In order to improve the performance of the liquid carbon dioxide energy storage (LCES) system, a coupled system including a coal-fired power plant and a LCES system is proposed in this paper. In the energy storage process, the condensate from the coal-fired power plant is used to absorb the heat of compression generated. In the energy release process, the condensate and feedwater are used to step-heat the high-pressure carbon dioxide entering the turbine inlet. The performance of the LCES subsystem is evaluated by the energy analysis, the conventional exergy analysis, and the advanced exergy analysis. Results show that the round-trip efficiency of the LCES subsystem can reach 60.52%, with an improvement of 2.35% compared with the single LCES system. The exergy efficiency of the LCES subsystem under the real cycle is 68.55% and under the unavoidable cycle is 84.16%, which indicates that the LCES subsystem has a great potential for improvement. The conventional exergy analysis indicates that the cold energy storage tank is the biggest exergy destruction component, accounting for 23.58% of the LCES subsystem exergy destruction. The split of the exergy destruction is carried out during the advanced exergy analysis, and the results show that the avoidable endogenous exergy destruction accounts for 47.44 % of all exergy destruction. The first turbine has the greatest avoidable endogenous exergy destruction, with 24.71%, indicating that it has the highest improvement potential. This paper may provide new ideas for the LCES system performance improvement.