JP2005071807A - Water-based lithium secondary battery - Google Patents

Water-based lithium secondary battery Download PDF

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JP2005071807A
JP2005071807A JP2003300208A JP2003300208A JP2005071807A JP 2005071807 A JP2005071807 A JP 2005071807A JP 2003300208 A JP2003300208 A JP 2003300208A JP 2003300208 A JP2003300208 A JP 2003300208A JP 2005071807 A JP2005071807 A JP 2005071807A
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lithium secondary
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Naruaki Okuda
匠昭 奥田
Itsuki Sasaki
厳 佐々木
Osamu Hiruta
修 蛭田
Yoji Takeuchi
要二 竹内
Yoshio Ukiyou
良雄 右京
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Toyota Central R&D Labs Inc
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based lithium secondary battery having large charge/discharge capacity, and having an excellent charge/discharge cycle characteristic. <P>SOLUTION: This water-based lithium secondary battery has a positive electrode 2, a negative electrode 3 and an aqueous electrolytic solution. The positive electrode 2 contains a lithium-manganese complex oxide of a defective layered structure represented by formula: Li<SB>2-x</SB>Mn<SB>1-y</SB>M<SB>y</SB>O<SB>3-z</SB>(wherein, M is one or more kinds selected from Fe, Al, Ni, and Co; 0<x≤0.9; 0≤y≤0.5; and 0<z≤0.9) as a positive electrode active material. The negative electrode 3 contains a substance having lower storage and desorption potential of lithium than the lithium-manganese complex oxide of the defective layered structure represented by the formula as a negative electrode active material. The aqueous electrolytic solution is prepared by dissolving a lithium salt into water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は、電解液として、リチウム塩を水に溶解してなる水溶液電解液を有する水系リチウム二次電池に関する。   The present invention relates to an aqueous lithium secondary battery having an aqueous electrolyte solution obtained by dissolving a lithium salt in water as an electrolyte solution.

電解液の溶媒として有機系溶媒を用いた非水系のリチウム二次電池は、高電圧でエネルギー密度が高く、また小型・軽量化が図れることから、パソコンや携帯電話等の携帯情報端末等を中心に情報機器や通信機器の分野で実用が進み、広く一般に普及するに至っている。また他の分野では、環境問題、資源問題から電気自動車の開発が急がれる中、このよなリチウム二次電池を電気自動車用電源として用いることが検討されている。   Non-aqueous lithium secondary batteries that use organic solvents as the solvent for the electrolyte solution are high voltage, high energy density, and can be reduced in size and weight, so they are mainly used in personal information terminals such as personal computers and mobile phones. In practical use in the field of information equipment and communication equipment, it has become widely popular. In other fields, the development of electric vehicles has been urgently caused by environmental problems and resource issues, and the use of such lithium secondary batteries as power sources for electric vehicles is being studied.

しかし、非水系のリチウム二次電池には、次のような問題が指摘されている。
即ち、非水系のリチウム二次電池は、電解液として有機溶媒等の非水系電解液を含有しているため、過充電や短絡等により引火や爆発の危険性を有している。そのため、特に高温度条件下での使用を余儀なくされる上記電気自動車の電源等として用いることについては、懸念がある。
また、非水系のリチウム二次電池は、その製造工程において徹底したドライ環境を維持する必要があるため、製造コストが高くなってしまう。したがって、この観点からも、特に電気自動車用の二次電池をにらんだ将来の量産化に対応しにくく、価格的にもきわめて高価になってしまうという問題があった。 However, the following problems have been pointed out for non-aqueous lithium secondary batteries.
That is, a non-aqueous lithium secondary battery contains a non-aqueous electrolyte solution such as an organic solvent as an electrolyte solution, and thus has a risk of ignition or explosion due to overcharge or short circuit. For this reason, there is a concern about using it as a power source for the above-mentioned electric vehicle that is inevitably used under high temperature conditions.
In addition, since the non-aqueous lithium secondary battery needs to maintain a thorough dry environment in the manufacturing process, the manufacturing cost increases. Therefore, from this point of view, there is a problem that it is difficult to cope with future mass production especially in view of a secondary battery for an electric vehicle, and the price is extremely high.

一方、電解液として水溶液電解液を用いた水系リチウム二次電池がある。この水系リチウム二次電池は、非水系のリチウム二次電池が有する上記の問題に対して非常に有利である。即ち、水系リチウム二次電池は、有機溶媒を含有していないため、非常に燃え難い。また、ドライ環境を必要としないため、製造コストを低くすることができる。さらに、一般的に水溶液電解液は非水系電解液に比べて導電性が高いため、水系リチウム二次電池は、非水系のリチウム二次電池に比べて内部抵抗が低くなるという利点がある。   On the other hand, there is an aqueous lithium secondary battery using an aqueous electrolyte as an electrolyte. This water-based lithium secondary battery is very advantageous for the above-mentioned problems of the non-aqueous lithium secondary battery. That is, the water-based lithium secondary battery does not contain an organic solvent and thus is very difficult to burn. In addition, since a dry environment is not required, the manufacturing cost can be reduced. Furthermore, since aqueous electrolytes generally have higher conductivity than non-aqueous electrolytes, aqueous lithium secondary batteries have the advantage of lower internal resistance than non-aqueous lithium secondary batteries.

しかし、水系リチウム二次電池は、水の電気分解反応が起こらない電位範囲で充放電をさせる必要があることから、非水系のリチウム二次電池と比較して大きな放電容量を確保することが難しいという欠点を抱えている。
したがって、水系リチウム二次電池においては、水溶液中で安定で、かつ水の電気分解により酸素や水素を発生しない電位範囲において、可逆的に大量のリチウムを吸蔵及び脱離できる活物質、つまり容量の大きい活物質を用いることが望まれている。 However, water-based lithium secondary batteries need to be charged / discharged in a potential range where no water electrolysis reaction occurs, so it is difficult to ensure a large discharge capacity compared to non-aqueous lithium secondary batteries. Have the disadvantages.
Therefore, in an aqueous lithium secondary battery, an active material that can absorb and desorb a large amount of lithium reversibly in a potential range that is stable in an aqueous solution and does not generate oxygen or hydrogen by electrolysis of water, that is, has a capacity. It is desired to use a large active material.

具体的には、正極活物質としては、ｐＨ７の水溶液電解液中で４．２Ｖまでにより多くのＬｉが引き抜ける材料が望まれている。なぜならば、中性、即ちｐＨが７の水溶液電解液を用いた場合には、理論上の水素発生電位及び酸素発生電位は、それぞれ２．６２Ｖ及び３．８５Ｖであり、さらにガス発生過電圧を考慮すると実際上の酸素ガス発生電位は４．２Ｖとなるからである。
また、水系リチウム二次電池においては、非水系のリチウム二次電池に比べて電位幅が小さいため、少しでもエネルギー密度の高くする必要がある。そのため、正負極ともに平坦な電位曲線をもつ活物質が望まれている。 Specifically, as the positive electrode active material, a material from which more Li can be extracted up to 4.2 V in an aqueous electrolyte solution having a pH of 7 is desired. This is because when a neutral aqueous solution, ie, pH 7 is used, the theoretical hydrogen generation potential and oxygen generation potential are 2.62 V and 3.85 V, respectively, and gas generation overvoltage is taken into consideration. This is because the actual oxygen gas generation potential is 4.2V.
In addition, since the potential width of the aqueous lithium secondary battery is smaller than that of the non-aqueous lithium secondary battery, it is necessary to increase the energy density as much as possible. Therefore, an active material having a flat potential curve for both positive and negative electrodes is desired.

現在までに、水系リチウム二次電池としては、Ｌｉ−Ｍｎ酸化物、Ｌｉ−Ｎｉ酸化物、Ｌｉ−Ｃｏ酸化物等を正極活物質として含有し、Ｌｉ−Ｍｎ酸化物、ＶＯ2、ＬｉＶ3Ｏ8等を負極活物質として含有するものが提案されている（特許文献１〜３参照）。 To date, water-based lithium secondary batteries include Li—Mn oxide, Li—Ni oxide, Li—Co oxide and the like as a positive electrode active material, and include Li—Mn oxide, VO 2 , LiV 3 O. The thing containing 8 etc. as a negative electrode active material is proposed (refer patent documents 1-3).

しかしながら、このような従来の水系リチウム二次電池の活物質は、電位の平坦性、放電容量、及び水溶液電解液中での安定性が未だ不充分であった。そのため、このような水系リチウム二次電池は、容量が小さく、充放電を繰り返し行うことにより容量劣化が起こりやすいという問題があった。それ故、現状の水系リチウム二次電池は、アイデア段階を抜けておらず、従来の非水系のリチウム二次電池等に取って代わる程の実用性を備えるには至っていない。
特開２００３−１７０５７号公報 特表平９−５０８４９０号公報 特開２０００−７７０７３号公報 However, the active material of such a conventional aqueous lithium secondary battery still has insufficient potential flatness, discharge capacity, and stability in an aqueous electrolyte. Therefore, such a water-based lithium secondary battery has a problem that the capacity is small, and capacity deterioration is likely to occur due to repeated charge and discharge. Therefore, the current aqueous lithium secondary battery has not gone through the idea stage and has not yet been practical enough to replace the conventional non-aqueous lithium secondary battery.
JP 2003-17057 A JP-T 9-508490 JP 2000-77073 A

本発明は、かかる従来の問題点に鑑みてなされたものであって、充放電容量が大きく、充放電サイクル特性に優れた水系リチウム二次電池を提供しようとするものである。   The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an aqueous lithium secondary battery having a large charge / discharge capacity and excellent charge / discharge cycle characteristics.

本発明は、正極と、負極と、水溶液電解液とを有する水系リチウム二次電池において、
上記正極は、一般式Ｌｉ2-xＭｎ1-yＭyＯ3-z（但し、Ｍは、Ｆｅ、Ａｌ、Ｎｉ、及びＣｏから選ばれる１種以上、０＜ｘ≦０．９、０≦ｙ≦０．５、０＜ｚ≦０．９）で表される欠損型層状構造のリチウムマンガン複合酸化物を正極活物質として含有し、
上記負極は、上記一般式で表される欠損型層状構造のリチウムマンガン複合酸化物よりも、リチウムの吸蔵・脱離電位が低い物質を負極活物質として含有し、
上記水溶液電解液は、リチウム塩を水に溶解してなることを特徴とする水系リチウム二次電池にある（請求項１）。 The present invention provides an aqueous lithium secondary battery having a positive electrode, a negative electrode, and an aqueous electrolyte solution.
The positive electrode has the general formula Li 2-x Mn 1-y M y O 3-z ( where, M is Fe, Al, Ni, and one or more selected from Co, 0 <x ≦ 0.9,0 ≦ y ≦ 0.5, 0 <z ≦ 0.9) containing a lithium-manganese composite oxide having a deficient layered structure as a positive electrode active material,
The negative electrode contains, as a negative electrode active material, a material having a lower lithium insertion / extraction potential than the lithium manganese composite oxide having a deficient layered structure represented by the above general formula,
The aqueous electrolyte solution is an aqueous lithium secondary battery obtained by dissolving a lithium salt in water (claim 1).

本発明において、最も注目すべき点は、一般式Ｌｉ2-xＭｎ1-yＭyＯ3-z（但し、Ｍは、Ｆｅ、Ａｌ、Ｎｉ、及びＣｏから選ばれる１種以上、０＜ｘ≦０．９、０≦ｙ≦０．５、０＜ｚ≦０．９）で表される欠損型層状構造のリチウムマンガン複合酸化物を正極活物質として含有する点にある。
上記の一般式で表される欠損型層状構造のリチウムマンガン複合酸化物は、例えばｐＨが７付近の水溶液電解液中において、水が分解して酸素を発生するまでの電位、即ち酸素発生電位（約４．２Ｖ）までに高い充放電容量を示すことができると共に、水溶液中で安定である。 In the present invention, the most noteworthy of the general formula Li 2-x Mn 1-y M y O 3-z ( where, M is, Fe, Al, Ni, and one or more selected from Co, 0 < x ≦ 0.9, 0 ≦ y ≦ 0.5, and 0 <z ≦ 0.9). The lithium manganese composite oxide having a deficient layer structure is included as a positive electrode active material.
The lithium-manganese composite oxide having a deficient layer structure represented by the above general formula has, for example, a potential until oxygen decomposes and generates oxygen in an aqueous electrolyte solution having a pH of around 7, that is, an oxygen generation potential ( It can exhibit a high charge / discharge capacity up to about 4.2 V) and is stable in an aqueous solution.

そのため、このような正極活物質を正極に含有し、上記のように構成した上記水系リチウム二次電池は、高い充放電容量を示すことができると共に、充放電を繰り返しても充放電容量が劣化し難く、充放電サイクル特性に優れたものになる。
また、上記一般式で表される欠損型層状構造のリチウムマンガン複合酸化物の基本組成はＬｉ2ＭｎＯ3であるが、この基本組成のリチウムマンガン複合酸化物はほとんど充放電反応を示さない。本発明においては、上記のごとく、欠損型層状構造のリチウムマンガン複合酸化物を正極活物質としているため、高い充放電容量を示すことができる。
このように、本発明によれば、充放電容量が大きく、充放電サイクル特性に優れた水系リチウム二次電池を提供することができる。 Therefore, the water based lithium secondary battery containing the positive electrode active material as described above and configured as described above can exhibit a high charge / discharge capacity, and the charge / discharge capacity deteriorates even after repeated charge / discharge. It is difficult to do so and has excellent charge / discharge cycle characteristics.
Further, the basic composition of the lithium manganese composite oxide having a deficient layered structure represented by the above general formula is Li 2 MnO 3 , but the lithium manganese composite oxide having this basic composition shows almost no charge / discharge reaction. In the present invention, as described above, since the lithium manganese composite oxide having a defect-type layered structure is used as the positive electrode active material, a high charge / discharge capacity can be exhibited.
Thus, according to the present invention, it is possible to provide an aqueous lithium secondary battery having a large charge / discharge capacity and excellent charge / discharge cycle characteristics.

本発明の水系リチウム二次電池において、正極は、一般式Ｌｉ2-xＭｎ1-yＭyＯ3-z（但し、Ｍは、Ｆｅ、Ａｌ、Ｎｉ、及びＣｏから選ばれる１種以上、０＜ｘ≦０．９、０≦ｙ≦０．５、０＜ｚ≦０．９）で表される欠損型層状構造のリチウムマンガン複合酸化物を正極活物質として含有する。 In the aqueous lithium secondary battery of the present invention, the positive electrode has the general formula Li 2-x Mn 1- y My O 3-z (where M is one or more selected from Fe, Al, Ni, and Co, 0 <x ≦ 0.9, 0 ≦ y ≦ 0.5, 0 <z ≦ 0.9) is contained as a positive electrode active material.

上記一般式Ｌｉ2-xＭｎ1-yＭyＯ3-zにおいて、ｘ＞０．９の場合には、可動するＬｉ量が不足し、充放電容量が減少するおそれがある。
また、ｙ＞０．５の場合には、酸化、還元する金属が少なくなり、充放電容量が減少するおそれがある。
また、ｚ＞０．９の場合には、欠損型Ｌｉ2ＭｎＯ3の構造を保持することが不可能になるおそれがある。 In the general formula Li 2-x Mn 1-y M y O 3-z, in the case of x> 0.9, the insufficient amount of Li to be movable, the charge and discharge capacity tends to be reduced.
Further, when y> 0.5, the amount of metal to be oxidized and reduced is reduced, and the charge / discharge capacity may be reduced.
Further, when z> 0.9, it may be impossible to maintain the structure of the defective Li 2 MnO 3 .

また、上記一般式においては、ｙ＝０とすることができる。
この場合には、上記一般式は、Ｌｉ2-xＭｎＯ3-z（０＜ｘ≦０．９、０＜ｚ≦０．９）で表される。そして、この場合においても、上記水系リチウム二次電池は、優れた初期放電容量及び充放電サイクル特性を示すことができる。 In the above general formula, y = 0 can be set.
In this case, the above general formula is expressed by Li 2-x MnO 3-z (0 <x ≦ 0.9, 0 <z ≦ 0.9). Even in this case, the water based lithium secondary battery can exhibit excellent initial discharge capacity and charge / discharge cycle characteristics.

また、上記一般式Ｌｉ2-xＭｎ1-yＭyＯ3-zにおいて、ｙは、０＜ｙ≦０．５であることが好ましい。
この場合には、上記一般式においてＭ（但し、Ｍは、Ｆｅ、Ａｌ、Ｎｉ、及びＣｏから選ばれる１種以上）が必須成分となり、上記水系リチウム二次電池の初期放電容量及び充放電サイクル特性を一層向上させることができる。 In the general formula Li 2-x Mn 1-y M y O 3-z, y is preferably 0 <y ≦ 0.5.
In this case, in the above general formula, M (where M is one or more selected from Fe, Al, Ni and Co) is an essential component, and the initial discharge capacity and charge / discharge cycle of the aqueous lithium secondary battery are as follows. The characteristics can be further improved.

また、上記一般式Ｌｉ2-xＭｎ1-yＭyＯ3-zで表されるリチウムマンガン複合酸化物としては、Ｍの種類や、ｘ、ｙ、及びｚの範囲を変えることにより、種々のものが存在する。上記水系リチウム二次電池においては、これらのうち１種類を正極活物質として正極に用いることもできるが、２種以上を混合して用いることもできる。さらに、上記一般式で表されるリチウムマンガン複合酸化物と公知の正極活物質とを混合したものを用いることもできる。 As the lithium manganese composite oxide represented by the general formula Li 2-x Mn 1-y M y O 3-z, the type and the M, x, by changing the range of y, and z, various There are things. In the aqueous lithium secondary battery, one of these can be used as the positive electrode active material for the positive electrode, but two or more can be mixed and used. Furthermore, what mixed the lithium manganese complex oxide represented by the said general formula and a well-known positive electrode active material can also be used.

また、本発明における、上記欠損型層状構造について説明する。
単斜晶の層状構造をとるＬｉ2ＭｎＯ3は、Ｍｎが４価で安定なため、Ｌｉが脱離し難く、電気化学的に安定である。したがって、一般に充放電反応を示さない。
しかし、酸素が欠損して欠損型層状構造になった場合には、Ｍｎが４価以下になるので、Ｍｎが４価になるまではＬｉの脱離が可能となる。そのため、可逆的な充放電反応を示すようになる。欠損型層状構造のリチウムマンガン複合酸化物は、多くの場合、酸素のみが欠損するのではなく、リチウムも欠損した組成で合成される。 The defect type layered structure in the present invention will be described.
In Li 2 MnO 3 having a monoclinic layered structure, Mn is tetravalent and stable, so Li is not easily detached and is electrochemically stable. Therefore, generally no charge / discharge reaction is exhibited.
However, when oxygen is deficient and a deficient layered structure is formed, Mn becomes tetravalent or less, so that Li can be desorbed until Mn becomes tetravalent. Therefore, a reversible charge / discharge reaction is exhibited. In many cases, a lithium-manganese composite oxide having a deficient layer structure is synthesized with a composition in which not only oxygen is deficient but also lithium is deficient.

次に、上記水系リチウム二次電池において、上記負極活物質は、上記一般式で表される欠損型層状構造のリチウムマンガン複合酸化物よりも、リチウムの吸蔵・脱離電位が低い物質である。
このような物質としては、例えばＬｉＶ2Ｏ4、ＬｉＶ3Ｏ8、ＶＯ2、ＦｅＯＯＨ等がある。 Next, in the aqueous lithium secondary battery, the negative electrode active material is a substance having a lower lithium insertion / extraction potential than the lithium manganese composite oxide having a deficient layered structure represented by the general formula.
Examples of such a substance include LiV 2 O 4 , LiV 3 O 8 , VO 2 , FeOOH and the like.

また、上記負極活物質としては、リチウムイオンを吸蔵・脱離できる炭素物質を用いることもできる。このような炭素物質としては、例えば天然あるいは人造の黒鉛、メソカーボンマイクロビーズ（ＭＣＭＢ）、フェノール樹脂等の有機化合物焼成体、コークス等の粉状体等が挙げられる。   Further, as the negative electrode active material, a carbon material capable of inserting and extracting lithium ions can be used. Examples of such a carbon material include natural or artificial graphite, mesocarbon microbeads (MCMB), a fired organic compound such as phenol resin, and a powdery material such as coke.

また、上記負極活物質は、スピネル構造のＬｉＶ2Ｏ4よりなることが好ましい（請求項２）。
この場合には、上記水系リチウム二次電池の充放電サイクル特性をさらに向上させることができる。ＬｉＶ2Ｏ4は、そのＬｉやＬｉ+に対する充放電の電位が水の電気分解により水素を発生する電位範囲から外れており２．４Ｖ付近にあるため、このＬｉＶ2Ｏ4を水系リチウム二次電池に適用すると、リチウムイオンを大量に吸蔵及び脱離できるからである。 The negative electrode active material is preferably made of LiV 2 O 4 having a spinel structure (claim 2).
In this case, the charge / discharge cycle characteristics of the water based lithium secondary battery can be further improved. LiV 2 O 4, therefore the potential of the charging and discharging of the Li and Li + is near 2.4V deviates from the potential scope for generating hydrogen by electrolysis of water, the LiV 2 O 4 aqueous lithium secondary This is because when applied to a battery, a large amount of lithium ions can be occluded and desorbed.

また、上記水系リチウム二次電池は、電解液として、リチウム塩を水に溶解してなる水溶液電解液を有する。
このようなリチウム塩としては、例えばＬｉＮＯ3、ＬｉＯＨ、ＬｉＣｌ、及びＬｉ2ＳＯ4等がある。これらのリチウム塩は、それぞれ単独で用いることもできるが、２種以上を併用することもできる。 Moreover, the said aqueous lithium secondary battery has aqueous solution electrolyte solution formed by melt | dissolving lithium salt in water as electrolyte solution.
Examples of such a lithium salt include LiNO 3 , LiOH, LiCl, and Li 2 SO 4 . These lithium salts can be used alone or in combination of two or more.

次に、上記水溶液電解液のｐＨは、６〜１０であることが好ましい（請求項３）。
上記水溶液電解液のｐＨが６未満の場合には、上記一般式で表されるリチウムマンガン複合酸化物が不安定となり、電池の容量やサイクル特性が低下するおそれがある。一方、ｐＨが１０を越える場合には、水の電気分解電位、即ち水素発生電位及び酸素発生電位がそれぞれ２．２１Ｖ及び３．４４Ｖまで低下する。そのため、正極や負極で酸素や水素が発生しやすくなるおそれがある。 Next, the pH of the aqueous electrolyte solution is preferably 6 to 10. (Claim 3)
When the pH of the aqueous electrolyte is less than 6, the lithium manganese composite oxide represented by the above general formula becomes unstable, and the battery capacity and cycle characteristics may be reduced. On the other hand, when the pH exceeds 10, the electrolysis potential of water, that is, the hydrogen generation potential and the oxygen generation potential are decreased to 2.21 V and 3.44 V, respectively. Therefore, oxygen and hydrogen may be easily generated at the positive electrode and the negative electrode.

また、上記水系リチウム二次電池においては、例えばリチウムを吸蔵・放出する正極及び負極と、これらの間に狭装されるセパレータと、正極及び負極間でリチウムを移動させる水溶液電解液などを主要構成要素として構成することができる。   The above-mentioned aqueous lithium secondary battery mainly includes, for example, a positive electrode and a negative electrode that store and release lithium, a separator that is sandwiched between them, and an aqueous electrolyte that moves lithium between the positive electrode and the negative electrode. Can be configured as an element.

上記水系リチウム二次電池において、正極は、例えば上記正極活物質に導電材及び結着剤を混合し、必要に応じて適当な溶剤を加えてペースト状の正極合材としたものを成形し、必要に応じて電極密度を高めるべく圧縮して形成することができる。
導電材は、正極の電気伝導性を確保するためのものであり、例えばカーボンブラック、アセチレンブラック、黒鉛等の炭素物質粉末状体を用いることができる。また、導電材としては、これらのうちの１種又は２種以上を用いることができる。 In the aqueous lithium secondary battery, the positive electrode is formed, for example, by mixing a conductive material and a binder into the positive electrode active material, and adding a suitable solvent as necessary to form a paste-like positive electrode mixture, If necessary, it can be compressed to increase the electrode density.
The conductive material is for ensuring the electrical conductivity of the positive electrode, and for example, a carbon material powder such as carbon black, acetylene black, and graphite can be used. Moreover, as a electrically conductive material, 1 type, or 2 or more types of these can be used.

結着剤は、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、ポリフッ化ビニリデン、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、ポリエチレンテレフタレート等の熱可塑性樹脂等を用いることができる。
これら活物質、導電材、結着剤を分散させる溶剤としては、例えばＮ−メチル−２−ピロリドン等の有機溶剤を用いることができる。 The binder plays a role of tying the active material particles and the conductive material particles. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber, or heat such as polypropylene, polyethylene, and polyethylene terephthalate. A plastic resin or the like can be used.
As a solvent for dispersing these active material, conductive material, and binder, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

負極は、上記正極と同様に、例えば上記負極活物質に導電材や結着剤を混合し、必要に応じて適当な溶媒を加えてペースト状にした負極合材を成形し、その後必要に応じてプレスして形成することができる。   As with the positive electrode, for example, the negative electrode active material is mixed with a conductive material or a binder, and if necessary, an appropriate solvent is added to form a paste-like negative electrode mixture. And press to form.

また、正極及び負極に狭装させるセパレータは、正極と負極とを分離し電解液を保持するものであり、例えばセルロース、ポリエチレン、及びポリプロピレン等の薄い微多孔膜を用いることができる。   In addition, the separator to be narrowly attached to the positive electrode and the negative electrode separates the positive electrode and the negative electrode and holds the electrolytic solution. For example, a thin microporous film such as cellulose, polyethylene, or polypropylene can be used.

また、上記水系リチウム二次電池の形状としては、例えばコイン型、円筒型、角型等がある。正極、負極、セパレータ及び水溶液電解液等を収容する電池ケースとしては、これらの形状に対応したものを用いることができる。   Examples of the shape of the water based lithium secondary battery include a coin shape, a cylindrical shape, and a square shape. As the battery case that accommodates the positive electrode, the negative electrode, the separator, the aqueous electrolyte, and the like, those corresponding to these shapes can be used.

（実施例１）
次に、本発明の実施例につき、説明する。
本例においては、欠損型層状構造のリチウムマンガン複合酸化物を合成し、これらの水系リチウム二次電池の正極活物質としての適性を調べる。即ち、まず、本例においては、欠損型層状構造のリチウムマンガン複合酸化物として、Ｌｉ1.6Ｍｎ0.8Ｆｅ0.2Ｏ3-z（０＜ｚ≦０．９）を合成し、これを正極活物質に用いて非水系のリチウム二次電池を作製する。次いで、この非水系のリチウム二次電池の電圧と容量の関係を調べることにより、Ｌｉ1.6Ｍｎ0.8Ｆｅ0.2Ｏ3-z（０＜ｚ≦０．９）の水系リチウム二次電池の正極活物質としての適性を評価する。 (Example 1)
Next, examples of the present invention will be described.
In this example, a lithium-manganese composite oxide having a defect-type layered structure is synthesized, and the suitability of these aqueous lithium secondary batteries as a positive electrode active material is examined. That is, first, in this example, Li 1.6 Mn 0.8 Fe 0.2 O 3-z (0 <z ≦ 0.9) was synthesized as a lithium manganese composite oxide having a deficient layer structure, and this was used as a positive electrode active material. A non-aqueous lithium secondary battery is produced. Next, by investigating the relationship between the voltage and capacity of this non - aqueous lithium secondary battery, the positive electrode active material of an aqueous lithium secondary battery of Li 1.6 Mn 0.8 Fe 0.2 O 3-z (0 <z ≦ 0.9) Assess suitability as

具体的には、まず、下記のようにして、正極活物質を合成した。
即ち、まず濃度１．０ＭのＭｎ（ＮＯ3）2水溶液と、濃度１．０ＭのＦｅ（ＮＯ3）3水溶液とをＦｅに対するＭｎのモル比が０．８０／０．２０となるような割合で混合し、混合水溶液を作製した。 Specifically, first, a positive electrode active material was synthesized as follows.
That is, the ratio of the Mn (NO 3 ) 2 aqueous solution having a concentration of 1.0M and the Fe (NO 3 ) 3 aqueous solution having a concentration of 1.0M to a molar ratio of Mn to Fe of 0.80 / 0.20. To prepare a mixed aqueous solution.

次いで、混合水溶液をスターラーで撹拌しつつ、この混合水溶液に濃度１．０ＭのＬｉＯＨ／３ｗｔ％Ｈ2Ｏ2水溶液を１５０ｍＬ混合し、５分間反応させて、リチウムマンガン複合酸化物の前駆体を析出させた。
続いて、前駆体を析出させた混合溶液をテフロン（登録商標）製の密閉容器に入れ、１００℃の温度で保持しつつ、２．４５ＧＨｚの電磁波を１５分間照射した。その後、室温まで放置した後、ろ過、水洗、乾燥して、欠損型層状構造のリチウムマンガン複合酸化物（Ｌｉ1.6Ｍｎ0.8Ｆｅ0.2Ｏ3-z）を作製した。これを試料Ｅとする。 Next, while stirring the mixed aqueous solution with a stirrer, 150 mL of a 1.0 M concentration LiOH / 3 wt% H 2 O 2 aqueous solution is mixed with this mixed aqueous solution and reacted for 5 minutes to precipitate a precursor of the lithium manganese composite oxide. I let you.
Subsequently, the mixed solution on which the precursor was deposited was put into a Teflon (registered trademark) sealed container and irradiated with an electromagnetic wave of 2.45 GHz for 15 minutes while being kept at a temperature of 100 ° C. Then, after standing to room temperature, filtered, washed with water, dried, lithium-manganese composite oxide of the defective layered structure (Li 1.6 Mn 0.8 Fe 0.2 O 3-z) were prepared. This is designated as Sample E.

次に、上記試料Ｅのリチウムマンガン複合酸化物を用いて、非水系のリチウム二次電池を作製した。
具体的には、まず、正極活物質としての上記試料Ｅを７０重量部、導電材としてのカーボンブラックを２５重量部、及び結着剤としてのポリエチレンテレフタレートを５重量部混合し、電極合材を作製した。そして、この電極合材１０ｍｇをφ１０ｍｍのペレットに成形し、これを正極とした。 Next, a non-aqueous lithium secondary battery was manufactured using the lithium manganese composite oxide of Sample E.
Specifically, first, 70 parts by weight of the sample E as a positive electrode active material, 25 parts by weight of carbon black as a conductive material, and 5 parts by weight of polyethylene terephthalate as a binder are mixed to obtain an electrode mixture. Produced. Then, 10 mg of this electrode mixture was formed into a 10 mm pellet, which was used as the positive electrode.

次いで、負極として金属リチウムを準備した。また、電解液として、エチレンカーボネートとジエチルカーボネートとを体積比１：１にて混合した混合溶媒に、ＰＦ6を溶解させて濃度１Ｍとした溶液を準備した。
次に、上記のようにして準備した正極と負極とで、厚さ２５μｍのポリエチレン製のセパレータを挟み、これをＣＲ２０１６型のコインセル用の電池ケース中に配置した。 Next, metallic lithium was prepared as a negative electrode. Further, as an electrolytic solution, a solution having a concentration of 1M was prepared by dissolving PF 6 in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1.
Next, a polyethylene separator having a thickness of 25 μm was sandwiched between the positive electrode and the negative electrode prepared as described above, and this was placed in a battery case for a CR2016 type coin cell.

さらに、電池ケース内の端部にガスケットを配置し、さらに電池ケース内に上記の電解液を適量注入して含浸させた。続いて、電池ケースを密封して、非水系のリチウム二次電池を作製した。これを電池Ｅとする。   Further, a gasket was disposed at the end of the battery case, and an appropriate amount of the above electrolyte was injected into the battery case for impregnation. Subsequently, the battery case was sealed to produce a non-aqueous lithium secondary battery. This is referred to as a battery E.

さらに、上記電池Ｅの優れた特性を明らかにするために、比較用として、市販のスピネル型のＬｉＭｎ1.5Ｎｉ0.5Ｏ4（以下、適宜試料Ｃという）を正極活物質として含有する非水系のリチウム二次電池を作製した。これを電池Ｃとする。
この電池Ｃは、正極活物質としてＬｉＭｎ1.5Ｎｉ0.5Ｏ4を用いた点を除いては、上記試料Ｅと同様にして作製したものである。 Furthermore, in order to clarify the excellent characteristics of the battery E, for comparison, non-aqueous lithium containing a commercially available spinel type LiMn 1.5 Ni 0.5 O 4 (hereinafter referred to as sample C as appropriate) as a positive electrode active material. A secondary battery was produced. This is referred to as a battery C.
The battery C was produced in the same manner as the sample E except that LiMn 1.5 Ni 0.5 O 4 was used as the positive electrode active material.

次に、上記電池Ｅ及び電池Ｃを、それぞれ温度２０℃の恒温槽内で、電流密度０．２ｍＡ／ｃｍ2にて、充電上限電圧４．５Ｖまで定電流充電し、次いで２０℃の恒温槽内で、電流密度０．２ｍＡ／ｃｍ2にて、放電下限電圧２．５Ｖまで定電流放電した。このとき、各電池の電圧及び容量を測定し、Ｌｉに対する電圧−容量曲線を作製した。これを図１に示す。なお、図１において、縦軸はＬｉに対する電位を示し、横軸は容量を示す。 Next, the battery E and the battery C were each charged in a constant current at a current density of 0.2 mA / cm 2 to a charge upper limit voltage of 4.5 V in a constant temperature bath at a temperature of 20 ° C., and then a constant temperature bath at 20 ° C. The battery was discharged at a constant current up to a discharge lower limit voltage of 2.5 V at a current density of 0.2 mA / cm 2 . At this time, the voltage and capacity of each battery were measured, and a voltage-capacity curve for Li was prepared. This is shown in FIG. In FIG. 1, the vertical axis represents the potential with respect to Li, and the horizontal axis represents the capacity.

図１より知られるごとく、電池Ｅにおいては、酸素ガス発生電位と目される４．２Ｖまでの容量が２００ｍＡｈ／ｇを越えており、酸素ガス発生電位までに高い容量を示した。一方、電池Ｃにおいては、酸素ガス発生電位と目される４．２Ｖまでの容量が約５ｍＡｈ／ｇであり、酸素ガス発生電位までの容量は非常に小さかった。
即ち、電池Ｅに用いた正極活物質（試料Ｅ）は、電池Ｃに用いた正極活物質（試料Ｃ）に比べて、酸素ガス発生電位までに４０倍以上の容量を発揮できることがわかる。
したがって、試料Ｅは、電解液として水溶液電解液を含有する水系リチウム二次電池に好適であることがわかる。 As is known from FIG. 1, in the battery E, the capacity up to 4.2 V regarded as the oxygen gas generation potential exceeded 200 mAh / g, and the capacity was high up to the oxygen gas generation potential. On the other hand, in the battery C, the capacity up to 4.2 V regarded as the oxygen gas generation potential was about 5 mAh / g, and the capacity up to the oxygen gas generation potential was very small.
That is, it can be seen that the positive electrode active material (sample E) used in battery E can exhibit a capacity 40 times or more up to the oxygen gas generation potential as compared with the positive electrode active material (sample C) used in battery C.
Therefore, it can be seen that Sample E is suitable for an aqueous lithium secondary battery containing an aqueous electrolyte as an electrolyte.

（実施例２）
本例は、実施例１にて作製した試料Ｅ、及び試料Ｃをそれぞれ正極活物質として用いて２種類の水系リチウム二次電池（電池Ｅａ及び電池Ｃａ）を作製し、その特性を評価した例である。
本例においては、水系リチウム二次電池として、図２に示すごとくＣＲ２０１６型コインセルを作製した。 (Example 2)
In this example, two types of water-based lithium secondary batteries (battery Ea and battery Ca) were produced using the samples E and C produced in Example 1 as positive electrode active materials, respectively, and their characteristics were evaluated. It is.
In this example, a CR2016 type coin cell was produced as an aqueous lithium secondary battery as shown in FIG.

図２に示すごとく、本例の水系リチウム二次電池１（電池Ｅａ）は、正極２と、負極３と、水溶液電解液とを有する。正極２は、Ｌｉ1.6Ｍｎ0.8Ｆｅ0.2Ｏ3-z（０＜ｚ≦０．９）で表される欠損型層状構造のリチウムマンガン複合酸化物を正極活物質として含有する。また、負極３は、上記の欠損型層状構造のリチウムマンガン複合酸化物よりも、リチウムの吸蔵・脱離電位が低い物質であるＬｉＶ2Ｏ4を負極活物質として含有する。また、水溶液電解液は、リチウム塩としてのＬｉＮＯ3を水に溶解してなる。 As shown in FIG. 2, the aqueous lithium secondary battery 1 (battery Ea) of this example includes a positive electrode 2, a negative electrode 3, and an aqueous electrolyte solution. The positive electrode 2 contains a lithium manganese composite oxide having a deficient layer structure represented by Li 1.6 Mn 0.8 Fe 0.2 O 3-z (0 <z ≦ 0.9) as a positive electrode active material. Further, the negative electrode 3 contains LiV 2 O 4 , which is a material having a lower lithium insertion / extraction potential than the above-described defect-type layered lithium manganese composite oxide, as a negative electrode active material. The aqueous electrolyte solution is obtained by dissolving LiNO 3 as a lithium salt in water.

また、本例の水系リチウム二次電池１において、上記正極及び負極は、これらの間にセパレータ４を狭装した状態で、電池ケース１１中に配置されている。また、電池ケース１１内には、水溶液電解液が注入されており、電池ケース１１内の端部には、ガスケット５が配置されている。また、電池ケース１１は封口板１２により密封されている。   Moreover, in the water based lithium secondary battery 1 of this example, the positive electrode and the negative electrode are disposed in the battery case 11 with the separator 4 interposed therebetween. In addition, an aqueous electrolyte solution is injected into the battery case 11, and a gasket 5 is disposed at an end in the battery case 11. The battery case 11 is sealed with a sealing plate 12.

次に、上記水系リチウム二次電池の作製方法につき、説明する。
まず、上記試料Ｅを用いて実施例１と同様にして正極を作製した。
また、負極としては、まず、負極活物質としてのＬｉＶ2Ｏ4を７０重量部、導電材としてのカーボンブラックを２５重量部、及び結着剤としてのポリエチレンテレフタレートを５重量部混合して負極合材を作製し、この負極合材２０ｍｇをφ１０ｍｍのペレットに成形したものを用いた。 Next, a method for producing the water based lithium secondary battery will be described.
First, a positive electrode was produced using the sample E in the same manner as in Example 1.
As the negative electrode, first, 70 parts by weight of LiV 2 O 4 as a negative electrode active material, 25 parts by weight of carbon black as a conductive material, and 5 parts by weight of polyethylene terephthalate as a binder were mixed to form a negative electrode composite. A material was prepared, and 20 mg of this negative electrode mixture was formed into a 10 mm diameter pellet.

なお、ＬｉＶ2Ｏ4は、ＬｉやＬｉ+に対する充放電電位が２．４Ｖ付近、即ち水の電気分解により水素発生を発生しない電位範囲内にある。したがって、このＬｉＶ2Ｏ4は、水素を発生しない電位範囲において、可逆的に大量のリチウムイオンを吸蔵・脱離することが可能であり、水系リチウム二次電池の負極活物質として好適なものである。 Note that LiV 2 O 4 has a charge / discharge potential with respect to Li or Li + in the vicinity of 2.4 V, that is, within a potential range where hydrogen generation does not occur due to water electrolysis. Therefore, this LiV 2 O 4 can reversibly absorb and desorb a large amount of lithium ions in a potential range where hydrogen is not generated, and is suitable as a negative electrode active material for an aqueous lithium secondary battery. is there.

また水溶液電解液としては、リチウム塩であるＬｉＮＯ3の飽和水溶液（ｐＨ≒７）を準備した。
次に、図２に示すごとく、上記正極２及び負極３の間に厚さ２５μｍのポリエチレン製のセパレータ４を挟み、これをＣＲ２０１６型の電池ケース１１内に配置した。 As an aqueous electrolyte solution, a saturated aqueous solution (pH≈7) of LiNO 3 which is a lithium salt was prepared.
Next, as shown in FIG. 2, a polyethylene separator 4 having a thickness of 25 μm was sandwiched between the positive electrode 2 and the negative electrode 3, and this was placed in a CR2016 type battery case 11.

さらに、電池ケース１１内の端部にガスケット５を配置し、さらに電池ケース１１内に上記の水溶液電解液を適量注入して含浸させた。続いて、封口板１２を配置し、電池ケース１１の端部をかしめ加工することにより、電池ケース１１を密封して水系リチウム二次電池１を作製した。これを電池Ｅａとする。   Further, the gasket 5 was disposed at the end in the battery case 11, and an appropriate amount of the above aqueous electrolyte solution was injected into the battery case 11 and impregnated. Subsequently, the sealing plate 12 was disposed, and the end portion of the battery case 11 was caulked, whereby the battery case 11 was sealed to produce the aqueous lithium secondary battery 1. This is designated as battery Ea.

また、本例においては、上記電池Ｅａの優れた特性を明らかにするために、比較用として、市販のスピネル型のＬｉＭｎ1.5Ｎｉ0.5Ｏ4（試料Ｃ）を正極活物質として含有する水系リチウム二次電池を作製した。これを電池Ｃａとする。
この電池Ｃａは、正極活物質としてＬｉＭｎ1.5Ｎｉ0.5Ｏ4を用いた点を除いては、上記試料Ｅａと同様にして作製したものである。 Further, in this example, in order to clarify the excellent characteristics of the battery Ea, for comparison, an aqueous lithium secondary battery containing a commercially available spinel type LiMn 1.5 Ni 0.5 O 4 (sample C) as a positive electrode active material is used. A secondary battery was produced. This is referred to as a battery Ca.
This battery Ca was produced in the same manner as the sample Ea except that LiMn 1.5 Ni 0.5 O 4 was used as the positive electrode active material.

次に、上記電池Ｅａ及び電池Ｃａについて、充放電サイクル試験を行った。
充放電サイクル試験は、各電池について、温度６０℃の条件下で、電流密度０．５ｍＡ／ｃｍ2の定電流にて電池電圧１．４Ｖまで充電し、その後、電流密度０．５ｍＡ／ｃｍ2の定電流にて電池電圧０．１Ｖまで放電する充放電を１サイクルとし、このサイクルを５０サイクル繰り返すことにより行った。各充放電サイクルにおいては、１．４Ｖまで充電した後、及び０．１Ｖまで放電した後に、充電休止時間及び放電休止時間をそれぞれ１分間ずつ設けた。そして、各サイクル毎に、それぞれの電池（電池Ｅａ及びＣａ）の放電容量を測定した。 Next, a charge / discharge cycle test was performed on the battery Ea and the battery Ca.
In the charge / discharge cycle test, each battery was charged to a battery voltage of 1.4 V at a constant current of 0.5 mA / cm 2 under a temperature of 60 ° C., and then the current density of 0.5 mA / cm 2. Charging / discharging to a battery voltage of 0.1 V at a constant current of 1 cycle was performed, and this cycle was repeated 50 times. In each charge / discharge cycle, after charging to 1.4 V and after discharging to 0.1 V, a charging pause time and a discharge pause time were provided for 1 minute each. And the discharge capacity of each battery (battery Ea and Ca) was measured for every cycle.

放電容量は、上記各サイクル毎の放電電流値（ｍＡ）を測定し、この放電電流値に放電に要した時間（ｈｒ）を乗じて得られた値を、電池内の正極活物質の重量（ｇ）で除することにより算出した。
上記充放電サイクル試験において、電池Ｅａ及び電池Ｃａの１サイクル目の充放電容量、即ち初期放電容量を下記の表１に示す。 The discharge capacity is determined by measuring the discharge current value (mA) for each cycle and multiplying this discharge current value by the time (hr) required for discharge to obtain the weight of the positive electrode active material in the battery ( Calculated by dividing by g).
In the charge / discharge cycle test, the charge / discharge capacities of the first cycle of the battery Ea and the battery Ca, that is, the initial discharge capacities are shown in Table 1 below.

また、各サイクル毎の放電容量を図３に示す。
なお、図３において、横軸はサイクル数（回）を示し、縦軸は放電容量（ｍＡｈ／ｇ）を示すものである。同図には、正極活物質として上記試料Ｅを用いて構成した電池を電池Ｅａとし、また上記試料Ｃを用いて構成した電池を電池Ｃａとして示してある。 Moreover, the discharge capacity for each cycle is shown in FIG.
In FIG. 3, the horizontal axis represents the number of cycles (times), and the vertical axis represents the discharge capacity (mAh / g). In the drawing, a battery configured using the sample E as a positive electrode active material is shown as a battery Ea, and a battery configured using the sample C is shown as a battery Ca.

Figure 2005071807
Figure 2005071807

表１より知られるごとく、電池Ｅａは、１２０ｍＡｈ／ｇを越える高い初期放電容量を示した。
一方、電池Ｃａにおいては、初期放電容量は約１０ｍＡｈ／ｇという非常に低いものであった。 As is known from Table 1, the battery Ea exhibited a high initial discharge capacity exceeding 120 mAh / g.
On the other hand, in the battery Ca, the initial discharge capacity was very low of about 10 mAh / g.

また、図３より知られるごとく、電池Ｅａにおいては、充放電を５０サイクル繰り返した後においても、初期放電容量の７５％以上の放電容量を維持しており、サイクル試験後も９０ｍＡｈ／ｇを越える高い放電容量を示した。
一方、電池Ｃａにおいては、充放電を５０サイクル繰り返した後、放電容量は、初期放電容量の５０％以下に低下し、サイクル試験後の放電容量は５ｍＡｈ／ｇを下回っていた。 As can be seen from FIG. 3, the battery Ea maintains a discharge capacity of 75% or more of the initial discharge capacity even after 50 cycles of charge / discharge, and exceeds 90 mAh / g even after the cycle test. High discharge capacity was shown.
On the other hand, in the battery Ca, after repeating 50 cycles of charge and discharge, the discharge capacity decreased to 50% or less of the initial discharge capacity, and the discharge capacity after the cycle test was less than 5 mAh / g.

本例の結果から、Ｌｉ1.6Ｍｎ0.8Ｆｅ0.2Ｏ3-zで表される欠損型層状構造のリチウムマンガン複合酸化物は、水系リチウム二次電池の正極活物質として非常に優れており、この正極活物質を用いて作製した電池Ｅａは、充放電容量が高く、充放電サイクル特性に優れていることがわかる。
また、本例においては、Ｍｎの２０％をＦｅで置換した組成であるＬｉ1.6Ｍｎ0.8Ｆｅ0.2Ｏ3-z（試料Ｅ）を正極活物質として用いたが、ＭｎのＦｅでの置換量が０〜５０％のリチウムマンガン複合酸化物を正極活物質として用いた場合についても、同様の結果が得られる。また、Ｆｅの代わりに、ＡｌやＣｏやＮｉにてＭｎを置換した場合についても同様の結果が得られる。 From the result of this example, the lithium manganese composite oxide having a deficient layer structure represented by Li 1.6 Mn 0.8 Fe 0.2 O 3-z is very excellent as a positive electrode active material of an aqueous lithium secondary battery. It can be seen that the battery Ea produced using the active material has a high charge / discharge capacity and excellent charge / discharge cycle characteristics.
In this example, Li 1.6 Mn 0.8 Fe 0.2 O 3-z (sample E) having a composition in which 20% of Mn was replaced with Fe was used as the positive electrode active material. Similar results are obtained when 0-50% lithium manganese composite oxide is used as the positive electrode active material. Similar results can be obtained when Mn is substituted with Al, Co, or Ni instead of Fe.

実施例１にかかる、各電池の容量と電位との関係を表す説明図。FIG. 3 is an explanatory diagram showing the relationship between the capacity and potential of each battery according to Example 1; 実施例２にかかる、水系リチウム二次電池の構成を示す断面図。Sectional drawing which shows the structure of the water based lithium secondary battery concerning Example 2. FIG. 実施例２にかかる、各電池の充放電サイクル試験の結果を示す説明図。Explanatory drawing which shows the result of the charging / discharging cycle test of each battery concerning Example 2. FIG.

符号の説明Explanation of symbols

１ 水系リチウム二次電池
２ 正極
３ 負極
４ セパレータ 1 Water-based lithium secondary battery 2 Positive electrode 3 Negative electrode 4 Separator

Claims (3)

正極と、負極と、水溶液電解液とを有する水系リチウム二次電池において、
上記正極は、一般式Ｌｉ2-xＭｎ1-yＭyＯ3-z（但し、Ｍは、Ｆｅ、Ａｌ、Ｎｉ、及びＣｏから選ばれる１種以上、０＜ｘ≦０．９、０≦ｙ≦０．５、０＜ｚ≦０．９）で表される欠損型層状構造のリチウムマンガン複合酸化物を正極活物質として含有し、
上記負極は、上記一般式で表される欠損型層状構造のリチウムマンガン複合酸化物よりも、リチウムの吸蔵・脱離電位が低い物質を負極活物質として含有し、
上記水溶液電解液は、リチウム塩を水に溶解してなることを特徴とする水系リチウム二次電池。 In an aqueous lithium secondary battery having a positive electrode, a negative electrode, and an aqueous electrolyte,
The positive electrode has the general formula Li 2-x Mn 1-y M y O 3-z ( where, M is Fe, Al, Ni, and one or more selected from Co, 0 <x ≦ 0.9,0 ≦ y ≦ 0.5, 0 <z ≦ 0.9) containing a lithium-manganese composite oxide having a deficient layered structure as a positive electrode active material,
The negative electrode contains, as a negative electrode active material, a material having a lower lithium insertion / extraction potential than the lithium manganese composite oxide having a deficient layered structure represented by the above general formula,
The aqueous electrolyte solution is obtained by dissolving a lithium salt in water. 請求項１において、上記負極活物質は、スピネル構造のＬｉＶ2Ｏ4よりなることを特徴とする水系リチウム二次電池。 2. The water based lithium secondary battery according to claim 1, wherein the negative electrode active material is made of LiV 2 O 4 having a spinel structure. 請求項１又は２において、上記水溶液電解液のｐＨは、６〜１０であることを特徴とする水系リチウム二次電池。   3. The aqueous lithium secondary battery according to claim 1, wherein the aqueous electrolyte solution has a pH of 6 to 10.
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