Cylindrical secondary battery

Abstract

The present invention relates to a cylindrical secondary battery having a large form factor applicable to medium-to-large devices such as automobiles, which exhibits excellent rapid charging characteristics, improves swelling problems caused by side reactions and gas generation, suppresses lithium precipitation, and has high capacity characteristics.

Description

Technology Field

[0001] The present invention relates to a cylindrical secondary battery having a large form factor applicable to medium-to-large devices such as automobiles, which exhibits excellent rapid charging characteristics, improves swelling problems caused by side reactions and gas generation, suppresses lithium precipitation, and has high capacity characteristics. Background Technology

[0002] Secondary batteries, which possess electrical characteristics such as high energy density and high applicability across product categories, are widely applied not only to portable devices but also to electric vehicles (EVs) or hybrid electric vehicles (HEVs) driven by electric power sources.

[0003] These secondary batteries are attracting attention as a new energy source for improving eco-friendliness and energy efficiency, as they not only have the primary advantage of being able to drastically reduce the use of fossil fuels but also the advantage of not generating any by-products from the use of energy.

[0004] Currently, widely used types of secondary batteries include lithium-ion batteries, lithium-polymer batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries. The operating voltage of these unit secondary battery cells, or unit battery cells, is approximately 2.5V to 4.5V. Therefore, if a higher output voltage is required, multiple battery cells are connected in series to form a battery pack. Additionally, depending on the charge / discharge capacity required for the battery pack, multiple battery cells are connected in parallel to form a battery pack. Accordingly, the number of battery cells included in the battery pack and the electrical connection type can be set in various ways depending on the required output voltage and / or charge / discharge capacity.

[0005] Meanwhile, cylindrical, prismatic, and pouch-type batteries are known as types of unit secondary batteries. Among these, in the case of a cylindrical secondary battery, an insulating separator is interposed between the positive and negative electrodes, and this is wound to form a jellyroll-shaped electrode assembly, which is then inserted into a battery can to constitute the battery. Additionally, a strip-shaped electrode tab may be connected to each of the positive and negative electrodes, and the electrode tab electrically connects the electrode assembly with the externally exposed electrode terminals. However, conventional cylindrical secondary batteries having such a structure have had problems such as high resistance, excessive heat generation, and poor current collection efficiency because current is concentrated in the strip-shaped electrode tab connected to the positive and / or negative electrodes.

[0006] However, resistance and heat generation were not major issues for small cylindrical secondary batteries with the form factors of the 18650 (cylindrical secondary battery with a diameter of 18 mm x a height of 65 mm) or 21700 (cylindrical secondary battery with a diameter of 21 mm x a height of 70 mm) that were commonly used in the past.

[0007] However, as increased driving range and faster charging speeds are required for electric vehicles in recent years, the development and use of larger cylindrical secondary batteries with larger form factors, such as the 46800 (a cylindrical secondary battery with a diameter of 46 mm x a height of 80 mm), are being considered. In addition, to improve the rapid charging characteristics of these larger cylindrical secondary batteries, so-called tab-less cylindrical secondary batteries are being developed, which utilize the current collector itself in the unoccupied portions of the positive and negative electrodes as an electrode tab instead of using a separate strip-shaped electrode tab.

[0008] The above-described enlarged cylindrical secondary battery not only exhibits relatively large capacity characteristics and energy density, but also has the advantage of increasing production efficiency and lowering production costs for cylindrical secondary batteries for electric vehicles. Furthermore, by applying the above-described tab-less structure, the electrical connection area and efficiency of the electrode tab and electrode terminal can be increased, thereby reducing current concentration on the electrode tab and increasing current collection efficiency, which can improve rapid charging characteristics.

[0009] However, in large-scale cylindrical secondary batteries with the above-mentioned tabless structure, a large current is applied to each electrode of the positive and / or negative electrode within a short period of time during processes such as rapid charging, so side reactions and the generation of gases resulting therefrom may occur seriously at each electrode. In particular, to realize large capacity characteristics and rapid charging characteristics, silicon-based negative electrode active materials are mainly mixed and used in the negative electrode of the above-mentioned large-scale cylindrical secondary battery. Since such silicon-based active materials can cause large volume changes and side reactions during charging and discharging, side reactions and gas generation at the negative electrode, as well as swelling and lithium precipitation phenomena resulting therefrom, may become even more serious problems.

[0010] Due to these problems, there is an urgent need to develop technology for large-scale cylindrical secondary batteries applicable to medium and large-sized devices such as automobiles that can improve rapid charging characteristics while reducing side reactions, gas generation, swelling, and lithium precipitation occurring in the anode. The problem to be solved

[0011] Accordingly, the present invention provides a cylindrical secondary battery having a large form factor applicable to medium and large-sized devices, exhibiting excellent rapid charging characteristics, improving swelling problems caused by side reactions and gas generation, suppressing lithium precipitation, and having high capacity characteristics.

[0012] The present invention also provides a battery pack comprising the cylindrical secondary battery. means of solving the problem

[0013] In order to solve these problems, according to one aspect of the present invention, cylindrical secondary batteries of the following embodiments are provided.

[0014] According to the first embodiment of the present invention,

[0015] A cylindrical secondary battery comprising: a positive electrode including a positive active material layer on a current collector, a negative electrode including a negative active material layer on a current collector, and a jellyroll-shaped electrode assembly in which a separator interposed between the positive electrode and the negative electrode is wound; and a battery can accommodating the electrode assembly.

[0016] The above cathode active material layer is,

[0017] A lower region in contact with the above-mentioned current collector and comprising, as an active material, a silicon-based compound and natural graphite, and

[0018] A mixed region in contact with the above lower region and comprising, as active materials, a silicon-based compound, natural graphite and artificial graphite, and

[0019] It comprises an upper layer region in contact with the above-mentioned mixed region and, as an active material, includes a silicon-based compound and artificial graphite, and

[0020] Based on the maximum diameter and maximum height of the above-mentioned battery can, a cylindrical secondary battery having a diameter of 35 mm or more and a height of 75 mm or more is provided.

[0021] According to the second embodiment of the present invention, in the first embodiment,

[0022] The above positive active material layer may include a lithium nickel-based transition metal oxide as an active material, wherein the nickel content is 80 to 100 mol% based on the total amount of transition metals.

[0023] According to the third embodiment of the present invention, in the second embodiment,

[0024] The above lithium nickel-based transition metal oxide may be represented by the following chemical formula 1:

[0025] [Chemical Formula 1]

[0026] Li 1+a (Ni b Co c Mn d Al e M f )O2

[0027] In the above chemical formula 1, -0.1≤a≤0.2, 0.8≤b≤1.0, 0.01≤c≤0.15, 0.01≤d≤0.15, 0.01≤e≤0.1, 0≤f≤0.05, and M is at least one selected from the group consisting of Mg, Ti, Zr, Nb and W.

[0028] According to the fourth embodiment of the present invention, in any one of the first to third embodiments,

[0029] The above negative electrode active material layer may have a thickness of 40 to 200 μm.

[0030] According to the fifth embodiment of the present invention, in any one of the first to fourth embodiments,

[0031] Based on the cross-sectional thickness at which the mixing region is formed with the largest thickness in the above-mentioned cathode active material layer, the mixing region may have a thickness of 20 to 80% of the total thickness of the cathode active material layer.

[0032] According to the sixth embodiment of the present invention, in any one of the first to fifth embodiments,

[0033] The above lower layer region may have a thickness of 10 to 40% of the total thickness of the cathode active material layer.

[0034] According to the seventh embodiment of the present invention, in any one of the first to sixth embodiments,

[0035] The above upper layer region may have a thickness of 10 to 40% of the total thickness of the cathode active material layer.

[0036] According to the eighth embodiment of the present invention, in any one of the first to seventh embodiments,

[0037] The above-mentioned mixing region may contain the natural graphite and artificial graphite in a weight ratio of 2:8 to 8:2 (natural graphite: artificial graphite).

[0038] According to the ninth embodiment of the present invention, in any one of the first to eighth embodiments,

[0039] The above-mentioned mixed region may have an active material distribution gradient in which the distribution ratio of the natural graphite decreases and the distribution ratio of the artificial graphite increases as it approaches the above-mentioned upper region.

[0040] According to the 10th embodiment of the present invention, in any one of the 1st to 9th embodiments,

[0041] The above natural graphite has a particle shape exhibiting a sphericity greater than 0.91 and may have an average particle size (D50) of 5 to 30 μm.

[0042] According to the 11th embodiment of the present invention, in any one of the 1st to 10th embodiments,

[0043] The artificial graphite above may include secondary particles formed by the aggregation of primary particles and a carbon coating layer formed on the surface of the secondary particles.

[0044] According to the 12th embodiment of the present invention, in any one of the 1st to 11th embodiments,

[0045] The carbon coating layer may be included in an amount of 0.5 to 10 weight percent based on the total weight of the artificial graphite.

[0046] According to the 13th embodiment of the present invention, in any one of the 1st to 12th embodiments,

[0047] The artificial graphite above may have an average particle size (D50) of 4 to 32 μm.

[0048] According to the 14th embodiment of the present invention, in any one of the 1st to 13th embodiments,

[0049] The above silicon-based compounds include Si, SiOx(0 <x≤2), Si-Y 합금(Y는 알칼리 금속, 알칼리 토금속, 13족 원소, Si를 제외한 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로부터 선택되는 원소이다.), 또는 이들 중 2종 이상을 포함할 수 있다.

[0050] According to the 15th embodiment of the present invention, in any one of the 1st to 14th embodiments,

[0051] The silicon-based compound may be included in an amount of 10 to 50 weight percent based on the total amount of active material included in the negative electrode active material layer.

[0052] According to the 16th embodiment of the present invention, in any one of the 1st to 15th embodiments,

[0053] In the above-described cathode active material layer, the lower layer region, the mixed region, and the upper layer region may each include the active material, the binder polymer, and the conductive material, respectively, and based on the total content (weight%) of each region, the lower layer region may include a greater content (weight%) of the binder polymer than the upper layer region.

[0054] According to the 17th embodiment of the present invention, in any one of the 1st to 16th embodiments,

[0055] The lower layer region may contain 1 to 1.2 weight percent of the binder polymer based on its total content (weight%), and the upper layer region may contain 0.5 to 0.9 weight percent of the binder polymer based on its total content (weight%).

[0056] According to the 18th embodiment of the present invention, in any one of the 1st to 17th embodiments,

[0057] The lower and upper regions may each contain the same or different binder polymers, and the binder polymer of the lower region may include styrene butadiene rubber (SBR) or a mixture of styrene butadiene rubber (SBR) and an acrylic copolymer.

[0058] According to the 19th embodiment of the present invention, in the 18th embodiment,

[0059] In the case of the mixture of the styrene butadiene rubber (SBR) and the acrylic copolymer, the styrene butadiene rubber may be included in a larger amount than the acrylic copolymer.

[0060] According to the 20th embodiment of the present invention, in any one of the 1st to 19th embodiments,

[0061] The binder polymer of the upper layer region may comprise a core-shell particle having a core portion made of styrene butadiene rubber and a shell portion made of an acrylic copolymer surrounding the outer side of the core portion; or a mixture of the core-shell particle and styrene butadiene rubber.

[0062] According to the 21st embodiment of the present invention, in the 20th embodiment,

[0063] The binder polymer in the upper layer region comprises a mixture of the core-shell particles and styrene butadiene rubber, and the core-shell particles may be included in a larger amount than the styrene butadiene rubber.

[0064] According to the 22nd embodiment of the present invention, in the 20th embodiment or the 21st embodiment,

[0065] The average particle size (D50) of the core-shell particles is 30 to 100 nm, and the average particle size of the styrene butadiene rubber may be 200 to 350 nm.

[0066] According to the 23rd embodiment of the present invention, in any one of the 1st to 22nd embodiments,

[0067] The above-mentioned negative electrode active material layer has a QBR (Quantified Binder Ratio) of 2.0 or less, and

[0068] The above QBR can be defined by the following mathematical formula:

[0069] QBR = Bs / Bf

[0070] In the above mathematical formula, Bs represents the average value of the Os atomic ratio in the surface region of the cathode active material layer from the outermost surface of the cathode active material layer up to within 15% of the total thickness of the cathode active material layer, and Bf represents the average value of the Os atomic ratio in the bottom region of the cathode active material layer from the interface of the cathode active material layer facing the current collector up to within 15% of the total thickness of the cathode active material layer.

[0071] The above Os atomic ratio is analyzed by EDS (Energy Dispersive Spectroscopy) after staining a cross-section of the above cathode active material with OsO4.

[0072] According to the 24th embodiment of the present invention, in any one of the 1st to 23rd embodiments,

[0073] In the above anode and cathode, there is a non-active portion in which an active material layer is not formed along one side (long side) end of the current collector in a direction parallel to the winding direction, and at least a portion of the current collector in this non-active portion may define an electrode tab that is electrically connected to an electrode terminal.

[0074] According to the 25th embodiment of the present invention, in the 24th embodiment,

[0075] At least a portion of the current collector defining the electrode tab can be processed into a plurality of segments that can be independently bent. Additionally, since these segments are connected to the electrode terminals with a wide contact area, the cylindrical secondary battery can have the structure of a tab-less secondary battery.

[0076] According to the 26th embodiment of the present invention, in any one of the first to 25 embodiments,

[0077] The ratio of the form factor, defined as the value obtained by dividing the diameter by the height, may be greater than 0.4.

[0078] According to the 27th embodiment of the present invention, in any one of the first to 26 embodiments,

[0079] The above cylindrical secondary battery may be a 46110 cell, a 48750 cell, a 48110 cell, a 48800 cell, or a 46800 cell.

[0080] According to the 28th embodiment of the present invention, a battery pack comprising a cylindrical secondary battery of any one of the first to 27 embodiments is provided.

[0081] According to the 29th embodiment of the present invention, a vehicle comprising the battery pack of the 28th embodiment is provided. Effects of the invention

[0082] According to an example of the present invention, a cylindrical secondary battery having a large form factor with a diameter of 35 mm or more and a height of 75 mm or more is provided, wherein the negative electrode active material layer is formed by dividing it into three or more regions according to the distribution of the active material.

[0083] Depending on the distribution of the active material in the negative electrode active material layer, the cylindrical secondary battery can suppress adverse reactions between the negative electrode and the electrolyte and gas generation even when a relatively large current is applied in a short period of time during rapid charging, and as a result, swelling, electrolyte consumption, and lithium precipitation phenomena can be significantly reduced. In addition, as a large amount of natural graphite is distributed in the lower layer region and the adjacent mixed region, the active material layer can have excellent adhesion and mechanical properties to the current collector.

[0084] Accordingly, the cylindrical secondary battery according to the present invention has a larger form factor than conventional batteries, while exhibiting excellent rapid charging characteristics and reduced swelling and lithium precipitation phenomena caused by reduced side reactions and gas generation. It can be very preferably applied as a secondary battery for medium-to-large devices, such as automobiles, that require large capacity and rapid charging characteristics. Brief explanation of the drawing

[0085] The following drawings attached to this specification illustrate preferred embodiments of the invention and serve to further enhance understanding of the technical concept of the invention together with the aforementioned description; therefore, the invention should not be interpreted as being limited only to the matters described in such drawings. FIG. 1 is a schematic plan view showing an example of a positive or negative electrode included in a cylindrical secondary battery of one embodiment. FIG. 2 is a schematic cross-sectional view showing an example of an electrode assembly included in a cylindrical secondary battery of one embodiment. FIG. 3 is a cutaway perspective view schematically showing an example of a cylindrical secondary battery of one embodiment. FIG. 4 is a schematic diagram showing an example of a battery pack including a cylindrical secondary battery of one embodiment, and FIG. 5 is a schematic diagram showing a vehicle including said battery pack. Figures 6a and 6b are electron microscope images of the cross-section of the negative electrode in the cylindrical secondary battery of Example 1, and Figure 6c is an electron microscope image of the cross-section of the negative electrode in the cylindrical secondary battery of Comparative Example 1. Figure 7 is the result of X-ray CT imaging of the cylindrical secondary battery of Example 1. Figure 8 is the X-ray CT scan result of the cylindrical secondary battery of Comparative Example 1. Figure 9 is the X-ray CT scan result of the cylindrical secondary battery of Comparative Example 2. FIGS. 10 to 12 are photographs showing the negative active material layer attached to the surface of the negative active material layer and the separator of each secondary battery as a result of disassembling the cylindrical secondary batteries of Example 1, Comparative Example 1, and Comparative Example 2. FIGS. 13a to 13d are graphs showing the results of a rapid charge / discharge test conducted on the cylindrical secondary batteries of Example 1 and Comparative Example 1 in Experimental Example 3. Figure 14 is a schematic diagram for calculating the QBR value of the cathode active material layer. FIG. 15a is a graph showing the change in normalized intensity of the Os component dyed in the binder polymer of the first cathode active material layer extracted and analyzed from EDS mapping at a distance from the surface of the first cathode active material layer of the cathode of Example 1 toward the current collector. FIG. 15b is a graph showing the change in normalized intensity of the Os component dyed in the binder polymer of the second cathode active material layer extracted and analyzed from EDS mapping at a distance from the surface of the second cathode active material layer of the cathode of Example 1 toward the current collector. Specific details for implementing the invention

[0086] Hereinafter, terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical idea of ​​the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0087] According to one embodiment of the invention, a cylindrical secondary battery comprising: a positive electrode having a positive active material layer on a current collector, a negative electrode having a negative active material layer on a current collector, and a jellyroll-shaped electrode assembly having a separator interposed between the positive electrode and the negative electrode; and a battery can accommodating the electrode assembly.

[0088] The above cathode active material layer is,

[0089] A lower region in contact with the above-mentioned current collector and comprising, as an active material, a silicon-based compound and natural graphite, and

[0090] A mixed region in contact with the above lower region and comprising, as active materials, a silicon-based compound, natural graphite and artificial graphite, and

[0091] It comprises an upper layer region in contact with the above-mentioned mixed region and, as an active material, includes a silicon-based compound and artificial graphite, and

[0092] Based on the maximum diameter and maximum height of the above-mentioned battery can, a cylindrical secondary battery having a diameter of 35 mm or more and a height of 75 mm or more is provided.

[0093] A cylindrical secondary battery having a large form factor with a diameter of 35 mm or more and a height of 75 mm or more is provided, wherein the negative active material layer is formed by dividing it into three or more regions according to the distribution of the active material.

[0094] The cylindrical secondary battery of the above embodiment has a larger form factor compared to previously known cylindrical secondary batteries, and the negative active material layer is formed by dividing it into three or more regions according to the distribution of the active material. More specifically, a silicon-based compound and natural graphite are distributed in the lower region in contact with the current collector, and a silicon-based compound and artificial graphite are distributed in the upper region in contact with the separator, and a mixed region containing a silicon-based compound, natural graphite, and artificial graphite is formed between the lower and upper regions.

[0095] As the above negative electrode active material layer basically includes a silicon-based compound as an active material, the cylindrical secondary battery of one embodiment can exhibit high capacity characteristics and energy density, and excellent rapid charging characteristics.

[0096] Additionally, compared to natural graphite, synthetic graphite offers more pathways for lithium ion movement, resulting in higher electrical efficiency and suitability for rapid charging. Furthermore, due to its stable isotropic structure, it exhibits minimal side reactions and swelling, offering advantages that are beneficial for the lifespan of secondary batteries. Conversely, while natural graphite shows inferior characteristics compared to synthetic graphite in terms of rapid charging performance and stability, and can cause relatively more side reactions, it possesses a relatively larger surface area and the presence of reactive sites on its surface, which are advantageous for improving adhesion to the current collector.

[0097] In a cylindrical secondary battery of one embodiment, artificial graphite is mainly distributed in the upper region of the active material layer where electrochemical reactions mainly occur during charging and discharging, and in the mixed region adjacent thereto, while natural graphite is mainly distributed in the lower region in contact with the current collector and in the mixed region adjacent thereto, thereby maximizing the advantages of these two active materials.

[0098] In other words, by distributing artificial graphite near the upper region where electrochemical reactions occur during charging and discharging, the occurrence of side reactions, swelling, and lithium precipitation phenomena during charging and discharging can be suppressed, while further improving rapid charging characteristics. Additionally, by distributing relatively stable artificial graphite together with silicon-based compounds in the upper region, silicon-based compounds, which exhibit significant side reactions and volume changes during charging and discharging, can be relatively buffered. Furthermore, by distributing natural graphite near the lower region in contact with the current collector, the adhesion of the negative electrode active material layer to the current collector can be significantly improved, and the overall durability of the secondary battery can be enhanced. Moreover, by mixing natural graphite and artificial graphite in the mixed region, the advantages of each active material described above can be further utilized, and the lithium ion storage capacity can be increased due to the large surface area, making it possible to provide a large-scale cylindrical secondary battery with greater capacity characteristics and energy density.

[0099] Consequently, in the cylindrical secondary battery of the above-described embodiment, due to the various characteristics described above, side reactions between the negative electrode and the electrolyte and gas generation can be suppressed even when a relatively large current is applied in a short period of time during rapid charging, etc., and as a result, swelling, electrolyte consumption, and lithium precipitation phenomena can be significantly reduced. In addition, the active material layer can have excellent adhesion and mechanical properties to the current collector.

[0100] Accordingly, the cylindrical secondary battery of one embodiment has a larger form factor than conventional batteries, while exhibiting excellent rapid charging characteristics and reduced swelling and lithium precipitation phenomena caused by reduced side reactions and gas generation, and can be very preferably applied as a secondary battery for medium-to-large devices such as automobiles that require large capacity and rapid charging characteristics.

[0102] Hereinafter, with reference to the attached drawings, a cylindrical secondary battery of one embodiment will be described in more detail for each component. FIG. 1 is a schematic plan view showing an example of a positive or negative electrode included in a cylindrical secondary battery of one embodiment, and FIG. 2 is a schematic cross-sectional view showing an example of an electrode assembly included in a cylindrical secondary battery of one embodiment.

[0103] As illustrated in FIGS. 1 and 2, the cylindrical secondary battery comprises a positive electrode and a negative electrode (13, 14) each having a positive or negative active material layer (18) formed on a current collector (17), and a jelly roll-shaped electrode assembly (10) in which a separator (15) interposed between the positive electrode and the negative electrode (13, 14) is wound.

[0104] At this time, the positive and negative electrodes (13, 14) have a non-active material layer (16) formed along one side (long side) end of each current collector (17) in a direction parallel to the winding direction, and at least some of the current collectors (17) in this non-active part (16) can define each electrode tab (11, 12) of the positive or negative electrode.

[0105] More specifically, referring to FIG. 1, at least a portion of the current collector (17) defining each electrode tab (11, 12) is processed into a plurality of segments that can be independently bent. These plurality of segments may have different shapes and sizes for each region, but are not particularly limited in this specification.

[0106] As described in more detail below, a plurality of segments formed in the above-mentioned non-electrode portion (16) can be electrically connected to each electrode terminal and act as electrode tabs (11, 12), and the cylindrical secondary battery of one embodiment may have the form of a so-called tab-less secondary battery without adding separate electrode tabs. Accordingly, compared to conventional batteries with separate electrode tabs, the electrical connection area with the electrode terminals and current collection efficiency can be greatly improved, and it can be a structure advantageous for large-capacity batteries requiring rapid charging.

[0107] However, in such a tabless structure and a large-sized cylindrical secondary battery, a large current can be applied to each electrode in a short period of time, so suppressing side reactions, swelling, and lithium precipitation phenomena may emerge as a major challenge along with improving relatively rapid charging characteristics. To solve this, in a cylindrical secondary battery of one embodiment, the negative electrode active material layer may be formed in a state divided into the lower layer region, the mixed region, and the upper layer region described above.

[0108] Each region of the cathode active material layer and its thickness can be verified by analyzing the cross-section of the corresponding active material layer using an electron microscope or the like. Additionally, the thickness of each region can be calculated by measuring the thickness of each region based on the cross-sectional thickness of the part where the mixed region is formed with the greatest thickness within the entire active material layer, as seen in the electron microscope image of the active material layer.

[0109] In a specific embodiment, the total thickness of the negative electrode active material layer is not particularly limited, but, for example, may be 40 to 200 μm.

[0110] Among these, the mixed region in which the natural graphite and artificial graphite are mixed may have a thickness of 20 to 80%, or 30 to 70%, or 40 to 60% of the total thickness of the negative electrode active material layer, the lower region may have a thickness of 10 to 40%, or 15 to 35%, or 20 to 30% of the total thickness of the negative electrode active material layer, and the upper region may have a thickness of 10 to 40%, or 15 to 35%, or 20 to 30% of the total thickness of the negative electrode active material layer.

[0111] In a more specific example, the thickness of the upper and / or lower layer regions may be 5 to 100 μm or 10 to 60 μm, respectively, and the thickness of the mixed region may be 20 to 180 μm or 25 to 150 μm.

[0112] As the distribution area of ​​natural graphite and artificial graphite is controlled by the thickness of each of these regions, the rapid charging characteristics of the cylindrical secondary battery of one embodiment can be further improved, and side reactions, gas generation, swelling, and lithium precipitation phenomena at the negative electrode can be further suppressed, while excellent capacity and lifespan characteristics of the cylindrical secondary battery can be exhibited.

[0113] In the above-described cathode active material layer, the mixed region may contain the natural graphite and artificial graphite in a weight ratio (natural graphite: artificial graphite) of 2:8 to 8:2, or 3:7 to 7:3, or 4:6 to 6:4. Additionally, this mixed region may have an active material distribution gradient in which the distribution ratio of the natural graphite decreases and the distribution ratio of the artificial graphite increases as it approaches the upper layer region. Due to the mixing ratio and distribution gradient within this mixed region, the effect of the mixture of natural graphite and artificial graphite in the mixed region can be maximized and expressed.

[0114] Meanwhile, the aforementioned cathode active material layer includes artificial graphite, natural graphite, and silicon-based compounds as active materials in each region.

[0115] Among these, artificial graphite is manufactured by mixing coke with a binder and calcining and heating it at a high temperature of over 2,500°C, so the crystallinity is intentionally increased during the manufacturing process, resulting in a uniform and stable internal structure. Although it cannot accommodate as many lithium ions as natural graphite, it has many pathways for lithium ion movement, making it advantageous for rapid charging, and it has the advantage of a relatively long charge / discharge lifespan.

[0116] However, artificial graphite is primarily used in the form of secondary particles. To this end, artificial graphite in the form of secondary particles can be obtained by generally aggregating coke, which is the material for primary particles, into secondary particles, and then graphitizing it through heat treatment. When following the above-mentioned conventional manufacturing method in which the size of the primary particles is not controlled, a large amount of fine particles that are not aggregated or that separate from the secondary particles even after aggregation occurs. Consequently, the anode adhesion (resistance to the detachment of anode active material particles from the anode) in the manufactured anode decreases, and the high-temperature storage performance of the battery may deteriorate. Furthermore, since fine particles are also contained within the secondary particles, the pores of the anode are not uniform, leading to a higher pore resistance of the anode and a decrease in the battery's lifespan characteristics and rapid charging performance. To solve these problems, a process of placing a carbon coating layer on the secondary particles has been used.

[0117] Accordingly, in one embodiment of the invention, the artificial graphite may include one or more types of artificial graphite that does not have a carbon coating layer on its surface and artificial graphite that has a carbon coating layer on its surface.

[0118] The above artificial graphite is generally manufactured by carbonizing raw materials such as coal tar, coal tar pitch, and petroleum-based heavy oils at 2,500°C or higher, and is used as a negative electrode active material after undergoing particle size adjustment such as grinding and secondary particle formation following such graphitization.

[0119] In the case of artificial graphite, crystals are randomly distributed within the particles, and compared to natural graphite, it has a lower degree of sphericity and a somewhat pointed shape.

[0120] Conventional spherical natural graphite may have inferior output characteristics compared to secondary particle artificial graphite because, based on active material particles, the Li ion migration distance is long and there are relatively few intercalation sites. Meanwhile, secondary particle artificial graphite is manufactured by assembling small primary particles into secondary particles with a particle size suitable for electrode manufacturing. Since it maintains the characteristics of the primary particles, such as the short Li migration distance and the large number of intercalation sites, it can have excellent rapid charging characteristics.

[0121] The artificial graphite used in one embodiment of the invention includes commercially widely used MCMB (mesophase carbon microbeads), MPCF (mesophase pitch-based carbon fiber), artificial graphite graphitized in block form, artificial graphite graphitized in powder form, etc., and the sphericity of the artificial graphite may be 0.91 or less, or 0.6 to 0.91, or 0.7 to 0.9.

[0122] Artificial graphite of secondary particles that does not have the carbon coating layer described above can be formed by assembling primary particles. That is, the secondary particles may be a structure formed by the primary particles aggregating with each other through an assembling process.

[0123] The artificial graphite of secondary particles having the carbon coating layer on its surface may include at least one of amorphous carbon and crystalline carbon as the carbon coating layer.

[0124] The above crystalline carbon can further improve the conductivity of the above cathode active material.

[0125] The crystalline carbon may include at least one selected from the group consisting of fullene, carbon nanotubes, and graphene.

[0126] The amorphous carbon can maintain the strength of the coating layer appropriately, thereby improving the output characteristics and rapid charging performance of the artificial graphite. The amorphous carbon may be a carbon-based material formed using at least one carbide selected from the group consisting of tar, pitch, and other organic materials, or a hydrocarbon as a source for chemical vapor deposition.

[0127] The above-mentioned other organic carbons may be carbons of organic materials selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or kedohexose and combinations thereof.

[0128] The above hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be metherine, etherine, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0129] The carbon coating layer may be included in an amount of 0.5% to 10.0% by weight based on the total weight of the artificial graphite having the carbon coating layer, specifically in an amount of 1% to 8% by weight, or 2% to 6% by weight. When the above range is satisfied, the capacity per weight of the negative electrode active material particle is secured, and the rapid charging performance of the artificial graphite can be improved.

[0130] The D50 of the artificial graphite not having a carbon coating layer on the surface may be 5㎛ to 35㎛, specifically 7㎛ to 33㎛, and more specifically 10㎛ to 30㎛.

[0131] The D50 of the artificial graphite having a carbon coating layer on the surface may be 4㎛ to 32㎛, specifically 6㎛ to 30㎛, and more specifically 8㎛ to 28㎛, or 8㎛ to 21㎛.

[0132] In this specification, the average particle size (D50) is the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size. The D50 can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to measure the difference in diffraction patterns according to particle size as the particles pass through a laser beam, thereby calculating the particle size distribution. The D50 can be measured by calculating the particle diameter at the point that is 50% of the cumulative distribution of the number of particles according to particle size in the measuring device.

[0133] Meanwhile, the above-mentioned natural graphite may generally exist as plate-like aggregates, i.e., flake-like natural graphite, prior to processing. The above-mentioned flake-like natural graphite is manufactured from natural graphite raw materials (e.g., those extracted from graphite ore), and specifically, it may be manufactured by crushing the natural graphite raw materials and undergoing processes such as removing impurities through base treatment and / or acid treatment, washing, drying, and sieving.

[0134] The above natural graphite may be spherical. The above spherical natural graphite may be manufactured by sphericalizing flaky natural graphite. The sphericalization may be performed, for example, using a vortex flow pulverizer. When the natural graphite is spherical, packing between active material particles can be achieved more smoothly, so the problem of thickness expansion of the negative electrode active material due to charging and discharging can be reduced to a superior level.

[0135] The natural graphite used in one embodiment of the invention may have a sphericity greater than 0.91 and less than or equal to 0.97, or between 0.93 and 0.97, or between 0.94 and 0.96.

[0136] The above natural graphite may have an average particle size (D50) of 5 to 30 μm, or 10 to 25 μm.

[0137] Natural graphite has soft physical properties that allow for easy deformation during rolling, making it easy to increase the filling rate. It also facilitates securing a contact area between active materials, which can be advantageous for securing adhesion. However, this makes it difficult to maintain pores in terms of the electrode structure, which can lead to blockages on the electrode surface or the creation of closed pores inside, thereby reducing electrolyte impregnation. On the other hand, artificial graphite has hard physical properties that result in reduced rolling performance, an inferior contact area between active materials compared to natural graphite, and relatively lower adhesion. Conversely, artificial graphite allows for easy pore maintenance, making it possible to implement an electrode structure that is advantageous for electrolyte impregnation.

[0138] In the above-described embodiment, in order to exhibit both the advantages of natural graphite and artificial graphite, the distribution gradient of these natural graphite and artificial graphite within the active material layer is controlled.

[0139] In this case, artificial graphite is included in the upper region of the cathode active layer or in a mixed region adjacent thereto, making electrolyte impregnation advantageous and ensuring adhesion through binder migration during electrode manufacturing. Meanwhile, natural graphite is included in the lower region or in a mixed region adjacent thereto, ensuring adhesion even if binder migration occurs to the upper region due to the active material properties of the natural graphite itself.

[0140] Generally, rapid charging involves increasing the current density initially and gradually decreasing it, which can take the form of a step charge in a broad sense. The negative electrode included in the secondary battery of the above-described embodiment can improve rapid charging performance by considering the characteristics of the current during such rapid charging. The overall electrode structure has secondary artificial graphite with excellent rapid charging performance on the electrode surface side where Li ions move, and electrolyte impregnation is also advantageous. Therefore, when a large number of Li ions move initially, charging proceeds rapidly from the surface, which can reduce the density of Li ions moving toward the current collector, thereby reducing the charging burden on the natural graphite. Subsequently, in the stage where the current density decreases, overall charging can proceed without difficulty.

[0141] Meanwhile, in order to form a mixed region in which natural graphite and artificial graphite are mixed within the above-mentioned negative electrode active material layer, the negative electrode active material layer may be formed by coating a slurry for a lower region containing a first negative electrode active material (natural graphite and a silicon-based compound) and a slurry for an upper region containing a second negative electrode active material (artificial graphite and a silicon-based compound) onto a current collector simultaneously or with a very short time difference, and then drying them simultaneously. At this time, the time interval between the steps of coating each slurry may be 1 hour or less, 50 minutes or less, 40 minutes or less, 30 minutes or less, 20 minutes or less, 10 minutes or less, 5 minutes or less, or 30 seconds or less for the slurry for the lower region. By controlling such time intervals, the thickness ratio of the mixed region can be optimized, thereby further improving the overall characteristics of the secondary battery of one embodiment.

[0142] Meanwhile, the silicon-based compounds included as active materials along with the aforementioned natural graphite and artificial graphite include Si, SiOx(0 <x≤2) 및 Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, Si를 제외한 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이다) 중 적어도 하나 이상을 포함할 수 있다. 또한 SiO2와 이들 중 적어도 하나를 혼합하여 사용할 수도 있다.

[0143] The above element Y may be selected from 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, or Po. Specifically, the silicon-based compound is SiOx(0 <x≤2)을 적용할 수 있다.

[0144] The silicon-based compound may be included in an amount of 10 to 50 weight% or 10 to 30 weight% based on the total amount of active material included in the negative electrode active material layer. More specifically, the weight ratio of the natural graphite to the silicon-based compound in the negative electrode active material of the lower layer region may be 1:1 to 10:1 or 1:1 to 10:3. Additionally, the weight ratio of the artificial graphite to the silicon-based compound in the negative electrode active material of the upper layer region may be 1:1 to 10:1 or 1:1 to 10:3. Furthermore, in the mixed region, the weight ratio of the total sum of the natural graphite and artificial graphite to the silicon-based compound may be 1:1 to 10:1 or 1:1 to 10:3.

[0145] When the weight ratio of the natural graphite and / or artificial graphite and the silicon-based compound each satisfies the above range, high capacity and high energy density of the secondary battery can be secured. If the content of the natural graphite or artificial graphite is contained in an excess amount exceeding the above weight ratio range, the energy density of the battery may decrease, and if the silicon-based compound is contained in an excess amount exceeding the above weight ratio range, the durability of the battery may decrease and side reactions may increase.

[0146] Meanwhile, in one embodiment of the invention described above, the current collector for the negative electrode used as a substrate for forming the negative electrode active material layer is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, a surface treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. may be used.

[0147] The thickness of the above-mentioned current collector is not particularly limited, but can have a thickness of 3 to 500 μm, which is typically applied.

[0148] Additionally, each region of the above-described cathode active material layer may include a binder polymer and a conductive material, respectively, in addition to the active material described above. In this case, the lower region and the upper region may include a binder polymer and a conductive material derived from each slurry for forming them, and the mixed region may include the binder polymer and conductive material derived from each slurry in a mixed form.

[0149] At this time, based on the total content (weight%) of each region, the lower region may contain a greater amount (weight%) of binder polymer than the upper region. Specifically, the lower region may contain 1 to 1.2 weight% or 1 to 1.6 weight% of binder polymer based on its total content (weight%), and the upper region may contain 0.5 to 0.9 weight% or 0.4 to 0.85 weight% of binder polymer based on its total content (weight%).

[0150] At this time, excellent adhesion and rapid filling performance can be achieved when the ratio of the weight percentage of the binder polymer in the lower layer region and the weight percentage of the binder polymer in the upper layer region satisfies the relationship and range described above.

[0151] Each binder polymer included in the above-mentioned cathode active material layer may independently use various types of binder polymers, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene butylene rubber (SBR), fluororubber, and acrylic copolymer. At this time, the binder polymers included in the lower layer region and the upper layer region, or in the slurry for forming them, may be the same or different from each other.

[0152] In addition, among the examples of the binder polymers mentioned above, carboxymethyl cellulose (CMC), carboxyethyl cellulose, polyvinylpyrrolidone, etc., may also serve as thickeners to further increase the dispersion stability of the slurry.

[0153] According to one embodiment of the invention, the binder polymer mainly included in the lower region of the negative electrode active material layer may be styrene butadiene rubber (SBR) alone, or a mixture of styrene butadiene rubber and an acrylic copolymer.

[0154] In this case, the acrylic copolymer may include an acrylic acid ester copolymer, an acrylonitrile copolymer, or both. Specifically, the acrylic acid ester copolymer may be a copolymer comprising a repeating unit derived from a (meth)acrylic acid ester monomer; and a repeating unit derived from a styrene monomer, a vinyl cyanide monomer, a (meth)acrylamide monomer, an unsaturated carboxylic acid monomer, or two or more of these monomers. In addition, the acrylonitrile copolymer may be a copolymer comprising: repeating units derived from an acrylonitrile monomer; and repeating units derived from a (meth)acrylic acid ester monomer, an ethylenically unsaturated carboxylic acid ester monomer, an unsaturated carboxylic acid monomer, a conjugated diene monomer, a (meth)acrylamide monomer, a nitrile monomer, or two or more of these monomers.

[0155] In addition, when the binder polymer for the lower layer region is a mixture of styrene butadiene rubber and an acrylic copolymer, the content of styrene butadiene rubber in the binder polymer may be greater than that of the acrylic copolymer. Specifically, the weight ratio of styrene butadiene rubber and the acrylic copolymer in the binder polymer for the lower layer region may be 51:49 to 99:1, or 70:30 to 99:1. Excellent adhesion can be achieved when the content of styrene butadiene rubber in the binder polymer is greater than that of the acrylic copolymer and satisfies this weight ratio range.

[0156] In addition, the binder polymer mainly included in the upper region of the cathode active material layer may be a core-shell particle alone having a core part made of styrene butadiene rubber and a shell part made of an acrylic copolymer surrounding the outer side of the core part, or it may be a mixture of the core-shell particle and styrene butadiene rubber.

[0157] When the binder polymer for the upper layer region is a mixture, the content of the core-shell particles may be greater than that of the styrene butadiene rubber. Specifically, the weight ratio of the core-shell particles to the styrene butadiene rubber in the second binder polymer may be 51:49 to 99:1, or 70:30 to 99:1. When the content of the core-shell particles in the binder polymer is greater than that of the styrene butadiene rubber and satisfies this weight ratio range, electrode processability may be improved, such as preventing electrode roll contamination and increasing electrode flexibility.

[0158] The average particle size of the core-shell particles may be 30 to 100 nm, and the average particle size of the styrene butadiene rubber may be 200 to 350 nm.

[0159] When the binder polymer for the upper layer region is a mixture, the average particle size of the styrene butadiene rubber is larger than the core-shell particles, and specifically, when the average particle size of the core-shell particles and the styrene butadiene rubber satisfies this range, electrode processability can be improved, such as preventing electrode roll contamination and increasing electrode flexibility.

[0160] The above core-shell particles may comprise 10 to 1 part by weight, or 6 to 2 parts by weight, of a shell part made of an acrylic copolymer surrounding the outer side of the core part, based on 100 parts by weight of a core part made of styrene butadiene rubber.

[0161] At this time, the acrylic copolymer constituting the shell portion may include an acrylic acid ester copolymer, an acrylonitrile copolymer, or both. Specifically, the acrylic acid ester copolymer may be a copolymer comprising a repeating unit derived from a (meth)acrylic acid ester monomer; and a repeating unit derived from a styrene monomer, a vinyl cyanide monomer, a (meth)acrylamide monomer, an unsaturated carboxylic acid monomer, or two or more of these monomers. Additionally, the acrylonitrile copolymer may be a copolymer comprising: repeating units derived from an acrylonitrile monomer; and repeating units derived from a (meth)acrylic acid ester monomer, an ethylenically unsaturated carboxylic acid ester monomer, an unsaturated carboxylic acid monomer, a conjugated diene monomer, a (meth)acrylamide monomer, a nitrile monomer, or two or more of these monomers.

[0162] Meanwhile, the conductive material included in the lower and upper regions, respectively, is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, carbon black such as carbon black, acetylene black, Ketjen black, channel black, Farness black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives may be used. Additionally, the conductive material included in the lower and upper regions, respectively, may be the same or different from one another.

[0164] According to one embodiment of the present invention, the negative electrode active material layer has a Quantified Binder Ratio (QBR) of 2.0 or less, and the QBR can be defined by the following mathematical formula:

[0165] QBR = Bs / Bf

[0166] In the above mathematical formula, Bs represents the average value of the Os atomic ratio in the surface region of the cathode active material layer from the outermost surface of the cathode active material layer up to within 15% of the total thickness of the cathode active material layer, and Bf represents the average value of the Os atomic ratio in the bottom region of the cathode active material layer from the interface of the cathode active material layer facing the current collector up to within 15% of the total thickness of the cathode active material layer.

[0167] The above Os atomic ratio is determined by staining the binder polymer contained in the cathode active material layer with OsO4 (Osmium tetraoxide) and then analyzing the cross-section of the cathode active material layer using Energy Dispersive X-ray Spectroscopy (EDS). That is, the above Os atomic ratio can be confirmed from the Os signal obtained from the EDS analysis results.

[0168] According to one embodiment of the present invention, the QBR can be calculated by the following method.

[0169] First, a cathode to be tested for QBR is selected, the cathode is prepared in a size of 1 cm X 1 cm, placed in a container containing OsO4 (Osmium tetraoxide), sealed, and after 3 hours, the cathode is removed and placed in a vacuum oven to be dried for 48 hours so that the binder polymer contained in the cathode active material layer can be dyed using OsO4.

[0170] Afterwards, a cross-section of the stained cathode is fabricated using argon ion milling. The components within the cathode active material layer of the fabricated cathode cross-section are mapped using an Energy Dispersive X-ray Spectroscopy (EDS) detector of a Scanning Electron Microscope (SEM).

[0171] A line profile is extracted in the direction of the thickness of the cathode active material layer from the EDS mapping results, and among the extracted line profile results, the average value (Bs) of the Os atomic ratio of the Os dyed binder polymer in the surface region of the cathode active material layer and the average value (Bf) of the Os atomic ratio of the Os dyed binder polymer in the bottom region of the cathode active material layer are extracted, and the QBR value is calculated using the following formula.

[0172] QBR = Bs / Bf

[0173] At this time, the surface region of the negative active material layer is a region from the outermost surface in the thickness direction of the negative active material layer to within 15% of the total thickness of the negative active material layer, and the bottom region of the negative active material layer is a region from the interface of the negative active material layer facing the current collector to within 15% of the total thickness of the negative active material layer.

[0174] Figure 14 is a schematic diagram for calculating the QBR value of the cathode active material layer.

[0175] At this time, the negative active material layer has a surface region (Es) of the negative active material layer extending from the outermost surface of the negative active material layer to within 15% of the total thickness of the negative active material layer based on the total thickness, and a bottom region (Ef) of the negative active material layer extending from the interface of the negative active material layer facing the current collector to within 15% of the total thickness of the negative active material layer.

[0176] Referring to Fig. 14, the X-axis represents the thickness of the cathode active material layer, i.e., the distance from the surface to the current collector, and the Y-axis represents the intensity of the Os atomic component. Line A represents the intensity of the Os atomic component of the Os-dyed binder polymer extracted by EDS mapping the cathode active material layer of the cathode cross-section, and Line B is a trend line representing the trend of Line A, which is a line formed by smoothing using the LOWESS smoothing method, i.e., the Locally-Weighted Scatterplot Smoother.

[0177] The above QBR value is a numerical value representing the uniformity of the binder polymer's distribution in the thickness direction within the cathode active material layer, based on the ratio of the content of the Os-dyed binder polymer contained in the surface region to the content of the Os-dyed binder polymer contained in the bottom region of the cathode active material layer. In this case, the binder polymer content can be inferred through the Os atomic components contained in the Os-dyed binder polymer.

[0178] According to one embodiment of the present invention, the QBR value may be 0.95 or higher, 0.97 or higher, 1.0 or higher, 1.2 or higher, 1.5 or higher, 1.6 or higher, 1.62 or lower, 1.7 or lower, 1.9 or lower, 1.95 or lower, and 2.0 or lower.

[0179] When the above QBR value satisfies this range, migration of the binder polymer to the negative electrode surface is suppressed, and the distribution of the binder in the thickness direction of the negative electrode active material layer is uniform, thereby improving the adhesion between the current collector and the electrode layer, and the conductivity on the surface of the negative electrode active material layer and the resulting charge / discharge rate can also be improved.

[0181] Meanwhile, according to one aspect of the invention, the method for manufacturing the cathode is,

[0182] A lower region slurry comprising the above-described first negative electrode active material, a binder polymer for the lower region, a conductive material, and a dispersion medium; and

[0183] A step of preparing an upper region slurry comprising the aforementioned second negative electrode active material and the binder polymer for the upper region, a conductive material, and a dispersion medium;

[0184] A step of coating a slurry for the lower layer region on one surface of a cathode current collector and coating a slurry for the upper layer region thereon; and

[0185] The method may include the step of simultaneously drying each of the coated slurries to form an active material layer. At this time, as previously described, in order to properly form a mixing region, each slurry in the coating step must be coated continuously or within a certain time interval.

[0186] The negative electrode active material (first negative electrode active material, second negative electrode active material), binder polymer, thickener, and conductive material included in each of the above slurries are as described above. In addition, the above dispersion medium may each independently use N-methylpyrrolidone, acetone, water, etc.

[0187] At this time, the lower layer region is formed by originating from the slurry for the coated lower layer region, the upper layer region is formed by originating from the slurry for the upper layer region, and the mixed region is formed by mixing these in a certain thickness ratio as described above.

[0188] For coating each slurry, a device such as a double slot die may be used. According to one embodiment of the present invention, when coating the slurry onto a negative electrode current collector, the coating speed may be 10 m / min or more, 20 m / min or more, or 30 m / min or more. When the coating speed of the slurry satisfies these ranges, drying proceeds before the binder polymer migrates, so the binder polymer can be uniformly distributed in the thickness direction of the negative electrode active material layer.

[0189] Additionally, the step of simultaneously drying each of the coated slurries to form an active material layer may include the step of simultaneously drying each of the coated slurries to remove the dispersion medium within the slurry, rolling, and then vacuum drying to form an active material layer.

[0190] At this time, rolling can be performed by a method commonly used in the field of the art, such as roll pressing, and, for example, can be performed at a pressure of 1 to 20 MPa and a temperature of 15 to 30°C. In addition, the rolling can be performed under conditions such that the porosity of the electrode (active material layer) after rolling is 20 to 40%, or 25 to 35%, or 20 to 30%, or 30 to 40%.

[0191] The step of drying the coated slurry above can be carried out, for example, at 70 to 90°C, or 75 to 85°C, or 80 to 85°C for 10 to 30 minutes, or 15 to 25 minutes, or 20 to 30 minutes, but such drying temperature and time can be appropriately adjusted depending on the type and content of the dispersion medium.

[0192] In addition, after rolling the dried slurry layer, it may be carried out by vacuum drying at a temperature of 100 to 170°C, or 120 to 150°C, or 130 to 150°C for about 3 to 10 hours, or 5 to 8 hours, but such drying temperature and time can be appropriately adjusted depending on the type and content of the dispersion medium.

[0193] The above-mentioned cathode active material layer may have a total ratio (weight%) of binder polymer of 1 to 3 weight%, or 1 to 2 weight%, or 2 to 3 weight%.

[0194] Meanwhile, the positive electrode included in the secondary battery of the above embodiment can be manufactured by mixing a positive electrode active material, a conductive material, a binder, and a solvent to prepare a slurry, and then directly coating it onto a positive electrode current collector, or by casting it onto a separate support and then laminating a film of the positive electrode active material peeled off from the support onto a positive electrode current collector.

[0195] The above-mentioned positive electrode active material may include a lithium-nickel-based transition metal oxide having a nickel content of 80 to 100 mol% based on the total amount of transition metals. In a specific example, the lithium-nickel-based transition metal oxide is represented by the following chemical formula 1, and

[0196] [Chemical Formula 1]

[0197] Li 1+a (Ni b Co c Mn d Al e M f )O2

[0198] In the above chemical formula 1,

[0199] -0.1≤a≤0.2, 0.8≤b≤1.0, 0.01≤c≤0.15, 0.01≤d≤0.15, 0.01≤e≤0.1, 0≤f≤0.05, and M is at least one selected from the group consisting of Mg, Ti, Zr, Nb and W.

[0200] In a more specific example, the nickel content of the lithium-nickel-based transition metal oxide may be 80 to 100 mol%, or 85 to 100 mol%, or 88 to 100 mol% based on the total amount of transition metal.

[0201] When the nickel content of the above lithium nickel-based transition metal oxide satisfies the range of 80 to 100 mol% based on the total amount of transition metal, it controls the resistance of the lower SOC region that affects the output of the secondary battery, thereby having a more effective effect on the high-loading electrode where the positive active material is highly coated, and is applicable to the realization of high-capacity, high-density EV batteries, but when the nickel content is low outside this range, there is a problem with capacity development.

[0202] The above-mentioned positive active material may be a single particle having unimodal characteristics on the particle size distribution curve, or a secondary particle formed by primary particles aggregating together through an assembly process. However, considering that in the above-mentioned large-scale tapless cylindrical secondary battery, it is necessary to further reduce resistance to improve rapid charging characteristics and to suppress side reactions and gas generation, it is more preferable to use the above-mentioned positive active material having the form of a single particle.

[0203] At this time, the D50 of the single-particle cathode active material may be 1 μm to 15 μm, or 2 μm to 8 μm, or 3 to 7 μm, thereby maximizing the effects such as reduced resistance, side reactions, and gas generation.

[0204] The above positive current collector is generally manufactured with a thickness of 3 to 300 μm and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, one selected from stainless steel, aluminum, nickel, titanium, and aluminum or stainless steel surface treated with carbon, nickel, titanium, or silver can be used, and specifically, aluminum can be used.

[0205] The above positive current collector may have fine irregularities formed on its surface to increase the adhesion of the positive active material, and can take various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0206] Meanwhile, the conductive material, binder polymer, and dispersion medium can be appropriately selected and used as exemplified during the manufacture of the cathode above.

[0207] The above-mentioned separator may be a porous polymer film made of a polyolefin-based polymer, such as a conventional porous polymer film used as a separator, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, used alone or in a laminate thereof. In addition, an insulating thin film having high ion permeability and mechanical strength may be used. The above-mentioned separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on the surface of the separator. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc., may be used, but is not limited thereto.

[0208] The above electrolyte comprises a lithium salt as an electrolyte and an organic solvent for dissolving it.

[0209] The above lithium salt may be used without limitation as long as it is one commonly used in electrolytes for secondary batteries, for example, as the anion of the above lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C -, (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One type selected from the group consisting of can be used.

[0210] The organic solvent included in the above electrolyte may be any commonly used solvent without limitation, and one or more selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran may be used.

[0211] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts in the electrolyte, so they can be used preferably. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0212] Optionally, the electrolyte may further include additives such as an overcharge prevention agent included in a conventional electrolyte.

[0213] Meanwhile, a cylindrical secondary battery according to one embodiment of the invention can be manufactured by forming an electrode assembly (10) by placing a separator (15) between a positive electrode (13) and a negative electrode (14), placing the electrode assembly (10) into a battery can, and then injecting an electrolyte.

[0214] Meanwhile, FIG. 3 schematically illustrates an example of the overall configuration of a cylindrical secondary battery of one embodiment. As described above with reference to FIG. 1 and 2, the cylindrical secondary battery of one embodiment basically comprises a positive electrode and a negative electrode (13, 14) in which each electrode tab (11, 12) is defined by a segment of the uncoated portion (16), and a separator (15) interposed between them is wound in one direction to form a jelly roll-shaped electrode assembly (10).

[0215] Referring to FIG. 3, the cylindrical secondary battery may further include: a battery can (20) that accommodates the electrode assembly (10) and is electrically connected to the electrode assembly (10); a through terminal (40) that penetrates one side of the battery can (20) and is electrically connected to the electrode assembly (10); and a cap plate (30) configured to cover the opening of the battery can (20).

[0216] Additionally, the through terminal (40) can be electrically connected to a segmented electrode tab (11) having positive polarity, and the battery can (20) can be electrically connected to a segmented electrode tab (12) having negative polarity.

[0217] Additionally, an insulating gasket (50) may be further provided to be interposed between the battery can (20) and the through terminal (40) to insulate the through terminal (40) and the battery can (20), and first and second current collection plates (60, 80) may be further provided to electrically connect the electrode tabs (11, 12), the through terminal (40), and the battery can (20). Additionally, an insulator (70) interposed between the first current collection plate and the battery can may be further provided.

[0218] A battery of this structure has a structure in which a negative electrode tab (12) is electrically connected to a battery can (20) through a second current collection plate (80) with a large area, and a positive electrode tab (11) is electrically connected to a through terminal (40) through a first current collection plate (60) with a large area, so that charge and current can move through the battery can (20) and the through terminal (40).

[0219] Accordingly, as the cylindrical secondary battery of one embodiment has such a stepless battery structure, the current / charge transfer path during charging / discharging can be minimized and improved rapid charging characteristics can be exhibited.

[0220] In addition, the above-mentioned cylindrical secondary battery may be a large-sized cylindrical secondary battery in which, for example, the ratio of the form factor (defined as the ratio of the diameter of the secondary battery to the height, i.e., the ratio of the diameter (Φ) to the height (H)) is approximately greater than 0.4, and may, for example, have a diameter of 35 mm or more and a height of 75 mm or more.

[0221] Here, the form factor refers to a value representing the diameter and height of a cylindrical secondary battery. In a more specific embodiment, the cylindrical secondary battery may be, for example, a 46110 cell, a 48750 cell, a 48110 cell, a 48800 cell, or a 46800 cell. In the numerical value representing the form factor, the first two digits represent the diameter of the cell, the next two digits represent the height of the cell, and the last digit 0 indicates that the cross-section of the cell is circular.

[0222] That is, according to specific embodiments, the cylindrical secondary battery of the above embodiment may be a cell in the shape of a cylinder, such that the diameter is approximately 46 mm, the height is approximately 110 mm, and the form factor ratio is approximately 0.418, 46110 cells, the diameter is approximately 48 mm, the height is approximately 75 mm, and the form factor ratio is approximately 0.640, 48750 cells, the diameter is approximately 48 mm, the height is approximately 110 mm, and the form factor ratio is approximately 0.418, 48110 cells, the diameter is approximately 48 mm, the height is approximately 80 mm, and the form factor ratio is approximately 0.600, or 46800 cells, the diameter is approximately 46 mm, the height is approximately 80 mm, and the form factor ratio is approximately 0.575.

[0223] Compared to existing 18650 cells and 21700 cells, this is a large-sized battery that has a large form factor and is advantageous for rapid charging, and can be preferably applied to medium and large devices such as automobiles.

[0224] Meanwhile, referring to FIG. 4, a battery pack (3) according to another embodiment of the invention includes a secondary battery assembly in which a plurality of cylindrical secondary batteries (1) according to one embodiment as described above are electrically connected, and a pack housing (2) that accommodates the same. In the drawings of this specification, components such as a busbar for electrical connection, a cooling unit, and a power terminal have been omitted for convenience of drawing.

[0225] Also, referring to FIG. 5, a vehicle (5) according to another embodiment of the invention may be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle, and includes a battery pack (3) according to the other embodiment. The vehicle (5) includes a four-wheeled vehicle and a two-wheeled vehicle. The vehicle (5) operates by receiving power from the battery pack (3) according to the other embodiment.

[0227] Hereinafter, the present invention will be described in detail with reference to examples to aid in understanding. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the following embodiments. The embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

[0229] Example 1: Manufacturing of a secondary battery

[0230] <Manufacturing of the Cathode>

[0231] A slurry for the lower layer was prepared by mixing 10 parts by weight of SiO (silicon oxide) and 50 parts by weight of natural graphite as the first cathode active material, 0.1 parts by weight of CNT as the first conductive material, and 1.4 parts by weight of styrene butadiene rubber (SBR) as the first binder polymer, and adding water.

[0232] 10 parts by weight of SiO (silicon oxide) and 50 parts by weight of artificial graphite as the second cathode active material, 0.1 parts by weight of CNT as the second conductive material, and 0.7 parts by weight of core-shell particles as the second binder polymer were mixed, and water was added to prepare an upper layer slurry.

[0233] The artificial graphite was in the form of a carbon coating layer disposed on secondary particles formed by the aggregation of primary artificial graphite particles. At this time, the D50 of the primary particles was 10 μm, and the average particle size (D50) of the first negative electrode active material, which was an artificial graphite in the form of secondary particles aggregated from the primary particles, was 20 μm. In the second negative electrode active material, the carbon coating layer on the secondary particles was included at 4.0 wt% based on the total weight of the second negative electrode active material. At this time, the average particle size (D50) of the second negative electrode active material was 21 μm.

[0234] In addition, the core-shell particle is composed of a core part made of styrene butadiene rubber and a shell part made of acrylic copolymer surrounding the outer side of the core part.

[0235] Subsequently, using a double slot die, the above lower layer slurry is applied to both sides of a copper (Cu) foil, which serves as a cathode current collector with a thickness of 10 μm, at a rate of 2.5 mAh / cm² 2 After applying with a loading amount, the upper layer slurry was applied onto the applied lower layer slurry continuously (without a separate time interval) with a loading amount of 2.5 mAh / cm2. At this time, the coating speed for applying the lower layer slurry and the upper layer slurry was 30 m / min each. Subsequently, the current collector coated with the slurries was dried at 80°C for 20 minutes to remove water from the slurry, the dried slurry layer was rolled, and then vacuum dried at approximately 130°C for 8 hours to manufacture the cathode.

[0236] Electron microscope images of such a cathode are shown in Figures 6a and 6b. Referring to Figures 6a and 6b, it was confirmed that cathode active material layers with thicknesses of approximately 70 μm and approximately 79 μm were formed on both sides of the 10 μm thick current collector, respectively (total thickness: 159 μm). Additionally, upon examination of the active material layer with a thickness of 70 μm, it was confirmed that its porosity was 30% and that it had an upper layer region with a thickness of 25 μm (a layer of artificial graphite + silicon oxide distribution), a mixed region with a thickness of 20 μm (a layer of artificial graphite and natural graphite mixed + silicon oxide), and a lower layer region with a thickness of 25 μm (a layer of natural graphite + silicon oxide distribution).

[0238] Manufacturing of the anode

[0239] A cathode was prepared by thoroughly mixing 97 parts by weight of the chemical formula Li[Ni0.86Mn0.05Co0.07]Al0.2O2 as a cathode active material with a Ni content of 86 mol% of the total transition metal, 1.4 parts by weight of polyvinylidene fluoride (PVdF) as a binder polymer, and 0.4 parts by weight of CNT as a conductive material in N-methylpyrrolidone (NMP), applying it to an Al foil 20 μm thick with a loading amount of 5 mAh / cm2, vacuum drying it at about 130°C for 8 hours, and rolling it to achieve a porosity of 30%.

[0241] Manufacture of Lithium Secondary Batteries

[0242] A non-aqueous electrolyte was prepared by dissolving LiPF6 to a concentration of 1.0 M in an organic solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in a composition of 3:3:4 (volume ratio).

[0243] An electrode assembly was prepared by interposing a porous polyethylene separator between the anode and cathode manufactured above, placed in a cylindrical case, and the electrolyte was injected to manufacture a lithium secondary battery (cylindrical battery). The form factor of the cylindrical battery was confirmed to be a 46800 cylindrical cell having a maximum diameter of 46 mm and a maximum height of 80 mm.

[0245] Comparative Example 1: Manufacturing of a secondary battery

[0246] A slurry was prepared by mixing 10 parts by weight of SiO (silicon oxide), 50 parts by weight of natural graphite, 50 parts by weight of artificial graphite as the first cathode active material, 0.1 parts by weight of CNT as the conductive material, and 1.2 parts by weight of styrene butadiene rubber (SBR) as the binder polymer, and adding water.

[0247] The artificial graphite was in the form of a carbon coating layer disposed on secondary particles formed by the aggregation of primary artificial graphite particles. At this time, the D50 of the primary particles was 10 μm, and the average particle size (D50) of the first negative electrode active material, which was an artificial graphite in the form of secondary particles aggregated from the primary particles, was 20 μm. In the second negative electrode active material, the carbon coating layer on the secondary particles was included at 4.0 wt% based on the total weight of the second negative electrode active material. At this time, the average particle size (D50) of the second negative electrode active material was 21 μm.

[0248] The above slurry is applied to both sides of a copper (Cu) foil, which serves as a cathode current collector with a thickness of 10㎛, at a rate of 5mAh / cm 2It was applied with a loading amount. At this time, the coating speed for applying the slurry was 30 m / min. The current collector coated with the slurry was vacuum dried at approximately 130°C for 8 hours, and rolled to achieve a porosity of 30% to produce a single-layer cathode. An electron microscope image of this cathode is shown in Fig. 6c. Referring to Fig. 6c, it was confirmed that the cathode active material layer formed on both sides of the current collector contained only regions where natural graphite, artificial graphite, and silicon oxide were mixed.

[0249] A positive electrode and a secondary battery (cylindrical battery) were manufactured in the same manner as in Example 1, except that the negative electrode manufactured in this way was used.

[0251] Comparative Example 2: Manufacturing of a secondary battery

[0252] A slurry was prepared by mixing 10 parts by weight of SiO (silicon oxide), 50 parts by weight of natural graphite, 50 parts by weight of artificial graphite as the first cathode active material, 0.1 parts by weight of CNT as the conductive material, and 1.05 parts by weight of styrene butadiene rubber (SBR) as the binder polymer, and adding water.

[0253] The artificial graphite was in the form of a carbon coating layer disposed on secondary particles formed by the aggregation of primary artificial graphite particles. At this time, the D50 of the primary particles was 10 μm, and the average particle size (D50) of the first negative electrode active material, which was an artificial graphite in the form of secondary particles aggregated from the primary particles, was 20 μm. In the second negative electrode active material, the carbon coating layer on the secondary particles was included at 4.0 wt% based on the total weight of the second negative electrode active material. At this time, the average particle size (D50) of the second negative electrode active material was 21 μm.

[0254] Subsequently, using a double slot die, the above-prepared slurry is applied to one side of a copper (Cu) foil serving as a cathode current collector with a thickness of 10 μm at a rate of 2.5 mAh / cm² 2 After applying with a loading amount of 2.5 mAh / cm², the same prepared slurry is applied onto the applied slurry. 2The slurry was applied with a loading amount. At this time, the coating speed for applying the lower layer slurry and the upper layer slurry was 30 m / min each. Subsequently, the current collector coated with the slurries was dried at 80°C for 20 minutes to remove water from the slurry, and after rolling the dried slurry layer, the cathode was manufactured by vacuum drying at approximately 130°C for 8 hours. At this time, the porosity of the manufactured cathode was 30%, and it had a double-layer structure with an upper layer region of 50 μm thickness and a lower layer region of 50 μm thickness, and a cathode active material layer with a total thickness of 100 μm.

[0255] A positive electrode and a secondary battery (cylindrical battery) were manufactured in the same manner as in Example 1, except that the negative electrode manufactured in this way was used.

[0257] Evaluation of characteristics of secondary batteries and cathodes

[0258] Experimental Example 1: Evaluation of Swelling Characteristics

[0259] For each example and comparative example, an initial (one-time) charge and discharge was performed on the lithium secondary battery (cylindrical battery) using an electrochemical charge / discharger. At this time, charging was performed by applying current at a current density of 1.5 C-rate up to a voltage of 4.47 V, and discharging was performed down to 3.0 V at the same current density.

[0260] Swelling characteristics were evaluated for each secondary battery that had undergone one cycle of charging and discharging. At this time, the swelling characteristics were calculated as the percentage of the changed diameter of the secondary battery after charging and discharging relative to the diameter of the initial secondary battery before charging and discharging, as shown in the following equation.

[0261] Swelling (%) = [(Secondary battery diameter after charge / discharge) - (Initial secondary battery diameter)] / (Initial secondary battery diameter) X 100

[0262] The results are shown in Table 1 below. In addition, the X-ray CT imaging results of the cylindrical secondary batteries of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Figures 7 to 9, respectively.

[0263] Example 1 Comparative Example 1 Comparative Example 2 Swelling (%) 9.30 12.40 11.60

[0264] Referring to Table 1 and Figures 7 to 9, it can be seen that although a crack occurred due to swelling of the negative electrode after the completion of the charge-discharge cycle, when the electrode structure is modified as in the example, the crack in the core part is improved and the swelling phenomenon is significantly reduced.

[0265] That is, in FIGS. 7 to 9, the middle part is the central part of the jelly roll (the part where the core is removed), and the cylindrical secondary batteries of Comparative Example 1 and Comparative Example 2, which have a negative electrode having only a single layer or double layer mixed with natural graphite and artificial graphite, have a large swelling phenomenon and the circular shape of the central part is distorted, whereas in the case of the cylindrical secondary battery of Example 1 (distribution of natural graphite and silicon-based compound in the lower layer region, distribution of natural graphite, artificial graphite and silicon-based compound in the mixed region, distribution of artificial graphite and silicon-based compound in the upper layer region), the swelling phenomenon is suppressed and the circular shape is maintained.

[0266] In addition, X-ray CT images of the cylindrical batteries of Example 1, Comparative Example 1, and Comparative Example 2, which underwent one cycle of charging and discharging, are shown in FIGS. 7 to 9, respectively.

[0267] In FIGS. 7 to 9, the center part is the central part of the jelly roll of the cylindrical battery (the part where the core has been removed). In the cylindrical battery of Example 1 in FIG. 7, the swelling phenomenon is suppressed and the circular shape is maintained, whereas in the cylindrical batteries of Comparative Examples 1 and 2 in FIGS. 8 and 9, only a region where artificial graphite and natural graphite are mixed exists in each negative electrode active material layer, so the swelling phenomenon is large and the circular shape of the central part of the jelly roll is distorted.

[0269] Experimental Example 2: Evaluation of Lithium Precipitation Phenomenon

[0270] After subjecting the lithium secondary batteries (cylindrical batteries) of each example and comparative example to one cycle of charging and discharging under the conditions of Experimental Example 1, each lithium secondary battery was disassembled, and photographs of the negative active material layer attached to the surface of the negative active material layer and the separator of each secondary battery are shown in FIGS. 10 to 12, respectively.

[0271] In FIGS. 10 to 12, the upper photograph shows the surface of the negative electrode active material layer, and the lower photograph shows the negative electrode active material layer attached to the separator. In the secondary batteries of Comparative Examples 1 and 2 in FIGS. 11 and 12, black lithium precipitates were observed on both the surface of the negative electrode active material layer and the negative electrode active material layer attached to the separator. On the other hand, no lithium precipitation was observed in the secondary battery of Example 1 in FIG. 10.

[0273] Experimental Example 3: Evaluation of Rapid Charging Characteristics

[0274] For each battery of Example 1 and Comparative Example 1, a rapid charge / discharge test was performed under conditions of 2.5C (4.1V, 0.05C) / 0.5C (3.0V), and the test results were shown in FIGS. 13a to 13d, respectively.

[0275] For reference, in FIGS. 13a to 13d, the solid line represents the evaluation result for Comparative Example 1, and the dotted line represents the evaluation result for Example 1. Additionally, FIG. 13a shows the change pattern of capacity characteristics per cycle during rapid charging and discharging, and FIG. 13b shows the 2.5C charging profile. Furthermore, FIGS. 13c and 13d are DCIR profiles showing the change patterns of voltage and resistance over time during rapid charging at SOC 50%.

[0276] Referring to FIG. 13a, it was confirmed that Example 1 exhibited superior capacity retention rate over cycles in a rapid charge-discharge test compared to Comparative Example 1. Additionally, referring to FIGs. 13c and 13d, it was confirmed that Example 1 suppressed overvoltage mitigation and interfacial resistance increase over time compared to Comparative Example 1.

[0277] From this, it was confirmed that the battery of Example 1 exhibits improved rapid charging characteristics compared to Comparative Example 1.

[0279] Experimental Example 4: Evaluation of Distribution Characteristics (QBR) of Cathode Binder Polymer

[0280] The cathode prepared in Example 1 was prepared in a size of 1 cm X 1 cm, placed in a container containing OsO4 (Osmium tetraoxide), sealed, and after 3 hours, the cathode was removed and placed in a vacuum oven to dry for 48 hours, thereby dyeing the binder polymer contained in the cathode active material layer using OsO4. At this time, the cathode had a cathode active material layer coated on both sides of the current collector, so the cathode active material layer formed on the upper surface of the current collector was referred to as the first cathode active material layer, and the cathode active material layer formed on the lower surface of the current collector was referred to as the second cathode active material layer.

[0281] Subsequently, a cross-section of the stained cathode was fabricated using argon ion milling. Then, the components within the first and second cathode active material layers of the fabricated cathode cross-section were mapped using an Energy Dispersive X-ray Spectroscopy (EDS) detector of a Scanning Electron Microscope (SEM).

[0282] Line profiles were extracted in the thickness direction of the first and second cathode active material layers from the EDS mapping results, and among the extracted line profile results, the average value (Bs) of the Os atomic ratio of the Os dyed binder polymer in the surface region of the first and second cathode active material layers and the average value (Bf) of the Os atomic ratio of the Os dyed binder polymer in the bottom region of the first and second cathode active material layers were extracted, and QBR values ​​were calculated using the following formula and the results are shown in Table 2.

[0283] QBR = Bs / Bf

[0284] At this time, the surface region of the first and second cathode active material layers is a region from the outermost surface in the thickness direction of the first and second cathode active material layers up to within 15% of the total thickness of the first and second cathode active material layers, and the bottom region of the first and second cathode active material layers is a region from the interface of the first and second cathode active material layers facing the current collector up to within 15% of the total thickness of the first and second cathode active material layers.

[0286] Bs Bf QBR First cathode active material layer 1.02 0.63 1.62 Second negative electrode active material layer 1.31 0.82 1.60

[0287] FIG. 15a is a graph showing the change in normalized intensity of the Os component dyed in the binder polymer of the first cathode active material layer extracted and analyzed from EDS mapping at a distance from the surface of the first cathode active material layer toward the current collector for the cathode of Example 1.

[0288] FIG. 15b is a graph showing the change in normalized intensity of the Os component dyed in the binder polymer of the second cathode active material layer extracted and analyzed from EDS mapping at a distance from the surface of the second cathode active material layer to the current collector direction for the cathode of Example 1.

[0289] In Figures 15a and 15b, the Binder line represents the intensity in each depth direction when the total Os component of the actually measured Os-stained binder polymer is normalized to 1, the Trend line is a trend line representing the trend of the Binder line, which is a line smoothed using the LOWESS smoothing method, i.e., the Locally-Weighted Scatterplot Smoother, and the Avg wt% line is a line that always shows a value of 1. Explanation of the symbols

[0291] 5: Cars 3: Battery Pack 2: Pack Housing 1: Cylindrical secondary battery 10: Electrode assembly 11, 12: Electrode (positive, negative) tabs 13: Bipolar 14: Cathode 15: Separator 16: Mujibu 17: The whole house 18: Active material layer 20: Battery can 30: Cap plate 40: Through-hole terminal 50: Insulation gasket 60: First collector plate 70: Insulator 80: Second current collector plate

Claims

Claim 1 A cylindrical secondary battery comprising: a positive electrode including a positive active material layer on a current collector, a negative electrode including a negative active material layer on a current collector, and a jellyroll-shaped electrode assembly in which a separator interposed between the positive electrode and the negative electrode is wound; and a battery can accommodating the electrode assembly, wherein the negative active material layer comprises a lower layer region in contact with the current collector and comprising a silicon-based compound and natural graphite as active materials, a mixed layer region in contact with the lower layer region and comprising a silicon-based compound, natural graphite and artificial graphite as active materials, and an upper layer region in contact with the mixed layer region and comprising a silicon-based compound and artificial graphite as active materials, wherein the mixed layer has an active material distribution gradient in which the distribution ratio of the natural graphite decreases and the distribution ratio of the artificial graphite increases as it approaches the upper layer region, and wherein the mixed layer has a diameter of 35 mm or more and a height of 75 mm or more based on the maximum diameter and maximum height of the battery can. Claim 2 A cylindrical secondary battery according to claim 1, characterized in that the positive active material layer comprises a lithium nickel-based transition metal oxide as an active material, wherein the nickel content is 80 to 100 mol% based on the total amount of transition metal. Claim 3 A cylindrical secondary battery according to claim 2, characterized in that the lithium-nickel-based transition metal oxide is represented by the following chemical formula 1: [Chemical Formula 1] Li 1+a (Ni b Co c Mn d Al e M f In the above formula 1, -0.1≤a≤0.2, 0.8≤b≤1.0, 0.01≤c≤0.15, 0.01≤d≤0.15, 0.01≤e≤0.1, 0≤f≤0.05, and M is at least one selected from the group consisting of Mg, Ti, Zr, Nb and W. Claim 4 A cylindrical secondary battery according to claim 1, characterized in that the negative electrode active material layer has a thickness of 40 to 200 μm. Claim 5 A cylindrical secondary battery according to claim 1, characterized in that, based on the cross-sectional thickness at which the mixing region is formed with the largest thickness in the negative electrode active material layer, the mixing region has a thickness of 20 to 80% of the total thickness of the negative electrode active material layer. Claim 6 A cylindrical secondary battery according to claim 5, characterized in that, based on the cross-sectional thickness in which the mixed region in the negative electrode active material layer is formed with the largest thickness, the lower layer region has a thickness of 10 to 50% of the total thickness of the negative electrode active material layer. Claim 7 A cylindrical secondary battery according to claim 5, characterized in that, based on the cross-sectional thickness in which the mixing region in the negative electrode active material layer is formed with the largest thickness, the upper layer region has a thickness of 10 to 50% of the total thickness of the negative electrode active material layer. Claim 8 A cylindrical secondary battery according to claim 1, characterized in that the mixing region comprises the natural graphite and artificial graphite in a weight ratio of 2:8 to 8:

2. Claim 9 A cylindrical secondary battery according to claim 1, characterized in that the natural graphite has a particle shape exhibiting a sphericity greater than 0.91 and has an average particle size (D50) of 5 to 30 μm. Claim 10 A cylindrical secondary battery according to claim 1, characterized in that the artificial graphite comprises secondary particles formed by the aggregation of primary particles and a carbon coating layer formed on the surface of the secondary particles. Claim 11 A cylindrical secondary battery according to claim 10, characterized in that the carbon coating layer is included in an amount of 0.5 to 10 weight percent based on the total weight of the artificial graphite. Claim 12 A cylindrical secondary battery according to claim 10, characterized in that the artificial graphite has an average particle size (D50) of 4 to 32 μm. Claim 13 In claim 1, the silicon-based compound is Si, SiOx(0 <x≤2), Si-Y 합금(Y는 알칼리 금속, 알칼리 토금속, 13족 원소, Si를 제외한 14족 원소, 전이금속, 희토류 원소 및 이들의 조합으로부터 선택되는 원소이다.), 또는 이들 중 2종 이상을 포함하는 것을 특징으로 하는 원통형 이차전지. Claim 14 A cylindrical secondary battery according to claim 1, characterized in that the silicon-based compound is included in an amount of 10 to 50 weight percent based on the total amount of active material included in the negative electrode active material layer. Claim 15 A cylindrical secondary battery according to claim 14, characterized in that the weight ratio of natural graphite to silicon-based compound in the negative electrode active material of the lower layer region is 1:1 to 10:1, and the weight ratio of artificial graphite to silicon-based compound in the negative electrode active material of the upper layer region is 1:1 to 10:

1. Claim 16 A cylindrical secondary battery according to claim 1, wherein the lower layer region, the mixed region, and the upper layer region each comprise the active material, the binder polymer, and the conductive material, and, based on the total content (weight%) of each region, the lower layer region comprises a greater content (weight%) of the binder polymer than the upper layer region. Claim 17 A cylindrical secondary battery according to claim 16, characterized in that the lower layer region comprises 1 to 1.2 weight% of a binder polymer based on its total content (weight%), and the upper layer region comprises 0.5 to 0.9 weight% of a binder polymer based on its total content (weight%). Claim 18 A cylindrical secondary battery according to claim 16, characterized in that the binder polymer of the lower layer region comprises styrene butadiene rubber (SBR) or a mixture of styrene butadiene rubber (SBR) and an acrylic copolymer. Claim 19 A cylindrical secondary battery according to claim 18, wherein the binder polymer of the lower layer region comprises a mixture of styrene butadiene rubber (SBR) and an acrylic copolymer, and the styrene butadiene rubber is included in a larger amount than the acrylic copolymer. Claim 20 A cylindrical secondary battery according to claim 16, wherein the binder polymer of the upper layer region comprises a core-shell particle having a core portion made of styrene butadiene rubber and a shell portion made of an acrylic copolymer surrounding the outer side of the core portion; or a mixture of the core-shell particle and styrene butadiene rubber. Claim 21 A cylindrical secondary battery according to claim 20, wherein the binder polymer of the upper layer region comprises a mixture of the core-shell particles and styrene butadiene rubber, and the core-shell particles are included in a larger content than the styrene butadiene rubber. Claim 22 A cylindrical secondary battery according to claim 20, characterized in that the average particle size (D50) of the core-shell particles is 30 to 100 nm and the average particle size of the styrene butadiene rubber is 200 to 350 nm. Claim 23 A cylindrical secondary battery according to claim 1, wherein the negative electrode active material layer has a QBR (Quantified Binder Ratio) of 2.0 or less, and the QBR is defined by the following mathematical formula: QBR = Bs / Bf. In the above mathematical formula, Bs represents the average value of the Os atomic ratio in the surface region of the negative electrode active material layer from the outermost surface of the negative electrode active material layer up to within 15% of the total thickness of the negative electrode active material layer, and Bf represents the average value of the Os atomic ratio in the bottom region of the negative electrode active material layer from the interface of the negative electrode active material layer facing the current collector up to within 15% of the total thickness of the negative electrode active material layer, and the Os atomic ratio is analyzed by EDS (Energy Dispersive Spectroscopy) after staining the cross-section of the negative electrode active material with OsO4. Claim 24 A cylindrical secondary battery according to claim 1, wherein the positive and negative electrodes have a non-active material layer formed along one end of a current collector in a direction parallel to the winding direction, and at least a portion of the current collector in the non-active portion defines an electrode tab. Claim 25 A cylindrical secondary battery according to claim 24, wherein at least a portion of the current collector defining the electrode tab is processed into a plurality of segments that can be independently bent. Claim 26 A cylindrical secondary battery according to claim 1, wherein the ratio of the form factor, defined as the value obtained by dividing the diameter by the height, is greater than 0.

4. Claim 27 In claim 26, the cylindrical secondary battery is a cylindrical secondary battery in which the cylindrical secondary battery is a 46110 cell, a 48750 cell, a 48110 cell, a 48800 cell, or a 46800 cell. Claim 28 A battery pack comprising a cylindrical secondary battery according to any one of claims 1 to 27. Claim 29 An automobile comprising the battery pack of paragraph 28.

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