Abstract:
A method for generation of phase-pure doped and undoped Li x  Mn y  O z  precursors. The method of this invention uses organic solutions instead of aqueous solutions or nonsolution ball milling of dry powders to produce phase-pure precursors. These precursors can be used as cathodes for lithium-polymer electrolyte batteries. Dopants may be homogeneously incorporated to alter the characteristics of the powder.

Description:
The United States Government has rights in this invention pursuant to Contract No. DE-AC04-76DP00789 between the Department of Energy and American Telephone and Telegraph Company. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     A method for the consistent generation of phase-pure, doped and undoped Li x  Mn y  O z  to be used, for example, in the manufacture of cathodes for lithium batteries has been actively sought. Standard preparation methods for these compounds use the mixed-oxide approach of heat treating a mixture of lithium and manganese salts or oxides (e.g., LiOH+MnO 2  ; Li 2  CO 3  +MnO 2  ; Li 2  CO 3  +Mn 2  O 3 ) to form the desired lithium manganese oxide phase. This invention uses organic solutions instead of aqueous solutions or non-solution ball milling of dry powders to produce phase-pure Li x  Mn y  O z   
     BACKGROUND ART 
     U.S. Pat. No. 5,135,732 (Barboux et al.) discloses the preparation of LiMn 2  O 4  compounds with aqueous solutions. 
     SUMMARY OF THE INVENTION 
     An object of this invention is a process for producing phase-pure, doped and undoped Li x  Mn y  O z  which can be used, for example, in the manufacture of cathodes for lithium batteries. 
     Another object of this invention is the preparation of Li x  Mn y  O z  using organic solvents instead of aqueous solutions or non-solution ball milling of dry powders. 
     A still further object of this invention is the formation of homogeneous solutions of lithium-manganese nitrates which can be precipitated as intimately mixed powders of lithium-manganese oxalates. 
     A still further object of this invention is the formation of homogeneous solutions of lithium-manganese doped nitrates which can be precipitated as intimately mixed powders of lithium-manganese doped oxalates. 
     A still further object of this invention is the controlled stoichiometric formation of Li x  Mn y  O z  compounds not feasible with current technology. 
     A still further object of this invention is the controlled introduction of transition metal dopants into Li x  Mn y  O z  compounds to control the characteristics of battery-cathode material made from these compounds. 
     To achieve the foregoing and other objects, and in accordance with the purpose of the present invention, as embodied and broadly described herein, the present invention is a method of preparing Li x  Mn y  O z  powder compounds using organic solutions instead of the currently used aqueous solutions or non-solution ball milling of dry powders. The method of the present invention readily produces phase-pure material which is being investigated for the manufacture of cathodes for lithium polymer electrolyte batteries. The intimate mixing produced by this chemical methodology results in powder compounds which have short component diffusion distances; therefore, significantly lower temperatures can be used to convert the compounds to desired mixed-oxide form. The method allows for controlled stoichiometric formation and doping of Li x  Mn y  O z  compounds which is not feasible with current technology. The controlled introduction of dopants to control the final characteristics of battery cathode material made from these compounds is easily realized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The accompanying drawing, which is incorporated in, and forms part of, the specification, illustrates embodiments of this invention and, together with the description, serve to explain the principles of the invention. 
     FIG. 1 shows the general steps for the production of doped and undoped Li x  Mn y  O z  compounds according to this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to a preferred embodiment of this invention, a system is provided for the generation of phase-pure, doped and undoped Li x  Mn y  O z  compounds to be used, for example, in the manufacture of cathodes in lithium batteries in a reproducible way. 
     As shown in FIG. 1, a preferred embodiment of this invention includes the preparation of precursors using organic solvents. The following example is provided as illustrative of the present invention and is not intended to limit its scope in any way: 
     Example 
     All reactions were handled under an inert atmosphere unless otherwise noted. Tetrahydrofuran (THF) and methanol were dried over, and distilled from, Na/benzophenone and CaO, respectively. All Fourier transform infrared (FT-IR) data were collected on pre-fired material. Aldrich Me 4  NOH·6H 2  O (tetramethyl ammonium hydroxide hexahydrate), H 2  C 2  O 4  (oxalic acid), Aldrich Mn(NO 3 ) 2  ·xH 2  O, Aldrich LiNO 3 , Aldrich Al(NO 3 ) 3  ·9H 2  O, Aldrich Ni(NO 3 ) 2  ·6H 2  O and Aldrich Co(NO 3 ) 2  ·6H 2  O were used as received. The values for molar solutions and volume ratios are approximate. 
     (Me 4  N) 2  C 2  O 4  : A 6.0M solution of Me 4  NOH·6H 2  O in methanol was added to a stirring 8.3M solution of H 2  C 2   4  in methanol in the volume ratio of 1.0:0.36, respectively. The reactants were stirred under argon for 24 hours. The solvent was removed in vacuo over a period of 12 hours using a warm water bath. The resulting white powder was used without further purification. 
     Mn(NO 3 ) 2  ·THF 0 .98 : A 3.4M solution of Mn(NO 3 ) 2  ·xH 2  O in THF was stirred for 12 hours and the solvent removed in vacuo over a period of 12 hours. The degree of substitution was proven by weight differential to be 1 Mn(NO 3 ) 2  :0.98 THF molecules. 
     LiMn 2  O 4  : A 0.87M solution of LiNO 3  in methanol was added to a stirring 0.42M solution of Mn(NO 3 ) 2  ·THf 0 .98 in methanol in the volume ratio of 1.0:4.4, respectively. This mixture was stirred for 10 min and one volume unit of a 0.29M solution of (Me 4  N) 2  C 2  O 4  in methanol was added by syringe to 0.26 volume unit of the mixture. A precipitate immediately formed. The resulting powder was separated from the solution by centrifugation and dried by rotary evaporation. This air-sensitive off-white powder was then placed in a ceramic boat and rapidly transferred, in air, to a furnace. The powder was fired at 0.2° C./min up to 200° C. and then heated at 5° C./min up to 600° C. and held at this temperature for 3 hours to facilitate crystallization. The resulting material has been shown by x-ray diffraction (XRD) to be phase-pure LiMn 2  O 4  : Fourier transform infrared (FT-IR) (KBr, cm -1 ) 3038 (w), 2966(w), 2587(w), 2485(w), 2383(w), 1676(m), 1630(mb), 1496(s), 1348(sb), 1266(m), 1095(m), 1046(w), 1019(m), 950(s), 833(w), 821(wb), 797(m), 497(w), 460(w), 408(w). 
     Li 2  Mn 2  O 4  : A method similar to the production of LiMn 2  O 4  was used except for the following change: 1.7M solution of LiNO 3  in methanol. 
     Li 3  Mn 2  O 4  : A method similar to the production of LiMn 2  O 4  was used except for the following change: 2.6M solution of LiNO 3  in methanol. 
     AlLi 8  Mn 15  O 32  : A 0.17M solution of Al(NO 3 ) 3  ·9H 2  O in methanol was added to a 1.3M solution of Mn(NO 3 ) 2  ·THF 0 .98 in methanol in the volume ratio of 1.0:4.4, respectively. 0.054 mole of LiNO 3  was added to this stirring solution. This mixture was stirred for 10 min. and one volume unit of a 1.9M solution of (Me 4  ND 2  C 2  O 4  in methanol was added to 0.26 volume unit of the mixture. A precipitate immediately formed. The resulting powder was separated from the solution by centrifugation and dried by rotary evaporation. This air-sensitive, off-white powder was then placed in a ceramic boat and rapidly transferred, in air, to a furnace. The powder was fired at 0.2° C./min up to 200° C. and then heated at 5° C./min up to 600° C. and held at this temperature for 3 hours to facilitate crystallization. The resulting material was shown by XRD to be a phase-pure AlLi 8  Mn 15  O 32  : FT-IR (KBr, cm -1 ) 3040(m), 2969(w), 2365(m), 2346(m), 1693(sb), 1631(sb), 1492(s), 1337(sb), 1044(w), 1023(w), 948(s), 920(wb), 833(m), 791(m), 669(w), 580(w), 495(m), 460(m), 418(w). 
     DLi 8  Mn 15  O 32  (D=dopant): A method similar to the production of AlLi 8  Mn 15  O 32  was used except for the substitution of: (a) a 0.17M solution of CoCNO 3 ) 2  ·6H 2  O in methanol for the 0.17M solution of Al(NO 3 ) 3  ·9H 2  O in methanol: FT-IR (KBr, cm -1 ) 3040(w), 2973(w), 2937(w), 2380(w), 1622(sb), 1494(s), 1347(sb), 1047(w), 949(m), 922(w), 831(w), 789(m), 744(w), 497(w), 459(w); (b) a 0.17M solution of Ni(NO 3 ) 2  ·6H 2  O in methanol for the 0.17M solution of Al(NO 3 ) 3  ·9H 2  O in methanol: FT-1R (KBr, cm -1 ) 3031(w), 2962(w), 2361(m), 2346(w), 1629(sb), 1497(s), 1350(sb), 1047(w), 1030(w), 1018(m), 948(s), 921(w), 833(w), 820(w), 798(m), 741(w), 669(w), 497(w), 459(w), 419(w). 
     D 2  Li 8  Mn 14  O 32  : A method similar to the production of A1Li 8  Mn 15  O 32  was used except for the substitution of: (a) a 0.36M solution of Al(NO 3 ) 3  ·9H 2  O in methanol for the 0.17M solution of Al(NO 3 ) 3  ·9H 2  O in methanol: FT-IR (KBr, cm -1 ) 3042(m), 2972(w), 2934(wb), 2382(m), 1653(sb), 1624(sb), 1494(s), 1348(sb), 1045(w), 1020(w), 950(s), 921(m), 833(m), 791(s), 705(w), 581(m), 493(s), 460(wb), 421(w); (b) a 0.37M solution of Co(NO 3 ) 2  ·6H 2  O in methanol for the 0.17M solution of Al(NO 3 ) 3  ·9H 2  O in methanol: FT-IR (KBr, cm -1 ) 3039(m), 2972(w), 2925(w), 2380(w), 1632(sb), 1497(s), 1347(sb), 1047(w), 1019(w), 948(s), 922(wb) 833(w), 798(m), 496(w), 460(w), 421(w); (c) a 0.37M solution of Ni(NO 3 ) 2  ·6H 2  O in methanol for the 0.17M solution of Al(NO 3 ) 3  ·9H 2  O in methanol: FT-IR CKbr, cm -1 ) 3037(w), 2968(w), 2922(w), 2364(w), 2335(w), 1634(mb), 1470(s), 1343(sb), 1024(w), 955(m), 832(w), 788(m), 745(w), 668(w), 494(w), 459(w), 420(w). 
     D 3  Li 8  Mn 13  O 32  : A method similar to the production of AlLi 8  Mn 15  O 32  was used except for the substitution of: (a) a 0.54M solution of Al(NO 3 ) 3  ·9H 2  O in methanol for the 0.17M solution of Al(NO 3 ) 3  ·9H 2  O in methanol: FT-IR (KBr, cm -1 ) 3038(m), 2972(w), 2380(wb), 2052(w), 1692(sb), 1627(sb), 1496(s), 1346(sb), 1046(w), 1021(m), 949(s), 917(m), 831(m), 794(s), 585(m), 492(s), 460(m), 416(w); (b) a 0.54M solution of Co(NO 3 ) 2  ·6H 2  O in methanol for the 0.17M solution of Al(NO 3 ) 3  ·9H 2  O in methanol: FT-IR (KBr, cm -1 ) 3037(w), 2973(w), 2363(w), 2342(w), 1678(m), 1636(s), 1502(s), 1344(sb), 1048(w), 1019(w), 949(s), 921(w), 833(w), 796(m), 669(w), 496(w), 459(w); (c) a 0.54M solution of Ni(NO 3 ) 2  ·6H 2  O in methanol for the 0.17M solution of Al(NO 3 ) 3  ·9H 2  O in methanol: FT-IR (KBr, cm -1 ) 3038(w), 2970(w), 2373(w), 1675(mb), 1628(mb), 1495(s), 1342(sb), 1045(w), 1018(w), 949(m), 921(w), 831(w), 750(m), 670(w), 459(w), 415(w). 
     The example discussed above is cited to illustrate a particular embodiment of this invention. It is contemplated that the use of the invention may involve components having different forms and compositions. For example, Li x  Mn y  O z  precursor compounds may be made with or without dopants. It is intended that the scope of the invention be defined by the claims appended hereto.