JP5810752B2 - Lithium titanate particle powder, negative electrode active material particle powder for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents
Lithium titanate particle powder, negative electrode active material particle powder for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery Download PDFInfo
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Description
本発明は、非水電解質二次電池用負極活物質として、優れた出力特性を有するチタン酸リチウム粒子粉末、該チタン酸リチウム粒子粉末を負極活物質として使用した非水電解質二次電池を提供する。 The present invention provides a lithium titanate particle powder having excellent output characteristics as a negative electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery using the lithium titanate particle powder as a negative electrode active material. .
近年、ＡＶ機器やパソコン等の電子機器のポータブル化、コードレス化が急速に進んでおり、これらの駆動用電源として小型、軽量で高エネルギー密度を有する二次電池への要求が高くなっている。このような状況下において、充放電電圧が高く、充放電容量も大きいという長所を有するリチウムイオン二次電池が注目されている。 In recent years, electronic devices such as AV devices and personal computers are rapidly becoming portable and cordless, and there is an increasing demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. Under such circumstances, a lithium ion secondary battery having advantages such as a high charge / discharge voltage and a large charge / discharge capacity has attracted attention.
このリチウムイオン二次電池において、近年、負極活物質にチタン酸リチウムを使用することが知られている。 In this lithium ion secondary battery, in recent years, it is known to use lithium titanate as a negative electrode active material.
チタン酸リチウム：Ｌｉ４Ｔｉ５Ｏ１２は、充放電によるリチウムイオン挿入・脱離反応における結晶構造変化が非常に小さいため、構造安定性が高く、信頼性の高い負極活物質として知られている。 Lithium titanate: Li 4 Ti 5 O 12 is known as a highly reliable negative electrode active material with high structural stability because the crystal structure change in the lithium ion insertion / extraction reaction due to charge / discharge is very small. .
従来から、チタン酸リチウム（Ｌｉ４Ｔｉ５Ｏ１２）を得るための製造法としては、リチウム塩とチタン酸化物をＬｉ／Ｔｉ比がほぼ０．８０となるように乾式または湿式混合した混合粉末（これらは、単なるリチウム塩とチタン酸化物の混合物である）を加熱焼成してＬｉ４Ｔｉ５Ｏ１２を得る、いわゆる固相反応法（乾式法）が知られている（特許文献１、２）。 Conventionally, as a manufacturing method for obtaining lithium titanate (Li 4 Ti 5 O 12 ), a mixed powder in which a lithium salt and a titanium oxide are dry or wet mixed so that a Li / Ti ratio is approximately 0.80. There is known a so-called solid phase reaction method (dry method) in which Li 4 Ti 5 O 12 is obtained by heating and firing (these are simply a mixture of a lithium salt and a titanium oxide) (Patent Documents 1 and 2). ).
この特許文献２では、粒子粉末を粉砕することで充填性を向上させ、電池特性を改善させることが開示されている。 In this patent document 2, it is disclosed that the filling property is improved by pulverizing the particle powder to improve the battery characteristics.
一方、チタンとリチウムの混合物を水熱処理して、その後加熱焼成してＬｉ４Ｔｉ５Ｏ１２を得る、液相反応＋固相反応法（湿式法）が知られている（特許文献３、４）。 On the other hand, a liquid phase reaction + solid phase reaction method (wet method) is known in which a mixture of titanium and lithium is hydrothermally treated and then heated and fired to obtain Li 4 Ti 5 O 12 (Patent Documents 3 and 4). ).
また、特許文献５では、結晶子径を小さくするほど、また、不純物相が少ないほどリチウムイオンの拡散速度が向上し、イオン伝導性および大電流特性（高率放電容量維持率）が向上することが開示されている。 Further, in Patent Document 5, the smaller the crystallite diameter and the smaller the impurity phase, the higher the lithium ion diffusion rate, and the higher the ion conductivity and large current characteristics (high rate discharge capacity retention rate). Is disclosed.
これまで、電池特性、特に、出力特性を向上させるためには、一次粒子や二次粒子の微細化が有効であることが報告されており、粒径や比表面積（ＢＥＴ法）を制御することが行われている。
近年、高い初期容量で且つ、従来よりも更に出力特性を向上させることのできるチタン酸リチウムは、最も要求されるところであり、より微細化が志向されている。
Until now, it has been reported that refinement of primary particles and secondary particles is effective for improving battery characteristics, particularly output characteristics, and controlling particle size and specific surface area (BET method). Has been done.
In recent years, lithium titanate, which has a high initial capacity and can further improve output characteristics as compared with the prior art, is the most demanded and further miniaturization is aimed at.
しかしながら、高い出力特性を目標にすると、粒子を微細化しても出力特性が向上するどころか、逆に悪化し、その要因が粒径や比表面積に依存しないケースが多々あった。 However, when high output characteristics are targeted, there are many cases in which the output characteristics are not improved even if the particles are miniaturized, but on the contrary, the cause is not dependent on the particle diameter or specific surface area.
そこで、高い初期容量であって、しかも、従来よりも更に出力特性を向上させることのできるチタン酸リチウム粒子粉末が望まれる。 Therefore, a lithium titanate particle powder having a high initial capacity and capable of further improving the output characteristics as compared with the prior art is desired.
本発明者らは、チタン酸リチウム粒子粉末のＸＲＤ測定を行い、リートベルト法により求められる結晶歪みと結晶子サイズとを制御することによって、出力特性（高率放電容量維持率）に優れた電池特性が得られることを見出して本発明をなすに至った。 The present inventors have performed an XRD measurement of lithium titanate particle powder and controlled the crystal strain and crystallite size required by the Rietveld method, whereby a battery having excellent output characteristics (high rate discharge capacity maintenance rate). The inventors have found that characteristics can be obtained, and have made the present invention.
前記技術的課題は、次の通りの本発明によって達成できる。 The technical problem can be achieved by the present invention as follows.
即ち、本発明は、スピネル構造を有するチタン酸リチウム粒子粉末において、該チタン酸リチウム粒子粉末のＸＲＤパターンのリートベルト解析による結晶歪みが０．００１５以下であり、且つ結晶子サイズが１００〜３００ｎｍであることを特徴とするチタン酸リチウム粒子粉末である（本発明１）。 That is, according to the present invention, in the lithium titanate particle powder having a spinel structure, the crystal strain by the Rietveld analysis of the XRD pattern of the lithium titanate particle powder is 0.0015 or less, and the crystallite size is 100 to 300 nm. It is a lithium titanate particle powder characterized by being (Invention 1).
また、本発明は、前記チタン酸リチウム粒子粉末からなる非水電解質二次電池用負極活物質粒子粉末である（本発明２）。 Moreover, this invention is the negative electrode active material particle powder for nonaqueous electrolyte secondary batteries which consists of the said lithium titanate particle powder (this invention 2).
また、本発明は、本発明２記載の負極活物質粒子粉末を９０重量部、導電助剤を５重量部、結合剤を５重量部の組成比で使用し、対極をリチウム金属としたセルにおいて、リチウムが放出される方向を充電としたときに、初期放電容量が１６５ｍＡｈ／ｇ以上であり、且つ、初期放電容量測定におけるＣ−レートを０．１Ｃとし、１０Ｃと０．１Ｃの割合にあたる出力特性が８５％以上である非水電解質二次電池用負極活物質粒子粉末である（本発明３）。 Further, the present invention provides a cell in which the anode active material particle powder according to the present invention 2 is used in a composition ratio of 90 parts by weight, a conductive additive is 5 parts by weight, a binder is 5 parts by weight, and the counter electrode is a lithium metal. When the charging direction is lithium, the initial discharge capacity is 165 mAh / g or more, and the C-rate in the initial discharge capacity measurement is 0.1 C, and the output corresponds to the ratio of 10 C and 0.1 C. This is a negative electrode active material particle powder for a nonaqueous electrolyte secondary battery having a characteristic of 85% or more (Invention 3).
また、本発明は、本発明２又は３に記載の負極活物質粒子粉末を使用した非水電解質二次電池である（本発明４）。 Moreover, this invention is a non-aqueous electrolyte secondary battery using the negative electrode active material particle powder of this invention 2 or 3 (this invention 4).
本発明に係るチタン酸リチウム粒子粉末は、適切な結晶歪み及び結晶子サイズを有する化合物であり、非水電解質二次電池に用いた場合に、優れた初期放電容量及び高出力特性を得られるので、非水電解質二次電池用の活物質粒子粉末として好適である。 The lithium titanate particle powder according to the present invention is a compound having appropriate crystal distortion and crystallite size, and when used in a non-aqueous electrolyte secondary battery, excellent initial discharge capacity and high output characteristics can be obtained. It is suitable as an active material particle powder for a non-aqueous electrolyte secondary battery.
本発明の構成をより詳しく説明すれば次のとおりである。 The configuration of the present invention will be described in more detail as follows.
本発明に係るチタン酸リチウム粒子粉末は、少なくともスピネル構造であり、一般化学式でＬｉ４Ｔｉ５Ｏ１２と記載できる化合物である。なお、本発明においては、後述する結晶歪み、結晶子サイズを有する範囲において、他の不純物相を含有してもよい。不純物相の総量は６％以下が好ましい。 The lithium titanate particle powder according to the present invention is a compound that has at least a spinel structure and can be described as Li 4 Ti 5 O 12 in a general chemical formula. In addition, in this invention, you may contain another impurity phase in the range which has the crystal | crystallization distortion and crystallite size which are mentioned later. The total amount of impurity phases is preferably 6% or less.
本発明ではチタン酸リチウム粒子粉末をＸＲＤ測定し、リートベルト解析によりチタン酸リチウム粒子粉末の結晶歪みと結晶子サイズを求めることができる。測定の条件は２θ／θで１０〜９０度を０．０２度ステップスキャンとした。 In the present invention, the lithium titanate particle powder is subjected to XRD measurement, and the crystal distortion and crystallite size of the lithium titanate particle powder can be obtained by Rietveld analysis. The measurement conditions were 2θ / θ, 10 to 90 degrees, and 0.02 degree step scan.
本発明に係るチタン酸リチウム粒子粉末は、ＸＲＤパターンからリートベルト解析を行うことで結晶歪みと結晶子サイズを算出することができる。結晶歪みが０．００１５を超えると、出力特性が悪くなる。結晶歪みの好ましい範囲は０．００１４以下であり、更に好ましい範囲は０．０００１〜０．００１３である。
また、結晶子サイズが８０〜３００ｎｍの範囲外である場合、出力特性が悪化する。結晶子サイズの好ましい範囲は９０〜２９０ｎｍであり、更に好ましい範囲は１００〜２８０ｎｍである。
The lithium titanate particle powder according to the present invention can calculate crystal distortion and crystallite size by performing Rietveld analysis from the XRD pattern. When the crystal strain exceeds 0.0015, the output characteristics deteriorate. A preferable range of crystal distortion is 0.0014 or less, and a more preferable range is 0.0001 to 0.0013.
Moreover, when the crystallite size is outside the range of 80 to 300 nm, the output characteristics are deteriorated. A preferable range of the crystallite size is 90 to 290 nm, and a more preferable range is 100 to 280 nm.
本発明では、チタン酸リチウム粒子粉末のＸＲＤパターンのリートベルト解析により、結晶歪みが０．００１５以下であり、且つ、結晶子サイズが８０〜３００ｎｍの範囲にあることが重要であり、主に２つの理由が挙げられる。 In the present invention, it is important by the Rietveld analysis of the XRD pattern of the lithium titanate particle powder that the crystal distortion is 0.0015 or less and the crystallite size is in the range of 80 to 300 nm. There are two reasons.
１点目は、ＢＥＴ比表面積の大小に関わらず結晶歪みが本発明の範囲にあると出力特性が大きくなることを見出した。一般的には出力特性を大きくする手法としてＢＥＴ比表面積が大きくなるような処方（例えば、粉砕度合いを上げて微粒子化する）が行われるが、粒子にダメージ（応力の残留や化学組成の変化）が発生するために粒子に歪みが残ってしまう。この歪みが本発明の範囲より大きいと急激に出力特性が悪化してしまうことが分かった。 The first point is that the output characteristics are increased when the crystal strain is within the range of the present invention regardless of the size of the BET specific surface area. In general, as a method for increasing the output characteristics, a prescription that increases the BET specific surface area (for example, increasing the degree of pulverization to make fine particles) is performed, but the particles are damaged (residual stress or change in chemical composition). Will cause distortion in the particles. It has been found that when this distortion is larger than the range of the present invention, the output characteristics deteriorate rapidly.
２点目は、結晶歪みが本発明の範囲にあったとしても、結晶子サイズが８０〜３００ｎｍの範囲外である場合には出力特性が悪化してしまう。即ち、結晶歪みが８０ｎｍ未満では電極塗料の分散性が悪化し、結晶歪みが３００ｎｍを超えるとＬｉのイオン拡散が悪化してしまい、結果的に出力特性が悪化してしまう。 Second, even if the crystal distortion is within the range of the present invention, the output characteristics are deteriorated when the crystallite size is outside the range of 80 to 300 nm. That is, when the crystal strain is less than 80 nm, the dispersibility of the electrode paint is deteriorated, and when the crystal strain exceeds 300 nm, Li ion diffusion is deteriorated, resulting in deterioration of output characteristics.
上記２点を満たす本発明のチタン酸リチウム粒子粉末であれば、出力特性（高率放電容量維持率）に優れるので、長期安定性に優れる結果になると考えられる。 If the lithium titanate particle powder of the present invention satisfying the above two points is excellent in output characteristics (high rate discharge capacity maintenance rate), it is considered that the long-term stability is excellent.
本発明に係るチタン酸リチウム粒子粉末のＢＥＴ法による比表面積は６〜３０ｍ２／ｇの範囲が好ましい。比表面積がこの範囲より小さいと、出力特性が悪化してしまう。またこの範囲より大きいと二次電池用活物質としての性能が低下する場合がある。より好ましい比表面積は７〜２０ｍ２／ｇである。 The specific surface area by the BET method of the lithium titanate particle powder according to the present invention is preferably in the range of 6 to 30 m 2 / g. When the specific surface area is smaller than this range, the output characteristics are deteriorated. On the other hand, if it is larger than this range, the performance as an active material for a secondary battery may deteriorate. A more preferable specific surface area is 7 to 20 m 2 / g.
次に、本発明に係るチタン酸リチウム粒子粉末の製造方法について述べる。 Next, the manufacturing method of the lithium titanate particle powder concerning this invention is described.
本発明に係るチタン酸リチウム粒子粉末の製造方法については特別限定されるものではないが、乾式法では、高温焼成により、一次粒子が大きくなり、それを粉砕して微粒子化する場合に、歪みが生じやすく、本発明で規定する出力特性を得ることは困難である。従って、強力な粉砕を行う必要のない湿式法が望ましい。 The production method of the lithium titanate particles according to the present invention is not particularly limited, but in the dry method, the primary particles become large due to high-temperature firing, and when the particles are pulverized into fine particles, distortion is caused. It is easy to occur, and it is difficult to obtain output characteristics defined by the present invention. Therefore, a wet method that does not require strong pulverization is desirable.
例えば、本発明に係るチタン酸リチウム粒子粉末は、少なくともＬｉ２ＴｉＯ３とＴｉＯ２との混合物を用いて、６５０℃以上８００℃未満で焼成することで得られる。 For example, the lithium titanate particle powder according to the present invention can be obtained by firing at 650 ° C. or more and less than 800 ° C. using at least a mixture of Li 2 TiO 3 and TiO 2 .
本発明に係るチタン酸リチウム粒子粉末の製造に用いるＬｉ２ＴｉＯ３は、ＪＣＰＤＳにおける指数付けでＬｉ２ＴｉＯ３の特定ができれば、その結晶構造に構造欠陥があったり、酸素欠損／酸素過剰があってもかまわない。 Li 2 TiO 3 to be used in the preparation of lithium titanate particles according to the present invention, if a particular Li 2 TiO 3 is in indexing in the JCPDS, or have structural defects in the crystal structure, there is an oxygen deficiency / oxygen excess It doesn't matter.
本発明において用いることができるＬｉ化合物は、特に限定されることなく各種のリチウム塩を用いることができるが、湿式法では、水酸化リチウムが好ましい。 The lithium compound that can be used in the present invention is not particularly limited, and various lithium salts can be used, but lithium hydroxide is preferable in the wet method.
本発明において用いることができるＴｉＯ２は、アナターゼ型とルチル型と、その混相があるが、アナターゼ型が好ましい。また、混合反応を行う場合は、反応性を向上させるために微粒子を用いると有利である。 TiO 2 that can be used in the present invention has an anatase type, a rutile type, and a mixed phase thereof, and an anatase type is preferable. In the case of performing a mixing reaction, it is advantageous to use fine particles in order to improve the reactivity.
また、Ｌｉ２ＴｉＯ３とＴｉＯ２との状態は、均一に混ざり合っている状態であれば、乾式での混合であったり、湿式でコートされている状態であったり、混合相のような状態になっていてもよい。 Moreover, if the state of Li 2 TiO 3 and TiO 2 is a uniformly mixed state, it may be a dry-type mixing, a wet-coated state, or a mixed phase state It may be.
この混合物は、湿式法では、温度、時間を制御することで調製できる。また、予め、Ｌｉ２ＴｉＯ３を生成させて、ＴｉＯ２と混合することでも調製できるが、焼成温度を高くする必要があるため、Ｌｉ／Ｔｉ比、ＢＥＴ比表面積の制御に配慮する必要がある。 This mixture can be prepared by controlling the temperature and time in the wet method. It can also be prepared by generating Li 2 TiO 3 in advance and mixing it with TiO 2. However, since it is necessary to increase the firing temperature, it is necessary to consider the control of the Li / Ti ratio and the BET specific surface area. .
なお、Ｌｉ２ＴｉＯ３とＴｉＯ２との混合物は、その製造条件において特に制限されるものではなく、酸化チタンと水酸化リチウムをＬｉ／Ｔｉ比のモル比で１．０を超え１．５未満に調整した反応懸濁液を８０℃以上１００℃未満の温度範囲で加熱し、５時間以上１５時間未満攪拌・熟成した後、反応懸濁液をろ過し乾燥することでも得ることができる。 In addition, the mixture of Li 2 TiO 3 and TiO 2 is not particularly limited in the production conditions, and titanium oxide and lithium hydroxide are in a molar ratio of Li / Ti ratio exceeding 1.0 and less than 1.5. It can also be obtained by heating the reaction suspension adjusted to 80 ° C. to less than 100 ° C., stirring and aging for 5 hours to less than 15 hours, and then filtering and drying the reaction suspension.
本発明に係るチタン酸リチウム粒子粉末の製造に用いるＬｉ２ＴｉＯ３とＴｉＯ２は、焼成後のＬｉ／Ｔｉ比で０．８０５〜０．８３０となるように調整することが好ましい。前記範囲に調整するためには、Ｌｉ２ＴｉＯ３とＴｉＯ２との混合比を調整したり、リチウム化合物を追加したりすることによって行うことができる。Ｌｉ／Ｔｉを０．８０より大きくする理由は、焼成後にＬｉ２ＴｉＯ３を残留させることにある。上記範囲より大きすぎると、初期放電容量が低下し、Ｌｉ２ＴｉＯ３残留物が更に多い場合には、得られたチタン酸リチウム粒子粉末の残留アルカリが多くなり、塗料のゲル化が起こる。 Li 2 TiO 3 and TiO 2 used in the production of the lithium titanate particles according to the present invention is preferably adjusted to be 0.805 to 0.830 in Li / Ti ratio after firing. To adjust the range, it can be carried out to adjust the mixing ratio of the Li 2 TiO 3 and TiO 2, by and add lithium compound. The reason why Li / Ti is made larger than 0.80 is that Li 2 TiO 3 remains after firing. When the amount is larger than the above range, the initial discharge capacity is reduced, and when the Li 2 TiO 3 residue is further increased, the residual alkali of the obtained lithium titanate particle powder increases, and the coating gels.
調製したＬｉ２ＴｉＯ３とＴｉＯ２との混合物を６５０℃以上８００℃未満で焼成する。焼成温度が６５０℃未満であるとＴｉＯ２が多量に残留してしまう。焼成温度が高すぎると、粒成長のためＢＥＴ比表面積が小さくなりすぎてしまい、結果として出力特性が損なわれてしまう。焼成温度は好ましくは６８０〜７８０℃である。 The prepared mixture of Li 2 TiO 3 and TiO 2 is fired at 650 ° C. or higher and lower than 800 ° C. If the firing temperature is less than 650 ° C., a large amount of TiO 2 remains. If the firing temperature is too high, the BET specific surface area becomes too small due to grain growth, resulting in a loss of output characteristics. The firing temperature is preferably 680 to 780 ° C.
焼成における雰囲気は、酸化性雰囲気であっても還元雰囲気であってもよいが、好ましくは酸化性雰囲気である。得られたチタン酸リチウム粒子粉末は、公知な技術の範囲において本発明において酸素欠損若しくは酸素過剰があってもよい。 The atmosphere in firing may be an oxidizing atmosphere or a reducing atmosphere, but is preferably an oxidizing atmosphere. The obtained lithium titanate particle powder may have oxygen deficiency or oxygen excess in the present invention within the scope of known techniques.
本発明に係るチタン酸リチウム粒子粉末は、非水電解質二次電池用負極活物質粒子粉末として用いることができる。 The lithium titanate particle powder according to the present invention can be used as a negative electrode active material particle powder for a non-aqueous electrolyte secondary battery.
次に、本発明に係るチタン酸リチウム粒子粉末を含有する負極、並びに非水電解質二次電池について述べる。 Next, the negative electrode containing the lithium titanate particle powder according to the present invention and the nonaqueous electrolyte secondary battery will be described.
本発明に係るチタン酸リチウム粒子粉末を含有する負極を製造する場合には、常法に従って、導電剤と結着剤とを添加混合する。導電剤としてはアセチレンブラック、カーボンブラック、黒鉛等が好ましく、結着剤としてはポリテトラフルオロエチレン、ポリフッ化ビニリデン等が好ましい。 When manufacturing the negative electrode containing the lithium titanate particle powder according to the present invention, a conductive agent and a binder are added and mixed according to a conventional method. As the conductive agent, acetylene black, carbon black, graphite and the like are preferable, and as the binder, polytetrafluoroethylene, polyvinylidene fluoride and the like are preferable.
本発明に係るチタン酸リチウム粒子粉末を含有する負極を用いて製造される二次電池は、正極、負極及び電解質から構成される。 The secondary battery manufactured using the negative electrode containing the lithium titanate particle powder according to the present invention includes a positive electrode, a negative electrode, and an electrolyte.
正極活物質としては、一般的な非水二次電池用の正極材であるコバルト酸リチウム、マンガン酸リチウム、ニッケル酸リチウム等を用いることができる。 As the positive electrode active material, lithium cobaltate, lithium manganate, lithium nickelate, etc., which are common positive electrode materials for non-aqueous secondary batteries, can be used.
また、電解液の溶媒としては、炭酸エチレンと炭酸ジエチルの組み合わせ以外に、炭酸プロピレン、炭酸ジメチル等のカーボネート類や、ジメトキシエタン等のエーテル類の少なくとも１種類を含む有機溶媒を用いることができる。 In addition to the combination of ethylene carbonate and diethyl carbonate, an organic solvent containing at least one of carbonates such as propylene carbonate and dimethyl carbonate and ethers such as dimethoxyethane can be used as the solvent for the electrolytic solution.
さらに、電解質としては、六フッ化リン酸リチウム以外に、過塩素酸リチウム、四フッ化ホウ酸リチウム等のリチウム塩の少なくとも１種類を上記溶媒に溶解して用いることができる。 Further, as the electrolyte, in addition to lithium hexafluorophosphate, at least one lithium salt such as lithium perchlorate and lithium tetrafluoroborate can be dissolved in the above solvent and used.
本発明に係るチタン酸リチウム粒子粉末を含有する電極を用いて製造した非水電解質二次電池は、後述する評価法で１．０Ｖ以上の初期放電容量が１６５ｍＡｈ／ｇ以上であり、１０Ｃ／０．１Ｃの比をとった出力特性は８５％以上である。 The non-aqueous electrolyte secondary battery manufactured using the electrode containing the lithium titanate particle powder according to the present invention has an initial discharge capacity of 1.0 V or higher by a later-described evaluation method of 165 mAh / g or more, and 10 C / 0. The output characteristic with a ratio of 1C is 85% or more.
なお、本発明に係るチタン酸リチウム粒子粉末は、正極活物質として用いることも可能である。 In addition, the lithium titanate particle powder according to the present invention can be used as a positive electrode active material.
本発明に係るチタン酸リチウム粒子粉末を正極活物質として用いる場合、非水電解質二次電池は、前記の電極、対極および電解質からなり、対極（負極）には金属リチウム、リチウム合金等、あるいはグラファイト、コークスなどの炭素系材料が用いられる。 When the lithium titanate particle powder according to the present invention is used as a positive electrode active material, the non-aqueous electrolyte secondary battery is composed of the above electrode, counter electrode and electrolyte, and the counter electrode (negative electrode) is metallic lithium, lithium alloy, or graphite. Carbonaceous materials such as coke are used.
＜作用＞
本発明において最も重要な点は、チタン酸リチウム粒子粉末の結晶歪みを抑えつつ結晶子サイズを本発明の範囲とすることである。仮に、高い出力特性を得るためにＢＥＴ比表面積を大きくしようとしても、良好な特性が得られるとは限らない。本発明においては、より高い出力特性（高率放電容量維持率）を得るためにはチタン酸リチウム粒子粉末の結晶歪みと結晶子サイズとを制御することが重要であることを見いだした。高い出力特性を得るための手段として活物質粒子粉末を微粒子にすることが、通常行われている。微粒子を得るための手段としては該粒子粉末に対して粉砕を行うことで達成できるが、結晶に歪みが残ってしまい、結局は高い出力特性を得ることができない。
<Action>
The most important point in the present invention is that the crystallite size is within the scope of the present invention while suppressing crystal distortion of the lithium titanate particle powder. Even if an attempt is made to increase the BET specific surface area in order to obtain high output characteristics, good characteristics are not always obtained. In the present invention, it has been found that it is important to control the crystal distortion and crystallite size of the lithium titanate particle powder in order to obtain higher output characteristics (high rate discharge capacity retention rate). As a means for obtaining high output characteristics, the active material particle powder is usually made into fine particles. As a means for obtaining fine particles, it can be achieved by pulverizing the particle powder. However, distortion remains in the crystal, and high output characteristics cannot be obtained after all.
本発明者らは、チタン酸リチウム粒子粉末について、単にＢＥＴ比表面積の大きさや粒子粉末の結晶子サイズのみではなく、結晶歪みという点にも着目し制御する方法を見出したことで、高い出力特性（高率放電容量維持率）を示すチタン酸リチウム粒子粉末を得ることが可能となった。 The inventors of the present invention have found a method for controlling lithium titanate particle powder not only by the size of the BET specific surface area and the crystallite size of the particle powder, but also by controlling the crystal distortion, thereby achieving high output characteristics. It became possible to obtain lithium titanate particle powder exhibiting (high rate discharge capacity maintenance rate).
本発明の代表的な実施の形態は、次の通りである。 A typical embodiment of the present invention is as follows.
ＢＥＴ比表面積は試料を窒素ガス下で１２０℃、４５分間乾燥脱気した後、マックソーブＨＭ Ｍｏｄｅｌ−１２０８ マウンテック（株）製を用いて測定した。 The BET specific surface area was measured by drying and deaerating the sample under nitrogen gas at 120 ° C. for 45 minutes, and then using a Macsorb HM Model-1208 manufactured by Mountec Co., Ltd.
試料のＸ線回折は、株式会社リガク製 ＳｍａｒｔＬａｂを用いて測定した。また、結晶歪みと結晶子サイズは、Ｘ線回折のデータを用いてリートベルト解析を行うことで算出した。リートベルト解析には、ＲＩＥＴＡＮ２０００を使用した。 The X-ray diffraction of the sample was measured using SmartLab manufactured by Rigaku Corporation. The crystal strain and crystallite size were calculated by performing Rietveld analysis using X-ray diffraction data. Rietan2000 was used for Rietveld analysis.
本発明に係る負極活物質粒子粉末については、２０３２型コインセルを用いて電池評価を行った。 About the negative electrode active material particle powder which concerns on this invention, battery evaluation was performed using the 2032 type | mold coin cell.
電池評価に係るコインセルについては、本発明に係るチタン酸リチウムを正極として用い、活物質量を９０重量％、導電材としてアセチレンブラックを２．５重量％、グラファイトを２．５重量％、バインダーとしてＮ−メチルピロリドンに溶解したポリフッ化ビニリデン５重量％とを混合した後、Ａｌ金属箔に塗布し１２０℃にて乾燥した。このシートを１６ｍｍΦに打ち抜いた後、３．０ｔ／ｃｍ２で圧延したものを正極に用いた。対極は１６ｍｍΦに打ち抜いた厚さが５００μｍの金属リチウムとし、電解液は１ｍｏｌ／ＬのＬｉＰＦ６を溶解したＥＣとＤＭＣを体積比で１：２で混合した溶液を用いて２０３２型コインセルを作製した。 For a coin cell according to battery evaluation, the lithium titanate according to the present invention is used as a positive electrode, the amount of active material is 90% by weight, acetylene black is 2.5% by weight as a conductive material, graphite is 2.5% by weight, and a binder is used. After mixing 5% by weight of polyvinylidene fluoride dissolved in N-methylpyrrolidone, it was applied to an Al metal foil and dried at 120 ° C. The sheet was punched out to 16 mmΦ and then rolled at 3.0 t / cm 2 to be used for the positive electrode. The counter electrode was made of metallic lithium having a thickness of 500 μm punched to 16 mmΦ, and the electrolyte was a 2032 type coin cell using a solution in which EC and DMC in which 1 mol / L LiPF 6 was dissolved were mixed at a volume ratio of 1: 2. .
充放電特性は、恒温槽で２５℃とした環境下で、充電をＬｉが放出される方向（電池として電圧が上がる方向）としたときに、放電は１．０Ｖまで０．１Ｃの電流密度にて行った（ＣＣ−ＣＣ操作）後、充電を３．０Ｖまで０．１Ｃの電流密度にて行った（ＣＣ−ＣＣ操作）。本操作の１回目の放電容量を測定した。 The charge / discharge characteristics are as follows. When charging is performed in the direction in which Li is released (in the direction in which the voltage increases as a battery) in an environment of 25 ° C. in a thermostatic chamber, the discharge is performed at a current density of 0.1 C up to 1.0 V. (CC-CC operation), charging was performed at a current density of 0.1 C up to 3.0 V (CC-CC operation). The first discharge capacity of this operation was measured.
出力特性（高率放電容量維持率）は、恒温槽で２５℃とした環境下で放電は１．０Ｖまで０．１Ｃの電流密度にて行った（ＣＣ−ＣＣ操作）後、充電は３．０Ｖまで０．１Ｃの電流密度にて行った（ＣＣ−ＣＣ操作）。このときの放電容量をａとする。次に、放電は１．０Ｖまで１０Ｃの電流密度にて行った（ＣＣ−ＣＣ操作）後、充電は３．０Ｖまで０．１Ｃの電流密度にて行った（ＣＣ−ＣＣ操作）。このときの放電容量をｂとするとき、出力特性は（ｂ／ａ×１００（％））とした。 The output characteristics (high rate discharge capacity maintenance rate) were as follows. Discharging was performed at a current density of 0.1 C up to 1.0 V (CC-CC operation) in an environment set to 25 ° C. in a constant temperature bath, and then charging was performed at 3. It was performed at a current density of 0.1 C up to 0 V (CC-CC operation). Let the discharge capacity at this time be a. Next, discharging was performed at a current density of 10 C up to 1.0 V (CC-CC operation), and charging was performed at a current density of 0.1 C up to 3.0 V (CC-CC operation). When the discharge capacity at this time is b, the output characteristic is (b / a × 100 (%)).
＜チタン酸リチウム粒子粉末の製造＞
実施例１
ＢＥＴ比表面積が６０ｍ２／ｇの酸化チタンと水酸化リチウムをＬｉ／Ｔｉ＝１．２の配合比で反応温度が９０℃で反応時間が１０時間の湿式反応を行い、濾過、乾燥した後、７６０℃で焼成し、粉砕して、チタン酸リチウム粒子粉末を得た。
<Manufacture of lithium titanate particle powder>
Example 1
Titanium oxide having a BET specific surface area of 60 m 2 / g and lithium hydroxide were subjected to a wet reaction with a reaction ratio of 90 ° C. and a reaction time of 10 hours at a compounding ratio of Li / Ti = 1.2, filtered and dried. Baking at 760 ° C. and pulverization gave lithium titanate particle powder.
実施例２
実施例１で得たチタン酸リチウムを更にボールミルにて１．５時間粉砕してチタン酸リチウム粒子粉末を得た。
Example 2
The lithium titanate obtained in Example 1 was further pulverized with a ball mill for 1.5 hours to obtain lithium titanate particle powder.
比較例１
実施例１で得たチタン酸リチウムを更にボールミルにて３時間粉砕してチタン酸リチウム粒子粉末を得た。
Comparative Example 1
The lithium titanate obtained in Example 1 was further pulverized with a ball mill for 3 hours to obtain lithium titanate particle powder.
実施例３
比較例１で得たチタン酸リチウム粒子粉末を６５０℃で再焼成を行ってチタン酸リチウム粒子粉末を得た。
Example 3
The lithium titanate particle powder obtained in Comparative Example 1 was refired at 650 ° C. to obtain lithium titanate particle powder.
参考例１
ＢＥＴ比表面積が３００ｍ２／ｇの酸化チタンと水酸化リチウムをＬｉ／Ｔｉ＝１．２の配合比で反応温度が９０℃で反応時間が１０時間の湿式反応を行い、濾過、乾燥した後、７００℃で焼成した後、ボールミルにて２時間粉砕して、チタン酸リチウム粒子粉末を得た。
Reference example 1
Titanium oxide having a BET specific surface area of 300 m 2 / g and lithium hydroxide were subjected to a wet reaction with a reaction ratio of 90 ° C. and a reaction time of 10 hours at a compounding ratio of Li / Ti = 1.2, filtered and dried. After firing at 700 ° C., the mixture was pulverized for 2 hours with a ball mill to obtain lithium titanate particle powder.
比較例２
ボールミルの処理時間を４時間とした以外は実施例４と同様にしてチタン酸リチウム粒子粉末を得た。
Comparative Example 2
A lithium titanate particle powder was obtained in the same manner as in Example 4 except that the treatment time of the ball mill was 4 hours.
比較例３
ＢＥＴ比表面積が３００ｍ２／ｇの酸化チタンと水酸化リチウムをＬｉ／Ｔｉ＝０．８３の配合比で乾式混合し、７９０℃で焼成した後、ボールミルにて１０時間粉砕して、チタン酸リチウム粒子粉末を得た。
Comparative Example 3
Titanium oxide having a BET specific surface area of 300 m 2 / g and lithium hydroxide were dry-mixed at a blending ratio of Li / Ti = 0.83, baked at 790 ° C., and then pulverized for 10 hours in a ball mill, and lithium titanate Particle powder was obtained.
得られたチタン酸リチウム粒子粉末の諸特性を表１に示す。 Table 1 shows various characteristics of the obtained lithium titanate particle powder.
実施例に示すとおり、本発明に係るチタン酸リチウム粒子粉末は、初期放電容量と出力特性（高率放電容量維持率）が共に高い特性を示すので、該チタン酸リチウム粒子粉末粒子粉末は非水電解質二次電池用の活物質として好適である。 As shown in the Examples, the lithium titanate particles according to the present invention, initial the discharge capacity and the output characteristics (high-rate discharge capacity retention ratio) exhibits a high characteristic co, the lithium titanate particles particles Non It is suitable as an active material for a water electrolyte secondary battery.
なお、前記実施例においては、本発明に係るチタン酸リチウム粒子粉末を正極活物質として用いた例を示しているが、本発明に係るチタン酸リチウム粒子粉末を負極活物質として用いた場合にも、非水電解質二次電池の活物質として、優れた特性を発揮できるものである。
In addition, in the said Example, although the example which used the lithium titanate particle powder which concerns on this invention as a positive electrode active material is shown, also when the lithium titanate particle powder which concerns on this invention is used as a negative electrode active material, As an active material of a nonaqueous electrolyte secondary battery, it can exhibit excellent characteristics.
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