In Situ Probing of Lithiation Dynamics Enabled by Strain‐Sensing Current Collector

ABSTRACT Lithiation dynamics govern the performance and degradation of lithium‐ion batteries, yet high‐fidelity operando probing of localized strain in the battery remains challenging due to the potential disruption of the cell structure with sensor implantation. Here, we present a strain‐sensing current collector (SSCC) that integrates patterned Constantan strain‐sensing units inside a copper current collector through UV‐assisted transfer printing and surface electroplating. The SSCC preserves continuous conductive copper surface and enables direct graphite coating, allowing the sensor‐embedded current collector to function as anode sheet in pouch cell. The SSCC achieves stable strain sensing after 60 days of electrolyte exposure, while showing negligible impact on cell electrochemical performance by delivering a capacity retention of 98.9% and Coulombic efficiency of 99.8% over 50 cycles. Based on electrode‐level strain readouts, the SSCC resolves staged graphite lithiation, asymmetric delithiation behavior, and rate‐dependent strain features during normal cycling. Under low‐temperature cycling, the SSCC captures pronounced irreversible strain drift associated with lithium plating, “dead‐Li” accumulation, and SEI thickening, as verified by post‐mortem characterizations. Moreover, frequency‐domain filtering enables decoupling of reversible lithiation strain from slowly evolving irreversible degradation strain. This work establishes a current‐collector‐integrated sensing strategy for in situ probing of electrochemical‐mechanical coupling dynamics in operating lithium‐ion batteries.