JP2006164689A - Electrode structure, secondary battery, and capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery or a capacitor, or an electric structure thereof having large capacity and high output power. <P>SOLUTION: The electrode structure is formed by a current collector material; and an electrode layer formed on the surface of the current collector material composed of conductive material mixed electrode activator particle, space forming particle; and a binder; including the conductive material mixed electrode activator particle having conductive material around electrode activator particle; the space forming particle with an average size larger than that of the conductive material mixed electrode activator particle by two times or more; and the binder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an electrode structure, a secondary battery, and a capacitor.

  A non-aqueous electrolyte secondary battery has an electrode structure in which a mixture of an electrode active material, a conductive material and a binder is applied to the surface of the current collector, and the electrode active material and the conductive material are adhered to the surface of the current collector by the adhesive strength of the binder. Was forming. Thus, in order to increase the conductivity of the electrode structure, if the particle size of the conductive material is widely distributed from large to small to form a dense structure, the amount of binder increases, which eventually increases the resistance of the electrode structure. Become. In addition, in order to increase the charge / discharge capacity of the secondary battery, the electrode active material has a dense structure in which the particle size of the electrode active material is widely distributed from large to small (see Patent Document 1). However, the electrolyte required for charging and discharging cannot sufficiently enter the electrode layer, and a large-capacity secondary battery cannot be obtained.

  Conventionally, there is a description that a conductive material is deposited on the surface of an electrode active material by vapor deposition or sputtering without using a binder, so that the surface coverage of the conductive material is 40% to 80% (patent) Reference 2). However, if the surface of the electrode active material is covered by 40% to 80%, there is a problem whether the characteristics and functions of the electrode active material can be sufficiently extracted. That is, when the conductive material covers the surface of the electrode active material, it is considered that the ion active material is prevented from being released and sucked, and the electrode active material coating blocks the reaction site of the electrode active material. Further, since the conductive material covering the electrode active material does not protrude from the surface of the electrode active material, it is considered difficult to increase the conductivity between the electrode active materials.

  In addition, the present applicant has invented conductive material mixed electrode active material particles that facilitate the release and suction of ions of the electrode active material and can increase the conductivity (see Patent Document 3).

JP 2003-109592 A JP 2000-58063 A International Publication Number WO 03/103076 A1

(1) The present invention provides a secondary battery or capacitor electrode structure having good performance.
(2) Alternatively, the present invention provides a secondary battery or capacitor having a large capacity and a high output.

(1) The present invention is at least twice as large as the average particle size of the current collector, the conductive material mixed electrode active material particles having conductive material attached around the electrode active material particles, and the conductive material mixed electrode active material particles An electrode structure comprising space-forming particles having an average particle diameter and a binder, wherein an electrode layer is formed on the surface of the current collector by the conductive material mixed electrode active material particles, the space-forming particles, and the binder.
(2) The electrode structure according to the present invention or the electrode structure according to (1), wherein the average particle diameter of the space-forming particles is three times or more larger than the average particle diameter of the conductive material mixed electrode active material particles. It is in.
(3) In the electrode structure according to (1), the space-forming particles have an average particle size of 10 μm or more, and the conductive material mixed electrode active material particles have an average particle size of 3 μm or less. In the electrode structure.
(4) In the electrode structure according to (1), the space-forming particles have an average particle size of 10 μm or more, and the conductive material mixed electrode active material particles have an average particle size of 1 μm or less. In the electrode structure.
(5) In the electrode structure according to (1), the space-forming particles have an average particle size of 10 μm or more, and the conductive material mixed electrode active material particles have an average particle size of 0.00. The electrode structure is 5 μm or less.

(1) Electrodes of battery or capacitor electrical parts Electrodes of batteries and capacitors (electric double layer capacitors and electric double layer capacitors) are those that can transfer electricity to and from ions or attract ions. is there. Therefore, the electrode is an electrode structure in which an electrode layer capable of transferring ions is formed on the surface of the current collector. Some electrode structures have electrode layers formed on the surface of a current collector. Note that “on the surface” may be in direct contact with the surface of the current collector 3, or may be disposed with another layer between the surface.

  The electrode layer is formed by bonding conductive material mixed active material particles and space forming particles with a small amount of binder. As shown in FIG. 1, the electrode structure 2 of a battery or a capacitor has an electrode layer 22 formed on the surface of a current collector 21. The conductive material mixed active material particles 51 are obtained by attaching a conductive material around the electrode active material particles without using a binder. The electrode active material particles can be applied to both positive electrode active material particles and negative electrode active material particles. The average particle diameter of the space-forming particles 52 is desirably twice or more larger than the average particle diameter of the electrode active material particles, and more preferably three times or more larger to form the electrode layer 22 when the electrode layer 22 is formed. A space where a large amount of electrolyte can enter can be formed without being dense, and the thick electrode layer 22 can be formed.

LiMn ₂ O ₄ or the like can be used as the positive electrode active material particles of the secondary battery, and graphite, hard carbon, or the like can be used as the negative electrode active material particles. Moreover, as the positive electrode active material particles and the negative electrode active material particles of the capacitor, electrode active material particles having a high surface area capable of adhering a large amount of ions such as lithium can be used. In an electrical component 1 of a secondary battery or a capacitor, a positive electrode structure and a negative electrode structure are disposed to face each other with a separator 4 interposed therebetween, and an electrolytic substance 3 such as an electrolytic solution is disposed therebetween.

(2) Electrode active material particles The electrode active material particles exchange ions. For example, in the case of a lithium battery, the positive electrode active material includes a lithium active material such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4. . Examples of the negative electrode active material include carbon materials and metals such as lithium metal.

A high surface area material can be used as the electrode active material particles of the capacitor. In particular, activated carbon obtained by activating a carbon material by a steam activation treatment method, a molten KOH activation treatment method, or the like is preferable. Examples of the activated carbon include coconut shell activated carbon, phenol activated carbon, petroleum coke activated carbon, polyacene, and the like, and one of these can be used alone or in combination of two or more. Among these, phenol-based activated carbon, petroleum coke-based activated carbon, and polyacene are preferable in realizing a large capacitance.

(3) Conductive Material The conductive material has high conductivity and increases the conductivity of the electrode structure 2. When the conductive material is in contact with the passive film of aluminum as the current collector 21, the conductive material is preferably a carbon material, and the conductivity of the passive film is considered to increase at the location where the carbon material is attached to the passive film. . Examples of the conductive material include carbon black, ketjen black, acetylene black, carbon whisker, natural graphite, artificial graphite, carbon fiber such as VGCF and carbon nanotube, and the like. Can be used. Among them, ketjen black which is a kind of carbon black is preferable.

(4) Conductive material mixed electrode active material particles The conductive material mixed electrode active material particles 51 are obtained by attaching a conductive material to the surface of the electrode active material particles without using a binder. The conductive material mixed electrode active material particles 51 can easily move electrons between the conductive material and the electrode active material particles, and can easily release and suck ions. The adhesion is considered to be a state in which the conductive material is bonded or attached in a cotton-like manner around the electrode active material particles. The cotton-like state means a state consisting of cotton-like, mold-like, beard-like, linear, thread-like and the like. In the conductive material mixed electrode active material particles 51, it is considered that a small cotton-like conductive material is bonded or attached around the electrode active material particles as dots. Here, the dot shape is not limited to a single point, and may be composed of a plurality of points, and is not covered in a planar shape so as not to substantially limit the release and suction of ions of the electrode active material particles. Say state. The conductive material mixed electrode active material particles 51 are shown in detail in International Publication No. WO 03/103076 A1.

(5) Space-Forming Particles The space-forming particles 52 are large-diameter particles for creating a space in which the electrolyte solution can easily enter the electrode layer 2. When the particle size is increased, a space surrounded by adjacent space-forming particles can be made larger, and the electrolytic solution can easily enter the space. Thereby, even if the electrode layer 2 is thickened, the electrolyte sufficiently enters the electrode layer 2 and near the current collector, and ions can be charged and discharged throughout the electrode layer 2. However, since the electrode layer 2 has conventionally increased the packing density by making the diameters of the electrode active material particles and the conductive material wide and dense from large to small, the electrolyte required for charging and discharging is contained in the electrode layer. However, even if the electrode layer was thickened, a large-capacity battery could not be obtained.

  The average particle diameter of the space forming particles 52 is larger than the average particle diameter of the conductive material mixed electrode active material particles 51, and preferably the average particle diameter is twice or more. If it is 2 times or more, the volume is 8 times or more, and the amount of electrolyte entering the space formed between adjacent space-forming particles can be increased. More preferably, the average particle size is 3 times or more. In that case, the average particle diameter of the space-forming particles is 10 μm or more, and the average particle diameter of the electrode active material particles is 3 μm or less. Alternatively, the average particle diameter of the space-forming particles is 5 μm or more, and the average particle diameter of the electrode active material particles is 1 μm or less. Alternatively, the average particle diameter of the space forming particles is 10 μm or more, and the average particle diameter of the electrode active material particles is 0.5 μm or less. When the electrode layer 22 is formed without using the space forming particles 52, the conductive material mixed electrode active material particles 51 become denser and the electrolyte becomes difficult to enter as the conductive material mixed electrode active material particles 51 have a smaller particle size. However, when the space-forming particles 52 are inserted, the conductive material mixed active material particles 51 cling around the space-forming particles 52, and a large space is formed between the adjacent space-forming particles 52, 52, and the electrolytic solution enters. It becomes easy. Moreover, since the amount of particles having a small particle size and a large surface area can be reduced with respect to the proportion of the space to be formed, the amount of the binder and the paste to be applied to the current collector 21 when the electrode layer 2 is formed. The amount of solvent to be reduced can be reduced relative to the proportion of space formed.

The space-forming particles 52 are preferably those that are not corroded by a substance constituting the electrode such as an electrolytic solution, such as carbon particles and electrode active material particles, and those that can obtain a large particle size. Furthermore, what has electrical conductivity like a carbon particle is preferable. In the case of carbon particles, mesocarbon microbead (MCMB) particles that are one type of graphite are preferred.

(6) Current collector The current collector 21 is made of a material having extremely high conductivity. As the positive electrode current collector 21, an aluminum foil is generally used, and as the negative electrode current collector 21, for example, copper foil or metal (in the case of a Li battery, Li metal) is used.

In the aluminum foil, an oxide film is naturally formed on the surface when the electrode is manufactured. When assembled as a battery or a capacitor and an electrolyte is injected and a current flows, a passive film may be formed on the surface. The passive film can prevent the current collector from being corroded by the electrolytic solution, and can improve the corrosion resistance of the current collector. On the other hand, since the passive film has an insulating property, the current of the electrode is limited. However, when the carbon material is in contact with the passive film, the passive film near the carbon material element is in contact with the passive film. It is considered that point defects are generated in the film, and conductivity is increased. The current collector 21 may be formed with the electrode layer 22 on one side or the electrode layer 22 on both sides. Whether it is single-sided or double-sided depends on how the electrode structure 2 is used in the electrical component 1 of a battery or capacitor.

(7) Electrode layer The electrode layer 22 has conductive material mixed electrode active material particles 51, space-forming particles 52, and a binder such as PVDF, and exchanges ions with the electrolyte. The ratio of the amount of the conductive material mixed electrode active material particles 51 and the space forming particles 52 may be such that the conductive material mixed electrode active material particles 51 are attached to the surface of the space forming particles 52, and between the adjacent space forming particles. The electrolytic solution can enter the space to be formed, and the conductive material mixed electrode active material particles 51 are not densely arranged. The porosity of the electrode layer 22 is, for example, 10% to 30%. Alternatively, the ratio of the volume of the electrode layer 22 to be closed is 40% to 60% for the space forming particles 52 and 40% to 20% for the conductive material mixed electrode active material particles 51. Alternatively, the proportion of the electrode layer 22 in the weight is 60% to 90% by weight of the space-forming particles 52 and 40% to 10% by weight of the conductive material mixed electrode active material particles 51.

(8) Electrolytic substance The electrolytic substance is a gel or solid in addition to the electrolytic solution, and ions can move between the positive electrode structure and the negative electrode structure. For example, dibutyl ether, 1,2-dimethoxyethane and the like can be mentioned.

(9) Separator The separator 4 prevents electrical contact between positive and negative electrode structures and allows ions to pass through. For example, a porous material such as polyethylene or polypropylene can be used.

  Hereinafter, the manufacturing method of electroconductive material mixed electrode active material particle is demonstrated.

(1) Conductive material mixed electrode active material particle manufacturing apparatus An example of a conductive material mixed electrode active material particle manufacturing apparatus is shown in FIG. FIG. 2 shows an L-shaped manufacturing apparatus (horizontal rotation type). The manufacturing apparatus includes a barrel 6 that rotates horizontally. The barrel 6 includes an entrance / exit 61 having a lid 62. This manufacturing apparatus is driven by a driving device such as a motor. The electrode active material particles, the conductive material, and the hard sphere 63 are taken in and out from the doorway 61. As the hard sphere 63 of this device, one having a large weight is suitable. A fluidized plate 64 is disposed inside the barrel 6. As the hard sphere 63, a steel sphere, a stainless sphere, a ceramic sphere, a Teflon (registered trademark) lining sphere, or the like can be used.

(2) Method of Using Conductive Material Mixed Electrode Active Material Particle Manufacturing Apparatus Electrode active material particles and conductive material powder to be processed at a time are put into barrel 6. When the barrel 6 is rotated in the direction of the arrow, the electrode active material particles and the conductive material are rotated and mixed together with the hard sphere 63 by the fluidized plate 64 and the like, and dropped together with the hard sphere 63 to be stirred and mixed. Thereby, an impact force is applied to the electrode active material particles and the conductive material, the conductive material is mixed with the electrode active material particles, and the conductive material mixed electrode active material particles 51 are obtained. The lid 62 is opened and taken out from the entrance / exit 61.

(3) Micrograph An electron micrograph (SEM) of a powder of lithium manganate LiMn ₂ O _{4 used as} a raw material is shown in FIG. This electron micrograph has a magnification of 10,000, and a 1 μm line segment is shown in the photograph to indicate the size. FIG. 3A shows part of one particle of lithium manganate, and one particle has a shape in which a large number of small crystals are combined. The surface of each bonded small crystal represents a clean plane. The corners of each small crystal that is bonded are sharp, with each plane intersecting.

An electron micrograph (SEM) of the treated conductive material mixed electrode active material 51 powder is shown in FIG. This electron micrograph has a magnification of 20,000 times, and a 1 μm line segment is shown in the photograph to indicate the size. In FIG. 3B, the surface of the lithium manganate is in a cotton-like state, which is different from the surface state before the treatment. A myriad of cotton-like conductive materials are mixed around lithium manganate. In particular, it seems that innumerable cotton-like conductive materials are attached to or electrically connected to the surfaces of the particles which are reduced by collision and destruction of the lithium manganate with the hard sphere. For example, when the conductive material mixed electrode active material 51 is used for the electrode layer 22, this cotton-like conductive material increases the conductivity between the electrode active material and the electrode active material, and the surface of the electrode active material is Since it is not coated with respect to the entry / exit of ions, the characteristics and functions as an electrode active material can be sufficiently extracted. Thereby, electrical conductivity can be raised, without using a lot of electrically conductive materials. As a result, when the electrode layer 22 is formed, the amount of the binder can be reduced without the binder being absorbed in a large amount by the conductive material.

  Hereinafter, examples of the lithium secondary battery will be described.

(1) Example 1
The conductive material mixed electrode active material particles 51 are prepared by mixing and pulverizing lithium manganate LM-9 (manufactured by JGC Chemical Co., Ltd.) as a positive electrode active material and Kettin Black (Ketchin Black International) as a conductive material. Lithium manganate LM-9 and Kettin Black (KB) are mixed at a weight ratio of 100 g: 20 g.

Conductive material mixed electrode active material particles (average particle size 0.3 μm) 51, carbon particles (average particle size 10 μm to 15 μm) which are space forming particles 52 (MCMB: manufactured by Osaka Gas Chemical Co., Ltd.), and PVDF which is a binder (Kureha Chemical Industry Co., Ltd.) and NMP (N-methyl 2-pyrrolidone) as a solvent are stirred with a mixer to form a mixture. Conductive material mixed electrode active material particles 51, carbon particles, and PVDF are mixed at a weight ratio of 10 g: 10 g: 2 g. The mixture is applied to an aluminum foil (made by Showa Denko KK), which is a current collector 21, with a thickness of approximately 25 μm by the doctor blade method. This is dried and rolled with a pressing device to form a positive electrode layer of approximately 20 μm to 21 μm on the current collector to produce a positive electrode structure. The conductive material mixed electrode active material particles 51 have a large particle diameter so as to be easily seen in FIG. 3B, but the average particle diameter is 0.3 μm.

(2) Example 2
In Example 2, lithium manganate LM-45 (average particle size: 15.8 μm) (manufactured by JGC Chemical Co., Ltd.) is used instead of the carbon particles of Example 1. The mixing ratio of these components is also the same. Conductive material mixed electrode active material particles, lithium manganate, and PVDF are mixed at a weight ratio of 10 g: 10 g: 2 g. The mixture is applied to an aluminum foil (manufactured by Showa Denko KK) as a current collector in a thickness of 25 μm by the doctor blade method. This is dried and rolled with a pressing device to form a positive electrode layer of approximately 20 μm to 21 μm on the current collector to produce a positive electrode structure.

(3) Lithium secondary battery As the lithium secondary battery, a hockey pack cell battery (HS cell: manufactured by Hosen Co., Ltd.) is used. The positive electrode is formed by punching a positive electrode layer 22 formed on the surface of the aluminum foil 21 into a circular coin shape. For example, as shown in FIG. 4, the positive electrode and the coin-shaped lithium metal 2 as a negative electrode are arranged to face each other with a separator 4 interposed therebetween. This is placed in the container of the hockey pack cell. Next, an electrolytic solution LiClO ₄ is injected into the container to produce a lithium secondary battery.

(4) Charging / discharging curve of lithium secondary battery The batteries of Examples 1 and 2 are charged. As a charging method, charging is performed at a C rate of 1 C as initial charging, charging is performed at a constant current, and then charging is performed at a constant voltage. This operation is repeated 4 times. When the initial capacity is stabilized, the battery is charged at a C rate of 1C, and when charging is completed, the battery is discharged at a C rate of 10C, 20C,. In addition, 1C means the speed of charging / discharging when the theoretical battery capacity is charged or discharged in one hour.

  The discharge characteristics of Examples 1 and 2 are shown in FIGS. In FIG. 5, the triangle marks indicate the characteristics of the first embodiment, and the circle marks indicate the characteristics of the second embodiment. FIG. 5A shows the ratio (%) of the discharge characteristic with 100% when the C rate is 1, and FIG. 5B shows the measured current amount (mAh). Example 1 shows that the change in the current amount is small with respect to the change in the C rate, and even when the C rate is close to 100, 50 to 60% of the charge amount can be taken out. On the other hand, Example 2 shows that when the C rate is small, a large amount of current can be extracted, and when the C rate is close to 100, 10% of the charged amount can be extracted. Since Example 2 uses an active material having a large diameter as the space-forming particles 52, it can be understood that a large current can be taken out because more active material is used than in Example 1. However, since the conductive material is not attached to the surface of the large-diameter active material like the conductive material mixed electrode active material particles 51, the amount of current decreases rapidly when the C rate is around 30-50. ing. When the C rate is close to 100, Example 2 shows that the amount of current is slightly smaller than that of Example 1, but can be taken out by the conductive material mixed electrode active material particles 51.

From this result, it can be seen that when the conductive material mixed electrode active material particles 51 and the space forming particles 52 are used in combination, extremely good characteristics can be obtained. Therefore, when a thick electrode active material layer is manufactured, a large amount of current can be obtained even if the C rate is increased. In particular, when carbon particles are used as the space forming particles 52, the electrolyte solution can be sufficiently filled and the conductivity can be further increased. When the electrode active material is used as the space forming particles 52, electrolysis can be achieved. The liquid can be sufficiently filled and a larger amount of current can be taken out.

Explanatory diagram of lithium secondary battery Illustration of conductive material mixed electrode active material particle manufacturing equipment Figure of micrograph of positive electrode active material and conductive material mixed electrode active material particles Illustration of a state in which a separator is interposed between a positive electrode and a negative electrode inside a hockey pack cell battery Explanatory diagram of battery discharge characteristics

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrical component of secondary battery or capacitor 2 ... Electrode structure 21 ... Current collector 22 ... Electrode layer 3 Electrolytic substance 4 Separator 51 ... Conductive material mixed active material 52・ Space forming particle 6... Barrel 61 of conductive material mixed electrode active material particle manufacturing apparatus ・ Barrel inlet / outlet 62 ・ Barrel lid 63 ・ Hard ball 64 ・ ・ Flow plate

Claims (7)

Current collector,
Conductive material mixed electrode active material particles in which a conductive material is attached around the electrode active material particles;
Space-forming particles having an average particle size that is at least twice as large as the average particle size of the conductive material mixed electrode active material particles;
With a binder,
An electrode structure in which an electrode layer is formed on the surface of a current collector with conductive material mixed electrode active material particles, space-forming particles, and a binder.
The electrode structure according to claim 1, wherein
Conductive material mixed electrode active material particles are formed by stirring and mixing electrode active material particles, conductive material, and hard spheres.
The electrode structure according to claim 1, wherein
An electrode structure in which the space-forming particles are carbon particles, the electrode active material of the conductive material mixed electrode active material particles is lithium manganate, and the conductive material of the conductive material mixed electrode active material particles is ketjen black.
The electrode structure according to claim 1, wherein
An electrode structure in which the space-forming particles are lithium manganate particles, the electrode active material of the conductive material mixed electrode active material particles is lithium manganate, and the conductive material of the conductive material mixed electrode active material particles is ketjen black.
A secondary battery in which the electrode structure according to claim 1 is used as a negative electrode, and the electrode structure is filled with an electrolytic solution.
A secondary battery in which the electrode structure according to claim 1 is used for a positive electrode and a negative electrode, and an electrolyte solution is filled in the electrode structure.
A capacitor, wherein the electrode structure according to claim 1 is used for a positive electrode and a negative electrode, and an electrolyte solution is filled in the electrode structure.