Air-zinc element. Zinc-air batteries - a breakthrough in energy storage? Do-it-yourself zinc air battery
Battery technology has improved significantly over the past 10 years, increasing the value of hearing aids and improving their performance. Ever since the digital processor dominated the CA market, the battery industry has exploded.The number of people using zinc-air batteries as a power source for hearing aids is increasing day by day. These batteries are environmentally friendly and, thanks to increased capacity They last much longer than other types of batteries. However, it is difficult to name the exact service life of the element used, it depends on many factors. At certain points, users have questions and complaints.<Радуга Звуков>will try to give an exhaustive answer to a very important question: so what does the battery life depend on?
ADVANTAGES...
For many years, mercury-oxide batteries have been the main source of power for hearing aids. However, in the mid 90s. it became clear that they were completely outdated. First, they contained mercury - an extremely harmful substance. Secondly, digital SA appeared and began to rapidly conquer the market, presenting fundamentally different requirements for the characteristics of batteries.
Mercury-oxide technology has been replaced by air-zinc technology. It is unique in that as one of the components (cathode) chemical element Power supply uses oxygen from the surrounding air, which enters through special holes. By removing mercury or silver oxide, which until now served as the cathode, from the battery case, more space was freed up for zinc powder. That's why zinc air battery is more energy intensive when compared different types batteries of the same size. With this ingenious solution, the zinc-air battery will remain unrivaled as long as its capacity is limited by the tiny volume of today's miniature SAs.
On the positive side of the battery, there are one or more holes (depending on its size) into which air enters. The chemical reaction during which the current is generated proceeds quite quickly and is completely completed within two to three months, even without loading the battery. Therefore, during the manufacturing process, these holes are covered with a protective film.
To prepare for work, it is necessary to remove the sticker and allow time for the active substance to saturate with oxygen (from 3 to 5 minutes). If you start using the battery immediately after opening, then activation will happen only in the surface layer of the substance, which will significantly affect the service life.
The size of the battery plays an important role. The larger it is, the more reserves of the active substance in it, and, therefore, the more accumulated energy. Therefore, a 675 size battery has the largest capacity, and a size 5 battery has the smallest. The battery capacity also depends on the manufacturer. For example, for batteries of size 675, it can vary from 440 mAh to 460 mAh.
AND FEATURES
First, the voltage supplied by a battery depends on how long it has been in use, or more specifically, on the degree to which it has been discharged. A new zinc-air battery can deliver up to 1.4 volts, but only for a short time. Then the voltage drops to 1.25 V, and holds for a long time. And at the end of the battery life, the voltage drops sharply to a value of less than 1 V.
Secondly, zinc-air batteries function better the warmer it is around. In this case, of course, you should not exceed the maximum temperature set for this type of battery. This applies to all batteries. But the peculiarity of zinc-air batteries is that their performance also depends on the humidity of the air. The chemical processes occurring in it depend on the presence of a certain amount of moisture. To put it simply, the hotter and more humid the better (this only applies to CA batteries!). And the fact that humidity has a negative effect on other components of the auditory system is another matter.
Thirdly, internal resistance batteries depends on a number of factors: temperature, humidity, operating time and technology used by the manufacturer. The higher the temperature and humidity, the lower the impedance, which has a beneficial effect on the functioning of the auditory system. The new 675th battery has an internal resistance of 1-2 ohms. However, at the end of the service life, this value can increase to 10 ohms, and for the 13th battery - up to 20 ohms. Depending on the manufacturer, this value can vary significantly, which creates problems when the maximum power specified in the data sheet is required.
If the critical current draw is exceeded, the final stage or the entire hearing system is switched off so that the battery can recover. If after<дыхательной паузы>the battery again begins to give current in an amount sufficient for operation, the SA is turned on again. In many hearing systems, reactivation is accompanied by sound signal, the same one that notifies you of a voltage drop in the battery. That is, in a situation where the CA turns off due to high current consumption, an alarm sounds when it is turned on again, although the battery may be completely new. This situation usually occurs when the hearing aid is receiving a very high input SPL and the hearing aid is set to full power.
Factors affecting service life
One of the main tasks facing batteries is to provide a constant supply of current throughout the life of the battery.
Battery life is primarily determined by the type of CA you use. As a rule, analog devices consume more current than digital ones, and powerful devices consume more than low-power devices. Typical current consumption values for medium power devices are from 0.8 to 1.5 mA, and for high-power and heavy-duty devices - from 2 to 8 mA.
Digital HAs are generally more economical than analog HAs of the same power. However, they have one disadvantage - at the moment of switching programs or automatic operation of complex signal processing functions (noise suppression, speech recognition, etc.), these devices consume significantly more current than in normal mode. The energy demand can rise and fall depending on what signal processing function it performs. this moment digital circuitry, and even whether correction of a patient's hearing loss requires different amplification for different SPL inputs.
The ambient acoustic situation also affects battery life. In a quiet environment, the acoustic signal level is usually low - about 30-40 dB. In this case, the signal entering the SA is also small. In a noisy environment, such as in the subway, train, at work or in a noisy street, the acoustic signal level can reach 90 dB or more (a jackhammer is about 110 dB). This leads to an increase in the level of the output signal of the SA and, accordingly, an increased current of its consumption. At the same time, the settings of the device also begin to affect - with a greater gain, the current consumption is also greater. Typically, ambient noise is concentrated in the low-frequency range, therefore, with greater suppression of the low-frequency range by the tone control, the current consumption also decreases.
The current consumption of medium-power devices does not depend too much on the level of the incoming signal, but for high-power and super-power SA the difference is quite large. For example, with an incoming signal with an intensity of 60 dB (at which the current consumption of the SA is normalized), the current strength is 2-3 mA. With an input signal of 90 dB (and the same SA settings), the current increases to 15-20 mA.
Battery Life Estimation Method
Typically, the battery life is estimated taking into account its nominal capacity and the estimated current consumption of the device, specified in the technical data (passport) for the device. Let's take a typical case: a 675 zinc-air battery with a typical capacity of 460 mAh.
When used in a medium power device with a current consumption of 1.4mA, the theoretical service life will be 460/1.4=328 hours. When wearing the device for 10 hours a day, this means more than a month of device operation (328/10=32.8).
When a powerful device is powered in a quiet environment (current consumption 2 mA), the service life will be 230 hours, that is, about three weeks with a 10-hour wear. But, if the environment is noisy, then the current consumption can reach 15-20 mA (depending on the type of device). In this mode, the service life will be 460/20=23 hours, i.e. less than 3 days. Of course, no one walks in such an environment for 10 hours, and the real mode will be mixed in terms of current consumption. So that given example simply illustrates the calculation methodology by giving extreme life values. Usually the battery life in a powerful device is in the range of two to three weeks.
Use hearing aid batteries (labeled or labeled) from well-known power supply manufacturers (GP, Renata, Energizer, Varta, Panasonic, Duracell Activair, Rayovac).
Don't break protective film batteries (do not open) until they are installed in the hearing aid.
Store batteries in blisters at room temperature and normal humidity. A wish<сберечь>a longer battery in the refrigerator can lead to the exact opposite result - the CA with a new battery will not work at all.
Before installing the battery in the device, keep it without film for 3-5 minutes.
Turn off the SA when not in use. Remove the power sources from the device at night and leave the battery compartment open.
The novelty promises to surpass lithium-ion batteries in terms of energy consumption 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, as it does not contain volatile substances and, accordingly, cannot ignite.
The main obstacle to creating rechargeable options from the network - that is, batteries - is the rapid degradation of the device: the electrolyte is deactivated, the oxidation-reduction reactions slow down and stop altogether after just a few recharge cycles.
To understand why this happens, we must first describe the principle of operation of air-zinc elements. The battery consists of air and zinc electrodes and electrolyte. During discharge, the air coming from outside, not without the help of catalysts, forms hydroxyl ions (OH -) in an aqueous electrolyte solution.
They oxidize the zinc electrode. During this reaction, electrons are released, forming a current. During battery charging, 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, due to which short circuits began to occur between the electrodes.
The novelty is devoid 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 the elements.
So far, the best performance of prototypes does not exceed hundreds of recharge cycles (photo by ReVolt).
ReVolt CEO James McDougall believes that the first products, unlike current prototypes, will be recharged up to 200 times, and will soon be able to reach the mark of 300-500 cycles. This indicator will allow the element to be used, for example, in cell phones or laptops.
The prototype of the new battery was developed at the Norwegian research foundation SINTEF, while ReVolt is commercializing the product (ReVolt illustration).
ReVolt is also developing zinc air batteries for electric vehicles. 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 goes through 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 this type of cell could be recharged between two and ten thousand times.
Electrochemical energy storage technologies are advancing rapidly. NantEnergy offers a budget zinc-air energy storage battery.
NantEnergy, led by California billionaire Patrick Soon-Shiong, has unveiled a Zinc-Air Battery that is significantly cheaper 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 energy sector. According to NantEnergy, its cost is less than one hundred dollars per kilowatt-hour.
The device of the zinc-air battery is simple. When charging, electricity converts zinc oxide into zinc and oxygen. In 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 with lithium-ion batteries are not affected by zinc-air batteries. In addition, the latter contain practically no elements harmful to the environment, and zinc is very easily recycled for recycling.
It is important to note that the NantEnergy device is not a prototype, but production model, which has been tested over the past six years "in thousands of different places". These batteries provided power to "more than 200 thousand people in Asia and Africa and were used in more than 1000 towers cellular communication around the world".
Such a low cost of energy storage system will allow "turning electrical network into a 24/7, 100% carbon-free system”, i.e. based entirely on renewable energy sources.
Zinc air batteries- this is not a novelty, they were invented back in the 19th century and have been widely used since the 30s of the last century. The main field of application of these power sources is hearing aids, portable radio stations, photographic equipment ... A certain 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 a battery can cycle over 1,000 times of charge and discharge without degrading performance.
Among other parameters specified by the company: 72 hours of autonomy and 20 years of system life.
To the number of cycles and other characteristics, of course, there are questions that need to be clarified. However, some energy storage experts believe in the technology. In a GTM survey last December, eight percent of respondents pointed to 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/kWh this year.
We often hear that the spread of variable renewable energy sources, solar and wind energy, is allegedly slowed down (will be slowed 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 agility (flexibility) of the power system, but not the only tool. In addition, as we can see, electrochemical energy storage technologies are developing at a rapid pace. published
If you have any questions on this topic, ask them to specialists and readers of our project.
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The entry 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 laptops and laptops. digital devices.
energy problem
and in recent years, the fleet of portable computers and various digital devices has increased significantly, many of which have appeared on the market quite recently. 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 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 batteries is only one side of the problem. Thus, as portable electronic devices develop, the density of mounting 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 larger screen size. All this leads to an increase in energy consumption. In addition, in the field of portable electronics, there is a clear trend towards further miniaturization. Taking into account the above factors, it becomes quite obvious that an increase in energy intensity, power, durability and reliability of used batteries 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 terms of functionality and performance to full-fledged laptops. 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 a full-fledged work in mobile environment 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 solutions to the problem of increasing the time battery life portable PCs is the transition from the now common nickel-metal hydride and lithium-ion batteries to chemical fuel cells 2 . The most promising from the point of view of application in portable electronic devices and PCs are fuel cells with a low operating temperature - 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 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 tightness and reliability of fuel cartridges. Secondly, to ensure an acceptable rate of chemical reactions in fuel cells with a low operating temperature, it is necessary to use catalysts. PEM and DMCF cells currently use catalysts made from platinum and its alloys, but the natural resources 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 involved in research in this direction has been able to find an acceptable alternative. Today, the so-called platinum problem is perhaps the most serious obstacle to the widespread use 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 found in the article “Fuel cells: a year of hope”, published in No. 1’2005.
3 Hydrogen gas PEM cells are equipped with a built-in converter to produce hydrogen from methanol.
Air-zinc 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 acquainted with the device and principle of operation of zinc-air cells, 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 design includes a cathode and an anode separated by an alkaline electrolyte and mechanical separators. A gas diffusion electrode (GDE) is used as a cathode, the permeable membrane of which makes it possible to obtain oxygen from atmospheric air circulating through it. The "fuel" is the zinc anode, which is oxidized in the process element work, and the oxidizing agent is oxygen obtained from atmospheric air entering through the “breathing holes”.
At the cathode, an oxygen electroreduction reaction 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 with the release of electrons, which 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 from the outside during operation.
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 mass production of zinc-air elements is deployed, 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 air-zinc elements are very environmentally friendly products. The materials used for their production do not poison the environment and can be reused after processing. The reaction products of air-zinc 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.
Of the operational properties of air-zinc elements, it is worth noting such advantages as low speed self-discharge in the non-activated state and a small change in the magnitude of the voltage as the discharge progresses (flat discharge curve).
A certain disadvantage of air-zinc elements is the influence of the relative humidity of the incoming air on the characteristics of the element. For example, for a zinc-air element designed for operation in conditions of 60% relative air humidity, with an increase in humidity to 90%, the service life decreases by about 15%.
From batteries to accumulators
Disposable batteries are the easiest zinc-air cell to implement. When creating zinc-air cells of large size and power (for example, designed to power the power plants of vehicles), the zinc anode cassettes can be made replaceable. In this case, to renew the energy reserve, it is enough to remove the cassette with used electrodes and install a new one instead. Spent electrodes can be recovered for reuse by 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. That is why most of the compact zinc air cells currently on the market are disposable. Single-use zinc-air batteries of small size are produced by Duracell, Eveready, Varta, Matsushita, GP, as well as the domestic enterprise Energia. The main scope of such power supplies is hearing aids, portable radio stations, photographic equipment, etc.
Many companies are now producing disposable zinc air batteries.
Several years ago, AER produced Power Slice zinc-air flat batteries for portable 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 (accumulators), 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 hampered by serious problems due to the chemical properties of zinc. Zinc oxide dissolves well in an alkaline electrolyte and, in dissolved form, is distributed throughout the 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 to a large extent: the zinc reduced from oxide is deposited on the anode surface in the form of ribbon crystals (dendrites), similar in shape to long spikes. The dendrites pierce through the separators, causing a short circuit inside the battery.
This problem aggravated by the fact that to increase the power, the anodes of air-zinc cells are made from crushed zinc powder (this allows you 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 cell performance.
To date, Zinc Matrix Power (ZMP) has achieved the greatest success in the field of compact zinc-air batteries. ZMP experts have developed a unique technology Zinc Matrix, which allowed to solve the main problems that arise in the process of charging batteries. The essence of this technology is the use of a polymeric binder, which provides unhindered penetration of hydroxide ions, but at the same time blocks the movement of zinc oxide dissolved in the electrolyte. Thanks to the use of this solution, it is possible to avoid a noticeable change 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 a high specific energy intensity, at least twice as high as those 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.
Zinc air battery prototype developed 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. Moreover, unlike lithium batteries air-zinc elements are much safer.
In conclusion, it is impossible not to mention one important event, which became a symbolic starting point for 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 clauses of this agreement, ZMP and Intel will join forces in the development of new technology rechargeable batteries for laptops. 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 appear on sale in 2006.
