A team of scientists from China and Germany may have found a solution for increasing efficiency as well as the capacity of li-ion batteries. Nano-sized cables made with titanium dioxide-coated carbon nanotubes promise to be cheap, reliable and do not depend on rare materials.

Within the framework of a joint project conducted by institutions including the German Max Planck Institute and the Chinese Academy of Sciences a paper has been published that proposes an “Efficient and Elegant Morphological Solution to the Lithium Storage Problem“.

It states that a special type of carbon nanocable in a battery’s construction would assist in considerably increasing its efficiency and capacity. Unlike other tested technologies that use titanium dioxide TiO₂-coated carbon nanotubes do not tend to fracture easily when repeatedly charged and discharged. Moreover, the nanocables appeared reliable showing almost no capacity loss after one hundred cycles. This is very useful for fabricating high-capacity batteries for electric vehicles.

The problem with the graphite anode

One of the main goals in battery research today is finding a replacement for the anode material graphite that is usually used in li-ion batteries today. The problem with this material is that it has a fairly low storage capacity and release rate. When the battery is in use the lithium ions held in the anode migrate to the cathode and release electrons, which power up the circuits the battery is connected to. The relatively low amounts of ions graphite can hold and release lead to a reduced efficiency and keep the lifetime of the batteries below a certain threshold.

Superior storage capacity and release rate for TiO₂

According to the chemists, the TiO₂-coated carbon nanotubes could be the alternative to make batteries that last longer and produce more power. However, the size of the tube is the important factor: “Titanium dioxide on its own is totally unsuitable for electrodes,”Joachim Maier, an expert at the Max Planck Institute for Solid State Research, in Stuttgart, Germany states. “Although it can hold lithium ions effectively, they are slow to diffuse through the structure - and it can take years to fill a millimetre-thick crystal. However, if the TiO₂ is only 10nm thick, it is filled in milliseconds," he added.

Moreover, the material is simple to produce and far cheaper than electrodes that are based on rare metals. The project team is therefore hoping that it can be more widely applied, perhaps for other energy storage devices such as super capacitors.

Background

Various research institutes, such as The National Natural Science Foundation of China, National Key Project on Basic Research(is this a programme or an institute?), the Chinese Academy of Sciences, and the Max Planck Society in Germany supported the work of the team. The paper “Symbiotic Coaxial Nanocables: Facile Synthesis and an Efficient and Elegant Morphological Solution to the Lithium Storage Problem” was published online 22 January in the ACS journal Chemistry of Materials.