JP4826877B2 - Electrode for electrochemical device and lithium secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for an electrochemical element enabling both high output and long life thereof, and a lithium secondary battery using the electrode. <P>SOLUTION: An electrode for an electrochemical element includes an activator and a conductive agent, wherein the conductive agent is oil furnace carbon black having &le;1.2 mg/g released amount of hydrogen (1,500&deg;C for 30 min) and &ge;130 cm<SP>3</SP>/100g 24M4DBP absorbing amount based on JIS K6217. A lithium secondary battery includes a positive electrode, a negative electrode and a nonaqueous electrolyte containing a lithium salt, and at least either the positive or negative electrode is the electrode for the electrochemical element. It becomes possible to establish higher performance of the electrochemical element by controlling physical property of the carbon black as the conductive agent and simultaneously to establish a higher output and a longer life of the lithium secondary battery by using the electrode for the electrochemistry element as the electrode of the lithium secondary battery. <P>COPYRIGHT: (C)2006,JPO&amp;NCIPI

Description

  The present invention relates to an electrode for an electrochemical element used for a capacitor, a lithium secondary battery, and the like, and a lithium secondary battery using the electrode for an electrochemical element.

  2. Description of the Related Art In recent years, along with the reduction in size and weight of electronic devices and the enhancement of functionality, development of capacitors and secondary batteries with high output and long life have been promoted as electrochemical elements used for these devices. Electrodes used in these electrochemical devices usually require an active material having a function of storing and releasing electrons, but this active material does not necessarily have high electron conductivity, or has an electron conductivity during use. In many cases, the active material alone does not function well because of a decrease. Therefore, in order to take a conductive path between the active materials or between the active material and the current collector, a conductive agent having an electron transfer function is usually mixed with the active material.

  As the conductive agent, a highly conductive carbonaceous material obtained by burning or firing organic substances at high temperatures is usually used, and it is known that the physical properties greatly affect the performance of the electrode and the electrochemical device.

  Hereinafter, a lithium secondary battery will be described as an example, but the type of the electrochemical device of the present invention is not limited as long as the effect of the conductive agent is not impaired.

  Among electrochemical devices, secondary batteries called lithium secondary batteries or lithium ion secondary batteries are excellent in energy density and output density, and can be reduced in size and weight. In addition, it is used as a power source for portable devices such as handy video cameras and hybrid electric vehicles.

  As the electrode active material of the lithium secondary battery, a compound capable of inserting and extracting lithium is used. More specifically, the positive electrode active material typically includes lithium manganese oxide having a spinel structure or a lithium transition metal oxide such as lithium cobalt oxide having a layered structure, and the negative electrode active material includes carbon material or graphite. Used.

  As the electrode, an electrode in which these active materials are attached to a current collector together with a conductive agent and a binder is used. In particular, since the positive electrode has a low electronic conductivity of the active material and does not work well without a conductive agent, it is necessary to add a conductive agent.

  As the conductive agent, carbon black such as acetylene black and ketjen black is widely used, but acetylene black is mainly used.

  However, in recent years, due to the demand for further weight reduction of electronic devices and higher performance such as long-time operation, lithium secondary batteries are required to have higher output and longer life. Accordingly, it is necessary to improve the active material used for the electrode and the conductive agent.

  Higher battery output means that even if the battery is charged / discharged at a higher current than before, the polarization is small and a high capacity can be extracted. This is because the conductive agent is an effective conductive path in the electrode. It is important to sufficiently form the original performance of the active material.

  On the other hand, extending the life of a battery means that even if the number of repeated charge / discharge cycles is increased, the deterioration of battery performance is suppressed. It must be able to withstand harsh chemical reactions.

Patent document 1 is mentioned as an example of the high output of a lithium secondary battery by improvement of a electrically conductive agent. In Patent Document 1, as a conductive agent, dibutyl phthalate (DBP) absorption of thereby achieving a high output by using a 250 cm ^3/100 g or less of carbon black based carbon material.

An example of extending the life of a lithium secondary battery by improving the conductive agent is, for example, Patent Document 2. In Patent Document 2, DBP absorption amount of 100 cm ^3/100 g or ^more, 400 cm 3/100 g or less, and _{I 2} adsorption amount 120 mg / g or more, by using the following carbon black 1500 mg / g, to obtain a longer life I'm trying.

Patent Document 3 describes the relationship between the production conditions of oil furnace carbon black, the particle size and the structure in paragraphs 0004 to 0008, and FIG. 2 shows the nitrogen adsorption specific surface area (N ₂ SA). The production limit of oil furnace black with 24M4DBP absorption is disclosed. In addition, although this patent document 3 describes the use as carbon black for long-life batteries, it does not describe a specific usage pattern. Moreover, about the amount of hydrogen which carbon black contains, and the volume specific resistance of carbon black itself, as shown in P552-555 of nonpatent literature 1 (April 15, 1995 carbon black association publication) and FIG. 1.7, It is disclosed that the resistance of carbon black itself decreases when the amount of hydrogen decreases.

  On the other hand, as the carbon black for conductive resin for imparting conductivity to the resin, the present applicant controls the conditions of the design of the manufacturing apparatus and the manufacturing process, thereby achieving ideal physical property values that could not be realized so far. A new oil furnace carbon black has been developed and a patent application has been filed earlier (Japanese Patent Application No. 2004-226894, hereinafter referred to as “prior application”).

The carbon black proposed in this prior application satisfies the following physical properties.
(1500 ° C. × 30 minutes) the dehydrogenation amount: 1.2 mg / g or less 24M4DBP ^absorption: 130 cm 3/100 g or more crystallite size Lc: 10~17Å
Nitrogen adsorption specific surface area (N ₂ SA): preferably 150 to 300 m ² / g
DBP absorption: preferably 150~400cm ³ / 100g

Physical properties of the primary carbon black that is provided conventionally is as shown in Table 1, from Table 1, those dehydrogenation weight and 24M4DBP absorption than 1.2 mg / g is more than 130 cm ^3/100 g is not It turns out that it was difficult to realize both.
The prior application of carbon black has realized both of these properties.

Japanese Patent Laid-Open No. 11-40139 JP 2001-110424 A JP 2002-121422 A Japanese Patent Application No. 2004-226894 "Carbon Black Handbook" <Third Edition>

  As described above, carbon black as a conductive agent blended in a lithium secondary battery electrode has been studied to improve its physical properties. However, recent electrochemical devices have higher output power or longer length. There is a demand for improving the lifespan and further improving both. In order to achieve both, it is necessary to design an advanced electrode. For this purpose, a high degree of design is required for the physical properties of carbon black as a conductive agent, and carbon black within the range of conventionally known physical properties is insufficient.

  The present invention uses such an oil furnace carbon black based on the physical property design of an oil furnace carbon black suitable for use in the electrode in order to satisfy both the demands of high output and long life of the electrochemical device. An object of the present invention is to provide an electrode for an electrochemical element capable of achieving both high output and long life of the electrochemical element, and a lithium secondary battery using the electrode for electrochemical element.

  The inventors of the present invention have proposed an oil furnace carbon black used as a conductive agent for an electrode for an electrochemical element, and electrochemical characteristics of the electrochemical element using the same, in order to achieve high output and long life of the electrochemical element. As a result of investigating the correlation of oil furnace carbon black, the dehydrogenation amount and 24M4DBP absorption amount of the physical properties of oil furnace carbon black greatly affect the output and life of electrochemical devices such as batteries. It has been found that oil furnace carbon black having a specific value can simultaneously improve the output and lifetime of an electrochemical device, and has led to the present invention.

The oil furnace carbon black used in the present invention is based on the carbon black described in the prior application. In other words, the prior application relates to carbon black newly developed mainly for conductive resins, but the present inventors have used oil furnace carbon black having substantially the same physical properties as a conductive agent for electrodes for electrochemical devices. It has been found that when used, it exhibits excellent characteristics.
That is, the gist of the present invention is as follows.

[1] An electrode for an electrochemical element comprising an active material and a conductive agent,
The weight ratio of the conductive agent to the active material weight is 0.5 wt% or more and 15 wt% or less,
The conductive agent is
Characterized in that it is obtained by the following measuring method (1500 ° C. × 30 minutes) the dehydrogenation amount is 1.2 mg / g or less, and 24M4DBP absorption conforming to JIS K6217 includes more oil furnace carbon black 130 cm ^3/100 g Electrode for electrochemical element.
(Measurement method)
0.5 g of carbon black is precisely weighed, put in an alumina tube, and decompressed to 0.01 Torr (1.3 Pa). Then, the decompression system is closed, and the carbon black is held in an electric furnace at 1500 ° C. for 30 minutes and exists in carbon black. Decomposes and volatilizes oxygen and hydrogen compounds. Volatile components are collected in a fixed-capacity gas collection tube through a quantitative suction pump. The amount of gas is determined from the pressure and temperature, the composition is analyzed by gas chromatography, the amount of hydrogen (H ₂ ) generated (mg) is determined, and the value converted to the amount of hydrogen per gram of carbon black is calculated (the unit is mg / g).
[2] The electrode for an electrochemical element according to [1], wherein the oil furnace carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 80 m ² / g or more and 300 m ² / g or less.
[3] The electrode for an electrochemical element according to [1] or [2], wherein the crystallite size Lc of the oil furnace carbon black is 10 to 40 mm.
[4] The electrode for an electrochemical element according to [1] to [3], wherein the active material contains at least a compound capable of inserting and extracting lithium.
[5] The electrode for an electrochemical element according to [4], wherein the compound capable of inserting and extracting lithium is a lithium transition metal composite oxide.
[6] The electrochemical device according to [5], wherein the lithium transition metal composite oxide has a crystal structure mainly identified by a layered structure and has a composition represented by the following formula (1): Electrode.
Li _{1 + α} Ni _x Mn _y Co _z M _{1-xy z} O ₂ (1)
(However, −0.1 ≦ α ≦ 0.2, 0 <x ≦ 0.5, 0 <y <1.0, 0 ≦ z ≦ 0.5, 0.8 ≦ x + y + z ≦ 1.0, M is one or more of Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, Nb, and Zr)
[7] The lithium transition metal composite oxide is formed by agglomerating primary particles to form secondary particles, and the shape of the secondary particles is spherical or elliptical spherical. [5] or [6] Electrode for chemical elements.
[8] A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a lithium salt,
At least one of a positive electrode and a negative electrode is the electrode for electrochemical elements as described in [4]-[7], The lithium secondary battery characterized by the above-mentioned.

  According to the present invention, by controlling the physical properties of oil furnace carbon black as a conductive agent, it is possible to improve the performance of an electrode for an electrochemical device using the same, and thus to improve the performance of the electrochemical device, In the case where this electrode for an electrochemical device is used as an electrode of a lithium secondary battery, it is possible to simultaneously achieve high output and long life of the lithium secondary battery, which has been considered difficult in the past.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention. The content of is not specified.

[Electrochemical element]
The electrochemical element in the present invention is a small battery or capacitor mainly used for electronic equipment or the like, but also includes an automobile battery, capacitor, fuel cell, etc., for which research has been actively conducted recently. Examples of the battery include primary batteries such as a lithium primary battery using manganese dioxide or graphite fluoride and lithium, a manganese dry battery and an alkaline dry battery, a secondary battery such as a nickel hydride secondary battery and a lithium secondary battery. An example of the capacitor is an electric double layer capacitor.

  As described above, the electrodes used in these electrochemical elements usually require an active material having a function of storing and releasing electrons, but the active material does not necessarily have high electron conductivity or is in use. In many cases, the active material alone does not function well because of a decrease in electron conductivity. Therefore, in order to take a conductive path between the active materials or between the active material and the current collector, a conductive agent having an electron transfer function is generally mixed.

  In the present invention, the physical properties of the conductive agent blended in the electrode are designed and controlled to provide a higher-performance electrode and thus an electrochemical element.

[Conductive agent]
The conductive agent according to the present invention is
(1500 ° C. × 30 minutes) the dehydrogenation amount (hereinafter, simply referred to as "the dehydrogenation amount".) Is 1.2 mg / g or less, and 24M4DBP absorption of 130 cm ^3/100 g or more oil furnace carbon conforming to JIS K6217 Black.

Conventionally known carbonaceous materials as conductive agents such as carbon black increase the amount of dehydrogenation when attempting to increase the nitrogen adsorption specific surface area, and conversely when attempting to keep the dehydrogenation amount low. Therefore, the 24M4DBP absorption amount is also reduced, and it is difficult to improve the life while increasing the conductivity of the conductive agent itself.
In the present invention, by adjusting the production conditions of the oil furnace carbon black and achieving the above dehydrogenation amount and 24M4DBP absorption range, the conductivity is increased and the high output is supported. An electrode with a long life, and thus an electrochemical element with high output and long life is realized.

The physical property parameters of the conductive agent in the present invention will be described below.
<(1500 ° C. × 30 minutes) Dehydrogenation amount>
(1500 ° C. × 30 minutes) The amount of dehydrogenation is the amount of hydrogen in the gas generated during the heating of carbon black at 1500 ° C. for 30 minutes in vacuum, and is specifically measured as described below. The

  The dehydrogenation amount of oil furnace carbon black (hereinafter also simply referred to as “carbon black”) which is a conductive agent in the present invention is 1.2 mg / g or less, preferably 1.1 mg / g or less, more preferably 1.0 mg. / G or less.

  The amount of dehydrogenation is greatly related to the thermal history received by the carbon black. If the heat treatment is insufficient, a large amount of hydrogen remains, which is considered to be largely related to conductivity. In the case of a large amount of dehydrogenation, carbonization on the surface of carbon black has not progressed, so that the conductivity cannot be improved in the electrode, and it is considered that an output cannot be obtained. In addition, when used in a battery, it also affects the electrochemical stability and is considered to influence the life. From these facts, it is generally considered that a smaller amount of dehydrogenation of carbon black is preferable. However, since it will lead to the cost increase at the time of manufacturing industrially when too small, generally 0.1 mg / g or more, More preferably, 0.3 mg / g or more is good.

(Measurement method)
About 0.5g of carbon black is precisely weighed, put in an alumina tube, depressurized to 0.01 Torr (1.3 Pa), then the decompression system is closed, and it is kept in an electric furnace at 1500 ° C. for 30 minutes. Decomposes and volatilizes oxygen and hydrogen compounds. Volatile components are collected in a fixed-capacity gas collection tube through a quantitative suction pump. The amount of gas is determined from the pressure and temperature, the composition is analyzed by gas chromatography, the amount of hydrogen (H ₂ ) generated (mg) is determined, and the value converted to the amount of hydrogen per gram of carbon black is calculated (the unit is mg / g).

<24M4 DBP absorption and DBP absorption>
DBP absorption amount is an amount that is defined in conformity with JIS K6217 (unit ^cm 3 / 100g).
24M4DBP absorption is the DBP absorption is another parameter, in compliance with DBP absorption as well as JIS K6217, a DBP absorption amount of the compression sample (units also ^cm 3 / 100g).

Oil furnace carbon blacks of the present invention fulfills the dehydrogenation amount, 24M4DBP absorption of 130 cm ^3/100 g or more, preferably 140cm ^3/100 g, more preferably not less than 145cm ³ / 100g.

If the absorption amount of 24M4DBP is less than the above lower limit, the structure is easily broken by stress at the time of electrode preparation, cycle, or stress at the time of storage, so that a sufficient conductive path is not formed and the capacity and output are reduced, or the formed conductive It is easy for the path to break and shorten the service life. The upper limit of the 24M4DBP absorption is not particularly limited, from the viewpoint of easy handling at the time of production of an electrode, usually less than 200 cm ^3/100 g.

  In general, carbon black forms secondary particles composed of a chain called a unique structure (aggregate structure) in which primary particles are arranged in a kitchen shape. Therefore, it is preferable that the carbon black has a developed structure because it is easy to secure a conductive path. Further, the conductivity is improved by reducing the primary particle size of carbon black. Furthermore, the conductivity is improved by reducing the amount of functional groups (oxygen compounds) on the surfaces of the primary particles of carbon black.

  Since DBP (dibutyl phthalate) is absorbed in the voids of the kitchen chain structure of the carbon black structure, the 24M4 DBP absorption amount and DBP absorption amount are important index values indicating the degree of structure development of the carbon black. is there.

  Unlike normal DBP absorption by absorbing DBP while carbon black is intact, 24M4 DBP absorption is measured by absorbing DBP after stressing carbon black and breaking easily broken parts. It is. When carbon black is used for the electrode, carbon black is usually subjected to various stresses during mixing with the active material or during electrode molding. Therefore, the 24M4DBP absorption is more important for indicating the carbon black structure than the DBP absorption. it is conceivable that.

And the 24M4DBP absorption amount of carbon black has a correlation with the amount of effective structure that forms the conductive path in the electrode, so it has a correlation with the improvement of the battery, and in addition, the cycle characteristics and storage characteristics of the electrochemical device Since it is considered to represent the abundance of structures that are not easily destroyed even when expansion and contraction of the active material and electrodes occur, there is a correlation with the lifetime. That is, it is considered that these electrochemical characteristics are difficult to extract unless the 24M4DBP absorption amount is large to some extent.
For this reason, in the present invention, the 24M4DBP absorption amount of carbon black is set to be equal to or greater than the predetermined value.

<Nitrogen adsorption specific surface area _(N 2 SA)>
The nitrogen adsorption specific surface area (N ₂ SA) is defined based on JIS K6217 (unit: m ² / g).

Regarding the nitrogen adsorption specific surface area (N ₂ SA) of the carbon black used in the present invention, the lower limit is preferably 80 m ² / g or more, more preferably 100 m ² / g or more, and further preferably 150 m ² / g or more. The upper limit is preferably 300 m ² / g or less, more preferably 290 m ² / g or less, and still more preferably 280 m ² / g or less.

In order to secure a conductive path between the active materials in the electrode of the electrochemical element and to obtain performance at high output, it is preferable that the specific surface area of the conductive agent is large. On the other hand, if the specific surface area is too large, there may be a problem in molding at the time of electrode preparation, an irreversible reaction due to an electrochemical side reaction or the like is likely to occur, and the life may be shortened.
Accordingly, the nitrogen adsorption specific surface area (N ₂ SA) of carbon black as the conductive agent is preferably within the above range.

<Crystallite size Lc>
The carbon black used in the present invention has a lower limit of the crystallite size Lc of 10 mm or more, more preferably 13 mm or more, and an upper limit of 40 mm or less, preferably 25 mm or less, and more preferably 17 mm or less. In the oil furnace carbon black, the conductivity of the electrode can be most enhanced by setting the crystallite size Lc within this specific range. If this value is too large or too low, sufficient conductivity may not be obtained.

  The crystallite size Lc according to the present invention is measured using an X-ray diffractometer (RINT-1500 type, manufactured by Rigaku Corporation). The measurement conditions are such that Cu is used for the tube, tube voltage is 40 KV, and tube current is 250 mA. The carbon black sample is filled in a sample plate attached to the apparatus, the measurement angle (2θ) is 10 ° to 60 °, the measurement speed is 0.5 ° / min, and the peak position and half width are calculated by the software of the apparatus. Further, silicon for X-ray standard is used for calibration of the measurement angle. Using the results thus obtained, Scherrer's equation: (Lc (Å) = K × λ / (β × cos θ) (where K: form factor constant 0.9, λ: wavelength of characteristic X-ray CuKα 1.5418 (Å), β: half width (radian), θ: peak position (degrees))).

<Manufacturing method>
The carbon black as the conductive agent in the present invention is an oil furnace carbon black produced by an oil furnace method.
A specific method for synthesizing carbon black having the above specific physical properties is as described in the prior application.

  An apparatus for producing carbon black by an oil furnace method is installed following a first reaction zone for burning a fuel to generate a high-temperature combustion gas flow, and a carbon black raw material hydrocarbon (hereinafter referred to as “oil”). A second reaction zone for introducing a carbon black production reaction and a cooling means for stopping the carbon black production reaction, which is subsequently installed in the second reaction zone. Reaction zone.

  In order to produce carbon black by this carbon black production apparatus, a high-temperature combustion gas flow is generated in the first reaction zone, and carbon black raw material hydrocarbon (oil) is sprayed in the second reaction zone. Carbon black is produced in the reaction zone. The gas stream containing carbon black is introduced into the third reaction zone, and is rapidly cooled by receiving water spray from the spray nozzle in the third reaction zone. The gas stream containing carbon black in the third reaction zone is then introduced into a collecting means such as a cyclone or a bag filter via a flue to collect the carbon black.

  Oil furnace carbon black can be manufactured by controlling the design and manufacturing conditions of such a manufacturing apparatus, the physical properties can be controlled relatively easily, and the physical properties when used for electrodes of electrochemical devices The design is advantageous over other conductive agents.

  For example, by adjusting the position of the carbon black raw material introduction nozzle in the second reaction zone described above and the position of the cooling water supply nozzle in the third reaction zone to make the carbon black residence time in the furnace a specific range, As described above, the carbon black 24M4DBP absorption amount and specific surface area are within a specific range, the crystallite size Lc is not excessively increased to a specific small value, and the dehydrogenation of the carbon black particle surface has progressed. That's fine. More specifically, the furnace temperature is set to 1500 ° C. to 2000 ° C., preferably 1600 ° C. to 1800 ° C., and the residence time of carbon black in the furnace, that is, the time required to move from the raw material introduction point to the reaction stop position (carbon black The time required for moving the raw material introduction position distance and the reaction stop position distance) may be 40 milliseconds to 500 milliseconds, preferably 50 milliseconds to 200 milliseconds. Further, in the case where the temperature in the furnace is lower than 1500 ° C., the residence time in the furnace exceeds 500 milliseconds and is 5 seconds or less, preferably 1 to 3 seconds.

  Since the carbon black according to the present invention has a particularly small amount of dehydrogenation, its production is carried out by a method in which the temperature of the high-temperature combustion gas flow in the furnace is set to a high temperature of 1700 ° C. or more, or downstream of the carbon black raw material supply nozzle. Further, it is preferable to introduce oxygen into the furnace to burn hydrogen or the like on the surface of the carbon black and to extend the residence time at a high temperature with this reaction heat. Such a method is preferable because crystallization in the vicinity of the surface of the carbon black and dehydrogenation inside the carbon black can be effectively performed.

[Electrode for Electrochemical Element]
The electrode for an electrochemical element of the present invention includes an active material and an oil furnace carbon black having the above specific properties as a conductive agent, and the conductive agent is electrochemically stable and high. By having conductivity, suitable performance can be obtained in any of the positive electrode, the negative electrode, and the capacitor electrode.

  In the electrode for an electrochemical element of the present invention, one kind of carbon black having physical properties within the range specified in the present invention may be used alone as the conductive agent. You may use the above together.

  In the present invention, the weight ratio of the conductive agent to the active material weight of the electrode is 0.5% by weight or more, particularly 1% by weight or more, and preferably 15% by weight or less, particularly preferably 12% by weight or less. If the proportion of the conductive agent is too small, the performance improvement effect may not appear, and if it is too large, the proportion of the active material is relatively reduced, and the capacity and output of the electrode may be reduced.

  When the electrochemical element is a battery, the electrode for an electrochemical element of the present invention may be a positive electrode or a negative electrode, and the active material in the electrode contains at least a compound capable of inserting and extracting lithium. It is preferable to do.

[Positive electrode for lithium secondary battery]
Next, the positive electrode for lithium secondary batteries is demonstrated among the electrodes for electrochemical elements of this invention.

  The positive electrode for a lithium secondary battery in the present invention has a positive electrode active material layer containing a specific carbon black as a conductive agent according to the present invention, an active material, and a binder (binder) on a current collector. It will be.

The positive electrode active material layer is usually pressure-bonded to a positive electrode current collector by mixing a conductive agent, a positive electrode active material, a binder, and a thickener used as necessary in a dry form into a sheet. Alternatively, these materials are dissolved or dispersed in a liquid medium to form a slurry, which is applied to the positive electrode current collector and dried.
The positive electrode active material layer obtained by coating and drying is preferably consolidated by a hand press, a roller press or the like in order to increase the packing density of the positive electrode active material.

  The thickness of the positive electrode active material layer is usually about 10 to 200 μm.

<Active material>
Lithium transition metal composite oxide is mentioned as a compound which can be generally occluded / released as a positive electrode active material. These include compounds having a layered structure such as LiNiO ₂ , LiMnO ₂ and LiCoO ₂ and compounds having a spinel structure typified by LiMn ₂ O ₄ . These are preferably used for the active material of the electrode of the present invention.

In particular, the positive electrode active material is preferably a lithium transition metal composite oxide having a crystal structure mainly identified by a layered structure and having a composition represented by the following formula (1).
Li _{1 + α} Ni _x Mn _y Co _z M _{1-xy z} O ₂ (1)
(However, −0.1 ≦ α ≦ 0.2, 0 <x ≦ 0.5, 0 <y <1.0, 0 ≦ z ≦ 0.5, 0.8 ≦ x + y + z ≦ 1.0, M is one or more of Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, Nb, and Zr)

In this compositional formula, the molar ratio of oxygen is set to ₂ for convenience when the sum of the molar ratios of Ni, Mn, Co, and M is 1 based on an analogy with LiCoO ₂ that is a layered lithium transition metal composite oxide. In actuality, it is determined by the balance between Li and the valence of each transition metal element cation, and the numerical value may slightly vary from 2. Strictly speaking, although there is an influence when there is oxygen deficiency or excess oxygen, the fluctuation value is usually smaller than 2 and is omitted.

  Α is a value representing the excess or deficiency of Li, and depends on the amount of Li raw material charged during synthesis. However, if α is too small, the electrochemical characteristics deteriorate, and if it is too large, the Li raw material contains excess alkali after synthesis. It is not preferable because it remains on the surface as a minute and causes deterioration and gas generation. Therefore, −0.1 ≦ α ≦ 0.2 is preferable, and 0.02 ≦ α ≦ 0.1 is more preferable.

  Even if z (the molar ratio of Co) is large, there is no problem in battery performance, but Co is valuable in terms of resources and the cost of Co raw material is high, so it is preferably 0.5 or less for economic reasons, and further 0 .35 or less is preferable.

  When x (molar ratio of Ni) is too large, the active material is likely to react with moisture in the air, or becomes thermally unstable in a charged state (a state in which lithium is electrochemically desorbed). 0.5 or less is preferable.

  M is added mainly for the purpose of improving safety during misuse, such as short-circuiting and overcharging of the battery. Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, Nb, and Zr Any one or more elements are preferable, and Al, Mg, Ti and the like are more effective and preferable. However, when the ratio of this element is large (when the value of x + y + z is small), the electrochemical capacity (mAh / g) at which the active material can occlude and release lithium is small, which is not preferable. Therefore, x + y + z is usually 0.80 or more, more preferably 0.90 or more, and further preferably 0.95 or more.

に属するものである。通常、ミラー指数（００３）のピーク面積とミラー指数（１０４）のピーク面積の比Ｉ（００３）／Ｉ（１０４）が、層状構造の発達度合いを表すパラメータとしてよく用いられる。本発明で用いるリチウム遷移金属酸化物のＩ（００３）／Ｉ（１０４）は通常１．０以上が好ましく、１．１以上であることがより好ましい。このパラメータが小さいと層状構造の発達が不十分で、活物質として十分機能しないおそれがある。 In the present invention, whether or not the lithium transition metal oxide has a layered structure is identified by powder X-ray diffraction measurement. Layered structure is a space group

Belongs to. Usually, the ratio I (003) / I (104) between the peak area of the Miller index (003) and the peak area of the Miller index (104) is often used as a parameter representing the degree of development of the layered structure. I (003) / I (104) of the lithium transition metal oxide used in the present invention is usually preferably 1.0 or more, and more preferably 1.1 or more. When this parameter is small, the layered structure is not sufficiently developed and may not function sufficiently as an active material.

  In addition, powder X-ray diffraction measurement uses CuKα ray, output 40 kV, 30 mA, Continuous mode, reading width 0.05 °, Divergence Slit 1 °, Scattering Slit 1 °, Receiving Slit 0.2 mm, scanning speed 3.0 ° / min. Measured.

  The composition (molar ratio: α, x, y, z) of the lithium transition metal oxide represented by the formula (1) is obtained by ICP emission analysis after dissolving the sample with an acid.

  The lithium transition metal oxide in the present invention is preferably formed by agglomerating primary particles to form secondary particles, and the shape of the secondary particles is preferably spherical or elliptical. In general, an electrochemical element expands and contracts due to charging and discharging thereof, and the stress easily breaks down due to the destruction of the active material and the disconnection of the conductive path due to the stress. Therefore, rather than a single particle active material consisting of only primary particles, it is considered preferable that the primary particles aggregate to form secondary particles because the stress of expansion and contraction is alleviated and deterioration is prevented. . In addition, spherical or oval spherical particles are less oriented during molding of the electrode than plate-like equiaxed particles, so that the expansion and contraction of the electrode during charging and discharging is small, and the electrode is produced. The mixing with the conductive agent is also preferable because it is easy to mix uniformly.

  Various methods are conceivable for producing a spherical or elliptical active material. For example, a raw material such as Ni, Mn, Co or the like is dissolved or pulverized and dispersed in a solvent such as water, and the pH is adjusted while stirring. There is a method in which a spherical coprecipitated hydroxide is prepared and recovered by adjustment, dried to obtain a precursor, and a Li source is added thereto and calcined at a high temperature to obtain an active material. Similarly, raw materials such as Ni, Mn, and Co are dissolved or pulverized and dispersed in a solvent such as water, and then spray-dried by spray drying or the like to obtain a spherical or elliptical precursor, to which a Li source is added. And a method of obtaining an active material by baking at a high temperature.

  The powder physical properties of the lithium transition metal composite oxide used in the present invention are described below.

(The bulk density)
First, the bulk density is preferably 1.2 g / cc or more, and more preferably 1.6 g / cc or more. If the bulk density is too low, the electrode density does not increase, so that there is a risk that the energy density of the battery will be lowered, and consequently the output will be lowered.
In the present invention, the bulk density is 5 to 10 g of lithium transition metal oxide powder placed in a 10 ml glass graduated cylinder and tapped 200 times with a stroke of about 20 mm. cc was determined.

(Median diameter d ₅₀ )
The median diameter d _{50 of the} particles (when the primary particles are aggregated to form secondary particles) is usually 3 μm or more, preferably 5 μm or more, more preferably 9 μm or more, and most preferably 10 μm or more. Usually, it is 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, and most preferably 15 μm or less. If the lower limit is not reached, a high bulk density product may not be obtained. If the upper limit is exceeded, it takes time to diffuse lithium in the particles. It is not preferable because a conductive agent, a binder, or the like is slurried with a solvent and may cause problems such as streaks when applied in a thin film.
The median diameter was measured by setting a refractive index of 1.24 using a known laser diffraction / scattering particle size distribution measuring device. In the present invention, LA-920 manufactured by HORIBA was used as a particle size distribution meter, and a 0.1 wt% sodium hexametaphosphate aqueous solution was used as a dispersion medium for measurement, and measurement was performed after ultrasonic dispersion for 5 minutes.

(Average primary particle size)
When primary particles are aggregated to form secondary particles, the average primary particle diameter of the lithium transition metal oxide is usually 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.3 μm. Above, most preferably 0.4 μm or more, usually 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and most preferably 0.6 μm or less. When the above upper limit is exceeded, it is difficult to form spherical secondary particles, which adversely affects the powder filling property, or the specific surface area is greatly reduced, so that there is a high possibility that the battery performance such as output characteristics will be reduced. Absent. On the other hand, if the value is below the lower limit, the crystal is usually undeveloped, which may cause problems such as inferior charge / discharge reversibility, which is not preferable.
In the present invention, the average primary particle size was determined from an SEM image observed at 30,000 times.

(BET specific surface area)
The BET specific surface area of the lithium transition metal composite oxide is 0.2 m ² / g or more, preferably 0.3 m ² / g or more, more preferably 0.4 m ² / g or more, 4.0 m ² / g or less, Preferably it is 2.5 m < ² > / g or less, More preferably, it is 1.5 m < ² > / g or less. If the BET specific surface area is smaller than this range, the battery performance tends to be lowered. If the BET specific surface area is larger, the bulk density is difficult to increase, or a problem is likely to occur in the coating property at the time of forming the positive electrode active material.
The specific surface area can be measured with a known BET type powder specific surface area measuring device. In the present invention, BET one-point method measurement by a continuous flow method was performed using an autosorb 1 manufactured by Cantachrome, using nitrogen as an adsorption gas and helium as a carrier gas. Specifically, the powder sample was heated and deaerated with a mixed gas at a temperature of 150 ° C., then cooled to liquid nitrogen temperature to adsorb the mixed gas, and then heated to room temperature with water to be adsorbed. Nitrogen gas was desorbed, the amount was detected by a thermal conductivity detector, and the specific surface area of the sample was calculated from this.

In the present invention, the positive electrode active material may be used alone or in combination of two or more in any combination and ratio.
The ratio of the positive electrode active material in the positive electrode active material layer is usually 75% by weight or more, preferably 80% by weight or more, and usually 98% by weight or less, preferably 95% by weight or less. When the proportion of the positive electrode active material is too low, the capacity and output of the battery are reduced. On the other hand, when the proportion is too high, the amount of the binder is relatively lowered and the mechanical strength of the electrode is lowered.

<Binder>
The binder used for manufacturing the positive electrode active material layer is not particularly limited, and in the case of a coating method, any material that can be dissolved or dispersed in a liquid medium used during electrode manufacturing may be used. , Polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose, and other resin polymers, SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine rubber, isoprene rubber, butadiene Rubber, rubbery polymer such as ethylene / propylene rubber, styrene / butadiene / styrene block copolymer and its hydrogenated product, EPDM (ethylene-propylene-diene terpolymer), styrene / ethylene / butadiene / ethylene copolymer Polymer, styrene / isopre Thermoplastic elastomeric polymers such as styrene block copolymers and hydrogenated products thereof, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymers, propylene / α-olefin copolymers, etc. Fluorine polymers such as soft resinous polymers, polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymers, alkali metal ions (especially lithium ions) Examples thereof include a polymer composition having ion conductivity. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

  The ratio of the binder in the positive electrode active material layer is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 3% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less. More preferably, it is 40% by weight or less, and most preferably 10% by weight or less. When the ratio of the binder is too low, the positive electrode active material cannot be sufficiently retained, and the mechanical strength of the positive electrode is insufficient, which may deteriorate battery performance such as cycle characteristics. On the other hand, if it is too high, the battery capacity and the conductivity may be reduced.

<Conductive agent>
The conductive agent is carbon black as described above, but in combination with it, there is no metal material such as copper or nickel, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, needle coke, etc. One or more carbon materials such as regular carbon may be used in combination.

As described above, the proportion of the conductive agent in the positive electrode active material layer is preferably 0.5% by weight or more, particularly 1% by weight or more, and 15% by weight or less, particularly 12% by weight or less based on the weight of the active material. If the proportion of the conductive agent is too small, the performance improvement effect may not appear, and if it is too large, the proportion of the active material is relatively reduced, and the capacity and output of the electrode may be reduced.
In order to sufficiently obtain the effect of the carbon black according to the present invention, when the conductive agent includes a conductive agent other than the above-described carbon black, the ratio is preferably 90% by weight or less of the total conductive agent amount. .

<Liquid medium>
As the liquid medium for forming the slurry, it is possible to dissolve or disperse the lithium nickel composite oxide powder that is the positive electrode active material, the conductive agent, the binder, and the thickener used as necessary. As long as it is a possible solvent, the type is not particularly limited, and either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N -N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran (THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. Can be mentioned. In particular, when an aqueous solvent is used, it is preferable to add a dispersant in addition to the thickener and make a slurry using a latex such as SBR.

  In addition, these solvents may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

<Current collector>
As the material for the positive electrode current collector, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, and carbon materials such as carbon cloth and carbon paper are usually used. Of these, metal materials are preferable, and aluminum is particularly preferable. As for the shape, in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, a foam metal, etc. Etc. Among these, metal thin films are preferable because they are currently used in industrialized products. In addition, you may form a thin film suitably in mesh shape.

  When a thin film is used as the positive electrode current collector, its thickness is arbitrary, but it is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 100 mm or less, preferably 1 mm or less, more preferably 50 μm or less. The range of is preferable. If the thickness is thinner than the above range, the strength required for the current collector may be insufficient. On the other hand, if it is thicker than the above range, the handleability may be impaired.

[Negative electrode for lithium secondary battery]
Next, the negative electrode for lithium secondary batteries is demonstrated among the electrodes for electrochemical elements of this invention.

  The negative electrode for a lithium secondary battery in the present invention is usually constituted by forming a negative electrode active material layer on a negative electrode current collector, similarly to the above-described positive electrode for a lithium secondary battery.

  As in the case of the positive electrode active material layer, the negative electrode active material layer is usually a negative electrode obtained by slurrying a negative electrode active material, a conductive agent, further a binder, and, if necessary, a thickener in a liquid medium. It can manufacture by apply | coating to a collector and drying. As the liquid medium forming the slurry, the binder, the thickener, and other conductive agents, the same materials as those described above for the positive electrode active material layer can be used at the same ratio.

<Active material>
The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions, but it can usually occlude and release lithium from the viewpoint of high safety. A carbon material is used.

  Although there is no restriction | limiting in particular as a carbon material, Graphite (graphite), such as artificial graphite and natural graphite, and the thermal decomposition thing of organic substance on various thermal decomposition conditions are mentioned. Examples of pyrolysis products of organic matter include coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, or carbide obtained by oxidizing these pitches, needle coke, pitch coke, phenol resin, crystalline cellulose, etc. And carbon materials obtained by partially graphitizing these, pitch-based carbon fibers, and the like. Among them, graphite is preferable, and particularly preferable is artificial graphite, purified natural graphite, or graphite material containing pitch in these graphites, which is manufactured by subjecting easy-graphite pitch obtained from various raw materials to high-temperature heat treatment. Therefore, those subjected to various surface treatments are mainly used. One of these carbon materials may be used alone, or two or more thereof may be used in combination.

  When a graphite material is used as the negative electrode active material, the d value (interlayer distance) of the lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method is usually 0.335 nm or more, and usually 0.340 nm or less, particularly What is 0.337 nm or less is preferable.

  Further, the ash content of the graphite material is usually 1% by weight or less, particularly 0.5% by weight or less, and particularly preferably 0.1% by weight or less, based on the weight of the graphite material.

  Further, the crystallite size (Lc) of the graphite material determined by X-ray diffraction by the Gakushin method is usually 30 nm or more, preferably 50 nm or more, and particularly preferably 100 nm or more.

  The median diameter of the graphite material determined by the laser diffraction / scattering method is usually 1 μm or more, especially 3 μm or more, more preferably 5 μm or more, especially 7 μm or more, and usually 100 μm or less, especially 50 μm or less, more preferably 40 μm or less, especially 40 μm or less. It is preferable that it is 30 micrometers or less.

Moreover, the BET specific surface area of the graphite material is usually 0.5 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1.0 m ² / g or more, and further preferably 1.5 m ² / g. or more, and usually 25.0 m ² / g or less, preferably 20.0 m ² / g, more preferably 15.0 m ² / g or less, still more preferably 10.0 m ² / g or less.

Further, when performing Raman spectroscopy using argon laser light for graphite material, and strength _{I A} of the peak _{P A} is detected in the range of 1580～1620Cm ^-1, it is detected in the range of 1350 ^-1 that intensity ratio _I a / _{I B} of the intensity _{I B} of a peak _{P B} is what is preferably 0 to 0.5. Further, the half width of the peak _{P A} is preferably 26cm ^-1 or less, 25 cm ^-1 or less is more preferable.

  In addition to the various carbon materials described above, other materials capable of inserting and extracting lithium can be used as the negative electrode active material. Specific examples of the negative electrode active material other than the carbon material include elements such as tin and silicon that form an alloy with lithium and a compound thereof, and lithium alloys such as lithium simple substance and lithium aluminum alloy. One of these materials other than the carbon material may be used alone, or two or more thereof may be used in combination. Moreover, you may use in combination with the above-mentioned carbon material.

<Current collector>
As a material of the negative electrode current collector, a metal material such as copper, nickel, stainless steel, nickel-plated steel, or a carbon material such as carbon cloth or carbon paper is used. Among these, in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, etc., and in the case of a carbon material, a carbon plate, a carbon thin film, a carbon cylinder, etc. are mentioned. Among these, metal thin films are preferable because they are currently used in industrialized products. In addition, you may form a thin film suitably in mesh shape.
When a metal thin film is used as the negative electrode current collector, the preferred thickness range is the same as the range described above for the positive electrode current collector.

[Lithium secondary battery]
Next, the lithium secondary battery of the present invention will be described.

  A lithium secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte using a lithium salt as an electrolytic salt, and one or both of the positive electrode and the negative electrode are the electrodes for an electrochemical element of the present invention described above. And

  The lithium secondary battery of the present invention may further include a separator that holds the nonaqueous electrolyte between the positive electrode and the negative electrode. In order to effectively prevent a short circuit due to contact between the positive electrode and the negative electrode, it is desirable to interpose a separator in this way.

  The lithium secondary battery of the present invention is usually produced by assembling the above-described positive electrode and / or negative electrode for the lithium secondary battery of the present invention, an electrolyte, and a separator used as necessary into an appropriate shape. . Furthermore, other components such as an outer case can be used as necessary.

<Electrolytes>
As the electrolyte, for example, known organic electrolytes, polymer solid electrolytes, gel electrolytes, inorganic solid electrolytes, and the like can be used. Among them, organic electrolytes are preferable. The organic electrolytic solution is configured by dissolving a solute (electrolyte) in an organic solvent.

  Here, the type of the organic solvent is not particularly limited. For example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, amines, esters, amides, phosphoric acid An ester compound or the like can be used. Typical examples are dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 4-methyl-2-pentanone, 1, 2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, benzonitrile, Examples include butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, and the like alone or in combination. Mixed solvents can be used.

  The organic solvent described above preferably contains a high dielectric constant solvent in order to dissociate the electrolytic salt. Here, the high dielectric constant solvent means a compound having a relative dielectric constant of 20 or more at 25 ° C. Among the high dielectric constant solvents, it is preferable that ethylene carbonate, propylene carbonate, and compounds in which hydrogen atoms thereof are substituted with other elements such as halogen or alkyl groups are contained in the electrolytic solution. The proportion of the high dielectric constant solvent in the electrolytic solution is preferably 10% by weight or more, more preferably 20% by weight or more, and most preferably 30% by weight or more. If the content of the high dielectric constant solvent is less than the above range, desired battery characteristics may not be obtained.

The type of the electrolytic salt is not particularly limited, and any conventionally known solute can be used. Specific examples include LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN (SO ₂ CF ₃ ) _2. , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) _{2 and the} like. Any one of these electrolytic salts may be used alone, or two or more thereof may be used in any combination and ratio.

  The lithium salt of the electrolytic salt is usually contained in the electrolytic solution so as to be 0.5 mol / L or more and 1.5 mol / L or less. Even if this concentration is less than 0.5 mol / L or more than 1.5 mol / L, the electric conductivity may be lowered, and the battery characteristics may be adversely affected. In particular, the lower limit is preferably 0.75 mol / L or more and the upper limit is 1.25 mol / L or less.

In addition, the electrolytic solution is good for enabling efficient charge and discharge of lithium ions on the negative electrode surface such as gas such as vinylene carbonate, vinyl ethylene carbonate, CO ₂ , N ₂ O, CO, SO ₂ , and polysulfide S _x ²⁻ A small amount of an additive for forming a thick film may be added.

Even when a polymer solid electrolyte is used, the type thereof is not particularly limited, and any known crystalline / amorphous inorganic substance can be used as the solid electrolyte. Examples of the crystalline inorganic solid electrolyte include LiI, Li ₃ N, Li _{1 + x} J _x Ti _2-x (PO ₄ ) ₃ (J = Al, Sc, Y, La), Li _0.5-3x RE _{0. .5 + x} TiO ₃ (RE = La, Pr, Nd, Sm) and the like. Examples of the amorphous inorganic solid electrolyte include oxide glasses such as 4.9LiI-34.1Li ₂ O-61B ₂ O ₅ and 33.3Li ₂ O-66.7SiO ₂ . Any one of these may be used alone, or two or more may be used in any combination and ratio.

<Separator>
When the above-described organic electrolyte is used as the electrolyte, a separator is interposed between the positive electrode and the negative electrode in order to prevent a short circuit between the electrodes. The material and shape of the separator are not particularly limited, but those that are stable with respect to the organic electrolyte used, have excellent liquid retention properties, and can reliably prevent short-circuiting between electrodes are preferable. Preferable examples include microporous films, sheets, nonwoven fabrics and the like made of various polymer materials. Specific examples of the polymer material include polyolefin polymers such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, and polybutene. In particular, from the viewpoint of chemical and electrochemical stability, which is an important factor for separators, polyolefin polymers are preferable. From the viewpoint of self-occluding temperature, which is one of the purposes of use of separators in batteries, polyethylene is preferred. Is particularly desirable.

  When using a separator made of polyethylene, it is preferable to use ultra-high molecular weight polyethylene from the viewpoint of maintaining high-temperature shape, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1,500,000. On the other hand, the upper limit of the molecular weight is preferably 5 million, more preferably 4 million, and most preferably 3 million. This is because if the molecular weight is too large, the fluidity becomes too low, and the pores of the separator may not close when heated.

<shape>
The shape of the lithium secondary battery of the present invention is not particularly limited, and can be appropriately selected from various commonly employed shapes according to the application. Examples of commonly used shapes include a cylinder type with a sheet electrode and separator in a spiral shape, a cylinder type with an inside-out structure combining a pellet electrode and a separator, and a coin type with stacked pellet electrodes and a separator. Can be mentioned. The method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

<Application>
The use of the lithium secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, watches, strobes, cameras, electric cars, electric scooters, electric bicycles, etc.

  The general embodiment of the lithium secondary battery of the present invention has been described above. However, the lithium secondary battery of the present invention is not limited to the above-described embodiment, and various modifications are possible as long as the gist thereof is not exceeded. Can be implemented.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

[Conductive agent]
The types and physical properties of the conductive agents used in the following examples and comparative examples are as follows.

Conductive agents CB-A to CB-D are oil furnace carbon blacks synthesized according to the method described in the prior application, CB-A; equivalent to Example 3 described in the prior application CB-B; Examples described in the prior application 4 equivalent to CB-C; equivalent to Comparative Example 4 described in the prior application CB-D; equivalent to Comparative Example 1 described in the prior application.
The conductive agent HS100 used in the comparative example is a commercially available product (acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd.), and is often used as a conductive agent for conventional positive electrodes for lithium batteries.

The physical properties of the conductive agent were determined according to the method described above (1500 ° C. × 30 minutes), dehydrogenation amount, 24M4 DBP absorption amount, nitrogen adsorption specific surface area (N ₂ SA), crystallite size Lc, DBP absorption amount. .

[Active material (lithium transition metal oxide)]
The types and physical properties of active materials (lithium transition metal oxides) used in the following examples and comparative examples are as follows.

The active material NMC is a lithium transition metal composite oxide synthesized by the method described below, and is represented by the composition formula Li _1.03 Ni _0.33 Mn _0.33 Co _0.34 O ₂ .
The active material C8G is a commercial product (lithium cobaltate manufactured by Nippon Kagaku Kogyo Co., Ltd.) and is a lithium cobalt oxide represented by the composition formula Li _1.03 CoO ₂ .

As the physical properties of the active material, X-ray diffraction measurement and composition (α, x, y, z) analysis are performed according to the above-described methods, and the bulk density (tap density), average primary particle diameter (SEM), median diameter d ₅₀ , BET specific surface area was measured.

(Synthesis of active material NMC)
Ni (OH) ₂ , Mn ₃ O ₄ and Co (OH) ₂ were weighed and mixed so as to have a molar ratio of Ni: Mn: Co = 1: 1: 1, and then pure water was added thereto. A slurry was prepared. While stirring the slurry, the solid content in the slurry was pulverized to a median diameter of 0.15 μm using a circulating medium agitation type wet pulverizer.

Next, the slurry was spray-dried with a spray dryer, and the pulverized LiOH powder was added to the obtained particulate powder and mixed well. This pre-firing mixture was charged into an alumina crucible, held and fired at 990 ° C. for 10 hours in an electric furnace (air heating / cooling rate 5 ° C./min), and then crushed to a composition of Li _1.03 Ni _0.33 Mn _0.33 A lithium transition metal composite oxide having a layered structure of Co _0.34 O ₂ was obtained.

This active material is mostly spherical or elliptical spherical particles in which primary particles are aggregated to form secondary particles. The average primary particle size is 0.5 μm by SEM observation, the median diameter d ₅₀ is 10 μm, and the bulk density is The surface area was 2.1 g / cc and the BET specific surface area was 0.7 m ² / g.

[Create test cell]
The test cell was prepared as follows.

<Types and combinations of conductive agents and active materials>
The types and combinations of positive electrode conductive agents and active materials in Examples and Comparative Examples are as follows.
Example 1 Conductive agent: CB-A / active material: NMC
Example 2 Conductive agent: CB-B / active material: NMC
Comparative Example 1 Conductive agent: CB-C / Active material: NMC
Comparative Example 2 Conductive agent: CB-D / Active material: NMC
Comparative Example 3 Conductive agent: HS100 / active material: NMC
Example 3 Conductive agent: CB-B / active material: C8G
Comparative Example 4 Conductive agent: HS100 / active material: C8G

<Creation of positive electrode>
First, the lithium transition metal composite oxide shown in Table 1 as the positive electrode active material, the conductive agent shown in Table 1, and the binder (PVdF / NMP solution; KF Polymer # 1320 manufactured by Kureha Chemical Industry Co., Ltd.) in a weight ratio. Active material: Conductive agent: PVdF (as solid content) = 94: 3: 3 Weighed and mixed so that the solid content was about 60% by weight, and dispersed with a homogenizer for 10 minutes. A slurry was obtained. Next, this slurry was applied onto an aluminum foil (thickness: 20 μm) as a current collector with a blade coater, and dried for 1 hour with a 120 ° C. ventilation dryer. Note that the amount of active material per unit area was adjusted to the desired basis weight by adjusting the gap of the blade coater during coating.
When this positive electrode was used as a test electrode for battery evaluation, it was punched into a circle with a punch of 9 mmφ or 12 mmφ, and then adjusted with a hand press so that the desired electrode density was obtained.
In this example and comparative example, the active material basis weight was about 25 to 28 mg / 12 mmφ, and the electrode density was about 3.1 g / cc with respect to the total weight of the mixture.
Strictly speaking, the basis weight when combined with the negative electrode in the cycle test was determined by calculating the weight balance between the negative electrode and the positive electrode, which will be described later.

<Creation of negative electrode>
First, graphite powder (d ₀₀₂ = 3.35 Å) having an average particle size of 9 μm as a negative electrode active material and a binder (PVdF / NMP solution; KF polymer # 1320 manufactured by Kureha Chemical Industry Co., Ltd.) in an active material ratio by weight. : PVdF (as solid content) = 92.5: 7.5 Weighed and mixed, and further added solvent NMP to a solid content of about 50% by weight and dispersed with a homogenizer for 10 minutes to form a uniform slurry. . Next, this slurry was applied onto a copper foil (thickness 20 μm) as a current collector with a blade coater, and dried for 1 hour with a 120 ° C. ventilation dryer. At this time, by adjusting the gap of the blade coater, the amount of active material per unit area was adjusted to a target weight.
When this negative electrode was used as a test electrode for battery evaluation, it was punched into a circular shape with a 12 mmφ punch, and then adjusted with a hand press to the desired electrode density.
In this example and comparative example, the active material weight was about 12 mg / 12 mmφ, and the electrode density was about 1.6 g / cc with respect to the total weight of the mixture.

<Create coin cell>
All 2032 type coin cells were used as test battery cells.
A separator was placed between the positive electrode, the negative electrode, or a Li metal foil punched with a punch, and an appropriate amount of electrolyte was added, followed by caulking using a coin cell caulking machine.
As an electrolytic solution, an electrolytic solution in which LiPF ₆ was dissolved at a rate of 1 mol / L in a solvent of EC (ethylene carbonate): DMC (dimethyl carbonate): EMC (ethyl methyl carbonate) = 3: 3: 4 (volume ratio) was used. A porous polyethylene film having a thickness of 25 μm was cut into a circle and used.
In addition, the member for battery preparation was vacuum-dried, and all the battery preparation was performed in Ar box so that it might not be influenced by moisture.

[Determining the capacity of the positive and negative electrodes]
The capacities of the positive electrode and the negative electrode were determined as follows.

<Initial charge capacity Qf of negative electrode>
First, in order to determine the initial charge capacity Qf (c) (mAh / g) of the negative electrode, a negative electrode is used as a test electrode, a counter electrode is used as a Li metal foil, a coin cell is assembled as described above, and the current density per active material weight is 0.2 mA. / Cm ² in the direction of occluding lithium ions in the negative electrode, that is, C (graphite) + xLi → C · Lix
A constant current is applied so that the reaction represented by the following occurs: Further, when the voltage reaches 3 mV so that lithium metal does not precipitate, the voltage is switched to a constant voltage, and when the current reaches about 0.05 mA, it stops and flows in total. The initial charge capacity Qf (c) was determined from the amount of electricity.
The negative electrode used in this example had an initial charge capacity Qf (c) of 390 mAh / g.

<Initial charge capacity Qs (c) and initial discharge capacity Qs (d) of positive electrode>
In order to obtain the initial charge capacity Qs (c) (mAh / g) and the initial discharge capacity Qs (d) (mAh / g) of the positive electrode, a coin cell is assembled as described above using the positive electrode as a test electrode and the counter electrode as a Li metal foil. , The current density per weight of the active material is 0.2 mA / cm ² , and the direction in which lithium ions are released from the positive electrode, that is, LiMeO ₂ → Li _1-m MeO ₂ + mLi (Me means transition metal)
A constant current was applied so that a charging reaction represented by the following occurs: the battery was stopped when 4.2 V was reached, and the initial charge capacity Qs (c) was determined from the amount of electricity that flowed during charging.
Furthermore, the direction in which lithium ions are occluded in the positive electrode at a current density of 0.2 mA / cm ² , that is, Li _1−a MeO ₂ + bLi → Li _{1−a + b} MeO _2.
A constant current was passed so as to cause the discharge reaction represented by the formula, and when the voltage reached 3.0 V, it was stopped, and the initial discharge capacity Qs (d) was determined from the amount of electricity that flowed during the discharge.
As for the positive electrode used in this example, NMC has an initial charge capacity Qs (c) = 169 mAh / g, an initial discharge capacity Qs (d) = 149 mAh / g, C8G has an initial charge capacity Qs (c) = 152 mAh / g, The initial discharge capacity Qs (d) was 149 mAh / g.

[Battery evaluation (characteristic evaluation test)]
The evaluation characteristic judgment test of the test battery cell was performed by the following method.

<Output characteristics evaluation>
Using the positive electrode (9 mmφ) as the test electrode and the Li metal foil (12 mmφ) as the counter electrode, a coin cell was prepared as described above and evaluated at 25 ° C.
As the evaluation of the output characteristic during discharging it was carried out constant-current discharge at 0.2 mA / cm ² and 11 mA / cm ^2. However, charging was unified at a constant current of 0.5 mA / cm ² up to 4.2 V, and discharging was cut at 3.0 V.
Superiority of the output takes the percentage of the discharge capacity of at 11 mA / cm ² to the discharge capacity at 0.2 mA / cm ^2, was determined to have a high output characteristic greater the value.

<Cycle characteristic evaluation (life test)>
A coin cell was prepared in the above manner using a combination of the positive electrode (12 mmφ) and the negative electrode (12 mmφ).
At this time, the balance between the weight of the positive electrode active material and the weight of the negative electrode active material was set so as to satisfy the following formula.
Negative electrode active material weight / positive electrode active material weight = 1.1 [Qs (c) / Qf (c)]

First, at 25 ° C., this coin cell battery was charged / discharged twice at a constant current of 0.2 C with an upper limit of 4.2 V and a lower limit of 3.0 V as initial conditioning. The definition of 1C was 1C = [Qs (d) × positive electrode active material weight] (mA). However, the discharge capacity (mAh) at the second cycle was redefined as 1 C (mA) and used for setting the current value during the cycle test.
In the cycle characteristic evaluation, a constant current charge / discharge cycle of 1 C having an upper limit of 4.2 V and a lower limit of 3.0 V was performed. However, at the time of charging, a constant voltage was applied at 4.2 V for 1 hour, and a pause of 10 minutes was inserted between the end of charging and the end of discharging.

  The superiority or inferiority of the life was determined by taking the ratio (%) of the discharge capacity at the 200th cycle to the discharge capacity in the initial cycle, and the greater the value, the better the life.

The battery evaluation results are summarized in Table 4.

From Table 4, when comparing the example using the same active material and the comparative example, it is clear that the example is superior to both the output characteristic and the cycle characteristic than the comparative example.
That the present invention, the dehydrogenation amount is 1.2 mg / g or less, and 24M4DBP absorption amount using 130 cm ^3/100 g or more carbon black as a conductive agent electrode, both output characteristics and cycle characteristics than conventional electrodes Can be seen to improve at the same time.
In the above-described embodiments, the electrode of the present invention is applied only to the positive electrode, but the same effect can be obtained when the electrode of the present invention is used for the negative electrode.

Claims (8)

An electrode for an electrochemical element comprising an active material and a conductive agent,
The weight ratio of the conductive agent to the active material weight is 0.5 wt% or more and 15 wt% or less,
The conductive agent is
Characterized in that it is obtained by the following measuring method (1500 ° C. × 30 minutes) the dehydrogenation amount is 1.2 mg / g or less, and 24M4DBP absorption conforming to JIS K6217 includes more oil furnace carbon black 130 cm ^3/100 g Electrode for electrochemical element.
(Measurement method)
0.5 g of carbon black is precisely weighed, put in an alumina tube, and decompressed to 0.01 Torr (1.3 Pa). Then, the decompression system is closed, and the carbon black is held in an electric furnace at 1500 ° C. for 30 minutes and exists in carbon black. Decomposes and volatilizes oxygen and hydrogen compounds. Volatile components are collected in a fixed-capacity gas collection tube through a quantitative suction pump. The amount of gas is determined from the pressure and temperature, the composition is analyzed by gas chromatography, the amount of hydrogen (H ₂ ) generated (mg) is determined, and the value converted to the amount of hydrogen per gram of carbon black is calculated (the unit is mg / g). _{2. The} electrode for an electrochemical element according to claim 1, wherein the oil adsorption carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 80 m ² / g or more and 300 m ² / g or less.   The electrode for an electrochemical element according to claim 1 or 2, wherein the crystallite size Lc of the oil furnace carbon black is 10 to 40 cm.   The electrode for an electrochemical element according to any one of claims 1 to 3, wherein the active material contains at least a compound capable of inserting and extracting lithium.   The electrode for an electrochemical element according to claim 4, wherein the compound capable of inserting and extracting lithium is a lithium transition metal composite oxide. 6. The electrode for an electrochemical element according to claim 5, wherein the lithium transition metal composite oxide has a crystal structure mainly identified by a layered structure and has a composition represented by the following formula (1).
Li _{1 + α} Ni _x Mn _y Co _z M _{1-xy z} O ₂ (1)
(However, −0.1 ≦ α ≦ 0.2, 0 <x ≦ 0.5, 0 <y <1.0, 0 ≦ z ≦ 0.5, 0.8 ≦ x + y + z ≦ 1.0, M is one or more of Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, Nb, and Zr)   The electricity according to claim 5 or 6, wherein the lithium transition metal composite oxide is formed by agglomerating primary particles to form secondary particles, and the shape of the secondary particles is spherical or elliptical. Electrode for chemical elements. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a lithium salt,
A lithium secondary battery, wherein at least one of the positive electrode and the negative electrode is the electrode for an electrochemical element according to any one of claims 4 to 7.