Auxetic‐Assisted Decoupling Strategy for High‐Sensitivity Multimodal Sensing of Temperature and Strain

Abstract Multimodal sensing in thermomechanically coupled environments, such as lithium–ion battery monitoring, remains constrained by inter‐modal interference and low sensitivity to environmental changes. This work presents a decoupling strategy using a modulus‐heterogeneous “rotating square” auxetic structure to vertically separate a thermoresistive temperature sensor array from a piezoelectric strain sensor array. This design near‐perfectly eliminates thermo‐mechanical crosstalk, enabling simultaneous detection of subtle thermal and mechanical variations over a wide temperature range. Specifically, the rigid regions of the auxetic structure rotate under tensile strain to isolate the temperature sensors from deformation, while the stretchable regions expand laterally to enhance in‐plane strain in the potassium sodium niobate (KNN)‐based piezoelectric layer, compensating for its intrinsically low d 31 coefficient. Benefiting from this architecture, the thermoresistive sensor provides stable, independent responses from 25 to 130 °C with 0.1 °C resolution. Simultaneously, the first developed piezoelectric unit, based on a lead‐free KNN ceramic framework, achieves 100% stretchability and reliably detects surface protrusions as small as 5 µm without thermal interference. When deployed on a pouch‐cell battery, the sensor array reliably detects both overheating and swelling, offering a compact and robust dual‐parameter sensing solution with strong potential for structural health monitoring in complex environments.