JP5190916B2 - Composite powder for electrode and method for producing the same - Google Patents

Description

  The present invention relates to a composite powder for electrodes and a method for producing the same.

  With the development of various devices and systems in recent years, there is an increasing demand for higher performance of batteries (primary batteries, secondary batteries, fuel cells, capacitors, etc.) as power sources. For example, lithium secondary batteries are widely used as high energy density secondary batteries that power electronic devices such as portable communication devices and laptop computers, and are used for driving motors in automobiles from the viewpoint of reducing environmental impact. It is also expected as a battery. For this reason, development of a lithium secondary battery having a high output and a high energy density corresponding to the high performance of these devices is required.

In particular, for vehicles, good charge / discharge characteristics at a high current density are required, but there is a problem that capacity deterioration and cycle deterioration occur when charge / discharge is repeated at a high current density. For example, an in-vehicle lithium secondary battery that uses aluminum-added lithium nickel cobalt oxide (LiNi _0.8 Co _0.15 Al _0.05 O ₂ ) as a positive electrode active material is well known. Such an in-vehicle lithium secondary battery has a large theoretical capacity of about 260 mAh / g. However, it has been pointed out that when charging / discharging is repeated at a high current density in an environment of 60 ° C., the electrical resistance of the positive electrode increases to cause cycle deterioration (Non-Patent Document 1).

  As the cause of the capacity deterioration and cycle deterioration, for example, the following reasons can be considered. That is, the conductive material may be separated from the electrode active material or the conductive network between the conductive materials may be disconnected due to the expansion / contraction of the electrode active material due to lithium desorption / insertion when charging / discharging is repeated at a high current density. Therefore, it is considered that the distribution of the conductive material becomes non-uniform (Non-Patent Document 2).

  In order to improve the above problems, (1) the electrode active material is atomized to shorten the diffusion distance of lithium ions in the electrode and increase the utilization of the active material. (2) The electrode active material is coated with a conductive material or Various methods have been considered, such as bonding to alleviate non-uniform distribution of the conductive material, and (3) strengthening the bonding between the conductive materials to maintain the conductive network.

  For example, in Patent Document 1, an electrode active material and a conductive material are mixed and subjected to a current treatment at a temperature of about 200 to 800 ° C. under a pressure of up to about 50 MPa using a graphite mold material. Is disclosed. This technique corresponds to the above (2), and the electrode active material and the conductive material are joined to alleviate the uneven distribution of the conductive material.

So far, the charge / discharge characteristics at high current density have been gradually improved, but in order to follow the high performance of various devices, further improvement of charge / discharge characteristics at high current density is required. . In order to meet such a demand, development of a technique for further strengthening the conductive network by further strengthening the bonding strength between the electrode active material and the conductive material is desired.
JP 2005-135723 A Y. Itou and Y. Ukyo, J. Power Sources, 146, 39 (2005). X. Zhang, PNRoss, Jr., R. Kostecki, F. Kong, S. Sloop, JBKerr, K. Striebel, EJCairns, and F. McLarnon, J. Electrochem. Soc., 148, A463 (2001).

The present invention can obtain an electrode with improved charge / discharge characteristics at a high current density without reducing the weight energy density and volume energy density, and the bonding strength between the electrode active material and the conductive material is improved. It aims at providing the composite powder for electrodes, and its manufacturing method.

  As a result of intensive studies, the present inventor has provided a raw material mixture containing a conductive material and an electrode active material to a mechanofusion process that applies at least a compressive force and a shearing force, whereby the electrode active material and the conductive material The present inventors have found that the above-mentioned object can be achieved by binding in advance and conducting current sintering under specific conditions, and have completed the present invention.

That is, this invention relates to the following composite powder for electrodes, and its manufacturing method.
1. A composite powder for an electrode having a structure in which electrode active materials are joined via a conductive material, the composite powder for an electrode,
(1) The electrode active material and the conductive material are previously bound by subjecting the raw material mixture containing the electrode active material and the conductive material to mechanofusion treatment,
(2) A composite powder for an electrode obtained by filling the raw material mixture after the binding into a conductive mold and sintering it by applying a direct current pulse current under a pressure of 60 MPa or more.
2. The composite powder for an electrode according to Item 1, wherein in the mechanofusion treatment, at least a compressive force and a shearing force are applied to the raw material mixture to bind the electrode active material and the conductive material. 3. The mechanofusion process is a process using a mechanofusion apparatus including a rotating casing and an inner piece fixed in the casing,
(1) The gap distance between the casing and the inner piece is 0.1 to 10 mm,
(2) When the raw material mixture is supplied into the casing, the raw material mixture is pressed against the inner wall surface of the casing by centrifugal force, and at least a compressive force and a shearing force are applied between the inner piece and the inner wall surface. The electrode active material and the conductive material are bound together,
(3) The composite powder for an electrode according to item 1, wherein the treatment is performed by rotating the casing at a speed of 1000 to 8000 rpm for 1 to 30 minutes after supplying the raw material mixture into the casing.
4). The composite powder for an electrode according to any one of Items 1 to 3, wherein the conductive mold contains tungsten carbide.
5. Item 5. The composite powder for an electrode according to any one of Items 1 to 4, wherein a DC pulse current is applied under a pressure of 150 MPa or more.
6). The electrode active material is composed of 1) a lithium-containing compound having an olivine structure, 2) a lithium-containing compound having a rock salt-like structure having a layered rock salt type or cubic rock salt type crystal structure, and 3) a lithium containing compound having a spinel structure. Item 6. The composite powder for an electrode according to any one of Items 1 to 5, which is at least one positive electrode active material selected from the group consisting of:
7). The electrode active material is lithium iron phosphate; lithium iron phosphate in which at least one selected from the group consisting of cobalt, manganese, and nickel is dissolved; lithium cobalt phosphate; at least one of manganese and nickel is in solid solution Cobalt lithium phosphate; lithium manganese phosphate; lithium manganese phosphate in solid solution; nickel lithium phosphate; lithium nickelate; lithium nickelate in solid solution of at least one of cobalt and aluminum; lithium cobaltate; iron At least one positive electrode active material selected from the group consisting of lithium acid; lithium ironate in which at least one of titanium and manganese is dissolved; lithium titanate; lithium manganate; and lithium manganate in which chromium is dissolved For an electrode according to any one of Items 1 to 5, If powder.
8). The electrode active material includes carbon, silicon, germanium, tin, lead, antimony, aluminum, indium, lithium, tin oxide, lithium titanate, lithium nitride, indium tin oxide, indium-tin alloy, lithium-aluminum. Item 6. The composite powder for an electrode according to any one of Items 1 to 5, which is at least one negative electrode active material selected from the group consisting of an alloy and a lithium-indium alloy.
9. A primary battery, a secondary battery, a fuel cell or a capacitor, comprising an electrode containing the composite powder for an electrode according to any one of Items 1 to 8.
10. A method for producing a composite powder for an electrode having a structure in which electrode active materials are joined together via a conductive material,
(1) The electrode active material and the conductive material are previously bound by subjecting the raw material mixture containing the electrode active material and the conductive material to mechanofusion treatment,
(2) A manufacturing method comprising filling the raw material mixture after the binding into a conductive mold and applying a direct current pulse current under a pressure of 60 MPa or more to sinter.
11. The manufacturing method according to Item 10, wherein in the mechanofusion treatment, at least a compressive force and a shearing force are applied to the raw material mixture to bind the electrode active material and the conductive material.
12 The mechanofusion process is a process using a mechanofusion apparatus including a rotating casing and an inner piece fixed in the casing,
(1) The gap distance between the casing and the inner piece is 0.1 to 10 mm,
(2) When the raw material mixture is supplied into the casing, the raw material mixture is pressed against the inner wall surface of the casing by centrifugal force, and at least a compressive force and a shearing force are applied between the inner piece and the inner wall surface. The electrode active material and the conductive material are bound together,
(3) The manufacturing method according to Item 10, wherein the treatment is performed by rotating the casing at a speed of 1000 to 8000 rpm for 1 to 30 minutes after supplying the raw material mixture into the casing.

Hereinafter, the composite powder for electrodes of the present invention and the production method thereof will be described in detail.

1. Electrode Composite Powder The electrode composite powder of the present invention is an electrode composite powder having a structure in which electrode active materials are joined together via a conductive material. As the structure, for example, a structure in which a conductive material adheres to the surface or electrode active materials covered with the conductive material are joined to each other can be given.

The composite powder for an electrode of the present invention having the above structure is
(1) The electrode active material and the conductive material are previously bound by subjecting the raw material mixture containing the electrode active material and the conductive material to mechanofusion treatment,
(2) It is obtained by filling the raw material mixture after the binding into a conductive mold and sintering it by applying a direct current pulse current under a pressure of 60 MPa or more.

  Since the composite powder for electrodes of the present invention is obtained by subjecting the raw material mixture to electro-sintering under a pressure of 60 MPa or more after the mechanofusion treatment, the bonding strength between the electrode active material and the conductive material is large, thereby the electrode active material. And the conductive network of the conductive material is strong. Such a composite powder for an electrode is useful as an electrode powder that can be applied to various batteries and capacitors because the conductive network is hardly damaged even when charging and discharging are repeated at a high current density. The composite powder for electrodes of the present invention is particularly useful for lithium secondary batteries.

  Hereinafter, the electrode composite powder of the present invention will be described with reference to the case where it is applied as an electrode material for a lithium secondary battery.

≪Electrode active material≫
It does not specifically limit as an electrode active material, The positive electrode and negative electrode active material conventionally applied to the battery and the capacitor can be used.

As specific examples of the electrode active material for lithium secondary battery, as the positive electrode active material, for example,
1) Lithium-containing compound having an olivine type structure,
2) Lithium-containing compounds having a rock salt related structure having a layered rock salt type or cubic rock salt type crystal structure,
3) a lithium-containing compound having a spinel structure,
Etc.

  Specifically, 1) Examples of lithium-containing compounds having an olivine type structure include lithium iron phosphate; lithium iron phosphate in which at least one of cobalt, manganese and nickel is dissolved; lithium cobalt phosphate; manganese and nickel And lithium cobalt phosphate in which at least one of them is dissolved; lithium manganese phosphate; lithium manganese phosphate in which nickel is dissolved, and lithium nickel phosphate.

  2) Examples of the lithium-containing compound having a rock salt-like structure having a layered rock salt type or cubic rock salt type crystal structure include lithium nickelate; lithium nickelate in which at least one of cobalt and aluminum is dissolved; lithium cobaltate; Examples thereof include lithium ferrate; lithium ferrate in which at least one of titanium and manganese is dissolved, lithium titanate, and the like.

  3) Examples of the lithium-containing compound having a spinel structure include lithium manganate; and lithium manganate in which chromium is dissolved.

  These positive electrode active materials can be used individually or in mixture of 2 or more types. In the present invention, by optimizing the manufacturing conditions of the composite powder for electrodes, even when a transition metal capable of taking an expensive number such as nickel, cobalt, manganese, etc. is used as an active material, the conductive material and the conductive material are strongly suppressed while suppressing the reduction. To form a composite powder for an electrode.

  Examples of the negative electrode active material include carbon, silicon, germanium, tin, lead, antimony, aluminum, indium, lithium, tin oxide, lithium titanate, lithium nitride, indium-dissolved tin oxide, indium-tin alloy, lithium -Aluminum alloy, lithium-indium alloy, etc. are mentioned. The negative electrode active materials can be used alone or in combination of two or more.

  A commercially available electrode active material may be used, but it can also be prepared. For example, lithium cobaltate can be prepared by a method in which cobalt carbonate and lithium carbonate are mixed and baked at 800 to 1000 ° C.

The iron-containing lithium manganate can be prepared, for example, by the following procedure. _{That, Fe (NO 3) 3 ·} 9H 2 and O and MnCl ₂ · 4H ₂ O mixed aqueous solution starting material, LiOH in water were kept at -10 ° C. - dropping to coprecipitate ethanol mixed solution After preparation, the precipitate is aged. LiOH.H ₂ O, KOH and KClO ₃ are added to the precipitate and mixed in distilled water, followed by hydrothermal treatment at 220 ° C. for 5 hours. After washing with water, the resulting precipitate and LiOH aqueous solution are mixed, dried, heated to 850 ° C. over 1 hour, and held for 1 minute. The fired product is washed, filtered, and dried to obtain iron-containing lithium manganate (for example, M. Tabuchi, Y.
Nabeshima, K. Ado, M. Shikano, H. Kageyama, and K. Tatsumi, IMLB 2006 Meeting Abstracts # 5 (2006)).

  The average particle size of the electrode active material (average particle size in the composite powder for electrodes) is not limited, but is preferably about 0.01 to 50 μm, more preferably about 0.02 to 30 μm. The average particle diameter of the electrode active material is approximately the same before and after being subjected to mechanofusion treatment and current sintering.

≪Conductive material≫
The conductive material (electron conductive powder) is not limited as long as it is a material having electronic conductivity. For example, carbon, a carbon-based conductive compound, iron, an alloy containing iron, copper, an alloy containing copper, aluminum, Examples thereof include alloys containing aluminum, iron oxide, and solid solutions having iron oxide as an end component. As a conductive material, these materials can be used alone or in combination of two or more.

  Among the conductive materials described above, the carbon-based conductive compound is a compound mainly having an electron conduction path such as a benzene skeleton and having carbon as a main component. For example, polyacene, polyparaphenylene, polythiophene and the like can be mentioned.

  Among the alloys, examples of the alloy containing iron include an Fe—Cr alloy, an Fe—Ni alloy, and an Fe—Mg alloy. Examples of the alloy containing copper include a Ni—Cu alloy, a Cu—Sn alloy, and a Cu—Zn alloy. Examples of the alloy containing aluminum include an Al—Zn alloy, an Al—Cu alloy, and an Al—Mg alloy. The ratio of each component in the alloy is not particularly limited and can be set as appropriate.

  As a solid solution having iron oxide as an end component, for example, a solid solution of iron, Zn, Mn, Ni, Al, Ti, Co or the like can be cited. The amount of solid solution is not particularly limited, and can be set as appropriate.

  Among the conductive materials, a carbon material is preferable. For example, acetylene black (AB) powder can be suitably used.

  The average particle diameter of the conductive material (average particle diameter in the composite powder for electrodes) is not limited, but is preferably about 0.005 to 10 μm, and more preferably about 0.01 to 1 μm. In addition, the average particle diameter of this electrically conductive material is substantially the same before and after the mechano-fusion treatment performed on the mixture with the electrode active material and the electric current sintering. The conductive material content in the composite powder for electrodes is preferably about 0.01 to 30% by weight, more preferably about 0.02 to 25% by weight.

≪Electrode composite powder≫
The composite powder for electrodes of the present invention has a structure in which the electrode active materials are joined via the conductive material. For example, there is a structure in which electrode active materials attached to the surface or covered with the conductive material are joined to each other.

The density of such composite powder for electrodes is not limited, but for example, the tap density is preferably 0.8 g / cm ³ or more, and more preferably 1 g / cm ³ or more. In addition, the tap density in this specification is a density measured after putting about 0.2 g of a sample (here, composite powder for electrodes) into a 25 ml graduated cylinder and tapping 100 times.

  The electrode composite powder of the present invention has a strong bonding strength (a strong conductive network) in the relationship between the electrode active material and the conductive material. The electrode active materials are joined to each other through a conductive material. Such a composite powder for electrodes is useful as an electrode material for various batteries and capacitors, and it is possible to produce an electrode with improved charge / discharge characteristics at a high current density without lowering the weight energy density and volume energy density. Can do.

  Specifically, the composite powder for electrodes of the present invention is useful as an electrode powder for primary batteries, secondary batteries, fuel cells, and capacitors.

  For example, when applied to an organic electrolyte battery, a positive electrode sheet and / or a negative electrode sheet are obtained after forming a layer made of a composite powder for electrodes on a metal foil (or metal mesh), and then the positive electrode sheet and the negative electrode By sandwiching a separator soaked with an electrolyte solution with a sheet, a lithium secondary battery excellent in charge / discharge cycle characteristics exhibiting a high capacity at a high current density can be produced. The electrode composite powder layer can be more easily formed on the metal foil (or metal mesh) by kneading a binder (for example, polyvinylidene fluoride) in the electrode composite powder.

  For example, when producing an organic electrolyte lithium secondary battery, an electrode mixture is formed by kneading a composite powder for an electrode and a binder (for example, polyvinylidene fluoride, etc.), and a positive electrode sheet and / or a negative electrode After the sheet is obtained, a lithium secondary battery excellent in charge / discharge cycle characteristics exhibiting a high capacity at a high current density can be produced by sandwiching a separator impregnated with an electrolytic solution between the positive electrode sheet and the negative electrode sheet.

2. Method for producing composite powder for electrode The method for producing a composite powder for an electrode of the present invention comprises:
(1) The electrode active material and the conductive material are previously bound by subjecting the raw material mixture containing the electrode active material and the conductive material to mechanofusion treatment,
(2) A step of filling the raw material mixture after the binding into a conductive mold, and applying a direct current pulse current under a pressure of 60 MPa or more to sinter.

  As a mixing ratio of the electrode active material and the conductive material in the raw material mixture, the amount of the conductive material may be 0.01 to 30% by weight of the total amount of the electrode active material and the conductive material, and 0.02 to 25% by weight. % Is preferred. When the amount of the conductive material is less than 0.01% by weight, the improvement of the electron conductivity of the electrode active material becomes insufficient, and good charge / discharge cycle characteristics may not be obtained. If it is 30% by weight or more, the weight output density and the volume output density of the battery decrease with a decrease in the weight ratio and volume ratio of the electrode active material, which is not preferable.

≪Mechanofusion process≫
The mechanofusion process is a process in which mechanical energy (mechanical strain force) is applied between a plurality of different particles to bind the different particles. In the present invention, at least a compression force and a shear force are applied to the raw material mixture. This is a process for binding the electrode active material and the conductive material.

  The above processing is usually performed by a mechanofusion apparatus as shown in the schematic diagram of FIG. The apparatus of FIG. 4 includes a casing (container) 1 that can rotate at high speed, a semi-cylindrical inner piece 2 (friction member), and a scraper 3 (scraping member) fixed inside the casing. 4 in FIG. 4 is a raw material mixture. Although not shown in FIG. 4, a cooler may be installed so as to surround the casing in order to prevent abnormal temperature rise due to frictional heat.

  When the raw material mixture is supplied into the casing 1 and the casing 1 is rotated at a high speed, the raw material mixture is pressed against the inner wall surface of the casing 1 by centrifugal force to form the layer 4. Although the rotation conditions of the casing 1 are not limited, 1000-8000 rpm is preferable and 2000-7000 rpm is more preferable. While the casing 1 is rotating, the raw material mixture receives at least a compressive force and a shearing force in a gap (clearance) between the inner piece 2 and the casing 1. The raw material mixture subjected to the mechanical strain is scraped off by the scraper 3 and mixed with the raw material mixture 4 again. By repeating this process continuously, the dispersibility of the electrode active material and the conductive material is made uniform, and the two are gradually strongly bonded.

  The clearance is preferably about 0.1 to 10 mm, and more preferably about 0.2 to 8 mm. Moreover, although processing time is set according to rotation conditions, about 1 to 30 minutes are preferable and about 1 to 25 minutes are more preferable. If the rotational speed is less than 1000 rpm or the processing time is less than 1 minute, the degree of binding may be insufficient. On the other hand, when the rotational speed exceeds 8000 rpm or the processing time exceeds 30 minutes, there is a possibility that the electrode active material or the conductive material is excessively deformed or modified due to a temperature rise.

  Examples of the mechanofusion apparatus include a powder and particle processing apparatus described in Japanese Patent Application Laid-Open No. 63-42728. Specifically, a mechanofusion system manufactured by Hosokawa Micron Corporation is suitable.

≪Electrical sintering method≫
The electric current sintering method (electric current joining method) may be a pressure sintering method in which a direct current pulse current referred to as a discharge plasma sintering method, a discharge sintering method, a plasma activated sintering method or the like is applied. Specifically, any material may be used as long as it conducts current sintering under pressure by filling a predetermined mold with a conductive mold and applying a pulsed ON-OFF direct current while applying pressure. Such an electric sintering apparatus and its operating principle are disclosed in, for example, Japanese Patent Laid-Open No. 10-251070.

  A schematic diagram of the spark plasma sintering machine is shown in FIG. A discharge plasma sintering machine 1 shown in FIG. 5 includes a die (die) 3 on which a sample 2 is loaded and a pair of upper and lower punches 4 and 5. The punches 4 and 5 are supported by punch electrodes 6 and 7, respectively, and a pulse current can be supplied through the punch electrodes 6 and 7 while pressing the sample 2 loaded on the die 3 as necessary. A pulse current is preferable as the type of current applied to the sample 2. The sample 2 and its vicinity (the die 3 and the upper and lower punches 4 and 5) are heated by pulse energization, and an energized sintered body is obtained by the effects of both the heating and the pulse current.

  Hereinafter, specific description will be given of a means for conducting current sintering under a pressure of 60 MPa or more after filling an electrode active material and a binder powder of a conductive material (also referred to as a “binding mixture”) into an electron conductive mold of the current sintering machine. I will explain it.

  The electron conductive mold used for the energization treatment is not particularly limited as long as it has electron conductivity and can withstand pressure conditions of 60 MPa or more. For example, tungsten carbide, iron, copper, an aluminum alloy (for example, an Al—Cu—Mg alloy) or the like can be preferably used. Among the above mold materials, tungsten carbide (WC) is a cemented carbide mold material, so that it has high pressure resistance and is preferable from the viewpoint of easily suppressing reduction of the electrode active material during current sintering.

  By applying a direct current pulse current to the electron conductive mold material, it is possible to utilize the discharge phenomenon generated in the particle gap of the filled binding mixture, and to activate the purification of the particle surface by discharge plasma, discharge impact pressure, etc. and the electric field. The generated electric field diffusion effect, the thermal diffusion effect due to Joule heat, the plastic deformation pressure due to pressurization, etc. serve as the driving force for particle bonding, and the electrode active materials are bonded together via the conductive material. Specifically, when a pulse current is applied, a part of the conductive material is vaporized and adheres (covers) to the surface of the electrode active material, and the conductive material in the form of particles adheres to it, which continuously occurs. Thus, the electrode active material is firmly bonded via the conductive material. Although it is conceivable that only a part of the electrode active material is sintered, it is considered that the electrode active materials are joined together via a conductive material rather than being sintered adjacent to each other.

  As a condition for supplying current, a current of 60 MPa or higher is applied to the binder mixture (under pressure). It is preferable to supply a pulse current. The pressure is 60 MPa or more, but 150 MPa or more (for example, 150 to 1000 MPa) or 300 MPa or more (for example, 300 to 1000 MPa) is more preferable. It may be 500 MPa or more (for example, 500 to 1000 MPa) as long as the pressure resistance condition is provided. In order to achieve sufficient bonding between the electrode active material and the conductive material, high pressure conditions are desirable, but the upper limit is about 50000 MPa.

  Further, the temperature of the die 3 (see FIG. 5) at the time of supplying current to the binding mixture can be appropriately selected according to the type and particle size of the electrode active material and the conductive material, but is usually 100 to 800. ° C, preferably about 150 to 700 ° C. If it is less than 100 degreeC, joining of an electrode active material and a electrically conductive material may become inadequate. Above 800 ° C., the electrode active material may be decomposed by reduction of the conductive material or the electron conductive mold material, which is not preferable. Therefore, heating at about 150 to 700 ° C. is preferable.

  The pulse current applied for heating may be a pulsed ON / OFF direct current having a pulse width of about 2 to 3 milliseconds and a period of about 3 Hz to 300 kHz. The current value varies depending on the type and size of the mold material. For example, about 300 to 1000 A is preferable when a tungsten carbide mold material having an inner diameter of 10 mm is used, and about 500 to 3000 A is preferable when a mold material having an inner diameter of 20 mm is used. During processing, the current value may be increased or decreased while monitoring the mold temperature, and the current value may be controlled so that a predetermined temperature can be managed, or the input electric energy amount (Wh value) may be controlled.

  The sintering time by electric current sintering varies depending on the amount of the binder mixture to be used, the sintering temperature, etc., and thus cannot be specified in general, but usually it should be kept in the above heating temperature range for about 1 minute to 2 hours. .

  In the electrode composite material of the present invention thus obtained, the weight ratio of the conductive material to the electrode composite material is about 1: 0.0001 to 0.3, preferably 1: 0.0002 to 0.25. Degree.

  The mixed powder that has been subjected to the electric current sintering treatment at a predetermined temperature is cooled, taken out from the mold material, and lightly pulverized with a mortar or the like, whereby the electrode active material to which the conductive material is bonded can be recovered. When a large amount of bonding processing is performed, the above process may be scaled up using a large mold material. Thus, the composite powder for electrodes of the present invention is obtained.

  In the above description, the method for producing the composite powder for an electrode by treating the binder mixture of the electrode active material and the conductive material by the electric current sintering method has been described. Incidentally, 1) a sheet obtained by winding the above-mentioned electrode active material and conductive material binding layer on a metal foil (or metal mesh), and a roll obtained by winding the sheet of the above 1) is electro-baked. In the case of processing by the sintering method, it is possible to efficiently produce an electrode material in which the composite powder for electrodes of the present invention adheres in layers on a metal foil. When a binder (for example, polyvinylidene fluoride) is added to the mixed powder, it becomes easier to form a composite powder layer for an electrode on a metal foil (or metal mesh). The addition amount of the binder is not particularly limited, and may be appropriately adjusted according to the types of the electrode active material and the conductive material. Normally, the binder is removed by electric sintering, but if it remains in a carbonized state, it may be handled in the same manner as the conductive material in the present invention.

  Since the composite powder for electrodes of the present invention is obtained by subjecting the raw material mixture to electro-sintering under a pressure of 60 MPa or more after the mechanofusion treatment, the bonding strength between the electrode active material and the conductive material is large, thereby the electrode active material. And the conductive network of the conductive material is strong. Such a composite powder for an electrode is useful as an electrode powder that can be applied to various batteries and capacitors because the conductive network is hardly damaged even when charging and discharging are repeated at a high current density. The composite powder for electrodes of the present invention is particularly useful for lithium secondary batteries.

  The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the examples.

Example 1
Iron-containing Li ₂ MnO ₃ (compositional formula Li _1.2 Fe _0.4 Mn _0.4 O ₂ ) was synthesized.

First, (a molar ratio of Fe: Mn = 1: 1) Fe (NO 3) 3 · 9H 2 O and MnCl ₂ · 4H ₂ O mixed aqueous solution of a starting material, LiOH in which this is controlled to -10 ° C. A coprecipitate was prepared by dropping into a water-ethanol mixed solution. Thereafter, the precipitate was aged overnight by stirring while sending air bubbles to the mixed solution. After filtration, LiOH.H ₂ O, KOH and KClO ₃ were added to the resulting coprecipitate and mixed in distilled water, followed by hydrothermal treatment at 220 ° C. for 5 hours. After washing with water, the resulting precipitate and a LiOH aqueous solution were mixed, dried, heated to 850 ° C. over 1 hour, and held for 1 minute. The fired product was washed, filtered, and dried to obtain the target iron-containing lithium manganate (Li _1.2 Fe _0.4 Mn _0.4 O ₂ ).

The iron-containing Li ₂ MnO ₃ was used as an electrode active material, a commercially available acetylene black (AB) powder was used as a conductive material, and both were mixed at a weight ratio of 97: 3 to obtain a raw material mixture. The specific surface area of the electrode active material was 21.8 m ² / g, and the spherical equivalent particle size was about 0.05 μm. The specific surface area of AB powder was about 70 m ² / g, and the spherical equivalent particle size was about 0.04 μm. Next, the raw material mixture was put into a mechanofusion apparatus AMS-Mini manufactured by Hosokawa Micron Co., Ltd., and a mechanofusion treatment was performed for 2 minutes with a clearance of 1 mm and a casing rotational speed of 6970 rpm.

Next, the bonded raw material mixture was filled in a WC type material having an inner diameter of 10 mm, set in an electric current sintering machine, depressurized to about 20 Pa, and then introduced with nitrogen gas to atmospheric pressure. Next, a pulse current of about 400 A (ON-OFF DC current with a pulse width of 2.5 milliseconds, cycle 29 Hz) was applied while the WC mold was pressed at about 500 MPa. The vicinity of the WC mold was heated at a heating rate of about 50 ° C./min, and reached 270 ° C. about 5 minutes after the start of pulse current application. After holding at this temperature for about 20 minutes, the current application and pressurization were stopped and the mixture was allowed to cool naturally. After cooling to room temperature, Li _1.2 Fe _0.4 Mn _0.4 O ₂ —AB composite powder (sintered body) was taken out of the mold material to obtain electrode powder.

  The composite powder is black, and in the X-ray diffraction pattern, a broad halo derived from AB is observed in the vicinity of 2θ = 26 °, and the other peaks are hexagonal layered rock salt type iron-containing lithium manganate unit cells (space Index was possible with group R3m).

≪Charge / discharge characteristics≫
Using the electrode powder as a positive electrode material of a lithium secondary battery, using lithium metal as a negative electrode, aluminum mesh as a current collector, and LiPF ₆ dissolved in an ethylene carbonate / dimethyl carbonate mixture as an electrolyte, A charge / discharge test was conducted by constant current measurement at a current density of 42.5 mA / g (1/3 C) to 3825 mA / g (30 C) and a cutoff of 2.0 to 4.8 V.

  FIG. 1 shows the discharge capacity of the lithium secondary battery as the capacity maintenance rate at each rate when the capacity at 1/3 C is 100%. At a rate of less than 5C, the case of only mechanofusion processing (Comparative Example 1), the case of only energization processing (Comparative Example 2), and the case of not performing any of mechanofusion and electroconductive sintering processing (Comparative Example 3) Although almost the same capacity was shown, an increase in capacity was recognized at a high current density of 5 C or more compared to these three cases. FIG. 2 shows discharge curves at 1C, 5C, and 20C, all of which have a higher discharge capacity than the three comparative examples, and are particularly characterized by a high discharge average potential at a high current density of 5C or more. -It suggests that the bonding between the conductive materials is good and the electron conductivity is sufficiently secured.

  From the above, it can be seen that the composite powder for an electrode of the present invention can be suitably used as a positive electrode material of a lithium secondary battery having a high current density and a high energy density and having excellent rate characteristics.

Comparative Example 1 (no energization process)
The same electrode active material Li _1.2 Fe _0.4 Mn _0.4 O ₂ as in Example 1 was used, and this and AB were weighed at a weight ratio of 97: 3. Mechanofusion treatment was performed for a minute.

  Using the obtained powder, a lithium secondary battery was produced in exactly the same manner as in Example 1, and a charge / discharge test was performed under the same conditions. As a result, as shown in FIGS. 1 and 2, although some increase in discharge capacity and average discharge voltage is recognized as compared with the case where the mechanofusion treatment is not performed (Comparative Example 3), the increase effect is as high as in the case of Example 1. It was found that the effect of improving the charge / discharge characteristics was small by the mechano-fusion method alone.

From the above, even if composite powder is prepared from Li _1.2 Fe _0.4 Mn _0.4 O ₂ and AB powder using the mechano-fusion method, the composite powder to which further energization treatment is applied can be bonded to both. It has been found that it is difficult to produce a lithium secondary battery that cannot be strengthened, exhibits a high energy density at a high current density, and has excellent charge / discharge characteristics.

Comparative Example 2 (without mechanofusion treatment)
Using the same electrode active material Li _1.2 Fe _0.4 Mn _0.4 O ₂ as in Example 1, this and AB were weighed at a weight ratio of 97: 3 and kneaded in an agate mortar. This was filled in a tungsten carbide jig having an inner diameter of 10 mm, and in the same manner as in Example 1, energization treatment was performed at 270 ° C. for 20 minutes under a pressure of 500 MPa.

  Using the obtained powder, a lithium secondary battery was produced in exactly the same manner as in Example 1, and a charge / discharge test was performed under the same conditions. As shown in FIG. 1 and FIG. 2, although the increase in the discharge capacity and the discharge average voltage is partially recognized as compared with the case where the energization process is not performed (Comparative Example 3), the increase effect is as high as in the case of Example 1. It was not recognized, and it turned out that the improvement effect of a charge / discharge characteristic is small only by energization processing.

From the above, even if a composite powder was produced from Li _1.2 Fe _0.4 Mn _0.4 O ₂ and AB powder using an electric current sintering method, the composite powder to which the mechano-fusion method was further added was more effective. It has been found that it is difficult to produce a lithium secondary battery that cannot enhance the bonding, exhibits a high energy density at a high current density, and has excellent charge / discharge characteristics.

Comparative Example 3 (without mechanofusion treatment / energization treatment)
Using the same electrode active material Li _1.2 Fe _0.4 Mn _0.4 O ₂ as in Example 1, this and AB were weighed at a weight ratio of 97: 3 and kneaded in an agate mortar.

  Using the obtained powder, a lithium secondary battery was produced in exactly the same manner as in Example 1, and a charge / discharge test was performed under the same conditions. As a result, as shown in FIGS. 1 and 2, compared to the case of Example 1, the discharge capacity and the discharge average voltage were low at any current density.

From the above, a lithium secondary battery having a high current density and high energy density and having excellent charge / discharge characteristics can be produced by simply mixing Li _1.2 Fe _0.4 Mn _0.4 O ₂ and AB powder. It turned out to be difficult.

Example 2
LiNi _0.8 Co _0.15 Al _0.05 O ₂ having an average particle size of 9.4 μm was prepared as an electrode active material.

LiNi _0.8 Co _0.15 Al _0.05 O ₂ and commercially available acetylene black (AB) powder were weighed to a weight ratio of 97: 3, and these were put into Mechanofusion AMS-Mini manufactured by Hosokawa Micron Corporation. Then, a mechanofusion treatment was performed for 10 minutes at a clearance of 1 mm and a casing rotation of 6970 rpm.

This was filled into a WC type material having an inner diameter of 10 mm, set in an electric current sintering machine, reduced in pressure to about 20 Pa, and then introduced with nitrogen gas to atmospheric pressure. Next, a pulse current of about 400 A (ON-OFF DC current with a pulse width of 2.5 milliseconds, cycle 29 Hz) was applied while the WC mold was pressed at about 500 MPa. The vicinity of the WC mold was heated at a rate of temperature increase of about 50 ° C./min, and reached 250 ° C. about 5 minutes after the start of pulse current application. After holding at this temperature for about 20 minutes, the current application and pressurization were stopped and the mixture was allowed to cool naturally. After cooling to room temperature, LiNi _0.8 Co _0.15 Al _0.05 O ₂ -AB composite powder (sintered body) was taken out of the mold material to obtain electrode powder.

  The composite powder is black, and in the X-ray diffraction pattern, a broad halo derived from AB is observed in the vicinity of 2θ = 26 °, and the other peaks are unit cells (space group of hexagonal layered rock salt type nickel cobalt oxide lithium). R3m).

≪Charge / discharge characteristics≫
Using the electrode powder as a positive electrode material of a lithium secondary battery, using lithium metal as a negative electrode, aluminum mesh as a current collector, and LiPF ₆ dissolved in an ethylene carbonate / dimethyl carbonate mixture as an electrolyte, A charge / discharge test was conducted by constant current measurement at a current density of 50 mA / g (1/3 C) to 9000 mA / g (60 C) and a cutoff of 2.0 to 4.2 V.

  FIG. 3 shows discharge curves of the lithium secondary battery at 1C, 10C, 30C, and 60C. At a rate of 10 C or less, a slightly lower capacity and a lower discharge average voltage are obtained compared to the case of only mechanofusion treatment (Comparative Example 4) and the case of not performing any of mechanofusion and current sintering treatment (Comparative Example 5). As shown, at a high current density of 30 C or higher, an increase in capacity and an improvement in discharge average voltage were recognized as compared with these two comparative examples. This suggests that the bonding between the active material and the conductive material is good and the electron conductivity is sufficiently ensured.

  From the above, it can be seen that the composite powder for an electrode of the present invention can be suitably used as a positive electrode material of a lithium secondary battery having a high current density and a high energy density and having excellent rate characteristics.

Comparative example 4 (no energization treatment)
The same electrode active material LiNi _0.8 Co _0.15 Al _0.05 O ₂ as in Example 2 was used, and this and AB were weighed at a weight ratio of 97: 3. Mechanofusion treatment was performed for a minute.

  Using the obtained powder, a lithium secondary battery was produced in exactly the same manner as in Example 2, and a charge / discharge test was performed under the same conditions. As shown in FIG. 3, although the increase in the discharge capacity and the discharge average voltage is recognized at a high current density of 30 C or more as compared with the case where the mechanofusion treatment is not performed (Comparative Example 5), the result is as high as in the case of Example 2. The increase effect was not recognized, and it was found that the mechano-fusion method alone had little effect on improving the charge / discharge characteristics.

From the above, even if a composite powder is produced from LiNi _0.8 Co _0.15 Al _0.05 O ₂ and AB powder using the mechanofusion method, the composite powder to which further energization treatment is applied can be bonded to both. It has been found that it is difficult to produce a lithium secondary battery that cannot be strengthened, exhibits a high energy density at a high current density, and has excellent charge / discharge characteristics.

Comparative Example 5 (without mechanofusion treatment / energization treatment)
Using the same electrode active material LiNi _0.8 Co _0.15 Al _0.05 O ₂ as in Example 2, this and AB were weighed at a weight ratio of 97: 3 and kneaded in an agate mortar.

  Using the obtained powder, a lithium secondary battery was produced in the same manner as in Example 2, and a charge / discharge test was performed under the same conditions. As a result, as shown in FIG. 3, the discharge capacity and the discharge average voltage were lower than those of Example 2 particularly at a high current density of 30 C or more.

From the above, a lithium secondary battery having high current density and high energy density and excellent charge / discharge characteristics can be produced by simply mixing LiNi _0.8 Co _0.15 Al _0.05 O ₂ and AB powder. It turned out to be difficult.

It is the figure which showed the discharge capacity in 1 / 3C-30C of the lithium secondary battery produced in Example 1 and Comparative Examples 1-3 by the capacity | capacitance maintenance factor which made the discharge capacity in 1 / 3C 100%. It is a figure which shows the discharge characteristic in 1C, 5C, and 20C of the lithium secondary battery produced in Example 1 and Comparative Examples 1-3. It is a figure which shows the discharge characteristic in 1C, 10C, 30C, 60C of the lithium secondary battery produced in Example 2 and Comparative Examples 4-5. It is the schematic of a mechanofusion apparatus. It is the schematic of a discharge plasma sintering machine.

Explanation of symbols

1. Casing 2. Inner piece (friction member)
3. Scraper
4). Raw material mixture

Claims (12)

A composite powder for an electrode having a structure in which electrode active materials are joined via a conductive material, the composite powder for an electrode,
(1) The electrode active material and the conductive material are previously bound by subjecting the raw material mixture containing the electrode active material and the conductive material to mechanofusion treatment,
(2) A composite powder for an electrode obtained by filling the raw material mixture after the binding into a conductive mold and sintering it by applying a direct current pulse current under a pressure of 60 MPa or more.   The composite powder for an electrode according to claim 1, wherein in the mechanofusion treatment, at least a compressive force and a shearing force are applied to the raw material mixture to bind the electrode active material and the conductive material. The mechanofusion process is a process using a mechanofusion apparatus including a rotating casing and an inner piece fixed in the casing,
(1) The gap distance between the casing and the inner piece is 0.1 to 10 mm,
(2) When the raw material mixture is supplied into the casing, the raw material mixture is pressed against the inner wall surface of the casing by centrifugal force, and at least a compressive force and a shearing force are applied between the inner piece and the inner wall surface. The electrode active material and the conductive material are bound together,
(3) The composite powder for an electrode according to claim 1, wherein the treatment is performed by rotating the casing at a speed of 1000 to 8000 rpm for 1 to 30 minutes after supplying the raw material mixture into the casing.   The composite powder for an electrode according to any one of claims 1 to 3, wherein the conductive mold contains tungsten carbide.   The composite powder for an electrode according to any one of claims 1 to 4, wherein a direct-current pulse current is passed under a pressure of 150 MPa or more.   The electrode active material is composed of 1) a lithium-containing compound having an olivine structure, 2) a lithium-containing compound having a rock salt-like structure having a layered rock salt type or cubic rock salt type crystal structure, and 3) a lithium containing compound having a spinel structure. The composite powder for an electrode according to any one of claims 1 to 5, which is at least one positive electrode active material selected from the group consisting of:   The electrode active material is lithium iron phosphate; lithium iron phosphate in which at least one selected from the group consisting of cobalt, manganese, and nickel is dissolved; lithium cobalt phosphate; at least one of manganese and nickel is in solid solution Cobalt lithium phosphate; lithium manganese phosphate; lithium manganese phosphate in solid solution; nickel lithium phosphate; lithium nickelate; lithium nickelate in solid solution of at least one of cobalt and aluminum; lithium cobaltate; iron At least one positive electrode active material selected from the group consisting of lithium acid; lithium ironate in which at least one of titanium and manganese is dissolved; lithium titanate; lithium manganate; and lithium manganate in which chromium is dissolved It is for the electrode according to any one of claims 1 to 5. If powder.   The electrode active material includes carbon, silicon, germanium, tin, lead, antimony, aluminum, indium, lithium, tin oxide, lithium titanate, lithium nitride, indium tin oxide, indium-tin alloy, lithium-aluminum. The composite powder for an electrode according to any one of claims 1 to 5, which is at least one negative electrode active material selected from the group consisting of an alloy and a lithium-indium alloy.   A primary battery, a secondary battery, a fuel cell or a capacitor, comprising an electrode containing the composite powder for an electrode according to claim 1. A method for producing a composite powder for an electrode having a structure in which electrode active materials are joined together via a conductive material,
(1) The electrode active material and the conductive material are previously bound by subjecting the raw material mixture containing the electrode active material and the conductive material to mechanofusion treatment,
(2) A manufacturing method comprising filling the raw material mixture after the binding into a conductive mold and applying a direct current pulse current under a pressure of 60 MPa or more to sinter.   The manufacturing method according to claim 10, wherein the mechanofusion treatment applies at least a compressive force and a shearing force to the raw material mixture to bind the electrode active material and the conductive material. The mechanofusion process is a process using a mechanofusion apparatus including a rotating casing and an inner piece fixed in the casing,
(1) The gap distance between the casing and the inner piece is 0.1 to 10 mm,
(2) When the raw material mixture is supplied into the casing, the raw material mixture is pressed against the inner wall surface of the casing by centrifugal force, and at least a compressive force and a shearing force are applied between the inner piece and the inner wall surface. The electrode active material and the conductive material are bound together,
(3) The manufacturing method according to claim 10, wherein the treatment is performed by rotating the casing at a speed of 1000 to 8000 rpm for 1 to 30 minutes after supplying the raw material mixture into the casing.

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