Storage Material Improves Energy Density Of Lithium-ion Battery

Researchers at the Institute for Chemistry & Technology of Materials at TU Graz have developed a new method that utilizes silicon for a lithium-ion battery. Its storage capacity is 10 times higher than the graphite substrate which has been used in batteries until now, and promises considerable improvements for battery and electric vehicles users.

High-performance energy storage technologies for the electric cars or mobile phone batteries and notebooks providing long battery times are visions of the future, one step nearer by scientists from Graz University of Technology.

Researchers at the Institute for Chemistry and Technology of Materials have developed a new method that utilises silicon for lithium-ion batteries. Its storage capacity is ten times higher than the graphite substrate which has been used up to now, and promises considerable improvements for users.

The new findings, which came to light in the NanoPoliBat EU project, have been recently submitted to the patent office by researchers together with their co-operation partner Varta Microbattery.

Modern electronic devices need more energy and even the automotive industry is hankering after increasingly powerful energy storage systems. The technological development of battery research has been inadequate for some time now. "A real revolution is needed for the development of the next generation. We need new storage materials for lithium-ion batteries," explains battery researcher Stefan Koller, who is familiar with the topic from his doctoral thesis. Together with colleagues from science and industry, he has managed to develop such a substrate material for electrochemical reactions at a low price.

In the newly developed process, researchers utilise a silicon-containing gel and apply it to the graphite substrate material. "In this way the graphite works as a buffer, cushioning the big changes in volume of the silicon during the uptake and transfer of lithium ions," explains Koller.

Silicon has a lithium-ion storage capacity some ten times higher than the up-to-now commercially used graphite. The new material can thus store more than double the quantity of lithium ions without changes to the battery lifetime.

This method is far cheaper than the previous ones in which silicon is separated in the gas phase. The challenge lies in the poor storage density of materials in the counter electrode in the whole battery, something which we have been doing intensive research on," says Koller.

Project Description NanoPoLiBat

The main objective of this work is to design functional nanomaterials as active materials, binder and separator for a very long life high rating polymer microbattery which can be used in high rate low voltage application. To overcome the current limitations of the components for lithium polymer batteries they should be newly re-designed and fine tuned. Nano-particulate electrode materials, electrode materials modified by surface layers in the nm- range (core-shell materials) and nano-structured composite electrodes and electrolytes-separators offer tremendous chances for realisation of this objective.

As positive electrode active material they select Li4Ti5O12 (lithiated state: Li7Ti5O12). This compound synthesised as nano-tubes and nano-fibres is characterised by extremely fast Li+-intercalation / de-intercalation and shows excellent capacity retentions even at very high C rates and in a wide temperatures range. It is by far superior compared to common commercialized micro- Li4Ti5O12.

Moreover intelligent composite electrodes require a well-designed spatial distribution of the various components. Simple mixing does not create optimised percolation patterns of conductive additives or other functional components. Self assembling of nano-particles on preconditioned surfaces can be used to create optimised 3-dimensional percolation patterns by use of the “binder-less” Substrate Induced Coagulation (SIC) in nano-thickness. Adequate electronic contacts for high-rate operation of these electrode materials can be made by SIC-coating.

The main project output is the understanding of the nano-material properties related to their synthesis structure and interaction to the metallic current collectors and to the other battery materials like conductive additives. Furthermore the different interfaces will be analysed and studied (electrodes to separator). The battery as demonstrator is the last proof of the developed nano-technology in the applied project.

In Asia and USA a considerable activity is directed towards the development of nano-material for an industrial use in the energy storage field. In order to be competitive with them we set up this network involving several European countries to establish on this future sector a nano-technology from the first material-developing and characterisation until the proof of their industrial viability. The economic yield of this project is the improvement of the infra-structure of nano-technology within the European Union and contributes to secure the European position with respect to future job opportunities.

The selected partners combine nicely basis-oriented work coming from the Universities Graz and Amiens and application-orientated institutes CSIC-ICMAB Barcelona and Fraunhofer Institute with the well-know company VARTA. The partners are situated in several European countries with an excellent infrastructure for working on their tasks.