微量Mg/F表面梯度渗透改善高电压LiCoO_(2)界面脆弱

Enhancement of the fragile interface of high voltage LiCoO_(2) by surface gradient permeation of trace amounts of Mg/F

采用高温固相法在1 050℃下烧结,制备了LiCoO_(2)低浓度梯度改性样品,分别为LiF掺杂包覆(LCOLF、LCO@LF)和MgF_(2)掺杂包覆(LCOMF、LCO@MF)。通过光电子能谱、透射电子显微镜和电化学技术等表征方法,对比分析材料形貌及电化学性能。结果表明,体相掺杂复合电极中,LCOLF热重测试显示出最优热稳定性,LCOMF晶体中(003)和(104)晶面间距收缩;45℃下1C倍率循环70圈后,LCOLF和LCOMF比容量分别为141.45和166.98 mAh·g^(-1),循环性能优于LiCoO_(2)。表面包覆复合电极中,LCO@LF和LCO@MF晶粒表面光洁且晶格氧键价都向更高结合能方向增强;LCO@MF构建了坚实且紧密的包覆层,循环70圈后,放电比容量和容量保持率分别为183 mAh·g^(-1)和91.26%(LCO@LF分别为154.38 mAh·g^(-1)和77.54%),循环性能显著优于体相掺杂。

Low-concentration gradient-modified samples of LiCoO_(2) were prepared by sintering at 1050℃using high-temperature solid-phase method,and were coated with LiF doping(LCOLF,LCO@LF)and MgF_(2) doping(LCOMF,LCO@MF).The material morphologies and electrochemical properties were compared and analyzed utiliz-ing characterization tests such as X-ray photoelectron spectroscopy,transmission electron microscopy,and electro-chemical techniques.The results show that in bulk-doping composite electrodes,the thermogravimetric test demon-strated that LCOLF had optimal thermal stability.In LCOMF crystals,crystal plane spacing of(003)and(104)con-tracted;after 70 cycles at 1C rate under 45℃,the specific capacities of LCOLF and LCOMF were 141.45 and 166.98 mAh·g^(-1) respectively,and their cycling performance was superior to that of the LiCoO_(2).In the surface-coated composite electrodes,LCO@LF and LCO@MF grains had clean surfaces and the bond valence of lattice oxygen was enhanced toward higher binding energy;LCO@MF built a solid and compact coating layer,and the specific capacity and capacity retention after 70 cycles were 183 mAh·g^(-1) and 91.26%(that of LCO@LF were respectively 154.38 mAh·g^(-1) and 77.54%).The cycling performance of surface-coated composite electrodes was significantly better than that of bulk-doping composite electrodes.