Aging-induced pressure characteristics and state-of-health estimation for large-format LFP batteries under multi-constraint operating conditions

Battery pressure is a critical indicator for battery state-of-health (SOH). In this work, long-term aging tests are conducted on large-format prismatic lithium-iron-phosphate (LFP) energy-storage cells via a custom-built multi-constraint test platform. Aging experiments under varied temperatures, pre-tightening forces and foam-buffer conditions are implemented to investigate reversible and irreversible pressure evolution during cell degradation. Experimental results show that ambient temperature, pre-tightening force and foam-buffer configuration significantly modulate reversible-pressure magnitude. Due to creep of cell components and foam materials, irreversible pressure does not increase monotonically with aging. Charging-pressure extrema of LFP cells strongly correlate with graphite phase transitions, and pressure differences between these extrema are well-correlated with SOH, showing promising potential as aging fingerprints for SOH estimation. Leave-one-condition-out cross-validation indicates that the model fusing pressure and voltage features delivers superior accuracy relative to the voltage-only counterpart. After excluding foam-buffer conditions, the mean absolute percentage error (MAPE) of the fused Elastic-Net model falls below 1%. This work clarifies pressure-related aging behaviours of large-format LFP cells under multi-constraint conditions and validates the feasibility of pressure signatures for enhanced SOH estimation, offering references for practical SOH evaluation of energy-storage batteries.