Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery (10) comprising a positive electrode (11), a negative electrode (12) and a non-aqueous electrolyte, characterized in that the positive electrode (11) has a positive electrode current collector (30) and a positive electrode additive layer (32) disposed on the surface of the positive electrode current collector (30), the positive electrode additive layer (32) comprising a positive electrode active material, a conductive agent and a binder, the positive electrode active material having an alkalinity of 0.5% by mass or more, the conductive agent having a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less, and the binder comprising a fluoropolymer.

Description

Technical Field

[0001] This invention relates to non-aqueous electrolyte secondary batteries. Background Technology

[0002] The positive electrode of a non-aqueous electrolyte secondary battery generally comprises: a positive electrode current collector as a metal foil, and a positive electrode binder layer containing positive electrode active material, conductive material, and binder material disposed on the positive electrode current collector. Patent Document 1 discloses a positive electrode using a fluoropolymer such as polyvinylidene fluoride (PVdF) as a binder.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2023 / 162942 Summary of the Invention

[0006] In recent years, against the backdrop of the widespread adoption of electric vehicles, there has been a pursuit of increasing the capacity of non-aqueous electrolyte secondary batteries. As a means to achieve this, increasing the Ni content in lithium-containing transition metal composite oxides within the positive electrode active material has been investigated.

[0007] However, generally speaking, lithium hydroxide and lithium carbonate tend to remain on the particle surface more easily in lithium transition metal composite oxides with high Ni content compared to those with low Ni content, resulting in a higher alkalinity. In the coating process of the positive electrode, the positive electrode active material is mixed with binders to create a positive electrode slurry. If the alkalinity of the positive electrode active material is high, the binder may deteriorate due to residual alkaline components, causing the positive electrode slurry to gel. If the positive electrode slurry gels, it is difficult to produce a positive electrode with a uniform coating of the slurry, which is undesirable from the perspective of ensuring battery performance.

[0008] The purpose of this invention is to suppress the gelation of the positive electrode slurry without increasing the resistance of the positive electrode, even when using a positive electrode active material with a high alkalinity.

[0009] The non-aqueous electrolyte secondary battery of one embodiment of the present invention is characterized in that it is a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode and a non-aqueous electrolyte, the positive electrode having a positive electrode current collector and a positive electrode additive layer disposed on the surface of the positive electrode current collector, the positive electrode additive layer having a positive electrode active material, a conductive agent and a binder, the positive electrode active material having an alkalinity of 0.5% by mass or more, the conductive agent having a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less, and the binder comprising a fluoropolymer.

[0010] According to one aspect of the non-aqueous electrolyte secondary battery of the present invention, even when using a positive electrode active material with a high alkalinity, the gelation of the positive electrode slurry can be suppressed without increasing the resistance of the positive electrode. Attached Figure Description

[0011] Figure 1 This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method. Detailed Implementation

[0012] Hereinafter, an example of an embodiment of the non-aqueous electrolyte secondary battery of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that configurations formed by selectively combining the constituent elements of the various embodiments and modifications described below are included within the scope of the present invention.

[0013] Hereinafter, as a non-aqueous electrolyte secondary battery, a cylindrical battery is illustrated, in which a wound electrode body 14 is housed in a bottomed cylindrical outer casing 16. However, the outer casing of the battery is not limited to a cylindrical outer casing. The secondary battery of the present invention can be, for example, a square battery with a square outer casing, a coin-shaped battery with a coin-shaped outer casing, or a pouch-type battery with an outer casing composed of a laminate containing a metal layer and a resin layer. Furthermore, the electrode body is not limited to a wound type; it can also be a stacked electrode body consisting of multiple positive electrodes and multiple negative electrodes alternately stacked with spacers between them.

[0014] Figure 1 This is a cross-sectional view of a non-aqueous electrolyte secondary battery 10, as an example of an embodiment. (See diagram below.) Figure 1 As shown, the non-aqueous electrolyte secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an outer casing 16 for housing the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 has a positive electrode 11, a negative electrode 12, and a spacer 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound into a spiral shape with the spacer 13 in between. The outer casing 16 is a bottomed cylindrical metal container with an opening at one end along the axial direction, and the opening of the outer casing 16 is blocked by a sealing body 17. Hereinafter, for ease of explanation, the sealing body 17 side of the battery will be referred to as "upper" and the bottom side of the outer casing 16 will be referred to as "lower".

[0015] The positive electrode 11, negative electrode 12, and spacer 13 constituting the electrode body 14 are all strip-shaped elongated bodies, and are alternately stacked in the radial direction of the electrode body 14 by being wound into a spiral. To prevent lithium deposition, the negative electrode 12 is formed to be one size larger than the positive electrode 11. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the length and width directions. The spacer 13 is formed to be at least one size larger than the positive electrode 11, for example, two pieces are arranged to clamp the positive electrode 11. The electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0016] Insulating plates 18 and 19 are respectively disposed above and below the electrode body 14. Figure 1 In the example shown, the positive lead 20 extends towards the sealing body 17 through the through hole in the insulating plate 18, and the negative lead 21 extends towards the bottom of the outer can 16 through the through hole in the insulating plate 19. The positive lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cover 27 of the top plate of the sealing body 17, which is electrically connected to the internal terminal plate 23, becomes the positive terminal. The negative lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative terminal.

[0017] A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness of the battery interior. A groove 22 is formed in the outer can 16, a portion of which protrudes inward and supports the sealing body 17. The groove 22 is preferably formed in a ring shape along the circumference of the outer can 16 and supports the sealing body 17 on its upper surface. The sealing body 17 is fixed to the upper part of the outer can 16 by the groove 22 and the open end of the outer can 16 that tightens the sealing body 17.

[0018] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cover 27 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a circular or annular shape, and all components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and the insulating member 25 is sandwiched between their respective peripheral portions. If the internal pressure of the battery rises due to abnormal heating, the lower valve body 24 deforms and breaks by pushing the upper valve body 26 upwards towards the cover 27, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cover 27.

[0019] The following is a detailed description of the positive electrode 11, negative electrode 12, spacer 13, and non-aqueous electrolyte constituting the electrode body 14, especially the positive electrode 11.

[0020] [positive electrode]

[0021] The positive electrode 11 has a positive current collector 30 and a positive electrode binder layer 32 disposed on the positive current collector 30. The positive current collector 30 can be a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film obtained by disposing of such metal on the surface. The positive electrode binder layer 32 contains a positive electrode active material, a conductive agent, and a binder. As detailed below, the positive electrode active material has an alkalinity of 0.5% by mass or more, and the binder contains a fluoropolymer. Furthermore, the conductive agent has a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less.

[0022] The positive electrode 11 can be formed on both sides of the positive electrode current collector 30 by coating a positive electrode paste containing positive electrode active material, conductive agent and binder onto the positive electrode current collector 30, drying the coating and then compressing it.

[0023] The positive electrode additive layer 32 contains, for example, a lithium-containing transition metal composite oxide as the positive electrode active material. The lithium-containing transition metal composite oxide contains, for example, secondary particles formed by the aggregation of primary particles. The particle size of the primary particles constituting the secondary particles of the lithium-containing transition metal composite oxide is, for example, 0.02 μm or more and 2 μm or less. The particle size of the primary particles is measured by the diameter of the circumscribed circle in a particle image observed by a scanning electron microscope (SEM). The median diameter (D50) of the secondary particles in the volumetric reference of the lithium-containing transition metal composite oxide is, for example, 2 μm or more and 30 μm or less. It should be noted that the median diameter (D50) in the volumetric reference refers to the particle size at which the cumulative frequency from the smaller particle size side in the volumetric particle size distribution reaches 50%, also known as the median diameter. The particle size distribution of the secondary particles of the lithium-containing transition metal composite oxide can be measured using a laser diffraction-type particle size distribution measuring device (e.g., Microtrac BEL Co., Ltd., MT3000II) with water as the dispersion medium.

[0024] The Ni content in the lithium-containing transition metal composite oxide is preferably 80 mol% or more relative to the total molar number of metal elements other than Li. Setting the Ni content to 80% or more can improve battery capacity. Furthermore, when the Ni content is 80% or more, lithium hydroxide and lithium carbonate tend to remain on the particle surface during the manufacturing process of the positive electrode active material, and the alkalinity of the positive electrode active material tends to increase. Therefore, when the Ni content is 80% or more, the gelation inhibition effect of the positive electrode slurry described later is more significantly achieved. The Ni content can be 82 mol% or more, or 85 mol% or more. Moreover, from the viewpoint of structural stabilization, the Ni content is preferably 99 mol% or less, and more preferably 95 mol% or less.

[0025] Lithium-containing transition metal composite oxides can be, for example, made of the general formula Li xNi a Co b Mn c Al d M e O2 (where 0.8 < x < 1.2, 0.8 ≤ a, 0 ≤ b ≤ 0.2, 0 ≤ c ≤ 0.2, 0 ≤ d < 0.2, 0 ≤ e ≤ 0.1, a + b + c + d + e = 1, and M is one or more elements selected from W, Mg, Mo, Nb, Ti, Si, Ca, Sr and Zr) represents a composite oxide.

[0026] In lithium-containing transition metal composite oxides, the Co content is between 0 mol% and 20 mol% relative to the total moles of metal elements other than Li, and Co is optional. In other words, lithium-containing transition metal composite oxides can also be free of Co. Including Co in lithium-containing transition metal composite oxides can improve the heat resistance of the battery.

[0027] In lithium-containing transition metal composite oxides, the content of Mn relative to the total moles of metal elements other than Li is between 0 mol% and 20 mol%, and Mn is an optional component. In other words, lithium-containing transition metal composite oxides may also be Mn-free. By including Mn in lithium-containing transition metal composite oxides, the crystal structure can be stabilized.

[0028] In lithium-containing transition metal composite oxides, the Al content is between 0 mol% and 20 mol% relative to the total moles of metal elements other than Li, and Al is optional. In other words, lithium-containing transition metal composite oxides can also be free of Al. The presence of Al in lithium-containing transition metal composite oxides stabilizes the crystal structure.

[0029] The content of elements constituting lithium-containing transition metal complex oxides can be determined by inductively coupled plasma optical emission spectrometry (ICP-AES), electron beam microanalyzer (EPMA), or energy dispersive X-ray diffraction (EDX).

[0030] Here, the alkalinity of the positive electrode active material is 0.5% by mass or more. It should be noted that in this specification, the alkalinity of the positive electrode active material refers to the amount of alkali dissolved in water when the positive electrode active material is stirred and dispersed in pure water at 25°C. Specifically, it is calculated using the following method: First, 1.0 g of the positive electrode active material is added to 30 ml of pure water, stirred for 1 hour, and filtered to remove solid components, obtaining an extract. Next, a hydrochloric acid aqueous solution of known concentration is added dropwise until the pH of the extract reaches 8.4, and the amount of hydrochloric acid added at this point is measured as α. Further, the same hydrochloric acid aqueous solution is added dropwise to the extract until the pH reaches 4.0, and the amount of hydrochloric acid added at this point is measured as β. In the neutralization titration method (Warder method), 2β corresponds to the amount of lithium carbonate (Li₂CO₃) in the positive electrode active material, and α-β corresponds to the total amount of lithium hydroxide (LiOH) in the positive electrode active material. Then, the sum of the amounts of lithium carbonate and lithium hydroxide is taken as the amount of alkali present in the positive electrode active material.

[0031] The alkalinity of the positive electrode active material can be 0.5% by mass or more, or it can be 0.6% by mass or more, or it can be 0.7% by mass or more. The upper limit of the alkalinity of the positive electrode active material is, for example, 3.0% by mass.

[0032] In addition to the positive electrode active material, the positive electrode binder layer 32 also contains a conductive agent with a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less. Here, when the alkali content of the positive electrode active material is 0.5% by mass or more, during the preparation of the positive electrode binder slurry, the fluoropolymer contained in the binder is prone to polyolefination due to residual alkali components. The polyolefinated fluoropolymer tends to aggregate in the positive electrode binder slurry and is difficult to disperse. As a result, the viscosity of the positive electrode binder slurry increases, and sometimes gelation occurs.

[0033] Therefore, in the past, methods to reduce the alkalinity in the positive electrode active material have been studied as a way to suppress gelation of the positive electrode slurry. One known method for reducing the alkalinity in the positive electrode active material is washing it with water after calcination. However, when washing the positive electrode active material with water after calcination, metallic elements such as Ni present on the particle surface of the positive electrode active material sometimes dissolve. As a result, the battery capacity decreases.

[0034] Therefore, the inventors investigated a method to suppress the gelation of the positive electrode slurry even without reducing the alkali content in the positive electrode active material. The results showed that the hydrogen content of the conductive agent has a significant impact on the gelation of the positive electrode slurry. Specifically, it was found that controlling the hydrogen content of the conductive agent to be above 1.0 mg / g and below 2.0 mg / g can suppress the gelation of the positive electrode slurry.

[0035] The hydrogen content of the conductive agent is 1.0 mg / g or more, preferably 1.1 mg / g or more, and more preferably 1.2 mg / g or more. When the hydrogen content of the conductive agent is 1.0 mg / g or more, surface functional groups that improve the dispersibility of the conductive agent are appropriately formed on the surface of the conductive agent, thereby improving the dispersibility of the conductive agent in the positive electrode slurry. In the positive electrode slurry, the binder tends to entangle with the conductive agent. Therefore, by improving the dispersibility of the conductive agent, the binder is also dispersed in the positive electrode slurry. As a result, the aggregation of the binder is suppressed, and the gelation of the positive electrode slurry is suppressed. It should be noted that the hydrogen content of the conductive agent is used as an indicator of the dispersibility of the conductive agent because the inventors have found a very good correlation between the hydrogen content of the conductive agent and the dispersibility of the conductive agent. It should be noted that the surface functional groups that improve the dispersibility of the conductive agent are, for example, hydroxyl or carboxyl groups.

[0036] Furthermore, the hydrogen content of the conductive agent can be 2.0 mg / g or less, preferably 1.9 mg / g or less, and more preferably 1.8 mg / g or less. When the hydrogen content of the conductive agent exceeds 2.0 mg / g, there is a tendency for the conductivity of the conductive agent to decrease. As a result, it is difficult to form a good conductive path, and the resistivity of the positive electrode binder layer 32 increases. Therefore, the hydrogen content of the conductive agent is preferably 1.1 mg / g or more and 1.9 mg / g or less, more preferably 1.2 mg / g or more and 1.8 mg / g or less. Alternatively, the hydrogen content of the conductive agent can also be 1.0 mg / g or more and 1.9 mg / g or less, or 1.0 mg / g or more and 1.8 mg / g or less. Alternatively, the hydrogen content of the conductive agent can also be 1.1 mg / g or more and 2.0 mg / g or less, or 1.2 mg / g or more and 2.0 mg / g or less.

[0037] The carbon monoxide content of the conductive agent is preferably 10 mg / g or more, more preferably 15 mg / g or more, and even more preferably 20 mg / g or more. Here, it is assumed that the carbon monoxide content of the conductive agent represents the amount of carboxyl groups present on the surface of the conductive agent. Therefore, when the carbon monoxide content of the conductive agent is 10 mg / g or more, a good conductive path is formed in the positive electrode binder layer 32, and the binder resistance of the positive electrode binder layer 32 decreases. On the other hand, if the amount of carboxyl groups on the surface of the conductive agent increases excessively, it becomes difficult to form a good conductive path between the conductive agents, and sometimes the binder resistance of the positive electrode binder layer 32 increases. Therefore, the carbon monoxide content of the conductive agent is preferably 50 mg / g or less, more preferably 45 mg / g or less, and even more preferably 40 mg / g or less. Thus, the carbon monoxide content of the conductive agent is preferably 10 mg / g or more and 50 mg / g or less, more preferably 15 mg / g or more and 45 mg / g or less, and even more preferably 20 mg / g or more and 40 mg / g or less.

[0038] The hydrogen and carbon monoxide content of the conductive agent can be determined, for example, by inactive gas melting-non-dispersive infrared absorption method (measuring device: EMGA-830 manufactured by Horiba Corporation).

[0039] From the viewpoint of forming a good conductive pathway in the positive electrode agent layer 32, the BET specific surface area of ​​the conductive agent is preferably 60 m². 2 / g or more, preferably 70m 2 / g or more, further preferably 80m 2 / g or more. On the other hand, if the BET specific surface area of ​​the conductive agent increases excessively, it becomes difficult to form good conductive pathways between the conductive agents, and sometimes the resistivity of the positive electrode binder layer 32 increases. Therefore, the BET specific surface area of ​​the conductive agent is preferably 150m². 2 / g or less, more preferably 140m 2 / g or less, more preferably 130m 2 / g or less. Therefore, the BET specific surface area of ​​the conductive agent is preferably 60m². 2 / g or more and 150m 2 / g or less, preferably 70m 2 / g or more and 140m 2 / g or less, more preferably 80m 2 / g or more and 130m 2 / g or less. The BET specific surface area was determined according to the BET method (nitrogen adsorption method) as described in JIS R1626.

[0040] As a conductive agent, materials selected from one or more of the following can be used: furnace black (FB), acetylene black (AB), Ketjen black (KB), carbon black (CB), carbon nanotubes (CNT), and graphene. From the viewpoint of setting the hydrogen content to 1.0 mg / g or more and 2.0 mg / g or less, furnace black is preferred as the conductive agent. Furthermore, the hydrogen content of the conductive agent can also be adjusted by performing surface treatment. Examples of such surface treatment include surface oxidation based on acid treatment using a strong acid. By immersing the conductive agent in a mixed acid of sulfuric acid and nitric acid and then heating it, carboxyl groups can be introduced onto the surface of the conductive agent.

[0041] The conductive agent exists, for example, in particulate form in the positive electrode binder layer 32. When the conductive agent is particulate, the average particle size of the primary particles of the conductive agent is preferably 25 nm or less, more preferably 20 nm or less. If the average particle size of the primary particles of the conductive agent exceeds 25 nm, it is difficult to form a good conductive path, and the binder resistance of the positive electrode binder layer 32 may sometimes increase. In addition, the lower limit of the average particle size of the primary particles of the conductive agent is, for example, 1 nm. It should be noted that the particle size of the primary particles of the conductive agent is measured by the diameter of the circumscribed circle in the particle image observed by a transmission electron microscope (TEM). In addition, the average particle size of the primary particles of the conductive agent can be obtained by arbitrarily selecting 100 particulate conductive agents, measuring the particle size of the primary particles, and arithmetically averaging the measured values.

[0042] In the positive electrode compound layer 32, the content of the conductive agent relative to the total mass of the positive electrode active material is preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and even more preferably 0.7% by mass or more. When the content of the conductive agent is 0.5% by mass or more, a good conductive path is formed in the positive electrode compound layer 32, and the compound resistance of the positive electrode compound layer 32 is reduced. In addition, from the viewpoint of ensuring the amount of positive electrode active material in the positive electrode compound layer 32 and realizing high battery capacity, the content of the conductive agent relative to the total mass of the positive electrode active material in the positive electrode compound layer 32 is preferably 2.0% by mass or less, more preferably 1.9% by mass or less, and even more preferably 1.8% by mass or less. Therefore, in the positive electrode compound layer 32, the content of the conductive agent relative to the total mass of the positive electrode active material is preferably 0.5% by mass or more and 2.0% by mass or less, more preferably 0.6% by mass or more and 1.9% by mass or less, and even more preferably 0.7% by mass or more and 1.8% by mass or less.

[0043] In the positive electrode mixture layer 32, the conductive agent may contain at least one of a conductive agent with a hydrogen content of less than 1.0 mg / g and a conductive agent with a hydrogen content of more than 2.0 mg / g, but it is preferable to use a conductive agent with a hydrogen content of 1.0 mg / g or more and less than 2.0 mg / g as the main component. More specifically, in the positive electrode mixture layer 32, the content of the conductive agent with a hydrogen content of 1.0 mg / g or more and less than 2.0 mg / g relative to the total mass of the conductive agent is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0044] In addition to the positive electrode active material and conductive agent, the positive electrode binder layer 32 also includes a binder. The binder contains at least a fluoropolymer such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVdF). Because fluoropolymers have strong adhesive properties, using a fluoropolymer as a binder suppresses the peeling of the positive electrode binder layer 32 from the positive electrode current collector 30. Furthermore, as mentioned above, in a positive electrode binder slurry containing a high-alkali positive electrode active material, the fluoropolymer undergoes polyene formation and is prone to aggregation. Therefore, the effects of the present invention are achieved when the binder contains a fluoropolymer.

[0045] In the positive electrode binder layer 32, the binder content relative to the total mass of the positive electrode active material is preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and even more preferably 0.7% by mass or more. When the binder content is 0.5% by mass or more, it further suppresses the peeling of the positive electrode binder layer 32 from the positive electrode current collector 30. From the viewpoint of ensuring the amount of positive electrode active material in the positive electrode binder layer 32 and achieving high battery capacity, the binder content relative to the total mass of the positive electrode active material in the positive electrode binder layer 32 is preferably 2.0% by mass or less, more preferably 1.9% by mass or less, and even more preferably 1.8% by mass or less. Therefore, in the positive electrode binder layer 32, the binder content relative to the total mass of the positive electrode active material is preferably 0.5% by mass or more and 2.0% by mass or less, more preferably 0.6% by mass or more and 1.9% by mass or less, and even more preferably 0.7% by mass or more and 1.8% by mass or less.

[0046] It should be noted that the adhesive may also contain adhesives other than the aforementioned fluoropolymers. Examples of adhesives other than fluoropolymers include polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. Furthermore, the adhesive may also be used in combination with the aforementioned resins and carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0047] [negative electrode]

[0048] The negative electrode 12 may, for example, have a negative electrode current collector 40 and a negative electrode flux layer 42 formed on the surface of the negative electrode current collector 40, or a metallic Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode current collector 40, and lithium metal may be deposited on the surface of the negative electrode current collector 40 through charging. When the negative electrode 12 has a negative electrode flux layer 42, the negative electrode flux layer 42 is preferably formed on both sides of the negative electrode current collector 40. The negative electrode current collector 40 may be a foil of a metal stable within the potential range of the negative electrode 12, such as copper or a copper alloy, or a film obtained by depositing such metal on the surface. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less.

[0049] The negative electrode mixture layer 42 contains, for example, a negative electrode active material and a binder. Regarding the thickness of the negative electrode mixture layer 42, for example, it is 10 μm or more and 150 μm or less on one side of the negative electrode current collector 40. The negative electrode 12 can be produced, for example, by coating a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. on the surface of the negative electrode current collector 40, drying the coating film, and then calendering to form the negative electrode mixture layer 42 on both sides of the negative electrode current collector 40.

[0050] As the negative electrode active material contained in the negative electrode mixture layer 42, there is no particular limitation as long as it can reversibly absorb and release lithium ions, and generally carbon materials such as graphite are used. The graphite can be any of natural graphite such as flaky graphite, massive graphite, and earthy graphite, massive artificial graphite, and artificial graphite such as graphitized mesophase carbon microbeads. In addition, as the negative electrode active material, metals alloyed with Li such as Si and Sn, metal compounds containing Si, Sn, etc., and lithium titanium composite oxides can also be used. In addition, materials obtained by providing a carbon coating film on these substances can also be used. For example, a Si-containing compound represented by SiO x (0.5 ≤ x ≤ 1.6), or a Si-containing compound in which Si fine particles are dispersed in a lithium silicate phase represented by Li 2y SiO （2+y） (0 < y < 2) can also be used in combination with graphite.

[0051] As the binder contained in the negative electrode mixture layer 42, for example, styrene-butadiene rubber (SBR), nitrile rubber (NBR), carboxymethyl cellulose (CMC) or its salt, polyacrylic acid (PAA) or its salt (PAA-Na, PAA-K, etc., and a partially neutralized salt can also be used), polyvinyl alcohol (PVA), etc. can be cited. These can be used alone or in combination of two or more.

[0052] [Spacer]

[0053] The spacer 13 uses a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, etc. As the material of the spacer 13, polyolefins such as polyethylene and polypropylene, cellulose, etc. are suitable. The spacer 13 can be a single-layer structure or can have a multilayer structure. In addition, a resin layer with high heat resistance such as an aromatic polyamide resin can be formed on the surface of the spacer 13.

[0054] On the interface between the spacer 13 and at least one of the positive electrode 11 and the negative electrode 12, a filler layer containing an inorganic filler can also be formed. As the inorganic filler, for example, oxides containing metal elements such as Ti, Al, Si, Mg, etc., phosphate compounds, etc. can be cited. The filler layer can be formed by coating a slurry containing the filler on the surface of the positive electrode 11, the negative electrode 12, or the spacer 13.

[0055] [Non-aqueous electrolytes]

[0056] Non-aqueous electrolytes possess ionic conductivity (e.g., lithium-ion conductivity). Non-aqueous electrolytes can be liquid electrolytes (electrolytes) or solid electrolytes.

[0057] Liquid electrolytes (electrolytes) may include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent may be, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may also contain halogen-substituted derivatives obtained by substituting at least a portion of the hydrogen atoms of these solvents with halogen atoms such as fluorine. Examples of halogen-substituted derivatives include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0058] Examples of the aforementioned esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0059] Examples of the aforementioned ethers include cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, and ethyl vinyl ether. Ethers, including butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and other chain ethers.

[0060] The preferred electrolyte salt is a lithium salt. Examples of lithium salts include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, and LiB. 10 Cl 10Examples of lithium salts include lower aliphatic carboxylic acids such as lithium Cl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO₂F₂), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium tetrafluoro(oxalate)phosphate. Examples of borates include lithium bis(oxalate)borate (LiBOB) and lithium difluoro(oxalate)borate (LiDFOB). Examples of imide salts include lithium difluorosulfonylimide (LiN(FSO₂)₂), lithium bis(trifluoromethanesulfonylimide) (LiN(CF₃SO₂)₂), lithium trifluoromethanesulfonate nonafluorobutanesulfonylimide (LiN(CF₃SO₂)(C₄F₉SO₂)), and lithium bis(pentafluoroethanesulfonylimide) (LiN(C₂F₅SO₂)₂). Among these, LiPF₆ is preferred from the perspective of ionic conductivity and electrochemical stability. Regarding the concentration of lithium salt, for example, it can be less than 4 moles per 1L of non-aqueous solvent, or less than 3 moles, preferably less than 1.8 moles, and more preferably more than 0.8 moles and less than 1.8 moles.

[0061] Non-aqueous electrolytes may also contain additives. Examples of additives include unsaturated carbonates, acid anhydrides, phenolic compounds, benzene compounds, nitrile compounds, isocyanate compounds, sulcolone compounds, sulfuric acid compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0062] Examples of unsaturated cyclic carbonates include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinyl ethylene carbonate, and divinyl ethylene carbonate. One type of unsaturated cyclic carbonate can be used alone, or two or more can be used in combination. A portion of the hydrogen atoms in the unsaturated cyclic carbonate can also be replaced by fluorine atoms. The anhydride can also be an anhydride formed by the intermolecular condensation of multiple carboxylic acid molecules, but is preferably an anhydride of a polycarboxylic acid. Examples of polycarboxylic acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0063] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0064] Examples of nitrile compounds include adiponitrile, heptanonitrile, propionitrile, and succinic anionyl. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and methylcyclohexane diisocyanate (BIMCH). Examples of sulcolactone compounds include propane sulcolactone and propene sulcolactone. Examples of sulfuric acid compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate compounds include trimethyl borate and tris(trimethylsilyl) borate. Examples of phosphate compounds include trimethyl phosphate and tris(trimethylsilyl) phosphate. Examples of phosphite compounds include trimethyl phosphite and tris(trimethylsilyl) phosphite.

[0065] As a solid electrolyte, examples include solid or gel-like polymer electrolytes and inorganic solid electrolytes. As an inorganic solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Polymer electrolytes may contain, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As a matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels. Examples of polymer materials include fluoropolymers, acrylic resins, and polyether resins.

[0066] Example

[0067] The present invention will be further illustrated below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0068] <Example 1>

[0069] [Preparation of positive electrode active material]

[0070] The [Ni] obtained by coprecipitation method 0.87 Co 0.09 Al 0.04 The complex hydroxide represented by (OH)₂ was calcined at 500°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. Next, lithium hydroxide monohydrate (LiOH·H₂O) was mixed such that the molar ratio of Li relative to the total amount of Ni, Co, and Al was 1:1.03, resulting in a mixture. This mixture was then subjected to an oxygen flow of 95% oxygen concentration (per 10 cm⁻¹). 3The mixture was calcined at a flow rate of 2 mL / min and 5 L / min per 1 kg of mixture, and then calcined at a heating rate of 2.0 °C / min from room temperature to 650 °C. The temperature was then increased from 650 °C to 740 °C at a heating rate of 0.5 °C / min to obtain a lithium-containing transition metal composite oxide. The alkali content of this lithium-containing transition metal composite oxide was determined using the above method, and the result was 0.6% by mass.

[0071] [The production of the positive electrode]

[0072] The above-mentioned positive electrode active material, furnace black (FB) with an average particle size of 18 nm as a conductive agent, and polyvinylidene fluoride (PVdF) powder as a binder were mixed in a mass ratio of 100:1:0.9, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was further added to prepare a positive electrode slurry. It should be noted that the hydrogen content and carbon monoxide content of the furnace black, determined using the above method, were 1.2 mg / g and 20 mg / g, respectively. Additionally, the BET specific surface area of ​​the furnace black was 100 m² / g. 2 / g.

[0073] Then, the positive electrode slurry was coated onto both sides of the positive electrode current collector formed from aluminum foil, and the coating was dried and compressed. Then, a specified electrode size was cut to fabricate a positive electrode with a positive electrode slurry layer formed on both sides of the positive electrode current collector. Furthermore, the thickness of the positive electrode slurry layer is 80 μm on each side of the positive electrode current collector.

[0074] [Evaluation of slurry viscosity]

[0075] For the cathode slurry prepared in the cathode fabrication process, the viscosity was measured 72 hours after preparation using a viscometer under the following conditions. When gelation occurs in the cathode slurry, the viscosity increases; therefore, this method can be used to evaluate whether gelation has occurred in the cathode slurry.

[0076] Viscosity measuring device: TV-22 type viscometer manufactured by Toki Sangyo Co., Ltd.

[0077] Rotation speed and measurement time: Rotation speed 2 rpm, measurement time 60 seconds

[0078] [Evaluation of peel strength]

[0079] The positive electrode, fabricated during the positive electrode manufacturing process, is cut to a specified size and used as a test piece. Using Nitto Denko double-sided tape #515, the positive electrode adhesive layer on one side of the test piece is adhered to a smooth stainless steel substrate, ensuring the substrate is horizontal. One end of the positive electrode current collector along the length of the test piece is fixed to the movable clamp of a tensile testing machine (A&D Tensilon RTC1210 universal testing machine). The machine is set to peel the positive electrode current collector at a 90° angle relative to the substrate surface of the stainless steel substrate. The movable clamp is then moved to peel the positive electrode adhesive layer from the positive electrode current collector at a speed of 100 mm / min. Throughout this process, the tensile direction remains at 90° relative to the substrate surface of the stainless steel substrate. The stable tensile strength at a peel length of 30 mm or more is recorded. This measurement is performed on five test pieces, and the average value is taken as the peel strength (N / m).

[0080] [Determination of the resistance of the compound]

[0081] For the positive electrode produced during the manufacturing process, the resistance of the mixture was measured using an electrode resistance meter (device name: RM2610) manufactured by Hioki Electric Co., Ltd. The measuring current was set to 100μA and the voltage range was set to 0.5V.

[0082] <Comparative Example 1>

[0083] Except that furnace black with hydrogen content of 0.6 mg / g and carbon monoxide content of 10 mg / g was used as a conductive agent, the positive electrode was prepared and evaluated in the same manner as in Example 1.

[0084] <Comparative Example 2>

[0085] Except that furnace black with hydrogen content of 2.4 mg / g and carbon monoxide content of 40 mg / g was used as a conductive agent, the positive electrode was prepared and evaluated in the same manner as in Example 1.

[0086] <Comparative Example 3>

[0087] Except for using furnace black with an average primary particle size of 28 nm as the conductive agent, the positive electrode was prepared and evaluated in the same manner as in Example 1. It should be noted that the hydrogen content and carbon monoxide content of this furnace black were measured using the above method, and the results were 2.4 mg / g and 40 mg / g, respectively. Furthermore, the BET specific surface area of ​​this furnace black was 62 m². 2 / g.

[0088] <Comparative Example 4>

[0089] Except for using acetylene black (AB) with an average primary particle size of 23 nm as the conductive agent, the positive electrode was prepared and evaluated in the same manner as in Example 1. It should be noted that the hydrogen content and carbon monoxide content of the acetylene black were measured using the above method, and the results were 0 mg / g and 0 mg / g, respectively. Furthermore, the BET specific surface area of ​​this acetylene black was 130 m². 2 / g.

[0090] <Comparative Example 5>

[0091] Except for using acetylene black (AB) with an average primary particle size of 30 nm as the conductive agent, the positive electrode was prepared and evaluated in the same manner as in Example 1. It should be noted that the hydrogen content and carbon monoxide content of the acetylene black were measured using the above method, and the results were 0 mg / g and 0 mg / g, respectively. Furthermore, the BET specific surface area of ​​the acetylene black was 63 m². 2 / g.

[0092] <Reference Example 1>

[0093] In the preparation of the positive electrode active material, the calcined lithium transition metal composite oxide was washed with distilled water for 2 hours and then dried in a vacuum dryer at 150°C for 4 hours. Except as described above, the positive electrode was prepared and evaluated in the same manner as in Example 1. The alkalinity of the lithium transition metal composite oxide in Reference Example 1 was determined using the above method, and the result was 0.1% by mass.

[0094] <Reference Example 2>

[0095] In the preparation of the positive electrode active material, the calcined lithium transition metal composite oxide was washed with distilled water for 2 hours and then dried in a vacuum dryer at 150°C for 4 hours. Except as described above, the positive electrode was prepared and evaluated in the same manner as in Comparative Example 4. The alkalinity of the lithium transition metal composite oxide in Reference Example 2 was determined using the above method, and the result was 0.1% by mass.

[0096] For the examples, comparative examples, and reference examples, the slurry viscosity, peel strength, and binder resistance are shown in Table 1. The slurry viscosity, peel strength, and binder resistance shown in Table 1 are expressed relative to 100 for the slurry viscosity, peel strength, and binder resistance of Comparative Example 1. Regarding slurry viscosity, a smaller value indicates lower viscosity; regarding peel strength, a larger value indicates greater peel strength; and regarding binder resistance, a smaller value indicates lower resistance.

[0097] [Table 1]

[0098]

[0099] As shown in Table 1, the positive electrode of the embodiment can achieve slurry viscosity, peel strength, and binder resistance equivalent to the positive electrode of the reference example with low alkali content. That is, it can be said that by setting the hydrogen content of the conductive agent to 1.0 mg / g or more and 2.0 mg / g or less, even when using a positive electrode active material with high alkali content, gelation of the positive electrode binder slurry can be suppressed without increasing resistance.

[0100] Furthermore, in Comparative Examples 1, 4, and 5, which used conductive agents with a hydrogen content of less than 1.0 mg / g, the slurry viscosity increased. It is speculated that this is because the conductive agents with a hydrogen content below 1.0 mg / g exhibit insufficient dispersibility, leading to binder aggregation and ultimately gelation of the positive electrode slurry.

[0101] Furthermore, in Comparative Examples 2 and 3, which used conductive agents with a hydrogen content exceeding 2.0 mg / g, the reactant resistance increased. This is presumably because conductive agents with a hydrogen content exceeding 2.0 mg / g do not readily form good conductive pathways between themselves.

[0102] The present invention is further illustrated by the following embodiments.

[0103] Configuration 1: A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has a positive current collector and a positive electrode binder layer disposed on the surface of the positive current collector, the positive electrode binder layer having a positive electrode active material, a conductive agent, and a binder, wherein the alkalinity of the positive electrode active material is 0.5% by mass or more, the hydrogen content of the conductive agent is 1.0 mg / g or more and 2.0 mg / g or less, and the binder comprises a fluoropolymer.

[0104] Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the carbon monoxide content of the conductive agent is 10 mg / g or more and 50 mg / g or less.

[0105] Configuration 3: A non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the conductive agent is furnace black.

[0106] Configuration 4: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein, in the above-mentioned positive electrode compound layer, the content of the above-mentioned conductive agent relative to the total mass of the positive electrode active material is 0.5% by mass or more and 2.0% by mass or less.

[0107] Configuration 5: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the average particle size of the primary particles of the conductive agent is 25 nm or less.

[0108] Configuration 6: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the BET specific surface area of ​​the conductive agent is 60 m². 2 / g or more and 150m 2 / g or less.

[0109] Configuration 7: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the positive electrode active material comprises a lithium-containing transition metal composite oxide containing Ni, and the proportion of Ni in the lithium-containing transition metal composite oxide is 80 mol% or more relative to the total molar number of metal elements other than Li.

[0110] Configuration 8: A non-aqueous electrolyte secondary battery according to Configuration 7, wherein the above-mentioned lithium-containing transition metal composite oxide is composed of the general formula Li x Ni a Co b Mn c Al d M e O2 (where 0.8 < x < 1.2, 0.8 ≤ a, 0 ≤ b ≤ 0.2, 0 ≤ c ≤ 0.2, 0 ≤ d < 0.2, 0 ≤ e ≤ 0.1, a + b + c + d + e = 1, and M is one or more elements selected from W, Mg, Mo, Nb, Ti, Si, Ca, Sr and Zr) represents O2.

[0111] Explanation of reference numerals in the attached figures

[0112] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Spacer, 14 Electrode body, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive lead, 21 Negative lead, 22 Groove section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cover, 28 Gasket, 30 Positive current collector, 32 Positive flux layer, 40 Negative current collector, 42 Negative flux layer.

Claims

1. A non-aqueous electrolyte secondary battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein, The positive electrode has a positive current collector and a positive electrode flux layer disposed on the surface of the positive current collector. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder. The alkalinity of the positive electrode active material is 0.5% by mass or more. The conductive agent has a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less. The adhesive comprises a fluoropolymer.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The carbon monoxide content of the conductive agent is above 10 mg / g and below 50 mg / g.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The conductive agent is furnace black.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein, In the positive electrode mixture layer, the content of the conductive agent is 0.5% by mass or more and 2.0% by mass or less relative to the total mass of the positive electrode active material.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The average particle size of the primary particles of the conductive agent is less than 25 nm.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The conductive agent has a BET specific surface area of ​​60 m². 2 / g or more and 150m 2 / g or less.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The positive electrode active material is a lithium-containing transition metal composite oxide containing Ni. The proportion of Ni in the lithium-containing transition metal composite oxide is more than 80 mol% relative to the total molar number of metal elements other than Li.

8. The non-aqueous electrolyte secondary battery according to claim 7, wherein, The lithium-containing transition metal composite oxide is composed of the general formula Li x Ni a Co b Mn c Al d M e O2 represents the formula, where 0.8 < x < 1.2, 0.8 ≤ a, 0 ≤ b ≤ 0.2, 0 ≤ c ≤ 0.2, 0 ≤ d < 0.2, 0 ≤ e ≤ 0.1, a + b + c + d + e = 1, and M is one or more elements selected from W, Mg, Mo, Nb, Ti, Si, Ca, Sr and Zr.

Images