A cylindrical battery

Abstract

The present invention provides a cylindrical battery, comprising a battery cell, the battery cell comprising a positive electrode sheet and a negative electrode sheet, the positive electrode sheet surface resistance is R1, the negative electrode sheet surface resistance is R2, wherein R1 and R2 satisfy the following relationship: 15≤R1 / R2≤1000; the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, the positive electrode active material is selected from at least one of a lithium iron phosphate positive electrode material, a nickel-cobalt-manganese ternary positive electrode material, a lithium iron manganese phosphate positive electrode material, a lithium-rich manganese-based positive electrode material, and a nickel-manganese oxide positive electrode material; the negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises graphite. The cylindrical battery provided by the present invention can effectively control the heat release of the cylindrical battery, reduce the heat release of the cylindrical battery, and improve the cycle performance and safety performance of the cylindrical battery.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium batteries, and in particular relates to a cylindrical battery. Background Art

[0002] Cylindrical batteries are the earliest mature industrialized lithium battery products. After more than 20 years of development, the production process of cylindrical batteries is mature, the production efficiency is high, and the cost is relatively low, so the cost of PACK is also relatively low. The lithium battery yield rate is higher than that of square lithium batteries and soft-pack lithium batteries, and its consistency and safety are also relatively good. Therefore, cylindrical batteries still account for a relatively large proportion in the current market. Further optimization of the cycle performance of cylindrical batteries is also a research focus in the current lithium battery industry.

[0003] The cylindrical shape of cylindrical batteries will result in low space utilization, poor radial heat conductivity, and uneven temperature distribution. These problems lead to poor heat dissipation performance of cylindrical batteries, especially the middle area of ​​the winding core is squeezed by the pole pieces in the outer and inner layers, making it more difficult to dissipate heat, resulting in difficulty in heat dissipation of cylindrical batteries. Long-term failure to dissipate heat in time will deteriorate battery stability and cycle performance, and degrade battery safety performance and service life. Summary of the invention

[0004] In order to solve the problems and shortcomings in the prior art, the present invention provides a cylindrical battery, which can effectively control the heat release of the cylindrical battery, reduce the heat release of the cylindrical battery, and improve the cycle performance and safety performance of the cylindrical battery.

[0005] The present invention provides a cylindrical battery, comprising a battery cell, wherein the battery cell comprises a positive electrode sheet and a negative electrode sheet, wherein the surface resistance of the positive electrode sheet is R1, and the surface resistance of the negative electrode sheet is R2, wherein R1 and R2 satisfy the following relationship: 15≤R1 / R2≤1000; the positive electrode sheet comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material is selected from at least one of a lithium iron phosphate positive electrode material and a nickel-cobalt-manganese ternary positive electrode material; the negative electrode sheet comprises a negative electrode active material layer, wherein the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises graphite.

[0006] The cylindrical battery is cylindrical in shape, with low space utilization and poor radial thermal conductivity. In particular, the middle area of ​​the winding core is squeezed by the pole pieces in the outer and inner areas, making it more difficult to dissipate heat. Therefore, cylindrical batteries have problems such as large temperature distribution differences and difficulty in heat dissipation. The difficulty in heat dissipation will affect the cycle performance and safety performance of the battery and shorten the service life of the battery. Specifically, on the one hand, because the positive electrode active material is usually a highly active material such as lithium iron phosphate positive electrode material, nickel-cobalt-manganese ternary positive electrode material, lithium iron manganese phosphate positive electrode material, manganese-rich lithium-based positive electrode material, nickel-manganese oxide lithium positive electrode material, etc., if the temperature inside the cylindrical battery rises too quickly and the internal temperature of the battery is too high, it will easily cause the activity of the positive electrode active material to fail, deteriorate the performance of the positive electrode active material, and lead to a decrease in the battery cycle performance. On the other hand, if the battery temperature inside the cylindrical battery is too high, it is easy to cause thermal runaway, increase safety risks such as battery fire or even explosion, and reduce the safety performance of the battery.

[0007] At present, in order to effectively dissipate heat for cylindrical batteries and improve their safety performance and cycle life, the following technical means are usually used: controlling the charging and discharging process of cylindrical batteries, optimizing battery structure design, installing battery monitoring systems, etc. However, these means usually improve the heat dissipation performance and stability of batteries by controlling the external conditions during battery charging and discharging. In this way, the batteries will still release a lot of heat, posing a greater safety hazard, and the high temperature of long-term charge and discharge cycles will still cause the battery cycle stability to decline.

[0008] The present invention can achieve the following effects by controlling the ratio of the surface resistance of the positive electrode sheet to the surface resistance of the negative electrode sheet in the cylindrical battery within a certain range, that is, directly controlling the resistance parameters of the positive and negative electrode sheets inside the cylindrical battery: first, it can ensure that the surface resistance of the positive electrode sheet will not be too large, avoiding excessive temperature rise of the positive electrode sheet causing the activity failure of the positive electrode active material; second, it can ensure that the surface resistance of the negative electrode sheet has a certain increase, because the negative electrode active material generally includes graphite, and the activity of graphite is relatively low. Properly increasing the surface resistance of the negative electrode sheet can increase the temperature of the negative electrode sheet, thereby effectively improving the activity of the negative electrode active material and improving the energy density and cycle life of the cylindrical battery. It is worth noting that in lithium batteries, the surface resistance of the positive electrode sheet is usually greater than the surface resistance of the negative electrode sheet. Therefore, the present invention further optimizes the ratio of the surface resistance of the positive electrode sheet to the surface resistance of the negative electrode sheet under this premise. DETAILED DESCRIPTION

[0009] The present invention provides a cylindrical battery, comprising a battery cell, wherein the battery cell comprises a positive electrode sheet and a negative electrode sheet, wherein the surface resistance of the positive electrode sheet is R1, and the surface resistance of the negative electrode sheet is R2, wherein R1 and R2 satisfy the following relationship: 15≤R1 / R2≤1000; the positive electrode sheet comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material is selected from at least one of a lithium iron phosphate positive electrode material and a nickel-cobalt-manganese ternary positive electrode material; the negative electrode sheet comprises a negative electrode active material layer, wherein the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises graphite.

[0010] The cylindrical battery is cylindrical in shape, with low space utilization and poor radial thermal conductivity. In particular, the middle area of ​​the winding core is squeezed by the pole pieces in the outer and inner areas, making it more difficult to dissipate heat. Therefore, cylindrical batteries have problems such as large temperature distribution differences and difficulty in heat dissipation. The difficulty in heat dissipation will affect the cycle performance and safety performance of the battery and shorten the service life of the battery. Specifically, on the one hand, because the positive electrode active material is usually a highly active material such as lithium iron phosphate positive electrode material, nickel-cobalt-manganese ternary positive electrode material, lithium iron manganese phosphate positive electrode material, lithium-rich manganese-based positive electrode material, and nickel-manganese oxide lithium positive electrode material, if the temperature inside the cylindrical battery rises too quickly and the temperature inside the battery is too high, it will easily cause the activity of the positive electrode active material to fail, deteriorate the performance of the positive electrode active material, and lead to a decrease in the battery cycle performance. On the other hand, if the battery temperature inside the cylindrical battery is too high, it is easy to cause thermal runaway, increase safety risks such as battery fire or even explosion, and reduce the safety performance of the battery.

[0011] At present, in order to effectively dissipate heat for cylindrical batteries and improve their safety performance and cycle life, the following technical means are usually used: controlling the charging and discharging process of cylindrical batteries, optimizing battery structure design, installing battery monitoring systems, etc. However, these means usually improve the heat dissipation performance and stability of batteries by controlling the external conditions during battery charging and discharging. In this way, the batteries will still release a lot of heat, posing a greater safety hazard, and the high temperature of long-term charge and discharge cycles will still cause the battery cycle stability to decline.

[0012] The present invention can achieve the following effects by controlling the ratio of the surface resistance of the positive electrode sheet to the surface resistance of the negative electrode sheet in the cylindrical battery within a certain range, that is, directly controlling the resistance parameters of the positive and negative electrode sheets inside the cylindrical battery: first, it can ensure that the surface resistance of the positive electrode sheet will not be too large, avoiding excessive temperature rise of the positive electrode sheet causing the activity failure of the positive electrode active material; second, it can ensure that the surface resistance of the negative electrode sheet has a certain increase, because the negative electrode active material generally includes graphite, and the activity of graphite is relatively low. Properly increasing the surface resistance of the negative electrode sheet can increase the temperature of the negative electrode sheet, thereby effectively improving the activity of the negative electrode active material and improving the energy density and cycle life of the cylindrical battery. It is worth noting that in lithium batteries, the surface resistance of the positive electrode sheet is usually greater than the surface resistance of the negative electrode sheet. Therefore, the present invention further optimizes the ratio of the surface resistance of the positive electrode sheet to the surface resistance of the negative electrode sheet under this premise.

[0013] Preferably, R1 satisfies: 0.5Ω≤R1≤3.0Ω. By ensuring that the positive electrode sheet surface resistance is within this numerical range, the positive electrode sheet can be controlled to have a smaller surface resistance, thereby preventing the positive electrode sheet from heating up too quickly during the cycle and ensuring the activity of the positive electrode active material. Because if the positive electrode sheet surface resistance is too high and the positive electrode sheet temperature is too high, it will easily cause the positive electrode active material to fail, thereby causing a decrease in the battery cycle stability. In addition, if the positive electrode sheet surface resistance is too large and the positive electrode sheet releases too much heat, it will also cause a decrease in the safety performance of the battery, which is likely to cause safety hazards.

[0014] Preferably, R2 satisfies: 3mΩ≤R2≤35mΩ. Controlling the negative electrode sheet surface resistance within this range is conducive to improving the performance of the negative electrode active material and promoting the negative electrode active material to exhibit better cycle performance during the charge and discharge process. At the same time, when the surface resistance of the negative electrode sheet is within the above range, it will not release a lot of heat, which can effectively reduce the occurrence of negative electrode side reactions, further optimize the negative electrode stability and battery cycle performance while ensuring the safety performance of the battery.

[0015] Preferably, the positive electrode active material is a nickel-cobalt-manganese ternary positive electrode material, in which the molar number of nickel element accounts for no less than 80% of the total molar number of nickel element, cobalt element and manganese element. When the positive electrode active material is a high-nickel nickel-cobalt-manganese ternary positive electrode material, it is more conducive to improving the activity and stability of the positive electrode active material, and the battery's charge and discharge cycle performance is better. Because generally speaking, in order to increase energy density, high-nickel ternary materials are preferred, and when the nickel content increases, the heat generation will increase, making the high-nickel ternary materials more easily deactivated. Therefore, for high-nickel materials, reasonable control of their surface resistance is more conducive to improving the stability of the positive electrode active material and optimizing the battery cycle performance.

[0016] Preferably. The positive electrode active material layer also includes a first conductive agent, the mass of the first conductive agent accounts for 0.5-2% of the mass of the positive electrode active material layer; the first conductive agent includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, super P, acetylene black, and graphene. Controlling the content of the first conductive agent in the positive electrode active material layer is conducive to regulating the surface resistance of the positive electrode sheet, so that the positive electrode sheet has a suitable surface resistance while not affecting the capacity of the positive electrode active material, thereby optimizing the battery cycle performance.

[0017] Preferably, the negative electrode active material also includes silicon-based materials, and the mass ratio of graphite to silicon-based materials is greater than 0 and less than or equal to 35%. The higher the silicon content, the greater the surface resistance of the negative electrode sheet. Controlling the mass ratio of graphite to silicon-based materials is conducive to regulating the surface resistance of the negative electrode sheet, while avoiding excessive silicon-based materials causing excessive volume expansion of the negative electrode active material layer, deteriorating the stability of the negative electrode material and the cycle performance of the battery.

[0018] Preferably, the negative electrode active material layer further includes a second conductive agent, the mass of the second conductive agent accounts for 0.5-3% of the mass of the negative electrode active material layer; the second conductive agent includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, super P, acetylene black, and graphene. Accordingly, further controlling the content of the second conductive agent in the negative electrode active material layer is conducive to regulating the surface resistance of the negative electrode sheet, so that the negative electrode sheet has a suitable surface resistance without affecting the performance of the negative electrode active material, thereby optimizing the battery cycle performance.

[0019] Preferably, after the battery cell is unfolded, the pole piece includes a non-lug area and a lug area; the lug area is provided with a plurality of lugs, and the pole piece includes a positive pole piece and a negative pole piece. The cylindrical battery is formed by winding the positive pole piece, the diaphragm, and the negative pole piece at the same time. Here, the pole piece includes a non-lug area and a lug area, which means that before the pole piece is wound, a lug will be formed on the pole piece in advance. The pole piece is provided with a winding start end and a winding end. The area from the winding start end of the pole piece to the first lug on the pole piece is the non-lug area, and the remaining area with lugs is the lug area. The lug area is provided with a plurality of lugs, and the plurality of lugs means that the number of lugs is greater than or equal to 2. Here, the lug area is provided with a plurality of lugs, which can refer to a certain distance between adjacent lugs during die cutting, that is, there is a gap between adjacent lugs in the lug area; it can also refer to cutting the lug area into sections to form a plurality of lugs, that is, the lugs are disconnected from each other.

[0020] After the pole piece is wound into a battery cell, a hollow winding core hole will be formed. The pole piece is provided with a non-ear area in order to avoid the pole ear being provided near the winding core hole. Because in cylindrical batteries, the pole ear usually needs to be folded and welded to the battery collector plate. If the pole ear is also provided near the winding core hole, the pole ear will block the winding core hole after folding. Therefore, in order to avoid the pole ear blocking the winding core hole, the pole piece is not provided with a pole ear near the winding core hole to ensure that the pole ear will not block the winding core hole after folding, so as to ensure the normal use of the cylindrical battery.

[0021] Preferably, the ratio of the length of the area without tabs to the length of the pole piece is 0.05 to 0.6; the length of the pole piece is 450 to 2000 mm.

[0022] Preferably, the tabs include a positive tab and a negative tab, and the positive tab and the negative tab are respectively arranged on the same side of the battery cell.

[0023] Preferably, the diameter of the cylindrical battery is ≥40 mm.

[0024] Preferably, the surface density of the positive electrode sheet is 220 to 800 g / m 2 , thickness is 60~220μm; surface density of negative electrode sheet is 150~250g / m 2 , thickness is 90~170μm.

[0025] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only embodiments of a part of the present invention, rather than all embodiments.

[0026] Example 1

[0027] (1) Preparation of positive electrode

[0028] The prepared 9-series Li[Ni x Co y Mn z ]O2 (wherein x≥0.9, x+y+z=1) positive electrode active material and conductive agent MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube), binder PVDF (polytetrafluoroethylene) are mixed in a mass ratio of 98.2:0.65:0.05:1.1, and then solvent NMP (N-methylpyrrolidone) is added thereto, and stirred under the action of a vacuum stirrer until the system is uniform to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the two surfaces of the positive electrode current collector aluminum foil, dried at room temperature and then transferred to an oven for further drying, and then cold pressed and cut to obtain a positive electrode sheet; and the surface density of the positive electrode sheet in this embodiment is controlled to be 364g / cm 2 , thickness is 115μm.

[0029] (2) Preparation of negative electrode sheet

[0030] The negative electrode active material graphite, silicon-based material (SiC), conductive agent SWCNT (single-walled carbon nanotube), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), binder SBR (styrene-butadiene rubber) are mixed in a mass ratio of 92.4:4:0.05:0.95:1:1.6, and then deionized water is added thereto as a solvent, and the mixture is stirred under the action of a vacuum stirrer until the system is uniform to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on both surfaces of the negative electrode current collector copper foil, dried, and then rolled and cut to obtain a negative electrode sheet; and the surface density of the negative electrode sheet in this embodiment is controlled to be 185 g / cm 2 , thickness is 122μm.

[0031] (3) Preparation of electrolyte

[0032] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0033] (4) Preparation of isolation membrane

[0034] A polyethylene film is selected as the separating film.

[0035] (5) Preparation of lithium-ion batteries

[0036] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then they are wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0037] In addition, in this embodiment, after the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, when the tabs are die-cut, the length of the electrode sheet in the tab area is controlled so that the length of the electrode sheet in the tab-free area accounts for 0.05 of the length of the electrode sheet.

[0038] Example 2

[0039] The difference between this embodiment and embodiment 1 is that, in the process of (1) preparing the positive electrode sheet, the mass ratio of 9-series LiNiCoMnO2 positive electrode active material, MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube), and binder PVDF (polytetrafluoroethylene) is 97.8:1:0.1:1.1; in the process of (2) preparing the negative electrode sheet, the conductive agent SWCNT (single-walled carbon nanotube) is not added, and the mass ratio of negative electrode active material graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.6:4:0:0.8:1:1.6; in the preparation of (5) lithium-ion batteries, after the positive electrode sheet, isolation membrane, and negative electrode sheet are stacked in order, when the tabs are die-cut, the length of the tab area is controlled so that the length of the tab area is 0.1 of the length of the tab; the rest is consistent with embodiment 1.

[0040] Example 3

[0041] The difference between this embodiment and embodiment 1 is that in the process of (1) preparing the positive electrode sheet, the surface density of the positive electrode sheet is adjusted to 450 g / cm 2 In the process of preparing the negative electrode sheet (2), the mass ratio of the negative electrode active material graphite, silicon-based material (SiC), conductive agent SWCNT (single-walled carbon nanotube), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.6:4:0:0.8:1:1.6, and the surface density of the negative electrode sheet is adjusted to 228 g / cm 2 ; In the preparation of (5) lithium-ion batteries, after the positive electrode sheet, isolation membrane, and negative electrode sheet are stacked in order, when the pole ears are die-cut, the length of the pole sheet in the area of ​​the pole ears is controlled so that the length of the pole sheet in the area without the pole ears accounts for 0.1 of the length of the pole sheet; the rest is consistent with Example 1.

[0042] Example 4

[0043] The difference between this embodiment and embodiment 1 is that, in the process of (1) preparing the positive electrode sheet, the mass ratio of 9-series LiNiCoMnO2 positive electrode active material, conductive agent MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube), and binder PVDF (polytetrafluoroethylene) is 98.1:0.65:0.15:1.1; in the process of (2) preparing the negative electrode sheet, the mass ratio of negative electrode active material graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.15:4:0.05:1.2:1:1.6; in the preparation of (5) lithium-ion batteries, after the positive electrode sheet, isolation membrane, and negative electrode sheet are stacked in order, when the tabs are die-cut, the length of the tab area is controlled so that the length of the tab area is 0.1 of the tab length; the rest is consistent with embodiment 1.

[0044] Example 5

[0045] The difference between this embodiment and embodiment 1 is that, in the process of (1) preparing the positive electrode sheet, the mass ratio of 9 series LiNiCoMnO2 positive electrode active material, conductive agent MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube), and binder PVDF (polytetrafluoroethylene) is 97.85:1:0.05:1.1; in the process of (2) preparing the negative electrode sheet, the conductive agent SWCNT (single-walled carbon nanotube) is not added, and the mass ratio of negative electrode active material graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.9:4:0.5:1:1.6; in the preparation of (5) lithium-ion battery, after the positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, when the tab is die-cut, the length of the tab area is controlled so that the length of the tab area is 0.1 of the tab length; the rest is consistent with embodiment 1.

[0046] Example 6

[0047] The difference between this embodiment and embodiment 1 is that in the process of (1) preparing the positive electrode sheet, the surface density of the positive electrode sheet is adjusted to 460 g / cm 2 In the process of preparing the negative electrode sheet (2), no conductive agent SWCNT (single-walled carbon nanotube) is added, and the mass ratio of the negative electrode active material graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.9:4:0.5:1:1.6, and the surface density of the negative and positive electrode sheets is adjusted to 234 g / cm 2; In the preparation of (5) lithium-ion batteries, after the positive electrode sheet, isolation membrane, and negative electrode sheet are stacked in order, when the pole ears are die-cut, the length of the pole sheet in the area of ​​the pole ears is controlled so that the length of the pole sheet in the area without the pole ears accounts for 0.1 of the length of the pole sheet; the rest is consistent with Example 1.

[0048] Example 7

[0049] The difference between this embodiment and embodiment 1 is that in the process of (1) preparing the positive electrode sheet, the 9-series LiNiCoMnO2 positive electrode active material is replaced with lithium iron phosphate positive electrode active material (LiFePO); in the preparation of (5) the lithium-ion battery, after the positive electrode sheet, the isolation membrane and the negative electrode sheet are stacked in order, when the tabs are die-cut, the length of the tab area is controlled so that the length of the tab area is 0.6 of the length of the tab; the rest is the same as embodiment 1.

[0050] Example 8

[0051] The difference between this embodiment and embodiment 1 is that in the process of (1) preparing the positive electrode sheet, the 9-series LiNiCoMnO2 positive electrode active material is replaced with lithium iron manganese phosphate positive electrode active material; the rest is consistent with embodiment 1.

[0052] Example 9

[0053] The difference between this embodiment and embodiment 1 is that in the process of (1) preparing the positive electrode sheet, the 9-series LiNiCoMnO2 positive electrode active material is replaced with a manganese-rich lithium-based positive electrode active material (LiMnO·LiMO); the rest is the same as embodiment 1.

[0054] Example 10

[0055] The difference between this embodiment and embodiment 1 is that in the process of (1) preparing the positive electrode sheet, the 9-series LiNiCoMnO2 positive electrode active material is replaced with a lithium nickel manganese oxide positive electrode active material (LiNi 0.5 Mn 1.5 O4); the rest is consistent with Example 1.

[0056] Embodiment 11

[0057] The difference between this embodiment and embodiment 1 is that, in the process of (1) preparing the positive electrode sheet, the mass ratio of 9 series LiNiCoMnO2 positive electrode active material, conductive agent MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube), and binder PVDF (polytetrafluoroethylene) is 98.1:0.7:0.05:1.1; in the process of (2) preparing the negative electrode sheet, the mass ratio of negative electrode active material graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.9:4:0.2:1.2:1:1.6; in the preparation of (5) lithium-ion batteries, after the positive electrode sheet, isolation membrane, and negative electrode sheet are stacked in order, when the tabs are die-cut, the length of the tab area is controlled so that the length of the tab area is 0.2 of the length of the tab; the rest is consistent with embodiment 1.

[0058] Example 12

[0059] The difference between this embodiment and embodiment 1 is that, in the process of (1) preparing the positive electrode sheet, the mass ratio of 9 series LiNiCoMnO2 positive electrode active material, conductive agent MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube), and binder PVDF (polytetrafluoroethylene) is 97.25:1:15.05:1.1; in the process of (2) preparing the negative electrode sheet, the conductive agent SWCNT (single-walled carbon nanotube) is not added, and the mass ratio of negative electrode active material graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 97.85:0.9:0.05:1.1; in the preparation of (5) lithium-ion batteries, after the positive electrode sheet, isolation membrane, and negative electrode sheet are stacked in order, when the tabs are die-cut, the length of the tab area is controlled so that the length of the tab area is 0.2 of the tab length; the rest is consistent with embodiment 1.

[0060] Embodiment 13

[0061] The difference between this embodiment and embodiment 1 is that, in the process of (1) preparing the positive electrode sheet, the mass ratio of 9 series LiNiCoMnO2 positive electrode active material, conductive agent MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube), and binder PVDF (polytetrafluoroethylene) is 97.85:0.9:0.05:1.1; in the process of (2) preparing the negative electrode sheet, the mass ratio of negative electrode active material graphite, silicon-based material (SiC), conductive agent SWCNT (single-walled carbon nanotube), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.1:4:0.3:1.5:1:1.6; in the preparation of (5) lithium-ion batteries, after the positive electrode sheet, isolation membrane, and negative electrode sheet are stacked in order, when the tabs are die-cut, the length of the tab area is controlled so that the length of the tab-free area accounts for 0.2 of the length of the tab; the rest is consistent with embodiment 1.

[0062] Embodiment 14

[0063] The difference between this embodiment and embodiment 1 is that in the preparation of (5) lithium-ion battery, after the above-mentioned positive electrode sheet, isolation membrane and negative electrode sheet are stacked in order, when the pole ear is die-cut, the length of the pole sheet in the area of ​​the pole ear is controlled so that the length of the area without the pole ear accounts for 0.9 of the length of the pole sheet.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 1 is that, in the process of (1) preparing the positive electrode sheet, the mass ratio of 9-series LiNiCoMnO2 positive electrode active material, conductive agent MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube), and binder PVDF is 96.9:1.5:0.5:1.1; in the process of (2) preparing the negative electrode sheet, the mass ratio of negative electrode active material graphite, silicon-based material (SiC), conductive agent SWCNT (single-walled carbon nanotube), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.45:4:0.05:0.9:1:1.6; the rest is consistent with Example 1.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 1 is that in the process of (1) preparing the positive electrode sheet, the mass ratio of 9 series LiNiCoMnO2 positive electrode active material and conductive agent MWCNT (multi-walled carbon nanotubes) and conductive agent SWCNT (single-walled carbon nanotubes) is 98.5:0.35:05:1.1, wherein the conductive agent single-walled carbon nanotubes, the surface density of the positive electrode sheet is adjusted to 654g / cm 2; In the process of (2) preparing the negative electrode sheet, the mass ratio of the negative electrode active material graphite, silicon-based material (SiC), conductive agent SWCNT (single-walled carbon nanotube), conductive agent SP (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.4:4:0.05:0.95:1:1.6; and the surface density of the negative electrode sheet is adjusted to 332g / cm 2 ; The rest is consistent with Example 1.

[0068] Test Case

[0069] 1. Experimental Construction Method

[0070] (1) The surface resistance of the positive electrode sheets and the negative electrode sheets in Examples 1 to 14 and Comparative Examples 1 to 2 was tested. The specific testing method is as follows:

[0071] The two-probe method is used to test the surface resistance of the positive and negative electrodes. When testing with the two-probe method, the terminals are placed at both ends of the sample. By inputting an AC voltage signal, the current at both ends of the sample is collected to obtain the sample resistance, and the sample resistivity is obtained through the conversion relationship.

[0072] (2) The cylindrical batteries assembled in Examples 1 to 14 and Comparative Examples 1 to 2 were tested for 3C rate charge and discharge cycle performance. The specific test method is as follows:

[0073] The battery is charged at 0.33C of its nominal capacity, and the fixed capacity is 1C. The nickel-cobalt-manganese ternary battery is fully charged to 4.25V at 3C, and then discharged at 1C to 2.5V, which is a charge and discharge cycle. With this charge and discharge mode, when the battery capacity is 80% of the initial fixed capacity, the number of cycles is recorded, which is the 3C rate cycle life of the battery. The charging and discharging mechanisms of lithium iron phosphate positive electrode material, lithium iron manganese phosphate positive electrode material, lithium-rich manganese-based positive electrode material, and lithium nickel manganese oxide positive electrode material are: lithium iron phosphate is charged to 3.65V at 0.5C and discharged to 2.5V at 1C; lithium iron manganese phosphate is charged to 4.25V at 0.5C and discharged to 2.5V at 1C; lithium-rich manganese-based is charged to 4.25V at 0.5C and discharged to 2.5V at 1C; lithium nickel manganese oxide is charged to 4.85V at 1C and discharged to 3.5V at 1C.

[0074] 2. Experimental results

[0075] The relevant parameters of the positive and negative electrode sheets and the cycle performance of the batteries in Examples 1 to 14 and Comparative Examples 1 to 2 are shown in Table 1.

[0076] Table 1 Related parameters of positive and negative electrodes and battery cycle performance in Examples 1 to 14 and Comparative Examples 1 to 2

[0077]

[0078]

[0079] It can be seen from Table 1 that when the ratio R2 of the positive electrode sheet resistance R1 to the negative electrode sheet resistance in the cylindrical battery is controlled to satisfy the relationship of R1 / R2=15-1000, the cylindrical battery can have a better charge and discharge cycle life at a 3C rate, and reference can be made to Examples 1-14. However, the ratio R2 of the positive electrode sheet resistance R1 to the negative electrode sheet resistance in Comparative Examples 1-2 does not satisfy the relationship of R1 / R2=15-1000, and the charge and discharge cycle life of the cylindrical battery at a 3C rate is significantly reduced relative to Examples 1-14. This shows that controlling the ratio R2 of the positive electrode sheet resistance R1 to the negative electrode sheet resistance in the cylindrical battery to satisfy the relationship of R1 / R2=15-1000 is conducive to improving the cycle life of the cylindrical battery. The reason is that when R1 and R2 satisfy the above relationship, on the one hand, it can ensure that the positive electrode sheet has a relatively low surface resistance, avoid the positive electrode sheet temperature rising too fast, and then ensure that the positive electrode active material will not fail due to high temperature, ensure the long-term and stable performance of the positive electrode active material, and optimize the battery cycle performance; on the other hand, it can ensure that the negative electrode sheet has a relatively high surface resistance, increase the temperature of the negative electrode surface resistance, and then increase the activity of the negative electrode active material, which is conducive to further optimizing the battery cycle performance.

[0080] Furthermore, comparing Examples 1, 3, and 13, Example 1 further satisfies the relationship that the surface resistances R1 and R2 of the positive and negative electrodes further satisfy R1 / R2=15-300, while Examples 3 and 13 do not satisfy this relationship, resulting in a decrease in the cycle performance of Examples 3 and 13. This shows that when the surface resistances R1 and R2 of the positive and negative electrodes further satisfy the relationship that R1 / R2=15-300, it is more conducive to taking into account the stability of the positive and negative active materials and the lithium ion transmission performance, and further promoting the improvement of the battery cycle performance.

[0081] Comparing Examples 1 and 4 to 6, the surface resistances R1 and R2 of the positive and negative electrode sheets in Example 1 further satisfy the relationship of R1 / R2=15 to 300 and satisfy the relationship of 0.5Ω≤R1≤3.0Ω, 3mΩ≤R2≤35mΩ, while the surface resistances R1 and R2 of the positive and negative electrode sheets in Examples 4 to 6 do not satisfy the relationship of 0.5Ω≤R1≤3.0Ω or 3mΩ≤R2≤35mΩ, resulting in a decrease in the cycle performance of the cylindrical batteries in Examples 4 to 6. This shows that further controlling the values ​​of R1 and R2 can further regulate the stability of the battery during the cycle and promote the improvement of the cycle performance. By observing Examples 1, 7, 8, 9, and 10, it can be found that when a variety of positive electrode active material types are used, these types of positive electrode active materials can all enable the cylindrical battery to have a better charge and discharge cycle life, indicating that limiting the ratio of the surface resistance of the positive electrode sheet to the negative electrode sheet within a specific range is beneficial to both the positive and negative electrode active materials having better activity and structural stability, thereby optimizing the cycle performance of the cylindrical battery.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention is described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the technical solutions of the present invention can be modified or equivalently replaced, but these modifications or replacements are all within the protection scope of the present invention.

Claims

1. A cylindrical battery, characterized in that: The battery cell includes a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet surface resistance is R1, and the negative electrode sheet surface resistance is R2, wherein R1 and R2 satisfy the following relationship: 15≤R1 / R2≤1000, and 0.5Ω≤R1≤3.0Ω, 3mΩ≤R2≤35mΩ; The positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material is selected from at least one of a lithium iron phosphate positive electrode material, a nickel-cobalt-manganese ternary positive electrode material, a lithium iron manganese phosphate positive electrode material, a lithium-rich manganese-based positive electrode material, and a lithium nickel manganese oxide positive electrode material; The negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises graphite; After the battery cell is unfolded, the positive electrode sheet and the negative electrode sheet independently include a non-tab area and a tab area; the tab area is provided with a plurality of tabs; The ratio of the length of the non-electrode lug region to the length of the electrode piece is 0.05 to 0.6; The length of the positive electrode sheet is 450 to 2000 mm, and the length of the negative electrode sheet is 450 to 2000 mm.

2. The cylindrical battery according to claim 1, characterized in that: R1 and R2 satisfy the following relationship: 15≤R1 / R2≤300.

3. The cylindrical battery according to claim 1, characterized in that: The positive electrode active material layer further includes a first conductive agent, the mass of the first conductive agent accounts for 0.5-2% of the mass of the positive electrode active material layer; The first conductive agent includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, superP, acetylene black, and graphene.

4. The cylindrical battery according to claim 1, characterized in that: The negative electrode active material further includes a silicon-based material, and the mass ratio of the silicon-based material to the graphite material is greater than 0 and less than or equal to 35%.

5. The cylindrical battery according to claim 1, characterized in that: The negative electrode active material layer further includes a second conductive agent, the mass of the second conductive agent accounts for 0.5 to 3% of the mass of the negative electrode active material layer; The second conductive agent includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, super P, acetylene black, and graphene.

6. The cylindrical battery according to claim 1, characterized in that: The surface density of the positive electrode sheet is 220 to 800 g / m 2 , thickness is 60~220μm; The surface density of the negative electrode sheet is 150 to 250 g / m 2 , thickness is 90~170μm.

7. The cylindrical battery according to claim 1, characterized in that: The positive electrode active material is the nickel-cobalt-manganese ternary positive electrode material. In the nickel-cobalt-manganese ternary positive electrode material, the nickel element accounts for no less than 80% of the total molar number of the nickel element, the cobalt element, and the manganese element.

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