JP2006269438A - Lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-ion secondary battery with excellent reliability which has an excellent charge/discharge property in an operation temperature from -20 to +25°C, and that, can maintain the same property for a long period. <P>SOLUTION: The lithium-ion secondary battery has a solvent of nonaqueous electrolyte solution composed of propylene carbonate, ethylene carbonate and diethyl carbonate. A propylene carbonate content X, an ethylene carbonate content Y and a diethyl carbonate content Z satisfy at the same time formula (1): 10≤X≤40, formula (2): 1≤Y≤20, formula (3): 30≤Z≤85, and formula (4): X+Y+Z=100. The nonaqueous electrolyte solution contains 3 to 6% by mass of a compound as expressed in formula (I), in which R1 and R2 may be the same or not and denote either a hydrogen atom or a hydrocarbon group with the carbon number of one to six. <P>COPYRIGHT: (C)2007,JPO&INPIT

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, a battery in which battery characteristics are improved by adding vinylene carbonate to a nonaqueous electrolyte solution using propylene carbonate as a solvent has been proposed (see, for example, Patent Documents 1 to 3). Also proposed is a battery that prevents reductive decomposition of propylene carbonate on the negative electrode surface by using a mixed solvent of propylene carbonate, ethylene carbonate and diethyl carbonate in the non-aqueous electrolyte solution and further adding 1,3-propane sultone. (For example, see Patent Document 4).

JP-A-11-67266 JP 2000-58125 A JP 2001-167797 A JP 11-339850 A

  However, in the conventional lithium ion secondary batteries described in Patent Documents 1 to 4 described above, the progress of the decomposition reaction of propylene carbonate has not been sufficiently prevented, particularly at low temperatures (-20 to + 25 ° C). The present inventors have found that the charge / discharge characteristics are not sufficiently obtained.

  Moreover, in the conventional lithium ion secondary battery, as described above, the decomposition of propylene carbonate occurs immediately after production, and during use or storage of the battery, gas is generated inside these cases, and the internal pressure rises. There was a problem. In addition, when the case is formed of a film, the case may swell during use or storage, or the case seal may be peeled off, resulting in liquid leakage. Was not obtained.

  The present invention has been made in view of the above-mentioned problems of the prior art, and can obtain excellent charge / discharge characteristics particularly in the operating temperature range of -20 to + 25 ° C. An object of the present invention is to provide a lithium ion secondary battery that can be maintained and has excellent reliability.

  As a result of intensive studies to achieve the above object, the present inventors have adjusted the component composition of the solvent of the non-aqueous electrolyte solution so as to satisfy the following conditions, It has been found that inclusion of a cyclic carbonate compound having a bond is extremely effective for achieving the above object, and the present invention has been achieved.

  That is, the lithium ion secondary battery of the present invention includes an anode, a cathode, an insulating separator disposed between the anode and the cathode, a nonaqueous electrolyte solution containing a lithium salt, an anode, a cathode, a separator, And a case of containing the nonaqueous electrolyte solution in a sealed state, and a lithium ion secondary battery, wherein the constituent components of the 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 solvent are represented by the following formulas (1) to (4). In the non-aqueous electrolyte solution, the compound represented by the following general formula (I) is simultaneously contained. Characterized in that it contains 6% by weight.

10 ≦ X ≦ 40 (1)
1 ≦ Y ≦ 20 (2)
30 ≦ Z ≦ 85 (3)
X + Y + Z = 100 (4)

In the above formula (I), R ¹ and R ² may be the same or different and each represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, and R ¹ and R ² are each A hydrogen atom is preferred.

  The lithium ion secondary battery of the present invention is a conventional battery with regard to charge / discharge characteristics at relatively high operating temperatures, such as high rate discharge characteristics and cycle characteristics, because the nonaqueous electrolyte solution is configured to satisfy the above conditions. The charge / discharge characteristics in a relatively low operating temperature (-20 to + 25 ° C.) range can be improved while maintaining the same level or higher. Furthermore, by adding a predetermined amount of a cyclic carbonate compound having a specific unsaturated double bond to the non-aqueous electrolyte solution, sufficiently high reliability can be obtained with further improvement of each characteristic.

  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. Further, it is possible to reversibly proceed doping and dedoping of lithium ions such as a conductive polymer and a counter anion (for example, ClO ₄ ⁻ ) of the lithium ions as an anode active material and / or a cathode active material. 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.

  In the lithium ion secondary battery of the present invention, the anode and the cathode each have a plate shape, and each includes an electron conductive porous body as a constituent material, and the separator has a plate shape. The nonaqueous electrolyte solution preferably has a shape and is made of an insulating porous body, and at least a part of the nonaqueous electrolyte solution is contained inside the anode, the cathode, and 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. The plate shape includes a flat plate shape and a curved plate shape.

  According to the present invention, an excellent charge / discharge characteristic can be obtained in an operating temperature range of −20 to + 25 ° C., and the charge / discharge characteristic can be maintained over a long period of time, and the lithium ion secondary battery has excellent reliability. Can be provided.

  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, a case 50 containing these in a sealed state, one end of the anode 10 being electrically connected to the anode 10, and the other end being external to the case 50 The anode lead 12 protrudes to the cathode 20, and the cathode lead 22 whose one end portion is electrically connected to the cathode 20 and the other end portion 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”.

  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 show the part of this film which has a mutually opposing surface formed when one rectangular film is bent as mentioned above, respectively. 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 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 can enter from the outside of the case to the inside of the case and from the inside of the case to the outside of the case From the viewpoint of effectively preventing the diffusion of the electrolyte component to the innermost layer, it has at least an innermost layer made of a synthetic resin that comes into contact with the non-aqueous electrolyte solution and a metal layer disposed above the innermost layer. A “composite packaging film” is preferred.

  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 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. 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. 7, the innermost layer and the innermost layer 3 layers having an outermost layer made of synthetic resin disposed on the outer surface side of the case 50 farthest from the surface and at least one metal layer disposed between the innermost layer and the outermost layer More preferably, it is composed of the above layers.

  The innermost layer is a layer having flexibility, and the constituent material can express the above-mentioned flexibility, and chemical stability (chemical reaction, It is not particularly limited as long as it is a synthetic resin that has chemical stability against oxygen and water (water in the air), and oxygen and water (water in the air). And the material which has the characteristic of the low permeability | transmittance with respect to the component of a nonaqueous electrolyte solution 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 is preferably a layer formed of a metal material having corrosion resistance against oxygen, water (water in the air) and a non-aqueous electrolyte solution. 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 counter anions of the lithium ions (for example, ClO ₄ ⁻ ). 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 interlayer distance d ₀₀₂ and the crystallite size Lc ₀₀₂ can be obtained by an X-ray diffraction method.

  In particular, when a carbon material is used as the anode active material, when propylene carbonate is used as the solvent, the amount of decomposition of propylene carbonate is large. However, by using a non-aqueous electrolyte solution as a constitution of the present invention, propylene carbonate is decomposed. It became possible to suppress sufficiently.

  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. Examples of the electron conductive porous material include raw coal (for example, fluid catalytic cracking of petroleum heavy oil). Examples thereof include carbon materials (for example, activated carbon) obtained by activating a petroleum coke produced from a delayed coker using a bottom oil of the apparatus or a residual oil of a vacuum distillation apparatus as a raw oil.

  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.

The cathode active material may be lithium ion occlusion and release, lithium ion desorption and insertion (intercalation), or doping and dedoping of lithium ions and a counter anion 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 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) Composites such as composite metal oxides, lithium vanadium compounds (LiV ₂ O ₅ ), olivine type LiMPO ₄ (wherein M represents Co, Ni, Mn or Fe), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), etc. 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 an organic solvent is used. As the lithium salt, for example, LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiClO ₄ , LiCoO ₂ or the like is used. The nonaqueous electrolyte solution 30 may be in the form of a gel.

Further, the organic solvent is composed of propylene carbonate, ethylene carbonate, and diethyl carbonate, and the content ratio X [volume%] of propylene carbonate, the content ratio Y [volume%] of ethylene carbonate, and diethyl in the solvent The carbonate content Z [volume%] simultaneously satisfies the conditions represented by the following formulas (1) to (4).
10 ≦ X ≦ 40 (1)
1 ≦ Y ≦ 20 (2)
30 ≦ Z ≦ 85 (3)
X + Y + Z = 100 (4)

  When the content X is less than the lower limit, the charge / discharge characteristics at low temperatures are insufficient. On the other hand, when the content exceeds the upper limit, the decomposition of propylene carbonate occurs and the reliability is insufficient. On the other hand, when the content Y is less than the lower limit, the decomposition of propylene carbonate occurs, resulting in insufficient reliability. On the other hand, when the content exceeds the upper limit, the charge / discharge characteristics at low temperatures are insufficient. On the other hand, 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 are insufficient, and when the content rate Z exceeds the upper limit value, the discharge capacity decreases.

  Further, the nonaqueous electrolyte solution 30 contains 3 to 6% by mass of a compound represented by the following general formula (I) based on the total mass of the nonaqueous electrolyte solution. When the content of this compound is less than the lower limit, the decomposition of propylene carbonate occurs and the reliability becomes insufficient. On the other hand, when the upper limit is exceeded, the high rate discharge characteristics and the charge / discharge characteristics at low temperatures become insufficient.

In formula (I), R ¹ and R ² may be the same or different, and are preferably a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms (an alkyl group, an alkenyl group, an alkynyl group, a phenyl group, Group is more preferable. The compound represented by the general formula (I) is particularly preferably vinylene carbonate in which R ¹ and R ² are each a hydrogen atom.

  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 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 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 batteries of Examples 1 to 10 and Comparative Examples 1 to 6 having the same configuration as the lithium ion secondary battery 1 shown in FIG.

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. Also in the production of the cathode, first, as a 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 (PC), ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 27: 3: 70 was used as a solvent, and LiPF ₆ was added as a solute at a ratio of 1.5 mol dm ⁻³ . Furthermore, non-aqueous electrolyte solution was obtained by adding vinylene carbonate (VC) so that it might become 5 mass% with respect to the solution which mixed the solvent and the solute.

  A laminated body (element body) was obtained by laminating a separator made of polyethylene between the obtained anode and cathode. The obtained laminate is put in an aluminum laminator pack, and a nonaqueous electrolyte solution is injected into the aluminum laminator pack and then vacuum-sealed to produce a lithium ion secondary battery (length: 115 mm, width: 87 mm, thickness: 3 mm). did. The aluminum laminator pack film has a synthetic resin innermost layer (layer made of modified polypropylene) in contact with the nonaqueous 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 to 10 and Comparative Examples 1 to 6)
Except that the volume ratio of PC, EC and DEC used as the solvent for the nonaqueous electrolyte solution was changed as shown in Table 1, and the addition amount of VC was changed as shown in the same table, it was the same as in Example 1. The lithium ion secondary battery of Examples 2-10 and Comparative Examples 1-6 was produced.

  Each battery characteristic was evaluated using the obtained lithium ion secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 6.

(Initial charge / discharge characteristics)
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 based on the ratio between the charge capacity and the discharge capacity. 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 Tables 2 to 4. A battery with a result exceeding 75% was evaluated as practically sufficient in initial charge / discharge characteristics.

(High rate discharge characteristics)
25 ° C., the ratio between 2C discharge capacity in the case of performing constant current discharge _{(5000mA) (A 2C),} 0.5C discharge capacity in the case of performing constant current discharge _{(1250mA) (A 0.5C)} Thus, high rate discharge characteristics were evaluated. The obtained results are shown in Tables 2 to 4. A battery with a result exceeding 60% was evaluated as practically sufficient for high rate discharge characteristics.

(Low temperature charge / discharge characteristics)
After carrying out constant current constant voltage charge to 4.2V at 25 degreeC and 1C (2500 mA), it hold | maintains at -20 degreeC for 3 hours, performs 1C discharge of 2.5V of cut-off, and -20 degreeC discharge capacity (A- ₂₀ ° C.) and were evaluated 25 ° C. discharge capacity _{(a 25} ° C.) and low-temperature discharge characteristics at a ratio of (hereinafter referred to as "low-temperature _{characteristics") (a -20 ℃ / a 25} ℃). Furthermore, the discharge capacity (A- ₁₀ ° C.) when the discharge was performed in the same manner as described above after being held at −10 ° C., the discharge capacity (A ₀ ° C.) at the discharge in the same manner as described above after being held at ₀ ° C. and 25 ° C. The low temperature characteristics (A- ₁₀ ° _{C./A 25} ° C.) and the low temperature characteristics (A ₀ ° C./A ₂₅ ° C.) were evaluated by the ratio with the discharge capacity (A ₂₅ ° C.). The obtained results are shown in Tables 2 and 3.

  It was confirmed that the batteries of Examples 1 to 6 had sufficient high rate discharge characteristics and sufficient low temperature characteristics. Moreover, since the batteries of Examples 7 to 10 had sufficient high rate discharge characteristics, it was estimated that the low temperature characteristics were sufficient, and thus the low temperature characteristics were not evaluated. In addition, the batteries of Comparative Examples 1 to 6 are not practical because the high-rate discharge characteristics are insufficient, and it is estimated that the low-temperature characteristics are insufficient. There wasn't.

(reliability)
Further, the lithium ion secondary battery was left at 90 ° C. for 4 hours, and the thickness before and after being left was compared (swelling at 90 ° C. storage). The results obtained are shown in Tables 2 and 4. The data shown in Tables 2 and 4 and expressed as “reliability” is the increase (F ₂ −F ₁ ) of the thickness (F ₂ ) after being left with respect to the thickness (F ₁ ) before leaving each battery. It is shown as a relative value {(F ₂ −F ₁ ) / F ₁ } (%). In addition, a battery with a result of less than 10% was evaluated as having practically sufficient reliability. In addition, about the battery of Examples 4-6, although data was not described, there was almost no increase in thickness.

  As is clear from the results shown in Tables 2 to 4, the lithium ion secondary batteries of Examples 1 to 10 are excellent in the initial charge / discharge characteristics and the high rate discharge characteristics, and further, at low temperatures (−20 ° C. to 25 ° C. It was confirmed that the charge / discharge characteristics at (° C.) were also excellent. Moreover, it was confirmed that the batteries of Examples 1 to 10 are excellent in reliability. Moreover, although not mentioned above, in the anodes of Examples 1 to 10, almost no expansion of graphite was observed.

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 (6)

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 constituent components of the solvent contained in the non-aqueous electrolyte solution are propylene carbonate, ethylene carbonate, and diethyl carbonate,
The propylene carbonate content X [vol%], the ethylene carbonate content Y [vol%], and the diethyl carbonate content Z [vol%] in the solvent are represented by the following formulas (1) to (4). ) At the same time,
The lithium ion secondary battery, wherein the non-aqueous electrolyte solution contains 3 to 6% by mass of a compound represented by the following general formula (I).
10 ≦ X ≦ 40 (1)
1 ≦ Y ≦ 20 (2)
30 ≦ Z ≦ 85 (3)
X + Y + Z = 100 (4)

[In Formula (I), R ¹ and R ² may be the same or different and each represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. ]   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 claim 2, 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 of any one of Claims 1-3. The anode and the cathode each have a plate-like shape, and each include an electron conductive porous body as a constituent material,
The separator has a plate-like shape and is made of an insulating porous body,
5. The non-aqueous electrolyte solution according to claim 1, wherein at least a part of the non-aqueous electrolyte solution is contained in the anode, the cathode, and the separator. Lithium ion secondary battery. 6. The lithium ion secondary battery according to claim 1, wherein R ¹ and R ² in the compound represented by the general formula (I) are hydrogen atoms.

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