Electrode slurry comprising thickeners having different aspect ratios, and electrode for secondary battery using same

Abstract

The present invention relates to an electrode slurry in which thickeners having different aspect ratios are mixed and applied, and to an electrode for a secondary battery using same. The electrode slurry is capable of reducing linear pressure and preventing a spring-back phenomenon while increasing interfacial adhesion between an active material layer and a current collector.

Description

Electrode slurry comprising thickeners with different aspect ratios and electrode for a secondary battery using the same

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2025-0010069 dated January 23, 2025, and all contents disclosed in the literature of said Korean patent applications are incorporated herein as part of this specification.

[0002] The present invention relates to an electrode slurry comprising thickeners with different aspect ratios and an electrode for a secondary battery using the same.

[0003]

[0004] Lithium-ion batteries are being widely applied not only to small devices such as portable electronic devices but also to medium and large-sized devices such as battery packs or power storage systems for hybrid and electric vehicles. In particular, with the recent increase in concern for environmental issues, the demand base for high-capacity batteries is expanding due to the growth of the market for devices employing high-capacity batteries, such as electric vehicles and hybrid electric vehicles, which can replace fossil fuel-using vehicles like gasoline and diesel cars that are major causes of air pollution.

[0005] Generally, a lithium secondary battery is a rechargeable power generation device composed of a stacked structure of a positive electrode, a separator, and a negative electrode. During charging, a lithium extraction reaction occurs in the positive electrode, where lithium contained in the positive electrode active material is oxidized and released, while a lithium insertion reaction occurs in the negative electrode, where lithium is reduced and enters the negative electrode active material. Since the extraction reaction in the positive electrode active material is generally faster than the insertion reaction in the negative electrode active material, performance characteristics such as charging and discharging speeds are primarily determined by the negative electrode.

[0006] Various attempts are being made to improve the performance of lithium-ion batteries. One such attempt is to increase the capacity of lithium-ion batteries. Methods to increase capacity include increasing the loading amount of the active material layer or increasing the active material content. However, as the rolling rate increases during the electrode manufacturing process, delamination of the interface between the active material layer and the current collector or springback after rolling may occur.

[0007] Therefore, there is a need for a technology that can prevent springback while increasing interfacial adhesion between the active material layer and the current collector.

[0008]

[0009] Accordingly, the present invention aims to provide an electrode slurry in which thickeners with different aspect ratios are mixed and applied, and an electrode for a secondary battery using the same.

[0010]

[0011] In order to solve the problem described above, in one embodiment, the electrode slurry according to the present invention comprises a first thickener having an aspect ratio of 100 or more; and a second thickener having an aspect ratio of 50 or less. In addition, the content of the first and second thickeners satisfies the following Formula 1.

[0012] [Formula 1]

[0013] 0.1 ≤ T1 / T2 ≤ 0.8

[0014] In the above Formula 1,

[0015] T1 represents the content (parts by weight) of the first thickener based on the solid content in the electrode slurry, and

[0016] T2 represents the content (parts by weight) of the second thickener based on the solid content in the electrode slurry.

[0017] In one example, the aspect ratio of the first thickener is in the range of 100 to 500. In addition, the aspect ratio of the second thickener is in the range of 1 to 50.

[0018] In a specific example, the first and second thickeners are each independently one or more of carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), polyurethane (PU), colloidal silica, polyethylene glycol (PEG), and alginate.

[0019] For example, the first thickener is a fibrous cellulose thickener. In a more specific example, the first thickener is a cellulose nanofiber (CNF).

[0020] As another example, the second thickener mentioned above is a block-type cellulose thickener.

[0021] In one embodiment, the electrode slurry comprises, based on solid content, 85 to 97 parts by weight of an active material; 0.1 to 5 parts by weight of a conductive material; 0.5 to 5 parts by weight of a binder; and 0.5 to 5 parts by weight of a thickener. The thickener comprises a first and a second thickener.

[0022] In a specific example, the combined content of the binder and the thickener is 2.6 parts by weight or more.

[0023]

[0024] The present invention also provides an electrode for a secondary battery manufactured using the electrode slurry described above. In one embodiment, the electrode for a secondary battery according to the present invention comprises a current collector; and an active material layer formed on one or both sides of the current collector. Here, the active material layer comprises a first thickener having an aspect ratio of 100 or more; and a second thickener having an aspect ratio of 50 or less. Additionally, the content of the first and second thickeners satisfies the following Formula 1.

[0025] [Formula 1]

[0026] 0.1 ≤ T1 / T2 ≤ 0.8

[0027] In the above Formula 1,

[0028] T1 represents the content (parts by weight) of the first thickener based on the solid content in the electrode slurry, and

[0029] T2 represents the content (parts by weight) of the second thickener based on the solid content in the electrode slurry.

[0030] In another embodiment, the combined content of the first and second thickeners is in the range of 0.1 to 5 parts by weight based on 100 parts by weight of the entire active material layer.

[0031] In a specific example, the first thickener is a fibrous cellulose thickener. Additionally, the second thickener is a sticky cellulose thickener.

[0032] For example, the first thickener is a cellulose nanofiber (CNF).

[0033] In one example, the active material layer comprises, based on solid content, 85 to 97 parts by weight of an active material; 0.1 to 5 parts by weight of a conductive material; 0.5 to 5 parts by weight of a binder; and 0.5 to 5 parts by weight of a thickener. Additionally, the thickener comprises a first and a second thickener.

[0034] In a specific example, the combined content of the binder and the thickener is 2.6 parts by weight or more.

[0035] In one embodiment, the electrode for a secondary battery according to the present invention is a negative electrode. The present invention provides a secondary battery comprising such a negative electrode. Furthermore, the secondary battery is a pouch-type secondary battery. As another example, the secondary battery is a cylindrical or prismatic secondary battery. The secondary battery is, for example, a battery for automobiles or an Energy Storage System (ESS).

[0036]

[0037] The electrode slurry and secondary battery electrode according to the present invention can lower the linear pressure during rolling and prevent springback phenomena without impairing the interfacial adhesion between the active material layer and the current collector.

[0038]

[0039] FIG. 1 is a graph showing the results of comparing and calculating the discharge capacity for cells according to embodiments and comparative examples of the present invention.

[0040]

[0041] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are to be described in detail in the detailed description.

[0042] However, this is not intended to limit the invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0043] In the present invention, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0044] In the present invention, "linear pressure" refers to a value calculated by dividing the pressure acting between the rolling roll and the electrode during the rolling process by the length of the electrode. That is, the linear pressure represents the magnitude of the pressure applied per unit length of the rolled electrode. Specifically, it refers to the magnitude of the pressure required to roll a specific loading amount to a certain thickness during electrode manufacturing.

[0045] In addition, in the present invention, 'spring back' refers to the rate of change in thickness of the cathode active material layer when the manufactured cathode is stored under specific conditions (e.g., stored at 25°C for 3 days).

[0046]

[0047] The present invention will be described in more detail below.

[0048]

[0049] In one embodiment, the electrode slurry according to the present invention comprises a first thickener having an aspect ratio of 100 or more; and a second thickener having an aspect ratio of 50 or less.

[0050] In the present invention, "aspect ratio" refers to the ratio of the major axis to the minor axis of a thickener particle or fiber structure. Thickeners with a high aspect ratio are often in a fibrous form and have a physically long and thin shape. Additionally, thickeners with a high aspect ratio tend to intertwine or form a network within a slurry and are effective in increasing viscosity. In contrast, thickeners with a low aspect ratio mainly have spherical or cubic particle shapes, intertwine less within a slurry, and may have a relatively smaller effect in increasing viscosity.

[0051] In one embodiment, the content of the first and second thickeners satisfies the following Formula 1.

[0052] [Formula 1]

[0053] 0.1 ≤ T1 / T2 ≤ 0.8

[0054] In the above Formula 1,

[0055] T1 represents the content (parts by weight) of the first thickener based on the solid content in the electrode slurry, and

[0056] T2 represents the content (parts by weight) of the second thickener based on the solid content in the electrode slurry.

[0057] The numerical value according to the above formula 1 is in the range of 0.1 to 0.8, 0.1 to 0.6, 0.1 to 0.4, 0.15 to 0.8, 0.2 to 0.4, or 0.2 to 0.3.

[0058] The first thickener mentioned above is a thickener with a relatively high aspect ratio. Increasing the content of the first thickener can increase the viscosity of the electrode slurry. Additionally, if the first thickener is in a fibrous form, the mechanical or structural strength and durability of the electrode can be improved. However, the first thickener is relatively expensive and may have poor dispersibility. In particular, the viscosity characteristics of the first thickener may change sensitively with changes in temperature or pH, and if the first thickener is added in excess, gelation of the electrode slurry is induced and problems such as reduced coating uniformity occur. Furthermore, the second thickener mentioned above is a case where the aspect ratio is relatively small, and is a general term for a non-linear or non-fibrous form or a point form.

[0059] By appropriately controlling the ratio of the first and second thickeners, the present invention can reduce linear pressure, prevent springback phenomena, and improve interfacial adhesion between the current collector and the active material layer.

[0060] In one embodiment, the aspect ratio of the first thickener is in the range of 100 to 500. Specifically, the aspect ratio of the first thickener is in the range of 100 to 300, 100 to 250, 100 to 200, 100 to 150, 100 to 120, 100 to 113, 105 to 115, or 111 to 120. The aspect ratio range of the first thickener is determined considering appropriate viscosity and dispersibility.

[0061] In addition, the aspect ratio of the second thickener is in the range of 1 to 50. Specifically, the aspect ratio of the second thickener is in the range of 1 to 30, 1 to 20, or 1 to 10. The case where the aspect ratio of the second thickener is 1 encompasses cases where it is spherical or dot-shaped, or cases where it is difficult to specify the aspect ratio as it is cubic. The aspect ratio range of the second thickener is intended to increase the dispersibility of the thickener and achieve stable viscosity.

[0062] In one embodiment, the first and second thickeners are each independently one or more of carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), polyurethane (PU), colloidal silica, polyethylene glycol (PEG), and alginate. Specifically, the first and second thickeners are each independently carboxymethylcellulose (CMC).

[0063] Specifically, the first thickener is a fibrous cellulose thickener. More specifically, the first thickener is a cellulose nanofiber (CNF). For example, the first thickener is carboxymethylcellulose (CMC) in the form of nanofibers.

[0064] Specifically, the second thickener is a sticky cellulose thickener. For example, the second thickener is a sticky carboxymethylcellulose (CMC).

[0065] The electrode slurry according to the present invention has a composition suitable for manufacturing into an electrode. For example, the electrode slurry is an anode slurry or a cathode slurry. In one embodiment, the electrode slurry comprises, based on solid content, 85 to 97 parts by weight of an active material; 0.1 to 5 parts by weight of a conductive material; 0.5 to 5 parts by weight of a binder; and 0.5 to 5 parts by weight of a thickener.

[0066] Specifically, the content of the thickener includes the content of the first and second thickeners. The content of the thickener is in the range of 0.5 to 5 parts by weight, 0.5 to 3 parts by weight, 0.5 to 2 parts by weight, or 0.6 to 1.5 parts by weight based on solid content.

[0067] In one embodiment, the electrode slurry is a cathode slurry. The cathode slurry includes, for example, a carbon-based active material as an active material. Specifically, the carbon-based active material includes one or more of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon made from tar and pitch, and graphitized coke. For example, the carbon-based active material may include graphite. The graphite may include one or more of natural graphite and artificial graphite. For example, the carbon-based active material may include natural graphite alone, or in some cases, may include a mixture of natural graphite and artificial graphite. Additionally, the cathode may further include a silicon-based active material as an active material.

[0068] As an example, the above cathode slurry may contain carbon black, carbon nanotubes, carbon fibers, etc., as conductive materials alone or in combination.

[0069] In addition, the above binder is a component that assists in the bonding of the cathode active material and the conductive material, as well as the bonding to the current collector, and can be appropriately applied within a range that does not degrade the electrical properties of the cathode. For example, the above binder is styrene butadiene rubber (SBR) or fluororubber.

[0070] The above-mentioned thickener is a mixed form of the first and second thickeners described above.

[0071] In addition, in the present invention, the combined content of the binder and the thickener can be controlled to be 2.6 parts by weight or more. The combined content of the binder and the thickener is based on the solid content in the electrode slurry. Specifically, the combined content of the binder and the thickener can be controlled to a range of 2.6 parts by weight to 8 parts by weight, a range of 2.6 parts by weight to 5 parts by weight, a range of 2.6 parts by weight to 3.5 parts by weight, or a range of 2.6 parts by weight to 3.2 parts by weight. If the combined content of the binder and the thickener is too low, sufficient interfacial adhesion with the current collector cannot be achieved, and conversely, if the content is too high, it may cause an excessive increase in viscosity or a decrease in the loading amount of the active material.

[0072] The composition of the cathode slurry will be explained in more detail later.

[0073]

[0074] Meanwhile, the process of manufacturing a cathode using a cathode slurry involves, for example, applying the cathode slurry onto a current collector and then drying and rolling the applied cathode slurry.

[0075] Here, the process of applying the cathode slurry is a step of coating the surface of a moving current collector by discharging the cathode slurry. The above step can be applied without particular limitation as long as it is a method commonly applied in the industry, but preferably, a die coating method can be used. The die coating method can be performed through a slot die equipped with a shim for controlling the discharge conditions of the cathode slurry. In this case, by controlling the shape of the shim, the loading amount and coating thickness of the cathode slurry applied on the cathode current collector can be easily controlled.

[0076] After the process of applying the cathode slurry, the process includes drying the cathode and rolling it. The process of drying the cathode involves drying the cathode slurry at a high temperature to form a cathode active material layer on a current collector. The process of drying the cathode can be performed, for example, by applying hot air at a temperature of 160°C to 250°C. The process of rolling the cathode can be performed by applying pressure to one or both sides of the cathode that has undergone the drying process. The method of applying pressure can be performed using a roll press or a plate press, etc. For example, the rolling step is performed by rolling with a roll press so that the rolling porosity of the cathode active material layer becomes 25±5%.

[0077]

[0078] In addition, the present invention provides an electrode for a secondary battery manufactured using the electrode slurry described above. In one embodiment, the electrode for a secondary battery according to the present invention comprises a current collector and an active material layer formed on one or both sides of the current collector. In addition, the active material layer comprises a first thickener having an aspect ratio of 100 or more; and a second thickener having an aspect ratio of 50 or less. In one example, the content of the first and second thickeners satisfies the following Formula 1.

[0079] [Formula 1]

[0080] 0.1 ≤ T1 / T2 ≤ 0.8

[0081] In the above Formula 1,

[0082] T1 represents the content (parts by weight) of the first thickener based on the solid content in the electrode slurry, and

[0083] T2 represents the content (parts by weight) of the second thickener based on the solid content in the electrode slurry.

[0084] The description regarding the content ratio or aspect ratio of the first and second thickeners mentioned above overlaps with what was previously stated.

[0085] In another embodiment, the content of the thickener is in the range of 0.5 to 5 parts by weight, 0.5 to 3 parts by weight, 0.5 to 2 parts by weight, or 0.6 to 1.5 parts by weight, based on 100 parts by weight of the total active material layer. The content range is determined considering the electrode capacity or process efficiency. Specifically, if the content of the thickener increases, the electrode capacity decreases. Conversely, if the content of the thickener deviates from the appropriate range, the viscosity or pH of the electrode slurry changes and process efficiency may decrease.

[0086] Specifically, the first thickener is a fibrous cellulose thickener. More specifically, the first thickener is a cellulose nanofiber (CNF). For example, the first thickener is carboxymethylcellulose (CMC) in the form of nanofibers.

[0087] Specifically, the second thickener is a sticky cellulose thickener. For example, the second thickener is a sticky carboxymethylcellulose (CMC).

[0088] In one embodiment, the active material layer comprises, based on solid content, 85 to 97 parts by weight of an active material; 0.1 to 5 parts by weight of a conductive material; 0.5 to 5 parts by weight of a binder; and 0.5 to 5 parts by weight of a thickener. Additionally, the thickener comprises a first and a second thickener.

[0089] In addition, the combined content of the binder and the thickener can be controlled to be 2.6 parts by weight or more. The combined content of the binder and the thickener is based on the solid content in the electrode slurry. Specifically, the combined content of the binder and the thickener can be controlled to a range of 2.6 to 8 parts by weight, a range of 2.6 to 5 parts by weight, a range of 2.6 to 3.5 parts by weight, or a range of 2.6 to 3.2 parts by weight.

[0090] The electrode for a secondary battery according to the present invention is a positive electrode or a negative electrode. For example, the electrode for a secondary battery according to the present invention is a negative electrode.

[0091]

[0092] secondary battery

[0093] In one example according to the present invention, the secondary battery may be a cylindrical, prismatic, or pouch-type secondary battery. For example, the secondary battery is a pouch-type secondary battery. The pouch-type secondary battery includes an electrode assembly in which a unit structure in which a positive electrode, a separator, and a negative electrode are stacked is repeated.

[0094] The above secondary battery includes an electrode assembly comprising a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes, and a case surrounding the electrode assembly.

[0095] The secondary battery according to the present invention includes an electrode assembly having a structure in which a plurality of positive electrodes and a plurality of negative electrodes are alternately arranged and a separator is located between them. The lithium secondary battery is equipped with the negative electrode of the present invention described above, and has the advantage of having excellent rapid charging performance by improving lithium ion diffusion ability, as well as high energy density.

[0096] The above-mentioned cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector and containing a cathode active material. Specifically, the cathode is manufactured by coating, drying, and rolling a cathode active material on the cathode current collector, and may optionally further include a conductive material, an organic binder polymer, a filler, etc., as needed.

[0097] The above-described cathode includes a carbon-based active material as the cathode active material. In one embodiment, the cathode active material layer includes a carbon-based active material as the active material. Specifically, the carbon-based active material includes one or more of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon made from tar and pitch, and graphitized coke. For example, the carbon-based active material may include graphite. The graphite may include one or more of natural graphite and artificial graphite. For example, the carbon-based active material may include natural graphite alone, or in some cases, may include a mixture of natural graphite and artificial graphite.

[0098] In one embodiment, the cathode further comprises a silicon-based active material as an active material. Specifically, the content of the silicon-based active material is in the range of 0.1 wt% to 30 wt% based on the total weight of the active material in the cathode active material layer. Specifically, the content of the silicon-based active material is in the range of 0.1 wt% to 30 wt%, 1 wt% to 30 wt%, 1 wt% to 10 wt%, 0.1 wt% to 5 wt%, 5 wt% to 30 wt%, or 6 wt% to 20 wt% based on the total weight of the active material contained in the cathode active material layer. The silicon-based active material has the advantage of increasing the cathode capacity compared to carbon-based active materials. On the other hand, the silicon-based active material has the problem of causing volume changes during the charging and discharging process. Therefore, it is desirable to control the content of the silicon-based active material by considering the application field or form of the secondary battery.

[0099] Specifically, the silicon-based active material is silicon (Si), silicon carbide (SiC), a carbon-silicon composite (Si / C), and silicon oxide (SiO₂). q ..., provided that it includes one or more of the following: , provided that 0.8≤q≤2.5). As one example, the active material may include graphite and silicon (Si)-containing particles together, and the graphite may include one or more of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure. The silicon (Si)-containing particles may include silicon (Si) particles as a main component as a metal component, silicon (Si) particles, silicon oxide (SiO, SiO2) particles, or a mixture of silicon (Si) particles and silicon oxide (SiO, SiO2) particles.

[0100] In addition, the silicon-based active material may be doped with Li, Mg, Al, Ca, or Ti, or form an alloy. Furthermore, the silicon-based active material may be surface-treated with a carbon coating layer or the like for the purpose of suppressing volume expansion during charging or improving electrical conductivity.

[0101] The above conductive material may include one or more types of carbon black such as acetylene black, Denka black, Ketjen black, Super-P, furnace black, lamp black, and thermal black; graphene; carbon nanotubes and carbon fibers, but is not limited thereto.

[0102] As an example, the above-mentioned cathode active material layer may contain carbon black, carbon nanotubes, carbon fibers, etc., as a conductive material, either alone or in combination.

[0103] At this time, the content of the conductive material may be 0.1 to 5 parts by weight per 100 parts by weight of the entire negative electrode active material layer. Specifically, the conductive material may be 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight per 100 parts by weight of the entire negative electrode active material layer. By controlling the content of the conductive material within the above range, the present invention can prevent the decrease in charging capacity caused by an increase in the resistance of the negative electrode due to a low content of the conductive material. Furthermore, the present invention can prevent problems such as a decrease in charging capacity due to a decrease in the content of the negative electrode active material caused by an excessive amount of conductive material exceeding the above range, or an increase in electrical resistance due to an increase in the loading amount of the negative electrode active material layer.

[0104] In addition, the binder is a component that assists in the bonding of the cathode active material and the conductive material, as well as the bonding to the current collector, and can be appropriately applied within a range that does not degrade the electrical properties of the cathode. For example, the binder may include one or more of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluororubber. For example, the binder is styrene butadiene rubber (SBR) or fluororubber.

[0105] The content of the binder may be 0.5 to 5 parts by weight per 100 parts by weight of the entire negative electrode active material layer. Specifically, the binder may be in the range of 0.5 to 5 parts by weight or 0.5 to 3 parts by weight per 100 parts by weight of the entire negative electrode active material layer. By controlling the content of the binder contained in the negative electrode active material layer to the above range, the present invention can prevent the adhesion of the active material layer from being reduced due to a low content of binder or the electrical properties of the negative electrode from being reduced due to an excessive amount of binder.

[0106] In addition, the above-mentioned negative electrode active material layer may further include the previously described thickener.

[0107] In addition, the cathode active material layer may have an average thickness of 100㎛ to 800㎛, and specifically, may have an average thickness of 100㎛ to 780㎛; 100㎛ to 550㎛; 120㎛ to 500㎛; 140㎛ to 200㎛ or 140㎛ to 160㎛.

[0108] In addition, the above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. may be used, and in the case of copper or stainless steel, surface-treated carbon, nickel, titanium, silver, etc. may be used.

[0109] In addition, the above-mentioned negative current collector, like the positive current collector, may form fine irregularities on its surface to strengthen the bonding force with the negative active material, and can take various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics. Furthermore, the average thickness of the above-mentioned negative current collector can be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured negative electrode.

[0110] In addition, the anode comprises an anode active material layer containing an anode active material on an anode current collector, and the anode active material layer may optionally further include a conductive material, a binder, other additives, etc., as needed.

[0111] The above-mentioned positive active material is a material capable of causing an electrochemical reaction on the positive current collector. The description of the positive active material is as previously mentioned.

[0112] In addition, the above-mentioned positive active material may be included in an amount of 85 parts by weight or more based on 100 parts by weight of the total positive active material layer. Specifically, the above-mentioned positive active material may be included in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more based on 100 parts by weight of the total positive active material layer.

[0113] In addition, the above-mentioned positive active material layer may further include a conductive material, a binder, other additives, etc., along with the positive active material.

[0114] At this time, the conductive material is used to improve the electrical performance of the anode, and while commonly used in the industry may be applied, specifically, it may include one or more of natural graphite; artificial graphite; carbon black such as acetylene black, Denka black, Ketjen black, Super-P, furnace black, lamp black, and thermal black; graphene; and carbon nanotubes.

[0115] In addition, the conductive material may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of each positive active material layer. Specifically, the conductive material may be included in an amount of 0.1 to 4 parts by weight; 2 to 4 parts by weight; 1.5 to 5 parts by weight; 1 to 3 parts by weight; 0.1 to 2 parts by weight; or 0.1 to 1 part by weight based on 100 parts by weight of each positive active material layer.

[0116] In addition, the binder serves to bind the positive active material, the positive additive, and the conductive material together, and any binder having this function can be used without particular limitation. Specifically, the binder may include one or more resins selected from polyvinylidenefluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidenefluoride.

[0117] In addition, the binder may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of each positive electrode active material layer. Specifically, the content of the binder is in the range of 1 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer; or in the range of 0.1 to 3 parts by weight.

[0118] The total thickness of the above positive active material layer is not particularly limited, but specifically may be in the range of 50㎛ to 800㎛, and more specifically may be in the range of 100㎛ to 800㎛; 80㎛ to 150㎛; 120㎛ to 170㎛; 150㎛ to 300㎛; 200㎛ to 600㎛; or 150㎛ to 390㎛.

[0119] In addition, the anode may be used as an anode current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of aluminum or stainless steel, surface-treated materials such as carbon, nickel, titanium, silver, etc. may be used. Furthermore, the average thickness of the current collector may be appropriately applied from 3㎛ to 500㎛, taking into consideration the conductivity and total thickness of the anode being manufactured.

[0120] In addition, the separator interposed between the positive and negative electrodes of the lithium secondary battery is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is one commonly used in the industry. Specifically, the separator may be one comprising one or more polymers selected from chemically resistant and hydrophobic polypropylene; polyethylene; and polyethylene-propylene copolymer. The separator may have the form of a porous polymer substrate, such as a sheet or nonwoven fabric, containing the aforementioned polymer, and in some cases, may have the form of a composite separator in which organic or inorganic particles are coated on the porous polymer substrate by an organic binder. Furthermore, the separator may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0121] Meanwhile, the secondary battery according to the present invention is not particularly limited, but may be a secondary battery of a form that includes a stack type; a zigzag type; or a zigzag-stack type electrode assembly.

[0122] In addition, the secondary battery according to the present invention may include a lithium salt-containing electrolyte. The lithium salt-containing electrolyte may consist of an electrolyte and a lithium salt, and the electrolyte may be a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0123] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfranc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, etc. may be used.

[0124] The above organic solid electrolyte may be, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer containing an ionic dissociator, etc.

[0125] As the above-mentioned inorganic solid electrolyte, for example, nitrides, halides, sulfates of Li such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc., may be used.

[0126] The above lithium salt is a substance that dissolves well in a non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylboronicate, imide, etc. may be used.

[0127] In addition, for the purpose of improving charge / discharge characteristics and flame retardancy, the electrolyte may be further enriched with, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, to impart non-flammability, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further enriched, carbon dioxide gas may be further enriched to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene Sultone), etc.

[0128] Meanwhile, in one embodiment, the present invention provides a module including the secondary battery described above to a battery pack including the module.

[0129] The above battery pack can be used as a power source for medium-to-large devices requiring high temperature stability, long cycle characteristics, and high rate characteristics. Specific examples of such medium-to-large devices include power tools that are powered by an electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems. More specifically, hybrid electric vehicles (HEVs) can be cited, but are not limited thereto.

[0130] Furthermore, the above-mentioned positive and negative electrodes may be wound into a jelly roll shape and stored in a cylindrical battery, a prismatic battery, or a pouch-type battery, or stored in a pouch-type battery in a folding or stack-and-folding form. For example, the secondary battery according to the present invention may be a pouch-type battery.

[0131] As described above, the secondary battery according to the present invention can be used in a battery module or battery pack comprising a plurality of unit cells. Specifically, it is useful in fields such as portable devices like mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0132]

[0133] The present invention will be explained in more detail below through examples and the like. However, the rights of the present invention are not limited thereto.

[0134]

[0135] Examples 1 to 4, Comparative Examples 1 to 2: Cathode preparation

[0136] A cathode slurry (solid content 54 wt%) was prepared by mixing carbon black as a cathode active material and conductive material, styrene-butadiene rubber (SBR) as a binder, and a thickener (carboxymethylcellulose, CMC) in distilled water. As the cathode active material, artificial graphite and natural graphite were mixed in a weight ratio of 80:20.

[0137] The above cathode slurry was applied to one surface of a cathode current collector (Cu thin film) with a thickness of 8 μm, and a cathode was manufactured by drying and rolling.

[0138] The composition of the above cathode slurry is as shown in Table 1 below. In addition, the type, content, and ratio of the thickener are as shown in Table 2 below. In Table 1 below, the first thickener is a fiber-type CMC thickener, and the second thickener is a stick-type CMC thickener.

[0139] Classification Cathode Active Material Content (Weight Ratio) Conductive Material Content (Weight Ratio) Binder Content (Weight Ratio) Thickener Content (Weight Ratio) Example 1 96.50.52.01.0 Example 2 96.50.52.01.0 Example 3 96.50.52.01.0 Example 4 97.00.51.51.0 Comparative Example 196.50.52.01.0 Comparative Example 296.50.52.01.0

[0140] Classification Content of 1st Thickener (Weight Ratio) 1st Thickener Aspect Ratio (NP Ratio) Content of 2nd Thickener (Weight Ratio) Thickener Ratio Example 1 0.2 10 50.8 0.25 Example 20.2 11 00.8 0.25 Example 3 0.2 11 50.8 0.25 Example 4 0.2 11 00.8 0.25 Comparative Example 10-10 Comparative Example 20.5 11 00.51

[0141] In Table 2 above, 'thickening agent ratio' represents the ratio value calculated by Formula 2 below.

[0142] [Equation 2]

[0143] T1 / T2

[0144] In the above formula 2, T1 represents the content (parts by weight) of the first thickener based on the solid content in the cathode slurry, and T2 represents the content (parts by weight) of the second thickener based on the solid content in the cathode slurry.

[0145]

[0146] Experimental Example 1: Comparison of Linear Pressure and Springback

[0147] For the cathodes according to Examples 1 to 4 and Comparative Examples 1 to 2, linear pressure and springback phenomena were compared and observed. Specifically, for each cathode, drying and roll pressing were performed, and the linear pressure applied during the manufacturing of the cathode was calculated for comparison so that the rolled porosity of the cathode active material layer became 25±5%. In addition, the manufactured cathodes were each stored for 3 days under conditions of 25°C. After storage, the rate of change in thickness of the cathode active material layer was compared for each cathode. The measurement results are shown in Table 3 below.

[0148] Separation Line Pressure Spring Bag Example 189% 65% Example 285% 60% Example 378% 56% Example 476% 70% Comparative Example 1100% 100%

[0149] In Table 3 above, the linear pressure and springback for each sample were set to 100% for Comparative Example 1 and expressed as a ratio relative to it.

[0150] Referring to Table 3 above, it can be seen that the cathodes of Examples 1 to 4 have a line pressure of 90% or less compared to the cathode of Comparative Example 1. In particular, it can be seen that the cathodes of Examples 3 and 4 have a line pressure of 80% or less compared to the cathode of Comparative Example 1. It was confirmed that the line pressure reduction effect is superior when the aspect ratio of the first thickener is in the range of 110 to 115.

[0151] In addition, it can be seen that the cathodes of Examples 1 to 4 have springback controlled to 70% or less of the linear pressure compared to the cathode of Comparative Example 1. In the cathode of Comparative Example 2, gelation was induced in the cathode slurry due to an increase in the content of the first thickener, and the experiment was stopped as a result. This indicates that gelation of the electrode slurry was induced when the first thickener with a high aspect ratio was excessively permeated, and it was confirmed that process efficiency was reduced and coating uniformity was not ensured due to the increase in the viscosity of the electrode slurry.

[0152]

[0153] Experimental Example 2: Measurement of Electrode Adhesion Strength

[0154] The adhesion strength between the active material layer and the current collector was measured for the cathodes prepared in Examples 1 to 4 and Comparative Example 1, respectively. Specifically, cathode specimens were prepared by cutting the cathodes prepared in the examples and comparative examples, respectively, to a length of 150 mm and a width of 20 mm. The prepared cathode specimens were attached to a slide glass in the longitudinal direction using double-sided tape. The slide glass was attached to an area corresponding to half of the longitudinal direction of each cathode specimen.

[0155] Next, each cathode specimen and the attached slide glass portion were fixed to the sample stage of a Universal Testing Machine (UTM) (LS5, AMETEK), and the cathode half without the attached slide glass was connected to the load cell of the UTM. The load applied to the load cell was measured while moving the load cell up to 50 mm at a speed of 100 mm / min. At this time, the minimum value of the load measured in the 20 mm to 40 mm section of the travel section was determined as the cathode adhesion strength (gf / 20 mm) of each specimen. After measuring five times for each specimen, the average value is shown in Table 4 below.

[0156] Adhesive strength (gf / 20mm) Example 191 Example 296 Example 398 Example 439 Comparative Example 145

[0157] Referring to Table 4 above, the cathodes of Examples 1 to 3 achieve excellent electrode adhesion of 90 gf / 20mm or higher. However, the cathode of Example 4 exhibited low adhesion of 39 gf / 20mm. This is attributed to the reduction in binder content during the manufacturing of the cathode of Example 4. Specifically, it was confirmed that it is necessary to control the combined content of the thickener and binder to a certain level or higher during cathode manufacturing. Additionally, the cathode of Comparative Example 1, which does not use the first thickener, was confirmed to exhibit electrode adhesion of approximately 45 gf / 20mm.

[0158]

[0159] Experimental Example 3: Comparison of Discharge Capacity

[0160] A Li metal / cathode cell was manufactured using the cathodes according to Examples 1 to 3 and Comparative Example 1. To measure the capacity of the manufactured secondary battery, the discharge capacity of each cell was calculated during the first cycle conducted at room temperature and 0.1C / 0.1C. The results of the calculation are shown in Table 5 and Figure 1 below. Table 5 and Figure 1 indicate the percentage increase or decrease in discharge capacity based on the discharge capacity of the cell containing the cathode according to Comparative Example 1.

[0161] Sectional Discharge Capacity Increase Rate (%) Example 1 + 1.35% Example 2 + 1.40% Example 3 + 1.92% Comparative Example 1 -

[0162] Referring to Table 5 and Figure 1, the cells containing the cathodes according to Examples 1 to 3 show a discharge capacity increase rate of at least 1.35%. In particular, the cell containing the cathode of Example 3 shows a discharge capacity increase rate of at least 1.9%.

[0163]

[0164] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and technical scope of the invention as described in the claims set forth below.

[0165] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

1. A first thickener having an aspect ratio of 100 or more; and It includes a second thickener with an aspect ratio of 50 or less, and The content of the first and second thickeners above is an electrode slurry satisfying the following Formula 1: [Formula 1] 0.1 ≤ T1 / T2 ≤ 0.8 In the above Formula 1, T1 represents the content (parts by weight) of the first thickener based on the solid content in the electrode slurry, and T2 represents the content (parts by weight) of the second thickener based on the solid content in the electrode slurry.

2. In Paragraph 1, The aspect ratio of the first thickener is in the range of 100 to 500, and An electrode slurry in which the aspect ratio of the second thickener is in the range of 1 to 50.

3. In Paragraph 1, The above first and second thickening agents are, respectively, independently. An electrode slurry comprising one or more of carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), polyurethane (PU), colloidal silica, polyethylene glycol (PEG), and alginate.

4. In Paragraph 1, An electrode slurry characterized in that the first thickener is a fibrous cellulose thickener.

5. In Paragraph 4, An electrode slurry characterized in that the first thickener is a cellulose nanofiber (CNF).

6. In Paragraph 1, An electrode slurry characterized in that the second thickener is a block-type cellulose thickener.

7. In Paragraph 1, The above electrode slurry, based on solid content, 85 to 97 parts by weight of active material; 0.1 to 5 parts by weight of conductive material; 0.5 to 5 parts by weight of binder; and It comprises 0.5 to 5 parts by weight of a thickener, The above-mentioned thickener is an electrode slurry comprising a first and a second thickener.

8. In Paragraph 7, An electrode slurry characterized by the combined content of the binder and the thickener being 2.6 parts by weight or more.

9. A current collector, and an active material layer formed on one or both sides of the current collector, and The above active material layer is, A first thickener having an aspect ratio of 100 or more; and It includes a second thickener having an aspect ratio of 50 or less, and The content of the first and second thickeners above satisfies the following formula 1 for a secondary battery electrode: [Formula 1] 0.1 ≤ T1 / T2 ≤ 0.8 In the above Formula 1, T1 represents the content (parts by weight) of the first thickener based on the solid content in the electrode slurry, and T2 represents the content (parts by weight) of the second thickener based on the solid content in the electrode slurry.

10. In Paragraph 9, An electrode for a secondary battery in which the combined content of the first and second thickeners is in the range of 0.5 to 5 parts by weight based on 100 parts by weight of the entire active material layer.

11. In Paragraph 9, The first thickener mentioned above is a fibrous cellulose thickener, and An electrode slurry characterized in that the second thickener is a block-type cellulose thickener.

12. In Paragraph 9, The electrode for a secondary battery is characterized in that the first thickener is a cellulose nanofiber (CNF).

13. In Paragraph 9, The above active material layer, based on solid content, 85 to 97 parts by weight of active material; 0.1 to 5 parts by weight of conductive material; 0.5 to 5 parts by weight of binder; and It comprises 0.5 to 5 parts by weight of a thickener, The above-mentioned thickener is an electrode for a secondary battery comprising a first and a second thickener.

14. In Paragraph 13, An electrode for a secondary battery characterized by the combined content of the binder and the thickener being 2.6 parts by weight or more.

15. In Paragraph 9, An electrode for a secondary battery characterized in that the above electrode is a negative electrode.

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