Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/02—Pretreatment of the material to be coated
  • C23C14/021—Cleaning or etching treatments
  • C23C14/022—Cleaning or etching treatments by means of bombardment with energetic particles or radiation
• • 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
  • H01M4/64—Carriers or collectors
  • H01M4/66—Selection of materials
  • H01M4/661—Metal or alloys, e.g. alloy coatings
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
  • C23C14/14—Metallic material, boron or silicon
  • C23C14/16—Metallic material, boron or silicon on metallic substrates or on substrates of boron or silicon
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/24—Vacuum evaporation
  • C23C14/28—Vacuum evaporation by wave energy or particle radiation
  • C23C14/30—Vacuum evaporation by wave energy or particle radiation by electron bombardment
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/56—Apparatus specially adapted for continuous coating; Arrangements for maintaining the vacuum, e.g. vacuum locks
  • C23C14/562—Apparatus specially adapted for continuous coating; Arrangements for maintaining the vacuum, e.g. vacuum locks for coating elongated substrates
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/02—Contacts characterised by the material thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/02—Contacts characterised by the material thereof
  • H01H1/021—Composite material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H11/00—Apparatus or processes specially adapted for the manufacture of electric switches
  • H01H11/04—Apparatus or processes specially adapted for the manufacture of electric switches of switch contacts
  • H01H11/041—Apparatus or processes specially adapted for the manufacture of electric switches of switch contacts by bonding of a contact marking face to a contact body portion
  • H01H11/045—Apparatus or processes specially adapted for the manufacture of electric switches of switch contacts by bonding of a contact marking face to a contact body portion with the help of an intermediate layer
• • 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
  • H01M10/04—Construction or manufacture in general
  • H01M10/0422—Cells or battery with cylindrical casing
  • H01M10/0427—Button cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/50—Current conducting connections for cells or batteries
  • H01M50/571—Methods or arrangements for affording protection against corrosion; Selection of materials therefor
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
  • H01R13/00—Details of coupling devices of the kinds covered by groups H01R12/70 or H01R24/00 - H01R33/00
  • H01R13/02—Contact members
  • H01R13/03—Contact members characterised by the material, e.g. plating, or coating materials
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
  • H01R39/00—Rotary current collectors, distributors or interrupters
  • H01R39/02—Details for dynamo electric machines
  • H01R39/18—Contacts for co-operation with commutator or slip-ring, e.g. contact brush
  • H01R39/20—Contacts for co-operation with commutator or slip-ring, e.g. contact brush characterised by the material thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
  • H01R4/00—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation
  • H01R4/58—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation characterised by the form or material of the contacting members
• • 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

• the present invention relates to a low electrical impedance contact element adapted to conduct current and designed to be able to operate in corrosive environments, said element being made of a metal strip product.
• Such a contact element may be of any type to be used in corrosive environments in which contact elements used in consumer batteries, such as coin cell batteries, may be mentioned as an example.
• Spring properties are requested in certain applications of such contact elements for obtaining a requested contact action, whereas such spring properties are not needed in other applications.
• the contact element is made of a material from a metal band product indicates that it is a question of comparatively thin contact elements, often with a thickness in the order of millimetres or less.
• contact elements of this type from a thin strip of Ti or a Ti alloy, in which the major part, such as at least 80 percent, consists of Ti, thanks to the excellent corrosion re- sistance properties of Ti and an acceptable low impedance of such a material, especially a low surface contact resistance in comparison with e.g. stainless steel thereof.
• the low tensile strength of Ti requires especially for applications requesting a considerable mechanical stability of a contact element a thickness of the element making it very expensive, since Ti is in itself an expensive material.
• the impedance of the element across the strip increases with the thickness, so that in spite of a low surface contact resistance the impedance may become higher than desirable for such contact elements which have to be comparatively stiff.
• the object of the invention is to provide a low electrical impedance contact adapted to conduct current and designed to be able to operate in corrosive environments reducing at least some of the problems mentioned above.
• the metal strip product comprises a strip substrate of steel with a tensile strength of at least 1000 MPa and on at least one side thereof coated by at least one coating layer of Ti or a Ti based alloy.
• Ti has a tensile strength of about 350 MPa, so that a said steel substrate results in the possibility to make a contact element of a predetermined mechanical stability substantially thinner than a contact element of Ti or a Ti based alloy, which also means that said coating layer of Ti or a Ti based alloy may be made considerably thinner resulting in a lower bulk resistance of the element without loosing the low surface contact resistance in comparison with stainless steel thanks to said coating layer and in considerable cost savings thanks to the reduced amount of Ti used.
• said at least one coating layer is essential pure Ti, which is suitable for obtaining said low surface contact resistance of the contact element.
• the thickness of said at least one coating layer is max 20 ⁇ m, and according to a further embodiment of the invention the thickness of said at least one coating layer is min 1 ⁇ m, preferably 2-10 ⁇ m and most preferred 3-6 ⁇ m. It has been found that the thickness of the coating layer should be within these limits, since a thinner coating layer will result in a higher surface contact resistance of the element and a thicker coating layer will increase the bulk resistance of the element without for that sake obtaining any lower surface contact resistance of the element.
• the substrate is coated by at least one said coating layer on both sides thereof. This makes the contact element well suited to be used in applications in which the entire environment of the element may be corrosive.
• the substrate is coated by at least two layers on a side thereof provided with said at least one coating layer.
• a bonding layer may then be used in order to further improve the adhesion of the coating layer to the substrate, and this bonding layer may be of another material than said at least one coating layer and applied in di- rect contact with the substrate.
• One or more coating layers of Ti or a Ti based alloy may then be applied upon said bonding layer.
• the thickness of said steel substrate is 0.05-5 mm, 0.05-2 mm or 0.05-1 mm, which are suitable thicknesses for contact elements of this type.
• said substrate is made of a steel with a Cr content of min 10%, preferably min 12%, more preferred min 13% and most preferred min 15%, which means that also the substrate material will have a good general corrosion resistance.
• said substrate is made of steel with a tensile strength of min 1300 MPa, preferably min 1700 MPa.
• a tensile strength of min 1300 MPa, preferably min 1700 MPa.
• said substrate is made of a spring steel, which makes the contact element suit- able to be used as a contact spring for for instance applying a contact pressure in a battery, and the contact element is according to another embodiment of the invention a current collector contact element of a coin cell battery.
• the mechanical, electrical and corrosion resistance properties of said steel sub- strate and Ti or the Ti based alloy coating may be particularly advantageously combined in such a current collector contact element.
• the invention also relates to a method for producing a metal strip product to be used as material for producing a low electrical impedance contact element according to the invention, and this method is characterized in that the steel substrate is etched by plasma assisted etching and then coated by at least one coating layer of Ti or a Ti based alloy on at least one side thereof by means of physical vapor deposition, preferably elec- tron-beam evaporation.
• the oxide layer formed on the steel substrate may be efficiently removed thereby enabling a very good adhesion of the coating to the substrate.
• the coating step is performed in a continuous roll-to-roll process, which opens up for a production at a much higher rate than batch-like processes.
• the invention also relates to a use of a metal strip product comprising a substrate of steel with a tensile strength of at least 1000 MPa and on at least one side thereof coated by at least one coating layer of Ti or a Ti based alloy for producing a low electrical impedance contact element according to the invention.
• a contact element for current conducting purposes in electrical devices, such as electrical switches, connectors and batteries, especially spring elements, may then be produced.
• the invention also relates to a coin cell battery having at least one contact element according to the invention, which may be produced to a lower cost than such batteries already known while reducing the electrical impedance of said at least one contact element therein.
• This coin cell battery may for instance be a Li/CF X battery.
• the invention also relates to a method of reducing the electrical impedance of contact elements adapted to conduct current in corrosive environments and having at least one surface formed by Ti or a Ti based alloy.
• a reduction of the electrical im- pedance of such contact elements is obtained by providing a substrate of a steel with a tensile strength of at least 1000 MPa and coating at least one side of this substrate by at least one coating layer of Ti or a Ti based alloy for producing such contact elements.
• Fig 1 shows a schematic cross-section of a contact element ac- cording to a first embodiment of the invention
• Fig 2 shows a contact element according to a second embodiment of the invention
• Fig 3 shows a mechanism of fatigue crack initiation in the coated material in a contact element according to the invention
• Fig 4 shows schematically a production line for manufacturing of a metal strip product in the form of a coated metal strip material to be used for manufacturing a contact element according to the invention
• Fig 5 shows a coin-cell type battery having contact elements in the form of current collector spring elements according to the present invention.
• Fig 1 shows a steel substrate 2 which is coated with a metallic coating layer 1 , 3 of Ti and/or a Ti based alloy on both sides of the steel strip.
• the thickness of the coating on the two sides may be the same or different.
• Titanium is a metal with many unique properties. It has found rapid growth in the industry, particularly owing to its high specific strength and corrosion resistance. Applications where these properties are explored can be found especially in aerospace, automotive and marine engineering, chemical processing, pulp and paper industry, and energy production and storage. Biomedical applications, such as surgical implants, have recently learned to take advantage of the metals inertness in the human body. Titanium's anti-bacteriological properties have also made it suitable in applications such as air-conditioning and food storage.
• titanium in specific chemical envi- ronments relates to its surface properties and makes it suitable as a material for a contact element to be used in corrosive environments.
• a thin titanium oxide film always present on the surface, is very dense and provides excellent corrosion resistance in a wide variety of special environments including chloride- containing environments, e.g. sea water and salt brines, moist chlorine gas, alkaline solutions, oxidizing acids, organic acids, inorganic salts, sulfur compounds, and in the human body.
• chloride- containing environments e.g. sea water and salt brines
• moist chlorine gas e.g. sea water and salt brines
• alkaline solutions e.g. oxidizing acids, organic acids, inorganic salts, sulfur compounds, and in the human body.
• titanium can be used in many cases when stainless steel does not provide adequate corrosion protection.
• Stainless steel is often used for e.g. springs and other demanding applications, where corrosion resistance needs to be combined with superior mechanical properties, such as mechanical strength, relaxation resistance and fatigue resistance.
• the corrosion resistance in stainless steel is principally achieved by alloying with chromium to a minimum of 10%, which results in a characteristic dense chromium oxide film on the surface.
• the chromium oxide film protects the steel from general corrosion in most oxidizing and reducing acids and in alkaline solutions.
• the corrosion resistance is, however, sometimes insufficient in chloride-containing environments, where aggressive chloride ions accelerate both pitting and crevice corrosion as well as stress corrosion cracking.
• the substrate may also be provided with additional coating layers 1a, 1 b, 1c as illustrated in Fig 2.
• These coating layers 1a, 1 b, 1 c may all be of Ti and/or Ti based alloys.
• one of the layers 1 c is a bonding layer in or- der to further improve the adhesion of the coating to the substrate.
• the bonding layer is in direct contact with the substrate.
• a suitable bonding layer metal is for example Ni.
• PVD Physical vapor deposition
• the final product in the form of a titanium-coated steel strip is suitable for use as low impedance contact elements in corrosive environments, especially as springs and in particular for conducting high current densities.
• a specific example is contact springs and container materials in certain batteries, such as coin cell batteries.
• the corrosion resistance of titanium can be regarded as complementary to stainless steel, and a titanium-coated stainless steel will therefore be stable in a wider range of different envi- ronments.
• the presence of titanium on the steel surface minimizes the probability of intergranular corrosion in the steel due to CrC formation, since carbon will preferentially react with titanium instead.
• a titanium coating makes the steel less sensitive to exterior carbonization.
• fatigue resistance is important for the intended application as spring. All metal components subjected to repeating load cycles have a maximum allowed stress. This stress is lower than the static tensile strength of the material. Under cyclic loading, failures can begin as microscopic cracks that grow for each load cycle if the local stress is high enough. The reason for increased local stresses that induce cracks is various defects in the material, such as surface defects, edge radius, non-metallic inclusions, and other internal defects. Hence, for a material to have good fatigue properties it must inter alia have a good surface standard, high metallurgical cleanliness, a suitable micro- structure, high static strength, high damping capacity and a suitable residual stress distribution.
• the fatigue properties of the metal substrate are improved due to the presence of the coating layers. Crack initiation under cyclic bending stresses generally starts mainly at surface defects. A coating creates a more homogenous surface and thereby improves the surface finish. This will reduce stress concentrators and decrease stress concentrations at the surface and lead to a transition of fatigue crack initiation from the surface of the substrate to the surface of the coating.
• Fig 3 shows a mechanism of fatigue crack initiation in a coated material.
• Fatigue cracks 4 start at the surface of the coating layer, and then propagate into the coating layer 1 , but stop at the interface 5 between the coating layer and the substrate layer 2.
• the interface 5 becomes a barrier for crack propagation.
• These micro cracks however, become new stress concentrators. Some of them can be high enough to cause a fa- tigue crack in initiation at the surface of the base material.
• the coating 1 therefore results in an increase of the resistance to fatigue crack initiation, which improves the fatigue properties of the material of the substrate 2.
• the fatigue properties are further improved if there is a plurality of coating layers as there will be a plurality of interfaces that acts as stops for crack propagation, especially if different coating layers have different density and/or composition.
• the substrate steel material to be coated should have a good general corrosion resistance. This means that the material should have a chromium content of at least 10% by weight, preferably minimum 12%, more preferred minimum 13% and most preferred minimum 15% chromium.
• the mate- rial must be alloyed in a way that allows for a high tensile strength, which shall be at least 1000 MPa, preferably minimum 1300 MPa, more preferred minimum 1500 MPa and most preferred minimum 1700 MPa.
• the mechanical strength may be achieved by cold deformation, such as for steels of the ASTM 200 and 300 series, or by thermal hardening as for hardenable martensitic chromium steels, e.g. certain ASTM 400 series steels.
• suitable substrate materials are precipitation hardenable (PH) steels of the type 13-8PH, 15-5PH, 17-4PH and 17-7PH.
• PH precipitation hardenable
• Yet another group of suitable substrate materials are stainless maraging steels that are characterized by a low carbon- and nitrogen-containing martensitic matrix that is hardened by the precipitation of substitutional atoms, such as copper, aluminium, titanium, nickel etc.
• the coating layer consists according to an embodiment of essentially pure titanium. Small amounts of alloy elements may then be present, but substantially pure (>99.9%) titanium is used. According to an alternative embodiment, the coating consists of a Ti based alloy. In this context, a Ti based alloy is considered to mean an alloy comprising at least 80%, preferably at least 90% by weight of Ti. The thickness of the coating layer is preferably less than 20 ⁇ m and minimum 1 ⁇ m, and more preferred in the range of 2-10 ⁇ m.
• the surface contact resistance is obviously lowered with an increasing thickness of the coating layer to a certain level, as of which it is not reduced any more, and since the electrical conductivity of Ti is mostly lower than that of a steel material used for said substrate it is from the electrical impedance point of view suitable to not increase the thickness of the coating layer above this level.
• This level is typically in the range of 3-6 ⁇ m.
• This stainless steel strip has preferably a thickness in the range of 0.05-5 mm, and mostly in the lower part of this range. It is provided by a roll 6 and delivered as a metal strip product 20 to another roll 7 after having been coated.
• the substrate should preferably first be cleaned from oil residues resulting from the previous production steps of the substrate, i.e. the rolling. This may for example be made in a degreasing bath 8. Thereafter, the substrate is introduced into the coating production line.
• An etching chamber 9 is placed as a first step in the production line, and the strip is here exposed to ion-assisted etching in order to remove the oxide scale on the steel strip and thereby to achieve good adhesion of the surface layer.
• the titanium layer is deposited by means of PVD in a chamber 10 in the second step of the roll-to-roll process.
• the PVD process may preferably be electron beam evaporation. However, as previously disclosed, electron beam evaporation is preferred.
• the corrosion resistance is related to the density of the coating layer and for further compacting the coating layer the coating process may be activated by a plasma introduced into the deposition chamber 10.
• the plasma will add energy (activate) to the titanium vapor and increase diffusion of the deposited atoms on the substrate surface. This will lead to a very dense, highly corrosion-resistance coating at a very small coating thickness.
• a dense pinhole-free titanium surface will for instance act as ca- thodic protection towards chloride-ion attack to many types of stainless steel.
• a plasma source can for example be based on a hollow cathode or an ion source.
• a coated product makes it possible to combine the excellent corrosion resistance of titanium and the excellent mechanical properties of steel.
• High strength stainless steel has in general superior mechanical properties compared to non-ferrous materials.
• the E-modulus of Ti is about 102 GPa, while it for a stan- dard AISI 301 -type stainless steel is about 185 GPa. This property is particularly beneficial for using this material for a contact spring element. It enables the production of springs with almost double the spring force for the same thickness of material.
• Fig 5 illustrates a coin cell battery 11 in the form of a primary (non-rechargeable) Li/CF X battery, in which spring contact elements 12, 13 are used as current collectors that conduct current from and adds pressure to the cathode 14 and the anode 15, respectively.
• Ti collectors have so far been used for their ability to withstand the chloride-containing environment in such batteries.
• These Li/CF X batteries are high-capacity non-rechargeable batteries particularly suited for low-power applications used above room temperature.
• Suitable applications are for instance medical implantable devices, such as drug-infusion pumps, neurostimulators and pacemakers, and also tire-pressure monitoring systems (TPMS) for cars.
• Ti for such spring current collectors has normally been chosen because, unlike other metals, such as Ni, it does not react with the CF x cathode material. This is especially true at elevated temperatures.
• the Ti current collectors are shaped like springs to provide pressure to the cell stack to accommodate for cell-stack volume changes during discharge. Lack of pressure may result in contact losses within the battery stack leading to impedance rise.
• the Ti spring properties are poor and the Ti needs to have a certain thickness to provide the right pressure.
• the Ti-coated steel is a very suitable alternative. The Ti-coating provides the right corrosion protection and the stainless steel provides a higher conductivity as well as a better stack pressure leading to a lower cell impedance.
• a set of coated spring steel materials suitable to act as a current collector spring towards the cathode in primary Li/CF X coin cell batteries were produced by electron-beam evaporation in a continuous roll-to-roll coating line.
• the substrate material was cleaned by degreasing in an alkaline solution and then etched prior to deposition. The etching was an integrated step in the coating line.
• the substrate materials used were stainless steel strip of grades EN 1.4310 (austenitic stainless steel) and ASTM 420 (marten- sitic chromium steel).
• the strip had a thickness of 0.08 mm.
• the surface roughness of the steel strip was less than 0.125 ⁇ m.
• the thickness of the titanium coating layers were in general approximately 2 or 3.5 ⁇ m.
• An overview of the samples produced is shown in Table 2.
• the table also includes mechanical properties compared to a Ti- spring reference of 0.10 mm thickness.
• Table 3 shows the relative impedance of identical Li/CF X coin-cells, which contain the different current collector materi- als. The cells were stored at elevated temperature (85°C and 110°) for 24 h. It can be concluded that the relative impedance is decreased with at least 20% when changing to Ti-coated stainless steel current collectors.
• Table 3 also includes the relative spring force, which is almost the same for the coated samples even though the strip thickness is substantially smaller. Table 3.
• the invention provides an efficient method of reducing the electrical impedance of contact elements, especially for spring applications, adapted to conduct current in corrosive environments and having at least one surface formed by Ti or a Ti based alloy.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Electrochemistry (AREA)
• Manufacturing & Machinery (AREA)
• Toxicology (AREA)
• Health & Medical Sciences (AREA)
• Composite Materials (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Battery Mounting, Suspending (AREA)
• Primary Cells (AREA)
• Cell Electrode Carriers And Collectors (AREA)

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Cited By (4)

Citations (8)

• 2007
  • 2007-02-23 SE SE0700476A patent/SE0700476L/sv not_active Application Discontinuation
• 2008
  • 2008-02-12 WO PCT/SE2008/050164 patent/WO2008103118A1/en active Application Filing

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