WO2020184157A1

WO2020184157A1 - Electrode and method for manufacturing electrode

Info

Publication number: WO2020184157A1
Application number: PCT/JP2020/007244
Authority: WO
Inventors: 大輔堀井; 典之宮本; 智志久保田; かおり小林
Original assignee: 日本ケミコン株式会社
Priority date: 2019-03-11
Filing date: 2020-02-21
Publication date: 2020-09-17
Also published as: JPWO2020184157A1; CN113519076A; KR20210135474A

Abstract

The present invention provides: an electrode having an excellent cycle service life, a high electrode density, and a low resistance; and a method for manufacturing the electrode. The electrode has an active material layer. The active material layer has electrode active material particles, oxidation-processed electroconductive carbon, electroconductive carbon different from the aforementioned electroconductive carbon, and fibrous carbon. The oxidation-processed electroconductive carbon and the different electroconductive carbon form a mixture. The electrode active material particles and the mixture form complexes in which at least a part of the surface of the electrode active material particles is covered by the mixture. The complexes and the fibrous carbon form a network structure in which the complexes are linked by the fibrous carbon.

Description

Electrodes and methods for manufacturing electrodes

The present invention relates to an electrode used in a power storage device and a method for manufacturing the electrode.

There are power storage devices such as secondary batteries, electric double layer capacitors, redox capacitors and hybrid capacitors. These power storage devices are widely studied for application as power sources for information devices such as mobile phones and laptop computers, motor drive power sources for low-emission vehicles such as electric vehicles and hybrid vehicles, and energy regeneration systems. In order to apply it to these application ranges, it is necessary to meet the demand for further improvement in performance and miniaturization of the power storage device. That is, the power storage device is required to further improve the energy density and the cycle life.

The power storage device is generally configured by sandwiching an electrolyte between a pair of electrodes. The electrode has an active material layer for energy storage. The electrode active material particles in the active material layer express their capacity by a Faraday reaction involving the transfer of electrons with ions in the electrolyte, or develop their capacity by a non-Faraday reaction such as polarization without the transfer of electrons. However, the electrode active material particles generally have low conductivity. Therefore, it has been studied to combine conductive carbon with the electrode active material particles and use the composite as a constituent of the active material layer.

Conductive carbon improves the conductivity of the electrode. That is, the conductive carbon contributes to the reduction of the direct current internal resistance (DCIR) and the equivalent series resistance (ESR) of the power storage device. However, conductive carbon does not contribute to the energy density of the power storage device. Therefore, it is better to reduce the conductive carbon in the composite as much as possible. In other words, it is better to increase the number of electrode active material particles per unit volume as much as possible while exhibiting good conductivity. Therefore, carbon nanotubes, which exhibit high conductivity even in a small amount, are attracting attention. The composite of carbon nanotubes and electrode active material particles can increase the electrode density. Further, this complex can obtain low DCIR and ESR even if the electrode density is increased.

However, it has been reported that the electrode active material particles and the electrolyte cause a side reaction to shorten the cycle life. Based on this report, it is desirable to coat part or all of the surface of the electrode active material particles with conductive carbon in order to improve the cycle life. For example, the surface of the mother particles of the composite oxide is mixed by mixing the mother particles of a lithium composite oxide such as LiCoO ₂ and the child particles of a carbon material such as acetylene black acting as a conductive agent while applying a compression and shearing action. Part or all of the particles are coated with child particles of carbon material (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 11-283623

The idea of covering a part or all of the surface of the electrode active material particles with acetylene black can improve the cycle life as compared with the composite of carbon nanotubes and the electrode active material particles. Moreover, although it is not as good as the composite of carbon nanotubes and electrode active material particles, the electrode density is also good.

However, the composite in which the electrode active material particles are coated with acetylene black falls below the characteristics of the composite of carbon nanotubes and the electrode active material particles in terms of resistance, and is originally intended to impart conductivity to the electrode active material particles. From the point of view, it must be said that it is inferior. As described above, an electrode having a high balance in cycle life, electrode density, and resistance is required, but such a proposal has not yet been made.

An object of the present invention is to provide an electrode having a good cycle life, a high electrode density, and a low resistance, and a method for manufacturing this electrode.

As a result of diligent studies by the inventors, when the electrode active material particles are covered with a mixture of oxidized conductive carbon and another conductive carbon (hereinafter, the mixture is also referred to as a conductive carbon mixture). The cycle life and electrode density were good. However, DCIR and ESR were significantly inferior to those in which the electrode active material particles were covered with acetylene black. Therefore, in order to suppress DCIR and ESR as much as possible, fibrous carbon such as carbon nanotubes was added to the active material composite formed by covering the electrode active material particles with a conductive carbon mixture. Then, instead of approaching the DCIR and ESR produced by the composite of carbon nanotubes and electrode active material particles, it was found that the DCIR and ESR are superior to those of the composite of carbon nanotubes and electrode active material particles.

The electrode according to the present invention was made based on this finding, and is an electrode having an active material layer in order to solve the above-mentioned problems. The active material layer is oxidized with the electrode active material particles. It is characterized by containing a conductive carbon mixture composed of the conductive carbon and the conductive carbon different from the oxidized conductive carbon, and fibrous carbon.

This mechanism is speculation and is not limited to this mechanism, but the goodness of DCIR and ESR of the present invention is presumed as follows. First, the active material composites are connected by fibrous carbon, which is an excellent electron path, like the composite of the electrode active material particles and the fibrous carbon. In the case of a composite of electrode active material particles and fibrous carbon, there is a problem in the transfer of local electrons called fibrous carbon and electrode active material particles. On the other hand, the electrode active material particles according to the present invention are densely coated with a conductive carbon mixture composed of an oxidation-treated conductive carbon and another conductive carbon to form an active material composite. Therefore, it is easy to transfer electrons from the conductive carbon mixture to the electrode active material particles. Therefore, this conductive carbon mixture once receives electrons from the fibrous carbon, and this conductive carbon mixture transfers electrons to the electrode active material particles, so that good DCIR and ESR can be achieved.

Therefore, in the electrode active material particles and the conductive carbon mixture, at least a part of the surface of the electrode active material particles is covered with the conductive carbon mixture to form an active material composite, and the active material is formed. The fibrous carbon may be arranged between the material composites to form a network structure.

The fibrous carbon may be carbon nanotubes. Further, the oxidized conductive carbon may contain a hydrophilic portion in 10% by mass or more of the total amount of the oxidized conductive carbon.

It is an electrode on the negative electrode side, and the electrode active material particles may be Si-based compound particles. Unlike other electrode active material particles, Si-based compound particles undergo electrode destruction, micronization of Si-based compound particles, thickening of SEI, or a combination of these due to large volume changes associated with the insertion and desorption of lithium ions. There is also a problem that the resistance is deteriorated or the capacity retention rate is lowered as the number of cycles elapses due to various factors. However, each electrode can solve this problem, provide an electrode having a good cycle life, a high electrode density, and a low resistance, and a method for manufacturing the electrode.

The Si-based compound particles may be particles of a compound represented by SiOx (0 ≦ x <2).

Further, the method for producing an electrode according to the present invention has been made based on this finding, and in order to solve the above problems, the electrode active material particles, the oxidized conductive carbon, and the oxidized conductive A slurry making step of preparing a slurry containing a conductive carbon mixture made of conductive carbon different from the conductive carbon and fibrous carbon, and an active material layer forming step of applying the slurry to a current collector are performed. It is characterized by including.

By this production method, the oxidized conductive carbon and another conductive carbon form a conductive carbon mixture, and the electrode active material particles and the conductive carbon mixture are formed on the surface of the electrode active material particles. At least a part thereof is covered with the conductive carbon mixture to form an active material composite, and the active material composite and the fibrous carbon are communicated with each other by the fibrous carbon. It forms a network structure.

In the slurry preparation step, the first mixing step of mixing the conductive carbon mixture and the electrode active material particles, and the active material composite obtained by the first step and the fibrous carbon are mixed. The second mixing step may be included.

According to the present invention, an electrode having a good balance between electrode density and low resistance can be obtained.

It is a schematic diagram which shows the 1st structure which each substance takes in an active material layer. It is a schematic diagram which shows the 2nd structure which each substance takes in an active material layer. It is various timing charts which show the manufacturing method of a slurry. It is an SEM photograph of the electrode of Example 1-1. It is an SEM photograph of the electrode of Example 2-1. It is a graph which shows the capacity maintenance rate according to the number of cycles of Example 1-4. It is a graph which shows the capacity maintenance rate according to the number of cycles of Example 3-1.

Hereinafter, embodiments of the electrode and the manufacturing method according to the present invention will be described in detail. The present invention is not limited to the embodiments described below.

(electrode)
The electrodes according to this embodiment are used in a power storage device. The power storage device is a passive element that charges and discharges electrical energy, and is roughly classified into a pair of electrodes and an electrolyte interposed between the electrodes. Examples of the power storage device in which the electrodes of the present embodiment are used include a secondary battery, an electric double layer capacitor, a redox capacitor and a hybrid capacitor, and may be used for one or both of the positive electrode or the anode or the negative electrode or the negative electrode of the pair of electrodes. Applies.

The electrode includes a current collector and an active material layer. The current collector is a conductor and also serves as a support substrate for the active material layer. The active material layer is formed on one side or both sides of the current collector. This active material layer is an energy storage layer.

As the current collector, for example, conductive materials such as platinum, gold, nickel, aluminum, titanium, steel, and carbon are used. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a net shape, an expanded metal shape, and a cylindrical shape can be adopted.

The active material layer contains electrode active material particles, oxidation-treated conductive carbon (hereinafter referred to as oxidation-treated carbon), conductive carbon different from oxidation-treated carbon, and fibrous carbon. The electrode active material particles express their capacity by a Faraday reaction involving the transfer of electrons with ions in the electrolyte, or by a non-Faraday reaction such as polarization without the transfer of electrons. Oxidized carbon, another conductive carbon and fibrous carbon are conductive aids in the active material layer.

(Electrode active material particles)
The electrode active material particles used for the positive electrode of the secondary battery include, first, layered rock salt type LiMO ₂ , layered Li ₂ MnO _3- LiMO ₂ solid solution, and spinel type LiM ₂ O ₄ (M in the formula is Mn, Fe. , Co, Ni or a combination thereof). Specific examples of these include LiCoO ₂ , LiNiO ₂ , LiNi _4/5 Co _1/5 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _1/2 Mn _1/2 O. ₂ , LiFeO ₂ , LiMnO ₂ , Li ₂ MnO _3- LiCoO ₂ , Li ₂ MnO _3- LiNiO ₂ , Li ₂ MnO _3- LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO _3- LiNi _1/2 Mn _1/2 O ₂ , Li ₂ MnO _3- LiNi _1/2 Mn _1/2 O _2- LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , LiMn _3/2 Examples include Ni _1/2 O ₄ . Also, sulfur and sulfides such as Li ₂ S, TiS ₂ , MoS ₂ , FeS ₂ , VS ₂ , Cr _1/2 V _1/2 S ₂ and sulphides such as NbSe ₃ , VSe ₂ , NbSe ₃ and Cr ₂ In addition to oxides such as O ₅ , Cr ₃ O ₈ , VO ₂ , V ₃ O ₈ , V ₂ O ₅ , V ₆ O 1 ₃ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiVOPO ₄ , LiV ₃ O ₅ , LiV ₃ O ₈ , MoV ₂ O ₈ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , LiFePO ₄ , LiFe _1/2 Mn _1/2 PO ₄ , LiMnPO ₄ , Li ₃ V ₂ (PO ₄ ) Examples thereof include composite oxides such as ₃ .

Examples of active materials used for the negative electrode of secondary batteries are Fe ₂ O ₃ , MnO, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , CoO, Co ₃ O ₄ , NiO, Ni ₂ O ₃ , and TIO. , TiO ₂ , SnO, SnO ₂ , SiO, SiO ₂ , RuO ₂ , WO, WO ₂ , ZnO and other oxides, Sn, Si, Al, Zn and other metals, LiVO ₂ , Li ₃ VO ₄ , Li ₄ Ti _Examples include composite oxides such as ₅ O _12, and nitrides such as Li _2.6 Co _0.4 N, Ge ₃ N ₄ , Zn ₃ N ₂ , and Cu ₃ N.

Examples of the electrode active material particles in the polarized electrode of the electric double-layer capacitor include carbon materials such as activated carbon, graphene, carbon nanofibers, carbon nanotubes, phenol resin carbides, polyvinylidene chloride carbides, and microcrystalline carbon having a large specific surface area. To. In the hybrid capacitor, the active material used for the positive electrode exemplified for the secondary battery can be used for the positive electrode, and in this case, the negative electrode is composed of a polarizing electrode using activated carbon or the like. Further, the negative electrode active material exemplified for the secondary battery can be used for the negative electrode, and in this case, the positive electrode is composed of a polarizable electrode using activated carbon or the like.

Examples of the electrode active material particles in the positive electrode of the redox capacitor include metal oxides such as RuO ₂ , MnO ₂ , and NiO, and examples of the electrode active material particles in the negative electrode include active materials such as RuO ₂ and activated charcoal. It is composed of a depolarizing material.

There is no limit to the shape and particle size of the electrode active material particles. However, the average particle size of the electrode active material particles is preferably more than 2 μm and 25 μm or less. The electrode active material particles having a relatively large average particle size improve the electrode density by themselves. The average particle size of the electrode active material particles means a 50% diameter (median diameter) in the measurement of the particle size distribution using a light scattering particle size meter.

Further, in the active material layer, fine particles having an average particle size of 0.01 to 2 μm as electrode active material particles and average particles larger than 2 μm and 25 μm or less capable of operating as an active material having the same poles as the fine particles It is preferable to mix with coarse particles having a diameter. By filling the coarse particles with fine particles, the electrode density is further increased, and the energy density of the power storage device is further improved. The mixing ratio of the coarse particles and the fine particles is preferably in the range of 80:20 to 95: 5 in terms of mass ratio, and more preferably in the range of 90:10 to 95: 5.

(Oxidized carbon)
The oxidized carbon is made of carbon having voids such as porous carbon powder, Ketjen black, furnace black having voids, carbon nanofibers and carbon nanotubes, and has a highly hydrophilic portion on the particle surface. The content of the hydrophilic portion is preferably 10% by mass or more of the total amount of the oxidized carbon. It is particularly preferable that the content of the hydrophilic portion is 12% by mass or more and 30% by mass or less of the whole.

The hydrophilic portion is brought about by the oxidation treatment, and is a portion in which a hydroxy group, a carboxy group or an ether bond is introduced into carbon, a portion in which a conjugated double bond of carbon is oxidized to generate a carbon single bond, and a portion. This is the part where the carbon-carbon bond is broken. 0.1 g of carbon is added to 20 mL of an aqueous ammonia solution having a pH of 11, and ultrasonic irradiation is performed for 1 minute, and the obtained solution is left to stand for 5 hours to precipitate a solid phase portion. It can be said that the portion dispersed in the aqueous ammonia solution having a pH of 11 without precipitating is the hydrophilic portion.

After leaving it to stand for 5 hours to precipitate the solid phase portion, the residual portion from which the supernatant has been removed is dried, and the weight of the dried solid is measured. The weight obtained by subtracting the weight of the solid after drying from the weight of the first carbon of 0.1 g is the weight of the hydrophilic portion dispersed in the aqueous ammonia solution at pH 11. The weight ratio of the weight of the hydrophilic portion to the weight of the first carbon of 0.1 g is the content of the hydrophilic portion in the carbon.

Since the oxidized carbon has a hydrophilic portion in this ratio, it easily spreads like a paste, easily extends along the surface of the electrode active material particles, easily enters the inside of the pores of the electrode active material particles, and is meticulous. Easy to change. Therefore, the oxidized carbon can come into contact with 80% or more, preferably 90% or more, particularly preferably 95% or more of the surface of the electrode active material particles. In addition, the paste-like state means a state in which grain boundaries are not recognized in the carbon primary particle size and non-particle-like amorphous carbon is connected in the SEM photograph taken at a magnification of 25,000 times. Further, the coverage may be calculated from an SEM photograph having a magnification of 25,000.

As the voids, it is desirable that the specific surface area measured by the BET method is 300 m ² / g or more, and if such voids are provided, it becomes easy to give the conductive carbon the property of changing into a paste by the oxidation treatment. Among them, spherical particles such as Ketjen black and furnace black having voids are preferable as the raw material. Even if oxidation treatment is performed using solid carbon as a raw material, it is difficult to obtain oxidation-treated carbon that changes into a paste.

(Another conductive carbon)
Another conductive carbon means to distinguish it from the oxidation-treated carbon, and the content of the hydrophilic portion is less than 10% by mass of the whole of the other conductive carbon, and it changes like a paste as compared with the oxidation-treated carbon. hard. If it is less than 10% by mass, it may be oxidized or unoxidized. This other conductive carbon is carbon black such as Ketjen black, acetylene black, furnace black, channel black, etc. used for electrodes of conventional power storage devices, fullerene, graphene, amorphous carbon, natural graphite, artificial graphite. Graphite, graphitized Ketjen black, mesoporous carbon, etc. are used.

As another conductive carbon, the particle shape is preferably spherical, and examples thereof include carbon black such as Ketjen black, acetylene black, furnace black, and channel black, fullerene, mesoporous carbon, and artificial graphite. Another conductive carbon does not easily change to a paste-like shape and maintains a spherical shape, so that a space that cannot be filled with the paste-like oxidation-treated carbon can be filled and the electrode active material particles can be densely filled with a conductive material. .. Further, it is preferable to use conductive carbon having a higher conductivity than the oxidized carbon, and it is particularly preferable to use acetylene black.

(Fibrous carbon)
Examples of the fibrous carbon include fibrous carbons such as carbon nanotubes, carbon nanofibers (hereinafter referred to as CNF), and vapor phase carbon fibers. The carbon nanotube may be a single-walled carbon nanotube (SWCNT) in which the graphene sheet is one layer, or a multi-walled carbon nanotube (MWCNT) in which two or more layers of graphene sheets are coaxially rolled and the tube wall is multi-walled. It may have been.

The outer diameter of this fibrous carbon is preferably in the range of 1 to 150 nm, preferably 1 to 70 nm, and further preferably 1 to 40 nm. The length of the fibrous carbon is preferably in the range of 1 to 500 μm, preferably 5 to 400 μm, and further preferably 5 to 200 μm. If it is smaller than these ranges, it becomes difficult for the electrode density to increase.

Further, as the number of layers of the graphene sheet of carbon nanotubes is smaller, the capacitance density of the carbon nanotubes themselves is higher. Therefore, carbon nanotubes having 50 or less layers, preferably 10 or less layers are preferable from the viewpoint of capacitance density. As for this fibrous carbon, an opening treatment or an activation treatment for making a hole in the tip or the wall surface of the fibrous carbon may be used.

The carbon nanotubes may be single-walled or multi-walled, but in the present invention, single-walled carbon nanotubes are more preferable. When the single-walled carbon nanotubes and the multi-walled carbon nanotubes are used in the same weight, the single-walled carbon nanotubes contain more carbon nanotubes than the multi-walled carbon nanotubes. Therefore, more networks can be constructed between the active material complexes, and the effect of reducing DCIR and ESR is further enhanced. By increasing the weight contained in the multi-walled carbon nanotubes, it is possible to increase the number of multi-walled carbon nanotubes and obtain the same DCIR and ESR reduction effect as the single-walled carbon nanotubes, but the multi-walled carbon nanotubes are more likely to clump and the electrodes The density is lower than that of single-walled carbon nanotubes. Further, when the content of the conductive auxiliary agent contained in the active material layer is constant, if a large amount of multi-walled carbon nanotubes is contained, the content of the conductive carbon mixture covering the active material is relatively reduced by that amount, and the cycle characteristics. The effect of improving is reduced. Therefore, single-walled carbon nanotubes are preferable in order to construct a network between active materials and reduce DCIR and ESR without impairing the cycle characteristics of conventional active materials.

The fibrous carbon is preferably 0.01% or more and 1.0% or less of the entire active material layer. This is because the effect of reducing DCIR and ESR appears from about 0.01%, while when it exceeds 1.0%, the proportion of the active material decreases and the capacity decreases.

(Structure of active material layer)
1 and 2 are schematic views showing the structure of the electrode active material particles, the oxidized carbon, another conductive carbon and the fibrous carbon taken in the active material layer. Part or all of the surface of the electrode active material particles 1 is coated with a mixture of oxidized carbon and another conductive carbon. A mixture of oxidized carbon and another conductive carbon is called a conductive carbon mixture 2. A double-shell structure particle composed of a conductive carbon mixture 2 and an electrode active material particle 1 having an inner shell as an electrode active material particle 1 and an outer shell as a conductive carbon mixture is referred to as an active material composite 3.

In the active material composite 3, the oxidized carbon spreads like a paste and adheres to the surface of the electrode active material particles 1. The oxidized carbon that spreads like a paste covers the surface of the electrode active material particles 1, is filled in the gaps between the electrode active material particles 1, and is extruded into the pores existing on the surface of the electrode active material particles 1. It is meticulously packed. The pores include gaps between the primary particles found in the secondary particles. Therefore, the amount of the electrode active material particles 1 per unit volume in the electrode increases, and the electrode density increases. However, the electrode of the present invention may contain oxidized carbon that has not changed into a paste.

Further, in the active material composite 3, the oxidation-treated carbon covers not only the surface of the electrode active material particles 1 but also the surface of another conductive carbon, and the electrode active material particles 1 involve the other conductive carbon. It is attached to. In other words, another conductive carbon is easily attached to the surface of the electrode active material particles 1 by the oxidation-treated carbon. Further, the other conductive carbon is covered with the oxidation-treated carbon to suppress aggregation. This other conductive carbon fills the gaps that could not be filled with the oxide-treated carbon that spreads like a paste, and improves the filling rate in the gaps.

Preferably, the oxidized carbon is present in the gaps having a width of 50 nm or less, inside the pores having a width of 50 nm or less, or both of them. Therefore, the coverage of the surface of the conductive carbon mixture 2 with respect to the electrode active material particles 1 is improved, the conductivity of the entire active material layer is improved, and the electrode density is improved. The width of the gap formed between the electrode active material particles 1 means the shortest distance among the distances between the adjacent electrode active material particles 1, and is present on the surface of the electrode active material particles 1. The width of the hole means the shortest distance between the opposing points of the opening of the hole.

In this active material composite 3, the mass ratio of the electrode active material particles 1 and the conductive carbon mixture 2 is preferably in the range of 90:10 to 99.5: 0.5, and is 95: 5 to 99. It is more preferably in the range of 1. If the proportion of the conductive carbon mixture 2 is less than the above range, the conductivity of the active material layer is insufficient, and the coverage of the electrode active material particles 1 by the gelatinized oxidation-treated carbon is lowered, resulting in cycle characteristics. Tends to decline. Further, when the ratio of the oxidized carbon is larger than the above range, the electrode density tends to decrease, and the energy density of the power storage device tends to decrease. Further, in the conductive carbon mixture 2, the ratio of the oxidized carbon to another conductive carbon is preferably in the range of 3: 1 to 1: 3 in terms of mass ratio, and 2.5: 1.5 to 1. A range of 5: 2.5 is more preferred.

As shown in FIGS. 1 and 2, the fibrous carbon 4 communicates between the active material composites 3. That is, the active material composite 3 and the fibrous carbon 4 adopt a network structure. The structure composed of the active material composite 3 and the fibrous carbon 4 is called a network structure 5. The network structure 5 can take the following two types.

First, as shown in FIG. 1, many conductive carbon mixtures 2 coat the electrode active material particles 1 and do not adhere to the fibrous carbon 4 so much, and the fibrous carbon 4 is an active material composite. It is in contact with the conductive carbon mixture 2 of the body 3. Further, as shown in FIG. 2, a part of the conductive carbon mixture 2 is coated with the electrode active material particles 1, but the other part of the conductive carbon mixture 2 is the surface of the fibrous carbon 4. It is also attached to. The conductive carbon mixture 2 adhering to the fibrous carbon 4 is in direct contact with the electrode active material particles 1, or the conductive carbon mixture 2 adhering to the fibrous carbon 4 and the electrode active material particles 1 are coated with conductivity. It is in contact with the carbon mixture 2.

It is presumed that both of these two types of network structures 5 contribute to lowering the resistance of the electrodes. First, the active material composites 3 are connected by fibrous carbon 4, which is an excellent electron path. The conductive carbon mixture 2 is responsible for the transfer of electrons carried by the fibrous carbon 4. Since both the fibrous carbon 4 and the conductive carbon mixture 2 use carbon as the main material, they are easy to fit on the contact surface and have good compatibility with electron transfer. Since the conductive carbon mixture 2 is closely adhered to the electrode active material particles 1, the electrode active material is compared with the transfer of electrons between the fibrous carbon 4 and the electrode active material particles 1. Electrons are easily transferred to particle 1. The fibrous carbon 4 is preferably 0.01% by mass or more of the entire active material layer. From about 0.01% by mass, the effect of reducing DCIR and ESR appears.

As described above, although it is a conductive additive, the conductive carbon different from the oxidation-treated carbon adheres closely to the electrode active material particles 1, and the fibrous carbon 4 is a conductive carbon with respect to the electrode active material particles 1. It is located via the mixture 2 and so as to communicate between the active material complexes 3. Therefore, the fibrous carbon 4 mainly functions as a highway that carries electrons close to the electrode active material particles 1, and the conductive carbon different from the oxidized carbon is the electrons of the electrode active material particles 1 and the fibrous carbon 4. It functions as a local transferor that mediates the transfer of electrons and directly transfers electrons to the electrode active material particle 1. As a result, a low resistance that cannot be achieved by the fibrous carbon 4 alone and that cannot be achieved by the electrode active material particles 1 coated with the conductive carbon different from the oxidized carbon can be realized.

In the network structure 5 shown in FIG. 1, the conductive carbon mixture 2 adheres less to the fibrous carbon 4. Therefore, the aggregation of the fibrous carbon 4 is small, and the fibrous carbon 4 between the electrode active material particles 1 can have a small volume. Therefore, the electrode density becomes even better. On the other hand, in the network structure 5 shown in FIG. 2, the fibrous carbon 4 is aggregated and the electrode density is lowered as compared with the network structure 5 in FIG. However, since the conductive carbon mixture 2 attached to the surface of the fibrous carbon 4 and the conductive carbon mixture 2 attached to the surface of the electrode active material particles 1 are in contact with each other, the transfer of electrons is further improved, and the electrode is used. Resistance goes down further.

Here, Si-based compound particles are suitable as the electrode active material particles 1 constituting the active material complex 3. The Si-based compound particles may be doped with a different element such as Ti or P, which is a compound represented by SiOx (0 ≦ x <2) such as Si or SiO, and the surface thereof is further coated with carbon. May be good.

In particular, SiO particles are suitable as the electrode active material particles 1. The SiO particles have a theoretical specific volume of approximately 2000 mAhg ^-1 per weight and an operating potential of approximately 0.5 V (vs. Li / Li ⁺ ). That is, the specific volume is much larger than that of graphite, and the operating potential is low like graphite, but it is not extremely low like graphite having an operating potential of about 0.05 V (vs. Li / Li ⁺ ). Therefore, the SiO particles are easily available and have a low environmental load, and are the electrode active material particles 1 on the negative electrode side of the lithium ion secondary battery and the electrode on the negative electrode side of the hybrid capacitor combined with the positive electrode having an electric double layer action. It is attracting attention as an active material particle 1.

However, the Si-based compound particles used as the electrode active material particles 1 on the negative electrode side expand and contract due to the insertion and detachment of lithium ions, and the Si particles contained in the Si-based compound particles have a volume change of about 300%. .. Therefore, the electrode is fragile, and the electrode active material particles 1 are easily cracked and pulverized. Further, SEI (Solid Electrolyte Interphase) is volumetrically formed on the surface of the Si-based compound particles used as the electrode active material particles 1 on the negative electrode side. SEI is a complex composed of an inorganic lithium compound or an organic compound formed by the reductive decomposition of the electrolytic solution, and suppresses the decomposition of the electrolytic solution beyond a certain level. When this SEI is destroyed by the expansion and contraction of the Si-based compound particles and a path of the electrolytic solution to the surface of the Si-based compound particles is generated, the SEI is further generated and the SEI around the Si-based compound particles becomes thicker. Too much.

Therefore, when Si-based compound particles are used as the electrode active material particles 1 on the negative electrode side, DCIR and ESR become high due to electrode destruction, micronization of Si-based compound particles, thickening of SEI film, or a combination of these factors. In addition, there is a problem that the capacity decreases as the number of cycles elapses. In addition, the Si-based compound particles used as the electrode active material particles 1 on the negative electrode side have a number of cycles due to side reactions such as decomposition of the electrolytic solution due to low operating voltage and precipitation of lithium metal due to rapid charging and discharging. There is also a phenomenon that the capacity decreases with each passing.

On the other hand, since the conductive carbon mixture 2 adheres closely to the electrode active material particles 1, it is difficult to be destroyed against the expansion and contraction of the Si-based compound particles. Therefore, it is difficult for the electrolytic solution to pass to the surface of the Si-based compound particles due to the expansion and contraction of the Si-based compound particles. This mechanism is speculative and is not limited to this mechanism alone, but by using Si-based compound particles as the electrode active material particles 1 and including the conductive carbon mixture 2 and the fibrous carbon 4, Si The electrode using the system compound particles as the electrode active material particles 1 has good electrode density and resistance, and the capacity retention rate is unlikely to decrease even after the number of cycles.

(Method of manufacturing electrodes)
In the network structure 5 as described above, firstly, a step of preparing a conductive carbon mixture, secondly, a step of preparing a slurry of an active material layer, and thirdly, a slurry is applied onto a current collector. It is manufactured through the process of rolling.

(Making process of conductive carbon mixture)
Oxidized carbon is produced by oxidation treatment of a carbon raw material. A known oxidation method can be used without particular limitation. For example, by treating the carbon raw material in a solution of acid or hydrogen peroxide, oxidized carbon can be obtained. As the acid, nitric acid, a mixture of nitric acid and sulfuric acid, an aqueous hypochlorous acid solution and the like can be used. Further, by heating the carbon raw material in an oxygen-containing atmosphere, steam, or carbon dioxide, oxidation-treated carbon can be obtained. Further, oxidation-treated carbon can be obtained by plasma treatment, ultraviolet irradiation, corona discharge treatment, and glow discharge treatment in an oxygen-containing atmosphere of the carbon raw material. As the strength of the oxidation treatment is increased, the proportion of hydrophilic portions increases.

Oxidized carbon containing 10% by mass or more of the total hydrophilic portion is
(A) A step of treating a carbon raw material having voids with an acid,
(B) Step of mixing the product after acid treatment with the transition metal compound,
(C) A step of pulverizing the obtained mixture to cause a mechanochemical reaction.
(D) A step of heating the product after the mechanochemical reaction in a non-oxidizing atmosphere, and
(E) It can be preferably obtained by a production method including a step of removing the transition metal compound and / or its reaction product from the product after heating.

In step (a), a carbon raw material having voids, preferably Ketjen black, is immersed in an acid and left to stand. Ultrasonic waves may be applied during this immersion. As the acid, an acid usually used for oxidation treatment of carbon such as nitric acid, a mixture of nitric acid and sulfuric acid, and an aqueous solution of hypochlorous acid can be used. The immersion time depends on the concentration of the acid and the amount of the carbon raw material to be treated, but is generally in the range of 5 minutes to 5 hours. The carbon after the acid treatment is thoroughly washed with water, dried, and then mixed with the transition metal compound in step (b).

Examples of the transition metal compound added to the carbon raw material in the step (b) include inorganic metal salts such as halides, nitrates, sulfates and carbonates of transition metals, formates, acetates, oxalates, methoxydos, ethoxydos and iso. Organic metal salts such as propoxide or mixtures thereof can be used. These compounds may be used alone or in combination of two or more. Compounds containing different transition metals may be mixed and used in predetermined amounts. Further, a compound other than the transition metal compound, for example, an alkali metal compound may be added together as long as the reaction is not adversely affected. Oxidized carbon is used by being mixed with electrode active material particles in the production of electrodes of power storage devices. Therefore, when a compound of an element constituting the active material is added to a carbon raw material, it can become an impurity with respect to the active material. It is preferable because it can prevent the mixing of elements.

In step (c), the mixture obtained in step (b) is pulverized to cause a mechanochemical reaction. Examples of crushers for this reaction include raikai, millstone grinders, ball mills, bead mills, rod mills, roller mills, stirring mills, planetary mills, vibration mills, hybridizers, mechanochemical compounding devices and jet mills. be able to. The crushing time depends on the crusher used, the amount of carbon to be processed, and the like, and is not strictly limited, but is generally in the range of 5 minutes to 3 hours. The step (d) is carried out in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere. The heating temperature and heating time are appropriately selected according to the transition metal compound used. In the subsequent step (e), the transition metal compound and / or the reaction product of the transition metal compound is removed from the heated product by means such as dissolution with an acid, and then thoroughly washed and dried. , It is possible to obtain an oxidation-treated carbon containing a hydrophilic portion of 10% by mass or more of the whole.

In this production method, in the step (c), the transition metal compound acts to promote the oxidation of the carbon raw material by the mechanochemical reaction, and the oxidation of the carbon raw material proceeds rapidly. By this oxidation, an oxidized carbon containing a hydrophilic portion of 10% by mass or more of the whole is obtained.

A conductive carbon mixture is obtained by dry-mixing another conductive carbon with the oxidized carbon produced in this manner. For dry mixing, a raikai device, a millstone grinder, a ball mill, a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibration mill, a hybridizer, a mechanochemical compounding device, and a jet mill can be used.

In the process of this dry mixing, the oxidized carbon adheres to the surface of another conductive carbon, the gelatinization of the oxidized carbon partially progresses, and at least a part of the oxidized carbon is changed to a paste. A conductive carbon mixture attached to the surface of another conductive carbon is obtained.

(Process for producing slurry of active material layer)
The slurry of the active material layer contains electrode active material particles, a conductive carbon mixture, and fibrous carbon which are the material sources of the network structure, and further contains a binder, a solvent, and a diluent. The diluent is added last. There are no particular restrictions on the mixing order or mixing method of the other mixing elements. However, with an emphasis on the electrode density shown in FIG. 1, a network structure in which the conductive carbon mixture 2 is less adhered to the fibrous carbon 4 is mainly included in the active material layer, or the low resistance shown in FIG. 2 is used. With emphasis, the preferred procedure differs depending on whether or not the active material layer mainly contains the network structure in which the conductive carbon mixture 2 adheres to the fibrous carbon 4 more than in the case shown in FIG.

FIG. 3 is a timing chart showing various slurry preparation methods. (A) to (c) of FIG. 3 mainly use the network structure shown in FIG. 1 as the main target product, and (d) to (f) of FIG. 3 mainly use the network structure shown in FIG. Use as the desired product.

The production methods (a) to (c) of FIG. 3 can be roughly classified into the active material composite after forming the active material composite by mixing the conductive carbon mixture and the electrode active material particles. Fibrous carbon is added and further mixed. Priority is given to adhering the conductive carbon mixture to the electrode active material particles, the conductive carbon mixture covering the electrode active material particles is sufficient, and the conductive carbon mixture adhering to the fibrous carbon is sufficient. It is small and difficult to aggregate.

In the production methods (d) to (f) of FIG. 3, the conductive carbon mixture and the fibrous carbon are simultaneously mixed with the electrode active material particles, or the fibrous carbon is the electrode active material particles first. Is mixed with. The chances of contact between the electrode active material particles of the conductive carbon mixture and the fibrous carbon are the same, and the conductive carbon mixture adheres to the fibrous carbon and easily aggregates, but the electrode active material particles and the fibrous carbon A conductive carbon mixture adheres to both of them.

(First slurry production method)
In the production method of (a) of FIG. 3, dry mixing of the conductive carbon mixture and the electrode active material particles and wet mixing of the fibrous carbon, the binder and the solvent are performed separately, and then both mixtures are combined into one. Mix Wet mixing is performed.

In the dry mixing of the conductive carbon mixture and the electrode active material particles, the oxidized carbon adheres to the surface of the electrode active material particles and covers the surface, so that the aggregation of the electrode active material particles is suppressed. In addition, due to the pressure applied to the oxidized carbon during the mixing process, at least a part of the oxidized carbon spreads like a paste and the surface of the electrode active material particles is partially covered, thereby forming an active material composite. To.

When the average particle size of the electrode active material particles is larger than 2 μm and 25 μm or less, the pressing force of the electrode active material particles promotes gelatinization of the oxidized carbon in the process of mixing with the oxidized carbon. Further, when the electrode active material particles are composed of fine particles and coarse particles, the oxidized carbon adheres not only to the coarse particles but also to the surface of the fine particles to cover the surface, so that the electrode active material particles are aggregated. Can be suppressed, and the mixed state of the electrode active material particles and the oxidized carbon can be made uniform.

For wet mixing of fibrous carbon, binder and solvent, it is desirable to use a dispersion in which fibrous carbon is dispersed in advance. As the binder to be mixed with the fibrous carbon, known binders such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, and carboxymethyl cellulose are used. The binder content is preferably 1 to 30% by mass with respect to the total amount of the electrode material. If it is 1% by mass or less, the strength of the active material layer is not sufficient, and if it is 30% by mass or more, inconveniences such as a decrease in the discharge capacity of the electrode and an excessive internal resistance occur. As the solvent, a solvent that does not adversely affect other components in the electrode material such as N-methylpyrrolidone can be used without particular limitation. The amount of the solvent is not particularly limited as long as each component in the mixture is uniformly mixed.

The wet mixing time varies depending on the total amount of the mixture and the mixing device used, but is generally between 1 and 60 minutes. Further, the kneading method with the binder and the solvent is not particularly limited, and may be carried out by hand mixing using a mortar, or may be carried out using a known wet mixing device such as a stirrer or a homogenizer. If the mixture is uniformly mixed, there is no problem even if the mixing time is short. However, it is preferable to refine the fibrous carbon by wet mixing, and it is preferable to use a wet mixing device known in this respect. The fibrous carbon is preferably miniaturized to a length of 20 nm to 200 nm in order to improve the electrode density.

Then, the mixed solution obtained by wet mixing and the active material composite obtained by dry mixing are mixed, and further wet-mixed. After the wet mixing, the mixed solution is diluted by further adding the solvent used in the wet mixing of the fibrous carbon and the binder to adjust the viscosity so that the slurry can be easily applied.

(Second slurry production method)
In the production method of FIG. 3B, the conductive carbon mixture and the electrode active material particles are dry-mixed to form an active material composite, and a binder and a solvent are added to shift to wet mixing. After the wet mixing is completed, the fibrous carbon dispersion is added to the mixture obtained by the wet mixing. Further, the mixed solution is diluted by further adding the solvent added together with the binder to adjust the viscosity so that the slurry can be easily applied.

(Third slurry production method)
In the production method (c) of FIG. 3, wet mixing of the binder, the conductive carbon mixture, and the solvent is performed, electrode active material particles are added to the mixed solution containing the conductive carbon mixture, and wet mixing is continued. , This produces an active material complex. After the wet mixing is completed, the fibrous carbon dispersion is added to the mixture obtained by the wet mixing. Further, the solvent added together with the binder and the conductive carbon mixture is further added to dilute the mixed solution and adjust the viscosity so that the slurry can be easily applied.

(Fourth slurry production method)
In the production method (d) of FIG. 3, wet mixing of a dispersion of a conductive carbon mixture and fibrous carbon, a binder, and a solvent is performed, and then electrode active material particles are added to continue the wet mixing. Then, the solvent used for the wet mixing of the fibrous carbon, the binder and the conductive carbon mixture is further added to dilute the mixed solution obtained by the wet mixing, and the viscosity is adjusted so that the slurry can be easily applied. ..

Since the conductive carbon mixture and the fibrous carbon first come into contact with each other, the conductive carbon mixture adheres to the surface of the fibrous carbon. The conductive carbon mixture that is not attached to the fibrous carbon adheres to the surface of the electrode active material particles at the stage of wet mixing in which the electrode active material particles are added. Further, the conductive carbon mixture adheres to the surface of the fibrous carbon while still adhering to the fibrous carbon, and further adheres to the electrode active material particles or the conductive carbon mixture adhering to the electrode active material particles. Due to the pressure applied to the oxidized carbon during the mixing process, the oxidized carbon adhering to the conductive carbon mixture also spreads like a paste, and the electrode active material particles and the fibrous carbon are integrally connected.

(Fifth slurry production method)
In the production method (e) of FIG. 3, wet mixing of the electrode active material particles, the conductive carbon mixture, the dispersion liquid of the fibrous carbon, the binder, and the solvent is performed. Then, the solvent used in the wet mixing is further added to dilute the mixed solution obtained by the wet mixing, and the viscosity is adjusted so that the slurry can be easily applied.

Since the conductive carbon mixture comes into contact with the fibrous carbon and the electrode active material particles at the same time, it adheres to both the surface of the fibrous carbon and the surface of the electrode active material particles. Due to the pressure applied to the oxidized carbon during the mixing process, the oxidized carbon adhering to the conductive carbon mixture also spreads like a paste, and the electrode active material particles and the fibrous carbon are integrally connected.

(6th slurry manufacturing method)
In the production method (f) of FIG. 3, wet mixing of the conductive carbon mixture, the binder and the solvent, and wet mixing of the fibrous carbon dispersion and the electrode active material particles are performed separately, and both mixtures are added. Further wet mixing is performed. Then, the mixture is diluted by further adding the solvent used in the wet mixing of the conductive carbon mixture, the binder and the solvent, and the viscosity is adjusted so that the slurry can be easily applied.

Since the conductive carbon mixture is added to the mixed fibrous carbon and the electrode active material particles, the fibrous carbon and the electrode active material particles come into contact with each other at the same time, so that the electrode active material is also on the surface of the fibrous carbon. It also adheres to the surface of the particles. Due to the pressure applied to the oxidized carbon during the mixing process, the oxidized carbon adhering to the conductive carbon mixture also spreads like a paste, and the electrode active material particles and the fibrous carbon are integrally connected.

(Process of applying slurry on the current collector and rolling)
After applying the slurry of the active material layer on the current collector and drying it, pressure is applied to the active material layer by rolling treatment to obtain an electrode. As pressure is applied to the active material layer, the oxidized carbon, which has at least partially changed to a paste, spreads further and becomes densified while covering the surface of the active material particles, and the active material particles approach each other. Oxidized carbon, which has changed into a paste, covers the surface of the active material particles and is extruded not only into the gaps formed between the adjacent active material particles but also into the pores existing on the surface of the active material particles. It is packed densely. Therefore, the amount of active material per unit volume of the electrode increases, and the electrode density increases. Further, the densely packed paste-like oxidation-treated carbon has sufficient conductivity to function as a conductive agent.

Further, when pressure is applied to the active material layer, the oxidized carbon on the electrode active material particles spreads like a paste by rolling, and a part of the oxidized carbon reaches the fibrous carbon existing between the active material composites. In addition, some continue to adhere to both the electrode active material particles and the fibrous carbon. Therefore, even after the rolling treatment is completed, some of the oxidation-treated carbons maintain a stretched state between the electrode active material particles and the fibrous carbons. Then, the role of mediating electrons between the fibrous carbon and the electrode active material particles becomes large, and the reduction in resistance is promoted. When the oxidized carbon is attached to both the electrode active material particles and the fibrous carbon, there is a high possibility that the oxidized carbon spreads between the electrode active material particles and the fibrous carbon by rolling, and the resistance is lowered. Is further promoted.

In addition, the coarse particles of the electrode active material particles have the effect of suitably pressing the oxidized carbon in the rolling process and rapidly changing the oxidized carbon into a paste-like state to make it densified, thus increasing the electrode density. Improve the energy density of power storage devices. In addition, while the fine particles of the electrode active material particles press the oxidized carbon that has been gelatinized at least in part in the rolling process, the gaps formed between the coarse particles that are adjacent to each other together with the oxidized carbon that has spread like paste Since it is extruded and filled, the electrode density is further increased, and the energy density of the power storage device is further improved.

The active material layer may be dried by reducing the pressure and heating as necessary to remove the solvent. The pressure applied to the active material layer by the rolling process is generally in the range of 50,000 to 1,000,000 N / cm2, preferably 100,000 to 500,000 N / cm2. Further, the temperature of the rolling process is not particularly limited, and the process may be performed at room temperature or under heating conditions.

Hereinafter, the present invention will be described in more detail based on Examples. The present invention is not limited to the following examples.

(Example 1-1)
10 g of Ketjen Black (trade name EC300J, manufactured by Ketjen Black International Co., Ltd., BET specific surface area 800 m2 / g) is added to 300 ml of 60% nitric acid, and the obtained liquid is irradiated with ultrasonic waves for 10 minutes and then filtered. Chen Black was recovered. The recovered Ketjen black was washed with water three times and dried to obtain an acid-treated Ketjen black.

And acid treatment Ketjenblack 3g, and 1.10g and 21.98g of Fe _(CH 3 COO), and 0.77g of Li _(CH 3 _COO), a _{_{_{C 6 H 8 O 7 · H}}} 2 O, CH 1.32 g of ₃ COOH, 1.31 g of H ₃ PO ₄ and 120 ml of distilled water were mixed, and the obtained mixture was stirred with a stirrer for 1 hour and then evaporated to dryness in air at 100 ° C. The mixture was collected. The resulting mixture was then introduced into a vibrating ball mill and pulverized at 20 Hz for 10 minutes. The pulverized powder was heated in nitrogen at 700 ° C. for 3 minutes to obtain a composite in which LiFePO ₄ was supported on the oxidized Ketjen black.

1 g of the obtained complex was added to 100 ml of an aqueous hydrochloric acid solution having a concentration of 30%, LiFePO ₄ in the complex was dissolved while irradiating the obtained solution with ultrasonic waves for 15 minutes, and the remaining solid was filtered and washed with water. And dried. A part of the dried solid was heated to 900 ° C. in air by TG analysis, and the weight loss was measured. Until it can be confirmed that the weight loss is 100%, that is, LiFePO ₄ does not remain, the steps of dissolving, filtering, washing and drying LiFePO _{4 with} the above-mentioned aqueous hydrochloric acid solution are repeated to remove the oxidized carbon from which LiFePO ₄ has been removed. Obtained.

Next, 0.1 g of the obtained oxidized carbon was added to 20 ml of an aqueous ammonia solution having a pH of 11, and ultrasonic irradiation was performed for 1 minute. The obtained liquid was left to stand for 5 hours to precipitate the solid phase portion. After the solid phase was precipitated, the residue from which the supernatant had been removed was dried, and the weight of the dried solid was measured. The weight ratio of the weight of the dried solid minus the weight of the first oxidized carbon of 0.1 g to the weight of the first oxidized carbon of 0.1 g is taken as the content of the "hydrophilic portion" in the oxidized carbon. did. As a result, the weight ratio of the hydrophilic portion of the oxidized carbon was 15% by mass.

Next, the obtained oxidation-treated carbon and acetylene black, which is a conductive carbon different from this oxidation-treated carbon, were mixed. That is, the obtained oxidized carbon and acetylene black (primary particle diameter 40 nm) were introduced into a ball mill at a mass ratio of 1: 1 and dry-mixed to obtain a conductive carbon mixture.

Using this conductive carbon mixture, the electrodes of Example 1-1 were produced by the first slurry production method shown in FIG. 3 (a). That is, the network structure of FIG. 1 was used as the target product.

That is, 1.94 parts by mass of the obtained conductive carbon mixture and 96 parts by mass of commercially available LiNi _0.5 Mn _0.3 Co _0.2 O ₂ particles (average particle size 5 μm) as electrode active material particles. And were mixed dryly, thereby producing an active material complex. On the other hand, 0.06 parts by mass of a single-walled carbon nanotube dispersion liquid (OCSiAl, product name: TUBALL BATT) as fibrous carbon and 2 parts by weight of polyvinylidene fluoride as a binder were used as an appropriate amount of N-methylpyrrolidone solvent. It was added and wet mixed. Then, the active material composite obtained by the dry mixing was added to the mixed solution obtained by the wet mixing, and the wet mixing was further continued.

Next, the mixed solution was diluted with N-methylpyrrolidone to form a slurry. This slurry was applied onto an aluminum foil, dried, and then rolled to obtain an electrode.

FIG. 4A is an SEM photograph of the electrode of Example 1-1 at a magnification of 10 k, and FIG. 4B distinguishes between the active material composite and fibrous carbon shown in the SEM photograph of FIG. 4A. It is an SEM photograph which performed the processing. In the photograph, the broken line is the border of the active material composite, and the solid line shows the axis of the fibrous carbon. As shown in FIG. 4, it can be seen that the electrode active material particles are covered with the conductive carbon mixture, and the active material composite is formed. Then, it can be seen that the carbon nanotubes extend so as to connect the active material composites to form a network structure.

(Example 2-1)
Using the conductive carbon mixture of Example 1-1, the electrode of Example 2-1 was produced by the fourth slurry production method shown in FIG. 3 (d). That is, the network structure of FIG. 2 was used as the target product.

Specifically, 1.94 parts by mass of the obtained conductive carbon mixture, 0.06 parts by mass of fibrous carbon, a single-walled carbon nanotube dispersion liquid (OCSiAl, product name: TUBALL BATT), and a binder. As a result, 2 parts by mass of polyvinylidene fluoride was added to an appropriate amount of N-methylpyrrolidone solvent and wet-mixed. Then, 96 parts by mass of commercially available LiNi _0.5 Mn _0.3 Co _0.2 O ₂ particles (average particle size 5 μm) were added as electrode active material particles, and wet mixing was continued.

FIG. 5A is an SEM photograph of the electrode of Example 2-1 at a magnification of 10 k, and FIG. 5B distinguishes between the active material complex and fibrous carbon shown in the SEM photograph of FIG. 5A. It is an SEM photograph which performed the processing. In the photograph, the broken line is the border of the active material composite, and the solid line shows the axis of the fibrous carbon. As shown in FIG. 5, it can be seen that the electrode active material particles are covered with the conductive carbon mixture, and the active material composite is formed. Then, it can be seen that the carbon nanotubes extend so as to connect the active material composites to form a network structure.

(Example 1-2)
The electrode of Example 1-2 uses the conductive carbon mixture of Example 1-1, and LiNi _0.3 Mn _0.3 Co _0.3 O ₂ particles (average particle size) are used as the electrode active material particles. It was changed to 10 μm) and produced by the first slurry production method shown in FIG. 3 (a). That is, the same network structure of FIG. 1 as in Example 1 was used as the target product.

Specifically, 1.94 parts by mass of the obtained conductive carbon mixture and 96 parts by mass of commercially available LiNi _0.3 Mn _0.3 Co _0.3 O ₂ particles (average particles) as electrode active material particles. A diameter of 10 μm) was added and dry mixing was carried out, whereby an active material complex was produced. On the other hand, 0.06 parts by mass of a single-walled carbon nanotube dispersion liquid (OCSiAl, product name: TUBALL BATT) as fibrous carbon and 2 parts by weight of polyvinylidene fluoride as a binder were used as an appropriate amount of N-methylpyrrolidone solvent. It was added and wet mixed. Then, the active material composite obtained by the dry mixing was added to the mixed solution obtained by the wet mixing, and the wet mixing was further continued.

(Example 1-3)
Using the conductive carbon mixture of Example 1-1, the electrodes of Example 1-3 were produced by the second slurry production method shown in FIG. 3 (b). That is, the same network structure of FIG. 1 as in Example 1-1 was used as the target product.

Specifically, 1.94 parts by mass of the obtained conductive carbon mixture and 96 parts by mass of commercially available LiNi _0.3 Mn _0.3 Co _0.3 O ₂ particles (average particles) as electrode active material particles. A diameter of 10 μm) was added and dry mixing was performed. Next, the result of the dry mixing and 2 parts by weight of polyvinylidene fluoride as a binder were added to an appropriate amount of N-methylpyrrolidone solvent and wet-mixed. To the result of the wet mixing, 0.06 parts by mass of a single-walled carbon nanotube dispersion liquid (OCSiAl, product name: TUBALL BATT) as fibrous carbon was added and diluted with N-methylpyrrolidone to form a slurry. This slurry was applied onto an aluminum foil, dried, and then rolled to obtain an electrode.

(Example 1-4)
Using the conductive carbon mixture of Example 1-1, the electrodes of Example 1-4 were produced by the third slurry production method shown in FIG. 3 (c). That is, the same network structure of FIG. 1 as in Example 1-1 was used as the target product.

Specifically, 1.94 parts by mass of the obtained conductive carbon mixture and 2 parts by weight of polyvinylidene fluoride as a binder were added to an appropriate amount of N-methylpyrrolidone solvent and wet-mixed. Next, 96 parts by mass of commercially available LiNi _0.3 Mn _0.3 Co _0.3 O ₂ particles (average particle size 10 μm) were added to the result of the dry mixing as electrode active material particles, and wet mixing was continued. , This produced an active material complex. Then, 0.06 parts by mass of a single-walled carbon nanotube dispersion liquid (OCSiAl, product name: TUBALL BATT) as fibrous carbon was added to the result of wet mixing and diluted with N-methylpyrrolidone to form a slurry. .. This slurry was applied onto an aluminum foil, dried, and then rolled to obtain an electrode.

(Example 2-2)
The electrode of Example 2-2 uses the conductive carbon mixture of Example 1-1, and LiNi _0.3 Mn _0.3 Co _0.3 O ₂ particles (average particle size) are used as the electrode active material particles. It was changed to 10 μm) and produced by the fourth slurry production method shown in FIG. 3 (d). That is, the network structure of FIG. 2 was used as the target product.

Specifically, 1.94 parts by mass of the obtained conductive carbon mixture, 0.06 parts by mass of fibrous carbon, a single-walled carbon nanotube dispersion liquid (OCSiAl, product name: TUBALL BATT), and a binder. As a result, 2 parts by mass of polyvinylidene fluoride was added to an appropriate amount of N-methylpyrrolidone solvent and wet-mixed. Then, 96 parts by mass of commercially available LiNi _0.3 Mn _0.3 Co _0.3 O2 particles (average particle size 10 μm) were added as electrode active material particles, and wet mixing was continued.

(Example 2-3)
Using the conductive carbon mixture of Example 1-1, the electrodes of Example 2-3 were produced by the fifth slurry production method shown in FIG. 3 (e). That is, the same network structure of FIG. 2 as in Example 2-1 was used as the target product.

Specifically, 96 parts by mass of commercially available LiNi _0.3 Mn _0.3 Co _0.3 O ₂ particles (average particle size 10 μm) as electrode active material particles and the obtained conductive carbon mixture 1. An appropriate amount of N-methyl contains 94 parts by mass, 0.06 parts by mass of a single-walled carbon nanotube dispersion liquid (OCSiAl, product name: TUBALL BATT) as fibrous carbon, and 2 parts by mass of polyvinylidene fluoride as a binder. It was added to a pyrrolidone solvent and wet mixed. Then, it was diluted with N-methylpyrrolidone to form a slurry. This slurry was applied onto an aluminum foil, dried, and then rolled to obtain an electrode.

(Example 2-4)
Using the conductive carbon mixture of Example 1-1, the electrodes of Example 2-4 were produced by the sixth slurry production method shown in FIG. 3 (f). That is, the same network structure of FIG. 2 as in Example 2-1 was used as the target product.

Specifically, 96 parts by mass of commercially available LiNi _0.3 Mn _0.3 Co _0.3 O ₂ particles (average particle size 10 μm) as electrode active material particles and 0.06 parts by mass of fibrous carbon are simple. A layered carbon nanotube dispersion (OCSiAl, product name: TUBALL BATT) was added and dry-mixed. Separately, 1.94 parts by mass of the obtained conductive carbon mixture and 2 parts by weight of polyvinylidene fluoride as a binder were added to an appropriate amount of N-methylpyrrolidone solvent, and wet mixing was performed. Then, both mixtures were added and further wet-mixed, and diluted with N-methylpyrrolidone to form a slurry. This slurry was applied onto an aluminum foil, dried, and then rolled to obtain an electrode.

(Evaluation of various characteristics 1)
The positive electrode densities of the electrodes of Examples 1-2 to 1-4 and Examples 2-2 to 2-4 were measured. The positive electrode density was measured by pressing the electrode at 1.5 t / cm ³ three times, cutting it into 1 cm ² , and measuring the weight and thickness. From there, the weight and thickness of the aluminum foil, which is the current collector, were subtracted, and the density was calculated.

In addition, the DCIR of the electrodes of Examples 1-2 to 1-4 and Examples 2-2 to 2-4 was measured. A laminated cell of a lithium ion secondary battery was prepared as follows for the measurement of DCIR. That is, a counter electrode with graphite attached to a copper foil was prepared, and a polyethylene terephthalate (PET) separator was interposed between the electrodes. As the electrolytic solution, a 1: 1 solution of 1 M LiPF ₆ in ethylene carbonate / diethyl carbonate was used. Then, constant current charging was performed at a charging rate of 25 ° C. and 1.0 C, then constant current discharging was performed at a discharge rate of 25 ° C. and 1 C, and the discharge curve was measured. DCIR was measured from this discharge curve.

In addition, the ESR of the electrodes of Examples 1-2 to 1-4 and Examples 2-2 to 2-4 was measured. A laminated cell of a lithium ion secondary battery was prepared as follows for the measurement of ESR. That is, a counter electrode with graphite attached to a copper foil was prepared, and a polyethylene terephthalate (PET) separator was interposed between the electrodes. As the electrolytic solution, a 1: 1 solution of 1 M LiPF ₆ in ethylene carbonate / diethyl carbonate was used. Then, constant current charging was performed at a charging rate of 0.5 C until the charging depth (SOC) became 50%, and then a value of 1 kHz was measured by AC impedance measurement.

The electrodes of the following Comparative Examples 1 to 3 were prepared as comparison targets, and the electrode densities, DCIR and ESR were measured under the same conditions as in each example. In the electrode of Comparative Example 1, 2 parts by mass of acetylene black was used instead of the conductive carbon mixture. Further, in the electrode of Comparative Example 1, fibrous carbon such as carbon nanotubes was not added. In the electrode of Comparative Example 1, other compositions, composition ratios, and production methods are the same as those of Example 1-1. In the electrode of Comparative Example 2, the addition amount of the same conductive carbon mixture as in Example 1-1 was 2 parts by mass, and fibrous carbon such as carbon nanotubes was not added. In the electrode of Comparative Example 2, other compositions, composition ratios, and production methods are the same as those of Example 1-1. Further, in the electrode of Comparative Example 3, the conductive carbon mixture was not added, and the conductive auxiliary agent was only 0.06 parts by mass of carbon nanotubes. In the electrode of Comparative Example 3, other compositions, composition ratios, and production methods are the same as those of Example 1-1. In the electrode of Comparative Example 4, 1.94 parts by mass of acetylene black was used instead of the conductive carbon mixture. Other compositions, composition ratios and production methods are the same as in Example 1-1.

Table 1 below shows various characteristics of the electrodes of Examples 1-2 to 1-4, 2-2 to 2-4, and Comparative Examples 1 to 4.
(Table 1)

As shown in Table 1, the electrodes of Examples 1-2 to 1-4 were superior to Comparative Example 1, Comparative Example 3 and Comparative Example 4 in terms of electrode density, and were equal to or higher than those of Comparative Example 2. Further, the electrodes of Examples 1-2 to 1-4 showed lower resistance than Comparative Example 2 as well as Comparative Example 3 in terms of DCIR and ESR. The electrodes of Examples 1-2 to 1-4 form an active material layer with the network structure shown in FIG. 1 according to the first to third slurry production methods shown in FIGS. 3A to 3C. It was done. In Comparative Example 2, the active material layer is formed by the active material composite of the conductive carbon mixture and the electrode active material particles, and the active material composite does not have a network structure.

Although the electrodes of Examples 2-2 to 2-4 were lower than the electrode densities of Comparative Example 2 and Comparative Example 3, they were higher than the electrode densities of Comparative Example 1 and had good electrode densities. Further, the electrodes of Examples 2-2 to 2-4 show lower resistance than Comparative Example 3 as well as Comparative Example 2 in terms of DCIR and ESR, and further, from Examples 1-2 to 1-4. Also showed low resistance. The electrodes of Examples 2-2 to 2-4 form an active material layer with the network structure shown in FIG. 2 according to the fourth to sixth slurry production methods shown in FIGS. 3 (d) to (f). It was done.

Based on the above, a slurry containing electrode active material particles, oxidation-treated carbon, conductive carbon different from conductive carbon, and fibrous carbon is prepared, and the slurry is oxidized by a manufacturing method of applying the slurry to a current collector. The treated carbon and another conductive carbon form a conductive carbon mixture, and the electrode active material particles and the conductive carbon mixture are such that at least a part of the surface of the electrode active material particles is the conductive carbon mixture. It was confirmed that the active material complex and the fibrous carbon were connected with each other by the fibrous carbon to form a network structure. ..

The electrode having the active material layer formed of this network structure has good electrode density and resistance, and in particular, the resistance may be better than the case where carbon nanotubes are contained as a conductive auxiliary agent. confirmed.

Further, in the slurry preparation step, the electrode active material particles are added to and mixed with the conductive carbon mixture of the oxidized carbon and another conductive carbon, and then the fibrous carbon is added to the active material composite and mixed. It was confirmed by the production method that a large amount of the conductive carbon mixture adhered to the electrode active material particles, while a network structure in which the amount of the conductive carbon mixture adhered to the fibrous carbon was small was obtained.

A large amount of the conductive carbon mixture adheres to the electrode active material particles, while the electrode has a particularly high electrode density according to the network structure in which the amount of the conductive carbon mixture adhered to the fibrous carbon is small. Was confirmed.

Further, in the slurry preparation step, the conductive carbon mixture and the fibrous carbon are added to the electrode active material particles at the same time, or the fibrous carbon and the electrode active material particles are mixed first, and then the conductive carbon mixture is added. It was confirmed that a network structure in which the conductive carbon mixture adheres to both the electrode active material particles and the fibrous carbon can be obtained by the production method.

Then, according to the network structure in which the conductive carbon mixture adheres to both the electrode active material particles and the fibrous carbon, it was confirmed that the electrode has a particularly low resistance.

(Cycle characteristics 1)
The capacity retention rate for each cycle of Examples 1-4 and Comparative Examples 1 to 4 was measured. A laminated cell of a lithium ion secondary battery was prepared as follows for measuring the capacity retention rate. That is, a counter electrode with graphite attached to a copper foil was prepared, and a polyethylene terephthalate (PET) separator was interposed between the electrodes. As the electrolytic solution, a 1: 1 solution of 1 M LiPF ₆ in ethylene carbonate / diethyl carbonate was used. Then, the lithium ion secondary battery was charged with a constant current of 4.2 V at 1 C, and then charged with a constant voltage current until the current became 0.02 CA. Then, constant current discharge was performed until it became 3.0 V at 1C, and the discharge capacity was calculated from the obtained discharge curve. The discharge cycle was performed 200 times, and the percentage with the initial discharge capacity was calculated as the capacity retention rate.

The result is shown in Fig. 6. FIG. 6 is a graph in which the horizontal axis represents the number of cycles and the vertical axis represents the capacity retention rate. As shown in FIG. 6, Example 1-4 maintains a capacity retention rate of 95% or more for at least 200 charge / discharge cycles. On the other hand, in Comparative Examples 2 to 4, the capacity retention rate dropped to 90% or less at the time of 200 charge / discharge cycles, and in Comparative Example 1, the deterioration of the capacity retention rate became steep after 110 charge / discharge cycles. When the charge / discharge cycle reached 200 times, the capacity retention rate became 80%.

From the above, the electrode in which at least a part of the surface of the electrode active material particles is covered with this conductive carbon mixture does not maintain good cycle characteristics, and a part or all of the surface of the electrode active material particles is provided with acetylene black. It was confirmed that the cycle life was also improved as compared with coating with.

(Si-based compound particles)
Using the conductive carbon mixture of Example 1-1, an electrode of Example 3-1 suitable for a negative electrode of a lithium ion secondary battery or a hybrid capacitor was prepared. The electrode active material particles of this electrode are SiO particles. This electrode is manufactured by the fourth slurry manufacturing method shown in FIG. 3D and has the network structure of FIG.

Specifically, a dispersion containing 2.5 parts by mass of the obtained conductive carbon mixture and 2.5 parts by mass of fibrous carbon as a multi-walled carbon nanotube dispersion liquid (JEIO, product name: JENO TUBE8). And 15 parts by weight of polyimide as a binder were added to an appropriate amount of N-methylpyrrolidone solvent and wet-mixed. Then, 80 parts by mass of SiO particles (manufactured by Osaka Titanium) having an average particle size of 5 μm were added as electrode active material particles, and wet mixing was continued. This mixed solution was diluted with N-methylpyrrolidone to form a slurry. This slurry was applied onto a copper foil, dried, and then rolled. After the rolling treatment, the electrodes were obtained by exposing them to an inert atmosphere at 350 ° C. for 1 hour.

(Evaluation of various characteristics 2)
The negative electrode density of the electrode of Example 3-1 was measured. The negative electrode density was calculated by the same preparation and the same method as the positive electrode density in Evaluation 1 of various characteristics. In addition, DCIR and ESR according to Example 3-1 were measured. The measurement conditions and measurement methods for DCIR and ESR are as follows.

A coin cell of a lithium ion secondary battery was made for the measurement of DCIR. That is, a lithium ion metal leaf was prepared as a counter electrode, and a polyethylene terephthalate (PET) separator was interposed between the electrodes. Further, 1 mora of LiPF ₆ was added as a solute to a solvent in which ethylene carbonate and diethyl carbonate were mixed at a weight ratio of 1: 1 to prepare an electrolytic solution. Then, constant current charging was performed up to SOC 50% at a charging rate of 25 ° C. and 0.2 C, then discharged at 25 ° C. for 10 seconds, and the voltage drop was measured. The discharge current value was plotted on the horizontal axis and the voltage drop was plotted on the vertical axis, and DCIR was calculated from the slope.

In the ESR, the coin cell is charged with a constant current at a charging rate of 0.2 C until the SOC becomes 50%, then the coin cell charged with the constant current is disassembled, and the electrodes taken out from the disassembled cell are laminated with a separator interposed therebetween. Then, a symmetric cell was prepared, and the ESR was confirmed by measuring the resistance value of 1 kHz by AC impedance measurement for the obtained symmetric cell.

The following electrodes of Comparative Example 5 and Comparative Example 6 were prepared as comparison targets, incorporated into a lithium ion secondary battery, and the electrode densities, DCIR and ESR were measured under the same conditions as in Example 3-1. In the electrode of Comparative Example 5, 5 parts by mass of acetylene black was used instead of the conductive carbon mixture. In the electrode of Comparative Example 6, 5 parts by mass of a conductive carbon mixture was used. In the electrodes of Comparative Example 5 and Comparative Example 6, fibrous carbon such as carbon nanotubes was not added. In Comparative Examples 5 and 6, the composition, composition ratio and production method of the other electrodes are the same as those in Example 3-1 and the composition, composition and composition ratio of the lithium ion secondary battery are the same as in Example 3-. It is the same as 1.

Table 2 below shows various characteristics of the electrodes of Example 3-1 and Comparative Example 5.
(Table 2)

As shown in Table 2, the electrodes of Example 3-1 were superior to Comparative Example 5 in terms of electrode density, and showed lower resistance than Comparative Example 5 in terms of DCIR and ESR. From the above, it was confirmed that when SiO particles were used as the electrode active material particles on the negative electrode side, the deterioration of the electrode density, DCIR and ESR due to the large volume change accompanying the insertion and removal of lithium ions was also solved. It was.

(Cycle characteristics 2)
A coin cell of a lithium ion secondary battery using the electrodes of Example 3-1 and Comparative Example 5 and Comparative Example 6 as the negative electrode was prepared, and the capacity retention rate for each cycle was measured. The composition, composition and composition ratio of the lithium ion secondary battery are the same as those in Evaluation 2 of various characteristics. The lithium ion secondary battery was charged at 0.3 C with a constant current to 0.01 V, and then charged with a constant current until the current became 0.015 CA. Then, constant current discharge was performed at 0.3 C until the voltage reached 1.5 V, and the discharge capacity was calculated from the obtained discharge curve. The discharge cycle was performed 50 times, and the percentage with the initial discharge capacity was calculated as the capacity retention rate.

The result is shown in Fig. 7. FIG. 7 is a graph in which the horizontal axis represents the number of cycles and the vertical axis represents the capacity retention rate. As shown in FIG. 7, Example 3-1 maintains a capacity retention rate of 95% or more for at least 50 charge / discharge cycles. On the other hand, in Comparative Example 5 and Comparative Example 6, the deterioration of the capacity retention rate became steep, and when the charge / discharge cycle reached 50 times, the capacity retention rate of Comparative Example 5 became 74.5%, and the capacity of Comparative Example 6 was reached. The maintenance rate was 89.5%.

From the above, it was confirmed that when SiO particles were used as the electrode active material particles on the negative electrode side, the decrease in the capacity retention rate due to the large volume change due to the insertion and removal of lithium ions was also solved.

Claims

An electrode having an active material layer
The active material layer contains electrode active material particles, a conductive carbon mixture composed of an oxidation-treated conductive carbon and a conductive carbon different from the oxidation-treated conductive carbon, and fibrous carbon. thing,
An electrode characterized by.
The electrode active material particles and the conductive carbon mixture form an active material composite in which at least a part of the surface of the electrode active material particles is covered with the conductive carbon mixture.
The fibrous carbon is arranged between the active material composites to form a network structure.
The electrode according to claim 1.
The fibrous carbon is a carbon nanotube.
The electrode according to claim 1 or 2.
The oxidized conductive carbon contains a hydrophilic portion in an amount of 10% by mass or more of the entire oxidized conductive carbon.
The electrode according to any one of claims 1 to 3.
It is the electrode on the negative electrode side,
The electrode active material particles are Si-based compound particles.
The electrode according to any one of claims 1 to 4.
The Si-based compound particles are particles of a compound represented by SiOx (0 ≦ x <2).
5. The electrode according to claim 5.
Preparation of a slurry to prepare a slurry containing the electrode active material particles, a conductive carbon composite composed of the oxidized conductive carbon and the conductive carbon different from the oxidized conductive carbon, and the fibrous carbon. Process and
The active material layer forming step of applying the slurry to the current collector, and
Including,
A method for manufacturing an electrode.
The slurry making step is
The first mixing step of mixing the conductive carbon mixture and the electrode active material particles, and
A second mixing step of mixing the active material composite obtained in the first step and the fibrous carbon, and
Including,
7. The method for manufacturing an electrode according to claim 7.