JP5942892B2 - Non-aqueous electrolyte, non-aqueous electrolyte secondary battery using the same, and secondary battery system using the non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte, a non-aqueous electrolyte secondary battery using the same, and a secondary battery system using the non-aqueous electrolyte secondary battery.

  Lithium ion secondary batteries, which are a type of non-aqueous electrolyte secondary battery, are compared to the electromotive force (about 1.5 V) of aqueous electrolyte secondary batteries (eg, nickel metal hydride batteries, nickel cadmium batteries, lead batteries). It has a very high electromotive force (3 V or more). Therefore, the lithium ion secondary battery is advantageous for reducing the size and weight of the battery and increasing the capacity and output, and has been widely used in small electronic devices such as portable personal computers and mobile phones. In recent years, the use of lithium ion secondary batteries has been expanded to large-scale electric devices (for example, power sources for automobiles such as HEV (hybrid vehicles) and EVs (electric vehicles), and power sources for power storage)).

  Non-aqueous electrolytes for lithium ion secondary batteries are widely prepared by dissolving an electrolyte (supporting salt) such as lithium hexafluorophosphate in a non-aqueous solvent such as ethylene carbonate (EC) or propylene carbonate (PC). Are known. However, since these non-aqueous solvents have flammability (for example, the flash point of EC and PC is 130 to 140 ° C.), in principle, they ignite if there is a fire type.

  On the other hand, in order to apply a lithium ion secondary battery to a large electric device, it is essential to realize a much higher output and capacity than in the case of a small electronic device. This leads to an increase in the absolute volume of the secondary battery. And since the problem of the heat_generation | fever accompanying it becomes large, it is important to ensure higher safety, and use of the non-aqueous electrolyte with little possibility of ignition is strongly desired. In response to such demands, research and development for avoiding non-aqueous electrolyte ignition by adding a flame retardant or an overcharge inhibitor to the non-aqueous electrolyte has been energetically advanced.

  As an electrolytic solution of a lithium ion secondary battery to which a flame retardant is added, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2006-004746) mainly includes a solute and a non-aqueous organic solvent that dissolves the solute, and has a specific structure. A non-aqueous electrolyte for a secondary battery containing 10 to 1000 ppm of a phosphorus-based compound having the above is disclosed. According to Patent Document 1, it is possible to provide a non-aqueous electrolyte and a secondary battery in which deterioration of battery performance during high-temperature storage and high-temperature continuous charging is suppressed, and a decrease in initial capacity is greatly reduced.

  On the other hand, as an electrolyte solution of a lithium ion secondary battery to which an overcharge inhibitor is added, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2005-135906) includes alkyl-substituted benzenes, aryl-substituted benzenes, and diaryl ethers. Alternatively, at least one aromatic compound selected from halogen-substituted anisoles is contained in a total amount of 0.5 to 10 wt% with respect to the total weight of the electrolytic solution, and fluorinated borate is added to the total weight of the electrolytic solution. On the other hand, a non-aqueous electrolyte characterized by containing 0.1 to 5 wt% is disclosed. According to Patent Document 2, a non-aqueous electrolyte that has a high overcharge prevention effect and a small decrease in charge / discharge characteristics after storage at high temperature, and a non-aqueous electrolyte that includes the non-aqueous electrolyte and is safe and has little decrease in battery characteristics after storage at high temperature. It is said that a lithium secondary battery can be provided.

  Patent Document 3 (Japanese Patent Laid-Open No. 2008-153096) includes a solvent containing a cyclic carbonate having two or more halogens as constituent elements, an electrolyte salt, and an aromatic compound. An electrolytic solution characterized in that the content of the compound is 0.1% by weight or more is disclosed. According to Patent Document 3, by using the electrolytic solution in an electrochemical device such as a battery, the decomposition reaction of the solvent and electrolyte salt that contributes to the ionic conductivity of the electrode reactant is suppressed, and functions as an overcharge inhibitor. Since the decomposition reaction of the aromatic compound is also suppressed, the overcharge characteristics can be improved and the storage characteristics can be improved.

  Further, Non-Patent Document 1 discloses a lithium ion secondary battery in which tri- (4-methoxythphenyl) phosphate is added to an electrolytic solution. According to Non-Patent Document 1, it is possible to provide a lithium ion secondary battery that is excellent in thermal stability and further prevents overcharging by reducing the flammability of the electrode.

JP 2006-004746 A Japanese Patent Laid-Open No. 2005-135906 JP 2008-153096 A

J. K. Feng, Y. L. Cao, X. P. Ai, and H. X. Yang, Electrochimica Acta. 53, 8265-8368, 2008

  As described above, the demand for higher capacity and higher output for lithium ion secondary batteries has been increasing in recent years. However, a lithium ion secondary battery using a conventional non-aqueous electrolyte to which a flame retardant or an overcharge preventing agent is added has a lithium ion secondary battery by adding a flame retardant component or an overcharge preventing component to the non-aqueous electrolyte. There is a problem that the required performance cannot be sufficiently satisfied with the battery performance (for example, initial capacity) of the secondary battery. That is, further improvements have been strongly desired in these respects.

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte capable of imparting flame retardancy and overcharge prevention without sacrificing battery characteristics (for example, initial capacity) of the non-aqueous electrolyte secondary battery. There is to do. In addition, by using the non-aqueous electrolyte, it is possible to provide a non-aqueous electrolyte secondary battery that is safer than the prior art while ensuring the same or better battery characteristics than the conventional one, and a secondary battery system using the same. is there.

  (I) One embodiment of the present invention is a nonaqueous electrolyte solution for a nonaqueous electrolyte secondary battery containing a nonaqueous solvent and an electrolyte, and the nonaqueous electrolyte solution has the following chemical formula (1) or A flame retardant comprising a compound represented by the chemical formula (2) is contained in the range of 5% by mass to 30% by mass with respect to the total mass of the non-aqueous electrolyte, and the three substituents (X1, X2) of the compound , X3) are one or two substituents (first substituent) that are involved in the polymerization reaction of the compound at a potential at which the secondary battery is overcharged. Of the three substituents (X1, X2, X3), the remaining substituents (second substituents) excluding the first substituent are compatible with the non-aqueous solvent and the flame retardant. Provided is a non-aqueous electrolyte characterized by being a substituent that contributes to improvement.

  (II) Another embodiment of the present invention is a nonaqueous electrolyte solution for a secondary battery containing a nonaqueous solvent and an electrolyte, and the nonaqueous electrolyte solution has the following chemical formula (1) or chemical formula ( 2) containing a flame retardant composed of a compound represented by 2) in a range of 5% by mass to 30% by mass with respect to the total mass of the non-aqueous electrolyte, and comprising three substituents (X1, X2, X3) of the compound ) Have one or two substituents (first substituents) having a phenyl group in the structure thereof, and among the three substituents (X1, X2, X3) of the compound, The remaining substituent (second substituent) excluding the first substituent is an organic group having 1 to 3 carbon atoms, and provides a nonaqueous electrolytic solution.

  (III) Still another embodiment of the present invention is a nonaqueous electrolytic solution having a positive electrode, a negative electrode, a separator partitioning the positive electrode and the negative electrode, and a nonaqueous electrolytic solution containing a nonaqueous solvent and an electrolyte. In the secondary battery, the non-aqueous electrolyte contains 5% by mass or more of a flame retardant composed of a compound represented by the following chemical formula (1) or chemical formula (2) with respect to the total mass of the non-aqueous electrolyte. 30% by mass or less, and one or two of the three substituents (X1, X2, X3) of the compound (first substituent) is overcharged by the secondary battery. The remaining substituents (excluding the first substituent) out of the three substituents (X1, X2, X3) of the compound at the electric potential to be involved in the polymerization reaction of the compound The second substituent) is a substituent that contributes to improving the compatibility between the non-aqueous solvent and the flame retardant. A non-aqueous electrolyte secondary battery is provided.

  (IV) Still another embodiment of the present invention is a nonaqueous electrolytic solution having a positive electrode, a negative electrode, a separator that partitions the positive electrode and the negative electrode, and a nonaqueous electrolytic solution containing a nonaqueous solvent and an electrolyte. In the secondary battery, the non-aqueous electrolyte contains 5% by mass or more of a flame retardant composed of a compound represented by the following chemical formula (1) or chemical formula (2) with respect to the total mass of the non-aqueous electrolyte. It is contained in the range of 30% by mass or less, and one or two of the three substituents (X1, X2, X3) of the compound (first substituent) is a phenyl group in the structure. Of the three substituents (X1, X2, X3) of the compound, the remaining substituents (second substituents) excluding the first substituent have 1 to 3 carbon atoms. Provided is a non-aqueous electrolyte secondary battery having the following organic group.

  (V) Still another aspect of the present invention provides a secondary battery system using the non-aqueous electrolyte secondary battery according to the above invention.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte which provides a flame retardance and overcharge prevention property can be provided, without sacrificing the battery characteristic of a nonaqueous electrolyte secondary battery. In addition, by using the non-aqueous electrolyte, it is possible to provide a non-aqueous electrolyte secondary battery that is safer than the prior art while ensuring the same or better battery characteristics than the conventional one, and a secondary battery system using the same. it can. Note that more specific problems, configurations, and effects related to the present invention will be described in detail in the following description of embodiments.

It is a cross-sectional schematic diagram which shows an example of the nonaqueous electrolyte secondary battery which concerns on this invention. It is a cross-sectional schematic diagram which shows an example of the secondary battery system which concerns on this invention.

  The inventors of the present invention diligently studied the flame retardant and overcharge inhibitor to be added with the aim of ensuring higher safety in the non-aqueous electrolyte secondary battery. As a result, a predetermined amount of a flame retardant composed of a compound having a specific substituent (phosphate ester or phosphite ester) is added to the non-aqueous electrolyte without sacrificing the battery characteristics of the secondary battery. The present inventors have found that flame retardancy and overcharge prevention can be imparted simultaneously. The present invention has been completed based on this finding.

The present invention can add the following improvements and changes to the non-aqueous electrolyte and non-aqueous electrolyte secondary battery described above.
(I) The difference between the Hansen solubility parameter of the non-aqueous solvent and the Hansen solubility parameter of the flame retardant is 4 or less. When the difference is 4 or less, the flame retardant can be dissolved in the electrolytic solution at a high concentration (for example, 10% by mass or more with respect to the total mass of the nonaqueous electrolytic solution). The difference is more preferably 3 or less, and further preferably 2 or less.
The Hansen solubility parameter (HSP) is one of the solubility indices indicating how much a certain substance dissolves in another certain substance. In the present invention, “(HSP) ² = (dD) ² + (dP ) ² + (dH) ² ”. In this relational expression, “dD” represents “energy derived from intermolecular dispersion force”, “dP” represents “energy derived from intermolecular polar force”, and “dH” represents “intermolecular hydrogen”. “Energy derived from binding force”, which is a property value of each species (see Charles M. Hansen, “Hansen Solubility Parameters: A User's Handbook, Second Edition”, CRC Press, Boca Raton FL, (2007)).
(Ii) The second substituent of the compound has in its structure at least one bond structure among a thioether group, a thiocarbonyl group, a carbonyl group, an ether group, a carboxyl group, and an amide group. .
(Iii) The non-aqueous electrolyte contains a surfactant.
(Iv) The flame retardant is filled in a microcapsule, and the microcapsule is held in the non-aqueous electrolyte.

Furthermore, the present invention can add the following improvements and changes to the non-aqueous electrolyte secondary battery described above.
(V) The microcapsules are held on the surface of the positive electrode and / or on the surface of the separator facing the positive electrode.
(Vi) A second flame retardant having a structure different from that of the flame retardant contained in the non-aqueous electrolyte is further added to the positive electrode, and the second flame retardant is added to the non-aqueous electrolyte. It is a poorly soluble compound.

  Hereinafter, embodiments according to the present invention will be described more specifically. However, the present invention is not limited to the embodiment taken up here, and can be appropriately combined and improved without departing from the technical idea of the present invention.

[Non-aqueous electrolyte]
As described above, the nonaqueous electrolytic solution according to the present invention contains a nonaqueous solvent and an electrolyte, and contains a flame retardant composed of a compound represented by the following chemical formula (1) or chemical formula (2).

  Chemical formula (1) is phosphorous acid triester, and chemical formula (2) is phosphoric acid triester. It is known that phosphorus has a function of preventing the combustion reaction of the electrolyte. The flame retardant added in the present invention has a function of preventing overcharge in addition to a function of preventing a combustion reaction.

  One or two of the three substituents (X1, X2, X3) of the compound constituting the flame retardant (first substituent) is a potential at which the nonaqueous electrolyte secondary battery is overcharged. And a substituent involved in the polymerization reaction of the compound. In other words, when a potential higher than the end-of-charge potential of the non-aqueous electrolyte secondary battery is applied to the flame retardant, the compounds are polymerized via the first substituent. On the other hand, of the three substituents (X1, X2, X3) of the compound, the remaining substituents (second substituents) excluding the first substituent are the phases of the non-aqueous solvent and the flame retardant. It is a substituent that contributes to improvement in solubility.

The first substituent preferably has a phenyl group in its structure. Examples thereof include a phenylcyclohexyl group (C ₆ H ₄ C ₆ H ₁₁ ), a biphenyl group (C ₆ H ₄ C ₆ H ₅ ), and halides thereof. When all of the three substituents (X1, X2, X3) of the above compound become the first substituent, the polarity of the entire compound is lowered and the compatibility with the nonaqueous solvent is lowered. On the other hand, when the molecular size of the compound becomes too large, the viscosity of the non-aqueous electrolyte is remarkably increased and the conductivity of the non-aqueous electrolyte is lowered. For these reasons, the first substituent is preferably one or two of the three substituents.

The second substituent is preferably an organic group having 1 to 3 carbon atoms. When the CH bonding group having a small number of carbon atoms forms an ester bond, the entire substituent becomes polar. Examples thereof include a methyl group (CH ₃ ), an ethyl group (CH ₂ CH ₃ ), and halides thereof. Furthermore, the second substituent has a thioether group (CS), a thiocarbonyl group (C = S), a carbonyl group (C = O), an ether group (CO), a carboxyl group (C = OO), And at least one bond structure of amide groups (NC = O). Thereby, the polarity of a 2nd substituent becomes still higher, As a result, the compatibility of a flame retardant and a nonaqueous solvent increases more. In addition, since the molecular size of the flame retardant is reduced, the flame retardant has an advantage of suppressing an increase in the viscosity of the non-aqueous electrolyte and not hindering the movement of lithium ions.

  When the non-aqueous electrolyte secondary battery is overcharged, the battery generates heat due to oxidation of the non-aqueous electrolyte on the positive electrode side and destruction of the crystal structure of the positive electrode material. Overcharging not only causes the non-aqueous electrolyte secondary battery to deteriorate rapidly but also may cause battery rupture and ignition. Therefore, prevention of overcharging is a very important issue from the viewpoint of ensuring the safety of the nonaqueous electrolyte secondary battery.

  As described above, the non-aqueous electrolyte according to the present invention acts so that the first substituent causes a polymerization reaction of the compound at a potential at which the non-aqueous electrolyte secondary battery is overcharged. This means that the current flowing into the secondary battery is consumed for the polymerization reaction of the compound. In other words, if the polymerization reaction is promoted at an overcharge potential and the current consumed by the polymerization reaction (oxidation current) is increased, the current (overcharge current) that overcharges the secondary battery is reduced. be able to. As a result, the progress of overcharge of the secondary battery can be prevented.

  Further, the polymerization reaction product forms a high resistance film on the positive electrode surface of the secondary battery. Thereby, since the electric current itself flowing into the secondary battery is suppressed, the progress of overcharge of the secondary battery can be prevented. It is more effective to prevent overcharge due to the polymerization reaction of the compound on the positive electrode side of the nonaqueous electrolyte secondary battery. The starting potential of the polymerization reaction is desirably higher in the range of 0.1 V or more and 1 V or less with respect to the upper limit potential (charge upper limit potential) of the positive electrode during normal charging. If the starting potential of the polymerization reaction is “less than charging upper limit potential +0.1 V”, the polymerization reaction of the flame retardant is likely to occur at the final stage of charging, which causes a reduction in the capacity of the secondary battery. On the other hand, when the polymerization reaction start potential is “over charge upper limit potential + 1 V”, it is difficult to suppress overcharge.

  The progress rate of the polymerization reaction of the compound is limited by the supply rate of the flame retardant to the positive electrode (that is, the concentration of the flame retardant added). The addition concentration of the flame retardant is preferably 5% by mass or more and 30% by mass or less with respect to the total amount of the non-aqueous electrolyte. When the addition concentration of the flame retardant is less than 5% by mass, the polymerization reaction cannot be promoted, and the effect of preventing overcharge of the secondary battery becomes insufficient. Moreover, when the addition concentration of the flame retardant is larger than 30% by mass, the electrical conductivity of the non-aqueous electrolyte is lowered, and the capacity as a secondary battery is lowered. In the present invention, the discharge current when evaluating the initial capacity of the secondary battery is 0.5 C (corresponding to 5 A in the case of a secondary battery with a rated capacity of 10 Ah) and 3 C (with a rated capacity of 10 Ah). In the case of a secondary battery, equivalent to 30 A).

Here, as a flame retardant to be added, the chemical formula (1) having a first substituent of a phenylcyclohexyl group (C ₆ H ₄ C ₆ H ₁₁ ) and a second substituent of a methyl group (CH ₃ ). Taking a compound (mono (cyclohexylbenzene) dimethyl phosphite) as an example, the mechanism of the polymerization reaction will be described. The polymerization reaction occurs when the first substituents in different molecules react with each other. The reaction formula is as shown in chemical formula (3) below.

In the above reaction, H of the benzene ring in the first substituent C ₆ H ₄ C ₆ H _{11 of} each molecule is oxidized to generate H ₂ . The benzene rings from which H is eliminated are bonded to each other, and two molecules undergo condensation polymerization to produce a polymerization reaction product.

In order for the polymerization reaction of the compound to proceed efficiently, it is desirable that the non-aqueous solvent of the non-aqueous electrolyte and the compound to be added have high compatibility. From this viewpoint, it is preferable that the difference between the Hansen solubility parameter (HSP _sol ) of the non-aqueous solvent and the Hansen solubility parameter (HSP _add ) of the flame retardant to be added is 4 or less. As described above, the Hansen solubility parameter (HSP) is defined as represented by the relational expression “(HSP) ² = (dD) ² + (dP) ² + (dH) ² ”.

When the difference between the HSP _{sol of the} non-aqueous solvent and the HSP _{add of} the flame retardant to be added is 4 or less, the compatibility between the non-aqueous solvent and the flame retardant increases, and the flame retardant concentration can be set higher. (For example, 10% by mass or more based on the total amount of the non-aqueous electrolyte). As a result, the effect of preventing the combustion reaction of the flame retardant and the effect of preventing overcharge are sufficiently exhibited. The difference in HSP is more preferably 3 or less, and even more preferably 2 or less.

  In order to increase the compatibility between the non-aqueous solvent and the flame retardant (to reduce the difference in HSP), a surfactant may be added to the non-aqueous electrolyte. As the surfactant to be added, it is preferable to select a surfactant that is not easily decomposed on the positive electrode or the negative electrode of the secondary battery. Surfactants include, for example, polyethylene glycol having a molecular weight of 50 to 300, those obtained by replacing the terminal OH group of the polyethylene glycol with a methyl group, polyoxyethylene glycerin fatty acid ester, polyethylene glycol fatty acid ester, solvitamin fatty acid ester, polyoxyethylene Examples include fatty acid amide, polyoxyethylene alkylamine, and perfluoroalkylamine oxide. Furthermore, alkyldimethylcarboxybetaine, alkylaminocarboxylate, and perfluoroalkylbetaine can be preferably used.

  As another form of addition of the flame retardant to the non-aqueous solvent, a part or all of the flame retardant can be filled in the microcapsule, and the microcapsule can be held in the non-aqueous electrolyte. By utilizing the microcapsules, a desired amount of flame retardant can be added while suppressing a decrease in the conductivity of the non-aqueous electrolyte during normal times. The material of the microcapsule is not particularly limited as long as it does not chemically react with the nonaqueous electrolytic solution. For example, a combination of gelatin and gum arabic, polylactic acid, melamine resin, urethane resin and the like can be suitably used.

  The non-aqueous solvent for the non-aqueous electrolyte is not particularly limited as long as it is not decomposed on the positive electrode or the negative electrode. For example, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane , Formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphoric acid triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone, tetrahydrofuran, 1,2-diethoxyethane, chloroethylene Carbonate and chloropropylene carbonate can be preferably used. When these non-aqueous solvents are used, the difference in HSP from the flame retardant of the present invention described above can be made 4 or less. Needless to say, other non-aqueous solvents can be used by adding a surfactant.

Next, an electrolyte (also referred to as a supporting salt) of the nonaqueous electrolytic solution will be described. The electrolyte used in the nonaqueous electrolyte solution, it is possible to use those conventional, for _{example, LiPF 6, LiBF 4, LiClO} 4, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiCF 3 SO ₃ , LiN (SO ₂ CF ₃ ) ₂ alone or a mixture thereof can be preferably used.

  When a solid polymer electrolyte (polymer electrolyte) is used, an ion conductive polymer such as ethylene oxide, acrylonitrile, polyvinylidene fluoride, methyl methacrylate, or hexafluoropropylene polyethylene oxide can be used as the electrolyte.

Furthermore, an ionic liquid can be used. For example, 1-ethyl-3-methylimidazolium-tetrafluoroborate (EMI-BF4), mixed complex of lithium salt, triglyme and tetraglyme (LiN (SO ₂ CF ₃ ) ₂ (LiTFSI)), N-methyl-N A cyclic quaternary ammonium cation such as propylpyrrolidinium and an imide anion such as bis (fluorosulfonyl) imide can be used for the electrolyte.

  About the density | concentration of these electrolytes, it is preferable to set it as the range of 0.8-2.0 mol / L with respect to the total volume of a nonaqueous solvent. The addition amount (% by mass) of the flame retardant is determined with respect to the entire electrolyte mass. Moreover, when utilizing a solid polymer electrolyte, it is preferable that the addition amount of the flame retardant of this invention is mass concentration with respect to the said solid polymer, and an addition ratio is the same as the case of a non-aqueous electrolyte. This is because the concentration of the flame retardant (that is, the rate at which the flame retardant forms a high-resistance film on the electrode surface) plays an important role with respect to the effects of the present invention.

  In the present invention, it is more preferable that the Hansen solubility parameter difference between the non-aqueous solvent and the flame retardant is small and the Hansen solubility parameter difference between the electrolyte and the flame retardant is small. The electrolyte is usually dissolved in a non-aqueous solvent. However, when the difference in Hansen solubility parameter between the electrolyte and the flame retardant is reduced, the electrolyte is more soluble in the flame retardant as well as the non-aqueous solvent. This is particularly effective when the flame retardant is added to the non-aqueous electrolyte at a high concentration (for example, when added at 10% by mass or more with respect to the total mass of the non-aqueous electrolyte). A decrease in conductivity can be prevented.

[Nonaqueous electrolyte secondary battery]
The configuration of the nonaqueous electrolyte secondary battery will be described. A non-aqueous electrolyte secondary battery is a general term for electrochemical devices that can store and use electrical energy by occlusion / release of ions to and from electrodes in the non-aqueous electrolyte. In this example, a lithium ion secondary battery will be described as a representative example.

  FIG. 1 is a schematic cross-sectional view showing an example of a non-aqueous electrolyte secondary battery according to the present invention. As shown in FIG. 1, the positive electrode 107 and the negative electrode 108 are wound in a state where the separator 109 is sandwiched so that they do not come into direct contact with each other to form an electrode group. The structure of the electrode group is not limited to winding in an arbitrary shape such as a cylindrical shape or a flat shape, and may be a laminate of strip-shaped electrodes.

  A positive electrode lead 110 is attached to the positive electrode 107, and a negative electrode lead 111 is attached to the negative electrode 108. The leads 110 and 111 can take any shape such as a wire shape, a foil shape, and a plate shape. A structure and material that can reduce electrical loss and ensure chemical stability are selected.

  The electrode group is accommodated in the battery container 102, and the inserted electrode group is connected to the battery container 102 by an insulating seal 112 installed on the top of the battery container 102 and an insulating seal (not shown) installed on the bottom. There is no direct contact. Furthermore, the pores of the separator 109 are impregnated with the non-aqueous electrolyte according to the present invention. After the electrode group is housed in the battery container 102 and sealed, the non-aqueous electrolyte according to the present invention is dropped from the liquid inlet 106, and after filling a predetermined amount, the liquid inlet 106 is sealed. The non-aqueous electrolyte injection method / procedure may be another method / procedure.

  As the shape of the battery container 102, a shape (for example, a cylindrical shape, a flat oblong column shape, a rectangular column, etc.) matching the shape of the electrode group is usually selected. As the insulating seal 112, any material that does not react with the non-aqueous electrolyte and has excellent airtightness (for example, a thermosetting resin, a glass hermetic seal, etc.) can be preferably used.

  The material of the battery container 102 is selected from materials that are corrosion resistant to the non-aqueous electrolyte, such as aluminum, stainless steel, and nickel-plated steel. The lid 103 can be attached to the battery container 102 by other methods such as caulking and bonding in addition to welding. It is also possible to provide a function as a safety mechanism to the injection port 106 used for injecting the non-aqueous electrolyte. As a safety mechanism, for example, there is a pressure valve that is released when the pressure inside the battery container exceeds a predetermined level.

  Current interruption mechanism using positive temperature coefficient resistance element in the middle of the positive electrode lead 110 or the negative electrode lead 111, the connection part between the positive electrode lead 110 and the positive electrode external terminal 104, or the connection part between the negative electrode lead 111 and the negative electrode external terminal 105 (Not shown) is preferably provided. When the current interruption mechanism is provided, when the temperature inside the battery becomes high, charging / discharging of the lithium ion secondary battery 101 can be stopped and the battery can be protected.

  The positive electrode 107 constituting the lithium ion secondary battery is coated and dried with a positive electrode mixture slurry containing a positive electrode active material on one side or both sides of a positive electrode current collector, and then compression-molded using a roll press machine or the like, It is produced by cutting into a predetermined size. As the positive electrode current collector, an aluminum foil having a thickness of 10 to 100 μm, an aluminum perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, a foamed aluminum plate, or the like is used. In addition to aluminum, stainless steel, titanium, etc. can be used as the material.

  Similarly, the negative electrode 108 constituting the lithium ion secondary battery is formed by applying and drying a negative electrode mixture slurry containing a negative electrode active material on one side or both sides of a negative electrode current collector, and then compression molding using a roll press or the like. Then, it is produced by cutting into a predetermined size. For the current collector of the negative electrode, copper foil with a thickness of 10 to 100 μm, copper perforated foil with a thickness of 10 to 100 μm and a hole diameter of 0.1 to 10 mm, expanded metal, foamed copper plate, etc. are used. In addition, stainless steel, titanium, nickel, and the like are also applicable.

  There is no particular limitation on the method for applying the positive electrode mixture slurry and the negative electrode mixture slurry, and conventional methods (for example, a doctor blade method, a dipping method, a spray method, etc.) can be used. Moreover, it is also possible to laminate | stack a several mixture layer on a collector by performing from application | coating to drying in multiple times.

  The positive electrode active material used for the positive electrode 107 is not particularly limited as long as it is a lithium compound that can occlude and release lithium ions. Examples thereof include lithium transition metal composite oxides such as lithium manganese oxide, lithium cobalt oxide, and lithium nickel oxide. Any one of these or a mixture of two or more of them can be used. A positive electrode mixture slurry is produced by mixing a positive electrode active material with a binder, a thickener, a conductive material, a solvent, and the like as necessary.

  The particle size of the positive electrode active material is defined to be equal to or less than the thickness of the mixture layer. When there are coarse particles having a particle size equal to or larger than the thickness of the mixture layer in the positive electrode active material powder, the coarse particles are previously removed by sieving classification, wind classification or the like, and particles having a thickness of the mixture layer thickness or less are prepared.

  The mixing ratio of the positive electrode active material and the binder is preferably in the range of 85:15 to 95: 5 by mass ratio. When the mass ratio of the positive electrode active material is less than 85/100, the energy density of the secondary battery decreases. On the other hand, when the mass ratio of the positive electrode active material exceeds 95/100, the maximum current value that can be charged and discharged decreases.

As the conductive agent for the positive electrode, conductive fibers (for example, vapor-grown carbon, carbon nanotubes, fibers produced by carbonizing pitch (by-products such as petroleum, coal, coal tar, etc.) at high temperature as raw materials, acrylic fibers A manufactured carbon fiber or the like is preferably used. Further, the conductive agent may be a material having a lower electrical resistance than the positive electrode active material, and a material that does not oxidize and dissolve at the charge / discharge potential (usually 2.5 to 4.2 V) of the positive electrode. Examples include corrosion resistant metals (such as titanium and gold), carbides (such as SiC and WC), and nitrides (such as Si ₃ N ₄ and BN). A carbon material having a high specific surface area (for example, carbon black or activated carbon) can also be used.

  The negative electrode active material used for the negative electrode 108 is not particularly limited as long as it is a material that can occlude and release lithium ions. For example, aluminum, silicon, tin, carbon materials (graphite, graphitizable carbon, non-graphitizable carbon natural graphite, artificial graphite, mesophase carbon, expanded graphite, carbon fiber, vapor grown carbon fiber, pitch-based carbonaceous material Materials, needle coke, petroleum coke, polyacrylonitrile-based carbon fiber, carbon black, amorphous carbon, etc.) can be used. Amorphous carbon is produced, for example, by thermally decomposing a 5-membered or 6-membered cyclic hydrocarbon or a cyclic oxygen-containing organic compound. Any one of these or a mixture of two or more of them can be used. Among these, since amorphous carbon is a material with a small volume change rate during insertion and extraction of lithium ions, it has high charge / discharge cycle characteristics, so that it contains amorphous carbon as a negative electrode active material. preferable. Further, in addition to the carbon material described above, a conductive polymer material (such as polyacene, polyparaphenylene, polyaniline, or polyacetylene) may be added. A negative electrode mixture slurry is prepared by mixing a negative electrode active material with a binder, a thickener, a conductive agent, a solvent, and the like as necessary.

  The mixing ratio of the negative electrode active material and the binder is preferably in the range of 90:10 to 99: 1 by mass ratio. When the mass ratio of the negative electrode active material is less than 90/100, the energy density of the secondary battery decreases. On the other hand, when the mass ratio of the negative electrode active material exceeds 99/100, the amount of the binder is too small and the capacity reduction due to the charge / discharge cycle becomes remarkable. As the negative electrode conductive agent, the same material as the positive electrode conductive agent can be used.

  There are no particular limitations on the binder, thickener, and solvent used in the positive electrode mixture slurry and the negative electrode mixture slurry, and the same ones as before can be used.

  The separator 109 is preferably a porous body (for example, a pore diameter of 0.01 to 10 μm and a porosity of 20 to 90%) because it is necessary to permeate lithium ions during charging and discharging of the secondary battery. As a material for the separator 109, a polyolefin polymer sheet (for example, polyethylene or polypropylene) or a multilayer structure sheet in which a polyolefin polymer sheet and a fluorine polymer sheet (for example, tetrafluoropolyethylene) are welded is used. It can be used suitably. Further, a mixture of ceramics and a binder may be formed in a thin layer on the surface of the separator 109.

  Further, when a solid polymer electrolyte (polymer electrolyte) is used as the electrolyte of the non-aqueous electrolyte described above, the separator 109 can be omitted.

  As described above, it is more effective to prevent overcharge due to the polymerization reaction of the compound on the positive electrode side of the non-aqueous electrolyte secondary battery. In addition, the nonaqueous electrolyte secondary battery according to the present invention can be filled in a microcapsule with part or all of the flame retardant and held at a desired location in the secondary battery. From these viewpoints, it is very effective to hold the microcapsules filled with the flame retardant on the surface of the non-aqueous electrolyte secondary battery and / or the surface of the separator facing the positive electrode. There is no particular limitation on the method of holding the microcapsules at those locations, and examples thereof include a method in which the microcapsules are mixed with a binder and applied to those locations. Even in this case, the total amount of the flame retardant in the secondary battery is adjusted to 5 to 30% by mass with respect to the non-aqueous electrolyte.

  Further, the non-aqueous electrolyte secondary battery according to the present invention includes another flame retardant (second flame retardant) in addition to the non-aqueous electrolyte (non-aqueous electrolyte containing a flame retardant) according to the present invention. It may be added to the positive electrode. At this time, the second flame retardant added to the positive electrode has a structure different from that of the flame retardant added to the non-aqueous electrolyte, and is preferably a compound that is hardly soluble in the non-aqueous electrolyte. It is more preferable that If the second flame retardant added to the positive electrode has the same structure as the flame retardant added to the non-aqueous electrolyte, the second flame retardant dissolves in the non-aqueous electrolyte and the amount of the flame retardant in the non-aqueous electrolyte Is excessive, and the electrical conductivity of the non-aqueous electrolyte is decreased.

  As the second flame retardant, conventional compounds can be used as long as they are hardly soluble compounds or insoluble compounds with respect to the non-aqueous electrolyte, and can be added within a range that does not lower the conductivity of the non-aqueous electrolyte. Although there is no special limitation in the addition method of the 2nd flame retardant to a positive electrode, a 2nd flame retardant can be coated on the positive electrode surface, for example using a spray coating method. In addition to the non-aqueous electrolyte according to the present invention described above, the safety of the non-aqueous electrolyte secondary battery can be further improved by adding the second flame retardant to the positive electrode.

[Secondary battery system]
The configuration of the secondary battery system will be described. The secondary battery system according to the present invention is defined as a system having at least two or more nonaqueous electrolyte secondary batteries connected in series or in parallel and having a charge / discharge control mechanism. FIG. 2 is a schematic cross-sectional view showing an example of the secondary battery system according to the present invention. As shown in FIG. 2, in this configuration, two lithium ion secondary batteries 101a and 101b are connected in series. The negative external terminal 105 of the lithium ion secondary battery 101a arranged on the right side of the paper in FIG. 2 is connected to the negative input terminal of the charge / discharge control mechanism 216 by the power cable 213. The positive external terminal 104 of the lithium ion battery 101a is connected to the negative external terminal 105 of the lithium ion secondary battery 101b disposed on the left side of the drawing via the power cable 214. The positive external terminal 104 of the lithium ion secondary battery 101b is connected to the positive input terminal of the charge / discharge control mechanism 216 by the power cable 215. With such a wiring configuration, the two lithium ion secondary batteries 101a and 101b can be charged or discharged while being controlled by the charge / discharge control mechanism 216. In FIG. 1 and FIG. 2, the same components are denoted by the same reference numerals.

  The charge / discharge control mechanism 216 exchanges power with the external device 219 via the power cables 217 and 218. The external device 219 includes various electric devices such as an external power source and a regenerative motor for supplying power to the charge / discharge control mechanism 216 in addition to an external load. Moreover, an inverter and a converter can be provided according to the kind of alternating current and direct current which an external apparatus respond | corresponds.

  The power generation device 222 is connected to the charge / discharge control mechanism 216 via the power cables 220 and 221. When the power generation device 222 is generating power, the charge / discharge control mechanism 216 shifts to the charge mode, supplies power to the external device 219, and charges surplus power to the lithium ion secondary batteries 101a and 101b. When the power generation amount of the power generator 222 is less than the required power of the external device 219, the charge / discharge control mechanism 216 shifts to the discharge mode so that power is supplied from the lithium ion secondary batteries 101a and 101b. The charge / discharge control mechanism 216 preferably stores a program so that such mode transition is automatically performed.

  As the power generation device 222, a power generation device that generates renewable energy (for example, a wind power generation device, a geothermal power generation device, or a solar cell) or a normal power generation device (for example, a fuel cell, a gas turbine generator, or the like) can be used. .

  The secondary battery system according to the present invention includes, for example, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric construction machine, a transport device, a construction machine, a care device, a light vehicle, an electric tool, a robot, and power of a remote island. It can be used as a power source for storage systems and space stations.

  The present invention is not limited to lithium ion batteries, and can be applied to electrochemical devices that use a non-aqueous electrolyte and store and use electrical energy by occluding and releasing ions to and from electrodes. Since this invention is excellent in safety | security, it is suitable for a large sized mobile body or a stationary battery system especially.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The present invention is not limited to these examples.

[Example 1]
(Preparation of B1-B19 lithium ion secondary batteries)
(1) Production of positive electrode First, a positive electrode active material (85 mass%, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), binder (8 mass%, polyvinylidene fluoride (PVDF), manufactured by Kureha Corporation) Then, a conductive agent (7% by mass, carbon black) and a solvent (1-methyl-2-pyrrolidone) were prepared to prepare a positive electrode mixture slurry.

  Next, this positive electrode mixture slurry was applied to one side of a positive electrode current collector (aluminum foil) having a thickness of 20 μm by using a doctor blade method and dried to form a positive electrode mixture layer. Then, it compression-molded with the roll press machine, cut | disconnected to the predetermined magnitude | size, and produced the positive electrode for lithium ion secondary batteries.

(2) Production of Negative Electrode electrode active material (98 wt%, graphite (lattice spacing d ₀₀₂ = from 0.35 to 0.36 nm, which was determined by XRD measurements (002))) and the binder (2% by weight, styrene-butadiene rubber (1 mass %) + Carboxylmethylcellulose (1% by mass) was added to water to prepare a negative electrode mixture slurry.

  Next, this negative electrode mixture slurry was applied to one side of a negative electrode current collector (copper foil) having a thickness of 20 μm using a doctor blade method and dried to form a negative electrode mixture layer. Then, it was compression-molded with a roll press and cut into a predetermined size to produce a negative electrode for a lithium ion secondary battery.

(3) Production of non-aqueous electrolyte As a non-aqueous solvent of the non-aqueous electrolyte, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio = 1: 1) was prepared. Next, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte was dissolved in the mixed solvent so as to be 1 mol / L. Finally, a flame retardant shown in Table 1 described later was added to and mixed with the mixed solution at a predetermined concentration to prepare a non-aqueous electrolyte. The addition amount of the flame retardant was a ratio (mass%) with respect to the mass of the entire electrolytic solution. The concentration of the electrolyte is a molar molar concentration with respect to the whole non-aqueous solvent (hereinafter the same).

  The difference in Hansen solubility parameter (HSP) between the non-aqueous solvent and the flame retardant is also shown in Table 1. For calculation of Hansen solubility parameters, commercially available calculation software was used (see Hansen Solubility Parameters: A User's Handbook).

When calculating the Hansen solubility parameter (HSP _add ) of the flame retardant, there is also an approximate HSP _add calculated for convenience by changing the oxygen position without changing the molecular weight. For example, “P (C ₆ H ₄ C ₆ H ₁₁ ) (OCH ₃ ) ₂ ” shown in Table 1 to be described later becomes “O = P (OCH ₃ ) ₂ (C ₆ H ₄ C ₆ H ₁₁ )”. HSP _add was calculated.

This approximation method was judged appropriate for the following reasons. The solubility parameter of trimethyl phosphite ((CH ₃ O) ₃ P) can be calculated by the method of “E. Stefanis and C. Panayiotou” (see the aforementioned Hansen Solubility Parameters: A User's Handbook). The solubility parameters of “(CH ₃ O) ₃ P” and “(CH ₃ O) ₂ (CH ₃ ) P = O” are “17.4” and “16.7”, respectively, and the difference between them is sufficiently small (almost consistent) Can be said). Therefore, for the flame retardants (B11 to B17, B52, B53, B55) for which the Hansen solubility parameter could not be directly calculated, HSP _add calculated by changing only the oxygen position was used.

(4) Production of Lithium Ion Secondary Battery The lithium ion secondary battery (rated capacity: 10 Ah) shown in FIG. Stainless steel was used for the battery container 102 and the lid 103, a porous polyethylene film having a thickness of 30 μm was used for the separator 109, and a glass hermetic seal was used for the insulating seal 112. In addition, as shown in FIG. 1, the separator 109 is also disposed between the positive electrode 107 and the battery container 102 and between the negative electrode 108 and the battery container 102, and the positive electrode 107 and the negative electrode 108 are short-circuited through the battery container 102. Not configured.

(Test evaluation)
(A) Charge / discharge test (initial capacity evaluation)
(A-1) When the discharge current is 0.5 C The following charge / discharge test was performed on the lithium ion secondary battery prepared above, and the initial capacity was evaluated. First, the fabricated battery was charged at a constant current corresponding to a 2-hour rate until the battery voltage reached 4.2 V from the open circuit state. After the battery voltage reached 4.2 V, 4.2 V was maintained until the current value was equivalent to 100 hours. Thereafter, charging was stopped and a 30-minute rest period was provided. Next, constant current discharge corresponding to a 2-hour rate was started, and the battery was discharged until the battery voltage reached 3.0 V. Thereafter, the discharge was stopped and a 30 minute rest period was provided. The process so far is referred to as initial aging. The discharge capacity obtained after repeating this initial aging three times was used as the initial capacity of the secondary battery. Five secondary batteries under the same conditions were manufactured, and the above test was performed in the same manner to calculate the average value of the initial capacity. With respect to the rated capacity, an initial capacity of 90% or more was evaluated as “pass”, and an initial capacity of less than 90% was evaluated as “fail”. The results are shown in Table 2 described later.

(A-2) When discharge current is 3 C After performing the above test, discharging was performed under the condition that only the discharge current was increased to 30 A without changing the charging conditions, and the initial capacity was calculated. This test is for confirming battery characteristics (high rate characteristics) when discharged at a high rate (large current). The results are also shown in Table 2.

  In addition, the time rate said here is defined as the electric current value which discharges the design discharge capacity of a battery in predetermined time (hereinafter, the same). For example, the 5-hour rate mentioned above is a current value for discharging the design capacity of the battery in 5 hours. More specifically, if the capacity of the battery is C (unit: Ah), the current value at the 5-hour rate is C / 5 (unit: A).

(B) Overcharge test (safety evaluation)
An overcharge test was performed on the secondary battery whose initial capacity was evaluated. The procedure of the overcharge test is shown below. The batteries B1 to B19 were recharged according to the initial aging charge conditions to a charge depth of 100%. From that state, the upper limit voltage 4.2 V was changed to 10 V, and overcharging was continued until 10 V was reached. During this time, the secondary battery that did not rupture or ignite was evaluated as “pass”, and the secondary battery that ruptured or ignited was evaluated as “fail”. The results are also shown in Table 2.

  As shown in Table 2, the non-aqueous electrolyte secondary batteries (B1 to B19) according to the present invention cleared all required levels in both the initial capacity (0.5 C discharge) and overcharge test items. You can see that In addition, the initial capacity (3 C discharge) achieved about 80% to about 90% of the rated capacity, and the non-aqueous electrolyte secondary batteries (B1 to B19) according to the present invention have excellent high-rate characteristics. In particular, flame retardants having a low molecular weight (B1, B2) and flame retardants having a substituent having a large number of oxygen or sulfur atoms (B8, B14, B16) were excellent.

  During the overcharge test, there was a tendency for the battery voltage to rise from around 4.4 V. This was considered due to the fact that the flame retardant (compound) added to the non-aqueous electrolyte started to undergo a polymerization reaction. After that, the voltage suddenly increased from 4.8 V and reached 10 V, and then the current became almost zero, making it impossible to charge. This was considered due to the fact that the polymerization product of the compound formed a high-resistance film on the positive electrode. From these facts, it was confirmed that the nonaqueous electrolytic solution according to the present invention has a function of preventing overcharge.

(Production and test evaluation of B51 lithium ion secondary battery)
A lithium ion secondary battery of B51 was prepared in the same manner as described above except that the non-aqueous electrolyte was prepared without adding a flame retardant, and a charge / discharge test and an overcharge test were performed. The test and evaluation results are shown in Table 4 described later.

(Production and test evaluation of B52 lithium-ion secondary battery)
Except that the amount of the flame retardant used in B1 to B4 (P (OC ₆ H ₄ C ₆ H ₁₁ ) (OCH ₃ ) ₂ ) was 2% by mass and the non-aqueous electrolyte was prepared, A B52 lithium ion secondary battery was prepared and subjected to a charge / discharge test and an overcharge test. The added flame retardant is also shown in Table 3, which will be described later, and the test / evaluation results are also shown in Table 4.

(Production and test evaluation of B53 lithium-ion secondary battery)
Except that the amount of the flame retardant used in B1 to B4 (P (OC ₆ H ₄ C ₆ H ₁₁ ) (OCH ₃ ) ₂ ) was 40% by mass and the non-aqueous electrolyte was prepared, A lithium ion secondary battery of B53 was prepared, and a charge / discharge test and an overcharge test were performed. The added flame retardant is also shown in Table 3, and the test and evaluation results are also shown in Table 4.

(Production and test evaluation of B54 lithium ion secondary battery)
A lithium ion secondary battery of B54 was prepared and charged in the same manner as described above except that 1% by mass of P (OC ₆ H ₅ C ₆ H ₁₁ ) ₃ was added as a flame retardant and a non-aqueous electrolyte was prepared. A discharge test and an overcharge test were performed. The added flame retardant is also shown in Table 3, and the test and evaluation results are also shown in Table 4.

(Production and test evaluation of B55 lithium-ion secondary battery)
A non-aqueous electrolyte was prepared by adding 5% by mass of P (OC ₆ H ₅ C ₆ H ₁₁ ) ₃ as a flame retardant. However, about 1/5 of the added flame retardant dissolved in the non-aqueous electrolyte, but most of the flame retardant remained undissolved. Therefore, the undissolved flame retardant was filtered off, and the filtrate was used as a non-aqueous electrolyte. Otherwise, a B55 lithium ion secondary battery was prepared in the same manner as described above, and a charge / discharge test and an overcharge test were performed. The added flame retardant is also shown in Table 3, and the test and evaluation results are also shown in Table 4.

  As can be seen from Tables 3 and 4, the safety evaluation (overcharge test) failed for B51 to which no flame retardant was added and for B52 in which the added concentration of the flame retardant was less than that of the present invention. On the other hand, in the case of B53 where the concentration of flame retardant added is larger than that of the present invention, the initial capacity is remarkably reduced.

  In B54, where the flame retardant deviates from the provisions of the present invention, the viscosity of the electrolyte was increased due to the large molecular size of the flame retardant, resulting in a decrease in lithium ion conductivity and a significant decrease in initial capacity. In B55, since the difference in HSP between the flame retardant and the non-aqueous solvent is 4.4 and larger than the provisions of the present invention, it is difficult to dissolve 5% by mass of the flame retardant in the non-aqueous electrolyte as described above. I found out that B55 showed the same battery characteristics as B54 as a result of using a non-aqueous electrolyte from which undissolved flame retardant was removed.

[Example 2]
The positive electrode used for the battery B1 was coated with P (OC ₆ H ₄ C ₆ H ₁₁ ) ₃ as a second flame retardant by a spray coating method to produce a lithium ion secondary battery B56. The amount of the second flame retardant added to the positive electrode was 1% with respect to the mass of the positive electrode active material. Dimethyl carbonate was used as the solvent for the second flame retardant. After coating, the coating was dried under vacuum to form a coating layer of P (OC ₆ H ₄ C ₆ H ₁₁ ) ₃ on the positive electrode surface. Table 5 shows the flame retardant used in B56, and Table 6 shows the test and evaluation results.

When a flame was brought close to the non-aqueous electrolyte prepared above, the non-aqueous electrolyte did not burn. This was considered to be due to the effect of P (OC ₆ H ₄ C ₆ H ₁₁ ) (OCH ₃ ) ₂ added to the non-aqueous electrolyte. In addition, as shown in Table 6, the non-aqueous electrolyte secondary battery (B56) of this example cleared all required levels in both the initial capacity (0.5 C discharge) and overcharge test items. did. Furthermore, even in the initial capacity (3 C discharge), less than 90% of the rated capacity has been achieved, and the non-aqueous electrolyte secondary battery (B25) of this example has excellent high-rate characteristics. confirmed.

[Example 3]
The flame retardant used in B1 to B4 (P (OC ₆ H ₄ C ₆ H ₁₁ ) (OCH ₃ ) ₂ ) is filled into gelatin-gum arabic microcapsules, mixed with a binder, and facing the positive electrode It was applied to the surface. Other than that was carried out similarly to Example 1, and produced the lithium ion secondary battery. The total amount of the flame retardant in the secondary battery (in the microcapsule + in the non-aqueous electrolyte) was adjusted to 10 mass% with respect to the non-aqueous electrolyte.

  After the initial aging, a secondary battery charged to a charging depth of 100% was placed in the oven, and the temperature was raised and maintained at 200 ° C. The battery container cracked by heating, and the non-aqueous electrolyte leaked from that portion, but the non-aqueous electrolyte did not burn. Similarly, after the initial aging, a secondary battery charged to a charging depth of 100% was put into a flame. The battery container cracked and the non-aqueous electrolyte leaked from it, but it did not burn and the secondary battery did not rupture.

  In any case, it was considered that the effect of the flame retardant was sufficiently exhibited because the microcapsules were melted by heating and the flame retardant was sufficiently diffused into the secondary battery. From the experiment of this example, it was proved that the flame retardant of the present invention has a function of preventing the combustion reaction of the non-aqueous electrolyte.

[Example 4]
A secondary battery system shown in FIG. 2 was produced using the secondary battery B1 prepared in Example 1, and a charge / discharge test, a cycle test, and an overcharge test were performed.

  An experiment was conducted in which power was supplied to the external device 219 while charging and discharging the lithium ion secondary batteries 101a and 101b in accordance with the power generation status of the power generation device 222. After charging at a rate of 2 hours, a discharge at a rate of 1 hour was performed to determine the initial discharge capacity. As a result, it was confirmed that a capacity of 99.5 to 100% of the design capacity 10 Ah of each of the secondary batteries 101a and 101b was obtained.

  Thereafter, a charge / discharge cycle test was performed under conditions of an environmental temperature of 20 to 30 ° C. First, when charging is performed at a current of 2 hours (5 A) and the depth of charge reaches 50% (5 Ah charged), a pulse of 5 seconds in the charging direction and a pulse of 5 seconds in the discharging direction Was applied to the secondary batteries 101a and 101b, and a pulse test was performed to simulate the acceptance of power from the power generator 222 and the supply of power to the external device 319. The magnitude of the current pulse was 15A for both.

  Subsequently, the remaining capacity of 5 Ah is charged with a current of 2 hours (5 A) until the voltage of each secondary battery reaches 4.2 V, and charging is terminated by performing constant voltage charging for 1 hour at that voltage. It was. Thereafter, the voltage of each secondary battery was discharged to 3.0 V at a current of 1 hour rate (10 A).

  When the above series of charge / discharge cycle tests were repeated 500 times, a capacity of 98 to 99% was obtained with respect to the initial discharge capacity. It was confirmed that the performance of the secondary battery system of this example hardly deteriorates even when a current pulse for power reception and power supply is applied to the secondary battery.

  Next, the secondary battery system was assembled with only the secondary battery 101a charged in advance to a charging depth of 100% and the secondary battery 101b discharged. From this state, the secondary battery 101b was charged to a charging depth of 100%. In the charging process, the secondary battery 101a was in an overcharged state, but charging to the secondary battery 101a was stopped by the overcharge preventing action by the polymerization reaction of the flame retardant of the present invention. As a result, it was confirmed that the secondary battery 101a did not rupture or ignite due to overcharging and exhibited high safety.

  As described above, according to the present invention, it has been confirmed that a non-aqueous electrolyte that provides flame retardancy and overcharge prevention can be provided without sacrificing the battery characteristics of the non-aqueous electrolyte secondary battery. It was. In addition, by using the non-aqueous electrolyte, it is possible to provide a non-aqueous electrolyte secondary battery that is safer than the prior art and a secondary battery system using the same while ensuring the same or better battery characteristics. Was confirmed.

  Note that the above-described embodiments and examples have been specifically described in order to help understanding of the present invention, and the present invention is not limited to having all the configurations described. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, a part of the configuration of each embodiment can be deleted, replaced with another configuration, or added with another configuration.

101, 101a, 101b ... lithium ion secondary battery, 102 ... battery container, 103 ... lid,
104 ... Positive electrode external terminal, 105 ... Negative electrode external terminal, 106 ... Injection port,
107 ... positive electrode, 108 ... negative electrode, 109 ... separator, 110 ... positive electrode lead wire,
111 ... Negative lead wire, 112 ... Insulating seal,
213, 214, 215, 217, 218, 220, 221 ... power cable, 216 ... charge / discharge control mechanism,
219 ... External equipment, 222 ... Power generator.

Claims (11)

A non-aqueous electrolyte for a secondary battery containing a non-aqueous solvent and an electrolyte,
The non-aqueous electrolyte includes a flame retardant composed of a compound represented by the following chemical formula (1) or chemical formula (2) in a range of 5% by mass to 30% by mass with respect to the total mass of the non-aqueous electrolyte. Contains,
One or two of the three substituents (X1, X2, X3) of the compound (first substituent) has a phenyl group in its structure,
Of the three substituents (X1, X2, X3) of the compound, the remaining substituents (second substituents) excluding the first substituent are organic groups having 1 to 3 carbon atoms. A non-aqueous electrolyte characterized in that the structure has at least one bond structure among a thioether group, a thiocarbonyl group, a carbonyl group, an ether group, a carboxyl group, and an amide group.

The non-aqueous electrolyte according to claim 1,
A non-aqueous electrolyte, wherein a difference between the Hansen solubility parameter of the non-aqueous solvent and the Hansen solubility parameter of the flame retardant is 4 or less. In the nonaqueous electrolytic solution according to claim 1 or 2,
The non-aqueous electrolyte includes a surfactant. In the nonaqueous electrolytic solution according to any one of claims 1 to 3,
The flame retardant is filled in a microcapsule,
The non-aqueous electrolyte, wherein the microcapsule is held in the non-aqueous electrolyte. A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, a separator that partitions the positive electrode and the negative electrode, and a non-aqueous electrolyte solution containing a non-aqueous solvent and an electrolyte,
The non-aqueous electrolyte includes a flame retardant composed of a compound represented by the following chemical formula (1) or chemical formula (2) in a range of 5% by mass to 30% by mass with respect to the total mass of the non-aqueous electrolyte. Contains,
One or two of the three substituents (X1, X2, X3) of the compound (first substituent) has a phenyl group in its structure,
Of the three substituents (X1, X2, X3) of the compound, the remaining substituents (second substituents) excluding the first substituent are organic groups having 1 to 3 carbon atoms. A non-aqueous electrolyte secondary characterized in that the structure has at least one bond structure among a thioether group, a thiocarbonyl group, a carbonyl group, an ether group, a carboxyl group, and an amide group battery.

The nonaqueous electrolyte secondary battery according to claim 5,
A nonaqueous electrolyte secondary battery, wherein a difference between a Hansen solubility parameter of the nonaqueous solvent and a Hansen solubility parameter of the flame retardant is 4 or less. The non-aqueous electrolyte secondary battery according to claim 5 or 6,
The non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte contains a surfactant. The nonaqueous electrolyte secondary battery according to any one of claims 5 to 7,
The flame retardant is filled in a microcapsule,
The non-aqueous electrolyte secondary battery, wherein the microcapsule is held in the non-aqueous electrolyte. The nonaqueous electrolyte secondary battery according to claim 8,
The non-aqueous electrolyte secondary battery, wherein the microcapsule is held on a surface of the positive electrode and / or a surface of the separator facing the positive electrode. The nonaqueous electrolyte secondary battery according to any one of claims 5 to 9,
A second flame retardant having a structure different from that of the flame retardant contained in the non-aqueous electrolyte is further added to the positive electrode;
The non-aqueous electrolyte secondary battery, wherein the second flame retardant is a compound that is hardly soluble in the non-aqueous electrolyte.   A secondary battery system using the nonaqueous electrolyte secondary battery according to claim 5.

Images