Of all the modern technologies we’ve come to take for granted, the rechargeable battery has to be one of the most important – after all, many of our electronic devices would not be able to work without it.
So how has the battery evolved and where is it headed? Let’s take a quick look at its history and future.
Lead acid batteries
Invented as far back as 1859 by Gaston Plante, the lead-acid model is the first battery that could be recharged by running an electrical current back into it.
The acid battery works by having a lead anode and cathode in a sulphuric acid bath.
This causes a reaction that releases electrons and produces lead sulfate.
The interesting thing about lead acid batteries is that the reaction can be reversed by passing a reverse current through it, essentially recharging the battery.
Lead acid batteries are still used in cars and motorcycles today but because of the relatively low charge they hold compared to their weight, not to mention the harmful chemicals, lead acid batteries are not practical for mobile devices.
Rise of NiCd
Nickel-cadmium (also known as NiCd or NiCad) were the first rechargeable batteries that were used in a variety of devices from remote control cars to cordless phones and early handphones.
Invented in 1899 by Waldemar Jungner, the battery uses electrodes made of nickel and cadmium in an alkaline bath of potassium hyrdoxide.
Nickel-cadmium has a terminal voltage of about 1.2 volts and a charge cycle of around 2,000, but it came with several disadvantages. The battery was toxic (due to cadmium) and suffered from the infamous memory effect (or voltage suppression if you want to get technical) – if a NiCd battery is repeatedly recharged before it was fully depleted, its voltage and capacity will be reduced.
Although it is possible to revive a NiCd battery to almost full capacity and voltage by completely discharging and recharging it several times but it was too tedious a process for most users.
NiCd is now uncommon thanks to the battery technology that follows.
The secret of NiMH
Nickel-metal Hydride (NiMH) cells have largely replaced NiCd as the default battery for most electronics devices that use AA- or AAA-sized battery.
Invented in 1967, NiMH use a complex alloy of various metals as well as nickel-hydroxide electrodes in an alkaline bath of potassium hydroxide.
NiMH batteries are less damaging to the environment compared to NiCd.
Contrary to popular belief, NiMH batteries also suffer from memory effect though not as badly as they only have to be discharged completely once in awhile to avoid the voltage suppression effect.
In 2005, Japanese electronics company Sanyo had a big breakthrough with its Eneloop battery, which is an NiMH battery with a very low discharge rate. The company claimed that the battery could retain up to 70% to 85% of its charge even after a year.
The Eneloop (and similar batteries) achieves this by having more efficient separators which keep the two electrodes apart to slow down electrical discharge.
It’s because of these separators that Eneloop batteries have a slightly lower capacity than regular NiMH batteries – the separators take up space that could have been used for chemicals to hold more charge.
In later batteries the company used thinner separators made of more advanced materials to increase the capacity of the battery.
Panasonic acquired Sanyo in 2009, and now Eneloop batteries are sold under the Panasonic brand name.
Age of lithium
Although research into lithium batteries began as early as 1912, the first rechargeable lithium-ion batteries were only created in 1985 and commercialised in 1991.
Lithium-ion batteries use a complex mix of materials – the cathode is made up of lithium molecules trapped within other compounds, while the anode is usually graphite or a mix of carbon and other compounds.
In fact, the chemistry is quite varied, with anodes, cathodes and the electrolyte solutions using a mix of lithium and other chemicals to offer different effects – more charge, more density, more stability or more resistance to overheating.
The batteries are widely used in today’s mobile devices because they can hold higher charge and have a very low discharge rate of only between 1.5% and 2% per month. A lithium battery has a charge cycle of about 1,000 cycles on average.
The lithium polymer variety is the same but the electrolyte is a solid polymer composite with laminated electrodes and separators which allow manufacturers, especially phone makers, to create a flexible battery that can be moulded to conform to the limited interior space of a smartphone.
Lithium-ion batteries’ biggest disadvantage is that they can be overcharged which can cause the lithium-ion cells to combust, often with very spectacular (if extremely dangerous) results.
In fact, lithium-ion batteries can combust so easily that even short-circuiting them by connecting the two terminals will cause them to catch fire and explode.
Most manufacturers prevent this by making the terminals recessed so it’s impossible for them to short circuit accidentally.
The future is wireless
The constant demand for more capacity and faster charging has accelerated research into many battery types.
Some of the technologies currently being researched are more efficient “super capacitors” which can be charged 50 times faster than current batteries.
Another possible battery technology is the Na-ion which is essentially made up of sodium-ion or salt – it can hold as much charge as lithium batteries but lasts almost twice as long as it can handle 2,000 charge cycles.
There are also solid-state batteries currently being researched by scientists at MIT and Samsung, which offer 20% to 30% improvement in power density compared to lithium-ion and can be recharged thousands of times before it degrades.
Beyond just battery technology, scientists are also researching more convenient ways to recharge our mobile devices.
One of the technologies that is already available now but that has yet to catch on is wireless charging.
There are essentially two types of wireless charging technologies, namely inductive charging and magnetic resonance charging.
Both technologies use the same principle – electricity flows though a tightly coiled wire which creates an electromagnetic field that transfers voltage to a nearby object.
Wireless charging is inherently less efficient than wired charging. Of the two technology, inductive charging method is the more efficient one but only works at very close range, typically less than 1.5in.
Magnetic resonance charging, which was demonstrated by Intel for its Rezence wireless charging technology at its annual IDF conference, works even when the charger and the device are separated by several inches, but is not as efficient as inductive charging.
Currently there are two competing standards – the Qi standard which is championed by the Wireless Power Consortium, and PMA which is headed by the AirFuel Alliance (which is made up to two formerly competing wireless standards).
While everyone is hoping that the two will merge, companies like Samsung have started supporting both wireless standards.