The FeS2 has abundant reserves and a high specific capacity (894 mAh g−1), commonly used to fabricate Li‐FeS2 primary batteries, like LiMx‐FeS2 thermal batteries (working at ≈500 °C). However, Li–FeS2 batteries struggle to function as rechargeable batteries due to serious issues such as pulverization and polysulfide shuttling. Herein, highly reversible solid‐state Li‐FeS2 batteries operating at 300 °C are designed. Molten salt‐based FeS2 slurry cathodes address the notorious electrode pulverization problem by encapsulating pulverized particles in time with e− and Li⁺ flow conductors. In addition, the solid electrolyte LLZTO tube serves as a hard separator and fast Li+ channel, effectively separating the molten electrodes to construct a liquid–solid–liquid structure instead of the solid–liquid–solid structure of LiMx‐FeS2 thermal batteries. Most importantly, these high‐temperature Li–FeS2 solid‐state batteries achieve FeS2 conversion to Li2S and Fe at discharge and further back to FeS2 at charge, unlike room‐temperature Li‐FeS2 batteries where FeS and S act as oxidation products. Therefore, these new‐type Li‐FeS2 batteries have a lower operating temperature than Li‐FeS2 thermal batteries and perform highly reversible electrochemical reactions, which can be cycled stably up to 2000 times with a high specific capacity of ≈750 mAh g−1 in the prototype batteries. This work reports Li–FeS2 secondary thermal batteries (240–300 °C) with a liquid–solid liquid structure. The liquid lithium anode and FeS2 slurry cathode are isolated using a U‐shaped LLZTO tube. The high battery reversibility is attributed to the reversible transition of Fe and Li2S to FeS2 at high temperatures and FeS2 pulverization. The FeS2 regeneration also avoids the production of polysulfides.