Battery Charging

I,m sure some of my old cordless drills had batteries that had memories and it was recommended to flatten them before recharging, more modern Lithium drill batteries can be topped up at any state of charge. So many different types of battery about now, it's confusing. I wouldn't like to let the bike or van battery get to low though.

 

Should you let your phone go completely flat before recharging? Why do lithium batteries explode? And aren't they bad for the environment?

Rechargeable batteries already power our phones, laptops and toothbrushes. With solar battery storage and electric cars set to take off, it's time to sort the battery fact from fiction.

Lithium ion batteries
A decade ago nicad (nickel cadmium) and nickel-metal hydride rechargeable batteries were pretty common in phones and laptops, but with the push for more energy in lighter, smaller mobile units, lithium ion batteries took over.

Lithium owes its market dominance to being a lightweight. At number three in the periodic table, it's the lightest metal, which really helps it store more energy for the same weight and volume.

Smart phones, tablets and new laptops all use lithium ion batteries. And with electric cars and the new solar storage systems using lithium ion batteries too, the technology will be around for a while.

And the high energy for its size and weight (energy density) isn't the only benefit that lithium batteries offer.

How rechargeable batteries work
Rechargeable batteries power devices the same way that disposable batteries do — by chemical reactions at the positive and negative electrodes. Those reactions allow positively charged ions to move from one electrode to the other inside the battery, and negative electrons to move through the wires in the circuit, producing a current.

But with rechargeable batteries, plugging your charger into an external power source forces these chemical reactions to happen in reverse. The positive ions (Li+ in lithium ion batteries) recombine with electrons at the surface of the negative electrode, ready to start all over again when the battery is connected to a circuit.


A typical lithium-ion rechargeable battery. The battery consists of a positive electrode (green) and a negative electrode (red), with a layer (yellow) separating them. When in use, lithium-ions (Li+, blue) travel from the negative electrode (anode) to the positive (cathode). During charging, the process is reversed and lithium ions are transferred back to the anode.

(Getty)
Charge away: lithium batteries don't have 'memory' problems
Back in the day, we all dutifully let our phones and seven-kilogram laptops go totally flat before recharging to avoid the dreaded battery 'memory' problem — where batteries held less and less charge over time if you recharged them before they were fully flat.

How to get the most out of lithium ion batteries:

• Don't fully discharge them — it shortens their lifespan.
• Their chemistry doesn't work over about 45 degrees Celsius, and operating at high temp shortens their life.
• If storing your device, charge it to about halfway before switching it off. Full charge puts stress on the electrode material.
• Check the manufacture date when you buy them — they start losing capacity to hold charge from day one.

The memory problem was caused by a build-up of crystals on the electrodes in the battery, leaving less room for the chemical reactions to take place there during charging. It was a real issue for nickel-based batteries, but with their different chemistry lithium ion batteries only show a very minor effect.

In fact, letting them run completely flat would actually destroy them, so the batteries in your devices have a circuit that shuts them down before they reach that point. Electric cars and solar storage systems have entire control systems devoted to avoiding death by discharge for individual batteries.

So recharge your devices whenever you like — but try to give them a full charge (let the battery go into the red) every now and then to recalibrate your battery level reading.

Complete discharge isn't the only enemy of lithium batteries — heat can also be pretty lethal for them.

... but they do occasionally blow up
The chemical reactions that are at the heart of all batteries generate some heat, and lithium-ion batteries have made headlines when that heat gets out of control and they catch fire — most recently in hoverboards and e-cigarettes. But they've also been behind fires in Boeings, Tesla electric cars and laptops in the past 10 years.

Manufacturers manage the heat with control systems, venting valves and fans to monitor and regulate the temperature the batteries are working at, and product recalls if things get out of hand.

The fire/explosion risk is not restricted to lithium ion batteries. Lead-acid (car) batteries, cans of petrol and all other energy dense materials can explode too.

But the push to make portable batteries lightweight adds an extra risk to lithium ion batteries. Components like the separators that keep the battery's positive and negative electrodes apart are built thin to keep battery weight down, but if they get pierced a short circuit can form between the electrodes and quickly heat things up. A spark from the short can set off a fire, and a build-up in pressure as the heat goes up can literally make the battery explode.

Lithium batteries don't age gracefully
From the moment they're made, lithium ion batteries start losing their ability to store charge and generate a voltage over time. It's called ageing, and it happens whether they're being used or not, so check the date of manufacture when you buy a lithium ion battery.

The ageing is caused by chemical changes at the electrodes. The positive electrode isn't a solid lump — it's made of microscopic particles of a lithium-based material. Over time those particles coalesce together forming bigger lumps, so there's less surface area for the lithium-releasing reaction when the battery is being used (discharging).

And recharging doesn't send 100 per cent of the lithium ions back to the negative electrode — some ions always get permanently stuck to the positive electrode. So over time there are fewer positive lithium ions 'in play' in the battery.

Environmental issues
Like all pieces of technology, lithium batteries come with the usual mining/manufacturing/processing baggage as part of their environmental impact.

In terms of toxicity to humans, lithium ion batteries are only half as toxic as lead-acid batteries per unit of energy. The biggest ticket item is the cobalt and nickel in the positive electrode (cathode) in some batteries, and the solvents used in making the electrodes. Keeping the batteries out of landfill by using a recycling program is the best way to stop these toxins from leaching into waterways.

From a greenhouse emission standpoint, their energy-heavy manufacture means lithium ion batteries take a long time to recoup the energy that went into making them, so maximising the battery's lifespan — avoiding excess heat and keeping the charge topped up — is important.

And with the biggest lithium deposits in some pretty stunning country in South America (Bolivia and Chile), there are concerns about the environmental damage done by mining.

The next small thing: alternatives to lithium ion batteries
There's no shortage of technological breakthroughs in the battery world — aluminium batteries, lithium-air batteries and redox flow batteries are all technologies that show lots of promise.

But it's a long road from exciting results in the laboratory to large scale manufacture and use. It took lithium ion batteries 20 years to go from a 1970s lab to commercial product, and another 15 years to really dominate the market.

That's longer than the lifespan of any existing rechargeable batteries, so for now at least, lithium ion batteries (and their more expensive lithium polymer cousins) are the go in the domestic world.

 

There you are, you can be helpful, just about confirms what I said.