Engineering liquid crystal elastomer unlocks high thermopower for fiber-shaped ionic thermoelectric capacitors

Ionic thermoelectric (i-TE) have become promising candidate for harvesting low-grade thermal energy. However, the development of n-type i-TE materials still lag far behind their p-type counterparts, which impedes the application. Herein, engineering a liquid crystal elastomer (LCE) from side-chain to main-chain structure, just swollen with single LiBF₄ or EMIM TFSI, enables the largest adjustable p-n (28.8 ~ -27.4 mV K^-1) span among current homologous materials below 30% RH. These high n- and p-type performance further ensure the successful integration of a homogeneous π-type fiber-shaped i-TE capacitor, where three p/n pairs yield an output voltage of 402.5 mV under a tiny temperature difference of 2.5 K. The areal energy density of per n-type fiber reaches 8.1 mJ m^-2. More importantly, the i-TE materials also exhibit excellent stability under loadings of cyclic stretching, long-term testing, or temperature-controlled cycling, highlighting its potential for efficient thermal-charge energy storage in flexible electronics and smart wearables.