KR20170038296A - Method for manufacturing of secondary battery and secondary battery - Google Patents

Abstract

The present invention relates to a method of manufacturing a secondary battery and a secondary battery, and more specifically, to a method of manufacturing a secondary battery, which comprises: after a secondary battery has been manufactured by varying the loading amount and porosity of a negative electrode active material layer, measuring the state of charging (SOC) up to the point where lithium starts to precipitate in a negative electrode during charging of the secondary battery (step 1); and selecting an optimal porosity of the negative electrode based on the value measured in the step 1, to manufacture a secondary battery having a negative electrode active material layer loading amount of x, and a state of charging of y (step 2). The method of manufacturing a secondary battery according to the present invention, based on the SOC value measured right before lithium starts to precipitate during charging of a secondary battery sample prepared by varying the loading amount and porosity of a negative electrode, can achieve an optimal porosity required to produce a secondary battery having a specific loading amount and SOC, and a high lithium diffusion resistance value, and can thus be used to manufacture a secondary battery having improved fast-charging properties.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a secondary battery,

The present invention relates to a method of manufacturing a secondary battery and a secondary battery.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing. 2. Description of the Related Art [0002] Recently, as technology development and demand for portable devices such as portable computers, portable phones, and cameras have increased, the demand for secondary batteries as energy sources has increased sharply. Among such secondary batteries, they exhibit high energy density and operating potential, Many studies have been made on a lithium secondary battery having a long self discharge rate, and it has been commercialized and widely used.

Generally, a secondary battery is composed of a cathode, a cathode, and an electrolyte. The lithium ion discharged from the cathode active material by the first charging is inserted into the anode active material such as carbon particles, Charge / discharge can be performed.

For example, a lithium secondary battery has a structure in which a lithium electrolyte is impregnated in an electrode assembly composed of a positive electrode containing a lithium transition metal oxide as an electrode active material, a negative electrode including a carbonaceous active material, and a porous separator. The positive electrode is prepared by coating a positive electrode mixture containing a lithium transition metal oxide on an aluminum foil, and the negative electrode is prepared by coating a copper foil with a negative electrode mixture containing a carbonaceous active material.

On the other hand, as the demand for rapid charging of a lithium secondary battery to be applied to an electric vehicle has recently increased, the need for research in terms of the design of the electrode used for rapid charging has increased.

When the amount of loading of the negative electrode is the same as that of the negative electrode, the diffusion resistance of the lithium ion is decreased and the rapid charging property is improved when the porosity of the negative electrode is increased. However, when the loading amount of the negative electrode increases, the area resistivity decreases and the accumulated diffusion resistance at the time of continuous charging increases, which adversely affects the rapid charging characteristics.

Therefore, there is a need to develop a method for controlling the optimum porosity as the cathode becomes highly loaded.

Japanese Laid-Open Patent Application No. 2014-126411

A first object of the present invention is to provide a method of manufacturing a secondary battery having a specific loading amount and a filling depth by measuring the charging depth according to the loading amount and the porosity of the anode active material layer, It is a way to do that.

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

In order to solve the above-described problems, the present invention provides a method of manufacturing a lithium secondary battery, comprising the steps of: preparing a sample of a secondary battery having different loading amounts and porosities of the active material layer of the negative electrode, Measuring (step 1); And a step (2) of selecting an optimum cathode porosity through the measurement value of the step 1 when the amount of loading of the active material layer of the cathode is x and the filling depth is y, And a manufacturing method thereof.

Further, the present invention is a negative electrode, a positive electrode and the negative electrode and in the separator, and a secondary battery including an electrolyte interposed between the cathode, the amount of loading of the active material layer of the negative electrode 3.04 mAh / cm ² to about 4.5 mAh / cm ^2, Wherein the porosity is from 33% to 37%, and the charging depth is from 40% to 80% at a C-rate of 1.4 to 1.8.

A method of manufacturing a secondary battery according to the present invention is a method of manufacturing a secondary battery having a different amount of loading and porosity of a negative electrode, charging the secondary battery sample, measuring the charging depth before the lithium precipitation occurs, It is possible to obtain an optimum pore value required for manufacturing a secondary battery having a high charging density and a high lithium diffusion resistance value, thereby manufacturing a secondary battery with improved rapid charging characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a guide map showing charge depth measurement values according to loading amount and porosity of a negative electrode according to Example 1 of the present invention. FIG.

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, But do not preclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

The method of manufacturing a secondary battery according to the present invention is characterized in that after manufacturing a secondary battery sample in which the loading amount and porosity of the negative electrode active material layer are different from each other, (Step 1); And a step (step 2) of selecting the optimum cathode porosity through the measurement value of step 1 when the amount of loading of the active material layer of the cathode is x and the depth of charge is y.

Hereinafter, a method of manufacturing a secondary battery according to the present invention will be described in detail for each step.

In the method of manufacturing a secondary battery according to the present invention, step 1 is a step of preparing a sample of a secondary battery having different loading amounts and porosities of a negative electrode active material layer, The charging depth before the charging is measured.

In step 1, it is possible to determine the value of charge depth up to the point where lithium precipitation occurs when the loading amount of the negative electrode and the porosity are different, and a graph is prepared based thereon to prepare a secondary battery excellent in rapid charging characteristics A guide map can be provided.

The loading amount of the negative electrode may mean the energy density per unit area of the active material layer of the negative electrode, and may be calculated using the electrode weight, the area of the electrode, the capacity of the active material, and the ratio of the active material in the active material layer.

The porosity is a parameter indicating the relative ratio of the volume of pores enclosed by the group consisting of at least one of the active material and the conductive material, based on the volume of the entire active material layer of the negative electrode. The porosity can be calculated by measuring the total mercury penetration (mL / g) with a mercury porosimeter (instrument: AutoPore VI 9500, Micromerities, USA).

The charging depth (SOC) is a parameter indicating a relative ratio of the charged capacity up to the present time based on the capacity when the secondary battery is fully charged (based on the available capacity), and can be measured through the charging / discharging device.

For example, in the preparation of the secondary battery sample, the secondary battery sample includes a negative electrode and a positive electrode, the negative electrode active material in the negative electrode active material layer is artificial graphite, and the positive electrode active material in the positive electrode active material layer is LiNi ₆ Co ₂ Mn ₂ O ₂ < / RTI >

The negative electrode may be prepared by coating a negative electrode active material, a conductive material, and a binder on a negative electrode current collector with a slurry prepared by mixing the negative electrode mixture with an organic solvent, followed by drying and rolling.

At this time, the loading amount can be controlled according to the weight of the negative electrode mixture including the negative electrode active material, the conductive material and the binder, and the porosity can be controlled in the step of coating, drying and rolling the slurry.

At this time, the loading amount of the secondary battery sample may be 3.0 mAh / cm ² to 4.5 mAh / cm ² , and specifically 3.04 mAh / cm ² , 3.31 mAh / cm ² , 3.63 mAh / cm ² , 4.02 mAh / cm ^{2 2} , 4.5 mAh / cm < ² >.

Further, if the porosity of the secondary battery sample of 3.04 mAh / cm ² with respect to the loading amount of each 25%, 28%, 31%, 34%, is 26% if 3.31 mAh / cm ^2, 29% , 31%, and 36%, of 3.63 mAh / cm ² is 26%, 30%, 32.7% , 36%, 4.02 mAh / cm when ^two has 26%, 29%, 32% , 34.5%, 4.5 mAh / cm < ² >, a total of 20 secondary battery samples of 25%, 29%, 32%, and 36% can be prepared for each loading amount and porosity.

However, in the production of the secondary battery sample, the numerical values of the porosity and loading amount of the negative electrode, the number of samples, the kind of the negative electrode active material and the positive electrode active material are not limited as described above, and the negative electrode active material And then, the negative electrode having different porosity and loading amount can be produced from the negative electrode active material.

On the other hand, the positive electrode may be prepared by applying a slurry prepared by mixing a positive electrode mixture containing a positive electrode active material, a conductive material and a binder to an organic solvent, and then drying and rolling the positive electrode current collector. The porosity and loading amount can be varied to produce a sample while the porosity and loading of the anode can have a constant value for all samples.

The cathode active material is not particularly limited, but a lithium transition metal oxide may be specifically used. Examples of the lithium transition metal oxide include a Li-Co-based composite oxide such as LiCoO ₂ , a Li-Ni-Co-Mn-based composite oxide such as LiNi _x Co _y Mn _z O ₂ , Li such as LiNiO ₂ Ni-based composite oxide, and Li-Mn-based composite oxide such as LiMn ₂ O ₄ , and these may be used singly or in combination.

The negative electrode active material is not particularly limited, but a carbonaceous material, lithium metal, silicon, or tin, in which lithium ions can be occluded and released, can be used. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

The current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used.

The conductive agent is not particularly limited as long as it has electrical conductivity without causing any chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) Various kinds of binder polymers such as sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid and polymers substituted with Li, Na or Ca, or various copolymers thereof are used .

The secondary battery sample may be a three-electrode cell. In the case of a secondary battery sample made of a three-electrode cell, the cathode profile can be separated separately and the lithium precipitation point can be predicted have.

After the secondary battery sample is prepared, the charge depth from the cathode to the lithium ion precipitation can be measured while charging the secondary battery sample at a specific C-rate.

When the lithium starts to precipitate from the cathode, the performance of the secondary battery deteriorates. Thus, by measuring the charge depth before the point, it is possible to determine the charge depth at which the performance of the secondary battery is not deteriorated Able to know.

In particular, the secondary battery sample may be charged at a C-rate of 1.4 to 1.8.

The present invention is for an optimal cathode design for rapid charging of a secondary battery for use in an electric vehicle. The charging depth can be measured when the charging speed is high in the above range, and the result can be applied to an electric vehicle.

The guide map can be created by plotting the above-mentioned pore values on the X-axis and the measured charge depth values on the Y-axis, and connecting the result values by a straight line for each amount of loading. Based on this result The porosity of the cathode can be selected.

In the method of manufacturing a secondary battery according to the present invention, step 2 is a step in which when the amount of loading of the active material layer of the negative electrode is x and the filling depth is y, the optimal cathode porosity .

In the step 2, a secondary battery having a specific loading amount and a charging depth and having a rapid charging characteristic without deteriorating the performance of the secondary battery, based on the specific loading amount measured in the step 1 and the optimum charging depth value according to the specific porosity, The cathode porosity for manufacturing the cathode can be selected.

For example, when the loading amount of the cathode of the secondary battery to be manufactured is set to 3.63 mAh / cm ² and the charge depth at 1.5 C-rate is set to 63.3%, based on the value on the graph prepared in the above step 1, The porosity value can be selected to be 33.3%.

On the other hand, after performing the step 2, the slurry prepared by mixing the negative electrode mixture containing the negative electrode active material, the conductive material and the binder in the organic solvent is coated on the current collector, followed by drying and rolling to obtain the optimal cathode porosity And a negative electrode. In the above step, a negative electrode is manufactured based on the value selected in step 2, and a secondary battery having improved rapid charging characteristics can be manufactured.

A secondary battery according to the present invention, a negative electrode, a positive electrode and in the secondary battery including a separator, and an electrolyte interposed between the negative electrode and the positive electrode, the amount of loading of the active material layer of the negative electrode 3.04 mAh / cm ² to about 4.5 mAh / cm ² , the porosity is from 33% to 37%, and the filling depth at a C-rate of 1.5 may be from 40% to 80%.

In the secondary battery within the above range, as the loading amount of the negative electrode increases, the porosity also increases, so that rapid charging characteristics can be further improved and lithium precipitation may not occur.

The negative electrode active material in the active material layer of the negative electrode of the secondary battery may be artificial graphite and the positive electrode active material in the active material layer of the positive electrode may be LiNi ₆ Co ₂ Mn ₂ O ₂ .

On the other hand, as the separator, a conventional porous polymer film conventionally used as a separator, such as 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 electrolytic solution may include a non-aqueous organic solvent and a metal salt.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

LiBCl ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ , LiBF ₄ , LiBF ₄ , LiBF ₄ , LiBF ₄ , _{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, 4-phenyl Lithium borate, imide and the like can be used.

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 which does not precipitate lithium and exhibits excellent charging characteristics even in a rapid charging environment of a middle- or large-sized device, it can be used for electric vehicles, hybrid electric vehicles, plug- And can be used as a power source for a medium and large-sized device selected from the group consisting of

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.

≪ Example 1 >

Step 1: Preparation of Secondary Battery Samples

A negative electrode mixture made of artificial graphite as a negative electrode active material, polyvinylidene difluoride (PVdF) as a binder and carbon black as a conductive material in an amount of 96% by weight, 3% by weight and 1% by weight, -2-pyrrolidone (NMP) to prepare an anode slurry.

The negative electrode slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to produce a negative electrode, followed by roll pressing to measure the amount of the negative electrode mixture, 20 cathodes with different degrees were prepared.

Amount of negative electrode mixture (g) Loading Amount (mAh / cm ² ) Porosity (%) Production Example 1 0.06 3.04 26 Production Example 2 29 Production Example 3 32 Production Example 4 35 Production Example 5 0.077 3.31 26 Production Example 6 29 Production Example 7 31 Production Example 8 36 Production Example 9 0.1 3.63 26 Production Example 10 29 Production Example 11 32.8 Production Example 12 36 Production Example 13 0.126 4.02 26 Production Example 14 29 Production Example 15 32 Production Example 16 34.5 Production Example 17 0.17 4.50 26 Production Example 18 29 Production Example 19 32 Production example 20 36

A positive electrode mixture of 92 wt% of LiNi ₆ Co ₂ Mn ₂ O ₂ as a positive electrode active material, 4 wt% of carbon black as a conductive material, and 4 wt% of PVDF as a binder was dissolved in N-methyl-2-pyrrolidone NMP) to prepare a positive electrode slurry. The positive electrode slurry was applied to an aluminum (Al) thin film of a positive electrode current collector having a thickness of 20 μm and dried to produce a positive electrode, followed by roll pressing.

One of the prepared positive electrode and the negative electrode, and the separation membrane were made of porous polyethylene. A reference electrode LTO is interposed between the working electrode and the counter electrode, the separator is disposed between the working electrode and the counter electrode, and a stacking method (Ethylene carbonate (EC) / ethylmethyl carbonate (EMC) = 1/2 (volume ratio) and lithium hexafluorophosphate (LiPF ₆ 1 mole) were injected into the assembled battery Secondary battery samples were prepared and 20 secondary battery samples were produced by different cathodes in the same manner.

Step 2: Depth of charge  Measure

The 20 secondary battery samples prepared in step 1 were charged to a point at which lithium was precipitated at 1.5 C-rate, and then the depth of charge was measured by an EC-Lab apparatus. At this point, the cathode profile was differentiated and represented by a dV / dQ curve at the point before lithium precipitation, and then the depth of charge at the point where the inflection point of the curve occurred was measured. The measured values were plotted on the graph as 20 points with the x-axis as the pore of the cathode and the Y-axis as the measured depth of charge, and then connected by a straight line to create the guide map of Fig.

Step 3: Production of secondary battery with improved rapid charging characteristics

When preparing a secondary battery having a loading depth of 3.63 mAh / cm < ² > and a charge depth at 1.5 C-rate of 63.3%, the porosity of the negative electrode Value was selected to be 33.3%.

Thus, 10 g of a negative electrode material mixture in which artificial graphite as a negative electrode active material, polyvinylidene difluoride (PVdF) as a binder and carbon black as a conductive material were respectively 96% by weight, 3% by weight and 1% by weight, Was added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare an anode slurry. Coating the cathode slurry to a thickness of 10 ㎛ the anode current collector, copper (Cu) thin film, subjected to a roll press (roll press) after producing the negative electrode through a drying, the loading amount of anode 3.63 mAh / cm ^2, and , And a porosity value of 33.3%.

A positive electrode mixture of 92 wt% of LiNi ₆ Co ₂ Mn ₂ O ₂ as a positive electrode active material, 4 wt% of carbon black as a conductive material, and 4 wt% of PVDF as a binder was dissolved in N-methyl-2-pyrrolidone NMP) to prepare a positive electrode slurry. The positive electrode slurry was applied to an aluminum (Al) thin film of a positive electrode current collector having a thickness of 20 μm and dried to produce a positive electrode, followed by roll pressing.

One of the prepared positive electrode and the negative electrode, and the separation membrane were made of porous polyethylene. A reference electrode LTO is interposed between the working electrode and the counter electrode, the separator is disposed between the working electrode and the counter electrode, and a stacking method is used to form a three-electrode cell (Ethylene carbonate (EC) / ethylmethyl carbonate (EMC) = 1/2 (volume ratio)) and lithium hexafluorophosphate (1 mole of LiPF ₆ ) were injected into the assembled battery to prepare a secondary battery.

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 (13)

A step (step 1) of measuring the depth of charge up to a point where lithium deposition occurs on the negative electrode while charging the secondary battery sample after manufacturing the secondary battery sample with different loading amounts and porosity of the active material layer of the negative electrode;
And a step (2) of selecting an optimum cathode porosity through the measurement value of the step 1 when the amount of loading of the active material layer of the cathode is x and the filling depth is y, Gt;
The method according to claim 1,
Wherein the secondary battery sample of step 1 includes a negative electrode and a positive electrode, the negative electrode active material in the negative electrode active material layer is artificial graphite, and the positive electrode active material in the positive electrode active material layer is LiNi ₆ Co ₂ Mn ₂ O ₂ . ≪ / RTI >
The method according to claim 1,
Wherein the loading amount of the secondary battery sample in the loading amount of step 1 is 3.0 mAh / cm ² to 4.5 mAh / cm ² .
The method according to claim 1,
The loading amount of the stage 1, characterized in that the amount of loading of the secondary battery samples, each ^{3.04 mAh / cm 2, 3.31 mAh} / cm 2, 3.63 mAh / cm 2, 4.02 mAh / cm 2, 4.5 mAh / cm 2 in contrast Gt; to < / RTI >
The method according to claim 1,
Wherein the porosity of the secondary battery sample having different porosity in the step 1 is 25% to 36%.
The method according to claim 1,
Wherein the secondary battery sample is made of a three-electrode cell.
The method according to claim 1,
Wherein the secondary battery sample is charged at a C-rate of 1.4 to 1.8.
The method according to claim 1,
After performing the step 2, a slurry prepared by mixing a negative electrode mixture containing an anode active material, a conductive material and a binder in an organic solvent is coated on a current collector, followed by drying and rolling to obtain an optimum cathode porosity A method for manufacturing a secondary battery, comprising the steps of: preparing a negative electrode;
A secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte,
Loading an amount of the active material layer of the negative electrode 3.04 mAh / cm ² to about 4.5 mAh / cm ^2,
The porosity is from 33% to 37%
Wherein the depth of charge of the secondary battery charged at a C-rate of 1.4 to 1.8 is 40% to 80%.
10. The method of claim 9,
Wherein the negative electrode active material in the negative electrode active material layer of the secondary battery is artificial graphite and the positive electrode active material in the active material layer of the positive electrode is LiNi ₆ Co ₂ Mn ₂ O ₂ .
10. A battery module comprising the secondary battery of claim 9 as a unit cell.
11. A battery pack comprising the battery module of claim 11 and used as a power source for a middle- or large-sized device.
13. The method of claim 12,
Wherein the middle- or large-sized device is selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle and a system for power storage.

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