Structures and Electrochemical Properties of Sn-Cl Co-Doped Li2MnO3 as Positive Materials for Lithium Ion Batteries
- 2020年第26卷 
以乙酸盐为原料，柠檬酸为络合剂，通过溶胶-凝胶的方法制备富锂阴极材料Li2MnO3，选用草酸亚锡(SnC2O4)为锡源，用Sn4+代替Mn4+，获得不同掺杂量的材料. 适当含量的Sn4+掺杂可以提高材料的放电比容量，在低电流下获得256.3 mAh·g-1的高放电比容量，但由于Sn4+离子半径过大，不能起到稳定结构的作用，材料的倍率性能较差. 在此基础上，选用氯化亚锡(SnCl2)进行掺杂改性，在材料中同时引入Sn4+和Cl-掺杂，获得了层状结构更完整的粉末样品. 通过共掺杂改性的阴极材料可以在20 mA·g-1的电流密度，经过80圈的循环仍然保持153 mAh·g-1的放电比容量，且此时还未出现衰减现象，库仑效率保持在96%以上；在400 mA·g-1的电流密度下提供的比容量可高达116 mAh·g-1，是未掺杂样品的2倍左右.Positive material Li2MnO3 shows the highest ratio of lithium to manganese among lithium-rich materials and exhibites the theoretical capacity up to 458 mAh·g-1, making it one of the most promising cathode materials. However, this material has the intrinsic low electrical conductivity and poor cycle stability. In this paper, Li2MnO3, the lithium-rich positive material, was prepared by sol-gel method using acetate as raw material and citric acid as a complexing agent. By using SnC2O4 as a tin source, Sn4+ instead of Mn4+ was introduced to obtain the materials with different doping amounts. The resultant solution was evaporated at 80 °C under vigorous stirring to get a viscous gel. Next, the resulting gel was dried at 120 °C for 12 h. Finally, the gathered precursor was calcined at 600 °C for 6 h under an air atmosphere to obtain the target material. It was found that the proper content of Sn4+ doping could increase the specific discharge capacity of the material, obtaining as high as 256.3 mAh·g-1 at low current, but had a detrimental influence on the rate performance. On this basis, SnCl2 was used for doping modification, and the Sn4+ and Cl- co-doping into Li2MnO3 revealed a better developed layered structure with high conductivity. The intensity of super lattice peak formed between 2θ = 20° and 30° was increased by Cl-doping, indicating the ordered Li/Mn in the TM layer. Especially, this Sn-Cl co-doped Li2MnO3 sample delivered the relatively high specific discharge capacity of approximate 160 mAh·g-1 after 80 cycles at 20 mA·g-1. At the high current density of 400 mA·g-1, this material provided the specific discharge capacity of 116 mAh·g-1, which is about twice that of the undoped sample.