JP2018174110A - Current collector and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which there is a possibility that bias in a temperature distribution of an electrode group cannot be avoided when a heat removal property in a thickness direction of an electrode plate is lowered due to thermal expansion of a battery, consequently, a temperature of a separator becomes nonuniform and it becomes difficult to uniformly advance shutdown.SOLUTION: Each of current collectors 22, 32 includes an anisotropic thermal conductor on a main thin metal plate. The anisotropic thermal conductor contains at least one of carbon nanotube, graphene, aluminum based STC, and copper based STC.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a current collector and a lithium ion secondary battery, and more particularly to a current collector for a lithium ion secondary battery excellent in heat removal and a lithium ion secondary battery including the current collector.

  Lithium ion secondary batteries have higher electromotive force, higher energy density, and better charge / discharge efficiency than lead batteries and nickel metal hydride batteries. There are expectations for a wide range of applications, from large storage batteries.

  By the way, it is known that a lithium ion secondary battery generates heat depending on a battery reaction at the time of charging and discharging and an internal resistance of the battery. In particular, it has been pointed out that a battery with a large output has a high internal temperature, and if the state continues for a long time, the battery life is shortened or the performance of the internal elements deteriorates.

In response to such indications, for example, Patent Document 1 proposes a mechanism in which a heat radiating plate is provided inside the battery can so as to be in contact with the can, and heat generated inside the battery is released to the outside to suppress the temperature rise inside the battery. ing.
Also, for example, in Patent Document 2, by increasing the thermal conductivity in the thickness direction of the separator that separates the positive electrode and the negative electrode (0.5 W / (m · k) or more) and improving the heat removal performance, A mechanism for suppressing temperature rise has been proposed.

  By the way, in a relatively large lithium ion secondary battery, it is known to use a porous polyethylene film or the like as a separator in order to improve safety during overcharge. This porous separator allows lithium ions to pass during normal charging and discharging, and prevents a short circuit between the positive electrode and the negative electrode. On the other hand, at the time of overcharging, the heat generated by the chemical reaction between the nonaqueous electrolyte solution and the active material causes the polyethylene to soften and melt and shut down (that is, the molten polyethylene closes the pores and blocks the passage of lithium ions). Thereby, since charging / discharging is interrupted | blocked, the rapid raise of battery temperature can be prevented beforehand.

  For example, in Patent Document 3, a metal shaft core made of the same material as the positive electrode or the negative electrode is disposed at the center of an electrode group in which a positive electrode plate and a negative electrode plate are wound with a porous separator interposed therebetween. A lithium ion secondary battery has been proposed in which one end is joined to either a positive electrode or a negative electrode connecting member. According to the present invention, by providing a metal shaft made of the same material as the positive electrode or the negative electrode, the temperature distribution of the entire electrode group is less biased, and the shutdown of the porous separator during overcharge proceeds substantially uniformly. Therefore, the safety of the battery is ensured.

JP 2011-113895 A JP 2006-269358 A JP 2006-40772 A

  However, in the conventional lithium ion secondary battery, although proposals such as improving the heat removal performance in the thickness direction of the electrode plate have been made by devising a separator or the like, the heat removal performance in the surface direction of the electrode plate is sufficient. If the heat removal performance in the thickness direction of the electrode plate is reduced due to the thermal expansion of the battery, it may not be possible to avoid the occurrence of bias in the temperature distribution of the electrode group as a result. It has been pointed out that the temperature of the separator is not uniform and it is difficult to proceed with the shutdown uniformly, and there is room for improvement.

  The present invention has been made in view of the above problems, and its purpose is to efficiently release the heat generated inside by the battery reaction, thereby efficiently releasing the heat generated inside to the outside of the battery, resulting in a temperature rise. Is to prevent. In addition, when overcharging, the structure of the lithium ion secondary battery can be significantly changed by making the temperature of the separator uniform, and by making the shutdown of the separator proceed uniformly, as heat is efficiently released. Not to improve safety.

The present invention provides the following means in order to solve the above problems.
(1) The current collector according to the first aspect of the present invention includes a metal thin plate as a main component and an anisotropic thermal conductor contained in the metal thin plate.

(2) The current collector according to the first aspect may include at least one of carbon nanotubes, graphene, aluminum-based STC, and copper-based STC as the anisotropic thermal conductor.

(3) The current collector according to the first aspect may have higher thermal conductivity in a predetermined direction along the surface of the metal thin plate than in a direction different from the predetermined direction.

(4) In the current collector according to the first aspect, the thermal conductivity in the predetermined direction may be 500 W / m · K or more.

(5) A lithium ion secondary battery according to a second aspect of the present invention includes a positive electrode current collector, a positive electrode having a positive electrode layer formed on a main surface of the positive electrode current collector, and a negative electrode current collector. A negative electrode having a negative electrode layer formed on the main surface of the negative electrode current collector, a separator interposed between and separated from the positive electrode and the negative electrode, and a non-aqueous electrolyte. In the secondary battery, at least one of the positive electrode current collector and the negative electrode current collector is any one of the current collectors (1) to (4).

(6) The current collector according to the third aspect of the present invention is made of an anisotropic thermal conductor, and has higher thermal conductivity in a predetermined direction along the surface than in a direction different from the predetermined direction. .

(7) In the current collector according to the third aspect, the anisotropic thermal conductor may be a graphite sheet.

(8) In the current collector according to the third aspect, the thermal conductivity in the in-plane direction of the graphite sheet may be 500 W / m · K or more.

(9) A lithium ion secondary battery according to a fourth aspect of the present invention includes a positive electrode current collector, a positive electrode having a positive electrode layer formed on a main surface of the positive electrode current collector, and a negative electrode current collector. A negative electrode having a negative electrode layer formed on the main surface of the negative electrode current collector, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. In the secondary battery, at least one of the positive electrode current collector and the negative electrode current collector is any one of the current collectors (6) to (8).

  According to the present invention, the heat removal property is maintained by releasing the heat in a direction different from the thickness direction of the current collector, for example, in the in-plane direction of the current collector. As a result, even if the heat removal performance in the thickness direction of the electrode plate is reduced due to the thermal expansion of the battery, the heat removal performance of the electrode is maintained without being greatly reduced. As a result, the bias of the temperature distribution of the entire electrode group is reduced, and the shutdown of the porous separator during overcharging proceeds almost uniformly, so that the safety of the battery can be ensured.

It is a cross-sectional schematic diagram of the lithium ion secondary battery concerning this embodiment. It is a schematic diagram which shows the planar shape of a positive electrode collector and a positive electrode collector.

  Hereinafter, the present embodiment will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios and the like of each component are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately modified and implemented without departing from the scope of the invention.

[Lithium ion secondary battery]
FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery according to this embodiment. A lithium ion secondary battery 100 shown in FIG. 1 mainly includes a laminated body 40, a case 50 that accommodates the laminated body 40 in a sealed state, and a pair of leads 60 and 62 connected to the laminated body 40.
Although not shown, the electrolyte solution is housed in the case 50 together with the laminate 40.

  The stacked body 40 is configured such that the positive electrode 20 and the negative electrode 30 separated by the separator 10 are arranged to face each other with the separator 10 interposed therebetween. The positive electrode 20 is obtained by providing a positive electrode active material layer 24 on a plate-like (film-like) positive electrode current collector 22. The negative electrode 30 is obtained by providing a negative electrode active material layer 34 on a plate-like (film-like) negative electrode current collector 32.

  The positive electrode active material layer 24 and the negative electrode active material layer 34 are in contact with both sides of the separator 10. Tabs 22a and 32a are formed at the ends of the positive electrode current collector 22 and the negative electrode current collector 32, respectively. The tabs 22a and 32a are connected to leads 60 and 62, respectively. The end extends to the outside of the case 50. In addition, although the case where the laminated body 40 is one in the case 50 is illustrated in FIG. 1, a plurality of laminated bodies may be laminated.

"Separator"
The separator 10 only needs to be formed of an electrically insulating porous structure, for example, a single layer of a film made of polyethylene, polypropylene, or polyolefin, a stretched film of a laminate or a mixture of the above resins, or cellulose, polyester, and Examples thereof include a fiber nonwoven fabric made of at least one constituent material selected from the group consisting of polypropylene.

"Positive electrode"
The positive electrode 20 includes a positive electrode current collector 22 and a positive electrode active material layer 24 provided on the positive electrode current collector 22.

(Positive electrode current collector)
For the positive electrode current collector 22, for example, a foil-like thin metal plate including an anisotropic heat conductor in a metal such as aluminum, copper, or nickel can be used. Examples of the anisotropic heat conductor contained in the metal thin plate include carbon nanotubes, graphene, aluminum-based STC, and copper-based STC. Here, STC is a composite material of graphite and copper or aluminum. STC has higher thermal conductivity than copper and aluminum, has anisotropy, and exhibits high heat transfer along the direction of graphite alignment. The thermal conductivity of the material used as these anisotropic heat conductors is preferably 1000 W / m · K or more.
The positive electrode current collector 22 contains at least one of these various anisotropic thermal conductors. The anisotropic thermal conductor included in the positive electrode current collector 22 is substantially aligned in one direction along the surface of the positive electrode current collector 22. Specifically, as shown in FIG. 2, the positive electrode current collector 22 is formed in a rectangular shape in plan view, and a tab 22a is formed at one end portion in the longitudinal direction. The positive electrode current collector 22 includes an anisotropic thermal conductor, most of which is from the other end in the longitudinal direction of the positive electrode current collector 22 toward one end where the tab 22a is formed. It is oriented in the direction of the arrow in FIG.
By including the various anisotropic thermal conductors so that their orientations are aligned in the longitudinal direction, the positive electrode current collector 22 has a higher heat transferability in the longitudinal direction than in the width direction. . The thermal conductivity in the longitudinal direction of the positive electrode current collector 22 is preferably secured to 500 W / m · K or more.
In addition, the positive electrode current collector 22 may be made of a graphite sheet that is an anisotropic heat conductor, instead of a metal thin plate that includes the various anisotropic heat conductors. The graphite sheet is obtained by processing graphite into a sheet shape and has high thermal diffusivity in the surface direction. Also in this case, the thermal conductivity in the in-plane direction of the positive electrode current collector 22 is preferably 500 W / m · K or more.

(Positive electrode active material layer)
The positive electrode active material layer 24 includes a positive electrode active material and a positive electrode binder, and includes a positive electrode conductive material as necessary.

(Positive electrode active material)
The positive electrode active material includes insertion and extraction of lithium ions, desorption and insertion of lithium ions (intercalation), or doping and dedoping of lithium ions and lithium ion counter anions (for example, PF ⁶⁻ ). An electrode active material that can be reversibly advanced can be used. As the positive electrode active material, for example, lithium cobalt oxide (LiCoO _2), lithium nickelate (LiNiO _2), lithium manganate (LiMnO _2), lithium manganese spinel (LiMn ₂ O _4), and the general formula: LiNi _x Co _y Mn _z M _a O ₂ (x + y + z + a = 1, 0 ≦ x <1, 0 ≦ y <1, 0 ≦ z <1, 0 ≦ a <1, M is Al, Mg, Nb, Ti, Cu, Zn, A composite metal oxide represented by one or more elements selected from Cr), a lithium vanadium compound (LiV ₂ O ₅ ), an olivine-type LiMPO ₄ (where M is Co, Ni, Mn, Fe, Mg, Nb) , Ti, Al, one or more elements selected from Zr or VO), LiNi _x Co _y Al _z O ₂ (0.9 <x + y + z <1.1), etc. Products, polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene and the like.

(Positive electrode conductive material)
Examples of the positive electrode conductive material include carbon powders such as carbon blacks, carbon nanotubes, carbon materials, metal fine powders such as copper, nickel, stainless steel, and iron, a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO. Can be mentioned. In addition, when sufficient electroconductivity is securable only with a positive electrode active material, the positive electrode active material layer 24 does not need to contain the electrically conductive material.

(Positive electrode binder)
The binder used for the positive electrode bonds the active materials to each other and bonds the active material to the positive electrode current collector 22. The material used as the binder may be any material as long as the above-described bonding is possible. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) , Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), Fluorine resin such as polyvinyl fluoride (PVF) can be used.

  In addition to the above, as the binder, for example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-) TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), Vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber The containing rubbers (VDF-CTFE-based fluorine rubber) vinylidene fluoride-based fluorine rubbers such as may be used.

Alternatively, an electron conductive conductive polymer or an ion conductive conductive polymer may be used as the binder. Examples of the electron conductive conductive polymer include polyacetylene. In this case, since the binder also functions as a conductive material, it is not necessary to add a conductive material. Examples of the ion conductive conductive polymer include monomers of polymer compounds (polyether polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphazenes, etc.), LiClO ₄ , LiBF ₄ , LiPF _{6, and the} like. Examples include a composite of a lithium salt or an alkali metal salt mainly composed of lithium. Examples of the polymerization initiator used for the combination include a photopolymerization initiator or a thermal polymerization initiator that is compatible with the above-described monomer.

  In addition, for example, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamideimide resin, acrylic resin, or the like may be used as the binder.

"Negative electrode"
The negative electrode 30 includes a negative electrode current collector 32 and a negative electrode active material layer 34 provided on the negative electrode current collector 32.

(Negative electrode current collector)
As the negative electrode current collector 32, the same material as the positive electrode current collector 22 can be used.
The negative electrode current collector 32 also includes at least one of the various anisotropic heat conductors exemplified in the description of the positive electrode current collector 22, and the directions are substantially aligned in one direction along the surface of the negative electrode current collector 32. It has been. Specifically, as shown in FIG. 2, the negative electrode current collector 32 has the same shape as the positive electrode current collector 22, and a tab 32a is formed at one end in the longitudinal direction. Many of the anisotropic thermal conductors included in the negative electrode current collector 32 are oriented in the direction from the other end in the longitudinal direction of the negative electrode current collector 32 toward one end where the tab 32a is formed. Has been.
By including the various anisotropic thermal conductors so that their orientations are aligned in their longitudinal direction, the negative electrode current collector 32 also has a higher heat transferability in the longitudinal direction than in the width direction. . The thermal conductivity in the longitudinal direction of the negative electrode current collector 32 is preferably secured to 500 W / m · K or more, as with the positive electrode current collector 22.
Further, similarly to the positive electrode current collector 22, a graphite sheet can be used for the negative electrode current collector 32 instead of the metal thin plate containing the various anisotropic heat conductors.

(Negative electrode active material layer)
The negative electrode active material layer 34 includes a negative electrode active material and a negative electrode binder, and optionally includes a negative electrode conductive material.

(Negative electrode active material)
As the negative electrode active material, a known negative electrode active material for lithium secondary batteries capable of inserting and extracting lithium ions can be used. Examples of the negative electrode active material include carbon materials such as metallic lithium, graphite capable of occluding and releasing lithium ions (natural graphite, artificial graphite), carbon nanotubes, non-graphitizable carbon, graphitizable carbon, and low-temperature calcined carbon. Metals that can be combined with lithium such as aluminum, silicon and tin, amorphous compounds mainly composed of oxides such as SiO _x (0 <x <2) and tin dioxide, lithium titanate (Li ₄ Ti ₅ And particles containing O ₁₂ ) and the like.

(Negative electrode conductive material)
As the same electric material used for the negative electrode, the same material as the positive electrode can be used. Note that in the case where sufficient conductivity can be ensured with only the negative electrode active material, the negative electrode active material layer 34 may not contain a conductive material.

(Negative electrode binder)
As the binder used for the negative electrode, the same binder as that for the positive electrode can be used.

"Electrolyte"
As the electrolytic solution, an electrolyte solution containing lithium salt (electrolyte aqueous solution, electrolyte solution using an organic solvent) can be used. However, since the electrolytic aqueous solution has a low decomposition voltage electrochemically, the withstand voltage during charging is limited to be low. Therefore, an electrolyte solution (nonaqueous electrolyte solution) using an organic solvent is preferable.

  The nonaqueous electrolytic solution has an electrolyte dissolved in a nonaqueous solvent, and may contain a cyclic carbonate and a chain carbonate as a nonaqueous solvent.

  As cyclic carbonate, what can solvate electrolyte can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, or the like can be used.

  The chain carbonate can reduce the viscosity of the cyclic carbonate. Examples thereof include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. In addition, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like may be mixed and used.

  The ratio of the cyclic carbonate and the chain carbonate in the non-aqueous solvent is preferably 1: 9 to 1: 1 by volume.

Examples of the electrolyte include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF _{2 SO 2) 2, LiN (} CF 3 SO 2) (C 4 F 9 SO 2), LiN (CF 3 CF 2 CO) 2, lithium salts such as LiBOB can be used. In addition, these lithium salts may be used individually by 1 type, and may use 2 or more types together. In particular, LiPF ₆ is preferably included from the viewpoint of the degree of ionization.

When LiPF ₆ is dissolved in a non-aqueous solvent, the concentration of the electrolyte in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L. When the concentration of the electrolyte is 0.5 mol / L or more, the lithium ion concentration of the nonaqueous electrolytic solution can be sufficiently secured, and a sufficient capacity can be easily obtained during charging and discharging. Moreover, by suppressing the electrolyte concentration to within 2.0 mol / L, it is possible to suppress an increase in the viscosity of the non-aqueous electrolyte, to sufficiently secure the mobility of lithium ions, and to obtain a sufficient capacity during charging and discharging. It becomes easy.

Even when LiPF ₆ is mixed with another electrolyte, the lithium ion concentration in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L, and the lithium ion concentration from LiPF ₆ is 50 mol%. More preferably, it is contained.

"Case"
The case 50 seals the laminated body 40 and the electrolytic solution therein. The case 50 is not particularly limited as long as it can suppress leakage of the electrolytic solution to the outside and entry of moisture and the like into the lithium ion secondary battery 100 from the outside.

  For example, as the case 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52 and a film such as polypropylene can be used as the polymer film 54. The material of the outer polymer film 54 is preferably a polymer material having a high melting point, such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP Etc.) are preferred.

"Lead"
The leads 60 and 62 are made of a conductive material such as aluminum. The leads 60 and 62 are welded to the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the separator 10 is sandwiched between the positive electrode active material layer 24 of the positive electrode 20 and the negative electrode active material layer 34 of the negative electrode 30, It inserts in case 50 with electrolyte solution, and the entrance of case 50 is sealed.

[Method for producing lithium ion secondary battery]
Next, a method for manufacturing the lithium ion secondary battery 100 will be specifically described.
First, a negative electrode active material, a binder, and a solvent are mixed to prepare a paint. A conductive material may be further added as necessary. As the solvent, for example, water, N-methyl-2-pyrrolidone or the like can be used. The constituent ratio of the negative electrode active material, the conductive material, and the binder is preferably 90 wt% to 98 wt%: 0 wt% to 3.0 wt%: 2.0 wt% to 5.0 wt% in mass ratio. These mass ratios are adjusted so as to be 100 wt% as a whole.

  The mixing method of these components constituting the paint is not particularly limited, and the mixing order is not particularly limited. The paint is applied to the negative electrode current collector 32. There is no restriction | limiting in particular as an application | coating method, The method employ | adopted when producing an electrode normally can be used. Examples thereof include a slit die coating method and a doctor blade method. Similarly, the positive electrode paint is applied on the positive electrode current collector 22 for the positive electrode.

Subsequently, the solvent in the paint applied on the positive electrode current collector 22 and the negative electrode current collector 32 is removed.
The removal method is not particularly limited. For example, the positive electrode current collector 22 and the negative electrode current collector 32 to which the paint is applied may be dried in an atmosphere of 80 ° C. to 150 ° C.

  Then, the electrode on which the positive electrode active material layer 24 and the negative electrode active material layer 34 are formed in this way is subjected to a press treatment by a roll press device or the like as necessary.

  Next, the positive electrode 20 having the positive electrode active material layer 24, the negative electrode 30 having the negative electrode active material layer 34, the separator 10 interposed between the positive electrode and the negative electrode, and the electrolytic solution are sealed in a case 50.

  For example, the positive electrode 20, the negative electrode 30, and the separator 10 are stacked, and the positive electrode 20 and the negative electrode 30 are heated and pressed with a press tool from a direction perpendicular to the stacking direction, and the positive electrode 20, the separator 10, and the negative electrode 30. Adhere. For example, the laminated body 40 is put into a bag-like case 50 prepared in advance.

  Finally, the lithium ion secondary battery is manufactured by injecting the electrolytic solution into the case 50. Instead of injecting the electrolytic solution into the case, the laminate 40 may be impregnated with the electrolytic solution.

  According to the present embodiment, the heat removal performance is maintained by releasing the heat in a direction different from the thickness direction of the current collector, for example, in the in-plane direction of the current collector. As a result, even if the heat removal performance in the thickness direction of the electrode plate is reduced due to the thermal expansion of the battery, the heat removal performance of the electrode is maintained without being greatly reduced. As a result, the temperature distribution in the entire electrode group is less biased, and the shutdown of the porous separator during overcharge proceeds almost uniformly. Therefore, according to the lithium ion secondary battery including the current collector according to the present embodiment, it is possible to ensure safety without adding new components or changing the structure of the battery significantly. it can.

  The embodiments of the present invention have been described in detail with reference to the drawings. However, the configurations and combinations of the embodiments in the embodiments are examples, and the addition and the omission of the configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible.

[Example 1]
An aluminum thin plate is prepared as a positive electrode current collector, 90% by weight of LiNi0.8Co0.15Al0.05O ₂ (hereinafter referred to as “NCA”) as a positive electrode active material, and 6% by weight of carbon powder as a conductive agent. As an adhesive, 4% by weight of PVDF (polyvinylidene fluoride) was prepared. Next, these were mixed with an N-methylpyrrolidone (NMP) solution to prepare a positive electrode slurry. This positive electrode slurry was applied on a thin aluminum plate by a doctor blade method, and then passed through a pressure roll to produce a positive electrode having an active material layer thickness of 55 μm.

  A thin plate made of copper-based STC (hereinafter referred to as “STC-Cu”) is prepared as a negative electrode current collector, MCMB (mesophase carbon microbeads) is 87% by weight as a negative electrode active material, and carbon powder is 3% as a conductive agent. %, And 10% by weight of PVDF was prepared as a binder. Next, these were mixed with an NMP solution to prepare a negative electrode slurry. This negative electrode slurry was applied to a STC-Cu thin plate by a doctor blade method, and then passed through a pressure roll to prepare a negative electrode having an active material layer thickness of 40 μm.

  An ethylene-methacrylic acid copolymer having a diameter of about 2 mm is spotted at the center of the positive electrode and the negative electrode, and a separator is disposed between the negative electrode and the positive electrode, and the negative electrode and the positive electrode are alternately disposed. While the resin was melted at 100 ° C., lamination was repeated to obtain a laminate comprising 10 positive electrodes and 11 negative electrodes. A polyethylene porous film having a film thickness of 12 μm was used as the separator.

  The obtained laminate was provided with a lead for taking out current, sealed together with a predetermined electrolyte and a predetermined amount in an aluminum laminate pack, and vacuum-sealed. Thereafter, heat pressing was performed at 80 ° C. to integrate the laminated body in the pack, and a lithium ion secondary battery having a 3456 size and a capacity of 1100 mAh was produced.

[Example 2]
As the positive electrode current collector, the same positive electrode (mainly composed of aluminum) as in Example 1 was produced.
A graphite sheet was prepared as a negative electrode current collector. Next, a negative electrode slurry having the same components as in Example 1 was applied on a graphite sheet by the same method as in Example 1, and then passed through a pressure roll to produce a negative electrode having the same film thickness as in Example 1.
In the following examples, the procedures for producing the laminate and producing the lithium ion secondary battery are the same as those in Example 1, and therefore description thereof is omitted.

[Example 3]
A thin plate made of STC-Al was prepared as a positive electrode current collector. Next, a positive electrode slurry having the same components as in Example 1 was applied on a STC-Al thin plate by the same method as in Example 1, and then passed through a pressure roll to produce a positive electrode having the same film thickness as in Example 1. did.
A copper thin plate was prepared as a negative electrode current collector. Next, a slurry having the same components as in Example 1 was prepared, and the slurry was applied on a copper thin plate by the same method as in Example 1, and then passed through a pressure roll to prepare a negative electrode.

[Example 4]
While producing the same positive electrode (mainly STC-Al) as Example 3 as a positive electrode current collector, the same negative electrode (mainly STC-Cu) as Example 1 was produced as a negative electrode current collector.

[Example 5]
The same positive electrode (mainly composed of STC-Al) as Examples 3 and 4 was prepared as a positive electrode current collector, and the same negative electrode (mainly composed of a graphite sheet) as Example 2 was prepared as a negative electrode current collector.

[Example 6]
As the positive electrode current collector, a thin plate made of a composite material (hereinafter referred to as “CNT aluminum composite material”) containing carbon fibers and carbon nanotubes in aluminum as a main body was prepared. Next, a positive electrode slurry having the same components as in Example 1 was applied on the thin plate made of the composite material by the same method as in Example 1, and then passed through a pressure roll to form a positive electrode having the same film thickness as in Example 1. Produced.
As the negative electrode current collector, the same negative electrode (mainly copper) as in Example 3 was produced.

[Example 7]
The same positive electrode as in Example 6 (mainly composed of a CNT aluminum composite) was produced as a positive electrode current collector, and the same negative electrode (mainly composed of STC-Cu) as in Examples 1 and 4 was produced as a negative electrode current collector. did.

[Example 8]
The same positive electrode (mainly composed of a CNT aluminum composite) as Examples 6 and 7 was produced as a positive electrode current collector, and the same negative electrode (mainly composed of a graphite sheet) as Examples 2 and 5 was used as a negative electrode current collector. Was made.

[Example 9]
A graphite sheet was prepared as a positive electrode current collector. Next, a positive electrode slurry having the same components as in Example 1 was applied onto a graphite sheet by the same method as in Example 1, and then passed through a pressure roll to produce a positive electrode having the same film thickness as in Example 1.
As the negative electrode current collector, the same negative electrode (mainly copper) as in Examples 3 and 6 was produced.

[Example 10]
The same positive electrode (mainly composed of a graphite sheet) as that of Example 9 was prepared as a positive electrode current collector, and the same negative electrode (mainly composed of STC-Cu) as that of Examples 1, 4, and 7 was prepared as a negative electrode current collector. did.

[Example 11]
The same positive electrode as in Examples 9 and 10 (mainly composed of a graphite sheet) was produced as a positive electrode current collector, and the same negative electrode as in Examples 2, 5, and 8 (mainly composed of a graphite sheet) as a negative electrode current collector Was made.

[Comparative example]
An aluminum thin plate was prepared as a positive electrode current collector. Next, a positive electrode slurry having the same components as in Example 1 was applied on an aluminum thin plate by the same method as in Example 1, and then passed through a pressure roll to produce a positive electrode having the same film thickness as in Example 1.
A copper thin plate was prepared as a negative electrode current collector. Next, a slurry having the same components as in Example 1 was prepared, and the slurry was applied on a copper thin plate by the same method as in Example 1, and then passed through a pressure roll to prepare a negative electrode.

The following measurements were performed for Examples 1 to 11 of the lithium ion secondary battery manufactured by the above procedure and a comparative example. The results are shown in Table 1.
(A) Thermal conductivity in the in-plane direction of the positive electrode current collector, that is, a predetermined direction along the surface of the positive electrode (see FIG. 2), and thermal conductivity in the thickness direction of the positive electrode current collector (B) Negative electrode current collector The thermal conductivity in the in-plane direction of the body, that is, the predetermined direction along the negative electrode surface (see FIG. 2), and the thermal conductivity in the thickness direction of the negative electrode current collector (C) The temperature of the battery surface during overcharging

  Here, for measuring the thermal conductivity in the in-plane direction of the positive electrode current collector and the negative electrode current collector, an optical alternating current method thermal diffusivity measuring device LaserPIT (manufactured by Advance Riko Co., Ltd.) was used. The thermal conductivity in the thickness direction of the positive electrode current collector and the negative electrode current collector was calculated by measuring and multiplying the thermal diffusivity and the heat capacity per unit volume, respectively. The thermal diffusivity was measured by a thermal diffusivity measuring apparatus (trade name “Eye Phase Mobile”, manufactured by Eye Phase Co.), and the heat capacity was measured by a differential scanning calorimeter (DSC).

From the measurement results shown in Table 1, when STC-Al is used for the positive electrode current collector, the thermal conductivity in the in-plane direction shows a high value of more than 200% compared to the comparative example, while the heat in the thickness direction The conductivity value decreased to about 13% of the comparative example (Examples 3, 4, and 5).
When a CNT aluminum composite material is used for the positive electrode current collector, the thermal conductivity in the in-plane direction shows a high value of more than 300% compared to the comparative example, while the thermal conductivity value in the thickness direction is the comparative example. (Examples 6, 7, and 8).
When a graphite sheet is used for the positive electrode current collector, the thermal conductivity in the in-plane direction shows a high value close to 700% compared to the comparative example, while the thermal conductivity value in the thickness direction is 8% of the comparative example. (Examples 9, 10, and 11).

In addition, when STC-Cu is used for the negative positive electrode current collector, the thermal conductivity in the in-plane direction shows a high value of more than 150% with respect to the comparative example, while the thermal conductivity value in the thickness direction is It decreased to about 9% of the comparative example (Examples 1, 4, 7, 10).
When a graphite sheet is used for the positive electrode current collector, the thermal conductivity in the in-plane direction is as high as 500% compared to the comparative example, while the thermal conductivity value in the thickness direction is 5% of the comparative example. (Examples 2, 5, 8, and 11).

  And when the temperature of the battery surface at the time of overcharge was compared, the lower value than the comparative example was shown in all the Examples. Among them, an example in which an anisotropic material made of any of STC-Cu, STC-Al, CNT aluminum composite, and graphite sheet is used for both the positive electrode current collector and the negative electrode current collector is the battery surface temperature during overcharge. (Examples 4, 5, 7, 8, 10, and 11), and the example in which the graphite sheet was used for both the positive electrode current collector and the negative electrode current collector showed the most remarkable effect ( Example 11).

  DESCRIPTION OF SYMBOLS 10 ... Separator, 20 ... Positive electrode, 22 ... Positive electrode collector, 22a ... Tab, 24 ... Positive electrode active material layer, 30 ... Negative electrode, 32 ... Negative electrode collector, 32a ... Tab, 34 ... Negative electrode active material layer, 40 ... Laminated body, 50 ... case, 52 ... metal foil, 54 ... polymer film, 60, 62 ... lead, 100 ... lithium ion secondary battery

Claims (9)

  A current collector comprising a metal thin plate as a main component and an anisotropic thermal conductor contained in the metal thin plate.   The current collector according to claim 1, comprising at least one of carbon nanotubes, graphene, aluminum-based STCs, and copper-based STCs as the anisotropic heat conductor.   The current collector according to claim 1, wherein the current collector has higher thermal conductivity in a predetermined direction along the surface of the metal thin plate than in a direction different from the predetermined direction.   The current collector according to claim 3, wherein the heat conductivity in the predetermined direction is 500 W / m · K or more. A positive electrode having a positive electrode current collector and a positive electrode layer formed on a main surface of the positive electrode current collector;
A negative electrode having a negative electrode current collector and a negative electrode layer formed on a main surface of the negative electrode current collector;
A separator that is interposed between the positive electrode and the negative electrode to separate them;
A lithium ion secondary battery comprising a non-aqueous electrolyte,
The lithium ion secondary battery in which at least one of the positive electrode current collector or the negative electrode current collector is the current collector according to any one of claims 1 to 4.   A current collector made of an anisotropic heat conductor and having higher thermal conductivity in a predetermined direction along the surface than in a direction different from the predetermined direction.   The current collector according to claim 6, wherein the anisotropic heat conductor is a graphite sheet.   The current collector according to claim 6 or 7, wherein the thermal conductivity in the predetermined direction is 500 W / m · K or more. A positive electrode having a positive electrode current collector and a positive electrode layer formed on a main surface of the positive electrode current collector;
A negative electrode having a negative electrode current collector and a negative electrode layer formed on a main surface of the negative electrode current collector;
A separator interposed between the positive electrode and the negative electrode with a gap therebetween,
A lithium ion secondary battery comprising a non-aqueous electrolyte,
The lithium ion secondary battery in which at least one of the positive electrode current collector or the negative electrode current collector is the current collector according to any one of claims 6 to 8.

Images