关键词: 锂离子电池, 正极材料, Li₂MnO₃, 草酸亚锡, 氯化亚锡, Sn-Cl共掺杂

Abstract:

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.

Key words: lithium ion battery, positive electrode material, Li₂MnO₃, SnC₂O₄, SnCl₂, Sn-Cl co-doping