JP2002175802A - Anode and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anode whose battery capacity and charging/discharging efficiency under high voltage and large-current charging conditions is improved. SOLUTION: An anode layer 13, containing compound particles 15 that contains two or more anode active material particles 14, a resin for integrating two or more anode active material particles 14, and an anode active material particles 16, and a collector 12 by which the anode layer 13 is held, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a negative electrode and a non-aqueous electrolyte secondary battery provided with the negative electrode.

[0002]

2. Description of the Related Art In recent years, due to advances in electronic technology, electronic devices have become more sophisticated, smaller, and more portable, and the demand for higher energy density of batteries used in these portable electronic devices has increased. Conventionally, nickel-cadmium batteries and lead batteries have been the mainstream for secondary batteries used in these electronic devices.However, these batteries have a low discharge potential and can sufficiently meet the demand for higher energy density. Did not.

Recently, research on a lithium ion secondary battery including a negative electrode containing a negative electrode active material capable of being doped and de-doped with lithium ions such as a carbon material, a positive electrode, and a non-aqueous electrolyte has been activated. I have. This secondary battery has an advantage that progress of self-discharge is slow and there is no memory effect. In addition, when a lithium-containing composite oxide having a high oxidation-reduction potential is used as an active material of the positive electrode, the battery voltage is increased, so that a battery having a high energy density can be realized.

[0004] As a carbon material of a lithium ion secondary battery, flaky graphite (graphite) is known.
Scaly graphites are relatively easily available, and have the advantage of higher crystallinity and higher true density than low-crystalline carbon materials.

However, scaly graphite is easily exposed to the negative electrode surface despite the fact that the surface on which lithium ions are actively absorbed and desorbed is not a large flat surface but a side surface. In the case of a negative electrode containing scale-like graphite, the use efficiency as a negative electrode active material, and the capacity and charge / discharge efficiency in charge / discharge at a high voltage and a large current are reduced. Furthermore, flaky, plate-like or fibrous graphite materials including flaky graphites require a larger amount of binder resin because of a large specific surface area as compared to those having a spherical shape, and the active material in the negative electrode Since the ratio must be reduced, there is a problem that a sufficient battery capacity cannot be obtained.

Japanese Patent Application Laid-Open No. 9-219190 discloses a lithium-containing composite oxide or carbon material.
A positive electrode mixture slurry or a negative electrode mixture slurry is prepared by mixing a fluorine-based binder resin in a solvent for dissolving the binder resin, and the slurry is spray-dried and dried to obtain a spherical positive electrode mixture powder or negative electrode mixture powder. It is disclosed that a positive electrode or a negative electrode is obtained by molding the powder.

However, when an attempt is made to use a negative electrode mixture powder supported on a current collector as a negative electrode, only a spherical powder such as a negative electrode mixture powder has a contact area with the current collector. Becomes insufficient and the adhesion between the current collector and the negative electrode mixture powder decreases, so that the negative electrode mixture powder easily peels from the current collector due to stress generated in the negative electrode due to charge and discharge. Further, the fluorine-based binder resin contained in the negative electrode mixture powder easily inhibits the lithium ion doping / undoping reaction of the carbon material. Therefore, a non-aqueous electrolyte secondary battery provided with such a negative electrode cannot obtain a high capacity retention ratio in charge and discharge at a high voltage and a large current.

On the other hand, JP-A-9-219188 discloses that a powder of a lithium-containing composite oxide or a carbon material coated with a protective film and a fluorine-based resin binder are mixed in a solvent for dissolving the binder resin. To produce a positive electrode or a negative electrode from the slurry obtained by mixing in, and that the protective film is formed of a resin that does not dissolve in both the nonaqueous solvent of the nonaqueous electrolyte and the solvent for dissolving the binder resin. Have been.

However, if the surface of the carbon material powder, which is the negative electrode active material, is coated with a protective film, direct contact between the non-aqueous solvent of the electrolytic solution and the carbon material powder is hindered. Even if it has conductivity, the reaction rate of the active material is reduced, making it difficult to perform charging and discharging with a high voltage and a large current and to obtain a high capacity retention rate.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a negative electrode and a non-aqueous electrolyte secondary battery having improved battery capacity and charge / discharge efficiency under high voltage and large current charging conditions.

[0011]

According to the present invention, there is provided a negative electrode comprising a plurality of negative electrode active material particles, a composite particle containing a resin for integrating the plurality of negative electrode active material particles, and a negative electrode containing the negative electrode active material particles. And a current collector carrying the negative electrode layer.

A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode comprises a plurality of negative electrode active material particles and a plurality of the plurality of negative electrode active material particles. It is characterized by comprising a composite layer containing a resin for integrating the negative electrode active material particles and a negative electrode layer containing the negative electrode active material particles, and a current collector on which the negative electrode layer is supported.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention comprises: an exterior material; a positive electrode housed in the exterior material; a negative electrode housed in the exterior material; And a non-aqueous electrolyte to be stored. The negative electrode includes a negative electrode layer including a plurality of negative electrode active material particles and a composite particle containing a resin for integrating the plurality of negative electrode active material particles, and a current collector on which the negative electrode layer is supported. However, the negative electrode layer further contains negative electrode active material particles that exist separately from the composite particles.

Hereinafter, the positive electrode, the negative electrode, the non-aqueous electrolyte, and the separator will be described.

1) The negative electrode composite particles are obtained by, for example, dispersing carbon material particles as negative electrode active material particles in a resin solution, and performing granulation by spray drying from the obtained dispersion (slurry). .

The spray drying includes, for example, a disk type spray drying apparatus, a parallel flow type pressure nozzle type spray drying apparatus,
It can be carried out using a spray-drying device such as a co-current type pressure nozzle type spray drying device or a counter-current type pressure nozzle type spray drying device.

As the carbon material particles constituting the composite particles, lithium-doped and undoped carbonaceous material particles or lithium-doped and undoped graphite material particles are used. Examples of carbonaceous material particles or graphite material particles that can be doped and dedoped with lithium include, for example, pyrolytic carbon, cokes, artificial graphites, glassy carbons,
Organic polymer compound fired bodies, carbon fibers, activated carbon and the like can be mentioned.

The shape of the carbon material particles constituting the composite particles can be, for example, scaly or plate-like. The shape of the carbon material particles constituting the composite particles may be one type, or may be two or more types such as a scale and a plate.

It is preferable that the flatness of the plate-like carbon material particles is set to be 2 or more and 5 or less as determined by the following equation (1). Further, it is desirable that the flaky carbon material particles have a flatness determined by the following equation (1), which is larger than 10 and equal to or smaller than 10,000.

Flatness = L / T (1) In the equation (1), L is a short diameter, that is, a diameter of a circle in which the carbon material particles are inscribed, and T is a thickness of the carbon material particles. I do.

As the carbon material particles constituting the composite particles, those containing at least one of a graphite material particle whose primary particle shape is plate-like and a graphite material particle whose primary particle shape is scale-like are preferable. Here, it is desirable that the graphite material particles have a (002) plane spacing d ₀₀₂ determined by powder X-ray diffraction of 0.336 nm or less.
A more preferred range is 0.3358 nm or less. Among them, flaky graphite (graphite) is preferable. Scaly graphite is relatively easy to obtain and has a higher true density because of higher crystallinity than a low-crystalline carbon material. For this reason, the negative electrode including the composite particles in which the flake graphite particles are integrated with the resin can increase the active material filling density, and can improve the energy density of the secondary battery.

As the resin, a resin having a function of binding the carbon material particles and not being dissolved in a non-aqueous solvent contained in a non-aqueous electrolyte described later can be used. As such a resin, for example, polyvinyl alcohol (PV
A), styrene butadiene rubber (SBR), polyethylene (PE), polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), hydroxyethyl methyl cellulose (HEMC) and the like. More preferably, the resin has a function of binding the composite particles and the current collector.

[0023] The content of the resin in the dispersion liquid is 0.1.
It is preferable that the content be in the range of 05 to 10% by weight. This is due to the following reasons. When the content of the resin is less than 0.05% by weight, the shape retention of the composite particles is reduced, and the shape of the composite particles is easily collapsed. On the other hand, when the content of the resin exceeds 10% by weight, the entire surface of the composite particles may be covered with the resin, and the removal and insertion of lithium ions may be hindered. A more preferred range of the resin content is 0.1 to
At 5% by weight, a more preferred range is 0.2 to 3% by weight.

It is preferable that the longest diameter of the primary particles of the carbon material particles constituting the composite particles be in the range of 0.1 μm or more and 50 μm or less. This is due to the following reasons. If the longest diameter is less than 0.1 μm, pulverization of the carbon material particles is likely to proceed, and the increase in the specific surface area tends to increase. Therefore, it is necessary to increase the amount of the resin added in anticipation of the increase in the specific surface area. There is a possibility that sufficient battery capacity cannot be obtained. On the other hand, the longest diameter is 50
If it exceeds μm, the longest diameter of the primary particles of the carbon material particles is
Since the size is close to the size of the composite particles to be formed, the granulated form may not be maintained and may be in a powder state. A desirable range of the longest diameter is 3 μm or more and 30 μm or less, and a more preferred range is 6 μm or more and 15 μm or less.

The composite particles preferably have an average particle diameter of 10 μm or more and 500 μm or less. This is due to the following reasons. When the average particle size is 10 μm or less, the size of the primary particles of the carbon material particles in the composite particles is reduced, so that the necessary resin addition amount may increase and the electrolyte impregnating property of the negative electrode decreases. There is fear. On the other hand, if the average particle size exceeds 500 μm, the adhesion between the composite particles and the current collector may be reduced, and the internal resistance of the negative electrode may increase. A preferable range of the average particle diameter is 20 μm.
m to 100 μm, more preferably 30
It is not less than μm and not more than 80 μm.

The shape of the composite particles can be, for example, spherical, massive, or the like.

For the negative electrode, for example, a negative electrode mixture slurry is prepared by mixing composite particles, carbon material particles, a binder and a solvent for dissolving the binder, and the slurry is applied to a current collector and dried. Alternatively, the negative electrode mixture slurry is poured into a flat vat or the like, powdered by hot air drying, and the obtained powder is pressed into a pellet. The pellet-shaped negative electrode can be used as a negative electrode of a coin-type non-aqueous electrolyte secondary battery.

The ratio of the composite particles to the total solid content in the negative electrode mixture slurry is preferably in the range of 2 to 80% by weight. This is due to the following reasons. When the ratio of the composite particles is less than 2% by weight, the carbon material powder that does not form the composite particles fills the pore structure serving as an electrolyte intrusion path, so that a high discharge capacity and excellent charge / discharge efficiency are obtained. May not be able to do so. On the other hand, if the ratio of the composite particles exceeds 80% by weight, the binding between the current collector and the composite particles is reduced, and the pore space in the negative electrode is increased. May decrease. A more preferable range of the ratio of the composite particles is 20 to 75% by weight, and a further preferable range is 50% by weight.
７０70% by weight.

Examples of the carbon material particles present separately from the composite particles include pyrolytic carbon, cokes, artificial graphites, natural graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, Activated carbon and the like can be mentioned. Among them, mesophase pitch-based carbon fibers are preferred. The mesophase pitch-based carbon fiber has a (002) plane spacing d ₀₀₂ determined by powder X-ray diffraction of 0.33.
The thickness is preferably 7 nm or less, and more preferably 0.3365 nm or less. The average fiber length of the mesophase pitch-based carbon fiber is preferably in the range of 10 to 30 μm, and more preferably 16 to 30 μm.
20 μm.

The shape of the carbon material particles present separately from the composite particles can be, for example, spherical, fibrous, scale-like or plate-like. The shape of such carbon material particles is 1
It is also possible to use two or more types such as a scale and a fiber.

The carbon material particles contained in the composite particles and the carbon material particles present separately from the composite particles may be of the same type or different types.

As the binder, those that dissolve in the solvent contained in the negative electrode mixture slurry can be used. Examples of such a binder include a fluororesin, polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), polyethylene (PE), carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), and hydroxyethylmethylcellulose ( HEMC) and the like. As such a fluorine-based resin, for example, polyvinylidene fluoride (P
VdF), poly (propylene hexafluoride), poly (ethylene trifluoride chloride), poly (propylene pentafluoride), or copolymers thereof. Among them, polyvinylidene fluoride (PVdF) is preferable.

Preferably, the amount of the binder in the solid content of the negative electrode mixture slurry is in the range of 0.3% by weight to 10% by weight. This is due to the following reasons. If the amount of the binder is less than 0.3% by weight, the moldability of the negative electrode or the adhesion between the negative electrode layer and the current collector may be reduced. On the other hand, when the amount of the binder exceeds 10% by weight, the amount of the active material may be relatively reduced, and the surface of the active material is coated with the binder, thereby preventing lithium ions from being inserted and removed. There is a risk that. A more preferable range of the amount of the binder is 1 to 8% by weight, and a further preferable range is 2 to 6% by weight.

When a fluoride resin is used as the binder, dimethylformamide, dimethylacetamide, methylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone and the like are used as the solvent for dissolving the binder. can do. In particular, PV as a binder
When dF is used, N-methyl-2-pyrrolidone is preferred. In addition, water can be used as a solvent for dissolving the binder in the case of a binder other than the above-mentioned fluoride-based resin, which can be turbid in water as a resin soluble in water or an emulsion. Examples of the binder dissolved in water include polyvinyl alcohol (PVA), polyethylene (PE),
Examples thereof include carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), and hydroxyethyl methyl cellulose (HEMC). On the other hand, as a binder which can be turbid in water as an emulsion, for example, styrene butadiene rubber (SBR)
And the like.

As the current collector, a porous conductive substrate or a non-porous conductive substrate can be used.
The current collector can be formed of, for example, copper, nickel, or the like. In particular, it is preferable to use a non-porous conductive substrate as the current collector.

2) Positive Electrode For the positive electrode, for example, a positive electrode mixture slurry is prepared by mixing a positive electrode active material, a conductive material and a binder in a binder dissolving solvent, and the slurry is used as a current collector. It is produced by applying and drying, or by pouring the positive electrode mixture slurry into a flat vat or the like, powdering by hot air drying, and press-molding the obtained powder into a pellet. The pellet-shaped positive electrode can be used as a positive electrode of a coin-type non-aqueous electrolyte secondary battery.

As the positive electrode active material, for example, lithium-containing composite oxide particles can be used. In particular,
As a lithium-containing composite oxide, the composition is Li _x MO
₂ (where M is a transition metal and the molar ratio x is 0.0
5 ≦ x ≦ 1.1).
Among the lithium-containing composite oxides represented by the above composition formulas, those using at least one selected from the group consisting of Co, Ni and Mn as M are preferable. The lithium-containing composite oxide in which M is Mn includes Li _x
Mn ₂ O ₄ and Li _x MnO ₂ are included.

Examples of the conductive material include carbon black and graphite. The shape of the conductive material is, for example, spherical, fibrous, granular, scaly,
It can be plate-shaped.

It is desirable to use a fluororesin as the binder. As such a fluororesin, for example,
Examples thereof include polyvinylidene fluoride (PVdF), polypropylene hexafluoride, polyethylene trifluoride chloride, polypropylene pentafluoride, and copolymers thereof. Among them, polyvinylidene fluoride (PVdF) is preferable.

As the solvent for dissolving the binder, for example,
Dimethylformamide, dimethylacetamide, methylformamide, tetrahydrofuran, N-methyl-2
-Pyrrolidone and the like can be used. In particular, when PVdF is used as a binder, N-methyl-2-
Preference is given to using pyrrolidone.

As the current collector, a porous conductive substrate or a non-porous conductive substrate can be used.
The current collector can be formed of, for example, aluminum, nickel, or the like. In particular, it is preferable to use a non-porous conductive substrate as the current collector.

3) Nonaqueous Electrolyte As the nonaqueous electrolyte, a liquid nonaqueous electrolyte (nonaqueous electrolyte) mainly composed of a nonaqueous solvent in which an electrolyte is dissolved, a gelled nonaqueous electrolyte, or the like can be used.

The gel non-aqueous electrolyte is prepared, for example, by the method described below. First, a paste prepared by mixing a polymer serving as a gelling agent, a non-aqueous solvent, and a lithium salt is formed into a film, and then dried. An electrode group is produced by interposing the obtained thin film between the positive electrode and the negative electrode. After the electrode group is impregnated with the liquid nonaqueous electrolyte, the thin film is plasticized under reduced pressure, so that the electrode group holds the gelled nonaqueous electrolyte.

The polymer preferably has thermoplasticity. Such polymers include, for example, polyvinylidene fluoride (PVdF), polyacrylonitrile (P
AN), polyethylene oxide (PEO), polyvinyl chloride (PVC), polymethyl methacrylate (PMM
A) and at least one selected from polyvinylidene fluoride hexafluoropropylene (PVdF-HFP) can be used.

Examples of the non-aqueous solvent include cyclic carbonates which are high dielectric constant solvents such as ethylene carbonate, propylene carbonate, butylene carbonate and γ-butyrolactone;
Examples thereof include low-viscosity solvents such as 2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. Above all,
A mixed solvent of ethylene carbonate and methyl ethyl carbonate can be preferably used. When a sheet including a resin layer is used as an exterior material, a non-aqueous solvent containing γ-butyrolactone is preferable because swelling of the exterior material during high-temperature storage can be suppressed.

As the electrolyte, for example, LiClO
_{4, LiAsF 6, LiPF 6,} LiBF 4, LiBr, C
H ₃ SO ₃ Li, CF ₃ SO ₃ Li, and the like can be given.

4) Separator A separator can be provided between the positive electrode and the negative electrode.

The separator can be formed from a porous sheet. As the porous sheet, for example, a porous film or a nonwoven fabric can be used. The porous sheet is preferably made of, for example, at least one material selected from polyolefin and cellulose. Examples of the polyolefin include polyethylene and polypropylene. Among them, a porous film made of polyethylene, polypropylene, or both is preferable because the safety of the secondary battery can be improved.

5) Exterior material The exterior material is, for example, a sheet containing a resin layer (for example,
(Laminate film), a resin film, a metal plate, or the like.

The resin layer contained in the sheet is, for example,
It can be formed from polyethylene, polypropylene or the like. As the sheet, it is desirable to use a sheet in which a metal layer and protective layers disposed on both sides of the metal layer are integrated. The metal layer serves to block moisture. Examples of the metal layer include aluminum, stainless steel, iron, copper, and nickel. Among them, aluminum which is lightweight and has a high function of blocking moisture is preferable. The metal layer may be formed from one type of metal, or may be formed from a combination of two or more types of metal layers. Of the two protective layers, a protective layer in contact with the outside serves to prevent damage to the metal layer. This external protective layer is formed of one type of resin layer or two or more types of resin layers. On the other hand, the inner protective layer has a role of preventing the metal layer from being corroded by the non-aqueous electrolyte. This internal protective layer is formed from one type of resin layer or two or more types of resin layers. Further, for the purpose of sealing the exterior material by heat sealing, a thermoplastic resin can be disposed on the surface of the internal protective layer (the inner surface of the sheet).

The resin film can be formed, for example, from a polyolefin such as polyethylene or polypropylene.

The metal plate is made of, for example, iron, stainless steel,
It can be formed from aluminum.

FIGS. 1 and 2 show a cylindrical non-aqueous electrolyte secondary battery which is an example of the non-aqueous electrolyte secondary battery according to the present invention.

For example, a bottomed cylindrical container 1 made of stainless steel has an insulator 2 disposed at the bottom. Electrode group 3
Are stored in the container 1. The electrode group 3 includes:
It has a structure in which a belt-like material in which a positive electrode 4, a separator 5 and a negative electrode 6 are laminated in this order is spirally wound.

The container 1 contains a liquid non-aqueous electrolyte (non-aqueous electrolyte). P with a hole in the center
TC element 7, safety valve 8 arranged on PTC element 7
And a hat-shaped positive electrode terminal 9 disposed on the safety valve 8
Is caulked and fixed to the upper opening of the container 1 via an insulating gasket 10. The positive electrode terminal 9 has a built-in safety mechanism serving as a gas vent hole (not shown). One end of the positive electrode lead 11 is connected to the positive electrode 4,
The other ends are connected to the PTC elements 7, respectively. The negative electrode 6 is connected to the container 1 as a negative terminal via a negative lead (not shown).

As shown in FIG. 2, the negative electrode 6 includes a current collector 12 formed of a non-porous conductive substrate, and a negative electrode layer 13 carried on the current collector 12. The negative electrode layer 13
Is a composite particle 15 in which a large number of flaky carbon material particles 14 are integrated into a sphere by a resin (not shown), and a fibrous carbon material particle 16 existing on the surface of the composite particle 15 or between the composite particles 15. And a binder (not shown) for bonding the composite particles 15 and the fibrous carbon material particles 16 to the current collector 12.

In the non-aqueous electrolyte secondary battery according to the present invention described above, a plurality of negative electrode active material particles (for example, carbon material particles) and the plurality of negative electrode active material particles (for example, carbon material particles) are integrated. And a negative electrode having a negative electrode layer including a composite particle containing a resin and negative electrode active material particles (for example, carbon material particles), and a current collector carrying the negative electrode layer.

(1) In such a negative electrode, a liquid non-aqueous electrolyte (non-aqueous electrolyte) can be quickly penetrated into the negative electrode while maintaining a high negative electrode density while increasing the voids in the negative electrode layer. In addition, the carbon material particles that exist separately from the composite particles have a high reaction rate because they are not integrated with the resin unlike the composite particles. As a result, the reaction rates of doping and undoping of lithium ions in the negative electrode can be improved.

(2) In the negative electrode according to the present invention, in addition to the contact between the composite particles, the contact area between the composite particle and other carbon material particles is ensured due to the presence of the carbon material particles that do not constitute the composite particles. can do. As a result, the electron conductivity of the negative electrode and the adhesion between the negative electrode layer and the current collector can be increased.

As a result of the above (1) and (2), since the utilization factor as a negative electrode is improved, a non-aqueous electrolyte secondary battery having high capacity and excellent charge / discharge efficiency can be realized.

In the nonaqueous electrolyte secondary battery according to the present invention, the carbon material particles contained in the composite particles may be a graphite material particle having a primary particle shape of plate-like and a flake-like graphite material particle having a primary particle shape of scaly. By including at least one of the above, the surface of such a composite particle is plate-like,
Since the side surfaces of the flaky graphite material particles are easily exposed, it is possible to selectively expose the side surfaces of the plate-like and flaky graphite material particles on the negative electrode surface by adopting the composite particle form. As a result, since the lithium ion occlusion / release speed of the negative electrode can be further improved, the charge / discharge efficiency at a high voltage and a large current can be increased. In addition, by integrating the plate-like, flaky graphite material particles with a resin, a plate-like,
Since the apparent specific surface area of the flaky graphite particles can be reduced, the amount of the resin added in the negative electrode layer can be reduced. Therefore, the occupation ratio of the negative electrode active material in the negative electrode layer can be increased, so that the battery capacity can be improved.

Further, for carbon material particles which are difficult to granulate due to an excessively large primary particle diameter such as fibrous carbon material particles, carbon material particles of a type different from the carbon material particles are formed. By adding the composite particles formed by granulation, the effect of the composite particles (such as improvement of the permeation rate and reaction rate of the non-aqueous electrolyte solution of the negative electrode, etc.) while taking advantage of the characteristics of the carbon material particles existing separately from the composite particles ) Can be obtained. In particular, by using mesophase pitch-based carbon fibers as carbon material particles that exist separately from the composite particles, there is a mesophase pitch-based carbon fiber between the composite particles, and both ends of the carbon fiber pierce the composite particles. Since the composite particles and the carbon material particles can be integrated with sufficient strength, the electron conductivity of the negative electrode can be improved, and the charge / discharge efficiency at a high voltage and a large current can be improved. Can be higher.

In particular, according to the present invention, the battery capacity and charge / discharge efficiency of a cylindrical non-aqueous electrolyte secondary battery under high-voltage and large-current charging conditions can be significantly improved.
This is presumed to be due to the mechanism described below.

The cylindrical non-aqueous electrolyte secondary battery includes an electrode group formed by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween, and a liquid non-aqueous electrolyte impregnated in the electrode group. (A non-aqueous electrolyte). When a porous negative electrode current collector of such a secondary battery is used, a tensile stress applied to the electrodes when a spiral electrode group is produced, and a remarkable expansion and expansion during charge / discharge compared to the positive electrode.
Since there is a concern that the negative electrode may be broken by shrinkage, the battery capacity may be reduced.

For this reason, a non-porous conductive substrate such as a copper foil is often used as a negative electrode current collector of a cylindrical non-aqueous electrolyte secondary battery. However, in the negative electrode in which the negative electrode layer is supported on both surfaces of the non-porous current collector, unlike the case where a porous current collector is used, the electrolytic solution passes through the current collector from one negative electrode layer, and There is no path that penetrates through the current collector of the negative electrode to reach the other negative electrode layer. Therefore, it is difficult to supply the nonaqueous electrolyte to the negative electrode active material existing near the surface of the negative electrode current collector, in addition to allowing the electrolyte to penetrate deeply from the negative electrode surface in the thickness direction of the negative electrode. It becomes more difficult to supply the nonaqueous electrolyte to the negative electrode active material present near the surface of the negative electrode current collector as the nonaqueous electrolyte secondary battery has a higher capacity and the density of the negative electrode layer increases.

As in the present invention, by using a material containing both the composite particles and the carbon material particles as the negative electrode layer carried on the non-porous current collector, the negative electrode layer can be maintained while maintaining high density. Can be increased to increase the electrolyte permeation rate of the negative electrode. Furthermore, the reaction rate of lithium ion doping and undoping, the electron conductivity, and the adhesion between the negative electrode layer and the current collector can be improved. As a result, the battery capacity and charge / discharge efficiency of a cylindrical nonaqueous electrolyte secondary battery using a nonporous negative electrode current collector under high-voltage and large-current charging conditions can be significantly improved.

[0067]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Negative Electrode> As the carbon material particles constituting the granulated particles, flaky graphite having a particle size of 6 μm corresponding to 90% of the lamination distribution curve (calculated according to the above-described formula (1)) The flatness of the primary particles to be obtained is 30 and the (002) plane spacing d ₀₀₂ obtained by powder X-ray diffraction is 0.3355 nm.
30% by weight and flaky graphite having a particle size of 15 μm corresponding to 90% of the lamination distribution curve (the primary particle flatness calculated by the above-mentioned formula (1) is 48 and is obtained by powder X-ray diffraction ( 002) The surface spacing d ₀₀₂ is 0.3
(356 nm) 70% by weight. On the other hand, carboxymethyl cellulose (CM) is used as a resin for forming granulated particles.
C) was dissolved in pure water to prepare a 2% by weight CMC aqueous solution.

The flatness of the primary particles of flaky graphite is calculated by the method described below.

That is, the carbon material particles are photographed with a scanning electron microscope (3000 times), and the thickness of the particles is measured from the cross-sectional image. The thickness is measured by measuring 30 particles with different particles for the carbon material particle group of the same sample, and the average value is defined as the particle thickness (T). On the other hand, the Feret diameter is measured for carbon material particles of the same kind of sample. The particle size measured at this time is an interval in which the particle image is sandwiched by two parallel lines, and the shortest distance between the parallel lines is measured as the minor axis. The minor axis is also measured with 30 different particles, and the average value is defined as the minor axis value (L). The flatness (L / T) is determined from the above particle thickness (T) and minor axis value (L).

A dispersion slurry having a solid content ratio of 25% by weight was prepared by adding a CMC aqueous solution to the above-mentioned carbon material particles, further adding pure water, and kneading. An SBR (styrene butadiene rubber) emulsion was added to the dispersion slurry and mixed so that the SBR was 0.6% by weight with respect to the carbon material particles. The obtained dispersion slurry is introduced into a spray dryer (manufactured by Okawara Processing Machine) having an inlet temperature of 250 ° C., an outlet temperature of 130 ° C., and an atomizer rotation speed of 25,000 per minute, and spray-drys the granulated particles. Obtained. FIG. 3 shows a scanning electron micrograph of the granulated particles. In the micrograph of FIG.
m.

As is clear from FIG. 3, the granulated particles obtained by the above-mentioned method have a spherical shape. It can also be seen that not only the flat surface of the flaky graphite but also the side surfaces are exposed on the surface of the granulated particles.

With respect to 20% by weight of the granulated particles, as a carbon material particle, a mesophase pitch-based carbon fiber manufactured by Petka Co., Ltd. (average fiber length: 18 μm, plane spacing of (002) plane obtained by powder X-ray diffraction) d ₀₀₂ is 0.336
2 nm) was added at 80% by weight, and a 2% by weight aqueous CMC solution was added as a binder so that the CMC amounted to 0.7 part by weight with respect to the whole powder particles. Subsequently, an emulsion of SBR (solid content of 48% by weight) was added. ) Was added so that the SBR solid content was 0.8 parts by weight based on the whole powder. Further, pure water was added so that the total solid content ratio was 58% by weight, and mixed to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to both surfaces of a copper foil having a thickness of 12 μm using a coater so as to have a weight of about 112 g / m ² after drying. After drying, the density was 1.4 with a roll press.
It was compressed to 5 g / cm ³ to obtain a strip-shaped negative electrode.
FIG. 4 shows a scanning electron micrograph of the negative electrode surface. In the photomicrograph of FIG. 4, 4 cm corresponds to 500 μm.

As is apparent from FIG. 4, the presence of granulated particles was observed in the negative electrode, and it was found that many pores were formed on the negative electrode surface.

<Preparation of Positive Electrode> To 100 parts by weight of LiCoO ₂ particles having a primary particle size of 3 μm as a positive electrode active material, 3 parts by weight of flaky graphite and 2.5 parts by weight of acetylene black were added as conductive materials, and PVdF was further added. Was dissolved in an N-methyl-2-pyrrolidone (NMP) solution so as to have a PVdF solid content of 4 parts by weight.
Next, NMP was added so that the solid content ratio became 68% by weight, and mixed to prepare a positive electrode mixture slurry. The obtained slurry was coated with a coater to a thickness of 15 μm.
Was coated on both sides of the aluminum foil, dried, and then compression-molded with a roll press to produce a belt-shaped positive electrode.

<Preparation of non-aqueous electrolyte> Ethylene carbonate
LiPF ₆ was dissolved at a concentration of 1 mol / L in a non-aqueous solvent consisting of 7% by weight and 60.3% by weight of ethyl methyl carbonate,
A non-aqueous electrolyte was prepared.

The strip-shaped negative electrode and positive electrode prepared as described above, and a separator made of a microporous polyethylene film having a thickness of 25 μm were sequentially laminated and multilayer-wound to produce a spirally wound electrode body. The spirally wound electrode body was housed in a nickel-plated iron battery can with insulating plates disposed on both upper and lower surfaces thereof. Next, a positive electrode lead made of aluminum was led out of the positive electrode current collector, and connected to the battery lid via a safety device having a PTC element as a current interrupting device. Further, a negative electrode lead made of nickel was led out of the negative electrode current collector and was welded to a battery can.

Subsequently, after injecting the electrolytic solution into the battery can, the battery lid is disposed in the battery can via a gasket, and the battery lid is swaged and fixed to the battery can, thereby obtaining the structure shown in FIG. , A cylindrical nonaqueous electrolyte secondary battery having a diameter of 18 mm, a height of 65 mm, and a theoretical capacity of 1850 mAh.

Example 2 A cylinder was prepared in the same manner as in Example 1 except that the mixing ratio of the granulated particles and the carbon material particles was 60% by weight of the granulated particles and 40% by weight of the carbon material particles. A non-aqueous electrolyte secondary battery was manufactured.

Example 3 Example 1 was repeated except that the atomizer rotation speed of the spray dryer was increased to 30,000 rotations per minute when forming the granulated particles of the negative electrode.
In the same manner as in the above, a cylindrical nonaqueous electrolyte secondary battery was manufactured.

Example 4 Example 1 was repeated except that the atomizer rotation speed of the spray dryer was reduced to 20,000 rotations per minute when forming the granulated particles of the negative electrode.
In the same manner as in the above, a cylindrical nonaqueous electrolyte secondary battery was manufactured.

Example 5 The blending ratio of the flaky graphite constituting the granulated particles was changed to 70% by weight of the flaky graphite having a particle diameter of 6 μm corresponding to 90% of the lamination distribution curve and 90% of the lamination distribution curve. A cylindrical non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the corresponding particle size was changed to 30% by weight of flaky graphite having a particle size of 15 μm.

Comparative Example 1 A flaky graphite powder having a particle size of 6 μm corresponding to 90% of the lamination distribution curve and a flaky graphite powder having a particle size of 15 μm corresponding to 90% of the lamination distribution curve were prepared by weight ratio. It was weighed so as to be 3: 7.
The total weight of the mixed powder was 20 parts by weight, and 80 parts by weight of mesophase pitch-based carbon fiber manufactured by Petka Corporation was prepared. In addition, a 2% by weight CMC aqueous solution was prepared as a binder, and pure water was prepared in such an amount that the solid content ratio in the negative electrode mixture slurry became 58%.

First, an aqueous CMC solution and pure water were mixed with a stirrer, and a mixed powder of flaky graphite and then a mesophase pitch-based carbon fiber were added thereto and mixed and dispersed. A negative electrode mixture slurry was prepared by adding and mixing the SBR emulsion (solid content: 48% by weight) so that the SBR solid content was 1.8 parts by weight based on the whole negative electrode active material powder. A negative electrode was produced in the same manner as in Example 1 except that the obtained slurry was used. FIG. 5 shows a scanning electron micrograph of the negative electrode surface. In the photomicrograph of FIG. 5, 4 cm corresponds to 500 μm.

As is clear from FIG. 5, the negative electrode contains no granulated particles, and although the presence of pores is recognized on the surface of the negative electrode, the size of the negative electrode is the same as that of Example 1 in FIG. It can be seen that it is smaller than the negative electrode.

From the obtained negative electrode, a cylindrical non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 described above.

Comparative Example 2 A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that only the same granulated particles as described in Example 1 were used as the negative electrode active material. Manufactured.

(Evaluation of Battery Performance) The cylindrical nonaqueous electrolyte secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2
℃, charging voltage is 4.2V, charging current is 360mA
After charging for 8 hours, the resultant was left at 20 ° C. for 7 days. Thereafter, the battery was discharged to 3.00 V at a discharge current of 1800 mA, and the discharge capacity was measured. The ratio of the discharge capacity to the measured charge capacity was calculated, and the result, expressed as a percentage, is shown in Table 1 below as charge / discharge efficiency.

(Confirmation of Microstructure of Negative Electrode) Also, the above-described battery performance evaluation test (at 20 ° C., charging voltage was 4.2 V,
After charging for 8 hours at a charging current of 360 mA, 20
C. for 7 days, and then discharge to 3.0 V at a discharge current of 1800 mA). For each of the cylindrical non-aqueous electrolyte secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2, The negative electrode was disassembled in the sealed glove box, the negative electrode was taken out, an adhesive tape was stuck to an arbitrary portion on the surface of the negative electrode layer, and then peeled off, and the negative electrode layer attached to the tape was observed with a scanning electron microscope. FIG. 6 shows a scanning electron micrograph of the positive electrode of Example 1. In the micrograph of FIG. 6, 12 mm corresponds to 100 μm.

As is clear from FIG. 6, the granulated particles in the negative electrode of Example 1 maintain the form of the granulated particles even after charge / discharge.

Further, among the negative electrodes taken out by disassembly, with respect to the negative electrodes of Examples 1 to 5, the microstructure at an arbitrary position on the negative electrode surface was measured with a scanning electron microscope at a magnification of 500.
Observation was performed in 10 visual fields at × 1, and the particle size of the confirmed granulated particle form and the longest diameter of the primary particles (primary particles of flaky graphite) observed in the granulated particles were measured from the obtained micrograph. The measurement diameter was the Feret diameter. For primary particles, 20 to 30 particles were measured for each visual field, and the particle size was measured by sandwiching the particle image of each visual field between two parallel lines and measuring the interval. The longest diameter of the primary particle diameter is determined for each visual field, the average of these longest diameters for 10 visual fields is calculated, and the result is shown in Table 1 below as the longest diameter of the primary particles.

On the other hand, as for the granulated particles, one particle is set for each visual field, the particle image shown in the photograph is sandwiched between two parallel lines, the distance between the particles is measured, and the particle image is orthogonal to the parallel lines. Sandwich the two parallel lines, measure the interval,
The particle size in two directions was measured. The average of the particle diameters in two directions is calculated for each visual field to obtain the granulated form particle diameter, and the average value of these granulated form particle diameters for 10 visual fields is calculated. The results are shown in Table 1 below.

[0093]

[Table 1]

As is evident from Table 1, two of Examples 1 to 5 provided with a negative electrode containing granulated particles (composite particles) composed of a number of carbon material particles integrated with a resin and a carbon material powder. The secondary battery had a larger discharge capacity than the secondary batteries of Comparative Examples 1 and 2, and an improvement of about 2% in charge / discharge efficiency was recognized.

In the above-described embodiment, an example in which the present invention is applied to a cylindrical non-aqueous electrolyte secondary battery has been described. However, in the present invention, a separator is interposed between a positive electrode and a negative electrode and spirally wound. Then, a rectangular non-aqueous electrolyte secondary battery, a coin-type non-aqueous electrolyte secondary battery, and a button in which the electrode group and the non-aqueous electrolyte formed into a flat shape by pressing are housed in a bottomed rectangular cylindrical metal container. -Type non-aqueous electrolyte secondary battery, an electrode group in which the positive electrode, the negative electrode, and the separator are integrated, and a sheet in which the non-aqueous electrolyte includes a resin layer (for example, a laminate film)
The present invention can be applied to a thin non-aqueous electrolyte secondary battery or the like stored in an exterior material.

[0096]

According to the present invention, it is possible to provide a negative electrode and a non-aqueous electrolyte secondary battery having improved battery capacity and charge / discharge efficiency under high voltage and large current charging conditions.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a cylindrical non-aqueous electrolyte secondary battery as an example of a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a schematic diagram showing an example of a fine structure of a negative electrode of the non-aqueous electrolyte secondary battery of FIG.

FIG. 3 is a scanning electron micrograph of granulated particles used for a negative electrode of the nonaqueous electrolyte secondary battery of Example 1.

FIG. 4 is a scanning electron micrograph of the negative electrode of the nonaqueous electrolyte secondary battery of Example 1.

FIG. 5 is a scanning electron micrograph of the negative electrode of the nonaqueous electrolyte secondary battery of Comparative Example 1.

FIG. 6 is a scanning electron micrograph of a negative electrode of the nonaqueous electrolyte secondary battery of Example 1 after a battery performance evaluation test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... container, 2 ... insulator, 3 ... electrode group, 4 ... positive electrode, 5 ... separator, 6 ... negative electrode, 10 ... insulating gasket, 12 ... current collector, 13 ... negative electrode layer, 14 ... flaky carbon material particle, 15: Composite particles, 16: Fibrous carbon material particles.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuyuki Sakurai, 8-8 Shinsugitacho, Isogo-ku, Yokohama, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Asako Sato, 8th Shinsugitacho, Isogo-ku, Yokohama, Kanagawa F-term (reference) at Toshiba Yokohama Office 5H029 AJ02 AJ03 AK03 AL06 AM03 AM04 AM05 AM07 BJ02 BJ14 DJ08 DJ16 DJ17 HJ05 5H050 AA02 AA08 BA17 CA08 CB07 DA03 DA11 EA10 EA23 EA24 EA28 FA17 HA05

Claims (12)

[Claims] 1. A negative electrode layer including a plurality of negative electrode active material particles, a composite particle containing a resin for integrating the plurality of negative electrode active material particles and a negative electrode active material particle, and a collector on which the negative electrode layer is supported. A negative electrode comprising: an electric body. 2. The negative electrode according to claim 1, wherein said negative electrode active material particles are carbon material particles. 3. The negative electrode according to claim 2, wherein the carbon material particles contained in the composite particles are composed of graphite material particles having a primary particle having a longest diameter of 0.1 μm or more and 50 μm or less. 4. An average particle diameter of the composite particles is 10 μm.
The thickness is not less than 500 μm.
The negative electrode as described. 5. The carbon material particles contained in the composite particles, wherein the primary particles have at least one of a plate-like graphite material particle and a primary particle having a flake-like graphite material particle. A method according to any one of claims 2 to 4,
The negative electrode as described. 6. The negative electrode according to claim 1, wherein the negative electrode active material particles are composed of mesophase pitch-based carbon fibers. 7. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is for integrating a plurality of negative electrode active material particles and the plurality of negative electrode active material particles. A non-aqueous electrolyte secondary battery, comprising: a negative electrode layer containing resin-containing composite particles and negative electrode active material particles; and a current collector on which the negative electrode layer is supported. 8. The non-aqueous electrolyte secondary battery according to claim 7, wherein the negative electrode active material particles are carbon material particles. 9. The non-aqueous material according to claim 8, wherein the carbon material particles contained in the composite particles are composed of graphite particles having a longest diameter of primary particles of 0.1 μm or more and 50 μm or less. Electrolyte secondary battery. 10. An average particle diameter of the composite particles is 10 μm.
The non-aqueous electrolyte secondary battery according to claim 9, wherein the length is not less than m and not more than 500 µm. 11. The carbon material particles contained in the composite particles, wherein the primary particles include at least one of a plate-like graphite particle and a primary particle having a scale-like graphite particle. The non-aqueous electrolyte secondary battery according to claim 8, wherein: 12. The non-aqueous electrolyte secondary battery according to claim 7, wherein the negative electrode active material particles are composed of mesophase pitch-based carbon fibers.