Dry electrode film, lithium secondary battery using same, and method for manufacturing same

Abstract

The present invention relates to: a dry electrode film which can be manufactured in a dry manner without a fiberizing process; a lithium secondary battery using same; and a method for manufacturing same. The dry electrode film according to the present invention comprises 80-99.9 wt% of an active material, 0.1-10 wt% of a rubber-based binder, and 10 wt% or less of a conductive material.

Description

Dry electrode film, lithium secondary battery using the same, and method for manufacturing the same

[0001] The present invention relates to a lithium secondary battery and a method for manufacturing the same, and more particularly, to a dry electrode film based on a rubber-based binder having amorphous rubber properties at room temperature, a lithium secondary battery using the same, and a method for manufacturing the same.

[0002] The advancement of the information society has led to the development of personal IT devices and computer networks, and the consequent increase in society's overall reliance on electrical energy. This has led to a growing demand for technologies that efficiently store and utilize this energy. Secondary battery-based technology is ideally suited for this diverse energy storage and utilization. Its miniaturization allows for application in personal IT devices and larger devices, such as electric vehicles and power storage devices.

[0003] Among these secondary battery technologies, lithium secondary batteries, theoretically capable of high operating voltage and capacity, are attracting attention due to their ability to achieve the highest energy density per weight and volume. Lithium secondary batteries typically consist of a positive electrode composed of a lithium-containing transition metal oxide, a negative electrode capable of storing lithium, an electrolyte that serves as a medium for transporting lithium ions, and a separator.

[0004] Here, the electrode is formed by including an active material and a binder, and a wet process or a dry process is used as the manufacturing method.

[0005] Dry electrode films manufactured using a dry process primarily use polytetrafluoroethylene (PTFE) as a binder, which involves a fiberization process. These dry electrode films are manufactured by kneading and grinding the active material and PTFE into a powder mixture for electrodes, which is then molded into electrode films.

[0006] However, PTFE used in the manufacture of dry electrode films has difficulties in application to negative electrodes due to problems with reduction stability and reactivity with lithium.

[0007] [Prior Art Literature]

[0008] [Patent Document]

[0009] Patent Publication No. 2022-0100240 (July 15, 2022)

[0010] Accordingly, the purpose of the present invention is to provide a dry electrode film that can be manufactured by a dry process without a fiberization process, a lithium secondary battery using the same, and a manufacturing method thereof.

[0011] Another object of the present invention is to provide a dry electrode film having good reduction stability and capable of suppressing side reactions with lithium, a lithium secondary battery using the same, and a method for manufacturing the same.

[0012] To achieve the above object, the present invention provides a dry electrode film comprising 80 to 99.9 wt% of an active material, 0.1 to 10 wt% of a rubber-based binder, and 10 wt% or less of a conductive material.

[0013] The above rubber-based binder includes at least one of styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylate butadiene rubber (ABR), methacrylate butadiene rubber, acrylonitrile-butadiene-styrene (ABS) rubber, and styrene-butadiene-styrene (SBS) rubber.

[0014] The above rubber binder has a glass transition temperature of 15 degrees or less and a melting point of 300 degrees or less.

[0015] The above rubber binder has a particle size of 1 nm to 1000 nm.

[0016] The above dry electrode film has a thickness of 50 ㎛ to 1000 ㎛.

[0017] The present invention also provides a lithium secondary battery comprising a cathode and a cathode, wherein at least one of the cathode and the cathode comprises the dry electrode film.

[0018] The lithium secondary battery according to the present invention further includes one of an electrolyte layer and a separator interposed between the negative electrode and the positive electrode.

[0019] The above electrolyte layer and separator may include the rubber-based binder.

[0020] The present invention also provides a method for producing a dry electrode film, comprising the steps of: preparing a mixture by mixing 80 to 99.9 wt% of an active material, 0.1 to 10 wt% of a rubber-based binder, and 10 wt% or less of a conductive material; and pressing the mixture with a roll mill to produce a dry electrode film.

[0021] In the step of preparing the above mixture, the active material and the conductive material can be mixed in a dispersion of the rubber-based binder and then vacuum-dried to prepare the mixture.

[0022] And the above-mentioned roll mill may be a three-roll mill having first to third rolls. The speed may increase from the first roll to the third roll, and the gaps between the first to third rolls may be the same.

[0023] According to the present invention, by using a rubber-based binder in the production of a dry electrode film, a dry electrode film can be produced in a dry manner without a fiberization process.

[0024] Since the rubber-based binder included in the dry electrode film according to the present invention exhibits amorphous rubber properties at room temperature, it can exhibit good reduction stability and suppress side reactions with lithium.

[0025] Figure 1 is a flow chart showing a method for manufacturing a dry electrode film for a lithium secondary battery according to the present invention.

[0026] FIG. 2 is a cross-sectional view showing a first example of an electrode including the dry electrode film of FIG. 1.

[0027] FIG. 3 is a cross-sectional view showing a second example of an electrode including the dry electrode film of FIG. 1.

[0028] Figure 4 is a graph showing the initial charge / discharge characteristics of a lithium secondary battery manufactured using a dry electrode film according to an example and comparative example of the present invention.

[0029] This invention is being filed with the support of the national research and development project below.

[0030] [Project ID] 2410004489

[0031] [Assignment Number] 20007045

[0032] Ministry of Trade, Industry and Energy

[0033] [Name of Project Management (Specialist) Institution] Korea Institute of Industrial Technology Planning and Evaluation

[0034] [Research Project Name] Automotive Industry Technology Development

[0035] [Research Project Name] (R) Development of a high-voltage battery system for electric vehicles with ultra-fast charging capability of approximately 1 minute.

[0036] [Name of the project performing organization] Korea Electronics Technology Institute

[0037] Research Period: September 1, 2019 - May 31, 2026

[0038]

[0039] It should be noted that in the following description, only the parts necessary for understanding the embodiments of the present invention are described, and the description of other parts will be omitted to the extent that it does not deviate from the gist of the present invention.

[0040] The terms and words used in this specification and claims described below should not be interpreted as limited to their conventional or dictionary meanings, but should be interpreted with meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to best describe his or her own invention. Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely preferred embodiments of the present invention and do not represent all of the technical idea of ​​the present invention. Therefore, it should be understood that there may be various equivalents and modified examples that can replace them at the time of this application.

[0041] Hereinafter, the present invention will be described in more detail with reference to the attached drawings.

[0042] The dry electrode film for a lithium secondary battery according to the present invention is based on a rubber-based binder having amorphous rubber properties at room temperature.

[0043] These dry electrode films comprise 80 to 99.9 wt% of an active material, 0.1 to 10 wt% of a rubber-based binder, and 10 wt% or less of a conductive material.

[0044] Here, the active material may be one of a positive electrode active material and a negative electrode active material. The active material includes at least one of activated carbon, carbon nanotube (CNT), graphite, silicon (Si), silicon oxide (Si oxide), lithium nickel manganese cobalt oxide (NCM), lithium iron phosphate (LFP), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), and lithium manganese nickel oxide (LNMO), but is not limited thereto.

[0045] For example, the negative active material is carbon such as non-graphitizable carbon, graphitic carbon, etc.; Li xFe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, group 2, group 3 of the periodic table, halogen; 0x≤1; 1≤y≤3; 1≤z≤8) and other metal composite oxides; lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; silicon-based oxides such as SiO, SiO / C, and SiO2; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. can be used, but are not limited thereto.

[0046] The cathode active material is not limited to a lithium transition metal oxide or lithium metal iron phosphate, a metal oxide form, and may be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); chemical formula LiMn 2-x M xLithium manganese composite oxides represented by O2 (wherein, M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (wherein, M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which a portion of the Li in the chemical formula is replaced by an alkaline earth metal ion; lithium metal phosphate LiMPO4 (wherein, M is M = Fe, CO, Ni, or Mn), disulfide compounds; Fe2(MoO4)3, etc., but are not limited thereto.

[0047] The conductive material is not particularly limited, as long as it is conductive and does not induce chemical changes in the battery. For example, the conductive material includes, but is not limited to, at least one of acetylene black, carbon black, carbon nanotubes (CNTs), and graphene. The conductive material may not be included in the dry electrode film.

[0048] And the rubber binder has a glass transition temperature of 15 degrees or lower. That is, the glass transition temperature must be lower than room temperature to exhibit amorphous rubber characteristics, which causes deformation of the rubber through pressure and bonding through contact.

[0049] Rubber-based binders have a melting point of less than 300 degrees. This means that if the binder is hard, it cannot be formed into a dry electrode film through rolling at room temperature.

[0050] Rubber-based binders have particle sizes ranging from 1 nm to 1,000 nm. This is because binder particle sizes exceeding 1,000 nm increase their relative volume relative to the active material, resulting in a decrease in surface area for the same amount of binder. Therefore, it is desirable for rubber-based binders to have as small a particle size as possible to ensure even adhesion to the surface of the active material.

[0051] Emulsion polymerization or suspension polymerization can be used as a method for manufacturing a rubber-based binder into nanoparticles, and other methods for manufacturing nanoparticles can be utilized.

[0052] These rubber-based binders include at least one of styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylate butadiene rubber (ABR), methacrylate butadiene rubber, acrylonitrile-butadiene-styrene (ABS) rubber, and styrene-butadiene-styrene (SBS) rubber.

[0053] The reasons for using a rubber-based binder in the dry electrode film according to the present invention are as follows. First, because the rubber-based binder possesses amorphous rubber properties at room temperature, it is possible to manufacture the dry electrode film using a dry process. Furthermore, while PTFE involves a fiberization process, the rubber-based binder does not, resulting in excellent reduction stability and suppression of side reactions with lithium.

[0054] Meanwhile, the dry electrode film according to the present invention may further include at least one of polyethylene oxide, polypropylene oxide, and polyalkylene carbonate as a binder, together with a rubber-based binder.

[0055] The dry electrode film according to the present invention can be applied to a lithium secondary battery. The lithium secondary battery includes a negative electrode and a positive electrode, and at least one of the negative electrode and the positive electrode includes a dry electrode film.

[0056] And the lithium secondary battery may include one of an electrolyte layer and a separator interposed between the negative electrode and the positive electrode. The electrolyte layer and the separator may include a rubber-based binder.

[0057] When a lithium secondary battery includes a separator, it is implemented as a liquid type secondary battery containing an electrolyte.

[0058] When a lithium secondary battery includes an electrolyte layer, it is implemented as an all-solid-state battery.

[0059]

[0060] The method for manufacturing a dry electrode film according to the present invention is described below with reference to FIG. 1. Here, FIG. 1 is a flow chart showing a method for manufacturing a dry electrode film for a lithium secondary battery according to the present invention.

[0061] First, in step S10, a mixture is prepared by mixing 80 to 99.9 wt% of the active material, 0.1 to 10 wt% of the rubber-based binder, and 10 wt% or less of the conductive material. That is, the mixture can be prepared by mixing the active material and the conductive material into a rubber-based binder dispersion and then vacuum-drying the mixture. The rubber-based binder dispersion can be prepared through emulsion polymerization or suspension polymerization.

[0062] And in step S20, the mixture is pressed into a roll mill to produce a dry electrode film. Here, the roll mill may be a three-roll mill having first to third rolls. The speed increases from the first roll to the third roll, and the gap between the first to third rolls may be the same. The gap may have a thickness of the dry electrode film to be produced, and may be, for example, 50 μm to 1000 μm.

[0063]

[0064] An electrode (30) including a dry electrode film according to the present invention can be implemented as shown in FIG. 2 or FIG. 3.

[0065] FIG. 2 is a cross-sectional view showing a first example of an electrode (30) including the dry electrode film (20) of FIG. 1.

[0066] Referring to FIG. 2, the electrode (30) according to the first example includes a current collector (10) and a dry electrode film (20) laminated on one surface of the current collector (10).

[0067] A metal foil with good electrical conductivity can be used as the current collector (10), for example, a copper foil can be used.

[0068] And the dry electrode film (20) can be bonded to one surface of the current collector (10) by a lamination method.

[0069] FIG. 3 is a cross-sectional view showing a second example of an electrode (30) including the dry electrode film (21, 23) of FIG. 1.

[0070] Referring to FIG. 3, the electrode (30) according to the second example includes a current collector (10) and a dry electrode film (21, 23) laminated on both sides of the current collector (10).

[0071] A metal foil with good electrical conductivity can be used as the current collector (10), for example, a copper foil can be used.

[0072] And the dry electrode film (21, 23) can be bonded to both sides of the current collector (10) by lamination.

[0073]

[0074] [Examples and Comparative Examples]

[0075] In order to confirm the electrochemical characteristics of the dry electrode film according to the present invention, dry electrode films according to examples and comparative examples were manufactured, and then lithium secondary batteries were manufactured using the manufactured dry electrode films.

[0076] [Example 1]

[0077] (1) Preparation of mixture for dry electrode film

[0078] A mixture was prepared by mixing artificial graphite, a 40 wt% aqueous dispersion of styrene butadiene rubber (SBR), and Super P carbon black at a solids ratio of 96:3:1 using a blender. The mixture was vacuum-dried in an oven at 120°C for 12 hours.

[0079]

[0080] (2) Dry electrode film

[0081] A dry electrode film was manufactured using the mixture manufactured in (1) above using a 3-roll mill. At this time, the temperature of the rolls was set to 50 degrees, the gap between the rolls was each set to 200 μm, the rotation speed of the first roll was set to 1 rpm, and the speed ratio of the first to third rolls was set to 1:1.2:1.44.

[0082] A dry electrode film of about 200 μm was manufactured through the manufacturing process of (2) above.

[0083]

[0084] (3) Battery manufacturing

[0085] The dry electrode film manufactured in the above (2) was bonded to copper foil by roll pressing, and then a coin half cell using lithium metal as the counter electrode was manufactured. At this time, the current density of the cathode was approximately 10 mAh / cm 2 It's about that much.

[0086] Polyolefin (PP) was used as the separator. 1M LiPF6in EC / DMC = 3:7 + 2% VC was used as the electrolyte.

[0087]

[0088] [Example 2]

[0089] A dry electrode film and battery were manufactured using the same method as Example 1, except that artificial graphite, styrene butadiene rubber, and carbon black were mixed in a weight ratio of 97:2:1 in terms of solid content.

[0090]

[0091] [Example 3]

[0092] A dry electrode film and battery were manufactured using the same method as Example 1, except that artificial graphite, styrene butadiene rubber, and carbon black were mixed in a weight ratio of 98:1:1 in terms of solid content.

[0093]

[0094] [Example 4]

[0095] A dry electrode film and battery were manufactured using the same method as Example 1, except that artificial graphite, styrene butadiene rubber, and carbon black were mixed in a weight ratio of 95:4:1 in terms of solid content.

[0096]

[0097] [Comparative Example 1]

[0098] A dry electrode film and battery were manufactured using the same method as Example 1, except that artificial graphite, styrene butadiene rubber, and carbon black were mixed in a weight ratio of 98.9:0.1:1 in terms of solid content.

[0099]

[0100] [Comparative Example 2]

[0101] PTFE was used as a binder. A dry electrode film and battery were manufactured using the same method as Example 1, except that artificial graphite, PVdF, and carbon black were mixed in a weight ratio of 97:2:1 in terms of solid content.

[0102]

[0103] [Comparative Example 3]

[0104] PTFE was used as a binder. A dry electrode film and battery were manufactured using the same method as Example 1, except that artificial graphite, PTFE, and carbon black were mixed in a weight ratio of 97:2:1 in terms of solid content.

[0105]

[0106] The initial charge / discharge characteristics of lithium secondary batteries manufactured using the dry electrode films according to the examples and comparative examples manufactured in this way were measured, and the measurement results are as shown in Table 1 and Fig. 4 below. Here, Fig. 4 is a graph showing the initial charge / discharge characteristics of lithium secondary batteries manufactured using the dry electrode films according to the examples and comparative examples of the present invention.

[0107]

[0108] It can be confirmed that it is impossible to manufacture an electrode using the dry electrode films of Comparative Examples 1 and 2.

[0109] Comparing Examples 1 and 2 with Comparative Example 3, it can be confirmed that both batteries operate well. However, it can be confirmed that Comparative Example 3 has a very low initial charge / discharge efficiency compared to Examples 1 and 2.

[0110] In this way, in the case of Comparative Example 3, it is judged that the lack of reduction stability and side reaction with lithium were due to PTFE used in the manufacture of the dry electrode film.

[0111] On the other hand, the reason why Examples 1 and 2 show better initial charge / discharge efficiency than Comparative Example 3 is believed to be due to the good reduction stability and suppression of side reactions with lithium by using styrene butadiene rubber as a binder in the production of the dry electrode film.

[0112]

[0113] Meanwhile, the embodiments disclosed in this specification and drawings are merely specific examples to aid understanding and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical concepts of the present invention are possible in addition to the embodiments disclosed herein.

[0114] [Explanation of symbols]

[0115] 10: Whole house

[0116] 20, 21, 23: Dry electrode film

[0117] 30: Electrode

Claims

1. A dry electrode film comprising 80 to 99.9 wt% of an active material, 0.1 to 10 wt% of a rubber-based binder, and 10 wt% or less of a conductive material.

2. In paragraph 1, A dry electrode film characterized in that the above rubber-based binder comprises at least one of styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylate butadiene rubber (ABR), methacrylate butadiene rubber, acrylonitrile-butadiene-styrene (ABS) rubber, and styrene-butadiene-styrene (SBS) rubber.

3. In paragraph 1, A dry electrode film characterized in that the above rubber-based binder has a glass transition temperature of 15 degrees or less and a melting point of 300 degrees or less.

4. In paragraph 1, A dry electrode film characterized in that the above rubber-based binder has a particle size of 1 nm to 1000 nm.

5. In paragraph 1, A dry electrode film, characterized in that the above dry electrode film has a thickness of 50 ㎛ to 1000 ㎛.

6. A lithium secondary battery including a cathode and anode, At least one of the cathode and anode comprises a dry electrode film, A lithium secondary battery comprising the above dry electrode film comprising 80 to 99.9 wt% of an active material, 0.1 to 10 wt% of a rubber-based binder, and 10 wt% or less of a conductive material.

7. In paragraph 6, Further comprising one of an electrolyte layer and a separator interposed between the cathode and the anode, A lithium secondary battery, characterized in that the electrolyte layer and separator include the rubber-based binder.

8. In paragraph 6, A lithium secondary battery, characterized in that the rubber-based binder comprises at least one of styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylate butadiene rubber (ABR), methacrylate butadiene rubber, acrylonitrile-butadiene-styrene (ABS) rubber, and styrene-butadiene-styrene (SBS) rubber.

9. A step of preparing a mixture by mixing 80 to 99.9 wt% of an active material, 0.1 to 10 wt% of a rubber-based binder, and 10 wt% or less of a conductive material; and A step of manufacturing a dry electrode film by pressing the above mixture with a roll mill; A method for producing a dry electrode film comprising:

10. In paragraph 9, A method for producing a dry electrode film, characterized in that the rubber-based binder comprises at least one of styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), acrylate butadiene rubber (ABR), methacrylate butadiene rubber, acrylonitrile-butadiene-styrene (ABS) rubber, and styrene-butadiene-styrene (SBS) rubber.

11. In the step of preparing the mixture in paragraph 9, A method for producing a dry electrode film, characterized in that the mixture is produced by mixing the active material and the conductive material in a dispersion of the rubber-based binder and then vacuum drying the mixture.

12. In paragraph 9, A method for manufacturing a dry electrode film, wherein the above-mentioned roll mill is a three-roll mill having first to third rolls, the speed increases from the first roll to the third roll, and the gaps of the first to third rolls are the same.

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