Electrode, method for manufacturing electrode, and secondary battery

Abstract

An electrode (100) comprises a current collector (10) and an active material (21). The current collector (10) comprises: a non-woven fabric (11) that is a porous body comprising voids; and an electrically conductive layer (12) that is provided on the surface of the non-woven fabric (11). The active material (21) is filled in the voids of the non-woven fabric (11) and is formed as a first surface layer (31) and a second surface layer (32) on both surfaces in a direction indicating the thickness of the current collector (10). The thicknesses (T1, T2) of the first surface layer (31) and the second surface layer (32) are less than or equal to the thickness (Tc) of the current collector (10) that is filled with the active material (21).

Description

Electrode, electrode manufacturing method, and secondary battery

[0001] The present invention relates to an electrode, a method for manufacturing an electrode, and a secondary battery.

[0002] Patent Document 1 discloses a current collector having a conductive nonwoven fabric and a secondary battery having the current collector as a constituent member. The surface of the nonwoven fabric is coated with a conductive film. This conductive film creates a three-dimensional network structure at the contact points between fibers or adjacent areas, providing porosity that allows the active material to easily penetrate.

[0003] JP 2012-109224 A

[0004] When the current collector described in Patent Document 1 is used in a lithium-ion battery, the active material repeatedly expands due to lithium absorption and contracts due to lithium desorption during charging and discharging. This expansion and contraction of the active material causes the active material to collapse (the breakdown of bonds between particles such as silicon that constitute the active material). The current collector described in Patent Document 1 has a layer of active material filled into the gaps between fibers of a nonwoven fabric, and a thicker layer of active material alone formed on both sides of the layer. That is, the current collector has a three-layer structure in which the layer of active material filled into the gaps between fibers of the nonwoven fabric is sandwiched between thicker layers of active material alone. The layer of active material alone accounts for more than two-thirds of the entire electrode made of the current collector. This poses a problem of a high possibility of active material collapse.

[0005] The present invention has been made in view of the above circumstances, and aims to provide an electrode, an electrode manufacturing method, and a secondary battery that can reduce the possibility of the active material collapsing.

[0006] In order to achieve the above object, an electrode according to a first aspect of the present invention is an electrode comprising a current collector and an active material, wherein the current collector comprises a porous body having voids and a conductive layer provided on the surface of the porous body, the active material is filled in the voids of the porous body and is formed as a first surface layer and a second surface layer on both sides of the current collector in the thickness direction, and the thicknesses of the first surface layer and the second surface layer are each equal to or less than the thickness of the current collector filled with the active material.

[0007] According to the present invention, it is possible to provide an electrode, an electrode manufacturing method, and a secondary battery that can reduce the possibility of the active material collapsing.

[0008] FIG. 1 is a cross-sectional view schematically showing an electrode according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the shape of the electrode according to the first embodiment of the present invention before charge, during charge, and during discharge. FIG. 3 is a diagram showing the manufacturing process of the electrode according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view schematically showing an electrode according to a second embodiment of the present invention. FIG. 5 is a graph showing the discharge capacity retention rate versus the number of cycles for batteries using a negative electrode manufactured by Manufacturing Method 1 in Examples and Comparative Examples of the present invention. FIG. 6 is a graph showing the discharge capacity retention rate versus the number of cycles for batteries using a negative electrode manufactured by Manufacturing Method 2 in Examples and Comparative Examples of the present invention. FIG. 7 is a graph showing the discharge capacity retention rate versus the number of cycles for batteries using a negative electrode manufactured by Manufacturing Method 3 in Examples and Comparative Examples of the present invention. FIG. 8 is a graph showing the discharge capacity retention rate versus the number of cycles for batteries using a negative electrode manufactured by Manufacturing Method 4 in Examples and Comparative Examples of the present invention. FIG. 9 is a graph showing the discharge capacity retention rate versus the number of cycles for batteries using a negative electrode manufactured by Manufacturing Method 5 in Examples and Comparative Examples of the present invention.

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrode according to an embodiment of the present invention will now be described with reference to the drawings.

[0010] First Embodiment As shown in FIG. 1, an electrode 100 according to a first embodiment includes a current collector 10 and a composite material 20 .

[0011] The current collector 10 includes a nonwoven fabric 11 and a conductive layer 12 formed on the surface of the nonwoven fabric 11. The current collector 10 is a conductor that collects and outputs current, and its thickness is shown as Tc in FIG. 1. The electrode 100 is composed of the current collector 10 having the thickness Tc, a first surface layer 31 having a thickness T1, and a second surface layer 32 having a thickness T2, which will be described later.

[0012] The nonwoven fabric 11 is formed by collecting and bonding a plurality of elongated fibrous bodies 11a to form a porous body with numerous voids, and is flexible. The nonwoven fabric 11, which is made of a plurality of collected fibrous bodies 11a, preferably has high heat resistance during subsequent plating processes, battery manufacturing, and use. For example, the nonwoven fabric 11 is preferably made of a synthetic resin having a melting point and thermal decomposition onset temperature of 140°C or higher. The nonwoven fabric 11 is formed from a resin such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), or polyolefin (PO). Nonwoven fabrics can be manufactured using a variety of methods, including wet spinning, dry spinning, wet-dry spinning, electrospinning, composite melt spinning, and meltblowing, but the manufacturing method is not particularly limited.

[0013] The structure of the nonwoven fabric must be lightweight and have a strong skeleton, while being able to contain as much active material as possible. The amount of active material required is determined by the battery design, so a nonwoven fabric with optimal porosity, fiber diameter, strength, etc. is selected based on the specifications.

[0014] The pore size of the voids is preferably large enough to allow the active material particles to easily penetrate. If the voids are too large relative to the active material, the active material cannot be retained inside the nonwoven fabric, which can hinder film formation of the composite. Furthermore, the amount of electrolyte captured increases, which can increase the battery weight and hinder battery performance. The optimal nonwoven fabric is selected depending on the film formation method of the composite, the state of the active material, and the viscosity or particle size of the composite.

[0015] If the nonwoven fabric is too thin, it will have the same structure as conventional copper foil, with a thick composite layer placed on the current collector. If the nonwoven fabric is too thick, plating will be more difficult and the composite will not be able to fill the voids. Although it depends on the battery design, a thickness of around 40 to 100 μm is considered appropriate, but the optimal thickness of the nonwoven fabric will be selected depending on the specifications.

[0016] The conductor layer 12 includes a first layer 12a and a second layer 12b. The first layer 12a is formed on the surface of the fibrous body 11a that constitutes the nonwoven fabric 11. The second layer 12b is formed on the first layer 12a. The first layer 12a and the second layer 12b are each formed by plating. Note that, in the plating of the first layer 12a, the metal that covers the surface of the fibrous body 11a also penetrates into the interior of the fibrous body 11a.

[0017] The first layer 12a and the second layer 12b preferably contain one or more elements selected from the group consisting of copper, nickel, aluminum, gold, silver, chromium, iron, cobalt, titanium, zinc, tin, indium, palladium, carbon, and silicon, and may also contain an alloy of these elements or a composite of one or more elements selected from the group consisting of carbon nanotubes (CNTs), carbon black, activated carbon, graphite, graphene, cellulose nanofibers, and carbon fibers.

[0018] The plating film thickness must be at least thick enough to completely cover the nonwoven fabric and make the entire surface conductive, but care must be taken to avoid it being too thick and increasing the weight.

[0019] The surface of the nonwoven fabric in the first layer 12a is hardened by plating with copper or nickel, etc. Therefore, in order to improve contact with the active material 21, the second layer 12b may be plated with soft tin or CNT composite plating.

[0020] The composite material 20 can be formed into a film by a "coating-type" film-forming method, in which a paste containing the active material 21, a solvent, a binder, a conductive additive, etc. is formed, and the paste is then coated on the current collector 10 and dried. Other methods for forming the composite material 20 include a "vapor deposition" film-forming method, in which energy is directly applied to the active material 21 to densely adhere it to the surface of the current collector foil. By forming the composite material 20 into a film on the current collector 10, the active material 21 fills the numerous voids formed in the nonwoven fabric 11. At the same time, a first surface layer 31 and a second surface layer 32, which are layers mainly composed of the composite material 20 (active material 21), are formed on both sides of the current collector 10 in the direction of the thickness Tc. The direction of the thickness Tc of the current collector 10 is the direction perpendicular to the plane of the current collector 10.

[0021] Known active materials used for the positive or negative electrodes of batteries can be used for the active material 21. The active material is selected based on the battery design, and examples of the active material include graphite, hard carbon, soft carbon, silicon (Si), SiO, sulfur, LTO (lithium titanate), Li metal, Na metal, and Zn metal.

[0022] Known materials used for battery electrolytes can be used as the electrolyte enclosed in the electrode 100. For example, not only electrolyte solutions in which various electrolyte salts are dissolved in solvents such as water, organic solvents, and ionic liquids, but also gel electrolytes in which electrolyte solutions are solidified with a gelling agent, and sulfide-based, oxide-based, and polymer-based solid electrolytes can be used.

[0023] As shown in FIG. 1 , in the electrode 100, the thickness of the current collector 10 is Tc, the thickness of the first surface layer 31 is T1, and the thickness of the second surface layer 32 is T2. The thickness of the electrode 100 is T = Tc + T1 + T2. Here, when the thickness index A = (Tc + T1 + T2) / Tc, a value A≦3.0 is preferable because, when the electrode 100 is used in a battery, a battery that exhibits little deterioration due to continuous charging and discharging is obtained. As the value of A increases above 3.0, the battery degradation due to continuous charging and discharging gradually increases. Furthermore, it is more preferable that the current collector 10 filled with the active material 21 has a thickness close to that of the electrode 100.

[0024] 2 shows the electrode 100 before charging, during charging, and during subsequent discharging when used as an electrode for a lithium-ion battery. Active material 21 fills the voids inside nonwoven fabric 11, which has a conductive layer 12 formed on its surface. This creates a conductive path (conductive pathway) through the nonwoven fabric in the areas where the active material 21 fills the voids in nonwoven fabric 11.

[0025] When the electrode 100 is charged, the active material 21 absorbs lithium and expands, causing the entire electrode 100 to expand. The nonwoven fabric 11 is flexible and follows the expansion of the active material 21. This maintains the skeleton and conductive paths of the nonwoven fabric 11 in the current collector 10. During discharge, lithium is released from the active material 21, causing the active material 21 to contract. The current collector 10 also follows the contraction, maintaining the original skeleton and conductive paths.

[0026] Next, a method for manufacturing the electrode 100 will be described with reference to Fig. 3. In this embodiment, a negative electrode is used as an example.

[0027] 3 relate to the production of current collector 10, and steps S21 to S23 relate to the production of composite material 20. Steps S11 to S14 and steps S21 to S23 may be performed in parallel.

[0028] In manufacturing the current collector 10, first, the nonwoven fabric 11 is selected and prepared (step S11). Here, it is preferable to select a nonwoven fabric with voids that encloses most of the composite material 20, including the amount of active material required for designing the battery. In addition, the material, size, thickness, etc. of the nonwoven fabric 11 are selected depending on the battery to be designed.

[0029] Next, the nonwoven fabric 11 is subjected to a conductive treatment (step S12), in which the surface of the fibrous body 11a of the nonwoven fabric 11 is subjected to a surface treatment using a primer, a conductive polymer, or the like.

[0030] Next, electroless plating is performed on the surface of the fibrous body 11a of the nonwoven fabric 11 after the conductive treatment to form the first layer 12a of the conductive layer 12 (step S13).

[0031] The first layer 12a, i.e., the conductive layer, can be formed on the fibrous body 11a of the nonwoven fabric 11 by wet plating such as electroless plating and electrolytic plating, vacuum deposition and sputtering, physical vapor deposition such as ion plating, and chemical vapor deposition such as plasma CVD and thermal CVD. Conductivity can also be imparted by coating with metal nanoparticles.

[0032] From the viewpoints of uniformity and productivity, electrolytic plating is preferable, but it is difficult to apply the plating directly to the nonwoven fabric 11. Therefore, in this embodiment, the nonwoven fabric 11 is subjected to a surface treatment and then subjected to electroless plating.

[0033] Next, electrolytic plating is performed (step S14) to form a second layer 12b on the surface of the first layer 12a of the fibrous body 11a in the nonwoven fabric 11. The second layer 12b can be electrolytic plating to obtain a required plating thickness, or surface treatment such as tin plating or composite plating to impart special functions.

[0034] Alternatively, after the nonwoven fabric 11 has been subjected to the conductive treatment (step S12), the electroless plating step (step S13) and the electrolytic plating step (step S14) may not be performed. The composite mixture application step (step S100) may then be performed. Furthermore, after the nonwoven fabric 11 has been subjected to the conductive treatment (step S12), either the electroless plating step (step S13) or the electrolytic plating step (step S14) may be performed. The composite mixture application step (step S100) may then be performed. As described above for step S14, instead of electrolytic plating, surface treatments such as tin plating or composite plating may be used to impart special functions.

[0035] The surface of the fibrous body 11a (nonwoven fabric 11) plated with copper, nickel, or the like on the first layer 12a becomes hard. Therefore, in order to ensure contact with the active material 21, the second layer 12b may be plated with soft tin or CNT composite plating.

[0036] In manufacturing the composite material 20, the battery is first designed (step S21). A film-forming method for the composite material and materials for the composite material are selected and prepared according to the design (step S22). The composite material includes an active material, a solvent, a binder, a conductive additive, etc., and the appropriate type, composition, etc. are selected depending on the application of the electrode 100.

[0037] Next, the composite materials are mixed to form a paste (step S23).

[0038] The current collector 10 having the plated nonwoven fabric 11 and the paste-like composite mixture are prepared as described above. Then, the composite mixture is applied to the current collector 10 (step S100). By applying the composite mixture, the voids in the current collector 10 are filled with the composite mixture, and layers that become the first surface layer 31 and the second surface layer 32 are formed on both surfaces of the current collector 10 in the direction of thickness Tc. The current collector 10 coated with the composite mixture is then dried and pressed to obtain an electrode 100 in which the nonwoven fabric 11 and the active material 21 are integrated.

[0039] When a current collector is used in a lithium-ion battery, the active material repeatedly expands due to lithium absorption and contracts due to lithium desorption during charging and discharging. This expansion and contraction of the active material causes breakdown of the active material (breakdown of bonds between particles such as silicon that constitute the active material). This causes a break in the conductive path formed by the active material, resulting in a decrease in battery capacity as the charge-discharge cycle increases. Silicon, which absorbs a large amount of lithium, is particularly susceptible to breakdown of the active material. In conventional technology, a layer of active material filled into the gaps between fibers of a nonwoven fabric is sandwiched between two thicker layers of active material alone, resulting in a three-layer structure. The active material-only layer accounts for more than two-thirds of the entire electrode made of the current collector. This increases the likelihood of active material breakdown.

[0040] In this embodiment, the substrate is replaced from the conventional metal foil with a resin nonwoven fabric 11. In addition to achieving low cost and light weight, most of the active material 21 is placed in the large irregularities or voids of the nonwoven fabric 11, and then dried and pressed to form an electrode in which the nonwoven fabric 11 and the active material 21 are integrated.

[0041] In the electrode 100 of this embodiment, a first surface layer 31 and a second surface layer 32, each thinner than the current collector 10, are formed on both sides of the current collector 10, which is a layer in which the active material 21 is filled into the gaps between the fibrous bodies 11a of the nonwoven fabric 11. That is, a three-layer structure is formed in which the layer in which the active material 21 is filled into the gaps between the fibrous bodies 11a of the nonwoven fabric 11 is sandwiched between the first surface layer 31 and the second surface layer 32, each thinner than the current collector 10. Here, the first surface layer 31 and the second surface layer 32 are layers primarily composed of the active material 21. Therefore, the first surface layer 31 and the second surface layer 32, which are layers primarily composed of the active material 21 (including layers consisting only of the active material 21), account for two-thirds or less of the entire electrode 100 made of the current collector 10. As a result, even when the active material 21 expands and contracts, the nonwoven fabric 11 on which the conductive layer 12 is formed follows the expansion and contraction of the active material 21, suppressing the collapse of the active material 21, which was a conventional problem, and maintaining electronic conduction. Therefore, according to the present embodiment, it is possible to obtain the electrode 100 that can reduce the possibility of breakdown of the active material 21. Furthermore, according to the present embodiment, it is possible to obtain the electrode 100 that can suppress a decrease in battery capacity when the number of charge / discharge cycles increases.

[0042] In addition to the above, a resistance reducing effect can be imparted by performing a conductive treatment or the above-mentioned CNT composite plating, or by further applying tin plating to the surface second layer 12b, which contributes to retaining the active material during expansion and contraction of the active material.

[0043] The present invention is also effective for metal anodes that undergo deposition and dissolution, such as metallic lithium. Conventional current collector foils, such as metal foils, have a limited reaction area, and needle-like metal deposits known as dendrites frequently cause short circuits in the battery.

[0044] In this embodiment, the substrate is replaced from a conventional metal foil with a resin nonwoven fabric 11, thereby increasing the reactive area of ​​the current collector foil. The increased reactive area of ​​the current collector foil allows metallic lithium to be deposited on the surface within the pores of the nonwoven fabric. As a result, short circuits due to dendrites can be significantly suppressed. This embodiment is effective regardless of whether or not a metallic lithium film is previously formed on the nonwoven fabric surface. Furthermore, to impart dendrite resistance, a thin film of silicon, carbon, inorganic oxide, solid electrolyte, or the like may be applied to the surface of the formed metallic lithium film.

[0045] Second Embodiment An electrode 100 according to a second embodiment will be described with reference to FIG.

[0046] In the second embodiment, the electrode 100 is formed by impregnating a conductor with an active material 21 and plating the surface of the fibrous body 11a constituting the nonwoven fabric 11 with a conductor layer 12 containing the active material 21. The voids in the nonwoven fabric 11 are filled with the conductor containing the active material 21. The first surface layer 31 and the second surface layer 32 are formed by the conductor containing the active material 21. The material of the conductor layer 12 other than the active material 21 is the same as in the first embodiment, and may contain tin or CNT. The relationship between the thickness of the entire electrode 100 and that of each part is the same as in the first embodiment.

[0047] According to the second embodiment, without producing a paste-like composite mixture, the voids in the nonwoven fabric 11 are filled by plating, and the first surface layer 31 and the second surface layer 32 are formed. According to the second embodiment, an electrode 100 having the same effect as that of the first embodiment can be obtained.

[0048] Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects of the present invention. These examples show one embodiment of the present invention, and the present invention is not limited to these examples in any way.

[0049] The electrode 100 used in the examples and the electrodes used in the comparative examples were produced by the following method, and batteries including the electrodes were evaluated.

[0050] (1) Manufacturing of the Current Collector First, a nonwoven fabric 11 was selected and prepared. By reducing the diameter of the fibrous body 11a of the nonwoven fabric 11, it was possible to make contact with a larger amount of the active material 21 and provide flexibility that could follow expansion and contraction. The thickness of the nonwoven fabric 11 was set to 60 μm because it was necessary to have a thickness that could encapsulate a large amount of the active material 21. The material of the nonwoven fabric 11 was selected to be PET or PBT, taking into consideration chemical resistance, heat resistance, cost, and plating adhesion. Based on the above conditions, samples were obtained from multiple nonwoven fabric manufacturers, and the nonwoven fabric 11 was selected based on the results of basic evaluation.

[0051] Next, the nonwoven fabric 11 was subjected to a conductive treatment and electroless plating. Since nonconductive resin nonwoven fabrics cannot be directly electroplated, some method was required to make them conductive. This method has long been established as a resin plating technique, and several manufacturers have marketed primers and other products. Here, the nonwoven fabric 11 was first set in a jig. The size of the nonwoven fabric 11 was A4 size. Next, a commercially available primer was applied to the nonwoven fabric 11 by immersion, followed by rinsing with pure water. The primer-coated nonwoven fabric 11 was then subjected to electroless copper plating (immersion at room temperature for 10 minutes), followed by rinsing with pure water. The copper-plated layer was then subjected to a rust prevention treatment (room temperature for 5 minutes), rinsing with pure water, and hot air drying (120°C for 2 minutes).

[0052] Next, CNT composite plating was performed on the surface of the first layer 12a of the conductor layer 12 to form the second layer 12b of the conductor layer 12. First, the copper-plated nonwoven fabric 11 was set in a jig. The nonwoven fabric 11 measured 150 mm x 200 mm. The nonwoven fabric 11 was then degreased (80°C for 1 minute) and washed with water. The nonwoven fabric 11 was then pickled (at room temperature for 30 seconds) and washed with water. The surface of the first layer 12a of the conductor layer 12 was then plated with CNT composite plating (at 30°C for 30 seconds) to form the second layer 12b, which was then washed with water. The second layer 12b of the conductor layer 12 was then subjected to rust prevention treatment (at room temperature for 1 minute), washed with water, and dried (at 120°C for 2 minutes).

[0053] Through the above steps, a current collector 10 including a nonwoven fabric 11 and a conductive layer 12 was manufactured. To evaluate the quality of the obtained current collector 10, the surface and cross section were observed using a metallurgical microscope and a scanning electron microscope, the thickness was measured using a micrometer, and the amount of copper co-deposited was measured using a fluorescent X-ray film thickness meter. Furthermore, to evaluate adhesion, mending tape was applied and peeled off to observe the peeling state of the plating film. Based on the results of the above evaluations, a current collector 10 suitable for battery evaluation was selected as a sample.

[0054] (2) Manufacturing of composite material 20 and manufacturing of electrode 100 Manufacturing method 1: Manufacturing of Si electrode by coating method Pure Si, which undergoes significant expansion and contraction during charging and discharging, was used as the active material 21. The materials for composite material 20 containing active material 21 were a mixture of 65% Si, 12% graphite, 12% conductive material, and 12% binder, and these materials were stirred and mixed to form a paste.

[0055] A paste of composite material 20 was placed on the current collector 10 and smoothed uniformly using a bar coater. During this process, it was confirmed that the active material particles penetrated into the voids of the nonwoven fabric 11. Subsequently, after drying, the mixture was pressed to a predetermined thickness using a roll press. This further forced the particles of active material 21 into the voids of the nonwoven fabric 11. The moisture in the electrode was then removed under vacuum at 120°C for 12 hours. After removing the moisture, the electrode was pre-doped with lithium to compensate for the lithium loss during charge and discharge that is unique to silicon. Specifically, an argon beam was applied to a Li target in the presence of an electrode containing Si under vacuum, depositing Li on the Si surface. The electrode 100 was manufactured through the above process.

[0056] Manufacturing method 2: Production of Si electrode by sputtering method The same pure Si was used as in Manufacturing method 1. Under vacuum, in the presence of current collector 10, an argon beam was applied to the Si target to deposit Si inside the voids of current collector foil 10. The subsequent steps of pressure pressing using a roll press and thereafter were the same as in Manufacturing method 1 to produce electrode 100.

[0057] Manufacturing method 3: Manufacturing of Li electrode by vapor deposition method Li was used as the active material 21. A Li target was heated in the presence of a current collector 10 under vacuum, and Li was deposited inside the voids of the current collector foil 10. Thereafter, the electrode was pressed to a predetermined thickness using a roll press in an air atmosphere with a dew point of -40°C or less. An electrode 100 was manufactured by the above steps.

[0058] Manufacturing method 4: Fabrication of sulfur electrode by coating method Sulfur, which expands and contracts significantly during charging and discharging, was used as the active material 21. The composite material 20 containing the active material 21 was a mixture of 60% sulfur, 20% graphite, 10% conductive material, and 10% binder, and these materials were mixed and stirred to form a paste.

[0059] A paste of composite material 20 was placed on the aluminum-plated current collector 10 and smoothed uniformly using a bar coater. During this process, it was confirmed that the active material particles had penetrated into the voids in the nonwoven fabric 11. Subsequently, after drying, the mixture was pressed to a predetermined thickness using a roll press. This further forced the particles of active material 21 into the voids in the nonwoven fabric 11. Thereafter, moisture was removed from within the electrode under vacuum at 100°C for 12 hours. Through the above process, an electrode 100 was manufactured.

[0060] Manufacturing Method 5: Production of Silver-Containing Carbon Anodeless Negative Electrode by Coating Method A paste (referred to as Coating Solution A) for a carbon coating layer for an anodeless negative electrode for an all-solid-state battery was prepared by the following method: A mixture of 30% 100-nanometer silver particles, 50% carbon black, and 20% binder was prepared, and these materials were stirred and mixed to form a paste.

[0061] Next, a sulfide solid electrolyte paste (referred to as coating solution B) was produced by the following method: 97% of an argyrodite-type sulfide solid electrolyte and 3% of a binder were mixed, and these materials were stirred and mixed in a butyl butyrate solvent to form a paste.

[0062] Coating liquid A was placed on the nickel-plated current collector 10 and spread evenly using a bar coater. In this process, it was confirmed that coating liquid A had penetrated into the voids in the nonwoven fabric 11. Subsequently, after drying, coating liquid B was similarly spread evenly using a bar coater, and it was confirmed that the solid electrolyte particles had penetrated into the voids in the nonwoven fabric 11. Subsequently, after drying, the electrode 100 was pressed at 500 MPa using a hydrostatic press. This further forced the particles of active material 21 into the voids in the nonwoven fabric 11. Through the above process, the electrode 100 was manufactured.

[0063] (3) Battery Production Using the above electrode 100, a single-sided laminate cell measuring 3 cm x 4 cm was produced. For the positive electrode, aluminum foil was used as the current collector 10, and lithium cobalt oxide (LCO) was used as the active material 21. For the negative electrode, the electrode 100 produced by the above Production Methods 1 to 3 was used. In addition, for comparison with the electrode 100, a negative electrode was also produced in which a composite slurry containing 65% Si was applied to a copper (Cu) foil current collector by Production Method 1, a negative electrode in which Si was vapor-deposited by Production Method 2, and a negative electrode in which Li was vapor-deposited by Production Method 3 were also produced.

[0064] (4) Evaluation of batteries using negative electrodes manufactured by Manufacturing Method 1 The coating thickness on the negative electrode was varied to examine the effect on battery characteristics. The coating thickness was determined by dividing the electrode thickness after composite coating by the thickness of the current collector substrate, using the aforementioned thickness index A = (Tc + T1 + T2) / Tc. The thickness index A of the examples was 1.2, 1.9, and 2.8, while the thickness index A of the comparative examples was 3.7, 4.5, 5.2, and 6.8 (Cu foil). Basic performance, including coating property evaluation, electrode penetration resistance test, peel strength test, and initial charge / discharge evaluation, was evaluated, confirming the suitability of the electrodes of the examples and comparative examples as battery materials. After confirmation, the electrodes of the examples and comparative examples were subjected to 50 cycles of continuous charge / discharge evaluation.

[0065] The results of the evaluation of continuous charge / discharge performance, performed under the conditions of 1C / 1C at 25°C, are shown in FIG. 5 along with the evaluation conditions. As shown in the figure, in the Example, the discharge capacity retention rate remained near 100% up to 50 cycles. In contrast, in the Comparative Example, the discharge capacity retention rate decreased with the number of cycles. Furthermore, the decrease in the discharge capacity retention rate in the Comparative Example became more pronounced as the thickness index A increased beyond 3.0. From the above results, in the Example where the thickness index A is ≦3.0, the breakdown of the active material 21 contained in the first surface layer 31 and the second surface layer 32 was suppressed. This is thought to have resulted in improved cycle characteristics compared to the Comparative Example.

[0066] (5) Evaluation of batteries using negative electrodes produced by Production Method 2: A nonwoven fabric was selected as an example of a sputtered negative electrode. Cu foil was selected as a comparative negative electrode. The battery characteristics of negative electrodes in which Si was attached to each current collector by sputtering were evaluated. The thickness index A of the nonwoven fabric and Cu foil was 1.1 for the example and 6.0 for the comparative example. As in the evaluation of Production Method 1 above (4), basic performance such as coatability evaluation, electrode penetration resistance test, peel strength test, and initial charge / discharge evaluation was evaluated, and it was confirmed that the electrodes of the example and comparative example were suitable as battery materials. After confirmation, the electrodes of the example and comparative example were subjected to a 50-cycle continuous charge / discharge evaluation.

[0067] The results of the evaluation of continuous charge-discharge performance, performed under the condition of 1C / 1C_25°C, are shown in Figure 6 along with the evaluation conditions. As shown in the figure, in the example, the discharge capacity retention rate remained near 100% up to 50 cycles.

[0068] (6) Evaluation of batteries using negative electrodes manufactured by Manufacturing Method 3 A nonwoven fabric was selected as an example of a negative electrode formed by vapor deposition. Cu foil was selected as a comparative example. The battery characteristics of negative electrodes in which Li was vapor-deposited on each current collector were evaluated. The thickness index A of the nonwoven fabric and Cu foil was 1.2 for the example and 6.3 for the comparative example, respectively. Basic performance, such as an electrode penetration resistance test, a peel strength test, and an initial charge / discharge evaluation, was evaluated, and it was confirmed that the electrodes of the example and comparative example were suitable as battery materials. After confirmation, the electrodes of the example and comparative example were subjected to a 50-cycle continuous charge / discharge evaluation.

[0069] The results of the evaluation of continuous charge / discharge performance, performed under the conditions of 1C / 1C at 25°C, are shown in Figure 7 along with the evaluation conditions. As shown in the figure, in the Example, the discharge capacity retention rate remained near 100% up to 50 cycles. In contrast, in the Comparative Example, a short circuit occurred early in the continuous charge / discharge cycle (around 10 cycles), resulting in a decrease in capacity. As in the Example, Li is encapsulated within the electrode. This is thought to be because Li deposition during charging proceeds within the nonwoven fabric, thereby suppressing lithium dendrite deposition on the separator surface.

[0070] (7) Evaluation of batteries using positive electrodes manufactured by Manufacturing Method 4: A nonwoven fabric was selected as an example of a sulfur positive electrode formed by the coating method. Al foil was selected as a comparative example. The battery characteristics of positive electrodes in which the sulfur positive electrode paste was coated on each current collector were evaluated. The thickness index A of the nonwoven fabric and Al foil was 1.5 for the example and 10.5 for the comparative example, respectively. Using Li metal as the negative electrode, basic performance such as initial charge / discharge evaluation was evaluated, and the electrodes of the example and comparative example were confirmed to be suitable as battery materials. After confirmation, the electrodes of the example and comparative example were subjected to 50 cycles of continuous charge / discharge evaluation.

[0071] The results of the evaluation of continuous charge-discharge performance, performed under conditions of 0.5 C / 0.5 C @ 25°C, are shown in Figure 8 along with the evaluation conditions. As shown in the figure, in the example, the discharge capacity retention rate was maintained at 80% or more after 50 cycles. In contrast, in the comparative example, the discharge capacity retention rate decreased with increasing cycle count. As in the Si negative electrode, the sulfur positive electrode also suppressed the breakdown of the active material 21 contained in the first surface layer 31 and the second surface layer 32, which is thought to have improved the continuous charge-discharge performance compared to the comparative example.

[0072] (8) As an evaluation example of a battery using a negative electrode manufactured by Manufacturing Method 5, a negative electrode was selected in which a carbon layer was coated on a nonwoven fabric and then a solid electrolyte was embedded. As a comparative example, a negative electrode was selected in which Coating Solution A of Manufacturing Method 5 was applied to SUS foil and dried, without forming a porous layer. A positive electrode was manufactured by coating lithium niobate-coated lithium cobalt oxide (LCO), an argyrodite-type solid electrolyte, a conductive material, and a binder onto an Al foil. A solid electrolyte layer was manufactured by mixing the argyrodite-type and a binder. The positive electrode, solid electrolyte layer, and negative electrode were stacked in this order and pressed at 500 MPa in an isostatic press to produce an all-solid-state battery. The thickness index A was 1.4 for both the Example and Comparative Example. The manufactured batteries were constrained at 4 MPa, and basic performance such as initial charge / discharge evaluation was evaluated. The electrodes of the Example and Comparative Example were confirmed to be suitable as battery materials. After confirmation, the electrodes of the example and comparative example were subjected to 50 cycles of continuous charge and discharge evaluation.

[0073] The results of the evaluation of continuous charge / discharge performance, performed under conditions of 0.5C / 0.5C at 60°C, are shown in Figure 9 along with the evaluation conditions. As shown in the figure, in the Example, the discharge capacity retention rate remained at 100% up to 50 cycles. In contrast, in the Comparative Example, the discharge capacity deteriorated from the early stage of continuous charge / discharge, and after about 20 cycles, the capacity became unstable, resulting in the occurrence of a short circuit. As with the negative electrode manufactured by Manufacturing Method 3, in the Example, it is assumed that Li deposition during charging proceeded within the nonwoven fabric, thereby suppressing the penetration of lithium dendrites into the solid electrolyte layer. Therefore, the effect of improving charge / discharge performance was confirmed even in all-solid-state batteries.

[0074] The present invention is not limited to the above-described embodiment, but various modifications and applications are possible.

[0075] In the embodiment, the thickness T1 of the first surface layer 31 and the thickness T2 of the second surface layer 32 are the same value, but they may be different thicknesses.

[0076] In the above embodiment, nonwoven fabric 11, which is a porous material, is used for current collector 10. In addition, a porous material having voids that can be filled with active material 21, such as a mesh, sponge, or cloth, may be used for current collector 10. Here, the mesh is, for example, a net-like member, and the sponge is, for example, a resin foam. In addition, the porous material may include one or more of nonwoven fabric, mesh, sponge, and cloth.

[0077] In the above embodiment, the coating method and the vapor deposition method are used to fill the active material 21 into the voids of the current collector 10. In addition to these, any method capable of filling the active material 21, such as electrolytic reduction or electroless plating, can be used.

[0078] In the first embodiment, the conductor layer 12 is formed as the first layer 12a and the second layer 12b, but it may also be formed as a single layer. In this case, tin plating or CNT composite plating may be applied for the above-mentioned purpose.

[0079] Although the above embodiments have exemplified Si and Li anodes for secondary batteries, the present invention can also be applied to cathodes using inorganic oxide active materials, sulfur, or organic active materials. The present invention can also be applied to next-generation batteries, including all-solid-state batteries, sodium-ion batteries, and zinc anode batteries.

[0080] This invention allows various embodiments and modifications without departing from the broad spirit and scope of this invention. Furthermore, the above-described embodiments are intended to explain this invention and do not limit the scope of this invention. That is, the scope of this invention is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of the invention equivalent thereto are considered to be within the scope of this invention.

[0081] In addition, this application claims priority based on Japanese Patent Application No. 2024-118422 filed on July 24, 2024, and the specification, claims, and drawings of Japanese Patent Application No. 2024-118422 are incorporated herein by reference.

[0082] The present invention can be applied to electrodes for secondary batteries.

[0083] 10 current collector, 11 nonwoven fabric, 11a fibrous body, 12 conductive layer, 12a first layer, 12b second layer, 20 composite, 21 active material, 31 first surface layer, 32 second surface layer, 100, 200 electrode, T thickness, Tc thickness, T1 thickness, T2 thickness.

Claims

1. An electrode comprising a current collector and an active material, wherein the current collector comprises a porous body having voids and a conductive layer provided on the surface of the porous body, the active material is filled into the voids of the porous body and is formed as a first surface layer and a second surface layer on both sides of the current collector in the thickness direction, and the thicknesses of the first surface layer and the second surface layer are each equal to or less than the thickness of the current collector filled with the active material.

2. The electrode according to claim 1, wherein the active material comprises a composite of one or more selected from the group consisting of graphite, hard carbon, soft carbon, silicon (Si), SiO, sulfur, LTO (lithium titanate), Li metal, Na metal, and Zn metal.

3. The electrode according to claim 1, wherein the current collector filled with the active material has a thickness close to that of the electrode.

4. The electrode according to claim 1, wherein (Tc + T1 + T2) / Tc≦3.0, where Tc is the thickness of the current collector filled with the active material, T1 is the thickness of the first surface layer, and T2 is the thickness of the second surface layer.

5. The electrode according to any one of claims 1 to 4, wherein the porous body comprises one or more of a nonwoven fabric, a mesh body, a sponge, and a cloth.

6. The electrode according to any one of claims 1 to 4, wherein the conductive layer contains one or more composites selected from the group consisting of carbon nanotubes, carbon black, activated carbon, graphite, graphene, cellulose nanofibers, and carbon fibers.

7. The electrode according to any one of claims 1 to 4, wherein the conductive layer contains one or more elements selected from the group consisting of copper, nickel, aluminum, gold, silver, chromium, iron, cobalt, titanium, zinc, tin, lithium, indium, palladium, carbon, and silicon.

8. The electrode according to any one of claims 1 to 4, wherein the conductive layer contains the active material and fills the voids.

9. A method for manufacturing an electrode comprising a current collector and a composite material containing an active material, comprising: a step of preparing a porous body having voids; a step of plating a conductive layer on the surface of the porous body to form the current collector comprising the porous body and the conductive layer; a step of preparing a paste-like composite material containing the active material; and a step of applying the composite material to the current collector to fill the voids in the porous body and forming a first surface layer and a second surface layer made of the composite material on both sides of the current collector in a thickness direction, wherein the thicknesses of the first surface layer and the second surface layer are each equal to or less than the thickness of the current collector filled with the composite material.

10. A method for manufacturing an electrode comprising a current collector and an active material, comprising: a step of preparing a porous body having voids; and a step of plating a conductive layer containing an active material onto the surface of the porous body and the voids to form the current collector comprising the porous body and the conductive layer, and a step of forming a first surface layer and a second surface layer made of the conductive layer containing the active material on both surfaces in the thickness direction of the current collector, wherein the thicknesses of the first surface layer and the second surface layer are each equal to or less than the thickness of the current collector filled with the conductive layer containing the active material.

11. A secondary battery comprising the electrode according to any one of claims 1 to 4.

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