Zinc air battery. Zinc-air batteries - a breakthrough in energy storage? From batteries to batteries
The new product promises to exceed lithium-ion batteries in energy intensity by three times and at the same time cost half as much.
Note that now zinc-air batteries are produced only in the form of disposable cells or “rechargeable” manually, that is, by changing the cartridge. By the way, this type of battery is safer than lithium-ion batteries, since it does not contain volatile substances and, accordingly, cannot ignite.
The main obstacle to the creation of rechargeable options - that is, batteries - is the rapid degradation of the device: the electrolyte is deactivated, oxidation-reduction reactions slow down and stop altogether after just a few recharge cycles.
To understand why this happens, we must first describe the operating principle of zinc air cells. The battery consists of air and zinc electrodes and electrolyte. During discharge, air coming from outside, with the help of catalysts, forms hydroxyl ions (OH -) in the aqueous electrolyte solution.
They oxidize the zinc electrode. During this reaction, electrons are released, forming a current. When charging the battery, the process goes in the opposite direction: oxygen is produced at the air electrode.
Previously, during the operation of a rechargeable battery, the aqueous electrolyte solution often simply dried out or penetrated too deeply into the pores of the air electrode. In addition, the deposited zinc was distributed unevenly, forming a branched structure, which caused short circuits to occur between the electrodes.
The new product is free of these shortcomings. Special gelling and astringent additives control the moisture and shape of the zinc electrode. In addition, scientists have proposed new catalysts, which also significantly improved the performance of elements.
So far, the best performance of prototypes does not exceed hundreds of recharge cycles (photo by ReVolt).
ReVolt chief executive James McDougall believes that the first products, unlike current prototypes, will recharge up to 200 times, and will soon be able to reach 300-500 cycles. This indicator will allow the element to be used, for example, in cell phones or laptops.
A prototype of the new battery was developed by the Norwegian research foundation SINTEF, and ReVolt is commercializing the product (illustration by ReVolt).
ReVolt also develops zinc-air batteries for electric Vehicle. Such products resemble fuel cells. The zinc suspension in them plays the role of a liquid electrode, while the air electrode consists of a system of tubes.
Electricity is generated by pumping the suspension through the tubes. The resulting zinc oxide is then stored in another compartment. When recharged, it continues along the same path, and the oxide turns back into zinc.
Such batteries can produce more electricity, since the volume of the liquid electrode can be much larger than the volume of the air electrode. McDougall believes that this type of cell will be able to recharge between two and ten thousand times.
Miniature zinc air batteries (galvanic “pills”) with a nominal voltage of 1.4 V are used for reliable and uninterrupted operation of analog and digital hearing aids, sound amplifiers and cochlear implants. The high environmental friendliness of microbatteries and the inability to leak ensure complete safety consumers. Our online store offers you to buy at affordable prices the widest range of high-quality batteries for in-canal, in-ear and behind-the-ear hearing aids.
Benefits of hearing aid batteries
The zinc-air battery body contains a zinc anode, an air electrode and an electrolyte. The catalyst for the oxidation reaction and the formation of electric current is atmospheric oxygen entering through a special membrane in the housing. This battery configuration provides a number of operational advantages:
- compactness and light weight;
- ease of storage and use;
- uniform charge release;
- low self-discharge (from 2% per year);
- long service life.
So that you can promptly replace worn-out batteries with new ones in devices of low, medium and high power, we sell batteries for hearing aids in St. Petersburg in convenient packages of 4, 6 or 8 pcs.
How to buy the right batteries for hearing aids
On our website you can always buy batteries for hearing amplification devices at retail and wholesale from well-known manufacturers Renata, GP, Energizer, Camelion. To correctly select the battery size, use our table, focusing on color protective film and type of device.
Attention! After removing the colored sealing sticker, you must wait a few minutes and only then insert the “pill” into the device. This time is necessary for a sufficient amount of oxygen to get inside the battery and for it to reach full power.Our prices are lower than our competitors because we buy directly from the manufacturer.
The release of compact zinc-air batteries into the mass market can significantly change the situation in the market segment of small-sized autonomous power supplies for laptop computers and digital devices.
Energy problem
and in recent years, the fleet of laptop computers and various digital devices has increased significantly, many of which have only recently appeared on the market. This process has accelerated noticeably due to the increase in popularity mobile phones. In turn, the rapid growth in the number of portable electronic devices 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 amount portable devices nutritional elements is only one side of the problem. Thus, as portable electronic devices develop, the density of the elements and the power of the microprocessors used in them increase; in just three years, the clock frequency of the PDA processors used has increased by an order of magnitude. Tiny monochrome screens are being replaced by color displays with high resolution and increased screen size. 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 these factors, it becomes quite obvious that increasing the energy intensity, power, durability and reliability of the batteries used is one of the most important conditions for ensuring the further development of portable electronic devices.
The problem of renewable autonomous power sources is very acute in the segment of portable PCs. Modern technologies make it possible to create laptops that are practically not inferior in their functionality and performance to full-fledged ones. desktop systems. However, the lack of sufficiently efficient autonomous power sources 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 for full work in mobile conditions this is clearly not enough (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 time battery life portable PCs is a shift from the currently common nickel-metal hydride and lithium-ion batteries to chemical fuel cells 2 . The most promising fuel cells from the point of view of application in portable electronic devices and PCs are fuel cells with low operating temperatures such as PEM (Proton Exchange Membrane) and DMCF (Direct Methanol Fuel Cells). 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 solely in rosy tones. The fact is that there are at least two obstacles to 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, to ensure acceptable rates of chemical reactions in fuel cells with low operating temperatures, it is necessary to use catalysts. Currently, catalysts made of platinum and its alloys are used in PEM and DMCF cells, but 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 direction have 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 portable PCs and electronic devices.
1 This refers to the operating time from a standard battery.
2 More information about fuel cells can be read in the article “Fuel cells: a year of hope”, published in No. 1’2005.
3 PEM cells operating on hydrogen gas are equipped with a built-in converter to produce hydrogen from methanol.
Zinc air elements
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 become familiar with the design and principle of operation of zinc-air elements, even in general terms, we can make a completely unambiguous conclusion that it is more correct to consider them as a separate class of autonomous power sources.
The zinc air cell cell design includes a cathode and anode separated by an alkaline electrolyte and mechanical separators. A gas diffusion electrode (GDE) is used as a cathode, the water-permeable membrane of which allows oxygen to be obtained from atmospheric air circulating through it. The “fuel” is the zinc anode, which is oxidized in the process element operation, and the oxidizing agent is oxygen obtained from atmospheric air entering through the “breathing holes”.
At the cathode, the electroreduction reaction 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 occurs, releasing electrons that return to the cathode through an 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 cell of a zinc-air cell is 1.45 V, which is very close to that of alkaline (alkaline) batteries. If necessary, to get more high voltage power supply, you can combine several series-connected cells into a battery.
Zinc is a fairly common and inexpensive material, so 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 elements are very environmentally friendly products. The materials used for their production do not poison 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 elements, it is worth noting such advantages as low speed self-discharge in the non-activated state and a small change in the voltage value as the discharge progresses (flat discharge curve).
A certain disadvantage of zinc air elements 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 for operation in conditions of relative air humidity of 60%, when the humidity increases to 90%, the service life decreases by approximately 15%.
From batteries to batteries
The easiest option for zinc-air cells to implement is disposable batteries. When creating zinc-air elements of large size and power (for example, intended to power vehicle power plants), zinc anode cassettes can be made replaceable. In this case, to renew the energy reserve, it is enough to remove the cassette with the used electrodes and install a new one in its place. Used electrodes can be restored for reuse using the electrochemical method 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 compact zinc air cells currently on the market are disposable. Disposable small-sized zinc-air batteries are produced by Duracell, Eveready, Varta, Matsushita, GP, as well as the domestic enterprise Energia. The main areas of application for such power sources are hearing aids, portable radios, photographic equipment, etc.
Currently, many companies produce disposable zinc air batteries
A few years ago, AER produced Power Slice zinc air batteries designed for laptop computers. These items were designed for Hewlett-Packard's Omnibook 600 and Omnibook 800 series laptops; 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, a zinc reduction reaction will occur at the anode. However, the practical implementation of such projects for a long time were hampered by serious problems caused by the chemical properties of zinc. Zinc oxide dissolves well in an alkaline electrolyte and, in dissolved form, is distributed throughout the entire volume of the electrolyte, moving away from the anode. Because of this, when charging from an external current source, the geometry of the anode changes significantly: the zinc recovered from zinc oxide is deposited on the surface of the anode in the form of ribbon crystals (dendrites), shaped like long spikes. The dendrites pierce through the separators, causing a short circuit inside the battery.
This problem aggravated by the fact that to increase power, the anodes of zinc-air cells are made from 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, having a negative impact on the performance of the cell.
To date, the greatest success in the field of creating compact zinc-air batteries has been achieved by Zinc Matrix Power (ZMP). ZMP specialists have developed a unique Zinc Matrix technology, which has solved the main problems that arise during battery charging. The essence of this technology is the use of a polymer binder, which ensures unhindered penetration of hydroxide ions, but at the same time blocks the movement of zinc oxide dissolving in the electrolyte. Thanks to the use of 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 a long operating time and high specific energy intensity, at least twice that of the best lithium-ion batteries. The specific energy intensity of zinc-air batteries reaches 240 Wh per 1 kg of weight, and the maximum power is 5000 W/kg.
According to 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 minimum possible thickness of such power supplies is only 3 mm. Experimental prototypes of zinc-air batteries for laptops have an energy capacity of 100 to 200 Wh.
A prototype of a zinc-air battery created by Zinc Matrix Power specialists
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. Moreover, unlike lithium batteries Zinc air cells are much safer.
In conclusion, it is impossible not to mention one important event, which became a symbolic starting point on the path to the commercialization of zinc-air cells: on June 9 last year, Zinc Matrix Power officially announced the signing of a strategic agreement with Intel Corporation. In accordance with the terms of this agreement, ZMP and Intel will combine their development efforts new technology rechargeable batteries for laptop PCs. Among the main goals of this work is to increase the battery life of laptops to 10 hours. According to the current plan, the first models of laptops equipped with zinc-air batteries should appear on sale in 2006.
Long time scope of application zinc air batteries did not go beyond medicine. Their high capacity and long service life (in an inactive state) allowed them to easily occupy the niche of disposable batteries for hearing aids. But in recent years there has been a large increase in interest in this technology among 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 container divided into compartments, on which air oxygen is adsorbed and reduced, as well as special removable cassettes filled with consumables anode, 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.
Air coming from 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
World zinc reserves are estimated to be approximately 1.9 gigatons. If we start global 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 kWh each. For example, it would 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 scheme for recycling waste zinc, are environmentally friendly products. The materials used here do not poison the environment and can be recycled. The reaction product of zinc air batteries (zinc oxide) is also absolutely safe for humans and their environment. It’s not for nothing that zinc oxide is used as the main component in 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 intensity of Zinc-Air reaches 450 Wh/kg, but the theoretical density can be 1350 Wh/kg!
Flaws
Since we don't drive electric vehicles with zinc-air batteries, there are disadvantages. Firstly, it is difficult to make such cells rechargeable with a sufficient number of discharge/charge cycles. During operation of a zinc-air battery, the electrolyte simply dries out or penetrates too deeply 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 gas 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, 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 require no more than 10 minutes. Even the super-fast ones will be able to replenish only 50% of their potential during the same time. Last year, the Korean company Leo Motors already demonstrated ZAI zinc-air batteries on its electric truck.
Swiss technology firm ReVolt is also working on improving the Zinc-Air battery. She proposed special gelling and astringent additives that control the moisture and shape of the zinc electrode, as well as new catalysts that significantly improve the performance of the cells.
However, engineers from both companies failed to overcome the mark of 200 Zinc-Air discharge/charge cycles. Therefore, it is too early to talk about zinc-air cells as electric vehicle batteries.
These elements have the highest density of all modern technologies. The reason for this was the components used in these batteries. These cells use atmospheric oxygen as a cathode reagent, which is reflected in their name. In order for air to react with the zinc anode, small holes are made in the battery body. Potassium hydroxide, which has high conductivity, is used as an electrolyte in these cells.
Originally created as non-rechargeable power supplies, zinc air cells characterized by a long and stable shelf life, at least if they are stored airtight, in an inactive state. In this case, over a year of storage, such elements lose about 2 percent of their capacity. Once air gets into the battery, these batteries won't last more than a month, whether you use them or not.
Some manufacturers have begun to use the same technology in rechargeable cells. Such elements have proven themselves best during long-term operation in low-power devices. The main disadvantage of these elements is their high internal resistance, meaning that to achieve high power, they must be of enormous size. This means the need to create additional battery compartments in laptops, comparable in size to the computer itself.
But it should be noted that they began to receive such use only recently. The first such product is a joint creation of Hewlett-Packard Co. and AER Energy Resources Inc. - PowerSlice XL - showed the imperfection of this technology when used in laptop computers. This battery, created for the HP OmniBook 600 laptop, weighed 3.3 kg - more than the computer itself. She provided only 12 hours of work. Energizer has also begun using this technology in its small button batteries used in hearing aids.
Recharging batteries is also not such an easy task. Chemical processes are very sensitive to electric current supplied to the battery. If the supplied voltage is too low, the battery will send current rather than receive it. If the voltage is too high, unwanted reactions may occur that can damage the element. For example, when the voltage increases, the current will necessarily increase, as a result the battery will overheat. And if you continue to charge the element after it is fully charged, explosive gases may begin to be released in it and even an explosion may occur.
Charging technologies
Modern devices for recharging - it's quite complicated electronic devices with different degrees of protection - both yours and your batteries. In most cases, each type of cell has its own charger. If you use the charger incorrectly, you can damage not only the batteries, but also the device itself, or even the systems powered by the batteries.
There are two operating modes chargers- With constant voltage and with direct current.
The simplest are constant voltage devices. They always produce the same voltage, and supply a current that depends on the battery's charge level (and other environmental factors). As the battery charges, its voltage increases, so the difference between the potential of the charger and the battery decreases. As a result, less current flows through the circuit.
All that is needed for such a device is a transformer (to reduce the charging voltage to the level required by the battery) and a rectifier (to rectify the alternating current into direct current, used to charge the battery). Such simple devices rechargers are used to charge car and ship batteries.
As a rule, lead batteries for sources are charged with similar devices. uninterruptible power supply. In addition, constant voltage devices are also used to recharge lithium-ion cells. Only there circuits have been added to protect the batteries and their owners.
The second type of charger provides a constant current and varies the voltage to provide the required amount of current. Once the voltage reaches full charge, charging stops. (Remember, tension, generated by the element, falls as the discharge progresses). Typically, such devices charge nickel-cadmium and nickel-metal hydride cells.
In addition to the required voltage level, chargers must know how long to recharge the cell. The battery can be damaged if you charge it for too long. Depending on the type of battery and the “intelligence” of the charger, several technologies are used to determine the charging time.
In the most simple cases For this purpose, the voltage generated by the battery is used. The charger monitors the battery voltage and turns off when the battery voltage reaches a threshold level. But this technology is not suitable for all elements. For example, for nickel-cadmium it is not acceptable. In these elements, the discharge curve is close to a straight line, and it can be very difficult to determine the threshold voltage level.
More “sophisticated” chargers determine the charging time based on temperature. That is, the device monitors the temperature of the cell, and turns off, or reduces the charge current, when the battery begins to heat up (which means it is overcharged). Typically, thermometers are built into such batteries that monitor the temperature of the element and transmit the corresponding signal to the charger.
Smart devices use both of these methods. They can switch from a high charge current to a small one, or they can support D.C. using special voltage and temperature sensors.
Standard chargers provide a charge current that is lower than the cell's discharge current. And chargers with a higher current value provide more current than the rated discharge current of the battery. Devices for continuous charging with low current use such a small current that it only prevents the battery from self-discharging (by definition, such devices are used to compensate for self-discharge). Typically, the charging current in such devices is one twentieth or one thirtieth of the rated discharge current of the battery. Modern charging devices can often operate at several charge currents. They use higher currents at first and gradually switch to lower ones as they approach full charge. If you are using a battery that can withstand low-current charging (nickel-cadmium batteries, for example, cannot), then at the end of the charging cycle the device will switch to this mode. Most laptop chargers and cell phones designed so that they can be permanently connected to the elements without causing harm to them.
