基于基团贡献法和柯普法则估算LiNi_xCo_yMn_zO₂ (x+y+z=1)正极材料的热容

LiNi_xCo_yMn_zO₂ (x+y+z=1, 0<x, y, z<1) ternary cathode material was one of the key materials in the field of lithium ion power battery. Its structure and electrochemical properties were well understood, but its heat capacity was rarely reported. In this paper, the CaAl₄O₇ was split according to the principle of the group contribution method, and the mathematical model of estimating the C_p of CaAl₄O₇ was proposed based on thermodynamic principle. In order to test the model, the C_{p, 298} of 54 kinds of solid inorganic compounds were estimated by the group contribution method and the Kopp's rule. Compared with the literature values, the absolute relative error of C_{p, 298} estimated by the group contribution method was within 5%, among which 43 kinds of solid inorganic compounds had the absolute relative error less than 2%. Based on the satisfactory results, a mathematical model for estimating the C_p of LiNi_xCo_yMn_zO₂cathode material for lithium ion power battery was constructed for LiNi_1/3Co_1/3Mn_1/3O₂, LiNi_0.5Co_0.2Mn_0.3O₂, LiNi_0.6Co_0.2Mn_0.2O₂ and LiNi_0.8Co_0.1Mn_0.1O₂, and then, the heat capacity of cathode materials LiNi_xCo_yMn_zO₂, such as LiNi_1/3Co_1/3Mn_1/3O₂, LiNi_0.5Co_0.2Mn_0.3O₂, LiNi_0.6Co_0.2Mn_0.2O₂ and LiNi_0.8Co_0.1Mn_0.1O₂ for lithium ion power battery cathode materials at 298 K were estimated, the estimated results of cathode material C_{p, 298} were 78.96, 78.69, 79.77 and 75.72 J•mol^-1•K^-1, respectively. Using Kopp's rule, the C_{p, 298} of LiNi_1/3Co_1/3Mn_1/3O₂, LiNi_0.5Co_0.2Mn_0.3O₂, LiNi_0.6Co_0.2Mn_0.2O₂ and LiNi_0.8Co_0.1Mn_0.1O₂ ternary materials were estimated, the results were 76.50, 76.38, 76.12 and 75.84 J•mol^-1•K^-1, respectively.