An integrated Janus hydrogel with different hydrophilicities and gradient pore structures for high-performance zinc-ion batteries

In zinc-ion batteries, the role of water in electrolytes is pivotal for enhancing the kinetics and capacity of the cathode; however, an excess of water leads to reduced stability of the cathode and corrosion of the Zn anode. Devising an electrolyte that meets the different water content requirements for both the cathode and anode holds promise for achieving superior performance but remains a persistent challenge. Herein, we have innovatively designed an integrated Janus hydrogel with different hydrophilicities on two surfaces and gradient pore structures within a bulk material. In the cross-sectional view, a gradient in pore size, ranging from large to small, is established in conjunction with a reduction in hydrophilicity. By employing the Janus hydrogel electrolyte, zinc-ion batteries demonstrate both high capacity and excellent cycling stability by facilitating sufficient H+ insertion in the cathode without the formation of by-products, while simultaneously mitigating water-induced corrosion in the zinc anode. Specifically, the coin-type Zn & Vert;(NH4)2V10O258H2O attains an extraordinary capacity of up to 307 mA h g-1 at 5 A g-1, with an impressive capacity retention of 88% after 1000 cycles. Moreover, the pouch cell with an area of 22.5 cm2 delivered a substantial capacity of 48 mA h and an excellent capacity retention of 85% after 150 cycles at 200 mA. Importantly, the pouch cell works reliably even when subjected to cutting, heavy loading or bending. A pioneering achievement is made in developing integrated Janus hydrogel electrolytes featuring gradient pores in cross-section and varying hydrophilicities on surfaces. This novel hydrogel enables Zn-ion batteries to exhibit excellent performance.