High‐safety and low‐cost aqueous zinc‐ion batteries (ZIBs) are an exceptionally compelling technology for grid‐scale energy storage, whereas the corrosion, hydrogen evolution reaction and dendrites growth of Zn anodes plague their...

Strategies on regulating Zn2+ solvation structure for dendrites-free and side reactions-suppressed zinc-ion batteries

The new‐generation flexible aqueous zinc‐ion batteries require enhanced mechanical properties and ionic conductivities at low temperature for practical applications. This fundamentally means that it is desired that the hydrogel electrolyte possesses antifreezing merits to resist flexibility loss and performance decrease at subzero temperatures. Herein, a highly flexible polysaccharide hydrogel is realized in situ and is regulated in zinc‐ion batteries through the Hofmeister effect with low‐concentration Zn(ClO4)2 salts to satisfy the abovementioned requirements. The chaotropic ClO4− anions, water, and polymer chains can form ternary and weak hydrogen bonding (HB), which enables the polymer chains to have improved mechanical properties, breaks the HB of water to remarkably decrease the electrolyte freezing point, and reduces the amounts of free water for effective side reactions and dendrite inhibition. Consequently, even at −30 °C, the Zn(ClO4)2 in situ optimized hydrogel electrolyte features a high ionic conductivity of 7.8 mS cm−1 and excellent flexibility, which enables a Zn/polyaniline (PANI) battery with a reversible capacity of 70 mA h g−1 under 5 A g−1 for 2500 cycles, and renderd the flexible full battery with excellent cycling performances under different bending angles. This work provides a new pathway for designing high‐performance antifreezing flexible batteries via the Hofmeister effect.

Antifreezing Hydrogel Electrolyte with Ternary Hydrogen Bonding for High‐Performance Zinc‐Ion Batteries

As one of the most competitive candidates for the next-generation energy storage systems, the emerging rechargeable zinc metal battery (ZMB) is inevitably influenced by beyond-room-temperature conditions, resulting in inferior performances. Although much attention has been paid to evaluating the performance of ZMBs under extreme temperatures in recent years, most academic electrolyte research has not provided adequate information about physical properties or practical testing protocols of their electrolytes, making it difficult to assess their true performance. The growing interest in ZMBs is calling for in-depth research on electrolyte behavior under harsh practical conditions, which has not been systematically reviewed yet. Hence, in this review, we first showcase the fundamentals behind the failure of ZMBs in terms of temperature influence and then present a comprehensive understanding of the current electrolyte strategies to improve battery performance at harsh temperatures. Last, we offer perspectives on the advance of ZMB electrolytes toward industrial application.

From room temperature to harsh temperature applications: Fundamentals and perspectives on electrolytes in zinc metal batteries

Zinc-ion batteries (ZIBs) feature high safety, low cost, environmental-friendliness, and promising electrochemical performance, and are therefore regarded as a potential technology to be applied in large-scale energy storage devices. However, ZIBs still face some critical challenges and bottlenecks. The electrolyte is an essential component of batteries and its properties affect the mass transport, energy storage mechanisms, reaction kinetics, and side reactions of ZIBs. The adjustment of electrolyte formulas usually has direct and obvious impacts on the overall output and performance. In this review, advanced electrolyte strategies are overviewed for optimizing the compatibility between cathode materials and electrolytes, inhibiting anode corrosion and dendrite growth, extending electrochemical stability windows, enabling wearable applications, and enhancing temperature tolerance. The underlying scientific mechanisms, electrolyte design principles, and recent progress are presented to provide a better understanding and inspiration to readers. In addition, a comprehensive perspective about electrolyte design and engineering for ZIBs is included.

Electrolyte Engineering Enables High Performance Zinc-Ion Batteries.

Electrolyte additive engineering for aqueous Zn ion batteries

Aqueous Zn-ion batteries own great potential on next generation wearable batteries due to the high safety and low cost. However, the uncontrollable dendrites growth and the negligible subzero temperature performance impede the batteries practical applications. Herein, it is demonstrated that dimethyl sulfoxide (DMSO) is an effective additive in ZnSO4 electrolyte for side reactions and dendrites suppression by regulating the Zn-ion solvation structure and inducing the Zn2+ to form the more electrochemical stable (002) basal plane, via the higher absorption energy of DMSO with Zn2+ and (002) plane. Moreover, the stable reconstructed hydrogen bonds between DMSO and H2 O dramatically lower the freezing point of the electrolyte, which significantly increases the ionic conductivity and cycling performance of the aqueous batteries at subzero temperatures. As a consequence, the symmetrical Zn/Zn cell can be kept stable for more than 2100 h at 20 °C and 1200 h at -20 °C without dendrite and by-products formation. The Zn/MnO2 batteries can perform steadily for more than 3000 cycles at 20 °C and 300 cycles at -20 °C. This work provides a facile and feasible strategy on designing high performance and dendrite free aqueous Zn-ion batteries for various temperatures.

Immunizing Aqueous Zn Batteries against Dendrite Formation and Side Reactions at Various Temperatures via Electrolyte Additives.

The safe, flexible, and environment-friendly Zn-ion batteries have aroused great interests nowadays. Nevertheless, flagrant Zn dendrite uncontrollably grows in liquid electrolytes due to insufficient surface protection, which severely impedes the future applications of Zn-ion batteries especially at high current densities. Gel electrolytes are emerging to tackle this issue, yet the required high modulus for inhibiting dendrite growth as well as concurrent poor interfacial contact with roughened Zn electrodes are not easily reconcilable to regulate the fragile Zn/Zn2+ interface. Here we demonstrate, such a conflict may be defeated by using a mechanoadaptive cellulose nanofibril-based morphing gel electrolyte (MorphGE), which synergizes bulk compliance for optimizing interfacial contact as well as high modulus for suppressing dendrite formation. Moreover, by anchoring desolvated Zn2+ on cellulose nanofibrils, the side reactions which induce dendrite formation are also significantly reduced. As a result, the MorphGE-based symmetrical Zn-ion battery demonstrated outstanding stability for more than 100 h at the high current density of 10 mA·cm−2 and areal capacity of 10 mA·h·cm−2, and the corresponding Zn-ion battery delivered a prominent specific capacity of 100 mA·h·g−1 for more than 500 cycles at 20 C. The present example of engineering the mechanoadaptivity of gel electrolytes will shed light on a new pathway for designing highly safe and flexible energy storage devices.

Tianyu Li

Papers

Immunizing Aqueous Zn Batteries against Dendrite Formation and Side Reactions at Various Temperatures via Electrolyte Additives.

Mechanoadaptive morphing gel electrolyte enables flexible and fast-charging Zn-ion batteries with outstanding dendrite suppression performance