Battery life is an explosive issue. Literally, as Samsung is discovering to its dismay. The company’s Galaxy Note 7 smartphone was praised upon release for best-in-class battery life, far outpacing its key competitor, the iPhones 6S and 7 Plus. Then it started blowing up. Samsung issued a recall and replace programme, and the replacements also started blowing up, forcing the company to suspend production entirely.
The affair marks the latest road block on the long fight to improve the batteries that power our electronics. While processing speed doubles around every 18 months, battery capacity takes almost a decade to improve to the same degree. That gap is starting to cause problems, but as Samsung has found to its cost, it’s not easy to fix.
A smartphone often lasts less than a day, a laptop sometimes only a few hours and an electric car struggles to go 350 miles. So why is it that battery life is still such a problem – and when are we going to fix it?
Inside that plastic and metal casing is a little box of chemicals ready to react and create electricity.
Photograph: BitchBuzz/FlickrBatteries are small containers of chemical energy. When a smartphone is plugged into the mains, electricity is used to reset a chemical reaction within the battery, transferring electrons from the negative anode to the cathode – the positive end of the battery.
Once charged, the battery can then create electricity by driving electrons through a circuit, in this case a smartphone, to the anode and will continue to do so until all of the electrons contained within the battery have transferred to the anode or a built-in switch disconnects the battery.
Inside a typical battery you have an anode, a cathode and electrolyte – something for the positive ions to travel through.
Lithium-ion batteries found in most smartphones and electronics have a metal oxide cathode made of a cobalt, nickel, manganese or iron mix, a porous graphite anode that holds lithium ions within it and a lithium salt electrolyte.
Positively charged lithium ions travel through the electrolyte from the anode to the cathode driving electrons through the smartphone as required and back to the anode.
Low battery symbol on the Nokia Lumia 800 in a jeans pocket.
Photograph: Martin Abegglen/FlickrThe principle of the battery may be simple, but the chemistry and technology to make it work is not. The major limiting factor for batteries is their energy density.
A battery can only generate as much electricity as its chemical components can store energy. Everything that is not the active material within the battery is effectively dead weight, including the casing, the controller chips, the wires to carry the current out – they all add weight but not power.
A typical lithium ion battery within a smartphone has an energy density around 150 Watt-hours per kilogram (Wh/kg). While Lithium ion battery energy density has improved since its introduction in the early 1990s, it is held back by its construction and chemistry.
The only way to immediately increase a smartphone’s battery life with current technology is to increase the power efficiency of the smartphone’s electronics and increase the size of the battery – but thinner and thinner smartphones demand thinner and thinner batteries.
Fully charged, or is it? Over time the battery can’t store as much energy as when new.
Photograph: Bastian Greshake/FlickrBattery life doesn’t stay constant for the entire life of a smartphone – it diminishes slowly over time, as the battery is discharged and recharged.
This is because the chemical reaction that produces the electricity causes thin layers of lithium to be laid down on the electrodes, which reduces the amount available to generate electricity and increases the internal resistance of the battery.
The higher the resistance the harder the battery has to work to maintain a usable voltage and so the amount of power it can produce per charge decreases. You might remember this bit from school:
Voltage = Current x Resistance (V=IR)
Battery exploding out of a 17in MacBook Pro battery casing due to swelling.
Photograph: J Aaron Farr/FlickrBatteries with much higher energy density than lithium-based cells are already available, but they aren’t safe enough for use in portable electronics.
“The more energy you put into a box, the more dangerous it’s going to be,” says Dr Billy Wu, lecturer at Imperial College London’s Dyson School of Design Engineering. “Safety is absolutely key and thermal management is crucial. If a battery heats up beyond 80C you hit what is called thermal runaway, where the components start to decompose, and that’s when it can explode.”
The specific cause of Samsung’s issues with exploding batteries is unknown, the company just cites “a battery cell issue”.
We’re stuck with the rechargeable lithium-ion battery for the time being.
Photograph: Razor512/FlickrIn the immediate term, battery advances will come by bringing existing lithium-ion technologies closer to their theoretical limits, which will increase the power density of batteries.
A typical lithium-ion battery using lithium manganese oxide has a theoretical power density of 280 Wh/kg, but the final product only has 150Wh/kg so there is certainly room for improvement.
“It’s about optimising the structure within the battery,” says Wu. “If you imagine inside your battery you have this porous structure full of the active material.”
“For higher power output, you need a more porous structure to increase the surface area and allow more lithium ions through at any one time, but because it’s got more holes it holds less active material, which in turn gives you lower capacity.”
New, advanced battery chemistries such as lithium-sulphur and lithium-silicon are also being worked on, with companies around the UK currently developing the technology.
A combination photo shows a Samsung Note 7 exploding as pressure is applied to its fully charged battery during a test at the Applied Energy Hub battery laboratory in Singapore, 6 October.
Photograph: Edgar Su/ReutersSolid state batteries are one possible future, where the liquid electrolyte in the battery is replaced by a solid substance, which will provide significant safety improvements.
“The main advantage of solid state batteries is that you can go back to using lithium as the anode material, which has really good power and energy density, but wasn’t safe with liquid electrolytes,” explains Wu.
Solid-state batteries will remove the need for the porous carbon anode and therefore removes more of the weight from the battery that doesn’t contribute to generating power.
Metal air batteries, using zinc, lithium or aluminium are also on the horizon, but are 20 years away from being available in a commercial application according to Wu.
A familiar sight for anyone with a smartphone, tablet or computer.
Photograph: Samuel Gibbs/The GuardianThere are a few things you can do to help prolong the life of your battery. The nature of the chemical reaction inside the battery means that it has to work harder in the last 20% of discharge and above 80% of charging.
Keeping a lithium ion battery roughly between 80% and 20% of charge will help it keep a greater amount of its capacity for longer. Smart power management systems are currently being developed that do just that when plugged into a wall overnight.
Batteries should never be left constantly plugged in, which is particularly applicable to laptops. They are kept in better working order if they are discharged and recharged every so often. Once a month should do it.
This article is about the type of electric cell. For the military weapon, see anti-aircraft warfare
AA cellsThe AA battery (or double-A battery) is a standard size single cell cylindrical dry battery. The IEC 60086 system calls the size R6, and ANSI C18 calls it 15.[1] It is named UM-3 by JIS of Japan.[2] Historically, it is known as D14 (hearing aid battery),[3] U12 – later U7 (standard cell), or HP7 (for zinc chloride 'high power' version) in official documentation in the United Kingdom, or a pen cell.[4]
AA batteries are common in portable electronic devices. An AA battery is composed of a single electrochemical cell that may be either a primary battery (disposable) or a rechargeable battery. Several different chemistries are used in their construction. The exact terminal voltage, capacity and practical discharge rates depend on cell chemistry; however, devices designed for AA cells will usually only take 1.2–1.5 V unless specified by the manufacturer.
Introduced in 1907 by The American Ever Ready Company,[5][third-party source needed] the AA battery size was standardized by the American National Standards Institute (ANSI) in 1947, but it had been in use in flashlights and electrical novelties before formal standardization. ANSI and IEC battery nomenclature gives several designations for cells in this size, depending on cell features and chemistry. Before being called AA batteries, they were commonly called Z batteries, as the ones produced by the Burgess Battery Company were sold as "Number Z" (meant to indicate them being smaller than the "Number 1", which was similar in size to a modern C battery).[citation needed] Due to their popularity in small flashlights, they are often called "penlight batteries".
Dimensions
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An AA cell measures 49.2–50.5 mm (1.94–1.99 in) in length, including the button terminal—and 13.5–14.5 mm (0.53–0.57 in) in diameter[citation needed]. The positive terminal button should be a minimum 1 mm high and a maximum 5.5 mm in diameter, the flat negative terminal should be a minimum diameter of 7 mm.[1] 14500 Lithium Batteries are longer if they feature a protection circuit up to 53 mm.
Alkaline AA cells have a weight of roughly 23 g (0.81 oz),[6] lithium AA cells around 15 g (0.53 oz),[7] and rechargeable Ni-MH cells around 31 g (1.1 oz).[8]
Chemistry and capacity
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Primary cells
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Primary (non-rechargeable) zinc–carbon (dry cell) AA batteries have around 400–900 milliampere hours capacity, with measured capacity highly dependent on test conditions, duty cycle, and cut-off voltage. Zinc–carbon batteries are usually marketed as "general purpose" batteries. Zinc-chloride batteries store around 1,000 to 1,500 mAh are often sold as "heavy duty" or "super heavy duty". Alkaline batteries from 1,700 mAh to 2,850 mAh cost more than zinc-chloride batteries, but hold additional charge. AA size alkaline batteries are termed as LR06 by IEC, and AM-3 by JIS.
Non-rechargeable lithium iron disulfide batteries are manufactured for devices that draw more current, such as digital cameras, where their high cost is offset by longer running time between battery changes and more constant voltage during discharge. The capacity of alkaline batteries is greatly reduced as the discharge current increases, however the capacity of a Li-FeS2 battery is not affected by high discharge currents nearly as much as alkaline batteries. Another advantage of lithium disulfide batteries compared to alkaline batteries is that they are less prone to leak. This is particularly important in expensive equipment, where a leaking alkaline battery can damage the equipment due to the corrosive electrolyte coming into contact with sensitive electronics. Lithium iron disulfide batteries are intended for use in equipment compatible with alkaline zinc batteries. Lithium-iron disulfide batteries can have an open-circuit voltage as high as 1.8 volts, but the closed-circuit voltage decreases, making this chemistry compatible with equipment intended for zinc-based batteries. A fresh alkaline zinc battery can have an open-circuit voltage of 1.6 volts, but a lithium iron disulfide battery with an open-circuit voltage below 1.7 volts is entirely discharged.[9]
Rechargeable cells
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Panasonic Eneloop 1.2 volt NiMH rechargeable cells in AA and AAARechargeable batteries in the AA size are available in multiple chemistries: nickel–cadmium (NiCd) with a capacity of roughly 600–1,000 mAh,[10] nickel–metal hydride (NiMH) in various capacities of 600–2,750 mAh[11][12] and lithium-ion. NiCd and NiMH provide 1.2 V; lithium-ion chemistry has a nominal voltage of 3.6–3.7 volts, and AA-sized cells of this voltage are coded 14500 rather than AA. AA-sized lithium-ion cells with circuitry to reduce the voltage to the 1.5V of standard replaceable cells are also made.
NiMH and lithium-ion AA/14500 cells can supply most of their capacity even when under a high current drain (0.5A and higher), unlike alkaline and zinc-chloride ("Heavy Duty"/"Super Heavy Duty") cells which drop to a small fraction of their low current capacity before even reaching 1 C.[13][14][15][16]
A Li-ion 1.5V AA-size battery, sold by the Chinese company Kentli as "Kentli PH5" since 2014 and with similar batteries later available from other suppliers is a AA-sized battery housing containing a rechargeable 3.7 V Li-ion cell with an internal buck converter at the positive terminal to reduce the output voltage to 1.5 V.[17] The Kentli batteries expose the normal 3.7 V Li-ion electrode in a ring around the AA electrode to allow charging by a special charger. It supplies the same 1.5 V as a fresh disposable alkaline AA cell, but with virtually no drop over the discharge cycle, unlike other disposable or rechargeable cells. Its lithium-ion chemistry provides a low self-discharge of 3% per month.[18] Its capacity at 250 mA drain is 1,700 mAh at 1.5 V, less than other chemistries, limited by the low efficiency of the step-down converter.[19] Some later Li-ion AA batteries advertise their capacity in milliwatt-hours (mWh) instead of the usual milliampere-hours (mAh), so a customer's attention is drawn to the figure, typically a claimed 3,000 or more, which is in reality 2,000 mAh.
By 2023, several brands of 1.5 V Li-ion rechargeable batteries in both AA and AAA sizes (with voltage converting circuitry in even the small AAA casing) were available. They use various charging methods, without the special Kentli ring third electrode. Some have special chargers—a charger for a 1.2 V cell will not provide sufficient voltage—but do not use a third electrode.[20] Others have a USB port built into the cell itself.[21]
NiZn
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Nickel-zinc cell (NiZn) rechargeable 1.65 V AA and AAA cells are also available, but not widely used. They require a charging circuit capable of supplying that voltage.
Comparison
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Chemistry IEC name ANSI/NEDA name Nominal voltage (V) Capacity under 50 mA constant drain (mAh) Max. energy at nominal voltage and 50 mA drain (Wh) Rechargeable Zinc–carbon R6 15D 1.50 400–1,700 2.55 No Alkaline LR6 15A 1.50 1,800–2,850 3.90 Some Li-FeS2 FR6 15LF 1.50 2,700–3,400 5.10 No Li-ion ??R15/50 14500 3.60–3.70 600–1,100 (1,600 mAh at 1.5V) 3.88 Yes LiFePO4 14500 3.2–3.3 600–1,000+ 2.80 Yes NiCd KR6 15K 1.20 600–1,000 1.20 Yes NiMH HR6 15H 1.20 600–2,750 3.42 Yes NiZn ZR6 ? 1.60–1.65 1,500–1,800 2.97 YesUse
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In 2011, AA cells accounted for approximately 60% of alkaline battery sales in the United States. In Japan, 58% of alkaline batteries sold were AA, known in that country as tansan (単三). In Switzerland, AA batteries totaled 55% in both primary and secondary (rechargeable) battery sales.[22][23][24]
See also
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References
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