JP5881468B2 - Positive electrode active material for lithium secondary battery and lithium secondary battery - Google Patents
Positive electrode active material for lithium secondary battery and lithium secondary battery Download PDFInfo
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Description
本発明は、リチウム二次電池用正極活物質およびリチウム二次電池に関し、特に、フッ化鉄粒子を含むリチウム二次電池用正極活物質およびこれを用いたリチウム二次電池に関する。 The present invention relates to a positive electrode active material for lithium secondary batteries and a lithium secondary battery, and more particularly to a positive electrode active material for lithium secondary batteries containing iron fluoride particles and a lithium secondary battery using the same.
最近、リチウム二次電池用の正極活物質として、フッ化金属を用いることが検討されている。例えば、特許文献１には、炭素でコートされたフッ化金属からなる正極活物質が提案されている。
フッ化金属の中でも、フッ化鉄は、安価で高い充放電容量を有し、熱安定性が高く、安全性に優れているため、次世代のリチウム二次電池用の正極活物質の材料として有望視されている。
Recently, the use of metal fluoride as a positive electrode active material for lithium secondary batteries has been studied. For example, Patent Document 1 proposes a positive electrode active material made of a metal fluoride coated with carbon.
Among metal fluorides, iron fluoride is inexpensive and has high charge / discharge capacity, high thermal stability, and excellent safety, so it can be used as a positive electrode active material for next-generation lithium secondary batteries. Promising.
しかしながら、フッ化鉄をリチウム二次電池用の正極活物質の材料として使用した場合、従来のリチウム二次電池と比較して、サイクル特性及び出力特性が低くなるという問題がある。
フッ化鉄を使用した正極活物質を用いたリチウム二次電池の出力特性が低い原因としては、フッ化鉄の電子伝導度が低いことが挙げられる。したがって、フッ化鉄粒子の表面に炭素膜を被覆して導電性を付与し、これを正極活物質として使用することで、出力特性の改善を図ることができる。
However, when iron fluoride is used as a material for a positive electrode active material for a lithium secondary battery, there is a problem that cycle characteristics and output characteristics are lowered as compared with conventional lithium secondary batteries.
The reason why the output characteristics of the lithium secondary battery using the positive electrode active material using iron fluoride is low is that the electronic conductivity of iron fluoride is low. Therefore, the carbon fluoride film is coated on the surface of the iron fluoride particles to impart conductivity, and by using this as a positive electrode active material, the output characteristics can be improved.
しかし、従来の技術では、フッ化鉄を使用した正極活物質を用いたリチウム二次電池において、十分な出力特性を得ることはできなかった。
本発明は上記事情に鑑みてなされたものであり、フッ化鉄粒子を含み、出力特性に優れたリチウム二次電池が得られるリチウム二次電池用正極活物質およびこれを用いたリチウム二次電池を提供することを課題とする。
However, in the conventional technology, sufficient output characteristics cannot be obtained in a lithium secondary battery using a positive electrode active material using iron fluoride.
The present invention has been made in view of the above circumstances, and includes a positive electrode active material for a lithium secondary battery that includes iron fluoride particles and that provides a lithium secondary battery with excellent output characteristics, and a lithium secondary battery using the same. It is an issue to provide.
本発明者は、上記課題を解決し、フッ化鉄を使用した正極活物質を用いたリチウム二次電池において、十分な出力特性を得るために鋭意検討した。
その結果、フッ化鉄を使用した正極活物質を用いた場合に、従来のリチウム二次電池と比較して出力特性が低くなる原因の一つが、フッ化鉄粒子におけるリチウムイオンのイオン拡散係数が低いためであることが分かった。
The present inventor has intensively studied in order to solve the above problems and to obtain sufficient output characteristics in a lithium secondary battery using a positive electrode active material using iron fluoride.
As a result, when a positive electrode active material using iron fluoride is used, one of the causes for the lower output characteristics compared to conventional lithium secondary batteries is the ion diffusion coefficient of lithium ions in the iron fluoride particles. It turns out that it is because it is low.
このため、本発明者は、フッ化鉄粒子におけるリチウムイオンのイオン拡散係数を補い、リチウム二次電池の出力特性を向上させるために、正極活物質に含有させるフッ化鉄粒子の粒径に着目して検討を重ねた。
その結果、フッ化鉄粒子の平均粒径を１μｍ以下とすることで、これを含む正極活物質を用いたリチウム二次電池の出力特性を向上できることが分かった。この理由は、フッ化鉄粒子を平均粒径１μｍ以下の微細なものとすることによって、フッ化鉄粒子におけるリチウムイオンの内部拡散経路が短縮されるためである。
For this reason, the present inventor paid attention to the particle size of the iron fluoride particles contained in the positive electrode active material in order to supplement the ion diffusion coefficient of lithium ions in the iron fluoride particles and improve the output characteristics of the lithium secondary battery. And repeated examination.
As a result, it was found that by setting the average particle size of the iron fluoride particles to 1 μm or less, the output characteristics of the lithium secondary battery using the positive electrode active material containing the particles can be improved. This is because the internal diffusion path of lithium ions in the iron fluoride particles is shortened by making the iron fluoride particles fine with an average particle diameter of 1 μm or less.
本発明者が、フッ化鉄からなる正極活物質を用いたリチウム二次電池の出力特性について調べた結果、フッ化鉄粒子の平均粒径が３５μｍである場合には、放電レート０．０５Ｃで放電したときに理論容量の２３％程度の放電容量しか得られなかったが、平均粒径を１μｍ以下とすることで、理論容量の７５％以上の良好な放電容量が得られることが分かった。さらに、本発明者は、フッ化鉄粒子の平均粒径を１μｍ以下とすることで、フッ化鉄粒子からなる正極活物質を用いたリチウム二次電池において、１５０ｍＡｈ／ｇ以上の十分な初期電気容量が得られることを確認し、本発明を完成した。即ち、本発明は以下に関する。 As a result of examining the output characteristics of the lithium secondary battery using the positive electrode active material made of iron fluoride by the present inventor, when the average particle size of the iron fluoride particles is 35 μm, the discharge rate is 0.05C. Although only a discharge capacity of about 23% of the theoretical capacity was obtained when discharged, it was found that a good discharge capacity of 75% or more of the theoretical capacity can be obtained by setting the average particle size to 1 μm or less. Furthermore, the inventor of the present invention has made it possible to achieve a sufficient initial electric current of 150 mAh / g or more in a lithium secondary battery using a positive electrode active material made of iron fluoride particles by setting the average particle size of the iron fluoride particles to 1 μm or less. After confirming that capacity was obtained, the present invention was completed. That is, the present invention relates to the following.
（１） 平均粒径が１μｍ以下のフッ化鉄粒子の表面に炭素膜が被覆されてなる一次粒子を含み、前記一次粒子が凝集されて二次粒子を形成していることを特徴とするリチウム二次電池用正極活物質。
（２） 前記一次粒子におけるフッ化鉄粒子と炭素膜との重量比は、フッ化鉄粒子：炭素膜＝70：30〜98：2であることを特徴とする（１）に記載のリチウム二次電池用正極活物質。
（３） 前記フッ化鉄粒子の最大粒径が５μｍ以下であることを特徴とする（１）又は（２）に記載のリチウム二次電池用正極活物質。
（４） 前記フッ化鉄粒子の平均粒径が０．１μｍ以上であることを特徴とする（１）〜（３）のいずれかに記載のリチウム二次電池用正極活物質。
(1) Lithium comprising primary particles in which the surface of iron fluoride particles having an average particle size of 1 μm or less is coated with a carbon film, and the primary particles are aggregated to form secondary particles Positive electrode active material for secondary battery.
(2) The weight ratio of the iron fluoride particles to the carbon film in the primary particles is iron fluoride particles: carbon film = 70: 30 to 98: 2. Positive electrode active material for secondary battery.
(3) The positive electrode active material for a lithium secondary battery according to (1) or (2), wherein the iron fluoride particles have a maximum particle size of 5 μm or less.
(4) The positive electrode active material for a lithium secondary battery according to any one of (1) to (3), wherein the iron fluoride particles have an average particle size of 0.1 μm or more.
（５） 正極と、負極と、電解質とを備えたリチウム二次電池であって、前記正極が、（１）〜（４）のいずれかに記載のリチウム二次電池用正極活物質を含むことを特徴とするリチウム二次電池。 (5) A lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the positive electrode active material for a lithium secondary battery according to any one of (1) to (4). Rechargeable lithium battery.
本発明のリチウム二次電池用正極活物質は、平均粒径が１μｍ以下のフッ化鉄粒子を含むものであるため、これを含む正極を備えたリチウム二次電池において、フッ化鉄粒子におけるリチウムイオンの内部拡散経路が短いものとなり、優れた出力特性が得られる。 Since the positive electrode active material for a lithium secondary battery of the present invention contains iron fluoride particles having an average particle diameter of 1 μm or less, in a lithium secondary battery including a positive electrode containing the same, lithium ion in the iron fluoride particles The internal diffusion path is short, and excellent output characteristics can be obtained.
以下、本発明のリチウム二次電池用正極活物質およびリチウム二次電池について、詳細に説明する。
「リチウム二次電池用正極活物質」
本実施形態のリチウム二次電池用正極活物質（以下、「正極活物質」という場合がある。）は、平均粒径が１μｍ以下のフッ化鉄粒子からなるものである。フッ化鉄粒子の平均粒径を１μｍ以下とすることで、これを含む正極を備えたリチウム二次電池において、正極活物質のフッ化鉄粒子におけるリチウムイオンの内部拡散経路が十分に短いものとなり、優れた出力特性が得られる。
Hereinafter, the positive electrode active material for a lithium secondary battery and the lithium secondary battery of the present invention will be described in detail.
"Positive electrode active material for lithium secondary battery"
The positive electrode active material for a lithium secondary battery of the present embodiment (hereinafter sometimes referred to as “positive electrode active material”) is made of iron fluoride particles having an average particle size of 1 μm or less. By setting the average particle size of the iron fluoride particles to 1 μm or less, the lithium ion internal diffusion path in the iron fluoride particles of the positive electrode active material is sufficiently short in the lithium secondary battery including the positive electrode including the same. Excellent output characteristics can be obtained.
フッ化鉄粒子の平均粒径が１μｍを超える場合、フッ化鉄粒子におけるリチウムイオンの内部拡散経路を短縮する効果が十分に得られない。フッ化鉄粒子の平均粒径は、リチウム二次電池の出力特性を向上させるためには、小さいほど好ましい。
しかし、平均粒径が０．１μｍ未満であるフッ化鉄粒子は、取り扱いしにくく、リチウム二次電池の生産性を低下させる恐れがある。このため、フッ化鉄粒子の平均粒径は、０．１μｍ以上であることが好ましい。
When the average particle diameter of the iron fluoride particles exceeds 1 μm, the effect of shortening the internal diffusion path of lithium ions in the iron fluoride particles cannot be sufficiently obtained. The average particle size of the iron fluoride particles is preferably as small as possible in order to improve the output characteristics of the lithium secondary battery.
However, the iron fluoride particles having an average particle size of less than 0.1 μm are difficult to handle and may reduce the productivity of the lithium secondary battery. For this reason, the average particle diameter of the iron fluoride particles is preferably 0.1 μm or more.
フッ化鉄粒子の最大粒径は、５μｍ以下であることが好ましい。フッ化鉄粒子の最大粒径が５μｍ以下である場合、フッ化鉄粒子におけるリチウムイオンの内部拡散経路の長い部分がなく、より効果的にリチウムイオンの内部拡散経路を短縮する効果が得られるため、リチウム二次電池の出力特性をより一層向上できる。 The maximum particle size of the iron fluoride particles is preferably 5 μm or less. When the maximum particle size of the iron fluoride particles is 5 μm or less, there is no long portion of the lithium ion internal diffusion path in the iron fluoride particles, and the effect of shortening the lithium ion internal diffusion path more effectively can be obtained. The output characteristics of the lithium secondary battery can be further improved.
フッ化鉄粒子の平均粒径は、湿式でのレーザー回折式装置を用いて測定できる。
また、フッ化鉄粒子の粒径は、測定前に分散液中で３分間以上超音波洗浄機を用いて測定する必要がある。
The average particle diameter of the iron fluoride particles can be measured using a wet laser diffraction apparatus.
In addition, the particle size of the iron fluoride particles needs to be measured in the dispersion using an ultrasonic cleaner for 3 minutes or more before measurement.
フッ化鉄粒子は、安価で高い充放電容量（理論容量：２３７ｍＡｈ／ｇ（インターカレーション反応のみ））を有するものであって、熱安定性が高く、安全性に優れているため、リチウム二次電池用の正極活物質の材料として好ましい。 The iron fluoride particles are inexpensive and have a high charge / discharge capacity (theoretical capacity: 237 mAh / g (intercalation reaction only)), and have high thermal stability and excellent safety. It is preferable as a material for a positive electrode active material for a secondary battery.
また、本実施形態の正極活物質は、フッ化鉄粒子の表面に炭素膜が被覆されてなる一次粒子を含み、一次粒子が凝集されて二次粒子とされているものであってもよい。
フッ化鉄粒子の表面に炭素膜が被覆されてなる一次粒子は、炭素膜によって導電性が向上されたものであるので、これを正極活物質として使用した場合、炭素膜が被覆されていないフッ化鉄粒子を正極活物質として使用した場合と比較して、高いサイクル特性，出力特性が得られる。
In addition, the positive electrode active material of the present embodiment may include primary particles in which the surface of iron fluoride particles is coated with a carbon film, and the primary particles are aggregated into secondary particles.
Since the primary particles obtained by coating the surface of the iron fluoride particles with a carbon film are those whose conductivity has been improved by the carbon film, when this is used as a positive electrode active material, the primary particles are not coated with the carbon film. High cycle characteristics and output characteristics can be obtained as compared with the case where iron halide particles are used as the positive electrode active material.
フッ化鉄粒子の表面に炭素膜が被覆されてなる一次粒子におけるフッ化鉄粒子と炭素膜との質量比（フッ化鉄粒子：炭素膜）は、特に限定されないが、７０：３０〜９８：２であることが好ましい。一次粒子のフッ化鉄粒子と炭素膜との質量比（フッ化鉄粒子：炭素膜）が上記範囲内である場合、十分な導電性を有し、容易に製造できるものとなる。フッ化鉄粒子の表面に炭素膜が被覆されていれば導電性向上効果は得られるが、一次粒子における炭素膜の質量比が上記範囲未満であると、フッ化鉄粒子の表面に炭素膜が被覆されていることによる導電性向上効果が十分に得られない恐れがある。また、一次粒子における炭素膜の質量比が上記範囲を超えると、一次粒子の生産性が低下するため好ましくない。 The mass ratio (iron fluoride particles: carbon film) between the iron fluoride particles and the carbon film in the primary particles obtained by coating the surface of the iron fluoride particles with the carbon film is not particularly limited, but is 70:30 to 98: 2 is preferable. When the mass ratio of the primary particles of iron fluoride particles to the carbon film (iron fluoride particles: carbon film) is within the above range, the particles have sufficient conductivity and can be easily manufactured. If the surface of the iron fluoride particles is coated with a carbon film, the effect of improving conductivity can be obtained, but if the mass ratio of the carbon film in the primary particles is less than the above range, There is a possibility that the effect of improving the conductivity due to the coating cannot be sufficiently obtained. Further, if the mass ratio of the carbon film in the primary particles exceeds the above range, the productivity of the primary particles decreases, which is not preferable.
フッ化鉄粒子の表面に炭素膜が被覆されてなる一次粒子の製造方法は、特に限定されないが、例えば、フッ化鉄粒子と炭素質材料とを機械的混合手段を用いて、乾式で混合することにより製造できる。
フッ化鉄粒子とともに混合される炭素質材料としては、導電性を有するものであればよく、例えば、アセチレンブラック、カーボンブラック、活性炭、ピレン、ジクロロベンゼンなどを用いることができる。
また、フッ化鉄粒子と炭素質材料との混合は、アルゴンガスなどの不活性ガス雰囲気下で行うことが好ましい。
The method for producing the primary particles in which the surface of the iron fluoride particles is coated with the carbon film is not particularly limited. For example, the iron fluoride particles and the carbonaceous material are mixed by a dry method using a mechanical mixing means. Can be manufactured.
Any carbonaceous material mixed with the iron fluoride particles may be used as long as it has conductivity. For example, acetylene black, carbon black, activated carbon, pyrene, dichlorobenzene and the like can be used.
The mixing of the iron fluoride particles and the carbonaceous material is preferably performed in an inert gas atmosphere such as argon gas.
機械的混合手段としては、遊星型ボールミル（planetary ball milling）などのボールミルを用いることができる。遊星型ボールミルは、自転運動と公転運動とによる粉砕エネルギーにより、フッ化鉄粒子と炭素質材料とを充分に混合できるものであるため好ましい。
フッ化鉄粒子と炭素質材料との混合時間は、５時間以上であることが好ましく、正極活物質に必要とされる導電性能などに応じて適宜決定できる。
As the mechanical mixing means, a ball mill such as a planetary ball milling can be used. The planetary ball mill is preferable because the iron fluoride particles and the carbonaceous material can be sufficiently mixed by the pulverization energy by the rotation motion and the revolution motion.
The mixing time of the iron fluoride particles and the carbonaceous material is preferably 5 hours or longer, and can be appropriately determined according to the conductive performance required for the positive electrode active material.
機械的混合手段を用いてフッ化鉄粒子と炭素質材料とを充分に混合することにより、フッ化鉄粒子の表面に炭素膜が均一に被覆される。フッ化鉄粒子の表面に形成した炭素膜は、ＳＥＭ（走査型電子顕微鏡）やＥＤＳ（エネルギー分散型Ｘ線分光）を用いて観察することにより確認できる。 By sufficiently mixing the iron fluoride particles and the carbonaceous material using a mechanical mixing means, the surface of the iron fluoride particles is uniformly coated with the carbon film. The carbon film formed on the surface of the iron fluoride particles can be confirmed by observing using SEM (scanning electron microscope) or EDS (energy dispersive X-ray spectroscopy).
このようにして得られたフッ化鉄粒子の表面に炭素膜が被覆されてなる一次粒子は、造粒することにより、一次粒子を凝集させた二次粒子とされていることが好ましい。
造粒方法としては、特に限定されないが、流動造粒機の流動層内で回転ロータによる転動作用と対向流パルスジェットの分散作用とにより、一次粒子とバインダーとを混合させて凝集させる方法などが挙げられる。
一次粒子を凝集させた二次粒子は、表面に炭素膜が被覆されていないフッ化鉄粒子や一次粒子と比較して、取り扱いが容易であるため、作業性に優れたリチウム二次電池用正極活物質となる。
The primary particles obtained by coating the surface of the iron fluoride particles thus obtained with a carbon film are preferably secondary particles obtained by agglomerating the primary particles by granulation.
The granulation method is not particularly limited, but a method of mixing and aggregating primary particles and a binder in a fluidized bed of a fluidized granulator for rolling operation by a rotating rotor and a dispersing action of a counterflow pulse jet, etc. Is mentioned.
The secondary particles, which are agglomerated primary particles, are easier to handle than iron fluoride particles and primary particles that are not coated with a carbon film on the surface, so the positive electrode for lithium secondary batteries has excellent workability. Become active material.
なお、本発明のリチウム二次電池用正極活物質は、表面に炭素膜が被覆されていないフッ化鉄粒子と、フッ化鉄粒子の表面に炭素膜が被覆されてなる一次粒子と、一次粒子が凝集されてなる二次粒子の３種から選ばれる１種のみからなるものであってもよいし、上記の３種から選ばれる２種以上を含むものであってもよい。
また、本発明のリチウム二次電池用正極活物質は、平均粒径が１μｍ以下のフッ化鉄粒子を含むものであればよく、例えば、従来のリチウム二次電池用正極活物質を含むものであってもよいし、本発明のリチウム二次電池用正極活物質とリチウム化合物とを反応させてなる反応物を含むものであってもよい。
The positive electrode active material for a lithium secondary battery of the present invention includes iron fluoride particles whose surfaces are not coated with a carbon film, primary particles whose surfaces are coated with a carbon film, and primary particles. May be composed of only one kind selected from three kinds of secondary particles formed by agglomeration, or may contain two or more kinds selected from the above three kinds.
Moreover, the positive electrode active material for lithium secondary batteries of this invention should just contain the iron fluoride particle whose average particle diameter is 1 micrometer or less, for example, includes the conventional positive electrode active material for lithium secondary batteries. It may contain the reaction material formed by making the positive electrode active material for lithium secondary batteries of this invention and a lithium compound react.
本発明において、所定の粒径範囲のフッ化鉄粒子を製造する方法としては、例えば、ジェットミルで粉砕する方法、風力分級法によって分級する方法が挙げられる。
ジェットミルで粉砕する方法としては、例えば、ジェットミル装置を用い、０．４ＭＰａ以上の空気圧で粉砕することにより、平均粒径が０．４〜０．７μｍ程度、最大粒径が０．７〜１．０μｍ程度のフッ化鉄粒子が得られる。
In the present invention, examples of the method for producing iron fluoride particles having a predetermined particle size range include a method of pulverizing with a jet mill and a method of classifying by an air classification method.
As a method of pulverizing with a jet mill, for example, by using a jet mill apparatus and pulverizing with an air pressure of 0.4 MPa or more, the average particle diameter is about 0.4 to 0.7 μm, and the maximum particle diameter is 0.7 to Iron fluoride particles of about 1.0 μm are obtained.
風力分級法によって分級する方法としては、例えば、原料として平均粒径２３μｍのフッ化鉄粒子を使用し、風力分級装置としてジグザグ分級機（１００ＭＺＲ）を用い、回転速度１８ｒｐｍ，風量２．０ｍ３／ｈで分級することにより、平均粒径が０．６μｍ程度、最大粒径が３μｍ程度のフッ化鉄粒子が得られる。
なお、本発明において、所定の粒径範囲のフッ化鉄粒子を製造する方法は、上記の方法のみに限定されるものではなく、平均粒径が１μｍ以下のフッ化鉄粒子が得られる方法であれば如何なる方法であってもよい。
As a classification method by an air classification method, for example, iron fluoride particles having an average particle diameter of 23 μm are used as a raw material, a zigzag classifier (100MZR) is used as an air classification device, a rotation speed is 18 rpm, an air volume is 2.0 m 3 / By classifying with h, iron fluoride particles having an average particle size of about 0.6 μm and a maximum particle size of about 3 μm are obtained.
In the present invention, the method of producing the iron fluoride particles having a predetermined particle size range is not limited to the above method, but a method of obtaining iron fluoride particles having an average particle size of 1 μm or less. Any method can be used.
「リチウム二次電池」
本実施形態のリチウム二次電池は、正極と、負極と、電解質とを備えている。
正極は、集電体（導体）の表面に、電極活物質と結着剤（バインダー）とを含む正極活物質層が形成されているものである。
本実施形態においては、正極の電極活物質として、本発明のリチウム二次電池用正極活物質が用いられている。
"Lithium secondary battery"
The lithium secondary battery of this embodiment includes a positive electrode, a negative electrode, and an electrolyte.
In the positive electrode, a positive electrode active material layer including an electrode active material and a binder (binder) is formed on the surface of a current collector (conductor).
In the present embodiment, the positive electrode active material for a lithium secondary battery of the present invention is used as the positive electrode active material.
正極の集電体（導体）としては、アルミニウム箔や銅箔などの導体箔や導体薄板、ステンレスなどの導体からなる金網などを用いることができる。
結着剤としては、ポリイミドやポリフッ化ビニルデン（ＰＶＤＦ）、フッ化エチレンフッ素樹脂（ＰＴＦＥ）などを用いることができる。
また、正極活物質層には、正極の電極活物質と結着剤（バインダー）に加えて、必要に応じて、導電助剤が含有されていてもよい。導電助剤としては、導電性を有する材料が適宜選択して用いられ、具体的には、アセチレンブラック、カーボンブラック、活性炭などが挙げられる。
As the positive electrode current collector (conductor), a conductor foil such as an aluminum foil or a copper foil, a conductor thin plate, or a wire mesh made of a conductor such as stainless steel can be used.
As the binder, polyimide, polyvinylidene fluoride (PVDF), fluoroethylene fluororesin (PTFE), or the like can be used.
Moreover, in addition to the electrode active material and binder (binder) of a positive electrode, the positive electrode active material layer may contain the conductive support agent as needed. As the conductive assistant, a conductive material is appropriately selected and used, and specific examples include acetylene black, carbon black, activated carbon and the like.
正極は、正極の電極活物質と、結着剤と、導電助剤と、必要に応じて含有されるＮ−メチルピロリドンなどの各種有機溶媒からなる溶媒とからなる混合物を、集電体の表面に塗工し、乾燥させることにより形成できる。 The positive electrode is a mixture of a positive electrode active material, a binder, a conductive additive, and a solvent composed of various organic solvents such as N-methylpyrrolidone, if necessary. It can be formed by coating and drying.
負極としては、例えば、集電体（導体）の表面に、電極活物質と結着剤（バインダー）とを含む負極活物質層が形成されているものを用いることができる。
負極の集電体（導体）としては、正極の集電体（導体）および結着剤と同じものを用いることができる。
負極の電極活物質としては、天然黒鉛、グラファイト、リチウム金属、リチウム合金、シリコン金属、シリコン薄膜などを使用できる。
As the negative electrode, for example, one having a negative electrode active material layer containing an electrode active material and a binder (binder) formed on the surface of a current collector (conductor) can be used.
As the negative electrode current collector (conductor), the same material as the positive electrode current collector (conductor) and the binder can be used.
As the electrode active material of the negative electrode, natural graphite, graphite, lithium metal, lithium alloy, silicon metal, silicon thin film and the like can be used.
また、負極活物質層には、負極の電極活物質と結着剤（バインダー）に加えて、必要に応じて、導電助剤が含有されていてもよい。負極の導電助剤としては、正極の導電助剤に使用可能な材料と同じ材料を用いることができる。
負極は、負極の電極活物質と、結着剤と、必要に応じて含有される導電助剤と、必要に応じて含有される水またはＮ−メチルピロリドンなどの各種有機溶媒からなる溶媒とからなる混合物を、集電体の表面に塗工し、乾燥させることにより形成できる。
また、負極は、集電体（導体）の表面に、リチウム金属箔などからなる負極の電極活物質が圧着されることにより貼り付けられたものであってもよい。
Moreover, in addition to the electrode active material and binder (binder) of a negative electrode, the negative electrode active material layer may contain the conductive support agent as needed. As the conductive additive for the negative electrode, the same materials that can be used for the conductive additive for the positive electrode can be used.
The negative electrode is composed of an electrode active material of the negative electrode, a binder, a conductive additive contained as necessary, and a solvent composed of various organic solvents such as water or N-methylpyrrolidone contained as necessary. The resulting mixture can be applied to the surface of the current collector and dried.
The negative electrode may be affixed to the surface of a current collector (conductor) by pressing a negative electrode active material made of lithium metal foil or the like.
電解質としては、例えば、炭酸エチレン、炭酸ジエチル、炭酸プロピルなどの有機溶媒に、六フッ化リン酸リチウムや四フッ化ホウ酸リチウムなどのリチウム塩を溶解した電解液などを用いることができる。電解液に含まれるリチウム塩は、リチウムイオンの供給源として作用して、正極と負極との間でのリチウムイオンの移動を促進するものである。
また、正極と負極との間には、必要に応じてポリエチレン、ポリプロピレンなどからなる樹脂フィルムなどからなるセパレータが配置されていてもよい。
As the electrolyte, for example, an electrolytic solution in which a lithium salt such as lithium hexafluorophosphate or lithium tetrafluoroborate is dissolved in an organic solvent such as ethylene carbonate, diethyl carbonate, or propyl carbonate can be used. The lithium salt contained in the electrolytic solution acts as a lithium ion supply source and promotes the movement of lithium ions between the positive electrode and the negative electrode.
In addition, a separator made of a resin film made of polyethylene, polypropylene, or the like may be disposed between the positive electrode and the negative electrode as necessary.
本実施形態の正極活物質は、平均粒径が１μｍ以下のフッ化鉄粒子を含むものである。このため、本実施形態の正極活物質を含む正極を備えた本実施形態のリチウム二次電池は、正極活物質のフッ化鉄粒子におけるリチウムイオンの内部拡散経路が十分に短いものとなり、優れた出力特性が得られる。 The positive electrode active material of the present embodiment includes iron fluoride particles having an average particle size of 1 μm or less. For this reason, the lithium secondary battery of the present embodiment including the positive electrode including the positive electrode active material of the present embodiment has a sufficiently short internal diffusion path of lithium ions in the iron fluoride particles of the positive electrode active material, and is excellent. Output characteristics can be obtained.
「実施例１」
以下に示す方法により平均粒径が０．６μｍ、最大粒径が１．３μｍであるフッ化鉄粒子を製造し、得られたフッ化鉄粒子を正極の電極活物質として使用して、以下に示す方法により正極を製造し、これを用いて、以下に示す方法により評価用セルを得た。
"Example 1"
According to the method shown below, iron fluoride particles having an average particle size of 0.6 μm and a maximum particle size of 1.3 μm are manufactured, and the obtained iron fluoride particles are used as an electrode active material for a positive electrode. The positive electrode was manufactured by the method shown, and the cell for evaluation was obtained by the method shown below using this.
「フッ化鉄粒子の製造方法」
原料として平均粒径２３μｍのフッ化鉄粒子を使用し、風力分級装置としてジグザグ分級機（１００ＭＺＲ）を用い、回転速度１８ｒｐｍ，風量２．０ｍ３／ｈで分級することにより、所定の平均粒径および最大粒径のフッ化鉄粒子を得た。
"Production method of iron fluoride particles"
By using iron fluoride particles having an average particle diameter of 23 μm as a raw material, and using a zigzag classifier (100MZR) as an air classifier, classification is performed at a rotational speed of 18 rpm and an air volume of 2.0 m 3 / h, thereby obtaining a predetermined average particle diameter And iron fluoride particles of maximum particle size were obtained.
「正極の製造方法」
メノウ乳鉢を用いて混合することにより、フッ化鉄粒子（正極の電極活物質）とアセチレンブラック（導電補助材）とＰＴＦＥ（バインダー）とを質量比で７０：２５：５＝正極の電極活物質：導電補助材:バインダーの割合で含む混合物の塊を得た。その後、混合物をステンレス金網からなる集電体の上に載置してプレス加工することにより、表面に正極活物質層を形成し、正極を得た。
"Method for manufacturing positive electrode"
By mixing using an agate mortar, iron fluoride particles (positive electrode active material), acetylene black (conductive auxiliary material), and PTFE (binder) in a mass ratio of 70: 25: 5 = positive electrode active material : Conductive auxiliary material: A lump of a mixture containing the binder was obtained. Thereafter, the mixture was placed on a current collector made of a stainless steel wire mesh and pressed to form a positive electrode active material layer on the surface, thereby obtaining a positive electrode.
「リチウム二次電池の製造方法」
負極として、ステンレス金網からなる集電体の表面に、３００μｍのリチウム金属からなる電極活物質が圧着されて貼り付けられてなるものを用い、電解質として炭酸エチレン（ＥＣ）と炭酸ジメチル（ＤＭＣ）とを混合比ＥＣ：ＤＭＣ＝１：２となるように混合した混合溶媒に六フッ化リン酸リチウム（ＬｉＰＦ６）を１（モル／Ｌ）の濃度になるように溶解したものを用い、正極と負極との間にセルガード２４００（商品名：Ｐｏｌｙ Ｐｏｒｅ社製）からなるセパレータを配置して、コイン型の評価用セルを得た。
"Production method of lithium secondary battery"
As the negative electrode, an electrode active material made of 300 μm lithium metal is pressure-bonded to the surface of a current collector made of stainless steel wire mesh, and ethylene carbonate (EC) and dimethyl carbonate (DMC) are used as electrolytes. Using a solution of lithium hexafluorophosphate (LiPF 6 ) dissolved to a concentration of 1 (mol / L) in a mixed solvent mixed so that the mixing ratio EC: DMC = 1: 2. A separator made of Celgard 2400 (trade name: manufactured by Poly Pore) was placed between the negative electrode and a coin-type evaluation cell.
「実施例２」
フッ化鉄粒子として平均粒径が０．４μｍ、最大粒径が０．７μｍであるものを製造したこと以外は、実施例１と同様にして、評価用セルを得た。
「実施例３」
フッ化鉄粒子として平均粒径が０．７μｍ、最大粒径が１．０μｍであるものを製造したこと以外は、実施例１と同様にして、評価用セルを得た。
"Example 2"
An evaluation cell was obtained in the same manner as in Example 1 except that an iron fluoride particle having an average particle size of 0.4 μm and a maximum particle size of 0.7 μm was produced.
"Example 3"
An evaluation cell was obtained in the same manner as in Example 1 except that iron fluoride particles having an average particle size of 0.7 μm and a maximum particle size of 1.0 μm were produced.
「実施例４」
実施例１と同様のフッ化鉄粒子の表面に、以下に示す方法により炭素膜を被覆して一次粒子とし、その後、以下に示す方法により一次粒子を凝集させて二次粒子とした。得られた二次粒子をリチウム二次電池用正極活物質として使用し、実施例１と同様にして、評価用セルを得た。
Example 4
The surface of the same iron fluoride particles as in Example 1 was coated with a carbon film by the following method to form primary particles, and then the primary particles were aggregated by the following method to obtain secondary particles. The obtained secondary particles were used as a positive electrode active material for a lithium secondary battery, and an evaluation cell was obtained in the same manner as in Example 1.
「炭素膜の被覆方法」
炭素質材料とフッ化鉄粒子とを湿式で混合させた後，エバポレータを用いて真空乾燥し、電気炉を用いてＡｒ雰囲気中で温度３００〜６５０℃で焼成し、フッ化鉄粒子の表面に炭素膜が被覆されてなる一次粒子を得た。炭素前駆体としては、酸素基を含まない芳香族炭化水素であるピレンを使用した。
"Coating method of carbon film"
After the carbonaceous material and the iron fluoride particles are wet mixed, they are vacuum dried using an evaporator and fired at a temperature of 300 to 650 ° C. in an Ar atmosphere using an electric furnace. Primary particles coated with a carbon film were obtained. As the carbon precursor, pyrene, which is an aromatic hydrocarbon containing no oxygen group, was used.
「一次粒子の凝集方法」
流動造粒機（商品名：アグロマスタ、ホソカワミクロン株式会社製）を使用して、一次粒子とバインダーとを混合させて凝集させることにより、一次粒子を凝集させて二次粒子とした。
"Aggregation method of primary particles"
Using a flow granulator (trade name: Agromaster, manufactured by Hosokawa Micron Co., Ltd.), the primary particles and the binder were mixed and aggregated to aggregate the primary particles into secondary particles.
「比較例１」
フッ化鉄粒子として平均粒径が７μｍ、最大粒径が２４μｍであるものを用いたこと以外は、実施例１と同様にして、評価用セルを得た。
「比較例２」
リチウム二次電池用正極活物質として三元系（ＬｉＮｉＣｏＭｎＯ２)を用いたこと以外は、実施例１と同様にして、評価用セルを得た。
"Comparative Example 1"
An evaluation cell was obtained in the same manner as in Example 1, except that iron fluoride particles having an average particle diameter of 7 μm and a maximum particle diameter of 24 μm were used.
"Comparative Example 2"
An evaluation cell was obtained in the same manner as in Example 1 except that a ternary system (LiNiCoMnO 2 ) was used as the positive electrode active material for the lithium secondary battery.
このようにして得られたリチウム二次電池について、以下に示す方法により、放電容量およびサイクル特性（容量維持率）を調べた。その結果を表１に示す。 The lithium secondary battery thus obtained was examined for discharge capacity and cycle characteristics (capacity maintenance ratio) by the following method. The results are shown in Table 1.
「放電容量の測定」
評価用セルの充放電を、測定温度を２５℃とし、電圧範囲を２．０〜４．５Ｖとし、電流密度を０．０５ｍＡ／ｃｍ２として行い、東洋システム社製の充放電装置ＴＯＳＣＡＴ３１００を用いて、初回放電容量（ｍＡｈ／ｇ）を測定した。
「サイクル特性の評価」
放電容量の測定と同様にして、評価用セルの充放電を１００サイクル行った後の放電容量を、放電容量の測定と同様にして測定し、初回放電容量を１００％とした場合における１００サイクル後の容量維持率（％）を求めた。
“Measurement of discharge capacity”
Charging / discharging of the evaluation cell is performed at a measurement temperature of 25 ° C., a voltage range of 2.0 to 4.5 V, a current density of 0.05 mA / cm 2 , and a charge / discharge device TOSCAT3100 manufactured by Toyo System Co., Ltd. is used. The initial discharge capacity (mAh / g) was measured.
"Evaluation of cycle characteristics"
Similarly to the measurement of the discharge capacity, the discharge capacity after 100 cycles of charging / discharging of the evaluation cell was measured in the same manner as the measurement of the discharge capacity, and after 100 cycles when the initial discharge capacity was 100%. The capacity retention rate (%) of was determined.
表１に示すように、平均粒径１μｍ以下のフッ化鉄粒子を含む実施例１〜実施例４では、フッ化鉄粒子の平均粒径が７μｍである比較例１と比較して、放電容量が高く、従来のリチウム二次電池用正極活物質を使用した比較例２と同等であった。
また、平均粒径が０．４μｍ、最大粒径が０．７μｍである実施例２では、フッ化鉄粒子の平均粒径が０．６μｍである実施例１と比較して、放電容量が高くなった。また、炭素被覆を施したフッ化鉄をリチウム二次電池用正極活物質として使用した実施例４においても、実施例１と比較して放電容量が高くなった。また、二次粒子をリチウム二次電池用正極活物質として使用した実施例４では、実施例１〜実施例３と比較して、容量維持率が高く、サイクル特性が優れていた。
As shown in Table 1, in Examples 1 to 4 including iron fluoride particles having an average particle diameter of 1 μm or less, the discharge capacity is compared with Comparative Example 1 in which the average particle diameter of the iron fluoride particles is 7 μm. It was high and was equivalent to the comparative example 2 using the conventional positive electrode active material for lithium secondary batteries.
Further, in Example 2 in which the average particle size is 0.4 μm and the maximum particle size is 0.7 μm, the discharge capacity is higher than that in Example 1 in which the average particle size of the iron fluoride particles is 0.6 μm. became. Further, in Example 4 in which iron fluoride coated with carbon was used as a positive electrode active material for a lithium secondary battery, the discharge capacity was higher than that in Example 1. Further, in Example 4 in which the secondary particles were used as the positive electrode active material for a lithium secondary battery, the capacity retention rate was higher and the cycle characteristics were excellent as compared with Examples 1 to 3.
Claims (5)
前記正極が、請求項１〜請求項４のいずれか一項に記載のリチウム二次電池用正極活物質を含むことを特徴とするリチウム二次電池。 A lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte,
The said positive electrode contains the positive electrode active material for lithium secondary batteries as described in any one of Claims 1-4, The lithium secondary battery characterized by the above-mentioned.
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