Abstract: In this research, a thermodynamic model for Carnot battery is established based on the non-linear relationship between temperature and enthalpy during the phase change of zeotropic mixtures. By comparing the non-linear thermodynamic model with the linear thermodynamic model, the accuracy of the non-linear thermodynamic model was verified,and by analyzing the Carnot battery model based on the linear temperature-enthalpy assumption, it was observed that the calculated pinch point temperature difference was larger. In the article, appropriate working fluids were selected to investigate the influence of their composition and boiling points on the system's round-trip efficiency and levelized cost of storage (LCOS) . The results revealed that as the number of working fluid components increased, both the round-trip efficiency and LCOS also increased. By adopting multi-component working fluids with significantly different boiling points and closely matched compositions, the maximum round-trip efficiency could be achieved. A unified evaluation criterion for multi-objective analysis of Carnot batteries was established, and a multi-objective comparison of working fluids was conducted. The optimal pure fluid, binary mixture, and ternary mixture were identified as R1224yd(Z) , R1233zd(E) -R1224yd(Z) , and R1233zd(E) -R1234ze(Z) -R1336mzz(Z) , respectively.This study established a nonlinear temperature-enthalpy model to effectively evaluate the performance of Carnot batteries. After the test, it was found that the physical properties of the working fluids will affect the round-trip efficiency and LCOS. By developing a multi-objective unified evaluation criterion, the optimal working fluids can be selected under multi-objective optimization.