Metal foils for electrochemical cell electrodes containing Ti, C and H based materials.

Abstract

To decrease the contact resistance between a piece of metal foil and an active substance deposited on its surface.SOLUTION: A piece of metal foil comprises a layer made of a material containing metal or alloy, carbon and hydrogen, and contains optionally oxygen on at least one side thereof. In the material, the atomic ratio of metal of the metal or alloy falls in a range of 10-60%, the atomic ratio of carbon is in a range of 35-70%, the atomic ratio of hydrogen is in a range of 2-20% and in the case of the material containing oxygen, the oxygen atomic ratio is 10% or less. The piece of metal foil can be used to fabricate a cathode of a lithium ion electrochemical cell. By depositing the layer, the internal resistance of the cell is reduced.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The technical field of the present invention relates to current collectors, and more particularly to current collectors used for the positive electrodes (cathodes) of electrochemical cells, preferably lithium-ion type electrochemical cells.

Background Art

[0002] Hereinafter, the term "cell (battery)" refers to an electrochemical cell. In this specification, the terms "cell" and "electrochemical cell" are used interchangeably.

[0003] Generally, an electrochemical cell includes an electrochemical assembly in which a cathode and an anode are alternately arranged with a separator impregnated with an electrolyte interposed therebetween. Each electrode generally comprises a current collector made of a metal that supports, on at least one side, an active material film containing at least one kind of active material, a binder, and an electron conductive material.

[0004] The cathode of a Li-ion battery is composed of a positive electrode active material composition coated on the surface of a current collector, and the current collector is usually made of aluminum or an aluminum-based alloy. When this aluminum foil is exposed to air, it is slightly oxidized and has an alumina (Al 2 O 3 ) layer on its surface. In the cell, this alumina layer comes into contact with the electrolyte and the salts in the electrolyte and is fluorinated to change to AlF 3 . Since this newly formed AlF 3 layer is an electrical insulator, it tends to increase the contact resistance between the positive electrode active material composition and the aluminum foil and inhibit the passage of electrons. In a Li-ion battery having a current collector with a cathode made of aluminum, it is recognized that the internal resistance increases with time when the current collector comes into contact with the electrolyte. The increase in internal resistance, on the one hand, degrades the electrical performance of the cell when used for charging and discharging at high current (or regime), and on the other hand, increases the heat generation during cycling.

[0005] A layer for suppressing loss of electrical conductivity between the above-described active material and the aluminum current collector may be deposited on the surface of the current collector. This layer may be a layer of a carbon-based material or a metal carbide (such as tungsten carbide) - based material. In this regard, U.S. Patent Application Publication No. 2011 / 0200884 (Patent Document 1) describes a method for reducing the contact resistance between an aluminum foil and an active material composition deposited on the surface of this foil. This method includes, under vacuum, a step of partially etching the aluminum oxide layer on the surface of the aluminum foil, and then a step of sputtering a metal or a metal carbide (usually tungsten (W) or tungsten carbide (WC)) on the surface of the partially etched foil.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the method of the prior art described above, many problems associated with the use of tungsten or its carbide are drawbacks. For example, tungsten is a relatively rare element, and the production of a WC sputtering target is costly and difficult to implement. Also, due to the large mass of W atoms, the compressive stress is high in a thin layer containing tungsten, which has an adverse effect on the aging and processing of the foil coated with a W - based material. For these reasons, a new method for reducing the contact resistance between an aluminum foil and an active material deposited on the surface of this foil is required.

Means for Solving the Problems

[0008] Therefore, the present invention is a metal foil provided with a layer made of a material containing a metal or an alloy, carbon, hydrogen, and optionally oxygen on at least one side, The atomic ratio of the metal in the metal or alloy in the material ranges from 10% to 60%, the atomic ratio of carbon in the material ranges from 35% to 70%, the atomic ratio of hydrogen in the material ranges from 2% to 20%, when oxygen is contained in the material, a metal foil is provided in which the atomic ratio of oxygen is 10% or less.

[0009] In one embodiment, the material contains nitrogen. In one embodiment, the atomic ratio of the metal in the metal or the alloy in the material ranges from 30% to 50%, preferably from 40% to 50%.

[0010] In one embodiment, the atomic ratio of carbon in the material ranges from 40% to 60%, preferably from 45% to 55%.

[0011] In one embodiment, the atomic ratio of hydrogen in the material ranges from 3% to 15%, preferably from 3% to 8%.

[0012] In one embodiment, the material contains oxygen, and the atomic ratio of oxygen in the material is 5% or less, preferably 2% or less, more preferably 1% or less.

[0013] In one embodiment, the atomic ratio of the metal in the metal or alloy in the material ranges from 40% to 50%, the atomic ratio of carbon in the material ranges from 40% to 55%, the atomic ratio of hydrogen in the material ranges from 3% to 8%, the atomic ratio of oxygen in the material is 5% or less.

[0014] In one embodiment, the metal of the material is selected from Ti, Cr, Zr, Fe, and Ni, preferably Ti.

[0015] In one embodiment, the alloy of the material consists of a plurality of metals selected from Ti, Zr, Fe, Cr, and Ni.

[0016] In one embodiment, the thickness of the layer ranges from 30 to 200 nm, or ranges from 50 to 150 nm, or ranges from 50 to 100 nm.

[0017] In one embodiment, the metal foil is made of aluminum or an aluminum-based alloy, or copper or a copper-based alloy.

[0018] The present invention also relates to a cathode of an electrochemical cell including the above foil. The conductive layer deposited on the above foil is stable over time in the organic electrolyte of a Li-ion battery. Due to the presence of this conductive layer, the contact between the cathode active material composition and the foil is improved, the internal resistance of the cell is reduced, the discharge capacity of the cell is improved, and the polarization of the cell is reduced.

[0019] Since the internal resistance of the cell is low, heat generation of the cell is reduced even when used in a cycle with a short rest phase or without a rest phase. Further, since the conductive layer exists on the surface of the foil, the surface of the foil is protected from alkaline corrosion even during aqueous solution treatment.

[0020] The present invention also relates to an electrochemical cell including a cathode and an anode, wherein the cathode or the anode includes the above metal foil.

[0021] In one embodiment, the electrochemical cell is selected from a lithium primary electrochemical cell (for example, a primary electrochemical cell of the LiCF x type), a lithium-ion secondary electrochemical cell with a liquid electrolyte, a lithium-ion secondary electrochemical cell with a solid electrolyte, a sodium-ion primary or secondary electrochemical cell, a lithium-sulfur secondary electrochemical cell, and a sodium-sulfur electrochemical cell.

[0022] The present invention also relates to a fuel cell including at least one bipolar plate having at least one of the above metal foils, wherein the metal foil includes a gas distribution channel on at least one side having the layer.

[0023] The present invention further relates to a method for forming a layer made of a material containing a metal or an alloy, carbon, and hydrogen on a metal foil, the method comprising: a) providing a substrate made of a metal foil; b) etching one side of the substrate by collision of ions generated by ionization of an inert gas; c) sputter depositing a material containing a metal or an alloy, carbon, hydrogen, and optionally oxygen on the etched side of the substrate, wherein the sputter deposition is performed using a target made of the metal or the alloy in a mixed gas of an inert gas and a hydrocarbon gas at 25°C, and the mixed gas optionally contains nitrogen.

[0024] In one embodiment, the metal of the material in step c) is titanium. In one embodiment, the method comprises only steps a) to c).

[0025] In one embodiment, the method does not include an annealing step for the metal foil coated with the material obtained at the end of step c). In one embodiment, the hydrocarbon is acetylene.

[0026] Furthermore, the present invention relates to a metal foil obtained by the above method. BRIEF DESCRIPTION OF THE DRAWINGS

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0028] (a) Production of Foil By the method according to the present invention, it is possible to produce a layer of the above material on the surface of a metal foil. This method a) a step of vacuum etching the surface of the metal foil; b) a step of vacuum depositing the material by sputtering and includes. Steps a) and b) are carried out in a spray chamber. This chamber includes a target and a support for supporting the above metal foil serving as a substrate, and an air inlet for gas injection is provided.

[0029] The target is made of a metal or an alloy that forms one of the components of the above layer material. The metal can be selected from Ti, Cr, Zr, Fe and Ni, and preferably Ti. The metals of the alloy are at least two kinds of metals, and are preferably selected from Ti, Cr, Zr, Fe and Ni. In one embodiment, the metal is neither Fe nor Ni, and the alloy does not contain Fe and / or does not contain Ni.

[0030] The substrate is made of a metal foil. The metal of the foil is preferably aluminum or an aluminum-based alloy, or may be copper or a copper-based alloy. Generally, the thickness of the foil is 50 μm or less. Usually, the minimum foil thickness is 5 μm. The foil thickness may be 10 μm or more, 15 μm or more, or 20 μm or more. Usually, the foil thickness is in the range of 5 - 35 μm.

[0031] Step a) of performing etching on the substrate includes polarizing the substrate and causing ions (plasma) formed by ionization of an inert gas to impinge on the surface of the substrate. Due to the impingement, the oxide layer on the surface of the foil is reduced and further removed. The step of performing etching improves the adhesion of the above-mentioned layer to the metal foil.

[0032] Step b) of performing sputtering is characterized by injecting into the chamber a mixed gas of an inert gas and a vapor-phase hydrocarbon, particularly at a temperature of 20 - 30°C. For example, this hydrocarbon may be selected from the group consisting of methane, ethylene, propane, acetylene, or some mixture of these gases. Acetylene is preferred because of its low H / C ratio. Preferably, the inert gas is argon. First, the chamber is evacuated, and then the mixed gas of the inert gas - hydrocarbon is injected. The injection rate and composition of the mixed gas may be varied. A potential difference is applied between the target and the chamber wall, and due to this potential difference, the mixed gas of the inert gas and the hydrocarbon is ionized to generate plasma. The positively charged plasma species are attracted to the target and impinge on the metal or alloy. Due to this impingement, the atoms of the metal or alloy of the target are sputtered. These atoms condense on the surface of the foil. By accumulating atoms on the surface of the foil, a thin layer composed of a material containing metal or alloy, carbon, hydrogen, and possibly oxygen can be gradually formed. In order to obtain layer uniformity, the foil may be rotated in front of the target during sputtering. Also, if necessary, in the step of performing sputtering, in addition to the hydrocarbon gas, nitrogen may be injected into the chamber. By injecting nitrogen gas, nitrogen can be introduced into the elemental composition of the material layer.

[0033] The substrate may be biased at a potential in the range of -100 to -500 V, preferably in the range of -150 to -450 V, and more preferably in the range of -200 to -400 V. The substrate may be biased in a pulse mode at a frequency in the range of 150 to 350 kHz or in the range of 200 to 300 kHz (for example, about 250 kHz). The substrate may be biased to a potential of -200 to -500 V. The flow rate of the hydrocarbon is a flow rate corresponding to the characteristics (size, throughput) of the enclosure used. This flow rate can be varied in the range of 2 to 50 sccm, or in the range of 2 to 25 sccm, or in the range of 5 to 20 sccm (under normal pressure and room temperature conditions, 1 sccm = 1 cm 3 / min). The flow rate of argon may be about 30 sccm. As the layer growth rate, a growth rate in the range of 1 to 15 nm / min, or in the range of 2 to 10 nm / min, or in the range of 4 to 10 nm / min can be achieved.

[0034] A person skilled in the art can understand how to vary the flow rate of the mixed gas of the inert gas and the hydrocarbon gas based on the characteristics of the spray chamber such as the target size, sputtering power, and further pump speed in order to obtain a material in which the atomic ratios of the metal elements, carbon, hydrogen, and oxygen contained in the metal or alloy are within specific limited ranges of 10 to 60%, 35 to 70%, 2 to 20%, and a maximum of 10% respectively.

[0035] When the deposition is completed, the foil is taken out from the chamber. The analysis of the elemental state in the above layer can be performed by fluorescence X-ray analysis on the surface of the foil, or by inductively coupled plasma analysis (ICP) or Rutherford backscattering spectroscopy (RBS). The exact hydrogen content in the material can be measured using the elastic recoil detection analysis (ERDA) method. The exact metal (especially titanium) content can be measured by Rutherford backscattering spectroscopy (RBS) method. The exact oxygen and carbon contents can be measured by nuclear reaction analysis (NRA) method. In some cases, the nitrogen content present in the material can be accurately measured by the RBS method.

[0036] The layer material may contain metals, carbon, hydrogen, and elements other than oxygen and nitrogen that may be contained in the metal or alloy. The abundance of these other elements is usually 2% or less, preferably 1% or less, in atomic ratio with respect to the amount of constituent elements of the material.

[0037] Generally, the thickness of the above layer is in the range of 25 to 200 nm, or 30 to 150 nm, or 40 to 150 nm, or 50 to 150 nm, or 50 to 100 nm. The layer thickness can be measured, for example, in a glass indicator by partially masking the substrate and measuring the step height using a profiler of the AlphaStep model manufactured by Tencor Instruments.

[0038] The electrical resistivity ρ (microohm meter [μΩ·m]) of the layer may be in the range of 0.5 to 14 μΩ·m, or 1 to 10 μΩ·m, or 2 to 10 μΩ·m, or 1 to 5 μΩ·m. The electrical resistivity of the layer can be evaluated by measuring the surface resistance R S (referred to as R "square") (ohm [Ω]) in an electrically insulating indicator (for example, an extremely thin glass slide) using a four-point probe (manufactured by Lucas Labs: S-302-6), and multiplying this R S by the thickness (m) of the layer. The dispersion of the measurement results is in the range of 5 to 10% for resistivity values in the range of 2 to 30 μΩ·m.

[0039] (b) Fabrication of the cathode: Hereinafter, the cathode of a liquid electrolyte lithium-ion secondary battery will be described, but it should be understood that the present invention is not limited to the method for fabricating the cathode of the following liquid electrolyte lithium-ion secondary battery. The present invention can be applied to the fabrication of the negative electrode (anode). Further, the present invention can be applied to the fabrication of electrodes of electrochemical cells other than liquid electrolyte lithium-ion secondary batteries. The present invention can be applied to, for example, primary lithium batteries (for example, LiCF xIt may also be applied to the production of current collectors used in the production of primary lithium batteries of the type, solid electrolyte lithium ion secondary batteries, liquid or solid electrolyte sodium ion primary or secondary batteries, lithium sulfur secondary batteries, and sodium sulfur batteries.

[0040] The present invention can be applied to the production of current collectors used in the electrodes of supercapacitors or fuel cells. Further, the present invention can also be applied to the production of gas distribution plates (also referred to as bipolar plates) of fuel cells.

[0041] One or both surfaces of the foil coated with the layer of the material obtained by the method according to the present invention are coated with a positive electrode active material composition. This positive electrode active material composition contains at least one type of positive electrode active material, usually at least one type of binder, and at least one type of substance having good electronic conductivity. The positive electrode active material composition can be obtained by a wet method, that is, a method including adding an aqueous solvent or an organic solvent to the active material composition. The positive electrode active material composition can also be obtained by a dry method, that is, without adding a solvent.

[0042] In the case of the wet method, the positive electrode active material composition, the binder, the electronic conductive component, and the solvent are mixed. The active material composition is deposited on a metal foil serving as a current collector by coating. The electrode is obtained by evaporating the solvent by drying.

[0043] Also, the positive electrode active material composition can be obtained by a dry method by mixing the active material, the binder, and the good electronic conductive substance in an extruder without using a solvent.

[0044] Subsequently, a calendaring process for adjusting the layer thickness of the deposited active material is performed on the electrode obtained by the dry or wet method. After the calendaring process, the layer thickness of the deposited active material is usually in the range of 25 to 300 μm. The amount of the active material in the dry state deposited on the current collector is usually 5 to 50 mg / cm per side 2Since it is within the range, the generator is suitable for high-power or high-energy applications.

[0045] The positive electrode active material of the cell is not particularly limited. The positive electrode active material composition can be selected from the group consisting of the following compounds i) to v) and mixtures thereof. Compound i): Formula Li x Mn 1-y-z M’ y M’’ z PO 4 (Compound represented by LMP) (wherein M’ and M’’ are different from each other and are selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, and 0.8 ≦ x ≦ 1.2; 0 ≦ y ≦ 0.6; 0 ≦ z ≦ 0.2). Compound ii): Formula Li x M 2-x-y-z-w M’ y M’’ z M’’’ w O 2 (Compound represented by LMO2) (wherein M, M’, M’’ and M’’’ are selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, W and Mo. However, M, or M’, or M’’, or M’’’ is selected from Mn, Co, Ni, or Fe, M, M’, M’’ and M’’’ are different from each other, 0.8 ≦ x ≦ 1.4; 0 ≦ y ≦ 0.5; 0 ≦ z ≦ 0.5; 0 ≦ w ≦ 0.2 and x + y + z + w < 2.2). Compound iii): Formula Li x Mn 2-y-z M’ y M’’ z O 4 (Compound represented by LMO) (wherein M’ and M’’ are selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, M’ and M’’ are different from each other, 1 ≦ x ≦ 1.4; 0 ≦ y ≦ 0.6; 0 ≦ z ≦ 0.2). Compound iv): Formula Li x Fe 1-y M y PO4 The compound shown in 4 (wherein M is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb, and Mo; 0.8 ≦ x ≦ 1.2; 0 ≦ y ≦ 0.6). Compound v): Formula xLi 2 MnO 3 ;(1 - x)LiMO 2 The compound shown in 2 (wherein M is selected from Ni, Co, and Mn; x ≦ 1).

[0046] An example of compound i) is LiMn 1-y Fe y PO 4 That is. A preferred example is LiMnPO 4 That is.

[0047] The formula showing compound ii) may be Li x M 2-x-y-z-w M’ y M’’ z M’’’ w O 2 (wherein 1 ≦ x ≦ 1.15, M is Ni, M’ is Mn, M’’ is Co, and M’’’ is selected from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, or a mixture thereof; 2 - x - y - z - w > 0; y > 0; z > 0; w ≧ 0).

[0048] The formula showing compound ii) may be LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O 2 That is. Also, the formula showing compound ii) may be Li x M 2-x-y-z-w M’ y M’’ z M’’’ w O 2It may also be (where 1≦x≦1.15, M is Ni, M’ is Co, M’’ is Al, M’’’ is selected from the group consisting of B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo or a mixture thereof, 2 - x - y - z - w>0; y>0; z>0; w≧0, and preferably, x = 1; 0.6≦2 - x - y - z≦0.85; 0.10≦y≦0.25; 0.05≦z≦0.15 and w = 0).

[0049] Compound ii) may be selected from 2 , LiCoO 2 , LiMnO 2 . Ni, Co and Mn may be substituted with one or more elements selected from the group consisting of Mg, Mn, Al, B, Ti, V, Si, Cr, Fe, Cu, Zn, Zr (except when it becomes LiMnO 2 ).

[0050] An example of compound iii) is LiMn 2 O 4 . An example of compound iv) is LiFePO 4 . An example of compound v) is Li 2 MnO 3 .

[0051] The positive electrode active material may be at least partially covered by a carbon layer.

[0052] The binder may be selected from carboxymethyl cellulose (CMC), styrene - butadiene copolymer (SBR), polytetrafluoroethylene (PTFE), polyamideimide (PAI), polyimide (PI), styrene - butadiene rubber (SBR), poly(acrylic acid) (PAA), polyvinyl alcohol, polyvinylidene fluoride (PVDF) and mixtures thereof.

[0053] The substance having the electron conductivity is usually carbon black.

[0054] A typical composition of the active material composition deposited on the metal foil may be as follows: 75 to 90 wt% (preferably 80 to 90 wt%) of the positive electrode active material composition, 5 to 15 wt% (preferably 10 wt%) of the binder, and 5 to 10 wt% (preferably 10 wt%) of carbon black.

[0055] (c) Fabrication of the anode The negative electrode active material is mixed with one or more binders (such as those described above), a solvent, and usually one or more components having high conductivity (such as carbon black). Thereby, the active material composition is deposited on one or both surfaces of the current collector. The current collector coated with the active material composition is laminated to adjust its thickness, and thus, the anode is obtained.

[0056] The active material composition deposited on the anode current collector may consist of 75 to 90% (preferably 80 to 85%) of the negative electrode active material, 5 to 15% (preferably 10%) of the binder, and 5 to 10% (preferably 7.5%) of carbon.

[0057] The negative electrode active material may be selected from the group consisting of i) carbon-based components (such as graphite), ii) lithium titanate (Li 4 Ti 5 O 12 etc.), iii) metals selected from lithium, aluminum, silicon, tin (preferably silicon), and alloys containing these metals (preferably lithium alloys).

[0058] (d) Fabrication of the cell: An electrochemical assembly is formed by interposing a separator between an anode and a cathode. This electrochemical assembly is inserted into a cell container. The cell container can be parallelepiped-shaped or cylindrical. In the case of a cylindrical cell, the electrochemical assembly is wound in a spiral shape and inserted into the cylindrical container. The container in which the electrochemical assembly is disposed is filled with an electrolyte containing at least one type of organic solvent and at least one type of lithium salt.

[0059] The electrochemical cell can be used as an electrical energy source for a hybrid vehicle or an electric vehicle. It can also be used in other fields such as power sources for communication devices, emergency lighting, railways, aircraft, etc., and power sources for portable electrical / electronic devices.

Example

[0060] Separate aluminum foils 1 to 9 were coated with a layer made of a material containing Ti, C, H, and optionally O of the above cell. During the sputtering step, the foil serving as the substrate was attached to the barrel-shaped part, and by rotating this barrel-shaped part, a uniform layer was deposited. The distance between the foil and the target was set to about 100 mm, and the foil was polarized in a pulse mode at a frequency of 250 kHz. A power of 6 kW was applied to the titanium target. The flow rate of argon was 30 cm 3 / min under normal temperature and pressure conditions, and the flow rate of acetylene was controlled by detecting the light emission from the plasma to obtain the desired composition. For ion assist deposition growth, power was supplied from a 430 W power source to an additional plasma source.

[0061] Different layers were produced on the above aluminum foil by changing the parameters (flow rate of acetylene (C 2 H 2 ), bias voltage of the aluminum substrate, and deposition rate of the layer). The compositions of these different layers and their production conditions are shown in Table 1, and the thicknesses of the layers and their resistivity are shown in Table 2.

[0062]

Table 1

[0063]

Table 2

[0064] A) Test of the stability of the foil in contact with the electrolyte at 60 °C: Foil 1 - 9 were immersed in a carbonate-based electrolyte at 60 °C for 3 weeks, and then analyzed by X-ray fluorescence spectrometry to measure the loss of carbon, titanium, and oxygen due to the progressive dissolution of the layer in contact with the electrolyte. The loss of carbon and titanium was evaluated by comparing the mass ratios of C / Al and Ti / Al before and after immersion. The values of carbon loss and titanium loss are shown in Figures 1 and 2, respectively.

[0065] As a result of this test, the following is shown. For foils 4, 5, 6, and 8, the carbon loss is 20% or less, and for foils 1, 2, 3, and 9, the carbon loss is at least 24%. For foils 4, 5, 6, and 8, the titanium loss is 15% or less, and for foils 1, 2, 3, and 9, the titanium loss is at least 43%.

[0066] The surface of foil 7 shows discoloration after immersion in the electrolyte. This discoloration is considered to reflect the change on the surface of the material layer due to the high oxygen atomic ratio (14.80%). Also, it can be seen that a significant amount of titanium (36%) was lost in the material layer of foil 7.

[0067] Therefore, foils 4, 5, 6, and 8 are the foils with the best stability against the electrolyte. In particular, for foils 4, 5, and 6, the loss of carbon or titanium is 10% or less.

[0068] B) Evaluation in 18650-sized lithium-ion cells Cathodes of 18650-sized lithium-ion cells were fabricated using different foils. The characteristics of the foils used in each of the tested cells are summarized in Table 3.

[0069]

Table 3

[0070] The active materials deposited on the positive electrode foils of each of Cells A to I included an active material composed of lithium iron phosphate (formula LiFePO 4 ), a carbon black-based electrical conductor, and a polyvinylidene fluoride (PVDF)-based binder. The density of the active material deposited on the foil, that is, the weight of the electrode, was 10.5 mg / cm per side 2 .

[0071] The anode was made to be a mixture of graphite, a binder, and a thickener applied to a copper foil as a current collector. By sandwiching a separator between the cathode and the anode, different electrochemical assemblies were formed. Each assembly was wound up and inserted into a cell container, and each container was filled with an organic electrolyte.

[0072] The electrical performance of Cells C to F of Series 2 and 3 according to the present invention was compared with the electrical performance of cells having bare positive electrode foils on both sides (Cells A and B of Series 1) and cells having both sides of the positive electrode foil coated with a 1.9-μm carbon layer (Cells G to I of Series 4).

[0073] B-1) Measurement of internal resistance: The internal resistance of each cell was measured. The measurement was performed using a reference cycle of charging and discharging in Regime C / 5. Here, C is the nominal capacity of the cell. During discharge, in order to set the cell charge state to about 50%, discharge pulses of 10 seconds were performed several times in a regime in the range of 2C to 10C. Using these pulses, the internal resistance Ri can be obtained using the following formula.

[0074]

Equation

[0075] In the formula, U C / 5is the voltage of the discharge cell in Regime C / 5 before the application of the discharge pulse, U regime is Discharge Regime I regime is the cell voltage 10 seconds after applying the discharge pulse in

[0076] Subsequently, by multiplying this internal resistance by the area of the cathode that coats the foil, the resistance expressed in Ω·cm 2 was obtained.

[0077] Figure 3 shows the values of the internal resistances of Cells A - I of Series 1 - 4 for different discharge regimes 2C - 10C. It can be seen that the cells with the highest internal resistance are Cells A and B that have bare foil on the cathode. The presence of a layer containing the material according to the present invention or a carbon layer on the positive electrode foil reduces the internal resistance of the cell. The internal resistances of Cells G, H, and I that have foil coated with carbon on the cathode are approximately 40% lower than the internal resistances of Cells A and B. The internal resistances of Cells C, D, E, and F according to the present invention are even lower than those of Cells G, H, and I.

[0078] B - 2) Measurement of cell capacity in different discharge regimes: Electrical tests were performed on Cells A - I and their capacities were evaluated. In this test, after charging the cells in Regime C / 5, discharging was performed in regimes ranging from C / 5 to 10C. Figure 4 shows the discharge capacity (mAh) per gram of the LiFePO 4 active material for each discharge regime. It can be seen that Cells A and B that have bare foil on the cathode have the lowest capacities. When the positive electrode foil is coated with either a carbon layer or a layer containing the material according to the present invention, a significant improvement in the discharge capacity is observed. This improvement is due to the reduction of the contact resistance of the active material by the presence of a layer on the surface of the positive electrode foil. The polarization of the electrode is significantly reduced by the layer containing the material according to the present invention compared to the carbon - based layer. Figure 4 shows that the capacity of the cells with a conductive layer on the positive electrode foil is improved compared to the cells with a bare positive electrode foil.

[0079] In the discharge regime 2C, the capacity increases by 10% for the foil coated with the material according to the present invention and by 9.4% for the foil coated with carbon. In the discharge regime 5C, the capacity increases by 19% for the foil coated with the material according to the present invention and by 16% for the foil coated with carbon. In the discharge regime 10C, the capacity increases by 72% for the foil coated with the material according to the present invention and by 51% for the foil coated with carbon. Therefore, the effect of the presence of the layer of the material according to the present invention becomes more prominent in a higher discharge regime than in a lower discharge regime.

[0080] B-3) Measurement of cell polarization: The charge curves in the regime C / 5 and the charge curves in the regime 10C of cells A, C, E, F and G were plotted. From this, the bias of the cell (the voltage difference between the charge voltage and the discharge voltage for a specific charge state of the cell) can be evaluated. It can be seen that cells C, E, F and G having a carbon layer or a layer of the material according to the present invention on the positive electrode foil have weaker polarization than cell A having a bare positive electrode foil. Cells C, E and F having a foil coated with the material according to the present invention as the cathode have smaller polarization than cell G having a foil coated with carbon as the cathode.

[0081] B-4) Analysis of cell aging: Thereafter, for cells A, C, D, F, H and I, after performing 500 charge-discharge cycles (charge C, discharge 2C) at room temperature, an aging test was conducted in which they were stored at 60 °C in a 100% charged state. During the 500 charge-discharge cycles and during storage at 60 °C, the internal resistance was measured at regular time intervals for the discharge pulse in the regime 5C according to the measurement conditions described in item B-1.

[0082] The change in the internal resistance of the cell during the aging test is shown in Fig. 6. From this, the following can be understood. At the start of the test, the internal resistance of cell A having a bare positive electrode foil is the highest (40 Ω·cm 2 ). The internal resistances of cells H and I whose positive electrode foils are covered with carbon are about 22 - 25 Ω·cm 2That is, the internal resistances of cells C, D, and F, in which the positive electrode foil is covered with the material according to the present invention, are lower than those of cells H and I, and are about 20 Ω·cm 2 It is. During the test, the internal resistances of cells C, D, and F according to the present invention have a lower increase rate than those of cells A, H, and I, and at the end of the test, they remain lower than the internal resistance of cell A at the start of the test. Therefore, the layer according to the present invention has aging resistance when the cell is used under either cycling conditions or storage conditions at high temperature.

Claims

1. A metal foil for an electrode of an electrochemical cell having a fluorine-containing electrolyte, comprising: a layer on at least one side of a material comprising a metal or alloy, carbon, hydrogen, and optionally oxygen; The metal or alloy is one or more selected from the group consisting of Ti, Cr, Zr, Ni, and Fe; the atomic ratio of the metal in the material or the metal in the alloy is in the range of 10 to 60%; The atomic ratio of carbon in the material is in the range of 35 to 70%, The atomic ratio of hydrogen in the material is in the range of 2 to 20%, When the material contains oxygen, the atomic ratio of oxygen in the metal foil is 10% or less.

2. The metal foil of claim 1 wherein the material further comprises nitrogen.

3. 3. The metal foil according to claim 1, wherein the atomic ratio of the metal in the material or the metal in the alloy is in the range of 30 to 50%.

4. The metal foil according to any one of claims 1 to 3, wherein the atomic ratio of carbon in the material is in the range of 40 to 60%.

5. 5. The metal foil according to claim 1, wherein the atomic ratio of hydrogen in the material is in the range of 3 to 15%.

6. 6. The metal foil according to claim 1, wherein the material contains oxygen, and the atomic ratio of oxygen in the material is 5% or less.

7. The metal foil according to any one of claims 3 to 6, the atomic ratio of the metal of the metal or alloy in the material is in the range of 40-50%; the atomic ratio of carbon in said material is in the range of 40-55%; the atomic ratio of hydrogen in said material is in the range of 3-8%; The atomic ratio of oxygen in said material is 5% or less.

8. The metal foil according to any one of claims 1 to 7, wherein the thickness of the layer is in the range of 30 to 200 nm, or in the range of 50 to 150 nm, or in the range of 50 to 100 nm.

9. 9. The metal foil according to claim 1, which is made of aluminum or an aluminum-based alloy, or copper or a copper-based alloy.

10. A cathode for an electrochemical cell comprising the metal foil of claim 9.

11. 10. An electrochemical cell comprising a cathode and an anode, the cathode or the anode comprising the metal foil of any one of claims 1 to 9.

12. 12. The electrochemical cell of claim 11, Lithium primary electrochemical cells, Liquid electrolyte lithium-ion secondary electrochemical cells, Solid electrolyte lithium-ion secondary electrochemical cells, Sodium ion type primary or secondary electrochemical cells, Lithium-sulfur secondary electrochemical cells, and Sodium-sulfur electrochemical cell An electrochemical cell selected from:

13. 10. A fuel cell comprising at least one bipolar plate having at least one metal foil according to any one of claims 1 to 9, said metal foil comprising gas distribution channels on at least one side having said layer.

14. A method for producing a layer of a material containing a metal or alloy, carbon, and hydrogen on a metal foil for use in an electrode of an electrochemical cell having a fluorine-containing electrolyte, comprising the steps of: a) providing a substrate made of a metal foil; b) etching one side of the substrate by bombardment with ions formed by ionization of an inert gas; c) sputter depositing a material comprising a metal or alloy, carbon, hydrogen, and optionally oxygen onto the etched side of the substrate; The sputter deposition is performed using a target made of the metal or the alloy, and includes a step of injecting a mixed gas of an inert gas and a hydrocarbon gas at 20 to 30° C. into a chamber; the atomic ratio of the metal or metals constituting the alloy in the material is in the range of 10 to 60%; The metal or alloy is one or more selected from the group consisting of Ti, Cr, Zr, Ni, and Fe; the atomic ratio of carbon in the material is in the range of 35 to 70%; the atomic ratio of hydrogen in the material is in the range of 2 to 20%; If oxygen is present in the material, its atomic ratio is 10% or less; The method, wherein the gas mixture optionally comprises nitrogen.

15. 15. The method of claim 14, wherein the sputter deposition is performed using a single target of the metal or the alloy, the alloy being carbon-free, and the carbon and hydrogen in the material deposited in step c) originate from the hydrocarbon gas.

16. 16. The method of claim 14 or 15, wherein the metal of the material in step c) is titanium.

17. 17. The method of any one of claims 14 to 16, wherein the hydrocarbon is acetylene.

18. 18. The method of any one of claims 14 to 17, which does not include the step of performing an annealing treatment.

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