Battery

Abstract

The present invention relates to the field of batteries, and in particular to a battery. The battery of the present invention comprises a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a first carbon nanotube, a recessed portion is formed on the surface of the negative electrode sheet, and a ratio of the depth of the recessed portion to the tube diameter of the first carbon nanotube is (300-5,000):1. The battery of the present invention can effectively mitigate the lithium precipitation problem of a negative electrode sheet, and has both high energy density and fast charging capability.

Description

Battery Technical Field

[0001] The present disclosure relates to the field of batteries, and in particular to batteries. Background Art

[0002] With the advent of the 5G era and the rapid development of lithium-ion battery technology, people have put forward higher requirements for the energy density and fast charging capabilities of lithium-ion batteries. High-energy-density fast-charging lithium batteries are the development trend of consumer lithium-ion batteries. In order to improve the energy density, related technologies usually increase the thickness of the positive and negative electrodes, which makes it easy for lithium ions to gather on the surface of the negative electrode, causing congestion, which seriously affects the service life of the lithium-ion battery. In order to improve this situation, holes are usually punched on the surface of the negative electrode. In addition, in order to improve the fast charging capability, related technologies usually use carbon nanotubes with better conductivity as a conductive agent. However, this will aggravate the lithium deposition phenomenon on the surface of the negative electrode. Even if holes are punched on the surface of the negative electrode, it cannot effectively alleviate the lithium deposition problem.

[0003] Therefore, it is very important to invent a battery that has both high energy density and fast charging capability and has a low risk of lithium plating. Summary of the Invention

[0004] The present disclosure aims to overcome the aforementioned problems of the prior art and provide a battery. By limiting the ratio of the diameter of the carbon nanotubes in the positive electrode sheet to the depth of the recessed portion on the negative electrode sheet, the battery disclosed herein can effectively alleviate the lithium deposition problem in the negative electrode sheet, thereby achieving both high energy density and fast charging capability.

[0005] The present disclosure provides a battery, which includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a first carbon nanotube. The surface of the negative electrode sheet has a concave portion, and the ratio of the depth of the concave portion to the diameter of the first carbon nanotube is (300-5000):1.

[0006] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art: the battery disclosed in the present disclosure limits the ratio of the diameter of the carbon nanotubes in the positive electrode sheet to the depth of the recess in the negative electrode sheet, so that the lithium insertion speed of the negative electrode sheet matches the lithium removal speed of the positive electrode sheet, that is, it can balance the kinetic performance of the two, thereby improving the problem of lithium deposition in the negative electrode sheet.

[0007] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG1 is a schematic diagram showing the width of a groove in an example of the present disclosure.

[0009] FIG2 is a schematic diagram showing the spacing of grooves in an example of the present disclosure.

[0010] FIG3 is a schematic diagram showing the morphology of a hole in an example of the present disclosure.

[0011] FIG4 is a schematic diagram of a groove in an example of the present disclosure. DETAILED DESCRIPTION

[0012] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0013] The present disclosure provides a battery, which may include a positive electrode sheet and a negative electrode sheet. The positive electrode sheet may include a first carbon nanotube. The surface of the negative electrode sheet may have a recess, and the ratio of the depth of the recess to the diameter of the first carbon nanotube may be (300-5000):1, for example, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 1000:1, 1100:1, 1200:1, 1300:1, 1400:1, 1500:1, 1600:1, 1700:1, 1800:1, 1900:1, 2000:1, 3000:1, 4000:1 or 5000:1.

[0014] In order to improve the energy density and fast charging capability of the battery, the related technology usually increases the thickness of the electrode and uses carbon nanotubes with excellent conductive properties as a conductive agent. However, this will cause lithium ions to accumulate on the surface of the negative electrode and lithium plating will occur, which will seriously affect the service life of the battery. Even if holes are punched on the surface of the negative electrode, the problem of lithium plating cannot be effectively alleviated. The inventors of the present disclosure have found through extensive research that by controlling the diameter of the carbon nanotubes in the positive electrode and the depth of the recess in the negative electrode so that the ratio of the two meets a specific range, the battery can improve the problem of lithium plating on the negative electrode while taking into account both energy density and fast charging capability. The reason may be that: setting a recess on the surface of the negative electrode sheet can improve the wettability of the electrolyte to the negative electrode active material near the negative electrode current collector, shorten the transmission distance of lithium ions, improve the kinetic performance of the negative electrode sheet, and thus increase the embedding speed of lithium ions in the negative electrode sheet; while carbon nanotubes play a role in enhancing the conductivity of the positive electrode sheet, and carbon nanotubes have a certain capillary effect, which can store electrolyte, improve the wetting effect of the electrolyte on the positive electrode sheet, increase the transmission speed of lithium ions in the positive electrode sheet, and improve the kinetic performance of the positive electrode sheet. However, at this time, the kinetic performance of the positive electrode sheet may not match the kinetic performance of the negative electrode sheet. The kinetic performance of the positive electrode sheet is better than that of the negative electrode sheet, that is, the release rate of lithium ions in the positive electrode sheet is greater than the embedding rate of lithium ions in the negative electrode sheet, resulting in the lithium ions not being able to be embedded in the negative electrode sheet in a timely manner, but accumulating on the surface of the negative electrode sheet, causing congestion, which further leads to the occurrence of lithium precipitation. If the ratio of the diameter of the carbon nanotubes in the positive electrode sheet to the depth of the recess in the negative electrode sheet is controlled, the kinetic performance of the positive electrode sheet can match the kinetic performance of the negative electrode sheet, that is, the speed at which the positive electrode sheet releases lithium ions matches the speed at which the negative electrode sheet embeds lithium ions, which significantly improves the fast charging capability of the battery and further improves the problem of lithium plating at the negative electrode.

[0015] In one embodiment, the ratio of the depth of the recess to the diameter of the first carbon nanotube is (600-2050):1. When the ratio of the depth of the recess to the diameter of the first carbon nanotube is (600-2050):1, the dynamic performance of the positive electrode sheet can be further matched with the dynamic performance of the negative electrode sheet, the fast charging capability of the battery is improved, and the lithium plating problem of the negative electrode sheet is alleviated.

[0016] In this disclosure, the depth of the recess has the conventional meaning in the art, and refers to the maximum vertical distance from any point within the recess to the surface of the negative electrode sheet. The depth of the recess can be measured by conventional methods in the art, such as using a 3D profilometer or a scanning electron microscope (SEM). For example, 20 recesses can be randomly selected from the entire negative electrode sheet, or all recesses can be selected, and the depth of each recess can be measured and averaged.

[0017] In the present disclosure, the diameter of the first carbon nanotube can be 2nm-20nm, for example, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm or 20nm.

[0018] In one example, the diameter of the first carbon nanotubes is 6 nm-16 nm.

[0019] Under the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the diameter of the first carbon nanotube is within a specific range, it can not only improve the overall conductivity of the battery, but also will not increase the risk of lithium plating at the negative electrode. When the diameter of the first carbon nanotube is too small (for example, less than 2nm), its capillary effect is not obvious, and it cannot store enough electrolyte, which will affect the transmission speed of lithium ions and reduce the kinetic performance of the positive electrode sheet, thereby reducing the conductivity of the battery; when the diameter is too large (for example, greater than 20nm), its capillary effect is also not obvious. Although it can store enough electrolyte compared to when the diameter is too small, the excess electrolyte will aggravate the occurrence of side reactions between the electrolyte and the positive electrode active material, thereby affecting the cycle capacity retention rate of the battery.

[0020] In the present disclosure, the diameter of the first carbon nanotube refers to the outer diameter of the first carbon nanotube, which can be obtained by conventional methods in the field, such as testing using SEM or transmission electron microscopy (TEM), and measuring the outer diameter of the carbon nanotube using a length measuring tool. For example, at least 20 carbon nanotubes are taken within the range of 100 μm×100 μm, the outer diameter of each carbon nanotube is measured, and the average value is taken.

[0021] In the present disclosure, the depth of the recess may be 5 μm-65 μm, for example, 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, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm or 65 μm.

[0022] In one example, the depth of the recess is 8 μm-30 μm.

[0023] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, the depth of the recess is within a specific range, which can not only improve the wettability of the electrolyte to the negative electrode active material, thereby increasing the insertion and extraction speed of lithium ions and improving the kinetic performance of the negative electrode sheet; it can also improve the utilization rate of the negative electrode active material, thereby improving the energy density of the battery.

[0024] <Positive electrode>

[0025] In the present disclosure, the ratio of the length of the first carbon nanotube to the depth of the recess may be (0.03-4):1, for example, 0.03:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 2:1, 3:1 or 4:1.

[0026] Under the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, by controlling the length of the carbon nanotubes in the positive electrode sheet and the depth of the recess in the negative electrode sheet so that the ratio of the two meets the specific range, the battery can further improve the problem of negative electrode lithium plating while taking into account both energy density and fast charging capability. The reason may be that: the provision of recesses on the surface of the negative electrode sheet can improve the wettability of the electrolyte to the negative electrode active material near the negative electrode current collector, shorten the transmission distance of lithium ions, improve the kinetic performance of the negative electrode sheet, and thus increase the insertion speed of lithium ions in the negative electrode sheet; and the carbon nanotubes play a role in enhancing the electrical conductivity in the positive electrode sheet, especially their length, which plays a vital role in improving the electrical conductivity, can improve the kinetic performance of the positive electrode sheet, and thus increase the release speed of lithium ions in the positive electrode sheet. If the ratio of the length of the carbon nanotubes in the positive electrode sheet to the depth of the recess in the negative electrode sheet is controlled, the two can produce an unexpected synergistic effect, so that the kinetic performance of the positive electrode sheet can be further matched with the kinetic performance of the negative electrode sheet, that is, the speed at which the positive electrode sheet releases lithium ions matches the speed at which the negative electrode sheet embeds lithium ions, significantly improving the battery's fast charging capability and effectively improving the problem of lithium plating in the negative electrode.

[0027] In one example, a ratio of the length of the first carbon nanotube to the depth of the recess is (0.1-2):1.

[0028] In the present disclosure, the length of the first carbon nanotube can be obtained by testing using conventional methods in the art, such as using SEM or TEM testing, and measuring the length of the carbon nanotube using a length measuring tool, for example, taking at least 20 carbon nanotubes within the range of 100 μm×100 μm, measuring the length of each carbon nanotube, and taking the average value.

[0029] In the present disclosure, the length of the first carbon nanotubes can be 0.2μm-32μm, for example, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm or 32μm.

[0030] In one example, the length of the first carbon nanotubes is 5 μm-20 μm.

[0031] Under the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, the length of the first carbon nanotube is within a specific range, which can not only improve the overall conductivity of the battery, but also will not increase the risk of lithium plating at the negative electrode. When the length of the first carbon nanotube is too short (for example, less than 0.2 μm), the overall conductivity of the battery will be affected; when the length of the first carbon nanotube is too long (for example, greater than 32 μm), it will be interrupted during the preparation of the positive electrode active material layer slurry, and the resulting cross-section will increase the risk of side reactions and affect the battery's cycle capacity retention rate; in addition, excessive length will cause the first carbon nanotubes to agglomerate, thereby affecting the battery's conductivity.

[0032] In the present disclosure, the first carbon nanotube may include at least one of a single-walled carbon nanotube and a multi-walled carbon nanotube.

[0033] In one example, the first carbon nanotubes include a combination of the single-walled carbon nanotubes and the multi-walled carbon nanotubes.

[0034] In the first carbon nanotubes, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes may be 1:(5-15), for example, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14 or 1:15.

[0035] In one example, in the first carbon nanotubes, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 1:(6-10).

[0036] Under the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the first carbon nanotube includes a combination of single-walled carbon nanotubes and multi-walled carbon nanotubes, it has a better effect than using single-walled carbon nanotubes or multi-walled carbon nanotubes alone. The reason may be that: through a large number of studies, it has been found that the conductivity of single-walled carbon nanotubes is much higher than that of multi-walled carbon nanotubes (the conductivity of single-walled carbon nanotubes per unit mass is about 10 times that of multi-walled carbon nanotubes). However, when the amount of single-walled carbon nanotubes is increased, they are more likely to agglomerate, resulting in their conductivity not being fully utilized; while the conductivity of multi-walled carbon nanotubes is relatively weak, it is much stronger than other conductive agents (such as conductive carbon black, etc.), and its dispersion ability is better; when the two are mixed, the easily dispersed multi-walled carbon nanotubes can disperse the agglomerated single-walled carbon nanotubes; so that the two interact with each other to obtain a good dispersion and an excellent conductive network; therefore, using the two and controlling the ratio can achieve an unexpected synergistic effect. The inventors of the present disclosure further discovered that single-walled carbon nanotubes have stronger conductivity than multi-walled carbon nanotubes, but single-walled carbon nanotubes are more prone to gassing. Controlling the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes can significantly improve the conductivity of the battery without affecting the battery's cycle performance.

[0037] In the present disclosure, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0038] The positive electrode conductive agent may include the first carbon nanotubes. Based on the total weight of the positive electrode conductive agent, the first carbon nanotubes may be present in an amount of 0.1% to 30%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 5%, 10%, 15%, 20%, 25%, or 30%.

[0039] In one example, based on the total weight of the positive electrode conductive agent, the content of the first carbon nanotubes is 9%-18%.

[0040] In one example, based on the total weight of the positive electrode conductive agent, the content of the first carbon nanotubes is 10%-15%.

[0041] Under the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotubes is within a specific range, the first carbon nanotubes in the positive electrode conductive agent have a specific mass content. Within this range, the positive electrode sheet has excellent conductivity. When the content of the first carbon nanotubes is too low (for example, less than 0.1%), after dispersion, the conductive agent is absent from the surface and vicinity of some of the positive electrode active materials, resulting in an imperfect conductive network of the entire positive electrode sheet, thereby reducing its conductivity and hindering the improvement of the battery's conductivity. When the content of the first carbon nanotubes is too high (for example, greater than 30%), the conductive agent will agglomerate, resulting in incomplete dispersion, which also affects the improvement of the battery's conductivity.

[0042] In the present disclosure, the positive electrode conductive agent may further include at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, and carbon fiber.

[0043] In one example, the positive electrode conductive agent includes conductive carbon black and the first carbon nanotubes.

[0044] In the present disclosure, the positive electrode active material may include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, and a lithium-rich manganese-based material. The positive electrode binder may include at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, polyacrylic acid, and polyethylene oxide.

[0045] In the present disclosure, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 80%-99.8% (for example, 80%, 85%, 90%, 95% or 99.8%), the content of the positive electrode conductor can be 0.1%-10% (for example, 10%, 7.5%, 5%, 2.5% or 0.1%), and the content of the positive electrode binder can be 0.1%-10% (for example, 10%, 7.5%, 5%, 2.5% or 0.1%).

[0046] In one example, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material is 90%-99%, the content of the positive electrode conductor is 1%-5%, and the content of the positive electrode binder is 1%-5%.

[0047] <Negative electrode>

[0048] In the present disclosure, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer on at least one side of the negative electrode current collector, and the recess may be located on the surface of the negative electrode active material layer.

[0049] In the present disclosure, the recessed portion extends in a direction approaching the negative electrode current collector.

[0050] In the present disclosure, the negative electrode active material layer may include a negative electrode active material. The negative electrode active material may include at least one of a carbon-based material and a silicon-based material. The carbon-based material may include at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon. The silicon-based material may include at least one of silicon, silicon-oxygen, silicon-carbon, and a silicon alloy.

[0051] In the present disclosure, the terms "silicon oxide" and "silicon carbon" have conventional meanings in the art. It is generally believed that the term "silicon oxide" refers to silicon oxide; and the term "silicon carbon" refers to a silicon-carbon composite material.

[0052] In one example, the silicon carbon includes a material in which silicon or partially oxidized silicon is filled (including partially filled or completely filled) in pores of porous amorphous carbon or porous crystalline carbon.

[0053] In one embodiment, the silicon-carbon comprises a material formed by coating carbon on the surface of silicon or partially oxidized silicon. Specific silicon-based materials have a certain inhibitory effect on battery expansion.

[0054] In one example, the negative electrode active material includes a carbon-based material.

[0055] In one example, the negative electrode active material includes a carbon-based material and a silicon-based material.

[0056] The negative electrode sheet (especially the silicon-doped negative electrode) will expand / contract in volume during the battery charge and discharge cycle, which will cause battery deformation and a decrease in conductivity. The inventors of the present disclosure have found that, under the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, by providing a recess in the negative electrode active material layer, the volume expansion of the negative electrode active material can be effectively alleviated, especially the volume expansion effect of silicon-based materials is more obvious. The recess provides space for the expansion of the negative electrode active material, so that the expansion part in the vertical direction is converted into expansion in the horizontal direction, thereby improving the expansion deformation of the battery.

[0057] In the present disclosure, based on the total weight of the negative electrode active material, the content of the silicon-based material can be 1%-65%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or 65%.

[0058] In one embodiment, based on the total weight of the negative electrode active material, the content of the silicon-based material is 3%-45%.

[0059] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the mass content of the silicon-based material in the negative electrode active material is within a specific range, the surface capacity of the negative electrode sheet can be increased, and the amount of negative electrode active material in the negative electrode sheet can be reduced, thereby reducing the thickness of the negative electrode sheet, improving the utilization rate of the negative electrode active material, further reducing the transmission path of lithium ions, and thereby improving the kinetic performance and energy density of the lithium-ion battery.

[0060] In the present disclosure, the negative electrode active material layer may further include a negative electrode conductive agent. The negative electrode conductive agent may include a second carbon nanotube.

[0061] When the ratio of the recess depth to the diameter of the first carbon nanotubes is within a specific range, the inclusion of carbon nanotubes in the negative electrode conductive agent can enhance the conductivity of the silicon-containing negative electrode sheet and further inhibit its expansion. This may be due to the inherently weak conductivity of the silicon-based material. Furthermore, volume expansion / contraction disrupts the structure, creating voids on the surface of the silicon-based material. This affects electrical contact with the negative electrode conductive agent, further deteriorating the conductivity of the negative electrode sheet. When the negative electrode conductive agent includes carbon nanotubes, firstly, the carbon nanotubes have excellent electrical conductivity, which can make up for the poor electrical conductivity of silicon-based materials and enhance the reactivity of silicon-based materials; secondly, the carbon nanotubes have a tubular structure and have a certain toughness. Their tubular structures can overlap with each other to form an elastic conductive network on the surface of the silicon-based material. This conductive network can not only enhance the electrical conductivity of the silicon-based material, but also inhibit the volume expansion of the silicon-based material to a certain extent. Moreover, since the conductive network has a certain elasticity, it can also reduce the gaps caused by the volume expansion / contraction of the silicon-based material, thereby further enhancing the electrical conductivity of the negative electrode sheet; finally, since the carbon nanotubes have a certain capillary effect and can store electrolyte, the conductive network formed by them can significantly improve the wettability of the electrolyte to the negative electrode sheet, increase the transmission speed of lithium ions, and enable lithium ions to be evenly embedded in the silicon-based material, avoiding lithium plating due to uneven lithium embedding.

[0062] In the present disclosure, the length of the second carbon nanotubes can be 0.2μm-32μm, for example, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm or 32μm.

[0063] In one example, the length of the second carbon nanotubes is 10 μm-20 μm.

[0064] Under the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, the length of the second carbon nanotube is within a specific range, which can not only improve the conductivity of the negative electrode sheet, but also further improve the lithium plating problem. When the length of the second carbon nanotube is too short (for example, less than 0.2 μm), it cannot form an effective conductive network on the surface of the silicon-based material, which will affect the conductivity of the negative electrode sheet and the inhibitory effect on the volume expansion of the silicon-based material; when the length of the second carbon nanotube is too long (for example, greater than 32 μm), it will affect the toughness of the conductive network formed by it, thereby affecting its inhibitory effect on the volume expansion of the silicon-based material; in addition, too long a length will cause the second carbon nanotubes to agglomerate, making it impossible to form an effective conductive network, which will also affect the conductivity of the negative electrode sheet and the inhibitory effect on the volume expansion of the silicon-based material.

[0065] In the present disclosure, the length of the second carbon nanotube can be measured by conventional methods in the art, such as using SEM or TEM, and measuring the length of the carbon nanotube by a length measuring tool, for example, taking at least 20 carbon nanotubes within the range of 100 μm×100 μm, measuring the length of each carbon nanotube, and taking the average value.

[0066] In the present disclosure, the diameter of the second carbon nanotubes can be 2nm-25nm, for example, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm or 25nm.

[0067] In one example, the diameter of the second carbon nanotubes is 5 nm-18 nm.

[0068] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, the diameter of the second carbon nanotube has a greater influence on the toughness of the conductive network formed by it. When it is within the specific range, the conductive network formed has strong toughness and good elasticity, which can effectively inhibit the expansion of the silicon-based material and reduce the gaps formed on the surface of the silicon-based material due to volume expansion / contraction, thereby improving the conductive performance of the negative electrode sheet.

[0069] In the present disclosure, the diameter of the second carbon nanotube refers to the outer diameter of the second carbon nanotube, which can be obtained by conventional methods in the field, such as SEM or TEM testing, and measuring the outer diameter of the carbon nanotube by a length measuring tool. For example, at least 20 carbon nanotubes are taken within the range of 100 μm×100 μm, the outer diameter of each carbon nanotube is measured, and the average value is taken.

[0070] In the present disclosure, the depth of the recess and the diameter of the second carbon nanotube can be (400-5000):1, for example, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 1000:1, 1500:1, 2000:1, 2500:1, 3000:1, 3500:1, 4000:1, 4500:1 or 5000:1.

[0071] In one example, the ratio of the depth of the concave portion to the diameter of the second carbon nanotube is (800-1670):1.

[0072] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the depth of the recess and the diameter of the second carbon nanotube satisfy the above relationship, the dynamic performance of the negative electrode sheet can be further improved, especially when the negative electrode sheet includes a silicon-based material. This may be because the recess is set on the negative electrode sheet so that the lithium ions released from the positive electrode sheet do not accumulate on the surface of the negative electrode sheet, but quickly migrate to the negative electrode active material near the negative electrode current collector through the recess. They can also quickly embed into the active material on the inner wall of the recess through the inner wall of the recess; however, the conductivity of the silicon-based material is weak. In order to increase its lithium insertion speed and improve its lithium insertion uniformity, it is necessary to control the depth of the recess and the diameter of the second carbon nanotube within a certain range.

[0073] In the present disclosure, the ratio of the length of the second carbon nanotube to the depth of the recess may be (0.03-3):1, for example, 0.03:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 2:1 or 3:1.

[0074] In one example, a ratio of the length of the second carbon nanotube to the depth of the recess is (0.3-1.5):1.

[0075] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the length of the second carbon nanotube and the depth of the recess satisfy the above relationship, the ability to suppress the expansion of the silicon-based material can be further improved. This may be because the recess is set for the negative electrode sheet so that the lithium ions released from the positive electrode sheet do not accumulate on the surface of the negative electrode sheet, but migrate to the negative electrode active material through the recess. Therefore, the depth of the recess is related to the position where the lithium ions are embedded in the negative electrode active material layer, and the position where the lithium ions are embedded in the negative electrode active material layer and the length of the carbon nanotube have a significant effect on the expansion of the silicon-based material; therefore, in order to improve the uniformity of lithium insertion and minimize the expansion of the silicon-based material, it is necessary to control the length of the second carbon nanotube and the depth of the recess within a certain range.

[0076] In the present disclosure, the shortest distance between the silicon-based particles located below the concave portion and a straight line parallel to the negative electrode current collector at the bottom of the concave portion is 3 μm to 15 μm.

[0077] In the present disclosure, the "silicon-based particles located below the recess" refer to the silicon-based particles in the following area, where the area extends from a straight line parallel to the negative electrode current collector at the bottom of the recess, to the negative electrode current collector, to the left of the perpendicular line from the leftmost point of the projection of the recess on the surface of the negative electrode sheet to the negative electrode current collector, and to the right of the perpendicular line from the rightmost point of the projection of the recess on the surface of the negative electrode sheet to the negative electrode current collector.

[0078] When the shortest distance from the silicon-based particles located below the recess to the straight line parallel to the negative electrode current collector at the bottom of the recess is 3μm-15μm, the expansion of the silicon-based particles can be suppressed, the penetration ability of lithium ions between the positive and negative electrodes can be improved, the electrical conductivity can be improved, and at the same time, the extension and fracture of the negative electrode current collector can be effectively avoided, thereby improving the safety performance of the battery.

[0079] In the present disclosure, the second carbon nanotube may include at least one of a single-walled carbon nanotube and a multi-walled carbon nanotube.

[0080] In one example, the second carbon nanotubes include a combination of the single-walled carbon nanotubes and the multi-walled carbon nanotubes.

[0081] In the second carbon nanotubes, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes may be 1:(5-15), for example, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14 or 1:15.

[0082] In one example, in the second carbon nanotubes, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 1:(6-10).

[0083] Under the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the second carbon nanotube includes a combination of single-walled carbon nanotubes and multi-walled carbon nanotubes, it has a better effect than using single-walled carbon nanotubes or multi-walled carbon nanotubes alone. The reason may be that: the conductivity of single-walled carbon nanotubes is better than that of multi-walled carbon nanotubes, but when the amount of single-walled carbon nanotubes is increased, they are more likely to agglomerate, resulting in their conductivity not being fully utilized; while the conductivity of multi-walled carbon nanotubes is relatively weak, it is much stronger than other conductive agents (such as conductive carbon black, etc.), and its dispersion ability is better; when the two are mixed, the easily dispersed multi-walled carbon nanotubes can break up the agglomerated single-walled carbon nanotubes; so that the two interact with each other to obtain good dispersion and an excellent conductive network; therefore, mixing the two and controlling the ratio can achieve an unexpected synergistic effect. The inventors of the present disclosure further discovered that single-walled carbon nanotubes have stronger conductivity than multi-walled carbon nanotubes, but single-walled carbon nanotubes are more prone to gassing. Controlling the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes can significantly improve the conductivity of the battery without affecting the battery's cycle performance.

[0084] In the present disclosure, the negative electrode conductive agent may further include conductive carbon black. The mass ratio of the conductive carbon black to the second carbon nanotubes may be (5-10):1, for example, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1.

[0085] In one example, the mass ratio of the conductive carbon black to the second carbon nanotubes is (6-8.5):1.

[0086] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the negative electrode conductive agent includes conductive carbon black and second carbon nanotubes, and the mass ratio of the two is within a specific range, the conductivity of the negative electrode sheet can be improved. The reason may be that the conductive carbon black is a point-like conductive distribution, while the carbon nanotubes are a line-like conductive distribution. The combination of the two (point-line combination) has a long-range conductive effect, especially for silicon-based materials with weaker conductivity, which can significantly improve their conductivity. In addition, the surface of the negative electrode sheet has a recess. When the silicon-based material is located on the inner wall of the recess, since part of the silicon-based material is exposed to the outside, the electrical contact of this part is destroyed, and its conductivity will become worse. At this time, the conductive agent with a long-range conductive effect can significantly improve its conductivity.

[0087] In the present disclosure, the negative electrode active material layer may further include a negative electrode binder and a thickener. The negative electrode binder may include at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, polytetrafluoroethylene, and polyethylene oxide. The thickener may include at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose.

[0088] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material may be 70%-99.7% (for example, 70%, 73%, 76%, 79%, 82%, 85%, 88%, 91%, 94%, 97% or 99.7%), the content of the negative electrode conductor may be 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1% or 0.1%), the content of the negative electrode binder may be 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1% or 0.1%), and the content of the thickener may be 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1% or 0.1%).

[0089] In one example, based on the total weight of the negative electrode active material layer, the content of the negative electrode active material is 88%-99%, the content of the negative electrode conductor is 0.2%-2.5%, the content of the negative electrode binder is 0.4%-5%, and the content of the thickener is 0.4%-4.5%.

[0090] In one example, based on the total weight of the negative electrode active material layer, the content of the negative electrode active material is 94%-98.7%, the content of the negative electrode conductor is 0.3%-1.8%, the content of the negative electrode binder is 0.5%-2.5%, and the content of the thickener is 0.5%-1.7%.

[0091] In the present disclosure, the negative active material layer may include N coating layers, where N≧1 (eg, N=1, 2, 3, 4, 5, 6, 7, or 8).

[0092] In the present disclosure, “the negative electrode active material layer includes N coating layers” refers to the number of layers of the negative electrode active material layer on one side of the negative electrode current collector.

[0093] When N=1, the number of negative electrode active material layers on one side of the negative electrode current collector is 1.

[0094] When N=2, the number of negative electrode active material layers on one side of the negative electrode current collector is two. In this case, the two negative electrode active material layers are a first negative electrode active material layer and a second negative electrode active material layer. The first and second negative electrode active material layers are stacked in the thickness direction of the negative electrode sheet. The slurries forming the first and second negative electrode active material layers can be the same or different. When the slurries forming the first and second negative electrode active material layers are different, their compositions are not particularly limited, as long as the mass content of the silicon-based material in the negative electrode active material is satisfied. In this case, the silicon-based material may be present only in the first negative electrode active material layer, only in the second negative electrode active material layer, or in both the first and second negative electrode active material layers. The ratio of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer is 1:(0.5-4), for example, 1:0.5, 1:1, 1:2, 1:3, or 1:4.

[0095] In one embodiment, the negative electrode active material layer is a single layer.

[0096] In one example, the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer sequentially stacked along a thickness direction of the negative electrode sheet.

[0097] In one example, the negative electrode active material layer includes a first negative electrode active material layer, a second negative electrode active material layer, and a third negative electrode active material layer sequentially stacked along the thickness direction of the negative electrode sheet.

[0098] In the present disclosure, the surface density of the negative electrode sheet can be 7 mg / cm 2 -22mg / cm 2 , for example 7mg / cm 2 、10mg / cm 2 、15mg / cm 2 , 20mg / cm 2 or 22 mg / cm 2 .

[0099] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the surface density of the negative electrode sheet is within a specific range, the ability of the negative electrode sheet to receive lithium ions can be improved; at the same time, providing a recess on the outer surface of the negative electrode sheet can shorten the transmission distance of lithium ions and increase the speed at which lithium ions are embedded in the negative electrode sheet, thereby further improving the charging speed of the battery and reducing the risk of lithium plating.

[0100] In the present disclosure, the thickness of the negative electrode active material layer is 35 μm-100 μm, for example, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm.

[0101] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the thickness of the negative electrode sheet is within a specific range and a recess is provided on the outer surface of the negative electrode sheet, it is possible to shorten the transmission distance of lithium ions, increase the speed at which lithium ions are embedded in the negative electrode sheet, and reduce the occurrence of lithium plating while increasing the energy density of the battery.

[0102] In the present disclosure, the thickness of the negative electrode active material layer refers to the thickness of the negative electrode active coating layer on one side of the negative electrode current collector.

[0103] <Concave>

[0104] In the present disclosure, the recess may include a hole and / or a groove.

[0105] In the present disclosure, the pores may have a pore size of 20 μm-150 μm, for example, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm or 150 μm.

[0106] In one example, the pores have a diameter of 35 μm to 90 μm.

[0107] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the pore diameter is within a specific range, it will not affect the adhesion between the negative electrode surface and the diaphragm. If the pore diameter is too large, the adhesion between this position and the diaphragm is relatively weak, and lithium plating problems caused by poor interface adhesion are likely to occur. If the pore diameter is too small, it will not absorb the electrolyte and quickly accommodate lithium ions, which may also cause lithium plating problems.

[0108] In the present disclosure, the pitch of the holes may be 50 μm-1000 μm, for example 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm or 1000 μm.

[0109] In one example, the pitch of the holes is 150 μm-450 μm.

[0110] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the spacing between the holes is small, the weight loss of the negative electrode sheet increases, which will bring more compensatory thickness, resulting in an overly thick battery and increased energy density loss; when the spacing between the holes is large, it is not conducive to the rapid dispersion of lithium ions and their rapid embedding into adjacent holes, resulting in lithium plating problems.

[0111] In the present disclosure, the pore diameter and spacing of the pores have the conventional meanings in the art. The pore diameter of the pore is generally considered to be the diameter of the regular circle when the shape of the projection of the pore on the negative electrode active material layer is a "regular circle"; when the shape of the projection of the pore on the negative electrode active material layer is a non-"regular circle" (such as an ellipse or an irregular curved polygon), the pore diameter of the pore is the diameter of an equivalent circle with the same area as the non-"regular circle". The spacing of the pores refers to the shortest distance between the edges of two adjacent pores on the negative electrode active material layer.

[0112] In the present disclosure, the pore diameter can be measured by conventional means in the art, for example, by randomly selecting 50 pores from the entire negative electrode sheet using SEM, measuring the pore diameter of each pore, and taking the average value. The pore spacing can be measured by conventional means in the art, for example, by randomly selecting 50 adjacent pores from the entire negative electrode sheet using SEM, measuring the spacing between each pair of adjacent pores, and taking the average value.

[0113] In the present disclosure, the width of the groove can be 35μm-185μm, for example, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm or 185μm.

[0114] In one example, the width of the groove is 40 μm-100 μm.

[0115] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the width of the groove is within a specific range, it will not affect the adhesion between the negative electrode surface and the diaphragm. If the width of the groove is too large, the adhesion between this position and the diaphragm is relatively weak, and lithium deposition problems caused by poor interface adhesion are likely to occur; if the width of the groove is too small, it will not absorb the electrolyte and quickly accommodate lithium ions, which may also cause lithium deposition problems.

[0116] In the present disclosure, the spacing of the grooves may be 0.1 mm to 3 mm, for example, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm or 3 mm.

[0117] In one example, the spacing between the grooves is 0.5 mm to 2 mm.

[0118] On the premise that the ratio of the depth of the recess to the diameter of the first carbon nanotube is within a specific range, when the spacing between the grooves is small, the weight loss of the negative electrode sheet increases, which will bring more compensatory thickness, resulting in an excessively thick battery and increased energy density loss; when the spacing between the grooves is large, it is not conducive to the rapid dispersion of lithium ions and their rapid embedding into adjacent grooves, resulting in lithium plating problems.

[0119] In this disclosure, the width and spacing of the grooves have the conventional meanings in this field. Regarding the width of the grooves, it is generally considered that the projection of the grooves on the negative electrode active material layer includes two long sides, and the width of the grooves refers to the average distance from one long side to the other long side in the length direction or width direction of the negative electrode sheet. Figure 1 shows a schematic diagram of the width of the grooves in an example of the present disclosure, where the two long sides of the grooves in Figures 1(a) to 1(c) are straight lines, and the two long sides of the grooves in Figure 1(d) are curved lines. In FIG1(a) and FIG1(b), the two long sides are arranged in parallel. Therefore, in the width direction of the negative electrode sheet, the distance d from any point on one long side to the other long side is equal. In this case, the width of the groove is the distance from any point on one long side to the other long side in the length direction or width direction of the negative electrode sheet. In FIG1(c), the two long sides of the groove are straight lines, but are not arranged in parallel. Therefore, the distance d from any point on one long side to the other long side is not equal. In this case, the width of the groove can be averaged, that is, 50 points (i.e., 50 points) are selected at equal distances on one long side based on the length of the side. The distance between each point is equal, so selecting points in this way can make the calculation result more accurate), measure the width corresponding to each point, and take the average value to obtain the width of the groove; in Figure 1(d), the two long sides are curved, so the distance d from any point on one long side to the other long side is not equal. In this case, the width of the groove can also be averaged, that is, 50 points are randomly selected on one long side (because the two long sides in Figure 1(d) are curved, there is no relationship between the two long sides in Figure 1(c), so 50 points can be randomly selected for measurement), measure the width corresponding to each point, and take the average value to obtain the width of the groove. The groove spacing is generally considered to be the average distance between the two adjacent long sides of two adjacent grooves on the negative electrode active material layer in the length direction or width direction of the negative electrode sheet. As shown in Figure 2, it is a schematic diagram of the spacing of the grooves in an example of the present disclosure, wherein Figure 2(a) shows the case where two adjacent long sides are straight and parallel, Figure 2(b) shows the case where two adjacent long sides are straight and non-parallel, and Figure 2(c) shows the case where two adjacent long sides are curved.In Figure 2(a), the two adjacent long sides are straight and parallel. Therefore, in the width direction, the distance from any point on one long side to the other long side is equal. In this case, the spacing of the grooves is the distance D from any point on one long side to the other long side in the width direction. In Figure 2(b), the two adjacent long sides are straight but not parallel. Therefore, the distance from any point on one long side to the other long side is not equal. In this case, the spacing of the grooves can be averaged, that is, on one long side, with the length of the side as the reference, 50 points are selected at equal distances (that is, the distance between each point is equal to the distance D between each point). The distance between the two points is equal, so selecting the points in this way can make the calculation result more accurate), measure the width corresponding to each point, and take the average value to get the spacing; in Figure 2(c), the two adjacent long sides are curved. Therefore, the distance from any point on one long side to the other long side is not equal. In this case, the spacing of the grooves can also be averaged, that is, 50 points are randomly selected on one long side (because the two long sides in Figure 2(c) are curved, there is no relationship between the two long sides in Figure 2(b), so 50 points can be randomly selected for measurement), measure the distance corresponding to each point, and take the average value to get the spacing.

[0120] In the present disclosure, the "groove width" can be measured by conventional means in the art, such as by SEM, selecting all grooves on the entire negative electrode sheet, measuring the width of each groove, and taking the average value. The "groove spacing" can be measured by conventional means in the art, such as by SEM, selecting all grooves on the entire negative electrode sheet, measuring the spacing between two adjacent grooves, and taking the minimum value.

[0121] In this disclosure, there are no specific limitations on the morphology of the holes. The holes can be straight blind holes, meaning that the projection of the holes on the negative electrode sheet is uniform throughout the thickness of the negative electrode sheet. Alternatively, the holes can be quasi-conical blind holes, meaning that the diameter of the holes farther from the negative electrode current collector is larger than the diameter of the holes closer to the negative electrode current collector. Figure 3 shows a schematic diagram of the morphology of the holes in one example of this disclosure, where Figure 3(a) shows a straight blind hole and Figure 3(b) shows a quasi-conical blind hole.

[0122] In the present disclosure, there is no particular limitation on the shape of the groove. The cross-section of the groove along the thickness direction of the negative electrode sheet can be rectangular or conical. FIG4 is a schematic diagram of a groove in an embodiment of the present disclosure. As can be seen from FIG4, the cross-section of the groove along the thickness direction of the negative electrode sheet can be rectangular or conical. In the present disclosure, the groove can be distributed along the length direction of the negative electrode sheet or along the width direction of the negative electrode sheet.

[0123] In the present disclosure, the vertical distance from the bottom of the recess to the negative electrode current collector is greater than 0 μm. When the vertical distance from the bottom of the recess to the negative electrode current collector is greater than 0, damage to the negative electrode current collector can be avoided, thereby affecting the electrochemical performance of the battery.

[0124] In the present disclosure, the components of the battery other than the positive electrode sheet and the negative electrode sheet (such as a separator and an electrolyte, etc.) can be conventionally selected in the art.

[0125] In one example, the lithium-ion battery further includes a separator and an electrolyte.

[0126] In the present disclosure, the separator may include a separator commonly used in the art, for example, at least one of a polyethylene film and a polypropylene film.

[0127] In the present disclosure, the electrolyte may include a lithium salt and an organic solvent. The lithium salt may include at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium oxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium bistrifluorosulfonylimide, and lithium bisfluorosulfonylimide. The organic solvent may include at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0128] The electrolyte may further include an additive, and the additive may include at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, methylene methanedisulfonate, propylene sultone, and succinic anhydride.

[0129] In the present disclosure, the battery can be assembled in accordance with conventional methods in the art.

[0130] In one example, the battery comprises a lithium-ion battery.

[0131] The battery disclosed herein has excellent cycle life and cycle expansion rate, and can significantly improve the problem of lithium plating.

[0132] It should be noted that the numerical expressions such as "first" and "second" in the present disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0133] The present disclosure will be described in detail below through examples. The examples described in this disclosure are only a portion of the examples of the present disclosure, not all of the examples. Based on the examples in this disclosure, all other examples obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this disclosure.

[0134] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0135] The following examples are provided to illustrate the batteries of the present disclosure.

[0136] Example 1

[0137] Prepare the battery as follows:

[0138] (1) Preparation of negative electrode sheet

[0139] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 85:15), the negative electrode conductive agent (conductive carbon black and carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes are in a mass ratio of 1:9, wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1, the carbon nanotubes have a diameter of 12 nm and a length of 13 μm), styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed in a mass ratio of 96.9:0.5:1.3:1.3, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a negative electrode slurry with a solid content of 45%. The negative electrode slurry is coated on a copper foil using a coating machine and dried at 100° C. A groove is made on the outer surface of the negative electrode active material layer, wherein the groove has a depth of 10 μm, a width of 50 μm, and a spacing of 1 mm to obtain a negative electrode sheet, wherein the width of the negative electrode sheet is 65 mm;

[0140] (2) Preparation of positive electrode sheet

[0141] Lithium cobalt oxide, a positive electrode conductive agent (conductive carbon black and carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes have a mass ratio of 1:9), wherein the mass ratio of conductive carbon black to carbon nanotubes is 7:1, the carbon nanotubes have a diameter of 16 nm and a length of 20 μm) and polyvinylidene fluoride are uniformly mixed in a mass ratio of 97.2:1.5:1.3, N-methylpyrrolidone (NMP) is added, and the mixture is passed through a 200-mesh sieve to obtain a positive electrode slurry with a solid content of 72%. The positive electrode slurry is coated on an aluminum foil using a coating machine and dried at 120° C. to obtain a positive electrode sheet with a width of 63 mm.

[0142] (3) Preparation of lithium-ion batteries

[0143] The negative electrode sheet obtained in step (1), the positive electrode sheet obtained in step (2) and a separator (polyethylene film, with a thickness of 9 μm) are wound to form a roll core, which is then wrapped with an aluminum-plastic film. After baking to remove moisture, an electrolyte is injected (propylene carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a weight ratio of 1:1:0.5:1, and 1 mol / L LiPF6 is added and mixed evenly), and a battery is obtained by a hot pressing process.

[0144] Example 2

[0145] Refer to Example 1, except that, step (1) and step (2) are specifically:

[0146] (1) Preparation of negative electrode sheet

[0147] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 85:15), the negative electrode conductive agent (conductive carbon black and carbon nanotubes (single-walled carbon nanotubes to multi-walled carbon nanotubes is 1:8), wherein the mass ratio of conductive carbon black to carbon nanotubes is 8:1, wherein the carbon nanotubes have a diameter of 15 nm and a length of 20 μm), styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed in a mass ratio of 96.9:0.5:1.3:1.3, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a negative electrode slurry with a solid content of 45%; the above-mentioned negative electrode slurry is coated on a copper foil using a coating machine, and dried at 100° C., and grooves are made on the outer surface of the negative electrode active material layer, wherein the grooves have a depth of 20 μm, a width of 95 μm, and a spacing of 1 mm, to obtain a negative electrode sheet, wherein the width of the negative electrode sheet is 65 mm;

[0148] (2) Preparation of positive electrode sheet

[0149] Lithium cobalt oxide, a positive electrode conductive agent (conductive carbon black and carbon nanotubes (the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes is 1:8), wherein the mass ratio of conductive carbon black to carbon nanotubes is 8:1, wherein the carbon nanotubes have a diameter of 10 nm and a length of 10 μm) and polyvinylidene fluoride are uniformly mixed in a mass ratio of 97.2:1.5:1.3, N-methylpyrrolidone (NMP) is added, and the mixture is passed through a 200-mesh sieve to obtain a positive electrode slurry with a solid content of 72%. The positive electrode slurry is coated on an aluminum foil using a coating machine and dried at 120°C to obtain a positive electrode sheet with a width of 63 mm.

[0150] Example 3

[0151] Refer to Example 1, except that, step (1) and step (2) are specifically:

[0152] (1) Preparation of negative electrode sheet

[0153] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 85:15), the negative electrode conductive agent (conductive carbon black and carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes are in a mass ratio of 1:10, wherein the mass ratio of conductive carbon black to carbon nanotubes is 6:1, wherein the carbon nanotubes have a diameter of 5 nm and a length of 12 μm), styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed in a mass ratio of 96.9:0.5:1.3:1.3, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a negative electrode slurry with a solid content of 45%; the above-mentioned negative electrode slurry is coated on a copper foil using a coating machine, and dried at 100° C., and grooves are made on the outer surface of the negative electrode active material layer, wherein the grooves have a depth of 8 μm, a width of 40 μm, and a spacing of 1 mm, to obtain a negative electrode sheet, wherein the width of the negative electrode sheet is 65 mm;

[0154] (2) Preparation of positive electrode sheet

[0155] Lithium cobalt oxide, a positive electrode conductive agent (conductive carbon black and carbon nanotubes (the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes is 1:10), wherein the mass ratio of conductive carbon black to carbon nanotubes is 6:1, wherein the carbon nanotubes have a diameter of 6 nm and a length of 12 μm) and polyvinylidene fluoride are uniformly mixed in a mass ratio of 97.2:1.5:1.3, N-methylpyrrolidone (NMP) is added, and the mixture is passed through a 200-mesh sieve to obtain a positive electrode slurry with a solid content of 72%. The positive electrode slurry is coated on an aluminum foil using a coating machine and dried at 120°C to obtain a positive electrode sheet with a width of 63 mm.

[0156] Example 4

[0157] Refer to Example 1, except that, step (1) and step (2) are specifically:

[0158] (1) Preparation of negative electrode sheet

[0159] The negative electrode active material (artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite and silicon oxide is 85:15), the negative electrode conductive agent (conductive carbon black and carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes are in a mass ratio of 1:

[0160] 6), wherein the mass ratio of conductive carbon black to carbon nanotubes is 8.5:1, wherein the carbon nanotubes have a diameter of 18 nm and a length of 10 μm), styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed uniformly in a mass ratio of 96.9:0.5:1.3:1.3, deionized water is added, and the mixture is passed through a 150-mesh sieve to obtain a negative electrode slurry having a solid content of 45%; the negative electrode slurry is coated on a copper foil using a coating machine, dried at 100° C., and grooves are made on the outer surface of the negative electrode active material layer, wherein the grooves have a depth of 26 μm, a width of 99 μm, and a spacing of 1 mm, to obtain a negative electrode sheet, wherein the width of the negative electrode sheet is 65 mm;

[0161] (2) Preparation of positive electrode sheet

[0162] Lithium cobalt oxide, a positive electrode conductive agent (conductive carbon black and carbon nanotubes (the mass ratio of single-walled carbon nanotubes to multi-walled carbon nanotubes is 1:6), wherein the mass ratio of conductive carbon black to carbon nanotubes is 8.5:1, wherein the carbon nanotubes have a diameter of 15 nm and a length of 5 μm) and polyvinylidene fluoride are uniformly mixed in a mass ratio of 97.2:1.5:1.3, N-methylpyrrolidone (NMP) is added, and the mixture is passed through a 200-mesh sieve to obtain a positive electrode slurry with a solid content of 72%. The positive electrode slurry is coated on an aluminum foil using a coating machine and dried at 120°C to obtain a positive electrode sheet with a width of 63 mm.

[0163] Example 5 group

[0164] This group of examples is carried out with reference to Example 1, except that the ratio of the depth of the recess to the diameter of the first carbon nanotube is changed by changing the diameter of the first carbon nanotube. Specifically:

[0165] In Example 5a, the first carbon nanotube has a diameter of 10 nm and a length of 20 μm;

[0166] In Example 5b, the first carbon nanotube has a diameter of 6 nm and a length of 20 μm;

[0167] In Example 5c, the first carbon nanotube has a diameter of 2 nm and a length of 20 μm;

[0168] In Example 5d, the diameter of the first carbon nanotube is 20 nm and the length is 20 μm.

[0169] Example 6

[0170] Example 6a is carried out in accordance with Example 2, except that the ratio of the depth of the recess to the diameter of the first carbon nanotube is changed by changing the diameter of the first carbon nanotube, that is, the diameter of the first carbon nanotube is 6 nm and the length is 10 μm;

[0171] Example 6b is carried out with reference to Example 3, except that the ratio of the recess depth to the diameter of the first carbon nanotube is changed by changing the diameter of the first carbon nanotube, that is, the diameter of the first carbon nanotube is 16 nm and the length is 12 μm.

[0172] Example 7 Group

[0173] This group of examples is carried out with reference to Example 1, except that the parameters for making the groove are changed, specifically:

[0174] In Example 7a, the grooves have a depth of 5 μm, a width of 35 μm, and a pitch of 1 mm;

[0175] In Example 7b, the grooves have a depth of 40 μm, a width of 170 μm, and a pitch of 1 mm.

[0176] Example 8 Group

[0177] This group of examples is carried out with reference to Example 1, except that the ratio of the depth of the recess to the length of the first carbon nanotube is changed by changing the length of the first carbon nanotube. Specifically:

[0178] In Example 8a, the first carbon nanotube has a diameter of 16 nm and a length of 10 μm;

[0179] In Example 8b, the first carbon nanotube has a diameter of 16 nm and a length of 5 μm;

[0180] In Example 8c, the first carbon nanotube has a diameter of 16 nm and a length of 30 μm;

[0181] In Example 8d, the diameter of the first carbon nanotube is 16 nm and the length is 0.5 μm.

[0182] Example 9 Group

[0183] This group of examples is carried out with reference to Example 1, except that the mass content of the first carbon nanotubes in the positive electrode conductive agent is changed. Specifically:

[0184] In Example 9a, the positive electrode conductive agent is a combination of conductive carbon black and carbon nanotubes, wherein the carbon nanotubes are a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes in a mass ratio of 1:9, and the mass ratio of conductive carbon black to carbon nanotubes is 5:1;

[0185] In Example 9b, the positive electrode conductive agent is a combination of conductive carbon black and carbon nanotubes, wherein the carbon nanotubes are a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes in a mass ratio of 1:9, and the mass ratio of conductive carbon black to carbon nanotubes is 10:1.

[0186] Example 10 Group

[0187] This group of examples is carried out with reference to Example 1, except that the negative electrode active material is changed, specifically:

[0188] In Example 10a, the negative electrode active material is artificial graphite;

[0189] In Example 10b, the negative electrode active materials are artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 95:5;

[0190] In Example 10c, the negative electrode active materials are artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 60:40;

[0191] In Example 10d, the negative electrode active material is artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 99:1;

[0192] In Example 10e, the negative electrode active materials are artificial graphite and silicon oxide, wherein the mass ratio of artificial graphite to silicon oxide is 40:60.

[0193] Example 11

[0194] The process is carried out with reference to Example 1, except that the negative electrode conductive agent is changed, specifically: the negative electrode conductive agent is conductive carbon black.

[0195] Example 12 Group

[0196] This group of examples is carried out with reference to Example 1, except that the ratio of the depth of the recess to the diameter of the second carbon nanotube is changed by changing the diameter of the second carbon nanotube. Specifically:

[0197] In Example 12a, the second carbon nanotube has a diameter of 5 nm and a length of 13 μm;

[0198] In Example 12b, the second carbon nanotube has a diameter of 18 nm and a length of 13 μm;

[0199] In Example 12c, the second carbon nanotube has a diameter of 2 nm and a length of 13 μm;

[0200] In Example 12d, the diameter of the second carbon nanotube is 25 nm and the length is 13 μm.

[0201] Example 13 Group

[0202] This group of examples is carried out with reference to Example 1, except that the ratio of the length of the second carbon nanotube to the depth of the recess is changed by changing the length of the second carbon nanotube. Specifically:

[0203] In Example 13a, the second carbon nanotube has a diameter of 12 nm and a length of 10 μm;

[0204] In Example 13b, the second carbon nanotube has a diameter of 12 nm and a length of 20 μm;

[0205] In Example 13c, the second carbon nanotube has a diameter of 12 nm and a length of 0.5 μm;

[0206] In Example 13d, the diameter of the second carbon nanotube is 12 nm and the length is 30 μm.

[0207] Example 14 Group

[0208] This group of examples is carried out with reference to Examples 1-4, except that pores are formed on the outer surface of the negative electrode active material layer. Specifically:

[0209] Example 14a was carried out in the same manner as Example 1, except that the pore depth was 10 μm, the pore diameter was 45 μm, and the spacing was 200 μm;

[0210] Example 14b was carried out in the same manner as Example 2, except that the pore depth was 20 μm, the pore diameter was 87 μm, and the spacing was 200 μm;

[0211] Example 14c was carried out in the same manner as Example 3, except that the pore depth was 8 μm, the pore diameter was 35 μm, and the spacing was 200 μm;

[0212] Example 14d is carried out with reference to Example 4, except that the hole depth is 26 μm, the hole diameter is 90 μm, and the spacing is 200 μm.

[0213] Example 15

[0214] The method is carried out in accordance with Example 1, except that the preparation process of the negative electrode sheet is adjusted to control the shortest distance from the silicon-based particles located below the recess to the straight line parallel to the negative electrode current collector at the bottom of the recess to be 3 μm-15 μm. Specifically, the coating speed of the negative electrode slurry is controlled to be 5 m / min-7 m / min, and the negative electrode sheet is dried in stages. The negative electrode sheet is baked at 60°C-80°C within 10 m of entering the oven to solidify it; and baked at 80°C-110°C within 20 m-30 m to allow the silicon-based particles at the bottom to move upward as the binder floats. Finally, the temperature of the negative electrode sheet 10 m out of the oven drops sharply to 50°C to plasticize and fix it.

[0215] Example 16

[0216] The process was carried out in accordance with Example 1, except that silicon 2 oxide was replaced with silicon-carbon material of the same mass (wherein the carbon content was approximately 13%).

[0217] Comparative Example 1

[0218] The process is carried out with reference to Example 1, except that the first carbon nanotube is changed. Specifically, the diameter of the first carbon nanotube is 35 nm and the length is 20 μm.

[0219] Comparative Example 2

[0220] The same procedure is carried out as in Example 1, except that the first carbon nanotube is changed. Specifically, the diameter of the first carbon nanotube is 1.5 nm and the length is 20 μm.

[0221] The parameters of Examples 1-16 and Comparative Examples 1-2 are shown in Table 1. In the above embodiments of the present disclosure, the surface density of the negative electrode sheet is 7 mg / cm 2 -22mg / cm 2, the thickness of the negative electrode active material layer is 35μm-100μm.

[0222] Table 1

[0223] Test Case

[0224] (1) Energy density test

[0225] The batteries prepared in the examples and comparative examples were subjected to energy density tests. The specific method is as follows: the battery discharge capacity was tested by 0.5C constant current constant voltage charge / 0.2C discharge at 25°C. Energy density = discharge capacity × average voltage / (thickness × width × height). The test results are recorded in Table 2.

[0226] (2) Cyclic capacity retention test

[0227] The batteries prepared in the examples and comparative examples were subjected to a cycle capacity retention test. The specific method is as follows: at a test temperature of 25°C, a 2C charge to 4.5V and a 0.05C / 1C discharge to 3.0V cycle test was performed for 800T. The test results are recorded in Table 2.

[0228] (3) Expansion rate test

[0229] The batteries prepared in the examples and comparative examples were subjected to an expansion rate test. The specific method is as follows: referring to the test method for the cycle capacity retention rate, a PPG thickness tester was used to test the thickness of the first fully charged battery and the thickness of the fully charged battery after completing 800T cycles. The expansion rate = (thickness of the fully charged battery after 800T cycles - thickness of the first fully charged battery) / thickness of the first fully charged battery. The results are recorded in Table 2.

[0230] (4) Lithium deposition test

[0231] The batteries prepared in the examples and comparative examples were subjected to a room temperature lithium deposition test. The specific method is as follows: at 25°C, the charging process is: first charging at a constant current of 4C to 4.48V, and then charging at a constant voltage until the current drops to 0.05C; the discharging process is: discharging at a constant current of 1C to 3.0V; and finally fully charging at 0.3C; after repeating 20 cycles, the battery is disassembled and the lithium deposition on the negative electrode sheet is observed. The results are recorded in Table 2, where the degree of lithium deposition is ranked from light to heavy as no lithium deposition, slight lithium deposition, lithium deposition, and severe lithium deposition.

[0232] Table 2

[0233] It can be seen from Table 2 that the battery disclosed herein has a higher cycle capacity retention rate, a lower expansion rate, and a better lithium deposition condition compared with the comparative example.

[0234] Comparing Example 5 with Example 1 and Example 6a with Example 2, it can be seen that when the ratio of the depth of the recess to the diameter of the first carbon nanotube is (600-2050):1, the cycle capacity retention rate of the battery can be improved, and expansion and lithium plating can be improved.

[0235] Compared with Example 3, Example 6b has similar cycle capacity retention rate, expansion rate and lithium deposition situation, but the charging speed of Example 6b is slower than that of Example 3.

[0236] Compared with Example 1, the depth of the concave portion of Example 7a becomes smaller, the energy density is higher than that of Example 1, while the cycle capacity retention rate, expansion rate and lithium deposition are worse than those of Example 1; compared with Example 1, the depth of the concave portion of Example 7b becomes larger, the energy density is lower than that of Example 1, and the cycle capacity retention rate, expansion rate and lithium deposition are close to those of Example 1.

[0237] Compared with Example 1, it can be seen that when the ratio of the length of the first carbon nanotube to the depth of the recess is (0.1-2):1, the cycle capacity retention rate of the battery can be improved, and expansion and lithium plating can be improved; the battery charging speed of Example 8d is slower than that of the example.

[0238] Compared with Example 1, it can be seen that the first carbon nanotubes in the positive electrode conductive agent have a specific mass content. Within this range, the positive electrode sheet has better conductivity and has a greater impact on the battery's cycle capacity retention rate, expansion rate and lithium plating.

[0239] Compared with Example 1, Example 11 shows that when the negative electrode conductive agent includes carbon nanotubes, the expansion of the silicon-containing negative electrode sheet can be further suppressed.

[0240] Compared with Example 1, Example 12 shows that when the depth of the concave portion and the diameter of the second carbon nanotube meet the ratio of (800-1670):1, the cycle capacity retention rate of the battery can be improved, and expansion and lithium plating can be improved.

[0241] Compared with Example 1, it can be seen that when the ratio of the length of the second carbon nanotube to the depth of the recess satisfies (0.3-1.5):1, the cycle capacity retention rate of the battery can be improved, and expansion and lithium plating can be improved.

[0242] Compared with Example 1, Example 15 shows that when the shortest distance from the silicon-based particles located below the concave portion to a straight line parallel to the negative electrode current collector at the bottom of the concave portion is 3 μm-15 μm, the expansion of the silicon-based particles can be suppressed.

[0243] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. A battery, characterized in that: The battery includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a first carbon nanotube. The surface of the negative electrode sheet has a concave portion. The ratio of the depth of the concave portion to the diameter of the first carbon nanotube is (300-5000):

1.

2. The battery according to claim 1, wherein The ratio of the depth of the concave portion to the diameter of the first carbon nanotube is (600-2050):

1.

3. The battery according to claim 1 or 2, wherein The diameter of the first carbon nanotubes is 2 nm to 20 nm, preferably 6 nm to 16 nm.

4. The battery according to any one of claims 1 to 3, wherein The depth of the concave portion is 5 μm-65 μm, preferably 8 μm-30 μm.

5. The battery according to any one of claims 1 to 4, wherein The ratio of the length of the first carbon nanotube to the depth of the concave portion is (0.03-4):1, preferably (0.1-2):

1.

6. The battery according to any one of claims 1 to 5, wherein The length of the first carbon nanotubes is 0.2 μm-32 μm, preferably 5 μm-20 μm.

7. The battery according to any one of claims 1 to 6, wherein The first carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes; Preferably, the first carbon nanotubes include a combination of the single-walled carbon nanotubes and the multi-walled carbon nanotubes; More preferably, in the first carbon nanotubes, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 1:(5-15); further preferably, it is 1:(6-10).

8. The battery according to any one of claims 1 to 7, wherein The positive electrode sheet includes a positive electrode conductive agent, and the positive electrode conductive agent includes the first carbon nanotubes; based on the total weight of the positive electrode conductive agent, the content of the first carbon nanotubes is 0.1%-30%, preferably 10%-15%; Preferably, the positive electrode conductive agent further comprises at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite and carbon fiber; More preferably, the positive electrode conductive agent includes conductive carbon black and the first carbon nanotubes.

9. The battery according to any one of claims 1 to 8, wherein The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer on at least one side of the negative electrode current collector, wherein the recess is located on the surface of the negative electrode active material layer; the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a carbon-based material and a silicon-based material; Preferably, the negative electrode active material comprises the carbon-based material and the silicon-based material, and the content of the silicon-based material is 1%-65% based on the total weight of the negative electrode active material; more preferably 3%-45%; Preferably, the silicon-based material comprises at least one of silicon-carbon, silicon-oxygen, silicon and silicon alloy; Preferably, the carbon-based material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon and soft carbon.

10. The battery according to claim 9, wherein The negative electrode active material layer further includes a negative electrode conductive agent, and the negative electrode conductive agent includes a second carbon nanotube; Preferably, the depth of the concave portion and the diameter of the second carbon nanotube are (400-5000):1; more preferably, (800-1670):

1.

11. The battery according to claim 10, wherein The ratio of the length of the second carbon nanotube to the depth of the recess is (0.03-3):1; preferably (0.3-1.5):1; Preferably, the length of the second carbon nanotubes is 0.2 μm-32 μm; more preferably 10 μm-20 μm; Preferably, the diameter of the second carbon nanotubes is 2 nm to 25 nm; more preferably, 5 nm to 18 nm.

12. The battery according to claim 10 or 11, wherein The negative electrode conductive agent also includes conductive carbon black; Preferably, the mass ratio of the conductive carbon black to the second carbon nanotubes is (5-10):1; more preferably (6-8.5):

1.

13. The battery according to any one of claims 10 to 12, wherein The second carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes; Preferably, the second carbon nanotubes include a combination of the single-walled carbon nanotubes and the multi-walled carbon nanotubes; More preferably, in the second carbon nanotubes, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 1:(5-15); further preferably, it is 1:(6-10).

14. The battery according to any one of claims 1 to 13, wherein The recess comprises a hole and / or a groove; Preferably, the pore diameter is 20 μm-150 μm; the spacing between the pores is 50 μm-1000 μm; Preferably, the width of the groove is 35 μm-185 μm; the spacing between the grooves is 0.1 mm-3 mm.

15. The battery according to any one of claims 9 to 14, wherein The shortest distance between the silicon-based particles located below the concave portion and a straight line parallel to the negative electrode current collector at the bottom of the concave portion is 3 μm to 15 μm; Preferably, the vertical distance from the bottom of the recess to the negative electrode current collector is greater than 0 μm; Preferably, the surface density of the negative electrode sheet is 7 mg / cm 2 -22mg / cm 2 The thickness of the negative electrode active material layer is 35 μm-100 μm.

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