These days, we all walk round with a smartphone and laptop – which has mainly been made possible by lithium-ion batteries. At the moment, these batteries still operate with a liquid electrolyte which limits miniaturisation. The flammable liquid also poses safety risk especially for use in wearables and medical implants. But because we also intend using sensors just about everywhere in our environment soon, we need to find a worthy successor to replace it. And this is the solid-state lithium-ion battery.
This new type of power unit will be more compact, as well as safer. And if you manage to combine this battery with thin film technology, it will also be possible to recharge that battery very quickly. This makes a handy solution for small batteries, which will always have a limited capacity, while in a larger format, this battery would also be suitable for flexible electronics and who knows, eventually maybe even for powering electric cars. In fact, you could say that it is the holy grail of rechargeable batteries.
The main problem with solid-state batteries is that we have not yet found the ideal electrolyte. Of course, we have made plenty of progress in this direction – just look at the many scientific papers that have already been published on the topic. But the fact remains that the world of batteries is still not much further down the road than the first generation of lithium solid-state batteries of the type that are used, for example in pacemakers. And which only deliver a very small amount of current.
Our research centre (imec) is on a quest to find the best electrolyte material for solid-state batteries and we are currently focusing on composite electrolytes. There are two other types of electrolytes, but they still have quite a few disadvantages. The first of these types, polymer electrolytes, do not have sufficient conductivity, while inorganic electrolytes require a high process temperature, which results in the electrodes becoming damaged.
Last year, we succeeded in developing a composite electrolyte that not only has good conductivity (2x10-4 S/cm), but is also compatible with the materials used for electrodes (lithium-manganese-oxide as a positive electrode and lithium-titanium-oxide as a negative electrode in our lab). This electrolyte is made mainly from silica, a material with which we have a great deal of experience in the chip industry.
Now the challenge is to combine our 3D electrodes and our silica-based composite electrolyte to produce a genuine 3D thin film solid-state battery. If everything goes to plan, we will have a first demonstration set ready in 2016. And hopefully we will then be able to demonstrate that 3D thin film solid-state batteries are more than just hype and are a real new step forward in battery technology that will enable us to produce ultra-small electronics and batteries that will charge up in no time at all!
Author profile:
Prof Dr Philippe Vereecken is an expert in electrochemistry and specifically in its use in electrochemical storage, nanomaterials synthesis and semiconductor processing.
