Polymer composite binder for lithium secondary battery electrode mixture and lithium secondary battery including same

Abstract

The present disclosure relates to a polymer composite binder for a lithium secondary battery electrode mixture, the polymer composite binder comprising a crystalline organic polymer and an ionic material. A polymer composite binder according to the present disclosure satisfies Nc < Np (Nc is the number of diffraction peaks located in a composite diffraction pattern which is a diffraction pattern in the 2θ range of 10 to 35° in the X-ray diffraction pattern of the polymer composite binder, and Np is the number of diffraction peaks located in a polymer diffraction pattern which is a diffraction pattern in the 2θ range of 10 to 35° in the X-ray diffraction pattern of a pristine organic polymer). The polymer composite binder according to the present disclosure can be included in an electrode to achieve uniform distribution of the binder and an excellent conductive network in the electrode, and effectively suppress volume expansion of the electrode.

Description

Polymer composite binder for lithium secondary battery electrode composites and lithium secondary battery including the same

[0001] The present invention relates to a polymer composite binder for a lithium secondary battery electrode composite, an electrode for a lithium secondary battery containing the same, and a lithium secondary battery.

[0002] Recently, as the required energy density of batteries has increased rapidly, the development of high-capacity lithium-ion batteries has become urgent. To this end, research is actively underway to replace conventional anode materials, such as graphite or silicon, with lithium metal, or to incorporate cathode materials with high energy density into the electrodes.

[0003] Binders are essential for bonding the positive and negative electrodes of lithium-ion batteries. The binder must be inert and insoluble in the electrolyte, while also possessing chemical stability to prevent degradation due to electrochemical oxidation. Furthermore, the binder must be designed to suppress electrode volume expansion to maintain battery performance and lifespan characteristics, while simultaneously enabling the development of a conductive network within the electrode.

[0004] Typically, fluorine-based polymers such as PVdF (Polyvinylidene fluoride), PVdF-based copolymers, and mixtures thereof are primarily used in the cathode. Specifically, while PVdF offers excellent electrochemical safety and superior adhesion performance, it requires large quantities and has a high unit cost, presenting many cost considerations. Additionally, using styrene-butadiene rubber or nitrile-butadiene rubber offers economic advantages due to its low unit cost and improved flexibility, which prevents physical cracking or non-uniformity of the cathode material during rolling; however, their insufficient adhesion results in poor bonding with the active material, and the electrode expands during multiple charge-discharge cycles, leading to a degradation of battery performance and lifespan characteristics.

[0005] In addition to the aforementioned problems, as the electrode thickness increases, the non-uniformity of the binder distribution intensifies, leading to non-uniform lithium ion flow characteristics and causing issues such as non-uniform charge / discharge characteristics along the thickness direction and polarization phenomena. Furthermore, as the electrode thickness increases, physical cracking or non-uniformity of the cathode material occurs during coating, drying, or rolling processes, making it difficult to secure stable battery performance and lifespan characteristics.

[0006] Accordingly, there is an urgent need to develop a binder that has excellent adhesion to the active material, possesses a superior conductive network within the electrode, and can maintain uniform distribution characteristics even within thick-film electrodes.

[0007] One objective of the present disclosure is to provide a polymer composite binder with excellent adhesion properties to current collectors or active materials, which has no cracking and significantly lower defect rates during the electrode manufacturing process, thereby offering excellent economic advantages.

[0008] Another objective of the present disclosure is to provide a polymer composite binder that has a very uniform distribution of binder even in a thick-film electrode and can form an excellent conductive network within the electrode.

[0009] Another objective of the present disclosure is to provide a lithium secondary battery having excellent battery performance and lifespan characteristics, in which the active material is uniformly distributed even in a thick-film electrode and volume expansion is effectively suppressed.

[0010] The polymer composite binder according to the present disclosure is a polymer composite binder for lithium secondary battery electrode composites, and comprises a crystalline organic polymer and an ionic material, satisfying Formula 1 below.

[0011] (Equation 1)

[0012] Nc < Np

[0013] In Equation 1, Nc is the number of diffraction peaks located in the composite diffraction pattern, which is the diffraction pattern in the 2θ range of 10 to 35° in the X-ray diffraction pattern of the polymer composite binder, and Np is the number of diffraction peaks located in the polymer diffraction pattern, which is the diffraction pattern in the 2θ range of 10 to 35° in the X-ray diffraction pattern of the pure (pristine) organic polymer.

[0014] In one embodiment, Np may be a natural number from 2 to 6 and Nc may be a natural number 0 or less than or equal to Np-1.

[0015] In one embodiment, the polymer composite binder may further satisfy Formula 2 below.

[0016] (Equation 2)

[0017] 20% ≤ I1 / I0×100 ≤ 50%

[0018] In Equation 2, I1 is the peak intensity of the diffraction peak having the strongest intensity in the composite diffraction pattern, and I0 is the peak intensity of the diffraction peak having the strongest intensity in the polymer diffraction pattern.

[0019] In one embodiment, the diffraction peak having the strongest intensity in each of the composite diffraction pattern and the polymer diffraction pattern may be located in the 2θ range of 19.7 to 20.7°.

[0020] In one embodiment, the polymer composite binder may further satisfy Formula 3 below.

[0021] (Equation 3)

[0022] 60% ≤ I2 / I1×100 ≤ 70%

[0023] In Equation 3, I1 is the peak intensity of the diffraction peak located at 19.7 to 20.7° in the composite diffraction pattern, and I2 is the peak intensity of the diffraction peak located at 17.7 to 18.7° in the composite diffraction pattern.

[0024] In one embodiment, the polymer composite binder may further satisfy Formula 4 below.

[0025] (Equation 4)

[0026] 80% ≤ I3 / I2×100 ≤ 98%

[0027] In Equation 4, I2 is the peak intensity of the diffraction peak located at 17.7 to 18.7° of the composite diffraction pattern, and I3 is the diffraction intensity of the composite diffraction pattern at a point 2θ, which is β°-1.5° from the peak center of the diffraction peak located at 17.7 to 18.7°.

[0028] In one embodiment, the organic polymer may be one or more selected from the group consisting of polyvinylidene fluoride (PVdF) and vinylidene fluoride-based copolymers.

[0029] In one embodiment, the ionic material may be an ionic organic compound or an ion-dissociable metal salt.

[0030] In one embodiment, the ionic material may contain fluorine.

[0031] In one embodiment, the ionic material may be any one or a combination of two or more selected from the group consisting of 1-ethyl-3-methylimidazoliium bis(trifluoromethylsulfonyl)imide (EMIm TFSI), poly(1-ethyl-3-vinylimidazoliium)bis(trifluoromethanesulfonyl)imide (p(EVIm TFSI)), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0032] In one embodiment, the ion-dissociable metal salt may be a sulfonyl group-containing metal salt selected from the following formula 1 or formula 2.

[0033] [Chemical Formula 1]

[0034]

[0035] [Chemical Formula 2]

[0036]

[0037] In the above chemical formulas 1 and 2, n is 1 or 2, A is an n-valent cation, and R1 to R3 are each independently a fluoro(C1-C7)alkyl or fluoro group.

[0038] In one embodiment, A may be lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium, or calcium.

[0039] The present disclosure includes an electrode for a lithium secondary battery comprising an electrode active material and the aforementioned polymer composite binder.

[0040] The present disclosure includes a lithium secondary battery comprising the aforementioned electrode.

[0041] The present disclosure comprises a binder solution for a lithium secondary battery electrode composite, wherein the binder solution has diffraction peaks located in the 2θ range of 19.7 to 20.7° and the 2θ range of 17.7 to 18.7° in the solid X-ray diffraction pattern obtained by volatilizing the solvent of the binder solution, and the intensity ratio obtained by dividing the peak intensity of the diffraction peak located at 17.7 to 18.7° by the peak intensity of the diffraction peak located at 19.7 to 20.7° is 60 to 70%.

[0042] In one embodiment, in the X-ray diffraction pattern of the solid phase, the number of diffraction peaks located in the 2θ range of 10 to 35° may be two.

[0043] The polymer composite binder according to the present disclosure has excellent adhesion properties with current collectors or active materials, so there are no cracks in the electrode manufacturing process and the defect rate of the manufactured electrode is significantly low, thereby providing excellent economic advantages.

[0044] Furthermore, the polymer composite binder according to the present disclosure has a very uniform distribution of the binder even in thick-film electrodes, forms an excellent conductive network within the electrode, induces a uniform distribution of the active material, and can effectively suppress the volume expansion of the electrode. Accordingly, the present disclosure can provide an electrochemical device capable of simultaneously satisfying excellent lifespan characteristics and stability by having excellent battery performance, such as excellent initial efficiency and capacity retention rate, and a low thickness increase rate.

[0045] The various and beneficial advantages and effects of the present invention are not limited to those described above and will be more easily understood in the process of explaining specific embodiments of the present invention.

[0046] The present invention will be explained in more detail below through specific examples or embodiments. However, the following specific examples or embodiments are merely references for explaining the present invention in detail, and the present invention is not limited thereto and may be implemented in various forms.

[0047] Unless otherwise defined in this specification, all technical and scientific terms have the same meaning as generally understood by those skilled in the art to which the present invention pertains. The terms used in the description herein are merely for the purpose of effectively describing specific embodiments and are not intended to limit the present invention.

[0048] Additionally, the singular form used in this specification may be intended to include the plural form unless specifically indicated otherwise in the context.

[0049] Additionally, units used herein without special reference are based on weight, and, for example, units of % or ratio mean weight % or weight ratio, and weight % means the weight percentage of any one component of the total composition that occupies the composition, unless otherwise defined.

[0050] Furthermore, in this specification and the appended claims, when a part such as a film (layer), region, or component is described as being on or above another part, it includes not only cases where it is directly above in contact with the other part, but also cases where another film (layer), other region, other component, etc. is interposed therein.

[0051] Additionally, numerical ranges used herein include lower and upper limits and all values ​​within the range, increments logically derived from the form and width of the defined range, all of which are limited values, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. Unless otherwise specifically defined in this specification, values ​​outside the numerical range that may occur due to experimental error or rounding are also included in the defined numerical range.

[0052] The term “comprising” in this specification is an open description having an equivalent meaning to expressions such as “comprising,” “containing,” “having,” or “characterizing,” and does not exclude elements, materials, or processes not additionally listed.

[0053] The term "porous binder scaffold" in this specification refers to a network structure uniformly formed in three dimensions by a binder (an organic polymer component contained in a polymer composite binder), wherein the binder forms a framework and pores are richly developed within the framework. The pores preferably have an open pore structure, and the porous network structure formed by the binder can serve as a support in which the cathode active material and the conductive material can be evenly distributed. The pores may have a diameter of 0.1 μm to 50 μm, specifically a diameter of 0.5 μm to 10 μm, but are not limited thereto.

[0054] In this specification, the term 'crystalline' in crystalline organic polymers refers to a semicrystalline polymer having both an amorphous region and a crystalline region, wherein the crystalline region includes a region in which regular chain folding occurs. A crystalline organic polymer may refer to a polymer having a degree of crystallization of at least 20%, specifically 30% or more, and substantially 80% or less. In this case, the degree of crystallization of a polymer may be calculated as the ratio (%) obtained by dividing the heat of fusion of the polymer measured by a differential scanning thermal analyzer by the heat of fusion of a polymer having 100% crystallization.

[0055] The polymer composite binder for a lithium secondary battery electrode composite according to the present disclosure comprises a crystalline organic polymer and an ionic material, and is characterized by satisfying Formula 1 below.

[0056] (Equation 1)

[0057] Nc < Np

[0058] In Equation 1, Nc is the number of diffraction peaks located in the composite diffraction pattern, which is the diffraction pattern in the 2θ range of 10 to 35° in the X-ray diffraction pattern of the polymer composite binder, and Np is the number of diffraction peaks located in the polymer diffraction pattern, which is the diffraction pattern in the 2θ range of 10 to 35° in the X-ray diffraction pattern of the pure (pristine) organic polymer. Here, the pure organic polymer refers to the organic polymer contained in the polymer composite binder, which is the pure organic polymer itself, in which no other foreign substances are intentionally added.

[0059] Equation 1 is derived from the fact that the organic polymer and the ionic substance contained in the polymer composite binder interact strongly with each other and form a composite, causing the physical properties of the organic polymer to differ from those of a pure organic polymer. In other words, Equation 1 is a property indicator in which the interaction between the organic polymer and the ionic substance manifests as a crystallographic property.

[0060] Specifically, based on the number of diffraction peaks in the X-ray diffraction pattern appearing in the same 2θ range of 10 to 35°, the number of diffraction peaks Nc of the polymer composite binder may be smaller than the number of diffraction peaks Np of the pure organic polymer. That is, the number of diffraction peaks Nc located in the 2θ range of 10 to 35° in the X-ray diffraction pattern of the polymer composite binder and the number of diffraction peaks Np located in the 2θ range of 10 to 35° in the X-ray diffraction pattern of the pure organic polymer may satisfy the relationship Nc < Np.

[0061] In a practical example, Np may be a natural number from 2 to 6 and Nc may be a natural number 0 or less than or equal to Np-1, or Np may be a natural number from 3 to 6 and Nc may be a natural number 0 or less than or equal to Np-2, or Np may be a natural number from 4 to 6 and Nc may be a natural number 0 or less than or equal to Np-3. In a more practical example, Np may be a natural number from 4 to 6 and Nc may be 1, 2, or 3.

[0062] As described above, the polymer composite binder, which is formed by strong interaction between an organic polymer and an ionic material, can exhibit excellent adhesion characteristics between current collectors and active materials. Furthermore, it offers significant economic advantages by being crack-free and having a significantly low defect rate during the electrode manufacturing process. Additionally, the polymer composite binder, formed by strong interaction between an organic polymer and an ionic material, can ensure a very uniform distribution of the binder even when incorporated into a thick-film electrode, and can form an excellent conductive network within the electrode. Moreover, the polymer composite binder, formed by strong interaction between an organic polymer and an ionic material, can very effectively suppress the volume expansion of the electrode after inclusion, thereby enabling the lithium secondary battery to possess excellent battery performance and lifespan characteristics.

[0063] In one embodiment, the polymer composite binder may further satisfy Formula 2 below.

[0064] (Equation 2)

[0065] 20% ≤ I1 / I0×100 ≤ 50%

[0066] In Equation 2, I1 is the peak intensity of the diffraction peak having the (relatively) strongest intensity in the composite diffraction pattern, and I0 is the peak intensity of the diffraction peak having the (relatively) strongest intensity in the polymer diffraction pattern. Specifically, I1 / I0×100 may be 20 to 50%, more specifically 30 to 45%.

[0067] Specifically, the composite diffraction pattern may have a first diffraction peak corresponding to the diffraction peak (hereinafter referred to as the main diffraction peak) having the relatively strongest diffraction intensity (I0) in the polymer diffraction pattern. In this case, "corresponding" may mean that the diffraction angle (2θ) of the first diffraction peak in the composite diffraction pattern is located within the range of ± 0.5° of the diffraction angle (2θ0) of the main diffraction peak in the polymer diffraction pattern. Furthermore, the statement that the diffraction peak is located within a specific 2θ range should not be interpreted as the entire region of the diffraction peak being located within a specific 2θ range, but rather as the center of the diffraction peak being located within a specific 2θ range. As a practical example, the diffraction peaks having the strongest intensity (the first diffraction peak and the main diffraction peak) in the composite diffraction pattern and the polymer diffraction pattern, respectively, may both be located within a 2θ range of 19.7 to 20.7°.

[0068] As shown in Equation 2, the peak intensity of the first diffraction peak (maximum diffraction intensity, I1) in the composite diffraction pattern may have a significantly lower intensity compared to the peak intensity of the main diffraction peak (maximum diffraction intensity, I0) in the polymer diffraction pattern. This low intensity implies that the organic polymer contained in the polymer composite binder has significantly lower crystallinity than the pure organic polymer. This low crystallinity may be due to complex formation resulting from the interaction between the organic polymer and the ionic material.

[0069] Crystallographic changes resulting from the complexation between an organic polymer and an ionic material can also cause an increase in the full width at half maximum (FWHM) of the first diffraction peak in the complex diffraction pattern. As a practical example, the full width at half maximum of the first diffraction peak may be 1.00° or more, more substantially 1.00 to 2.00°, 1.30 to 1.80°, or 1.45 to 1.60°.

[0070] In one embodiment, the polymer composite binder may further satisfy Formula 3 below.

[0071] (Equation 3)

[0072] 60% ≤ I2 / I1×100 ≤ 70%

[0073] In Equation 3, I1 is the peak intensity of the diffraction peak located at 19.7 to 20.7° in the composite diffraction pattern, and I2 is the peak intensity of the diffraction peak located at 17.7 to 18.7° in the composite diffraction pattern.

[0074] Specifically, the composite diffraction pattern may include a diffraction peak located at 19.7 to 20.7° and a diffraction peak located at 17.7 to 18.7°, and the intensity ratio (I2 / I1×100, %) obtained by dividing the peak intensity I2 of the diffraction peak located at 17.7 to 18.7° by the peak intensity I1 of the diffraction peak located at 19.7 to 20.7° may be 60 to 70%, specifically 65 to 69%. At this time, the diffraction peak located at 19.7 to 20.7° may be the aforementioned first diffraction peak.

[0075] Alternatively, the complex diffraction pattern may have two or more diffraction peaks, substantially two diffraction peaks, and the two diffraction peaks may be a diffraction peak located at 19.7 to 20.7° (corresponding to the first diffraction peak) and a diffraction peak located at 17.7 to 18.7° (collectively referred to as the second diffraction peak).

[0076] When the crystal structure of an organic polymer within a polymer composite binder is broken or distorted due to the interaction between the organic polymer and the ionic substance, the weaker the diffraction plane in the polymer diffraction pattern, the greater the impact of such breakage or distortion of the crystal structure. Accordingly, the ratio of the intensity of another diffraction peak to the intensity of the first diffraction peak in the composite diffraction pattern can also indicate the degree of interaction between the organic polymer and the ionic substance. The aforementioned intensity ratio between I1 and I2 may indicate that strong interaction between the organic polymer and the ionic substance occurred homogeneously throughout the polymer composite binder.

[0077] In one embodiment, the polymer composite binder may further satisfy Formula 4 below.

[0078] (Equation 4)

[0079] 80% ≤ I3 / I2×100 ≤ 98%

[0080] In Equation 4, I2 is the peak intensity of the diffraction peak located at 17.7 to 18.7° of the composite diffraction pattern, and I3 is the diffraction intensity of the composite diffraction pattern at a point 2θ, which is β°-1.5° from the peak center of the diffraction peak located at 17.7 to 18.7°.

[0081] The more homogeneously the strong interaction between the organic polymer and the ionic substance occurs throughout the organic polymer, the greater the peak broadening can appear, as well as a decrease in the diffraction intensity of the second diffraction peak.

[0082] Equation 4 indicates the degree of broadening of the second diffraction peak, which is substantially free from the influence of the first diffraction peak and has a relatively weak diffraction intensity. The diffraction intensity I3 at 2θ of β° - 1.5° may be 80 to 98% of I2, specifically 85 to 98%, more specifically 90 to 98%, and even more specifically 92 to 97%. Such an intensity ratio of I3 / I2 implies that the crystal structure of the diffraction plane(s) contributing to the second diffraction peak is severely distorted and warped, and the regularity of the structure is severely impaired throughout the organic polymer contained in the polymer composite binder.

[0083] Experimentally, the composite diffraction pattern and the polymer diffraction pattern may be raw data obtained using an X-ray diffraction device (Rigaku SmartLab high resolution powder XRD) under conditions of Cu Kα rays, 40 kV, 200 mA, and a scan rate of 0.04 ° / min.

[0084] The aforementioned change in crystallinity is due to strong interactions between organic polymers and ionic substances, and is a result of the polymer composite binder differing merely from a mixture of organic polymers and ionic substances.

[0085] According to one embodiment, the organic polymer may be a fluorine-based polymer and / or a copolymer of a fluorine-based and a hydrocarbon-based polymer. According to one embodiment, the organic polymer may be one or more combinations selected from the group consisting of polyvinylidene fluoride (PVdF) and vinylidene fluoride-based copolymers. Representative examples of vinylidene fluoride-based copolymers include, but are not limited to, one or more combinations selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polyvinylidene fluoride-tetrafluoroethylene copolymer (PVdF-TrFE), polyvinylidene fluoride-polymethyl methacrylate (PVdF-PMMA), and polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE). The above organic polymer may have a weight-average molecular weight of 10,000 g / mol or more, and may be, without limitation, 5,000,000 g / mol or less. For example, the weight-average molecular weight of the organic polymer may be 10,000 to 5,000,000 g / mol or 20,000 to 1,000,000 g / mol, but is not limited thereto.

[0086] According to one embodiment, the ionic material may be included in an amount of 0.01 to 200 parts by weight, specifically 1 to 100 parts by weight, more specifically 10 to 100 parts by weight, and even more specifically 15 to 80 parts by weight, with respect to 100 parts by weight of the organic polymer, but is not limited thereto. The organic polymer and the ionic material may be homogeneously composited and uniformly distributed within the polymer composite binder. Specifically, the ionic material may be present mixed with the organic polymer at a molecular level. To ensure that the ionic material and the organic polymer included in the polymer composite binder are mixed (complexed) at a molecular level and have stronger interactions as described below, this may be achieved through heat treatment in a solid phase.

[0087] According to one embodiment, the ionic material may be an ionic organic compound or an ion-dissociable metal salt. The ionic organic compound may be an ionic liquid or an ionic polymer. The ionic organic compound may refer to a hydrocarbon ligand in which the cation and anion are hydrocarbon-based or contain heteroelements, and is not limited to being cyclic or acyclic. An example of such a hydrocarbon ligand or a hydrocarbon ligand containing heteroelements may be a ligand (cationic group) containing a straight-chain or branched substituted imidazolium, ammonium, pyrrolidinium, or piperidinium cation, such as PF6 - , BF4 - , CF3SO3 - , (CF3SO2)2N - , (C2F5SO2)2N - , (C6F5SO2)2N - or (CN)2N - Examples include ligands (anionic groups) including the back.

[0088] According to one embodiment, the ionic material may contain fluorine. The fluorine may be located in the anionic group of the ionic material. The fluorine-containing anionic group is, for example, PF6 - , BF4 - , CF3SO3 - , (CF3SO2)2N - , (C2F5SO2)2N - or (C6F5SO2)2N - It may include.

[0089] According to one embodiment, the ionic material may be any one or more combinations selected from the group consisting of 1-ethyl-3-methylimidazoliium bis(trifluoromethylsulfonyl)imide (EMIm TFSI), poly(1-ethyl-3-vinylimidazoliium)bis(trifluoromethanesulfonyl)imide (p(EVIm TFSI)), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0090] The above ion-dissociable metal salt may be an ion-dissociable lithium salt, specifically an ion-dissociable fluorine-containing lithium salt. The above 'ion-dissociable' means dissociating into metal cations and anions in a solvent used as an electrolyte for a lithium secondary battery.

[0091] According to one embodiment, the ion-dissociable metal salt may be a sulfonyl group-containing metal salt selected from the following formula 1 or formula 2.

[0092] [Chemical Formula 1]

[0093]

[0094] [Chemical Formula 2]

[0095]

[0096] In the above chemical formulas 1 and 2, n is independently 1 or 2; A is independently an n-valent cation; and R1 to R3 are each independently a fluoro(C1-C7)alkyl or fluoro group.

[0097] According to one embodiment, A may be lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium, or calcium, and specifically may be lithium.

[0098] Furthermore, the present disclosure provides a method for manufacturing the aforementioned polymer composite binder. In the manufacturing method, the specific type of organic polymer, the specific type of ionic material, and the content between the two materials are identical or similar to those described above in the polymer composite binder. Accordingly, the method for manufacturing the polymer composite binder includes all the details described above in the polymer composite binder.

[0099] A method for manufacturing a polymer composite binder according to one embodiment can be manufactured by a step of compounding a mixture comprising an organic polymer and an ionic material at a temperature of 150 to 250°C, specifically at a temperature of 200 to 250°C and a speed of 30 to 80 rpm. At this time, it is sufficient for the compounding to be performed using a compounding extruder equipped with a mixer commonly used in the polymer field.

[0100] In addition, the present disclosure provides an electrode for a lithium secondary battery, wherein the electrode comprises an electrode active material, a polymer composite binder as described above, and optionally a conductive material.

[0101] In addition, the present disclosure provides a lithium secondary battery comprising an electrode as described above. The electrode may be a positive electrode or a negative electrode, and the active material included in the positive electrode or the negative electrode may be selected from materials known in the art without limitation. The conductive material may also be selected from materials known in the art without limitation as a material used to improve the conductivity of the positive electrode or the negative electrode.

[0102] The above-mentioned polymer composite binder may be included as a component of a slurry composition to be included in a positive electrode or a negative electrode. For example, to manufacture a positive electrode, a composition comprising positive electrode active material particles containing lithium oxide, a conductive material, and a polymer composite binder may be prepared first. To achieve a viscosity suitable for coating, the conditions of the manufacturing method may be modified, such as by adjusting the order of input sequentially or alternately, adjusting the temperature of input, or adjusting the amount of input at each step. An electrode may be manufactured through a conventional process of coating, drying, and rolling the aforementioned composition (slurry) onto a current collector.

[0103] As the above-mentioned polymer composite binder is included in the electrode, a porous binder scaffold can be formed, and the binder can form a framework while having an open pore structure with abundantly developed pores. By having a scaffold structure as described above, the positive active material and the conductive material can be uniformly distributed throughout the electrode, thereby significantly improving the electrochemical properties of the electrode.

[0104] The above-mentioned polymer composite binder can function as a precursor that induces the formation of a porous binder scaffold within the electrode, and can reduce the defect rate of the electrode and maintain consistent electrode quality by ensuring that there is almost no variation in the electrochemical properties of the electrode during each individual manufacturing process.

[0105] The polymer composite binder in the electrode may be included in an amount of 0.01% to 20% by weight, specifically 0.1% to 10% by weight, based on dry weight relative to the total weight of the electrode.

[0106] Likewise, to manufacture the cathode, carbon-based, silicon-based, lithium metal, or a mixture thereof may be used as the cathode active material.

[0107] A lithium secondary battery may comprise a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, and an electrolyte that conducts lithium ions, or may comprise a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive and negative electrodes. The solvent, electrolyte salt, or concentration of electrolyte salt, and solid electrolyte in the separator and electrolyte may be materials or compositions that are conventionally adopted in lithium secondary batteries.

[0108] The present disclosure includes a binder solution for a lithium secondary battery electrode composite comprising the aforementioned polymer composite binder and solvent.

[0109] The present disclosure comprises a binder solution for a lithium secondary battery electrode composite, wherein the binder solution has diffraction peaks located in the 2θ range of 19.7 to 20.7° and the 2θ range of 17.7 to 18.7° in the solid X-ray diffraction pattern obtained by volatilizing the solvent of the binder solution, and the intensity ratio obtained by dividing the peak intensity of the diffraction peak located at 17.7 to 18.7° by the peak intensity of the diffraction peak located at 19.7 to 20.7° is 60 to 70%.

[0110] In one embodiment, the X-ray diffraction pattern of the solid obtained by volatilizing the solvent of the binder solution may be substantially the same as the composite diffraction pattern of the polymer composite binder described above. The solid obtained by volatilizing the solvent of the binder solution may be a powder obtained by drying the binder solution while stirring at 120°C.

[0111] In one embodiment, the binder solution may contain 1 to 20 weight%, specifically 2 to 15 weight%, of a polymer composite binder, but is not limited thereto.

[0112] In one embodiment, any material known in the art may be selected without limitation as the solvent of the active material slurry for manufacturing the electrode as the solvent of the binder solution. Representative examples of solvents contained in the binder solution include dimethylsulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, or water, but are not limited thereto.

[0113] The present invention will be explained in more detail below based on the following examples and comparative examples. However, the following examples and comparative examples are merely illustrative of the present invention and are not intended to limit the present invention.

[0114]

[0115] [Physical Property Evaluation]

[0116] (1) Binder-to-current collector adhesion (Adhesion) (N / 20mm)

[0117] A polymer binder composite containing organic polymers and ionic materials of the examples and comparative examples was mixed with N-methyl-2-pyrrolidone (NMP) to produce a mixture (polymer binder composite content 8 wt%), which was then applied onto an electrode current collector and dried to prepare a current collector coated with a binder composition. The current collector coated with the binder composition was cut to a width of 20 mm, and a 180° peel-off evaluation was performed using 3M Scotch tape with a Universal Test Machine (UTM). A higher result value was evaluated as indicating superior adhesion between the current collector and the binder composition.

[0118] (2) Binder-electrode active material cohesion (N / 20mm)

[0119] The anodes prepared according to the examples and comparative examples were cut to a width of 20 mm, and a 180° peel-off evaluation was performed using 3M Scotch tape with a UTM. A higher result value was evaluated as indicating superior bonding strength between the polymer binder composite and the electrode active material.

[0120] (3) Solid content (%)

[0121] The solid and liquid components in the slurry composition prepared according to the examples and comparative examples were distinguished and the input amounts of each were recorded, and the solid content was measured by calculating (input amount of solid component) / (input amount of solid component + input amount of liquid component).

[0122] (4) Initial efficiency (%)

[0123] The electrochemical elements of the examples and comparative examples were charged to 4.4V at a rate of 0.1 C-rate under constant current / constant voltage (CC / CV) conditions at 25°C and then cut off. Subsequently, they were discharged to 3.0V at a rate of 0.1 C-rate (CC conditions). The percentage of the value obtained by dividing the discharge capacity by the charge capacity was calculated and expressed as the initial efficiency in the table below.

[0124] (5) Battery performance evaluation

[0125] The electrochemical elements of the examples and comparative examples were charged to 4.4V at a rate of 0.2 C-rate under constant current / constant voltage (CC / CV) conditions at 25°C and then cut off. Subsequently, they were discharged to 3.0V at a rate of 0.2 C-rate (CC conditions). After 50 cycles, the battery life capacity retention rate and the electrode thickness increase rate were calculated using the following formula and are shown in the table below. The thickness increase rate was calculated from the positive electrode recovered from the battery after 50 cycles.

[0126] [Meal] 50 th Capacity retention rate = [50 th Discharge capacity / 1 st Discharge Capacity] × 100 (%)

[0127] [Formula] Electrode thickness increase rate = [(50 th [Charged electrode thickness - Initial electrode thickness) / (Initial electrode thickness - Electrode current collector thickness)] × 100 (%)

[0128] [Preparation Example 1]

[0129] A polymer composite binder was prepared by mixing 100 parts by weight of polyvinylidene fluoride (PVdF, Solvay, Solef 5130) as an organic polymer with 50 parts by weight of 1-ethyl-3-methylimidazolidium bis(trifluoromethylsulfonyl)imide (EMIm TFSI) as an ionic material and compounding through an extruder at 230°C and 50 rpm.

[0130] [Preparation Example 2]

[0131] A polymer composite binder was prepared in the same manner as in Preparation Example 1, except that lithium bis(trifluoromethanesulfonyl)imide was used as the ionic material.

[0132] [Example 1]

[0133] The cathode active material, the conductive material, and the polymer composite binder of Preparation Example 1 were sequentially added to an N-methyl-2-pyrrolidone solvent and stirred. Specifically, as the cathode active material, LiNi with an average particle size of 5 μm was used. 0.9 Mn 0.05 Co 0.05 O295 wt%, 2 wt% carbon black (Super-P) with an average particle size of 40 nm as a conductive material, and 3 wt% of the polymer composite binder of Preparation Example 1 were added to finally prepare an anode material slurry composition having a solid content of 76 wt%.

[0134] The above cathode material slurry composition was applied to an aluminum thin film with a thickness of 20 μm using a doctor blade, dried with hot air at 100°C, vacuum dried at 130°C for 24 hours, and rolled with a roll press to produce a cathode with a porous binder scaffold structure of a total thickness of 70 μm in which cathode active material particles are evenly distributed.

[0135] A cathode material was prepared by mixing 96 wt% of natural graphite with an average particle size of 20 μm as the cathode active material, 1 wt% of carbon black (Super-P) with an average particle size of 40 nm as the conductive material, and 1.5 wt% each of CMC (carboxymethylcellulose) and SBR (styrene-butadiene rubber) as binders (total 100 wt%). A cathode material slurry (100 wt%) was prepared by adding the cathode material to 40 wt% of distilled water so that the cathode material made up 60 wt%. The cathode material slurry was applied to a copper thin film with a thickness of 20 μm using a doctor blade, hot-air dried at 100°C, vacuum dried at 130°C for 24 hours, and rolled with a roll press to produce a cathode according to the example having a cathode active material layer with a thickness of 65 μm.

[0136] [Example 2]

[0137] A cathode material slurry composition, a cathode, and a negative electrode were prepared in the same manner as in Example 1, except that the polymer composite binder prepared in Preparation Example 2 was used.

[0138] [Comparative Example 1]

[0139] The cathode active material, conductive material, and organic polymer were sequentially added to a single solvent of N-methyl-2-pyrrolidone. Specifically, LiNi with an average particle size of 5 μm was used as the cathode active material. 0.9 Mn 0.05 Co 0.05 O295 wt%, 2 wt% carbon black (Super-P) with an average particle size of 40 nm as a conductive material, 2 wt% polyvinylidene fluoride, and 1 wt% lithium bis(trifluoromethanesulfonyl)imide were added to prepare a cathode material slurry composition having a solid content of 76 wt%. Subsequently, the process was carried out in the same manner as in Example 1, and a cathode and an anode were prepared.

[0140] Scanning Electron Microscope (SEM) analysis of the anode surfaces prepared in Examples 1 and 2 confirmed that the anode active material layer was evenly coated on the current collector without mechanical deformation, that the anode active material particles were evenly distributed throughout, and that the binder composition formed a uniform scaffold structure in the voids between the particles. On the other hand, the anode prepared in Comparative Example 1 was found to have a non-uniform microstructure and pore distribution with the binders clumping together.

[0141] In addition, the cross-sections of the anodes prepared in Example 1, Example 2, and Comparative Example 1 were X-ray CT scanned to analyze the distribution of carbon black, which is a conductive material. As a result, it was found that in the anode of Comparative Example 1, as the anode active material layer became thicker, a phenomenon occurred in which the conductive material moved upwards toward the electrode, and non-uniformity in the distribution of the conductive material in the thickness direction was observed. On the other hand, in the anode of the example, it was confirmed that the distribution of the conductive material was uniform in the first active material layer corresponding to the 1 / 3 point in the thickness direction of the anode active material layer from the boundary between the anode current collector and the anode active material layer, the second active material layer corresponding to the 1 / 3 point to the 2 / 3 point in the thickness direction, and the third active material layer from the 2 / 3 point in the thickness direction to the surface. In addition, when the distribution of the conductive material content (vol%) in the first active material layer, the second active material layer, and the third active material layer was quantified based on the X-ray CT scan results, the deviation of the conductive material concentration according to the following formula in the anode according to the above example was found to be very low, at about 9% or less, and through this, it was confirmed that the conductive material in the anode active material layers of Example 1 and Example 2 is very uniformly distributed.

[0142] [ceremony]

[0143] (|C0- C n | / C0) × 100

[0144] In the above Equation 1,

[0145] C0 is the average concentration (vol%) of the conductive material throughout the entire cathode active material layer;

[0146] C n is the concentration (vol%) of the conductive material in the n-th active material layer.

[0147] [Manufacturing of Electrochemical Devices]

[0148] An electrochemical device was manufactured according to the following method using the anode and cathode of the above examples and comparative examples.

[0149] A battery assembly was manufactured by laminating the above-mentioned anode and cathode with a separator (thickness 13 μm, SC13-D4-BP, Gellec), and the assembly was placed into a battery pouch film (153 μm, DNP) formed to fit the battery assembly and sealed. Subsequently, an electrochemical device was manufactured by injecting a liquid electrolyte containing 1 mole of LiPF6 dissolved in a solvent mixed with ethylene carbonate and dimethyl carbonate in a 1:1 volume ratio.

[0150] The results of measuring the adhesion between the binder and the current collector (aluminum) using the polymer composite binder used in the example and the binder used in the comparative example, and the bonding strength of the electrodes prepared according to the example and comparative example, are shown in Table 1 below.

[0151] (Table 1)

[0152]

[0153] As shown in Table 1 above, Examples 1 and 2 of the present invention demonstrate that the adhesion between the polymer composite binder and the current collector, as well as the binding strength between the polymer composite binder and the electrode active material within the positive active material layer, are significantly improved through the action of the ionic material within the polymer composite binder. On the other hand, Comparative Example 1 is a case where the organic binder and the ionic material are each introduced into the slurry, and the organic binder and the ionic material are not composited, exhibiting very poor adhesion and binding strength.

[0154] According to the conditions described above, after obtaining the X-ray diffraction pattern of the polymer composite binder used in Example 1 (composite diffraction pattern) and the X-ray diffraction pattern of polyvinylidene fluoride (polymer diffraction pattern), respectively, the number of diffraction peaks appearing in the 2θ range of 10 to 35° in the polymer diffraction pattern (Np), the number of diffraction peaks appearing in the 2θ range of 10 to 35° in the composite diffraction pattern (Nc), the intensity ratio (I1 / I0×100, %) obtained by dividing the maximum intensity I1 of the diffraction peak exhibiting the greatest intensity in the composite diffraction pattern (diffraction peak located at 20.1°) by the maximum intensity I0 of the diffraction peak exhibiting the greatest intensity in the polymer diffraction pattern (diffraction peak located at 19.9°), the full width at half maximum (FWHM) of the diffraction peak exhibiting the greatest intensity in the composite diffraction pattern, and the two diffraction peaks appearing in the composite diffraction pattern (18.1°, Table 2 summarizes the intensity ratio between (located at 20.1°) (I2 / I1×100, % where I2 is the maximum intensity of the diffraction peak located at 18.1°) and the intensity ratio obtained by dividing I3, the diffraction intensity at the 2θ point between 18.1° and 1.5° in the complex diffraction pattern, by I2 (I3 / I2×100, %).

[0155] (Table 2)

[0156]

[0157] It was confirmed that even when the process of dissolving the polymer composite binder in a solvent to form a solution, then evaporating the solvent from the solution to recover the polymer composite binder, and then dissolving the recovered polymer composite binder in a solvent again is repeated, the physical properties of the polymer composite binder including the composite diffraction pattern remain substantially the same, and it was also confirmed that the X-ray diffraction characteristics of the polymer composite binder of Example 2 are substantially similar to the X-ray diffraction characteristics of the polymer composite binder of Example 1.

[0158] [Performance Evaluation of Electrochemical Devices]

[0159] The initial efficiency of the electrochemical device according to the above examples and comparative examples was evaluated and is shown in Table 3 below.

[0160] (Table 3)

[0161]

[0162] As shown in Table 3 above, the initial efficiency of the electrochemical devices manufactured in the above examples and comparative examples was evaluated. It was confirmed that the initial efficiency of the above examples was higher than that of the above comparative examples.

[0163] The results of measuring the 50-cycle capacity retention rate and electrode thickness increase rate of the electrochemical devices manufactured according to the above examples and comparative examples are shown in Table 4 below.

[0164] (Table 4)

[0165]

[0166] As shown in Table 4 above, it can be confirmed that the electrode manufactured in the embodiment of the present invention effectively suppresses changes in electrode thickness and improves the lifespan characteristics of the battery by adhering between the electrode active material and the electrode current collector during the charge-discharge cycle and stably maintaining the binding between the electrode active material particles.

[0167] On the other hand, in the case of Comparative Example 1, it can be seen that the battery life characteristics were degraded due to severe changes in electrode thickness during charge-discharge cycles caused by the low adhesion characteristics of the binder.

[0168] Through this, the cathode according to the embodiment exhibits excellent adhesion characteristics by using a polymer composite binder and can have a cathode active material layer with the cathode material uniformly coated. Furthermore, it can be confirmed that a lithium secondary battery containing the cathode can maintain excellent lifespan characteristics by exhibiting excellent battery performance, such as superior initial efficiency and capacity retention rate, as well as a low thickness increase rate.

[0169] As described above, the present invention has been explained by limited embodiments, but this is provided merely to aid in a more comprehensive understanding of the invention. The present invention is not limited to the above embodiments, and those skilled in the art can make various modifications and variations from this description.

[0170] Accordingly, the scope of the present invention is not limited to the described embodiments, and all things equivalent to or having equivalent variations to the claims set forth below, as well as the claims set forth below, shall be considered to fall within the scope of the concept of the present invention.

Claims

1. A polymer composite binder for a lithium secondary battery electrode composite comprising a crystalline organic polymer and an ionic material, satisfying Formula 1 below. (Equation 1) Nc < Np (In Equation 1, Nc is the number of diffraction peaks located in the composite diffraction pattern, which is the diffraction pattern in the 2θ range of 10 to 35° in the X-ray diffraction pattern of the polymer composite binder, and Np is the number of diffraction peaks located in the polymer diffraction pattern, which is the diffraction pattern in the 2θ range of 10 to 35° in the X-ray diffraction pattern of the pure (pristine) organic polymer.) 2. In Paragraph 1, A polymer composite binder for a lithium secondary battery electrode composite, wherein Np is a natural number from 2 to 6 and Nc is a natural number of 0 or Np-1 or less.

3. In Paragraph 1, A polymer composite binder for lithium secondary battery electrode composites that further satisfies Formula 2 below. (Equation 2) 20% ≤ I1 / I0×100 ≤ 50% (In Equation 2, I1 is the peak intensity of the diffraction peak having the strongest intensity in the composite diffraction pattern, and I0 is the peak intensity of the diffraction peak having the strongest intensity in the polymer diffraction pattern) 4. In Paragraph 3, A polymer composite binder for a lithium secondary battery electrode composite, wherein the diffraction peak having the strongest intensity in each of the composite diffraction pattern and the polymer diffraction pattern is located in the 2θ range of 19.7 to 20.7°.

5. In Paragraph 1, A polymer composite binder for lithium secondary battery electrode composites that further satisfies Formula 3 below. (Equation 3) 60% ≤ I2 / I1×100 ≤ 70% (In Equation 3, I1 is the peak intensity of the diffraction peak located at 19.7 to 20.7° in the complex diffraction pattern, and I2 is the peak intensity of the diffraction peak located at 17.7 to 18.7° in the complex diffraction pattern) 6. In Paragraph 1, A polymer composite binder for lithium secondary battery electrode composites that further satisfies Formula 4 below. (Equation 4) 80% ≤ I3 / I2×100 ≤ 98% (In Equation 4, I2 is the peak intensity of the diffraction peak located at 17.7 to 18.7° of the composite diffraction pattern, and I3 is the diffraction intensity of the composite diffraction pattern at a point 2θ, which is β° - 1.5° from β°, the peak center of the diffraction peak located at 17.7 to 18.7°.) 7. In Paragraph 1, The above organic polymer is one or more selected from the group consisting of polyvinylidene fluoride (PVdF) and vinylidene fluoride-based copolymers, a polymer composite binder for a lithium secondary battery electrode composite.

8. In Paragraph 1, The above ionic material is a polymer composite binder for lithium secondary battery electrode composites, which is an ionic organic compound or an ion-dissociable metal salt.

9. In Paragraph 1, A polymer composite binder for lithium secondary battery electrode composites, wherein the above ionic material contains fluorine.

10. In Paragraph 8, The above ionic material is a polymer composite binder for a lithium secondary battery electrode composite, wherein the ionic material is any one or a combination of two or more selected from the group consisting of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIm TFSI), poly(1-ethyl-3-vinylimidazolium)bis(trifluoromethanesulfonyl)imide (p(EVIm TFSI)), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

11. In Paragraph 8, A polymer composite binder for a lithium secondary battery electrode composite, wherein the above ion-dissociable metal salt is a sulfonyl group-containing metal salt selected from the following Chemical Formula 1 or Chemical Formula 2. [Chemical Formula 1] [Chemical Formula 2] (In the above chemical formulas 1 and 2, n is 1 or 2 and; A is an n-valent cation; R1 to R3 are each independently a fluoro(C1-C7)alkyl or fluoro group) 12. In Paragraph 11 A is a polymer composite binder for lithium secondary battery electrode composites, wherein A is lithium, sodium, zinc, copper, aluminum, silver, gold, cesium, indium, magnesium, or calcium.

13. An electrode for a lithium secondary battery comprising an electrode active material and a polymer composite binder according to any one of claims 1 to 12.

14. A lithium secondary battery comprising an electrode according to paragraph 13.

15. A binder solution for lithium secondary battery electrode composites, and In the X-ray diffraction pattern of the solid phase obtained by volatilizing the solvent of the above binder solution, diffraction peaks are located in the 2θ range of 19.7 to 20.7° and the 2θ range of 17.7 to 18.7°, respectively, and A binder solution for a lithium secondary battery electrode composite, wherein the intensity ratio obtained by dividing the peak intensity of a diffraction peak located at 17.7 to 18.7° by the peak intensity of a diffraction peak located at 19.7 to 20.7° is 60 to 70%.

16. In Paragraph 15, A binder solution for a lithium secondary battery electrode composite, wherein in the X-ray diffraction pattern of the above solid phase, the number of diffraction peaks located in the 2θ range of 10 to 35° is two.

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