JP6120382B2 - Negative electrode for lithium secondary battery and lithium secondary battery including the same - Google Patents

Description

  The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode. More specifically, the negative electrode includes a multilayer active material layer in which the negative electrode active material has different rolling density and average particle size, and The present invention relates to a lithium secondary battery including the same.

  As the price of energy sources rise due to the depletion of fossil fuels and the concern about environmental pollution is amplified, environmentally friendly alternative energy sources have become indispensable factors for future life. Therefore, research on various power production technologies using natural energy such as nuclear power, solar power, wind power, tidal power, etc. has been continued, and a power storage device for more efficiently using the energy thus produced. Is also of great interest.

  In particular, with the development of technology and demand for mobile devices, the demand for secondary batteries as an environmentally friendly alternative energy source is increasing rapidly. The secondary battery has recently been used as a power source for devices that require large-capacity power, such as an electric vehicle (EV) or a hybrid electric vehicle (HEV), such as a power auxiliary power source via a grid. The range of use is also expanding in applications.

  In order to be used as a power source for the devices that require a large amount of electric power, it has a characteristic capable of exhibiting a large output in a short time and at least 10 years even under severe conditions in which charging and discharging with a large current is repeated in a short time. High energy density, excellent safety and long life characteristics are inevitably required, such as having to be used.

  Traditionally, lithium metal has been used as the negative electrode for secondary batteries, but the structural and electrical properties are maintained while the battery short-circuit associated with the formation of dendrite and the danger of explosion due to this are known. However, carbon-based compounds capable of reversible lithium ion intercalation and desorption are being substituted.

  The carbon-based compound has a very low discharge potential of about −3 V with respect to the standard hydrogen electrode potential, and is excellent due to the very reversible charge / discharge behavior due to the uniaxial orientation of the graphite plate layer. The electrode life characteristics (cycle life) are shown. In addition, when charging Li ions, the electrode potential is 0 V Li / Li +, which can show a potential almost similar to that of pure lithium metal, so that higher energy can be obtained when configuring a battery with an oxide-based positive electrode There is an advantage that you can.

  The negative electrode for a secondary battery is prepared by preparing a negative electrode active material slurry in which a carbon material as the negative electrode active material 13 and, if necessary, a conductive material and a binder are mixed, and then using the slurry as an electrode such as a copper foil. The current collector 11 is manufactured by a method of applying a single layer and drying. At this time, at the time of applying the slurry, the active material powder is pressed against the current collector, and a rolling process is performed in order to make the thickness of the electrode uniform (see FIG. 1).

  However, in the conventional electrode rolling process, the ratio of the surface pores is reduced while the surface depression is deepened as compared with the inside of the negative electrode active material.

  This phenomenon is further deepened when the electrode thickness is thick, and it becomes difficult to impregnate the electrolyte solution up to the inside of the electrode. Deteriorating battery performance and life characteristics.

  The problem to be solved by the present invention is to provide a negative electrode having improved ion mobility into the electrode by including a multilayer active material layer in the negative electrode.

  Moreover, this invention provides the lithium secondary battery which the charging characteristic and lifetime characteristic of the battery improved by including the said negative electrode.

In order to solve the above problems, according to one embodiment of the present invention,
An electrode current collector; and a multilayer active material layer formed on the electrode current collector, wherein the multilayer active material layer is formed on the electrode current collector and includes a first negative electrode active material 1 And a second negative electrode active material layer formed on the primary negative electrode active material layer and having a relatively lower rolling density and a relatively larger average particle size than the first negative electrode active material. comprises secondary negative-electrode active material layer containing a substance, the first negative active material and the second negative electrode active material, are both crystalline system-carbon, the crystalline carbon include natural with spherical or similar sphere Including graphite, artificial graphite, or a mixture thereof, the ratio of the average particle size of the first negative electrode active material and the second negative electrode active material is 1: 9 to 5: 5.1, A negative electrode is provided.

  In addition, according to an embodiment of the present invention, a lithium secondary battery including the negative electrode is provided.

  The negative electrode according to an embodiment of the present invention includes a multilayer active material layer including two types of negative electrode active materials having different rolling densities and average particle sizes of the negative electrode active material on the electrode current collector. Since the porosity of the electrode surface can be improved later and the ion mobility to the inside of the electrode can be improved, the charging characteristics and life characteristics of the lithium secondary battery can be improved.

It is a schematic diagram of the negative electrode structure which consists of a conventional single layer active material layer. It is a schematic diagram of the negative electrode structure which consists of a multilayer active material layer based on one Example of this invention. 6 is a graph obtained by measuring charging characteristics of Example 1 and lithium secondary batteries of Comparative Examples 1 and 2 according to Experimental Example 2. FIG. 5 is a graph showing the life characteristics of lithium secondary batteries of Example 1 and Comparative Example 1 measured according to Experimental Example 3 according to negative electrode density. 5 is a graph showing the life characteristics of lithium secondary batteries of Example 1 and Comparative Example 1 measured according to Experimental Example 3 according to negative electrode density.

  The present invention will be described in detail below.

  A negative electrode according to an embodiment of the present invention includes an electrode current collector 21; and a multilayer active material layer formed on the electrode current collector, as shown in the schematic diagram of FIG. The material layer includes a primary negative electrode active material layer (A) including a first negative electrode active material 23; and a second material having a relatively lower rolling density and a relatively larger average particle size than the first negative electrode active material. A secondary negative electrode active material layer (B) including the negative electrode active material 24 can be included.

  The negative electrode according to an embodiment of the present invention includes a multilayer active material layer including two types of negative electrode active materials having different rolling densities and average particle sizes of the negative electrode active material on the electrode current collector. Since the porosity of the electrode surface can be improved later and the ion mobility to the inside of the electrode can be improved, the charging characteristics and life characteristics of the lithium secondary battery can be improved.

  First, the electrode current collector was stainless steel; aluminum; nickel; titanium; calcined carbon; copper; stainless steel surface-treated with carbon, nickel, titanium, or silver; aluminum-cadmium alloy; surface-treated with a conductive material And one or more selected from the group consisting of a non-conductive polymer; and a conductive polymer.

  In the negative electrode of the present invention, the first negative electrode active material and the second negative electrode active material have a theoretical maximum limit capacity of 372 mAh / g (844 mAh / cc) so as to ensure a high energy density. Mention may be made of some crystalline carbons such as natural graphite and artificial graphite; amorphous carbons such as soft carbon and hard carbon; or mixtures thereof.

  Specifically, the first negative electrode active material and the second negative electrode active material may be the same (same type) natural graphite and crystalline carbon such as artificial graphite each having a spherical shape or a similar spherical shape. It may be.

  In the negative electrode according to an embodiment of the present invention, the average particle size ratio of the first negative electrode active material: second negative electrode active material may be 1: 9 to 5: 5.1. Alternatively, it may be 1: 1.3 to 1: 4. As a non-limiting example, the average particle size of the first negative electrode active material may be about 20 μm or less, specifically, for example, in the range of 10 μm to 18 μm.

The average particle size of the negative electrode active material according to an embodiment of the present invention can be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of about several millimeters from a submicron region, and can obtain results of high reproducibility and high resolution. The average particle size (D ₅₀ ) of the negative electrode active material can be defined by the particle size based on 50% of the particle size distribution.

  In the negative electrode according to one embodiment of the present invention, the rolling density ratio of the first negative electrode active material: second negative electrode active material may be 1.1: 1 to 3: 1 under a pressure of 12 to 16 MPa, preferably It should be between 1.1: 1 and 1.5: 1.

  According to an embodiment of the present invention, a rolling density of the first negative electrode active material and the second negative electrode active material satisfies a rolling density ratio of the first negative electrode active material and the second negative electrode active material satisfying the range. As long as it is not particularly limited. However, for example, the rolling density of the first negative electrode active material preferably has a density of 1.4 to 1.85 g / cc under a pressure of 12 to 16 MPa, and the rolling density of the second negative electrode active material is from 12 It preferably has a density of 1.4 to 1.6 g / cc under a pressure of 16 MPa.

  The rolling density is a comparison of the degree of particle deformation of the negative electrode active material. When rolling at the same pressure, the lower the rolling density value, the better the compressive strength. The measurement of the rolling density of the first negative electrode active material and the second negative electrode active material can be performed using, for example, a powder resistance measuring device MCP-PD51 of Mitsubishi Chemical. In the case of the powder resistance measuring device, a constant amount of negative electrode active material powder is put into a cylinder type load cell and force is continuously applied. At this time, the density measured while the particles are pressed was measured. Is. The larger the particle strength, the less the pressure is applied at the same pressure, and the lower the rolling density can be.

  In the negative electrode according to an embodiment of the present invention, the compressive strength ratio of the first negative electrode active material: the second negative electrode active material may be 2: 8 to 5: 5.1 under a pressure of 12 to 16 MPa. The range may be from 2: 8 to 4: 7.

  The porosity of the primary negative electrode active material layer, for example, the ratio of 0.1 to 10 μm voids is about 10 to 50% by weight. The porosity in the volume is about 10 to 50% by weight. At this time, in the secondary negative electrode active material layer, the size and / or porosity of the void may be relatively larger or higher than that of the primary negative electrode active material layer. For example, when the primary negative electrode active material layer and the secondary negative electrode active material layer have the same porosity of 27%, the size of the gap between the active material of the primary negative electrode active material layer is 0. 4 to 3 μm, and the size of the gap between the active materials of the secondary negative electrode active material layer may be 0.5 to 3.5 μm.

  That is, the negative electrode of the present invention is relatively rolled on the primary negative electrode active material layer composed of the first negative electrode active material having a relatively high rolling density and a smaller average particle size than the second negative electrode active material. By forming a secondary negative electrode active material layer composed of a second negative electrode active material having a low density and a large average particle size, the porosity of the surface of the negative electrode active material layer is increased, and the negative electrode active material layer is formed during the rolling process. Surface damage can be prevented, and the void structure inside the electrode can be improved.

  On the other hand, when forming an electrode composed of a single-layer active material layer as in the prior art, pressure can be transmitted to the inside of the electrode due to the characteristics of a single negative electrode active material layer with low stress because it is soft during the rolling process. Since this is not possible, only the negative electrode active material located on the electrode surface is heavily pressurized. For example, even when the electrode is formed only with a single layer active material layer having a low rolling density and a large average particle size like the second negative electrode active material, the single negative electrode active material layer having a low stress during the rolling process is used. Depending on the characteristics, only the negative electrode active material located on the electrode surface is heavily pressurized. As a result, the porosity between the negative electrode active materials in the vicinity of the electrode surface can be reduced, and ion mobility into the electrode can be reduced. Such a phenomenon can become more serious as the electrode thickness of the negative electrode increases or the density increases.

  However, as in the present invention, two or more negative electrode active materials having different rolling density and average particle size and high stress, in particular, the rolling density of the secondary negative electrode active material layer is relative to that of the primary negative electrode active material layer. If a negative electrode active material that is extremely low is used, the dent phenomenon on the electrode surface during rolling can be alleviated as the compressive strength of the negative electrode active material applied in the vicinity of the electrode surface increases. Accordingly, the porosity of the electrode surface, that is, the secondary negative electrode active material layer is further increased as compared with the inside of the electrode, that is, the primary negative electrode active material layer. Can be improved (see FIG. 2).

  The first and second negative electrode active materials of the present invention may further include a conductive material and a binder as necessary.

  At this time, examples of the conductive material include nickel powder, cobalt oxide, titanium oxide, and carbon. Examples of carbon include any one selected from the group consisting of ketjen black, acetylene black, furnace black, graphite, carbon fiber, and fullerene, or a mixture of two or more thereof.

  In addition, the binder may be any binder resin that has been used in lithium secondary batteries, such as polyvinylidene fluoride, carboxymethylcellulose, methylcellulose, and sodium polyacrylate. Any one selected or a mixture of two or more of these may be used.

  According to another embodiment of the present invention, a step of applying a first negative electrode active material slurry containing a first negative electrode active material and a binder resin on an electrode current collector; drying the first negative electrode active material slurry; Forming a primary negative electrode active material layer; applying a second negative electrode active material slurry containing a second negative electrode active material and a binder resin on the primary negative electrode active material layer; drying the second negative electrode active material slurry And forming a secondary negative electrode active material layer; and rolling the electrode current collector on which the primary and secondary negative electrode active material layers are formed.

  In the method, the second negative electrode active material slurry may be applied before the first negative electrode active material slurry is dried. That is, the step of applying the first negative electrode active material slurry and the second negative electrode active material slurry may be continued without a drying step, and the steps of drying and rolling the applied slurry are also performed simultaneously. May be.

  The rolling process may be performed under the same process conditions as those of a normal electrode manufacturing method.

  In the method of the present invention, the size of voids in the primary negative electrode active material layer before the rolling step is about 1 to 20 μm, and the porosity of the total volume of the primary negative electrode active material layer is about 50%. It is. However, after the rolling process, the size of the void inside the primary negative electrode active material layer is about 0.1 to 3 μm, and the porosity of the total volume of the primary negative electrode active material layer is about 10% to about 50%. is there.

  In addition, the size of the voids in the secondary negative electrode active material layer before the rolling step is about 1 to 30 μm, and the porosity in the total volume of the secondary negative electrode active material layer is about 50%. However, after the rolling process, the size of the void in the secondary negative electrode active material layer is about 0.1 to 5 μm, and the porosity of the total volume of the secondary negative electrode active material layer is about 10% to 50%. .

  In the primary negative electrode active material layer and the secondary negative electrode active material layer, the porosity ratio before rolling is 5: 5.1 to 4: 6, and the porosity ratio after rolling is 5: 5.1 to 2 : 8.

  In addition, the size and / or porosity of the void in the secondary negative electrode active material layer may be relatively larger or higher than that of the primary negative electrode active material layer. For example, the primary negative electrode active material layer When the ratio of the porosity of the secondary negative electrode active material layer is 4: 6 (20%: 30%), the size of the void of the primary negative electrode active material layer is 0.4 to 3 μm. The size of the voids in the active material layer may be 0.5 to 3.5 μm.

  Usually, in a negative electrode to which a negative electrode active material is applied, a void having a size of 0.1 to 10 μm plays a role of improving the moisture content rate of the electrolytic solution and the transmission rate of lithium ions. If a negative electrode consisting of only a single layer active material layer is used as in the prior art, the density increases after the rolling step while the porosity on the negative electrode, for example, the proportion of voids of 5 μm or more is reduced to 50% or less. It will be.

  The measurement of the porosity is not particularly limited, and can be measured by, for example, a BET (Brunauer-Emmett-Teller) measurement method or a mercury permeation method (Hg porosimeter) according to an embodiment of the present invention.

  In the present invention, by providing a negative electrode composed of a multilayer active material layer using two types of negative electrode active materials having different rolling densities and average particle sizes, the porosity of the upper portion of the negative electrode remains in the lower portion of the negative electrode even after the rolling process. Since it is relatively high, the density of the upper part of the negative electrode is lowered. Accordingly, it is possible to easily impregnate the electrode with the electrolytic solution and further improve the ion mobility. Furthermore, it is possible to maintain the form of the active material in which the electrode surface is easily broken or not recessed during the rolling process for manufacturing the electrode.

  The present invention also provides a lithium secondary battery manufactured by enclosing the negative electrode, the positive electrode, a separator, and an electrolyte in a battery case by a general method.

  The positive electrode may be used without limitation as long as it is a normal positive electrode used in the manufacture of a lithium secondary battery. For example, a positive electrode active material powder, a slurry obtained by mixing a binder and a conductive material is used as an electrode current collector. After coating and drying, it can be rolled and molded.

Examples of the positive electrode active material include 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. preferable. In addition, it is preferable to use a material capable of inserting and extracting lithium, such as TiS, MoS, an organic disulfide compound, or an organic polysulfide compound.

  Examples of the binder include polyvinylidene fluoride, carboxymethylcellulose, methylcellulose, sodium polyacrylate, and the like, and examples of the conductive material include conductive auxiliary materials such as acetylene black, furnace black, graphite, carbon fiber, and fullerene. Can be mentioned.

  As the separator, any separator can be used as long as it is used for a lithium secondary battery. For example, polyethylene, polypropylene, or a multilayer film thereof, polyvinylidene fluoride, polyamide, glass fiber, and the like are given as examples. be able to.

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

  Nonaqueous solvents constituting the organic electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, gamma butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide. , Dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl Carbonate, diisopropyl carbonate, dibutyl carbonate, diethylene glycol Nonaqueous solvents such as dimethyl ether, mixed solvents in which two or more of these solvents are mixed, and those conventionally known as solvents for lithium secondary batteries can be cited as examples, particularly propylene carbonate, ethylene What mixed one in dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate in what contained one in carbonate and butyl carbonate is preferable.

Examples of the lithium salt, 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 Use one or more lithium salts selected from among CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate and lithium 4-phenylborate Can do.

  The polymer electrolyte includes polyethylene oxide, polypropylene oxide, polyacetonitrile, polyvinylidene fluoride, polymethacrylate, polymethyl methacrylate, and the like that are excellent in swelling property with respect to the organic electrolyte and the organic electrolyte. An example in which a polymer is contained can be given.

  Since the secondary battery according to the present invention exhibits high energy density, high output characteristics, improved safety and stability, it can be preferably used particularly as a constituent battery of a medium- or large-sized battery module. Therefore, the present invention further provides a medium-to-large battery module including the secondary battery as described above as a unit battery.

  Such medium and large-sized battery modules are preferably applicable to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices.

Examples of the present invention and comparative examples will be described below. However, the following examples describe preferred examples of the present invention, and the present invention is not limited to the following examples.
[Mode for Carrying Out the Invention]

(Example 1)
When a pressure of 12.3 MPa is applied, 97.3 parts by weight of the first negative electrode active material (artificial graphite) having a negative electrode density of 1.79 g / cc and 0.7 parts by weight of a conductive material (Super-P), a thickener (Carboxymethylcellulose) 1.0 part by weight and binder (styrene butadiene rubber) 1.0 part by weight were mixed to prepare a first negative electrode active material slurry.

  Next, when a pressure of 12.3 MPa was applied, 97.3 parts by weight of a second negative electrode active material (artificial graphite) having a negative electrode density of 1.51 g / cc and 0.7 parts by weight of a conductive material (Super-P) were increased. A second negative electrode active material slurry was prepared by mixing 1.0 part by weight of a sticking agent (carboxymethylcellulose) and 1.0 part by weight of a binder (styrene butadiene rubber).

  After sequentially applying the first negative electrode active material slurry and the second negative electrode active material slurry on the copper current collector, the slurry is dried to form a multilayer active material layer in which the primary and secondary negative electrode active material layers are laminated. did.

  Next, the negative electrode on which the multilayer active material layer was formed was rolled by a roll press. At this time, the negative electrode density was 1.6 g / cc. Further, another negative electrode having a negative electrode density of 1.64 g / cc was obtained by the same method.

Next, 97.2 parts by weight of a positive electrode active material (LiCoO ₂ ), 1.5 parts by weight of a binder (polyvinylidene fluoride) and 1.3 parts by weight of a conductive material (Super-P) are dispersed in N-methylpyrrolidone to form a positive electrode. An active material slurry was produced. The slurry was applied on an aluminum current collector and then rolled with a roll press to produce a positive electrode (positive electrode density: 3.4 g / cc).

A polyethylene separator was inserted between the negative electrode and the positive electrode, and this was put in a battery case, and then an electrolyte solution was injected to manufacture a secondary battery. At this time, a secondary battery was manufactured using a mixed solution of ethylene carbonate / ethyl methyl carbonate and diethyl carbonate (1/2/1 volume ratio) in which 1.0 M LiPF ₆ was dissolved.

(Comparative Example 1)
When a pressure of 12.3 MPa is applied, 97.3 parts by weight of a negative electrode active material (artificial graphite) having a rolling density of 1.51 g / cc, 0.7 parts by weight of a conductive material (Super-P), a thickener (carboxy A negative electrode active material slurry was prepared by mixing 1.0 part by weight of methyl cellulose) and 1.0 part by weight of a binder (styrene butadiene rubber).

  After apply | coating the said negative electrode active material slurry on a copper electrical power collector, this was dried and the single layer active material layer was formed. Thereafter, two types of negative electrodes and secondary batteries having negative electrode densities of 1.6 g / cc and 1.64 g / cc were manufactured in the same manner as in Example 1.

(Comparative Example 2)
A negative electrode having a negative electrode density of 1.6 g / cc and a negative electrode active material having a negative electrode density of 1.79 g / cc was used in the same manner as in Comparative Example 1 except that a negative electrode active material having a negative electrode density of 1.79 g / cc was used. A secondary battery was manufactured.

(Experimental example 1. Measurement of rolling density and average particle size)
The rolling density of the negative electrode active material particles produced in Example 1 and Comparative Examples 1 and 2 was measured using a MCP-PD51 powder resistance measuring instrument manufactured by Mitsubishi Chemical.

  In the case of the powder resistance measuring device, a certain amount of negative electrode active material powder is put into a cylinder type load cell, and a force is continuously applied. At this time, the density measured while the particles are pressed is measured. It is. Therefore, as the strength of the negative electrode active material particles increases, the negative electrode active material particles are not sufficiently pressed at the same pressure, and the density appears lower. At this time, the applied pressure appeared at about 12 to 16 MPa.

  The average particle size of the negative electrode active materials prepared in Example 1 and Comparative Examples 1 and 2 was measured using a laser diffraction method.

The rolling density and average particle size measured as described above are shown in Table 1 below.

(Experimental example 2. Charging characteristics)
In order to evaluate the charging characteristics of the secondary batteries manufactured in Example 1, Comparative Example 1 and Comparative Example 2, the secondary batteries manufactured in Example 1, Comparative Example 1 and Comparative Example 2 were constant current at 23 ° C. After charging at 0.1 C to 4.2 V and 0.05 C under constant voltage (CC / CV) conditions, the battery was discharged at 0.1 C to 3 V under constant current (CC) conditions, and the capacity was measured twice. After that, it was charged at 4.2C under constant current / constant voltage (CC / CV) conditions at 0.5C to 0.05C, then discharged at 0.2C up to 3V under constant current (CC) conditions, and 0.5C- Rate charge characteristics were measured. The results are shown in FIG.

  That is, when FIG. 3 is examined, if the constant current of 0.5 C-rate is charged, the constant current charging time of the battery of Example 1 appears longer than the batteries of Comparative Example 1 and Comparative Example 2. . Therefore, it is confirmed that the charging characteristics of the battery of Example 1 including the negative electrode including the multilayer active material layer are more excellent than those of Comparative Examples 1 and 2 including the negative electrode including the single layer active material layer. I was able to.

(Experimental example 3. Life characteristics)
After performing under the conditions of the experimental example 2, after charging at 4.2C to constant current / constant voltage (CC / CV) conditions to 0.2C to 0.05C, to 3V under constant current (CC) conditions. The discharge was performed at 0.2 C, and this was repeated 80 cycles. The results of the life characteristics against this are shown in FIGS.

  At this time, FIG. 4 shows the life characteristics of the secondary battery having the negative electrode density of 1.6 g / cc in Example 1 and Comparative Examples 1 and 2, and FIG. 5 shows the negative electrode in Example 1 and Comparative Example 1. The lifetime characteristics of a secondary battery having a density of 1.64 g / cc were shown.

  First, considering FIG. 4, when the negative electrode density is as low as 1.6 g / cc, the batteries of Comparative Examples 1 and 2 having a negative electrode including a single layer active material layer, and a multilayer active material layer are included. It can be confirmed that all the batteries of Example 1 equipped with the negative electrode exhibit similar levels of life characteristics.

  However, considering FIG. 5, when the negative electrode density increases to 1.64 g / cc, the negative electrode density is high in the case of the electrode of Example 1 including the electrode including the multilayer negative electrode active material layer. However, while the negative electrode life characteristics were maintained excellent, in the case of the battery of Comparative Example 1 provided with the electrode including the single-layer negative electrode active material layer, it was confirmed that the life characteristics deteriorated as the negative electrode density increased.

  Therefore, the electrode of Example 1 provided with the electrode including the multilayer active material layer obtained from the present invention has improved ion mobility and improved speed and cycle characteristics as compared with the electrode of Comparative Example 1. I understand.

  The negative electrode according to an embodiment of the present invention includes a multilayer active material layer including two types of negative electrode active materials having different rolling densities and average particle sizes of the negative electrode active material on the electrode current collector. Since the porosity of the electrode surface can be improved and ion mobility into the electrode can be improved later, it can be usefully applied to a lithium secondary battery.

11, 21 Electrode current collector 13 Negative electrode active material 23 First negative electrode active material 24 Second negative electrode active material
A Primary negative electrode active material layer
B Secondary negative electrode active material layer

Claims (12)

An electrode current collector; and a multilayer active material layer formed on the electrode current collector,
The multilayer active material layer is formed on the electrode current collector and includes a first negative electrode active material layer including a first negative electrode active material; and
A secondary negative electrode active material formed on the primary negative electrode active material layer and including a second negative electrode active material having a lower rolling density and a relatively larger average particle size than the first negative electrode active material. Including a material layer,
The first negative active material and the second negative electrode active material, are both crystalline system-carbon,
The crystalline carbon includes natural graphite having a spherical shape or a similar spherical shape, artificial graphite, or a mixture thereof.
The negative electrode characterized in that the ratio of the average particle size of the first negative electrode active material and the second negative electrode active material is 1: 9 to 5: 5.1. Wherein the ratio of the size of the first negative electrode active material and the average particle of the second negative electrode active material 1: 1.3 to 1: negative electrode according to claim 1, characterized in that a 4. Rolling density ratio of the second negative electrode active material and the first negative electrode active material, 1.1 to 12 at a pressure of 16 MPa: 1 to 3: according to claim 1 or 2, characterized in that one Negative electrode. The compressive strength ratio of the first negative active material and the second negative electrode active material, 2 to 12 at a pressure of 16 MPa: 8 to 5: any of claims 1 to 3, characterized in that 5.1 The negative electrode according to Item 1. The porosity of the secondary negative active material layer, the negative electrode according to claim 1, any one of 4, wherein the greater than the porosity of the primary negative electrode active material layer. The primary negative electrode active material layer and the second negative active material layer, the negative electrode according to claim 1, any one of 5, characterized in that each further comprising a conductive material and a binder. Applying a first negative electrode active material slurry containing a first negative electrode active material and a binder resin on the electrode current collector;
Drying the first negative electrode active material slurry to form a primary negative electrode active material layer;
Applying a second negative electrode active material slurry containing a second negative electrode active material and a binder resin on the primary negative electrode active material layer;
Rolling the second negative electrode active material slurry to form a secondary negative electrode active material layer; and rolling the electrode negative electrode current collector on which the primary negative electrode active material and the secondary negative electrode active material layer are formed. Including
The first negative active material and the second negative electrode active material, are both crystalline system-carbon,
The crystalline carbon includes natural graphite having a spherical shape or a similar spherical shape, artificial graphite, or a mixture thereof.
The method for producing a negative electrode, wherein the ratio of the average particle size of the first negative electrode active material and the second negative electrode active material is 1: 9 to 5: 5.1. Applying a first negative electrode active material slurry containing a first negative electrode active material and a binder resin on the electrode current collector;
Applying a second negative electrode active material slurry containing a second negative electrode active material and a binder resin on the first negative electrode active material slurry;
Drying the first and second negative electrode active material slurries to form a multilayer negative electrode active material layer including a primary negative electrode active material layer and a secondary negative electrode active material layer; and the multilayer negative electrode active material layer is formed. Rolling into an electrode current collector,
The first negative active material and the second negative electrode active material, are both crystalline system-carbon,
The crystalline carbon includes natural graphite having a spherical shape or a similar spherical shape, artificial graphite, or a mixture thereof.
The method for producing a negative electrode, wherein the ratio of the average particle size of the first negative electrode active material and the second negative electrode active material is 1: 9 to 5: 5.1. The method for producing a negative electrode according to claim 7 or 8 , wherein a porosity of the secondary negative electrode active material layer is relatively larger than a porosity of the primary negative electrode active material layer. 10. The method of manufacturing a negative electrode according to claim 9 , wherein a porosity ratio before rolling of the primary negative electrode active material layer and the secondary negative electrode active material layer is from 5: 5.1 to 4: 6. 11. . Porosity ratio after rolling of the primary negative electrode active material layer and the second negative active material layer, 5: 5.1 to 2: a negative electrode according to claim 9 or 10, characterized in that it is 8 Production method. The lithium secondary battery containing the negative electrode of any one of Claim 1 to 6 .