The development of a high specific capacity and stable manganese (Mn)-based cathode material is very attractive for aqueous zinc-ion (Zn²⁺) batteries (ZIBs). However, the inherent low electrical conductivity and volume expansion challenges limit its stability improvement. Here, a mesoporous ZnMn₂O₄ (ZMO) nanocage (N-ZMO) coupled with nitrogen doping and oxygen vacancies is prepared by defect engineering and rational structural design as a high-performance cathode material for rechargeable ZIBs. The oxygen vacancies enhance the electrical conductivity of the material and the nitrogen doping releases the strong electrostatic force of the material to maintain a higher structural stability. Interestingly, N-ZMO exhibits excellent ability of Zn²⁺ storage (225.4 mAh·g⁻¹ at 0.3 A·g⁻¹), good rate, and stable cycling performance (88.4 mAh·g⁻¹ after 1,000 cycles at 3 A·g⁻¹). Furthermore, a flexible quasi-solid-state device with high energy density (261.6 Wh·kg⁻¹) is assembled, demonstrating long-lasting durability. We believe that the strategy in this study can provide a new approach for developing aqueous ZIBs.

High-performance energy storage and sensing devices have been undergoing rapid development to meet the demand for portable and wearable electronic products, which require flexibility, extensibility, small volume and lightweight. In this study, we construct a lightweight and flexible self-powered sensing system by integrating a highly stretchable strain sensor with a high-performance asymmetric supercapacitor based on ZnSe/CoSe₂//ECNT (ECNT: electrochemically activated carbon nanotube film). The ZnSe/CoSe₂ two-dimentional nanosheets on carbon nanotube (CNT) films are synthesized through a simple and efficient strategy derived from ZnCo-based metal-organic frameworks (MOFs). The density functional theory (DFT) simulations show the higher conductivity of the ZnSe/CoSe₂/CNT electrode than the CoSe₂/CNT electrode. Due to the synergistic properties of self-supported two-dimentional ZnSe/CoSe₂ nanosheets with high specific surface area and the high pathway of one-dimention CNTs, the nanocomposite electrode provides efficient transmission and short paths for electron/ion diffusion. The asymmetric supercapacitor provides a stable output power supply to the sensors that can precisely respond to strain and pressure changes. The sensor can also be attached to a garment for measuring a variety of joint movements.

Electrochemical conversion reactions provide more selections for Na-storage materials, but the reaction suffers from low reversibility and poor cyclability. Introducing an electrochemically inactive component is a common strategy, but the effect is quite limited since it could not stabilize the structure during long-term cycling. In this study, a new approach is developed using an amino group-functioned hyperbranched polymer (AHP) as a template and electrode additive for the design of high-performance FeSe₂-AHP composite with chemical interaction. The assembled FeSe₂-AHP composite nanoneedles were prepared by the selenylation of FeS-AHP composite microflowers and entirely inherit the polymer network from the precursor. The amino groups of AHP in composite coordinate with iron cations to achieve uniform polymer dispersion in the composite, and maintain the molecular level mixed state during the long-term cycling. Moreover, the in-situ constructed uniform 3D elastic polymer network effectively accommodates volume expansion and alleviates nanoparticle aggregation during sodiation/de-sodiation. FeSe₂-AHP composite provides a superior rate capability (584.8 mAh·g^-1 at 20 A·g^-1) and a remarkable cyclability with a capacity retention rate of 93.3% after 2, 000 cycles. FeSe₂-AHP composite shows a high pseudocapacitive behavior for the abundant nanometer interface established by AHP, enhancing the solid-state Na⁺ diffusion. The FeSe₂-AHP anode is also compatible with Na₃V₂(PO₄)₃/C cathode in a full Na-ion battery, which provides a high-power performance (powering 51 LEDs). The work herein highlights an innovative and efficient strategy for conversion-type material design and demonstrates the function of chemical interaction of polymer additive in the enhancement of long-term cyclability for conversion electrode.