KR20130108275A - Battery assembly - Google Patents

Abstract

The present invention provides an assembled battery in which deterioration of battery performance due to overdischarge does not occur even without using a protection circuit. The present invention relates to a battery unit in which a plurality of unit cells are connected to each other, wherein the unit cell is a sodium ion secondary battery having a positive electrode, a negative electrode, and an electrolyte containing a positive electrode active material capable of doping and dedoping sodium ions.

Description

Battery pack {BATTERY ASSEMBLY}

The present invention relates to a battery assembly in which a plurality of unit cells are connected in series and / or in parallel.

Among the nonaqueous electrolyte secondary batteries, the lithium ion secondary battery is usually LiMO in the positive electrode.₂ It is a secondary battery using oxides, such as (M is transition metals, such as Co, Mn, and Ni), and the compound of low electric potentials, such as a carbon material and lithium, as a negative electrode. Recently, a battery pack in which a plurality of unit cells are connected in series and / or in parallel as a power source for an electric vehicle, a power leveling power source, or the like is used. In particular, in order to obtain high capacity at a high voltage, a lithium secondary battery is often used as such a secondary battery. have. The unit cells constituting the assembled battery come in various forms such as cylindrical, rectangular, and laminate.

By the way, commercially available lithium ion secondary batteries (single cells) are usually used in the range of 3 to 4 V so that battery performance does not deteriorate. Discharge (over-discharge) greatly deteriorates the characteristics of the lithium ion secondary battery.

In particular, when the battery voltage falls below a predetermined lower limit voltage due to overdischarge, copper current may be eluted from the current collector of the negative electrode, resulting in poor current collection with the negative electrode active material, deterioration of the positive electrode due to excessive insertion of lithium ions into the positive electrode, There is a problem that capacity decreases by alloying aluminum, which is a current collector of a positive electrode material.

In the case of charging or discharging a plurality of lithium ion secondary batteries (single cells) in series, the battery voltage is balanced by the capacity difference or internal resistance difference of each battery, and even if the battery voltage of the entire battery pack is within a predetermined range, Some of the unit cells constituting the may become an overcharged state or an overdischarged state.

For example, when discharging an assembled battery in which three single cells of a lithium ion secondary battery having a lower limit voltage of 3.0 V are connected in series, the assembled battery is discharged so that the total battery voltage is 9.0 V. At this time, when the capacity of the three unit cells is not the same, some unit cells may be 3.0 V or less, and other unit cells may be 3.0 V or more. A unit cell with a voltage of 3.0 V or less becomes overdischarged and battery performance is significantly reduced.

In order to avoid the problem of overdischarge in such a battery pack, the battery pack is usually provided with a temperature sensor for detecting the temperature of each unit cell, a voltmeter for detecting the voltage of each unit cell, etc., in addition to the unit cell. Moreover, it is known to provide the control apparatus with the temperature and voltage detected by these temperature sensors and a voltmeter through a signal line, and to control an assembled battery by a control apparatus (for example, refer Unexamined-Japanese-Patent No. 3773350). ).

Each sensor and control device is an electronic circuit component necessary not only to control the end condition of charge / discharge of the assembled battery, but also to avoid overcharge and overdischarge of the unit cells constituting the assembled battery.

Japanese Patent No. 3773350

However, when each sensor and control device is installed in the assembled battery, a problem arises in that the total volume of the assembled battery becomes large and the energy density in the assembled battery decreases. In particular, when the number of unit cells constituting the assembled battery increases, the cost of the assembled battery is also greatly increased.

Under these circumstances, an object of the present invention is to provide an assembled battery in which deterioration of battery performance due to over discharge is hardly generated even without using a protection circuit.

The present invention is as follows.

<1> An assembled battery in which a plurality of unit cells are connected to each other, wherein the unit cells are sodium ion secondary batteries having a positive electrode, a negative electrode, and an electrolyte containing a positive electrode active material capable of doping and dedoping sodium ions.

The assembled battery as described in said <1> whose <2> above-mentioned positive electrode active material is a sodium transition metal compound which can dope and dedope sodium ions.

<3> The assembled battery according to <2>, wherein the sodium transition metal compound is an oxide represented by NaM ¹ O ₂ (M ¹ represents one or more transition metal elements).

The assembled battery in any one of said <1> to <3> containing <4> at least 1 parallel connection.

According to the present invention, there is provided an assembled battery in which deterioration of battery performance due to overdischarge does not occur even without using a protection circuit.

The assembled battery of the present invention is a battery in which a plurality of unit cells (hereinafter, simply referred to as "unit cells") including a sodium ion secondary battery are connected. The plurality of unit cells are electrically connected to each other.

Hereinafter, a unit cell serving as a structural unit of the assembled battery of the present invention includes a positive electrode capable of doping and dedoping sodium ions, a negative electrode capable of doping and dedoping sodium ions, and an electrolyte. It has a separator to separate.

Hereinafter, the component in a unit cell is demonstrated.

(1) positive electrode

The positive electrode is composed of a positive electrode current collector and a positive electrode mixture supported on the positive electrode current collector. The positive electrode mixture contains a positive electrode active material and, if necessary, a conductive material or a binder.

Examples of the positive electrode active material include doped and dedoped sulfides such as TiS ₂ , oxides such as Fe ₃ O ₄ , sulfates such as Fe ₂ (SO ₄ ) ₃ , phosphates such as FePO _4, and fluorides such as FeF ₃ . Although it may be a material which can be used, it is especially preferable that it is a sodium transition metal compound which is a compound of sodium and a transition metal element. In addition, the transition metal element in a sodium transition metal compound can be selected arbitrarily, 1 or more types, Specifically, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, etc. are mentioned.

As a sodium transition metal compound, for example

An oxide represented by Na _x M ¹ O _y (M ¹ represents one or more transition metal elements, and x and y are values satisfying 0.4 <x <2 and 1.9 <y <2.1);

Silicates represented by Na _b M ² _c Si ₁₂ O ₃₀ , such as Na ₆ Fe ₂ Si ₁₂ O ₃₀ and Na ₂ Fe ₅ Si ₁₂ O ₃₀ (M ² represents one or more transition metal elements, and b and c represent 2 ≤ b ≤ 6, 2 ≤ c ≤ 5);

Silicates represented by Na _d M ³ _e Si ₆ O ₁₈ , such as Na ₂ Fe ₂ Si ₆ O ₁₈ and Na ₂ MnFeSi ₆ O ₁₈ (M ³ represents one or more transition metal elements, and d and e represent 3 ≦ d 6, 1 ≦ e ≦ 2;

Silicate represented by Na _f M ⁴ _g Si ₂ O ₆ , such as Na ₂ FeSiO ₆ (M ⁴ represents at least one element selected from the group consisting of transition metal elements, Mg, and Al, and f and g are 1 ≦ f ≤ 2, 1 ≤ g ≤ 2);

NaFePO _4, NaMnPO _4, NaNiPO ₄ such as a phosphate represented by the NaM ⁶ _a PO ₄ (M ⁶ represents a transition metal element at least one);

Phosphates such as Na ₃ Fe ₂ (PO ₄ ) ₃ ;

Sulfates such as NaFeSO ₄ F;

Borate salts such as NaFeBO ₄ and Na ₃ Fe ₂ (BO ₄ ) ₃ ;

Fluorides represented by Na _h M ⁵ F ₆ , such as Na ₃ FeF ₆ and Na ₂ MnF ₆ (M ⁵ represents one or more transition metal elements, and h is a value satisfying 2 ≦ h ≦ 3)

These can be mentioned, These can be used 1 type or in mixture of 2 or more types.

Among them, preferably in the oxide represented by NaM ¹ O ₂ (M ¹ represents a transition metal element at least one). A preferred specific example, NaMnO ₂ having a structure of α-NaFeO ₂ type, ₂ and NaNiO NaCoO ₂ and _{NaFe 1 -pq Mn p Ni q O} 2 (p, q is a value satisfying the following relationship, 0≤p + q Oxides such as ≦ 1, 0 ≦ p ≦ 1, and 0 ≦ q ≦ 1).

As said sodium transition metal compound, a part of said transition metal element can also be substituted by metal elements other than the said transition metal element in the range which does not impair the effect of invention significantly. By substitution, the characteristic of the assembled battery of this invention may improve. Examples of metals other than the transition metal elements include Li, K, Ag, Mg, Ca, Sr, Ba, Al, Ga, In, Zn, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Metal elements, such as Ho, Er, Tm, Yb, and Lu, are mentioned.

What is necessary is just to be a thing with high electroconductivity and to be easy to process into a thin film as a positive electrode electrical power collector, and metals, such as Al, Ni, stainless steel, Cu, etc. can be used. Examples of the shape of the positive electrode current collector include thin, flat, mesh, net, lath, punched metal, or embossed, or a combination thereof (for example, a mesh flat). have.

As the conductive material, a carbon material can be used, and examples of the conductive material include fibrous carbon materials such as graphite powder, carbon black, and carbon nanotubes.

<Binder>

As a binder used for the said positive electrode, the polymer of a fluorine compound is mentioned, for example. As a fluorine compound, For example, fluorinated alkyl (C1-C18) (meth) acrylate, perfluoroalkyl (meth) acrylate [For example, perfluoro dodecyl (meth) acrylate, perfluoro n Octyl (meth) acrylate, perfluoro n-butyl (meth) acrylate];

Perfluoroalkyl substituted alkyl (meth) acrylates [eg, perfluorohexylethyl (meth) acrylate and perfluorooctylethyl (meth) acrylate];

Perfluorooxyalkyl (meth) acrylates [eg, perfluorododecyloxyethyl (meth) acrylate and perfluorodecyloxyethyl (meth) acrylate];

Fluorinated alkyl (C18 to C18) crotonates;

Fluorinated alkyl (1-18 carbon atoms) maleate and fumarate;

Fluorinated Alkyl (C18 to C18) Itaconate and Fluorinated Alkyl Substituted Olefin (C2 to C10, C1 to C17) [For example, perfluorohexylethylene, tetrafluoroethylene, trifluoro Ethylene, polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), and hexafluoropropylene].

As an example other than the polymer of the fluorine compound of a binder, the addition polymer of the monomer containing the ethylenic double bond which does not contain a fluorine atom is mentioned. As such a monomer, it is (cyclo) alkyl (C1-C22) (meth) acrylate [for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate and octadecyl (meth) acrylate ];

Aromatic ring-containing (meth) acrylates [eg, benzyl (meth) acrylate and phenylethyl (meth) acrylate];

Mono (meth) acrylate of alkylene glycol or dialkylene glycol (C2-4 of an alkylene group) [for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate And diethylene glycol mono (meth) acrylate];

(Poly) glycerol (polymerization degree 1 to 4) mono (meth) acrylate;

Polyfunctional (meth) acrylates [eg, (poly) ethylene glycol (polymerization degree 1 to 100) di (meth) acrylate, (poly) propylene glycol (polymerization degree 1 to 100) di (meth) acrylate, 2, (Meth) acrylic acid ester monomers such as 2-bis (4-hydroxyethylphenyl) propanedi (meth) acrylate and trimethylolpropane tri (meth) acrylate];

(Meth) acrylamide monomers, such as (meth) acrylamide and (meth) acrylamide derivatives [for example, N-methylol (meth) acrylamide and diacetone acrylamide];

Cyano group-containing monomers such as (meth) acrylonitrile, 2-cyanoethyl (meth) acrylate and 2-cyanoethylacrylamide;

Styrene monomers such as styrene and styrene derivatives having 7 to 18 carbon atoms (for example, α-methylstyrene, vinyltoluene, p-hydroxystyrene and divinylbenzene);

Diene monomers such as alkadienes having 4 to 12 carbon atoms (for example, butadiene, isoprene and chloroprene);

Carboxylic acid (2 to 12 carbon atoms) vinyl esters [for example, vinyl acetate, vinyl propionate, vinyl butyrate and vinyl octanoate];

Alkenyl ester monomers such as carboxylic acid (2 to 12 carbon atoms) (meth) allyl ester [for example, acetic acid (meth) allyl, propionic acid (meth) allyl and octanoic acid (meth) allyl];

Epoxy group-containing monomers such as glycidyl (meth) acrylate and (meth) allyl glycidyl ether;

Monoolefins of monoolefins (2 to 12 carbon atoms) [for example, ethylene, propylene, 1-butene, 1-octene and 1-dodecene];

Chlorine, bromine or iodine atom containing monomers;

Halogen atom-containing monomers other than fluorine such as vinyl chloride and vinylidene chloride;

(Meth) acrylic acid, such as acrylic acid and methacrylic acid;

And conjugated double bond-containing monomers such as butadiene and isoprene.

Moreover, copolymers, such as an ethylene vinyl acetate copolymer, a styrene butadiene copolymer, or an ethylene propylene copolymer, may be sufficient as an addition polymer, for example. In addition, the carboxylic acid vinyl ester polymer may be partially or completely saponified. The binder may be a copolymer of a fluorine compound and a monomer containing an ethylenic double bond containing no fluorine atom.

Other examples of the binder include polysaccharides and derivatives thereof such as starch, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl hydroxyethyl cellulose and nitrocellulose; Phenolic resin; Melamine resin; Polyurethane resin; Urea resin; Polyamide resins; Polyimide resin; Polyamideimide resin; Petroleum pitch; Coal pitch is mentioned.

Especially as a binder, the polymer of a fluorine compound is preferable, and polytetrafluoroethylene which is a polymer of tetrafluoroethylene is especially preferable. Moreover, the above-mentioned multiple types of binder can also be used as a binder. In addition, in the application | coating process to a positive electrode electrical power collector, a thickener or a viscosity reducer can also be used in order to make application to a positive electrode electrical power collector easy.

As a method of supporting the positive electrode mixture on the positive electrode current collector, a method of press molding or a method of pasting using an organic solvent or the like to apply a paste onto the positive electrode current collector, drying and pressing, etc. may be mentioned. As a method of apply | coating a positive mix to a positive electrode electrical power collector, the slit die coating method, the screen coating method, the bar coating method, etc. are mentioned, for example.

(2) negative electrode

The negative electrode may have a material capable of doping and dedoping sodium ions at a potential lower than that of the positive electrode, and examples thereof include an electrode in which a negative electrode mixture containing a negative electrode material is supported on a negative electrode current collector, or an electrode made of a negative electrode material alone. . Examples of the negative electrode material include carbon materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, or alloys, and materials capable of doping and dedoping sodium ions at a potential lower than that of the positive electrode. In addition, these negative electrode materials can also be mixed and used.

The said negative electrode material is illustrated below. Specifically, as the carbon material, doping and dedoping of sodium ions at a potential lower than that of the positive electrode among graphites such as natural graphite and artificial graphite, coke, carbon black, pyrolytic carbon, carbon fiber, and organic polymer compound fired body Possible materials are mentioned. These carbon materials, oxides, sulfides and nitrides may be used in combination, or may be either crystalline or amorphous. In addition, these carbon materials, oxides, sulfides and nitrides are mainly supported on the negative electrode current collector and used as the negative electrode.

The shape of the carbon material may be, for example, flaky like natural graphite, spherical like mesocarbon microbeads, fibrous like graphitized carbon fiber, or fine powder aggregates.

Moreover, sodium metal, a silicon metal, a tin metal is mentioned specifically as said metal which can do the doping and dedoping of sodium ion at the electric potential lower than a positive electrode. Further, as the alloy capable of doping and dedoping sodium ions at a potential lower than that of the positive electrode, sodium alloys such as Na-Al, Na-Ni, Na-Si, silicon alloys such as Si-Zn, Sn-Mn, and Sn- More tin alloy such as Co, Sn-Ni, Sn- Cu, Sn-La, can also include alloys such as _{Cu 2 Sb, La 3 Ni 2} Sn 7. These metals and alloys are mainly used alone as a negative electrode (for example, in a thin phase).

The said negative electrode mixture may contain a binder as needed. A thermoplastic resin is mentioned as a binder, Specifically, the thing similar to the binder used for positive electrodes, such as PVdF, a thermoplastic polyimide, carboxymethylcellulose, polyethylene, a polypropylene, is mentioned. In the case where the electrolyte solution does not contain ethylene carbonate which will be described later, when the negative electrode mixture containing polyethylene carbonate is used, the cycle characteristics and the large current discharge characteristics of the obtained battery may be improved.

Cu, Ni, stainless steel, etc. are mentioned as a negative electrode electrical power collector, Cu is preferable at the point which is difficult to form an alloy with sodium, and is easy to process into a thin film.

Examples of the shape of the negative electrode current collector include thin, flat, mesh, net, lath, punched metal, embossed, or combinations thereof (for example, mesh-like flat plates). have. Unevenness by etching may be formed on the surface of the negative electrode current collector.

(3) electrolyte

Next, the electrolyte will be described. Examples of the electrolyte include NaClO ₄ , NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN (SO ₂ CF ₃ ) ₂ , lower aliphatic carboxylate, NaAlCl ₄ , and the like. Mixtures of species or more may be used. Among these, it is preferred to use in that it comprises at least one member selected from the group consisting of _{NaPF 6, NaAsF 6, NaSbF 6} , NaBF 4, NaCF 3 SO 3 and NaN (SO ₂ CF _{3) 2} containing fluorine. In the present invention, the electrolyte is preferably used as a state (liquid) dissolved in an organic solvent, that is, as a nonaqueous electrolyte.

Examples of the organic solvent in the nonaqueous electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, and vinylene carbonate. Carbonates such as nate, 4-trifluoromethyl-1,3-dioxolan-2-one and 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethylether, 2,2,3,3-tetrafluoropropyldifluoromethylether, tetrahydrofuran, 2-methyltetrahydro Ethers such as furan; Esters such as methyl formate, methyl acetate and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; Amides such as N, N-dimethylformamide and N, N-dimethylacetamide; Carbamates such as 3-methyl-2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propanesultone; Or what introduce | transduced the fluorine substituent further into the said organic solvent can be used. As an organic solvent, you may mix and use 2 or more types in these.

The concentration of the electrolyte in the nonaqueous electrolyte is usually about 0.1 mol / L to 2 mol / L, and preferably about 0.3 mol / L to 1.5 mol / L.

In the present invention, the electrolyte may be used as a polymer electrolyte in which the nonaqueous electrolyte is retained in the polymer compound, that is, as a gel electrolyte or as a solid electrolyte. As a solid electrolyte, the organic solid electrolyte which hold | maintained the said electrolyte in the high molecular compound containing at least 1 sort (s) of a polyethylene oxide type high molecular compound, a polyorganosiloxane chain, or a polyoxyalkylene chain can be used, for example. In addition, Na ₂ S-SiS ₂ , Na ₂ S-GeS ₂ , NaTi ₂ (PO ₄ ) ₃ , NaFe ₂ (PO ₄ ) ₃ , Na ₂ (SO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₂ (PO ₄ ), Fe ₂ (MoO ₄ ) ₃ , inorganic solid electrolytes such as β-alumina, β ″ -alumina and NASICON may be used.

(4) Separator

As the separator, for example, a material having a form such as a porous film, a nonwoven fabric, a woven fabric, or the like containing a material such as polyolefin resin such as polyethylene or polypropylene, a fluorine resin or a nitrogen-containing aromatic polymer can be used. It can also be set as a separator using 2 or more types, and the said material may be laminated | stacked. As a separator, the separator as described in Unexamined-Japanese-Patent No. 2000-30686, Unexamined-Japanese-Patent No. 10-324758, etc. are mentioned, for example. The thickness of the separator is preferably as thin as the mechanical strength is maintained in that the volume energy density of the battery becomes high and the internal resistance becomes small. The thickness of the separator is usually about 5 to 200 m, preferably about 5 to 40 m.

The separator preferably has a porous film containing a thermoplastic resin. In a sodium secondary battery, it is usually important to cut off the current when the abnormal current flows in the battery due to a short circuit between the positive electrode and the negative electrode, and to prevent the excessive current from flowing (shut down). Therefore, the separator should be shut down at a low temperature as far as possible when the normal operating temperature is exceeded (if the separator has a porous film containing a thermoplastic resin) and the micropores of the porous film are shut off, and then to some extent after shutdown. Even if the temperature inside the battery rises to a high temperature, it is not likely to be ruptured by the temperature, and it is required to maintain the shut down state, in other words, to have high heat resistance.

As a separator, by using the separator containing the laminated porous film which laminated | stacked the heat-resistant porous layer containing a heat resistant resin, and the porous film containing a thermoplastic resin, it becomes possible to prevent a heat wave film further. Here, the heat resistant porous layer may be laminated on both surfaces of the porous film.

A single cell can be manufactured by impregnating the electrolyte group containing the organic solvent containing electrolyte after accommodating the electrode group obtained by laminating | stacking and winding the positive electrode, the separator, and the negative electrode mentioned above in a container, such as a battery tube.

As a shape of the said electrode group, the shape in which the cross section at the time of cut | disconnecting this electrode group in the direction perpendicular | vertical to the axis | shaft of a winding is a circle, an ellipse, a rectangle, a rounded rectangle, etc. are mentioned, for example. Moreover, as a shape of a battery, shapes, such as a paper type, coin type, cylinder shape, a square, are mentioned, for example.

(Battery pack)

The assembled battery of the present invention is formed by connecting a plurality of unit cells using the unit cells described above as a structural unit, connecting the unit cells only in series, connecting the unit cells only in parallel, and combining the unit cells in series and parallel connection. It includes everything that is connected. The unit cell has a variety of forms, such as cylindrical, rectangular, laminate.

It is preferable that the assembled battery of the present invention includes at least one parallel connection in order to make it less likely to cause deterioration due to over discharge. Moreover, it is more preferable that the group of cells including at least one parallel connection and having a parallel relationship have the same number of unit cells.

(connect)

Busbars, leads, rings, nuts, etc. made of metals such as copper, nickel, aluminum, or alloys thereof may be used for the connection between the unit cells, but any metal other than these may be used to achieve the object of the present invention. It does not specifically limit because it becomes.

As the welding method thereof, spot welding, ultrasonic vibration welding, or the like can be used.

(arrangement)

In the assembled battery of the present invention, a battery group in which a plurality of unit cells are connected in series or in parallel is housed in a case.

It is preferable that the said case contains synthetic resin, such as polypropylene, from a viewpoint of weight reduction of an assembled battery and ensuring strength.

It is preferable that the case has an air inlet and an air outlet. By providing an air inlet and an air outlet, the release of heat inside the assembled battery is promoted, and an abnormal temperature rise of the assembled battery can be avoided. In addition, it is possible to further reduce the overheating of the assembled battery by promoting the circulation of air inside the assembled battery using a cooling fan.

Moreover, it is also possible to indirectly radiate the inside of an assembled battery by radiating the heat of the exterior case of an assembled battery with a cooling apparatus, such as a cooling fan.

(Circuit member)

The battery pack according to the present invention may be provided with a temperature sensor for detecting the temperature of each unit cell, a voltmeter for detecting the voltage of each unit cell, and the like, as necessary. Moreover, you may have a control apparatus which controls an assembled battery based on the information of the temperature and voltage detected by these temperature sensors and a voltmeter.

The assembled battery may have a control device for preventing overcharging and overdischarging of the battery. By having the said control apparatus, overcharge and overdischarge of a battery can be prevented and the life of a battery can be improved. In addition, in the assembled battery in the present invention, an overdischarge prevention device is not necessarily required.

Example

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is changed.

Comparative Example 1

(1) Production of the positive electrode

Lithium hydroxide (LiOH: manufactured by Wako Junyaku Kogyo Co., Ltd .: purity of 95% or more), nickel oxide (II) (NiO: manufactured by Kogaku Chemical Co., Ltd., manufactured by Kagaku Gensho Show: purity: 99%), cobalt oxide (II, III ) (Co ₃ O ₄ : Co., Ltd. Kogaku Kengku Gensho Show: Purity 90% or more), the Li: Ni: Co molar ratio is 1: 0.8: 0.2 and weighed for 4 hours using a dry ball mill. Mixing over gave a raw material mixture. Charging the obtained raw material mixture in an alumina boat, and by heating in an oxygen atmosphere using an electric furnace maintained at 750 ℃ over a period of 6 hours to obtain a positive electrode active material A ^1. In addition, using acetylene black (manufactured by Denki Chemical Co., Ltd.) as a conductive agent and PVdF (manufactured by Kureha Co., Ltd.) as a binder, the positive electrode active material A ¹ , the conductive agent and the binder were used as the positive electrode active material A ^1. : Conductor: Binder = 85: 10: 5 (weight ratio), each weighed so as to have a composition to obtain a positive electrode mixture. First, the positive electrode active material A ¹ and the conductive agent are sufficiently mixed with an agate mortar, and N-methyl-2-pyrrolidone (NMP: manufactured by Tokyo Kasei Kogyo Co., Ltd.) is appropriately added, followed by addition of PVdF. The mixture was mixed so as to be uniform to obtain a slurry. The obtained slurry was apply | coated to the thickness of 100 micrometers using an applicator on the aluminum foil of thickness 40 micrometers which is a positive electrode electrical power collector, and this was put into a drier, and it dried sufficiently, removing NMP, and obtained the positive electrode sheet. The positive electrode sheet was consolidated using a roll press. Also, the Al foil welded by an ultrasonic welding machine, and to do this as an electrode lead wire to obtain a positive electrode B ^1.

(2) production of negative electrode

Using natural graphite and artificial graphite as negative electrode materials, PVdF (manufactured by Kureha Co., Ltd.) as a binder was weighed so that the weight ratio of natural graphite: artificial graphite: binder was 58.8: 39.2: 2 to obtain a negative electrode mixture, dissolving the binder in the solvent, NMP, was added to the carbon material C ¹ is applied to a slurry to a 100 ㎛ thickness by an applicator on a copper foil of the negative electrode current collector having a thickness of 10 ㎛, and put it in the dryer to remove the NMP The negative electrode sheet was obtained by drying sufficiently, making it dry. The negative electrode sheet was consolidated using a roll press. In addition, welding the Ni foil by ultrasonic welding, and to do this as an electrode lead wire to obtain a negative electrode D ^1.

(3) Production of unit cell

The positive electrode B ¹ was placed on the side where the positive electrode mixture was applied upward, and the polypropylene porous membrane (thickness 20 μm) as a separator and the side on which the negative electrode mixture was applied were laminated downward to be the negative electrode D ¹ to obtain an electrode group. . The electrode group was inserted into a battery case (Al laminate pack) containing a 10 μm thick film.

A non-aqueous electrolyte was prepared by dissolving LiPF ₆ in a ratio of 1.5 mol / L in an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate. By the vacuum laminating sealing injected into the non-aqueous electrolyte in a battery case after the electrode group is inserted, and to prepare a sodium ion secondary battery E ^1. In addition, the assembly of the test battery was performed in the glove box of argon atmosphere. The weight was combined so that the charging capacity of the negative electrode per unit area became 1 or more and 2 or less with respect to the charging capacity of the positive electrode per unit area.

Here, "the charge capacity of a positive electrode per unit area" means charging with a constant current to 4.2V (relative to a lithium counter electrode) at a current value of 0.1 C, and calculating the charge capacity per unit area by such a charge. In addition, "the charge capacity of a negative electrode per unit area" means charging with a constant current to 0.5 mV (relative to a lithium counter electrode) with a current value of 0.05 C, and calculates the charge capacity per unit area by such a charge.

(4) fabrication of battery pack

The same batteries E ² , E ³ , E ⁴ , and E ⁵ as in lithium ion secondary battery E ¹ were produced, and all were connected in parallel to obtain assembled battery F ¹ .

The constant current charge / discharge test was performed under the following conditions.

Charge / discharge condition:

Charging performed CC (constant current: constant current) charging to 0.1V at 0.1 C rate (speed of full charge in 10 hours). The discharge was carried out at the same rate as the charging rate described above, and cut off at a voltage of 3.0V. Charging and discharging after the next cycle were performed at the same speed as the above charging rate, and were cut off at the charge voltage of 4.2 V and the discharge voltage of 3.0 V as in the first cycle. A total of 10 cycles of charge / discharge tests were performed, and the discharge capacity of the 10th cycle was made into discharge capacity 1.

Over discharge condition:

Charging performed CC charging at 0.1 C rate to 4.2V using the battery which performed 10 cycles. The discharge was subjected to CC discharge to a voltage of 0.01 V at the same rate as the charging rate, followed by 100 h of CV (constant voltage: constant voltage) discharge at a voltage of 0.01 V. Charging and discharging after the next cycle were performed at the same speed as the above charging rate, and CC charging and discharging was performed by cutting off at 4.2 V of charging voltage and 3.0 V of discharge voltage. The charge and discharge test after overdischarge was repeated three cycles in total.

The assembled battery F ¹ was subjected to the constant current charge / discharge test and the overdischarge test under the above charge / discharge conditions, and the retention rate of the discharge capacity of each cycle was measured.

Discharge capacity retention rate (%) = discharge capacity / discharge capacity 1 * 100

As a result, after the overdischarge, the discharge capacity retention rate drastically decreased.

Example 1

(1) Production of the positive electrode

Sodium carbonate (Na ₂ CO ₃ : Wako Junyaku Kogyo Co., Ltd .: purity 99.8%), manganese oxide (IV) (MnO ₂ : Kabukishi Kagaku Genshusho manufacture: purity 99.9%), iron oxide (II, III) (Fe ₃ O _4: whether or sikki manufactured gojyun FIG Chemical Gen kkyusyo prepared: purity: 99%), and nickel oxide (II) (NiO: whether or sikki manufactured gojyun FIG Chemical Gen kkyusyo manufactured by using the 99% pure) Then, the molar ratio of Na: Mn: Fe: Ni was 1: 0.4: 0.2: 0.4, and the mixture was mixed with a dry ball mill over 4 hours to obtain a raw material mixture. Obtained by charging the raw material mixture in an alumina boat, heated in an air atmosphere by using an electric furnace and maintained throughout at 900 ℃ for 6 hours, and the positive electrode active material ^{_{A 2 (NaMn 0 .4 Fe 0}} .2 Ni 0 .4 O 2) Got. In addition, using acetylene black (manufactured by Denki Chemical Co., Ltd.) as a conductive agent and PVdF (manufactured by Kureha Co., Ltd.) as a binder, the positive electrode active material A ² , the conductive agent and the binder were used as the positive electrode active material A ^2. : Conductive agent: Binder = It was weighed so that it might become a composition of 85: 10: 5 (weight ratio), respectively, and the positive mix was obtained. First, the positive electrode active material A ² and the conductive agent are sufficiently mixed with agate induction, and an appropriate amount of N-methyl-2-pyrrolidone (NMP: manufactured by Tokyo Kasei Kogyo Co., Ltd.) is added thereto, followed by addition of PVdF. The slurry was obtained by mixing to be uniform. The obtained slurry was apply | coated to the thickness of 100 micrometers using an applicator on the aluminum foil of 40 micrometers thickness which is a positive electrode collector, this was put into a drier, and it dried sufficiently, removing NMP, and the positive electrode sheet was obtained. The positive electrode sheet was consolidated using a roll press. Also, the Al foil welded by an ultrasonic welding machine, and by this to obtain a positive-electrode lead wire B ^2.

(2) production of negative electrode

Resorcinol and benzaldehyde were polymerized.

Into a four-necked flask, 200 g of resorcinol, 1.5 L of methyl alcohol, and 194 g of benzaldehyde were added and cooled with ice, and 36.8 g of 36% hydrochloric acid was added dropwise while stirring. It heated up at 65 degreeC after completion | finish of dripping, and kept warm at the same temperature after that for 5 hours. 1 L of water was added to the obtained polymerization reaction mixture, and the precipitate was collected by filtration, washed with water until the filtrate became neutral, and dried, followed by tetraphenylcalix [4] resorcinene (hereinafter sometimes referred to as PCRA). g was obtained. PCRA was put into a rotary kiln, the atmosphere was made into an air atmosphere, and it heated at 300 degreeC for 1 hour, Subsequently, the atmosphere of a rotary kiln was substituted by argon, and it heated at 1000 degreeC for 4 hours. Next, the carbon material C ² was obtained as a negative electrode active material by grinding with a ball mill (agate ball, 28 rpm, 5 minutes). The carbon material C ² and PVdF as a binder are weighed to have a composition of carbon material C ² : binder = 95: 5 (weight ratio) to obtain a negative electrode mixture, and the binder is dissolved in NMP, which is a solvent, and then carbon material C ² The slurry which was added and slurried was apply | coated in thickness of 100 micrometers using the applicator on the copper foil of thickness 10 micrometers which is a negative electrode collector, this was put into a drier, and it dried sufficiently, removing NMP, and the negative electrode sheet was obtained. The negative electrode sheet was consolidated using a roll press. In addition, welding the Ni foil by ultrasonic welding, and to do this as an electrode lead wire to obtain a negative electrode D ^2.

(3) Production of unit cell

The electrode group was obtained by laminating the aluminum foil downward so that the positive electrode B ² was disposed, the polypropylene porous membrane (thickness 20 μm) as a separator, and the copper foil upward so as to be the negative electrode D ² . The electrode group was inserted into a battery case (Al laminate pack) containing a 10 μm thick film.

Injecting the electrolyte solution NaClO ₄ / propylene carbonate, a non-aqueous electrolyte is 1 M as in a battery case after inserting the electrode assembly, and by a vacuum laminate sealed to prepare a sodium ion secondary battery E ^6. In addition, the assembly of the test battery was performed in the glove box of argon atmosphere. The weight was combined so that the charging capacity of the negative electrode per unit area was 1 or more and 2 or less, preferably 1.0 or more and 1.2 or less, more preferably 1.0 or more and 1.1 or less with respect to the charging capacity of the positive electrode per unit area.

Here, "the charge capacity of a positive electrode per unit area" means charging to 4.0 V (relative to a sodium counter electrode) by a constant current with a current value of 0.1 C, and calculating the charge capacity per unit area by such a charge. In addition, "the charge capacity of a negative electrode per unit area" means charging with a constant current to 0.5 mV (relative to a sodium counter electrode) at a current value of 0.05 C, and calculates the charge capacity per unit area by such a charge.

(4) fabrication of battery pack

The same batteries E ⁷ , E ⁸ , E ⁹ , and E ¹⁰ as in sodium ion secondary battery E ⁶ were produced, and all were connected in parallel to obtain assembled battery F ² .

The constant current charge / discharge test was performed under the following conditions.

Charge / discharge condition:

Charging performed CC (constant current: constant current) charging at 0.1 C rate (speed of full charge in 10 hours) to 4.0V. The discharge was carried out at the same rate as the above charging rate and interrupted at a voltage of 1.5V. Charging and discharging after the next cycle were performed at the same speed as the above charging rate, and were cut off at a charge voltage of 4.0 V and a discharge voltage of 1.5 V as in the first cycle. A total of 10 cycles of charge / discharge tests were performed, and the discharge capacity of the 10th cycle was made into discharge capacity 1.

Over discharge condition:

The battery which carried out 10 cycles was charged by CC charging at 0.1 C rate to 4.0V. The discharge was subjected to CC discharge to a voltage of 0.01 V at the same rate as the charging rate, followed by 100 h of CV (constant voltage: constant voltage) discharge at a voltage of 0.01 V. Charging and discharging after the next cycle were performed at the same speed as the above charging rate, and CC charging and discharging was performed by cutting off at a charge voltage of 4.0 V and a discharge voltage of 1.5 V. The charge and discharge test after overdischarge was repeated three cycles in total.

With respect to the battery F ^2, subjected to the charging and discharging conditions, a constant current charging and discharging test, the over-discharge test, and measuring the retention rate of discharge capacity at each cycle.

Discharge capacity retention rate (%) = discharge capacity / discharge capacity 1 * 100

As a result, the discharge capacity retention rate did not decrease as compared with Comparative Example 1 even after overdischarge.

Example 2

(1) Production of the positive electrode

In a polypropylene beaker, 120 g of potassium hydroxide was added to 700 mL of distilled water and dissolved by stirring to prepare an aqueous potassium hydroxide solution (precipitant aqueous solution). In a separate polypropylene beaker, 100 g of iron (II) sulfate, 71.0 g of nickel (II) sulfate, and 65.1 g of manganese (II) sulfate pentahydrate were added to 700 mL of distilled water and dissolved by stirring. A mixed aqueous solution containing, iron, nickel and manganese was obtained. The slurry which produced the precipitate was obtained by adding the said mixed aqueous solution to this, stirring the said precipitant aqueous solution. Subsequently, the slurry was filtered, washed with distilled water, and the solids were recovered. The solid was dried at 100 ° C. to obtain a precipitate (molar ratio of Mn: Fe: Ni is 0.3: 0.4: 0.3). Using a precipitate and sodium hydroxide, the molar ratio of Na: Mn: Fe: Ni was 1: 0.3: 0.4: 0.3, and then dry mixed using an agate mortar to obtain a mixture. Then, into the mixture to the alumina sintering vessel, by using an electric furnace, maintained for 12 hours at 850 ℃ nitrogen atmosphere firing the mixture, cooled to room temperature, the positive electrode active material ^{_{A 3 (NaMn 0 .3 Fe 0}} . ₄ Ni _{0 .3} O ₂₎ was obtained.

The positive electrode active material A ³ , acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) and a binder (VT470, manufactured by Daikin Kogyo Co., Ltd.) as a conductive material were prepared as the positive electrode active material: conductive material: binder = 90: 5: Each was weighed so as to have a composition of 5 (weight ratio). After that, first, the positive electrode active material A ³ and the conductive material are sufficiently mixed with agate induction, and N-methyl-2-pyrrolidone (NMP: manufactured by Tokyo Kasei Kogyo Co., Ltd.) is added to the mixture, and a binder is further added. The mixture was added and mixed with agate mortar so as to be uniform, thereby obtaining a positive electrode mixture paste. The positive electrode mixture paste was applied to a thickness of 100 μm using an applicator on a 20 μm thick aluminum foil as a current collector. After drying the coated current collector at 60 degreeC for 2 hours, the electrode sheet was rolled at 0.5 MPa using the roll press (SA-602, Tester Sangyo Co., Ltd. product) using the roll press (SA-602, Tester Sangyo Co., Ltd. product). The electrode sheet was punched into a circular shape having a diameter of 1.45 cm with an electrode puncher, and vacuum dried at 150 ° C. for 8 hours to obtain positive electrodes B ³ and B ⁴ having slightly different weights per unit area. Weight per unit area refers to the weight of active substance per unit area.

(2) production of negative electrode

A negative electrode mixture paste was prepared using a carbon material C ³ (manufactured by Nippon Carbon Corporation, trade name: Nikka Biz ICB-0510) as a negative electrode active material, sodium polyacrylate (manufactured by Wako, polymerization degree 22,000 to 70,000) as a binder, and water as a solvent. It was. A binder aqueous solution prepared by dissolving the binder in water was prepared, weighed so as to have a composition of negative electrode active material C ³ : binder: water = 97: 3: 150 (weight ratio), and a dispermat (manufactured by VMA-GETZMANN) The mixture mixture was stirred and mixed to obtain a negative electrode mixture paste. The rotation conditions of the rotor blade were 2,000 rpm, and 5 minutes. The obtained negative electrode mixture paste was coated on copper foil using a doctor blade, dried at 60 ° C. for 2 hours, and then cut into an electrode having a width of 4 cm using a roll press (SA-602, manufactured by Tester Sangyo Co., Ltd.). The electrode sheet was obtained by rolling to 0.5 MPa using. The electrode sheet was punched into a circular shape having a diameter of 1.50 cm with an electrode puncher, and vacuum dried at 100 ° C. for 8 hours to obtain negative electrodes D ³ and D ⁴ that were slightly different in weight per unit area.

(3) Production of unit cell

Place the positive electrode B ³ with the aluminum foil facing downward in the recess of the lower part of the coin cell (manufactured by Hoosen Kabukishi Co., Ltd.) so that the polypropylene porous membrane (thickness 20 µm) as the separator and the negative electrode D ³ face the copper foil upward. by laminating, and injecting a non-aqueous NaClO ₄ / propylene carbonate electrolyte solution of 1 M as the caulking by combining the upper part was produced in the sodium ion secondary battery E ^11. In addition, the assembly of the test battery was performed in the glove box of argon atmosphere. In the same manner, sodium ion secondary battery E ¹² was obtained using positive electrode B ⁴ and negative electrode D ⁴ .

In sodium ion secondary battery E ¹¹ , the charging capacity of the negative electrode per unit area was 1.07 with respect to the charging capacity of the positive electrode per unit area. In sodium ion secondary battery E ¹² , the charging capacity of the negative electrode per unit area was 1.05 with respect to the charging capacity of the positive electrode per unit area.

Here, the "charging capacity of the positive electrode per unit area" is charged to a constant current of 4.0 V (relative to the sodium counter electrode) at a current value of 0.1 C (speed of full charge in 10 hours), and the charging capacity per unit area is calculated by this charging. I say that. In addition, "the charge capacity of the negative electrode per unit area" is charged to a constant current to 0.5 mV (relative to the sodium counter electrode) at a current value of 0.05 C (speed of full charge in 20 hours), and by this charging, the charge capacity per unit area is obtained. It is to calculate.

(4) fabrication of battery pack

Sodium ion secondary battery E ¹¹ and battery E ¹² were connected in parallel, and assembled battery F ³ was obtained.

The assembled battery F ³ was subjected to the constant current charge / discharge test under the following conditions.

Charge / discharge condition:

Charging performed CC (constant current: constant current) charging at 0.1 C rate to 4.0V. The discharge was carried out at the same rate as the above charging rate and interrupted at a voltage of 1.5V. Charging and discharging after the next cycle were performed at the same speed as the above charging rate, and were cut off at a charge voltage of 4.0 V and a discharge voltage of 1.5 V as in the first cycle. A total of 10 cycles of charge / discharge tests were performed, and the discharge capacity of the 10th cycle was made into discharge capacity 1.

Over discharge condition:

The battery which carried out 10 cycles was charged by CC charging at 0.1 C rate to 4.0V. The discharge was subjected to CC discharge to a voltage of 0.01 V at the same rate as the charging rate, followed by 100 h of CV (constant voltage: constant voltage) discharge at a voltage of 0.01 V. Charging and discharging after the next cycle were performed at the same speed as the above charging rate, and CC charging and discharging was performed by cutting off at a charge voltage of 4.0 V and a discharge voltage of 1.5 V. The charge and discharge test after overdischarge was repeated three cycles in total.

The assembled battery F ³ was subjected to the constant current charge / discharge test and the overdischarge test under the above charge and discharge conditions, and the retention rate of the discharge capacity of each cycle was measured.

Discharge capacity retention rate (%) = discharge capacity / discharge capacity 1 * 100

As a result, the discharge capacity retention rate of each cycle after overdischarge was 100%.

The battery pack according to the present invention has the effect that deterioration of battery performance due to overdischarge is unlikely to occur, and is useful as a power source for an electric vehicle, a power leveling power source, or the like.

Claims (4)

An assembled battery in which a plurality of unit cells are connected to each other,
An assembled battery according to claim 1, wherein the unit cell is a sodium ion secondary battery having a positive electrode, a negative electrode, and an electrolyte containing a positive electrode active material capable of doping and undoping sodium ions. The battery pack according to claim 1, wherein the positive electrode active material is a sodium transition metal compound capable of doping and dedoping sodium ions. The battery pack according to claim 2, wherein the sodium transition metal compound is an oxide represented by NaM ¹ O ₂ (M ¹ represents one or more transition metal elements). The battery pack according to any one of claims 1 to 3, comprising at least one parallel connection.