KR101977973B1 - Negative electrode for fast charging, battery comprising the same and fabricating methods thereof - Google Patents

Abstract

A cathode improved in structure so as not to cause Li-plating during rapid charging and a manufacturing method thereof are provided. The negative electrode according to the present invention comprises a negative electrode collector; And an anode active material layer containing carbon-based particles formed on the anode current collector, wherein micropores having a diameter of 1 탆 or less are present in the carbon-based particles and an area occupied by the micropores is within the entire range of the anode active material layer 60% to 85% of the pore area.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a negative electrode capable of rapid charging, a secondary battery including the negative electrode,

The present invention relates to a secondary battery and a method of manufacturing the same, and more particularly, to a negative electrode having a structure improved so as to rapidly charge a battery while increasing the life of the battery, a secondary battery including the same, and a method of manufacturing the same.

2. Description of the Related Art In recent years, demand for portable electronic products such as notebooks and portable telephones has been rapidly increasing, and research on high performance secondary batteries capable of repeated charging and discharging has been actively conducted as demands for electric carts, electric wheelchairs, . In addition, demand for hybrid electric vehicles (HEV) and electric vehicles (EVs) is increasing worldwide, as carbon energy has recently become depleted and environmental concerns have increased. As a result, much attention and research have been focused on vehicle batteries, which are core parts of HEVs and EVs, and it is urgent to develop rapid charging technology that can charge batteries quickly. Rapid charging is especially important for EVs without additional energy sources.

The process of charging the battery includes charging the battery with electric charge and energy, and such a process must be carefully controlled. In general, excessive C-rate or charging voltage can permanently degrade the performance of the battery and ultimately cause complete failure or can lead to unexpected disturbances such as leakage or explosion of highly corrosive chemicals.

The conventional battery charging system includes a constant current (CC) system in which charging is performed at a constant current from the beginning to the completion of charging, a constant voltage (CV) system in which charging is performed at a constant voltage from the beginning to the completion of charging, And a constant current-constant voltage (CC-CV) system charging at a constant voltage at the end. The CC method is most advantageous for rapid charging. The larger the charging current is, the better the charge is completed quickly. However, if the battery is charged continuously with a large current, the charging efficiency is lowered and the life of the battery is also affected.

Li-plating phenomenon in which Li is not intercalated into the cathode during rapid charging due to a high charge current density is a problem. Precipitated Li may cause side reactions with electrolytes, change of the kinetic balance of the battery, and the like, which may cause battery degeneration in the future. Therefore, there is a need for a technique to achieve rapid charging without causing Li-plating.

Disclosure of Invention Technical Problem [8] The present invention provides a negative electrode and a method for producing the negative electrode, wherein the structure is improved so as not to cause Li-plating during rapid charging.

Another problem to be solved by the present invention is to provide a secondary battery including such an anode capable of rapid charging and having a long life, and a method of manufacturing the same.

According to an aspect of the present invention, there is provided a negative electrode comprising: an anode current collector; And an anode active material layer containing carbon-based particles formed on the anode current collector, wherein micropores having a diameter of 1 탆 or less are present in the carbon-based particles and an area occupied by the micropores is within the entire range of the anode active material layer 60% to 85% of the pore area.

The porosity of the negative electrode active material layer may be 30% to 35%.

The secondary battery according to the present invention includes such a cathode.

The method for manufacturing a negative electrode according to the present invention includes the steps of: forming a negative electrode active material layer containing carbon-based particles on a negative electrode current collector; Rolling the negative electrode current collector having the negative electrode active material layer at least twice; And drying the rolled negative electrode current collector.

The rolling may be performed at a pressure not considering spring back after the cathode collector is dried. The pressures of the at least two times of rolling may be the same.

In particular, the at least twice rolling may be to generate and / or relocate micropores having a diameter of 1 탆 or less within the carbon-based particles while maintaining the shape of the carbon-based particles.

And drying the negative electrode current collector before the rolling step.

The present invention also provides a method for manufacturing a secondary battery including such a cathode manufacturing method.

According to the present invention, fine pores having a diameter of 1 탆 or less occupy a large area in the negative electrode active material layer, thereby reducing the diffusion resistance of lithium ions. Since lithium diffusion is facilitated, lithium intercalation of the negative electrode occurs well during rapid charging, and Li-plating can be prevented from occurring.

Since the secondary battery including the negative electrode according to the present invention can be charged without causing Li-plating, there is no problem such as a side reaction between deposited Li and the electrolyte, a change in the kinetic mechanical balance of the battery, It can prevent and ensure long life. In addition, rapid charging can be achieved because the battery can be charged at a high charging rate within a limit that does not cause Li-plating.

In addition, according to the manufacturing method of the present invention, it is possible to control the micropores in the anode active material only by changing the rolling process without changing the anode active material, and thus the cathode and the secondary battery can be economically produced while utilizing existing process lines as they are .

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a schematic cross-sectional view of a secondary battery anode according to the present invention.
2 is a flowchart of a method of manufacturing a cathode according to the present invention.
3 is a schematic view of a secondary battery according to the present invention.
4 is an SEM photograph of a section of a cathode of an embodiment of the present invention.
5 is an image of the pore size in the SEM photograph of FIG.
6 is a graph showing the number of pore size counts from the image of FIG.
7 is a graph showing the area of the cathode according to Comparative Example and the cathode of the present invention according to the pore size.
8 is an electrochemical test result of a three electrode cell including a cathode of the comparative example and the embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It is provided to let you know. The shape of the elements and the like in the drawings are exaggerated in order to emphasize a clearer explanation.

In the case of rapid charging of the CC system, degradation of the cell due to Li-plating of the cathode surface becomes the most problematic. Li-plating has the disadvantage that the higher the charge current density (charge rate or charge current) and the lower the temperature, the better the charge current density is lowered to prevent the target charge rate from being achieved.

Li-plating occurs when lithium ions can not be intercalated into the cathode. Therefore, to prevent Li-plating, lithium ions should be uniformly intercalated into the cathode. For uniform intercalation, the lithium ion diffusion property of the negative electrode is a very important factor when charging. In order to improve the lithium ion diffusion characteristics, the cathode structure is an important factor, so the cathode porosity should be increased. However, the porosity of the cathode increases the energy density of the cell.

The present invention proposes a secondary battery improved in pore structure of a negative electrode so that rapid charging can be improved at a level similar to that of a conventional negative electrode, and a manufacturing method thereof. The secondary battery including the negative electrode according to the present invention can rapidly charge the battery without causing Li-plating, thereby shortening the charging time.

In the present invention, the pore structure of the cathode is optimized in order to improve the rapid charging characteristics of the secondary battery while maintaining a high energy density. It is proposed that micropores having a diameter of 1 탆 or less are formed on the multiple surfaces of the negative electrode active material layer, rather than in a limited region of the negative electrode active material layer, with diameters exceeding 1 탆 at the same or similar porosity.

1 is a schematic cross-sectional view of a secondary battery anode according to the present invention.

1, a cathode 10 according to the present invention includes a cathode current collector 20 and a cathode active material layer 30 formed on the cathode current collector 20. The anode active material layer 30 includes carbon-based particles 40.

Micropores P having a diameter of 1 탆 or less are present inside the carbon-based particles 40 and the area occupied by these micropores P is 60% to 85% of the total pore area. At this time, the porosity of the negative electrode active material layer 30 may be 30% to 35%.

In the present invention, pores having a diameter of 1 m or less are referred to as micropores (P). When the porosity is high (when the pores are large), the diffusion of Li is easy. However, since it is impossible to increase the porosity of the cathode in a state where the footprint of the cell is fixed, It is easy to form more fine pores P than the liquid pores L.

Large pores L and fine pores P may exist in the negative electrode active material layer 30 of the negative electrode 10 according to the present invention such that the blood vessels are composed of aorta and capillary blood vessels. The micropores P that are uniformly distributed in the negative electrode active material layer 30 may flow into the negative electrode like a capillary in the electrolytic solution Dissociated lithium ions) can be easily moved, it is advantageous if the micropores P having a diameter of 1 mu m or less are large. Further, it is advantageous that the fine pores P are uniformly formed in the negative electrode active material layer 30.

In the present invention, such fine pores P are present in the carbon-based particles 40 such that they occupy a large portion of the total pore area, and are uniformly distributed over the entire surface of the anode active material layer 30. In this case, Can have the same energy density as the conventional lithium ion battery, and at the same time, the lithium ion diffusion can be improved and the rapid charging property can be improved.

If the area occupied by the fine pores P is smaller than 60% of the total pore area, the effect of improving the lithium ion diffusion characteristics due to the fine pores P may be insignificant. If the area occupied by the micro pores (P) is larger than 85% of the total pore area, the area of the large pores (L) is not sufficient, which may be detrimental to electrolyte impregnation. Therefore, the area occupied by the micropores P is set to 60% to 85% of the total pore area. This area can be controlled by changing the rolling process during the manufacturing process of the negative electrode 10, without changing the carbon-based particles 40 constituting the negative electrode active material layer 30. This will be described later.

The porosity of the negative electrode active material layer 30 is 30% to 35%. If the porosity of the negative electrode active material layer 30 is less than 30%, there is a fear that diffusion of lithium ions or electrolyte impregnation may not be performed smoothly. When the porosity of the negative electrode active material layer 30 is larger than 35%, it is not preferable from the viewpoint of energy density. The porosity of the negative electrode active material layer 30 can be controlled by various parameters such as particle size, porosity, tap density, other additives, rolling process, etc. of the carbon particles 40 constituting the negative electrode active material layer 30.

2 is a flowchart of a method of manufacturing a cathode according to the present invention. The cathode manufacturing method according to the present invention may include the steps as shown in Fig.

Referring to FIG. 2, a negative electrode active material layer is applied to the negative electrode collector 20 to form a negative electrode active material layer 30 (S10). Here, the anode current collector 20 can be any metal that has high conductivity and can easily adhere to the slurry of the anode active material and is not reactive in the voltage range of the battery. The negative electrode current collector 20 may be made of copper, gold, nickel or a copper alloy or a combination thereof. The negative electrode current collector 20 may be made of a material such as a metal, May be stacked and used.

The negative electrode active material used in the present invention includes carbon-based particles (40) capable of intercalating and deintercalating lithium ions. Concretely, the carbon-based particles 40 may be both low-crystalline carbon and high-crystallinity carbon. 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 negative electrode active material may further include a conductive material, a binder, and a high boiling point solvent, and the slurry in which the slurry is mixed is applied to the negative electrode current collector 20 to form the negative electrode active material layer 30. The method of uniformly applying the slurry on the negative electrode current collector 20 can be selected from known methods in consideration of the characteristics of materials and the like or can be carried out by a new suitable method. For example, it is preferable to distribute the paste on the current collector and uniformly disperse the paste using a doctor blade or the like. In some cases, a method of performing the distribution and dispersion processes in a single process may be used. Other methods such as die casting, comma coating, and screen printing may be employed, or they may be formed on a separate substrate and then joined to the current collector by a pressing or lamination method.

The conductive material is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in an electrochemical device. In general, carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material and the like can be used. Commercially available conductive materials include acetylene black series (manufactured by Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (MMM). For example, acetylene black, carbon black and graphite.

The binder that can be included in the negative electrode active material has a function of holding the negative electrode active material in the negative electrode current collector 20 and also connecting the negative electrode active materials. All the binders used in the conventional lithium secondary battery can be used without limitation have.

For example, it is possible to use vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, styrene Various types of binder polymers such as styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like can be used.

When the anode active material layer 30 is formed on the anode current collector 20 as described above, the primary drying step S15 is performed. The primary drying step (S15) is performed in order to remove the solvent and the like contained in the negative electrode active material slurry so as to be in a state suitable for rolling.

Next, the negative electrode current collector 20 is rolled at least twice. In the present embodiment, the primary rolling (S20) and the secondary rolling (S30) are performed.

In the steps S20 and S30, the negative electrode active material may be adhered to the negative electrode current collector 20 by passing the negative electrode current collector 20 coated with the negative electrode active material between two or more rotating rolls. At this time, the rotating roll may be in a high temperature state, thereby further improving the adhesive force between the negative electrode active material and the negative electrode current collector 20.

The negative electrode or positive electrode is generally prepared by applying a slurry containing an electrode active material and a binder to a metal current collector, followed by drying and rolling. When a carbonaceous material is used as a negative electrode active material, there is no problem such as side reactions, and it is safe and can be manufactured in various forms by using a powder form. However, since the electric capacity is low, The density is increased. In the present invention, particularly, the rolling is divided into two or more times in the production of the negative electrode.

Generally, there is a so-called springback phenomenon in which the electrodes are swollen after a certain period of time during rolling and after electrode drying. Therefore, in the case of the conventional one-time rolling, a pressure of 120 to 130% is applied in consideration of such springback. That is, a large force is applied so as to be smaller than the target electrode thickness so as to achieve a desired target thickness only when the spring is released later. For example, if the target electrode thickness is 151 占 퐉, the pressure when the thickness is 151 占 퐉 immediately after rolling can be 100% pressure. In the conventional one-time rolling, considering the spring back, The pressure of 120 to 130% is applied. At this time, the thickness considering the spring back varies depending on the experiential value, becomes about 10 to 20 탆, and the pressure set in consideration of spring back is 20 to 30% when the spring back is not taken into consideration (100% A further pressure will be applied.

In the case of two or more rolling operations according to the present invention, 100% pressure is applied without considering such springback. That is, if the target electrode thickness is 151 탆, immediately after rolling, primary pressure is applied by 100% pressure so that the thickness becomes 151 탆. After the primary rolling, secondary rolling is carried out at a pressure of 100% at a target thickness of 151 탆 without considering spring back. When the target thickness is the same as the conventional one, the rolling is performed twice or more with a smaller pressure than the conventional one.

In general, the microporosity of the rolled electrode active material layer is reduced due to the rolling process of the electrode current collector. However, the present invention is not limited to the rolled negative active material layer 30 ) Can be increased.

In particular, the pressure applied to the surface of the electrode is the largest at the time of rolling, and the porosity decreases and the density increases as the surface gets closer to the inside of the electrode. Therefore, even if a certain level of porosity is secured in the inside of the electrode, the porosity of the electrode surface is very low, so that the electrolyte can not penetrate into the electrode. In the present invention, since the rolling is performed at a pressure lower than that in the prior art, there is less possibility of occurrence of such a problem, and thus a certain level of porosity can be ensured evenly on the surface and inside of the electrode after rolling.

If the carbon-based particles containing the fine pores are selected in order to make the fine pores P exist in the whole of the negative electrode active material layer 30, the ratio of the ratio of the rolled negative electrode active material The surface area is increased and a new edge surface protrudes accordingly, which may lead to an electrolyte side reaction. However, in the present invention, micro-pores (P) in the carbon-based particles (40) are formed and / or rearranged through two or more rolling processes, and there is no need to change the raw material carbon-based particles. Therefore, even in the rolling process, the anode active material is not easily broken, so that there is no side reaction of the electrolyte solution, so that a negative electrode having excellent swelling suppression characteristics can be manufactured.

Then, the rolled negative electrode collector 20 may be secondarily dried (S40). Preferably, in step S40, the anode current collector 20 may be dried by heating under vacuum at a temperature of about 150 ° C to 300 ° C for about 1 hour to about 15 hours. However, the present invention is not limited thereto It is not. The secondary drying step (S40) can be performed at a higher temperature and a longer time than the primary drying step (S15). The secondary drying step (S40) can be carried out for relaxation of stress due to complete drying and rolling of the anode current collector 20, and diffusion of generated and re-arranged micropores (P).

The negative electrode 10 manufactured by the above steps may have a negative electrode active material layer 30 having a thickness of 1 탆 to 180 탆 or 30 탆 to 150 탆. When the negative electrode active material layer 30 satisfies such a thickness range, the amount of the active material in the negative electrode active material layer 30 is sufficiently secured, the battery capacity can be prevented from being reduced, and the cycle characteristics and the rate characteristics can be improved have. However, it is not limited to such a thickness.

In the negative electrode active material layer 30 of the negative electrode 10, the area occupied by the micropores P having a diameter of 1 m or less increases by the rolling process change, and diffusion of lithium ions can be performed quickly and smoothly. The secondary battery including the secondary battery is improved in lifetime characteristics because the Li-plating is suppressed even after rapid charging. As described above, in the present invention, the area of the micro pores can be increased by changing the rolling process, and the rapid charging characteristics of the secondary battery can be improved by the micro pores.

3 is a schematic view of a secondary battery according to the present invention. Referring to FIG. 3, the secondary battery 100 according to the present invention includes the cathode 10 according to the present invention as described above. The secondary battery 100 includes a cathode 50, a cathode 10, and a separator 60. Forming an electrode assembly (70) between the anode (50) and the cathode (10) with the separator (60) interposed therebetween; Storing the electrode assembly (70) in a battery case (80); And injecting an electrolyte into the battery case 80, and the like.

The anode 50 may be a conventional anode used in the manufacture of a lithium secondary battery. For example, a slurry obtained by mixing a cathode active material, a binder and a conductive material is applied to a cathode current collector, followed by drying, can do.

As the cathode active material, for example, any one selected from the group consisting of LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ and V ₂ O ₅ , or a mixture of two or more thereof is preferable. It is also preferable to use those capable of intercalating and deintercalating lithium such as TiS, MoS, an organic disulfide compound or an organic polysulfide compound.

Examples of the binder include polyvinylidene fluoride, carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, and conductive materials such as acetylene black, furnace black, graphite, carbon fiber, and fullerene. .

As the separator 60, any material may be used as long as it is used in a lithium secondary battery. Examples of the separator 60 include polyethylene, polypropylene, or a multilayer film thereof, polyvinylidene fluoride, polyamide, glass fiber, . A separator composition is prepared by mixing a polymer resin, a filler and a solvent, and then the separator composition is directly coated on the electrode and dried to form a separator film, or after the separator composition is cast on a support and dried, And then laminating the separator film on top of the electrode.

As the structure of the electrode assembly 70, various examples such as a winding type, a stack type, a stack and a folding type are possible.

Here, the type of the battery case 80 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. The figure shows a pouch type.

Examples of the electrolytic solution include an organic electrolytic solution or a polymer electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent.

Examples of the non-aqueous solvent constituting the organic electrolytic solution include propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, gamma butyrolactone, dioxolane, But are not limited to, methanol, ethanol, propanol, isopropanol, n-butanol, isopropanol, n-butanol, A nonaqueous solvent such as a carbonate, a methylpropyl carbonate, a methyl isopropyl carbonate, an ethylbutyl carbonate, a dipropyl carbonate, a diisopropyl carbonate, a dibutyl carbonate, a diethylene glycol, a dimethyl ether and the like, A mixed solvent, and a solvent conventionally known as a solvent for a lithium secondary battery, It is a mixture of propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate that comprises one of, one of the methyl ethyl carbonate, diethyl carbonate, is preferred.

The lithium salt may be 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, One or more lithium salts selected from CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium and lithium 4-phenylborate can be used.

The polymer electrolytic solution may be prepared by dissolving the (co) polymer such as polyethylene oxide, polypropylene oxide, polyacetonitrile, polyvinylidene fluoride, polymethacrylate, polymethylmethacrylate and the like having excellent swelling property against the organic electrolytic solution and the organic electrolytic solution Included are, for example.

Since the secondary battery 100 according to the present invention includes the cathode 10 having improved lithium diffusion characteristics, it can be rapidly charged without the problem of Li-plating, and thus can be used for a vehicle battery in which rapid charging is particularly required , And thus can be preferably used as a constituent battery of a middle- or large-sized battery module. Accordingly, the present invention may also provide a middle- or large-sized battery module including the above-described secondary battery 100 as a unit battery. Such a middle- or large-sized battery module can be suitably applied to a power source requiring a high output and a large capacity, such as an electric vehicle, a hybrid electric vehicle, and a power storage device.

Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples. It should be understood, however, that the embodiments of the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Comparative Example

As a conventional method, a 130% pressure was applied in consideration of spring back, and then rolled once and subjected to heat treatment (VD) under vacuum to prepare a negative electrode. The target electrode thickness was 151 mu m.

Example

Without considering springback, 100% pressure was applied, rolled twice, and heat treated (VD) under vacuum to produce a negative electrode. The target electrode thickness was 151 mu m.

Table 1 shows the results of comparison of the thickness and porosity according to the rolling order of the negative electrode of the comparative example subjected to the single rolling and the negative electrode of the embodiment of the present invention subjected to the double rolling.

<Table 1>

As a result, the thickness of the electrode before VD was similar to that of conventional rolling after VD, but after VD it was about 5 ㎛ difference by springback. This is negligible.

The porosity was 32% for the comparative example and 30.5% for the example of the present invention.

4 is an SEM photograph of a section of a cathode of an embodiment of the present invention.

FIG. 5 shows an image of the pore diameter in this SEM photograph. Referring to FIG. 5, it can be seen that the white circles are large pores at the grain boundaries between the carbon-based particles. In the inside of the carbon-based particles, it can be seen that fine pores having diameters of 1 μm or less are uniformly distributed in red and green.

From this image, the number of pore diameters is counted to obtain the graph of FIG. In the comparative example, the number of pore diameters is also counted in the same manner and shown together in Fig.

As a result of the electrode image analysis as described above, it was found that the porosity of the example was 30.5%, which is lower than that of the comparative example, but the number of micropores of 1 μm or less was larger than that of the comparative example.

FIG. 7 is a graph showing the area of the cathode according to Comparative Example and Inventive Example cathode according to the pore diameter. FIG.

((D / 2) ^ 2 * 3.14) by using the pore diameter, which is the x-axis of the graph in FIG. 6, the area of pores of 1 μm or less in the comparative example having a small pore diameter becomes small, On the contrary.

Table 2 summarizes the analysis results of FIG. 6 and FIG.

<Table 2>

In the case of the present invention, the porosity is slightly smaller than that of the comparative example, but the pore area of 1 μm or less is about 1.9 times larger than that of the comparative example. As described above, the area occupied by pores of 1 mu m or less in the total pore area of the present invention is larger than that of the comparative example. Since micropores having a size of 1 탆 or less contribute to the diffusion of lithium ions, the lithium ion diffusion of the negative electrode according to the present invention is smooth and intercalation occurs uniformly, and thus Li-plating can be suppressed as much as possible.

Each of the three electrode pouch cells was fabricated to include the negative electrode of the comparative example and the present invention example, and the diffusion resistance and rapid charging property of the negative electrode were confirmed while charging at a C-rate as high as 1.6C.

FIG. 8 is a result of such electrochemical experiment for a triode electrode cell including a cathode of the comparative example and the embodiment of the present invention. In FIG. 8, the hollow square is OCV, the hollow circles and the X-axis are voltage drops due to the interfacial resistance of each three-electrode cell, the thick solid line is the voltage profile of the negative electrode when the comparative three- The dotted line is the voltage profile of the negative electrode when charging the three electrode cell of the embodiment.

Generally, at the time of charging, as the Li is intercalated in the negative electrode active material, the stage is lowered and the negative electrode potential is lowered. At this time, if the charge current density is increased, the stage is not observed well, but the negative potential continuously falls due to the intercalation of Li and the increase of resistance. 8, it is confirmed that the cathode potential drops as the charging progresses at a high charging current.

However, the reaction in which Li is intercalated into the negative electrode active material during charging and the reaction in which Li-plating is generated are competitive reactions. The inventors of the present invention found through repeated experiments that Li is not intercalated into the negative electrode active material when Li-plating is generated during charging, and the negative electrode potential remains constant after the point. That is, a point where the negative electrode potential does not fall and becomes constant when charging is determined as the point of occurrence of Li-plating.

Referring to FIG. 8, it can be seen that as the filling progresses, the porosity of the embodiment is low, but the diffusion resistance is small and the overpotential is small. It can be seen that the point where Li-plating of the cathode occurs is confirmed at SOC which is 6% higher than the comparative example in the case of the present invention. That is, the comparative example can charge by a small amount of SOC at the same charge current density, but according to the present invention, since the same charge current density can be charged up to a higher SOC without Li-plating, The embodiment of the present invention is more effective in terms of rapid charging that must be performed.

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, but many variations and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the appended claims.

10: cathode
20: cathode collector
30: Negative electrode active material layer
40: carbon-based particles
L: Large pore
P: fine pore
50: anode
60: Separator
70: electrode assembly
80: Battery case
100: secondary battery

Claims (9)

delete delete delete Forming a negative electrode active material layer containing carbon-based particles on the negative electrode current collector;
Rolling the negative electrode current collector having the negative electrode active material layer at least twice; And
And drying the rolled negative electrode current collector,
Wherein the rolling is performed at a pressure not considering spring back after the drying of the negative electrode collector,
The respective pressures of the at least two times of rolling are the same,
Wherein the at least twice rolling is to form and / or relocate fine pores having a diameter of 1 m or less in the carbon-based particles while maintaining the shape of the carbon-based particles. delete delete delete 5. The method of claim 4,
Further comprising the step of drying the negative electrode collector before the rolling step. Producing a negative electrode by the method of claim 4;
Forming an electrode assembly between the negative electrode and the positive electrode with a separator interposed therebetween;
Storing the electrode assembly in a battery case; And
And injecting an electrolyte into the battery case.

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