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Nanotechnology for advanced rechargeable polymer lithium batteries

Final Report Summary - NANOPOLIBAT (Nanotechnology for advanced rechargeable polymer lithium batteries)

The project NANOPOLIBAT was engaged in the design and fine tuning of active materials, binders and separators for a very long life, high-rating rechargeable polymer microbattery for low voltage applications. Intelligent composite electrodes require a well-designed spatial distribution of the various components, which cannot be achieved by simple mixing. The alternative being explored is the self-assembly of nano-particles on preconditioned surfaces. Nano-particulate electrode materials, electrode materials modified by surface layers in the nm range (core shell materials) and nano-structured composite electrodes and electrolytes all offer opportunities to overcome the limitations of current lithium polymer microbatteries. They reduce transport limitations within the materials, and decrease the over-potential required for intercalation / de-intercalation reactions of the Li-ions.

An advanced nano-ceramic / organic hybrid polymer (Ormocer) combined with a promising new conductive salt is being used to produce a separator with high lithiumion conductivity and adequate electrochemical stability. The hybrid is also applied as binder for electrode materials. The goal is to build up a battery with the newly developed nano-materials, in order to deliver a final demonstrator proving the concept for future technologies such solar energy storage and the powering of smart cards.

Nano-silicon / graphite blends that show higher capacities than standard graphite have been developed. In the opening year, a first sample containing 10 % nano-Si was synthesised, showing a specific capacity of 600 mAh/g.

A study of the properties of Li-titanate (Li8Ti5O13) as a cathode material was carried out. This showed excellent capacity retention at various charge / discharge rates and temperatures, and proved to be safer than other common electrode materials. In the form of nano-tubes and nano-fibres, it is characterised by extremely fast Lions-intercalation / de-intercalation.

The conductivity of a polymer-salt complex electrolyte was measured at 10^6 Sccm at 25 degrees Celsius and 6 x 10^6 Sccm at 80 degrees Celsius. Test were undertaken to measure the effect of plastisation by a non-volatile tonic liquid on conductivity and battery performance. Samples of the ionic liquid were also made available to partners for testing with the li-titanate cathode material, nano-Si / C anode and Ormocer based binder. A first generation solvent-free polymer electrolyte gave conductivity of around 10^5 cOhm ccm.

A nano-Si/C-compound was successfully formulated. This invention was protected by a patent application. From the three ways of making nano-TiO2 the best was chosen, but has to be improved in further projects. The IL-electrolyte was improved significantly. The best of several candidates was formulated and characterised. The combination of Ormocer with the C-anode could not be used successfully. Further investigations are necessary.