JP2004111109A - Electrode material for secondary battery, electrode for secondary battery containing the electrode material, and lithium ion secondary battery using the electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode material for a secondary battery useful for realizing a secondary battery especially with excellent initial efficiency and cycle property, an electrode for a secondary battery containing the electrode material and a lithium ion secondary battery using the electrode. <P>SOLUTION: A material used when manufacturing an electrode for a secondary battery contains spheroidal graphite particles with an acid functional group of 1.0 milliequivalent/kg or less and conductive carbonaceous microparticles relatively finer than and different from the spheroidal graphite particles in a mixed state. <P>COPYRIGHT: (C)2004,JPO

Description

【００６４】
上記実験例１〜７で得られた球状化黒鉛粒子または混合粉を二次電池用電極材料として用いて、コイン型のリチウムイオン二次電池を作製し、負極の性能として初期効率とサイクル特性を評価した。
【００６５】
リチウムイオン二次電池（コイン型）用の負極は、次に示す様に作成した。上記実験例１〜７で得られた球状化黒鉛粒子（または混合粉）１００質量部に対して、バインダーとしてカルボキシメチルセルロース（ダイセル化学社製、商品名：ＣＭＣ−１１５０）１質量部およびスチレンブタジエンゴム粉末（日本合成ゴム社製）１質量部を混合し、これに純水１００質量部を加えてスラリー状にした。得られたスラリーを厚さ１８μｍの銅箔上に塗布し、乾燥機（１００℃）で１時間乾燥した。乾燥後の膜を直径１．６ｃｍの円形に打ち抜いたのち、銅箔を除く塗布量を測定すると２０ｍｇであった。この膜をローラープレス機で、銅箔上に塗布した塗布物の密度が１．６ｇ／ｃｃとなるようにプレスしてリチウムイオン二次電池用の負極を作製した。
【００６６】
リチウムイオン二次電池（コイン型）用の正極は、初期効率を算出するために作製するリチウムイオン二次電池用の正極としてはリチウム箔を用い、サイクル特性を算出するために作製するリチウムイオン二次電池用の正極としてはＬｉＣｏＯ_２を活物質とする電極を用いた。ＬｉＣｏＯ_２を活物質とする電極は、次に示す方法で作成した。
【００６７】
ＬｉＣｏＯ_２９０質量部に対して、バインダーとしてポリフッ化ビニリデン１２％溶液（ＰＶｄＦ、クレハ化学社製、商品名：ＫＦＰ−１３２０）４１．７質量部、導電材としてケッチェンブラック（ケッチェンブラックインターナショナル社製、商品名：ケッチェンブラック）５質量部を夫々混合し、これにＮ−メチル−２−ピロリドン（三菱化学社製）２００質量部を加えてスラリー状にする。得られたスラリーを厚さ３０μｍのアルミ箔上に塗布し、乾燥機（１００℃）で１時間乾燥した。乾燥後の膜を直径１．６ｃｍの円形に打ち抜いたのち、アルミ箔を除く塗布量を測定すると４５ｍｇであった。この膜をローラープレス機で、アルミ箔上に塗布した塗布物の密度が２．８ｇ／ｃｃとなるようにプレスしてリチウムイオン二次電池用の正極を作製した。
【００６８】
負極と正極を、セパレータを介して対向させ、ステンレス製セルに組み込み電池を作製した。電解液としては、エチレンカーボネート（ＥＣ）とジメチルカーボネート（ＤＭＣ）を容積比１：１で混合した溶媒に、ＬｉＰＦ_６を１Ｍの割合で溶解したもの（三菱化学社製、商品名：ソルライト）を用いた。セパレータはＣｅｌｇａｒｄ社製の「セルガード＃３５０１（商品名）」を用いた。なお、電池の組み立てはアルゴンガス雰囲気下で行なった。
【００６９】
負極の性能を評価するために電池の初期効率を算出した。電池の充電は、電流値０．７４ｍＡで０Ｖまで充電した後、０Ｖの定電位で電流値が０．２ｍＡとなるまで行なった。電池の放電は、電流値０．７４ｍＡで１．０Ｖになるまで行なった。一回目の充電容量と放電容量から下記（２）式で計算した。算出結果を表１に示す。なお、電池の正極はリチウム箔である。
【００７０】
【数１】

【００７１】
また、負極の性能を評価するために電池のサイクル特性を算出した。電池の充電は、電流値６．４ｍＡで４．２Ｖまで充電した後、４．２Ｖの定電圧で電流値が０．２ｍＡとなるまで行なった。電池の放電は、電流値６．４ｍＡで３．０Ｖとなるまで行なった。サイクル特性は、１サイクル目の放電容量と充放電を２００サイクル繰り返したときの放電容量から下記（３）式で算出した。算出結果を表１に併せて示す。なお、電池の正極はＬｉＣｏＯ_２を活物質とする電極である。
【００７２】
【数２】

【００７３】
表１から明らかな様に、実験例１〜３は、本発明で規定する何れかの要件を満足しておらず、特にサイクル特性が悪い。一方、実験例４〜７は、本発明の要件を満足しており、初期効率は実験例３と同程度の特性を維持しつつサイクル特性が飛躍的に向上している。
【００７４】
【発明の効果】
本発明によれば、二次電池用電極材料であって、初期効率およびサイクル特性に優れた二次電池を実現するために有用な二次電池用電極材料を提供することができる。また、本発明では、該電極材料を含む二次電池用電極および該電極を用いたリチウムイオン二次電池を提供することができる。
【図面の簡単な説明】
【図１】球状化黒鉛粒子の製造に使用される装置を例示する概略説明図である。
【符号の説明】
１　槽　　　　　　　　　　　　　２　フィーダー
３　対向ノズル　　　　　　　　　４　分級機
５　吹き上げノズル[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrode material for a secondary battery, an electrode for a secondary battery including the electrode material, and a lithium ion secondary battery using the electrode.
[0002]
[Prior art]
Recently, along with the miniaturization of electronic devices and the like, a battery serving as a power source is also required to be miniaturized. In particular, a lithium ion secondary battery is receiving attention from the viewpoint of increasing the capacity of the battery. Among the lithium ion secondary batteries, those using a carbon material for the negative electrode are also useful in that a large capacity is easily obtained, and a safe and high voltage is easily obtained. However, when a carbon material is used for the negative electrode, there is a problem that the cycle characteristics deteriorate.
[0003]
Therefore, a technique has been proposed in which an electrode obtained by uniformly dispersing copper fine particles in a carbon material is used as the negative electrode to increase the utilization rate of the negative electrode and improve the cycle characteristics (for example, see Patent Document 1). Also disclosed is a technology for increasing the charge / discharge cycle life by using an electrode in which the negative electrode active material is a mixture of at least one of massive graphite and flaky graphite and mesophase small spherical carbon powder as an electrode for a nonaqueous electrolyte secondary battery. (See, for example, Patent Document 2). However, as a result of investigations by the present inventors, in these electrodes, the electric capacity required at the time of initial charging is higher than the electric capacity required for discharging, and the initial charging efficiency (hereinafter, sometimes referred to as “initial efficiency”). Has a problem).
[0004]
By the way, carbon materials used for batteries include natural graphite and artificial graphite. Generally, various functional groups (for example, carboxyl group, phenol group, lactone group, carbonyl group, etc.) exist on the surface of the carbon material. Therefore, this functional group reacts with the electrolytic solution at the time of the first charge to cause a side reaction, and the charge capacity is lost, so that the initial efficiency is deteriorated.
[0005]
In order to solve such a problem, a technique has been proposed in which the amount of functional groups present on the surface of the carbon material is reduced by heat-treating the raw material of the carbon material in a vacuum or a reducing atmosphere (for example, Patent Document 3). reference.). However, in this technique, the following problem arises because flaky graphite particles are used as the carbon material. That is, when forming an electrode, it is common to apply a slurry obtained by mixing crushed natural graphite or artificial graphite with a solvent and a binder (binder) to an object, When flake-like graphite particles are used, the fluidity of the slurry becomes poor and the coating workability is significantly impaired.
[0006]
The present inventors have conducted studies with a view to further improving such a problem, and as a result, when flake-like natural graphite particles are spheroidized by crushing and reaggregating, the flake-like natural graphite particles are originally formed. The inventors have found that the slurry characteristics are improved while maintaining the advantages possessed, and that the decrease in the discharge capacity at a large discharge current value can be suppressed. .).
[0007]
However, as pointed out in Patent Document 3, when a large amount of a functional group is present on the surface of the spheroidized graphite particles, the functional group reacts with the electrolytic solution at the time of the first charge, causing a decrease in the initial efficiency. In addition, when flake graphite is pulverized and re-agglomerated to form a spheroid, the slurry properties are improved, but the graphite particle surface becomes smooth, so the number of contacts between graphite particles or between graphite particles and binder particles is reduced, and the conductive component is reduced. Adhesion between the members deteriorates, and the conductivity decreases, causing a decrease in cycle characteristics.
[0008]
[Patent Document 1]
JP-A-9-245798
[Patent Document 2]
JP 2001-236950 A
[Patent Document 3]
JP-A-8-148185
[Patent Document 4]
JP-A-11-263612
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of such problems, and an object of the present invention is to provide a secondary battery electrode material that is particularly useful for realizing a secondary battery excellent in initial efficiency and cycle characteristics. An object of the present invention is to provide an electrode material for a secondary battery. Another object of the present invention is to provide a secondary battery electrode including the electrode material and a lithium ion secondary battery using the electrode.
[0010]
[Means for Solving the Problems]
The secondary battery electrode material according to the present invention which can solve the above-mentioned problem is a material used when manufacturing a secondary battery electrode, and has an acidic functional group content of 1.0 meq / kg or less. The point is that the spheroidized graphite particles and conductive carbonaceous fine particles which are relatively finer than the spheroidized graphite particles and are different from the spheroidized graphite particles are mixed and contained.
[0011]
As the spheroidized graphite particles, flake graphite is pulverized and then re-agglomerated, and a particle having an average particle diameter of 10 μm or more is used. At this time, the conductive carbonaceous fine particles have an average particle diameter of 10 μm. It is preferable to use one having a particle diameter of less than (not including 0 μm).
[0012]
In the present invention, the total amount of acidic functional groups in the mixed powder obtained by mixing the spheroidized graphite particles and the conductive carbonaceous fine particles is preferably 2.5 meq / kg or less.
[0013]
As the conductive carbonaceous fine particles, flaky graphite fine particles and / or carbon black can be suitably used, and flaky graphite fine particles: 1 to 20% (meaning “% by mass”; the same applies hereinafter) and / or carbon black. : 0.1 to 2.0% (meaning "% by mass"; the same applies hereinafter).
[0014]
The secondary battery electrode containing the secondary battery electrode material has a low reaction with the electrolytic solution at the time of the first charging, has a high conductivity, and has a lithium ion secondary electrode having the secondary battery electrode as a negative electrode. The secondary battery has excellent initial efficiency and cycle characteristics.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have studied from various angles in order to solve the problems as described above. As a result, the amount of acidic functional groups contained in the spheroidized particles obtained by pulverizing and reaggregating the flaky graphite is suppressed to a predetermined amount or less, and is relatively finer than the spheroidized graphite particles, and The inventors have found that the above problem can be solved satisfactorily by mixing conductive carbonaceous fine particles different from the spheroidized graphite particles, and have completed the present invention. Hereinafter, the configuration, operation and effect of the present invention will be described in detail.
[0016]
The electrode material for a secondary battery of the present invention is obtained by pulverizing flaky graphite, reaggregating the flake graphite, and spheroidizing the graphite. As described above, after the flake graphite is pulverized, the flake graphite particles are re-agglomerated, and the spheroidized graphite particles have good fluidity when mixed with a solvent or a binder.
[0017]
Here, the spherical shape means not only a true spherical shape such as a soccer ball or a tennis ball, but also an elliptical shape such as a rugby ball, and in the present invention, refers to a shape having a circularity of about 0.86 or more. . However, since the circularity is an index calculated by projecting three-dimensional graphite particles on a two-dimensional plane, for example, when calculating the circularity of commonly available flaky natural graphite particles, it is about 0.84, Although similar to the circularity of the graphite particles of the present invention, the flaky graphite particles (raw material) are planar particles, whereas the actual shape of the secondary battery electrode material of the present invention is three-dimensional and completely different.
[0018]
The spheroidized graphite particles can be obtained by pulverizing the flake graphite and then reaggregating them, but the specific method for producing the spheroidized graphite particles is not particularly limited. For example, it can be manufactured by the method proposed by the present inventors (JP-A-11-263612) or a method similar thereto. Hereinafter, an example of the manufacturing method will be described with reference to the drawings.
[0019]
FIG. 1 is a schematic explanatory view of an apparatus used for producing spheroidized graphite particles, wherein 1 is a tank, 2 is a feeder, 3 is an opposed nozzle, 4 is a classifier, and 5 is a blow-up nozzle.
[0020]
Scaly graphite (raw material) is supplied into the tank 1 from a feeder 2 provided in the tank 1. The feeder 2 is preferably provided as a hopper type at an appropriate location in the tank 1, and can be used as an outlet for spheroidized graphite particles. Further, the feeder 2 may be provided with a screw type at the lower part of the tank 1. The amount of the raw material supplied into the tank 1 may be determined in consideration of the capacity of the tank 1.
[0021]
An opposing nozzle 3 is provided at the lower side of the tank 1 through the tank wall, and a jet stream is blown from the opposing nozzle 3 to form a collision area on the lower side in the tank 1. The flaky graphite entering the airflow in the collision area collides with each other, re-aggregates while being pulverized, and becomes spherical.
[0022]
It is preferable to provide a plurality (for example, three to four) of the opposed nozzles 3. The speed of the jet airflow blown from the opposed nozzle 3, the blown gas amount, the tank pressure, and the like are set so as to achieve smooth collision and flow, and the flake graphite is spheroidized by appropriately setting the operation time. For example, the nozzle discharge pressure is about 0.01 to 0.50 MPa, and the blowing gas amount is 0.2 to 1.0 Nm.³/ Min, the tank pressure is about -10 to 30 kPa, and the operation time is about 1 to 100 minutes. The gas blown from the opposed nozzle 3 may be air, nitrogen, water vapor, or the like, and the temperature in the tank 1 may be about 0 to 60 ° C.
[0023]
Gas convection occurs in the tank 1, and particles that collide with each other in the collision area on the lower side of the tank 1 and are blown upward along the convection in the tank 1, and then settle again. That is, the particles are blown up near the center of the tank 1, fall down along the wall of the tank 1, and circulate in the tank 1.
[0024]
By providing a classifier 4 at the upper part of the tank 1, fine powder below the classification limit can be discharged out of the tank 1. Although a known classifier may be provided as the classifier 4, a high-speed rotating classifier is generally used. The amount discharged at this time depends on the particle size of the flaky graphite used as a raw material.
[0025]
The above operation is preferably performed in a batch. When air is blown into the tank 1 from a blow-up nozzle 5 provided at the bottom of the tank 1, spheroidized graphite particles can be collected from the feeder 2.
[0026]
As a raw material of the spheroidized graphite particles, flaky natural graphite or artificial graphite can be used. For example, flaky natural graphite is generally used in a purity of more than 85% to 99% and is used as it is. Good. If necessary, it is preferable to further increase the purity by a known method. There are various particle sizes of the flaky graphite as a raw material, and as described later, in order to control the average particle size of the spheroidized graphite particles obtained by spheroidizing the flaky graphite to 10 μm or more, It is preferable to use flaky graphite (raw material) having a diameter of about 10 to 60 μm.
[0027]
By the way, when the spheroidized graphite particles produced by the above method are used as an electrode material, it has become clear that the initial efficiency of the obtained secondary battery is unexpectedly low. Therefore, when pursuing the cause of the decrease in the initial efficiency of the secondary battery, when a large amount of functional groups are present on the surface of the spheroidized graphite particles, the functional groups react with the electrolytic solution at the time of the first charge to reduce the initial efficiency. I found something to cause. Further, when the reaction between the functional group and the electrolytic solution was further examined, it was found that among the functional groups, particularly, the acidic functional group greatly affected the reduction in the initial efficiency. That is, the acidic functional group refers to functional groups such as a carboxyl group, a phenol group, a lactone group, and a carbonyl group, and it has been found that these functional groups are particularly easy to react with the electrolytic solution.
[0028]
In addition, when spheroidal graphite is pulverized and then reagglomerated and spheroidized graphite particles are used as an electrode material, the cycle characteristics of the obtained secondary battery are unexpectedly low. The reason for this is, as described above, that the scale-like graphite is agglomerated and formed into a spheroid, thereby reducing the contact points between the particles and deteriorating the adhesion, and the conductivity of the electrode itself is considered to be reduced. .
[0029]
Therefore, the present inventors have found that if the amount of acidic functional groups present on the surface of spheroidized graphite particles can be suppressed to a predetermined amount or less and the number of contacts between graphite particles can be increased, the initial efficiency and cycle characteristics as a secondary battery can be improved. We thought that it could be greatly improved, and proceeded with research along that line. As a result, the amount of acidic functional groups contained in the spheroidized graphite particles is suppressed to a predetermined amount or less to inactivate the graphite particles, and is relatively finer than the spheroidized graphite particles. It has been found that the mixing of conductive carbonaceous fine particles different from the particles significantly improves both the initial efficiency and the cycle characteristics of the secondary battery.
[0030]
That is, if conductive carbonaceous fine particles that are relatively finer than the spheroidized graphite particles are mixed with the spheroidized graphite particles, the number of contact points between the particles increases, whereby the adhesion becomes better, the conductivity increases, and the cycle characteristics are improved. improves. However, since the conductive carbonaceous fine particles themselves also have an acidic functional group as described later, when the conductive carbonaceous fine particles and the spheroidized graphite particles are mixed, the amount of the acidic functional groups in the entire mixed powder increases, and the initial amount increases. This leads to lower efficiency. Therefore, when the spheroidized graphite particles are mixed with the conductive carbonaceous fine particles and used, the amount of the acidic functional groups in the mixed powder as a whole can be kept at a low level by using the acidic carbonaceous fine particles themselves. In consideration of the amount of the functional group, it is necessary to keep the amount of the acidic functional group of the spheroidized graphite particles small. In the present invention, "conductive carbonaceous fine particles" refers to particles other than spheroidized graphite particles obtained by pulverizing flaky graphite and then reaggregating the same (details will be described later).
[0031]
However, the amount of the conductive carbonaceous fine particles depends on the type, but as described later, it is relatively small up to about 20%, and the amount of acidic functional groups contained therein is relatively small. Is mainly governed by the amount of acidic functional groups of the spheroidized graphite particles.
[0032]
For this reason, in the present invention, it is important to suppress the amount of acidic functional groups of the spheroidized graphite particles to 1.0 meq / kg or less. That is, if the amount of acidic functional groups present on the surface of the spheroidized graphite particles is 1.0 meq / kg or less, a mixed powder obtained by mixing the spheroidized graphite particles with conductive carbonaceous fine particles is used as an electrode for a secondary battery. Even when used as a raw material, the amount of acidic functional groups in the whole mixed powder can be suppressed to a sufficiently low level of about 2.5 meq / kg or less. As a result, the reaction between the acidic functional group and the electrolytic solution at the time of the first charging is suppressed, and the initial efficiency can be increased. The amount of the acidic functional group present on the surface of the spheroidized graphite particles is desirably controlled to preferably 0.5 meq / kg or less, and the amount of the acidic functional group as the whole mixed powder is preferably 1.5 meq. / Kg or less. Note that the equivalent means the number of moles of reacted ions.
[0033]
The method for suppressing the amount of acidic functional groups present on the surface of the spheroidized graphite particles to a desired amount or less is not particularly limited. For example, if the spheroidized graphite particles are heated under a non-oxidizing atmosphere, the spheroidized graphite particles are present on the surface of the graphite particles. The acidic functional group can be easily decomposed and removed. As the non-oxidizing atmosphere, an inert gas is preferable.₂, He or the like can be suitably used. The temperature at which the spheroidized graphite particles are heated is not particularly limited as long as the acidic functional groups can be decomposed and removed, but may be, for example, 600 ° C. or higher, preferably 800 ° C. or higher.
[0034]
As a means for quantifying the amount of the acidic functional group, for example, the following method proposed by Boehm et al. Can be mentioned.
[0035]
<The method of Boehm et al.>
10 g of spheroidized graphite particles and 0.01 mol / L of C₂H₅After stirring 50 g of the ONa aqueous solution in the flask for 2 hours, it is left at room temperature for 22 hours. After standing, the mixture is further stirred for 30 minutes and then filtered to collect the filtrate. 25 mL of the collected filtrate is subjected to neutralization titration with a 0.01 mol / L HCl aqueous solution, and the amount (mL) of the HCl aqueous solution required until the pH reaches 4.0 is measured. The amount of the acidic functional group (milli-equivalent / kg) is calculated from the amount of the HCl aqueous solution and the following formula (1).
Amount of acidic functional group = (amount of 25-HCl aqueous solution) × 2 (1)
[0036]
In the present invention, in addition to the use of spheroidized graphite particles in which the amount of acidic functional groups is suppressed to a predetermined amount or less as described above, relatively finer than the spheroidized graphite particles, and the spheroidized graphite particles It is important to mix and use different conductive carbonaceous fine particles.
[0037]
In the present invention, the conductive carbonaceous fine particles are carbonaceous fine particles that indicate conductivity, and examples thereof include flaky graphite fine particles, carbon black, and fibrous graphite fine particles. In the present invention, in particular, flaky graphite fine particles and carbon black can be suitably used. Each of them can be used alone, or a mixture of any of these can be used. However, the conductive carbonaceous fine particles in the present invention do not include spheroidized graphite particles obtained by pulverizing flaky graphite and then reaggregating the flake graphite to form a spheroid.
[0038]
As the conductive fine particles, for example, it is conceivable to use metal fine particles. However, inactive metal fine particles reduce the battery capacity, and active metal fine particles cause a new problem of cycle deterioration of the metal itself. Therefore, the present invention employs conductive carbonaceous fine particles.
[0039]
The spheroidized graphite particles and the conductive carbonaceous fine particles can be easily distinguished by observing an electron micrograph taken at a magnification of, for example, 600 using a scanning electron microscope.
[0040]
When the flaky graphite fine particles are mixed with the spheroidized graphite particles as the conductive carbonaceous fine particles, it is preferable to mix 1 to 20% with respect to the spheroidized graphite particles. This is because if the content is 1% or more, the number of contacts between particles increases, and the purpose of improving cycle characteristics is effectively exhibited. It is more preferable to mix 3% or more. However, if the mixing amount exceeds 20%, the number of fine particles having a small particle diameter increases, so that the surface area becomes too large, causing a problem of reduced safety. Becomes too dense, the voids between the particles are reduced, and the permeability of the electrolyte to the inside of the electrode is deteriorated, leading to deterioration of the cycle characteristics. In addition, since the flaky graphite fine particles themselves also have an acidic functional group, if the mixing amount exceeds 20%, the amount of acidic functional groups in the entire mixed powder increases, which causes a decrease in initial efficiency. More preferably, the mixing amount is 15% or less, and further preferably, the mixing amount is 10% or less.
[0041]
When carbon black is mixed with the spheroidized graphite particles as conductive carbonaceous fine particles, it is preferable to mix 0.1 to 2.0% with respect to the spheroidized graphite particles. Since carbon black has a smaller particle size than the flaky graphite fine particles, the desired effect can be obtained by mixing a small amount of 0.1% or more as compared with the flaky graphite fine particles. More preferably, the content is 0.3% or more. However, if the mixing amount is too large, a problem such as a decrease in the binding property of the electrode or a decrease in the initial efficiency due to an increase in the amount of the acidic functional group occurs. , More preferably, 1.0% or less.
[0042]
The flaky graphite fine particles and the carbon black may be used alone and mixed with the spheroidized graphite particles, respectively, or may be mixed in an arbitrary ratio and used in combination with the spheroidized graphite particles. At this time, when the flaky graphite fine particles and carbon black are used in combination as the conductive carbonaceous fine particles, the amount of the acidic functional groups of the entire mixed powder obtained by mixing the mixed conductive carbonaceous fine particles and the spheroidized graphite particles, It is desirable to mix the mixed conductive carbonaceous fine particles at an arbitrary ratio so as to be 2.5 meq / kg or less.
[0043]
The size of the conductive carbonaceous fine particles only needs to be relatively smaller than the spheroidized graphite particles. The reason for using conductive carbonaceous fine particles that are relatively smaller than spheroidized graphite particles is that relatively small conductive carbonaceous fine particles are interposed between relatively large spheroidized graphite particles so that the particles can contact each other. Is increased, and the conductivity is increased. Here, "relatively" means that when the average particle diameter of the spheroidized graphite particles and the conductive carbonaceous fine particles is compared, the conductive carbonaceous fine particles need only be smaller. . Specifically, the difference between the average particle diameter of the spheroidized graphite particles and the conductive carbonaceous fine particles may be about 1 μm or more, more preferably about 5 μm or more, and further preferably about 10 μm or more.
[0044]
In the present invention, it is preferable to use a mixture of spheroidized graphite particles having an average particle diameter of 10 μm or more and conductive carbonaceous fine particles having an average particle diameter of less than 10 μm (not including 0 μm). This is because the use of the spheroidized graphite particles having an average particle diameter of 10 μm or more improves the liquid permeability of the electrolytic solution into the inside of the electrode constituted by the particles and increases the reaction efficiency at the electrode. More preferably, it is desirable to use spheroidized graphite particles having an average particle diameter of 15 μm or more, further preferably 20 μm or more. The upper limit of the average particle diameter of the spheroidized graphite particles is not particularly limited. The upper limit is preferably about 40 μm. On the other hand, the conductive carbonaceous fine particles preferably have an average particle diameter of less than 10 μm. This is because it efficiently penetrates between the spheroidized graphite particles and effectively exerts the effect of improving the conductivity by increasing the number of contacts. The more preferable average particle diameter of the conductive carbonaceous fine particles is 6 μm or less. The lower limit of the average particle diameter of the conductive carbonaceous fine particles is not particularly limited, but if the average particle diameter of the conductive carbonaceous fine particles is too small, it cannot contribute to an increase in contact between particles, so the lower limit is about 0.5 μm. Is good.
[0045]
In the present invention, a mixture of spheroidized graphite particles and conductive carbonaceous fine particles so as to satisfy the above requirements can be used as various secondary battery electrode materials. It is preferably used as a material. Examples of the non-aqueous secondary battery include a lithium ion secondary battery.
[0046]
When producing an electrode using the electrode material for a secondary battery of the present invention, it is common to mix and mold with a binder, and the obtained electrode is used as an electrode for various secondary batteries. be able to. Although there are various types of secondary batteries, the secondary battery electrode of the present invention is suitable as a nonaqueous secondary battery electrode. There are various types of non-aqueous secondary batteries, but the secondary battery electrode of the present invention exhibits particularly excellent performance as a negative electrode of a lithium ion secondary battery because graphite can absorb a large amount of lithium ions. I do.
[0047]
As the negative electrode material of the lithium ion secondary battery comprising the secondary battery electrode of the present invention as a negative electrode, in addition to the spheroidized graphite particles of the present invention, as a binder, for example, carboxymethyl cellulose, styrene butadiene rubber, polyvinylidene fluoride ( PVdF), polytetrafluoroethylene, or the like may be mixed to form a negative electrode.
[0048]
As a positive electrode material in a lithium ion secondary battery, for example, LiCoO₂And LiNiO₂, LiNi_1-yCo_yO₂, LiMnO₂, LiMn₂O₄, LiFeO₂Are used. As the binder for the positive electrode, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), or the like can be used.
[0049]
Examples of the electrolyte in the lithium ion secondary battery include an organic solvent such as ethylene carbonate (EC), and an organic solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), 1,2-dimethoxyethane, and 1,2. -LiPF in a mixed solvent with a low boiling point solvent such as diethoxymethane, ethoxymethoxyethane, etc.₆And LiBF₄, LiClO₄, LiCF₃SO₃, LiAsF₆For example, a solution in which an electrolyte solute (electrolyte salt) is dissolved is used.
[0050]
As the separator in the lithium ion secondary battery, for example, a nonwoven fabric, cloth, microporous film, or the like mainly containing a polyolefin such as polyethylene or polypropylene is used.
[0051]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are not intended to limit the present invention, and may be appropriately modified and implemented within a range that can conform to the purpose of the preceding and the following. It is possible and they are all included in the technical scope of the present invention.
[0052]
A negative electrode of a lithium ion secondary battery was manufactured using the spheroidized graphite particles or mixed powder obtained in Experimental Examples 1 to 7 below.
[0053]
Experimental example 1
Chinese flaky natural graphite (average particle diameter: 25 μm, purity: 99% or more) was pulverized using a counter jet mill “100AFG” manufactured by Hosokawa Micron Corporation and reagglomerated to form a spheroid.
[0054]
FIG. 1 is a schematic explanatory view of a counter jet mill “100AFG” (a device for producing spheroidized graphite particles) manufactured by Hosokawa Micron Corporation. The inside of the tank 1 is cylindrical, and three opposing nozzles 3 (nozzle inner diameter: 2.5 mm) are arranged on the lower side of the tank 1 so as to face each other so as to face the center. At the top of the tank 1, a high-speed rotating classifier is arranged as an example of the classifier 4. The number of rotations of the high-speed classifier is 20,000 rpm. The feeder 2 is provided on the side wall of the tank 1, and a blow-up nozzle 5 is provided at the bottom of the tank 1. FIG. 1 shows only one opposing nozzle.
[0055]
200 g of the scaly natural graphite was introduced from the feeder 2 and spheroidized under the following conditions. The spheroidizing conditions were as follows: the nozzle discharge air pressure of the opposing nozzle 3 was 0.13 MPa, the operation time was 10 minutes, and the temperature in the tank 1 was 25 ° C. The average particle size of the obtained spheroidized graphite particles was 28 μm.
[0056]
Experimental example 2
The spheroidized graphite particles obtained in Experimental Example 1 were mixed with 3% of flaky graphite fine powder from China (average particle size: 6 μm) to obtain a mixed powder.
[0057]
Experimental example 3
The spheroidized graphite particles obtained in Experimental Example 1 were heat-treated at 1200 ° C. for 2 hours in a nitrogen atmosphere. The heat-treated spheroidized graphite particles are hereinafter referred to as “heat-treated spheroidized graphite particles”.
[0058]
Experimental example 4
The spheroidized graphite particles obtained in Experimental Example 1 were heat-treated at 1200 ° C. for 2 hours in a nitrogen atmosphere. The spheroidized graphite particles after the heat treatment were mixed with 3% of flaky graphite fine powder from China (average particle diameter: 6 μm) to obtain a mixed powder.
[0059]
Experimental example 5
The spheroidized graphite particles obtained in Experimental Example 1 were heat-treated at 1200 ° C. for 2 hours in a nitrogen atmosphere. The spheroidized graphite particles after the heat treatment were mixed with 5% of flaky graphite fine powder from China (average particle size: 6 μm) to obtain a mixed powder.
[0060]
Experimental example 6
The spheroidized graphite particles obtained in Experimental Example 1 were heat-treated at 1200 ° C. for 2 hours in a nitrogen atmosphere. 0.5% of carbon black (trade name “3050B”, average particle diameter: 0.04 μm) manufactured by Mitsubishi Chemical Corporation was mixed with the spheroidized graphite particles after the heat treatment to obtain a mixed powder.
[0061]
Experimental example 7
The spheroidized graphite particles obtained in Experimental Example 1 were heat-treated at 1200 ° C. for 2 hours in a nitrogen atmosphere. To the spheroidized graphite particles after the heat treatment, 3% of flaky graphite fine powder (average particle diameter: 6 μm) produced in China and carbon black (trade name “3050B”, average particle diameter: 0.04 μm) manufactured by Mitsubishi Chemical Corporation were added. 5% was mixed to obtain a mixed powder.
[0062]
The amount of the acidic functional group of the spheroidized graphite particles (or the spheroidized graphite particles after the heat treatment) obtained in Experimental Examples 1 to 7 was measured by the above-mentioned method of Boehm et al. In addition, the amount of acidic functional groups of the mixed powder mixed with the spheroidized graphite particles (after the heat treatment) and the flaky graphite fine powder and / or carbon black was similarly measured, and Table 1 shows the amount of acidic functional groups of the entire mixed powder. Indicated.
[0063]
[Table 1]

[0064]
Using the spheroidized graphite particles or the mixed powder obtained in the above Experimental Examples 1 to 7 as an electrode material for a secondary battery, a coin-type lithium ion secondary battery was produced, and the initial efficiency and cycle characteristics were evaluated as the performance of the negative electrode. evaluated.
[0065]
A negative electrode for a lithium ion secondary battery (coin type) was prepared as follows. Based on 100 parts by mass of the spheroidized graphite particles (or mixed powder) obtained in Experimental Examples 1 to 7, 1 part by mass of carboxymethyl cellulose (manufactured by Daicel Chemical Industries, Ltd., trade name: CMC-1150) and styrene-butadiene rubber One part by mass of a powder (manufactured by Nippon Synthetic Rubber Co., Ltd.) was mixed, and 100 parts by mass of pure water was added thereto to form a slurry. The obtained slurry was applied on a copper foil having a thickness of 18 μm, and dried for 1 hour in a drier (100 ° C.). After the dried film was punched out into a circular shape having a diameter of 1.6 cm, the coating amount excluding the copper foil was measured and found to be 20 mg. This film was pressed with a roller press so that the density of the coating material applied on the copper foil was 1.6 g / cc, to produce a negative electrode for a lithium ion secondary battery.
[0066]
The positive electrode for a lithium ion secondary battery (coin type) uses a lithium foil as a positive electrode for a lithium ion secondary battery, which is manufactured to calculate initial efficiency, and a lithium ion secondary battery, which is manufactured to calculate cycle characteristics. LiCoO as the positive electrode for the secondary battery₂Was used as an active material. LiCoO₂Was prepared by the following method.
[0067]
LiCoO₂For 90 parts by mass, 41.7 parts by mass of a polyvinylidene fluoride 12% solution (PVdF, manufactured by Kureha Chemical Co., Ltd., trade name: KFP-1320) as a binder, and Ketjen Black (Ketjen Black International Co., Ltd.) as a conductive material (Trade name: Ketjen Black) 5 parts by mass are mixed, and 200 parts by mass of N-methyl-2-pyrrolidone (manufactured by Mitsubishi Chemical Corporation) are added to form a slurry. The obtained slurry was applied on an aluminum foil having a thickness of 30 μm, and dried for 1 hour in a drier (100 ° C.). After the dried film was punched into a circular shape having a diameter of 1.6 cm, the coating amount excluding the aluminum foil was measured to be 45 mg. This film was pressed with a roller press so that the density of the coating material applied on the aluminum foil was 2.8 g / cc, to produce a positive electrode for a lithium ion secondary battery.
[0068]
The negative electrode and the positive electrode were opposed to each other with a separator interposed therebetween, and the battery was built in a stainless steel cell. As an electrolyte, LiPF was mixed with a solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 1: 1.₆(Mitsubishi Chemical Corp., trade name: Sollite) was used. As a separator, "Celgard # 3501 (trade name)" manufactured by Celgard was used. The battery was assembled in an argon gas atmosphere.
[0069]
The initial efficiency of the battery was calculated to evaluate the performance of the negative electrode. After charging the battery to 0 V at a current value of 0.74 mA, the battery was charged at a constant potential of 0 V until the current value reached 0.2 mA. The battery was discharged at a current value of 0.74 mA until the voltage reached 1.0 V. It was calculated from the first charge capacity and discharge capacity by the following equation (2). Table 1 shows the calculation results. The positive electrode of the battery is a lithium foil.
[0070]
(Equation 1)

[0071]
In addition, the cycle characteristics of the battery were calculated in order to evaluate the performance of the negative electrode. After charging the battery to 4.2 V at a current value of 6.4 mA, the battery was charged at a constant voltage of 4.2 V until the current value reached 0.2 mA. The battery was discharged until the voltage reached 3.0 V at a current value of 6.4 mA. The cycle characteristics were calculated from the discharge capacity at the first cycle and the discharge capacity obtained when charge / discharge was repeated for 200 cycles, using the following equation (3). The calculation results are also shown in Table 1. The positive electrode of the battery is LiCoO₂Is an electrode using as an active material.
[0072]
(Equation 2)

[0073]
As is clear from Table 1, Experimental Examples 1 to 3 do not satisfy any of the requirements defined in the present invention, and particularly have poor cycle characteristics. On the other hand, Experimental Examples 4 to 7 satisfy the requirements of the present invention, and the cycle efficiency is dramatically improved while maintaining the same initial efficiency as that of Experimental Example 3.
[0074]
【The invention's effect】
According to the present invention, it is possible to provide an electrode material for a secondary battery, which is an electrode material for a secondary battery and useful for realizing a secondary battery having excellent initial efficiency and cycle characteristics. Further, in the present invention, it is possible to provide an electrode for a secondary battery containing the electrode material and a lithium ion secondary battery using the electrode.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view illustrating an apparatus used for producing spheroidized graphite particles.
[Explanation of symbols]
1 tank 2 feeder
3 opposed nozzle 4 classifier
5 blowing nozzle

Claims (7)

A material used when manufacturing an electrode for a secondary battery,
Spheroidized graphite particles having an acidic functional group content of 1.0 meq / kg or less;
An electrode material for a secondary battery, comprising conductive carbonaceous fine particles that are relatively finer than the spheroidized graphite particles and different from the spheroidized graphite particles in a mixed state. The spheroidized graphite particles are obtained by pulverizing flaky graphite and then reaggregating the particles, wherein the average particle size is 10 μm or more, and the average particle size of the conductive carbon fine particles is less than 10 μm. 2. The electrode material for a secondary battery according to item 1. The electrode material for a secondary battery according to claim 1 or 2, wherein the total amount of acidic functional groups in the mixed powder obtained by mixing the spheroidized graphite particles and the conductive carbonaceous fine particles is 2.5 meq / kg or less. The electrode material for a secondary battery according to any one of claims 1 to 3, wherein the conductive carbonaceous fine particles are flaky graphite fine particles and / or carbon black. As the conductive carbonaceous fine particles,
It contains flaky graphite fine particles: 1 to 20% (meaning “% by mass”; the same applies hereinafter) and / or carbon black: 0.1 to 2.0% (meaning “% by mass”; the same applies hereinafter). The electrode material for a secondary battery according to claim 4. An electrode for a secondary battery, comprising the electrode material for a secondary battery according to claim 1. A lithium ion secondary battery comprising the secondary battery electrode according to claim 6 as a negative electrode.

Images