Aqueous Asymmetric Pseudocapacitor Featuring High Areal Energy and Power Using Conjugated Polyelectrolytes and Ti3C2Tx MXene

Despite the development of various pseudocapacitive materials, full-cell pseudocapacitors have yet to surpass the power density of conventional electric double layer capacitors (EDLCs), primarily due to the lack of high-rate pseudocapacitive materials for positive electrodes. This work reports a solid-state conjugated polyelectrolyte (CPE), namely CPE-K, that achieves ultrahigh-rate charge storage as a positive electrode, facilitated by a co-ion desorption mechanism. Used without additives or binders, CPE-K retains 70% of its capacitance at 100 A g ^− 1 with a mass loading of 2.8 mg cm ^− 2 and exhibits an ultra-long cycling life of 100,000 cycles. Increasing the electrode thickness fourfold has minimal impact on ion diffusivity and accessibility, yielding a high areal capacitance of 915 mF cm ^− 2 . When paired with Ti ₃ C ₂ T _x , a well-known high-rate pseudocapacitive negative electrode, the device leverages the redox-active potentials of both materials, achieves a device voltage of 1.5 V and supports operation rates up to 10 V s⁻¹ or 50 A g⁻¹. This configuration enables the pseudocapacitor to deliver an areal power of 160 mW cm ^− 2 , exceeding the previously unparalleled power of EDLCs, while significantly increasing the areal energy (up to 71 µWh cm ^− 2 ). The high areal performance, combined with the additive-free and water-based fabrication process, makes micro-pseudocapacitors promising for on-chip and wearable energy storage applications.