Negative electrode active material layer, battery, and method for manufacturing a negative electrode active material layer

Abstract

To provide an anode active material layer capable of improving the discharge capacity and resistance of a battery, and a method for manufacturing the anode active material layer.SOLUTION: An anode active material layer for a battery includes a carbon-based anode active material and a binder that covers the carbon-based anode active material. The content of the binder is 4.0 to 9.0 mass% with respect to the total amount of the anode active material layer, and the coverage of the anode active material by the binder is 8.0 to 25%. A method for manufacturing an anode active material layer includes mixing a carbon-based anode active material and a binder of 4.0 to 9.0 mass% with respect to the total amount of the anode active material layer to prepare a negative electrode mixture, and coating the anode mixture onto a substrate by a dry process to form the anode active material layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a negative electrode active material layer, a battery, and a method for manufacturing a negative electrode active material layer. [Background technology]

[0002] Lithium-ion secondary batteries typically have an electrode active material layer containing electrode active material on a current collector. The performance of a battery using this electrode active material layer can be stable if it is formed uniformly. Generally, this electrode active material layer is manufactured by supplying a slurry-like electrode material, in which the electrode active material is dispersed in a liquid medium, to a current collector, drying it, and then compacting it. On the other hand, there are also known manufacturing methods for electrode active material layers (dry methods) that eliminate the use of a liquid medium and the drying process, resulting in energy savings and lower costs.

[0003] For example, Patent Document 1 discloses a method for manufacturing an electrode, which includes (a) preparing granules containing an active material powder and a binder, (b) supplying the granules to the surface of a roll, (c) charging the granules, (d) transporting the granules from a first region to a second region by the rotation of the roll, (e) causing the granules to fly from the second region to the third region by forming a first electric field between the second region and the third region, and (f) causing the granules to fly from the third region to the substrate by forming a second electric field between the third region and the substrate, wherein in the vertical direction, the second region is located lower than the first region, in a direction intersecting the vertical direction, the third region is located away from the second region, and in the vertical direction, the substrate is located lower than the third region, and an active material layer is formed when the granules adhere to the substrate. According to the electrode manufacturing method of Patent Document 1, it is possible to reduce uneven coating. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-016208 [Overview of the project] [Problems that the invention aims to solve]

[0005] The dry process eliminates the drying step, allowing for energy-efficient and low-cost production of electrode active material layers. However, batteries containing electrode active material layers produced by the dry process still have room for improvement in terms of discharge capacity and resistance.

[0006] Therefore, the object of this disclosure is to provide a negative electrode active material layer that can improve the discharge capacity and resistance of a battery. [Means for solving the problem]

[0007] This disclosure aims to achieve the above objectives by the following means:

[0008] <Aspect 1> A negative electrode active material layer for a battery, The above-mentioned negative electrode active material layer includes a carbon-based negative electrode active material and a binder coating the carbon-based negative electrode active material. The binder content is 4.0 to 9.0% by mass relative to the total amount of the negative electrode active material layer, and The coverage rate of the negative electrode active material by the above binder is 8.0 to 25%. A negative electrode active material layer for batteries. <Aspect 2> The negative electrode active material layer according to Aspect 1, wherein the content of the binder is 6.0 to 9.0% by mass of the total amount of the negative electrode active material layer. <Aspect 3> The negative electrode active material layer according to aspect 1, wherein the content of the binder is 7.0 to 8.0% by mass relative to the total amount of the negative electrode active material layer. <Aspect 4> The negative electrode active material layer according to any one of aspects 1 to 3, wherein the binder is polyvinylidene fluoride. <Aspect 5> A battery having the negative electrode active material layer described in any one of aspects 1 to 4. <Aspect 6> A method for manufacturing a negative electrode active material layer according to any one of aspects 1 to 4, Adjusting a negative electrode composite material by mixing a carbon-based negative electrode active material and a binder of 4.0 to 9.0% by mass with respect to the total amount of the negative electrode active material layer, and Forming the negative electrode active material layer by applying the negative electrode composite material onto a substrate by a dry process, A method for manufacturing a negative electrode active material layer, comprising: <Aspect 7> The manufacturing method according to Aspect 6, wherein the dry process is electrostatic coating. <Aspect 8> The average particle size of the carbon-based negative electrode active material is 5 to 30 μm, and The average particle size of the binder is 100 nm to 500 nm. The manufacturing method according to Aspect 6 or 7.

Advantages of the Invention

[0009] According to the negative electrode active material layer of the present disclosure, the discharge capacity and resistance of the battery can be improved.

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present disclosure.

[0011] Regarding the present disclosure, "composite material" means a composition that can form a negative electrode (positive electrode) active material layer as it is or by further containing other components. Also, regarding the present disclosure, "composite material slurry" means a slurry that contains a dispersion medium in addition to the "composite material" and can form a negative electrode (positive electrode) active material layer by coating and drying it.

[0012] 《Negative Electrode Active Material Layer》 The negative electrode active material layer for a battery of the present disclosure is The negative electrode active material layer includes a carbon-based negative electrode active material and a binder that coats the carbon-based negative electrode active material, The content of the binder is 4.0 to 9.0% by mass with respect to the total amount of the negative electrode active material layer, and The coverage rate of the negative electrode active material by the binder is 8.0 to 25%.

[0013] The negative electrode active material layer of this disclosure can improve the discharge capacity and resistance of the battery.

[0014] The negative electrode active material layer for batteries of this disclosure comprises a carbon-based negative electrode active material and a binder coating the carbon-based negative electrode active material. The Disclosers have conducted studies and found that when the amount of binder and the coating rate of the negative electrode active material by the binder are within a specific range, the discharge capacity and resistance of the battery can be improved.

[0015] Although the details of the mechanism that improved the battery's discharge capacity and resistance are not clear, it is presumed to be due to the following mechanism. Generally, it is known that a film (Solid Electrolyte Interphase (hereinafter referred to as SEI)) is formed on the surface of the negative electrode active material during battery charging and discharging. By setting the binder amount of the negative electrode active material layer to 4% or more, the surface of the negative electrode active material is partially covered with the binder, suppressing SEI formation and thereby suppressing the increase in irreversible capacity. On the other hand, by setting the binder amount to 9% or less and the binder coverage rate of the negative electrode active material to 8.0-25%, it is thought that excessive coating of the surface of the negative electrode active material with the binder is prevented, thereby suppressing the increase in contact resistance between the negative electrode active materials.

[0016] <Composition of the negative electrode active material layer> The negative electrode active material layer includes a carbon-based negative electrode active material and a binder coating the carbon-based negative electrode active material.

[0017] The negative electrode active material layer may optionally contain conductive additives, solid electrolytes, etc.

[0018] (Carbon-based negative electrode active material) The carbon-based negative electrode active material is not particularly limited and may be any carbon material capable of intercalating and releasing metal ions such as lithium ions. The carbon material is not particularly limited and examples include hard carbon, soft carbon, or graphite.

[0019] The average particle size of the carbon-based anode active material is not particularly limited, but 5 to 30 μm is preferred from the viewpoint of obtaining a anode active material layer with high discharge capacity and low resistance. The average particle size of the carbon-based anode active material may also be 5 μm or more, 7 μm or more, 9 μm or more, 11 μm or more, 13 μm or more, or 15 μm or more, and may be 30 μm or less, 28 μm or less, 26 μm or less, 24 μm or less, 22 μm or less, or 20 μm or less. Here, the average particle size can be determined by observation using a scanning electron microscope (SEM).

[0020] (Binder) The binder is not particularly limited. For example, the binder may be, but is not limited to, materials such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), polytetrafluoroethylene (PTFE), or styrene-butadiene rubber (SBR), or a combination thereof. Although the binder is not particularly limited, polyvinylidene fluoride and polytetrafluoroethylene are preferred in terms of oxidation-reduction resistance and binding properties, with polyvinylidene fluoride being more preferred.

[0021] The average particle size of the binder is not particularly limited, but may be between 100 nm and 500 nm. The average particle size of the binder may be 100 nm or more, 120 nm or more, or 140 nm or more, and may be 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, or 250 nm or less. Here, the average particle size can be determined by observation using a scanning electron microscope (SEM).

[0022] (Conductive additive) The conductive additive is not particularly limited. For example, the conductive additive may be VGCF (Vapor Grown Carbon Fiber), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), carbon nanofibers (CNF), etc., but is not limited to these.

[0023] (solid electrolyte) The material of the solid electrolyte is not particularly limited. For example, the solid electrolyte may be a sulfide solid electrolyte, an oxide solid electrolyte, a polymer electrolyte, etc., but is not limited thereto.

[0024] Examples of sulfide solid electrolytes include, but are not limited to, sulfide-based amorphous solid electrolytes, sulfide-based crystalline solid electrolytes, or argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li2S-P2S5 systems (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2 (Li 13 GeP3S 16 , Li 10 GeP2S 12 , etc.), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x PS 6-x Cl x , etc.; or combinations thereof can be cited, but are not limited thereto.

[0025] Examples of oxide solid electrolytes include, but are not limited to, Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO 4-x N x (LiPON), etc., but are not limited thereto.

[0026] The sulfide solid electrolyte and oxide solid electrolyte may be glass or crystallized glass (glass ceramic).

[0027] Examples of polymer electrolytes include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

[0028] (Negative electrode current collector layer) The negative electrode active material layer may be formed on the negative electrode current collector layer. The material used for the negative electrode current collector layer is not particularly limited, but any material that can be used as a negative electrode current collector for a battery can be appropriately adopted. For example, it may be copper, copper alloy, stainless steel (SUS), nickel, or these metals plated, coated, or deposited with nickel, chromium, and carbon, etc., but is not limited to these.

[0029] <Binder content in the negative electrode active material layer> The binder content in the negative electrode active material layer is 4.0 to 9.0% by mass relative to the total amount of the negative electrode active material layer.

[0030] The binder content of the negative electrode active material layer is not particularly limited, but from the viewpoint of improving discharge capacity and resistance, it is preferably 6.0 to 9.0% by mass, and more preferably 7.0 to 8.0% by mass, relative to the total amount of the negative electrode active material layer.

[0031] The binder content in the negative electrode active material layer may be 4.0% by mass or more, 4.5% by mass or more, 5.0% by mass or more, 5.5% by mass or more, 6.0% by mass or more, 6.5% by mass or more, or 7.0% by mass or more, and may be 9.0% by mass or less, 8.5% by mass or less, or 8.0% by mass or less.

[0032] <Coverage of negative electrode active material by binder> The coverage rate of the negative electrode active material by the binder is 8.0 to 25%.

[0033] The coverage rate of the negative electrode active material by the binder may be 8.0% or more, 10% or more, 12% or more, 14% or more, 16% or more, or 18% or more, or 25% or less, 23% or less, or 21% or less, from the viewpoint of improving discharge capacity and resistance.

[0034] Coating of the negative electrode active material with a binder means that the binder is present on the surface of the negative electrode active material, typically in an attached or bonded state, and a portion of the binder may extend into the interior of the negative electrode active material.

[0035] The coverage rate of the negative electrode active material by the binder can be determined by energy-dispersive X-ray spectroscopy (EDX). Specifically, the side surface of the negative electrode active material layer is observed using a scanning electron microscope (SEM), and then elements present only in the binder, such as fluorine atoms when PVdF is used as the binder, are mapped using EDX. The areas of the binder and negative electrode active material are calculated by binarizing the image data obtained from the mapping. The coverage rate (%) of the negative electrode active material by the binder can be calculated as the ratio of the binder area to the area of ​​the negative electrode active material.

[0036] "battery" The battery of this disclosure includes the negative electrode active material layer of this disclosure.

[0037] The battery of this disclosure may be a liquid-type battery containing an electrolyte as an electrolyte layer, or it may be a solid-state battery having a solid electrolyte layer as an electrolyte layer. In this disclosure, "solid-state battery" means a battery using at least a solid electrolyte as the electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as the electrolyte. Furthermore, the battery of this disclosure may be an all-solid-state battery, i.e., a battery using only a solid electrolyte as the electrolyte.

[0038] (liquid battery) In the case of a liquid-type battery, the battery of this disclosure may further include an electrolyte as the positive electrode active material layer and an electrolyte layer, and may include a separator between the positive electrode active material layer and the negative electrode active material layer.

[0039] (Cathode active material layer) The positive electrode active material layer may contain, as needed, a binder, a conductive additive, and a solid electrolyte in addition to the positive electrode active material.

[0040] The material of the positive electrode active material is not particularly limited. For example, the positive electrode active material can be lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), nickel-cobalt-lithium manganese oxide (NCM), LiCO 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, Li 1+x Mn 2-x-y M y Heteroatomic-substituted Li-Mn spinel, LiNi x Co y Al z It may be O2(NCA), etc., but is not limited to these.

[0041] For details regarding the binder, conductive additive, and solid electrolyte, please refer to the description in "<Composition of the negative electrode active material layer>" above.

[0042] (Positive electrode current collector layer) The positive electrode active material layer may be formed on the positive electrode current collector layer. The material used for the positive electrode current collector layer is not particularly limited, but any material that can be used as a positive electrode current collector for a battery can be appropriately adopted. For example, aluminum, stainless steel (SUS), chromium, gold, platinum, iron, titanium, and zinc, as well as these metals plated, coated, or deposited with nickel, chromium, and carbon, etc., are acceptable, but are not limited to these.

[0043] (electrolyte) The electrolyte is not particularly limited, but it preferably contains a supporting salt and a solvent.

[0044] Examples of lithium-ion conductive electrolyte supporting salts (lithium salts) include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3.

[0045] The solvent used in the electrolyte is not particularly limited, but examples include non-aqueous solvents and aqueous solvents.

[0046] Examples of non-aqueous solvents include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), and linear esters (linear carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte may be used alone or in combination of two or more. Preferably, the electrolyte contains two or more solvents.

[0047] Examples of aqueous solvents include those containing water as a solvent, and may also contain solvents other than water. Examples of solvents other than water include one or more organic solvents selected from ethers, carbonates, nitriles, alcohols, ketones, amines, amides, sulfur compounds, and hydrocarbons.

[0048] (Separator) The separator is not particularly limited, but for example, nonwoven fabrics such as polyolefin, polyamide, and polyimide can be used.

[0049] (solid battery) In the case of a solid-state battery, the battery of this disclosure may further include a positive electrode active material layer and a solid electrolyte layer as an electrolyte layer.

[0050] The positive electrode active material layer may contain, as necessary, a binder, a conductive additive, and a solid electrolyte, in addition to the positive electrode active material. Refer to the description under "(Liquid-based batteries)".

[0051] The solid electrolyte layer may contain a binder or other components in addition to the solid electrolyte, as needed. The solid electrolyte and binder can be described in the section above under "<Composition of the Negative Electrode Active Material Layer>".

[0052] Method for producing the negative electrode active material of this disclosure The negative electrode active material layer of this disclosure can be manufactured by a method comprising the following steps: The negative electrode mixture is prepared by mixing a carbon-based negative electrode active material with a binder in an amount of 4.0 to 9.0% by mass relative to the total amount of the negative electrode active material layer, and The above-mentioned negative electrode mixture is applied to the substrate using a dry method to form the above-mentioned negative electrode active material layer.

[0053] The method for manufacturing a negative electrode active material layer according to this disclosure makes it possible to obtain a negative electrode active material layer that contributes to improving the discharge capacity and resistance of a battery. Furthermore, in the method for manufacturing a negative electrode active material layer according to this disclosure, the negative electrode active material layer can be manufactured by placing the negative electrode mixture in powder form on a current collector. In other words, unlike conventional methods, it is possible to use materials that do not contain solvents, thus eliminating the step of removing the solvent.

[0054] <Negative electrode mixture> The negative electrode composite material includes a carbon-based negative electrode active material and a binder. The negative electrode composite material may also optionally contain a conductive additive and a solid electrolyte.

[0055] The negative electrode mixture may be in a dry or wet state. That is, the negative electrode mixture may contain a solvent (liquid). However, the negative electrode mixture is different from the negative electrode mixture slurry (particle dispersion). In the negative electrode mixture, the solvent forms droplets, and the solvent (liquid) is dispersed in the powder (solid). On the other hand, in the negative electrode mixture slurry, the solvent is the dispersion medium, and the powder (solid) is dispersed in the solvent (liquid).

[0056] For information on the carbon-based anode active material and binder contained in the anode composite material, please refer to the description in "<Composition of the Anode Active Material Layer>". Furthermore, for information on the binder content, please refer to the description in "<Binder Content of the Anode Active Material Layer>".

[0057] For information regarding the conductive additives and solid electrolytes optionally included in the negative electrode composite material, please refer to the description in "<Composition of the negative electrode active material layer>".

[0058] The negative electrode composite material can be obtained, for example, by mixing a mixture containing a carbon-based negative electrode active material and a binder using a multi-purpose small-scale mixing and grinding machine, but is not limited to this method.

[0059] (Dry construction method) The dry construction method is not particularly limited as long as it is a method of forming an electrode active material layer on a current collector using the above-mentioned negative electrode composite material. The dry construction method is not particularly limited, but examples include electrostatic coating and rolling film formation.

[0060] Electrostatic coating methods include, but are not limited to, electrostatic screen deposition. Specifically, a high voltage is applied between the electrostatic screen and the current collector to generate an electrostatic field between the electrostatic screen and the current collector. When an electrically charged electrode mixture is dropped into the electrostatic field through an opening in the electrostatic screen, a Coulomb force is generated in the electrode mixture, attracting it towards the current collector (the counter electrode) and coating it, thereby forming an electrode active material layer. Alternatively, as a rolling deposition method, for example, lamination of a self-supporting electrode active material layer onto the current collector can be considered, but is not limited to this method.

[0061] (base material) The material used for the base material is not particularly limited, but any material that can be used as a negative electrode current collector for a battery can be appropriately adopted. For example, copper, copper alloys, stainless steel (SUS), nickel, and these metals may be plated, coated, or vapor-deposited with nickel, chromium, and carbon, but are not limited to these. [Examples]

[0062] The present disclosure will be further described with reference to the following embodiments, but the scope of the present disclosure is not limited to these embodiments.

[0063] Example 1 <Fabrication of the negative electrode active material layer A1> 95.0 parts by mass of graphite (particle size 20 μm) as the negative electrode active material and 5.0 parts by mass of polyvinylidene fluoride (PVdF) (particle size 150 nm) as the binder were placed in an MP mixer (multipurpose small mixing and grinding machine) and compounded at a rotation speed of 10,000 rpm for 2 minutes to obtain a negative electrode composite material. Next, the obtained negative electrode composite material was deposited onto a Cu foil (8 μm) as the negative electrode current collector using an electrostatic screen deposition method under conditions of a voltage of 0.5 kV and a distance of 1 cm between the current collector foil and the screen. Subsequently, both sides of the negative electrode composite material deposited on the Cu foil were sandwiched between flat plates heated at 160°C and pressed with a load of 5 tons for 1 minute. This obtained a negative electrode active material layer A1 in which the negative electrode composite material was fixed to the Cu foil.

[0064] <Coverage of negative electrode active material layer A1> The side surface of the negative electrode active material layer A1 was observed using SEM, and fluorine atoms present only in PVdF as a binder were mapped using EDX. Next, the binder area was calculated by binarizing the obtained images. The binder coverage was calculated from the binder area relative to the particle area. The binder coverage of the negative electrode active material layer A1 was 10.1%.

[0065] <Fabrication of positive electrode active material layer B1> A positive electrode slurry was prepared by mixing lithium nickel-cobalt-manganate (NCM) (particle size 3-10 μm) (97.5 parts by mass) as the positive electrode active material, acetylene black (1.5 parts by mass) as a conductive additive, PVdF (1.0 part by mass) as a binder, and an appropriate amount of NMP as a dispersion medium. The obtained positive electrode slurry was applied to an Al foil (12 μm) as the positive electrode current collector and dried to create a positive electrode active material layer B1 on the positive electrode current collector.

[0066] <Making Battery C1> The negative electrode active material layer A1 and the positive electrode active material layer B1 were placed opposite each other with a separator in between and housed in a container. Next, 1.14 M LiPF6 / ethylene carbonate (EC):dimethyl carbonate (DMC):ethyl methyl carbonate (EMC) (30:34:36 volume%) was injected into the container as an electrolyte, and the container was sealed to fabricate battery C1.

[0067] <Cell capacity of battery C1> Battery C1 was discharged under constant current and constant voltage conditions (current 0.3C, voltage from 4.25V to 2.5V, cut-off current 1 / 20C), and its discharge capacity was calculated. The discharge capacity of battery C1 was 190mAh / g.

[0068] <Reaction resistance of battery C1> The State of Charge (SOC) of battery C1 was adjusted to 50%. Next, the AC impedance of battery C1 was measured, and the response resistance was calculated from the Cole-Cole plot. The response resistance of battery C1 was 0.33Ω.

[0069] Example 2 <Fabrication of the negative electrode active material layer A2> A negative electrode active material layer A2 was fabricated on a Cu foil using the same method as in Example 1, except that graphite (particle size 20 μm) (92.5 parts by mass) was used as the negative electrode active material and PVdF (particle size 150 nm) (7.5 parts by mass) was used as the binder. The binder coverage of electrode active material layer A2 was 20.0%.

[0070] <Making Battery C2> Battery C2 was fabricated using the same method as in Example 1, "<Fabrication of Battery C1>", except that negative electrode active material layer A2 was used instead of negative electrode active material layer A1. The cell capacity and reaction resistance of battery C2 are shown in Table 1 below.

[0071] Comparative Example 1 <Fabrication of the negative electrode active material layer a1> A negative electrode active material layer A2 was fabricated on a Cu foil using the same method as in Example 1, "<Fabrication of negative electrode active material layer A1>", except that graphite (particle size 20 μm) (97.5 parts by mass) was used as the negative electrode active material and PVdF (particle size 150 nm) (2.5 parts by mass) was used as the binder. The binder coverage of electrode active material layer a1 was 4.0%.

[0072] <Making battery c1> Battery c1 was fabricated in the same manner as in Example 1, "<Fabrication of Battery C1>", except that negative electrode active material layer a1 was used instead of negative electrode active material layer A1. The cell capacity and reaction resistance of battery c1 are shown in Table 1 below.

[0073] Comparative Example 2 <Fabrication of the negative electrode active material layer a2> A negative electrode active material layer A2 was fabricated on a Cu foil using the same method as in Example 1, "<Fabrication of negative electrode active material layer A1>", except that graphite (particle size 20 μm) (90.0 parts by mass) was used as the negative electrode active material and PVdF (particle size 150 nm) (10.0 parts by mass) was used as the binder. The binder coverage of electrode active material layer a1 was 28.0%.

[0074] <Making battery c2> Battery c2 was fabricated in the same manner as in Example 1, "<Fabrication of Battery C1>", except that negative electrode active material layer a2 was used instead of negative electrode active material layer A1. The cell capacity and reaction resistance of battery c2 are shown in Table 1 below.

[0075] [Table 1]

[0076] Batteries were fabricated using negative electrode active material layers with different binder amounts prepared by a dry process, and positive electrode active material layers prepared from positive electrode composite slurry. The discharge capacity and reaction resistance were then evaluated.

[0077] Battery C1, which included a negative electrode active material layer A1 with a binder content of 5.0%, and battery C2, which included a negative electrode active material layer A2 with a binder content of 7.5%, were batteries with low reaction resistance and high discharge capacity (Examples 1 and 2).

[0078] However, battery c1 containing a negative electrode active material layer a1 with a binder content of 2.5% had low reaction resistance but low discharge capacity (Comparative Example 1). It is thought that when the binder content is low and the coverage rate of the negative electrode active material by the binder is low, SEI forms on the graphite surface, increasing irreversible capacity, which in turn reduces discharge capacity.

[0079] Furthermore, battery c2, which included a negative electrode active material layer a2 with a binder content of 10.0%, had a high discharge capacity but high resistance (Comparative Example 2). It is thought that when the binder content is high and the coverage of the negative electrode active material by the binder is high, the conduction of lithium ions is inhibited by the binder, thereby increasing the reaction resistance.

[0080] While this disclosure describes a negative electrode active material layer, a method for manufacturing the negative electrode active material layer, and preferred embodiments of a battery, those skilled in the art will understand that modifications can be made without departing from the scope of the claims.

Claims

1. A negative electrode active material layer for a battery, The negative electrode active material layer includes a carbon-based negative electrode active material and a binder coating the carbon-based negative electrode active material. The binder content is 4.0 to 9.0% by mass relative to the total amount of the negative electrode active material layer, and The coverage rate of the negative electrode active material by the binder is 8.0 to 25%. A negative electrode active material layer for batteries.

2. The negative electrode active material layer according to claim 1, wherein the content of the binder is 6.0 to 9.0% by mass with respect to the total amount of the negative electrode active material layer.

3. The negative electrode active material layer according to claim 1, wherein the content of the binder is 7.0 to 8.0% by mass with respect to the total amount of the negative electrode active material layer.

4. The negative electrode active material layer according to claim 1, wherein the binder is polyvinylidene fluoride.

5. A battery having the negative electrode active material layer according to any one of claims 1 to 4.

6. A method for producing a negative electrode active material layer according to any one of claims 1 to 4, The negative electrode mixture is prepared by mixing a carbon-based negative electrode active material with a binder in an amount of 4.0 to 9.0% by mass relative to the total amount of the negative electrode active material layer, and The anode composite material is applied to the substrate by a dry method to form the anode active material layer. A method for producing a negative electrode active material layer, including the above.

7. The manufacturing method according to claim 6, wherein the dry method is electrostatic coating.

8. The average particle size of the carbon-based negative electrode active material is 15 to 30 μm, and The manufacturing method according to claim 6, wherein the average particle size of the binder is 100 nm to 500 nm.

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