JP6447652B2 - Current collector for lithium secondary battery and lithium secondary battery - Google Patents

Description

  The present invention relates to a current collector for a lithium secondary battery and a lithium secondary battery.

  Lithium secondary batteries can achieve high capacity, and are widely used from mobile batteries such as mobile phones and notebook computers to automobile batteries and large-sized power storage batteries.

  Unlike a lithium ion secondary battery in which charging and discharging is performed by inserting and desorbing lithium ions into and from a material constituting the electrode, the lithium secondary battery performs charging and discharging by depositing and dissolving lithium metal. Since lithium metal has a very low potential, lithium secondary batteries are expected to be able to achieve a high theoretical capacity density.

  Lithium secondary batteries deposit metallic lithium during charging. Metallic lithium may precipitate on the tree (form dendrite) with the deposition start point as a root. The metallic lithium deposited on the tree dissolves when the lithium secondary battery is discharged. There is no problem if the metallic lithium dissolves in order from the metallic lithium branch portion deposited on the tree, but the root portion may dissolve first. In this case, the lithium metal that has lost its base floats in the non-aqueous electrolyte and cannot conduct. Since the metallic lithium floating in the non-aqueous electrolyte cannot conduct, it cannot contribute to the subsequent charge / discharge. As a result, the cycle characteristics of the lithium secondary battery are reduced.

  Patent Document 1 states that by providing pores of 3 μm or less on the surface of the current collector, increasing the specific surface area of the current collector, the effective current density is reduced, and metallic lithium forms dendrites. It is described that it can be suppressed.

JP-A-8-321310

  Patent Document 1 does not allow the formation of dendrites. Therefore, it is described that the specific surface area of the current collector is preferably as large as possible in order to prevent the formation of dendrites. As the specific surface area increases, the effective current density is reduced, and the difference in current density between the portion where the pores are formed and the other portion is reduced. If the in-plane current density difference is reduced, the probability that dendrites are formed decreases.

  However, it is still difficult to completely prevent dendrite formation. When the lithium secondary battery operates, external factors such as temperature and vibration are added. These external causes are the cause of locally increasing current density, and when the current density is locally increased, dendrites are formed.

  When an external factor is applied in a state where the effective current density on the surface of the current collector is averaged, the probability that the current density increases is uniform in any part, and the place where the dendrite is formed cannot be controlled. As a result, dendrite is formed in the charge / discharge process, and the root of metallic lithium grown on the tree may be dissolved. That is, in the lithium secondary battery using the current collector described in Patent Document 1, the cycle characteristics may not be sufficient.

  This invention is made | formed in view of the said problem, and it aims at providing the lithium secondary battery excellent in cycling characteristics.

The present inventors have accepted that the formation of dendrites, and have investigated that even if dendrites are formed, they are difficult to dissolve from the root. And it discovered that metallic lithium grew selectively in a pore by making the diameter and density of the pore formed in the surface into a predetermined range. As a result, the base part of the dendrite is present in the pores, and even when the dendrite is formed, it has been found that dissolution can be prevented from starting from the root of the lithium metal grown on the tree.
That is, in order to solve the above problems, the following means are provided.

(1) The current collector for a lithium secondary battery according to the first aspect is a metal film having a plurality of pores provided on a surface thereof, and the density of the pores on the surface of the metal film is 2 × 10 ⁶ pieces / m ² or more and 8 × 10 ¹³ pieces / m ² or less, and the average diameter of the pores is 0.02 μm or more and 1 μm or less.

(2) In the current collector for a lithium secondary battery according to the above aspect, the average depth of the pores may be 0.05 μm or more and 3.0 μm or less.

(3) In the current collector for a lithium secondary battery according to the above aspect, the average volume of the pores may be 1.5 × 10 ⁻⁴ μm ³ or more and 3.9 × 10 ⁻¹ μm ³ or less. .

(4) In the current collector for a lithium secondary battery according to the above aspect, the metal film may be any one selected from the group consisting of copper, nickel, titanium, stainless steel, platinum, and alloys thereof.

(5) In the current collector for a lithium secondary battery according to the above aspect, the pores may have a sulfur compound therein.

(6) The lithium secondary battery according to the second aspect uses the current collector for a lithium secondary battery according to the above aspect as a negative electrode, a positive electrode facing the negative electrode, and lithium ions between the negative electrode and the positive electrode And an electrolyte solution responsible for conduction.

(7) In the lithium secondary battery according to the above aspect, the electrolytic solution has a metal ion or complex contained in the current collector, and the electrolytic solution is 1 mass ppm or more and 1000 mass ppm or less. Metals may be included.

  According to the current collector for a lithium secondary battery according to the above aspect, a lithium secondary battery having excellent cycle characteristics can be obtained.

It is a cross-sectional schematic diagram of the lithium secondary battery concerning this embodiment. It is the image which image | photographed the surface of the electrical power collector concerning this embodiment with the scanning electron microscope (SEM). It is the figure which showed typically the charging / discharging process of the negative electrode vicinity of the lithium secondary battery concerning this embodiment.

  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 of the respective components 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.

“First Embodiment”
[Lithium secondary battery]
FIG. 1 is a schematic cross-sectional view of a lithium secondary battery according to the first embodiment. A lithium secondary battery 100 illustrated in FIG. 1 includes a power generation unit 40, an exterior body 50, and leads 60 and 62. The exterior body 50 accommodates the power generation unit 40 in a sealed state. One end of the pair of leads 60 and 62 is connected to the power generation unit 40, and the other end extends to the outside of the exterior body 50. Although not shown, the electrolyte is housed in the exterior body 50 together with the power generation unit 40.

(Power generation part)
In the power generation unit 40, the positive electrode 20 and the negative electrode 30 are disposed to face each other with the separator 10 interposed therebetween. In FIG. 1, the case where there is one power generation unit 40 in the exterior body 50 is illustrated, but a plurality of power generation units 40 may be stacked. In the positive electrode 20, a positive electrode active material layer 24 is provided on a plate-like (film-like) positive electrode current collector 22.

<Negative electrode>
The negative electrode 30 has a lithium metal through a current collector and a charge / discharge process. Metal lithium is deposited on the surface of the current collector during charging, and metal lithium deposited on the surface is eluted during discharging. That is, the negative electrode 30 includes the current collector and metallic lithium during charging, and the negative electrode 30 during discharging. In preparation for the shortage of the amount of lithium contributing to charging / discharging, a lithium foil may be provided on one surface of the current collector from the initial state before charging / discharging.

  FIG. 2 is an image obtained by photographing the surface of the current collector according to the present embodiment with a scanning electron microscope (SEM). As shown in FIG. 2, a plurality of pores 32 are provided on the surface of the current collector 31.

  FIG. 3 is a diagram schematically illustrating a charge / discharge process in the vicinity of the negative electrode of the lithium secondary battery according to the present embodiment. FIG. 3A shows an initial state. When the lithium secondary battery is charged from the initial state, metallic lithium 33 is deposited in the pores 32.

  As shown in FIG. 3B, the metallic lithium 33 is selectively deposited in the pores 32. This is probably because the voltage tends to concentrate on the edge portion of the pore 32 and metal lithium is likely to precipitate. As an image in which the metallic lithium 33 is selectively deposited in the pores 32, the metallic lithium 33 generated at the edge portions of the pores 32 falls into the pores 32 from the edge portions, and nuclei grows there. An image in which the inside of the pore 32 is buried, a metal lithium 33 is formed on the inner surface of the pore 32, and the nucleus is grown, so that the inside of the pore 32 having a small volume is buried first.

  When charging is continued as it is, as shown in FIG. 3C, the metallic lithium 33 grows in a dendritic shape (dendrites are formed). The energy that the metallic lithium 33 nucleates is larger than the energy that the metallic lithium 33 nucleates. Therefore, dendrite grows from metallic lithium 33 (FIG. 3B) grown in the pores 32.

  Next, when the lithium secondary battery is discharged, the metal lithium 33 is eluted. As shown in FIG. 3C, the base of the metallic lithium 33 is protected by the current collector 31 that forms the pores 32. Therefore, it is suppressed that elution progresses from the base of the metal lithium 33 at the time of discharge. As a result, the elution proceeds in order from the branch portion of the metallic lithium 33 grown in a dendritic shape (FIG. 3D).

  When the metal lithium 33 is eluted from the root, the metal lithium 33 that has lost the root floats in the electrolytic solution and cannot conduct. Since this metallic lithium 33 cannot conduct, it cannot contribute to subsequent charging / discharging. On the other hand, by growing the metal lithium 33 in the pores 32, the root of the metal lithium 33 is protected, and the amount of metal lithium floating in the electrolytic solution is reduced. That is, the decrease in the amount of lithium that can be used in the charge / discharge process is suppressed, and the cycle characteristics of the lithium secondary battery are improved.

The density of the pores 32 on the surface of the current collector 31 is 2 × 10 ⁶ / m ² or more and 8 × 10 ¹³ / m ² or less, and 7 × 10 ⁹ / m ² or more and 8 × 10 ¹³ / More preferably, it is m ² or less.

  As described above, the metallic lithium 33 first grows in the pores 32 during charging, whereby the root of the metallic lithium 33 can be protected (see FIG. 3C). If the density of the pores 32 is low, it is conceivable that the metal lithium 33 is deposited even in portions other than the pores 32. Since the root of the metal lithium 33 deposited on the portion other than the pore 32 is exposed, elution proceeds from the root, and sufficient cycle characteristics of the lithium secondary battery cannot be obtained.

  On the other hand, when the density of the pores 32 is high, the effective current density applied to the surface of the current collector 31 is averaged. What mainly constitutes the surface of the current collector 31 is the pore 32, and the current density difference formed between the flat portion and the pore 32 is averaged. The metal lithium 33 is selectively deposited in the pores 32 because there is a current density difference between the flat portion and the pores 32. When the current density is made uniform on the surface of the current collector 31, the place where the metal lithium 33 is deposited is not limited to the pores 32. As a result, metallic lithium 33 from which lithium is eluted from the root during discharge is generated, and sufficient cycle characteristics of the lithium secondary battery cannot be obtained.

  The average diameter of the pores on the surface of the current collector 31 is 0.02 μm or more and 1 μm or less, preferably 0.1 μm or more and 0.8 μm or less, and preferably 0.3 μm or more and 0.7 or less. More preferred.

  The average diameter of the pores 32 is obtained from an image taken with an SEM. First, a 10,000 times image of an arbitrary surface of the current collector 31 is taken with an SEM. Then, ten diameters of the pores 32 in the photographed image are measured. Since the pore 32 is not a perfect circle, it has a circumscribed circle diameter. The same operation is performed five times while changing the shooting location, and the average of them is obtained.

  When the average diameter of the pores 32 exceeds 1 μm, the cycle characteristics of the lithium secondary battery are degraded. The reason is not clear, but the following reasons are possible.

  The diameter of the base of the metal lithium 33 that grows from the pores 32 is increased, and the length of the metal lithium 33 that is deposited in a dendritic manner is also increased. The increase in the diameter of the metal lithium 33 is considered to be advantageous for the cycle characteristics of the lithium secondary battery because the metal lithium 33 is difficult to be cut off during discharge.

  However, metallic lithium does not maintain the same diameter when it deposits in a dendritic shape, and it becomes thinner or thicker depending on the location. The portion with the reduced diameter is easy to cut during discharge. When the length of the metal lithium 33 is increased, the probability that a portion in which the diameter of the metal lithium 33 precipitated in a dendritic shape is reduced is increased. Therefore, if the average diameter of the pores 32 is too large, the probability that the metal lithium 33 deposited in a dendritic shape will be cut at the time of elution increases, and the cycle characteristics are considered to deteriorate.

  Further, when the lithium secondary battery is charged and discharged, the volume of the negative electrode 30 changes greatly. The volume change of the negative electrode 30 applies stress to the current collector 31. If the average diameter of the pores 32 is too large, the current collector 31 may be cracked or broken due to stress. If the current collector 31 is cracked or broken, it may not be possible to quickly exchange electrons, and the battery characteristics may deteriorate.

  On the other hand, sufficient cycle characteristics cannot be obtained even when the average diameter of the pores 32 is less than 0.02 μm. If the average diameter of the pores 32 is too small, the pores 32 are immediately filled with the metal lithium 33. Further, in the charging process, when the metal lithium 33 generated at the edge portion falls into the pore 32 from the edge portion and is considered to be a nucleus that grows there, the average diameter of the pore 32 is too small and the metal lithium 33 is removed from the edge portion. It is conceivable that it does not fall into the pore 32. As a result, it is conceivable that the metallic lithium 33 is deposited from an arbitrary place and the cycle characteristics are deteriorated.

  The average depth of the pores 32 is preferably 0.05 μm or more and 3.0 μm or less, preferably 0.1 μm or more and 2.0 μm or less, and more preferably 0.3 μm or more and 1.0 μm or less. preferable.

  The average depth of the pores 32 is determined from an image taken with a cross-sectional SEM. First, the current collector 31 is cut at an arbitrary location, and an image of 10,000 times the cross section is taken with an SEM. Then, the depth of the pore 32 existing in the photographed image is measured. The same operation is performed five times while changing the shooting location, and the average of them is obtained.

  If the average depth of the pores 32 is too shallow, the protection of the roots of the metal lithium 33 deposited therefrom will not be sufficient. As a result, the probability that metal lithium 33 from which lithium elutes from the root during discharge is generated increases. On the other hand, if the average depth of the pores 32 is too deep, the strength of the current collector 31 decreases. If the current collector 31 is cracked or broken, electrons cannot be exchanged quickly and the battery characteristics are deteriorated.

The average volume of the pores 32 is preferably at 1.5 × ^{10 -4} μm ³ or more 3.9 × ^{10 -1} μm ³ or less, 9.8 × ^{10 -3} μm ³ or more 9.8 × 10 ^- More preferably, it is ² μm ³ or less.

  The average volume of the pores 32 is determined from the average diameter and the average depth of the pores 32. When the average volume of the pores 32 is small, the pores 32 are immediately filled with the metal lithium 33. Assuming that the amount of metallic lithium 33 deposited when fully charged is constant, when the amount of metallic lithium 33 present in the pores 32 decreases, the amount of metallic lithium 33 deposited relatively in a dendritic manner increases. . As the amount of metallic lithium 33 deposited in a dendritic state increases, the probability that the amount of metallic lithium floating in the electrolytic solution will increase accordingly.

  The current collector 31 is a metal film having excellent electrical conductivity. As described above, the metal lithium 33 is deposited on one surface of the current collector 31. Therefore, the metal constituting the current collector 31 is preferably a material that is difficult to form an alloy with lithium. Specifically, it is preferably one selected from the group consisting of copper, nickel, titanium, stainless steel, platinum, and alloys thereof, and copper is particularly preferable.

  The current collector 31 may have a sulfur compound inside the pores 32. “Having a sulfur compound” means that sulfur element (S) is detected in energy dispersive X-ray analysis (EDS analysis).

  When the sulfur element is present in the pores 32, the cycle characteristics of the lithium secondary battery are improved. Although the reason for this is not clear, it is considered that, for example, a sulfur element and a metal element constituting the current collector are combined to suppress corrosion of the metal element constituting the current collector.

<Positive electrode>
The positive electrode 20 includes a positive electrode current collector 22 and a positive electrode active material layer 24 provided on one surface thereof (see FIG. 1). The positive electrode current collector 22 only needs to be made of a conductive material. For example, a thin metal plate of aluminum, copper, or nickel foil can be used.

The positive electrode active material used for the positive electrode active material layer 24 includes insertion and extraction of lithium ions, desorption and insertion (intercalation) of lithium ions, or counter anions (for example, PF ₆ ⁻ ) of lithium ions and lithium ions. An electrode active material capable of reversibly proceeding doping and dedoping can be used.

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} a2 ( x + y + z + a = 1, 0 ≦ x <1, 0 ≦ y <1, 0 ≦ z <1, 0 ≦ a <1, M is one or more selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr Element)), lithium vanadium compound (LiV ₂ O ₅ ), olivine-type LiMPO ₄ (where M is selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr) are shown one or more elements or VO), lithium titanate _{(Li 4 Ti 5 O 12)} , LiNi x Co y Al z O 2 (0.9 <x + y + z <1 1) a composite metal oxide such as polyacetylene, polyaniline, polypyrrole, polythiophene, and the like polyacene.

  The positive electrode active material layer 24 may have a conductive material. Examples of the conductive material include carbon powder such as carbon black, carbon nanotube, carbon material, fine metal powder such as copper, nickel, stainless steel and iron, a mixture of carbon material and fine metal powder, and conductive oxide such as ITO. It is done. In the case where sufficient conductivity can be ensured with only the positive electrode active material, the positive electrode active material layer 24 may not include a conductive material.

  The positive electrode active material layer 24 includes a binder. A well-known thing can be used for a binder. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Fluorine resins such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF).

  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.

<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.

(Electrolyte)
The electrolytic solution is impregnated in the power generation unit 40. As the electrolytic solution, an electrolyte solution containing lithium salt or the like (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.

  In the non-aqueous electrolyte solution, an electrolyte is dissolved in a non-aqueous solvent, and a cyclic carbonate and a chain carbonate may be contained as a non-aqueous solvent.

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

  An ionic liquid may be used as the non-aqueous electrolyte solution. An ionic liquid is a salt which is liquid even below 100 ° C. obtained by a combination of a cation and an anion. Since the ionic liquid is a liquid composed only of ions, the ionic liquid has a strong electrostatic interaction and is characterized by non-volatility and nonflammability. The lithium secondary battery 100 using an ionic liquid as an electrolyte is excellent in safety.

  The electrolytic solution preferably has a metal ion or complex contained in the current collector 31. Moreover, it is preferable that the content is 1 mass ppm or more and 1000 mass ppm or less in conversion of the mass of a metal.

  When the metal which comprises the electrical power collector 31 is contained in electrolyte solution, the corrosion of the electrical power collector 31 is suppressed by the chemical equilibrium of the metal ion or complex, and the electrical power collector 31. FIG.

(Exterior body)
The exterior body 50 seals the power generation unit 40 and the electrolyte therein. The outer package 50 is not particularly limited as long as it can prevent leakage of the electrolyte to the outside and entry of moisture and the like into the lithium secondary battery 100 from the outside.

  For example, as the outer package 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. For example, the material of the outer polymer film 54 is preferably a polymer 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 20 and the negative electrode 30, respectively, and the separator 10 is sandwiched between the positive electrode 20 and the negative electrode 30 and inserted into the outer package 50 together with the electrolyte, and the entrance of the outer package 50 is sealed. .

  As described above, in the lithium secondary battery according to this embodiment, the current collector constituting the negative electrode has pores satisfying a predetermined density and a predetermined average diameter. Therefore, metallic lithium is selectively deposited from the pores, and the base of the deposited metallic lithium is protected by the current collector that forms the pores. Therefore, elution is suppressed from proceeding from the base of metallic lithium during discharge, and the cycle characteristics of the lithium secondary battery are improved.

[Method for producing lithium secondary battery]
A method for manufacturing the lithium secondary battery 100 according to the present embodiment will be described. First, the positive electrode 20 and the negative electrode 30 are produced.

  The positive electrode 20 is produced by applying a paint containing a positive electrode active material on the positive electrode current collector 22 and drying it. The coating material containing a positive electrode active material contains a positive electrode active material, a binder, and a solvent, and a conductive material is mixed as necessary. As the solvent, for example, water, N-methyl-2-pyrrolidone, or the like can be used.

  The composition ratio of the positive electrode active material, the conductive material, and the binder in the paint is preferably 80 wt% to 98 wt%: 0.1 wt% to 10 wt%: 0.1 wt% to 10 wt% in mass ratio. These mass ratios are adjusted so as to be 100 wt% as a whole. The mixing method of the components constituting the paint is not particularly limited, and the mixing order is not particularly limited.

  Then, the prepared paint is applied to the positive electrode current collector 22. 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.

  Subsequently, the solvent in the paint applied to the positive electrode current collector 22 is removed. The removal method is not particularly limited. For example, the positive electrode current collector 22 to which the paint is applied may be dried in an atmosphere of 80 ° C. to 150 ° C. And the positive electrode 20 in which the positive electrode active material layer 24 was formed on the positive electrode collector 22 is obtained.

  For the negative electrode 30, a metal film used as the current collector 31 is prepared. A commercially available metal film can be used. The pores 32 are formed on the surface of the prepared metal film (current collector 31). The means for forming the pores 32 is not particularly limited. For example, the metal compound may be subjected to a reduction treatment to remove elements constituting the compound. Alternatively, the pores 32 may be formed by pressing a stamper having predetermined protrusions on the metal film and then performing an acid treatment or the like. Further, the pores 32 may be directly drawn using means such as electron beam lithography.

  When a sulfur compound is formed inside the pores 32 of the current collector 31, the current collector 31 is immersed in an electrolyte containing sulfur, and a voltage is applied to the current collector 31 to reduce and decompose the electrolyte containing sulfur. By doing so, the sulfur element is attached to the surface of the current collector 31.

  Next, the produced positive electrode 20 and negative electrode 30 are stacked with the separator 10 interposed between them, and sealed in the outer package 50 together with the electrolytic solution. For example, the positive electrode 20, the negative electrode 30, and the separator 10 are stacked, and the power generation unit 40 is placed in a bag-shaped exterior body 50 that is manufactured in advance. The electrolytic solution may be injected into the outer package 50 or may be impregnated in the power generation unit 40.

  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
First, a positive electrode was prepared. NCA (composition formula: Li _1.0 Ni _0.78 Co _0.19 Al _0.03 O ₂ ) was prepared as the positive electrode active material, carbon black as the conductive material, and PVDF as the binder. These were mixed in a solvent to prepare a paint, and applied onto a positive electrode current collector made of aluminum foil. The mass ratio of the positive electrode active material, the conductive material, and the binder was 95: 2: 3. After application, the solvent was removed.

Next, a negative electrode was prepared. The negative electrode used copper foil as a current collector. A stamper having projections of 7 × 10 ⁹ pieces / m ² was produced using electron beam lithography, and the stamper was pressed against the copper foil surface. Then, the copper foil after the stamper was pressed was subjected to an acid treatment to expand the holes formed by the stamper and produce the pores.

  The prepared electrode facing the current collector was immersed in a thiocyanate solution, and a voltage was applied between the current collector and the counter electrode. The surface of the current collector after the voltage application treatment was washed and subjected to EDS analysis. As a result, sulfur element was detected in the pores.

And the produced positive electrode and the negative electrode were laminated | stacked through the separator, and the electric power generation part was produced. The number of stacked positive and negative electrodes was one. For the separator, a laminate of polyethylene and polypropylene was used. The obtained power generation part was impregnated with a non-aqueous electrolyte and then enclosed in the exterior body. N-methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide (P ₁₃ -FSI) is used as the electrolyte, and lithium bis (trifluoromethanesulfonyl) imide (Li-TFSI) is used so as to have a concentration of 1 mol / L. ) Was used. The obtained lithium secondary battery was charged and discharged, and the capacity retention rate was measured. The capacity retention rate of the lithium secondary battery means the capacity ratio of the discharge capacity at the 100th discharge to the discharge capacity at the first discharge.

(Examples 2 and 3 and Comparative Examples 1 and 2)
Examples 2 and 3 and Comparative Examples 1 and 2 differ from Example 1 in that the diameter of the pores was changed. The diameter of the pores was adjusted by changing the time during which the copper foil was subjected to acid treatment. The other conditions were the same as in Example 1, and the capacity retention rate of the lithium secondary battery was measured.

(Examples 4 and 5 and Comparative Examples 3 and 4)
Examples 4 and 5 and Comparative Examples 3 and 4 differ from Example 1 in that the density of the pores was changed. The density of the pores was changed by changing the density of the stamper protrusions pressed against the copper foil. The other conditions were the same as in Example 1, and the capacity retention rate of the lithium secondary battery was measured.

(Examples 6 and 7)
Examples 6 and 7 differ from Example 1 in that the density of the pores and the diameter of the pores were changed. The other conditions were the same as in Example 1, and the capacity retention rate of the lithium secondary battery was measured.

(Examples 8 to 11)
Examples 8 to 11 differ from Example 1 in that the pore diameter was changed to 0.02 μm, the pore density was changed to 2 × 10 ⁹ pores / m ² , and the pore depth was changed. The depth of the pores was changed by changing the pressure when pressing the stamper against the copper foil. The other conditions were the same as in Example 1, and the capacity retention rate of the lithium secondary battery was measured.

(Examples 12 and 13)
In Examples 12 and 13, the diameter of the pores was changed to 0.02 μm, the density of the pores was changed to 2 × 10 ⁹ pieces / m ^2, and the amount of copper ions contained in the electrolytic solution was changed. The content of copper ions was adjusted by the content of triethylenetetramine copper complex. The other conditions were the same as in Example 1, and the capacity retention rate of the lithium secondary battery was measured.

  The results of capacity retention rates of the lithium secondary batteries of Examples 1 to 13 and Comparative Examples 1 to 4 are summarized in Table 1 below.

When Examples 1 to 3 and Comparative Examples 1 and 2 were compared, it was confirmed that the capacity retention rate was excellent when the pore diameter was in the range of 0.02 μm to 1.0 μm. Further, when Examples 1, 4, and 5 are compared with Comparative Examples 2 and 3, the capacity retention rate is excellent when the pore density is in the range of 2 × 10 ⁶ / m ^{2 to} 8 × 10 ¹³ / m ^2. Was confirmed. Further, when Examples 1 and 8 to 11 were compared, it was confirmed that the capacity retention rate was particularly excellent when the depth of the pores was within a predetermined range. Further, from Examples 1, 12, and 13, it was confirmed that the capacity retention rate was particularly excellent when the copper ion concentration in the electrolytic solution was within a predetermined range.

DESCRIPTION OF SYMBOLS 10 ... Separator, 20 ... Positive electrode, 22 ... Positive electrode collector, 24 ... Positive electrode active material layer, 30 ... Negative electrode, 31 ... Current collector, 32 ... Fine pore, 33 ... Metal lithium, 40 ... Power generation part, 50 ... Exterior Body, 60, 62 ... lead, 100 ... lithium secondary battery

Claims (7)

A negative electrode used for a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode includes a negative electrode current collector, lithium metal is deposited on the negative electrode current collector during charging, and lithium metal dissolves during discharge A current collector,
A metal film having a plurality of pores on the surface,
The density of the pores on the surface of the metal film is 2 × 10 ⁶ pieces / m ² or more and 8 × 10 ¹³ pieces / m ² or less,
The negative electrode current collector for a lithium secondary battery, wherein the average diameter of the pores is 0.02 μm or more and 1 μm or less. 2. The negative electrode current collector for a lithium secondary battery according to claim 1, wherein an average depth of the pores is 0.05 μm or more and 3.0 μm or less. 3. The negative electrode current collector for a lithium secondary battery according to claim 1, wherein an average volume of the pores is 1.5 × 10 ⁻⁴ μm ³ or more and 3.9 × 10 ⁻¹ μm ³ or less. The metal film is copper, nickel, titanium, platinum and their alloys, as well as any one selected from the group consisting of stainless steel, a lithium secondary battery according to any one of claims 1 to 3 Negative electrode current collector. The negative electrode current collector for a lithium secondary battery according to any one of claims 1 to 4, wherein the pores have a sulfur compound therein. Using the negative electrode current collector for a lithium secondary battery according to any one of claims 1 to 5 as a negative electrode ,
A lithium secondary battery comprising: a positive electrode facing the negative electrode; and an electrolyte solution that conducts lithium ions between the negative electrode and the positive electrode. The electrolytic solution has a metal ion or complex contained in the current collector,
The lithium secondary battery according to claim 6, wherein the electrolytic solution contains 1 to 1000 ppm by mass of the metal.