JP6489252B1 - Negative electrode current collector, negative electrode and lithium secondary battery - Google Patents

Abstract

An object of the present invention is to provide a lithium secondary battery in which volume expansion is suppressed and an anode current collector and an anode suitable for the lithium secondary battery. An anode current collector according to one aspect of the present invention has at least one crystal particle selected from the group consisting of copper, nickel, stainless steel, and titanium, and the average crystallite size of the crystal particle is 380 Å or more and 4000 Å or less. [Selected figure] Figure 1

Description

  The present invention relates to a negative electrode current collector, a negative electrode and a lithium secondary battery.

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

  A lithium secondary battery using metal lithium for the negative electrode performs charge and discharge by depositing and dissolving lithium metal. Since lithium metal has a very low potential, lithium secondary batteries are expected to achieve high theoretical capacity density.

  One of the problems of lithium secondary batteries is volumetric expansion during charge and discharge. For example, in Patent Document 1, volume expansion occurs when dendrite (metal lithium is precipitated on a tree with the deposition start point as a root) is formed and disappears, and this volume expansion causes a part of the electrode to be cut and the battery It is stated that it causes the decrease of capacity.

  Patent Documents 2 and 3 describe means for suppressing this dendrite. Patent Document 2 uses an amorphous metal or an amorphous alloy substantially free of grain boundaries on the metal deposition surface as a negative electrode current collector. It is described in Patent Document 2 that the difference between the grain boundaries and the orientation plane is the cause of the non-uniformity of the current distribution during charge and discharge, and the use of this negative electrode current collector can suppress dendrite.

  Patent Document 3 uses, for a lithium secondary battery, a negative electrode current collector having a metal deposition surface with a surface roughness (Rz) of 10 μm or less. It is described in patent documents 3 that non-uniformity of current distribution at the time of charge and discharge can be prevented, and dendrite can be controlled by smoothing a metal precipitation side.

Unexamined-Japanese-Patent No. 11-224689 gazette JP 2001-250559 A JP 2001-243957 A

  Dendrite is one of the major causes of volumetric expansion of lithium secondary batteries, but volumetric expansion of lithium secondary batteries is not caused by dendrite alone. For example, when the amount of decomposition gas in which the electrolytic solution is decomposed is large, the lithium secondary battery is largely expanded in volume. That is, in the lithium secondary batteries described in Patent Documents 2 and 3, the volumetric expansion could not be sufficiently suppressed. Moreover, even when the negative electrode current collectors described in Patent Documents 2 and 3 were used, generation of dendrite could not be sufficiently suppressed.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide a lithium secondary battery in which volume expansion is suppressed, and a negative electrode current collector and a negative electrode that are suitable for the lithium secondary battery.

The present inventors focused attention on the crystallite size constituting crystal particles and found that when the crystallite size is in a predetermined range, it is possible to suppress the volume expansion of the lithium secondary battery.
That is, in order to solve the above-mentioned subject, the following means are provided.

(1) The negative electrode current collector according to the first aspect has at least one crystal particle selected from the group consisting of copper, nickel, stainless steel, and titanium, and the average crystallite size of the crystal particle is 380 Å or more and 4000 Å. It is below.

(2) In the negative electrode current collector according to the above aspect, the half width d1 in the (200) plane and the half width d2 in the (220) plane in the X-ray diffraction measurement satisfy 1.1 ≦ d2 / d1 ≦ 1.4. May satisfy the relationship of

(3) In the negative electrode current collector according to the above aspect, the size of the crystal particle may be 1.5 μm or more and 2.5 μm or less.

(4) The negative electrode according to the second aspect includes the negative electrode current collector according to the above aspect.

(5) The negative electrode according to the above aspect may include metallic lithium as a negative electrode active material layer on at least one surface of the negative electrode current collector.

(6) The lithium secondary battery according to the third aspect includes the negative electrode according to the above aspect, a positive electrode facing the negative electrode, and a separator located between the negative electrode and the positive electrode.

  When the negative electrode current collector according to the above aspect is used, a lithium secondary battery in which volume expansion is suppressed can be obtained.

It is a cross-sectional schematic diagram of the lithium secondary battery concerning this embodiment.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may show enlarged features for convenience for the purpose of clarifying the features of the present invention, and the dimensional ratio of each component may be different from the actual one. is there. The materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not limited to them, and can be appropriately changed and implemented without changing the gist of the invention.

First Embodiment
[Lithium secondary battery]
FIG. 1 is a schematic cross-sectional view of the lithium secondary battery according to the first embodiment. The lithium secondary battery 100 shown 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. Further, although not shown, the electrolytic solution is accommodated in the exterior body 50 together with the power generation unit 40.

(Power generation unit)
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. Although FIG. 1 illustrates the case where one power generation unit 40 is provided in the exterior body 50, a plurality of power generation units 40 may be stacked.

<Negative electrode>
The negative electrode 30 includes a negative electrode current collector 32 and a negative electrode active material layer 34. In the case where precipitation of lithium metal and dissolution reaction are used in the negative electrode 30, the negative electrode active material layer 34 may not be in the initial state. This is because lithium ions in the electrolytic solution are deposited as metallic lithium on one surface of the negative electrode current collector 32. On the other hand, since the deposited metal lithium remains when charging is performed once or more, the layer containing the metal lithium can be regarded as the negative electrode active material layer 34. Also, in preparation for the shortage of the amount of lithium contributing to charge and discharge, lithium foil may be provided on one surface of the current collector from the initial state before charge and discharge.

  On the other hand, when alloying or de-alloying reaction is used in the negative electrode, Si, Sn or the like is used as the negative electrode active material layer 34. When Si is alloyed, the volume is quadrupled, and therefore, it is required to suppress volumetric expansion.

  The negative electrode current collector 32 has at least one crystal particle selected from the group consisting of copper, nickel, stainless steel, and titanium. The negative electrode current collector 32 is preferably a metal foil of at least one of these metals. Each of these metals is excellent in conductivity and can quickly output electrons generated through the lead 60 to the outside.

  The average crystallite size of the crystal particles constituting the negative electrode current collector 32 is 380 Å or more and 4000 Å or less, and preferably 380 Å or more and 800 Å or less. Here, the term "crystallite" refers to the largest group that can be regarded as a single crystal, and one crystal particle is composed of a plurality of crystallites. The average crystallite size is determined from the half width of the diffraction peak in X-ray diffraction according to Scheller's equation. The wavelength of the X-ray used for measurement was 1.54 Å, the Bragg angle (half of the diffraction angle) was 35 ° to 40 °, and the diffraction peak used for measurement of the half width was 74.14 ° at 2θ.

  When the average crystallite size of the crystal particles is within the above range, the volumetric expansion of the lithium secondary battery 100 is suppressed. Although the reason why the volume expansion is suppressed is not clear, it is considered that one of the major factors is that the reaction field at the time of charge and discharge reaction becomes appropriate when the average crystallite size is within the predetermined range. .

  When the average crystallite size of the crystal particles is small, the reaction area between the electrolytic solution and the crystallites increases, and the reaction site increases. Ideally, the energy given should be used for all the lithium deposition and dissolution reactions, but if there are too many reaction sites, these reactions can not catch up, and the excess energy decomposes the electrolyte. The decomposed electrolyte becomes a gas, which is a major cause of volume expansion.

  On the other hand, when the average crystallite size of the crystal grains is large, the size of the crystal grains tends to be large. When the size of the crystal particle is large, the conductivity in the negative electrode current collector 32 becomes nonuniform in the plane, the precipitation state of lithium becomes nonuniform, and the surface state of the precipitation surface becomes rough. Then, the reaction occurs locally, lithium precipitation and dissolution reaction can not catch up, and excess energy decomposes the electrolyte. The decomposed electrolyte becomes a gas, which is a major cause of volume expansion.

  On the other hand, when the average crystallite size of the crystal particles is within the above range, the reaction field contributing to the precipitation and dissolution reaction of lithium is stabilized in the plane of the negative electrode 30, and the decomposition reaction of the electrolyte occurs. It can be suppressed.

  Further, when the average crystallite size of the crystal particles is in the above range, the generation of dendrite can also be suppressed. Dendrite is one of the causes of volumetric expansion.

  When the average crystallite size of the crystal particles is small, the metal element constituting the crystal particles is easily diffused. The diffused metal element reacts with an element (active material) constituting the negative electrode active material layer 34 to be alloyed. As described above, even when the negative electrode active material layer 34 is not present in the initial state, metal lithium becomes the negative electrode active material layer 34 after one or more times of charging, so an alloying reaction between the diffused metal element and the metal lithium occurs. .

  When an alloying reaction occurs in the negative electrode active material layer 34, the active material expands in volume. When the active material expands in volume, compressive stress is generated in the negative electrode active material layer 34. The compressive stress is particularly strong at the particle interface of the active material, and makes the pressure distribution in the plane of the negative electrode active material layer 34 uneven. The precipitation state of lithium is strongly influenced by the state of the precipitation surface. For example, in a portion under high pressure, metallic lithium tends to grow in a direction intersecting with the deposition surface so as to release the pressure. The metallic lithium deposited in the direction intersecting the deposition surface is dendrite.

  When the average crystallite size of the crystal particles is 380 Å or more, the diffusion of the metal element constituting the crystal particles can be sufficiently suppressed.

  In the negative electrode current collector 32, it is preferable that the half width d1 in the (200) plane and the half width d2 in the (220) plane in the X-ray diffraction measurement satisfy the relationship of 1.10 ≦ d2 / d1 ≦ 1.40. It is preferable to satisfy the relationship of 1.25 <d2 / d1 ≦ 1.40.

  The average crystallite size of the negative electrode current collector 32 varies depending on the sintered state, and is small in unsintered state and large in the sintered state. Moreover, the X-ray diffraction measurement result of the negative electrode current collector 32 shows that the crystallinity of the (200) plane is high in the unsintered state (half width d1 is narrow) and the crystallinity of the (220) plane is high in the sintered state Price range d2 is narrow). It is considered that when the metal element constituting the negative electrode current collector 32 crystal-grows, the average crystallite size increases and the X-ray diffraction conditions change.

  When the half width d1 in the (200) plane and the half width d2 in the (220) plane in the X-ray diffraction satisfy the above relationship, the volumetric expansion of the lithium secondary battery 100 is suppressed. The cause of this is not clear, but in addition to the average crystallite size of the crystal particles, it is thought that the reaction field is stabilized by the orientation state of the crystal becoming a specific state, and the decomposition of electrolyte and the dendrite are suppressed. Be

  The size of the crystal particles of the negative electrode current collector 32 is preferably 1.5 μm or more and 2.5 μm or less, and more preferably 1.5 μm or more and 1.7 μm or less. The volume expansion of the lithium secondary battery 100 is further suppressed when the size of the crystal particles is in the above range.

  The size of the crystal particle is the size of a particle that can be regarded as one particle in observation with a scanning electron microscope (SEM) or the like, and is calculated from a 5000 × or 10000 × planar image captured by the SEM. Specifically, the major axis length and the minor axis length of ten arbitrarily selected crystal grains in the field of view of the image are measured, and the average value thereof is determined. The average of the minor axis length and the major axis length of the measured crystal grain corresponds to the size of the crystal grain.

  The crystal particles of the negative electrode current collector 32 preferably have a columnar shape. The aspect that the shape of the crystal grain is columnar is an aspect in which the average major axis length of ten arbitrarily selected crystal grains is divided by the average minor axis length in a cross-sectional image of 5000 times or 10000 times captured by SEM. It means that the ratio is 1.4 or more. When the orientation state of the crystallites constituting the crystal particles changes, the reaction state of precipitation and dissolution of metal lithium changes. As a result, volumetric expansion of the lithium secondary battery 100 is further suppressed.

<Positive electrode>
The positive electrode 20 has 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 may be made of a material having conductivity, and 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 lithium ion absorption and release, lithium ion desorption and insertion (intercalation), or lithium ion and lithium ion counter anion (for example, PF ₆ ⁻ ) An electrode active material capable of reversibly advancing doping and de-doping can be used.

For example, lithium cobaltate (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, Cr Complex metal oxide represented by the 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 powders such as carbon blacks, carbon nanotubes, carbon materials, metal fine powders such as copper, nickel, stainless steel and iron, mixtures of carbon materials and metal fine powders, and conductive oxides such as ITO. Be When sufficient conductivity can be ensured only with the positive electrode active material, the positive electrode active material layer 24 may not contain the conductive material.

  The positive electrode active material layer 24 also contains 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-tetrafluorocarbon And fluorine resins such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF).

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

<Separator>
The separator 10 may 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, cellulose, polyester, A non-woven fabric made of at least one component selected from the group consisting of polypropylene can be mentioned.

(Electrolyte solution)
The electrolytic solution is impregnated in the power generation unit 40. As the electrolytic solution, an electrolytic solution containing a lithium salt or the like (aqueous electrolytic solution, non-aqueous electrolytic solution using an organic solvent) can be used. However, since the aqueous electrolytic solution has a low decomposition voltage electrochemically, the useful voltage at the time of charge is limited to a low level. Therefore, it is preferable that it is the electrolyte solution (non-aqueous electrolyte solution) which uses an organic solvent.

  The non-aqueous electrolyte solution has an electrolyte dissolved in a non-aqueous solvent, and may contain a cyclic carbonate and a linear carbonate as the non-aqueous solvent.

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

  Chain carbonates can reduce the viscosity of cyclic carbonates. For example, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate can be mentioned. 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 cyclic carbonate to linear carbonate in the non-aqueous solvent is preferably 1: 9 to 1: 1 by volume.

  An ionic liquid may also be used as the non-aqueous electrolyte solution. An ionic liquid is a salt which is liquid at less than 100 ° C. obtained by the combination of a cation and an anion. Since the ionic liquid is a liquid consisting only of ions, it has strong electrostatic interaction, and is characterized as being non-volatile and non-combustible. The lithium secondary battery 100 using an ionic liquid as an electrolytic solution is excellent in safety.

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

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

"Lead"
The leads 60 and 62 are formed of a conductive material such as aluminum. The leads 60 and 62 are respectively welded to the positive electrode 20 and the negative electrode 30, and the separator 10 is inserted between the positive electrode 20 and the negative electrode 30 together with the electrolytic solution and inserted into the outer package 50, and the inlet of the outer package 50 is sealed. Do.

  As described above, in the lithium secondary battery according to the present embodiment, the average crystallite size of the negative electrode current collector 32 is within the predetermined range. Therefore, the reaction site is stabilized, decomposition of the electrolytic solution and dendrite are suppressed, and volumetric expansion of the lithium secondary battery 100 is suppressed.

[Method of manufacturing lithium secondary battery]
A method of 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 manufactured.

  The positive electrode 20 is produced by applying and drying a paint containing a positive electrode active material on the positive electrode current collector 22. A paint containing a positive electrode active material contains a positive electrode active material, a binder and a solvent, and a conductive material is mixed as needed. As the solvent, for example, water, N-methyl-2-pyrrolidone and 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 to be 100 wt% in total. The method of mixing the components constituting the paint is not particularly limited, and the order of mixing is also not particularly limited.

  Then, the prepared paint is applied to the positive electrode current collector 22. There is no restriction | limiting in particular as a coating method, The method employ | adopted when producing an electrode normally can be used. For example, a slit die coating method or a doctor blade method may be mentioned.

  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. Then, the positive electrode 20 in which the positive electrode active material layer 24 is formed on the positive electrode current collector 22 is obtained.

  The negative electrode 30 prepares a metal foil used as the negative electrode current collector 32. The prepared metal foil is sintered to adjust the average crystallite size of crystal particles constituting the metal film. There is a certain correlation between the average crystallite size of the crystal grains and the sintering temperature, and the average crystallite size increases as the sintering temperature increases. Therefore, if a precise calibration curve can be prepared, a predetermined negative electrode current collector 32 can be obtained by sintering the metal foil according to the calibration curve. In order to set the average crystallite size to 380 Å or more and 4000 Å or less, the sintering temperature is preferably set to about 200 ° C. to 350 ° C.

  On the other hand, in the sintering furnace, the average crystallite size often fluctuates even when sintered under the same conditions due to temperature distribution and various factors. It is difficult to strictly control the average crystallite size in the region of 380 Å or more and 4000 Å or less. Therefore, after sintering, the average crystallite size is measured by X-ray diffraction, and the one that is within the specific range is used as the negative electrode current collector 32.

  When sintering the metal film, it is preferable to sinter in a reducing atmosphere or vacuum. For example, copper is easily oxidized. By sintering in a reducing atmosphere or vacuum, the formation of copper oxide in the negative electrode current collector 32 can be suppressed, and the nonuniformity of the conductivity can be further suppressed.

  When Si, Sn or the like other than metallic lithium is used as the negative electrode active material layer 34, a solvent containing the negative electrode active material, a binder and a solvent is applied to the negative electrode current collector 32, and the solvent is removed. When removing the solvent, the negative electrode current collector 32 may be sintered.

  Subsequently, the produced positive electrode 20 and the negative electrode 30 are stacked via the separator 10 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 the bag-like exterior body 50 manufactured in advance. The electrolytic solution may be injected into the exterior body 50 or may be impregnated into the power generation unit 40.

  The embodiments of the present invention have been described in detail with reference to the drawings, but the respective configurations and the combinations thereof and the like in the respective embodiments are merely examples, and additions and omissions of configurations are possible within the scope of the present invention. , Permutations, and other modifications are possible.

Example 1
First, a positive electrode was prepared. NCA as a positive electrode active material (composition _{formula: Li 1.0 Ni 0.78 Co 0.19 Al} 0.03 O 2), carbon black as a conductive material was prepared PVDF as a binder. These were mixed in a solvent to prepare a paint, which was applied on 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.

  Then, a negative electrode current collector was prepared. The copper foil was sintered at a set temperature of 200 ° C., and the average crystallite size was determined by X-ray diffraction. Then, one having an average crystallite size of 380 Å was used as a negative electrode current collector.

And the produced positive electrode and negative electrode were laminated | stacked through the separator, and the electric power generation part was produced. The number of stacked layers of the positive electrode and the negative electrode was one. For the separator, a laminate of polyethylene and polypropylene was used. The obtained power generation unit was impregnated with a non-aqueous electrolyte and then enclosed in an outer package. As an electrolytic solution, N-methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide (P ₁₃ -FSI) is used, and lithium bis (trifluoromethanesulfonyl) imide (Li-TFSI) is prepared to have a concentration of 1 mol / L. ) Was used. And charge and discharge of the obtained lithium secondary battery were performed, and the expansion coefficient with respect to the lithium secondary battery at the time of discharge of the lithium secondary battery at the time of charge was calculated | required. The expansion coefficient was determined by “volume difference of lithium secondary battery between charging and discharging” / “volume of lithium secondary battery at discharging” × 100.

(Examples 2 to 5)
Example 2 differs from Example 1 in that the one having an average crystallite size of 400 Å is selected as the negative electrode current collector, and the example 3 selects one having an average crystallite size of 500 Å as the negative electrode current collector The point is different from Example 1, Example 4 is different from Example 1 in that an average crystallite size of 600 Å is selected as a negative electrode current collector, and Example 5 has an average crystallite size of 800 Å. Is different from Example 1 in that the negative electrode current collector was selected. The other conditions were the same as in Example 1 and the number of cycles was determined.

(Examples 6 to 9)
Examples 6 to 9 differ from Example 1 in that the copper foil was sintered at a set temperature of 350 ° C. In Example 6, the one having an average crystallite size of 1,000 Å was selected as the negative electrode current collector, and in Example 7, the one having an average crystallite size of 2,000 Å was selected as the negative electrode current collector. One having a size of 3000 Å was selected as a negative electrode current collector, and in Example 9, one having an average crystallite size of 4000 Å was selected as a negative electrode current collector. The other conditions were the same as in Example 1 to determine the expansion rate.

(Comparative example 1)
Comparative Example 1 is different from Example 1 in that the copper foil was used in an unsintered state. In Comparative Example 1, one having an average crystallite size of 300 Å was selected as a negative electrode current collector. The other conditions were the same as in Example 1 to determine the expansion rate.

(Comparative Examples 2 and 3)
Comparative Examples 2 and 3 differ from Example 1 in that the copper foil was sintered at a set temperature of 100 ° C. And in Comparative Example 2, one having an average crystallite size of 340 Å was selected as a negative electrode current collector, and in Comparative Example 3, one having an average crystallite size of 360 Å was selected as a negative electrode current collector. The other conditions were the same as in Example 1 to determine the expansion rate.

(Comparative Examples 4 to 6)
Comparative Examples 4 to 6 are different from Example 1 in that the copper foil was sintered at a set temperature of 350 ° C. And in Comparative Example 4, one having an average crystallite size of 4200 Å is selected as the negative electrode current collector, and in Comparative Example 5, one having an average crystallite size of 4500 Å is selected as the negative electrode current collector. One having a size of 5000 Å was used as a negative electrode current collector. The other conditions were the same as in Example 1 to determine the expansion rate.

  As shown in Table 1, the expansion coefficient of the lithium secondary battery was suppressed when the average crystallite size was in the range of 380 Å to 4000 Å.

(Examples 10 to 20)
Next, the average crystallite size was fixed at 800 Å, and the relationship between the half width d1 in the (200) plane and the half width d2 in the (220) plane in the X-ray diffraction measurement was changed. These relationships are considered to change depending on the sintering conditions, but since no clear control factor is unknown, the surface of the negative electrode current collector after sintering at a set temperature of 200 ° C. is measured by X-ray diffraction. The relationship is extracted that satisfies the relationship of the following examples. The other conditions were the same as in Example 5 to determine the expansion rate.

(Examples 21 to 29)
The average crystallite size was then fixed at 800 Å and the crystal grain size was changed. The crystal grain size was controlled by changing the sintering time and the degree of vacuum in the sintering furnace. The other conditions were the same as in Example 5 to determine the expansion rate.

DESCRIPTION OF REFERENCE NUMERALS 10 separator 20 positive electrode 22 positive electrode current collector 24 positive electrode active material layer 30 negative electrode 32 negative electrode current collector 34 negative electrode active material layer 40 power generation unit 50 exterior body 60, 62 lead 100 lithium secondary battery

Claims (5)

An anode current collector for a lithium secondary battery using metallic lithium for the anode,
It consists of copper and has crystal grains of copper ,
The negative electrode current collector, wherein an average crystallite size of the crystal particle is 380 Å or more and 4000 Å or less.
  The negative electrode collector according to claim 1, wherein the half width d1 in the (200) plane and the half width d2 in the (220) plane in the X-ray diffraction measurement satisfy the relationship of 1.1 ≦ d2 / d1 ≦ 1.4. Collector.   The negative electrode current collector according to claim 1, wherein the size of the crystal particle is 1.5 μm or more and 2.5 μm or less.   The negative electrode provided with the negative electrode collector as described in any one of Claims 1-3. A lithium secondary battery using metallic lithium for the negative electrode,
The negative electrode according to claim 4 ;
A positive electrode facing the negative electrode,
A lithium secondary battery comprising a separator positioned between the negative electrode and the positive electrode.

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