Negative electrode for secondary battery, and secondary battery

Abstract

This negative electrode (12) for a secondary battery is provided with a negative electrode current collector (40) and a negative electrode mixture layer (42) provided on the negative electrode current collector (40), and is characterized in that the negative electrode mixture layer (42) has a negative electrode active material and a dicarboxylic acid component containing a dicarboxylic acid and / or an acid anhydride thereof. When the negative electrode mixture layer (42) is bisected in the thickness direction into a lower half region (42a) on the negative electrode current collector (40) side and an upper half region (42b) on the surface side, the content (CA) of the dicarboxylic acid component in the lower half region (42a) and the content (CB) of the dicarboxylic acid component in the upper half region (42b) satisfy the relationship CA > CB.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode for a secondary battery and a secondary battery. Background Art

[0002] In recent years, as high-power, high-energy-density secondary batteries, for example, secondary batteries that include a positive electrode, a negative electrode, and a nonaqueous electrolyte and that perform charge and discharge by transferring lithium ions or the like between the positive electrode and the negative electrode have been widely used.

[0003] For example, Patent Documents 1 and 2 disclose a negative electrode for a secondary battery in which a negative electrode composite material layer containing a negative electrode active material and a dicarboxylic acid is disposed on a negative electrode current collector.

[0004] In addition, for example, Patent Document 3 discloses a negative electrode active material comprising: particles formed of silicon oxide represented by SiOx (0.3≤x≤1.6) and a resin coating covering the surface of the particles, wherein the resin coating is a copolymer of acrylic acid and acid monomers such as methacrylic acid, itaconic acid, fumaric acid, and maleic acid.

[0005] In addition, for example, Patent Document 4 discloses a method for manufacturing a negative electrode composition, which includes a process of suspending an electrode active material, a binder and an electron conductivity generator in an aqueous medium, wherein the aqueous medium is a non-buffered acidic medium with a pH of 1 or a buffered acidic medium with a pH of less than 4 obtained by adding a strong base and an organic acid, and fumaric acid is used as the organic acid.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2011-249058

[0009] Patent Document 2: Japanese Patent Application Publication No. 2004-335379

[0010] Patent Document 3: Japanese Patent Application Publication No. 2012-164624

[0011] Patent Document 4: Japanese Patent Application No. 2012-516531 Summary of the invention

[0012] However, the inventors of the present invention have conducted in-depth research and found that by containing a dicarboxylic acid such as fumaric acid in the negative electrode composite material layer, the interface resistance between the negative electrode composite material layer and the negative electrode collector tends to decrease. However, it is also known that in the negative electrode for a secondary battery containing a dicarboxylic acid in the negative electrode composite material layer, the problem of reduced bonding force (closed force) between the particles of the negative electrode active material in the negative electrode composite material layer will occur. It is believed that if the bonding force (closed force) between the particles of the negative electrode active material in the negative electrode composite material layer is reduced, the particles of the negative electrode active material isolated from the conductive path will increase.

[0013] Therefore, the purpose of the present disclosure is to provide a negative electrode for a secondary battery and a secondary battery having the negative electrode for a secondary battery, wherein the negative electrode for a secondary battery can reduce the interface resistance between the negative electrode composite material layer and the negative electrode collector, and can suppress the reduction of the bonding force (closeness) between the particles of the negative electrode active material in the negative electrode composite material layer.

[0014] A negative electrode for a secondary battery as one embodiment of the present disclosure is characterized in that it comprises: a negative electrode collector and a negative electrode composite material layer provided on the negative electrode collector, the negative electrode composite material layer comprising: a negative electrode active material and a dicarboxylic acid component comprising at least one of a dicarboxylic acid and an anhydride thereof, and when the negative electrode composite material layer is divided into two equal parts in the thickness direction into a lower half region on the negative electrode collector side and an upper half region on the surface side, the content of the dicarboxylic acid component in the lower half region (C A ) and the content of the dicarboxylic acid component in the region of the upper half (C B ) satisfies C A >C B relationship.

[0015] Moreover, a secondary battery as one aspect of the present disclosure is characterized by including the above-mentioned negative electrode for a secondary battery.

[0016] According to one embodiment of the present disclosure, a negative electrode for a secondary battery and a secondary battery having the negative electrode for a secondary battery can be provided, wherein the negative electrode for a secondary battery can reduce the interface resistance between the negative electrode composite material layer and the negative electrode collector and can suppress the reduction of the bonding force (adhesion force) between the particles of the negative electrode active material in the negative electrode composite material layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a cross-sectional view of a secondary battery as an example of an embodiment.

[0018] Figure 2 It is a cross-sectional view of a negative electrode as an example of an embodiment. DETAILED DESCRIPTION

[0019] A negative electrode for a secondary battery as one embodiment of the present disclosure is characterized in that it comprises: a negative electrode collector and a negative electrode composite material layer provided on the negative electrode collector, the negative electrode composite material layer comprising: a negative electrode active material and a dicarboxylic acid component comprising at least one of a dicarboxylic acid and an anhydride thereof, and when the negative electrode composite material layer is divided into two equal parts in the thickness direction into a lower half region on the negative electrode collector side and an upper half region on the surface side, the content of the dicarboxylic acid component in the lower half region (C A ) and the content of the dicarboxylic acid component in the region of the upper half (C B ) satisfies C A >C B In addition, according to the negative electrode for a secondary battery as one mode of the present disclosure, the interface resistance between the negative electrode composite material layer and the negative electrode current collector can be reduced, and the bonding force (adhesion force) between the particles of the negative electrode active material in the negative electrode composite material layer can be suppressed. The mechanism of exerting the above effect is not clear, but it can be considered as follows.

[0020] It is believed that a film derived from a dicarboxylic acid will be formed on the surface of the negative electrode active material. For example, the functional groups on the surface of the negative electrode active material chemically bond with the carboxyl groups of the dicarboxylic acid, so that the carboxylic acid is adsorbed on the negative electrode active material to form a film. For example, if the functional groups on the surface of the negative electrode active material are hydroxyl groups, they will hydrogen bond with the carboxyl groups. In addition, it is believed that the electronic conductivity of the negative electrode active material is improved by the film derived from the dicarboxylic acid formed on the surface of the negative electrode active material, which is closely related to the reduction of the interface resistance between the negative electrode composite material layer and the negative electrode collector. In addition, it is believed that a film derived from the dicarboxylic acid will also be formed on the surface of the negative electrode collector. For example, when the negative electrode collector is a Cu-based negative electrode collector such as Cu foil, Cu reacts with the carboxyl group, and a film derived from the dicarboxylic acid is formed on the surface of the negative electrode collector. Furthermore, it is believed that the electron conductivity of the negative electrode current collector is improved by forming a film derived from a dicarboxylic acid on the surface of the negative electrode current collector, destroying the oxide film of the negative electrode current collector, and this is closely related to the reduction of the interface resistance between the negative electrode composite material layer and the negative electrode current collector.

[0021] In addition, the content of the dicarboxylic acid component in the lower half region (C A ) and the content of the dicarboxylic acid component in the upper half region (C B ) satisfies C A >C B In the case of a relationship between the dicarboxylic acid component and the case where the dicarboxylic acid component is uniformly present in the negative electrode composite material layer (C A =C B), even if the content of the dicarboxylic acid component is a small amount, it is possible to reduce the interface resistance between the negative electrode composite material layer and the negative electrode current collector. In addition, it is believed that the content of the dicarboxylic acid component in the negative electrode composite material layer is suppressed, which is closely related to suppressing the reduction of the binding force (adhesion force) between the particles of the negative electrode active material in the negative electrode composite material layer.

[0022] Furthermore, it is believed that: when using an unsaturated dicarboxylic acid as a dicarboxylic acid, due to the contribution of the π electron cloud of the carbon-carbon double bond portion, the interface resistance between the negative electrode composite material layer and the negative electrode collector is further greatly reduced and is closely related. In addition, it is believed that: in terms of reducing the interface resistance between the negative electrode composite material layer and the negative electrode collector, a combination of an unsaturated dicarboxylic acid and a Cu-based negative electrode collector is preferred. Through this combination, the content of the dicarboxylic acid component in the negative electrode composite material layer can be further reduced, so the effect of suppressing the reduction of the bonding force (closed force) between the particles of the negative electrode active material in the negative electrode composite material layer can be further improved.

[0023] Hereinafter, an example of an embodiment will be described in detail with reference to the accompanying drawings. It should be noted that the secondary battery of the present disclosure is not limited to the embodiment described below. In addition, the accompanying drawings referred to in the description of the embodiment are schematic diagrams.

[0024] Figure 1 It is a cross-sectional view of a secondary battery as an example of an embodiment. Figure 1 The secondary battery 10 shown has: a wound electrode body 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, a non-aqueous electrolyte, insulating plates 18 and 19 respectively arranged above and below the electrode body 14, and a battery case 15 for accommodating the above components. The battery case 15 is composed of a case body 16 in a cylindrical shape with a bottom and a sealing body 17 that blocks the opening of the case body 16. It should be noted that, instead of the wound electrode body 14, other types of electrode bodies such as a laminated electrode body in which a positive electrode and a negative electrode are alternately laminated with a separator interposed therebetween can be used. In addition, as the battery case 15, examples include cylindrical, square, coin-shaped, button-shaped, etc. metal cases, resin cases formed by laminating resin sheets (so-called laminated types), etc.

[0025] The nonaqueous electrolyte is, for example, an electrolyte having lithium ion conductivity, and may be a liquid electrolyte (electrolyte) or a solid electrolyte.

[0026] Liquid electrolyte (electrolyte) for example comprises non-aqueous solvent and electrolyte salt dissolved in non-aqueous solvent. Non-aqueous solvent can use ester, ether, nitrile, amide and these 2 kinds of mixed solvent etc. for example. As an example of non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and their mixed solvent etc. can be cited. Non-aqueous solvent can also contain halogen substitution (for example, fluoroethylene carbonate etc.) formed by at least a part of hydrogen of these solvents being replaced by halogen atom such as fluorine. Electrolyte salt uses lithium salt such as LiPF6 for example.

[0027] In addition, as a solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As an inorganic solid electrolyte, well-known materials in all-solid lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte, for example, comprises a lithium salt and a matrix polymer, or comprises 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 is gelled is used. As a polymer material, fluororesins, acrylic resins, polyether resins, etc. can be listed. It should be noted that the non-aqueous electrolyte is an example, and an aqueous electrolyte can also be used as long as it is applicable.

[0028] The outer shell body 16 is, for example, a metal container in a cylindrical shape with a bottom. A gasket 28 is provided between the outer shell body 16 and the sealing body 17 to ensure the airtightness inside the battery. The outer shell body 16 has, for example, a bulging portion 22 in which a part of the side surface bulges inwardly and supports the sealing body 17. The bulging portion 22 is preferably formed in an annular shape along the circumferential direction of the outer shell body 16, and the sealing body 17 is supported by its upper surface.

[0029] The sealing body 17 has a structure in which a partially opened metal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cover 27 are stacked in order from the electrode body 14 side. The components constituting the sealing body 17 have, for example, a disc shape or a ring shape, and the 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 to each other at their respective central portions, and an insulating member 25 is sandwiched between their respective peripheral portions. When the internal pressure of the secondary battery 10 rises due to heat release such as an internal short circuit, the lower valve body 24 is deformed and broken in a manner such that the upper valve body 26 is pushed upward toward the cover 27 side, and the current path between the lower valve body 24 and the upper valve body 26 is cut off. When the internal pressure rises further, the upper valve body 26 breaks, and the gas is discharged from the opening of the cover 27.

[0030] Figure 1In the secondary battery 10 shown, the positive electrode lead 20 attached to the positive electrode 11 extends to the sealing body 17 side through the through hole of the insulating plate 18, and the negative electrode lead 21 attached to the negative electrode 12 extends to the bottom side of the outer shell body 16 through the outer side of the insulating plate 19. The positive electrode lead 20 is connected to the bottom plate of the sealing body 17, that is, the lower surface of the partially opened metal plate 23 by welding or the like, and the top plate of the sealing body 17, that is, the cover 27 electrically connected to the partially opened metal plate 23, becomes the positive terminal. The negative electrode lead 21 is connected to the bottom inner surface of the outer shell body 16 by welding or the like, and the outer shell body 16 becomes the negative terminal.

[0031] Hereinafter, the positive electrode 11 , the negative electrode 12 , and the separator 13 will be described in detail.

[0032] [negative electrode]

[0033] Figure 2 1 is a cross-sectional view of a negative electrode as an example of an embodiment. The negative electrode 12 includes a negative electrode current collector 40 and a negative electrode composite material layer 42 provided on the negative electrode current collector 40. The negative electrode composite material layer 42 may be provided on one surface of the negative electrode current collector 40 or on both surfaces of the negative electrode current collector 40.

[0034] The negative electrode current collector 40 is made of, for example, a foil of a metal such as copper that is stable in the potential range of the negative electrode, or a thin film having the metal disposed on the surface.

[0035] The negative electrode composite material layer 42 contains: a negative electrode active material, and a dicarboxylic acid component including at least one of a dicarboxylic acid and its anhydride. It should be noted that, hereinafter, at least one of a dicarboxylic acid and its anhydride is sometimes referred to as a dicarboxylic acid and / or its anhydride. The negative electrode composite material layer 42 preferably includes a binding material, a conductive material, and the like. The negative electrode 12 is made, for example, by the following method: preparing a negative electrode composite material slurry including a negative electrode active material, a dicarboxylic acid component, a binding material, and the like, applying the negative electrode composite material slurry to the negative electrode collector 40, drying to form a negative electrode composite material layer 42, and rolling the negative electrode composite material layer 42 so as to be able to make it. It should be noted that the details of the method for making the negative electrode composite material layer 42 will be described later.

[0036] In this embodiment, Figure 2 When the negative electrode composite material layer 42 shown in the figure is divided into two equal parts in the thickness direction into a lower half region 42a on the negative electrode current collector 40 side and an upper half region 42b on the surface side, the content of the dicarboxylic acid component in the lower half region 42a (C A ) and the content of the dicarboxylic acid component in the upper region 42b (C B ) satisfies C A >C B In addition, by satisfying C A >CB , so that as mentioned above, the interface resistance between the negative electrode composite material layer 42 and the negative electrode current collector 40 can be reduced, and the bonding force (closed force) between the particles of the negative electrode active material in the negative electrode composite material layer 42 can be suppressed. It should be noted that dividing the negative electrode composite material layer 42 into two equal parts in the thickness direction means that when the stacking direction of the negative electrode current collector 40 and the negative electrode composite material layer 42 is set as the thickness direction of the negative electrode composite material layer 42, the negative electrode composite material layer 42 is divided into two halves at the middle Z of the thickness. In addition, the negative electrode composite material layer 42 is divided into two equal parts in the thickness direction, and the negative electrode composite material layer 42 that is closer when viewed from the negative electrode current collector 40 is set as the region 42a of the lower half, and the negative electrode composite material layer 42 that is farther away when viewed from the negative electrode current collector 40 is set as the region 42b of the upper half. In addition, the content of the dicarboxylic acid component in the region 42a of the lower half (C A ) refers to the ratio (mass %) of the mass of the dicarboxylic acid component contained in the lower half region 42a to the mass of the lower half region 42a. In addition, the content of the dicarboxylic acid component in the upper half region 42b (C B ) refers to the ratio (mass %) of the mass of the dicarboxylic acid component contained in the upper half region 42b relative to the mass of the upper half region 42b.

[0037] The content of dicarboxylic acid components in the upper half (C B ) relative to the content of the dicarboxylic acid component in the lower half region 42a (C A ) ratio (C B / C A ), for example, from the perspective of further reducing the interface resistance between the negative electrode composite material layer 42 and the negative electrode collector 40, or further suppressing the reduction of the bonding force (adhesion force) between the particles of the negative electrode active material in the negative electrode composite material layer 42, it is preferably greater than 0 and less than 0.7, more preferably greater than 0 and less than 0.5, and more preferably greater than 0 and less than 0.3.

[0038] The content of the dicarboxylic acid component in the lower region 42a (C A ), for example, from the perspective of further reducing the interface resistance between the negative electrode composite material layer 42 and the negative electrode current collector 40, or further suppressing the decrease in the bonding force (adhesion force) between the particles of the negative electrode active material in the negative electrode composite material layer 42, it is preferably 0.1 mass % or more and 2 mass % or less, and more preferably 0.4 mass % or more and 1.5 mass % or less. In addition, the content of the dicarboxylic acid component in the upper half region (C B), for example, from the perspective of further reducing the interface resistance between the negative electrode composite material layer 42 and the negative electrode collector 40, or further suppressing the reduction of the bonding force (adhesion force) between the particles of the negative electrode active material in the negative electrode composite material layer 42, it is preferably greater than 0 mass % and less than 1.4 mass %.

[0039] Dicarboxylic acid and / or its anhydride, for example, aliphatic dicarboxylic acid and / or its anhydride, or aromatic dicarboxylic acid and / or its anhydride, etc. can be listed. Aliphatic dicarboxylic acid and / or its anhydride, for example, saturated dicarboxylic acid and / or its anhydride, unsaturated dicarboxylic acid and / or its anhydride, etc. can be listed. These can be used alone, or two or more can be used in combination. Among these, for example, from the aspect of further reducing the interface resistance of the negative electrode composite material layer 42 and the negative electrode collector 40, unsaturated dicarboxylic acid and / or its anhydride are preferred.

[0040] Unsaturated dicarboxylic acids include, for example, fumaric acid, maleic acid, itaconic acid, mesaconic acid, methylene succinic acid, citraconic acid, glutaconic acid, tetrahydrophthalic acid, 2-allylmalonic acid, isopropylidene succinic acid, etc. Among these, for example, from the aspect of further reducing the interface resistance between the negative electrode composite material layer 42 and the negative electrode collector 40, fumaric acid, mesaconic acid, and methylene succinic acid are preferred. In addition, these can be used alone or in combination of two or more.

[0041] A method for calculating the content of dicarboxylic acid components from the negative electrode 12 after manufacture is described. First, the negative electrode composite material layer 42 of the upper region 42b is cut, and the cut sample is placed in an alcohol solution to dissolve the dicarboxylic acid components contained in the sample. It should be noted that the dicarboxylic acid components contained in the negative electrode composite material layer 42 are sometimes combined with lithium or the like and exist in the form of dicarboxylates, but in this case, it is desirable to use pure water instead of the alcohol solution. In addition, by using the solution after the dicarboxylic acid components are dissolved to perform GCMS measurement, the dicarboxylic acid components are quantified, and the content of the dicarboxylic acid components in the upper region 42b (C B ). In addition, the negative electrode composite material layer 42 of the lower half region 42a is cut, and the same steps as above are performed to calculate the content of the dicarboxylic acid component in the lower half region 42a (C A ).

[0042] The negative electrode active material is, for example, a material that can reversibly absorb and release lithium ions. Specifically, carbon materials, metals that can form alloys with lithium, alloys containing the metals, or compounds containing the metals can be listed. As carbon materials, graphite materials such as natural graphite and artificial graphite can be listed. As metals that can form alloys with lithium, alloys containing the metals, or compounds containing the metals, known materials such as Si-containing materials, Sn-containing materials, and Ti-containing materials can be listed. For example, from the perspective of high capacity of the battery, charge and discharge cycle characteristics, etc., the negative electrode active material preferably includes a graphite material and a Si-containing material.

[0043] Examples of Si-containing materials include Si, Si alloys, and Si compounds. In addition, the Si-containing material may be, for example, a composite particle including an ion-conducting phase and a silicon phase (in one viewpoint, silicon particles) dispersed in the ion-conducting phase. The ion-conducting phase is a phase that conducts ions, and examples thereof include a silicate phase, a carbon phase, and a silicon oxide phase. For example, from the perspective of charge and discharge cycle characteristics, the Si-containing material preferably includes at least one of a first composite particle having a carbon phase and a silicon phase dispersed in the aforementioned carbon phase, a second composite particle having a silicate phase and a silicon phase dispersed in the aforementioned silicate phase, and a third composite particle having a silicon oxide phase and a silicon phase dispersed in the aforementioned silicon oxide phase.

[0044] The carbon phase may be composed of amorphous carbon, for example. Examples of amorphous carbon constituting the carbon layer include hard carbon, soft carbon, and other amorphous carbon. Amorphous carbon is the average interplanar spacing d of the (002) plane measured by X-ray diffraction. 002 Carbon materials exceeding 0.34nm.

[0045] The main component (for example, 95% by mass or more and 100% by mass or less) of the silicon oxide phase may be silicon dioxide. The composition of the composite particles including the silicon oxide phase and the silicon phase dispersed therein may be composed of SiO x Indicates. SiO x It has a structure in which silicon particles are dispersed in amorphous SiO 2. The content ratio x of oxygen to silicon is, for example, preferably 0.5≤x<2.0, and more preferably 0.8≤x≤1.5.

[0046] The silicate phase may satisfy the following conditions (1) and / or (2).

[0047] (1) The silicate phase contains at least one selected from the group consisting of alkali metal elements and Group 2 elements (Group 2 elements of the long-form periodic table).

[0048] (2) The silicate phase contains an element L. The element L is at least one selected from the group consisting of B, Al, Zr, Nb, Ta, V, lanthanoids, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, and W. It should be noted that the lanthanoids are a general term for 15 elements from lanthanum (La) with an atomic number of 57 to lutetium (Lu) with an atomic number of 71.

[0049] Regarding the above-mentioned condition (1), examples of alkali metal elements include lithium (Li), potassium (K), and sodium (Na). Examples of Group 2 elements include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). By including alkali metal elements and / or Group 2 elements, the irreversible capacity of the silicate phase is sometimes reduced. The silicate phase containing lithium (hereinafter sometimes referred to as "lithium silicate phase") is preferred, for example, in terms of small irreversible capacity and high initial charge and discharge efficiency.

[0050] The lithium silicate phase may be an oxide phase containing Li, Si and O, and may contain other elements. The atomic ratio of O to Si in the lithium silicate phase: O / Si is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase: Li / Si is, for example, greater than 0 and less than 4.

[0051] The lithium silicate phase may contain the formula: Li 2z SiO (2+z) The lithium silicate phase represented by (0<z<2) can also be composed of this lithium silicate phase. Z preferably satisfies the relationship of 0<z<1, and more preferably z=1 / 2 (that is, Li2Si2O5).

[0052] In addition, the Si-containing material may include composite particles including an ion-conducting phase and a silicon phase dispersed in the ion-conducting phase, and a coating layer covering at least a portion of the surface of the composite particles.

[0053] The coating present on the surface of the composite particles includes, for example, a conductive layer. By forming a conductive layer on the surface of the composite particles, the conductivity of the Si-containing material can sometimes be improved. As a conductive material constituting the conductive layer, a conductive material containing carbon is preferred. Examples of conductive materials containing carbon include conductive carbon materials. Examples of conductive carbon materials include carbon black, graphite, and amorphous carbon (non-crystalline carbon) with low crystallinity. Amorphous carbon is preferred in terms of its large buffering effect on the silicon phase that undergoes volume changes during charge and discharge. Amorphous carbon can be easily graphitized carbon (soft carbon) or difficult to graphitize carbon (hard carbon). Examples of carbon black include acetylene black, Ketjen black, etc. The thickness of the conductive layer can be, for example, in the range of 1 to 200 nm. The thickness of the conductive layer can be measured by cross-sectional observation of the Si-containing material using SEM or TEM (transmission electron microscope).

[0054] For example, from the perspective of increasing battery capacity or charge-discharge cycle characteristics, the content of the Si-containing material is preferably 1 mass % to 20 mass % and more preferably 5 mass % to 15 mass % relative to the total mass of the negative electrode active material.

[0055] As the binding material, for example, fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or its salt, polyacrylic acid (PAA) or its salt (which may be PAA-Na, PAA-K, etc., or partially neutralized salt), polyvinyl alcohol (PVA), etc. can be listed. These can be used alone or in combination of two or more.

[0056] Examples of the conductive material include carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphite and other carbon particles, etc. These may be used alone or in combination of two or more.

[0057] An example of a method for making the negative electrode composite material layer 42 is described. For example, a negative electrode active material, a dicarboxylic acid, a binding material and a solvent such as water are mixed together to prepare a negative electrode composite material slurry for the lower half region 42a. In addition, separate from the slurry, the negative electrode active material, the binding material, and the dicarboxylic acid as required are mixed together with a solvent such as water to prepare a negative electrode composite material slurry for the upper half region 42b. It should be noted that when a dicarboxylic acid is added to the negative electrode composite material slurry for the upper half region 42b, the content of the dicarboxylic acid in the slurry is adjusted to be less than the content of the dicarboxylic acid in the negative electrode composite material slurry for the lower half region 42a. Then, the negative electrode composite material slurry for the lower half region 42a is applied to both sides of the negative electrode collector 40, and after drying, the negative electrode composite material slurry for the upper half region 42b is applied to the coating formed by the negative electrode composite material slurry for the lower half region 42a, and dried, thereby forming the negative electrode composite material layer 42. In the above method, after the negative electrode composite material slurry for the lower half area 42a is applied and dried, the negative electrode composite material slurry for the upper half area 42b is applied. However, the negative electrode composite material slurry for the upper half area 42b may be applied after the negative electrode composite material slurry for the lower half area 42a is applied and before drying, or the negative electrode composite material slurry for the lower half area 42a and the negative electrode composite material slurry for the upper half area 42b may be applied at the same time.

[0058] The drying temperature of the negative electrode composite material slurry is preferably, for example, lower than the temperature at which the dicarboxylic acid decomposes / gasifies (e.g., sublimates). In the present disclosure, it is not prohibited to set the drying temperature of the negative electrode composite material slurry to be above the temperature at which the dicarboxylic acid decomposes / gasifies, but when drying is performed at a temperature above the temperature at which the dicarboxylic acid decomposes / gasifies, it is necessary to prevent the dicarboxylic acid from completely disappearing from the negative electrode composite material layer 42.

[0059] For the mixing of raw materials when obtaining the negative electrode composite material slurry, for example, a shredder, a pin mill, a bead mill, a microparticle compounding device (a device that generates a shear force between a rotor with a special shape rotating at high speed inside a tank and a collision plate), a granulator, a twin-screw extruder mixer, a planetary mixer and the like can be listed.

[0060] The negative electrode composite material slurry is applied using, for example, a slot die coater, a reverse roll coater, a lip coater, a blade coater, a knife coater, a gravure coater, a dip coater, or the like.

[0061] The coating film is rolled, for example, by rolling the coating film several times at a predetermined linear pressure using a roll press until the coating film reaches a predetermined thickness.

[0062] [positive electrode]

[0063] The positive electrode 11 is composed of, for example, a positive electrode current collector such as a metal foil and a positive electrode composite material layer formed on the positive electrode current collector. The positive electrode current collector can be made of a foil of a metal such as aluminum that is stable within the potential range of the positive electrode, or a film in which the metal is arranged on the surface. The positive electrode composite material layer includes, for example, a positive electrode active material, a binding material, a conductive material, and the like.

[0064] The positive electrode 11 can be produced, for example, by applying a positive electrode composite material slurry containing a positive electrode active material, a binding material, a conductive material, etc. on a positive electrode collector, drying it to form a positive electrode composite material layer, and then performing a compression process of compressing the positive electrode composite material layer using a calender roller, etc., so as to produce it.

[0065] Examples of positive electrode active materials include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Lithium transition metal oxides are, for example, Li x CoO2、Li x NiO2、Li x MnO2、Li x Co y Ni 1-y O2、Li x Co y M 1-y O z , Li x Ni 1- y My O z , Li x Mn2O4、Li x Mn 2-y M y O4, LiMPO4, Li2MPO4F (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0<x≤1.2, 0<y≤0.9, 2.0≤z≤2.3). These can be used alone or in combination. From the perspective of achieving a high capacity of the secondary battery, the positive electrode active material preferably contains Li x NiO2、Li x Co y Ni 1-y O2、Li x Ni 1-y M y O z Lithium nickel composite oxides such as (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x≤1.2, 0<y≤0.9, 2.0≤z≤2.3).

[0066] Examples of the conductive material include carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphite and other carbon particles, etc. These may be used alone or in combination of two or more.

[0067] Examples of the binder include fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (which may be PAA-Na, PAA-K, etc., or partially neutralized salts), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0068] [Separator]

[0069] The separator 13 may be made of, for example, a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, nonwoven fabrics, and the like. Suitable materials for the separator 13 include olefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. In addition, it may be a multilayer separator comprising a polyethylene layer and a polypropylene layer, or a separator having a surface coated with materials such as an aramid resin and ceramics. Specific embodiments

[0071] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to the following examples.

[0072] <Example>

[0073] [Production of negative electrode]

[0074] Graphite particles were mixed in an amount of 90 parts by mass and Si-containing materials were mixed in an amount of 10 parts by mass to form a negative electrode active material. 98 parts by mass of negative electrode active material, 1 part by mass of carboxymethyl cellulose, 1 part by mass of styrene-butadiene rubber, and 1.46 parts by mass of fumaric acid were mixed and mixed with any water to prepare a negative electrode composite material slurry for the lower half region. In addition, 98 parts by mass of the above negative electrode active material, 1 part by mass of carboxymethyl cellulose, 1 part by mass of styrene-butadiene rubber, and 0.72 parts by mass of fumaric acid were mixed and mixed with any water to prepare a negative electrode composite material slurry for the upper half region.

[0075] The negative electrode composite material slurry for the lower half area is applied to both sides of the copper foil. After the coating is dried, the negative electrode composite material slurry for the upper half area is applied on the coating, dried, and the coating is rolled by a calendering roller, thereby producing a negative electrode having a negative electrode composite material layer formed on both sides of the negative electrode collector. The coating thickness of each negative electrode composite material slurry is set to the same thickness. In addition, the drying temperature is set to 150°C to suppress the sublimation of fumaric acid. Therefore, it is estimated that the content of fumaric acid in the lower half area (C A ) is the same as the fumaric acid content in the solid content of the negative electrode composite material slurry used in the lower half region, which is 1.46 mass %. In addition, it is estimated that the fumaric acid content in the upper half region (C B ) has the same fumaric acid content in the solid content of the negative electrode composite material slurry as that used in the upper half region, which is 0.72 mass %.

[0076] <Comparative Example 1>

[0077] 98 parts by mass of the above-mentioned negative electrode active material, 1 part by mass of carboxymethyl cellulose, and 1 part by mass of styrene-butadiene rubber were mixed and mixed with any water to prepare a negative electrode composite material slurry. The negative electrode composite material slurry was coated on both sides of a copper foil, and after the coating film was dried, the coating film was rolled by a calendering roller, thereby preparing a negative electrode having a negative electrode composite material layer formed on both sides of the negative electrode current collector. The content of fumaric acid in the lower half of the negative electrode composite material layer (C A ) and the fumaric acid content in the upper part (C B ) are all 0 mass %.

[0078] <Comparative Example 2>

[0079] The negative electrode was prepared in the same manner as in Example 1 except that the negative electrode composite material slurry used in Comparative Example 1 was used as the negative electrode composite material slurry for the lower half region and the amount of fumaric acid added in the preparation of the negative electrode composite material slurry for the upper half region was set to 0.75 parts by mass. A ) is 0 mass %, and the content of fumaric acid in the upper half region (C B ) is 0.75 mass %.

[0080] <Comparative Example 3>

[0081] 98 parts by mass of the above-mentioned negative electrode active material, 1 part by mass of carboxymethyl cellulose, 1 part by mass of styrene-butadiene rubber, and 1.57 parts by mass of fumaric acid were mixed and mixed with any water to prepare a negative electrode composite material slurry. The negative electrode composite material slurry was applied to both sides of the copper foil, and after the coating film was dried, the coating film was rolled by a calendering roller, thereby producing a negative electrode having a negative electrode composite material layer formed on both sides of the negative electrode collector. The drying temperature was set to 150°C to suppress the sublimation of fumaric acid. Therefore, the content of fumaric acid in the lower half of the negative electrode composite material layer (C A ) and the fumaric acid content in the upper part (C B ) were all 1.57 mass %.

[0082] [Interface resistance (Ω·cm 2 )]

[0083] The interface resistance (Ω·cm) between the negative electrode composite material layer and the negative electrode current collector in each negative electrode of Example and Comparative Examples 1 and 2 was measured using an electrode resistance measurement system RM2610 manufactured by HIOKI Corporation. 2 The principle of measuring the interface resistance is based on Japanese Patent Application Publication No. 2016-27311. Table 1 summarizes the results of the interface resistance between the negative electrode composite material layer and the negative electrode current collector in each negative electrode of Example and Comparative Examples 1 and 2.

[0084] [Table 1]

[0085]

[0086] [Measurement of Binding Strength (Adhesion Strength) Between Particles of Negative Electrode Active Material]

[0087] The adhesion (closed force) between the particles of the negative electrode active material in the negative electrode composite material layer of each negative electrode in the embodiment, comparative example 1, and 3 was measured using a viscosity tester TAC-II manufactured by RHESCA CO., LTD. The specific measurement conditions are as follows. The prepared negative electrode was cut into a specified size (2cm×3cm) as a test sample. Then, a double-sided tape #515 manufactured by Nitto Corporation was attached to the front end of a metal rod with a bonding area of ​​2mmφ, and it was pressed on the test sample with a preload of 400gf for 10 seconds, and then peeled off at a speed of 600mm / min. At this time, a part of the particles of the negative electrode active material will be adhered to the surface of the aforementioned tape, and the particles of the negative electrode active material in the negative electrode composite material layer will be pulled apart and peeled off. The stress required for peeling at this time is taken as the adhesion (closed force) between the particles of the negative electrode active material in the negative electrode composite material layer. Table 2 summarizes the results of the binding force (closed force) between the particles of the negative electrode active material in the negative electrode composite material layer in each negative electrode of the embodiment and comparative examples 1 and 3. In Table 2, the value of the binding force (closed force) between the particles of the negative electrode active material of comparative example 1 is used as a reference (100), and the values ​​of the binding force (closed force) between the particles of the negative electrode active material of other embodiments and comparative example 3 are expressed as relative values.

[0088] [Table 2]

[0089]

[0090] In the negative electrode composite material layer, the content of the dicarboxylic acid component in the lower half region (C A ) and the content of dicarboxylic acid components in the upper half (C B ) satisfies C A >C B Compared with Comparative Example 1 not containing a dicarboxylic acid component, the interface resistance between the negative electrode composite material layer and the negative electrode current collector is reduced, and the bonding force (adhesion force) between the particles of the negative electrode active material in the negative electrode composite material layer is the same. It should be noted that the embodiment satisfying C A <C B Compared with Comparative Example 1, the interface resistance between the negative electrode composite material layer and the negative electrode current collector was not reduced and was the same as that of Comparative Example 2. In addition, both the lower half region and the upper half region contain dicarboxylic acid components but satisfy C A =C B In Comparative Example 3, which shows a relationship of , the binding force (adhesion force) between the negative electrode active material particles in the negative electrode composite material layer is also reduced by 15% compared with Comparative Example 1.

[0091] [appendix] (1)

[0093] A negative electrode for a secondary battery, comprising: a negative electrode current collector and a negative electrode composite material layer disposed on the negative electrode current collector.

[0094] The negative electrode composite material layer comprises: a negative electrode active material and a dicarboxylic acid component including at least one of a dicarboxylic acid and an anhydride thereof.

[0095] When the negative electrode mixture layer is divided into two equal parts in the thickness direction into a lower half region on the negative electrode current collector side and an upper half region on the surface side, the content of the dicarboxylic acid component in the lower half region (C A ) and the content of the dicarboxylic acid component in the region of the upper half (C B ) satisfies C A >C B relationship. (2)

[0097] The secondary battery negative electrode according to (1) above, wherein the content (C B ) relative to the content of the dicarboxylic acid component in the lower half region (C A ) ratio (C B / C A ) is greater than or equal to 0 and less than or equal to 0.7. (3)

[0099] The secondary battery negative electrode according to (2) above, wherein the content of the dicarboxylic acid component in the upper half region (C B ) relative to the content of the dicarboxylic acid component in the lower half region (C A ) ratio (C B / C A ) is greater than or equal to 0 and less than or equal to 0.5. (4)

[0101] The secondary battery negative electrode according to any one of (1) to (3), wherein the content of the dicarboxylic acid component in the lower half region (C A ) is 0.1 mass % or more and 2 mass % or less. (5)

[0103] The secondary battery negative electrode according to any one of (1) to (4), wherein the content of the dicarboxylic acid component in the lower half region (C A ) is 0.4 mass % or more and 1.5 mass % or less. (6)

[0105] The secondary battery negative electrode according to any one of (1) to (5), wherein the content (C B ) is 0 mass % or more and 1.4 mass % or less. (7)

[0107] The secondary battery negative electrode according to any one of (1) to (6) above, wherein the dicarboxylic acid is an unsaturated dicarboxylic acid. (8)

[0109] The secondary battery negative electrode according to any one of (1) to (7) above, wherein the negative electrode active material comprises a graphite material and a Si-containing material. (9)

[0111] The secondary battery negative electrode according to the above (7), wherein the unsaturated dicarboxylic acid includes at least any one of fumaric acid, mesaconic acid, and methylenesuccinic acid. (10)

[0113] A negative electrode for a secondary battery according to any one of (1) to (9) above, wherein the Si-containing material comprises at least any one of a first composite particle, a second composite particle and a third composite particle, wherein the first composite particle has a carbon phase and a silicon phase dispersed in the carbon phase, the second composite particle has a silicate phase and a silicon phase dispersed in the silicate phase, and the third composite particle has a silicon oxide phase and a silicon phase dispersed in the silicon oxide phase. (11)

[0115] The negative electrode for a secondary battery according to the above (10), wherein the silicate phase of the second composite particle contains a compound of the formula: Li 2z SiO (2+z) Lithium silicate phase shown by (0<z<2). (12)

[0117] A secondary battery comprising the secondary battery negative electrode according to any one of (1) to (11) above.

[0118] Description of Reference Numerals

[0119] 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 battery casing, 16 casing body, 17 sealing body, 18, 19 insulating plate, 20 positive electrode lead, 21 negative electrode lead, 22 bulge, 23 partially opened metal plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cover, 28 gasket, 40 negative electrode collector, 42 negative electrode composite material layer, 42a lower half area, 42b upper half area.

Claims

1. A negative electrode for a secondary battery, comprising: a negative electrode current collector and a negative electrode composite material layer disposed on the negative electrode current collector, The negative electrode composite material layer comprises: a negative electrode active material and a dicarboxylic acid component including at least one of a dicarboxylic acid and an anhydride thereof. When the negative electrode composite material layer is divided into two equal parts in the thickness direction into a lower half region on the negative electrode current collector side and an upper half region on the surface side, the content C of the dicarboxylic acid component in the lower half region is A The content C of the dicarboxylic acid component in the upper half region B Satisfy C A >C B relationship.

2. The negative electrode for a secondary battery according to claim 1, wherein The content C of the dicarboxylic acid component in the upper half region B The content C of the dicarboxylic acid component in the lower half region A Ratio C B / C A It is greater than or equal to 0 and less than or equal to 0.

7.

3. The negative electrode for a secondary battery according to claim 2, wherein: The content C of the dicarboxylic acid component in the upper half region B The content C of the dicarboxylic acid component in the lower half region A Ratio C B / C A It is greater than or equal to 0 and less than or equal to 0.

5.

4. The negative electrode for a secondary battery according to any one of claims 1 to 3, wherein The content C of the dicarboxylic acid component in the lower half region A It is 0.1 mass % or more and 2 mass % or less.

5. The negative electrode for a secondary battery according to any one of claims 1 to 3, wherein The content C of the dicarboxylic acid component in the lower half region A It is 0.4 mass % or more and 1.5 mass % or less.

6. The negative electrode for a secondary battery according to any one of claims 1 to 3, wherein The content C of the dicarboxylic acid component in the upper half region B It is 0 mass % or more and 1.4 mass % or less.

7. The negative electrode for a secondary battery according to any one of claims 1 to 3, wherein The dicarboxylic acid is an unsaturated dicarboxylic acid.

8. The negative electrode for a secondary battery according to any one of claims 1 to 3, wherein The negative electrode active material includes a graphite material and a Si-containing material.

9. The negative electrode for a secondary battery according to claim 7, wherein The unsaturated dicarboxylic acid includes at least any one of fumaric acid, mesaconic acid, and methylene succinic acid.

10. The negative electrode for a secondary battery according to any one of claims 1 to 3, wherein The Si-containing material includes at least any one of a first composite particle, a second composite particle, and a third composite particle, wherein the first composite particle has a carbon phase and a silicon phase dispersed in the carbon phase, the second composite particle has a silicate phase and a silicon phase dispersed in the silicate phase, and the third composite particle has a silicon oxide phase and a silicon phase dispersed in the silicon oxide phase.

11. The negative electrode for a secondary battery according to claim 10, wherein The silicate phase of the second composite particle comprises the formula: Li 2z SiO (2+z) The lithium silicate phase shown, wherein 0<z<2. 12 . A secondary battery comprising the negative electrode for a secondary battery according to claim 1 .

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