WO2024253470A1 - Electrochemical device comprising high-capacity positive electrode - Google Patents

Abstract

The present invention relates to an electrochemical device comprising a high-capacity positive electrode and capable of satisfying excellent battery performance, lifetime characteristics, and stability. The electrochemical device according to the present invention comprises a positive electrode, a negative electrode, and an electrolyte, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer, wherein the capacity per area of the positive electrode active material layer formed on one surface of the positive electrode current collector is 3 mAh/cm2 or more, and a lithium metal is not precipitated on the surface of the negative electrode during charging at a rate of 2.0 C.

Description

Electrochemical device containing a high-capacity cathode

The present invention relates to an electrochemical device including a high-capacity cathode.

Recently, as the energy density of batteries required has increased rapidly, the development of high-capacity lithium batteries has become urgent. To this end, research on replacing existing anode materials such as graphite or silicon with lithium metal or on anode-free batteries has been proposed, but it is difficult to meet the increasingly increasing battery performance requirements by only changing the anode material. Accordingly, in addition to changing the anode material, research on thick-film anodes with increased thickness of the anode active material layer by increasing the density/high loading of the anode active material is actively being conducted.

However, as the positive electrode active material layer becomes thicker, problems such as physical cracks or unevenness of the positive electrode material occur during the manufacturing process, and thus it is difficult to secure stable battery performance and life characteristics, so there is a practical limit to increasing the thickness.

As a specific example, the above-mentioned thick-film type positive electrode has a fundamental problem that the positive electrode material is unevenly distributed. This causes uneven flow characteristics of lithium ions, and causes problems such as uneven charge/discharge characteristics in the thickness direction and polarization phenomena. In addition, the battery performance deteriorates due to the increase in the movement distance of lithium ions as the thickness of the positive electrode increases, and furthermore, such uneven flow characteristics of lithium ions further aggravate the problem of lithium metal precipitation and dendrite formation on the surface of lithium metal, graphite, and silicon negative electrodes, which not only shortens the life of the battery, but also lowers the stability of the battery.

In addition, as the electric vehicle market has grown rapidly recently, research and development on rapid charging is being focused on shortening the charging time to make drivers more active. However, there is still a problem that when rapid charging with high current is performed, the precipitation of lithium metal and the formation of dendrites on the surface of the cathode are further accelerated, which increases the overvoltage and reduces the capacity realization rate, deteriorates the battery performance, and makes it difficult to secure the stability of the battery.

Therefore, there is an urgent need for research and development of an electrochemical device that can simultaneously secure excellent battery performance, life characteristics, and stability by effectively suppressing lithium metal precipitation, lithium plating, and lithium dendrite formation during rapid charging while including a high-capacity thick-film cathode and having high capacity realization rate and low overvoltage.

According to one aspect of the present invention, it is an object to provide an electrochemical device which exhibits excellent capacity realization rate and low overvoltage because lithium metal is not deposited on the surface of a cathode even during high-speed charging, and can simultaneously satisfy excellent battery performance, high energy density, life characteristics, and stability.

The tasks of the present invention are not limited to the above-described contents. Those with ordinary knowledge in the technical field to which the present invention belongs will have no difficulty in understanding additional tasks of the present invention from the overall contents of this specification.

An electrochemical device according to one embodiment of the present invention comprises a cathode, an anode, and an electrolyte, wherein the cathode comprises a cathode current collector and a cathode active material layer, and the cathode active material layer formed on one surface of the cathode current collector has a capacity per area of 3 mAh/cm2 or more, and is characterized in that lithium metal is not deposited on the surface of the anode when charged at a charge rate of 2.0C.

An electrochemical device according to one embodiment, wherein the cathode active material layer comprises a porous binder scaffold and cathode active material particles.

In an electrochemical device according to one embodiment, the anode may have a porosity of less than 25%.

In an electrochemical device according to one embodiment, the cathode active material layer may be included in an amount of 50 wt% or more with respect to the total weight of the electrochemical device.

In an electrochemical device according to one embodiment, the positive electrode may be a thick-film positive electrode having a capacity per area of a positive electrode active material layer formed on one surface of a positive electrode current collector of 3.5 to 10 mAh/cm2.

In an electrochemical device according to one embodiment, the positive electrode active material particles may be included in an amount of 80 to 99 wt% with respect to the total weight of the positive electrode active material layer.

In an electrochemical device according to one embodiment, the negative electrode may include a negative electrode active material layer containing 50 wt% or more of a graphite-based active material.

In an electrochemical device according to one embodiment, the electrochemical device may further include a separator.

In an electrochemical device according to one embodiment, the cathode active material layer may have cathode active material particles evenly dispersed therein, and a porous binder scaffold may be present in the empty spaces between the particles.

In an electrochemical device according to one embodiment, the porous binder scaffold may be included in an amount of 0.01 to 40 parts by weight per 100 parts by weight of the cathode active material particles.

In an electrochemical device according to one embodiment, the porous binder scaffold may further include a conductive material.

In an electrochemical device according to one embodiment, when a cross-section of the positive electrode active material layer is analyzed by X-ray CT, a deviation of a conductive material concentration (C1) of a first active material layer corresponding to a point 1/3 of the thickness of the positive electrode active material layer from the boundary between the positive electrode current collector and the positive electrode active material layer, a conductive material concentration (C2) of a second active material layer corresponding to a point from the point 1/3 to the point 2/3 of the thickness of the positive electrode active material layer, and a conductive material concentration (C3) of a third active material layer from the point 2/3 of the thickness of the positive electrode active material layer to the surface may be 10% or less.

In an electrochemical device according to one embodiment, the conductive material may be one or a combination of two or more selected from the group consisting of carbon black, carbon nanotubes, and VGCF.

In an electrochemical device according to one embodiment, the porous binder scaffold may include one or two or more selected from the group consisting of a fluorine-based resin, a rubber-based material, a polyolefin-based resin, an acrylic-based resin, an imide-based resin, and a cellulose-based resin.

In an electrochemical device according to one embodiment, the positive electrode active material layer may further include a metal salt.

In an electrochemical device according to one embodiment, the metal salt may be included in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of the positive electrode active material particles.

In an electrochemical device according to one embodiment, the metal salt may be contained in or surface-adsorbed in at least one of a porous binder scaffold and positive electrode active material particles.

In an electrochemical device according to one embodiment, the metal salt may be a sulfonyl group-containing metal salt selected from the following chemical formula 1 or chemical formula 2.

[Chemical Formula 1]

[Chemical formula 2]

In the above chemical formulas 1 and 2,

n is 1 or 2;

A is a cation of valence n;

R ₁ to R ₃ are each independently a fluoro(C1-C7) alkyl or a fluoro group.

In an electrochemical device according to one embodiment, A may be lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium or calcium.

In an electrochemical device according to one embodiment, the electrochemical device may have a 0.1C discharge capacity realization ratio relative to the design capacity of 0.9 or more.

In an electrochemical device according to one embodiment, the anode may have an electrode tortuosity (τ) of 10 or less, calculated by the following relationship.

[Relationship]

τ (Tortuosity) = (K _electrolyte /K _electrode )×(Porosity)

(In the above formula, K _electrolyte represents the ionic conductivity of the electrolyte, K _electrode represents the ionic conductivity of the anode, and Porosity represents the porosity of the anode.)

In an electrochemical device according to one embodiment, the electrochemical device may have a capacity realization rate of 90% or more according to a charge rate of 1.5 C-rate.

An electrochemical device according to one embodiment of the present invention comprises a high-capacity thick-film cathode in which a cathode material is uniformly distributed, and can satisfy excellent life characteristics and stability at the same time. Specifically, the electrochemical device according to one embodiment can effectively suppress the occurrence of a polarization phenomenon even when a thick-film type cathode is employed, and can implement uniform charge/discharge characteristics. In addition, the electrochemical device does not cause lithium metal to be precipitated on the surface of the anode even when fast-charging with a current amount twice or more of its self-capacity, and exhibits excellent capacity implementation rate and low overvoltage, so that stability and life characteristics can be secured at the same time.

Unless otherwise defined, technical and scientific terms used in this specification have the meaning commonly understood by a person of ordinary skill in the art to which this invention belongs, and descriptions of well-known functions and configurations that may unnecessarily obscure the gist of the present invention in the following description or accompanying drawings are omitted.

The embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art. Therefore, the scope of the present invention is not limited to the embodiments described below.

The terminology used in the description of the present invention is for the purpose of describing embodiments of the present invention only and should not be taken to be limiting. Unless clearly used otherwise, the singular form includes the plural form.

The term "comprises," as used herein, is an open-ended description equivalent to the expressions "comprises," "contains," "has," or "characterized by," and does not exclude additional elements, materials, or processes not listed herein.

Units used herein, unless otherwise specified, are based on weight, and as an example, units of % or ratio mean weight% or weight ratio, and weight% means the weight % that any one component occupies in the composition among the entire composition, unless otherwise defined.

In addition, the numerical range used in this specification includes the lower and upper limits and all values within that range, the increments logically derived from the shape and width of the defined range, all doubly defined values, and all possible combinations of the upper and lower limits of the numerical range defined in different shapes. Unless otherwise specifically defined herein, values outside the numerical range that may arise due to experimental error or rounding of values are also included in the defined numerical range.

In this specification, terms such as ‘top’, ‘upper part’, ‘top surface’, ‘bottom’, ‘lower part’, ‘bottom’, and ‘side’ are based on the drawings, and may actually vary depending on the direction in which elements or components are arranged.

Additionally, throughout the specification, when we say that a part is 'connected' to another part, this includes not only cases where it is 'directly connected', but also cases where it is 'indirectly connected' with other elements in between.

In this specification, the present invention is described in detail through each embodiment according to the present invention, but each embodiment described in the specification should be considered not only to mean one embodiment but also to mean a combination with other embodiments. Therefore, the citation of a claim in the scope of the patent claims is only an example, and the technical idea of the present invention should not be interpreted only as a combination with the cited claim, and a combination with various claims is also included in the scope of the technical idea of the present invention.

The term "porous binder scaffold" as used herein refers to a structure in which a mesh structure is uniformly formed three-dimensionally by a binder, in which the binder forms a framework and pores are abundantly developed within the framework. The pores preferably have an open pore structure, and the porous mesh structure formed by the binder can act as a support in which positive electrode active material particles and a conductive material can be evenly distributed. The pores may have a diameter of 0.1 ㎛ to 50 ㎛, and specifically, may have a diameter of 0.5 ㎛ to 10 ㎛. More specifically, the porous binder scaffold may be a support including fibers formed by self-assembly of an organic binder and a conductive material as a unit structure, and including a thin inner wall structure formed by secondary self-assembly of the fibrous unit structure. In other words, the binder scaffold is an open-cell foam formed by the inner wall structure, and the inner space can be partitioned by the inner wall structure. More specifically, the inner wall structure can be a porous inner wall, and the inner space can include a large number of pores compared to the pores formed in the inner wall structure. Positive active material particles can be positioned in the inner space. More specifically, the positive active material particles can be positioned in the inner space and be fixed by contact with the porous inner wall structure. The binder scaffold structure can form a conductive network superior to a fibrous mesh structure, and can have excellent adhesion to the positive active material particles.

In order to meet the performance requirements of next-generation lithium batteries, it is necessary to replace the existing anode material with lithium metal or make it anode-free, and in addition, to increase the thickness of the anode active material layer by increasing the density/high loading of the anode active material to combine it with a thick film anode to further increase the capacity.

However, in the case of a thick-film positive electrode in which the thickness of the positive electrode active material layer is increased by making the positive electrode active material dense/loaded, as the thickness of the positive electrode active material layer increases, the components constituting the positive electrode active material layer are distributed unevenly, which easily causes cracks to occur on the surface during the positive electrode manufacturing process, and the transfer of lithium ions in the positive electrode active material layer is not smooth, which reduces the output performance, lifespan, and safety of the electrochemical device. In addition, an electrochemical device including such a conventional thick-film positive electrode still has a problem in that lithium metal precipitation and dendrite formation on the negative electrode surface are further accelerated during rapid charging accompanied by high current.

The present invention has solved the problems of the prior art as described above, and an electrochemical device according to one embodiment of the present invention includes a thick-film type high-capacity cathode, and exhibits excellent capacity realization rate and low overvoltage by effectively suppressing lithium precipitation at a high charge rate, and can simultaneously satisfy excellent battery performance, high energy density, life characteristics, and stability.

According to one embodiment of the present invention, an electrochemical device includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode collector and a positive electrode active material layer, and the positive electrode active material layer formed on one surface of the positive electrode collector has a capacity per area of 3 mAh/cm2 or more, and is characterized in that lithium metal is not deposited on the surface of the negative electrode when charged at a charge rate of 2.0 C. At this time, whether lithium metal is deposited can be determined through direct observation with the naked eye or indirect observation using an optical microscope (or a scanning electron microscope). Alternatively, whether lithium metal is deposited can be determined through the negative electrode potential during the charging process when charging and discharging under constant current (CC) conditions. If the negative electrode potential drops below 0 V, it is considered that lithium plating has occurred, and in contrast, if it is above 0 V, it can be determined that lithium plating has not occurred.

Specifically, the positive electrode may have a capacity per area of a positive electrode active material layer formed on one surface of a positive electrode current collector of 3 mAh/cm ² or more, 3.5 mAh/cm ² or more, and, but not limited to, 15 mAh/cm ² or less, and may be a thick film positive electrode having a capacity of 3 to 15 mAh/cm ² , 3.5 to 10 mAh/cm ² , 3.5 to 9 mAh/cm ² , or 3.8 to 8 mAh/cm ² .

According to one embodiment, the electrochemical device may include a cathode active material layer in an amount of 50 wt% or more, 55 wt% or more, or 60 wt% or more, or 95 wt% or less, or 90 wt% or less, or 88 wt% or less, or 50 to 90 wt%, or 60 to 90 wt%, or 60 to 85 wt%, based on the total weight.

Additionally, the positive electrode active material particles may be included in an amount of 70 to 99 wt%, 80 to 99 wt%, or 85 to 99 wt% with respect to the total weight of the positive electrode active material layer.

In addition, the positive electrode may have a positive electrode active material layer thickness of 50 ㎛ or more, or 100 ㎛ or more, or 200 ㎛ or more, or 2,000 ㎛ or less, or 1,500 ㎛ or less, or 1,000 ㎛ or less, and may be a thick-film positive electrode having a thickness of 150 to 2,000 ㎛, or 100 to 2,000 ㎛, or 100 to 1,000 ㎛, or 100 to 500 ㎛, or 200 to 500 ㎛.

Additionally, the positive electrode may be a thick-film positive electrode having a positive electrode active material layer composite density (g/cc) of 2.0 to 4.5, or 3.0 to 4.0, or 3.2 to 4.0.

In addition, the electrode may have an electrode tortuosity ( τ ) calculated by the following relationship of 10 or less, 9 or less, 8 or less, 7 or less, or 6 or less, and may be, but is not limited to, 1 or more. Specifically, the electrode tortuosity may be 1 to 10, 2 to 9, 3 to 8, 4 to 7, or 5 to 6.

[Relationship]

τ (Tortuosity) = (K _electrolyte /K _electrode )×(Porosity)

In the above formula, K _electrolyte represents the ionic conductivity of the electrolyte, K _electrode represents the ionic conductivity of the anode, and Porosity represents the porosity of the anode.

An electrochemical device including such a cathode has excellent ion conductivity due to a relatively short ion transfer path within the electrode, and can have excellent battery performance, for example, excellent rate characteristics.

Specifically, the electrochemical device according to one embodiment may have a capacity realization rate according to a charge rate of 1.5 C-rate of 89.5% or more, 90% or more, 90.5% or more, 91% or more, and, but not limited to, 99.9% or less. Here, the capacity realization rate according to the charge rate means the percentage of the discharge capacity according to the charge rate divided by the initial discharge capacity.

In addition, the electrochemical device according to one embodiment may have a 0.1C discharge capacity implementation ratio relative to the design capacity of 0.8 or more, 0.85 or more, 0.9 or more, 0.95 or more, and may be from 0.8 to 1.0, or from 0.9 to 1.0, or from 0.95 to 1.0. Here, the design capacity means a theoretical value calculated from the total weight of the positive active material included in the cell and the reversible discharge capacity of the positive active material.

The anode according to one embodiment may have a porosity of less than 25%, less than or equal to 20%, less than or equal to 15%, and, but not limited to, greater than or equal to 10%, specifically greater than or equal to 10% and less than 25%, from 15 to 24% or from 15 to 20%.

The above "porosity" means the ratio of the volume occupied by pores to the total volume in a certain structure, and uses its unit vol%, and can be used interchangeably with terms such as porosity, porosity, etc. The measurement of porosity is not particularly limited. For example, it can be measured by the BET (Brunauer-Emmett-Teller) measurement method using nitrogen gas or the mercury penetration method (Hg porosimeter) and ASTM D-2873. Alternatively, the true density of the anode can be calculated from the density (apparent density) of the anode and the composition ratio of materials included in the anode and the density of each component, and the porosity of the anode can be calculated from the difference between the apparent density and the true density (net density).

That is, the positive electrode active material layer according to one embodiment does not generate cracks at all even though it is high-density/high-loaded, and the positive electrode material can be very evenly distributed in the thickness direction, and the uniform flow characteristics of lithium ions and uniform charge/discharge characteristics in the thickness direction can be effectively maintained.

The above positive electrode active material layer may include a porous binder scaffold and positive electrode active material particles.

Here, the porous binder scaffold means a mesh structure in which the binder forms a skeleton and pores are richly developed within the skeleton, and the porous mesh structure can serve as a support in which positive electrode materials such as positive electrode active material particles and conductive materials can be evenly distributed. That is, in the positive electrode according to one embodiment, cracks do not occur even when the positive electrode is thickened by making the binder component microporous, and the positive electrode material is very evenly distributed, so that excellent battery performance can be maintained.

According to one embodiment, a cathode active material layer can realize excellent mechanical properties even using a small amount of binder since the binder forms a porous scaffold structure, and thus the content of cathode active material particles can be further increased, thereby realizing an even better energy density.

According to one embodiment, the porous binder scaffold may be included in an amount of 0.01 to 40 parts by weight, or 0.01 to 20 parts by weight, or 0.01 to 10 parts by weight, or 0.01 to 5 parts by weight, or 0.01 to 1 part by weight, relative to 100 parts by weight of the positive electrode active material particles.

The above porous binder scaffold may be any polymer binder commonly used in the relevant technical field, and either an aqueous polymer binder or a non-aqueous polymer binder may be used. Specifically, the polymer binder may be a fluorine-based resin, a rubber-based material, a polyolefin-based resin, an acrylic resin, an imide-based resin, a cellulose-based resin, or the like. More specifically, the polymer binder is selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, polyvinylpyrrolidone, polyacrylonitrile, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyvinylacetate, ethylene-co-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile styrene butadiene copolymer, polyimide, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, Examples include, but are not limited to, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluoroelastomer, or mixtures thereof.

The above cathode active material particles may use a compound capable of reversibly intercalating and deintercalating lithium (lithiated intercalation compound).

Specifically, one or more of a composite oxide of a metal selected from cobalt, manganese, nickel, and combinations thereof and lithium may be used, and a specific example thereof may be a compound represented by one of the following chemical formulas.

Li _a A _1-b B _b D ₂ (wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li _a E _1-b B _b O _2-c D _c (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _2-b B _b O 4 _-c D _c (wherein 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _1-bc Co _b B _c D _α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α T _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Co _b B _c O _2-α T ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b B _c O _2-α T _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _1-bc Mn _b B _c O _2-α T ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (wherein 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); LiV ₂ O ₅ ; LiIO ₂ ; and LiNiVO ₄ ; In the above chemical formulas, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn or a combination thereof; T is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; and J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

Additionally, the positive electrode active material layer according to one embodiment may further include a conductive material, in which case the conductive material may be contained or adsorbed in the porous binder scaffold.

The above conductive material is not particularly limited as long as it is commonly used in the relevant technical field, but as a non-limiting example, it may be a carbon-based conductive material, and the carbon-based conductive material may include a point-shaped carbon-based conductive material, a linear carbon-based conductive material, a plate-shaped carbon-based conductive material, or a mixture thereof. The point-shaped carbon-based conductive material may include acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon black, etc., the linear carbon-based conductive material may include carbon nanotubes, conductive carbon fibers, etc., and the plate-shaped carbon-based conductive material may include graphene, etc.

According to one embodiment, the above-described challenging material may be one or a combination of two or more selected from the group consisting of carbon black, carbon nanotubes, and VGCF (Vapor Grown Carbon Fiber, VGCF).

In addition, the positive electrode active material layer according to one embodiment may further include a metal salt, and the metal salt may be contained in or surface-adsorbed to at least one of the porous binder scaffold and the positive electrode active material particles. Specifically, the metal ion of the metal salt may be a metal ion (active ion) involved in an electrochemical reaction, and the salt may induce effective complexation of the carbon-based conductive material and the binder, and may remain contained in or surface-adsorbed to at least one of the porous binder scaffold structure and the positive electrode active material, and may remain in a crystal phase unique to the salt.

The metal salt may be included in an amount of 0.01 to 50 parts by weight, or 0.01 to 30 parts by weight, or 0.01 to 10 parts by weight, or 0.01 to 10 parts by weight, or 0.01 to 1 part by weight, based on 100 parts by weight of the positive electrode active material particles.

In addition, the weight ratio of the binder: metal salt is not particularly limited, but may be 1:0.1 to 1, 1:0.1 to 0.8, or 1:0.2 to 0.6.

The above metal salt may be a metal salt containing a sulfonyl group, in which case it may remain in the positive electrode to further improve the electrochemical properties of the positive electrode and further improve wettability with respect to a liquid electrolyte.

The molecular weight (g/mole) of the above sulfonyl group-containing metal salt may be 1000 or less, specifically 500 or less, more specifically 400 or less, and may have a molecular weight of 20 or more, 50 or more, or 100 or more. In addition, the number of anions per molecule of the above sulfonyl group-containing metal salt may be 1 to 4, specifically 1 to 3, more specifically 1 to 2.

Specifically, the metal salt may be selected from the following chemical formula 1 or chemical formula 2, but is not limited thereto.

[Chemical Formula 1]

[Chemical formula 2]

(In the above chemical formulas 1 and 2,

n is 1 or 2;

A is a cation of valence n;

R ₁ to R ₃ are each independently a fluoro(C1-C7) alkyl or a fluoro group.)

For example, R ₁ to R ₃ can each independently be F, CFH ₂ , CF ₂ H, CF ₃ , C ₂ F ₅ , C ₃ F ₇ , C ₄ F ₉ or C ₅ H ₁₁ .

For example, the above A is a monovalent cation or a divalent cation, and the monovalent cation may be an alkali metal ion, and the divalent cation may be an alkaline earth metal ion or a post-transition metal ion. may be selected. Specifically, the A may be lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium or calcium.

For example, the sulfonyl group-containing metal salt may be one or more selected from lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(perfluoroethanesulfonyl)imide, zinc trifluoromethanesulfonate, zinc di[bis(trifluoromethylsulfonyl)imide], and the like.

When a cross-section of the positive electrode active material layer according to one embodiment is analyzed by X-ray CT, the deviation of the conductive material concentration (C ₁ ) of the first active material layer corresponding to 1/3 of the thickness direction of the positive electrode active material layer from the boundary between the positive electrode current collector and the positive electrode active material layer, the conductive material concentration (C ₂ ) of the second active material layer corresponding to 1/3 to 2/3 of the thickness direction of the positive electrode active material layer, and the conductive material concentration (C ₃ ) of the third active material layer from 2/3 of the thickness direction of the positive _electrode active material layer to the surface may be 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 1% or less, and, but not limited to, 0.1% or more. Specifically, the deviation may be 0.1 to 10%, 0.1 to 7%, or 0.1 to 3%.

That is, the positive electrode active material layer is characterized by a positive electrode material such as a conductive material and positive electrode active material particles being very uniformly distributed in the thickness direction as the thickness of the positive electrode active material layer increases by forming a porous binder scaffold by microporousizing the binder component.

The above cathode is not particularly limited as long as it is commonly used in electrochemical devices.

In one embodiment, the negative electrode includes a negative electrode active material layer containing a negative electrode active material, and the negative electrode active material may be a material commonly used in a negative electrode of a lithium secondary battery. Specifically, the negative electrode active material may be a material capable of lithium intercalation. More specifically, the negative electrode active material may be one or more selected from, but is not limited to, lithium (metallic lithium), graphitizable carbon, non-graphitizable carbon, graphite, silicon, Sn alloy, Si alloy, Sn oxide, Si oxide, Ti oxide, Ni oxide, Fe oxide (FeO), lithium-titanium oxide (LiTiO ₂ , Li ₄ Ti ₅ O ₁₂ ), mixtures thereof, or composites thereof.

According to one embodiment, the negative electrode may include a negative electrode active material layer containing 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, and not limited to 99 wt% or less of a graphite-based active material, specifically 50 to 99 wt%, 60 to 99 wt%, 70 to 99 wt%, 80 to 99 wt%, or 90 to 99 wt%.

At this time, the graphite-based active material may be artificial graphite or natural graphite. As a non-limiting example, the graphite-based active material may be natural graphite.

According to another embodiment, the negative electrode may include a negative current collector, or a negative current collector and lithium metal.

That is, an electrochemical device according to one embodiment may be a lithium metal battery including the above-described thick-film positive electrode; a negative electrode including a negative electrode current collector and lithium metal formed on the negative electrode current collector; and an electrolyte.

In addition, an electrochemical device according to one embodiment may be an anode-free lithium battery including the above-described thick-film positive electrode; a negative electrode current collector; and an electrolyte.

The above positive and negative electrodes may be provided by forming the positive active material layer and the negative active material layer on a positive current collector and a negative current collector, respectively. The positive current collector and the negative current collector may be any positive current collector or negative current collector used in a typical lithium secondary battery. In detail, the positive current collector or the negative current collector may be any material that has excellent conductivity and is chemically stable during charge and discharge of the battery. Specifically, the positive current collector or the negative current collector may be any material that is conductive, such as graphite, graphene, titanium, copper, platinum, aluminum, nickel, silver, gold, aluminum, or carbon nanotubes, but the present invention is not limited thereto.

The above electrolyte may be a liquid electrolyte, a solid electrolyte or a combination thereof, and specifically may be a liquid electrolyte, and the liquid electrolyte may include a non-aqueous organic solvent and a lithium salt.

The above non-aqueous organic solvent may be selected from a cyclic carbonate solvent, a linear carbonate solvent, and a mixed solvent thereof, and the cyclic carbonate solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and mixtures thereof, and the linear carbonate solvent may be selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, and mixtures thereof. Specifically, the non-aqueous organic solvent may be a mixed solvent of a cyclic carbonate solvent and a linear carbonate solvent, and a mixing volume ratio of the cyclic carbonate solvent: linear carbonate solvent may be mixed and used in a volume ratio of 1:1 to 9, or 1:1 to 4.

The lithium salt may be one or a mixture of two or more selected from the group consisting of LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ , LiN(SO ₃ CF ₃ ) ₂ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiCl and LiI, but is not limited thereto. The concentration of the lithium salt may be included in a range of 0.6 M to 2.0 M.

For example, the liquid electrolyte may have a ratio of the amount of electrolyte injected to the capacity of the electrochemical device according to one embodiment (g/Ah) of less than 3.0, less than 2.0, less than 1.5, less than 1.2, or less than 1.1. In addition, the liquid electrolyte may be included in a weight ratio of 15 to 30, or a weight ratio of 15 to 25, or a weight ratio of 15 to 20, with respect to 100 parts by weight of the positive electrode.

That is, the positive electrode of the electrochemical device according to one embodiment has excellent wettability with respect to the electrolyte, so that the amount of electrolyte used can be reduced while realizing a further improved energy density.

In addition, the electrochemical device according to one embodiment may further include a separator, and the separator is not limited to one commonly used in the relevant technical field, but as a non-limiting example, for example, may be selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene or a combination thereof, may be in the form of a non-woven fabric or a woven fabric, and may optionally be used in a single-layer or multi-layer structure.

According to one embodiment of the present invention, the means for forming a porous binder scaffold by microporousing the binder component is not particularly limited, but may be, for example, using a pore former when preparing a cathode material slurry, and the pore former may be, for example, a mixed solvent of two or more having different solubility parameters, a metal salt, or a combination thereof.

The above mixed solvent may be, specifically, a mixed solvent of a first solvent and a second solvent having different solubility parameters, and the first solvent and the second solvent may have different solubilities with respect to the binder due to the different solubility parameters. Due to the different solubilities between the solvents, solidification of the binder may occur in a state where the solvent remains during the drying process of the cathode material slurry, and porosity of the binder component may occur in the cathode due to volatilization of the residual solvent during and/or after solidification of the binder.

The difference in the solubility parameters between the first solvent and the second solvent may be 0.1 to 20, or 0.1 to 10, or 0.1 to 5, or 1 to 5, and specifically, may be 0.5 or more, 1 or more, 2 or more, 3 or more, or 4 or more, and may be 15 or less, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, or 5 or less.

Here, the solubility parameter (based on 25°C) may be based on a known value through the Hansen solubility parameter for each substance (e.g., Charles Hansen, "Hansen Solubility Parameters: A User's Handbook" CRC Press (2007), "The CRC Handbook and Solubility Parameters and Cohesion Parameters," Allan F. M. Barton (1999)), etc.) or a value calculated by commercial software such as Molecular Modeling Pro or Dynacomp Software, and the Hansen solubility parameter for each substance is a value that is already known to those skilled in the art or can be easily calculated.

For example, when a solvent having excellent solubility in the binder is referred to as a first solvent and a solvent having poor solubility in the binder is referred to as a second solvent, the second solvent can act as a pore former, and the degree of porosity of the binder can be controlled by controlling the relative amounts of the first solvent and the second solvent. For example, the weight ratio of the first solvent to the second solvent can be 1:0.1 to 10, 1:0.1 to 5, 1:0.1 to 1, or 1:0.1 to 0.5, but is not necessarily limited thereto.

According to one embodiment of the present invention, a method for manufacturing an electrochemical device is provided, comprising a positive electrode, an negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode collector and a positive electrode active material layer, and a positive electrode active material layer formed on one surface of the positive electrode collector has a capacity per area of 3 mAh/cm2 or more, and lithium metal is not deposited on the surface of the negative electrode when charged at a charge rate of 2.0C.

According to one embodiment, the method for manufacturing the electrochemical device includes the steps of manufacturing a positive electrode including a current collector and a positive electrode active material layer on the current collector; the step of manufacturing a negative electrode; the step of assembling the positive electrode and the negative electrode; and the step of injecting an electrolyte. Since the positive electrode, the negative electrode, and the electrolyte are the same as those described above, a detailed description thereof will be omitted.

According to one embodiment, the step of manufacturing the positive electrode may include a step of applying a positive electrode slurry including the positive electrode active material particles, a conductive material, a binder, and a metal salt as described above onto a current collector; and a step of drying the applied positive electrode slurry.

The application of the cathode slurry may be performed by one or more methods selected from spin coating, roll coating, spray coating, dip coating, flow coating, doctor blade, dispensing, inkjet printing, offset printing, stencil printing, screen printing, pad printing, gravure printing, reverse gravure printing, gravure offset printing, flexography printing, stencil printing, imprinting, xerography, slot die coating, bar coating, and roll-to-roll coating, but is not limited thereto.

After the application of the cathode slurry is performed, a step of drying the slurry application (the applied cathode slurry) can be performed. The drying can be performed by applying energy, or can be performed through natural drying or vacuum drying without separately applying energy. The applied energy can be thermal energy, light energy, or thermal and light energy, and the application of thermal and light energy can include sequential application or simultaneous application. When light energy is applied, the light can be near-infrared light, which is a heat ray.

The above drying can be performed in a multi-stage manner, and the drying method of each stage can be the same or different. As a non-limiting example, hot air drying can be performed first, followed by vacuum drying second.

The above drying temperature is not particularly limited as long as it is a temperature capable of drying the cathode material slurry. As a non-limiting example, the drying temperature may be performed at a temperature of 90 to 180° C., 100 to 160° C., 100 to 140° C., or 100 to 130° C. The drying time may be appropriately adjusted in proportion to the amount of the cathode material slurry applied.

The cathode material slurry can be prepared by mixing the cathode active material particles, the conductive material, the organic binder, and the ionic material described above in the mixed solvent described above. When preparing the cathode material slurry, the order of adding the cathode active material particles, the conductive material, the organic binder, and the ionic material is not particularly limited. For example, the cathode material slurry can be prepared by simultaneously adding and mixing the cathode active material particles, the conductive material, the organic binder, and the ionic material to the solvent. As another example, the cathode material slurry can be prepared by first adding the cathode active material particles to a mixture in which the conductive material, the organic binder, and the ionic material are mixed. The cathode material slurry prepared in this way can form a more stable porous binder scaffold structure when dried later to form a cathode active material layer.

In one embodiment, the cathode material slurry preparation step may include a step of preparing an active material mixture by mixing an ionic material (metal salt) and cathode active material particles, a step of mixing the active material mixture, a conductive material, and a binder into the cathode material mixture described above in the mixed solvent.

The step of preparing the above active material mixture may include a step of mixing an ionic material and positive electrode active material particles and then calcining them.

The above mixing may mean mechanical mixing through a stirring device such as a rotary mixer, and the mixing speed (rpm) and mixing time may be appropriately adjusted according to the amount of ionic material and positive electrode active material particles introduced.

The above-mentioned calcination can be performed at a temperature below the melting point of the ionic material, and is not particularly limited as long as it is a temperature higher than room temperature (20±5°C) and a temperature below the melting point (MP) of the ionic material. Non-limitingly, the temperature of the above-mentioned calcination may be 0.5 (MP) or more and less than 1 (MP), 0.5 (MP) to 0.9 (MP), or 0.6 (MP) to 0.8 (MP) with respect to the melting point (MP) of the ionic material. As a non-limiting example, when the ionic material is lithium trifluoromethanesulfonate, the above-mentioned calcination can be performed at a temperature of 150 to 300°C, 160 to 250°C, or 180 to 220°C.

Here, the heating rate during the firing may be, but is not limited to, 1 to 30°C/min, 1 to 15°C/min, 1 to 10°C/min, or 3 to 7°C/min.

The time for which the above-mentioned calcination is performed can be appropriately adjusted depending on the amount of the active material mixture introduced, and can be performed for, but not limited to, 10 to 180 minutes, 20 to 150 minutes, or 30 to 90 minutes.

Hereinafter, the present invention will be specifically described through examples. However, it should be noted that the examples described below are only intended to illustrate and concretize the present invention, and are not intended to limit the scope of the rights of the present invention. This is because the scope of the rights of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[Example 1]

1) Manufacturing of positive electrode

1 wt% of lithium trifluorometal sulfonate and 95 wt% of positive electrode active material particles having an average particle size of 5 ㎛ (LiNi _0.9 Mn _0.05 Co _0.05 O ₂ ) were pre-mixed using a rotary mixer at 2000 rpm for 3 minutes, placed in a furnace, and heated to 200 ℃ at a heating rate of 5 ℃/min, then fired by maintaining it at that temperature for 1 hour, and then naturally cooling the fired product to room temperature (25±5 ℃) to produce an active material mixture (96 wt%). The active material mixture was mixed with 2 wt% of carbon black (Super-P) having an average particle size of 40 nm as a conductive material and 2 wt% of polyvinylidene fluoride as a binder to produce a positive electrode material (total 100 wt%). A slurry of positive electrode material (total 100 wt%) was prepared by adding 60 wt% of the above-mentioned positive electrode material to a mixed solvent containing 32.5 wt% of N-methyl-2-pyrrolidone and 7.5 wt% of propylene carbonate. The positive electrode slurry was applied to a 20 ㎛ thick aluminum thin film using a doctor blade, dried with hot air at 100 ° C., vacuum-dried at 130 ° C. for 24 hours, and rolled using a roll press to prepare a positive electrode including a 55 ㎛ thick positive electrode active material layer in which positive electrode active material particles are evenly distributed within a porous binder scaffold structure.

The positive electrode active material loading of the above positive electrode was 4.1 mAh/cm2, and the composite density was 3.6 g/cc.

2) Manufacturing of cathode

A mixture of 96 wt% of natural graphite with an average particle size of 20 ㎛ as an anode active material, 1 wt% of carbon black (Super-P) with an average particle size of 40 nm as a conductive material, and 1.5 wt% of CMC (carboxymethyl cellulose) and SBR (styrene-butadiene rubber) as a binder (total 100 wt%) was used as the anode material. The anode material slurry was prepared by adding 60 wt% of the above anode material to 40 wt% of distilled water. The above anode material slurry was applied onto a 10 ㎛ thick copper thin film using a doctor blade, dried with hot air at 100 ° C., vacuum dried at 130 ° C. for 24 hours, and rolled using a roll press to prepare an anode including an 80 ㎛ thick anode active material layer.

The negative active material loading of the above negative electrode was 4.5 mAh/cm2, and the composite density was 1.65 g/cc.

3) Manufacturing of electrochemical devices

The manufactured positive and negative electrodes and separator (thickness 13 ㎛, SC13-D4-BP, Gelec) were laminated to manufacture a battery assembly, and an aluminum battery tab (0.1 T × 7 mm) was ultrasonically welded to the non-coated portion of the positive electrode assembly, and a nickel battery tab (0.1 T × 7 mm) was welded to the non-coated portion of the negative electrode assembly, respectively. Then, the battery assembly was placed in a formed battery pouch film (153 ㎛, DNP) and sealed. Thereafter, an electrochemical device was manufactured by injecting 2.72 g/Ah of a liquid electrolyte containing 1 mol of LiPF ₆ dissolved in a solvent containing ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1.

[Example 2]

In the above Example 1, an electrochemical device was manufactured in the same manner as in the above Example 1, except that lithium poly(1-ethyl-3-methylimidazolium)bis(trifluoromethanesulfonyl)imide (PVIm[TFSI]) was used instead of lithium trifluorometalsulfonate when manufacturing the positive electrode.

[Example 3]

In the above Example 1, an electrochemical device was manufactured in the same manner as in the above Example 1, except that a mixture of trimethylolpropane ethoxylate triacrylate and lithium trifluoromethanesulfonate in a 50:50 mass% mixture was used instead of lithium trifluoromethanesulfonate when manufacturing the positive electrode.

[Example 4]

An electrochemical device was manufactured in the same manner as in Example 1, except that cesium bis(trifluoromethanesulfonyl)imide was used instead of lithium trifluoromethanesulfonate when manufacturing the positive electrode.

[Comparative Example 1]

In the above Example 1, when manufacturing the positive electrode, 95 wt% of LiNi _0.9 Mn _0.05 Co _0.05 O ₂ having an average particle size of 5 μm as a positive electrode active material, 2 wt% of carbon black (Super-P) having an average particle size of 40 nm as a conductive material, and 3 wt% of polyvinylidene fluoride as a binder were mixed (total 100 wt%) to form a positive electrode material, and an electrochemical device was manufactured in the same manner as in Example 1, except that the positive electrode material was added to 40 wt% of N-methyl-2-pyrrolidone to form 60 wt% to prepare a positive electrode material slurry.

<Evaluation 1. Electrochemical device performance evaluation>

1-1. Initial efficiency (%)

The electrochemical devices of the examples and comparative examples were charged at 0.1 C-rate to 4.4 V under constant current/constant voltage (CC/CV) conditions at 25°C and then cut-off. Thereafter, they were discharged at 0.1 C-rate to 3.0 V (CC conditions). The percentage of the discharge capacity divided by the charge capacity was calculated and presented as the initial efficiency in Table 1 below. In addition, the capacity per unit area of the positive electrode was measured under 0.1C/0.1C conditions and in the voltage range of 3.0-4.4 V and presented in Table 1 below.

Referring to Table 1 above, it was confirmed that the initial efficiency of the example was higher than the initial efficiency of the comparative example. In addition, the positive electrode according to the example was confirmed to have a capacity per area of about 4 mAh/cm2 under 0.1C/0.1C conditions and a voltage range of 3.0-4.4 V.

1-2. Capacity realization rate (%) and average charging voltage (V) according to charging rate

(1) Capacity implementation rate (%)

The electrochemical devices of Examples and Comparative Examples were charged at different C-rates of 0.5, 1.0, 1.5, 2.0, and 3.0 under constant current (CC) conditions at 25°C up to 4.4 V, and then cut-off. Thereafter, they were discharged at 0.2 C-rate to 3.0 V (CC conditions). The percentage of the discharge capacity according to each charge rate divided by the initial discharge capacity was calculated to calculate the capacity realization rate according to the charge rate, and the results are shown in Table 2 below. The initial discharge capacity is obtained by charging the electrochemical device at 0.2 C-rate up to 4.4 V under the constant current/constant voltage conditions, cut-off, and then discharging at 0.2 C-rate to 3.0 V.

(2) Average charging voltage (V)

The electrochemical devices of the examples and comparative examples were charged at constant current (CC) conditions at 25°C up to 4.4 V at different C-rates of 0.5, 1.0, 1.5, 2.0, and 3.0, and then cut-off. The resulting charging graphs were integrated to calculate the charging energy, and the value obtained by dividing the charging energy by the charging capacity at each charging rate was calculated, and the average charging voltage according to the charging rate is shown in Table 3 below.

Referring to Tables 2 and 3 above, it was confirmed that the electrochemical device of the above example exhibited a higher capacity implementation rate at charge rates of 1.5, 2.0, and 3.0, and a lower overvoltage at the average charge voltage, compared to the comparative example.

1-3. Lithium-Plating Evaluation

The electrochemical devices of Examples and Comparative Examples were charged at different C-rates of 0.5, 1.0, 1.5 and 2.0 up to 4.4 V under constant current (CC) conditions at 25°C, and then cut-off was performed. The fully charged cells were disassembled, and the Li deposited on the cathode surface was observed using a scanning electron microscope. The results are shown in Table 4 below.

Referring to Table 4, in the case of the electrochemical device of the above example, compared to the comparative example, when the lithium secondary battery was evaluated at a charge rate of 2.0C, the surface of the negative electrode was observed with a scanning electron microscope and lithium was not precipitated. On the other hand, in the case of the comparative example, lithium metal was confirmed to be precipitated. Through this, it was confirmed that the electrochemical device according to the example can simultaneously implement excellent capacity implementation rate and low overvoltage compared to the comparative example at a high charge rate of 2.0C or higher. That is, it can be seen that the electrochemical device according to the present invention can maintain excellent life characteristics by suppressing the lithium precipitation phenomenon of the negative electrode during rapid charging.

As a result of the above evaluation, it was confirmed that the electrochemical device according to the present invention has high initial efficiency and exhibits excellent capacity realization at a high charging rate of 2.0C or higher, thereby realizing excellent battery performance and life characteristics.

Furthermore, the electrochemical device has uniform lithium ion flow characteristics even when charged with a current more than twice its magnetic capacity, and lithium is not deposited on the surface of the negative electrode, effectively suppressing lithium plating, thereby providing a product with improved safety.

<Evaluation 2. Bipolar property evaluation>

2-1. Bipolar porosity

The density (apparent density) of the anode was measured using a thickness gauge (equipment name: S-HITE, manufacturer: TESA) and a scale (equipment name: EX125, manufacturer: OHAUS), and the true density of the anode was calculated from the composition ratio of the materials included in the anode and the density of each component. The porosity of the anode was calculated from the difference between the apparent density and the true density (net density), which can be expressed by the following relationship, and is shown in Table 5 below.

[Relationship]

Volume of each component in the anode (cc) = measured weight of the anode (g) * composition of the material (%) / true density of the material (g/cc)

Porosity (%) = 1 - (volume of active material in positive electrode + volume of conductive material in positive electrode + volume of binder in positive electrode + volume of additive in positive electrode) / measured apparent volume of positive electrode

2-2. Bipolar Appearance Evaluation

The appearance of the surfaces of the positive electrodes manufactured in Example 1 and Comparative Example 1 was evaluated using a scanning electron microscope (SEM) analysis. In the case of the positive electrode manufactured in Comparative Example 1, it was confirmed that numerous cracks occurred on the electrode appearance due to uneven distribution of the conductive agent/binder during slurry coating and drying. On the other hand, in the case of the positive electrode of Example 1, it was confirmed that no cracks occurred on the electrode appearance because the positive electrode active material coating layer was evenly applied on the current collector without mechanical deformation and a uniform binder scaffold structure was formed in the direction of the entire electrode thickness.

In addition, when observing the cross-section of the positive electrode manufactured in Example 1 using a scanning electron microscope, it was confirmed that the positive electrode active material particles were evenly distributed throughout and that the binder formed a uniform scaffold structure in the empty spaces between the particles. On the other hand, in the case of the positive electrode manufactured in the comparative example, it was found that the binders were clumped together and had an uneven microstructure and pore distribution.

2-3. Bipolar X-ray CT analysis

The cross-sections of the positive electrodes manufactured in Example 1 and Comparative Example 1 were X-ray CT scanned to analyze the distribution of the conductive material, carbon black, in the thickness direction. It was confirmed that the positive electrode of Comparative Example 1 had an uneven distribution of the conductive material in the thickness direction. On the other hand, the positive electrode of Example 1 had a uniform distribution of the conductive material in the first active material layer corresponding to 1/3 of the thickness direction from the boundary between the positive electrode current collector and the positive electrode active material layer, the second active material layer from the 1/3 to the 2/3 point in the thickness direction, and the third active material layer from the 2/3 point in the thickness direction to the surface. In addition, the distribution of the conductive material content (vol%) in the first active material layer, the second active material layer, and the third active material layer according to the X-ray CT scan results was quantified, and the results are shown in Table 6 below. Referring to Table 6, the positive electrode according to Example 1 showed a very low value of 0.57% or less in the deviation of the conductive material concentration according to Equation 1 below, and through this, it was confirmed that the positive electrode active material layer of Example 1 had the conductive material very uniformly distributed.

[Formula 1]

(|C ₀ - C _n |/C ₀ ) × 100

In the above equation 1,

C ₀ is the average concentration (vol%) of the conductive material throughout the positive electrode active material layer;

C _n is the conductive material concentration (vol%) of the nth active material layer.

2-4. Evaluation of ionic conductivity within the anode

A symmetric cell was manufactured using the positive electrodes manufactured in the Examples and Comparative Examples, and a liquid electrolyte containing 1 mol of LiPF ₆ dissolved in a solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 was injected to manufacture a cell for measuring ionic conductivity. The ionic resistance was measured through impedance analysis of the cell for measuring ionic conductivity, and the ionic conductivity value inside the positive electrode was calculated, and the results are shown in Table 7 below.

2-5. Evaluation of the electrode tortuosity of the anode

The measured ionic conductivity values in the anode were used to calculate the electrode curvature of the anode using the MacMullin number (N _m ) formula. N _m can be defined as follows:

N _m = K _electrolyte / K _electrode = Tortuosity / Porosity

K _electrolyte refers to the ionic conductivity of the liquid electrolyte, and K _electrode refers to the ionic conductivity of the anode according to the examples and comparative examples measured at 25 ℃. The liquid electrolyte was prepared by adding 1 M LiPF ₆ to a cosolvent containing ethylene carbonate (EC)/diethyl carbonate (DEC) in a volume ratio of 1:1. The ionic conductivity of the anode was calculated by measuring the conductivity in the thickness direction of the electrode after filling the anode with a 1 M LiPF ₆ EC/DEC solution. The porosity was measured using a mercury porosimeter (Mercury Porosimet, AutoPore V, Micromeritics) according to ASTM D 4284-83. Specifically, a pre-weighed anode sample was placed in a mercury porosimeter cell, and the cell was filled with mercury up to a given pressure range (30 psia to 60,000 psia) to measure the pore volume inside the anode. The final curvature was calculated from the measured porosity and McMullin number. The measured electrode curvature is shown in Table 7 below.

As shown in Table 7 above, it was confirmed that the anode according to the example formed a uniform binder scaffold structure in the empty space between the particles, thereby reducing the curvature value within the electrode compared to the anode according to the comparative example.

Although the present invention has been described by limited embodiments, this has only been provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and those with ordinary skill in the art to which the present invention pertains can make various modifications and variations from this description. Therefore, the spirit of the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the following claims, as well as variations equivalent to the claims, are considered to fall within the scope of the spirit of the present invention.

Claims (22)

Contains a positive electrode, a negative electrode and an electrolyte, The above positive electrode includes a positive electrode current collector and a positive electrode active material layer, The capacity per area of the positive electrode active material layer formed on one side of the positive electrode current collector is 3 mAh/cm2 or more, An electrochemical device characterized in that lithium metal is not deposited on the surface of the cathode when charged at a charge rate of 2.0C. In the first paragraph, An electrochemical device, wherein the positive electrode active material layer comprises a porous binder scaffold and positive electrode active material particles. In paragraph 1, The above cathode is an electrochemical device having a porosity of less than 25%. In paragraph 1, An electrochemical device, wherein the cathode active material layer is included in an amount of 50 wt% or more based on the total weight of the electrochemical device. In paragraph 1, An electrochemical device, wherein the positive electrode is a thick film positive electrode having a capacity per area of a positive electrode active material layer formed on one surface of a positive electrode current collector of 3.5 to 10 mAh/cm2. In the second paragraph, An electrochemical device, wherein the positive electrode active material particles are included in an amount of 80 to 99 wt% based on the total weight of the positive electrode active material layer. In paragraph 1, An electrochemical device, wherein the negative electrode includes a negative electrode active material layer containing 50 wt% or more of a graphite-based active material. In paragraph 1, An electrochemical device further comprising a separator. In the second paragraph, An electrochemical device, wherein the positive electrode active material layer comprises positive electrode active material particles evenly dispersed therein, and a porous binder scaffold exists in the empty space between the particles. In the second paragraph, An electrochemical device, wherein the porous binder scaffold is included in an amount of 0.01 to 40 parts by weight based on 100 parts by weight of the positive electrode active material particles. In the second paragraph An electrochemical device, wherein the porous binder scaffold further comprises a conductive material. In the second paragraph An electrochemical device, wherein when a cross-section of the positive electrode active material layer is analyzed by X-ray CT, a deviation of a conductive material concentration (C1) of a first active material layer corresponding to a point 1/3 of the thickness of the positive electrode active material layer from the boundary between the positive electrode current collector and the positive electrode active material layer, a conductive material concentration (C2) of a second active material layer corresponding to a point from the point 1/3 to the point 2/3 of the thickness of the positive electrode active material layer, and a conductive material concentration (C3) of a third active material layer from the point 2/3 of the thickness of the positive electrode active material layer to the surface is 10% or less. In Article 11 An electrochemical device wherein the above-mentioned challenge material is one or a combination of two or more selected from the group consisting of carbon black, carbon nanotubes, and VGCF. In Article 9 An electrochemical device, wherein the porous binder scaffold comprises one or more selected from the group consisting of a fluorine-based resin, a rubber-based material, a polyolefin-based resin, an acrylic-based resin, an imide-based resin, and a cellulose-based resin. In Article 9, An electrochemical device, wherein the positive electrode active material layer further comprises a metal salt. In Article 15, An electrochemical device, wherein the metal salt is contained in an amount of 0.01 to 50 parts by weight based on 100 parts by weight of the positive electrode active material particles. In Article 15, An electrochemical device, wherein the metal salt is contained in or surface-adsorbed in at least one of a porous binder scaffold and positive electrode active material particles. In Article 15, An electrochemical device, wherein the metal salt is a sulfonyl group-containing metal salt selected from the following chemical formula 1 or chemical formula 2. [Chemical Formula 1]

[Chemical formula 2]

In the above chemical formulas 1 and 2, n is 1 or 2; A is a cation of valence n; R ₁ to R ₃ are each independently a fluoro(C1-C7) alkyl or a fluoro group. In Article 18 The above A is an electrochemical device comprising lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium or calcium. In paragraph 1, The above electrochemical device is an electrochemical device having a 0.1C discharge capacity implementation ratio of 0.9 or more compared to the design capacity. In paragraph 1, The above-mentioned positive electrode is an electrochemical device having an electrode tortuosity (τ) of 10 or less, calculated by the following relationship. [Relationship] τ (Tortuosity) = (K _electrolyte /K _electrode )×(Porosity) (In the above formula, K _electrolyte represents the ionic conductivity of the electrolyte, K _electrode represents the ionic conductivity of the anode, and Porosity represents the porosity of the anode.) In paragraph 1, The above electrochemical device is an electrochemical device having a capacity realization rate of 90% or more according to a charge rate of 1.5 C-rate.