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A ll A bout Part 2: by Dr David Maddison Batteries Battery technology is being actively researched worldwide in an attempt to find a better way to store energy from solar panels and wind generators and for powering the latest generation of technology. This article will look at some of that upcoming tech, and will also describe the ‘tried and true’ lead-acid battery in more detail. I n the first article in this series, we gave the history of cell and battery technology, listed some common battery types and explained some of the theory behind them. This article will describe lead-acid batteries in more detail (as they are still in widespread use) and discuss some of the more obscure battery types. A third and final part, to be published next month, will cover electric vehicle batteries, how to characterise batteries and take certain measurements. It will conclude with some miscellaneous battery facts. More about lead-acid batteries Lead-acid batteries might seem ‘primitive’, but they are still very useful. A major reason for this is that they are inexpensive compared to their capabilities, especially capacity and current delivery. Many decades of research has led to them being almost perfected, and many different sub-types are available to suit various applications. Lead-acid car batteries, in particular, are subject to many myths because they need to be replaced regularly (sometimes at a relatively high cost), and when they fail, it is usually at the most inconvenient time. 12 Silicon Chip How a lead-acid battery works Let’s start by considering just one cell of a standard ‘flooded’ lead-acid battery. A typical “12V” battery has six cells in series, each developing about 2V. The essential components of such a battery are (see Figs.31-33): • A spongy, porous lead plate anode that provides a large surface area to assist in the dissolution of the lead (negative) • A lead dioxide plate for the cathode (positive) • Sulfuric acid electrolyte The lead plate is usually alloyed with antimony or calcium for strength. The two plates are kept apart with a porous non-conductive membrane such as fibreglass. In a fully charged state, a lead-acid battery has one lead plate, one lead dioxide plate and a high concentration of aqueous sulfuric acid. Both plates develop a lead sulfate (PbSO4) layer as the battery discharges, and the aqueous sulfuric acid becomes very weak, almost like water. It is essential to realise that, unlike most metal oxides, lead dioxide is electrically conductive. However, lead sulfate is a poor conductor and that is why a discharged lead-acid battery has a higher internal resistance than a fully charged one. During discharge, the following Fig.31: the basic layout of a lead-acid battery. The positive and negative plates are supported by grids made of lead alloyed with calcium or antimony for strength. The active material that fills the grid of a charged positive plate is red-brown lead dioxide, while on a charged negative plate, the grid is filled with sponge lead. Original source: Jorge Omar Gil Posada, CC BY 4.0 Australia's electronics magazine siliconchip.com.au Assures reserve electrolyte capacity. To protect against leakage and corrosion. Safety Valve Relieves excess pressure. Sealed Terminal Post Prevents acid leakage. Reduces corrosion; extends battery life. ► Hi-Impact Case and Cover Fig.32; a cutaway of a lead-acid battery (in this case, an AGM or absorbed glass mat type) showing the internal plate structure. Note how multiple pairs of plates are interleaved to increase the battery’s current capacity, both for charging and discharging. AGM means that the electrolyte is absorbed into a glass mat separator between each pair of plates, making them spill-proof and more robust. Cast On Strap Using auto welding system to weld plate group; to ensure the stability of the product. Special Grid Design Withstands severe vibration. Assures maximum conductivity. Absorbed Glass Mat Separator Makes the battery spill-proof. Valve regulated design eliminates fluid loss. Special Active Material Using exclusive materials to prolong battery life and dependability. reaction occurs at the negative (anode) plate. The PbSO4 formed sticks to the lead electrode and coats it. Two electrons are produced in this reaction (2e-). Pb(s) + HSO4(aq) → PbSO4(s) + H+(aq) + 2e− During discharge, the following reaction occurs at the positive (cathode) plate. The PbO2 of the plate is reduced to Pb metal and then reacts with the SO42- of the acid to produce PbSO4 (lead sulfate) which coats the electrode. Two electrons from the above reaction are consumed. The overall reaction at the cathode is: PbO2(s) + HSO4(aq) + 3H+(aq) + 2e− → PbSO4(s) + 2H2O(l) Combining the two ‘half reactions’ above into one chemical equation we get: Pb(s) + PbO2(aq) + 2H2SO4(aq) → 2PbSO4(s) + 2H2O(l) In other words, both the lead and lead dioxide become lead sulfate, while at the same time, the sulfuric acid becomes watery. This reaction produces a cell siliconchip.com.au potential of 2.05V. The actual voltage in a real battery will be slightly different depending on several factors. The above reactions are reversed during the charging process, and the lead sulfate is converted to the lead or lead dioxide of the original electrode. At the same time, the weak watery acid reverts to a strong acid. Most of the energy in a lead-acid battery is stored as the potential energy of the sulfuric acid. More precisely, most of the energy comes from the H+ (free protons) in the acid reacting with the O2 (oxygen ions) of the PbO2 to form water, H2O. One way to judge the quality of a lead-acid battery Arguably, you can judge the quality of a lead-acid battery by its weight. The heavier it is compared to another of similar capacity, the more lead has been used and the longer the expected life of the plates. Batteries from one manufacturer are often sold in multiple grades, perhaps three. Those of the cheapest grade have a short warranty, while the more expensive types come with longer warranties. The difference is due to the more robust construction and more materials Australia's electronics magazine Fig.33: lead plates for manufacturing lead-acid batteries. You can see the grid structure (which appears to be hexagonal), and the brown colour of the lead oxide is also apparent, in contrast to the grey metallic lead. in the more expensive battery, especially more lead. However, for a counterpoint to this, see Fig.34 on the next page! The efficiency of lead-acid batteries This can vary according to the construction method. Flooded batteries are around 70% energy efficient, meaning that only about 70% of the electricity used to charge them is recovered during discharge. Sealed lead-acid batteries (‘gel cells’) can be 95% efficient. Charging efficiency also depends on the temperature and the charging current/rate. Also, a lower discharge rate will achieve more of the rated capacity than a higher rate, because of losses from heating and gas formation. Lead-acid batteries are one of the world’s most recycled items, especially car batteries. Lead-acid battery life Battery life is shortened by high temperatures (hence many batteries these days being relocated from the engine bay to the boot, or under the seat), a high rate of discharge, a high depth of discharge or storing the battery at too low a voltage. February 2022  13 A special deep-cycle battery should be used to achieve a long life if the battery will frequently be deeply discharged. Utilising a lead-acid battery’s full rated capacity (Ah) will shorten its life. In general, a standard lead-acid battery should not be discharged more than 50% of its rated capacity, preferably less – see Table 1. If more capacity is needed, use a bigger battery. A deep cycle battery can tolerate a higher depth of discharge, but shallower discharging is still better. Over-discharge or excessive temperatures cause ‘battery sulfation’ and degradation of the plates (hence thicker, heavier lead plates lasting longer). When excessive sulfation occurs, it is usually permanent, although some claim it can be reversed if the battery has only been excessively sulfated for a short time. This is the subject of endless debates. (We have published multiple “battery zappers” which intend to fix sulfation; some swear by them.) Stored batteries should be maintained on a float charge at the voltage recommended by the manufacturer, or at least their voltage checked periodically and recharged as necessary. A typical float charge voltage is in the range of 13.2-13.8V, but check the manufacturer’s recommendation. The problem with silvercalcium batteries The silver-calcium lead-acid battery is a relatively new type of lead-acid battery with a much longer life than other types. The author had one in a car that lasted about ten years, more than three times the life of a typical car battery. The problem with these batteries is that they require a higher than typical charging voltage of 14.4V to 14.8V (the standard lead-acid charging range is more like 14-14.4V). Unless a vehicle’s charging system is designed (or modified) to be used with these batteries, they will be inadequately charged and will eventually sulfate and have a short life. Because of the silver content, these batteries are more expensive than others, but the author’s opinion is that they will be cheaper in the long run because of their extended life as long as they are charged to the correct voltage. Problems with swapping batteries For certain car brands and models, 14 Silicon Chip Fig.34: contrary to what we said elsewhere, a heavier lead-acid battery is not always a sign of a better battery. This unfortunate person found a small battery inside their big battery case, with the empty space filled with concrete... especially those made in the last ten years, replacing the battery isn’t as simple as disconnecting the old one and connecting the new one. When the battery of a modern car is changed, many settings can be lost and have to be reprogrammed, and certain systems such as power windows might need to be resynchronised. For example, here is the procedure required when changing the battery on some Mercedes models. You might save a small fortune doing this yourself compared to getting a dealer to do it! siliconchip.com.au/link/abc6 You can also maintain settings in various cars by carefully jumpering power to the battery leads during replacement to avoid complete power loss. See the YouTube video titled “How to change your car battery without losing your radio code and dashboard setting. HD” at https://youtu. be/9HREVVZAqNI In certain post-2002 BMWs, a new battery requires registration with the car engine control module so that the charging system knows about the new battery and its capacity, type and charging voltage. This even has to be done if the new battery is the same type as the old one. See: siliconchip. com.au/link/abc7 In modern cars, there is some controversy as to whether the negative or positive lead should be removed first when replacing a battery (or if it even matters). In old cars, it used to be negative first. Some say positive first on modern vehicles to avoid a voltage spike through the car’s electronics. We don’t think it makes any Australia's electronics magazine difference. However, there is an advantage when jumping a car or charging its battery to making the final (negative) connection to an exposed area of the chassis or engine, rather than directly to the battery. Besides making it easier to make solid contact, this has the advantage that any spark generated during connection or (probably more importantly) disconnection is away from the battery and therefore unlikely to ignite any hydrogen gas which might have evolved from the battery. Note that car batteries have gotten quite a lot more expensive as the demands placed on them have multiplied. Modern cars have electric power steering, stop/start systems, high-compression engines and many electrical accessories. As a result, they need higher-capacity batteries that can be discharged and recharged faster, deeper and more frequently. Automotive battery parameters (lead-acid) The primary purpose of an automotive battery is to start the engine, which requires a very high current for a short time (usually many hundreds of amps for a few seconds). Once the engine starts, the alternator keeps the battery charged and provides power for functions such as ignition, engine and vehicle management, radio and lighting. Car batteries are not designed to be deeply discharged; this will degrade battery life. They also generally aren’t intended to run accessories for long periods with the engine off, although siliconchip.com.au Table 1 – Regular Wet Lead Acid Battery Voltage (12V nominal) 100% 12.70V 95% 12.60V 90% 12.50V 80% 12.42V 70% 12.32V 60% 12.20V 50% 12.06V 40% 11.90V 30% 11.75V 20% 11.58V 10% 11.31V <10% (fully discharged) 10.50V or less special deep-cycle/starting ‘hybrid’ batteries can do that without significantly shortening their life. When buying an automotive leadacid battery, you will see various specifications quoted, as follows: CCA (cold cranking amperes) The current that a battery can deliver at about -18°C (0°F) for 30 seconds while supplying at least 7.2V. Current delivery drops with temperature, which is why this is measured at such a low temperature. Under more temperate conditions, current delivery will be significantly higher than this. CA (cranking amperes) As for CCA but at 0°C (32°F). HCA (hot cranking amperes) As for CCA but at 26.7°C (80°F). Group size Refers to standard battery sizes established by the (American) Battery Council International and specifies the terminal size, location, and polarity, but not the current rating or capacity. ETN (European type number) A numbering scheme for car batteries (replacing the DIN number) that specifies the voltage, capacity, CCA and dimensions. The first digit is voltage: 1 or 2 is 6V while 5, 6 or 7 is 12V; the second and third digits are the nominal 20hr continuous discharge capacity; the fourth, fifth and six digits are a unique code that gives details such as physical size, endurance, terminal configuration and clamping parts; the seventh, eighth and ninth digits give the CCA rating. For example, 536-040-030 refers to a 12V 36Ah battery with a unique code number of 040 rated at 300 CCA (the siliconchip.com.au Comments Cycling in this zone gives a reasonable battery life expectancy. Occasionally dropping into this zone is OK but will shorten battery life if done repeatedly. Avoid discharging this deeply as permanent damage will occur. 030). Confusingly, if the Ah capacity is 100 or more, its leading digit (‘1’ for ratings ≥ 100Ah, or ‘2’ for ≥ 200Ah) gets added to the first digit of the ETN, so 660 in the first three digits would mean 12V and 160Ah. JIS (Japanese Industrial Standard) A sizing standard used for Japanese and Korean cars. It is simpler than group size (US) or ETN (Europe) and consists of four groups of characters. For example, a 55 B 24 L battery has a 55 performance rating for starting and capacity (higher is better), B refers to 129mm width and 203mm total height, 24 is the length in cm and L means that the negative terminal is on the left side with the terminals closest to you. RC (reserve capacity) The time in minutes that a battery ► State of Charge (SoC) Notes: Readings are taken with no load using a voltmeter after resting for more than two hours. Battery temperature is held steady at 25°C. Batteries just taken off charger will have a significantly higher voltage until the surface charge decays over two hours or more. will deliver 25A continuously at 26.7°C (80°F) before its voltage drops below 10.5V. Amp-hours (Ah) The constant current a battery can produce over a 20hr period (current × hours) at 26.7°C (80°F). Charging a lead-acid battery Lead-acid batteries are charged in various stages of constant current or voltage (see Fig.35). The voltage used depends on multiple factors such as construction method and exact chemistry but is usually 2.30V-2.45V per cell. Even very similar batteries from different manufacturers can have slightly different charging requirements. The charging voltage is a compromise, as too low a voltage will result in slow charging and sulfation, and too high a voltage will result in gassing and plate corrosion. Manufacturers recommend a specific float charge to maintain stationary batteries at around 2.25V-2.27V for flooded leadacid batteries at 25°C. Lead-acid batteries should be stored fully charged. Note that common float chargers Fig.35: a typical charging cycle for a lead-acid battery. The curve shape is generally the same for different lead-acid variations, but the voltages, currents, and times will vary. Larger batteries will have a higher initial current; the end of the bulk charge stage is when it draws less than about 5% of the initial constant current. Australia's electronics magazine February 2022  15 maintain 2.3V/cell or 13.8V for a typical battery. A car battery is called “12V” since the nominal cell voltage from electrochemistry is 2.05V and six cells give 12.3V. However, the charging voltage is usually from 13.8V to 14.7V (but generally closer to 14.4V). An attempt to charge a lead-acid battery at 12.3V will not work; it must be at the manufacturer’s (higher) recommended voltage. Note that charging voltages are usually specified at room temperature (25°C). Manufacturers also typically specify a temperature coefficient in mV/°C. It is negative for lead-acid batteries, so the charge voltage reduces at higher temperatures and increases at lower temperatures (charging usually stops at 0°C). What liquid should you add to a lead-acid battery? Only distilled water should ever be added to a car battery. The sulfuric acid is not consumed and more does not need to be added. An exception to adding acid is in ‘dry’ lead-acid batteries that, for reasons of safer shipping and longer storage life, have no acid or other liquid in them at all. When you buy these, you get a special container of acid to go with them and add it before use. Such batteries are available in the USA and UK, among other countries. A YouTube video about doing this titled “How to fill a dry battery with sulfuric acid (Yuasa)” – https://youtu. be/89Nf3IJcFJQ The author has not Fig.36: a drawing of a lead-acid “B” radio battery, circa 1920, in a rubber box and with glass cells. Moisture could be absorbed into the porous rubber, and leaking acid could also establish conductive pathways that drain the battery. This one was made by the Willard Storage Battery Co. 16 Silicon Chip seen such batteries in Australia, and sadly, in Victoria (possibly other states as well), sulfuric acid is a restricted chemical. The author has such a battery and was unable to buy acid to fill it. The myth of leaving a car battery on concrete The myth is that a car battery will go flat quickly if stored on a concrete floor. There is no truth to this for modern car batteries. What flattens these batteries in storage is gradual self-­ discharge. Lead-acid batteries have low self-discharge rates, but they can still lose around 5% of their capacity per month, more at higher temperatures. Lead-acid batteries should be connected to a trickle charger for storage or regularly topped up to the recommended storage voltage. The problem with storing them on a concrete floor happened with much older generations of car batteries. Early batteries had glass cell cases encased in a timber box (see Fig.36). Water or moisture that gathered on a concrete floor caused the timber case to warp, possibly breaking the glass. Later generations of car batteries utilised porous rubber cases with added carbon, and moisture or leaking acid could create unwanted conductive pathways between cells. For comparison, other battery chemistry self-discharge rates are: ● Lithium-metal primary cells: 10% in 5 years ● Alkaline cells: 2%-3% per year ● Nickel-based batteries: 10%-15% per month after 10%-15% in the first 24 hours ● Lithium-ion: 1-2% per month after 5% in the first 24 hours Typically, the self-discharge rate doubles for every 10°C increase in temperature, so keep stored batteries cool (small batteries can be kept in a refrigerator). In Western countries, this is the point at which the battery is recycled. But in some places, you can take your old battery to a battery rebuilder, and they will reform it into a new battery, perhaps while you wait. See the videos titled “Dead Car Battery Restoration” at https://youtu.be/UvtsBuqLC1g and “How Battery Plates are Made & Restoration of an Old Battery” at https:// youtu.be/VEvPjOKkPyE Lithium-ion car starter batteries Lithium-ion batteries are available as direct replacements for lead-acid batteries in conventional cars. They are lighter in weight (eg, a 120Ah leadacid battery weighs about 30kg compared to 8kg for lithium-ion) and will tolerate a deeper discharge without damage than conventional batteries. Some of these batteries require special charging compared with leadacid types and normally could not be directly replaced; however, some versions contain internal electronics to make them compatible with conventional charging systems. They are also claimed to last longer, say 2000 complete discharge cycles for lithium starter battery compared to 500 for lead-acid. The self-discharge rate can also be lower. However, we recommend that you take caution if you are considering replacing your car battery with a lithium-­ion type, as we have heard stories of vehicle fires started by such batteries. The safest type to use would be LiFePO4 as they generally do not catch fire if abused. You can see a teardown of a lithium-­ ion starter battery at siliconchip.com. au/link/abbq Note that small lithium-ion battery packs are also available for emergency jump-starting, and these generally work very well (but you have to charge them every few months). Other car battery myths Unusual battery types Numerous online videos purport to show how to restore a failed car battery and chemical additives are available that claim to do this. These will generally not work, as the typical reason for failure is the physical destruction of the battery plates. There is no way to restore disintegrated plates without disassembling the battery, melting the lead, recasting it and making it into a new battery. Here we describe some other interesting or important types of batteries not already covered, although there are too many types to cover them all. Australia's electronics magazine Aluminium-air batteries Aluminium-air batteries have occasionally been in the news, typically promoted as the “1000 mile (1600km) car battery”. These batteries are not rechargeable. siliconchip.com.au What can you salvage from used batteries? They are similar to zinc-air batteries as a current is produced by reacting aluminium with atmospheric oxygen. This results in aluminium oxide (Al2O3), and when depleted, this would be collected and converted back to Al2O3 by the input of energy. You can make your own aluminium-­ air battery; several videos show how. For example, see the one titled “Aluminum Air Battery Build 2.0” at https://youtu.be/8wEmjwfHqRI You can recover useful items from certain batteries and cells. For example, in non-alkaline carbon-zinc batteries, there is a carbon rod that can be reused for various projects (see below). It can be used as an electrode for electrochemical experiments or even for making a carbon arc lamp. The best carbon rods are obtained from D cells or 6V lantern batteries. These batteries also have a zinc case and manganese dioxide filling, both useful in many amateur chemical experiments. Brand new lithium disposable batteries have a coiled-up sheet of lithium metal in them; see the video titled “Get Lithium Metal From an Energizer Battery” at https://youtu.be/BliWUHSOalU Used laptop battery packs are a good source of 18650 (18mm diameter, 65mm tall) lithium cells for torches or other uses. Battery packs often fail due to just one or two bad cells, so the rest can be reused. Older laptop battery packs used 18650 cells, and many of these packs are still in service. When they inevitably fail, they can be a good source of 18650 cells. Take care during disassembly; there are many online tutorials about how to get the cells out. Warning: the contents of many batteries, including lithium metal, are hazardous. Take appropriate precautions when dealing with chemicals and look at numerous web pages or videos dealing with battery salvage. Ambri liquid metal battery According to Ambri (https://ambri. com), “the liquid metal battery [comprises] a liquid calcium-alloy anode, a molten salt electrolyte and a cathode comprised of solid particles of antimony, enabling the use of low-cost materials and a low number of steps in the cell assembly process”. Fig.37 shows the reactions involved in this type of battery. We described this type of battery in the April 2020 article on Grid-scale Energy Storage (siliconchip.com.au/Article/13801). The battery system is tolerant of over-charging and over-discharging and is not subject to thermal runaway, electrolyte decomposition or outgassing. The batteries have to be started using heaters. They are packaged in 3m (10ft) shipping containers. The battery system is intolerant of movement, as this causes unwanted mixing of the liquid layers. So they are only suitable for stationary applications such as grid-scale storage. The batteries need to stay hot; once heaters start them, the ongoing charge/ discharge cycles will keep them hot as they are kept in insulated containers. The operating temperature of the battery is over 240°C. Left: carbon rods salvaged from zinccarbon batteries (non-alkaline types). Source: W. Oelen (CC BY-SA 3.0) Future developments of liquid metal batteries include those with lower operating temperatures, possibly using a gallium-based liquid metal cathode and a sodium-potassium liquid metal anode. Gallium is liquid at room temperature but very expensive. The dissolving battery Scientists at Iowa State University have developed a battery that dissolves in water (see Fig.38). It is part of the emerging field of “transient electronics”, devices that are designed to have just a short life and then dispose of themselves after their function has been performed. The 1mm x 5mm x 6mm battery pictured provides 2.5V and dissipates after 30 minutes of immersion in water. It uses a lithium-ion chemistry and would power a calculator for 15 minutes. Flow batteries Flow batteries are a type of battery (strictly, a rechargeable fuel cell) in which the electroactive chemicals are a liquid that flows through an electrochemical cell. The electrolyte is stored 1. Charged State Ca and Sb separated Liquid Metal Calcium (Ca) alloy (negative electrode) Ca Solid antimony (Sb) particles (positive electrode) Sb 2. Discharging 4. Charging Batteries absorb power from the grid e− Half-reactions (3) CaSbx → Ca2+ + Sbx + 2e− (4) Ca2+ + 2e− → Ca Overall charge reaction CaSbx + Energy → Ca + Sbx e− siliconchip.com.au Half-reactions Ca Ca²+ Sb Ca Ca²+ Sb Fig.37: the charging and discharging reactions for the Ambri liquid metal battery. Batteries provide power to the grid CaCl2-based salt electrolyte e− CaSb (1) Ca → Ca2+ + 2e− (2) Ca2+ + Sbx + 2e− → CaSbx e− Overall discharge reaction Ca + Sbx → CaSbx + Energy 3. Discharged State Ca and Sb form an intermetallic alloy Australia's electronics magazine Fig.38: the Iowa State University “transient battery” provides a voltage and current while it dissolves in water. February 2022  17 Fig.40: images and diagrams showing the operation of the alkaline fuel cells used on Apollo spacecraft and the Space Shuttle. They generate electricity from the reaction of hydrogen and oxygen gases. in tanks and continuously supplied to the cell to generate electricity or be recharged. In contrast, a traditional cell has the electrolyte permanently stored around the cell instead of in external tanks. Advantages include scalability, deep discharge capability, low self-­ discharge, relatively low cost and long cycle life. Disadvantages include complexity, added failure points (eg, pumps), difficulties with handling possibly toxic liquids, low energy density and low charge and discharge rates. Flow batteries were mentioned in our article on Grid-scale Energy Storage (April 2020). A vanadium redox flow battery was unsuccessfully tested in Australia as Fig.39: an Australian-made Gelion zinc-bromide cell using non-flow technology. 18 Silicon Chip Fig.41: a cross-section of the Licerion lithium-metal battery, which works similarly to a lithium-ion battery, but with several significant benefits claimed. part of the King Island (Tas) Renewable Energy Integration Project. The Federal Government is now backing the world’s largest vanadium flow battery in the Flinders Ranges, of 8MWh capacity. Redflow (https://redflow.com) is an Australian manufacturer of zinc-­ bromine flow batteries. They make batteries of all sizes, from residential to grid-scale (also mentioned and shown in the April 2020 article). Gelion (https://gelion.com) is another Australian manufacturer of zinc-bromide cells but uses a non-flow technology, shown in Fig.39. They are also developing Li-Si, Li-S and Li-Si-S battery systems. is an example of a molten salt battery. They use a molten salt electrolyte such as LiCl-rich LiCl-LiBr-KBr, operating at a temperature of 375-500°C. The negative electrode is a lithium alloy with aluminium or silicon, while the positive electrode is a sulfide of iron (such as FeS or FeS2), nickel, cobalt or other metals. These batteries have high power and energy density, are tolerant of overcharge, overdischarge and freezing, and are relatively safe. The downside is their high operating temperature and the thermal management that goes with that. Sodium-sulfur and sodium-­ nickel chloride batteries are further examples of this type. Fuel cells Lithium-metal “Licerion” batteries Fuel cells are not strictly batteries, although they have a similar function and may be subject to a separate article in future. Unlike batteries, they do not run flat or need recharging as their fuel is continuously supplied. Like batteries, they are electrochemical cells. Fuel cells were used on Apollo Spacecraft and the Space Shuttle (see Fig.40). We published a three-part series on fuel cell technology in the May, June & July 2002 issues, so for more details, refer to those articles (siliconchip.com. au/Series/226). Lithium alloy-iron / metal batteries A lithium alloy/metal sulfide battery Australia's electronics magazine Licerion is a trademark of Sion Power for their lithium-metal batteries. They are stated to have increased charge density, increased cycle life, better safety and fast charging capability compared to other batteries used in electric vehicles. They are still under development (see Fig.41). According to Sion Power, they have solved many of the problems with lithium-ion, lithium-sulfur and early lithium-metal batteries. “The solution was to pair a proprietary lithium metal anode technology with conventional lithium-ion cathodes. By eliminating the cathode graphite, Sion Power achieved the combination of siliconchip.com.au Fig.42: the movement of ions in a Li-S cell during discharge. Original source: Wikimedia user Egibe (CC BYSA 4.0) Fig.43: this experimental lithiumsulfur cell from Monash University in Melbourne looks similar to a typical lithium-polymer cell. ultra-high energy with long cycle life.” Lithium-sulfur battery Lithium-sulfur (Li-S) batteries are seen as a replacement for lithium-ion batteries because they theoretically have a much higher energy density and do not use expensive cobalt, most of which comes from politically unstable areas (see Figs.42-44). Serious problems with Li-S batteries are the low conductivity of the sulfur electrode, a large volume change of 80% during charging and discharging (leading to the eventual destruction of the electrode) and the permanent loss of sulfur in the electrolyte due to unwanted reactions (the “polysulfide shuttle” effect). In Australia, research is underway on these types of batteries at both Deakin University and Monash University. Deakin is working with Australian company Li-S Energy Ltd (www.lis.energy), using boron nitride nanotubes to enhance cell performance. At Monash, work is underway to use ordinary sugar to stabilise and improve the performance of Li-S batteries. Sion Power was a world leader in commercial Li-S technology, and in 2014 their cells were used to power the Airbus Defence and Space Zephyr 7 HAPS flight which set a record for continuous unrefuelled flight of over 14 days. During that flight, solar cells on the wings recharged the batteries. siliconchip.com.au They have now announced they are moving on to lithium metal technology with batteries they call “Licerion”. US company Lyten (https://lyten. com) is another company working on developing Li-S batteries. They are developing batteries for electric vehicles that also use graphene. See our September 2013 article on graphene at siliconchip.com.au/Article/4393 They are using a technique they call “Sulfur-Caging” to improve the stability of cell components to overcome problems with existing Li-S batteries. They see this as a major breakthrough. Lyten says their batteries will have three times the gravimetric energy density of Li-ion batteries and a life of 1400 charge/discharge cycles. The batteries do not suffer from thermal runaway or combust when damaged and have no critical metals like nickel and cobalt that originate in conflicted countries. A wide variety of battery form factors are possible, as well as a high charge rate: up to 3C, meaning the charge current is three times the Ah rating of the battery (eg, charging a 10Ah battery at 30A). They have an operating temperature range of -30°C to 60°C, and up to 100% depth of discharge is possible. See the YouTube video titled “This Startup Says Its Lithium Sulfur Batteries Have No Rival!” at https://youtu. be/9LfaIppP1Us Mercury batteries Mercury batteries (Fig.45) are now banned in many regions due to the toxicity of mercury (and the cadmium used in some types). Nevertheless, they were important battery types from 1942 to the 1990s, especially in military equipment during the second world war. They had the advantage of a long shelf life and a constant voltage of 1.35V during discharge. Note: Since 1990, IUPAC (which names chemical elements) has stated that sulfur should be spelled with an ‘f’ worldwide. Fig.44: several Lyten Li-S batteries, including 18650 (18mm diameter, 65mm tall) cells at right. Australia's electronics magazine February 2022  19 Fig.45: the cross-section of a typical (obsolete) mercury cell. Original source: Ted Ankara College Library and Information Center A special version containing cadmium had a voltage of 0.9V and was usable at temperatures as high as 180°C. Many cameras, hearing aids, cardiac pacemakers and early electronic watches used mercury batteries, while large mercury battery packs for industrial applications were also available. For devices that still require mercury batteries, there are a few options. Cameras designed before 1975 often used cadmium sulfide photoresistors for light metering, powered by mercury batteries, commonly a 1.35V PX625 type. Light meters designed for mercury batteries often did not have voltage regulation as the battery voltage remained so constant. This poses a problem for substitute batteries which are unlikely to have such a stable voltage. For light meters that included voltage regulation, a 1.5V alkaline PX625A can be used, or a 1.66V silver-oxide S625PX. If the device has no voltage regulation, a 1.35V zinc-air battery can be used, but it will run flat in weeks once the battery is unsealed. Of course, the battery must fit physically. Some vendors make mechanical adaptors for alkaline or silver oxide, including voltage regulation circuitry (see Fig.46). Wein makes a zinc-air cell converted to the same shape as Fig.46: a Kanto MR-9 adaptor in the shape of a PX625 mercury cell (left), which accepts an SR43 silver oxide cell (right). Source: Wikimedia user huzu1959 (CC BY 2.0) the original PX625. Mercury PX625 cells are still made in Russia and sold online. PX640 is another type of mercury battery that was used in cameras. Two (2.7V total) were used in cameras such as the Yashica TL Electro. Adaptors are made to use two SR44 batteries with a total voltage of 3.1V. A diode is used to lower the voltage delivered to 2.7V. Older “insect eye” type of exposure meters are likely to be selenium cells that don’t require a battery. Zinc-air batteries Zinc-air batteries rely on the chemical reaction between oxygen in the air and a zinc electrode to create a current. They have a very high energy density but must be kept sealed to exclude oxygen before use. They are available in sizes from hearing aid batteries to electric vehicles and even grid-scale energy storage (see Fig.47). They produce 1.35V-1.40V. The batteries can be either rechargeable or non-rechargeable. Rechargeable types rely on replacing the zinc oxide with fresh zinc, or electrolytically converting the oxide back to zinc. Other metal-air batteries Fig.47: the zinc-air regenerative fuel cell system for large scale energy storage by Zinc8 (www.zinc8energy.com). Zinc oxide particles are converted to zinc in the regenerator and put in the storage tank until needed, whereupon they are delivered to the fuel stack. Oxidised particles are returned to the storage tank for later regeneration. 20 Silicon Chip Australia's electronics magazine We already mentioned aluminium-­ air and zinc-air batteries. There are also air batteries based on lithium, sodium, potassium, magnesium, calcium and iron. These other types are proposed and of possible future interest only; they have no present commercial applications. The US military used BA-4286 non-rechargeable magnesium-air batteries from 1968 to 1984 until lithium thionyl chloride batteries replaced them. The cost of the magnesium siliconchip.com.au Fig.48: “reversible rusting”, the basis of Form Energy’s iron-air battery. battery was comparable to a zinc-air battery, and they were superior to zinc-carbon batteries. Iron-air batteries are being investigated for grid-scale energy storage. US company Form Energy (website: https://formenergy.com) is developing this technology. Their batteries use “reversible rusting” of iron in combination with oxygen and water to produce or store electricity (see Fig.48). During discharge, atmospheric oxygen causes the iron to rust, while during charging, the rust is converted back to iron and oxygen is released. Form Energy has not supplied specific details of the electrochemistry involved. Advantages claimed are extremely low cost (one-tenth that of lithium-ion for large scale batteries), safety and scalability to grid size. For more information, see the video at https://vimeo.com/575943459 Microbial fuel cells Microbial fuel cells use biological materials as “fuel”, digested by special bacteria. This process involves oxidation or reduction of the biological material, and electrons are collected and used to power a circuit. The idea was conceived in 1911 by Michael Cressé Potter but attracted little interest at the time. Then in 1931, Barnett Cohen made a cell that produced 35V at 2mA. In 2007, the University of Queensland and Foster’s Brewing used wastewater from brewing to power a microbial fuel cell, or a “beer battery”, as one might call it [remember Dick Smith’s Beer-Powered Radio? – Editor]. Although plans called for a 2kW fuel cell to be produced, we could not find any results published for this siliconchip.com.au Fig.49: a No.6 dry cell on a 7mm grid with a AA cell for comparison. Source: Wikipedia user Militoy (CC BY-SA 3.0) experiment. There are online plans about building your own microbial fuel cell, at Instructables: siliconchip. com.au/link/abbr – PDF – siliconchip. com.au/link/abbs The No.6 dry cell I have fond childhood memories of these large 1.5V cells – see Fig.49. They were typically used in bell ringing systems, telephone systems, alarms, ignition systems, some clocks and school science experiments. My late father was a bank manager and the bank alarm system, which would be regarded as primitive by modern standards, used these cells in backup batteries. They were replaced every few months and the old ones discarded, and he would bring them home to me. They were ideal for my experiments, such as making electromagnets or making wire glow red hot. They conveniently had screw terminals which made it very easy to attach wires. These cells are no longer available, although apparently, there are some copies on eBay that produce the wrong voltage. They are still used in certain vintage products such as “self-winding” clocks from the Self Winding Clock Company (1886-1970) – see https://w. wiki/4NaT A US seller makes authentic-looking replacements with modern innards, available from siliconchip.com.au/ link/abbt The original cells were 67mm in diameter and 172mm tall, with a capacity of 35-40Ah. There are original used cells on eBay; they are almost certainly depleted, but they attract good money from collectors. Nuclear batteries During the 1960s, nuclear batteries utilising plutonium-238 were seriously considered for powering artificial hearts (see Fig.50). However, no such hearts were ever implanted. Fig.50: the operating principle of a betavoltaic device. The beta represents an electron or positron emission via nuclear decay. The spontaneously created electron-hole pairs in the semiconductor and the loss of the beta particle from the emitter cause a current to flow through the load. Australia's electronics magazine February 2022  21 Fig.51: a rendering of the proposed nuclear diamond battery. Many people are sceptical about its viability. Fig.52: the operational scheme of sodium-sulfur cell. Note the use of a solid polymer electrolyte and the test tube shaped design. Nuclear powered pacemakers were made but have been discontinued. They would still operate after 88 years, compared to a conventional lithium battery at 10-15 years. We discussed this in our October 2016 article on “Implantable Medical Devices” (page 31; siliconchip.com. au/Article/10329). The nuclear pacemaker battery is a betavoltaic device. It is essentially like a solar cell, but instead of being struck by photons from the sun, it is struck by beta particles (electrons or positrons) from a radioactive source. Radioactive sources can produce some combination of alpha (helium-4 nucleus), beta (electron/positron) or gamma (electromagnetic) radiation, so not all radioactive substances are suitable. A different type of nuclear “battery” used on spacecraft is the radioisotope thermoelectric generator (RTG). These were used on the Pioneer and Voyager spacecraft (December 2018; siliconchip.com.au/Article/11329), Mars rovers (July 2021; siliconchip. com.au/Article/14916) and many other spacecraft. A “diamond” nuclear battery is a recent development (Fig.51). It is a betavoltaic device made of irradiated graphite nuclear waste. The graphite waste containing radioactive carbon14 is converted to a diamond-like coating and acts as the beta particle source, producing a tiny current for thousands of years. Australian YouTuber David L. Jones has stated this battery is not viable in his video titled “EEVblog #1333 - Nano Diamond Self-Charging Battery DEBUNKED!” at https://youtu.be/ 22 Silicon Chip uzV_uzSTCTM and so has YouTuber Thunderf00t in the video “NUCLEAR Diamond Battery: BUSTED!” at https:// youtu.be/JDFlV0OEK5E Sodium-sulfur batteries The sodium-sulfur battery uses molten sulfur as the positive electrode and molten sodium as the negative, with solid sodium alumina as the electrolyte (see Figs.52 & 53). The battery operates at over 300°C. These batteries are used at over 190 sites in Japan for large-scale energy storage, plus some sites in Europe, North America and the UAE. NGK Insulators Ltd commercially produces these batteries in Japan. A 200kW/1200kWh battery fits into a 6m/20ft shipping container and has a life of 15 years or 4500 charge/discharge cycles. + terminal − terminal This type of battery was an early candidate for electric cars and was also tested on a Space Shuttle flight. It is a candidate for a Venus landing mission due to its high-temperature operation. Silver-oxide batteries Silver-oxide primary cells comprise a silver oxide cathode and zinc anode. They are primarily sold in the form of button cells to power watches and other small devices where the cost of the silver is not excessive. There is also a silver-zinc battery that is rechargeable and had the highest energy density before the development of lithium-ion batteries. They are mostly restricted to military and aerospace applications because of their expense. The Lunar Rover used in the Apollo missions used two 36V silver-oxide 192 battery cells fuse − pole (sodium) safety tube solid electrolyte (Beta alumina) + pole (sulfur) sand thermally insulated lid radiated heat duct main pole heater Battery Module Battery Cell 6 NAS battery moldules containerised NAS battery units (800kW) power conversion system container controller Battery Container Battery System Fig.53: this shows how sodium-sulfur batteries are configured for large-scale storage, such as in power grids. NAS is the trade name for this battery. Australia's electronics magazine siliconchip.com.au non-rechargeable batteries of 121Ah capacity each, giving a range of 92km. Sodium-ion batteries Sodium-ion batteries are under development. They are similar to lithium-­ion batteries but without the supply or cost problems of lithium, cobalt, copper and nickel. However, they currently have a low energy density and a short life. Sodium-ion batteries were initially developed alongside lithium-ion batteries until it became apparent that lithium-ion batteries were superior. But there has been a resurgence of interest due to the aforementioned supply and cost problems. Solid-state batteries Solid-state batteries use solid electrodes and solid electrolytes instead of a liquid or gel (see Fig.54). They were first experimented with in the 19th century but were not practical until recent developments in solid electrolyte materials and electrodes. They have a higher energy density than conventional Li-ion batteries and are of particular interest for electric vehicles as they use non-­flammable electrolytes. Experiments with Li-S as a cathode material and a solid lithium anode are looking promising. The Weston Cell The Weston Cell was invented in 1893 and was used as a calibration standard for EMF and voltmeters from 1911 until 1990 (see Figs.55 & 56). It uses cadmium and mercury to produce a stable voltage of 1.018638V for an “unsaturated” cell design. The Fig.55: a Weston Cell from NIST, the National Institute of Standards and Technology in the USA. voltage produced is very slightly temperature-­dependent, according to a known formula. “Saturated” Weston Cells are less temperature-dependent, but they lose about 80μV per year, so they need to be calibrated regularly. Today the Josephson voltage standard, a superconducting integrated circuit, has mostly replaced the Weston Cell. Electrolytic cells The inverse of a battery/cell is an electrolytic cell. They consume energy rather than produce it and are typically used to decompose chemical compounds. Common examples are the decomposition of water into hydrogen and oxygen (“electrolysis”), the electrolytic refining of aluminium by the Fig.56: how a Weston Cell is constructed. Cd is cadmium, Hg is mercury, SO4 is sulfate and H2O is water. Original source: Paweł Grzywocz (CC BY-SA 2.5) Hall–Héroult process and electrolytic rust removal (see our article on “How To Remove Rust By Electrolysis” from October 2014 – siliconchip.com.au/ Article/8041). Recharging a battery is also an electrolytic process; essentially, a rechargeable cell switches between being a regular cell and an electrolytic cell depending on the direction of current flow. Next month In the third and final part of the series next month, we’ll cover electric vehicle batteries in more detail. We’ll also describe concepts like battery internal resistance, depth of discharge, lifespan, storage charge and temperature, battery protection and have some battery trivia. SC Fig.54: a solid-state battery is much like a conventional battery but with a solid electrolyte. Original source: Wikimedia user Luca Bertoli (CC BY-SA 4.0) Fig.57: a Diesel-powered electric car charging station on the Nullarbor. “Range anxiety” is a concern for many EV owners. We’ll have more details on electric vehicle batteries in the third and final part of this series next month. siliconchip.com.au Australia's electronics magazine February 2022  23