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The mass market entry of compact zinc air batteries has the potential to make a significant difference in the small-sized battery pack for laptop computers and digital devices.
Energy problem
and in recent years, the fleet of portable computers and various digital devices has grown significantly, many of which have recently appeared on the market. This process has accelerated markedly due to the increasing popularity of mobile phones. In turn, the rapid growth in the number of portable electronic devices has caused a serious increase in demand for autonomous sources of electricity, in particular for various types of batteries and accumulators.
However, the need to provide a huge number of portable devices with batteries is only one side of the problem. So, with the development of portable electronic devices, the assembly density of the elements and the power of the microprocessors used in them increase - in just three years, the clock frequency of the used PDA processors has increased by an order of magnitude. Tiny monochrome screens are being replaced by high-resolution, larger-screen color displays. All this leads to an increase in energy consumption. In addition, there is a clear trend towards further miniaturization in the field of portable electronics. Taking into account the above factors, it becomes quite obvious that an increase in energy intensity, power, durability and reliability of the used batteries is one of the most important conditions for ensuring the further development of portable electronic devices.
The problem of renewable sources of autonomous power supply is very acute in the segment of portable PCs. Modern technologies make it possible to create laptops that are practically not inferior in their functional equipment and performance to full-fledged desktop systems. However, the lack of sufficiently effective sources of autonomous power supply deprives laptop users of one of the main advantages of this type of computer - mobility. A good indicator for a modern laptop equipped with a lithium-ion battery is a battery life of about 4 hours 1, but this is clearly not enough for full-fledged work in mobile conditions (for example, a flight from Moscow to Tokyo takes about 10 hours, and from Moscow to Los Angeles - almost 15).
One of the options for solving the problem of increasing the battery life of portable PCs is the transition from the now widespread nickel-metal hydride and lithium-ion batteries to chemical fuel cells 2. Low operating temperature fuel cells such as PEM (Proton Exchange Membrane) and DMCF (Direct Methanol Fuel Cells) are the most promising for applications in portable electronic devices and PCs. An aqueous solution of methyl alcohol (methanol) 3 is used as fuel for these elements.
However, at this stage, it would be too optimistic to describe the future of chemical fuel cells exclusively in pink colors. The fact is that at least two obstacles stand in the way of the mass distribution of fuel cells in portable electronic devices. Firstly, methanol is a rather toxic substance, which implies increased requirements for the tightness and reliability of fuel cartridges. Secondly, catalysts must be used to ensure an acceptable rate of passage of chemical reactions in fuel cells with a low operating temperature. Currently, catalysts made from platinum and its alloys are used in PEM and DMCF cells, but the natural reserves of this substance are small and its cost is high. It is theoretically possible to replace platinum with other catalysts, but so far none of the teams engaged in research in this area has been able to find an acceptable alternative. Today, the so-called platinum problem is perhaps the most serious obstacle to the widespread adoption of fuel cells in laptop PCs and electronic devices.
1 This refers to the operating time from the standard battery.
2 Read more about fuel cells in the article "Fuel Cells: A Year of Hope" published in # 1'2005.
3 PEM cells fueled by gaseous hydrogen are equipped with an integrated converter for the production of hydrogen from methanol.
Zinc air cells
Although the authors of a number of publications consider zinc air batteries and accumulators to be one of the subtypes of fuel cells, this is not entirely true. Having familiarized yourself with the device and the principle of operation of zinc-air cells, even in general terms, one can make a completely unambiguous conclusion that it is more correct to consider them as a separate class of autonomous power supplies.
The zinc air cell cell design includes a cathode and an anode, separated by an alkaline electrolyte and mechanical separators. A gas diffusion electrode (GDE) is used as the cathode, the permeable membrane of which allows oxygen to be obtained from the atmospheric air circulating through it. The "fuel" is the zinc anode, which is oxidized during the operation of the cell, and the oxidizing agent is oxygen obtained from the atmospheric air entering through the "breathing holes".
At the cathode, the reaction of electroreduction of oxygen occurs, the products of which are negatively charged hydroxide ions:
O 2 + 2H 2 O + 4e 4OH -.
Hydroxide ions move in the electrolyte to the zinc anode, where the zinc oxidation reaction takes place with the release of electrons, which return to the cathode through the external circuit:
Zn + 4OH - Zn (OH) 4 2– + 2e.
Zn (OH) 4 2– ZnO + 2OH - + H 2 O.
It is quite obvious that zinc air cells do not fall under the classification of chemical fuel cells: firstly, they use a consumable electrode (anode), and secondly, the fuel is initially placed inside the cell, and is not supplied during operation from the outside.
The voltage between the electrodes of one zinc air cell is 1.45 V, which is very close to that of alkaline (alkaline) batteries. If necessary, to obtain a higher supply voltage, several cells connected in series can be combined into a battery.
Zinc is a fairly common and inexpensive material, due to which, when deploying mass production of zinc air cells, manufacturers will not experience problems with raw materials. In addition, even at the initial stage, the cost of such power supplies will be quite competitive.
It is also important that zinc air cells are very environmentally friendly products. The materials used for their production do not pollute the environment and can be reused after recycling. The reaction products of zinc-air elements (water and zinc oxide) are also absolutely safe for humans and the environment - zinc oxide is even used as the main component of baby powder.
Among the operational properties of zinc-air cells, it is worth noting such advantages as a low self-discharge rate in an unactivated state and a small change in the voltage value during discharge (flat discharge curve).
A certain disadvantage of zinc-air cells is the influence of the relative humidity of the incoming air on the characteristics of the element. For example, for a zinc air cell designed to operate at 60% RH, the service life decreases by about 15% as the humidity rises to 90%.
From batteries to rechargeable batteries
Disposable batteries are the easiest zinc air cell option to implement. When creating zinc-air cells of large size and power (for example, intended for powering power plants of vehicles), zinc anode cassettes can be made replaceable. In this case, to renew the energy supply, it is enough to remove the cassette with the spent electrodes and install a new one instead. Used electrodes can be recovered for reuse electrochemically at specialized enterprises.
If we talk about compact batteries suitable for use in portable PCs and electronic devices, then the practical implementation of the option with replaceable zinc anode cassettes is impossible due to the small size of the batteries. This is why most of the compact zinc air cells currently on the market are disposable. Small size single-use zinc-air batteries are produced by Duracell, Eveready, Varta, Matsushita, GP, as well as the domestic company Energia. The main area of application of such power sources is hearing aids, portable radios, photographic equipment, etc.
Many companies now make disposable zinc air batteries
Several years ago, AER produced Power Slice zinc-air batteries for laptop computers. These items were designed for Hewlett-Packard's Omnibook 600 and Omnibook 800 series notebooks; their battery life ranged from 8 to 12 hours.
In principle, there is also the possibility of creating rechargeable zinc-air cells (batteries), in which, when an external current source is connected, the zinc reduction reaction will proceed at the anode. However, the practical implementation of such projects has long been hampered by serious problems associated with the chemical properties of zinc. Zinc oxide dissolves well in an alkaline electrolyte and in dissolved form is distributed throughout the electrolyte volume, moving away from the anode. Because of this, when charging from an external current source, the geometry of the anode changes significantly: zinc oxide recovered from oxide is deposited on the surface of the anode in the form of ribbon crystals (dendrites), similar in shape to long spikes. Dendrites pierce the separators, causing a short circuit inside the battery.
This problem is aggravated by the fact that in order to increase the power, the anodes of the zinc-air cells are made of crushed powdered zinc (this allows to significantly increase the surface area of the electrode). Thus, as the number of charge-discharge cycles increases, the surface area of the anode will gradually decrease, adversely affecting cell performance.
To date, Zinc Matrix Power (ZMP) has achieved the greatest success in compact zinc air batteries. ZMP specialists have developed a unique Zinc Matrix technology, which has solved the main problems arising in the process of battery charging. The essence of this technology is the use of a polymer binder, which ensures the unhindered penetration of hydroxide ions, but at the same time blocks the movement of zinc oxide dissolving in the electrolyte. By using this solution, it is possible to avoid noticeable changes in the shape and surface area of the anode for at least 100 charge-discharge cycles.
The advantages of zinc-air batteries are long operating time and high specific energy consumption, at least twice as high as those of the best lithium-ion batteries. The specific energy consumption of zinc-air batteries reaches 240 Wh per 1 kg of weight, and the maximum power is 5000 W / kg.
According to the ZMP developers, today it is possible to create zinc-air batteries for portable electronic devices (mobile phones, digital players, etc.) with an energy capacity of about 20 Wh. The smallest possible thickness of such power supplies is only 3 mm. Experimental prototypes of zinc-air batteries for notebooks have an energy capacity of 100 to 200 Wh.
Zinc Air Prototype Battery by Zinc Matrix Power
Another important advantage of zinc air batteries is the complete absence of the so-called memory effect. Unlike other types of batteries, zinc air cells can be recharged at any charge level without compromising their energy capacity. In addition, zinc air cells are much safer than lithium batteries.
In conclusion, one cannot fail to mention one important event that became a symbolic starting point for the commercialization of zinc air cells: on June 9 of last year, Zinc Matrix Power officially announced the signing of a strategic agreement with Intel Corporation. Subject to the terms of this agreement, ZMP and Intel will join forces to develop a new laptop battery technology. Among the main goals of these works is to increase the battery life of laptops up to 10 hours. According to the existing plan, the first models of notebooks equipped with zinc-air batteries should go on sale in 2006.
Long time scope zinc air batteries did not go beyond medicine. Their high capacity and long (inactive) lifespan have allowed them to seamlessly occupy the niche of disposable hearing aid batteries. But in recent years, there has been a great increase in interest in this technology from automakers. Some believe that an alternative to lithium has been found. Is it so?
A zinc-air battery for an electric vehicle can be arranged as follows: electrodes are inserted into a compartment divided into compartments, on which air oxygen is adsorbed and reduced, as well as special removable cassettes filled with anode consumable material, in this case, zinc granules. A separator is placed between the negative and positive electrodes. An aqueous solution of potassium hydroxide or a solution of zinc chloride can be used as an electrolyte.
The air entering from the outside with the help of catalysts forms hydroxyl ions in the aqueous electrolyte solution, which oxidize the zinc electrode. During this reaction, electrons are released, forming an electric current.
Advantages
According to some estimates, world reserves of zinc are about 1.9 gigatons. If we start the world production of zinc metal now, then in a couple of years it will be possible to assemble a billion zinc-air batteries with a capacity of 10 kW * h each. For example, it will take more than 180 years to create the same amount under current lithium mining conditions. The availability of zinc will also reduce the price of batteries.
It is also very important that zinc air cells, having a transparent recycling scheme for waste zinc, are environmentally friendly products. The materials used here do not pollute the environment and can be recycled. The reaction product of zinc air cells (zinc oxide) is also absolutely safe for humans and their environment. It is not for nothing that zinc oxide is used as the main component for baby powder.
The main advantage, thanks to which electric vehicle manufacturers look at this technology with hope, is the high energy density (2-3 times higher than that of li-ion). Already, the energy consumption of Zinc-Air reaches 450 W * h / kg, but the theoretical density can be 1350 W * h / kg!
Flaws
Since we do not drive electric vehicles with zinc air batteries, then there are also disadvantages. First, it is difficult to make such cells rechargeable with a sufficient number of discharge / charge cycles. During the operation of the zinc air battery, the electrolyte simply dries out, or penetrates too deep into the pores of the air electrode. And since the deposited zinc is distributed unevenly, forming a branched structure, short circuits often occur between the electrodes.
Scientists are trying to find a way out. The American company ZAI solved this problem by simply replacing the electrolyte and adding fresh zinc cartridges. Naturally, this will require a developed infrastructure of filling stations, where the oxidized active material in the anode cassette will be replaced with fresh zinc.
And although the economic component of the project has not yet been worked out, the manufacturers claim that the cost of such "charging" will be significantly lower than refueling a car with an internal combustion engine. In addition, the process of changing the active material will take no more than 10 minutes. Even superfast ones will be able to replenish only 50% of their potential during the same time. Last year, Korean company Leo Motors already demonstrated ZAI zinc air batteries on its electric truck.
Electrochemical energy storage technologies are advancing rapidly. NantEnergy offers a low cost zinc-air energy accumulator.
NantEnergy, led by Californian billionaire Patrick Soon-Shiong, has unveiled the Zinc-Air Battery, which costs significantly less than its lithium-ion counterparts.
Zinc-air energy accumulator
The battery, "protected by hundreds of patents", is intended for use in energy storage systems in the power industry. According to NantEnergy, the cost is below $ 100 per kilowatt hour.
The device of the zinc-air battery is simple. When charged, electricity converts zinc oxide into zinc and oxygen. During the discharge phase in the cell, zinc is oxidized by air. One battery, enclosed in a plastic case, is not much larger than a briefcase.
Zinc is not a rare metal, and the resource constraints discussed in relation to lithium-ion batteries are not affected by zinc-air batteries. In addition, the latter practically do not contain elements harmful to the environment, and zinc is very easily recyclable for secondary use.
It is important to note that the NantEnergy device is not a prototype, but a production model that has been tested “in thousands of different locations” over the past six years. These batteries have provided power to "over 200,000 people in Asia and Africa and have been used in over 1,000 cell towers around the world."
Such a low cost of the energy storage system will make it possible to "transform the electrical grid into a fully carbon-free system operating around the clock," that is, based entirely on renewable energy sources.
Zinc-air batteries are not new, they were invented in the 19th century and have been widely used since the 30s of the last century. The main area of application of these power sources is hearing aids, portable radios, photographic equipment ... A specific scientific and technical problem due to the chemical properties of zinc was the creation of rechargeable batteries. Apparently, this problem has been largely overcome today. NantEnergy has achieved that the battery can repeat the charge and discharge cycle over 1000 times without degrading performance.
Other parameters indicated by the company include 72 hours of autonomy and 20 years of system life.
There are, of course, questions about the number of cycles and other characteristics that need to be clarified. However, some energy storage experts believe in technology. In a GTM survey last December, eight percent of respondents cited zinc batteries as a technology that could replace lithium-ion in energy storage systems.
Earlier, the head of Tesla, Elon Musk, reported that the cost of lithium-ion cells (cells) produced by his company could fall below $ 100 / kW * h this year.
We often hear that the spread of variable renewable energy sources, solar and wind energy, is allegedly slowed down (will slow down) due to the lack of cheap energy storage technologies.
This, of course, is not the case, since energy storage is only one of the tools for increasing the maneuverability (flexibility) of the power system, but not the only tool. In addition, as we can see, electrochemical energy storage technologies are developing rapidly. published
If you have any questions on this topic, ask them to the specialists and readers of our project.
The invention relates to the field of primary zinc-air chemical current sources (VTsKhIT) and can be used as stand-alone power sources. According to the invention, VTsKhIT with a liquid alkaline electrolyte, refueled in VTSKhIT immediately after manufacture or immediately before use, contains a housing with a cover equipped with positive and negative current-carrying terminals and a filling hole closed with a plug, one or more gaseous diffusion cathodes electrically connected to the positive terminal and equipped with gas chambers with a system of "breathing" holes, a zinc anode in the form of a briquette of zinc powder, connected to the negative terminal, and an interelectrode separator made of a porous dielectric material, while the anode is made of several flat porous briquettes, placed with a gap relative to each other , electrically connected in parallel, while the planes of the briquettes are installed in the VTsKhIT perpendicular to the surface of the cathodes. Anode briquettes can be made by dry pressing of zinc powders and an expander swelling in an electrolyte with an effort providing the maximum density of briquettes with a minimum of 10–20% residual porosity, and wrapped in an interelectrode separator. Each anode briquette with a separator is placed in the seats of two cups made of corrugated and perforated polymeric material, while a cavity is formed between the bottom of the cup and the surface of the briquette, the direction of the corrugations at the bottom of the cup is at an angle to the longitudinal axis. The volume of electrolyte charged in VTsKhIT is in relation to the total mass of zinc in the anode as 0.4 ÷ 0.6 cm 3 / g. The physical parameters of the "breathing" holes (section, length) are selected based on the value of the limiting current, which is 3-4 times the nominal discharge current. A capillary matrix made of a highly porous elastic hydrophilic material resistant in an alkaline electrolyte can be placed in the gaps between the briquettes and the cathodes, the pore size of which is larger than the pore size in the discharged anode briquette, and the total pore volume is greater than the volume of the electrolyte charged in the VTSKhIT. The cathode adheres tightly to the capillary matrix and is made by pressing a partially hydrophobized mixture of powders of technical carbon and activated carbon onto a mesh. The technical result of the invention is to increase the utilization rate of the active mass. 6 c.p. f-ly, 2 dwg.
Drawings for RF patent 2349991
The invention relates to the field of primary zinc-air chemical current sources (VTsKhIT) and can be used as stand-alone power supplies.
Known primary VTsKhIT containing a positive electrode (cathode), made by pressing briquettes from powders of carbon black (soot, graphite) and manganese dioxide with an addition to the mixture of alkaline electrolyte (Battery "Liman", Specifications TU 16-729.374-82, ILEV. 563212.003 THAT). The disadvantage of this known VTsKhIT is the low current density in a continuous discharge mode.
Of the known VTSKHIT, the closest in technical essence and the achieved technical result is VTSKHIT with a liquid alkaline electrolyte, charged into the cell immediately after manufacture or immediately before use, containing a housing with a lid equipped with positive and negative current-carrying terminals and a filling hole closed with a plug, one or several gaseous diffusion cathodes hermetically mounted into the cell body, electrically connected to the positive terminal, equipped with gas chambers and a system of "breathing" holes, a zinc anode in the form of a zinc powder briquette connected to the negative terminal, and an interelectrode separator made of porous dielectric material (see http://www.itpower.co.uk/investire/zmcrep/pdf: WP Report "Investigation on Storage Technologies for Intermittent Renewable Energies", Storage Technology Report, WPST9-Metal-air systems. Materials 2002. ). The disadvantages of this VTsKhIT are:
The limitation on the thickness (or mass) of the anode briquette, which, after reaching a certain value, leads to the appearance of equalizing currents inside the anode briquette, which, in addition to the main discharge current of the cell, lead to additional dissolution of zinc in the frontal zone of the anode, and electrochemical deposition of the same amount of zinc in deep or its back layers. In the zone of zinc deposition, the porosity of the anode decreases and the specific content of the electrolyte there decreases. This phenomenon leads to the passivation of zinc in the deep layers of the anode and the shutdown of part of the sections of the anode material from the operation of the element;
Inefficient use of the anode material (zinc) in the negative electrode due to the use of powdered zinc with a large specific surface area. Such powders are characterized by increased self-discharge, which, over a long operating time (thousands of hours), leads to an unproductive loss of a significant (up to 30%) amount of the active anode material.
The technical result of the invention is to increase the utilization rate of the active mass and increase, due to this, the specific capacity of VTsKhIT.
The specified technical result is achieved by the fact that a zinc-air primary chemical current source (VTsKhIT) with a liquid alkaline electrolyte, refueled in VTsKhIT immediately after manufacture or immediately before use, contains a housing with a lid equipped with positive and negative current-carrying terminals and a filling hole closed with a plug , one or more, gas diffusion cathodes, electrically connected to the positive terminal and equipped with gas chambers with a system of "breathing" holes, a zinc anode in the form of a zinc powder briquette connected to the negative terminal, and an interelectrode separator made of a porous dielectric material, while the anode is made of several flat porous briquettes, placed with a gap relative to each other, electrically connected in parallel, while the planes of the briquettes are installed in the VTsKhIT perpendicular to the surface of the cathodes. Such implementation of VTsKhIT allows to increase the utilization factor of the active mass and the specific capacity.
It is advisable that the anode briquettes were made by dry pressing of zinc powders and an expander swelling in the electrolyte with an effort that ensures the maximum density of briquettes with a minimum of 10–20% residual porosity, and wrapped in an interelectrode separator. With such a manufacture of briquettes, it is possible to limit the flow of electrolyte into the depth of the briquette and, thus, to reduce the corrosion of zinc during the operation of the cell. The surface layers of zinc in the briquettes remain accessible for the discharge processes of the operating element. As the surface layers of zinc in the anode briquettes are triggered due to swelling in the electrolyte of the expander, the porosity of the briquettes in this zone increases. The increase in porosity contributes to the further penetration of the electrolyte deep into the briquettes and the normal passage of the anode discharge process. The use of a separator around the briquette prevents coloring of the anode briquettes, which is possible when the expander swells.
It is advisable that each anode briquette with a separator was placed in the seats of two cups made of corrugated and perforated polymeric material, while a cavity is formed between the bottom of the cup and the surface of the briquette, the direction of the corrugations at the bottom of the cup is at an angle to the longitudinal axis of the cup. Such an arrangement of briquettes in VTsKhIT contributes to the preservation of sufficient ionic conductivity of the electrolyte along the briquettes during the entire period of the anode discharge. This conductivity eliminates or sharply reduces the effect of the action of equalizing currents in briquettes and contributes to the almost complete use of zinc in the anode during the operation of VTsKhIT.
It is advisable that the volume of electrolyte charged in the VTsKhIT was in relation to the total mass of zinc in the anode as 0.4 ÷ 0.6 cm 3 / g. This ratio between electrolyte and zinc, established in practice, ensures the possibility of maximum use of the volume of VCHIT or the achievement of maximum capacity.
It is advisable that the physical parameters of the "breathing" holes (section, length), providing the rated discharge current, be determined as (1 / 3-1 / 4) of the value of the limiting discharge current. This ratio is determined by the fact that the value of the discharge current, in addition to the load of the cell, depends on the amount of oxygen entering the operating cell. With a lack of air at the cathode, the limiting current is realized, when, at a constant electrical load, the discharge current and the voltage of the VTsKhIT simultaneously decrease. Excessive air flow into the element does not lead to an increase in the VTsKhIT voltage, but increases the mass transfer of the element with the environment. In this case, either the electrolyte may dry out if there is dry air around the cell, and the VTsKhIT breaks down, or excessive absorption of atmospheric moisture by the electrolyte if there is humid air around, which will cause the electrolyte to leak from the cell. Both cases are not standard for VTsKhIT. The measure of the amount of air entering the VTsKhIT is the value of the limiting current, which is determined by the parameters of the "breathing" holes (section, length). In practice, by changing the parameters of the "breathing" holes, the value of the limiting current is selected, which should be 3-4 times higher than the nominal discharge current of the VTsKhIT.
A variant of VTsKhIT is a variant in which instead of cups made of perforated and corrugated film material, a capillary matrix made of highly porous elastic hydrophilic material resistant to alkaline electrolyte was placed between the briquettes and cathodes. The capillary matrix should have a pore size larger than the pore size in the discharged anode briquette, and the total pore volume should be larger than the volume of the electrolyte charged to the VTsKhIT. If these conditions are met, the presence of electrolyte in the capillary (electrolyte) matrix will be ensured in an amount that ensures high conductivity of the electrolyte at any stage of the VCHIT discharge and the optimal specific amount of electrolyte in the anode briquettes (0.4-0.6 cm 3 / g).
The main feature of the use of a capillary matrix is the possibility of installing cathodes in the cell without hermetically separating their gas chambers from the anodes. The hydrophilic electrolyte matrix due to the forces of capillary pressure (in the hydrophilic matrix the pressure is negative), the entire electrolyte is contained in the matrix, does not flow out of it and, thus, ensures its absence in the gas chambers of the cathodes and the possibility of free flow of air into the VCHIT.
The absence of free electrolyte in the anode chamber of the cell allows the use of cathodes in which there is no liquid-blocking hydrophobic layer. Such a cathode has only an active layer, on which the electrochemical reaction of air oxygen reduction takes place. It is advisable that the cathode adheres tightly to the capillary matrix and is made by pressing a partially hydrophobized mixture of powders of technical carbon and activated carbon onto a grid. Electrodes of this type have a smaller thickness, which makes it possible to increase the volume of the anode chamber and, consequently, increase the capacity of the VTsKhIT.
The analysis of the prior art showed that the claimed set of essential features set forth in the claims is unknown. This allows us to conclude that it meets the "novelty" criterion.
To check the compliance of the claimed invention with the criterion of "inventive step", an additional search was carried out for known technical solutions in order to identify features that coincide with the distinguishing features of the prototype of the claimed technical solution. It was found that the claimed technical solution does not follow explicitly from the prior art. Therefore, the claimed invention meets the "inventive step" criterion.
The essence of the invention is illustrated by drawings and a description of the design of the VTsKhIT.
Figure 1 shows the design of the VTsKhIT, made according to the proposed invention.
Figure 2 shows a variation of the design of VTsKhIT with a capillary matrix.
Cathodes (2) are hermetically mounted in the cell body (1) in its opposite side walls. The design of the cathodes is also similar to the prototype cathodes. The cathodes in the cell are located with an active layer inside the cell. They are mounted in the cell body in such a way that chambers (16) are formed between the body wall and the cathode. These chambers are necessary for even distribution of air over the entire surface of the cathode. Each air chamber communicates with the surrounding atmosphere by at least two "breathing" holes (13) located in its lower and upper parts. Spacers (4) are installed between the cathode and the wall of the element in the air chamber, which prevent the cathode from bending due to internal pressure. The active layer of the cathode is protected from contact with the anode by an interelectrode separator (3). Anode briquettes (6), made by dry pressing of zinc powders and an expander (starch, carboxymethyl cellulose, carbopol), are equipped with current collectors (15), which are located in the middle of each briquette. Each briquette is wrapped in a porous separator (7) made of a dielectric material such as non-woven polypropylene. Anode briquettes are installed in the internal volume of the element vertically with gaps between themselves and are located perpendicular to the surfaces of the cathodes. Each anode briquette (6) with a separator (7) is placed in two cups (14) made of corrugated and perforated polymeric material, which have a seating surface for placing briquettes in them and an additional cavity that creates a chamber between its bottom and the surface of the briquette; the direction of the corrugations on the bottom of the cup is at an angle (12) (approximately 45 °) to its longitudinal axis. The depth of the cavity of the cup ensures tight packing of the anode briquettes in the cups into the internal volume of the element (5).
From above, the anode briquettes are covered with an inner cover (8). The entire element is equipped with a cover (9), on which there are current leads from the electrodes, a filling plug (11) and a liquid electrolyte level damper (10). The cover (9) is hermetically mounted on the cell body. The design of the element provides the possibility of its backup use. VTSKHIT is made dry-charged and is driven by filling it through a filling plug with a liquid alkaline electrolyte. Without electrolyte with sealed "breathing" holes, the cell can be stored without loss of quality for several years. The VTsKhIT works as follows. After filling the cell through the filling hole, closed with a stopper (11), with liquid alkaline electrolyte and de-preserving it by opening the "breathing" holes, a voltage will appear at the output terminals of the cell.
When the cell is turned on for discharge, electrochemical reactions will occur on the electrodes, which are described in the introduction to this invention. Air from the environment through the "breathing" holes first enters the gas chamber of the cathode, then, due to diffusion through the pores of the hydrophobic liquid-blocking layer, it penetrates into its active layer, where oxygen is ionized. Due to the consumption of oxygen, a heavy component of air, the composition of the air changes and its density decreases. Due to this, a convective air flow from bottom to top is created in the gas chamber of the cathode. The exhaust air comes out through the upper "breathing" opening, and to replace it, a portion of fresh air is sucked into the chamber through the lower "breathing" opening. Thus, the consumption of oxygen at the cathode ensures a continuous supply of new portions of air to the electrochemical reaction zone. Another system of "breathing" holes is possible, which uses the cell cover or the upper level of the cell body. In this system, fresh air is sucked into the cell through a tube located in the gas chamber of the cathode and connecting an opening in the cover or in the upper part of the housing with the lower level of the gas chamber of the cathode. Outlets are located either in the cover or in the upper part of the housing. The convective movement of air in the cathode chamber in this system will be similar to the previous one. The intensity of the convective air flow is determined by the rate of oxygen absorption by the electrochemical reaction of the cell discharge, i.e. the magnitude of the discharge current. Thus, an automatic link is provided between the discharge current and the magnitude of the convective air flow. The degree of this relationship is determined by the flow resistance (diameter and length) of the "breathing" holes. Insufficient cross-section of these holes creates a deceleration of the convective air flow and will limit the amount of oxygen or, equivalently, limit the value of the discharge current of the cell. If the cross-section of the holes is greater than the nominal, the value of the discharge current will not increase, but the intensity of the convective flow will increase, and with it the intensity of mass exchange of the element with the environment. As a result, the volume of electrolyte in the cell may change. It will either increase if the ambient humidity is above the average (calculated) value, or decrease in a drier atmosphere. The physical parameters of the "breathing" holes (section, length) are selected empirically based on the value of the limiting current, which should be 3-4 times the nominal discharge current.
The value of the limiting current is determined such that the voltage of the element, which is under the discharge to a constant resistance, does not stabilize, but decreases monotonically.
At the anode, zinc particles that are closest to the cathodes are oxidized. Simultaneously with this process, the expander particles interact with the electrolyte. The expander swells in the electrolyte and increases in volume. The swollen expander particles push the adjacent zinc particles and increase the local electrolyte content, thus reducing the negative effect of the accumulating discharge product - zinc oxide. Zinc oxide precipitates from the electrolyte solution in the discharge zone when it is oversaturated with zincates. Due to the fact that the anode briquettes were pressed by pressure until they reach their natural maximum density, the inner regions of the anode briquettes are practically inaccessible to the electrolyte. These "dry" areas do not interact with the electrolyte and therefore do not undergo corrosive processes. An additional effect of reducing corrosion processes is the use of zinc powder obtained by spraying the melt. Such powders do not have a large specific surface area and, therefore, the rate of their interaction with the electrolyte is greatly underestimated. The discharge processes of the anodes undergo their outer layers, which, due to swelling of the expander in the electrolyte, increase in volume and gradually fill the cavities of the cups. As the discharge zone of the anode deepens, the resistance of the electrolyte in the pores of the discharged zone increases. Parallel to the streamlines passing through the pores of the discharged zone, there are gaps between the briquettes filled with free electrolyte. In this case, the ionic discharge current is distributed over the anode briquettes in such a way that the external surfaces of the anode briquettes are connected to the discharge process and their discharge flows from the outer surfaces into the briquettes. The thickness of the briquettes is less than their overall dimensions and therefore the discharge occurs from the periphery to the center of the briquettes. This effect provides the conditions for the complete discharge of zinc in briquettes. The increasing anode briquettes in the limit fill the entire volume of the cups. The inclined arrangement of the corrugations to the axis of the cups creates a guaranteed minimum clearance equal to twice the height of the corrugation between adjacent cups. The stiffness of the corrugated bottom of the cups is sufficient to maintain a minimum gap between the briquettes until the zinc is completely discharged in the briquettes. The conductivity of the electrolyte in this gap maintains the discharge mode of the briquettes from the front to the center. The upward expansion of the anode briquettes is limited by the inner cover (8). This cover keeps free space in the upper part of the cell, in which an additional volume of electrolyte can accumulate, formed, for example, due to the absorption of water vapor from the atmosphere by the electrolyte, if the latter has for a long time a relative humidity higher than the calculated one for the areas of intended use of the cells.
A type of element design, in which anode briquettes with a separator are placed in cups, is a design with capillary matrices shown in Fig. 2, in which a capillary matrix is placed in the gaps between the briquettes and cathodes, made of a highly porous elastic hydrophilic material stable in an alkaline electrolyte, size whose pores are larger than the pore size in the discharged briquette, and the pore volume is larger than the volume of the electrolyte charged into the cell. Capillary matrices (14) are placed between the anode briquettes (6) and hold the entire volume of electrolyte required for the cell to operate.
The electrolyte in the matrix is retained by capillary forces. The use of a capillary matrix increases the reliability of the current source, since in this case the fundamental possibility of filling the gas chamber with electrolyte is eliminated, which can enter the gas chamber of the cathode due to a breach of the tightness of the cathode embedment unit in the element. When the gas chamber is filled with electrolyte, its "breathing" openings are blocked and air access to the cathode stops. The absence of oxygen in the cathode stops the electrochemical process of current generation and thus turns off the cell. The matrix material is non-conductive and does not chemically interact with the electrolyte. It also enables the matrix to deform elastically under the action of a compressive force. The pore size in the matrix should be such that, on the one hand, the volume of electrolyte in the upper part of the cell should be maintained in an amount that allows the discharge of adjacent sections of zinc briquettes, on the other hand, the size of its pores should be large pores that are formed in the discharged zone anode briquette. If these conditions are met, the ionic conductivity of the system is preserved: the capillary matrix is an anode briquette at any degree of discharge of the briquettes. The anode briquettes expanding during the discharge squeeze the capillary matrices and squeeze the electrolyte from the matrices into the briquettes. This process maintains the constancy of the electrolyte volume in the joint porous matrix-briquette system. When using a capillary matrix, the cathode can be freely (not hermetically sealed) installed in the cell body, while ensuring its tight fit to the matrix. Using the property of the capillary matrix to absorb the electrolyte, it is possible to use a cathode tightly adjacent to the capillary matrix, made by pressing a partially hydrophobized mixture of powders of technical carbon and activated carbon onto a mesh. Such an electrode is easier to manufacture and no less active during the operation of the element. The absence of electrolyte leakage provides a physical phenomenon - capillary pressure, which has a negative value for a hydrophilic matrix. The use of capillary arrays eliminates the need for corrugated and perforated cups. During the discharge of the cell, the electrolyte is kept by the matrix all the time in accordance with the physical law of capillary equilibrium of the system of porous media and gives it to the anode briquettes in proportion to their degree of discharge (the degree of increase in volume). The resistance of the electrolyte in the highly porous matrix is lower than the resistance in the pores of the discharged zone of the anodes. For this reason, the discharge ion current is distributed over the anode briquettes in the same way as in cells with free electrolyte, when the external surfaces of the anode briquettes are connected to the discharge process and their discharge flows from the outer surfaces into the briquettes. The thickness of the briquettes is chosen relatively small, therefore, their discharge occurs almost completely with a high efficiency of zinc utilization (KPI). The practically achieved values of KPI are at the level of 0.92-0.95. The use of all the design features of the high capacity zinc air cell described in this invention allows specific energy levels of up to 500 Wh / kg and 1100 Wh / L to be achieved.
Based on the foregoing, it can be concluded that the declared VTSHIT can be implemented in practice with the achievement of the declared technical result, i.e. it meets the criterion "industrial applicability".
CLAIM
1. Zinc-air primary chemical current source (VTsKhIT) with a liquid alkaline electrolyte, refueled in VTsKhIT immediately after manufacture or immediately before use, containing a housing with a lid equipped with positive and negative current-carrying terminals and a filling hole closed with a plug, one or more, gas diffusion cathodes electrically connected to the positive terminal and equipped with gas chambers with a system of "breathing" holes, a zinc anode in the form of a briquette of zinc powder connected to the negative terminal, and an interelectrode separator made of a porous dielectric material, characterized in that the anode is made of several flat porous briquettes, placed with a gap relative to each other, electrically connected in parallel, while the planes of the briquettes are installed in VTsKhIT perpendicular to the surface of the cathodes.
2. VTsKhIT according to claim 1, characterized in that the anode briquettes are made by dry pressing of zinc powders and an expander swelling in the electrolyte with an effort providing the maximum density of briquettes with a minimum 10% -20% residual porosity, and wrapped in an interelectrode separator.
3. VTSKHIT according to claim 1, characterized in that each anode briquette with a separator is placed in the seats of two cups made of corrugated and perforated polymeric material, while a cavity is formed between the bottom of the cup and the surface of the briquette, the direction of the corrugations at the bottom of the cup is at an angle to its longitudinal axis.
4. VTsKhIT according to claim 1, characterized in that the volume of electrolyte charged in VTsKhIT is in relation to the total mass of zinc in the anode as 0.4 ÷ 0.6 cm 3 / g.
5. VTsKhIT according to claim 1, characterized in that the physical parameters of the "breathing" holes (section, length) are selected based on the value of the limiting current, which is 3-4 times the nominal discharge current.
6. VTsKhIT according to claim 1, characterized in that a capillary matrix made of a highly porous, elastic, resistant in an alkaline electrolyte, hydrophilic material is placed in the gaps between the briquettes and the cathodes, the pore size of which is larger than the pore size in the discharged anode briquette, and the total volume pores are larger than the volume of electrolyte charged to the VTsKhIT.
7. VTsKhIT according to claim 1 or 6, characterized in that the cathode adheres tightly to the capillary matrix and is made by pressing on the mesh a partially hydrophobized mixture of powders of technical carbon and activated carbon.
