Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery (10) comprises a positive electrode (11), a negative electrode (12), and a non-aqueous electrolyte, the non-aqueous electrolyte secondary battery being characterized in that: the positive electrode (11) includes a positive electrode current collector (30) and a positive electrode mixture layer (32) disposed on the surface of the positive electrode current collector (30); the positive electrode mixture layer (32) has a positive electrode active material, a conductive agent, and a binder; the alkali content of the positive electrode active material is 0.5 mass% or more; the hydrogen content of the conductive agent is 1.0 mg / g to 2.0 mg / g; and the binder includes a fluorine-containing polymer.

Description

Non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] A positive electrode of a non-aqueous electrolyte secondary battery generally includes a positive electrode current collector, which is a metal foil, and a positive electrode mixture layer, which includes a positive electrode active material, a conductive material, and a binder, and is provided on the positive electrode current collector. Patent Document 1 discloses a positive electrode that uses a fluorine-containing polymer such as polyvinylidene fluoride (PVdF) as a binder.

[0003] International Publication No. 2023 / 162942

[0004] In recent years, with the spread of electric vehicles and other factors, there has been a demand for higher-capacity non-aqueous electrolyte secondary batteries. As a method for achieving higher capacity non-aqueous electrolyte secondary batteries, increasing the Ni content in the lithium-containing transition metal composite oxide contained in the positive electrode active material has been considered.

[0005] However, in general, lithium-containing transition metal composite oxides with a high Ni content tend to have lithium hydroxide or lithium carbonate remaining on the particle surface, resulting in a higher alkali content, compared to lithium-containing transition metal composite oxides with a low Ni content. In the coating process for producing a positive electrode, a positive electrode active material is mixed with a binder and other components to produce a positive electrode mixture slurry. In this process, if the positive electrode active material has a high alkali content, the remaining alkaline components can easily cause the binder to deteriorate, resulting in gelation of the positive electrode mixture slurry. Gelling of the positive electrode mixture slurry makes it difficult to produce a positive electrode in which the positive electrode mixture slurry is uniformly applied, which is undesirable from the perspective of ensuring battery performance.

[0006] An object of the present disclosure is to suppress gelation of a positive electrode mixture slurry without increasing the resistance of the positive electrode, even when a positive electrode active material with a large amount of alkali is used.

[0007] A nonaqueous electrolyte secondary battery according to one aspect of the present disclosure is a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer disposed on a surface of the positive electrode current collector, the positive electrode mixture layer has a positive electrode active material, a conductive agent, and a binder, the alkali content of the positive electrode active material being 0.5 mass% or more, the hydrogen content of the conductive agent being 1.0 mg / g or more and 2.0 mg / g or less, and the binder containing a fluorine-containing polymer.

[0008] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, even when a positive electrode active material with a large amount of alkali is used, gelation of the positive electrode mixture slurry can be suppressed without increasing the resistance of the positive electrode.

[0009] 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention;

[0010] Hereinafter, an example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. Note that configurations obtained by selectively combining the respective components of the multiple embodiments and variations described below are included within the scope of the present disclosure.

[0011] In the following, a cylindrical battery in which a wound electrode assembly 14 is housed in a cylindrical outer can 16 with a bottom is exemplified as a nonaqueous electrolyte secondary battery, but the battery outer can is not limited to a cylindrical outer can. The secondary battery according to the present disclosure may be, for example, a prismatic battery with a prismatic outer can, a coin battery with a coin-shaped outer can, or a pouch-type battery with an outer can made of a laminate sheet including a metal layer and a resin layer. Furthermore, the electrode assembly is not limited to a wound type, and may be a stacked type electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.

[0012] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte, and an outer can 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 16 is a cylindrical metal container with a bottom and an open end in the axial direction, and the opening of the outer can 16 is closed by a sealing member 17. For ease of explanation, the sealing member 17 side of the battery will be referred to as the "top" and the bottom side of the outer can 16 will be referred to as the "bottom."

[0013] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the length and width directions. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and, for example, two separators 13 are arranged to sandwich the positive electrode 11. The electrode assembly 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.

[0014] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes through a through hole in the insulating plate 19 and extends toward the bottom side of the outer can 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0015] A gasket 28 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior can 16 has a groove 22 formed on its side surface that protrudes inward and supports the sealing body 17. The groove 22 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior can 16 by the groove 22 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0016] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0017] The positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte that constitute the electrode assembly 14 will be described in detail below, with the positive electrode 11 being particularly described below.

[0018] [Positive Electrode] The positive electrode 11 has a positive electrode current collector 30 and a positive electrode mixture layer 32 disposed on the positive electrode current collector 30. The positive electrode current collector 30 can be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on its surface. The positive electrode mixture layer 32 includes a positive electrode active material, a conductive agent, and a binder. As will be described in detail later, the alkali content of the positive electrode active material is 0.5 mass% or more, and the binder includes a fluorine-containing polymer. The hydrogen content of the conductive agent is 1.0 mg / g or more and 2.0 mg / g or less.

[0019] The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like onto the positive electrode current collector 30, drying the coating, and then compressing it to form a positive electrode mixture layer 32 on both sides of the positive electrode current collector 30.

[0020] The positive electrode mixture layer 32 contains, for example, a lithium-containing transition metal composite oxide as a positive electrode active material. The lithium-containing transition metal composite oxide contains, for example, secondary particles formed by 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 as the diameter of a circumscribed circle in a particle image observed with a scanning electron microscope (SEM). The volume-based median diameter (D50) of the secondary particles of the lithium-containing transition metal composite oxide is, for example, 2 μm or more and 30 μm or less. The volume-based median diameter (D50) refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also referred to 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 particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0021] The Ni content in the lithium-containing transition metal composite oxide is preferably 80 mol% or more relative to the total number of moles of metal elements excluding Li. By setting the Ni content to 80% or more, the battery capacity can be improved. Furthermore, when the Ni content is 80% or more, lithium hydroxide or lithium carbonate is likely to remain on the particle surface during the preparation process of the positive electrode active material, and the alkali content of the positive electrode active material tends to increase. Therefore, when the Ni content is 80% or more, the effect of suppressing gelation of the positive electrode mixture slurry, described below, is more significantly exhibited. The Ni content may be 82 mol% or more, or may be 85 mol% or more. Furthermore, from the viewpoint of structural stabilization, the Ni content is preferably 99 mol% or less, more preferably 95 mol% or less.

[0022] The lithium-containing transition metal composite oxide is, for example, a compound represented by the general formula Li ｘ Ni ａ Co ｂMn ｃ Al ｄ M ｅ O ２ (wherein 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 the group consisting of W, Mg, Mo, Nb, Ti, Si, Ca, Sr, and Zr).

[0023] The content of Co in the lithium-containing transition metal composite oxide is 0 mol % or more and 20 mol % or less relative to the total number of moles of metal elements excluding Li, and Co is an optional component. In other words, the lithium-containing transition metal composite oxide does not need to contain Co. By containing Co, the lithium-containing transition metal composite oxide can improve the heat resistance of the battery.

[0024] The content of Mn in the lithium-containing transition metal composite oxide is 0 mol % or more and 20 mol % or less relative to the total number of moles of metal elements excluding Li, and Mn is an optional component. In other words, the lithium-containing transition metal composite oxide does not need to contain Mn. By containing Mn, the lithium-containing transition metal composite oxide can stabilize its crystal structure.

[0025] The content of Al in the lithium-containing transition metal composite oxide is 0 mol % or more and 20 mol % or less relative to the total number of moles of metal elements excluding Li, and Al is an optional component. In other words, the lithium-containing transition metal composite oxide does not need to contain Al. By containing Al, the lithium-containing transition metal composite oxide can stabilize its crystal structure.

[0026] The content of the elements constituting the lithium-containing transition metal composite oxide can be measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), or the like.

[0027] Here, the positive electrode active material has an alkali content of 0.5 mass% or more. In this specification, the alkali content of the positive electrode active material refers to the amount of alkali eluted into water when the positive electrode active material is stirred and dispersed in pure water at 25°C, and is specifically calculated by the following measurement method. First, 1.0 g of the positive electrode active material is placed in 30 ml of pure water, stirred for 1 hour, and filtered to remove solids to obtain an extract. Next, a hydrochloric acid solution of a known concentration is added dropwise until the pH of the extract reaches 8.4, and the amount of hydrochloric acid added at this time is measured. Furthermore, the same hydrochloric acid solution is added dropwise to the extract until the pH reaches 4.0, and the amount of hydrochloric acid added at this time is measured. In neutralization titration (Warder method), 2β is determined as the amount of lithium carbonate (Li ２ CO ３ ), and α-β corresponds to the total amount of lithium hydroxide (LiOH) in the positive electrode active material. The sum of the amount of lithium carbonate and the amount of lithium hydroxide is the amount of alkali present in the positive electrode active material.

[0028] The alkali content of the positive electrode active material may be 0.5% by mass or more, but may also be 0.6% by mass or more, or 0.7% by mass or more. The upper limit of the alkali content of the positive electrode active material is, for example, 3.0% by mass.

[0029] The positive electrode mixture layer 32 contains, in addition to the positive electrode active material, a conductive agent having a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less. When the alkali content of the positive electrode active material is 0.5 mass % or more, the fluorine-containing polymer contained in the binder is likely to undergo polyenization due to the residual alkali component during preparation of the positive electrode mixture slurry. The polyenized fluorine-containing polymer is likely to aggregate and be difficult to disperse in the positive electrode mixture slurry. As a result, the viscosity of the positive electrode mixture slurry increases, which may cause gelation.

[0030] Therefore, in the past, methods for reducing the amount of alkali in the positive electrode active material have been considered as a method for suppressing gelation of the positive electrode mixture slurry. For example, a method of washing the positive electrode active material with water after calcination is known as a method for reducing the amount of alkali in the positive electrode active material. However, when washing the positive electrode active material with water after calcination, metal elements such as Ni present on the particle surface of the positive electrode active material may be eluted. As a result, the battery capacity decreases.

[0031] Therefore, the present inventors investigated a method for suppressing gelation of the positive electrode mixture slurry without performing a treatment to reduce the alkali content in the positive electrode active material, and found that the hydrogen content of the conductive agent significantly affects the gelation of the positive electrode mixture slurry. Specifically, they found that gelation of the positive electrode mixture slurry can be suppressed by controlling the hydrogen content of the conductive agent to 1.0 mg / g or more and 2.0 mg / g or less.

[0032] The hydrogen content of the conductive agent may be 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 conductive agent surface, thereby improving the dispersibility of the conductive agent in the positive electrode mixture slurry. In the positive electrode mixture slurry, the binder tends to become entangled with the conductive agent. Therefore, by improving the dispersibility of the conductive agent, the binder is also dispersed in the positive electrode mixture slurry. As a result, aggregation of the binder is suppressed, and gelation of the positive electrode mixture slurry is suppressed. Note that the hydrogen content of the conductive agent is used as an indicator of the dispersion characteristics of the conductive agent because the inventors have found a very good correlation between the hydrogen content of the conductive agent and the dispersion characteristics of the conductive agent. Note that the surface functional group that improves the dispersibility of the conductive agent is, for example, a hydroxyl group or a carboxyl group.

[0033] The hydrogen content of the conductive agent may be 2.0 mg / g or less, preferably 1.9 mg / g or less, and more preferably 1.8 mg / g or less. If the hydrogen content of the conductive agent exceeds 2.0 mg / g, the conductivity of the conductive agent tends to decrease. As a result, it becomes difficult to form a good conductive path, and the mixture resistance of the positive electrode mixture 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, and more preferably 1.2 mg / g or more and 1.8 mg / g or less. The hydrogen content of the conductive agent may 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. The hydrogen content of the conductive agent may 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.

[0034] 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. It is presumed that the carbon monoxide content of the conductive agent indicates the amount of carboxy 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 mixture layer 32, and the mixture resistance of the positive electrode mixture layer 32 is reduced. On the other hand, if the amount of carboxy groups on the surface of the conductive agent is excessively increased, it becomes difficult to form a good conductive path between the conductive agents, and the mixture resistance of the positive electrode mixture layer 32 may actually increase. 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. Therefore, 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.

[0035] The hydrogen content and carbon monoxide content of the conductive agent can be measured, for example, by an inert gas fusion-non-dispersive infrared absorption method (measuring device: EMGA-830 manufactured by Horiba, Ltd.).

[0036] The BET specific surface area of ​​the conductive agent is set to 60 m from the viewpoint of forming a good conductive path in the positive electrode mixture layer 32. ２ / g or more, and ２ / g or more is more preferable, and 80m ２ / g or more is more preferable. On the other hand, if the BET specific surface area of ​​the conductive agent is excessively increased, it becomes difficult to form a good conductive path between the conductive agents, and the mix resistance of the positive electrode mix layer 32 may increase. Therefore, the BET specific surface area of ​​the conductive agent is preferably 150 m ２ / g or less, and ２ / g or less is more preferable, and 130m ２ Therefore, the BET specific surface area of ​​the conductive agent is 60 m ２ / g or more, 150m ２ / g or less, and ２ / g or more, 140m ２ / g or less is more preferable, and ２ / g or more, 130m ２ The BET specific surface area is measured in accordance with the BET method (nitrogen adsorption method) described in JIS R1626.

[0037] The conductive agent may be, for example, one or more materials selected from the group consisting of carbon black (CB) such as furnace black (FB), acetylene black (AB), and ketjen black (KB), carbon nanotubes (CNT), and graphene. Among these, furnace black is preferably used as the conductive agent from the viewpoint of achieving a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less. The hydrogen content of the conductive agent may also be adjusted by subjecting it to a surface treatment. Examples of the surface treatment include surface oxidation using a strong acid. Carboxy groups can be introduced onto the surface of the conductive agent by immersing the conductive agent in a mixed acid of sulfuric acid and nitric acid and then heat-treating it.

[0038] The conductive agent is present in the positive electrode mixture layer 32 in a granular form, for example. When the conductive agent is granular, 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 becomes difficult to form a good conductive path, and the mixture resistance of the positive electrode mixture layer 32 may increase. The lower limit of the average particle size of the primary particles of the conductive agent is, for example, 1 nm. The particle size of the primary particles of the conductive agent is measured as the diameter of a circumscribed circle in a particle image observed with a transmission electron microscope (TEM). The average particle size of the primary particles of the conductive agent is determined by randomly selecting 100 granular conductive agents, measuring the particle size of the primary particles, and arithmetically averaging the measured values.

[0039] In the positive electrode mixture layer 32, the content of the conductive agent relative to the total mass of the positive electrode active material is preferably 0.5 mass% or more, more preferably 0.6 mass% or more, and even more preferably 0.7 mass% or more. When the content of the conductive agent is 0.5 mass% or more, a good conductive path is formed in the positive electrode mixture layer 32, and the mixture resistance of the positive electrode mixture layer 32 is reduced. Furthermore, from the viewpoint of ensuring the amount of positive electrode active material in the positive electrode mixture layer 32 and realizing a high capacity battery, the content of the conductive agent relative to the total mass of the positive electrode active material in the positive electrode mixture layer 32 is preferably 2.0 mass% or less, more preferably 1.9 mass% or less, and even more preferably 1.8 mass% or less. Therefore, in the positive electrode mixture layer 32, the content of the conductive agent relative to the total mass of the positive electrode active material is preferably 0.5 mass% or more and 2.0 mass% or less, more preferably 0.6 mass% or more and 1.9 mass% or less, and even more preferably 0.7 mass% or more and 1.8 mass% or less.

[0040] The positive electrode mixture layer 32 may contain, as the conductive agent, at least one of a conductive agent having a hydrogen content of less than 1.0 mg / g and a conductive agent having a hydrogen content of more than 2.0 mg / g, but preferably contains a conductive agent having a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less as a main component. More specifically, in the positive electrode mixture layer 32, the content of the conductive agent having a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less relative to the total mass of the conductive agents is preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 99 mass% or more.

[0041] The positive electrode mixture layer 32 contains a binder in addition to a positive electrode active material and a conductive agent. The binder includes at least a fluorine-containing polymer such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVdF). Because fluorine-containing polymers have strong binding properties, using a fluorine-containing polymer as a binder prevents the positive electrode mixture layer 32 from peeling off from the positive electrode current collector 30. Furthermore, as described above, in a positive electrode mixture slurry containing a positive electrode active material with a high alkali content, the fluorine-containing polymer is prone to polyenation and aggregation. Therefore, the effects of the present disclosure are exhibited when the binder includes a fluorine-containing polymer.

[0042] In the positive electrode mixture layer 32, the content of the binder relative to the total mass of the positive electrode active material is preferably 0.5 mass% or more, more preferably 0.6 mass% or more, and even more preferably 0.7 mass% or more. When the content of the binder is 0.5 mass% or more, peeling of the positive electrode mixture layer 32 from the positive electrode current collector 30 is further suppressed. From the viewpoint of ensuring the amount of positive electrode active material in the positive electrode mixture layer 32 and realizing a high capacity battery, the content of the binder relative to the total mass of the positive electrode active material in the positive electrode mixture layer 32 is preferably 2.0 mass% or less, more preferably 1.9 mass% or less, and even more preferably 1.8 mass% or less. Therefore, in the positive electrode mixture layer 32, the content of the binder relative to the total mass of the positive electrode active material is preferably 0.5 mass% or more and 2.0 mass% or less, more preferably 0.6 mass% or more and 1.9 mass% or less, and even more preferably 0.7 mass% or more and 1.8 mass% or less.

[0043] The binder may contain a binder other than the above-mentioned fluorine-containing polymer. Examples of binders other than the fluorine-containing polymer include polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, etc. Furthermore, the binder may be a combination of the above-mentioned resin with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), etc.

[0044] [Negative Electrode] The negative electrode 12 may have, for example, a negative electrode current collector 40 and a negative electrode mixture layer 42 formed on the surface of the negative electrode current collector 40, or a metal 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 upon charging. When the negative electrode 12 has a negative electrode mixture layer 42, the negative electrode mixture 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 that is stable within the potential range of the negative electrode 12, such as copper or a copper alloy, or a film having such a metal disposed on its surface. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less.

[0045] The anode mixture layer 42 includes, for example, a anode active material and a binder. The thickness of the anode mixture layer 42 is, for example, 10 μm or more and 150 μm or less on one side of the anode current collector 40. The anode 12 can be produced, for example, by applying an anode mixture slurry including the anode active material, the binder, etc. to the surface of the anode current collector 40, drying the coating, and then rolling the coating to form the anode mixture layer 42 on both sides of the anode current collector 40.

[0046] The negative electrode active material contained in the negative electrode mixture layer 42 is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally, a carbon material such as graphite is used. The graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, or artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. Furthermore, as the negative electrode active material, metals that alloy with Li, such as Si and Sn, metal compounds containing Si, Sn, and lithium-titanium composite oxides, may also be used. Furthermore, these may be coated with a carbon film. For example, SiO ｘ (0.5≦x≦1.6) or Li２ｙ SiO （２＋ｙ） A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2) may be used in combination with graphite.

[0047] Examples of the binder contained in the negative electrode mixture layer 42 include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0048] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0049] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides and phosphate compounds containing metal elements such as Ti, Al, Si, and Mg. The filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0050] [Non-aqueous electrolyte] The non-aqueous electrolyte has ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0051] The liquid electrolyte (electrolytic solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent that can be used include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the halogen-substituted compound include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0052] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene 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).

[0053] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methyl phenyl ether. and chain ethers such as 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, and tetraethylene glycol dimethyl ether.

[0054] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ Among these, LiPF is preferred from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ The concentration of the lithium salt may be, for example, 4 mol or less, or 3 mol or less, preferably 1.8 mol or less, and more preferably 0.8 mol or more and 1.8 mol or less, per 1 L of the non-aqueous solvent.

[0055] The non-aqueous electrolyte may contain an additive such as an unsaturated carbonate ester, an acid anhydride, a phenol compound, a benzene compound, a nitrile compound, an isocyanate compound, a sultone compound, a sulfate compound, a borate ester compound, a phosphate ester compound, or a phosphite ester compound.

[0056] 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, vinylethylene carbonate, and divinylethylene carbonate. One type of unsaturated cyclic carbonate may be used alone, or two or more types may be used in combination. Some of the hydrogen atoms in the unsaturated cyclic carbonate may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by intermolecular condensation of multiple carboxylic acid molecules, but is preferably an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0057] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0058] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanatomethylcyclohexane (BIMCH). Examples of sultone compounds include propane sultone and propene sultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethyl borate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethyl phosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethyl phosphite and tris(trimethylsilyl)phosphite.

[0059] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0060] Hereinafter, the present disclosure will be further described with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0061] Example 1 Preparation of Positive Electrode Active Material [Ni ０．８７ Co ０．０９ Al ０．０４ ](OH) ２The composite hydroxide represented by the formula (1) was calcined at 500°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. Next, lithium hydroxide monohydrate (LiOH·H) was added to the composite hydroxide represented by the formula (1) so that the molar ratio of Li to the total amount of Ni, Co, and Al was 1:1.03. ２ O) was mixed to obtain a mixture. Then, this mixture was placed under an oxygen flow (10 cm) with an oxygen concentration of 95%. ３ The mixture was heated from room temperature to 650°C at a temperature increase rate of 2.0°C / min under a flow rate of 2 mL / min per kg of the mixture and 5 L / min per kg of the mixture, and then heated from 650°C to 740°C at a temperature increase rate of 0.5°C / min, and fired to obtain a lithium-containing transition metal composite oxide. The alkali content of the lithium-containing transition metal composite oxide was measured by the method described above and was found to be 0.6 mass%.

[0062] [Preparation of Positive Electrode] The positive electrode active material, furnace black (FB) as a conductive agent having an average primary particle size of 18 nm, 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 added to prepare a positive electrode mixture slurry. The hydrogen content and carbon monoxide content of the furnace black were measured using the above-mentioned method and were found to be 1.2 mg / g and 20 mg / g, respectively. The BET specific surface area of ​​the furnace black was 100 m ２ / g.

[0063] The positive electrode mixture slurry was then applied to both sides of a positive electrode current collector made of aluminum foil, and the coating was dried and compressed. The resulting film was then cut to a predetermined electrode size to produce a positive electrode having a positive electrode mixture layer formed on both sides of the positive electrode current collector. The thickness of the positive electrode mixture layer was 80 μm on each side of the positive electrode current collector.

[0064] [Evaluation of Slurry Viscosity] The viscosity of the positive electrode mixture slurry prepared in the production of the positive electrode was measured 72 hours after preparation using a viscosity measuring device under the following conditions. If gelation of the positive electrode mixture slurry occurs, the slurry viscosity increases, so this method can be used to evaluate whether or not the positive electrode mixture slurry has gelled. Viscosity measuring device: TV-22 viscometer manufactured by Toki Sangyo Co., Ltd. Rotation speed and measurement time: rotation speed 2 rpm, measurement time 60 seconds

[0065] [Evaluation of Peel Strength] The positive electrode prepared in the positive electrode preparation step was cut to a predetermined size to prepare a test specimen. Using Nitto Denko double-sided tape #515, the positive electrode mixture layer on one side of the test specimen was attached to a stainless steel substrate with a smooth surface, and the stainless steel substrate to which the test specimen was fixed was positioned horizontally. One end of the positive electrode current collector in the longitudinal direction of the test specimen was fixed to a movable jig of a tensile tester (A&D Corporation's Tensilon universal testing machine RTC1210). The positive electrode current collector was set to peel off in a direction 90° relative to the substrate surface of the stainless steel substrate, and the movable jig was then moved to peel off the positive electrode mixture layer of the test specimen from the positive electrode current collector at a speed of 100 mm / min. At this time, the tensile direction was always maintained at 90° relative to the substrate surface of the stainless steel substrate to which the test specimen was fixed. A stable tensile strength value was read when 30 mm or more of the test specimen had peeled off. The above measurements were carried out on five test pieces, and the average value of the measured values ​​was taken as the peel strength (N / m).

[0066] [Measurement of Mixture Resistance] The mix resistance of the positive electrode prepared in the positive electrode preparation was measured using an electrode resistance measuring instrument (device name: RM2610) manufactured by Hioki E.E. Corp. The measurement current was set to 100 μA and the voltage range was set to 0.5 V.

[0067] Comparative Example 1 A positive electrode was prepared and evaluated in the same manner as in Example 1, except that furnace black having a hydrogen content and a carbon monoxide content of 0.6 mg / g and 10 mg / g, respectively, was used as the conductive agent.

[0068] Comparative Example 2 A positive electrode was prepared and evaluated in the same manner as in Example 1, except that furnace black having a hydrogen content and a carbon monoxide content of 2.4 mg / g and 40 mg / g, respectively, was used as the conductive agent.

[0069] Comparative Example 3 A positive electrode was prepared and evaluated in the same manner as in Example 1, except that furnace black with an average primary particle size of 28 nm was used as the conductive agent. The hydrogen content and carbon monoxide content of the furnace black were measured by the above-mentioned method and were found to be 2.4 mg / g and 40 mg / g, respectively. The BET specific surface area of ​​the furnace black was also found to be 62 m ２ / g.

[0070] Comparative Example 4 A positive electrode was prepared and evaluated in the same manner as in Example 1, except that acetylene black (AB) with an average primary particle size of 23 nm was used as the conductive agent. The hydrogen content and carbon monoxide content of the acetylene black were measured by the above-mentioned method and were found to be 0 mg / g and 0 mg / g, respectively. The BET specific surface area of ​​the acetylene black was 130 m ２ / g.

[0071] Comparative Example 5 A positive electrode was prepared and evaluated in the same manner as in Example 1, except that acetylene black (AB) with an average primary particle size of 30 nm was used as the conductive agent. The hydrogen content and carbon monoxide content of the acetylene black were measured by the above-mentioned method and were found to be 0 mg / g and 0 mg / g, respectively. The BET specific surface area of ​​the acetylene black was 63 m ２ / g.

[0072] Reference Example 1 A positive electrode was prepared and evaluated in the same manner as in Example 1, except that in the preparation of the positive electrode active material, the fired lithium-containing 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. The alkali content of the lithium-containing transition metal composite oxide of Reference Example 1 was measured by the method described above and was found to be 0.1 mass %.

[0073] Reference Example 2 A positive electrode was prepared and evaluated in the same manner as in Comparative Example 4, except that in the preparation of the positive electrode active material, the fired lithium-containing 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. The alkali content of the lithium-containing transition metal composite oxide of Reference Example 2 was measured by the method described above and was found to be 0.1 mass %.

[0074] The slurry viscosity, peel strength, and mix resistance of the Examples, Comparative Examples, and Reference Examples are shown in Table 1. The slurry viscosity, peel strength, and mix resistance shown in Table 1 are expressed relative to the slurry viscosity, peel strength, and mix resistance of Comparative Example 1, which are set to 100. A smaller value for the slurry viscosity means a lower viscosity, a larger value for the peel strength means a higher peel strength, and a smaller value for the mix resistance means a lower resistance.

[0075]

[0076] As shown in Table 1, the positive electrodes of the examples achieve slurry viscosity, peel strength, and mixture resistance equivalent to those of the positive electrodes of the reference examples, which have a small amount of alkali. In other words, by setting the hydrogen content of the conductive agent to 1.0 mg / g or more and 2.0 mg / g or less, it can be said that gelation of the positive electrode mixture slurry can be suppressed without increasing resistance, even when a positive electrode active material with a large amount of alkali is used.

[0077] Furthermore, the positive electrodes of Comparative Examples 1, 4, and 5, which used a conductive agent with a hydrogen content of less than 1.0 mg / g, had increased slurry viscosity. This is presumably because the conductive agent with a hydrogen content of less than 1.0 mg / g did not have sufficient dispersibility, causing aggregation of the binder, which resulted in gelation of the positive electrode mixture slurry.

[0078] Furthermore, the positive electrodes of Comparative Examples 2 and 3, which used conductive agents with hydrogen contents exceeding 2.0 mg / g, exhibited increased mixture resistance. This is presumably because conductive agents with hydrogen contents exceeding 2.0 mg / g have difficulty forming good conductive paths between conductive agents.

[0079] The present disclosure is further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer disposed on the surface of the positive electrode current collector, the positive electrode mixture layer having a positive electrode active material, a conductive agent, and a binder, the positive electrode active material having an alkali content of 0.5 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 including a fluorine-containing polymer. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the conductive agent has a carbon monoxide content of 10 mg / g or more and 50 mg / g or less. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the conductive agent is furnace black. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the content of the conductive agent in the positive electrode mixture layer is 0.5 mass % or more and 2.0 mass % or less relative to the total mass of the positive electrode active material. Configuration 5: The nonaqueous 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. Configuration 6: The BET specific surface area of ​​the conductive agent is 60 m ２ / g or more, 150m ２ / g or less. Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the positive electrode active material has 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 number of moles of metal elements excluding Li. Configuration 8: The lithium-containing transition metal composite oxide is represented by the general formula Li ｘ Ni ａ Co ｂ Mn ｃ Al ｄ M ｅ O ２ (wherein 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 the group consisting of W, Mg, Mo, Nb, Ti, Si, Ca, Sr, and Zr).

[0080] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode current collector, 32 Positive electrode mixture layer, 40 Negative electrode current collector, 42 Negative electrode mixture 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 electrode current collector and a positive electrode mixture layer disposed on a surface of the positive electrode current collector, the positive electrode mixture layer has a positive electrode active material, a conductive agent, and a binder, the positive electrode active material has an alkali amount of 0.5 mass% or more, the conductive agent has a hydrogen content of 1.0 mg / g or more and 2.0 mg / g or less, and the binder includes a fluorine-containing polymer.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the carbon monoxide content of the conductive agent is 10 mg / g or more and 50 mg / g or less.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the conductive agent is furnace black.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the conductive agent in the positive electrode mixture layer is 0.5 mass % or more and 2.0 mass % or less with respect to the total mass of the positive electrode active material.

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

6. The BET specific surface area of ​​the conductive agent is 60 m ２ / g or more, 150m ２ 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the capacitance is 0.1 to 0.5 μm.

7. The nonaqueous electrolyte secondary battery according to claim 1, 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 number of moles of metal elements excluding Li.

8. The lithium-containing transition metal composite oxide has the general formula Li ｘ Ni ａ Co ｂ Mn ｃ A ｄ M ｅ O ２ 8. The nonaqueous electrolyte secondary battery according to claim 7, wherein: (wherein 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 the group consisting of W, Mg, Mo, Nb, Ti, Si, Ca, Sr, and Zr).

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