Title of Invention

"A SOLID STATE THERMAL PROCESS FOR THE PREPARATION OF LITHIUM CATHODE MATERIALS"

Abstract

The present invention relates to a novel process based on solid state thermal reaction for the preparation of cathode materials for lithium secondary batteries such as rocking chair and intercalated batteries. The solid state reaction takes place between solid lithium oxide (Li20) and a metal compound selected from oxides and nitrates. The metal is selected from nickel and cobalt. Urea or ammonium nitrate may be added to the reaction mixture in order to generate heal. LiNiO2 and LiCoO2 are formed.

Full Text

PROCESS FOR PREPARING CATHODE MATERIAL FOR LITHIUM BATTERIES Field of the invention The present invention relates to a novel process based on solid state thermal reaction for the preparation of cathode materials for lithium secondary batteries such as rocking chair and intercalated batteries. Background of the invention Lithium compounds such as lithium cobaltate (LiCoOj) and lithium nickelate (LiN02) are widely used as cathode material for both lithium secondary cells and thin film microbatteries due to its high reversibility to lithium ions, high cell capacity and less fading capacity over LiMnaO^ In general, lithium cobaltate materials are prepared by solid state thermal method and soft chemistry (like sol-gel) methods. The common materials for the preparation of this cathode lithium cobaltate (LiCoOj) are any one of the lithium salts viz. lithium nitrate or lithium hydroxide, lithium acetate lithium carbonate with cobalt nitrate or cobalt oxide. Soft chemistry methods are mainly used to prepare the intercalation compounds at low temperatures and to reduce the particle size of the compounds. But the soft chemistry routes are multi-step procedures, prolonged time for calcination and expensive. Prolonged heating time, mechanical grinding and intermittent cooling are major drawbacks of solid state thermal procedures. Other preparation methods are also available in literature for preparation of lithium cobaltate like pulsed laser deposition, sputtering and electrostatic spray deposition. Lithium nickelate is also useful as a cathode in lithium secondary cells of high voltage to replace present low energy density secondary storage cells. In the art it is known to prepare lithium nickelate by reacting lithium nitrate, or lithium hydroxides or any other lithium salts with lithium nitrates, acetates, hydroxides or sulphates by a sol-gel process at a temperature in the.range-of 350 - 500°C. However, separation of the final product requires several steps. In the preparation of intercalation compounds, any one of the following disadvantages are observed in the above conventional procedures. 1. Side reactions occur i.e., unexpected product. 2. Unreacted material is left behind which acts as impurity. 3. Partial reactions occur. 4. Several steps are needed for preparation. 5. Controlled conditions required. 6. Long calcination time 7. Nonhomogeneous reactant distribution during heating i.e., undesirable phases are formed. Reference: 1. "Synthesis and electrochemical properties of LiCoCh spinel catho.des"-S. Choi and A. Manthiram, Journal of the Elecfrochemical Society, Vol. 149(2) (2002) A162-166. 2. "Fabrication of LiCo02 thin films by sol-gel method and characterization as positive electrodes for Li/ LiCoO2 cells " -M.N. Kim, H. Chung, Y. Park, J. Kirn^ J. Son, K. Park andH. Kim, Journal of Power Sources, Vol. 99(2001) 34-40. '3. "High temperature combustion synthesis and electrochemical characterization of LiNiOi, LiCoC-2 and LiMniO^ for lithium ion secondary batteries" - M.M. Rao, C. Liebenow, M. Jayalakshmi, M. Wulff, U. -Guth and F. Scholz, Journal of Solid State Electrochemistry, Vol. 5, Issue 5(2001) 348-354. 4. "Lithiated cobaltates for lithium - ion batteries- Structure, morphology and electrochemistry of oxides grown by solid state reaction, wet chemistry and film deposition" C. Julien and S. Gastro-Garcia, Journal of Power Sources, Vol. 97-98 (2001) 290-293. 5. "Electrochemical characterization of layered LiCoOz films prepared by electrostatic deposition", Won-Sub Yoon, Sung-Ho Ban, Kyung-Keun Lee, Kwang-Bum Kim, Min Dyu Kim and Jay Min Lee, Journal of Power Sources, Vol. 97-98 (2001) 282-286. 6. "Emulsion-derived lithium manganese oxide powder for positive electrodes in lithium ion batteries" Chung-Hsin Lu and Shang-Wei Lin, Journal of Power Sources, Vol. 93 (2001) 14-19. 7. "Cobalt doped chromium oxides as cathode materials for secondary, batteries for secondary lithium batteries" Dong Zhang, Branko N. Popov, Yury M. Poddrahansky, Pankaj Arora and Ralph E. White, Journal of Power Sources, Vol. 83 (1999) 121-127. 8. "Synthesis and electrochemical studies of spinel phase LiMnjCU cathode materials prepared by the Pechini process"- W. Liu, G.C. Farrington, F. Chaput and B. Dunn, Journal, of the Electrochemical Society., Vol. 143, No.3(1996) 879-884. 9. "Synthesis of electrochemical characterisation of LiMO2 (M = Ni, Nio.7sCoo.2s) for rechargeable lithium ion batteries", Chun-Chieh Chang, N. Scarr and P. M Kumta, J. of Solid Stale Ionics, Vol 112, 329 - 344 (1998). 10. "Structural and electrochemical properties of LiNio.3Coo.7O2 synthesized by different low temperature techniques", C. Julien, S. S. Michael and S. Ziolkewicz, International Journal of Materials, Vol. 1 (1999), 29-37 "Synthesis and characterization of LiCoNi(l-y) V04 lithium insertion materials", S. Panero, P. Reale, F. Bonno, B. Serosati, M. Arrabito, D. Mazza and N. Pennazi, J. of Solid State Ionics", Vol. 128, 43 - 52, (2000). "Preparation and characterization of high density spherical LiNi0.8CoO2 cathode material for lithium secondary batteries", Jierond Ying, ChunrongWan, Changyin Jiang and Yangxing Li, J. of Power Sources" Vol 99, (2001), 78-84. "High temperature combustion synthesis and electrochemical characterization of LiNi02l LioO2 and LiMn204 for lithium ion secondary batteries", M.M. Rao, C. Liebnow, M. Jayalakshmi, M. Wulff, U. Guth and F. Scholz, J. of Solid State Electrochemistry", Vol 5, Issue 5, 348 - 354(2002). Objects of the invention The main object of the invention is to provide a process for the preparation of lithium cathode materials which overcomes the disadvantages of the prior art enumerated above. It is another object of the invention to provide a process for the manufacture of lithium cathode materials which does not result in impurities. It is a further object of the invention to provide a process for the manufacture of lithium cathode materials which does not result in impurities. It is further object of the invention to provide a process for the manufacture of lithium cathode materials which does not involve a multiplicity of steps. Summary of the invention Accordingly the present invention relates to a solid state thermal process for the preparation of lithium cathode materials of the general formula LiM02 wherein M is Ni or Co which comprises preparing a solid mixture of Lithium oxide and CO3O4 in stoichiometric proportions adding urea or ammonium nitrate as a self heat generating material to prepare a uniform reaction mixture and heating the reaction mixture at a temperature in the range of 400° to 750°C to recover lithium cobaltate. In one embodiment of the invention, the metal oxide is Co3O4 and the Lithium oxide and the cobalt (II) oxide are mixed in stoichiometric condition. In another embodiment of the invention, the reactants are heated at a temperature in the range of 450° to 750°C. In further embodiment of the invention, the reactants are of analytical reagent grade. In another embodiment of the invention, the metal nitrate is nickel nitrate. In a further embodiment of the invention, urea or ammonium nitrate is added to the reaction mixture of lithium oxide and cobalt (II) oxide as self heat generating materials and ground well. In yet another embodiment of the invention the ratio of LizO + CosCX mixture and urea or ammonium nitrate additive is 1:3. In a further embodiment of the invention, the process comprises mixing solid lithium oxide and cobalt (II) oxide, mixing urea in the resultant mixture and grinding the final mixture, introducing the resultant mixture in a furnace and heating at a temperature in the range of 450 to 750°C to obtain lithium cobaltate. In one embodiment of the invention, the LJ2O is mixed with CosO^ in the following preferred proportions Li2O: CosO^ = 0.16: 0.84 (for I gram) In another embodiment of the invention, the process comprises mixing solid lithium oxide and nickel nitrate and heating to a temperature in the range of 450 to 750°C to obtain lithium nickelate. In another embodiment of the invention, the lithium oxide and nickel nitrate are mixed in the ratio of 1:2. Detailed description of the invention The present invention provides a simple single step reaction for the preparation of cathode materials for lithium secondary cells such as lithium cobaltate and lithium nickelate. The process comprises solid state mixing of the lithium oxide with the corresponding metal compound and heating with or without the addition of urea. The preferred temperature range for the heating which is carried out continuously in a furnace is 500 to 750°C for a period of about 8 hours. The products formed were examined by X-ray diffraction for confirmation. The following reaction occurs during the thermal process when the metal is cobalt. 3Li2O + 2Co304 + (O) -> 6UCo02 LijO is mixed with CoaO4 in the following desired proportions Li2O : CosCU = 0.16: 0.84 (for 1 gram). It is preferred that the reaction takes place in an electric furnace. The materials used are all in the solid state. Preparation of LiCoOz through solid state thermal reaction: (A) Li20 solid state material is allowed to react with solid CosC^ under controlled conditions at moderate temperature which yields fairly very good sample of spinel structure useful as a very good intercalating cathode. Stoichiometric amount of Pure AR sample of CosCU is mixed with pure AR sample of Li2O in the cationic ratio of Li:Co is (1:1) for the preparation of LiCoOz. This mixture is thoroughly mixed with urea in the ratio of 1:3 (mixture: urea). This uniform mixture was preheated at 300°C for 3 hours. In order to obtain a better homogeneous mixture, this mixture is ground well with double distilled water free ethylene carbonate (EC). This mixture was again heated to 700°C for 5 hours continuously to yield lithium cobaltate (LiCoO2) which is evidenced by X-ray analysis (Figure la). (B) LijO solid state material is allowed to react with solid €0364 under controlled conditions at moderate temperature which yields fairly very good sample of spinel structure useful as a very good intercalating cathode. Stoichiometric amount of Pure AR sample of 00364 and pure AR sample of Li20 in the cationic ratio of Li:Co is (1:1) for the preparation of LiCoOj. This mixture is thoroughly mixed with ammonium nitrate in the ratio of 1:3 (mixture: ammonium nitrate). This uniform mixture was preheated at 300°C for 3 hours. In order to obtain a better homogeneous mixture, this mixture is ground well with double distilled water free ethylene carbonate (EC). Again this mixture was heated to 700°C for 5 hours continuously to yield lithium cobaltate (LiCoC2) which is evidenced by X-ray analysis (Figure Ib). The following reaction occurs during the thermal process. 3Li20 + 2Co304 + (0) - 6LiCo02 Preparation of LiNiOz through solid state thermal reaction: (A) LJ20 solid state material is allowed to react with solid Ni(NOs)2 under controlled conditions at moderate temperature which yields fairly very good sample of spinel structure useful as a very good intercalating cathode. Pure AR sample of Ni(NOs)2 is mixed with pure AR sample of L/i/zO in the ratio of 2:1 such that an uniform mixture is formed. This mixture when heated to 600°C for 12 hours continuously yields lithium nickelate LiNiO2 which is evidenced by X-ray analysis (Figure 2). (B) LiaO solid state material is allowed to react with solid Ni(N03)2 under controlled conditions at moderate temperatures which yields fairly very good sample of spinel structure useful as a very good intercalating cathode. Ni(N03)2 is mixed with lithium salt Li2O in the ratio of 2:1 such that an uniform mixture is formed. The mixture when heated continuously at a temperature of about 500°C yields lithium nickelate confirmed by X-ray analysis (Figure 2). The following reaction occurs during the thermal process. Li2O + Ni(N03)2 + (0) -» 2LiNiO2 + 4N02 + 202 The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. Exampie-1 AR pure dry Li2O is mixed with AR pure dry Co304 in the ratio of 0.16: 0.84 in a pestle and mortar arrangement and then the mix is further mixed with 3 times the weight of urea and then introduced in an electric furnace. This mixture was heated first for 3 hours at 300°C and then again heated at 700°C for 5 hours. Components Compositions Li20 0.16g Go304 0.84 g Urea 3.00 g. Pre heating temperature .- 300°C Final temperature 700°C Time . 8 hours Particle size of the product 10-20 um Nature of the product Black Efficiency of the process > 90% Example-2 Pure dry AR Li2O is mixed with pure dry AR Co304 in the molar ratio of 0.16: 0.84 in a pestle and mortar arrangement and then the mix is further mixed with 3 times the weight of ammonium nitrate. The final mixture was heated first for 3 hours at 300°C and then heated at 700°C for 5 hours. Components Compositions Li20 0.16g Co304 0.84 g Ammonium nitrate 3.00 g Pre heating.temperature 300°C Final temperature 700°C Time 8 hours Particle size of the product 10-20 pro Nature of the product Black Efficiency of the process 90% molecular weight ratio Example-3 AR pure dry Li20 is mixed with AR pure dry Ni(NQ3}2 in the molar ratio of 1:2 in a pestle and mortar arrangement and the mix is then introduced in an electric furnace. This mixture is heated for 12 hours at 600°C. Components Compositions Li20 0.5 g N5(NO3)2 1-Og Pre heating temperature 100°C Final temperature 600°C Time 12 hours Particle size of the product 10-20 urn Nature of the product Black Efficiency of the process 80% Example-4 Pure dry AR LijO is mixed with pure dry AR Ni(NOs)2 in the molar ratio of 1:2 in a pestle and mortar arrangement and the mix is then introduced into an electric furnace and heated for 12 hours continuously at 500°C. Components Compositions Li20 0.5 g Ni(NO3)2 1.0 g Pre heating temperature 100°C Final temperature 500°C Tune 12 hours Particle size of the product 10-20 um Nature of the product Black Efficiency of the process 80% in LiM02, XRD spectra at 500°C. The peak at 26 = 68° is not well formed and the peak at 29 = 31 ° is present when compared to the standard. The main advantages of the present invention are 1. It is a single step solid state thermal process 2. Li2O is used to react with CosC^to form LiCo02 and with Ni(N03)2 to obtain LiNi02 of high capacity cathode for intercalation. 3. Heating time is considerably less, and hence considerable-heating time can be saved. We claim: 1. A solid state thermal process for the preparation of lithium cathode materials of the general formula LiMO2 wherein M is Ni or Co which comprises preparing a solid mixture of Lithium oxide and CO3O4 in stoichiometric proportions adding urea or ammonium nitrate as a self heat generating material to prepare a uniform reaction mixture and heating the reaction mixture at a temperature in the range of 400° to 750°C to recover lithium cobaltate. 2. A process as claimed in claim 1 wherein the reactants are of analytical reagent grade. 3. A process as claimed in claims 1-2, wherein the ratio of Li2O + Co3O4 mixture and urea or ammonium nitrate additive is 1 : 3. 4. A process as claimed in claims 1-3 wherein the Li2O is mixed with Co3O4 in the following proportion Li2O : Co3O4 = 0.16 : 0.84 ( per gram). 5. A process as claimed in claims 1-4 wherein no side reaction occur. 6. A solid state thermal process for the preparation of Lithium Cathode material as substantially herein described with reference to the examples.

Documents:

2756-DELNP-2004-Abstract (08-08-2008).pdf

2756-delnp-2004-abstract.pdf

2756-DELNP-2004-Claims (08-08-2008).pdf

2756-delnp-2004-claims.pdf

2756-DELNP-2004-Correspondence-Others (08-08-2008).pdf

2756-delnp-2004-correspondence-others.pdf

2756-delnp-2004-description (complete)-08-08-2008.pdf

2756-delnp-2004-description (complete).pdf

2756-delnp-2004-drawings.pdf

2756-DELNP-2004-Form-1-(08-08-2008).pdf

2756-delnp-2004-form-1.pdf

2756-delnp-2004-form-18.pdf

2756-DELNP-2004-Form-2-(08-08-2008).pdf

2756-delnp-2004-form-2.pdf

2756-DELNP-2004-Form-3-(08-08-2008).pdf

2756-delnp-2004-form-3.pdf

2756-delnp-2004-form-5.pdf

2756-DELNP-2004-Petition-137-(08-08-2008).pdf