Critical review of phase-engineered 1 T/2H MoS2 cathode materials for enhanced Zn-ion diffusion with tactically designed Zn anodes for aqueous Zn-ion battery

A semi-interpenetrating network polymer coating for dendrite-free Zn anodes

Electrochemical Energy Storage with Mediator-Ion Solid Electrolytes

Recent progress and perspectives on aqueous Zn-based rechargeable batteries with mild aqueous electrolytes

The physical chemistry of electrolytic solutions: by Herbert S. Harned and Benton S. Owen. Second edition, 645 pages, diagrams, 16 × 24 cm. New York, Reinhold Publishing Corp., 1950. Price, $10.00

A hybrid aqueous Na-Zn ion battery derived from the Na3V2(PO4)3 cathode is one of the most promising systems among aqueous batteries because it exhibits higher energy density than a pure Zn ion battery due to different ion intercalation mechanisms related to various electrolytes. However, it is more difficult to improve the electrochemical performance of the hybrid aqueous Na-Zn ion battery versus Zn ion battery. In addition, searching for suitable protective interphase film-forming electrolyte additives in order to increase cycling stability and developing a new electrolyte recipe to improve the low temperature performance are significant and still big challenges for the hybrid aqueous Na-Zn battery. Herein, the introduction of protective interphase film-forming additives (VC), an economical 10 M NaClO4-0.17 M Zn(CH3COO)2-2 wt % VC electrolyte, was proposed. Based on such an electrolyte, the carbon-coated single crystalline Na3V2(PO4)3 nanofiber//Zn aqueous Na-Zn hybrid battery involving high energy, long cycle, and outstanding low temperature performance was successfully obtained. For example, it delivered a remarkable output voltage of 1.48 V and excellent cycle stability (retained 84% after 1000 cycles). The capacities were 94.4 mA h/g at 0.2 A/g at -10 °C and 90.0 mA h/g at 0.2 A/g at -20 °C, respectively.

Lithium-ion batteries (LIBs) have become essential for storing electrical energy in portable electronics and electric vehicles due to their high energy density, light weight, and excellent reversibility and cyclability. Despite their widespread use across various electronic devices, their use in Energy Storage Systems (ESS) with substantial capacities is limited by safety concerns. This is because enhancing storage capacity also increases the volume of flammable organic solvents. As a result, there have been significant research efforts toward developing safer alternatives, such as aqueous batteries, with aqueous Zn-ion batteries (AZIBs) being a representative example. Compared to conventional LIBs, ZIBs are more cost-effective, safer, and environmentally friendly. However, the practical application of AZIBs faces significant challenges, particularly regarding Zn dendrite growth, corrosion, and the hydrogen evolution reaction (HER) on the Zn anode side, which critically reduces the cyclability of ZIBs. To mitigate these challenges, several solutions have been proposed, such as modifying the Zn ion hydration structure, using water-in-salt electrolytes, and adding additives to modulate the properties of the Zn surface. In this presentation, we will introduce organic additives aimed at regulating the electrochemical Zn growth to enhance the cyclability of the Zn anode. These organic additives influence the kinetics of the Zn deposition/dissolution processes and alter the morphology of the Zn deposits. We will discuss the effect of organic additives on Zn growth and the cyclability of Zn||Zn symmetric cells in relation to the molecular structure and adsorption behavior of the additives. By considering all results, we will determine which functional group is critical for controlling Zn growth and propose the most effective organic additive for enhancing the performance of AZIBs.

A key aspect of any future battery technology development is safety. Although lithium-based batteries are ubiquitous, there are still challenges related to their energy density, cycle life, cost and safety. In regard to safety, compared with organic electrolyte, aqueous rechargeable batteries may provide a safer alternative for reliable, low-cost and large-scale energy storage systems. As seen from the penetration test in Fig. 1a-1b, the battery with organic electrolyte catches fire, yet the battery with aqueous electrolyte is relatively safe. Moreover, aqueous batteries have high ion conductivity and cost effectiveness. Generally, the cell voltage and energy density of aqueous batteries are lower than those of organic-based batteries (e.g. Li-ion) because of the relatively smaller electrochemical stability window of water. Among all the metals that are stable in water, zinc is the most active and has the lowest possible operating potential. This means using Zn anode can increase overall cell voltage of aqueous batteries. Moreover, zinc is globally available, inexpensive (3.19 USD kg-1), and has high capacity (820 Ah kg-1 and 5854 Ah L-1). Zinc-based aqueous batteries also possess the stability to be operated in ambient air. Accordingly, Zn aqueous rechargeable batteries are promising to become a safer energy storage system. Among zinc-based aqueous batteries, Zn-air batteries have high theoretical volumetric energy density, which is around three times that of conventional Li-ion batteries (LIB). Zn anodes have been investigated in neutral/mild acidic aqueous electrolytes. Yet in order to pair them with oxygen cathode to reach the highest energy density, alkaline aqueous electrolyte is ideal, in which the oxygen electrode has low polarization. In alkaline aqueous electrolyte, Zn anode undergoes a Zn (s) ↔ Zn(OH)4 2- (aq) ↔ ZnO (s) conversion. This solid-solute-solid transformation and insulating discharge product ZnO lead to three vital challenges: 1) ZnO passivates Zn surface and prevents further discharging, leading to low Zn utilization; 2) ZnO is insulating and can hardly be charged back to Zn; 3) diffusion of Zn(OH)4 2- causes the loss of active material and change of electrode morphology. Thus, anode modification and protection are needed to alleviate the passivation and dissolution. We firstly designed a Zn mesh@GO anode (Fig 1c). Graphene oxide (GO) layers on the Zn mesh surface deliver electrons across insulating ZnO and can slow down the Zn dissolution. However, the utilization of zinc is still low because passivation problem is not completely solved. Through SEM investigation, critical passivation size was found to be ~ 2 µm. Thus, we further designed a lasagna-inspired ZnO@GO anode (Fig 1d). ZnO nanoparticles are encapsulated by GO. ZnO lasagna structure has three features: 1) the size of ZnO nanoparticles is smaller than the critical size of passivation; 2) the fabrication of ZnO lasagna anode starts with commercially available ZnO nanoparticles (~100 nm), and is compatible with the roll-to-roll process, which is ideal for large-scale manufacturing; 3) GO allows permeation of OH- and water, and prevents loss of Zn active material through blocking bigger Zn(OH)4 2-. As a result, such lasagna anode achieves a high volumetric capacity of 2308 Ah/L and a remarkable capacity retention of 86% after 150 cycles. In contrast, the open-structured ZnO nanoparticle anode, without the protection of GO, completely died after 90 cycles. Figure 1

As an alternative for lithium ion batteries, aqueous energy storage system has recently attracted tremendous attentions due to the low cost, non-flammable and non-toxic materials.[1] Among various aqueous batteries, aqueous Zn ion batteries are particularly advantageous owing to a high-capacity Zn metal anode (819mAh/g).[2] However, limited cathode materials have been explored for reversible Zn2+-ion intercalation, and most of which exhibit poor rate capabilities and inadequate cycling performance, or limited specific capacity. α-MoO3, as a typical layered transition metal oxide, has been extensively studied as electrode material for lithium batteries due to the advantages of high capacity, low cost, abundant resources and non-toxic.[3] Based on our research, we have found α-MoO3 can be used as host material (cathode) for zinc ions as well owing to the large interlayer space. However, the capacity fading in the initial cycles is still significant and unavoidable. The reason for irreversible capacity fading of MoO3 in the initial cycles can be attributed to its unstable structural prosperity. Recently, pre-intercalation has been demonstrated as an effective way to improve the electrochemical performance for zinc-ion batteries. For example, Linda et.al has reported vanadium oxide bronze pillared by interlayer Zn2+ ions and water can supply the remarkable performance.[2] However, the related research of α-MoO3 as electrode for zinc-ion is still blank. For the first time, we have studied the electrochemical performance of zinc pre-intercalation α-MoO3 as cathode material for zinc batteries and investigated the electrochemical mechanism during charging and discharging. The zinc pre-intercalation α-MoO3 can supply the initial specific capacity as high as 300 mAh/g, exhibiting great potential for application as high-performance cathode material for zinc-ion batteries. Reference 1. Pan, H.; Shao, Y.; Yan, P. F.; Cheng, Y. W.; Han, K. S.; Nie, Z. M., Wang, C. M., Yang, J. H.; Li, X. L.; Bhattacharya, P.; Mueller, K. T.; Reversible Aqueous Zinc/Manganese Oxide Energy Storage From Conversion Reactions. Nature Energy, 2016, 1, 16039. 2. Kundu, D.; Adams, B. D.; Duffort, V.; Vajargah, S. H.; Nazar, L. F.; A High-Capacity and Long-life Aqueous Rechargeable Zinc Battery Using a Metal Oxide Intercalation Cathode. Nature Energy. 2016,1,16119. 3. Dong, Y. F.; Xu, X. M.; Li, S., Han, C. H.; Zhao, K. N.; Zhang, L.; Niu, C. J.; Huang, Z.; Mai, L. Q.; Inhibiting Effect of Na+ Pre-Intercalation in MoO3 Nanobelts with Enhanced Electrochemical Performance. Nano Energy. 2015, 15, 145.

A Na-rich manganese hexacyanoferrate hollow nano-cube with low crystal water and few defects for efficient Zn ion storage in aqueous batteries

The potential application of rechargeable multivalent ion batteries in portable devices and renewable energy grid integration have gained substantial research interest in aqueous Zn-ion batteries (ZIBs). Compared to Li-based batteries, ZIBs offer lower costs, higher energy density, and safety that make them more attractive for energy storage in grid integration applications. Currently, more research is required to find a suitable cathode material for ZIBs with high capacity and structural stability during charge/discharge cycling. Vanadium phosphate (VOP) compounds as cathode material for ZIBs have been of particular interest, owing to vanadium’s diverse oxidation states. In this present work, two VOP compounds, [H0.6(VO)3(PO4)3(H2O)3].4H2O and VOPO4.2H2O, were synthesized from phosphoric acid and different sources of vanadium via a simple hydrothermal method. Various characterization techniques were carried out, revealing the layered structure of both products and high purity of [H0.6(VO)3(PO4)3(H2O)3].4H2O. Zn/VOP batteries were prepared using Zn metal as counter and reference electrode and 3 M ZnSO4.7H2O as electrolyte. Electrochemical tests were conducted to evaluate the cycling performance of VOPs as cathode material for aqueous Zn-ion batteries. Based on the results, both compounds have shown highly reversible Zn-ion intercalation and deintercalation. VOPO4.2H2O achieved a higher specific capacity of up to 85 mAh/g during discharging, as opposed to 65 mAh/g for the hydrated VOP complex. However, [H0.6(VO)3(PO4)3(H2O)3].4H2O is more stable with higher reproducibility than VOPO4.2H2O during cycling. Nevertheless, more research is still required to enhance the specific capacity and improve the cycling performance of VOP-based cathodes for their prospective use in aqueous ZIBs.

Aqueous Zn-ion batteries (ZIBs) are promising candidates for large-scale energy storage due to high safety, abundant reserves, low-cost, and high energy density. However, the reversibility of the metallic Zn anode in the mild electrolyte is still unsatisfactory, due to the Zn dendrite growth, hydrogen evolution, and corrosion passivation. Herein, a Zn-In alloying powder solvent free electrode is proposed to replace the Zn foil in ZIBs. The novel Zn anodes are constructed by a solvent-free manufacturing process with carbons, forming a 3D Zn deposition network and providing uniformly electric field distribution. The In on the Zn powder surface can increase the overpotential for hydrogen evolution and further improve the morphology of Zn deposition against dendrite growth. The Zn solvent-free electrodes enable the Zn-MnO2 batteries with high cathode loading mass of 10-20mg cm-2 to achieve >380 stable cycles. Furthermore, the assembled soft package batteries of 2.4 Ah (52Wh kg-2) is evaluated and the capacity retention is maintained at 80% after 200 cycles at a high areal capacity of 5 mAh cm-2 without gas evolution. This work offers a workable strategy to develop a durable Zn anode for the eventually commercial applications of aqueous Zn-Mn secondary batteries.

Owing to the advantages of low cost, rich resources, and intrinsic safety, aqueous Zn-ion batteries have attracted broad attention as the promising energy storage technology for large-scale smart grids. The cathodes for aqueous Zn-ion batteries have developed rapidly, including Mn-based cathodes, V-based cathodes, and halogen cathodes. High specific capacity and long cycling lifespan have been achieved. However, when the mass loading for cathode materials is scaled up to the practical level, the cycling stability and rate property of aqueous Zn-ion batteries are very unsatisfactory. Therefore, in this review, we deeply analyze the key issues that limit the electrochemical performance of high-loading cathodes for aqueous Zn-ion batteries. Subsequently, we comprehensively summarize the effective solutions to the above issues, including (1) rational binder design, (2) three-dimensional cathode design, (3) cathode material structural optimization, and (4) interface engineering for Zn anodes. Finally, we give a critical perspective from commercial application for the future development of high-loading cathodes for high-energy-density aqueous Zn-ion batteries.

An in-depth understanding of improvement strategies and corresponding characterizations towards Zn anode in aqueous Zn-ions batteries

Rechargeable aqueous zinc-ion (Zn-ion) batteries are widely regarded as important candidates for next-generation energy storage systems for low-cost renewable energy storage. However, the development of Zn-ion batteries is currently facing significant challenges due to uncontrollable Zn dendrite growth and severe parasitic reactions on Zn metal anodes. Herein, we report an effective strategy to improve the performance of aqueous Zn-ion batteries by leveraging the self-assembly of bovine serum albumin (BSA) into a bilayer configuration on Zn metal anodes. BSA's hydrophilic and hydrophobic fragments form unique and intelligent ion channels, which regulate the migration of Zn ions and facilitate their desolvation process, significantly diminishing parasitic reactions on Zn anodes and leading to a uniform Zn deposition along the Zn (002) plane. Notably, the Zn||Zn symmetric cell with BSA as the electrolyte additive demonstrated a stable cycling performance for up to 2400 hours at a high current density of 10 mA cm-2. This work demonstrates the pivotal role of self-assembled protein bilayer structures in improving the durability of Zn anodes in aqueous Zn-ion batteries.

Lithium-ion batteries (LIBs) are indispensable for storing electrical energy in portable electronics and electric vehicles, thanks to their high energy density, light weight, and excellent reversibility and cyclability. Despite their successful integration into various electronic devices, their application in Energy Storage Systems (ESS) with substantial capacities is hindered by safety concerns. This is because increasing the energy storage capacity inevitably leads to a higher volume of flammable organic solvents. Therefore, significant research efforts have been directed towards aqueous batteries to develop safer alternatives, including representative Zn-ion batteries (ZIBs). Compared to conventional LIBs, ZIBs offer cost-effectiveness, high safety, and environmental friendliness. However, the practical application of aqueous Zn ion batteries (AZIBs) is hindered by several issues, particularly concerning Zn dendrite growth, corrosion, and the hydrogen evolution reaction (HER) on the Zn anode side, which critically reduce the cyclability of ZIBs. To mitigate these challenges, several solutions have been proposed, including the modification of the Zn ion hydration structure, the use of water-in-salt electrolytes, and the addition of additives to modulate the properties of the Zn surface. This presentation will introduce organic additives aimed at controlling the electrochemical Zn growth to enhance the cyclability of the Zn anode. These organic additives influence both the kinetics of the Zn deposition/dissolution processes and the properties of Zn deposits. We will discuss the effect of organic additives on Zn growth and the cyclability of Zn||Zn symmetric cells based on the molecular structure and adsorption behavior of the additives. By considering all results, we will determine which functional group is critical for controlling Zn growth and suggest the optimal organic additive for AZIBs.