JP5708933B2 - Secondary battery system - Google Patents

Description

  The present invention relates to a secondary battery system including a plurality of secondary batteries.

  2. Description of the Related Art In recent years, secondary batteries mounted on automobiles, robots, and the like, including portable electronic devices such as notebook computers and digital cameras, have been developed. And the lithium ion secondary battery which has a high energy density among secondary batteries attracts attention.

  When overcharging occurs in a lithium ion secondary battery, there is a risk of heat generation, smoke generation, and ignition as a result of elution and decomposition of the active material, corrosion of the electrode, and further deposition of metallic lithium and the accompanying short circuit. In particular, when a large number of lithium ion secondary batteries are connected in series, the current concentrates on a specific lithium ion secondary battery due to variations in the capacity and impedance of each lithium ion secondary battery, or due to differences in the state of charge, Overcharge is likely to occur. Therefore, it is common to provide a protection circuit that monitors the state of charge of a lithium ion secondary battery and cuts off the connection between the charging circuit and the lithium ion secondary battery when the battery is overcharged. For example, Patent Document 1 discloses a secondary battery pack including a protection circuit provided with a fuse.

JP 2006-73457 A

  However, in Patent Document 1, although it is considered that there is a certain effect in that overcharge can be prevented by providing a protection circuit, each lithium ion secondary battery is connected in series when a plurality of lithium ion secondary batteries are connected in series. Since the protection circuit is provided in the ion secondary battery, there is a problem that a space for installing the protection circuit component is necessary and costly.

  The present invention has been made in view of such problems, and it is possible to simplify a protection circuit provided in each lithium ion secondary battery and to provide a secondary battery system that can be miniaturized. Objective.

  The inventor has been studying an organic active material secondary battery in which an active material responsible for an electrode reaction is an organic material. The organic active material secondary battery has the lowest internal resistance at the charge / discharge voltage (oxidation / reduction voltage of the active material), and the internal resistance tends to increase rapidly regardless of whether it is higher or lower than the charge / discharge voltage. And this inventor clarified that combining this organic active material secondary battery with a lithium ion secondary battery has the effect of suppressing the voltage variation of a large number of lithium ion secondary batteries connected in series. .

  The secondary battery system according to the present invention is made based on such knowledge, and is charged and discharged by the electrode reaction of the first active material, and the reaction product or product of the first active material or the electrode reaction is A plurality of lithium ion secondary batteries that are lithium transition metal oxides and an organic active material that is charged and discharged by an electrode reaction between the second active material and the second active material or a reaction product or product of the electrode reaction is an organic material A lithium-ion secondary battery and an organic active material secondary battery are connected in series.

  In the secondary battery system according to the present invention, a plurality of lithium ion secondary batteries are connected in series, and a predetermined lithium ion secondary battery and an organic active material secondary battery among the plurality of lithium ion secondary batteries are connected in series. It is preferable that it is connected to.

  In the secondary battery system according to the present invention, it is preferable that the second active material or the reaction product or product of the electrode reaction of the organic active material secondary battery is a neutral radical compound.

  In the secondary battery system according to the present invention, the neutral radical compound is preferably a nitroxyl radical-based stable radical compound.

  In the secondary battery system according to the present invention, the nitroxyl radical-based stable radical compound is preferably a compound containing 2,2,6,6-tetramethylpiperidine-N-oxyl radical in the molecular structure.

  In the secondary battery system according to the present invention, the number of lithium ion secondary batteries is preferably larger than the number of organic active material secondary batteries.

  Moreover, in the secondary battery system which concerns on this invention, it is preferable that the number of lithium ion secondary batteries is a ratio of 100 or less with respect to one organic active material secondary battery.

  According to the present invention, since the lithium ion secondary battery and the organic active material secondary battery are connected in series, the capacity variation, the internal impedance variation, or the charge state difference among the plurality of lithium ion secondary batteries. As a result, even if current concentration on a specific secondary battery or overcharge associated therewith occurs, an increase in voltage can be prevented by the presence of the organic active material secondary battery. Therefore, it is possible to provide a secondary battery system in which the protection circuit can be simplified and the size can be reduced.

It is a figure which shows the voltage-current curve of a lithium ion secondary battery and an organic active material secondary battery. It is a circuit diagram which shows the secondary battery system which concerns on this invention. It is a circuit diagram which shows the secondary battery system which concerns on this invention.

  Hereinafter, modes for carrying out the present invention will be described.

  FIG. 1 is a diagram of voltage-current curves of a lithium ion secondary battery and an organic active material secondary battery used in the present invention. A lithium ion secondary battery and an organic active material secondary battery are both secondary batteries that are charged and discharged by an electrode reaction of the active material.

  Since the active material of the secondary battery is reversibly oxidized or reduced by charging / discharging, it has different structures depending on the charged state, discharged state, or intermediate state. Therefore, the active material becomes a substance (reactant) that causes a chemical reaction in the electrode reaction, or becomes a substance and an intermediate product (product) generated as a result of the electrode reaction.

A lithium ion secondary battery is a battery in which an active material or a reaction product or product of an electrode reaction is a lithium transition metal oxide, and a lithium ion in an electrolyte moves between a positive electrode and a negative electrode, and a charge / discharge reaction proceeds. It is. Examples of the lithium transition metal oxide include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO ₄ , Li ₂ FePO ₄ F, LiCO _1/3 Ni _1/3 Mn _1/3 O _{2 and the} like, Alternatively, a plurality of combinations are used.

  An organic active material secondary battery is a battery in which an active material or a reaction product or product of an electrode reaction is an organic material. In general, an organic active material secondary battery includes a positive electrode including an active material and a conductive agent, a negative electrode, and an electrolyte. And the charging / discharging voltage of an organic active material secondary battery is dependent on the molecular structure of the site | part in which oxidation-reduction reaction is performed.

  In addition, the active material of a lithium ion secondary battery and an organic active material secondary battery may contain not only one type of active material but also a plurality of active materials.

1 (A) is the voltage of the lithium ion secondary battery - a view of the current curve, the charge and discharge voltage is V _a. When the voltage is increased, the internal resistance of the lithium ion secondary battery decreases, and current easily flows. And when it exceeds predetermined voltage value _Vb , the tendency for an electric current to flow rapidly will be shown.

  In general, when a plurality of lithium ion secondary batteries are connected in series and charged, the applied voltage differs depending on the state of charge, temperature, etc. of each battery, and overcharge is caused in some batteries. In particular, since the temperature of these batteries increases as the charging proceeds, there is a possibility that the internal resistance decreases and the voltage substantially applied to the batteries further increases, resulting in a vicious circle.

FIG. 1 (B) is a diagram of a voltage-current curve of an organic active material secondary battery using a compound containing 2,2,6,6-tetramethylpiperidine-N-oxy radical in the molecular structure as an active material, The charge / discharge voltage is V _c . In the organic active material secondary battery, since the internal resistance is the smallest at V _c , current easily flows. And even if the voltage is larger or smaller than V _c , there is a tendency that the current hardly flows because the internal resistance rapidly increases.

  FIG. 2 is an example of a circuit diagram showing a secondary battery system according to the present invention. The secondary battery system 1 includes two assembled batteries 2, and the assembled batteries 2 are connected in series with each other. The dotted line portion in the figure indicates the assembled battery 2. In the present embodiment, the assembled battery 2 includes three lithium ion secondary batteries 3 and one organic active material secondary battery 4. In this embodiment, since the charge / discharge voltage of each of the lithium ion secondary battery and the organic active material secondary battery is 3.6 V, charging is performed by applying a voltage of 28.8 V or more to the secondary battery system 1. Progresses.

In the present invention, one or more organic active material secondary batteries 4 are connected in series with the lithium ion secondary battery 3. At this time, since the voltages applied to the plurality of lithium ion secondary batteries 3 vary, a voltage deviating from V _c is applied to the organic active material secondary battery 4. At this time, as shown in FIG. 1B, the current flowing through the organic active material secondary battery 4 is reduced. As a result, the current flowing through the entire circuit is reduced, and overcharging of the lithium ion secondary battery 3 can be suppressed. Therefore, the conventional protection circuit connected to each lithium ion secondary battery 3 can be further simplified, and the overall size of the secondary battery system 1 can be reduced.

  In the present embodiment, the organic active material secondary battery is connected to one end of the plurality of lithium ion secondary batteries, but may be connected between the plurality of lithium ion secondary batteries.

  In this embodiment, a plurality of lithium ion secondary batteries are connected in series, and a predetermined lithium ion secondary battery and an organic active material secondary battery among the plurality of lithium ion secondary batteries are connected in series. . The number of lithium ion secondary batteries and organic active material secondary batteries is not particularly limited, but the number of lithium ion secondary batteries is preferably larger than the number of organic active material secondary batteries. In this case, the overall energy density of the secondary battery system is improved.

  Moreover, it is preferable that the number of lithium ion secondary batteries is a ratio of 100 or less to one organic active material secondary battery. In this case, the effect of the present invention is remarkable.

  Further, the difference in charge / discharge voltage between the lithium ion secondary battery and the organic active material secondary battery is not particularly defined, but is preferably 0.5 V or less. In this case, the effect of the present invention is remarkable.

  In addition, the reaction product or product of the electrode reaction of the organic active material secondary battery is preferably a neutral radical compound. In this case, the progress of the charge / discharge reaction is facilitated. Examples of neutral radical compounds include various nitroxy radicals, nitrogen radicals, oxygen radicals, thioaminyl radicals, sulfur radicals, boron radicals and the like, with nitroxy radical-based stable radical compounds being particularly preferred.

  Among the nitroxy radical-based stable radical compounds, since the charge / discharge reaction is stable, the compound may contain a 2,2,6,6-tetramethylpiperidine-N-oxyl radical structure in the molecular structure. preferable. Examples of such a molecule containing a 2,2,6,6-tetramethylpiperidine-N-oxyl radical structure include, for example, polymer compounds represented by chemical formulas (1) to (6) and those having a part of the repeating unit. Such as a copolymer.

  FIG. 3 is another example of a circuit diagram showing a secondary battery system according to the present invention. In FIG. 3, unlike FIG. 2, the assembled battery 2 is connected in parallel. Even in this case, the overcharge of the lithium ion secondary battery 3 can be suppressed.

  In the present invention, the secondary battery system may be provided with a voltage control circuit, a battery remaining amount monitoring circuit, a display circuit, and the like as necessary.

  Next, an example of the manufacturing method of said organic active material secondary battery is explained in full detail.

  First, a positive electrode is formed. For example, an active material, a conductive agent, and a binder are mixed, an organic solvent is added to form a slurry, and the slurry is applied on the positive electrode current collector by an arbitrary coating method and dried to form a positive electrode. To do.

  Here, the conductive agent is not particularly limited, and examples thereof include carbonaceous fine particles such as graphite, carbon black, and acetylene black, carbon fibers such as vapor grown carbon fiber (VGCF), carbon nanotube, and carbon nanohorn, Examples thereof include conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyacene. Further, two or more kinds of conductive agents may be mixed and used. In addition, as for the content rate of the electrically conductive agent in a positive electrode, 10-80 mass% is desirable.

  The binder is not particularly limited, and examples thereof include various resins such as polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, and carboxymethyl cellulose.

  Further, the organic solvent is not particularly limited, and examples thereof include basic solvents such as dimethyl sulfoxide, dimethylformamide, N-methyl-2-pyrrolidone, propylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone, acetonitrile. , Non-aqueous solvents such as tetrahydrofuran, nitrobenzene, and acetone, and protic solvents such as methanol and ethanol.

  Further, the type of organic solvent and its blending amount, the type of binder and its blending amount, etc. can be arbitrarily set in consideration of the required characteristics and productivity of the secondary battery.

Next, an electrolyte is prepared. The electrolyte is interposed between the positive electrode (active material) and the negative electrode as the counter electrode, and transports charge carriers between the two electrodes. As such an electrolyte, for example, 10 ⁻⁵ to 10 ⁻¹ S at room temperature. For example, an electrolyte solution in which an electrolyte salt is dissolved in an organic solvent is used. Examples of the electrolyte salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO _2). ) ₃ , LiC (C ₂ F ₅ SO ₂ ) _{3 and the} like.

  Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone. Can be mentioned.

  A solid electrolyte may be used as the electrolyte. Examples of the polymer compound used for the solid electrolyte include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-monofluoroethylene copolymer, and fluoride. Vinylidene fluoride polymers such as vinylidene-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and acrylonitrile-methyl methacrylate Copolymer, Acrylonitrile-methyl acrylate copolymer, Acrylonitrile-ethyl methacrylate copolymer, Acrylonitrile-ethyl acrylate copolymer, Acrylonitrile-methacrylic acid copolymer, Acrylonitrile-a Acrylic acid copolymer, an acrylonitrile - acrylonitrile polymers such as vinyl acetate copolymer and polyethylene oxide, ethylene oxide - propylene oxide copolymers, and polymers such as these acrylates body or methacrylate products thereof. Moreover, you may use what made these polymer compounds contain electrolyte solution and made it gelatinous as electrolyte. Alternatively, only a polymer compound containing an electrolyte salt may be used as an electrolyte as it is.

  Next, the positive electrode is impregnated with the electrolyte, and the negative electrode is opposed to the negative electrode through the separator impregnated with the electrolyte, followed by sealing the exterior to produce an organic active material secondary battery.

  In the present invention, needless to say, the battery shape is not particularly limited. Examples of battery shapes include cylindrical, square, and sheet types. Also, the exterior method is not particularly limited. Examples of the exterior method include a metal case, a mold resin, and an aluminum laminate film.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible in the range which does not deviate from a summary.

DESCRIPTION OF SYMBOLS 1 Secondary battery system 2 Assembly battery 3 Lithium ion secondary battery 4 Organic active material secondary battery

Claims (7)

A lithium ion secondary battery that is charged and discharged by an electrode reaction of a first active material, and wherein a reaction product or product of the first active material or the electrode reaction is a lithium transition metal oxide;
An organic active material secondary battery that is charged and discharged by an electrode reaction of a second active material, and wherein the second active material or the reaction product or product of the electrode reaction is an organic material;
Including
The lithium ion secondary battery and the organic active material secondary battery are connected in series ,
The secondary battery system, wherein the second active material is a compound containing 2,2,6,6-tetramethylpiperidine-N-oxyl radical in the molecular structure .   A plurality of the lithium ion secondary batteries are connected in series, and a predetermined lithium ion secondary battery and the organic active material secondary battery among the plurality of lithium ion secondary batteries are connected in series. The secondary battery system according to claim 1. The secondary battery system according to claim 1 or 2, wherein a reaction product or product of an electrode reaction of the second active material of the organic active material secondary battery is a neutral radical compound.   The secondary battery system according to claim 3, wherein the neutral radical compound is a nitroxyl radical-based stable radical compound.   The secondary battery system according to claim 4, wherein the nitroxyl radical-based stable radical compound is a compound containing 2,2,6,6-tetramethylpiperidine-N-oxyl radical in the molecular structure. . 6. The secondary battery system according to claim 1 , wherein the number of the lithium ion secondary batteries is larger than the number of the organic active material secondary batteries. The number of the lithium ion secondary battery is characterized in that the the proportion of 100 or less for one organic active material secondary battery, the secondary according to any one of claims 1 to 6 Battery system.

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