Interface Coordination Stabilizing Reversible Redox of Zinc for High-Performance Zinc-Iodine Batteries.

Electrochemical Energy Storage with Mediator-Ion Solid Electrolytes

The eminent global energy crisis and growing ecological concerns in the past two decades lead to intensive development in the fields of clean energy sources such as wind and solar power. The successful penetration of green energy technologies highly depends on the deployment of large scale energy storage systems (ESS) with low cost, safe, and longevity. Lithium ion batteries (LIB) have been well acknowledged as EES with high energy density and long cycling life, and are superior to other conventional batteries. However, their inherent safety and cost issues related to the use of expensive, toxic and flammable organic electrolyte and superfast charging performance are still challenges for their applications in large-scale EES such as electric vehicles and smart grids [1]. To meet the needs of EES, batteries based on aqueous electrolytes are attractive candidates compared to the present LIB utilizing flammable and expensive organic electrolytes because of their improved safety and low cost. For these reasons, aqueous batteries, including Pb-Acid, Ni-Cd and Ni-MH batteries, are widely used in many markets such as electric scooters and automatically guided vehicles. However, the Pb-Acid batteries and Ni-Cd batteries raise the problem of toxic heavy-metal pollution, while the market of Ni-MH batteries is limited by its high cost due to the use of rare-earth metal for anodes [2]. So it is necessary to develop a new type of aqueous battery with qualities of low cost, safety, environmental benignity, long cycle life and acceptable energy density. Zn is an ideal anode for aqueous rechargeable batteries due to its abundance in the nature and possesses a high theoretical capacity (820 mAh/g) and a low negative potential (-0.762 V vs. SHE). Various rechargeable Zn-based batteries have been investigated (Ni-Zn, Zn-air and Zn-Br flow battery etc.) [3]. Recently, a promising aqueous Zn-LiMn2O4 (LMO) rechargeable battery system has attracted attentions as a low cost, ecologically friendly and safe battery. The estimated energy density of the system is 50-80 Wh/kg, which is comparable to conventional aqueous systems such as Lead-Acid batteries [4]. However, shape change and dendritic shorting of the Zn electrode prevent the commercialization of these battery technologies [3]. Herein, we present an innovative design of aqueous battery based on Zn-LMO system, which used the concept of immobilized Zn2+ions to prevent the metal dendrite in Zn-based batteries and optimized a nontoxic, high conductivity, noncorrosive, and low-cost neutral aqueous solution as electrolyte. Therefore, this new design of Zn-LMO aqueous battery exhibits an improved rate capability and delivers good cycling performance while still maintaining an acceptable energy density. As shown in Fig.1 and Fig.2, the Zn-LMO pouch cell provides a high discharge capacity of 120 mAh/g (based on the weight of LMO) at 0.5C at room temperature with an average discharge potential of 1.88 V. The system showed a good rate capability, maintaining 99, 92.5, and 74.3% of the 0.5C value at rates of 1C, 2C, and 4C, respectively. In addition, the battery also exhibited an excellent good cycle performance even at higher temperature of 60℃（Fig.2）which were attributed to the well optimized negative, positive and electrolyte combination and composition. Given the unique advantages (performance, scalability, low cost, safety and environmental benignity) of this cell, it’s optimal for stationary storage applications of renewable energies, such as solar and wind, and energy integration into the grid. Fig. 1. Charge/Discharge profiles (25℃) of Zn-LMO battery at various current densities from 0.5C to 4C. Cut voltage is 1.5 V-2.3 V. Fig. 2. Cycle performances and coulombic efficiency (25℃ and 60℃) of Zn-LMO battery at 4C. Reference [1] J.M. Tarascon, Nature 414 (2001) 359. [2] F. Beck, Electrochimica Acta 45 (2000) 2467. [3] X.G. Zhang, Encyclopedia of Electrochemical Power Sources (2009) 454. [4] J. Yan, Journal of Power Sources 216 (2012) 222. Figure 1

Chitosan modified filter paper separators with specific ion adsorption to inhibit side reactions and induce uniform Zn deposition for aqueous Zn batteries

ConspectusFrequent safety accidents of lithium-ion batteries (LIBs) originating from the utilization of flammable electrolytes urges the battery community to develop a safe substitute. This safety background is a boom for aqueous batteries (ABs) which employ aqueous electrolytes to address safety concerns. Recently, ABs have experienced a rapid advance because various battery chemistries have been successively developed, e.g., aqueous Zn batteries (AZBs), aqueous LIBs, aqueous sodium-ion battery, etc. Impeded by the narrow voltage window of aqueous electrolytes, however, the majorities of cathode materials with high operation potential employed in traditional nonaqueous batteries are excluded from the range of ABs cathodes, leading to a low energy density. Directly using metal as an anode is likely to improve the energy density, whereas most of the reported metal anodes, e.g., lithium, sodium, magnesium, etc., cannot run in aqueous electrolytes. One exceptional case is the Zn metal anode that permits theoretically high energy density AZBs due to triple merits: (1) the Zn metal anode exhibits a low redox potential (−0.76 V vs standard hydrogen electrode, SHE), taking the best advantage of the limited voltage window of aqueous electrolytes; (2) Zn metal anode with mild protection can easily maintain its chemical stability in aqueous medium; (3) Zn metal anode releases a high specific capacity of 820 mAh g–1. AZBs thus exhibit a rapid development, especially in developing high specific capacity cathode materials such as MnO2 and V2O5, and the corresponding structure modification. Despite these spurring achievements, the overall energy density of the whole AZB device is still unsatisfactory.In this Account, we initially present the energy density state of AZBs, where a detailed discussion is given to the energy bottleneck of current cathode materials. Meanwhile, the corresponding strategies that are considered as the first-stage attempt to enhance energy density are discussed, including mediating interlayer spacing, introducing oxygen vacancy, and using high-voltage cathode materials. Due to the unsatisfactory energy density, we then propose a systemic methodology of cathode engineering to renew the energy blueprint of AZBs. Specifically, we show the high possibility of employing conversion-type cathodes with the capability of multiple-electron transfer reaction, e.g., sulfur, selenium, iodine, etc., to remarkably enhance the energy density of AZBs. In addition, strengthening the utilization of cathode active material such as the activation, stabilization, or introduction of metal active centers is highlighted as a branch of cathode engineering to address the energy density issue of AZBs. Finally, we attempt to summarize the remaining challenges and possible solutions to address the energy density issue of AZBs, such as reducing the proportion of electrochemically inactive materials, increasing the cathode loading mass, and avoiding the excessive usage of Zn anode. Overall, we believe this Account can shed light on the promising directions to design a practical high energy density AZBs.

V2O5 nanopaper as a cathode material with high capacity and long cycle life for rechargeable aqueous zinc-ion battery

An electrolyte additive for interface regulations of both anode and cathode for aqueous zinc-vanadium oxide batteries

During the past decades, aqueous rechargeable batteries have been receiving much attention on account of the merits of cost efficiency, high safety, and environmental benignity. Compared to metal‐ions (such as Li+, Na+, K+, Mg2+, Zn2+, Al3+ etc.) as charge carriers in aqueous ion batteries, nonmetal charge carriers not only form covalent–ionic bonds in framework, but also act as reversible redox centers. Moreover, nonmetal charge carriers have advantages of low costs and high volumetric energy densities. Recently, huge efforts have been contributed to performance improvements in aqueous nonmetal cation batteries via a variety of methods. Herein, the recently reported cathode, anode materials, and newly proposed electrochemical reaction mechanisms for rechargeable aqueous nonmetal cation batteries are reviewed.

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

Synergistic effect of the co-solvent induced interfacial chemistries in aqueous Zn batteries

Current Li-ion batteries dominate the market but face great challenges with respect to safety, cost and the higher energy and power densit requirements of electrical vehicles and stationary energy storage. Relevant for mobile electrical transport, Li-O2 batteries in theory offer the highest specific energy among all the lithium electrochemical energy storage systems. Research efforts have been made to address the challenges that impede the functioning of this battery, which include low round trip efficiency, low specific capacity and poor cycling stability. To understand the origin of these issues, attaining a deeper understanding of the mechanism behind the electrochemical reactions is of vital importance. This also forms the foundation for exploring ideal oxygen cathodes and better electrolytes. The aqueous zinc batteries are another potential candidate for large scale electric energy storage owing to its low-cost, high operational safety, and environmental benignity. However, it is not easy to find a suitable insertion cathode for ZIBs, because the electrostatic interaction between divalent Zn ions. The development of host materials for ZIBs is still in its infancy, and in-depth understanding of the electrochemical processes involved is paramount at this early stage. The focus of this thesis is on attaining mechanistic insight into the electrochemical processes occurring in working Li-O2 and aqueous zinc batteries, which guides the choice/design of proper electrode materials for these next generation battery systems.

Na-containing manganese-based cathode materials synthesized by sol-gel method for zinc-based rechargeable aqueous battery

CONNEXX SYSTEMS developed a novel hybrid energy storage system, bindbattery™, with a unique overcharge protection capability, high power and high energy capability and long cycle life at low cost without complex battery management system. bindbattery™ consists of lithium-ion battery units and aqueous electrolyte battery units. The two units are connected in parallel and form a virtual cell. The multiple virtual cells are connected in series and in parallel to meet specifications of each application. An aqueous electrolyte battery could be chosen from a nickel-hydride battery, lead-acid battery or other form of aqueous batteries depending on requirements of applications. Hybridization with an aqueous electrolyte battery makes bindbattery™ tolerable to abusive conditions such as reverse directional high current pulse or overcharge current. Benefits of bindbattery™ include: 1) Safety: The lithium-ion battery is protected from the devastating overcharge by aqueous batteries connected in parallel. The aqueous battery unit consumes overcharge energy through the aqueous electrolyte decomposition (electrolysis). The oxygen evolved at the positive electrode recombines with hydrogen on the negative electrode and reforms water. By connecting the lead-acid battery and lithium-ion battery in parallel, the lead-acid battery effectively protects lithium-ion battery from overcharge by absorbing the overcharge current through the chemical reaction. Thus, bindbattery™ does not require complex electronic protection circuit to protect from overcharge. In other words, the bindbattery™ configuration makes the battery system intrinsically safe. This simplifies construction of the bindbattery™, and reduces both the cost and the weight and makes the battery suitable for large scale stationary applications. 2) Power performance: As a result of high power characteristics of both high power lithium-ion batteries and lead-acid batteries, bindbattery™ has a high power capability. 3) Cycle life improvement: The lead-acid battery is an inexpensive battery but its cycle life is poor compared to the lithium-ion battery. The lithium-ion battery has higher discharge voltage than the lead-acid battery, therefore lithium-ion battery discharges prior to the lead-acid battery in bindbattery™. Thus bindbattery™ provides an excellent cycle life in the same manner as the lithium-ion battery. 4) High energy density: bindbattery™ can provide a larger energy compared to the lead-acid battery alone as a result of the hybridization with lithium-ion battery. 5) Low temperature performance improvement: The lead-acid battery has excellent low temperature capability. At subzero temperature, lithium-ion battery is not able to discharge immediately. In bindbattery™, the lead-acid battery discharges first and provides warm-up time for the lithium-ion battery. 6) Float charge capability: Like other aqueous batteries, bindbattery™ can be used in the float-charge mode. 7) Cost improvement: Use of lead-acid battery as an aqueous battery units lowers the cost significantly. Elimination of electrical protection switches and battery management units contribute to the cost reduction. These unique features make bindbattery™ the most suitable energy storage system for stationary applications including storage system for renewable energy, demand shifting and frequency regulation. We developed 20 kWh bindbattery™ module for stationary applications such as solar energy or wind energy storage. The module will comprise a larger scale storage system by connecting multiple of the modules in parallel or in series. The simplified control method and low cost also make bindbattery™ a remarkable choice for car applications.

<i>N</i> -Heterocycles Extended π-Conjugation Enables Ultrahigh Capacity, Long-Lived, and Fast-Charging Organic Cathodes for Aqueous Zinc Batteries

Long lifespan and high-rate Zn anode boosted by 3D porous structure and conducting network

Aqueous zinc-ion batteries, in terms of integration with high safety, environmental benignity, and low cost, have attracted much attention for powering electronic devices and storage systems. However, the interface instability issues at the Zn anode caused by detrimental side reactions such as dendrite growth, hydrogen evolution, and metal corrosion at the solid (anode)/liquid (electrolyte) interface impede their practical applications in the fields requiring long-term performance persistence. Despite the rapid progress in suppressing the side reactions at the materials interface, the mechanism of ion storage and dendrite formation in practical aqueous zinc-ion batteries with dual-cation aqueous electrolytes is still unclear. Herein, we design an interface material consisting of forest-like three-dimensional zinc-copper alloy with engineered surfaces to explore the Zn plating/stripping mode in dual-cation electrolytes. The three-dimensional nanostructured surface of zinc-copper alloy is demonstrated to be in favor of effectively regulating the reaction kinetics of Zn plating/stripping processes. The developed interface materials suppress the dendrite growth on the anode surface towards high-performance persistent aqueous zinc-ion batteries in the aqueous electrolytes containing single and dual cations. This work remarkably enhances the fundamental understanding of dual-cation intercalation chemistry in aqueous electrochemical systems and provides a guide for exploring high-performance aqueous zinc-ion batteries and beyond.