Li_(2)TiO_(3)包覆提高LiNi_(0.5)Mn_(0.5)O_(2)的电化学性能

Improving electrochemical performance of LiNi_(0.5)Mn_(0.5)O_(2)by coating Li_(2)TiO_(3)

结合共沉淀法、溶剂热法和固相法,将Li_(2)TiO_(3)包覆在LiNi_(0.5)Mn_(0.5)O_(2)正极材料表面,合成z Li_(2)TiO_(3)@LiNi_(0.5)Mn_(0.5)O_(2)(z=0、0.03、0.05和0.08)正极材料。通过XRD、SEM和透射电子显微镜(TEM)对合成材料的结构、形貌和元素分布等进行分析。Li_(2)TiO_(3)均匀地包覆在LiNi_(0.5)Mn_(0.5)O_(2)的表面,减缓LiNi_(0.5)Mn_(0.5)O_(2)材料的团聚程度;包覆过程中,少量的Ti^(4+)掺杂进入材料的内部,可降低锂镍混排程度。以40 mA/g(0.2C)在2.5~4.5 V充放电,0.03Li_(2)TiO_(3)@LiNi_(0.5)Mn_(0.5)O_(2)的电化学性能较好。与LiNi_(0.5)Mn_(0.5)O_(2)正极材料相比,包覆Li_(2)TiO_(3)不仅将电极的放电比容量由125.44 mAh/g提高到138.40 mAh/g,而且将容量保持率由76.66%提升到89.23%(循环120次时)。这是因为具有三维结构的Li_(2)TiO_(3)包覆层和Ti^(4+)掺杂可降低锂镍混排,减轻极化,降低迁移电阻,增加材料的结构稳定性,提高Li^(+)的迁移速率。

zLi_(2)TiO_(3)@LiNi_(0.5)Mn_(0.5)O_(2)(z=0,0.03,0.05 and 0.08)cathode materials were synthesized by Li_(2)TiO_(3)coating on the surface of LiNi_(0.5)Mn_(0.5)O_(2)cathode materials uniformly by a combinative strategy of co-precipitation,hydrothermal and solid phase method.By means of XRD,SEM and transmission electron microscopy(TEM),the structure,morphology and element distribution of the synthetic materials were systematically analyzed.Li_(2)TiO_(3)was uniformly coated on the surface of LiNi_(0.5)Mn_(0.5)O_(2),which could retard the agglomeration degree of LiNi_(0.5)Mn_(0.5)O_(2).A small amount of Ti^(4+)was doped into the interior of the material during coating process,which might reduce the degree of Li/Ni cation mixing.0.03 Li_(2)TiO_(3)@LiNi_(0.5)Mn_(0.5)O_(2)showed better electrochemical perfor-mance at 0.2C in 2.5-4.5V.Compared with LiNi_(0.5)Mn_(0.5)O_(2)cathode material,Li_(2)TiO_(3)coating could not only increase the discharge capacity of the pristine electrode from 125.44 mAh/g to 138.40 mAh/g,but also enhance the capacity retention of the pristine electrode from 76.66%to 89.23%in 120 cycles.The reasons were three-dimensional structured Li_(2)TiO_(3)coating and Ti^(4+)doping could reduce Li/Ni cation mixing,polarization and migration resistance;also could increase structural stability and migration rate of Li^(+).