JP4224987B2 - Non-aqueous electrolyte battery - Google Patents

Description

【００６２】
なお、各実施例及び各比較例では、高温保存後の放電容量維持率を以下のようにして測定した。各実施例及び各比較例における高温貯蔵後の放電容量維持率を測定する際は、各実施例及び各比較例の電池に対し、２３℃雰囲気中、１Ｃ、上限電圧４．２Ｖの定電流定電圧充電を２．５時間行った後に、２３℃雰囲気中、１Ｃの電流値で３Ｖまでの定電流放電を行い、初回放電容量を測定した。次に、各実施例及び各比較例の電池を、８５℃雰囲気中で４０時間保存した後に、初回の充放電と同様の条件で充放電を行い、高温保存後の放電容量を測定した。そして、高温保存後の放電容量維持率は、以上のようにして測定した初回放電容量に対する高温保存後の放電容量の比率である。
【００６３】
表１に示す評価結果から、非水電解液にＬｉＢＦ_４を０．０１モル／リットル以上、０．１モル／リットル以下の範囲で含有させた実施例１〜実施例３では、非水電解液にＬｉＢＦ_４を含有させていない比較例１に比べ、高温保存後の放電容量維持率が大きくなっていることわかる。
【００６４】
比較例１では、非水電解液にＬｉＢＦ_４が含有されていないことから、高温保存した際に正極と非水電解液が反応して非水電解液が分解し、非水電解液が劣化することから、高温保存後の電池容量が低下してしまう。
【００６５】
また、表１に示す評価結果から、非水電解液にＬｉＢＦ_４を０．０１モル／リットル以上、０．１モル／リットル以下の範囲で含有させた実施例１〜実施例３では、非水電解液にＬｉＢＦ_４を０．１５モル／リットル含有させた比較例２に比べ、高温保存後の放電容量維持率が大きくなっていることわかる。
【００６６】
比較例２では、非水電解液に含有されるＬｉＢＦ_４の量が多すぎて、充放電及び高温保存された際に負極表面にホウ素化合物が被膜として形成されてしまう。これにより、比較例２では、負極表面に形成されたホウ素化合物の被膜がリチウムイオンの移動を妨げることから、高温保存後の電池容量が小さくなる。
【００６７】
これらの比較例に対し、実施例１〜実施例３では、非水電解液に含有されるＬｉＢＦ_４が０．０１モル／リットル以上、０．１モル／リットル以下の範囲であり、ＬｉＢＦ_４の含有量が適切であることから、高温保存された際の非水電解液の分解を抑えると共に、負極表面にホウ素化合物の被膜が形成されてしまうことを防ぐことができる。したがって、実施例１〜実施例３では、高温保存後の電池容量を低下することが防止されて高温保存後の放電容量維持率が大きくなる。
【００６８】
以上のことから、電池を作製する際に、非水電解液にＬｉＢＦ_４を０．０１モル／リットル以上、０．１モル／リットル以下の範囲で含有させることは、高温保存後の電池容量の低下が防止された優れた電池を製造する上で大変有効であることがわかる。
【００６９】
さらに、表１に示す評価結果から、正極活物質にリチウム・ニッケル複合酸化物とリチウム・マンガン複合酸化物との混合物を用いた実施例１〜実施例５では、正極活物質をリチウム・ニッケル複合酸化物だけとする比較例３に比べ、高温保存後の放電容量維持率が大きくなっていることわかる。
【００７０】
比較例３では、正極活物質とするリチウム・ニッケル複合酸化物が電池容量を大きくするものの、充電状態においては非水電解液との反応性が高く、非水電解液の酸化分解により高温保存後の容量が低下してしまう。
【００７１】
さらにまた、表１に示す評価結果から、正極活物質にリチウム・ニッケル複合酸化物とリチウム・マンガン複合酸化物との混合物を用いた実施例１〜実施例５では、正極活物質をリチウム・マンガン複合酸化物だけとする比較例４に比べ、高温保存後の放電容量維持率が大きくなっていることわかる。
【００７２】
比較例４では、正極活物質とするリチウム・マンガン複合酸化物が非水電解液との反応性は比較的低いものの、高温保存の際に非水電解液に含まれる酸の影響でＭｎの価数が変化しやすく、高温保存後の電池容量が低下してしまう。
【００７３】
これらの比較例に対し、実施例１〜実施例５では、正極活物質に用いたリチウム・ニッケル複合酸化物とリチウム・マンガン複合酸化物との混合物のうち、リチウム・ニッケル複合酸化物が電池容量を大きくし、更に非水電解液中の酸の生成も抑制するため、リチウム・マンガン複合酸化物の高温保存による劣化を抑制する。また、実施例１〜実施例５では、正極活物質に用いたリチウム・マンガン複合酸化物が電解液の酸化反応を低下させる。これにより、実施例１〜実施例５では、高温保存後の電池容量を低下することが防止されて高温保存後の放電容量維持率が大きくなる。
【００７４】
以上のことから、電池を作製する際に、正極活物質をしてリチウム・ニッケル複合酸化物とリチウム・マンガン複合酸化物との混合物を用いることは、高温保存後の電池容量の低下が防止された優れた電池を製造する上で大変有効であることがわかる。
【００７５】
【発明の効果】
以上の説明から明らかなように、本発明によれば、正極活物質にリチウム・ニッケル複合酸化物とリチウム・マンガン複合酸化物との混合物を用いることで高いエネルギー密度と高い安全性とが図られつつ、電解質塩にＬｉＢＦ_４を含有させることで高温保存時に正極と非水電解質とが反応して非水電解質が劣化することを抑制できる。したがって、本発明によれば、高いエネルギー密度と、高い安全性と、高温保存による電池特性の低下がない優れた高温保存特性とを兼ね備えた非水電解質電池を得ることができる。
【図面の簡単な説明】
【図１】本発明に係るリチウムイオン二次電池の内部構造を示す断面図である。
【符号の説明】
１ リチウムイオン二次電池、２ 電池素子、３ 外装缶、４ 非水電解液、５ 正極、６ 負極、７ セパレータ、８ 正極集電体、９ 正極合剤層、１０正極端子、１１ 負極集電体、１２ 負極合剤層、１３ 負極端子、１４ａ，１４ｂ 絶縁板、１５ 電流遮断用薄板、１６ 電池蓋、１７ 絶縁ガスケット、１８ センターピン、１９ 安全弁、２０ ＰＴＣ素子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nonaqueous electrolyte battery that includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, and whose battery characteristics are greatly improved.
[0002]
[Prior art]
In recent years, for example, a lightweight and high energy density secondary battery has been developed as a power source for electronic devices such as a notebook personal computer, a portable phone, and a camera-integrated VTR (video tape recorder). Examples of the secondary battery having a high energy density include a lithium ion secondary battery having an energy density higher than that of a lead battery, a nickel cadmium battery, a nickel hydrogen battery, or the like.
[0003]
In this lithium ion secondary battery, a negative electrode active material such as a carbonaceous material capable of intercalating lithium ions between carbon materials such as graphite is used for the negative electrode, and the crystal structure is stable for the positive electrode. A positive electrode active material such as lithium-cobalt composite oxide that can increase the battery capacity is used. In this lithium ion secondary battery, a battery reaction is performed by moving lithium ions between a negative electrode and a positive electrode by a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent. However, in this lithium ion secondary battery, the lithium-cobalt composite oxide used for the positive electrode active material has a problem that the resource of cobalt is scarce.
[0004]
Further, in the lithium ion secondary battery, it is also possible to use a lithium / nickel composite oxide instead of the lithium / cobalt composite oxide which is scarce in resources as the positive electrode active material. The lithium-nickel composite oxide has a larger battery capacity per unit volume than the lithium-cobalt composite oxide, and can achieve a higher energy density. However, the lithium-nickel composite oxide has a relatively unstable crystal structure, which may reduce battery safety.
[0005]
[Problems to be solved by the invention]
In order to solve the above-described problems, a lithium ion secondary battery using a mixture of a lithium / nickel composite oxide and a lithium / manganese composite oxide as a positive electrode active material has also been proposed. A lithium ion secondary battery using such a positive electrode active material can have both high energy density, which is an advantage of a lithium / nickel composite oxide, and high safety, which is an advantage of a lithium / manganese composite oxide. .
[0006]
However, in this lithium ion secondary battery, when stored at a high temperature, the positive electrode using a mixture of a lithium / nickel composite oxide and a lithium / manganese composite oxide as a positive electrode active material reacts with the non-aqueous electrolyte. The battery characteristics may be deteriorated, for example, the non-aqueous electrolyte is deteriorated by oxidative decomposition and the battery capacity is reduced.
[0007]
Therefore, the present invention has been proposed in view of such a conventional situation, and an object thereof is to provide a nonaqueous electrolyte battery in which deterioration of battery characteristics due to high-temperature storage is prevented.
[0008]
[Means for Solving the Problems]
The nonaqueous electrolyte battery according to the present invention includes LiBF as an electrolyte salt in the nonaqueous electrolyte.₄By containing, the battery characteristics are prevented from deteriorating when stored at high temperature.
[0009]
  That is, the nonaqueous electrolyte battery according to the present invention includes a positive electrode including a positive electrode mixture layer having a positive electrode active material capable of doping / dedoping lithium, and a negative electrode having a negative electrode active material capable of doping / dedoping lithium. A negative electrode including a mixture layer and a non-aqueous electrolyte containing an electrolyte salt, wherein the positive electrode active material is a mixture of a lithium / nickel composite oxide and a lithium / manganese composite oxide,The negative electrode active material is graphite,The electrolyte salt is LiPF₆And LiBF₄Containing at leastAnd the above LiBF ₄ Is contained in the range of 0.01 mol / liter or more and 0.1 mol / liter or less..
[0010]
  In this non-aqueous electrolyte battery, high energy density and high safety are achieved by using a mixture of lithium / nickel composite oxide and lithium / manganese composite oxide as the positive electrode active material,Using negative electrode active material and highly reactive graphite with electrolyte,LiPF as electrolyte salt₆And LiBF₄ContainsAnd LiBF ₄ Is contained in the range of 0.01 mol / liter or more and 0.1 mol / liter or less.LiPF₆Efficiently moves lithium ions, LiBF₄Suppresses deterioration of the nonaqueous electrolyte caused by the reaction between the positive electrode and the nonaqueous electrolyte during high temperature storage.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a nonaqueous electrolyte battery to which the present invention is applied will be described. A configuration example of a lithium ion secondary battery (hereinafter referred to as a battery) is shown in FIG. 1 as the nonaqueous electrolyte battery. The battery 1 has a structure in which a battery element 2 serving as a power generation element is sealed together with a non-aqueous electrolyte 4 inside an outer can 3.
[0012]
The battery element 2 has a configuration in which a strip-like positive electrode 5 and a strip-like negative electrode 6 are wound in close contact via a separator 7.
[0013]
In the positive electrode 5, a positive electrode mixture layer 9 containing a positive electrode active material is formed on a positive electrode current collector 8. A positive electrode terminal 10 is connected to the positive electrode 5 at a predetermined position of the positive electrode current collector 8 so as to protrude from one end in the width direction of the positive electrode current collector 8. For the positive electrode terminal 10, for example, a strip-shaped metal piece made of aluminum or the like is used.
[0014]
  The positive electrode 5 uses a mixture of a lithium / nickel composite oxide and a lithium / manganese composite oxide as a positive electrode active material. Specifically, for example, LiNiO₂, Li_xNi_yCo_1-yO₂(X and y differ depending on the charge / discharge state of the battery, and usually 0 <x <1, 0.7 <y <1.0It is. ), Li_xNi_1-yM_yO₂(X and y differ depending on the charge / discharge state of the battery, and usually 0 <x <1, 0.7 <y <1.0And M is any one or more of transition metals. Lithium / nickel composite oxides represented by chemical formulas such as₂O₄, Li_xMn_2-yM ’_yO₄(X is 0.9 or more, y is 0 or more, 0.5 or less, M ′ is Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B , Ga, In, Si, or Ge). A mixture with a spinel-type lithium-manganese composite oxide represented by the chemical formula:
[0015]
In the positive electrode 5, for example, LiCoO is added to the above-described mixture of the lithium / nickel composite oxide and the lithium / manganese composite oxide.₂, Li_xMO₂(Where x is in the range of 0.5 or more and 1.1 or less, and M is any one or more of transition metals other than Ni and Mn). It is also possible.
[0016]
In the positive electrode 5, for example, a net-like or foil-like aluminum is used as the positive electrode current collector 8. In the positive electrode 5, as a binder contained in the positive electrode mixture layer 9, a known resin material that is usually used for this type of nonaqueous electrolyte battery can be used. Specifically, examples of the binder include polyvinylidene fluoride. Moreover, in the positive electrode 5, the well-known thing normally used for this kind of nonaqueous electrolyte battery can be used as a electrically conductive material contained in the positive mix layer 9. FIG. Specifically, examples of the conductive material include carbon black and graphite.
[0017]
In the positive electrode 5, by using a mixture of a lithium / nickel composite oxide and a lithium / manganese composite oxide as a positive electrode active material, the lithium / nickel composite oxide with a large amount of lithium improves battery capacity, and It acts to suppress the generation of acid in the water electrolyte 4. In the positive electrode 5, the lithium / manganese composite oxide has a relatively stable crystal structure, thereby improving safety and reducing the oxidation reaction of the nonaqueous electrolyte solution 4. 4 acts to suppress the degradation of 4.
[0018]
In the negative electrode 6, a negative electrode mixture layer 12 containing a negative electrode active material is formed on a negative electrode current collector 11. A negative electrode terminal 13 is connected to the negative electrode 6 at a predetermined position of the negative electrode current collector 10 so as to protrude from one end in the width direction of the negative electrode current collector 10. For the negative electrode terminal 13, for example, a strip-shaped metal piece made of copper, nickel, or the like is used.
[0019]
In the negative electrode 6, the negative electrode active material is a material that can be doped / undoped with lithium, and examples thereof include a metal capable of forming an alloy with lithium or a compound of this metal. Specifically, for example, chemical formula D_sE_tLi_u(D is one or more metal elements and / or semiconductor elements that can be combined with lithium, E is one or more metal elements and / or semiconductor elements other than lithium and D, s is greater than 0, t and u Is not less than 0.) SiB4, SiB as compounds represented by the chemical formula₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂CoSi₂NiSi₂, CaSi₂, CrSi₂, Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂Any one or more of these are used.
[0020]
In the negative electrode 6, in addition to the above-described compounds, for example, a carbonaceous material capable of doping / dedoping lithium ions can be used. Examples of the carbonaceous material include graphites such as artificial graphite and natural graphite, non-graphitizable carbon, pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound fired bodies, carbon fibers, activated carbon, carbon Blacks etc. are mentioned, and any one or more of these are used. Of these carbonaceous materials, the cokes are, for example, pitch coke, needle coke, petroleum coke and the like, and the organic polymer compound fired body is a polymer material such as phenol resin or furan resin at a predetermined temperature. And carbonized by firing. These carbonaceous materials can be used by mixing one or more of the above-described compounds. In this case, the carbonaceous material also functions as a conductive material.
[0021]
In addition, in the negative electrode 6, in addition to the above-described compounds and carbonaceous materials, for example, a polymer such as polyacetylene or polypyrrole, an oxide such as iron oxide, ruthenium oxide, molybdenum oxide, or tin oxide is used as the negative electrode active material. It is also possible.
[0022]
In the negative electrode 6, for example, net-like or foil-like copper is used as the negative electrode current collector 11. In the negative electrode 6, as the binder contained in the negative electrode mixture layer 12, a known resin material that is usually used for this type of nonaqueous electrolyte battery can be used. Specifically, examples of the binder include polyvinylidene fluoride.
[0023]
In the battery element 2, the separator 7 separates the positive electrode 5 and the negative electrode 6, and a known material that is usually used as an insulating porous film of this type of nonaqueous electrolyte battery can be used. Specifically, for example, a polymer film such as polypropylene or polyethylene is used. Moreover, from the relationship between lithium ion conductivity and energy density, the thickness of the separator 7 is preferably as thin as possible, and the thickness is set to 30 μm or less.
[0024]
The outer can 3 is a bottomed cylindrical container, for example, and has a rectangular bottom surface and a flat circular bottom surface. Further, when the outer can 3 is electrically connected to the negative electrode 6, the outer can 3 is formed of a conductive metal such as iron, stainless steel, nickel, or the like. When the outer can 3 is made of, for example, iron, nickel plating or the like is applied to the surface thereof.
[0025]
As the nonaqueous electrolytic solution 4, for example, a solution in which an electrolyte salt is dissolved in a nonaqueous solvent is used. As the non-aqueous solvent, for example, a cyclic carbonate compound, a cyclic carbonate compound in which hydrogen is substituted with a halogen group or a halogenated acrylic group, a chain carbonate compound, or the like is used. Specifically, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3 as nonaqueous solvents -Dioxolane, 4methyl 1,3 dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole, acetate ester, butyrate ester, propionate ester, etc., and any one or more of these are used. In particular, as the non-aqueous solvent, propylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, and dipropyl carbonate are used from the viewpoint of voltage stability.
[0026]
In the nonaqueous electrolytic solution 4, the electrolyte salt includes at least LiPF.₆And LiBF₄Are mixed and used. Thus, in the battery 1, LiPF is used as the electrolyte salt.₆And LiBF₄By adding LiPF, LiPF with high ionic conductivity₆Acts to move lithium ions appropriately and to obtain a high battery capacity. Further, in the battery 1, LiBF contained in the electrolyte salt₄However, when stored at a high temperature, the nonaqueous electrolyte solution 4 is prevented from being decomposed by the reaction between the positive electrode 5 and the nonaqueous electrolyte solution 4, and acts to prevent a decrease in battery capacity due to high temperature storage.
[0027]
In the non-aqueous electrolyte 4, the above-described LiPF₆And LiBF₄Besides, for example, LiClO as an electrolyte salt₄, LiAsF₆, LiB (C₆H₅)₄, LiCF₃SO₃, LiCH₃SO₃, LiN (CF₃SO₂)₂, LiSbF₆LiClO₄LiCl, LiBr, etc., and any one or more of these may be LiPF.₆And LiBF₄It can also be used as a mixture.
[0028]
In addition, the nonaqueous electrolytic solution 4 includes LiBF, which is an electrolyte salt.₄In a range of 0.01 mol / liter to 0.1 mol / liter. LiBF for non-aqueous electrolyte 4₄In the battery 1, LiBF contained in the non-aqueous electrolyte 4 is contained in an amount of less than 0.01 mol / liter.₄Therefore, it is difficult to suppress the decomposition of the nonaqueous electrolytic solution 4 when stored at a high temperature. On the other hand, LiBF with respect to the non-aqueous electrolyte 4₄In the battery 1, LiBF contained in the non-aqueous electrolyte solution 4 is contained in an amount of more than 0.1 mol / liter.₄As a result, a boron compound film is formed on the surface of the negative electrode 6 during charging and storage at high temperatures. For this reason, in the battery 1, since the coating of the boron compound formed on the surface of the negative electrode 6 hinders the movement of lithium ions, the battery characteristics are deteriorated such as a reduction in battery capacity.
[0029]
Therefore, in the battery 1, the LiBF is different from the non-aqueous electrolyte 4.₄Is contained in the range of 0.01 mol / liter or more and 0.1 mol / liter or less to suppress decomposition of the non-aqueous electrolyte 4 when stored at a high temperature, and a boron compound film is formed on the surface of the negative electrode 6. It is possible to prevent the formation.
[0030]
The battery 1 having the above configuration is manufactured as follows. First, the positive electrode 5 is produced. When the positive electrode 5 is produced, a positive electrode mixture coating liquid containing a positive electrode active material containing at least a mixture of a lithium / nickel composite oxide and a lithium / manganese composite oxide, a conductive material, and a binder is prepared. Then, the positive electrode mixture coating solution is uniformly applied on both main surfaces of the positive electrode current collector 8 made of, for example, an aluminum foil, dried, and then compressed to form the positive electrode mixture layer 9, and The positive electrode terminal 10 is attached to a predetermined position by cutting, for example, by ultrasonic welding. In this way, the elongated positive electrode 5 is produced.
[0031]
Next, the negative electrode 6 is produced. When producing the negative electrode 6, a negative electrode mixture coating liquid containing a negative electrode active material and a binder is prepared, and the two main surfaces of the negative electrode current collector 11 made of, for example, copper foil are used as the negative electrode mixture coating liquid. After uniformly coating and drying on top, the negative electrode mixture layer 12 is formed by compression, cutting into a predetermined dimension, and the negative electrode terminal 13 is attached to a predetermined position by, for example, ultrasonic welding. In this way, a long negative electrode 6 is produced.
[0032]
Next, the battery element 2 is manufactured by laminating the positive electrode 5 and the negative electrode 6 obtained as described above via a long separator 7 and winding the laminate many times. At this time, the battery element 2 has a configuration in which the positive electrode terminal 10 protrudes from one end surface in the width direction of the separator 8 and the negative electrode terminal 13 protrudes from the other end surface.
[0033]
Next, insulating plates 14a and 14b are installed on both end faces of the battery element 2, and the battery element 2 is housed in an iron outer can 3 having nickel plating or the like inside. Then, in order to collect current of the negative electrode 6, the portion of the negative electrode terminal 13 protruding from the battery element 2 is welded to the bottom of the outer can 3 or the like. As a result, the outer can 3 is electrically connected to the negative electrode 6 and becomes an external negative electrode of the battery 1. Further, in order to collect the current of the positive electrode 5, the portion protruding from the battery element 2 of the positive electrode terminal 10 is welded to the current interrupting thin plate 15 to electrically connect the battery lid 16 via the current interrupting thin plate 15. Connect to. The current interrupting thin plate 15 interrupts the current according to the battery internal pressure. As a result, the battery lid 16 conducts the positive electrode 5 and becomes the external positive electrode of the battery 1.
[0034]
Next, the nonaqueous electrolytic solution 4 is injected into the outer can 3 in which the battery element 2 is accommodated. This non-aqueous electrolyte solution 4 is at least LiPF.₆And LiBF₄An electrolyte salt containing is dissolved in a non-aqueous solvent. Next, the battery lid 16 is fixed by caulking the opening of the outer can 3 through the insulating gasket 17 coated with asphalt, and the cylindrical battery 1 is manufactured.
[0035]
The battery 1 is provided with a center pin 18 that serves as a shaft for winding the battery element 2, and vents the internal gas when the internal pressure of the battery becomes higher than a predetermined value. There are provided a safety valve 19 and a PTC (positive temperature coefficient) element 20 for preventing temperature rise inside the battery.
[0036]
In the battery 1 manufactured in this way, a mixture of lithium / nickel composite oxide and lithium / manganese composite oxide is used as the positive electrode active material, so that the lithium / nickel composite oxide of the mixture increases the battery capacity. In addition, since generation of acid in the non-aqueous electrolyte 4 is also suppressed, deterioration due to high temperature storage of the lithium / manganese composite oxide is suppressed. In this battery 1, the lithium-manganese composite oxide having a stable crystal structure used for the positive electrode active material improves safety and reduces the oxidation reaction of the non-aqueous electrolyte 4, thereby reducing the non-aqueous electrolyte 4. Deterioration of the battery and the deterioration of battery characteristics are suppressed.
[0037]
In this battery 1, LiBF is used as an electrolyte salt.₄By suppressing the decomposition of the non-aqueous electrolyte solution 4 caused by the reaction between the positive electrode 5 and the non-aqueous electrolyte solution 4 during high-temperature storage, an excellent high temperature without a decrease in battery capacity when stored at a high temperature Storage characteristics can be obtained.
[0038]
Therefore, this battery 1 combines high energy density, high safety, and excellent high-temperature storage characteristics.
In the above example, the battery 1 using the non-aqueous electrolyte 4 has been described. However, the present invention is not limited to this, and instead of the non-aqueous electrolyte 4, for example, a polymer solid electrolyte, a gel electrolyte, or the like The present invention can also be applied to a non-aqueous electrolyte battery using a solid electrolyte.
[0039]
The polymer solid electrolyte is, for example, at least the LiPF described above.₆And LiBF₄And a polymer compound that imparts ionic conductivity by containing the electrolyte salt. Examples of the polymer compound used for the polymer solid electrolyte include silicon, polyether-modified siloxane, polyacryl, polyacrylonitrile, polyphosphazene, polyethylene oxide, polypropylene oxide, and composite polymers, cross-linked polymers, modified polymers, and the like, acrylonitrile. Ether polymers such as butadiene rubber, polyacrylonitrile-butadiene styrene rubber, acrylonitrile-polyethylene chloride-propylene-diene-styrene resin, acrylonitrile-vinyl chloride resin, acrylonitrile-methacrylate resin, acrylonitrile-acrylate resin, polyethylene oxide cross-linked product Any one of them or a mixture of two or more of them may be used.
[0040]
Examples of the polymer compound used in the polymer solid electrolyte include acrylonitrile, vinyl acetate, methyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, itaconic acid, methyl hydroxide acrylate, ethyl hydroxide acrylate, A copolymer obtained by copolymerizing any one or more of acrylamide, vinyl chloride, vinylidene fluoride, poly (vinylidene fluoride), poly (vinylidene fluoride-co-hexafluoropropylene), poly (vinylidene fluoro) Ride-co-tetrafluoroethylene), poly (vinylidene fluoride-co-trifluoroethylene) and the like are also included, and any one or a combination of these may be used.
[0041]
The gel electrolyte is composed of the non-aqueous electrolyte 4 described above and a matrix polymer that absorbs the non-aqueous electrolyte 4 and gels. As the matrix polymer used for the gel electrolyte, for example, any of the above-described polymer compounds that absorbs the nonaqueous electrolytic solution 4 and gels can be used. Specifically, examples of the matrix polymer include fluorine-based polymers such as poly (vinylidene fluoride) and poly (vinylidene fluoride-co-hexafluoropropylene), and ethers such as poly (ethylene oxide) and a crosslinked product thereof. Polymer, poly (acrylonitrile) and the like, and any one or a combination of these may be used. In particular, it is preferable to use a fluorine-based polymer having good redox stability as the matrix polymer.
[0042]
In the above-described embodiment, the cylindrical battery 1 has been described as an example. However, the present invention is not limited to this example. For example, a coin type, a square type, a button type, or the like is made of metal as an exterior material. The present invention can also be applied to non-aqueous electrolyte batteries having various shapes and sizes, such as batteries using containers and the like, thin batteries, and batteries using a laminate film as an exterior material.
[0043]
【Example】
Hereinafter, examples and comparative examples in which lithium ion secondary batteries are actually manufactured as nonaqueous electrolyte batteries to which the present invention is applied will be described.
[0044]
<Example 1>
In Example 1, first, a positive electrode was produced. When producing the positive electrode, 60 parts by weight of lithium / nickel composite oxide and 40 overlapping parts of lithium / manganese composite oxide were mixed to obtain a mixture. Then, 92 parts by weight of the mixture obtained as described above as the positive electrode active material, 5 parts by weight of graphite as the conductive material, and 3 parts by weight of polyvinylidene fluoride (hereinafter referred to as PVdF) as the binder. Were uniformly dispersed in N-methyl-2-pyrrolidone (hereinafter referred to as NMP) to prepare a positive electrode mixture coating solution. Next, this positive electrode mixture coating solution is uniformly applied onto a 20 μm thick aluminum foil serving as a positive electrode current collector, dried, and then compressed by a roll press to form a positive electrode mixture layer with predetermined dimensions. The positive electrode terminal made of aluminum was attached to the positive electrode current collector by ultrasonic welding. In this way, a long positive electrode was produced.
[0045]
Next, a negative electrode was produced. When preparing the negative electrode, 92 parts by weight of graphite as a negative electrode active material and 8 parts by weight of PVdF as a binder were uniformly dispersed in NMP to prepare a negative electrode mixture coating liquid. And after apply | coating this negative electrode mixture coating liquid uniformly on 15-micrometer-thick copper foil used as a negative electrode collector, and drying, it compresses with a roll press machine, forms a negative electrode mixture layer, and cut | disconnects to a predetermined dimension. Then, a negative electrode terminal made of nickel was attached to the negative electrode current collector by ultrasonic welding. In this way, a long negative electrode was produced.
[0046]
Next, in order to produce a battery element, a laminate made of a porous polyethylene film having a thickness of 25 μm is interposed between the positive electrode and the negative electrode obtained as described above, and this laminate is subjected to multiple cycles. Turned. In this way, a battery element was produced. At this time, the positive electrode terminal was led out from one end surface of the obtained battery element, and the negative electrode terminal was led out from the other end surface.
[0047]
Next, the positive electrode terminal derived from the produced battery element was welded to the battery lid, the negative electrode terminal was welded to the outer can made of nickel-plated iron, and the battery element was housed in the outer can.
[0048]
Next, LiPF is used as an electrolyte salt for a mixed solvent in which ethylene carbonate, propylene carbonate, and dimethyl carbonate are mixed so that the volume mixing ratio is 1: 2: 7.₆A non-aqueous electrolyte solution was prepared in which was dissolved at 1.2 mol / liter. Furthermore, LiBF as an electrolyte salt is added to this non-aqueous electrolyte.₄Was dissolved so as to contain 0.01 mol / liter.
[0049]
Next, LiPF as the electrolyte salt₆And LiBF₄Non-aqueous electrolyte containing water is injected into the outer can, and the battery lid is pressed into the opening of the outer can through an insulating gasket coated with asphalt to caulk the opening of the outer can. Fixed to.
[0050]
A cylindrical lithium ion secondary battery having a diameter of 18 mm and a height of 65 mm was produced as described above. In the following description, a lithium ion secondary battery is simply referred to as a battery for convenience.
[0051]
<Example 2>
In Example 2, LiBF is used as the non-aqueous electrolyte.₄Was added in the same manner as in Example 1 except that 0.05 mol / liter was added.
[0052]
<Example 3>
In Example 3, LiBF was used as the non-aqueous electrolyte.₄A battery was fabricated in the same manner as in Example 1, except that 0.1 mol / liter was added.
[0053]
<Example 4>
In Example 4, when producing a positive electrode, a positive electrode was produced using a mixture in which 90 parts by weight of lithium / nickel composite oxide and 10 overlapping parts of lithium / manganese composite oxide were mixed as a positive electrode active material. did. And the battery was produced like Example 2 except having used this positive electrode.
[0054]
<Example 5>
In Example 5, when producing a positive electrode, a positive electrode was produced using a mixture in which 10 parts by weight of a lithium / nickel composite oxide and 90 parts of a lithium / manganese composite oxide were mixed as a positive electrode active material. did. And the battery was produced like Example 2 except having used this positive electrode.
[0055]
<Comparative example 1>
In Comparative Example 1, LiBF was used as the non-aqueous electrolyte.₄A battery was fabricated in the same manner as in Example 1 except that the content of was not included.
[0056]
<Comparative example 2>
In Comparative Example 2, LiBF was used as the non-aqueous electrolyte.₄Was made in the same manner as in Example 1 except that 0.15 mol / liter was added.
[0057]
<Comparative Example 3>
In Comparative Example 3, when producing the positive electrode, the positive electrode was produced using only the lithium / nickel composite oxide as the positive electrode active material. And the battery was produced like Example 2 except having used this positive electrode.
[0058]
<Comparative example 4>
In Comparative Example 4, when producing the positive electrode, the positive electrode was produced using only the lithium / manganese composite oxide as the positive electrode active material. And the battery was produced like Example 2 except having used this positive electrode.
[0059]
And the discharge capacity maintenance factor after high-temperature preservation | save was measured about the battery of Example 1- Example 5 produced as mentioned above and Comparative Example 1- Comparative Example 4. FIG.
[0060]
Hereinafter, Table 1 shows the evaluation results of the discharge capacity retention rate after high-temperature storage in each Example and each Comparative Example.
[0061]
[Table 1]

[0062]
In each example and each comparative example, the discharge capacity retention rate after high-temperature storage was measured as follows. When measuring the discharge capacity retention rate after high-temperature storage in each example and each comparative example, the constant current constant of 1 C and the upper limit voltage of 4.2 V in a 23 ° C. atmosphere was measured for the batteries of each example and each comparative example. After voltage charging for 2.5 hours, a constant current discharge of up to 3 V was performed at a current value of 1 C in an atmosphere at 23 ° C., and the initial discharge capacity was measured. Next, the batteries of each Example and each Comparative Example were stored in an atmosphere at 85 ° C. for 40 hours, and then charged / discharged under the same conditions as the first charge / discharge, and the discharge capacity after high-temperature storage was measured. The discharge capacity retention rate after high temperature storage is the ratio of the discharge capacity after high temperature storage to the initial discharge capacity measured as described above.
[0063]
From the evaluation results shown in Table 1, LiBF was added to the non-aqueous electrolyte.₄In Example 1 to Example 3 containing 0.01 mol / liter or more and 0.1 mol / liter or less, LiBF was added to the non-aqueous electrolyte.₄It can be seen that the discharge capacity retention rate after high-temperature storage is higher than that of Comparative Example 1 in which no is contained.
[0064]
In Comparative Example 1, LiBF was used as the non-aqueous electrolyte.₄Does not contain, the positive electrode and the non-aqueous electrolyte react when stored at high temperatures, the non-aqueous electrolyte decomposes, and the non-aqueous electrolyte deteriorates, reducing the battery capacity after storage at high temperatures. End up.
[0065]
Further, from the evaluation results shown in Table 1, LiBF was added to the non-aqueous electrolyte.₄In Example 1 to Example 3 containing 0.01 mol / liter or more and 0.1 mol / liter or less, LiBF was added to the non-aqueous electrolyte.₄It can be seen that the discharge capacity retention rate after high-temperature storage is larger than that of Comparative Example 2 in which 0.15 mol / liter is contained.
[0066]
In Comparative Example 2, LiBF contained in the non-aqueous electrolyte₄When the amount is too large and charged and discharged and stored at a high temperature, a boron compound is formed as a coating on the negative electrode surface. As a result, in Comparative Example 2, the boron compound film formed on the negative electrode surface hinders the migration of lithium ions, so that the battery capacity after high-temperature storage is reduced.
[0067]
In contrast to these comparative examples, in Examples 1 to 3, LiBF contained in the nonaqueous electrolytic solution₄Is in the range of 0.01 mol / liter or more and 0.1 mol / liter or less, and LiBF₄Accordingly, the decomposition of the non-aqueous electrolyte during high-temperature storage can be suppressed, and a boron compound film can be prevented from being formed on the negative electrode surface. Therefore, in Examples 1 to 3, it is prevented that the battery capacity after high-temperature storage is reduced, and the discharge capacity retention rate after high-temperature storage is increased.
[0068]
From the above, when producing a battery, LiBF was added to the non-aqueous electrolyte.₄In the range of 0.01 mol / liter or more and 0.1 mol / liter or less, it is very effective in manufacturing an excellent battery in which the battery capacity is prevented from being reduced after high-temperature storage. Recognize.
[0069]
Furthermore, from the evaluation results shown in Table 1, in Examples 1 to 5 in which a mixture of a lithium / nickel composite oxide and a lithium / manganese composite oxide was used as the positive electrode active material, the positive electrode active material was a lithium / nickel composite. It can be seen that the discharge capacity retention rate after high-temperature storage is higher than in Comparative Example 3 in which only the oxide is used.
[0070]
In Comparative Example 3, although the lithium-nickel composite oxide as the positive electrode active material increases the battery capacity, it is highly reactive with the non-aqueous electrolyte in the charged state, and after high-temperature storage by oxidative decomposition of the non-aqueous electrolyte. The capacity of will decrease.
[0071]
Furthermore, from the evaluation results shown in Table 1, in Examples 1 to 5 in which a mixture of lithium / nickel composite oxide and lithium / manganese composite oxide was used as the positive electrode active material, the positive electrode active material was lithium / manganese. It can be seen that the discharge capacity retention rate after high-temperature storage is higher than in Comparative Example 4 in which only the composite oxide is used.
[0072]
In Comparative Example 4, although the lithium-manganese composite oxide used as the positive electrode active material has a relatively low reactivity with the non-aqueous electrolyte, the value of Mn is affected by the acid contained in the non-aqueous electrolyte during high-temperature storage. The number tends to change, and the battery capacity after high-temperature storage is reduced.
[0073]
In contrast to these comparative examples, in Examples 1 to 5, the lithium-nickel composite oxide is a battery capacity among the mixture of the lithium-nickel composite oxide and the lithium-manganese composite oxide used for the positive electrode active material. In addition, the generation of acid in the non-aqueous electrolyte is also suppressed, so that deterioration due to high-temperature storage of the lithium-manganese composite oxide is suppressed. In Examples 1 to 5, the lithium-manganese composite oxide used for the positive electrode active material reduces the oxidation reaction of the electrolytic solution. Thereby, in Example 1- Example 5, it is prevented that the battery capacity after high temperature preservation | save is reduced, and the discharge capacity maintenance factor after high temperature preservation | save becomes large.
[0074]
From the above, when a battery is manufactured, using a mixture of a lithium / nickel composite oxide and a lithium / manganese composite oxide as a positive electrode active material prevents a decrease in battery capacity after high-temperature storage. It turns out that it is very effective in manufacturing the outstanding battery.
[0075]
【The invention's effect】
As is apparent from the above description, according to the present invention, high energy density and high safety can be achieved by using a mixture of lithium / nickel composite oxide and lithium / manganese composite oxide as the positive electrode active material. While the electrolyte salt is LiBF₄It can suppress that a positive electrode and a nonaqueous electrolyte react at the time of high temperature preservation | save, and a nonaqueous electrolyte deteriorates. Therefore, according to the present invention, it is possible to obtain a non-aqueous electrolyte battery having high energy density, high safety, and excellent high-temperature storage characteristics that do not deteriorate battery characteristics due to high-temperature storage.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an internal structure of a lithium ion secondary battery according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery, 2 Battery element, 3 Exterior can, 4 Non-aqueous electrolyte, 5 Positive electrode, 6 Negative electrode, 7 Separator, 8 Positive electrode collector, 9 Positive electrode mixture layer, 10 Positive electrode terminal, 11 Negative electrode current collector Body, 12 negative electrode mixture layer, 13 negative electrode terminal, 14a, 14b insulating plate, 15 thin plate for current interruption, 16 battery cover, 17 insulating gasket, 18 center pin, 19 safety valve, 20 PTC element

Claims (4)

A positive electrode comprising a positive electrode mixture layer having a positive electrode active material capable of doping / dedoping lithium;
A negative electrode comprising a negative electrode mixture layer having a negative electrode active material capable of doping / dedoping lithium;
A non-aqueous electrolyte containing an electrolyte salt,
The positive electrode active material is a mixture of lithium / nickel composite oxide and lithium / manganese composite oxide,
The negative electrode active material is graphite,
The electrolyte salt contains at least LiPF ₆ and LiBF ₄ and contains the LiBF ₄ in a range of 0.01 mol / liter to 0.1 mol / liter. battery. The lithium-nickel composite oxide is LiNiO ₂ , Li _x Ni _y Co _1-y O ₂ (0 <x <1, 0.7 <y < 1.0 ), Li _x Ni _{1- y My} O _2. The nonaqueous electrolyte according to claim 1, wherein the nonaqueous electrolyte is at least one represented by a chemical formula (0 <x <1, 0.7 <y < 1.0 , M is one or more of transition metals). battery. The lithium-manganese composite oxide is LiMn ₂ O ₄ , Li _x Mn _2-y M ′ _y O ₄ (x is 0.9 or more, y is 0 or more, 0.5 or less, M ′ is Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, or Ge). The nonaqueous electrolyte battery according to claim 1.   The nonaqueous electrolyte battery according to claim 1, further comprising ethylene carbonate and dimethyl carbonate as a solvent.

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