Powder for electrode, method for manufacturing dry electrode using same, and lithium secondary battery comprising dry electrode manufactured therefrom

Abstract

The present invention relates to a powder for an electrode, a method for manufacturing a dry electrode using same, and a lithium secondary battery comprising an electrode manufactured therefrom, the powder for an electrode comprising an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure, wherein the powder for an electrode has a circularity of 0.30 to 0.65, and the powder for an electrode has a convexity of 0.54 to 0.71.

Description

Powder for electrodes, a method for manufacturing a dry electrode using the same, and a lithium secondary battery including a dry electrode manufactured therefrom

[0001] The present invention relates to a powder for electrodes, a method for manufacturing a dry electrode using the same, and a lithium secondary battery comprising a dry electrode manufactured therefrom.

[0002]

[0003] Secondary batteries are used not only in small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable game devices, power tools, and E-bikes, but also in large products requiring high output such as electric vehicles and hybrid vehicles, as well as in power storage devices that store surplus power or new and renewable energy and backup power storage devices.

[0004] Typically, a secondary battery is manufactured by applying an electrode active material slurry to a positive electrode current collector and a negative electrode current collector to form an electrode active material layer, then manufacturing a positive electrode and a negative electrode through drying and rolling processes, and then stacking them on both sides of a separator to form an electrode assembly of a predetermined shape, and then housing the electrode assembly in a battery case, injecting an electrolyte, and sealing.

[0005] Meanwhile, during the drying process of the electrode active material slurry, defects such as pinholes or cracks may be induced in the electrode active material layer formed on the current collector as the solvent contained in the slurry evaporates. In addition, since the inner and outer parts of the electrode active material slurry are not dried uniformly during the drying process, there is a risk that the electrode quality may deteriorate due to a powder floating phenomenon caused by the difference in solvent evaporation rates, that is, powders in the parts that dry first rise and form a gap with the parts that dry relatively later.

[0006] To solve the above problem, drying devices capable of controlling the evaporation rate of the solvent are being considered so that the inside and outside of the electrode active material slurry can be dried uniformly; however, these drying devices are very expensive and require significant cost and time to operate, which is disadvantageous in terms of manufacturing processability.

[0007] On the other hand, the solvent included in conventional electrode active material slurries is N-methyl-2-pyrrolidone (NMP), which has a high boiling point and requires high thermal energy and a very long drying oven to dry, making it very unfavorable for mass production. In addition, N-methyl-2-pyrrolidone (NMP) is a toxic substance and is harmful to living organisms, so it has the disadvantage of not being environmentally friendly.

[0008] Therefore, there is a recent trend of active research on dry electrodes that manufacture electrodes without using solvents. The above-mentioned dry electrode is generally manufactured by laminating a free-standing type electrode composite film, which is manufactured in a sheet form and includes an electrode active material, a binder, a conductive material, etc., onto a current collector. This electrode composite film includes a process of first mixing the electrode active material, a carbon material as a conductive material, and a fiberizable binder together using a blender or similar device, then fiberizing the binder by applying shear force through a process such as jet-milling or kneading, and finally calendering the obtained mixture into a film form to manufacture a free-standing film.

[0009] However, as mentioned above, since the electrode is manufactured without using a solvent, unlike wet electrodes, it is difficult to perform pre-dispersion of the conductive material, and there is a disadvantage that dispersion of the electrode components is not easy in a solvent-free environment. In particular, if the dispersibility of the conductive material among the electrode components is low, there is a problem that the contact area with the active material is reduced, thereby degrading the battery performance.

[0010] In addition, conventional dry LFP electrodes contain 10% or more by weight of active material with a particle size of 1 μm or less, making it difficult to manufacture a dry electrode film, and it is difficult to predict the possibility of film formation based on existing mixed powder characteristics such as particle size distribution, tap density, and binder crystallinity.

[0011]

[0012] One objective of the present invention is to solve the above-mentioned problems by providing an electrode powder that can predict whether film formation is possible in a calendering process and improve the processability of the calendering process by designing the electrode powder to have a specific range of roundness and convexity.

[0013] In addition, one objective of the present invention is to provide a method for manufacturing a dry electrode by first mixing an electrode active material, a fiberizable binder, and a conductive material, and then performing kneading, grinding, and sheet forming processes under specific temperature, time, and speed conditions, in order to manufacture the dry electrode using the electrode powder and a composite electrode film containing the same.

[0014] In addition, one objective of the present invention is to solve the above-mentioned problems by providing a lithium secondary battery comprising a dry electrode manufactured by using the above-mentioned manufacturing method performed under specific conditions.

[0015]

[0016] [1] According to one embodiment, the present invention provides an electrode powder comprising an electrode active material, a conductive material and a binder having a three-dimensional fiber network structure, wherein the electrode powder has a circularity of 0.3 to 0.65 and a convexity of 0.54 to 0.71.

[0017] [2] In the above [1], the electrode powder may have a circularity of 0.38 to 0.58.

[0018] [3] In the above [1], the electrode powder may have a convexity of 0.60 to 0.67.

[0019] [4] In the above [1], the electrode active material may contain at least 10% by weight of particles with a particle size of 1 μm or less relative to the electrode active material.

[0020] [5] In the above [1], the electrode active material is a positive active material, and the positive active material may include a lithium complex metal compound containing one or more selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe).

[0021] [6] In the above [1], the electrode active material is a positive active material, and the positive active material may include a lithium metal phosphate-based compound represented by the following chemical formula 1.

[0022] [Chemical Formula 1]

[0023] Li 1+x [Fe 1-y M y ]PO4

[0024] In the above chemical formula 1, M comprises one or more selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤x≤0.5, 0≤y<1.

[0025] [7] In the above [1], the degree of crystallization of the binder may be 20% or less.

[0026] [8] In the above [1], the volume cumulative average particle size D of the electrode powder 50 It can be 150㎛ to 700㎛.

[0027]

[0028] [9] According to another embodiment, a method for manufacturing a dry electrode is provided, comprising: a first step of mixing an electrode active material, a fiberizable binder, and a conductive material to form a composite composition; a second step of kneading the composite composition to form a mixed aggregate containing a fiberized binder; a third step of crushing the mixed aggregate to form an electrode powder; and a fourth step of rolling the electrode powder to form a sheet to produce an electrode composite film; wherein the electrode powder has a three-dimensional fiber network structure inside due to the binder, the electrode powder has a circularity of 0.30 to 0.65, and the electrode powder has a convexity of 0.54 to 0.71.

[0029]

[0010] In the above [9], the mixing of the first step can be performed at a rotational speed of 100 rpm to 2,000 rpm.

[0030]

[0011] In the above [9], the mixing of the second step can be performed at a rotational speed of 20 rpm to 250 rpm.

[0031]

[0012] In the above [9], the grinding of the third step can be performed under conditions where the rotational speed of the grinding equipment is 1,000 rpm to 12,000 rpm.

[0032]

[0033]

[0013] According to another embodiment, a lithium secondary battery may be provided that includes a structure in which a plurality of electrodes and a separator are alternately stacked, and at least one of the electrodes is manufactured by the dry electrode manufacturing method described above.

[0034]

[0035] Using the electrode powder according to the present invention allows for the prediction of whether the electrode composite film will form during the sheet forming step performed in the process of manufacturing a dry electrode, and facilitates the control of conditions in the roll rolling process, thereby improving processability. Specifically, when the electrode powder satisfies specific range values ​​for sphericity and convexity during dry electrode manufacturing, it eliminates issues with appearance characteristics caused by cracks or streaks in the film during the calendering process, which is a sheet forming process, thereby significantly reducing the defect rate. Furthermore, it minimizes the problem of increased trial errors due to forming failures during the optimization of process conditions for improving mechanical properties, thereby further enhancing process efficiency.

[0036] In addition, when the electrode powder contains a lithium metal phosphate-based material as an active material in which particles with a particle size of 1 μm or less are mixed in at least 10 weight percent of the total, it is possible to realize a dry electrode with excellent unit cost competitiveness, high density, and high loading characteristics, thereby providing improved process efficiency in next-generation energy technology fields such as energy storage systems (ESS) and electric vehicle cells.

[0037]

[0038] Figure 1 is a photograph showing the shape of a particle obtained to measure the degree of sphericity of the electrode powder of Example 1 of the present invention.

[0039] Figure 2 is a photograph showing the shape of a particle obtained to measure the convexity of the electrode powder of Example 1 of the present invention.

[0040] Figure 3 is a photograph showing the shape of a particle obtained to measure the degree of sphericity of the electrode powder of Example 2 of the present invention.

[0041] Figure 4 is a photograph showing the shape of a particle obtained to measure the convexity of the electrode powder of Example 2 of the present invention.

[0042] Figure 5 is a photograph showing the shape of a particle obtained to measure the degree of sphericity of the electrode powder of Comparative Example 1 of the present invention.

[0043] Figure 6 is a photograph showing the shape of a particle obtained to measure the convexity of the electrode powder of Comparative Example 1 of the present invention.

[0044] Figure 7 is a photograph showing the shape of a particle obtained to measure the degree of sphericity of the electrode powder of Comparative Example 2 of the present invention.

[0045] Figure 8 is a photograph showing the shape of a particle obtained to measure the convexity of the electrode powder of Comparative Example 2 of the present invention.

[0046]

[0047] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0048] In this specification, "composite composition" refers to a mixture comprising an electrode active material, a conductive material, and a fiberizable binder, which is physically mixed to form a uniform dispersed phase. As a product of the mixing process according to this specification, it may be a powdered mixture and may substantially not involve a solvent. Here, "substantially not involving a solvent" means that no solvent is introduced or only a minute amount of solvent is introduced during the mixing of the composite composition.

[0049] In this specification, "mixed aggregate" refers to a product of a mixing process (kneading process) according to this specification in which the powdered mixture is converted into a paste-like aggregate as the binder is fiberized under shear force, and the product may have a solid content of 100%.

[0050] In this specification, "powder for electrode" refers to a material in which the mixed aggregate is crushed to form a powder with a smaller particle size, and may mean an electrode material in powder form comprising an electrode active material, a binder, and optionally a conductive material.

[0051] In this specification, the term "electrode composite film" may refer to a free-standing type single sheet manufactured using an "electrode composite" comprising an electrode active material, a conductive material, and a binder without the involvement of a solvent, or an electrode composite layer laminated onto a current collector. In this specification, the term "free-standing type" means that it can maintain an independent form without relying on other components and can be moved or handled on its own. As described below, the electrode composite film may be formed by compressing the electrode powder. For example, the electrode powder may have a shape forming a layered structure by being accumulated by compression.

[0052] In this specification, "powder-sheeting film" refers to a film formed from the time the powder for the electrode passes through the first rolling roll in a roll-to-roll process to form a sheet shape until it passes through the last rolling roll in the process. It may be a self-supporting sheet, but may be a sheet with relatively weak self-supporting capacity. Here, "powder-sheeting" refers to the process in which the powder for the electrode is formed into a self-supporting sheet shape by the rolling roll of the roll-to-roll process, and "sheeting" refers to a process performed during the process of manufacturing the powder-sheeting film into an electrode composite film, which may refer to the process of rolling the powder-sheeting film.

[0053] In this specification, "volume cumulative average particle size D 50 In the particle size distribution curve, it refers to the particle size corresponding to 50% of the cumulative volume. The above D 50For example, it can be measured using the laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0054] In this specification, the porosity can be calculated using the following mathematical formula A.

[0055] [Mathematical Formula A]

[0056] Porosity (%) = {1 - (Electrode Density / True Density)} × 100

[0057] In the above mathematical formula A, the true density is the calculated density derived from the density and mass ratio of each constituent material forming the electrode composite film under the assumption that it does not contain pores, and the electrode density is the measured density of the electrode composite film obtained by sampling the film of a certain size.

[0058] In this specification, "three-dimensional fiber network structure" refers to a structure formed by the fiberization of a binder during the process in which an electrode powder is manufactured from a composite composition comprising an electrode active material and a binder, and then sheet-formed into an electrode composite film, wherein a plurality of fibers are connected in the up, down, left, and right directions at a plurality of points. The three-dimensional fiber network structure may refer to various forms of structures capable of functioning as a support that enables the electrode composite film to be a self-standing film by forming a framework of fine fibrous binders. At this time, the electrode active material and, optionally, a conductive material may be accommodated within the pores formed in the three-dimensional fiber network structure.

[0059]

[0060] The present invention will be described in detail below.

[0061] A lithium secondary battery comprising an electrode powder according to the present invention, a method for manufacturing a dry electrode using the same, and a dry electrode manufactured therefrom comprises at least one of the configurations disclosed below, and may comprise any combination of technically feasible configurations among the configurations below.

[0062]

[0063] Powder for electrodes

[0064] An electrode powder according to one embodiment of the present invention is an electrode powder comprising an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure, wherein the electrode powder has a circularity of 0.30 to 0.65 and the electrode powder has a convexity of 0.54 to 0.71.

[0065] Unlike wet electrodes, which are formed by applying a slurry of electrode active material, binder, and conductive material to an electrode current collector and then processing it using a liquid medium such as a solvent and a dispersion medium, dry electrodes are manufactured using electrode powders formed by mixing, kneading, and / or grinding electrode active material, binder, and conductive material without a liquid medium.

[0066] The electrode composite film to be finally formed is manufactured through a step of rolling electrode powder to form a sheet. Specifically, a roll-to-roll process (calendering process) is performed to apply pressure by passing the electrode powder between rollers to form an electrode composite film of a uniform thickness, and additional post-processing is carried out to achieve desired mechanical and electrochemical performance by applying physical properties such as thickness and density.

[0067] As mentioned above, the formation and physical properties of the electrode composite film are inevitably influenced by the physical properties of the electrode powder, as the film is formed by undergoing a sheet molding process performed under specific pressure and temperature conditions. Specifically, if the bonding between the electrode active material, conductive material, and binder constituting the electrode powder is not properly achieved, the electrode composite film may not be formed or may be formed incompletely. Furthermore, if the crystallinity and fiberization of the binder are not properly controlled, even if the electrode composite film is formed, it may quickly peel off from the current collector, leading to a deterioration in lifespan characteristics.

[0068] If an electrode composite film is not formed from the electrode powder, the previous processes lead to economic losses, and batteries using an incomplete electrode composite film not only suffer from reduced energy efficiency but can also lead to safety issues.

[0069] Accordingly, the present invention aims to resolve the phenomenon in which a self-standing electrode composite film is not formed due to uneven compression during sheet molding by controlling the shape characteristics of the electrode powder, specifically the sphericity and convexity. In other words, the invention is characterized by designing the electrode powder so that the particle shape characteristics of the electrode powder, specifically the sphericity and convexity, satisfy a specific range, thereby preventing the above-mentioned problems from occurring. Through this, the efficiency of the process and the reliability of the battery can be further improved by making it possible to predict whether the electrode composite film will be formed into a film.

[0070] The electrode powder according to the present invention is an electrode particle comprising an electrode active material, a conductive material, and a binder having a three-dimensional fiber network. Detailed descriptions such as the roles, materials, and content ratios of the electrode active material, conductive material, and binder will be provided later.

[0071] The electrode powder according to the present invention comprises a binder having a three-dimensional fiber network. The three-dimensional fiber network structure is a structure formed by the fiberization of the binder during the process of manufacturing the electrode powder from a composite composition comprising an electrode active material and a binder, and may refer to a structure in which a plurality of fibers are connected in the up, down, left, and right directions at a plurality of points. The three-dimensional fiber network structure may refer to various forms of structures that can function as a support, enabling the finally manufactured electrode composite film to be a self-standing film, by having the fine fibrous binder form a framework. At this time, the electrode active material and, optionally, a conductive material may be accommodated within the pores formed in the three-dimensional fiber network structure.

[0072] The degree of crystallization of the binder included in the electrode powder of the present invention may be 20% or less, specifically 18% or less, more specifically 16% or less, more specifically 15% or less, and 3% or more, specifically 5% or more, more specifically 7% or more. When the degree of crystallization of the binder included in the electrode powder satisfies the above range, the three-dimensional fiber network structure of the electrode powder of the present invention is formed more stably, and the mechanical and electrochemical properties of the electrode composite film can be further improved.

[0073] The electrode powder according to the present invention may have a circularity of 0.30 to 0.65, specifically 0.32 to 0.62, more specifically 0.35 to 0.60, more specifically 0.38 to 0.58, even more specifically 0.40 to 0.56, and even more specifically 0.42 to 0.53. If the circularity of the electrode powder is less than 0.30, the powder flowability may be poor, causing a problem where holes are formed in the film, and if it exceeds 0.65, the bonding strength between the powders is insufficient, causing a problem where it cannot be manufactured.

[0074] The electrode powder according to the present invention may have a convexity of 0.54 to 0.71, specifically 0.56 to 0.70, more specifically 0.58 to 0.69, more specifically 0.59 to 0.68, and even more specifically 0.60 to 0.67. If the convexity of the electrode powder is less than 0.54, the powder flowability may be poor, causing a problem where holes are formed in the film, and if it exceeds 0.71, the bonding strength between the powders is insufficient, causing a problem where it cannot be manufactured.

[0075] Meanwhile, the sphericity and convexity according to the present invention are determined by sieving and dispersing the electrode powder through a particle shape analyzer (e.g., Morphologies 4, Malvern), and then determining the particle size as the volume-cumulative average particle size (D 50 ) More than 100 electrode powders of the level ) can be selected, and the average value of the sphericity and convexity of the corresponding particles calculated through the following Equations 2 and 3 can be used.

[0076] [Equation 2]

[0077] Circularity = CE perimeter / Perimeter

[0078] (CE perimeter = the circumference of a circle with the same area as the particle, Perimeter = the circumference measured along the actual boundary of the particle)

[0079] [Equation 3]

[0080] Convexity = Convex Hull Perimeter / Perimeter

[0081] (Convex Hull Perimeter = the perimeter of the smallest convex polygon formed by connecting the outer points of the particle, Perimeter = the perimeter measured along the actual boundary of the particle)

[0082] Volume cumulative average particle size (D) of the electrode powder according to the present invention 50 The range may be 150㎛ to 700㎛, specifically 200㎛ to 500㎛, more specifically 230㎛ to 470㎛, and even more specifically 260㎛ to 440㎛. When the above range is satisfied, the mechanical properties of the electrode powder may be excellent, and subsequently, excellent physical properties can be secured when manufacturing the electrode composite film.

[0083] Hereinafter, the composition of the electrode powder according to the present invention will be explained in more detail.

[0084]

[0085] (1) Electrode active material

[0086] The electrode powder according to the present invention includes an electrode active material.

[0087] The above electrode active material may be a positive electrode active material or a negative electrode active material.

[0088] The above-mentioned positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and may include a lithium complex metal compound containing one or more selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe).

[0089] Specifically, it may include a lithium composite transition metal oxide comprising lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite transition metal oxide may be a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 CoY1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are each atomic fractions of independent elements, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.) any one or more of these compounds may be included.

[0090] Among these, the lithium metal oxides mentioned above include LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni) 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15)O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), lithium nickel-cobalt-aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), or lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 It may be )O2), etc., and any one of these or a mixture of two or more of them may be used.

[0091] In addition, the above positive active material may include a lithium metal phosphate-based compound containing iron, specifically lithium iron phosphate, and may be represented, for example, by the following chemical formula 1.

[0092] [Chemical Formula 1]

[0093] Li 1+a Fe 1-x M x PO4

[0094] In the above chemical formula 1, M is one or more selected from Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤a≤0.5, 0≤x<1.

[0095] When the above-mentioned positive electrode active material is a lithium metal phosphate-based compound, particularly a lithium iron phosphate, the disadvantage is that the capacity is relatively smaller compared to lithium nickel-based oxides, even though safety is guaranteed. However, according to one embodiment of the present invention, a dry electrode capable of high loading can be implemented, so it is possible to implement a lithium secondary battery with excellent safety and improved capacity, and excellent cost competitiveness.

[0096] However, the positive active material according to the present invention is not limited to the compounds described above.

[0097] The above-mentioned negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0098] As for the carbon material capable of reversibly intercalating / deintercalating the above lithium ions, any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries may be used without particular limitation, and representative examples include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the above crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the above amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0099] As the above metal or alloy of these metals and lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of these metals and lithium may be used.

[0100] The above metal composite oxides include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1) and Sn x Me 1-x Me y O z(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 로 이루어진 군에서 선택되는 것이 사용될 수 있다.

[0101] Materials capable of doping and dedoping the above lithium include Si and SiO x (0 <x≤2), Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), Sn, SnO2, Sn-Y(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po 및 이들의 조합으로 이루어진 군에서 선택될 수 있다.

[0102] Examples of the above transition metal oxides include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0103] According to one embodiment of the present invention, the electrode active material may contain 10 weight percent or more of particles with a particle size of 1 μm or less relative to the electrode active material. In conventional batteries using lithium metal phosphate-based compounds as positive electrode active materials, the particle size of the positive electrode active material is basically small, and since 10 weight percent or more of fine particles with a particle size of 1 μm or less are contained relative to the electrode active material, there was a significant difficulty in forming it into a self-standing electrode composite film.

[0104] In order to solve the above difficulties, the inventors of the present invention devised a method for predicting whether an electrode composite film can be formed by quantifying the shape characteristics of the electrode powder, namely sphericity and convexity, as described above. As a result, it became possible to form an electrode composite film that can stand on its own even if particles with a particle size of 1 μm or less are included in an amount of 10% by weight or more relative to the electrode active material.

[0105] Meanwhile, by using a lithium metal phosphate-based compound as an electrode active material that contains at least 10 weight percent of fine particles with a particle size of 1 μm or less, which are basically small in size, the manufacturing cost of the battery can be further reduced.

[0106] According to one embodiment of the present invention, the volume cumulative average particle size D of the electrode active material 50 The value may be 0.1㎛ to 10㎛, and preferably, the volume cumulative average particle size D of the electrode active material 50 The particle size may be 0.5㎛ to 8㎛, and more preferably, the volume cumulative average particle size D of the electrode active material 50 The particle size may be 0.8㎛ to 5㎛. When the above range is satisfied, it may be easy to form a film when manufacturing an electrode composite film using the electrode powder, and the average particle size may be suitable for maximizing low resistance characteristics due to excellent conductive material dispersibility.

[0107] According to one embodiment of the present invention, a coating layer comprising carbon (C) may be further included, formed on the electrode active material. When the above conditions are satisfied, ion conductivity and electron conductivity can be improved.

[0108] According to one embodiment of the present invention, the electrode active material may be included in an amount of 80 to 99 parts by weight based on the total weight of the electrode powder, specifically 85 to 98 parts by weight, and more specifically 90 to 97 parts by weight. Satisfying the above range is desirable in terms of increasing the capacity and energy density of the electrode.

[0109]

[0110] (2) Challenge material

[0111] The above electrode powder includes a conductive material.

[0112] The above conductive material is a component for further improving the conductivity of the electrode active material, and such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite or artificial graphite with a highly developed crystal structure; conductive fibers such as carbon-based fibers (e.g., carbon nanotubes, carbon nanofibers, carbon fibers) or metallic fibers; fluorocarbon powder; metallic powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive polymers such as polyphenylene derivatives, etc. may be used. In detail, to ensure uniform mixing of the conductive material and to improve conductivity, it may include one or more selected from the group consisting of graphite powder, carbon black, and carbon nanotubes. The above conductive material may be included in an amount of 0.1 to 10 parts by weight based on the total weight of the electrode powder, and preferably in an amount of 0.1 to 5.0 parts by weight. Satisfying the above range is desirable in that it can form an excellent conductive path while also achieving an excellent capacity density.

[0113]

[0114] (3) Binder

[0115] The above electrode powder includes a binder.

[0116] The above binder is not specified as long as it is fibrillable, and fibrillation refers to a process of dividing a polymer into smaller fibers. For example, this can be performed using mechanical shear force, and the surface of the polymer fiber thus fibrillated is loosened to generate a large number of fine fibers (fibrils). Preferably, such a binder may include one or more selected from the group consisting of polytetrafluoroethylene (PTFE) and polyolefins, more preferably may include polytetrafluoroethylene (PTFE), and even more preferably may be polytetrafluoroethylene (PTFE). When the above conditions are satisfied, excellent dispersibility of the conductive material can be achieved, while the resistance can be appropriately reduced.

[0117] Meanwhile, the above-mentioned polytetrafluoroethylene (PTFE) may be included in an amount of 60% by weight or more based on the total weight of the binder. At this time, the binder may additionally include one or more of PEO (polyethylene oxide), PVdF (polyvinylidene fluoride), PVdF-HFP (polyvinylidene fluoride-cohexafluoropropylene), and polyolefin-based binders.

[0118] According to one embodiment of the present invention, the binder may be included in an amount of 0.1 to 10 parts by weight relative to the total weight of the powder for the electrode, and preferably in an amount of 0.1 to 5.0 parts by weight. Satisfying the above range is desirable in that it can achieve a degree of fiberization suitable for manufacturing a self-standing sheet while also having excellent resistance characteristics.

[0119]

[0120] Meanwhile, the electrode powder according to the present invention may additionally include fillers to suppress the expansion of the electrode, although this is not essential. The fillers are not particularly limited as long as they are fibrous materials that do not cause chemical changes in the battery, but, for example, at least one selected from olefinic polymers such as polyethylene and polypropylene; and fibrous materials such as glass fibers and carbon fibers may be included.

[0121]

[0122] Method for manufacturing a dry electrode

[0123] Hereinafter, a method for manufacturing a dry electrode according to the present invention will be described.

[0124] A method for manufacturing a dry electrode according to one embodiment of the present invention comprises: a first step of mixing an electrode active material, a fiberizable binder, and a conductive material to form a composite composition; a second step of kneading the composite composition to form a mixed aggregate containing a fiberized binder; a third step of crushing the mixed aggregate to form the aforementioned electrode powder; and a fourth step of rolling the electrode powder to form a sheet to produce an electrode composite film.

[0125] As mentioned above, dry electrodes are manufactured in a different way than wet electrodes, and in this case, the physical properties of the electrode powder must be considered important, and in order for the electrode powder to have particle shape characteristics such as sphericity and convexity within a specific range, the process variables in the manufacturing process as mentioned above must be finely controlled.

[0126] Furthermore, even when using the electrode powder according to the present invention, the control of process variables in the molding sheet process must be fully achieved to realize the effect of predicting whether the electrode composite film is formed into a film, which the present invention intends to implement; therefore, the present invention provides an advantageous example of process variables in the molding sheet process.

[0127] Hereinafter, the method for manufacturing a powder for electrodes according to the present invention will be described in detail step by step.

[0128]

[0129] Stage 1

[0130] The first step is to form a composite composition by mixing an electrode active material, a fiberizable binder, and a conductive material.

[0131] The above electrode active material, fiberizable binder, and conductive material are omitted as they have been described above.

[0132] The above mixing is performed so that the electrode active material and the binder can be uniformly distributed, and since they are mixed in powder form, they can be mixed by various methods that enable simple mixing, without limitation. However, since the present invention is manufactured as a powder for electrodes that does not use a solvent, the above mixing can be performed by dry mixing, and the materials can be mixed by introducing them into a device such as a mixer or blender.

[0133] According to one embodiment of the present invention, the mixing of the first step may be performed for 1 to 30 minutes, preferably for 2 to 25 minutes, and more preferably for 3 to 20 minutes. When performed within the above range, the electrode active material and the fiberizable binder may be uniformly mixed, thereby improving battery performance.

[0134] According to one embodiment of the present invention, the mixing of the first step can be performed at a rotational speed of 100 rpm to 2,000 rpm, specifically at 150 rpm to 1,800 rpm, more specifically at 200 rpm to 1,700 rpm, and even more specifically at 250 rpm to 1,650 rpm. When performed within the above range, the electrode active material and the fiberizable binder can be uniformly mixed, and the over-fiberization of the binder can be prevented, thereby improving battery performance.

[0135] In addition, according to one embodiment of the present invention, the rotational speed of the first step may not be fixed at a single rotational speed. For example, the mixing of the first step may be divided into two or more steps and performed at different rotational speeds. By performing mixing with different rotational speeds, the degree to which the composite composition is uniformly mixed can be controlled more finely.

[0136]

[0137] Phase 2

[0138] The second step is to knead the composite composition to form a mixed aggregate containing a fiberized binder. That is, the second step may be a fiberization process for fiberizing the binder.

[0139] In particular, since the electrode active material, conductive material, and binder are not mixed all at once, but rather a composite composition in which the electrode active material and binder are already mixed is mixed together with the conductive material, the poor dispersion of the conductive material caused by interference from the binder can be overcome.

[0140] The above fiberization process can be performed, for example, through mechanical milling or kneading, and there are no special limitations as long as it is performed generally, but preferably, it can be performed by high-temperature, low-shear kneading, and can be performed through a kneader such as a twin-screw extruder, for example. Through such kneading, the binder is fiberized, and the electrode active material and conductive material powders are combined or connected to form a mixed aggregate with 100% solid content.

[0141] The above mixing can be performed at a rotational speed of 20 rpm to 250 rpm, specifically 25 rpm to 200 rpm, more specifically 30 rpm to 180 rpm, and even more specifically 35 rpm to 150 rpm. When the above range is satisfied, appropriate fiberization proceeds, and the characteristics of the battery can be improved.

[0142] In addition, the above mixing can be performed at high temperature and high motor load, and specifically, at a motor load rate of 5% or more compared to no load.

[0143] More specifically, the above mixing can be performed at a temperature of 50°C to 300°C, specifically 80°C to 280°C, and more specifically 100°C to 260°C. When mixing is performed at a high temperature such as the above range, the fiberization of the binder and agglomeration by mixing can be effectively achieved, and the problem of breakage of the fiberized binder can be appropriately prevented.

[0144] In addition, the motor load rate can be performed at 5% or more relative to the no-load, specifically at 8% to 100% relative to the no-load, and more specifically at 10% to 80% relative to the no-load. When performed within the above range, the problem of breakage of the binder undergoing fiberization can be adequately prevented, and the problem of the density of the aggregate becoming too high can be prevented.

[0145] That is, according to the present invention, when a high-temperature, low-shear mixing process is performed under powder packing conditions of high temperature and motor no-load or higher instead of high-shear mixing, the effect intended by the present invention can be achieved.

[0146]

[0147] Stage 3

[0148] The third step is to crush the above-mentioned mixed aggregate to form the aforementioned electrode powder.

[0149] Although the mixed aggregate prepared through the above kneading process may be immediately pressurized to form a sheet (sheeting, e.g., a calendering process), in this case, the aggregate may need to be pressed under high pressure and high temperature to produce a thin film. Consequently, problems may arise where the film density becomes too high or a uniform film cannot be obtained. Therefore, the mixed aggregate prepared as described above is crushed to produce a powder for electrodes.

[0150] The device used for the above grinding is not particularly limited, but preferably can be performed with a device such as a blender or a grinder.

[0151] The grinding above may be performed at a rotational speed of the grinding equipment of 1,000 rpm to 12,000 rpm, specifically 1,500 rpm to 10,000 rpm, and more specifically 2,000 rpm to 8,000 rpm. When performed within the above range, sufficient grinding can be achieved to produce powder of a size suitable for film formation, and a large amount of fine powder may not be generated in the aggregate.

[0152]

[0153] Stage 4

[0154] The fourth step is to manufacture an electrode composite film by rolling the electrode powder and forming it into a sheet. The fourth step may be to form the electrode composite film by heat-pressing the electrode powder.

[0155] Specifically, an electrode composite film in the form of a self-standing sheet can be manufactured by heat-pressing the electrode powder using rolling rolls in a roll-to-roll process (calendering process, sheeting process) that includes two or more pairs of rolling rolls.

[0156] The above roll-to-roll process (calendar process) may include a roll press section, and the roll press section may have rolling rolls arranged in pairs facing each other, and multiple such pairs of rolling rolls may be arranged continuously in the roll press section. When multiple rolling rolls are arranged continuously, the temperature of each roll and the peripheral speed ratio (ratio of the rotational speeds of a pair of rolls) can be appropriately adjusted.

[0157] Meanwhile, the temperature of the rolling roll into which the electrode powder is first fed may be important, specifically the temperature of the rolling roll in which the electrode composite film is manufactured in the fourth step. At this time, the temperature of the rolling roll may be 20°C to 200°C, specifically 25°C to 170°C, and more specifically 30°C to 150°C. When the above range is satisfied, the electrode powder containing the fiberized binder can be more organically bonded as it is formed into the electrode composite film during mixing, and accordingly, the overall three-dimensional fiber network structure can be formed robustly and uniformly.

[0158] The roll diameter may be 80 mm to 600 mm, specifically 100 mm to 500 mm, more specifically 150 mm to 400 mm, and the rotational speed ratio of the roll may be 1 to 3.0, specifically 1 to 2.5, more specifically 1 to 2.3. When the above range is satisfied, an electrode composite film can be formed from the electrode powder according to the present invention, and the thickness of the electrode composite film to be realized by the present invention can be achieved.

[0159] In addition, the electrode composite film manufactured above can be fed back into a roll press section to be adjusted to an appropriate thickness and heated and pressed 1 to 10 times.

[0160] The thickness of the electrode composite film formed through the above fourth step may be 50㎛ to 200㎛, specifically 70㎛ to 150㎛, more specifically 80㎛ to 130㎛. When the above range is satisfied, the mechanical properties of the electrode composite film can be secured while simultaneously improving the energy density.

[0161]

[0162] In addition, the method for manufacturing a dry electrode according to the present invention may include the step of laminating the electrode composite film on one or both sides of a current collector and laminating the resulting product.

[0163] The above lamination may be performed by rolling and attaching the electrode composite film onto a current collector. The above lamination may be performed by a roll press method using a lamination roller, wherein the lamination roller may be maintained at a temperature of 40°C to 160°C.

[0164]

[0165] The above dry electrode may preferably be a positive electrode, and the above current collector may be conductive without causing chemical changes in the battery, and is not particularly limited. For example, the above current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0166] The thickness of the above current collector may be 8㎛ to 20㎛, but is not limited thereto. In addition, fine irregularities may be formed on the surface of the above current collector to increase the adhesion of the composite film.

[0167] The above-mentioned current collector may be used with a conductive primer coated wholly or partially on the surface to lower resistance and improve adhesion. Here, the conductive primer may comprise a conductive material and a binder, and the conductive material is not limited to any material that exhibits conductivity, but may be, for example, a carbon-based material. The binder may include solvent-soluble fluorine-based (including PVDF and PVDF copolymers), acrylic binders, and water-based binders.

[0168]

[0169] lithium secondary battery

[0170] A lithium secondary battery according to the present invention comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein one or more selected from the positive electrode and the negative electrode are dry electrodes according to the dry electrode manufacturing method of the present invention. Preferably, the lithium secondary battery may comprise a dry electrode, a separator, and an electrolyte according to the dry electrode manufacturing method of the present invention.

[0171] The separator according to one embodiment of the present invention separates the positive and negative electrodes and provides a pathway for the movement of lithium ions. It can be used without special limitations as long as it is used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0172] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0173] Specifically, the electrolyte may include an organic solvent and a lithium salt. The organic solvent may be used without special limitations as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0174] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0175] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, 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, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 10.0 weight% based on the total weight of the electrolyte.

[0176] In addition, since the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0177] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0178] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0179]

[0180] Examples

[0181] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0182] Example 1: Preparation of powder for electrodes

[0183] 95.5 wt% of LFP oxide as the positive active material, 0.5 wt% of activated carbon as the conductive material, and 4.0 wt% of polytetrafluoroethylene (PTFE) as the binder were introduced into a mixer, and a composite composition was prepared by mixing at 500 rpm for 3 minutes and at 1500 rpm for 5 minutes.

[0184] The above composite composition was fed into a kneader to produce a mixed aggregate at a temperature of 180°C and a speed of 100 rpm. The above mixed aggregate was fed into a grinding mill and ground under conditions of a rotor of 3000 rpm and a ring blower of 30 Hz to produce a powder for electrodes.

[0185]

[0186] Example 2: Preparation of powder for electrodes

[0187] A composite composition identical to that of Example 1 was fed into a kneader and mixed at a speed of 40 rpm for 15 minutes to produce a mixed aggregate, and the mixed aggregate was fed into an impact mill and ground at a speed of 5000 rpm to produce a powder for electrodes.

[0188]

[0189] Comparative Example 1: Preparation of powder for electrodes

[0190] A powder for electrodes was prepared by mixing the same composite composition as in Example 1 in a mixer for 2 hours without undergoing a separate kneading and grinding process.

[0191]

[0192] Comparative Example 2: Preparation of powder for electrodes

[0193] A composite composition identical to that of Example 1 was fed into a kneader and mixed at a temperature of 180°C and a speed of 160 rpm to produce a mixed aggregate, and the mixed aggregate was fed into an impact mill and ground at a speed of 10,000 rpm to produce a powder for electrodes.

[0194]

[0195] Comparative Example 3: Preparation of powder for electrodes

[0196] A composite composition identical to that of Example 1 was fed into a kneader and mixed at a temperature of 180°C and a speed of 160 rpm to produce a mixed aggregate, and the mixed aggregate was fed into a grinding mill and ground under conditions of a rotor of 3000 rpm and a ring blower of 30 Hz to produce a powder for electrodes.

[0197]

[0198] Comparative Example 4: Preparation of powder for electrodes

[0199] A composite composition identical to that of Example 1 was fed into a kneader and mixed at a speed of 40 rpm for 30 minutes to produce a mixed aggregate, and the mixed aggregate was fed into an impact mill and ground at a speed of 10,000 rpm to produce a powder for electrodes.

[0200]

[0201] The content, mixing conditions, and grinding conditions of the mixed powders of Examples 1 and 2 and Comparative Examples 1 to 4 are summarized and shown in Table 1 below.

[0202] Mixed Powder Content Mixing Condition Grinding Condition Active Material Conductive Material Binder Temperature (°C) Rotation Speed ​​(rpm) Rotation Speed ​​(rpm) Example 1 95.50.54 180 100 3,000 Example 2 95.50.54 180 40 5,000 Comparative Example 1 95.50.54 --- Comparative Example 2 95.50.54 180 160 10,000 Comparative Example 3 95.50.54 180 160 3,000 Comparative Example 4 95.50.54 180 40 10,000

[0203] Experimental Example 1: Measurement of characteristics of electrode powder

[0204] For the following items, the physical properties of the electrode powders of the above examples and comparative examples were measured in the following manner.

[0205] 1) Degree of crystallinity of binder: 9 mg of the electrode powder prepared in Examples 1–2 and Comparative Examples 1–4 was placed in a Differential Scanning Calorimeter (DSC), and the melting point (Tm) and heat of fusion (ΔHm) were measured while increasing the temperature from 30°C to 360°C at a rate of 10°C / min under a nitrogen atmosphere, and calculated according to Equation 1 below. Meanwhile, the 100% crystallization heat of the PTFE binder (ΔHm o ) was set to 85.4J / g.

[0206] [Equation 1]

[0207] Binder crystallinity (%) = (ΔHm / ΔHm o ) x 100

[0208] The calculation results are shown in Table 2 below.

[0209] 2) Average particle size (D 50 In the present invention, "average particle size D50" refers to the particle size corresponding to 50% of the volume cumulative amount of the volume cumulative particle size distribution of the powder to be measured, and can be measured using the laser diffraction method. For example, the powder to be measured can be measured by dispersing it in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Mastersizer 3000, Malvern), irradiating it with ultrasound of approximately 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then determining the particle size corresponding to 50% of the volume cumulative amount. The measurement results are shown in Table 2 below.

[0210] 3) Tap density: The electrode powders prepared in Examples 1-2 and Comparative Examples 1-4 were placed in a powder measuring instrument (Powderpro A1, Better size instrument Co.) and the density was measured after 1250 tappings.

[0211] 4) Sphericity: The electrode powders prepared in Examples 1–2 and Comparative Examples 1–4 were sieved and dispersed using a particle shape analyzer (Morphologies 4, Malvern), and the particle size was the volume-cumulative average particle size (D 50 More than 100 electrode powders of the level were selected, images of the particles were acquired to measure the circumference of the particles, and the boundary region between the electrode and the electrolyte was extracted from the images and the length of the boundary along it was measured to calculate the degree of sphericity defined by Equation 2 below.

[0212] [Equation 2]

[0213] Circularity = CE perimeter / Perimeter

[0214] (CE perimeter = the circumference of a circle with the same area as the particle, Perimeter = the circumference measured along the actual boundary of the particle)

[0215] The calculated sphericity values ​​are shown in Table 2 below.

[0216] 5) Convexity

[0217] The electrode powders prepared in Examples 1 and 2 and Comparative Examples 1 to 4 were sieved and dispersed using a particle shape analyzer (Morphologies 4, Malvern), and the particle size was the volume-cumulative average particle size (D 50 More than 100 electrode powders of the level were selected, images of the particles were acquired to measure the length of the particle's perimeter, and the Convex Hull of the particle was extracted from the image and the length of its boundary was measured to calculate the convexity defined by Equation 3 below.

[0218] [Equation 3]

[0219] Convexity = Convex Hull Perimeter / Perimeter

[0220] (Convex Hull Perimeter = the perimeter of the smallest convex polygon formed by connecting the outer points of the particle, Perimeter = the perimeter measured along the actual boundary of the particle)

[0221] The calculated convexity values ​​are shown in Table 2 below.

[0222] Binder Crystallinity (%) Particle Size D 50 (㎛) Sphericity Convexity Example 1 1.2 270 0.4 270.623 Example 2 13.8 20 20.48 90.652 Comparative Example 1 35 250 0.63 20.760 Comparative Example 2 2.1 25 50.59 20.725 Comparative Example 3 2.1 38 20.27 30.526 Comparative Example 4 4.5 236 0.80 50.783

[0223] Experimental Example 2: Measurement of film formation

[0224] The electrode powders prepared in Examples 1 and 2 and Comparative Examples 1 to 5 were sheeted in a roll-to-roll process using a calendering roll (roll diameter: 200 mm, roll temperature: 100°C, roll rotation speed ratio: 1.6) to produce an electrode composite film.

[0225] Film formation status Example 10 Example 20 Comparative Example 1X Comparative Example 2X Comparative Example 3X Comparative Example 4X

[0226] As can be seen in Table 3 above, in the case of Examples 1 and 2 manufactured using the aforementioned electrode powder manufacturing method, the sphericity and convexity ranges of the aforementioned electrode powder were satisfied and formed into a film. On the other hand, when manufacturing an electrode composite film using the electrode powders of Comparative Examples 1 to 4, it was confirmed that the film was not formed, or even if a film was manufactured, the surface was torn, making it impossible to wind into a film, and the defect rate increased.

[0227] Specifically, Comparative Example 1 is an electrode powder having an upper limit of the numerical range of convexity according to the present invention, Comparative Example 2 is an electrode powder having a convexity exceeding the upper limit of the numerical range of convexity according to the present invention, Comparative Example 3 is an electrode powder having a value less than the lower limit of the numerical range of sphericity according to the present invention, and Comparative Example 4 is an electrode powder having sphericity and convexity values ​​that both exceed the upper limit of their respective numerical ranges.

[0228] This means that the electrode powder can be manufactured without defects in the electrode manufacturing process only if it satisfies both the numerical ranges of the shape characteristics of the electrode powder particles according to the present invention, namely sphericity and convexity.

Claims

1. A powder for electrodes comprising an electrode active material, a conductive material, and a binder having a three-dimensional fiber network structure, The above electrode powder has a circularity of 0.30 to 0.65, and The above electrode powder is an electrode powder having a convexity of 0.54 to 0.

71.

2. In Claim 1, The above electrode powder is an electrode powder having a circularity of 0.38 to 0.

58.

3. In Claim 1, The above electrode powder is an electrode powder having a convexity of 0.60 to 0.

67.

4. In Claim 1, The above electrode active material is a powder for electrodes containing at least 10 weight percent of particles with a particle size of 1 μm or less relative to the electrode active material.

5. In Claim 1, The above electrode active material is a positive electrode active material, and The above positive active material is a powder for an electrode comprising a lithium composite metal compound containing one or more selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn) and iron (Fe).

6. In Claim 1, The above electrode active material is a positive electrode active material, and The above positive electrode active material is a powder for electrodes comprising a lithium metal phosphate-based compound represented by the following chemical formula 1: [Chemical Formula 1] Li 1+a [Fe 1-x M x ]PO4 In the above chemical formula 1, M comprises one or more selected from the group consisting of Mn, Co, Ni, Al, Mg, and Ti, and -0.5≤x≤0.5, 0≤y<1.

7. In Claim 1, A powder for electrodes having a crystallinity of 20% or less of the binder.

8. In Claim 1, Volume cumulative average particle size D of the above electrode powder 50 Powder for electrodes having a thickness of 150㎛ to 700㎛.

9. A first step of forming a composite composition by mixing an electrode active material, a fiberizable binder, and a conductive material; A second step of kneading the above composite composition to form a mixed aggregate containing a fiberized binder; A third step of crushing the above-mentioned mixed aggregate to form a powder for electrodes; and A fourth step of manufacturing an electrode composite film by rolling and sheet-forming the above electrode powder; comprising The above electrode powder is provided with a three-dimensional fiber network structure inside by the binder, and The above electrode powder has a circularity of 0.30 to 0.65, and The above electrode powder has a convexity of 0.54 to 0.

71. Method for manufacturing a dry electrode.

10. In Claim 9, A method for manufacturing a dry electrode, wherein the mixing in the first step is performed at a rotational speed of 100 rpm to 2,000 rpm.

11. In Claim 9, A method for manufacturing a dry electrode, wherein the mixing in the second step is performed at a rotational speed of 20 rpm to 250 rpm.

12. In Claim 9, A method for manufacturing a dry electrode, wherein the grinding in the third step is performed under conditions where the rotational speed of the grinding equipment is 1,000 rpm to 12,000 rpm.

13. A structure comprising a plurality of electrodes and a separator alternately stacked, and A lithium secondary battery, wherein at least one of the above electrodes is manufactured by the method for manufacturing a dry electrode of claim 9.

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