Lithium ion secondary battery

Abstract

To provide a lithium ion secondary battery having a high output in a wide range from a low SOC to a high SOC, and excellent storage characteristics (a capacity retention ratio) while ensuring a battery capacity.SOLUTION: A lithium ion secondary battery includes a positive electrode and a negative electrode, and the negative electrode includes a current collector and a negative electrode active material layer provided on at least one surface of the current collector. The negative electrode active material layer has a negative electrode active material containing graphite particles (A) and graphite particles (B) carrying amorphous carbon fine particles. The number of amorphous carbon fine particles per unit area of the surface of the graphite particles (B) obtained based on a SEM observation image is 0.4 particles / μm2 or more in the graphite particles (B) carrying amorphous carbon fine particles. The graphite particles constituting the graphite particles (A) and the graphite particles (B) carrying the amorphous carbon fine particles are graphite particles coated with amorphous carbon, an average particle diameter of the amorphous carbon fine particles is 0.05 μm or more and 0.5 μm or less. One of the graphite particles (A) and the graphite particles (B) is an artificial graphite.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a lithium-ion secondary battery.

Background Art

[0002] In the automotive industry, fuel consumption regulations and environmental regulations are being strengthened in various countries and regions. To comply with these regulations, the technological development of electric vehicles powered by batteries that do not emit carbon dioxide and fuel cell vehicles powered by hydrogen as fuel sources has attracted attention. However, regarding electric vehicles, there are problems such as insufficient charging infrastructure and longer charging times compared to refueling. Regarding fuel cell vehicles, there are problems such as the need for a large amount of cost for infrastructure development of hydrogen stations and high costs of fuel cells. Therefore, PHEVs (Plug-in Hybrid Electric Vehicles) and HEVs (Hybrid Electric Vehicles) that use both an internal combustion engine and a battery as power sources and have low carbon dioxide emissions are strong candidates for meeting fuel consumption regulations and environmental regulations.

[0003] In PHEVs and HEVs, lithium-ion secondary batteries are generally used. Patent Document 1 describes a positive electrode active material containing lithium nickel manganese tungsten composite oxide particles having a hexagonal layered structure, which enables high capacity and high output of a lithium-ion secondary battery. Patent Document 2 describes that, as a negative electrode active material constituting a non-aqueous electrolyte secondary battery, it contains coated graphite particles in which the surface of the graphite particles is coated with a coating layer containing a first amorphous carbon and a second amorphous carbon, the second amorphous carbon particles are dispersed inside the layer made of the first amorphous carbon, the first amorphous carbon is a fired product of pitch, and the second amorphous carbon is carbon black, etc.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] In a PHEV or HEV, there is a need for a lithium-ion secondary battery that has a sufficient capacity retention rate and a small increase in resistance even in a region where the state of charge (SOC) is low, and can supply a stable output. The technologies described in Patent Documents 1 and 2 do not aim to improve the output in the low SOC region, and a technology for supplying a stable output is required.

[0006] The present invention has been made in view of such problems, and an object thereof is to provide a lithium-ion secondary battery that has a high output in a wide range from low SOC to high SOC while ensuring battery capacity and also has good storage characteristics (capacity retention rate). [Means for Solving the Problems]

[0007] As one aspect of the present embodiment, it includes a positive electrode and a negative electrode, the negative electrode has a current collector and a negative electrode active material layer provided on at least one surface of the current collector, the negative electrode active material layer has a negative electrode active material including graphite particles (A) and graphite particles (B) on which amorphous carbon fine particles are supported, the number of amorphous carbon fine particles per unit area of the surface of the graphite particles (B) on which the amorphous carbon fine particles are supported is 0.4 particles / μm 2 or more based on the SEM observation image, the graphite particles constituting the graphite particles (A) and the graphite particles (B) on which the amorphous carbon fine particles are supported are particles of graphite coated with amorphous carbon, the average particle diameter of the amorphous carbon fine particles is 0.05 μm or more and 0.5 μm or less, Examples of the lithium ion secondary battery include those in which either one of the graphite particles (A) and the graphite particles (B) is artificial graphite.

[0008] This specification incorporates the disclosure of Japanese Patent Application No. 2021-133832, which is the basis of the priority of this application.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a lithium ion secondary battery that has a high output in a wide range from a low state of charge (SOC) to a high SOC while ensuring the battery capacity and also has good storage characteristics.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described with reference to the drawings as appropriate. The following description shows specific examples of the content of the present invention, and the present invention is not limited to these descriptions, and various changes and modifications can be made by those skilled in the art within the scope of the technical idea disclosed in this specification. Also, in all the drawings for explaining the present invention, those having the same function are denoted by the same reference numerals, and the repeated description thereof may be omitted. In addition, the dimensional ratios in the drawings may be different from the actual ratios for convenience of explanation, and a part of the members may be omitted from the drawings. Further, in the present application, the numerical range represented by the symbol "~" includes the numerical values described before and after the symbol "~" as the lower limit value and the upper limit value, respectively.

[0012] The lithium-ion secondary battery 100 according to the embodiment shown in FIGS. 1 and 2 includes a battery can 1 and a battery lid 6. The battery can 1 includes a rectangular bottom surface 1d, a pair of relatively large opposing wide side surfaces 1b rising from the bottom surface 1d, a pair of relatively small opposing narrow side surfaces 1c, and a side surface including the narrow side surfaces 1c, and an opening 1a that is open upward at the upper ends of the wide side surfaces 1b and the narrow side surfaces 1c. Here, the upward direction means the Z direction in FIGS. 1 and 2.

[0013] The opening 1a of the battery can 1 is sealed by the battery lid 6. The battery lid 6 is in a substantially rectangular flat plate shape and is welded so as to close the opening 1a of the battery can 1 to seal the battery can 1.

[0014] A gas discharge valve 10 is integrally provided on the battery lid 6. When the pressure inside the battery can 1 rises, the gas discharge valve 10 cracks and gas is discharged from the inside of the battery can 1, and the pressure inside the battery can 1 decreases. Thereby, the safety of the lithium-ion secondary battery 100 is ensured.

[0015] A liquid injection port 9 for injecting an electrolytic solution into the battery can 1 is formed in the battery lid 6. The liquid injection port 9 is sealed by a liquid injection plug 11 after the electrolytic solution is injected into the battery can 1. The liquid injection plug 11 is joined to the battery lid 6 by laser welding to seal the liquid injection port 9 and seal the lithium-ion secondary battery 100.

[0016] A positive electrode side through hole 46 and a negative electrode side through hole 26 are further formed in the battery lid 6.

[0017] A positive electrode external terminal 14 and a negative electrode external terminal 12 are provided above the battery lid 6. A positive electrode current collector plate 44 and a negative electrode current collector plate 24 are provided inside the battery can 1 below the battery lid 6.

[0018] Examples of the material for forming the positive electrode external terminal 14 and the positive electrode current collector plate 44 include an aluminum alloy, and examples of the material for forming the negative electrode external terminal 12 and the negative electrode current collector plate 24 include a copper alloy.

[0019] The positive electrode external terminal 14 and the negative electrode external terminal 12 each have a welded joint portion to which a bus bar or the like is welded. The welded joint portion has a rectangular parallelepiped block shape that protrudes upward from the battery lid 6. The lower surface of the welded joint portion faces the surface of the battery lid 6, the upper surface of the welded joint portion is located at a predetermined height, and is substantially parallel to the battery lid 6.

[0020] The positive electrode current collector plate 44 has a rectangular plate-shaped positive electrode current collector plate base portion 41 facing the lower surface of the battery lid 6, and a positive electrode side connection end portion 42 extending from the side end of the positive electrode current collector plate base portion 41 along the wide side surface 1b of the battery can 1 toward the bottom surface 1d side. Similarly, the negative electrode current collector plate 24 has a rectangular plate-shaped negative electrode current collector plate base portion 21 facing the lower surface of the battery lid 6, and a negative electrode side connection end portion 22 extending from the side end of the negative electrode current collector plate base portion 21 along the wide side surface 1b of the battery can 1 toward the bottom surface 1d side. Positive electrode side opening holes 43 and negative electrode side opening holes 23 are respectively formed in the positive electrode current collector plate base portion 41 and the negative electrode current collector plate base portion 21.

[0021] A positive electrode connection portion 14a and a negative electrode connection portion 12a are provided so as to protrude respectively from the lower surfaces of the positive electrode external terminal 14 and the negative electrode external terminal 12. The positive electrode connection portion 14a and the negative electrode connection portion 12a are integrally formed with the positive electrode external terminal 14 and the negative electrode external terminal 12 respectively.

[0022] The positive electrode connection portion 14a has a cylindrical shape that can be inserted into the positive electrode side through hole 46 of the battery lid 6 and the positive electrode side opening hole 43 of the positive electrode current collector plate base portion 41. Similarly, the negative electrode connection portion 12a has a cylindrical shape that can be inserted into the negative electrode side through hole 26 of the battery lid 6 and the negative electrode side opening hole 23 of the negative electrode current collector plate base portion 21. The positive electrode connection portion 14a passes through the positive electrode side through hole 46 of the battery lid 6 and the positive electrode side opening hole 43 of the positive electrode current collector plate base portion 41 to penetrate the battery lid 6 and the positive electrode current collector plate base portion 41. The positive electrode external terminal 14 and the positive electrode current collector plate 44 are electrically connected via the positive electrode connection portion 14a and are fixed to the battery lid 6. Similarly, the negative electrode connection portion 12a passes through the negative electrode side through hole 26 of the battery lid 6 and the negative electrode side opening hole 23 of the negative electrode current collector plate base portion 21 to penetrate the battery lid 6 and the negative electrode current collector plate base portion 21. The negative electrode external terminal 12 and the negative electrode current collector plate 24 are electrically connected via the negative electrode connection portion 12a and are fixed to the battery lid 6.

[0023] The positive electrode external terminal 14 is electrically connected to the winding group 3, which will be described later, via the positive electrode connection portion 14a and the positive electrode current collector plate 44. Similarly, the negative electrode external terminal 12 is electrically connected to the winding group 3 via the negative electrode connection portion 12a and the negative electrode current collector plate 24. During charging of the lithium ion secondary battery 100, electricity is supplied from an external power source to the winding group 3 via the positive electrode external terminal 14, the positive electrode connection portion 14a, the positive electrode current collector plate 44, and the negative electrode external terminal 12, the negative electrode connection portion 12a, and the negative electrode current collector plate 24. During discharging of the lithium ion secondary battery 100, electricity is supplied from the winding group 3 to an external load via the positive electrode external terminal 14, the positive electrode connection portion 14a, the positive electrode current collector plate 44, and the negative electrode external terminal 12, the negative electrode connection portion 12a, and the negative electrode current collector plate 24.

[0024] In order to electrically insulate the positive electrode current collector plate 44, the negative electrode current collector plate 24, the positive electrode external terminal 14, and the negative electrode external terminal 12 from the battery lid 6, a gasket 5 is provided between each of the positive electrode external terminal 14 and the negative electrode external terminal 12 and the battery lid 6, and an insulating plate 7 is provided between each of the positive electrode current collector plate 44 and the negative electrode current collector plate 24 and the battery lid 6. Examples of the materials for the insulating plate 7 and the gasket 5 include resin materials having insulating properties such as polybutylene terephthalate, polyphenylene sulfide, and perfluoroalkoxy fluororesin.

[0025] An electrolytic solution and the winding group 3 are housed in the battery can 1.

[0026] The electrolytic solution is injected into the battery can 1 from the liquid injection port 9. As the electrolytic solution, for example, a non-aqueous electrolytic solution in which a lithium salt such as lithium hexafluorophosphate (LiPF6) is dissolved in a carbonic ester-based organic solvent such as ethylene carbonate can be used.

[0027] As shown in FIG. 3, the wound group 3 has a negative electrode 32, a positive electrode 34, and two separators 33 and 35. The separator 35, the negative electrode 32, the separator 33, and the positive electrode 34 are stacked in this order and wound flat. The separator 35 is located on the outermost periphery of the wound group 3, and the negative electrode 32 is located inside it. The two separators 33 and 35 electrically insulate the positive electrode 34 and the negative electrode 32.

[0028] The wound group 3 has a pair of opposing end faces 3a and 3b perpendicular to the winding axis, and a side face 3c between the pair of end faces 3a and 3b. The side face 3c has a pair of opposing curved portions with a semicircular cross-section and a flat portion continuously formed between the pair of curved portions. The wound group 3 is disposed in the battery can 1 such that the flat portion of the side face 3c is substantially parallel to the wide side face 1b of the battery can 1.

[0029] The positive electrode 34 has a positive electrode current collector 34a and a positive electrode active material layer 34b formed on at least one side, preferably both sides, of the positive electrode current collector 34a.

[0030] The positive electrode current collector 34a is formed of any material having high conductivity and not alloying with lithium ions. The positive electrode current collector 34a may have a plate-like (sheet-like) shape. For example, an aluminum foil can be used as the positive electrode current collector 34a. A portion (hereinafter referred to as the "positive electrode current collector exposed portion") 34c not covered with the positive electrode active material layer 34b is provided at one end of the positive electrode current collector 34a. The positive electrode current collector exposed portion 34c is provided at the end face 3a of the wound group 3 and in its vicinity. The positive electrode current collector exposed portion 34c faces and is electrically connected to the positive electrode side connection end portion 42 of the positive electrode current collecting plate 44. In the present invention, the positive electrode active material layer and the negative electrode active material layer are also referred to as the positive electrode active material layer and the negative electrode active material layer, respectively.

[0031] <Positive electrode> The positive electrode 34 has a positive electrode mixture layer 34b on at least one side, preferably both sides, of the positive electrode foil which is the positive electrode current collector 34a, and a positive electrode current collector exposed portion 34c where the positive electrode active material mixture is not applied is provided at one end in the width direction of the positive electrode foil. In the present invention, the positive electrode is also referred to as the cathode. Further, in the description of the positive electrode, the positive electrode current collector is also simply referred to as the current collector.

[0032] The positive electrode 34 has a positive electrode mixture layer 34b formed on at least one side, preferably both sides, of the positive electrode current collector 34a. The positive electrode mixture layer 34b contains a positive electrode active material. As the positive electrode active material, for example, a composite oxide of nickel, cobalt, and manganese can be used. Further, as the positive electrode active material, one of the preferred embodiments is to use a ternary lithium-containing composite oxide represented by the following general composition formula (1). Li 1+X M A O2(1) (In the formula, X satisfies -0.15 ≤ X ≤ 0.15, and M A represents an element group including at least one selected from the group consisting of Mn and Al, Ni, and Co)

[0033] The ternary lithium-containing composite oxide represented by the general composition formula (1) has high thermal stability and stability in a high potential state, and by applying the oxide, the safety and various battery characteristics of the lithium-ion secondary battery can be improved.

[0034] The positive electrode mixture layer 34b may further contain at least one, preferably both, of a binder and a conductive agent.

[0035] As the binder, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, polyacrylonitrile, polyvinyl fluoride, polypropylene fluoride, chloroprene fluoride, butyl rubber, nitrile rubber, styrene butadiene rubber (SBR), polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylic resins, or a mixture thereof can be used.

[0036] As the conductive agent, a carbon-based material can be used. The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. Examples of crystalline carbon include artificial graphite, natural graphite (e.g., flake graphite), or a mixture thereof. Examples of amorphous carbon include carbon black (e.g., acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, or a mixture thereof).

[0037] The positive electrode 34 can be formed, for example, as follows. The positive electrode active material, and optionally a binder and a conductive agent, are dispersed in a solvent (e.g., N-methyl-2-pyrrolidone (NMP), water) to prepare a paste-like or slurry-like positive electrode mixture composition. This positive electrode mixture composition is applied to the surface (one side or both sides) of the positive electrode current collector 34a, dried, and, if necessary, calendered to form the positive electrode mixture layer 34b. Thereby, the positive electrode 34 is obtained. However, the positive electrode is not limited to that manufactured by the above manufacturing method, and may be manufactured by other methods.

[0038] <Negative electrode> In one aspect of this embodiment, the negative electrode of the lithium-ion secondary battery has a current collector and a negative electrode active material layer provided on at least one side of the current collector, and the negative electrode active material layer has a negative electrode active material containing graphite particles (A) and graphite particles (B) carrying amorphous carbon fine particles, and the graphite particles (B) carrying the amorphous carbon fine particles have 0.4 amorphous carbon fine particles per unit area / μm 2 or more.

[0039] In another aspect of this embodiment, the negative electrode of the lithium-ion secondary battery has a current collector and a negative electrode active material layer provided on at least one side of the current collector. The negative electrode active material layer has a negative electrode active material, a binder that holds the negative electrode active material, and a negative electrode additive containing copper oxide, and the negative electrode active material contains a negative electrode active material containing amorphous carbon.

[0040] The negative electrode 32 has a negative electrode current collector 32a and a negative electrode mixture layer 32b formed on at least one side, preferably both sides, of the negative electrode current collector 32a. In the present invention, the negative electrode is also referred to as a negative electrode. In the description of the negative electrode, the negative electrode current collector is also simply referred to as a current collector.

[0041] The negative electrode current collector 32a is formed of any material having high conductivity and not alloying with lithium ions. At one end of the negative electrode current collector 32a, a portion not covered with the negative electrode mixture layer 32b (hereinafter referred to as the "negative electrode current collector exposed portion") 32c is provided. The negative electrode current collector exposed portion 32c is provided on the end face 3b of the winding group 3 and its vicinity. The negative electrode current collector exposed portion 32c faces and is electrically connected to the negative electrode side connection end portion 22 of the negative electrode current collector plate 24.

[0042] The portion of the negative electrode 32 where the negative electrode mixture layer 32b is applied is larger in the width direction than the portion where the positive electrode mixture layer 34b of the positive electrode 34 is applied. Thus, it is preferable that the portion where the positive electrode mixture layer 34b is applied is configured to be sandwiched between the portions where the negative electrode mixture layer 32b is applied. One preferred embodiment is that the positive electrode current collector exposed portion 34c and the negative electrode current collector exposed portion 32c are each bundled in a flat portion and connected by welding or the like. Note that the separators 33 and 35 are wider in the width direction than the portion where the negative electrode mixture layer 32b is applied, but since they are wound around the positions where the current collectors at the ends of the positive electrode current collector exposed portion 34c and the negative electrode current collector exposed portion 32c are exposed, there is no hindrance when bundling and welding.

[0043] The negative electrode mixture layer 32b contains a negative electrode active material and may further contain at least one, preferably both, of a negative electrode additive and a binder.

[0044] As the negative electrode active material, in one aspect, there is provided a negative electrode active material including graphite particles (A) and graphite particles (B) supporting amorphous carbon fine particles. Further, as the negative electrode active material, in another aspect, there is provided a negative electrode active material including amorphous carbon.

[0045] Examples of the graphite particles constituting the graphite particles (A) and the graphite particles (B) supporting amorphous carbon fine particles include natural graphite particles and artificial graphite particles, and natural graphite particles are preferred. Examples of natural graphite include flaky graphite, massive graphite, and earthy graphite. The graphite particles (A) and the graphite particles constituting the graphite particles (B) supporting amorphous carbon fine particles may be the same type of graphite particles or different types of graphite particles.

[0046] Examples of negative electrode active materials other than graphite include carbon-based materials such as non-graphitizable carbon (hard carbon) and graphitizable carbon (soft carbon).

[0047] Regarding graphite, those having the graphite surface coated with amorphous carbon may be used. By coating with amorphous carbon, the reaction with excess electrolyte can be prevented. Examples of amorphous carbon include pitch. That is, it is a preferred aspect that the graphite particles constituting the graphite particles (A) and the graphite particles (B) supporting amorphous carbon fine particles are graphite particles coated with amorphous carbon, and more preferably pitch-coated graphite particles. Further, it is a particularly preferred aspect that the graphite particles constituting the graphite particles (A) and the graphite particles (B) supporting amorphous carbon fine particles are natural graphite particles coated with amorphous carbon.

[0048] Graphite particles (B) supporting amorphous carbon fine particles. Examples of the supported amorphous carbon fine particles that constitute the graphite particles (B) include carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Note that the supported amorphous carbon fine particles mean the amorphous carbon scattered on the surface of the graphite particles, which is different from the aforementioned coating. The coating means covering all or part of the surface of the graphite particles as a plane.

[0049] The graphite particles (B) supporting amorphous carbon fine particles have 0.4 particles / μm or more of amorphous carbon fine particles per unit area 2 and preferably 0.4 to 2.4 particles / μm 2 and more preferably 0.8 to 2.0 particles / μm 2 In this embodiment, when the graphite particles carry a small amount of amorphous carbon fine particles, that is, when the number of amorphous carbon fine particles per unit area is less than 0.4 particles / μm 2 the graphite particles supporting the amorphous carbon fine particles do not correspond to (B). Graphite particles supporting less than 0.4 particles / μm of amorphous carbon fine particles per unit area 2 may be used as graphite particles (A).

[0050] As the graphite particles (A), its average particle diameter is preferably 4 μm or more and 12 μm or less, and more preferably 5 μm or more and 10 μm or less.

[0051] As the graphite particles (B) supporting amorphous carbon fine particles, its average particle diameter is preferably 4 μm or more and 12 μm or less, and more preferably 5 μm or more and 10 μm or less. Note that the average particle diameter of the graphite particles (A) and the average particle diameter of the graphite particles (B) supporting amorphous carbon fine particles may be the same or different.

[0052] The supported amorphous carbon fine particles that constitute the graphite particles (B) with supported amorphous carbon fine particles preferably have an average particle diameter smaller than the average particle diameter of the graphite particles (A) and the average particle diameter of the graphite particles that constitute the graphite particles (B) with supported amorphous carbon fine particles. The average particle diameter of the amorphous carbon fine particles is preferably 0.05 μm or more and 0.5 μm or less, more preferably 0.1 μm or more and 0.4 μm or less.

[0053] As the negative electrode active material containing graphite particles (A) and graphite particles (B) with supported amorphous carbon fine particles, for example, as shown in FIG. 4, it is preferable that the graphite particles (A) 50 and the graphite particles (B) 52 with supported amorphous carbon fine particles (the amorphous carbon fine particles 56 are supported on the graphite particles 54) are present in the negative electrode active material layer in a mixed state. In FIG. 4, the description of the components constituting the negative electrode active material layer other than (A) and (B) is omitted.

[0054] When the negative electrode active material contains graphite particles (A) and graphite particles (B) with supported amorphous carbon fine particles, the mass ratio (graphite particles (A) / graphite particles (B) with supported amorphous carbon fine particles) is preferably 0.25 or more and 5 or less, more preferably 0.5 or more and 2 or less.

[0055] When the negative electrode active material contains a negative electrode active material containing amorphous carbon, it is a preferred embodiment that the negative electrode active material containing amorphous carbon contains graphite particles (B) with supported amorphous carbon fine particles.

[0056] Also, for example, as part of the negative electrode active material, a material obtained by mixing a carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc. as a conductive aid with a graphite material, and a material obtained by coating and compositing these conductive aids with a graphite material after mixing, or a material obtained by mixing hard carbon (hard carbon) or easily graphitizable carbon (soft carbon) with graphite may be used. The shape of the negative electrode active material is not particularly limited, and for example, it may have a spherical shape, a flaky shape, a fibrous shape, or a shape obtained by pulverizing these.

[0057] As a result of intensive studies by the present inventors, by using a negative electrode active material containing graphite particles (A) and graphite particles (B) supporting amorphous carbon fine particles, a lithium ion secondary battery can ensure the capacity of the battery and reduce the internal resistance in a wide range from a low SOC region to a high SOC region, so that it has high output and good storage characteristics.

[0058] Further, as a result of intensive studies by the present inventors, since the negative electrode active material contains a negative electrode active material containing amorphous carbon, and the negative electrode active material layer has a negative electrode active material, a binder for holding the negative electrode active material, and a negative electrode additive containing copper oxide, a lithium ion secondary battery can ensure the capacity of the battery and reduce the internal resistance in a wide range from a low SOC region to a high SOC region, so that it has high output and good storage characteristics.

[0059] Furthermore, it is preferable that the negative electrode active material layer has copper oxide. By having the copper oxide in an amount of 0.5 wt% or more and 15 wt% or less based on 100 wt% in total of the negative electrode active material and copper oxide, more preferably, a lithium ion secondary battery can ensure the capacity of the battery and reduce the internal resistance in a wide range from a low SOC region to a high SOC region, so that it has high output and good storage characteristics, which is preferable.

[0060] Copper oxide is included as a negative electrode additive. The copper oxide may be copper(I) oxide (Cu2O), copper(II) oxide (CuO), or a mixture thereof. That is, the copper oxide may be at least one copper oxide selected from Cu2O and CuO. The negative electrode additive may be particulate. The shape of the particulate negative electrode additive is not particularly limited, and may have, for example, a spherical shape, a flaky shape, a fibrous shape, or a shape obtained by pulverizing these. The particulate negative electrode additive may be particles containing copper(I) oxide (Cu2O), copper(II) oxide (CuO), or a mixture thereof, or may be particles consisting essentially of copper(I) oxide (Cu2O), copper(II) oxide (CuO), or a mixture thereof. These various particulate negative electrode additives may be used alone or in combination.

[0061] In the negative electrode binder layer 32b, the negative electrode active material and the negative electrode additive may exist as separate particles not compounded with each other. Thereby, the negative electrode active materials can be electrically connected well without being inhibited by the negative electrode additive having a high electrical resistance, and an increase in the internal resistance of the lithium ion secondary battery can be suppressed. The negative electrode additive may have an average particle diameter smaller than the average particle diameter of the negative electrode active material, and may have an average particle diameter of 1 to 10 μm. Thereby, the negative electrode active materials can be electrically connected well without being inhibited by the negative electrode additive having a high electrical resistance, so that an increase in the internal resistance of the lithium ion secondary battery can be suppressed. The average particle diameters of the negative electrode active material and the negative electrode additive are determined based on SEM observation images.

[0062] As the binder for the negative electrode binder layer 32b, the same materials as those exemplified as the materials that can be used as the binder for the positive electrode binder layer 34b can be used.

[0063] The negative electrode binder layer 32b may further have a dispersant. As the dispersant, carboxymethyl cellulose (CMC) can be used.

[0064] The negative electrode 32 can be formed, for example, as follows. First, a negative electrode active material, a negative electrode additive containing copper oxide, a binder, and optionally a dispersant are prepared. The negative electrode active material and the negative electrode additive may be in particulate form. The negative electrode active material and the negative electrode additive may be separate particles that are not compounded with each other. The negative electrode active material, the negative electrode additive, the binder, and optionally the dispersant are dispersed in a solvent (e.g., N-methyl-2-pyrrolidone (NMP), water) to prepare a paste-like or slurry-like mixture. The prepared mixture is applied to the surface (one side or both sides) of the negative electrode current collector 32a, dried, and, if necessary, subjected to a calendaring process to form the negative electrode mixture layer 32b. Thereby, the negative electrode 32 is obtained. However, the negative electrode is not limited to those manufactured by the above manufacturing method and may be manufactured by other methods.

[0065] The separators 33 and 35 have an insulating function of preventing a short circuit between the positive electrode 34 and the negative electrode 32 and a function of holding the non-aqueous electrolyte. As the separators 33 and 35, for example, a porous sheet made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, or a laminated sheet thereof (e.g., a sheet having a three-layer structure of PP / PE / PP) can be used.

[0066] A layer containing an inorganic material (e.g., alumina particles, etc.) and a binder may be provided on one side or both sides of the separators 33 and 35. Thereby, even when the lithium-ion secondary battery 100 is used in an abnormal state (for example, when the temperature of the lithium-ion secondary battery rises to 160 °C or higher due to overcharging, crushing, etc.), melting of the separators 33 and 35 is prevented and the insulating function can be maintained. Therefore, the safety of the lithium-ion secondary battery 100 is improved.

[0067] If necessary, a shaft core (not shown) may be arranged on the innermost circumference of the winding group 3. As the shaft core, a resin sheet or the like having a higher bending rigidity than any of the positive electrode current collector, the negative electrode current collector, and the separators 33 and 35 can be used.

[0068] An insulating protection film (not shown) may be optionally wound around the winding group 3. The insulating protection film is composed of, for example, a single sheet of synthetic resin such as PP (polypropylene) or a plurality of film members, and has a length that can be wound around with the direction parallel to the flat surface of the winding group 3 and perpendicular to the winding axis direction as the winding center.

Example

[0069] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[0070] [Examples 1 to 11, Comparative Examples 1 to 4] As the positive electrode active material, Li 1.0 Ni 0.33 Co 0.33 Mn 0.33 O2 powder, acetylene black as a conductive aid, and polyvinylidene fluoride (PVdF) as a binder were prepared.

[0071] The positive electrode active material, conductive agent, and binder were mixed at a weight ratio of 90:5:5. N-methyl-2-pyrrolidone (NMP) was added to the obtained mixture to adjust the viscosity, and a positive electrode slurry was obtained.

[0072] As the positive electrode current collector, an aluminum foil with a thickness of 15 μm was prepared. Uncoated portions that would become welding portions (positive electrode current collector exposed portions 34c) were left on both sides of the positive electrode current collector, and a layer of the positive electrode slurry was formed by simultaneous coating of two layers (front and back) using the positive electrode slurry by a slot die coating method. Next, the layer of the positive electrode slurry was dried and pressed to form a positive electrode mixture layer 34b, and the positive electrode 34 shown in FIG. 3 was produced.

[0073] Pitch-coated natural graphite particles (negative electrode active material A) as the negative electrode active material, pitch-coated natural graphite particles supporting amorphous carbon fine particles (negative electrode active material B), copper(I) oxide (Cu2O) particles (negative electrode additive C) as the negative electrode additive, styrene-butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the dispersant were prepared. However, the negative electrode active material A used in Example 2 had a small amount of amorphous carbon fine particles supported thereon, and the negative electrode active material A used in Comparative Example 4 had amorphous carbon fine particles supported thereon.

[0074] The negative electrode active material A, negative electrode active material B, negative electrode additive C, binder, and dispersant were mixed so that the total of the negative electrode active material A, negative electrode active material B, and negative electrode additive C: binder: dispersant had a weight ratio of 100:1:1. The respective usage amounts (total 100 wt%) and specifications of the negative electrode active material A, negative electrode active material B, and negative electrode additive C are shown in Table 1. Note that the copper(I) oxide particles used as the negative electrode additive C are simply denoted as Cu2O in Table 1. Ion-exchanged water was added to the obtained mixture to adjust the viscosity, and a negative electrode slurry was obtained.

[0075] Uncoated portions to be welding parts (negative electrode current collector exposed portions 32c) were left on both sides of a copper foil with a thickness of 10 μm, and a layer of the negative electrode slurry was formed by simultaneously coating two layers (front and back) using the negative electrode slurry by a slot die coating method. Next, the layer of the negative electrode slurry was dried and pressed to form a negative electrode mixture layer 32b, and a negative electrode 32 shown in FIG. 3 was produced.

[0076] Subsequently, separators 33 and 35 were sandwiched between the produced positive electrode 34 and negative electrode 32, and a winding group 3 was produced with a configuration as shown in FIG. 3. The positive electrode side connection end portions 42 and negative electrode side connection end portions 22 of the positive electrode current collector plate 44 and negative electrode current collector plate 24 connected to the battery lid 6 and the uncoated portions (positive electrode current collector exposed portion 34c, negative electrode current collector exposed portion 32c) of the winding group 3 were welded, the winding group 3 was covered with an insulating protection film, enclosed in a battery can 1, and the battery lid 6 and the battery can 1 were welded (see FIGS. 1 and 2).

[0077] Subsequently, as a non-aqueous electrolyte, an electrolyte solution was prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 1:2. After injecting the prepared electrolyte solution from the injection port 9, it was sealed with the injection plug 11 to fabricate a lithium-ion secondary battery.

[0078] After initial formation by charging and discharging the fabricated lithium-ion secondary battery, the battery capacity, the direct current resistance (DCR) at SOC, and the capacity retention rate after storage were measured.

[0079] <Battery capacity> For the battery capacity, constant voltage - constant current charging (CC - CV charging) was performed at a charging current of 1C for a total of 2.5 hours until the battery voltage reached 4.2V. After a 30-minute rest, constant current discharging (CC discharging) was performed at a discharging current of 0.02C until the battery voltage reached 2.9V to obtain the initial capacity. The initial capacities (relative values) of the lithium-ion secondary batteries of each example and comparative example, normalized with the initial capacity of the lithium-ion secondary battery of Comparative Example 1 as 100, are shown as the capacity in Table 1.

[0080] <dcr> The relationship between the SOC-open circuit voltage (OCV) was obtained by discharging the battery capacity in 5% increments from 4.2 V, resting for 2 hours, and using the voltage after the rest as the OCV to obtain the relationship with the SOC.

[0081] For the DCR at SOC 25% which is the low SOC region, charging was performed at a constant current of 1C in the CC-CV mode from SOC 0% to SOC 25% based on the SOC-OCV relationship. Next, the lithium-ion secondary battery was held in a thermostat at -10°C for 5 hours. Then, the lithium-ion secondary battery was discharged at a constant current of 5C for 10 seconds, and the voltage drop value due to the discharge was measured. Furthermore, similar constant current discharges were performed at discharge currents of 10C and 15C. The discharge current was plotted on the horizontal axis and the voltage drop value on the vertical axis, and the slope of the graph was determined as the DCR. The DCR (relative value) of each example and comparative example of the lithium-ion secondary battery, with the DCR of the lithium-ion secondary battery of Comparative Example 1 normalized to 100, is shown in Table 1. The smaller the value of the DCR at SOC 25%, the lower the internal resistance of the lithium-ion secondary battery in the low SOC region.

[0082] For the DCR at SOC 75% which is the high SOC region, charging was performed at a constant current of 1C in the CC-CV mode from SOC 0% to SOC 75% based on the SOC-OCV relationship. Next, the lithium-ion secondary battery was held in a thermostat at -10°C for 5 hours. Then, the lithium-ion secondary battery was discharged at a constant current of 5C for 10 seconds, and the voltage drop value due to the discharge was measured. Furthermore, similar constant current discharges were performed at discharge currents of 10C and 15C. The discharge current was plotted on the horizontal axis and the voltage drop value on the vertical axis, and the slope of the graph was determined as the DCR. The DCR (relative value) of each example and comparative example of the lithium-ion secondary battery, with the DCR of the lithium-ion secondary battery of Comparative Example 1 normalized to 100, is shown in Table 1. The smaller the value of the DCR at SOC 75%, the lower the internal resistance of the lithium-ion secondary battery in the high SOC region.

[0083] <Capacity retention rate after storage> The relationship between the SOC-open circuit voltage (OCV) was obtained by discharging the battery capacity in 5% increments from 4.2 V, resting for 2 hours, and using the voltage after the rest as the OCV to obtain the relationship with the SOC.

[0084] From the relationship between SOC and OCV, CC-CV charging was performed at a charging current of 1C from SOC 0% to SOC 80%. Then, the temperature of the thermostat was controlled to 70°C and maintained for 30 days. After that, constant-current discharge (CC discharge) was performed at a discharge current of 1C until the battery voltage reached 2.9V. Subsequently, constant-voltage - constant-current charging (CC-CV charging) was performed at a charging current of 1C for a total of 2.5 hours until the battery voltage reached 4.2V. After a 30-minute pause, constant-current discharge (CC discharge) was performed at a discharge current of 0.02C until the battery voltage reached 2.9V to obtain the capacity after storage. The capacity retention rate after storage was calculated as (capacity after storage / initial capacity) × 100. The capacity retention rates (relative values) of the lithium-ion secondary batteries of each example and comparative example, with the capacity retention rate of the lithium-ion secondary battery of Comparative Example 1 standardized as 100, are shown in Table 1.

[0085] The configurations of the negative electrode active material and negative electrode additive of each lithium-ion secondary battery of the examples and comparative examples, and the above evaluation results are shown in Table 1. From Table 1, it was suggested that in the examples to which the present application was applied, it was possible to achieve both the reduction of DCR in the low SOC region and the high SOC region and the maintenance of the storage capacity retention rate while ensuring the battery capacity. On the other hand, in the comparative examples, either the reduction of DCR or the maintenance of the storage capacity retention rate was poor, and both could not be achieved.

[0086] By adopting the above-described configuration as the negative electrode for a lithium-ion secondary battery, it is possible to provide a lithium-ion secondary battery with high output in a wide range from low SOC to high SOC and good storage characteristics.

[0087]

Table 1

[0088] Those skilled in the art can use the above description to make the most of the present disclosure. The claims and embodiments disclosed herein are merely illustrative and exemplary, and should not be construed as limiting the scope of the present disclosure in any way. With the help of the present disclosure, changes can be made to the details of the above embodiments without departing from the basic principles of the present disclosure. In other words, various modifications and improvements to the embodiments specifically disclosed in the above specification are within the scope of the present disclosure.

[0089] The upper limit value and / or the lower limit value of the numerical range described in this specification can respectively define a preferred range by any combination. For example, the upper limit value and the lower limit value of the numerical range can be arbitrarily combined to define a preferred range, the upper limit values of the numerical range can be arbitrarily combined to define a preferred range, and the lower limit values of the numerical range can also be arbitrarily combined to define a preferred range.

[0090] Throughout this specification, it should be understood that the singular form includes the plural concept thereof unless otherwise specifically stated. Therefore, the singular articles (for example, in English, "a", "an", "the", etc.) should be understood to include the plural concept thereof unless otherwise specifically stated. All publications, patents, and patent applications cited in this specification are hereby incorporated herein by reference in their entirety.

Description of Reference Numerals

[0091] 1 ··· Battery can 1a ··· Opening 1b ··· Wide side 1c ··· Narrow side 1d ··· Bottom surface 3 ··· Wound group 5 ··· Gasket 6 ··· Battery cover 7 ··· Insulating plate 9 ··· Liquid injection port 10 ··· Gas discharge valve 11 ··· Liquid injection plug 12 ··· Negative electrode external terminal 12a ··· Negative electrode connection part 14 ··· Positive electrode external terminal 14a ··· Positive electrode connection part 21 ··· Negative electrode current collector base 22 ··· Negative electrode side connection end 23 ··· Negative electrode side opening hole 24 ··· Negative electrode current collector 26 ··· Negative electrode side through hole 32 ··· Negative electrode 32a ··· Negative electrode current collector 32b ··· Negative electrode mixture layer 32c ··· Negative electrode current collector exposed part 33 ··· Separator 34 ··· Positive electrode 34a ··· Positive electrode current collector 34b ··· Positive electrode mixture layer 34c ··· Positive electrode current collector exposed part 35 ··· Separator 41 ··· Positive electrode current collector base 42 ··· Positive electrode side connection end 43 ··· Positive electrode side opening hole 44 ··· Positive electrode current collector 46 ··· Positive electrode side through hole 50 ··· Graphite particles (A) 52 ··· Graphite particles (B) supported by amorphous carbon fine particles 54 ··· Graphite particles 56 ··· Amorphous carbon fine particles 100 ··· Lithium ion secondary battery< / dcr>

Claims

1. A lithium-ion secondary battery comprising a positive electrode and a negative electrode, wherein the negative electrode has a current collector and a negative electrode active material layer provided on at least one side of the current collector, the negative electrode active material layer having a negative electrode active material containing graphite particles (A) and graphite particles (B) on which amorphous carbon fine particles are supported, The graphite particles (B) on which the amorphous carbon fine particles are supported have 0.4 or more amorphous carbon fine particles per unit area of the surface of the graphite particles (B) determined based on the SEM observation image. ２ and more, the graphite particles constituting the graphite particles (A) and the graphite particles (B) on which the amorphous carbon fine particles are supported being particles of graphite coated with amorphous carbon, the average particle diameter of the amorphous carbon fine particles being 0.05 μm or more and 0.5 μm or less, and either one of the graphite particles (A) and the graphite particles (B) being artificial graphite.

2. A lithium-ion secondary battery comprising a positive electrode and a negative electrode, wherein the negative electrode has a current collector and a negative electrode active material layer provided on at least one side of the current collector, the negative electrode active material layer having a negative electrode active material containing graphite particles (A) and graphite particles (B) on which amorphous carbon fine particles are supported, The graphite particles (B) carrying the amorphous carbon fine particles have the number of amorphous carbon fine particles per unit area on the surface of the graphite particles (B) determined based on the SEM observation image of 0.4 particles / μm ２ or more, the graphite particles constituting the graphite particles (A) and the graphite particles (B) on which the amorphous carbon fine particles are supported being particles of graphite coated with amorphous carbon, the average particle diameter of the amorphous carbon fine particles being 0.05 μm or more and 0.5 μm or less, and the graphite particles (A) having a larger average particle diameter than the graphite particles (B).

3. A lithium-ion secondary battery comprising a positive electrode and a negative electrode, wherein the negative electrode has a current collector and a negative electrode active material layer provided on at least one side of the current collector, the negative electrode active material layer having a negative electrode active material containing graphite particles (A) and graphite particles (B) on which amorphous carbon fine particles are supported, The graphite particles (B) on which the amorphous carbon fine particles are supported have 0.4 or more amorphous carbon fine particles per unit area of the surface of the graphite particles (B) determined based on the SEM observation image. ２ or more, the graphite particles constituting the graphite particles (A) and the graphite particles (B) on which the amorphous carbon fine particles are supported being particles of graphite coated with amorphous carbon, the average particle diameter of the amorphous carbon fine particles being 0.05 μm or more and 0.5 μm or less, and the graphite particles (B) having a larger average particle diameter than the graphite particles (A).

4. The lithium-ion secondary battery according to any one of claims 1 to 3, wherein the graphite particles (A) are artificial graphite, and the graphite particles (B) are natural graphite.

5. The lithium-ion secondary battery according to any one of claims 1 to 3, wherein the graphite particles (A) are natural graphite, and the graphite particles (B) are artificial graphite.

6. The lithium-ion secondary battery according to any one of claims 1 to 3, wherein the negative electrode active material layer has copper oxide.

7. The copper oxide is Cu ２ The lithium ion secondary battery according to claim 6, which is at least one copper oxide selected from CuO and CuO.

8. The lithium ion secondary battery according to claim 6, wherein the negative electrode active material layer contains copper oxide in an amount of 0.5 wt% or more and 15 wt% or less based on 100 wt% in total of the negative electrode active material and the copper oxide.

9. The lithium ion secondary battery according to claim 7, wherein the negative electrode active material layer contains copper oxide in an amount of 0.5 wt% or more and 15 wt% or less based on 100 wt% in total of the negative electrode active material and the copper oxide.

10. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the mass ratio of the graphite particles (A) to the graphite particles (B) supporting the amorphous carbon fine particles (graphite particles (A) / graphite particles (B) supporting the amorphous carbon fine particles) is 0.25 or more and 5 or less.

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