Bendable quasi-solid-state aqueous sodium-ion batteries operated at -30 °C.

Aqueous sodium-ion batteries (ASIBs) have garnered considerable attention for large-scale energy storage because of inherent safety and the Na abundance. Nonetheless, the solidification of aqueous electrolytes under sub-zero conditions results in diminished ionic conductivity and increased viscosity, hindering the electrochemical performance and versatility of ASIBs. Herein, we introduce a novel freeze-tolerant ASIB using antifreezing ethylene glycol-polyacrylamide-sodium perchlorate hydrogel electrolyte, paired with new couple of Na3MnTi(PO4)3 cathode and Fe-based anode. The addition of ethylene glycol in the electrolyte enhances ionic conductivity at cold temperatures and optimizes electrode capacity by reduced hydrogen bonding within the water molecules and a decline in free water activity. The pronounced interaction between ethylene glycol and water, combined with the cooperative effect of the crosslinked polyacrylamide network, enables the hydrogel electrolyte to effectively suppress water solidification and maintain better water-retaining capability, achieving remarkable mechanical extensibility and good ionic conductivity (2.5 mS cm-1) at - 40 °C. Consequently, the ASIB equipped with hydrogel electrolyte delivers high energy density of 43.6 Wh kg-1 and retains 64 % at - 30 °C. Furthermore, the flexible ASIB demonstrates robust mechanical durability when bent or compressed, efficiently powering electronic devices even at - 30 °C. Our findings will pave the way for advancing low-temperature ASIBs with hydrogel-based electrolytes.

Electrolyte Concentration Regulation Boosting Zinc Storage Stability of High-Capacity K0.486V2O5 Cathode for Bendable Quasi-Solid-State Zinc Ion Batteries.

Vanadium-based cathodes have attracted great interest in aqueous zinc ion batteries (AZIBs) due to their large capacities, good rate performance and facile synthesis in large scale. However, their practical application is greatly hampered by vanadium dissolution issue in conventional dilute electrolytes. Herein, taking a new potassium vanadate K0.486V2O5 (KVO) cathode with large interlayer spacing (~ 0.95 nm) and high capacity as an example, we propose that the cycle life of vanadates can be greatly upgraded in AZIBs by regulating the concentration of ZnCl2 electrolyte, but with no need to approach "water-in-salt" threshold. With the optimized moderate concentration of 15 m ZnCl2 electrolyte, the KVO exhibits the best cycling stability with ~ 95.02% capacity retention after 1400 cycles. We further design a novel sodium carboxymethyl cellulose (CMC)-moderate concentration ZnCl2 gel electrolyte with high ionic conductivity of 10.08 mS cm-1 for the first time and assemble a quasi-solid-state AZIB. This device is bendable with remarkable energy density (268.2 Wh kg-1), excellent stability (97.35% after 2800 cycles), low self-discharge rate, and good environmental (temperature, pressure) suitability, and is capable of powering small electronics. The device also exhibits good electrochemical performance with high KVO mass loading (5 and 10 mg cm-2). Our work sheds light on the feasibility of using moderately concentrated electrolyte to address the stability issue of aqueous soluble electrode materials.

Designing Polymer-in-Salt Electrolyte and Fully Infiltrated 3D Electrode for Integrated Solid-State Lithium Batteries.

Solid-state lithium batteries (SSLBs) are promising owing to enhanced safety and high energy density but plagued by the relatively low ionic conductivity of solid-state electrolytes and large electrolyte-electrode interfacial resistance. Herein, we design a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based polymer-in-salt solid electrolyte (PISSE) with high room-temperature ionic conductivity (1.24×10-4  S cm-1 ) and construct a model integrated TiO2 /Li SSLB with 3D fully infiltration of solid electrolyte. With forming aggregated ion clusters, unique ionic channels are generated in the PISSE, providing much faster Li+ transport than common polymer electrolytes. The integrated device achieves maximized interfacial contact and electrochemical and mechanical stability, with performance close to liquid electrolyte. A pouch cell made of 2 SSLB units in series shows high voltage plateau (3.7 V) and volumetric energy density comparable to many commercial thin-film batteries.

Surface and Interface Engineering of Nanoarrays toward Advanced Electrodes and Electrochemical Energy Storage Devices.

The overall performance of electrochemical energy storage devices (EESDs) is intrinsically correlated with surfaces and interfaces. As a promising electrode architecture, 3D nanoarrays (3D-NAs) possess relatively ordered, continuous, and fully exposed active surfaces of individual nanostructures, facilitating mass and electron transport within the electrode and charge transfer across interfaces and providing an ideal platform for engineering. Herein, a critical overview of the surface and interface engineering of 3D-NAs, from electrode and interface designs to device integration, is presented. The general merits of 3D-NAs and surface/interface engineering principles of 3D-NA hybrid electrodes are highlighted. The focus is on the use of 3D-NAs as a superior platform to regulate the interface nature and unveiling new mechanism/materials without the interference of binders. The engineering and utilization of the surface of 3D-NAs to develop flexible/solid-state EESDs with 3D integrated electrode/electrolyte interfaces, or 3D triphase interfaces involving other active species, which are characteristic of (quasi-)solid-state electrolyte infiltration into the entire device, are also considered. Finally, the challenges and future directions of surface/interface engineering of 3D-NAs are outlined. In particular, potential strategies to obtain electrode charge balance, optimize the multiphase solid-state interface, and attain 3D solid electrolyte infiltration are proposed.

Scalable Wire-Type Asymmetric Pseudocapacitor Achieving High Volumetric Energy/Power Densities and Ultralong Cycling Stability of 100 000 Times.

Wire-shaped asymmetric pseudocapacitors with both pseudocapacitive cathode and anode are promising in facilitating device assembly and provide highly efficient power sources for wearable electronics. However, it is a great challenge to simultaneously obtain high energy and power as well as ultralong cycling life for practical demands of such devices. Herein, a device design with new cathode/anode coupling is proposed to achieve excellent comprehensive performance in a wire-type quasi-solid-state asymmetric pseudocapacitor (WQAP). The hierarchical α-MnO2 nanorod@δ-MnO2 nanosheet array cathode and MoO2@C nanofilm anode are directly grown on flexible tiny Ti wires by well-established hydrothermal and electrodeposition techniques, which ensures rapid charge/mass transport kinetics and the sufficient utilization of pseudocapacitance. The nanoarray/film electrode also facilitates integration with gel electrolyte of polyvinyl alcohol-LiCl, guaranteeing the durability. The resulting WQAP with 2.0 V voltage delivers high volumetric energy and power densities (9.53 mWh cm-3 and 22720 mW cm-3, respectively) as well as outstanding cycling stability over 100 000 times, surpassing all the previously reported WQAPs. In addition, the device can be facilely connected in parallel or in series with minimal internal resistance, and be fabricated at the 1 m scale with excellent flexibility. This work opens the way to develop high-performance integrated wire supercapacitors.

One-pot growth of Co(OH)2 nanowire bundle arrays on in situ functionalized carbon cloth for robust flexible supercapacitor electrodes.

A one-pot route for coaxial growth of crystallized Co(OH)2 nanowire arrays on flexible carbon cloth (Co(OH)2/CC) has been developed for high-performance bendable pseudocapacitive electrodes. The hydrothermal process is found to result in in situ generation of hydrophilic groups on CC (in situ functionalized), changing its wettability and simultaneously helping the nucleation of Co(OH)2. Electrochemical tests evidence that the Co(OH)2/CC can function as a high-performance electrode with a high areal capacitance up to ∼1.13 F cm-2, excellent cycling performance (nearly 100% capacitance retention after programmed 4000 cycles) and good rate capability (retaining 46.7% of its maximum capacitance at a high current density of 40.8 mA cm-2). More importantly, detailed bending tests further demonstrate that the electrode possesses a good mechanical endurance. Even with an extreme bending radius, the majority of the nanowire arrays can still survive and the electrode shows small changes in capacitance (only 7.5% loss) and impendance (<11%) compared to the unbent state. The unique mechanical merits of array architecture for robust flexible electrode design are put forward. Our work provides a direct strategy to grow ordered nanoarray energy storage electrodes with in situ functionalization of the current collector to achieve robust mechanical and electrical adhesion.