JP3643522B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

【０１５９】
【表２】

【０１６０】
【表３】

【０１６１】
【表４】

【０１６２】
表１〜表４から明らかなように、実施例１〜６，１０〜１３の電池は、比較例１〜５に比べ、高容量でかつ安全性が高く、さらにサイクル寿命特性にも優れる。
【０１６３】
実施例１４〜１８
組成がＬｉＮｉ_0.8Ｃｏ_0.14Ａｌ_0.06Ｏ₂で表され、かつ前述した方法で測定されるｐＨが１０．８、１１．２、１１．４、１１．８、１２．０である５種類のリチウムニッケルコバルトアルミニウム複合酸化物粉末を用意した。各複合酸化物を正極活物質として使用すること以外は、前述した実施例１と同様にして正極を作製した。
【０１６４】
＜負極の作製＞
メソフェーズピッチ系炭素繊維に３０００℃で熱処理を施し、炭素質物としてメソフェーズピッチ系炭素繊維の黒鉛質材料を用意した。前記炭素繊維は、平均繊維径が１０μｍで、平均繊維長が３０μｍで、平均アスペクト比が２０で、平均面間隔（ｄ₀₀₂）が０．３３５８ｎｍであった。前記炭素質物の粉末９３重量％と、結着剤としてポリフッ化ビニリデン（ＰＶｄＦ）７重量％と、ＮＭＰ溶液とを加えて混合し、スラリーを調製した。得られたスラリーを厚さが１０μｍの銅箔からなる集電体の両面に塗布し、乾燥し、プレスすることにより電極密度が１．３５ｇ／ｃｍ³の負極を作製した。
【０１６５】
＜液状非水電解質の調製＞
２４体積％のエチレンカーボネート（ＥＣ）と７５体積％のγ−ブチロラクトン（γＢＬ）と１体積％のビニレンカーボネート（ＶＣ）の混合溶媒に四フッ化ホウ酸リチウム（ＬｉＢＦ₄）を１．５モル／Ｌ溶解して液状非水電解質を調製した。
【０１６６】
前記正極と前記負極の間に前述した実施例１で説明したのと同様なセパレータを介在させて渦巻き状に捲回した後、偏平状に成形し、厚さ２．７ｍｍ、幅３０ｍｍ、高さ５０ｍｍの偏平型電極群を作製した。次いで、前記電極群に９０℃で１２ｋｇ／ｃｍ²の圧力でプレスを施した。
【０１６７】
収納容器として実施例１で説明したのと同様なラミネートフィルムを用意し、これを袋状に成形した。これに前記偏平形状の電極群を収納した後、前記液状非水電解質を２ｇ注入し、厚さが２．７ｍｍ、幅が３２ｍｍ、高さが５５ｍｍの薄型非水電解質二次電池を組み立てた。
【０１６８】
実施例１９
メソフェーズ小球体に３０００℃で熱処理を施し、炭素質物としてメソフェーズ小球体の黒鉛質材料を用意した。前記メソフェーズ小球体は、平均粒径が６μｍで、長径に対する短径の比が０．９で、平均面間隔（ｄ₀₀₂）が０．３３６０ｎｍであった。このような球状炭素質物を用いること以外は、前述した実施例１４と同様にして薄型非水電解質二次電池を製造した。
【０１６９】
実施例２０
炭素質物として３０００℃で熱処理したメソフェーズピッチ系炭素繊維５０重量％と、粒状の黒鉛５０重量％との混合粉末を用意した。前記炭素繊維は、平均繊維径が１０μｍで、平均繊維長が３０μｍで、平均アスペクト比が２０で、平均面間隔（ｄ₀₀₂）が０．３３５８ｎｍであった。一方、前記粒状黒鉛は、平均粒径が１０μｍで、長径（major radius）に対する短径（minor radius）の比が０．６で、平均面間隔（ｄ₀₀₂）が０．３３５５ｎｍであった。このような炭素質物を用いること以外は、前述した実施例１４と同様にして薄型非水電解質二次電池を製造した。
【０１７０】
得られた実施例１４〜２０の電池について、０．５Ｃで４．２Ｖの定電圧充電を３時間行った後、０．５Ｃで３Ｖまで放電した際の容量をそれぞれ求め、その結果を下記表５に示す。
【０１７１】
また、実施例１４〜２０の電池について、４．４Ｖまで過充電し、針刺しの安全性性能試験を行い、電池温度と収納容器の膨れ率を測定し、その結果を下記表５に示す。
【０１７２】
さらに、実施例１４〜２０の電池について、０．５Ｃで４．２Ｖの定電圧充電を３時間行った後、０．５Ｃで３Ｖまで放電する充放電サイクル試験を行い、初期容量の８０％容量になるときの充放電サイクル数を調べ、その結果を下記表５に示す。
【０１７３】
【表５】

【０１７４】
表５から明らかなように、正極活物質のｐＨが高くなるほど、収納容器の膨れが大きくなることがわかる。また、負極活物質として繊維状炭素質物を含む負極を備えた実施例１４の二次電池は、実施例１９、２０の二次電池に比べてサイクル寿命が長いことがわかる。
【０１７５】
【発明の効果】
以上詳述したように本発明によれば、安全性を確保しつつ、高容量で、さらにサイクル寿命特性にも優れた薄型非水電解質二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明に係る非水電解質二次電池の一例を示す断面図。
【図２】図１のＡ部を示す拡大断面図。
【符号の説明】
１…収納容器、
２…電極群、
３…セパレータ、
４…正極層、
５…正極集電体、
６…負極層、
７…負極集電体、
１２…正極、
１３…負極、
Ｔ…収納容器の外壁の厚さ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
Currently, thin lithium ion secondary batteries are commercialized as non-aqueous electrolyte secondary batteries for portable devices such as mobile phones. This battery is made of lithium cobalt oxide (LiCoO ₂ ), A negative electrode containing a graphite material or a carbonaceous material, a separator composed of a porous film disposed between the positive electrode and the negative electrode, and a lithium salt dissolved in an organic solvent. A liquid nonaqueous electrolyte and a storage container made of a cylindrical or rectangular can are provided.
[0003]
With the reduction in size and thickness of portable devices, there is a demand for thinner and lighter batteries, but it is somewhat difficult to put into practical use a battery having the above configuration and a thickness of 4 mm or less.
[0004]
Therefore, an electrode group composed of a positive electrode, a negative electrode, and a polymer electrolyte layer disposed between the positive electrode and the negative electrode, and the electrode group are housed, and the thickness is 0.25 mm or less. A nonaqueous electrolyte secondary battery including a storage container made of a laminate film has been proposed and is being developed. The secondary battery provided with the polymer electrolyte layer can ensure the adhesion between the electrode and the electrolyte layer even if the thickness of the film material of the storage container is reduced.
[0005]
On the other hand, the following proposals have been made to reduce the thickness of a non-aqueous electrolyte secondary battery including a liquid non-aqueous electrolyte.
[0006]
JP-A-10-177865 includes a positive electrode, a negative electrode, a separator having an opposing surface holding an electrolytic solution, an electrolytic solution phase, a polymer gel phase containing an electrolytic solution, and a polymer solid phase, A lithium ion secondary battery including an adhesive resin layer for joining the positive electrode and the negative electrode to the opposing surface of the separator is described.
[0007]
In JP-A-10-189054, a positive electrode is formed by forming a positive electrode active material layer on a positive electrode current collector, and a negative electrode is formed by forming a negative electrode active material layer on a negative electrode current collector. Preparing a binder resin solution containing polyvinylidene fluoride as a main component by dissolving polyvinylidene fluoride in a solvent, applying the binder resin solution to a separator, and applying the binder resin solution to one side of the separator; A step of disposing the negative electrode on the other surface and drying the contacted electrode, evaporating the solvent to form a battery stack, and impregnating the battery stack with an electrolyte. A method for manufacturing a lithium ion secondary battery is described.
[0008]
Japanese Patent Laid-Open No. 10-172606 discloses a positive electrode and a separator formed by bonding a positive electrode active material layer to a current collector, and a negative electrode and a separator formed by bonding a negative electrode active material layer to a current collector. , By disposing an adhesive resin layer on each, the bonding strength between the positive electrode active material layer and the separator is equal to or higher than the bonding strength between the positive electrode active material layer and the current collector, and the negative electrode active material layer and the separator It is described that the bonding strength is equal to or higher than the bonding strength between the negative electrode active material layer and the current collector.
[0009]
The lithium ion secondary battery described in each of the above publications can ensure the adhesion between the positive electrode and the separator and the adhesion between the negative electrode and the separator even when the outer wall of the storage container is thinned, Since a non-aqueous electrolyte can be used, the volume energy density and the large current discharge characteristic can be made higher than those of a secondary battery including a polymer electrolyte.
[0010]
By the way, from the viewpoint of further increasing the capacity of the non-aqueous electrolyte secondary battery, lithium cobalt composite oxide (LixCoO) that has been conventionally used as a positive electrode active material. ₂ Lithium nickel composite oxide (LixNiO) ₂ ) Is being considered. For example, Japanese Patent Laid-Open No. 63-121258 discloses a lithium nickel composite oxide into which a different element (Al, Sn, In, B, P, Si, etc.) is introduced. In addition, J.H. Power Sources, 43-44, 595 (1993) includes lithium-nickel-cobalt composite oxide (Li _x Ni _1-y Co _y O ₂ ) Is disclosed. Furthermore, J. et al. Electrochem. Soc. , 142, 4033 (1995) describes that the lithium nickel composite oxide into which Al is introduced has relatively high thermal stability.
[0011]
However, a non-aqueous electrolyte secondary battery including a positive electrode containing the above-described lithium nickel composite oxide or lithium nickel cobalt composite oxide as an active material and a storage container having an outer wall thickness of 0.25 mm or less has a capacity. Although improved, there is a problem that it is inferior in safety.
[0012]
That is, a secondary battery having a storage container having an outer wall thickness of 0.25 mm or less has a phenomenon such as gas generation inside the battery or a temperature rise compared to the case where the thickness exceeds 0.25 mm. It tends to lead to accidents such as deformation, gas blowout or ignition. For this reason, in a secondary battery provided with a storage container having an outer wall thickness of 0.25 mm or less, it is necessary to extremely reduce gas generation and temperature rise inside the battery. However, since the lithium nickel composite oxide and the lithium nickel cobalt composite oxide are inferior in thermal stability to the lithium cobalt composite oxide, the battery internal temperature rapidly increases due to an internal short circuit or the like. When the temperature reaches from 100 ° C to 100 ° C, oxygen gas is generated. This oxygen gas reacts with the organic solvent in the non-aqueous electrolyte to cause oxidative decomposition of the non-aqueous electrolyte. Therefore, the battery temperature and the internal pressure of the battery further rise, and there is a risk that the gas will blow out from the battery or cause ignition Becomes higher.
[0013]
[Problems to be solved by the invention]
The objective of this invention is improving both the capacity | capacitance and safety | security of a nonaqueous electrolyte secondary battery provided with the storage container with thin thickness.
[0014]
[Means for Solving the Problems]
The nonaqueous electrolyte secondary battery according to the present invention includes a storage container, a positive electrode that is stored in the container and includes a positive electrode active material, a negative electrode that is stored in the container and includes a negative electrode active material, and the container A non-aqueous electrolyte housed inside,
The storage container is formed of a film material having a thickness of 0.25 mm or less,
The positive electrode active material is Oxide having a composition represented by the following formula (2) And the pH of the positive electrode active material is in the range of 10-12.
Li _x Ni _1-yz Co _z M _y O ₂ (2)
Where M is Al or at least one element selected from the group consisting of Al and B, Sn and Nb, and the atomic ratios x, y and z are 0 <x ≦ 1.2, 0.004. ≤ y ≤ 0.2, 0 <z ≤ 0.3 And the atomic ratio of Al is 0.04 or more and 0.15 or less. .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
A nonaqueous electrolyte secondary battery according to the present invention includes a storage container, a positive electrode that is stored in the container and includes a positive electrode active material, and a negative electrode active material that is stored in the container and that occludes and releases lithium ions. And a nonaqueous electrolyte housed in the container.
[0018]
The outer wall of the storage container is a film material having a thickness of 0.25 mm or less. The positive electrode active material is a first oxide containing at least one element M, Li and Ni selected from the group consisting of Al, B, Sn and Nb, or contains the elements M, Li, Ni and Co. A second oxide. The element M contained in each oxide consists of at least one selected from the group consisting of Al, B, Sn, and Nb.
[0019]
Hereinafter, the positive electrode, the negative electrode, the nonaqueous electrolyte, and the storage container will be described.
[0020]
1) Positive electrode
The positive electrode includes a current collector and a positive electrode layer that is supported on one or both surfaces of the current collector and includes the positive electrode active material.
[0021]
It can be said that the positive electrode active material is a compound (composite oxide) in which the element M is introduced into a part of the crystal structure of a lithium nickel composite oxide or a lithium nickel cobalt composite oxide.
[0022]
In the first oxide and the second oxide, the most preferable element among the elements M is Al. A secondary battery including an oxide containing Al as the element M as the positive electrode active material can improve the charge / discharge efficiency of the positive electrode and can further increase safety.
[0023]
In the first oxide, when the atomic ratio of Ni is 1, it is preferable that the atomic ratio of the element M is in the range of 0.005 to 0.2. This is due to the following reason. When the atomic ratio of the element M is less than 0.005, the thermal stability of the positive electrode active material is lowered, and it may be difficult to avoid the expansion and ignition of the storage container at the time of a short circuit. On the other hand, if the atomic ratio of the element M exceeds 0.2, a high battery capacity may not be obtained. Moreover, it is preferable to use Al, B, or both Al and B as the element M, and to make the atomic ratio of the element M within a range of 0.02 to 0.15. By adopting such a configuration, the thermal stability and battery capacity of the positive electrode active material can be further improved.
[0024]
The composition of the first oxide is preferably represented by the following formula (1) because a high capacity can be obtained.
[0025]
Li _a Ni _1-b M _b O ₂ (1)
M is at least one element selected from the group consisting of Al, B, Sn, and Nb, and the atomic ratios a and b satisfy 0 <a ≦ 1.2 and 0.004 ≦ b ≦ 0.17. Each is shown.
[0026]
The atomic ratio a of Li in the composition formula (1) varies depending on the charge amount and discharge amount of the nonaqueous electrolyte secondary battery within a range of greater than 0 and 1.2 or less.
[0027]
A more preferable range of the atomic ratio b of the element M is 0.01 or more and 0.12 or less. Most preferably, the element M is Al, B, or both Al and B, and the atomic ratio b is in the range of 0.02 to 0.1.
[0028]
In the second oxide, when the total amount of the atomic ratio of Ni and the atomic ratio of Co is 1, it is desirable that the atomic ratio of the element M be in the range of 0.005 to 0.2. This is due to the following reason. When the atomic ratio of the element M is less than 0.005, the thermal stability of the positive electrode active material is lowered, and it may be difficult to avoid the expansion and ignition of the storage container at the time of a short circuit. On the other hand, if the atomic ratio of the element M exceeds 0.2, a high battery capacity may not be obtained. Moreover, it is preferable to use Al, Nb, or both Al and Nb as the element M, and to make the atomic ratio of the element M within a range of 0.02 to 0.15. By adopting such a configuration, the thermal stability and battery capacity of the positive electrode active material can be further improved.
[0029]
The composition of the second oxide is preferably represented by the following formula (2) because a high capacity can be obtained.
[0030]
Li _x Ni _1-yz Co _z M _y O ₂ (2)
M is at least one element selected from the group consisting of Al, B, Sn, and Nb, and the atomic ratios x, y, and z are 0 <x ≦ 1.2, 0.004 ≦ y ≦ 0. 17, 0 <z ≦ 0.3, respectively.
[0031]
The atomic ratio x of Li in the composition formula (2) is greater than 0 and varies within the range of 1.2 or less depending on the charge amount and discharge amount of the nonaqueous electrolyte secondary battery.
[0032]
A more preferable range of the atomic ratio y of the element M is 0.01 or more and 0.12 or less. Most preferably, the element M is Al, Nb, or both Al and Nb, and the atomic ratio y is in the range of 0.02 to 0.1.
[0033]
The cobalt molar ratio z is preferably greater than 0 and less than or equal to 0.3. This is due to the following reason. By containing cobalt in the oxide, the thermal stability of the positive electrode active material can be improved, so that the safety of the secondary battery can be further improved. However, when the molar ratio z of cobalt exceeds 0.3, the characteristics of the oxide may be close to those of lithium cobalt oxide, which may make it difficult to obtain a high battery capacity. A more preferable range of the molar ratio z is greater than 0 and 0.25 or less, and a more preferable range is 0.1 or more and 0.25 or less.
[0034]
The positive electrode active material preferably has a pH (powder pH) in the range of 10 to 12. This is due to the following reason. Since the first oxide and the second oxide are synthesized from a raw material compound containing a lithium compound, lithium carbonate, lithium salt such as lithium oxide, that is, alkali is an unreacted substance or impurity Remain as If each oxide is washed with water, the alkali remaining in the oxide can be removed to reduce the pH, but the oxide is decomposed. On the other hand, when the pH exceeds 12, the reaction between the residual alkali content in the first oxide and the second oxide and the nonaqueous solvent of the nonaqueous electrolyte is likely to occur, and the amount of carbon dioxide generated is increased. There is a fear. A more preferable range of the pH is 10.5 to 11.8.
[0035]
The first oxide and the second oxide are synthesized by, for example, a solid phase method, a coprecipitation method, or a hydrothermal synthesis method.
[0036]
This positive electrode is produced, for example, by suspending a positive electrode active material, a conductive agent and a binder in an appropriate solvent, and applying this suspension to a current collector, drying and pressing to form a strip electrode.
[0037]
The binder has a function of binding between powders or particles contained in the positive electrode layer. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), or the like can be used. In particular, it is desirable to use a thermosetting resin, specifically PVdF is desirable.
[0038]
Examples of the conductive agent include acetylene black, carbon black, and graphite.
[0039]
The blending ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.
[0040]
As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, aluminum, stainless steel, or nickel. The thickness of the current collector is preferably 5 to 20 μm. This is because the electrode strength and weight reduction can be balanced within this range.
[0041]
The thickness of one surface of the positive electrode layer is preferably in the range of 10 to 150 μm. Accordingly, when the positive electrode current collector is supported on both surfaces, the total thickness of the positive electrode layer is desirably in the range of 20 to 300 μm. A more preferable range on one side is 30 to 100 μm. Within this range, large current discharge characteristics and cycle life are improved.
[0042]
The positive electrode may contain an adhesive polymer for bonding the positive electrode and the separator. The polymer having adhesiveness is desirably a polymer that can maintain high adhesiveness in a state where the nonaqueous electrolytic solution is retained. Furthermore, it is more preferable that such a polymer has high lithium ion conductivity. Specific examples include polyacrylonitrile (PAN), polyacrylate (PMMA), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), and polyethylene oxide (PEO). In particular, polyvinylidene fluoride (PVdF) is preferable. Polyvinylidene fluoride (PVdF) can hold a non-aqueous electrolyte and partly gelate when the non-aqueous electrolyte is included, so that the ionic conductivity in the positive electrode can be further improved.
[0043]
The polymer having adhesiveness preferably has a porous structure having fine pores in the gaps of the positive electrode, the negative electrode, and the separator. It is desirable that the polymer having adhesiveness having a porous structure can hold a large amount of the non-aqueous electrolyte and is evenly dispersed and scattered in the electrode group.
[0044]
2) Negative electrode
The negative electrode includes a current collector and a negative electrode layer that is supported on one or both surfaces of the current collector and includes a negative electrode active material.
[0045]
The negative electrode active material is preferably a carbonaceous material that absorbs and releases lithium ions. Examples of the carbonaceous materials include graphite materials such as graphite, coke, carbon fiber, spherical carbon, and granular carbon, carbonaceous materials such as coke, carbon fiber, spherical carbon, and granular carbon, thermosetting resin, isotropic pitch, Graphite material, thermosetting resin, isotropic pitch, mesophase obtained by heat-treating mesophase pitch, mesophase pitch-based carbon fiber, vapor-grown carbon fiber, mesophase small sphere, etc. at 2000-3000 ° C. Examples thereof include carbonaceous materials obtained by heat-treating pitch, mesophase pitch-based carbon fiber, vapor-grown carbon fiber, mesophase microspheres, etc. at 500 to 2000 ° C. Of the carbonaceous materials, mesophase pitch-based carbon fiber graphite materials, mesophase pitch-based carbon fiber carbonaceous materials, mesophase microsphere carbonaceous materials, mesophase microsphere carbonaceous materials, and granular graphite materials are preferred. is there. Among such carbonaceous materials, it is more preferable to use carbonaceous material a or carbonaceous material b described below.
[0046]
The carbonaceous material a is obtained by setting the temperature of the heat treatment to 2000 ° C. or more, and the surface spacing d of the (002) plane. ₀₀₂ Is a graphite material having a graphite crystal of 0.34 nm or less. The shape of the graphite material is preferably granular. A nonaqueous electrolyte secondary battery including a negative electrode containing the carbonaceous material a can greatly improve battery capacity and large current characteristics. Surface spacing d ₀₀₂ Is more preferably 0.336 nm or less.
[0047]
The carbonaceous material b is at least one selected from a fibrous graphite material that has been heat-treated at 2000 ° C. or higher and a spherical graphite material that has been heat-treated at 2000 ° C. or higher. Among these, mesophase pitch-based carbon fiber graphite materials, vapor-grown carbon fibers such as carbon whiskers, and mesophase microsphere graphite materials are preferable. The negative electrode including the carbonaceous material b has a density of 1.3 g / cm. ^Three Since the interface impedance between the negative electrode and the separator can be reduced even when increased to the above, the large current discharge characteristics and the rapid charge / discharge cycle performance of the secondary battery can be improved.
[0048]
The shape of the carbonaceous material can be, for example, fibrous, spherical, or granular. The negative electrode layer includes one or more carbonaceous materials selected from the group consisting of fibrous carbonaceous materials, spherical carbonaceous materials, and granular carbonaceous materials, thereby maintaining the interface resistance of the negative electrode at a low value over a long period of time. Therefore, the charge / discharge cycle life can be improved. When a liquid non-aqueous electrolyte or a gel non-aqueous electrolyte is used as the non-aqueous electrolyte, it is preferable to use a fibrous carbonaceous material as the negative electrode active material. A negative electrode including a fibrous carbonaceous material as a negative electrode active material can quickly impregnate a high-viscosity non-aqueous solution called the non-aqueous solvent in which the electrolyte is dissolved. Cycle life can be greatly improved.
[0049]
The average fiber length of the fibrous carbonaceous material is preferably in the range of 5 to 200 μm. A more preferable range is 10 to 50 μm.
[0050]
The average fiber diameter of the fibrous carbonaceous material is preferably in the range of 0.1 to 20 μm. A more preferable range is 1 to 15 μm.
[0051]
The average aspect ratio of the fibrous carbonaceous material is preferably in the range of 1.5 to 200. A more preferable range is 1.5 to 50. However, the aspect ratio is the ratio of the fiber length (fiber length / fiber diameter) to the fiber diameter.
[0052]
The average particle diameter of the spherical carbonaceous material is preferably in the range of 1 to 100 μm. A more preferable range is 2 to 40 μm.
[0053]
The ratio of the minor radius to the major radius of the spherical carbonaceous material (minor radius / major axis) is preferably 1/10 or more. A more preferable range is 1/2 or more.
[0054]
The granular carbonaceous material means a carbonaceous material powder having a shape in which a ratio of a minor radius to a major radius (minor radius / major axis) is in a range of 1/100 to 1. A more preferable range of the ratio is 1/10 to 1.
[0055]
The average particle size of the granular carbonaceous material is preferably in the range of 1 to 100 μm. A more preferable range is 2 to 50 μm.
[0056]
This negative electrode is produced, for example, by adding a binder to the negative electrode active material, suspending these in an appropriate solvent, applying this suspension to a current collector, drying and pressing to form a strip electrode. The A conductive agent may be further added to the suspension.
[0057]
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. Can be used. Among them, a thermosetting resin is desirable, and among these resins, PVdF is preferable.
[0058]
The blending ratio of the carbonaceous material and the binder is preferably in the range of 90 to 98% by weight of the carbonaceous material and 2 to 20% by weight of the binder. In particular, the carbonaceous material is 10 to 110 g / m on one side in a state where a negative electrode is produced. ² It is preferable to be in the range. The packing density is 1.2 to 1.5 g / cm. ^Three It is desirable to be in the range.
[0059]
As the current collector, a conductive substrate having a porous structure or a nonporous conductive substrate can be used. These conductive substrates can be formed from, for example, copper, stainless steel, or nickel. The thickness of the current collector is preferably 5 to 20 μm. This is because within this range, the electrode strength and weight reduction can be balanced.
[0060]
The thickness of the negative electrode active material layer is preferably in the range of 10 to 150 μm. Accordingly, when the negative electrode current collector is supported on both surfaces, the total thickness of the negative electrode active material layer is in the range of 20 μm to 300 μm. A more preferable range of the thickness of one side is 30 to 100 μm. Within this range, the large current discharge characteristics and cycle life are greatly improved.
[0061]
The negative electrode may contain an adhesive polymer for bonding the negative electrode and the separator. The polymer having adhesiveness is desirably a polymer that can maintain high adhesiveness in a state where the nonaqueous electrolytic solution is retained. Furthermore, it is more preferable that such a polymer has high lithium ion conductivity. Specifically, the same thing as having demonstrated with the positive electrode mentioned above can be mentioned.
[0062]
The area of the negative electrode is preferably larger than the area of the positive electrode. With such a configuration, since the negative electrode end can be extended from the positive electrode end, current concentration at the negative electrode end can be suppressed, and the cycle performance and safety of the secondary battery can be increased. Can do.
[0063]
As the negative electrode active material, in addition to the carbonaceous material that occludes / releases lithium ions described above, a material containing a metal oxide, metal sulfide, or metal nitride, or a material made of lithium metal or a lithium alloy is used. be able to.
[0064]
Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide.
[0065]
Examples of the metal sulfide include tin sulfide and titanium sulfide.
[0066]
Examples of the metal nitride include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride.
[0067]
Examples of the lithium alloy include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy.
[0068]
3) Non-aqueous electrolyte
This non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.
[0069]
As the non-aqueous electrolyte, a liquid non-aqueous electrolyte prepared by dissolving an electrolyte in a non-aqueous solvent, or a gel electrolyte obtained by combining the liquid non-aqueous electrolyte and a polymer material can be used.
[0070]
Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC), trifluoropropylene carbonate (TFPC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate. (DEC), ethyl propionate, methyl propionate, γ-butyrolactone (BL), acetonitrile (AN), ethyl acetate (EA), toluene, xylene, methyl acetate (MA) and the like. These non-aqueous solvents can be used alone or in the form of a mixture of two or more.
[0071]
The volume ratio of γ-butyrolactone (γBL) in the non-aqueous solvent is preferably 50% by volume or more of the whole non-aqueous solvent. Since the non-aqueous electrolyte provided with such a non-aqueous solvent has high thermal stability, abnormal heat generation of the battery can be suppressed and safety can be further improved. If the volume ratio of γBL is less than 50% by volume, the amount of gas generated at a high temperature increases, which may make it difficult to suppress the expansion of the storage container. Furthermore, when the solvent mixed with γBL is a cyclic carbonate (for example, ethylene carbonate), the volume ratio of the cyclic carbonate becomes relatively high, so that the solvent viscosity increases, the conductivity decreases, and the charge / discharge cycle characteristics. And the large current discharge characteristics deteriorate. In addition, if the volume ratio of γBL exceeds 95% by volume, a reaction between the negative electrode and γBL may occur, which may reduce charge / discharge cycle characteristics and safety. Therefore, the volume ratio of γBL in the non-aqueous solvent is 50%. It is preferable to be in the range of ~ 95% by volume. A more preferable range of the volume ratio of γBL is 55 volume% or more and 75 volume% or less. Within this range, the effect of suppressing gas generation during high-temperature storage becomes higher.
[0072]
As the solvent mixed with γBL, a cyclic carbonate is desirable in terms of increasing the charge / discharge efficiency of the negative electrode. As the cyclic carbonate, propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC), trifluoropropylene carbonate (TFPC) and the like are desirable. In particular, when EC is used as a solvent mixed with γBL, charge / discharge cycle characteristics and large current discharge characteristics can be improved. In addition, the other solvent mixed with γBL is preferably a mixed solvent of EC and at least one solvent selected from the group consisting of PC, VC, TFPC, diethyl carbonate (DEC), and methyl ethyl carbonate (MEC). It is desirable in terms of enhancing the discharge cycle characteristics.
[0073]
Further, from the viewpoint of lowering the solvent viscosity, the low viscosity solvent may contain 20% by volume or less. Examples of the low viscosity solvent include chain carbonate, chain ether, and cyclic ether.
[0074]
Specific examples of more preferable combinations of the non-aqueous solvent of the present invention include γBL and EC, γBL and PC, γBL and EC and DEC, γBL and EC and MEC, or γBL and EC and VC, and these combinations include EC. In this case, the volume ratio of EC is desirably 5 to 50% by volume. Moreover, the volume ratio of DEC, MEC, or VC can be 0.5-10 volume%.
[0075]
In the present invention, it is desirable to add a surfactant such as trioctyl phosphate in the range of 0.01 to 3% in order to improve the wettability with the separator.
[0076]
Examples of the electrolyte include lithium perchlorate (LiClO). _Four ), Lithium hexafluorophosphate (LiPF) ₆ ), Lithium tetrafluoroborate (LiBF) _Four ), Lithium hexafluoroarsenide (LiAsF) ₆ ), Lithium trifluorometasulfonate (LiCF) _Three SO _Three ), Bistrifluoromethylsulfonylimide lithium [LiN (CF _Three SO ₂ ) ₂ And the like. Among them, LiPF ₆ , LiBF _Four Is preferably used.
[0077]
The amount of the electrolyte dissolved in the non-aqueous solvent is preferably 0.5 to 2 mol / L.
[0078]
The gel-like non-aqueous electrolyte is prepared by, for example, mixing the non-aqueous solvent, the electrolyte, the polymer, and the gelling agent, followed by heat treatment to cause gelation.
[0079]
As the polymer, at least one polymer selected from polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), polyvinyl chloride (PVC), and polyacrylate (PMMA) is used. it can.
[0080]
When using a liquid nonaqueous electrolyte, the amount of the liquid nonaqueous electrolyte is preferably 0.2 to 0.6 g per 100 mAh of battery unit capacity. This is due to the following reason. If the liquid nonaqueous electrolytic mass is less than 0.2 g / 100 mAh, the ionic conductivity of the positive electrode and the negative electrode may not be sufficiently maintained. On the other hand, if the liquid non-aqueous electrolytic mass exceeds 0.6 g / 100 mAh, the electrolytic mass becomes large, and sealing with a film container may be difficult. A more preferable range of the liquid nonaqueous electrolytic mass is 0.4 to 0.55 g / 100 mAh.
[0081]
4) Storage container
In this storage container, an electrode group and a non-aqueous electrolyte are stored.
[0082]
The shape of the storage container can be, for example, a bottomed cylindrical shape, a bottomed rectangular tube shape, a bag shape, or the like.
[0083]
Examples of the film material constituting the storage container include a metal film, a resin sheet such as a thermoplastic resin, and a sheet in which a resin layer such as a thermoplastic resin is coated on one or both sides of a flexible metal layer. Etc. can be formed. The resin sheet and the resin layer can be formed from one type of resin or two or more types of resin, respectively. Meanwhile, the metal layer can be formed of one kind of metal or two or more kinds of metals. Moreover, the said metal film can be formed from aluminum, iron, stainless steel, nickel, etc., for example.
[0084]
The film material constituting the outer wall of the storage container has a thickness of 0.25 mm or less. A particularly desirable thickness range is 0.05 mm to 0.2 mm. This achieves a thinner and lighter battery.
[0085]
In particular, a sheet composed of a flexible metal layer and a resin layer laminated on one or both sides of the metal layer is lightweight, high in strength, and penetrates a substance such as moisture from the outside. Can be prevented, which is desirable. The storage container constituted by the sheet is sealed by, for example, heat sealing. For this reason, it is desirable to arrange a thermoplastic resin on the inner surface of the storage container. The melting point of the thermoplastic resin is preferably 120 ° C or higher, more preferably 140 ° C to 250 ° C. Examples of the thermoplastic resin include polyolefins such as polyethylene and polypropylene. In particular, it is desirable to use polypropylene having a melting point of 150 ° C. or higher because the sealing strength of the heat seal portion is increased. On the other hand, the metal layer is preferably formed of aluminum which prevents water from entering the battery.
[0086]
When a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte is used as the nonaqueous electrolyte, a separator can be disposed between the positive electrode and the negative electrode. Hereinafter, the separator will be described.
[0087]
5) Separator
A porous separator is used as the separator. As a material of the separator, for example, a porous film containing polyethylene, polypropylene, or polyvinylidene fluoride (PVdF), a synthetic resin nonwoven fabric, or the like can be used. Among these, a porous film made of polyethylene, polypropylene, or both is preferable because it can improve the safety of the secondary battery.
[0088]
The thickness of the separator is preferably 30 μm or less. If the thickness exceeds 30 μm, the distance between the positive and negative electrodes may be increased and the internal resistance may be increased. Further, the lower limit value of the thickness is preferably 5 μm. If the thickness is less than 5 μm, the strength of the separator is remarkably lowered and an internal short circuit is likely to occur. The upper limit value of the thickness is more preferably 25 μm, and the lower limit value is more preferably 10 μm.
[0089]
The separator preferably has a thermal shrinkage rate of 20% or less when stored at 120 ° C. for 1 hour. If the thermal shrinkage rate exceeds 20%, it may be difficult to make the adhesive strength between the positive and negative electrodes and the separator sufficient. The thermal shrinkage rate is more preferably 15% or less.
[0090]
The separator preferably has a porosity in the range of 30 to 70%. This is due to the following reason. If the porosity is less than 30%, it may be difficult to obtain high electrolyte retention in the separator. On the other hand, if the porosity exceeds 60%, sufficient separator strength may not be obtained. A more preferable range of the porosity is 35 to 70%.
[0091]
The separator has an air permeability of 500 seconds / 100 cm. ^Three The following is desirable. Air permeability is 500 seconds / 100cm ^Three If it exceeds 1, it may be difficult to obtain high lithium ion mobility in the separator. The lower limit of the air permeability is 30 seconds / 100 cm. ^Three It is preferable to make it. Air permeability is 30 seconds / 100cm ^Three If it is less than this, there is a possibility that sufficient separator strength cannot be obtained. The upper limit of air permeability is 150 seconds / 100cm ^Three More preferably, the lower limit is 50 seconds / 100 cm. ^Three More preferred.
[0092]
Both end portions orthogonal to the longitudinal direction of the separator extend from 0.25 mm to 2 mm from both end portions orthogonal to the longitudinal direction of the negative electrode, respectively, and an adhesive polymer exists in the extended portion of the separator. Is desirable. With such a configuration, the strength of the extending portion of the separator can be increased, so that a short circuit when an impact is applied to the battery can be suppressed. Furthermore, when the battery is present under high temperature conditions (100 ° C. or higher), the shrinkage of the separator can be suppressed, so that a short circuit can be suppressed and safety can be improved.
[0093]
The peel strength between the separator and the positive electrode layer and the peel strength between the separator and the negative electrode layer are each preferably 10 gf / cm or less. Thereby, the resistance of the electrochemical reaction between each active material layer and the separator can be reduced, and the battery performance can be improved. A more preferable range of each peel strength is 5 gf / cm or less, and a more preferable range is 2 gf / cm or less. However, a peel strength of 0 gf / cm between the separator and the positive electrode layer means that the separator and the positive electrode are not integrated, and a peel strength between the negative electrode layer and the separator is 0 gf / cm, It means that the negative electrode and the separator are not integrated.
[0094]
In order to have a peel strength within this range, the positive and negative electrodes and the separator are integrated by thermosetting in a state where the adhesive polymer is scattered at the interface between the positive electrode layer and the separator or the negative electrode layer and the separator, Alternatively, it is desirable that the positive electrode, the negative electrode, and the separator be integrated by thermosetting in a state in which an adhesive polymer is present in the voids of the positive electrode layer, the negative electrode layer, and the separator (including the binder). In this case, an adhesive polymer is scattered or hardly present at the interface between the positive electrode layer and the separator, and the negative electrode active material layer and the separator, and the electrochemical reaction is not inhibited. Therefore, large current performance, low temperature performance, and cycle performance can be greatly improved.
[0095]
Peel strength is measured by the 180 degree peel strength method. That is, as the measuring apparatus, a product manufactured by Fudo Kogyo Co., Ltd., having a trade name of Rheo meater and a model number of NRM / 1010J-CW is used. First, the secondary battery is disassembled, and a target laminate (for example, a laminate in which a negative electrode current collector, a negative electrode layer, and a separator are laminated in this order) is taken out. This laminate still retains the non-aqueous electrolyte. The width of the laminate was 20 mm and the length was 50 mm. This laminate is placed on the support base with the current collector side down. Next, a double-sided tape is attached to the upper surface of the laminate. This double-sided tape is manufactured by Sumitomo 3M Co., Ltd. under the trade name Scotch. NO. 665-3-24, the base material is transparent hard vinyl chloride, and the adhesive material is an acrylic resin-based adhesive material. The adhesion area between the laminate and the double-sided tape is 20 × 30 mm. The double-sided tape is pulled at a rate of 2 cm per minute in a direction parallel to the top surface of the laminate to peel the separator from the negative electrode layer. The force required to peel the separator fluctuates at the beginning of peeling, and the traction force when this force becomes constant is taken as the peeling strength between the negative electrode layer and the separator.
[0096]
Hereinafter, an example of a method for producing a nonaqueous electrolyte secondary battery according to the present invention (for example, a method for producing a thin lithium ion secondary battery having a structure shown in FIGS. 1 and 2 described later) will be described. However, the manufacturing method of the nonaqueous electrolyte secondary battery according to the present invention is not limited to the following embodiment.
[0097]
(First step)
An electrode group is prepared by interposing a porous sheet as a separator between the positive electrode and the negative electrode.
[0098]
(Second step)
The electrode group is stored in the bag-shaped storage container through the opening on the laminated surface. A polymer having adhesiveness is dissolved in a solvent, and the obtained solution is injected into the electrode group in the storage container through the opening, and the electrode group is impregnated with the solution.
[0099]
As the solvent, it is desirable to use an organic solvent having a boiling point of 200 ° C. or lower. An example of such an organic solvent is dimethylformamide (boiling point 153 ° C.). If the boiling point of the organic solvent exceeds 200 ° C., the drying time may be prolonged when the heating temperature described below is set to 100 ° C. or lower. The lower limit of the boiling point of the organic solvent is preferably 50 ° C. If the boiling point of the organic solvent is less than 50 ° C., the organic solvent may evaporate while the solution is injected into the electrode group. The upper limit of the boiling point is more preferably 180 ° C., and the lower limit of the boiling point is further preferably 100 ° C.
[0100]
The concentration of the polymer having adhesiveness in the solution is preferably in the range of 0.05 to 2.5% by weight. This is due to the following reason. If the concentration is less than 0.05% by weight, it may be difficult to bond the positive and negative electrodes and the separator with sufficient strength. On the other hand, if the concentration exceeds 2.5% by weight, it may be difficult to obtain a sufficient porosity to hold the non-aqueous electrolyte, and the interface impedance of the electrode may be significantly increased. As the interfacial impedance increases, the capacity and large current discharge characteristics are significantly reduced. A more preferable range of the concentration is 0.1 to 1.5% by weight.
[0101]
The injection amount of the solution is preferably in the range of 0.1 to 2 mL per 100 mAh of battery capacity when the concentration of the polymer having adhesiveness of the solution is 0.1 to 2.5% by weight. This is due to the following reason. When the injection amount is less than 0.1 mL, it may be difficult to sufficiently improve the adhesion between the positive electrode, the negative electrode, and the separator. On the other hand, if the injection amount exceeds 2 mL, the internal resistance of the battery may be increased, and it may be difficult to improve the discharge capacity, large current discharge characteristics, and charge / discharge cycle characteristics. A more preferable range of the injection amount is 0.15 to 1 mL per 100 mAh of battery capacity.
[0102]
(Third step)
The electrode group is 0.05 kg / cm at a high temperature of 30 ° C. or higher under reduced pressure (including vacuum) or normal pressure. ² 10 kg / cm ² Under the following pressure, the electrode group is pressurized to a predetermined thickness to form the electrode group.
[0103]
It is preferable to perform this molding step in a range of 60 ° C. to 100 ° C. in a reduced pressure atmosphere (including vacuum), since it can also serve as a drying step.
[0104]
A more preferable pressure is 0.01 to 2 kg / cm. ² It is. A more preferable temperature is 60 ° C to 100 ° C.
[0105]
As the pressing method, a press such as a flat plate press or a roll press, or insertion into a holder having a predetermined thickness can be employed. The pressurization may be applied to the electrode group covered with the storage container, or may be applied to the bare electrode group.
[0106]
(4th process)
After injecting a non-aqueous electrolyte into the electrode group in the storage container, the thin non-aqueous electrolyte secondary battery is assembled by sealing the opening of the storage container.
[0107]
In the manufacturing method described above, the solution in which the adhesive polymer is dissolved is injected after the electrode group is stored in the storage container. However, the injection may be performed without storing the electrode group in the storage container. In this case, first, an electrode group is produced by interposing a separator between the positive electrode and the negative electrode. After impregnating the electrode group with the solution, 0.005 kg / cm at 30 ° C. or higher ² 10 kg / cm ² The electrode group is heated and dried while being pressed at the following pressure to evaporate the solvent of the solution and form the electrode group with a predetermined thickness. After storing such an electrode group in a storage container, a thin nonaqueous electrolyte secondary battery can be manufactured by injecting a nonaqueous electrolyte and performing sealing or the like. An adhesive may be applied to the outer periphery of the electrode group before storage. Thereby, an electrode group and a storage container can be adhere | attached.
[0108]
In the above-described manufacturing method, the positive electrode, the negative electrode, and the separator are integrated with an adhesive polymer. However, the integration method is not limited to this, and for example, a binder contained in the positive electrode and the negative electrode is added. A thermosetting method can be employed. That is, the separator is interposed between the positive electrode and the negative electrode and wound into a flat shape, or the positive electrode and the negative electrode are bent one or more times with the separator interposed therebetween. By applying heat and pressure to the obtained flat product, the binder contained in the positive electrode and the negative electrode is thermally cured, and the positive electrode, the negative electrode, and the separator are integrated to obtain an electrode group. The heating and pressing can be performed under the same conditions as described in the third step described above.
[0109]
A thin lithium ion secondary battery which is an example of a non-aqueous electrolyte secondary battery according to the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a thin lithium ion secondary battery as an example of a nonaqueous electrolyte secondary battery according to the present invention, and FIG. 2 is an enlarged cross-sectional view showing part A of FIG.
[0110]
As shown in FIG. 1, the electrode group 2 is accommodated in the storage container 1 which consists of a sheet | seat containing a resin layer, for example. The electrode group 2 has a structure in which a laminate composed of a positive electrode, a separator, and a negative electrode is wound into a flat shape. T indicates the thickness (wall thickness) of the outer wall of the storage container 1. From the lower side of FIG. 2, the laminate includes the separator 3, the positive electrode layer 4, the positive electrode current collector 5, and the positive electrode layer 12 including the positive electrode layer 4, the separator 3, the negative electrode layer 6, the negative electrode current collector 7, and the negative electrode layer 6. The negative electrode 13 provided with the separator 3, the positive electrode layer 4, the positive electrode current collector 5, the positive electrode 12 provided with the positive electrode layer 4, the separator 3, the negative electrode layer 6 and the negative electrode 13 provided with the negative electrode current collector 7 were laminated in this order. Has a structured. The negative electrode current collector 7 is located on the outermost periphery of the electrode group 2. The adhesive layer 8 is disposed between the surface of the electrode group 2 and the inner surface of the storage container 1. The nonaqueous electrolyte is accommodated in the storage container 1. One end of the belt-like positive electrode lead 10 is connected to the positive electrode current collector 5 of the electrode group 1, and the other end is extended from the storage container 1. On the other hand, one end of the strip-shaped negative electrode lead 11 is connected to the negative electrode current collector 7 of the electrode group 1 and the other end is extended from the storage container 1.
[0111]
Further, the positive electrode 12, the negative electrode 13, and the separator 3 exist at the gaps of the positive electrode layer 4, the separator 3, and the negative electrode layer 6, the boundary between the positive electrode layer 4 and the separator 3, and the boundary between the negative electrode layer 6 and the separator 3. Are integrated by a polymer having adhesive properties. The polymer having adhesiveness present in the positive electrode layer 4 and the negative electrode layer 6 can also serve as a binder.
[0112]
Since the adhesive layer 8 can bond and integrate the storage container 1 and the electrode group 2, battery deformation can be reduced. The adhesive layer 8 can be formed from the above-described polymer having adhesiveness. The adhesive layer 8 may have a porous structure. The porous adhesive layer 8 can hold the non-aqueous electrolyte in the gap. Although the adhesive layer 8 is formed on the entire surface of the electrode group 2 in FIG. 1 described above, the adhesive layer 8 may be formed on a part of the electrode group 2. When the adhesive layer 8 is formed on a part of the electrode group 2, it is preferable to form it on at least the surface corresponding to the outermost periphery of the electrode group. Further, the adhesive layer 8 may not be provided.
[0113]
The total amount of the polymer having adhesiveness contained in the battery (including those used in the adhesive part) is preferably 0.1 to 6 mg per 100 mAh of battery capacity. This is due to the following reason. If the total amount of the polymer having adhesiveness is less than 0.1 mg per 100 mAh of battery capacity, it may be difficult to sufficiently improve the adhesion between the positive electrode, the separator and the negative electrode. On the other hand, if the total amount exceeds 6 mg per 100 mAh of battery capacity, the lithium ion conductivity of the secondary battery may decrease and the internal resistance may increase, improving the discharge capacity, large current discharge characteristics, and charge / discharge cycle characteristics. It can be difficult to do. A more preferable range of the total amount of the polymer having adhesiveness is 0.2 to 1 mg per 100 mAh of battery capacity.
[0114]
The non-aqueous electrolyte secondary battery according to the present invention described above includes a storage container, a positive electrode that is stored in the container and includes a positive electrode active material, and a negative electrode that is stored in the container and stores and releases lithium ions. A negative electrode containing an active material; and a non-aqueous electrolyte housed in the container. The outer wall of the storage container is a film material having a thickness of 0.25 mm or less. The positive electrode active material is a first oxide containing at least one element M, Li and Ni selected from the group consisting of Al, B, Sn and Nb, or the elements M, Li, Ni and Co. It is the 2nd oxide to contain. The pH of the positive electrode active material is in the range of 10-12.
[0115]
According to such a secondary battery, safety can be improved while securing a high battery capacity.
[0116]
That is, the first oxide and the second oxide can increase the battery capacity. At the same time, since the first oxide and the second oxide are relatively excellent in thermal stability, the thermal decomposition reaction when the battery internal temperature rises due to an internal short circuit or the like hardly occurs, and the amount of oxygen gas generated Less is. In addition, when a large current flows due to an internal short circuit or the like and the internal temperature of the battery rises, the reaction between the residual alkali in the positive electrode active material and the nonaqueous electrolyte can be suppressed, so the amount of carbon dioxide generated is reduced. can do. As a result, an increase in internal pressure of the secondary battery can be suppressed.
[0117]
The nonaqueous electrolyte secondary battery according to the present invention includes a storage container, a positive electrode stored in the container and containing a positive electrode active material, a negative electrode active material stored in the container and occluding and releasing lithium ions. A negative electrode containing a substance; and a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent. The outer wall of the storage container is a film material having a thickness of 0.25 mm or less. The positive electrode active material is a first oxide containing at least one element M, Li and Ni selected from the group consisting of Al, B, Sn and Nb, or the elements M, Li, Ni and Co. It is the 2nd oxide to contain. The non-aqueous solvent contains 50% by volume or more of γ-butyrolactone.
[0118]
According to such a secondary battery, safety can be improved while securing a high battery capacity.
[0119]
That is, the first oxide and the second oxide can increase the battery capacity. At the same time, since the first oxide and the second oxide are relatively excellent in thermal stability, the thermal decomposition reaction when the battery internal temperature rises due to an internal short circuit or the like hardly occurs, and the amount of oxygen gas generated Less is. On the other hand, since the non-aqueous electrolyte contains γ-butyrolactone that is difficult to oxidatively decompose in a non-aqueous solvent in an amount of 50% by volume or more, the reaction between the generated oxygen and the non-aqueous solvent can be minimized. Therefore, when a large current flows due to an internal short circuit or the like and the battery internal temperature rises, it is possible to suppress an increase in internal pressure, and it is possible to avoid an excessive increase in the battery temperature. Can be prevented, and the safety of the secondary battery can be improved.
[0120]
In the secondary battery according to the present invention, when the pH of the positive electrode active material is within the range of 10 to 12, when a large current flows due to an internal short circuit or the like and the internal temperature of the battery rises, Since the reaction between the residual alkali content and the non-aqueous electrolyte can be suppressed, the amount of carbon dioxide generated can be reduced. As a result, an increase in internal pressure of the secondary battery can be sufficiently suppressed.
[0121]
In the secondary battery according to the present invention, when using a liquid non-aqueous electrolyte or a gel-like non-aqueous electrolyte as the non-aqueous electrolyte, the negative electrode resistance is reduced by using a negative electrode containing a fibrous carbonaceous material. Therefore, the cycle life of the secondary battery can be further improved.
[0122]
That is, the liquid nonaqueous electrolyte has a relatively high viscosity because the volume ratio of γ-butyrolactone in the nonaqueous solvent is 50% by volume or more. On the other hand, the electrode group in which the gel-like non-aqueous electrolyte is held is prepared by placing a gel-like non-aqueous electrolyte precursor containing an electrolyte, a non-aqueous solvent and a polymer between the positive electrode and the negative electrode, and then impregnating the liquid non-aqueous electrolyte. It is produced by performing a heat treatment. Since the negative electrode containing a fibrous carbonaceous material can be impregnated quickly with a high-viscosity liquid non-aqueous electrolyte, the negative electrode resistance can be lowered and the cycle life of the secondary battery can be improved.
[0123]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings described above.
[0124]
(Example 1)
<Preparation of positive electrode>
First, the composition is LiNi _0.75 Co _0.15 Al _0.1 O ₂ And a nickel-nickel-cobalt-aluminum composite oxide powder having a pH of 11.0 measured by the method described below.
[0125]
That is, 2 g of the positive electrode active material was added to 100 mL of pure water, and the pH at 25 ° C. was continuously measured with a pH measuring device while setting the stirring speed to 3 revolutions per second. The pH value of the positive electrode active material for obtaining the pH value when the change in pH value with time was not observed, specifically, when the pH change per minute became 0.001 or less was taken.
[0126]
Next, 91% by weight of the lithium nickel cobalt aluminum composite oxide powder was mixed by adding 2% by weight of acetylene black, 3% by weight of graphite, 4% by weight of polyvinylidene fluoride (PVdF), and an N-methylpyrrolidone (NMP) solution. A slurry was prepared. The obtained slurry was applied to an aluminum foil current collector having a thickness of 10 μm, dried, and then pressed to obtain an electrode density of 3.0 g / cm. ^Three Thus, a positive electrode having a thickness of 120 μm was obtained. The peel strength between the positive electrode active material layer and the current collector was measured by the 180-degree peel strength method described above, and found to be 15 gf / cm.
[0127]
<Production of negative electrode>
Mesophase pitch-based carbon fiber heat-treated at 3000 ° C. as a carbonaceous material (fiber diameter is 8 μm, average fiber length is 20 μm, average spacing (d ₀₀₂ ) Is 0.3360 nm), 93% by weight of a powder, 7% by weight of polyvinylidene fluoride (PVdF) as a binder, and an NMP solution were added and mixed to prepare a slurry. The obtained slurry was applied on both sides of a current collector made of a copper foil having a thickness of 10 μm, dried and pressed to obtain an electrode density of 1.35 g / cm. ^Three Thus, a negative electrode in which a negative electrode layer having a thickness of 45 μm was supported on both surfaces of the current collector was produced. Therefore, the total thickness of the negative electrode layer is 90 μm. When the peel strength between the negative electrode layer and the current collector was measured by the 180-degree peel strength method described above, it was 12 gf / cm.
[0128]
<Preparation of flat electrode group>
Thickness 27μm, porosity 50%, air permeability 90 seconds / 100cm ^Three A polyethylene separator was prepared. The separator was interposed between the positive electrode and the negative electrode and wound into a spiral shape, and then formed into a flat shape to produce a flat electrode group having a thickness of 2.7 mm, a width of 30 mm, and a height of 50 mm.
[0129]
<Preparation of liquid nonaqueous electrolyte>
Lithium tetrafluoroborate (LiBF) in a mixed solvent of ethylene carbonate (EC) and γ-butyrolactone (γBL) (mixed volume ratio 40:60) _Four ) Was dissolved at 1.5 mol / L to prepare a liquid non-aqueous electrolyte.
[0130]
<Formation of electrode group>
A laminate film having a thickness of 0.1 mm in which both sides of an aluminum foil were covered with polypropylene was prepared as a storage container, and this was formed into a bag shape. The flat electrode group was housed in this, and both sides of the battery were sandwiched between holders so that the battery thickness was fixed at 2.7 mm. At this time, the pressure applied to the electrode group is 0.5 kg / cm. ² Met. Polyvinylidene fluoride (PVdF), which is an adhesive polymer, was dissolved in 0.3% by weight in dimethylformamide (DMF) (boiling point: 153 ° C.), which is an organic solvent. The obtained solution was poured into the electrode group in the laminate film so as to have a battery capacity of 0.6 mL, and the solution was allowed to penetrate into the electrode group and adhered to the entire surface of the electrode group.
[0131]
Next, the electrode group in the laminate film is vacuum-dried at 80 ° C. for 12 hours to evaporate the organic solvent, and to retain the polymer having adhesiveness in the voids of the positive electrode, the negative electrode, and the separator, and the electrode group A porous adhesive part was formed on the surface of the film.
[0132]
2 g of the liquid nonaqueous electrolyte is injected into the electrode group in the laminate film, and has the structure shown in FIGS. 1 and 2 described above, and has a thickness of 2.7 mm, a width of 32 mm, and a height of 55 mm. An electrolyte secondary battery was assembled.
[0133]
Example 2
Composition is LiNi _0.75 Co _0.15 Al _0.1 O ₂ And a nickel-nickel-cobalt-aluminum composite oxide powder having a pH of 11.5 measured by the method described above. A positive electrode was produced in the same manner as in Example 1 described above except that this composite oxide was used as the positive electrode active material. Between this positive electrode and the negative electrode similar to that described in Example 1 above, a separator similar to that described in Example 1 described above is interposed and wound into a spiral shape, and then formed into a flat shape. A flat electrode group having a thickness of 2.7 mm, a width of 30 mm, and a height of 50 mm was produced.
[0134]
After the flat electrode group is stored in the same storage container as described in Example 1, it is 1 kg / cm from the thickness direction of the electrode group using the holder described above. ² Molding was performed at a pressure of. Subsequently, the electrode group in the laminate film was vacuum-dried at 80 ° C. for 12 hours. A thin nonaqueous electrolyte secondary battery having a thickness of 2.7 mm, a width of 32 mm, and a height of 55 mm is injected into the electrode group in the laminate film by 2 g of the same liquid nonaqueous electrolyte as described in Example 1. Assembled.
[0135]
Example 3
LiNi having a pH of 11.2 as a positive electrode active material _0.75 Co _0.1 Al _0.15 O ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0136]
Example 4
LiNi having a pH of 11.5 as a positive electrode active material _0.8 Co _0.15 Al _0.04 B _0.01 O ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0137]
Example 5
LiNi having a pH of 11.5 as a positive electrode active material _0.8 Co _0.14 Al _0.04 B _0.01 Nb _0.01 O ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0138]
Example 6
LiNi having a pH of 12.0 as a positive electrode active material _0.8 Co _0.14 Al _0.05 Sn _0.01 O ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0139]
reference Example 7
LiNi having a pH of 11.5 as a positive electrode active material _0.9 Al _0.1 O ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0140]
reference Example 8
LiNi having a pH of 11.0 as a positive electrode active material _0.77 Al _0.2 B _0.03 O ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0141]
reference Example 9
LiNi having a pH of 11.8 as a positive electrode active material _0.77 Al _0.2 Sn _0.03 O ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0142]
Example 10
<Preparation of gel-like nonaqueous electrolyte>
A paste prepared by mixing a liquid non-aqueous electrolyte similar to that described in Example 1 and a solution obtained by dissolving polyvinylidene fluoride hexafluoropropylene (PVdF-HEP) in tetrahydroxyfuran (THF). Was prepared. The obtained paste was applied to a substrate and then dried to obtain a thin film.
[0143]
<Preparation of positive electrode>
LiNi having a pH of 11.2 as a positive electrode active material _0.75 Co _0.15 Al _0.1 O ₂ A positive electrode was produced in the same manner as in Example 1 except that was used.
[0144]
<Production of electrode group>
The positive electrode described above and the negative electrode similar to that described in Example 1 were wound in a spiral shape through the thin film therebetween, and then formed into a flat shape to produce an electrode group.
[0145]
This electrode group was immersed in the liquid non-aqueous electrolyte described above, and the thin film was plasticized under reduced pressure to obtain an electrode group in which a gel-like non-aqueous electrolyte layer was interposed between the positive electrode and the negative electrode.
[0146]
A laminated film similar to that described in Example 1 is formed into a bag shape, and the electrode group is accommodated in the bag. The thin non-aqueous electrolyte has a thickness of 2.7 mm, a width of 32 mm, and a height of 55 mm. A secondary battery was assembled.
[0147]
Example 11
LiNi having a pH of 10.8 as a positive electrode active material _0.75 Co _0.15 Al _0.1 O ₂ As a liquid nonaqueous electrolyte, lithium hexafluorophosphate (LiPF) is mixed in a mixed solvent of 48 volume% ethylene carbonate (EC), 50 volume% propylene carbonate (PC), and 2 volume% vinylene carbonate (VC). ₆ A non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 2 except that 1.5 mol / L was dissolved.
[0148]
Example 12
LiNi having a pH of 11.4 as a positive electrode active material _0.75 Co _0.15 Al _0.1 O ₂ A thin nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 11 except that was used.
[0149]
Example 13
LiNi having a pH of 12.0 as a positive electrode active material _0.75 Co _0.15 Al _0.1 O ₂ A thin nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 11 except that was used.
[0150]
Comparative Example 1
LiNiO having a pH of 12.2 as a positive electrode active material ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0151]
Comparative Example 2
LiNi having a pH of 12.1 as a positive electrode active material _0.8 Co _0.2 O ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0152]
Comparative Example 3
LiNi having a pH of 12.3 as a positive electrode active material _0.75 Co _0.15 Al _0.1 O ₂ LiPF in a mixed solvent of EC and MEC (mixing volume ratio 50:50) as a liquid non-aqueous electrolyte ₆ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that 1 mol / L dissolved was used.
[0153]
Comparative Example 4
LiNi having a pH of 12.2 as a positive electrode active material _0.75 Co _0.15 Al _0.1 O ₂ And LiPF as a liquid non-aqueous electrolyte in a mixed solvent of EC and γ-butyrolactone (mixing volume ratio 60:40) _Four A thin nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that 1.5 mol / L dissolved was used.
[0154]
Comparative Example 5
LiCoO having a pH of 10.5 as a positive electrode active material ₂ A thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that.
[0155]
Examples 1 to 1 obtained above 6,10-13 and Reference Examples 7-9 And about the battery of Comparative Examples 1-5, after performing the constant voltage charge of 4.2V at 0.5C for 3 hours, the capacity | capacitance at the time of discharging to 3V at 0.5C was calculated | required, respectively, and the result was shown in following Table 3, 4 shows.
[0156]
Examples 1 to 6,10-13 and Reference Examples 7-9 And about the battery of Comparative Examples 1-5, it overcharges to 4.4V, the safety performance test of a needle stick is performed, the battery temperature and the swelling rate of a storage container are measured, and the result is shown to the following Tables 3 and 4.
[0157]
Furthermore, Examples 1 to 6,10-13 and Reference Examples 7-9 The batteries of Comparative Examples 1 to 5 were subjected to a constant voltage charge of 4.2 V at 0.5 C for 3 hours, and then a charge / discharge cycle test was performed to discharge to 3 V at 0.5 C to obtain 80% capacity of the initial capacity. The number of charging / discharging cycles at this time was examined and the results are shown in Tables 3 and 4 below.
[0158]
[Table 1]

[0159]
[Table 2]

[0160]
[Table 3]

[0161]
[Table 4]

[0162]
As apparent from Tables 1 to 4, Examples 1 to 6,10-13 Compared with Comparative Examples 1-5, this battery has a high capacity, high safety, and excellent cycle life characteristics.
[0163]
Examples 14-18
Composition is LiNi _0.8 Co _0.14 Al _0.06 O ₂ And 5 types of lithium nickel cobalt aluminum composite oxide powders having a pH of 10.8, 11.2, 11.4, 11.8, 12.0 measured by the method described above were prepared. A positive electrode was produced in the same manner as in Example 1 described above except that each composite oxide was used as a positive electrode active material.
[0164]
<Production of negative electrode>
The mesophase pitch-based carbon fiber was heat-treated at 3000 ° C. to prepare a mesophase pitch-based carbon fiber graphitic material as a carbonaceous material. The carbon fiber has an average fiber diameter of 10 μm, an average fiber length of 30 μm, an average aspect ratio of 20, and an average spacing (d ₀₀₂ ) Was 0.3358 nm. A slurry was prepared by adding 93% by weight of the carbonaceous powder, 7% by weight of polyvinylidene fluoride (PVdF) as a binder, and an NMP solution. The obtained slurry was applied on both sides of a current collector made of a copper foil having a thickness of 10 μm, dried and pressed to obtain an electrode density of 1.35 g / cm. ^Three A negative electrode was prepared.
[0165]
<Preparation of liquid nonaqueous electrolyte>
Lithium tetrafluoroborate (LiBF) in a mixed solvent of 24% by volume ethylene carbonate (EC), 75% by volume γ-butyrolactone (γBL) and 1% by volume vinylene carbonate (VC) _Four ) Was dissolved at 1.5 mol / L to prepare a liquid non-aqueous electrolyte.
[0166]
A separator similar to that described in Example 1 described above is interposed between the positive electrode and the negative electrode and wound into a spiral shape, then formed into a flat shape, a thickness of 2.7 mm, a width of 30 mm, and a height. A 50 mm flat electrode group was prepared. Next, 12 kg / cm at 90 ° C. is applied to the electrode group. ² The press was performed at a pressure of.
[0167]
A laminate film similar to that described in Example 1 was prepared as a storage container and formed into a bag shape. After storing the flat electrode group in this, 2 g of the liquid nonaqueous electrolyte was injected to assemble a thin nonaqueous electrolyte secondary battery having a thickness of 2.7 mm, a width of 32 mm, and a height of 55 mm.
[0168]
Example 19
The mesophase spherules were heat treated at 3000 ° C. to prepare mesophase spherulitic graphite materials as carbonaceous materials. The mesophase spherules have an average particle size of 6 μm, a ratio of the minor axis to the major axis of 0.9, and an average interplanar spacing (d ₀₀₂ ) Was 0.3360 nm. A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 14 described above except that such a spherical carbonaceous material was used.
[0169]
Example 20
A mixed powder of 50% by weight of mesophase pitch-based carbon fiber heat-treated at 3000 ° C. and 50% by weight of granular graphite was prepared as a carbonaceous material. The carbon fiber has an average fiber diameter of 10 μm, an average fiber length of 30 μm, an average aspect ratio of 20, and an average spacing (d ₀₀₂ ) Was 0.3358 nm. On the other hand, the granular graphite has an average particle diameter of 10 μm, a ratio of a minor radius to a major radius of 0.6, and an average interplanar spacing (d ₀₀₂ ) Was 0.3355 nm. A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 14 described above except that such a carbonaceous material was used.
[0170]
The obtained batteries of Examples 14 to 20 were each charged with a constant voltage of 4.2 V at 0.5 C for 3 hours and then discharged to 0.5 V at 0.5 C, and the results are shown in the table below. As shown in FIG.
[0171]
Moreover, about the battery of Examples 14-20, it overcharges to 4.4V, the safety performance test of a needle stick is performed, battery temperature and the swelling rate of a storage container are measured, The result is shown in following Table 5.
[0172]
Further, the batteries of Examples 14 to 20 were subjected to a constant voltage charge of 4.2 V at 0.5 C for 3 hours, and then a charge / discharge cycle test in which the battery was discharged to 3 V at 0.5 C was performed. The number of charge / discharge cycles at the time of becoming is examined, and the results are shown in Table 5 below.
[0173]
[Table 5]

[0174]
As can be seen from Table 5, the higher the pH of the positive electrode active material, the greater the swelling of the storage container. Moreover, it turns out that the secondary battery of Example 14 provided with the negative electrode containing a fibrous carbonaceous material as a negative electrode active material has a long cycle life compared with the secondary battery of Examples 19 and 20.
[0175]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a thin non-aqueous electrolyte secondary battery having high capacity and excellent cycle life characteristics while ensuring safety.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a nonaqueous electrolyte secondary battery according to the present invention.
FIG. 2 is an enlarged cross-sectional view showing a portion A in FIG.
[Explanation of symbols]
1 ... Storage container,
2 ... Electrode group,
3 ... Separator,
4 ... positive electrode layer,
5 ... positive electrode current collector,
6 ... negative electrode layer,
7 ... negative electrode current collector,
12 ... positive electrode,
13 ... negative electrode,
T: The thickness of the outer wall of the storage container.

Claims (12)

A storage container, a positive electrode stored in the container and including a positive electrode active material, a negative electrode stored in the container and including a negative electrode active material, and a nonaqueous electrolyte stored in the container. ,
The storage container is formed of a film material having a thickness of 0.25 mm or less,
The non-aqueous electrolyte secondary battery, wherein the positive electrode active material includes an oxide having a composition represented by the following formula (2) , and the pH of the positive electrode active material is in the range of 10-12.
_{Li x Ni 1-yz Co z} M y O 2 (2)
Where M is Al or at least one element selected from the group consisting of Al and B, Sn and Nb, and the atomic ratios x, y and z are 0 <x ≦ 1.2, 0.004. ≦ y ≦ 0.2,0 <z ≦ 0.3 and shows respectively the atomic ratio of Al is 0.04 or more and 0.15 or less. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein, in the composition formula (2), the element M is composed of Al and Nb, and the atomic ratio y satisfies 0.02 ≦ y ≦ 0.1. . The nonaqueous electrolyte secondary battery according to claim 1 , wherein the positive electrode active material has a pH in a range of 10.5 to 11.8 . The non-aqueous electrolyte secondary battery according to claim 1 , wherein the non-aqueous electrolyte is a liquid non-aqueous electrolyte or a gel-like non-aqueous electrolyte . The non-aqueous electrolyte secondary battery according to claim 1 , wherein the film material is a sheet including a resin layer . The nonaqueous electrolyte secondary battery according to claim 1 , wherein the nonaqueous electrolyte contains a nonaqueous solvent containing 50% by volume or more of γ-butyrolactone . The non-aqueous solvent, ethylene carbonate (EC), propylene carbonate (PC) and a non according to claim 6, further comprising at least one or more solvents selected from the group consisting of vinylene carbonate (VC) Water electrolyte secondary battery. The negative electrode, the fibrous carbonaceous material, non-aqueous electrolyte secondary battery according to claim 1, characterized in that it comprises one or more carbonaceous material is selected from the group consisting of spherical carbonaceous material and particulate carbonaceous material. The non-aqueous electrolyte secondary battery according to claim 8, wherein an average aspect ratio of the fibrous carbonaceous material is in a range of 1.5 to 200 . 9. The nonaqueous electrolyte secondary battery according to claim 8 , wherein the granular carbonaceous material has a ratio of a minor axis to a major axis (minor axis / major axis) in a range of 1/100 to 1 . 9. The nonaqueous electrolyte secondary battery according to claim 8 , wherein the spherical carbonaceous material has a ratio of a minor axis to a major axis (minor axis / major axis) of 1/10 or more . The negative electrode non-aqueous electrolyte secondary battery according to claim 1 comprising the lithium-titanium oxide.

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