The invention generally relates to the field of solid state chemistry and particularly to method for obtaining ultra thin composition of lithium metal phosphate.

BACKGROUND
Lithium metal phosphates have been a potential source for cathode materials in lithium ion batteries. The Lithium metal phosphates are environmentally safe and cost less for production of lithium batteries and demonstrate high theoretical capacity. However  lithium metal phosphates have poor intrinsic Li+/e- conductivities and long term cycling lead to structural instability. Normally  lithium metal phosphate compositions are coated with a conductive material  for example  carbon compound to enhance the electronic conductivity. The coated carbon is mostly in the amorphous form. The source of amorphous carbon is usually from metal and phosphate precursors employed during the synthesis of lithium metal phosphate. Additionally  the source of carbon can be a structure directing agent  example surfactant  employed during the synthesis of lithium metal phosphate. Alternatively nanostructures of the carbon-lithium metal phosphate compositions have been synthesized for enhancing the electrical conductivity. However  the above mentioned compositions has certain disadvantages which include but are not limited to poor electronic conductivity; structural instability of LMP during long battery cycling; compatibility with various types of binders; compatibility with all forms of electrolytes: conventional liquids to all forms of soft matter electrolytes especially polymer electrolytes synthesized using various techniques including those using low melting point solids e.g. plastic crystalline electrolytes including room temperature ionic liquids. Hence there is a need for a composition that overcomes the above mentioned disadvantages.

BRIEF DESCRIPTION OF DRAWINGS:
So that the manner in which the recited features of the invention can be understood in detail  some of the embodiments are illustrated in the appended drawings. It is to be noted  however  that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope  for the invention may admit to other equally effective embodiments.
FIG.1 shows a graph obtained from thermo-gravimetric analysis of a lithium iron phosphate composition having different loading of carbon structures  according to an embodiment of the invention.
FIG. 2 shows a graph of galvanostatic performance of a lithium iron phosphate composition with extended carbon structures  according to an embodiment of the invention.
FIG.3 shows a graph comparing the galvanostatic performance of a lithium iron phosphate composition with amorphous carbon and a lithium iron phosphate composition with extended carbon structure  according to an embodiment of the invention.
FIG.4 shows a graph comparing the conductivity of a lithium iron phosphate composition with amorphous carbon and a lithium iron phosphate composition with extended carbon structure  according to an embodiment of the invention.
FIG.5 shows a raman spectra of a lithium iron phosphate composition indicating quality of incorporated extended carbon structures  according to an embodiment of the invention.

SUMMARY OF THE INVENTION
One aspect of the invention includes a method for obtaining ultrathin composition of lithium metal phosphates. The method includes obtaining aqueous solution of lithium precursor and at least one metal precursor. The aqueous solutions of lithium precursor and metal precursor are then mixed in the ratio of 1:1 to 1:2 at a temperature in the range of 60oC -70oC to obtain a sol. To the sol obtained  extended carbon structures  for example  carbon nanotubes  in the range of <1% of the total weight of the composition  is added. The sol including the multi walled carbon nanotube is then dried at a temperature in the range of 65oC -80oC to obtain a gel. The gel is annealed at a temperature in the range of 800oC -900oC for time duration in the range of 8-12 hours to obtain multi-walled carbon nanotube composition of lithium metal phosphate.
DETAIL DESCRIPTION OF THE INVENTION:
Various embodiments of the invention provide a method for obtaining ultrathin compositions of lithium metal phosphates. Initially an aqueous solution of lithium precursor along with at least one metal precursor is obtained. In an embodiment of the invention  the lithium precursor is lithium phosphate  lithium acetate and lithium oxalate. A predetermined quantity of lithium precursor is added to a predetermined quantity of phosphoric acid to obtain a mixture. The mixture obtained is heated at a predetermined temperature under constant stirring for a predetermined duration of time to obtain a lithium precursor solution. The ratio of addition of the lithium precursor to the phosphoric acid is in the range of 1:1 to 1:2. In an example of the invention  1M lithium phosphate is added to 2M of phosphoric acid and heated at 60oC under constant stirring for about an hour to obtain a lithium precursor solution. The metal precursor is chosen from the group comprising of ferric citrate  ferric oxalo-dehydrate  manganese acetate  nickel acetate  cobalt acetate. A predetermined quantity of metal precursor is heated at a predetermined temperature under constant stirring for a predetermined duration of time to obtain a metal precursor solution. In an example of the invention  1M ferric citrate is heated at 70oC under constant stirring for about an hour to obtain a metal precursor solution.
The aqueous solutions of lithium precursor and metal precursor obtained by the method discussed herein above are then mixed in the ratio ranging between 1:1 to 1:2 at a temperature in the range of 60-70oC to obtain a sol. To the sol obtained  extended carbon nanostructures  example commercial carbon nanotubes (multi walled  single walled  double walled) in the range of <1% of the total weight of the composition  is added. The sol including the multi walled carbon nanotube is then dried at a temperature in the range of 65-80oC to obtain a gel. The gel is annealed at a temperature in the range of 800 -900oC for time duration in the range of 8-12hrs to obtain multi-walled carbon nanotube composition of lithium metal phosphate.

Example 1: Synthesis of lithium iron phosphates:
25-100 ml aqueous solution having 0.03M to 1M concentration of Ferric salts precursor example  ferric citrate  is heated at 70 to 80oC with constant stirring for 1 hour. 35-100 ml aqueous solution having 0.01M to 1M of Lithium precursor  example  lithium phosphate  Li3PO4  is mixed with phosphoric acid  H3PO4  in the concentration range of 0.02M to 2M and heated at a temperature in the range 60 to 70°C under constant stirring for 1 hour. The ratio of Li3PO4: H3PO4 is maintained in a range of 1:1 to 1:2. The two solutions obtained as herein are mixed together. Iron (Fe) to LiH2PO4 ratio is maintained at a molar ratio of 1:1 and final solution is heated at 60-70 °C with constant stirring for one hour until formation of clear sol. A predetermined amount of multi-walled and/or single-walled carbon nanotube  x  is added into above solution at a ratio 0 = x = 1 wt %. Finally  sol is dried at a temperature of 60oC to 70°C for 24 hours to form a Xerogel. The Xerogel is annealed at 700°C for 7 hr to obtain a black color carbon coated LiFePO4 /C.

Example 2: Synthesis of lithium manganese phosphate
25-100 ml aqueous solution having 0.02M to 1M concentration of Manganese acetate is mixed with citric acid in the molar ratio of 1:2 and heated at a temperature range of 70oC to 80oC with constant stirring for 1 hour. 25-100 ml aqueous solution having 0.01M to 1M concentration of Lithium precursor  example  lithium phosphate  Li3PO4  is mixed with phosphoric acid in the molar ratio of 1:2 and heated at a temperature of 60oC to 70°C under constant stirring for 1 h. The two solutions described herein above are mixed together. The ratio of manganese to lithium phosphate is maintained at a molar ratio in the range of 1:1 to 2:1. The solution obtained is heated at a temperature in the range of 60oC to 70 °C with constant stirring for 30 min until formation of a clear sol. A predetermined amount of multi-walled and/or single-walled carbon nanotube  x  is added into above solution at a ratio 0 = x =1 wt. The sol is dried at 75oC for 24 h to form xerogel. The xerogel is annealed at 800oC to 9000C for 10 hours to obtain a black color carbon coated LiMnPO4.
Characterization of carbon nanotube compositions of lithium metal phosphates:
The carbon nanotube compositions of lithium metal phosphates obtained by the process described herein above are characterized to determine stability and performance established through methods which include but are not limited to thermogravimetry  electrochemical and physico-chemical characterization.
FIG.1 shows a graph obtained from thermo-gravimetric analysis of a lithium iron phosphate composition having different loading of carbon structures  according to an embodiment of the invention. Thermo-gravimetric analysis  TGA  measures the weight loss as a function of temperature and signifies changes in sample composition as a function of temperature. The TGA data was recorded by heating the samples under air starting from room temperature   for example in the range of 220C to 26 0C  to 750 0C. The rate of heating was in the range of 30C to 5 0Cmin-1. The graph shows profiles obtained for lithium iron phosphate (LFP) with multi-walled carbon nanotubes with l concentration of the carbon nanotubes ? 1 wt %. Graph 1 (a) LFP coated with amorphous carbon (LFP-C)  1(b) LFP coated with amorphous carbon and 0.5 wt % of multi-walled carbon nanotubes  1(c) LFP coated with amorphous carbon and 1.0 wt % of multi-walled carbon nanotubes. The weight losses in the temperature range room temperature to nearly 200 0C signify loss of adsorbed water whereas weight loss at higher temperatures is due to the carbonization of the precursors. This process contributes to the formation of amorphous carbon in the composite lithium iron phosphate.
FIG. 2 shows a graph of galvanostatic performance of a lithium iron phosphate composition with extended carbon structures  according to an embodiment of the invention. Room temperature galvanostatic measurements were done at temperatures in the range of 220C to 26 0C and at constant current. Charge and discharge specific capacities versus cycle number with different types of carbon were plotted. In this example the galvanostatic performance of LFP-single walled carbon nanotubes (SWCNT)/multi walled carbon nanotubes (MWCNT) performed at current= 30 mAg-1 are shown. The amount of SWCNT/MWCNT is 0.5 wt % of the composition. The charge and discharge cycling was done using the composite LFP-C/CNT as the cathode and lithium as the anode. The electrolyte varied from commercial liquid electrolytes (1 M LiPF6-EC:DMC; 1 M LiTFSI-EC:DMC) to soft matter electrolytes especially based on ionic liquid/plastic crystalline based polymer electrolytes.
FIG.3 shows a graph comparing the galvanostatic performance of a lithium iron phosphate composition with amorphous carbon and a lithium iron phosphate composition with extended carbon structure  according to an embodiment of the invention. temperature galvanostatic measurements were done at temperatures in the range of 220C to 26 0C and at constant current. Charge and discharge specific capacities versus cycle number with different types of carbon were plotted. In this example the galvanostatic performance of LFP-amorphous carbon (LFP-C) and LFP-multi walled carbon nanotubes (LFP-MWCNT) at various currents are shown. The amount of MWCNT is 0.5 wt % in the composite samples. The charge and discharge cycling was done using the composite LFP-C/CNT as the cathode and lithium as the anode. The electrolyte varied from commercial liquid electrolytes (1 M LiPF6-EC:DMC; 1 M LiTFSI-EC:DMC) to soft matter electrolytes especially based on ionic liquid/plastic crystalline based polymer electrolytes.
FIG.4 shows a graph comparing the conductivity of a lithium iron phosphate composition with amorphous carbon and a lithium iron phosphate composition with extended carbon structure  according to an embodiment of the invention. Current versus voltage (I-V) plots for lithium iron phosphate with and without extended carbon structures are plotted. In this example the I-V plots for LFP coated with amorphous carbon (LFP-C) and LFP coated with multi walled carbon nanotubes (LFP-MWCNT) are shown. The I-V plots were obtained by scanning various regions of the composite electrode cast on aluminum current collector using a micromanipulator in combination with an optical microscope and I-V measuring setup. The LFP material with carbon nanotubes has a lower sample resistance compared to the LFP without nanotubes.
FIG.5 shows a raman spectra of a lithium iron phosphate composition indicating quality of incorporated extended carbon structures  according to an embodiment of the invention. Micro-Raman spectra (WITEC) of lithium iron phosphate coated with amorphous carbon (LFP–C) and lithium iron phosphate coated with carbon nanotubes (LFP–CNT) electrodes in the range of 150-4000 cm-1 were obtained using an excitation wavelength of 514.5 nm laser (laser power ? 1 mW). Only LFP-CNT samples show D and G bands indicating presence of carbon nanotubes.
The present invention involves an integrated synthesis of lithium metal phosphates  referred to as LMP. The LMP synthesized has various morphologies and dimensions. The LMP are electronically wired with optimum content of various extended carbon nanostructures e.g. carbon sheets/scrolls  carbon nanotube (CNT). Examples of carbon nanotube include but are not limited single walled nanotube; double-walled nanotube; multi-walled carbon nanotube and graphene including graphene oxides.
The synthesis technique employed here is not a mechanical mixture of carbon structures with porous LMP as reported in prior art. The coating with extended carbon structures resulted with excellent cyclability and rate capability desired for applications ranging from daily life as well as niche applications e.g. electric and space vehicles. The battery performance of the extended carbon nanostructures-lithium metal phosphate CNT-LMP were much superior compared to the carbon coated LMP of prior art. This is attributed to the very efficient percolating pathways for the electrons provided by the extended carbon structures compared to the amorphous carbon. Apart from improvements in electronic conductivity  LMP structure stabilizes considerably in the presence of the extended nanostructures. So  by coating the LMP with extended carbon structures advantageously improves the electrochemical performance and structural stability of the composition
The invention provides ultra thin compositions of lithium metal phosphates. The compositions demonstrate rate capability of ? 1C with LMP- wired extended carbon structures and compatibility in lithium based batteries and hybrid super capacitors. Further  the compositions also demonstrate structural stability of LMP during long battery cycling; compatibility with various types of binders; compatibility with all forms of electrolytes: conventional liquids to all forms of soft matter electrolytes especially polymer electrolytes synthesized using various techniques including those using low melting point solids e.g. plastic crystalline electrolytes including room temperature ionic liquids
The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art  the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

I Claim:
1. A method for obtaining ultrathin composition of lithium metal phosphates comprising
i. obtaining an aqueous solution of at least one lithium precursor;
ii. obtaining an aqueous solution of at least one metal precursor;
iii. mixing the aqueous solutions of lithium precursor and metal precursor to obtain a sol;
iv. adding a predetermined quantity of extended carbon structures to the sol to obtain a gel; and
v. annealing the gel at a predetermined temperature;
wherein the annealed gel yields extended carbon structure integrated composition of lithium metal phosphate.
2. The method according to claim 1  wherein the concentration range of lithium precursor to the metal precursor is in the range of 1:1 to 1:2.
3. The method according to claim 1  wherein the sol is obtained by heating the mixture at a temperature in the range of 60oC to 70oC.
4. The method according to claim 1  wherein the extended carbon nanostructures is added in the concentration range upto 1% of the total weight of the composition.
5. The method according to claim 1  wherein the gel is obtained by drying the sol including the extended carbon nanostructures at a temperature in the range of 65-80oC.
6. The method according to claim 1  wherein the annealing of the gel is performed in the presence of argon gas at a temperature in the range of 800oC to 900oC.
7. The method according to claim 1  wherein the annealing of the gel is performed in the presence of argon-reducing gas at a temperature in the range of 800oC to 900oC.
8. The method according to claim 1  wherein the time duration for annealing of the gel is in the range of 8-12 h.
9. The composition as described in the specification and as illustrated in the drawings.