CN117039194A - Cylindrical battery - Google Patents

Abstract

The invention provides a cylindrical battery, which includes a battery core. The battery core includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet resistance is R1 and the negative electrode sheet resistance is R2. R1 and R2 satisfy the following relationship: 15≤R1/R2≤ 1000; The positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. The positive electrode active material is selected from the group consisting of lithium iron phosphate positive electrode material, nickel cobalt manganese ternary positive electrode material, lithium iron manganese phosphate positive electrode material, and lithium-rich manganese-based positive electrode. material and lithium nickel manganate cathode material; the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes graphite. The cylindrical battery provided by the 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

A cylindrical battery

Technical field

The invention belongs to the technical field of lithium batteries, and specifically relates to a cylindrical battery.

Background technique

Cylindrical batteries are the earliest mature industrialized lithium battery products. After more than 20 years of development, now the cylindrical battery production process is mature, the production efficiency is high, and the cost is relatively low. Therefore, the cost of PACK is also relatively low. The finished lithium battery The efficiency is higher than that of prismatic lithium batteries and soft-pack lithium batteries, and its consistency and safety are also relatively excellent. Therefore, cylindrical batteries still account for a relatively large proportion in the current market field. Further optimization of the cycle performance of cylindrical batteries is also an important step for current lithium batteries. Research focus in the battery industry.

The cylindrical shape of cylindrical batteries will cause low space utilization, poor radial heat conduction, and uneven temperature distribution. These problems lead to poor heat dissipation performance of cylindrical batteries. In particular, the middle area of the roll core is squeezed by the outer and inner area pole pieces, making it more difficult to dissipate heat, making it difficult for cylindrical batteries to dissipate heat. The long-term inability to dissipate heat in time will worsen the stability and cycle performance of the battery, and degrade the safety performance and service life of the battery.

Contents of the invention

In order to solve the problems and deficiencies in the prior art, the present invention provides a cylindrical battery that 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.

The invention provides a cylindrical battery, which includes a battery core. The battery core includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet resistance is R1 and the negative electrode sheet resistance is R2. R1 and R2 satisfy the following relationship: 15≤R1/ R2≤1000; the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material is selected from at least one of lithium iron phosphate positive electrode materials and nickel cobalt manganese ternary positive electrode materials; the negative electrode sheet includes negative electrode active materials layer, the negative active material layer includes negative active material, and the negative active material includes graphite.

The shape of the cylindrical battery is cylindrical, with low space utilization and poor radial heat conduction. In particular, the middle area of the core is squeezed by the outer and inner electrodes, making it more difficult to dissipate heat. Therefore, there is a large difference in temperature distribution in cylindrical batteries. , heat dissipation difficulties and other problems. The difficulty in dissipating heat 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 cathode active material is usually a highly active material such as lithium iron phosphate cathode material, nickel cobalt manganese ternary cathode material, lithium iron manganese phosphate cathode material, manganese-rich lithium-based cathode material, lithium nickel manganese oxide cathode material Materials, etc. If the internal temperature of the cylindrical battery rises too quickly and the internal temperature of the battery is too high, it will easily cause the failure of the activity of the positive active material, deteriorate the performance of the positive 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 can easily cause thermal runaway, increase safety risks such as battery fire or even explosion, and reduce the safety performance of the battery.

At present, in order to enable cylindrical batteries to effectively dissipate heat and improve the safety performance and cycle life of cylindrical batteries, the following technical means are usually used: controlling the charge and discharge process of cylindrical batteries, optimizing the battery structure design, and installing battery monitoring systems. However, these methods usually improve the heat dissipation performance and stability of the battery by controlling the external conditions during battery charging and discharging. In this way, the battery will still generate a lot of heat, which poses a major safety hazard, and the high temperature of long-term charging and discharging cycles will still cause The battery cycling stability deteriorates.

By controlling the ratio of the positive electrode sheet resistance and the negative electrode sheet resistance 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, the present invention can achieve the following effects: First, the positive electrode sheet can be guaranteed The surface resistance will not be too large to prevent the positive electrode sheet from overheating and causing the activation failure of the positive electrode active material; secondly, it can ensure that the surface resistance of the negative electrode sheet increases to a certain extent, because the negative electrode active material generally includes graphite, and graphite has low activity. Appropriately increasing the surface resistance of the negative electrode sheet can increase the temperature of the negative electrode sheet, which can effectively increase the activity of the negative electrode active material and improve the energy density and cycle life of the cylindrical battery. It is worth noting that in lithium batteries, the sheet resistance of the positive electrode sheet is usually greater than the sheet resistance of the negative electrode sheet. Therefore, the present invention is based on this premise to further optimize the ratio of the sheet resistance of the positive electrode sheet to the sheet resistance of the negative electrode sheet.

Detailed ways

The invention provides a cylindrical battery, which includes a battery core. The battery core includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet resistance is R1 and the negative electrode sheet resistance is R2. R1 and R2 satisfy the following relationship: 15≤R1/ R2≤1000; the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material is selected from at least one of lithium iron phosphate positive electrode materials and nickel cobalt manganese ternary positive electrode materials; the negative electrode sheet includes negative electrode active materials layer, the negative active material layer includes negative active material, and the negative active material includes graphite.

The shape of the cylindrical battery is cylindrical, with low space utilization and poor radial heat conduction. In particular, the middle area of the core is squeezed by the outer and inner electrodes, making it more difficult to dissipate heat. Therefore, there is a large difference in temperature distribution in cylindrical batteries. , heat dissipation difficulties and other problems. The difficulty in dissipating heat 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 cathode active material is usually a highly active material such as lithium iron phosphate cathode material, nickel cobalt manganese ternary cathode material, lithium iron manganese phosphate cathode material, lithium-rich manganese-based cathode material, lithium nickel manganate cathode material Materials, if the internal temperature of the cylindrical battery rises too fast and the internal temperature of the battery is too high, it will easily cause the failure of the activity of the positive active material, deteriorate the performance of the positive 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 can easily cause thermal runaway, increase safety risks such as battery fire or even explosion, and reduce the safety performance of the battery.

At present, in order to enable cylindrical batteries to effectively dissipate heat and improve the safety performance and cycle life of cylindrical batteries, the following technical means are usually used: controlling the charge and discharge process of cylindrical batteries, optimizing the battery structure design, and installing battery monitoring systems. However, these methods usually improve the heat dissipation performance and stability of the battery by controlling the external conditions during battery charging and discharging. In this way, the battery will still generate a lot of heat, which poses a major safety hazard, and the high temperature of long-term charging and discharging cycles will still cause The battery cycling stability deteriorates.

By controlling the ratio of the positive electrode sheet resistance and the negative electrode sheet resistance 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, the present invention can achieve the following effects: First, the positive electrode sheet can be guaranteed The surface resistance will not be too large to prevent the positive electrode sheet from overheating and causing the activation failure of the positive electrode active material; secondly, it can ensure that the surface resistance of the negative electrode sheet increases to a certain extent, because the negative electrode active material generally includes graphite, and graphite has low activity. Appropriately increasing the surface resistance of the negative electrode sheet can increase the temperature of the negative electrode sheet, which can effectively increase the activity of the negative electrode active material and improve the energy density and cycle life of the cylindrical battery. It is worth noting that in lithium batteries, the sheet resistance of the positive electrode sheet is usually greater than the sheet resistance of the negative electrode sheet. Therefore, the present invention is based on this premise to further optimize the ratio of the sheet resistance of the positive electrode sheet to the sheet resistance of the negative electrode sheet.

Preferably, R1 satisfies: 0.5Ω≤R1≤3.0Ω. Ensuring that the positive electrode sheet resistance is within this value range can control the positive electrode sheet to have a smaller sheet resistance, prevent the positive electrode sheet from heating up too quickly during the cycle, and ensure the activity of the positive electrode active material. Because if the positive electrode sheet resistance is too high and the temperature of the positive electrode sheet is too high, it will easily cause the failure of the positive electrode active material, thereby causing a decrease in battery cycle stability. In addition, if the positive electrode sheet resistance is too large and the positive electrode sheet generates too much heat, it will also cause the battery safety performance to decrease and easily cause safety hazards.

Preferably, R2 satisfies: 3mΩ≤R2≤35mΩ. Controlling the negative electrode sheet resistance within this range will help improve the performance of the negative electrode active material and promote the negative electrode active material to show better cycle performance during the charge and discharge process. At the same time, the surface resistance of the negative electrode sheet is within the above range and does not generate 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, and ensure the safety performance of the battery.

Preferably, the cathode active material is a nickel-cobalt-manganese ternary cathode material. In the nickel-cobalt-manganese ternary cathode material, the proportion of the number of moles of nickel element in the total number of moles of nickel element, cobalt element, and manganese element is not less than 80%. When the cathode active material is a high-nickel nickel-cobalt-manganese ternary cathode material, it is more conducive to improving the activity and stability of the cathode active material, and the battery has better charge and discharge cycle performance. Because generally speaking, in order to increase energy density, high-nickel ternary materials are preferred. When the nickel content increases, the heat generation will increase, making high-nickel ternary materials more likely to be deactivated. Therefore, for high-nickel materials, it is reasonable to Controlling the surface resistance is more conducive to improving the stability of the cathode active material and optimizing the battery cycle performance.

Preferably. The positive active material layer also includes a first conductive agent, the mass of the first conductive agent accounts for 0.5 to 2% of the mass of the positive active material layer; the first conductive agent includes multi-walled carbon nanotubes, single-walled carbon nanotubes At least one of tube, super P, acetylene black, and graphene. Controlling the content of the first conductive agent in the positive active material layer is conducive to regulating the surface resistance of the positive electrode sheet, so that the positive electrode sheet has an appropriate surface resistance without affecting the capacity of the positive electrode active material and optimizing the battery cycle performance.

Preferably, the negative active material further includes a silicon-based material, and the mass ratio of graphite to the silicon-based material is greater than 0 and less than or equal to 35%. The higher the silicon content, the greater the sheet resistance of the negative electrode sheet. Controlling the mass ratio of graphite to silicon-based materials is conducive to regulating the sheet resistance of the negative electrode, while avoiding excessive volume expansion of the negative electrode active material layer caused by excessive silicon-based materials. Deteriorate the stability of the anode material and the cycle performance of the battery.

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

Preferably, after the battery core is unfolded, the pole piece includes a tab-free area and a tab area; the tab area is provided with a plurality of tabs, and the pole piece includes a positive electrode piece and a negative electrode piece. The cylindrical battery is formed by winding the positive electrode sheet, separator, and negative electrode sheet at the same time. The electrode sheet here includes the tab-free area and the tab area. It means that before the electrode sheet is wound, the tabs will be formed on the electrode sheet in advance. The electrode sheet is set There is a winding start end and a winding end end. The area from the winding start end of the pole piece to the first tab on the pole piece is the tab-free area, and the remaining areas with tabs are the tab area. The tab area To provide a plurality of poles, the plurality of poles means that the number of poles is greater than or equal to 2. Here, the plurality of tabs in the tab area can mean that there is a certain distance between adjacent tabs during die cutting, that is, there are gaps between adjacent tabs in the tab area; it can also mean that the tab area is segmented. Cut open to form multiple poles, that is, the poles are disconnected from each other.

After the pole piece is wound into a battery core, a hollow core hole will be formed. The tab-free area on the pole piece is to avoid placing tabs near the winding core hole, because in cylindrical batteries, tabs usually need to be turned over. After folding, it is welded together with the battery current collecting plate. If the tabs are also installed close to the core hole, the tabs will cover the core hole after being folded. Therefore, in order to prevent the tabs from blocking the core hole, the pole pieces are not provided with tabs near the core hole to ensure that the tabs will not block the core hole after being folded, ensuring the normal use of the cylindrical battery.

Preferably, the ratio of the length of the tab-free area to the length of the pole piece is 0.05-0.6; the length of the pole piece is 450-2000 mm.

Preferably, the pole tabs include a positive pole tab and a negative pole tab, and the positive pole tab and the negative pole tab are respectively arranged on the same side of the battery core.

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

Preferably, the area density of the positive electrode sheet is 220-800g/m ² and the thickness is 60-220 μm; the area density of the negative electrode sheet is 150-250g/m ² and the thickness is 90-170 μm.

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 examples.

Example 1

(1) Preparation of positive electrode sheet

_{The prepared} 9-series Li[ _NixCoyMnz ] _O2 (where Wall carbon nanotubes) and the binder PVDF (polytetrafluoroethylene) are mixed at a mass ratio of 98.2:0.65:0.05:1.1, and then the solvent NMP (N-methylpyrrolidone) is added to it and stirred under the action of a vacuum mixer. Until the system is uniform, the positive electrode slurry is obtained; the positive electrode slurry is evenly coated on both surfaces of the positive electrode current collector aluminum foil, dried at room temperature, then transferred to the oven to continue drying, and then cold pressed and cut to obtain the positive electrode sheet. ; And in this embodiment, the area density of the positive electrode sheet is controlled to 364g/cm ² and the thickness is 115 μm.

(2) Preparation of negative electrode sheet

Combine the negative 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 (single-walled carbon nanotube). Styrene rubber) are mixed according to the mass ratio of 92.4:4:0.05:0.95:1:1.6, and then the solvent deionized water is added to it, and the system is stirred under the action of a vacuum mixer until the system is homogeneous to obtain a negative electrode slurry; The material 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 in this embodiment, the surface density of the negative electrode sheet is controlled to be 185g/cm ² and the thickness is 122 μm.

(3) Preparation of electrolyte

Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) at a volume ratio of 1:1:1 to obtain an organic solvent, and then dissolve the fully dried lithium salt LiPF ₆ In the mixed organic solvent, an electrolyte solution with a concentration of 1 mol/L was prepared.

(4) Preparation of isolation film

Selected from polyethylene film as isolation film.

(5) Preparation of lithium-ion batteries

Stack the above-mentioned positive electrode sheet, isolation film and negative electrode sheet in order, so that the isolation film is between the positive and negative electrode sheets to play the role of isolation, and then wind it to obtain a bare battery core; place the bare battery core in the outer packaging shell , after drying, the electrolyte is injected, and through processes such as vacuum packaging, standing, formation, and shaping, a lithium-ion battery is obtained.

In addition, in this embodiment, after the positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, when die-cutting the tabs, the length of the pole tabs in the tab area is controlled so that the length of the pole tabs in the tab-free area accounts for 0.05 of the length of the pole tabs. .

Example 2

The difference between this embodiment and Example 1 is that in (1) the process of preparing the cathode sheet, the 9-series LiNiCoMnO ₂ cathode active material, MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube), The binder PVDF (polytetrafluoroethylene) has a mass ratio of 97.8:1:0.1:1.1; in (2) the process of preparing the negative electrode sheet, the conductive agent SWCNT (single-walled carbon nanotube) is not added, and the negative electrode active material The mass ratio of graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethylcellulose), and binder SBR (styrene-butadiene rubber) is 92.6:4:0:0.8: 1:1.6; In the preparation of (5) lithium-ion battery, after stacking the positive electrode sheet, separator, and negative electrode sheet in order, when die-cutting the tabs, control the length of the tabs in the tab area so that there are no tabs. The length of the regional pole piece accounts for 0.1 of the length of the pole piece; the rest is consistent with Example 1.

Example 3

The difference between this embodiment and Example 1 is that in (1) the process of preparing the positive electrode sheet, the areal density of the positive electrode sheet is adjusted to 450g/cm ² ; in the process of (2) preparing the negative electrode sheet, the negative electrode active material graphite , the quality of silicon-based materials (SiC), conductive agent SWCNT (single-walled carbon nanotubes), conductive agent SP (carbon black), thickener CMC (carboxymethylcellulose), and binder SBR (styrene-butadiene rubber) The ratio ^of After stacking, when die-cutting the tabs, control the length of the pole piece in the removed tab area so that the length of the pole piece in the tab-free area accounts for 0.1 of the length of the pole piece; the rest is consistent with Example 1.

Example 4

The difference between this embodiment and Example 1 is that in (1) the process of preparing the positive electrode sheet, the 9-series LiNiCoMnO ₂ positive electrode active material, the conductive agent MWCNT (multi-walled carbon nanotube), the conductive agent SWCNT (single-walled carbon nanotube) ) and the binder PVDF (polytetrafluoroethylene) in a mass ratio of 98.1:0.65:0.15:1.1; in (2) the process of preparing the negative electrode sheet, the negative active material graphite, silicon-based material (SiC), conductive agent SP The mass ratio of (carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber) is 92.15:4:0.05:1.2:1:1.6; in (5) lithium-ion battery During preparation, after stacking the positive electrode sheet, separator, and negative electrode sheet in order, when die-cutting the tabs, control the length of the pole tabs in the tab area so that the length of the pole tabs without tabs accounts for 0.1 of the pole tab length; the rest Consistent with Example 1.

Example 5

The difference between this embodiment and Example 1 is that in (1) the process of preparing the positive electrode sheet, the 9-series LiNiCoMnO ₂ positive electrode active material, the conductive agent MWCNT (multi-walled carbon nanotube), the conductive agent SWCNT (single-walled carbon nanotube) ), the mass ratio of the binder PVDF (polytetrafluoroethylene) is 97.85:1:0.05:1.1; in (2) the process of preparing the negative electrode sheet, the conductive agent SWCNT (single-walled carbon nanotube) is not added, and The mass ratio of the negative active material graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethylcellulose), and binder SBR (styrene-butadiene rubber) is 92.9:4:0.5 :1:1.6; In the preparation of (5) lithium-ion batteries, after stacking the positive electrode sheet, separator film, and negative electrode sheet in order, when die-cutting the tabs, control the length of the tabs in the tab area to make the electrodeless The length of the pole piece in the ear region accounts for 0.1 of the length of the pole piece; the rest is consistent with Example 1.

Example 6

The difference between this embodiment and Example 1 is that in (1) the process of preparing the positive electrode sheet, the areal density of the positive electrode sheet was adjusted to 460g/cm ² ; in (2) the process of preparing the negative electrode sheet, no conductive agent was added SWCNT (single-walled carbon nanotube), and negative active materials graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethylcellulose), binder SBR (styrene-butadiene rubber) ) is 92.9:4:0.5:1:1.6, and the areal density of the negative and positive electrode sheets is adjusted to 234g/cm ² ; in (5) the preparation of the lithium-ion battery, the positive electrode sheet, isolation film, and negative electrode sheet are After the order is stacked, when die-cutting the tabs, control the length of the pole piece in the removed tab area so that the length of the pole piece in the tab-free area accounts for 0.1 of the length of the pole piece; the rest is consistent with Example 1.

Example 7

The difference between this embodiment and Example 1 is that in (1) the process of preparing the cathode sheet, the 9-series LiNiCoMnO ₂ cathode active material is replaced with lithium iron phosphate cathode active material (LiFePO); in (5) the lithium ion battery During preparation, after stacking the positive electrode sheet, separator, and negative electrode sheet in order, when die-cutting the tabs, control the length of the tab area removed so that the length of the tab area without tab accounts for 0.6 of the length of the tab; the rest Consistent with Example 1.

Example 8

The difference between this embodiment and Example 1 is that in (1) the process of preparing the cathode sheet, the 9-series LiNiCoMnO ₂ cathode active material is replaced by the lithium iron manganese phosphate cathode active material; the rest is consistent with Example 1.

Example 9

The difference between this embodiment and Example 1 is that in (1) the process of preparing the cathode sheet, the 9-series LiNiCoMnO ₂ cathode active material is replaced with a manganese-rich lithium-based cathode active material (LiMnO·LiMO); the rest is the same as in Example 1 consistent.

Example 10

The difference between this embodiment and Example 1 is that in (1) the process of preparing the cathode sheet, the 9-series LiNiCoMnO ₂ cathode active material is replaced by the lithium nickel manganate cathode active material (LiNi _0.5 Mn _1.5 O ₄ ); the rest are the same as Same as Example 1.

Example 11

The difference between this embodiment and Example 1 is that in (1) the process of preparing the cathode sheet, the 9-series LiNiCoMnO ₂ cathode active material and the conductive agent MWCNT (multi-walled carbon nanotube), the conductive agent SWCNT (single-walled carbon nanotube) tube) and binder PVDF (polytetrafluoroethylene) according to the mass ratio of 98.1:0.7:0.05:1.1; in (2) the process of preparing the negative electrode sheet, the negative electrode active material graphite, silicon-based material (SiC), conductive agent The mass ratio of SP (carbon black), thickener CMC (carboxymethylcellulose), and binder SBR (styrene-butadiene rubber) is 92.9:4:0.2:1.2:1:1.6; in (5) lithium-ion battery In the preparation, after stacking the positive electrode sheet, separator, and negative electrode sheet in order, when die-cutting the tabs, control the length of the pole tabs in the cutout tab area so that the length of the pole tabs in the non-pole tab area accounts for 0.2 of the pole piece length; The rest is consistent with Example 1.

Example 12

The difference between this embodiment and Example 1 is that in (1) the process of preparing the positive electrode sheet, the 9-series LiNiCoMnO ₂ positive electrode active material, the conductive agent MWCNT (multi-walled carbon nanotube), the conductive agent SWCNT (single-walled carbon nanotube) ) and the binder PVDF (polytetrafluoroethylene) are in a mass ratio of 97.25:1:15.05:1.1; in (2) the process of preparing the negative electrode sheet, no conductive agent SWCNT (single-walled carbon nanotubes) is added, and the negative electrode The mass ratio of active material graphite, silicon-based material (SiC), conductive agent SP (carbon black), thickener CMC (carboxymethylcellulose), and binder SBR (styrene-butadiene rubber) is 97.85:0.9:0.05: 1.1; In the preparation of (5) lithium-ion battery, after stacking the positive electrode sheet, separator film, and negative electrode sheet in order, when die-cutting the tabs, control the length of the pole tabs in the tab area so that there is no tab area. The piece length accounts for 0.2 of the pole piece length; the rest is consistent with Example 1.

Example 13

The difference between this embodiment and Example 1 is that in (1) the process of preparing the positive electrode sheet, the 9-series LiNiCoMnO ₂ positive electrode active material, the conductive agent MWCNT (multi-walled carbon nanotube), the conductive agent SWCNT (single-walled carbon nanotube) ), the binder PVDF (polytetrafluoroethylene) is in a mass ratio of 97.85:0.9:0.05:1.1; in (2) the process of preparing the negative electrode sheet, the negative active material graphite, silicon-based material (SiC), conductive agent The mass ratio of SWCNT (single-walled carbon nanotubes), conductive agent SP (carbon black), thickener CMC (carboxymethylcellulose), and binder SBR (styrene-butadiene rubber) is 92.1:4:0.3:1.5: 1:1.6; In the preparation of (5) lithium-ion battery, after stacking the positive electrode sheet, separator, and negative electrode sheet in order, when die-cutting the tabs, control the length of the tabs in the tab area so that there are no tabs. The length of the region accounts for 0.2 of the length of the pole piece; the rest is consistent with Example 1.

Example 14

The difference between this embodiment and Embodiment 1 is that in (5) the preparation of the lithium-ion battery, after the above-mentioned positive electrode sheet, separator film, and negative electrode sheet are stacked in order, when the tabs are die-cut, the tab area is controlled to be removed The length of the pole piece is such that the length of the area without tabs accounts for 0.9 of the length of the pole piece.

Comparative example 1

The difference between this comparative example and Example 1 is that in (1) the process of preparing the cathode sheet, the 9-series LiNiCoMnO ₂ cathode active material, conductive agent MWCNT (multi-walled carbon nanotube), conductive agent SWCNT (single-walled carbon nanotube) ) and the binder PVDF according to the mass ratio of 96.9:1.5:0.5:1.1; in (2) the process of preparing the negative electrode sheet, the negative electrode active material graphite, silicon-based material (SiC), conductive agent SWCNT (single-walled carbon nanoparticles The mass ratio of pipe), 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 are with Same as Example 1.

Comparative example 2

The difference between this comparative example and Example 1 is that in (1) the process of preparing the cathode sheet, the 9-series LiNiCoMnO ₂ cathode active material and the conductive agent MWCNT (multi-walled carbon nanotube), the conductive agent SWCNT (single-walled carbon nanotube) ) according to the mass ratio of 98.5:0.35:05:1.1, in which the conductive agent single-walled carbon nanotubes are used to adjust the area density of the positive electrode sheet to 654g/cm ² ; in (2) the process of preparing the negative electrode sheet, the negative electrode active material Graphite, silicon-based material (SiC), conductive agent SWCNT (single-walled carbon nanotube), conductive agent SP (carbon black), thickener CMC (carboxymethylcellulose), binder SBR (styrene-butadiene rubber) The mass ratio is 92.4:4:0.05:0.95:1:1.6; and the areal density of the negative electrode sheet is adjusted to 332g/cm ² ; the rest is consistent with Example 1.

test case

1. Experiment construction method

(1) Test the surface resistance of the positive electrode sheet and the negative electrode sheet in Examples 1 to 14 and Comparative Examples 1 to 2. The specific test method is as follows:

The two-probe method is used to test the surface resistance of the positive and negative electrodes. During the two-probe method test, the terminals are placed at both ends of the sample, and the current at both ends of the sample is collected by inputting an AC voltage signal to obtain the sample resistance. The sample is obtained through the conversion relationship. Resistivity.

(2) Test the 3C rate charge and discharge cycle performance of the cylindrical batteries assembled in Examples 1 to 14 and Comparative Examples 1 to 2. The specific test methods are as follows:

The nominal capacity of the battery is 0.33C, and the fixed capacity is 1C capacity; among them, the nickel-cobalt-manganese ternary element is fully charged to 4.25V at a current of 3C, and then discharged at 1C to 2.5V. It is a charge and discharge cycle. According to this charge and discharge system, when the battery capacity is 80% of the initial fixed capacity, record the number of cycles at this time, which is the 3C rate cycle life of the battery. The charge and discharge mechanisms of lithium iron phosphate cathode materials, lithium iron manganese phosphate cathode materials, lithium-rich manganese-based cathode materials, and lithium nickel manganese oxide cathode materials are: charging lithium iron phosphate to 3.65V at 0.5C, and discharging 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 base 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. Discharge to 3.5V at 1C.

2.Experimental results

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.

Table 1 Related parameters of positive and negative electrode sheets and battery cycle performance in Examples 1 to 14 and Comparative Examples 1 to 2

It can be seen from Table 1 that when the ratio R2 of the positive electrode sheet resistance R1 and the negative electrode sheet resistance in the cylindrical battery is controlled to satisfy the relationship of R1/R2 = 15 to 1000, the cylindrical battery can be charged from a better state at a 3C rate. For the discharge cycle life, please refer to Examples 1 to 14. In Comparative Examples 1 to 2, the ratio R1 of the positive electrode sheet resistance to the negative electrode sheet resistance R2 does not satisfy the relationship of R1/R2 = 15 to 1000. The charge and discharge cycle life of the cylindrical battery at a 3C rate is lower than that of Examples 1 to 14. The words are obviously reduced. This shows that controlling the ratio R1 of the positive electrode sheet resistance R1 to the negative electrode sheet resistance R2 in the cylindrical battery satisfies the relationship of R1/R2 = 15 to 1000, which is beneficial 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 temperature of the positive electrode sheet from heating up too fast, and thus ensure that the positive electrode active material will not cause activity failure due to high temperature. It ensures the long-term stable performance of the positive active material and optimizes 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, thereby increasing the activity of the negative active material, which is conducive to further optimization Battery cycle performance.

Furthermore, comparing Examples 1, 3, and 13, Example 1 further satisfies the relational expression R1/R2=15-300 for the surface resistances R1 and R2 of the positive and negative electrode sheets, while Examples 3 and 13 do not satisfy this relation. formula, 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 electrode sheets further satisfy the relationship of R1/R2=15~300, it will be more conducive to balancing the stability of the positive and negative active materials and the lithium ion transmission performance, and further promote the battery cycle. Performance improvements.

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=15~300 and satisfy the various requirements of 0.5Ω≤R1≤3.0Ω and 3mΩ≤R2≤35mΩ. The relationship expression, and the surface resistances R1 and R2 of the positive and negative electrode sheets in Examples 4 to 6 do not satisfy the relationship expression of 0.5Ω≤R1≤3.0Ω or 3mΩ≤R2≤35mΩ, resulting in the cylindrical batteries in Examples 4 to 6. cycle performance has declined. 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 cycle performance. Observing Examples 1, 7, 8, 9, and 10, it can be found that when using a variety of cathode active material types, these types of cathode active materials can make the cylindrical battery have a better charge and discharge cycle life, indicating that the The ratio of the area resistance of the positive electrode sheet and the negative electrode sheet is limited to a specific range, which is beneficial to both the positive and negative electrode active materials having better activity and structural stability, and optimizing the cycle performance of the cylindrical battery.

The above embodiments are only used to illustrate the technical solutions of the present invention and do not limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be carried out. modifications or equivalent substitutions, but these modifications or substitutions are within the protection scope of the present invention.

Claims (11)

1. A cylindrical battery, characterized in that: it includes a battery core, and the battery core includes a positive electrode sheet and a negative electrode sheet, Take the positive sheet resistance as R1 and the negative sheet resistance as R2. Among them, R1 and R2 satisfy the following relationship: 15≤R1/R2≤1000; The positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. The positive electrode active material is selected from the group consisting of lithium iron phosphate positive electrode material, nickel cobalt manganese ternary positive electrode material, lithium iron manganese phosphate positive electrode material, rich At least one of lithium manganese-based cathode materials and lithium nickel manganese oxide cathode materials; The negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes graphite. 2. The cylindrical battery of claim 1, wherein R1 and R2 satisfy the following relationship: 15≤R1/R2≤300. 3. The cylindrical battery according to claim 1, wherein R1 satisfies: 0.5Ω≤R1≤3.0Ω. 4. The cylindrical battery according to claim 2, wherein R2 satisfies: 3mΩ≤R2≤35mΩ. 5. The cylindrical battery of claim 1, wherein the positive active material layer further includes a first conductive agent, and the mass of the first conductive agent accounts for 0.5 in the mass of the positive active material layer. ~2%; The first 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 of claim 1, wherein the negative 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%. 7. The cylindrical battery of claim 1, wherein the negative active material layer further includes a second conductive agent, and the mass of the second conductive agent accounts for 0.5 in the mass of the negative active material layer. ~3%; The second conductive agent includes at least one of multi-walled carbon nanotubes, single-walled carbon nanotubes, super P, acetylene black, and graphene. 8. The cylindrical battery of claim 1, wherein after the battery core is deployed, the pole piece includes a tab-free area and a tab area; The pole area is provided with a plurality of poles; The pole piece includes the positive pole piece and the negative pole piece. 9. The cylindrical battery of claim 8, wherein the ratio of the length of the tab-less area to the length of the pole piece is 0.05 to 0.6; The length of the pole piece is 450-2000mm. 10. The cylindrical battery according to claim 1, characterized in that: the areal density of the positive electrode sheet is 220-800g/ ^m2 , and the thickness is 60-220 μm; The negative electrode sheet has an area density of 150-250g/m ² and a thickness of 90-170 μm. 11. The cylindrical battery of claim 1, wherein the positive active material is the nickel-cobalt-manganese ternary cathode material, and in the nickel-cobalt-manganese ternary cathode material, the nickel element is in the nickel element, the cobalt element, and the nickel element. The proportion of the total number of moles of elements and manganese elements is not less than 80%.