Synthesis of nanosized, electrochemically active lithium transition metal phosphates

The increasing interest to develop new types of Li-ion batteries is motivated by the amplified need of batteries with high charge and discharge rates. Lithium transition metal phosphates are promising candidates to challenge this need. Before LiMnPO4 can be used as active material, research has to challenge two different aspects. First of all, for this material a crystallite size reduction is very important to improve the rate performance. And second, the electronic conductivity has to be improved. In this doctoral thesis, nanocrystalline LiMnPO4 and LiFePO4 were successfully obtained by a wet chemical hydrothermal synthesis. A phosphate-based surfactant, and glycine, an amino acid, were used as structure-directing additives. The results demonstrate that the additives have intense effects on controlling the nucleation and growth of LiMnPO4, resulting in nanocrystalline LiMnPO4. Furthermore, two methods to increase the ionic and electronic conductivity were developed, at first by a wet chemical hydrothermal carbon coating synthesis with glucose and second by a novel impregnation synthesis, in which carbon was used as a host material to obtain a carbon/LiMnPO4 composite. The results displayed that via the first method a carbon shell is formed around the particles. In addition, the second method showed promising results with samples comprising a three dimensional carbon fibre network impregnated with LiMnPO4. At last, amorphous LiMnPO4 was synthesized by a newly developed non-aqueous sol-gel method at ambient conditions. This material consists of three-dimensionally connected nanometer-sized particles that can be transformed into a crystalline substance by heat treatment. The last chapter of this thesis deals with the application of thus prepared materials in Li-ion rechargeable batteries. The performed electrochemical measurements illustrated that some samples showed very promising electrochemical properties