FIELD OF INVENTION: A process for preparing nanostructured LiFePO4 -C and it derivatives. The invention particularly relates to a process of making LiFePO4-C and LiFe1-x Mx PO4-YNY -C (Where, M = Ti, Zr, B, V and N = S, F, CI Br etc) composite cathode materials for application in lithium-ion batteries. Background of the Invention: Lithium-ion battery technology has become increasingly important in recent years because it provides lightweight, compact, high energy density batteries for powering appliances in the rapidly growing electronic industries. These batteries are also considered as power sources for future electric vehicles [Evs] and hybrid electric vehicles (HEVs).A typical commercial lithium commercial lithium-ion cell consists of a layered UCoO2 as cathode, LiPF6 in EC/DMC as electrolyte and graphite anode. However, the capacity and rate performance of today's lithium-ion batteries are limited which hinders its application in green vehicles technology. Therefore, all battery scientists are focused on overcoming the technical barriers associated with future battery technology, namely cost, performance, safety and life. To the fulfillments of above, improvements on the cathode materials are critical for achieving high energy density lithium-ion batteries. Considerable efforts are presently being directed towards the replacement of the high-cost, toxic LiCoO2 cathode with more affordable and sustainable materials. Promising candidates are lithum manganese oxide, lithium vanadium oxide and lithium iron phosphates. Particularly, the phosphor-olivine, LiFePO4 (LEP), which in a lithium cell may be reversely delithiated to FePO4, has emerged as the candidate cathode material for next generation EVs and HEVs technology. This material is cheap, environmentally benign, and has a reasonably high capacity (170mAhg-1), i.e., approaching that of LiCoO2. However, LiFePO4 is an insulator type material having more than 3 eV band gap energy which retards its C-rate performance during high discharge rate performance during high discharge rate condition and also, low temperature capacity loss. Therefore, to increase its conductivity, a thin layer of carbon coating is suggested to achieve a minimum conductivity during solid state lithium intercalation. In another approach, it has been observed that doping can also improve its conductivity during charge transfer process. It has been observed in many cases that sulfur doping at Oxygen site may increase the lattice volume of cathode materials facilitating Li-on conduction during charge-discharge process. Sulfur doping also helps in stabilizing the structure giving a good support to the Metal-S bond and may play a major role during high and low temperature operation. This is due to the fact that during charge-discharge process at high and low temperature, the structural strain is maximum in the lattice. Sulfur as its volume is comparatively larger than oxygen, it enlarge the lattice which in turn helps in charge transfer process. Therefore, accessible capacity as high and low temperature is more than that of pristine LiFePO4-C composite. There are number of wet chemical methods such as co-precipitation, hydrothermal, sol-gel etc that are found in various literatures for making nanostructures LiFePO4-C composite and its derivatives. However, most of them are laboratory based methods that are either not facile or having lots of complications for process up-scaling and executing in bulk. The material produced using conventional industrial solid state process has several disadvantages such as inhomogenity, irregular and inconsistent particle morphology, larger particle size, poor control of stoichiometry etc while working in range of particles of submicron sized. Therefore, an advanced solid state process has been invented in this work to counter all the disadvantages related to conventional solid state process of preparing particularly nano-structured LiFePO4 -C and LiFe1- xMxPO4-yNy-C. Reference may be laid to Patent Number WO2008067677 also published as CN101636861A (Applicant: Phostech Lithium Inc.) wherein they claim involving the formation of a complex oxide (LFP) that is prepared by the solid state reaction of precursors under reducing atmosphere utilizing different raw materials for the introduction of Li, PO4 3- and Fe to obtain the lithium iron phosphate based electrode active materials involving multiple steps of nanogrinding and pyrolysis. It is well known that conventional solid state process has its own demerits like multi time grinding, inhomogenity, etc. Therefore production of nano LFP-C and its derivatives is very difficult in using the conventional solid state process. Again, it should be noted that too high a pyrolysis temperature has a tendency to result in the formation of grains which are fine but solidly agglomerated. US 2008/0241690 Patent Number teaches of a process of preparing crystalline LiFePO4 powder from a water based mixture having a Ph range between 6-10 containing water miscible boiling point elevation additives and Li, Fe precursor component. The process requires a stringent control of Ph and the use of co-solvent like DMSO. Upon heating DMSO as above 100° C (212° F), sulfur dioxide is evolved from this substance. Hazardous thermo-oxidative degradation products from DMSO include formaldehyde, methyl mercaptan and sulfur dioxide which are toxic and bad for human safety as well as environment. Reference may also be laid to Patent Number US 2002/0192137A1 relates to the production of nanoscale and submicron particles of LifePO4 and LiFe1-xMnxPO4 (0.4< x <) by a laser pyrolysis method. However, laser pyrolysis methods. However, laser pyrolysis methods are relatively expensive process, and powders produced by such method are not suitable for cost conscious applications like electric vehicles and hybrid electric vehicles technology. Further, US Patent Number 20090072203 also teaches of a process for preparing a carbon-coated Li-containing olivine or NASICON powder, comprising the steps of preparing a water-based solution comprising, as solutes, one or more Li-containing olivine or NASICON precursor compounds and polymerizing the monomer compounds in a single step, heat treating the obtained precipitate in a neutral or reducing environment so as to form a Li- containing olivine or NASICON crystalline phase and decompose the polymer compound. The process is multi step and not an in-situ coating process which may lead to non-uniform carbon coating of Li- containing olivine or nasicon powder. Reference may be lead to Unites States Patent Number 7670721 wherein they describes a process for the manufacture of a lithium insertion electrode comprising the steps of: providing an equimolar aqueous solution of Li1+, Mn+ and PO43- prepared by dissolving components which are susceptible to coexist as solutes in an aqueous system and which, upon heating at a temperature below 500o C, decompose to form a pure homogenous Li and M phosphate precursor; evaporating water form the solution, thereby producing a solid mixture; decomposing the solid mixture at a temperature below 500 oC to form a pure homogenous Li and M phosphate precursor ; annealing the precursor at a temperature of less than 600 oC in an inert of reducing atmosphere, thereby forming a LiMPO4 powder of olivine structure; providing a mixture of the LiMPO4 powder and a conductive carbon bearing powder. However, the above- mentioned process is behind the scope of our process and composition. The process directly describes about the process of manufacturing doped LiFePO4 or LiMPO4, whereas present process is dealing with the composition of co-doped (both cationic and anionic doping) LiFePO4. Similarly Unites States Patent Number 7101521 relates to a method for the preparation of a cathode active material comprising: mixing, milling and sintering materials for synthesis of a compound represented by the general formula LixFePO4, where 0