Long-circulation negative electrode slurry, negative electrode sheet, preparation method thereof, and cylindrical battery

Abstract

The application provides a long-cycle negative electrode slurry, a negative electrode sheet and a preparation method thereof, and a cylindrical battery. The long-cycle negative electrode slurry comprises a solvent and a negative electrode active material, wherein the negative electrode active material comprises 93-97.3 parts of low-expansion multi-layer artificial graphite, 0.5-2.5 parts of a first conductive agent, 1-2 parts of a thickening agent, and 1.2-2.5 parts of a first binder. The long-cycle negative electrode slurry has a large interlayer spacing and a low expansion coefficient, so that the lithium battery has small lithium ion deintercalation resistance and good kinetic performance during the charging and discharging process, the stress in the lithium battery is reduced, the electrolyte can easily enter the lithium battery, the problem of lithium precipitation failure caused by the difficulty of electrolyte infiltration during the cycle process is effectively prevented, the phenomenon of repeated rupture and repair of the SEI film of the negative electrode caused by expansion during the cycle process of the lithium battery is alleviated, the cycle performance of the lithium battery is improved, and the production cost is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a long-cycle negative electrode slurry, a negative electrode sheet, a preparation method thereof, and a cylindrical battery. BACKGROUND

[0002] Lithium batteries have been widely used in various energy storage products. With the rapid development of modern energy storage products, people have increasingly high requirements for the cycle life of lithium batteries, and most of the lithium batteries on the market have a cycle life of 3000-6000 times, which cannot better meet people's demand for high-performance lithium batteries.

[0003] In order to improve the cycle life of lithium batteries, improvements are mainly made from four aspects of the positive electrode, the negative electrode, the separator and the electrolyte to improve the cycle life of lithium batteries. At present, the negative electrode material of lithium battery is mostly carbon material. Since there are many types of carbon materials and the performance improvement space is large, researching high-performance and low-cost carbon negative electrode material is one of the effective ways to improve the performance of lithium ion batteries and reduce the cost of batteries.

[0004] Artificial graphite belongs to a kind of carbon material. Since artificial graphite has more advantages than natural graphite, artificial graphite is widely used in lithium battery negative electrode materials. For example, CN113764622B2 discloses a preparation method of a low-expansion lithium battery silicon-carbon negative electrode sheet. Artificial graphite, Si-CNT precursor and sucrose are mixed to obtain silicon-carbon powder, and then the silicon-carbon powder, water-based composite binder, graphene, dispersant and pure water are mixed and dispersed into negative electrode slurry to prepare a low-expansion lithium battery silicon-carbon negative electrode sheet, so that the Si-CNT precursor is uniformly distributed in the artificial graphite, which can effectively reduce the expansion of the silicon-carbon negative electrode sheet and improve the cycle life of the battery. However, the doped Si element not only increases the production cost, but also the effect of improving the cycle life of lithium battery is not ideal, which still cannot meet people's demand for high-performance lithium batteries.

[0005] Also, CN106450336A discloses a lithium ion battery negative electrode slurry. Artificial graphite, binder, thickener and additive are compounded and used according to the mass ratio of (80-98):(1.0-5.0):(0.5-5.0):(0.5-10.0), and it can be seen from CN106450336A that the lithium battery starts to decay after 700 times of 1C charge-discharge cycle, so that the cycle life of the lithium battery still has deficiencies, which still cannot meet people's demand for high-performance lithium batteries. Figure 1 SUMMARY

[0006] ​The application aims to overcome the defects in the prior art, and provide a long-cycle negative electrode slurry with good cycle performance and low production cost, a negative electrode sheet, a preparation method thereof, and a cylindrical battery.

[0007] The application aims to achieve the above-mentioned purpose by the following technical solutions.

[0008] A long-cycle negative electrode slurry comprises a solvent and a negative electrode active material, wherein the negative electrode active material comprises the following components in the following mass fractions:

[0009]

[0010] In one of the embodiments, the interlayer spacing of the low-swelling multi-layer artificial graphite is 0.337 nm to 0.340 nm.

[0011] In one of the embodiments, the thickening agent comprises at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0012] A preparation method of a negative electrode sheet comprises the following steps:

[0013] The low-swelling multi-layer artificial graphite, the first conductive agent, the thickening agent, the first binder and the solvent are mixed to obtain the long-cycle negative electrode slurry in any one of the above-mentioned embodiments.

[0014] The long-cycle negative electrode slurry is coated on a negative electrode current collector.

[0015] The negative electrode current collector after coating is subjected to a drying operation to obtain a negative electrode semi-product.

[0016] The negative electrode semi-product is subjected to N times of rolling operations to obtain the negative electrode sheet, wherein N is less than or equal to 2, and N is a positive integer.

[0017] A negative electrode sheet is prepared by the preparation method of the negative electrode sheet in any one of the above-mentioned embodiments.

[0018] A cylindrical battery comprises a shell and a roll core, wherein the roll core is arranged in the shell, the roll core comprises a positive electrode sheet, a separator, an electrolyte and the negative electrode sheet in any one of the above-mentioned embodiments, the negative electrode sheet, the separator and the positive electrode sheet are arranged in sequence, and the electrolyte is filled in the shell.

[0019] In one of the embodiments, the active material of the positive electrode sheet comprises the following components:

[0020] Lithium iron phosphate 92 parts to 97.7 parts;

[0021] Second conductive agent 1 part to 4 parts;

[0022] Second binder 1.3 parts to 4 parts.

[0023] In one of the embodiments, the diaphragm comprises at least one of a ceramic diaphragm, a PP diaphragm and a PE diaphragm.

[0024] In one of the embodiments, the diaphragm has a thickness of 7-25 um.

[0025] In one of the embodiments, the shell has a diameter of 20-60 mm and a height of 65-200 mm.

[0026] Compared with the prior art, the present application has at least the following advantages:

[0027] The long-cycle negative electrode slurry has the following advantages: the interlayer spacing of the low-expansion multi-layer artificial graphite is relatively large, on the one hand, which helps the solvent to well wet the surface of the low-expansion multi-layer artificial graphite, so that the first conductive agent, the thickening agent and the first binder can be well mixed with the low-expansion multi-layer artificial graphite to obtain a uniform and stable long-cycle negative electrode slurry, and on the other hand, the lithium ion deintercalation resistance is small and the kinetic performance is good during the charging and discharging process of the lithium battery, so that the lithium ion can be well deintercalated in the negative electrode material, thereby preventing the negative electrode material from collapsing, and improving the cycle performance of the lithium battery. In addition, the expansion rate of the low-expansion multi-layer artificial graphite is low, on the one hand, which makes the negative electrode expand less after charging and discharging, thereby reducing the stress inside the lithium battery, helping the electrolyte to easily enter the inside of the lithium battery, effectively preventing the problem of lithium precipitation failure caused by the difficulty of electrolyte wetting during the cycle process of the lithium battery, and on the other hand, which is beneficial to alleviate the phenomenon of repeated rupture and repair of the SEI film of the negative electrode caused by expansion during the cycle process of the lithium battery, thereby reducing the consumption of active lithium, and further improving the cycle performance of the lithium battery, i.e. the capacity retention rate of the lithium battery can still remain above 100% when the lithium battery is charged and discharged at 1C for 757 times, and the capacity retention rate can still remain 80% when the lithium battery is cycled for 10000 times, which breaks through the phenomenon that the traditional lithium battery starts to decay when cycled at 1C for 700 times, to realize long cycle of the lithium battery, and well meet the demand of people for high-performance lithium batteries. In addition, the low-expansion multi-layer artificial graphite does not contain metal elements, thereby reducing the production cost. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0029] Figure 1 Flow chart of the negative electrode sheet of an embodiment of the present application.

[0030] Figure 2 A sectional view of a negative plate in one direction according to an embodiment of the present application. DETAILED DESCRIPTION

[0031] For the purposes of promoting an understanding of the principles of the application, reference will now be made to the embodiments illustrated in the drawings. It is expressly understood that the drawings are for illustration only and that the application can be embodied in many different forms. In the drawings:

[0032] It is to be understood that where the terms "fixed" or "attached" are used herein, they are to be interpreted broadly to include direct attachment between two elements as well as attachment through intervening elements. Where the terms "connected" or "coupled" are used herein, they are to be interpreted broadly to include both direct connections between two elements and connections through intervening elements. As used herein, the terms "vertical", "horizontal", "left", "right", and the like, are merely used for the purpose of illustration and are not intended to be limiting.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0034] The present application provides a long-circulation negative electrode slurry, comprising a solvent and a negative electrode active material, the negative electrode active material comprising the following components in the following mass fractions: low-expansion multi-layer artificial graphite 93-97.3 parts; first conductive agent 0.5-2.5 parts; thickening agent 1-2 parts; first binder 1.2-2.5 parts.

[0035] The long-cycle negative electrode slurry has the following advantages. The interlayer spacing of the low-expansion multi-layer artificial graphite is relatively large, which helps the solvent to wet the surface of the low-expansion multi-layer artificial graphite well, so that the first conductive agent, the thickening agent and the first binder can be well mixed with the low-expansion multi-layer artificial graphite to obtain a uniform and stable long-cycle negative electrode slurry. In addition, the lithium ion deintercalation resistance is small and the kinetic performance is good during the charging and discharging process of the lithium battery, so that the lithium ion can be well deintercalated in the negative electrode material, thereby preventing the negative electrode material from collapsing and improving the cycle performance of the lithium battery. In addition, the expansion rate of the low-expansion multi-layer artificial graphite is low, which helps to reduce the stress inside the lithium battery after charging and discharging, makes the electrolyte more easily enter the inside of the lithium battery, effectively prevents the problem of lithium precipitation failure caused by the difficulty of electrolyte wetting during the cycle process of the lithium battery, and helps to alleviate the phenomenon of repeated rupture and repair of the SEI film of the negative electrode caused by expansion during the cycle process of the lithium battery, thereby reducing the consumption of active lithium and improving the cycle performance of the lithium battery. That is, the capacity retention rate of the lithium battery can still be maintained at more than 100% when the lithium battery is charged and discharged at 1C for 757 cycles, and the capacity retention rate can still be maintained at 80% when the lithium battery is cycled for 10,000 times, which breaks through the phenomenon that the traditional lithium battery starts to decay when it is charged and discharged at 1C for 700 cycles. The long-cycle lithium battery can meet the needs of people for high-performance lithium batteries.

[0036] In order to better understand the technical solutions and beneficial effects of the present application, the present application will be further described in detail below in combination with specific embodiments:

[0037] The long-cycle negative electrode slurry of one embodiment comprises a solvent and a negative electrode active material, and the negative electrode active material comprises the following components in the following mass fractions: low-expansion multi-layer artificial graphite 93-97.3 parts; first conductive agent 0.5-2.5 parts; thickening agent 1-2 parts; and first binder 1.2-2.5 parts.

[0038] It can be understood that there are still many problems with conventional artificial graphite, such as small interlayer spacing and high expansion rate. In order to improve the cycle performance of lithium batteries, either the amount of artificial graphite is increased, or the artificial graphite is modified, such as patent CN113764622 B2, or a plurality of different types of carbon sources are mixed for use, such as patent CN106450336A. However, the traditional method still has the phenomenon of poor cycle performance of lithium batteries, and still cannot well meet people's demand for high-performance lithium batteries. Therefore, the present application is prepared by compounding 93-97.3 parts of low-expansion multi-layer artificial graphite, 0.5-2.5 parts of a first conductive agent, 1-2 parts of a thickening agent, and 1.2-2.5 parts of a first binder. Since the interlayer spacing of the low-expansion multi-layer artificial graphite is relatively large, for example, in one embodiment, the interlayer spacing of the low-expansion multi-layer artificial graphite is 0.337-0.340 nm, on the one hand, it helps the solvent to wet the surface of the low-expansion multi-layer artificial graphite well, so that the first conductive agent, the thickening agent and the first binder can be well mixed with the low-expansion multi-layer artificial graphite to obtain a uniform and stable long-cycle negative electrode slurry, on the other hand, the lithium ion deintercalation resistance is small and the kinetic performance is good during the charging and discharging process of the lithium battery, so that the lithium ion can be well deintercalated in the negative electrode material, thereby preventing the negative electrode material from collapsing, and thus improving the cycle performance of the lithium battery.

[0039] Further, since the low-expansion multi-layer artificial graphite has a low expansion rate, on the one hand, the negative electrode expands less after charging and discharging, thereby reducing the stress inside the lithium battery, helping the electrolyte to easily enter the inside of the lithium battery, effectively preventing the problem of lithium precipitation failure due to the difficulty of electrolyte wetting during the cycle process, on the other hand, the low expansion rate helps to maintain the interlayer spacing structure of the low-expansion multi-layer artificial graphite, so that the lithium ion can be better deintercalated on the negative active material, on the other hand, it is beneficial to alleviate the phenomenon of repeated rupture and repair of the SEI film of the negative electrode caused by expansion during the cycle process of the lithium battery, thereby reducing the consumption of active lithium, and thus improving the cycle performance of the lithium battery, i.e. the capacity retention rate of the lithium battery can still be maintained at more than 100% when the 1C charging and discharging cycle is 757 times, and there is no attenuation phenomenon, and the capacity retention rate can still be maintained at 80% when the cycle is 10000 times, breaking through the phenomenon of attenuation of traditional lithium batteries when the 1C charging and discharging cycle is 700 times, to realize the long cycle of lithium batteries, and well meet people's demand for high-performance lithium batteries. In addition, the low-expansion multi-layer artificial graphite does not contain metal elements, thereby reducing the production cost.

[0040] It should be noted that, in actual application, due to the characteristics of the cylindrical battery itself (the winding setting of the winding core), if a conventional artificial graphite with a high expansion rate is used, the cylindrical battery will expand greatly after charging and discharging, thereby causing the stress inside the winding core to increase, so that lithium ions are difficult to diffuse uniformly in the active material inside the winding core, and further causing the local stress of the entire winding core to be too large to cause the electrolyte to be more difficult to enter the inside of the winding core in the cycle process, and further unable to better ensure that the electrolyte can fully soak on the active material inside the winding core, thereby greatly reducing the cycle energy difference of the cylindrical battery. Therefore, in the present application, due to the addition of low-expansion multi-layer artificial graphite to the negative electrode active material, the expansion rate of the lithium battery in the cycle process is smaller, thereby reducing the stress inside the winding core, so that the electrolyte is more easily entered into the inside of the winding core in the cycle process of the cylindrical battery, effectively preventing the phenomenon of lithium precipitation failure caused by the difficulty of the electrolyte to soak the negative electrode active material in the cycle process. Therefore, the long-cycle negative electrode slurry of the present application is particularly suitable for cylindrical batteries.

[0041] It should also be noted that, compared with conventional artificial graphite, their interlayer spacing is usually 0.3354 nm-0.3360 nm, which is relatively smaller than the interlayer spacing of the low-expansion multi-layer artificial graphite of the present application, 0.337 nm-0.340 nm. When the low-expansion multi-layer artificial graphite with more and larger interlayer spacing is coated on the negative electrode current collector, the lithium ion deintercalation resistance is small and the kinetic performance is good during the charging and discharging process of the lithium battery, so that the lithium ion can be well deintercalated in the negative electrode material, thereby preventing the negative electrode material from collapsing, and further improving the cycle performance of the lithium battery. That is, when more low-expansion multi-layer artificial graphite is coated on the negative electrode current collector, a large amount of change can be formed, thereby greatly improving the cycle performance of the lithium battery.

[0042] In one embodiment, the thickening agent includes at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0043] In one embodiment, the low-expansion multi-layer artificial graphite is provided by a Jiangxi Zichen supplier manufacturer.

[0044] In one embodiment, the first conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, carbon nanotubes, graphene, conductive graphite, and VGCF (Vapour Grown-carbon Fibres).

[0045] In one embodiment, the first binder includes at least one of butadiene styrene rubber and polyacrylic acid.

[0046] The present application also provides a preparation method of a negative electrode sheet, which includes part or all of the following steps:

[0047] S100, mixing the low-expansion multi-layer artificial graphite, the first conductive agent, the thickening agent, the first binder and the solvent to obtain the long-cycle negative electrode slurry of any one of the above embodiments.

[0048] It can be understood that first, the low-expansion multi-layer artificial graphite, the first conductive agent, the thickening agent, the first binder and the solvent are weighed according to the formula of the long-cycle negative electrode slurry, and then the weighed low-expansion multi-layer artificial graphite, the first conductive agent, the thickening agent, the first binder and the solvent are mixed to obtain the long-cycle negative electrode slurry. Further, in this embodiment, the solvent is deionized water, so that the deionized water can better wet the low-expansion multi-layer artificial graphite and will not introduce new impurities, so that the first conductive agent, the thickening agent and the first binder can be well mixed with the low-expansion multi-layer artificial graphite to obtain a uniform and stable long-cycle negative electrode slurry, so as to ensure that a negative electrode slurry with stable structure is obtained.

[0049] S200, coating the long-cycle negative electrode slurry on the negative electrode current collector for standby use.

[0050] S300, drying the coated negative electrode current collector to obtain a negative electrode semi-finished product, so as to effectively remove the solvent in the negative electrode slurry and ensure that a negative electrode sheet with good conductivity and safety is prepared.

[0051] S400, performing N times of rolling operation on the negative electrode semi-finished product to obtain the negative electrode sheet, wherein N≤2 and N is a positive integer.

[0052] It can be understood that since the low-expansion multi-layer artificial graphite has low expansion and relatively large interlayer spacing, the thickness of the negative electrode slurry coated on the negative electrode current collector is relatively large, and the particles in the negative electrode slurry are relatively loose. If the negative electrode semi-finished product is not subjected to rolling operation, the impedance of the negative electrode sheet will be large, which is not conducive to the conduction of lithium ions, and thus the cycle performance of the lithium battery is reduced. Therefore, the negative electrode semi-finished product is subjected to rolling operation, which can improve the energy density of the lithium battery and reduce the impedance of the negative electrode sheet, so as to prepare a lithium battery with high energy density and good cycle performance, so that the user can better pack the core into the shell.

[0053] It should be noted that by performing N times of rolling operation on the negative electrode semi-product, where N≤2, N is a positive integer, so as to realize the secondary classification compression of the negative electrode semi-product. Specifically, when performing the first rolling operation on the negative electrode semi-product, the negative electrode slurry farthest from the current collector part is first compressed, and then the force is gradually transmitted to the negative electrode slurry close to the current collector. It is equivalent to having a pre-compression state in the innermost layer of the negative electrode slurry, so as to realize the first compaction operation of the negative electrode semi-product, so as to effectively avoid the phenomenon that the particles in the negative electrode slurry are loose, thereby improving the compaction density of the negative electrode semi-product. Then, when performing the second rolling operation, since the rebounding force of the negative electrode slurry after the first rolling operation is not large, under the condition of ensuring that the compaction density of the negative electrode sheet can be improved, the structure of the low-expansion multi-layer artificial graphite in the negative electrode material can still maintain the original structure form, that is, the phenomenon that the particles of the low-expansion multi-layer artificial graphite in the negative electrode material are easily broken during the rolling process is effectively avoided, so as to ensure that the negative electrode sheet has high energy density and good cycle performance. It is worth mentioning that if the number of rolling operations on the negative electrode semi-product exceeds 2 times, that is, the number of rolling is too much, the particles on the surface of the electrode sheet are broken due to multiple times of roller contact, resulting in the falling off of the surface powder; on the other hand, the production efficiency is low, and the production cost is high.

[0054] It should be noted that although the compaction density of the negative electrode sheet is improved after the second rolling, when the negative electrode sheet of the present application is wound with the positive electrode sheet and the separator to form a roll core, there is a relatively dense phenomenon inside the roll core, that is, the diameter of the innermost roll layer of the roll core is relatively small and the outer layer is dense, so that the active material inside the roll core still has the phenomenon that the local stress is large and the electrolyte is difficult to infiltrate. Therefore, when performing the second rolling operation on the negative electrode semi-product after the drying operation, the following specific steps are included: the first rolling operation is performed on the negative electrode semi-product, and the second rolling operation is performed on the negative electrode semi-product. A non-rolled area is reserved at one end of the negative electrode semi-product, so that the non-rolled area is the starting point of winding. In this way, when winding with the non-rolled area as the starting point, the diameter of the innermost roll layer of the roll core is relatively large, thereby effectively improving the density of the roll core and maintaining the original structure of the low-expansion multi-layer artificial graphite in the innermost roll layer. In this way, on the one hand, a cylindrical battery with high energy density can be obtained, and on the other hand, the stress at the center of the roll core can be reduced, so that the electrolyte can more easily enter the inside of the roll core during the cycle process, thereby effectively improving the phenomenon that the electrolyte is difficult to infiltrate during the cycle process.

[0055] It can be understood that if the length of the non-rolled area is relatively long, the stress difference between the inside and outside of the core is relatively large, which is not conducive to the infiltration of the electrolyte into the negative electrode slurry, and therefore, in one embodiment, the number of turns after winding the non-rolled area is ≤2, which on the one hand ensures that the cylindrical battery has a high energy density, and on the other hand ensures the stress at the center of the core, so that the electrolyte can more easily enter the inside of the core during the cycle process, effectively improving the phenomenon that the electrolyte is difficult to infiltrate during the cycle process.

[0056] In one embodiment, first, the first rolling device is used to perform the first rolling operation on the negative electrode semi-product, that is, to perform the first overall rolling operation on the negative electrode semi-product to obtain a negative electrode sheet with high energy density, and then the second rolling device is used to perform the second rolling operation on the negative electrode semi-product, and the second rolling device is provided with a preset rolling area and a non-rolled area to perform the second special rolling operation on the negative electrode semi-product, so that a non-rolled area is reserved at one end of the negative electrode semi-product, and the non-rolled area serves as the starting point for winding. Thus, when winding starts from the non-rolled area, the diameter of the innermost winding layer inside the core is relatively large, effectively improving the density of the core inside and maintaining the original structure of the low-expansion multi-layer artificial graphite at the innermost winding layer. This, on the one hand, ensures that the cylindrical battery has a high energy density, and on the other hand, better reduces the stress at the center of the core, so that the electrolyte can more easily enter the inside of the core during the cycle process, effectively improving the phenomenon that the electrolyte is difficult to infiltrate during the cycle process. Further, using the first rolling device and the second rolling device to roll the negative electrode semi-product respectively is conducive to mass production.

[0057] The above method for preparing the negative electrode sheet first coats the long-cycle negative electrode slurry on the negative electrode current collector, which not only improves the conductivity of the negative electrode sheet, but also effectively avoids the phenomenon that the SEI film of the negative electrode is repeatedly broken and repaired due to high expansion during the cycle process of the lithium battery, thereby reducing the consumption of active lithium and improving the cycle performance of the lithium battery. Then, the coated negative electrode current collector is subjected to drying and secondary rolling operations to obtain a negative electrode sheet with high compaction density, low expansion, and good cycle performance.

[0058] As Figure 2As shown, in one embodiment, the negative electrode sheet 10 comprises a negative electrode current collector 200 and a coating layer 100, the coating layer 100 is arranged on the negative electrode current collector 200, the coating layer is formed with a first compacted coating area 110 and a second compacted coating area 120, the first compacted coating area 110 is formed by a first rolling operation, and the second compacted coating area 120 is formed by a second rolling operation. In this way, the first compacted coating area 110 can be used as the starting point of winding, so that the diameter of the innermost winding layer of the core is relatively large, effectively improving the phenomenon of densification in the core, thereby helping the electrolyte to flow into the inside of the core, and ensuring that the low-expansion multi-layer artificial graphite of the innermost winding layer of the core can maintain the original structure, which can not only ensure a cylindrical battery with high energy density, but also better reduce the stress at the center of the core, so as to ensure that the electrolyte can more easily enter the inside of the core during the cycle process, effectively improving the phenomenon that the electrolyte is difficult to infiltrate during the cycle process.

[0059] The application also provides a cylindrical battery, comprising a shell and a core, the core is arranged in the shell, the core comprises a positive electrode sheet, a separator, an electrolyte and the negative electrode sheet of any one of the above embodiments, the negative electrode sheet, the separator and the positive electrode sheet are sequentially wound and arranged, and the electrolyte is filled in the shell.

[0060] It can be understood that by applying the negative electrode sheet prepared by the application to a cylindrical battery, specifically, the negative electrode sheet, the separator and the positive electrode sheet are sequentially stacked and wound, so as to ensure that the lithium battery has good cycle performance, that is, the capacity retention rate can still be maintained at more than 100% when the 1C charge-discharge cycle is 757 times, and the capacity retention rate can still be maintained at 80% when the cycle is 10000 times, which breaks the phenomenon that the traditional lithium battery starts to decay when the 1C charge-discharge cycle is 700 times, realizes long cycle of the lithium battery, and well meets the demand of people for high-performance lithium batteries.

[0061] In the present embodiment, firstly, the negative electrode sheet, the separator and the positive electrode sheet are stacked in sequence, and then the first compacted coating area of the negative electrode sheet is taken as the starting point of winding to perform winding arrangement, so as to ensure that the diameter of the innermost winding layer of the winding core is relatively large, thereby effectively improving the phenomenon of the relatively compacted inside of the winding core, and ensuring that the low-expansion multi-layer artificial graphite of the innermost winding layer of the winding core can maintain the original structural form, so that on the one hand, a cylindrical battery with high energy density can be ensured, and on the other hand, the stress at the center position of the winding core can be better reduced, so as to ensure that the electrolyte can more easily enter the inside of the winding core in the cycle process of the lithium battery, thereby effectively improving the phenomenon that the electrolyte is difficult to infiltrate in the cycle process, and then the winding core is placed in the shell, and finally the electrolyte is injected into the shell and sealed, thereby obtaining the lithium battery. Especially, when the negative electrode sheet and the positive electrode sheet of the present application are used in cooperation with the ceramic separator, the cycle performance of the lithium battery can be greatly improved, that is, when the 1C charge-discharge cycle is 757 times, the capacity retention rate can still be maintained at more than 100%, and no attenuation phenomenon occurs, and when the cycle is 10000 times, the capacity retention rate can still be maintained at 80%. Further, in one of the embodiments, the thickness of the separator is 7um-25um.

[0062] In one of the embodiments, the separator can also be a PP separator and a PE separator

[0063] In one of the embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material, the positive electrode current collector is attached with a functional pattern layer, and the positive electrode active material is coated on the functional pattern layer, and the positive electrode active material comprises the following components: lithium iron phosphate 92-97.7 parts; a second conductive agent 1-4 parts; a second binder 1.3-4% parts, so that when the negative electrode sheet, the positive electrode sheet and the ceramic separator are used in cooperation, the cycle performance of the lithium battery can be greatly improved.

[0064] It should be noted that, since the rolling type is used when the negative electrode sheet is rolled, the first compacted coating area and the second compacted coating area on the negative electrode sheet are circular arc transition areas, so that when the negative electrode sheet and the positive electrode sheet, the separator are wound, the circular arc transition areas can form a relatively wide flow passage in the inside of the winding core, so that not only the stress in the inside of the winding core is small, but also more electrolyte can flow into the inside of the winding core, thereby effectively avoiding the problem that the electrolyte is difficult to infiltrate in the cycle process of the lithium battery, and further improving the long cycle performance of the lithium battery.

[0065] In a more preferred embodiment, the diameter of the shell is 20mm-60mm, and the height is 65mm-200mm, so as to ensure that the long cycle negative electrode slurry can better adapt to the cylindrical battery with large diameter, so as to ensure that the stress in the inside of the winding core of the cylindrical battery with large diameter is small, so as to ensure that the electrolyte can more easily enter the inside of the winding core in the cycle process of the lithium battery, thereby improving the cycle performance of the lithium battery.

[0066] In one of the embodiments, the second conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, carbon nanotube, and VGCF (Vapour Grown-carbon Fibres). Further, in one of the embodiments, the second binder is polyvinylidene fluoride.

[0067] Compared with the prior art, the present application has at least the following advantages:

[0068] The long cycle negative electrode slurry described above, due to the relatively large interlayer spacing of the low-expansion multi-layer artificial graphite, on the one hand, helps the solvent to well wet the surface of the low-expansion multi-layer artificial graphite, so that the first conductive agent, the thickening agent and the first binder can well mix with the low-expansion multi-layer artificial graphite, obtaining a uniform and stable long cycle negative electrode slurry, on the other hand, makes the lithium ion deintercalation resistance small and the kinetic performance good during the charging and discharging process of the lithium battery, so that the lithium ion can well deintercalate in the negative electrode material, thereby preventing the negative electrode material from collapsing, and further improving the cycle performance of the lithium battery. In addition, due to the low expansion rate of the low-expansion multi-layer artificial graphite, on the one hand, the negative electrode expands less after charging and discharging, thereby reducing the stress inside the lithium battery, helping the electrolyte to more easily enter the inside of the lithium battery, effectively preventing the problem of lithium precipitation failure caused by the difficulty of electrolyte wetting during the cycle process of the lithium battery, on the other hand, it is beneficial to alleviate the phenomenon of repeated rupture and repair of the SEI film of the negative electrode caused by expansion during the cycle process of the lithium battery, thereby reducing the consumption of active lithium, and further improving the cycle performance of the lithium battery, i.e. the capacity retention rate of the lithium battery can still remain above 100% when 1C charging and discharging cycle is 757 times, without the phenomenon of attenuation, and the capacity retention rate can still remain 80% when the cycle is 10000 times, breaking through the phenomenon of attenuation of traditional lithium battery when 1C charging and discharging cycle is 700 times, to realize the long cycle of the lithium battery, to well meet the demand of people for high-performance lithium battery. In addition, the low-expansion multi-layer artificial graphite does not incorporate metal elements, thereby reducing the production cost.

[0069] The following examples illustrate some specific embodiments. If % is mentioned, it means percent by weight. It should be noted that the following examples do not exhaust all possible cases, and the materials used in the following examples can be obtained from commercial channels if not specifically stated.

[0070] Example 1

[0071] Positive electrode: 96.8 parts of lithium iron phosphate, 1.6 parts of conductive carbon black, 1.6 parts of polyvinylidene fluoride, using 54 parts of N-methyl pyrrolidone as a solvent to prepare a uniformly dispersed slurry, coating on the positive electrode current collector with a functional layer and drying to obtain a positive electrode sheet;

[0072] The negative electrode: 93.5 parts of low-expansion multi-layer artificial graphite, 2.5 parts of conductive carbon black, 2.0 parts of lithium carboxymethyl cellulose, 2.0 parts of polyacrylic acid, and 82 parts of deionized water as a solvent to prepare a long-cycle negative electrode slurry, which is coated on the negative electrode current collector and then dried to obtain a negative electrode semi-finished product. The negative electrode semi-finished product is then rolled once to obtain a negative electrode sheet with a coating thickness of 170 um.

[0073] The prepared negative electrode sheet, positive electrode sheet, and separator are sequentially stacked and wound to obtain a winding core. Finally, the winding core, shell, and electrolyte are assembled into a lithium battery.

[0074] Example 2

[0075] The positive electrode: 96.8 parts of lithium iron phosphate, 0.5 parts of conductive graphite, 0.7 parts of conductive carbon black, and 2 parts of polyvinylidene fluoride are uniformly dispersed in 54 parts of N-methyl pyrrolidone as a solvent to prepare a slurry, which is coated on the positive electrode current collector with a functional layer and then dried to obtain a positive electrode sheet.

[0076] The negative electrode: 96.5 parts of low-expansion multi-layer artificial graphite, 0.6 parts of conductive carbon black, 1.1 parts of sodium carboxymethyl cellulose, and 1.8 parts of butadiene-styrene rubber are prepared into a long-cycle negative electrode slurry with 82 parts of deionized water as a solvent, which is coated on the negative electrode current collector and then dried to obtain a negative electrode semi-finished product. The negative electrode semi-finished product is then rolled twice to obtain a negative electrode sheet with a coating thickness of 170 um.

[0077] The prepared negative electrode sheet, positive electrode sheet, and separator are sequentially stacked and wound to obtain a winding core. Finally, the winding core, shell, and electrolyte are assembled into a lithium battery.

[0078] Example 3

[0079] 95 parts of lithium iron phosphate, 1 part of carbon nanotubes, 2 parts of conductive carbon black, and 2 parts of polyvinylidene fluoride are uniformly dispersed in 54 parts of N-methyl pyrrolidone as a solvent to prepare a slurry, which is coated on the positive electrode current collector with a functional layer and then dried to obtain a positive electrode sheet.

[0080] 97.0 parts of low-expansion multi-layer artificial graphite, 0.4 parts of carbon nanotubes, 0.5 parts of conductive carbon black, 1.0 parts of sodium carboxymethyl cellulose, and 1.1 parts of polyacrylic acid are prepared into a long-cycle negative electrode slurry with 82 parts of deionized water as a solvent, which is coated on the negative electrode current collector and then dried to obtain a negative electrode semi-finished product. The negative electrode semi-finished product is then rolled twice to obtain a negative electrode sheet with a coating thickness of 170 um.

[0081] The prepared negative electrode sheet, positive electrode sheet and separator are stacked in sequence, then the first compacted coating area of the negative electrode sheet is taken as the starting point of winding to perform winding operation to obtain a winding core, and finally the winding core, shell and electrolyte are assembled into a lithium battery.

[0082] Comparative Example 1

[0083] The difference from Example 2 is that 96.5 parts of low-expansion multi-layer artificial graphite in Example 2 is replaced by 96.5 parts of conventional artificial graphite, and the rest remains unchanged.

[0084] Comparative Example 2

[0085] The difference from Example 2 is that the 2 times of rolling operation in Example 2 is replaced by 3 times of rolling operation, and the rest remains unchanged.

[0086] The negative electrode sheets obtained in Examples 1-3 and Comparative Examples 1-2 are subjected to full-charge rebound detection to obtain the detection data in Table 1 as follows:

[0087] Table 1 Full-charge rebound data of negative electrode sheet

[0088]

[0089] The cycle performance test is performed on Examples 1-3 and Comparative Examples 1-2, i.e. 1C charge / 1C discharge cycle data, to obtain the data in Table 2 as follows:

[0090] Table 2 Cycle data

[0091]

[0092] From the comparison of Examples 1-3 and Comparative Example 1 in Tables 1 and 2, it can be seen that since the conventional artificial graphite is used in Comparative Example 1, the full-charge rebound rate of the negative electrode sheet is higher than that of Examples 1-3, and thus the capacity retention rate of Comparative Example 1 is less than 100% at 500 cycles, while the full-charge rebound rate of the negative electrode sheet is relatively suitable due to the use of low-expansion multi-layer artificial graphite in Examples 1-3, so that Examples 1-3 can achieve 0 decay at 1000 cycles, and can maintain a capacity retention rate of more than 80% at 12000 cycles, thereby realizing long cycle of the lithium battery. Among them, the comprehensive indicators of Example 2 are the best.

[0093] From the comparison of Example 2 and Comparative Example 2 in Tables 1 and 2, it can be seen that since the rolling times of Comparative Example 2 is greater than 2 times, the structure of the low-expansion multi-layer artificial graphite is damaged, and thus the full-charge rebound rate of Comparative Example 2 is greater than that of Example 2, and the capacity retention rate of Comparative Example 2 is less than 80% at 6000 cycles.

[0094] From the comparison of Example 1 and Examples 2-3, it can be seen that, because the negative electrode sheets of Examples 2-3 have the first compacted coating area and the second compacted coating area formed in the second rolling operation, and the first compacted coating area is wound, the full-charge rebound data rate of the negative electrode sheets of Examples 2-3 is relatively appropriate, and the capacity retention rate can still be maintained at more than 85% after 1200 cycles.

[0095] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a restriction on the scope of the patent. It should be pointed out that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, which are all within the protection scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A cylindrical battery, comprising a casing and a winding core, wherein the winding core is disposed within the casing, characterized in that, The core includes a positive electrode, a separator, an electrolyte, and a negative electrode. The negative electrode sheet includes a negative electrode current collector and a coating layer. The coating layer is disposed on the negative electrode current collector. The coating layer forms a first compacted coating area and a second compacted coating area. The first compacted coating area is formed by a first rolling operation, and the second compacted coating area is formed by a second rolling operation. The negative electrode, the separator, and the positive electrode are stacked in sequence and wound around the uncompacted area of ​​the first compacted coating area as the starting point. The electrolyte is then injected into the housing. The method for preparing the negative electrode sheet includes the following steps: Low-expansion multilayer artificial graphite, a first conductive agent, a thickener, a first binder, and a solvent are mixed to obtain a long-cycle negative electrode slurry. The long-cycle negative electrode slurry is coated onto the negative electrode current collector; The coated negative electrode current collector is dried to obtain a negative electrode semi-finished product. The negative electrode semi-finished product is subjected to a second rolling operation to obtain the negative electrode sheet; wherein, the first rolling operation rolls the negative electrode semi-finished product completely, and the second rolling operation leaves an unrolled area at one end of the negative electrode semi-finished product to form the unrolled area. The long-cycle negative electrode slurry includes a solvent and a negative electrode active material, wherein the negative electrode active material comprises the following parts by mass: Low-expansion multilayer artificial graphite, 93 to 97.3 parts; The first conductive agent is 0.5 to 2.5 parts; Thickener 1 to 2 parts; The first adhesive is 1.2 to 2.5 parts; The interlayer spacing of the low-expansion multilayer artificial graphite is 0.337nm~0.340nm.

2. The cylindrical battery according to claim 1, characterized in that, The thickener includes at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

3. The cylindrical battery according to claim 1, characterized in that, The active material of the positive electrode includes the following components: Lithium iron phosphate: 92-97.7 parts; 1 to 4 parts of the second conductive agent; The second adhesive is 1.3 to 4% of the total amount.

4. The cylindrical battery according to claim 1, characterized in that, The diaphragm includes at least one of ceramic diaphragm, PP diaphragm and PE diaphragm.

5. The cylindrical battery according to claim 1, characterized in that, The thickness of the diaphragm is 7µm to 25µm.

6. The cylindrical battery according to claim 1, characterized in that, The diameter of the shell is 20mm~60mm and the height is 65mm~200mm.

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