Electrode and secondary battery

Abstract

The purpose of the present invention is to provide: an electrode, especially a negative electrode, that has excellent rate characteristics when applied in a battery; and a battery comprising the electrode.　The present invention is a negative electrode including a current collector and an active material layer that is provided to the surface of the current collector and contains an active material, a conduction auxiliary agent, and a binder, wherein the negative electrode is characterized in that: the active material contains non-spherical particles; and the diffraction intensity ratio I(002) / I(110) of the peak intensity I(002) on the 002 plane and the peak intensity I(110) on the 110 plane as observed in X-ray diffraction of the active material layer, is 100-300.

Description

Anodes and secondary batteries

[0001] The present invention relates to a negative electrode and a secondary battery.

[0002] Electrodes used in lithium-ion batteries and the like have an electrode active material layer formed on a current collector. There are many methods for forming an active material on a current collector when producing an electrode. However, these methods can be broadly divided into wet methods and dry methods, depending on whether or not the electrode mixture containing the active material is slurried. In the wet method, an active material, a polymer, a solvent, and the like are mixed to obtain a slurry, and the resulting slurry is applied to a current collector and dried to form an electrode. On the other hand, in the dry method, an electrode is formed without undergoing a step of applying a slurry of a solvent and an active material. For example, an electrode is formed by forming granules containing the active material in advance and pressing them onto a current collector.

[0003] Patent Document 1 discloses a technique in which granules containing an active material are formed in advance and then transferred onto a current collector. Patent Document 1 describes mixing granulated powder with flat active material particles and specifying the particle size and aspect ratio of the flat active material particles in order to prevent poor formation of an active material layer using the granulated powder. Patent Document 2 also discloses an invention in which a magnetic field is applied before pressing to orient elongated graphite in the electrode mixture substantially perpendicular to the current collector foil in order to prevent excessive densification of the electrode mixture layer even when high-pressure pressing is performed and to increase peel strength.

[0004] JP 2016-100127 A JP 2013-131379 A

[0005] In order to meet the demand for rapid charge / discharge in lithium-ion secondary batteries, it is desirable to use electrodes with excellent rate characteristics, i.e., electrodes that can withstand large current charge / discharge. Patent Document 1 describes how mixing flat graphite particles with granules prevents agglomeration and produces a homogeneous electrode, adjusting the spacing between the rolling rolls to adjust the desired thickness and porosity of the active material layer. However, the electrode disclosed in Patent Document 1 may not sufficiently improve its rate characteristics. Patent Document 2 also applies pressure preferentially to elongated graphite particles oriented approximately perpendicular to the current collector foil to prevent the electrode mixture from being crushed. However, the method disclosed in Patent Document 2 does not apply pressure to particles other than those oriented perpendicularly, which may result in the granules falling off the active material layer or current collector foil. Therefore, it is presumed that the electrode disclosed in Patent Document 2 also has insufficient rate characteristics.

[0006] The inventors have conducted studies and found that in a negative electrode including an active material layer using granules composed of an active material containing non-spherical particles, a conductive additive, and a binder, by appropriately adjusting the orientation of the active material, it is possible to obtain a negative electrode with good rate characteristics in which the active material layer is less likely to fall off from the current collector.

[0007] The present invention has been made in view of the above circumstances, and provides a negative electrode having an active material layer that has high adhesion to a current collector, and a secondary battery that uses the negative electrode and has good rate characteristics.

[0008] That is, the present invention provides the following anode and secondary battery: 1. An anode comprising: a current collector; and an active material layer provided on the surface of the current collector, the active material layer including an active material, a conductive additive, and a binder, wherein the active material comprises non-spherical particles, and wherein the active material layer has a diffraction intensity ratio I(002) / I(110) of a peak intensity I(002) in the 002 plane to a peak intensity I(110) in the 110 plane measured by X-ray diffraction method, the diffraction intensity ratio I(002) / I(110) being 100 or more and 300 or less.

[0009] 2. A secondary battery in which a plurality of negative electrodes and positive electrodes described in 1 above are stacked with separators interposed therebetween, optionally wound together, and housed in an outer container, and a positive electrode terminal electrically connected to the positive electrode and a negative electrode terminal electrically connected to the negative electrode are drawn out from the outer container.

[0010] According to the present invention, it is possible to provide a secondary battery having good rate characteristics and a negative electrode used therein.

[0011] Hereinafter, an embodiment of the present invention will be described.

[0012] One embodiment of the present invention is a negative electrode including a current collector and an active material layer provided on a surface of the current collector, the active material layer including an active material, a conductive additive, and a binder, wherein the active material includes non-spherical particles, and the active material layer has a diffraction intensity ratio I(002) / I(110) of a peak intensity I(002) in the 002 plane to a peak intensity I(110) in the 110 plane measured by X-ray diffraction method, I(002) / I(110), of 100 to 300.

[0013] In one embodiment, the negative electrode refers to, but is not particularly limited to, a negative electrode used in a non-aqueous secondary battery material. The negative electrode is composed of a current collector and an active material layer provided on the surface of the current collector, and the active material layer includes an active material, a conductive additive, and a binder. The current collector can be made of metal, such as copper, nickel, titanium, or stainless steel. The current collector is preferably made of a planar metal, particularly a metal foil. The current collector will be described in detail below.

[0014] In one embodiment, the active material includes non-spherical particles. "Non-spherical" generally refers to shapes that are not spherical. While not all active material particles are necessarily non-spherical, they may be. The active material particles may include both spherical and non-spherical particles. A carbon-based active material can be used as the active material. Examples of the carbon-based active material include natural graphite, artificial graphite, hard carbon, soft carbon, carbon black, and any mixture thereof. Natural graphite includes natural graphite particles coated with amorphous carbon, while artificial graphite includes artificial graphite particles coated with amorphous carbon. These natural graphite and artificial graphite particles may be primary particles, particles formed by agglomeration of primary particles to form secondary particles, or mixtures thereof. The negative electrode active material may also be a mixture of a carbon-based active material and a silicon-based active material. The negative electrode active material may include metal materials such as aluminum, lithium, silver, bismuth, calcium, cerium, indium, magnesium, tin, zinc, and nickel. The negative electrode active material will be described in detail later.

[0015] The conductive additive is a material for reducing the resistance of the electrode. Examples of the conductive additive include carbon black such as acetylene black and ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, carbon nanotubes, carbon nanofibers, carbon nanobrushes, and other carbon fibers. The conductive additive will be described in detail later.

[0016] Examples of binders include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF); conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin. In addition, the binder may be polyacrylic acid, polymethacrylic acid, lithium polyacrylate, sodium polyacrylate, potassium polyacrylate, sodium polymethacrylate, potassium polymethacrylate; polyethyl acrylate, polyethyl acrylate, polybutyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polyacrylamide, polyacrylonitrile, or any mixture thereof. Furthermore, the binder may be a cellulose derivative, such as carboxymethyl cellulose (hereinafter referred to as "CMC"), or a metal salt of carboxymethyl cellulose (e.g., sodium carboxymethyl cellulose, potassium carboxymethyl cellulose). Binders will be described in detail below.

[0017] In one embodiment, the active material layer is composed of granules. The granules include an active material, a conductive additive, and a binder, and are aggregates of these. In one embodiment, the active material layer has the following characteristic: the diffraction intensity ratio I(002) / I(110) of the peak intensity I(002) in the 002 plane to the peak intensity I(110) in the 110 plane, as measured by X-ray diffraction, is 100 or more and 300 or less. Here, X-ray diffraction is a method of irradiating a material with monochromatic X-rays using CuKα rays as an X-ray source and measuring the spectrum of the scattered X-rays, and peaks specific to the structure of the material irradiated with X-rays are observed. In one embodiment, X-rays are incident on the active material layer, and the scattered X-ray spectrum is measured, focusing on the intensities of the (002) plane diffraction peak detected at a diffraction angle 2θ of approximately 26 to 27 degrees and the (110) plane diffraction peak detected at a diffraction angle 2θ of approximately 70 to 80 degrees. Focus is placed on the ratio of the peak intensity I(002) in the (002) plane to the peak intensity I(110) in the (110) plane. The diffraction intensity ratio I(002) / I(110) is preferably 100 or more and 300 or less. A diffraction intensity ratio I(002) / I(110) of 100 or more and 300 or less means that the granules constituting the active material layer are not excessively oriented. Maintaining the number of voids (paths) that connect the current collector, which serves as a path for lithium ions, to the surface of the active material layer is important for improving the rate characteristics of a secondary battery using the negative electrode of one embodiment.

[0018] To obtain an active material layer having a structure that exhibits the above-described diffraction intensity ratio observed by X-ray diffraction, it is preferable to first form granules in which the active material, conductive additive, and binder are aggregated, and then laminate the granules on a current collector to form the active material layer. Here, the granules refer to particles (granules) obtained by aggregating a mixture of the active material, conductive additive, binder, and, optionally, a solvent. In one embodiment, the active material layer used in the negative electrode is formed by applying granules in which the active material, conductive additive, and binder are aggregated to the surface of the current collector using a dry coating method. After forming the granules, the active material layer can be pressed to obtain the desired density by appropriately adjusting the pressing conditions. It is believed that the granules gradually break down during pressing of the active material layer, preventing excessive orientation of the active material particles. Compared to an active material layer formed by a wet coating method using a slurry containing a mixture of an active material, a conductive additive, and a binder, the active material layer in one embodiment formed using granules has a larger or similar number of pore paths extending in the thickness direction of the active material layer. The length of the pore paths can also be adjusted by changing the pressing conditions, such as the number of presses and pressure, while keeping the particle size of the active material and the amount of binder the same (i.e., using the same granules). Even in an active material layer formed using granules, if the density is increased without adjusting the pressing conditions, the granules will be crushed back to the original active material particle state, resulting in the orientation of the active material. This will result in a deterioration in the rate characteristics of a secondary battery using a negative electrode containing such an active material layer.

[0019] The average particle size of the granules is preferably 15 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more, and is preferably 90 μm or less, more preferably 80 μm or less, and even more preferably 70 μm or less. In one embodiment, the average particle size of the granules means the particle size at 50% of the integrated value (median size: D50) in the particle size distribution (volume basis) measured by a laser diffraction scattering method.

[0020] From the viewpoint of adhesion of the conductive additive to the active material surface, the average particle size of the active material particles is preferably 1.0 μm or more, more preferably 1.5 μm or more, and even more preferably 2.0 μm or more. It is also preferably 20.0 μm or less, more preferably 10.0 μm or less, and even more preferably 5.0 μm or less. In one embodiment, the average particle size of the active material particles refers to the particle size at 50% of the integrated value (median diameter: D50) in the particle size distribution (volume basis) measured by a laser diffraction scattering method.

[0021] The negative electrode active material includes a carbon-based active material. The carbon-based active material is preferably natural graphite, artificial graphite, hard carbon, soft carbon, or any mixture thereof. Here, graphite is a carbon material with hexagonal plate-like crystals and is sometimes called graphite. Natural graphite and artificial graphite include natural graphite coated with amorphous carbon and artificial graphite coated with amorphous carbon.

[0022] Here, amorphous carbon refers to a carbon material that is amorphous as a whole and has a random network structure of microcrystals, which may partially have a structure similar to graphite. Examples of amorphous carbon include carbon black, coke, activated carbon, carbon fiber, carbon nanotubes, hard carbon, soft carbon, and mesoporous carbon. When using artificial graphite, it is preferable that the interlayer distance d value (d002) is 0.33 nm or more.

[0023] The crystalline structure of artificial graphite is generally thinner than that of natural graphite. When artificial graphite is used as a negative electrode active material for nonaqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, it must have an interlayer distance that allows lithium ions to be inserted. The interlayer distance that allows lithium ions to be inserted and removed can be estimated by the d value (d002), and if the d value is 0.33 nm or more, lithium ions can be inserted and removed without any problems. In addition, the negative electrode active material may include a silicon-based active material (A) containing SiOx (where x is a number that satisfies 0.5≦x≦1.6) and a carbon-based active material.

[0024] The aspect ratio of the negative electrode active material is preferably 1.1 or more and 5 or less. Creating granules primarily composed of a negative electrode active material with an aspect ratio within this range facilitates adjusting the orientation of the active material layer through the pressing conditions, resulting in stable electrical characteristics of secondary batteries using negative electrodes with an active material layer with such adjusted orientation. When the aspect ratio of the negative electrode active material is less than 1.1, the active material particles are packed too densely, making it impossible to adjust the orientation of the active material layer. This makes it difficult to obtain excellent rate characteristics in secondary batteries using such negative electrodes. On the other hand, when granules are formed using an active material with an aspect ratio greater than 5, adjusting the pressing conditions to achieve the desired density tends to result in excessively long path lengths in the active material layer, resulting in poor rate characteristics in secondary batteries using such negative electrodes, regardless of how much the orientation is adjusted. The orientation of the active material layer can be determined by the diffraction intensity ratio I(002) / I(110) of the active material layer. The diffraction intensity ratio I(002) / I(110) of the active material layer is more preferably 50 or more, and even more preferably 100 or more. The diffraction intensity ratio I(002) / I(110) of the active material layer is more preferably 300 or less, and even more preferably 125 or less. Note that as the anisotropy of the orientation of the active material layer increases, the diffraction intensity I(002) decreases and the diffraction intensity I(110) increases.

[0025] In one embodiment, when the total amount of the granules is 100 parts by mass, the content of the active material is preferably 95.0 parts by mass or more, more preferably 96 parts by mass or more, even more preferably 97 parts by mass or more, and preferably 99.5 parts by mass or less, more preferably 99.0 parts by mass or less, and even more preferably 98.5 parts by mass or less. The proportion of the active material involved in forming the granules is at least 95% or more, preferably 97% or more, and even more preferably 99% or more.

[0026] The conductive additive preferably includes at least one selected from the group consisting of carbon black, carbon nanofibers, and carbon nanotubes. The carbon black used as the conductive additive preferably has an aggregate structure in which nanoparticle-sized carbons are linked together like beads. Examples of carbon black that can be used include acetylene black and ketjen black. The conductive additive can also be carbon nanotubes, which are formed from a substance composed of carbon atoms, such as graphene, into a cylindrical shape with a diameter of several nanometers and a length of several millimeters. In particular, bundles of single-walled carbon nanotubes, each of which has a substantially single layer around the cylinder, or multi-walled carbon nanotubes, each of which has multiple layers around the cylinder, can be used.

[0027] In one embodiment, when the total amount of the granules is 100 parts by mass, the content of the conductive additive is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.3 parts by mass or more, and preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, even more preferably 0.5 parts by mass or less.

[0028] In one embodiment, the granules further contain a binder. Preferably, the conductive additive and binder are present on the surface of the active material particles, and the binder and conductive additive are present on the surface and inside of the granules. In this way, when the granules are pressed, the pores between the active material particles are not excessively crushed or oriented, and a desired density can be obtained.

[0029] The binder may include, for example, polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polytetrafluoroethylene, polyimide, polyamideimide, polyamide, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyvinyl alcohol, polyvinyl butyral, or two or more of these, but is not limited to these, and can be changed appropriately depending on the solvent.

[0030] In one embodiment, when the total amount of the granules is 100 parts by mass, the content of the binder is preferably 0.5 parts by mass or more, more preferably 0.7 parts by mass or more, even more preferably 1.0 part by mass or more, and preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 2.0 parts by mass or less.

[0031] A method for producing a negative electrode according to one embodiment preferably includes the steps of spraying a dispersion of a conductive additive onto the active material particles while mixing and stirring the active material particles to form granules, and placing the granules on a current collector and pressing them. The method for forming the granules is not particularly limited, and examples include spray granulation, agitation granulation, fluidized bed granulation, rolling granulation, extrusion granulation, and compression granulation. These granulation methods may be selected or combined as desired. Examples of spray granulation methods include spray-drying granulation. In the spray-drying granulation method, for example, a dispersion of a negative electrode active material and a conductive additive is sprayed into high-temperature gas in a spray dryer to form granules. In the agitation granulation method, for example, a dispersion of a conductive additive is sprayed onto the negative electrode active material particles while mixing and stirring the negative electrode active material to form granules. The average particle size of the granulated particles is preferably 15 μm or more, more preferably 20 μm or more, even more preferably 40 μm or more, and preferably 90 μm or less, more preferably 80 μm or less, and even more preferably 70 μm or less. The average particle size of the granulated particles refers to the particle size at 50% of the integrated value (median diameter: D50) in the particle size distribution (volume basis) measured by a laser diffraction scattering method. By adjusting the number of times and pressure of pressing the active material layer containing the granules thus formed, it is possible to obtain high adhesion between the current collector and the active material layer, maintain the desired pore paths between the active material particles, and obtain the desired electrode density.

[0032] By applying a dispersion containing a highly dispersed conductive additive and binder to active material particles without the addition of other organic solvents, an active material with a uniformly dispersed conductive additive on its surface can be prepared. The diameter of the granules formed varies depending on the equipment used to mix and stir these materials, but it can be controlled by adjusting the amount and timing of spraying the dispersion of conductive additive and binder, as well as the mixing and stirring times. In addition, by classifying the formed granules through a sieve, it is possible to obtain granules with any particle size distribution.

[0033] In one embodiment, the material of the current collector is not particularly limited, but when the current collector is a positive electrode current collector, aluminum foil is preferred. When the current collector is a negative electrode current collector, a material selected from the group consisting of copper, stainless steel, nickel, titanium, or an alloy thereof is preferred, with copper being particularly preferred. The shape of the current collector layer is not particularly limited, and may be foil, flat, or mesh-like. For example, the thickness is 0.001 mm or more and 0.5 mm or less.

[0034] When granules are placed on the surface of a current collector or a current collector and pressed, the pressing method is not particularly limited as long as it can form electrode granules containing an electrode active material on the current collector. In one embodiment, a roll-type pressure molding method is preferably used. In the roll-type pressure molding method, a long current collector is arranged so that the current collector passes between a pair of rolls while the current collector is unwound from a rolled body and wound up. The granules are supplied onto the current collector before passing through the rolls and compressed as they pass between the rolls to form an electrode sheet. To adjust the amount of granules supplied, it is preferable to smooth the surface with a squeegee or the like before supplying the granules between the rolls to increase their thickness. It is preferable to previously form a current collector surface layer containing a binder to enhance adhesion to the granules on the current collector. By adjusting the number of times, pressure, temperature, etc., of pressing the electrode sheet, it is possible to adjust the adhesion between the active material layer and the current collector and the length of the voids between the active material particles.

[0035] A second embodiment of the present invention is a secondary battery in which a plurality of the above-described negative electrodes and positive electrodes are stacked with a separator interposed therebetween, optionally wound, and housed in an outer container, with a positive electrode terminal electrically connected to the positive electrode and a negative electrode terminal electrically connected to the negative electrode extending from the outer container. The secondary battery of the second embodiment can be fabricated using the above-described negative electrode according to a known method. In the second embodiment, the positive electrode refers to, but is not particularly limited to, a positive electrode used in a non-aqueous secondary battery material. For example, the positive electrode is composed of a positive electrode current collector and a positive electrode active material layer provided on the surface of the positive electrode current collector, and the active material layer includes a positive electrode active material, a conductive additive, and a binder. The positive electrode active material layer including the positive electrode active material, the conductive additive, and the binder can be formed on at least one surface of the positive electrode current collector. The positive electrode current collector can be stainless steel, aluminum, nickel, titanium, or a positive electrode current collector whose aluminum surface is surface-treated with carbon, nickel, titanium, or silver.

[0036] The positive electrode active material may be a composite oxide of lithium and a transition metal, such as lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-nickel-manganese composite oxide, lithium-nickel-cobalt composite oxide, lithium-nickel-aluminum composite oxide, lithium-nickel-cobalt-aluminum composite oxide, lithium-nickel-manganese-cobalt composite oxide, lithium-nickel-manganese-aluminum composite oxide, or lithium-nickel-cobalt-manganese-aluminum composite oxide; TiS, FeS, MoS ２ transition metal sulfides such as MnO, V ２ O ５ , V ６ O １３ , TiO ２and one or more transition metal oxides selected from the group consisting of olivine-type lithium phosphates. The olivine-type lithium phosphates contain, for example, one or more elements selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, Nb, and Fe, as well as lithium, phosphorus, and oxygen. These compounds may have some elements partially substituted with other elements to improve their properties. Among these, the positive electrode active material is preferably a Li-based phosphate having an average particle size of 3 to 15 μm. ａ Ni ｂ Mn ｃ Co ｄ M ｘ O ２ (wherein a, b, c, d, and x satisfy 0.9≦a≦1.2, 0<b<1, 0<c≦0.5, 0<d≦0.5, 0≦x≦0.3, and b+c+d=1, and M is at least one element selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr) is preferably used. Examples of binders that form the positive electrode and material layer together with the positive electrode active material include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF); conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin. Examples of conductive additives include carbon black such as acetylene black and ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, carbon fibers such as carbon nanofibers, carbon nanotubes, and carbon nanobrushes. In addition, electrode additives commonly used for electrode formation, such as thickeners, dispersants, and stabilizers, can be used appropriately in the positive electrode active material layer.

[0037] In the second embodiment, the separator may be, for example, a porous separator. The separator may be in the form of a membrane, a film, a nonwoven fabric, or the like. Examples of the porous separator include polyolefin-based porous separators such as polypropylene-based and polyethylene-based separators; and porous separators formed from polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride-hexafluoropropylene copolymer, or the like.

[0038] The separator may contain inorganic particles such as ceramic particles, or may further include a layer containing inorganic particles.

[0039] In the secondary battery of the second embodiment, a plurality of negative electrodes and positive electrodes are stacked with a separator interposed therebetween, optionally wound, and housed in an outer container. The secondary battery is formed by extending a positive electrode terminal electrically connected to the positive electrode and a negative electrode terminal electrically connected to the negative electrode from the outer container. The outer container can be, for example, a flexible film having a resin layer on both sides of a metal layer such as aluminum as a base material, or a metal can made of aluminum, iron, stainless steel, or the like. The positive electrode terminal can be made of aluminum or an aluminum alloy, and the negative electrode terminal can be made of copper, a copper alloy, or a nickel-plated copper or copper alloy.

[0040] The shape of the secondary battery according to the second embodiment may be, for example, a square, cylindrical, coin, or button shape housed in an outer container such as an aluminum can, an iron can, a stainless steel can, etc. A pouch-shaped secondary battery housed in an outer container mainly made of an aluminum film is also preferred.

[0041] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0042] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0043] <Production of Negative Electrode> (Examples 1 to 4 and Comparative Example 1) Separately from the formation of the conductive layer and adhesive layer, granulated particles for the negative electrode active material layer were prepared. A negative electrode dispersion was prepared by highly dispersing negative electrode active material particles, including artificial graphite with an average particle size of 12 μm and silicon monoxide with an average particle size of 5 μm, single-walled carbon nanotubes (SWCNT) as a conductive additive, and polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) as binders, together with a solvent. The negative electrode dispersion prepared by the above procedure was then sprayed into a spray dryer by rotating an atomizer at a predetermined rotation speed to obtain granules. The mass ratio of artificial graphite / silicon monoxide / SWCNT / PAA / SBR was 93.45:4.0:0.05:0.5:2.0. The artificial graphite was manufactured by Nippon Graphite Industries Co., Ltd., the PAA was manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., and the SWCNT was manufactured by OCSiAl.

[0044] Next, a predetermined amount of the resulting granules was applied to a current collector traveling from the unwinding side to the winding side of an electrode coater while smoothing the surface with a squeegee. An adhesive auxiliary layer containing carbon black and binders (CMC and SBR) had been previously formed on the surface of the current collector. After the granules were applied to the current collector, the amount of granules applied to the press roll was adjusted by the squeegee roll before the granules were compressed by the press roll. The granules were then passed through the press rolls to form an active material layer of the desired density. Negative electrodes with different diffraction intensity ratios I(002) / I(110) were prepared.

[0045] (Comparative Example 2) A slurry containing graphite as a negative electrode active material, acetylene black as a conductive additive, and styrene-butadiene copolymer rubber (SBR) as a binder was prepared, and the slurry was applied to copper foil as a negative electrode current collector using a die coater, dried, and then pressed with a roll press to a density of 1.65 g / cm ３ The graphite used was from Nippon Graphite Industries Co., Ltd. <Battery Production> As the positive electrode active material, LiNi ０．９２ Mn ０．０３ Co ０．０５ O ２The slurry containing carbon black as a conductive additive and polyvinylidene fluoride (PVDF) as a binder was applied to an aluminum foil as a positive electrode current collector, and then pressed to a density of 3.5 g / cm ３ A positive electrode of 1000 .mu.m was obtained.

[0046] The eight positive electrode layers and nine negative electrode layers of each of the previously obtained examples or comparative examples were stacked via a polyolefin-based porous separator, and a negative electrode terminal electrically connected to each negative electrode and a positive electrode terminal electrically connected to each positive electrode were provided to obtain a laminate. Next, a mixed solvent of ethylene carbonate and diethyl carbonate (ethylene carbonate:diethyl carbonate=3:7 (volume ratio)) was added with LiPF as an electrolyte. ６ The electrolyte solution in which the above was dissolved to a concentration of 1.0 mol / L was placed together with the obtained laminate in a container with a flexible film as a case, and the container was sealed with the positive electrode terminal and the negative electrode terminal extended to the outside, thereby obtaining a secondary battery.

[0047] <Rate characteristics> The prepared battery was charged at a constant current of 0.2 C up to 4.2 V, and after reaching 4.2 V, the charge was switched to a constant voltage and charged down to 0.015 C, and discharged at a constant current of 0.2 C and 3 C down to 2.5 V, and the rate characteristics were determined as 3 C / 0.2 C, which is the ratio of the capacity at 2.5 V between the 3 C discharge and the 0.2 C discharge. Generally, the capacity tends to decrease more easily as the current value increases, so the closer the current value is to 100%, the better the rate characteristics are.

[0048] <Diffraction Intensity Ratio> The diffraction intensity ratio I (002) / I (110) was calculated, which is the ratio of the peak intensity I (002) in the 002 plane to the peak intensity I (110) in the 110 plane by X-ray diffraction of the active material layer. Using an X-ray diffractometer (SmartLab 9kW, Rigaku), the (002) and (110) diffraction peaks of the active material layers of the negative electrodes of the examples and comparative examples were measured, and the diffraction intensity ratio I (002) / I (110) was calculated from the respective peak top intensities. In the X-ray diffraction method, the X-ray source was CuKα ray / 40 KV / 20 mA, and the step width was 0.02 °.

[0049]

[0050] As shown in Table 1, secondary batteries (Examples 2, 3, and 4) using negative electrodes with active material layers having diffraction intensity ratios of 100 to 300 exhibited favorable rate characteristics. The rate characteristics of the secondary battery (Example 1) using a negative electrode with an active material layer having a diffraction intensity ratio of 50 were somewhat poor. This is presumably because the density of the active material layer after pressing could not be increased sufficiently to achieve a diffraction intensity ratio of 50 in the active material layer using the granules of the present invention, resulting in insufficient contact of the conductive additive between the active material particles and making it somewhat difficult to follow rapid charge / discharge. On the other hand, negative electrodes with active material layers having a diffraction intensity ratio of more than 400 have fewer paths perpendicular to the current collector surface and negative electrode surface, and relatively more paths parallel to the current collector surface and electrode surface. This is thought to have lengthened the path length of lithium ions and deteriorated the rate characteristics.

[0051] The electrode for a lithium ion secondary battery and the lithium ion secondary battery of the present invention have been described in detail above, but the present invention is not limited to the above-mentioned embodiments and examples, and various improvements and modifications may be made without departing from the spirit and scope of the present invention.

Claims

1. A negative electrode comprising: a current collector; and an active material layer provided on a surface of the current collector, the active material layer comprising an active material, a conductive additive and a binder; wherein the active material comprises non-spherical particles; and a diffraction intensity ratio I(002) / I(110) of a peak intensity I(002) in a 002 plane to a peak intensity I(110) in a 110 plane, as measured by an X-ray diffraction method, of the active material layer is 100 or more and 300 or less.

2. The negative electrode according to claim 1, wherein the active material layer includes granules in which the active material, the conductive additive, and the binder are aggregated.

3. The negative electrode according to claim 1 or 2, wherein the aspect ratio of the non-spherical particles is 1.1 or more and 5 or less.

4. A secondary battery in which the negative electrode according to any one of claims 1 to 3 and a positive electrode are stacked in multiple layers with a separator between them, optionally rolled up, and housed in an outer container, with a positive electrode terminal electrically connected to the positive electrode and a negative electrode terminal electrically connected to the negative electrode being pulled out from the outer container.

Images