JP2019106374A - Negative electrode for lithium ion battery, and lithium ion battery - Google Patents

Abstract

To provide: a negative electrode for a lithium ion battery, which is high in the mechanical strength of cohering particles and superior in energy density and cycle characteristics; and a lithium ion battery arranged by use thereof.SOLUTION: A negative electrode for a lithium ion battery comprises: a negative electrode current collector; and a negative electrode active material layer including cohering particles resulting from agglomeration of primary particles made of silicon and/or a silicon compound, and disposed on the negative electrode current collector. In the negative electrode, the cohering particles are arranged by binding the primary particles to one another with a binding resin for cohering particle granulation; the binding resin for cohering particle granulation is a (meth)acrylic acid (co)polymer of which the acid value is 680-850; and the negative electrode active material layer is a non-binding body which does not include a binder for binding the cohering particles to one another.SELECTED DRAWING: Figure 1

Description

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

In recent years, reduction of carbon dioxide emissions is strongly desired for environmental protection. In the automobile industry, there are high hopes for reducing carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and the development of motor-drive secondary batteries that hold the key to their practical application is keen It has been done. As secondary batteries, attention has been focused on lithium ion batteries (also referred to as lithium ion secondary batteries) capable of achieving high energy density and high power density.

In order to increase the energy density of lithium ion batteries, attention has been focused on active materials having higher theoretical capacity, that is, materials capable of storing more lithium ions per unit volume. However, when the amount of lithium ions that can be stored per unit volume increases, the volume change associated with insertion and desorption of lithium ions also increases. Therefore, self-destruction of the material may occur due to the volume change, and the active material layer is easily peeled off from the surface of the current collector, so that it is difficult to improve the cycle characteristics.

For example, in Patent Document 1, after the negative electrode active material is granulated with a binder for granulation, a method for suppressing self-destruction due to volume change of the negative electrode active material by fixing to the copper foil surface with a binder for coating Is disclosed.

JP, 2013-235684, A

However, in the negative electrode described in Patent Document 1, mechanical strength (also referred to as granulation strength) of particles granulated by the granulation binder is insufficient. If the mechanical strength is insufficient, the granules break at the time of volume change to generate fine powder, and the cycle characteristics are deteriorated. As a cause of insufficient granulation strength, it is considered that the acid value of the binder for granulation described in Patent Document 1 is as low as about 30 to 600.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a lithium ion battery negative electrode having high mechanical strength of aggregated particles and excellent energy density and cycle characteristics, and a lithium ion battery using the same. To aim.

The present inventors reached the present invention as a result of earnestly examining in order to solve the above-mentioned subject.
That is, the present invention is a negative electrode for a lithium ion battery in which a negative electrode active material layer including aggregated particles formed by aggregation and binding of primary particles composed of silicon and / or silicon compound is disposed on a negative electrode current collector. The aggregated particles are formed by binding the primary particles to each other with the aggregation resin for aggregation particle granulation, and the aggregation resin for aggregation particle granulation has (meth) acrylic acid having an acid value of 680 to 850. (Co) polymer, wherein the negative electrode active material layer is a non-binding body not containing a binder that binds the aggregated particles to each other; a lithium ion battery negative electrode comprising the same It relates to a lithium ion battery.

The negative electrode for a lithium ion battery of the present invention has high mechanical strength of aggregated particles, and is excellent in energy density and cycle characteristics.

FIG. 1 is a cross-sectional view schematically showing an example of the lithium ion battery negative electrode of the present invention.

Hereinafter, the present invention will be described in detail.
In addition, in this specification, when describing as a lithium ion battery, it is considered as the concept also containing a lithium ion secondary battery.

The lithium ion battery negative electrode of the present invention is a lithium ion battery in which a negative electrode active material layer including agglomerated particles formed by aggregation and binding of primary particles consisting of silicon and / or silicon compound is disposed on a negative electrode current collector. In the negative electrode, the aggregated particles are formed by binding the primary particles to each other by the aggregation resin for aggregation particle granulation, and the aggregation resin for aggregation particle granulation has an acid value of 680 to 850 ( It is a (meth) acrylic acid (co) polymer, and the negative electrode active material layer is characterized in that it is a non-binding body which does not contain a binder for binding the aggregated particles to each other.

In the negative electrode for a lithium ion battery of the present invention, primary particles composed of silicon and / or silicon compound are aggregated and bound to form aggregated particles.
The agglomerated particles are formed by the primary particles being agglomerated and bound to each other by the (meth) acrylic acid (co) polymer having an acid value of 680 to 850, so that the agglomerated particles have high mechanical strength. Therefore, pulverization of aggregated particles due to volume change can be suppressed, and cycle characteristics are improved.

Furthermore, in the negative electrode for a lithium ion battery of the present invention, the negative electrode active material layer is a non-binding body which does not contain a binder for binding the aggregated particles to each other.
If the negative electrode active material layer is a non-binding body that does not contain a binder that binds the aggregated particles to one another, the aggregated particles in the negative electrode active material layer move freely to some extent without being constrained by adjacent aggregated particles. can do. Therefore, even if expansion or contraction of the aggregated particles occurs, the aggregated particles can absorb the volume change by moving in the negative electrode active material layer, and the negative electrode active material layer is peeled off from the current collector. Can be suppressed.
Furthermore, since the primary particles are bound to each other by the binder resin for aggregation particle granulation, even if the primary particles are self-destructed due to expansion and contraction, they are hardly isolated electrically.
In addition, the non-binding body which does not contain the binder which binds the aggregated particles to each other is not bound to each other either by the binder resin for aggregation particle granulation or by the known binder.
Here, a known binder is a known solvent-drying type binder for lithium ion batteries (starch, polyvinylidene fluoride, etc.) used to bind and fix active material particles to each other, and active material particles and current collector. (Polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, styrene-butadiene copolymer, etc.), which are dried and solidified by volatilizing the solvent component to form active material particles It means what firmly fixes the active material particles and the current collector.

In the negative electrode for a lithium ion battery of the present invention, in the aggregated particles constituting the negative electrode active material layer, primary particles are aggregated and bound to each other by the aggregated particle granulation resin.
However, the negative electrode active material layer is a non-binding body that does not contain a binder that causes aggregated particles to be bound to each other.
That is, since the agglomerated particles are not bound to each other, they can move in the negative electrode active material layer, but the primary particles constituting the agglomerated particles are bound to each other by the binder resin for agglomerated particle granulation. Primary particles can not move in aggregated particles.

In the lithium ion battery negative electrode of the present invention, whether or not aggregated particles are present can be confirmed by observing a cross section of the lithium ion battery negative electrode with a scanning electron microscope (SEM).
In addition, an electrode prepared by a known method of applying a slurry obtained by adding a conductive auxiliary to a mixture of a negative electrode active material, a binder and a solvent according to need, and drying it (hereinafter also referred to as cast electrode) In the case where the negative electrode active material particles are dispersed separately, the whole is solidified by the binding agent, and aggregated particles can not be confirmed. In the cast electrode, a slurry in which the negative electrode active material is uniformly dispersed is preferably prepared and uniformly coated, and the embodiment is different from the present invention in which the negative electrode active material is used as aggregated particles. In addition, even if there is a portion where a plurality of negative electrode active material particles are locally gathered in the cast electrode, the entire negative electrode active material layer can be solidified by the binder, and the negative electrode active material can be gathered. It is different from the agglomerated particles herein because there is no boundary as particles.

The example of a structure of the negative electrode for lithium ion batteries of this invention is demonstrated using FIG.
FIG. 1 is a cross-sectional view schematically showing an example of the lithium ion battery negative electrode of the present invention.
The negative electrode 1 for lithium ion batteries shown in FIG. 1 has a negative electrode active material layer 20 disposed on a negative electrode current collector 10.
The negative electrode active material layer 20 includes aggregated particles 60 formed by aggregation of primary particles 30, and further includes a non-aqueous electrolyte 70 and a conductive material 80.
The aggregated particles 60 are formed by binding the primary particles 30 to each other by the aggregated particle granulation binder resin 40.
Since the binder resin 40 for agglomerated particle granulation is a (meth) acrylic acid (co) polymer having an acid value of 680 to 850, the mechanical strength of the agglomerated particles 60 is high.
Furthermore, the negative electrode active material layer 20 is a non-binding body in which the aggregated particles 60 are not bound to each other by the aggregated particle granulation binder resin 40 which is a binder.
Since the agglomerated particles 60 are not bound to each other by the binder resin 40 for agglomerated particle granulation, the agglomerated particles 60 are free to some extent in the negative electrode active material layer 20 even when the volume of the agglomerated particles 60 changes. The negative electrode active material 20 as a whole can be inhibited from changing in volume.
In addition, in the lithium ion battery negative electrode 1 shown in FIG. 1, for example, the aggregated particles 60 are in contact with each other as in the region surrounded by the broken line b in FIG. A conductive path in the negative electrode active material layer 20 is constructed by bringing the aggregated particles 60 into contact with each other via the conductive material 80 as in the region.

In addition, as shown in FIG. 1, at least a part of the aggregated particles 60 may have a void 50. When the agglomerated particles 60 have the voids 50, the volume change of the agglomerated particles 60 can be suppressed by the voids 50 in the agglomerated particles 60 even if the volume of the primary particles 30 changes. Furthermore, the air gap 50 may be filled with the non-aqueous electrolyte 70.

In the negative electrode for a lithium ion battery of the present invention, silicon and / or a silicon compound refer to silicon and a silicon compound, and may be a mixture of silicon and a silicon compound.

Primary particle
The primary particles consist of silicon and / or silicon compounds.
As a silicon compound, silicon oxide (SiOx), silicon-carbon composite (the surface of carbon particles is coated with silicon and / or silicon carbide, the surface of silicon particles or silicon oxide particles is coated with carbon and / or silicon carbide And silicon alloys) and silicon alloys (silicon-aluminum alloy, silicon-lithium alloy, silicon-nickel alloy, silicon-iron alloy, silicon-titanium alloy, silicon-manganese alloy, silicon-copper alloy and silicon-tin alloy) Etc) etc.].
Among these, silicon oxide is desirable.

As silicon described above, those available from Aldrich and Shin-Etsu Chemical Co., Ltd. can be used, and as silicon compounds, silicon monoxide available from Osaka Titanium Technologies Co., Ltd. and Shin-Etsu Chemical Co., Ltd., etc. What coated the surface of the silicon oxide particle which can be obtained from Shin-Etsu Chemical Co., Ltd. with carbon [KSC-1064 (volume average particle diameter 5 micrometers)] etc. can be used.
In addition, silicon and silicon compounds described in JP-A-2017-191771 and JP-A-2017-191707 can be used.

The volume average particle size of the primary particles is not particularly limited, but is preferably 0.1 to 20 μm, and more preferably 0.1 to 10 μm.
If the volume average particle size of the primary particles is less than 0.1 μm, the contact resistance between the primary particles in the aggregated particles may increase. On the other hand, when the volume average particle size of the primary particles exceeds 20 μm, the volume average particle size of the aggregated particles becomes too large, which is not preferable.
The volume average particle diameter of the primary particles can be measured by the microtrack method after the aggregated particles are dispersed in a solvent in which the binder resin for aggregation particle granulation is dissolved and the primary particles are separated from the aggregated particles. .

The primary particles may be coated primary particles coated at least at a part of the surface thereof with a coating layer containing a coating resin.
When the periphery of the primary particles is covered by the covering layer, expansion of the agglomerated particles can be suppressed by volume expansion of silicon and / or silicon compound, which contributes to suppression of expansion of the electrode. In addition, since primary particles function as a negative electrode active material, coated primary particles are also referred to as coated negative electrode active material particles.

As resin for coating | cover which comprises a coating layer, what was described as Unexamined-Japanese-Patent No. 2017-054703 as resin for non-aqueous secondary battery active material coating can be used suitably, and resin for coating and a primary particle are mixed. The coated primary particles are obtained by The coating layer may further contain a conductive material as necessary, and the same conductive assistant as that used in the later-described resin current collector can be suitably used.

[Aggregated particle]
The aggregated particles are formed by binding primary particles to one another by the binder resin for aggregation particle granulation.
The volume average particle size of the aggregated particles is preferably 200% or more of the volume average particle size of the primary particles and 50% or less of the thickness of the negative electrode active material layer.
If the volume average particle size of the aggregated particles is less than 200% of the volume average particle size of the primary particles, the number of primary particles constituting the aggregated particles may be too small to exhibit a sufficient function as the aggregated particles. On the other hand, when the volume average particle diameter of the aggregated particles exceeds 50% of the thickness of the negative electrode active material layer, the shape of the aggregated particles is reflected on the surface of the negative electrode active material layer, and the smoothness of the surface of the negative electrode active material layer It may be lost.

The volume average particle diameter of the aggregated particles is not particularly limited, but is preferably 30 to 100 μm. When the volume average particle diameter of the agglomerated particles is less than 30 μm, the number of primary particles constituting the agglomerated particles may be too small to exhibit a sufficient function as the agglomerated particles. On the other hand, when the volume average particle diameter of the aggregated particles exceeds 100 μm, the shape of the aggregated particles may be reflected on the surface of the negative electrode active material layer, and the smoothness of the surface of the negative electrode active material layer may be lost.

The volume average particle size of the aggregated particles is measured by the microtrack method (laser diffraction / scattering method) after separating the aggregated particles by dispersing the negative electrode active material layer in a dispersion medium in which the binder resin for aggregation particle granulation is not dissolved. It can confirm by doing. The microtrack method is a method of obtaining a particle size distribution using scattered light obtained by irradiating particles with laser light.

The particle distribution of the aggregated particles is not particularly limited, but it is desirable that the cumulative 10% particle diameter (also referred to as d10) in the particle diameter cumulative distribution curve on a volume basis is 1 μm or more.
That d10 of the agglomerated particles is 1 μm or more means that the ratio of the number of agglomerated particles having a particle diameter of less than 1 μm is 10% or more among all the agglomerated particles.
When the ratio of agglomerated particles having a particle size of less than 1 μm is 10% or more, the agglomerated particles having a particle size of less than 1 μm are arranged in the gaps between agglomerated particles having a relatively large particle size. The quality is good.
On the other hand, if d10 of the agglomerated particles is less than 1 μm, that is, if the ratio of agglomerated particles having a particle diameter of less than 1 μm is less than 10%, gaps are easily formed between agglomerated particles having relatively large particle diameters. The contact between the two may be reduced, and internal resistance may increase.
The particle diameter cumulative distribution curve of the agglomerated particles can be determined by the microtrack method.

In the negative electrode for lithium ion batteries of the present invention, the ratio of the binder resin for aggregation particle granulation to the aggregation particles is not particularly limited, but the ratio of the weight of the binder resin for aggregation particle granulation to the weight of aggregation particles is 10 to 10 It is desirable to be 30% by weight.
If the ratio of the binder resin for granulation particle granulation to the weight of the aggregation particles is in the above range, the strength of the aggregation particles becomes good, and the electric resistance value of the aggregation particles can be lowered.
When the ratio of the weight of the binder resin for aggregation particle granulation to the weight of the aggregation particles is less than 10% by weight, the weight ratio of the binder resin for aggregation particle granulation to the aggregation particles is too small, and the volume of primary particles It becomes difficult to suppress the volume change of the electrode by expansion. When the weight ratio of the binder resin for aggregation particle granulation to the weight of the aggregation particles exceeds 30% by weight, the weight ratio of the binder resin for aggregation particle granulation to the aggregation particles is too large, and the energy density decreases. Resulting in.

In the negative electrode for a lithium ion battery of the present invention, it is preferable that the aggregated particles further have a conductive aid in addition to the primary particles and the binder resin for aggregated particle granulation.
The proportion of the weight of the conductive aid to the weight of the agglomerated particles is more preferably 10 to 50% by weight.
When the agglomerated particles have a conductive aid and the weight ratio of the conductive aid is in the above range, excellent conductivity can be imparted to the agglomerated particles while maintaining a sufficient energy density.
When the proportion of the weight of the conductive aid is less than 10% by weight, sufficient conductivity may not be imparted to the agglomerated particles, and internal resistance may increase. If the proportion of the weight of the conductive additive exceeds 50% by weight, the proportion of primary particles in the agglomerated particles relatively decreases, and the energy density decreases.

The conductive aid is selected from materials having conductivity.
Specifically, metals [nickel, aluminum, stainless steel (SUS), silver, copper and titanium etc.], carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black etc.), etc. And mixtures thereof, but not limited thereto.
These conductive aids may be used alone or in combination of two or more. Also, these alloys or metal oxides may be used. From the viewpoint of electrical stability, it is preferably aluminum, stainless steel, carbon, silver, copper, titanium and a mixture thereof, more preferably silver, aluminum, stainless steel and carbon, and still more preferably carbon. Moreover, as these conductive support agents, conductive materials (metals of the above-mentioned conductive support agents) may be coated around the particulate ceramic material or resin material by plating or the like.

The shape and size of the conductive additive are not particularly limited, but it is desirable that the volume average particle diameter of the conductive additive be 0.001 to 0.4 times the volume average particle diameter of the primary particles constituting the agglomerated particles. .
The volume average particle size of the conductive additive can be measured by the microtrack method.

The shape (form) of the conductive aid is not limited to the particle form, and may be a form other than the particle form, and may be a form such as a carbon nanotube that has been put to practical use as a so-called filler-based conductive resin composition Good.

The conductive aid may be a conductive fiber whose shape is fibrous.
Examples of conductive fibers include carbon fibers such as PAN-based carbon fibers and pitch-based carbon fibers, conductive fibers obtained by uniformly dispersing conductive metals and graphite in synthetic fibers, and metals such as stainless steel. The metal fiber which carried out fiberization, the electroconductive fiber which coat | covered the surface of the organic fiber with metal, the electroconductive fiber which coat | covered the surface of the organic fiber with resin containing an electroconductive substance etc. are mentioned. Among these conductive fibers, carbon fibers are preferred. In addition, a polypropylene resin into which graphene is incorporated is also preferable.
When the conductive aid is a conductive fiber, the average fiber diameter is preferably 0.1 to 20 μm.

In the aggregated particles, voids may be present in which neither the primary particles nor the binder resin for aggregated particle granulation, nor any of the other configurations described above are arranged.
If voids exist in the agglomerated particles, it is easy to suppress the volumetric expansion of the agglomerated particles.

[Binder resin for agglomerated particle granulation]
In the negative electrode for a lithium ion battery of the present invention, the binder resin for aggregation particle granulation bonds primary particles constituting the aggregation particles to each other.
The binder resin for aggregation particle granulation preferably has a swelling degree of 120% or less with respect to the non-aqueous electrolyte.

The resin constituting the binder resin for aggregated particle granulation is a (meth) acrylic acid (co) polymer.
When the binder resin for aggregation particle granulation uses (meth) acrylic acid (co) polymer as a binder resin for aggregation particle granulation, the strength of the aggregation particles is excellent.
In the present specification, (meth) acrylic acid means acrylic acid and / or methacrylic acid, and (co) polymer means polymer or copolymer.

The (meth) acrylic acid (co) polymer contains methyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate as monomers in addition to acrylic acid and methacrylic acid. It may be a copolymer.

From the viewpoint of adhesion to the Si-based active material, the total weight of acrylic acid and methacrylic acid in the (meth) acrylic acid (co) polymer is 70 to 100% by weight of the total (meth) acrylic acid copolymer Is preferred.

The acid value of the (meth) acrylic acid (co) polymer is 680 to 850, and more preferably 680 to 800.
When the acid value of the (meth) acrylic acid (co) polymer is 680 to 850, the adhesion to the negative electrode active material particles and the conductive aid becomes good, so the granulation strength becomes high, and the aggregation structure is changed when the volume changes. Since maintenance can be performed, it is possible to suppress the loss of the negative electrode active material particles from the aggregated particles.

When a (meth) acrylic acid (co) polymer is used as a binder resin for agglomerated particle granulation, one obtained by polymerizing the above-mentioned monomers by a known method may be used, and can be obtained from the market (Meth) acrylic acid (co) polymers may be used.
As the (meth) acrylic acid (co) polymer available from the market, in addition to polyacrylic acid produced by Toagosei Co., Ltd., reagents produced by Wako Pure Chemical Industries, Ltd. can be used. As the (meth) acrylic acid (co) polymer which can be used, not only one sold as a binder but also one sold as a dispersant can be used in the same manner.

The agglomerated particles described above may be coated agglomerated particles in which at least a part of the surface of the agglomerated particles is covered by the coating layer.
As a covering layer which constitutes covering aggregation particles, the thing similar to a covering layer which constitutes covering primary particles can be used suitably, for example, aggregation particles are carried out by the same method as a method of creating covering primary particles from primary particles. Coated agglomerated particles can be made from

In the negative electrode for a lithium ion battery of the present invention, the negative electrode active material layer is a non-binding body which contains the above-mentioned aggregated particles but does not contain a binder which binds the aggregated particles to each other.

The thickness of the negative electrode active material layer is not particularly limited, but is preferably 150 to 600 μm, and more preferably 200 to 600 μm.

In the present specification, the void refers to the void of the negative electrode active material layer in a state in which the negative electrode is not impregnated with the non-aqueous electrolyte.
The porosity of the negative electrode active material layer is not particularly limited, but is preferably 35 to 50%.
When the porosity of the negative electrode active material layer is less than 35%, the number of voids is too small, and it becomes difficult to alleviate the volume change of the agglomerated particles due to the volume expansion of the primary particles involved in charge and discharge. On the other hand, when the porosity of a negative electrode active material layer exceeds 50%, the mechanical strength of a negative electrode active material layer may fall.
The porosity of the negative electrode active material layer can be measured by image analysis by X-ray computed tomography (CT) or the like.
However, when the negative electrode active material layer contains an electrolytic solution and other components, and the X-ray CT image of the negative electrode active material layer containing voids can not be obtained, the porosity is a constant volume of the negative electrode active material layer. The sum of the volume values of each component obtained by dividing the weight of each constituting solid component (excluding the electrolyte) by the true density of each component is subtracted from the volume of the negative electrode active material layer to obtain a further negative electrode active It can be calculated by dividing by the volume of the material layer.

The negative electrode active material layer may contain, in addition to the aggregated particles, a conductive material, carbon-based negative electrode active material particles, a non-aqueous electrolytic solution, and the like.
As the conductive material, the same conductive assistant as an optional component of the agglomerated particles can be suitably used. The conductive support agent is a component constituting the above-described aggregated particles, and is integrally contained in the aggregated particles, while the conductive material is present separately from the aggregated particles in the negative electrode active material layer. It can be distinguished.

[Carbon-based negative electrode active material particles]
The negative electrode for a lithium ion battery of the present invention may further contain carbon-based negative electrode active material particles.
Examples of carbon-based negative electrode active material particles include carbon-based materials (eg, graphite, non-graphitizable carbon, amorphous carbon, resin fired bodies (eg, those obtained by firing and carbonizing phenol resin and furan resin), coke (eg, pitch) Coke, needle coke, petroleum coke and the like), conductive polymers (for example, polyacetylene and polypyrrole and the like) and the like.

The volume average particle diameter of the carbon-based negative electrode active material particles is not particularly limited, but is preferably 1 to 40 μm.
In addition, the carbon-based negative electrode active material particles may be carbon-based coated negative electrode active material particles in which at least a part of the surface is covered with a covering layer.
As the coating layer constituting the carbon-based coated negative electrode active material particles, the same one as the coating layer constituting the coated primary particles can be suitably used.

It is desirable that the carbon-based negative electrode active material particles and the carbon-based coated negative electrode active material particles be contained in the negative electrode active material layer separately from the aggregated particles, without being used as a material for forming the aggregated particles.
Although the ratio of the weight of the agglomerated particles based on the total weight of the agglomerated particles and the carbon-based negative electrode active material particles is not particularly limited, it is preferably 2 to 50% by weight.

The carbon-based coated negative electrode active material particles can be obtained by the same method as the above-described coated primary particles. The coating layer may contain a conductive material, and the same conductive assistant as the resin current collector to be described later can be suitably used.

[Non-aqueous electrolyte]
As a non-aqueous electrolyte, the non-aqueous electrolyte containing electrolyte and a non-aqueous solvent used for manufacture of a lithium ion battery can be used.

As the electrolyte, those used in known non-aqueous electrolytes can be used, and preferred examples include lithium salts of inorganic acids such as LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ and LiClO _4. Sulfonylimide electrolytes having a fluorine atom such as electrolyte, LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ , fluorine such as LiC (CF ₃ SO ₂ ) ₃ The sulfonyl methide type electrolyte which has an atom etc. are mentioned. Among these, preferred are sulfonylimide electrolytes having a fluorine atom from the viewpoint of ion conductivity at high concentration and thermal decomposition temperature, and LiN (FSO ₂ ) ₂ is more preferred. LiN (FSO ₂ ) ₂ may be used in combination with other electrolytes, but is preferably used alone.

The electrolyte concentration of the non-aqueous electrolytic solution is not particularly limited, but is preferably 1 to 5.0 mol / L, and preferably 1.2 to 5.0 mol / L, from the viewpoints of handleability of the non-aqueous electrolytic solution and battery capacity. Is more preferably 1.5 to 4.0 mol / L, and particularly preferably 2.0 to 3.0 mol / L.

The non-aqueous electrolytic solution preferably has a degree of swelling of 120% or less, more preferably 115% or less, of the binder resin for aggregating particulate particles in the non-aqueous electrolytic solution. .
The swelling degree of the binder resin for aggregation particle granulation with respect to the non-aqueous electrolyte can be measured by the following method.
The resin solution in which the binder resin for agglomerated particle granulation is dissolved is applied on a horizontal glass plate and naturally dried for half a day at room temperature. Next, after standing for 3 hours in a reduced pressure drier heated to 150 ° C., after cooling to room temperature, a binder resin for aggregated particle granulation cut into a size of 10 × 40 × 0.2 mm is used as a test piece Then, this test piece is immersed in a non-aqueous electrolyte at 50 ° C. for 3 days to obtain a saturated liquid absorption state.
Then, swelling degree can be calculated | required by a following formula from the weight change before and behind liquid absorption of a test piece.
Swelling degree [%] = [(weight of test piece after liquid absorption) / (weight of test piece before liquid absorption)] × 100

As the non-aqueous solvent, those used in known non-aqueous electrolytes can be used, and examples thereof include lactone compounds, cyclic or linear carbonates, linear carboxylic esters, cyclic or linear ethers, and phosphoric esters. Nitrile compounds, amide compounds, sulfones and the like and mixtures thereof can be used.

Examples of lactone compounds include 5-membered rings (such as γ-butyrolactone and γ-valerolactone) and 6-membered ring lactone compounds (such as δ-valerolactone).

Examples of cyclic carbonates include propylene carbonate, ethylene carbonate and butylene carbonate.
Examples of chain carbonates include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl n-propyl carbonate, ethyl n-propyl carbonate and di-n-propyl carbonate.

Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate and methyl propionate.
Examples of cyclic ethers include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane and 1,4-dioxane.
Examples of the chain ether include dimethoxymethane and 1,2-dimethoxyethane.

As phosphoric acid esters, trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, tripropyl phosphate, tributyl phosphate, tri (trifluoromethyl) phosphate, tri (trichloromethyl) phosphate, Tri (trifluoroethyl) phosphate, tri (triperfluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphosphoran-2-one, 2-trifluoroethoxy-1,3,2- Examples include dioxaphospholan-2-one and 2-methoxyethoxy-1,3,2-dioxaphospholan-2-one.
Acetonitrile etc. are mentioned as a nitrile compound. As an amide compound, N, N- dimethylformamide (it describes as DMF hereafter) etc. are mentioned.
Examples of sulfones include linear sulfones such as dimethylsulfone and diethylsulfone and cyclic sulfones such as sulfolane.
A non-aqueous solvent may be used individually by 1 type, and may use 2 or more types together.

Among non-aqueous solvents, lactone compounds, cyclic carbonates, chain carbonates and phosphates are preferable from the viewpoint of battery power and charge-discharge cycle characteristics, and it is preferable not to contain nitrile compounds. Further preferred are lactone compounds, cyclic carbonates and chain carbonates, and particularly preferred are mixed solutions of cyclic carbonates and chain carbonates. Most preferred is a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), or a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC).
When the non-aqueous solvent contains a cyclic carbonate, the volume ratio of the cyclic carbonate in the non-aqueous solvent is preferably 50% by volume or more.

[Anode current collector]
The negative electrode current collector is not particularly limited, but a known metal current collector and a resin current collector composed of a conductive material and a resin (described in JP 2012-150905, etc.) and the like are preferable. It can be used for
The metal current collector is, for example, selected from the group consisting of copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony and alloys containing at least one of these, and stainless steel alloys Metal materials, and these metal materials may be used in the form of thin plates, metal foils, etc., and the above metal materials are formed on the surface of the substrate by a method such as sputtering, electrodeposition, coating, etc. It may be.

The conductive material constituting the resin current collector is selected from materials having conductivity.
Specifically, metals [nickel, aluminum, stainless steel (SUS), silver, copper and titanium etc.], carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black etc.), etc. And mixtures thereof, but not limited thereto.
These conductive materials may be used alone or in combination of two or more. Also, these alloys or metal oxides may be used. From the viewpoint of electrical stability, it is preferably aluminum, stainless steel, carbon, silver, copper, titanium and a mixture thereof, more preferably silver, aluminum, stainless steel and carbon, and still more preferably carbon. Further, as the conductive material, a conductive material (a metal of the above-described conductive materials) may be coated by plating or the like around a particle-based ceramic material or a resin material.

The average particle size of the conductive material is not particularly limited, but is preferably 0.01 to 10 μm, more preferably 0.02 to 5 μm, from the viewpoint of the electrical properties of the battery. More preferably, it is 03 to 1 μm. In addition, "the particle diameter of an electrically-conductive material" means the largest distance among the distances between any two points on the outline of an electrically-conductive material. As the value of “average particle diameter”, using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM), as an average value of particle diameters of particles observed in several to several tens of visual fields The calculated value shall be adopted.

The shape (form) of the conductive material is not limited to the particle form, and may be a form other than the particle form, and is a form that is put into practical use as a so-called filler-based conductive resin composition such as carbon nanofiller or carbon nanotube. It may be.

The conductive material may be a conductive fiber whose shape is fibrous.
Examples of conductive fibers include carbon fibers such as PAN-based carbon fibers and pitch-based carbon fibers, conductive fibers obtained by uniformly dispersing conductive metals and graphite in synthetic fibers, and metals such as stainless steel. The metal fiber which carried out fiberization, the electroconductive fiber which coat | covered the surface of the organic fiber with metal, the electroconductive fiber which coat | covered the surface of the organic fiber with resin containing an electroconductive substance etc. are mentioned. Among these conductive fibers, carbon fibers are preferred. In addition, a polypropylene resin into which graphene is incorporated is also preferable.
When the conductive material is a conductive fiber, the average fiber diameter is preferably 0.1 to 20 μm.

Examples of the resin constituting the resin current collector include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyether nitrile (PEN), and polytetratetra Fluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin or a mixture of these, etc. Can be mentioned.
From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and polycycloolefin (PCO) are preferred, and more preferably polyethylene (PE), polypropylene (PP) and polymethylpentene (PMP).

[Lithium ion battery]
The lithium ion battery of the present invention is a battery using the lithium ion battery negative electrode of the present invention, and is combined with the electrode serving as the counter electrode of the lithium ion battery negative electrode of the present invention. It can manufacture by the method etc. which inject | pours electrolyte solution and seals a cell container.
Further, in the negative electrode for a lithium ion battery of the present invention in which the negative electrode active material layer is formed only on one side of the negative electrode current collector, a positive electrode active material layer made of a positive electrode active material is formed on the other side of the negative electrode current collector. It is also possible to manufacture a bipolar electrode, laminate the bipolar electrode with a separator, store it in a cell container, inject a non-aqueous electrolyte, and seal the cell container.

The separator may be a microporous film made of polyethylene or polypropylene, a laminated film of a porous polyethylene film and a porous polypropylene, a non-woven fabric made of synthetic fibers (such as polyester fibers and aramid fibers) or glass fibers, and silica on their surfaces. And separators for known lithium ion batteries such as those to which ceramic fine particles such as alumina and titania are attached.
As the non-aqueous electrolytic solution, those described for the lithium ion battery negative electrode of the present invention can be suitably used.

The electrode used as a counter electrode of the said negative electrode for lithium ion batteries (positive electrode) can use the positive electrode used for a well-known lithium ion battery.

The lithium ion battery of the present invention is characterized by comprising the lithium ion battery negative electrode of the present invention. Since the lithium ion battery of the present invention is equipped with the lithium ion battery negative electrode of the present invention, it is excellent in energy density and cycle characteristics.

[Method of producing negative electrode for lithium ion battery]
Then, the method to manufacture the negative electrode for lithium ion batteries of this invention is demonstrated.
As a method for producing the negative electrode for a lithium ion battery of the present invention, for example, it is preferable to use aggregated particles and a conductive material optionally used as the weight of water or a solvent (nonaqueous solvent used for nonaqueous electrolyte or nonaqueous electrolyte). Based on the dispersion liquid dispersed at a concentration of 30 to 60% by weight is applied to the negative electrode current collector with a coating device such as a bar coater, and then dried as necessary to remove water or solvent. The obtained negative electrode active material layer may be pressed by a pressing machine if necessary, and the obtained negative electrode active material layer may be impregnated with a predetermined amount of non-aqueous electrolyte solution as necessary.
The negative electrode active material layer obtained from the dispersion does not have to be formed directly on the negative electrode current collector, and, for example, the negative electrode active material layer obtained by applying the dispersion to the surface of an aramid separator or the like It may be arranged to be in contact with the negative electrode current collector.
Moreover, the drying which is carried out as necessary after applying the dispersion can be carried out using a known dryer such as a normal wind type dryer, and the drying temperature is the dispersion medium (water or solvent) contained in the dispersion. It can be adjusted according to the type.
A binder such as polyvinylidene fluoride (PVdF) contained in a known lithium ion battery is not added to the above-mentioned dispersion liquid. When a binder contained in a known negative electrode for a lithium ion battery is added to the above-mentioned dispersion liquid, aggregated particles are mutually bonded in the negative electrode active material layer, and a non-bonded body can not be obtained. .
In the conventional negative electrode for a lithium ion battery, it is necessary to maintain the conductive path by fixing the negative electrode active material in the negative electrode with a binder. However, in the case of the negative electrode for a lithium ion battery of the present invention using aggregated particles, since the conductive path can be maintained without fixing the aggregated particles in the negative electrode active material layer, it is not necessary to add a binder. By not adding the binder, the aggregated particles are not immobilized in the negative electrode, and the ability to relax the volume change of the primary particles is further improved.

Examples of known binders for lithium ion batteries include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene and the like. The binder is not added at the stage of preparing the above-mentioned dispersion liquid at the time of producing the negative electrode for a lithium ion battery of the present invention.
However, the above-mentioned binder for lithium ion batteries may be included as a component which constitutes a binder resin for agglomerated particle granulation. In this case, since the binder for lithium ion batteries is a binder resin for aggregate particle granulation which constitutes aggregate particles, it can be clearly distinguished from the binder added when preparing the dispersion liquid.

In the above method, the pressure for pressing the dried slurry is not particularly limited, but if the pressure is too high, a sufficient amount of voids can not be formed in the negative electrode active material layer, and if the pressure is too low It is preferable to press at 1 to 200 MPa, since no effect by the press is observed.

In the negative electrode for a lithium ion battery of the present invention, when the dispersion is water or a non-aqueous solvent and the applied dispersion is dried, the non-aqueous electrolyte is impregnated in the negative electrode active material layer obtained after drying. The weight of the non-aqueous electrolytic solution impregnated into the negative electrode active material layer can be adjusted according to the amount of voids in the negative electrode active material layer and the electrolyte concentration of the non-aqueous electrolytic solution.

Impregnation of the non-aqueous electrolyte into the negative electrode active material layer can be carried out by a method such as dropping the non-aqueous electrolyte onto the surface of the negative electrode active material layer formed by the above method using a syringe etc. .

[Method of producing aggregated particles]
The method for producing the agglomerated particles is not particularly limited, but a known granulator (agitation granulator, compression granulator, etc.) may be used for the agglomerated particle granulation binder resin, the primary particles, and the conductive auxiliary agent optionally used. If necessary, the mixture obtained by removing the solvent by mixing under reduced pressure and removing the solvent by reduced pressure drying etc. may be crushed, and classified with a sieve etc. as necessary so as to obtain the desired particle size. .

In the mixing of the binder resin for aggregated particle granulation, the primary particles, and the conductive auxiliary agent optionally used, a solvent (such as water and an organic solvent) may be used in combination.
When a solvent is used in combination, the solvent may be used as a solvent of the resin solution in which the binder resin for aggregating aggregated particles is dissolved, and the resin solution, the primary particles, and the conductive auxiliary agent used as needed may be mixed. The solvent may be added as it is when mixing the binder resin for aggregation particle granulation, the primary particles, and the conductive auxiliary agent optionally used.
The total amount of the solvents used in combination may be used as a solvent for the resin solution, or may be divided into a solvent used as a part of the resin solution and a solvent to be added and mixed as it is.

The method (order) of the mixing of the binder resin for aggregation particle granulation, the primary particles, and the conductive auxiliary agent / solvent used as required is not particularly limited, and, for example, described in (Method 1) to (Method 6) below The method is mentioned.
(Method 1) A method in which a binder resin for aggregation particle granulation, which is in a powdery state, a primary particle and a conductive additive are simultaneously charged and mixed.
(Method 2) A method in which a binder resin for agglomerated particle granulation, which is in a powdery state, primary particles and a conductive additive are simultaneously charged and mixed, and then a solvent is further added with stirring and further mixed.
(Method 3) A method in which primary particles in a powder state and a conductive support agent are simultaneously charged and mixed in a resin solution in which a binder resin for aggregation particle granulation in a powder state is dispersed in a solvent.
(Method 4) While stirring a resin solution in which a binder resin for agglomerated particles in powder form is dispersed in a solvent, first, primary particles in powder form are added and mixed, and then after being stirred, a conductive aid How to put in and mix.
(Method 5) While stirring a resin solution in which a binder resin for agglomerated particles in powder form is dispersed in a solvent, first, a conductive additive is added and mixed, and then primary particles in powder form are stirred. How to put in and mix.
(Method 6) A primary particle slurry is obtained by first adding and mixing primary particles in a powder state while stirring a resin solution in which a binder resin for agglomerated particle granulation in a powder state is dispersed in a solvent. Thereafter, the primary particle slurry is dropped or divided and mixed while stirring the conductive aid.

As described above, since the conductive auxiliary is an optional component that may be used if necessary, a method obtained by excluding the step of adding the conductive auxiliary from the methods described in (Method 1) to (Method 6) above Even in such a case, it is possible to obtain aggregated particles constituting the negative electrode for a lithium ion battery of the present invention. Note that (Method 4) to (Method 6) excluding the step of adding the conductive aid are substantially the same.

In the above (Method 3) to (Method 4), a solvent may be further added to the mixture of the resin solution, the primary particles and the conductive aid.

The solvent used in the above (Method 2) to (Method 6) is not particularly limited as long as it dissolves the binder resin for aggregation particle granulation and the wettability of the resin solution to the used negative electrode active material is good. I will not. The solvents used in (Method 2) to (Method 6) include both the solvent constituting the resin solution and the solvent added separately from the resin solution.

In the case of using the above resin solution, the content of the binder resin for aggregation particle granulation contained in the resin solution is based on the weight of the resin solution from the viewpoint of the wettability to the negative electrode active material particles and the conductive additive. 0.1 to 60 weight% is preferable, and 1 to 40 weight% is more preferable.

In the above (Method 2), the solid content concentration at the time of mixing the solvent, the binder resin for agglomerated particle granulation, the primary particles, and the conductive additive is the viewpoint of the wettability to the negative electrode active material particles and the conductive additive From the viewpoint of the total weight of the solvent, the binder resin for agglomerated particle granulation, the primary particles, and the conductive additive, it is preferably 10 to 90% by weight, and more preferably 30 to 90% by weight.

In the above (Method 2) to (Method 6), the solid content concentration at the time of mixing the resin solution, the primary particles, the conductive auxiliary agent and the solvent is from the viewpoint of the wettability of the resin solution to the primary particles and the conductive auxiliary agent. It is preferable that it is 0.1 to 90 weight% based on the total weight of a solvent, the binder resin for aggregation particle granulation, a primary particle, and a conductive support agent, and 0.5 to 60 weight% is more preferable.

The solid content concentration of the primary particle slurry used in the above (Method 6) is 20 to 90% by weight based on the total weight of the primary particle slurry from the viewpoint of the wettability of the resin solution to the primary particles and the conductive additive Is preferable, and 40 to 80% by weight is more preferable.

The binder resin for aggregation particle granulation, the primary particles, the conductive auxiliary agent, and the solvent can be mixed using a known mixing and stirring apparatus, and even if it is a container rotation type mixing apparatus which does not use a stirring blade It may be a stirring-type mixing device using blades. Among them, a stirring-type mixing apparatus is preferable, and a twin-screw stirring-type granulator and the like are more preferable.

The step of mixing the binder resin for aggregation particle granulation, the primary particles, the conductive auxiliary agent, and the solvent is performed by sampling the contents and performing until the volume average particle diameter of the aggregation particles becomes a target volume average particle diameter Is preferred.

When mixing a solvent, a binder resin for aggregation particle granulation, a primary particle, and a conductive auxiliary agent optionally used to obtain an aggregation particle, the solvent may be further distilled off if necessary during or after mixing. . When distilling off the solvent during mixing, it can be performed by reducing pressure and / or heating the inside of the mixing device while mixing with the mixing device, and when performing after mixing, the pressure reduction of the inside of the mixing device after mixing It can carry out by transferring the contents after heating and / or mixing to another dryer, and reducing pressure and / or heating.
The pressure and temperature of the mixing apparatus and dryer for distilling off the solvent may be adjusted according to the boiling point and vapor pressure of the solvent used.

When distilling off the solvent by depressurizing and / or heating the inside of the mixing device while mixing with the mixing device, the contained solvent may be continuously distilled off at once, and a part of the solvent was distilled off It is preferable to stop evaporation of the solvent at a point in time and resume evaporation of the solvent after mixing for a predetermined time (after confirming by weight change that the target solvent has been completely evaporated). When distillation of the solvent is stopped by distilling off the solvent by stopping the evaporation of the solvent by resuming evaporation of the solvent after mixing for a predetermined period of time, the solvents having different boiling points are used as solvents. It is preferable to use in combination.

The aggregated particles can be obtained by mixing the binder resin for aggregation particle granulation, the primary particles, the conductive auxiliary agent used as needed, the solvent used as needed, and the solvent used as needed, if necessary, by distilling off the solvent. These may be further crushed and / or classified as required.

The crushing can be performed using a known crusher, a known powder mixer, or the like.

Classification can be performed by screening or the like. When sieving is performed, the sieve to be used has an opening which is 200% or more of the volume average particle size of the primary particles and / or 50% or less of the thickness of the negative electrode active material layer described below. It is preferable to select the size to be

The volume average particle diameter of the agglomerated particles can be changed as appropriate by changing the conditions of the above-mentioned crushing and the classification conditions using a sieve or the like.
In addition, from the viewpoint of suppressing electrical isolation inside the electrode and improving durability, it is preferable that the cumulative 10% particle diameter in the particle diameter cumulative distribution curve of the obtained aggregated particles on a volume basis be 1 μm or more .

EXAMPLES The present invention will now be specifically described by way of Examples, but the present invention is not limited to the Examples unless departing from the gist of the present invention. Unless otherwise stated, parts mean parts by weight and% mean% by weight.

[Production of resin current collector]
In a twin-screw extruder, polypropylene [trade name "Sun Aroma PL 500A", Sun Aroma Co., Ltd. product] 70 parts, carbon nanotube [trade name: "FloTube 9000", CNano company] 25 parts and dispersant [trade name "Yumex 1001" And 5 parts of Sanyo Chemical Industries, Ltd.] were melt-kneaded under the conditions of 200 ° C. and 200 rpm to obtain a resin mixture.
The obtained resin mixture was passed through a T-die extrusion film forming machine, and it was stretched and rolled to obtain a conductive film for a resin current collector having a film thickness of 100 μm. Next, the obtained conductive film for a resin current collector was cut into 3 cm × 3 cm, nickel deposition was performed on one side, and then a resin current collector to which a terminal (5 mm × 3 cm) for current extraction was connected was obtained. .

[Preparation of Primary Particles]
Silicon oxide particles for lithium ion battery anode [Shin-Etsu Chemical Co., Ltd., volume average particle diameter of primary particles: 5 μm] is placed in a horizontal heating furnace, and methane gas is passed in the horizontal heating furnace at 1100 ° C./1000 Pa, Chemical vapor deposition operation with an average residence time of about 2 hours was carried out to obtain silicon oxide particles (volume average particle diameter 6 μm) (N-1) having a carbon content of 2% by weight and a surface covered with carbon.
The obtained (N-1) was magnified and observed with a microscope to confirm that aggregates were not formed, and this was used as primary particles for obtaining the following aggregated particles.

[Preparation of resin solution for coating]
In a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel and a nitrogen gas inlet, 407.9 parts of DMF was charged and the temperature was raised to 75 ° C. Next, a monomer combination liquid containing 242.8 parts of methacrylic acid, 97.1 parts of methyl methacrylate, 242.8 parts of 2-ethylhexyl methacrylate and 116.5 parts of DMF, and 2,2′-azobis (2,4-dimethylvalero) An initiator solution of 1.7 parts of nitrile) and 4.7 parts of 2,2'-azobis (2-methylbutyronitrile) dissolved in 58.3 parts of DMF is stirred while blowing nitrogen into a four-necked flask In the lower portion, radical polymerization was continuously performed by dropping the solution for 2 hours with a dropping funnel. After completion of the addition, the reaction was continued at 75 ° C. for 3 hours. Then, the temperature was raised to 80 ° C. and the reaction was continued for 3 hours to obtain a copolymer solution having a resin solid concentration of 50% by weight. To this was added 789.8 parts of DMF to obtain a coating resin solution having a solid concentration of 30% by weight.

[Preparation of carbon-based coated negative electrode active material particles]
68.2 parts of hard carbon for lithium ion battery negative electrode (manufactured by JFE Chemical Co., Ltd., volume average particle diameter 20 μm) (N-2) is placed in universal mixer high speed mixer FS25 (manufactured by Earth Technica Co., Ltd.), and room temperature While stirring at 720 rpm, 33.3 parts of the coating resin solution was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes. Thereafter, the pressure was reduced to 0.01 MPa while maintaining the stirring, and then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of vacuum, and the volatile matter was distilled off while maintaining the degree of stirring, the pressure and the temperature for 8 hours The carbon-based coated negative electrode active material particles (N-3) were obtained.

Example 1
[Preparation of aggregated particles]
25 parts by weight of 60 parts of silicon oxide particles (N-1) which are primary particles and polyacrylic acid [PHO (non-crosslinked type) acid number 780 made by Wako Pure Chemical Industries, Ltd.] which is a binder resin for aggregation particle granulation 80% aqueous dispersion and acetylene black (Denka Co., Ltd. Denka Black Li-400: volume average particle diameter 48 nm) 20 parts of a biaxial stirring type granulator (Akira Kiko Co.) The solvent was removed by mixing at 2000 rpm for 10 minutes using a Balance Granule, followed by heating for 3 hours in a vacuum oven set at 100 ° C.
The resulting mixture was crushed in a mortar to obtain agglomerated particles.
The above-mentioned aggregated particles for a non-aqueous electrolyte prepared by dissolving LiN (FSO ₂ ) ₂ at a ratio of 2 mol / L in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (volume ratio 1: 1) The degree of swelling of the binder resin for granulation was 110%.

[Measurement of particle generation rate of particle diameter 20 μm or less after ultrasonic irradiation]
Aggregated particles were charged into propylene carbonate so that the solid content was 2% by weight, and ultrasonic waves (40 kHz) were applied for 5 minutes with an ultrasonic cleaner [ASU-20M manufactured by As One Co., Ltd.]. Thereafter, the particle size distribution is measured with a laser diffraction / scattering particle size distribution measuring apparatus (MT3300 EXII manufactured by Microtrac Bell Co., Ltd.) to determine the ratio of particles having a particle size of 20 μm or less. The following particle generation rates were determined.
The lower the particle generation rate with a particle diameter of 20 μm or less after the ultrasonic wave irradiation, the higher the mechanical strength of the aggregated particles, and the less the generation of fine powder due to the volume change associated with charge and discharge.

[Preparation of negative electrode active material slurry]
After adding 100 parts of the aggregated particles and 15 parts of acetylene black (denka black Li-400 manufactured by Denka Co., Ltd.) as the conductive material to 3000 parts of the non-aqueous electrolyte, a planetary stirring type mixing and kneading apparatus {Awatori Nritaro It mixed for 5 minutes at 1000 rpm using [made by Corporation | KK Shinky]}, and produced the negative electrode active material slurry.

[Fabrication of negative electrode active material layer]
The obtained negative electrode active material slurry is dropped on a 23 mm φ aramid non-woven fabric (2415 R, manufactured by Nippon Byuren) fitted with a φ 15 mm mask so that the weight per unit area is 20 mg / cm ² and suction filtration (decompression) The negative electrode active material layer was produced by laminating on the aramid non-woven fabric and pressing for about 10 seconds at a pressure of 5 MPa.
The thickness of the negative electrode active material layer measured by the contact film thickness meter was 225 μm.
Also, the total value of the volume of each component obtained by dividing the weight of each solid component (excluding the electrolyte) constituting the negative electrode active material layer by the true density of each component is subtracted from the volume of the negative electrode active material layer Thus, the volume of the void occupied in the negative electrode active material layer was determined. Then, the porosity of the negative electrode active material layer was determined by dividing the volume of the void occupied in the negative electrode active material layer by the volume of the negative electrode active material layer. The porosity of the negative electrode active material layer was 48%.

[Preparation of exterior material]
Two copper foils (3 cm × 3 cm, thickness 17 μm) with terminals (5 mm × 3 cm) are sequentially laminated in the direction in which the two terminals come out in the same direction, and these are laminated with two commercially available heat sealable aluminum laminate films The battery case was prepared by sandwiching (10 cm × 8 cm) and heat-sealing one side where the terminal was exposed.

[Production of battery]
The resin current collector was disposed on the copper foil of the packaging material, the negative electrode active material layer from which the aramid nonwoven fabric was peeled off was disposed thereon, and 100 μL of the non-aqueous electrolyte was added. A separator (5 cm × 5 cm, 23 μm thickness, made of Celgard # 3501 polypropylene) was disposed on the negative electrode active material layer, and 100 μL of a non-aqueous electrolyte was added. The lithium foil and the negative electrode active material layer were laminated via a separator, and 100 μL of a non-aqueous electrolyte was added. Furthermore, the resin current collector was laminated on lithium foil, and the covering material was covered so that the copper foil of the covering material might overlap. Of the outer periphery of the packaging material, heat seal the two sides orthogonal to the previously heat sealed side, and seal the laminated cell by heat sealing the remaining opening while vacuuming the inside of the cell using a vacuum sealer. Thus, a half cell for evaluation (hereinafter, also referred to as a battery for evaluation) according to Example 1 having the negative electrode for a lithium ion battery of the present invention was obtained.

[Measurement of battery characteristics]
The prepared battery for evaluation was subjected to a charge / discharge test according to the following method using a charge / discharge measurement apparatus "HJ0501SM" (manufactured by Hokuto Denko Co., Ltd.), and silicon and silicon compounds per gram (hereinafter referred to as The discharge capacity carried by the silicon-based active material (initially the discharge capacity of the silicon-based active material) and the ratio of the discharge capacity of the half cell at the 10th discharge to the discharge capacity of the half cell at the first discharge (10 cycles) The eye volume maintenance rate was also determined by the following method. The results are shown in Table 1.

[Measurement conditions of charge and discharge test]
In this charge / discharge test, lithium ions are inserted into the negative electrode to decrease the potential of the evaluation battery as a half cell [ie, a normal lithium ion battery using a positive electrode active material instead of metallic lithium as the positive electrode In the case of a full cell), the direction of the current to be charged is referred to as charging. The test was conducted at 45 ° C. as described below, with a 10 minute dwell between charge and discharge.
Set the prepared evaluation battery in the charge and discharge measurement device (HJ0501SM manufactured by Hokuto Denko Co., Ltd.), charge to 0 V with a current of 0.05 C at a constant current constant voltage charging method under the condition of 45 ° C 10 A pause for a minute was done. Thereafter, it was discharged to 1.5 V at a current of 0.05 C, and charged to 0 V at a current of 0.05 C again after 10 minutes of rest. After that, charging to 0 V at 0.05 C and discharging to 1.5 V at 0.05 C, which are performed with the above-described 10-minute rest time, were repeated a total of 10 times.

[Initial discharge capacity of silicon-based active material]
As described above, the initial discharge capacity of the silicon-based active material means the capacity of 1 g of silicon-based active material, and from the discharge capacity of the evaluation battery obtained by the following method, lithium among the raw materials used for the electrode It was obtained by dividing the value obtained by dividing the discharge capacity carried by the conductive additive, which is a raw material capable of causing an insertion reaction, by the weight of the silicon-based active material used for battery preparation.
The discharge capacity of the conductive support agent in the evaluation battery was changed to the agglomerated particles in Example 1 to prepare a half cell for capacity calculation using the conductive support agent, and the charge / discharge test was performed in the same manner as the evaluation battery. The capacity per 1 g of the conductive additive was determined, and the value was calculated by multiplying the weight ratio of the conductive additive used in the preparation of the battery for evaluation to the weight ratio of the battery for evaluation.

[10th cycle capacity maintenance rate]
It calculated with the following formula.
10th cycle capacity retention rate (%) = [(10th discharge capacity of the evaluation battery) / (first discharge capacity of the evaluation battery) x 100]

[Production of Binder Resin A for Agglomerated Particle Granulation]
150 parts of DMF was charged into a four-necked flask provided with a stirrer, a thermometer, a reflux condenser, a dropping funnel and a nitrogen gas inlet, and the temperature was raised to 75 ° C. Then, a monomer composition containing 70 parts of acrylic acid, 20 parts of methacrylic acid, 10 parts of methyl methacrylate and 50 parts of DMF, 0.3 parts of 2,2'-azobis (2,4-dimethylvaleronitrile), An initiator solution in which 0.8 parts of 2,2′-azobis (2-methylbutyronitrile) is dissolved in 30 parts of DMF is stirred for 2 hours with a dropping funnel under stirring while blowing nitrogen into a four-necked flask. The radical polymerization was carried out continuously dropwise. After completion of the addition, the reaction was continued at 75 ° C. for 3 hours. Then, the temperature was raised to 80 ° C. and the reaction was continued for 3 hours to obtain a copolymer solution having a resin concentration of 30%. The obtained copolymer solution was transferred to a Teflon (registered trademark) vat, dried under reduced pressure at 150 ° C. and 0.01 MPa for 3 hours, and DMF was distilled off to obtain a copolymer. The copolymer was roughly crushed with a hammer and then further crushed in a mortar to obtain a powdery binder resin A for granulation particle granulation.

[Manufacture of binder resin B for agglomerated particle granulation]
Production of Binder Resin A for Agglomerated Particles Except that 70 parts of acrylic acid, 20 parts of methacrylic acid and 10 parts of methyl methacrylate were changed to 83 parts of acrylic acid and 17 parts of 2-ethylhexyl methacrylate Binder resin B for aggregation particle granulation was manufactured in the procedure similar to the above.

<Examples 2 to 11 and Comparative Examples 1 to 2>
The amount of primary particles added in the preparation of aggregated particles, the type and amount of conductive aid, the type and amount of binder resin for aggregation particle granulation, the type and amount of conductive material, the porosity of the negative electrode active material layer, The procedure was carried out in the same manner as Example 1, except that the thickness and the type and amount of addition of carbon-based negative electrode active material particles were changed as shown in Table 1 when used in combination with carbon-based negative electrode active material particles. Lithium ion batteries according to Examples 2 to 11 and lithium ion batteries according to Comparative Examples 1 and 2 were obtained. In Comparative Example 2, the aggregated particles were not formed, and the primary particles (N-1) were used as they were as the material constituting the negative electrode active material.
The battery characteristics of the lithium ion batteries according to Examples 2 to 11 and Comparative Examples 1 and 2 were also measured in the same manner as Example 1, and the initial discharge capacity and the 10th cycle capacity retention rate of the silicon-based active material were measured. .
However, the first discharge capacity of the silicon-based active material in Examples 5 to 8 in which the carbon-based negative electrode active material particles are used in combination is the lithium ion among the raw materials used for the electrode from the first discharge capacity of the evaluation battery. It obtained by dividing the value which remove | divided the capacity | capacitance which the conductive support agent and carbon-type negative electrode active material particle which are the raw materials which can carry out an insertion reaction each into was divided by the weight of the silicon type active material used for battery preparation.
The capacity of the conductive support agent in the evaluation battery was calculated in the same manner as the calculation of the initial discharge capacity of the silicon-based active material in Example 1, and the capacity of the carbon-based negative electrode active material particles was the conductive support agent. In place of the carbon-based negative electrode active material particles, the volume was calculated in the same manner as the capacity of the conductive support agent.
The descriptions of compound names and conditions etc. in Table 1 correspond as follows.
AB: Denka Co., Ltd. Denka Black Li-400
KB: Lion Corporation Ketjen Black EC300J
PAA: Wako Pure Chemical Industries, Ltd. PHA (non-crosslinked type) acid number 780 Number average molecular weight: about 1,000,000 PAA 10% Cross-linked product: Wako Pure Chemical Industries, Ltd. 10 CLPAH acid value 740 number average molecular weight: about 1,000,000 Resin A: Binder resin for agglomerated particle granulation A Acid value 680 Number average molecular weight: about 100,000 Resin B: Binder resin for agglomerated particle granulation B Acid value 640 Number average molecular weight: about 100,000 (N-1): Silicon oxide particles (volume average particle diameter: 6 μm) which are primary particles obtained by [Preparation of primary particles]
(N-2): Hard carbon for lithium ion battery negative electrode (manufactured by JFE Chemical Co., Ltd., volume average particle diameter: 20 μm)
(N-3): Carbon-based coated negative electrode active material particles produced using (N-2) (volume average particle diameter: 20 μm)
(N-4): Graphite for lithium ion battery negative electrode [Hitachi Chemical Co., Ltd. MAGD-20, volume average particle diameter 20 μm]

From the results of Table 1, the lithium ion battery using the lithium ion battery negative electrode of the present invention using aggregated particles in which the acid value of the binder resin for aggregated particle granulation is 680 to 850 has initial discharge characteristics and 10 It was found that the cycle capacity retention rate was excellent. From this, it is understood that the lithium ion battery negative electrode of the present invention is excellent in energy density and cycle characteristics. In the lithium ion batteries according to Examples 1 to 11, since the particle generation rate of the particle diameter of 20 μm or less after the ultrasonic wave irradiation is low, the mechanical strength of the aggregated particles is high, and fine powder is generated due to the volume change associated with charge and discharge. It is considered difficult. Furthermore, it was found from the results of Examples 5 to 8 that even when the agglomerated particles were used in combination with the carbon-based negative electrode active material, the battery characteristics of the agglomerated particles were not deteriorated.

The negative electrode for lithium ion batteries of the present invention is particularly useful as an electrode for bipolar secondary batteries and lithium ion secondary batteries used for mobile phones, personal computers, hybrid vehicles and electric vehicles.

DESCRIPTION OF SYMBOLS 1 negative electrode 10 for lithium ion battery negative electrode collector 20 negative electrode active material layer 30 primary particle 40 binder resin for aggregation particle granulation 50 void 60 aggregation particle 70 non-aqueous electrolyte 80 conductive material

Claims (6)

A negative electrode for a lithium ion battery, comprising: a negative electrode active material layer including an agglomerated particle formed by aggregation and binding of primary particles composed of silicon and / or silicon compound disposed on an anode current collector,
The aggregated particles are formed by binding the primary particles to each other with a binder resin for aggregation particle granulation,
The binder resin for aggregating aggregated particles is a (meth) acrylic acid (co) polymer having an acid value of 680 to 850,
The negative electrode active material layer is a non-binding body that does not contain a binder that binds the aggregated particles to each other. The negative electrode for a lithium ion battery according to claim 1, wherein a ratio of a weight of the binder resin for granulation of aggregated particles to a weight of the aggregated particles is 10 to 30% by weight. The thickness of the said negative electrode active material layer is 150-600 micrometers, The negative electrode for lithium ion batteries of Claim 1 or 2. The lithium ion battery negative electrode further comprises a non-aqueous electrolyte containing an electrolyte and a non-aqueous solvent,
The non-aqueous solvent comprises cyclic carbonate,
The volume ratio of the cyclic carbonate to the non-aqueous solvent is 50% by volume or more,
The electrolyte concentration is 1.2 to 5.0 mol / L,
The negative electrode for a lithium ion battery according to any one of claims 1 to 3, wherein a degree of swelling of the binder resin for granulation of aggregated particles with respect to the non-aqueous electrolytic solution is 120% or less. The porosity of the said negative electrode active material layer is 35 to 50%, The negative electrode for lithium ion batteries in any one of Claims 1-4. A lithium ion battery comprising the negative electrode for a lithium ion battery according to any one of claims 1 to 5.

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