Battery monomer, battery device and power utilization device

Abstract

The invention relates to a battery monomer, a battery device and a power utilization device. A negative electrode material layer of the battery monomer comprises a first negative electrode film layer and a second negative electrode film layer; the first negative electrode film layer is closer to the negative electrode current collector than the second negative electrode film layer; the first negative electrode film layer comprises a first negative electrode active material and a first conductive agent, the first negative electrode active material comprises natural graphite, and the first conductive agent comprises a single-walled carbon nanotube; the second negative electrode film layer comprises a second negative electrode active material and a second conductive agent, the second negative electrode active material comprises artificial graphite, and the second conductive agent comprises a multi-walled carbon nanotube. The battery monomer provided by the invention has good cycle stability.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a battery cell, a battery device and an electrical device. Background Art

[0002] Secondary batteries represented by lithium-ion batteries have been widely used in recent years. With the development of related technologies and the increase in demand, higher requirements have been placed on the cycle life of secondary batteries.

[0003] The negative electrode is one of the key components in secondary batteries. Graphite, as a commonly used active material for the negative electrode, is prone to expansion and contraction during the charging and discharging process, which can easily lead to a decrease in the stability of the battery during the cycle, thereby deteriorating the cycle performance. Summary of the invention

[0004] The purpose of the present application is to provide a battery cell, a battery device and an electrical device. The battery cell improves the cycle performance of the battery mainly by using a negative electrode sheet including a first negative electrode film layer and a second negative electrode film layer.

[0005] To this end, the present application provides a battery cell, which includes a positive electrode sheet, a separator and a negative electrode sheet;

[0006] The negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; the negative electrode material layer includes a first negative electrode film layer and a second negative electrode film layer; the first negative electrode film layer is closer to the negative electrode current collector than the second negative electrode film layer;

[0007] The first negative electrode film layer includes a first negative electrode active material and a first conductive agent, the first negative electrode active material includes natural graphite, and the first conductive agent includes single-walled carbon nanotubes;

[0008] The second negative electrode film layer includes a second negative electrode active material and a second conductive agent, wherein the second negative electrode active material includes artificial graphite, and the second conductive agent includes multi-walled carbon nanotubes.

[0009] Natural graphite has a higher gram capacity than artificial graphite, but it has more surface defects and is prone to side reactions with the electrolyte. By using natural graphite in the first negative electrode film layer close to the negative electrode current collector and artificial graphite in the second negative electrode film layer far away from the current collector, it not only plays a role in increasing the gram capacity, but also reduces the side reactions between the negative electrode active material and the electrolyte, which is beneficial to improving the cycle performance of the battery. In addition, multi-walled carbon nanotubes are not easy to bend or kink compared to single-walled carbon nanotubes. The application of multi-walled carbon nanotubes in the second negative electrode film layer can better inhibit the expansion rebound of artificial graphite during the cycle, which is further beneficial to improving the cycle performance. Single-walled carbon nanotubes have the characteristics of good elasticity, high mechanical properties and excellent thermal conductivity. Using them in the first negative electrode film layer can improve the bonding force between the first negative electrode film layer and the negative electrode current collector and reduce the problem of film stripping during the cycle; and in the case of high current charging and discharging of the battery, the temperature near the negative electrode current collector is high. The use of single-walled carbon nanotubes has good tolerance, which is beneficial to improving the cycle stability of the battery during multiple charge and discharge.

[0010] In some embodiments, a thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 3-7:3-7.

[0011] When the above thickness ratio is adopted, the gram capacity of the negative electrode material and the cycle stability can be better taken into account.

[0012] In some embodiments, the thickness of the second negative electrode film layer is greater than the thickness of the first negative electrode film layer.

[0013] Since artificial graphite particles have high crystallinity and good consistency, when the thickness of the second negative electrode film layer is thicker, it is beneficial to further improve the fast charging performance and cycle life of the battery.

[0014] In some embodiments, the mass percentage of the multi-walled carbon nanotubes in the second negative electrode film layer is 0.05% to 2%.

[0015] When the mass proportion of multi-walled carbon nanotubes is greater than or equal to 0.05%, it can play an excellent role in inhibiting the expansion and rebound of graphite. Moreover, if the mass proportion of multi-walled carbon nanotubes does not exceed 2%, the artificial graphite can have a higher mass proportion, which is conducive to maintaining a good energy density.

[0016] In some embodiments, the multi-walled carbon nanotubes satisfy at least one of the following conditions:

[0017] The diameter of the multi-walled carbon nanotubes is 5 to 80 nm;

[0018] The length of the multi-walled carbon nanotubes is 1 to 50 μm;

[0019] The specific surface area of ​​the multi-walled carbon nanotubes is 150 to 300 m2 / g.

[0020] When the multi-walled carbon nanotubes used have the above-mentioned higher diameter or larger specific surface area, their conductivity is higher, which is beneficial to enhancing the conductivity of the negative electrode material layer. When the multi-walled carbon nanotubes have the above-mentioned length, their strength and toughness are higher, which can better inhibit the expansion and rebound of graphite particles during the cycle process, which is beneficial to improving the cycle performance of the battery.

[0021] In some embodiments, the mass percentage of the single-walled carbon nanotubes in the first negative electrode film layer is 0.05% to 1%.

[0022] When the mass proportion of single-walled carbon nanotubes in the first negative electrode film layer is greater than 0.05%, it can significantly improve the cohesion and reduce film peeling, which is beneficial to the stability of the battery during recycling. In addition, due to the high cost of single-walled carbon nanotubes, when the cost is comprehensively considered, the mass proportion of single-walled carbon nanotubes can be made not more than 1%.

[0023] In some embodiments, the single-walled carbon nanotubes satisfy at least one of the following conditions:

[0024] The diameter of the single-walled carbon nanotube is 1 to 5 nm;

[0025] The length of the single-walled carbon nanotube is 1 to 500 μm;

[0026] The specific surface area of ​​the single-walled carbon nanotube is 250 to 500 m 2 / g.

[0027] In the embodiments of the present application, when the single-walled carbon nanotubes have the above-mentioned longer length, smaller tube diameter and / or larger specific surface area, their conductivity is better, and the carbon-carbon bonds enable them to have a higher current carrying capacity, so that they can form a three-dimensional conductive network even at a lower dosage, further improving the current density of the first negative electrode film layer and reducing the impedance between the negative electrode material layer and the negative electrode current collector.

[0028] In some embodiments, the artificial graphite satisfies at least one of the following conditions:

[0029] In the second negative electrode film layer, the mass proportion of the artificial graphite is 95% to 99.5%;

[0030] The volume average particle size Dv50 of the artificial graphite is 5 μm to 20 μm;

[0031] The specific surface area of ​​the artificial graphite is 0.5m 2 / g to 1.3m 2 / g;

[0032] The powder compaction density of the artificial graphite under a force of 20000N is 1.5g / cm 3 Up to 1.9g / cm 3 .

[0033] When the mass proportion of artificial graphite in the second negative electrode film layer is within the above range, it is beneficial for the battery to have a higher energy density. When the volume average particle size Dv50 of artificial graphite is within the above range, it is beneficial for the negative electrode active material to better transmit ions and electrons, thereby achieving fast charging. When the specific surface area of ​​artificial graphite is within the above range, there are more active sites on the negative electrode surface, which can enable the battery to have a higher fast charging capability; when the powder compaction density of the artificial graphite under a force of 20,000 N is within the above range, the battery can have a higher energy density and improved cycle performance.

[0034] In some embodiments, the natural graphite satisfies at least one of the following conditions:

[0035] In the first negative electrode film layer, the mass proportion of the natural graphite is 95% to 99.5%;

[0036] The volume average particle size Dv50 of the natural graphite is 5 μm to 25 μm;

[0037] The specific surface area of ​​the natural graphite is 0.8 m 2 / g to 2.0m 2 / g;

[0038] The powder compaction density of the natural graphite under a force of 20000N is 1.5g / cm 3 Up to 1.9g / cm 3 .

[0039] When the mass proportion of natural graphite in the first negative electrode film layer is within the above range, it is beneficial for the battery to have a higher energy density. When the volume average particle size Dv50 of natural graphite is within the above range, it is beneficial for the negative electrode active material to better transmit ions and electrons, reduce the impedance of the pole piece, improve the battery's current carrying capacity and power, and reduce the temperature rise during charging and discharging. When the specific surface area of ​​natural graphite is within the above range, the particles are more tightly bound, which can prevent the active material from falling off the current collector surface during the cycle, and enable the battery to have a higher fast charging capability; when the powder compaction density of the artificial graphite under a force of 20000N is within the above range, the battery can have a higher energy density and improved cycle performance.

[0040] In some embodiments, the specific surface area of ​​the negative electrode material layer is 0.8 m 2 / g to 2.5m 2 / g.

[0041] When the specific surface area of ​​the negative electrode material layer is within the above range, there are more active sites on the negative electrode surface in contact with the electrolyte, which can enable the battery to have a higher rapid charging capability.

[0042] In some embodiments, the compaction density of the negative electrode material layer is 1.4 g / cm 3 ~1.8g / cm 3 .

[0043] When the negative electrode material layer has the above-mentioned higher compaction density, it is beneficial to improve the energy density of the battery. It is generally believed that higher compaction may lead to more significant expansion and rebound of the negative electrode material, thereby easily deteriorating the cycle performance. However, in the embodiment of the present application, under the above-mentioned compaction conditions, the rebound of the negative electrode active material during the battery cycle can also be well suppressed, so as not to deteriorate the cycle performance.

[0044] In some embodiments, the first negative electrode film layer and the second negative electrode film layer further contain a binder;

[0045] The mass proportion of the binder in the first negative electrode film layer is smaller than the mass proportion of the binder in the second negative electrode film layer.

[0046] Compared with the first negative electrode film layer, the second negative electrode film layer has a higher degree of infiltration with the electrolyte, and has relatively more lithium insertion and extraction reactions during the charge and discharge process. Therefore, in the later stage of the battery cycle, the volume change of the second negative electrode film layer is greater. By using a higher content of binder in the second negative electrode film layer, it is helpful to improve the cohesion, thereby reducing the shedding of the second negative electrode film layer during the cycle.

[0047] A second aspect of the present application provides a battery device, which includes the battery cell described in the first aspect of the present application.

[0048] In a third aspect of the present application, an electrical device is provided, which includes the battery cell described in the first aspect of the present application, or the battery device described in the second aspect of the present application.

[0049] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only used to illustrate the preferred embodiments and are not to be considered as limiting the present application. In the accompanying drawings:

[0051] Figure 1is a schematic diagram of a battery cell according to an embodiment of the present application;

[0052] Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0053] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0054] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0055] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0056] Figure 6 is a schematic diagram of an electrical device using a battery cell as a power source according to an embodiment of the present application;

[0057] Description of reference numerals:

[0058] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 end cover. DETAILED DESCRIPTION

[0059] The exemplary embodiments of the present disclosure will be described in more detail below. It should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0060] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0062] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0063] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0064] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0065] In recent years, secondary batteries have made great progress. With the development of related technologies and the increase in demand, higher requirements have been put forward for the cycle life of secondary batteries. The negative electrode is one of the key components in secondary batteries. Graphite, as a commonly used active material for the negative electrode, is prone to expansion and contraction during the charging and discharging process, which can easily lead to a decrease in the stability of the battery during the cycle, thereby deteriorating the cycle performance.

[0066] In the prior art, there are reports on adding carbon nanotubes into the negative electrode to improve the conductivity and the expansion of graphite. However, the effect of improving the battery cycle life is still relatively limited.

[0067] In the embodiments of the present application, the cycle performance of the battery is comprehensively improved mainly by applying a layered coating structure in the negative electrode sheet and combining different negative electrode active materials and conductive agents in different layers.

[0068] The solutions described in the embodiments of the present application are applicable to battery cells, battery devices using the battery cells, and electrical devices using the battery cells or battery devices.

[0069] Battery Cell

[0070] In the embodiment of the present application, the battery cell may be a secondary battery. A secondary battery refers to a battery cell that can be continuously used by activating active materials by charging after the battery cell is discharged.

[0071] The battery cell may be a lithium ion battery, a sodium ion battery, a sodium lithium ion battery, a lithium metal battery, a sodium metal battery, a lithium sulfur battery, a magnesium ion battery, a nickel hydrogen battery, a nickel cadmium battery, a lead storage battery, etc. In some embodiments, the battery cell is a lithium ion battery.

[0072] [Electrode assembly]

[0073] A battery cell generally includes an electrode assembly. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator, which is arranged between the negative electrode sheet and the positive electrode sheet. During the charge and discharge process of the battery cell, active ions (such as lithium ions) are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which can prevent the positive and negative electrodes from short-circuiting, and at the same time allow active ions to pass through.

[0074] [Negative electrode]

[0075] In some embodiments, a battery cell is provided, which includes a positive electrode sheet, a separator, and a negative electrode sheet;

[0076] The negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; the negative electrode material layer includes a first negative electrode film layer and a second negative electrode film layer; the first negative electrode film layer is closer to the negative electrode current collector than the second negative electrode film layer;

[0077] The first negative electrode film layer includes a first negative electrode active material and a first conductive agent, the first negative electrode active material includes natural graphite, and the first conductive agent includes single-walled carbon nanotubes (SWCNT);

[0078] The second negative electrode film layer includes a second negative electrode active material and a second conductive agent, wherein the second negative electrode active material includes artificial graphite, and the second conductive agent includes multi-walled carbon nanotubes (MWCNTs).

[0079] Natural graphite has a higher gram capacity than artificial graphite, but it has more surface defects and is prone to side reactions with the electrolyte. By using natural graphite in the first negative electrode film layer close to the negative electrode current collector and artificial graphite in the second negative electrode film layer far away from the current collector, it not only plays a role in increasing the gram capacity, but also reduces the side reactions between the negative electrode active material and the electrolyte, which is beneficial to improving the cycle performance of the battery. In addition, multi-walled carbon nanotubes are not easy to bend or kink compared to single-walled carbon nanotubes. The application of multi-walled carbon nanotubes in the second negative electrode film layer can better inhibit the expansion rebound of artificial graphite during the cycle, which is further beneficial to improving the cycle performance. Single-walled carbon nanotubes have the characteristics of good elasticity, high mechanical properties and excellent thermal conductivity. Using them in the first negative electrode film layer can improve the bonding force between the first negative electrode film layer and the negative electrode current collector and reduce the problem of film stripping during the cycle; and in the case of high current charging and discharging of the battery, the temperature near the negative electrode current collector is high. The use of single-walled carbon nanotubes has good tolerance, which is beneficial to improving the cycle stability of the battery during multiple charge and discharge.

[0080] In some embodiments, the ratio of the thickness of the first negative electrode film layer to the second negative electrode film layer is 3-7:3-7, for example, it can be about 1:1, 3:4, 3:5, 1:2, 3:7, 4:3, 4:5, 2:3, 4:7, 5:3, 5:4, 5:6, 5:7, 2:1, 3:2, 6:5, 6:7, 7:3, 7:4, 7:5, 7:6, etc.

[0081] When the above thickness ratio is adopted, the gram capacity of the negative electrode material and the cycle stability can be better taken into account. In some embodiments, the thickness of the first negative electrode film layer and the second negative electrode film layer can be independently selected from 30 μm to 300 μm, for example, can be selected from about 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 170 μm, 190 μm, 200 μm, 250 μm, 300 μm, etc.

[0082] In some embodiments, the thickness of the second negative electrode film layer is greater than the thickness of the first negative electrode film layer.

[0083] Since artificial graphite particles have high crystallinity and good consistency, they can make the electrode have higher energy density and cycle stability. Therefore, when the thickness of the second negative electrode film layer is thicker, it is beneficial to further improve the fast charging performance and cycle life of the battery.

[0084] In some embodiments, in the second negative electrode film layer, the mass proportion of multi-walled carbon nanotubes is 0.05% to 2%, for example, it can be selected from about 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.

[0085] When the mass proportion of multi-walled carbon nanotubes is greater than or equal to 0.05%, it can play an excellent role in inhibiting the expansion and rebound of graphite. Moreover, if the mass proportion of multi-walled carbon nanotubes does not exceed 2%, the artificial graphite can have a higher mass proportion, which is conducive to maintaining a good energy density.

[0086] In some embodiments, the multi-walled carbon nanotubes satisfy at least one of the following conditions:

[0087] The diameter of the multi-walled carbon nanotubes is 5 to 80 nm, for example, about 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, etc.;

[0088] The length of the multi-walled carbon nanotubes is 1 to 50 μm, for example, about 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, etc.;

[0089] The specific surface area of ​​the multi-walled carbon nanotubes is 150 to 300 m 2 / g, for example, about 150 m 2 / g, 160m 2 / g, 170m 2 / g, 180m 2 / g, 190m 2 / g, 200m 2 / g, 210m 2 / g, 220m 2 / g, 230m2 / g, 240m 2 / g, 250m 2 / g, 260m 2 / g, 270m 2 / g, 280m 2 / g, 290m 2 / g、300m 2 / g, etc.

[0090] When the multi-walled carbon nanotubes used have the above-mentioned higher diameter or larger specific surface area, their conductivity is higher, which is beneficial to enhancing the conductivity of the negative electrode material layer. When the multi-walled carbon nanotubes have the above-mentioned length, their strength and toughness are higher, which can better inhibit the expansion and rebound of graphite particles during the cycle process, which is beneficial to improving the cycle performance of the battery.

[0091] In some embodiments, in the first negative electrode film layer, the mass proportion of single-walled carbon nanotubes is 0.05% to 1%; for example, it can be about 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0092] When the mass proportion of single-walled carbon nanotubes in the first negative electrode film layer is greater than 0.05%, it can significantly improve the cohesion and reduce film peeling, which is beneficial to the stability of the battery during recycling. In addition, due to the high cost of single-walled carbon nanotubes, when the cost is comprehensively considered, the mass proportion of single-walled carbon nanotubes can be made not more than 1%.

[0093] In some embodiments, the single-walled carbon nanotubes satisfy at least one of the following conditions:

[0094] The diameter of the single-walled carbon nanotube is 1 to 5 nm, for example, about 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, etc.;

[0095] The length of the single-walled carbon nanotube is 1 to 500 μm, for example, about 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, etc.;

[0096] The specific surface area of ​​the single-walled carbon nanotube is 250 to 500 m 2 / g, for example, about 250 m 2 / g, 275m 2 / g、300m 2 / g, 325m 2 / g, 350m 2 / g, 375m 2 / g, 400m 2 / g, 425m 2 / g, 450m 2 / g, 475m 2 / g、500m 2 / g, etc.

[0097] In the embodiments of the present application, the single-walled carbon nanotubes are relatively long (1 to 500 μm, for example, 50 to 200 μm), have relatively small diameters (1 to 5 nm, for example, 1 to 3 nm) and / or have relatively large specific surface areas. When the diameter of the carbon nanotubes is thinner, the length is longer, and the specific surface area is larger, the conductivity is better. The carbon-carbon bonds enable them to have a higher current carrying capacity, so that they can form a three-dimensional conductive network even at a lower dosage, thereby further increasing the current density of the first negative electrode film layer and reducing the impedance between the negative electrode material layer and the negative electrode current collector.

[0098] In some embodiments, the artificial graphite satisfies at least one of the following conditions:

[0099] In the second negative electrode film layer, the mass proportion of the artificial graphite is 95% to 99.5%, for example, about 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, etc.;

[0100] The volume average particle size Dv50 of the artificial graphite is 5 μm to 20 μm, for example, about 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc.;

[0101] The specific surface area of ​​the artificial graphite is 0.5m 2 / g to 1.3m 2 / g, for example, about 0.5 m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, etc.

[0102] The powder compaction density of the artificial graphite under a force of 20000N is 1.5g / cm 3 Up to 1.9g / cm3 , for example, about 1.5 g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 wait.

[0103] When the mass proportion of artificial graphite in the second negative electrode film layer is within the above range, it is beneficial for the battery to have a higher energy density. When the volume average particle size Dv50 of artificial graphite is within the above range, it is beneficial for the negative electrode active material to better transmit ions and electrons, thereby achieving fast charging. When the specific surface area of ​​artificial graphite is within the above range, there are more active sites on the negative electrode surface, which can enable the battery to have a higher fast charging capability. When the powder compaction density of artificial graphite under a force of 20,000N is within the above range, the battery can have a higher energy density and improved cycle performance.

[0104] The volume average particle size Dv50 is well known in the art and can be measured using instruments and methods well known in the art, for example, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0105] The specific surface area of ​​the graphite material can be detected according to conventional methods in the art. For example, the specific surface area of ​​artificial graphite and natural graphite is detected according to the following method:

[0106] ① Sample pretreatment: Place the graphite powder sample to be tested into a sample tube and heat it in a vacuum to remove impurities and moisture on the sample surface. ② Determination of adsorption isotherm: At a certain temperature (usually liquid nitrogen temperature, 77K), allow the adsorbent gas (such as nitrogen) to contact the sample and measure the adsorption amount under different pressures. By changing the pressure, the adsorption isotherm can be obtained, that is, the relationship curve between the adsorption amount and the relative pressure (P / P0). According to the adsorption isotherm, the BET equation is used to calculate the adsorption amount V of the monolayer m and constant C. Through these parameters, the specific surface area of ​​the sample can be calculated. ③ Calculation of specific surface area: V m To convert to actual specific surface area, the cross-sectional area of ​​a specific adsorbent molecule is usually used as a reference. For example, for nitrogen adsorption, the cross-sectional area of ​​a nitrogen molecule is usually 0.162 nm 2 .

[0107] The compaction density of the powder can be detected according to conventional methods in the art. For example, the compaction density of the powder of artificial graphite and natural graphite under a force of 20000N is detected according to the following method:

[0108] First, you need to prepare a certain amount of graphite powder sample, usually 1 to 2 grams.

[0109] Pressurization: Use a press machine to apply the above force to the graphite powder for compaction, and maintain the pressure for 10 seconds; Decompression: After pressurization, the pressure is released to 3MPa, and the pressure is maintained for 10 seconds again to simulate the stress state of the powder in the real electrode; after decompression, the height h of the block material is measured to calculate the compaction density. This method can calculate the rebound amount of the powder compaction density, which is closer to the stress state in actual application. The calculation formula of compaction density is ρ=m / (h×S); where ρ is the compaction density, m is the mass of the powder material, h is the height of the block material, and S is the cross-sectional area of ​​the block material.

[0110] In some embodiments, the natural graphite satisfies at least one of the following conditions:

[0111] In the first negative electrode film layer, the mass proportion of the natural graphite is 95% to 99.5%, for example, about 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, etc.;

[0112] The volume average particle size Dv50 of the natural graphite is 5 μm to 25 μm, for example, about 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, etc.;

[0113] The specific surface area of ​​the natural graphite is 0.8 m 2 / g to 2.0m 2 / g, for example, about 0.8 m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2m 2 / g, etc.

[0114] The powder compaction density of the natural graphite under a force of 20000N is 1.5g / cm 3 Up to 1.9g / cm3 , for example, about 1.5 g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 wait.

[0115] When the mass proportion of natural graphite in the first negative electrode film layer is within the above range, it is beneficial for the battery to have a higher energy density. When the volume average particle size Dv50 of natural graphite is within the above range, it is beneficial for the negative electrode active material to better transmit ions and electrons, reduce the impedance of the pole piece, improve the battery's current carrying capacity and power, and reduce the temperature rise during charging and discharging. When the specific surface area of ​​natural graphite is within the above range, the particles are more tightly bonded, which can prevent the active material from falling off the collector surface during the cycle and enable the battery to have a higher rapid charging capability. When the powder compaction density of artificial graphite under a force of 20,000N is within the above range, the battery can have a higher energy density and improved cycle performance.

[0116] In some embodiments, the specific surface area of ​​the negative electrode material layer is 0.8 m 2 / g to 2.5m 2 / g, for example, about 0.8 m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2m 2 / g, 2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, etc.

[0117] When the specific surface area of ​​the negative electrode material layer is within the above range, there are more active sites on the negative electrode surface in contact with the electrolyte, which can enable the battery to have a higher rapid charging capability.

[0118] The specific surface area can be detected by the methods commonly used in the art. For example, a certain area of ​​the negative electrode plate is cut as a sample, nitrogen is used as the adsorbent, helium or hydrogen is used as the carrier gas, the two gases are mixed in a certain proportion, a specified relative pressure is reached, and then flowed through the solid material. When the sample tube is placed in liquid nitrogen for insulation, the sample physically adsorbs the nitrogen in the mixed gas, while the carrier gas is not adsorbed. At this time, an adsorption peak appears on the screen. When the liquid nitrogen is taken away, the sample tube is back to room temperature, the adsorbed nitrogen is desorbed, and a desorption peak appears on the screen. Finally, a known volume of pure nitrogen is injected into the mixed gas to obtain a correction peak. According to the peak area of ​​the correction peak and the desorption peak, the adsorption amount of the sample at the relative pressure can be calculated. By changing the mixing ratio of nitrogen and carrier gas, the adsorption amount under several relative pressures of nitrogen can be measured, so that the specific surface area can be calculated according to the BET formula.

[0119] In some embodiments, the compaction density of the negative electrode material layer is 1.4 g / cm 3 ~1.8g / cm 3 , for example, can be about 1.4 g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 wait.

[0120] When the negative electrode material layer has the above-mentioned higher compaction density, it is beneficial to improve the energy density of the battery. It is generally believed that higher compaction may lead to more significant expansion and rebound of the negative electrode material, thereby easily deteriorating the cycle performance. However, in the embodiment of the present application, under the above-mentioned compaction conditions, the rebound of the negative electrode active material during the battery cycle can also be well suppressed, so as not to deteriorate the cycle performance.

[0121] The compaction density of the negative electrode material layer can be detected by a method commonly used in the art. For example, the following method is used for detection herein: the compaction density is calculated by measuring the weight and thickness of the negative electrode material layer per unit area. The calculation formula for the compaction density is: compaction density of the negative electrode material layer = surface density of the negative electrode material layer / thickness of the negative electrode material layer.

[0122] In some embodiments, the first negative electrode film layer and the second negative electrode film layer further contain a binder;

[0123] The mass proportion of the binder in the first negative electrode film layer is smaller than the mass proportion of the binder in the second negative electrode film layer.

[0124] Compared with the first negative electrode film layer, the second negative electrode film layer has a higher degree of infiltration with the electrolyte, and has relatively more lithium insertion and extraction reactions during the charge and discharge process. Therefore, in the later stage of the battery cycle, the volume change of the second negative electrode film layer is greater. By using a higher content of binder in the second negative electrode film layer, it is helpful to improve the cohesion, thereby reducing the shedding of the second negative electrode film layer during the cycle.

[0125] In some embodiments, the binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0126] In some embodiments, the negative electrode plate further includes a primer layer disposed between the negative current collector and the negative electrode material layer. The primer layer may be a primer layer for batteries known in the art, and is generally formed by a primer slurry including a conductive agent, a binder, a dispersant, and deionized water. The conductive agent, the binder, and the dispersant may be a conductive agent, a binder, and a dispersant for batteries known in the art. By further including a primer layer, the bonding force between the active material and the current collector may be increased, so that the pole piece is not prone to powdering or film removal during the charge and discharge process.

[0127] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0128] In some embodiments, the negative electrode active material does not contain other materials except artificial graphite and natural graphite.

[0129] In some embodiments, the negative electrode active material may further include at least one of the following materials: soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0130] In some embodiments, the negative electrode material layer may optionally further include other conductive agents. For example, the first conductive agent and the second conductive agent may also independently include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene and carbon nanofibers.

[0131] In some embodiments, the negative electrode material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0132] In some embodiments, the negative electrode sheet may be prepared in the following manner: providing a slurry for forming a first negative electrode film layer, which comprises dispersing a first negative electrode active material, a first conductive agent, and any other components (such as a binder, etc.) in a solvent (such as deionized water), that is, preparing a first negative electrode slurry;

[0133] Providing a slurry for forming a second negative electrode film layer, which comprises dispersing a second negative electrode active material, a second conductive agent and any other components (such as a binder, etc.) in a solvent (such as deionized water), that is, preparing a second negative electrode slurry;

[0134] The first negative electrode slurry is coated on the negative electrode current collector, dried, and then coated with the second negative electrode slurry. After drying, cold pressing and other processes, a negative electrode sheet can be obtained.

[0135] [Positive electrode]

[0136] The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode material layer includes a positive electrode active material.

[0137] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0138] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0139] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may adopt a positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, sodium transition metal oxides, polyanionic compounds, Prussian blue compounds and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0140] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The sodium transition metal oxide is, for example, Na xMO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 <x≤1。

[0141] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si; n represents (YO4) n- valence state.

[0142] Polyanionic compounds can also be those with sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si, and n represents (YO4) n- valence state; the halogen may be at least one of F, Cl and Br.

[0143] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) m+ and an optional halogen anion. Y can be at least one of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0144] Polyanionic compounds include NaFePO4, Na3V2(PO4)3, NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0145] The Prussian blue compound may be a compound having sodium ions, transition metal ions and cyanide ions (CN-). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The Prussian blue compound may be, for example, Na a Me b Me'c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 <a≤2,0<b<1,0<c<1。

[0146] In some embodiments, the positive electrode material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0147] In some embodiments, the positive electrode material layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0148] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0149] [Electrolytes]

[0150] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0151] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0152] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0153] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0154] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0155] [Isolator]

[0156] In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0157] In some embodiments, the separator is a separator. The present application has no particular limitation on the type of separator, and any known separator with a porous structure having good chemical stability and mechanical stability can be selected.

[0158] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without special restrictions. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without special restrictions. The separator can be a separate component located between the positive and negative electrodes, or it can be attached to the surface of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be coated on the surface of the separator.

[0159] In some embodiments, the separator is a solid electrolyte, which is disposed between the positive electrode and the negative electrode and serves to transmit ions and isolate the positive and negative electrodes.

[0160] [Structure of electrode assembly]

[0161] The electrode assembly may be a wound structure, a laminated structure, or a mixed structure of a wound structure and a laminated structure.

[0162] In some embodiments, the electrode assembly is a wound structure, wherein the positive electrode sheet and the negative electrode sheet are wound into the wound structure.

[0163] In some embodiments, the electrode assembly is a laminate structure.

[0164] As an example, a plurality of positive electrode sheets and a plurality of negative electrode sheets may be provided respectively, and the plurality of positive electrode sheets and the plurality of negative electrode sheets may be alternately stacked.

[0165] As an example, a plurality of positive electrode sheets may be provided, and the negative electrode sheet is folded to form a plurality of stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0166] As an example, both the positive electrode sheet and the negative electrode sheet are folded to form a plurality of stacked folded sections.

[0167] As an example, a plurality of separators may be provided, each of which is provided between any adjacent positive electrode sheets or negative electrode sheets.

[0168] As an example, the separator may be disposed continuously, and may be disposed between any adjacent positive electrode sheets or negative electrode sheets by folding or winding.

[0169] In some embodiments, the shape of the electrode assembly can be cylindrical, flat, or polygonal.

[0170] In some embodiments, the electrode assembly is provided with tabs, which can lead current out of the electrode assembly. The tabs include a positive tab and a negative tab.

[0171] [shell]

[0172] In some embodiments, the battery cell may include a shell. The shell may be a steel shell, an aluminum shell, a plastic shell (such as polypropylene), a composite metal shell (such as a copper-aluminum composite shell) or an aluminum-plastic film, etc. In some embodiments, the shell may be a sealed structure or a non-sealed structure. As an example, when the shell is a non-sealed structure, the shell plays a role in protecting the electrode assembly, and a sealed bag is also included between the shell and the electrode assembly, and the sealed bag is used to encapsulate the electrode assembly and the electrolyte. Specifically, the sealed bag may be a bag-shaped insulating member or an aluminum-plastic film. When the shell is a sealed structure, it is used to encapsulate components such as the electrode assembly and the electrolyte.

[0173] As an example, the battery cell may be a cylindrical battery cell, a prismatic battery cell, a soft-pack battery cell or a battery cell of other shapes, and the prismatic battery cell includes a square-shell battery cell, a blade-shaped battery cell, a multi-prismatic battery, and the multi-prismatic battery is, for example, a hexagonal battery, etc., and the present application has no particular limitation. For example, Figure 1 The battery cell 5 is a square case as an example.

[0174] In some embodiments, reference Figure 2 The housing includes an end cap 53 and a shell 51, the shell 51 is provided with an opening, and the end cap 53 is provided to cover the opening. The shell 51 may be provided with one or more openings. One or more end caps 53 may also be provided. The positive electrode sheet, the negative electrode sheet and the separator may be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is encapsulated in a receiving cavity enclosed by the shell 51 and the end cap 53. The electrolyte is impregnated in the electrode assembly 52.

[0175] [Electrode terminal]

[0176] In some embodiments, at least one electrode terminal is disposed on the housing, and the electrode terminal is electrically connected to the electrode tab. The electrode terminal may be directly connected to the electrode tab, or may be indirectly connected to the electrode tab through a current collecting member. The electrode terminal may be disposed on an end cap, or may be disposed on the housing.

[0177] [Pressure relief mechanism]

[0178] In some embodiments, a pressure relief mechanism is provided on the housing, and the pressure relief mechanism is used to discharge the internal gas of the battery cell.

[0179] As an example, when the internal pressure or temperature of the battery cell reaches a predetermined threshold, it is actuated to release the internal pressure or temperature. When the internal pressure or temperature of the battery cell reaches a predetermined threshold, the pressure relief mechanism performs an action or a weak structure provided in the pressure relief mechanism is destroyed, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies according to different design requirements. The threshold may depend on one or more materials of the positive electrode plate, negative electrode plate, electrolyte and separator in the battery cell.

[0180] As an example, the pressure relief mechanism may be integrally formed with the housing.

[0181] As an example, the pressure relief mechanism may also be separately provided and connected to the housing.

[0182] The "actuation" mentioned in this application means that the pressure relief mechanism is in action or activated to a certain state, so that the internal pressure and temperature of the battery cell can be released. The action produced by the pressure relief mechanism may include but is not limited to: the components in the pressure relief mechanism move to form an exhaust channel, at least a part of the pressure relief mechanism ruptures, breaks, is torn or opened, etc. When the pressure relief mechanism is actuated, the high-temperature and high-pressure substances inside the battery cell will be discharged from the actuated part as emissions. In this way, the battery cell can be depressurized and cooled under controllable pressure or temperature, thereby avoiding potential more serious accidents.

[0183] In some embodiments, when the outer shell is a non-sealed structure, the pressure relief mechanism can be set as a through hole to discharge the gas inside the battery cell.

[0184] The emissions from the battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode sheets, fragments of separators, high-temperature and high-pressure gases produced by the reaction, flames, and the like.

[0185] Battery device

[0186] The battery apparatus mentioned in the embodiments of the present application may include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly may include multiple battery cells, which are connected in series, in parallel or in mixed connection through a busbar component.

[0187] In some embodiments, a battery cell assembly is generally formed by arranging a plurality of battery cells.

[0188] As an example, the battery cell assembly may be a battery module, which is formed by arranging and fixing a plurality of battery cells to form an independent module. As an example, the battery module may be formed by bundling a plurality of battery cells by a cable tie. Figure 3 This is a battery module 4 as an example. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner.

[0189] In some embodiments, the battery device may be a battery pack, which includes a case and one or more battery cell assemblies, wherein the battery cell assemblies are accommodated in the case.

[0190] As an example, the battery cell assembly may be a battery module, and the battery cell assembly may be accommodated in the box by fixing the battery module in the box. Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a box and a plurality of battery modules 4 disposed in the box. The box includes an upper box 2 and a lower box 3. The upper box 2 can cover the lower box 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0191] As an example, the battery cell assembly may also be housed in the case by directly fixing a plurality of battery cells to the case.

[0192] As an example, the box may include a first box and a second box. The first box and the second box are buckled together to form a closed space inside the box to accommodate the battery cell assembly. The closed here means covered or closed, which can be sealed or unsealed. The first box can be a top cover or a bottom plate.

[0193] As an example, the box body may include a top cover, a frame and a bottom plate. The top cover and the bottom plate are respectively connected to the frame, so that a closed space is formed inside the box body to accommodate the battery cell assembly.

[0194] In some embodiments, the box body can be used as a part of the chassis structure of the vehicle. For example, part of the box body can become at least a part of the floor of the vehicle, or part of the box body can become at least a part of the cross beam and longitudinal beam of the vehicle.

[0195] Electrical devices

[0196] The technical solutions described in the embodiments of the present application are applicable to various electrical devices that use battery cells, such as mobile phones, portable devices, laptop computers, electric vehicles, electric toys, electric tools, vehicles, ships and spacecraft, for example, spacecraft include airplanes, rockets, space shuttles and spacecraft, etc. Figure 6 The power consumption device is taken as an example, and the power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0197] Example 1

[0198] This embodiment provides a lithium ion battery, and the preparation method thereof includes:

[0199] (I) Negative electrode

[0200] 1. Premixed suspension

[0201] Suspension A:

[0202] Single-walled carbon nanotubes (3 nm in diameter, 300 μm in length, and 350 m in specific surface area) were used. 2 / g) and styrene-butadiene rubber (SBR) as a binder are added into a stirring tank in a mass ratio of 1:2 for stirring, and deionized water as a solvent is dispersedly added during the stirring process. After stirring evenly, a suspension A is prepared, in which the mass proportion of the single-walled carbon nanotubes is 5%.

[0203] Suspension B:

[0204] In addition to replacing single-walled carbon nanotubes with multi-walled carbon nanotubes (15 nm in diameter, 30 μm in length, and 250 m in specific surface area), 2 / g), a suspension B was prepared according to the same preparation method as the suspension A, wherein the weight proportion of the multi-walled carbon nanotubes was 5%.

[0205] 2. Preparation of negative electrode slurry

[0206] Negative electrode slurry A:

[0207] Natural graphite (particle size Dv50: 17 μm, specific surface area: 1.8 m 2 / g, the compacted density of the powder under a force of 20000N is 1.6g / cm 3 ), carboxymethyl cellulose (CMC) as a thickener, and suspension A are mixed and stirred evenly to prepare negative electrode slurry A, wherein the mass ratio of natural graphite, thickener, binder, and single-walled carbon nanotubes is 95:2:2:1.

[0208] Negative electrode slurry B:

[0209] Artificial graphite (particle size Dv50 of 10 μm, specific surface area of ​​1.0 m 2 / g, the compacted density of the powder under a force of 20000N is 1.55g / cm 3 ), carboxymethyl cellulose (CMC) as a thickener, and suspension B are mixed and stirred evenly to prepare negative electrode slurry B, wherein the mass ratio of artificial graphite, thickener, binder, and multi-walled carbon nanotubes is 95:2:2:1.

[0210] 3. Preparation of negative electrode sheet

[0211] The negative electrode slurry A used to form the first negative electrode film layer is applied to the surface of the copper foil used as the negative electrode current collector, and then dried to obtain the negative electrode sheet A; the negative electrode slurry B used to form the second negative electrode film layer is applied to the surface of the negative electrode sheet A, and then dried, cold pressed, and cut to obtain the negative electrode sheet. The thickness of the first negative electrode film layer is 80 μm, and the thickness of the second negative electrode film layer is 80 μm; the specific surface area of ​​the negative electrode sheet is 1.5 m 2 / g, compacted density is 1.6g / cm 3 .

[0212] (ii) Positive electrode

[0213] Lithium iron phosphate (LiFePO4) as the positive electrode active material, PVDF as the binder and conductive carbon as the conductive agent are dispersed and dissolved in N-methyl-2-pyrrolidone (NMP) as a solvent in a mass ratio of 97:2:1 to form a uniformly dispersed positive electrode slurry, and then the positive electrode slurry is evenly coated on aluminum foil as the positive electrode current collector, and then dried, cold pressed and cut to obtain the positive electrode sheet.

[0214] (III) Electrolyte

[0215] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly in a volume ratio of 3:7, and LiPF6 with a final concentration of 12.5% ​​was added and dissolved in the organic solvent and stirred evenly.

[0216] (IV) Isolation Film

[0217] Polypropylene film is used as the isolation film.

[0218] (V) Lithium-ion battery

[0219] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrodes to play an isolating role, and then wound to obtain a bare cell, the tabs are welded to the bare cell, and the bare cell is placed in an aluminum shell and baked at 60°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery then goes through the processes of static, hot and cold pressing, formation, shaping, capacity testing, etc. to obtain a lithium-ion battery product.

[0220] The following tests were performed and the results are recorded in Table 1 and Table 5:

[0221] 1. Specific surface area of ​​negative electrode material layer

[0222] Cut a 0.8cm×0.8cm negative electrode piece as a sample and put it into a sample tube. Nitrogen is used as the adsorbent and helium is used as the carrier gas. The two gases are mixed in a certain ratio of nitrogen and helium to reach a specified relative pressure, and then flow through the solid material. When the sample tube is placed in liquid nitrogen for insulation, the sample physically adsorbs the nitrogen in the mixed gas, while the carrier gas is not adsorbed. At this time, an adsorption peak appears on the screen. When the liquid nitrogen is taken away, the sample tube is back to room temperature, and the adsorbed nitrogen desorbs, and a desorption peak appears on the screen. Finally, a known volume of pure nitrogen is injected into the mixed gas to obtain a correction peak. According to the peak area of ​​the correction peak and the desorption peak, the adsorption amount of the sample at the relative pressure can be calculated. By changing the mixing ratio of nitrogen and carrier gas, the adsorption amount under several relative pressures of nitrogen can be measured, so that the specific surface area can be calculated according to the BET formula.

[0223] 2. Compaction density of negative electrode material layer

[0224] The compaction density is calculated by measuring the weight and thickness of the negative electrode material layer. The calculation formula of the compaction density is: compaction density of the negative electrode material layer = surface density of the negative electrode material layer / thickness of the negative electrode sheet.

[0225] 3. Negative electrode cohesion test:

[0226] Take the negative electrode and cut a sample with a width of 30mm and a length of 90mm with a blade. Stick a low-viscosity green tape with a width of 20mm and a length greater than the sample length of 80mm flat on the test surface, and roll it three times in the same direction with a roller. Turn on the power of the tensile testing machine (Shenzhen Sansi Testing Equipment Co., Ltd.), the indicator light is on, adjust the limit block to the appropriate position, fix the sample vertically on the tensile testing machine fixture, set the force sensor parameters to 500N, pre-tension, reset the force and displacement to zero, start the test and record the test data.

[0227] 4. Cycle 500cls expansion force test

[0228] Two rigid steel plates are used to restrain the battery cell and the rigid pressure sensor at a certain distance to simulate the stress of the battery in the module. The rigid pressure sensor is sandwiched between the third steel plate and the battery cell. The battery is charged and discharged in a cycle test under the above restraint method. During the process, the expansion force of the battery cell cycle is measured through the sensor acquisition system.

[0229] 5. Battery DCR test

[0230] At 25°C, charge the battery to 3.8V at 1 / 3C constant current, then charge at 3.8V constant voltage to a current of 0.05C, leave for 5 minutes, and then discharge at 1 / 3C to 2.0V. The resulting capacity is recorded as the initial capacity C0. Charge the battery to 0.5C0 at 1 / 3C0, record the voltage as V1 after 30 minutes of rest, and then discharge at 3C0 for 30S, record the terminal voltage V2, and the 30SDCR of the fresh battery is R = (V1-V2) / 3C0. After the above battery is charged at 1 / 3C and discharged at 1 / 3C for 1000 cycles, the 30SDCR is tested again with the same steps, that is, the 30SDCR of the battery after 1000 cycles is obtained, and the DCR growth rate is calculated.

[0231] Comparative Example 1

[0232] The same preparation and testing methods as in Example 1 were used except that the second film layer was not included and the thickness of the first film layer was 160 μm. The results are shown in Table 1.

[0233] Comparative Example 2

[0234] The same preparation and testing methods as in Example 1 were used except that the first film layer was not included and the thickness of the second film layer was 160 μm. The results are shown in Table 1.

[0235] Table 1

[0236]

[0237] By comparing Example 1 with Comparative Examples 1 to 2, it can be seen that by adopting the first negative electrode film layer and the second negative electrode film layer, the cohesion of the negative electrode sheet is increased, and the cycle performance of the battery is improved.

[0238] Embodiments 2 to 4

[0239] Except that the thicknesses of the first negative electrode film layer and the second negative electrode film layer are as shown in Table 2, the preparation and testing are carried out in the same manner as in Example 1. The results are as shown in Table 2.

[0240] Table 2

[0241]

[0242] From the above results, it can be seen that when the ratio of the thickness of the first negative electrode film layer to the second negative electrode film layer is 3-7:3-7, the cycle performance can be significantly improved compared with Comparative Examples 1 and 2. In particular, when the second negative electrode film layer is thicker, the battery can still have a lower DCR after cycling, reflecting a better cycle life.

[0243] Embodiments 5 to 7

[0244] The preparation and testing were carried out in the same manner as in Example 1, except that the ratio of the binder to the carbon nanotubes in the suspension and the ratio of each group in the negative electrode slurry were adjusted so that the mass ratio of each component in the negative electrode sheet was as shown in Table 3. The results are shown in Table 3.

[0245] Table 3

[0246]

[0247] By comparing Example 5 and Example 7 with Example 1, it can be seen that when the mass proportion of the binder in the second negative electrode film layer is higher than the mass proportion of the binder in the first negative electrode film layer, it is further beneficial to improve the cohesion of the electrode sheet and improve the problem of cyclic expansion.

[0248] Embodiments 8 to 11

[0249] Except that the parameters of the carbon nanotubes are shown in Table 4, the same method as in Example 1 was used for preparation and testing. The results are shown in Table 4.

[0250] Table 4

[0251]

[0252]

[0253] Embodiments 12 to 15

[0254] Except that the relevant parameters of natural graphite, artificial graphite and negative electrode sheet are shown in Table 5, the same preparation and testing as in Example 1 are carried out, and the results are shown in Table 5.

[0255] Table 5

[0256]

[0257] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A battery cell, characterized in that: It includes a positive electrode sheet, a separator and a negative electrode sheet; The negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; the negative electrode material layer includes a first negative electrode film layer and a second negative electrode film layer; the first negative electrode film layer is closer to the negative electrode current collector than the second negative electrode film layer; The first negative electrode film layer includes a first negative electrode active material and a first conductive agent, the first negative electrode active material includes natural graphite, and the first conductive agent includes single-walled carbon nanotubes; The second negative electrode film layer includes a second negative electrode active material and a second conductive agent, wherein the second negative electrode active material includes artificial graphite, and the second conductive agent includes multi-walled carbon nanotubes.

2. The battery cell according to claim 1, characterized in that: The thickness ratio of the first negative electrode film layer to the second negative electrode film layer is 3-7:3-7.

3. The battery cell according to claim 1, characterized in that: The thickness of the second negative electrode film layer is greater than the thickness of the first negative electrode film layer.

4. The battery cell according to any one of claims 1 to 3, characterized in that: In the second negative electrode film layer, the mass proportion of the multi-walled carbon nanotubes is 0.05% to 2%.

5. The battery cell according to any one of claims 1 to 4, characterized in that: The multi-walled carbon nanotubes at least meet at least one of the following conditions: The diameter of the multi-walled carbon nanotubes is 5 to 80 nm; The length of the multi-walled carbon nanotubes is 1 to 50 μm; The specific surface area of ​​the multi-walled carbon nanotubes is 150 to 300 m 2 / g.

6. The battery cell according to any one of claims 1 to 5, characterized in that: In the first negative electrode film layer, the mass proportion of the single-walled carbon nanotubes is 0.05% to 1%.

7. The battery cell according to any one of claims 1 to 6, characterized in that: The single-walled carbon nanotubes at least meet at least one of the following conditions: The diameter of the single-walled carbon nanotube is 1 to 5 nm; The length of the single-walled carbon nanotube is 1 to 500 μm; The specific surface area of ​​the single-walled carbon nanotube is 250 to 500 m 2 / g.

8. The battery cell according to any one of claims 1 to 7, characterized in that: The artificial graphite satisfies at least one of the following conditions: In the second negative electrode film layer, the mass proportion of the artificial graphite is 95% to 99.5%; The volume average particle size Dv50 of the artificial graphite is 5 μm to 20 μm; The specific surface area of ​​the artificial graphite is 0.5m 2 / g to 1.3m 2 / g; The powder compaction density of the artificial graphite under a force of 20000N is 1.5g / cm 3 Up to 1.9g / cm 3 .

9. The battery cell according to any one of claims 1 to 8, characterized in that: The natural graphite satisfies at least one of the following conditions: In the first negative electrode film layer, the mass proportion of the natural graphite is 95% to 99.5%; The volume average particle size Dv50 of the natural graphite is 5 μm to 25 μm; The specific surface area of ​​the natural graphite is 0.8 m 2 / g to 2.0m 2 / g; The powder compaction density of the natural graphite under a force of 20000N is 1.5g / cm 3 Up to 1.9g / cm 3 .

10. The battery cell according to any one of claims 1 to 9, characterized in that: The specific surface area of ​​the negative electrode material layer is 0.8 m 2 / g to 2.5m 2 / g.

11. The battery cell according to any one of claims 1 to 10, characterized in that: The compaction density of the negative electrode material layer is 1.4 g / cm 3 ~1.8g / cm 3 .

12. The battery cell according to any one of claims 1 to 11, characterized in that: The first negative electrode film layer and the second negative electrode film layer further contain a binder; The mass proportion of the binder in the first negative electrode film layer is smaller than the mass proportion of the binder in the second negative electrode film layer.

13. A battery device, characterized in that: A battery cell comprising the battery cell according to any one of claims 1 to 12.

14. An electrical device, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 12, or the battery device according to claim 13.

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