JP2010073489A - Electrolyte excellent in thermal stability and secondary battery prepared using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte for high voltage, which has high thermal stability and can be used in an onboard normal secondary battery, and to provide a secondary battery prepared using the electrolyte. <P>SOLUTION: The electrolyte is used for the secondary battery including positive and negative electrodes occluding and desorbing alkali metal ions and the electrolyte. The electrode concerned contains only glyme as the solvent for the electrolyte and an alkali metal salt as a solute for the electrolyte and is characterized in that at least part of the glyme and the alkali metal salt forms a complex. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrolyte suitable for use in a secondary battery, particularly a vehicle. More specifically, the present invention relates to an electrolytic solution excellent in thermal stability and electrochemical stability, and further relates to a secondary battery using the electrolytic solution.

  In recent years, in order to cope with air pollution and global warming, reduction of carbon dioxide emissions has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done. This is because in these so-called electric vehicles, it is indispensable to use a power supply device capable of discharging and charging.

  As the secondary battery for driving the motor, a secondary battery such as a lithium ion battery or a nickel metal hydride battery, an electric double layer capacitor, or the like is used. Among them, lithium ion secondary batteries are attracting attention because they have the highest theoretical energy among all the batteries and have high durability against repeated charging and discharging, and are currently being developed rapidly. .

In order to improve the performance of secondary batteries such as lithium ion secondary batteries, various studies have been made on the components thereof, but the same applies to the electrolyte. In general, an organic solvent such as ethylene carbonate or propylene carbonate is used as a solvent for the electrolytic solution. For example, in order to reduce the solvating ability of an organic solvent and suppress decomposition at the negative electrode, an electrolytic solution to which glymes are added as a plasticizer for a polymer solid electrolyte has been proposed (see Patent Document 1 below). .
JP-A-8-106920

  Regarding the electrolyte for secondary batteries, the thermal stability is also being improved. As the capacity and output of batteries increase, the requirements for safety are becoming stricter, so it is important to ensure the thermal stability of the electrolyte. However, conventional electrolyte solutions have a trade-off relationship in which electrical characteristics such as ion conductivity and electrochemical stability are reduced when thermal stability is improved. In order to make this relationship compatible, for example, a complicated battery control system needs to be added. Therefore, realization of an electrolytic solution that is applicable to a secondary battery and excellent in thermal stability and electrochemical stability is desired.

  In order to solve the above problems, the electrolytic solution provided by the present invention contains only glyme as a solvent of the electrolytic solution and an alkali metal salt as a solute of the electrolytic solution. Furthermore, at least a part of the glyme and the alkali metal salt forms a complex in the electrolytic solution. Moreover, the electrolyte solution of this invention can be used for the secondary battery containing the positive electrode and negative electrode which occlude / desorb an alkali metal ion.

  The electrolyte solution of the present invention forms a complex structure in which an alkali metal salt and glyme contain a complex by using only glyme as a solvent. As a result, excellent thermal stability and good electrical characteristics derived from electrochemical stability are compatible with the electrolyte.

  The electrolyte solution of the present invention will be described in detail below.

  The electrolytic solution of the present invention uses only glyme as a solvent. Glyme is a general term for linear glycol diethers. Glyme is polar in the molecule and is suitable for dissolving alkali metal salts used in batteries. However, since glyme has an ether structure, it has generally been considered that it has poor oxidation resistance and is difficult to combine with the positive electrode material of a battery. In addition, in order to achieve a voltage of a level normally used for secondary batteries for vehicles and the like, it is difficult to use only glyme as a solvent of the electrolyte because the oxidation potential is low when the electrolyte is used. This was the conventional technical common sense. However, as a result of the experiment, the present inventors have been able to charge and discharge together with a commonly used positive electrode material even when only glyme is used as the solvent of the electrolytic solution, and obtain an oxidation potential sufficient for the use of the secondary battery. I found out that In addition, it has been found that an electrolytic solution using only glyme exhibits excellent thermal stability at the same time.

  The reason why the electrolyte solution exhibits a sufficient oxidation potential and excellent thermal stability even when only glyme is used as the solvent is presumed as follows. When glyme and an alkali metal salt are mixed, the oxygen part of the ether structure of glyme is coordinated to the alkali metal ion, and it is considered that a complex is formed in at least a part of the electrolytic solution. By this complex formation, the electrolytic solution is considered to have improved oxidation resistance and at the same time improved thermal stability. However, it is assumed that the complex formation in the electrolytic solution does not necessarily determine a clear form such that the alkali metal ions and glyme have a specific structure of 1: 1 and are liberated from others. It seems that the whole of the glyme ether part and alkali metal ions form a complex structure while including a form like a 1: 1 complex while maintaining a weak bond with each other. Such a whole group is considered to contribute to the improvement of oxidation resistance, that is, electrochemical stability and thermal stability.

  In the electrolytic solution of the present invention, the mixing ratio of alkali metal salt to glyme, that is, the alkali metal salt / glyme is preferably 0.70 to 1.25 in terms of mole, more preferably 0.8 to 1. 2. Within such a range, a high oxidation potential can be realized more reliably. In particular, the oxidation potential of an electrolyte used for a secondary battery for vehicle mounting or the like usually requires a high voltage of at least about 4.5V. As described above, the electrolytic solution using glyme has a low oxidation potential, and conventionally, application to a normal battery has not been considered. However, when the mixing ratio is as described above, the electrolytic solution can sufficiently realize an oxidation potential of 4.5 V or more, and can be used for a normal secondary battery. When the mixing ratio range of alkali metal salt / glyme is 0.70 to 1.25 in terms of mole, the electrochemical stability of the electrolytic solution is easily secured, and an oxidation potential of 4.5 V or more can be realized. Be certain. The reason for this is that if the mixing ratio is within this range, the complex structure in the electrolyte as described above is most effectively contributing to the electrochemical stability. If the mixing ratio is less than 0.70, glyme may be oxidized and decomposed on the positive electrode. On the other hand, when the mixing ratio exceeds 1.25, the alkali metal salt may not be completely dissolved and may be deposited in the electrolytic solution.

  The glyme used in the electrolytic solution of the present invention is preferably at least one of the following chemical formulas. A glyme may be used individually by 1 type, or may be used with the form of a 2 or more types of mixture.

  Here, R is any one of an alkyl group having 1 to 9 carbon atoms which may be substituted with fluorine, a phenyl group which may be substituted with a halogen atom, and a cyclohexyl group which may be substituted with a halogen atom. Yes, x is 1-5. By using such a glyme, the thermal stability, ionic conductivity, and electrochemical stability of the electrolytic solution can be further improved.

  Examples of the alkyl group in the above formula include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, pentyl group, isopentyl group, hexyl group, heptyl group, octyl group, and nonyl group. These alkyl groups may be substituted at any position with fluorine. When the number of alkyl groups exceeds 9, the polarity of glyme becomes weak, so that the solubility of the alkali metal salt tends to decrease. For this reason, the alkyl group preferably has a smaller number of carbon atoms, preferably a methyl group or an ethyl group, and most preferably a methyl group.

  The phenyl group which may be substituted with a halogen atom is not particularly limited, but 2-chlorophenyl group, 3-chlorophenyl group, 4-chlorophenyl group, 2,4-dichlorophenyl group, 2-bromophenyl group, 3- Examples include bromophenyl group, 4-bromophenyl group, 2,4-dibromophenyl group, 2-iodophenyl group, 3-iodophenyl group, 4-iodophenyl group, 2,4-iodophenyl group and the like.

  The cyclohexyl group which may be substituted with a halogen atom is not particularly limited, but 2-chlorocyclohexyl group, 3-chlorocyclohexyl group, 4-chlorocyclohexyl group, 2,4-dichlorocyclohexyl group, 2-bromocyclohexyl group. Group, 3-bromocyclohexyl group, 4-bromocyclohexyl group, 2,4-dibromocyclohexyl group, 2-iodocyclohexyl group, 3-iodocyclohexyl group, 4-iodocyclohexyl group, 2,4-diiodocyclohexyl group and the like. Can be mentioned.

  X representing the number of repeating ethylene oxide units is preferably 1 to 5, more preferably 2 to 5, and most preferably 3 or 4. When x is in the range of 1 to 5, electrochemical stability is easily ensured when the electrolyte is used, and the electrolyte can withstand high voltages. According to experiments, when x is 3 or 4, the oxidation potential is the highest and is suitable for a secondary battery.

  In the electrolytic solution of the present invention, any glyme represented by the above chemical formula can be preferably used, but the oxidation potential of the electrolytic solution varies depending on the type of glyme. For this reason, considering application to a secondary battery as described above, it is preferable to adjust the mixing ratio and the like so that the oxidation potential is 4.5 to 5.3 V. The oxidation potential is more preferably 5.0 to 5.3V.

The alkali metal salt used in the electrolytic solution of the present invention can be represented by MX, where M is an alkali metal and X is a substance that becomes a counter anion. There is no restriction | limiting in particular as an alkali metal, Any alkali metal currently used as a supporting salt and an active material can be used for a normal battery. Specific examples include Li, Na, K, Rb, and Cs. More preferred are Li, Na and K, and most preferred is Li from the viewpoint of versatility. X is not particularly limited, but Cl, Br, I, BF ₄ , PF ₆ , CF ₃ SO ₃ , ClO ₄ , CF ₃ CO ₂ , AsF ₆ , SbF ₆ , AlCl ₄ , N (CF ₃ SO ₂ ) _2, and _{N (CF 3 CF 2 SO 2} ) 2 and the like. Preferred are BF ₄ , PF ₆ , ClO ₄ , N (CF ₃ SO ₂ ) ₂ and N (CF ₃ CF ₂ SO ₂ ) ₂ . N (CF ₃ SO ₂ ) ₂ and N (CF ₃ CF ₂ SO ₂ ) ₂ are more preferable from the viewpoint of solubility in glyme and ease of forming a complex structure. The said alkali metal salt may be used individually by 1 type, and may be used in the form of a mixture of 2 or more types.

  The electrolytic solution of the present invention may contain any additive such as a plasticizer in addition to the above-mentioned glyme and alkali metal salt. Examples of the plasticizer include carbonates such as propylene carbonate, ethylene carbonate, vinylene carbonate, and 4-fluoroethylene carbonate. However, the additive is preferably 1% by mass or less based on the entire electrolytic solution so as not to prevent complex formation between glyme and the alkali metal salt. Moreover, as a kind of additive, it is preferable to add an additive having a polarity lower than that of glyme so as not to excessively affect the complex formation.

  Hereinafter, a secondary battery to which the electrolytic solution of the present invention can be applied will be described. First, basic configurations of a non-bipolar secondary battery and a bipolar secondary battery, which are typical forms of secondary batteries, will be described with reference to the drawings.

[Battery overall structure]
FIG. 1 schematically shows the overall structure of a flat (stacked) secondary battery (hereinafter also simply referred to as a non-bipolar secondary battery), which is a typical embodiment of the battery of the present invention. FIG.

  As shown in FIG. 1, the non-bipolar secondary battery 10 of the present embodiment has a configuration in which a power generation element (battery element) 17 is housed and sealed by a battery exterior material 22. A positive electrode (positive electrode active material layer) 12 is formed on both surfaces of the positive electrode current collector 11, and a negative electrode (negative electrode active material layer) 15 is formed on both surfaces of the negative electrode current collector 14 (one side for the lowermost layer and the uppermost layer of the power generation element). Is formed. The power generation element (battery element) 17 has a configuration in which a positive electrode plate, an electrolyte layer 13 and a negative electrode plate are laminated. At this time, the positive electrode (positive electrode active material layer) 12 on one surface of one positive electrode plate and the negative electrode (negative electrode active material layer) 15 on one surface of one negative electrode plate adjacent to the one positive electrode plate face each other through the electrolyte layer 13. A plurality of layers are stacked.

  As a result, the adjacent positive electrode (positive electrode active material layer) 12, electrolyte layer 13, and negative electrode (negative electrode active material layer) 15 constitute one unit cell layer 16. Therefore, it can be said that the secondary battery 10 of the present embodiment has a configuration in which a plurality of single battery layers 16 are stacked and electrically connected in parallel. A positive electrode (positive electrode active material layer) 12 is formed on only one side of the outermost positive electrode current collector 11 a located in both outermost layers of the power generation element (battery element; laminate) 17. The arrangement is changed from that of FIG. 1, and the outermost layer negative electrode current collector (not shown) is positioned on both outermost layers of the power generation element (battery element) 17. In addition, a negative electrode (negative electrode active material layer) 15 may be formed.

  Further, the positive electrode tab 18 and the negative electrode tab 19 that are electrically connected to the positive electrode plate and the negative electrode plate are ultrasonically applied to the positive electrode current collector 11 and the negative electrode current collector 14 of each electrode plate via the positive electrode terminal lead 20 and the negative electrode terminal lead 21. It is attached by welding or resistance welding. Each lead has a structure that is sandwiched between heat-sealed portions and exposed to the outside of the battery exterior material 22.

  FIG. 2 schematically shows the overall structure of a bipolar flat (stacked) secondary battery (hereinafter also simply referred to as a bipolar secondary battery), which is another typical embodiment of the battery of the present invention. FIG.

  As shown in FIG. 2, in the bipolar secondary battery 30 of the present embodiment, a substantially rectangular power generation element (battery element) 37 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior member 42. It has a structure. The power generation element (battery element) 37 includes an electrolyte layer 35 sandwiched between one or two or more bipolar electrodes 34, and a positive electrode (positive electrode active material layer) 32 and a negative electrode (negative electrode active) of adjacent bipolar electrodes 34. The material layer) 33 is opposed to the material layer 33. Here, the bipolar electrode 34 has a structure in which a positive electrode (positive electrode active material layer) 32 is provided on one surface of the current collector 31 and a negative electrode (negative electrode active material layer) 33 is provided on the other surface. That is, the bipolar secondary battery 30 has a positive electrode (positive electrode active material layer) 32 on one surface of the current collector 31 and a negative electrode (negative electrode active material layer) 33 on the other surface. And a power generation element (battery element) 37 having a structure in which a plurality of sheets 34 are stacked with an electrolyte layer 35 interposed therebetween.

  The adjacent positive electrode (positive electrode active material layer) 32, electrolyte layer 35, and negative electrode (negative electrode active material layer) 33 constitute one unit cell layer 36. Therefore, it can be said that the bipolar secondary battery 30 has a configuration in which the single battery layers 36 are stacked. Further, a seal portion (insulating layer) 43 is disposed around the unit cell layer 36 in order to prevent liquid junction due to leakage of the electrolyte from the electrolyte layer 35. By providing the seal portion (insulating layer) 43, the adjacent current collectors 31 can be insulated and a short circuit due to contact between the adjacent electrodes (the positive electrode 32 and the negative electrode 33) can be prevented.

  In addition, the positive electrode side electrode 34a and the negative electrode side electrode 34b located in the outermost layer of the power generation element (battery element) 37 may not have a bipolar electrode structure. A structure in which the positive electrode (positive electrode active material layer) 32 or the negative electrode (negative electrode active material layer) 33 of only one side necessary for the outermost layer current collectors 31a and 31b (or terminal plates) may be arranged. A positive electrode (positive electrode active material layer) 32 may be formed on only one side of the positive electrode side outermost layer current collector 31 a located in the outermost layer of the power generation element (battery element) 37. Similarly, a negative electrode (negative electrode active material layer) 33 may be formed only on one side of the outermost current collector 31b on the negative electrode side located in the outermost layer of the power generation element (battery element) 37. Further, in the bipolar secondary battery 30, a positive electrode tab 38 and a negative electrode tab 39 are provided on the positive electrode side outermost layer current collector 31a and the negative electrode side outermost layer current collector 31b at both upper and lower ends, respectively, and a positive electrode terminal lead 40 and It is joined via the negative terminal lead 41. However, the positive electrode side outermost layer current collector 31 a may be extended to form a positive electrode tab 38, which may be derived from a laminate sheet that is the battery exterior material 42. Similarly, the negative electrode side outermost layer current collector 31b may be extended to form a negative electrode tab 39, which may be similarly derived from the battery outer packaging material.

  In the bipolar secondary battery 30, the power generation element (battery element; laminated body) 37 is enclosed in the battery exterior member 42 in order to prevent external impact and environmental degradation during use, and the positive electrode tab 38. It is preferable that the negative electrode tab 39 be taken out of the battery exterior member 42. The basic configuration of the bipolar secondary battery 30 can be said to be a configuration in which a plurality of stacked unit cell layers 36 are connected in series.

  As described above, with respect to each constituent requirement and manufacturing method of the non-bipolar secondary battery and the bipolar secondary battery, the basic configuration is the same except that the electrical connection form (electrode structure) in the secondary battery is different. Is the same. Moreover, an assembled battery and a vehicle can also be comprised using the non-bipolar secondary battery and / or bipolar secondary battery of this invention. Next, each member of the above secondary battery will be described.

[Current collector]
The current collector is made of foil, mesh, expanded grid (expanded metal), punched metal, or the like using a conductive metal material such as nickel, copper, and stainless steel (SUS). The mesh opening, wire diameter, number of meshes, etc. are not particularly limited, and conventionally known ones can be used. Further, not limited to metals, a conductive resin or a resin containing a conductive filler may be used as a current collector. The general thickness of the current collector is 5 to 30 μm. However, a current collector having a thickness outside this range may be used.

[Active material layer]
An active material layer is formed on the current collector. The active material layer is a layer containing an active material that plays a central role in the charge / discharge reaction. When the electrode is used as a positive electrode, the active material layer includes a positive electrode active material. On the other hand, when the electrode is used as a negative electrode, the active material layer includes a negative electrode active material. Hereinafter, the positive electrode active material layer and the negative electrode active material layer are collectively referred to as an active material layer. Similarly, the positive electrode active material and the negative electrode active material are collectively referred to as an active material.

The positive electrode active material contained in the positive electrode acts to occlude and desorb alkali metal ions. As the positive electrode active material, a lithium transition metal composite oxide is preferable, and examples thereof include a Li—Mn composite oxide such as LiMn ₂ O ₄ and a Li—Ni composite oxide such as LiNiO ₂ . More specifically, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFePO ₄ , LiCo _0.5 Ni _0.5 O ₂ , LiNi _0.7 Co _0.2 Mn _0.1 O ₂ are preferably mentioned. In addition to lithium, any alkali metal ion can be used without limitation as long as it is a substance that electrochemically inserts and desorbs, and examples thereof include sodium. In some cases, two or more positive electrode active materials may be used in combination.

  The negative electrode active material contained in the negative electrode acts to occlude and desorb alkali metal ions. The negative electrode active material is preferably at least one selected from the group consisting of lithium, carbon, silicon, aluminum, tin, zinc and magnesium. More specifically, metal materials such as lithium titanate, lithium metal, lithium aluminum alloy, lithium tin alloy, lithium silicon alloy, natural graphite, artificial graphite, carbon black, acetylene black, graphite, activated carbon, carbon fiber, coke, Conventionally known negative electrode materials such as crystalline carbon materials such as soft carbon and hard carbon, and carbon materials such as amorphous carbon materials can be used. Among these, it is desirable to use a carbon material or lithium or a lithium transition metal composite oxide because a battery excellent in capacity and output characteristics can be constituted. In some cases, two or more negative electrode active materials may be used in combination.

  The average particle diameter of the active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 50 μm, and further preferably 1 to 20 μm. However, forms outside these ranges can also be employed. The average particle diameter of the active material can be measured by laser diffraction particle size distribution measurement (laser diffraction scattering method).

  Moreover, the content of the active material in the active material layer is preferably 70 to 98% by mass, more preferably 80 to 98% by mass with respect to the total mass of the active material layer. If the content of the active material is within the above range, it is preferable because the energy density can be increased.

  The thickness of the active material layer (the thickness of one surface of the coating layer) is preferably 20 to 500 μm, more preferably 20 to 300 μm, and still more preferably 20 to 150 μm.

  The active material layer may contain other materials, for example, a binder, a conductive additive, a supporting salt, and the like. The compounding ratio of these components is not particularly limited, and can be adjusted by appropriately referring to known knowledge about secondary batteries.

  A conductive assistant means the additive mix | blended in order to improve electroconductivity. Examples of the conductive assistant include carbon powder such as graphite, and various carbon fibers such as vapor grown carbon fiber (VGCF). As the supporting salt, those contained in the electrolytic solution can be used similarly.

  The binder contained in the active material layer includes polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE). Styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or mixtures thereof.

[Electrolyte layer]
Examples of the electrolyte layer include a separator or gel electrolyte containing the above-described electrolytic solution of the present invention.

  As a separator, the porous sheet and nonwoven fabric which consist of a polymer which absorbs and hold | maintains the said electrolyte solution can be mentioned, for example.

  The porous sheet is composed of, for example, a microporous polymer. Examples of the polymer constituting such a porous sheet include polyolefins such as polyethylene (PE) and polypropylene (PP); laminates having a three-layer structure of PP / PE / PP, polyimide, and aramid. In particular, a polyolefin-based microporous separator is preferable because it has a property of being chemically stable with respect to an organic solvent and can keep the reactivity with the electrolyte solution low.

  The thickness of the separator cannot be uniquely defined because it varies depending on the application. However, in the use of a secondary battery for driving a motor of a vehicle, it is desirable that the thickness is 4 to 60 μm in a single layer or multiple layers. Further, it is desirable that the fine pore diameter of the separator is 1 μm or less (usually a pore diameter of about 10 nm), and the porosity is 20 to 80%.

  As the nonwoven fabric, cotton, rayon, acetate, nylon (registered trademark), polyester; polyolefins such as PP and PE; conventionally known materials such as polyimide and aramid are used alone or in combination. The bulk density of the non-woven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated electrolytic solution. The porosity of the nonwoven fabric separator is preferably 50 to 90%. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm. When the thickness is less than 5 μm, the electrolyte retention deteriorates, and when it exceeds 200 μm, the resistance increases.

  The gel electrolyte has a configuration in which an electrolytic solution is injected into a matrix polymer made of an ion conductive polymer. As the electrolytic solution, the above-described electrolytic solution of the present invention is used. Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), and vinylidene fluoride-hexafluoropropylene (VDF-HEP). And poly (methyl methacrylate (PMMA), copolymers thereof, etc. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

[Insulation layer]
Insulating layers (sealing parts) are used to prevent secondary current collectors in the secondary battery from coming into contact with each other and short-circuiting due to slight unevenness at the end of the laminated electrode. It arrange | positions at the peripheral part of a battery layer. As the sealing material constituting the insulating layer, it should have insulating properties, sealing properties against falling off of the solid electrolyte, sealing properties against moisture permeation from the outside (sealing property), heat resistance at the battery operating temperature, etc. That's fine. For example, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber and the like can be used. Of these, urethane resins and epoxy resins are preferred from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming properties), economy, and the like.

[tab]
The material of the tab (positive electrode tab and negative electrode tab) can be aluminum, copper, nickel, stainless steel, alloys thereof, or the like. These are not particularly limited, and known materials conventionally used as tabs can be used.
[Battery exterior materials]
As the battery exterior material, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element (battery element) using a laminate film containing aluminum can be used. For example, a laminate film having a three-layer structure in which polypropylene, aluminum, and nylon (registered trademark) are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto. [Battery]
The present invention also provides an assembled battery using the battery.

  The assembled battery of the present invention is formed by connecting a plurality of lithium ion secondary batteries of the present invention. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series. In the assembled battery of the present invention, the non-bipolar lithium ion secondary battery and the bipolar lithium ion secondary battery of the present invention are used, and these are combined in series, in parallel, or in series and in parallel. Thus, an assembled battery can be configured.

  FIG. 3 is an external view of a typical embodiment of the assembled battery according to the present invention, FIG. 3A is a plan view of the assembled battery, FIG. 3B is a front view of the assembled battery, and FIG. 3C is an assembled battery. FIG.

  As shown in FIG. 3, an assembled battery 300 according to the present invention forms a small assembled battery 250 in which a plurality of lithium ion secondary batteries according to the present invention are connected in series or in parallel to be detachable. The battery pack 300 may further include a plurality of detachable small battery packs 250 connected in series or in parallel. The small assembled battery 250 that can be attached and detached is connected to each other using an electrical connection means such as a bus bar, and the assembled battery 250 is stacked in a plurality of stages using a connection jig 310.

[vehicle]
The present invention also provides a vehicle equipped with the battery or the assembled battery.

  The vehicle of the present invention is equipped with the bipolar secondary battery of the present invention or an assembled battery formed by combining a plurality of these. The bipolar secondary battery of the present invention or an assembled battery formed by combining a plurality of these is used as a power source for driving a vehicle. The bipolar secondary battery or the assembled battery of the present invention is used in a vehicle such as a hybrid vehicle, a fuel cell vehicle, and an electric vehicle (for example, a four-wheeled vehicle (a commercial vehicle such as a passenger car, a truck, a bus, a light vehicle)). In addition, because it is used for motorcycles (including motorcycles and tricycles), it becomes a long-life and highly reliable automobile. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  FIG. 4 is a conceptual diagram of a vehicle equipped with the above assembled battery. As shown in FIG. 4, in order to mount the assembled battery 300 on a vehicle such as the electric vehicle 400, the battery pack 300 is mounted under the seat at the center of the vehicle body of the electric vehicle 400. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 300 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or an engine room in front of the vehicle. The electric vehicle 400 using the assembled battery 300 as described above has high durability and can provide sufficient output even when used for a long period of time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance. A vehicle equipped with the assembled battery of the present invention can be widely applied to a hybrid vehicle, a fuel cell vehicle and the like in addition to an electric vehicle as shown in FIG.

  Then, the manufacturing method of the electrolyte solution of this invention and a secondary battery using the same is demonstrated.

[Production method]
(1) Electrolytic Solution The electrolytic solution of the present invention can be prepared by mixing and dissolving an alkali metal salt in glyme which is a solvent, and there is no particular limitation on the mixing method and the like. In mixing, it is preferable to mix in an inert gas atmosphere, for example, an atmosphere of nitrogen gas, helium gas, argon gas, or the like, in order to prevent water from being mixed. More preferably, it is in an argon gas atmosphere. The temperature during mixing is preferably 20 to 80 ° C. Further, in order to dissolve the alkali metal salt, stirring may be performed using a stirrer or the like. Conditions such as selection of the type of glyme and the mixing ratio of alkali metal salt and glyme are as described above.

(2) Formation of Positive Electrode Active Material Layer The positive electrode active material is usually obtained as a slurry (positive electrode slurry) and applied to the surface of the current collector. The positive electrode slurry contains a positive electrode active material, and optionally includes a conductive additive, a binder, a polymerization initiator, an electrolytic solution, a supporting salt, a slurry viscosity adjusting solvent, and the like. The positive electrode slurry can be prepared by mixing these materials in a solvent at a predetermined ratio.

  The binder can be mixed in the positive electrode slurry by a method in which the binder is mixed with a solid content such as an active material in a powder state and then mixed with a solvent. Or you may mix in the slurry for positive electrodes by the method of making it dissolve in a small amount of solvent previously, and adding to the mixture containing an active material and a solvent.

  The kind of solvent and the mixing means are not particularly limited, and conventionally known knowledge can be referred to as appropriate. As an example of the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide and the like can be used.

  Subsequently, the prepared slurry for positive electrode is applied to one surface of the current collector to form a coating film. The application means for applying the positive electrode slurry is not particularly limited. For example, commonly used means such as an applicator and a self-propelled coater may be employed. A thin layer can be formed by using screen printing, an inkjet method, a doctor blade method, or a combination thereof as the application means.

  Thereafter, the coating film formed on the surface of the current collector is dried. Thereby, the solvent in a coating film is removed. The drying means for drying the coating film is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. For example, heat treatment is exemplified. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the coating amount of the positive electrode slurry and the volatilization rate of the solvent of the slurry. For drying, a vacuum dryer or the like can be used. The drying conditions are determined according to the applied positive electrode slurry and cannot be uniquely defined, but are usually 40 to 150 ° C. and 5 minutes to 20 hours.

(3) Formation of negative electrode active material layer A negative electrode active material (negative electrode slurry) is applied to the surface of the current collector. The negative electrode slurry is a solution containing a negative electrode active material. As other components, a conductive additive, a binder, a polymerization initiator, an electrolytic solution, a supporting salt, a slurry viscosity adjusting solvent, and the like are optionally included. About the raw material used and addition amount, it is as having mentioned above.

  The negative electrode slurry is applied on the current collector in the same manner as in the case of forming the positive electrode active material layer. Thereafter, the current collector coated with the negative electrode slurry is dried to remove the contained solvent. The drying is the same as in the case of forming the positive electrode active material layer.

(4) Pressing step The current collector formed with the positive electrode active material layer and the current collector formed with the negative electrode active material layer by the above procedure are improved in surface smoothness and thickness uniformity, and It is preferable to perform a pressing operation so as to obtain a desired film thickness.

  The press operation may be either a cold press roll method or a hot press roll method. In the case of a hot-rolling method, if an electrolyte supporting salt or a polymerizable polymer is contained in the active material layer, it is desirable to carry out at a temperature below which they decompose. The press pressure is preferably 20 to 100 t / m, more preferably 30 to 80 t / m, and even more preferably 40 to 70 t / m in linear pressure. However, conditions such as the pressing pressure and time vary depending on the material and the desired film thickness, and are not particularly limited to this range.

The roll press machine is not particularly limited, and a conventionally known roll press machine such as a calendar roll can be appropriately used. However, other conventionally known press devices and press techniques such as a flat plate press may be used as appropriate.

(6) Formation of electrolyte layer As described above, the electrolyte layer can be constituted by holding the electrolytic solution of the present invention in the separator. To constitute the electrolyte layer, the separator may be impregnated with the electrolytic solution. For example, the electrolytic solution may be preliminarily soaked in the separator. Each separator may be impregnated. In order to provide the electrolyte layer in the secondary battery, it can be manufactured by various conventionally known manufacturing methods, for example, a method in which a separator in which an electrolytic solution is immersed is sandwiched between bipolar electrodes, a vacuum injection method, or the like.

  A polymer gel electrolyte layer in which a polymer gel electrolyte is held in a separator can also be used. In this case, the separator is impregnated with, for example, a pregel solution comprising a matrix polymer and the electrolytic solution of the present invention, an alkali metal salt, a polymerization initiator and the like as a raw material for the polymer gel electrolyte. Then, it manufactures by making it superpose | polymerize (acceleration of a crosslinking reaction) simultaneously with heat drying in inert atmosphere.

  Alternatively, an electrolyte layer laminated between the electrodes or a part thereof (an electrolyte membrane having about half the electrolyte layer thickness) is prepared. In this case, the pregel solution is produced by coating a suitable film such as a polyethylene terephthalate (PET) film or a polypropylene film and polymerizing (accelerating the crosslinking reaction) simultaneously with curing or heat drying in an inert atmosphere. The

  For curing or heat drying, a vacuum dryer (vacuum oven) or the like can be used. The conditions for heat drying are determined according to the solution or the pregel solution and cannot be uniquely defined, but are usually 30 to 110 ° C. and 0.5 to 12 hours.

(7) Lamination of electrode and electrolyte layer As described above, when the electrode and the electrolyte layer are produced separately, both are sufficiently heated and dried under high vacuum. Thereafter, a plurality of each may be cut into an appropriate size as desired. A predetermined number of these electrodes and electrolyte layers are overlapped to produce a secondary battery main body (electrode laminate). The number of electrode stacks is determined in consideration of battery characteristics required for the secondary battery. The step of obtaining the secondary battery by laminating the electrode and the electrolyte layer is preferably performed in an inert atmosphere from the viewpoint of preventing moisture and the like from entering the battery. For example, the bipolar battery may be manufactured under an argon atmosphere or a nitrogen atmosphere.

(8) Formation of Insulating Layer In order to form the insulating layer, for example, an epoxy resin (precursor solution) or the like is applied around the electrode forming portion of the electrode stack with a predetermined width. At this time, the voltage detection tab, the electrode terminal plate, the electrode lead, the electrode tab, or the current collector portion to which these need to be connected are masked in advance using a releasable masking material or the like. Thereafter, an epoxy resin or the like is cured to form an insulating layer, and then the masking material is peeled off.

(9) Connection of terminal plate, electrode lead and tab (terminal) A positive electrode tab and a negative electrode tab are joined (electrically connected) to the outermost current collectors of the secondary battery body (battery laminate), respectively. To do. As a method for joining the tabs, ultrasonic welding or the like having a low joining temperature can be preferably used. However, the method is not limited to this, and a conventionally known joining method can be appropriately used.

(10) Packing (battery completion)
Finally, in order to prevent external impact and environmental degradation, the entire battery stack is sealed in a battery can or sealed with a battery exterior material such as an aluminum laminate film to complete a bipolar battery. At the time of sealing, one end of the positive electrode tab and the negative electrode tab is taken out of the battery.

  The structure of the secondary battery of the present invention is not particularly limited, and when it is distinguished by the form and structure, any conventionally known form such as a stacked (flat) battery or a wound (cylindrical) battery is used.・ Applicable to structures.

Example 1
The following triethyl glycol dimethyl ether (hereinafter referred to as G3) was used as a glyme as a solvent for the electrolytic solution. As the alkali metal salt, a lithium salt represented by the following chemical formula (hereinafter referred to as LiTFSI) was used.

  G3 and LiTFSI were converted to a molar ratio of 25 ° C. so that the Li / G3 ratio was 0.05, 0.50, 0.70, 0.90, 1.00, 1.05, 1.25. Each was mixed under an argon gas atmosphere. Therefore, seven types of electrolyte solutions were prepared. The mixing ratio was confirmed by NMR measurement using trifluorotoluene as a reference substance.

(Example 2)
Tetraethyl glycol dimethyl ether (hereinafter referred to as G4) shown below was used as a glyme as a solvent for the electrolytic solution. As the alkali metal salt, LiTFSI similar to that used in Example 1 was used.

  G4 and LiTFSI at 25 ° C. so that the molar ratio of Li / G4 is 0.05, 0.50, 0.70, 0.90, 1.00, 1.05, 1.25 Seven types of electrolytes were prepared by mixing in an argon gas atmosphere. The mixing ratio was confirmed by NMR measurement using trifluorotoluene as a reference substance.

(Example 3)
In Example 3, using the same G3 and LiTFSI as in Example 1, mixing was performed so that the Li / G3 ratio was 2.0 in terms of molarity, thereby preparing an electrolytic solution.

Example 4
In Example 4, using the same G4 and LiTFSI as in Example 2, mixing was performed so that the Li / G4 ratio was 2.0 in terms of molarity, thereby preparing an electrolytic solution.

(Comparative Example 1)
In Comparative Example 1, for comparison with Example 1, the alkali metal salt was not dissolved and only G3 similar to the solvent of Example 1 was used.

(Comparative Example 2)
In Comparative Example 2, for comparison with Example 2, the alkali metal salt was not dissolved and only G4 similar to the solvent of Example 1 was used.

(Conductivity evaluation)
The electroconductivity (ionic conductivity) of the electrolyte solutions obtained in Examples 1 to 4 was measured and evaluated by the AC impedance method. As the impedance analyzer, EG8 / PAR and VMPs Multi Potentiostat manufactured by Princeton Applied Research were used as an evaluation apparatus. The measurement conditions were a measurement frequency range of 500 kHz to 1 Hz and an applied voltage of 10 mV. Regarding the conductivity, in Examples 1 and 2, measurement was performed on an electrolyte solution having a mixing ratio of 1: 1 (molar ratio) of glyme and alkali metal salt. The measurement results are shown in Table 1 below.

(Thermal stability evaluation)
Evaluation of the thermal stability of the electrolyte solutions obtained in Examples 1 to 4 and Comparative Examples 1 to 2 was performed by thermogravimetry using a TG / DTA6200 manufactured by Seiko Instrument. The measurement was performed by a method of increasing the temperature from room temperature to 550 ° C. at a rate of temperature increase of 10 ° C./min, and a method of determining weight loss over time with the temperature fixed at 100 ° C. Regarding the thermal stability, in Examples 1 and 2, measurement was performed on an electrolyte solution having a mixing ratio of 1: 1 (molar ratio) of glyme and alkali metal salt. The measurement results are shown in Table 1 below.

  As can be seen from Table 1, when Examples 1 and 3 in which the solvent is G3 and Comparative Example 1 are compared, the thermal stability is such that the temperature at which the weight decreases by 5% indicates that the electrolyte of the present invention is the solvent only. It is higher than the case. In addition, the time to 10% weight loss at 100 ° C. is significantly longer than that of the solvent of the present invention alone. Therefore, it can be seen that the electrolytic solution of the present invention is excellent in thermal stability because glyme and alkali metal salt form a complex. In particular, Example 1 in which the mixing ratio of the alkali metal salt to glyme is within a range of 0.70 to 1.25 in terms of moles is assured to have the same degree of conductivity as compared to Example 3. It can be seen that the thermal stability is further improved.

  Further, when Examples 2 and 4 in which the solvent is G4 and Comparative Example 2 are compared, it can be seen that there is a tendency similar to that in the case where the solvent is G3. That is, with respect to thermal stability, the temperature at which the weight is reduced by 5% is higher than that in the case where the electrolytic solution of the present invention is a solvent alone. It is longer than just the case. Therefore, it can be seen that the electrolytic solution of the present invention is excellent in thermal stability by forming a complex between glyme and alkali metal salt even if the kind of glyme is different. In particular, Example 2 in which the mixing ratio of the alkali metal salt to glyme is in the range of 0.70 to 1.25 in terms of mole is ensuring the same degree of conductivity as compared to Example 4. It can be seen that the thermal stability is further improved.

(Electrochemical stability evaluation)
The electrochemical stability of the seven types of mixing ratio electrolytes obtained in Examples 1 and 2 was evaluated by the linear sweep voltammetry method. EG8 / PAR, VMPs Multi Potentiostat manufactured by Princeton Applied Research, Inc. was used as an evaluation apparatus. In this case, the measurement was performed with a two-electrode cell in which the working electrode was platinum and the counter electrode and reference electrode was lithium. The measurement results are shown in the graph of FIG.

  The horizontal axis of the graph of FIG. 5 represents the mixing molar ratio of Li / G3 or Li / G4, and the vertical axis represents the oxidation potential of the electrolytic solution. Although the oxidation potential varies depending on the type of solvent, it can be seen that the electrolytic solution of the present invention can realize an oxidation potential of 4.5 V or more required for a vehicle secondary battery. Moreover, in order to obtain the electrolyte solution which can endure such a high voltage, it turns out that it is suitable that the mixing ratio of the alkali metal salt with respect to a glyme is the range of 0.70-1.25 in molar conversion.

(Example 5)
The electrolyte used LiTFSI as the alkali metal salt and G3 as the solvent, and was mixed in an argon gas atmosphere at 25 ° C. so that the ratio of LiTFSI to G3 was 1.0 in terms of molar ratio.

LiCoO ₂ was used as the positive electrode active material, acetylene black was used as the conductive auxiliary agent, and polyvinylidene fluoride (PVdF) was used as the binder. These materials were mixed so that LiCoO ₂ or LiFePO ₄ : acetylene black: PVdF was in a mass ratio of 85: 9: 6. At this time, an appropriate amount of N-methylpyrrolidone (NMP) was used as a solvent and mixed in a paste form. The obtained mixture was applied on an aluminum foil (thickness 10 μm) as a current collector so that the thickness after pressing was about 20 μm. The current collector coated with the paste was sufficiently dried at 0.1 MPa and 80 ° C. for 24 hours and then pressed to obtain a positive electrode.

  The electrolyte prepared as described above was immersed in a polyolefin separator having a thickness of 20 μm at 25 ° C. for 30 minutes. This separator was sandwiched between the produced positive electrode and a negative electrode in which metallic lithium (thickness: 200 μm) was attached to a stainless steel disk (thickness: 7 mm). These were placed in a battery can made of SUS304 and sealed.

  The secondary battery obtained as described above was subjected to a charge / discharge test to determine the discharge capacity. The charge / discharge evaluation was carried out with a constant current charge at a rate of 0.125C and a charge / discharge voltage range of 3.0-4.2V. The discharge condition was 0.125C. The above evaluation was carried out in a thermostatic bath kept constant at 30 ° C. The evaluation results are shown in Table 2 below. In Table 2, “-” indicates that the measurement was completed because the discharge capacity was reduced.

(Example 6)
In Example 6, a secondary battery was produced in the same manner as in Example 5 except that LiFePO ₄ was used as the positive electrode active material. About the obtained secondary battery, the same charging / discharging test as Example 5 was implemented. The results are shown in Table 2 below.

(Example 7)
In Example 7, a secondary battery was produced in the same manner as in Example 5 except that G4 was used as a solvent for the electrolytic solution. About the obtained secondary battery, the same charging / discharging test as Example 5 was implemented. The results are shown in Table 2 below.

(Example 8)
In Example 8, a secondary battery was fabricated in the same manner as in Example 5 except that G4 was used as the solvent for the electrolytic solution and LiFePO ₄ was used as the positive electrode active material. About the obtained secondary battery, the same charging / discharging test as Example 5 was implemented. The results are shown in Table 2 below.

Example 9
In Example 9, a secondary battery was fabricated in the same manner as in Example 5 except that LiTFSI and G3 of the electrolytic solution were mixed in a molar ratio of 4.0 (Li / G3). About the obtained secondary battery, the same charging / discharging test as Example 5 was implemented. The results are shown in Table 2 below.

(Example 10)
In Example 10, the secondary electrolyte was LiTFSI and G3 in the same manner as in Example 5 except that the mixing ratio was 4.0 (Li / G3) in terms of mole and LiFePO ₄ was used as the positive electrode active material. A battery was produced. About the obtained secondary battery, the same charging / discharging test as Example 5 was implemented. The results are shown in Table 2 below.

(Example 11)
In Example 11, G4 was used as the solvent of the electrolytic solution, and LiTFSI and G4 of the electrolytic solution were changed to a molar ratio of 4.0 (Li / G4). A secondary battery was produced. About the obtained secondary battery, the same charging / discharging test as Example 5 was implemented. The results are shown in Table 2 below.

Example 12
Example 12 was carried out except that G4 was used as the solvent of the electrolytic solution, LiFePO ₄ was used as the positive electrode active material, and LiTFSI and G4 of the electrolytic solution were mixed in a molar ratio of 4.0 (Li / G4). A secondary battery was fabricated in the same manner as in Example 5. About the obtained secondary battery, the same charging / discharging test as Example 5 was implemented. The results are shown in Table 2 below.

  From the results in Table 2, it can be seen that all the secondary batteries of the present invention exhibited stable cycle characteristics up to about 10 cycles. Among them, Examples 5 to 8 in which the mixing ratio of the alkali metal salt and glyme is in the range of 0.7 to 1.25 in terms of mole show particularly excellent cycle characteristics, and stable charge / discharge of 200 cycles or more is achieved. I understand that I can do it. This is presumably because the formation of a complex structure between the lithium salt and G3 or G4 contributed to the electrochemical stability of the electrolytic solution.

1 is a schematic cross-sectional view schematically showing the overall structure of a non-bipolar secondary battery that is an embodiment of the present invention. 1 is a schematic cross-sectional view schematically showing the entire structure of a bipolar secondary battery which is an embodiment of the present invention. FIG. 3A is a plan view, FIG. 3B is a front view, and FIG. 3C is a side view of an embodiment of an assembled battery according to the present invention. It is a conceptual diagram of the vehicle carrying the assembled battery of this invention. It is a result of electrochemical stability evaluation of the electrolyte solution obtained in Examples 1 and 2.

Explanation of symbols

10 Non-bipolar secondary battery,
11 positive electrode current collector,
11a Outermost layer positive electrode current collector,
12, 32 positive electrode,
13, 35 electrolyte layer,
14 negative electrode current collector,
15, 33 negative electrode,
16, 36 cell layer,
17, 37 Power generation element,
18, 38 positive electrode tab,
19, 39 negative electrode tab,
20, 40 Positive terminal lead,
21, 41 Negative terminal lead,
22, 42 Battery exterior material,
30 Bipolar secondary battery,
31 current collector,
31a positive electrode side outermost layer current collector,
31b negative electrode side outermost layer current collector,
34 Bipolar electrode,
34a Positive electrode side electrode 34b Negative electrode side electrode,
43 Sealing part (insulating layer),
250 small battery pack,
300 battery packs,
310 connection jig,
400 Electric car.

Claims (10)

An electrolyte used for a secondary battery including a positive electrode and a negative electrode that absorb and desorb alkali metal ions and an electrolyte,
Only glyme as a solvent for the electrolyte,
An alkali metal salt as a solute of the electrolyte,
And at least a part of the glyme and the alkali metal salt forms a complex.   2. The electrolytic solution according to claim 1, wherein a mixing ratio of the alkali metal salt to the glyme is 0.70 to 1.25 in terms of mole.   The electrolytic solution according to claim 1 or 2, wherein an oxidation potential of the electrolytic solution is 4.5 to 5.3V. The grime has the following formula

Here, R is any one of an alkyl group having 1 to 9 carbon atoms which may be substituted with fluorine, a phenyl group which may be substituted with a halogen atom, and a cyclohexyl group which may be substituted with a halogen atom. X is 1-5,
The electrolytic solution according to claim 1, wherein the electrolytic solution is at least one type represented by The alkali metal salt is represented by MX, where M is an alkali metal, X is Cl, Br, I, BF ₄ , PF ₆ , CF ₃ SO ₃ , ClO ₄ , CF ₃ CO ₂ , AsF ₆ , SbF. _{6, AlCl 4, N (CF} 3 SO 2) 2 and _{N (CF 3 CF 2 SO 2} ) electrolyte solution according to claim 1 is at least one selected from the group consisting of _2.   The secondary battery containing the electrolyte solution as described in any one of Claims 1-5 and the positive electrode and negative electrode which occlude / desorb an alkali metal ion.   The secondary battery according to claim 6, wherein the positive electrode includes a positive electrode active material that occludes and desorbs alkali metal ions, and the positive electrode active material includes at least one lithium transition metal composite oxide.   The negative electrode includes a negative electrode active material that occludes and releases alkali metal ions, and the negative electrode active material includes at least one selected from the group consisting of lithium, carbon, silicon, aluminum, tin, zinc, and magnesium. Or the secondary battery according to 7.   The assembled battery in which the secondary battery as described in any one of Claims 6-8 was connected two or more.   A vehicle equipped with the secondary battery according to any one of claims 6 to 8 or the assembled battery according to claim 9 as a driving power source.

Images