Classifications

• • 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
  • H01M10/052—Li-accumulators
• • 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
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • 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
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • 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
  • H01M4/362—Composites
• • 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
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • 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
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • 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
  • H01M2004/021—Physical characteristics, e.g. porosity, surface area
• • 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 non-fully delithiatable cathode compositions for rechargeable lithium batteries. In other aspects, this invention also relates to processes for preparing the compositions, to compositions produced thereby, to lithium electrochemical cells comprising the compositions, and to lithium batteries comprising the cells.
• BACKGROUND Rechargeable (secondary) lithium batteries typically comprise an anode, an electrolyte, and a cathode that contains lithium in the form of a lithium transition metal oxide.
• lithium transition metal oxides that have been used for cathodes include lithium cobalt oxide, lithium vanadium oxide, lithium nickel oxide, and various lithium manganese oxides. Sulfides or phosphates have also been used.
• Lithium cobalt oxide (LiCoO 2 ) is the most widely used cathode active material in commercial secondary lithium ion batteries. It has a theoretical capacity of about 280 mAh/g.
• cathode active materials that are "fully delithiatable" (fully delithiated during charging of the cell).
• cathode active materials such as LiCoO 2 (which typically has only half of its lithium removed when charged (for example, to Lio.s CoO 2 ))
• no additional capacity can be obtained with these materials by increasing the voltage range of the charge.
• At least one attempt has been made to prevent degradation of LiCoO 2 cathodes during charging or overdischarging. This involved electrochemically forming a protective film on the cathode after battery assembly.
• lithium transition metal oxide cathode active materials have been directed at improving their structural and/or thermal stability and have generally involved multiple steps (for example, coating, drying, and/or heat treatment steps). Such treatments have included, for example, the use of starting coating materials such as aluminum alkoxides, which form hydroxides (electrochemically active) at low temperatures and chemically bond to the cathode active material at higher temperatures.
• this invention provides such a composition, which consists essentially of (a) at least one non-fully delithiatable cathode active material; and (b) at least one electrochemically inactive metal oxide; the cathode active material and the metal oxide being present only as separate phases that have essentially no chemical bonding between them (no mixed phase).
• the composition consists essentially of a blend of particles of component (a) and particles of component (b).
• non-fully delithiatable cathode active materials can be electrochemically stabilized by the addition of electrochemically inactive metal oxides.
• simple physical blending or mixing of particles of the cathode active material and particles of the metal oxide produces a cathode composition that exhibits surprisingly enhanced capacity and cycling capability (relative to the cathode active material alone).
• the cathode composition is especially advantageous when used at voltages higher than the stable voltage window of the cathode active material (that is, voltages above the point where the material exhibits a sharp drop in capacity due to oxidative and reductive degradation through reaction with electrolyte) and enables access to the extra capacity of the material.
• this invention also provides a process for preparing the cathode composition of the invention, the process comprising the step of mixing (preferably, by dry blending) particles of component (a) and particles of component (b); a composition produced by the process; a lithium electrochemical cell comprising the composition; and a lithium battery comprising at least one lithium electrochemical cell.
• Figure 1 is a plot of capacity versus number of cycles for the cathode compositions described in Comparative Example 1 (no alumina) and Examples 1, 2, and 3 (various amounts of added alumina).
• Figure 2 is a plot of capacity versus number of cycles for the cathode compositions described in Comparative Example 1 and Example 2 (cycling in a broader voltage window of 3.0 V to 4.5 V and 4.55 V(versus Li)).
• Figure 3 is a plot of differential capacity versus voltage for the cathode composition described in Comparative Example 1 (cycling in a broader voltage window of 3.0 V to 4.5 V(versus Li)).
• Figure 4 is a plot of differential capacity versus voltage for the cathode composition described in Comparative Example 1 (cycling in a broader voltage window of 3.0 V to 4.55 V(versus Li)).
• Figure 5 is a plot of differential capacity versus voltage for the cathode composition described in Example 2 (cycling in a broader voltage window of 3.0 V to 4.5 N(versus Li)).
• Figure 6 is a plot of differential capacity versus voltage for the cathode composition described in Example 2 (cycling in a broader voltage window of 3.0 N to 4.55 N(versus Li)).
• Figure 7 is a plot of 10msec cell impedance versus number of cycles for the cathode compositions described in Comparative Example 1 and Example 2.
• Figure 8 is a plot of 15 min cell impedance versus number of cycles for the cathode compositions described in Comparative Example 1 and Example 2.
• Figure 9 is a plot of capacity versus number of cycles for the cathode compositions described in Comparative Example 2 and Example 4.
• Figure 10 is a scanning electron micrograph of the cathode composition described in Comparative Example 1 at lOOOx magnification.
• Figure 11 is a scanning electron micrograph of the cathode composition described in Example 2 at lOOOx magnification.
• Figure 12 is a scanning electron micrograph of the cathode composition described in Example 3 at lOOOx magnification.
• lithium electrochemical cell and “lithium battery” mean a cell or battery that uses lithium either as the negative electrode (in a metallic form or in an alloy form with other metals) or as the active cation species. Examples include a cell or battery with a lithium metal negative electrode; a cell or battery with graphite as the active negative electrode into which lithium ion intercalates during chargmg; and a cell or battery with a lithium alloy as the negative electrode;
• non-fully delithiatable cathode active material means an electrochemically active cathode material that cannot be fully delithiated during charging of a cell or battery without undergoing a change of structure (for example, full delithiation of LiNiO 2 provides NiO 2 , which is unstable and converts to NiO and oxygen);
• electrochemically inactive means a material that does not intercalate or alloy lithium and does not undergo reduction and oxidation under the charging/discharging operating conditions of a cell or battery;
• Non-fully Delithiatable Cathode Active Material useful in the cathode composition of the invention are those that are non-fully delithiatable.
• Representative examples of such materials include lithium transition metal oxides such as LiV 3 O 8 and LiMO 2 , where M represents one or more metals selected from the group consisting of nickel, aluminum, cobalt, and manganese (for example, LiCoO 2 , LiNiO 2 , oxides comprising nickel and aluminum, and oxides comprising nickel and manganese such as LiNio. 37 5Coo.25Mn 0 . 375 O 2 , LiNio. 1 Coo.sMno.
• cathode active materials include LiCoO 2 and lithium oxides comprising nickel and manganese (with LiCoO 2 and LiNio.3 75 C ⁇ o. 25 Mno. 37 sO 2 being more preferred and LiCoO 2 being most preferred) and mixtures thereof.
• Materials that are not "non-fully delithiatable" and thus not useful in the cathode composition of the invention include , for example, LiTiO 2 , LiTiS 2 , LiSnO, LiMoO 3 , LiCrO 3 , LiPbO, LiFe 2 0 3 , LiAg 2 N 4 O ⁇ , LiCF x , LiN 2 0 5 , LiFeS 2 , and LiMn 2 O .
• the cathode active material is in the form of particles (more preferably, substantially spherical particles). Large particles are generally desirable.
• suitable particles include microparticles (less than about 100 micrometers in average diameter, where "diameter” refers not only to the diameter of substantially spherical particles but also to the longest dimension of non-spherical particles).
• the average diameter of the particles preferably ranges from about 1 micrometer to about 20 micrometers, more preferably from about 5 micrometers to about 10 micrometers.
• Electrochemically Inactive Metal Oxide Metal oxides suitable for use in the cathode composition of the invention are those that are electrochemically inactive.
• the metal oxides are also electrically non- conductive, lithium ion permeable, relatively low in density, thermally stable, and relatively electrochemically and chemically inert to reaction with typical battery electrolytes.
• the metal oxides can be either hydrophobic or hydrophilic in nature. Representative examples of useful metal oxides include the hydrophobic and hydrophilic forms of Al 2 O 3 , SiO 2 , MgO, TiO 2 , SnO 2 , B 2 O 3 , Fe 2 O 3 ,Zr ⁇ 2, and mixtures thereof.
• Preferred metal oxides include Al 2 O 3 , SiO 2 , and mixtures thereof (with Al 2 O 3 being more preferred).
• the metal oxide is in the form of particles (more preferably, substantially spherical particles). Small, relatively non-agglomerated particles are generally desirable. Suitable particles generally include nanoparticles (less than about 100 nanometers in average diameter, where "diameter” refers not only to the diameter of substantially spherical particles but also to the longest dimension of non-spherical particles).
• the average diameter of the particles is less than about 30 nanometers, more preferably less than about 15 nanometers.
• the cathode composition of the invention can be prepared by mixing the cathode active material and the metal oxide.
• a method of mixing that is capable of providing an intimate mixture or blend of the particles of each of the two components is utilized (for example, use of a mortar and pestle, a ball mill, a jet mill, a rod mill, or a high shear blender).
• Mixing can be carried out in the presence of one or more inert solvents (for example, hydrocarbons such as heptane and hexane, or ketones such as 2-butanone), if desired, with subsequent solvent removal.
• inert solvents for example, hydrocarbons such as heptane and hexane, or ketones such as 2-butanone
• the cathode composition "consists essentially" of the cathode active material and the metal oxide. That is, the cathode composition can further comprise conventional cathode additives, if desired, provided that the additives do not significantly interfere with the intimate contact of the cathode active material and the metal oxide (that is, the additives do not react with the metal oxide and do not displace the metal oxide from the surface of the cathode active material. Poly(alkylene oxides), for example, cannot be included in the composition, as they tend to complex with the metal oxide and prevent it from intimately contacting the cathode active material. Thus, the cathode composition comprises the cathode active material and the metal oxide, with the proviso that no poly(alkylene oxide) is present.
• Useful non-interfering additives include binders such as polyvinylidenefluoride (PNDF), polytetrafluoroethylene, ethylene-propylene-diene (EPDM) terpolymer, emulsified styrene-butadiene rubber (SBR), and the like; and conductive agents such as carbon (for example, NULCA ⁇ VXC-72 (Cabot Corporation)) and the like.
• PNDF polyvinylidenefluoride
• EPDM ethylene-propylene-diene
• SBR emulsified styrene-butadiene rubber
• conductive agents such as carbon (for example, NULCA ⁇ VXC-72 (Cabot Corporation)) and the like.
• the conventional additives can be added prior to mixing the cathode active material and the metal oxide, but, preferably, they are added after the cathode active material and the metal oxide have been mixed. This facilitates the intimate mixing of the active material and the oxide.
• the cathode active particles are in contact with metal oxide particles.
• the amount of metal oxide that can be included in the composition will vary, depending upon the particle sizes, chemical nature, and surface morphology of the cathode active material and the metal oxide. However, for the preferred particle sizes set forth above, the metal oxide can generally be present in the composition in amounts ranging from about 1 to about 10 percent by weight, based on the total weight of the composition. Conventional additives can be present in amounts up to about 10 percent by weight (based on the total weight of the composition).
• the metal oxide of the composition of the invention does not exist as a film or shell covering a core of the cathode active material, and there is essentially no chemical bonding between them. Rather, the composition is a physical mixture of the two components, which exist as separate phases with no mixed phase
• the cathode composition of the invention can be used to prepare lithium electrochemical cells (comprising the composition, a non-aqueous electrolyte, and an anode) and lithium batteries comprising one or more of the electrochemical cells.
• Such cells and batteries when cycled above the stable voltage window of the cathode active material (for example, above 4.3 volts for LiCoO 2 ), generally exhibit a greater capacity and cycle life than the same cell or battery comprising a corresponding cathode composition without inactive metal oxide.
• the cathode composition can be applied (for example, by coating or extrusion) to a current collector or electrolyte or other substrate.
• the resulting cathode film can then be assembled into a cell or battery in a conventional manner with electrolyte, separator, and anode.
• the separator can comprise a porous, non-conductive material (for example, microporous polyethylene film having a thickness of about 25 micrometers and a porosity of about 40 percent).
• Suitable anodes include lithium metal, graphite, and lithium alloy compositions (for example, of the type described in U.S. Patent No. 6,203,944 (Turner) entitled “Electrode for a Lithium Battery” and U.S. Patent No. 6,225,017 (Turner) entitled “Electrode Material and Compositions”).
• Graphite is commonly used.
• the electrolyte can be a liquid, a gel, or a solid (often a liquid).
• solid electrolytes include polymeric electrolytes such as polyethylene oxide, polytetrafluoroethylene, fluorine-containing copolymers, and combinations thereof.
• liquid electrolytes include ethylene carbonate, diethylene carbonate, propylene carbonate, and combinations thereof.
• gel electrolytes are blends of the liquid and solid electrolytes.
• the electrolyte generally further comprises a lithium electrolyte salts.
• suitable salts include LiPF 6 , LiBF 4 , and LiClO .
• the electrolyte can also further comprise one or more conventional additives (for example, anode-stabilizing additives).
• PVDF polyvinylidene fluoride
• NMP N-methyl-2-pyrrolidinone
• additional NMP Burdick and Jackson, Muskegon, MI
• the resulting mixture was blended in a four-blade, air-driven, high shear mixer for 20 minutes.
• the resulting solution was coated on to an Al foil with a 15-mil (0.381 mm) gap die. The coated sample was then dried in an air convection oven at 120°C for lhr, followed by drying in a vacuum oven at 120°C for 12 hrs.
• Disks of 16-mm diameter were punched out for use as cathodes in 2325 coin cells.
• Each 2325 cell consisted of an 18-mm diameter disk of aluminum spacer (31 -mil (0.787 mm) thick), a 16-mm diameter disk of cathode, a 20-mm diameter microporous separator (CELGARD 2400, Celgard Inc., Charlotte, NC), 18-mm diameter x
• Tulsa, OK at room temperature using the following cycling protocol: Charge at 30 mA/g (of cathode active material) rate to 4.5 N. Hold at 4.5 N until current reaches 0.1 rnA. Discharge at 30 mA g (of cathode active material) rate to 3.6 N. Rest for 15 minutes. Repeat. Cell performance (specific capacity based on the cathode active material) is shown in Figure 1.
• Example 1 except that 1J55 g of LiCoO 2 was blended with 0.045 g fumed alumina (ALUMINUM OXIDE C, Degussa, Franfurt, Germany) by mortar and pestle before mixing with the SUPER S and PVDF. Electrochemical evaluation was performed essentially as described in Comparative Example 1. Cell performance is shown in Figure 1.
• LiCoO 2 Treated With 5 Weight Percent Alumina (Based on the Weight of LiCoO 2 and Alumina)
• a cathode composition and coin cells were prepared essentially as in Example 1, except that 1.11 g LiCoO 2 was blended with 0.09 g fumed alumina by mortar and pestle before mixing with the SUPER S and PVDF. Electrochemical evaluation was performed essentially as described in Comparative
• Example 1 Cell performance is shown in Figure 1.
• Example 2 using the following cycling protocol with set voltage and relaxation after charge to evaluate cell impedances: Charge at 30 mA/g (of cathode active material) rate to
• LiCoO 2 Treated With 10 Weight Percent Alumina (Based on the Weight of LiCoO 2 and Alumina)
• a cathode composition and coin cells were prepared essentially as in Example 1, except that 1.62 g LiCoO 2 was blended with 0.18 g fumed alumina by mortar and pestle before mixing with the SUPER S and PVDF. Electrochemical evaluation was performed essentially as described in Comparative Example 1. Cell performance is described in Figure 1.
• a cathode composition and coin cells were prepared essentially as in Example 2, except that 1.71 g of LiNio.3 75 Co 0 . 2S M11 0 . 375 O 2 was blended with 0.09 g fumed alumina by mortar and pestle before mixing with the SUPER S and PVDF. Electrochemical evaluation was performed essentially as described in Comparative Example 1. Cell performance is shown in Figure 9.

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