Batteries and cathodes containing carbon nanotubes

The disclosure relates to cathodes that contain carbon nanotubes and batteries containing such cathodes.

Cathodes for batteries useful in implantable medical devices typically contain active materials, carbon black or graphite and polymeric binder. Such materials are typically mixed together and pressed to form a cathode. The combinations of active materials, carbon or graphite and binder are chosen to minimize volume and maximize the volumetric capacity of the cathode. As batteries for implantable medical devices decrease in size, a desire exists to increase the volumetric capacity of such batteries.

In one embodiment, a battery comprises a lithium metal anode, an electrolyte, and a cathode containing carbon nanotubes, and a cathode active material selected from include silver vanadium oxide (SVO), carbon monofluoride (CFx), manganese dioxide (MnO 2 ), vanadium pentoxide (V 2 O 5 ), copper fluoride (CuF 2 ) and copper silver vanadium oxide (Cu x Ag 2-x V 4 O 11 ) and mixtures of all or any of them, the cathode active material being present in the cathode in an amount of at least 80% by weight.

In another embodiment, a cathode comprises carbon nanotubes and a cathode active material selected from include silver vanadium oxide (SVO), carbon monofluoride (CFx), manganese dioxide (MnO 2 ), vanadium pentoxide (V 2 O 5 ), copper fluoride (CuF 2 ) and copper silver vanadium oxide (Cu x Ag 2-x V 4 O 11 ) and mixtures of all or any of them, the cathode active material being present in the cathode in an amount of at least 80% by weight.

In another embodiment, a battery comprises a lithium metal anode, an electrolyte and a cathode comprising a cathode composition containing carbon nanotubes, carbon monofluoride (CFx) and silver vanadium oxide, the silver vanadium oxide and CFx combined being present the composition in an amount of at least 80% by weight of the composition.

In another embodiment, a cathode consists essentially of an active material selected from the group consisting of silver vanadium oxide (SVO), manganese dioxide (MnO 2 ), vanadium pentoxide (V 2 O 5 ), copper silver vanadium oxide (Cu x Ag 2-x V 4 O 11 )), and copper fluoride (CuF 2 ) and mixtures of any of them, carbon monofluoride (CFx), and conductive additive consisting essentially of carbon nanotubes and carbon black or graphite or both, wherein the active material and the carbon monofluoride combined is present in an amount of at least 80% by weight.

In another embodiment, a battery consists essentially of an anode consisting essentially of lithium metal and a current collector, an electrolyte, a separator; and a cathode consisting essentially of carbon nanotubes, one or more active materials, carbon black or graphite or both carbon black and graphite, a binder, and a current collector.

In another embodiment, a battery consists essentially of an anode consisting essentially of lithium metal and a current collector, an electrolyte, a separator; and a cathode consisting essentially of CFx, SVO, carbon nanotubes, carbon black or graphite or both carbon black and graphite, a binder, and a current collector.

FIG. 1 is a depiction of a plot of the Delivered Capacity versus Discharge Voltage for one embodiment composition of a battery compared to a sample of a known composition of a battery.

“Carbon nanotubes” includes single walled carbon nanotubes and multi-walled carbon nanotubes (MWNT) and mixtures of both.

Carbon monofluoride, often referred to as carbon fluoride, polycarbon monofluoride, CFx, or (CFx)n or graphite fluoride is a solid, structural, non-stoichiometric fluorocarbon of empirical formula CFx, wherein x is 0.01 to 1.9, 0.1 to 1.5, or 1.1. One commercially available carbon monofluoride is (CFx)n where 0<x<1.25 (and n is the number of monomer units in the polymer, which can vary widely).

Silver vanadium oxide includes compounds having the general formula Ag x V y O z wherein x=0 to 2; y=1 to 4; and z=4 to 11, for example, AgV 2 O 5 , Ag 2 V 4 O 11 , Ag 0.35 V 2 O 5.8 , Ag 0.74 V 2 O 5.37 and AgV 4 O 5.5 .

Applicant has discovered that the use of carbon nanotubes in cathode materials can provide a battery having increased longevity over batteries that contain a cathode that uses conventional conductive additives such as carbon black or graphite.

Applicant has found that the use of carbon nanotubes in place of carbon black or graphite in cathodes such as CFx/SVO cathodes allows for the use of higher amounts of active materials in a cathode composition while maintaining physical integrity, in the case of a pressed or pellet cathode. Particularly, the ratio of CFx (capacity of 786 mAh/g) active material to SVO (capacity of 270 mAh/g) active material can be increased when carbon nanotubes are used instead of graphite or carbon black. Applicant has found that the use of carbon black or graphite in cathodes where the CFx to SVO ratio is increased results in cathodes having higher resistance, lower physical integrity and lower density. The use of carbon nanotubes results in pressed cathodes having a desired density and conductivity to maximize stored capacity (mAh) and maintaining power capability (W/cm^2) and cathodes having a higher volumetric capacity than cathodes using the same active materials and binder, but containing carbon black or graphite conductive additive.

The electrochemical cells or batteries described in this application include a cathode (positive polarity), an anode (negative polarity), an electrolyte and a separator. The cathodes described in this application generally contain active materials, conductive additive and binder.

Active materials in the battery are the source of energy and power. Useful active materials include silver vanadium oxide (SVO), carbon monofluoride (CFx), manganese dioxide (MnO 2 ), vanadium pentoxide (V 2 O 5 ), and copper silver vanadium oxide (Cu x Ag 2-x V 4 O 11 ) and mixtures of all or any of them. In another embodiment, useful active materials consist essentially of silver vanadium oxide (SVO), carbon monofluoride (CFx), manganese dioxide (MnO 2 ), vanadium pentoxide (V 2 O 5 ), copper silver vanadium oxide (Cu x Ag 2-x V 4 O 11 ), and copper fluoride (CuF 2 ) and mixtures of all or any of them and do not include any other active materials. In another embodiment, active materials are selected from the group consisting of silver vanadium oxide (SVO), carbon monofluoride (CFx), manganese dioxide (MnO 2 ), vanadium pentoxide (V 2 O 5 ), copper silver vanadium oxide (Cu x Ag 2-x V 4 O 11 ) and copper fluoride (CuF 2 ) and mixtures of all or any of them and may be selected from a group consisting of any subgroup of the above group.

Conductive additives are used for improving the conductivity of the cathode. Useful conductive additives include carbon nanotubes as defined above and carbon black or graphite as a co-additive. In another embodiment, useful conductive additives consist essentially of carbon nanotubes and may contain carbon black or graphite or both as a co-additive and does not include any other conductive additives.

Binders are used to hold or bind all of the materials mixed together to form a solid cathode which holds its shape without cracking or breaking. Useful binders are typically polymers or polymeric materials. Useful binders include poly(tetrafluoroethylene) (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC).

Cathodes are typically made by combining one or more active materials, carbon nanotubes and a binder into a cathode composition and then pressing the composition onto a metallic current collector.

The anode is a metal and typically is or comprises lithium metal. The anode metal is typically pressed onto a metallic current collector. In another embodiment, the anode consists essentially of lithium metal pressed onto a metallic current collector and contains no other active anode material.

Separators are typically in the form of a film and are used to separate an anode from a cathode, but allow an electrolyte to permeate. Useful materials that can be used to make separators include polymer films such as polyethylene, polypropylene, poly(tetrafluoroethylene), and polyvinyl chloride, and nonwoven fibers such as nylon, polyesters and glass, and ceramics.

Useful electrolytes for use in the electrochemical cells described in this application are non-aqueous. The electrolyte may be a 1:1 mixture of propylene carbonate (PC) to dimethoxyethane (DME) in a 1.0 molar (M) lithium salt such as lithium hexafluoroarsenate (LiAsF6), or 1:1 mixture of ethylene carbonate (EC) to diethylene carbonate (DEC) (EC:DEC) in a 1.0 molar (M) salt of lithium hexafluorophosphate (LiPF6). The electrolyte may include a polypropylene carbonate solvent and a lithium bis-oxalatoborate salt (sometimes referred to as LiBOB). The electrolyte may include one or more of a polyvinylidene fluoride (PVDF) copolymer, a PVDF-polyimide material, and organosilicon polymer, a thermal polymerization gel, a radiation cured acrylate, a particulate with polymer gel, an inorganic gel polymer electrolyte, an inorganic gel-polymer electrolyte, a PVDF gel, polyethylene oxide (PEO), a glass ceramic electrolyte, phosphate glasses, lithium conducting glasses, lithium conducting ceramics, and an inorganic ionic liquid or gel, among others.

Current collectors are metallic and include those made from or comprising titanium, aluminum, nickel and combinations and alloys of any of them.

Cathode active materials are present in the cathode composition in an amount of at least 80% by weight. The cathode active materials are present in a cathode composition in an amount that ranges from 80% to 97% by weight, the range including any individual amount or any range of amounts within such range. In other embodiments, the cathode active materials are present in a cathode composition in an amount that ranges from 92% to 95% by weight, the range including any individual amount or any range of amounts within such range. In other embodiments, the cathode active materials are present in a cathode composition in an amount of at least 90% by weight or in an amount of at least 93% by weight.

Conductive additives, for example, carbon nanotubes are present in the cathode composition in an amount of from 1% to 10% by weight, the range including any individual amount or any range of amounts within such range. In other embodiments, conductive additives are present in the cathode composition in an amount of from 1% to 6% by weight, 2% to 5% by weight, and 2% to 4% by weight.

Binders are present in the cathode composition in an amount of from 1% to 15% by weight, the range including any individual amount or any range of amounts within such range. In other embodiments, binders are present in the cathode composition in an amount of from 3% to 10% by weight, 3% to 7% by weight, and 4% to 6% by weight.

In one example of a cathode composition, CFx is present in the cathode compositions described in this application in an amount of from 20 to 80 percent by weight of the cathode composition, and SVO is present in the cathode compositions described in this application in an amount of from 60 to 20 percent by weight, the ranges including any individual amount or any range of amounts within such range. The capacity ratio ((mAh/g) CFx/(mAh/g) SVO) of such compositions containing CFx and SVO active materials range from 1 to 1 to 10 to 1.

The cathode compositions described in this application are useful for making cathodes for batteries, for example batteries for use in medical devices.

Glossary:

Abbreviation Material Comments SVO Silver Vanadium Oxide Ag 2 V 4 O 11 CFx Carbon Mono fluoride CF 1.0 Carbon Carbon black Commercially available such as SUPER-P carbon black form TIMCAL America Inc. or acetylene black CNT Carbon Nanotubes Multi-walled Binder Polytetrafluoroethylene PTFE aqueous emulsion (PTFE) such as commercially available from Daikin Corporation. Term Definition Determined Specific Capacity Capacity (mAh)/g Calculated cathode Capacity Ratio Capacity (mAh/g) Calculated CFx/Capacity (mAh/g) SVO Pressed Density g/cm 3 Calculated Volumetric mAh/cm 3 Calculated Capacity Stored Capacity Total available battery Calculated capacity (mAh)

Sample Preparation:

Cathode mixtures were generally prepared by mixing CFx, SVO, Carbon (or CNT) and Binder in water and isopropyl alcohol. The mixture was then heated at a temperature of 150° C. for 4 hours or longer to remove the water and isopropyl alcohol.