JP2021150065A - Active material layer, electrode, and lithium ion secondary battery - Google Patents

Abstract

To provide a lithium ion secondary battery superior in discharge rate characteristic.SOLUTION: The active material layer comprises at least an active material and a binder. The active material includes a first active substance of a main component, and a second active substance which is a subcomponent different from the first active substance in composition. The proportion of the first active substance is 60% of a total quantity of the active substances or more and less than 100%, and the proportion of the second active substance is more than 0% of the total quantity of the active substances and less than 5%.SELECTED DRAWING: Figure 1

Description

The present invention relates to an active material layer, electrodes and a lithium ion secondary battery.

Lithium-ion secondary batteries are also widely used as a power source for mobile devices such as mobile phones and laptop computers, and hybrid cars. With the development of these fields, lithium ion secondary batteries are required to have higher performance.

For example, Patent Document 1 discloses a lithium secondary battery in which a film made of a mixture of two or more kinds is formed on the surface of a positive electrode. Patent Document 1 discloses that the coating film suppresses the decomposition of the electrolytic solution due to the reaction between the active material and the electrolytic solution, and improves the cycle characteristics.

Further, for example, Patent Document 2 describes a positive electrode in which an active material is coated with a predetermined metal, an intermetallic compound, or an oxide. It is described that the safety of the battery is improved by absorbing oxygen by the metal coating the active material.

Japanese Unexamined Patent Publication No. 8-236114 Japanese Unexamined Patent Publication No. 11-16566

Discharge rate characteristics are one of the indicators of battery performance. The discharge rate is the speed required from full charge to reaching the final voltage. The discharge rate characteristic is the ratio of the discharge capacity when the discharge rate is accelerated to the discharge capacity when discharging at a predetermined discharge rate. A battery with excellent discharge rate characteristics can be discharged rapidly.

The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a lithium ion secondary battery having excellent discharge rate characteristics.

The following means are provided to solve the above problems.

(1) The active material layer according to the first aspect has at least an active material and a binder, and the active material is a first active material as a main component and a sub-component having a composition different from that of the first active material. With a second active material, the ratio of the first active material is 60% or more and less than 100% of the total active material, and the ratio of the second active material is larger than 0% of the total active material 5 Less than%.

(2) In the active material layer according to the above aspect, the primary active material may be secondary particles in which a plurality of primary particles are aggregated, and the secondary active material may be primary particles.

(3) In the active material layer according to the above aspect, the particle size of the first active material may be 0.6 times or more and 1.5 times or less the particle size of the second active material.

(4) In the active material layer according to the above aspect, the reaction potential of the second active material may be higher than the reaction potential of the first active material.

(5) In the active material layer according to the above embodiment, the second active material is represented by Li _a Co _{1- y My} O ₂ ... (1), where a is 0.8 ≦ a ≦ 1.2. , Y satisfies 0 ≦ y <0.5, and M may be at least one of Ni, Mn, Fe, Mg, Zr, Al, Ti, Zn, Cu, Ca, and Na.

(6) The electrode according to the second aspect includes a current collector and an active material layer according to the above aspect laminated on at least one surface of the current collector.

(7) The lithium ion secondary battery according to the third aspect includes the electrodes according to the above aspect.

The lithium ion secondary battery according to the above aspect has excellent discharge rate characteristics.

It is a schematic diagram of the lithium ion secondary battery which concerns on 1st Embodiment.

Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, the featured portion may be enlarged for convenience in order to make the feature easy to understand, and the dimensional ratio of each component may be different from the actual one. The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

"Lithium-ion secondary battery"
FIG. 1 is a schematic view of a lithium ion secondary battery according to the first embodiment. The lithium ion secondary battery 100 shown in FIG. 1 includes a power generation element 40, an exterior body 50, and a non-aqueous electrolytic solution (not shown). The exterior body 50 covers the periphery of the power generation element 40. The power generation element 40 is connected to the outside by a pair of connected terminals 60 and 62. The non-aqueous electrolyte solution is housed in the exterior body 50.

(Power generation element)
The power generation element 40 includes a positive electrode 20, a negative electrode 30, and a separator 10.

<Separator>
The separator 10 is sandwiched between the positive electrode 20 and the negative electrode 30. The separator 10 isolates the positive electrode 20 and the negative electrode 30 and prevents a short circuit between the positive electrode 20 and the negative electrode 30. Lithium ions can pass through the separator 10.

The separator 10 has, for example, an electrically insulating porous structure. The separator 10 is selected from, for example, a monolayer of a film made of polyolefin such as polyethylene or polypropylene, a stretched film of a laminate or a mixture of the above resins, or a group consisting of cellulose, polyester, polyacrylonitrile, polyamide, polyethylene and polypropylene. Examples thereof include fibrous polypropylene made of at least one constituent material.

The separator 10 may be, for example, a solid electrolyte. The solid electrolyte is, for example, a polymer solid electrolyte, an oxide-based solid electrolyte, or a sulfide-based solid electrolyte. The polymer solid electrolyte is, for example, a polyethylene oxide-based polymer in which an alkali metal salt is dissolved. Oxide-based solid electrolytes include, for example, Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ (ceramic type), Li _1.07 Al _0.69 Ti _1.46 (PO _{4 ) 3} (glass). Ceramics), Li _0.34 La _0.51 TiO _2.94 (perovskite type), Li ₇ La ₃ Zr ₂ O ₁₂ (garnet type), Li _2.9 PO _3.3 N _0.46 (amorphous, LIPON) , 50Li ₄ SiO ₄・ 50Li ₂ BO ₃ (glass), 90Li ₃ BO ₃・ 10Li ₂ SO ₄ (glass ceramics). The sulfide-based solid electrolyte is, for example, Li _3.25 Ge _0.25 P _0.75 S ₄ (crystal), Li ₁₀ GeP ₂ S ₁₂ (crystal, LGPS), Li ₆ PS ₅ Cl (crystal, algyrodite type). , Li _9.54 Si _1.74 P _1.44 S _11.7 Cl _0.3 (crystal), Li _3.25 P _0.95 S ₄ (glass ceramics), Li ₇ P ₃ S ₁₁ (glass ceramics) _{, 70Li 2 S · 30P 2 S} 5 ( _{glass), 30Li 2 S · 26B 2} S 3 · 44LiI ( _{glass), 50Li 2 S · 17P 2} S 5 · 33LiBH 4 ( _{glass), 63Li 2 S · 36SiS 2} · Li ₃ PO ₄ (glass), 57Li ₂ S / 38SiS _2.5 Li ₄ SiO ₄ (glass).

<Positive electrode>
The positive electrode 20 has a positive electrode current collector 22 and a positive electrode active material layer 24. The positive electrode active material layer 24 is formed on at least one surface of the positive electrode current collector 22.

[Positive current collector]
The positive electrode current collector 22 is, for example, a conductive plate material. The positive electrode current collector 22 is, for example, a thin metal plate such as aluminum, copper, nickel, titanium, or stainless steel.

[Positive electrode active material layer]
The positive electrode active material layer 24 has, for example, a positive electrode active material, a conductive auxiliary agent, and a binder.

The positive electrode active material can reversibly proceed with the occlusion and release of lithium ions, the desorption and insertion (intercalation) of lithium ions, or the doping and dedoping of lithium ions and counter anions.

The positive electrode active material comprises at least two or more kinds of active materials. The positive electrode active material includes, for example, a first active material as a main component and a second active material as a sub component. The abundance ratio of the second active material is extremely small as compared with the first active material. The second active material is present in the positive electrode active material layer 24 in a very small amount.

The proportion of the first active material in the entire positive electrode active material is 60% or more and less than 100%, preferably 60% or more and 99% or less, more preferably 80% or more and 99% or less, and further preferably 96. % Or more and 98% or less. The proportion of the second active material in the entire positive electrode active material is greater than 0% and less than 5%, preferably 0.5% or more and 4.5% or less, and more preferably 1% or more and 4% or less. .. When the positive electrode active material is composed of the first active material and the second active material, the total ratio of the first active material and the second active material is 100%. When there are three or more types of positive electrode active materials, the total ratio of the first active material and the second active material is less than 100%.

The composition of the first active material is different from that of the second active material. The reaction potential of the second active material is, for example, higher than the reaction potential of the first active material. The reaction potential is the electrical potential energy at which the lithium intercalation reaction occurs, and is the reaction potential with respect to the equilibrium potential of Li. For example, a spinel compound (hereinafter referred to as LMO), a manganese phosphate compound (hereinafter referred to as LMP), lithium cobalt oxide (hereinafter referred to as LCO), and a nickel-cobalt-manganese ternary compound (hereinafter referred to as LMP). , NMC), nickel-cobalt-aluminum ternary compound (hereinafter referred to as NCA), lithium iron phosphate (hereinafter referred to as LFP), sulfur-based compound and lithium titanium oxide (hereinafter referred to as LFP). The reaction potential of (referred to as LTO) satisfies the relationship of LMO> LMP> LCO> NMC ≈ NCA> LFP> sulfur compound> LTO.

The second active material is, for example, _a compound represented by Li a Co _{1- y My} O ₂ ... (1). a satisfies 0.8 ≦ a ≦ 1.2, y satisfies 0 ≦ y <0.5, and M is Ni, Mn, Fe, Mg, Zr, Al, Ti, Zn, Cu, Ca, Na. At least one of them. In the above formula (1), the case where y = 0 is LCO.

For example, the first active material may be secondary particles, and the second active material may be primary particles. Secondary particles are particles in which a plurality of primary particles are aggregated. For example, in cross-sectional observation with a transmission electron microscope (TEM), if a grain boundary is visible in the particle, it is a secondary particle, and if the grain boundary is not visible, it is a primary particle.

The particle size of the first active material is, for example, 0.6 times or more and 1.5 times or less, preferably 0.9 times or more and 1.1 times or less the particle size of the second active material. Here, the particle size is the average particle size of 10 or more particles. If the particles are irregular, half the sum of the length of the major axis and the length of the minor axis is regarded as the particle size. When secondary particles are formed, it is the particle size of the secondary particles.

The binder binds the positive electrode active materials in the positive electrode active material layer 24 to each other. A known binder can be used. The binder is, for example, a fluororesin. The fluororesin includes, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and the like. Ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF) and the like.

In addition to the above, the binder is, for example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based). Fluororesin), Vinylidene Fluoride-Pentafluoropropylene Fluororesin (VDF-PFP Fluororubber), Vinylidene Fluoride-Pentafluoropropylene-Tetrafluoroethylene Fluororesin (VDF-PFP-TFE Fluororesin), Vinylidene Fluoro Vinylidene fluoride-based fluoropolymers such as Ride-Perfluoromethyl Vinyl Ether-Tetrafluoroethylene Fluororesin (VDF-PFMVE-TFE Fluororesin) and Vinylidene Fluoride-Chlorotrifluoroethylene Fluororesin (VDF-CTFE Fluororesin) It may be rubber.

The conductive auxiliary agent enhances the conductivity between the positive electrode active materials in the positive electrode active material layer 24. The conductive auxiliary agent is, for example, carbon powder such as carbon black, carbon nanotube, carbon material, metal fine powder such as copper, nickel, stainless steel, iron, a mixture of carbon material and metal fine powder, and conductive oxide such as ITO. .. The conductive auxiliary agent is preferably a carbon material such as carbon black. When sufficient conductivity can be ensured only by the active material, the positive electrode active material layer 24 may not contain a conductive auxiliary agent.

Further, the positive electrode active material layer 24 may contain a solid electrolyte or a gel electrolyte. The solid electrolyte is similar to that which can be used for, for example, a separator.

<Negative electrode>
The negative electrode 30 has, for example, a negative electrode current collector 32 and a negative electrode active material layer 34. The negative electrode active material layer 34 is formed on at least one surface of the negative electrode current collector 32.

[Negative electrode current collector]
The negative electrode current collector 32 is, for example, a conductive plate material. As the negative electrode current collector 32, the same one as the positive electrode current collector 22 can be used.

[Negative electrode active material layer]
The negative electrode active material layer 34 contains a negative electrode active material. Further, if necessary, a conductive material, a binder, and a solid electrolyte may be contained.

The negative electrode active material may be any compound that can occlude and release ions, and a known negative electrode active material used in a lithium ion secondary battery can be used. The negative electrode active material is, for example, a carbon material such as metallic lithium, a lithium alloy, graphite capable of storing and releasing ions (natural graphite, artificial graphite), carbon nanotubes, non-graphitizable carbon, easily graphitized carbon, and low-temperature calcined carbon. , A semi-metal or metal that can be combined with metals such as lithium such as aluminum, silicon, tin and germanium, _{and amorphous compounds mainly composed of oxides such as SiO x} (0 <x <2) and tin dioxide. , Lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and the like.

The negative electrode active material layer 34 may contain, for example, silicon, tin, and germanium as described above. Silicon, tin, and germanium may exist as a simple substance element or as a compound. The compound is, for example, an alloy, an oxide, or the like. As an example, when the negative electrode active material is silicon, the negative electrode 30 may be called a Si negative electrode. The negative electrode active material may be, for example, a simple substance of silicon, tin, or germanium, or a mixed system of a compound and a carbon material. The carbon material is, for example, natural graphite. Further, the negative electrode active material may be, for example, a simple substance of silicon, tin, germanium or a compound whose surface is coated with carbon. The carbon material and the coated carbon enhance the conductivity between the negative electrode active material and the conductive auxiliary agent. When the negative electrode active material layer contains silicon, tin, and germanium, the capacity of the lithium ion secondary battery 100 increases.

The negative electrode active material layer 34 may contain, for example, lithium as described above. Lithium may be metallic lithium or a lithium alloy. The negative electrode active material layer 34 may be metallic lithium or a lithium alloy. Lithium alloys include, for example, Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Sb, Pb, In, Zn, Ba, It is an alloy of lithium and one or more elements selected from the group consisting of Ra, Ge, and Al. As an example, when the negative electrode active material is metallic lithium, the negative electrode 30 may be called a Li negative electrode. The negative electrode active material layer 34 may be a lithium sheet.

The negative electrode 30 may be only the negative electrode current collector 32 without having the negative electrode active material layer 34 at the time of fabrication. When the lithium ion secondary battery 100 is charged, metallic lithium is deposited on the surface of the negative electrode current collector 32. The metallic lithium is a simple substance lithium in which lithium ions are precipitated, and the metallic lithium functions as a negative electrode active material layer 34.

As the conductive material and the binder, the same ones as those of the positive electrode 20 can be used. The binder in the negative electrode 30 may be, for example, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamide-imide resin, acrylic resin or the like, in addition to those listed in the positive electrode 20. Cellulose may be, for example, carboxymethyl cellulose (CMC).

(Terminal)
The terminals 60 and 62 are connected to the positive electrode 20 and the negative electrode 30, respectively. The terminal 60 connected to the positive electrode 20 is a positive electrode terminal, and the terminal 62 connected to the negative electrode 30 is a negative electrode terminal. The terminals 60 and 62 are responsible for electrical connection with the outside. The terminals 60 and 62 are formed of a conductive material such as aluminum, nickel, or copper. The connection method may be welding or screwing. It is preferable to protect the terminals 60 and 62 with insulating tape in order to prevent a short circuit.

(Exterior body)
The exterior body 50 seals the power generation element 40 and the non-aqueous electrolytic solution inside. The exterior body 50 suppresses leakage of the non-aqueous electrolytic solution to the outside and invasion of water or the like into the inside of the lithium ion secondary battery 100 from the outside.

The exterior body 50 has, for example, as shown in FIG. 1, a metal foil 52 and a resin layer 54 laminated on each surface of the metal foil 52. The exterior body 50 is a metal laminate film in which a metal foil 52 is coated with a polymer film (resin layer 54) from both sides.

As the metal foil 52, for example, an aluminum foil can be used. A polymer film such as polypropylene can be used for the resin layer 54. The material constituting the resin layer 54 may be different between the inside and the outside. For example, a polymer having a high melting point, for example, polyethylene terephthalate (PET), polyamide (PA) or the like is used as the outer material, and polyethylene (PE), polypropylene (PP) or the like is used as the material of the inner polymer film. be able to.

(Non-aqueous electrolyte)
The non-aqueous electrolytic solution is sealed in the exterior body 50 and impregnated in the power generation element 40.
The non-aqueous electrolyte solution has, for example, a non-aqueous solvent and an electrolyte. The electrolyte is dissolved in a non-aqueous solvent.

The non-aqueous solvent contains, for example, a cyclic carbonate and a chain carbonate. Cyclic carbonate solvates the electrolyte. Cyclic carbonates are, for example, ethylene carbonate, propylene carbonate and butylene carbonate. The cyclic carbonate preferably contains at least propylene carbonate. The chain carbonate reduces the viscosity of the cyclic carbonate. The chain carbonate is, for example, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate. The non-aqueous solvent may also include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane and the like. ..

In the non-aqueous solvent, for example, a part of hydrogen of the cyclic carbonate or the chain carbonate may be replaced with fluorine. For example, it may have fluoroethylene carbonate, difluoroethylene carbonate and the like.

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

The electrolyte is, for example, a lithium salt. Electrolytes include, for example, LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF _2). SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , LiBOB and the like. One type of lithium salt may be used alone, or two or more types may be used in combination. From the viewpoint of the degree of ionization, the electrolyte preferably contains _{LiPF 6.}

The non-aqueous solvent may have, for example, a room temperature molten salt. The room temperature molten salt is a salt obtained by a combination of a cation and an anion and is in a liquid state even at a temperature lower than 100 ° C. Since the room temperature molten salt is a liquid consisting of only ions, it has strong electrostatic interactions and is characterized by being non-volatile and non-flammable.

Examples of the cation component of the room temperature molten salt include nitrogen-based cations containing nitrogen, phosphorus-based cations containing phosphorus, and sulfur-based cations containing sulfur. These cation components may contain one kind alone or a combination of two or more kinds.
Examples of the nitrogen-based cation include chain or cyclic ammonium cations such as imidazolium cation, pyrrolidinium cation, piperidinium cation, pyridinium cation, and azoniaspiro cation.
Examples of phosphorus-based cations include chain or cyclic phosphonium cations.
Examples of sulfur-based cations include chain or cyclic sulfonium cations.
As a cation component, N-methyl-N-propyl-pyrrolidinium (P13), which is a nitrogen-based cation, has high lithium ion conduction and wide redox resistance, especially when a lithium imide salt is dissolved. ) Is preferable.

The anionic component of the ambient temperature molten _{^{salt, AlCl 4 -, NO 2 -}} , NO 3 -, I -, BF 4 -, PF 6 -, AsF 6 -, SbF 6 -, NbF 6 -, TaF 6 -, F ( HF) _2.3 ⁻ , p−CH ₃ PhSO ₃ ⁻ , CH ₃ CO ₂ ⁻ , CF ₃ CO ₂ ⁻ , CH ₃ SO ₃ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , C _{3 F 7 CO 2, C 4} F 9 SO 3 -, (FSO 2) 2 N - ( bis (fluorosulfonyl) _{imide) (FSI), (CF 3} SO 2) 2 N - ( bis (trifluoromethanesulfonyl) imide ) (TFSI), (C ₂ F ₅ SO ₂ ) ₂ N ⁻ (bis (pentafluoroethanesulfonyl) imide), (CF ₃ SO ₂ ) (CF ₃ CO) N ⁻ ((trifluoromethanesulfonyl) (trifluoromethanecarbonyl) ) Imid), (CN) ₂ N ⁻ (dicyanoimide) and the like. These anion components may contain one kind alone or a combination of two or more kinds.

"Manufacturing method of lithium ion secondary battery"
First, the positive electrode 20 is manufactured. The positive electrode 20 is prepared by mixing a positive electrode active material, a binder and a solvent to prepare a paste-like positive electrode slurry. At least two types of positive electrode active material, a first active material and a second active material, are prepared. The amount of the second active material mixed with the first active material is very small. The method of mixing these components constituting the positive electrode slurry is not particularly limited, and the mixing order is also not particularly limited. Next, the positive electrode slurry is applied to the positive electrode current collector 22. The coating method is not particularly limited. For example, the slit die coat method and the doctor blade method can be mentioned.

Subsequently, the solvent in the positive electrode slurry coated on the positive electrode current collector 22 is removed. The removal method is not particularly limited. For example, the positive electrode current collector 22 coated with the positive electrode slurry is dried in an atmosphere of 80 ° C. to 150 ° C. Next, the obtained coating film is pressed to increase the density of the positive electrode active material layer 24, whereby the positive electrode 20 is obtained. As the pressing means, for example, a roll press machine, a hydrostatic press machine or the like can be used.

Next, the negative electrode 30 is manufactured. The negative electrode 30 can be manufactured in the same manner as the positive electrode 20. The negative electrode 30 prepares a paste-like negative electrode slurry by mixing the negative electrode active material, the binder, and the solvent. The negative electrode 30 is obtained by applying the negative electrode slurry to the negative electrode current collector 32 and drying it. When the negative electrode active material is metallic lithium, a lithium foil may be attached to the negative electrode current collector 32.

Next, the separator 10 is laminated so that the separator 10 is located between the produced positive electrode 20 and the negative electrode 30, and the power generation element 40 is produced. When the power generation element 40 is a wound body, the positive electrode 20, the negative electrode 30, and the separator 10 are wound around one end side as an axis.

Finally, the power generation element 40 is enclosed in the exterior body 50. The non-aqueous electrolyte solution is injected into the exterior body 50. The non-aqueous electrolytic solution is impregnated into the power generation element 40 by reducing the pressure, heating, or the like after injecting the non-aqueous electrolytic solution. By applying heat or the like to seal the exterior body 50, the lithium ion secondary battery 100 can be obtained.

In the lithium ion secondary battery 100 according to the first embodiment, the discharge rate characteristic is improved by slightly adding the second active material as a sub-component to the first active material as the main component. The cause of this is not clear, but it is considered that the positive electrode active material layer 24 contains a small amount of the second active material having a different reaction potential, which causes a concentration gradient of Li ions in the active material layer. It is considered that the charge / discharge reaction is promoted and the discharge rate characteristics are improved by promoting the movement of Li ions according to the concentration gradient of Li ions. Further, when the primary particles were contained in the active material, the discharge rate tended to improve. In particular, this tendency was remarkable when the secondary active material was the primary particles.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations thereof in the respective embodiments are examples, and the configurations are added or omitted within the range not deviating from the gist of the present invention. , Replacements, and other changes are possible.

"Example 1"
(Preparation of positive electrode)
A positive electrode active material, a conductive material, and a binder were mixed to prepare a positive electrode mixture. The conductive material was carbon black, and the binder was polyvinylidene fluoride (PVDF). The mass ratio of the positive electrode active material, the conductive material, and the binder was 90: 5: 5. As the positive electrode active material, LiNi _0.33 Mn _0.33 Co _0.33 O ₂ (denoted as NMC333 in Table 1) was used as the first active material, and LiCoO ₂ (LCO in Table 1) was used as the second active material. Notation) was used. The abundance ratio of the first active material to the second active material was 99.5% for the first active material and 0.5% for the second active material. This positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. Then, a positive electrode slurry was applied to one surface of an aluminum foil having a thickness of 15 μm so that the basis weight after drying was about 10.0 mg / cm ^2. After coating, it was dried at 100 ° C. to remove the solvent to form a positive electrode active material layer on one surface of the aluminum foil. After drying, a positive electrode slurry was applied to the other surface of the aluminum foil so that the basis weight after drying was about 10.0 mg / cm ^2. After coating, it was dried at 100 ° C. to remove the solvent to form positive electrode active material layers on both sides of the aluminum foil.

(Preparation of negative electrode)
The negative electrode active material, the conductive material, and the binder were mixed to prepare a negative electrode mixture. Graphite was used as the negative electrode active material, styrene-butadiene rubber (SBR) was used as the binder, and carboxymethyl cellulose (CMC) was added as a thickener. The mass ratio of the negative electrode active material, the binder and the thickener was 95: 3: 2. This negative electrode mixture was dispersed in distilled water to prepare a negative electrode slurry. Then, a negative electrode slurry was applied to one surface of a copper foil having a thickness of 10 μm so that the basis weight after drying was about 6.0 mg / cm ^2. After coating, it was dried at 100 ° C. to remove the solvent to form a negative electrode active material layer on one surface of the copper foil. After drying, a negative electrode slurry was applied to the other surface of the copper foil so that the basis weight after drying was about 6.0 mg / cm ^2. After coating, it was dried at 100 ° C. to remove the solvent to form negative electrode active material layers on both sides of the copper foil.

(Creation of cell)
The prepared negative electrode and positive electrode were punched into a predetermined shape, and alternately laminated via a polypropylene separator having a thickness of 25 μm, and 9 negative electrodes and 8 positive electrodes were laminated to prepare a laminated body. A cross section was cut using a laminate prepared in the same procedure as a sample, and the morphology of the first active material and the second active material was confirmed by TEM. The first active material was a secondary particle, and the second active material was a primary particle.

An opening was formed by inserting the laminate into the exterior of the aluminum laminate film and heat-sealing it except for one peripheral portion. A non-aqueous electrolyte solution was injected into the outer body. In the non-aqueous electrolyte solution, 1.5 MOL / L of _{lithium hexafluorophosphate (LiPF 6} ) was dissolved in a solvent in which equal amounts of ethylene carbonate (EC) and dimethyl carbonate (DEC) were mixed. Then, the remaining one place was sealed with a heat seal while reducing the pressure with a vacuum sealer to prepare a lithium ion secondary battery according to Example 1.

(Battery evaluation: discharge rate characteristics)
The discharge rate characteristics of the manufactured lithium-ion battery were evaluated. The discharge rate characteristic is 3C (constant at 25 ° C) when the discharge capacity is 100% when the discharge rate is 1C (current value at which the discharge ends in 1 hour when constant current discharge is performed at 25 ° C). The ratio (%) of the discharge capacity at (the current value at which the discharge ends in 20 minutes when the current is discharged) was determined as the discharge rate characteristic.

As an evaluation condition of the discharge rate characteristic, the prepared cell was charged and ^{discharged for the first time at a current density of 0.15 mA / cm 2} , and the actual capacity of the prepared cell was measured. Based on the obtained actual capacity, the current densities at the discharge rates 1C and 3C were determined.

After the initial charge and discharge, constant current charging was performed at 0.5 C to 4.3 V, and then constant voltage charging was performed until the current density reached 0.02 C. After charging, after a pause of 5 minutes, constant current discharge was performed at 1C to 2.8 V, the discharge capacity at 1C was measured, and a pause of 5 minutes was inserted after the measurement.

Then, after constant current charging at 0.5 C to 4.3 V, constant voltage charging was performed until the current density reached 0.02 C. After charging, after a pause of 5 minutes, constant current discharge was performed at 3C to 2.8V, and the discharge capacity at 3C was measured.

"Examples 2 to 5, Comparative Examples 1 and 2"
Examples 2 to 5 and Comparative Examples 1 and 2 are different from Example 1 in that the abundance ratio of the first active material and the second active material is changed. Comparative Example 1 comprises only the first active material.
In Comparative Example 1, the first active material was 100.0% and the second active material was 0.0%.
In Example 2, the first active material was 99.0%, and the second active material was 1.0%.
In Example 3, the first active material was 97.0%, and the second active material was 3.0%.
In Example 4, the first active material was 96.0% and the second active material was 4.0%.
In Example 5, the first active material was 96.5% and the second active material was 4.5%.
In Comparative Example 2, the first active material was 95.0% and the second active material was 5.0%.
The discharge rate characteristics of Examples 2 to 5 and Comparative Examples 1 and 2 were measured. Table 1 shows the ratios of the rate characteristics of Examples 2 to 5 and Comparative Example 2 when the rate characteristic of Comparative Example 1 is 100%. That is, the rate characteristics of Examples 2 to 5 and Comparative Example 2 shown in Table 1 are relative values to the rate characteristics of Comparative Example 1.

"Examples 6 to 10, Comparative Examples 3 and 4"
In Examples 6 to 10 and Comparative Examples 3 and 4, LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (referred to as NMC622 in Table 1) was used as the first active material. 1 to 5 are different from Comparative Examples 1 and 2.
The discharge rate characteristics of Examples 6 to 10 and Comparative Examples 3 and 4 were measured. Table 1 shows the ratios of the rate characteristics of Examples 6 to 10 and Comparative Example 4 when the rate characteristics of Comparative Example 3 are set to 100%. That is, the rate characteristics of Examples 6 to 10 and Comparative Example 4 shown in Table 1 are relative values to the rate characteristics of Comparative Example 3.

"Examples 11 to 15, Comparative Examples 5 and 6"
In Examples 11 to 15 and Comparative Examples 5 and 6, LiNi _0.85 Co _0.10 Al _0.05 O ₂ (denoted as NCA in Table 1) was used as the first active material. 1 to 5 are different from Comparative Examples 1 and 2.
The discharge rate characteristics of Examples 11 to 15 and Comparative Examples 5 and 6 were measured. Table 1 shows the ratios of the rate characteristics of Examples 11 to 15 and Comparative Example 6 when the rate characteristics of Comparative Example 5 were set to 100%. That is, the rate characteristics of Examples 11 to 15 and Comparative Example 6 shown in Table 1 are relative values to the rate characteristics of Comparative Example 5.

"Examples 16 to 20, Comparative Examples 7 and 8"
Examples 16 to 20 and Comparative Examples 7 and 8 are different from Examples 1 to 5 and Comparative Examples 1 and 2 in _{that LiFePO 4 (referred to as LFP in Table 2) is used as the first active material.}
The discharge rate characteristics of Examples 16 to 20 and Comparative Examples 7 and 8 were measured. Table 2 shows the ratios of the rate characteristics of Examples 16 to 20 and Comparative Example 8 when the rate characteristics of Comparative Example 7 were set to 100%. That is, the rate characteristics of Examples 16 to 20 and Comparative Example 8 shown in Table 2 are relative values to the rate characteristics of Comparative Example 7.

"Examples 21 to 25, Comparative Examples 9 and 10"
In Examples 21 to 25 and Comparative Examples 9 and 10, LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (referred to as NMC811 in Table 2) was used as the first active material. 1 to 5 are different from Comparative Examples 1 and 2.
The discharge rate characteristics of Examples 21 to 25 and Comparative Examples 9 and 10 were measured. Table 2 shows the ratios of the rate characteristics of Examples 21 to 25 and Comparative Example 10 when the rate characteristics of Comparative Example 9 were set to 100%. That is, the rate characteristics of Examples 21 to 25 and Comparative Example 10 shown in Table 2 are relative values to the rate characteristics of Comparative Example 9.

"Examples 26 to 30, Comparative Examples 11 and 12"
In Examples 26 to 30 and Comparative Examples 11 and 12, the first active material is LiCoO ₂ (referred to as LCO in Table 3), and the second active material is LiMn ₂ O ₄ having a spinel structure (LMO in Table 3). Notation) is different from Examples 1 to 5 and Comparative Examples 1 and 2.
The discharge rate characteristics of Examples 26 to 30 and Comparative Examples 11 and 12 were measured. Table 3 shows the ratios of the rate characteristics of Examples 26 to 30 and Comparative Example 12 when the rate characteristics of Comparative Example 11 were set to 100%. That is, the rate characteristics of Examples 26 to 30 and Comparative Example 12 shown in Table 3 are relative values to the rate characteristics of Comparative Example 11.

"Examples 31 to 35, Comparative Examples 13 and 14"
Examples 31 to 35 and Comparative Examples 13 and 14 are different from Examples 26 to 30 and Comparative Examples 11 and 12 in that the second active material is NMC333.
The discharge rate characteristics of Examples 31 to 35 and Comparative Examples 13 and 14 were measured. Table 3 shows the ratios of the rate characteristics of Examples 31 to 35 and Comparative Example 14 when the rate characteristics of Comparative Example 13 were set to 100%. That is, the rate characteristics of Examples 31 to 35 and Comparative Example 14 shown in Table 3 are relative values to the rate characteristics of Comparative Example 13.

"Examples 36-40, Comparative Examples 15 and 16"
Examples 36 to 40 and Comparative Examples 15 and 16 are different from Examples 26 to 30 and Comparative Examples 11 and 12 in that the second active material is NMC622.
The discharge rate characteristics of Examples 36 to 40 and Comparative Examples 15 and 16 were measured. Table 3 shows the ratios of the rate characteristics of Examples 36 to 40 and Comparative Example 16 when the rate characteristics of Comparative Example 15 were set to 100%. That is, the rate characteristics of Examples 36 to 40 and Comparative Example 16 shown in Table 3 are relative values to the rate characteristics of Comparative Example 15.

"Examples 41-45, Comparative Examples 17 and 18"
Examples 41 to 45 and Comparative Examples 17 and 18 are different from Examples 26 to 30 and Comparative Examples 11 and 12 in that _{the second active material is LiFePO 4 (referred to as LFP in Table 1).}
The discharge rate characteristics of Examples 41 to 45 and Comparative Examples 17 and 18 were measured. Table 4 shows the ratios of the rate characteristics of Examples 41 to 45 and Comparative Example 18 when the rate characteristics of Comparative Example 17 were set to 100%. That is, the rate characteristics of Examples 41 to 45 and Comparative Example 18 shown in Table 4 are relative values to the rate characteristics of Comparative Example 17.

"Examples 46 to 50, Comparative Examples 19 and 20"
Examples 46 to 50 and Comparative Examples 19 and 20 are different from Examples 1 to 5 and Comparative Examples 1 and 2 in that three types of active materials are used. The first active material was LCO, the second active material was NMC333, and the third active material was NMC622. The abundance ratio of the first active material was fixed at 62%, and the abundance ratio of the second active material and the third active material was changed.

In Comparative Example 19, the first active material was 62.0%, the second active material was 0.0%, and the third active material was 38.0%.
In Example 46, the first active material was 62.0%, the second active material was 0.5%, and the third active material was 37.5%.
In Example 47, the first active material was 62.0%, the second active material was 1.0%, and the third active material was 37.0%.
In Example 48, the first active material was 62.0%, the second active material was 3.0%, and the third active material was 35.0%.
In Example 49, the first active material was 62.0%, the second active material was 4.0%, and the third active material was 34.0%.
In Example 50, the first active material was 62.0%, the second active material was 4.5%, and the third active material was 33.5%.
In Comparative Example 20, the first active material was 62.0%, the second active material was 5.0%, and the third active material was 33.0%.
The discharge rate characteristics of Examples 46 to 50 and Comparative Examples 19 and 20 were measured. Table 4 shows the ratios of the rate characteristics of Examples 46 to 50 and Comparative Example 20 when the rate characteristics of Comparative Example 19 were set to 100%. That is, the rate characteristics of Examples 46 to 50 and Comparative Example 20 shown in Table 4 are relative values to the rate characteristics of Comparative Example 19.

"Examples 51-56"
Examples 51 to 53 are different from Example 3 in that the forms of the first active material and the second active material are changed.
Examples 54 to 56 are different from Example 8 in that the forms of the first active material and the second active material are changed.
The discharge rate characteristics of Examples 51 to 56 were measured. The results are shown in Table 5. The rate characteristics of Examples 51 to 53 in Table 5 are relative values to Comparative Example 1, and the rate characteristics of Examples 54 to 56 are relative values to Comparative Example 3. Table 5 shows the results of Example 3 and Example 8 for comparison.

"Examples 57 to 70"
Examples 57 to 63 are different from Example 3 in that the relationship between the particle sizes of the first active material and the second active material is changed.
Examples 64 to 70 are different from Example 8 in that the forms of the first active material and the second active material are changed.
The discharge rate characteristics of Examples 57 to 70 were measured. The results are shown in Table 6. The rate characteristics of Examples 57 to 63 are relative values to Comparative Example 1, and the rate characteristics of Examples 64 to 70 are relative values to Comparative Example 3. Table 6 shows the results of Example 3 and Example 8 for comparison.

10 Separator 20 Positive electrode 22 Positive electrode current collector 24 Positive electrode active material layer 30 Negative electrode 32 Negative electrode current collector 34 Negative electrode active material layer 40 Power generation element 50 Exterior body 52 Metal leaf 54 Resin layer 60, 62 Terminal 100 Lithium ion secondary battery

Claims (7)

Have at least an active material and a binder,
The active material includes a first active material as a main component and a second active material as a sub-component having a composition different from that of the first active material.
The ratio of the first active material is 60% or more and less than 100% of the total active material.
The active material layer in which the proportion of the second active material is greater than 0% and less than 5% of the total active material. The primary active material is a secondary particle in which a plurality of primary particles are aggregated.
The active material layer according to claim 1, wherein the second active material is primary particles. The active material layer according to claim 1 or 2, wherein the particle size of the first active material is 0.6 times or more and 1.5 times or less the particle size of the second active material. The active material layer according to any one of claims 1 to 3, wherein the reaction potential of the second active material is higher than the reaction potential of the first active material. The second active material is represented by Li _a Co _{1- y My} O ₂ ... (1).
a satisfies 0.8 ≦ a ≦ 1.2, y satisfies 0 ≦ y <0.5, and
The active material layer according to any one of claims 1 to 4, wherein M is at least one of Ni, Mn, Fe, Mg, Zr, Al, Ti, Zn, Cu, Ca, and Na. With the current collector
An electrode comprising the active material layer according to any one of claims 1 to 5, which is laminated on at least one surface of the current collector. A lithium ion secondary battery comprising the electrode of claim 6.

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