble Na_0.55Mn₂O₄·1.5H₂O, which derives from the oxidation of Mn(OH)₂ by O₂ and a final transformation into Na_0.7MnO_2.05.