JP5862490B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

In recent years, along with the development of portable electronic devices such as mobile phones and notebook computers, and the practical application of electric vehicles, secondary batteries with small and light weight and high capacity are required. Currently, as a high-capacity secondary battery, a lithium ion secondary battery using lithium cobaltate (LiCoO ₂ ) as a positive electrode material and a carbon-based material as a negative electrode material is commercialized.

  Lithium ion secondary batteries are required to have higher capacities, and higher positive electrode potentials are being studied. However, when driven at a high voltage, there has been a problem that battery characteristics after repeated charge and discharge, in other words, cycle characteristics are extremely deteriorated.

  The cause is considered to be that an oxidative decomposition of the electrolyte or electrolyte occurs in the vicinity of the positive electrode during charging, and metal components such as an active material constituting the positive electrode are eluted by an acid generated by the oxidative decomposition. It is also considered that the electrolyte and electrolyte decomposition products accumulate in the electrodes and in the gaps in the separator, resulting in resistance to lithium ion conduction and thus the output is reduced.

  Various studies have been conducted to improve cycle characteristics in a high-voltage usage environment. For example, in Patent Document 1, lithium cobaltate to which at least one of Mg, Al, Ti, and Zr is added as a positive electrode active material is used, and in combination with this positive electrode active material, lithium phosphate is contained in the positive electrode, and further a separator A nonaqueous electrolyte secondary battery having an average pore diameter of 0.05 μm to 0.2 μm has been proposed. In Patent Document 1, it is considered that when the potential of the positive electrode is increased, a low-oxidation substance is generated on the negative electrode side, which moves to the positive electrode and reacts with the positive electrode to deteriorate the cycle characteristics, and the low-oxidation substance moves to the positive electrode. It has been studied to suppress this. It is considered that the lithium cobaltate added with different elements has high stability at a high potential, and lithium phosphate further enhances the stability of the positive electrode at high potential. Further, by regulating the average pore diameter of the separator within the above range, it is possible to suppress the movement of the low oxidizing substance generated on the negative electrode side to the positive electrode side. Further, it is described that by combining this positive electrode active material, lithium phosphate and a separator, the cycle characteristics of the nonaqueous electrolyte secondary battery are improved even when used at a high potential. Patent Document 1 does not describe the discharge capacity.

The Patent Document 2, a cathode active _{material, Li x PO y (1 ≦} x ≦ 4,1 ≦ y ≦ 4) and a lithium phosphate compound represented by the non-aqueous electrolyte secondary comprising a _Al 2 _{O 3} A positive electrode material for a battery has been proposed. By arranging the lithium phosphate compound and Al ₂ O _{3 in} the vicinity of the positive electrode active material, the oxidation state of the transition metal in the positive electrode active material changes, so that the electrolytic solution is decomposed and the transition metal is eluted, and the positive electrode active material It is estimated that the destruction of the crystal structure is reduced. In the example of Patent Document 2, by combining Li ₃ PO ₄ , Al ₂ O ₃ and a positive electrode active material (LiCoO ₂ ), the charge / discharge cycle characteristics are improved while maintaining the initial discharge capacity even at a high potential. Is disclosed.

However, since lithium phosphate (Li ₃ PO ₄ ) has low lithium ion conductivity, it is expected to cause a decrease in output characteristics.

JP 2008-251218 A JP 2008-71569 A

  The present invention has been made in view of such circumstances, and an object thereof is to provide a lithium ion secondary battery capable of improving cycle characteristics while maintaining an initial capacity under a high voltage use environment. And

  As a result of intensive studies by the present inventors, it is possible to improve the cycle characteristics while maintaining the initial capacity of the lithium ion secondary battery even in a high voltage use environment by including a specified amount of lithium phosphate glass in the positive electrode. I found it.

That is, the lithium ion secondary battery of the present invention is a lithium ion secondary battery having a positive electrode, a negative electrode, a separator, and an electrolyte solution. The positive electrode has a general formula: LiCo _p Ni _q Mn _r D _S O ₂ (D is It is a doping component and 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) 100% by mass of a positive electrode active material containing a composite metal oxide and a lithium phosphate glass and a total of the positive electrode active material and the lithium phosphate glass %, So that the content of the lithium phosphate glass is 0.1 mass% or more and less than 3 mass%, and the charging potential of the positive electrode is 4.4 V or more and 4.6 V or less on the basis of lithium. And

  The content of the lithium phosphate glass is preferably 2% by mass or less.

The lithium phosphate glass has a general formula: xLi ₂ O-yMO _u -zP ₂ O ₅ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 1 ≦ u ≦ 2, x + y + z = 1, M is preferably at least one selected from Si, Ge, Ti, Al and Zr).

  In the lithium phosphate glass, M in the general formula preferably contains at least Si.

The positive electrode active material is LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , and the lithium phosphate glass is represented by the general formula: 9 / 13Li ₂ O-3 / 13SiO ₂ -1 / 13P ₂ O ₅ It is preferable to have a composition.

  Since the lithium ion secondary battery of the present invention has a positive electrode active material that is highly stable even at a high potential, the initial capacity is high even in a high voltage environment. Furthermore, since the lithium ion secondary battery of the present invention contains lithium phosphate glass in the positive electrode, the stability of the positive electrode active material is further enhanced in a high voltage use environment. Moreover, since the lithium ion secondary battery of this invention contains lithium phosphate glass in a positive electrode, decomposition | disassembly of the electrolyte solution produced by contact with a positive electrode active material and electrolyte solution can be suppressed, and cycling characteristics can be improved. Further, since lithium phosphate glass has high lithium ion conductivity, an increase in resistance can be suppressed even if lithium phosphate glass is contained in the positive electrode. Therefore, the lithium ion secondary battery of the present invention can improve cycle characteristics while maintaining the initial capacity even under a high voltage use environment.

It is a schematic diagram explaining the positive electrode material used for the lithium ion secondary battery of this embodiment. It is a graph which compares the initial capacity of the lithium ion secondary battery produced by the Example and comparative example of this invention, the capacity | capacitance after a cycle, and a capacity | capacitance maintenance factor.

  The lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, a separator, and an electrolytic solution.

The positive electrode has the general _{formula: LiCo p Ni q Mn r D} s O 2 (D is the doping component, at least one element selected Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe and Na A positive electrode active material containing a composite metal oxide represented by p + q + r + s = 1, 0 ≦ p ≦ 1, 0 ≦ q <1, 0 ≦ r <1, 0 ≦ s <1), and lithium phosphate glass The total content of the positive electrode active material and the lithium phosphate glass is 100% by mass, so that the content of the lithium phosphate glass is 0.1% by mass or more and less than 3% by mass.

  The positive electrode active material and the lithium phosphate glass are referred to as a positive electrode material.

The positive electrode active material has a general formula: LiCo _p Ni _q Mn _r D _S O ₂ (D is a doping component, and 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).

  The composite metal oxide has high stability even at a high potential. Since the composite metal oxide is excellent in thermal stability and low in cost, by including the composite metal oxide, an inexpensive lithium ion secondary battery having good thermal stability can be obtained.

Examples of the composite metal oxide include LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , Li _1.0 Ni _0.6 Co _0.2 Mn _0.2 O ₂ , and Li _1.0 Ni _{0.5. Co 0.2 Mn 0.3 O 2, LiCoO} 2, it is possible to use a _{LiNi 0.8 Co 0.2 O 2, LiCoMnO} 2. Among them, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ is preferable from the viewpoint of thermal stability.

  The positive electrode active material preferably has a powder shape with an average particle diameter of 1 μm to 20 μm. If the average particle size of the positive electrode active material is smaller than 1 μm, the specific surface area of the positive electrode active material is increased and the reaction area with the electrolyte is increased. Therefore, it is not preferable that the average particle size of the positive electrode active material is smaller than 1 μm. If the average particle diameter of the positive electrode active material is larger than 20 μm, the resistance when the lithium ion secondary battery is made increases, and the output characteristics of the lithium ion secondary battery are lowered. .

  The average particle size of the positive electrode active material can be measured by a particle size distribution measurement method.

Lithium phosphate glass contains Li as a skeleton of P ₂ O ₅ having an amorphous structure. Lithium phosphate glass has lithium ion conductivity. Lithium phosphate glass may contain an element selected from Si, Ge, Ti, Al, and Zr in addition to Li. By containing these elements, the thermal stability and ion conductivity of the lithium phosphate glass can be further increased. In particular, the lithium phosphate glass preferably contains Si. When the lithium phosphate glass contains Si, thermal stability can be improved, and lithium ion conductivity can be improved.

  Here, the lithium phosphate glass refers to a material in a glass form containing lithium phosphate in the system. Vitrification makes it easy to place the active material, which is advantageous in terms of structure. In addition, when a material containing lithium phosphate is contained in the positive electrode, lithium ions are easily conducted through the material containing lithium phosphate, so that the electrolyte and the positive electrode active material may be in direct contact with each other. It is presumed that there is an effect of preventing the decomposition of the electrolytic solution, and that the elution of transition metals and the destruction of the crystal structure of the positive electrode active material are reduced.

  In addition, since the phosphoric acid-based material has a strong bond with oxygen, it is considered that the release of oxygen radicals due to oxidative decomposition of the phosphoric acid-based material itself is small, and it can be said that the phosphoric acid-based material is suitable for high voltage applications.

The lithium phosphate glass has a general formula: xLi ₂ O-yMO _u -zP ₂ O ₅ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 1 ≦ u ≦ 2, x + y + z = 1, M is preferably at least one selected from Si, Ge, Ti, Al and Zr).

Lithium phosphate glass includes Li ₂ O—P ₂ O ₅ , Li _3.6 Si _0.6 P _0.4 O ₄ , LiGe ₂ (PO ₄ ) ₃ , and Li (Ti, Al, Zr) (PO ₄ ) It is preferable that at least one component selected from ₃ is included.

  The lithium phosphate glass preferably has a powder shape with an average particle size of 50 nm to 500 nm. If the average particle size of the lithium phosphate glass is smaller than 50 nm, the effect of suppressing the decomposition of the electrolyte is reduced, which is not preferable. If the average particle size of the lithium phosphate glass is larger than 500 nm, it is in the vicinity of the positive electrode active material. Since it becomes difficult to arrange at least one lithium phosphate glass, it is not preferable. When the average particle diameter of the lithium phosphate glass is several nm, the lithium phosphate glass aggregates when mixed with the positive electrode active material, and the lithium phosphate glass is not disposed near the surface of the positive electrode active material. Therefore, it is not preferable.

  The average particle size of the lithium phosphate glass can be measured by a particle size distribution measurement method.

  When the total amount of the positive electrode active material and the lithium phosphate glass is 100% by mass, the content of the lithium phosphate glass is 0.1% by mass or more and less than 3% by mass. By including the lithium phosphate glass in the above range, the lithium ion secondary battery can improve the cycle characteristics while maintaining the initial capacity even in a high voltage use environment.

  When the content of the lithium phosphate glass is less than 0.1% by mass, the effect of improving the cycle characteristics is not observed. When the content of the lithium phosphate glass is 3% by mass or more, since the lithium phosphate glass has high hygroscopicity, the positive electrode material is gelled at the time of slurry preparation, resulting in poor coatability. difficult. The content of the lithium phosphate glass is more preferably 2% by mass or less.

  The positive electrode active material is a powder, the lithium phosphate glass is a powder, and the positive electrode active material and the lithium phosphate glass are at least one lithium phosphate near the surface of one powder of the positive electrode active material. It is preferable that the powder of the system glass is arranged.

  Here, being arranged in the vicinity means that the lithium phosphate glass may adhere to the surface of the positive electrode active material, and there is a small gap between the positive electrode active material and the lithium phosphate glass. Refers to the state that may be. This arrangement state can be confirmed, for example, by observation with an electron microscope.

  FIG. 1 is a schematic diagram illustrating a positive electrode material used in the lithium ion secondary battery of this embodiment. FIG. 1 shows that three lithium phosphate glass 2 powders are arranged in the vicinity of the surface of one positive electrode active material 1 powder.

  The average particle size of the positive electrode active material powder is preferably larger than the average particle size of the lithium phosphate glass powder. When the size of the positive electrode active material is larger than the size of the lithium phosphate glass, the lithium phosphate glass is likely to be disposed near the surface of the positive electrode active material.

  In particular, the positive electrode active material is a powder having an average particle diameter of 1 μm to 20 μm, and the lithium phosphate glass is preferably a powder having an average particle diameter of 50 nm to 500 nm.

  When the average particle diameter of the positive electrode active material is 2 to 400 times the average particle diameter of the lithium phosphate glass, the lithium phosphate glass is more easily disposed near the surface of the positive electrode active material.

  In the lithium ion secondary battery having the positive electrode material, lithium ion conduction is likely to occur on the surface of the positive electrode active material in the vicinity of the lithium phosphate glass having high lithium ion conductivity. The action that the electrolyte solution is decomposed by the contact between the positive electrode active material and the electrolyte solution is accompanied by the conduction of lithium ions. Therefore, the action that the electrolyte solution is decomposed by the contact between the positive electrode active material and the electrolyte solution is Lithium phosphate glass with high ion conductivity is likely to occur on the surface of the positive electrode active material in the vicinity. However, since the electrolytic solution cannot contact the surface of the positive electrode active material on the surface of the positive electrode active material in the vicinity of the lithium phosphate glass, decomposition of the electrolytic solution is suppressed. Therefore, the decomposition of the electrolytic solution is likely to occur selectively on the surface of the positive electrode active material on which the lithium phosphate glass is disposed, but the decomposition of the electrolytic solution is selectively suppressed because the lithium phosphate glass is disposed. Cheap.

  In addition, as described above, since the decomposition of the electrolytic solution is selectively suppressed along with the conduction of lithium ions, a part of the surface can be obtained even if lithium phosphate glass is not disposed on the entire surface of the positive electrode active material. If the lithium phosphate glass is arranged in the vicinity, the decomposition of the electrolytic solution is suppressed.

  In the case of the present application, when the total amount of the positive electrode active material and the lithium phosphate glass is 100% by mass, the content of the lithium phosphate glass is 0.1% by mass or more and less than 3% by mass. From the content, it is unlikely that the lithium phosphate glass is disposed on the entire surface of the positive electrode active material. Resistance when lithium ions are conducted from a solid lithium phosphate glass to a solid cathode active material is higher than that when lithium ions are conducted from a liquid electrolyte to a solid cathode active material . Therefore, in the conduction of lithium ions, when lithium ions are conducted from the electrolytic solution to the positive electrode active material, the lithium phosphate glass existing therebetween becomes a resistance component. If the lithium phosphate glass is disposed on the entire surface of the positive electrode active material, it is assumed that the capacity of the battery is reduced.

  The mixing method of the positive electrode active material and the lithium phosphate glass is preferably dry mixing. In the dry mixing method, mixing may be performed using a mortar and a pestle, for example, mixing may be performed using a known mixing device such as a ball milling device, or the like may be appropriately combined. Depending on the mixing conditions during mixing, the lithium phosphate glass and the positive electrode active material are crushed to reduce the average particle size. Therefore, for use as a material, the positive electrode active material is preferably a powder having an average particle size of 1 μm to 20 μm, and the lithium phosphate glass is preferably a powder having an average particle size of 50 nm to 1 μm.

  Mixing is performed until a lithium phosphate glass powder having an average particle size of 50 nm to 500 nm is disposed in the vicinity of a part of the surface of the positive electrode active material powder having an average particle size of 1 μm to 20 μm. It is preferable to do.

  If the lithium phosphate glass is crushed until the particle size reaches several nanometers during mixing, the crushed lithium phosphate glass aggregates, and the lithium phosphate glass is in the vicinity of the surface of the positive electrode active material. Since it is not arranged, it is not preferable.

  A desirable mixing condition is to mix for about 30 minutes using a mortar and pestle and then mix in an agitator for about 10 minutes at 2000 rpm.

  The positive electrode is formed by adhering a positive electrode active material layer containing the positive electrode material to a current collector. The positive electrode active material layer may contain a binder and, if necessary, a conductive additive in addition to the positive electrode material.

  The binder plays the role of anchoring the positive electrode active material, the lithium phosphate glass and, if necessary, the conductive additive to the current collector, such as polyvinylidene fluoride, polytetrafluoroethylene, fluororubber, etc. Fluorine-containing resins, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins can be used.

  The conductive assistant is added 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 as conductive aids Two or more kinds can be added in combination. The amount of the conductive auxiliary agent used is not particularly limited, but can be, for example, about 1 to 30 parts by mass with respect to 100 parts by mass of the active material contained in the positive electrode.

  A current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a secondary battery. Examples of the material used for the current collector include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins. The current collector can take the form of a foil, a sheet, a film, or the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector.

  The current collector preferably has a thickness of 5 μm to 100 μm.

  For the positive electrode, a composition for forming a positive electrode active material layer containing the above positive electrode material is prepared, and after adding a suitable solvent to the above composition to make a paste, it is applied to the surface of the current collector, and then dried. Accordingly, it can be formed by compression so as to increase the electrode density.

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

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

  The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. A negative electrode active material layer contains a negative electrode active material and a binder, and contains a conductive support agent as needed. The current collector, binder and conductive additive are the same as those described for the positive electrode.

  As the negative electrode active material, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, an elemental compound that has an element that can be alloyed with lithium, or a polymer material 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 capable of alloying lithium is preferably silicon (Si) or tin (Sn).

Examples of elemental compounds having elements 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 , _{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. The elemental compound having an element capable of alloying with lithium is preferably a silicon compound or a tin compound. The silicon compound is preferably SiO _x (0.5 ≦ x ≦ 1.5). As the tin compound, for example, a tin alloy (Cu-Sn alloy, Co-Sn alloy, or the like) can be used.

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

  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.

  For example, cyclic esters, chain esters, and ethers can be used as the solvent. 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 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. Examples of ethers that can be used include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, and the like.

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.

For example, as an electrolytic solution, 0.5 mol / l to 1.7 mol / l of 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, and dimethyl carbonate. A solution dissolved at a certain concentration can be used.

  The lithium ion secondary battery of the present invention is used in a high voltage environment. Specifically, in the lithium ion secondary battery of the present invention, the charging potential of the positive electrode is 4.4 V or more and 4.6 V or less on the basis of lithium. In the present invention, when the charge potential of the positive electrode is 4.4 V or higher with respect to lithium, the effect is remarkably exhibited. However, when the charge potential of the positive electrode exceeds 4.6 V on the basis of lithium, the stability of the positive electrode active material decreases, and the discharge characteristics deteriorate. Accordingly, the charging potential of the positive electrode is preferably in the above range.

  The lithium ion secondary battery can be mounted on a vehicle. Since the lithium ion secondary battery has excellent cycle performance while maintaining the initial capacity, a vehicle equipped with the lithium ion secondary battery can be a high performance vehicle.

  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.

  As mentioned above, although embodiment of the lithium ion secondary battery of this invention was described, this invention is not limited to the said 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.

<Production of laminated lithium-ion secondary battery>
Example 1
[Production of positive electrode]
LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ having an average particle diameter of 10 μm as the positive electrode active material and Li _3.6 Si _0.6 P _0.4 O ₄ glass having an average particle diameter of 1 μm as the lithium phosphate glass. (General formula: 9 / 13Li ₂ O-3 / 13SiO ₂ -1 / 13P ₂ O ₅ ) was prepared.

LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and _Li 3.6 _Si 0.6 _P 0.4 _{O 4} when the sum of the glass is 100 mass% _Li 3.6 _{Si 0.6} P _0.4 O ₄ glass was mixed so as to be 0.1% by mass. For mixing, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and Li _3.6 Si _0.6 P _0.4 O ₄ glass were put in a mortar at the above ratio, and the contents were mixed with a pestle for 30 minutes. Then, it put into the rotation revolution mixer, and stirred at 2000 rpm for 8 minutes, and obtained the mixture.

The mixture had an average particle size an average particle diameter in a portion near the surface of the _LiCo 1/3 _Ni 1/3 _Mn 1/3 _{O 2} of 10μm is 500nm of _Li 3.6 _Si 0.6 _P 0.4 _{O 4} Glass is arranged, and five Li _3.6 Si _0.6 P _0.4 O ₄ near the surface of _one LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ powder. It was confirmed by a scanning electron microscope (SEM) that the glass had been placed.

  The mixture was mixed with the conductive additive and the binder as described below to prepare a slurry. A composition for forming a positive electrode active material layer by mixing the above mixture, acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder so as to be 94 parts by mass, 3 parts by mass, and 3 parts by mass, respectively. I made a thing. This positive electrode active material layer forming composition was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry.

An aluminum foil having a thickness of 20 μm was prepared as a current collector. The slurry was placed on the current collector and applied to the current collector using a doctor blade so that the slurry became a film. The obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then the current collector and the coating material on the current collector were firmly bonded to each other by a roll press. At this time, the electrode density was set to 2.8 g / cm ² . The joined product was heated with a vacuum dryer at 120 ° C. for 6 hours, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and used as the positive electrode of Example 1 having a thickness of about 50 μm.

[Production of negative electrode]
The negative electrode was produced as follows.

  97 parts by mass of graphite powder, 1 part by mass of acetylene black as a conductive additive, 1 part by mass of styrene-butadiene rubber (SBR) and 1 part by mass of carboxymethylcellulose (CMC) as a binder are mixed, and this mixture is mixed. A slurry was prepared by dispersing in an appropriate amount of ion-exchanged water. This slurry was applied to a copper foil having a thickness of 20 μm as a negative electrode current collector so as to form a film using a doctor blade, and the current collector coated with the slurry was dried and pressed. It was heated with a vacuum dryer for a time, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and a negative electrode having a thickness of about 45 μm was obtained.

[Production of laminated lithium-ion secondary battery]
A laminate-type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode of Example 1 above. 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. As an electrolytic solution, a solution obtained by dissolving 1 mol of LiPF ₆ in a solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 3: 7 (volume ratio) 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.

(Example 2)
In the positive electrode material, when the total of LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and Li _3.6 Si _0.6 P _0.4 O ₄ glass is 100 mass%, Li _3.6 Si A laminated lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that _0.6 P _0.4 O ₄ glass was mixed so as to be 0.5 mass%.

(Example 3)
In the positive electrode material, when the total of LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and Li _3.6 Si _0.6 P _0.4 O ₄ glass is 100 mass%, Li _3.6 Si A laminated lithium ion secondary battery of Example 3 was produced in the same manner as in Example 1 except that _0.6 P _0.4 O ₄ glass was mixed so as to be 1.0% by mass.

(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 Li _3.6 Si _0.6 P _0.4 O ₄ glass was not added as the positive electrode material.

(Comparative Example 2)
In the positive electrode material, when the total of LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and Li _3.6 Si _0.6 P _0.4 O ₄ glass is 100 mass%, Li _3.6 Si _A positive electrode was produced in the same manner as in Example 1 except that _0.6 P _0.4 O ₄ glass was mixed so as to be 3.0% by mass, but the slurry gelled when the slurry was applied to the current collector. The slurry could not be applied to the current collector due to poor coating properties. Therefore, a positive electrode could not be produced.

<Initial capacity measurement>
The initial capacities of the laminated lithium ion secondary batteries of Example 1, Example 2, Example 3, and Comparative Example 1 were measured. Based on the capacity when the voltage range is 4.5V-3.0V, the current rate for discharging in 1 hour was set to 1C rate.

  CCCV charge (constant current constant voltage charge) was performed at 25 ° C. with a voltage of 4.5V. The voltage was held for 1 hour. The discharge was a CC discharge (constant current discharge) at a voltage of 3.0 V and a 1 C rate. The discharge capacity at this time was measured and used as the initial capacity.

<Cycle characteristic evaluation>
Following the initial capacity measurement, the cycle characteristics of the laminated lithium ion secondary batteries of Example 1, Example 2, Example 3 and Comparative Example 1 were evaluated. As an evaluation of the cycle characteristics, a cycle test in which charge and discharge were repeated under the following conditions was performed. Charging was CCCV charging (constant current constant voltage charging) at a 1C rate at 55 ° C. and a voltage of 4.5V. The voltage was held for 1 hour. Discharging performed CC discharge (constant current discharge) at 3.0V and 1C rate. This charging / discharging was made into 1 cycle, and the cycle test was done to 25 cycles. Thereafter, the temperature was returned to 25 ° C., and the discharge capacity was measured at a 1 C rate. This discharge capacity was taken as the post-cycle capacity. The capacity retention rate (%) was obtained by the following formula.

Capacity maintenance rate (%) = capacity after cycle / initial capacity × 100
Table 1 shows the initial capacity, post-cycle capacity, and capacity retention rate of each example and comparative example. A graph for comparing the results is shown in FIG.

From the results of Table 1 and FIG. 2, the results of Comparative Example 1 and Example 1 are compared. Compared to Comparative Example 1, Example 1 showed an initial capacity that was not much different from the initial capacity of Comparative Example 1, and the capacity retention rate increased compared to Comparative Example 1. Similarly, Example 2 and Example 3 showed an initial capacity that was not much different from the initial capacity of Comparative Example 1, and the capacity retention rate was increased as compared with Comparative Example 1. The capacity retention _ratio, the higher the content of Li _3.6 Si _{0.6 P} 0.4 _{O 4} glass has a high value. Here, as shown in Comparative Example 2, when the content of Li _3.6 Si _0.6 P _0.4 O ₄ glass is set to 3.0% by mass, the slurry is gelled and a positive electrode can be produced. There wasn't. Therefore, it was found that the content of Li _3.6 Si _0.6 P _0.4 O ₄ glass is preferably 0.1% by mass or more and less than 3.0% by mass. From the experimental results, it was found that Examples 1 to 3 were superior to Comparative Example 1 in both initial capacity and cycle characteristics even under a high voltage use environment.

  1: Positive electrode active material, 2: Lithium phosphate glass.

Claims (3)

The positive electrode, the negative electrode, a lithium ion secondary battery having a separator and an electrolyte,
Positive electrode has the general _{formula: LiCo p Ni q Mn r D} s O 2 (D is the doping component, at least one of Al, Mg, Ti, Sn, Zn, W, Zr, Mo, selected from Fe and Na A positive electrode active material comprising a composite metal oxide represented by p + q + r + s = 1, 0 ≦ p ≦ 1, 0 ≦ q <1, 0 ≦ r <1, 0 ≦ s <1),
Lithium phosphate glass,
Including
When the total amount of the positive electrode active material and the lithium phosphate glass is 100% by mass, the content of the lithium phosphate glass is 0.1% by mass or more and less than 3% by mass,
The lithium phosphate glass has a composition represented by the general formula: 9 / 13Li ₂ O-3 / 13SiO ₂ -1 / 13P ₂ O ₅
The lithium ion secondary battery, wherein a charging potential of the positive electrode is 4.4 V or more and 4.6 V or less on the basis of lithium. Positive electrode active _material, a lithium ion secondary battery according to LiCo _1/3 Ni _{1/3 Mn} 1/3 _{O 2} der Ru請 Motomeko 1. The lithium ion secondary battery according to claim 1 or 2, wherein the content of the lithium phosphate glass is 2 mass% or less.

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