The effect of potassium fluoride on zinc batteries

Potassium fluoride has a great impact on zinc batteries

Potassium fluoride is an inorganic salt with the chemical formula KF. It is a white crystalline powder with a salty taste and is hygroscopic. It is soluble in water and insoluble in ethanol.

Chinese name

Potassium fluoride[2]

Foreign name

Potassium fluoride[2]

Chemical formula

KF[2]

Molecular weight

58.097[2]

CAS registration number

7789- 23-3[2]

Basic information

Chemical formula: KF

Molecular weight: 58.097

CAS number: 7789-23-3

EINECS number: 232-151-5

Physical and chemical properties

Physical properties

Melting point: 858℃

Density: 2.48g/cm3

Boiling point: 1505℃

Refractive index: 1.363

Vapor pressure: 922mmHg at 25°C

Appearance: white crystalline powder

Solubility: soluble in water, hydrofluoric acid, liquid ammonia, insoluble in alcohol[1]

Chemical Properties

It decomposes slightly when heated to sublimation temperature, but molten potassium fluoride is highly active and can corrode refractory materials. It can form the adduct KF·H2O2 with hydrogen peroxide. There are two types of hydrates: KF·2H2O and KF·4H2O. When the temperature is lower than 40.2°C, the dihydrate (KF·2H2O) can be crystallized in the aqueous solution, which is a monoclinic crystal. It can autodissolve in the crystallization water at 41°C.

Calculated chemical data

Reference value for hydrophobic parameter calculation (XlogP): None

Number of hydrogen bond donors: 0[2]

Number of hydrogen bond acceptors: 1[2]

Number of rotatable chemical bonds: 0[2]

Number of tautomers: 0

Topology Molecular polarity Surface area: 0[2]

Number of heavy atoms: 2[2]

Surface charge: 0[2]

Complexity: 2[ 2]

Number of isotope atoms: 0[2]

Determine the number of atomic stereocenters: 0[2

The remaining zinc electrode components include zinc oxide , and optionally bismuth oxide, aluminum oxide, indium and potassium fluoride or calcium. More zinc particles can be added at this stage. These retained zinc electrode components are available in powder form.

Zinc (Zinc) is a chemical element, its chemical symbol is Zn, its atomic number is 30, and it is located in the 4th period and Group IIB of the periodic table of chemical elements. Zinc is a light gray transition metal and the fourth most "common" metal. In modern industry, zinc is an irreplaceable and important metal in battery manufacturing. In addition, zinc is also one of the essential trace elements for the human body and plays an extremely important role.

Chinese name

Zinc

Foreign name

zinc

Molecular weight

65.38

CAS registration number

7440-66-6

Melting point

419.53 ℃

Chemical element controlled zinc Zn, a metal often used as a "wedding dress" for other metals, can also make people stronger 02:33

Zinc [xīn]

Element No. 30 in the periodic table

This entry is polysemous, with ***3 meanings

Science Popularization in China?|?This entry is reviewed by the "Science Popularization in China" Science Encyclopedia Entry Compilation and Application Work Project

Zinc is a chemical element, its chemical symbol is Zn, its atomic number is 30, and it is located in the 4th period and IIB of the periodic table of chemical elements. clan. Zinc is a light gray transition metal and the fourth most "common" metal. In modern industry, zinc is an irreplaceable and important metal in battery manufacturing. In addition, zinc is also one of the essential trace elements for the human body and plays an extremely important role.

Chinese name

Zinc

Foreign name

zinc

Molecular weight

65.38

CAS registration number

7440-66-6

Melting point

419.53 ℃

Wireless portable devices such as The popularity of power tools has increased the need and requirements for rechargeable batteries with high energy density that can also provide high power. As power and energy density requirements increase, so does the need for high cycle life rechargeable electrodes. Alkaline zinc electrodes are known for their high voltage, low equivalent weight, and low cost. The fast electrochemical kinetics associated with the charge and discharge processes allow zinc electrodes to deliver both high power and high energy density. The low redox potential associated with zinc electrodes renders the electrode unstable with respect to hydrogen evolution. Primary alkaline batteries using zinc solve this problem by alloying the zinc with specific elements and using gas inhibitors. The purity of the materials in contact with the zinc is important and also limits the extent to which the zinc is exposed to any hydrogen evolution catalyst. Differences in starting materials for primary and rechargeable batteries affect the technology and effectiveness of anti-corrosion approaches. The zinc primary battery is prepared in a charged state, while the zinc secondary battery is prepared in a deep discharge state. In zinc primary batteries, the active material is metallic zinc in the form of a gel powder formed with particles of 100 to 300 microns. In zinc secondary batteries, the active material is zinc oxide (ZnO) containing a small amount of zinc metal and with a particle size between 0.2 and 0.3 microns. The size of the small zinc oxide particles used in the negative electrode of rechargeable batteries results in a surface area that is on the order of twice that of the particles in zinc electrodes used in primary batteries. Once formed after initial charge, the corrosion rate in secondary batteries is significantly higher. Improvements in rechargeable zinc electrode compositions and production processes continue to be sought to minimize corrosion and improve manufacturability.

The active material used in the negative electrode of rechargeable zinc alkaline electrochemical cells is made of zinc metal particles coated with tin and/or lead. Zinc particles can be coated by adding salts of lead and tin to a mixture containing zinc particles, a thickener and water. The remaining zinc electrode components such as zinc oxide (ZnO), bismuth oxide (Bi2O3), dispersants, and binders such as polytetrafluoroethylene (Teflon) are then added. Metallic zinc can be coated in the presence of zinc oxide as well as other electrode components. The obtained slurry/paste has stable viscosity and is easy to handle during the zinc electrode manufacturing process. In addition, zinc electrodes are less likely to outgas when cobalt is present in the electrolyte. Batteries made from electrodes produced according to the present invention show much less hydrogen release than conventional batteries, with a reduction of up to 60-80%. Cycle life and storage life are also improved because the zinc conductive matrix remains intact and self-discharge is reduced. In one aspect, the invention relates to a nickel zinc battery with a zinc negative electrode. The electrodes include zinc powder particles coated with lead, tin, or both, having a size of less than about 100 microns, less than about 40 microns, about 25 microns, or about 5-15 microns. Metallic zinc particles are added to the electrode to create and maintain a conductive matrix during cycling. Lead and tin, which are more inert than zinc, will not discharge at zinc potential and will protect the zinc particles they coat. The electrode can maintain good connectivity during discharge. Only small amounts of lead and tin are used. According to various embodiments, lead may be less than about 0.05% of the zinc electrode active material, and tin may be less than about 1% of the zinc electrode active material. Nickel-zinc batteries also include a nickel positive electrode. The positive electrode may contain cobalt and/or cobalt compounds, which may be coated on the nickel hydroxide particles, or added separately in the form of cobalt metal, cobalt oxide, cobalt hydroxide, cobalt oxyhydroxide, and/or other cobalt compounds. Positive electrode. The positive electrode may also include uncoated nickel hydroxide particles. Another aspect of the invention relates to a method of preparing a zinc negative electrode for a nickel-zinc battery. The method includes coating lead and/or tin on zinc metal particles (preferably in a slurry), using the zinc particles to form an active material slurry/paste, and incorporating the active material into the zinc electrode. According to various embodiments, at least one soluble tin salt and at least one soluble lead salt are added to zinc metal particles in a liquid medium, preferably water, to coat the zinc particles. The liquid medium may also include thickeners (thixotropic agents), and/or binders. Tin and lead can be used to coat zinc particles. The tin salt may be one or more of tin sulfate, tin acetate, tin fluoroborate, tin chloride, and tin nitrate. The lead salt may be one or more of lead acetate, lead chloride, lead fluoroborate, or lead nitrate.

The coating operation results in a slurry that can be used to form active materials. In some embodiments, the slurry can be treated before being added to the active material. For example, the slurry can be concentrated, heated or washed. The zinc particle slurry may also include some residual tin and lead salts in solution. The residual tin and lead salts can then be coated with the electrochemically formed zinc (after battery formation) to further protect the zinc from corrosion. An active material slurry/paste is formed with a slurry of zinc particles. Add the remaining zinc electrode components to the slurry. These components may include zinc oxide, bismuth oxide, dispersants, binders and liquids. Other additives such as insoluble corrosion inhibitors may also be included. These components may be in pre-stirred powder form when added to the slurry, thereby forming a slurry or paste that can be processed after mixing. One aspect of preparing negative electrodes is the stability of the slurry and paste during the preparation time period. The slurry/paste needs to be stable during the time period from slurry preparation to application to the substrate, which can take 4-6 hours or more. The addition of trace amounts of lead and tin was found to stabilize the slurry/paste. In certain embodiments, soluble lead and tin may be added separately. For example, the pre-dissolved tin salt solution can be added to the active material paste after the remaining zinc electrode components. The lead concentration in the paste can be up to about 0.05% by weight, and the tin concentration can be up to about 1% by weight. Testing at a temperature of 60°C showed that outgassing due to corrosion of zinc in a fully charged battery was reduced by 60-80% when the battery incorporated zinc electrodes. Less outgassing reduces self-discharge and pressure in the battery, which results in reduced electrolyte leakage and visible swelling. Zinc particles are added to the electrode during preparation to create and maintain a conductive matrix in the electrode during cycling. The metallic zinc particles used are larger than zinc oxide particles and have a size less than about 100 microns, or less than 40 microns. The size of the metallic zinc particles prevents complete discharge leaving an intact inner core, although its metallic character results in a loss of connectivity due to an insulating surface oxide. Maintaining an inert but conductive layer of tin and lead on the surface of the zinc particles will help maintain the integrity of the zinc particles. In another aspect, the present invention relates to zinc electrodes fabricated. The electrode includes a conductive substrate layer and an active material layer having zinc oxide, zinc particles coated with lead and/or tin, bismuth oxide and a binder. Zinc particles may be coated using the methods described herein, or pre-coated with specific amounts of lead and/or tin. The lead concentration in the active material may be up to about 0.05% by weight, and the tin concentration may be up to about 1% by weight. These and other features and advantages are discussed further below with reference to the corresponding drawings.

Figure IA is an exploded view of a cylindrical battery cell suitable for use in conjunction with various embodiments of the present invention.

Figure IB is a cross-sectional view of a cylindrical battery cell suitable for incorporating various embodiments of the present invention. Figure 2 is a cross-sectional view of the different layers of the separator. Figure 3 is a graph comparing the viscosity of negative active material pastes with and without tin and lead coatings on zinc particles. Figure 4A is a bar graph showing the effect of lead on the corrosion rate of zinc in alkaline solution. Figure 4B is a bar graph showing the effect of lead on zinc corrosion rate in an alkaline solution with cobalt. Figure 5 shows the corrosion reduction percentage for different amounts of tin and lead in the negative electrode paste. Figure 6A is a graph of discharge capacity for a cell with lead-coated zinc particles and a control cell with uncoated zinc particles. Figure 6B is a graph of discharge capacity for a cell with tin-coated zinc particles and a control cell with uncoated zinc particles. Figure 7 is a graph of discharge capacity for a cell with zinc particles coated with lead and tin and a control cell with uncoated zinc particles. DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention are disclosed in the context of preparing zinc-zinc oxide negative electrodes and in the context of zinc-zinc oxide negative active materials for nickel-zinc batteries. Those skilled in the art will appreciate that the following detailed description of the present invention is illustrative only and is not intended to be limiting in any way. Other embodiments of the present invention will readily demonstrate the advantages of the present disclosure to those skilled in the art. For example, the invention can be used with other rechargeable batteries, such as silver-zinc or zinc-air batteries. In this article, the terms "battery" and "cell" are used interchangeably. Introduction The present invention provides an improved method of preparing a negative electrode for use in rechargeable zinc batteries. The present invention makes the preparation process more controllable. The resulting rechargeable batteries of the present invention have one or more of the following characteristics: long storage life, long cycle life, low leakage, and little or no bulging. Conventional nickel positive electrodes include cobalt particles in the active material.

The cobalt particles are provided as cobalt metal and/or cobalt oxide (or sometimes cobalt hydroxide or cobalt oxyhydroxide). The inventors realized that dissolved cobalt may migrate from the positive electrode before the formation process of the battery is completed. Migration can occur during the period between filling the cell with electrolyte and applying the first charge, or during the first charge as part of the electrochemical cell formation process. Cobalt migration is less of a problem for sintered positive electrodes than for smeared positive electrodes. The source of cobalt also affects whether it will dissolve in the electrolyte and migrate to the positive electrode. Generally, freely added cobalt/cobalt compounds migrate more easily than cobalt that is coated on or incorporated into other particles, such as the nickel hydroxide particles that make up a typical positive electrode. The inventor found that cobalt at the negative electrode can catalyze the evolution of hydrogen in the negative electrode. A particular feature of the invention is the attenuation of this catalytic effect of cobalt. Sealed rechargeable Ni-Zn batteries have been developed for high-power applications such as power tools and hybrid electric vehicles. These batteries display exceptional high-rate charging and discharging capabilities and a maximum power density of over 2000W/kg. The impact of soluble cobalt species on this type of battery is particularly detrimental by accelerating hydrogen evolution during battery operation and storage. Accelerated hydrogen evolution can lead to cell-to-cell imbalance in multi-cell batteries and may promote the development of dendritic short circuits, which can lead to early failure. Alkaline electrolytes have been developed to examine dendrite growth, but their effectiveness is diminished in the presence of cobalt contamination. Examples of advanced alkaline electrolytes for rechargeable nickel-zinc batteries are disclosed in US Patent Publication US20060127761 entitled "Electrolyte Composition For Nickel-Zinc Batteries" by Jeffrey Phillips, which is incorporated herein by reference.

The electrochemical reaction of nickel-zinc storage battery is dominated by the following reaction for the charging process of nickel hydroxide positive electrode in alkaline electrochemical battery Ni (OH) 2+0Γ — Ni00H+H2e"(l)alkali In rechargeable zinc electrodes, the starting active material is ZnO powder or a mixture of zinc and zinc oxide powders dissolved in KOH solution to form zincate (Zn( OH)42-), which is reduced to zinc metal during charging. The reaction at the zinc electrode can be written as follows Zn20H>H20 - Zn (OH) -2e- +40F (3) Therefore, the net electrode reaction at the negative electrode is ZnO+H22e" - Zn+20H>2θ" (4) Therefore, the total Ni/Zn battery reaction can be expressed as

Zn+2Ni00H+H20 = Zn2Ni (OH) 2 (5) During the discharge of the zinc electrode, the metal zinc donates electrons to form zincate. At the same time, the concentration of zincate in the KOH solution increases. The increase results in the precipitation of zincate to form ZnO, as shown in Reaction 103. These transformations and aggregation that occur at the zinc electrode are a major factor in the eventual loss of electrode activity. Zinc Batteries, White Patent Publication US20060207084 and US Patent Publication US20060127761 disclose technical improvements to eliminate zincate aggregation in separators in Ni-Zn batteries. Nickel batteries and battery components shown in Figures IA and IB are implemented in accordance with the present invention. A schematic diagram of the main components of a cylindrical power cell, while Figure IA shows an exploded view of the cell providing alternating layers of electrodes and electrolytes in a cylindrical assembly 101 (also called a "winding body"). The negative and positive manifolds 103 and 105 are connected to opposite ends of the cylindrical assembly 101 and serve as internal terminals. , while the negative current collecting plate is electrically connected to the negative electrode, and the positive current collecting plate is electrically connected to the positive electrode. In the illustrated embodiment, the negative current collecting plate 103 is included for use as external terminals. Connect the negative collector plate 103 to the connector 107 of the lid 109. The positive collector plate 105 is welded or otherwise electrically connected to the tank 113.

In other embodiments, the negative collector pan is connected to the tank and the positive collector pan is connected to the lid. The positive current collecting plate 103 and the negative current collecting plate 105 are shown with perforations which may be used to facilitate bonding to the winding body and/or the passage of electrolyte from one part of the cell to another. In other embodiments, the disk may use slots (radial or circumferential), trenches, or other structures to promote bonding and/or electrolyte distribution. A flexible gasket 111 is placed on the surrounding bead 115 and is provided along the perimeter of the upper portion of the can 113 adjacent the lid 109 . The gasket 111 is used to electrically isolate the tank 113 and the lid 109 . In some embodiments, bead 115 (on which gasket 111 is located) is coated with a polymer coating. The gasket can be made of any material that electrically isolates the lid from the tank. Preferably, the material does not deform significantly at high temperatures; one such material is nylon. In other embodiments, it may be desirable to use relatively hydrophobic materials to reduce the driving forces that cause the alkaline electrolyte to creep and eventually leak from the cell at seams or other available exit locations. An example of a less wettable material is polypropylene. After filling the tank or other container with the electrolyte, the container is sealed to isolate the electrode and electrolyte from the environment, as shown in Figure IB. Gaskets are usually sealed by crimping. In some embodiments, sealants are used to prevent leaks. Examples of suitable sealants include asphalt sealant, tar, and VERSAMID? available from Cognis of Cincinnati, OH. In some embodiments, the cell is configured to operate in an electrolyte "lean" state. Additionally, in certain embodiments, the nickel-zinc batteries of the present invention use a lean electrolyte format. Such batteries have relatively low amounts of electrolyte relative to the amount of active electrode material. They can be easily distinguished from flooded batteries which have free liquid electrolyte in the internal area of ??the battery. As described in U.S. Patent Application No. US2006-0240317A1, filed April 26, 2005, entitled "Nickel Zinc Battery Design," which is incorporated herein by reference, it may be desirable to use a The battery operates under lean conditions. A lean cell is generally understood to be a cell in which the total void volume in the electrode stack of the cell is not completely occupied by the electrolyte. In a typical embodiment, the void volume of a lean cell after electrolyte filling may be at least about 10% of the total void volume before filling. The battery cells of the present invention may have any of a variety of different shapes and sizes. For example, the cylindrical cells of the present invention may have the diameter and length of conventional AAA cells, M cells, A cells, C cells, etc. In some applications, custom battery designs are appropriate. In a specific embodiment, the cell size is a sub-C cell size of 22 mm in diameter and 43 mm in length. Please note that the present invention is also applicable to relatively small prismatic battery formats, as well as to various larger format batteries for various non-portable applications. The shape of a battery pack typically used for power tools or lawn tools, for example, will determine the size and shape of the battery cells. The invention also relates to a battery pack comprising one or more nickel zinc battery cells of the invention and suitable housing, contacts, conductive wires to allow charging and discharging in an electrical device. Note that the embodiment shown in Figures IA and IB has the opposite polarity than a conventional Ni-Cd cell, since the lid is negative and the can is positive. In a conventional power battery, the polarity of the battery is such that the lid is positive and the can or container is negative. That is, the positive electrode of the battery assembly is electrically connected to the cover and the negative electrode of the battery assembly is electrically connected to the can housing the battery assembly. In some embodiments of the present invention, including the embodiments shown in Figures IA and IB, the polarity of the battery is reversed from that of a conventional battery. Therefore, the negative electrode is electrically connected to the lid, and the positive electrode is electrically connected to the tank. It will be appreciated that in certain embodiments of the invention, the polarity remains the same as a conventional design, ie with a positive cover. The can can be a container that serves as the outer cladding or casing of the final battery. In a conventional battery, the can is the negative terminal, which is typically nickel-plated steel. As noted, the can can be a negative terminal or a positive terminal.

In embodiments where the can is negative, the can material may have a similar composition to that used for conventional nickel-cadmium batteries, such as steel, as long as the material is coated with another material that is potentially compatible with the zinc electrode. For example, a negative acting tank may be coated with a material such as copper to prevent corrosion. In embodiments where the can is positive and the lid negative, the can can have a similar composition to that used for conventional nickel-cadmium cells, typically nickel-plated steel. In some embodiments, the interior of the tank may be coated with materials to facilitate hydrogen recombination. Any material that catalyzes hydrogen recombination can be used. An example of such a material is silver oxide. A vent cover allows the battery to vent gases generated during charging and discharging from the battery, although the battery is normally sealed from the environment. A typical nickel-cadmium battery outgasses at a pressure of about 200 pounds per square inch (PSI). In some embodiments, nickel zinc cells are designed to operate at this pressure or even higher pressures (eg, up to about 300 PSI) without venting. This promotes the recombination of any oxygen and hydrogen produced within the cell. In certain embodiments, the battery is constructed to maintain an internal pressure up to about 450 PSI or even up to about 600 PSI. In other embodiments, nickel-zinc cells are designed to vent gases at relatively low pressures. This may be appropriate when the design promotes controlled release of hydrogen and/or oxygen gases within the battery without their recombination. Some details of the structure of the vent cover and tray, as well as the support substrate itself, can be found in the following patent applications (which are incorporated herein by reference for all purposes) PCT/US2006/015807 and 2004 filed on April 25, 2006 PCT/US2004/026859 filed on August 17, 2019 (Publication W02005/020353 A3). Electrode and Separator Structure Figure 2 shows the layers in a negative electrode-separator-positive electrode sandwich structure that can be used in roll or prismatic cell structures. Separator 205 mechanically and electrically separates the negative electrode (components 201 and 203) from the positive electrode (components 207 and 209) while allowing ionic current to flow between the electrodes. The negative electrode includes an electrochemically active layer 201 and an electrode substrate 203. The electrochemically active layer 201 of the zinc negative electrode generally includes zinc oxide and/or zinc metal as the electrochemically active material. Layer 201 may also include other additives or electrochemically active compounds such as calcium zincate, bismuth oxide, aluminum oxide, indium oxide, hydroxyethyl cellulose and dispersants. Zinc negative electrode compositions according to specific embodiments will be described in detail below. The negative electrode substrate 203 should be electrochemically compatible with the negative electrode material 201 .

Great impact

Potassium fluoride can react chemically with zinc, and the reaction is relatively strong.