KR20190125281A - Rechargeable lithium battery - Google Patents

Abstract

An embodiment of the present invention provides a lithium secondary battery which has excellent adhesive properties between a separator and an electrode, and is excellent in stability, lifetime characteristics, high temperature storage properties, etc. The lithium secondary battery of the present invention comprises: a cathode including a cathode active material; an anode including an anode active material; an electrolyte including a lithium salt and a non-aqueous organic solvent; and a separator positioned between the cathode and the anode, wherein the anode active material includes an Si-based material and a carbonaceous material, the carbonaceous material includes amorphous carbon, the non-aqueous organic solvent includes a cyclic carbonate including ethylene carbonate, propylene carbonate or a combination thereof, and a linear carbonate including ethyl methyl carbonate and diethyl carbonate, the cyclic carbonate and the linear carbonate are included at a volume ratio of 1:1 to 1:9, the electrolyte additionally includes an additive including at least one selected from fluoroethylene carbonate, vinyl ethylene carbonate, propane sultone, succinonitrile, and adiponitrile, the separator includes a porous substrate and a coating layer which is positioned on at least one surface of the porous substrate, the coating layer includes a fluorine-based polymer, ceramic or a combination thereof, and the ceramic is Al_2O_3, Al(OH)_3, or a combination thereof.

Description

Lithium Secondary Battery {RECHARGEABLE LITHIUM BATTERY}

It relates to a lithium secondary battery.

In the lithium secondary battery, a separator made of a porous film is interposed between the positive electrode and the negative electrode, and an electrolyte solution in which lithium salt is dissolved is impregnated in the gap of the film. This lithium secondary battery has excellent characteristics of high capacity and high energy density.

However, when the contraction and expansion of the positive and negative electrodes are repeated by the charge / discharge cycle of the battery, or when the calorific value increases due to the abnormal operation of the battery, the battery temperature may increase rapidly. In this case, a short contraction may occur between the electrodes due to the rapid contraction or breakage of the separator.

Accordingly, at least one surface of the separator has been proposed to coat the heat-resistant inorganic particles with a binder to secure the stability of the battery.

However, as the content of the heat resistant inorganic particles is increased, the content of the binder may be relatively low, thereby decreasing the adhesion between the separator and the electrode.

One embodiment of the present invention provides a lithium secondary battery excellent in adhesion between the separator and the electrode, excellent in stability, lifespan characteristics, high temperature storage.

According to one embodiment of the present invention, a positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; Electrolyte solution containing a lithium salt and a non-aqueous organic solvent; And a separator disposed between the cathode and the anode, the separator including a porous substrate and a coating layer disposed on at least one surface of the porous substrate, wherein the anode active material comprises a Si-based material, and the non-aqueous organic solvent is ethylene carbonate. , And a cyclic carbonate including propylene carbonate or a combination thereof, wherein the cyclic carbonate is included in an amount of 20 to 60% by volume based on the total amount of the non-aqueous organic solvent, and the coating layer comprises a fluorine-based polymer, ceramic, or a combination thereof. It provides a lithium secondary battery comprising.

According to another embodiment, a positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; Electrolyte solution containing a lithium salt and a non-aqueous organic solvent; And a separator positioned between the positive electrode and the negative electrode, wherein the negative electrode active material includes a Si-based material and a carbon-based material, and the carbon-based material includes amorphous carbon, and the non-aqueous organic solvent. Is a cyclic carbonate comprising ethylene carbonate, propylene carbonate or a combination thereof, and a linear carbonate comprising ethylmethyl carbonate and diethyl carbonate, wherein the cyclic carbonate and the linear carbonate have a volume ratio of 1: 1 to 1: 9 The additive includes at least one selected from fluoroethylene carbonate, vinylethylene carbonate, propane sultone, succinonitrile, and adiponitrile, and the separator may be formed on at least one surface of the porous substrate and the porous substrate. Including a coating layer located, the coating Comprises a fluorinated polymer, a ceramic, or a combination thereof, and the ceramic provides an _{Al 2 O 3, Al (OH} ) 3 or a combination of a lithium secondary battery.

The Si-based material may include Si, silicon oxide, Si-C composite, silicon-based alloy, or a combination thereof.

The non-aqueous organic solvent may further include a linear carbonate comprising ethylmethyl carbonate, dimethyl carbonate or a combination thereof.

The electrolyte may further include an additive, and the additive may include fluoroethylene carbonate, vinylethylene carbonate, propane sultone, succinonitrile, adipononitrile, or a combination thereof.

The additive may be included in an amount of 5 to 30 parts by weight based on 100 parts by weight of the non-aqueous organic solvent.

The porous substrate may include polyethylene, polypropylene, aramid, polyimide, or a combination thereof.

The fluorine-based polymer may include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer, or a combination thereof.

It is possible to improve the characteristics of the battery by increasing the adhesiveness between the electrode and the separator while securing the stability, lifespan characteristics, high temperature storage properties of the battery.

1 is a schematic view showing a rechargeable lithium battery according to one embodiment.
Figure 2 is a graph showing the compressive strength measurement results of the gel prepared by dissolving the coating layer in the electrolyte of the lithium secondary battery according to Example 4.
3 is a graph showing the results of evaluation of the adhesion between the negative electrode and the separator of the lithium secondary battery according to Example 4.
4 is a graph showing evaluation results of room temperature life of lithium secondary batteries according to Examples 2, 4, 6, 8, Comparative Example 1, and Comparative Example 2. FIG.
5 is a graph showing the results of high temperature storage evaluation of lithium secondary batteries according to Examples 2, 4, 6, 8, Comparative Example 1, and Comparative Example 2. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

A rechargeable lithium battery according to one embodiment is described with reference to FIG. 1.

1 is a schematic view showing a rechargeable lithium battery according to one embodiment.

Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment may include an electrode assembly 10, a battery container 20 containing the electrode assembly 10, and a current formed in the electrode assembly 10. It may include an electrode tab 13 that serves as an electrical passage for guiding to the outside. Two surfaces of the battery container 20 are sealed by overlapping surfaces facing each other. In addition, an electrolyte is injected into the battery container 20 containing the electrode assembly 10.

The electrode assembly 10 is composed of a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode.

Specifically, the negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer includes a negative electrode active material.

The negative electrode active material may use a Si-based material. The Si-based material may be Si, silicon oxide, Si-C composite, silicon-based alloy, or a combination thereof. The Si-C composite refers to a composite prepared by mixing Si and carbon, for example, but is not limited to Si-nano wire, Si-nano particles, and the like. The silicon-based alloy may be, for example, an alloy of 'Si' and 'alkali metals, alkaline earth metals, Group 13-16 elements, transition metals, rare earth elements, or combination metals thereof (excluding Si)', but are not limited thereto. no.

The negative electrode active material may be used in combination with a carbon-based material, an alloy of lithium metal, or a combination thereof.

The carbonaceous material may use crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate, flake, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (soft carbon) Or hard carbon, mesophase pitch carbide, calcined coke, or the like.

Examples of the alloy of the lithium metal include lithium and metals of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, or Sn. Alloys can be used.

The negative electrode active material layer also includes a binder, and optionally may further include a conductive material.

The binder adheres the anode active material particles to each other well, and also serves to adhere the anode active material to the current collector well, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, and carboxylation. Polyvinylchloride, polyvinylfluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic ray Tied styrene-butadiene rubber, epoxy resin, nylon, and the like may be used, but is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and may be used as long as it is an electronic conductive material without causing chemical change in the battery to be constructed. Examples thereof include natural graphite, artificial graphite, carbon black, acetylene black, and ketjen black. Carbon-based materials such as carbon fibers; Metal materials such as metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive polymers such as polyphenylene derivatives; Or a conductive material containing a mixture thereof.

The current collector may be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam (foam), copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

Hereinafter, the positive electrode will be described.

The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector.

As the positive electrode active material, a compound (lithiated intercalation compound) capable of reversible intercalation and deintercalation of lithium may be used. Specifically, one or more of complex oxides of metal and lithium of cobalt, manganese, nickel or a combination thereof may be used, and specific examples thereof may be a compound represented by any one of the following formulas. Li _a A _1-b R _b D ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0 ≦ b ≦ 0.5); Li _a E _1-b R _b O _2-c D _c (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, and 0 ≦ c ≦ 0.05); LiE _2-b R _b 0 _4-c D _c (wherein 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li _a Ni _1-bc Co _b R _c D _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2); Li _a Ni _1-bc Co _b R _c O _2-α Z _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05 and 0 <α <2); Li _a Ni _1-bc Co _b R _c O _2-α Z ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05 and 0 <α <2); Li _a Ni _1-bc Mn _b R _c D _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, and 0 <α ≦ 2); Li _a Ni _1-bc Mn _b R _c O _2-α Z _α (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05 and 0 <α <2); Li _a Ni _1-bc Mn _b R _c O _2-α Z ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05 and 0 <α <2); Li _a Ni _b E _c G _d O ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, and 0.001 ≦ d ≦ 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (wherein 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, and 0.001 ≦ e ≦ 0.1); Li _a NiG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); Li _a Mn ₂ G _b O ₄ (wherein 0.90 ≦ a ≦ 1.8 and 0.001 ≦ b ≦ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiTO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≦ f ≦ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≦ f ≦ 2); And LiFePO ₄ .

In the above formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or combinations thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof and T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

Of course, what has a coating layer on the surface of this compound can also be used, or the compound and the compound which have a coating layer can also be used in mixture. The coating layer may include an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element as the coating element compound. The compounds constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof may be used. The coating layer forming process may use any coating method as long as it does not adversely affect the physical properties of the positive electrode active material by using such elements in the compound (for example, spray coating, dipping, etc.). Details that will be well understood by those in the field will be omitted.

The positive electrode active material layer also includes a binder and a conductive material.

The binder adheres the positive electrode active material particles to each other well, and also serves to adhere the positive electrode active material to the current collector well, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and polyvinyl. Chloride, carboxylated polyvinylchloride, polyvinylfluoride, polymer comprising ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon and the like can be used, but is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and any battery can be used as long as it is an electronic conductive material without causing chemical change in the battery. For example, natural graphite, artificial graphite, carbon black, acetylene black, and ketjen. Black, carbon fiber; Metal powders, such as copper, nickel, aluminum, silver, metal fiber, etc. can be used, and 1 type (s) or 1 or more types can be mixed and used for conductive materials, such as a polyphenylene derivative.

Al may be used as the current collector, but is not limited thereto.

The negative electrode and the positive electrode are each prepared by mixing an active material, a conductive material and a binder in a solvent to prepare an active material composition, and applying the composition to a current collector. Since such an electrode manufacturing method is well known in the art, detailed description thereof will be omitted. N-methylpyrrolidone may be used as the solvent, but is not limited thereto.

The electrolyte solution may include a lithium salt and a non-aqueous organic solvent.

The non-aqueous organic solvent dissolves the lithium salt and serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, alcohol or aprotic solvent. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), and ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used, and the ester solvent may be methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methylpropionate. , Ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone and the like may be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran may be used as the ether solvent, and cyclohexanone may be used as the ketone solvent. have. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol solvent, and as the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, Amides, such as nitriles, dimethylformamide, and dioxolanes, such as 1,3-dioxolane, and sulfolanes, such as 1,3-dioxolane, and the like.

The non-aqueous organic solvents may be used alone or in mixture of one or more, and the mixing ratio in the case of mixing one or more may be appropriately adjusted according to the desired battery performance.

Specifically, the non-aqueous organic solvent may include a cyclic carbonate including ethylene carbonate, propylene carbonate or a combination thereof. More specifically, the cyclic carbonate may be included in 20 to 60% by volume with respect to the total amount of the non-aqueous organic solvent.

In addition, in the case of the carbonate-based solvent, a cyclic carbonate and a linear carbonate may be mixed and used. The linear carbonate may comprise ethylmethyl carbonate, dimethyl carbonate or a combination thereof. In this case, the cyclic carbonate and the linear carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that the performance of the electrolyte may be excellent.

Specifically, 20 to 60% by volume of ethylene carbonate (EC) and propylene carbonate (PC), 10 to 70% by volume of ethyl methyl carbonate (EMC), and 10 to 70% by volume of diethyl carbonate (DEC) may be used. .

Specifically, 20 to 30% by volume of ethylene carbonate (EC), 0 to 15% by volume of propylene carbonate (PC), 25 to 50% by volume of ethyl methyl carbonate (EMC), and 30% by volume of diethyl carbonate (DEC) Can be used.

When the cyclic carbonate is included in the non-aqueous organic solvent in an amount of 20 to 60% by volume with respect to the total amount of the non-aqueous organic solvent, the polymer layer coated on the surface of the separator is easily dissolved in the electrolyte, and thus the compressive strength of the separator and adhesion between the electrode and the separator As a result, the separator may be prevented from being rapidly shrunk or deformed even during charging and discharging, thereby improving lifespan characteristics of the battery.

The non-aqueous organic solvent may further include the aromatic hydrocarbon organic solvent in the carbonate solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1: 1 to about 30: 1.

As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon compound of Formula 1 may be used.

[Formula 1]

In Formula 1, R ₁ to R ₆ are each independently hydrogen, halogen, an alkyl group of C1 to C10, a haloalkyl group of C1 to C10, or a combination thereof.

The aromatic hydrocarbon organic solvent is benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene , 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2, 4-trichlorobenzene, iodobenzene, 1,2-dioodobenzene, 1,3-dioodobenzene, 1,4-dioiobenzene, 1,2,3-triiodobenzene, 1,2,4 -Triiodobenzene, toluene, fluorotoluene, 1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3-trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene, 1,2,4 -Trichlorotoluene, iodotoluene, 1,2-dioodotoluene, 1,3-dioodotoluene, 1,4-diaodotol Ene, 1,2,3-tree-iodo toluene, 1,2,4-iodo toluene, xylene, or may be a combination thereof.

The non-aqueous organic solvent may further include vinylene carbonate or an ethylene carbonate compound represented by the following Formula 2 to improve battery life.

[Formula 2]

In Formula 2, R ₇ and R ₈ are each independently hydrogen, a halogen group, a cyano group (CN), a nitro group (NO ₂ ) or a fluoroalkyl group of C1 to C5, and at least one of R ₇ and R ₈ Is a halogen group, cyano group (CN), nitro group (NO ₂ ) or a fluoroalkyl group of C1 to C5.

Representative examples of the ethylene carbonate compound include difluoro ethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, and the like. When the vinylene carbonate or the ethylene carbonate-based compound is further used, the amount thereof may be appropriately adjusted to improve life.

The electrolyte may further include an additive, and the additive may be fluoroethylene carbonate, vinylethylene carbonate, propane sultone, succinonitrile, adiponitrile, or a combination thereof.

Specifically, the additive may be included in 5 to 30 parts by weight based on 100 parts by weight of the non-aqueous organic solvent.

When the fluoroethylene carbonate is included in the non-aqueous organic solvent within the above range, the content of the cyclic carbonate in the electrolyte is increased, thereby improving the flame retardancy of the electrolyte and increasing stability as well as causing decomposition reactions on the electrode surface. A stable passivation film can be formed, thereby improving the life characteristics of the battery.

The lithium salt is a substance that dissolves in the electrolyte and acts as a source of lithium ions in the battery to enable operation of the basic lithium secondary battery and to promote the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of the lithium salt are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y +1} SO ₂ ), where x and y are natural numbers, LiCl, LiI, LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate (LiBOB) or combinations thereof The lithium salt may be used in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is in the above range, the separator, the electrolyte, the electrolyte additive, and the lithium salt may be used. Electrolytes including the like and the like have an appropriate conductivity and viscosity can exhibit excellent electrolyte performance, lithium ions can move effectively.

Hereinafter, the separator will be described.

The method of manufacturing the separator includes applying a slurry including an inorganic compound and a binder polymer to at least one surface of the porous substrate, and drying the slurry to form a coating layer.

The binder polymer may be a mixed form of the first binder polymer and the second binder polymer having different particle sizes, or may be a mixed form of the solvent-soluble binder polymer and the emulsion binder polymer.

Drying the slurry may be performed by, for example, hot air drying, infrared drying, or the like, and may be dried at a drying rate of about 30 to 70% / min.

Here, the drying rate means a rate at which about 30 to 70% of the solvent contained in the slurry is dried, and may be determined by drying temperature, air supply amount, exhaust amount, wind speed, heating method, and the like.

By drying at the drying rate of the said range, as mentioned above, the binder polymer can fully move to the surface part side, and it can prevent that a crack and a deformation generate | occur | produce in a surface part by rapid drying.

It is preferable to dry at a drying rate of about 40 to 60% / min within the above range.

The drying temperature can be determined depending on various factors such as the solvent used and the atmosphere when the drying is carried out. The drying temperature may be, for example, about 45 ℃ to 110 ℃, may be about 50 ℃ to 90 ℃ within the range, may be about 60 ℃ to 80 ℃ within the range. By carrying out drying in the above temperature range, the solvent can be removed without excessive shrinkage of the porous substrate.

The separator is positioned between the positive electrode and the negative electrode, and includes a porous substrate and a coating layer disposed on at least one surface of the porous substrate, and the coating layer may include a fluorine-based polymer, a ceramic, or a combination thereof.

Specifically, the porous substrate may include polyethylene, polypropylene, aramid, polyimide, or a combination thereof.

When the porous substrate is polyethylene, polypropylene, aramid, polyimide, or a combination thereof, coating of the coating layer may be easy.

Specifically, the fluorine-based polymer may include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer, or a combination thereof.

Specifically, the ceramic may include Al ₂ O ₃ , MgO, TiO ₂ , Al (OH) ₃ , Mg (OH) ₂ , Ti (OH) _4, or a combination thereof.

Since the separator has improved adhesion by using a fluorine-based polymer, ceramic, or a combination thereof, in particular, in a pouch-type battery in which a flexible packaging material such as a laminate film is used, the separator is more stably bound between the electrode and the separator to detach and detach the electrode and the separator. The gap can be prevented and the position of the separator can be fixed.

In addition, the fluorine-based polymer, ceramic, or a combination thereof can be more easily dissolved in the electrolyte composition and form a polymer gel, thereby preventing the separator from rapidly contracting or deforming even during charging and discharging, thereby improving battery life characteristics. Can be.

The thickness of the entirety of the separator may be determined according to the capacity of the target battery. For example, the thickness of the separator may be about 10 to about 30 μm. The thickness of the polymer coating layer may be 0.1 to 5㎛ based on one surface. When the thickness of the polymer coating layer is smaller than the above range, sufficient heat resistance may not be obtained. In addition, when the thickness of the polymer coating layer is larger than the above range, the polymer coating layer increases the overall thickness of the separator, thereby reducing the capacity of the battery.

The separator manufactured by the manufacturing method separates the positive electrode and the negative electrode and provides a passage for moving lithium ions, as described above.

Hereinafter, the lithium secondary battery including the positive electrode, the negative electrode, the electrolyte solution, and the separator will be described.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separator and electrolyte used, and may be classified into a cylindrical shape, a square shape, a coin type, a pouch type, and the like according to a shape. Depending on the size, it can be divided into bulk type and thin film type. Specifically, the lithium secondary battery according to one embodiment of the present invention may be a pouch type battery. Since the structure and manufacturing method of these batteries are well known in the art, detailed description thereof will be omitted.

Hereinafter, examples and comparative examples of the present invention are described. However, the following examples are only examples of the present invention and the present invention is not limited to the following examples.

Example 1

(1) N-methylpyrrolidone (NMP) solvent containing 97.0% by weight of LiCoO ₂ as a positive electrode active material, 1% by weight of Denka Black as a conductive material, and 2% by weight of polyvinylidene fluoride (PVdF) as a binder. It was added to the prepared positive electrode active material composition. The positive electrode active material composition was applied to an aluminum (Al) thin film, dried, and roll pressed to prepare a positive electrode.

(2) 97% by weight of the negative electrode active material (SiO _x (x is 1.0 to 1.5) + 97% by weight of Graphite), 1% by weight of carboxymethylcellulose as a thickener, and 2% by weight of styrene-butadiene rubber as a binder in distilled water It was added to prepare a negative electrode active material composition. The negative electrode active material composition was coated on a copper foil, dried, and subjected to roll press to prepare a negative electrode.

(3) 1.15 M LiPF ₆ and fluoroethylene carbonate (FEC) in a mixed solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 20:50:30. 5 parts by weight (based on 100 parts by weight of the mixed solvent) were added to prepare an electrolyte solution.

(4) Polyvinylidene fluoride (PVdF) was dissolved in acetone, and then gravure coated on both surfaces of a 9 μm-thick polyethylene (PE) separator substrate. The thickness of the coating layer was 1.5 μm on one side.

(5) After preparing an electrode assembly using the positive electrode, the negative electrode and the separator, the electrode assembly is placed in a battery container, the electrolyte is injected into the battery container and sealed, and charged to 3.8V to coat the negative electrode. Was formed.

Subsequently, the PVdF layer coated on the separator was gelled through a heat press process to close the separator and the electrode plate, and a pouch-type battery was manufactured by vacuum sealing.

Example 2

A pouch type battery was manufactured in the same manner as in Example 1, except that ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 30:40:30 instead of 20:50:30.

Example 3

A pouch type battery was manufactured in the same manner as in Example 2, except that 7 parts by weight was used instead of 5 parts by weight.

Example 4

A pouch type battery was manufactured in the same manner as in Example 2, except that 10 parts by weight of fluoroethylene carbonate was used instead of 5 parts by weight of fluoroethylene carbonate.

Example 5

A pouch type battery was manufactured in the same manner as in Example 2, except that 15 parts by weight instead of 5 parts by weight of fluoroethylene carbonate were used.

Example 6

A pouch type battery was manufactured in the same manner as in Example 2, except that 20 parts by weight of fluoroethylene carbonate was used instead of 5 parts by weight.

Example 7

A pouch type battery was manufactured in the same manner as in Example 2, except that 30 parts by weight of fluoroethylene carbonate was used instead of 5 parts by weight.

Example 8

The above examples were mixed with ethylene carbonate, propylene carbonate, ethylmethyl carbonate and diethyl carbonate in a volume ratio of 30: 15: 25: 30 instead of a volume ratio of 20:50:30, and 10 parts by weight of fluoroethylene carbonate was used. In the same manner as in 1, a pouch-type battery was manufactured.

Comparative Example 1

A pouch type battery was manufactured in the same manner as in Example 1, except that ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 10:60:30 instead of 20:50:30.

Comparative Example 2

A pouch-type battery was manufactured in the same manner as in Example 1, except that the polyethylene separator without a coating layer was used.

Evaluation 1: Compressive Strength Evaluation

After weighing 1.5 wt% of the electrolyte solution and PVdF powder according to Examples 1 to 8 and Comparative Example 1 in a vial, dissolving PVdF in an oven at 100 ° C, lowering the temperature to room temperature again, diameter 20mm, height 15mm A cylindrical gel of was prepared.

The prepared gel was placed between the upper and lower envils of the Instron 3344 property tester, and the compressive strength was measured by compressing the gel to a break point at a speed of 100 mm / min. The compressive strength evaluation test results are shown in Table 1 and FIG. 2.

2 shows the compressive strength value according to the compressed distance when compressed to the break point of the gel including the electrolyte according to Example 4.

As shown in Table 1 and Figure 2, the gel containing the electrolyte according to Examples 1 to 8, it can be confirmed that has a superior compressive strength compared to the gel containing the electrolyte according to Comparative Examples 1 and 3. have.

Evaluation 2: Adhesion Evaluation

After preparing the negative electrode plate and the separator prepared in the preparation example to a width of 45mm, length 60mm, put into a pouch bag and inject the electrolyte solution according to Examples 1 to 8 and Comparative Example 1, the negative electrode plate and the separator as an electrolyte solution After impregnation and heat press, the adhesive force between the negative electrode plate and the separator was evaluated by peeling test at a speed of 10 mm / min using an Instron 3344 property tester.

The measured value was converted into force per unit width (N / mm) with respect to the length (45 mm) in the width direction of the specimen.

The adhesion test results are shown in Table 1 and FIG. 3.

3 is a result of using the electrolyte according to Example 4.

As shown in Table 1 and Figure 3, in the case of the electrolyte solution according to Examples 1 to 8, it can be seen that to improve the adhesion between the negative electrode plate and the separator than the electrolyte solution according to Comparative Example 1. This is because the adhesion between the PVdF component and the negative electrode plate coated on the separator is improved by using the appropriate electrolyte composition according to the present invention.

Electrolyte
(vol%) Lithium salt
(M) additive
(Parts by weight) Compressive strength
(MPa) Adhesion
(N / mm) EC PC EMC DEC LiPF ₆ FEC Example 1 20 0 50 30 1.15 5 1.64 0.007 Example 2 30 0 40 30 1.15 5 1.76 0.009 Example 3 30 0 40 30 1.15 7 1.79 0.010 Example 4 30 0 40 30 1.15 10 1.84 0.013 Example 5 30 0 40 30 1.15 15 1.89 0.015 Example 6 30 0 40 30 1.15 20 1.95 0.018 Example 7 30 0 40 30 1.15 30 2.11 0.025 Example 8 30 15 40 30 1.15 10 2.03 0.021 Comparative Example 1 10 0 60 30 1.15 5 1.38 0.003

Evaluation 3: room temperature evaluation

The battery according to Examples 1 to 8, Comparative Example 1, and Comparative Example 2 (having a capacity of 1C = 1600mAh) was performed 350 times under the following charging and discharging conditions, and the capacity retention rate was% based on the capacity of the first cycle. Indicated.

Charge: 0.7C / 4.3V, 0.025C cut-off under CC-CV

Discharge: 0.5C, 3.0V cut-off under CC conditions

The results of the room temperature evaluation test are shown in Table 2 and FIG. 4.

4 is a result according to Examples 2, 4, 6, 8, and Comparative Example 1.

As shown in Table 2 and FIG. 4, the life characteristics of Examples 1 to 8 including a high cyclic carbonate and a coating layer are higher than those of Comparative Example 1 having a low cyclic carbonate content and Comparative Example 2 that do not include a coating layer. The higher the fluoroethylene carbonate content in the same electrolyte composition, the better the life characteristics.

Since fluoroethylene carbonate acts as an additive to form a film of the negative electrode to improve the life and at the same time belong to the cyclic carbonate can be seen that the life characteristics improve as the content increases.

This is a result of the difference in the content of the cyclic carbonate having high solubility in PVdF, the higher the content of the cyclic carbonate has a higher solubility in PVdF, which has a positive effect on the improvement of the compressive strength and the adhesion between the plate and the separator.

In the case of Example 8, the content of the cyclic carbonate is higher than those of Examples 4 to 7, but due to the high viscosity of the ethylene carbonate and propylene carbonate seems to have slightly reduced life characteristics.

Evaluation 4: high temperature storage evaluation

After charging the battery according to Examples 1 to 8, Comparative Example 1, and Comparative Example 2 in the conditions of 0.7C / 4.3V, 0.025C cut-off under CC-CV conditions for 30 days at 60 ℃ The thickness was measured every 5 days to indicate the degree of battery swelling (cell thickness increase rate) in%.

Experimental results of the room temperature evaluation are shown in Table 2 and FIG. 5.

5 is a result according to Examples 2, 4, 6, 8, and Comparative Example 1.

As shown in Table 2 and FIG. 5, Examples 1 to 8 having a high cyclic carbonate content have a higher adhesive force between the electrode plate and the separator than Comparative Example 1 having a low cyclic carbonate content. Not easily deformed, improved high temperature storage characteristics. In addition, Examples 1 to 8 including the coating layer was superior to the high temperature storage characteristics than Comparative Example 2 without the coating layer.

Electrolyte
(vol%) Lithium salt
(M) additive
(Parts by weight) Room temperature
(% @ 350 times) Battery thickness increase rate
(% @ 30 days) EC PC EMC DEC LiPF ₆ FEC Example 1 20 0 50 30 1.15 5 72.7 19.0 Example 2 30 0 40 30 1.15 5 81.0 17.3 Example 3 30 0 40 30 1.15 7 82.3 11.2 Example 4 30 0 40 30 1.15 10 86.2 10.3 Example 5 30 0 40 30 1.15 15 86.4 10.7 Example 6 30 0 40 30 1.15 20 86.8 11.4 Example 7 30 0 40 30 1.15 30 87.4 13.5 Example 8 30 15 40 30 1.15 10 84.9 9.4 Comparative Example 1 10 0 60 30 1.15 5 NG 20.5 Comparative Example 2 30 0 40 30 1.15 10 NG 27.3

It can be seen from the evaluations 1 to 4 that proper control of the electrolyte composition and the fluoroethylene carbonate content is necessary to improve the battery life and the high temperature storage characteristics.

10: electrode assembly
13: electrode tab
20: battery container
100: lithium secondary battery

Claims (9)

A positive electrode including a positive electrode active material;
A negative electrode including a negative electrode active material;
Electrolyte solution containing a lithium salt and a non-aqueous organic solvent; And
A lithium secondary battery comprising a separator located between the positive electrode and the negative electrode,
The anode active material includes a Si-based material and a carbon-based material,
The carbonaceous material includes amorphous carbon,
The non-aqueous organic solvent comprises a cyclic carbonate comprising ethylene carbonate, propylene carbonate or a combination thereof, and a linear carbonate comprising ethylmethyl carbonate and diethyl carbonate,
The cyclic carbonate and the linear carbonate are included in a volume ratio of 1: 1 to 1: 9,
The additive includes at least one selected from fluoroethylene carbonate, vinylethylene carbonate, propane sultone, succinonitrile and adiponitrile,
The separator includes a porous substrate and a coating layer disposed on at least one surface of the porous substrate, wherein the coating layer includes a fluorine-based polymer, a ceramic, or a combination thereof, and the ceramic may be Al ₂ O ₃ , Al (OH) _3, or a combination thereof. Lithium secondary battery.
The method of claim 1,
The ethyl methyl carbonate is included in 10 to 70% by volume based on the total amount of the non-aqueous organic solvent, the diethyl carbonate is included in 10 to 70% by volume relative to the total amount of the non-aqueous organic solvent. .
The method of claim 1,
The cyclic carbonate is a lithium secondary battery that is contained in 20 to 60% by volume based on the total amount of the non-aqueous organic solvent.
The method of claim 3,
The cyclic carbonate is a lithium secondary battery that is contained in 30 to 60% by volume based on the total amount of the non-aqueous organic solvent.
The method of claim 1,
The linear carbonate is a lithium secondary battery that is contained in 40 to 80% by volume relative to the total amount of the non-aqueous organic solvent. The method of claim 1,
The Si-based material is Si, silicon oxide, Si-C composite, silicon-based alloy, or a combination thereof.
The method of claim 1,
The additive is a lithium secondary battery 5 to 30 parts by weight based on 100 parts by weight of the non-aqueous organic solvent.
The method of claim 1,
The porous substrate is a lithium secondary battery comprising polyethylene, polypropylene, aramid, polyimide, or a combination thereof.
The method of claim 1,
The separator has a thickness of 10 μm to 30 μm.

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