JP2014116077A - Lithium ion secondary battery, secondary battery system including the same, nonaqueous electrolytic solution for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery having battery performance (for example, initial capacity) equivalent to the conventional ones, and having high safety capable of complying with such requirements as increased capacity/output, and a secondary battery system including the lithium ion secondary battery.SOLUTION: A lithium ion secondary battery according to the present invention includes a nonaqueous electrolytic solution containing an electrolyte comprising a lithium compound, a nonaqueous solvent, and a flame retarder. A lithium concentration in the nonaqueous electrolytic solution is 0.5 mol/L or more and 2.5 mol/L or less, the flame retarder includes trimethyl phosphite and dimethyl phosphite, and the total content of the trimethyl phosphite and the dimethyl phosphite is 1 mass% or more and 60 mass% or less relative to the amount of the nonaqueous electrolytic solution.

Description

  The present invention relates to a lithium ion secondary battery, a secondary battery system using the same, and a non-aqueous electrolyte for a lithium ion 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, a much higher output and capacity are required 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 a technique for adding a flame retardant to a non-aqueous electrolyte, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2011-165606) includes a positive electrode containing olivine type lithium iron phosphate and occlusion and release of lithium ions. A non-aqueous solvent, a lithium salt dissolved in the non-aqueous solvent, and an electrolyte containing 5 to 50% by mass of a phosphite represented by a specific formula A lithium ion secondary battery is disclosed. According to Patent Document 1, it is possible to provide a non-aqueous electrolyte for a lithium ion secondary battery and a lithium ion secondary battery in which both safety and cycle characteristics are improved.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2006-004746) discloses a secondary battery that mainly comprises a solute and a non-aqueous organic solvent that dissolves the solute, and contains 10 to 1000 ppm of a phosphorus compound having a specific structure. Non-aqueous electrolytes are disclosed. According to Patent Document 2, 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.

  Patent Document 3 (Japanese Patent Laid-Open No. 2007-299542) includes a negative electrode that can occlude and release lithium ions, a positive electrode, and a non-aqueous electrolyte, and the negative electrode includes Si atoms, Sn atoms, and Pb atoms. A non-aqueous electrolyte used in a non-aqueous electrolyte secondary battery containing a negative electrode active material having at least one atom selected from the group, comprising a carbonate having at least one of an unsaturated bond and a halogen atom, and a specific A non-aqueous electrolytic solution characterized by containing at least an organic phosphorus compound having a structure is disclosed. According to Patent Document 3, a non-aqueous electrolyte secondary battery having a high charge capacity, excellent characteristics for a long period of time, and particularly excellent discharge capacity retention rate can be produced.

  Patent Document 4 (Japanese Patent Laid-Open No. 58-206078) discloses at least a polymer compound having a conjugated double bond in the main chain or a conductive polymer compound obtained by doping a dopant in the polymer compound. In a battery used for one electrode, a battery characterized by using a phosphate ester compound having a specific structure as an organic solvent of an electrolytic solution is disclosed. According to Patent Document 4, it is possible to provide a secondary battery having a large energy density, good voltage flatness, little self-discharge, and a long repeated life.

  Patent Document 5 (Japanese Patent Laid-Open No. 2011-096462) is characterized in that a non-aqueous electrolyte solution containing an electrolyte and a non-aqueous solvent contains a halogen-containing phosphate ester compound represented by a specific formula. A non-aqueous electrolyte solution is disclosed. According to Patent Document 5, by using the above electrolyte as a battery electrolyte, gas generation during high-temperature storage in a charged state of the battery is suppressed, and charge / discharge characteristics, in particular, high-temperature storage voltage and capacity are excellent. A battery can be obtained.

  Patent Document 6 (Patent No. 3512114) discloses an organic electrolyte solution for an organic electrolyte battery using a negative electrode made of an alkali metal or a compound containing an alkali metal, which contains a fluorine atom and has a three-membered ring structure or An organic electrolyte for an organic electrolyte battery characterized by using a cyclic ether having a 4-membered ring structure as a solvent is disclosed. According to Patent Document 6, as a solvent for an organic electrolyte solution for a specific organic electrolyte battery, a cyclic ether having a 3-membered ring structure or a 4-membered ring structure containing fluorine atoms in which some or all of hydrogen atoms are substituted with fluorine atoms Can reduce the reactivity with the electrode and obtain a highly stable organic electrolyte solution for an organic electrolyte battery. By using the organic electrolyte solution, an organic electrolyte solution having excellent storage properties can be obtained. A battery can be obtained. Further, by using an organic fluorine-containing lithium salt containing two or more carbon atoms as an electrolyte and using a cyclic ether containing a fluorine atom as a solvent, the organic electrolyte battery has high stability and high ionic conductivity. An organic electrolyte solution can be obtained, and by using the organic electrolyte solution, an organic electrolyte battery having excellent storability and low internal resistance can be obtained.

JP 2011-165606 A JP 2006-004746 A JP 2007-299542 A JP 58-206078 A JP 2011-096462 A Japanese Patent No. 3512114

  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 lithium ion secondary battery having high safety that does not deteriorate battery performance (for example, initial capacity) and can meet the demand for large capacity and high output, and a secondary battery using the lithium ion secondary battery. It is to provide a battery system. Another object of the present invention is to provide a non-aqueous electrolyte for a lithium ion secondary battery for realizing such a highly safe lithium ion secondary battery.

(I) One aspect of the present invention is a non-aqueous electrolyte solution for a lithium ion secondary battery containing an electrolyte comprising a lithium compound, a flame retardant, and a non-aqueous solvent,
The lithium concentration in the non-aqueous electrolyte is 0.5 mol / L or more and 2.5 mol / L or less,
The flame retardant includes trimethyl phosphite and dimethyl phosphite,
The trimethyl phosphite is a compound represented by the following chemical formula (1):
The dimethyl phosphite comprises a compound represented by the following chemical formula (2) and / or a compound represented by the following chemical formula (3),
The total content of the trimethyl phosphite and the dimethyl phosphite is 1% by mass or more and 60% by mass or less with respect to the non-aqueous electrolyte.

(II) Another aspect of the present invention is a lithium ion secondary battery having a non-aqueous electrolyte containing an electrolyte comprising a lithium compound, a flame retardant, and a non-aqueous solvent,
Provided is a lithium ion secondary battery, wherein the non-aqueous electrolyte is the non-aqueous electrolyte described above.

(III) Still another aspect of the present invention is a secondary battery system in which at least two lithium ion secondary batteries are connected in series or in parallel.
The lithium ion secondary battery has a nonaqueous electrolytic solution containing an electrolyte composed of a lithium compound, a flame retardant, and a nonaqueous solvent,
The secondary battery system is characterized in that the non-aqueous electrolyte is the non-aqueous electrolyte described above.

  ADVANTAGE OF THE INVENTION According to this invention, the battery performance (for example, initial stage capacity | capacitance) can be provided, and the non-aqueous electrolyte for lithium ion secondary batteries with high safety | security can be provided. In addition, according to the present invention, by using the non-aqueous electrolyte, it is possible to provide a high-capacity lithium ion secondary battery capable of increasing the capacity and output without sacrificing battery performance. And a secondary battery system using the lithium ion secondary battery can be provided.

It is a cross-sectional schematic diagram which shows an example of the lithium ion 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 to be added with the aim of simultaneously achieving both battery performance (initial capacity, large capacity, high output) and safety in the lithium ion secondary battery. As a result, a flame retardant containing trimethyl phosphite and dimethyl phosphite is included in the non-aqueous electrolyte so as to have a predetermined addition amount without sacrificing the battery performance of the lithium ion secondary battery. And found that safety can be ensured. The present invention has been completed based on this finding.

The present invention can add the following improvements and changes to the above-described non-aqueous electrolyte, lithium ion secondary battery, and secondary battery system.
(I) The total content of the trimethyl phosphite and the dimethyl phosphite is 1% by mass or more and 10% by mass or less with respect to the non-aqueous electrolyte.
(Ii) The content of trimethyl phosphite is 0.9 mass% or more and 9.9 mass% or less with respect to the non-aqueous electrolyte, and the total content of dimethyl phosphite is based on the non-aqueous electrolyte. 0.1% by mass or more and 1% by mass or less.
(Iii) The lithium compound is at least one selected from LiPF ₆ , LiBF ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , and lithium bis (pentafluoroethanesulfonyl) imide. .
(Iv) The lithium ion secondary battery includes a solid polymer gel electrolyte in which the nonaqueous electrolyte is impregnated in a solid polymer.

  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 an electrolyte made of a lithium compound and a nonaqueous solvent, and further contains a flame retardant made of trimethyl phosphite and dimethyl phosphite. Trimethyl phosphite is a compound represented by the following chemical formula (1), and dimethyl phosphite is a compound represented by the following chemical formula (2) and / or a compound represented by the following chemical formula (3). The dimethyl phosphite represented by the chemical formula (2) and the dimethyl phosphite represented by the chemical formula (3) are in an isomer relationship with each other. In the non-aqueous electrolyte according to the present invention, both dimethyl phosphites are obtained over time. Reaches a chemical equilibrium state in which

  Addition of trimethyl phosphite mainly has an effect of making the non-aqueous electrolyte itself flame-retardant (an effect of suppressing / preventing non-aqueous electrolyte ignition). On the other hand, the addition of dimethyl phosphite is mainly caused by the decomposition of dimethyl phosphite on the surface of the positive electrode of the battery when the battery becomes hot due to overcharge of the secondary battery or internal short circuit. A high-resistance film is formed, and the effect of suppressing overcharge current and short-circuit current is achieved.

  The flame retardant of the present invention has the two effects of improving the flame retardancy of the non-aqueous electrolyte and preventing abnormal heat generation by suppressing excessive current (overcharge current and short circuit current) exceeding the range of use of the battery. Therefore, a lithium ion secondary battery that is safer than the prior art can be provided. Both trimethyl phosphite and dimethyl phosphite have both of the above effects (improving flame retardancy and preventing abnormal heat generation), but trimethyl phosphite improves flame retardancy, dimethyl phosphite It has a stronger effect in preventing abnormal heat generation, and a synergistic effect is obtained at a specific mixing ratio. That is, according to the present invention, by using two kinds of flame retardants at the same time, it becomes possible to further increase the level of safety of the battery than when used alone.

  Trimethyl phosphite is conventionally known as a flame retardant for non-aqueous electrolytes, and can enhance the self-extinguishing properties of non-aqueous electrolytes. However, the single addition of trimethyl phosphite has a problem in that the effect of flame retardancy of the electrolyte solution itself decreases when the secondary battery becomes hot and the trimethyl phosphite decomposes.

Therefore, the present inventors focused on the group bonded to the phosphorus (P) atom with respect to the decomposition of the flame retardant. As understood from the chemical formula (1), trimethyl phosphite has _three methoxy groups (CH ₃ O—) bonded to the P atom. The decomposition process of trimethyl phosphite is considered to be a stepwise reaction in which the CH ₃ O group is eliminated stepwise and decomposes.

On the other hand, as shown in chemical formula (2) and chemical formula (3), dimethyl phosphite has two CH ₃ O groups bonded to P atoms, and one bond of P atoms is hydrogen (H). Alternatively, it is bonded to a hydroxyl group (—OH). The decomposition process of dimethyl phosphite is also considered to be a stepwise reaction in which the CH ₃ O group is desorbed stepwise and decomposes.

As the CH ₃ O group decomposition process, the oxygen (O) atom is left on the P atom side and the methyl group (CH ₃ ) is released, or the P atom is left as a CH ₃ O group without leaving an O atom. It is unclear whether dimethyl phosphite with a small number of CH ₃ O groups is easier to decompose than trimethyl phosphite in any elementary process.

  Further, since dimethyl phosphite is easily oxidized in the battery environment, conventionally, it has not been considered as a compound to be actively used as a flame retardant for non-aqueous electrolytes. In contrast, the present invention uses dimethyl phosphite and trimethyl phosphite in combination to actively utilize the decomposition of dimethyl phosphite, thereby preventing abnormal heat generation for lithium ion secondary batteries. It gives an effect.

  As described above, dimethyl phosphite decomposes at a high temperature to form a high resistance film on the positive electrode. Although details of the decomposition reaction are unknown, for example, when the oxygen (O) component desorbed from the positive electrode and dimethyl phosphite chemically react as shown in the following reaction formula (a) and reaction formula (b) Conceivable.

(CH ₃ O) ₂ PH (= O) + xO ₂ → PO _2x-1 + 2CO ₂ + 7H ⁺ + 7e ^- Reaction formula (a)
(CH ₃ O) ₂ P (OH) + xO ₂ → PO _2x-1 + 2CO ₂ + 7H ⁺ + 7e ^- Reaction formula (b)
Here, “x” represents the number of moles of oxygen molecules desorbed from the positive electrode, and “2x-1” represents the ratio of oxygen atoms bonded to one phosphorus atom. “X” satisfies “13/8 ≦ x ≦ 7/4” (that is, the oxidation number of P in PO _2x-1 is 4.5 or more and 5 or less). The dimethyl phosphite shown on the left side of the reaction formula (b) may be the isomer “(CH ₃ O) ₂ PH (═O)”, and oxidation of P of the dimethyl phosphite of the present invention. The number is considered 4.5.

The phosphorus oxide (PO _2x-1 ) generated by the above chemical reaction forms a high-resistance film on the surface of the positive electrode of the secondary battery and inhibits the transmission (migration) of lithium ions serving as current carriers inside the battery. In addition, the formation of a high-resistance film prevents the nonaqueous solvent molecules of the electrolytic solution from electrochemically reacting with the oxygen of the positive electrode on the surface of the positive electrode and oxidatively decomposing. As a result, excessive current (overcharge current and short circuit current) can be suppressed, and abnormal heat generation due to oxidative decomposition of nonaqueous solvent molecules can be prevented.

In the above description, the formation of a high-resistance film on the positive electrode has been described. However, when the temperature becomes high, a reduction reaction occurs on the negative electrode. Specifically, lithium (Li) and dimethyl phosphite react to form Li ₃ P, Li ₃ PO ₄ or the like on the negative electrode, thereby inactivating lithium ions. Thereby, the excess current (overcharge current or short circuit current) between the positive electrode and the negative electrode is further suppressed.

  In a phosphite used as a flame retardant, generally, as the molecular weight increases, the viscosity of the electrolytic solution increases and the electrical conductivity decreases (the mobility of lithium ions decreases). In addition, the higher the molecular weight of the ester-bonded alkyl group or aryl group (the greater the number of carbon atoms constituting the group), the greater the heat of decomposition reaction. Reduce the effect. Furthermore, when the molecular weight of the flame retardant increases, its vapor pressure also decreases, so that the ignition suppression effect of the electrolyte (the combustion suppression effect of the electrolyte against an external flame) also decreases.

  The phosphite used in the present invention (trimethyl phosphite and dimethyl phosphite) has a low molecular weight because the ester-bonded alkyl group is a methyl group, while suppressing an increase in the viscosity of the electrolyte, The content of can be increased. As a result, it is possible to suppress the decrease in the conductivity of the non-aqueous electrolyte and improve the safety while maintaining the battery performance equivalent to the conventional one. In addition, since the flame retardant used in the present invention has a low molecular weight, the heat of decomposition reaction is small and the vapor pressure is high as compared with conventional flame retardants. For this reason, while suppressing the temperature rise of the electrolyte solution accompanying decomposition | disassembly of a flame retardant, the ignition suppression effect of electrolyte solution improves.

  In the non-aqueous electrolyte for a lithium ion secondary battery according to the present invention, the total content of trimethyl phosphite and dimethyl phosphite described above is 1% by mass or more and 60% by mass or less based on the non-aqueous electrolyte. It is preferable that it is the range of these. When the total content is less than 1% by mass, the safety is relatively insufficient as compared with the optimum range described above. On the other hand, if the total content is larger than 60% by mass, the conductivity of the electrolytic solution is lowered and the battery characteristics are greatly lowered. The upper limit of the total content is appropriately set within the above range depending on the characteristics required for the lithium ion secondary battery (for example, the balance between battery characteristics and safety), but 1% by mass from the viewpoint of the initial capacity More preferably, it is 10 mass% or less.

  Furthermore, as a distribution of trimethyl phosphite and dimethyl phosphite, when the total amount of the flame retardant is 10% by mass, the content of trimethyl phosphite is 0.9% by mass to 9.9% with respect to the non-aqueous electrolyte. It is preferably in the range of mass% or less, and the content of dimethyl phosphite is preferably in the range of 0.1 mass% or more and 1 mass% or less with respect to the non-aqueous electrolyte. Accordingly, it is possible to provide a nonaqueous electrolytic solution that suppresses decomposition of trimethyl phosphite, has high flame retardancy, and suppresses abnormal heat generation due to excessive current.

  In addition, in a lithium ion secondary battery, it should be avoided that a water | moisture content mixes in a non-aqueous electrolyte. If moisture is present in the non-aqueous electrolyte, the electrolyte and water chemically react with each other, causing the electrolyte to decompose and causing battery performance to deteriorate. In addition, the chemical reaction between the electrolyte and water generates hydrogen halide such as hydrogen fluoride (HF) and damages the positive and negative electrodes of the secondary battery, resulting in a decrease in the capacity of the secondary battery. It becomes a factor. On the other hand, trimethyl phosphite used as a flame retardant is difficult to quantitatively analyze the amount of mixed water. Conventionally, trimethyl phosphite has been used in a state where the amount of mixed water is unclear. On the other hand, in this invention, after performing sufficient water removal process with respect to trimethyl phosphite and dimethyl phosphite, they were utilized. This is considered to be one reason why the content of the flame retardant can be increased as compared with the conventional case.

The electrolyte to be contained in the nonaqueous electrolytic solution is not particularly limited as long as it does not decompose on the positive electrode or the negative electrode used in the lithium ion secondary battery according to the present invention described later, and a conventional electrolyte can be used. For example, the _{LiPF 6, LiBF 4, LiClO 4} , LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB (CN) 4, LiN (SO 2 F) 2, LiN (SO 2 CF 3) 2 It can be suitably used. Alternatively, an imide salt of lithium (for example, lithium trifluoromethanesulfonimide, lithium bis (pentafluoroethanesulfonyl) imide) may be used.

  The lithium concentration by the electrolyte in the nonaqueous electrolytic solution is preferably 0.5 mol / L or more and 2.5 mol / L or less. In the present specification, “lithium concentration” means the concentration of all “lithium” present in the non-aqueous electrolyte, and “lithium” includes lithium ions generated by ionization of the electrolyte. Shall also be included. When the lithium concentration is less than 0.5 mol / L, the conductivity of the non-aqueous electrolyte is lowered, and the battery characteristics of the lithium ion secondary battery are lowered. On the other hand, the upper limit of the lithium concentration is not particularly limited as long as the added electrolyte is completely dissolved. However, when the lithium concentration exceeds 2.5 mol / L, the capacity decreases due to the increase in the viscosity of the electrolytic solution, which is not preferable.

  The non-aqueous solvent contained in the non-aqueous electrolyte is not particularly limited as long as it does not decompose on the positive electrode or the negative electrode used in the lithium ion secondary battery according to the present invention described later, and a conventional non-aqueous solvent is used. it can. 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, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone, tetrahydrofuran, 1,2-diethoxyethane, chloroethylene carbonate, chloropropylene carbonate Etc. are suitable.

The non-aqueous electrolyte according to the present invention can use an ionic liquid instead of the above-mentioned “electrolyte + non-aqueous solvent” on the condition that trimethyl phosphite and dimethyl phosphite are not decomposed. . Examples of the ionic liquid include 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF ₄ , C ₆ H ₁₁ N ₂ BF ₄ ), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI, LiN (SO ₂ CF ₃ ) ₂ ), triethylene glycol dimethyl ether (triglyme, C ₈ H ₁₈ O ₄ ) and tetraethylene glycol dimethyl ether (tetraglyme, C ₁₀ H ₂₂ O ₅ ) mixed complex, cyclic quaternary ammonium series P ₁₃ -FSI (C ₈ H ₁₈ NF) consisting of an ion (eg, N-methyl-N-propylpyrrolidinium (P ₁₃ )) and an imide anion (eg, bis (fluorosulfonyl) imide (FSI)) ₂ NO ₄ S ₂ ) Ionic liquid can be used.

  Further, in the present invention, a polymer gel electrolyte can be used in addition to the above-described combination of the nonaqueous electrolytic solution (“electrolyte + nonaqueous solvent”). The polymer gel electrolyte is formed by impregnating a solid polymer with a nonaqueous electrolytic solution (“electrolyte + nonaqueous solvent”) to form a gel. The polymer gel electrolyte has an advantage that higher lithium ion conductivity can be obtained than the polymer electrolyte alone. By using the non-aqueous electrolyte containing the flame retardant of the present invention, it becomes possible to provide a polymer gel electrolyte having high conductivity and flame retardancy.

  As the solid polymer, an ion conductive polymer such as ethylene oxide, acrylonitrile, polyvinylidene fluoride, methyl methacrylate, or polyethylene oxide of hexafluoropropylene can be used.

[Lithium ion secondary battery]
The configuration of the lithium ion secondary battery according to the present invention will be described. The lithium ion secondary battery according to the present invention is a polymer gel electrolyte obtained by impregnating a solid polymer with the above-described non-aqueous electrolyte containing the flame retardant of the present invention or the non-aqueous electrolyte containing the flame retardant of the present invention. There is the biggest feature in using.

  FIG. 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery 101 according to the present invention. As shown in FIG. 1, the positive electrode 107 and the negative electrode 108 are laminated 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 outermost separator 109 insulates between the electrode group and the battery container 102. The structure of the electrode group is not limited, and for example, the electrode group may be wound in a cylindrical shape or a flat shape.

  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 housed in the battery container 102 and sealed by a battery lid 103 installed on the upper part of the battery container 102. The battery lid 103 is provided with a positive external terminal 104 and a negative external terminal 105 via an insulating seal 112. Further, the above-described non-aqueous electrolyte (not shown) according to the present invention is injected into the battery container 102. 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. More specifically, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are representative examples. In addition, LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn, Ta, x = 0.01 to 0.2), Li ₂ Mn ₃ MO ₈ (M = Fe, Co, Ni, Cu, Zn), Li _1-x A _x Mn ₂ O ₄ (However, A = Mg, Ba, B, Al , Fe, Co, Ni, Cr, Zn, Ca, x = 0.01 to 0.1), LiNi _1-x M _x O ₂ (where M = Co, Fe, Ga and x = 0.01 to 0.2 ), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-x M _x O ₂ (where M = Ni, Fe, Mn, x = 0.01 to 0.2), LiNi _1-x M _x O ₂ (However, M = Mn, Fe, Co, Al, Ga, Ca, Mg and x = 0.01 to 0.2), Fe (MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , LiMnPO _{4 and the} like can be listed. it can. 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 material (eg, graphite, graphitizable carbon, non-graphitizable carbon natural graphite, artificial graphite, mesophase carbon, expanded graphite, carbon fiber, vapor grown carbon fiber, pitch system Carbonaceous materials, needle coke, petroleum coke, polyacrylonitrile-based carbon fiber, carbon black, amorphous carbon) and oxides (eg lithium titanate, titanium oxide, iron oxide, vanadium oxide, antimony oxide) are available is there. 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 maximum current value that can be charged and discharged decreases. 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. The separator 109 can be omitted when a solid polymer electrolyte is used as the “electrolyte + nonaqueous solvent” of the nonaqueous electrolytic solution described above.

  Since the lithium ion secondary battery according to the present invention uses the non-aqueous electrolyte described above, it is possible to increase the capacity and output without sacrificing battery performance (for example, initial capacity) and safety. High lithium ion secondary battery can be provided. Specific examples of battery performance will be described later.

[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 secondary battery 101a is connected to the negative terminal 105 of the lithium ion secondary battery 101b by the power cable 214. Further, 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 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-B18 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 Negative electrode active material (98% by mass, graphite ((002) interplanar spacing d ₀₀₂ = 0.35 to 0.36 nm determined by XRD measurement, average particle size 15 to 16 μm)), binder (2% by mass, Styrene butadiene rubber (1% by mass) + carboxymethyl cellulose (1% by mass)), conductive agent (7% by mass, carbon black) and solvent (1-methyl-2-pyrrolidone) were prepared 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) Preparation of non-aqueous electrolyte As a non-aqueous solvent for the non-aqueous electrolyte, a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (volume ratio = 1: 1: 1) Was formulated. 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. In the table, the content of the flame retardant is a mass concentration (% by mass) with respect to the entire non-aqueous electrolyte. The concentration of the electrolyte is a volume molar concentration with respect to the non-aqueous solvent (hereinafter the same).

The trimethyl phosphite ((CH ₃ O) ₃ P) and dimethyl phosphite ((CH ₃ O) ₂ POH) used as flame retardants were dehydrated in advance as follows. In a glove box filled with argon gas, molecular sieves were charged into trimethyl phosphite or dimethyl phosphite at room temperature and left for one week. Each immersion liquid was filtered to obtain anhydrous trimethyl phosphite and anhydrous dimethyl phosphite.

(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 fluororesin 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)
About the lithium ion secondary battery prepared above, the following charging / discharging tests were implemented and initial capacity was evaluated. First, the fabricated battery was charged with a charging current of 5 A from the open circuit state until the battery voltage reached 4.2 V. After the battery voltage reached 4.2 V, 4.2 V was maintained until the current value decreased to 0.1 A. Thereafter, charging was stopped and a 30-minute rest period was provided. Next, discharging with a discharge current of 5 A was started and 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. Note that the variation in the measured values was approximately within ± 0.1 Ah with respect to the average value. 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 1 described later.

(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. B1-B18 batteries 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 1.

As shown in Table 1, the lithium ion secondary batteries (B2 to B10, B13 to B16) according to the present invention have cleared all the required levels in both the initial capacity and overcharge test items. I understand that. In particular, the total content of trimethyl phosphite ((CH ₃ O) ₃ P) and dimethyl phosphite ((CH ₃ O) ₂ POH) in the flame retardant is 1% by mass to 10% by mass, The lithium ion secondary batteries (B2 to B7) in which CH ₃ O) ₃ P is 0.9 mass% to 9.9 mass% and (CH ₃ O) ₂ POH is 0.1 mass% to 1 mass% have initial capacity The (average) was 9.9 Ah, the highest value.

On the other hand, in the sample (B1) in which the amount of CH ₃ O) ₃ P added was less than 1% by mass, the secondary battery ruptured in the overcharge test, and the safety was rejected. In addition, in the samples (B11, B12, B17, B18) in which the total amount of (CH ₃ O) ₃ P and (CH ₃ O) ₂ POH is greater than 60% by mass, the initial capacity of the secondary battery is not acceptable. there were.

[Example 2]
(Production and test evaluation of lithium ion secondary batteries B21-B26)
The concentration of lithium hexafluorophosphate (LiPF ₆ ) in the non-aqueous electrolyte is 0.2 mol / L (Sample B21), 0.5 mol / L (Sample B22), 1.5 mol / L (Sample B23), 2.0 mol / Except that L (sample B24), 2.5 mol / L (sample B25), and 3 mol / L (sample B26) were used, a lithium ion secondary battery of B21 to B26 was prepared in the same manner as in Example 1, A charge / discharge test and an overcharge test were performed. Table 2 shows the specifications of the secondary battery and the battery characteristic results.

As shown in Table 2, it can be seen that the lithium ion secondary batteries (B22 to B25) according to the present invention have cleared all the required levels in both the initial capacity and overcharge test items. On the other hand, the sample (B21) in which the concentration of the electrolyte (LiPF ₆ ) was 0.2 mol / L failed in the initial capacity of the secondary battery. This was considered due to a decrease in the conductivity of the non-aqueous electrolyte. In addition, the sample (B26) having an electrolyte concentration of 3 mol / L failed in both the initial capacity and overcharge test items. The initial capacity decreased because the viscosity of the electrolyte increased. In addition, the overcharge test was considered to have failed because the amount of heat generated due to the decomposition of the electrolyte may have increased.

  From the above results, in the lithium ion secondary battery according to the present invention, the electrolyte concentration in the nonaqueous electrolytic solution is preferably 0.5 mol / L or more, and if it is 2.5 mol / L or less, it is verified that it is at least a pass level. It was done.

[Example 3]
(Production and test evaluation of B31-B33 lithium ion secondary batteries)
Except having used the mixed electrolyte which mixed multiple types of lithium compound, it carried out similarly to Example 1, produced the lithium ion secondary battery of B31-B33, and implemented the charging / discharging test and the overcharge test. LiPF ₆ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ and lithium bis (pentafluoroethanesulfonyl) imide (LiBETI) were used as the lithium compound, and two of them were mixed. The two lithium compounds A and B and their mixing ratio (ratio of their respective molar concentrations, [A] / [B]) are [LiPF ₆ ] / [LiN (SO ₂ F) ₂ ] = [0.8 mol / L ] / [0.2 mol / L] (Sample B31), [LiPF ₆ ] / [LiN (SO ₂ CF ₃ ) ₂ ] = [0.8 mol / L] / [0.2 mol / L] (Sample B32), [LiPF ₆ ] / [LiBETI] = [0.8 mol / L] / [0.2 mol / L] (Sample B33). Table 3 shows the specifications of the secondary battery and the battery characteristic results.

  As shown in Table 3, it can be seen that all the lithium ion secondary batteries B31 to B33 have cleared all the required levels in both the initial capacity and overcharge test items. From this result, it was demonstrated that in the lithium ion secondary battery according to the present invention, a plurality of types of lithium compounds can be mixed as the electrolyte in the nonaqueous electrolytic solution.

[Example 4]
(Production and test evaluation of B41-B45 lithium ion secondary batteries)
Except that a mixture of LiPF ₆ and LiBF ₄ was used as the electrolyte, B41 to B45 lithium ion secondary batteries were produced in the same manner as in Example 1, and a charge / discharge test and an overcharge test were performed. The mixing ratio of the added LiPF ₆ and LiBF ₄ (ratio of molar concentration of each, [LiPF ₆ ] / [LiBF ₄ ]) is [0.9 mol / L] / [0.1 mol / L] (Sample B31), [ 0.7 mol / L] / [0.3 mol / L] (Sample B32), [0.5 mol / L] / [0.5 mol / L] (Sample B33), [0.3 mol / L] / [0.7 mol / L] (Sample B34) and [0.1 mol / L] / [0.9 mol / L] (sample B35). Table 4 shows the specifications of the secondary battery and the battery characteristic results.

As shown in Table 4, it can be seen that all the lithium ion secondary batteries B41 to B45 cleared all the required levels in both the initial capacity and overcharge test items. From this result, it was confirmed that in the lithium ion secondary battery according to the present invention, even when a plurality of types of lithium compounds are mixed and used as the electrolyte in the non-aqueous electrolyte, they can be mixed at an arbitrary ratio. . In addition, the tendency that the initial capacity slightly decreases as the concentration of LiBF ₄ is increased is considered to be because the conductivity of LiBF ₄ is lower than that of LiPF ₆ .

[Example 5]
(Production and test evaluation of B51-B55 lithium ion secondary batteries)
In this example, a lithium ion secondary battery was produced using a polymer gel electrolyte. Specifically, a polymer sheet of polyethylene oxide (average molecular weight 7000 to 8000, thickness 3 μm) is used, and the polymer sheet is impregnated with the non-aqueous electrolyte containing the flame retardant of the present invention. An electrolyte was prepared. A non-aqueous electrolyte (including a flame retardant) of 130 to 150% by mass with respect to the mass of the polymer sheet was impregnated. Other than that was carried out similarly to Example 1, the lithium ion secondary battery of B51-B55 was produced, and the charging / discharging test and the overcharge test were implemented. Table 5 shows the specifications of the secondary battery and the battery characteristic results.

  As shown in Table 5, it can be seen that the lithium ion secondary batteries (B51 to B55) according to the present invention have cleared all required levels in both items of the initial capacity and the overcharge test. From this, it was proved that the effects of the present invention can be obtained even with a solid polymer gel electrolyte if the flame retardant of the present invention is added.

[Example 6]
The secondary battery system shown in FIG. 2 was produced using the lithium ion secondary battery B5 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 219. The magnitudes of the current pulses were both 20 A.

  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 hardly deteriorates even when a current pulse of 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 toward a charging depth of 100%. During the charging process, the secondary battery 101a is in an overcharge environment, but the secondary battery 101a is charged by the overcharge prevention action by decomposition of dimethyl phosphite, which is a flame retardant component of the present invention, and formation of a high resistance film. Has been stopped. 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, a highly safe lithium ion secondary battery having battery performance (for example, initial capacity) equivalent to that of the prior art and capable of meeting demands for large capacity and high output is provided. It was confirmed that a non-aqueous electrolyte for realization could be provided. Further, by using the non-aqueous electrolyte, it is possible to provide a high-capacity lithium-ion secondary battery capable of increasing the capacity and output without sacrificing battery performance, and further, It was confirmed that a secondary battery system using a lithium ion secondary battery can be provided.

  The present invention is not limited to the above-described embodiments and examples, and includes various modifications. For example, the above-described embodiments have been specifically described in order to help understanding of the present invention, and are not limited to having all the configurations described. Further, a part of the configuration of the 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 (14)

A lithium ion secondary battery having a non-aqueous electrolyte containing an electrolyte comprising a lithium compound, a non-aqueous solvent and a flame retardant,
The lithium concentration in the non-aqueous electrolyte is 0.5 mol / L or more and 2.5 mol / L or less,
The flame retardant includes trimethyl phosphite and dimethyl phosphite,
The lithium ion secondary battery, wherein a total content of the trimethyl phosphite and the dimethyl phosphite is 1% by mass to 60% by mass with respect to the non-aqueous electrolyte. The lithium ion secondary battery according to claim 1,
The lithium ion secondary battery, wherein a total content of the trimethyl phosphite and the dimethyl phosphite is 10% by mass or less based on the non-aqueous electrolyte. The lithium ion secondary battery according to claim 2,
The content of trimethyl phosphite is 0.9 mass% or more and 9.9 mass% or less with respect to the non-aqueous electrolyte,
Content of the said dimethyl phosphite is 0.1 to 1 mass% with respect to the said non-aqueous electrolyte, The lithium ion secondary battery characterized by the above-mentioned. The lithium ion secondary battery according to any one of claims 1 to 3,
The lithium compound is at least one selected from LiPF ₆ , LiBF ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , and lithium bis (pentafluoroethanesulfonyl) imide. Lithium ion secondary battery. The lithium ion secondary battery according to any one of claims 1 to 4,
A lithium ion secondary battery comprising a solid polymer gel electrolyte in which the nonaqueous electrolyte is impregnated in a solid polymer. A secondary battery system in which at least two lithium ion secondary batteries are connected in series or in parallel,
The lithium ion secondary battery has a nonaqueous electrolytic solution containing an electrolyte composed of a lithium compound, a nonaqueous solvent, and a flame retardant,
The lithium concentration in the electrolyte is 0.5 mol / L or more and 2.5 mol / L or less,
The flame retardant includes trimethyl phosphite and dimethyl phosphite,
A secondary battery system, wherein a total content of the trimethyl phosphite and the dimethyl phosphite is 1% by mass to 60% by mass with respect to the non-aqueous electrolyte. The secondary battery system according to claim 6,
The secondary battery system, wherein a total content of the trimethyl phosphite and the dimethyl phosphite is in a range of 10% by mass or less with respect to the non-aqueous electrolyte. The secondary battery system according to claim 7,
The content of trimethyl phosphite is 0.9 mass% or more and 9.9 mass% or less with respect to the non-aqueous electrolyte,
A secondary battery system, wherein a content of the dimethyl phosphite is 0.1% by mass or more and 1% by mass or less with respect to the non-aqueous electrolyte. The secondary battery system according to any one of claims 6 to 8,
The lithium compound is at least one selected from LiPF ₆ , LiBF ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , and lithium bis (pentafluoroethanesulfonyl) imide. Rechargeable battery system. The lithium ion secondary battery system according to any one of claims 6 to 9,
The lithium ion secondary battery includes a solid polymer gel electrolyte in which the non-aqueous electrolyte is impregnated in a solid polymer. A non-aqueous electrolyte for a lithium ion secondary battery containing an electrolyte comprising a lithium compound, a flame retardant, and a non-aqueous solvent,
The lithium concentration in the non-aqueous electrolyte is 0.5 mol / L or more and 2.5 mol / L or less,
The flame retardant includes trimethyl phosphite and dimethyl phosphite,
A nonaqueous electrolytic solution, wherein a total content of the trimethyl phosphite and the dimethyl phosphite is 1% by mass to 60% by mass with respect to the nonaqueous electrolytic solution. The non-aqueous electrolyte according to claim 11,
The nonaqueous electrolyte solution, wherein a total content of the trimethyl phosphite and the dimethyl phosphite is 10% by mass or less with respect to the nonaqueous electrolyte solution. In the non-aqueous electrolyte according to claim 12,
The content of trimethyl phosphite is 0.9 mass% or more and 9.9 mass% or less with respect to the non-aqueous electrolyte,
A nonaqueous electrolytic solution, wherein a content of the dimethyl phosphite is 0.1% by mass or more and 1% by mass or less with respect to the nonaqueous electrolytic solution. The nonaqueous electrolytic solution according to any one of claims 11 to 13,
The lithium compound is at least one selected from LiPF ₆ , LiBF ₄ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , and lithium bis (pentafluoroethanesulfonyl) imide. Non-aqueous electrolyte.

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