JP2019160782A - Negative electrode and lithium ion secondary battery - Google Patents

Abstract

To provide a negative electrode capable of improving quick charge characteristics and a lithium ion secondary battery using the negative electrode.SOLUTION: A negative electrode is provided with a negative electrode active material layer having a negative electrode active material on a negative electrode current collector, and the negative electrode active material contains a carbon material, and the reflectance Ra at a wavelength of 550 nm on the surface of the negative electrode active material layer is 7.0≤Ra≤14.8%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a negative electrode and a lithium ion secondary battery.

  Lithium ion secondary batteries are widely applied as power sources for portable electronic devices because they are lighter and have a higher capacity than nickel cadmium batteries, nickel metal hydride batteries, and the like. It is also a promising candidate as a power source for use in hybrid vehicles and electric vehicles. With the recent miniaturization and higher functionality of portable electronic devices, further increase in capacity is expected for lithium ion secondary batteries that serve as these power sources.

  The capacity of the lithium ion secondary battery mainly depends on the active material of the electrode. Various negative electrode active materials have been proposed, but because of their high capacity and excellent discharge potential flatness, artificial graphite and graphite obtained by graphitization of natural graphite, coke, etc. Graphite carbon materials such as mesophase pitch and graphitized carbon fiber are used.

  In recent years, demand for not only high capacity but also rapid discharge has been increasing in order to respond to new applications such as power tools and full-scale spread of hybrid vehicles. (Patent Literature 1, Patent Literature 2 and Patent Literature 3).

JP 2010-135314 A JP 2009-59676 A JP 2008-59903 A

  However, even in the negative electrode active materials described in Patent Document 1, Patent Document 2, and Patent Document 3 described above, the discharge capacity and the quick charge characteristics are not sufficient.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a negative electrode and a lithium ion secondary battery having good quick charge characteristics.

As a result of intensive studies, the present inventors have determined that a negative electrode provided with a negative electrode active material layer having a specific negative electrode active material on the negative electrode current collector has a reflectance Ra of a wavelength of 550 nm on the surface of the negative electrode active material layer. It was found that by setting the range, high quick charge characteristics can be obtained.
That is, in order to solve the above problems, the following means are provided.

  The negative electrode according to the first aspect includes a negative electrode active material layer having a negative electrode active material on a negative electrode current collector, the negative electrode active material includes a carbon material, and reflection at a surface of the negative electrode active material layer has a wavelength of 550 nm. The rate Ra is 7.0 ≦ Ra ≦ 14.8%.

  The quick charge characteristic is improved by adjusting the reflectance Ra on the surface of the negative electrode active material layer within a predetermined range. Although the effect is not clear, the reflectance of the negative electrode active material layer surface is considered to reflect the smoothness of the negative electrode active material layer surface and the surface compression state of the negative electrode active material on the negative electrode active material layer surface. .

  That is, in addition to an increase in the reaction field with the electrolytic solution on the surface of the negative electrode active material layer, the negative electrode active material surface on the negative electrode active material layer surface is compressed, thereby impregnating an excessive amount of electrolytic solution on the negative electrode active material surface. In addition to suppression, it is presumed that high rapid charge characteristics can be obtained by achieving both high reactivity and suppression of side reactions.

  In addition, regardless of the surface compression state of the negative electrode active material layer, it is considered that the quick charge characteristics are also improved when the reflectance Ra on the negative electrode active material layer surface is controlled within a predetermined range.

  This is because the reflectance Ra on the surface of the negative electrode active material layer is not only to suppress side reactions on the surface of the negative electrode active material layer, but also the permeability of the electrolyte from the surface of the negative electrode active material layer to the inside of the negative electrode active material layer. It is considered that rapid charging characteristics are improved by achieving both improvements.

In the negative electrode according to the above aspect, the density da in the negative electrode active material layer may be 1.35 ≦ da ≦ 1.62 g / cm ³ .

In the negative electrode according to the above aspect, the supported amount La per unit area in the negative electrode active material layer may be 7.8 ≦ La ≦ 12.5 mg / cm ² .

  In the negative electrode according to the above aspect, porosity Pa in the negative electrode active material layer may be 26.5 ≦ Pa ≦ 31.3%.

  In the negative electrode according to the aspect, the negative electrode active material may contain a carbon material having a graphite structure.

  The negative electrode having the above reflectance has particularly good rapid charge characteristics when a carbon material having a graphite structure is used as the negative electrode active material. This is presumed to be because both the impregnation of the electrolyte and the suppression of side reactions can be achieved without excessively reducing the lithium ion desorption sites on the negative electrode active material layer surface.

  A lithium ion secondary battery according to a second aspect includes the negative electrode of the above aspect, a positive electrode, a separator, and a non-aqueous electrolyte, and the non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte. The non-aqueous solvent contains ethylene carbonate, and the content of the ethylene carbonate is 10 to 30 vol. %.

  The content of ethylene carbonate is 10 to 30 vol. % Quick charge characteristics can be obtained by combining the electrolyte solution. It is presumed that this is because a part of the electrode surface is decomposed and an excellent film can be formed while suppressing excessive decomposition of ethylene carbonate as a film component.

  In the lithium ion secondary battery according to the second aspect, the ratio solvent contains propylene carbonate, and the content of the propylene carbonate is 10 to 20 vol. The ratio Le / Lp between the ethylene carbonate content Le and the propylene carbonate content Lp may be 1 ≦ Le / Lp ≦ 3.

  The content of propylene carbonate is 10 to 20 vol. %, And a high quick charge characteristic can be obtained by combining an electrolytic solution in which the content ratio with ethylene carbonate is 1.0 ≦ La / Lp ≦ 3.0.

  The present invention can provide a negative electrode capable of improving quick charge characteristics and a lithium ion secondary battery using the negative electrode.

It is a cross-sectional schematic diagram of the lithium ion 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.

(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 nonaqueous electrolyte 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 are disposed 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. Leads 62 and 60 are connected to the ends of the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the ends of the leads 60 and 62 extend to the outside of the case 50. In FIG. 1, the case 50 has one laminated body 40 in the case 50, but a plurality of laminated bodies 40 may be laminated.

(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.

  The positive electrode according to the present embodiment includes a positive electrode active material layer having a positive electrode active material on a positive electrode current collector.

  The positive electrode active material layer according to the present embodiment can be used without any problem as long as it uses a conventional positive electrode active material, and the electrode density dc in the positive electrode active material layer and the positive electrode active material layer The supported amount Lc per unit area, the porosity Pc in the positive electrode active material layer, and the like can be appropriately adjusted depending on the positive electrode active material used.

(Positive electrode active material)
The positive electrode active material according to the present embodiment is not particularly limited, and is represented by, for example, LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.2 Co _0.8 O _2. An existing positive electrode active material typified by a lithium-containing transition metal oxide containing Ni, Mn, and Co as main components can be used.

Among these, lithium containing Co or Ni as a main component as a transition metal represented by LiCoO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ It is preferable to use a contained transition metal oxide.

  In addition, the positive electrode active material according to the present embodiment does not need to be the oxygen amount of the stoichiometric composition of the existing compound, and widely includes oxygen-deficient materials. In other words, those identified as the same composition system by X-ray diffraction or the like are targeted.

  Therefore, in the positive electrode active material according to this embodiment, a part of Ni or Co may be substituted with a different element, and at least a part of the concentration gradient of the element in the positive electrode active material or the surface of the positive electrode active material is oxidized. It may be covered with an object, carbon or the like.

  Moreover, the positive electrode active material layer according to the present embodiment may contain a plurality of positive electrode active materials having different compositions.

The positive electrode active material having different compositions and the positive electrode active material, lithium nickel oxide (LiNiO _2), lithium manganate (LiMnO _2), lithium manganese spinel (LiMn ₂ O _4), and the general _formula: LiNi x _Co y M _{z O 2 (x + y +} z = 1,0.5 ≦ x <1,0 ≦ y <1,0 ≦ z <1, M is Al, Mg, Nb, Ti, Cu, Zn, 1 or more selected from Cr Element)), lithium vanadium compound (LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiV ₂ O ₅ , Li ₂ VP ₂ O ₇ ), olivine-type LiMPO ₄ (where M is , Co, showing Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr, at least one element selected from V), multiple such as lithium titanate _{(Li 4} Ti _{5 O 12)} Metal oxides, polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc., and the existing positive electrode active material a lithium ion capable of occluding and releasing it.

  In addition to the positive electrode active material, the positive electrode active material layer according to the present embodiment may include members such as a conductive additive and a binder.

(Conductive aid)
Examples of the conductive aid 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.

(Binder)
The binder binds the active materials to each other and also binds the active materials to the current collector 22. The binder is not particularly limited as long as the above-described bonding is possible. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoro Ethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride A fluororesin such as (PVF) is 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-HFPPTFE-based) Fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride Ride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber It may be used vinylidene fluoride-based fluorine rubbers such as rubber (VDF-CTFE-based fluorine rubber).

  Further, 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 those obtained by combining a polymer compound such as polyethylene oxide and polypropylene oxide with a lithium salt or an alkali metal salt mainly composed of lithium.

  The contents of the positive electrode active material, the conductive material, and the binder in the positive electrode active material layer 24 are not particularly limited. The constituent ratio of the positive electrode active material in the positive electrode active material layer 24 is preferably 90.0% or more and 98.0% or less in terms of mass ratio. The constituent ratio of the conductive material in the positive electrode active material layer 24 is preferably 1.0% to 3.0% by mass ratio, and the constituent ratio of the binder in the positive electrode active material layer 24 is 2. It is preferably 0% or more and 5.0% or less.

  By making content of a positive electrode active material and a binder into the said range, it can prevent that the quantity of a binder is too small and it becomes impossible to form a strong positive electrode active material layer. In addition, the amount of the binder that does not contribute to the electric capacity increases, and the tendency that it is difficult to obtain a sufficient volume energy density can be suppressed.

  In addition, by setting the content of the positive electrode active material and the conductive material in the above range, sufficient electronic conductivity can be obtained in the positive electrode active material layer, and high volume energy density and output characteristics can be obtained.

(Positive electrode current collector)
The positive electrode current collector 22 may be a conductive plate material, and for example, a metal thin plate such as aluminum, copper, or nickel foil, or an alloy thin plate thereof may be used. Among these, it is preferable to use an aluminum metal thin plate having a light weight.

(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.

  The negative electrode according to the present embodiment includes a negative electrode active material layer having a negative electrode active material on a negative electrode current collector, the negative electrode active material includes a carbon material, and a reflectance at a wavelength of 550 nm on the surface of the negative electrode active material layer. Ra is preferably 7.0 ≦ Ra ≦ 14.8%.

  By using the negative electrode according to the present embodiment, high rapid charge characteristics can be obtained. This is considered to reflect the smoothness on the surface of the negative electrode active material layer and the surface compression state of the negative electrode active material on the surface of the negative electrode active material layer, and the reflectance Ra on the surface of the negative electrode active material layer is 7.0 ≦ Ra. It is estimated that rapid charge characteristics are improved by using a negative electrode in the range of ≦ 14.8%.

The negative electrode according to the present embodiment, it is preferable that the density da of the anode active material layer is ^{1.35 ≦ dc ≦ 1.62g / cm 3} , a 1.40 ≦ dc ≦ 1.60g / cm ³ More preferred.

In the negative electrode according to this embodiment, the supported amount La per unit area in the negative electrode active material layer is preferably 4.5 ≦ La ≦ 12.5 mg / cm ² , and 6.0 ≦ La ≦ 12.0 mg / cm ^{2. 2} is more preferable.

  In the negative electrode according to this embodiment, the porosity Pa in the negative electrode active material layer is preferably 26.5 ≦ Pc ≦ 31.3%, and more preferably 26.0 ≦ Pa ≦ 31.0%. .

  The negative electrode according to the present embodiment more preferably satisfies the density da in the negative electrode active material layer and the value of the porosity Pa in the negative electrode active material layer at the same time.

  By simultaneously satisfying da and Pa in the negative electrode active material layer, it is possible not only to suppress excessive impregnation of the electrolyte solution, and to achieve both high reactivity and suppression of side reactions, but also the electrolyte solution inside the negative electrode active material layer. It is presumed that high rapid charging characteristics can be obtained by increasing the diffusion effect.

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

(Negative electrode active material)
As the material for the negative electrode active material, various materials that are used as negative electrode active materials for known lithium secondary batteries can be used. Examples of the material of the negative electrode active material include, for example, carbon materials such as graphite, hard carbon, soft carbon, MCMB, silicon, silicon-containing compounds such as silicon oxide represented by SiO _x (0 <x <2), Examples thereof include lithium metal, metals that form alloys with lithium, alloys thereof, amorphous compounds mainly composed of oxides such as tin dioxide, and lithium titanate (Li ₄ Ti ₅ O ₁₂ ). Examples of the metal that forms an alloy with metallic lithium include aluminum, silicon, tin, and germanium.

  As the negative electrode active material according to the present embodiment, it is preferable to use a carbon material having a graphite structure, and it is particularly preferable to use at least one of artificial graphite and natural graphite.

  Moreover, the negative electrode active material layer according to the present embodiment may contain negative electrode active materials having a carbon composition having a graphite structure as a main component and different compositions. Among them, a metal or a semimetal that forms an alloy with lithium typified by silicon and these alloys exhibit high charge / discharge capacity, and therefore, it is preferable to use a mixture of a carbon material having a graphite structure.

  When negative electrode active materials having different compositions are contained, the content of the carbon material having a graphite structure is 70.0% by mass or more with respect to the total of the carbon materials having a graphite structure and the negative electrode active materials having different compositions. Is more preferably 90.0% by mass or more, and particularly preferably 95.0% by mass or more.

(Negative electrode 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. Among these, carbon powders such as acetylene black and ethylene black are particularly preferable. In the case where sufficient conductivity can be ensured with only the negative electrode active material, the lithium ion secondary battery 100 may not include a conductive additive.

(Binder)
As the binder, the same as the positive electrode can be used. 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.

  The contents of the negative electrode active material, the conductive material, and the binder in the negative electrode active material layer 34 are not particularly limited. The constituent ratio of the negative electrode active material in the negative electrode active material layer 34 is preferably 90.0% or more and 98.0% or less in terms of mass ratio. The constituent ratio of the conductive material in the negative electrode active material layer 34 is preferably 0% or more and 3.0% or less in terms of mass ratio, and the constituent ratio of the binder in the negative electrode active material layer 34 is 2.0% by mass ratio. It is preferably 5.0% or less.

  By making content of a negative electrode active material and a binder into the said range, it can prevent that the quantity of a binder is too small and it becomes impossible to form a strong negative electrode active material layer. In addition, the amount of the binder that does not contribute to the electric capacity increases, and the tendency that it is difficult to obtain a sufficient volume energy density can be suppressed.

  Further, by setting the contents of the negative electrode active material and the conductive material in the above ranges, sufficient electronic conductivity can be obtained in the negative electrode active material layer, and high volume energy density and output characteristics can be obtained.

(Negative electrode current collector)
The negative electrode current collector 32 may be any conductive plate material, and for example, a metal thin plate such as aluminum, copper, or nickel foil, or an alloy thin plate thereof may be used. Among these, it is preferable to use a copper metal thin plate.

  Instead of providing the negative electrode active material layer 34, lithium ions may be deposited as metallic lithium on the surface of the negative electrode current collector 32 during charging, and the metallic lithium deposited during discharging may be dissolved as lithium ions. In this case, since the negative electrode active material layer 34 is not necessary, the volume energy density of the battery can be improved. In that case, a copper foil can be used as the negative electrode current collector 32.

  A high charge rate characteristic can be obtained by using the positive electrode 20 and the negative electrode 30 in the lithium ion secondary battery according to the present embodiment in the above-described manner.

(Separator)
The separator 18 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.

(Nonaqueous electrolyte solution)
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.

  The cyclic carbonate is not particularly limited as long as it can solvate the electrolyte, and a known cyclic carbonate can be used. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), or the like can be used.

  The chain carbonate is not particularly limited as long as the viscosity of the cyclic carbonate can be reduced, and a known chain carbonate can be used. Examples thereof include diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). 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 non-aqueous solvent according to this embodiment contains ethylene carbonate, and the content of the ethylene carbonate is 10 to 30 vol. % Is preferred.

  It is presumed that this is because a part of the electrode surface is decomposed and an excellent film can be formed while suppressing excessive decomposition of ethylene carbonate as a film component.

  The non-aqueous solvent according to this embodiment contains propylene carbonate, and the content of the propylene carbonate is 10 to 20 vol. Preferably, the ratio Le / Lp of the ethylene carbonate content Le and the propylene carbonate content Lp is 1.0 ≦ Le / Lp ≦ 3.0.

  Further, the nonaqueous electrolytic solution according to the present embodiment may be used in combination with a gel electrolyte or a solid electrolyte.

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 Lithium salts such as CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , 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 conductivity.

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 conductivity 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.

(Measurement of reflectance)
The reflectance Ra according to the present embodiment can be measured using a commercially available spectrocolorimeter or the like.

  The reflectance Ra at a wavelength of 550 nm on the surface of the negative electrode active material layer according to the present embodiment can be controlled by post-processing after molding the negative electrode active material layer and molding conditions.

  As a method for controlling the reflectance, it is possible to change the rolling pressure according to the rolling pressure at the time of electrode rolling, the number of rolling, the heating condition at the time of rolling, and the like. It can also be controlled by the material and surface shape of the rolling plate and rolling roll used during rolling.

  Moreover, you may grind | polish the surface of the electrode obtained after the obtained rolling, and may give a topcoat. In the case of applying a top coat, it is preferable to use a conductive top coat liquid in order to suppress deterioration of battery characteristics.

(Method for producing positive electrode 20 and negative electrode 30)
Next, a method for manufacturing the positive electrode 20 and the negative electrode 30 according to this embodiment will be described.

  A binder and a solvent are mixed with the positive electrode active material or the negative electrode active material. If necessary, a conductive additive may be further added. As the solvent, for example, water, N-methyl-2-pyrrolidone or the like can be used. The mixing method of the components constituting the paint is not particularly limited, and the mixing order is not particularly limited. The paint is applied to the current collectors 22 and 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, For example, the slit die-coating method and a doctor blade method are mentioned.

  Subsequently, the solvent in the paint applied on the current collectors 22 and 32 is removed. The removal method is not particularly limited, and the current collectors 22 and 32 to which the paint is applied may be dried, for example, 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. The reflectance on the surfaces of the positive electrode active material layer 24 and the negative electrode active material layer 34 can be controlled by adjusting the pressing pressure, the number of times of pressing, and the shape of the pressing material of the pressing device.

  Through the above steps, an electrode in which the electrode active material layers 24 and 34 are formed on the current collectors 22 and 32 is obtained.

(Method for producing lithium ion secondary battery)
Then, the manufacturing method of the lithium ion secondary battery which concerns on this embodiment is demonstrated. The method for manufacturing a lithium ion secondary battery according to the present embodiment includes a positive electrode 20 containing the active material, a negative electrode 30, a separator 10 interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution containing a lithium salt. And a step of enclosing the outer body 50 in the exterior body 50.

  For example, the positive electrode 20 including the active material described above, 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. 20, the separator 10 and the negative electrode 30 are brought into close contact with each other. Then, for example, a lithium ion secondary battery can be manufactured by putting the laminate 40 into a bag-shaped outer package 50 prepared in advance and injecting a non-aqueous electrolyte solution containing the lithium salt. Instead of injecting the nonaqueous electrolyte solution containing the lithium salt into the outer package, the laminate 40 may be impregnated in advance with the nonaqueous electrolyte solution containing the lithium salt.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same function and effect. Are included in the technical scope.

  As mentioned above, although embodiment concerning this invention was described in detail, it is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above-described embodiment, the laminated film type lithium ion secondary battery has been described. However, the present invention can be similarly applied to a lithium ion secondary battery having a structure in which a positive electrode, a negative electrode, and a separator are wound or folded. it can. Furthermore, it can apply suitably also about lithium ion secondary batteries, such as a cylindrical shape, a square shape, and a coin type, as a battery shape.

  Hereinafter, based on the above-described embodiment, the present invention will be described in more detail using examples and comparative examples.

Example 1
(Preparation of negative electrode)
90 parts by weight of graphite powder as a negative electrode active material, 2.5 parts by weight of styrene-butadiene rubber as a binder, 1.5 parts by weight of carboxymethylcellulose as a thickener, and carbon black (Super-P) as a conductive assistant 6.0 parts by weight was weighed and dispersed in water to prepare a slurry. The obtained slurry was applied on a copper foil having a thickness of 15 μm, and the solvent was removed by drying at a temperature of 120 ° C. for 30 minutes. Then, the press process was performed with the linear pressure of 700 kgf / cm using the roll press apparatus which heated the roll for rolling to 82 degreeC. After the press treatment, air cooling was defined as one cycle, and a three-cycle press treatment was performed.

  A negative electrode was produced by punching into an electrode size of 18 mm × 22 mm using a mold.

  As a result of measuring the reflectance Ra at a wavelength of 550 nm on the surface of the obtained negative electrode active material layer using a spectrocolorimeter (manufactured by KONICA MINOLTA: SPECTRO PHOTOMETER CM-5), Ra was 7.0%.

The obtained positive electrode was cut into a 10 cm ² square, and the density da of the negative electrode active material layer, the supported amount La per unit area, and the porosity Pa were calculated. As a result, da = 1.51 g / cm ³ , La = 9. It was 5 mg / cm ² and Pa = 28.5%.

(Production of counter electrode)
As a counter electrode, a metal lithium foil was pressure-bonded on a copper foil punched out to an electrode size of 19 mm × 23 mm using a mold to prepare a counter electrode.

(Nonaqueous electrolyte solution)
LiPF ₆ as an electrolyte is dissolved to 1.3 mol / L in a non-aqueous solvent in which ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) are mixed as a non-aqueous electrolyte solution. Used. The volume ratio of EC, PC, and EMC in the non-aqueous solvent was EC: PC: EMC = 10: 10: 80.

(Separator)
A polyethylene microporous membrane having a thickness of 20 μm (porosity: 40%, shutdown temperature: 134 ° C.) was prepared.

(Production of battery cells)
The negative electrode and the counter electrode were laminated via a polyethylene separator to produce an electrode laminate. This was used as one electrode body, and an electrode laminate composed of four layers was produced by the same production method. In addition, since the said negative electrode and a counter electrode are equipped with each mixture layer on both surfaces, they are comprised with three negative electrodes, two counter electrodes, and four separators. Further, in the negative electrode of the electrode laminate, a negative electrode lead made of nickel is attached to the protruding end of the copper foil not provided with the negative electrode mixture layer, and the metal lithium foil is not crimped on the counter electrode of the electrode laminate. A nickel counter electrode lead was attached to the protruding end of the copper foil by an ultrasonic fusion machine. The negative electrode lead and the counter electrode lead were fused to an aluminum laminate film for an exterior body, and the laminate film was folded to insert the electrode laminate into the exterior body. An opening was formed by heat-sealing except for one side around the exterior body, and a non-aqueous electrolyte was injected from this opening. Then, the opening part of the exterior body was sealed by heat sealing while reducing the pressure with a vacuum sealing machine, and the laminate type battery cell in Example 1 was produced. The battery cell was produced in a dry room.

(Example 2)
In the production of the negative electrode, the battery cell of Example 2 was produced in the same manner as in Example 1 except that the roll for rolling during the press treatment was heated to 88 ° C.

(Example 3)
In the production of the negative electrode, a battery cell of Example 3 was produced in the same manner as in Example 1 except that the roll for rolling during the press treatment was heated to 91 ° C.

Example 4
In the production of the negative electrode, a battery cell of Example 4 was produced in the same manner as in Example 1 except that the roll for rolling during the press treatment was heated to 97 ° C.

(Example 5)
In the production of the negative electrode, a battery cell of Example 5 was produced in the same manner as in Example 1 except that the roll for rolling during the press treatment was set to 105 ° C.

(Example 5)
In the production of the negative electrode, a battery cell of Example 5 was produced in the same manner as in Example 1 except that the roll for rolling during the press treatment was set to 105 ° C.

(Example 5)
In the production of the negative electrode, a battery cell of Example 5 was produced in the same manner as in Example 1 except that the roll for rolling during the press treatment was set to 105 ° C.

(Example 6)
In the production of the negative electrode, a battery cell of Example 5 was produced in the same manner as in Example 1 except that the roll for rolling during the press treatment was heated to 105 ° C. and the number of presses was 5 cycles.

(Example 7)
In the production of the negative electrode, a battery cell of Example 5 was produced in the same manner as in Example 1 except that the roll for rolling during the press treatment was heated to 111 ° C. and the number of presses was 3 cycles.

(Example 8)
In the production of the negative electrode, the battery cell of Example 8 was produced in the same manner as in Example 3 except that the linear pressure during the press treatment was 450 kgf / cm.

Example 9
In the production of the negative electrode, a battery cell of Example 9 was produced in the same manner as in Example 3 except that the linear pressure during the press treatment was 510 kgf / cm.

(Example 10)
In the production of the negative electrode, a battery cell of Example 10 was produced in the same manner as in Example 3 except that the linear pressure during the press treatment was 670 kgf / cm.

(Example 11)
In the production of the negative electrode, the battery cell of Example 11 was produced in the same manner as in Example 3 except that the linear pressure during the press treatment was 800 kgf / cm.

(Example 12)
In the production of the negative electrode, a battery cell of Example 12 was produced in the same manner as in Example 3 except that the linear pressure during the press treatment was 1000 kgf / cm.

(Example 13)
In the production of the negative electrode, the battery cell of Example 13 was prepared in the same manner as in Example 3, except that the amount of slurry applied was adjusted so that the supported amount La per unit area was 4.0 mg / cm _2. Produced. It was 4.2 mg / cm < ² > when the load amount La per unit area of the produced negative electrode was measured.

(Implementation 14)
In the production of the negative electrode, the battery cell of Example 14 was prepared in the same manner as in Example 3, except that the amount of slurry applied was adjusted so that the supported amount La per unit area was 4.5 mg / cm _2. Produced. It was 4.5 mg / cm < ² > when the loading amount La per unit area of the produced negative electrode was measured.

(Example 15)
In the production of the negative electrode, the battery cell of Example 15 was prepared in the same manner as in Example 3 except that the amount of slurry applied was adjusted so that the supported amount La per unit area was 7.5 mg / cm _2. Produced. It was 7.8 mg / cm < ² > when the loading amount La per unit area of the produced negative electrode was measured.

(Implementation 16)
In the production of the negative electrode, the battery cell of Example 16 was prepared in the same manner as in Example 3 except that the amount of slurry applied was adjusted so that the supported amount La per unit area was 8.0 mg / cm _2. Produced. It was 8.0 mg / cm < ² > when the load amount La per unit area of the produced negative electrode was measured.

(Example 17)
In the production of the negative electrode, the battery cell of Example 17 was prepared in the same manner as in Example 3, except that the amount of slurry applied was adjusted so that the supported amount La per unit area was 12.0 mg / cm _2. Produced. It was 11.9 mg / cm < ² > when the loading amount La per unit area of the produced negative electrode was measured.

(Example 18)
In the production of the negative electrode, the battery cell of Example 18 was prepared in the same manner as in Example 3, except that the amount of slurry applied was adjusted so that the supported amount La per unit area was 12.5 mg / cm _2. Produced. When the carrying amount La per unit area of the produced negative electrode was measured, it was 12.5 mg / cm ² .

(Example 19)
In the production of the negative electrode, the battery cell of Example 18 was prepared in the same manner as in Example 3, except that the amount of slurry applied was adjusted so that the supported amount La per unit area was 13.0 mg / cm _2. Produced. It was 12.9 mg / cm < ² > when the loading amount La per unit area of the produced negative electrode was measured.

(Example 20)
A battery cell of Example 21 was produced in the same manner as in Example 1 except that in the production of the negative electrode, a mixture of 20 parts by weight of graphite powder and 80 parts by weight of silicon oxide was used as the negative electrode active material.

(Example 21)
In the production of the negative electrode, a battery cell of Example 21 was produced in the same manner as in Example 2 except that 20 parts by weight of graphite powder and 80 parts by weight of silicon oxide were mixed as the negative electrode active material.

(Example 22)
In the production of the negative electrode, a battery cell of Example 22 was produced in the same manner as in Example 3 except that 20 parts by weight of graphite powder and 80 parts by weight of silicon oxide were mixed as the negative electrode active material.

(Example 23)
In the production of the negative electrode, a battery cell of Example 23 was produced in the same manner as in Example 4 except that 20 parts by weight of graphite powder and 80 parts by weight of silicon oxide were mixed as the negative electrode active material.

(Example 24)
In the production of the negative electrode, a battery cell of Example 24 was produced in the same manner as in Example 5 except that 20 parts by weight of graphite powder and 80 parts by weight of silicon oxide were mixed as the negative electrode active material.

(Example 25)
In the production of the negative electrode, a battery cell of Example 25 was produced in the same manner as in Example 6 except that 20 parts by weight of graphite powder and 80 parts by weight of silicon oxide were mixed as the negative electrode active material.

(Example 26)
In the production of the negative electrode, a battery cell of Example 26 was produced in the same manner as in Example 7 except that 20 parts by weight of graphite powder and 80 parts by weight of silicon oxide were mixed as the negative electrode active material.

(Comparative Example 1)
In the production of the negative electrode, a battery cell of Comparative Example 1 was produced in the same manner as in Example 1 except that the rolling roll during the press treatment was heated to 76 ° C.

(Comparative Example 2)
In production of the negative electrode, a battery cell of Comparative Example 2 was produced in the same manner as in Example 1 except that the roll for rolling during the press treatment was heated to 111 ° C. and the number of presses was 5 cycles.

(Comparative Example 3)
In the production of the negative electrode, a battery cell of Comparative Example 3 was produced in the same manner as in Comparative Example 1, except that 20 parts by weight of graphite powder and 80 parts by weight of silicon oxide were mixed as the negative electrode active material.

(Comparative Example 4)
In the production of the negative electrode, a battery cell of Comparative Example 4 was produced in the same manner as in Comparative Example 2, except that 20 parts by weight of graphite powder and 80 parts by weight of silicon oxide were mixed as the negative electrode active material.

(Preparation of positive electrode)
Weighing 88.0 parts by weight of LiFePO ₄ as a positive electrode active material, 6.0 parts by weight of PVDF (HSV-800) as a binder, and 6.0 parts by weight of Ketjen black (ECP300J) as a conductive assistant, A slurry was prepared by dispersing in N-methyl-2-pyrrolidone (NMP) as a solvent. The obtained slurry was applied onto an aluminum foil having a thickness of 15 μm, and the solvent was removed by drying at a temperature of 120 ° C. for 30 minutes. Then, the press process was performed with the linear pressure of 2000 kgf / cm using the roll press apparatus.

  A positive electrode for evaluation was produced by punching into an electrode size of 18 mm × 22 mm using a mold.

(Example 27)
A battery cell of Example 27 was produced in the same manner as in Example 1 except that the counter electrode was changed to the positive electrode for evaluation and the counter electrode lead made of nickel was changed to the positive electrode lead made of aluminum.

(Example 28)
A battery cell of Example 28 was fabricated in the same manner as Example 2 except that the counter electrode was changed to the positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 29)
A battery cell of Example 29 was produced in the same manner as in Example 3 except that the counter electrode was changed to a positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 30)
A battery cell of Example 30 was produced in the same manner as in Example 4 except that the counter electrode was changed to a positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 31)
A battery cell of Example 31 was produced in the same manner as in Example 5 except that the counter electrode was changed to the positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 32)
A battery cell of Example 32 was produced in the same manner as in Example 6 except that the counter electrode was changed to a positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 33)
A battery cell of Example 33 was made in the same manner as Example 7 except that the counter electrode was changed to the positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 34)
A battery cell of Example 34 was made in the same manner as Example 20 except that the counter electrode was changed to the positive electrode for evaluation and the nickel counter electrode lead was changed to the aluminum positive electrode lead.

(Example 35)
A battery cell of Example 35 was made in the same manner as Example 21 except that the counter electrode was changed to the positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 36)
A battery cell of Example 36 was fabricated in the same manner as Example 22 except that the counter electrode was changed to the positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 37)
A battery cell of Example 37 was fabricated in the same manner as in Example 23, except that the counter electrode was changed to the positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 38)
A battery cell of Example 38 was made in the same manner as Example 24, except that the counter electrode was changed to a positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 39)
A battery cell of Example 39 was made in the same manner as Example 25 except that the counter electrode was changed to a positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Example 40)
A battery cell of Example 40 was produced in the same manner as in Example 26 except that the counter electrode was changed to a positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Comparative Example 5)
A battery cell of Comparative Example 5 was produced in the same manner as Comparative Example 1 except that the counter electrode was changed to a positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Comparative Example 6)
A battery cell of Comparative Example 6 was fabricated in the same manner as Comparative Example 2 except that the counter electrode was changed to the positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Comparative Example 7)
A battery cell of Comparative Example 7 was produced in the same manner as Comparative Example 3 except that the counter electrode was changed to the positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

(Comparative Example 8)
A battery cell of Comparative Example 8 was produced in the same manner as Comparative Example 4 except that the counter electrode was changed to a positive electrode for evaluation and the nickel counter electrode lead was changed to an aluminum positive electrode lead.

  For the negative electrodes used in Examples 2 to 40 and Comparative Examples 1 to 8, the reflectance Ra at a wavelength of 550 nm on the surface of the negative electrode active material layer was measured in the same manner as in Example 1. Further, the density da of the negative electrode active material layer, the supported amount La per unit area, and the porosity Pa were also measured in the same manner as in Example 1. The results of Examples 2 to 26 and Comparative Examples 1 to 4 are shown in Table 1 together with the results of Example 1, and the results of Examples 27 to 40 and Comparative Examples 5 to 8 are shown in Table 2.

(Example 41)
As in Example 3, except that the volume ratio of EC, PC, and EMC was set to EC: PC: EMC = 20: 10: 70 as the nonaqueous solvent of the nonaqueous electrolyte solution. The battery cell of Example 41 was produced.

(Example 42)
As in Example 3, except that the volume ratio of EC, PC, and EMC was EC: PC: EMC = 30: 10: 60 was used as the nonaqueous solvent for the nonaqueous electrolyte solution. The battery cell of Example 42 was produced.

(Example 43)
As in Example 3, except that the volume ratio of EC, PC, and EMC was EC: PC: EMC = 20: 20: 60 as the nonaqueous solvent for the nonaqueous electrolyte solution. The battery cell of Example 43 was produced.

(Example 44)
The battery cell of Example 44 was obtained in the same manner as in Example 3 except that the volume ratio of EC to EMC was set to EC: EMC = 30: 70 as the nonaqueous solvent for the nonaqueous electrolyte solution. Produced.

(Example 45)
The battery cell of Example 45 was obtained in the same manner as in Example 3 except that the volume ratio of EC to EMC was set to EC: EMC = 20: 80 as the nonaqueous solvent for the nonaqueous electrolyte solution. Produced.

(Example 46)
The battery cell of Example 46 was obtained in the same manner as in Example 3 except that the volume ratio of EC to EMC was set to EC: EMC = 10: 90 as the nonaqueous solvent for the nonaqueous electrolyte solution. Produced.

(Example 47)
As in Example 3, except that the volume ratio of EC, PC, and EMC was EC: PC: EMC = 40: 10: 50 as the nonaqueous solvent for the nonaqueous electrolyte solution. The battery cell of Example 47 was produced.

(Example 48)
As in Example 3, except that the volume ratio of FEC, PC, and EMC was set to FEC: PC: EMC = 10: 10: 80 as the nonaqueous solvent of the nonaqueous electrolyte solution. The battery cell of Example 48 was produced.

  When the nonaqueous solvent used in Examples 41 to 48 was analyzed by gas chromatography-mass spectrometry, it was confirmed that the composition of the nonaqueous solvent was equivalent to the charged composition. Table 2 shows the ratio Le / Lp between the ethylene carbonate content Le and the propylene carbonate content Lp in the non-aqueous solvent obtained by gas chromatography-mass spectrometry.

(Measurement of quick charge characteristics)
Using the manufactured battery cell of Example 1, constant current charging was performed at a current density of 0.1 C until the voltage reached 2.5 V (vs. Li ^/ Li ⁺ ), and the current density was further increased to 0.05 C. Constant voltage charging was performed at 2.5 V (vs. Li ^/ Li ⁺ ) until it decreased. After a 5-minute rest period, constant current discharge was performed until the voltage became 0.05 V (vs. Li ^/ Li ⁺ ) at a current density of 0.1 C, and initial charge / discharge was performed.

After the initial charge and discharge, constant current charging is performed until the voltage reaches 2.5 V (vs. Li ^/ Li ⁺ ) at a current density of 0.2 C, and further, 2.5 V (until the current density decreases to 0.05 C ( vs. Li ^/ Li ⁺ ) was subjected to constant voltage charging, and the charge capacity at 0.2 C was measured.

After measuring the charge capacity at 0.2 C, after resting for 5 minutes, constant current discharge was performed at a current density of 0.1 C until the voltage reached 0.01 V (vs. Li ^/ Li ⁺ ), and the battery cell was discharged. It was.

The discharged battery cells are charged at a constant current density of 2.0 C until the voltage reaches 2.5 V (vs. Li ^/ Li ⁺ ), and further 2.5 V until the current density decreases to 0.05 C. Constant voltage charging was performed at (vs. Li ^/ Li ⁺ ), and the initial charge capacity at 2.0 C was measured.

After measuring the initial charge capacity at 2.0 C, constant current discharge was performed until the voltage reached 0.05 V (vs. Li ^/ Li ⁺ ) at a current density of 0.5 C, and the voltage was 2 at a current density of 2.0 C. a constant current charging until it reaches the .5V (vs.Li/Li ^+), to carry out constant-voltage charge at 2.5V (vs.Li/Li ⁺⁾ further to the current density is reduced to 0.05C One cycle was measured, and the charge capacity after 100 cycles at 2.0 C was measured.

The ratio of the charge capacity after 100 cycles at 2.0 C with respect to the initial charge capacity at 2.0 C was calculated as a rapid charge characteristic using the formula (Equation 1) to evaluate the rapid charge characteristic.
(Equation 1)
Rapid charge characteristics (%) = (initial charge capacity at 2.0 C / charge capacity after 100 cycles at 2.0 C) * 100

  The battery cells of Examples 2 to 26, Examples 41 to 48, and Comparative Examples 1 and 2 were evaluated for quick charge characteristics in the same manner as the battery cell of Example 1.

The produced battery cells of Examples 27 to 40 and Comparative Examples 3 and 4 have a constant current charge and constant voltage charge voltage of 4.0 V (vs. Li ^/ Li ⁺ ) and a constant current discharge voltage of 2.5 V ( (vs. Li ^/ Li ⁺ ) The quick charge characteristics were evaluated in the same manner as in the battery cell of Example 1, except that the change was made as follows.

  Table 1 shows the results of the quick charge characteristics of the battery cells of Examples 1 to 26 and Comparative Examples 1 and 2, Table 2 shows the results of the quick charge characteristics of Examples 27 to 40 and Comparative Examples 3 and 4. Example 41 The results of the fast charge characteristics of -48 battery cells are listed in Table 3.

  In Table 1, as shown from the results of Examples 1 to 7 and Comparative Examples 1 and 2, the negative electrode whose reflectance Ra at a wavelength of 550 nm on the surface of the negative electrode active material layer is 7.0 ≦ Ra ≦ 14.8% It has been confirmed that the quick charge characteristics are greatly improved by using. In addition, the results of Examples 8 to 19 indicate that the density da of the negative electrode active material layer, the loading amount La of the negative electrode active material layer, and the porosity Pa of the negative electrode active material layer each contribute to the quick charge characteristics. In particular, it can be seen that the quick charge characteristics are improved particularly in a specific range.

  Further, from the results of Examples 20 to 26 and Comparative Examples 3 and 4, when a mixture of graphite and silicon oxide was used as the negative electrode active material, the reflectance Ra at a wavelength of 550 nm on the surface of the negative electrode active material layer was similarly obtained. It was confirmed that the rapid charge characteristics were greatly improved by using a negative electrode with 7.0 ≦ Ra ≦ 14.8%.

  Moreover, about the battery cell of Examples 1-26 and Comparative Examples 1-4 which evaluated the quick charge characteristic, the battery cell after evaluation was each disassembled in the glove box in argon atmosphere, a negative electrode was taken out, and dimethyl carbonate was used. Washed and dried. After drying, the reflectance Ra at a wavelength of 550 nm on the surface of the negative electrode active material layer was measured, and it was confirmed that there was no change before and after the evaluation.

  In Table 2, from the results of Examples 27 to 33 and Comparative Examples 5 and 6, the reflectance Ra at a wavelength of 550 nm on the surface of the negative electrode active material layer was found in the evaluation of the battery cell using a normal positive electrode instead of the counter electrode. It was confirmed that the rapid charge characteristics were greatly improved by using a negative electrode with 7.0 ≦ Ra ≦ 14.8%. Further, from the results of Examples 34 to 40 and Comparative Examples 7 and 8, it was confirmed that the rapid charge characteristics were also greatly improved when a mixture of graphite and silicon oxide was used as the negative electrode active material. That is, it was confirmed that the improvement of the quick charge characteristic according to the present invention is an effect obtained by using a specific negative electrode.

  Moreover, about the battery cell of Examples 27-40 and Comparative Examples 5-8 which evaluated the quick charge characteristic, the battery cell after evaluation was respectively disassembled in the glove box in argon atmosphere, a negative electrode was taken out, and dimethyl carbonate was used. Washed and dried. After drying, the reflectance Ra at a wavelength of 550 nm on the surface of the negative electrode active material layer was measured, and it was confirmed that there was no change before and after the evaluation.

  In Table 3, ethylene carbonate (EC) is contained as a non-aqueous solvent liquid, and the content thereof is 10 to 30 vol. As a volume ratio in the non-aqueous solvent. It can be seen that high rapid charge characteristics are exhibited when the content is 1%.

  In addition, when propylene carbonate (PC) is contained in the non-aqueous solvent and the ratio Le / Lp of the content Le of ethylene carbonate and the content Lp of propylene carbonate is 1 ≦ Le / Lp ≦ 3, it is particularly rapid. It can be seen that the charging characteristics are improved.

  According to the present invention, it is possible to provide a negative electrode capable of improving quick charge characteristics and a lithium ion secondary battery using the negative electrode. These are suitably used as a power source for portable electronic devices, and are also used as electric vehicles and household and industrial storage batteries.

DESCRIPTION OF SYMBOLS 10 Separator 20 Positive electrode 22 Positive electrode collector 24 Positive electrode active material layer 30 Negative electrode 32 Negative electrode collector 34 Negative electrode active material layer 40 Laminate 50 Case 52 Metal foil 54 Polymer film 60, 62 Lead 100 Lithium ion secondary battery

Claims (7)

A negative electrode active material layer having a negative electrode active material on a negative electrode current collector,
The negative electrode active material includes a carbon material,
The negative electrode whose reflectance Ra of wavelength 550nm in the surface of the said negative electrode active material layer is 7.0 <= Ra <= 14.8%. The negative electrode according to claim 1, wherein a density da in the negative electrode active material layer is 1.35 ≦ da ≦ 1.62 g / cm ³ . The negative electrode according to claim 1, wherein a loading amount La per unit area of the negative electrode active material layer is 4.5 ≦ La ≦ 12.5 mg / cm ² .   The negative electrode according to claim 1, wherein the negative electrode active material layer has a porosity Pa of 26.5 ≦ Pa ≦ 31.3%.   The negative electrode according to any one of claims 1 to 4, wherein the carbon material contains a carbon material having a graphite structure.   A negative electrode according to any one of claims 1 to 5, a positive electrode, a separator, and a nonaqueous electrolyte solution, wherein the nonaqueous electrolyte solution includes a nonaqueous solvent and an electrolyte. The aqueous solvent contains ethylene carbonate, and the content of the ethylene carbonate is 10 to 30 vol. % Lithium ion secondary battery.   The non-aqueous solvent contains propylene carbonate, and the content of the propylene carbonate is 10 to 20 vol. The lithium ion content according to claim 6, wherein the ratio Le / Lp of the content Le of ethylene carbonate and the content Lp of propylene carbonate is 1.0 ≦ Le / Lp ≦ 3.0. Next battery.

Images