The K2FeO4/TiB2 battery has a significant advantage of battery capacity due to their multi-electron discharge reaction both of the cathode K2FeO4 (3e−) and the anode TiB2 (6e−). However, the more positive reduction potential of TiB2 anode results in a lower discharge voltage plateau of K2FeO4/TiB2 battery, compared with the K2FeO4/Zn battery. The simple modification of Fe(VI) cathode with CuO additive was used to improve the cathode reduction kinetics and decrease the polarization potential in the discharge process. Another electrocatalysis media RuO2 with excellent electric conductivity is used as additive in K2FeO4 cathode to demonstrate which effect is more important for the discharge voltage plateau, electrocatalysis or electron conductivity of additives. The results show that the 5% CuO additive modified K2FeO4/TiB2 battery exhibits an enhanced discharge voltage plateau (1.5 V) and a higher cathode specific capacity (327 mAh/g). The advanced discharge voltage plateau can be due to the electrocatalysis of additives on the electrochemical reduction kinetics of Fe(VI) cathode in the whole discharge process, rather than the good electronic conductivity of additives.