KR100497249B1 - Lithium ion secondary battery - Google Patents

Abstract

The present invention relates to a lithium ion secondary battery, the lithium ion secondary battery comprising a negative electrode comprising a polymer substrate, a current collector and a negative electrode active material layer; A positive electrode including a positive electrode active material capable of occluding and detaching lithium ions; And electrolyte solutions.

The lithium ion secondary battery of the present invention has an excellent energy density.

Description

Lithium ion secondary battery {LITHIUM ION SECONDARY BATTERY}

[Industrial use]

The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery having a high energy density.

[Prior art]

Lithium secondary batteries, which are in the spotlight as power sources of recent portable small electronic devices, exhibit high energy density by showing a discharge voltage that is twice as high as that of a battery using an alkaline aqueous solution using an organic electrolyte solution.

As a cathode active material of a lithium secondary battery, an oxide composed of lithium and a transition metal having a structure capable of intercalating lithium, such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNi _1-x Co _x O ₂ (0 <X <1) Was mainly used.

Lithium metal was initially used as a negative electrode active material. However, due to a problem of dendrites occurring and a very short lifespan, various types of carbon-based carbonaceous materials including artificial graphite, natural graphite, and hard carbon, which can be inserted / desorbed of lithium, have recently been used. The material is being used. However, the carbon-based anode active material can solve the problem of dendrites and has excellent voltage flatness and good life characteristics at low potential, but due to high reactivity with the organic electrolyte and low diffusion rate of lithium in the material, power ( There are problems such as power characteristics, initial irreversible control, and electrode swelling during charging and discharging.

Accordingly, researches for using lithium alloy as a negative electrode active material to solve the problem of dendrites have a long life. U. S. Patent No. 6,051, 340 describes a negative electrode comprising a metal that is not alloyed with lithium and a metal that is alloyed with lithium. In this patent, the metal that is not alloyed with lithium serves as a current collector, and the metal that is alloyed with lithium forms an alloy with lithium ions taken out of the anode during charging, and the alloy serves as a negative electrode active material, The negative electrode contains lithium during charging.

However, even with the lithium alloy described above, it was difficult to obtain satisfactory battery characteristics.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a lithium ion secondary battery including a negative electrode having an excellent energy density.

In order to achieve the above object, the present invention is a negative electrode comprising a polymer substrate, a current collector and a negative electrode active material layer; A positive electrode including a positive electrode active material capable of occluding and detaching lithium ions; And it provides a lithium ion secondary battery comprising an electrolyte solution.

Hereinafter, the present invention will be described in more detail.

In the present invention, a negative electrode of a lithium ion secondary battery uses a lithium vapor deposited on a current collector instead of a conventional carbon material. As shown in FIG. 1, the negative electrode of the present invention is composed of a polymer substrate 1, current collector layers 3, 3 'formed on the polymer substrate, and negative electrode active material layers 5, 5' formed on the current collector layer. do. The polymer substrate includes a polymer selected from the group consisting of polyethylene terephthalate, polyimide, polyethylene naphthalate, polypropylene, polyethylene, and polyester. 1-30 micrometers is preferable, as for the thickness of the said polymer base material, 2-25 micrometers is more preferable, and its 3-20 micrometers are the most preferable. When the thickness of the polymer substrate is less than 1 μm, handling is difficult, and when larger than 30 μm, there is a problem that the energy density is reduced.

The polymer substrate may further include a silicone release agent.

The current collector is formed of a material that does not form an alloy with lithium, and examples of such materials include those selected from the group consisting of Ni, Ti, Cu, Ag, At, Pt, Fe, Co, Cr, W, and Mo. Can be. 10 kPa-10 micrometers are preferable, as for the thickness of the said electrical power collector, 100 kPa-9 micrometers are more preferable, and 200 kPa-8 micrometers are the most preferable. If the thickness of the current collector is less than 100 kV, the current collector capacity may be deteriorated, and if the current collector is larger than 10 µm, the energy density is reduced, which is not preferable.

The negative electrode active material layer includes lithium metal, an alloy of lithium metal, or a material capable of reversibly forming a compound with lithium. As a material capable of forming an alloy or a compound with the lithium, those selected from the group consisting of Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In, and Zn may be used.

In addition, the negative electrode active material layer may further include a protective film on the surface. The passivation layer may be a single layer or a multilayer formed of one selected from the group consisting of a polymer material, an inorganic material, or a mixture thereof.

The inorganic material may be LiPON (Lithium Phosphorus Oxy-Nitride, Li _2.9 PO _3.3 N _0.46 ), Li ₂ CO ₃ , Li ₃ N, Li ₃ PO ₄ or Li ₅ PO ₄ .

The thickness of the protective film formed of the inorganic material is preferably 10 kPa to 10,000 kPa. When the thickness of the protective film is thinner than 10 kW, the thickness of the protective film may be too thin, so that the protective film may be physically damaged. When the protective film is thicker than 10,000 kW, the ion conductivity and energy density may be reduced.

Further, the polymer material forming the protective film may be polyvinylidene fluoride, copolymer of polyvinylidene fluoride and hexafluoropropylene, poly (vinyl acetate), poly (vinyl butyral-co-vinyl alcohol-co- Vinyl acetate), poly (methylmethacrylate-co-ethyl acrylate), polyacrylonitrile, polyvinyl chloride co-vinyl acetate, polyvinyl alcohol, poly (1-vinylpyrrolidone-co-vinyl acetate), Cellulose acetate, polyvinylpyrrolidone, polyacrylate, polymethacrylate, polyolefin, polyurethane, polyvinyl ether, acrylonitrile-butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene-styrene, sulfonated Styrene / ethyl-butylene / styrene triblock polymer, polyethylene oxide and mixtures thereof can do.

The thickness of the protective film formed of the polymer material is preferably 100 μm to 10 μm. When the thickness of the protective film formed of the polymer material is thinner than 100 Å, it may be too thin to physically damage the protective film, and when the protective film is thicker than 10 μm, there is a problem of lowering ion conductivity and energy density.

The negative electrode of the present invention having the above-described configuration forms a current collector on the polymer substrate by depositing a current collector material on one or both surfaces of the polymer substrate, such as a film form, and the negative electrode active material on the current collector formed on the polymer substrate. Prepare by vapor deposition. The deposition process may be performed by any method capable of depositing the current collector material and the negative electrode active material, and representative examples thereof may be sputtering, electron beam evaporation, and vacuum thermal evaporation. ), Laser ablation, chemical vapor deposition, thermal evaporation, plasma chemical vapor deposition, laser chemical vapor deposition, and jet vapor deposition. The deposition process is carried out by heating at a high vacuum of 10 ^-6 Torr or more for both the current collector and the negative electrode active material deposition, and the deposition atmosphere is carried out in a dry room with little moisture.

The lithium ion secondary battery of the present invention including the negative electrode includes a positive electrode including a positive electrode active material that reversibly occludes and desorbs lithium ions.

The positive electrode of a lithium ion secondary battery including the negative electrode of the present invention includes a positive electrode active material capable of intercalating and deintercalating lithium ions. Representative examples of the positive electrode active material may be selected from the group consisting of the following formula (1) to (12).

[Formula 1]

Li _x Mn _1-y M _y A ₂

[Formula 2]

Li _x Mn _1-y M _y O _2-z X _z

[Formula 3]

Li _x Mn ₂ O _4-z X _z

[Formula 4]

Li _x Co _1-y M _y A ₂

[Formula 5]

Li _x Co _1-y M _y O _2-z X _z

[Formula 6]

Li _x Ni _1-y M _y A ₂

[Formula 7]

Li _x Ni _1-y M _y O _2-z X _z

[Formula 8]

Li _x Ni _1-y Co _y O _2-z X _z

[Formula 9]

Li _x Ni _1-yz Co _y M _z A _α

[Formula 10]

Li _x Ni _1-yz Co _y M _z O _2-α X _α

[Formula 11]

Li _x Ni _1-yz Mn _y M _z A _α

[Formula 12]

Li _x Ni _1-yz Mn _y M _z O _2-α X _α

(Wherein 0.90 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, M is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V and At least one element selected from the group consisting of rare earth elements, A is an element selected from the group consisting of O, F, S and P, and X is F, S or P.)

In the lithium ion secondary battery of the present invention, the electrolyte solution contains an organic solvent and a lithium salt. As the organic solvent, benzene, fluorobenzene, toluene, dimetalformamide, dimethyl acetate, trifluorotoluene, xylene, cyclohexane, tetrahydrofuran, 2-methyltetrahydrofuran, cyclohexanone, ethanol, iso Propyl alcohol, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methylpropyl carbonate, methylpropionate, ethylpropionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxyethane, 1,3-dioxolane, digly One or more selected from the group consisting of lym, tetraglyme, ethyl carbonate, propyl carbonate, ν-butyrolactone and sulfolane may be used. The mixing ratio in the case of mixing more than one can be appropriately adjusted according to the desired battery performance, which can be widely understood by those skilled in the art.

As the lithium salt, one or more lithium salts selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) _2, and LiAsF ₆ may be used. have. They are dissolved in organic solvents and act as a source of lithium ions in the cell to enable operation of the basic lithium ion secondary battery and to promote the movement of lithium ions between the positive and negative electrodes.

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

(Comparative Example 1)

A positive electrode active material slurry was prepared by mixing a LiCoO ₂ positive electrode active material, a polyvinylidene fluoride binder, and a super-P conductive material in an N-methylpyrrolidone mixed solvent at a 94/3/3 weight ratio. The slurry was coated on an aluminum current collector, dried, and rolled using a rolling mill to prepare a positive electrode plate.

The negative electrode active material slurry was prepared by mixing the carbon negative electrode active material and the polyvinylidene fluoride binder in an N-methylpyrrolidone mixed solvent in a 94/6 weight ratio. The negative electrode active material slurry was coated on a copper current collector, dried, and rolled using a rolling mill to prepare a negative electrode plate.

The battery was assembled using the positive plate and the negative plate. The battery produced had a specification of 4.5 cm in height, 3.7 cm in width, and 0.4 cm in thickness and had a capacity of 650 mAh. In this case, a mixed solution of ethylene carbonate / dimethyl carbonate and ethylmethyl carbonate (3/3/4 vol. Volume) in which 1.0 M LiPF ₆ was dissolved was used.

(Example 1)

1000 Å of copper was deposited on both sides of a polyethylene terephthalate film having a thickness of 5 μm. A negative electrode plate was prepared by depositing 5 μm each of lithium on both surfaces of a copper-deposited polyethylene terephthalate film.

A battery was manufactured using the negative electrode and the positive electrode of Comparative Example 1.

The battery is 4.5cm high, 3.7cm wide and 0.25cm thick, with a capacity of 650mAh.

(Example 2)

A lithium ion secondary battery of 650 mAh having a specification of 4.5 cm in height, 3.7 cm in width, and 0.27 cm in thickness was manufactured by using a negative electrode manufactured by depositing lithium at 15 μm on both sides of a copper-deposited polyethylene terephthalate film. Except that was carried out in the same manner as in Example 1.

(Example 3)

A lithium ion secondary battery of 650 mAh having a specification of 4.5 cm in height, 3.7 cm in width, and 0.31 cm in thickness was fabricated using a negative electrode manufactured by depositing lithium at 30 μm on both sides of a copper-deposited polyethylene terephthalate film. Except that was carried out in the same manner as in Example 1.

(Example 4)

A lithium ion secondary battery of 650 mAh having a specification of 4.5 cm in height, 3.7 cm in width, and 0.35 cm in thickness was manufactured using a negative electrode prepared by depositing lithium at 45 μm on both sides of a copper-deposited polyethylene terephthalate film. Except that was carried out in the same manner as in Example 1.

The battery measures 4.5cm high, 3.7cm wide and 0.35cm thick, and has a capacity of 650mAh.

(Example 5)

A lithium ion secondary battery of 650 mAh having a specification of 4.5 cm in height, 3.7 cm in width, and 0.38 cm in thickness was fabricated using a cathode prepared by depositing 60 μm of lithium on both sides of a copper-deposited polyethylene terephthalate film. Except that was carried out in the same manner as in Example 1.

After charging the lithium ion secondary batteries of Examples 1 to 5 and Comparative Example 1 at 0.2C and discharging at 0.2C, the capacity, Wh / kg, Wh / kg increase rate, Wh / l and Wh / l increase rate were measured. The results are shown in Table 1 below.

Capacity (mAh) Wh / kg % Increase in Wh / kg Wh / l % Increase in Wh / l Comparative Example 1 650 152 - 361 - Example 1 650 215 41 578 60 Example 2 650 211 39 535 48 Example 3 650 206 35 466 29 Example 4 650 202 33 413 14 Example 5 650 198 30 380 5

As shown in Table 1, it can be seen that the batteries of Examples 1 to 5 in which copper was deposited on polyethylene terephthalate and lithium was again deposited were higher in mass energy density and volumetric energy density than in Comparative Example 1.

The lithium ion secondary battery of the present invention has an excellent energy density.

1 is a cross-sectional view schematically showing the structure of a cathode of the present invention.

Claims (24)

A negative electrode including a polymer substrate, a current collector, and a negative electrode active material layer, and including a protective film formed of a material selected from the group consisting of a polymer material, an inorganic material, and a mixture thereof; A positive electrode including a positive electrode active material capable of occluding and detaching lithium ions; And Electrolyte Including, The polymer substrate is selected from the group consisting of polyethylene terephthalate, polyimide, polyethylene naphthalate, polypropylene, polyethylene, and polyester, The polymeric materials include polyvinylidene fluoride, copolymers of polyvinylidene fluoride and hexafluoropropylene, poly (vinyl acetate), poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate), poly (methyl Methacrylate-co-ethyl acrylate), polyacrylonitrile, polyvinyl chloride co-vinyl acetate, polyvinyl alcohol, poly (1-vinylpyrrolidone-co-vinyl acetate), cellulose acetate, polyvinylpyrroly Don, polyacrylate, polymethacrylate, polyolefin, polyurethane, polyvinyl ether, acrylonitrile-butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene-styrene, sulfonated styrene / ethyl-butylene / Styrene triblock polymer, polyethylene oxide and mixtures thereof, The inorganic material is a lithium ion secondary battery selected from the group consisting of LiPON, Li ₂ CO ₃ , Li ₃ N, Li ₃ PO ₄ and Li ₅ PO ₄ . The lithium ion secondary battery of claim 1, wherein the negative electrode active material is selected from the group consisting of lithium metal, an alloy of lithium metal, and a material capable of reversibly forming a compound with lithium. delete The lithium ion secondary battery of claim 1, wherein the protective layer is a single layer or a double layer. delete The lithium ion secondary battery of claim 1, wherein the protective film made of the inorganic material has a thickness of about 10 to 10,000 kPa. delete The lithium ion secondary battery of claim 1, wherein the protective film made of the polymer material has a thickness of about 100 μm to about 10 μm. The lithium ion secondary battery of claim 1, wherein the negative electrode active material layer has a thickness of 1 to 100 μm. The lithium ion secondary battery of claim 9, wherein the negative electrode active material layer has a thickness of 2 to 90 μm. The lithium ion secondary battery of claim 10, wherein the negative electrode active material layer has a thickness of 3 to 80 μm. The method of claim 2, wherein the material capable of forming an alloy or reversibly compound with lithium is Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In and Zn The lithium ion secondary battery which is chosen. The lithium ion secondary battery of claim 1, wherein the current collector is formed of a material that does not form an alloy with lithium. The lithium ion secondary battery of claim 13, wherein the current collector is selected from the group consisting of Ni, Ti, Cu, Ag, At, Pt, Fe, Co, Cr, W, and Mo. The lithium ion secondary battery of claim 1, wherein the current collector has a thickness of 10 μm to 10 μm. The lithium ion secondary battery of claim 15, wherein the current collector has a thickness of 100 μs to 9 μm. The lithium ion secondary battery of claim 16, wherein a thickness of the current collector is 200 kW to 8 μm. delete The lithium ion secondary battery of claim 1, wherein the polymer substrate further comprises a silicon release agent. The lithium ion secondary battery of claim 1, wherein the polymer substrate has a thickness of 1 to 30 μm. The lithium ion secondary battery of claim 20, wherein the polymer substrate has a thickness of 2 to 25 μm. The lithium ion secondary battery of claim 21, wherein the polymer substrate has a thickness of 3 to 20 μm. The method of claim 1, wherein the electrolyte is benzene, fluorobenzene, toluene, dimetalformamide, dimethyl acetate, trifluorotoluene, xylene, cyclohexane, tetrahydrofuran, 2-methyltetrahydrofuran, cyclohexanone , Ethanol, isopropyl alcohol, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methylpropyl carbonate, methylpropionate, ethylpropionate, methyl acetate, ethyl acetate, propyl acetate, dimethoxyethane, 1,3-diox A lithium ion secondary battery comprising an organic solvent selected from the group consisting of solan, diglyme, tetraglyme, ethyl carbonate, propyl carbonate, ν-butyrolactone and sulfolane. The lithium ion secondary of claim 1, wherein the electrolyte includes a lithium salt selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , LiBF _6, and LiClO ₄ . battery.