Metal foil for electrochemical cell electrodes comprising materials based on Ti, C and H

Abstract

A metal foil comprising a layer of material on at least one side thereof, the material comprising: a metal or metal alloy, carbon, hydrogen, and optionally oxygen, wherein the atomic percentage of the metal of the metal or alloy in the material ranges from 10% to 60%, the atomic percentage of carbon in the material ranges from 35% to 70%, the atomic percentage of hydrogen in the material ranges from 2% to 20%, and the atomic percentage of oxygen, when present, in the material is less than or equal to 10%. The metal foil can be used to fabricate a cathode for a lithium-ion electrochemical cell. Deposition of the layer reduces the internal resistance of the cell.

Description

Technical Field

[0001] The technical field of the invention is that of current collectors, in particular those intended for positive electrodes (or cathodes) of electrochemical cells, preferably of the lithium-ion type. Background Art

[0002] The term "battery" as used herein below refers to an electrochemical cell. In this specification, the terms "battery" and "electrochemical cell" are used interchangeably.

[0003] Electrochemical cells typically include an electrochemical assembly comprising alternating cathodes and anodes surrounding an electrolyte-impregnated separator. Each electrode is composed of a metallic current collector supporting, on at least one side thereof, an active material film comprising at least one active material and typically a binder and a conductive compound.

[0004] The cathode of a lithium-ion battery consists of a cathode active material composition coated on a current collector, which is generally composed of aluminum or an aluminum-based alloy. The aluminum foil is slightly oxidized in contact with air and therefore has an aluminum oxide Al2O3 layer on its surface. In the battery, the aluminum oxide layer will fluorinate and convert into AlF3 in contact with the electrolyte and the salt in the electrolyte. This new AlF3 layer is electrically insulating. Therefore, it tends to prevent electrons from passing through by increasing the contact resistance between the cathode active material composition and the aluminum foil. It can be seen that the internal resistance of a lithium-ion battery with a cathode whose current collector is made of aluminum will increase over time as the current collector contacts the electrolyte. When the battery is charged or discharged at a high current (or state), the increase in internal resistance leads to a decrease in the electrical performance of the battery on the one hand, and to higher heat generation during the cycle on the other hand.

[0005] In order to reduce the loss of electrical conductivity between the active material composition and the aluminum current collector, a layer can be deposited on the surface of the current collector. This layer can be based on carbon or on a metal carbide such as tungsten carbide. In this regard, US 2011 / 0200884 describes a process for reducing the contact resistance between an aluminum foil and an active material composition deposited on the surface of the foil. The process is carried out under vacuum and comprises a step of partially etching the aluminum oxide layer on the surface of the aluminum foil, followed by a step of sputtering a metal or metal carbide, typically tungsten (W) or tungsten carbide (WC), on the partially etched surface of the foil.

[0006] A drawback of this prior art is that the use of tungsten or its carbide presents numerous problems. For example, tungsten is very rare in batteries, and manufacturing sputtering targets from WC is expensive and difficult. Furthermore, due to the high mass of the W atoms, compressive stresses are high in thin layers containing tungsten. This can be detrimental to the aging and handling of foils coated with this material. For these reasons, novel methods are being sought to reduce the contact resistance between aluminum foil and the active material composition deposited on the foil surface. Summary of the Invention

[0007] To this end, the present invention provides a metal foil comprising, on at least one side thereof, a layer of material comprising:

[0008] - metal or metal alloy,

[0009] -carbon,

[0010] -hydrogen,

[0011] and optionally oxygen,

[0012] The atomic percentage of the metal in the material, metallic or alloyed, ranges from 10% to 60%,

[0013] The atomic percentage of carbon in the material ranges from 35% to 70%,

[0014] The atomic percentage of hydrogen in the material ranges from 2% to 20%,

[0015] The atomic percentage of oxygen present in the material is less than or equal to 10%.

[0016] According to one embodiment, the material further comprises nitrogen.

[0017] According to one embodiment, the atomic percentage of the metal, metallic or alloyed, in the material ranges from 30% to 50%, preferably from 40% to 50%.

[0018] According to one embodiment, the atomic percentage of carbon in the material ranges from 40% to 60%, preferably from 45% to 55%.

[0019] According to one embodiment, the atomic percentage of hydrogen in the material ranges from 3% to 15%, preferably from 3% to 8%.

[0020] According to one embodiment, the material comprises oxygen, and the atomic percentage of oxygen in the material is less than or equal to 5%, preferably less than or equal to 2%, and more preferably less than or equal to 1%.

[0021] According to one embodiment,

[0022] - the atomic percentage of metal in the material, metallic or alloyed, ranges from 40% to 50%,

[0023] - the atomic percentage of carbon in the material ranges from 40% to 55%,

[0024] - the atomic percentage of hydrogen in the material ranges from 3% to 8%, and

[0025] - The atomic percentage of oxygen in the material is less than or equal to 5%.

[0026] According to one embodiment, the metal of the material is selected from Ti, Cr, Zr, Fe, Ni, preferably Ti.

[0027] According to one embodiment, the alloy of the material consists of several metals selected from Ti, Zr, Fe, Cr and Ni.

[0028] According to one embodiment, the layer thickness ranges from 30 nm to 200 nm or from 50 nm to 150 nm or from 50 nm to 100 nm.

[0029] According to one embodiment, the metal foil is made of aluminum or an aluminum-based alloy, or copper or a copper-based alloy.

[0030] The invention also relates to a cathode of an electrochemical cell comprising a foil as described above.

[0031] The conductive layer deposited on the foil is stable over time in the organic electrolyte of lithium-ion batteries. The presence of this conductive layer improves the contact between the cathode active material and the foil, which leads to:

[0032] -The internal resistance of the battery is low,

[0033] -The battery has a good discharge capacity,

[0034] - The polarization of the battery is lower.

[0035] Due to the lower internal resistance of the battery, the battery heats up less when used in cycles with few or no rest phases. In addition, the presence of a conductive layer on the foil protects its surface from alkaline corrosion during aqueous treatment.

[0036] The invention also relates to an electrochemical cell comprising a cathode and an anode, the cathode or the anode comprising a metal foil as described above.

[0037] According to an embodiment, the electrochemical cell is selected from:

[0038] -Lithium primary electrochemical cells, such as LiCF x Type,

[0039] -Liquid electrolyte lithium-ion type secondary electrochemical cells,

[0040] - solid electrolyte lithium-ion type secondary electrochemical battery,

[0041] - primary or secondary electrochemical cells of the sodium ion type,

[0042] - lithium-sulfur secondary electrochemical cells, and

[0043] -Sodium-sulfur type electrochemical cell.

[0044] The invention also relates to a fuel cell comprising at least one bipolar plate comprising at least one metal foil as described above, wherein the metal foil comprises gas distribution channels on at least one side comprising said layer.

[0045] The invention also relates to a process for producing a layer of a material comprising a metal or a metal alloy, carbon and hydrogen on a metal foil, the method comprising the following steps:

[0046] a) providing a substrate consisting of a metal foil,

[0047] b) etching one side of the substrate by bombardment with ions generated by ionization of an inert gas,

[0048] c) sputter depositing on the etched side of the substrate a material comprising:

[0049] - metal or metal alloy,

[0050] -carbon,

[0051] -hydrogen,

[0052] and optionally oxygen,

[0053] Sputtering is carried out at a temperature of 25° C. in a mixture of inert gas and hydrocarbon gas, the mixture optionally containing nitrogen, using a target consisting of the metal or the metal alloy.

[0054] According to one embodiment, the metal of the material of step c) is titanium.

[0055] According to one embodiment, the process consists only in steps a) to c).

[0056] According to one embodiment, the process does not comprise a step of annealing the metal foil coated with the material obtained at the end of step c).

[0057] According to one embodiment, the hydrocarbon is acetylene.

[0058] Finally, the invention relates to a metal foil obtained by the process described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] [ Figure 1 ] shows the carbon loss in the layer for each of foils 1 to 9 after immersing the foil in an organic electrolyte maintained at 60° C. for three weeks.

[0060] [ Figure 2 ] represents, for each of foils 1 to 9, the loss of titanium in the layer after immersing the foil in an organic electrolyte maintained at 60° C. for three weeks.

[0061] [ Figure 3 ] represents the values of the internal resistance of batteries A to I measured for different discharge states from 2C to 10C for a depth of discharge of about 50%.

[0062] [ Figure 4 ] represents the values of discharge capacity of batteries A to I measured for different discharge states from C / 5 to 10C.

[0063] [ Figure 5 ] shows the charging curves of batteries A, C, E, F and G at state C / 5 and the discharging curves at state 10C.

[0064] [ Figure 6 ] shows the change in internal resistance of cells A, C, D, F, H, and I during an aging test consisting of 500 charge / discharge cycles (C charge, 2C discharge) at room temperature, followed by storage of the cells at 100% state of charge (SOC) at 60°C. For a depth of discharge of approximately 50%, the internal resistance was measured by applying a discharge pulse at state 5C for 10 seconds. DETAILED DESCRIPTION

[0065] a) Foil Manufacturing:

[0066] The process according to the invention makes it possible to obtain a layer of material on a metal foil. It comprises:

[0067] a) vacuum etching of the foil surface, then

[0068] b) A step of vacuum depositing the material by sputtering.

[0069] Steps a) and b) are carried out in a spray chamber. The chamber comprises a target, a support for receiving a foil serving as a substrate, and is provided with an inlet for injecting a gas.

[0070] The target is composed of a metal or metal alloy that is one of the components of the layer material. The metal can be selected from Ti, Cr, Zr, Fe and Ni, preferably Ti. The metals of the alloy are preferably at least two metals selected from Ti, Cr, Zr, Fe and Ni. In one embodiment, the metal is neither Fe nor Ni, and the metal alloy does not include Fe and / or does not include Ni.

[0071] The substrate is composed of a metal foil. The metal of the foil is preferably aluminum or an aluminum-based alloy. It can also be copper or a copper-based alloy. The thickness of the foil is typically less than or equal to 50 μm. The minimum foil thickness is typically 5 μm. The thickness can be greater than or equal to 10 μm, greater than or equal to 15 μm, or greater than or equal to 20 μm. Typically, the foil has a thickness ranging from 5 μm to 35 μm.

[0072] The step a) of etching the substrate consists of polarizing the substrate and bombarding its surface with ions (plasma) from an ionized inert gas. The bombardment reduces or even eliminates the oxide layer on the surface of the foil. The etching step improves the adhesion of this layer to the metal foil.

[0073] Step b) of sputtering is characterized in particular in that a mixture of an inert gas and a gaseous hydrocarbon is injected into the chamber at a temperature of 20° C. to 30° C. By way of example, the hydrocarbon can be selected from methane, ethylene, propane, acetylene, or a mixture of several of these gases. Acetylene is preferred because of its low H / C ratio. Preferably, the inert gas is argon. The chamber is first evacuated, and then the inert gas-hydrocarbon mixture is injected. The injection rate of the mixture and its composition can vary. A potential difference is applied between the target and the walls of the chamber. This potential difference causes the mixture of inert gas and hydrocarbon to ionize, forming a plasma. The positively charged plasma species are attracted to the target and collide with the metal or metal alloy. This collision causes atoms of the metal or metal alloy of the target to be sputtered. These atoms condense on the surface of the foil. The accumulation of atoms on the surface of the foil allows a thin layer of material comprising the metal or metal alloy, carbon, hydrogen, and optionally oxygen to gradually form. To achieve layer uniformity, the foil can be rotated in front of the target during sputtering. Optionally, in addition to the hydrocarbon gas, nitrogen can be injected into the chamber during the sputtering step. The injection of nitrogen allows the incorporation of chemical element nitrogen into the material layer.

[0074] The substrate may be biased at a potential in the range of -100 V to -500 V, preferably -150 V to -450 V or even -200 V to -400 V. The substrate may be biased in pulsed mode at a frequency in the range of 150 kHz to 350 kHz or 200 kHz to 300 kHz, for example about 250 kHz. The substrate may be biased to a potential in the range of -200 V to -500 V. The hydrocarbon flow rate depends on the characteristics of the housing used (size, pumping). The flow rate may vary from 2 sccm to 50 sccm, or from 2 sccm to 25 sccm, or from 5 sccm to 20 sccm (under standard pressure and temperature conditions, 1 sccm = 1 cm 3 The argon flow rate may be approximately 30 sccm. A layer growth rate of 1 nm / min to 15 nm / min, or 2 nm / min to 10 nm / min, or 4 nm / min to 10 nm / min may be achieved.

[0075] A person skilled in the art knows how to vary the flow rate of the mixture of inert gas and hydrocarbon gas, depending on the characteristics of the spray chamber, such as target size, sputtering power or even pumping rate, in order to obtain a material whose atomic percentage of metal, atomic percentage of carbon, atomic percentage of hydrogen and atomic percentage of oxygen in the metal or alloy falls within the specified ranges, i.e., 10% to 60%, 35% to 70%, 2% to 20% and up to 10%, respectively.

[0076] At the end of the deposition, the foil is removed from the chamber. The properties of the chemical elements present in the layer can be analyzed by X-ray fluorescence on the surface of the foil or by inductively coupled plasma spectroscopy (ICP) or Rutherford backscattering spectroscopy (RBS). The precise hydrogen content of the material can be measured using the elastic recoil detection analysis (ERDA) technique. The precise metal content, especially titanium, can be measured by the Rutherford backscattering spectroscopy (RBS) technique. The precise oxygen and carbon content can be measured by nuclear reaction analysis (NRA). The nitrogen content, optionally present in the material, can be accurately measured by RBS.

[0077] The layer material may include chemical elements other than the metal, carbon, hydrogen, and optionally oxygen and nitrogen contained in the metal or alloy. These other chemical elements are generally present in an amount of 2% or less of the atomic weight of the chemical elements constituting the material, preferably in an amount of 1% or less.

[0078] The thickness of the layer is typically in the range of 25 nm to 200 nm, or 30 nm to 150 nm, or 40 nm to 150 nm, or 50 nm to 150 nm, or 50 nm to 100 nm. The layer thickness can be measured, for example, on a glass indicator by partially masking the substrate and measuring the step height using an AlphaStep profilometer manufactured by Tencor Instruments.

[0079] The resistivity p of the layer (in micro-ohms x meters [μΩ x m]) can range from 0.5 μΩ·m to 14 μΩ·m, or from 1 μΩ·m to 10 μΩ·m, or from 2 μΩ·m to 10 μΩ·m, or from 1 μΩ·m to 5 μΩ·m. The resistivity of the layer can be assessed on an electrically insulating indicator, such as a very thin sheet of glass, by measuring the surface resistance R□, also known as R "squared," in ohms [Ω], using a Lucas Labs S-302-6 4-point meter, and then multiplying R□ by the thickness of the layer in m. For resistivity values between 2 μΩ·m and 30 μΩ·m, the dispersion of the measured values is approximately 5% to 10%.

[0080] b) Cathode manufacturing:

[0081] The following description is made with reference to the cathode of a liquid electrolyte lithium ion type secondary battery. However, it should be understood that the present invention is not limited to the manufacture of cathodes of liquid electrolyte lithium ion type secondary batteries. It can be applied to the manufacture of negative electrodes (anodes). It can be applied to the manufacture of electrodes of electrochemical cells other than liquid electrolyte lithium ion secondary batteries. For example, the present invention can be applied to the production of current collectors intended to be used in the manufacture of the following batteries:

[0082] - Primary lithium batteries, such as LiCF x Type,

[0083] - solid electrolyte lithium-ion secondary batteries,

[0084] - primary or secondary batteries of the sodium ion type with liquid or solid electrolyte,

[0085] - lithium-sulfur secondary batteries, and

[0086] -Sodium-sulfur batteries.

[0087] The invention can be applied to the production of current collectors intended to be used in supercapacitor electrodes or in fuel cell electrodes.The invention can also be applied to the production of gas distribution plates, also known as bipolar plates, for fuel cells.

[0088] One or more sides of the foil coated with the material layer obtained by the method according to the present invention are coated with a cathode active material composition. The cathode active material composition comprises at least one cathode active material, typically at least one binder, and at least one good electron conducting compound. The cathode active material composition can be obtained by a wet process, i.e., by a process comprising adding an aqueous or organic solvent to the active material composition. The cathode active material composition can also be obtained by a dry process, i.e., without the introduction of a solvent.

[0089] Typically, in a wet process, a cathode active material, a binder, an electron-conducting compound, and a solvent are mixed. The active material composition is deposited by coating on a metal foil serving as a current collector. The electrode is dried to evaporate the solvent, thereby obtaining the electrode.

[0090] The positive electrode active material composition can also be obtained by a dry process of mixing the active material, the binder, and the good electron-conducting compound in an extruder without using a solvent.

[0091] The electrode obtained by the dry or wet process then undergoes a calendering step in which the thickness of the layer of deposited active material composition is adjusted. After calendering, the thickness of the layer of deposited active material composition is generally between 25 μm and 300 μm. The amount of dry active material composition deposited on the current collector is generally from 5 mg / cm 2 / side changes to 50mg / cm2 / side, making the generator suitable for high power or high energy applications.

[0092] The cathode active material of the battery is not particularly limited. It can be selected from the following:

[0093] -Li x Mn 1-y-z M' y M” z Compound i) of PO4(LMP), wherein M' and M" are different from each other and are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, wherein 0.8≤x≤1.2; 0≤y≤0.6; 0≤z≤0.2;

[0094] -Li x M 2-x-y-z-w M' y M” z M"' w ii) a compound of O2(LMO2), wherein M, M', M", and M'' are selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, W, and Mo, provided that 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; wherein 0.8≤x≤1.4; 0≤y≤0.5; 0≤z≤0.5; 0≤w≤0.2; and x+y+z+w<2.2;

[0095] -Li x Mn 2-y-z M' y M” z Compound iii) of O4(LMO), wherein M' and M" are selected from 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, and 1≤x≤1.4; 0≤y≤0.6; 0≤z≤0.2;

[0096] -Li x Fe 1-y M y Compound iv) of PO4, wherein M is selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; and 0.8≤x≤1.2; 0≤y≤0.6;

[0097] - compounds of the formula xLi2MnO3; (1-x)LiMO2 v), wherein M is selected from Ni, Co and Mn and x≤1,

[0098] or a mixture of compounds i) to v).

[0099] An example of compound i) is LiMn 1-y Fe y PO4. A preferred embodiment is LiMnPO4.

[0100] Compound ii) may have the formula Li x M 2-x-y-z-w M' y M” z M"' w O2, wherein 1≤x≤1.15; M represents Ni; M' represents Mn; M" represents Co and M"" is selected from B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo or a mixture thereof; 2-xyzw>0; y>0; z>0; w≥0.

[0101] Compound ii) may have the formula LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2.

[0102] Compound ii) may also have the formula Li x M 2-x-y-z-w M' y M” z M"' w O2, wherein 1≤x≤1.15; M represents Ni; M' represents Co; M" represents Al and M'" is selected from B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo or mixtures thereof; 2-xyzw>0; y>0; z>0; w≥0. Preferably, x=1; 0.6≤2-xyz≤0.85; 0.10≤y≤0.25; 0.05≤z≤0.15 and w=0.

[0103] Compound ii) can also be selected from LiNiO2, LiCoO2, LiMnO2, and Ni, Co and Mn can be replaced by one or more of the batteries selected from Mg, Mn (except LiMnO2), Al, B, Ti, V, Si, Cr, Fe, Cu, Zn, and Zr.

[0104] An example of compound iii) is LiMn2O4.

[0105] An example of compound iv) is LiFePO4.

[0106] An example of compound v) is Li2MnO3.

[0107] The cathode active material may be at least partially covered by a carbon layer.

[0108] 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.

[0109] The electron-conducting compound is typically carbon black.

[0110] A typical composition of the active material deposited on the metal foil may be as follows:

[0111] - 75% to 90% by mass, preferably 80% to 90% by mass of cathode active material;

[0112] - 5 to 15% by mass, preferably 10% by mass, of binder(s);

[0113] - 5 to 10% by mass, preferably 10% by mass, of carbon black.

[0114] c) Anode manufacturing:

[0115] The anode active material is mixed with one or more binders such as those mentioned above, a solvent, and one or more compounds generally having high electrical conductivity, such as carbon black. This results in an active material composition deposited on one or both sides of a current collector. The current collectors coated with the active material composition are laminated to adjust their thickness. Thus, an anode is obtained.

[0116] The active material composition deposited on the anode current collector may be the following:

[0117] - 75% to 90%, preferably 80% to 85% anode active material;

[0118] - 5% to 15%, preferably 10% of binder;

[0119] - 5% to 10%, preferably 7.5% carbon.

[0120] The anode active material may be selected from:

[0121] i) carbon-based compounds, such as graphite;

[0122] ii) Lithium oxides of titanium, such as Li4Ti5O 12 ;

[0123] iii) Metals selected from the group consisting of lithium, aluminum, silicon, tin, preferably silicon, and alloys containing these metals, preferably lithium alloys.

[0124] d) Battery manufacturing:

[0125] An electrochemical assembly is formed by inserting a separator between an anode and a cathode. The electrochemical assembly is inserted into a battery container. The battery container can be parallelepiped or cylindrical. In the case of a cylindrical battery, the electrochemical assembly is wound into a spiral and inserted into the cylindrical container. The container containing the electrochemical assembly is filled with an electrolyte comprising at least one organic solvent and at least one lithium salt.

[0126] Electrochemical cells can be used as a source of electrical energy for hybrid or electric vehicles. They can also be used in other areas, such as powering telecommunications equipment, emergency lighting, railways, aviation, and powering portable electrical or electronic devices.

[0127] Example

[0128] Different aluminum foils 1 to 9 were coated with a layer of material comprising the battery's Ti, C, H, and optionally O. During the sputtering step, the foil used as a substrate was mounted on a barrel-shaped component that was rotated to allow uniform deposition of the layer. The distance between the foil and the target was approximately 100 mm. The foil was polarized in pulsed mode at a frequency of 250 kHz. The power applied to the titanium target was 6 kW. Under standard temperature and pressure conditions, the argon flow rate was 30 cm 3 / min. The acetylene flow rate was adjusted by monitoring the luminescence from the plasma to obtain the desired composition. The other plasma source was powered by a 430W power supply for ion-assisted deposition growth. Different layers of aluminum foil were produced by varying the following parameters: acetylene C2H2 flow rate, bias voltage of the aluminum substrate, and layer deposition rate. The compositions of the different layers and the operating conditions for their production are shown in Table 1. The thicknesses of the different layers and their resistivities are shown in Table 2.

[0129] [Table 1]

[0130]

[0131] *The examples are not part of this invention

[0132] [Table 2]

[0133] Foil Number Thickness (nm) Resistivity (μΩ·m) 1 110 2.5 2 90 1.9 3 110 8.8 4 95 2.7 5 55 2.2 6 100 2.4 7 170 21 8 140 20 9 35 27

[0134] A) Stability test of foil in contact with electrolyte at 60°C:

[0135] Foils 1 to 9 were immersed in a carbonate-based electrolyte at 60°C for 3 weeks and then analyzed by X-ray fluorescence after immersion. The loss of carbon, titanium, and oxygen due to the gradual dissolution of the layer in contact with the electrolyte was measured. The loss of carbon and titanium was evaluated by comparing the mass percentages C / Al and Ti / Al before and after immersion. The values of carbon loss and titanium loss are respectively Figure 1 and Figure 2 Shown in.

[0136] The results of this test showed that:

[0137] - For foils 4, 5, 6 and 8, carbon loss is less than 20%,

[0138] - For foils 1, 2, 3 and 9, the carbon loss is at least 24%.

[0139] - for foils 4, 5, 6 and 8, titanium loss less than or equal to 15%,

[0140] - For foils 1, 2, 3 and 9, the titanium loss is at least 43%.

[0141] The surface of foil 7 shows a color change after immersion in the electrolyte. This change in color probably reflects a change in the surface of the material layer, which can be explained by the high atomic percentage of oxygen (14.80%). In addition, it can be noted that the material layer of foil 7 has lost a significant amount of titanium (36%).

[0142] Therefore, foils 4, 5, 6 and 8 are the foils with the best stability to the electrolyte. In particular, foils 4, 5 and 6 have a carbon loss or titanium loss of no more than 10%.

[0143] B) Evaluated in 18650 lithium-ion batteries

[0144] Different foils were used in the manufacture of cathodes for 18650 size lithium-ion batteries. Table 3 summarizes the properties of the foils used in the different batteries tested.

[0145] [Table 3]

[0146]

[0147] The active material composition deposited on each of the cathode foils of cells A to I included an active material composed of lithium iron phosphate of the formula LiFePO4, an electrical percolant based on carbon black, and a binder based on polyvinylidene fluoride (PVdF). The density of the active material composition deposited on the foil, i.e., the electrode weight, was 10.5 mg / cm 2 / side.

[0148] The anode consists of a mixture of graphite, a binder, and a thickener, coated on a current collector (copper foil). Separators are inserted between the cathode and anode to form the various electrochemical components. Each component is coiled and placed in a battery container. Each container is filled with an organic electrolyte.

[0149] The electrical performance of cells C to F of series 2 and 3 according to the invention was compared with the electrical performance of cells with both sides of the cathode foil exposed (cells A and B of series 1) and with the electrical performance of cells with both sides of the cathode foil covered with a 1.9 μm carbon layer (cells G to I of series 4).

[0150] B-1) Measurement of internal resistance:

[0151] The internal resistance of each battery was measured. This measurement was performed using a reference cycle consisting of charging and then discharging at a regime of C / 5, where C is the nominal capacity of the battery. During discharge, several 10-second discharge pulses, each at a regime between 2C and 10C, were performed to bring the battery's state of charge to approximately 50%. These pulses made it possible to calculate the internal resistance Ri by applying the following formula:

[0152] [Mathematical formula 1]

[0153] Ri=(U C / 5 -U 状态 ) / I 状态

[0154] in:

[0155] U C / 5 represents the voltage of the discharged battery at state C / 5 before the discharge pulse is applied.

[0156] U 状态 Indicates that in the discharge state I 状态 The battery voltage after applying the discharge pulse for 10 seconds.

[0157] The internal resistance is then multiplied by the cathode area coated on the foil to obtain the value in Ω×cm 2 Indicates the resistance.

[0158] Figure 3The internal resistance values of batteries A through I for series 1 through 4 are shown for different states of discharge, ranging from 2C to 10C. It can be seen that the batteries with the highest internal resistance are batteries A and B, which have bare cathode foil. The presence of a layer comprising a material according to the present invention, or a carbon layer, on the cathode foil results in a reduction in the internal resistance of the battery. Batteries G, H, and I, whose cathodes comprise carbon-coated foil, have an internal resistance approximately 40% lower than that of batteries A and B. Batteries C, D, E, and F, according to the present invention, have even lower internal resistance than batteries G, H, and I.

[0159] B-2) Measurement of battery capacity at different discharge states :

[0160] Batteries A to I were subjected to electrical testing to evaluate their capacity. The test involved charging the batteries at state C / 5, followed by discharging at states between C / 5 and 10C. Figure 4 The discharge capacity of the LiFePO4 active material in mAh per gram is shown for each discharge state. It can be seen that cells A and B, whose cathodes consist of bare foil, have the lowest capacity. A significant improvement in discharge capacity is observed when the cathode foil is covered with a carbon layer or a layer comprising the material according to the present invention. This improvement is attributed to the fact that the presence of the layer on the surface of the cathode foil reduces the contact resistance with the active material. The layer comprising the material according to the present invention reduces the polarization of the electrode to a greater extent than the carbon-based layer. Figure 4 shows the improved capacitance of a cell with a conductive layer on the cathode foil compared to a cell with a bare cathode foil:

[0161] - In discharge state 2C: for the foil coated with the material according to the invention, the increase in capacity is 10%, whereas for the foil coated with carbon, the increase in capacity is 9.4%.

[0162] - In discharge state 5C: for the foil coated with the material according to the invention, the increase in capacity is 19%, while for the foil coated with carbon, the increase in capacity is 16%.

[0163] - In discharge state 10C: for the foil coated with the material according to the invention, the increase in capacity is 72%, while for the foil coated with carbon, the increase in capacity is 51%.

[0164] Therefore, the benefit of the presence of the layer of material according to the invention is more pronounced in high discharge states than in low discharge states.

[0165] B-3) Measure the polarization of the battery:

[0166] The charge curves for batteries A, C, E, F, and G at state C / 5 and the discharge curves at state 10C are plotted. This allows the battery's bias voltage, which is the voltage difference between the charge and discharge voltages for a given state of charge, to be estimated. It can be seen that batteries C, E, F, and G, whose cathode foils include a carbon layer or a layer of the material according to the present invention, have weaker polarization than battery A, whose cathode foil is bare. Batteries C, E, and F, whose cathodes include foils coated with the material according to the present invention, have lower polarization than battery G, whose cathode includes a carbon-coated foil.

[0167] B-4) Research on battery aging:

[0168] Batteries A, C, D, F, H, and I were then subjected to an aging test consisting of 500 charge / discharge cycles at room temperature (C charge, 2C discharge) followed by storage at 60°C at 100% state of charge. The internal resistance was measured periodically during the 500 charge / discharge cycles and during storage at 60°C, according to the measurement conditions described in paragraph B-1, for a discharge pulse at state 5C. Figure 6 The change in internal resistance of the cells during the aging test is shown in FIG. 1 . It can be seen that: - at the beginning of the test, the internal resistance of cell A with exposed cathode foil is the highest (40 Ω×cm 2 The internal resistance of cells H and I with carbon-coated cathode foil is approximately 22Ω×cm 2 to 25Ω×cm 2 The cathode foils of cells C, D and F coated with the material according to the present invention had a resistance of about 20 Ω x cm 2 The internal resistance of batteries H and I is lower than that of batteries I.

[0169] The internal resistance of batteries C, D and F according to the invention increased more slowly during the test than the internal resistance of batteries A, H and I and remained lower at the end of the test than the internal resistance of battery A at the beginning of the test.

[0170] The layer according to the invention is therefore resistant to aging both when the battery is used under cycling conditions and under high-temperature storage conditions.

Claims

1. A cathode or anode of an electrochemical cell comprising a metal foil comprising, on at least one side thereof, a layer of a material comprising: -Ti, -carbon, -hydrogen, and optionally oxygen, The atomic percentage of Ti in the material ranges from 40% to 50%, The atomic percentage of carbon in said material ranges from 40% to 55%, The atomic percentage of hydrogen in said material ranges from 3% to 8%, Oxygen is present in the material at an atomic percentage of less than or equal to 5%.

2. The cathode or anode according to claim 1, wherein The material also includes nitrogen.

3. The cathode or anode according to claim 1 , wherein: The atomic percentage of carbon in the material ranges from 45% to 55%.

4. The cathode or anode according to claim 1 , wherein The layer thickness is from 30 nm to 200 nm.

5. The cathode or anode according to claim 1, wherein The layer thickness is from 50 nm to 150 nm.

6. The cathode or anode according to claim 1, wherein The layer thickness is from 50 nm to 100 nm.

7. The cathode or anode according to one of claims 1 to 2, wherein the metal foil is made of aluminum or an aluminum-based alloy, or copper or a copper-based alloy.

8. An electrochemical cell comprising a cathode and an anode, the cathode or the anode being the cathode or anode according to one of claims 1 to 7.

9. The electrochemical cell according to claim 8, selected from: - lithium primary electrochemical cells, -Liquid electrolyte lithium-ion type secondary electrochemical cells, - solid electrolyte lithium-ion type secondary electrochemical battery, - primary or secondary electrochemical cells of the sodium ion type, - lithium-sulfur secondary electrochemical cells, and -Sodium-sulfur type electrochemical cell. 10 . A fuel cell comprising a cathode and an anode, the cathode or the anode being the cathode or the anode according to claim 1 .

11. A method for producing a layer of a material comprising Ti, carbon and hydrogen on a metal foil, the method comprising the steps of: a) providing a substrate consisting of a metal foil, b) etching one side of the substrate by bombardment with ions generated by ionization of an inert gas, c) sputter depositing on the etched side of the substrate a material comprising: -Ti, -carbon, -hydrogen, and optionally oxygen, The atomic percentage of Ti in the material ranges from 40% to 50%, The atomic percentage of carbon in said material ranges from 40% to 55%, The atomic percentage of hydrogen in said material ranges from 3% to 8%, The atomic percentage of oxygen present in the material is less than or equal to 5%, The sputtering is performed using a single target composed of the Ti, and the sputtering comprises injecting a mixture of an inert gas and a hydrocarbon gas into a chamber at a temperature of 20° C. to 30° C., the mixture optionally containing nitrogen, wherein the carbon and hydrogen in the material deposited in step c) originate from the hydrocarbon gas.

12. The method according to claim 11, wherein The hydrocarbon is acetylene.

13. The method of claim 11, wherein the atomic percentage of carbon in the material ranges from 45% to 55%.

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