JP6048751B2 - Current collector for lithium ion secondary battery, electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a current collector for a lithium ion secondary battery, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  In lithium ion secondary batteries, lithium-containing metal composite oxides such as lithium cobalt composite oxide are mainly used as the positive electrode active material, and carbon materials are mainly used as the negative electrode active material. The positive and negative electrode plates are prepared by dispersing the active material, binder resin, and conductive additive in a solvent to form a slurry on a metal foil as a current collector. After forming the agent layer, it is produced by compression molding with a roll press. Since the current collector itself needs to have conductivity, a metal foil such as copper or aluminum is used as the current collector of the lithium ion secondary battery.

  In the lithium ion secondary battery having such a configuration, there is a problem that the current collector is corroded by the action of the electrolytic salt contained in the electrolytic solution and the cycle characteristics are deteriorated. In recent years, it has been desired that the lithium ion secondary battery can be used even in a high voltage use environment (in this specification, use at a voltage of 4.3 V or higher is defined as high voltage use). The metal current collector is more susceptible to corrosion in a high voltage environment.

Studies are underway to form a protective layer on the current collector in order to improve cycle characteristics in a high voltage environment. For example, Patent Document 1 describes a current collector on which a protective film containing a compound selected from Al iodide, TiN, Ti ₂ O ₃ , SnO ₂ , In ₂ O ₃ , RuO _{2 and the} like as a constituent component is formed. ing. These protective films are formed by ion sputtering or vacuum deposition. Film formation by such a dry process is not preferable in that the film stress at the time of film formation tends to remain on the current collector and the film formation is increased in area. Therefore, it is preferable to form the protective film by a wet process. When a film is formed by a wet process, the protective film needs to contain an organic binder.

  For example, Patent Document 2 describes a laminated current collector in which a conductive protective layer containing polytetrafluoroethylene and a conductive filler is provided on a current collector. The organic binder contained in the protective layer generally decreases the conductivity of the protective layer. When the conductivity decreases, the resistance of the electrode increases and the output characteristics of the battery decrease.

  Therefore, a current collector for a lithium ion secondary battery having a protective layer containing an organic binder that hardly lowers the conductivity of the protective layer is desired.

JP 2004-55247 A JP2012-84523A

  The present invention has been made in view of such circumstances, and a current collector for a lithium ion secondary battery capable of improving cycle characteristics without deteriorating output characteristics even under a high voltage use environment, It aims at providing the electrode for lithium ion secondary batteries, and a lithium ion secondary battery.

  As an organic binder used for a protective layer of a laminated current collector, a resin that is stable in a wide potential region, that is, has a wide potential window has been conventionally studied. However, as a result of intensive studies by the present inventors, the use of polyethylene glycol, which has not been studied so far because it does not have a wide potential window, makes it possible to use a secondary lithium ion as an organic binder for the protective layer of the current collector. It has been found that the cycle characteristics can be improved without degrading the output characteristics of the battery.

That is, the current collector for a lithium ion secondary battery of the present invention has a current collector body, and a coat layer that is disposed on the surface of the current collector body and includes conductive particles and a binder for the coat layer. The binder for the coat layer has a compound represented by the general formula: HO— (CH ₂ —CH ₂ —O) _n —H (n ≧ 3), and the molecular weight of the compound is from 180 to 5,000,000. Features.

  The molecular weight of the compound is preferably 180 or more and 50,000 or less.

The conductive particles include indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), zinc peroxide (ZnO ₂ ), tin oxide (II) (SnO), tin oxide (IV) (SnO ₂ ), tin oxide ( VI) (SnO ₃ ), titanium dioxide (TiO ₂ ), dititanium trioxide (Ti ₂ O ₃ ), ruthenium oxide (RuO ₂ ), nickel oxide (NiO), tantalum oxide (Ta ₂ O ₃ ), tungsten oxide ( III) (W ₂ O ₃ ), tungsten oxide (IV) (WO ₂ ), tungsten oxide (VI) (WO ₃ ), chromium oxide (Cr ₂ O ₃ ), titanium nitride (TiN), germanium nitride (Ge ₃ N) ₄ ), lanthanum nitride (LaN), tungsten carbide (WC), tantalum carbide (TaC), titanium carbide (TiC), carbon (C), indium oxide (In ₂ O ₃ ), Zn, Mo, W, Ti , With addition of at least one element selected from Zr, Sn and H, tin oxide (IV) (SnO ₂ ) with addition of at least one element selected from F, W, Ta, Sb, P and B It is preferable that at least one selected from zinc oxide (ZnO) to which at least one element selected from Ga, Al and B is added and titanium dioxide (TiO ₂ ) to which Nb element is added.

  The thickness of the coat layer is preferably 10 nm to 1000 nm.

  The coating layer binder is further selected from polyacrylic acid (PAA), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and polyvinylidene fluoride (PVDF). Preferably, at least one of them is included.

  The electrode for a lithium ion secondary battery of the present invention is characterized by having the above-described current collector for a lithium ion secondary battery.

  The lithium ion secondary battery of this invention has the said electrode for lithium ion secondary batteries, It is characterized by the above-mentioned.

The current collector for a lithium ion secondary battery of the present invention has a coat layer disposed on the surface of the current collector body. The coat layer has a compound represented by the general formula: HO— (CH ₂ —CH ₂ —O) _n —H (n ≧ 3), and the coat layer binder has a molecular weight of 180 to 5,000,000. Conductive particles. The lithium ion secondary battery of the present invention has the above-described current collector for a lithium ion secondary battery, so that the cycle characteristics can be improved without deteriorating the output characteristics even when used in a high voltage use environment. it can.

It is a schematic diagram explaining the electrode for lithium ion secondary batteries of this embodiment. The observation result of the scanning electron microscope (SEM) of the cross section of the positive electrode of the lamination-type lithium ion secondary electron of Example 1 is shown. It is the graph which compared the measurement result by a gas chromatograph mass spectrometer (GC-MS) about the powder of polyethyleneglycol (PEG) and the coating layer of the collector after conditioning of the lithium ion secondary battery of Example 1.

<Current collector for lithium ion secondary battery>
The current collector for a lithium ion secondary battery of the present invention has a current collector body, and a coat layer that is disposed on the surface of the current collector body and includes conductive particles and a binder for a coat layer.

The current collector for a lithium ion secondary battery of the present invention has a compound in which the binder for the coating layer is represented by the general formula: HO— (CH ₂ —CH ₂ —O) _n —H (n ≧ 3) Is characterized by a molecular weight of 180 to 5,000,000.

  The current collector body refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. In the current collector for a lithium ion secondary battery of the present invention, since the coat layer is disposed on the surface of the current collector body, the current collector body is prevented from being corroded by an electrolytic salt or the like. Examples of materials that can be used for the current collector body include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins. The current collector body can take the form of a foil, a sheet, a film and the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector body.

  The thickness of the current collector body is preferably 10 μm to 100 μm.

  The thickness of the coat layer is preferably 10 nm to 1000 nm, and more preferably 20 nm to 500 nm. If the thickness of the coat layer is 10 nm or more, the surface of the current collector body can be protected by the coat layer, and corrosion of the current collector body due to the electrolytic solution can be effectively suppressed. When the thickness of the coat layer is 1000 nm or less, the volume occupied by the current collector in the lithium ion secondary battery can be made appropriate. If the volume occupied by the current collector in the lithium ion secondary battery becomes too large, the amount of the active material must be reduced, which leads to a decrease in battery capacity, which is not preferable.

In particular, when an aluminum foil is used as the current collector body, the effect of the coat layer is great. On the surface of the aluminum foil, there is usually a passive film such as Al ₂ O ₃ formed by a natural reaction with oxygen in the atmosphere and AlF ₃ formed by a reaction with an electrolytic salt in the electrolytic solution. This passive film is an insulator, and the number of digits of the specific resistance (Ωcm) is about 10 ⁸ . The aluminum foil is protected from the electrolytic salt by the passive film, but since the passive film is a high resistance film, the electrode using the current collector having the passive film on the surface has high resistance, and the electrode was used. Batteries are said to have reduced output characteristics. In the current collector for a lithium ion secondary battery according to the present invention, since the coat layer is disposed on the surface of the current collector body, the passive film is hardly formed. Therefore, it can suppress that a high resistance layer is formed in the surface of a collector main body by a coat layer.

  The coat layer includes conductive particles and a binder for the coat layer.

  The conductive particles are required to have conductivity, resistance to organic solvents, corrosion resistance to oxidation-reduction reactions, and low reaction activity. Oxides, carbides, and nitrides can be used as materials that satisfy such conditions.

For example, indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), zinc peroxide (ZnO ₂ ), tin oxide (II) (SnO), tin oxide (IV) (SnO ₂ ), oxidation can be used as conductive particles. Tin (VI) (SnO ₃ ), titanium dioxide (TiO ₂ ), dititanium trioxide (Ti ₂ O ₃ ), ruthenium oxide (RuO ₂ ), nickel oxide (NiO), tantalum oxide (Ta ₂ O ₃ ), oxidation Tungsten (III) (W ₂ O ₃ ), tungsten oxide (IV) (WO ₂ ), tungsten oxide (VI) (WO ₃ ), chromium oxide (Cr ₂ O ₃ ), titanium nitride (TiN), germanium nitride (Ge) ₃ N ₄ ), lanthanum nitride (LaN), tungsten carbide (WC), tantalum carbide (TaC), titanium carbide (TiC), carbon (C), indium oxide (In ₂ O ₃ ), Zn, M o, W, Ti, Zr, Sn and H added, at least one element selected from F, W, Ta, Sb, P and B added to tin oxide (IV) (SnO ₂ ) At least one selected from an element added, zinc oxide (ZnO) added at least one element selected from Ga, Al and B, and titanium dioxide (TiO ₂ ) added an Nb element is used. be able to.

Among indium oxide (In ₂ O ₃ ) added with at least one element selected from Zn, Mo, W, Ti, Zr, Sn, and H, indium oxide (In ₂ O ₃ ) contains Zn element or Sn element. Those added are preferred. As a material obtained by adding Zn element indium oxide _(In 2 _{O 3),} indium zinc oxide and the like, as the addition of Sn element indium oxide _(In 2 _{O 3),} it includes indium tin oxide. In ₂ O ₃ —ZnO (IZO) is preferable as the indium zinc oxide, and In ₂ O ₃ —SnO ₂ (ITO) is preferable as the indium tin oxide.

F tin oxide _{(IV) (SnO 2),} W, Ta, Sb, among those prepared by adding at least one element selected from P and B, tin oxide _{(IV) (SnO 2),} F element, Sb element , Ta elements or P elements added are preferable. As a material obtained by adding F element tin oxide _(IV) (SnO 2), include fluorine tin oxide, as the addition of Sb element tin oxide _(IV) (SnO 2), antimony tin oxide Examples of tin oxide (IV) (SnO ₂ ) added with Ta element include tantalum tin oxide, and tin oxide (IV) (SnO ₂ ) added with P element includes phosphorus tin oxide. Is mentioned. Fluorine tin oxide is preferably fluorine-added tin oxide (FTO), antimony tin oxide is preferably antimony-added tin oxide (ATO), tantalum tin oxide is preferably tantalum-added tin oxide (TaTO), and phosphorus tin oxide is preferred. Phosphorus-doped tin oxide (PTO) is preferred.

  Examples of zinc oxide (ZnO) with Ga element added include gallium zinc oxide, zinc oxide (ZnO) with Al element added, aluminum zinc oxide, and zinc oxide (ZnO). Boron zinc oxide is mentioned as an element to which B element is added. Gallium-doped zinc oxide (GZO) is preferred as the gallium zinc oxide, aluminum-doped zinc oxide (AZO) is preferred as the aluminum zinc oxide, and boron-doped zinc oxide (BZO) is preferred as the boron zinc oxide.

An example of the titanium dioxide (TiO ₂ ) added with an Nb element is titanium niobium oxide. The titanium niobium oxide is preferably TiO ₂ ; Nb.

Among the conductive particles, SnO ₂ is particularly preferable. SnO ₂ has sufficient electrical conductivity and is resistant to oxygen, electrolytes and electrolyte salts in the atmosphere, and exhibits its resistance even at high voltages. SnO ₂ is also excellent in oxidation resistance.

The conductive particles preferably have a powder specific resistance of 1E + 3 Ωcm or less. The conductive particles may preferably have an average particle diameter _{D 50} is 10 nm to 1000 nm. If the average particle diameter D ₅₀ of the conductive particles is 10nm or more, the resistance is not too high between the conductive particles, a suitable conductive can have a coating layer. The average particle diameter D ₅₀ and 1000nm larger than the conductive particles, is not preferred since the film thickness of the coating layer becomes too thick.

The binder for the coat layer causes the conductive particles and the conductive particles and the current collector body to adhere to each other in the coat layer. The binder for a coat layer has a compound represented by the general formula: HO— (CH ₂ —CH ₂ —O) _n —H (n ≧ 3), and the molecular weight of the compound is from 180 to 5,000,000.

  Polyethylene glycol is a polymer compound having a structure in which ethylene glycol is polymerized. Polyethylene glycol used as a raw material has a low molecular weight to some extent in the coating layer manufacturing process, battery manufacturing process, and battery operating process. Therefore, the polyethylene glycol having a low molecular weight is contained in the coat layer from the polyethylene glycol used as a raw material when the coat layer is formed. However, even if the molecular weight is lowered, it can be detected by analysis such as GC-MS that the binder for the coat layer has the compound represented by the above general formula.

  In general, since polyethylene glycol is easily electrolyzed, it has not been studied as a binder for a coat layer of a current collector of a lithium ion secondary battery. When the above-mentioned compound is contained in the coat layer of the current collector as a binder for the coat layer, the reason is not clearly understood, but the cycle characteristics are suppressed while suppressing the increase in the resistance of the electrode of the lithium ion secondary battery. Can be improved.

  Polyethylene glycols have various degrees of polymerization. As the degree of polymerization increases, the polyethylene glycol changes from a liquid at room temperature to a solid at room temperature. The polyethylene glycol used as a raw material when the coating layer is produced preferably has a molecular weight of 180 to 5,000,000. If polyethylene glycol having a molecular weight within this range is used, the conductive particles can be satisfactorily bound to the current collector body. Those having a molecular weight greater than 5000 are solid lumps at room temperature. Further, when the molecular weight is larger than 50,000, it is necessary to heat the solution when dissolved in water, so that the handleability is poor. Therefore, it is more preferable that the polyethylene glycol used as the raw material when the coat layer is produced has a molecular weight of 50,000 or less.

  Furthermore, the molecular weight of polyethylene glycol used as a raw material when the coating layer is produced is preferably 1000 or more. This is because when the molecular weight is 1000 or more, the viscosity of polyethylene glycol is higher, and the coat layer is easily disposed on the current collector body.

The molecular weight of the compound represented by the general formula: HO— (CH ₂ —CH ₂ —O) _n —H (n ≧ 3) is from 180 to 5,000,000, and the molecular weight of the compound is from 180 to 50,000. Preferably there is. When the molecular weight of the compound is in the above range, the conductive particles can be favorably bound to the current collector body.

The presence of the compound represented by the general formula: HO— (CH ₂ —CH ₂ —O) _n —H (n ≧ 3) can be confirmed by a gas chromatograph mass spectrometer (GC-MS). GC-MS is an analyzer in which a gas chromatograph (GC) and a mass spectrometer (MS) are integrated. In the GC section, the measurement sample is separated through a separation tube called a column, and the compound is separated to appear as a plurality of components. The mass spectrum is measured by the MS part. By analyzing the mass spectrum, it is possible to analyze what kind of compound the separated peak is. The measurement data of GC-MS is displayed as a chromatogram with the detection time on the horizontal axis and the detection intensity on the vertical axis. In other words, components can be identified by comparing chromatograms. The molecular weight can be measured using a technique such as GPC (Gel Permeation Chromatography).

  Here, an example of measurement conditions by GC-MS is described below.

GC-MS device name: manufactured by Agilent Technologies, model number G1099A, accessory Agilent 5973 MSD,
GC measurement conditions: Agilent 122-1032 (model number), DB-1, 0.25 mm × 30 mm × 0.25 μm, inlet conditions are split / splitless 320 ° C., carrier gas is helium, oven conditions are Initial temperature 40 ° C, maximum temperature 350 ° C, equilibration time 3 minutes, post temperature 300 ° C, runtime 26 minutes, transfer line temperature 320 ° C,
MS measurement conditions: scan mode, solvent waiting time is 0 minute, MS temperature is 230 ° C. (ion source), 150 ° C. (quadrupole), and scan range is 20-800 amu.

  A pyrolyzer can be used for gasification of the measurement sample. From the viewpoint of analysis, the gasification temperature should be higher than the thermal decomposition temperature of polyethylene glycol, or lower than the temperature at which polyvinylidene fluoride (PVDF) or the like generally used as a binder for the active material layer decomposes. Still good. Measurement conditions are not limited to these measurement conditions.

According to the GC-MS, the presence of the compound represented by the general formula: HO— (CH ₂ —CH ₂ —O) _n —H (n ≧ 3) is the current collector for the lithium ion secondary battery of the present invention. It can be confirmed even when the body is incorporated in a lithium ion secondary battery. Specifically, even when the coat layer is arranged on the current collector body, it is represented by the general formula: HO— (CH ₂ —CH ₂ —O) _n —H (n ≧ 3) even if measured by GC-MS. The presence of the compound can be confirmed, and after preparing the electrode using the current collector for the lithium ion secondary battery of the present invention, the active material layer is peeled off from the electrode, and the surface on the current collector body side The presence is confirmed even if measured. In addition, after producing a lithium ion secondary battery using the electrode for lithium ion secondary battery of the present invention, the lithium ion secondary battery is disassembled and the active material layer is peeled off from the electrode, The presence of the surface residue is also confirmed. In addition, after the conditioning treatment of the lithium ion secondary battery of the present invention, the electrode after the conditioning is disassembled, and the active material layer is peeled off from the current collector for the lithium ion secondary battery of the present invention. The compound can also be confirmed by measuring the residue on the surface.

Here, the presence of the compound represented by the general formula: HO— (CH ₂ —CH ₂ —O) _n —H (n ≧ 3) is difficult to confirm even when observed with a scanning electron microscope (SEM). This is because the compound may be decomposed by an electron beam when observed by SEM.

  The coating layer binder is further selected from polyacrylic acid (PAA), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and polyvinylidene fluoride (PVDF). Preferably, at least one of them is included. By using these resins in combination, the adhesion of the coat layer to the current collector body is further improved. In addition, when these resins are used in combination, the coatability of the coating layer slurry to the current collector body is improved during the production of the coating layer.

  The method for disposing the coat layer on the current collector body is not particularly limited, but the following method can be employed.

  Polyethylene glycol, which is a raw material for the binder for the coat layer, and conductive particles are mixed in a solvent to form a slurry for the coat layer. Furthermore, the above-mentioned resin may be further added as a raw material for the coating layer binder to form a coating layer slurry. Here, the polyethylene glycol may be mixed with the solvent first, and then the conductive particles may be mixed. Alternatively, the conductive particles may be mixed with the solvent first, and then the polyethylene glycol may be mixed. In addition, polyethylene glycol and conductive particles may be mixed in a solvent at the same time. Further, the above-described resin may be mixed at any time.

  As the solvent, water or an organic solvent can be used. As the organic solvent, ethanol, methanol, benzene, dichloromethane, or the like can be used, and any other solvent that can dissolve polyethylene glycol even in a trace amount can be used. Water contains a small amount of inorganic salt or the like, and can be used even when the pH is in the range of pH 4 to pH 9. However, from the viewpoint of the corrosion of the current collector body to be used, the water preferably has a pH of pH 6 to pH 8 from which impurities such as distilled water and ion exchange water are removed. Moreover, you may use what mixed the organic solvent and water by arbitrary ratios as a solvent.

  Here, the conductive particles are preferably dispersed in the slurry for the coating layer. When the conductive particles are dispersed, the conductive particles are easily disposed in the entire coat layer in the finished coat layer. In order to disperse the conductive particles in the slurry for the coat layer, when the solvent is water, the addition amount of polyethylene glycol, which is an organic substance, and other binder resin may be appropriately adjusted so that the conductive particles do not aggregate.

  In the slurry for the coating layer, the blending amount of the conductive particles and the raw material for the binder for the coating layer is preferably from 1: 1 to 100: 1 in terms of mass ratio.

  When the blending amount is within this range, the conductive particles in the finished coat layer are favorably bound to each other, and the conductive particles and the current collector main body are bound by the binder for the coat layer. Moreover, the resistance increase of the electrode can be appropriately suppressed.

  In addition, when using together other binder resin mentioned above as a raw material of the binder for coat layers according to polyethyleneglycol, it is preferable to add 0.1-100 other binder resin with respect to polyethyleneglycol 100 by mass ratio. If another binder resin is added within this range, the binding between the conductive particles and the current collector body and the conductive particles can be improved while appropriately suppressing the increase in resistance of the electrodes.

  Next, the slurry for the coat layer is applied to the current collector body. As a coating method, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used.

  Thereafter, the current collector body to which the slurry for the coating layer is applied is dried to produce the current collector for the lithium ion secondary battery of the present invention.

<Electrode for lithium ion secondary battery>
The electrode for a lithium ion secondary battery of the present invention has the above-described current collector for a lithium ion secondary battery. The current collector for a lithium ion secondary battery of the present invention may be used for a positive electrode or a negative electrode. In particular, when the current collector for a lithium ion secondary battery of the present invention is used for a positive electrode in which the current collector body is severely corroded, a great effect is achieved.

  In the electrode for a lithium ion secondary battery, an active material layer formed by binding an active material with a binder is disposed on the surface of a current collector for a lithium ion secondary battery. The active material layer may further contain a conductive additive as necessary.

As the positive electrode active material, a lithium-containing compound or another metal compound can be used. Examples of the lithium-containing compound, for example, lithium-cobalt composite oxide having a layered structure, the lithium nickel composite oxide having a layered structure, the lithium manganese composite oxide having a spinel structure represented by the general _{formula: Li a Co p Ni q Mn} r D _s O _x (D is at least one selected from Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe, and Na, p + q + r + s = 1, 0 <p <1, 0 ≦ q <1, 0 ≦ r <1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s) ≦ 0.2) things, the general formula: olivine-type lithium phosphate compound oxide represented by LiMPO ₄ (at least one M is selected Mn, Fe, Co and Ni), the general _formula: Li 2 _MPO 4 F Fluoride olivine-type lithium phosphate compound oxide represented (at least one M is selected Mn, Fe, Co and Ni), the general _formula: Li 2 MSiO silicate lithium composite oxide represented by ₄ ( M may be at least one selected from Mn, Fe, Co, and Ni. Examples of other metal compounds include oxides such as titanium oxide, vanadium oxide, and manganese dioxide, and disulfides such as titanium sulfide and molybdenum sulfide.

The positive electrode active material is preferably made of a lithium-containing oxide represented by the chemical formula: LiMO ₂ (M is at least one selected from Ni, Co, and Mn), and further has a general formula: Li _a Co _p Ni _{q Mn r D s O x (} D is at least one selected Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe and Na, p + q + r + s = 1,0 <p <1,0 ≦ Lithium having a layered structure represented by q <1, 0 ≦ r <1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s) ≦ 0.2) It is preferably made of a cobalt-containing composite metal oxide.

Examples of the lithium-containing oxide include LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _{0. 3} O ₂ , LiCoO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiCoMnO ₂ can be used. Among these, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ are preferable in terms of thermal stability.

The positive electrode active material preferably has an average particle diameter _{D 50} is a powder shape is 1 m to 20 m. When the average particle diameter D ₅₀ of the positive electrode active material is small, the specific surface area of the positive electrode active material is increased. Thus, the reaction area of the average particle diameter D ₅₀ of the positive electrode active material is too small and the positive electrode active material and the electrolyte becomes excessive increase it, as a result, are accelerated decomposition of the electrolytic solution, the lithium ion secondary Battery cycle characteristics deteriorate. Therefore, the average particle diameter _{D 50} of the positive electrode active material is preferably at least 1 [mu] m. When the average particle diameter D ₅₀ of the positive electrode active material is larger than 20 μm, the resistance of the lithium ion secondary battery is increased, and the output characteristics of the lithium ion secondary battery are lowered. The average particle diameter D ₅₀ of the positive electrode active material can be measured by particle size distribution measurement method. The average particle diameter D ₅₀ is that the particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50%. That is, the average particle diameter D ₅₀ means the median size measured by volume.

  As the negative electrode active material, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, a compound that includes an element that can be alloyed with lithium, a polymer material, or the like can be used.

  Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, coke, graphite, glassy carbon, organic polymer compound fired body, carbon fiber, activated carbon, or carbon black. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

  Elements that can be alloyed with lithium are Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn. , Pb, Sb, Bi may be included. Among them, the element that can be alloyed with lithium is preferably silicon (Si) or tin (Sn).

Examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , and CaSi. _{2, CrSi 2, Cu 5 Si} , FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO or LiSnO can be used. As the compound having an element that can be alloyed with lithium, a silicon compound or a tin compound is preferable. As the silicon compound, SiO _x (0.5 ≦ x ≦ 1.5) is preferable. As the tin compound, for example, a tin alloy (Cu—Sn alloy, Co—Sn alloy, etc.) can be used.

  As the polymer material, polyacetylene, polypyrrole, or the like can be used.

The negative electrode active material is preferably in powder form. If the anode active material is in powder form, it is preferable that the average particle size _{D 50} of the negative electrode active material is 0.1μm or more 30μm or less. The average particle diameter D ₅₀ of the negative electrode active material 0.1μm smaller, the specific surface area of the powder of the negative electrode active material is increased, the contact area of the powder of the anode active material and the electrolyte solution is increased, the decomposition of the electrolyte solution Advances and the cycle characteristics deteriorate. The average particle diameter D ₅₀ of the negative electrode active material is larger than 30 [mu] m, the conductivity of the whole electrode becomes uneven, since the charge and discharge characteristics decrease undesirably. The average particle diameter D ₅₀ can be measured by particle size distribution measurement method.

  The binder plays a role of connecting the positive electrode active material or the negative electrode active material and the conductive additive to the current collector for the lithium ion secondary battery of the present invention. As the binder, for example, fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene, polyethylene and polyvinyl acetate resins, imide resins such as polyimide and polyamideimide, alkoxy Silyl group-containing resins and rubbers such as styrene butadiene rubber (SBR) can be used.

  The conductive auxiliary agent is added to the active material layer as necessary in order to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (AB), ketjen black (registered trademark) (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used alone or in combination of two or more as conductive aids. Can be used. Although there are no particular limitations on the amount of conductive aid used, for example, it can be about 1 to 30 parts by mass with respect to 100 parts by mass of the active material contained in the electrode.

  In order to dispose the active material layer on the surface of the current collector for the lithium ion secondary battery of the present invention, an active material layer forming composition containing an active material, a binder, and, if necessary, a conductive additive is prepared. Further, an appropriate solvent may be added to the composition to form a paste, which may be applied to the surface of the current collector for a lithium ion secondary battery and then dried. In addition, you may compress the electrical power collector in which the active material layer is arrange | positioned so that an electrode density may be raised as needed.

  As a method for applying the composition for forming an active material layer, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used.

  As a solvent for adjusting the viscosity, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used.

  FIG. 1 shows a schematic diagram for explaining an electrode for a lithium ion secondary battery of the present embodiment. As shown in FIG. 1, a coat layer 2 is disposed on the current collector body 1, and an active material layer 3 is disposed on the surface of the coat layer 2. The coating layer 2 includes conductive particles 21 and a coating layer binder 22, and the coating layer binder 22 includes the conductive particles 21 and the conductive particles 21 and the current collector body 1 in the coating layer 2. Adhere closely.

<Lithium ion secondary battery>
The lithium ion secondary battery of this invention has the said electrode for lithium ion secondary batteries, It is characterized by the above-mentioned. As for an electrode, the positive electrode or the negative electrode may be the electrode for lithium ion secondary batteries, and both the positive electrode and the negative electrode may be the electrodes for lithium ion secondary battery. The lithium ion secondary battery having the above-mentioned electrode for lithium ion secondary battery has excellent cycle characteristics without deteriorating output characteristics even under a high voltage use environment.

  The lithium ion secondary battery of the present invention includes a separator and an electrolytic solution as a battery component in addition to the above-described electrode for a lithium ion secondary battery.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. As the separator, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramics can be used.

  The electrolytic solution includes a solvent and an electrolyte dissolved in the solvent.

  As the solvent, for example, cyclic esters, chain esters, and ethers can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters that can be used include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. As ethers, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane can be used.

As the electrolyte dissolved in the electrolytic solution, for example, a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used.

As the electrolytic solution, for example, a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 in} a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate, or the like is from 0.5 mol / l to 1.7 mol / l. A solution dissolved at a certain concentration can be used.

  The lithium ion secondary battery can be mounted on a vehicle. Since the lithium ion secondary battery has excellent cycle characteristics, a vehicle equipped with the lithium ion secondary battery has high performance in terms of life and output.

  The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.

  The embodiments of the current collector for lithium ion secondary battery, the electrode for lithium ion secondary battery, and the lithium ion secondary battery of the present invention have been described above, but the present invention is not limited to the above embodiment. . The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described in more detail with reference to examples.

<Formation of coat layer on current collector body>
An aluminum foil having a thickness of 20 μm was prepared as a current collector body.

Prepare SnO ₂ powder with an average particle diameter D ₅₀ of 20 nm as conductive particles and polyethylene glycol (PEG), polyacrylic acid (PAA), and polytetrafluoroethylene (PTFE) with a molecular weight of 20,000 as a binder for the coating layer. did. Moreover, ion-exchange water was prepared as a viscosity adjusting solvent.

(Current collector A)
A slurry for a coating layer was prepared by mixing with ion-exchanged water so that the mass ratio of SnO ₂ : PEG was 20: 1. The coating layer slurry was placed on an aluminum foil and applied using a doctor blade. The aluminum foil after the coating layer slurry was applied was dried at 200 ° C., and this was used as current collector A. The current collector A is composed of an aluminum foil as a current collector body and a coat layer disposed on the surface of the aluminum foil. The thickness of the coat layer of current collector A was 300 nm.

(Current collector B)
A current collector B was produced in the same manner as the current collector A except that the mass ratio of SnO ₂ : PAA was 20: 1.

(Current collector C)
A current collector C was produced in the same manner as the current collector A except that the mass ratio of SnO ₂ : PTFE was 10: 1.

(Current collector D)
The aluminum foil itself was used as the current collector D without forming a coat layer.

(Current collector E)
A current collector E was produced in the same manner as the current collector A, except that the mass ratio of SnO ₂ : PEG: PAA was 20: 1: 0.1.

<Production of laminated lithium-ion secondary battery>
Example 1
The laminated lithium ion secondary battery of Example 1 was produced as follows.

(Creation of positive electrode)
88 parts by mass, 6 parts by mass, and 6 parts by mass of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ as a positive electrode active material, acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder, respectively. The mixture was mixed at a ratio of part by mass, and this mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode active material layer slurry.

The positive electrode active material layer slurry was applied to the surface of the current collector A in a film form using a doctor blade. The current collector A to which the positive electrode active material layer slurry was applied was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then pressed by a roll press to obtain a bonded product. At this time, the electrode density was set to 3.2 g / cm ² . The joined product was heated with a vacuum dryer at 120 ° C. for 6 hours, and then cut into a predetermined shape (rectangular shape of 25 mm × 30 mm) to obtain a positive electrode having a positive electrode active material layer having a thickness of about 45 μm.

(Preparation of negative electrode)
As the negative electrode active material, SiO (manufactured by Aldrich) having an average particle diameter D ₅₀ of 4 μm and graphite (natural graphite (manufactured by Hitachi Chemical Co., Ltd.) having an average particle diameter D ₅₀ of 20 μm) were prepared. As a binder resin, an alkoxy group-containing silane-modified polyamideimide resin (Arakawa Chemical Industries, Ltd., trade name Composeran, product number H900-2) was prepared. KB (Ketjen Black) manufactured by Ketjen Black International Co., Ltd. was prepared as a conductive aid.

  The negative electrode active material, the conductive auxiliary agent, and the binder resin were mixed at a mass ratio of SiO: graphite: conductive auxiliary agent: binder resin = 22: 60: 3: 15. Here, when the total of the mass of graphite and the mass of SiO is 100 mass%, the mixing ratio of SiO is 27 mass%. An appropriate amount of NMP was added as a solvent to the above mixture to prepare a slurry, which was then slurried for the negative electrode active material layer.

A 20 μm copper foil was prepared as a current collector for the negative electrode, and the slurry for negative electrode active material layer was applied to the copper foil in a film form using a doctor blade. The copper foil coated with the negative electrode active material layer slurry was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then pressed by a roll press to obtain a bonded product. At this time, the electrode density was set to 1.6 g / cm ² . The bonded product was heated with a vacuum dryer at 200 ° C. for 2 hours, and then cut into a predetermined shape (26 mm × 31 mm rectangular shape) to form a negative electrode having a negative electrode active material layer thickness of 20 μm.

A laminate type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode. Specifically, a rectangular sheet (27 × 32 mm, thickness 25 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. 1 mol / liter of LiPF ₆ was added to a solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) as an electrolytic solution in EC: EMC: DMC = 3: 3: 4 (volume ratio). A solution dissolved so as to be 1 was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. The laminated lithium ion secondary battery of Example 1 was produced through the above steps.

  In addition, the prepared laminate type lithium ion secondary battery was subjected to a conditioning process before cycle measurement. In the conditioning process, the manufactured laminated lithium ion secondary battery was charged stepwise to 4.5V, finally charged to 4.5V at a 1C rate, and then CV charged for 5 hours. Then, after discharging to 2.5 V at a 0.33 C rate, CV discharging was performed at 2.5 V for 5 hours.

(Example 2)
A laminated lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that the current collector E was used instead of the current collector A in Example 1.

(Comparative Example 1)
A laminated lithium ion secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the current collector D was used instead of the current collector A in Example 1.

(Comparative Example 2)
A laminated lithium ion secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the current collector B was used instead of the current collector A in Example 1.

(Comparative Example 3)
A laminated lithium ion secondary battery of Comparative Example 3 was produced in the same manner as in Example 1 except that the current collector C was used instead of the current collector A in Example 1.

<Cycle characteristic evaluation>
The cycle characteristics of the laminated lithium ion secondary batteries of Examples 1-2 and Comparative Examples 1-3 were evaluated. As an evaluation of the cycle characteristics, a cycle test in which charging and discharging were repeated under the following conditions was performed, and the discharge capacity of each cycle was measured. When charging, CC charging (constant current charging) was performed at 60 ° C. at a 1C rate and a voltage of 4.5V. When discharging, CC discharge (constant current discharge) was performed at a rate of 2.5 V and 1 C. This charging / discharging was made into 1 cycle, and the cycle test was done to 200 cycles. The discharge capacity of the first cycle was measured, and the initial discharge capacity (mAh / g) per mass of the positive electrode active material was calculated. The capacity retention rate after 200 cycles was determined by the following formula.
Capacity retention rate (%) = (discharge capacity after 200 cycles / initial discharge capacity) × 100

<Cell resistance evaluation>
The initial cell resistances of the laminated lithium ion secondary batteries of Examples 1-2 and Comparative Examples 1-3 were measured. The cell resistance (Ω) was measured at 3C rate for 10 seconds at a voltage (3.6 V) at 20% SOC (State of charge). The cell resistance after the cycle test was measured in the same manner, and the cell resistance after 200 cycles was measured. The rate of change in cell resistance after 200 cycles was determined by the following equation.

Cell resistance change rate (%) = (cell resistance after 200 cycles / initial cell resistance) × 100
The results are shown in Table 1.

  As can be seen from Table 1, compared to the initial discharge capacity of the laminated lithium ion secondary battery of Comparative Example 1, the laminated lithium ion secondary batteries of Example 1, Example 2, Comparative Example 2 to Comparative Example 3 were compared. None of the initial discharge capacities were changed. That is, even when the coating layer used in the laminated lithium ion secondary batteries of Example 1, Example 2, Comparative Example 2 and Comparative Example 3 was disposed on the current collector body, the initial discharge capacity did not decrease.

  In addition, looking at the capacity maintenance rate after 200 cycles, the capacity maintenance rates of the laminated lithium ion secondary batteries of Example 1 and Example 2 were compared with the capacity maintenance rate of the laminated lithium ion secondary battery of Comparative Example 1. And greatly improved. In addition, the capacity retention rate of the laminated lithium ion secondary battery of Example 1 was higher than the capacity retention rates of the laminated lithium ion secondary batteries of Comparative Example 2 and Comparative Example 3. The reason for this is unknown, but the laminate type lithium ion secondary battery having a coating layer using PEG as a raw material for the coating layer binder has a high capacity maintenance rate of 71% and 70% even after the cycle test. showed that.

  In addition, looking at the cell resistance change rate (%), the cell resistance change rate of the laminated lithium ion secondary battery of Example 1 and Example 2 is the cell resistance change rate of the laminate type lithium ion secondary battery of Comparative Example 1. Almost unchanged, the cell resistance change rate of the laminated lithium ion secondary batteries of Comparative Example 2 and Comparative Example 3 was significantly lower. From this, it was found that a coating layer using PEG as a binder for the coating layer hardly has an increase in cell resistance even after a cycle test.

<Scanning Electron Microscope (SEM) Observation of Positive Electrode of Laminated Lithium Ion Secondary Battery of Example 1>
The cross section of the positive electrode of the laminated lithium ion secondary battery of Example 1 was observed with a scanning electron microscope (SEM). The observed positive electrode was used at the time of producing the laminate cell.

  FIG. 2 shows the observation result of the cross section of the positive electrode of the laminated lithium ion secondary electron of Example 1 with a scanning electron microscope (SEM). As can be seen from FIG. 2, the coat layer 2 is disposed on the surface of the current collector body 1, and the active material layer 3 is disposed on the surface of the coat layer 2. Here, when the coating layer 2 is viewed, powders that can be seen as a plurality of conductive particles are arranged in the coating layer 2 with gaps in some places, but the coating layer binder cannot be clearly observed. Since it is presumed that PEG decomposes when it hits an electron beam, it could not be confirmed by SEM observation whether PEG was actually arranged.

<Measurement by GC-MS>
Thus, it was confirmed that PEG remained on the surface of the current collector body even after the lithium ion secondary battery was moved.

  The laminated lithium ion secondary battery of Example 1 after being conditioned is disassembled, the positive electrode active material layer is peeled off from the positive electrode current collector body, and the coating layer remaining on the current collector body surface is collected It was measured by GC-MS.

  The measurement conditions by GC-MS are described below. GC-MS apparatus: manufactured by Agilent Technologies Inc., model number G1099A, accessory Agilent 5973 MSD, GC conditions: columns used are Agilent 122-1032 (model number), DB-1, 0.25 mm × 30 mm × 0.25 μm, Inlet conditions are split / splitless 320 ° C., carrier gas is helium, oven conditions are initial temperature 40 ° C., maximum temperature 350 ° C., equilibration time 3 minutes, post temperature 300 ° C., runtime 26 minutes, transfer line temperature 320 ° C. MS measurement conditions: scan mode, solvent waiting time was 0 minutes, MS temperature was 230 ° C. (ion source), 150 ° C. (quadrupole), and scan range was 20-800 amu. Gasification of the measurement sample was performed at 280 ° C. using a pyrolyzer.

  The results are shown in FIG. 3 together with GC-MS measurement data of PEG powder having a molecular weight of 20,000.

  From FIG. 3, the peak of the data obtained by measuring the surface of the current collector main body was observed at the same position as the peak of the data measured with the PEG powder. These peaks were identified as the following chemical formula (1), chemical formula (2), and chemical formula (3). The same component as PEG powder was detected from Example 1, and it was confirmed that PEG remained on the current collector foil even after conditioning.

  1: current collector body, 2: coat layer, 21: conductive particles, 22: binder for coat layer, 3: active material layer.

Claims (6)

A current collector body;
A coating layer disposed on the surface of the current collector body and comprising conductive particles and a coating layer binder;
The coat layer binder general _{formula: HO- (CH 2 -CH 2 -O} ) has a compound represented by n -H (n ≧ 3), the molecular weight of the compound Ri der 180 or 5,000,000 ,
The conductive particles include indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), zinc peroxide (ZnO ₂ ), tin oxide (II) (SnO), tin oxide (IV) (SnO ₂ ), tin oxide. (VI) (SnO ₃ ), titanium dioxide (TiO ₂ ), dititanium trioxide (Ti ₂ O ₃ ), ruthenium oxide (RuO ₂ ), nickel oxide (NiO), tantalum oxide (Ta ₂ O ₃ ), tungsten oxide (III) (W ₂ O ₃ ), tungsten oxide (IV) (WO ₂ ), tungsten oxide (VI) (WO ₃ ), chromium oxide (Cr ₂ O ₃ ), titanium nitride (TiN), germanium nitride (Ge ₃₎ N ₄ ), lanthanum nitride (LaN), tungsten carbide (WC), tantalum carbide (TaC), titanium carbide (TiC), indium oxide (In ₂ O ₃ ), Zn, Mo, W, Ti, Zr, One added with at least one element selected from Sn and H, one added with at least one element selected from F, W, Ta, Sb, P and B to tin oxide (IV) (SnO ₂ ), zinc oxide Lithium ion 2 which is at least one selected from those obtained by adding at least one element selected from Ga, Al and B to (ZnO) and those obtained by adding Nb element to titanium dioxide (TiO ₂ ). Secondary battery current collector.   The current collector for a lithium ion secondary battery according to claim 1, wherein the compound has a molecular weight of 180 or more and 50,000 or less. The current collector for a lithium ion secondary battery according to claim 1 or 2 , wherein the coat layer has a thickness of 10 nm to 1000 nm. The coating layer binder is further composed of polyacrylic acid (PAA), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and polyvinylidene fluoride (PVDF). The current collector for a lithium ion secondary battery according to any one of claims 1 to 3 , comprising at least one selected. The electrode for lithium ion secondary batteries which has the collector for lithium ion secondary batteries as described in any one of Claims 1-4 . The lithium ion secondary battery which has an electrode for lithium ion secondary batteries of Claim 5 .