KR20150037408A - A composition for preparing anode comprising low temperature additives and a electrochemical device comprising the same - Google Patents

Abstract

The present invention relates to a composition for preparing a negative electrode comprising low temperature additives and an electrochemical device manufactured using the same. More specifically, the present invention provides: a carbon-based negative electrode material, which has a superior output characteristic at low temperature by inclusion of low temperature additives such as lithium titanium oxide (LTO) into a carbon-based negative electrode material to provide high output not only at room temperature but also at low temperature; and an electrode and electrochemical device manufactured using the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a composition for forming a negative electrode containing a low-temperature additive, and to an electrochemical device using the same. BACKGROUND OF THE INVENTION < RTI ID = 0.0 >

The present invention relates to a composition for forming a negative electrode containing a low-temperature additive and an electrochemical device manufactured using the same. More particularly, the present invention relates to a carbon-based anode material that includes a low-temperature additive such as lithium-titanium oxide (LTO) in a carbonaceous anode material and provides excellent output at low temperatures as well as room temperature, to provide.

As technology development and demand for mobile devices have increased, there has been a rapid increase in the demand for secondary batteries as energy sources. Among such secondary batteries, much research has been conducted on lithium batteries with high energy density and discharge voltage, . In addition, as interest in environmental issues grows, many researches on electric vehicles and hybrid electric vehicles that can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, which are one of the major causes of air pollution, are being conducted. Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage.

The lithium secondary battery has a structure in which a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode coated with an active material on a current collector. Lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium composite oxide and the like are mainly used as the cathode active material, and carbonaceous materials are mainly used as the anode oxide.

In order to use such a lithium secondary battery as a power source for an electric vehicle and a hybrid electric vehicle in addition to a cellular phone, a notebook computer, a PDA, and the like, performance that can operate under harsh conditions is required. For example, since mobile devices and electric vehicles used in the outside must be able to operate at low temperatures such as in winter, a typical example of the requirements as the power source is an excellent output characteristic at a low temperature. Especially, when the power can not be provided at a low temperature, the driving of the power system becomes unreasonable, and if the minimum output required for starting can not be attained, the vehicle operation itself may not be possible.

Improvement of the low temperature output characteristics of the lithium secondary battery is mainly attempted by improving the electrolyte and the cathode material. Up to now, a method of improving the low temperature output by changing the active material such as adoption of amorphous carbon as the anode active material for HEV has been considered. However, if the active material is changed, there is a problem that the available cell voltage range is changed or the profile pattern is changed, resulting in a decrease in the high temperature characteristics and the capacity of the battery.

Therefore, there is a demand for a technique capable of achieving an improvement in the low-temperature output characteristic in an easy way without substantially causing the deterioration of the high-temperature characteristics and the capacity of the battery.

In order to solve the above technical problems, the present invention provides a carbonaceous anode material having improved low-temperature output characteristics while minimizing deterioration of high-temperature characteristics and capacity.

The present invention also provides a negative electrode comprising the negative electrode material and an electrochemical device comprising the negative electrode.

Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The present invention provides a composition for forming a negative electrode for a lithium ion battery, which comprises a negative electrode active material, a binder, an organic solvent, and a low temperature property improving additive. Here, the low temperature property improving additive may be lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ , LTO).

Here, the content of the low temperature property improving additive may be 2 to 50% by weight based on 100% by weight of the composition for forming a negative electrode.

Here, the composition may further comprise at least one conductive agent selected from the group consisting of polyacetylene, polyaniline, polypyrrole, polythiophene and polysulfuronitrile, copper, silver, palladium and nickel.

Here, the anode active material may be a carbonaceous material.

Here, the carbon material may be low crystalline carbon and / or highly crystalline carbon.

The negative active material may be at least one selected from the group consisting of Si, Sn, Li, Mg, Al, Ca, Ce, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Pd, (Me) which is at least one selected from the group consisting of In, Sb, Pt, Au, Hg, Pb and Bi and / or at least two metals (Me) .

The present invention also provides a lithium ion battery having a current collector and a negative electrode active material layer formed by applying the composition on at least one surface of the current collector and drying the same.

Here, the lithium ion battery includes a negative electrode, a positive electrode, and a non-aqueous electrolyte, and the negative electrode uses the composition for forming the negative electrode according to the present invention.

Here, the lithium ion battery may have an operating range of 2.5 V or more.

According to an aspect of the present invention, there can be provided a carbon-based anode material having improved low-temperature output characteristics while minimizing deterioration of high-temperature characteristics and capacity, and a cathode and an electrochemical device employing the same. And can be suitably used as a unit battery for a battery or a battery pack. In particular, it can be used as an automobile power source such as an electric vehicle or a hybrid electric vehicle requiring a high output at a low temperature without requiring a separate internal combustion engine for heating at a low temperature.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 shows SOC and OCV of an electrode using an anode composition according to the present invention.
FIG. 2 is a graph showing a comparison of charging peaks of a battery using a negative electrode composition not containing LTO and a battery using the negative electrode composition according to the present invention.
3 is a graph showing the effect of improving the low temperature output of a battery using the anode composition according to the present invention.
FIG. 4 is a graph showing the effect of improving the charge transfer resistance at low temperature in the battery using the anode composition according to the present invention, as compared with the comparative example.
5 shows the effect of improving the room temperature output of the battery using the negative electrode composition according to the present invention.
FIG. 6 is a graph showing the effect of improving the charge transfer resistance at room temperature as compared with the battery using the negative electrode composition according to 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 embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

The present invention provides a negative electrode composition for a secondary battery comprising a negative electrode active material, a binder, an organic solvent, and an additive for improving low temperature characteristics.

In one embodiment of the present invention, the secondary battery may be a lithium ion battery for a hybrid electric vehicle (HEV). HEV supports automobile engine output by battery. In the past, Ni / MH battery was mainly installed, but it is decreasing from 2011, and lithium-ion battery with higher energy density than Ni / MH is replacing it. However, it is still required to solve the low-temperature output characteristic problem of the lithium ion battery for HEV.

In order to improve low-temperature characteristics of a lithium ion battery for HEV, the present invention is characterized in that the composition for forming a negative electrode contains an additive for improving low-temperature characteristics. According to a specific embodiment of the present invention, the additive for improving low-temperature characteristics is titanium oxide (TiO ₂ ) or lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ , LTO). Of these, lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ , LTO) is preferable. However, the present invention is not limited thereto.

Lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ , LTO) is generally used as an electrode material for lithium batteries. It is capable of high-speed charging and discharging, has almost no irreversible reaction (initial efficiency: 95% It has an advantage of excellent safety. However, it has a drawback that the operating voltage is in the range of 1.3 to 1.6 V and the reversible capacity is as small as about 170 mAh / g. Generally, the operating range of the HEV lithium ion battery is from 2.5V to 4.3V, and the available voltage of the cathode is less than 1.0V. Therefore, LTO does not contribute to charging / discharging when the lithium ion battery for HEV is designed to be below 1.0V. That is, since the EV lithium-ion battery does not act as an active material, it does not affect the inherent characteristics of the battery such as SOC and OCV (see FIGS. 1 and 2). However, when discharging at a high C-rate at a low temperature, overpotential is largely applied to the cathode, and the LTO is discharged to a very small amount, and the effect of low temperature output is improved due to the gradual slope of the profile of the low temperature discharge due to this effect (FIGS. 3 and 4 Reference). In addition, since LTO has high conductivity and high specific surface area, the charge transfer resistance is lowered at room temperature and low temperature, and thereby the output of the battery is improved (see FIGS. 5 and 6). In addition, LTO has high conductivity, excellent stability, excellent low-temperature characteristics, and has an excellent cycle life due to its extremely small volume expansion because it is an oxide having a three-dimensional structure. According to this feature, when LTO is mixed with the anode material, the conductivity of the anode electrode is increased to lower the charge transfer resistance of the battery, thereby improving the room temperature and low temperature output.

In one embodiment of the present invention, the content of the low temperature property improving additive such as LTO is 2 to 50% by weight, more preferably 2 to 30% by weight based on 100% by weight of the composition for forming a negative electrode of the present invention, . When the content of the additive for improving low-temperature characteristics is more than 30% by weight, irreversible is increased more than necessary and cathode loading is increased. According to a specific embodiment of the present invention, the LTO has an average primary particle diameter of 0.5 to 20 탆, preferably 1 to 10 탆. If the average particle diameter exceeds 10 mu m, there may be a disadvantage that the output decreases. Or when the average particle diameter is less than 1 mu m, there is a problem that the electrode BET increases more than necessary.

In one preferred embodiment of the present invention, the negative electrode active material used in the composition for forming a negative electrode for a secondary battery of the present invention generally includes a carbon material capable of intercalating and deintercalating lithium ions, lithium, a lithium alloy, silicon, Tin, tin alloy, or the like, 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 low crystalline carbon are soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, graphite, pyrolytic carbon, High-temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes are representative.

The carbon material preferably has a specific surface area of 10 m ² / g or less. If the specific surface area of the carbon material is more than 10 m ² / g, the initial efficiency of the cathode may be lowered. In the present invention, the lower limit of the specific surface area of the carbonaceous material is not particularly limited. The preferred lower limit is 2 m < ² > / g, but this is merely an example and is not limiting.

The carbon material may have a particle diameter of 5 탆 to 100 탆, preferably 5 탆 to 40 탆. If the average particle diameter of the carbon material is less than 5 탆, the initial efficiency of the cathode may be deteriorated due to the fine powder of carbon material. If the average particle diameter exceeds 100 탆, the processability of the anode slurry may be decreased and scratches may be increased.

In addition, according to one embodiment of the present invention, the negative electrode active material includes at least one selected from the group consisting of Si, Sn, Li, Mg, Al, Ca, Ce, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, (Me) and / or two or more metals (Me) which are at least one selected from the group consisting of Nb, Pd, Ag, Cd, In, Sb, Pt, Au, Hg, And may form a complex with the material.

The content of the negative electrode active material is 50 to 95% by weight, more preferably 70% by weight or more, based on 100% by weight of the composition for forming a negative electrode of the present invention.

As the polymer binder used in the negative electrode composition for a lithium secondary battery of the present invention, a commonly used binder may be used without limitation. For example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, SBR (styrene butadiene rubber), and the like can be used. The polymer binder resin may be contained in an amount of 0.1 to 10% by weight based on 100% by weight of the composition for forming a negative electrode.

The organic solvent used in the composition for forming a negative electrode for a lithium secondary battery of the present invention can be used without limitation as long as it is used in the art as an organic solvent for a composition for forming a negative electrode.

In addition, the anode forming composition for a lithium ion battery of the present invention may further include a conductive material within a range of 0.1 wt% to 10 wt%, preferably 0.5 wt% to 2 wt%, based on 100 wt% of the composition. Wherein the conductive material is at least one selected from the group consisting of carbon black, acetylene black, ketjen black, carbon fiber, polyacetylene, polyaniline, polypyrrole, polythiophene and polysulfuronitrile, copper, silver, palladium and nickel .

The negative electrode composition of the present invention may further contain a thickener to control the viscosity of the formed composition. The thickening agent is not particularly limited, for example, (Carboxymethyl cellulose).

The lithium ion battery according to the present invention is manufactured as a lithium secondary battery by injecting a non-aqueous electrolyte into the electrode structure composed of the negative electrode, the positive electrode, and the separator interposed between the positive electrode and the negative electrode. In addition to the negative electrode according to the present invention, the positive electrode, the separator, and the nonaqueous electrolyte may be those conventionally used in the production of lithium secondary batteries.

The nonaqueous electrolyte solution according to the present invention comprises an ionizable lithium salt and an organic solvent.

The lithium salt contained as an electrolyte in a non-aqueous liquid electrolyte of the present invention can be used without limitation, those which are commonly used in a lithium secondary battery electrolyte, such as the lithium salt, the anion is 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 ^- .

Examples of the organic solvent included in the non-aqueous electrolyte of the present invention include those commonly used in an electrolyte for a lithium secondary battery, such as an ether, an ester, an amide, a linear carbonate, a cyclic carbonate, etc., Two or more of them may be used in combination.

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, 2,3-pentylene carbonate, vinylene carbonate, and halides thereof, or a mixture of two or more thereof. Specific examples of the linear carbonate compound include a group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate Any one selected, or a mixture of two or more thereof 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, can be preferably used because they have high permittivity as a high viscosity organic solvent and dissociate the lithium salt in the electrolyte well, and dimethyl carbonate and diethyl carbonate When a low viscosity and a low dielectric constant linear carbonate are mixed in an appropriate ratio, an electrolyte having a high electric conductivity can be prepared, and thus it can be more preferably used.

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.

Also, in the positive electrode, the negative electrode and the separator forming the electrode structure, in addition to the negative electrode prepared according to the present invention, the positive electrode and the separator may be those conventionally used in the manufacture of lithium secondary batteries.

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 < 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 ) O ₄ (0.5 <x <1.3, 0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), Li _x Mn _{2 -z} Ni _z O ₄ 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.

The composition for forming an anode may be the same as the binder used in the negative electrode.

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.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

3 g of LTO (Posco ESM, T30 grade), 0.6 g of carbon black, 0.7 g of aqueous SBR as a binder and 3 g of LTO were mixed as a negative active material. These were mixed with water to prepare an anode slurry. The prepared electrode slurry was coated on one side of a copper current collector and dried at about 60 ° C for one day, and then a negative electrode having a size of 13.33 cm ² was produced.

Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3: 4: 3 and LiPF ₆ was added to the nonaqueous electrolyte solvent to prepare a 1M LiPF ₆ nonaqueous electrolyte solution.

An NMC 622 100% electrode was used as an anode. A polyolefin separator was interposed between the cathode and the anode, and the electrolyte was injected to prepare a pouch-type mono cell.

Comparative Example

30 g of spherical natural graphite, 0.6 g of carbon black as a conductive agent, and 0.7 g of aqueous SBR as a binder were mixed as an anode active material. These were mixed with water to prepare an anode slurry. The prepared electrode slurry was coated on one side of a copper current collector and dried at about 60 ° C for one day, and then a negative electrode having a size of 13.33 cm ² was manufactured.

Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3: 4: 3 and LiPF ₆ was added to the nonaqueous electrolyte solvent to prepare a 1M LiPF ₆ nonaqueous electrolyte solution.

An NMC 622 100% electrode was used as an anode. A polyolefin separator was interposed between the cathode and the anode, and the electrolyte was injected to prepare a pouch-type mono cell.

Experimental Example

The cells of the examples and comparative examples were charged with a constant current up to 4 V and then charged with a constant voltage until the current reached 0.1 at 4 V. Then, discharging was performed at a constant current up to 2.8 V.

OCV  And SOC  Character rating

FIG. 1 is a graph showing SOC and OCV of electrodes in Examples and Comparative Examples and comparing charging peaks of batteries of Examples and Comparative Examples. As can be seen from the graphs of FIGS. 1 and 2, the battery of the embodiment including LTO, which is a low temperature property improving additive, is fully charged (FIG. 2) It does not work at discharge. Also, it can be seen that the OCV and the SOC in the embodiment are not substantially different from the comparative example.

Low temperature output improvement effect

FIG. 3 shows that the battery of the embodiment improved the low temperature output compared with the comparative example, and FIG. 4 shows that the charge transfer resistance at the low temperature of the battery of the embodiment is improved as compared with the comparative example. In the case of the battery of the embodiment, when the battery is discharged at a low C-rate at a low temperature, the overpotential is largely applied to the cathode, and the conductivity of the LTO improves, thereby gentle slope of the low temperature discharge profile is obtained. .

Room temperature output improvement effect

Fig. 5 and Fig. 6 show that the room temperature output of the battery is improved as compared with the comparative example. It can be seen that the charge transfer resistance is lowered in the embodiment, and the output is greatly improved as compared with the comparative example. Particularly, in the case of Examples, it was confirmed that the output at SOC at room temperature was significantly improved as compared with Comparative Example.

Claims (10)

Anode active material;
bookbinder; And
And a low temperature property improving additive.
The method according to claim 1,
Wherein the low temperature property improving additive is lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ , LTO).
The method according to claim 1,
Wherein the content of the low temperature property improving additive is 2 to 50% by weight based on 100% by weight of the composition for forming a negative electrode.
The method according to claim 1,
The negative electrode composition for lithium ion battery according to claim 1, further comprising at least one conductive agent selected from the group consisting of polyacetylene, polyaniline, polypyrrole, polythiophene and polysulfuronitrile, copper, silver, palladium and nickel .
The method according to claim 1,
Wherein the negative electrode active material is a carbon material.
6. The method of claim 5,
Wherein the carbon material is a low-carbon and / or highly-crystalline carbon material.
6. The method of claim 5,
The negative electrode active material may be selected from the group consisting of Si, Sn, Li, Mg, Al, Ca, Ce, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Pd, Ag, (Me) which is at least one selected from the group consisting of Sb, Pt, Au, Hg, Pb and Bi and / or at least two kinds of metals (Me) A composition for forming a negative electrode for a battery.
A negative electrode for a lithium ion battery comprising a current collector and a negative electrode active material layer formed by applying the negative electrode composition of any one of claims 1 to 7 on at least one side of the current collector and drying the same.
A lithium secondary battery comprising a negative electrode, a positive electrode and a non-aqueous electrolyte, wherein the negative electrode is the negative electrode according to claim 8.
10. The method of claim 9,
Wherein the lithium ion battery has a working range of 2.5 V or more.

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