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.

Although zinc metal anodes have some intrinsic advantages for aqueous zinc ion batteries, the notorious dendrites hamper its practical applications. Herein, a charge‐enriched strategy through MXene‐based polypyrrole (MXene‐mPPy) layers is explored toward dendrite‐free Zn metal anode. The MXene‐mPPy layers composed of mesoporous PPy on both sides of Ti3C2Tx‐MXene exhibit an exceptional charge enrichment ability (149 F g−1, 5 mV s−1), which is beneficial not onlying terms of accumulating the charge levels, but also to homogenize the dispersions of electric field and ion flux as used as an artificial interface on a Zn anode. Thus, a dendrite‐free Zn anode with an ultralong cycling lifespan up to 2500 h and superior rate capability is achieved, which is further applied as an anode for aqueous zinc ion batteries with a long‐term span over 3000 cycles at 10 A g−1.

Charge‐Enriched Strategy Based on MXene‐Based Polypyrrole Layers Toward Dendrite‐Free Zinc Metal Anodes

Aqueous Zn metal batteries have attracted much attention due to their high intrinsic capacity, high safety, and low cost. Nevertheless, uncontrollable dendrite growth and adverse side reactions of Zn anodes seriously hinder their further application. Herein, a three‐dimensional (3D) porous graphene‐carbon nanotubes scaffold decorated with metal–organic framework derived ZnO/C nanoparticles (3D‐ZGC) is fabricated as the host for dendrite‐free Zn‐metal composite anodes. The zincophilic ZnO/C nanoparticles act as preferred deposition sites with low nucleation barriers to induce homogeneous Zn deposition. The mechanically robust 3D scaffold with high conductivity not only suppresses the formation of dendritic Zn by reducing the local current density and homogenizing Zn2+ ion flux, but also inhibits volume changes during the long‐term plating/stripping process. As a result, the 3D‐ZGC composite anodes afford unprecedented Zn plating‐stripping stability at an ultrahigh current density of 20 mA cm‐2 for 1500 cycles with low overpotential (<65 mV) when used in a symmetric cell. When coupled with MnO2 cathodes, the assembled Zn@3D‐ZGC//MnO2 full batteries deliver an enhanced cycling stability for up to 6000 cycles at 2000 mA g‐1, demonstrating the potential of the 3D‐ZGC composite anode for advanced Zn metal batteries.

A MOF‐Derivative Decorated Hierarchical Porous Host Enabling Ultrahigh Rates and Superior Long‐Term Cycling of Dendrite‐Free Zn Metal Anodes

Aqueous zinc (Zn)-ion batteries are regarded as promising candidates for large-scale energy storage systems because of their high safety, low cost, and environmental benignity. However, the dendrite issue of Zn anode hinders their practical application. Herein, a freestanding, lightweight, and zincophilic MXene/nanoporous oxide heterostructure engineered separator is designed to stabilize a Zn metal anode. The nanoporous oxides prepared by a one-step vacuum distillation technique afford the advantages of large surface area, high porosity, and homogeneous porous structure. The zincophilic MXene@oxides layer can homogenize the electric field distribution, facilitate ion diffusion kinetics, reduce local current density, and promote even Zn ionic flux, which will regulate uniform Zn deposition and suppress side reactions. Accordingly, dendrite-free Zn anodes with stable cyclability are achieved for over 500 h at an ultrahigh area capacity of 10 mAh cm-2. Besides, flexible, long-lifespan, and high-rate N/S-doped three-dimensional MXene@MnO2||Zn full cells are constructed with the engineered separator. Moreover, this strategy can be successfully extended to lithium, sodium, potassium, and magnesium metal batteries, indicating that separator regulation is a universal approach to overcome the challenges of metal batteries.

Highly Reversible Zn Metal Anodes Enabled by Freestanding, Lightweight, and Zincophilic MXene/Nanoporous Oxide Heterostructure Engineered Separator for Flexible Zn-MnO2 Batteries.

The practical implementation of Zn metal anodes with high volumetric capacity is seriously plagued by the dendritic growth and accompanying interfacial parasitic reactions. Herein, high yield carbon dots (CDs) with abundant polar functional groups (CHO and CN), as a functional artificial interface layer, are rationally designed to optimize electrolyte/Zn interfaces with large‐scale viability. Of particular note, the quantum‐sized CDs with strong Zn affinity can effectively ameliorate the electric field distribution and ensure that more Zn2+ is adsorbed onto the whole electrode, which are beneficial for lowering the barrier of Zn2+ nucleation and inducing homogeneous Zn deposition, thus rendering a dendrite‐free Zn anode, as extensively confirmed by in situ optical microscope observation and finite element simulation. Meanwhile, the dense and insoluble coating layer with abundant polar functional groups is conducive to arousing the repulsion effect, which is good for shielding the active water and SO42−, thus eliminating the water‐mediated parasitic reactions and improving Zn2+ reaction kinetics. More importantly, the electrochemically stable CDs layer endows the Zn anode with a prolonged lifespan of 3000 h at 1 mA cm−2. This feasible and efficient fabrication of functional CDs layer opens a new avenue for stable dendrite‐free metal anodes.

High‐Yield Carbon Dots Interlayer for Ultra‐Stable Zinc Batteries

Rechargeable aqueous zinc-ion batteries (RZIBs) provide a promising complementarity to the existing lithium-ion batteries due to their low cost, non-toxicity and intrinsic safety. However, Zn anodes suffer from zinc dendrite growth and electrolyte corrosion, resulting in poor reversibility. Here, we develop an ultrathin, fluorinated two-dimensional porous covalent organic framework (FCOF) film as a protective layer on the Zn surface. The strong interaction between fluorine (F) in FCOF and Zn reduces the surface energy of the Zn (002) crystal plane, enabling the preferred growth of (002) planes during the electrodeposition process. As a result, Zn deposits show horizontally arranged platelet morphology with (002) orientations preferred. Furthermore, F-containing nanochannels facilitate ion transport and prevent electrolyte penetration for improving corrosion resistance. The FCOF@Zn symmetric cells achieve stability for over 750 h at an ultrahigh current density of 40 mA cm−2. The high-areal-capacity full cells demonstrate hundreds of cycles under high Zn utilization conditions. Rechargeable aqueous zinc-ion batteries are promising but the zinc anode suffers from dendrite growth and electrolyte corrosion. Here, the authors develop a fluorinated covalent organic framework film as a protective layer for aqueous zinc anode battery.

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Horizontally Arranged Zinc Platelet Electrodeposits Modulated by Fluorinated Covalent Organic Framework Film for High-Rate and Durable Aqueous Zinc Ion Batteries

The invention relates to an in-situ assembled polyvinyl alcohol composite carbon-based hydrophobic oil-absorption material and a preparation method thereof. The in-situ assembled polyvinyl alcohol composite carbon-based hydrophobic oil-absorption material has good hydrophobic and oleophobic properties (the water contact angle reaches up to 146 degrees) and relatively high adsorption rate and mechanical strength; and meanwhile, through simple compression, the material can be recycled. The preparation method is green, environment-friendly and low-cost. The material has potential application value in the environmental protection fields of adsorption of oils and organic solvents and the like.

In-situ assembled polyvinyl alcohol composite carbon-based hydrophobic oil-absorption material and preparation method thereof

The invention relates to a co-alkali system in-situ self-assembly cellulose/graphene compound fiber and a preparing method thereof. The compound fiber is composed of a graphene dispersing liquid and acellulose solution. A solvent of the cellulose solution is composed of a strong base composition, urine or thiourea and water. The preparing process mainly includes the steps of conducting intercalation, activation, shearing and stripping and co-alkali solution dispersing to obtain high-concentration graphene dispersing liquid, cooling a co-alkali solvent until the temperature reaches -12 DEG C to -4 DEG C, conducting stirring at a high speed and rapidly dissolving natural or regenerated cellulose with the molecular weight smaller than 10*104 to obtain a high-dissolubility transparent cellulose concentrated solution. After the cellulose solution and the graphene dispersing liquid are mixed in proper proportion under the alkali system, the self-assembly, traction, oiling and drying are conducted with a 3-5 wt% dilute acid coagulating bath to prepare the cellulose/graphene compound fiber. Operation is simple, the prepared material can be used for the fields of wearable self-power-generation intelligent fabrics, antistatic textile materials, flexible intelligent sensing materials or electromagnetic shielding fabrics or the like.

Wu Tianqi

Papers

Horizontally Arranged Zinc Platelet Electrodeposits Modulated by Fluorinated Covalent Organic Framework Film for High-Rate and Durable Aqueous Zinc Ion Batteries

In-situ assembled polyvinyl alcohol composite carbon-based hydrophobic oil-absorption material and preparation method thereof

Co-alkali system in-situ self-assembly cellulose/graphene compound fiber and preparing method thereof