JP2004319287A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery having excellent safety capable of surely clearing a 150°C heating test regulated in UL1642 even with a capacity of 1300-5000mAh. <P>SOLUTION: This lithium ion secondary battery 1 mainly comprises an anode 10 and a cathode 20 opposed to each other; a separator 40 having insulating property, which is arranged adjacently between the anode and the cathode; an electrolytic solution 30 containing lithium ion; and a case 50 for storing them in a sealed state, with a capacity of 1,300-5,000 mAh. The anode has a porous anode active material layer including an anode active material, and the cathode has a porous cathode active material layer including a cathode active material. The anode active material is an electron conductive carbonaceous material having a BET specific surface area of 0.5-1.5 m<SP>2</SP>/g. The separator is formed including a synthetic resin, and its thermal contraction rate at 90°C of 0.1-3%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００９４】
【表２】

【００９５】
表１に示した結果から明らかなように、実施例１及び実施例２のリチウムイオン二次電池は、ＵＬ１６４２規定の１５０℃加熱試験を確実にクリアすることのできる優れた安全性を有することが確認された。
【００９６】
【発明の効果】
以上説明したように、本発明によれば、容量を１３００〜５０００ｍＡｈとする場合であっても、ＵＬ１６４２規定の１５０℃加熱試験を確実にクリアすることのできる優れた安全性を有するリチウムイオン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】本発明のリチウムイオン二次電池の好適な一実施形態を示す正面図である。
【図２】図１に示すリチウムイオン二次電池の内部をアノード１０の表面の法線方向からみた場合の展開図である。
【図３】図１に示すリチウムイオン二次電池を図１のＸ１−Ｘ１線に沿って切断した場合の模式断面図である。
【図４】図１に示すリチウムイオン二次電池を図１のＸ２−Ｘ２線に沿って切断した場合の要部を示す模式断面図である。
【図５】図１に示すリチウムイオン二次電池を図１のＹ−Ｙ線に沿って切断した場合の要部を示す模式断面図である。
【図６】図１に示すリチウムイオン二次電池のケースの構成材料となるフィルムの基本構成の一例を示す模式断面図である。
【図７】図１に示すリチウムイオン二次電池のケースの構成材料となるフィルムの基本構成の別の一例を示す模式断面図である。
【図８】図１に示すリチウムイオン二次電池のアノードの基本構成の一例を示す模式断面図である。
【図９】図１に示すリチウムイオン二次電池のカソードの基本構成の一例を示す模式断面図である。
【符号の説明】
１…リチウムイオン二次電池、１０…アノード、１２…アノード用リード線、１４…絶縁体、２０…カソード、２２…カソード用リード線、２４…絶縁体、３０…電解質溶液、４０…セパレータ、５０…ケース、６０…素体。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium ion secondary battery.
[0002]
[Prior art]
2. Description of the Related Art In recent years, the performance of electronic devices, particularly small electronic devices such as mobile phones, notebook computers, and PDAs (Personal Digital Assistants), has been remarkably improved, and power consumption tends to increase year by year as the devices spread. Accordingly, development of a battery having a high energy density as a power supply mounted on such an electronic device is desired. As one of such batteries, a lithium ion secondary battery has been widely adopted as a power source for portable equipment because of its high energy density and the like.
[0003]
A lithium ion secondary battery is mainly composed of a cathode, an anode, a separator, and an electrolyte solution (including a gel-like solid electrolyte and a solid polymer electrolyte), and has battery characteristics such as higher voltage and higher energy density. Various studies have been made to further improve the size and to reduce the size and weight. In order to improve the battery characteristics in this way, the energy density of the lithium ion secondary battery is very high compared to other batteries, so it is also necessary to ensure sufficient safety of the battery during use or storage. It becomes important. This safety is particularly important when a flammable non-aqueous electrolyte solution (an electrolyte solution containing an organic solvent) is used as the electrolyte solution.
[0004]
As standardized in the safety evaluation test of the lithium ion secondary battery, there is "UL1642" or "UL2054" of the United States UL (Underwriters Laboratories) standard.
[0005]
From the viewpoint of improving the battery characteristics, it is desirable to configure an electrode having a high activity against the electrode reaction, but from the viewpoint of safety, the reaction between the electrode and the components of the electrolyte solution, the reaction between the components of the electrolyte solution, and the like are suppressed. It is desirable to apply such a contrivance to the electrode or the electrolyte. As described above, the improvement of battery characteristics (capacity, energy density, output characteristics, etc.) and the securing of battery safety are in a trade-off relationship, and a lithium ion secondary battery having desired excellent battery characteristics and safety is provided. Developing batteries is not easy.
[0006]
For example, by providing a negative electrode having a negative electrode active material layer having a BET specific surface area of 0.5 to 2.0 m ² / g, it was intended to obtain good discharge characteristics while maintaining high safety and reliability. Lithium ion secondary batteries have been proposed (for example, see Patent Document 1).
[0007]
[Patent Document 1]
Patent No. 3139390 [0008]
[Problems to be solved by the invention]
However, even in the conventional lithium ion secondary battery described in Patent Literature 1, the capacity of the battery (particularly, a battery using a non-aqueous electrolyte solution as the electrolyte solution) is set to 1300 to 5000 mAh. The present inventors have found that, when intended, it is extremely difficult to reliably pass the 150 ° C. heating test of the above safety evaluation test standard “UL1642”, and it is impossible to obtain reliable safety. .
[0009]
Batteries that cannot reliably pass the “UL1642” 150 ° C heating test generate gas inside when the temperature inside the battery rises due to abnormal heat generation in the battery during use or storage. Then, the internal pressure rises, and problems such as liquid leakage and ignition may occur. In particular, when the case is formed from a flexible film, the above problem is likely to occur because the seal portion of the case is peeled off.
[0010]
The present invention has been made in view of the above-mentioned problems of the related art, and has an excellent safety that can reliably clear the 150 ° C. heating test specified in UL1642 even when the capacity is set to 1300 to 5000 mAh. It is an object of the present invention to provide a lithium ion secondary battery having a property.
[0011]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to achieve the above object, and as a result, when the capacity of the lithium ion secondary battery is particularly set to 1300 to 5000 mAh, the battery configuration is changed to a battery temperature in a 150 ° C. heating test specified in UL1642. The temperature at which a short-circuit phenomenon starts to be observed between the anode and the cathode (hereinafter referred to as “short-circuit start temperature”) of 125 ° C. or higher ensures that the 150 ° C. heating test specified in UL1642 is reliably cleared. I can do it. Further, the present inventors have found that it is extremely effective to achieve the above object by making the structure of the battery satisfy the following conditions, and have reached the present invention.
[0012]
That is, the present invention provides a plate-shaped cathode having a porous anode active material layer including a porous anode active material layer including an anode active material facing each other, and a plate-shaped cathode including a porous cathode active material layer including a cathode active material. It is disposed between the anode and the cathode, and has a plate-shaped separator having an insulating property, an electrolyte solution containing lithium ions, and a case accommodating the anode, the cathode, the separator, and the electrolyte solution in a sealed state. The anode active material is an electron conductive carbon material having a BET specific surface area of 0.5 to 1.5 m ² / g, and the separator is made of synthetic resin as a constituent material. A lithium ion secondary battery characterized in that it is formed so as to have a heat shrinkage at 90 ° C. of 0.1 to 3%.
[0013]
Since the lithium ion secondary battery of the present invention has the anode having the above configuration and a separator having a heat shrinkage in the above range, the short-circuit initiation temperature in the 150 ° C. heating test specified in UL1642 should be 125 ° C. or more. Can be easily and reliably performed. Therefore, even when the capacity is set to 1300 to 5000 mAh, a lithium ion secondary battery having excellent safety which can surely pass the 150 ° C. heating test specified in UL1642 can be provided.
[0014]
Here, in the present invention, “thermal shrinkage at 90 ° C.” refers to a separator obtained by punching a predetermined area (area of the main surface) S1 at room temperature (25 ° C.) under a temperature condition of 90 ° C. It is a reduction rate (100 × S2 / S1) of the area of the main surface calculated by measuring the area S2 of the main surface that has been exposed to the atmosphere for 1 hour and then reduced by the thermal shrinkage of the separator obtained thereafter.
[0015]
In the present invention, the fact that the heat shrinkage at 90 ° C. is less than 0.1% is achieved by mixing a filler such as SiO ₂ or Al ₂ O ₃ into a resin as a constituent material of the separator to suppress the shrinkage. Is also very difficult. If the “heat shrinkage at 90 ° C.” exceeds 3%, the short-circuit start temperature during the 150 ° C. heating test is less than 125 ° C., and the heating test cannot be cleared.
[0016]
In addition, the inventors have determined that a separator having a melting point of 120 ° C. or higher (preferably, a separator having a melting point of 120 to 180 ° C.) can be used as long as the separator has a heat shrinkage in the above range. I found it. As described above, in the present invention, since a separator having a melting point lower than the temperature of the 150 ° C. heat test can be used, the selection range of the constituent materials of the separator can be widened, and the manufacturing cost can be easily reduced. .
[0017]
Here, in the present invention, when the capacity exceeds 5000 mAh, the mass and volume of the components (electrodes, electrolytes, separators, and gel-like synthetic resin layers) of the battery become large, and these are sufficient to accommodate these in a sealed state. A case having mechanical strength cannot be formed. On the other hand, when the capacity is less than 1300 mAh, it becomes impossible to supply a sufficient power required as a power source of an electronic device (especially a small electronic device) to be mounted.
[0018]
In the present invention, if the BET specific surface area of the anode active material (electron conductive carbon material) is less than 0.5 m ² / g, a sufficient electrode reaction speed of the anode cannot be secured, and the electron to be mounted Sufficient power supply cannot be performed promptly in response to fluctuations in load demands required from devices (especially small electronic devices). On the other hand, when the BET specific surface area exceeds 1.5 m ² / g, the reaction activity of the electrode becomes too high, and besides the desired anode electrode reaction, for example, side reactions such as decomposition reaction of the electrolyte solution component occur simultaneously and It becomes easy to proceed quickly, and it is no longer possible to ensure sufficient and reliable safety.
[0019]
Here, in the present invention, the electrodes serving as the anode and the cathode serve as a reaction field capable of reversibly proceeding an electron transfer reaction in which lithium ions (or metallic lithium) participate as redox species. Further, "promoting the electron transfer reaction reversibly" means that the electron transfer reaction proceeds reversibly within a range of a battery life required as a power supply or an auxiliary power supply of a device to be mounted. .
[0020]
The anode active material contained in the anode as a constituent material and the cathode active material contained in the cathode as a constituent material represent substances that contribute to the electron transfer reaction. The anode active material and the cathode active material may be a carbon material or a metal oxide having a structure capable of inserting and extracting lithium ions or desorbing and inserting (intercalating) lithium ions. In addition, it is possible to reversibly perform doping and undoping of a lithium ion such as a conductive polymer and a counter anion of the lithium ion (for example, ClO ₄ ⁻ ) as an anode active material and / or a cathode active material. The structure may be such that the substance is used alone or together with another active material.
[0021]
For convenience of description, in this specification, the “anode” in the case of “anode active material” refers to a material based on the polarity at the time of battery discharge (negative electrode active material), and is referred to as “cathode active material”. The "cathode" in this case is also based on the polarity at the time of discharging the battery (positive electrode active material). Specific examples of the anode active material and the cathode active material will be described later.
[0022]
In the present invention, the electrolyte solution may include an organic solvent as a solvent. In particular, in the present invention, even when a non-aqueous electrolyte solution containing an organic solvent is used as the electrolyte solution, a lithium ion secondary battery having excellent safety that can reliably pass the 150 ° C. heating test specified in UL1642. A battery can be provided.
[0023]
Further, in the present invention, from the viewpoint of more securely securing the capacity in the above range, and more reliably obtaining the effects of the present invention described above, the carbon material serving as the anode active material has a layered crystal structure similar to graphite. And the interlayer distance d _{002 of the} carbon material determined by the X-ray diffraction method is 0.335 to 0.338 nm or less, and the crystallite size Lc ₀₀₂ of the carbon material determined by the X-ray diffraction method Is preferably 30 to 120 nm.
[0024]
In the present invention, the melting point of the separator is preferably 120 to 180 ° C from the viewpoint of more reliably obtaining the effects of the present invention described above. Further, in this case, the separator preferably has one or more porous films containing a polyolefin having a melting point of 130 to 140 ° C.
[0025]
In the case of a separator made of a porous membrane containing polyolefin, when the battery is at an abnormally high temperature, the internal pores are blocked by melting of the separator, so that it becomes difficult for current to flow, and the progress of the abnormal reaction is more reliably suppressed. be able to. From the viewpoint of more reliably exerting the so-called shutdown function of the separator, the porous film containing polyolefin is more preferably a porous film made of polyolefin. Further, from a similar viewpoint, in this case, the polyolefin is preferably at least one selected from the group consisting of polyethylene and polypropylene.
[0026]
In the lithium ion secondary battery of the present invention, the case is preferably formed of a flexible film (hereinafter, referred to as a “film”).
[0027]
When the case is formed from a film in this manner, the shape of the lithium ion secondary battery itself can be made thin. Therefore, the original volume energy density can be easily improved, and the energy density per unit volume of the installation space where the lithium ion secondary battery is to be installed (hereinafter referred to as “the volume of the space to be installed, The volume energy density) can be easily improved.
[0028]
Note that the “volume energy density” of a lithium ion secondary battery is essentially the total volume of a portion (“element body” to be described later) composed of an electrode and a separator of the lithium ion secondary battery and contributing to power generation or a whole including a container. It is defined as the ratio of the total output energy to the product. On the other hand, the “volume energy density based on the volume of the space to be installed” is defined as the lithium with respect to the apparent volume calculated based on the maximum length, maximum width, and maximum thickness of the lithium ion secondary battery. It means the ratio of the total output energy of the ion secondary battery. Actually, when a lithium ion secondary battery is mounted on a small electronic device, it is necessary to improve the volume energy density based on the volume of the space to be installed together with the improvement of the original volume energy density described above. This is important from the viewpoint of effectively utilizing the limited space in the device while the dead space is sufficiently reduced.
[0029]
When the case is formed from a flexible film, the case is preferably formed using at least a pair of films opposed to each other. Thereby, a case with high airtightness can be manufactured more easily.
[0030]
Further, in this case, from the viewpoint of improving the tightness of the case, a composite packaging film having at least an innermost layer made of a synthetic resin in which the film comes into contact with the electrolyte solution and a metal layer disposed above the innermost layer. It is preferable that
[0031]
In the lithium ion secondary battery of the present invention, it is preferable that at least a part of the electrolyte solution is contained in the anode, the cathode, and the inside of the separator. By adopting such a configuration, the volume energy density based on the volume of the space to be installed can be further improved.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the lithium ion secondary battery of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding parts will be denoted by the same reference characters, without redundant description.
[0032]
FIG. 1 is a front view showing a preferred embodiment of the lithium ion secondary battery of the present invention. FIG. 2 is a developed view when the inside of the lithium ion secondary battery shown in FIG. 1 is viewed from the normal direction of the surface of the anode 10. FIG. 3 is a schematic cross-sectional view of the lithium ion secondary battery shown in FIG. 1 taken along the line X1-X1 in FIG. FIG. 4 is a schematic cross-sectional view showing a main part when the lithium ion secondary battery shown in FIG. 1 is cut along the line X2-X2 in FIG. FIG. 5 is a schematic cross-sectional view showing a main part when the lithium ion secondary battery shown in FIG. 1 is cut along the line YY in FIG.
[0033]
As shown in FIGS. 1 to 5, the lithium ion secondary battery 1 is mainly disposed adjacent to a plate-shaped anode 10 and a plate-shaped cathode 20 facing each other, and between the anode 10 and the cathode 20. Plate-like separator 40, an electrolyte solution containing lithium ions (a non-aqueous electrolyte solution in the present embodiment), a case 50 for accommodating them in a sealed state, and one end electrically connected to anode 10 The anode lead 12 has the other end protruding outside the case 50 and the cathode 20 has one end electrically connected and the other end protruding outside the case 50. And a cathode lead 22.
[0034]
Here, the “anode” 10 and the “cathode” 20 are determined based on the polarity at the time of discharging of the lithium ion secondary battery 1 for convenience of explanation. Therefore, during charging, the “anode 10” becomes the “cathode” and the “cathode 20” becomes the “anode”.
[0035]
The lithium ion secondary battery 1 has a capacity of 1300 to 5000 mAh, and has a configuration described below in order to achieve the above-described object of the present invention.
[0036]
Hereinafter, details of each component of the present embodiment will be described with reference to FIGS.
[0037]
The case 50 is formed using a pair of films (a first film 51 and a second film 52) facing each other. Here, as shown in FIG. 2, the first film 51 and the second film 52 in the present embodiment are connected. That is, the case 50 in the present embodiment bends a rectangular film made of one composite packaging film at a bending line X3-X3 shown in FIG. 2, and sets a pair of opposing edges of the rectangular film ( The edge 51B of the first film 51 and the edge 52B) of the second film 52 in the drawing are overlapped and formed by using an adhesive or performing heat sealing.
[0038]
The first film 51 and the second film 52 indicate portions of the film having surfaces facing each other when a single rectangular film is bent as described above. Here, in this specification, the respective edges of the first film 51 and the second film 52 after being joined are referred to as “seal portions”.
[0039]
This eliminates the need to provide a seal portion for joining the first film 51 and the second film 52 at the portion of the fold line X3-X3, so that the seal portion in the case 50 can be further reduced. As a result, the volume energy density based on the volume of the space in which the lithium ion secondary battery 1 is to be installed can be further improved.
[0040]
In the case of the present embodiment, as shown in FIGS. 1 and 2, one end of each of the anode lead 12 and the cathode lead 22 connected to the anode 10 is connected to the edge 51B of the first film 51 described above. It is arranged so as to protrude to the outside from a seal portion where the second film and the edge portion 52B of the second film are joined.
[0041]
As described above, the films constituting the first film 51 and the second film 52 are films having flexibility. Since the film is lightweight and easily thinned, the shape of the lithium ion secondary battery itself can be made thin. Therefore, the original volume energy density can be easily improved, and the volume energy density based on the volume of the space in which the lithium ion secondary battery is to be installed can be easily improved.
[0042]
This film is not particularly limited as long as it is a flexible film. However, while ensuring sufficient mechanical strength and lightness of the case, moisture and air can enter the inside of the case 50 from the outside of the case 50 and enter the inside of the case 50. From the viewpoint of effectively preventing the electrolyte component from escaping from the case 50 to the outside, the innermost layer made of synthetic resin that comes into contact with the non-aqueous electrolyte solution, and the metal layer disposed above the innermost layer It is preferable that the “composite packaging film” has at least
[0043]
As a composite packaging film that can be used as the first film 51 and the second film 52, for example, a composite packaging film having a configuration shown in FIGS. The composite packaging film 53 shown in FIG. 6 is disposed on the innermost layer 50a made of a synthetic resin that comes into contact with the nonaqueous electrolyte solution on the inner surface F53, and on the other surface (outer surface) of the innermost layer 50a. And a metal layer 50c to be formed. The composite packaging film 54 shown in FIG. 7 has a configuration in which an outermost layer 50b made of a synthetic resin is further disposed on the outer surface of the metal layer 50c of the composite packaging film 53 shown in FIG.
[0044]
The composite packaging film that can be used as the first film 51 and the second film 52 includes one or more synthetic resin layers including the innermost layer described above, and two or more layers including a metal layer such as a metal foil. Although it is not particularly limited as long as it is a composite packaging material having a layer, from the viewpoint of more reliably obtaining the same effect as described above, the innermost layer 50a and the innermost layer 50a as in the composite packaging film 54 shown in FIG. An outermost layer 50b made of a synthetic resin disposed on the outer surface side of the case 50 farthest from the layer 50a, and at least one metal layer disposed between the innermost layer 50a and the outermost layer 50b More preferably, it is composed of three or more layers having a thickness of 50c.
[0045]
The innermost layer 50a is a layer having flexibility, and its constituent material is capable of exhibiting the above-mentioned flexibility, and is chemically stable to a nonaqueous electrolyte solution used (chemical reaction). Any synthetic resin having the property of not dissolving and swelling) and chemical stability against oxygen and water (moisture in air) is not particularly limited. ) And materials having low permeability to components of the non-aqueous electrolyte solution. For example, engineering plastics, and thermoplastic resins such as polyethylene, polypropylene, modified polyethylene acid, modified polypropylene acid, polyethylene ionomer, and polypropylene ionomer are exemplified.
[0046]
In addition, "engineering plastic" means a plastic having excellent mechanical properties, heat resistance, and durability as used in mechanical parts, electric parts, housing materials, and the like.For example, polyacetal, polyamide, Examples include polycarbonate, polyoxytetramethyleneoxyterephthaloyl (polybutylene terephthalate), polyethylene terephthalate, polyimide, and polyphenylene sulfide.
[0047]
Further, in the case where a layer made of a synthetic resin such as the outermost layer 50b is further provided in addition to the innermost layer 50a as in the composite packaging film 54 shown in FIG. The same constituent material as that of the innermost layer 50a may be used.
[0048]
The metal layer 50c is preferably a layer formed of a metal material having corrosion resistance to oxygen, water (moisture in air) and a non-aqueous electrolyte solution. For example, a metal foil made of aluminum, an aluminum alloy, titanium, chromium, or the like may be used.
[0049]
The method of sealing all the seal portions in the case 50 is not particularly limited, but is preferably a heat seal method from the viewpoint of productivity.
[0050]
Next, the anode 10 and the cathode 20 will be described. FIG. 8 is a schematic sectional view showing an example of a basic configuration of the anode 10 of the lithium ion secondary battery 1 shown in FIG. FIG. 9 is a schematic cross-sectional view showing an example of the basic configuration of the cathode 20 of the lithium ion secondary battery 1 shown in FIG.
[0051]
As shown in FIG. 8, the anode 10 includes a current collector 16 and an anode active material-containing layer 18 formed on the current collector 16. As shown in FIG. 9, the cathode 20 includes a current collector 26 and a cathode active material-containing layer 28 formed on the current collector 26.
[0052]
The current collector 16 and the current collector 26 are not particularly limited as long as they are good conductors capable of sufficiently transferring charges to the anode active material containing layer 18 and the cathode active material containing layer 28. A current collector used for a secondary battery can be used. For example, the current collector 16 and the current collector 26 include metal foils such as aluminum and copper.
[0053]
Further, the anode active material containing layer 18 of the anode 10 is mainly composed of an anode active material, a conductive auxiliary, and a binder.
[0054]
The anode active material absorbs and releases lithium ions, desorbs and inserts (intercalates) lithium ions, or performs doping and undoping of lithium ions and a counter anion of the lithium ions (for example, ClO ₄ ⁻ ). The material is not particularly limited as long as it is an electron conductive carbon material that can be reversibly advanced and has a BET specific surface area of 0.5 to 1.5 m ² / g. Examples of such a carbon material include carbon materials such as natural graphite, artificial graphite, and low-temperature fired carbon. Among them, a carbon material having a layered crystal structure similar to graphite, the interlayer distance d _{002 of the} carbon material determined by the X-ray diffraction method is 0.335 to 0.338 nm or less, and determined by the X-ray diffraction method. More preferably, the carbon material has a crystallite size Lc ₀₀₂ of 30 to 120 nm. Examples of the carbon material satisfying such conditions include artificial graphite and MCF (mesocarbon fiber).
[0055]
The conductive assistant is not particularly limited, and a known conductive assistant can be used. For example, carbon blacks, carbon materials, metal fine powders such as copper, nickel, stainless steel, iron, etc., a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO can be used.
[0056]
The binder is not particularly limited as long as the binder can bind the particles of the anode active material and the particles of the conductive assistant. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), ethylene-tetrafluoro Fluororesins such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF). Further, this binder contributes not only to the binding between the particles of the anode active material and the particles of the conductive auxiliary agent, but also to the binding to the foil (current collector 16).
[0057]
The cathode active material containing layer 28 of the cathode 20 is a layer having a porous cathode active material layer containing the cathode active material. More specifically, similarly to the anode active material-containing layer 18, it is mainly composed of a cathode active material, a conductive additive, and a binder.
[0058]
The cathode active material absorbs and releases lithium ions, desorbs and inserts (intercalates) lithium ions, or performs doping and dedoping of lithium ions with counter anions of the lithium ions (for example, ClO ₄ ⁻ ). There is no particular limitation as long as it can reversibly proceed, and a known electrode active material can be used. For example, it is represented by lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and a general formula: LiNi _x Co _y Mn _z O ₂ (x + y + z = 1). Composite of metal oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (where M represents Co, Ni, Mn or Fe), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), etc. Metal oxides.
[0059]
Further, for each component other than the cathode active material contained in the cathode active material containing layer 28, the same material as that constituting the anode active material containing layer 18 can be used. Also, the binder contained in the cathode active material containing layer 28 not only binds to the cathode active material particles and the conductive auxiliary particles, but also binds to the foil (current collector 26). It has also contributed. Further, it is preferable that the cathode active material containing layer 28 also contains an electron conductive porous body.
[0060]
The current collector 28 of the cathode 20 is electrically connected to one end of a cathode lead 22 made of, for example, aluminum, and the other end of the cathode lead 22 extends outside the case 50. On the other hand, the current collector 18 of the anode 10 is also electrically connected to one end of the anode lead 12 made of, for example, copper or nickel, and the other end of the anode lead 12 extends outside the case 50.
[0061]
The separator 40 disposed between the anode 10 and the cathode 20 is formed so as to include an insulating synthetic resin as a constituent material, and has a heat shrinkage at 90 ° C. of 0.1 to 3%. Is formed. As described above, the melting point of the separator 40 is 120 to 180 ° C. from the viewpoint of ensuring that the short-circuit start temperature in the 150 ° C. heating test defined by UL1642 is 125 ° C. or more and ensuring sufficient battery safety. Is preferred. Further, in this case, the separator 40 preferably has one or more porous films containing a polyolefin having a melting point of 130 to 140 ° C.
[0062]
In the case of the separator 40 made of a porous film containing polyolefin, when the lithium ion secondary battery 1 is at an abnormally high temperature, the internal pores are closed by the melting of the separator 40, so that the current becomes difficult to flow, and abnormal reaction occurs. Progress can be suppressed more reliably.
[0063]
From the viewpoint of more reliably exerting the so-called shutdown function of the separator 40, the porous film containing polyolefin is more preferably a porous film made of polyolefin. Further, from a similar viewpoint, in this case, the polyolefin is preferably at least one selected from the group consisting of polyethylene and polypropylene.
[0064]
More specifically, the separator 40 may be formed by using one film made of polyethylene or one film made of polypropylene, or may be made of a laminate in which a plurality of films made of polyethylene are stacked. It may be a laminate formed by laminating a plurality of films made of polypropylene, or a laminate formed by combining a film made of one or more polyethylene and a film made of one or more polypropylene. Good. Further, the separator 40 may be subjected to processing such as stretching for suppressing deformation due to heat. Further, the thickness of the separator 40 is preferably 10 to 30 μm from the viewpoint of ensuring safety and reducing the size of the battery.
[0065]
The electrolyte solution 30 is filled in the internal space of the case 50, and a part of the electrolyte solution 30 is contained in the anode 10, the cathode 20, and the separator 40. As the electrolyte solution 30, a solution in which a lithium salt is dissolved in an organic solvent is used. As the lithium salt, for example, LiBF ₄ , LiPF ₆ , LiClO ₄ or the like is used. The electrolyte solution 30 may be in a gel state by adding a gelling agent or the like.
[0066]
Further, as the organic solvent, a solvent used in a known lithium ion secondary battery can be used. For example, propylene carbonate, ethylene carbonate, diethyl carbonate and the like are preferable. These may be used alone, or two or more kinds may be used by mixing at an arbitrary ratio.
[0067]
Further, as shown in FIGS. 1 and 2, the portion of the anode lead 12 that comes into contact with the sealing portion of the sealing bag formed by the edge 51 </ b> B of the first film 51 and the edge 52 </ b> B of the second film 52 includes: An insulator 14 for preventing contact between the anode lead 12 and a metal layer in the composite packaging film constituting each film is coated. Furthermore, the cathode lead 22 and each film are formed in the portion of the cathode lead 22 that comes into contact with the sealing portion of the enclosing bag formed by the edge 51B of the first film 51 and the edge 52B of the second film 52. An insulator 24 for preventing contact with the metal layer in the composite packaging film is coated.
[0068]
Although the configuration of the insulator 14 and the insulator 24 is not particularly limited, for example, each of them may be formed of a synthetic resin. The insulator 14 and the insulator 24 may not be disposed as long as the contact of the metal layer in the composite packaging film with the anode lead 12 and the cathode lead 22 can be sufficiently prevented.
[0069]
Next, a method for manufacturing the above-described case 50 and the lithium ion secondary battery 1 will be described.
[0070]
The method for producing the element body 60 (a laminate in which the anode 10, the gel-like synthetic resin layer 71, the separator 40, the gel-like synthetic resin layer 72, and the cathode 20 are sequentially laminated in this order) is not particularly limited, and is known. A known method employed for the manufacture of the lithium ion secondary battery of the present invention can be used.
[0071]
When preparing the anode 10 and the cathode 20, first, the above-described respective constituent components are mixed and dispersed in a solvent in which the binder can be dissolved to prepare a coating liquid for forming an electrode (such as a slurry). The solvent is not particularly limited as long as the binder can be dissolved therein and the conductive auxiliary agent can be dispersed. For example, N-methyl-2-pyrrolidone or N, N-dimethylformamide is used. Can be.
[0072]
Next, the electrode-forming coating liquid is applied on the surface of the current collector, dried, and rolled to form an active material-containing layer on the current collector, and the production of the anode 10 and the cathode 20 is completed. Here, the method of applying the electrode forming coating liquid to the surface of the current collector is not particularly limited, and may be appropriately determined according to the material and shape of the current collector. Examples include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method.
[0073]
The anode lead 12 and the cathode lead 22 are electrically connected to the produced anode 10 and cathode 20, respectively.
[0074]
Next, the separator 40 is disposed between the anode 10 and the cathode 20 in a contact state (preferably, a non-adhesion state), and the element body 60 is completed.
[0075]
Next, an example of a method for manufacturing the case 50 will be described. First, when the first film and the second film are composed of the above-described composite packaging film, a known production method such as a dry lamination method, a wet lamination method, a hot melt lamination method, or an extrusion lamination method is used. It is produced using.
[0076]
For example, a film to be a synthetic resin layer constituting the composite packaging film, and a metal foil made of aluminum or the like are prepared. The metal foil can be prepared, for example, by rolling a metal material.
[0077]
Next, a composite packaging film (multilayer film) is formed by bonding a metal foil via an adhesive onto a film to be a layer made of a synthetic resin so as to preferably have the above-described configuration of a plurality of layers. Is prepared. Then, the composite packaging film is cut into a predetermined size, and one rectangular film is prepared.
[0078]
Next, as described above with reference to FIG. 2, one film is bent, and the sealing portion 51B (the edge portion 51B) of the first film 51 and the sealing portion 52B (the edge portion) of the second film 51 are bent. 52B) is heat-sealed by a desired sealing width under a predetermined heating condition using, for example, a sealing machine. At this time, in order to secure an opening for introducing the element body 60 into the case 50, a part where heat sealing is not performed is provided. Thus, the case 50 having the opening is obtained.
[0079]
Then, the element body 60 to which the anode lead 12 and the cathode lead 22 are electrically connected is inserted into the case 50 having the opening. Then, the electrolyte solution 30 is injected. Subsequently, with a part of the anode lead 12 and a part of the cathode lead 22 inserted into the case 50, the opening of the case 50 is sealed using a sealing machine. Thus, the fabrication of the case 50 and the lithium ion secondary battery 1 is completed. In addition, the lithium ion secondary battery of the present invention is not limited to such a shape, and may be a cylindrical shape or the like.
[0080]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
[0081]
The lithium ion secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 3 having the same configuration as the lithium ion secondary battery 1 shown in FIG.
[0082]
(Example 1)
First, an anode was produced. In the production of the anode, first, MCF (90 parts by mass, specific surface area: 1.0 m ² · g ⁻¹ ) as an anode active material, carbon black (2 parts by mass) as a conductive additive, and polyvinylidene fluoride as a binder (PVDF) (8 parts by mass) was mixed and dispersed in a solvent N-methyl-pyrrolidone (NMP) to obtain a slurry. The obtained slurry was applied to an electrolytic copper foil as a current collector by a doctor blade method, and dried at 110 ° C. Rolling was performed after drying to obtain an anode.
[0083]
Next, a cathode was produced. In the production of the cathode, LiNi _{(x = 1/3)} Co _{(y = 1/3)} Mn _{(z = 1/3)} O ₂ (x + y + z = 1) (90 parts by mass) as the positive electrode active material Carbon black (6 parts by mass) as an auxiliary and PVDF (4 parts by mass) as a binder were mixed and dispersed in NMP to obtain a slurry. The obtained slurry was applied to an aluminum foil as a current collector, dried, and rolled to obtain a cathode.
[0084]
Next, a non-aqueous electrolyte solution was prepared. A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3: 7 is used as a solvent, and LiPF ₆ is added as a solute so that the molar concentration thereof is 2.0 mol / L. An aqueous electrolyte solution was obtained.
[0085]
Next, a separator containing polyethylene as a main component (trade name: “S4823”, manufactured by Asahi Kasei Corporation, thickness: 23 μm) was prepared. Further, as a result of analysis by DSC (differential scanning calorimetry), the melting point of the separator containing polyethylene as a main component (trade name: “S4823”, manufactured by Asahi Kasei Corporation) was 135 ° C. Further, the heat shrinkage at 90 ° C. of this separator was 2.5% (horizontal: −1.5%, vertical: −1%).
[0086]
Next, a laminate (element body) was obtained by laminating the separator between the anode and the cathode. The obtained laminate is placed in an aluminum laminator pack, a non-aqueous electrolyte solution is injected into the aluminum laminator pack, vacuum sealed, and hot-pressed at 80 ° C. to make the lithium-ion secondary battery having a capacity of 2500 mAh (vertical). : 87 mm, width: 115 mm, thickness 3 mm). The film of the aluminum laminator pack is composed of a synthetic resin innermost layer (a layer made of modified polypropylene), a metal layer made of aluminum foil, and a layer made of polyamide, which are sequentially laminated in this order in contact with the nonaqueous electrolyte solution. The obtained laminate was used. Then, two composite packaging films were laminated and the edges thereof were heat-sealed.
[0087]
(Example 2)
A lithium ion secondary battery was manufactured in the same procedure and under the same conditions as in Example 1 except that the anode was formed using the anode having the anode active material shown in Table 1 and the electrolyte solution having the composition shown in Table 2.
[0088]
(Comparative Examples 1 to 3)
Except for using the anode having the anode active material shown in Table 1 and the electrolyte solution having the composition shown in Table 2, the lithium ion secondary batteries of Comparative Examples 1 to 5 were manufactured in the same procedure and under the same conditions as in Example 1. Produced.
[0089]
In addition, as the separator of Comparative Example 1, a separator containing polyethylene as a main component (trade name: “H6022”, manufactured by Asahi Kasei Corporation) was used. Further, as a result of analysis by DSC (differential scanning calorimetry), the melting point of a separator containing polyethylene as a main component (trade name: “H6022”, manufactured by Asahi Kasei Corporation, thickness: 27 μm) was 135 ° C. Furthermore, the heat shrinkage at 90 ° C. of this separator was 5.0% (horizontal: −2.0%, vertical: −3%).
[0090]
As the separator of Comparative Example 2, a separator containing polyethylene as a main component (trade name: “S6722”, manufactured by Asahi Kasei Corporation) was used. Further, as a result of analysis by DSC (differential scanning calorimetry), the melting point of the separator containing polyethylene as a main component (trade name: “S6722”, manufactured by Asahi Kasei Corporation; thickness: 20 μm) was 135 ° C. Further, the heat shrinkage of this separator at 90 ° C. was 5.6% (horizontal: −2%, vertical: −3.6%).
[0091]
[UL1642 specified 150 ° C heating test]
Each of the obtained lithium ion secondary batteries of Example 1 and Example 2 and Comparative Examples 1 to 3 was subjected to a UL1642 standard 150 ° C. heating test to evaluate the safety of each. In the heating test at 150 ° C. specified in UL1642, each battery (in a state where the charging at 4.2 V has been completed) is placed in a thermostat, and the temperature is raised from room temperature to 150 ° C. at a heating rate of 5 ° C./min. C. for 1 hour. Table 1 shows the results. The short-circuit initiation temperature of each battery in a 150 ° C. heating test defined by UL1642 was also measured, and the results are shown in Table 1.
[0092]
In addition, among the results of the 150 ° C. heating test shown in Table 1, “2” indicates the evaluation result that “the battery did not rupture or ignite during the test”, and “1” indicates that the battery ruptured or failed during the test. It fired ".
[0093]
[Table 1]

[0094]
[Table 2]

[0095]
As is clear from the results shown in Table 1, the lithium ion secondary batteries of Examples 1 and 2 have excellent safety that can reliably pass the 150 ° C. heating test specified in UL1642. confirmed.
[0096]
【The invention's effect】
As described above, according to the present invention, even when the capacity is set to 1300 to 5000 mAh, a lithium ion secondary battery having excellent safety that can surely pass the 150 ° C. heating test specified in UL1642 is surely cleared. A battery can be provided.
[Brief description of the drawings]
FIG. 1 is a front view showing a preferred embodiment of a lithium ion secondary battery of the present invention.
FIG. 2 is a developed view when the inside of the lithium ion secondary battery shown in FIG. 1 is viewed from the normal direction of the surface of the anode 10.
FIG. 3 is a schematic cross-sectional view of the lithium-ion secondary battery shown in FIG. 1 taken along line X1-X1 in FIG.
FIG. 4 is a schematic cross-sectional view showing a main part when the lithium ion secondary battery shown in FIG. 1 is cut along the line X2-X2 in FIG.
5 is a schematic cross-sectional view showing a main part when the lithium ion secondary battery shown in FIG. 1 is cut along the line YY in FIG.
6 is a schematic cross-sectional view showing an example of a basic configuration of a film serving as a constituent material of the case of the lithium ion secondary battery shown in FIG.
FIG. 7 is a schematic cross-sectional view showing another example of the basic structure of the film serving as the constituent material of the case of the lithium ion secondary battery shown in FIG.
8 is a schematic sectional view showing an example of a basic configuration of an anode of the lithium ion secondary battery shown in FIG.
9 is a schematic cross-sectional view showing an example of a basic configuration of a cathode of the lithium ion secondary battery shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 10 ... Anode, 12 ... Lead wire for anode, 14 ... Insulator, 20 ... Cathode, 22 ... Lead wire for cathode, 24 ... Insulator, 30 ... Electrolyte solution, 40 ... Separator, 50 ... case, 60 ... elementary body.

Claims (11)

A plate-like cathode having a porous anode active material layer including a porous anode active material layer including an anode active material opposed to each other, and a porous cathode active material layer including a cathode active material;
A plate-shaped separator that is disposed between the anode and the cathode and has an insulating property,
An electrolyte solution containing lithium ions,
A case for housing the anode, the cathode, the separator and the electrolyte solution in a sealed state,
Has,
Capacity is 1300-5000 mAh,
The anode active material is an electron conductive carbon material having a BET specific surface area of 0.5 to 1.5 m ² / g,
The separator is formed including a synthetic resin as a constituent material, and has a heat shrinkage at 90 ° C. of 0.1 to 3%;
A lithium ion secondary battery characterized by the above-mentioned. The lithium ion secondary battery according to claim 1, wherein the electrolyte solution includes an organic solvent as a solvent. The carbon material serving as the anode active material has a layered crystal structure similar to graphite,
An interlayer distance d _{002 of the} carbon material determined by an X-ray diffraction method is 0.335 to 0.338 nm or less, and
The crystallite size Lc ₀₀₂ of the carbon material determined by X-ray diffraction is 30 to 120 nm,
The lithium ion secondary battery according to claim 1, wherein: The lithium ion secondary battery according to any one of claims 1 to 3, wherein the melting point of the separator is 120C or more. The lithium ion secondary battery according to claim 4, wherein the separator has one or more porous films containing a polyolefin having a melting point of 130 to 140C. The lithium ion secondary battery according to claim 5, wherein the polyolefin is at least one selected from the group consisting of polyethylene and polypropylene. The lithium ion secondary battery according to any one of claims 1 to 6, wherein the case is formed of a flexible film. The lithium ion secondary battery according to claim 7, wherein the case is formed using at least a pair of the films facing each other. 8. The film according to claim 7, wherein the film is a composite packaging film having at least an innermost layer made of a synthetic resin in contact with the electrolyte solution and a metal layer disposed above the innermost layer. Or the lithium ion secondary battery according to 8. The lithium ion according to any one of claims 5 to 9, wherein at least a part of the electrolyte solution is contained inside the anode, the cathode, and the separator. Secondary battery. The lithium ion secondary battery according to any one of claims 1 to 10, wherein a short-circuit start temperature in a 150 ° C heating test defined in UL1642 is 125 ° C or more.

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