Preparation and electrochemical characterization of LiMnPO4/single-walled carbon nanotube composites as cathode material for Li-ion battery

We investigated the synthesis of the nanocrystalline LiMnPO4 and its composites with single-walled carbon nanotubes (SWNTs) in order to apply them as cathode material in Li-ion battery. Two synthesis routes, precipitation and sol-gel, have been evaluated with regard to elemental composition, crystal size and crystal structure. Precipitation of LiMnPO4 from aqueous solution produces microcrystalline material with low specific surface area of 5 m(2)/g. Sol-gel procedure and in situ incorporation of SWNTs reduce the particle size to less than 100 nm and enhances specific surface area by factor of 10. Both materials have been used to prepare a cathode and the electrochemical performance of assembled battery has been tested. Whereas the electrical conductivity of the composite increases by 5 orders of magnitude upon addition of 1 wt.% of SWNTs, the battery capacity with a value of 20 mAh/g (theoretical 175 mAh/g) still appears low. We found out that incorporation of LiMnPO4 nanocrystals in a dense SWNT network (bucky paper) improves significantly the battery performance, and capacity approaching 150 mAh/g can be achieved. Our experiments provides the proof of principle that individual nanosize particles of LiMnPO4 can be sufficiently separated by conducting SWNTs to prevent their agglomeration, and electrically wired in a network for efficient electronic and ionic transport through the cathode. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim