Performance analysis and optimization of a side-contact plate for refrigerant direct cooling thermal management in energy storage batteries

Large-format prismatic lithium iron phosphate (LFP) cells used in stationary energy storage conduct heat poorly across their thickness, so the bottom-contact cooling plates inherited from indirect liquid-cooling designs must drive heat across the full cell height, leaving a steep vertical temperature gradient (Δ T _z) that promotes uneven current distribution and localized aging. This work develops a side-contact refrigerant direct cooling (RDC) plate that places the evaporating refrigerant against the broad cell faces, and evaluates it through coupled experiment and simulation. An R134a two-phase model based on the Mixture formulation is calibrated against a custom flow-boiling test rig, predicting pressure drop and wall temperature to within 7.66% and 8.70%, respectively. Using this validated model, the side and bottom-contact configurations are compared under identical conditions: relocating the cooling interface reduces Δ T _z from 28.34°C to 1.66°C and raises the mass-specific heat-exchange index ( η _m ) to 5.1 times that of the bottom-cooled baseline at a 1 P discharge rate. A shunt-parallel serpentine channel is then designed, and its geometry and refrigerant flow rate are optimized by response surface methodology to balance temperature uniformity against the pumping penalty. Finally, the saturation temperature is shown to have an optimum at 22°C, where the vapour-quality distribution along the channel gives the best temperature uniformity, with the maximum temperature spread limited to 1.15°C. These results offer quantitative design guidance for next-generation RDC thermal management in grid-scale battery systems.