Summary
For the electrochemical enclosure of lithium (Li) ions in the layer structure of graphite, a specific capacity of 372 mAh/g has already been proven. Similar behaviour is expected for carbon nanofibres (CNF).
The project's aim was therefore the electrochemical determination of Li accumulation in CNF. To this end, the project partners prepared electrodes by producing thin-film electrodes first on copper foil and later on nickel-foam electrodes. The samples were activated by adding Li salts. During a modification step, changes to the electrode preparation and CNF pretreatment (such as grinding of the samples or adding silicon oxide (SiO)) were intended to resolve adhesion issues and to minimise undesired irreversible capacities. The work programme further included electrochemical measurements for investigation of the various CNF samples' Li storage capacities.
Results:
- Plasma-treated CNF displayed high Li charge and discharge capacities. They proved comparable to standard graphite. Suitability for use in Li-ion batteries is given.
- For electrode preparation, use of nickel-foam electrodes proved more practical in terms of processing capacity and adhesion of the used CNF.
- Though activation of the samples by heating or adding Li salts with subsequent tempering reduced the irreversible capacities, it also reduced the charge and discharge capacities and is therefore not recommended.
- Careful grinding of the CNF in a planetary ball mill lead to better adhesion but also to a further increase in irreversible capacity.
- C/SiO composite materials possess a higher storage capacity than graphite, are mechanically stable and also highly promising materials.
- Addition of the spreading agent isopropyl myristate substantially improved the processing capacity, adhesion and, in some cases, the CNF's capacities.
