CN117597792A

CN117597792A - Electrode for electrochemical device including dry electrode film and method of manufacturing the same

Info

Publication number: CN117597792A
Application number: CN202280046692.6A
Authority: CN
Inventors: 姜声旭; 韩在成; 申东穆; 申东午; 尹景焕; 刘光虎
Original assignee: LG Energy Solution Ltd
Current assignee: LG Energy Solution Ltd
Priority date: 2021-08-06
Filing date: 2022-08-04
Publication date: 2024-02-23
Also published as: KR20230022129A; KR102661426B1; WO2023014127A1; CA3227840A1

Abstract

A method for manufacturing a dry electrode is disclosed. The method allows the degree of microfibrillation of the binder resin to be determined from the crystallinity of the binder resin. On the basis of this, the processing conditions of the electrode mixed powder or the electrode film can be controlled. In this way, the processing conditions can be easily and effectively checked and controlled. Further, the method for manufacturing a dry electrode includes a kneading step and a pulverizing step at a low speed and a high temperature using a kneader. Therefore, the problem of flow path blockage due to component aggregation is avoided, and mass production is facilitated.

Description

Electrode for electrochemical device including dry electrode film and method of manufacturing the same

Technical Field

The present application claims priority from korean patent application No. 10-2021-0104169 filed on 8.6 of 2021, the disclosure of which is incorporated herein by reference.

The present disclosure relates to an electrode for an electrochemical device including a dry electrode film and a method of manufacturing the same. The present disclosure also relates to the dry electrode film and a method of manufacturing the dry electrode film. Furthermore, the present disclosure relates to a mixed powder for an electrode for manufacturing a dry electrode film and a method of preparing the mixed powder for an electrode.

Background

As the use of fossil fuels has increased, the demand for alternative and clean energy sources has also increased. As part of an attempt to meet such a demand, the most actively studied field is the field of power generation and storage using electrochemistry. Currently, typical examples of electrochemical devices using electrochemical energy include secondary batteries, and their application range is also expanding. As a representative of such secondary batteries, lithium secondary batteries have been used in recent years not only as an energy source for mobile instruments but also as a power source for electric vehicles and hybrid vehicles, which are capable of replacing vehicles such as gasoline vehicles and diesel vehicles that use fossil fuels and are regarded as one of the main causes of air pollution. In addition, such lithium secondary batteries are expanded even as auxiliary power sources of electric power by forming a Grid (Grid). The process of manufacturing such a lithium secondary battery is roughly divided into an electrode forming step, an electrode assembly forming step, and an aging step. The electrode forming step is further classified into an electrode mixture mixing step, an electrode coating step, a drying step, a pressing step, a slitting step, a winding step, and the like. Among these steps, the electrode mixture mixing step is a step of mixing the components for forming the electrode active layer actually performing the electrochemical reaction in the electrode. In particular, an electrode active material as an essential element of an electrode is mixed with a binder for bonding between powder particles and for adhering to a current collector, a solvent for imparting viscosity and dispersing powder, and the like to prepare a slurry having fluidity.

Such a composition mixed for forming an electrode active layer is also referred to as an electrode mixture (electrode mixture) in a broad sense. After the above steps are completed, an electrode coating step of coating the electrode mixture onto a current collector having conductivity and a drying step of removing a solvent contained in the electrode mixture are performed, and then the resulting electrode is pressed to a predetermined thickness.

Meanwhile, defects such as pinholes or cracks may be generated in the initially formed electrode active layer due to evaporation of the solvent contained in the electrode mixture during the drying step. In addition, since the electrode active layer is dried unevenly at the inside and outside thereof due to the difference in the evaporation rate of the solvent, a powder floating phenomenon occurs. In other words, the powder present in the earlier dried portion floats up, and when a gap is formed with the relatively later dried portion, the electrode quality is lowered.

Accordingly, in order to solve the above-mentioned problems, a drying apparatus capable of uniformly drying the inside and outside of the electrode active layer and controlling the evaporation rate of the solvent has been considered. However, such a drying apparatus is expensive, requires a large amount of cost and time to operate, and is therefore disadvantageous in terms of manufacturing workability. Accordingly, recently, active researches have been conducted to manufacture a dry electrode without using any solvent.

In general, dry electrodes are obtained by laminating a free-standing film, which includes an active material, a binder and a conductive material and is prepared in a film form, onto a current collector. First, an active material, a carbonaceous material as a conductive material, and a binder capable of being fibrillated are mixed using a stirrer, the binder is fibrillated by a high shear mixing (High Shear Mixing) process such as Jet-milling, and the resulting mixture is then calendered to form a film, thereby providing a free-standing film. Then, the free-standing film obtained after the calendering was laminated onto a current collector to obtain a dry electrode.

However, when an active material having brittleness is subjected to such a high shear mixing process, a large amount of fine powder having a small powder size is formed, resulting in deterioration of mechanical properties or electrochemical properties. Further, when such high shear mixing is excessively performed, the resulting binder fiber may be cut, resulting in deterioration of flexibility of the free-standing film.

Therefore, there is an urgent need to develop a technique for manufacturing a dry electrode capable of solving the above-described problems. In particular, it is required to provide a method capable of quantitatively analyzing the mixing uniformity of a mixture containing components for manufacturing a dry electrode film or the state of a binder (degree of fibrosis, etc.), and establishing processing conditions.

Disclosure of Invention

Technical problem

The present disclosure is designed to solve the problems of the prior art, and thus aims to provide a dry electrode exhibiting minimized micronization of an active material and maximized binder fiber, and a method of manufacturing the dry electrode.

The present disclosure is also directed to a dry electrode having improved mechanical properties, such as flexibility and strength, and a method of manufacturing the dry electrode.

Further, the present disclosure aims to provide a method of manufacturing a dry electrode using processing conditions based on crystallinity of a binder resin.

Technical proposal

According to a first embodiment of the present disclosure, there is provided an electrode for an electrochemical device, including a dry electrode film obtained by a dry manufacturing process without using a solvent, wherein the dry electrode film includes an electrode active material, a conductive material, and a binder resin, and the binder resin contained in the dry electrode film has a crystallinity of 10% or less.

According to a second embodiment of the present disclosure, there is provided an electrode for an electrochemical device as defined in the first embodiment, wherein the dry electrode film has a tensile strength in the Machine Direction (MD) of 0.5MPa or more.

According to a third embodiment of the present disclosure, there is provided an electrode for an electrochemical device as defined in the first embodiment or the second embodiment, wherein the dry electrode film has a tensile elongation of 2% or more.

According to a fourth embodiment of the present disclosure, there is provided an electrode for an electrochemical device as defined in any one of the first to third embodiments, wherein the electrode film has a porosity of 20 to 50% by volume.

According to a fifth embodiment of the present disclosure, there is provided a method for manufacturing an electrode for an electrochemical device as defined in any one of the first to fourth embodiments, the method comprising the steps of: (a) Preparing a powdery mixture including an electrode active material, a conductive material, and a binder resin;

(b) Kneading (kneading) the powdery mixture at 70 ℃ to 200 ℃ to prepare a mixture block;

(c) Crushing the mixture block to obtain a mixed powder for an electrode; and

(d) Calendering the mixed powder for an electrode to obtain a free-standing dry electrode film, wherein the binder resin contained in the dry electrode film obtained from step (d) has a crystallinity (d) of 10% or less.

According to a sixth embodiment of the present disclosure, there is provided the method for manufacturing an electrode for an electrochemical device as defined in the fifth embodiment, wherein the binder resin contained in the mixed powder for an electrode obtained from step (c) has a crystallinity (c) of 20% or less.

According to a seventh embodiment of the present disclosure, there is provided the method for manufacturing an electrode for an electrochemical device as defined in the fifth or sixth embodiment, wherein the binder resin contained in the mixture obtained from step (a) has a crystallinity (a) of 50% or less.

According to an eighth embodiment of the present disclosure, there is provided the method for manufacturing an electrode for an electrochemical device as defined in any one of the fifth to seventh embodiments, wherein step (a) is performed at 500rpm to 30,000 rpm.

According to a ninth embodiment of the present disclosure, there is provided the method for manufacturing an electrode for an electrochemical device as defined in any one of the fifth to eighth embodiments, wherein step (b) is performed at a rotation speed of 100rpm or less.

According to a tenth embodiment of the present disclosure, there is provided the method for manufacturing an electrode for an electrochemical device as defined in any one of the fifth to ninth embodiments, wherein step (b) is at 0.5kgf/cm ² To 10kgf/cm ² Is carried out under pressure of (2).

According to an eleventh embodiment of the present disclosure, there is provided the method for manufacturing an electrode for an electrochemical device as defined in any one of the fifth to tenth embodiments, wherein step (b) is performed at atmospheric pressure or more.

According to a twelfth embodiment of the present disclosure, there is provided an electrode for an electrochemical device as defined in any one of the first to fourth embodiments, wherein the binder resin comprises Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (Polyvinylidene fluoride, PVDF), polyolefin, or a mixture of two or more thereof.

According to a thirteenth embodiment of the present disclosure, there is provided an electrode for an electrochemical device as defined in any one of the first to fourth embodiments, the electrode further comprising a current collector, wherein the dry electrode film is disposed on at least one surface or both surfaces of the current collector.

According to a fourteenth embodiment of the present disclosure, there is provided a method for manufacturing the electrode for an electrochemical device as defined in any one of the fifth to eighth embodiments, the method further comprising the steps of preparing a current collector, disposing the dry electrode film on at least one surface of the current collector, and laminating.

According to a fifteenth embodiment of the present disclosure, there is provided a secondary battery comprising the dry electrode as defined in any one of the first to fourth embodiments, wherein the dry electrode is a positive electrode, and an electrode assembly including the positive electrode, a negative electrode and a separator is housed in a battery case together with a lithium-containing nonaqueous electrolyte.

According to a sixteenth embodiment of the present disclosure, there is provided an energy storage system comprising the secondary battery as defined in the fifteenth embodiment as a unit cell.

According to a seventeenth embodiment of the present disclosure, there is provided a method of preparing a mixed powder for an electrode for manufacturing a dry electrode film, the method including the steps of: (a) Preparing a powdery mixture including an electrode active material, a conductive material, and a binder resin;

(c) Crushing the mixture block to obtain a mixed powder for an electrode,

wherein the binder resin contained in the mixed powder for an electrode has a crystallinity of 20% or less,

and the binder resin comprises Polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof.

According to an eighteenth embodiment of the present disclosure, there is provided a mixed powder for an electrode, which is obtained by the method as defined in the seventeenth embodiment, and which includes an electrode active material, a conductive material, and a binder resin, wherein the binder resin includes Polytetrafluoroethylene (PTFE), PVDF, polyolefin, or a mixture of two or more thereof, and the binder resin contained in the electrode mixture has a crystallinity of 20% or less.

According to a nineteenth embodiment of the present disclosure, there is provided a method for manufacturing a dry electrode film, comprising the step of calendaring a mixed powder for an electrode to obtain a free-standing dry electrode film, wherein the mixed powder for an electrode is the same as defined in the seventeenth embodiment, and a binder resin contained in the dry electrode film has a crystallinity (d) of 10% or less.

According to a twentieth embodiment of the present disclosure, there is provided a dry electrode film obtained by the method as defined in the nineteenth embodiment and having a tensile strength of 0.5MPa or more, a tensile elongation of 2% or more, and a porosity of 20 to 50% by volume in the Machine Direction (MD).

Advantageous effects

The method for manufacturing a dry electrode according to the present disclosure uses a pulverizing step after a high-temperature low-shear mixing step during manufacturing of a mixed powder for an electrode, and thus can minimize micronization of an active material and prevent fiber binder cutting. In addition, in manufacturing a dry electrode by using the mixed powder for an electrode, mechanical properties such as flexibility and strength of the dry electrode can be improved.

Further, the method for manufacturing a dry electrode according to the present disclosure may determine the degree of microfibrillation of the binder resin from the crystallinity of the binder resin during each step and determine whether each step is completed. On the basis of this, the processing conditions of the electrode mixed powder or the electrode film can be controlled. In this way, the processing conditions and the process completion time can be easily and effectively checked and controlled.

Further, the method for manufacturing a dry electrode according to the present disclosure includes a low-shear kneading step and a pulverizing step using a Kneader (Kneader). Therefore, the binder resin will be well microfibrillated and there is no problem of blocking the flow path due to aggregation of the components, which is advantageous for mass production.

Drawings

Fig. 1 is a graph showing the results of thermogravimetric analysis using Differential Scanning Calorimetry (DSC) according to example 1.

Fig. 2 is a graph showing the results of thermogravimetric analysis using Differential Scanning Calorimetry (DSC) according to example 2.

Fig. 3 is a flow chart illustrating the manufacture of a dry electrode according to the present disclosure.

Detailed Description

Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Before the description, it is to be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It will be further understood that the terms "comprises" and/or "comprising," or "includes" and/or "including," when used in this specification, do not exclude the presence of other elements, and are intended to specify the presence of additional elements, unless otherwise specified.

In one aspect of the present disclosure, an electrode for an electrochemical device and a method of manufacturing the same are provided. For example, the electrochemical device may be a secondary battery, in particular a lithium ion secondary battery.

According to the present disclosure, an electrode includes a dry electrode film obtained by a dry manufacturing process that disperses electrode components without using a solvent during manufacturing of the electrode. The dry electrode film includes an electrode active material, a conductive material, and a binder resin, and the binder resin contained in the dry electrode film has a crystallinity of 10% or less. For example, the crystallinity may be 5% or less.

When the crystallinity is 10% or less, the binder resin is highly fibrillated to secure flexibility of the dry electrode film. Therefore, as will be described later, a strip-like dry electrode film is easily manufactured in a rolling process applying a roll-to-roll continuous process. Further, when the electrode film is wound in a roll shape or unwound after the electrode film is manufactured, the electrode film stably maintains its shape without any breakage such as breakage or cracking. In addition, such a crystallinity range is advantageous in ensuring that the binding force to the current collector reaches a predetermined level or more.

Further, according to the present disclosure, the dry electrode film preferably has a tensile strength of 0.5MPa or more in the Machine Direction (MD). Meanwhile, the dry electrode film may have a tensile strength of 10.0MPa or less, 5.0MPa or less, or 3.0MPa or less in the Machine Direction (MD). When the tensile strength satisfies the above range, sufficient mechanical strength can be ensured at the time of manufacturing the free-standing dry electrode, so that both manufacturing and handling are easy. On the other hand, when the above range is not reached, the mechanical strength is weak and breakage is easy. On the other hand, when the tensile strength is too high, the tensile elongation increases together, so that the process efficiency deteriorates as shown below, and the film thickness becomes uneven.

Meanwhile, the dry electrode film preferably has a tensile elongation of 2% or more.

The dry electrode film may have a tensile elongation of 30% or less, 20% or less, or 10% or less.

When the tensile elongation satisfies the above range, sufficient morphological stability and flexibility can be ensured at the time of manufacturing the free-standing dry electrode, and thus manufacturing and handling are easy. When the tensile elongation is too low, flexibility and morphological stability are low, and thus the dry electrode film is easily broken during manufacture or transportation. On the other hand, when the tensile elongation exceeds the above range, the flexibility may be excessively increased, so that the dry electrode film may be excessively stretched from roll to roll in a rolling process as described later, and the thickness of the resulting film may be uneven.

Meanwhile, the dry electrode film may have a porosity of 20 to 50% by volume.

In another aspect of the present disclosure, a method for manufacturing the electrode is provided. In the method for manufacturing the electrode, the crystallinity of the binder resin contained in the dry electrode film is controlled to 10% or less. In one aspect of the present disclosure, the crystallinity of the binder resin contained in the dry electrode film is 10% or less or is absent (zero).

According to an embodiment, the method for manufacturing the electrode comprises the steps of:

(a) Preparing a powdery mixture (blend) including an electrode active material, a conductive material, and a binder resin;

(b) Kneading (kneading) the powdery mixture to prepare a mixture block;

(c) Crushing the mixture block to obtain a mixed powder for an electrode; and

(d) The mixed powder for electrodes was calendered to obtain a free-standing (free standing type) dry electrode film.

In another aspect, in one embodiment of the present invention, step (b) may be performed at a temperature of 70 ℃ to 200 ℃. For example, the object to which the kneading process is applied (e.g., powdery mixture) may be controlled at a temperature of 70 ℃ to 200 ℃.

In the method, the binder resin contained in the powdery mixture obtained from step (a) has a crystallinity (a) of 60% or less, preferably 50% or less. Further, the binder resin contained in the mixed powder for an electrode obtained from step (c) has a crystallinity (c) of 20% or less, and the binder resin contained in the dry electrode film obtained from step (d) has a crystallinity (d) of 10% or less.

In an embodiment of the present invention, the completion of the process of each of steps (a) to (d) may be determined by measuring the crystallinity of the resultant obtained in each step. If the crystallinity of the binder resin in the product of each process step satisfies the predetermined crystallinity of each step, the current step is terminated and the next step is started.

Specifically, in step (a), when it is determined that the crystallinity of the binder resin of the powdery mixture is 60% or less, preferably 50% or less, the process of step (a) is terminated, and the obtained powdery mixture is added to step (b).

Further, in step (c), when it is determined that the crystallinity of the binder resin in the mixed powder for electrode is 20% or less, the process of step (c) is terminated, and then the obtained mixed powder for electrode is added to step (d).

Further, in the step (d), when the crystallinity of the binder resin in the obtained dry electrode film satisfies 10% or less, the preparation is considered to be completed.

Alternatively, for each of steps (a), (b) and (d), the process conditions for controlling the crystallinity to a desired predetermined value may be established by experiment, and then the predetermined process conditions established by the experiment may be applied to each step.

According to the present disclosure, crystallinity can be determined by using differential scanning calorimetry (differential scanning calorimetry, DSC) and is based on the temperature at the point in time (peak temperature) at which the highest enthalpy is exhibited upon crystallization. In particular, the crystallinity is calculated by DSC based on the following equation 1, and the melting enthalpy (. DELTA.H) _m ) Divided by the melting enthalpy (. DELTA.H) of theoretically complete crystallization (crystallinity 100%) _m ⁰ ) (melt balance heat) as a percentage. In this context, the melting enthalpy value (. DELTA.H) for a theoretical complete crystallization of the polymer _m ⁰ ) Reference will be made to the handbook of polymers (J. Brandrep et al, 2003) or academic journal, for example, the handbook of polymers. For example, PTFE has a melting enthalpy value of 85.4J/g (Polymer 46, 2005, pp 8872-8882) for theoretical complete crystallization. Meanwhile, in general, thermal analysis of polymers such as DSC can be measured and calculated according to ASTM D3418-21.

[ mathematics 1]

X _c (％)＝(ΔH _m ÷ΔH _m ⁰ )×100

Hereinafter, a method for manufacturing a dry electrode according to the present disclosure will be explained in more detail.

First, a powdery mixture including an electrode active material, a conductive material, and a binder is prepared (step a).

Herein, mixing for preparing a powdery mixture is performed to obtain a uniform mixture of the electrode active material, the conductive material, and the binder resin, and the crystallinity of the binder resin in the powdery mixture is preferably controlled to 50% or less. Since the components are mixed in a powder state, the mixing method is not particularly limited, but various methods may be used as long as the method allows the components to be uniformly mixed. However, since the present disclosure is intended to provide a dry electrode without using a solvent, mixing may be performed through a dry mixing process. For example, the mixing may be performed by introducing the ingredients into an instrument such as a mixer or blender.

According to an embodiment of the present disclosure, the mixing time is not particularly limited, but the mixing may be performed for 1 second to 20 minutes. For example, the mixing may be performed for 1 second to 10 minutes. Meanwhile, the mixing speed is not particularly limited, but may be appropriately controlled in the range of about 500rpm to 30,000 rpm. For example, the mixing speed is controlled in the range of 500rpm to 20,000 rpm.

In another aspect, in an embodiment of the present disclosure, the temperature of the powdered mixture may be controlled to 70 ℃ or less, or 60 ℃ or less. When the mixing temperature exceeds 70 ℃, it may be difficult to obtain a uniform mixture due to adhesion of materials to the mixing device. On the other hand, the lower limit of the temperature of the mixture is not particularly limited, and in an embodiment of the present invention, may be performed at a temperature of 20 ℃ or more.

In particular, the mixing may be performed in a mixer at 500rpm to 20,000rpm at 70 ℃ or lower for 30 seconds to 10 minutes, or at 5,000rpm to 20,000rpm at 70 ℃ or lower for 30 seconds to 2 minutes, specifically at 1000rpm to 15,000rpm or 10,000rpm to 15,000rpm at 60 ℃ or lower for 30 seconds to 1 minute or 30 seconds to 7 minutes, to achieve high uniformity and control of crystallinity of the binder resin.

According to the present disclosure, the crystallinity of the binder resin in the mixture obtained from the mixing step is 60% or less, preferably 50% or less. Meanwhile, when the crystallinity of the binder resin in the resulting mixture is more than 60% or more than 50%, it is preferable to lengthen the mixing time and/or the rotational speed (rpm) to pulverize the binder cake into primary particles so as to prevent aggregation of the binder cake and to perform partial fibrillation.

If the crystallinity of the powdery mixture obtained in step (a) is not within the above-mentioned range and is not high, the binder resin is not easily fibrillated in a low-shear kneading (step b) process described later. Further, fibers cannot be sufficiently formed on the surface of the adhesive, or the process time required for fiberizing the adhesive resin increases.

On the other hand, when the mixing time is too long, the mixing speed is too high, or both, there is a risk that the electrode active material is micronized/damaged or the fibers are cut off instead. At the same time and/or independently of this, there is a risk that non-uniform binder fibrosis may be caused. In view of this, in an embodiment of the present invention, the crystallinity of the binder resin in the powdery mixture may be controlled to 30% or more, 35% or more, or 40% or more.

According to the present disclosure, the binder resin is not particularly limited as long as it can be fibrillated through the step (a) and/or the step (b).

Meanwhile, the binder resin may be fibrillated in the step (a), but the fibers formed in the step (a) are thick, and it is difficult to fine to achieve the tensile elongation and tensile strength required for the dry electrode. In the present invention, preferably, the microfibrillation of the binder resin is mainly performed by (b), which will be described later.

Fibrosis refers to a process of finely dividing a polymer, and for example, fibrosis can be performed by using mechanical shear force or the like. The fibrillated polymer fibers are disintegrated by the surface to form a multitude of microfibers (fibrils). Non-limiting examples of the binder resin may include Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyolefin, or a mixture of two or more thereof, particularly, the binder resin includes Polytetrafluoroethylene (PTFE), and more particularly, the binder resin is Polytetrafluoroethylene (PTFE). In particular, the amount of Polytetrafluoroethylene (PTFE) may be 30 wt% or more based on the total weight of the binder resin. Meanwhile, the binder resin may further include polyethylene oxide PEO (polyethylene oxide) and/or PVDF-HFP (polyvinylidene fluoride-co-fluoroopylene) in addition to the above components.

The dry electrode may be a positive electrode, and the electrode active material may be a positive electrode active material.

The positive electrode active material may include any one selected from lithium transition metal oxides, lithium metal iron phosphorus oxides, and metal oxides, and is not particularly limited. Specific examples of the positive electrode active material include at least one selected from the group consisting of: layered compounds, such as lithium cobalt oxide (LiCoO) ₂ ) And lithium nickel oxide (LiNiO) ₂ ) Or those substituted with one or more transition metals; lithium manganese oxide, e.g. of formula Li _1+x Mn _2-x O ₄ (wherein x is 0-0.33), liMnO ₃ 、LiMn ₂ O ₃ And LiMnO ₂ Those represented; lithium copper oxide (Li) ₂ CuO ₂ ) The method comprises the steps of carrying out a first treatment on the surface of the Vanadium oxides, such as LiV ₃ O ₈ 、LiV ₃ O ₄ 、V ₂ O ₅ Or Cu ₂ V ₂ O ₇ The method comprises the steps of carrying out a first treatment on the surface of the From chemical formula LiNi _1-x M _x O ₂ (wherein M is Co, mn, al, cu, fe, mg, B or Ga and x is 0.01 to 0.3), such as Li (Ni, co, mn, al) O ₂ Wherein Ni accounts for 50% or more of the metals other than Li; from chemical formula LiMn _2-x M _x O ₂ (wherein M is Co, ni, fe, cr, zn or Ta and x is 0.01-0.1) or Li ₂ Mn ₃ MO ₈ Lithium manganese composite oxide represented by (wherein M is Fe, co, ni, cu or Zn)The method comprises the steps of carrying out a first treatment on the surface of the LiMn in which Li is partially substituted by alkaline earth metal ions ₂ O ₄ The method comprises the steps of carrying out a first treatment on the surface of the Lithium metal phosphorus oxide LiMPO ₄ (wherein M is Fe, co, ni or Mn); a disulfide compound; and Fe (Fe) ₂ (MoO ₄ ) ₃ The method comprises the steps of carrying out a first treatment on the surface of the Or the like. However, the scope of the present disclosure is not limited thereto.

In one variation, the dry electrode may be a negative electrode and the active material may be a negative electrode active material. Specific examples of the anode active material include: carbon, such as non-graphitizing carbon or graphite-based carbon; metal composite oxides, such as Li _x Fe ₂ O ₃ (0≤x≤1)、Li _x WO ₂ (0.ltoreq.x.ltoreq.1) and Sn _x Me _1-x Me’ _y O _z (Me: mn, fe, pb, ge; me': al, B, P, si, an element of group 1, 2 or 3 of the periodic Table of the elements, halogen; 0)<x is less than or equal to 1; y is more than or equal to 1 and less than or equal to 3; z is more than or equal to 1 and less than or equal to 8); lithium metal; a lithium alloy; silicon-based alloy; a tin-based alloy; silicon oxides, such as SiO, siO/C and SiO ₂ The method comprises the steps of carrying out a first treatment on the surface of the Metal oxides, such as SnO, snO ₂ 、PbO、PbO ₂ 、Pb ₂ O ₃ 、Pb ₃ O ₄ 、Sb ₂ O ₃ 、Sb ₂ O ₄ 、Sb ₂ O ₅ 、GeO、GeO ₂ 、Bi ₂ O ₃ 、Bi ₂ O ₄ And Bi (Bi) ₂ O ₅ The method comprises the steps of carrying out a first treatment on the surface of the Conductive polymers such as polyacetylene; li-Co-Ni type material; or the like.

More particularly, the dry electrode may be a positive electrode. Thus, the active material may be a positive electrode active material, specific examples of which include lithium transition metal oxide, lithium nickel manganese cobalt oxide partially substituted with other transition metal, lithium iron phosphorus oxide, or the like.

The conductive material is not particularly restricted so long as it has conductivity without causing any chemical change in the corresponding battery. Specific examples of the conductive material include: graphite, such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; metal powder such as carbon fluoride powder, aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium dioxide; conductive polymers such as polyphenylene derivatives; or the like. In particular, the conductive material may include at least one selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes, more particularly activated carbon, to uniformly mix the conductive material and improve conductivity.

The mixing ratio of the electrode active material, the conductive material, and the binder resin may be 80 to 98 wt%: 0.5 to 10 wt.%: 0.5 to 10% by weight (active material: conductive material: binder), in particular 85 to 98% by weight: 0.5 to 5 wt.%: 0.5 to 10% by weight.

When the content of the binder resin is too high beyond the above-defined range, the binder resin may excessively fibrillate during the subsequent kneading step, thereby adversely affecting the entire process. When the binder content is too low, sufficient fiberization is not possible, and therefore the components cannot be aggregated to such an extent that the components form a mixture block, it is difficult to manufacture a dry electrode film, or the physical properties of the dry electrode film are undesirably deteriorated.

Further, when the content of the conductive material is too high beyond the above-defined range, the content of the active material is relatively reduced, resulting in a decrease in capacity. When the content of the conductive material is too low, sufficient conductivity cannot be ensured, or the physical properties of the dry electrode film undesirably deteriorate.

Meanwhile, a filler may be further introduced into the mixture as an ingredient for suppressing expansion of the electrode, as appropriate. The filler is not particularly restricted so long as it is a fibrous material while not causing any chemical changes in the corresponding battery. Specific examples of fillers include: olefin polymers such as polyethylene or polypropylene; fibrous materials such as glass fibers or carbon fibers; or the like.

In an embodiment of the present invention, the crystallinity of the binder resin in the powdery mixture obtained from step (a) is checked, when the measured crystallinity is 60% or less, preferably 50% or less, step (a) is terminated, and then the obtained product may be added to step (b). In performing the processes (a) to (d), crystallinity may be measured at each step.

Alternatively, in another embodiment, the process conditions of step (a) are confirmed by an experiment in which the crystallinity of the binder resin of the powdery mixture can be controlled to 60% or less, or 50% or less, and then the predetermined process conditions confirmed by the experiment can be applied to step (a).

Next, the mixture obtained as described above is subjected to a kneading step to fibrillate the binder resin (step b).

In this kneading step sequence, as described later, since a relatively low shearing force and a relatively high temperature are applied, problems such as micronization/damage of the electrode active material or cutting of the binder fiber do not occur, and mixed particles for electrodes in which the binder resin has been microfibrillated can be obtained. Furthermore, the fiberizing binder has a high uniformity in the thickness and/or length of the fibers.

The kneading method is not particularly limited. According to an embodiment of the present disclosure, kneading may be performed using a Kneader (Kneader). For example, as the kneader, a twin-screw extruder, a single-screw extruder, a batch kneader, a continuous kneader, or the like can be used.

The kneading step is provided to bond or interconnect the electrode active material with the conductive material powder particles while fiberizing the binder resin, so that a mixture block (mixed block) having a solid content of 100% can be formed.

In particular, the kneading in step (b) may be performed at a rate controlled to 10rpm to 100 rpm. For example, kneading may be performed at a rate controlled to 20rpm to 70rpm within the above-defined range.

For example, kneading may be performed for 1 minute to 30 minutes. For example, kneading may be performed at a rate of 20rpm to 70rpm within the above-defined range for 3 minutes to 10 minutes.

Meanwhile, kneading may be performed with the shear rate controlled to 5/s to 1000/s. According to an embodiment of the present disclosure, kneading may be performed for 1 to 30 minutes, and the shear rate may be controlled in the range of 10 to 500/s.

In addition, the kneading step may be performed at a high temperature under pressure conditions equal to or higher than ambient pressure.

In particular, kneading can be carried out at 70℃to 200℃and in particular at 90℃to 150 ℃. The temperature may be the temperature inside the kneader or the temperature of the object to be kneaded. Alternatively, both temperatures may be controlled within the above-described ranges.

When kneading is performed at a low temperature lower than the above-defined temperature range, the fiberization of the binder cannot be performed during kneading and a lump is formed by sufficient kneading. Therefore, a film cannot be easily formed during rolling. On the other hand, when kneading is performed at too high a temperature, the binder may be rapidly fibrillated, and the resultant fibers may be cut by excessive shearing force, which is undesirable.

In addition, the ratio of the pressure to the flow rate may be 0.5kgf/cm ² To 10kgf/cm ² In particular 1kgf/cm ² To 8kgf/cm ² For example, ambient pressure or more, 8kgf/cm ² Or less under pressure. When kneading is performed at an excessively high pressure outside the above-defined pressure range, there is a problem that: the resulting fibers may be cut due to the application of excessive shear and pressure, and the density of the mixture mass may be excessively increased, which is undesirable. In other words, according to the present disclosure, when the low-shear mixing step is performed at a high temperature under a pressure condition equal to or higher than the ambient pressure instead of the high-shear kneading, it is possible to achieve a desired effect. Or may be kneaded under an ambient pressure or more, particularly a pressure of 1atm to 3atm or 1.1atm to 3 atm.

Meanwhile, in an embodiment of the present invention, the process conditions in the kneading step may be controlled according to the characteristics of the material used in the present invention. In the specific embodiment, the process conditions may be appropriately adjusted according to the particle diameter of the electrode active material particles. When the particle diameter of the electrode active material particle is large, fibrosis can be performed relatively easily as compared with an electrode active material having a smaller particle diameter. Thus, when the particle size of the electrode active material is large, a relatively low rotational speed and/or shear rate may be applied, and when the particle size is small, a relatively high rotational speed and/or shear rate may be applied. On the other hand, even in the case of temperature or pressure, adjustment can be made in consideration of these material characteristics.

Then, the mixture block obtained in the kneading step (b) is pulverized to obtain a mixed powder for an electrode (step c).

In particular, the block of mixture prepared by kneading step (b) may be directly subjected to calendering to prepare a sheet. However, in this case, it is necessary to press the mixture blocks under strong pressure at high temperature to convert them into films. As a result, there arises a problem that the density of the dry electrode film is too high, or a film uniform in thickness or density cannot be obtained. Thus, according to the present disclosure, the mixture pieces obtained in step (b) are subjected to a comminution step.

In this context, the pulverizing step may be performed by using a known pulverizing apparatus such as a stirrer or a grinder, but is not particularly limited. According to embodiments of the present disclosure, the pulverizing step may be performed at a rate controlled to be 100rpm to 30,000 or 3000rpm to 30,000 rpm. Meanwhile, the pulverizing time may be appropriately controlled in the range of 1 second to 10 minutes. However, the pulverizing speed and time are not limited to the above-defined ranges. In particular, the pulverization may be performed at a rate of 500rpm to 20,000rpm or 5000rpm to 20000rpm for 30 seconds to 10 minutes, or at a rate of 700rpm to 18000rpm or 10000rpm to 18000rpm for 30 seconds to 5 minutes or 30 seconds to 1 minute.

When the pulverization is performed at an ultra-low rpm or in an ultra-short time exceeding the above-defined range, the pulverization cannot be sufficiently performed, and there arises a problem that the particle size of the powder is insufficient for film formation. When the pulverization is performed at ultra-high rpm or for an ultra-long time, a large amount of fine powder is undesirably generated from the mixture cake.

In an embodiment of the present invention, in view of film formation, the particle diameter of the electrode mixture powder obtained in step (c) may preferably be in the range of 30 μm to 180 μm.

In one embodiment of the present invention, particle size may be measured by applying a particle size distribution analyzer (PSA) (Model Mastersizer 300,Malvem Instruments LTD). Specifically, the particle diameter is measured by irradiating laser light and detecting the degree of scattering of the light scattered by the particles with the incident laser light. As the measurement method, a wet method of dispersing particles in a solvent for measurement and a dry method of measuring particles in a powder state can be employed.

Meanwhile, according to the present disclosure, the binder resin contained in the mixed powder for an electrode has a crystallinity (c) of 20% or less, which is lower than the crystallinity (a) of the binder resin contained in the powdery mixture. On the other hand, it may be higher than the crystallinity (d) of the binder resin contained in the dry electrode film after calendering. That is, the crystallinity can be reduced by the calendaring step.

When the binder resin has a crystallinity (c) of more than 20%, it is difficult to obtain a homogeneous film in the subsequent calendering step. If the resultant mixed powder for an electrode has a crystallinity higher than 20%, the kneading time can be controlled, for example, preliminary fiberization of the binder resin can be performed by controlling process conditions such as at least one of the kneading time, temperature, rotational speed (rpm) and shear rate, and thus the crystallinity can be controlled. For example, the kneading time may be increased to carry out the binder resin fiberization and control the crystallinity of the binder resin.

In an embodiment of the present invention, the crystallinity (c) of the binder resin in the mixed powder for an electrode obtained in step (c) is preferably 20% or less. When the crystallinity (c) exceeds 20%, the fibrillation is insufficient, and the tensile strength and tensile elongation of the dry electrode obtained by the rolling step are lowered, as will be described later.

In an embodiment of the present invention, the crystallinity (c) of the binder resin in the mixed powder for an electrode obtained in step (c) is measured, and when the measured crystallinity is 20% or less, step (c) is terminated, and then the obtained product may be added to step (d). When the processes (a) to (d) are performed, crystallinity may be measured at each step.

Alternatively, in another embodiment, the process condition of step (c) is confirmed experimentally, wherein the crystallinity of the binder resin of the mixed powder may be controlled to 20% or less, and then the predetermined process condition may be applied to step (c).

Once the mixed powder for an electrode is obtained in the above manner, a dry electrode is manufactured using the mixed powder for an electrode (step d). Specifically, the mixed powder for electrodes obtained by completing the pulverizing step is subjected to calendaring to obtain a dry electrode film.

Calendering refers to processing the electrode mix powder into a film. For example, the rolling step may be a step of pressing the electrode powder into a film shape having an average thickness of 50 μm to 300 μm.

According to an embodiment of the present disclosure, the rolling may be performed by using a rolling apparatus including a rolling unit having two rolls opposite to each other. The calendering device may comprise at least one roll-in unit. For example, a plurality of rolling units may be arranged in succession to perform a plurality of steps of pressing the mixed powder for the electrode. Meanwhile, at least one of the respective independent calender rolls in the calender has a temperature of 50 ℃ to 200 ℃. In combination therewith or independently thereof, the two rolls in the at least one roll-in unit may have a speed ratio controlled in the range of 1:1 to 1:3.

After the rolling step is performed, a dry electrode film as an electrode mixture may be prepared. Such a dry electrode film is also called a free standing film or a self-supporting film. Such a dry electrode film may have sufficient mechanical strength to be used in the manufacturing process of an energy storage device without any external support element such as a current collector, support web, or other structure. Alternatively, it may be combined with a support member such as a current collector and used to manufacture a battery.

Meanwhile, according to an embodiment of the present disclosure, the binder resin in the resulting dry electrode film exhibits a crystallinity (d) of 10% or less. When the dry electrode film exhibits crystallinity higher than 10%, the crystallinity may be controlled by adjusting the gap or the rotation speed ratio between the two rolls in the roll pressing unit. For example, the degree of adhesive fibrosis may be increased by decreasing the gap and/or increasing the speed ratio.

In an embodiment of the present invention, the crystallinity of the binder resin in the dry electrode film obtained in step (d) is measured, and when the measured crystallinity is 10% or less, step (d) is terminated. When the processes (a) to (d) are performed, crystallinity may be measured at each step.

Alternatively, in another embodiment, the process condition of step (d) is confirmed experimentally, wherein the crystallinity of the binder resin of the dry electrode film may be controlled to 10% or less, and then the predetermined process condition may be applied to step (d).

The resulting dry electrode film contained no solvent and therefore had little flowability. Thus, the dry electrode film can be easily handled and can be processed into a desired shape for manufacturing various types of electrodes. In addition, when an electrode is manufactured using the dry electrode film according to the present disclosure, a drying step of removing a solvent may be omitted. Therefore, it is possible to remarkably improve the manufacturing workability of the electrode and solve problems occurring in the method of manufacturing the dry electrode according to the related art, such as micronization of the active material or cutting of the fibrillated binder.

Further, the binder resin contained in the dry electrode film according to the present disclosure shows crystallinity controlled to 10% or less, and has increased flexibility. Therefore, when the dry electrode film is wound and stored, or rewound, it advantageously does not cause breakage or cracking. In addition, mechanical strength such as tensile strength and tensile elongation can be improved by such increased flexibility.

Meanwhile, according to the present disclosure, the dry electrode film may have a porosity of 20% to 50%. Within the above-defined range, the porosity may be controlled to 45% or less, or 40% or less. When the porosity satisfies the above-defined range, various advantages are provided. On the other hand, when the porosity is too low beyond the above-defined range, it is difficult to impregnate the dry electrode film with the electrolyte, which is not preferable in terms of both life and output characteristics. When the porosity is too high, the volume of the dry electrode film required to achieve the same capacity increases, and is also not preferable in terms of energy density per unit volume. According to an embodiment of the present disclosure, the porosity may be calculated by using an actual density calculated based on an actual density and composition of each component after measuring the apparent density of the dry electrode film according to the following mathematical formula 2:

[ math figure 2]

Porosity (%) = {1- (apparent density/actual density) } ×100

Then, according to the present disclosure, after the calendaring, a lamination step of forming a dry electrode film on at least one surface of the current collector may be performed. The lamination step may be a step of pressing and attaching the dry electrode film to a current collector. Lamination may also be performed using laminating rollers, which may be maintained at a temperature of 20 ℃ to 200 ℃.

Meanwhile, according to an embodiment of the present disclosure, the dry electrode obtained as described above may have a size smaller than Is particularly +.>Or less, and more particularly +.>Or less bending resistance. As described above, the dry electrode film according to the present disclosure results in less cutting of the fibrillated adhesive, and thus may provide improved flexibility. The bending resistance can be determined by a standard method defined in JIS K5600-5-1. In particular, the bending resistance can be determined by contacting the dry electrode with test bars having different diameters and lifting both ends to determine whether cracking occurs, and measuring the minimum diameter at which cracking does not occur. />

In addition, the electrode active material loading of the dry electrode film may be 3mAh/cm ² To 15mAh/cm ² In particular 4mAh/cm ² To 10mAh/cm ² 。

Herein, the electrode active material loading is a value calculated according to the following equation 3:

[ math 3]

Electrode active material loading (mAh/cm) ² ) =capacity of electrode active material (mAh/g) ×weight ratio of electrode active material in dry electrode film (wt%) ×weight of dry electrode film per unit area (g/cm) ² )

Meanwhile, the current collector is not particularly restricted so long as it has high conductivity without causing any chemical change in the corresponding battery. Specific examples of the current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. In addition, fine surface irregularities may be formed on the surface of the current collector to enhance the binding force with the positive electrode active material. The current collector may be used in various shapes including films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, or the like.

In addition, the current collector may be fully or partially coated with a conductive primer in order to reduce surface resistance and improve adhesion. Herein, the conductive primer may include a conductive material and an adhesive. The conductive material is not particularly limited as long as it has conductivity, and specific examples thereof include carbonaceous materials. The binder may include a solvent-soluble fluorine-based binder (including PVDF and PVDF copolymers), an acrylic binder, an aqueous binder, or the like.

In yet another aspect of the present disclosure, there is provided a dry electrode obtained by the method for manufacturing a dry electrode. The electrode further comprises a current collector, wherein the dry electrode film is disposed on at least one surface or both surfaces of the current collector. Also provided is a secondary battery including the dry electrode, wherein the dry electrode is a positive electrode, and an electrode assembly including the positive electrode, a negative electrode and a separator is accommodated in a battery case together with a lithium-containing non-aqueous electrolyte, and an energy storage system including the secondary battery as a unit cell.

Herein, the structure of the secondary battery and the structure of the energy storage system are the same as those known to those skilled in the art, and a description thereof will be omitted herein.

In yet another aspect of the present disclosure, a system for manufacturing a dry electrode is provided. The system comprises: a mixer unit configured to mix components of a mixture including an electrode active material, a conductive material, and a binder resin; a kneader (kneader) unit configured to knead the mixture to prepare a mixture block; a pulverizer unit configured to pulverize the mixture block to form a mixed powder for an electrode; a calender (calender) unit configured to form the electrode powder into a dry electrode film; and a lamination unit configured to laminate the dry electrode film with a current collector.

Each unit of the system and each step performed by the apparatus may be preliminarily set as processing conditions that cause the binder resin to achieve the crystallinity defined above in each step.

In addition, after each step is performed, a sample may be taken to determine crystallinity, and then, when the crystallinity does not meet the criteria, a correction may be made to the preset processing conditions.

For example, when the crystallinity of the powder mixture obtained from the mixer unit after the crystallinity is determined is higher than 50%, or when the crystallinity of the mixed powder for electrodes after the crystallinity is determined is higher than 20%, the processing time per step can be increased. Further, when the crystallinity of the electrode film obtained after the rolling step is higher than 10%, the crystallinity may be controlled by reducing the gap between the respective rolls of the rolling unit, or by increasing the rotation speed ratio of the rolls.

The blender unit is configured as a mixer for mixing the ingredients. As described above, the components of the mixture may be mixed at a rate of 500rpm to 30,000 rpm.

The kneader unit is configured to form the mixture into a mixture block by kneading and to perform fiberization of the binder. For this purpose, the kneader unit may be set to a temperature of 70 ℃ to 200 ℃ and a pressure condition equal to or higher than the ambient pressure. In particular, the kneader unit may be set to 90℃to 150℃and 0.5kgf/cm ² To 10kgf/cm ² More particularly, 1kgf/cm ² To 8kgf/cm ² 。

The pulverizer unit is configured to pulverize the mixture block obtained by the kneader unit to form a mixed powder for an electrode, and may include a stirrer or a grinder.

The calender unit is configured to press the electrode powder so that it can be molded into a film shape. According to an embodiment of the present disclosure, the calender may include a rolling unit having two rolls opposite to each other, wherein a plurality of rolling units may be continuously arranged to perform a plurality of steps of pressing the powder.

The lamination unit functions to attach and compress the dry electrode film formed by the calender unit to at least one surface of the current collector. For example, the lamination unit may include a roll-in unit.

The porosity of the dry electrode film according to the present disclosure may be determined by a calender and a laminating roller. The structures of the stirrer unit, kneader unit, calender unit and lamination unit are generally known to those skilled in the art, and a description thereof will be omitted herein.

Fig. 3 is a flow chart illustrating the manufacture of a dry electrode according to the present disclosure. Referring to fig. 3, first, an electrode active material, a binder resin, and a conductive material are blended to prepare a powdery mixture, and crystallinity of the binder resin is determined. If the crystallinity of the binder resin is 50% or less, the powdery mixture is introduced into the next kneading step. However, if the crystallinity is higher than 50%, the powdery mixture may be further subjected to a mixing step to prolong the mixing time. In this context, the binder mass may be crushed into primary particles and coarse fibrillation performed.

Next, the resultant powdery mixture was kneaded to obtain a mixture block, which was then pulverized to obtain a mixed powder for an electrode. If the binder resin in the obtained mixed powder for an electrode exhibits crystallinity of 20% or less, the mixed powder for an electrode is introduced into the next rolling step. However, if the crystallinity is higher than 20%, the mixed powder for an electrode is returned to the kneading step.

Then, the obtained electrode was subjected to calendaring with the mixed powder to obtain a dry electrode film. If the binder resin in the resulting dry electrode film exhibits crystallinity of 10% or less, the dry electrode film is introduced into a lamination step to obtain an electrode. However, when the crystallinity is higher than 10%, the gap between the respective rollers, the rotation speed ratio of the respective rollers, or both are adjusted to control the crystallinity. Meanwhile, the processing conditions for satisfying the crystallinity required for each step during the electrode manufacturing may also be established using the flowchart shown in fig. 3.

The present disclosure will be explained in detail below with reference to examples, comparative examples and test examples so that the present disclosure fully conveys the scope of the present invention to those skilled in the art.

Example 1

First, li (Ni, co, mn, al) O as a positive electrode active material ₂ Activated carbon and Polytetrafluoroethylene (PTFE) were introduced into a stirrer in a weight ratio of 96:1:3, and then mixed at 15000rpm for 1 minute to prepare a powdery mixture. Next, the kneader was stabilized at a temperature of 150℃and the mixture was introduced into the kneader at a rate of 25rpm at 1kgf/cm ² The kneader was operated for 5 minutes under to obtain a mixture block. The mixture block was introduced into a stirrer and pulverized at 10000rpm for 30 seconds to obtain a mixed powder for an electrode. Then, the mixed powder for electrodes was introduced into a laboratory calender (roll diameter: 200mm, roll temperature: 100 ℃, roll rotation speed ratio: 1.5) to obtain a dry electrode film. The particle size of the positive electrode active material ranges from about 5 μm to about 12 μm.

Example 2

First, lithium iron phosphate (LFP), activated carbon, and Polytetrafluoroethylene (PTFE) as positive electrode active materials were introduced into a stirrer in a weight ratio of 94:1.5:4.5, and then mixed at 10000rpm for 1 minute to prepare a powdery mixture. Next, the kneader was stabilized at a temperature of 150℃and the mixture was introduced into the kneader at a rate of 50rpm at 1kgf/cm ² The kneader was operated for 5 minutes under to obtain a mixture block. The mixture block was introduced into a stirrer and pulverized at 10000rpm for 20 seconds to obtain a mixed powder for an electrode. The mixed powder for electrode was then introduced into a laboratory calender (roll diameter: 200mm, roll temperature: 1)00 ℃, roller rotation speed ratio: 1.75 To obtain a dry electrode film. The particle size of the positive electrode active material ranges from about 2 μm to about 3 μm.

Example 3

First, li (Ni, co, mn, al) O as a positive electrode active material ₂ Activated carbon and Polytetrafluoroethylene (PTFE) were introduced into a stirrer at a weight ratio of 96:1:3, and then mixed at 15,000rpm for 1 minute to prepare a powdery mixture. The particle size of the positive electrode active material ranges from about 5 μm to about 12 μm.

Next, the kneader was stabilized at a temperature of 150℃and the mixture was introduced into the kneader at a rate of 25rpm at 1kgf/cm ² The kneader was operated for 2 minutes under to obtain a mixture block. The mixture block was introduced into a stirrer and pulverized at 10000rpm for 30 seconds to obtain a mixed powder for an electrode. Then, the mixed powder for electrodes was introduced into a laboratory calender (roll diameter: 200mm, roll temperature: 100 ℃, roll rotation speed ratio: 1.5) to obtain a dry electrode film.

Comparative example 1

First, lithium iron phosphate (LFP), activated carbon, and Polytetrafluoroethylene (PTFE) as positive electrode active materials were introduced into a stirrer at a weight ratio of 94:1.5:4.5, and then mixed at 10,000rpm for 1 minute to prepare a powdery mixture. Next, the kneader was stabilized at a temperature of 150℃and the mixture was introduced into the kneader at a rate of 25rpm at 1kgf/cm ² The kneader was operated for 2 minutes under to obtain a mixture block. The mixture block was introduced into a stirrer and pulverized at 10000rpm for 20 seconds to obtain a mixed powder for an electrode. Then, the mixed powder for electrodes was introduced into a laboratory calender (roll diameter: 200mm, roll temperature: 100 ℃, roll rotation speed ratio: 1.75) to obtain a dry electrode film. The particle size of the positive electrode active material ranges from about 2 μm to about 3 μm.

Comparative example 2

First, li (Ni, co, mn, al) O as a positive electrode active material ₂ Activated carbon and Polytetrafluoroethylene (PTFE) were introduced into a stirrer in a weight ratio of 96:1:3, and then mixed at 400rpm for 2 minutes to prepare a powdery mixture.

Next, the kneader was stabilized at a temperature of 150℃and the mixture was introduced into the kneaderAnd at a rate of 25rpm at 1kgf/cm ² The kneader was operated for 5 minutes under to obtain a mixture block. The mixture block was introduced into a stirrer and pulverized at 10,000rpm for 30 seconds to obtain a mixed powder for an electrode. Then, the mixed powder for electrodes was introduced into a laboratory calender (roll diameter: 200mm, roll temperature: 100 ℃, roll rotation speed ratio: 1.5) to obtain a dry electrode film. The particle size of the positive electrode active material ranges from about 5 μm to about 12 μm.

Comparative example 3

First, li (Ni, co, mn, al) O as a positive electrode active material ₂ Activated carbon and Polytetrafluoroethylene (PTFE) were introduced into a stirrer at a weight ratio of 96:1:3, followed by mixing at 15,000rpm for 1 minute, and the resultant was placed into a super mixer and mixed at 800rpm for 30 seconds to prepare a powdery mixture. In both steps, the temperature was controlled at 23℃and the pressure at 85psi. The powdery mixture was then introduced into a laboratory calender (roll diameter: 200mm, roll temperature: 100 ℃, roll rotation speed ratio: 1.5) to obtain a dry electrode film. The particle size of the positive electrode active material ranges from about 5 μm to about 12 μm.

TABLE 1

TABLE 2

/>

As can be seen from table 1, the mixtures according to each of examples 1 to 3 showed crystallinity of 50% or less, then the mixed powders for electrodes showed crystallinity of 20% or less, and the dry electrode films showed crystallinity of 10% or less. Fig. 1 is a graph showing the results of thermogravimetric analysis using Differential Scanning Calorimetry (DSC) according to example 1. As can be seen from fig. 1, each of the mixed powder for electrodes (ringing) and the dry electrode film (Sheet) which were subsequently processed showed lower crystallinity than the powdery mixture (Mixing). Further, fig. 2 is a graph showing the result of thermogravimetric analysis using Differential Scanning Calorimetry (DSC) according to example 2. It can also be seen from example 2 that each of the subsequently processed mixed powder for electrode (ringing) and dry electrode film (Sheet) showed lower crystallinity than the powdery mixture (Mixing). Further, each of the dry electrode films according to the embodiments exhibits a tensile strength of 0.5MPa or more and a tensile elongation of 2% or more. Meanwhile, PTFE in fig. 2 represents a specific crystallinity of 100% PTFE determined before processing PTFE, which is provided for the purpose of comparison with the crystallinity of PTFE after processing.

In comparative examples 1 and 2, the crystallinity of the binder resin of the obtained electrode mixture powder exceeded 20%. This means that the obtained electrode mixed powder is not sufficiently fibrillated, and it is difficult to produce a sheet-like dry electrode film by a subsequent calendering process. In particular, in comparative example 2, the crystallinity of the binder resin in the powdery mixture exceeds 60%, and therefore, sufficient fiberization is not achieved even if the subsequent process is performed. In comparative example 3, the kneading process according to the present invention was not applied, and thus, the fine fiberization was not sufficiently achieved.

Determination of crystallinity

For each of the examples and comparative examples, samples were taken from each of the powdery mixture, the mixed powder for electrodes, and the dry electrode film to measure the crystallinity of each. Next, about 5mg to 12mg of each sample was weighed, and a differential scanning calorimeter (differential scanning calorimetry, DSC) of TA corporation was introduced to determine crystallinity (Xc), and then melting point (Tm) and heat of fusion (Δhm) were measured in a temperature range of 25 ℃ to 360 ℃ at a heating rate of 10 ℃/min under a nitrogen atmosphere.

Melting point (Tm) and melting enthalpy (Δhm) were analyzed based on the temperature (peak temperature) at the point in time at which the highest enthalpy was shown during melting using the treis program of TA. The crystallinity of each sample was determined by DSC according to equation 1 given above, and the melting enthalpy (. DELTA.H _m ) Removal ofWith melting enthalpy (. DELTA.H) of theoretical complete crystallization (100% crystallinity) _m ⁰ ) Calculated, expressed in%. Heat of fusion of 100% adhesive crystals (Δhf ₀ ) The value is 85.4J/g (Polymer 46, 2005, pp 8872-8882).

Determination of tensile Strength and tensile elongation

The dry electrode films obtained from each of the examples and comparative examples were cut into widths of 10 mm. Then, the tensile strength and the tensile elongation were measured three times at a tensile rate of 5mm/min by using a tensile strength tester. The results are shown as the average of three measurements. Tensile strength is the stress applied until fracture occurs, and tensile elongation represents the percentage (% of the change in length to the original length) of the specimen that is stretched until fracture occurs.

Claims

1. An electrode for an electrochemical device, comprising a dry electrode film obtained by a dry manufacturing process without using a solvent, wherein the dry electrode film comprises an electrode active material, a conductive material, and a binder resin, and the binder resin contained in the dry electrode film has a crystallinity of 10% or less.

2. The electrode for an electrochemical device according to claim 1, wherein the dry electrode film has a tensile strength of 0.5MPa or more in a Machine Direction (MD).

3. The electrode for an electrochemical device according to claim 1, wherein the dry electrode film has a tensile elongation of 2% or more.

4. The electrode for an electrochemical device according to claim 1, wherein the electrode film has a porosity of 20 to 50% by volume.

5. A method for manufacturing the electrode for an electrochemical device according to claim 1, the method comprising the steps of:

(a) Preparing a powdery mixture including an electrode active material, a conductive material, and a binder resin;

(c) Crushing the mixture block to obtain a mixed powder for an electrode; and

6. The method for manufacturing an electrode for an electrochemical device according to claim 5, wherein the binder resin contained in the mixed powder for an electrode obtained from step (c) has a crystallinity (c) of 20% or less.

7. The method for manufacturing an electrode for an electrochemical device according to claim 5, wherein the binder resin contained in the mixture obtained from step (a) has a crystallinity (a) of 50% or less.

8. The method for manufacturing an electrode for an electrochemical device according to claim 5, wherein step (a) is performed at 500rpm to 30,000 rpm.

9. The method for manufacturing an electrode for an electrochemical device according to claim 5, wherein step (b) is performed at a rotation speed of 100rpm or less.

10. The method for manufacturing an electrode for an electrochemical device according to claim 5, wherein step (b) is performed at 0.5kgf/cm ² To 10kgf/cm ² Is carried out under pressure of (2).

11. The method for manufacturing an electrode for an electrochemical device according to claim 5, wherein step (b) is performed at atmospheric pressure or more.

12. The electrode for an electrochemical device according to claim 1, wherein the binder resin comprises Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (Polyvinylidene fluoride, PVDF), polyolefin, or a mixture of two or more thereof.

13. The electrode for an electrochemical device according to claim 1, further comprising a current collector, wherein the dry electrode film is provided on at least one surface or both surfaces of the current collector.

14. The method for manufacturing an electrode for an electrochemical device according to claim 5, further comprising the steps of preparing a current collector, disposing the dry electrode film on at least one surface of the current collector, and laminating.

15. A secondary battery comprising the dry electrode of claim 1, wherein the dry electrode is a positive electrode, and an electrode assembly comprising the positive electrode, a negative electrode, and a separator is contained in a battery case together with a lithium-containing nonaqueous electrolyte.

16. An energy storage system comprising the secondary battery according to claim 15 as a unit cell.

17. A method of preparing a mixed powder for an electrode for use in manufacturing a dry electrode film, the method comprising the steps of:

(c) Crushing the mixture block to obtain a mixed powder for an electrode,

wherein the binder resin contained in the mixed powder for an electrode has a crystallinity of 20% or less, and the binder resin includes Polytetrafluoroethylene (PTFE), polyolefin, or a mixture thereof.

18. A mixed powder for an electrode obtained by the method of claim 17 and comprising an electrode active material, a conductive material, and a binder resin, wherein the binder resin comprises Polytetrafluoroethylene (PTFE), PVDF, polyolefin, or a mixture of two or more thereof, and the binder resin contained in the electrode mixture has a crystallinity of 20% or less.

19. A method for manufacturing a dry electrode film, comprising a step of calendaring a mixed powder for an electrode to obtain a free-standing dry electrode film, wherein the mixed powder for an electrode is the same as defined in claim 17, and the binder resin contained in the dry electrode film has a crystallinity (d) of 10% or less.

20. A dry electrode film obtained by the method of claim 19 and having a tensile strength of 0.5MPa or greater, a tensile elongation of 2% or greater, and a porosity of 20 to 50% by volume in the Machine Direction (MD).