The US institution of energy has made progress in development of a new lithium-ion battery using spongy silicon which doubles the capacity of the battery. This battery can hold at least twice as much power as any conventional battery within laptops and mobile phones today. This type of battery is looking to be coming to our commercial products fairly soon and will revolutionize the market of mobile electric based goods. Now these aren’t the most powerful batteries out there at the moment, but its their design and physical properties that we are going to be discussing here.
What’s it made of?
Nanotechnology is the magic here, as it is made from a nano-structured silicon sponge. However let’s take a step back and understand what’s out there now. In almost every (LIB) Lithium-Ion Battery there consists of a graphite electrode, an electrolyte (usually lithium salt) and a metal oxide electrode, this oxide will usually have lithium in it too.
When you charge a LIB the energy given to the graphite electrode which is the anode, absorbs the lithium ions. When the battery is discharging there is a chemical reaction that causes the ions to flow out of the graphite into the metal oxide electrode which is the cathode.
The biggest drawback to this type of battery is how many ions can fit into an anode, and for graphite this isn’t too much. However scientists have looked into silicon as a new type of battery, if you compare this to lithium the silicon atoms are larger than carbon atoms. After you wade through the complex maths the silicon can potentially hold up to 10 times more energy as graphite. The only problem here is that the silicon absorbs so many ions its physical shape can increase up to 4 times its original size, in comparison to lithium batteries which are solid and tough ( because they are also volatile).
Where are we now?
The researchers within the DOE’s PNNL have successfully fabricated a silicon electrode that expands only 30% instead of 400%. This is great news for us as the 30% means that LIB designs can use this type of material without exploding. How it does this is due to the development of mesoporous silicon sponge. This basically means a piece of silicon that has many holes inside of it, what they did was quite clever as for the silicon expanding, it will expand into the holes in its structure before it physically expands to the user.
Porous silicon anode has an energy density of 750 mAh per gram! This is twice as much as graphite, and its structure seems to be able to with stand a lot of charge / discharge cycles. Over 1000 of these cycles the battery managed to retain over 80% of its initial power absorb rates. So due to this the team has been trying to developing the battery for commercial use, but they must account for the production process of the electrode which isn’t quite as streamlined as they want it to be “yet”!
Anything out there now?
There are already some batteries being shipped like this from a company called Amprius, who have started shipping out batteries with a silicon anode however it isn’t as powerful as the team have developed here about 50% of the strength. This isn’t bad but we are still eager to what the systems are going to be like over the next couple of years, as this could provide the resolution the mobile market so desperately needs and wants. Below is a picture of the output the team received over the charge cycles of silicon, you can see there is virtually no gradient within these lines! This is very impressive!
