Lithium iron phosphate (LiFePO4) is a widely utilized cathode material in lithium-ion batteries, prized for its safety, low cost, and extensive cycling lifespan. However, its low compaction density limits its application in batteries requiring high volumetric energy density. The inclusion of conductive carbon black in electrodes, while increasing porosity, also exacerbates side reactions due to its high specific surface area. In this study, the use of liquid metal (GaIn) nanoparticles is explored as a substitute for carbon black in electrode formulations. GaIn nanoparticles' stable oxide film prevents oxidation at cathode potential. Additionally, liquid metal improves the particle interface to a solid-liquid interface, reducing particle friction and providing a lubricating effect, resulting in a denser electrode structure. As a result, the porosity of LiFePO4 electrodes prepared with liquid metal is reduced, leading to a 20.7% increase in volumetric energy density. Moreover, GaIn-containing batteries exhibit fewer side reactions, especially at elevated temperatures in both liquid and solid battery configurations. Solid-state batteries employing GaIn nanoparticles demonstrate a specific capacity of 144 mAh g−1 at 0.5C, showcasing superior cycling performance compared to traditional formulations. This underscores the potential of GaIn to elevate the performance of LiFePO4 batteries.