A four-electron Zn-I2 aqueous battery enabled by reversible I\u2212/I2/I+ conversion

Electrochemical Energy Storage with Mediator-Ion Solid Electrolytes

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

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

Iodine (I2 ) shows great promising as the active material in aqueous batteries due to its distinctive merits of high abundance in ocean and low cost. However, in conventional aqueous I2 -based batteries, the energy storage mechanism of I- /I2 conversion is only two-electron redox reaction, limiting their energy density. Herein, six-electron redox chemistry of I2 electrodes is achieved via the synergistic effect of redox-ion charge-carriers and halide ions in electrolytes. The redox-active Cu2+ ions in electrolytes induce the conversion between Cu2+ ions and I2 to CuI at low potential. Simultaneously, the Cl- ions in electrolytes activate the I2 /ICl redox couple at high potential. As a result, in our case, I2 -based battery system with six-electron redox is developed. Such energy storage mechanism with six-electron redox leads to high discharge potential and capacity, excellent rate capability, as well as stable cycling behavior of I2 electrodes. Impressively, six-electron-redox I2 cathodes can match various aqueous metal (e.g. Zn, Mn and Fe) anodes to construct metal||I2 hybrid batteries. These hybrid batteries not only deliver enhanced capacities, but also exhibit higher operate voltages, which contributes to superior energy densities. Therefore, this work broadens the horizon for the design of high-energy aqueous I2 -based batteries.

Aqueous Li-Ion Batteries: Now in Striking Distance

Three kinds of secondary batteries, nickel metal hydride, Li-ion and Na/S battery were commercialized in Japan for the first time. Among them, Li-ion battery became the most popular power sources for PDA, because of the highest energy density. However, Li-ion battery is difficult to use for large-scale batteries, because its organic electrolytes are flammable, expensive and less conductive. Recently, aqueous electrolyte has been recognized as an attractive alternative and much attention has been paid to its development, because it has 3 big advantages about the conductivity, nonflammability and cost. In addition, water is an ideal solvent that dissolves a lot of various salts. Here, the most important thing is the selection of electrode active materials to avoid decomposition of the aqueous electrolyte. An aqueous Li-ion battery with LiMn2O4 cathode and VO2 anode was first reported by J. R. Dahn's group [1]. Since them, several combinations of cathodes and anodes have been reported as aqueous Li-ion battery. Theoretically, higher cell voltage more than 1.2 V cannot be obtained in the aqueous battery. So, it is unnecessary to dare to use Li in the aqueous batteries. Nevertheless, there is few report about aqueous Na-ion battery, in comparison with aqueous Li-ion battery. As one of the few exceptions, aqueous sodium-ion hybrid device with Na0.44MnO2cathode and active carbon anode was first proposed by Carnegie Mellon University, 4 years ago [2]. In this presentation, we introduce the aqueous Na-ion battery with pyrophosphate Na2FeP2O7 cathode and NASICON-type NaTi2(PO4)3 anodes. Because these polyanionic electrodes have flat voltage plateaus at 3.0 V and 2.1 V vs. Na/Na+, respectively. These redox voltages are almost located within the potential window of the aqueous electrolyte. In addition, Fe and Ti are the first and the second cheapest redox couple in transition metals, respectively.

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

Aqueous rechargeable zinc batteries are very attractive for energy storage applications due to their low cost and high safety. However, low operating voltages limit their further development. For the first time, this work proposes a unique approach to increase the voltages of aqueous zinc batteries by using tri‐functional metallic bipolar electrode with good electrochemical activity and ultrahigh electronic conductivity, which not only participates in redox reactions, but also functions as an electrical highway for charge transport. Furthermore, bipolar electrode can replace expensive ion selective membrane to separate electrolytes with different pH; thus, redox couples with higher potential in acid condition and couple with lower potential in alkaline condition can be employed together, leading to high voltages of aqueous zinc batteries. Herein, two types of metallic bipolar electrodes of Cu and Ag are utilized based on three kinds of aqueous zinc batteries: Zn–MnO2, Zn–I2, and Zn–Br2. The voltage of aqueous Zn–MnO2 battery is raised to 1.84 V by employing one Cu bipolar electrode, which shows no capacity attenuation after 3500 cycles. Moreover, the other Ag bipolar electrode can be adopted to successfully construct Zn–I2 and Zn–Br2 batteries exhibiting much higher voltages of 2.44 and 2.67 V, which also show no obvious capacity degradation for 1000 and 800 cycles, representing decent cycle stability. Since bipolar electrode can be applied in a large family of aqueous batteries, this work offers an elaborate high‐voltage concept based on tri‐functional metallic bipolar electrode as a model system to open a door to explore high‐voltage aqueous batteries.

A free-sealed high-voltage aqueous polymeric sodium battery enabling operation at −25°C

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.

Make past serve present: A novel aqueous Lead-Bromine battery with high energy density

Deciphering the energy storage mechanism of CoS2 nanowire arrays for High-Energy aqueous copper-ion batteries

Orbital energy level engineering: 3d high-spin Mn's d-electron mediating electronic structure of VO2 boosting highly durable aqueous ammonium ion batteries.

A new perylene-based tetracarboxylate as anode and LiMn2O4 as cathode in aqueous Mg-Li batteries with excellent capacity