Development of nanomaterials for high power lithium batteries (NANOBATT)

Sonochemistry process was developed to obtain nanosized vanadium oxides, able to deliver high specific capacities (around 300mAh/g). V3O7.H2O with a grain size of about 6nm was obtained, leading to 50nm V2O5 particles after thermal treatment. Electrochemical measurements indicate high specific capacities (300mAh/g) and long cycle life.

The high energy ball milling device, the Simoloyer, was applied for the project work of mechanosynthesis of anode materials and cathode materials. The machines used for the laboratory experiments were Simoloyer CM01 which possesses 0.5l and 2l milling volumes. During the modification of the FeAlSiB based anode material by Simoloyer the particle size was essentially reduced and the amorphous structure could be kept without any change. The mechanosynthesis from ferrous and lithium phosphate to Lithium iron sulphate was very successful. Particle size of each synthesized materiel was measured by laser diffraction meter Coulte LS200. The D50 of the particle sizes ranges between 1.5 to 9µm. For the future industrial application the production process will be scaled up from the laboratory machine with 2l milling volumes up to 400l.

State of the Art processes (practical & industrial) all relates to the high temperature (>500°C) synthesis of LiFePO4 compounds using either expensive raw materials such as Iron(II) oxalate or intermediate substances not commercially available or unstable. Moreover, for compounds requiring doping and/or substitution of Iron by another element, State of the Art processes require the preparation and use of separate raw material. Some recipes impose also the synthesis of new non available specific compounds. ERACHEM studied several processes for this type of materials. The proposed process is very useful for the battery community for at least three reasons: - Uses low cost, readily available raw materials - Iron(II) sulphate, Mn(II) sulphate. - The generic process proposed for the intermediate compound can accommodate any suitable composition or proportion of metals contrary to the State of Art methods. - Once this highly homogeneous intermediate compound is prepared, the synthesis of the Olivine active phase (doped and or/substituted) can be done at a much lower temperature than the State of Art preparation methods (+/- 350°C).

The synthesis, using rapid solidification of the metallic melts (melt spinning technique), of new types of metal based amorphous and nanostructured alloys and compounds. The synthesized alloys contained: - One or more inactive elements, not more than 50 atom percent, which does not alloy with lithium, selected from Ni, Fe, Cu, Mn; - One or more active elements, not less than 50 atom percent, which alloy with lithium, selected from Si, Al, Ag, Ge. The characterization of structure and microstructure properties of synthesized alloys was performed using XRD, SEM and TEM. The dissemination consisted in scientific communications in journals and at conferences.

The result consists in the achievement of two optimised grades of LiFePO4 and Li4Ti5O12 as electrode materials for high power lithium batteries. This LiFePO4 grade is able to deliver up to 80% of its capacity (165mAh/g) at continuous 10C rate. The other features of LiFePO4 are maintained: high cycle life (1000s of cycles), high safety/stability in the charged state, prolonged calendar life. Moreover this cheap material delivers similar energy density to LiCoO2 material. CEA optimised synthesis procedure leads to top performances in term of rate capability of the material compared to grades from other sources in the world. Part of the synthesis development is the subject of a patent, the remaining part is still a secret know-how. Li4Ti5O12 grade is developped to find an optimum in term of tap density:rate capability ratio. This material is able to deliver 80% of its capacity (170mAh/g) at continuous 10C rate with a rather good tap density of 1.7 g/cm³ (for comparison high surface area Li4Ti5O12 0.7g/cm³). Both materials are then suitable for high power application. Their expected low-cost is favourable to their use in large systems (HEV, EV) and consumer application such as power tools and electric bicycles.

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