Design Strategies for Aqueous Zinc Metal Batteries with High Zinc Utilization: From Metal Anodes to Anode-Free Structures

A solid solution alloy current collector to stabilize zinc metal anodes

Dendrite growth limits the performance of aqueous zinc-metal batteries. Here, we present a Cu-In solid solution alloy current collector, where indium enhances zinc affinity and lowers nucleation overpotential, enabling dendrite-free zinc deposition. The Zn@Cu-In anode demonstrates stable cycling at high current densities.

Self-adsorbing electrolyte additive promoting Zn(002) deposition on Zn anode for aqueous zinc-ion battery

The poor cycling stability of aqueous zinc-ion batteries (AZIBs), caused by zinc dendrite growth and surface corrosion-induced passivation at the zinc anode, significantly hinders their practical development. In this work, 7-(2,3-dihydroxypropyl)theophylline (DHTP) is introduced as a functional additive into Zn(CF3SO3)2 (ZOT) electrolyte to regulate the anode-electrolyte interface and mitigate side reactions. Theoretical calculations and experimental characterizations reveal that DHTP preferentially adsorbs on the zinc anode, reducing direct water contact and thereby suppressing hydrogen evolution and corrosion reactions. Notably, DHTP exhibits the lowest adsorption energy on the Zn(002) crystal plane, which optimizes Zn2+ diffusion and deposition behavior, guiding the preferential growth of the Zn(002) plane. Benefiting from this, the Zn||Zn symmetric cell with DHTP achieves stable cycling for over 800 h at 1 mA cm-2 and 1 mAh cm-2, outperforming the bare electrolyte. Furthermore, the Zn||NaV3O8·1.5H2O full cell demonstrates exceptional durability of 9,000 cycles with a remarkable capacity retention of 89 % under a high current density of 10 A g-1. This molecular adsorption strategy based on DHTP provides a novel approach to constructing highly reversible zinc anodes for advanced AZIBs.

Salt-Based Electrolyte Additives for Regulating the Interface Chemistry of Zinc Metal Anodes in High-Performance Aqueous Zinc Batteries

Aqueous zinc-metal batteries (AZMBs) are emerging as a promising green and low-cost energy storage solution, distinguished by their high safety and environmental friendliness. However, the industrialization of AZMBs is currently hindered by significant challenges, particularly uncontrollable dendritic growth and side reactions at the zinc metal anode interface, which severely limit their large-scale application. To address these issues, salt-based electrolyte additives have emerged as a straightforward, economical, and practical solution. This review systematically classifies and analyzes the working mechanisms of inorganic, organic, and ammonium salt-based additives, elucidating their roles in regulating solvation structures, hydrogen bond networks, pH levels, interfacial protective layers, electric fields, and Zn2+ deposition behaviors. These additives enhance anode stability and mitigate side reactions, thereby improving overall electrochemical performance. Additionally, the review offers valuable insights into future directions for the development of salt-based electrolyte additives, providing essential guidance for advancing research in this field.

Tailoring Water-in-DMSO Electrolyte for Ultra-stable Rechargeable Zinc Batteries

Rechargeable zinc batteries (RZBs) are hindered by two primary challenges: instability of Zn anode and deterioration of the cathode structure in traditional aqueous electrolytes, largely attributable to the decomposition of active H2O. Here, we design and synthesize a non-flammable water-in-dimethyl sulfoxide electrolyte to address these issues. X-ray absorption spectroscopy, in situ techniques and computational simulations demonstrate that the activity of H2O in this electrolyte is extremely compressed, which not only suppresses the side reactions and increases the reversibility of Zn anode, but also diminishes the cathode dissolution and proton intercalation. The hybrid solid-electrolyte interface (SEI), formed in situ, helps Zn-Zn symmetric cell a prolonged lifespan exceeding 10000 h at 0.5 mA cm-2 and 600 h at a 60 % discharge depth. The versatility of this electrolyte endows the Zn-VO2 full batteries ultra-stable cycling performance. This work provides insights into electrolyte structure-property relationships, and facilitates the design of high-performance RZBs.

Suppressing Hydrogen Evolution and Dendrite Formation on a Zn Anode by Coating In2O3 with Tailored Affinity to H* and Zn

To suppress the hydrogen evolution reaction (HER) and dendrite formation on the Zn anode in aqueous Zn-ion batteries, a submicrometer In2O3 coating on the Zn anode (referred to as Zn@In2O3) was constructed via magnetron sputtering. Density functional theory (DFT) and experimental data show that the In2O3 coating suppresses the HER because of its weaker interactions with H* compared with Zn, inhibiting the Volmer step. At the same time, the In2O3 coating exhibits a moderate affinity for Zn*, higher than that on Zn but lower than that at the In2O3-Zn interface, thus facilitating the desolvation of the hydrated Zn2+ ions while promoting its deposition on the Zn substrate beneath the In2O3 coating. The resultant suppression of side reactions and dendrite growth significantly enhance the reversible plating/stripping of Zn. The optimized Zn@In2O3 stably cycles over 6400 h with a low voltage hysteresis of 9.5 mV at 1 mA cm-2 and 1 mAh cm-2 in symmetric cells. The average Coulombic efficiency of Zn plating/stripping is increased from 95.8 to 99.6% owing to the In2O3 coating. Moreover, when coupled with the Mn0.15V2O5·nH2O cathode, the Zn@In2O3 battery maintains a capacity retention of 78.6% after 2000 cycles at 5 A g-1. This facile and economical modification of Zn anodes provides an idea for realizing the practical application of AZIBs.

Intrinsic Ion Concentration Difference Induced Antipolyelectrolyte Effect for Promoting Stability of Zn Anodes

Aqueous zinc-ion batteries have gained significant attention due to their high safety and low cost. However, the cation concentration gradient at the anode/electrolyte interface often causes serious Zn dendrites and side reactions. Herein, cross-linked ion channels were constructed on the anode surface by the antipolyelectrolyte effect of zwitterionic polymer carboxymethyl chitosan (CMCHS) molecules, which is induced by the transient ion concentration difference at the initial Zn2+ deposition process. The CMCHS channels endow the anode surface with homogeneous ions and electron distributions. Simultaneously, CMCHS molecules enter into Zn2+ solvation structures and H2O molecules are removed, limiting the activity of solvated H2O molecules. Therefore, the dendrite growth and water activity are significantly suppressed, resulting in the excellent electrochemical performance of Zn anodes. An average Coulombic efficiency of 99.58% is achieved, which is much superior to the case in the conventional ZnSO4 electrolyte. To illustrate the feasibility of the CMCHS-contained electrolyte, Zn||V2O5 full batteries were assembled and exhibited enhanced electrochemical performance.

Exploring cyclodextrin-driven advancements in aqueous Zn-ion battery: A review

The growing demand for sustainable and efficient energy storage solutions has emphasized the value of aqueous zinc-ion batteries (AZIBs) as a safer and less expensive alternative to lithium-ion batteries. Despite their potential, AZIBs confront considerable obstacles, particularly the production of zinc dendrites and side reactions such hydrogen evolution, which limit their cycling stability and practical applicability. In this review, we explore the prospective function of cyclodextrins (CDs), a type of supramolecular carbohydrate polymer, in addressing such challenges. CDs, with their unique capacity to form inclusion complexes, provide an innovative approach for controlling zinc deposition, limiting dendrite development, and minimizing parasitic interactions. We present a detailed assessment of recent improvements in the use of CDs to change electrolytes and the electrode/electrolyte interface, resulting in improved electrochemical performance of AZIBs. This review focuses on CDs' potential as multifunctional additives for improving zinc anode stability, extending battery life, and facilitating large-scale AZIB adoption.

Anode-Free Zinc-Bromine Batteries Enabled by a Simple Prenucleation Strategy

The design of anode-free zinc (Zn) batteries with high reversibility at high areal capacity has received significant attention recently, which is quietly challenging yet. Here, a Zn alloyed interface through electroplating is introduced, providing homogeneous Zn prenucleation sites to stabilize subsequent Zn nucleation and plating. By employing Zn-Cu alloy as a module, the complementary simulations and characterizations confirm that the prenucleation alloyed interfaces achieve a homogeneous electric field distribution and greatly enhance the stability of the Zn anode. Accordingly, the Zn//Zn-Cu@Cu half-cells show a long cycle life of over 900 h and an average Coulombic efficiency (CE) of 99.8% at an areal capacity of 10 mAh cm-2. The assembled anode-free zinc-bromine (Zn-Br2) battery exhibits an attractive stable cycling of 11 000 cycles at 1 mAh cm-2, while over 1000 cycles at the higher areal capacity of 10 mAh cm-2. Excitingly, the Zn-Br2 pouch cell with a capacity of 1000 mAh operates stably over 50 cycles, and achieves successful integration with photovoltaic systems. This anode-free Zn-Br2 batteries constructed through a prenucleation strategy offer new insights into the potential for large-scale energy storage applications.

Current status and advances in zinc anodes for rechargeable aqueous zinc-air batteries

To promote sustainable development and reduce fossil fuel consumption, there is a growing demand for high-performance, cost-effective, safe and environmentally friendly batteries for large-scale energy storage systems. Among the emerging technologies, zinc-air batteries (ZABs) have attracted significant interest. By integrating the principles of traditional zinc-ion batteries and fuel cells, ZABs offer remarkably high theoretical energy density at lower production cost compared to the current state-of-the-art lithium-ion batteries (LIBs). However, the critical challenge remains in developing high-performance zinc anode. Herein, this review provides a comprehensive analysis of the current status and advancements in zinc anodes for rechargeable aqueous ZABs. We begin by highlighting the major challenges and underlying mechanisms associated with zinc anodes including issues such as uneven zinc deposition, dendrite growth and hydrogen evolution reaction. Then, this review discusses the recent advancements in zinc anode modifications, focusing on strategies such as alloying, surface porosity and zincophilicity. By reviewing the latest research, we also identify existing gaps and pose critical questions that need further exploration to push the field forward. The goal of this review is to inspire new research directions and promote the development of more efficient zinc anodes.

Enhancing Zn Deposition Reversibility on MXene Current Collectors by Forming ZnF2-Containing Solid-Electrolyte Interphase for Anode-Free Zinc Metal Batteries

Anode-free aqueous zinc metal batteries (AZMBs) offer significant potential for energy storage due to their low cost and environmental benefits. Ti3C2Tx MXene provides several advantages over traditional metallic current collectors like Cu and Ti, including better Zn plating affinity, lightweight, and flexibility. However, self-freestanding MXene current collectors in AZMBs remain underexplored, likely due to challenges with Zn deposition reversibility. This study investigates the combination of a Ti3C2Tx self-freestanding film with advanced electrolyte engineering, specifically examining the effects of Li-salt and propylene carbonate (PC) as additives on Zn plating reversibility. While using Li+ ions as an additive alone facilitates uniform Zn deposition on bulk metals through the electrostatic shielding effect, the addition of Li-salt negatively impacts Zn plating uniformity on Ti3C2Tx. Meanwhile, using PC additive alone forms an organic SEI layer on Ti3C2Tx and causes Zn agglomeration. The use of both additives together results in a ZnF2-containing hybrid SEI layer with improved interfacial kinetics, promoting more uniform Zn deposition. This approach achieves an average Coulombic efficiency (CE) of 96.8% over 150 cycles (a maximum CE of 97.8%). The study highlights the strategic difference in electrolyte design, emphasizing the need for tailored approaches to optimize Zn deposition on MXenes, contrasting with traditional metallic current collectors.

Minimizing Zn Loss Through Dual Regulation for Reversible Zinc Anode Beyond 90% Utilization Ratio

Large-scale energy storage devices experience explosive development in response to the increasing energy crisis. Zinc ion batteries featuring low cost, high safe, and environment friendly are considered promising candidates for next-generation energy storage devices. However, their practical application suffers from the limited anode lifespan under a high zinc utilization ratio, which can be attributed to aggravated Zn loss caused by zinc conversion reactions and "dead" Zn. Herein, n-propyl alcohol is reported to stabilize the Zn anode under the high depth of discharge through dual regulation of water activity inhibition and zinc-ion plating regulation. The modified electrolyte exhibits a 76.43% cut in corrosion current benefited from low water activity and benefits SEI surface. The "dead" Zn content is also reduced by 26 times as a result of dendrite-free zinc ion plating. Thus, the highly reversible zinc plating/stripping with 99.62% CE is achieved for ≈3600 cycles. Moreover, the lifespan of Zn/Zn cells is greatly increased even under a high depth of discharge (310 h, 90%DOD and 120 h, 95.18% DOD). In Zn/NH4V4O10 full cells, the improved anode reversibility enables a remarkable capacity retention of 92.16% after 400 cycles with a low N/P ratio of 2.5.

Long cycle life aqueous zinc-ion battery enabled by a ZIF-N protective layer with electron-withdrawing group and zincophilicity on the Zn anode

Aqueous zinc-ion batteries (AZIBs) have garnered attention from researchers for their high theoretical capacity, safety, and low cost. However, the uncontrolled growth of zinc (Zn) dendrites and spontaneous corrosion reactions on the Zn anode significantly compromise the cycle life of AZIBs. This paper proposes the utilization of a novel zeolitic imidazole framework (ZIF-N) material with zincophilicity and hydrophilicity for modifying the Zn anode of AZIBs. ZIF-N incorporates numerous electron-withdrawing nitro groups at the Zn/ZIF-N interface to regulate the uneven electron distribution on the Zn anode. The modified Zn anode (Zn@ZIF-N) exhibits a lower polarization ratio (32.18 mV at 4 mA cm-2) and an extended cycle life (over 700 h at 4 mA cm-2). At a current density of 1 mA cm-2, the battery composed of a Zn@ZIF-N anode and NVO (NaV3O8) achieves a cycle life of 1600 cycles. This work provides a straightforward and cost-effective strategy for modifying the Zn anode to prolong the cycle life of AZIBs.

Pyrrolic-Nitrogen Chemistry in 1-(2-hydroxyethyl)imidazole Electrolyte Additives toward a 50,000-Cycle-Life Aqueous Zinc-Iodine Battery

Rechargeable aqueous zinc iodine (Zn-I2) batteries offer benefits such as low cost and high safety. Nevertheless, their commercial application is hindered by hydrogen evolution reaction (HER) and polyiodide shuttle, which result in a short lifespan. In this study, 1-(2-hydroxyethyl)imidazole (HEI) organic molecules featuring pyrrole-N groups are introduced as dually-functional electrolyte additives to simultaneously stabilize Zn anode and confine polyiodide through ion-dipole interactions. The pyrrole-N groups in HEI can preserve the interfacial pH equilibrium at Zn anode by reversibly capturing H+ ions and dynamically neutralizing OH- ions, thereby suppressing the HER. Notably, the H2 evolution rate at the Zn anode is reduced to a mere 2.20 μmol h-1 cm-2. Furthermore, the pyrrole-N moieties in HEI effectively curtail the polyiodide shuttle at I2 cathode, which show adsorption energies of -0.174 eV for I2, -0.521 eV for I3 -, and -0.768 eV for I-, as indicated by density functional theory calculations. Electrochemical testing demonstrates that the Zn//Zn symmetric cell maintains stable cycling for up to 4,200 hours at 1 mA cm-2. Most strikingly, at a high I2 mass loading of 9.7 mg cm-2, the Zn-I2 battery achieves an extraordinary cycle life of 50,000 cycles.

Untangling the Role of Capping Agents in Manipulating Electrochemical Behaviors Toward Practical Aqueous Zinc-Ion Batteries

Long-standing challenges including notorious side reactions at the Zn anode, low Zn anode utilization, and rapid cathode degradation at low current densities hinder the advancement of aqueous zinc-ion batteries (AZIBs). Inspired by the critical role of capping agents in nanomaterials synthesis and bulk crystal growth, a series of capping agents are employed to demonstrate their applicability in AZIBs. Here, it is shown that the preferential adsorption of capping agents on different Zn crystal planes, coordination between capping agents and Zn2+ ions, and interactions with metal oxide cathodes enable preferred Zn (002) deposition, water-deficient Zn2+ ion solvation structure, and a dynamic cathode-electrolyte interface. Benefiting from the multi-functional role of capping agents, dendrite-free Zn plating and stripping with an improved Coulombic efficiency of 99.2% and enhanced long-term cycling stability are realized. Remarkable capacity retention of 91% is achieved for cathodes after more than 500 cycles under a low current density of 200 mA g-1, marking one of the best cycling stabilities to date. This work provides a proof-of-concept of capping agents in manipulating electrochemical behaviors, which should inspire and pave a new avenue of research to address the challenges in practical energy storage beyond AZIBs.

Recent Progress in Aqueous Zinc-ion Batteries at High Zinc Utilization

Aqueous zinc ion batteries (AZIBs) are promising candidates for next-generation energy storage systems due to their low cost, high safety, and environmental friendliness. As the critical component, Zn metal with high theoretical capacity (5855 mAh cm-3), low redox potential (-0.76 V vs. standard hydrogen electrode), and low cost has been widely applied in AZIBs. However, the low Zn utilization rate (ZUR) of Zn metal anode caused by the dendrite growth, hydrogen evolution, corrosion, and passivation require excess Zn installation in current AZIBs, thus leading to increased unnecessary battery weight and decreased energy density. Herein, approaches to the historical progress toward high ZUR AZIBs through the perspective of electrolyte optimization, anode protection, and substrate construction are comprehensively summarized, and an in-depth understanding of ZUR is highlighted. Specifically, the main challenges and failure mechanisms of Zn anode are analyzed. Then, the persisting issues and promising solutions in the reaction interface, aqueous electrolyte, and Zn anode are emphasized. Finally, the design of 100 % ZUR AZIBs free of Zn metal is presented in detail. This review aims to provide a better understanding and fundamental guidelines on the high ZUR AZIBs design, which can shed light on research directions for realizing high energy density AZIBs.

The challenges and strategies towards high-performance anode-free post-lithium metal batteries

With the merits of high theoretical energy density and ease of manufacture, anode-free post-lithium metal batteries have drawn extensive attention and have been rapidly emerging in recent years. However, the poor reversibility of metal anodes has severely hindered the realization of high-performance anode-free batteries. In this review, the critical challenges and strategies for achieving high-performance anode-free metal batteries are first elucidated. Then, the significant research studies devoted to promoting the reversibility of metal anodes for anode-free post-lithium (including sodium-, potassium- and zinc-) metal batteries are exclusively discussed to extract the principles for their practical implementation. Additionally, remedial solutions of supplying metal to the anode for improving the cyclability of anode-free batteries are also introduced. Finally, we summarize the advancements in anode-free post-lithium metal batteries, and propose some promising directions in this area. This review aims to provide a more comprehensive understanding towards the strategies for achieving highly reversible anode-free post-lithium metal batteries and a timely overview of the latest developments in this emerging field.

Sieving-type Electric Double Layer with Hydrogen Bond Interlocking to Stable Zinc Metal Anode

The stability of aqueous zinc metal batteries is significantly affected by side reactions and dendrite growth on the anode interface, which primarily originate from water and anions. Herein, we introduce a multi H-bond site additive, 2, 2'-Sulfonyldiethanol (SDE), into an aqueous electrolyte to construct a sieving-type electric double layer (EDL) by hydrogen bond interlock in order to address these issues. On the one hand, SDE replaces H2O and SO4 2- anions that are adsorbed on the zinc anode surface, expelling H2O/SO4 2- from the EDL and thereby reducing the content of H2O/SO4 2- at the interface. On the other hand, when Zn2+ are de-solvated at the interface during the plating, the strong hydrogen bond interaction between SDE and H2O/SO4 2- can trap H2O/SO4 2- from the EDL, further decreasing their content at the interface. This effectively sieves them out of the zinc anode interface and inhibits the side reactions. Moreover, the unique characteristics of trapped SO4 2- anions can restrict their diffusion, thereby enhancing the transference number of Zn2+ and promoting dendrite-free deposition and growth of Zn. Consequently, utilizing an SDE/ZnSO4 electrolyte enables excellent cycling stability in Zn//Zn symmetrical cells and Zn//MnO2 full cells with lifespans exceeding 3500 h and 2500 cycles respectively.

An Ion-Pumping Quasi-Solid Electrolyte Enabled by Electrokinetic Effects for Stable Aqueous Zinc Metal Batteries

The practical application of aqueous zinc (Zn) metal batteries (ZMBs) is hindered by the complicated hydrogen evolution, passivation reactions, and dendrite growth of Zn metal anodes. Here, an ion-pumping quasi-solid electrolyte (IPQSE) with high Zn2+ transport kinetics enabled by the electrokinetic phenomena to realize high-performance quasi-solid state Zn metal batteries (QSSZMBs) is reported. The IPQSE is prepared through the in situ ring-opening polymerization of tetramethylolmethane-tri-β-aziridinylpropionate in the aqueous electrolyte. The porous polymer framework with high zeta potential provides the IPQSE with an electrokinetic ion-pumping feature enabled by the electrokinetic effects (electro-osmosis and electrokinetic surface conduction), which significantly accelerates the Zn2+ transport, reduces the concentration polarization and overcomes the diffusion-limited current. Moreover, the Zn2+ affinity of the polymer and hydrogen bonding interactions in the IPQSE changes the Zn2+ coordination environment and reduces the amount of free H2O, which lowers the H2O activity and inhibits H2O-induced side reactions. Consequently, the highly reversible and stable Zn metal anodes are achieved. The assembled QSSZMBs based on the IPQSE display excellent cycling stability with high capacity retention and Coulombic efficiency. The high-performance quasi-solid state Zn metal pouch cells are demonstrated, showing great promise for the practical application of the IPQSE.

Ultra-Stable Aqueous Zinc Anodes: Enabling High-Performance Zinc-Ion Batteries via a ZnSiF6-Derived Protective Interphase

Zinc-ion batteries (ZIBs) hold immense promise as next-generation energy storage solutions, however, the practical application of zinc anodes is hindered by dendrite formation and parasitic side reactions. Engineering a stable solid- eletrolyte interphase (SEI) is crucial for addressing these issues. This study proposes a novel strategy to enhance Zn anode performance by incorporating a ZnSiF6 additive into a standard ZnSO4 (ZSO) electrolyte. The ZnSiF6 additive facilitates the formation of a stable, fluorine-rich SEI on the Zn anode surface. Characterization reveals a hierarchical SEI structure, primarily composed of porous alkali zinc sulfate (ZHS) with embedded ZnF2. This unique architecture promotes rapid zinc ion desolvation and efficient transport, enhances corrosion resistance, and mitigates hydrogen evolution. Consequently, ZnSiF6-modified cells exhibit exceptional cycling stability, exceeding 3000 hours at 0.5 mA cm-2 and 560 hours at 10 mA cm-2, significantly outperforming ZSO-based cells. The modified cells also achieve high areal capacities (10 mAh cm-2), indicating superior zinc utilization. This work provides key insights for designing stable electrode/electrolyte interfaces, contributing to the development of high-performance aqueous ZIBs.

Planar Deposition via In Situ Conversion Engineering for Dendrite-Free Zinc Batteries

Owing to the considerable capacity, high safety, and abundant zinc resources, zinc-ion batteries (ZIBs) have been garnering much attention. Nonetheless, the unsatisfactory cyclic lifespan and poor reversibility originate from side reactions and dendrite obstacles to their practical applications. In addition to inhibiting the corrosion of aqueous electrolytes, regulating planar deposition is a key strategy to enhance their long-term stability. Herein, an in situ conversion strategy is reported to construct a protective "dual-layer" structure (VZSe/V@Zn) on zinc metal, consisting of the VSe2-ZnSe outer layer with low lattice mismatch to Zn (002) plane, and corrosion-resistant nanometallic V inner layer. Such design integrates superior interfacial ionic/electronic transfer, corrosion resistance, and unique planar deposition regulation capability. The as-prepared VZSe/V@Zn demonstrates remarkable durability of 238 h at 50 mA cm-2 with a high depth of discharge (68.3% DOD) in the Zn||Zn symmetric cell. Even in the anode-free system, the as-prepared protective layer can extend the cycle life up to 2000 cycles, with an outstanding capacity retention of 93.1% and ultra-high average coulombic efficiency of 99.998%. This work delineates an effective strategy for fabricating lattice-matching protective layers, with profound implications for elucidating zinc deposition mechanisms and paving the way for the development of high-performance zinc batteries.

A Crystalline-Water Electrolyte Enabled High Depth-of-Discharge Anodes in Aqueous Zinc Metal Batteries

Aqueous zinc metal batteries are regarded as a promising energy storage solution for a green and sustainable society in the future. However, the practical application of metallic zinc anode is plagued by the thermodynamic instability issue of water molecules in conventional electrolytes, which leads to severe dendrite growth and side reactions. In this work, an ultra-thin and high areal capacity metallic zinc anode is achieved by utilizing crystalline water with a stable stoichiometric ratio. Unlike conventional electrolytes, the designed electrolyte can effectively suppress the reactivity of water molecules and diminish the detrimental corrosion on the metallic zinc anode, while preserving the inherent advantages of water molecules, including great kinetic performance in electrolytes and H+ capacity contribution in cathodes. Based on the comprehensive performance of the designed electrolyte, the 10 µm Zn||10 µm Zn symmetric cell stably ran for 1000 h at the current density of 1 mA cm-2, and the areal capacity of 1 mAh cm-2, whose depth-of-discharge is over 17.1%. The electrochemical performance of the 10 µm Zn||9.3 mg cm-2 polyaniline (PANI) full-cell demonstrates the feasibility of the designed electrolyte. This work provides a crucial understanding of balancing activity of water molecules in aqueous zinc metal batteries.

Achieving a balance of rapid Zn2+ desolvation and hydrogen evolution reaction inertia at the interface of the Zn anode

It is difficult to achieve fast kinetics of Zn2+(H2O)6 desolvation as well as HER inertia at the same electrolyte/Zn interface during long-term cycling of Zn plating/stripping in aqueous Zn-ion batteries. Herein, an effective interface construction strategy with hydrophilic transition metal oxides was proposed to achieve that balance using a CeO2 layer coating. The hydrophilic CeO2 layer can bring a balance between improving the access to the anode surface for Zn2+(H2O)6 electrolyte ions, providing uniform Zn2+ nucleation sites and HER inertia. What's more, Zn corrosion can be significantly inhibited benefiting from this coating layer. The efficiency of aqueous Zn-ion batteries showed a great enhancement. Ultra-long plating/stripping stability up to 1600 h and excellent recovery (returning to 0.5 from 20 mA cm-2) for the symmetric CeO2@Zn system were observed. A full cell with the MnO2 cathode (CeO2@Zn//MnO2) with good reversibility and stability (∼600 cycles) was fabricated for practical application. Our work provides a fundamental understanding and an essential solution to deal with the balance between rapid desolvation and inhibition of the hydrogen evolution reaction, which is important for promoting the practical application of rechargeable Zn batteries.

Molecule Engineering of Sugar Derivatives as Electrolyte Additives for Deep-Reversible Zn Metal Anode

The cycling performance of zinc-ion batteries is greatly affected by dendrite formation and side reactions on zinc anode, particularly in scenarios involving high depth of discharge (DOD) and low negative/positive capacity (N/P) ratios in full cells. Herein, drawing upon principles of host-guest interaction chemistry, we investigate the impact of molecular structure of electrolyte additives, specifically the -COOH and -OH groups, on the zinc negative electrode through molecular design. Our findings reveal that molecules containing these groups exhibit strong adsorption onto zinc anode surfaces and chelate with Zn2+, forming a H2O-poor inner Helmholtz plane. This effectively suppresses side reactions and promotes dendrite-free zinc deposition of exposed (002) facets, enhancing stability and reversibility of an average coulombic efficiency of 99.89 % with the introduction of Lactobionic acid (LA) additive. Under harsh conditions of 92 % DOD, Zn//Zn cells exhibit stable cycling at challenging current densities of 15 mA ⋅ cm-2. Even at a low N/P ratio of 1.3, Zn//NH4V4O10 full cells with LA electrolyte exhibit high-capacity retention of 73 % after 300 cycles, significantly surpassing that of the blank electrolyte. Moreover, in a conversion type Zn//Br static battery with a high areal capacity (~5 mAh ⋅ cm-2), LA electrolyte sustains an improved cycling stability of 700 cycles.

Highly Reversible and Dendrite-Free Zinc Anodes Enabled by PEDOT Nanowire Interfacial Layers for Aqueous Zinc-Ion Batteries

The aqueous zinc-ion batteries (ZIBs) have gained increasing attention because of their high specific capacity, low cost, and good safety. However, side reactions, hydrogen evolution reaction, and uncontrolled zinc dendrites accompanying the Zn metal anodes have impeded the applications of ZIBs in grid-scale energy storage. Herein, the poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires as an interfacial layer on the Zn anode (Zn-PEDOT) are reported to address the above issues. Our experimental results and density functional theory simulation reveal that the interactions between the Zn2+ and S atoms in thiophene rings of PEDOT not only facilitate the desolvation of hydrated Zn2+ but also can regulate the diffusion of Zn2+ along the thiophene molecular chains and induce the dendrite-free deposition of Zn along the (002) surface. Consequently, the Zn||Cu-PEDOT half-cell exhibits highly reversible plating/stripping behavior with an average Coulombic efficiency of 99.7% over 2500 cycles at 1 mA cm-2 and a capacity of 0.5 mAh cm-2. A symmetric Zn-PEDOT cell can steadily operate over 1100 h at 1 mA cm-2 (1 mAh cm-2) and 470 h at 10 mA cm-2 (2 mAh cm-2), outperforming the counterpart bare Zn anodes. Besides, a Zn-PEDOT||V2O5 full cell could deliver a specific capacity of 280 mAh g-1 at 1 A g-1 and exhibits a decent cycling stability, which are much superior to the bare Zn||V2O5 cell. Our results demonstrate that PEDOT nanowires are one of the promising interfacial layers for dendrite-free aqueous ZIBs.

Enhancing Zinc Electrode Stability Through Pre-Desolvation and Accelerated Charge Transfer via a Polyimide Interface for Zinc-Ion Batteries

Aqueous zinc-based energy storage devices possess superior safety, cost-effectiveness, and high energy density; however, dendritic growth and side reactions on the zinc electrode curtail their widespread applications. In this study, these issues are mitigated by introducing a polyimide (PI) nanofabric interfacial layer onto the zinc substrate. Simulations reveal that the PI nanofabric promotes a pre-desolvation process, effectively desolvating hydrated zinc ions from Zn(H2O)6 2+ to Zn(H2O)4 2+ before approaching the zinc surface. The exposed zinc ion in Zn(H2O)4 2+ provides an accelerated charge transfer process and reduces the activation energy for zinc deposition from 40 to 21 kJ mol-1. The PI nanofabric also acts as a protective barrier, reducing side reactions at the electrode. As a result, the PI-Zn symmetric cell exhibits remarkable cycling stability over 1200 h, maintaining a dendrite-free morphology and minimal byproduct formation. Moreover, the cell exhibits high stability and low voltage hysteresis even under high current densities (20 mA cm-2, 10 mAh cm-2) thanks to the 3D porous structure of PI nanofabric. When integrated into full cells, the PI-Zn||AC hybrid zinc-ion capacitor and PI-Zn||MnVOH@SWCNT zinc-ion battery achieve impressive lifespans of 15000 and 600 cycles with outstanding capacitance retention. This approach paves a novel avenue for high-performance zinc metal electrodes.

Enhancing the Cycle Life of Zinc-Iodine Batteries in Ionic Liquid-Based Electrolytes

Aqueous zinc-iodine (Zn-I2) batteries are gaining significant attention due to their low-cost, high safety and high theoretical capacity. Nevertheless, their long cycle and durability have been hampered due to the use of aqueous media that, over time, lead to Zn dendrite formation, hydrogen evolution reaction, and polyiodide dissolution. Xiao et al. recently reported the addition of an imidazolium-based ionic liquid (IL) to an aqueous electrolyte and found that the IL plays a key role in modifying the solvation of Zn2+ ions in the bulk electrolyte and the inner Helmholtz plane, repelling H2O molecules away from the Zn anode surface. UV/Vis and NMR spectroscopy also indicates a strong interaction between imidazolium cation [EMIM]+ and I3 -, thereby reducing polyiodide shuttling and enhancing the cycle life of the battery. Overall, a capacity decay rate of only 0.01 % per cycle after over 18,000 cycles at 4 A g-1, is observed, making the use of IL additives in aqueous electrolytes highly promising candidates for Zn-I2 batteries.

Lamellar Nanoporous Metal/Intermetallic Compound Heterostructure Regulating Dendrite-Free Zinc Electrodeposition for Wide-Temperature Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries are attractive post-lithium battery technologies for grid-scale energy storage because of their inherent safety, low cost and high theoretical capacity. However, their practical implementation in wide-temperature surroundings persistently confronts irregular zinc electrodeposits and parasitic side reactions on metal anode, which leads to poor rechargeability, low Coulombic efficiency and short lifespan. Here, this work reports lamellar nanoporous Cu/Al2Cu heterostructure electrode as a promising anode host material to regulate high-efficiency and dendrite-free zinc electrodeposition and stripping for wide-temperatures aqueous zinc-ion batteries. In this unique electrode, the interconnective Cu/Al2Cu heterostructure ligaments not only facilitate fast electron transfer but work as highly zincophilic sites for zinc nucleation and deposition by virtue of local galvanic couples while the interpenetrative lamellar channels serving as mass transport pathways. As a result, it exhibits exceptional zinc plating/stripping behaviors in aqueous hybrid electrolyte of diethylene glycol dimethyl ether and zinc trifluoromethanesulfonate at wide temperatures ranging from 25 to -30 °C, with ultralow voltage polarizations at various current densities and ultralong lifespan of >4000 h. The outstanding electrochemical properties enlist full cell of zinc-ion batteries constructed with nanoporous Cu/Al2Cu and ZnxV2O5/C to maintain high capacity and excellent stability for >5000 cycles at 25 and -30 °C.