High performance lithium or lithium ion cell

Abstract

Graphite sheeting having a thickness of less than 250 micrometers and in-plane conductivity of at least 100 S/cm when employed as a cathode current collector in a lithium or lithium ion cell containing a fluorinated lithium imide or methide electrolyte salt imparts high thermal resistance, excellent electrochemical stability, and surprisingly high capacity retention at high rates of discharge.

What is claimed is:  
     
         1 . A lithium or lithium-ion electrochemical cell, the cell comprising an anode comprising an anode active material, an anode current collector in electronically conductive contact with said anode; a cathode exhibiting an upper charging voltage in the range of 3 to 5 volts with respect to a Li/Li +  reference electrode, said cathode comprising a lithium insertion transition metal oxide, phosphate, or sulfate in electronically conductive contact with a cathode current collector comprising graphite, said cathode current collector having a thickness of less than 250 micrometers, said graphite being characterized by a bulk density of 0.08-2.25 g/cc, an electrical conductivity of at least 500 Siemens/cm, and said electronically conductive contact being characterized by a resistance of less than 50 ohm-cm 2 ; an ion-permeable membrane as a separator between said cathode and anode; and an electrolyte solution being in ionically conductive contact with said anode and cathode, the electrolyte solution comprising an aprotic polar solvent or a polymer, and a lithium compound at a concentration in the range of 0.2 up to 3 molar, said lithium compound being represented by the formula  
       R f   1 SO 2 X − (Li + )YZ a    
       wherein X is C or N, a=0 or 1 with the proviso that a=1 when X is C and a=0 when X is N; wherein when a=1, Y and Z independently are electron-withdrawing groups selected from the group consisting of CN, SO 2 R f   2 , SO 2 R, P(O)(OR) 2 , CO 2 R, P(O)R 2 , C(O)R f   3 , C(O)R, cycloalkenyl groups formed therewith, and, H, with the proviso that Y and Z cannot both be H; wherein further R f   1 ,R f   2  and R f   3  are perfluoroalkyl radicals of 1-4 carbons optionally substituted with one or more ether oxygens; R is an alkyl group of 1-6 carbons optionally substituted with one or more ether oxygens, or an aryl group optionally further substituted; or wherein, when a=0, Y is an electron-withdrawing group represented by the formula —SO 2 R f   6  where R f   6  is the radical represented by the formula —(R f   4  SO 2 N − (Li + )SO 2 ) m R f   5  where m=0 or 1, and R f   4  is —C n F 2n — and R f   5  is —C n F 2n+1  where n=1-4, optionally substituted with one or more ether oxygens.  
     
     
         2 . The electrochemical cell of  claim 1  wherein the anode active material is carbon selected from the group consisting of graphite microbeads, natural graphites, carbon fibers, or graphitic flakes.  
     
     
         3 . The electrochemical cell of  claim 1  wherein the anode active material or the lithium insertion transition metal oxide, phosphate, or sulfate, or both, are in particulate form said particulates ranging in size from 1 to 100 micrometers in average equivalent spherical diameter.  
     
     
         4 . The electrochemical cell of  claim 1  wherein the cathode exhibits an upper charging voltage in the range of 3.5 to 4.5 volts with respect to a Li/Li +  ref. electrode.  
     
     
         5 . The electrochemical cell of  claim 1  wherein the lithium insertion transition metal oxide, phosphate or sulfate is selected from the group consisting of LiCoO 2 , spinel LiMn 2 O 4 , chromium-doped spinel lithium manganese oxides, layered LiMnO 2 , LiNiO 2 , LiNi x Co 1-x O 2  where x is 0<x<1, vanadium oxides, LiFePO 4 , and LiFeTi(SO 4 ) 3 .  
     
     
         6 . The electrochemical cell of  claim 5  wherein the lithium insertion transition metal oxide, phosphate, or sulfate is a lithium insertion transition metal oxide selected from the group consisting of LiCoO 2 , LiMn 2 O 4 , LiNiO 2 , LiNi x Co 1-x O 2  where x is 0<x<1, and derivatives thereof.  
     
     
         7 . The electrochemical cell of  claim 1  wherein the cathode current collector comprising graphite is a graphite sheet having a purity of >95%.  
     
     
         8 . The electrochemical cell of  claim 7  wherein the graphite sheet is characterized by a bulk density in the range of 0.8 to 1.4 grams per cubic centimeter.  
     
     
         9 . The electrochemical cell of  claim 1  wherein the graphite sheet has a thickness of less than 75 micrometers.  
     
     
         10 . The electrochemical cell of  claim 1  wherein the graphite sheet is characterized by an electrical conductivity of at least 1000 Siemens per centimeter in the plane of the sheet.  
     
     
         11 . The electrochemical cell of  claim 1  wherein the cathode current collector comprising graphite further comprises an adhesion promoter.  
     
     
         12 . The electrochemical cell of  claim 1  wherein the electrolyte solution comprises an organic carbonate.  
     
     
         13 . The electrochemical cell of  claim 12  wherein the organic carbonate is selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethylcarbonate, and mixtures thereof.  
     
     
         14 . The electrochemical cell of  claim 1  wherein the concentration of the lithium compound in the electrolyte solution is in the range of 0.5 to 2 molar.  
     
     
         15 . The electrochemical cell of  claim 1  wherein the concentration of the lithium compound in the electrolyte solution is in the range of 0.8 to 1.2 molar.  
     
     
         16 . The electrochemical cell of  claim 1  wherein the lithium compound is represented by the formula  
       CF 3 SO 2 N − (Li + )SO 2 CF 3    
     
     
         17 . A process for forming an electrochemical cell, the process comprising forming a melt processible composition by combining in a vessel provided with a mixing means a first polymer, a mixture of one or more polar aprotic liquids, and a lithium compound; mixing said composition at least until it is plastically formable; and, forming a sheet from said plastically formable composition by the application of heat and/or pressure thereto; layering said sheet with a graphite current collector sheet, an ion-permeable separator sheet, an anode sheet comprising an anode active material and a second polymer, and an anode current collector sheet, said graphite current collector sheet having a bulk density of 0.08-2.25 g/cc, a thickness of less than 250 micrometers and a conductivity of at least 500 Siemens/cm; and, consolidating said layered sheets so that the layers are in electrically and/or ionically conductive contact as necessary to form an electrochemical cell, said lithium compound being represented by the formula  
       R f   1 SO 2 X − (Li + )YZ a    
       wherein X is C or N, a=0 or 1 with the proviso that a=1 when X is C and a=0 when X is N; wherein when a=1, Y and Z independently are electron-withdrawing groups selected from the group consisting of CN, SO 2 R f   2 , SO 2 R, P(O)(OR) 2 , CO 2 R, P(O)R 2 , C(O)R f   3 , C(O)R, cycloalkenyl groups formed therewith, and, H, with the proviso that Y and Z cannot both be H; wherein further R f   1 , R f   2  and R f   3  are perfluoroalkyl radicals of 1-4 carbons optionally substituted with one or more ether oxygens; R is an alkyl group of 1-6 carbons optionally substituted with one or more ether oxygens, or an aryl group optionally further substituted; or wherein, when a=0, Y is an electron-withdrawing group represented by the formula —SO 2 R f   6  where R f   6  is the radical represented by the formula —(R f   4  SO 2 N − (Li + )SO 2 ) m R f   5  where m=0 or 1, and R f   4  is —C n F 2n — and R f   5  is —C n F 2n+1  where n=1-4, optionally substituted with one or more ether oxygens.  
     
     
         18 . The process of  claim 17  wherein the step of consolidating said layered sheets to form an electrochemical cell comprises the application of heat and/or pressure.  
     
     
         19 . The process of  claim 17  wherein the anode active material or the lithium insertion transition metal oxide, phosphate, or sulfate, or both, are in particulate form said particulates ranging in size from 1 to 100 micrometers in average equivalent spherical diameter.  
     
     
         20 . The process of  claim 17  herein the lithium insertion transition metal oxide, phosphate, or sulfate is a lithium insertion transition metal oxide is selected from the group consisting of LiCoO 2 , LiMn 2 O 4 , LiNiO 2 , LiNi x Co 1-x O 2  where x is 0<x<1, and derivatives thereof.  
     
     
         21 . The process of  claim 17  wherein the cathode current collector comprising graphite is a graphite sheet having a purity of >95%.  
     
     
         22 . The process of  claim 21  wherein the graphite sheet is characterized by a bulk density in the range of 0.8 to 1.4 grams per cubic centimeter.  
     
     
         23 . The process of  claim 17  wherein the graphite sheet has a thickness of less than 75 micrometers.  
     
     
         24 . The process of  claim 17  wherein the graphite sheet is characterized by an electrical conductivity of at least 1000 Siemens per centimeter in the plane of the sheet.  
     
     
         25 . The process of  claim 17  wherein the cathode current collector comprising graphite further comprises an adhesion promoter.  
     
     
         26 . The process of  claim 17  wherein the electrolyte solution comprises an organic carbonate.  
     
     
         27 . The process of  claim 26  wherein the organic carbonate is selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethylcarbonate, and mixtures thereof.  
     
     
         28 . The process of  claim 17  wherein the concentration of the lithium compound in the electrolyte solution is in the range of 0.5 to 2 molar.  
     
     
         29 . The process of  claim 17  wherein the lithium compound is represented by the formula  
       CF 3 SO 2 N − (Li + )SO 2 CF 3    
     
     
         30 . The process of  claim 17  wherein said first and said second polymers are selected from the group consisting of polyvinylidene fluoride and copolymers thereof, and ionomers having pendant groups comprising fluorinated sulfonate, imide or methide lithium salts and mixtures thereof.  
     
     
         31 . The process of  claim 30  wherein said first and said second polymers are polyvinylidene fluoride or copolymers thereof.  
     
     
         32 . The process of  claim 17  wherein said ion-permeable separator sheet comprises a polymeric component selected from the group consisting of microporous sheeting, solvent swellable polymers, gelled polymer electrolytes, polyethers, fluorinated ionomers, and combinations thereof.  
     
     
         33 . The process of  claim 17  wherein said ion-permeable separator sheet comprises polyvinylidene fluoride or copolymers of vinylidene fluoride with a monomer selected from the group consisting of hexafluoropropylene, perfluoromethyl vinyl ether, perfluoroethylvinylether, and perfluoropropyl vinyl ether.  
     
     
         34 . The process of  claim 17  wherein said ion-permeable separator sheet comprises a microporous polyolefin sheet.  
     
     
         35 . The process of  claim 17  wherein said ion-permeable separator sheet comprises an ionomer comprising a backbone of repeat units derived from vinylidene fluoride and a perfluoroalkenyl monomer having an ionic pendant roup represented by the formula:  
       —(O—CF 2 CFR) a O—CF 2 (CFR′) b SO 3   − Li +   
       wherein R and R′ are independently selected from F, Cl or a perfluorinated alkyl group having 1 to 10 carbon atoms, a=0, 1 or 2, b=0 to 6, and the imide and methide derivatives thereof.  
     
     
         36 . The electrochemical cell of  claim 1  wherein the cathode current collector is a graphite sheet having a purity of >95%, a bulk density in the range of 0.8 to 1.4 grams per cubic centimeter, a thickness of less than 75 micrometers; and, an electrical conductivity of at least 1000 Siemens per centimeter in the plane of the sheet; and the electrolyte solution is a 0.5-2 molar solution of a lithium compound in an organic carbonate selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethylcarbonate, and mixtures thereof; the lithium compound being represented by the formula  
       CF 3 SO 2 N − (Li + )SO 2 CF 3    
     
     
         37 . The process of  claim 17  wherein the cathode current collector is a graphite sheet having a purity of >95%, a bulk density in the range of 0.8 to 1.4 grams per cubic centimeter, a thickness of less than 75 micrometers; and, an electrical conductivity of at least 1000 Siemens per centimeter in the plane of the sheet; the aprotic liquid is an organic carbonate selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethylcarbonate, and mixtures thereof; and the lithium compound, represented by the formula  
       CF 3 SO 2 N − (Li + )SO 2 CF 3 ,  
       is present in an amount such that when combined with said organic carbonate will provide a solution of lithium compound in organic carbonate of 0.5 to 2 molar.