JP4109168B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

  In recent years, the development of electronic devices, particularly portable electronic devices has been remarkable, and accordingly, development of a battery having a high energy density is desired. As such a battery, a lithium ion secondary battery is widely used as a power source for portable devices because of its extremely high energy density. A lithium ion secondary battery is mainly composed of a cathode, an anode, a separator, and a non-aqueous electrolyte solution, and various studies for further improvement of the battery characteristics have been made.

  For example, the nonaqueous solvent of the nonaqueous electrolyte solution has a relatively low melting point, a relatively high conductivity, a relatively wide potential window (electrochemical window), and a high temperature even when the electrolyte is dissolved. Those capable of obtaining ionic conductivity are preferred, and propylene carbonate is preferably used from this viewpoint. However, when a negative electrode (anode) using a carbon material such as highly crystallized graphite as a constituent material is provided, the decomposition of propylene carbonate proceeds at the cathode {electrode functioning as a negative electrode during discharge} particularly during charging. There was a problem to do.

  As the decomposition of propylene carbonate proceeds, gas is generated, and as a result, the carbon material of the negative electrode is peeled off and decomposed, and the battery characteristics such as capacity and charge / discharge cycle characteristics gradually deteriorate during use. Further, as the decomposition of propylene carbonate proceeds, decomposition products are deposited on the negative electrode, and it is considered that the above-described deterioration in battery characteristics further proceeds due to the influence of this deposit.

  Therefore, a battery intended to suppress reductive decomposition on the negative electrode surface of propylene carbonate by adding a cyclic sulfate to a nonaqueous electrolyte solution containing propylene carbonate as a nonaqueous solvent has been proposed (for example, Patent Document 1).

Also, when improving battery characteristics, the energy density of lithium ion secondary batteries is very high compared to other batteries, so it is also important to ensure the safety of batteries during use or storage. It becomes. Ensuring this safety is particularly important when using a flammable non-aqueous electrolyte solution (an electrolyte solution containing an organic solvent) as the electrolyte solution. As standardized in the safety evaluation test of the lithium ion secondary battery, there is "UL1642" or "UL2054" of US UL (Underwriters Laboratories) standard.
JP-A-10-189042

  However, in the conventional lithium ion secondary battery described in Patent Document 1 described above, the decomposition reaction of propylene carbonate proceeds with the use of the battery, and the charge / discharge characteristics deteriorate. For this reason, the present inventors have found that the charge / discharge cycle characteristics for maintaining the charge / discharge characteristics over a long period are insufficient and sufficient high-rate discharge characteristics are not obtained.

  Further, the conventional lithium ion secondary battery described in Patent Document 1 described above has a problem that gas is generated inside these cases and the internal pressure is increased, particularly during use or storage at a high temperature. In particular, when the case is formed of a film, the case may rupture and ignite during use or storage of the battery, and the 150 ° C. heating test of the safety evaluation test standard “UL1642” is ensured. The present inventors have found that it is difficult to clear and reliable safety is not obtained.

  The present invention has been made in view of the above-described problems of the prior art, and has a lithium ion secondary battery having excellent safety and practically sufficient charge / discharge cycle characteristics and high rate discharge characteristics. The purpose is to provide.

  As a result of intensive studies to achieve the above object, the inventors of the present invention include a specific compound as a nonaqueous solvent for a nonaqueous electrolyte solution and a specific cyclic sulfate ester in the solution. Has been found to be extremely effective for achieving the above object, and the present invention has been achieved.

［式（Ｉ）中、Ｒ¹及びＲ²は、それぞれ独立に水素原子及び炭素数１〜３の炭化水素基からなる群より選ばれる少なくとも一種を表す。但し、Ｒ¹及びＲ²は、それぞれ同時に水素原子ではない。］ That is, the lithium ion secondary battery of the present invention comprises an anode,
A cathode,
An insulating separator disposed between the anode and the cathode;
A non-aqueous electrolyte solution containing a lithium salt;
A case for containing the anode, cathode, separator, and nonaqueous electrolyte solution in a sealed state;
A lithium ion secondary battery having
The components of the nonaqueous solvent contained in the nonaqueous electrolyte solution are propylene carbonate, ethylene carbonate, and diethyl carbonate,
The content ratio X [volume%] of propylene carbonate, the content ratio Y [volume%] of ethylene carbonate, and the content ratio Z [volume%] of diethyl carbonate in the non-aqueous solvent are the following formulas (1) to (4). Satisfy the conditions shown at the same time,
A lithium ion secondary battery characterized in that the nonaqueous electrolyte solution contains 2 to 15% by mass of a compound represented by the following general formula (I).
10 ≦ X ≦ 50 (1)
1 ≦ Y ≦ 20 (2)
30 ≦ Z ≦ 85 (3)
X + Y + Z = 100 (4)

[In Formula (I), R ¹ and R ² each independently represent at least one selected from the group consisting of a hydrogen atom and a hydrocarbon group having 1 to 3 carbon atoms. However, R ¹ and R ² are not simultaneously hydrogen atoms. ]

In the present invention, the compound represented by the general formula (I) is 4-methyl-1,3,2-dioxathiolane-2,2-dioxide (in the compound represented by the general formula (I)). R ¹ is a methyl group) or 4-ethyl-1,3,2-dioxathiolane-2,2-dioxide (R ¹ in the compound represented by the general formula (I) is preferably an ethyl group). .

  Here, in the present invention, the electrodes serving as the anode and the cathode serve as a reaction field capable of reversibly proceeding with an electron transfer reaction involving lithium ions (or metallic lithium) as a redox species. Further, “reversing the electron transfer reaction” means that the electron transfer reaction proceeds reversibly within the range of battery life required as a power source or auxiliary power source for the device to be mounted. .

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 indicate 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 occluding and releasing lithium ions or desorbing and inserting (intercalating) lithium ions. In addition, doping and dedoping of lithium ions such as a conductive polymer and a counter anion (eg, ClO ₄ ⁻ ) of the lithium ions as an anode active material and / or a cathode active material can proceed reversibly. It is good also as a structure which uses a substance alone or with another active material.

  For convenience of explanation, in this specification, “anode” in the case of “anode active material” is 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 battery discharge (positive electrode active material). Specific examples of the anode active material and the cathode active material will be described later.

  In the lithium ion secondary battery of the present invention, the case is formed of a flexible film (hereinafter referred to as “film”), and is formed using at least a pair of films facing each other. Preferably, the film is a composite packaging film having at least a synthetic resin innermost layer that contacts the non-aqueous electrolyte solution and a metal layer disposed above the innermost layer.

  When the case is thus formed from a film, the shape of the lithium ion secondary battery itself can be made into a thin film. Therefore, the original volume energy density can be easily improved, and the energy density per unit volume of the installation space in which the lithium ion secondary battery is to be installed (hereinafter referred to as “the volume of the space to be installed as a reference). Volume energy density ”) can be easily improved.

  Note that the “volume energy density” of a lithium ion secondary battery originally means the entire volume of the portion (“elementary body” to be described later) that contributes to power generation consisting of electrodes and separators of the lithium ion secondary battery or the whole including the container. It is defined as the ratio of the total output energy to the product. On the other hand, “volume energy density based on the volume of the space to be installed” refers to lithium with respect to the apparent volume required based on the maximum vertical, maximum horizontal, and maximum thickness of the lithium ion secondary battery. It means the ratio of the total output energy of the ion secondary battery. In fact, when a lithium ion secondary battery is mounted on a small electronic device, it is possible to improve the volume energy density based on the volume of the space to be installed in addition to the improvement of the original volume energy density described above. This is important from the viewpoint of effectively using the limited space in the device with the dead space sufficiently reduced.

  Moreover, in this invention, metal cases, such as a metal can exterior body, may be sufficient as a case other than what is formed from the above-mentioned composite packaging film. Thereby, it can apply to uses, such as a case where mechanical strength higher than a composite packaging film is requested | required with respect to a case.

  According to the present invention, it is possible to provide a lithium ion secondary battery having excellent safety and practically sufficient charge / discharge cycle characteristics and high rate discharge characteristics.

  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 are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a front view showing a preferred embodiment of a lithium ion secondary battery of the present invention. FIG. 2 is a development 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. 3 is a schematic cross-sectional view of the lithium ion secondary battery shown in FIG. 1 cut along the line X1-X1 in FIG. 4 is a schematic cross-sectional view showing the main part when the lithium ion secondary battery shown in FIG. 1 is cut along the line X2-X2 of 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 of FIG.

  As shown in FIGS. 1 to 5, the lithium ion secondary battery 1 is mainly disposed adjacent to each other between the plate-like anode 10 and the plate-like cathode 20 facing each other, and the anode 10 and the cathode 20. A plate-like separator 40, a non-aqueous electrolyte solution 30, a case 50 containing these in a sealed state, one end of the case 50 being electrically connected to the anode 10, and the other end of the case 50 The anode lead 12 protrudes to the outside, and the cathode lead 22 whose one end is electrically connected to the cathode 20 and the other end protrudes to the outside of the case 50. 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. Accordingly, during charging, “anode 10” becomes “cathode” and “cathode 20” becomes “anode”. The plate shape includes a flat plate shape and a curved plate shape.

  And the lithium ion secondary battery 1 has the structure demonstrated below, in order to achieve the objective of this invention described previously.

  Details of each component of the present embodiment will be described below with reference to FIGS.

  The case 50 is formed by using a pair of films (a first film 51 and a second film 52) that face each other. Here, as shown in FIG. 2, the first film 51 and the second film 52 in this embodiment are connected. That is, the case 50 in the present embodiment is formed by folding a rectangular film made of a single composite packaging film along a fold line X3-X3 shown in FIG. 2 and a pair of edges of the rectangular film facing each other ( The edge 51B of the first film 51 and the edge 52B of the second film 52 in the figure are overlapped to form an adhesive or heat seal.

  And the 1st film 51 and the 2nd film 52 respectively show the part of this film which has a mutually opposing surface formed when the sheet-like rectangular film 53 is bend | folded as mentioned above. Here, in this specification, each edge part of the 1st film 51 after bonding and the 2nd film 52 is called "seal part."

  Thereby, since it becomes unnecessary to provide the seal part for joining the 1st film 51 and the 2nd film 52 in the part of bending line X3-X3, the seal part in case 50 can be reduced more. 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.

  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 the edge portion 51 </ b> B of the first film 51 described above. And the edge portion 52B of the second film 52 are arranged so as to protrude to the outside from the sealed portion.

  Moreover, the film which comprises the 1st film 51 and the 2nd film 52 is a film which has flexibility as stated above. Since the film is lightweight and can be easily thinned, the shape of the lithium ion secondary battery itself can be made into a thin film. 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.

  The film is not particularly limited as long as it is a flexible film. However, while ensuring sufficient mechanical strength and light weight of the case, moisture and air intrusion into the case 50 from the outside of the case 50 and the inside of the case 50 can be achieved. From the viewpoint of effectively preventing the electrolyte component from escaping to the outside of the case 50, an innermost layer made of synthetic resin that contacts the nonaqueous electrolyte solution 30 and a metal layer disposed above the innermost layer It is preferably a “composite packaging film” having at least

  Examples of the composite packaging film that can be used as the first film 51 and the second film 52 include a composite packaging film having a configuration shown in FIGS. 6 and 7. The composite packaging film 53 shown in FIG. 6 has an innermost layer 50a made of a synthetic resin that contacts the nonaqueous electrolyte solution 30 on the inner surface F53, and the other surface (outer surface) of the innermost layer 50a. And a metal layer 50c to be disposed. Further, the composite packaging film 54 shown in FIG. 7 has a configuration in which an outermost layer 50b made of synthetic resin is further arranged on the outer surface of the metal layer 50c of the composite packaging film 53 shown in FIG.

  The composite packaging film that can be used as the first film 51 and the second film 52 includes two or more layers including one or more synthetic resin layers including the innermost layer described above and a metal layer such as a metal foil. Although it will not specifically limit if it is the composite packaging material which has a layer, From the viewpoint of acquiring the same effect as the above more reliably, like the composite packaging film 54 shown in FIG. The innermost layer 50a in contact, the outermost layer 50b made of synthetic resin disposed on the outer surface side of the case 50 farthest from the innermost layer 50a, the innermost layer 50a and the outermost layer 50b And at least one metal layer 50c disposed between the two and more layers.

  The innermost layer 50a is a layer having flexibility, and the constituent material thereof can express the above-mentioned flexibility, and the chemical stability (chemical properties) with respect to the non-aqueous electrolyte solution 30 to be used. It is not particularly limited as long as it is a synthetic resin having a chemical stability with respect to oxygen and water (moisture in the air), and oxygen, water (in the air) A material having a property of low permeability to moisture and components of the non-aqueous electrolyte solution 30 is preferable. Examples thereof include engineering plastics and thermoplastic resins such as polyethylene, polypropylene, polyethylene acid modified products, polypropylene acid modified products, polyethylene ionomers, and polypropylene ionomers.

  The “engineering plastic” means a plastic having excellent mechanical properties, heat resistance, and durability used in mechanical parts, electrical parts, housing materials, etc., for example, polyacetal, polyamide, Examples include polycarbonate, polyoxytetramethyleneoxyterephthaloyl (polybutylene terephthalate), polyethylene terephthalate, polyimide, polyphenylene sulfide, and the like.

  Further, when a synthetic resin layer 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. Constituent materials similar to the innermost layer may be used.

  The metal layer 50 c is preferably a layer formed of a metal material having corrosion resistance against oxygen, water (water in the air), and the non-aqueous electrolyte solution 30. For example, a metal foil made of aluminum, aluminum alloy, titanium, chromium, or the like may be used.

  Moreover, the sealing method of all the sealing parts in the case 50 is not particularly limited, but the heat sealing method is preferable from the viewpoint of productivity.

  Next, the anode 10 and the cathode 20 will be described. FIG. 8 is a schematic cross-sectional view showing an example of the basic configuration of the anode of the lithium ion secondary battery shown in FIG. FIG. 9 is a schematic cross-sectional view showing an example of the basic configuration of the cathode of the lithium ion secondary battery shown in FIG.

  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.

  The current collector 16 and the current collector 26 are not particularly limited as long as they are good conductors that can sufficiently transfer charges to the anode active material-containing layer 18 and the cathode active material-containing layer 28. The current collector used for the secondary battery can be used. For example, the current collector 16 and the current collector 26 include metal foils such as aluminum and copper.

  The anode active material-containing layer 18 of the anode 10 is mainly composed of an anode active material, a conductive auxiliary agent, and a binder.

The anode active material includes insertion and extraction of lithium ions, desorption and insertion (intercalation) of lithium ions, or doping and dedoping of lithium ions and a counter anion (for example, ClO ₄ ⁻ ) of the lithium ions. A known anode active material can be used without particular limitation as long as it can proceed reversibly. Examples of such an active material include a combination with carbon materials such as natural graphite and artificial graphite (non-graphitizable carbon, graphitizable carbon, low-temperature calcined carbon, etc.), lithium such as Al, Si, and Sn. be metallic, amorphous compounds mainly oxides of SiO _2, SnO ₂ or the like, and lithium titanate (Li ₄ Ti ₅ O ₁₂₎ is.

Among these, a carbon material is preferable, and an interlayer distance d ₀₀₂ of the carbon material is 0.335 to 0.338 nm, and a crystallite size Lc ₀₀₂ of the carbon material is more preferably 30 to 120 nm. Examples of the carbon material satisfying such conditions include artificial graphite and MCF (mesocarbon fiber). The size Lc ₀₀₂ of the interlayer distance d ₀₀₂ and crystallite can be determined by X-ray diffraction method.

  In particular, when a carbon material is used as the anode active material, when propylene carbonate is used as the non-aqueous solvent, the amount of decomposition of propylene carbonate is large. However, when the non-aqueous electrolyte solution 30 is configured as the present invention, It has become possible to sufficiently suppress the decomposition of.

  The conductive auxiliary agent is not particularly limited, and a known conductive auxiliary agent can be used. Examples thereof include carbon blacks, carbon materials, metal fine powders such as copper, nickel, stainless steel and iron, a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO.

  The binder is not particularly limited as long as it can bind the particles of the anode active material and the conductive aid particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Examples thereof include fluorine resins such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF). In addition, the binder contributes not only to the binding of the anode active material particles and the conductive aid particles, but also to the foil (current collector 16).

  The anode active material-containing layer 18 preferably contains an electron conductive porous material, and examples of the electron conductive porous material include carbon black such as acetylene black and ketjen black.

  The cathode active material-containing layer 28 of the cathode 20 is mainly composed of a cathode active material, a conductive aid, and a binder, like the anode active material-containing layer 18.

Cathode active material includes insertion and extraction of lithium ions, desorption and insertion (intercalation) of lithium ions, or doping and dedoping of lithium ions and counter anions of the lithium ions (for example, ClO ₄ ⁻ ). If it can be made to advance reversibly, it will not specifically limit, A well-known electrode active material can be used. For example, lithium cobalt oxide (LiCoO _2), lithium nickel oxide (LiNiO _2), lithium manganese spinel (LiMn ₂ O _4), and the general formula: represented by _{LiNi x Co y Mn z O 2} (x + y + z = 1) Composite metal oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (where M represents Co, Ni, Mn or Fe), composite such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ) A metal oxide is mentioned.

  Furthermore, each component other than the cathode active material contained in the cathode active material-containing layer 28 can use the same material as that constituting the anode active material-containing layer 18. Further, the binder contained in the cathode active material-containing layer 28 is not only used for binding the particles of the cathode active material and the particles of the conductive additive, but also for binding to the foil (current collector 26). It also contributes. Further, the cathode active material-containing layer 28 preferably contains an electron conductive porous body.

  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 to the outside of the case 50. On the other hand, the current collector 18 of the anode 10 is also electrically connected to one end of an anode lead 12 made of, for example, copper or nickel, and the other end of the anode lead 12 extends to the outside of the enclosing bag 14.

  The separator 40 disposed between the anode 10 and the cathode 20 is not particularly limited as long as it is formed of an insulating porous body, and a separator used in a known lithium ion secondary battery may be used. it can. For example, as the insulating porous body, at least one constituent material selected from the group consisting of a laminate of films made of polyethylene, polypropylene or polyolefin, a stretched film of a mixture of the above resins, or cellulose, polyester and polypropylene The fiber nonwoven fabric which consists of is mentioned.

The nonaqueous electrolyte solution 30 is filled in the internal space of the case 50, and a part of the nonaqueous electrolyte solution 30 is contained in the anode 10, the cathode 20, and the separator 40. As the non-aqueous electrolyte solution 30, a lithium salt dissolved in a non-aqueous solvent (organic solvent) is used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN. Salts such as (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ are used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together. The nonaqueous electrolyte solution 30 may be gelled by adding a gelling agent such as a gel polymer.

In addition, the nonaqueous electrolyte solution 30 is composed of propylene carbonate, ethylene carbonate, and diethyl carbonate as the nonaqueous solvent, and the content rate X [volume%] of propylene carbonate in the nonaqueous solvent includes ethylene carbonate. The ratio Y [volume%] and the content ratio Z [volume%] of diethyl carbonate simultaneously satisfy the conditions represented by the following formulas (1) to (4).
10 ≦ X ≦ 50 (1)
1 ≦ Y ≦ 20 (2)
30 ≦ Z ≦ 85 (3)
X + Y + Z = 100 (4)

  When the content ratio X is less than the lower limit value, the charge / discharge characteristics at low temperatures tend to be insufficient. On the other hand, when the upper limit value is exceeded, decomposition of propylene carbonate occurs and reliability is insufficient. Tend to be. On the other hand, when the content Y is less than the lower limit, propylene carbonate is decomposed and the reliability tends to be insufficient. On the other hand, when the content exceeds the upper limit, the temperature is low (−20 ° C. to 25 ° C. ) Tend to be insufficient. Further, when the content rate Z is less than the lower limit value, the high rate discharge characteristics and the charge / discharge characteristics at low temperature tend to be insufficient. On the other hand, when the content rate exceeds the upper limit value, the discharge capacity tends to decrease. There is. When diethyl carbonate is included, battery swelling during high-temperature storage (90 ° C.) can be reduced and excellent low-temperature characteristics compared to the case where other chain carbonates such as dimethyl carbonate and ethyl methyl carbonate are included. And rate characteristics can be obtained.

  In addition, the non-aqueous electrolyte solution 30 contains 2 to 15% by mass of a compound represented by the following general formula (I). As a result, the charge / discharge characteristics and the high rate discharge characteristics are further improved, and the safety is improved.

上記式（Ｉ）中、Ｒ¹及びＲ²は、それぞれ独立に水素原子及び炭素数１〜３の炭素数１〜３の炭化水素基（アルキル基、アルケニル基、アルキニル基が好ましく、アルキル基がより好ましい。）からなる群より選ばれる少なくとも一種を表す。但し、Ｒ¹及びＲ²は、それぞれ同時に水素原子ではない。また、上記式（Ｉ）で表される化合物としては、４−メチル−１，３，２−ジオキサチオラン−２，２−ジオキサイド、又は、４−エチル−１，３，２−ジオキサチオラン−２，２−ジオキサイドが特に好ましい。

In the above formula (I), R ¹ and R ² are each independently a hydrogen atom and a hydrocarbon group having 1 to 3 carbon atoms (an alkyl group, an alkenyl group or an alkynyl group is preferred, And more preferably at least one selected from the group consisting of: However, R ¹ and R ² are not simultaneously hydrogen atoms. Examples of the compound represented by the above formula (I) include 4-methyl-1,3,2-dioxathiolane-2,2-dioxide, or 4-ethyl-1,3,2-dioxathiolane-2, 2-Dioxide is particularly preferred.

  When the content of the compound represented by the above general formula (I) is less than 2% by mass, it is difficult to clear the 150 ° C. heating test of the safety evaluation test standard “UL1642”, and reliable safety is ensured. Can't get. On the other hand, if it exceeds 15% by mass, the capacity is lowered, and at the same time, the rate characteristics become insufficient.

  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 encapsulating bag composed of the edge portion 51 </ b> B of the first film 51 and the edge portion 52 </ b> B of the second film 52 includes: An insulator 14 for preventing contact between the anode lead 12 and the 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 encapsulating bag composed of 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.

  The configurations of the insulator 14 and the insulator 24 are not particularly limited. For example, the insulator 14 and the insulator 24 may be made of a synthetic resin. It should be noted that the insulator 14 and the insulator 24 may not be disposed as long as the metal layer in the composite packaging film can be sufficiently prevented from contacting the anode lead 12 and the cathode lead 22 respectively.

  Next, a method for manufacturing the case 50 and the lithium ion secondary battery 1 described above will be described.

  The manufacturing method of the element body 60 (a stacked body in which the anode 10, the separator 40, and the cathode 20 are sequentially stacked in this order) is not particularly limited, and is a known method that is adopted for manufacturing a known lithium ion secondary battery. Can be used.

  When the anode 10 and the cathode 20 are manufactured, first, the above-described constituent components are mixed and dispersed in a solvent in which the binder can be dissolved to prepare an electrode-forming coating solution (slurry or the like). The solvent is not particularly limited as long as the binder can be dissolved and the conductive additive can be dispersed. For example, N-methyl-2-pyrrolidone or N, N-dimethylformamide is used. Can do.

  Next, the electrode forming coating solution is applied onto the surface of the current collector, dried and rolled to form an active material-containing layer on the current collector, thereby completing the production of the anode 10 and the cathode 20. Here, the method for applying the electrode-forming coating solution to the surface of the current collector is not particularly limited, and may be appropriately determined according to the material, shape, and the like of the current collector. Examples thereof 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.

  The anode lead 12 and the cathode lead 22 are electrically connected to the produced anode 10 and cathode 20, respectively. The separator 40 is disposed between the anode 10 and the cathode 20 in a contacted state (non-adhered state), and the element body 60 is completed.

  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 composite packaging film described above, known production methods such as a dry lamination method, a wet lamination method, a hot melt lamination method, an extrusion lamination method, etc. It is produced using.

  For example, a film that becomes 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.

  Next, a composite packaging film (multilayer film) is preferably obtained by laminating a metal foil via an adhesive on a film that becomes a layer made of a synthetic resin so as to have a configuration of a plurality of layers described above. Is made. Then, the composite packaging film is cut into a predetermined size to prepare one rectangular film.

  Next, as described above with reference to FIG. 2, one film is folded, and the seal portion 51B (edge portion 51B) of the first film 51 and the seal portion 52B (edge portion) of the second film 52B) is heat-sealed by a desired seal 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. As a result, the case 50 having an opening is obtained.

  Then, an element body 60 in which the anode lead 12 and the cathode lead 22 are electrically connected is inserted into the case 50 having an opening. Then, the nonaqueous electrolyte solution 30 is injected. Subsequently, with the anode lead 12 and the cathode lead 22 partially inserted into the case 50, the opening of the case 50 is sealed using a sealing machine. In this way, the production of the case 50 and the lithium ion secondary battery 1 is completed. 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.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these Examples at all.

  The lithium ion secondary battery of Examples 1-8 and Comparative Examples 1-3 which have the structure similar to the lithium ion secondary battery 1 shown in FIG. 1 with the procedure shown below was produced.

(Example 1)
First, an anode was produced. In the production of the anode, first, artificial graphite (90 parts by mass) as an anode active material, carbon black (2 parts by mass) as a conductive auxiliary agent, and polyvinylidene fluoride (PVDF) (8 parts by mass) as a binder are mixed. The slurry was dispersed in N-methyl-pyrrolidone (NMP) as a solvent 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. After drying, rolling was performed to obtain an anode.

Next, a cathode was produced. In the production of the cathode, first, as the positive electrode active material, LiNi _{(x = 1/3)} Co _{(y = 1/3)} Mn _{(z = 1/3)} O ₂ (x + y + z = 1) (90 parts by mass), conductive Carbon black (6 parts by mass) as an auxiliary agent 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.

Next, a non-aqueous electrolyte solution was prepared. A mixture of propylene carbonate (hereinafter, sometimes referred to as PC), ethylene carbonate (hereinafter, sometimes referred to as EC) and diethyl carbonate (hereinafter, sometimes referred to as DEC) at a volume ratio of 2: 1: 7 is used as a non-aqueous solvent. LiPF ₆ was added as a solute at a rate of 1.5 mol dm ⁻³ . Further, 4-methyl-1,3,2-dioxathiolane-2,2-dioxide (hereinafter sometimes referred to as MDTD) is added as a non-aqueous electrolyte solution to the mixed solution of the non-aqueous solvent and the solute. It added so that it might become 2 mass% with respect to the whole quantity, and the nonaqueous electrolyte solution was obtained.

  A laminated body (element body) was obtained by laminating a separator made of polyethylene between the obtained anode and cathode. The obtained laminate is placed in an aluminum laminate pack, a nonaqueous electrolyte solution is injected into the aluminum laminate pack, and then vacuum-sealed to produce a lithium ion secondary battery (length: 115 mm, width: 87 mm, thickness: 3 mm). did. The film of the aluminum laminate pack has a synthetic resin innermost layer (layer made of modified polypropylene) in contact with the non-aqueous electrolyte solution, a metal layer made of aluminum foil, and a layer made of polyamide in this order. The laminated body used was used. And two sheets of this composite packaging film were piled up, and the edge part was heat-sealed and produced.

(Examples 2-8 and Comparative Examples 1-3)
The lithium ion secondary of Examples 2 to 8 and Comparative Examples 1 to 3 were the same as Example 1 except that the type and content of the additive added to the nonaqueous electrolyte solution were changed as shown in Table 1. A battery was produced. In Table 1, EDTD represents 4-ethyl-1,3,2-dioxathiolane-2,2-dioxide, and DTD represents 1,3,2-dioxathiolane-2,2-dioxide.

  Each battery characteristic was evaluated using the obtained lithium ion secondary battery of Examples 1-8 and Comparative Examples 1-3.

(Initial charge / discharge characteristics evaluation test)
After the production of the lithium ion secondary battery, the first charge was performed at 25 ° C., and the discharge was performed immediately after that. The initial charge / discharge characteristics were evaluated by the ratio between the charge capacity and the discharge capacity at that time. In addition, charge performed constant current constant voltage charge to 4.2V at 0.2C (500mA), and discharge performed constant current discharge to 2.5V at 0.2C. The obtained results are shown in Table 1. A battery having a result of 80% or more was evaluated as having practically sufficient initial charge / discharge characteristics.

(Charge / discharge cycle characteristics evaluation test)
After the battery was prepared, the discharge capacity A2 after 100 times of charging / discharging at 25 ° C. was measured. The charge / discharge cycle characteristics were evaluated by the ratio {100 × (A2 / A1)} [%] of the discharge capacities A1 and A2 after the first charge / discharge. In addition, charge performed constant current constant voltage charge to 4.2V at 1C (2500mA), and discharge performed constant current discharge to 2.5V at 1C (2500mA). The obtained results are shown in Table 1. A battery having a result of 80% or more was evaluated as having practically sufficient charge / discharge cycle characteristics. In Examples 6-7 and Comparative Examples 2-3, no particular measurement was performed. From the results of the initial charge / discharge characteristics, it is presumed that charge / discharge cycle characteristics are practically sufficient in Examples 6-7. . Moreover, in Comparative Examples 2-3, it is inferred that the charge / discharge cycle characteristics are practical.

(High rate discharge characteristics evaluation test)
25 ° C., and 2C discharge capacity (A _2C) in the case of performing constant current discharge (5000 mA), the ratio of 0.5C discharge capacity in the case of performing constant current discharge (1250mA) (A _0.5C) High rate discharge characteristics were evaluated. As a result, in Examples 1 to 8, the high-rate discharge characteristics were 60% or more, and it was confirmed that they had practically sufficient characteristics. Specifically, it was 64.8% in Example 3, 64.2% in Example 6, and 61.2% in Example 7. On the other hand, in Comparative Examples 1 to 3, the high rate discharge characteristic was less than 60%, which was confirmed to be insufficient in practical use. Specifically, in Comparative Example 3, the high rate discharge characteristic was 54.6%.

(Safety evaluation test)
About each of the obtained lithium ion secondary battery of Examples 1-8 and Comparative Examples 1-3, the 150 degreeC heating test of UL1642 regulation was performed, and each safety | security was evaluated. In the 150 ° C. heating test specified by UL 1642, each battery (in a state in which charging at 4.2 V has been completed) is placed in a constant temperature bath, and the temperature is increased from room temperature to 150 ° C. at a temperature rising rate of 5 ° C./min. This was carried out by holding at 1 ° C for 1 hour. Table 1 shows the results. Of the results of the 150 ° C. heating test shown in Table 1, “2” indicates an evaluation result that “the battery did not rupture or ignite during the test”, and “1” indicates “the battery ruptured or failed during the test. The evaluation result is “I fired”.

  As is clear from the results shown in Table 1, the lithium ion secondary batteries of Examples 1 to 8 have excellent initial charge / discharge characteristics, practically sufficient charge / discharge cycle characteristics, and high rate discharge characteristics. Was confirmed. It was also confirmed that it has excellent safety.

  The lithium ion secondary battery of the present invention is useful as a power source for electronic devices, particularly portable electronic devices.

It is a front view which shows suitable one Embodiment of the lithium ion secondary battery of this invention. FIG. 2 is a development view when the inside of the lithium ion secondary battery shown in FIG. 1 is viewed from the normal direction of the surface of an anode 10. It is a schematic cross section at the time of cut | disconnecting the lithium ion secondary battery shown in FIG. 1 along the X1-X1 line | wire of FIG. It is a schematic cross section which shows the principal part at the time of cut | disconnecting the lithium ion secondary battery shown in FIG. 1 along the X2-X2 line | wire of FIG. It is a schematic cross section which shows the principal part at the time of cut | disconnecting the lithium ion secondary battery shown in FIG. 1 along the YY line of FIG. It is a schematic cross section which shows an example of the basic composition of the film used as the constituent material of the case of the lithium ion secondary battery shown in FIG. It is a schematic cross section which shows another example of the basic composition of the film used as the constituent material of the case of the lithium ion secondary battery shown in FIG. It is a schematic cross section which shows an example of the basic composition of the anode of the lithium ion secondary battery shown in FIG. It is a schematic cross section which shows an example of the basic composition of the 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 for anode, 14 ... Insulator, 20 ... Cathode, 22 ... Lead for cathode, 24 ... Insulator, 30 ... Nonaqueous electrolyte solution, 40 ... Separator, 50 ... case, 60 ... element.

Claims (5)

An anode,
A cathode,
An insulating separator disposed between the anode and the cathode;
A non-aqueous electrolyte solution containing a lithium salt;
A case for containing the anode, the cathode, the separator, and the nonaqueous electrolyte solution in a sealed state;
A lithium ion secondary battery having
The components of the nonaqueous solvent contained in the nonaqueous electrolyte solution are propylene carbonate, ethylene carbonate, and diethyl carbonate,
The propylene carbonate content X [volume%], the ethylene carbonate content Y [volume%], and the diethyl carbonate content Z [volume%] in the non-aqueous solvent are represented by the following formulas (1) to (1): (4) is satisfied at the same time,
The non-aqueous electrolyte solution contains 2 to 15% by mass of a compound represented by the following general formula (I).
10 ≦ X ≦ 50 (1)
1 ≦ Y ≦ 20 (2)
30 ≦ Z ≦ 85 (3)
X + Y + Z = 100 (4)

[In Formula (I), R ¹ and R ² each independently represent at least one selected from the group consisting of a hydrogen atom and a hydrocarbon group having 1 to 3 carbon atoms. However, R ¹ and R ² are not simultaneously hydrogen atoms. ] The compound represented by the general formula (I) is 4-methyl-1,3,2-dioxathiolane-2,2-dioxide, or 4-ethyl-1,3,2-dioxathiolane-2,2-dioxide. The lithium ion secondary battery according to claim 1, wherein: The lithium ion secondary battery according to claim 1, wherein the case is formed of a flexible film. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the case is formed using at least a pair of the films facing each other. The film is a composite packaging film having at least an innermost layer made of a synthetic resin that comes into contact with the nonaqueous electrolyte solution and a metal layer disposed above the innermost layer. The lithium ion secondary battery according to claim 3 or 4 .

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