Model For The Calculation Of The Thermodynamic Properties Of Ternary And Lithium-Rich Cathode Materials

Ternary cathode LiNi_xCo_yMn_zO₂（x+y+z=1,0<x,y,z<1）materials is one of the key materials in the field of lithium ion power battery and is widely used in the field of new energy vehicles.The lithium-rich layered cathode materials may be used as a new high specific energy lithium-ion batteries cathode Li_1+xM_1-xO₂（0<x<1）materials due to their high specific capacity,excellent cycling ability and new electrochemical charging and discharging mechanism.Research on ternary LiNi_xCo_yMn_zO₂ materials and lithium-rich cathode Li_1+xM_1-xO₂ materials has mainly focused on their structure and electrochemical properties and rarely on their thermodynamic properties.The development of novel lithium-rich materials with high energy density and capacity is dependent on the intrinsic relationship among the s tructure,thermodynamic properties,and electrochemical properties of such materials.Insufficient understanding of the thermodynamic properties of ternary LiNi_XCo_yMn_zO₂ materials and lithium-rich cathode Li_1+xM_1-xO₂ materials limits the development and utilization of novel LiNi_xCo_yMn_zO₂ materials and Li_1+XM_1-xO₂ materials.Given the lack of thermodynamic data on LiNi_xCo_yMn_zO₂ materials and Li_1+xM_1-xO₂ materials,the mathematical models for estimating the standard molar enthalpy of formation(△H_f,298^θ),standard molar gibbs free energy of formation(△G_f,298^θ)and constant pressure heat capacity（Cp）of ternary LiNi_xCo_yMn_zO₂ materials and lithium-rich Li_1+xMi_1-xO₂ materials are constructed based on group contribution method.The △H_f,298^θ,△G_f,298^θand C_p,298 of common LiNi_xCo_yMn_zO₂ materials and lithium-rich Li_1+xM_1-xO₂ materials were also estimated.In this paper,the CaAl₄O₇ was split according to the basis of the group contribution method,the mathematical models for estimating the △H_f,298^θ,△G_f,298^θand Cp of CaAl₄O₇ were proposed in accordance with thermodynamic principles.The group contribution method was used to estimate the △H_f,298^θ and △G_f,298^θ of 56 solid inorganic compounds to determine the reliability and applicability of the model.The estimated and reported values of △H_f,298^θ were compared[25].The absolute values of relative errors were within 4%,the absolute values of the relative errors of 43 kinds of solid inorganic compounds were less than 2%.The estimated and reported values of△H_f,298^θ were also compared.The absolute values of relative errors were within 4%,the absolute values of the relative errors of 42 kinds of solid inorganic compounds were less than 2%.The C_p,298 values of 54 solid inorganic compounds were likewise estimated[26].The absolute values of the relative errors of C_p,298 were within 5%of the values in the literature.The absolute values of the relative errors of 43 kinds of solid inorganic compounds were less than 2%.The C_p,298 values of the 54 selected solid inorganic compounds were estimated in accordance with Kopp’s rule.The absolute values of relative errors of C_p,298 were within 11%of those reported in the literature,and the absolute values of the relative errors of 33 solid inorganic compounds were less than 3%.Among them,12 kinds of solid inorganic compounds had absolute values of the relative errors of between 3%and 5%.This method has a better calculation effect than Kopp’s rule estimation.The results show that the mathematical model of the correlation between group parameters and physical properties is correct,the experimental data selected by fitting the group parameters were accurate and reliable,and the group division method was appropriate.Mathematical models for estimating the △H_f,298^θ,△G_f,298^θand C_p,298 of ternary LiNi_xCo_yMn_zO₂ materials and three types of Li_1+xM（1-x）O₂ materials were constructed for the first time on the basis of the satisfactory results Three main types of lithium-rich cathode materials are currently available:（1）lithium-rich layered xLi₂MnO₃·（1-x）LiMO₂（0<x<1,M=Ni,Co,Cr,Fe,Al,Mg,Ni-Co,Ni-Mn,Ni-Co-Mn-.·）cathode material;（2）lithium-rich manganese-based xLi[Li_1/3Mn_2/3]O₂·（l-x）LiMO₂（0<x<1,M=Ni,Co,Cr,Fe,Al,Mg,Ni-Co,Ni-Mn,Ni-Co-Mn…）solid solution material;and（3）layered spinel xLi[Li_1/3Mn_2/3]O₂·（1-x）LiMn₂O)₄（0<x<1）composite solid solution material and layered spinel xLi[Li_1/3Mn_2/3]O₂·（1-x）LiNi_0.5Mn_1.5O₄（0<x<1）composite solid solution material.Combining the XPS experimental data analysis results,the estimated values of the△H_f,298^θ,△G_f,298^θ and C_p,298 of ternary materials LiNi_0.6Co_0.2Mn_0.2O₂,LiNi_0.5Co_0.2Mn_0.3O₂,LiNi_0.8Co_0.1Mn_0.1O₂ and LiNi_1/3Co_1/3Mn_1/3O₂ are-705.39 kJ·mol^-1,-703.90 kJ·mol-,-695.67 kJ·mol^-1,-705.17 kJ·mol^-1;-647.98 kJ.mol^-1,-640.04 kJ·mol^-1,-631.10 kJ·mol^-1,-642.41 kJ·mol^-1;78.96 J·mol^-1·K^-1、78.69 J·mol^-1·K^-1、79.77 J-mol^-1·K^-1 and 75.72 J·mol^-1-K^-1,respectively.The mathematical models for estimating the △H_f,298^θ,△G_f,298^θ,and Cp of three types of lithium-rich materials were constructed in accordance with the satisfactory results,and the △H_f,298^θ,△G_f,298^θ,and C_p,298 of the common 63 lithium-rich materials were estimated.Based on the experimental and analytical basis,the LiNi_1/3Co_1/3Mn_1/3O₂-NaHSO₄·H₂O system was used to predict the chemical reactions that may occur during the roasting reaction,and the standard gibbs free energy of possible chemical reactions.The relationship between change and temperature was calculated as △rG_T^θ,LiNi_1/3Co_1/3Mn_1/3O₂ decomposes at a temperature higher than 1637 K to form Li₂O,NiO,CoO,MnO,and O₂,When NaHSO₄·H₂O is higher than 649 K decomposes into SO₃,and Li₂O,NiO,CoO,and MnO react with SO₃ to form Li₂SO₄,CoSO4,NiSO₄,and MnSO₄.