Converting low‐grade waste heat into usable electricity and storing it simultaneously requires a new technology that realize the directional migration of electrons or ions under temperature difference and enrichment on the electrodes. Although the urgent demand of energy conversion‐storage (ECS) has emerged in the field of wearable electronic, achieving the integrated bi‐functional device remains challenge due to the different mechanisms of electrical transportation and storage. Here, we report an ionic thermoelectric supercapacitor that relies on the synergistic functions of thermoelectricity and supercapacitor in the thermoelectric ionogel electrolyte and high‐performance hydrogel electrodes to enhance the ECS performance under a thermal gradient. The thermoelectric electrolyte is composed of polyacrylamide hydrogel and sodium carboxymethyl cellulose (PMSC), possessing cross‐linked network with excellent cation selectivity, while the ionic thermoelectric properties are further improved in the presence of NaCl. The corresponding Seebeck coefficient and ionic conductivity of the NaCl–PMSC electrolyte reach 17.1 mV K−1 and 26.8 mS cm−1, respectively. Owing to good stretchability of both gel‐based electrolyte and electrode, the full‐stretchable integrated ECS device, termed ionic thermoelectric supercapacitor, presents promising thermal‐charge storage capability (~1.3 mC, ΔT ≈ 10 K), thus holds promise for wearable energy harvesting.

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