JP2011113655A - Lithium secondary battery - Google Patents

Lithium secondary battery Download PDF

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JP2011113655A
JP2011113655A JP2009266293A JP2009266293A JP2011113655A JP 2011113655 A JP2011113655 A JP 2011113655A JP 2009266293 A JP2009266293 A JP 2009266293A JP 2009266293 A JP2009266293 A JP 2009266293A JP 2011113655 A JP2011113655 A JP 2011113655A
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positive electrode
garnet
active material
secondary battery
type oxide
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JP5381640B2 (en
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Hiroshi Sawada
博 佐和田
Shingo Ota
慎吾 太田
Hidehito Matsuo
秀仁 松尾
Tetsuo Kobayashi
哲郎 小林
Masahiko Asaoka
賢彦 朝岡
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Toyota Central R&D Labs Inc
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

<P>PROBLEM TO BE SOLVED: To further increase cycle characteristics and thermal stability of a lithium secondary battery. <P>SOLUTION: The lithium secondary battery 10 includes a positive electrode sheet 13 having a positive electrode active material 12a, a negative electrode sheet 18 having a negative electrode active material, and a nonaqueous electrolyte 20 interposed between the positive electrode sheet 13 and the negative electrode sheet 18 to conduct lithium. In the lithium secondary battery 10, the positive electrode active material 12a and a lithium ion conducting garnet type oxide 12b are contained in the positive electrode sheet 13. The garnet type oxide may be expressed by a composition formula Li<SB>5+X</SB>La<SB>3</SB>(Zr<SB>X</SB>,A<SB>2-X</SB>)O<SB>12</SB>(wherein A is one or more elements selected from the group of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga and Ge, and X is 1.4≤X<2). The garnet type oxide 12b may be present in at least one or more of a positive electrode, a negative electrode and the electrolyte. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

本発明は、リチウム二次電池に関する。   The present invention relates to a lithium secondary battery.

従来、リチウム二次電池としては、リチウムイオンを伝導する固体電解質としてのガラスセラミックスＬｉ1+XＴｉ2ＳｉXＰ3-XＯ12・ＡｌＰＯ4（以下、オハラ電解質という）を正極又は負極に含有するものが提案されている（例えば、特許文献１参照）。この電池では、高温環境下での保存性や充放電サイクル特性を向上することができるとしている。また、固体電解質二次電池において、固体電解質に非プロトン性溶媒を添加し、固体電解質であるＬｉ1+X+YＡｌXＴｉ2-XＳｉYＰ3-YＯ12を電極に混入することにより、電解液にリチウム塩を用いないようにしたものが提案されている（例えば、特許文献２参照）。また、電極に混入する固体電解質をＬｉ0.35Ｌａ0.65ＴｉＯ3とし、正負極の短絡時の安定性を高めたものが提案されている（例えば、特許文献３参照）。 Conventionally, as a lithium secondary battery, glass ceramics Li 1 + X Ti 2 Si X P 3-X O 12 .AlPO 4 (hereinafter referred to as OHARA electrolyte) as a solid electrolyte that conducts lithium ions are included in the positive electrode or the negative electrode. Have been proposed (see, for example, Patent Document 1). This battery is said to be able to improve storage stability and charge / discharge cycle characteristics in a high temperature environment. In a solid electrolyte secondary battery, an aprotic solvent is added to the solid electrolyte, and Li 1 + X + Y Al X Ti 2-X Si Y P 3-Y O 12 as a solid electrolyte is mixed into the electrode. Therefore, a solution in which a lithium salt is not used in the electrolytic solution has been proposed (see, for example, Patent Document 2). In addition, a solid electrolyte mixed in the electrode is Li 0.35 La 0.65 TiO 3 and the stability when the positive and negative electrodes are short-circuited is improved (see, for example, Patent Document 3).

特開２００８−１１７５４２号公報JP 2008-117542 A 特開２００１−１５５７７７号公報JP 2001-155777 A 特開平１０−１１６６３２号公報Japanese Patent Laid-Open No. 10-116632

しかしながら、上述の特許文献１のリチウム二次電池では、高温環境下での保存性や充放電サイクル特性を向上することができるものの、オハラ電解質はリチウム金属基準において１．５Ｖ以下の範囲で還元性を示すように電位窓が狭いことがあり、更なる改良が望まれていた。また、特許文献２のリチウム二次電池では、固体電解質二次電池のリチウム伝導性を向上することはできるが、電池の高温安定性については検討されていなかった。また、特許文献３のリチウム二次電池では、正負極の短絡時の安定性を高めることはできるものの、サイクル特性の向上や高温安定性はまだ十分でなく、更なる向上を図ることが望まれていた。   However, although the lithium secondary battery of Patent Document 1 described above can improve storage stability and charge / discharge cycle characteristics in a high-temperature environment, the OHARA electrolyte is reducible within a range of 1.5 V or less on a lithium metal basis. As shown, the potential window may be narrow, and further improvements have been desired. In the lithium secondary battery of Patent Document 2, the lithium conductivity of the solid electrolyte secondary battery can be improved, but the high temperature stability of the battery has not been studied. Further, in the lithium secondary battery of Patent Document 3, although the stability at the time of short-circuiting of the positive and negative electrodes can be improved, the improvement of the cycle characteristics and the high temperature stability are not yet sufficient, and further improvement is desired. It was.

本発明は、このような課題に鑑みなされたものであり、サイクル特性及び熱的安定性をより向上することができるリチウム二次電池を提供することを主目的とする。   This invention is made | formed in view of such a subject, and it aims at providing the lithium secondary battery which can improve cycling characteristics and thermal stability more.

上述した目的を達成するために鋭意研究したところ、本発明者らは、Ｚｒ，Ｎｂを含みリチウムイオンを伝導するガーネット型酸化物を正極に含むものとすると、サイクル特性及び熱的安定性をより向上することができることを見いだし、本発明を完成するに至った。   As a result of diligent research to achieve the above-described object, the present inventors have improved the cycle characteristics and thermal stability when the garnet-type oxide containing Zr and Nb and conducting lithium ions is included in the positive electrode. It has been found that it can be done, and the present invention has been completed.

即ち、本発明のリチウム二次電池は、リチウムを吸蔵・放出する正極活物質を有する正極と、リチウムを吸蔵・放出する負極活物質を有する負極と、前記正極と前記負極との間に介在しリチウムを伝導する電解液と、を備え、前記正極、前記負極及び前記電解液のうち少なくとも１以上にリチウムイオンを伝導するガーネット型酸化物が存在するものである。   That is, the lithium secondary battery of the present invention is interposed between a positive electrode having a positive electrode active material that occludes and releases lithium, a negative electrode having a negative electrode active material that occludes and releases lithium, and the positive electrode and the negative electrode. An electrolyte solution that conducts lithium, and at least one of the positive electrode, the negative electrode, and the electrolyte solution has a garnet-type oxide that conducts lithium ions.

本発明のリチウム二次電池は、サイクル特性及び熱的安定性をより向上することができる。このような効果が得られる理由は明らかではないが、以下のように推測される。例えば、リチウムイオンを伝導するガーネット型酸化物は、電位窓が広く、高温でも安定で、リチウムイオン伝導度が高いことがある。このガーネット型酸化物がリチウム二次電池内に存在することから、熱的安定性を高めたり、サイクル特性を高めたりすることができる。例えば、電位窓が広いため、過充電及び過放電などの環境下にさらされても、電池性能へ悪影響を与えにくいと考えられる。また、例えば、このガーネット型酸化物を電極に含ませたものとすると、活物質の表面の一部を覆うことにより電解液−活物質間の副反応などを抑制することができると考えられる。また、このガーネット型酸化物を電解液に入れたものにおいては、より化学的に安定な固体電解質で電解液を置き換えるため、電解液−活物質間の副反応などを抑制することができると考えられる。このように、本発明のリチウム二次電池では、リチウムイオンを伝導するガーネット型酸化物の電池内の存在により、サイクル特性及び熱的安定性をより向上することができるものと推察される。   The lithium secondary battery of the present invention can further improve cycle characteristics and thermal stability. The reason why such an effect is obtained is not clear, but is presumed as follows. For example, a garnet oxide that conducts lithium ions may have a wide potential window, be stable even at high temperatures, and have high lithium ion conductivity. Since this garnet-type oxide is present in the lithium secondary battery, it is possible to improve thermal stability and cycle characteristics. For example, since the potential window is wide, it is considered that the battery performance is hardly adversely affected even when exposed to an environment such as overcharge and overdischarge. Further, for example, when this garnet-type oxide is included in the electrode, it is considered that a side reaction between the electrolytic solution and the active material can be suppressed by covering a part of the surface of the active material. In addition, in the case where this garnet-type oxide is put in an electrolytic solution, the electrolytic solution is replaced with a more chemically stable solid electrolyte, so that side reactions between the electrolytic solution and the active material can be suppressed. It is done. Thus, in the lithium secondary battery of the present invention, it is presumed that the cycle characteristics and the thermal stability can be further improved by the presence of the garnet-type oxide conducting lithium ions in the battery.

リチウム二次電池１０の構造の一例を示す説明図である。2 is an explanatory diagram showing an example of a structure of a lithium secondary battery 10. FIG. リチウム二次電池３０の構造の一例を示す説明図である。3 is an explanatory diagram showing an example of a structure of a lithium secondary battery 30. FIG. 実験例１，３，５，７のＸＲＤパターンを示すグラフである。It is a graph which shows the XRD pattern of Experimental example 1,3,5. 実験例１〜７（４を除く）の格子定数のＸ値依存性を示すグラフである。It is a graph which shows the X value dependence of the lattice constant of Experimental examples 1-7 (except 4). 実験例１〜７のリチウムイオン伝導度のＸ値依存性を示すグラフである。It is a graph which shows the X value dependence of the lithium ion conductivity of Experimental Examples 1-7. ガーネット型酸化物の結晶構造に含まれる部分構造の説明図である。It is explanatory drawing of the partial structure contained in the crystal structure of a garnet-type oxide. ガーネット型酸化物の結晶構造の説明図であり、（ａ）は全体像、（ｂ）は六面体のＬｉＯ6（ＩＩ）を露出させた様子を示す。Is an explanatory view of the crystal structure of garnet-type oxide, showing a state in which to expose the (a) Overview, the (b) LiO the hexahedron 6 (II). 実験例１，３，５〜７のＬｉＯ4（Ｉ）結晶構造のＸ値依存性を示すグラフであり、（ａ）は酸素イオンが形成する三角形の辺ａ，ｂのＸ値依存性を示し、（ｂ）は該三角形の面積のＸ値依存性を示す。It is a graph which shows X value dependence of LiO4 (I) crystal structure of Experimental example 1, 3, 5-7, (a) shows X value dependence of the sides a and b of the triangle which an oxygen ion forms. , (B) shows the X value dependency of the area of the triangle. 実験例１，３，５〜７の各回折強度を（２２０）回折強度で規格化したときの規格化後強度のＸ値依存性を示すグラフである。It is a graph which shows X value dependence of the intensity | strength after normalization when each diffraction intensity of Experimental example 1, 3, 5-7 is normalized by (220) diffraction intensity. 実験例１，３，５〜７の（０２４）の規格化後強度のＸ値依存性を示すグラフである。It is a graph which shows X value dependence of the intensity | strength after normalization of (024) of Experimental example 1,3,5-7. 実験例１〜７のアレニウスプロットのグラフである。It is a graph of the Arrhenius plot of Experimental Examples 1-7. 実験例１〜７の活性化エネルギーのＸ値依存性を示すグラフである。It is a graph which shows the X value dependence of the activation energy of Experimental Examples 1-7. 実験例５の室温大気中での化学的安定性を示すグラフである。10 is a graph showing chemical stability in a room temperature atmosphere of Experimental Example 5. 実験例５の電位窓の測定結果を示すグラフである。10 is a graph showing measurement results of a potential window of Experimental Example 5.

本発明のリチウム二次電池は、リチウムを吸蔵・放出する正極活物質を有する正極と、リチウムを吸蔵・放出する負極活物質を有する負極と、正極と負極との間に介在しリチウムを伝導する電解液と、を備え、正極、負極及び電解液のうち少なくとも１以上にリチウムイオンを伝導するガーネット型酸化物が存在するものである。例えば、リチウムイオンを伝導するガーネット型酸化物は、正極に存在しているものとしてもよいし、負極に存在しているものとしてもよいし、電解液に存在しているものとしてもよい。更に、本発明のリチウム二次電池は、正極と負極との間にセパレータを備え、リチウムイオンを伝導するガーネット型酸化物は、このセパレータに存在しているものとしてもよい。また、本発明のリチウム二次電池において、リチウムイオンを伝導するガーネット型酸化物は、粉末状で存在していてもよいし、正極、負極及びセパレータの少なくとも１以上に積層された積層体として存在してもよい。このように、リチウムイオンを伝導するガーネット型酸化物がリチウム二次電池の中に含まれているものとすればよい。こうすれば、熱的及び化学的に安定なガーネット型酸化物により電解液を置き換えるなどして、サイクル特性及び熱的安定性をより向上することができる。本実施形態では、説明の便宜のため、リチウムイオンを伝導するガーネット型酸化物を正極に備えたものを主として説明する。   The lithium secondary battery of the present invention conducts lithium by interposing between a positive electrode having a positive electrode active material that occludes and releases lithium, a negative electrode having a negative electrode active material that occludes and releases lithium, and the positive electrode and the negative electrode. And at least one of the positive electrode, the negative electrode, and the electrolyte includes a garnet-type oxide that conducts lithium ions. For example, the garnet oxide that conducts lithium ions may be present in the positive electrode, may be present in the negative electrode, or may be present in the electrolyte. Furthermore, the lithium secondary battery of the present invention may include a separator between the positive electrode and the negative electrode, and the garnet oxide that conducts lithium ions may be present in the separator. Moreover, in the lithium secondary battery of the present invention, the garnet-type oxide that conducts lithium ions may exist in the form of a powder, or as a laminate that is laminated on at least one of the positive electrode, the negative electrode, and the separator. May be. Thus, the garnet-type oxide that conducts lithium ions may be included in the lithium secondary battery. In this case, the cycle characteristics and the thermal stability can be further improved by replacing the electrolytic solution with a thermally and chemically stable garnet oxide. In the present embodiment, for convenience of explanation, a case where a garnet-type oxide that conducts lithium ions is provided on a positive electrode will be mainly described.

本発明のリチウム二次電池に含まれるリチウムイオンを伝導するガーネット型酸化物は、少なくともＺｒを含有していることが好ましく、少なくともＺｒ及びＮｂを含有していることがより好ましく、少なくともＺｒ、Ｎｂ及びＬａを含有していることが更に好ましい。こうすれば、リチウムイオンの伝導性をより高めることができる。このリチウムイオンを伝導するガーネット型酸化物は、組成式Ｌｉ5+XＬａ3（ＺｒX，Ａ2-X）Ｏ12（式中、ＡはＳｃ，Ｔｉ，Ｖ，Ｙ，Ｎｂ，Ｈｆ，Ｔａ，Ａｌ，Ｓｉ，Ｇａ及びＧｅからなる群より選ばれた１種類以上の元素、Ｘは１．４≦Ｘ＜２）で表されるものとしてもよい。ここで用いるガーネット型酸化物は、Ｘが１．４≦Ｘ＜２を満たすため、公知のガーネット型酸化物Ｌｉ7Ｌａ3Ｚｒ2Ｏ12（つまりＸ＝２）と比べて、リチウムイオン伝導度が高くなり且つ活性化エネルギーも小さくなる。例えば、ＡがＮｂの場合、伝導度が２．５×１０-4Ｓｃｍ-1以上、活性化エネルギーが０．３４ｅＶ以下になる。したがって、この酸化物を含むリチウム二次電池によれば、リチウムイオンが伝導しやすく、抵抗が低くなり、電池の出力が向上する。また、活性化エネルギーが小さい、つまり温度に対する伝導度の変化の割合が小さいため、電池の出力が安定する。また、Ｘが１．６≦Ｘ≦１．９５を満たせば、伝導度がより高く、活性化エネルギーがより低くなるため、より好ましい。更に、Ｘが１．６５≦Ｘ≦１．９を満たせば、伝導度がほぼ極大、活性化エネルギーがほぼ極小となるため、一層好ましい。なお、Ａとしては、ＮｂやＮｂとイオン半径が同等のＴａが好ましい。 The garnet-type oxide that conducts lithium ions contained in the lithium secondary battery of the present invention preferably contains at least Zr, more preferably contains at least Zr and Nb, and at least Zr, Nb. And La is further preferred. In this way, the conductivity of lithium ions can be further increased. The garnet-type oxide that conducts lithium ions has the composition formula Li 5 + X La 3 (Zr X , A 2−X ) O 12 (where A is Sc, Ti, V, Y, Nb, Hf, Ta). , Al, Si, Ga, and Ge, one or more elements selected from the group consisting of X, X may be represented by 1.4 ≦ X <2). Since the garnet-type oxide used here satisfies X ≦ 1.4 ≦ X <2, the lithium ion conductivity is higher than that of the known garnet-type oxide Li 7 La 3 Zr 2 O 12 (that is, X = 2). Increases and the activation energy also decreases. For example, when A is Nb, the conductivity is 2.5 × 10 −4 Scm −1 or more and the activation energy is 0.34 eV or less. Therefore, according to the lithium secondary battery containing this oxide, lithium ions are easily conducted, the resistance is lowered, and the output of the battery is improved. Further, since the activation energy is small, that is, the rate of change in conductivity with respect to temperature is small, the output of the battery is stabilized. Further, it is more preferable that X satisfies 1.6 ≦ X ≦ 1.95 because conductivity is higher and activation energy is lower. Furthermore, it is more preferable that X satisfies 1.65 ≦ X ≦ 1.9 because the conductivity is almost maximum and the activation energy is almost minimum. As A, Nb or Ta having an ion radius equivalent to that of Nb is preferable.

あるいは、本発明のリチウム二次電池に含まれるリチウムイオンを伝導するガーネット型酸化物は、組成式Ｌｉ7Ｌａ3Ｚｒ2Ｏ12のＺｒサイトがＺｒとはイオン半径の異なる元素で置換され、ＸＲＤにおける（２２０）回折の強度を１に規格化したときの（０２４）回折の規格化後の強度が９．２以上であるものとしてもよい。（０２４）回折の規格化後の強度が９．２を超えると、ＬｉＯ4（Ｉ）の四面体の酸素イオンが形成する三角形が正三角形に近づき、その三角形の面積が大きくなるため、公知のガーネット型酸化物Ｌｉ7Ｌａ3Ｚｒ2Ｏ12（つまりＸ＝２）と比べて、伝導度が高くなり且つ活性化エネルギーも小さくなる。例えば、ＡがＮｂの場合、伝導度が２．５×１０-4Ｓｃｍ-1以上、活性化エネルギーが０．３４ｅＶ以下になる。したがって、この酸化物をリチウム二次電池に用いた場合、リチウムイオンが伝導しやすくなるため、電池の出力が向上する。また、活性化エネルギーが小さい、つまり温度に対する伝導度の変化の割合が小さいため、電池の出力が安定する。また、（０２４）回折の規格化後の強度が１０．０以上であれば、伝導度がより高く、活性化エネルギーがより低くなるため、より好ましい。更に、（０２４）回折の規格化後の強度が１０．２以上であれば、伝導度がほぼ極大、活性化エネルギーがほぼ極小となるため、一層好ましい。なお、Ｚｒとはイオン半径の異なる元素としては、Ｓｃ，Ｔｉ，Ｖ，Ｙ，Ｎｂ，Ｈｆ，Ｔａ，Ａｌ，Ｓｉ，Ｇａ及びＧｅからなる群より選ばれた１種類以上の元素が挙げられ、このうち、ＮｂやＮｂとイオン半径が同等のＴａが好ましい。 Alternatively, in the garnet-type oxide that conducts lithium ions contained in the lithium secondary battery of the present invention, the Zr site of the composition formula Li 7 La 3 Zr 2 O 12 is substituted with an element having an ionic radius different from that of Zr. The intensity after normalization of (024) diffraction when the intensity of (220) diffraction is normalized to 1 may be 9.2 or more. (024) When the intensity after diffraction standardization exceeds 9.2, the triangle formed by the LiO 4 (I) tetrahedral oxygen ions approaches an equilateral triangle, and the area of the triangle increases. Compared with the garnet-type oxide Li 7 La 3 Zr 2 O 12 (that is, X = 2), the conductivity is increased and the activation energy is also decreased. For example, when A is Nb, the conductivity is 2.5 × 10 −4 Scm −1 or more and the activation energy is 0.34 eV or less. Therefore, when this oxide is used for a lithium secondary battery, lithium ions are easily conducted, so that the output of the battery is improved. Further, since the activation energy is small, that is, the rate of change in conductivity with respect to temperature is small, the output of the battery is stabilized. Moreover, if the intensity | strength after normalization of (024) diffraction is 10.0 or more, since conductivity is higher and activation energy becomes lower, it is more preferable. Further, it is more preferable that the strength after normalization of (024) diffraction is 10.2 or more, because the conductivity is almost maximum and the activation energy is almost minimum. The element having an ionic radius different from that of Zr includes one or more elements selected from the group consisting of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, and Ge. Among these, Nb and Ta having the same ion radius as Nb are preferable.

ここで、リチウムイオンを伝導するガーネット型酸化物は、主としてガーネット型の構造を有していればよく、例えば、固体電解質として他の構造が一部含まれていたり、例えばＸ線回折のピーク位置がシフトしているなどガーネットからみて歪んだ構造を含むものとしてもよい。また、組成式で示しているが、リチウムイオンを伝導するガーネット型酸化物には他の元素や構造などが一部含まれていてもよい。   Here, the garnet-type oxide that conducts lithium ions only needs to have a garnet-type structure. For example, the garnet-type oxide may include a part of other structures as a solid electrolyte, for example, a peak position of X-ray diffraction. It is also possible to include a structure that is distorted when viewed from the garnet, such as is shifted. In addition, as shown by the composition formula, the garnet-type oxide that conducts lithium ions may contain some other elements and structures.

このリチウムイオンを伝導するガーネット型酸化物は、正極活物質とガーネット型酸化物との全体に対して５０重量％以下の範囲で正極に含まれていることが好ましく、３０重量％以下の範囲で正極に含まれていることがより好ましく、２０重量％以下の範囲で正極に含まれていることが更に好ましく、１０重量％以下の範囲で正極に含まれていることが最も好ましい。ガーネット型酸化物の含有量が５０重量％以下では、活物質が相対的に少なくなってしまうのを抑制可能であり、電池容量の低下をより抑制することができ、３０重量％以下では電池容量の低下を更に抑制することができる。また、ガーネット型酸化物を電極に含ませる場合は、活物質の平均粒径よりもガーネット型酸化物の平均粒径が小さい方が、活物質の表面をガーネット型酸化物によってより覆いやすく、好ましい。なお、平均粒径は、電子顕微鏡（ＳＥＭ）による観察により求めた粒径の平均値とする。   The garnet-type oxide that conducts lithium ions is preferably contained in the positive electrode in a range of 50% by weight or less with respect to the whole of the positive electrode active material and the garnet-type oxide, and in a range of 30% by weight or less. More preferably, it is contained in the positive electrode in a range of 20% by weight or less, and most preferably in the positive electrode in a range of 10% by weight or less. When the content of the garnet-type oxide is 50% by weight or less, it is possible to suppress the decrease of the active material, and it is possible to further suppress the decrease in battery capacity. Can be further suppressed. Further, when the garnet-type oxide is included in the electrode, it is preferable that the average particle diameter of the garnet-type oxide is smaller than the average particle diameter of the active material because the surface of the active material is more easily covered with the garnet-type oxide. . In addition, let an average particle diameter be the average value of the particle diameter calculated | required by observation with an electron microscope (SEM).

本発明のリチウム二次電池の正極は、例えば正極活物質とガーネット型酸化物と導電材と結着材とを混合し、適当な溶剤を加えてペースト状の正極材としたものを、集電体の表面に塗布乾燥し、必要に応じて電極密度を高めるべく圧縮して形成してもよい。正極活物質としては、遷移金属元素を含む硫化物や、リチウムと遷移金属元素とを含む酸化物などを用いることができる。具体的には、ＴｉＳ2、ＴｉＳ3、ＭｏＳ3、ＦｅＳ2などの遷移金属硫化物、Ｌｉ(1-x)ＭｎＯ2（０＜ｘ＜１など、以下同じ）、Ｌｉ(1-x)Ｍｎ2Ｏ4などのリチウムマンガン複合酸化物、Ｌｉ(1-x)ＣｏＯ2などのリチウムコバルト複合酸化物、Ｌｉ(1-x)ＮｉＯ2などのリチウムニッケル複合酸化物、ＬｉＶ2Ｏ3などのリチウムバナジウム複合酸化物、Ｖ2Ｏ5などの遷移金属酸化物などを用いることができる。これらのうち、リチウムの遷移金属複合酸化物、例えば、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎＯ2、ＬｉＶ2Ｏ3などが好ましい。導電材は、正極の電池性能に悪影響を及ぼさない電子伝導性材料であれば特に限定されず、例えば、天然黒鉛（鱗状黒鉛、鱗片状黒鉛）や人造黒鉛などの黒鉛、アセチレンブラック、カーボンブラック、ケッチェンブラック、カーボンウィスカ、ニードルコークス、炭素繊維、金属（銅、ニッケル、アルミニウム、銀、金など）などの１種又は２種以上を混合したものを用いることができる。これらの中で、導電材としては、電子伝導性及び塗工性の観点より、カーボンブラック及びアセチレンブラックが好ましい。結着材は、活物質粒子及び導電材粒子を繋ぎ止める役割を果たすものであり、例えば、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）、フッ素ゴム等の含フッ素樹脂、或いはポリプロピレン、ポリエチレン等の熱可塑性樹脂、エチレン−プロピレン−ジエンマー（ＥＰＤＭ）、スルホン化ＥＰＤＭ、天然ブチルゴム（ＮＢＲ）等を単独で、あるいは２種以上の混合物として用いることができる。また、水系バインダーであるセルロース系やスチレンブタジエンゴム（ＳＢＲ）の水分散体等を用いることもできる。正極活物質、導電材、結着材を分散させる溶剤としては、例えばＮ−メチルピロリドン、ジメチルホルムアミド、ジメチルアセトアミド、メチルエチルケトン、シクロヘキサノン、酢酸メチル、アクリル酸メチル、ジエチルトリアミン、Ｎ，Ｎ−ジメチルアミノプロピルアミン、エチレンオキシド、テトラヒドロフランなどの有機溶剤を用いることができる。また、水に分散剤、増粘剤等を加え、ＳＢＲなどのラテックスで活物質をスラリー化してもよい。増粘剤としては、例えば、カルボキシメチルセルロース、メチルセルロースなどの多糖類を単独で、あるいは２種以上の混合物として用いることができる。塗布方法としては、例えば、アプリケータロールなどのローラコーティング、スクリーンコーティング、ドクターブレイド方式、スピンコーティング、バーコータなどが挙げられ、これらのいずれかを用いて任意の厚さ・形状とすることができる。集電体としては、アルミニウム、チタン、ステンレス鋼、ニッケル、鉄、焼成炭素、導電性高分子、導電性ガラスなどのほか、接着性、導電性及び耐酸化性向上の目的で、アルミニウムや銅などの表面をカーボン、ニッケル、チタンや銀などで処理したものを用いることができる。これらについては、表面を酸化処理することも可能である。集電体の形状については、箔状、フィルム状、シート状、ネット状、パンチ又はエキスパンドされたもの、ラス体、多孔質体、発泡体、繊維群の形成体などが挙げられる。集電体の厚さは、例えば１〜５００μｍのものが用いられる。 The positive electrode of the lithium secondary battery of the present invention is obtained by mixing a positive electrode active material, a garnet-type oxide, a conductive material and a binder, and adding a suitable solvent to form a paste-like positive electrode material. It may be applied and dried on the surface of the body, and may be compressed to increase the electrode density as necessary. As the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used. Specifically, transition metal sulfides such as TiS 2 , TiS 3 , MoS 3 , FeS 2 , Li (1-x) MnO 2 (0 <x <1, etc., the same shall apply hereinafter), Li (1-x) Mn Lithium manganese composite oxide such as 2 O 4 , lithium cobalt composite oxide such as Li (1-x) CoO 2 , lithium nickel composite oxide such as Li (1-x) NiO 2 , lithium such as LiV 2 O 3 Vanadium composite oxides, transition metal oxides such as V 2 O 5, and the like can be used. Of these, lithium transition metal composite oxides such as LiCoO 2 , LiNiO 2 , LiMnO 2 , and LiV 2 O 3 are preferable. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black, carbon black, What mixed 1 type (s) or 2 or more types, such as ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. The binder serves to bind the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resin such as fluorine rubber, or polypropylene, Thermoplastic resins such as polyethylene, ethylene-propylene-dienemer (EPDM), sulfonated EPDM, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used. Examples of the solvent for dispersing the positive electrode active material, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, and N, N-dimethylaminopropyl. Organic solvents such as amine, ethylene oxide, and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape. Current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, and aluminum, copper, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance. A surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous, foam, and formed fiber group. The thickness of the current collector is, for example, 1 to 500 μm.

本発明のリチウム二次電池の負極は、例えば負極活物質と導電材と結着材とを混合し、適当な溶剤を加えてペースト状の負極材としたものを、集電体の表面に塗布乾燥し、必要に応じて電極密度を高めるべく圧縮して形成してもよい。負極活物質としては、リチウム、リチウム合金、スズ化合物などの無機化合物、リチウムイオンを吸蔵・放出可能な炭素質材料、導電性ポリマーなどが挙げられるが、このうち炭素質材料が安全性の面から見て好ましい。この炭素質材料は、特に限定されるものではないが、コークス類、ガラス状炭素類、グラファイト類、難黒鉛化性炭素類、熱分解炭素類、炭素繊維などが挙げられる。このうち、人造黒鉛、天然黒鉛などのグラファイト類が、金属リチウムに近い作動電位を有し、高い作動電圧での充放電が可能であり電解質塩としてリチウム塩を使用した場合に自己放電を抑え、且つ充電時おける不可逆容量を少なくできるため、好ましい。また、負極に用いられる導電材、結着材、溶剤などは、それぞれ正極で例示したものを用いることができる。負極の集電体には、銅、ニッケル、ステンレス鋼、チタン、アルミニウム、焼成炭素、導電性高分子、導電性ガラス、Ａｌ−Ｃｄ合金などのほか、接着性、導電性及び耐還元性向上の目的で、例えば銅などの表面をカーボン、ニッケル、チタンや銀などで処理したものも用いることができる。これらについては、表面を酸化処理することも可能である。集電体の形状は、正極と同様のものを用いることができる。   The negative electrode of the lithium secondary battery of the present invention is prepared by, for example, mixing a negative electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like negative electrode material on the surface of the current collector. It may be dried and compressed to increase the electrode density as necessary. Examples of negative electrode active materials include inorganic compounds such as lithium, lithium alloys and tin compounds, carbonaceous materials capable of occluding and releasing lithium ions, and conductive polymers. Among these, carbonaceous materials are used from the viewpoint of safety. It is preferable to see. The carbonaceous material is not particularly limited, and examples thereof include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Of these, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and suppresses self-discharge when a lithium salt is used as an electrolyte salt. In addition, the irreversible capacity during charging can be reduced, which is preferable. In addition, as the conductive material, binder, solvent, and the like used for the negative electrode, those exemplified for the positive electrode can be used. The negative electrode current collector includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., as well as improved adhesion, conductivity and reduction resistance. For the purpose, for example, a copper surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. The shape of the current collector can be the same as that of the positive electrode.

本発明のリチウム二次電池の電解液としては、支持塩を含む非水系電解液や水溶液系電解液などを用いることができる。非水電解液の溶媒としては、カーボネート類、エステル類、エーテル類、ニトリル類、フラン類、スルホラン類及びジオキソラン類などが挙げられ、これらを単独又は混合して用いることができる。具体的には、カーボネート類としてエチレンカーボネートやプロピレンカーボネート、ビニレンカーボネート、ブチレンカーボネート、クロロエチレンカーボネートなどの環状カーボネート類や、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネート、エチル−ｎ−ブチルカーボネート、メチル−ｔ−ブチルカーボネート、ジ−ｉ−プロピルカーボネート、ｔ−ブチル−ｉ−プロピルカーボネートなどの鎖状カーボネート類、γ−ブチルラクトン、γ−バレロラクトンなどの環状エステル類、ギ酸メチル、酢酸メチル、酢酸エチル、酪酸メチルなどの鎖状エステル類、ジメトキシエタン、エトキシメトキシエタン、ジエトキシエタンなどのエーテル類、アセトニトリル、ベンゾニトリルなどのニトリル類、テトラヒドロフラン、メチルテトラヒドロフラン、などのフラン類、スルホラン、テトラメチルスルホランなどのスルホラン類、１，３−ジオキソラン、メチルジオキソランなどのジオキソラン類などが挙げられる。このうち、環状カーボネート類と鎖状カーボネート類との組み合わせが好ましい。この組み合わせによると、充放電の繰り返しでの電池特性を表すサイクル特性が優れているばかりでなく、電解液の粘度、得られる電池の電気容量、電池出力などをバランスの取れたものとすることができる。   As the electrolytic solution of the lithium secondary battery of the present invention, a non-aqueous electrolytic solution containing a supporting salt or an aqueous electrolytic solution can be used. Examples of the solvent for the nonaqueous electrolytic solution include carbonates, esters, ethers, nitriles, furans, sulfolanes and dioxolanes, and these can be used alone or in combination. Specifically, as carbonates, cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t -Chain carbonates such as butyl carbonate, di-i-propyl carbonate, t-butyl-i-propyl carbonate, cyclic esters such as γ-butyllactone and γ-valerolactone, methyl formate, methyl acetate, ethyl acetate, Chain esters such as methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; Examples include furans such as lan, methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, the combination of cyclic carbonates and chain carbonates is preferable. According to this combination, not only the cycle characteristics representing the battery characteristics in repeated charge and discharge are excellent, but also the viscosity of the electrolyte, the electric capacity of the obtained battery, the battery output, etc. should be balanced. it can.

本発明のリチウム二次電池に含まれている支持塩は、例えば、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＡｓＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＮ（ＣＦ3ＳＯ2）2、ＬｉＣ（ＣＦ3ＳＯ2）3、ＬｉＳｂＦ6、ＬｉＳｉＦ6、ＬｉＡｌＦ4、ＬｉＳＣＮ、ＬｉＣｌＯ4、ＬｉＣｌ、ＬｉＦ、ＬｉＢｒ、ＬｉＩ、ＬｉＡｌＣｌ4などが挙げられる。このうち、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＡｓＦ6、ＬｉＣｌＯ4などの無機塩、及びＬｉＣＦ3ＳＯ3、ＬｉＮ（ＣＦ3ＳＯ2）2、ＬｉＣ（ＣＦ3ＳＯ2）3などの有機塩からなる群より選ばれる１種又は２種以上の塩を組み合わせて用いることが電気特性の点から見て好ましい。この支持塩は、非水電解液中の濃度が０．１ｍｏｌ／Ｌ以上５ｍｏｌ／Ｌ以下であることが好ましく、０．５ｍｏｌ／Ｌ以上２ｍｏｌ／Ｌ以下であることがより好ましい。支持塩の濃度が０．１ｍｏｌ／Ｌ以上では、十分な電流密度を得ることができ、５ｍｏｌ／Ｌ以下では、電解液をより安定させることができる。また、この非水電解液には、リン系、ハロゲン系などの難燃剤を添加してもよい。 The supporting salt contained in the lithium secondary battery of the present invention is, for example, LiPF 6 , LiBF 4 , LiAsF 6 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiC (CF 3 SO 2 ) 3 , Examples include LiSbF 6 , LiSiF 6 , LiAlF 4 , LiSCN, LiClO 4 , LiCl, LiF, LiBr, LiI, and LiAlCl 4 . Among these, from the group consisting of inorganic salts such as LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , and organic salts such as LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiC (CF 3 SO 2 ) 3. It is preferable from the viewpoint of electrical characteristics to use a combination of one or two or more selected salts. The supporting salt preferably has a concentration in the non-aqueous electrolyte of 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. If the concentration of the supporting salt is 0.1 mol / L or more, a sufficient current density can be obtained, and if it is 5 mol / L or less, the electrolytic solution can be made more stable. Moreover, you may add flame retardants, such as a phosphorus type and a halogen type, to this non-aqueous electrolyte.

本発明のリチウム二次電池は、負極と正極との間にセパレータを備えていてもよい。セパレータとしては、リチウム二次電池の使用範囲に耐えうる組成であれば特に限定されないが、例えば、ポリプロピレン製不織布やポリフェニレンスルフィド製不織布などの高分子不織布、ポリエチレンやポリプロピレンなどのオレフィン系樹脂の薄い微多孔膜が挙げられる。これらは単独で用いてもよいし、複数を混合して用いてもよい。   The lithium secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium secondary battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a thin fine olefin resin such as polyethylene or polypropylene is used. A porous membrane is mentioned. These may be used alone or in combination.

本発明のリチウム二次電池の形状は、特に限定されないが、例えばコイン型、ボタン型、シート型、積層型、円筒型、偏平型、角型などが挙げられる。また、こうしたリチウム二次電池を複数直列に接続して電気自動車等に用いる大型のものなどに適用してもよい。図１は、本発明のリチウム二次電池１０の一例を示す模式図である。このリチウム二次電池１０は、集電体１１に正極合材１２を形成した正極シート１３と、集電体１４の表面に負極合材１７を形成した負極シート１８と、正極シート１３と負極シート１８との間に設けられたセパレータ１９と、正極シート１３と負極シート１８との間を満たす非水電解液２０と、を備えたものである。このリチウム二次電池１０では、正極シート１３と負極シート１８との間にセパレータ１９を挟み、これらを捲回して円筒ケース２２に挿入し、正極シート１３に接続された正極端子２４と負極シートに接続された負極端子２６とを配設して形成されている。また、このリチウム二次電池１０では、正極活物質１２ａとリチウムイオンを伝導するガーネット型酸化物１２ｂとが正極合材１２に含まれている。   The shape of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Further, a plurality of such lithium secondary batteries connected in series may be applied to a large battery used for an electric vehicle or the like. FIG. 1 is a schematic diagram showing an example of a lithium secondary battery 10 of the present invention. The lithium secondary battery 10 includes a positive electrode sheet 13 in which a positive electrode mixture 12 is formed on a current collector 11, a negative electrode sheet 18 in which a negative electrode mixture 17 is formed on the surface of the current collector 14, and the positive electrode sheet 13 and the negative electrode sheet. 18 and a non-aqueous electrolyte 20 that fills between the positive electrode sheet 13 and the negative electrode sheet 18. In this lithium secondary battery 10, the separator 19 is sandwiched between the positive electrode sheet 13 and the negative electrode sheet 18, and these are wound and inserted into the cylindrical case 22, and the positive electrode terminal 24 connected to the positive electrode sheet 13 and the negative electrode sheet are connected. A connected negative electrode terminal 26 is provided. In the lithium secondary battery 10, the positive electrode mixture 12 includes a positive electrode active material 12 a and a garnet-type oxide 12 b that conducts lithium ions.

以上詳述した本実施形態のリチウム二次電池では、サイクル特性及び熱的安定性をより向上することができる。このような効果が得られる理由は明らかではないが、例えば、リチウムイオンを伝導するガーネット型酸化物は、電位窓が広く、高温でも安定で、リチウムイオン伝導度が高いことがあり、このガーネット型酸化物がリチウム二次電池内に存在することから、熱的安定性を高めたり、サイクル特性を高めたりすることができると考えられる。例えば、電位窓が広いため、過充電及び過放電などの環境下にさらされても、電池性能へ悪影響を与えにくいと考えられる。また、例えば、このガーネット型酸化物を電極に含ませたものとすると、活物質の表面の一部を覆うことにより電解液−活物質間の副反応などを抑制することができると考えられる。また、ガーネット型酸化物を電解液に入れたものにおいては、より化学的に安定な固体電解質で電解液を置き換えるため、電解液−活物質間の副反応などを抑制することができると考えられる。また、このガーネット型酸化物は、例えば組成式Ｌｉ5+XＬａ3（ＺｒX，Ｎｂ2-X）Ｏ12（１．４≦Ｘ＜２）とすることができ、こうすれば、サイクル特性及び熱的安定性をより向上することができる。 In the lithium secondary battery of this embodiment described in detail above, the cycle characteristics and the thermal stability can be further improved. The reason why such an effect is obtained is not clear. For example, a garnet oxide that conducts lithium ions has a wide potential window, is stable at high temperatures, and may have high lithium ion conductivity. Since the oxide is present in the lithium secondary battery, it is considered that thermal stability can be improved and cycle characteristics can be improved. For example, since the potential window is wide, it is considered that the battery performance is hardly adversely affected even when exposed to an environment such as overcharge and overdischarge. Further, for example, when this garnet-type oxide is included in the electrode, it is considered that a side reaction between the electrolytic solution and the active material can be suppressed by covering a part of the surface of the active material. In addition, in the case where a garnet-type oxide is put in an electrolytic solution, the electrolytic solution is replaced with a more chemically stable solid electrolyte, so that it is considered that side reactions between the electrolytic solution and the active material can be suppressed. . Further, the garnet-type oxide, for example the composition formula Li 5 + X La 3 (Zr X, Nb 2-X) O 12 may be a (1.4 ≦ X <2), In this way, the cycle characteristics In addition, the thermal stability can be further improved.

なお、本発明は上述した実施形態に何ら限定されることはなく、本発明の技術的範囲に属する限り種々の態様で実施し得ることはいうまでもない。   It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

例えば、上述した実施形態では、リチウムイオンを伝導するガーネット型酸化物が粉末状で正極活物質と共に正極に存在するものとしたが、上述のようにガーネット型酸化物が正極上に層状に存在するものとしてもよい。本発明のリチウム二次電池において、正極を作製する方法としては、例えば、気相法や固相法により集電体上に正極活物質を形成するものとしてもよい。気相法としては、ＰＬＤ（パルスレーザー堆積）やスパッタリング、蒸着、ＣＶＤ（ＭＯ−ＣＶＤなどを含む）などが挙げられる。固相法としては、焼結法やゾルゲル法、ドクターブレード法、スクリーン印刷法、スラリーキャスト法、粉体の圧着などが挙げられる。このように形成した正極活物質上にこのガーネット型酸化物を層上に形成してもよい。こうしても、サイクル特性及び熱的安定性をより向上することができる。なお、負極上に層状のガーネット型酸化物を形成する場合も同様である、   For example, in the above-described embodiment, the garnet-type oxide that conducts lithium ions is in powder form and is present in the positive electrode together with the positive electrode active material. However, as described above, the garnet-type oxide is present in layers on the positive electrode. It may be a thing. In the lithium secondary battery of the present invention, as a method for producing the positive electrode, for example, a positive electrode active material may be formed on the current collector by a vapor phase method or a solid phase method. Examples of the vapor phase method include PLD (pulse laser deposition), sputtering, vapor deposition, and CVD (including MO-CVD). Examples of the solid phase method include a sintering method, a sol-gel method, a doctor blade method, a screen printing method, a slurry cast method, and a powder pressure bonding method. The garnet-type oxide may be formed on the layer on the positive electrode active material thus formed. Even in this case, cycle characteristics and thermal stability can be further improved. The same applies when a layered garnet-type oxide is formed on the negative electrode.

上述した実施形態では、リチウムイオンを伝導するガーネット型酸化物が正極に存在するものとしたが、図２に示すように、このガーネット型酸化物が負極に存在するものとしてもよい。図２は、別の本発明のリチウム二次電池３０の一例を示す模式図である。このリチウム二次電池３０は、集電体３１に正極合材３２を形成した正極シート３３と、集電体３４の表面に負極合材３７を形成した負極シート３８と、正極シート３３と負極シート３８との間に設けられたセパレータ１９と、正極シート３３と負極シート３８との間を満たす非水電解液２０と、を備えたものである。このリチウム二次電池３０では、負極活物質３７ａとリチウムイオンを伝導するガーネット型酸化物３７ｂとが負極合材３７に含まれている。こうしても、サイクル特性及び熱的安定性をより向上することができる。このリチウムイオンを伝導するガーネット型酸化物は、負極活物質とガーネット型酸化物との全体に対して５０重量％以下の範囲で負極に含まれていることが好ましく、３０重量％以下の範囲で負極に含まれていることがより好ましく、２０重量％以下の範囲で負極に含まれていることが更に好ましく、１０重量％以下の範囲で負極に含まれていることが最も好ましい。ガーネット型酸化物の含有量が５０重量％以下では、活物質が相対的に少なくなってしまうのを抑制可能であり、電池容量の低下をより抑制することができ、３０重量％以下では電池容量の低下を更に抑制することができる。なお、正極、負極、電解液及びセパレータのうち少なくとも１以上にリチウムイオンを伝導するガーネット型酸化物が存在するものとすればよい。   In the embodiment described above, the garnet-type oxide that conducts lithium ions is present in the positive electrode. However, as shown in FIG. 2, the garnet-type oxide may be present in the negative electrode. FIG. 2 is a schematic view showing an example of another lithium secondary battery 30 of the present invention. The lithium secondary battery 30 includes a positive electrode sheet 33 in which a positive electrode mixture 32 is formed on a current collector 31, a negative electrode sheet 38 in which a negative electrode mixture 37 is formed on the surface of a current collector 34, a positive electrode sheet 33, and a negative electrode sheet. 38, and the non-aqueous electrolyte 20 that fills the space between the positive electrode sheet 33 and the negative electrode sheet 38. In the lithium secondary battery 30, a negative electrode active material 37 a and a garnet-type oxide 37 b that conducts lithium ions are included in the negative electrode mixture 37. Even in this case, cycle characteristics and thermal stability can be further improved. The garnet-type oxide that conducts lithium ions is preferably contained in the negative electrode in a range of 50% by weight or less with respect to the whole of the negative electrode active material and the garnet-type oxide, and in a range of 30% by weight or less. More preferably, it is contained in the negative electrode, more preferably in the range of 20% by weight or less, and most preferably in the negative electrode in the range of 10% by weight or less. When the content of the garnet-type oxide is 50% by weight or less, it is possible to suppress the decrease of the active material, and it is possible to further suppress the decrease in battery capacity. Can be further suppressed. Note that at least one of the positive electrode, the negative electrode, the electrolytic solution, and the separator may have a garnet oxide that conducts lithium ions.

以下には、本発明のリチウム二次電池を具体的に作製した例を実験例として説明する。   Below, the example which produced the lithium secondary battery of this invention concretely is demonstrated as an experiment example.

［ガーネット型酸化物の作製］
ガーネット型酸化物Ｌｉ5+XＬａ3（ＺｒX，Ｎｂ2-X）Ｏ12（Ｘ＝０〜２）は、Ｌｉ2ＣＯ3、Ｌａ（ＯＨ）3、ＺｒＯ2、およびＮｂ2Ｏ5を出発原料に用いて合成を行った。ここで、実験例１〜７のＸの値は、それぞれＸ＝０，１．０，１．５，１．６２５，１．７５，１．８２５，２．０とした（表１参照）。はじめに、出発原料を化学量論比になるように秤量し、エタノール中にて遊星ボールミル（３００ｒｐｍ／ジルコニアボール）で１時間、混合・粉砕を行った。出発原料の混合粉末をボールとエタノールから分離したのち、Ａｌ2Ｏ3製のるつぼ中にて、９５０℃、１０時間大気雰囲気で仮焼を行った。その後、本焼結でのＬｉの欠損を補う目的で、仮焼した粉末に、Ｌｉ5+XＬａ3（ＺｒX，Ｎｂ2-X）Ｏ12（Ｘ＝０〜２）の組成中のＬｉ量に対して Ｌｉ換算で１０ａｔ．％になるようにＬｉ2ＣＯ3を過剰添加した。この混合粉末を、混合のためエタノール中にて遊星ボールミル（３００ｒｐｍ／ジルコニアボール）で１時間処理した。得られた粉末を再び９５０℃、１０時間大気雰囲気の条件下で再度仮焼した。その後、成型したのち、１２００℃、３６時間大気中の条件下で本焼結を行い、ガーネット型酸化物（実験例１〜７）を作製した。 [Production of garnet-type oxide]
Garnet-type oxides Li 5 + X La 3 (Zr X , Nb 2−X ) O 12 (X = 0 to 2) are composed of Li 2 CO 3 , La (OH) 3 , ZrO 2 , and Nb 2 O 5 . The starting material was used for synthesis. Here, the values of X in Experimental Examples 1 to 7 were set to X = 0, 1.0, 1.5, 1.625, 1.75, 1.825, and 2.0, respectively (see Table 1). First, starting materials were weighed so as to have a stoichiometric ratio, and mixed and pulverized in ethanol with a planetary ball mill (300 rpm / zirconia balls) for 1 hour. After the mixed powder of the starting material was separated from the balls and ethanol, calcination was performed in an air atmosphere at 950 ° C. for 10 hours in an Al 2 O 3 crucible. Thereafter, in order to make up for the loss of Li in the main sintering, the calcined powder was mixed with Li 5 + X La 3 (Zr X , Nb 2−X ) O 12 (X = 0 to 2) in the composition. 10 at. Li 2 CO 3 was excessively added so as to be a%. This mixed powder was treated in a planetary ball mill (300 rpm / zirconia ball) for 1 hour in ethanol for mixing. The obtained powder was again calcined again at 950 ° C. for 10 hours under atmospheric conditions. Then, after shaping | molding, main sintering was performed on the conditions in 1200 degreeC and the air | atmosphere for 36 hours, and the garnet-type oxide (Experimental Examples 1-7) was produced.

［ガーネット酸化物の物性の測定及び結果］
１．相対密度
電子天秤にて測定した乾燥重量をノギスを用いて測定した実寸から求めた体積で除算することにより、各試料の測定密度を算出した。また、理論密度を算出し、測定密度を理論密度で除算し１００を乗算した値を相対密度（％）とした。実験例１〜７の相対密度は、８８〜９２％であった。 [Measurement and results of physical properties of garnet oxide]
1. Relative density The measured density of each sample was calculated by dividing the dry weight measured with an electronic balance by the volume determined from the actual size measured with calipers. The theoretical density was calculated, and the value obtained by dividing the measured density by the theoretical density and multiplying by 100 was taken as the relative density (%). The relative densities of Experimental Examples 1 to 7 were 88 to 92%.

２．相及び格子定数
各試料の相及び格子定数は、ＸＲＤの測定結果から求めた。ＸＲＤの測定は、ＸＲＤ測定器（ブルカー（Ｂｕｒｕｋｅｒ）製、Ｄ８ＡＤＶＡＮＣＥ）を用いて、試料粉末をＣｕＫα、２θ：１０〜１２０°，０．０１°ｓｔｅｐ／１ｓｅｃ．の条件で測定した。結晶構造解析は、結晶構造解析用プログラム：Ｒｉｅｔａｎ−２０００（Ｍａｔｅｒ． Ｓｃｉ． Ｆｏｒｕｍ， ｐ３２１−３２４（２０００），１９８）を用いて解析を行った。代表例として実験例１，３，５，７つまりＬｉ5+XＬａ3（ＺｒX，Ｎｂ2-X）Ｏ12（Ｘ＝０，１．５，１．７５，２）のＸＲＤパターンを図３に示す。図３から、各試料は不純物を含まず単相であることがわかる。また、実験例１〜３，５〜７につき、ＸＲＤパターンより求めた格子定数のＸ値依存性を図４に示す。図４から、Ｚｒの割合が増えるほど格子定数が増大することがわかる。これは、Ｚｒ4+のイオン半径（ｒZr4+＝０．７９Å）がＮｂ5+のイオン半径（ｒNb5+＝０．６９Å）よりも大きいためである。格子定数が連続的に変化していることから、ＮｂはＺｒサイトに置換されていると考えられる（全率固溶が可能と考えられる）。 2. Phase and lattice constant The phase and lattice constant of each sample were determined from the XRD measurement results. The XRD measurement was performed using an XRD measuring instrument (D8ADVANCE, manufactured by Bruker, Inc.) using CuKα, 2θ: 10-120 °, 0.01 ° step / 1 sec. It measured on condition of this. Crystal structure analysis was performed using a crystal structure analysis program: Rietan-2000 (Matter. Sci. Forum, p321-324 (2000), 198). As representative examples, XRD patterns of Experimental Examples 1, 3, 5 and 7, that is, Li 5 + X La 3 (Zr X , Nb 2−X ) O 12 (X = 0, 1.5, 1.75, 2) are illustrated. 3 shows. FIG. 3 shows that each sample does not contain impurities and is a single phase. Moreover, the X value dependence of the lattice constant calculated | required from the XRD pattern about Experimental example 1-3, 5-7 is shown in FIG. FIG. 4 shows that the lattice constant increases as the ratio of Zr increases. This ionic radius of Zr 4+ (r Zr4 + = 0.79Å ) is larger than the ionic radius of the Nb 5+ (r Nb5 + = 0.69Å ). Since the lattice constant is continuously changed, it is considered that Nb is substituted for the Zr site (it is considered that full solid solution is possible).

３．伝導度
伝導度は、恒温槽中にてＡＣインピーダンスアナライザーを用い（周波数：０．１Ｈｚ〜１ＭＨｚ、振幅電圧：１００ｍＶ）、ナイキストプロットの円弧より抵抗値を求め、この抵抗値から算出した。ＡＣインピーダンスアナライザーで測定する際のブロッキング電極にはＡｕ電極を用いた。Ａｕ電極は市販のＡｕペーストを８５０℃、３０分の条件で焼き付けることで形成した。実験例１〜７つまりＬｉ5+XＬａ3（ＺｒX，Ｎｂ2-X）Ｏ12（Ｘ＝０〜２）の２５℃での伝導度のＸ値依存性を図５に示す。図５から、伝導度は、Ｘが１．４≦Ｘ＜２のとき、公知のＬｉ7Ｌａ3Ｚｒ2Ｏ12（つまりＸ＝２、実験例７）に比べて高くなり、Ｘが１．６≦Ｘ≦１．９５のとき、実験例７に比べて一段と高くなり、Ｘが１．６５≦Ｘ≦１．９の範囲のとき、ほぼ極大値（６×１０-4Ｓｃｍ-1以上）を取ることがわかる。上記１．で述べたとおり、各試料の相対密度は８８〜９２％であったことから、伝導度がＸ値に応じて変化するのは、密度による影響ではないと考えられる。 3. Conductivity Conductivity was calculated from a resistance value obtained from an arc of a Nyquist plot using an AC impedance analyzer in a thermostatic chamber (frequency: 0.1 Hz to 1 MHz, amplitude voltage: 100 mV). An Au electrode was used as a blocking electrode when measuring with an AC impedance analyzer. The Au electrode was formed by baking a commercially available Au paste at 850 ° C. for 30 minutes. FIG. 5 shows the X value dependence of the conductivity at 25 ° C. of Experimental Examples 1 to 7, that is, Li 5 + X La 3 (Zr X , Nb 2−X ) O 12 (X = 0 to 2). From FIG. 5, the conductivity becomes higher when X is 1.4 ≦ X <2, compared with the known Li 7 La 3 Zr 2 O 12 (that is, X = 2, Experimental Example 7). When 6 ≦ X ≦ 1.95, the value is higher than that of Experimental Example 7, and when X is in the range of 1.65 ≦ X ≦ 1.9, it is almost a maximum value (6 × 10 −4 Scm −1 or more). I can see that Above 1. As described above, since the relative density of each sample was 88 to 92%, it is considered that the change in conductivity according to the X value is not an influence of the density.

ここで、ニオブを適量添加することで、伝導度が向上した理由について考察する。ガーネット型酸化物の結晶構造には、図６に示すように、リチウムイオンが酸素イオンと４配位してなる四面体のＬｉＯ4（Ｉ）と、リチウムイオンが酸素イオンと６配位してなる八面体のＬｉＯ6（II）と、ランタンイオンが酸素イオンと８配位してなる十二面体のＬａＯ8（Ｉ）と、ジルコニウムイオンが酸素イオンと６配位してなる八面体のＺｒＯ6とが含まれている。この結晶構造の全体像を図７（ａ）に示す。この図７（ａ）の結晶構造では、六面体のＬｉＯ6（II）は八面体のＺｒＯ6と十二面体のＬａＯ8とによって囲まれているため見えない状態となっている。図７（ｂ）は、図７（ａ）の結晶構造からＬｉＯ8（Ｉ）を削除して六面体のＬｉＯ6（II）を露出させた様子を示す。このように、６配位しているリチウムイオンは、６個の酸素イオンと、３個のランタンイオンと、２個のジルコニウムイオンに囲まれた位置にあり、恐らく、伝導性にはほとんど寄与していないと考えられる。一方、４配位しているリチウムイオンは、酸素イオンを頂点とする四面体を形成している。リートベルド（Ｒｉｅｔｖｅｌｄ）構造解析より求めたＬｉＯ4（Ｉ）四面体構造の変化を図８に示す。ＬｉＯ4（Ｉ）四面体を形成する酸素イオン間距離は二つの長さがある。ここでは長尺の二辺をａ、短尺の一辺をｂとする。図８（ａ）に示すように、長尺の辺ａは、Ｎｂの置換量によらずほとんど一定の値を示すのに対し、短尺の辺ｂは、Ｎｂを適量置換することで長くなっている。つまり、酸素イオンが形成する三角形はＮｂを適量置換することで、正三角形に近付きつつ面積は増大している（図８（ｂ）参照）。このことから、適量のＮｂをＺｒと置換すると、伝導するリチウムイオン周りの構造（酸素イオンが形成している四面体）が最適となり、リチウムイオンの移動を容易にする効果があると考えられる。なお、Ｚｒと置換する元素は、Ｎｂ以外の元素、たとえばＳｃ，Ｔｉ，Ｖ，Ｙ，Ｈｆ，Ｔａなどであっても、同様の構造変化が見込まれることから、同様の効果が得られる。 Here, the reason why the conductivity is improved by adding an appropriate amount of niobium will be considered. As shown in FIG. 6, the crystal structure of the garnet-type oxide includes tetrahedral LiO 4 (I) in which lithium ions are 4-coordinated with oxygen ions, and lithium ions are 6-coordinated with oxygen ions. Octahedral LiO 6 (II), dodecahedron LaO 8 (I) in which lanthanum ions are 8-coordinated with oxygen ions, and octahedral ZrO in which zirconium ions are 6-coordinated with oxygen ions 6 and included. An overall image of this crystal structure is shown in FIG. In the crystal structure of FIG. 7A, hexahedral LiO 6 (II) is surrounded by octahedral ZrO 6 and dodecahedron LaO 8 , so that it cannot be seen. FIG. 7B shows a state in which LiO 8 (I) is deleted from the crystal structure of FIG. 7A to expose hexahedral LiO 6 (II). Thus, the lithium ions that are six-coordinated are in a position surrounded by six oxygen ions, three lanthanum ions, and two zirconium ions, and probably contribute almost to conductivity. It is thought that it is not. On the other hand, the tetracoordinated lithium ions form a tetrahedron with the oxygen ions at the vertices. FIG. 8 shows changes in the LiO 4 (I) tetrahedral structure obtained from the Rietveld structural analysis. The distance between oxygen ions forming the LiO 4 (I) tetrahedron has two lengths. Here, a long side is a, and a short side is b. As shown in FIG. 8A, the long side a shows an almost constant value regardless of the amount of Nb replacement, whereas the short side b becomes longer by replacing Nb with an appropriate amount. Yes. That is, the triangle formed by the oxygen ions is replaced with an appropriate amount of Nb, and the area increases while approaching the regular triangle (see FIG. 8B). From this, it is considered that when an appropriate amount of Nb is substituted with Zr, the structure around the conducting lithium ions (tetrahedron formed by oxygen ions) is optimized, and the effect of facilitating the movement of lithium ions is obtained. Even if the element substituted for Zr is an element other than Nb, such as Sc, Ti, V, Y, Hf, Ta, etc., the same effect can be obtained because the same structural change is expected.

ここで、ＸＲＤの回折ピークの強度は、ＬｉＯ4（Ｉ）四面体構造を反映して変化する。すなわち、ＺｒサイトをＮｂで置換することによりＬｉＯ4（Ｉ）四面体をなす三角形が上述したように変化するため、当然、ＸＲＤの各回折ピークの強度比も変化するのである。実験例１〜３，５，７の各試料の（２２０）回折の強度を１に規格化したときの各回折の規格化後強度のＸ値依存性を図９に示す。代表的なピークとして（０２４）回折の規格化後強度に注目する（図１０参照）。（０２４）回折に関して言えば、公知のＬｉ7Ｌａ3Ｚｒ2Ｏ12（つまりＸ＝２、実験例７）に比べて伝導度が高くなる１．４≦Ｘ＜２に対応する規格化後強度は９．２以上であり、一段と伝導度が高くなる１．６≦Ｘ≦１．９５に対応する規格化後強度は１０．０以上であり、伝導度がほぼ極大値を取る１．６５≦Ｘ≦１．９に対応する規格化後強度は１０．２以上であることがわかる。 Here, the intensity of the diffraction peak of XRD changes reflecting the LiO 4 (I) tetrahedral structure. That is, by replacing the Zr site with Nb, the triangle forming the LiO 4 (I) tetrahedron changes as described above, and naturally the intensity ratio of each diffraction peak of XRD also changes. FIG. 9 shows the X-value dependency of the normalized intensity of each diffraction when the intensity of (220) diffraction of each sample of Experimental Examples 1 to 3, 5, and 7 is normalized to 1. As a typical peak, pay attention to the intensity after normalization of (024) diffraction (see FIG. 10). In terms of diffraction, the normalized strength corresponding to 1.4 ≦ X <2 where the conductivity is higher than that of the known Li 7 La 3 Zr 2 O 12 (that is, X = 2, Experimental Example 7). Is 9.2 or more, the normalized strength corresponding to 1.6 ≦ X ≦ 1.95 where the conductivity is further increased is 10.0 or more, and the conductivity is almost maximum 1.65 ≦ It can be seen that the normalized strength corresponding to X ≦ 1.9 is 10.2 or more.

４．活性化エネルギー（Ｅａ）
活性化エネルギー（Ｅａ）はアレニウス（Ａｒｒｈｅｎｉｕｓ）の式：σ＝Ａｅｘｐ（−Ｅａ／ｋＴ）（σ：伝導度、Ａ：頻度因子、ｋ：ボルツマン定数、Ｔ：絶対温度）を用い、アレニウスプロットの傾きより求めた。代表例として実験例１〜７のＬｉ5+XＬａ3（ＺｒX，Ｎｂ2-X）Ｏ12（Ｘ＝０〜２）の伝導度の温度依存性（アレニウスプロット）を図１１に示す。図１１には、併せてＬｉイオン伝導性酸化物の中でも特に高い伝導度を示すガラスセラミックスＬｉ1+XＴｉ2ＳｉXＰ3-XＯ12・ＡｌＰＯ4（オハラ電解質、Ｘ＝０．４）とＬｉ1.5Ａｌ0.5Ｇｅ1.5（ＰＯ4）3（ＬＡＧＰ）の伝導度の温度依存性（いずれも文献値）を示す。実験例１〜７につき、アレニウスプロットより求めた活性化エネルギーＥａ（２５℃）のＸ値依存性を図１２に示す。図１２から、Ｘが１．４≦Ｘ＜２のとき、Ｌｉ7Ｌａ3Ｚｒ2Ｏ12（つまりＸ＝２、実験例７）より低い活性化エネルギーＥａ（つまり０．３４ｅＶ未満）を示すことから、広い温度域で伝導度が安定した値をとるといえる。また、Ｘが１．５≦Ｘ≦１．９のときには活性化エネルギーが０．３２ｅＶ以下となり、特にＸが１．７５のときに極小値０．３ｅＶとなった。０．３ｅＶという値は既存のＬｉイオン伝導性酸化物中で最も低い値と同等の値である（オハラ電解質：０．３ｅＶ、ＬＡＧＰ：０．３１ｅＶ）。 4). Activation energy (Ea)
The activation energy (Ea) is calculated using the Arrhenius equation: σ = Aexp (−Ea / kT) (σ: conductivity, A: frequency factor, k: Boltzmann constant, T: absolute temperature) Obtained from the slope. As a typical example, the temperature dependence (Arrhenius plot) of the conductivity of Li 5 + X La 3 (Zr X , Nb 2−X ) O 12 (X = 0 to 2) in Experimental Examples 1 to 7 is shown in FIG. FIG. 11 also shows glass ceramics Li 1 + X Ti 2 Si X P 3 -X O 12 .AlPO 4 (Ohara electrolyte, X = 0.4) that exhibits particularly high conductivity among Li ion conductive oxides. And Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) conductivity dependence on temperature (both are literature values). FIG. 12 shows the X value dependency of the activation energy Ea (25 ° C.) obtained from the Arrhenius plot for Experimental Examples 1-7. From FIG. 12, when X is 1.4 ≦ X <2, the activation energy Ea (that is, less than 0.34 eV) is lower than Li 7 La 3 Zr 2 O 12 (that is, X = 2, Experimental Example 7). Therefore, it can be said that the conductivity has a stable value in a wide temperature range. In addition, when X is 1.5 ≦ X ≦ 1.9, the activation energy is 0.32 eV or less, and particularly when X is 1.75, the minimum value is 0.3 eV. The value of 0.3 eV is equivalent to the lowest value among the existing Li ion conductive oxides (Ohara electrolyte: 0.3 eV, LAGP: 0.31 eV).

５．化学的安定性
ガーネット型酸化物Ｌｉ6.75Ｌａ3Ｚｒ1.75Ｎｂ0.25Ｏ12（つまりＸ＝１．７５、実験例５）の室温大気中での化学的安定性を調べた。具体的には、大気中に放置したＬｉ6.75Ｌａ3Ｚｒ1.75Ｎｂ0.25Ｏ12の伝導度の経時変化（０〜７日）の有無を確認することで行った。その結果を図１３に示す。バルクの抵抗成分が大気中に放置していた時間によらず一定であることから、ガーネット型酸化物は室温大気中でも安定と言える。 5. Chemical Stability The chemical stability of the garnet-type oxide Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 (that is, X = 1.75, Experimental Example 5) in the room temperature atmosphere was examined. Specifically, it was performed by confirming the presence or absence of a change with time in the conductivity of Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 left in the atmosphere (0 to 7 days). The result is shown in FIG. Since the bulk resistance component is constant regardless of the time it has been left in the air, it can be said that the garnet-type oxide is stable even in the air at room temperature.

６．電位窓
ガーネット型酸化物Ｌｉ6.75Ｌａ3Ｚｒ1.75Ｎｂ0.25Ｏ12（つまりＸ＝１．７５、実験例５）の電位窓を調べた。電位窓は、Ｌｉ6.75Ｌａ3Ｚｒ1.75Ｎｂ0.25Ｏ12のバルクペレットの片面に金を、もう片面にＬｉメタルを貼り付け、０〜５．５Ｖ（対Ｌｉ+）および−０．５Ｖ〜９．５Ｖ（対Ｌｉ+）の範囲で電位をスイープ（１ｍＶ／ｓｅｃ．）させることで調べた。その測定結果を図１４に示す。電位を０〜５．５Ｖの範囲で走査しても、電流は全く流れなかった。このことからＬｉ6.75Ｌａ3Ｚｒ1.75Ｎｂ0.25Ｏ12は０〜５．５Ｖの範囲で安定と言える。走査する電位を−０．５ 〜９Ｖに広げると、０Ｖを境にして、酸化・還元電流が流れた。これはリチウムの酸化・還元に起因すると思われる。また、約７Ｖ以上でわずかに酸化電流が流れ始めた。しかし、流れる酸化電流量が非常に微弱であること、目視で色に変化が無いことなどから、流れる酸化電流は電解質の分解ではなく、セラミックス中に含まれている微量の不純物や粒界の分解が原因だと考えている。 6). Potential window The potential window of the garnet-type oxide Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 (that is, X = 1.75, Experimental Example 5) was examined. The potential window was formed by bonding gold on one side of a bulk pellet of Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 and Li metal on the other side, and 0 to 5.5 V (vs. Li + ) and −0.5 V to 9. The potential was swept (1 mV / sec.) In the range of 5 V (vs. Li + ). The measurement results are shown in FIG. Even when the potential was scanned in the range of 0 to 5.5 V, no current flowed. From this, it can be said that Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 is stable in the range of 0 to 5.5V. When the scanning potential was expanded to -0.5 to 9V, an oxidation / reduction current flowed around 0V. This is probably due to the oxidation and reduction of lithium. Further, a slight oxidation current began to flow at about 7 V or more. However, because the amount of flowing oxidation current is very weak and there is no visual change in color, the flowing oxidation current is not the decomposition of the electrolyte, but the decomposition of trace amounts of impurities and grain boundaries contained in the ceramics. I think that is the cause.

［リチウム二次電池の作製・評価方法］
正極活物質として、層状Ｎｉ系活物質である、平均粒径が１０μｍ程度であるＬｉＮｉ0.80Ｃｏ0.15Ａｌ0.05Ｏ2を用いた。この正極活物質と、所定割合の上記ガーネット型酸化物Ｌｉ6.75Ｌａ3Ｚｒ1.75Ｎｂ0.25Ｏ12（つまりＸ＝１．７５、実験例５）とを混合し、正極／固体電解質混合物を作製した。このガーネット型酸化物は、平均粒径が３μｍ程度になるよう粉砕したものを用いた。この平均粒径は、電子顕微鏡を用いて観察した領域内にある各粒子の短径と長径とを計測し、この短径と長径との平均値を１つの粒径とし、全粒子の平均値を算出することにより求めた。なお、ガーネット型酸化物を電極に含ませる場合は、活物質の平均粒径よりもガーネット型酸化物の平均粒径が小さい方が、活物質の表面をガーネット型酸化物がより覆いやすく、好ましい。この正極／固体電解質混合物を８５重量％、導電材としてのカーボンブラックを１０重量％、結着材としてのポリフッ化ビニリデンを５重量％混合し、正極合材を作製した。この正極合材をＮ−メチル−２−ピロリドン（ＮＭＰ）で分散させてペーストとし、この正極合材ペーストを厚さ２０μｍのアルミニウム箔の両面に塗工乾燥させ、ロールプレスして高密度化し、正極シート電極とした。なお、正極シート電極は５２ｍｍ×４５０ｍｍとし、正極活物質の付着量は片面あたり７ｍｇ／ｃｍ2程度とした。次に、人造黒鉛を負極活物質とした。この負極活物質を９５重量％、結着材としてのポリフッ化ビニリデンを５重量％混合し、負極合材を作製した。この負極合材をＮ−メチル−２−ピロリドン（ＮＭＰ）で分散させてペーストとした。この負極合材ペーストを厚さ１０μｍの銅箔集電体の両面に塗工乾燥させ、ロールプレスして高密度化し、負極シート電極とした。なお、負極シート電極は５４ｍｍ×５００ｍｍとし、負極活物質の付着量は片面あたり５ｍｇ／ｃｍ2程度とした。電解液は、ＬｉＰＦ6を、エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）との混合溶媒（体積比３：７）に１ｍｏｌ／Ｌ濃度で溶解したものを用いた。作製した正・負極シート電極をセパレータ（東燃タピルス製、ＰＥ２５μｍ厚、幅５８ｍｍ品）を介してロール状に捲回し、１８６５０電池缶に挿入し、上記の電解液を注入したあと、トップキャップを密閉することによりリチウム二次電池を作製した。 [Production and evaluation method of lithium secondary battery]
As the positive electrode active material, a layered Ni-based active material, LiNi 0.80 Co 0.15 Al 0.05 O 2 having an average particle size of about 10 μm was used. This positive electrode active material was mixed with a predetermined proportion of the garnet-type oxide Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 (that is, X = 1.75, Experimental Example 5) to prepare a positive electrode / solid electrolyte mixture. This garnet-type oxide used was pulverized so as to have an average particle size of about 3 μm. This average particle diameter is obtained by measuring the short diameter and the long diameter of each particle in the region observed using an electron microscope, and setting the average value of the short diameter and the long diameter as one particle diameter. Was calculated by calculating. When the garnet-type oxide is included in the electrode, it is preferable that the average particle diameter of the garnet-type oxide is smaller than the average particle diameter of the active material, because the surface of the active material is more easily covered with the garnet-type oxide. . 85% by weight of this positive electrode / solid electrolyte mixture, 10% by weight of carbon black as a conductive material, and 5% by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. This positive electrode mixture is dispersed with N-methyl-2-pyrrolidone (NMP) to form a paste, and this positive electrode mixture paste is coated and dried on both surfaces of an aluminum foil having a thickness of 20 μm, and is densified by roll pressing. A positive electrode sheet electrode was obtained. The positive electrode sheet electrode was 52 mm × 450 mm, and the amount of positive electrode active material deposited was about 7 mg / cm 2 per side. Next, artificial graphite was used as the negative electrode active material. The negative electrode active material was mixed with 95% by weight and 5% by weight of polyvinylidene fluoride as a binder to prepare a negative electrode mixture. This negative electrode mixture was dispersed with N-methyl-2-pyrrolidone (NMP) to obtain a paste. This negative electrode mixture paste was applied to and dried on both sides of a 10 μm thick copper foil current collector, and roll pressed to increase the density to obtain a negative electrode sheet electrode. The negative electrode sheet electrode was 54 mm × 500 mm, and the amount of the negative electrode active material attached was about 5 mg / cm 2 per side. The electrolytic solution used was LiPF 6 dissolved in a mixed solvent (volume ratio 3: 7) of ethylene carbonate (EC) and diethyl carbonate (DEC) at a concentration of 1 mol / L. The prepared positive and negative electrode sheet electrodes are rolled into a roll through a separator (product of Tonen Tapirs, PE 25 μm thick, 58 mm wide), inserted into a 18650 battery can, and after injecting the above electrolyte, the top cap is sealed Thus, a lithium secondary battery was produced.

［実験例８〜１１］
上記リチウム二次電池において、正極活物質とガーネット型酸化物との重量比が９９：１となるように、即ち、正極活物質とガーネット型酸化物との全体に対してガーネット型酸化物が１重量％正極に含まれるように配合して得られたリチウム二次電池を実験例８とした。また、正極活物質とガーネット型酸化物との重量比が９０：１０となるように、即ち、正極活物質とガーネット型酸化物との全体に対してガーネット型酸化物が１０重量％正極に含まれるように配合して得られたリチウム二次電池を実験例９とした。また、正極活物質とガーネット型酸化物との重量比が７０：３０となるように、即ち、正極活物質とガーネット型酸化物との全体に対してガーネット型酸化物が３０重量％正極に含まれるように配合して得られたリチウム二次電池を実験例１０とした。また、正極活物質とガーネット型酸化物との重量比が５０：５０となるように、即ち、正極活物質とガーネット型酸化物との全体に対してガーネット型酸化物が５０重量％正極に含まれるように配合して得られたリチウム二次電池を実験例１１とした。 [Experimental Examples 8 to 11]
In the lithium secondary battery, the weight ratio of the positive electrode active material and the garnet oxide is 99: 1, that is, the garnet oxide is 1 in the whole of the positive electrode active material and the garnet oxide. A lithium secondary battery obtained by blending so as to be included in the weight percent positive electrode was used as Experimental Example 8. Further, the positive electrode active material and the garnet oxide have a weight ratio of 90:10, that is, the garnet oxide is contained in the positive electrode by 10% by weight with respect to the total of the positive electrode active material and the garnet oxide. The lithium secondary battery obtained by blending as described above was designated as Experimental Example 9. The positive electrode active material and the garnet oxide have a weight ratio of 70:30, that is, 30% by weight of the garnet oxide is contained in the positive electrode with respect to the whole of the positive electrode active material and the garnet oxide. The lithium secondary battery obtained by blending as described above was designated as Experimental Example 10. The positive electrode active material and the garnet oxide have a weight ratio of 50:50, that is, the garnet oxide is contained in the positive electrode by 50% by weight with respect to the total of the positive electrode active material and the garnet oxide. The lithium secondary battery obtained by blending as described above was designated as Experimental Example 11.

［実験例１２］
また、上記リチウム二次電池において、正極活物質とガーネット型酸化物との重量比が１００：０となるように、即ち、ガーネット型酸化物を添加せずに得られたリチウム二次電池を実験例１２とした。 [Experimental example 12]
Further, in the above lithium secondary battery, the lithium secondary battery obtained so that the weight ratio of the positive electrode active material and the garnet oxide was 100: 0, that is, without adding the garnet oxide was tested. Example 12 was adopted.

（初期容量）
作製した電池について、０．２Ｃ（１００ｍＡ）の電流で、上限４．１Ｖ、下限３．０Ｖとして充放電を５サイクル実行するコンディショニングを行った。次に、２０℃の温度条件下で電流密度０．２ｍＡ／ｃｍ2の定電流・低電圧充電方式で充電上限電圧である４．１Ｖまで７時間かけて充電した。次いで、電流密度０．１ｍＡ／ｃｍ2の定電流で放電下限電圧である３．０Ｖまで放電を実施した。このときの正極活物質当たりの放電容量（ｍＡｈ／ｇ）を電池初期容量とした。 (Initial capacity)
About the produced battery, the conditioning which performs charging / discharging 5 cycles with an electric current of 0.2C (100mA) as an upper limit of 4.1V and a minimum of 3.0V was performed. Next, the battery was charged over 7 hours to a charging upper limit voltage of 4.1 V by a constant current / low voltage charging method with a current density of 0.2 mA / cm 2 under a temperature condition of 20 ° C. Next, discharging was performed to a discharge lower limit voltage of 3.0 V at a constant current of a current density of 0.1 mA / cm 2 . The discharge capacity (mAh / g) per positive electrode active material at this time was defined as the battery initial capacity.

（容量維持率）
作製した電池について、２ｍＡ／ｃｍ2の定電流で充電上限電圧である４．１Ｖまで充電し、次いで電流密度２ｍＡ／ｃｍ2の定電流で放電下限電圧である３．０Ｖまで放電を行う充放電を１サイクルとし、このサイクルを６０℃の温度条件下で５００サイクル行った。この充放電サイクル試験前後において、２０℃の温度条件下で、電流密度０．２ｍＡ／ｃｍ2での放電容量を測定し、充放電サイクル試験後の放電容量を、充放電サイクル試験前の放電容量で除したものに１００を乗じて容量維持率（％）を求めた。 (Capacity maintenance rate)
Charging / discharging the prepared battery at a constant current of 2 mA / cm 2 to a charge upper limit voltage of 4.1 V, and then discharging at a constant current density of 2 mA / cm 2 to a discharge lower limit voltage of 3.0 V 1 cycle, and this cycle was performed 500 times under a temperature condition of 60 ° C. Before and after the charge / discharge cycle test, the discharge capacity at a current density of 0.2 mA / cm 2 was measured under a temperature condition of 20 ° C., and the discharge capacity after the charge / discharge cycle test was determined as the discharge capacity before the charge / discharge cycle test. The capacity retention rate (%) was calculated by multiplying the value divided by 100 by 100.

（ＤＳＣ発熱開始温度評価）
正極活物質を加圧密閉セルにて４．２Ｖまで充電したあと、正極活物質５ｍｇと電解液（ＬｉＰＦ6／ＥＣ＋ＤＥＣ（３：７））３ｍｇをＤＳＣ測定用容器に封入し、示差走査熱量計（ＮＴ０６−０１０６，Ｒｉｇａｋｕ社製）を用いて昇温速度５℃／ｍｉｎで室温から４８０℃まで発熱挙動を測定した。発熱開始温度は、熱流量ピークの立ち上がりが最大値の１／２となる温度とした。標準的活物質である実験例１２の発熱開始温度を基準としてその温度差をＤＳＣ評価の結果とした。 (DSC heat generation start temperature evaluation)
After the positive electrode active material is charged to 4.2 V in a pressure sealed cell, 5 mg of the positive electrode active material and 3 mg of the electrolyte (LiPF 6 / EC + DEC (3: 7)) are sealed in a DSC measurement container, and a differential scanning calorimeter (NT06-0606, manufactured by Rigaku) was used to measure the exothermic behavior from room temperature to 480 ° C. at a heating rate of 5 ° C./min. The heat generation start temperature was a temperature at which the rise of the heat flow peak was ½ of the maximum value. The temperature difference was determined as the result of DSC evaluation based on the heat generation start temperature of Experimental Example 12 which is a standard active material.

（実験結果）
実験例８〜１２のリチウム二次電池について、表２に正極活物質とガーネット型酸化物との重量比、初期容量（ｍＡｈ／ｇ）、容量維持率（％）及び発熱開始温度（℃）をまとめた。実験例８〜１１のリチウム二次電池では、実験例１２に比して容量維持率がより高くなることが明らかとなった。したがって、粉体としてガーネット型酸化物（Ｌｉ6.75Ｌａ3Ｚｒ1.75Ｎｂ0.25Ｏ12）を正極に存在させると、サイクル特性が向上することが明らかとなった。また、実験例８〜１１のリチウム二次電池では、実験例１２に比して発熱開始温度がより高くなることが明らかとなった。したがって、粉体としてガーネット型酸化物（Ｌｉ6.75Ｌａ3Ｚｒ1.75Ｎｂ0.25Ｏ12）を正極に存在させると熱的により安定とすることができることが明らかとなった。しかしながら、ガーネット型酸化物が５０重量％含む実験例１１では、正極活物質量が低下することにより、初期容量が低下することがわかった。このため、ガーネット型酸化物は、５０重量％以下であることが好ましく、３０重量％以下であることがより好ましく、１０重量％以下であることが更に好ましいことがわかった。 (Experimental result)
For the lithium secondary batteries of Experimental Examples 8 to 12, Table 2 shows the weight ratio of the positive electrode active material and the garnet oxide, the initial capacity (mAh / g), the capacity retention rate (%), and the heat generation start temperature (° C.). Summarized. In the lithium secondary batteries of Experimental Examples 8 to 11, it was revealed that the capacity retention rate was higher than that of Experimental Example 12. Therefore, it has been clarified that when a garnet type oxide (Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 ) is present as a powder in the positive electrode, the cycle characteristics are improved. Moreover, in the lithium secondary batteries of Experimental Examples 8 to 11, it became clear that the heat generation start temperature is higher than that of Experimental Example 12. Therefore, it has been clarified that when a garnet-type oxide (Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 ) is present as a powder in the positive electrode, it can be more thermally stabilized. However, in Experimental Example 11 in which the garnet-type oxide was 50% by weight, it was found that the initial capacity was reduced due to a decrease in the amount of the positive electrode active material. For this reason, it was found that the garnet-type oxide is preferably 50% by weight or less, more preferably 30% by weight or less, and even more preferably 10% by weight or less.

このように、サイクル特性、熱的安定性を向上する理由は、Ｚｒ及びＮｂを含みリチウムイオンを伝導するガーネット型酸化物が正極活物質の表面の一部を覆うことにより、正極活物質と電解液との接触面積が減少し、正極活物質−電解液間の発熱反応が抑制されたためであると推察された。例えば、Ｚｒ及びＮｂを含むガーネット型酸化物は、高いリチウム伝導度を有しており、電池の出力特性低下などの懸念が少ない。また、大気中でも安定であるから、大気中の水分と反応したり吸収したりしにくい。また、０Ｖ〜９．５Ｖの広い電位窓を有するため、充放電を行っても電池内で安定に存在できる。即ち、低電位の負極に混入又は接触可能であるし、高電位の正極に混入又は接触可能であるし、正負極に混入又は接触可能である。また、過放電が起きて正極の電位が下がりすぎたり負極の電位が上がりすぎたりしてもガーネット型酸化物は安定であるため、電極に悪影響を与えにくい。   Thus, the reason for improving the cycle characteristics and the thermal stability is that the garnet-type oxide containing Zr and Nb and conducting lithium ions covers a part of the surface of the positive electrode active material, so that the positive electrode active material and the electrolysis are electrolyzed. It was speculated that this was because the contact area with the liquid decreased and the exothermic reaction between the positive electrode active material and the electrolyte was suppressed. For example, a garnet-type oxide containing Zr and Nb has a high lithium conductivity, and there are few concerns such as a reduction in battery output characteristics. Further, since it is stable in the air, it is difficult to react with or absorb moisture in the air. Moreover, since it has a wide electric potential window of 0 V to 9.5 V, it can stably exist in the battery even if charging and discharging are performed. That is, it can be mixed or contacted with the low potential negative electrode, can be mixed or contacted with the high potential positive electrode, and can be mixed or contacted with the positive and negative electrodes. In addition, even if overdischarge occurs and the potential of the positive electrode is too low or the potential of the negative electrode is too high, the garnet-type oxide is stable and thus does not adversely affect the electrode.

なお、本実験例では、正極活物質とリチウムイオンを伝導するガーネット型酸化物とを混合して正極に存在させたものを検討したが、負極活物質とこのガーネット型酸化物とを混合して負極に存在させても同様の効果を奏するものと推察された。また、セパレータ内にこのガーネット型酸化物を存在させた場合についても、電解液を固体電解質で一部置き換えるものとして、同様の効果が期待できる。また、ガーネット型酸化物の粉体を正極内に混入するものとしたが、正極、負極及びセパレータのうち少なくとも１以上にガーネット型酸化物を積層させるものとしても同様の効果が期待できる。   In this experimental example, the positive electrode active material and a garnet-type oxide that conducts lithium ions were mixed and present in the positive electrode. However, the negative-electrode active material and this garnet-type oxide were mixed. It was presumed that the same effect was obtained even if it was present in the negative electrode. Further, even when this garnet-type oxide is present in the separator, the same effect can be expected by replacing the electrolytic solution with a solid electrolyte. Moreover, although the garnet-type oxide powder is mixed in the positive electrode, the same effect can be expected when a garnet-type oxide is laminated on at least one of the positive electrode, the negative electrode, and the separator.

１０，３０ リチウム二次電池、１１，１４，３１，３４ 集電体、１２，３２ 正極合材、１２ａ 正極活物質、１２ｂ，３７ｂ ガーネット型酸化物、１３，３３ 正極シート、１７，３７ 負極合材、１８，３８ 負極シート、１９ セパレータ、２０ 非水電解液、２２ 円筒ケース、２４ 正極端子、２６ 負極端子、３７ａ 負極活物質。   10, 30 Lithium secondary battery, 11, 14, 31, 34 Current collector, 12, 32 Positive electrode mixture, 12a Positive electrode active material, 12b, 37b Garnet type oxide, 13, 33 Positive electrode sheet, 17, 37 Negative electrode combination Material, 18, 38 Negative electrode sheet, 19 Separator, 20 Nonaqueous electrolyte, 22 Cylindrical case, 24 Positive electrode terminal, 26 Negative electrode terminal, 37a Negative electrode active material.

Claims (3)

リチウムを吸蔵・放出する正極活物質を有する正極と、
リチウムを吸蔵・放出する負極活物質を有する負極と、
前記正極と前記負極との間に介在しリチウムを伝導する電解液と、
を備え、
前記正極、前記負極及び前記電解液のうち少なくとも１以上にリチウムイオンを伝導するガーネット型酸化物が存在する、リチウム二次電池。 A positive electrode having a positive electrode active material that absorbs and releases lithium;
A negative electrode having a negative electrode active material that absorbs and releases lithium; and
An electrolytic solution that is interposed between the positive electrode and the negative electrode and conducts lithium;
With
A lithium secondary battery in which a garnet-type oxide that conducts lithium ions is present in at least one of the positive electrode, the negative electrode, and the electrolyte. 前記ガーネット型酸化物は、組成式Ｌｉ5+XＬａ3（ＺｒX，Ａ2-X）Ｏ12（式中、ＡはＳｃ，Ｔｉ，Ｖ，Ｙ，Ｎｂ，Ｈｆ，Ｔａ，Ａｌ，Ｓｉ，Ｇａ及びＧｅからなる群より選ばれた１種類以上の元素、Ｘは１．４≦Ｘ＜２）で表される、請求項１に記載のリチウム二次電池。 The garnet-type oxide has a composition formula of Li 5 + X La 3 (Zr X , A 2−X ) O 12 (where A is Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, The lithium secondary battery according to claim 1, wherein one or more elements selected from the group consisting of Ga and Ge, X is represented by 1.4 ≦ X <2). 前記ガーネット型酸化物は、前記正極活物質と該ガーネット型酸化物との全体に対して３０重量％以下の範囲で前記正極に含まれている、
請求項１又は２に記載のリチウム二次電池。 The garnet-type oxide is contained in the positive electrode in a range of 30% by weight or less based on the whole of the positive electrode active material and the garnet-type oxide.
The lithium secondary battery according to claim 1 or 2.
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