고온에서 H2WO4 코팅된 Li[Ni0.8Co0.15Al0.05]O2의 수명 향상에 관한 연구

Abstract

To improve cycling performance of the Li[Ni0.8Co0.15Al0.05]O2 at high temperature (55 ℃), we make homogeneously coated H2WO4 layer on to the surface of Li[Ni0.8Co0.15Al0.05]O2 materials via dry coating method. The morphology of the H2WO4-coated Li[Ni0.8Co0.15Al0.05]O2 was analyzed using scanning electron microscope (SEM) and transmission electron microscopy (TEM) instruments and we found that the surface of the Li[Ni0.8Co0.15Al0.05]O2 was uniformly coated by H2WO4 with a thickness of 10-20nm. At high temperature, the H2WO4-coated Li[Ni0.8Co0.15Al0.05]O2 electrode delivered discharge capacity of 206.4 mAh g-1 while the pristine delivered as slightly lower capacity of 204.5 mAh g-1 and provided a high capacity retention of 90.3% after 100 cycles, compared of 86.1% for pristine. Through the comparison of the impedance results for both pristine and H2WO4-coated Li[Ni0.8Co0.15Al0.05]O2 electrode, both surface (Rsf) and charge transfer (Rct) resistances were reduce by the H2WO4 coating layer. In addition, The H2WO4 coating layer possesses good thermal stability; The pristine shows a relatively large exothermic peak at 221.1 ℃ with a corresponding heat generation of 896.4 J g-1. In the case of the H2WO4-coated Li[Ni0.8Co0.15Al0.05]O2, however, the exothermic peak shifts to more a higher temperature (245.0 ℃) with lower heat generation (509.7 J g-1).