Electrode, cell, module, and pack

Abstract

Provided are an electrode (10), a cell (20), a module (31), and a pack (30) that make it possible to improve the energy density and output characteristics of an electric power storage device. The electrode includes a current collector (11), and a mixture layer (12) that is bonded to the current collector. The mixture layer contains a Si-containing substance (14) that contains silicon, and a carbon-based active material (15). The ratio R1 of the area of the Si-containing substance to the sum of the area of the Si-containing substance and the area of the carbon-based active substance in a range (16), within the mixture layer, that has a thickness of 5 μm from the interface (13) between the mixture layer and the current collector is 10-40%, said range appearing in a cross-section in the lamination direction of the mixture layer. The cell includes an electrode including a lithiated mixture layer.

Description

Electrodes, cells, modules and packs

[0001] The present invention relates to electrodes, cells, modules and packs that contain a carbon-based active material and a silicon-containing material.

[0002] In an electrode including a composite layer containing a carbon-based active material and a silicon-containing material and a current collector, Patent Document 1 discloses a prior art in which the proportion of the material in the surface layer farthest from the current collector to the total of the carbon-based active material and the material is 50 mass % or more. In the prior art, when pre-doping is performed to pre-load the electrode with Li ions, attaching a metallic lithium foil to the surface layer facilitates diffusion of Li ions into the composite layer.

[0003] JP 2015-46220 A

[0004] The prior art leaves room for improvement in the energy density (energy per unit mass or unit volume that can be extracted from a charged electricity storage device) and output characteristics of electricity storage devices that include electrodes.

[0005] The present invention has been made to solve this problem, and has an object to provide an electrode, a cell, a module, and a pack that can improve the energy density and output characteristics of an electricity storage device.

[0006] A first aspect of the present invention to achieve this object is an electrode comprising a current collector and a composite layer attached to the current collector, the composite layer comprising a Si-containing material containing silicon and a carbon-based active material, wherein the ratio R1 of the area of ​​the Si-containing material to the total area of ​​the Si-containing material and the carbon-based active material in a range of 5 μm in thickness from the interface between the composite layer and the current collector, which appears in a cross section of the composite layer, is 10% or more and 40% or less.

[0007] In a second aspect, in the first aspect, the ratio R1 is 20% or more and 40% or less.

[0008] In a third aspect, in the first or third aspect, the carbon-based active material is one or more selected from porous carbon, natural graphite, artificial graphite, graphitizable carbon, non-graphitizable carbon, and carbon fiber.

[0009] In a fourth aspect, in any one of the first to third aspects, the Si-containing substance is at least one selected from silicon and silicon oxide.

[0010] In a fifth aspect, in any one of the first to fourth aspects, the current collector is made of one or more materials selected from copper, aluminum, and stainless steel.

[0011] A sixth aspect is a cell including an electrode according to any one of the first to fifth aspects, wherein the electrode includes a lithiated composite layer.

[0012] A seventh aspect includes a plurality of cells according to the sixth aspect.

[0013] The eighth aspect includes a plurality of modules according to the seventh aspect.

[0014] According to the present invention, the ratio R1 of the area of ​​the Si-containing material to the total area of ​​the silicon-containing material and the carbon-based active material in a 5 μm-thick region of the composite layer from the interface between the composite layer and the current collector, as seen in a cross section of the composite layer in the stacking direction, is 10% or more and 40% or less. Since the ionic conductivity and electronic conductivity of the pre-doped electrode are improved in the 5 μm-thick region from the interface of the composite layer, the energy density and output characteristics of the power storage device can be improved.

[0015] 1A and 1B are cross-sectional views of an electrode in one embodiment, a cross-sectional view of a cell, a perspective view of a pack, and an exploded perspective view of a module.

[0016] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of an electrode 10 according to one embodiment. The electrode 10 includes a current collector 11 and a composite layer 12 attached to the current collector 11. There are no particular limitations on the material of the current collector 11, but examples include Cu, Al, a Cu alloy, an Al alloy, and stainless steel. There are also no particular limitations on the shape of the current collector 11. The current collector 11 may be a porous foil having a plurality of holes penetrating the current collector 11.

[0017] The composite layer 12 includes a silicon-containing material 14 and a carbon-based active material 15. There are no particular limitations on the material of the Si-containing material 14 as long as it contains silicon and is capable of absorbing and releasing Li. Examples of the material of the Si-containing material 14 include Si, a Si-Li alloy, and a compound containing Si and O as constituent elements (hereinafter referred to as "SiOx" where 0.5≦X≦1.5).

[0018] SiOx (silicon oxide) is an oxide of silicon, amorphous SiO ２ Examples of such a material include those having a structure in which microcrystalline or amorphous Si is dispersed in a matrix. SiOx has poor electrical conductivity, so it is preferable to provide a conductive layer covering the surface of SiOx or to combine SiOx with a conductive material. Granulation is an example of a method for combining SiOx with a conductive material. Examples of materials for the conductive layer include metals such as Pt and Os, and carbon. Examples of conductive materials include graphite, low-crystalline carbon, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon black, carbon nanotubes, carbon fiber, and fibrous or coiled metals.

[0019] When the conductivity of the Si-containing material 14 is low, a conductive agent is mixed and dispersed in the composite layer 12 to create a conductive network in order to reduce the amount of isolated Si-containing material 14. Examples of the conductive agent include carbon black, acetylene black, ketjen black, carbon nanotubes, and fibrous or coiled metals.

[0020] The Si-containing material 14 has a particle diameter (median diameter) of, for example, 0.2 to 20 μm, at which the cumulative value of the volumetric undersize cumulative distribution obtained by particle size distribution measurement using a laser diffraction / scattering method is 50%, in order to ensure the utilization rate of the Si-containing material 14.

[0021] There are no particular limitations on the carbon-based active material 15 as long as it contains carbon and is capable of absorbing and releasing Li. Examples of the carbon-based active material 15 include porous carbon, natural graphite, artificial graphite, graphitizable carbon, non-graphitizable carbon, and carbon fiber. The carbon-based active material 15 preferably contains particles with a volume-based median diameter of 1-30 μm determined by particle size distribution measurement using a laser diffraction / scattering method. This is to ensure the capacity of the electrode 10.

[0022] In a cell with Li as the carrier ion, the silicon-containing electrode 10 has a Li metal reference potential (Li ＋ / Li), and exhibits a high capacity density. However, silicon forms irreversible Si-O-Li bonds and consumes Li ions, resulting in a large irreversible capacity. To reduce the irreversible capacity, there is a technology (pre-doping) in which an amount of Li ions equivalent to at least a portion of the irreversible capacity is reacted with the electrode 10 before assembling the cell, thereby pre-loading the electrode 10 with Li ions. Pre-doping the electrode 10 with Li ions lowers the potential of the negative electrode, increasing the cell voltage and thus increasing the energy density.

[0023] In the composite layer 12, in a range 16 of 5 μm thickness from the interface 13 between the current collector 11 and the composite layer 12, the ratio R1 of the area of ​​the Si-containing material 14 to the total area of ​​the Si-containing material 14 and the carbon-based active material 15 that appear in the cross section of the composite layer 12 is 10% or more and 40% or less. This improves the ionic conductivity of the pre-doped electrode 10 in the range 16. Furthermore, when a Li alloy is formed in the Si-containing material 14 that has absorbed Li ions by pre-doping, Si-Si bonds are broken, and the electron density increases. As a result, the electronic conductivity of the range 16 is improved.

[0024] In addition to the conductivity between carbon-based active material 15 and current collector 11 in region 16, the conductivity between Si-containing material 14 and current collector 11 reduces the resistance of electrode 10 while maintaining the capacitance of electrode 10, improving the output characteristics of cell 20 (described below) and increasing the maximum power that can be extracted from charged cell 20. Furthermore, the increase in the potential of electrode 10 during discharge can be suppressed, allowing the voltage of cell 20 to be increased, thereby achieving a high energy density.

[0025] If the proportion R1 of range 16 is 20% or more and 40% or less, the ionic conductivity and electronic conductivity of range 16 are further improved, which is advantageous for improving the output characteristics of cell 20.

[0026] On the other hand, if the proportion R1 of range 16 is less than 10%, it becomes difficult to improve the electronic conductivity of range 16, and therefore the output characteristics tend not to improve. If the proportion R1 of range 16 exceeds 40%, the expansion of Si-containing material 14 that has absorbed Li ions by pre-doping tends to make range 16 more likely to peel off from current collector 11, and furthermore, the potential of electrode 10 tends to increase during discharge, which tends to lower the cell voltage and degrade the output characteristics.

[0027] The ratio R2 of the area of ​​Si-containing material 14 to the total area of ​​Si-containing material 14 and carbon-based active material 15 that appear in the cross section of composite layer 12 as a whole is preferably 10% or more and 40% or less, and more preferably 20% or more and 40% or less, because this can reduce peeling of composite layer 12 from current collector 11 due to expansion of Si-containing material 14 that has absorbed Li ions by pre-doping.

[0028] The Si-containing material 14 and the carbon-based active material 15 appearing in the cross section of the composite layer 12 can be identified using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). By image analysis of the cross section in the stacking direction of the composite layer 12 obtained using the SEM, the cross-sectional areas of the Si-containing material 14 containing Si and the carbon-based active material 15 containing C can be measured individually, and the ratios R1 and R2 can be calculated.

[0029] The ratio R2 can be calculated by individually measuring the cross-sectional areas of the Si-containing material 14 and the carbon-based active material 15 within a rectangular area of, for example, 100 μm in length and 240 μm in width on the image. The image is set so that the width of the image is approximately parallel to the interface 13. When the thickness of the composite layer 12 is less than 100 μm, an image with a length of 100 μm cannot be obtained. Therefore, the length of the image is set to the thickness of the composite layer 12, and when the area of ​​the image is 24,000 μm, the length of the image is set to the thickness of the composite layer 12. ２ Set the horizontal length of the image so that

[0030] The ratio R1 can be calculated by measuring the cross-sectional areas of the Si-containing material 14 and the carbon-based active material 15 individually within a rectangular area 16 that is 5 μm long and 240 μm wide in the image including the interface 13. The image is set so that the width of the image is along the interface 13.

[0031] The electrode 10 is manufactured, for example, as follows. First, a slurry containing the Si-containing material 14 and the carbon-based active material 15 as essential components, and optionally containing a binder and a thickener, is prepared. The ratio of the Si-containing material 14 to the carbon-based active material 15 is set in the range of 1:9 to 3:7 (volume ratio).

[0032] Examples of binders include fluororesins, acrylic resins, polyolefins, and rubbers. Examples of fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene copolymers. Examples of polyolefins include polyethylene and polypropylene. Examples of rubbers include styrene-butadiene rubbers. Examples of thickeners include carboxymethyl cellulose. Examples of dispersion media include organic solvents such as N-methyl-2-pyrrolidone and water.

[0033] The prepared slurry is applied to current collector 11, and then the slurry is dried to obtain electrode 10 in which composite layer 12 is formed on current collector 11. After drying, composite layer 12 may be rolled with a roller or the like.

[0034] Next, Li is supplied to electrode 10, and pre-doped with Li ions in an amount corresponding to at least a portion of the irreversible capacity. Pre-doping can be exemplified by a method in which current collector 11 and metallic lithium are short-circuited with a separator disposed between composite layer 12 and metallic lithium, and electrode 10, the separator, and metallic lithium are immersed in an electrolyte solution. Electrons flow from metallic lithium to current collector 11 due to the potential difference between current collector 11 and metallic lithium, and at the same time, the metallic lithium is ionized and released into the electrolyte solution, and the Li ions in the electrolyte solution are supported by composite layer 12.

[0035] Pre-doping with Li ions results in an electrode 10 in which the mixture layer 12 is lithiated. During pre-doping, a current may be passed between the current collector 11 and metallic lithium. The lithiation of the mixture layer 12 means that some of the atoms constituting the mixture layer 12 have been replaced with lithium atoms, that is, the mixture layer 12 contains lithium.

[0036] 2 is a cross-sectional view of a cell 20. The cell 20 is an electrochemical element that uses Li as a carrier ion. In this embodiment, the cell 20 is a lithium ion capacitor. The cell 20 includes, in order, an electrode 10 (negative electrode), a separator 21, and a positive electrode 22.

[0037] 2 shows a cell 20 having one set of electrode 10, separator 21, and positive electrode 22, but the present invention is not limited to this and may include a plurality of sets of these. Furthermore, the cell 20 is not limited to a stacked structure, but may have a wound structure in which the electrode 10 and the positive electrode 22 are stacked with the separator 21 interposed therebetween and wound.

[0038] The positive electrode 22 is formed by stacking a current collector 23 and a composite layer 24. Examples of the material of the current collector 23 include a metal selected from Ni, Ti, Fe, and Al, an alloy containing two or more of these elements, and stainless steel.

[0039] The composite layer 24 contains an active material such as graphite or activated carbon, and a conductive agent. Examples of the conductive agent include carbon black, acetylene black, ketjen black, and carbon fiber. The active material may be any material that can reversibly support anions, and is not limited to graphite or activated carbon.

[0040] The mixture layer 24 may contain a binder that binds the active material and the conductive agent. Examples of the binder include fluororesin, polyolefin, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ether, and rubber such as styrene-butadiene rubber. Examples of the fluororesin include vinylidene fluoride polymer, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer.

[0041] The separator 21 is made of a porous material that is durable against the active material and electrolyte solution contained in the positive electrode 22 and the electrode 10, and that is non-electron-conductive while allowing lithium ions to pass through. Examples of the separator 21 include nonwoven fabrics and porous films made of cellulose, polypropylene, polyethylene, etc.

[0042] The electrolyte solution contains a lithium salt dissolved in a solvent. The lithium salt is a compound used to transfer lithium ions between the positive electrode 22 and the electrode 10. The anion of the lithium salt is a halide ion (I － , Cl － ,Br － etc.), SCN － , BF4 － , BF3 (CF ３ ) ― , B.F. ３ (C ２ F ５ ) － , P.F. ６ － , ClO ４ － , SbF ６ － , N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ２ F ５ ) ２ － , B(C ６ H ５ ) ４ － , B(O ２ C ２ H ４ ) ２ － , C(SO ２ F) ３ － , C(SO ２ CF ３ ) ３ － , C.F. ３ COO － , C.F. ３ SO ２ O － , C ６ F ５ SO ２ O － , B(O ２ C ２ O ２ ) ２ － is exemplified.

[0043] The solvent for the electrolyte solution is not particularly limited as long as it is liquid in the temperature range in which the cell 20 is used. Examples of the solvent include carbonate esters, aliphatic carboxylic acid esters, phosphate esters, γ-lactones, ethers, nitriles, sulfolane, dimethyl sulfoxide, fluorous solvents, and ionic liquids. Mixtures of these solvents are also acceptable.

[0044] The cell 20 is manufactured, for example, as follows: A slurry is prepared by dispersing an active material and a conductive agent in a solution in which a binder is dissolved. The slurry is then applied to a current collector 23 and dried to obtain a green sheet (cathode sheet) for the positive electrode 22. The separator 21, the positive electrode sheet, and the electrode 10 are each cut to a predetermined shape, and then the positive electrode sheet, separator 21, and electrode 10 are stacked in this order. Terminals 35 and 36 (see FIG. 4) are connected to the current collectors 11 and 23, respectively, and the resulting product is sealed in a case 34 (see FIG. 4) together with an electrolyte solution, thereby obtaining the cell 20 including the positive electrode 22, separator 21, and electrode 10 (negative electrode) in this order.

[0045] 3 is a perspective view of the pack 30. The pack 30 includes a module 31 including a plurality of cells 20 (see FIG. 2). In the pack 30 of this embodiment, the plurality of modules 31 and an ECU (Electronic Control Unit) 32 are housed in a housing 33. An example of the material of the housing 33 is metal. The modules 21 and ECU 32 are fixed to the wall of the housing 33. The plurality of modules 31 are connected in series or in parallel.

[0046] 4 is an exploded perspective view of the module 31. The module 31 includes a plurality of cases 34 each enclosing a cell 20 (see FIG. 2). A terminal 35 connected to the current collector 11 of the electrode 10 (negative electrode) and a terminal 36 connected to the current collector 23 of the positive electrode 22 are drawn out of the case 34. The plurality of terminals 35, 36 are connected in series or in parallel. The case 34 may be of a laminated or cylindrical shape without any restrictions.

[0047] An ECU (not shown) may be provided in the module 31. The voltages and temperatures of the multiple cells 20 are input to the ECU. When the temperatures of the cells 20 are input to the ECU, a thermometer is provided that detects the temperature of the case 34 and inputs the temperature to the ECU. The ECU provided in the module 31 adjusts the voltage of each cell 20, for example.

[0048] The ECU 32 of the pack 30 (see FIG. 3 ) detects and monitors the state quantities (voltage and temperature) of the cells 20 of the module 31. The monitoring of the cells 20 may involve determining whether the state quantities are abnormal values, and stopping charging and discharging of the cells 20 if the state quantities are abnormal values. While the present embodiment illustrates a case in which one ECU 32 detects the state quantities of multiple modules 31, this is not limiting. It is of course possible to provide an ECU 32 for each module 31. The pack 30 may also be provided with a cooling circuit (not shown) for cooling the modules 31.

[0049] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0050] (Preparation of electrode) 100 parts by mass of a mixture of graphite particles (carbon-based active material) and carbon-covered silicon particles (silicon-containing material) mixed in various ratios, 1 part by mass of carbon black (conductive agent), 5 parts by mass of styrene butadiene rubber (binder), and 1 part by mass of carboxymethyl cellulose (thickener) were added to 107 parts by mass of pure water and mixed with a mixer to prepare a slurry. A current collector made of 8 μm thick copper foil was placed on the electrode, and the combined mass of graphite and silicon was 6.5 mg / cm. ２ The slurry was applied so as to form a composite layer having a thickness of about 100 μm, followed by vacuum drying at 70° C. for 1 hour, thereby obtaining an electrode in Sample No. 1-9.

[0051] (Pre-doping of Li ions into the electrode) A separator and a metallic lithium foil (counter electrode) pressed onto copper foil were attached in this order on the electrode composite layer to prepare a half cell. The half cell was immersed in the electrolyte, then evacuated and sealed. Pre-doping was performed by passing a current between the copper foil of the electrode and the copper foil of the counter electrode of the half cell, charging at a constant current of 0.1 C to 0 V at 25°C, and then charging at a constant voltage of 0.01 C. The electrolyte was prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in a lithium salt (1 mol / dm ３ ) dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate.

[0052] (Cell Fabrication) After removing the lithiated electrode from the half cell, a separator and an activated carbon electrode (counter electrode) were attached in that order on the lithiated composite layer to fabricate a cell. 4 mL of electrolyte was poured into the cell, which was then vacuum degassed to remove excess electrolyte, and the cell (lithium ion capacitor) was then sealed in a vacuum.

[0053] (Calculation of energy density) The cell was charged at 25° C. at a rate of 1 C to U1 = 3.8 V, and then charged at a constant voltage of 3.8 V for 30 minutes, and then discharged at a rate of 1 C to U2 = 2.2 V. The current I (A) during discharge, the voltage change ΔU from the start of discharge to the end of discharge, and the elapsed time Δt were substituted into equation (1) to determine the capacitance C, and the energy density was calculated from equation (2).

[0054] C = I · Δt / ΔU ... formula (1) Energy density = 0.5 · C · (U1 ２ -U2 ２ ) / 3600...Formula (2)

[0055] (Calculation of power) The cell was charged at 25° C. at a rate of 50 C to U1 = 3.8 V, and then charged at a constant voltage of 3.8 V for 30 minutes, and then discharged at a rate of 50 C to U2 = 2.2 V. The voltage drop at the start of discharge was divided by the current during discharge to determine the resistance R, and the power was calculated using equation (3).

[0056] Power = U1 ２ / (4・R)...Formula (3)

[0057] (Calculation of ratios R1 and R2) After cutting the pre-doped electrode perpendicular to the current collector, an image of the cross section of the composite layer 12 was obtained using an SEM, and the area of ​​the Si-containing material 14 containing Si and the area of ​​the carbon-based active material 15 containing C in a rectangular range of 100 μm long x 240 μm wide of the image were measured using image analysis software imageJ 1.53k. The ratio R2 of the area of ​​the Si-containing material 14 to the total area of ​​the Si-containing material 14 and the carbon-based active material 15 was calculated. Similarly, the area of ​​the Si-containing material 14 containing Si and the area of ​​the carbon-based active material 15 containing C in a rectangular range 16 of 5 μm long x 240 μm wide of the image including the interface 13 were measured using image analysis software imageJ 1.53k, and the ratio R1 of the area of ​​the Si-containing material 14 to the total area of ​​the Si-containing material 14 and the carbon-based active material 15 was calculated.

[0058] (Judgment) The energy density and power of the cell of sample No. 9, in which R1 = R2 = 0%, were used as a reference, and the energy density and power of the cells of sample Nos. 1-8 relative to No. 9 were calculated. The energy density of cell No. 9 was set to 100%, and samples with an energy density of 101% or more were rated as A, and samples with an energy density of less than 101% were rated as C. The power of cell No. 9 was set to 100%, and samples with a power of 110% or more were rated as A, samples with a power of 101% or more but less than 110% were rated as B, and samples with a power of less than 101% were rated as C.

[0059] Table 1 shows the ratio R1 (%), ratio R2 (%), energy density (%), and power (%) of the cells of Sample Nos. 1-9, as well as the lower of the energy density rating (A or C) and power rating (A, B, or C) of the cells of Sample Nos. 1-8.

[0060]

[0061] As shown in Table 1, Samples 1-6, in which R1 was 10% or more and 40% or less, had both an energy density and power of 101% or more compared to Sample No. 9. In contrast, Sample No. 7, in which R1 was 41%, had an energy density of 81% and a power of 45% compared to Sample No. 9. It was revealed that when R1 was 10% or more and 40% or less, the energy density and output characteristics of the cell could be improved.

[0062] Sample No. 3-6, in which R1 was 20% or more and 40% or less, had a power of 110% or more compared to Sample No. 9. It was revealed that when R1 was 20% or more and 40% or less, the output characteristics of the cell could be further improved.

[0063] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0064] In the embodiment, the cell 20 has been described as including a positive electrode 22 in which a composite material layer 24 is provided on one side of a current collector 23, and an electrode 10 (negative electrode) in which a composite material layer 12 is provided on one side of a current collector 11, but this is not necessarily limited to this. For example, it is of course possible to apply each element in the embodiment to a cell including an electrode layer (so-called bipolar electrode) in which a composite material layer 12 and a composite material layer 24 are provided on both sides of a current collector 23. A so-called bipolar structure cell can be obtained by alternately stacking bipolar electrodes and separators 21 and housing the resultant in a case (not shown).

[0065] In the embodiment, the electrode 10 has been described in which the composite layer 12 is provided on one side of the current collector 11, but this is not necessarily limited to this. It is of course possible to provide the composite layer 12 on both sides of the current collector 11.

[0066] In the embodiment, a lithium ion capacitor has been described as an example of the cell 20 including the electrode 10, but the present invention is not necessarily limited to this. Other cells (electricity storage devices) including the electrode 10 include secondary batteries such as lithium ion batteries.

[0067] REFERENCE SIGNS LIST 10 Electrode 11 Current collector 12 Composite layer 13 Interface 14 Si-containing material 15 Carbon-based active material 16 Area 20 Cell 30 Pack 31 Module

Claims

1. An electrode comprising a current collector and a composite layer attached to the current collector, the composite layer comprising a Si-containing material containing silicon and a carbon-based active material, wherein a ratio R1 of the area of ​​the Si-containing material to the sum of the area of ​​the Si-containing material and the area of ​​the carbon-based active material in a range of 5 μm thick from the interface between the composite layer and the current collector, which appears in a cross section of the composite layer in the stacking direction, is 10% or more and 40% or less.

2. The electrode according to claim 1, wherein said ratio R1 is 20% or more and 40% or less.

3. An electrode according to claim 1 or 2, wherein the carbon-based active material is one or more selected from the group consisting of porous carbon, natural graphite, artificial graphite, graphitizable carbon, non-graphitizable carbon, and carbon fiber.

4. The electrode according to claim 1 or 2, wherein the Si-containing substance is at least one selected from the group consisting of silicon and silicon oxide.

5. The electrode according to claim 1 or 2, wherein the current collector is made of one or more materials selected from the group consisting of copper, aluminum, and stainless steel.

6. A cell comprising an electrode according to claim 1 or 2, said electrode comprising a lithiated composite layer.

7. A module comprising a plurality of cells according to claim 6.

8. A pack containing a plurality of modules according to claim 7.

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