Positive electrode and lithium battery including same

Abstract

The invention relates to a positive electrode and a lithium battery including the same. The positive electrode includes: a positive electrode active material including a lithium transition metal oxide; a conductive material; and a binder, in which the lithium transition metal oxide includes nickel and a transition metal other than nickel, in which the lithium transition metal oxide has a layered crystal structure, in which the nickel content is 30 mol% or more, and the lithium transition metal oxide has a specific surface area of 1-10 [mu] m based on the total number of moles of the transition metal of the lithium transition metal oxide. Wherein the conductive material comprises a linear carbon conductive material, the binder comprises a first binder and a second binder, the first binder comprises fluorine and a polar functional group, the second binder does not comprise fluorine, and the amount of the linear carbon conductive material is 0.1 weight percent or more. Based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

Description

[0001] This application is a divisional application of Chinese Invention Application (Invention Title: Positive Electrode and Lithium Battery Comprising the Same, Application Date: August 28, 2019; Application No.: 201910800396.0).

[0002] Cross - reference to related applications

[0003] This application claims the priority and benefits of Korean Patent Application No. 10 - 2018 - 0101564, filed on August 28, 2018 with the Korean Intellectual Property Office, and all benefits arising therefrom, the content of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present disclosure relates to a positive electrode and a lithium battery comprising the same. Background Art

[0005] Lithium batteries have been used as power sources for various high - performance applications such as electronic devices and electric vehicles. For high - performance electronic devices and electric vehicles, lithium batteries with high energy density and high capacity are required.

[0006] High - capacity positive electrode active materials can be used to provide lithium batteries with high capacity.

[0007] Although positive electrode active materials including nickel provide high discharge capacity, electrolyte side reactions can deteriorate the lifespan and thermal stability of lithium batteries.

[0008] As the loading of the positive electrode mixture increases, the discharge capacity can increase; however, the thickness of the positive electrode can also increase. A positive electrode with an increased thickness can have reduced flexibility and thus can easily crack during the winding process or the charge / discharge process in the manufacture of lithium batteries.

[0009] Therefore, there is still a need for a positive electrode including a positive electrode active material containing nickel and having an increased loading, and a battery including the same. Summary of the Invention

[0010] Provide a positive electrode having improved physical properties due to including an adhesive with a new composition and a linear carbon conductive material.

[0011] Provide a lithium battery including the positive electrode and having improved lifespan characteristics.

[0012] Provide a lithium battery having improved energy density due to including a positive electrode including a high - capacity positive electrode active material and having an increased loading.

[0013] Additional aspects will be set forth in part in the following description, and in part will be obvious from the description, or may be learned by practice of the presented embodiments.

[0014] According to an aspect of one embodiment, a positive electrode includes: a positive electrode active material including a lithium transition metal oxide; a conductive material; and a binder, wherein the lithium transition metal oxide includes nickel and a transition metal other than nickel and has a layered crystal structure, wherein the content of nickel is 30 mole percent or greater, based on the total mole number of the transition metals of the lithium transition metal oxide, wherein the conductive material includes a linear carbon conductive material, wherein the binder includes a first binder containing fluorine and a polar functional group, and a second binder not including fluorine, and wherein the amount of the linear carbon conductive material is 0.1 weight percent or greater, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

[0015] According to an aspect of another embodiment, a lithium battery includes: the positive electrode; a negative electrode; and an electrolyte disposed between the positive electrode and the negative electrode.

[0016] A method of manufacturing the positive electrode is also disclosed, the method including: providing a positive electrode active material including a lithium transition metal oxide, a conductive material, and a binder, wherein the lithium transition metal oxide includes nickel and a transition metal other than nickel, wherein the content of nickel is 30 mole percent or greater, based on the total mole number of the transition metals of the lithium transition metal oxide, and wherein the lithium transition metal oxide has a layered crystal structure, the conductive material includes a linear carbon conductive material, wherein the amount of the linear carbon conductive material is 0.1 weight percent or greater, based on the total combined weight of the positive electrode active material, the conductive material, and the binder, the binder includes a first binder containing fluorine and a polar functional group, and a second binder not including fluorine; combining the positive electrode active material, the conductive material, the binder, and a solvent to form a composition; disposing the composition on a current collector; and removing the solvent to manufacture the positive electrode.

[0017] A method of manufacturing a lithium battery is also disclosed, the method including: manufacturing a positive electrode using the above method; disposing the positive electrode on a separator and a negative electrode; and bringing the positive electrode, the separator, and the negative electrode into contact with an electrolyte to manufacture the lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] These and / or other aspects will become apparent and more readily appreciated by reference to the following description of embodiments in conjunction with the accompanying drawings, in which:

[0019] Figure 1 is a graph of three-point bending force (Newtons, N) versus displacement (millimeters, mm), which illustrates the results of a flexure (bending) performance test on positive electrodes prepared according to Example 1 and 4 and Comparative Example 1;

[0020] Figure 2It is a photograph showing the bending property of the positive electrode prepared according to Example 1;

[0021] Figure 3 It is a graph of capacity retention rate (percentage, %) against the number of cycles, which shows the evaluation results of the life characteristics at room temperature of the positive electrodes prepared according to Example 1 and Comparative Example 2;

[0022] Figure 4 It is a graph of capacity retention rate (percentage, %) against the number of cycles, which shows the evaluation results of the life characteristics at room temperature of the positive electrodes prepared according to Examples 1 and 2 and Comparative Example 3; and

[0023] Figure 5 It is a schematic diagram of an embodiment of a lithium battery. Detailed Embodiment

[0024] The embodiments will now be described in detail. Examples thereof are illustrated in the accompanying drawings, wherein like reference numerals always denote like elements. In this regard, the present embodiments may have different forms and should not be construed as limited to the description set forth herein. Accordingly, the embodiments are described below only to illustrate aspects by referring to the accompanying drawings. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Expressions such as "at least one (each) of..." modify the entire list of elements when preceding or following the list of elements, rather than modifying individual elements of the list.

[0025] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present disclosure. Expressions used in the singular include the plural expressions unless they have a distinctly different meaning in the context. Hereinafter, it will be understood that terms such as "comprising (including)" or "having" are intended to indicate the presence of features, quantities, operations, components (parts), portions, elements, materials, or combinations thereof disclosed in the specification, and are not intended to preclude the possibility that one or more other features, quantities, operations, components (parts), portions, elements, materials, or combinations thereof may exist or may be added. As used herein, a forward slash, i.e., " / ", may be interpreted as "and" or "or".

[0026] In the figures, for clarity, the thickness of layers and regions may be enlarged or reduced. Throughout the specification, like reference numerals denote like elements. Throughout the specification, it will be understood that when an element such as a layer, region, or plate is referred to as being "on" another element, it may be directly on the other element or intervening elements may also be present therebetween. It will be understood that although terms such as first, second, etc. may be used herein to describe various components (parts), these components (parts) should not be limited by these terms. These terms are only used to distinguish one component (part) from another.

[0027] In addition, relative terms such as "lower" or "bottom" and "upper" or "top" may be used herein to describe a relationship of one element to another element as shown in the figures. It will be understood that relative terms are intended to include different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in one of the figures is turned over, an element described as on the "lower" side of another element will be oriented on the "upper" side of the other element. Thus, depending on the specific orientation of the figure, the exemplary term "lower" can include both the "lower" and "upper" orientations. Similarly, if the device in one of the figures is turned over, an element described as "beneath" or "under" another element will be oriented "above" the other element. Thus, the exemplary terms "beneath" or "under" can include both above and beneath orientations.

[0028] As used herein, "about" or "approximately" includes the stated value and means within an acceptable deviation range for the specific value as determined by one of ordinary skill in the art in view of the measurements discussed and the error associated with the measurement of the specific quantity (i.e., the limitations of the measurement system). For example, "about" can mean within one or more standard deviations of the stated value, or within ±30%, 20%, 10%, or 5%.

[0029] Unless otherwise defined, all terms (including technical and scientific terms) in the specification may be defined as commonly understood by one of ordinary skill in the art. Terms defined in commonly used dictionaries may not be interpreted idealistically or exaggeratedly unless clearly defined. In addition, unless explicitly stated to the contrary, the word "comprising" will be understood to mean including the stated elements but not excluding any other elements.

[0030] The C-rate is the discharge rate of a single cell and is obtained by dividing the total capacity of the single cell by the total discharge time of 1 hour. For example, the C-rate of a battery with a discharge capacity of 1.6 ampere-hours will be 1.6 amperes.

[0031] Hereinafter, the positive electrode according to an exemplary embodiment of the present disclosure and a lithium battery including the same will be disclosed in further detail.

[0032] According to one embodiment, the positive electrode includes a positive electrode active material, a conductive material, and a binder. The positive electrode active material includes a lithium transition metal oxide containing nickel and a transition metal other than nickel and having a layered crystal structure, and the content of nickel is 30 mole percent (mol%) or more, based on the total mole number of the transition metals in the lithium transition metal oxide, that is, the total content of nickel and the transition metal other than nickel. The conductive material includes a linear carbon conductive material, and the binder includes a first binder containing fluorine and a polar functional group and a second binder not including fluorine. The amount of the linear carbon conductive material is 0.1 weight percent (wt%) or more, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

[0033] Since the positive electrode includes the linear carbon conductive material in an amount of 0.1 wt% or more and the first binder containing a polar functional group, both the adhesion strength and the flexibility are improved, thereby improving the cycle characteristics and the energy density. In addition, by including the second binder not containing fluorine, the positive electrode can have improved dispersibility of the linear carbon conductive material.

[0034] The aspect ratio of the linear carbon conductive material is 2 or greater. The linear carbon conductive material may include carbon nanotubes (CNTs), carbon nanofibers, carbon nanorods, or a combination thereof. However, embodiments are not limited thereto, and any suitable linear carbon conductive material may be used. The aspect ratio (length-to-width ratio) of the linear carbon conductive material may be 2 or greater, 3 or greater, 4 or greater, 5 or greater, 10 or greater, 20 or greater, 50 or greater, or 100 or greater, for example, about 2 to about 1,000,000, about 10 to about 100,000, or about 100 to about 10,000. When the linear carbon conductive material has such an aspect ratio, the linear carbon conductive material can be three-dimensionally dispersed in the positive electrode to form a conductive network, even when present in a small amount, such as about 3 wt% (based on the total combined weight of the positive electrode active material, the conductive material, and the binder), thereby improving the conductivity of the positive electrode. The linear carbon conductive material may be, for example, carbon nanotubes. Examples of the carbon nanotubes may include single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, rope carbon nanotubes, or a combination thereof. For example, the carbon nanotubes may have a diameter of about 5 nanometers (nm) to about 50 nm and a length of about 1 micrometer (μm) to about 50 μm. The aspect ratio of the conductive material may be the ratio of the major (larger) dimension to the minor (smaller) dimension of the conductive material. For example, the aspect ratio of the carbon nanotubes may be the ratio of the length of the carbon nanotubes to the diameter. Moreover, the amount of the linear carbon conductive material included in the positive electrode may be 0.1 wt% or greater, 0.3 wt% or greater, 0.5 wt% or greater, 0.7 wt% or greater, 0.9 wt% or greater, 1 wt% or greater, or 1.3 wt% or greater, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. For example, the amount of the linear carbon conductive material included in the positive electrode may be about 0.1 wt% to about 5 wt%, about 0.1 wt% to about 4 wt%, about 0.1 wt% to about 3 wt%, about 0.3 wt% to about 3 wt%, about 0.5 wt% to about 3 wt%, about 0.7 wt% to about 3 wt%, about 0.9 wt% to about 3 wt%, about 1 wt% to about 3 wt%, or about 1.3 wt% to about 3 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

[0035] In addition to the linear carbon conductive material, the exemplary conductive material may further include a particulate carbon conductive material. The aspect ratio of the particulate carbon conductive material may be less than about 2, less than about 1.8, or less than about 1.5. The aspect ratio of the particulate carbon conductive material may be from about 1.01 to less than about 2, from about 1.05 to about 1.8, or from about 1.1 to about 1. Examples of the particulate carbon conductive material may include carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal carbon black, natural graphite, artificial graphite, or a combination thereof. However, the embodiments are not limited thereto, and any suitable particulate carbon conductive material may also be used. The particulate carbon conductive material may be, for example, carbon black. The weight ratio of the linear carbon conductive material to the particulate carbon conductive material may be from about 90:10 to about 10:90, from about 90:10 to about 50:50, from about 90:10 to about 60:40, from about 85:15 to about 60:40, or from about 80:20 to about 60:40, based on the total weight of the linear carbon and the particulate carbon. When the weight ratio of the linear carbon conductive material to the particulate carbon conductive material is within the above range, the dispersibility of the conductive material is improved and the conductivity of the positive electrode is further improved, even when there is a small amount of the conductive material, such as about 5 wt%, thereby reducing the internal resistance.

[0036] In the positive electrode, the amount of the conductive material may be from about 0.1 wt% to about 5 wt%, from about 0.3 wt% to about 4 wt%, from about 0.5 wt% to about 4 wt%, from about 1.0 wt% to about 4 wt%, from about 1.0 wt% to about 3 wt%, from about 1 wt% to about 2.5 wt%, or from about 1.0 wt% to about 2 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. When the positive electrode includes the conductive material within the above range, the adhesion, flexibility, and conductivity of the positive electrode are further improved. As a result, the cycle characteristics of the lithium battery including the positive electrode are further improved.

[0037] The first binder containing fluorine and a polar functional group may include repeating units derived from a monomer containing a polar functional group, repeating units derived from vinylidene fluoride (1,1-difluoroethylene), and optionally repeating units derived from a fluorine-containing monomer (other than vinylidene fluoride), particularly tetrafluoroethylene (tetrafluoroethylene), hexafluoropropylene (hexafluoropropylene), chlorotrifluoroethylene (1-chloro-1,2,2-trifluoroethylene), a monomer including a fluoro vinyl group (1-fluoro vinyl group, 2-fluoro vinyl group, or a combination thereof), a perfluoroalkyl vinyl ether (C n F 2n+1 -OCF=CF2, where n = 1 - 12 or 1 - 6), or a combination thereof.

[0038] In the first binder, the polar functional group may include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, a salt thereof, or a combination thereof. However, the embodiments are not limited thereto, and any suitable polar functional group may be used in the first binder. Among the polar functional groups, for example, in terms of the adhesion property to the positive electrode active material and the adhesion property between the positive electrode active material layer and the current collector, a carboxylic acid group or a sulfonic acid group (or a salt thereof) may be selected. For example, in terms of the efficiency of capturing transition metal ions eluted from a nickel-rich lithium transition metal oxide, a carboxylic acid group may be selected.

[0039] For example, the first binder may be a copolymer of a monomer containing a polar functional group and a vinylidene fluoride monomer; or the first binder may be a copolymer of a monomer containing a polar functional group, a vinylidene fluoride monomer, and a fluorine-containing monomer other than the vinylidene fluoride monomer as described above. Examples of the first binder may include a monomer containing a polar functional group-vinylidene fluoride copolymer, a monomer containing a polar functional group-vinylidene fluoride-hexafluoropropylene copolymer, or a monomer containing a polar functional group-vinylidene fluoride-chlorotrifluoroethylene copolymer. However, these embodiments are not limited thereto, and any suitable fluorine-containing binder including a polar functional group may be used. In particular, the first binder may be a polyvinylidene fluoride (PVDF) binder including a carboxylic acid group (-COOH) (for example, a carboxyl group) or a salt thereof.

[0040] In the first binder, the amount of the optional fluorine-containing monomer (a monomer other than the vinylidene fluoride monomer) may be, for example, 5 mol% or less based on the total monomer content of the first binder. In the first binder, if the optional fluorine-containing monomer is present, the amount of the repeating unit derived from the fluorine-containing monomer (that is, a combination of the vinylidene fluoride monomer and the optional fluorine-containing monomer) may be, for example, 50 mol% or more to less than 100 mol%, 60 mol% or more to less than 100 mol%, 70 mol% or more to less than 100 mol%, 80 mol% or more to less than 100 mol%, or 90 mol% or more to less than 100 mol% based on the total monomer content of the first binder, and the remaining repeating units may be derived from the monomer containing a polar functional group. In the first binder, the amount of the repeating unit derived from the fluorine-containing monomer may be, for example, 90 mol% to 99.9 mol% based on the total monomer content of the first binder. When the first binder includes the repeating unit derived from the fluorine-containing monomer within the above range, improved chemical stability can be obtained.

[0041] In addition, in the first binder, the amount of the repeating unit derived from the monomer containing a polar functional group may be, for example, up to about 10 mol%, or about 0.1 mol% to about 9 mol%, or about 0.1 mol% to about 8 mol%, or about 0.1 mol% to about 7 mol%, or about 0.1 mol% to about 5 mol%. When the first binder includes the repeating unit derived from the monomer containing a polar functional group within the above range, the solvent tolerance to the electrolyte is further improved.

[0042] In the first binder, the amount of the repeating unit derived from the vinylidene fluoride monomer may be, for example, about 50 mol% or more, about 60 mol% or more, about 70 mol% or more, about 80 mol% or more, or about 90 mol% or more, based on the total monomer content of the first binder, where the maximum amount is 100 mol% minus the mol% of the monomer containing a polar functional group and the optional fluorine-containing monomer (if present).

[0043] In an embodiment, the weight-average molecular weight of the first binder may be 1,000,000 daltons or more, or about 1,000,000 daltons to about 2,000,000 daltons, or about 1,000,000 daltons to about 1,800,000 daltons, or about 1,000,000 daltons to about 1,500,000 daltons, or about 1,000,000 daltons to about 1,200,000 daltons. The weight-average molecular weight of the first binder can be measured by gel permeation chromatography using polystyrene standards. When the first binder has a weight-average molecular weight within the above range, the adhesion between the positive electrode active material and the current collector is further increased.

[0044] For example, the amount of the first binder may be up to about 2 wt%, or up to about 1.5 wt%, 1 wt%, up to about 0.5 wt%, about 0.2 wt%, or up to about 0.1 wt% or less, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. For example, the amount of the first binder may be about 0.01 wt% to about 2 wt%, about 0.01 wt% to about 1.5 wt%, about 0.01 wt% to about 1.0 wt%, about 0.01 wt% to about 0.5 wt%, about 0.01 wt% to about 0.2 wt%, or about 0.01 wt% to about 0.1 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. When the positive electrode includes the first binder within the above range, the adhesion between the positive electrode active material and the electrode plate is further improved, and the lithium battery including the positive electrode may have improved cycle characteristics.

[0045] Exemplary embodiments of the positive electrode may further include a second fluorine-containing binder that does not contain polar functional groups, i.e., a third binder, wherein the third binder includes fluorine and wherein the third binder does not include polar functional groups. The third binder may include units derived from vinylidene fluoride. For example, the third binder may be a homopolymer of vinylidene fluoride monomer, or a copolymer of vinylidene fluoride monomer and tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluorine-containing vinyl monomer, perfluoroalkyl vinyl ether, or a combination thereof. The alkyl group of the perfluoroalkyl vinyl ether may be a C1 to C10, or C2 to C8 perfluorinated alkyl group. In particular, the third binder may be a vinylidene fluoride homopolymer, a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-chlorotrifluoroethylene copolymer, etc. However, these embodiments are not limited thereto, and any suitable binder that includes fluorine and does not include polar functional groups may be used for the third binder. In particular, the third binder may be a polyvinylidene fluoride (PVDF) binder. In the third binder, the amount of repeating units derived from vinylidene fluoride monomer may be, for example, about 50 mol% or greater, about 60 mol% or greater, about 70 mol% or greater, about 80 mol% or greater, or about 90 mol% or greater, based on the total monomer content of the third binder. In an embodiment, the weight-average molecular weight of the third binder may be about 1,000,000 daltons or less, about 100,000 daltons to about 1,000,000 daltons, about 200,000 daltons to about 900,000 daltons, about 300,000 daltons to about 800,000 daltons, about 500,000 daltons to about 700,000 daltons, or about 670,000 daltons to about 700,000 daltons. When the weight-average molecular weight of the third binder is within the above range, the dispersibility of the positive electrode active material in the positive electrode including the first binder is further improved.

[0046] For example, the amount of the third binder that does not include polar functional groups may be about 2 wt% or less, about 1.5 wt% or less, about 1 wt% or less, about 0.5 wt% or less, about 0.2 wt% or less, or about 0.1 wt% or less, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. For example, the amount of the third binder that does not include polar functional groups may be from about 0.01 wt% to about 2 wt%, from about 0.01 wt% to about 1.5 wt%, from about 0.01 wt% to about 1.0 wt%, from about 0.01 wt% to about 0.5 wt%, from about 0.01 wt% to about 0.2 wt%, or from about 0.01 wt% to about 0.1 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. When the positive electrode includes the third binder within the above range, the dispersibility of the positive electrode active material in the positive electrode is further improved, and the cycle characteristics of the lithium battery including the positive electrode are further improved.

[0047] For example, the weight ratio of the first binder to the third binder that does not include polar functional groups may be from about 90:10 to about 10:90, from about 80:20 to about 20:80, from about 70:30 to about 30:70, or from about 60:40 to about 40:60, based on the total weight of the first binder and the third binder. When the weight ratio of the first binder to the third binder is within the above range, the dispersibility of the positive electrode active material is improved, and the adhesion between the positive electrode active material and the electrode plate is further improved.

[0048] Although not wishing to be bound by theory, it is understood that the first binder and the third binder that does not include polar functional groups maintain an appropriate viscosity when dissolved in a non-aqueous solvent to improve the dispersibility of the positive electrode active material and provide improved adhesion between the positive electrode active material particles and between the positive electrode active material and the current collector, thus improving the dimensional stability of the positive electrode. Therefore, delamination of the positive electrode mixture from the positive electrode current collector or cracking in the positive electrode mixture is prevented during charging and discharging, and thus the lithium battery including the positive electrode has improved cycle characteristics.

[0049] The second binder without fluorine included in the exemplary embodiment of the positive electrode may include a cyano group. For example, the second binder including a cyano group may include repeating units derived from acrylonitrile-containing monomers and repeating units derived from olefin-containing monomers. For example, the acrylonitrile-containing monomer may be acrylonitrile, methacrylonitrile, etc. The olefin-containing monomer may be 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, 1,4-hexadiene, ethylene, propylene, 1-butene, etc. The second binder may be, for example, a hydrogenated binder that does not include (e.g., is substantially free of) any double bonds in the main chain or backbone. In particular, the second binder may be a hydrogenated acrylonitrile-butadiene rubber (NBR). In the second binder, the amount of the repeating units derived from the acrylonitrile-containing monomer may be, for example, about 1 wt% to about 70 wt%, about 2 wt% to about 50 wt%, about 5 wt% to about 30 wt%, or about 10 wt% to about 25 wt%, based on the total weight of the second binder. In the second binder, the amount of the repeating units derived from the olefin-containing monomer may be, for example, about 30 wt% to about 99 wt%, about 50 wt% to about 98 wt%, about 70 wt% to about 95 wt%, or about 75 wt% to about 90 wt%, based on the total weight of the second binder. When the second binder includes acrylonitrile-containing monomers and / or olefin-containing monomers within the above ranges, the dispersibility of the linear carbon conductive material is further improved. For example, the weight average molecular weight of the second binder without fluorine may be about 100,000 daltons to about 1,000,000 daltons, about 100,000 daltons to about 800,000 daltons, about 100,000 daltons to about 600,000 daltons, about 100,000 daltons to about 500,000 daltons, or about 100,000 daltons to about 300,000 daltons. When the second binder has a weight average molecular weight within the above ranges, the flexibility of the positive electrode is further improved. The glass transition temperature (Tg) of the second binder may be about -40 °C to about 30 °C, about -40 °C to about 25 °C, about -40 °C to about 20 °C, about -40 °C to about 15 °C, or about -40 °C to about 5 °C. When the second binder in the positive electrode has a glass transition temperature as described above, it is easier to form a bonding network in the positive electrode through the second binder.

[0050] For example, the amount of the second binder that does not include fluorine may be about 2 wt% or less, about 0.1 wt% to about 2 wt%, about 0.1 wt% to about 1.5 wt%, about 0.1 wt% to about 1.0 wt%, about 0.1 wt% to about 0.7 wt%, about 0.1 wt% to about 0.5 wt%, or about 0.1 wt% to about 0.3 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. When the positive electrode includes the second binder within the above range, the flexibility and conductivity of the positive electrode are further improved, and a lithium battery including the positive electrode has further improved cycle characteristics.

[0051] Exemplary embodiments of the positive electrode may further include a fourth binder, wherein the fourth binder includes a cyanoalkyl group and wherein the fourth binder does not include fluorine. Different from the second binder in which the cyano group may be directly bonded to the main chain, in the fourth binder, the cyano group may be bonded to a side chain of the polymer, and thus, although not wishing to be bound by theory, it is understood that heat generated by side reactions between the nickel-rich lithium transition metal oxide and the electrolyte can be prevented. In an embodiment, it is understood that the fourth binder reduces the heat of the positive electrode and inhibits the deterioration of the nickel-rich lithium transition metal oxide in the positive electrode. Accordingly, the positive electrode including the fourth binder has improved thermal stability. Moreover, a lithium battery including the positive electrode has improved thermal stability and cycle characteristics. In particular, the high-temperature cycle characteristics of the lithium battery are improved.

[0052] For example, the amount of the fourth binder that does not include fluorine may be about 2 wt% or less, or about 0.1 wt% to about 2 wt%, about 0.1 wt% to about 1.5 wt%, about 0.1 wt% to about 1.0 wt%, about 0.1 wt% to about 0.7 wt%, about 0.1 wt% to about 0.5 wt%, or about 0.1 wt% to about 0.3 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. When the positive electrode includes the fourth binder within the above range, the thermal stability of the positive electrode is further improved, and the cycle characteristics of a lithium battery including the positive electrode are also further improved.

[0053] For example, the fourth binder that does not include fluorine may be a cyano polymer in which a cyanoalkyl group is bonded to a hydroxyl group-containing polymer compound. The cyano polymer can be obtained by substituting a hydroxyl group of a polymer compound represented by A-OH with a cyanoalkyl group, or by bonding a cyanoalkyl group to the hydroxyl group, and refers to a random copolymer in which A-OH and A-O-RCN (where -RCN is a cyano (C1-C10 alkyl) group and A is the remainder of the polymer) are non-uniformly bonded to each other.

[0054] For example, the fourth binder may include cyanoalkyl polyvinyl alcohol, cyanoalkyl pullulan (amylopectin), cyanoalkyl cellulose, cyanoalkyl hydroxyethyl cellulose, cyanoalkyl starch, cyanoalkyl dextrin, cyanoalkyl collagen, cyanoalkyl carboxymethyl cellulose, or a combination thereof. However, the embodiments are not limited thereto, and any suitable cyano resin may also be used. The number of carbon atoms included in the alkyl group R included in the cyanoalkyl may be 1 to 10, 2 to 8, or 3 to 6.

[0055] In particular, the fourth binder may include cyanoethyl polyvinyl alcohol, cyanoethyl pullulan (amylopectin), cyanoethyl cellulose, cyanoethyl hydroxyethyl cellulose, cyanoethyl starch, cyanoethyl dextrin, cyanoethyl collagen, cyanoethyl carboxymethyl cellulose, or a combination thereof.

[0056] In particular, the fourth binder may be, for example, cyanoethyl polyvinyl alcohol represented by Formula 1.

[0057] Formula 1

[0058]

[0059] In Formula 1, n and m are each independently the mole fraction in the repeating unit, 0 ≤ n < 1, 0 < m < 1, n + m = 1, and x is 2.

[0060] It is understood that the second binder including a cyano group and / or the fourth binder including a cyanoalkyl improve the dispersibility of the linear carbon conductive material in the positive electrode, and also improve the flexibility of the positive electrode. Therefore, the internal resistance of the positive electrode including the second binder and the fourth binder is reduced, and the occurrence of cracking during the battery manufacturing process is suppressed. In addition, the internal resistance of the lithium battery including the positive electrode is reduced, and the occurrence of cracking caused during the winding process or the charge and discharge process of the lithium battery is also suppressed, thereby improving the cycle characteristics of the lithium battery.

[0061] The total amount of the binder including the first binder, the second binder, optionally the third binder, and optionally the fourth binder may be about 0.01 wt% to about 5 wt%, about 0.01 wt% to about 4 wt%, about 0.01 wt% to about 3 wt%, about 0.01 wt% to about 2 wt%, about 0.1 wt% to about 2 wt%, about 0.1 wt% to about 1.5 wt%, about 0.1 wt% to about 1 wt%, or about 0.1 wt% to about 0.5 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. When the positive electrode includes the binder within the above range, the flexibility, adhesion, and / or cycle characteristics of the positive electrode are further improved.

[0062] The positive electrode active material includes a lithium transition metal oxide containing nickel and a transition metal other than nickel and having a layered crystal structure. In an embodiment, the layered crystal structure is an α-NaFeO2-type structure, for example, the structure adopted by LiCoO2 and LiNi (1-x) Co x O2 (where 0 < x < 1).

[0063] In the lithium transition metal oxide, the amount of nickel can be, for example, about 30 mol% or more, about 50 mol% or more, about 60 mol% or more, about 70 mol% or more, about 80 mol% or more, about 82 mol% or more, about 85 mol% or more, about 87 mol% or more, or about 90 mol% or more, based on the total number of moles of the lithium transition metal oxide. When the positive electrode active material includes a nickel content within the above range, the discharge capacity of the positive electrode is further increased.

[0064] For example, the lithium transition metal oxide can be a compound represented by Formula 2.

[0065] Formula 2

[0066] Li a Ni x Co y M z O 2-b A b

[0067] In Formula 2, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.3 ≤ x < 1, 0 < y ≤ 0.4, 0 < z ≤ 0.4, x + y + z = 1, M is manganese (Mn), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B), or a combination thereof, and A is F, S, Cl, Br, or a combination thereof. For example, 0.5 ≤ x < 1, 0 < y ≤ 0.4, and 0 < z ≤ 0.4. For example, 0.6 ≤ x < 1, 0 < y ≤ 0.4, and 0 < z ≤ 0.4. For example, 0.7 ≤ x < , 0 < y ≤ 0.3, and 0 < z ≤ 0.3. For example, 0.8 ≤ x < 1, 0 < y ≤ 0.2, and 0 < z ≤ 0.2. For example, 0.83 ≤ x < 0.97, 0 < y ≤ 0.15, and 0 < z ≤ 0.15. For example, 0.85 ≤ x < 0.95, 0 < y ≤ 0.1, and 0 < z ≤ 0.1. For example, 0.7 ≤ x < 0.99, 0 < y ≤ 0.3, and 0 < z ≤ 0.3.

[0068] For example, the lithium transition metal oxide can be a compound represented by Formula 3 or 4.

[0069] Formula 3

[0070] LiNi x Co y Mn z O2

[0071] In Formula 3, 0.3 ≤ x < 1, 0 < y ≤ 0.4, and 0 < z ≤ 0.4. For example, 0.5 ≤ x < 1, 0 < y ≤ 0.4, 0 < z ≤ 0.4. For example, 0.6 ≤ x < 1, 0 < y ≤ 0.4, and 0 < z ≤ 0.4. For example, 0.7 ≤ x < 1, 0 < y ≤ 0.3, and 0 < z ≤ 0.3. For example, 0.82 ≤ x ≤ 0.95, 0 < y ≤ 0.15, and 0 < z ≤ 0.15. For example, 0.85 ≤ x ≤ 0.95, 0 < y ≤ 0.1, and 0 < z ≤ 0.1. For example, 0.8 ≤ x < 0.99, 0 < y ≤ 0.2, and 0 < z ≤ 0.1.

[0072] Formula 4

[0073] LiNi x’ Co y’ Al z’ O2

[0074] In Formula 4, 0.3 ≤ x’ < 1, 0 < y’ ≤ 0.4, and 0 < z’ ≤ 0.4. For example, 0.5 ≤ x’ < 1, 0 < y’ ≤ 0.4, 0 < z’ ≤ 0.4. For example, 0.6 ≤ x’ < 1, 0 < y’ ≤ 0.4, and 0 < z’ ≤ 0.4. For example, 0.7 ≤ x’ < 1, 0 < y’ ≤ 0.3, and 0 < z’ ≤ 0.3. For example, 0.82 ≤ x’ ≤ 0.95, 0 < y’ ≤ 0.15, and 0 < z’ ≤ 0.15. For example, 0.85 ≤ x’ ≤ 0.95, 0 < y’ ≤ 0.1, and 0 < z’ ≤ 0.1. For example, 0.8 ≤ x’ < 0.99, 0 < y’ ≤ 0.2, and 0 < z’ ≤ 0.1.

[0075] In particular, the lithium transition metal oxide may be LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.88 Co 0.08 Mn 0.04 O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al0.05 O2, LiNi 0.8 Co 0.1 Al 0.1 O2, or LiNi 0.88 Co 0.1 Al 0.02 O2. The lithium transition metal oxide may additionally be doped with a doping element such as Al.

[0076] In an embodiment, the positive electrode active material may have a bimodal particle size (grain size) distribution, for example, having two peaks in the particle size distribution obtained by light scattering. When the lithium transition metal oxide has a bimodal particle size distribution, the bulk density of the positive electrode including the lithium transition metal oxide is further increased. The amount of the positive electrode active material may be about 70 wt% to about 99.9 wt%, about 80 wt% to about 99.9 wt%, about 90 wt% to about 99.9 wt%, about 95 wt% to about 98.9 wt%, or about 97 wt% to about 98.9 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. When the positive electrode includes the positive electrode active material within the above range, the discharge capacity of the positive electrode is further increased.

[0077] Since the positive electrode including the linear carbon conductive material and the first binder has improved flexibility and increased adhesion, the occurrence of cracking caused by an increase in the thickness of the positive electrode is prevented. Moreover, since the positive electrode includes a nickel-rich lithium transition metal oxide, the discharge capacity is increased. Therefore, the positive electrode may have improved cycle characteristics and a load of about 3 milliamperes per square centimeter (mAh / cm 2 ) or greater, and a lithium battery including the positive electrode may have improved cycle characteristics and an energy density of about 500 watt-hours per liter (Wh / L) or greater. For example, the load of the positive electrode may be about 3.5 mAh / cm 2 or greater, about 4 mAh / cm 2 or greater, about 4.3 mAh / cm 2 or greater, about 4.5 mAh / cm 2 or greater, about 5 mAh / cm 2 or greater, 5.5 mAh / cm 2 or greater, or about 6 mAh / cm 2 or greater, for example about 3 mAh / cm 2 to about 30 mAh / cm 2 、about 3.5 mAh / cm 2 to about 20 mAh / cm 2 、or about 4 mAh / cm 2 to about 15 mAh / cm 2. For example, the weight per unit area of the positive electrode may be about 40 milligrams per square centimeter (mg / cm 2 ) or greater, about 45 mg / cm 2 or greater, about 50 mg / cm 2 or greater, or about 55 mg / cm 2 or greater, for example, about 40 mg / cm 2 to about 400 mg / cm 2 , about 50 mg / cm 2 to about 350 mg / cm 2 , or about 60 mg / cm 2 to about 300 mg / cm 2 . For example, the pressing density of the positive electrode may be about 3 grams per cubic centimeter (g / cc) or greater, about 3.2 g / cc or greater, about 3.4 g / cc or greater, about 3.6 g / cc or greater, about 3.8 g / cc or greater, or about 4 g / cc or greater, for example, about 3 g / cc to about 30 g / cc, about 4 g / cc to about 25 g / cc, or about 5 g / cc to about 20 g / cc.

[0078] In an embodiment, after being bent by 90° or more, 100° or more, 110° or more, 120° or more, 130° or more, 140° or more, 150° or more, or even after being bent to the maximum mechanical bending limit of a Universal Test Machine in a flexural property test according to ASTM D790, the positive electrode does not break or rupture. In a flexural property test according to ASTM D790 (e.g., a three-point bending test where the electrode sample has a width of 20 mm, a length of 15 mm, and a 10 mm spacing between two points), the positive electrode has a maximum flexural strength of about 1 Newton (N) or less, about 0.9 N or less, about 0.8 N or less, about 0.7 N or less, about 0.68 N or less, about 0.66 N or less, or about 0.64 N or less, for example, about 0.1 N to about 1 N, about 0.2 N to about 0.95 N, or about 0.3 N to about 0.9 N for a force applied in a direction perpendicular to the sample. Due to the positive electrode having such a low maximum flexural strength, the occurrence of rupture can be prevented during the winding process or the charge and discharge process of a lithium battery including the positive electrode. In a 180° peel strength test according to ASTM D3330 (where the electrode sample has a width of 25 mm), the positive electrode has a peel strength of about 0.3 gram-force per millimeter (gf / mm) or more, about 1 gf / mm or more, about 5 gf / mm or more, about 10 gf / mm or more, about 15 gf / mm or more, about 20 gf / mm or more, about 25 gf / mm or more, or about 30 gf / mm or more, for example, about 0.3 gf / mm to about 300 gf / mm, about 1 gf / mm to about 250 gf / mm, or about 2 gf / mm to about 200 gf / mm. Due to the positive electrode having such a high peel strength, i.e., an increased adhesive force, delamination, rupture, etc. caused during the winding process or the charge and discharge process of a lithium battery including the positive electrode are prevented. Furthermore, even after being bent, for example, by 90° or more, 100° or more, 110° or more, 120° or more, 130° or more, 140° or more, 150° or more, 160° or more, or 170° or more in a manual finger pressure / bending test for evaluating mechanical limits, the positive electrode does not break. Due to the positive electrode having excellent flexibility, the occurrence of rupture caused during the winding process or the charge and discharge process of the lithium battery can be prevented. Therefore, although the positive electrode has an increased load, due to the improved flexibility and increased adhesive force of the positive electrode, the occurrence of rupture is prevented during the winding process or the charge and discharge process of the lithium battery.

[0079] A lithium battery according to another embodiment includes: the above-mentioned positive electrode containing a linear carbon conductive material and a first binder; a negative electrode; and an electrolyte disposed between the positive electrode and the negative electrode.

[0080] The lithium battery including the positive electrode containing the above-mentioned binder and linear carbon conductive material provides both increased energy density and improved cycling characteristics. For example, by using a positive electrode having improved cycling characteristics and a load of about 4 mAh / cm 2 or greater, the lithium battery can have improved cycling characteristics and a high energy density of about 500 Wh / L or greater. For example, the energy density of the lithium battery can be about 500 Wh / L or greater, about 550 Wh / L or greater, about 600 Wh / L or greater, about 650 Wh / L or greater, about 700 Wh / L or greater, or about 800 Wh / L or greater. The lithium battery is suitable for high-energy applications such as electric vehicles.

[0081] The lithium battery may include a lithium-ion battery, a lithium-ion polymer battery, and a lithium-sulfur battery. Moreover, the shape and structure of the lithium battery are not particularly limited. Throughout the specification, the lithium battery refers to a lithium secondary battery unless otherwise specified. Moreover, the lithium battery can be an all-solid-state (solid) battery.

[0082] For example, the lithium battery can be manufactured according to the following method, but the embodiment is not limited thereto, and any other suitable method can also be used.

[0083] First, prepare the positive electrode.

[0084] Mix a positive electrode active material, a conductive material, a binder, and a solvent to prepare a positive electrode active material composition. Subsequently, directly coat the positive electrode active material composition on a positive electrode current collector to prepare a positive electrode. Alternatively, cast the positive electrode active material composition on a separate carrier and laminate the film separated from the carrier on a metal current collector to prepare a positive electrode.

[0085] The positive electrode active material for use in the positive electrode active material composition includes such a lithium transition metal oxide that contains nickel and another transition metal that does not include nickel, wherein the total amount of nickel in the lithium transition metal oxide including nickel can be 50 mol% or more, based on the total number of moles of the lithium transition metal oxide. For example, the nickel-rich lithium transition metal oxide can be the lithium transition metal oxide represented by Formula 2-4 as shown above. The conductive material for use in the positive electrode active material composition includes a single linear carbon conductive material, or a mixture of the linear carbon conductive material and a particulate carbon conductive material. The binder for use in the positive electrode active material composition can include the first binder, the second binder, the third binder, and the fourth binder as described above. The solvent for use in the positive electrode active material composition can be N-methylpyrrolidone, acetone, or water, without limitation thereto, and any suitable solvent can be used. Moreover, the amount of the solvent can be about 10 parts by weight to about 100 parts by weight, based on 100 parts by weight of the positive electrode active material.

[0086] For example, the positive electrode active material composition can be prepared as follows: using the nickel-rich lithium transition metal oxide as the positive electrode active material, a mixture of carbon nanotubes and carbon black as the conductive material, a mixture of polyvinylidene fluoride (PVDF), polyvinylidene fluoride (PVDF) including a carboxylic acid group (-COOH) (for example, a carboxyl group), hydrogenated acrylonitrile-butadiene rubber (NBR), and cyanoethylated polyvinyl alcohol (PVA-CN) as the binder, and N-methylpyrrolidone (NMP) as the solvent. For example, the positive electrode can be prepared as follows: preparing a solid material including 97.7 wt% of the positive electrode active material, 1 wt% of the conductive material, and 1.3 wt% of the binder, and adding a solvent to the solid material such that the amount of the solvent is 70 wt% of the solid material, thereby preparing a positive electrode active material slurry, and further coating the slurry onto a positive electrode current collector and drying and rolling the slurry. The amounts of the positive electrode active material, the conductive material, the binder, and the solvent are as described above with reference to the positive electrode.

[0087] The thickness of the positive electrode current collector is, for example, about 3 micrometers (μm) to about 50 μm. Any suitable current collector that does not cause undesirable chemical changes in the lithium battery and has suitable electrical conductivity can be used without limitation. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector may have a surface on which irregularities are formed to improve the adhesion of the current collector to the positive electrode active material. The positive electrode current collector can be used in any of a variety of forms including films, sheets, foils, meshes, porous structures, foams, and nonwoven fabrics. In particular, the positive electrode current collector can be aluminum foil. The positive electrode of the all-solid-state battery may further include a solid electrolyte.

[0088] Next, a negative electrode is prepared.

[0089] A negative electrode active material, a conductive material, a binder, and a solvent are mixed to prepare a negative electrode active material composition. Subsequently, the negative electrode active material composition is directly coated on a negative electrode current collector and dried to prepare a negative electrode. Alternatively, the negative electrode active material composition is cast on a separate carrier and a film separated from the carrier is laminated on a metal current collector to prepare a negative electrode.

[0090] The negative electrode active material may include lithium metal, a metal / metalloid capable of alloying with lithium, a transition metal oxide, a non-transition metal oxide, a carbonaceous material, or a combination thereof. However, the embodiments are not limited thereto, and any suitable material for the negative electrode active material of a lithium battery can also be used. For example, the metal / metalloid capable of alloying with lithium may be Si, Sn, Al, Ge, Pb, Bi, Sb, a Si-Y' alloy (where Y' is an alkali metal, an alkaline earth metal, a Group 13-16 element, a transition metal, a rare earth element, or a combination thereof (excluding Si)), or a Sn-Z alloy (where Z is an alkali metal, an alkaline earth metal, a Group 13-16 element, a transition metal, a rare earth element, or a combination thereof (excluding Sn)). In this regard, the elements Y' and Z may each independently be 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, or a combination thereof. For example, the transition metal oxide may be lithium titanate oxide, vanadium oxide, or lithium vanadium oxide. For example, the non-transition metal oxide may be SnO2 or SiO x(0 < x < 2). Examples of the carbonaceous material may include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include natural graphite or artificial graphite, which are in the form of plates, flakes, spheres, or fibers. Examples of the amorphous carbon include soft carbon (carbon sintered at low temperature), hard carbon, mesophase pitch carbonized product, sintered coke, or a combination thereof.

[0091] Examples of the binder for the negative electrode active material composition may include polyvinylidene fluoride, polyvinylidene chloride, polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyaniline, acrylonitrile-butadiene-styrene (ABS), phenolic resin, epoxy resin, polyethylene terephthalate, polytetrafluoroethylene (PTFE), polyphenylene sulfide, polyamideimide, polyetherimide, polyvinyl sulfone (polyethylene sulfone), polyamide, polyacetal, polyphenylene ether, polybutylene terephthalate, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and combinations thereof, and are not limited thereto, and any suitable binder may be used.

[0092] The conductive material, the binder, and the solvent for the negative electrode active material composition may be the same as those for the positive electrode active material composition. The amounts of the negative electrode active material, the conductive material, the binder, and the solvent may be any suitable amounts for a lithium battery. A plasticizer may be further added to the positive electrode active material composition and / or the negative electrode active material composition to form pores within the electrode mixture. For example, the negative electrode may be prepared by: preparing a solid material including 94 wt% of the negative electrode active material, 3 wt% of the conductive material, and 3 wt% of the binder, and adding a solvent to the solid material such that the amount of the solvent is 70 wt% of the solid material, thereby preparing a negative electrode active material slurry, and further coating the slurry onto a negative electrode current collector and drying and rolling the slurry.

[0093] The thickness of the negative electrode current collector is, for example, about 3 μm to about 500 μm. Any current collector that does not cause undesirable chemical changes in the lithium battery and has high electrical conductivity can be used without limitation. For example, copper, stainless steel, aluminum, nickel, calcined carbon, or copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The negative electrode current collector may have a surface on which irregularities are formed to improve the adhesion of the current collector to the negative electrode active material. The negative electrode current collector can be used in any of various forms including a film, sheet, foil, net, porous structure, foam, and nonwoven fabric. In particular, the negative electrode current collector can be a copper foil. The negative electrode of the all-solid-state battery may further include a solid electrolyte.

[0094] Next, a separator to be inserted between the positive electrode and the negative electrode is prepared.

[0095] Any suitable separator for a lithium battery can be used. Any suitable separator having low resistance to ion migration of the electrolyte and excellent electrolyte retention ability can be used. Examples of the separator may include glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), and combinations thereof, each of which may be a nonwoven or woven fabric. For example, a wound separator including polyethylene or polypropylene can be used in a lithium-ion battery, and a separator having excellent electrolyte retention ability can be used in a lithium-ion polymer battery.

[0096] For example, the separator can be prepared according to the following method.

[0097] A polymer resin, a filler, and a solvent can be mixed to prepare a separator composition. Then, the separator composition can be directly coated on the electrode and then dried to form a separator. Alternatively, the separator composition can be cast on a carrier and then dried to form a separator film, and the separator film separated from the carrier can be laminated on the electrode to form the separator. The polymer resin used for manufacturing the separator is not particularly limited and can be any suitable material used as an adhesive for the electrode. Examples of the polymer resin used for preparing the separator may include a vinylidene fluoride / hexafluoropropylene copolymer, PVDF, polyacrylonitrile, polymethyl methacrylate, and any mixture thereof.

[0098] Subsequently, an electrolyte located between the positive electrode and the negative electrode is prepared.

[0099] For example, the electrolyte may be an organic electrolyte. For example, the organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent. For example, the organic solvent may be any organic solvent commonly used in the art. Examples of the organic solvent include propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, and any mixture thereof. The lithium salt may be any lithium salt commonly used in the art. For example, the lithium salt is LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(where x and y are natural numbers), LiCl, LiI, or any mixture thereof.

[0100] In addition to the above organic electrolytes, other exemplary electrolytes further include non-aqueous electrolytes, organic solid electrolytes, inorganic solid electrolytes, etc. Examples of the organic solid electrolytes include polyethylene derivatives, poly(ethylene oxide) derivatives, poly(propylene oxide) derivatives, phosphate esters polymers, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers including ionic dissociating groups. Examples of the inorganic solid electrolytes include nitride solid electrolytes, oxynitride solid electrolytes, and sulfide solid electrolytes. Examples of the inorganic solid electrolytes include Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2.

[0101] Refer to Figure 5, the exemplary lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, negative electrode 2, and separator 4 are wound or folded and then accommodated in a battery case 5. Subsequently, an electrolyte is injected into the battery case 5 and the battery case 5 is sealed by a cap assembly 6, thereby completing the manufacture of the lithium battery 1. The battery case 5 may have a cylindrical shape, a rectangular shape, or a film shape. Although not shown in the figures, another exemplary lithium battery may be manufactured as follows: using a battery assembly prepared by disposing a separator between a positive electrode and a negative electrode. The battery assemblies are stacked in a dual-cell battery structure and immersed in an organic electrolyte, and then the obtained product is accommodated in a bag and sealed to complete the manufacture of a lithium-ion polymer battery. Moreover, a plurality of battery assemblies are stacked to form a battery pack, and the battery pack can be used in any high-capacity and high-output device applications. For example, the battery pack can be used in laptop computers, smartphones, and electric vehicles. The lithium battery can also be used in: power tools that operate when receiving energy from a battery-driven motor; electric vehicles (EVs) such as hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs); electric motorcycles such as electric bicycles and electric scooters; electric golf carts; and systems for energy storage, and is not limited thereto.

[0102] Throughout the specification, the term "alkyl" refers to a fully saturated branched or unbranched (or straight-chain or linear) hydrocarbon group.

[0103] Examples of "alkyl" may include, but are not limited to: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, 3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl, and n-heptyl.

[0104] At least one hydrogen atom of "alkyl" may be replaced by: a halogen atom, a C1-C20 alkyl group substituted by a halogen atom (e.g., CF3, CHF2, CH2F, and CCl3), a C1-C20 alkoxy group, a C2-C20 alkoxyalkyl group, a hydroxyl group, a nitro group, a cyano group, an amino group, an amidino group, a hydrazino group, a hydrazono group, a carboxylic acid group and its salts, a sulfonyl group, a sulfamoyl group, a sulfonic acid group and its salts, a phosphoric acid group and its salts, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C1-C20 heteroalkyl group, a C6-C20 aryl group, a C7-C20 aralkyl group, a C6-C20 heteroaryl group, a C7-C20 heteroaralkyl group, a C6-C20 heteroaryloxy group, a C6-C20 heteroaryloxyalkyl group, or a C6-C20 heteroaralkyl group.

[0105] The term "halogen" includes fluorine, bromine, chlorine, and iodine. The term "cyano" refers to -CN. The term "cyanoalkyl" refers to -R-CN, where R is "alkyl".

[0106] In the following, one or more embodiments of the present disclosure will be described in detail with reference to the following examples. These examples are not intended to limit the purpose and scope of one or more embodiments of the present disclosure.

[0107] Example

[0108] Preparation of Cathode and Lithium Battery

[0109] Comparative Example 1: 96 wt% nickel cobalt manganese oxide (NCM), 2 wt% carbon black (CB), 0.2 wt% modified PVDF (m-PVDF), 1.6 wt% PVDF, and 0.2 wt% NBR, without CNT (weight ratio of active material: conductive material: binder = 96:2:2)

[0110] Granular carbon black (KETJENBLACK ECP, EC300J, AkzoNobel) having an aspect ratio of less than 2 as a conductive material was added to a first solution (NBR) containing a second binder (non-fluorinated binder), and the carbon black-containing mixture was stirred several times at 2000 revolutions per minute (rpm) for 10 minutes using a planetary centrifugal mixer (hereinafter referred to as a Thinky mixer, Thinky Corporation, USA) to prepare a conductive material slurry.

[0111] A second solution including a first binder (binder containing fluorine and polar groups) (m-PVDF, modified PVDF including carboxyl group (-COOH), SOLEF 5130, weight average molecular weight = 1,000,000 g / mol, Solvay, Belgium) and LiNi as a cathode active material 0.88 Co 0.08 Mn 0.04 O2 was added to the conductive material slurry, and the mixture was stirred at 1000 rpm for 5 minutes using a Thinky mixer to prepare a first active material slurry.

[0112] A third solution containing a third binder (fluorine-containing binder without polar groups) (PVDF, SOLEF 6020, weight average molecular weight = 700,000 g / mol, Solvay, Belgium) was added to the first active material slurry, and the mixture was stirred at 1000 rpm for 5 minutes using a Thinky mixer to prepare a second active material slurry.

[0113] The second active material slurry was coated onto an aluminum foil with a thickness of 12 μm, dried at 110 °C for 2 hours, and roll-pressed to prepare a positive electrode plate having a loading (or capacity per unit area) of 6.0 mAh / cm 2 and a mixture density of 3.6 g / cc.

[0114] The weight ratio of the positive electrode active material, the conductive material, and the binder included in the positive electrode is 96:2:2, and the weight ratio of a first binder (m-PVDF) containing a polar group and fluorine, a third binder (PVDF) not containing a polar group and containing fluorine, and a second binder (NBR) not containing fluorine included in the binder is 0.2:1.6:0.2.

[0115] Carbon nanotubes were not used. The amount of the first binder (m-PVDF) is 0.2 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

[0116] A coin cell battery (CR2032 type) was prepared using the positive electrode plate. In the preparation of the coin cell battery, Li metal was used as the counter electrode, a polyethylene separator with a thickness of 20 μm (separator, 20) was used, and an electrolyte prepared as follows was used: 0.5 wt% vinylene carbonate (VC) was dissolved in a mixed solvent of fluoroethylene carbonate (FEC):ethylene carbonate (EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC) mixed in a volume ratio of 7:7:46:40, and 1.15 M LiPF6 was dissolved in the solvent.

[0117] Comparative Example 2: 95 wt% NCM, 2.5 wt% CB, 2.5 wt% PVDF, without NBR (weight ratio of active material:conductive material:binder = 95:2.5:2.5)

[0118] A positive electrode plate was prepared in the same manner as in Comparative Example 1, except that: the weight ratio of the positive electrode active material, the conductive material, and the binder included in the positive electrode is 95:2.5:2.5, and the weight ratio of the first binder (m-PVDF), the third binder (PVDF), and the second binder (NBR) included in the binder is 0:2.5:0.

[0119] Carbon nanotubes were not used. The first binder was not used.

[0120] A coin cell battery was prepared in the same manner as in Comparative Example 1.

[0121] Comparative Example 3: 97.7 wt% NCM, 1.86 wt% CNT+CB, 0.1 wt% PVDF, and 0.34 wt% NBR, 1.3% CNT, without m-PVDF (weight ratio of active material:conductive material:binder = 97.7:1.86:0.44)

[0122] The positive electrode plate was prepared in the same manner as in Comparative Example 1, except that: the weight ratio of the positive electrode active material, conductive material, and binder included in the positive electrode was 97.7:1.86:0.44, and the weight ratio of the first binder (m-PVDF), third binder (PVDF), and second binder (NBR) included in the binder was 0.0:0.1:0.34.

[0123] The amount of CNT was 1.3 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. The first binder was not used.

[0124] The coin cell battery was prepared in the same manner as in Comparative Example 1.

[0125] Example 1: 97.7 wt% NCM, 1.86 wt% CNT+CB, 0.1 wt% m-PVDF, and 0.34 wt% NBR, 1.3 wt% CNT (weight ratio of active material:conductive material:binder = 97.7:1.86:0.44)

[0126] The positive electrode plate was prepared in the same manner as in Comparative Example 1, except that: the weight ratio of the positive electrode active material, conductive material, and binder included in the positive electrode was 97.7:1.86:0.44, and the weight ratio of the first binder (m-PVDF), third binder (PVDF), and second binder (NBR) included in the binder was 0.1:0.0:0.34.

[0127] The amount of CNT was 1.3 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. The amount of the first binder was 0.1 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

[0128] The coin cell battery was prepared in the same manner as in Comparative Example 1.

[0129] Example 2: 97.7 wt% NCM, 1.86 wt% CNT+CB, 0.05 wt% m-PVDF, 0.05 wt% PVDF, and 0.34 wt% NBR, 1.3 wt% CNT (weight ratio of active material:conductive material:binder = 97.7:1.86:0.44)

[0130] The positive electrode plate was prepared in the same manner as in Comparative Example 1, except that: the weight ratio of the positive electrode active material, the conductive material, and the binder included in the positive electrode was 97.7:1.86:0.44, and the weight ratio of the first binder (m-PVDF), the third binder (PVDF), and the second binder (NBR) included in the binder was 0.05:0.05:0.34.

[0131] The amount of CNT was 1.3% by weight, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. The amount of the first binder was 0.05% by weight, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

[0132] The coin cell battery was prepared in the same manner as in Comparative Example 1.

[0133] Example 3: 97.7% by weight of NCM, 1.0% by weight of CNT + CB, 0.2% by weight of m-PVDF, 0.9% by weight of PVDF, and 0.2% by weight of NBR, 0.7% by weight of CNT (weight ratio of active material:conductive material:binder = 97.7:1.0:1.3)

[0134] The positive electrode plate was prepared in the same manner as in Comparative Example 1, except that: a mixture of linear carbon nanotubes having an aspect ratio of 10 or greater and particulate carbon black (Ketjenblack ECP, EC300J, AkzoNobel) having an aspect ratio of less than 2, mixed at a weight ratio of 7:3, was used instead of the single carbon black as the conductive material, and the weight ratio of the positive electrode active material, the conductive material, and the binder included in the positive electrode was 97.7:1:1.3, and the weight ratio of the first binder (m-PVDF), the third binder (PVDF), and the second binder (NBR) included in the binder was 0.2:0.9:0.2.

[0135] The amount of CNT was 0.7% by weight. The amount of the first binder was 0.2% by weight, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

[0136] The coin cell battery was prepared in the same manner as in Comparative Example 1.

[0137] Example 4: 97.7% by weight of NCM, 1.3% by weight of CNT + CB, 0.2% by weight of m-PVDF, 0.54% by weight of PVDF, and 0.26% by weight of NBR, 0.9% by weight of CNT (weight ratio of active material:conductive material:binder = 97.7:1.3:1.0)

[0138] The positive electrode plate was prepared in the same manner as in Comparative Example 1, except that: the weight ratio of the positive electrode active material, the conductive material, and the binder included in the positive electrode was 97.7:1.3:1, and the weight ratio of the first binder (m-PVDF), the third binder (PVDF), and the second binder (NBR) included in the binder was 0.2:0.54:0.26.

[0139] The amount of CNT was 0.9 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. The amount of the first binder was 0.2 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

[0140] The coin cell battery was prepared in the same manner as in Comparative Example 1.

[0141] Example 5: 97.7 wt% NCM, 1.57 wt% CNT+CB, 0.2 wt% m-PVDF, 0.22 wt% PVDF, and 0.31 wt% NBR, 1.1 wt% CNT (weight ratio of active material:conductive material:binder = 97.7:1.57:0.73)

[0142] The positive electrode plate was prepared in the same manner as in Comparative Example 1, except that: the weight ratio of the positive electrode active material, the conductive material, and the binder included in the positive electrode was 97.7:1.57:0.73, and the weight ratio of the first binder (m-PVDF), the third binder (PVDF), and the second binder (NBR) included in the binder was 0.2:0.22:0.31.

[0143] The amount of CNT was 1.1 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder. The amount of the first binder was 0.2 wt%, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

[0144] The coin cell battery was prepared in the same manner as in Comparative Example 1.

[0145] Evaluation of Example 1: Evaluation of peel strength

[0146] The peel strength of the positive electrode plates prepared according to Example 1, 3, and 4 and Comparative Example 1 was evaluated in accordance with ASTM D3330. A UTM, Instron 3345 was used as the measuring device.

[0147] The positive electrode plates prepared according to Example 1, 3, and 4 and Comparative Example 1, in which the active material layer is located on both surfaces of the current collector, were each cut into a size of 25 mm × 150 mm, and 20 samples of each positive electrode plate were prepared. After coating the adhesive on the glass substrate at room temperature, the positive electrode plate was adhered to the adhesive and roll-pressed. After folding one end of the positive electrode plate by 180 degrees, the force applied to the sample was measured while pulling the sample at a rate of 100 mm / min in the direction opposite to the one end. The evaluation results are shown in Table 1 below. The fracture incidence rate is the number of samples in which the positive electrode active material layer located on one surface of the positive electrode plate that does not contact the adhesive breaks during the process of folding the positive electrode plate by 180 degrees, expressed as a percentage. The peel strength is the average value of 20 samples.

[0148] Table 1

[0149] Peeling strength [gf / mm] Fracture incidence rate [%] Example 1 30.32 0 Example 3 0.44 90 Example 4 1.35 35 Comparative Example 1 0.0 100

[0150] As shown in Table 1, the peel strength of the positive electrodes prepared according to Example 1, 3, and 4 is greater than that of the positive electrode prepared according to Comparative Example 1.

[0151] Therefore, although the positive electrodes prepared according to Example 1, 3, and 4 contain a lower amount of binder than the positive electrode prepared according to Comparative Example 1, it is confirmed that, compared with the positive electrode of Comparative Example 1, the positive electrode active material layer has a much greater peel strength, the current collector has a better adhesion, and / or the positive electrode active material layer has a better cohesion.

[0152] Moreover, when the positive electrode active material layer of Comparative Example 1 has a fracture incidence rate of 100%, the positive electrode active material layers of Example 1, 3, and 4 have a lower fracture incidence rate of 90% or less, and the positive electrode active material layer of Example 1 does not break.

[0153] Therefore, it is confirmed that, compared with the positive electrode of Comparative Example 1, the positive electrodes of Example 1, 3, and 4 have better flexibility despite having a lower binder content.

[0154] Evaluation Example 2: Evaluation of Flexural Strength

[0155] The flexural strength (3-point bending test) of the positive electrode plates prepared according to Example 1, 3, and 4 and Comparative Example 1 was measured according to ASTM D790.

[0156] The positive electrode plates prepared according to Example 1, Example 3, Example 4, and Comparative Example 1 were each cut into a size of 15 mm × 20 mm. According to the three-point bending test, each sample was placed between a first point and a second point spaced 10 mm apart, and a probe was used to squeeze the center (the third point) of the sample at a constant rate in the thickness direction of the sample to evaluate its bending performance. The force applied to the sample was measured while moving at a rate of 5 mm / minute in the thickness direction. The measurement results are shown in Table 2 and Figure 1 and 2 . The maximum bending force (maximum bending strength) is the maximum force applied to the sample for the moving distance of the probe.

[0157] Table 2

[0158] Maximum bending force [N] Example 1 0.62 Example 3 0.85 Example 4 0.95 Comparative Example 1 1.3

[0159] As shown in Table 2 and Figure 1 , the maximum bending forces of the positive electrodes according to Example 1, Example 3, and Example 4 are lower than those of the positive electrode according to Comparative Example 1.

[0160] As Figure 1 shown, although the maximum bending force of the positive electrode according to Example 1 is lower than that of the positive electrode according to Example 4, the slope of the positive electrode according to Example 1 is gentler than that of the positive electrode according to Example 4.

[0161] Therefore, it was confirmed that the positive electrodes according to Example 1, Example 3, and Example 4 have better flexibility although they have a lower binder content compared to the positive electrode according to Comparative Example 1.

[0162] In addition, as Figure 2 shown, the positive electrode according to Example 1 does not break even after the bending test and even after being finger-pressed to a large bending / bending angle (two samples on the left: 90 degrees and two samples on the right: 180 degrees), but remains bent.

[0163] Evaluation of Example 3: Evaluation of Impedance

[0164] The lithium batteries prepared according to Example 1, Example 3, Example 5, and Comparative Example 2 were charged at a constant current of 0.2C at 25 °C until the voltage reached 4.35 volts (V) (relative to Li), and then while maintaining the voltage of 4.35V in the constant voltage mode, the charging process was cut off at a current of 0.05C. Subsequently, the lithium batteries were discharged at a constant current of 0.2C until the voltage reached 2.8V (relative to Li) (formation operation).

[0165] The lithium battery that has undergone the formation operation is charged at a constant current of 0.5C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is terminated at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium battery is discharged at a constant current of 0.5C until the voltage reaches 2.8V (relative to Li) (the first cycle). This charge / discharge cycle is repeated 50 times. The lithium battery is allowed to stand for 20 minutes after each charge / discharge cycle.

[0166] After 50 cycles of the charge / discharge cycle are terminated, the lithium battery is charged at a constant current of 0.5C at 45°C until the voltage reaches 4.35V (relative to Li), and then the charging process is completed by terminating the charging at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode.

[0167] The impedance of each of the charged lithium batteries is measured using an impedance analyzer (Biologic VMP3, potentiostatic electrochemical impedance spectroscopy). The measurement is performed using an alternating current with an amplitude of 10 mV in the frequency range from about 1 MHz to about 100 mHz. The interfacial resistance in ohms is measured from the obtained Nyquist plot, and the results are shown in Table 3 below.

[0168] Table 3

[0169] Interface resistance [ohm] Example 1 4.90 Example 3 6.52 Example 5 6.48 Comparative Example 2 6.94

[0170] As shown in Table 3, the lithium batteries including the positive electrodes according to Examples 1, 3, and 5 have lower impedance than the lithium batteries including the positive electrode according to Comparative Example 2.

[0171] That is, since the positive electrodes according to Examples 1, 3, and 5 include 0.1 wt% or more of the linear carbon conductive material, the interfacial resistance is significantly reduced.

[0172] Evaluation of Example 4: Evaluation of charge / discharge characteristics (room temperature of 25°C), according to the CNT content

[0173] The lithium batteries prepared according to Example 1 and Comparative Example 2 are charged at a constant current of 0.2C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is terminated at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium batteries are discharged at a constant current of 0.2C until the voltage reaches 2.8V (relative to Li) (formation operation).

[0174] The lithium battery that has undergone the formation operation is charged at a constant current of 0.5C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is terminated at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium battery is discharged at a constant current of 0.5C until the voltage reaches 2.8V (relative to Li) (the first cycle). This charge / discharge cycle is repeated 50 times. The lithium battery is left standing for 20 minutes after each charge / discharge cycle.

[0175] The charge / discharge test results are shown in Table 4 below and Figure 3 in. The capacity retention rate at the 50th cycle is defined as in Equation 1 below.

[0176] Equation 1

[0177] Capacity retention rate = [Discharge capacity at the 50th cycle / Discharge capacity at the first cycle] × 100%

[0178] Table 4

[0179] CNT content [wt%] Capacity retention rate [%] Example 1 1.3 92 Comparative Example 2 0 3.2

[0180] As shown in Table 4 and Figure 3 in, compared with the lithium battery according to Comparative Example 2, the life characteristics of the lithium battery according to Example 1, which has an improved energy density due to including a positive electrode with a load of 6 mAh / cm 2 are significantly improved at room temperature.

[0181] Although the lithium battery according to Comparative Example 2 exhibits a capacity retention rate similar to that of the lithium battery according to Example 1 until about 30 cycles, the capacity retention rate rapidly decreases after about 30 cycles.

[0182] Therefore, it is confirmed that when the amount of the linear carbon conductive material in the positive electrode is less than 0.1 wt%, the life characteristics at room temperature rapidly deteriorate.

[0183] Evaluation of Example 5: Evaluation of charge / discharge characteristics (room temperature of 25°C), according to the m-PVDF content

[0184] The lithium batteries prepared according to Examples 1 and 2 and Comparative Example 3 are charged at a constant current of 0.2C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is terminated at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium batteries are discharged at a constant current of 0.2C until the voltage reaches 2.8V (relative to Li) (formation operation).

[0185] The lithium battery that has undergone the formation operation is charged at a constant current of 0.5C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is cut off at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium battery is discharged at a constant current of 0.5C until the voltage reaches 2.8V (relative to Li) (the first cycle). The charge / discharge cycle is repeated 50 times. The lithium battery is left standing for 20 minutes after each charge / discharge cycle.

[0186] The charge / discharge test results are shown in Table 5 below and Figure 4 in. The capacity retention rate at the 50th cycle is defined as in Equation 2 below.

[0187] Equation 2

[0188] Capacity retention rate = [Discharge capacity at the 50th cycle / Discharge capacity at the first cycle] × 100%

[0189] Table 5

[0190] m-PVDF content [wt%] Capacity retention rate [%] Example 1 0.1 92 Example 2 0.05 92 Comparative Example 3 0.0 3

[0191] As shown in Table 5 and Figure 4 in, compared with the lithium battery according to Comparative Example 3, the life characteristics of the lithium batteries according to Examples 1 and 2 including the positive electrode with a load of 6 mAh / cm 2 are significantly improved at room temperature.

[0192] Although the lithium battery according to Comparative Example 3 exhibits a capacity retention rate similar to that of the lithium batteries according to Examples 1 and 2 until about 30 cycles, the capacity retention rate rapidly decreases after about 30 cycles.

[0193] Therefore, it is confirmed that when the positive electrode does not include the fluorine-based first binder containing polar functional groups, the life characteristics at room temperature rapidly deteriorate.

[0194] Evaluation Example 6: Evaluation of high-rate performance at room temperature

[0195] The lithium batteries prepared according to Examples 1 and 3 and Comparative Example 1 are charged at a constant current of 0.1C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is cut off at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium batteries are discharged at a constant current of 0.1C until the voltage reaches 2.8V (relative to Li) (the first cycle, formation operation).

[0196] The lithium battery that has undergone the first cycle is charged at a constant current of 0.2C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is cut off at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium battery is discharged at a constant current of 0.2C until the voltage reaches 2.8V (relative to Li) (the second cycle).

[0197] The lithium battery that has undergone the second cycle is charged at a constant current of 0.2C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is cut off at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium battery is discharged at a constant current of 0.5C until the voltage reaches 2.8V (relative to Li) (the third cycle).

[0198] The lithium battery that has undergone the third cycle is charged at a constant current of 0.2C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is cut off at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium battery is discharged at a constant current of 1.0C until the voltage reaches 2.8V (relative to Li) (the fourth cycle).

[0199] The lithium battery that has undergone the fourth cycle is charged at a constant current of 0.2C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is cut off at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium battery is discharged at a constant current of 2.0C until the voltage reaches 2.8V (relative to Li) (the fifth cycle).

[0200] The lithium battery that has undergone the fifth cycle is charged at a constant current of 0.2C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is cut off at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium battery is discharged at a constant current of 3.0C until the voltage reaches 2.8V (relative to Li) (the sixth cycle).

[0201] The lithium battery that has undergone the sixth cycle is charged at a constant current of 0.2C at 25°C until the voltage reaches 4.35V (relative to Li), and then the charging process is cut off at a current of 0.05C while maintaining the voltage of 4.35V in the constant voltage mode. Subsequently, the lithium battery is discharged at a constant current of 0.5C until the voltage reaches 2.8V (relative to Li) (the seventh cycle).

[0202] The lithium battery is allowed to stand for 20 minutes after each charge / discharge cycle.

[0203] The charge / discharge test results are shown in Table 6 below. The high-rate performance is defined by Equations 3 and 4 below respectively.

[0204] Equation 3

[0205] High-rate performance at 2C [%] = [Discharge capacity at the 5th cycle (2C rate) / Discharge capacity at the 2nd cycle (0.2C rate)] × 100%

[0206] Equation 4

[0207] High-rate performance at 3C [%] = [Discharge capacity at the 6th cycle (3C) / Discharge capacity at the 2nd cycle (0.2C rate)] × 100%

[0208] Table 6

[0209] CNT content [wt%] 2C high-rate performance [%] 3C high-rate performance [%] Example 1 1.3 86.5 62.3 Example 3 0.7 75.8 46.8

[0210] As shown in Table 6, the lithium batteries according to Examples 1 and 3 including 0.1 wt% or more of the linear carbon conductive material have good high-rate performance. In addition, compared with the lithium battery according to Comparative Example 1 that does not include the linear carbon conductive material (which is not shown in Table 6), the lithium batteries according to Examples 1 and 3 have enhanced high-rate performance.

[0211] Moreover, compared with the lithium battery according to Example 3 having a small amount of the linear carbon conductive material, the lithium battery according to Example 1 including 1.0 wt% or more of the linear carbon conductive material has significantly improved high-rate performance.

[0212] In addition, although not shown in the figures, the lithium battery according to Comparative Example 1 that does not include the linear carbon conductive material has worse cycle characteristics than the lithium batteries according to Examples 1 and 3.

[0213] According to one embodiment, the positive electrode may have improved flexibility and improved adhesion due to including the first binder and the linear carbon conductive material.

[0214] According to another embodiment, the lithium battery may have improved life characteristics due to including a positive electrode having improved flexibility and improved adhesion.

[0215] According to another embodiment, the lithium battery may have improved energy density by including a positive electrode having improved flexibility and improved adhesion, including the nickel-rich lithium transition metal oxide and having an increased load.

[0216] It should be understood that the embodiments described herein are to be considered in a descriptive sense only and not for purposes of limitation. The description of features or aspects within each embodiment should typically be considered applicable to other similar features or aspects in other embodiments.

[0217] Although the embodiments have been described with reference to the accompanying drawings, those of ordinary skill in the art will understand that various changes in form and detail may be made therein without departing from the spirit and scope defined by the appended claims.

Claims

1. A positive electrode, wherein the positive electrode comprises: a positive electrode active material comprising a lithium transition metal oxide; a conductive material; and a binder, wherein the lithium transition metal oxide comprises nickel and a transition metal other than nickel, wherein the lithium transition metal oxide has a layered crystal structure, wherein the content of nickel is 30 mole percent or more, based on the total mole number of the transition metals of the lithium transition metal oxide, wherein the conductive material is a single linear carbon conductive material, or a mixture of a linear carbon conductive material and a particulate carbon conductive material, and the particulate carbon conductive material is carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal carbon black, or a combination thereof, wherein the linear carbon conductive material comprises carbon nanotubes, carbon nanofibers, carbon nanorods, or a combination thereof, wherein the binder is composed of a first binder containing fluorine and a polar functional group and a second binder not containing fluorine, and wherein the amount of the linear carbon conductive material is 0.1 weight percent or more, based on the total combined weight of the positive electrode active material, the conductive material, and the binder, wherein the amount of the first binder is 0.2 weight % or less, based on the total combined weight of the positive electrode active material, the conductive material, and the binder, wherein the amount of the second binder is 0.26 weight % to 2 weight %, based on the total combined weight of the positive electrode active material, the conductive material, and the binder.

2. The positive electrode according to claim 1, wherein the aspect ratio of the linear carbon conductive material is 2 or more, and wherein the aspect ratio of the particulate carbon conductive material is less than 2.

3. The positive electrode according to claim 1, wherein the weight ratio of the linear carbon conductive material to the particulate carbon conductive material is 90:10 to 10:

90.

4. The positive electrode according to claim 1, wherein the first binder comprises: a repeating unit comprising a polar functional group; a repeating unit derived from vinylidene fluoride; and optionally, a repeating unit derived from tetrafluoroethylene, hexafluoropropylene, trichlorofluoroethylene, a fluorine-containing vinyl monomer, a perfluoroalkyl vinyl ether, or a combination thereof, wherein the weight-average molecular weight of the first binder is 1,000,000 daltons or more.

5. The positive electrode according to claim 1, wherein the polar functional group of the first binder comprises a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, a salt thereof, or a combination thereof.

6. The positive electrode according to claim 1, wherein the second binder comprises a cyano group.

7. The positive electrode according to claim 1, wherein the second binder comprises a repeating unit derived from an acrylonitrile-containing monomer and a repeating unit derived from an olefin-containing monomer.

8. The positive electrode according to claim 1, wherein the lithium transition metal oxide is a compound represented by Formula 2: Formula 2 Li a Ni x Co y M z O 2-b A b Among them, In Formula 2, 1 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.3 ≤ x < 1, 0 < y ≤ 0.4, 0 < z ≤ 0.4, x + y + z = 1, M comprises manganese, vanadium, magnesium, gallium, silicon, tungsten, molybdenum, iron, chromium, copper, zinc, titanium, aluminum, boron, or a combination thereof, and A is F, S, Cl, Br, or a combination thereof.

9. The positive electrode according to claim 1, wherein the lithium transition metal oxide is a compound represented by Formula 3 or 4: Formula 3 LiNi x Co y Mn z O2 Formula 4 LiNi x’ Co y ’ Al z’ O2 Among them, In Formula 3, 0.3 ≤ x < 1, 0 < y ≤ 0.4, and 0 < z ≤ 0.4, and wherein, in Formula 4, 0.3 ≤ x' < 1, 0 < y' ≤ 0.4, and 0 < z' ≤ 0.

4.

10. The positive electrode according to claim 1, wherein the amount of the positive electrode active material is 95 weight percent to 98.9 weight percent, the amount of the conductive material is 1 weight percent to 4 weight percent, and the amount of the binder is 0.01 weight percent to 2 weight percent, based on the total combined weight of the positive electrode active material, the conductive material, and the binder, and wherein the loading of the positive electrode is 3 milliampere-hours per square centimeter or greater.

11. The positive electrode according to claim 10, wherein the loading of the positive electrode is 5 milliampere-hours per square centimeter or greater.

12. The positive electrode according to claim 1, wherein during a flexural performance test conducted according to ASTM D790, the positive electrode has a bending motion range of 90 degrees or greater.

13. The positive electrode according to claim 1, wherein the maximum bending strength of the positive electrode obtained from the flexural performance test conducted according to ASTM D790 is 1 Newton or less.

14. The positive electrode according to claim 1, wherein the peel strength of the positive electrode obtained from a 180-degree peel strength test conducted according to ASTM D3330 is 0.3 grams-force per millimeter or greater.

15. A lithium battery, comprising: the positive electrode according to any one of claims 1-14; a negative electrode; and an electrolyte located between the positive electrode and the negative electrode.

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