KR20170008479A - Secondary battery, and battery pack comprising the same - Google Patents

Abstract

The present invention relates to a secondary battery and a battery pack comprising the same, and more specifically, to a secondary battery which includes a positive electrode, a negative electrode, and an electrolyte and in which one or more of the positive electrode and the negative electrode include dioctyl sodium sulfosuccinate. According to the present invention, the secondary battery includes dioctyl sodium sulfosuccinate in the electrodes and the compound reduces surface tension of a nonaqueous organic solvent, and thus the electrodes and wettability are desirable for an electrolyte having a high-concentration lithium salt and desirable wettability is exhibited for the positive electrode obtained by performing high-density rolling on a lithium nickel-manganese-cobalt oxide. Accordingly, provided is an effect in which the secondary battery exhibits uniform charging/discharging and life span characteristics.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a secondary battery and a battery pack including the secondary battery.

The present invention relates to a secondary battery and a battery pack including the same.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, Batteries have been commercialized and widely used.

The performance of such a secondary battery is affected by smooth movement of lithium ions in the electrode coating layer and uniform reaction thereof.

In order to transfer lithium ions, the electrolyte must penetrate quickly and uniformly to the micropores in the electrode. In the wettability of the electrolyte, the anode mainly acts as a bottle neck.

When the wettability of the electrolyte is lowered in the case of the anode, insertion and desorption of lithium ions may locally and nonuniformly proceed, and local overcharge and overdischarge regions may be formed in this process. Such overcharging and overdischarging areas may cause problems such as formation of unnecessary byproducts in the battery, or deterioration of the performance of the battery by generating gas, and operation of the safety device in the battery may occur if the battery is severely damaged.

Furthermore, non-uniform electrolyte wettability generally increases the resistance of the electrode, so that rapid capacity decrease may occur at the beginning of the life of a lithium secondary battery used for applications requiring high rate discharge.

In particular, as the lithium secondary battery market has recently increased, the production rate of the mass production line is inevitably increased due to a rapid increase in the amount of water, and the rate of electrolyte injection must also be increased, so that the wettability of the electrolyte to the electrode is required to be improved.

Korean Patent Publication No. 10-2004-0096773

A first object of the present invention is to provide a secondary battery including an electrode having improved wettability with respect to an electrolyte solution.

A second technical object of the present invention is to provide a battery module and a battery pack including the secondary battery.

In order to solve the above problems, the present invention provides a positive electrode comprising a positive electrode, a negative electrode and an electrolyte,

Wherein at least one of the positive electrode and the negative electrode comprises dioctyl sodium sulfosuccinate.

The present invention also provides a battery module and a battery pack including the secondary battery.

The secondary battery according to the present invention comprises dioctyl sodium sulfosuccinate in an electrode and the compound lowers the surface tension of the non-aqueous organic solvent, so that the electrode has excellent wettability with the electrode even in the case of an electrolyte having a high lithium salt concentration , And an anode obtained by rolling lithium-nickel-manganese-cobalt oxide at high density can exhibit excellent wettability.

Therefore, there is an effect that the secondary battery exhibits uniform charge / discharge and lifetime characteristics.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The 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 appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, the terms "comprising," "comprising," or "having ", and the like are intended to specify the presence of stated features, integers, But do not preclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

Generally, non-aqueous electrolytic solutions of lithium secondary batteries are mainly composed of nonconjugated organic solvents such as ethylene carbonate, diethyl carbonate, and 2-methyltetrahydrofuran. Such electrolytic solution is a polar solvent having a polarity enough to dissolve and dissolve an electrolyte salt, and is an aprotic solvent having no active hydrogen, and has high viscosity and surface tension. Therefore, the non-aqueous electrolytic solution of the lithium secondary battery has a low affinity with the electrode material including the polytetrafluoroethylene and the polyvinylidene fluoride binder or the like, so that the electrode material can not be easily wetted. Further, the wettability may be deteriorated when an electrolyte solution having a high lithium salt concentration or a high compression density of the electrode is used. Such deterioration of the wettability property is one of the main causes of inefficiently increasing the manufacturing process time of the battery.

According to an embodiment of the present invention, there is provided a secondary battery comprising a cathode, a cathode, and an electrolyte, wherein at least one of the anode and the cathode comprises dioctyl sodium sulfosuccinate.

Dioctyl sodium sulfosuccinate contained in the electrode lowers the surface tension of the electrolytic solution, so that the electrolytic solution can penetrate into the electrode quickly and uniformly.

The dioctyl sodium sulfosuccinate is ionized with dioctyl sulfosuccinate and sodium (Na ⁺ ) in contact with the electrolytic solution, and dioctyl sulfosuccinate is electrostatically bound to the non-aqueous organic solvent The surface tension of the non-aqueous organic solvent can be lowered. As a result, the electrolyte can permeate into the electrode more quickly.

The anode may include a cathode active material and a binder together with dioctyl sodium sulfosuccinate. The cathode active material may be a lithium nickel-manganese-cobalt oxide represented by the following general formula (1), but is not limited thereto.

[Chemical Formula 1]

LiNi _x Co _y Mn _z O ₂ (where 0.5 <x <0.9, 0.01 <y <0.2, 0.01 <z <0.3, and x + y + z = 1)

When the lithium nickel-manganese-cobalt oxide having the above composition is used as the cathode active material, the capacity reduction rate is alleviated in the early stage of the battery cycle (particularly at a high rate discharge cycle).

In addition, when the lithium nickel-manganese-cobalt oxide is used as the cathode active material, the compression density of the electrode manufactured by performing strong rolling at the time of manufacturing the electrode is increased. When such an electrode having a high compression density is used, Since the space through which the electrolyte can penetrate is smaller, penetration of the electrolyte solution may be more difficult. However, in the present invention, dioctyl sodium sulfosuccinate in the electrode remarkably lowers the surface tension of the electrolytic solution, so that it quickly and uniformly penetrates into the high-density electrode, thereby exhibiting excellent wettability between the electrolytic solution and the electrode.

At this time, the compression density of the anode may be 3.1 g / cc to 4.0 g / cc. This may be a value that is higher than the compression density of 1 g / cc to 3 g / cc of the electrode in the conventional secondary battery.

The compression density refers to the density of the anode after coating the anode slurry on the current collector and then pressing it at a constant pressure. Higher compression densities mean that more of the cathode active material is on the current collector under the same volume. The life characteristics of the secondary battery can be further improved in the range of the compression density.

The binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), carboxyl methyl cellulos, and mixtures thereof. Although the binder has poor affinity with non-aqueous organic solvents and the like, it is contained in the electrode together with the dioctyl sodium sulfosuccinate of the present invention, thereby lowering the viscosity and surface tension of the non-aqueous organic solvent. And an excellent wettability between the electrolyte and the electrolyte.

The electrolytic solution includes a lithium salt and a non-aqueous organic solvent. At this time, the non-aqueous organic solvent is a polar solvent having a polarity enough to dissolve and dissociate the lithium salt effectively, an aprotic solvent having no active hydrogen, and a high viscosity and surface tension. In the present invention, by incorporating dioctyl sodium sulfosuccinate into the electrode, even when a non-aqueous organic solvent containing a lithium salt having a higher concentration is used, the viscosity of the electrolytic solution is not lowered and excellent wettability with the electrode can be exhibited.

At this time, the concentration of the lithium salt to the electrolytic solution may be 1.6 M to 3 M, specifically 1.7 to 3 M. This may be a value higher than 0.5 M to 1.5 M, which is the concentration of the lithium salt in the electrolytic solution in the conventional secondary battery.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, Tetrahydrofuran, tetrahydrofuran, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Examples of the organic solvent include methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, Propylenic organic solvents such as methylmethyl, ethylpropionate and the like can be used. Particularly, when a cyclic carbonate such as ethylene carbonate or fluoro-ethylene carbonate is used, it is not only decomposed in the cell but is stable, and also has an excellent effect of lowering the surface tension due to dioctyl sodium sulfosuccinate, The wettability can be improved.

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

The negative electrode may include a negative electrode active material, the binder, and the like. The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1 - x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based material, and the like.

According to one embodiment of the present invention, there is provided a surface tension modifier comprising a cathode active material represented by the following formula (1), polyvinylidene fluoride, carboxylmethyl cellulose and a mixture thereof, and dioctyl sodium sulfosuccinate Lt; RTI ID = 0.0 &gt; slurry. &Lt; / RTI &gt;

[Chemical Formula 1]

LiNi _x Co _y Mn _z O ₂ (where 0.5 <x <0.9, 0.01 <y <0.2, 0.01 <z <0.3, and x + y + z = 1)

Since the positive electrode slurry includes a surface tension regulator containing dioctyl sodium sulfosuccinate, the surface tension of the non-aqueous organic solvent can be lowered. Thus, the positive electrode prepared using the positive electrode slurry has a wettability characteristic with the electrolyte great.

The surface tension regulator may further include one selected from the group consisting of ethanol, water, and a mixture thereof. The surface tension regulator may include 70 to 80 wt% of dioctyl sodium sulfosuccinate based on the total weight of the surface tension regulator You can use the included.

On the other hand, the surface tension regulator may be included in an amount of 0.5 to 5% by weight based on the total weight of the cathode slurry. If the amount of the surface tension regulator is less than 0.5 wt%, the wetting property between the electrode and the electrolyte is insufficient. When the amount of the surface tension regulator is more than 5 wt%, the energy density of the electrode decreases, There may be a problem of increase.

According to an embodiment of the present invention, there is provided a method of manufacturing a positive electrode slurry, comprising the steps of: (1) coating the positive electrode slurry on a current collector; Roll pressing the slurry-coated current collector (step 2); And drying the roll-pressed slurry-coated current collector at a temperature of 60 ° C to 80 ° C (Step 3).

 In the method for producing an anode according to the present invention, Step 1 is a step of coating a positive electrode slurry on a current collector.

In step 1, the positive electrode slurry may be thinly coated on a current collector having a predetermined thickness. Here, the current collector may have a thickness of about 10 m to 100 m, and the current collector may be any one selected from aluminum foil, aluminum mesh, and copper foil, and the positive electrode slurry coated on the current collector, May have a thickness of about 50 to 200 mu m, but the present invention is not limited thereto.

In the method for producing an anode according to the present invention, Step 2 is a step of roll pressing the current collector coated with the slurry.

In the roll pressing step, the current collector coated with the active material as described above is passed through the heated rollers so that the adhesion between the active material and the active material, the adhesion between the active material and the current collector can be improved, Can be increased. At this time, the compression density of the anode produced by roll-pressing at a pressure of 8 MPa to 15 MPa may be 3.1 g / cc to 4.0 g / cc.

Even if a roll press is performed at a somewhat higher pressure to produce a high capacity positive electrode having a high compression density, the positive electrode and the electrolyte can exhibit high wettability due to dioctyl sodium sulfosuccinate contained in the positive electrode slurry.

In the anode manufacturing method according to the present invention, step 3 is a step of drying the roll-pressed slurry-coated current collector at a temperature of 60 ° C to 80 ° C.

The solvent of the positive electrode slurry may be removed and drying may be carried out in a vacuum atmosphere to remove water entrained during the process. At this time, it is necessary to perform drying at a temperature of 60 ° C to 80 ° C due to dioctyl sodium sulfosuccinate in the cathode slurry to prevent deformation of the compound and to remain as residues in the electrode.

According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having a low electrode resistance and exhibiting uniform charge / discharge and lifetime characteristics, it is possible to use a power tool, an electric vehicle (EV), a hybrid electric vehicle Vehicle, an electric vehicle including a plug-in hybrid electric vehicle (PHEV), or a power storage system.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

&Lt; Example 1 >

Step 1: Preparation of positive electrode slurry

LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ 92% by weight, 3% by weight of the conductive agent of carbon black (carbon black), polyvinylidene fluoride (PVdF) 3% by weight of a binder, BASF's WE3475 (ethanol 5% by weight, a surface tension adjusting agent, water 15% by weight , 2% by weight of dioctyl sodium sulfosuccinate (including 80% by weight) and N-methyl-2-pyrrolidone (NMP) as a solvent were mixed to prepare a positive electrode slurry.

Step 2: Preparation of positive electrode

The positive electrode slurry was applied to an aluminum (Al) thin film as a positive electrode current collector having a thickness of 15 m, followed by performing a roll press at a pressure of 4 MPa and drying at a temperature of 70 캜 to obtain a negative electrode having a compression density of 1.5 g / cc. At this time, the compression density of the anode was measured by taking the electrode of a specific area, measuring the mass and thickness of the electrode, and subtracting the mass and thickness of the aluminum metal as the current collector.

Step 3: Preparation of secondary battery

Graphite was used as the cathode. On the other hand, LiPF ₆ was added to a nonaqueous electrolyte solvent prepared by mixing ethylene carbonate and diethyl carbonate as electrolytes in a volume ratio of 30:70 to prepare a 1.5 M LiPF ₆ nonaqueous electrolyte solution. After the positive electrode and the negative electrode thus prepared were interposed with a mixed separator of polyethylene and polypropylene, a jelly roll cell was fabricated, and the nonaqueous electrolytic solution thus prepared was injected to prepare a lithium secondary 18650 circular battery.

&Lt; Comparative Example 1 &

A secondary battery was fabricated in the same manner as in Example 1 except that the surface tension modifier was not included in the step 1 of Example 1.

&Lt; Examples 2 to 7 and Comparative Examples 2 to 7 >

In Example 1, a secondary battery was manufactured in the same manner as in Example 1, except that the experiment was conducted in accordance with the conditions shown in Table 1 below.

Roll press condition Anode compression density Lithium salt concentration Surface tension modifier Example 1 4 MPa 1.5 g / cc 1.0 M ○ Comparative Example 1 Χ Example 2 7 MPa 2.5 g / cc 1.0 M ○ Comparative Example 2 Χ Example 3 9 MPa 3.1 g / cc 1.0 M ○ Comparative Example 3 Χ Example 4 15 MPa 4.0 g / cc 1.0 M ○ Comparative Example 4 Χ Example 5 7 MPa 2.5 g / cc 0.5 M ○ Comparative Example 5 Χ Example 6 7 MPa 2.5 g / cc 1.6 M ○ Comparative Example 6 Χ Example 7 7 MPa 2.5 g / cc 3.0 M ○ Comparative Example 7 Χ

<Experimental Example 1> Wettability and Resistance Characteristics

LiPF ₆ was added to the nonaqueous electrolyte solvent prepared by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 30:70 to the positive electrodes prepared in Examples 1 to 8 and Comparative Examples 1 to 8, Aqueous electrolyte solution was dropwise added to the electrode, and then the time when all of the electrode was absorbed into the electrode was measured. Further, the resistances of the electrodes prepared according to Examples 1 to 4 and Comparative Examples 1 to 4 were measured with a resistance meter, and the results are shown in Tables 2 and 3. [

Anode compression density Wetting time (sec) Electrical Resistance (Ω) Example 1 1.5 g / cc 100 0.119 Comparative Example 1 101 0.121 Example 2 2.5 g / cc 198 0.085 Comparative Example 2 200 0.081 Example 3 3.1 g / cc 270 0.051 Comparative Example 3 275 0.048 Example 4 4.0 g / cc 420 0.023 Comparative Example 4 433 0.022

Lithium salt concentration Wetting time (sec) Example 5 0.5 M 177 Comparative Example 5 178 Example 2 1.0 M 198 Comparative Example 2 200 Example 6 1.6 M 248 Comparative Example 6 261 Example 7 3.0 M 294 Comparative Example 7 311

As shown in Tables 2 and 3, the wetting time of the electrodes according to the present invention is improved because the wetting time of the embodiments is lower than that of the comparative examples.

Specifically, when the anode compaction density was 1.5 g / cc, the wetting time of the comparative example was consumed by 1% longer than that of the Example, 1.01% at 2.5 g / cc, 1.85% at 3.1 g / cc, 4.0 g / cc is consumed 3.09% longer.

When the lithium salt concentration is 0.5 M, the wetting time of the comparative example is consumed by 0.5% longer than that of the comparative example, and it is consumed by 1% at 1.0 M, 5.24% at 1.6 M and 5.78% at 3.0 M .

Thus, when the compression density of the anode is 3.1 g / cc or more, or when the lithium salt concentration of the electrolyte is 1.6 M or more, the improvement effect of the wettability of the anode is particularly high at 1.8% and 5% or more.

In addition, it can be seen that the resistance of the anode shows an equivalent increase in the level of 4 to 5% when the anode density is increased when dioctyl sodium sulfosuccinate is included.

As a result, when the compression density is not less than 3.1 g / cc or the lithium salt concentration of the electrolyte is not less than 1.6 M, excellent wettability can be obtained without being affected by the increase in the resistance of the anode due to the addition of dioctyl sodium sulfosuccinate .

&Lt; Experimental Example 2 > Life characteristics

The following experiments were conducted to examine the life characteristics of the secondary batteries manufactured in Example 1 and Comparative Example 1. [

The lifetime characteristics of the lithium secondary battery were evaluated by charging and discharging at 0.1 C for the first cycle, charging at 0.5 C and discharging at 2.0 C. The ratio of the 49th cycle discharge capacity to the first cycle discharge capacity was measured and the results are shown in Table 4.

Life characteristics (%) Example 1 96 Comparative Example 1 90

- Life characteristics: (49th cycle discharge capacity / first cycle discharge capacity) 100

As shown in Table 4, it can be seen that the lifetime characteristic of Example 1 was improved by 6.6% as compared with Comparative Example 1. As a result, the wettability of the electrode according to the present invention is improved, so that the lifetime characteristics of the secondary battery are increased.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

Claims (12)

An anode, a cathode, and an electrolytic solution,
Wherein at least one of the positive electrode and the negative electrode comprises dioctyl sodium sulfosuccinate.
The method according to claim 1,
Wherein the anode comprises a cathode active material,
Wherein the cathode active material is a lithium nickel-manganese-cobalt oxide expressed by the following general formula (1).
[Chemical Formula 1]
LiNi _x Co _y Mn _z O ₂ (where 0.5 <x <0.9, 0.01 <y <0.2, 0.01 <z <0.3, and x + y + z = 1)
The method according to claim 1,
And the compression density of the anode is 3.1 g / cc to 4.0 g / cc.
The method according to claim 1,
Wherein the electrolyte solution comprises a lithium salt and a non-aqueous organic solvent,
Wherein the non-aqueous organic solvent is a cyclic carbonate,
Wherein the lithium salt has a concentration of 1.6 M to 3.0 M with respect to the electrolytic solution.
The method according to claim 1,
Wherein at least one of the positive electrode and the negative electrode includes a binder,
Wherein the binder is one selected from the group consisting of polyvinylidene fluoride (PVDF), carboxyl methyl cellulos, and mixtures thereof.
The method according to claim 1,
The dioctyl sodium sulfosuccinate is contacted with an electrolyte to be ionized with dioctyl sulfosuccinate and sodium (Na ⁺ ), and dioctyl sulfosuccinate is electrostatically bound to the non-aqueous organic solvent Secondary battery.
A positive electrode slurry comprising a surface tension modifier comprising a positive electrode active material represented by the following formula (1), a binder that is polyvinylidene fluoride, carboxylmethyl cellulose, and a mixture thereof, and dioctyl sodium sulfosuccinate.
[Chemical Formula 1]
LiNi _x Co _y Mn _z O ₂ (where 0.5 <x <0.9, 0.01 <y <0.2, 0.01 <z <0.3, and x + y + z = 1)
8. The method of claim 7,
Wherein the surface tension modifier comprises 70 to 80% by weight of dioctyl sodium sulfosuccinate based on the total weight of the surface tension modifier.
8. The method of claim 7,
Wherein the surface tension regulator is contained in an amount of 0.5 to 5 wt% based on the total weight of the cathode slurry.
A battery module comprising the secondary battery of claim 1 as a unit cell.
A battery pack comprising the battery module of claim 10 and used as a power source of the device.
12. The method of claim 11,
Wherein the device is a mobile electronic device, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage device.