EP1149427A1 - Cathode active material for lithium electrochemical cells - Google Patents

Cathode active material for lithium electrochemical cells

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Publication number
EP1149427A1
EP1149427A1 EP00906108A EP00906108A EP1149427A1 EP 1149427 A1 EP1149427 A1 EP 1149427A1 EP 00906108 A EP00906108 A EP 00906108A EP 00906108 A EP00906108 A EP 00906108A EP 1149427 A1 EP1149427 A1 EP 1149427A1
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EP
European Patent Office
Prior art keywords
formula
lithium
compound according
electrochemical cell
cathode
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Application number
EP00906108A
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German (de)
English (en)
French (fr)
Inventor
Yeong-Chang Yoo
Do-Young Seung
Isobel Davidson
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National Research Council of Canada
Samsung Advanced Institute of Technology
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Individual
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Publication of EP1149427A1 publication Critical patent/EP1149427A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • This invention relates to a compound of molecular formula L xCrdon yMn, y O 4 +2 , wherein 2.2 ⁇ x ⁇ 4, O ⁇ y ⁇ 2 and z > 0, and to the use of this compound as a cathode material in secondary lithium and lithium ion cells.
  • the impetus for this invention was the recent, great increase in demand for rechargeable batteries that combine high specific and volumetric energy density and with low cost and thermal stability.
  • a lithium ion cell is a rechargeable electrochemical cell in which the electrochemically active components in both the cathode and the anode are lithium intercalation compounds.
  • the intercalation compound serves as a host structure for lithium ions, which are either stored or released depending on the polarity of an externally applied potential.
  • a lithium ion cell consists of a lithium intercalation cathode with an oxidizing potential and a lithium intercalation anode with a reducing potential.
  • a lithium intercalation material is able to reversibly store and release lithium ions in response to an electrochemical potential. On discharge, in a lithium ion cell, lithium ions move from the anode to the cathode, and thereby, generate an electrochemical current.
  • Typical anodes for a lithium ion cell are made from carbonaceous materials such as graphite or petroleum cokes.
  • Typical cathodes are made from transition metal oxides or sulphides.
  • lithium ion cells are normally built in the fully discharged state with lithium present only in the cathode and not in the anode. In this state usually both the anode and the cathode materials are air stable. Assembling the cell in the discharged state means that the ultimate capacity of the cell depends on the amount of lithium initially present in the
  • cathode For example, cathodes based on LiMnU2 have twice the
  • a lithium-poor lithium-manganese spinel structure for use in secondary electrochemical cells having a molecular formula of Li q M x Mn y O 2 where q is 0 to 1 .3, is described in US Patent No: 5, 169,736. More recently, the amount of lithium in such mixed metal oxides has been increased.
  • a single phase compound of molecular formula Li 2 Cr x Mn 2. x O 4 , wherein 0 ⁇ x ⁇ 2, and its use in secondary lithium ion cells is described.
  • compositions Li 2 Cr x Mn 2 x O 4 in which 1 .0 ⁇ x ⁇ 1 .5 was described by Dahn, Zheng and Thomas (J. Electrochem. Soc, 145, 851 - 859, March 1 998). These materials were made using a sol-gel technique followed by heating in an inert atmosphere to temperatures ranging from 500 to 1 100 °C. In this study a maximum discharge capacity of 1 50 mAh/g at a low current density ( 1 .5 mA/g) was found for a sample of composition Li 2 Cr, 25 Mn 0 75 O 4 which had been prepared at 700 °C.
  • the same sample cycled at 1 5 mA/g showed a capacity of about 1 37 mAh/g.
  • the materials prepared at 700 °C were all found by powder x-ray diffraction to have a 5 layered structure like LiCoO 2 with a hexagonal unit cell symmetry.
  • the volume of the crystallographic unit cells varied from 68.6 to 71 .9 cubic angstroms per formula unit of Li 2 Cr x Mn 2 x O 4 .
  • the compounds were characterized by Reitveld refinement of crystallographic unit cell dimensions from powder x-ray diffraction data.
  • the symmetry and space group of the compounds was found to depend on the composition and processing temperature.
  • Table 1 of the patent (US 5,858,324) .
  • Table 1 of the patent summarizes the structure refinements and chemical analyses for the 37 samples studied. Only two of the examples (samples 22 and 23) of Li y Cr x Mn 2 x O 4 + z have compositions in which y is greater than 2.0. The value of x ranges from 0.5 to 1 .5 and the value of z as reported in table 6 is zero.
  • Example 23 demonstrated a discharge capacity of 1 1 7 mAh/g only slightly better than that of example 3-3 at 106 mAh/g. This small difference in the discharge capacities of the two examples falls within the normal range of variability between cells containing identical cathodes.
  • a novel compound of molecular formula I Li x Cr ⁇ Mn 2 v O 4 + z wherein 2.2 ⁇ x ⁇ 4.0, 0 ⁇ y ⁇ 2 and z > 0, is provided.
  • x be in the range of about 2.2 to about 4, it is more preferred that x be in the range of 2.2 to 3.6.
  • y be in the middle and lower end of the range, i.e. about 0.1 to about 1 .75
  • useful compounds according to the invention toward the upper end of the range, i.e. up to about 1 .9 are included.
  • z be > 0, it is more preferable that 0 ⁇ z ⁇ 2.6.
  • R -3 m structure being smaller than that of LiCrO 2 i.e. smaller than 104.9 cubic angstroms, and yet further characterized by the average cation to anion bond distance being smaller than that of LiCrO 2 . This value is available in the literature.
  • a secondary lithium ion electrochemical cell comprising a lithium intercalation anode, a suitable non-aqueous electrolyte including a lithium salt, a cathode of a compound of formula I as defined above as initial active material, and a separator between anode and cathode is provided.
  • the anode of the present invention serves as the recipient for Li + ions.
  • the anode can be of any intercalation compound, which is capable of intercalating lithium and has an electrode potential sufficiently reducing to provide an adequate cell voltage over a range of lithium intercalation.
  • Specific examples include transition metal oxides such as MoO 2 or WO 2 [Auborn and Barberio, J. Electrochem. Soc. 134 638 (1 987)], the disclosure of which is incorporated herein by reference, transition metal sulfides (see also US Patent No: 4,983,476) or carbon products obtained by the pyrolysis of organic compounds.
  • transition metal oxides such as MoO 2 or WO 2 [Auborn and Barberio, J. Electrochem. Soc. 134 638 (1 987)]
  • transition metal sulfides see also US Patent No: 4,983,476
  • carbon products obtained by the pyrolysis of organic compounds As will be apparent hereinafter, various commercially available carbonaceous materials of predetermined structural characteristics have proven
  • the cathode of molecular formula I as defined above is an intercalation compound with an electrochemical potential sufficiently positive of the anode to produce a useful overall cell voltage. The greater the potential, the greater the resulting energy density.
  • the cathode generally serves as the initial reservoir of lithium. The capacity of the cell will be limited by the amount of lithium, available for deintercalation, present in the cathode. In most cases, only a proportion of the lithium present, during fabrication of the cathode, can be reversibly deintercalated.
  • the non-aqueous electrolyte of the present invention can be liquid, paste-like or solid.
  • the electrolyte could be a solid or gelled polymer.
  • Polymers useful for electrolytes in lithium cells include polyvinylidene fluoride (PVDF), with and without co-polymers, and polyethylene oxide (PEO).
  • the electrolyte typically includes a lithium salt in a liquid organic solvent.
  • Lithium salts useful for this purpose include LiAsF 6 , LiPF 6 , LiBF 4 , LiCIO 4 , LiBr, LiAICI 4 , LiCF 3 SO 3 , LiC(CF 3 SO 2 ) 3 , LiN(CF 3 SO 2 ) 2 , and mixtures thereof.
  • LiAsF 6 should be used with caution due to its toxicity.
  • a water-free solvent for these salts there can be used alone or in mixture with others an organic solvent of the group propylene carbonate, ethylene carbonate, 2-methyl tetrahydrofuran, tetrahydrofuran, dimethoxyethane, diethoxyethane, dimethyl carbonate, diethyl carbonate, methyl acetate, methylformate, ⁇ - butyrolactone, 1 ,3-dioxolane, sulfolane, acetonitrile, butyronitrile, trimethylphosphate, dimethylformamide and other like organic solvents.
  • the electrolyte solution can also contain additives such as Crown ethers eg.
  • FIG. 1 is a x-ray diffraction pattern of a sample prepared according to example 1 .
  • FIGS. 2 to 6 show specific capacities versus voltage or cycle number for electrochemical cells prepared according to example 1 .
  • FIG. 7 overlays x-ray diffraction patterns of samples described in example 1 .
  • FIGS. 8 and 9 show the voltage profiles of electrochemical cells prepared according to example 1 .
  • FIG. 10 is a plot of capacity versus cycle number for an electrochemical cell cycled under the conditions described in example 1 .
  • FIG. 1 1 is a x-ray diffraction pattern for the sample of example 2.
  • FIG. 1 2 provides the discharge voltage profiles of cells assembled and tested as described in example 2.
  • FIG. 1 3 is a SEM micrograph of a sample prepared according to example 2.
  • FIG. 14 is a plot of specific capacity for a cell prepared and tested as described in example 3.
  • FIGS. 1 5 -1 6 are overlays of x-ray diffraction patterns of the samples prepared according to example 3.
  • FIGS. 1 7 - 20 show specific capacities as a function of either voltage or cycle number for electrochemical cells prepared ant tested according to example 4.
  • FIG. 21 is a x-ray diffraction pattern of a sample prepared as described in example 5.
  • FIG. 22 is a plot of voltage versus capacity for an electrochemical cell assembled and tested according to example 5.
  • FIG. 23 is a x-ray diffraction pattern of a sample made according to example 6.
  • FIG. 24 shows SEM micrographs for samples described in example 6.
  • FIGS. 25 - 26 are plots of specific capacities for electrochemical cells assembled and tested as described in example 6.
  • the present invention relates to discovery of related phases with higher lithium content, and in some cases higher oxygen contents.
  • these phases exhibit both a high capacity and a sloping, single-plateau voltage curve. They are synthesized at temperatures in the range of 600 to 800 °C. Since they are prepared at moderate temperatures it is advisable to establish thoroughly homogeneous mixing of the precursors prior to firing. Consequently techniques which are known to be very effective at preparing homogeneous mixtures of fine powders have been employed. These include co-precipitation, spray-drying and polymer complexation. All three of these techniques have been shown to work and are described in detail in the subsequent examples. The first two techniques were found to produce materials with exceptionally high capacities and rate capabilities.
  • the materials provided in this invention exhibit a large discharge capacity in a sloping, single-plateau voltage curve at potentials greater than 2.5 volts relative to the potential of metallic lithium.
  • the idea of these processes is to prepare a uniform mixture of finely divided metals salts, which can serve as precursors for the synthesis of lithiated transition metal oxides containing one or more transition metals.
  • a uniform mixture of finely divided metals salts which can serve as precursors for the synthesis of lithiated transition metal oxides containing one or more transition metals.
  • Mn(CH 3 CO 2 ) 2 and Cr 3 (OH) 2 (CH 3 CO 2 ) 7 were employed.
  • any combination of water-soluble metal salts which can be decomposed thermally to the metal oxides could be used.
  • Suitable salts include metal nitrates, sulfates, hydroxides, oxyhydroxides, formates, citrates, and other organic salts.
  • a lithium containing precursor such as lithium hydroxide, lithium nitrate, lithium sulfate, lithium acetate, lithium carbonate, lithium oxide or lithium chloride could also be intimately mixed with the transition metal salts before thermal decomposition to the oxides.
  • the lithium precursor can be reacted with the transition metal oxides prepared by thermal decomposition of the mixed metal salts.
  • the composite hydroxides are mixed with lithium compounds such as lithium hydroxide, lithium oxide or lithium carbonate and heat-treated at particular temperature range in an Argon atmosphere to make the cathode active material Li x Cr y Mn 2 . v O 4 +z where 2.2 ⁇ x ⁇ 4, 0 ⁇ y ⁇ 2 and z > 0.
  • Co-precipitation procedures can be used to prepare a range of Li x Cr v Mn 2 y O 4 +2 materials.
  • the co-precipitation method starts by preparing mixed metal hydroxides from soluble metal salts such as nitrates, sulfates, acetates or chlorides.
  • the metal salts are dissolved in de-ionized water, and then mixed with an aqueous alkali solution under controlled conditions of temperature, pH, and concentration.
  • the resulting metal hydroxides are mixed with a source of lithium such as lithium oxide, lithium hydroxide or lithium carbonate and fired at a variety of processing temperatures in an inert atmosphere.
  • the heat treatment is used to complete the reaction and to control the oxidation state of each transition metal.
  • the oxidation states of the transition metals are critical to the material's crystal structure and electrochemical performance. The temperature of the heat treatment and the oxygen content within the reaction vessel will affect the oxidation states of the transition metals.
  • co-precipitation of a Cr-Mn composite hydroxide can be prepared as follows.
  • An aqueous solution containing a mixture of water-soluble chromium and manganese salts such as chromium nitrate and manganese nitrate or chromic sulfate hydrate and manganese sulfate is prepared by mixing the transition metal salts with de-ionized water.
  • the co-precipitation of Cr hydroxide and Mn hydroxide is caused by controlled addition of an alkali aqueous solution containing an alkali such as ammonium hydroxide, potassium hydroxide, sodium hydroxide, lithium hydroxide or mixtures thereof into the aqueous solution of transition metal salts.
  • the Cr-Mn composite hydroxide is collected by filtering the deposits and rinsing them with water.
  • the resulting composite hydroxide is then dried in an oven at 100°C.
  • the dried composite hydroxide is then mixed with a source of lithium such as lithium oxide, lithium hydroxide or lithium carbonate and the mixture is heat-treated in Argon for 24 hours at various temperatures between 600 and 1000°C. Characterization by powder X- ray diffraction and typical electrochemical data for materials prepared by the co-precipitation method is provided in the example 4.
  • the materials with the best electrochemical performance were those that were heat-treated at 650 - 750 °C.
  • lithium compounds include lithium oxides or any compounds that can be thermally decomposed to the oxide such as lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, or lithium acetate.
  • the mixtures were carefully dried and calcined in air and then heat-treated in an argon atmosphere to form the active cathode materials.
  • the compounds of formula I are further characterised by characteristic X-ray powder diffraction patterns. More specifically, the
  • X-ray powder diffraction patterns of compounds of Formula I are similar to that of LiCrO 2 with the exception that the reflections are shifted to higher diffraction angles, corresponding to smaller crystallographic unit cell size. It can be expected that the volume of the crystallographic unit cell will decrease with increasing lithium content. The increase in lithium content is effectively a partial substitution of lithium atoms for transition metal atoms and must be balanced by the partial oxidation of the remaining transition metals. The oxidation state of the manganese might, for example, be increased from + 3 to + 4 by the substitution of lithium atoms for transition metal atoms. This would result in a decrease in the crystallographic unit cell volume because the weighted average of the ionic radii of the cations will have decreased. That is substituting Li + and Mn +4 in the 1 :2 ratio, which would maintain charge balance, for Cr + 3 or Mn 3 + will result in a smaller average ionic radius.
  • the X-ray powder diffraction patterns of compounds of formula I 5 resemble the diffraction pattern of LiCrO 2 , which has a hexagonal unit cell with a crystallographic structure belonging to the space group R -3 m. Although the crystallographic structure of compounds of formula I have not been determined in detail, the X-ray diffraction patterns can be approximately indexed to hexagonal crystallographic unit cells like that of0 LiCrO 2 . Comparison of crystallographic unit cell dimensions between related structures provides information about relative bond distances and oxidation states. Volumetric comparisons of related crystal structures are most useful between crystallographic volumes that contain the same number of atoms. Since Li x Cr y Mn 2 .
  • v O 4 +z phases do not necessarily contain an equal number of 5 cations and anions, the quantity of cation or anion sites in the crystal structure must be chosen for making volumetric comparisons. After normalization to the same quantity of anion sites, the crystallographic unit cell volumes of Li x Cr y Mn 2 . v O 4 +z compounds are smaller than that of LiCrO 2 .
  • the corresponding crystallographic unit cell volumes are 104.9 A 3 for LiCrO 2 and 102.1 A 3 for 5 Li 3 Cr 1 , based on a hexagonal R -3m structure.
  • Li 3 1 Cr, 34 Mn 0 66 O 5 8 from Table 4 in the examples to follow has a crystallographic unit cell volume of 102.92 A 3 .
  • the crystallographic unit cell volume of Li 2 CrMnO 4 for a similar number of atomic sites is 107.69 A 3 (J. Power Sources, vol. 81 -82, p. 406-41 1 ,
  • the invention relates to a compound having the formula Li x Cr y Mn 2. y O 4 +z wherein 2.2 ⁇ x ⁇ 4, 0 ⁇ y ⁇ 2, and z > 0 and an electrode composition containing this compound.
  • the initial composition has the formula Li x Cr Y Mn 2 y O 4 + z wherein 2.2 ⁇ x ⁇ 4, 0 ⁇ y ⁇ 2, and z > 0, and in the course of utilizing the compound as an electrode, the composition can vary in x from 4 to 0.
  • x be in the upper end of the range, i.e. about 2.2 to about 4, and more preferably in the range of 2.5 to 3.6
  • useful intermediate compounds through the middle of the range where x is about 2, to the lower end of the range where x is near 0 are also within the scope of this invention.
  • these intermediate compounds are formed by cycling an appropriate cell starting with a cathode of a material of formula I in which x is about 2.2 to about 4.
  • compounds of the present invention have exceptionally good chemical stability. Greater chemical stability often results in enhanced safety in electrochemical cells.
  • the preferred negative electrode is based on a carbonaceous product. Suitable carbonaceous materials include:
  • isotropic graphite composed of a mixture of graphite and carbonized pitch with a degree of graphitization greater than or equal to 0.4 and heat treated fluid coke and commercial graphite whose first lithium electrochemical intercalation is performed at or above 50°C, as per US Patent No: 5,028,500.
  • Typical electrodes in the present invention are fabricated from 70 -
  • a conductivity enhancer such as Super S carbon black and/or graphite
  • a binder such as poly(vinylidene fluoride) (PVDF) or Kynar Flex ® .
  • PVDF poly(vinylidene fluoride)
  • Kynar Flex ® a binder
  • Other conductivity enhancers such as Shawinigan Acetylene Black, graphites or other conductive materials may be used.
  • other binders such as Teflon ® , ethylene propylene diene monomer (EPDM), polyolefins or elastomers may be substituted for Kynar Flex.
  • the compounds of the invention have the following distinguishing characteristics. They contain a greater molar percentage of lithium than previously known related materials and therefore have a greater theoretical capacity in use as cathodes in a lithium ion cells. They are characterized by their composition, crystallographic unit cell dimensions, x-ray diffraction patterns, and shape of their voltage curves. When used as cathodes in secondary lithium or lithium ion cells, the compounds of the invention exhibit significant enhancement in discharge capacities relative to related cathode materials. In addition, secondary lithium or lithium ion cells with cathodes based on the compounds of the invention exhibit a broader operational voltage range. It is expected that a broader operational voltage range will facilitate higher currents and faster recharging times.
  • a mass of 2.8 g of this oxide was slurried with 1 3 ml of a 4M solution of lithium hydroxide in de- ionized water and heated treated in an alumina crucible in a tube furnace under a flow of air.
  • the heating regime was controlled to heat the sample slowly, over 5.5 hours, to 450 °C, hold at 450 °C for 2 hours and then allow the sample to cool slowly in the furnace to room temperature.
  • Figure 1 is a x-ray diffraction pattern of the sample after heat-treatment.
  • the diffraction pattern can be compared to that of LiCrO 2 as indicated by the bar diagram under the diffraction pattern.
  • the diffraction pattern of the Li x Cr y Mn 2 . y O 4 + z sample is similar to that of LiCrO 2 but there are differences in the relative intensities of the peaks and the peaks of Li x Cr y Mn 2 y O 4 +z are shifted to higher angle relative to those of LiCrO 2 .
  • Chemical analysis of the sample by atomic absorption found the composition to be Li(3.30 ⁇ 0.25)Mn(1 .06 ⁇ 0.08)Cr(0.94 ⁇ 0.05)0(5.54 ⁇ 0.28), with the oxygen content estimated by difference.
  • Electrodes were prepared from a mixture of 0.456 g of active material, 0.047 g of Super S carbon black, and 0.049 g of graphite (Lonza S4). The mixture was formed into a slurry with 1 .206 g of a binder solution containing 3 weight percent of Kynar Flex 2801 in n- methyl pyrrolidinone (NMP) and cast as a film on aluminum foil by the doctor blade method. The cast was dried in air at low heat on a hot plate and then at 1 1 0 °C for twenty minutes in a convection oven.
  • NMP n- methyl pyrrolidinone
  • Electrode discs of 1 .27 cm diameter were punched from the cast and densified by pressing each disc with a force of 500 lbs. on a hydraulic press.
  • the electrodes typically had a thickness between 0.008 to 0.01 3 cm after pressing.
  • the electrochemical cycling was carried out in 2325 coin cells each containing an internal spring and spacer to maintain an adequate pressure on the electrode stack.
  • the anodes were lithium (Foote Mineral) discs of 1 .65 cm diameter and 0.05 cm thickness and electrolyte containing 1 M LiPF 6 in 1 : 1 ethylene carbonate (EC) : dimethyl carbonate (DMC) (Mitsubishi Chemical) .
  • the voltage profile for the first seven cycles of a cell cycled at 3.6 mA/g between 2.5 and 4.3 volts is shown in figure 2.
  • the initial discharge capacity was 1 80 mAh/g and the average output voltage was 3.41 volts.
  • a plot of discharge capacity versus cycle number for this cell is provided in figure 3.
  • Another cell cycled between 2.5 and 4.5 volts produced discharge capacities of 1 87 to 200 mAh/g at 3.6 mA/g and 145 to147 mAh/g at 14.4 mA/g as shown in figure 4.
  • Figure 5 is a plot of capacity versus cycle number for a similar cell cycled at 7.2 mA/g from 2.5 volts to initially 4.3 volts and later 4.5 volts.
  • Figure 7 shows a comparison of the powder x-ray diffraction patterns of the material before and after washing.
  • An electrode cast was made of the washed sample in a similar manner as the unwashed sample.
  • the electrode cast of the washed sample contained 0.406 g active material, 0.050 g Super S, 0.054 g graphite and 1 .286 g of a 3 weight percent solution of Kynar Flex 2801 in NMP. Electrodes discs were punched from this cast and tested in coin cells in a manner similar to the previous examples. This cast was used in a cell cycled at 7.2 mA/g between 2.5 and 4.5 volts. The cell had a discharge capacity of 1 82 mAh/g on the first cycle. Figure 8 shows the capacity and voltage profile of this cell.
  • FIG. 9 A voltage versus capacity plot for another cell containing a cathode punched for the same cast is shown in figure 9. This cell was cycled at 3.6 mA/g between 2.5 and 4.7 volts on the first cycle and between 2.75 and 4.7 volts for subsequent cycles.
  • Figure 10 is a plot of discharge capacity versus cycle number for the same cell. As can be seen in the figure this cell could be cycled to 4.7 volts over 30 cycles without severe capacity loss and retained discharge capacities in excess of 1 85 mAh/g.
  • an intimate mixture of manganese and chromium salts was prepared by spray drying a 1 liter solution containing 24.677 g of manganese acetate (Aldrich) and 22.075 g of chromium acetate hydroxide (Aldrich) .
  • the metal salts were calcined at 475 °C for 4 hours in air.
  • a quantity of the product of the calcination, 4.014 g, was combined with 20.85 ml of a 4 M aqueous solution of LiOH (Anachemia) as a slurry. The mixture was slowly heated to 450°C in air and held at that temperature for 2 hours.
  • FIG. 1 2 shows the voltage versus capacity profiles for cells with these cathodes cycled at the indicated current densities.
  • the charge and discharge capacities at the 1 st , 1 5 th , 30 th and 50 th cycles for cells cycled at various current densities are tabulated in table 1 .
  • Two SEM micrographs of the product from the spray-drying procedure are provided in figure 1 3.
  • Table 1 Charge and discharge capacities for the 1 st , 1 5 th , 30 ,h and 50 th cycle of cells cycled between 2.5 and 4.5 volts at the indicated current densities.
  • the x-ray diffraction patterns of the manganese-rich series of samples A to J are shown in figure 16.
  • the discharge capacities for the 1 st , 10 th and 20 th cycles of cells with cathodes based on the manganese-rich materials cycled between 2.5 and 4.5 volts at a current density of 7.2 mA/g are listed in table 3.
  • the manganese-rich materials exhibited very stable discharge capacities over the first twenty cycles.
  • a cell with a cathode of composition Li 3 -iMni 07Cr 0 93 ⁇ 66 had a capacity of 175 mAh/g on the 20 th cycle while those of compositions Li 2 eMn-i ⁇ oCr 0 9 o0 4 5 and Li 3 ⁇ Mn ⁇ i5Cro 8 5 ⁇ 4 7 had capacities of 145 and 150 mAh/g by the 20 th cycle.
  • Figure 1 8 is a plot of discharge capacity versus cycle number for the same cell. As can be seen in the figure a capacity near 21 5 mAh/g was sustained for more than 40 cycles. The same sample was also evaluated in another coin cell at a higher current density. Figure 1 9 plots the discharge capacity for the first 100 cycles of a cell cycled between 2.5 and 4.5 volts at a current density of 14.4 mA/g. A discharge capacity near 1 50 mAh/g was maintained for 100 cycles. The second sample was tested in a similar manner as previous examples. A coin cell with a cathode comprised of the second sample was cycled between 2.5 and 4.5 volts at 3.6 mA/g. The discharge capacity of the first 32 cycles as shown in figure 20 is, after the first few cycles, remarkably constant at about 210 mAh/g.
  • a process for preparing a Cr-Mn hydroxide through co-precipitation according to present invention is described.
  • An aqueous solution of 2M concentration in chromium nitrate was prepared by adding a specified quantity (according to the targeted Cr/Mn ratio) of manganese nitrate to the solution with the final composition adjusted using water.
  • Slowly pouring caustic alkali aqueous solution containing 6 M sodium hydroxide into the concentrated transition metal nitrate solution caused the co- precipitation of Cr hydroxide and Mn hydroxide.
  • the precipitation was finished when the pH of the mixed solution reached a value of 10.
  • the Cr-Mn double hydroxide was obtained by filtering the deposits and the rinsing with water.
  • Lithium hydroxide was used as the Li compound.
  • the Cr-Mn double hydroxide obtained through the co-precipitation method described above was mixed with lithium hydroxide, and the mixture was placed in an alumina crucible and fired in a horizontal tube furnace under a flow of argon gas. The sample was fired for 24 hours at 650 - 700°C. After the firing the product was gradually cooled to room temperature and milled to a powder to be used as the cathode active material.
  • each sample was examined by an X-ray diffraction method.
  • the cathodes were prepared by casting and drying a slurry made from 85wt% active material with 1 0wt% acetylene black and 5wt% polyvinyiidene fluoride (PVdF) in NMP.
  • the substrate was Al foil and the diameter of punched cathodes was 1 0 mm.
  • the anodes were prepared by punching lithium metal film, having the thickness of 0.8 mm and the diameter of 1 2 mm.
  • the diameters of the electrodes were chosen to fit a commercial coin cell case of the type #201 6. These coin cells have a diameter of 20 mm and a height of 1 .6 mm.
  • the cell stack consisted of a three-layer sandwich of the cathode, a cell separator, and a lithium anode.
  • the separator used was a polypropylene film.
  • the electrolyte used was a 50/50 mixture by volume of ethylene carbonate and dimethyl carbonate containing 1 M LiPF6.
  • the cells were assembled and crimped in a helium filled glove box.
  • the coin cells were charged and discharged with the current density of 3.6 mA/g and the voltage range was 4.3-2.5V.
  • Figure 22 shows the charge and discharge curves of active material having above formula.
  • Table 4 represents the results of charge and discharge capacity of several different formulas.
  • the atomic ratios of Li, Cr, and Mn were determined by AA analysis. Oxygen contents were determined by difference.
  • the lattice parameters: a, b and c are in Angstrom units and the unit cell volumes are in units of cubic Angstroms.
  • Another sample was prepared by the co-precipitation process described in example 5 using chromium sulfate, Cr 2 (SO 4 ) 3 xH 2 O, and manganese sulfate, MnSO 4 H 2 O, instead of nitrate salts.
  • the precipitation of the mixed transition metal hydroxide was initiated by the controlled addition of ammonium hydroxide.
  • the mixed hydroxide was combined with lithium hydroxide monohydrate and heated at 650 °C in a flow of argon gas for 24 hours.
  • a x-ray diffraction pattern of the product is provided in figure 23.
  • Figure 25 and 26 are plots of discharge capacity versus cycle number for four cells containing cathodes comprised of compounds made by the co- precipitation process from either nitrate or sulfate salts. All the cells were cycled between voltage limits of 2.5 to 4.3 volts. The two in figure 25 were cycled at 3.6 mA/g while those in figure 26 were tested at a current density of 14.5 mA/g. The compositions as determined from atomic absorption are indicated in the figures 24 through 26.

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  • Inorganic Chemistry (AREA)
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  • Inorganic Compounds Of Heavy Metals (AREA)
EP00906108A 1999-10-08 2000-02-28 Cathode active material for lithium electrochemical cells Withdrawn EP1149427A1 (en)

Applications Claiming Priority (3)

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US15830399P 1999-10-08 1999-10-08
US158303P 1999-10-08
PCT/CA2000/000194 WO2001028010A1 (en) 1999-10-08 2000-02-28 Cathode active material for lithium electrochemical cells

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JP5236878B2 (ja) * 2003-05-28 2013-07-17 ナショナル リサーチ カウンシル オブ カナダ リチウムセルおよびバッテリー用の酸化リチウム電極
US9446963B2 (en) 2012-06-06 2016-09-20 Johnson Controls Technology Company System and methods for a cathode active material for a lithium ion battery cell

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US5858324A (en) * 1997-04-17 1999-01-12 Minnesota Mining And Manufacturing Company Lithium based compounds useful as electrodes and method for preparing same
DE19727611A1 (de) * 1997-06-28 1999-02-04 Merck Patent Gmbh Verfahren zur Herstellung vom Lithiummanganmischoxiden und deren Verwendung
US6117596A (en) * 1997-09-04 2000-09-12 Samsung Electronics Co., Ltd. Organic electrolyte and lithium secondary cell employing the same
JP3625630B2 (ja) * 1997-11-10 2005-03-02 日本電信電話株式会社 コバルト酸化物正極材料の製造方法、及びその方法により製造したコバルト酸化物正極材料を用いる電池

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