One]The present invention relates to a secondary battery including a structure in which unit cells having reduced thickness in one direction are radially assembled, and to a device including the same.
[2]This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0133561 on October 25, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.
background
[3]
As the price of energy sources increases due to the depletion of fossil fuels and interest in environmental pollution is increased, the demand for eco-friendly alternative energy sources is increasing. In particular, as technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. As the demand for secondary batteries diversifies and increases, there is a demand for new types of secondary batteries.
[4]
In addition, in the case of a lithium secondary battery, lithium ions in an electrolyte generally exhibit high ionic conductivity in a specific concentration range, and when the concentration is thinner or thicker than this, the ionic conductivity is reduced. The concentration of the electrolyte or the concentration of lithium ions inside the lithium secondary battery is not constant, and the concentrations of lithium ions near the positive electrode and the negative electrode behave in opposite directions depending on the operating conditions of the battery.
[5]
Therefore, there is a need for a new type of secondary battery technology that solves these problems.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[6]
The present invention has been devised to solve the above problems, and an object of the present invention is to provide a new type of secondary battery including a structure in which unit cells having reduced thickness in one direction are radially assembled, and a device for the same.
means of solving the problem
[7]
In one example, in the secondary battery according to the present invention, n unit cells (n is an integer greater than or equal to 5) are radially assembled about a central axis based on a horizontal cross-sectional structure to form a battery, and each unit cell includes , based on the horizontal cross-sectional structure, the cell thickness is reduced in the central axis direction from the outer end forming the outer peripheral surface of the battery.
[8]
In a specific example, in the secondary battery, the k-th unit cell (k is an integer between 1 and n-1) and the k+1-th unit cell are adjacent to each other and face each other, and the first unit cell and the n-th unit cell (n is an integer) An integer between 5 and 10000) unit cells are also adjacent to each other and face each other. The n value may vary depending on the size of the applied device, and in the case of a mobile or small device, n can be manufactured within 1000, and when a large cell such as an automobile is used, the n value is 1000 or more to a range that satisfies 10000 Unit cells may be aggregated.
[9]
In one example, the secondary battery has a cylindrical structure in which n units (n is an integer greater than or equal to 5) are radially assembled about a central axis based on a horizontal cross-sectional structure to form a hollow, and the inner and outer diameters of the battery The diameter ratio ranges from 1:1.1 to 100.
[10]
In another example, each unit cell forming the battery, based on the horizontal cross-sectional structure, the thickness of the inner end in the center direction forming the inner peripheral surface of the battery (D in ) and the outer end forming the outer peripheral surface of the battery The ratio (D out : D in ) of the thickness (D out ) is in the range of 1:1.1 to 100.
[11]
In a specific example, in each unit cell forming the battery, at least one electrode of the positive electrode and the negative electrode decreases the distance between the electrode and the electrode from the outer end forming the outer circumferential surface of the battery to the center direction based on the horizontal cross-sectional structure is a structure that
[12]
In another specific example, in each unit cell forming the battery, the positive electrode and the negative electrode each have a structure in which a mixture layer including an active material is applied on a metal current collector, and at least one electrode of the positive electrode and the negative electrode has a horizontal cross-sectional structure Based on , the thickness of the mixture layer applied on the metal current collector in the central axis direction from the outer end forming the outer circumferential surface of the battery is reduced.
[13]
In another specific example, in each unit cell forming the battery, the positive electrode and the negative electrode each have a structure in which a mixture layer including an active material is applied on a metal current collector, and at least one electrode of the positive electrode and the negative electrode has a horizontal cross-sectional structure Based on , the density of the mixture layer applied on the metal current collector in the central axis direction from the outer end forming the outer circumferential surface of the battery increases.
[14]
In one example, each unit cell includes a positive electrode and a negative electrode, a first separator is interposed between the positive electrode and the negative electrode, and a second separator is interposed between the unit cell and the unit cell.
[15]
In a specific example, each of the positive electrode and the negative electrode has a structure in which a mixture layer including an active material is laminated on one surface of a current collector in a direction facing the first separator.
[16]
In one example, in each unit cell forming a battery, a metal current collector forming at least one electrode of a positive electrode and a negative electrode has a porous structure in which a through-thick hole is formed.
[17]
In a specific example, in each unit cell forming the battery, the metal current collector forming at least one electrode of the positive electrode and the negative electrode has a porous structure in which a through-hole is formed, and the area fraction in which the through-hole is formed is 10 to 80 % range. For example, a metal current collector having a porous structure in which a through-thick hole is formed is in the form of a mesh.
[18]
In another example, the present invention provides a device including the secondary battery described above. Specifically, the device includes a mobile electronic device, a wearable device, a power tool that moves with power by a battery-based motor, a drone, and an electric vehicle. , EV), Hybrid Electric Vehicle (HEV), Plug-in Hybrid Electric Vehicle (PHEV), E-bike, Electric Scooter (E-scooter), Electric Golf It may be an electric golf cart or a system for power storage.
Effects of the Invention
[19]
A secondary battery and a device including the same according to the present invention present a new structure in which unit cells having a thickness decreasing in one direction are radially assembled, and when a current collector having a through-hole in the thickness direction is applied, the change in the concentration of the electrolyte in the battery can be reduced to improve the performance of the battery.
Brief description of the drawing
[20]
1 is a schematic diagram showing a cross-sectional structure of a secondary battery according to an embodiment of the present invention.
[21]
2 and 3 are partially enlarged views each showing a cross-sectional structure in a horizontal direction and a vertical direction of an electrode assembly according to an embodiment of the present invention.
[22]
4 and 5 are graphs showing results of comparative evaluation of voltage and temperature changes during charging and discharging of a secondary battery according to an embodiment of the present invention, respectively.
Modes for carrying out the invention
[23]
Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in the present specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventor must properly understand the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention based on the principle that it can be defined in
[24]
In addition, in the present invention, the meaning of "cylindrical" or "circular" includes not only a case of a physical cylinder or circular shape, but also a case that the overall shape is cylindrical or close to a circular shape. For example, when the cross-sectional shape of the battery is n-shaped, when n is 5 or more or 10 or more, it should be interpreted as being included in the circle category.
[25]
[26]
In the present invention, based on the horizontal cross-sectional structure, n unit cells (n is an integer greater than or equal to 5) are radially assembled about a central axis to form a battery, and each unit cell is, based on the horizontal cross-sectional structure, of the battery Provided is a secondary battery having a structure in which a cell thickness is reduced in a central axis direction from an outer end forming an outer circumferential surface. In the secondary battery according to the present invention, a plurality of unit cells are radially assembled to form a battery. The shape of the secondary battery, based on the horizontal cross-sectional structure, may have an outer circumferential surface of a circular shape or a shape close thereto, an n-shaped shape, or a sector shape.
[27]
The number n of unit cells assembled in the secondary battery is an integer of 5 or more, and specifically ranges from 5 to 10000, 5 to 100, 100 to 1000, 1000 to 10000, 500 to 5000, or 3000 to 10000. The number n of the unit cells can be variously designed according to the shape, structure, or required physical properties of the battery.
[28]
In one embodiment, in the secondary battery, a k-th unit cell (k is an integer between 1 and n-1) and a k+1-th unit cell are adjacent to each other and have a facing structure. Also, the first unit cell and the n-th unit cell (n is an integer between 5 and 10000) are also adjacent to each other and face each other. For example, in the secondary battery, a plurality of unit cells may be radially assembled to form a cylindrical structure. In this case, the outer peripheral surface of the cylindrical structure is determined by the number of unit cells, and may form a circle or an n-gonal shape based on the cross-section.
[29]
In one embodiment, the secondary battery may have a structure in which a hollow penetrating in a vertical direction is formed in the center of the secondary battery as a whole, and the external appearance has a thin cylindrical shape. Specifically, the secondary battery has a cylindrical structure in which a hollow is formed by radially gathering n unit cells (n is an integer greater than or equal to 5) about a central axis based on a horizontal cross-sectional structure. In addition, in the secondary battery, the ratio of the inner diameter to the outer diameter of the battery is in the range of 1:1.1 to 100. The diameter ratio of the inner diameter and the outer diameter of the secondary battery is calculated based on the average value of the inner diameter and the outer diameter, respectively. In a specific example, in the secondary battery, the diameter ratio of the inner diameter and the outer diameter of the battery is in the range of 1:1.1 to 100, in the range of 1:1.5 to 80, in the range of 1:2 to 50, in the range of 1:10 to 100, or in the range of 1:30 to 100. am.
[30]
In another embodiment, each unit cell forming the battery, based on the horizontal cross-sectional structure, the thickness of the inner end in the center direction forming the inner peripheral surface of the battery (D in ) and the outer end forming the outer peripheral surface of the battery The ratio (D out : D in ) of the thickness (D out ) is in the range of 1:1.5 to 10. In a specific example, the ratio (D out : D in ) is in the range of 1:1.1 to 100, in the range of 1:1.5 to 80, in the range of 1:2 to 50, in the range of 1:10 to 100, or in the range of 1:30 to 100.
[31]
The unit cell included in the secondary battery according to the present invention has a form in which the thickness decreases in one direction. This is a form differentiated from conventional prismatic batteries, pouch-type batteries, or cylindrical batteries. Existing secondary batteries have a difference in external shape, but the unit cells constituting each battery are manufactured to have a uniform overall thickness, but are merely stacked or wound differently. In one embodiment, in each unit cell forming the battery, any one or more electrodes of the positive electrode and the negative electrode, based on the horizontal cross-sectional structure, the distance between the electrode and the electrode in the center direction from the outer end forming the outer peripheral surface of the battery This is a decreasing structure.
[32]
In addition, by applying a structure in which the unit cell having a thickness decreasing in one direction and a unit cell having a uniform thickness are aggregated together, a secondary battery applicable to various types of devices can be manufactured. For example, in the case of a mobile smart watch, a rechargeable battery that can be stored inside the watch band may be applied, and the watch band may be formed in a form in which a straight section area and a curved section area are combined. In this case, by using a secondary battery having a structure in which unit cells having a uniform thickness are assembled in a straight section region of the watch band and unit cells having a thickness decreasing in one direction are assembled in a curved section region, a secondary battery of a desired shape can be easily manufactured can be manufactured.
[33]
In a specific embodiment, in each unit cell forming the battery, the positive electrode and the negative electrode each have a structure in which a mixture layer including an active material is applied on a metal current collector, and at least one electrode of the positive electrode and the negative electrode has a horizontal cross-sectional structure. As a reference, the thickness of the mixture layer applied on the metal current collector in the central axis direction from the outer end forming the outer circumferential surface of the battery is reduced. That is, in the present invention, by designing to increase or decrease the thickness of the mixture layer loaded on the current collector in one direction, thickness orientation can be imparted to the unit cell.
[34]
In another specific embodiment, in each unit cell forming the battery, the positive electrode and the negative electrode each have a structure in which a mixture layer including an active material is applied on a metal current collector, and at least one electrode of the positive electrode and the negative electrode has a horizontal cross-section Based on the structure, the density of the mixture layer applied on the metal current collector in the central axis direction from the outer end forming the outer circumferential surface of the battery increases. As described above, in the present invention, when the thickness of the mixture layer loaded on the current collector is designed to increase or decrease in one direction, capacity non-uniformity may occur depending on the position or direction of the unit cell. In the present invention, by designing to decrease or increase the density of the mixture layer loaded on the current collector in one direction, it is possible to compensate for the capacity non-uniformity according to the thickness orientation of the unit cell. For example, in a region where the thickness of the mixture layer laminated on the current collector is thin, the density of the mixture layer may be set high. The density orientation of the mixture layer can be realized by pressing or reducing pressure in one direction when the mixture layer is uniformly loaded on the current collector and pressurized using a roller.
[35]
In one embodiment, each unit cell constituting the secondary battery according to the present invention includes a positive electrode and a negative electrode, a first separator is interposed between the positive electrode and the negative electrode, and a second separator is disposed between the unit cell and the unit cell This is an intervening structure. In this case, each of the positive electrode and the negative electrode may have a structure in which a mixture layer including an active material is laminated on one surface of a current collector in a direction facing the first separator.
[36]
Specifically, in each unit cell forming the battery, the metal current collector forming at least one electrode of the positive electrode and the negative electrode has a porous structure in which a through-hole is formed. In the secondary battery according to the present invention, by applying a current collector having a through-hole in the thickness direction to the unit cell, it is possible to reduce the change in the concentration of the electrolyte or lithium ions in the battery, thereby improving the performance of the battery. In the present invention, the lithium ion concentration in the electrolyte can be uniformly maintained within a certain range by applying the current collector having the through-hole in the thickness direction to the unit cell. Through this, it is possible to increase the performance of the battery by reducing the overvoltage factors related to the electrolyte among the overvoltage factors of the battery.
[37]
In one embodiment, in each unit cell forming the battery, the metal current collector forming at least one electrode of the positive electrode and the negative electrode has a porous structure in which a thickness through-hole is formed, and the area fraction in which the through-hole is formed is 10 to 80%. Specifically, the area fraction in which the through-holes are formed is in the range of 10 to 80%, 10 to 70%, 10 to 50%, 20 to 90%, 30 to 90%, or 30 to 60%. By controlling the number to the area fraction per unit area of ​​the through-holes in the above range, it is possible to reduce the deformation rate of the current collector without significantly lowering the mechanical strength and to reduce the range of change in the electrolyte concentration or lithium ion concentration in the battery.
[38]
In a specific example, the through-holes have a structure in which 10 to 500 are formed per unit area of ​​10 cm x 10 cm. Specifically, the through-holes are 10 to 300, 10 to 200, 10 to 100, 10 to 70, 30 to 50, 50 to 500, 100 to 200, 50 to 300, 100 to 300 per unit area. 500, 30 to 200, or 10 to 200 structures are formed. For example, the metal current collector has a mesh shape.
[39]
In the present invention, the secondary battery is, for example, a lithium secondary battery. The lithium secondary battery may include, for example, the electrode assembly described above; a non-aqueous electrolyte for impregnating the electrode assembly; and a battery case containing the electrode assembly and the non-aqueous electrolyte.
[40]
The positive electrode has a structure in which a positive electrode mixture layer is laminated on one or both surfaces of a positive electrode current collector. The positive active material may be each independently a lithium-containing oxide, and may be the same or different. As the lithium-containing oxide, a lithium-containing transition metal oxide may be used. In one example, the positive electrode mixture layer includes a conductive material and a binder polymer in addition to the positive electrode active material, and, if necessary, may further include a positive electrode additive commonly used in the art.
[41]
The current collector used for the positive electrode is a metal with high conductivity, and any metal that can be easily adhered to the positive electrode active material slurry and has no reactivity in the voltage range of the secondary battery may be used. Specifically, non-limiting examples of the current collector for the positive electrode include a foil made of aluminum, nickel, or a combination thereof. Specifically, the current collector for the positive electrode is formed of the metal component described above and includes a metal plate having a through hole in the thickness direction, and an ion conductive porous reinforcing material filled in the through hole of the metal plate.
[42]
The anode may include a carbon material, lithium metal, silicon or tin as an anode mixture layer. When a carbon material is used as the negative electrode active material, both low crystalline carbon and high crystalline carbon may be used. Soft carbon and hard carbon are typical low-crystalline carbons, and high-crystalline carbons include natural graphite, Kish graphite, pyrolytic carbon, and liquid-crystal pitch-based carbon fiber. (mesophase pitch based carbon fiber), carbon microspheres (mesocarbon microbeads), liquid crystal pitches (Mesophase pitches), and high-temperature calcined carbon such as petroleum and coal-based cokes (petroleum orcoal tar pitch derived cokes) are representative.
[43]
Non-limiting examples of the current collector used for the negative electrode include a foil made of copper, gold, nickel, or a copper alloy, or a combination thereof. In addition, the current collector may be used by stacking substrates made of the above materials. Specifically, the current collector for the negative electrode is formed of the metal component described above and includes a metal plate having a through hole in the thickness direction, and an ion conductive porous reinforcing material filled in the through hole of the metal plate.
[44]
In addition, the negative electrode may include a conductive material and a binder commonly used in the art.
[45]
As the first and second separators, any porous substrate used in a lithium secondary battery may be used, for example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto. Examples of the polyolefin-based porous membrane include polyethylene, such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, and polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, respectively, individually or in a mixture thereof. One membrane is mentioned.
[46]
According to an embodiment of the present invention, as the electrolyte, a non-aqueous electrolyte including a non-aqueous electrolyte may be used. Examples of the non-aqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma-butylo. Lactone, 1,2-dimethoxyethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile , nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate may be used. However, it is not particularly limited thereto, and a plurality of electrolyte components typically used in the field of lithium secondary batteries may be added or subtracted within an appropriate range.
[47]
In addition, the present invention provides a device including the secondary battery described above. In a specific example, the device is a mobile electronic device, a wearable device, a power tool that moves by being powered by a battery-based motor, a drone, an electric vehicle, EV), Hybrid Electric Vehicle (HEV), Plug-in Hybrid Electric Vehicle (PHEV), E-bike, Electric Scooter (E-scooter), Electric Golf Cart (electric golf cart) or power storage system.
[48]
For example, when the secondary battery of the present invention is included in a smart watch, which is a mobile electronic device, compared to the conventional pouch-type battery in which several thin electrodes need to be stacked on a flat surface, the secondary battery of the present invention is hollow by itself. Since it can be manufactured in a molded structure, it is suitable for manufacturing in response to the band shape of a watch. In addition, since it is possible to achieve high capacity compared to its size, it can be applied to ultra-small devices such as wireless earphones. On the other hand, since the size can be easily adjusted according to the number of unit cells assembled, it can be applied to a large cylindrical battery for electric vehicles.
[49]
[50]
Hereinafter, the present invention will be described in more detail with reference to examples and drawings. However, the configurations described in the drawings and embodiments described in this specification are only one embodiment of the present invention and do not represent all of the technical spirit of the present invention, so at the time of the present application, various equivalents and It should be understood that there may be variations.
[51]
[52]
Example 1
[53]
100 parts by weight of NCM (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) as a cathode active material, 1.5 parts by weight of carbon black (FX35, Denka) as a conductive material, and 2.3 parts by weight of polyvinylidene fluoride (KF9700, Kureha) as a binder polymer as a solvent It was added to N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture layer slurry. The positive electrode mixture layer slurry was coated on one surface of an aluminum current collector having through-holes in the thickness direction in a loading amount of 640 mg/25 cm 2 , and then vacuum dried to obtain a positive electrode. In the aluminum current collector, the through-holes are formed in an area fraction of about 40%, and have a structure in which about 50 are formed per unit area of ​​10 cm x 10 cm. In addition, the positive electrode mixture layer was pressed to be sequentially reduced to a thickness of about 40% in one direction.
[54]
The negative electrode is 100 parts by weight of artificial graphite (GT, Zichen (China)) as an anode active material, 1.1 parts by weight of carbon black (Super-P) as a conductive material, 2.2 parts by weight of styrene-butadiene rubber, and 0.7 parts by weight of carboxymethyl cellulose as a solvent. was added to to prepare a negative active material slurry, and then coated, dried and compressed on one surface of a copper current collector having a through-hole in the thickness direction. The copper current collector has a structure in which the through-holes are formed at an area fraction of about 40% and about 50 per unit area of ​​10 cm x 10 cm. In addition, the positive electrode mixture layer was pressed to be sequentially reduced to a thickness of about 40% in one direction.
[55]
On the other hand, polypropylene was uniaxially stretched using a dry method to prepare a separator having a microporous structure having a melting point of 165° C. and a width of 200 mm on one side. The first separator was interposed between the positive electrode and the negative electrode, and unit cells having a structure in which the second separator was positioned on the outside of the positive electrode and the negative electrode were repeatedly assembled to prepare an electrode assembly. The electrode assembly has a structure in which 50 unit cells are radially assembled about a central axis based on a horizontal cross-sectional structure.
[56]
After the electrode assembly was embedded in a hollow cylindrical battery case, 1M LiPF 6 carbonate-based electrolyte solution was injected to complete the battery.
[57]
1 shows a cross-sectional structure of the manufactured secondary battery. Also, FIG. 2 is a partially enlarged view of a horizontal cross-sectional structure of an electrode assembly included in a secondary battery, and FIG. 3 is a partially enlarged view of a vertical cross-sectional structure of an electrode assembly included in a secondary battery.
[58]
Referring to FIG. 1 , a secondary battery 100 according to an embodiment of the present invention has a structure in which 50 unit cells are radially assembled about a central axis based on a horizontal cross-sectional structure. In addition, each unit cell has a structure in which the cell thickness decreases in the central axis direction from the outer end forming the outer circumferential surface of the battery based on the horizontal cross-sectional structure.
[59]
Referring to FIG. 2 , the unit cells constituting the secondary battery include a negative electrode current collector 110 , a negative electrode mixture layer 111 , a first separator 131 , a positive electrode mixture layer 121 , a positive electrode current collector 120 and a second It has a structure in which two separators 132 are sequentially stacked. In addition, the negative electrode current collector 110 and the positive electrode current collector 120 have a structure in which a through-hole is formed in a thickness direction. The negative electrode mixture layer 111 and the positive electrode mixture layer 121 each have thicknesses of the mixture layers 111 and 121 applied on the metal current collectors 110 and 120 in the central axis direction from the outer end forming the outer circumferential surface of the battery. It is a structure in which the density decreases while the density increases.
[60]
Referring to FIG. 3 , the unit cells constituting the secondary battery include a negative electrode current collector 110 , a negative electrode mixture layer 111 , a first separator 131 , a positive electrode mixture layer 121 , a positive electrode current collector 120 and a second The structure in which the two separators 132 are sequentially stacked is continuously repeated. In addition, the negative electrode current collector 110 and the positive electrode current collector 120 have a structure in which a through-hole is formed in a thickness direction. A plurality of through-holes are formed in the negative electrode current collector 110 and the positive electrode current collector 120 , and these through-holes promote the smooth flow of lithium ions.
[61]
[62]
Example 2
[63]
A secondary battery was manufactured in the same manner as in Example 1, except that the aluminum and copper current collectors each had a mesh structure.
[64]
[65]
Comparative Example 1
[66]
A positive electrode and a negative electrode were manufactured in the same manner as in Example 1, except that a through-thickness hole was not formed in the positive and negative current collectors, respectively, and a thickness gradient of the positive and negative electrode mixture layers was not formed.
[67]
On the other hand, polypropylene was uniaxially stretched using a dry method to prepare a separator having a microporous structure having a melting point of 165° C. and a width of 200 mm on one side. The first separator was interposed between the positive electrode and the negative electrode, and unit cells having a structure in which the second separator was positioned on the outside of the positive electrode and the negative electrode were repeatedly assembled to prepare an electrode assembly. The electrode assembly has a structure in which 50 unit cells are sequentially aggregated.
[68]
After the electrode assembly was embedded in a hollow prismatic battery case, 1M LiPF 6 carbonate-based electrolyte solution was injected to complete the battery.
[69]
[70]
Experimental Example 1: Evaluation of secondary battery properties
[71]
Physical properties of each of the secondary batteries prepared in Example 1 and Comparative Example 1 were evaluated. Specifically, charging and discharging were performed for each secondary battery, and voltage and temperature changes were measured during charging and discharging, respectively. Charging and discharging of the secondary battery was performed at 20°C and 1C conditions.
[72]
The result of evaluating the voltage change during charging and discharging of the secondary battery is shown in FIG. 4 , and the result of evaluating the temperature change during charging and discharging of the secondary battery is shown in FIG. 5 .
[73]
First, referring to FIG. 4 , it can be seen that the secondary battery according to Example 1 has a high discharge voltage and a low charge voltage, as compared to Comparative Example 1. Through this, it can be seen that the secondary battery according to Example 1 provides higher power when applied to a product, and requires lower charging power when charging.
[74]
Referring to FIG. 5 , it can be seen that the secondary battery according to Example 1 has a lower temperature during charging and discharging and a significantly smaller change in the secondary battery compared to Comparative Example 1. Accordingly, the secondary battery according to Example 1 has a lower required cooling performance, and a more compact design is possible.
[75]
Therefore, it can be applied to various mobile devices and wearable devices, and in particular, small devices such as wireless earphones and smart watches, in particular, require long-term use while being limited by the weight and volume of secondary batteries. It is particularly suitable for devices that
[76]
In addition, due to its excellent output, it can be used for power tools that move with power by a battery-based motor, and can be used in drones, electric vehicles (EVs), hybrid electric vehicles (HEVs), Electric vehicles including Plug-in Hybrid Electric Vehicles (PHEVs), electric bicycles (E-bikes), electric two-wheeled vehicles including electric scooters (E-scooters), and electric golf carts ), etc., are suitable not only for transportation means using high-output electricity, but also for electricity storage systems.
[77]

[78]
100: secondary battery
[79]
110: negative electrode current collector
[80]
111: negative electrode mixture layer
[81]
120: positive electrode current collector
[82]
121: positive electrode mixture layer
[83]
131: first separator
[84]
132: second separator

WE CLAIMS

Based on the horizontal cross-sectional structure, n unit cells (n is an integer greater than or equal to 5) are radially assembled about the central axis to form a battery, and each unit cell forms the outer peripheral surface of the battery based on the horizontal cross-sectional structure A secondary battery having a structure in which the cell thickness decreases from the outer end to the central axis direction.
[Claim 2]
The method of claim 1, wherein the k-th (k is an integer between 1 and n-1) unit cell and the k+1-th unit cell are adjacent to each other and face each other, and the first unit cell and the n-th unit cell (n is 5 to 10000) A secondary battery in which the unit cells are also adjacent to each other and face each other.
[Claim 3]
The battery according to claim 1, wherein the secondary battery has a cylindrical structure in which n unit cells (n is an integer equal to or greater than 5) are radially assembled about a central axis based on a horizontal cross-sectional structure to form a hollow, and the inner and outer diameters of the battery The diameter ratio of the secondary battery is in the range of 1:1.1 to 100.
[Claim 4]
According to claim 1, wherein each unit cell forming the battery, based on the horizontal cross-sectional structure, the thickness of the inner end of the center direction forming the inner peripheral surface of the battery (D in ) and the thickness of the outer end forming the outer peripheral surface of the battery (D out ) The ratio (D out : D in ) is a secondary battery, characterized in that 1:1.1 ~ 100 range.
[Claim 5]
The distance between the electrode and the electrode according to claim 1, wherein in each unit cell forming the battery, at least one electrode of a positive electrode and a negative electrode has a horizontal cross-sectional structure from an outer end forming an outer circumferential surface of the battery to the center direction A secondary battery with this decreasing structure.
[Claim 6]
The method of claim 1, wherein in each unit cell forming the battery, the positive electrode and the negative electrode each have a structure in which a mixture layer including an active material is applied on a metal current collector, and at least one electrode of the positive electrode and the negative electrode has a horizontal cross-sectional structure A secondary battery having a structure in which the thickness of the mixture layer applied on the metal current collector is reduced in the central axis direction from the outer end forming the outer peripheral surface of the battery.
[Claim 7]
The method of claim 6, wherein in each unit cell forming the battery, the positive electrode and the negative electrode each have a structure in which a mixture layer including an active material is applied on a metal current collector, and at least one electrode of the positive electrode and the negative electrode has a horizontal cross-sectional structure A secondary battery having a structure in which the density of the mixture layer applied on the metal current collector increases in the central axis direction from the outer end forming the outer circumferential surface of the battery.
[Claim 8]
The secondary battery according to claim 1, wherein each unit cell includes a positive electrode and a negative electrode, a first separator is interposed between the positive electrode and the negative electrode, and a second separator is interposed between the unit cell and the unit cell.
[Claim 9]
The secondary battery according to claim 8, wherein each of the positive and negative electrodes has a structure in which a mixture layer including an active material is laminated on one surface of a current collector in a direction facing the first separator.
[Claim 10]
The secondary battery according to claim 1, wherein in each unit cell forming the battery, the metal current collector forming at least one electrode of the positive electrode and the negative electrode has a porous structure in which a through-thick hole is formed.
[Claim 11]
The method according to claim 10, wherein in each unit cell forming the battery, the metal current collector forming at least one electrode of the positive electrode and the negative electrode has a porous structure in which a thickness through-hole is formed, and the area fraction in which the through-hole is formed is 10 to 80% of the secondary battery.
[Claim 12]
The secondary battery according to claim 10, wherein the porous metal current collector has a mesh shape.
[Claim 13]
A device comprising the secondary battery according to claim 1 .
[Claim 14]
14. The method of claim 13, wherein the device is a mobile electronic device, a wearable device, a power tool that is powered by a battery-based motor, a drone, and an electric vehicle (Electric). Vehicle, EV), Hybrid Electric Vehicle (HEV), Plug-in Hybrid Electric Vehicle (PHEV), E-bike, Electric Scooter (E-scooter), Electric A device, characterized in that the golf cart (electric golf cart) or system for power storage.