Method for producing a negative electrode for a secondary battery with non-aqueous electrolytes

Abstract

Method for producing a negative electrode for a secondary battery with non-aqueous electrolytes, comprising the method: the mixing of negative electrode active material particles with ferroelectric particles to form first composite particles, wherein the ferroelectric particles are attached to the negative electrode active material particles (S101), wherein a mixing ratio of the ferroelectric particles is 5 wt% to 40 wt% with respect to a total mass of the negative electrode mixed layer; the mixing of initial composite particles with a binder to produce granular particles (S102); the application of pressure to an aggregate of granular particles to form a plate-shaped negative electrode mixed layer (S103); and the arrangement of the negative electrode mixed layer on a main surface of a negative electrode current collector foil (S104).

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to a method for producing a negative electrode for a secondary battery with non-aqueous electrolytes. 2. State of the art

[0002] In the Japanese patent application with publication number 2013-055049 (JP 2013-055049 A), a process for composite particles for an electrode is disclosed, comprising a process of: a step of producing a slurry by dispersing an electrode active material, a binder and an antioxidant in water; and a step of spray drying to granulate the slurry.

[0003] Composite particles are already known that are obtained by mixing an electrode active material and a binder (in JP 2013-055049 A, an antioxidant) with an additive. According to the prior art, it is known that the effect of an additive, as long as it is present, corresponds to the amount of the additive present. However, according to the present investigation of the present inventors, an additive has been found that exhibits its effect by arranging the additive in a specific configuration within the composite particles.

[0004] Furthermore, the published patent applications KR 10 2007 0 081 831 A, US 2011 / 0244322 A1 and US 2014 / 0023922 A1 disclose electrode active material from the prior art. SUMMARY OF THE INVENTION

[0005] Taking into account the circumstances described above, it is an object of the invention to create a negative electrode for a secondary battery with non-aqueous electrolytes that has improved high-load (high-current) properties.

[0006] A method for producing a negative electrode for a secondary battery with non-aqueous electrolytes comprises: a first step of mixing negative electrode active material particles with ferroelectric particles to form first composite particles, wherein the ferroelectric particles are attached to the negative electrode active material particles, wherein a mixing ratio of the ferroelectric particles is 5 wt% to 40 wt% with respect to a total mass of the negative electrode mixed layer; a second step of mixing first composite particles with a binder to produce granular particles; a third step of applying pressure to an aggregate of the granular particles to form a plate-shaped negative electrode mixed layer; and a fourth step of arranging the negative electrode mixed layer on a major surface of a negative electrode current collector foil.

[0007] In the manufacturing process according to [1], the ferroelectric particles, acting as an additive, exert a catalytic effect that reduces the reaction resistance between the lithium (Li) ions and the negative electrode active material particles. Consequently, an improvement in high-load properties can be expected. The reason for this is considered to be that the ferroelectric particles promote the desolvation of solvated Li ions and reduce the activation energy of an incorporation reaction of the Li ions into the negative electrode active material particles.

[0008] According to the investigation of the present inventors, the ferroelectric particles can exhibit the catalytic effect described above sufficiently when they are deposited directly onto the surfaces of the negative electrode active material particles. However, with a prior art manufacturing process, it is difficult to achieve the deposition state described above. That is, the binder is located between the negative electrode active material particles and the ferroelectric particles, since the negative electrode active material particles, the binder, and the ferroelectric particles are collectively mixed together, resulting in insufficient catalytic effect. It can be said that, apart from their catalytic effect, the ferroelectric particles are simply resistors.Therefore, the addition of ferroelectric particles in the state-of-the-art manufacturing process can lead to a deterioration of the high-load properties. Considering the circumstances described above, it is difficult to determine the catalytic effect of the ferroelectric particles using state-of-the-art methods.

[0009] In the manufacturing process according to [1], as described with reference to the first step, the ferroelectric particles are attached to the negative electrode active material particles by substantial mixing of the negative electrode active material particles and the ferroelectric particles together, without inserting the binder component between the negative electrode active material particles and the ferroelectric particles. Furthermore, the binder is mixed with the mixture (first composite particles) from the first step. Therefore, by mixing the negative electrode active material particles with the ferroelectric particles without adding a binder component, the proportion of ferroelectric particles that are directly attached to the negative electrode active material particles can be increased. In this case, "binder component" refers to an adhesive resin component.

[0010] However, if the composite particles are dispersed in a solvent (to form a “sludge” or “paste”), the ferroelectric particles detach from the surfaces of the negative electrode active material particles after mixing, and no catalytic effect is achieved. Therefore, in the manufacturing process according to [1], as described above with reference to steps two to four, the negative electrode mixed layer can be formed without producing the sludge. Consequently, the state in which the ferroelectric particles are directly attached to the surfaces of the negative electrode active material particles can be maintained until the negative electrode mixed layer is obtained.

[0011] The mixing ratio of the ferroelectric particles is 5 wt% to 40 wt% of the total mass of the negative electrode mixture. Adjusting the mixing ratio to 5 wt% or higher can be expected to improve the high-load properties. Adjusting the mixing ratio to 40 wt% or lower can prevent a reduction in the peel strength of the negative electrode mixture.

[0012] The ferroelectric particles are preferably barium titanate particles. A significant catalytic effect can be expected from barium titanate particles.

[0013] The first step is preferably carried out by mixing the components using a dry process. This suppresses the aggregation of the ferroelectric particles and increases the proportion of ferroelectric particles that are directly attached to the negative electrode active material particles.

[0014] The second step preferably comprises: a step of forming second composite particles, which consist of a plurality of first composite particles, by mixing the first composite particles and a first binder; and a step of forming granule particles, which consist of a plurality of second composite particles, by mixing the second composite particles and a second binder. Forming the granule particles in these two steps improves the dispersibility of the binder and enhances the peel strength of the negative electrode composite layer.

[0015] According to the invention, a negative electrode for a secondary battery with non-aqueous electrolytes with improved high-load properties can be created. BRIEF DESCRIPTION OF THE DRAWING

[0016] The features and advantages as well as the technical and industrial significance of the exemplary embodiments of the invention are described below with reference to the accompanying drawing, in which the same reference numerals indicate the same elements, and in which the following applies: Fig. Figure 1 is a flowchart showing the summary of a process for producing a negative electrode for a secondary battery with non-aqueous electrolytes according to an embodiment of the invention; Fig. Figure 2 is a schematic diagram showing an example configuration of the negative electrode for a secondary battery with non-aqueous electrolytes according to the embodiment of the invention; Fig. Figure 3 is a schematic diagram showing an example of a third step and a fourth step according to the embodiment of the invention; Fig. Figure 4 is a flowchart that summarizes a process for manufacturing a secondary battery with non-aqueous electrolytes according to the embodiment of the invention; Fig. Figure 5 is a schematic diagram showing an example configuration of a positive electrode according to the embodiment of the invention; Fig. Figure 6 is a schematic diagram showing an example configuration for an electrode group according to the embodiment of the invention; Fig. Figure 7 is a schematic diagram showing an example configuration of a secondary battery with non-aqueous electrolytes according to the embodiment of the invention; Fig. 8 is a schematic sectional view along line VIII-VIII in Fig. 7; Fig. Figure 9 is a graph showing an example of the relationship between the mixing ratio of ferroelectric particles and a low-temperature charging resistor; Fig. Figure 10 is a graph showing an example of the relationship between the mixing ratio of ferroelectric particles and the peel strength of a negative electrode mixed layer; and Fig. Figure 11 is a graph showing a relationship between the D50 of a binder and the low-temperature charging resistance. DETAILED DESCRIPTION OF THE EXECUTION FORMS

[0017] One embodiment of the invention (hereinafter referred to as "the embodiment") is described in detail below. However, the embodiment is not limited to the following description. In the following description, the "negative electrode for a secondary battery with non-aqueous electrolytes" is simply referred to as the "negative electrode." The "secondary battery with non-aqueous electrolytes" is also simply referred to as the "battery." Method for producing a negative electrode for a secondary battery with non-aqueous electrolytes

[0018] Fig. Figure 2 is a schematic diagram showing an example configuration of a negative electrode according to the embodiment. A negative electrode 20 is an elongated, ribbon-shaped plate element. The negative electrode 20 comprises: a negative electrode current collector foil 21; and a negative electrode mixed layer 22 arranged on both main surfaces of the negative electrode current collector foil 21. The negative electrode current collector foil 21 is, for example, a copper (Cu) foil. The negative electrode 20 has a foil exposure section Ep, in which the negative electrode current collector foil 21 is exposed, for connection to an external terminal.

[0019] Fig. Figure 1 is a flowchart that summarizes a process for manufacturing the negative electrode according to the embodiment. As shown in Fig. As shown in Figure 1, the process for manufacturing a negative electrode for a secondary battery with non-aqueous electrolytes comprises a first step (S101), a second step (S102), a third step (S103), and a fourth step (S104). The individual steps are described below. First step (p. 101)

[0020] In the first step, the negative electrode active material particles and the ferroelectric particles are mixed together to form initial composite particles in which the ferroelectric particles are attached to the negative electrode active material particles. Here, each of the initial composite particles refers to a composite particle in which one or more ferroelectric particles are attached to a negative electrode active material particle. As a specific process in the first step, for example, a powder of negative electrode active material particles and a powder of ferroelectric particles can be mixed together using a mixer.By substantially mixing the negative electrode active material particles and the ferroelectric particles without the addition of a binder component, the proportion of ferroelectric particles that are directly attached to the negative electrode active material particles can be increased.

[0021] The mixer is not limited in any particular way. For example, the mixer could be a planetary mixer, the HIGH-SPEED MIXER (product name, manufactured by EARTHTECHNICA CO., Ltd.), or the HIGH FLEX GRAL (product name, manufactured by EARTHTECHNICA CO., Ltd.). The mixing conditions can be modified appropriately according to the production quantity, powder properties, and the like. However, it is preferred that the first step be carried out by mixing the components using a dry process. That is, it is preferred that no solvent be used in the first step. If the components are mixed using a wet process, it is unlikely that the ferroelectric particles will adhere to the negative electrode active material particles due to the aggregation of the ferroelectric particles.Whether the ferroelectric particles attach to the negative electrode active material particles or not can be checked, for example, by observing the first composite particles with a scanning electron microscope (SEM). Ferroelectric particles

[0022] In this description, ferroelectric particles refer to particles made of a material with a dielectric constant of 100 or higher. A higher dielectric constant of the ferroelectric particles is preferred. The dielectric constant of the ferroelectric particles is preferably 500 or higher and more preferably 1000 or higher. The upper limit of the dielectric constant of the ferroelectric particles is not specifically restricted. For example, the upper limit of the dielectric constant of the ferroelectric particles can be 10000.

[0023] Considering chemical stability in the battery, it is preferred that the ferroelectric particles be formed from an inorganic compound. Examples of ferroelectric particles that can be used are barium titanate (BaTiO3) particles, lithium niobate (LiNbO3) particles, potassium niobate (KNbO3) particles, cadmium niobate (Cd2Nb2O7) particles, and titanium oxide (TiO2) particles. One type of these ferroelectric particles can be used alone, or two or more types can be used in combination. That is, the ferroelectric particles can be at least one selected from BaTiO3 particles, LiNbO3 particles, KNbO3 particles, Cd2Nb2O7 particles, and TiO2 particles. With regard to the dielectric constant, it is preferred that the ferroelectric particles be BaTiO3 particles.

[0024] The powder properties of the ferroelectric particles are not specifically restricted. However, to effectively bind the ferroelectric particles to the negative electrode active material particles, it is preferred that the D50 of the ferroelectric particles be set lower than that of the negative electrode active material particles. In this description, "D50" refers to a particle size corresponding to a cumulative value of 50% of a volume particle size distribution measured using a laser diffraction scattering method. The D50 of the ferroelectric particles can, for example, be set to approximately 0.01 times or 0.1 times that of the negative electrode active material particles. The D50 of the ferroelectric particles is, for example, 100 nm to 1.0 µm.

[0025] The mixing ratio of the ferroelectric particles is 5 wt% to 40 wt% of the desired total mass of the negative electrode mixture. By adjusting the mixing ratio to 5 wt% or higher, an improvement in the high-load properties can be expected. From this perspective, the lower limit of the mixing ratio is preferably 10 wt% and even more preferably 20 wt%. By adjusting the mixing ratio to 40 wt% or lower, a reduction in the peel strength of the negative electrode mixture can be suppressed. From this perspective, the upper limit of the mixing ratio is preferably 30 wt%. Negative electrode active material particles

[0026] The negative electrode active material particles are not restricted in any particular way. For example, the negative electrode active material particles can be particles formed from a carbon-based negative electrode active material, such as graphite or coke, or particles formed from an alloy of a negative electrode active material made of silicon (Si), tin (Sn), or the like. The D50 of the negative electrode active material particles can be, for example, approximately 1 µm to 30 µm, and preferably 5 µm to 20 µm. The mixing ratio of the negative electrode active material particles can be, for example, 56 wt% to 96 wt% with respect to the desired total mass of the negative electrode mixture. Second step (p. 102)

[0027] The second step is performed after the first. In the second step, the initial compound particles and a binder are mixed together to form granules. The granules contain the majority of the initial compound particles. The granules can be formed directly by granulating the initial compound particles or by subsequent multi-stage granulation. That is, the second step can include: a step of forming the second compound particles using the majority of the initial compound particles; and a step of forming the granules using the majority of the second compound particles.

[0028] In the second step, for example, the formation of second composite particles can be carried out by mixing the first composite particles with a first binder. The second composite particles contain the majority of the first composite particles. In the second composite particles, adjacent first composite particles are bonded together by the first binder. The first binder is applied to sections of the surfaces of the negative electrode active material particles to which no ferroelectric particles are attached, or it is applied to the ferroelectric particles that are attached to the negative electrode active material particles. As a specific operation in this step, for example, a powder of the first composite particles, a powder of the first binder, and a solvent are mixed together using a mixer. First binder

[0029] The first binder preferably exhibits a thickening effect when dispersed in the solvent. By mixing the components together while applying a shear stress of a certain magnitude using the thickening binder, the density of the second composite particles or granules can be increased. For example, carboxymethylcellulose (CMC), polyacrylic acid (PAA), polyacrylonitrile (PAN), or polyvinylidene fluoride (PVDF) can be used as the first binder. The first binder can be a powder or can be pre-dispersed or dissolved in the solvent. If a powder is used as the first binder, the D50 of the first binder can be adjusted to approximately 0.01 to 1.0 times the D50 of the negative electrode active material particles.Consequently, the area of ​​the surface sections of the ferroelectric particles covered with the first binder can be reduced, thereby further reducing the battery resistance. The D50 of the first binder, which is a powder, is, for example, 200 µm or less, preferably 0.1 µm to 10 µm, and more preferably 0.1 µm to 1 µm. The mixing ratio of the first binder can be, for example, 0.5 wt% to 2 wt% with respect to the desired total mass of the negative electrode mixed layer.

[0030] The solvent can be selected according to the type of first binder. Examples of solvents that can be used include water, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMA). The amount of solvent used during the formation of the second composite particles can be adjusted, for example, so that the solids content of the second composite particles is 90 wt% to 95 wt%. Within the range described above, a predetermined level of shear stress can be applied to the mixture while suppressing the aggregation of the ferroelectric particles.

[0031] After the second composite particles have been formed as described above, a step of forming granule particles can be carried out by mixing the second composite particles with a second binder. The granule particles obtained as described above contain the majority of the second composite particles. In the granule particles, adjacent second composite particles can be bonded together by the first binder or bonded together by the second binder, which is different from the first. As a specific operation in this step, a powder of the second composite particles and a solvent can be mixed together. Alternatively, a powder of the second composite particles, a powder of the second binder, and a solvent can be mixed together. Second binder L3-P3

[0032] A second binder with stronger bonding properties than the first is preferably used, as this improves the peel resistance of the negative electrode composite layer. Examples of suitable second binders include styrene-butadiene rubber (SBR), acrylic rubber (AR), urethane rubber (UR), or polytetrafluoroethylene (PTFE). The second binder can be a powder or pre-dispersed or dissolved in the solvent. The mixing ratio of the second binder can be, for example, 0.5 wt% to 2 wt% of the desired total mass of the negative electrode composite layer.

[0033] The solvents described above as examples can be used. The amount of solvent used during the formation of the granular particles can be adjusted, for example, so that the solids content of the granular particles is 70 wt% or more and less than 90 wt%. This allows for the formation of dense granular particles while suppressing the aggregation of ferroelectric particles.

[0034] After the formation of the granular particles, the particle distribution and the particle shape of the granular particles can be adjusted by classification, extrusion granulation or the like. Third Step (p. 103)

[0035] In the third step, pressure is applied to an aggregate of the granular particles to form a plate-shaped negative electrode mixture. This aggregate (powder) of granular particles is also referred to as the "granulated body". Fig. Figure 3 is a schematic diagram showing an example of step 3 and step 4 (described below). These steps can be illustrated using a diagram in Fig. The transfer forming device 90 shown in step 3 is used. Steps 3 and 4, along with the operation of the transfer forming device 90, are described below.

[0036] The aggregate of granule particles obtained in the third step is fed to a feeding device 95 of the transfer forming device 90. An aggregate 22a of granule particles is guided from the feeding device 95 onto an A-roller 91 or a B-roller 92. Fig. Figure 3 shows the directions of rotation of the respective roller elements. The aggregate 22a of granule particles is transported along the direction of rotation of roller A 91 or roller B 92 and reaches a gap between roller A 91 and roller B 92. In this gap, pressure is exerted on the aggregate 22a of granule particles by roller A 91 and roller B 92. Consequently, the aggregate 22a of granule particles is formed into the plate-shaped negative electrode mixture 22. The coating mass (area mass) and thickness of the negative electrode mixture 22 are adjusted by the gap between roller A 91 and roller B 92. The coating mass and thickness of the negative electrode mixture can be adjusted as appropriate according to the specifications of a battery. The thickness of the negative electrode mixed layer can, for example, be 50 µm to 150 µm.In this example, the aggregate of granule particles is formed into a plate-like shape using the two rollers. However, a forming process is not limited to this example, provided the aggregate of granule particles can be formed into a plate-like shape. The plate-like negative electrode mixture layer can, for example, be formed using a flat press. Fourth step (p. 104)

[0037] In the fourth step, the negative electrode mixed layer is arranged on a main surface of the negative electrode current collector foil. As in Fig. As shown in Figure 3, the negative electrode mixed layer 22 obtained in the third step is transported along the direction of rotation of the B-roller 92. The negative electrode current collector foil 21 is transported along the direction of rotation of the C-roller 93. In a gap between the B-roller 92 and the C-roller 93, pressure is exerted by the B-roller 92 and the C-roller 93 on the negative electrode mixed layer 22 and the negative electrode current collector foil 21. Consequently, the negative electrode mixed layer 22 is transferred to the main surface of the negative electrode current collector foil 21 and pressed against it. In this way, the negative electrode mixed layer 22 is positioned on the main surface of the negative electrode current collector foil 21. The solvent remaining in the negative electrode mixed layer can then be evaporated using a hot air drying oven.The negative electrode mixed layer 22 can also be arranged on the other main surface opposite the main surface on which the negative electrode mixed layer 22 is formed, with respect to the main surfaces of the negative electrode current collector foil 21. Subsequently, the negative electrode 20 is, as in . Fig. 2 is shown, completed by processing the negative electrode mixed layer and the negative electrode current collector foil to obtain predetermined dimensions.

[0038] At the negative electrode 20, a state is maintained in which the ferroelectric particles are deposited onto the surfaces of the negative electrode active material particles. Therefore, the ferroelectric particles exhibit sufficient catalytic activity during an intercalation reaction of Li ions onto the negative electrode active material particles. Consequently, an improvement in high-load properties can be expected. A significant increase in effectiveness can be anticipated, particularly in a low-temperature environment where the reaction resistance is high. Method for manufacturing a secondary battery with non-aqueous electrolytes

[0039] According to the embodiment, a method for manufacturing a secondary battery with non-aqueous electrolytes is created. Fig. Figure 4 is a flowchart summarizing the manufacturing process. The process for manufacturing a secondary battery with non-aqueous electrolytes comprises a negative electrode manufacturing step (S100), a positive electrode manufacturing step (S200), an electrode assembly manufacturing step (S300), an outer body receiving step (S400), and a liquid injection step (S500). Of these steps, the negative electrode manufacturing step (S100) has been described above in "Process for Manufacturing a Negative Electrode for a Secondary Battery with Non-Aqueous Electrolytes" and is therefore not repeated. The other steps, with the exception of the negative electrode manufacturing step, are described below. Positive electrode manufacturing step (S200)

[0040] Fig. Figure 5 is a schematic diagram showing an example configuration of a positive electrode according to the embodiment. In the positive electrode manufacturing step, for example, a Fig. A positive electrode 10 is produced as shown in Figure 5. The positive electrode 10 comprises: a positive electrode current collector foil 11; and a positive electrode mixed layer 12 arranged on both main surfaces of the positive electrode current collector foil 11. The positive electrode current collector foil 11 is, for example, an aluminum (Al) foil. The positive electrode 10 has a foil exposure section Ep, in which the positive electrode current collector foil 11 is exposed, for connection to an external terminal. The thickness of the positive electrode mixed layer can be, for example, approximately 50 µm to 150 µm.

[0041] The positive electrode 10 can be produced using a method known in the art. For example, the positive electrode 10 can be produced as follows: A positive electrode mixture slurry containing a positive electrode active material is prepared. The positive electrode mixture slurry is applied to both main surfaces of the positive electrode current collector foil 11. Drying of the slurry coating film forms the positive electrode mixture layer 12. The positive electrode mixture layer 12 is pressed to adjust its thickness. The positive electrode current collector foil 11 and the positive electrode mixture layer 12 are processed to have predetermined dimensions.

[0042] Positive electrode mixture sludge can be produced by kneading a positive electrode active material, a conductive material, and a binder together in a solvent. Examples of positive electrode active materials include LiCoO2, LiNiO2, or a compound with the formula LiNi. a Co b O2 represented compound (where a+b=1, 0 <a<1, und 0<b<1), LiMnO2, LiMn2O4, eine mit der Formel LiNi a Co b Mn c O2 represented compound (where a+b+c=1, 0 <a<1, 0<b<1, und 0<c<1), oder LiFePO4 verwendet werden. Als die mit der Formel LiNi a Co b Mn c The compound represented by O2 can, for example, be LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 can be used.

[0043] The conductive material can be, for example, carbon black (AB) or graphite. The mixing ratio of the conductive material can be, for example, approximately 1 wt% to 10 wt% of the total mass of the positive electrode composite layer. The binder can be, for example, PVDF or PTFE. The mixing ratio of the binder can also be, for example, approximately 1 wt% to 10 wt% of the total mass of the positive electrode composite layer. The solvent can be, for example, NMP. Electrode group manufacturing step (S300)

[0044] Fig. Figure 6 is a schematic diagram showing an example configuration of an electrode assembly according to the embodiment. In the electrode assembly manufacturing step, a Fig. Electrode group 80, as shown in Figure 6, is manufactured. For example, the positive electrode 10 and the negative electrode 20 are laminated with separators 40 arranged between them to obtain a laminate, and the laminate is wound. Consequently, an elliptically wound electrode group is obtained. In this case, the foil exposure sections Ep of the positive electrode 10 and the negative electrode 20 are arranged at end sections in a direction extending along a winding axis Aw. The wound electrode group is pressed such that its outer shape is formed into a flat shape. In this way, the electrode group 80 is obtained.

[0045] The separator can be, for example, a microporous membrane made of a polyolefin material. Specifically, the separator can be a microporous membrane made of polyethylene (PE), polypropylene (PP), or the like. The separator can have a single-layer or multi-layer structure. The thickness of the separator can be, for example, 5 µm to 40 µm. The pore size and porosity of the separator can be adjusted to achieve a desired air permeability. External body imaging step (S400)

[0046] Fig. Figure 7 is a schematic diagram showing an example configuration of a battery according to the embodiment. Fig. 8 is a schematic sectional view along line VIII-VIII in Fig. 7. During the external body imaging step, the in Fig. The electrode assembly 80 shown in Figure 8 is enclosed in the outer body 50. The outer body 50 comprises a square housing 52 and a cover 54. The outer body 50 is made, for example, of an aluminum alloy. A positive electrode terminal 70 and a negative electrode terminal 72 are provided on the cover 54. The outer body 50 may, for example, contain a safety valve, a current-interrupting device, and a liquid injection port (all of which are not shown in the drawing). In a state where the positive electrode terminal 70 and a negative electrode terminal 72 are connected, the electrode assembly 80 is enclosed in the square housing 52. The square housing 52 and the cover 54 are joined together, for example, by laser welding. Liquid injection step (S500)

[0047] In the liquid injection step, an electrolyte solution is injected into the outer body. The electrolyte solution can be injected, for example, through a liquid injection port provided on the outer body.

[0048] The electrolyte solution is an electrolyte solution in which a carrier electrolyte is dissolved in a non-aqueous solvent. Examples of non-aqueous solvents that can be used include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and γ-butyrolactone (γBL); as well as chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). One of these non-aqueous solvents can be used alone, or two or more types can be used in combination. When a mixture of a cyclic carbonate and a chain carbonate is used, the volume ratio of the cyclic carbonate to the chain carbonate is preferably about 1:9 to 5:5.

[0049] Examples of carrier electrolytes include lithium salts such as LiPF6, LiBF4, LiClO4, LiAsF6, Li(CF3SO2)2N, and LiCF3SO3. One of these carrier electrolytes can be used alone, or two or more can be used in combination. The concentration of the carrier electrolytes can range from approximately 0.5 mol / L to 2.0 mol / L.

[0050] By sealing the liquid injection port with a predetermined agent after the injection of the electrolyte solution, the outer body 50 is sealed. In this way, the secondary battery can be manufactured with non-aqueous electrolytes 100.

[0051] The embodiment described above uses a square battery as an example. However, the embodiment is not limited to square batteries. It can, for example, be applied to a cylindrical battery or a laminate battery.

[0052] The embodiment is described below using the examples. However, the embodiment is not limited to the following examples. [Experiment 1: Investigation of a method for adding ferroelectric particles]

[0053] Negative electrodes and batteries were manufactured under various conditions, as described below. Here, manufacturing condition A corresponds to the examples, and manufacturing conditions B and C correspond to the comparison examples. Manufacturing condition A

[0054] Under manufacturing condition A, five negative electrodes were produced, while the mixing ratio of the ferroelectric particles was changed to 5 wt%, 10 wt%, 20 wt%, and 40 wt% with respect to the total mass of the negative electrode mixed layer.

[0055] First, the following material was prepared: Negative electrode active material particles: Graphite Ferroelectric particles: BaTiO3 particles First binder: CMC (D50: 200µm) Second binder: SBR Solvent: Water Negative electrode current collector foil: Cu foil 1. First step (p. 101)

[0056] A planetary mixer was prepared. The negative electrode active material particles and the ferroelectric particles were added to a mixing vessel of the planetary mixer and dried using a drying process. Consequently, the first composite particles were formed, in which the ferroelectric particles were bonded to the negative electrode active material particles. The mixing ratio of the ferroelectric particles was 5 wt% of the desired total mass of the negative electrode composite layer. 2. Second step (p. 102)

[0057] The first binder and solvent were added to the mixing vessel, and the components were further mixed. This caused the first binder to bind to the first composite particles, forming a second composite particle. The amount of solvent was adjusted so that the solids content of the second composite particle was 92% by weight.

[0058] The second binder and the solvent were added to the mixing vessel, and the components were further mixed. This resulted in the formation of granular particles using the majority of the second composite particles. The amount of solvent was adjusted so that the solids content of the granular particles was 75% by weight. 3. Third step (p. 103)

[0059] Using the in Fig. In the transfer forming device 90 shown in Figure 3, an aggregate of the granule particles obtained as described above was formed into a plate-shaped negative electrode mixed layer. 4. Fourth step (p. 104)

[0060] Using the in Fig. In the transfer forming device 90 shown in Figure 3, the negative electrode mixture obtained as described above was arranged on a main surface of the negative electrode current collector foil. Consequently, a negative electrode was produced in which the mixing ratio of the ferroelectric particles was 5 wt% with respect to the total mass of the negative electrode mixture. Furthermore, negative electrodes were produced using the same method as described above, except that the mixing ratio was changed to 10 wt%, 20 wt%, 30 wt%, and 40 wt%. Manufacturing condition B

[0061] Manufacturing condition B corresponds to the comparative examples in which a negative electrode mixed layer was formed from a slurry without the formation of granular particles. That is, under manufacturing condition B, steps one through four were not carried out according to the embodiment. In particular, a negative electrode was manufactured as follows.

[0062] The negative electrode active material particles, the ferroelectric particles, the first binder, and the solvent were added together to the mixing vessel of the planetary mixer and kneaded. Subsequently, the second binder and the solvent were also added and kneaded together. Consequently, a negative electrode mixture slurry was formed. The solids content of the negative electrode mixture slurry was adjusted to 50 wt%. Using a nozzle coating device, the negative electrode mixture slurry was applied to a main surface of the negative electrode current collector foil and dried. Consequently, a negative electrode mixture layer was formed. In this way, five negative electrodes were produced, while the mixing ratio of the ferroelectric particles was varied to 5 wt%, 10 wt%, 20 wt%, and 40 wt% with respect to the total mass of the negative electrode mixture layer. Manufacturing condition C

[0063] Manufacturing condition C corresponds to the comparative examples in which a negative electrode mixture was formed from a slurry without the formation of granular particles. Furthermore, manufacturing condition C corresponds to the comparative examples in which no ferroelectric particles were added to the negative electrode mixture. In particular, negative electrodes in which the ferroelectric particle mixture ratio was 0 wt% with respect to the total mass of the negative electrode mixture were produced using the same process as in manufacturing condition B, except that no ferroelectric particles were added. Production of a secondary battery with non-aqueous electrolytes

[0064] Using the various negative electrodes produced as described above, batteries were manufactured as described above (see e.g. Fig. 4) The structure of the batteries was modified appropriately according to the mixing ratio of the ferroelectric particles. Evaluation 1. Measuring the low-temperature charging resistance

[0065] The state of charge (SOC) of each battery was set to 60%. The battery was placed in a thermostatically controlled chamber set to -15°C. A voltage increase was measured by performing a pulse charge in the same environment as described above. The low-temperature charging resistance was calculated based on the ratio between the current value and the voltage increase during the pulse charge. The results are presented in Fig. Figure 9 shows that the lower the low-temperature charging resistance, the higher the high-load performance.

[0066] Fig. Figure 9 is a graph showing an example of the relationship between the mixing ratio of ferroelectric particles and the low-temperature charging resistance. Fig. Figure 9 shows the horizontal axis representing the mixing ratio of the ferroelectric particles, and the vertical axis representing the low-temperature charging resistance. As the Fig. As can be seen from Figure 9, under manufacturing condition A, the low-temperature charging resistance was lower the higher the mixing ratio of the ferroelectric particles was. Under manufacturing condition A, the proportion of ferroelectric particles directly attached to the surfaces of the negative electrode active material particles was high. Therefore, it is assumed that the catalytic effect of the ferroelectric particles has been demonstrated.

[0067] On the other hand, under manufacturing condition B, the low-temperature charging resistance was higher the higher the mixing ratio of the ferroelectric particles, as shown in the comparative examples. Under manufacturing condition B, the negative electrode active material particles, the ferroelectric particles, and the binder were completely mixed together during the production of the negative electrode. Therefore, it is assumed that the catalytic effect of the ferroelectric particles was reduced, since the binder was positioned between the negative electrode active material particles and the ferroelectric particles.Furthermore, it is assumed that adhesion of the ferroelectric particles to the negative electrode active material particles was unlikely due to the aggregation of the ferroelectric particles, or that detachment of the ferroelectric particles from the surfaces of the negative electrode active material particles was likely, since the negative electrode active material particles, the ferroelectric particles, and the binder were dissolved in the solvent to form the sludge. Consequently, it is assumed that the ferroelectric particles acted as simple resistors, causing an increase in resistance.

[0068] Again Fig. As can be seen from Figure 9, the effect of reducing the low-temperature charging resistance under manufacturing condition A was confirmed when the mixing ratio of the ferroelectric particles was 5 wt% to 40 wt% with respect to the total mass of the negative electrode mixed layer. The higher the mixing ratio of the ferroelectric particles, the lower the low-temperature charging resistance. When the mixing ratio of the ferroelectric particles is 20 wt% or higher, the low-temperature charging resistance is extremely low. Therefore, it can be said that the mixing ratio of the ferroelectric particles is preferably 5 wt% or higher, more preferably 10 wt% or higher, and even more preferably 20 wt% or higher. 2. Measuring the peel strength of the negative electrode mixed layer

[0069] The peel strength of the negative electrode mixture layer was measured for each of the negative electrodes produced under manufacturing condition A. The peel strength was measured using a 90° peel test based on the Japanese industrial standard "JIS Z 0237: Testing methods of pressure-sensitive adhesive tapes and sheets". The results are presented in Fig. Figure 10 shows that with increasing peel strength, it is less likely that the negative electrode mixed layer will detach from the negative electrode current collector foil, which is preferable.

[0070] Fig. Figure 10 is a graph showing an example of the relationship between the mixing ratio of the ferroelectric particles and the peel strength of the negative electrode mixed layer. Fig. Figure 10 shows the horizontal axis representing the mixing ratio of the ferroelectric particles, and the vertical axis representing the peel strength of the negative electrode mixed layer. As the Fig. As can be seen from section 10, the peel strength of the negative electrode mixed layer gradually decreases with increasing mixing ratio of the ferroelectric particles, and if the mixing ratio of the ferroelectric particles exceeds 30 wt%, the peel strength of the negative electrode mixed layer decreases considerably. Accordingly, considering the peel strength, it can be said that the mixing ratio of the ferroelectric particles is preferably 30 wt% or lower. In particular, in a battery with a wound electrode assembly, where the effect of the peel strength is high, it is preferred that the mixing ratio be set to 30 wt% or less. Experiment 2: Investigation of the D50 of the first binder

[0071] In Experiment 2, the effect of D50 of the first binder was investigated in a state where the mixing ratio of the ferroelectric particles was set to 20 wt%. Here, production conditions A1 and A2 correspond to the examples, and production condition D corresponds to the comparison examples. Manufacturing condition A1

[0072] Under the same conditions as in manufacturing condition A, a negative electrode was produced using CMC with a D50 of 200 µm as the first binder. Manufacturing condition A2

[0073] A negative electrode was produced using the same procedure as in manufacturing condition A1, except that CMC with a D50 of 1 µm was used as the first binder. Manufacturing condition D

[0074] Manufacturing condition D corresponds to the comparative examples where the first step according to the embodiment was not carried out. In particular, a negative electrode was manufactured as follows.

[0075] The negative electrode active material particles, the ferroelectric particles, and the first binder were added to the mixing vessel of the planetary mixer, and the components were mixed together using a drying process. CMC with a D50 of 200 µm was used as the first binder. The solvent was added, and the components were further mixed. This resulted in the formation of the composite particles. Subsequently, the second binder and the solvent were added to the mixing vessel, and the components were further mixed. This resulted in the formation of the granular particles using the majority of the composite particles. Under the same conditions as in manufacturing condition A, an aggregate of the granular particles was formed into a plate-like negative electrode composite layer.The negative electrode mixed layer was arranged on a main surface of the negative electrode current collector foil. Evaluation

[0076] Using the same procedure as in Experiment 1, a battery was obtained that uses the negative electrode obtained as described above, and its low-temperature charging resistance was measured. The results are presented in Fig. 11 shown. Fig. Figure 11 is a graph showing the relationship between the D50 of the first binder and the low-temperature charging resistance. It was calculated using Fig. 11. It was found that the low-temperature charging resistance can be reduced by decreasing the particle size of the CMC as the first binder. It is assumed that it is unlikely that the ferroelectric particles will be coated by reducing the particle size of the CMC to a smaller size than that of the negative electrode active material particles or the first composite particles with the CMC.

[0077] The D50 of the CMC under manufacturing condition D and the D50 of the CMC under manufacturing condition A1 were the same. Furthermore, the first step of the embodiment under manufacturing condition D was not carried out; however, a negative electrode mixed layer was formed without sludge formation. However, as in Fig.As shown in Figure 11, the low-temperature charging resistance is higher than that under manufacturing condition A1 according to the examples. Based on the above results, it can be assumed that if the negative electrode active material particles and the ferroelectric particles are mixed together using a binder, the binder is likely to be positioned between the negative electrode active material particles and the ferroelectric particles, thereby reducing the catalytic activity of the ferroelectric particles. Therefore, it is necessary to mix the negative electrode active material particles and the ferroelectric particles together, as described in the embodiment, without the intervening binder component, in order to achieve sufficient catalytic activity of the ferroelectric particles.

[0078] The embodiment and examples disclosed herein are in every respect merely exemplary and are not limited in any particular way. The scope of protection of the invention is not defined by the foregoing description, but by the claims.

Claims

[1] Method for producing a negative electrode for a secondary battery with non-aqueous electrolytes, comprising the method: the mixing of negative electrode active material particles with ferroelectric particles to form first composite particles, wherein the ferroelectric particles are attached to the negative electrode active material particles (S101), wherein a mixing ratio of the ferroelectric particles is 5 wt% to 40 wt% with respect to a total mass of the negative electrode mixed layer; the mixing of initial composite particles with a binder to produce granular particles (S102); the application of pressure to an aggregate of granular particles to form a plate-shaped negative electrode mixed layer (S103); and the arrangement of the negative electrode mixed layer on a main surface of a negative electrode current collector foil (S104). [2] Method for producing a negative electrode for a secondary battery with non-aqueous electrolytes according to claim 1, wherein the ferroelectric particles are barium titanate particles. [3] Method for producing a negative electrode for a secondary battery with non-aqueous electrolytes according to claim 1 or claim 2, wherein the negative electrode active material particles and the ferroelectric particles are mixed together by a dry process to form first composite particles in which the ferroelectric particles are attached to the negative electrode active material particles (S101). [4] Method for producing a negative electrode for a secondary battery with non-aqueous electrolytes according to any one of claims 1 to 3, wherein The binder comprises a first binder and a second binder which differs from the first binder. the mixing of the first composite particles with a binder to form granular particles includes (S102): Formation of second composite particles, comprising a plurality of first composite particles, by mixing the first composite particles and the first binder; and Formation of the granular particles, which comprise a plurality of second composite particles, by mixing the second composite particles and the second binder.

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