CN111406330B

CN111406330B - Zinc electrode for battery

Info

Publication number: CN111406330B
Application number: CN201880071313.2A
Authority: CN
Inventors: D·R·罗利森; J·F·帕克; J·W·朗; J·S·柯
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 2017-10-30
Filing date: 2018-10-30
Publication date: 2024-02-23
Anticipated expiration: 2038-10-30
Also published as: EP3704754A2; WO2019089505A2; JP2021501446A; WO2019089505A3; JP7275127B2; CN111406330A; EP3704754A4; KR20200066695A

Abstract

An article having a continuous zinc mesh and a continuous mesh of void spaces extending through the zinc mesh. The zinc mesh is a fused monolithic structure. A method of: providing an emulsion having zinc powder and a liquid phase; drying the emulsion to form a sponge; annealing and/or sintering the sponge to form an annealed and/or sintered sponge; heating the annealed and/or sintered sponge in an oxidizing atmosphere to form an oxidized sponge having zinc oxide on the surface of the oxidized sponge; the zinc oxide is electrochemically reduced to form a zinc metal sponge.

Description

Zinc electrode for battery

The present application claims priority from U.S. patent application No.15797181, filed on 10 months 30 of 2017, which is a partial continuation-in-patent application of U.S. patent No.9802254, issued on 31 of 10 months of 2017. The present application is also a continuation of the section of U.S. application No.13832576 filed on day 3, month 15 of 2013, which claims the benefit of U.S. provisional application No.61730946 filed on day 11, month 28 of 2012. These applications, as well as all other publications and patent documents referred to throughout this non-provisional application, are incorporated herein by reference.

Technical Field

The present disclosure relates generally to porous zinc electrodes for batteries and other uses.

Background

In order to meet the urgent needs of the growing energy market (including electric automobiles and portable electronic devices), research on battery technology is performed, and it is expected to overcome some disadvantages of lithium ion batteries. Although lithium ion batteries have the advantages of low self-discharge, no memory effect and most important rechargeability, the widespread use of lithium ion-based energy storage suffers from safety, manufacturing cost and lower specific energy density (specific energy densities) relative to other promising battery technologies<200W h kg ^–1 ) Is described (see Lee et al, "Metal-air batteries with high energy density: li-air vectors Zn-air" adv. Energy Mater.2011,1, 34-50). For example, zinc-air batteries have a relatively high practical specific energy density (400 Wh kg ^-1 ) And has the advantage of an inexpensive and environmentally friendly active material (zinc) that is coupled to an air breathing cathode that consumes molecular oxygen without the need to store it within the battery (see neburghlov et al, "A review on air cathodes for zinc-air fuel cells" j.power Sources 2010,195,1271-1291). Although successful as primary batteries in certain commercial applications (e.g., hearing aid market), the further use of zinc-air is limited in its charging capability, insufficient pulse power, and low theoretical discharge capacity utilization<60%) of the obstruction. These limitations are inherent to the electrochemical behavior of zinc (Zn) in the traditional anode form factor for commercial zinc-air batteries.

When a zinc-air cell containing zinc powder as a negative electrode mixed with a gelling agent, an electrolyte and a binder is discharged, metallic zinc is oxidized and reacts with hydroxide ions of the electrolyte to form soluble zincate ions. The dissolved zincate ions begin to diffuse from their point of generation (point of electrogeneration) until supersaturation is reached, and then precipitate rapidly and dehydrate to form semiconducting zinc oxide (ZnO) (see Cai et al, "Spectroelectrochemical studies on dissolution and passivation of zinc electrodes in alkaline solutions" j. Electrochem. Soc.1996,143, 2125-2131). Upon electrochemical recharging, the resulting zinc oxide is reduced to zinc metal, although in a different shape than upon initial discharge. This shape change becomes more pronounced as the number of charge and discharge cycles increases, eventually leading to dendrites growing out of the negative electrode until they pierce the separator and cause a short circuit, thereby terminating the operation of the battery.

Disclosure of Invention

Disclosed herein is an electrochemical cell comprising: an anode current collector; an anode in electrical contact with the anode current collector; an electrolyte; a cathode current collector; a cathode comprising silver or silver oxide in electrical contact with an anode current collector; a separator between the anode and the cathode. The anode is manufactured by the following method: providing a mixture comprising metallic zinc powder and a liquid phase emulsion; drying the mixture to form a sponge; annealing and/or sintering the sponge in an inert atmosphere or under vacuum at a temperature below the melting point of zinc to form an annealed and/or sintered sponge having a metallic zinc surface; the annealed and/or sintered sponge is heated in an oxidizing atmosphere at a temperature above the melting point of zinc to form an oxidized sponge comprising zinc oxide shells on the surface of the oxidized sponge. The anode includes: a continuous grid comprising metallic zinc; a continuous void space grid extending through the zinc grid; a metallic zinc bridge connecting the metallic zinc particle cores. The electrolyte fills the void space.

Drawings

A more complete understanding of the present invention will be readily obtained by reference to the following description of exemplary embodiments and the accompanying drawings.

The top of fig. 1 shows a photograph of a 3D zinc sponge after heating first in argon and then in air and the middle and bottom show scanning electron micrographs showing the molten, through-connected porous grid of the monolith and the surface structure of the individual particles in the sponge.

Fig. 2 shows: comparison of the zinc sponge after heating (left: A, C, E) and after electrochemical reduction step (right: B, D, F) as measured by electrochemical impedance spectroscopy (electrochemical impedance spectroscopy) (A, B); x-ray diffraction (C, D); and scanning electron micrographs (E, F).

The top of fig. 3 shows the discharge potential at increasing applied current for 10 minutes at 5mA-200mA in a half cell configuration and the bottom shows the linear relationship of steady state discharge voltage with increasing applied current.

The top of FIG. 4 shows a full-cell zinc-air cell demonstration using the zinc sponge anode and carbon/potassium manganese ore (cryptomelane)Prepared by a composite air cathode, and the bottom shows three zinc-air cells at a discharge current density of-5 mA cm ^–2 、–10mA cm ^–2 And-24 mA cm ^–2 A discharge curve at.

FIG. 5 shows a graph of a Zn/ZnO sponge symmetric cell at the top and at +24mAcm at the bottom ^–2 And-24 mA cm ^–2 Charge-discharge cycle data for up to 45 scans at alternating additional loads.

FIG. 6 shows SEM for single particles of fully reduced all-metal zinc sponge at the top and SEM at the bottom, which demonstrates at + -24mA cm ^–2 After 45 scanning charge/discharge cycles, a compact ZnO coating is formed on the surface of the Zn sponge; note that no macroscopic size is observed>10 μm) of dendrites.

Fig. 7 shows the cell construction of a high power Ag-Zn prototype cell comprising a zinc sponge anode.

FIG. 8 shows power cycling of an Ag-Zn cell using Zn sponge electrodes, with an applied current in the range of 15-500mA (about 15-500mA cm ^–2 ；0.2–5.6A g ^–1 ). The legend lists the platforms (plateaus) in the same order from top to bottom.

FIG. 9 shows that a silver zinc cell comprising a zinc sponge anode (5.5 mA cm ^–2 ) Can reach 96% of theoretical Zn utilization and can be recharged to the initial capacity (5.5 mA cm ^–2 ) 97% of (3).

Fig. 10 schematically illustrates the effect of repeated cycling on the disclosed zinc structure.

Fig. 11 schematically illustrates the effect of repeated cycling on the zinc structure of the prior art.

Detailed Description

In the following description, for purposes of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that the present subject matter may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods and apparatuses are omitted so as not to obscure the present disclosure with unnecessary detail.

The basic requirements of zinc-containing secondary batteries are twofold. For the zinc-air case, the air breathing cathode structure must contain a catalyst for the Oxygen Reduction Reaction (ORR) of the cell discharge and for the Oxygen Evolution Reaction (OER) of the reverse reaction after charging. The zinc anode composite needs additives that inhibit dendrites or its structure must be designed so that the current density is uniformly distributed throughout the zinc structure, thereby reducing the formation of dendrites and the potential for eventual shorting of the cell. The present disclosure focuses on this redesign of zinc structures to investigate the use of these zinc sponges for secondary zinc-containing battery systems.

Disclosed herein is a method of replacing a powder bed zinc anode with a highly porous, monolithic and 3D through-connected zinc sponge as a negative electrode for use in current and yet to be developed high performance zinc-containing batteries. Typically, zinc sponges are manufactured by forming a slurry of zinc powder in a two-phase mixture in the presence of an emulsion stabilizer to produce a high viscosity but pourable mixture that is dried in a mold and then heat treated to produce a solid monolithic electrode. Due to the interconnected pore network (between 10-75 μm in size), zinc sponge may exhibit a larger surface area, which may lead to an increase in power density achievable relative to commercial zinc-containing batteries. After the electrochemical reduction step, the device-ready electrode is 3D interconnected, highly conductive, highly porous, immersed in electrolyte, reasonably structured, and provides a desirable platform for rechargeable batteries using zinc anodes or primary batteries where higher utilization of zinc is required. The all-metal sponge-like mesh provides an electronic environment that improves current distribution, thereby inhibiting dendrite formation that leads to electrical shorting. Preliminary characteristics of the zinc sponge anode in a full cell configuration, as well as evaluations in a full cell zinc-air cell prototype (prototypes), and demonstration of chargeable without detrimental dendrite formation are shown. U.S. patent application publication No.20160093890 is incorporated herein by reference, and all materials and methods disclosed therein are applicable to the presently disclosed subject matter.

The 3D all-metal, highly conductive path allows for improved current distribution throughout the electrode structure, avoiding non-uniform reaction sites and higher local current densities in the discharge-charge cycle, while higher local current densities stimulate dendrite formation (see Zhang, "Electrochemical thermodynamics and kinetics," Corrosion and Electrochemistry of zinc 1996,1st Ed.; arora et al, "Battery separators" chem. Rev.2004,104, 4419-4462). In addition, the highly porous zinc mesh allows for a limited volume element with a high surface-electrolyte volume, as well as faster concomitant saturation of zincate and faster dehydration to ZnO upon discharge, thereby minimizing shape changes.

The electrode comprises two bicontinuous interpenetrating grids. One is solid and comprises zinc and the other is void space. Thus, the electrode is a porous zinc structure, which may be in the form of what is commonly referred to as a sponge. Zinc grids may contain zinc both on the surface and inside the grid. That is, it does not coat zinc on a non-zinc porous substrate, and it may always be pure zinc or near pure zinc. The zinc mesh may also include zinc oxide and/or zinc oxyhydroxide formed on the surface when the electrode is discharged in the cell. The zinc mesh is a three-dimensional fused monolithic structure. The structure cannot be made simply by pressing zinc particles together. Such a pressed material will not melt the zinc particles together, as the pressed particles can be separated from each other. The zinc mesh may have less than 5wt.% or even less than 1wt.% zinc oxide. A lower percentage of zinc oxide may result in an electrode with better performance, but the electrode may not be completely free of zinc oxide because zinc may spontaneously oxidize in air.

As used herein, void space refers to the volume within a structure that is not a zinc mesh nor any other material attached thereto. The void space may be filled with a gas or liquid, such as an electrolyte, and is still referred to as a void space.

An exemplary method of manufacturing an electrode begins with providing an emulsion of zinc powder in a liquid phase. Any particle size of zinc powder may be used including, but not limited to, 100 μm or less. Smaller particle sizes may lead to better electrode performance. The liquid phase of the emulsion may be any liquid or mixture thereof that can evaporate and in which zinc powder can be emulsified. A mixture of water and decane is a suitable liquid phase. Emulsification may be improved by adding emulsifiers and/or emulsion stabilizers. One suitable emulsifier is sodium lauryl sulfate and one suitable emulsion stabilizer is carboxymethyl cellulose. Other such suitable emulsifiers and emulsion stabilizers are known in the art. Zinc metal can be alloyed with indium and bismuth or other dopants or emulsifying additives to inhibit gas evolution and sponge corrosion, which can improve electrode performance. The mixture of zinc and emulsion may have a viscosity of, for example, 2-125 Pa-s, 2-75 Pa-s, or 50-125 Pa-s.

The zinc powder may be a mixture of two or more different zinc powders having different average particle sizes. For example, the average particle size of the first zinc powder may be in the range of 20-75 microns. The average particle size of the second zinc powder may be in the range of 2 to 20 microns. The combination of the two zinc powders will produce an average pore per linear inch (linear inch) representing the weighted contribution of the two sources. When multiple types of zinc powder are mixed, the particle size distribution profile will exhibit at least two maxima. Note that in this particle size distribution, any portion of the zinc powder used to make the electrode should not be omitted. After analysis of all zinc in the emulsion, the particle size will have at least two maxima. The use of multiple particle sizes can result in higher zinc bulk density and increased specific energy in the monolith.

The emulsion was introduced into a vessel which determines the size and shape of the Zn/ZnO monolith required, and then dried to remove the liquid components. The dried emulsion produces a porous solid body comprising Zn/ZnO particles and voids, referred to herein as a "sponge"; because the zinc powder particles do not fuse together, the porous object may be fragile.

The mold may comprise a metal substrate, screen or foil (e.g., tin) or an alloyed substrate, screen or foil (e.g., tin coated copper) capable of maintaining the temperature reached in the subsequent heat treatment step. This operation produces an electrode in which the metal melts to another metal. Applications for this operation include, but are not limited to, electrically connecting a sponge electrode to a current collector to be used in an electrochemical cell (e.g., battery). In this process, the bottom of the mould is open and placed on a metal screen (tin-coated copper) of a size that does not allow the zinc particles to pass through and comprising a metal that is able to withstand the temperatures reached in the subsequent heat treatment step (bottom). The average opening size of the screen may be smaller than d of the zinc powder ₅₀ Particle size.

Next, the sponge is annealed and/or sintered at a low partial pressure of oxygen to form an annealed and/or sintered sponge. Such conditions may be found in an inert atmosphere (e.g., argon or nitrogen flow) or in vacuum, all of which contain a trace amount of oxygen. Annealing and/or sintering is performed at a temperature below the melting point of zinc, and may be at least two thirds of the melting point of zinc. The temperature ramp may be, for example, 2 ℃/min, and the residence time may be, for example, at least 30 minutes. Annealing and/or sintering melts the zinc particles into a monolithic structure without causing sufficient melting to significantly alter the overall morphology. The structure is still a sponge. Any annealing and/or sintering conditions that melt the zinc particles together may be used. Exemplary conditions include, but are not limited to, annealing and/or sintering in argon at peak temperatures of 200 to 410 ℃. The fused structure comprises metallic zinc and interconnecting bridges that fuse the particles together.

Next, the annealed and/or sintered sponge is heated in an oxidizing atmosphere to produce zinc oxide on the surface of the partially oxidized sponge. The heating is performed at a temperature above the melting point of zinc. This second heating step may increase the strength of the sponge for further processing, such as incorporating it into a battery or other device. Since zinc oxide does not melt and decompose at a temperature much higher than the melting point of zinc, the sponge structure can be maintained even at high temperatures. A zinc oxide shell is formed covering the molten zinc mesh, typically leaving metallic zinc bridges and the powder particle core within the shell. Some or all of the bridges may be partially or fully converted to zinc oxide, but the physical bridges are not destroyed. In the zinc oxide shell, the metallic zinc can be melted without changing the form of the sponge, and at the same time, the structure and the strength of the fusion bridge can be further increased. Any heating conditions that form zinc oxide may be used. Exemplary conditions include, but are not limited to, heating in air at 420 to 650, 700 ℃, at least above the melting point of zinc, or at least 150 ℃ above the melting point of zinc for 30 minutes.

Next, the sponge is returned to the inert atmosphere at a temperature equal to or above the melting point of the metal, for example, at 420 to 650, 700 ℃, at least above the melting point of zinc or at least 150 ℃ or more, 30 minutes above the melting point of zinc. This third heating step can further improve the strength and interconnectivity of the sponge by terminating the additional oxide formation and further melting the metal core of the sponge skeleton, while the shape is protected by the oxide formed on the surface in the previous step. The transition back to the inert atmosphere prevents further conversion to zinc oxide to maintain a significant amount of zinc in the core.

Optionally, the zinc oxide is then electrochemically reduced to zinc to form a zinc metal sponge. The sponge comprises interpenetrating zinc and a network of void spaces. The reduction may be performed after the electrodes are placed in the intended device (e.g., battery). Any electrochemical conditions for reducing zinc oxide may be used. For example, this can be accomplished by applying a negative voltage to the oxidized sponge until the open circuit potential for zinc is less than 5 mV. As noted above, the fuse bridge typically retains and converts back to metallic zinc. Some zinc oxide may be present on the surface of the zinc mesh because some zinc oxidizes even at room temperature.

This structure differs from the structure made by a single heating step, which is heating the dried emulsion in vacuo at a high temperature above the melting point of zinc. Since the vacuum is not perfect and there is always an indefinite molecular oxygen present, this heating will rapidly form a zinc oxide shell on each zinc particle before the metallic zinc bridge is formed to fuse the particles together. Absent these bridges, such structures are very fragile and may have less electrical interconnectivity than the presently disclosed structures.

The final electrode may be used in an electrochemical cell. Such a battery may include an anode current collector, an anode comprising a zinc sponge electrode in electrical contact with the anode current collector, an electrolyte filling the void space, a cathode current collector, and a separator between the anode and the cathode. The electrochemical cell may be a zinc-air, silver-zinc or zinc-manganese oxide cell, or any other cell containing a zinc electrode. The construction of such cells is known in the art. Zinc oxide and/or zinc oxyhydroxide can form on the surface of a zinc mesh when the anode of a battery is fully or partially discharged.

Fig. 10 schematically shows the zinc sponge structure and the effect of repeated cycles. The top image shows a monolithic non-periodic structure in which the entire three-dimensional (3D) volume of the sponge is an interconnected core of conductive metal. As used herein, "aperiodic" means that the structure does not conform to a regular or geometric pattern and is generally uniform; the use in combination with 3D wiring structures can ensure a more uniform current distribution than other zinc powder formulations known in the art. All void spaces are created by the same mechanism that dries the mixture. No other method (e.g., template) is used to create voids of different sizes or types. The boundaries between the original zinc particles are not necessarily discernable. The structure is metal-interconnected in three dimensions. The lower panel shows that all surfaces of the Zn sponge structure are lined with zinc oxide upon discharge. Charging removes the zinc oxide and restores the structure to a substantially all-metallic form. As described in Parker et al, science,356,415-418 (2007), incorporated herein by reference, this cycle can be repeated multiple times without forming large scale dendrites.

The aperiodic structure can be formed by naturally filling the metallic zinc powder by sedimentation of well-mixed emulsions (containing well-distributed zinc particles) during slow evaporation of the emulsion to form a consolidated, friable molded shape factor. After removal from the mold, the consolidated, template-free void-solid shape is annealed in a non-oxidizing atmosphere at a temperature just below the melting point of the original metal powder to ensure that the inter-particle atomic scale bridges formed as organic components of the original emulsion are thermally decomposed into volatile species for removal from the air-solid structure of the original emulsion-consolidated monolithic object. Calcining the annealed void-solid shapes in an oxidizing atmosphere at 650 ℃ (hundreds of degrees celsius above the melting point of the original metallic zinc powder) ensures that the internal metallic zinc melts and flows, while the annealed void-solid shaped void-solid structures are captured by zinc oxide crust at the annealed solid grids, which maintains the annealed porous structure by preventing the oxide coated solid grids from collapsing or sinking into the voids. The general size of the void cell in the final porous monolithic form factor can be determined by the particle size used to prepare the zinc emulsion. This can result in a pore size of 1-100 microns, with a pore size of 160-6000 microns per linear inch, or on average, greater than 300 microns per linear inch. The first zinc powder may create an average pore region with a pore size in the range of 169-635 microns per linear inch. The second zinc powder produced a region having an average pore size per linear inch of between 635 and 6350 microns. The combination of the two zinc powders will produce an average pore per linear inch representing a weighted contribution from both sources.

Fig. 11 schematically shows an example of a zinc structure of the prior art and the effect of repeated cycles. The special properties of zinc powder (usually loosely associated with the binder and gelling agent) lead to non-uniform current distribution. The lower view shows that repeated discharge and charge results in uneven formation of zinc oxide, thereby resulting in uneven generation of zinc upon charge. A portion of the structure containing zinc oxide after discharge may no longer be connected to the circuit so that the load of the battery is directed to a narrow area, which may lead to the formation of dendritic zinc (McBreen, "Rechargeable Zinc Batteries" j. Electric. Chem.1980,168, 415-432).

Other prior art zinc structures (e.g., arance, U.S. patent No. 3287166) can be made using porous polymer foam as a template. The template is filled with slurry and burned off to render the voids in the original template solid. The solids in the template become a wide range of voids. The macropores may be about millimeters in diameter with a total pore per linear inch of less than 50 millimeters.

Other possible applications include the use of zinc sponge in various battery systems containing zinc as the negative electrode. Full-cell batteries (e.g., silver-zinc, nickel-zinc, zinc-carbon, zinc-air, etc.) can be prepared without altering the zinc sponge manufacturing process described herein, with or without the addition of electrolyte additives. The full cell described herein may utilize a nylon screw cap as a cell seat. An alternative is to include any battery support that contains zinc as an electrode component. Other alternatives include manufacturing procedures designed to produce 3D, through-connected zinc structures in an effort to produce porous zinc monoliths with uniform current distribution as a means of inhibiting dendrite formation, enhancing cyclability, and/or increasing zinc utilization of primary or secondary zinc-containing cells.

A suitable electrolyte is KOH. Any number and density of cells that produce functionality may be used.

The development of zinc-containing batteries capable of high power operation and enhanced charge capacity requires redesigning the structure of the zinc electrode to provide a high surface area electrochemical interface and support improved current distribution, thereby inhibiting overgrowth of electrodeposited Zn and detrimental dendrite formation. Conventional powder bed zinc composites are mainly used as negative electrodes in commercial zinc-containing batteries (e.g., zinc-air) with low theoretical specific capacity utilization (< 60%) of zinc, high electrolyte additive content, non-uniform current distribution, limited chargeability. The electrodes disclosed herein describe the preparation of new zinc anodes that significantly ameliorate these disadvantages.

By forming the zinc powder emulsion in two subsequent steps (annealing and/or sintering) and electrochemical reduction steps, a strong, expandable monolithic zinc sponge can be produced that can be readily used in a variety of devices having zinc-containing cells. The resulting zinc sponge includes two interpenetrating, co-continuous grids of zinc metal and voids, thereby improving current distribution throughout the electrode structure. This feature inherent to the 3D architecture of the anode prevents the formation of concentration gradients that would otherwise lead to disproportionate reaction centers, leading to dendrite growth, inevitably creating battery defects. The primary zinc-air cell used in the examples below utilized greater than 20% more zinc than commercial powder bed zinc anode composites, providing a higher specific energy, another feature desired for metal grids that improved current distribution. In addition, the highly porous mesh co-continuous with the zinc metal mesh allows the use of a limited volume element with a high surface to electrolyte volume ratio, thereby promoting faster saturation of zincate and faster dehydration to ZnO upon discharge, thereby minimizing shape changes. This idea, together with the dendrite suppression effect brought about by the improved current distribution, allows for achieving a rechargeable performance, which is not achieved with zinc anodes in commercial zinc-air batteries.

The following examples are given to illustrate specific applications. These specific examples are not intended to limit the scope of the disclosure in this application.

Example 1

Manufacture of monolithic zinc sponge-a typical method of manufacture of zinc sponge electrodes is to form an emulsion of zinc powder in water and decane. In a small beaker or scintillation vial (scintillation vial), 6.0g of zinc powder was added, which also contained 300-ppm indium and 285-ppm bismuth (from Grillo-Werke AG). Indium and bismuth additives are necessary to increase the overpotential for hydrogen evolution in alkaline electrolytes while eliminating the need for toxic additives such as lead and mercury(Glaeser, U.S. Pat. No. 5240793). Water (1.027 mL) and decane (2.282 mL), as well as sodium dodecyl sulfate (6.3 mg) and carboxymethyl cellulose (0.253 g), as emulsifying agents, were added. These components are used to form zinc emulsions (Drillet et al., "Development of a Novel Zinc/Air Fuel Cell with a Zn Foam Anode, aPVA/KOH Membrane, and aMnO 2/SiOC-based Air Cathode" ECS Trans.2010,28,13-24) that are subsequently used to make zinc electrodes that have been previously described. The mixture was stirred rapidly at 1200rpm for more than 15 minutes to ensure complete absorption of zinc into the emulsion. The free flowing but viscous emulsion was poured into a cylindrical polyethylene mold and air dried overnight. The diameter of the mould used in the example is 1.15cm, so that zinc sponge with the thickness of 1-4mm can be produced; however, this process may scale to other sizes and shapes. After 16-24 hours of drying, the mold was inverted to release the zinc monolith, which was brittle at this stage. To strengthen the zinc sponge, the sample was transferred to a tube furnace and placed in flowing argon at 2℃for a minute ^–1 It was heated to an annealing temperature of 400 c and held for 2 hours. The argon stream is then removed, the tube is opened to ambient air, and the second step: at 2 ℃ for min ^–1 Heat to 650 ℃ and hold for 2h. The last step: the surface of the annealed zinc particles is encapsulated with a ZnO needle shell, which is necessary to impart additional reinforcing properties to the zinc sponge. After 2 hours, the tube was allowed to cool without any rate control. The resulting monolith was characterized by Scanning Electron Microscopy (SEM) as shown in figure 1.

Example 2

Zinc sponge as negative electrode in zinc-air batteries-it is intended to introduce oxides into the zinc sponge, improving mechanical integrity, allowing to reduce the risk of breakage in daily operations; however, the oxide layer on zinc reduces the initial capacity upon discharge and introduces contact resistance when the zinc-containing cell is assembled (see Nyquist plot (Nyquist plot) of Electrochemical Impedance Spectroscopy (EIS) in fig. 2A). For electrochemical reduction of the ZnO coating, a sponge was used as part of the working electrode in a half-cell, three-electrode configuration with a Pt counter electrode in 6M KOH and a zinc quasi-reference electrode (quasi-reference electrode). Placing zinc sponge on tinned copper meshIn the encapsulation to form the working electrode. (tin contacts are used because tin is galvanically compatible with zinc and inhibits corrosion of the electrode that would otherwise propagate to other current collectors (e.g., nickel, copper, etc.)) in a typical experimental sequence, the Open Circuit Potential (OCP) of the cell is measured relative to a metallic zinc quasi-reference electrode, and then an initial EIS measurement is performed. The initial OCP is typically over 40mV relative to Zn, and the actual impedance (R _CT ) Much higher than the expected resistance of the metal contact, consistent with the presence of poorly conducting zinc oxide coatings on zinc sponges. The oxide coated sponge can be electrochemically reduced to the metallic zinc counterpart by applying a constant potential of-50 mV for 30 minutes, followed by additional EIS and OCP measurements. This sequence was repeated until the open circuit potential stabilized at or near 0mV, indicating complete reduction to zinc metal. The charge transfer resistance of the electro-reduced zinc sponge is reduced to less than 0.2cm compared to a heated zinc sponge ^–2 While the resistance value exceeds 60cm ^–2 (FIG. 2A, B). The conversion of ZnO to Zn metal was confirmed using X-ray diffraction (Rigaku, fig. 2C, 2D), which indicates the loss of ZnO reflection, leaving only metallic zinc after electro-reduction. In addition, after reduction, the porosity or mechanical strength of the zinc monolith is not significantly lost; however, a measurable mass loss was noted due to the loss of oxygen mass when ZnO was reduced to Zn, and the loss of alkaline electrolyte due to some corrosion of zinc to form soluble products. Based on twelve control experiments, the average mass loss associated with this electrochemical reduction step was 23.9±3.4% using the annealed and oxidized zinc sponge subjected to the heat treatment described above. Fig. 2E, 2F highlight the morphological changes after the reduction step, effectively removing the zinc oxide shell associated with the prepared sponge.

The above reduction step successfully reduces the amount of zinc oxide present in the sponge, which would otherwise limit capacity and increase resistance when incorporated into a zinc-containing battery. The half cell test configuration can quality check the impedance characteristics of the anode before it is used in a full cell, but it can also be used as a useful tool to study the power capacity of zinc sponge as an anode. For example, by1C ^TM Epoxy resin a monolithic zinc sponge (1.15 cm diameter; 3.5mm thick) was attached to the tin current collector, the epoxy resin completely surrounding all ingredients except the surface of the zinc sponge. A reduction voltage of-50 mV relative to zinc was applied for 50 minutes, and then a zinc sponge was discharged (i.e., oxidized) at a constant current (5 mA) for 10 minutes to measure a steady-state discharge voltage. As shown in fig. 3, this operation is repeatedly performed as the applied current increases. Constant current experiments revealed a linear relationship of steady-state discharge voltage with applied current. Even at the imposed 200mA (193 mA cm ^–2 ) The overpotential required to maintain this current density is also only 230mV. The ability to maintain a low overpotential even at high loads (current densities) is an enabling feature of zinc sponge architecture. Conventional Zinc-containing cells, including Zinc-air cells, typically operate at a voltage drop of up to 500mV relative to open circuit voltage (Linden, "Zinc/air cells" Handbook of batteries.1984,2nd Ed.).

Once the zinc sponge is completely reduced to Zn ⁰ Can be used as the negative electrode of the full cell. The zinc-air cell prototype used for the preliminary test was based on a 1.8 cm nylon screw cap (Hillman Group) that snapped into a 6mm hole in the top surface to serve as the venting face of the cell. A platinum wire was attached to the tin current collector and used as the negative terminal during battery testing. After a separate electrochemical reduction step, the zinc sponge still impregnated with 6M KOH was immersed in a gel electrolyte synthesized from 6g polyacrylic acid dissolved in 100ml6M KOH. To prepare the full Zn-air cell, excess gel was wiped off the gel-impregnated zinc sponge, leaving only a thin coating. The viscous gel electrolyte ensures that the zinc sponge slows down the evaporation rate of the solvent while the liquid electrolyte is sufficiently permeable. A zinc sponge was placed on a tin current collector and then covered with a water compatible separator sized slightly larger than the diameter of the zinc sponge (1.15 cm). The positive electrode terminal comprises Ketjen carbon black, potassium manganese ore andis adhered to a piece of nickelOn the net and attached to a strip of platinum wire. The results of a typical zinc-air full cell using these zinc sponge anodes are shown in fig. 4. In these examples, at-5.0, -10 and-24 mA cm ^–2 All initial OCP measurements were higher than 1.4V before discharging the full cell. The average discharge voltages of these cells were 1.25, 1.19 and 1.13V, respectively, and the cutoff voltage of each cell was 0.9V. At-5, -10 and-24 mA cm ^–2 The specific capacities obtained under discharge are 728, 682 and 709mAh g _Zn ^–1 Specific energy densities of 907, 834 and 816Wh kg, respectively _Zn ^–1 The corresponding zinc utilization rates for these cells were 89%, 83% and 86%, respectively. These metrics are an improvement over standard commercial zinc powder composite anodes that typically utilize only 50-60% of theoretical zinc specific capacity (Zhang, "Fibrous zinc anodes for high power batteries," j.power sources 2006,163, 591).

Example 3

Reversibility of zinc sponge anode-to investigate the reversibility of 3D zinc sponge in cell construction, without having an optimized cathode (e.g., dual-function catalysis of ORR or OER), symmetrical electrochemical cells were used that contained Zn/ZnO sponge separated from all-metal Zn sponge by a water-compatible separator. Zn/ZnO sponges were prepared by electroreduction of some ZnO present in the heated sponge in 10 minute increments applied at-50 mV relative to zinc. EIS and OCP were measured after each cycle. R in EIS _CT Down to 0.5 Ω cm ^–2 Below, the reduction of the sponge terminated, but the OCP remained greater than 30mV compared to Zn, indicating that the whole sponge lattice had high conductivity, but ZnO remained. As described in example 2, the second heated sponge was reduced in 30 minute increments of-50 mV relative to Zn until it was fully reduced to an all metal zinc sponge with an OCP very close to 0mV relative to Zn. For the symmetrical cell construction, the negative electrode is an all-metal Zn sponge in electrical contact with a tin foil current collector and the positive electrode is a Zn/ZnO sponge electrode also in contact with a tin foil current collector. Both sponge electrodes have been pre-impregnated with 6M KOH and separated by a water compatible separator (see fig. 5). For evaluating symmetrical batteriesFor 1 hour-24 mA cm ^–2 To reduce some of the ZnO in the Zn/ZnO sponge, which is coupled with oxidation of Zn in the opposite sponge. Then in a second step +24mA cm is applied ^–2 To initiate the reverse reaction. The complete symmetrical cell was measured at.+ -.24 mA cm ^–2 Cycling until one of the steps exceeds a threshold of + -100 mV. No electrical shorts were observed. In this example, the symmetrical cell cycled 45 charge and discharge cycles at a depth of discharge of about 23%. For analysis after cycling, the electrodes were removed from the cell, rinsed thoroughly, and dried overnight in vacuo. Scanning electron micrograph shows that the sponge retains its porosity after cycling (fig. 6). In addition, no visible signs of shape change, dendrite formation or uneven deposition were observed. The circulation of the zinc sponge forms a layer of dense zinc or zinc oxide on the surface of the monolithic particles, rather than flower-like dendrites, which suggests improved recyclability due to the firm linear, well plumbed zinc sponge framework.

Example 4

Preparation of monolithic Zinc sponge with increased bulk Density-higher bulk Density (1.79-2.14 g cm) ^–3 ) An example of the preparation of a zinc (Zn) sponge electrode starts with the formation of a zinc powder emulsion in water and decane. In a small vessel, an emulsifier (sodium dodecyl sulfate, 21 mg) and an emulsion stabilizer (carboxymethyl cellulose, 0.844 g) were added to a stirred mixture of deionized water (2.054 mL) and decane (4.565 mL) and stirred at 300rpm for 10 minutes. Zn metal powder (20 g) was added to the mixture. In this example, the powder is a mixture comprising Zn particles of two sources: (i) Zinc powder having an average particle size of about 50 μm and containing 300ppm of indium and 300ppm of bismuth; (ii) Zinc powder having an average particle size of < 20 μm and containing 200ppm of indium and 200ppm of bismuth. For the Zn sponge prepared in this example, the large particles account for 30wt.% of the powder mixture, while the small particles account for the remaining 70wt.%, although other proportions may be used. Indium and bismuth additives were introduced by manufacturers to reduce the overpotential for hydrogen evolution in alkaline electrolytes while eliminating the need for toxic additives such as lead and mercury (Glaeser, U.S. patent No. 5240793).After Zn was added to the stirred oil/water mixture, the stirring rate was slowly increased to 1200rpm and stirred at 1200rpm for at least 15 minutes to ensure complete absorption of Zn powder into the emulsion. The free flowing but viscous emulsion was transferred as a 0.5mL aliquot into a polyethylene mold 1.15cm in diameter and allowed to stand dry overnight at ambient atmosphere and temperature, in this example 16 hours. After drying, the mold was inverted to release the Zn monolith; the shape of the released zinc at this stage is brittle. To strengthen the zinc sponge, the sample is transferred to a cuvette oven and subjected to a flowing inert atmosphere (e.g., argon) at 2℃for a minute ^–1 It was heated to an annealing temperature of 410 c and held for 2 hours (m.p. _Zn =419.5 ℃). The inert gas flow is then removed, the test tube is opened to ambient air, and then in a second step in static air at 2℃for a minute ^–1 Heated to 665 deg.c and held for 2 hours. This step encapsulates the surface of the annealed Zn particle frame with a thermally grown ZnO shell, which imparts additional reinforcing properties to the Zn sponge. After 2 hours, the tube was allowed to cool without any rate control. The monoliths obtained have a bulk density of from 1.79 to 2.14g cm ^–3 (density 25-30% relative to non-porous zinc metal) and is therefore referred to herein as "Zn 30").

Example 5

Zinc sponge as negative electrode for high-power silver-zinc cell-conversion of heat-treated zinc sponge to metallic Zn in electrochemical reduction step ⁰ After the analogue, the zinc sponge of example 4 was thoroughly rinsed with deionized water, dried and reweighed to accurately evaluate the capacity of the Zn active material prior to prototype testing. Will be about 1cm ² Immersing in 6M KOH, placing it on a tin current collector, then placing four separators on top: microporous filters (e.g. Celgard 3501), two layersAnd a layer of nonwoven fabric (e.g., freudenberg 700/28K). Prior to the assembly of the battery cell,non-wovenThe cloth-making separator has also been immersed in 6M KOH electrolyte. The positive terminal comprises silver oxide (Ag) in mechanical contact with a piece of Pt or Ag foil attached to a platinum wire _x O) cathode. By combining Ag with _x O (0.5 g) was pressed into an Ag screen (in a 1cm particle mold) to 7000psi to make Ag _x And an O cathode. All battery materials were contained in a 1.8 cm nylon screw cap (Hillman Group). An expanded view of the battery assembly is shown in fig. 7.

While silver-zinc cells using zinc sponge anodes may also be used for rechargeable applications, ag-Zn cell prototypes of the present example have been prepared to demonstrate the power capacity of Zn sponge. In this example, the temperature is measured at 15, 25, 50, 100, 200, 300, 400, and 500mA (about 15-500mA cm ^–2 Corresponding to a mass normalized value of 0.2-5.6Ag ^–1 ) The open circuit voltage was measured to be about 1.66V before discharging the Ag-Zn cell. The lower limit voltage of the example battery of fig. 8 was set to 1.0V and never reached within the checked current density range, indicating no power limitation at the specified load. The total specific capacity of the eight power offsets totaled 246mAh g _Zn ^–1 Corresponding to a depth of discharge of 30% relative to the total amount of theoretical Zn active material present, it is highlighted that each power step shown in this example is a continuous load, rather than a pulse of sub-second order. The corresponding specific power (current x average voltage) transferred by the battery ranges from 260W kg to 5800W kg _Zn ^–1 Depending on the applied current density. In the packaged and optimized Ag-Zn cell, assuming that 20% of the cell contains Zn sponge anode, the specific power is about 50-1200W kg depending on the applied current density ^-1 。

Example 6

Zinc sponge as negative electrode for high capacity rechargeable silver-zinc cell-after electrochemical reduction step, the heat treated zinc sponge is converted to metallic Zn ⁰ The analogue was then rinsed thoroughly with deionized water the zinc sponge of example 4, dried, and re-weighed to accurately evaluate the capacity of the Zn active material prior to prototype testing. About 1-cm used in this example ² The total mass of the reduced zinc sponge was 0.101g. Once immersed in 6M KOH electrolyte, the Ag-Zn cell will be according to the previousExamples are built. By a current density of about 5.5mA cm ^–2 (C/15) the ability of a Zn sponge anode to discharge to a high Zn mass normalized capacity and charge without causing dendrites was investigated by thoroughly discharging an Ag-Zn cell and then charging at the same rate (FIG. 9). The cell was discharged at an average voltage of 1.50V and reached 96% dod _Zn (787mAh g _Zn ^–1 ；1181Wh kg _Zn ^–1 ) And can be charged from this extreme depth to 97% capacity. No dendritic shorts were observed.

Obviously, many modifications and variations are possible in light of the above teaching. It is, therefore, to be understood that the claimed subject matter may be practiced otherwise than as specifically described. For example, any reference to claim elements in the singular using the articles "a," "an," "the," or "said" should not be construed as limiting the element to the singular.

Claims

1. An article for a rechargeable battery, comprising:

a continuous grid comprising metallic zinc; and

continuous grids that intersect the void space of the zinc grid;

wherein the zinc mesh comprises a fused monolithic structure;

wherein the article comprises a metallic zinc bridge connecting metallic zinc particle cores; and

wherein the article is manufactured by the steps of:

providing a mixture comprising metallic zinc powder and a liquid phase emulsion;

wherein the particle size distribution of all metallic zinc powders used to make the article has two maxima, one of which is in the range of 2-20 microns and the other of which is in the range of 20-75 microns;

drying the mixture to form a sponge;

sintering the sponge in an inert atmosphere or under vacuum at a temperature below the melting point of zinc to form a sintered sponge having a metallic zinc surface; and

the sintered sponge is heated in an oxidizing atmosphere at a temperature above the melting point of zinc to form a zinc oxide shell on the surface of the sintered sponge.

2. The article of claim 1, wherein the surface of the zinc mesh and the interior of the zinc mesh each comprise zinc.

3. The article of claim 1, wherein the surface of the zinc mesh comprises one or more of zinc oxide and zinc oxide oxyhydroxide.

4. The article of claim 1, wherein the zinc mesh is uniformly conductive.

5. The article of claim 1, wherein the inert atmosphere is argon or nitrogen.

6. The article of claim 1, wherein the article is further manufactured by: and (3) reducing zinc oxide.

7. The article of claim 1, wherein the void space comprises a pore size of 10-75 microns.

8. An electrochemical cell for a rechargeable battery, comprising:

an anode current collector;

an anode comprising the article of claim 1 in electrical contact with the anode current collector;

an electrolyte filling the void space;

a cathode current collector;

a cathode in electrical contact with the anode current collector; and

a separator between the anode and the cathode.

9. The electrochemical cell of claim 8, wherein the electrochemical cell is a zinc-air cell.

10. The electrochemical cell of claim 8, wherein the anode can be oxidized and reduced for at least 45 cycles without formation of zinc dendrites.

11. A method of manufacturing a rechargeable battery, comprising:

providing a mixture comprising a metallic zinc powder and an emulsion of a liquid phase;

wherein the particle size distribution of all metallic zinc powders has two maxima, one of which is in the range of 2-20 microns and the other of which is in the range of 20-75 microns;

drying the mixture to form a sponge;

sintering the sponge at a temperature below the melting point of zinc to form a sintered sponge; and

12. The method of claim 11, wherein the emulsion of the liquid phase comprises water and decane.

13. The method of claim 11, wherein the emulsion comprises an emulsifier and an emulsion stabilizer.

14. The method of claim 13, wherein the emulsifier is sodium dodecyl sulfate and the emulsion stabilizer is carboxymethyl cellulose.

15. The method of claim 11, wherein the sintering is performed under argon at a peak temperature of 200-410 ℃.

16. The method of claim 11, wherein the heating is performed in air at a peak temperature greater than 420 ℃.

17. The method according to claim 11,

wherein the sintering is performed in an inert atmosphere or vacuum; and

wherein the sintered sponge has a metallic zinc surface.

18. The method of claim 17, wherein the inert atmosphere is argon or nitrogen.

19. The method of claim 11, further comprising:

and (3) reducing zinc oxide.

20. The method of claim 19, wherein the zinc oxide is reduced by applying a negative voltage to the oxidized sponge until the open circuit potential for zinc is less than 5 mV.