JP6026359B2 - Lithium titanate negative electrode active material - Google Patents
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Description
本発明は、良好な電池特性を発現できるチタン酸リチウム負極活物質に関する。 The present invention relates to a lithium titanate negative electrode active material capable of exhibiting good battery characteristics.
従来より、電池の性能を高めるべく、正極材料や負極材料として導電性の高い物質が用いられる。近年では、リチウムイオン電池等の次世代電池が益々台頭してきているが、かかる電池における負極材料としては、カーボン系材料を用いるのが主流ではあるものの、例えば非特許文献１に記載されるチタン酸リチウム化合物を用いることも検討されつつある。かかるチタン酸リチウム化合物を次世代電池の負極材料として採用するには、そのもの自体の導電性が低いため、粒子を微細化することによって良好な電池物性の発現を確保する必要がある。 Conventionally, a highly conductive substance is used as a positive electrode material or a negative electrode material in order to improve battery performance. In recent years, next-generation batteries such as lithium ion batteries have been increasingly used. As a negative electrode material in such batteries, a carbon-based material is mainly used, but for example, titanic acid described in Non-Patent Document 1 The use of lithium compounds is also being studied. In order to employ such a lithium titanate compound as a negative electrode material for a next-generation battery, it is necessary to ensure good battery physical properties by making the particles finer because the conductivity of the lithium titanate compound itself is low.
しかしながら、単にチタン酸リチウム化合物の粒子を微細化するのみでは、タップ密度が減少する傾向にあり、所望の電池特性を十分に発現できないおそれがある。 However, simply refining the particles of the lithium titanate compound tends to reduce the tap density, and there is a possibility that desired battery characteristics cannot be sufficiently exhibited.
したがって、本発明の課題は、リチウムイオン電池の負極材料として、優れた電池物性を発現し得るチタン酸リチウム負極活物質を提供することにある。 Therefore, the subject of this invention is providing the lithium titanate negative electrode active material which can express the outstanding battery physical property as a negative electrode material of a lithium ion battery.
そこで本発明者らは、種々検討したところ、特定の処理を施すことにより得られるチタン酸リチウム負極活物質であれば、タップ密度が大きく、優れた電池物性を発現できることを見出し、本発明を完成させるに至った。 Accordingly, the present inventors have made various studies and found that a lithium titanate negative electrode active material obtained by performing a specific treatment has a large tap density and can exhibit excellent battery properties, thereby completing the present invention. I came to let you.
すなわち、本発明は、チタン酸リチウム化合物及び導電性炭素を混合した後、さらに圧縮力及びせん断力を付加しながら混合する処理を経ることにより得られるチタン酸リチウム負極活物質を提供するものである。 That is, the present invention provides a lithium titanate negative electrode active material obtained by mixing a lithium titanate compound and conductive carbon and then mixing them while adding compressive force and shear force. .
本発明のチタン酸リチウム負極活物質は、チタン酸リチウム化合物と導電性炭素とが極めて均一に分散され、かつ空隙が低減された粒子であるため、タップ密度が大きく、リチウムイオン電池の性能向上に大いに寄与することが期待される。 Since the lithium titanate negative electrode active material of the present invention is a particle in which a lithium titanate compound and conductive carbon are dispersed extremely uniformly and with reduced voids, the tap density is large and the performance of the lithium ion battery is improved. It is expected to contribute greatly.
以下、本発明について詳細に説明する。
本発明のチタン酸リチウム負極活物質は、チタン酸リチウム化合物及び導電性炭素を混合した後、さらに圧縮力及びせん断力を付加しながら混合する処理を経ることにより得られる。かかる処理を経ることにより、チタン酸リチウム化合物と導電性炭素とが均一に分散したまま堅固に凝集して粒子（以下、「複合体粒子」ともいう）を形成することにより、空隙が低減された複合体粒子を得ることができる。また、導電性炭素を変形又は延展させながらチタン酸リチウム化合物が呈する粒子（以下、「一次粒子」ともいう）の表面に付着させ、導電性炭素の層を形成させることもできる。圧縮力及びせん断力を付加しながら混合する処理は、周速２５〜４０ｍ／ｓで回転するインペラを備える密閉容器を用いるのが好ましい。かかる容器内にチタン酸リチウム化合物及び導電性炭素を投入し、容器を稼動させることにより、圧縮力及びせん断力を付加しながら混合する処理が可能となる。かかるインペラを備える密閉容器内では、インペラの回転によってこれらチタン酸リチウム化合物及び導電性炭素が均一に混合されるとともに、インペラと容器内壁との間で圧縮力を付加されながらせん断力も付加されることとなる。インペラの周速は、得られる複合体粒子のタップ密度を高める観点から、好ましくは２５〜４０ｍ／ｓであり、より好ましくは２７〜３５ｍ／ｓである。
Hereinafter, the present invention will be described in detail.
The lithium titanate negative electrode active material of the present invention is obtained by mixing a lithium titanate compound and conductive carbon and then mixing them while adding compressive force and shearing force. By undergoing such treatment, the voids were reduced by forming particles (hereinafter also referred to as “composite particles”) by firmly aggregating the lithium titanate compound and the conductive carbon while being uniformly dispersed. Composite particles can be obtained. Alternatively, a conductive carbon layer can be formed by attaching to the surface of particles (hereinafter also referred to as “primary particles”) exhibited by a lithium titanate compound while deforming or extending the conductive carbon. It is preferable to use an airtight container provided with an impeller that rotates at a peripheral speed of 25 to 40 m / s for the process of mixing while applying a compressive force and a shearing force. By putting a lithium titanate compound and conductive carbon into such a container and operating the container, it is possible to perform a mixing process while applying compressive force and shearing force. In a closed container equipped with such an impeller, the lithium titanate compound and conductive carbon are uniformly mixed by the rotation of the impeller, and a shearing force is also applied while a compressive force is applied between the impeller and the inner wall of the container. It becomes. The peripheral speed of the impeller is preferably 25 to 40 m / s, more preferably 27 to 35 m / s, from the viewpoint of increasing the tap density of the resulting composite particles.
なお、得られる複合体粒子の均一性を高める観点、およびインペラを備える密閉容器内での処理時間を短縮化する観点から、かかる密閉容器内へチタン酸リチウム化合物及び導電性炭素を投入する前に、予めこれらを混合してもよい。 In addition, from the viewpoint of increasing the uniformity of the obtained composite particles and shortening the processing time in the closed container equipped with the impeller, before introducing the lithium titanate compound and the conductive carbon into the closed container. These may be mixed in advance.
このような圧縮力及びせん断力を付加しながら混合することのできる密閉容器を備える装置としては、高速せん断ミル、ブレード型混練機等が挙げられ、具体的には、例えば、微粒子複合化装置 ノビルタ（ホソカワミクロン社製）を好適に用いることができる。かかる装置を用いることにより、容易に所定の圧縮力とせん断力を付加しながらの混合処理を行うことができ、このような処理を施すのみで本発明のチタン酸リチウム負極活物質を得ることができる。
上記混合の処理条件としては、処理温度が、好ましくは５〜８０℃、より好ましくは１０〜５０℃であり、処理時間が、好ましくは５〜９０分、より好ましくは１０〜６０分である。処理雰囲気としては、特に限定されないが、不活性ガス雰囲気下、または還元ガス雰囲気下が好ましい。
Examples of the apparatus provided with a closed container that can be mixed while applying such compressive force and shearing force include a high-speed shear mill, a blade-type kneader, and the like. (Manufactured by Hosokawa Micron Corporation) can be preferably used. By using such an apparatus, it is possible to easily perform a mixing process while applying a predetermined compressive force and shearing force, and the lithium titanate negative electrode active material of the present invention can be obtained only by performing such a process. it can.
As the processing conditions for the mixing, the processing temperature is preferably 5 to 80 ° C., more preferably 10 to 50 ° C., and the processing time is preferably 5 to 90 minutes, more preferably 10 to 60 minutes. The treatment atmosphere is not particularly limited, but is preferably an inert gas atmosphere or a reducing gas atmosphere.
上記密閉容器内に投入するチタン酸リチウム化合物と導電性炭素との質量比は、得られる電池物性を高める観点から、好ましくは９７：３〜８５：１５であり、より好ましくは９５：５〜８８：１２であり、さらに好ましくは９３：７〜９０：１０である。 The mass ratio of the lithium titanate compound and the conductive carbon charged into the closed container is preferably 97: 3 to 85:15, more preferably 95: 5 to 88, from the viewpoint of improving the physical properties of the obtained battery. : 12, and more preferably 93: 7 to 90:10.
なお、電池物性をより高める観点から、得られた複合体粒子を焼成してもよい。焼成条件は、不活性ガス雰囲気下又は還元条件下に４００℃以上、好ましくは４００〜８００℃で１０分〜３時間、好ましくは０．５〜１．５時間行うのが好ましい。 In addition, you may bake the obtained composite particle from a viewpoint of improving battery physical property more. The firing conditions are 400 ° C. or higher, preferably 400 to 800 ° C. for 10 minutes to 3 hours, preferably 0.5 to 1.5 hours under an inert gas atmosphere or reducing conditions.
上記チタン酸リチウム化合物は、チタン酸化合物及びリチウム化合物を焼成することにより得られる一次粒子であるのが好ましい。
用い得るチタン酸化合物としては、酸化チタン、オルトチタン酸やメタチタン酸等の含水酸化チタンが挙げられる。これらは１種単独で用いてもよく、２種以上組み合わせて用いてもよい。なかでも、電池物性を高める観点から、酸化チタンが好ましい。
用い得るリチウム化合物としては、リチウム酸化物又はリチウム水酸化物が挙げられる。具体的には、例えば、炭酸リチウム、水酸化リチウム、硝酸リチウム、酸化リチウム、シュウ酸リチウム、酢酸リチウム等が挙げられる。これらは１種単独で用いてもよく、２種以上組み合わせて用いてもよい。なかでも、電池物性を高める観点から、炭酸リチウムが好ましい。
The lithium titanate compound is preferably primary particles obtained by firing a titanate compound and a lithium compound.
Examples of titanic acid compounds that can be used include hydrous titanium oxide such as titanium oxide, orthotitanic acid, and metatitanic acid. These may be used alone or in combination of two or more. Among these, titanium oxide is preferable from the viewpoint of improving battery physical properties.
Examples of the lithium compound that can be used include lithium oxide and lithium hydroxide. Specific examples include lithium carbonate, lithium hydroxide, lithium nitrate, lithium oxide, lithium oxalate, and lithium acetate. These may be used alone or in combination of two or more. Among these, lithium carbonate is preferable from the viewpoint of improving battery physical properties.
これらチタン酸化合物及びリチウム化合物を焼成してチタン酸リチウム化合物の一次粒子を得る方法としては、例えばＪｏｕｒｎａｌ ｏｆ Ｐｏｗｅｒ Ｓｏｕｒｃｅ ２２１（（２０１３），ｐ１２２−１２７）に記載の方法を用いることができる。 As a method for obtaining primary particles of the lithium titanate compound by firing the titanate compound and the lithium compound, for example, a method described in Journal of Power Source 221 ((2013), p122-127) can be used.
具体的には、例えば、まずチタン酸化合物及びリチウム化合物を粉体のまま混合・粉砕し、或いは水やエタノール等のアルコールを溶媒として用いて混合・粉砕すればよい。混合・粉砕する処理には、例えばボールミルやビーズミル等を用いることができる。次いで、乾燥することにより混合物を得る。
次に得られた混合物を焼成する。焼成条件は、例えば焼成温度７００〜９００℃、焼成時間８〜２４時間である。また、焼成する際、窒素やアルゴン等の不活性ガス雰囲気下としてもよく、酸素雰囲気下、或いは大気雰囲気下としてもよい。
得られた焼成物を粉砕することにより、原料となるチタン酸リチウム化合物を得ることができる。
Specifically, for example, first, the titanate compound and the lithium compound may be mixed and pulverized as powder, or may be mixed and pulverized using an alcohol such as water or ethanol as a solvent. For the mixing / pulverization treatment, for example, a ball mill or a bead mill can be used. Next, the mixture is obtained by drying.
Next, the obtained mixture is fired. The firing conditions are, for example, a firing temperature of 700 to 900 ° C. and a firing time of 8 to 24 hours. Further, when firing, an inert gas atmosphere such as nitrogen or argon may be used, or an oxygen atmosphere or an air atmosphere may be used.
By pulverizing the obtained fired product, a lithium titanate compound as a raw material can be obtained.
チタン酸リチウム化合物が有する平均粒径Ｘは、複合体粒子としての均一性を高めて得られる電池物性の向上を図る観点から、好ましくは２０〜２００ｎｍであり、より好ましくは２０〜１５０ｎｍであり、さらに好ましくは２０〜１００ｎｍである。なお、かかる平均粒径Ｘは、試料を溶媒によって均一分散させ、動的光散乱法の粒度分析計（ナノトラックUPA-EX150、日機装株式会社製）により測定される値を意味する。 The average particle size X of the lithium titanate compound is preferably 20 to 200 nm, more preferably 20 to 150 nm, from the viewpoint of improving battery physical properties obtained by increasing the uniformity as composite particles. More preferably, it is 20-100 nm. The average particle diameter X means a value measured by a dynamic light scattering particle size analyzer (Nanotrack UPA-EX150, manufactured by Nikkiso Co., Ltd.) after uniformly dispersing the sample with a solvent.
上記導電性炭素としては、カーボンブラックが好ましく、具体的には、例えば、アセチレンブラック、ケッチェンブラック、チャンネルブラック、ファーネスブラック、ランプブラック、サーマルブラック等が挙げられる。なかでも、良好な導電性を付与する観点から、アセチレンブラック、ケッチェンブラックが好ましい。また、これら導電性炭素の形状としては、チタン酸リチウム化合物の一次粒子の少なくとも一部の表面を導電性炭素からなる層で被覆させて得られる電池物性をより高める観点から、中空形状を呈するもの、又は空隙を含む形状を呈するものであるのが好ましい。 Carbon black is preferable as the conductive carbon, and specific examples include acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Of these, acetylene black and ketjen black are preferred from the viewpoint of imparting good conductivity. The conductive carbon has a hollow shape from the viewpoint of further improving the physical properties of the battery obtained by coating at least a part of the surface of the primary particles of the lithium titanate compound with a layer made of conductive carbon. Or a shape including voids is preferred.
また、本発明で用いる導電性炭素は、チタン酸リチウム化合物の一次粒子が有する平均粒径Ｘ以下の平均粒径Ｙを有するのが好ましい。導電性炭素がこのような平均粒径を有することにより、かかる導電性炭素がチタン酸リチウム化合物の粒子と粒子の間隙に効率的に配置されて、空隙が低減された均一性の高い複合体粒子を得ることができる。 In addition, the conductive carbon used in the present invention preferably has an average particle size Y that is equal to or less than the average particle size X of the primary particles of the lithium titanate compound. Since the conductive carbon has such an average particle diameter, the conductive carbon is efficiently arranged in the gap between the lithium titanate compound particles and the particles, and the composite particles have high uniformity with reduced voids. Can be obtained.
チタン酸リチウム化合物が有する平均粒径Ｘと導電性炭素が有する平均粒径Ｙとの比（Ｘ／Ｙ）は、より効率的にチタン酸リチウム化合物の粒子と粒子の間隙に配置される観点、及び得られる電池物性の向上を図る観点から、好ましくは１〜２０であり、より好ましくは１．５〜１０である。また、導電性炭素が有する平均粒径Ｙは、同様の観点から、好ましくは１０〜１００ｎｍであり、より好ましくは１０〜５０ｎｍである。なお、かかる平均粒径Ｙは、上記チタン酸リチウム化合物の平均粒径Ｘと同様の方法により測定される値を意味する。 The ratio (X / Y) of the average particle diameter X possessed by the lithium titanate compound and the average particle diameter Y possessed by the conductive carbon is a viewpoint in which the lithium titanate compound particles are more efficiently disposed between the particles, And from a viewpoint of aiming at the improvement of the battery physical property obtained, Preferably it is 1-20, More preferably, it is 1.5-10. Moreover, the average particle diameter Y which electroconductive carbon has becomes like this. Preferably it is 10-100 nm, More preferably, it is 10-50 nm. In addition, this average particle diameter Y means the value measured by the method similar to the average particle diameter X of the said lithium titanate compound.
本発明のチタン酸リチウム負極活物質のタップ密度は、好ましくは０．８〜２．５ｇ／ｃｍ3であり、より好ましくは１．０〜２．５ｇ／ｃｍ3であり、さらに好ましくは１．２〜２．５ｇ／ｃｍ3である。したがって、本発明のチタン酸リチウム負極活物質は、極めて空隙が低減されてなり、これらチタン酸リチウム化合物と導電性炭素とが非常に均一に分散してなる粒子であるため、これを負極材料として用いれば、得られる電池物性の向上を容易に図ることが可能となる。なお、チタン酸リチウム負極活物質のタップ密度とは、重量既知の粉体試料ｍ（g）を入れた測定用容器を機械的にタップし、体積変化が認められなくなった時の粉体体積Ｖ（ｃｍ3）を読み取り、式 ｍ/Ｖ を用いて計算された値を平均したものを意味する。 The tap density of the lithium titanate negative electrode active material of the present invention is preferably 0.8 to 2.5 g / cm 3 , more preferably 1.0 to 2.5 g / cm 3 , and still more preferably 1. 2 to 2.5 g / cm 3 . Therefore, the lithium titanate negative electrode active material of the present invention is a particle in which voids are extremely reduced, and these lithium titanate compound and conductive carbon are dispersed very uniformly. If used, it is possible to easily improve the physical properties of the battery obtained. The tap density of the lithium titanate negative electrode active material is the powder volume V when no change in volume is recognized by mechanically tapping a measuring container containing a powder sample m (g) of known weight. (Cm 3 ) is read, and the value calculated using the formula m / V is averaged.
また、本発明のチタン酸リチウム負極活物質におけるチタン酸リチウム化合物及び導電性炭素は、これらの均一性及び分散性を高める観点、及び得られる電池物性をより高める観点から、チタン酸リチウム化合物の一次粒子の少なくとも一部の表面を、導電性炭素からなる層が被覆してなるのが好ましい。導電性炭素からなる層は、一次粒子の少なくとも一部の表面を被覆していてもよく、一次粒子のほぼ全表面を被覆していてもよい。これにより、チタン酸リチウム化合物の一次粒子及び導電性炭素の各々が凝集するのを抑制することができ、導電性炭素がより緻密かつ均一に分散した複合体粒子であるチタン酸リチウム負極活物質が得られ、導電性をより高めることが可能となる。 Moreover, the lithium titanate compound and the conductive carbon in the lithium titanate negative electrode active material of the present invention are primary components of the lithium titanate compound from the viewpoint of enhancing the uniformity and dispersibility thereof and the physical properties of the obtained battery. It is preferable that at least a part of the surface of the particle is covered with a layer made of conductive carbon. The layer made of conductive carbon may cover at least a part of the surface of the primary particles, or may cover almost the entire surface of the primary particles. Thereby, the primary particles of the lithium titanate compound and the conductive carbon can be prevented from aggregating, and the lithium titanate negative electrode active material which is a composite particle in which the conductive carbon is more densely and uniformly dispersed is obtained. As a result, the conductivity can be further increased.
導電性炭素からなる層の厚みは、好ましくは０．１〜５．０ｎｍであり、より好ましくは０．５〜３．０ｎｍである。 The thickness of the layer made of conductive carbon is preferably 0.1 to 5.0 nm, more preferably 0.5 to 3.0 nm.
また、本発明のチタン酸リチウム負極活物質が有する平均粒径Ｚは、得られるリチウムイオン電池において優れた電池物性を保持しつつ軽量化を図る観点から、５〜５０μｍであって、好ましくは５〜３０μｍであり、より好ましくは５〜２０μｍである。このように、本発明のチタン酸リチウム負極活物質は、均一に分散したチタン酸リチウム化合物と導電性炭素とを含有しつつも微細な複合体粒子であるため、これを用いて負極を形成することにより、優れた電池物性を有するリチウムイオン電池を得ることができる。なお、かかる平均粒径Ｚは、上記平均粒径Ｘ及びＹと同様の方法により測定される値を意味する。 The average particle size Z of the lithium titanate negative electrode active material of the present invention is 5 to 50 μm, preferably 5 from the viewpoint of weight reduction while maintaining excellent battery properties in the obtained lithium ion battery. It is -30 micrometers, More preferably, it is 5-20 micrometers. Thus, since the lithium titanate negative electrode active material of the present invention is a fine composite particle containing a uniformly dispersed lithium titanate compound and conductive carbon, a negative electrode is formed using this. Thus, a lithium ion battery having excellent battery properties can be obtained. In addition, this average particle diameter Z means the value measured by the method similar to the said average particle diameter X and Y.
なお、本発明のチタン酸リチウム負極活物質は、本発明の効果を阻害しない範囲内で、リチウム原子、チタン原子又は酸素原子以外の原子によりドープされていてもよい。ドープ可能な原子としては、Ｂｅ、Ｍｇ、Ｃａ、Ｓｃ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ａｌ、Ｓｉ、Ｇａ、Ｇｅ、Ｙ、Ｓｎ、Ｃｅ、Ｅｕ、Ｌａ、Ｗ、Ｒｕ等が挙げられる。 In addition, the lithium titanate negative electrode active material of the present invention may be doped with an atom other than a lithium atom, a titanium atom, or an oxygen atom as long as the effects of the present invention are not impaired. The atoms that can be doped include Be, Mg, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Si, Ga, Ge, Y, Sn, Ce, Eu, La, and W. , Ru and the like.
このようにして得られた本発明のチタン酸リチウム負極活物質を用いてリチウムイオン電池を製造する方法は特に限定されず、公知の方法をいずれも使用できる。例えば、かかるチタン酸リチウム負極活物質を結着剤や溶剤等の添加剤とともに混合して塗工液を得る。この際、必要に応じて、さらに導電助剤を添加して混合してもよい。かかる結着剤としては、特に限定されず、公知の剤をいずれも使用できる。具体的には、ポリテトラフルオロエチレン、ポリビニリデンフルオライド、ポリビニルクロライド、エチレンプロピレンジエンポリマー等が挙げられる。また、かかる導電助剤としては、特に限定されず、公知の剤をいずれも使用できる。具体的には、アセチレンブラック、ケッチェンブラック、天然黒鉛、人工黒鉛、繊維状炭素等が挙げられる。次いで、かかる塗工液をアルミ箔等の負極集電体上に塗布し、乾燥させて負極とする。 The method for producing a lithium ion battery using the thus obtained lithium titanate negative electrode active material of the present invention is not particularly limited, and any known method can be used. For example, the lithium titanate negative electrode active material is mixed with additives such as a binder and a solvent to obtain a coating liquid. At this time, if necessary, a conductive additive may be further added and mixed. The binder is not particularly limited, and any known agent can be used. Specific examples include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, and ethylene propylene diene polymer. Moreover, it does not specifically limit as this conductive support agent, Any well-known agent can be used. Specific examples include acetylene black, ketjen black, natural graphite, artificial graphite, and fibrous carbon. Subsequently, this coating liquid is apply | coated on negative electrode collectors, such as aluminum foil, and it is made to dry and is set as a negative electrode.
本発明のチタン酸リチウム負極活物質は、リチウムイオン電池の負極として非常に優れた放電容量を発揮する点で有用である。かかる負極を適用できるリチウム電池としては、正極と負極と電解液とセパレータを必須構成とするものであれば特に限定されない。 The lithium titanate negative electrode active material of the present invention is useful in that it exhibits a very excellent discharge capacity as a negative electrode of a lithium ion battery. A lithium battery to which such a negative electrode can be applied is not particularly limited as long as it has a positive electrode, a negative electrode, an electrolytic solution, and a separator as essential components.
ここで、正極については、リチウムイオンを充電時には放出し、かつ放電時には吸蔵することができれば、その材料構成で特に限定されるものではなく、公知の材料構成のものを用いることができる。例えば、原料を水熱反応させることにより得られる各種オリビン型化合物を好適に用いることが好ましい。 Here, as for the positive electrode, as long as lithium ions can be released during charging and occluded during discharging, the material configuration is not particularly limited, and a known material configuration can be used. For example, it is preferable to suitably use various olivine compounds obtained by hydrothermal reaction of the raw materials.
電解液は、有機溶媒に支持塩を溶解させたものである。有機溶媒は、通常リチウムイオン二次電池の電解液の用いられる有機溶媒であれば特に限定されるものではなく、例えば、カーボネート類、ハロゲン化炭化水素、エーテル類、ケトン類、ニトリル類、ラクトン類、オキソラン化合物等を用いることができる。 The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent that is usually used for an electrolyte solution of a lithium ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones An oxolane compound or the like can be used.
支持塩は、その種類が特に限定されるものではないが、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4及びＬｉＡｓＦ6から選ばれる無機塩、該無機塩の誘導体、ＬｉＳＯ3ＣＦ3、ＬｉＣ（ＳＯ3ＣＦ3）2及びＬｉＮ（ＳＯ3ＣＦ3）2、ＬｉＮ（ＳＯ2Ｃ2Ｆ5）2及びＬｉＮ（ＳＯ2ＣＦ3）（ＳＯ2Ｃ4Ｆ9）から選ばれる有機塩、並びに該有機塩の誘導体の少なくとも１種であることが好ましい。 The type of the supporting salt is not particularly limited, but an inorganic salt selected from LiPF 6 , LiBF 4 , LiClO 4 and LiAsF 6 , a derivative of the inorganic salt, LiSO 3 CF 3 , LiC (SO 3 CF 3 ) 2 and LiN (SO 3 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 and LiN (SO 2 CF 3 ) (SO 2 C 4 F 9 ), and organic salt derivatives It is preferable that it is at least 1 type of these.
セパレータは、正極及び負極を電気的に絶縁し、電解液を保持する役割を果たすものである。たとえば、多孔性合成樹脂膜、特にポリオレフィン系高分子（ポリエチレン、ポリプロピレン）の多孔膜を用いればよい。 The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film may be used.
以下、本発明について、実施例に基づき具体的に説明するが、本発明はこれら実施例に限定されるものではない。 EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
［製造例１］
酸化チタン及び炭酸リチウムを用い、Ｊｏｕｒｎａｌ ｏｆ Ｐｏｗｅｒ Ｓｏｕｒｃｅ ２２１（（２０１３），ｐ１２２−１２７）に記載の方法にしたがって、混合・粉砕、焼成処理（焼成温度８００℃、焼成時間１０時間）を行い、チタン酸リチウム化合物の一次粒子（平均粒径１００ｎｍ）を得た。
[Production Example 1]
In accordance with the method described in Journal of Power Source 221 ((2013), p122-127) using titanium oxide and lithium carbonate, mixing, pulverization, and baking treatment (baking temperature of 800 ° C., baking time of 10 hours) are performed. Primary particles (average particle size 100 nm) of the lithium acid compound were obtained.
［実施例１］
製造例１で得られたチタン酸リチウム化合物の一次粒子９３．０ｇとケッチェンブラック（ライオン社製、平均粒径３０ｎｍ）７．０ｇとを予め混合して混合物を得て、得られた混合物を微粒子複合化装置 ノビルタ（ホソカワミクロン社製）に投入し、２５〜３５℃で３０分間混合して、複合体粒子Ａを得た。得られた複合体粒子Ａの平均粒径は２０μｍであり、タップ密度は１．４５ｇ／ｃｍ3であった。
得られた複合体粒子ＡのＳＥＭ像を図１に示す。
[Example 1]
93.0 g of primary particles of the lithium titanate compound obtained in Production Example 1 and 7.0 g of Ketjen Black (manufactured by Lion Corporation, average particle size of 30 nm) were mixed in advance to obtain a mixture. Fine particle composite apparatus Nobilta (manufactured by Hosokawa Micron Corporation) was charged and mixed at 25 to 35 ° C. for 30 minutes to obtain composite particles A. The obtained composite particles A had an average particle size of 20 μm and a tap density of 1.45 g / cm 3 .
The SEM image of the obtained composite particle A is shown in FIG.
［比較例１］
製造例１で得られたチタン酸リチウム化合物の一次粒子２．６３ｇ、ケッチェンブラック（ライオン社製、平均粒径３０ｎｍ）０．０９ｇ及び分散安定化剤（カルボキシメチルセルロース、ダイセルファインケム社製）を加えた水３０ｇを、遊星ボールミル（遊星型ボールミルＰ−５、フリッチュ社製）のジルコニア製ポットにジルコニア製ボールとともに投入し、２５〜７０℃で２４０分間混合して乾燥し、複合体粒子Ｂを得た。得られた複合体粒子Ｂの平均粒径は、２μｍであり、タップ密度は０．９３ｇ／ｃｍ3であった。
[Comparative Example 1]
Add 2.63 g of primary particles of the lithium titanate compound obtained in Production Example 1, 0.09 g of Ketjen Black (Lion, average particle size 30 nm) and a dispersion stabilizer (carboxymethylcellulose, manufactured by Daicel Finechem) 30 g of water was put into a zirconia pot of a planetary ball mill (Planet Ball Mill P-5, manufactured by Fritsch) together with zirconia balls, mixed at 25 to 70 ° C. for 240 minutes, and dried to obtain composite particles B It was. The obtained composite particles B had an average particle size of 2 μm and a tap density of 0.93 g / cm 3 .
［試験例１］
実施例１及び比較例１で得られた複合体粒子を用い、リチウムイオン二次電池の負極を作製した。実施例１及び比較例１で得られた複合体、ケッチェンブラック（導電剤）、ポリフッ化ビニリデン（粘結剤）を重量比８０：１０：１０の配合割合で混合し、これにＮ−メチル−２−ピロリドンを加えて充分混練し、負極スラリーを調製した。負極スラリーを厚さ２０μｍのアルミニウム箔からなる集電体に塗工機を用いて塗布し、８０℃で１２時間の真空乾燥を行った。その後、φ１４ｍｍの円盤状に打ち抜いてハンドプレスを用いて１６ＭＰａで２分間プレスし、負極とした。
[Test Example 1]
Using the composite particles obtained in Example 1 and Comparative Example 1, a negative electrode of a lithium ion secondary battery was produced. The composite obtained in Example 1 and Comparative Example 1, ketjen black (conductive agent), and polyvinylidene fluoride (binding agent) were mixed at a weight ratio of 80:10:10, and this was mixed with N-methyl. -2-Pyrrolidone was added and sufficiently kneaded to prepare a negative electrode slurry. The negative electrode slurry was applied to a current collector made of an aluminum foil having a thickness of 20 μm using a coating machine, and vacuum dried at 80 ° C. for 12 hours. Thereafter, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a negative electrode.
次いで、上記の負極を用いてコイン型リチウムイオン二次電池を構築した。正極には、リチウム箔を用いた。電解液には、エチレンカーボネート及びエチルメチルカーボネートを体積比１：１の割合で混合した混合溶媒に、ＬＩＰＦ6を１ｍｏｌ／ｌの濃度で溶解したものを用いた。セパレータには、ポリプロピレンなどの高分子多孔フィルムなど、公知のものを用いた。これらの電池部品を露点が−５０℃以下の雰囲気で常法により組み込み収容し、コイン型リチウム二次電池（ＣＲ−２０３２）を製造した。 Next, a coin-type lithium ion secondary battery was constructed using the negative electrode. Lithium foil was used for the positive electrode. As the electrolytic solution, a solution obtained by dissolving LIPF 6 at a concentration of 1 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 1 was used. As the separator, a known one such as a polymer porous film such as polypropylene was used. These battery components were assembled and housed in a conventional manner in an atmosphere with a dew point of −50 ° C. or lower to produce a coin-type lithium secondary battery (CR-2032).
製造したリチウムイオン二次電池を用いて定電流密度での充放電試験を行い、充放電容量を測定した。このときの充電条件は電流０．１ＣＡ（１７．５ｍＡ／ｇ）、電圧２．５Ｖの定電流充電とし、放電条件は電流０．１ＣＡ、終止電圧１．０Ｖの定電流放電とした。温度は全て３０℃とした。 A charge / discharge test at a constant current density was performed using the manufactured lithium ion secondary battery, and a charge / discharge capacity was measured. The charging conditions at this time were constant current charging with a current of 0.1 CA (17.5 mA / g) and a voltage of 2.5 V, and the discharging conditions were constant current discharging with a current of 0.1 CA and a final voltage of 1.0 V. All temperatures were 30 ° C.
上記結果より、実施例１で得られた複合体粒子Ａは、比較例１で得られた複合体粒子Ｂに比して、極めて均一性が高い上に空隙が低減されてなるため、タップ密度が非常に大きく、これを用いた二次電池において優れた電池物性を示すことがわかる。一方、比較例１で得られた複合体粒子Ｂは、微細な粒子ではあるものの、十分な量の導電性炭素を含有していない上に空隙が多いためにタップ密度が小さくなり、電池物性の低下を招いたものと考えられる。 From the above results, the composite particle A obtained in Example 1 is extremely uniform and has reduced voids as compared to the composite particle B obtained in Comparative Example 1. Therefore, the tap density It can be seen that the secondary battery using the same exhibits excellent battery properties. On the other hand, although the composite particle B obtained in Comparative Example 1 is a fine particle, it does not contain a sufficient amount of conductive carbon and has many voids, so that the tap density is reduced, and the battery physical properties are reduced. This is thought to have caused a decline.
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