JP4304577B2 - Electrolyte and secondary battery using the same - Google Patents

Description

【００５８】
電池缶１１の内部に電解液を注入したのち、ガスケット１７を介して電池蓋１４を電池缶１１にかしめることにより、実施例１−１〜１−４について直径１８ｍｍ、高さ６５ｍｍの円筒型二次電池を得た。
【００５９】
実施例１−１〜１−４に対する比較例１−１として、添加剤を加えなかったことを除き、他は実施例１−２と同様にして二次電池を作製した。また、実施例１−１〜１−４に対する比較例１−２として、添加剤としてＭｇＣｌ₂ を用いたことを除き、他は実施例１−２と同様にして二次電池を作製した。
【００６０】
作製した実施例１−１〜１−４および比較例１−１，１−２の二次電池について、充放電を１００サイクル行い、容量維持率を求めた。その際、充電は、１Ａの定電流で電池電圧が４．２Ｖに達するまで行ったのち、４．２Ｖの定電圧で充電時間の総計が１サイクル目では２０時間、２サイクル目以降では５時間に達するまで行い、放電は、１サイクル目〜１００サイクル目のいずれでも１．５Ａの定電流で電池電圧が２．５Ｖに達するまで行った。容量維持率は、２サイクル目の放電容量と１００サイクル目の放電容量とから、（１００サイクル目の放電容量／２サイクル目の放電容量×１００）として求めた。得られた結果を表１に示す。
【００６１】
また、充放電を２サイクル行ったのち再度充電を行ったものを、５０℃で１週間保存したのち、放電を行い、引き続き１サイクル充放電を行って、保存後容量維持率を求めた。その際、充電は、１サイクル目では充電時間の総計が２０時間、２，３サイクル目では充電時間の総計が５時間とした以外は上述の条件と同様の条件で行った。放電は、１サイクル目〜４サイクル目のいずれでも上述の条件で行った。保存後容量維持率としては、保存前の２サイクル目の放電容量と保存後の４サイクル目の放電容量とから、（２サイクル目の放電容量／４サイクル目の放電容量×１００）として求めた。得られた結果を表１に示す。
【００６２】
表１から分かるように、Ｍｇ（ＰＦ₆ ）₂ を用いた実施例１−１〜１−４はいずれも、Ｍｇ（ＰＦ₆ ）₂ を用いていない比較例１−１に比べて、容量維持率および保存後容量維持率の両方について高い値が得られた。
【００６３】
また、比較例１−１，１−２を比較すると分かるように、添加剤としてフッ素を含有しない塩を用いた比較例１−２は、比較例１−１に比べて、容量，容量維持率および保存後容量維持率のいずれについても低かった。これは、フッ素を含有しない塩は、上記溶媒に溶解しにくいためと考えられる。
【００６４】
すなわち、電解液がマグネシウムのフッ素含有塩を含むようにすれば、サイクル特性および保存特性を向上させることができることが分かった。
【００６５】
更に、実施例１−１〜１−４から分かるように、容量維持率および保存後容量維持率は、リチウムに対するマグネシウムの含有量が増加すると大きくなり極大値を示したのち小さくなる傾向が見られた。すなわち、マグネシウムの含有量は、リチウムの含有量の２０原子％以下であることが好ましいことが分かった。
【００６６】
（実施例２−１，参考例２−２，２−３，実施例２−４，２−５，参考例２−６〜２−８）
添加剤の種類を表２に示したように変えたことを除き、他は実施例１−２と同様にして二次電池を作製した。実施例２−１，参考例２−２，２−３，実施例２−４，２−５，参考例２−６〜２−８の二次電池についても実施例１−２と同様にして、容量維持率および保存後容量維持率を求めた。その結果を実施例１−２および比較例１−１，１−２の結果と共に表２に示す。
【００６７】
【表２】

【００６８】
表２から分かるように、実施例２−１，参考例２−２，２−３，実施例２−４，２−５，参考例２−６〜２−８は、実施例１−２と同様に、比較例１−１，１−２に比べて、容量維持率および保存後容量維持率の両方について高い値が得られた。また、その効果は、実施例１−２，２−１および参考例２−２，２−３を比較すると、または、実施例２−４，２−５および参考例２−６を比較すると分かるように、ヘキサフルオロリン酸塩またはテトラフルオロホウ酸塩を用いたものにおいて特に大きかった。
【００６９】
すなわち、電解液が２族元素（マグネシウムまたはカルシウム）のフッ素含有塩を含むようにすれば、サイクル特性および保存特性を向上させることができ、特に、上記した２族元素のヘキサフルオロリン酸塩またはテトラフルオロホウ酸塩を含むようにすれば、より高い効果を得ることができることが分かった。
【００７０】
（実施例３−１）
鍍金により、スズ−ニッケル（Ｓｎ−Ｎｉ）合金よりなる負極活物質層２２Ｂを形成したことを除き、他は実施例１−２と同様にして二次電池を作製した。負極活物質層２２Ｂは、具体的には、次のようにして形成した。まず、表面を清浄した圧延銅箔よりなる負極集電体２２Ａをスズ−ニッケル合金鍍金浴中に浸漬して、負極集電体２２Ａをカソードとして通電することにより、スズ−ニッケル合金を厚み約３μｍとなるように析出させた。次いで、それを、水洗し、乾燥させたのち２００℃において２４時間熱処理した。
【００７１】
なお、負極２２の総厚みは２４μｍであった。また、この負極２２についても実施例１−２と同様にしてＸＰＳ（X-ray Photoelectron Spectroscopy；Ｘ線光電子分光法）およびＡＥＳ（ Auger Electron Spectroscopy；オージェ電子分光法）により分析したところ、負極活物質層２２Ｂが、負極集電体２２Ａとの界面の少なくとも一部において負極集電体２２Ａと合金化していることが確認された。
【００７２】
また、実施例３−１に対する比較例３−１として、添加剤を加えなかったことを除き、他は実施例３−１と同様にして二次電池を作製した。作製した実施例３−１および比較例３−１の二次電池についても、実施例１−２と同様にして、容量維持率および保存後容量維持率を求めた。その結果を表３に示す。
【００７３】
【表３】

【００７４】
表３から分かるように、Ｍｇ（ＰＦ₆ ）₂ を用いた実施例３−１は、用いていない比較例３−１に比べて容量維持率および保存後容量維持率の両方について高い値が得られた。すなわち、負極活物質を合金としても、また、負極活物質層２２Ｂを液相法である鍍金により形成しても、電解液に２族元素（マグネシウムまたはカルシウム）のフッ素含有塩を含むようにすれば、サイクル特性および保存特性を向上させることができることが分かった。
【００７５】
（実施例４−１）
電子ビーム蒸着法により、非晶質ケイ素よりなる厚み３μｍの負極活物質層２２Ｂを形成したことを除き、他は実施例１−２と同様にして二次電池を作製した。なお、負極２２の総厚みは２４μｍであった。また、この負極２２についても実施例１−２と同様にしてＸＰＳ（X-ray Photoelectron Spectroscopy；Ｘ線光電子分光法）およびＡＥＳ（ Auger Electron Spectroscopy；オージェ電子分光法）により分析したところ、負極活物質層２２Ｂが、負極集電体２２Ａとの界面の少なくとも一部において負極集電体２２Ａと合金化していることが確認された。
【００７６】
また、実施例４−１に対する比較例４−１として、添加剤を加えなかったことを除き、他は実施例４−１と同様にして二次電池を作製した。作製した実施例４−１および比較例４−１の二次電池についても実施例１−２と同様にして容量維持率および保存後容量維持率を求めた。その結果を表４に示す。
【００７７】
【表４】

【００７８】
表４から分かるように、Ｍｇ（ＰＦ₆ ）₂ を用いた実施例４−１は、用いていない比較例４−１に比べて容量維持率および保存後容量維持率の両方について高い値が得られた。すなわち、負極活物質にケイ素を用いても、電解液に２族元素（マグネシウムまたはカルシウム）のフッ素含有塩を含むようにすれば、サイクル特性および保存特性を向上させることができることが分かった。
【００７９】
なお、上記実施例では、負極活物質層２２Ｂを、電子ビーム蒸着法以外の気相法、電解鍍金以外の液相法、または焼結法により形成しても、同様の結果を得ることができる。更に、上記実施例では、電解液を用いる場合について説明したが、ゲル状の電解質を用いても同様の結果を得ることができる。
【００８０】
以上、実施の形態および実施例を挙げて本発明を説明したが、本発明は上記実施の形態および実施例に限定されるものではなく、種々変形可能である。例えば、上記実施の形態および実施例では、液状の電解質である電解液、またはいわゆるゲル状の電解質を用いる場合について説明したが、他の電解質を用いるようにしてもよい。他の電解質としては、イオン伝導性を有する固体電解質、固体電解質と電解液とを混合したもの、あるいは固体電解質とゲル状の電解質とを混合したものが挙げられる。
【００８１】
また、上記実施の形態および実施例では、負極集電体２２Ａに負極活物質層２２Ｂを形成するようにしたが、負極集電体と負極活物質層との間に、他の層を形成するようにしてもよい。
【００８２】
更に、上記実施の形態および実施例では、負極活物質層２２Ｂを気相法，液相法および焼結法からなる群のうちの少なくとも１つの方法により形成するようにしたが、負極活物質層は、塗布により形成したもの、具体的には、負極活物質と必要に応じてポリフッ化ビニリデンなどの結着剤を含んだものでもよい。但し、気相法，液相法および焼結法からなる群のうちの少なくとも１つの方法により形成したものの方が、塗布により形成したものに比べて表面積が小さので、２族元素（マグネシウムまたはカルシウム）のフッ素含有塩の効果を有効に引き出すことができるので好ましい。
【００８４】
更にまた、上記実施の形態および実施例では、巻回構造を有する円筒型の二次電池について説明したが、本発明は、巻回構造を有する楕円型あるいは多角形型の二次電池、または正極および負極を折り畳んだりあるいは積み重ねた構造を有する二次電池についても同様に適用することができる。また、いわゆる角型，コイン型あるいはボタン型、またはフィルム状の外装部材を用いた他の形状を有する二次電池についても適用することができる。
【００８５】
【発明の効果】
以上説明したように本発明の電解質または二次電池によれば、負極が、ケイ素またはスズの単体および化合物からなる群のうちの少なくとも１種を含むと共に、電解質が、リチウムのフッ素含有塩と、２族元素（マグネシウムまたはカルシウム）のフッ素含有塩とを含み、その２族元素のフッ素含有塩が、ヘキサフルオロリン酸塩およびテトラフルオロホウ酸塩のうちの少なくとも１種を含むようにしたので、２族元素のフッ素含有塩の解離により生じた２族元素のイオンが負極に吸着して吸着層が形成される、あるいは負極において充電時に還元され、薄い被膜が形成される。よって、負極における副反応を抑制することができ、サイクル特性および保存特性を向上させることができる。
【００８６】
特に、本発明の電解質または二次電池では、２族元素の含有量をリチウム原子の含有量の２０原子％以下とするようにすれば、より高い効果を得ることができる。
【００８７】
また、本発明の二次電池では、負極集電体との界面の少なくとも一部において負極集電体と合金化している負極活物質層を有するように、または、負極集電体に気相法，液相法および焼結法からなる群のうちの少なくとも１つの方法により形成された負極活物質層を有するようにすれば、電解質におけるイオンの円滑な移動を妨げることなく、負極に吸着層あるいは薄い被膜を形成することができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る二次電池の構成を表す断面図である。
【図２】図１に示した電極素子の一部を拡大して表す断面図である。
【符号の説明】
１１…電池缶、１２，１３…絶縁板、１４…電池蓋、１５…安全弁機構、１５Ａ…ディスク板、１６…熱感抵抗素子、１７…ガスケット、２０…電極素子、２１…正極、２１Ａ…正極集電体、２１Ｂ…正極活物質層、２２…負極、２２Ａ…負極集電体、２２Ｂ…負極活物質層、２３…セパレータ、２４…センターピン、２５…正極リード、２６…負極リード[0001]
BACKGROUND OF THE INVENTION
  The present invention includes an electrolyte together with a positive electrode and a negative electrode.secondaryThe present invention relates to a battery and an electrolyte used therefor.
[0002]
[Prior art]
With recent advances in electronic technology, small portable electronic devices such as camera-integrated video tape recorders, mobile phones, and laptop computers have been developed, and they are small, lightweight, and have a high energy density as a power source for using them. There is a strong demand for the development of secondary batteries having the following characteristics.
[0003]
So far, secondary batteries using graphite materials using intercalation reaction of lithium (Li) between graphite layers, or carbonaceous materials applying lithium insertion / extraction action into pores as negative electrode active materials Has been developed and widely used.
[0004]
On the other hand, with the recent improvement in performance of portable electronic devices, the demand for the capacity of the secondary battery has become stronger. In addition, with the widespread use of portable electronic devices, various demands on characteristics have been made. For example, as the device usage time becomes longer, higher capacity is required, and further improvement in cycle characteristics is strongly desired so that the battery can be used repeatedly many times. In addition, since battery users' storage conditions are diversified, high performance has been required for storage characteristics.
[0005]
As a battery that meets such a demand, there is a battery that uses a light metal such as lithium metal as a negative electrode active material. However, in this battery, light metal tends to precipitate as dendrite on the negative electrode during the charging process, and the current density becomes very high at the tip of the dendrite, so the life is shortened due to decomposition of the electrolyte and the dendrite grows excessively. As a result, there is a problem that an internal short circuit of the battery occurs.
[0006]
On the other hand, a secondary battery using an alloying reaction between a metal and lithium has been proposed. As a negative electrode active material used for such a secondary battery, there are a lithium-lead alloy (for example, see Patent Documents 1 to 4) and a bismuth soot-lead-cadmium alloy (for example, see Patent Documents 5 and 6). However, the use of lead (Pb), bismuth (Bi) and cadmium (Cd) is not preferable from the viewpoint of global environmental protection in recent years. In addition, an alloy of lithium and silicon (Si) (for example, refer to Patent Documents 7 to 11), an alloy of lithium, aluminum (Al), and tin (Sn) (for example, refer to Patent Document 12), Although there are alloys of tin and zinc (Zn) (see, for example, Patent Document 13), all of them have a drawback that they are greatly expanded and contracted with insertion and extraction of lithium, so that cycle deterioration is severe.
[0007]
In addition, a tin alloy containing 1 mass% to 55 mass% of phosphorus (P) (see, for example, Patent Document 14), a tin-containing phase that occludes lithium, manganese (Mn), iron (Fe), cobalt (Co ), Nickel (Ni) or copper (Cu) containing a mixture with a phase that does not occlude lithium (for example, see Patent Document 15), but these also have sufficient cycle characteristics. Absent. In addition, Cu₂NiSn or Mg₂There is Sn (for example, see Patent Document 16), but Cu₂In NiSn, nickel adversely affects the human body, and Mg₂In Sn, magnesium (Mg) is oxygen (O₂) And generate heat and are difficult to handle in the air. In addition, there is an alloy of tin and copper. However, in a battery using this alloy (for example, see Patent Document 17), the discharge capacity at the first cycle is 300 mAh / g, which is compared with the current carbonaceous material. It was too low to be put to practical use.
[0008]
Thus, while optimization of the composition of the negative electrode active material has been studied, a battery whose characteristics are improved by an additive has also been developed. For example, there is a battery in which an alkaline earth salt, particularly carbonate, oxalate, nitrate, acetate, phosphate, or borate is added to a positive electrode, a negative electrode, or an electrolytic solution (see Patent Document 18).
[0009]
[Patent Document 1]
Japanese Examined Patent Publication No. 3-53743
[Patent Document 2]
Japanese Patent Publication No. 5-34787
[Patent Document 3]
Japanese Patent Publication No. 7-73044
[Patent Document 4]
Japanese Patent Publication No. 8-138654
[Patent Document 5]
Japanese Examined Patent Publication No. 4-47431
[Patent Document 6]
Japanese Examined Patent Publication No. 3-64987
[Patent Document 7]
Japanese Patent Laid-Open No. 7-302588
[Patent Document 8]
JP-A-10-199524
[Patent Document 9]
JP 7-326342 A
[Patent Document 10]
Japanese Patent Laid-Open No. 10-255768
[Patent Document 11]
JP-A-10-302770
[Patent Document 12]
JP-A-61-66369
[Patent Document 13]
Japanese Patent Laid-Open No. Sho 62-145650
[Patent Document 14]
JP-A-8-273602
[Patent Document 15]
Japanese Patent Application Laid-Open No. 11-86854
[Patent Document 16]
Japanese Patent Laid-Open No. 10-223221
[Patent Document 17]
JP-A-10-308207
[Patent Document 18]
JP-A-9-180758
[0010]
[Problems to be solved by the invention]
However, because these salts have low solubility in the electrolyte solution, sufficient effects cannot be obtained even when added to the electrolyte solution, and when added to the positive electrode or the negative electrode, the content of the active material is reduced, the capacity, etc. There is a disadvantage that the gas is decomposed and gas is generated because the carbonate anion and acetate anion constituting the salt are not sufficiently stable against oxidation or reduction atmosphere.
[0011]
  The present invention has been made in view of such problems, and its purpose is to improve cycle characteristics and storage characteristics.secondaryThe object is to provide a battery and an electrolyte used therefor.
[0012]
[Means for Solving the Problems]
[0013]
  An electrolyte according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the negative electrode is used for a secondary battery including at least one member selected from the group consisting of a simple substance and a compound of silicon or tin, a fluorine-containing salt of lithium, and a long period Group 2 elements in the periodic table(Magnesium or calcium)The fluorine-containing salt of the Group 2 element includes at least one of hexafluorophosphate and tetrafluoroborate.
[0014]
  The secondary battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, the negative electrode includes at least one member selected from the group consisting of a simple substance and a compound of silicon or tin, the electrolyte includes a fluorine-containing salt of lithium, a long period Group 2 elements in the periodic table(Magnesium or calcium)The fluorine-containing salt of the Group 2 element includes at least one of hexafluorophosphate and tetrafluoroborate.
[0015]
  In the electrolyte and secondary battery according to the present invention, a group 2 element containing at least one of hexafluorophosphate and tetrafluoroborate(Magnesium or calcium)The fluorine-containing salt of this group dissociates into ions of group 2 elements and fluorine-containing anions, and the ions of group 2 elements are adsorbed on, for example, the negative electrode to form an adsorption layer, or are reduced at the time of charging in the negative electrode to form a thin film It is thought that it is formed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
The electrolyte according to an embodiment of the present invention includes, for example, a solvent and an electrolyte salt dissolved in the solvent. Examples of the solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane. 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propyl nitrile, anisole, acetic acid ester or propionic acid ester can be used. Any one kind of solvent may be used, but two or more kinds may be mixed and used.
[0018]
The electrolyte salt includes a fluorine-containing salt of lithium. It is because the solubility with respect to the said solvent is high and stability is also high. As a fluorine-containing salt of lithium, LiAsF₆, LiPF₆, LiBF_Four, LiCF_ThreeSO_Three, LiN (CF_ThreeSO₂)₂, LiN (C₂F_FiveSO₂)₂Or LiN (C_FourF₉SO₂) (CF_ThreeSO₂Are preferred, among which LiPF₆Or LiBF_FourIs particularly preferred. Any one of the fluorine-containing salts of lithium may be used, or a mixture of two or more may be used.
[0019]
In addition, as the electrolyte salt, a fluorine-containing salt of lithium may be used alone, but in order to obtain characteristics according to the purpose, it may be used by mixing with another electrolyte salt. Examples of other electrolyte salts include LiClO._Four, LiCH_ThreeSO_ThreeLiCl or LiBr is preferred.
[0020]
The electrolyte also contains a fluorine-containing salt of a group 2 element in the long-period periodic table as an additive. Since this fluorine-containing salt has high solubility in the above-described solvent, it dissociates into ions of group 2 elements and fluorine-containing anions in the electrolyte, and the ions of group 2 elements are adsorbed on the negative electrode in, for example, a battery and adsorbed layer This is because it is considered that it is reduced at the time of charging in the negative electrode to form a thin film, thereby suppressing undesirable side reactions in the negative electrode. Another reason is that the fluorine-containing anion is stable in an oxidizing or reducing atmosphere.
[0021]
As a fluorine-containing salt of a group 2 element, Mg (PF₆)₂, Mg (BF_Four)₂, Mg (CF_ThreeSO_Three)₂, Mg [N (CF_ThreeSO₂)₂]₂, Mg [N (C₂F_FiveSO₂)₂]₂, Mg [N (C_FourF₉SO₂) (CF_ThreeSO₂]]₂, Mg [C (CF_ThreeSO₂)₂]_Three, Ca (PF₆)₂, Ca (BF_Four)₂, Ca (CF_ThreeSO_Three)₂, Ca [N (CF_ThreeSO₂)₂]₂, Ca [N (C₂F_FiveSO₂)₂]₂, Ca [N (C_FourF₉SO₂) (CF_ThreeSO₂]]₂Or Ca [C (CF_ThreeSO₂)₂]_ThreeIn particular, Mg (PF₆)₂Or Ca (PF₆)₂Hexafluorophosphate such as Mg or BF_Four)₂Or Ca (BF_Four)₂Most preferred are tetrafluoroborate salts such as It is because it is excellent in stability against oxidation and reduction. In addition, any 1 type may be used for the fluorine-containing salt of a Group 2 element, but 2 or more types may be mixed and used.
[0022]
In this electrolytic solution, the content of the group 2 element is preferably 30 atomic percent or less of the lithium content, and more preferably 20 atomic percent or less. If the amount is too large, for example, when used in a battery as described later, a decrease in battery capacity, a decrease in cycle characteristics, and a storage characteristic are observed. The reason for this is not yet clear, but it is considered that the amount of group 2 element ions reduced on the negative electrode is too large, which inhibits charge and discharge of lithium.
[0023]
The content of the group 2 element is preferably 0.001 atomic% or more of the lithium content, and more preferably 0.01 atomic% or more. It is because the effect mentioned above is not remarkable when there are too few.
[0024]
The electrolyte may be a liquid so-called electrolytic solution composed of these electrolyte salt, solvent, additive, and the like, but may further include a polymer compound that holds them, and may be in the form of a gel. .
[0025]
Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and polyhexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, poly Examples thereof include siloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, and polycarbonate. In particular, from the viewpoint of electrochemical stability, a polymer compound having a polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide structure is preferable.
[0026]
Some of these polymer compounds do not have ionic conductivity, but some of them can dissociate electrolyte salts and have ionic conductivity, either of which may be used. However, the polymer salt that can dissociate the electrolyte salt and has ionic conductivity also functions as a solvent.
[0027]
This electrolyte can be produced, for example, by dissolving a fluorine-containing salt of lithium and a fluorine-containing salt of a group 2 element in a solvent. Moreover, when setting it as a gel form, it can manufacture, for example by mixing and drying this electrolyte solution with a high molecular compound and a dilution solvent. Alternatively, for example, the electrolytic solution can be mixed with a monomer that is a starting material of the polymer compound, and the monomer can be polymerized.
[0028]
This electrolyte is used for a secondary battery as follows, for example.
[0029]
FIG. 1 shows a cross-sectional structure of the secondary battery. This secondary battery is a so-called cylindrical type, and has an electrode element 20 in which a strip-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. is doing. The battery can 11 is made of, for example, iron (Fe) plated with nickel, and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the electrode element 20.
[0030]
At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the electrode element 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.
[0031]
The electrode element 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum or the like is connected to the positive electrode 21 of the electrode element 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.
[0032]
FIG. 2 shows an enlarged part of the electrode element 20 shown in FIG. The positive electrode 21 includes, for example, a positive electrode current collector 21A and a positive electrode active material layer 21B provided on the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, aluminum, nickel, stainless steel, or the like.
[0033]
The positive electrode active material layer 21B includes, for example, a positive electrode active material, and may include a conductive additive such as a carbonaceous material and a binder such as polyvinylidene fluoride as necessary. Examples of the positive electrode active material include a general formula Li_xMIO₂A lithium-containing metal composite oxide represented by This is because the lithium-containing metal composite oxide can generate a high voltage and has a high density, so that it is possible to further increase the capacity of the secondary battery. MI is one or more kinds of transition metals, and for example, at least one of cobalt and nickel is preferable. x varies depending on the charge / discharge state of the battery and is usually a value in the range of 0.05 ≦ x ≦ 1.10. As a specific example of such a lithium-containing metal composite oxide, LiCoO₂Or LiNiO₂Etc. In addition, any 1 type may be used for a positive electrode active material, and 2 or more types may be mixed and used for it.
[0034]
The negative electrode 22 includes, for example, a negative electrode current collector 22A and a negative electrode active material layer 22B provided on the negative electrode current collector 22A. The negative electrode current collector 22A is preferably made of, for example, copper, stainless steel, nickel, titanium (Ti), tungsten (W), molybdenum (Mo), aluminum, or the like, and in particular, alloyed with the negative electrode active material layer 22B. In some cases, it may be more preferable to use a metal that is likely to cause oxidization. For example, as will be described later, when the negative electrode active material layer 22B includes at least one member selected from the group consisting of a simple substance and a compound of silicon or tin, copper, titanium, aluminum, nickel, or the like can be cited as a material that is easily alloyed. . The negative electrode current collector 22A may be composed of a single layer, but may be composed of a plurality of layers. In that case, the layer in contact with the negative electrode active material layer 22B may be made of a metal material that is easily alloyed with the negative electrode active material layer 22B, and the other layers may be made of another metal material.
[0035]
The negative electrode active material layer 22B is formed by, for example, at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method, and includes a negative electrode active material. Thereby, it is possible to suppress destruction due to expansion / contraction of the negative electrode active material layer 22B due to charge / discharge, and it is possible to integrate the negative electrode current collector 22A and the negative electrode active material layer 22B. The conductivity can be improved. In addition, the coating type negative electrode formed by coating the negative electrode active material layer, specifically, unlike the conventional coating type negative electrode including the negative electrode active material and a binder such as polyvinylidene fluoride as necessary, the binding type Agents and voids can be reduced or eliminated, and a thin film can be formed.
[0036]
The negative electrode active material layer 22B is preferably alloyed with the negative electrode current collector 22A at least at a part of the interface with the negative electrode current collector 22A. Specifically, it is preferable that the constituent element of the negative electrode current collector 22A is diffused in the negative electrode active material layer 22B, the constituent element of the negative electrode active material is diffused in the negative electrode current collector 22A, or they are mutually diffused at the interface. This alloying often occurs simultaneously with the formation of the anode active material layer 22B by a vapor phase method, a liquid phase method, or a sintering method, but it may also occur by further heat treatment. Note that in this specification, the above-described element diffusion is also included in one form of alloying.
[0037]
The negative electrode active material preferably contains at least one member selected from the group consisting of a simple substance and a compound of silicon or tin. The simple substance and compound of silicon or tin can form an alloy with lithium and have a large ability to occlude and release lithium. Depending on the combination, the energy density of the negative electrode 22 may be higher than that of conventional graphite. Because it can. The silicon or tin compound may be crystalline or amorphous, but is preferably an amorphous or microcrystalline aggregate. The term “amorphous” or “microcrystal” as used herein means that the half width of the peak of a diffraction pattern obtained by X-ray diffraction analysis using CuKα as characteristic X-rays is 0.5 ° or more at 2θ and 30 at 2θ. It has a broad pattern from ° to 60 °.
[0038]
Examples of silicon or tin compounds include SiB_Four, SiB₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu_FiveSi, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si_ThreeN_Four, Si₂N₂O, SiO_a(0 <a ≦ 2), SnO_b(0 <b ≦ 2), SnSiO_ThreeLiSiO or LiSnO.
[0039]
The thickness of the negative electrode 22 including the thickness of the negative electrode current collector 22A is preferably 10 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less. If it is too thin, the proportion of the negative electrode current collector 22A in the negative electrode 22 increases, and a decrease in battery capacity is observed. On the other hand, if it is too thick, the negative electrode active material layer 22B is caused by silicon or tin expansion / contraction due to charge / discharge. This is because there is a case where the destruction of this occurs.
[0040]
The separator 23 is for preventing a short circuit due to physical contact between the positive electrode 21 and the negative electrode 22 while allowing lithium ions to pass through, and is made of, for example, a microporous polyolefin film such as a polyethylene film or a polypropylene film. ing. This separator 23 preferably has a function of blocking the current by closing the hole at 120 ° C. or higher for ensuring safety and cutting off the current.
[0041]
The separator 23 is impregnated with the electrolyte according to the present embodiment. As a result, in this secondary battery, ions of group 2 elements in the electrolyte are adsorbed on the negative electrode 22 to form an adsorption layer, or are reduced at the time of charging in the negative electrode 22 to form a thin film, which is not preferable in the negative electrode 22. Side reactions are suppressed. In particular, when the fluorine-containing salt of the group 2 element is present in an excessive amount in the electrolyte, there is a risk of hindering the smooth movement of lithium ions, but the negative electrode 22 according to the present embodiment has the negative electrode active material layer 22B. At least part of the interface with the negative electrode current collector 22A is alloyed with the negative electrode current collector 22A, or formed by at least one method of the group consisting of a vapor phase method, a liquid phase method, and a sintering method. Since the surface area is relatively small, an effective adsorption layer or film can be formed on the anode 22 without using a large amount of a fluorine-containing salt of a Group 2 element. In addition, it is thought that the thickness of this adsorption layer or a film is a thing which does not inhibit the entrance / exit of lithium to the negative electrode 22, and can suppress a side reaction.
[0042]
For example, the secondary battery can be manufactured as follows.
[0043]
First, for example, a positive electrode active material, a conductive additive, and a binder are mixed to prepare a positive electrode mixture, and then the positive electrode mixture is dispersed in a dispersion medium such as N-methyl-2-pyrrolidone. A slurry is obtained. Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 21A and dried, and then compression-molded to form the positive electrode active material layer 21B to produce the positive electrode 21.
[0044]
Next, the negative electrode active material layer 22B is deposited on the negative electrode current collector 22A by depositing at least one member selected from the group consisting of a simple substance and a compound of silicon or tin, for example, on the negative electrode current collector 22A by a vapor phase method or a liquid phase method. Form. Further, after forming a precursor layer containing a particulate negative electrode active material on the negative electrode current collector 22A, the negative electrode active material layer 22B may be formed by a sintering method in which the precursor layer is sintered. The negative electrode active material layer 22B may be formed by combining two or three of the phase method and the sintering method. Thus, by forming the negative electrode active material layer 22B by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method, in some cases, at least at the interface with the negative electrode current collector 22A In part, a negative electrode active material layer 22B alloyed with the negative electrode current collector 22A is formed. Note that in order to further alloy the interface between the negative electrode current collector 22A and the negative electrode active material layer 22B, heat treatment may be further performed in a vacuum atmosphere or a non-oxidizing atmosphere. In particular, when the negative electrode active material layer 22B is formed by plating, which will be described later, the negative electrode active material layer 22B may be difficult to be alloyed even at the interface with the negative electrode current collector 22A. preferable. In addition, even in the case of forming by the vapor phase method, the characteristics may be improved by alloying the interface between the negative electrode current collector 22A and the negative electrode active material layer 22B. It is preferable to perform a heat treatment.
[0045]
As the vapor phase method, a physical deposition method or a chemical deposition method can be used depending on the type of the negative electrode active material. Specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, a thermal CVD method, or the like. (Chemical Vapor Deposition; chemical vapor deposition) method or plasma CVD method can be used. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. As for the sintering method, a known method can be used, for example, an atmosphere sintering method, a reaction sintering method, or a hot press sintering method can be used. However, vacuum deposition, sputtering, CVD, electrolytic plating or electroless plating is preferable.
[0046]
After producing the positive electrode 21 and the negative electrode 22, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, an electrolyte is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is completed.
[0047]
In this secondary battery, when charged, lithium ions are released from the positive electrode 21 and inserted in the negative electrode 22 through the electrolyte. On the other hand, when discharging is performed, for example, lithium ions are separated from the negative electrode 22 and inserted into the positive electrode 21 through the electrolyte. In this embodiment, since the electrolyte contains a fluorine-containing salt of a group 2 element, ions of the group 2 element generated by dissociation of the fluorine-containing salt of the group 2 element are adsorbed on the negative electrode 22 to form an adsorption layer. Alternatively, it is reduced at the time of charging in the negative electrode 22 to form a thin film, and side reactions in the negative electrode 22 are suppressed.
[0048]
As described above, in the present embodiment, since the electrolyte contains the fluorine-containing salt of the group 2 element, the ions of the group 2 element generated by the dissociation of the fluorine-containing salt of the group 2 element are adsorbed on the negative electrode 22 and adsorbed. A layer is formed or reduced at the time of charging in the negative electrode 22 to form a thin film. Therefore, side reactions in the negative electrode 22 can be suppressed, and cycle characteristics and storage characteristics can be improved.
[0049]
In particular, if the content of the group 2 element is 20 atomic% or less of the lithium content, or the electrolyte is a fluorine-containing salt of the group 2 element, hexafluorophosphate and tetrafluoroborate If at least one of them is included, a higher effect can be obtained.
[0050]
Furthermore, the negative electrode 22 has a negative electrode active material layer 22B provided on the negative electrode current collector 22A and alloyed with the negative electrode current collector 22A at least at a part of the interface with the negative electrode current collector 22A. If the negative electrode active material layer 22B formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method is provided in the electric body 22A, smooth lithium ion movement is prevented. In addition, an adsorption layer or a thin film can be formed on the negative electrode 22.
[0051]
The secondary battery according to the present embodiment includes, for example, a headphone stereo, a video deck, a liquid crystal television, a portable CD (compact disc) player, an MD (mini disc) player, a notebook personal computer, a mobile phone, and an electric shaver. , Transceivers, electronic notebooks, calculators, radios, toys, game machines, watches, pacemakers, etc. Furthermore, it can also be used in combination with a generator such as a solar cell or a fuel cell.
[0052]
【Example】
Furthermore, specific embodiments of the present invention will be described in detail with reference to FIGS.
[0053]
(Examples 1-1 to 1-4)
First, LiNi with an average secondary particle size of 15 μm, which is a positive electrode active material_0.8Co_0.19Al_0.01O₂A positive electrode mixture was prepared by mixing 91% by mass, 6% by mass of graphite as a conductive additive, and 3% by mass of polyvinylidene fluoride as a binder, and this positive electrode mixture was then mixed with N-methyl-2. -Dispersed in pyrrolidone to obtain a positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to a positive electrode current collector 21A made of aluminum having a thickness of 20 μm, dried, and compression-molded with a roller press to form the positive electrode active material layer 21B, thereby producing the positive electrode 21. . After that, a positive electrode lead 25 having an insulating tape attached to one end of the positive electrode current collector 21A was attached.
[0054]
Further, after forming a 3 μm thick layer of tin by electron beam evaporation on both surfaces of the negative electrode current collector 22A of 18 μm thick made of electrolytic copper foil, 1 × 10 1^-FiveTorr (approximately 1.33 × 10^-3A negative electrode active material layer 22B was formed by heat treatment at 200 ° C. for 24 hours at a degree of vacuum of Pa), and a negative electrode 22 having a total thickness of 24 μm was produced. When the obtained negative electrode 22 was analyzed by XPS (X-ray Photoelectron Spectroscopy) and AES (Auger Electron Spectroscopy), the negative electrode active material layer 22B and the negative electrode current collector 22A were analyzed. It was confirmed that at least a part of the interface was alloyed with the negative electrode current collector 22A. After producing the negative electrode 22, a negative electrode lead 26 was attached to one end of the negative electrode current collector 22A.
[0055]
Subsequently, the positive electrode 21 and the negative electrode 22 were laminated | stacked via the separator 23 which consists of a 30-micrometer-thick microporous polyethylene film, and the electrode element 20 was produced by winding up this.
[0056]
After producing the electrode element 20, the electrode element 20 is sandwiched between the pair of insulating plates 12 and 13, the positive electrode lead 25 is welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to the battery can 11. It was stored in an iron battery can 11. After that, the center pin 24 was inserted into the center of the electrode element 20. Next, an electrolytic solution was injected into the battery can 11. The electrolyte includes LiPF, which is an electrolyte salt, in a solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 1.₆And additive Mg (PF₆)₂The thing which added and was used. At that time, LiPF₆The content of was 1 mol / l. Mg (PF₆)₂The content of was changed as shown in Table 1 in Examples 1-1 to 1-4. That is, the content of magnesium in the electrolytic solution is the value shown in Table 1 in Examples 1-1 to 1-4 with respect to lithium.
[0057]
[Table 1]

[0058]
After injecting the electrolyte into the battery can 11, the battery lid 14 is caulked to the battery can 11 via the gasket 17, so that the cylinders of Examples 1-1 to 1-4 have a diameter of 18 mm and a height of 65 mm. A secondary battery was obtained.
[0059]
As Comparative Example 1-1 with respect to Examples 1-1 to 1-4, a secondary battery was fabricated in the same manner as Example 1-2, except that no additive was added. Further, as Comparative Example 1-2 for Examples 1-1 to 1-4, MgCl as an additive₂A secondary battery was fabricated in the same manner as in Example 1-2 except that was used.
[0060]
About the produced secondary battery of Examples 1-1 to 1-4 and Comparative Examples 1-1 and 1-2, 100 cycles of charging / discharging was performed, and the capacity retention rate was obtained. At that time, charging is performed at a constant current of 1 A until the battery voltage reaches 4.2 V, and then at a constant voltage of 4.2 V, the total charging time is 20 hours for the first cycle, and 5 hours for the second and subsequent cycles. Discharge was performed until the battery voltage reached 2.5 V at a constant current of 1.5 A in any of the first to 100th cycles. The capacity retention rate was determined as (discharge capacity at 100th cycle / discharge capacity at second cycle × 100) from the discharge capacity at the second cycle and the discharge capacity at the 100th cycle. The obtained results are shown in Table 1.
[0061]
Moreover, after charging / discharging for 2 cycles, what was charged again was preserve | saved at 50 degreeC for 1 week, discharged, and 1 cycle charging / discharging was performed continuously, and the capacity | capacitance maintenance factor after a preservation | save was calculated | required. At that time, the charging was performed under the same conditions as described above except that the total charging time was 20 hours in the first cycle and the total charging time was 5 hours in the second and third cycles. The discharge was performed under the above conditions in any of the first to fourth cycles. The capacity retention rate after storage was calculated as (second cycle discharge capacity / fourth cycle discharge capacity × 100) from the second cycle discharge capacity before storage and the fourth cycle discharge capacity after storage. . The obtained results are shown in Table 1.
[0062]
As can be seen from Table 1, Mg (PF₆)₂In Examples 1-1 to 1-4 using Mg, Mg (PF₆)₂Higher values were obtained for both the capacity retention ratio and the post-storage capacity retention ratio as compared to Comparative Example 1-1 in which no was used.
[0063]
Further, as can be seen by comparing Comparative Examples 1-1 and 1-2, Comparative Example 1-2 using a salt that does not contain fluorine as an additive is higher in capacity and capacity retention than Comparative Example 1-1. In addition, both of the capacity retention ratios after storage were low. This is presumably because a salt containing no fluorine is difficult to dissolve in the solvent.
[0064]
That is, it has been found that cycle characteristics and storage characteristics can be improved if the electrolyte contains a fluorine-containing salt of magnesium.
[0065]
Furthermore, as can be seen from Examples 1-1 to 1-4, the capacity retention rate and the post-storage capacity retention rate tend to increase as the magnesium content relative to lithium increases and then show a maximum value and then decrease. It was. That is, it was found that the magnesium content is preferably 20 atomic% or less of the lithium content.
[0066]
(Example 2-1Reference Examples 2-2, 2-3, Examples 2-4, 2-5, Reference Example 2-6~ 2-8)
  A secondary battery was fabricated in the same manner as in Example 1-2, except that the type of additive was changed as shown in Table 2. Example 2-1Reference Examples 2-2, 2-3, Examples 2-4, 2-5, Reference Examples 2-6 toFor the secondary battery of 2-8, the capacity retention rate and the post-storage capacity retention rate were determined in the same manner as in Example 1-2. The results are shown in Table 2 together with the results of Example 1-2 and Comparative Examples 1-1 and 1-2.
[0067]
[Table 2]

[0068]
  As can be seen from Table 2, Example 2-1Reference Examples 2-2, 2-3, Examples 2-4, 2-5, Reference Example 2-6As for Example 2-8, the high value was obtained about both the capacity | capacitance maintenance factor and the capacity | capacitance maintenance factor after a preservation | save compared with Comparative Examples 1-1 and 1-2 similarly to Example 1-2. The effect is also the same as in Examples 1-2 and 2-1.And Reference Example 2-2Compare 2-3, or Example 2-4, 2-5 and reference examplesAs can be seen by comparing 2-6, it was particularly large in those using hexafluorophosphate or tetrafluoroborate.
[0069]
  That is, the electrolyte is a group 2 element(Magnesium or calcium)If the fluorine-containing salt is included, cycle characteristics and storage characteristics can be improved.AboveIt has been found that a higher effect can be obtained by including a hexafluorophosphate or tetrafluoroborate of a group 2 element.
[0070]
(Example 3-1)
A secondary battery was fabricated in the same manner as in Example 1-2, except that the anode active material layer 22B made of a tin-nickel (Sn—Ni) alloy was formed by plating. Specifically, the negative electrode active material layer 22B was formed as follows. First, a negative electrode current collector 22A made of rolled copper foil having a cleaned surface is immersed in a tin-nickel alloy plating bath, and the negative electrode current collector 22A is energized as a cathode, whereby the tin-nickel alloy has a thickness of about 3 μm. It was made to precipitate so that it might become. Next, it was washed with water, dried and then heat treated at 200 ° C. for 24 hours.
[0071]
The total thickness of the negative electrode 22 was 24 μm. The negative electrode 22 was analyzed by XPS (X-ray Photoelectron Spectroscopy) and AES (Auger Electron Spectroscopy) in the same manner as in Example 1-2. It was confirmed that the layer 22B was alloyed with the negative electrode current collector 22A at least at a part of the interface with the negative electrode current collector 22A.
[0072]
Further, as Comparative Example 3-1, compared with Example 3-1, a secondary battery was fabricated in the same manner as Example 3-1, except that the additive was not added. For the fabricated secondary batteries of Example 3-1 and Comparative Example 3-1, the capacity retention rate and the post-storage capacity retention rate were determined in the same manner as in Example 1-2. The results are shown in Table 3.
[0073]
[Table 3]

[0074]
  As can be seen from Table 3, Mg (PF₆)₂In Example 3-1 using, a higher value was obtained for both the capacity retention rate and the post-storage capacity retention rate than Comparative Example 3-1, which was not used. That is, even if the negative electrode active material is an alloy, and the negative electrode active material layer 22B is formed by plating which is a liquid phase method, the group 2 element is contained in the electrolytic solution.(Magnesium or calcium)It was found that the cycle characteristics and the storage characteristics can be improved by including the fluorine-containing salt.
[0075]
(Example 4-1)
A secondary battery was fabricated in the same manner as in Example 1-2, except that the negative electrode active material layer 22B made of amorphous silicon was formed by electron beam evaporation. The total thickness of the negative electrode 22 was 24 μm. The negative electrode 22 was analyzed by XPS (X-ray Photoelectron Spectroscopy) and AES (Auger Electron Spectroscopy) in the same manner as in Example 1-2. It was confirmed that the layer 22B was alloyed with the negative electrode current collector 22A at least at a part of the interface with the negative electrode current collector 22A.
[0076]
Further, as Comparative Example 4-1 with respect to Example 4-1, a secondary battery was fabricated in the same manner as in Example 4-1, except that the additive was not added. For the fabricated secondary batteries of Example 4-1 and Comparative Example 4-1, the capacity retention ratio and the post-storage capacity retention ratio were determined in the same manner as in Example 1-2. The results are shown in Table 4.
[0077]
[Table 4]

[0078]
  As can be seen from Table 4, Mg (PF₆)₂In Example 4-1, which used, a higher value was obtained for both the capacity retention rate and the post-storage capacity retention rate than Comparative Example 4-1, which was not used. That is, even if silicon is used for the negative electrode active material, the group 2 element is used in the electrolyte.(Magnesium or calcium)It was found that the cycle characteristics and the storage characteristics can be improved by including the fluorine-containing salt.
[0079]
  In the above embodiment,,negativeSimilar results can be obtained even if the polar active material layer 22B is formed by a vapor phase method other than the electron beam evaporation method, a liquid phase method other than electrolytic plating, or a sintering method. Furthermore, although the case where the electrolytic solution is used has been described in the above embodiment, the same result can be obtained even when a gel electrolyte is used.
[0080]
Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the case where an electrolytic solution which is a liquid electrolyte or a so-called gel electrolyte is used has been described, but another electrolyte may be used. Examples of other electrolytes include solid electrolytes having ionic conductivity, a mixture of a solid electrolyte and an electrolyte solution, and a mixture of a solid electrolyte and a gel electrolyte.
[0081]
In the above embodiment and examples, the negative electrode active material layer 22B is formed on the negative electrode current collector 22A. However, another layer is formed between the negative electrode current collector and the negative electrode active material layer. You may do it.
[0082]
  Furthermore, in the above embodiment and example, the negative electrode active material layer 22B is formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method. May be formed by coating, specifically, may include a negative electrode active material and, if necessary, a binder such as polyvinylidene fluoride. However, since the surface area of the one formed by at least one of the group consisting of the vapor phase method, the liquid phase method, and the sintering method is smaller than that formed by coating, the group 2 element(Magnesium or calcium)This is preferable because the effect of the fluorine-containing salt can be effectively brought out.
[0084]
  Furthermore, in the above embodiments and examples, a cylindrical secondary battery having a winding structure has been described. However, the present invention relates to an elliptical or polygonal secondary battery having a winding structure, or a positive electrode. The present invention can be similarly applied to a secondary battery having a structure in which the negative electrode is folded or stacked. Further, it can be applied to a secondary battery having a so-called square shape, coin shape, button shape, or other shape using a film-shaped exterior member..
[0085]
【The invention's effect】
  As described above, according to the electrolyte or secondary battery of the present invention, the negative electrode includes at least one member selected from the group consisting of a simple substance and a compound of silicon or tin, and the electrolyte includes a fluorine-containing salt of lithium, Group 2 element(Magnesium or calcium)And the fluorine-containing salt of the group 2 element contains at least one of hexafluorophosphate and tetrafluoroborate, so that the fluorine-containing salt of the group 2 element Group II element ions generated by dissociation are adsorbed on the negative electrode to form an adsorbed layer, or reduced at the time of charging in the negative electrode to form a thin film. Therefore, side reactions in the negative electrode can be suppressed, and cycle characteristics and storage characteristics can be improved.
[0086]
  In particular,The present inventionOf electrolyte orsecondarybatteryThenThe content of group 2 elements should be 20 atomic percent or less of the lithium atom content.if,A higher effect can be obtained.
[0087]
  Also,The present inventionofsecondarybatteryThenThe negative electrode current collector has a negative electrode active material layer alloyed with the negative electrode current collector at least at a part of the interface with the negative electrode current collector, or the negative electrode current collector is obtained from a vapor phase method, a liquid phase method, and a sintering method. So as to have a negative electrode active material layer formed by at least one method of the groupifAn adsorption layer or a thin film can be formed on the negative electrode without hindering the smooth movement of ions in the electrolyte.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the invention.
2 is an enlarged cross-sectional view showing a part of the electrode element shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disk board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20 ... Electrode element, 21 ... Positive electrode, 21A ... Positive electrode Current collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode current collector, 22B ... Negative electrode active material layer, 23 ... Separator, 24 ... Center pin, 25 ... Positive electrode lead, 26 ... Negative electrode lead

Claims (9)

An electrolyte is provided with a positive electrode and a negative electrode,
The negative electrode includes at least one selected from the group consisting of a simple substance and a compound of silicon (Si) or tin (Sn),
The electrolyte includes a fluorine-containing salt of lithium and a fluorine-containing salt of a group 2 element (magnesium or calcium) in the long-period periodic table,
The fluorine-containing salt of the group 2 element includes at least one of hexafluorophosphate and tetrafluoroborate. The fluorine-containing salts of lithium include LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiN (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ), and the fluorine-containing salt of the group 2 element is Mg (PF ₆ ) ₂ , Ca (PF ₆ ) ₂ , Mg (BF ₄ ) _2. The secondary battery according to claim 1, comprising at least one member selected from the group consisting of Ca (BF ₄ ) ₂ and Ca (BF ₄ ) ₂ .   The secondary battery according to claim 1, wherein a content of the group 2 element in the electrolyte is 20 atomic% or less of a content of the lithium.   The secondary battery according to claim 1, wherein the negative electrode has a thickness of 10 μm to 100 μm.   The negative electrode has a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector and alloyed with the negative electrode current collector at least at a part of an interface with the negative electrode current collector. The secondary battery as described. The negative electrode has a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector by at least one method selected from the group consisting of a gas phase method, a liquid phase method, and a sintering method. The secondary battery according to 1. An electrolyte is provided together with a positive electrode and a negative electrode, and the negative electrode is used for a secondary battery including at least one member selected from the group consisting of a simple substance and a compound of silicon or tin,
A fluorine-containing salt of lithium, and a fluorine-containing salt of a group 2 element (magnesium or calcium) in the long-period periodic table,
The fluorine-containing salt of the group 2 element includes at least one of hexafluorophosphate and tetrafluoroborate. The fluorine-containing salts of lithium include LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiN (C ₄ F ₉ SO _2. ) (CF ₃ SO ₂ ), and the fluorine-containing salt of the group 2 element is Mg (PF ₆ ) ₂ , Ca (PF ₆ ) ₂ , Mg (BF ₄ ) _2. The electrolyte according to claim 7, comprising at least one member selected from the group consisting of Ca (BF ₄ ) ₂ and Ca (BF ₄ ) ₂ .   The electrolyte according to claim 7, wherein the content of the Group 2 element is 20 atomic% or less of the content of lithium.

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