KR101440347B1 - Anode Having Multi-Layer Structure for Secondary Battery and Lithium Secondary Battery Including The Same - Google Patents

Abstract

The present invention relates to a negative electrode for a secondary battery having a multi-layer structure and a lithium secondary battery comprising the same, and more particularly, to a negative electrode for a secondary battery comprising a first negative electrode active material layer including a first negative electrode active material coated in contact with a surface of a current collector; And a second negative electrode active material layer coated on the first negative electrode active material layer and including a second negative electrode active material having a relatively high charge / discharge potential and relatively high hydrophilicity relative to the first negative electrode active material, And a lithium secondary battery including the negative electrode.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode for a secondary battery and a lithium secondary battery including the negative electrode. 2. Description of the Related Art Anode Having Multi-Layer Structure for Secondary Battery and Lithium Secondary Battery Including The Same [

The present invention relates to a negative electrode for a secondary battery having a multilayer structure and a lithium secondary battery including the negative electrode. More particularly, the present invention relates to a negative electrode for a secondary battery comprising a first negative electrode mixture layer containing a first negative electrode active material coated in contact with a surface of a current collector, And a second negative electrode active material layer coated on the first negative electrode active material layer and including a second negative electrode active material having a relatively high charge / discharge potential and relatively high hydrophilicity than the first negative electrode active material layer And a lithium secondary battery including the negative electrode.

The increase in the price of energy sources due to the depletion of fossil fuels, the increase of interest in environmental pollution, and the demand for environmentally friendly alternative energy sources are becoming indispensable factors for future life. Various researches on various power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, in the case of a lithium secondary battery, the demand for an energy source is rapidly increasing due to an increase in technology development and demand for a mobile device. Recently, the use of a lithium secondary battery as a power source for an electric vehicle (EV) and a hybrid electric vehicle , And the area of use is also expanding for applications such as power assisted power supply through gridization.

A lithium secondary battery used as a power source of an electric vehicle (EV) or a hybrid electric vehicle (HEV) has a high energy density and a characteristic capable of exhibiting a large output in a short period of time, and also, under severe conditions, It is inevitably required to have safety and long-term life characteristics far superior to conventional small-sized lithium secondary batteries.

In addition, a lithium secondary battery used as a large-capacity power storage device must have a long life with a high energy density and efficiency. In addition, since the ignition or explosion accident is linked to a large accident when the system malfunctions due to high performance and large capacity, Is a particularly important task.

In this connection, a negative electrode of a conventional lithium secondary battery is mainly composed of a carbonaceous compound capable of intercalating and desorbing reversible lithium ions while maintaining structural and electrical properties as a negative electrode active material.

Specifically, the carbon-based compound has a very low discharge potential of about -3 V with respect to the standard hydrogen electrode potential and exhibits a highly reversible charge-discharge behavior due to the uniaxial orientation of the graphite plate layer (graphene layer) And when the Li-ion is charged, the electrode potential can exhibit a potential similar to that of a pure lithium metal as 0V Li / Li ⁺ . Therefore, when forming the battery with the oxide-based anode, Energy can be obtained.

However, the negative electrode made of such a carbon-based compound has the following problems.

First, since the carbon-based compound has a theoretical maximum capacity of 372 mAh / g (844 mAh / cc), it is difficult to cope with a sufficient role as a energy source for a rapidly changing next generation mobile device.

Secondly, since the chemical potential of the carbon-based compound is similar to that of metal lithium at the time of inserting and desorbing lithium ions, lithium precipitation occurs due to overpotential even at a slightly high charging current, As the discharge is repeated, the acceleration is further accelerated, resulting in a capacity shortage caused by the dendrite as well as the capacity deterioration, thereby significantly affecting safety.

Third, when the amount of lithium charged into the cathode exceeds the amount of lithium that can be received by the overcharge of the battery, the temperature rises and the exothermic reaction occurs. This is because of the earliest reaction among the thermodynamic reactions occurring inside the battery It can be a major trigger such as ignition and explosion of the battery.

Fourth, the surface of the hydrophobic electrode has a great influence on the electrode wetting of the electrolyte during production of the battery, and the electrode wettability time affects the productivity of the battery.

In order to solve the above-mentioned problems, recently, research on Li ₄ Ti ₅ O ₁₂ and an anode material by a Li alloy reaction using silicon (Si), tin (Sn) Is going on.

However, silicon, for example, has a theoretical maximum capacity of about 4020 mAh / g (9800 mAh / cc, specific gravity: 2.23), which is very advantageous over graphite materials. And has a disadvantage that the volume change during charging and discharging is very large.

In addition, Li ₄ Ti ₅ O ₁₂ has a very low structural change during charge and inversion and is excellent in life characteristics due to a zero-strain material, forms a relatively high voltage band, and the generation of dendrite It is known as an excellent material for safety and stability. It has the advantage of having a rapid charging electrode characteristic that can be charged in a few minutes. However, the capacity is very low, There is a problem that the energy density is very low.

In addition, Patent Application Publication Nos. 2010-0008785, 2008-0112977, 2010-0086367, 2006-0028327 disclose an anode active material in which a titanium-containing oxide is placed or coated on the surface of a carbonaceous anode active material However, the production of an anode active material having a titanium-containing oxide on the surface thereof is difficult to be mixed with each other due to the opposite characteristics of the two materials, and there is a problem in that the process cost is increased.

Therefore, there is an urgent need to develop an anode having high safety and stability, a high output characteristic and a high energy density, which can be used as a high capacity power source.

On the other hand, high wetting characteristics become more important as large-sized devices such as mid- and large-sized devices are made for high capacity, and the formation of dendritic crystals occurs from the surface of the electrode. Therefore, in the case of simple mixing of a carbonaceous anode active material and a titanium- There is a problem that it is not easy to maximize the wettability.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application have continued intensive research and various experiments and have found that the formation of dendrites, the wetting of electrolytes, and the electrochemical reaction with electrolytes result from the surface reaction of the electrodes. When a second negative electrode material mixture containing a second negative electrode active material having a relatively high charge / discharge potential and a large hydrophilicity relative to the first active material in the first negative electrode material mixture is coated on the first negative electrode material mixture applied on the surface of the current collector . Safety and stability are improved, and at the same time a high energy density is achieved, and the present invention has been accomplished.

Accordingly, an object of the present invention is to provide a negative electrode for a secondary battery having improved safety and stability, a high energy density and a high output characteristic, and a lithium secondary battery including the negative electrode.

In order to solve the above-mentioned problems, a negative electrode for a secondary battery according to the present invention includes: a first negative electrode mixture layer including a first negative electrode active material coated in contact with a surface of a current collector; And a second negative electrode active material layer coated on the first negative electrode active material layer and including a second negative electrode active material having a relatively high charge / discharge potential and relatively high hydrophilicity than the first negative electrode active material; Layer structure including a multi-layer structure.

Therefore, the negative electrode for a secondary battery according to the present invention is formed by applying a second negative electrode material mixture containing a second negative electrode active material having a relatively higher charge / discharge potential than the first negative electrode active material in the first negative electrode material mixture on the first negative electrode material mixture , The formation of dendrites is prevented and safety is improved.

Specifically, the second negative electrode mixture formed on the surface of the negative electrode which directly reacts with the electrolyte acts as a kind of buffer for charging a large amount of current by allowing lithium to be charged in the negative electrode mixture when the lithium is charged in the negative electrode. Therefore, the formation of dendrites by repetitive charging and discharging is prevented on the surface of the second negative electrode active material having a higher charge / discharge potential than the first negative electrode active material similar to the charge / discharge potential of the lithium metal.

The negative electrode for a secondary battery according to the present invention may further comprise a second negative electrode active material containing a second negative electrode active material having a relatively larger hydrophilicity than the first negative electrode active material in the first negative electrode mixture, Thereby improving the wetting property.

Specifically, the second negative electrode mixture formed on the surface of the negative electrode which directly reacts with the electrolyte serves to lower the surface tension to easily impregnate the electrolyte solution on the surface of the negative electrode. The first negative electrode active material, which is relatively hydrophobic compared to the second negative electrode active material In the negative electrode active material, the permeated electrolyte is permeated to the surface portion of the negative electrode collector by the capillary phenomenon, thereby improving the wettability of the electrolyte.

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If the affinity of the second negative electrode active material with respect to the electrolyte, for example, the electrolyte impregnation rate, is not greater than the above range relative to the first negative electrode active material, it may be difficult to exhibit the desired effects of the present invention as described above. I do not.

The first negative electrode active material may preferably be at least one selected from the group consisting of crystalline graphite and low crystalline carbon. In one preferred example, the mixture may be a mixture of a flaky crystalline graphite carbon-based compound and a low-crystalline carbon-based compound.

Generally, in the crystalline carbon-based compound, the path through which lithium ions are inserted and desorbed into the layered structure of carbon is limited to approximately two dimensions, while the low-crystalline carbonaceous compound has such a limited path for insertion of lithium ions And relatively high in rate characteristics. However, the amorphous carbon-based compound has an irreversible capacity of about 20 to 30% and has a very high disadvantage.

On the other hand, as described above, the first negative electrode active material includes a flaky crystalline carbon-based compound having a relatively small irreversible capacity in the amorphous carbon-based compound, thereby completing the above-mentioned disadvantages.

In some cases, the first anode active material may be in the form of a crystalline graphite core coated with low-crystalline carbon.

The first negative electrode active material may be spherical, and the crystalline graphite may be natural graphite or artificial graphite. The low crystalline carbon is particularly limited as long as carbon atoms have an amorphous crystal structure and exhibit excellent rate characteristics For example, a hard carbon, a coke, a needle coke or a soft carbon obtained by carbonizing a pitch can be used, which is obtained by pyrolyzing a phenol resin or a furan resin.

Accordingly, the negative electrode for a secondary battery according to the present invention can have a high energy density by using a carbon-based compound having a high energy density as a first negative electrode active material.

Meanwhile, the second negative electrode active material may preferably be a titanium-containing oxide. The titanium-containing oxide may be at least one selected from the group consisting of lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) and titanium dioxide (TiO ₂ ), preferably lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ).

In some cases, the second negative electrode active material may be a mixture of lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) and titanium dioxide (TiO ₂ ), wherein the content ratio thereof is in the range of 10: 90:10. ≪ / RTI >

Accordingly, the negative electrode for a secondary battery according to the present invention uses the titanium-containing oxide as the second negative electrode active material to maintain the structural stability during repetitive charging and discharging, thereby improving cycle characteristics.

The negative electrode includes a first negative electrode mixture layer and a second negative electrode mixture layer which are prepared by preparing a paste by adding and stirring the negative electrode active material to a dispersion and then applying and drying the paste on the negative electrode collector, The additive layers may optionally further include components such as a conductive agent, a binder and a filler.

In the process, since the anode mixture layer of the multi-layer structure according to the present invention can be formed by a single double coating process, the process can be simplified and the process cost can be reduced.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, various copolymers, and the like can be given as examples of the polypropylene resin .

The conductive agent is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. For example, graphite carbon black such as natural graphite or artificial graphite, acetylene black, ketjen black, channel black, Carbon black such as black, lamp black, summer black, etc. Carbon fiber and conductive fiber such as metal fiber Carbon fluoride, metal powder such as aluminum and nickel powder Conductive metal oxide such as zinc oxide and conductive whiskey titanium oxide such as potassium titanate Polyphenylene A conductive material such as a derivative may be used. Concrete examples of commercially available conductive agents include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC series (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by Timcal).

In some cases, a filler may be optionally added as a component to suppress the expansion of the negative electrode. Such a filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and for example, a fibrous material such as an olefin polymer glass fiber such as polyethylene or polypropylene or carbon fiber is used.

Typical examples of the dispersion include isopropyl alcohol, N-methyl pyrrolidone (NMP), and acetone.

The method of applying the paste of the electrode material to the metal material in a uniform manner can be selected from known methods in consideration of the characteristics of the material and the like or can be carried out by a new suitable method. For example, it is preferable that the paste is uniformly dispersed on a current collector by using a doctor blade or the like. In some cases, a method of performing the distribution and dispersion processes in a single process may be used. In addition, a method such as die casting, comma coating, screen printing, or the like may be employed, or may be formed on a separate substrate, and then pressed or laminated by a pressing or laminating method. .

Drying of the paste applied on the metal plate is preferably performed in a vacuum oven at 50 to 200 DEG C for 1 to 3 days.

The present invention also relates to a positive electrode comprising at least one selected from the above-described negative electrode, positive electrode active materials for lithium secondary batteries represented by the following Chemical Formulas 1 and 2, and a porous separator interposed between the negative electrode and the positive electrode And an electrode assembly for a secondary battery.

Li _x (Ni _v Mn _w Co _y M _z ) O _{2 -te t} (1)

In this formula,

0 < = x < = 0.9, 0 &

M is at least one metal or transition metal cation of +2 to +4 oxidation number and A is -1 or -2 valent anion.

Li _a Mn _2-b M ' _b O _4-c A' _c (2)

In this formula,

0.8 <a? 1.3, 0? B? 0.5, 0? C? 0.3;

M 'is at least one metal or transition metal cation of +2 to +4 oxidation number and A' is an anion of -1 or -2 valence.

In the above formula (1), transition metals such as Ni, Mn and Co may be substituted with metals having a +2 to +4 oxidation number and / or other transition metal (M) elements, preferably Al, Mg and Ti , And in this case, the preferable substitution amount may be 0.3? Z? 0.6.

M 'in Formula 2 may be one or more selected from the group consisting of Co, Mn, Ni, Al, Mg, and Ti.

In the above formulas (1) and (2), the oxygen ion may be substituted by an anion (A, A ') having an oxidation number of -1 or -2 in a predetermined range, wherein A and A' , Halogen such as Cl, Br, I, S, and N.

By substituting these anions, the binding force with the transition metal is improved and the structural transition of the compound is prevented, so that the lifetime of the battery can be improved. On the other hand, if the substitution amount of the anions A and A 'is too large (t > 0.2), the life characteristic is deteriorated due to the incomplete crystal structure.

In one preferred example, the positive electrode active material of Formula 1 includes a mixed transition metal of Ni and Mn, wherein the average oxidation number of the total transition metals except lithium is greater than +3, Or a lithium transition metal oxide having a layered structure satisfying the same or larger than the content.

In another preferred embodiment, the cathode active material of Formula 1 may be Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ or Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ .

The method of producing the positive electrode according to the present invention is not particularly limited, and one example will be described below.

The binder and the conductive agent are added to the composite cathode active material in an amount of 1 to 20% by weight and the mixture is stirred to prepare a paste. The paste is applied to a metal plate for a current collector, compressed and dried to produce a laminated electrode can do.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used.

Like the negative electrode current collector, the current collector may have fine unevenness on the surface thereof to increase the adhesive force of the positive electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m, and the thickness is generally 5 to 300 mu m. As such a separation membrane, for example, a sheet made of olefin-based polymer glass fiber such as polypropylene, which is chemically resistant and hydrophobic, polyethylene or the like, nonwoven kraft paper, or the like is used. Representative examples currently on the market include the Celgard ^R 2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separation membrane to improve the stability of the cell. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

The present invention also provides a lithium secondary battery in which the above-mentioned electrode assembly is impregnated with an electrolyte. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing non-aqueous electrolyte is composed of a nonaqueous electrolyte and lithium. As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate , Gamma -butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, Diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane A non-protonic organic solvent such as an ether, a methyl pyrophosphate, or an ethyl propionate is used as the solvent, a sulfone, a methyl sulfolane, a 1,3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, .

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate, imide, and the like can be used.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, a halogen-containing solvent such as carbon tetrachloride, ethylene trifluoride or the like may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate ), PRS (Propene sultone), and the like.

The secondary battery according to the present invention exhibits high energy density, high output characteristics, improved safety and stability, and thus can be preferably used as a constituent battery of a middle- or large-sized battery module. Accordingly, the present invention also provides a middle- or large-sized battery module including the above-described secondary battery as a unit battery.

Such a middle- or large-sized battery module can be suitably applied to a power source requiring a high output and a large capacity, such as an electric vehicle, a hybrid electric vehicle, and a power storage device.

The configuration of the middle- or large-sized battery module and the method of manufacturing the middle- or large-sized battery module are well known in the art, and a description thereof will be omitted in the specification.

The negative electrode for a secondary battery according to the present invention is formed by applying a second negative electrode mixture containing a second negative electrode active material having a relatively higher charge / discharge potential on the first negative electrode active material than the first negative electrode active material, thereby preventing the formation of dendrites Thereby improving safety.

Also, the negative electrode for a secondary battery according to the present invention improves the wetting of the electrolyte by applying a second negative electrode mixture containing a second negative electrode active material having a relatively larger hydrophilicity on the first negative electrode active material than the first negative electrode active material .

Also, the negative electrode for a secondary battery according to the present invention has a high energy density by using a carbon-based compound as a first negative electrode active material and a titanium-containing oxide that maintains structural stability during repeated charge and discharge with the second negative electrode active material The cycle characteristics can be improved.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (17)

A first negative electrode mixture layer including a first negative electrode active material coated in contact with a surface of a current collector; And
A second negative electrode active material layer coated on the first negative electrode active material layer and comprising a second negative electrode active material having a relatively high charge / discharge potential and relatively high hydrophilicity than the first negative electrode active material;
Wherein the first anode active material has a crystalline graphite core coated with low crystalline carbon and the second anode active material is a lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) And titanium dioxide (TiO ₂ ), and the content ratio thereof is in the range of 10:90 to 90:10 based on the weight ratio. delete delete delete delete The negative electrode for a secondary battery according to claim 1, wherein the first negative electrode active material is spherical. The negative electrode for a secondary battery according to claim 1, wherein the crystalline graphite is natural graphite or artificial graphite. The negative electrode for a secondary battery according to claim 1, wherein the low crystalline carbon is hard carbon or soft carbon. delete delete delete A positive electrode comprising at least one selected from the group consisting of a negative electrode according to claim 1, a positive electrode active material for lithium secondary batteries represented by the following general formulas (1) and (2), and a porous separator interposed between the negative electrode and the positive electrode The electrode assembly for a secondary battery
Li _x (Ni _v Mn _w Co _y M _z ) O _{2 -te t} (1)
In this formula,
0 < = x < = 0.9, 0 &
M is at least one metal or transition metal cation of +2 to +4 oxidation numbers
A is an anion of -1 or -2 valence.
Li _a Mn _2-b M ' _b O _4-c A' _c (2)
In this formula,
0.8 <a? 1.3, 0? B? 0.5, 0? C? 0.3;
M 'is at least one metal or transition metal cation of +2 to +4 oxidation number and A' is an anion of -1 or -2 valence. A lithium secondary battery comprising the electrode assembly of claim 12. The battery module according to claim 13, wherein the lithium secondary battery is used as a unit battery. An electric vehicle characterized by using the battery module according to claim 14 as a power source. The power storage device according to claim 14, wherein the battery module is used as a power source. A hybrid electric vehicle characterized by using the battery module according to claim 14 as a power source.