KR20170103212A - Electrode assembly and Lithium secondary battery with extended life by comprising the same - Google Patents

Abstract

According to the present invention, when the capacity of a lithium secondary battery is reduced to a certain level or less, a lithium particle layer included in an electrode assembly is activated by raising the temperature of the lithium secondary battery to 60C or more, and lithium ions are supplemented in the battery, thereby extending the service life without degrading the performance of the battery. An electrode assembly for a lithium secondary battery comprises a positive electrode, a separator, a lithium particle layer, another separator, and a negative electrode, which are sequentially laminated.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrode assembly and a lithium secondary battery having the same,

The present invention relates to an electrode assembly and a lithium secondary battery having improved life span thereof.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing.

The secondary battery may be used in the form of a single battery cell or in the form of a battery module in which a plurality of unit cells are electrically connected to each other depending on the type of an external device used. For example, a small device such as a cellular phone can operate for a predetermined period of time at the output and capacity of one battery cell, while a medium or large device such as a notebook computer, a portable DVD, a mini PC, an electric vehicle, The use of a battery module including a plurality of battery cells is required because of problems of output and capacity.

Conventionally, a nickel-cadmium battery or a hydrogen ion battery is used as a secondary battery, but recently, a lithium ion battery and a lithium polymer battery having high energy density are widely used. Such secondary batteries have been in increasing demand due to the advantages described above.

Particularly, the lithium secondary battery has a working voltage of 3.6 V or higher and is used as a power source of a portable electronic device or several series connected in series to be used in a high-output hybrid vehicle. In comparison with a nickel-cadmium battery or a nickel-metal hydride battery, And the energy density per unit weight is also excellent, and the demand is rapidly increasing.

Such a lithium secondary battery mainly uses a lithium-based oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material. Generally, a battery using a liquid electrolyte is referred to as a lithium ion battery, and a battery using a polymer electrolyte is referred to as a lithium polymer battery, which is classified as a liquid electrolyte cell and a polymer electrolyte cell, depending on the type of the electrolyte. In addition, the lithium ion secondary battery is manufactured in various shapes. Typical shapes include a cylindrical shape, a square shape, and a pouch shape.

A typical electrode assembly in which such a lithium secondary battery constitutes is schematically shown in Fig.

1, the electrode assembly 100 includes a separator interposed between an anode 10 and a cathode 30. The electrode assembly 100 is accommodated in a battery case (not shown) An electrolytic solution may be injected thereinto.

As the charge / discharge cycle of the lithium secondary battery progresses, dendrites are formed on the surface of the negative electrode, thereby causing side reactions such as the consumption of usable lithium ions. With such side reactions, the capacity of the lithium secondary battery is reduced and the output of the lithium secondary battery is lowered during discharging, resulting in a reduction in the life of the lithium secondary battery.

Therefore, it is necessary at the present time to maintain the excellent battery performance and extend the service period even if the lithium secondary battery is repeatedly charged and discharged.

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

More specifically, an object of the present invention is to provide an electrode assembly and a lithium rechargeable battery including the electrode assembly, which solve the problem of lithium ion reduction caused by repetition of charging and discharging.

Another problem to be solved by the present invention is to provide a lithium rechargeable battery having an extended life while maintaining excellent performance by solving the above problems.

Another object of the present invention is to provide a method for treating lithium secondary battery so that the life of the lithium secondary battery is prolonged.

According to one aspect of the present invention, there is provided an electrode assembly for a lithium secondary battery in which an anode, a separator, a lithium particle layer, a separator, and a cathode are sequentially laminated.

Wherein the lithium particle layer comprises a mesh-shaped substrate; And a plurality of lithium particles inside the mesh of the base material and at the upper and lower portions of the mesh.

The mesh-shaped substrate may be formed by arranging a plurality of thin and long wires in parallel and another thin and long plurality of wires arranged in parallel so as to be perpendicular to the wires.

The substrate in the mesh form may be formed from one or more polymers selected from polyethylene, polypropylene and polyvinyl chloride.

The substrate in the mesh form may be formed from one or more metals selected from aluminum, copper and stainless steel.

The lithium particle layer may have a thickness of 10 to 50 mu m.

The lithium particles include lithium metal in particle form; And a coating surrounding the lithium metal.

The lithium particles may have an average particle diameter of 0.1 to 1 占 퐉.

The coating material may be decomposed at a temperature of 60 ° C or higher.

The coating material may be selected from polyurethane, polycarbonate or mixtures thereof.

The coating material may be coated with lithium metal in the form of particles in a thickness of 10 nm to 100 nm.

According to another aspect of the present invention, there is provided a lithium secondary battery including the above-described electrode assembly for a lithium secondary battery.

The lithium secondary battery may include an end of life (EOL) indicator.

According to still another aspect of the present invention, there is provided a method of manufacturing a lithium secondary battery, comprising: identifying an EOL indicator from the lithium secondary battery; And raising the temperature of the lithium secondary battery by the high temperature aging method at a temperature of 50 to 60 DEG C for 48 to 72 hours.

According to one aspect of the present invention, there is provided an electrode assembly in which lithium particles contained in a lithium particle layer at a temperature of 60 DEG C or higher are activated by coating removal to replenish lithium ions.

Therefore, the lithium secondary battery according to an embodiment of the present invention can replenish lithium ions in the lithium particle layer included in the electrode assembly, so that there is no problem of reduction in output or lifetime due to lithium ion reduction.

Further, according to a method according to an embodiment of the present invention, the end of life (EOL) indication provided in the lithium secondary battery is confirmed, and the lifetime of the lithium secondary battery is reduced by simply treating the lithium battery to reach a predetermined temperature range There is an advantage that it can be improved.

1 schematically shows a cross section of a conventional electrode assembly including an anode, a cathode, and a separator interposed between the anode and the cathode.
2 schematically shows a cross section of an electrode assembly according to an embodiment of the present invention in which an anode, a separator, a lithium particle layer, a separator, and a cathode are sequentially laminated.
Fig. 3 schematically shows a mesh-shaped substrate for adhering and fixing lithium particles in a lithium particle layer according to an embodiment of the present invention.
4 schematically shows the structure of a lithium particle adhered and fixed to a mesh-shaped substrate in a lithium particle layer according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor may designate the concept of a term appropriately in order to describe its own invention in the best way possible. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the constitution described in the embodiments of the present invention is merely an embodiment of the present invention, and does not represent all the technical ideas of the present invention, so that various equivalents and modifications It should be understood.

As used herein, the term " electrode assembly " includes not only an anode, a separator and a cathode sequentially stacked as shown in Fig. 1 but also a cathode, a separator, a lithium particle layer, a separator, It is understood that the present invention also includes a form in which the layers are sequentially stacked.

2, an electrode assembly 200 according to an embodiment of the present invention includes a positive electrode 10, a separator 20, a lithium particle layer 40, a separator 20 ', and a negative electrode 30 sequentially May be stacked.

Further, the lithium particle layer 40 includes a base material 41 in the form of a mesh; And a plurality of lithium particles 42 in the mesh of the base material and at the upper and lower portions of the mesh.

The lithium particle layer 40 may have a thickness of about 10 to 50 [mu] m. If the thickness of the lithium particle layer 40 is less than about 10 탆, the required amount of lithium particles can not be supported. If the thickness of the lithium particle layer 40 is greater than about 50 탆, the thickness of the electrode assembly becomes unnecessarily large.

One embodiment of the mesh-like substrate 41 is shown in Fig.

According to Fig. 3, one embodiment of the mesh-like base material 41 comprises a plurality of thin and long wires 411 arranged in parallel, and another thin and long wire 411 perpendicular to these wires in parallel So that a mesh shape can be formed. Pores 412 are formed in the substrate 41 by intersection of a plurality of wires 411. The intersection of the wires can be fixed by welding or the like.

The mesh-like substrate may be made from any material that is electrically inactive and can be coated with lithium particles, and may be a polymer or metal as a non-limiting example. Non-limiting examples of the polymer include polyethylene, polypropylene, and polyvinyl chloride. Non-limiting examples of the metal include, but are not limited to, aluminum, copper, and stainless steel.

The substrate may have a two-dimensional thin film shape formed by entanglement of a plurality of thin and long wires to form a mesh shape. The thickness of the substrate and the length of the wire cross-section may independently have a thickness of about 10 to 50 mu m, but are not limited thereto. The thickness of the substrate may be substantially equal to the thickness of the wire or may be slightly thicker than the wire due to the intersection point between the wires.

The wire constituting the substrate may have various cross-sectional shapes such as circular, square, triangular, polygonal and stripe shapes, but is not limited thereto.

As the base material has a mesh shape, the formation of the thick film is facilitated, the electrolyte impregnation amount is increased, and even if it is formed as a thick film, flexibility of the current collector of the conventional porous structure can be obtained.

4 shows an embodiment of the lithium particles 42 covering the inside of the mesh and the upper and lower portions of the mesh.

4, the lithium particles 42 include lithium metal 421 in the form of particles; And a coating material (422) surrounding the lithium metal (421).

Although the lithium particle is not particularly limited in terms of its shape, it is preferable that the lithium particle is better coated on the base material, and furthermore, it is preferable that the lithium particle is a spherical or nearly spherical in terms of filling (tap density) and leveling of the lithium particle layer Shape or an elliptical shape is preferable.

In addition, the lithium particles are not particularly limited in terms of the average particle size, but may be an average of 0.1 to 1 占 퐉 in terms of satisfactorily adhering the lithium particles to the substrate and allowing the lithium particles to be impregnated into the electrolyte as large as possible after the coating material is removed. It is preferable to have a particle diameter.

The surface of the lithium metal in the form of particles is electrochemically inert and coated with a coating that decomposes at a temperature of 60 ° C or higher. Non-limiting examples of such coatings include, but are not limited to, polyurethane, polycarbonate.

The coating material may be coated on the lithium metal in the form of particles by a method such as electroless plating, chemical vapor deposition, physical vapor deposition, or wet coating, but is not limited thereto.

The coating material may be coated with lithium metal in the form of particles in a thickness of 10 nm to 100 nm. In the case where the thickness is thicker than the upper limit value, even when the temperature reaches 60 캜 or higher, it is not decomposed well, and the supply of lithium ions from lithium particles may not be smoothly performed. In addition, when the thickness is thinner than the lower limit, the coating material is removed from the lithium particles at a point earlier than desired, and lithium ions can be supplied from the lithium particles at an unnecessary point in time.

The lithium particle layer of the present invention can be produced by electrochemically dispersing lithium particles in an inert solvent, applying the lithium particle dispersion to a mesh-shaped substrate, and then drying.

Non-limiting examples of the solvent include water, a solvent selected from the group consisting of dimethylformamide (DMF), dimethylacetamide, dimethyl sulfoxide (DMSO), alcohol, acetone and N-methylpyrrolidone One or a mixture of two or more thereof, but is not limited thereto.

The lithium particle dispersion may further include a binder polymer. The binder polymer can be used without any particular limitation as long as it is ordinarily used in the art, and examples thereof include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, Polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorocarbon rubber and But are not limited to, various copolymers thereof.

The binder polymer may be included in an amount of 1 to 5 parts by weight based on 100 parts by weight of lithium particles. If the content of the binder polymer is less than 1 part by weight, the lithium particles can not be properly fixed to the mesh-shaped base material. If the amount is more than 5 parts by weight, the electrical resistance can be unnecessarily increased.

Non-limiting examples of the method of applying the lithium particle dispersion to a mesh-shaped substrate include die coating, roll coating, dip coating, or Mayer BAR coating. It is not.

The electrode assembly of the present invention is characterized in that the positive electrode, the separator, the lithium particle layer, the separator, and the negative electrode are sequentially laminated, and the positive electrode, negative electrode and separator constituting the electrode assembly are all those conventionally used for manufacturing a lithium secondary battery .

As a specific example, the cathode active material include lithium-containing transition and the metal oxide is preferably used, for example, _{Li x CoO 2 (0.5 <x} <1.3), Li x NiO 2 (0.5 <x <1.3), Li x MnO _{2 (0.5 <x <1.3)} , Li x Mn 2 O 4 (0.5 <x <1.3), Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 < b <1, 0 <c < 1, a + b + c = 1), Li x Ni 1 - y Co y O 2 (0.5 <x <1.3, 0 <y <1), Li x Co 1 - y Mn _{y O 2 (0.5 <x <} 1.3, 0≤y <1), Li x Ni 1 - y Mn y O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c 2, a + b + c = 2), Li _x Mn _{2 - z} Ni _z O ₄ (0.5 < x <1.3, 0 <z <2 ), Li x Mn 2 - z Co z O 4 (0.5 <x <1.3, 0 <z <2), Li x CoPO 4 (0.5 <x <1.3) and Li _x FePO ₄ (0.5 < x < 1.3), or a mixture of two or more thereof. The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

As the anode active material, a carbon material, lithium metal, silicon or tin, which lithium ions can be occluded and released, can be used, and metal oxides such as TiO ₂ and SnO ₂ having a potential with respect to lithium of less than ₂ V are also possible. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

The anode and / or the cathode may include a binder, and examples of the binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile ), Polymethylmethacrylate, and the like can be used.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer A porous polymer film made of a high molecular weight polymer may be used alone or in a laminated manner, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber or the like may be used. It is not.

In order to improve mechanical strength of the separator and safety of the lithium secondary battery, the porous polymer substrate may further include a porous coating layer including inorganic particles and a polymeric binder on at least one surface of the porous polymer substrate. Here, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied lithium secondary battery (for example, 0 to 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having a high dielectric constant are used as the inorganic particles, the dissociation of the electrolyte salt, for example, the lithium salt in the liquid electrolyte, can be increased, and the ion conductivity of the electrolyte can be improved.

The polymer binder may be selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-co-chlorotrifluoroethylene ), Polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylpyrrolidone, Polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene, polyethylene oxide, polyarylate, cellulose acetate ), Cellulose acetate butyrate, cell Cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan (which may be referred to as &quot; pullulan, and carboxyl methyl cellulose, or a mixture of two or more thereof, but is not limited thereto.

In the porous coating layer, the polymeric binder is coated on a part or the entire surface of the inorganic particles, and the inorganic particles are connected and fixed to each other by the polymeric binder in an adhered state, and an interstitial volume an interstitial volume between the inorganic particles is formed, and an interstitial volume between the inorganic particles becomes an empty space to form pores. This void space becomes the pores of the porous coating layer, and it is preferable that these pores are equal to or smaller than the average particle diameter of the inorganic particles.

Meanwhile, the electrolyte salt included in the nonaqueous electrolyte solution which can be used in the present invention is a lithium salt. The lithium salt can be used without limitation as those conventionally used in an electrolyte for a lithium secondary battery. For example is the above lithium salt anion ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF _{^{4 -, (CF 3) 3}} PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 - _{, (CF 3 SO 2) 2} N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, ( ^{_{CF 3 SO 2) 3 C -}} , CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - from the group consisting of It can be any one selected.

Examples of the organic solvent included in the above-mentioned non-aqueous electrolyte include those commonly used in electrolytic solutions for lithium secondary batteries, such as ether, ester, amide, linear carbonate, cyclic carbonate, etc., Can be mixed and used.

Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a mixture thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Propylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

Specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate And mixtures of two or more of them may be used as typical examples, but the present invention is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, are high-viscosity organic solvents having a high dielectric constant and can dissociate the lithium salt in the electrolyte more easily. In addition, such cyclic carbonates can be used as dimethyl carbonate and diethyl carbonate When a low viscosity, low dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having a higher electric conductivity can be produced.

As the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used , But is not limited thereto.

Examples of the ester in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone, ε-caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.

The injection of the non-aqueous electrolyte may be performed at an appropriate stage of the production process of the lithium secondary battery, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the lithium secondary battery or at the final stage of assembling the lithium secondary battery.

The outer shape of the lithium secondary battery according to an embodiment of the present invention including the electrode assembly is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, or a coin shape using a can.

According to another aspect of the present invention, there is provided a method of manufacturing a lithium secondary battery, comprising: confirming an end of life (EOL) indicator provided in the lithium secondary battery; And a method for increasing the lifetime of the lithium secondary battery by raising the temperature of the lithium secondary battery at 50 to 60 ° C for 48 to 72 hours by the high temperature aging method.

The level of the EOL can be determined as needed, and can generally be prepared to be displayed when 80% or less of the original capacity is reached.

When the lithium secondary battery is treated at a temperature lower than 50 캜, the coating material of the lithium particles may not be removed. When the battery is treated at a temperature higher than 60 캜, battery performance may be deteriorated due to side reactions .

If the treatment time of the lithium secondary battery is less than 48 hours at the temperature in the above-mentioned range, the coating material of lithium particles may not be sufficiently removed, and if the treatment time is longer than 72 hours, undesirable side reactions may occur.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention.

Claims (14)

An electrode assembly for a lithium secondary battery, comprising a positive electrode, a separator, a lithium particle layer, a separator, and a negative electrode sequentially laminated.
The method according to claim 1,
Wherein the lithium particle layer comprises a mesh-shaped substrate; And a plurality of lithium particles inside the mesh of the base material and at upper and lower portions of the mesh.
3. The method of claim 2,
Wherein the mesh-shaped base member is formed by arranging a plurality of thin and long wires in parallel and another thin and long plurality of wires arranged in parallel so as to be perpendicular to the wires.
3. The method of claim 2,
Wherein the mesh-shaped base material is formed from one or more polymers selected from polyethylene, polypropylene, and polyvinyl chloride.
3. The method of claim 2,
Wherein the mesh-shaped base material is formed from one or more metals selected from aluminum, copper and stainless steel.
The method according to claim 1,
Wherein the lithium particle layer has a thickness of 10 to 50 占 퐉.
3. The method of claim 2,
The lithium particles include lithium metal in particle form; And a coating material surrounding the lithium metal.
8. The method of claim 7,
Wherein the lithium particles have an average particle diameter of 0.1 to 1 占 퐉.
8. The method of claim 7,
Wherein the coating material is decomposed at a temperature of 60 ° C or higher.
8. The method of claim 7,
Wherein the coating material is selected from polyurethane, polycarbonate, or a mixture thereof.
8. The method of claim 7,
Wherein the coating material has a thickness of 10 nm to 100 nm and is coated with lithium metal in particle form.
12. A lithium secondary battery comprising the electrode assembly for a lithium secondary battery according to any one of claims 1 to 11.
13. The method of claim 12,
A lithium rechargeable battery having an end of life (EOL) indicator.
Confirming the EOL indicator from the lithium secondary battery according to claim 13; And
Increasing the temperature of said lithium secondary battery by said high temperature aging method at a temperature of 50 to 60 DEG C for 48 to 72 hours;
Wherein the lithium secondary battery is a lithium secondary battery.

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