LiTi_(2)(PO_(4))_(3)修饰高镍单晶三元正极材料增强结构稳定性

LiTi_2(PO_(4))_(3) modifies high nickel single crystal ternary cathode materials to enhance structural stability

单晶LiNi_(1-x-y)Co_(x)Mn_(y)O_(2)(SCNCM,1-x-y>0.9)正极材料由于其特殊的晶体结构,与多晶NCM材料相比,具有更优越的循环寿命。然而,SCNCM在长循环过程中由于严重的副反应和不可逆相变,导致严重的容量退化。具有较高扩散系数的LiTi_(2)(PO_(4))_(3)(LTP)可以增强Li^(+)在电极和电解质之间的传递,并防止与空气和电解质的副反应。为了优化SCNCM的电化学性能,采用液相混合和固相烧结相结合的方法对其进行表面包覆,提高单晶SCNCM循环性能。X射线衍射(XRD)和高分辨透射电子显微镜(HRTEM)结果证实,SCNCM表面包覆一层30~50 nm的LTP涂层,改性后的样品在长循环后仍然可以保持良好的层状结构。具体地说,包覆0.8%(质量分数)LTP的SCNCM正极在0.5 C循环100圈后,放电比容量为151.2 mAh/g。

Single crystalline LiNi_(1-x-y)Co_(x)Mn_(y)O_(2)(SCNCM,1-x-y0.9) cathode material has superior cycle life compared with spherical secondary particle NCM due to its special crystal structure.However,SCNCM is accompanied by severe capacity degradation during long cycling due to severely exacerbated side reactions and irreversible phase transitions.It has been reported that LiTi_(2)(PO_(4))_(3)(LTP) with a higher diffusion coefficient can enhance Li^(+) transport between electrodes and electrolytes and prevent side reactions with air and electrolytes.In this thesis,in order to optimize the electrochemical performance of SCNCM,liquid phase mixing and solid phase sintering were used to coat the surface of SCNCM to improve the cycle performance of single crystalline SCNCM.X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) results confirmed that the surface of SCNCM was coated with a 30~50 nm LTP coating,and the modified samples can still maintain a good layered structure after long cycles.Specifically,the SCNCM cathode coated with 0.8%LTP exhibited a discharge capacity of151.2 mAh/g after 100 cycles at 0.5 C.