Negative electrode sheet and lithium ion battery

Abstract

The present disclosure provides a negative electrode sheet and a lithium ion battery. The negative electrode sheet comprises: a current collector; and a negative active material layer formed on the current collector; wherein the negative active material layer comprises at least two negative active material layers in sequence from inside to outside, the negative active material layers comprise negative active materials selected from natural graphite or artificial graphite, and the at least two negative active material layers comprise at least one negative active material layer containing natural graphite and at least one negative active material layer containing artificial graphite. The negative electrode sheet of the present disclosure can achieve a good balance between maintaining high energy density, high fast charging capability and controlling cost due to the simultaneous use of natural graphite and artificial graphite.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery technology, and in particular to a negative electrode sheet and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are a new type of green power source with advantages such as high energy, high battery voltage, wide operating temperature range, long storage life, and no memory effect. They have been widely used in military and civilian small electrical appliances, as well as pure electric and hybrid new energy vehicles.

[0003] In existing technologies, lithium-ion battery anodes typically require the use of artificial graphite as the active material because it has advantages over natural graphite, such as more balanced performance, better cycle performance, and better compatibility with electrolytes. This makes it more conducive to achieving high energy density and fast charging capability, but it also inevitably leads to high cost.

[0004] Therefore, how to reduce the manufacturing cost of the negative electrode while maintaining high energy density and fast charging capability has become an important problem that urgently needs to be solved. Summary of the Invention

[0005] This disclosure is made in view of the above-mentioned technical problems, and its purpose is to provide a negative electrode sheet that uses both artificial graphite and natural graphite as negative electrode active materials to achieve a good balance between maintaining high energy density, high fast charging capability and cost control.

[0006] Therefore, the first aspect of this disclosure provides a negative electrode sheet, which includes:

[0007] Current collector; and

[0008] A negative electrode active material layer is formed on the current collector;

[0009] The negative electrode active material layer comprises at least two negative electrode active material layers from the inside out. The negative electrode active material layers include negative electrode active materials selected from natural graphite or artificial graphite, and the at least two negative electrode active material layers include at least one negative electrode active material layer containing natural graphite and at least one negative electrode active material layer containing artificial graphite.

[0010] The negative electrode active material layer formed on the current collector includes cases where the negative electrode active material layer is directly disposed on the current collector, and cases where the negative electrode active material layer is indirectly disposed on the current collector, such as cases where other layers are disposed between the negative electrode active material layer and the current collector.

[0011] By simultaneously introducing natural graphite and artificial graphite into the negative electrode active material layer, the advantages of high energy density of artificial graphite and low cost of natural graphite can be combined, thus achieving a compromise performance balance.

[0012] In any embodiment, the negative electrode active material layer comprises, from the inside out, a first negative electrode active material layer and a second negative electrode active material layer, wherein the negative electrode active material in the first negative electrode active material layer includes natural graphite, and the negative electrode active material in the second negative electrode active material layer includes artificial graphite.

[0013] In any embodiment, one or more blind holes are provided in the first negative electrode active material layer, and the opening of the blind hole is located on the outside of the first negative electrode active material layer, that is, the opening of the blind hole is located on the side of the first negative electrode active material layer away from the current collector.

[0014] By setting blind holes in the first negative electrode active material layer, artificial graphite in the second negative electrode active layer can penetrate into the first negative electrode active material layer, thereby forming an efficient lithium intercalation channel and improving fast charging capability.

[0015] In any embodiment, the depth of the blind hole is 1-80% of the thickness of the first negative electrode active material layer, preferably 10-70%, more preferably 20-60%; and / or

[0016] The diameter of the blind hole is 20-300 μm, preferably 80-150 μm; and / or

[0017] The spacing between the blind holes is 100-1000 μm, preferably 400-500 μm; and / or

[0018] The hole formation rate is 0.1%-10%, preferably 2%-4%.

[0019] In any implementation, the blind holes are uniformly distributed.

[0020] In any embodiment, the thickness of the first negative electrode active material layer is 10-200 μm, preferably 50-100 μm.

[0021] In any embodiment, the thickness of the second negative electrode active material layer is 10-200 μm, preferably 50-100 μm.

[0022] In any embodiment, the thickness of the first negative electrode active material layer is greater than the thickness of the second negative electrode active material layer.

[0023] In any embodiment, the median particle size of the natural graphite is 5-20 μm; and / or

[0024] The median particle size of the artificial graphite is 5-20 μm.

[0025] In any embodiment, the negative electrode active material layer comprises, from the inside out, a first negative electrode active material layer, a second negative electrode active material layer, and a third negative electrode active material layer. The negative electrode active material in the first negative electrode active material layer includes artificial graphite, the negative electrode active material in the second negative electrode active material layer includes natural graphite, and the negative electrode active material in the third negative electrode active material layer includes artificial graphite.

[0026] In any embodiment, the system consisting of the first negative electrode active material layer and the second negative electrode active material layer is provided with one or more blind holes, the opening of the blind hole being located on the outside of the second negative electrode active material layer, that is, the opening of the blind hole being located on the side of the second negative electrode active material layer away from the current collector.

[0027] By setting blind holes in the system composed of the first negative electrode active material layer and the second negative electrode active material layer, artificial graphite in the third negative electrode active material layer can penetrate into the first negative electrode active material layer and the second negative electrode active material layer, thereby forming an efficient lithium intercalation channel that connects the innermost and outermost layers and improves fast charging capability.

[0028] In any embodiment, the depth of the blind hole is 1-80% of the thickness of the second negative electrode active material layer plus the thickness of the first negative electrode active material layer, preferably 10-70%, more preferably 30-60%; and / or

[0029] The diameter of the blind hole is 20-500 μm, preferably 100-150 μm; and / or

[0030] The spacing between the blind holes is 100-1500 μm, preferably 400-500 μm; and / or

[0031] The hole formation rate is 0.1%-10%, preferably 2%-4%.

[0032] In any implementation, the blind holes are uniformly distributed.

[0033] In any embodiment, the thickness of the first negative electrode active material layer is 10-100 μm, preferably 60-100 μm.

[0034] In any embodiment, the thickness of the second negative electrode active material layer is 10-200 μm, preferably 60-100 μm.

[0035] In any embodiment, the thickness of the third negative electrode active material layer is 10-100 μm, preferably 20-40 μm.

[0036] In any embodiment, the thickness of the second negative electrode active material layer is greater than the thickness of the first negative electrode active material layer and / or the third negative electrode active material layer.

[0037] In any embodiment, the median particle size of the artificial graphite in the negative electrode active material of the first negative electrode active material layer is 5-20 μm; and / or

[0038] The median particle size of the natural graphite in the negative electrode active material of the second negative electrode active material layer is 5-20 μm; and / or

[0039] The median particle size of the artificial graphite in the negative electrode active material of the third negative electrode active material layer is 5-20 μm.

[0040] A second aspect of this disclosure provides a method for preparing a negative electrode sheet, comprising:

[0041] At least two negative electrode slurries containing negative electrode active materials are stacked and coated onto a current collector and then dried to obtain the negative electrode sheet;

[0042] The negative electrode active material is selected from natural graphite or artificial graphite, and the at least two negative electrode slurries containing negative electrode active materials include at least one negative electrode slurry containing natural graphite and at least one negative electrode slurry containing artificial graphite.

[0043] In any implementation, the method includes:

[0044] A first negative electrode slurry containing a negative electrode active material is coated onto a current collector and dried to form a first negative electrode active material layer, wherein the negative electrode active material includes natural graphite; and

[0045] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0046] To obtain the negative electrode sheet.

[0047] In any implementation, the method includes:

[0048] A first negative electrode slurry containing a negative electrode active material and a chemical pore-forming agent is coated onto a current collector and dried and pore-forming is performed to form a first negative electrode active material layer containing one or more blind pores. The negative electrode active material includes natural graphite, and the openings of the blind pores are located on the outer side of the first negative electrode active material layer.

[0049] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0050] To obtain the negative electrode sheet.

[0051] In any implementation, the method includes:

[0052] A first negative electrode slurry containing a negative electrode active material is coated onto a current collector and dried to form a first negative electrode active material layer, wherein the negative electrode active material includes natural graphite.

[0053] Physical pore-forming is performed on the first negative electrode active material layer to form a first negative electrode active material layer containing one or more blind holes, wherein the openings of the blind holes are located on the outer side of the first negative electrode active material layer; and

[0054] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer containing one or more blind pores and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0055] To obtain the negative electrode sheet.

[0056] In any embodiment, the depth of the blind hole is 1-80% of the thickness of the first negative electrode active material layer, preferably 10-70%, more preferably 20-60%; and / or

[0057] The diameter of the blind hole is 20-300 μm, preferably 80-150 μm; and / or

[0058] The spacing between the blind holes is 100-1000 μm, preferably 400-500 μm and / or

[0059] The hole formation rate is 0.1%-10%, preferably 2%-4%.

[0060] In any implementation, the blind holes are uniformly distributed.

[0061] In any embodiment, the thickness of the first negative electrode active material layer is 10-200 μm, preferably 50-100 μm.

[0062] In any embodiment, the thickness of the second negative electrode active material layer is 10-200 μm, preferably 50-100 μm.

[0063] In any embodiment, the median particle size of the natural graphite is 5-20 μm; and / or

[0064] The median particle size of the artificial graphite is 5-20 μm.

[0065] In any implementation, the method includes:

[0066] A first negative electrode slurry containing a negative electrode active material is coated onto a current collector and dried to form a first negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0067] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes natural graphite; and

[0068] A third negative electrode slurry containing a negative electrode active material is coated onto the second negative electrode active material layer and dried to form a third negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0069] To obtain the negative electrode sheet.

[0070] In any implementation, the method includes:

[0071] A first negative electrode slurry containing a negative electrode active material and a chemical pore-forming agent is coated onto a current collector and semi-dried at low temperature to form a semi-dried first negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0072] A second negative electrode slurry containing a negative electrode active material is coated onto the semi-dried first negative electrode active material layer and dried at high temperature to create pores, thereby forming a second negative electrode active material layer and forming one or more blind pores in the system composed of the first and second negative electrode active material layers. The negative electrode active material includes natural graphite, and the openings of the blind pores are located on the outer side of the second negative electrode active material layer.

[0073] A third negative electrode slurry containing a negative electrode active material is coated onto the second negative electrode active material layer and dried to form a third negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0074] To obtain the negative electrode sheet.

[0075] In any implementation, the method includes:

[0076] A first negative electrode slurry containing a negative electrode active material is coated onto a current collector and dried to form a first negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0077] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes natural graphite.

[0078] Physical pore-forming is performed on the system composed of the first negative electrode active material layer and the second negative electrode active material layer to form one or more blind holes, the openings of which are located on the outer side of the second negative electrode active material layer; and

[0079] A third negative electrode slurry containing a negative electrode active material is coated onto the second negative electrode active material layer and dried to form a third negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0080] To obtain the negative electrode sheet.

[0081] In any embodiment, the depth of the blind hole is 1-80% of the thickness of the second negative electrode active material layer plus the thickness of the first negative electrode active material layer, preferably 10-70%, more preferably 30-60%; and / or

[0082] The diameter of the blind hole is 20-500 μm, preferably 100-150 μm; and / or

[0083] The spacing between the blind holes is 100-1500 μm, preferably 400-500 μm; and / or

[0084] The hole formation rate is 0.1%-10%, preferably 2%-4%.

[0085] In any implementation, the blind holes are uniformly distributed.

[0086] In any embodiment, the thickness of the first negative electrode active material layer is 10-100 μm, preferably 60-100 μm.

[0087] In any embodiment, the thickness of the second negative electrode active material layer is 10-200 μm, preferably 60-100 μm.

[0088] In any embodiment, the thickness of the third negative electrode active material layer is 10-100 μm, preferably 20-40 μm.

[0089] In any embodiment, the median particle size of the artificial graphite in the negative electrode active material of the first negative electrode active material layer is 5-20 μm; and / or

[0090] The median particle size of the natural graphite in the negative electrode active material of the second negative electrode active material layer is 5-20 μm; and / or

[0091] The median particle size of the artificial graphite in the negative electrode active material of the third negative electrode active material layer is 5-20 μm.

[0092] A third aspect of this disclosure provides a lithium-ion battery comprising a negative electrode sheet as described in the first aspect above, or a negative electrode sheet prepared by the method described in the second aspect above. Typically, the lithium-ion battery in this disclosure includes a battery cell, a battery module, a battery pack, etc. Attached Figure Description

[0093] Figure 1 This is a schematic diagram of the hole formation in the method of Embodiment 1 of this disclosure, wherein the meanings of the reference numerals are as follows: 101: current collector; 105: second negative electrode active material layer; 106: first negative electrode active material layer; 107: blind hole; 108: third negative electrode active material.

[0094] Figure 2 This is a schematic diagram of the hole-forming method in Embodiment 4 of this disclosure, wherein the meanings of the reference numerals are as follows: 101: current collector; 102: first negative electrode active material layer; 103: blind hole; 104: blind hole channel. Detailed Implementation

[0095] The negative electrode sheet of this disclosure, its preparation method, and embodiments of lithium-ion batteries containing the negative electrode sheet are described in detail below with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter of the claims.

[0096] In this disclosure, "range" is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" is a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer greater than or equal to 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0097] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0098] Unless otherwise specified, all steps in this disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0099] Unless otherwise specified, the terms “comprising,” “including,” “having,” “containing,” or any other variations thereof used in this disclosure are intended to cover non-exclusive inclusion.

[0100] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0101] Unless otherwise specified, the indefinite articles “a” and “an” preceding an element or component in this disclosure do not impose any limitation on the quantity requirement (i.e., the number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity is clearly intended to define the singular form.

[0102] Furthermore, numerous expressions will be mentioned in the following description, which are defined to have the following meanings.

[0103] The term "negative electrode" refers to the electrode in a battery that has a lower potential and undergoes an oxidation reaction.

[0104] The term "current collector" refers to any conductive substrate that can conduct current to the electrodes during the discharge or charging of a lithium-ion battery.

[0105] The term "negative electrode active material" refers to an active material that can be intercalated (also known as "doped") with lithium.

[0106] The term "natural graphite" refers to graphite that forms naturally in nature.

[0107] The term "artificial graphite" refers to graphite that is synthesized or processed.

[0108] The term "from the inside out" refers to extending outwards from the current collector as the inner layer.

[0109] The term "blind via" refers to a via that connects the surface layer and the inner layer without penetrating the entire layer.

[0110] The term "system consisting of the first negative electrode active material layer and the second negative electrode active material layer" refers to considering the first negative electrode active material layer and the second negative electrode active material layer as a single, integrated layer.

[0111] The term "pore formation rate" refers to the ratio of the total volume of blind pores to the volume of the negative electrode active material layer.

[0112] The term "lithium-ion battery" refers to a type of rechargeable battery in which lithium ions move from the anode to the cathode during discharge and from the cathode to the anode during charging.

[0113] The term "median particle size" refers to D50, which is the particle size corresponding to 50% of the cumulative particle size distribution of a sample. The median particle size in this disclosure is determined using a particle size analyzer-laser diffraction method, and for details, please refer to the standard GB / T19077-2016.

[0114] Negative electrode sheet

[0115] To at least partially address one or more of the aforementioned problems and other potential problems, a first exemplary embodiment of this disclosure provides a negative electrode sheet comprising:

[0116] Current collector; and

[0117] A negative electrode active material layer is formed on the current collector;

[0118] The negative electrode active material layer comprises at least two negative electrode active material layers from the inside out. The negative electrode active material layers include negative electrode active materials selected from natural graphite or artificial graphite, and the at least two negative electrode active material layers include at least one negative electrode active material layer containing natural graphite and at least one negative electrode active material layer containing artificial graphite.

[0119] In some embodiments, the negative electrode active material layer comprises, from the inside out, a first negative electrode active material layer and a second negative electrode active material layer, wherein the negative electrode active material in the first negative electrode active material layer includes natural graphite, and the negative electrode active material in the second negative electrode active material layer includes artificial graphite.

[0120] In some embodiments, one or more blind holes are provided in the first negative electrode active material layer, and the openings of the blind holes are located on the outside of the first negative electrode active material layer.

[0121] In some embodiments, the depth of the blind via is 1-80%, 10-70%, or 20-60% of the thickness of the first negative electrode active material layer, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%. %, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or any value between these; and / or

[0122] The aperture of the blind hole is 20-300μm or 80-150μm, for example, it can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 260μm, 270μm, 280μm, 290μm, 300μm or any value between these values; and / or

[0123] The spacing between the blind holes is 100-1000 μm or 400-500 μm, for example, it can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm. m, 290μm, 300μm, 310μm, 320μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, 4 10μm, 420μm, 430μm, 440μm, 450μm, 460μm, 470μm, 480μm, 490μm, 500μm, 510μm, 520μm, 530μm m, 540μm, 550μm, 560μm, 570μm, 580μm, 590μm, 600μm, 610μm, 620μm, 630μm, 640μm, 650μm, 6 60μm, 670μm, 680μm, 690μm, 700μm, 710μm, 720μm, 730μm, 740μm, 750μm, 760μm, 770μm, 780μm μm, 790μm, 800μm, 810μm, 820μm, 830μm, 840μm, 850μm, 860μm, 870μm, 880μm, 890μm, 900μm, 910μm, 920μm, 930μm, 940μm, 950μm, 960μm, 970μm, 980μm, 990μm, 1000μm or any value between these values; and / or

[0124] The hole formation rate of the blind hole is 0.1%-10% or 2%-4%, for example, it can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value between these values.

[0125] In some embodiments, the blind holes are evenly distributed.

[0126] There are no particular limitations on the thickness of the first negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the first negative electrode active material layer is 10-200 μm or 50-100 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm or any value between these values.

[0127] There are no particular limitations on the thickness of the second negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the second negative electrode active material layer is 10-200 μm or 50-100 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm or any value between these values.

[0128] Preferably, the thickness of the first negative electrode active material layer is greater than the thickness of the second negative electrode active material layer. This configuration can better reduce costs.

[0129] There are no particular limitations on the particle size of the natural graphite, and those commonly used in the art can be used. Typically, the median particle size of the natural graphite is 5-20 μm, for example, it can be 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 or any value between these values.

[0130] There are no particular limitations on the particle size of the artificial graphite, and those commonly used in the art can be used. Typically, the median particle size of the natural graphite is 5-20 μm, for example, it can be 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 or any value between these values.

[0131] There are no particular limitations on the composition of the first negative electrode active material layer and the second negative electrode active material layer; those commonly used in the art can be used. Typically, the first negative electrode active material layer and the second negative electrode active material layer each include:

[0132] 90-97% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0133] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0134] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, or any value between these values; and

[0135] 1-3% by weight of negative electrode thickener, for example, it can be 1% by weight, 2% by weight, 3% by weight or any value between these values;

[0136] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode thickener.

[0137] The negative electrode active material is selected from natural graphite or artificial graphite.

[0138] There are no particular limitations on the negative electrode conductive agent; those commonly used in the art can be used. Typically, the negative electrode conductive agent is selected from one or more of the following group: conductive carbon black, carbon nanotubes, vapor-generated carbon fibers, Ketjen black, and graphene.

[0139] There are no particular limitations on the negative electrode binder; those commonly used in the art can be used. Typically, the negative electrode binder is styrene-butadiene rubber and / or lithium polyacrylate.

[0140] There are no particular limitations on the negative electrode thickener; those commonly used in the art can be used. Typically, the negative electrode thickener is selected from one or more of the following group: sodium carboxymethyl cellulose, polyvinylidene fluoride, lithium polyacrylate, and polyacrylonitrile.

[0141] In some embodiments, the negative electrode active material layer comprises, from the inside out, a first negative electrode active material layer, a second negative electrode active material layer, and a third negative electrode active material layer. The negative electrode active material in the first negative electrode active material layer includes artificial graphite, the negative electrode active material in the second negative electrode active material layer includes natural graphite, and the negative electrode active material in the third negative electrode active material layer includes artificial graphite.

[0142] In some embodiments, the system consisting of the first negative electrode active material layer and the second negative electrode active material layer is provided with one or more blind holes, the openings of which are located on the outside of the second negative electrode active material layer.

[0143] In some embodiments, the depth of the blind hole is 1-80%, 10-70%, or 30-60% of the thickness of the second negative electrode active material layer plus the thickness of the first negative electrode active material layer. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, or 34%. 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or any value between these; and / or

[0144] The diameter of the blind hole is 20-500μm or 100-150μm, for example, it can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 2 60μm, 270μm, 280μm, 290μm, 300μm, 310μm, 320μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, 210μm, 410μm, 420μm, 430μm, 440μm, 450μm, 460μm, 470μm, 480μm, 490μm, 500μm or any value between these; and / or

[0145] The spacing between the blind holes is 100-1500 μm, preferably 400-500 μm, and can be, for example, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm, 290 μm. 300μm, 310μm, 320μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, 410μm, 420μm, 4 30μm, 440μm, 450μm, 460μm, 470μm, 480μm, 490μm, 500μm, 510μm, 520μm, 530μm, 540μm, 550μm, 560 μm, 570μm, 580μm, 590μm, 600μm, 610μm, 620μm, 630μm, 640μm, 650μm, 660μm, 670μm, 680μm, 690μm m, 700μm, 710μm, 720μm, 730μm, 740μm, 750μm, 760μm, 770μm, 780μm, 790μm, 800μm, 810μm, 820μm, 830μm, 840μm, 850μm, 860μm, 870μm, 880μm, 890μm, 900μm, 910μm, 920μm, 930μm, 940μm, 950μm, 960μm, 970μm, 980μm, 990μm, 1000μm, 1100μm, 1200μm, 1300μm, 1400μm, 1500μm or any value between these; and / or

[0146] The hole formation rate of the blind hole is 0.1%-10% or 2%-4%, for example, it can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value between these values.

[0147] In some embodiments, the blind holes are evenly distributed.

[0148] There are no particular limitations on the thickness of the first negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the first negative electrode active material layer is 10-100 μm or 60-100 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or any value between these values.

[0149] There are no particular limitations on the thickness of the second negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the second negative electrode active material layer is 10-200 μm or 60-100 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm or any value between these values.

[0150] There are no particular limitations on the thickness of the third negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the third negative electrode active material layer is 10-100 μm or 20-40 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or any value between these values.

[0151] Preferably, the thickness of the second negative electrode active material layer is greater than the thickness of the first negative electrode active material layer and / or the third negative electrode active material layer. This configuration can better reduce costs.

[0152] There are no particular limitations on the particle size of the natural and artificial graphite; those commonly used in the art can be used. Typically, the median particle size of the artificial graphite in the negative electrode active material of the first negative electrode active material layer is 5-20 μm, for example, it can be 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 or any value between these values; and / or

[0153] The median particle size of the natural graphite in the negative electrode active material of the second negative electrode active material layer is 5-20 μm, for example, it can be 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 or any value between these values; and / or

[0154] The median particle size of the artificial graphite in the negative electrode active material of the third negative electrode active material layer is 5-20 μm, for example, it can be 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 or any value between these values.

[0155] There are no particular limitations on the composition of the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer; those commonly used in the art can be used. Typically, each of the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer comprises:

[0156] 90-97% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0157] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0158] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0159] 1-3% by weight of negative electrode thickener, for example, it can be 1% by weight, 2% by weight, 3% by weight or any value between these values;

[0160] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode thickener.

[0161] The negative electrode active material is selected from natural graphite or artificial graphite.

[0162] There are no particular limitations on the negative electrode conductive agent; those commonly used in the art can be used. Typically, the negative electrode conductive agent is selected from one or more of the following group: conductive carbon black, carbon nanotubes, vapor-generated carbon fibers, Ketjen black, and graphene.

[0163] There are no particular limitations on the negative electrode binder; those commonly used in the art can be used. Typically, the negative electrode binder is styrene-butadiene rubber and / or lithium polyacrylate.

[0164] There are no particular limitations on the negative electrode thickener; those commonly used in the art can be used. Typically, the negative electrode thickener is selected from one or more of the following group: sodium carboxymethyl cellulose, polyvinylidene fluoride, lithium polyacrylate, and polyacrylonitrile.

[0165] Methods for preparing negative electrode sheets

[0166] To at least partially address one or more of the aforementioned problems and other potential problems, a second exemplary embodiment of this disclosure provides a method for preparing a negative electrode sheet, comprising:

[0167] At least two negative electrode slurries containing negative electrode active materials are stacked and coated onto a current collector and then dried to obtain the negative electrode sheet;

[0168] The negative electrode active material is selected from natural graphite or artificial graphite, and the at least two negative electrode slurries containing negative electrode active materials include at least one negative electrode slurry containing natural graphite and at least one negative electrode slurry containing artificial graphite.

[0169] In some embodiments, the method includes:

[0170] A first negative electrode slurry containing a negative electrode active material is coated onto a current collector and dried to form a first negative electrode active material layer, wherein the negative electrode active material includes natural graphite; and

[0171] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0172] To obtain the negative electrode sheet.

[0173] There are no particular limitations on the composition of the first and second negative electrode slurries mentioned above; those commonly used in the art can be used. Typically, each of the first and second negative electrode slurries comprises:

[0174] The composition can be 5-30% by weight, for example, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight, 30% by weight, or any value between these values; and

[0175] Solvents in the range of 70-95 wt%, for example, can be 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or any value between these values;

[0176] The composition comprises:

[0177] 90-97% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0178] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0179] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, or any value between these values; and

[0180] 1-3% by weight of negative electrode thickener, for example, it can be 1% by weight, 2% by weight, 3% by weight or any value between these values;

[0181] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode thickener.

[0182] In some embodiments, the method includes:

[0183] A first negative electrode slurry containing a negative electrode active material and a chemical pore-forming agent is coated onto a current collector and dried and pore-forming is performed to form a first negative electrode active material layer containing one or more blind pores. The negative electrode active material includes natural graphite, and the openings of the blind pores are located on the outer side of the first negative electrode active material layer.

[0184] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0185] To obtain the negative electrode sheet.

[0186] In one embodiment, the first negative electrode slurry comprises:

[0187] The composition can be 5-30% by weight, for example, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight, 30% by weight, or any value between these values; and

[0188] Solvents in the range of 70-95 wt%, for example, can be 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or any value between these values;

[0189] The composition comprises:

[0190] 85-95% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0191] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0192] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0193] 1-3% by weight of negative electrode thickener, for example, 1% by weight, 2% by weight, 3% by weight, or any value between these values; and

[0194] 1-10% by weight of pore-forming agent, for example, can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight or any value between these values;

[0195] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder, negative electrode thickener, and pore-forming agent.

[0196] In one embodiment, the second negative electrode slurry comprises:

[0197] The composition can be 5-30% by weight, for example, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight, 30% by weight, or any value between these values; and

[0198] Solvents in the range of 70-95 wt%, for example, can be 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or any value between these values;

[0199] The composition comprises:

[0200] 90-97% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0201] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0202] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, or any value between these values; and

[0203] 1-3% by weight of negative electrode thickener, for example, it can be 1% by weight, 2% by weight, 3% by weight or any value between these values;

[0204] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode thickener.

[0205] In some embodiments, the method includes:

[0206] A first negative electrode slurry containing a negative electrode active material is coated onto a current collector and dried to form a first negative electrode active material layer, wherein the negative electrode active material includes natural graphite.

[0207] Physical pore-forming is performed on the first negative electrode active material layer to form a first negative electrode active material layer containing one or more blind holes, wherein the openings of the blind holes are located on the outer side of the first negative electrode active material layer; and

[0208] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer containing one or more blind pores and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0209] To obtain the negative electrode sheet.

[0210] There are no particular limitations on the composition of the first and second negative electrode slurries mentioned above; those commonly used in the art can be used. Typically, each of the first and second negative electrode slurries comprises:

[0211] The composition can be 5-30% by weight, for example, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight, 30% by weight, or any value between these values; and

[0212] Solvents in the range of 70-95 wt%, for example, can be 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or any value between these values;

[0213] The composition comprises:

[0214] 90-97% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0215] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0216] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, or any value between these values; and

[0217] 1-3% by weight of negative electrode thickener, for example, it can be 1% by weight, 2% by weight, 3% by weight or any value between these values;

[0218] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode thickener.

[0219] In some embodiments, the depth of the blind via is 1-80%, 10-70%, or 20-60% of the thickness of the first negative electrode active material layer, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or 36%. 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or any value between these; and / or

[0220] The aperture of the blind hole is 20-300μm or 80-150μm, for example, it can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 260μm, 270μm, 280μm, 290μm, 300μm or any value between these values; and / or

[0221] The spacing between the blind holes is 100-1000 μm or 400-500 μm, for example, it can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm. m, 290μm, 300μm, 310μm, 320μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, 4 10μm, 420μm, 430μm, 440μm, 450μm, 460μm, 470μm, 480μm, 490μm, 500μm, 510μm, 520μm, 530μm m, 540μm, 550μm, 560μm, 570μm, 580μm, 590μm, 600μm, 610μm, 620μm, 630μm, 640μm, 650μm, 6 60μm, 670μm, 680μm, 690μm, 700μm, 710μm, 720μm, 730μm, 740μm, 750μm, 760μm, 770μm, 780μm μm, 790μm, 800μm, 810μm, 820μm, 830μm, 840μm, 850μm, 860μm, 870μm, 880μm, 890μm, 900μm, 910μm, 920μm, 930μm, 940μm, 950μm, 960μm, 970μm, 980μm, 990μm, 1000μm or any value between these values; and / or

[0222] The hole formation rate of the blind hole is 0.1%-10% or 2%-4%, for example, it can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value between these values.

[0223] In some embodiments, the blind holes are evenly distributed.

[0224] There are no particular limitations on the thickness of the first negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the first negative electrode active material layer is 10-200 μm or 50-100 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm or any value between these values.

[0225] There are no particular limitations on the thickness of the second negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the second negative electrode active material layer is 10-200 μm or 50-100 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm or any value between these values.

[0226] There are no particular limitations on the particle size of the natural graphite, and those commonly used in the art can be used. Typically, the median particle size of the natural graphite is 5-20 μm, for example, it can be 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 or any value between these values.

[0227] There are no particular limitations on the particle size of the artificial graphite, and those commonly used in the art can be used. Typically, the median particle size of the natural graphite is 5-20 μm, for example, it can be 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 or any value between these values.

[0228] In one embodiment, the method includes:

[0229] A first negative electrode slurry containing a negative electrode active material is coated onto a current collector and dried to form a first negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0230] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes natural graphite; and

[0231] A third negative electrode slurry containing a negative electrode active material is coated onto the second negative electrode active material layer and dried to form a third negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0232] To obtain the negative electrode sheet.

[0233] There are no particular limitations on the composition of the first, second, and third negative electrode slurries mentioned above; those commonly used in the art can be used. Typically, each of the first, second, and third negative electrode slurries comprises:

[0234] The composition can be 5-30% by weight, for example, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight, 30% by weight, or any value between these values; and

[0235] Solvents in the range of 70-95 wt%, for example, can be 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or any value between these values;

[0236] The composition comprises:

[0237] 90-97% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0238] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0239] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, or any value between these values; and

[0240] 1-3% by weight of negative electrode thickener, for example, it can be 1% by weight, 2% by weight, 3% by weight or any value between these values;

[0241] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode thickener.

[0242] In one embodiment, the method includes:

[0243] A first negative electrode slurry containing a negative electrode active material and a chemical pore-forming agent is coated onto a current collector and semi-dried at low temperature to form a semi-dried first negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0244] A second negative electrode slurry containing a negative electrode active material is coated onto the semi-dried first negative electrode active material layer and dried at high temperature to create pores, thereby forming a second negative electrode active material layer and forming one or more blind pores in the system composed of the first and second negative electrode active material layers. The negative electrode active material includes natural graphite, and the openings of the blind pores are located on the outer side of the second negative electrode active material layer.

[0245] A third negative electrode slurry containing a negative electrode active material is coated onto the second negative electrode active material layer and dried to form a third negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0246] To obtain the negative electrode sheet.

[0247] In one embodiment, the first negative electrode slurry comprises:

[0248] The composition can be 5-30% by weight, for example, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight, 30% by weight, or any value between these values; and

[0249] Solvents in the range of 70-95 wt%, for example, can be 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or any value between these values;

[0250] The composition comprises:

[0251] 85-95% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0252] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0253] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0254] 1-3% by weight of negative electrode thickener, for example, 1% by weight, 2% by weight, 3% by weight, or any value between these values; and

[0255] 1-10% by weight of pore-forming agent, for example, can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight or any value between these values;

[0256] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder, negative electrode thickener, and pore-forming agent.

[0257] There are no particular limitations on the composition of the second and third negative electrode slurries mentioned above; those commonly used in the art can be used. Typically, the second and third negative electrode slurries each include:

[0258] The composition can be 5-30% by weight, for example, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight, 30% by weight, or any value between these values; and

[0259] Solvents in the range of 70-95 wt%, for example, can be 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or any value between these values;

[0260] The composition comprises:

[0261] 90-97% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0262] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0263] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, or any value between these values; and

[0264] 1-3% by weight of negative electrode thickener, for example, it can be 1% by weight, 2% by weight, 3% by weight or any value between these values;

[0265] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode thickener.

[0266] In one embodiment, the method includes:

[0267] A first negative electrode slurry containing a negative electrode active material is coated onto a current collector and dried to form a first negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0268] A second negative electrode slurry containing a negative electrode active material is coated onto the first negative electrode active material layer and dried to form a second negative electrode active material layer, wherein the negative electrode active material includes natural graphite.

[0269] Physical pore-forming is performed on the system composed of the first negative electrode active material layer and the second negative electrode active material layer to form one or more blind holes, the openings of which are located on the outer side of the second negative electrode active material layer; and

[0270] A third negative electrode slurry containing a negative electrode active material is coated onto the second negative electrode active material layer and dried to form a third negative electrode active material layer, wherein the negative electrode active material includes artificial graphite.

[0271] To obtain the negative electrode sheet.

[0272] There are no particular limitations on the composition of the first, second, and third negative electrode slurries mentioned above; those commonly used in the art can be used. Typically, each of the first, second, and third negative electrode slurries comprises:

[0273] The composition can be 5-30% by weight, for example, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight, 30% by weight, or any value between these values; and

[0274] Solvents in the range of 70-95 wt%, for example, can be 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, or any value between these values;

[0275] The composition comprises:

[0276] 90-97% by weight of negative electrode active material, for example, it can be 90% by weight, 91% by weight, 92% by weight, 93% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight or any value between these values;

[0277] 1-5% by weight of negative electrode conductive agent, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value between these values;

[0278] 1-5% by weight of negative electrode binder, for example, it can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, or any value between these values; and

[0279] 1-3% by weight of negative electrode thickener, for example, it can be 1% by weight, 2% by weight, 3% by weight or any value between these values;

[0280] The above weight percentages are based on the total weight of the negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode thickener.

[0281] There are no particular limitations on the negative electrode conductive agent used in the above methods; those commonly used in the art can be used. Typically, the negative electrode conductive agent is selected from one or more of the following group: conductive carbon black, carbon nanotubes, vapor-generated carbon fibers, Ketten black, and graphene.

[0282] There are no particular limitations on the negative electrode binders used in the above methods; those commonly used in the art can be employed. Typically, the negative electrode binder is styrene-butadiene rubber and / or lithium polyacrylate.

[0283] There are no particular limitations on the negative electrode thickeners used in the above methods; those commonly used in the art can be used. Typically, the negative electrode thickener is selected from one or more of the following group: sodium carboxymethyl cellulose, polyvinylidene fluoride, lithium polyacrylate, and polyacrylonitrile.

[0284] There are no particular limitations on the pore-forming agents used in the above methods; those commonly used in the art can be used. Typically, the pore-forming agent is selected from one or more of the following group: hydrogen peroxide, urea, ammonium carbonate, ammonium bicarbonate, ammonium carbamate, dicalcium phosphate, naphthalene, and p-diphenylsulfonyl hydrazine oxide (OBSH), preferably ammonium bicarbonate.

[0285] In some embodiments, the depth of the blind hole is 1-80%, 10-70%, or 30-60% of the thickness of the second negative electrode active material layer plus the thickness of the first negative electrode active material layer. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, or 34%. 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or any value between these; and / or

[0286] The diameter of the blind hole is 20-500μm or 100-150μm, for example, it can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 2 60μm, 270μm, 280μm, 290μm, 300μm, 310μm, 320μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, 210μm, 410μm, 420μm, 430μm, 440μm, 450μm, 460μm, 470μm, 480μm, 490μm, 500μm or any value between these; and / or

[0287] The spacing between the blind holes is 100-1500μm or 400-500μm, for example, it can be 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 260μm, 270μm, 280μm, 290μm, 30μm, etc. 0μm, 310μm, 320μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, 410μm, 420μm, 430 μm, 440μm, 450μm, 460μm, 470μm, 480μm, 490μm, 500μm, 510μm, 520μm, 530μm, 540μm, 550μm, 560μm m, 570μm, 580μm, 590μm, 600μm, 610μm, 620μm, 630μm, 640μm, 650μm, 660μm, 670μm, 680μm, 690μm , 700μm, 710μm, 720μm, 730μm, 740μm, 750μm, 760μm, 770μm, 780μm, 790μm, 800μm, 810μm, 820μm, 830μm, 840μm, 850μm, 860μm, 870μm, 880μm, 890μm, 900μm, 910μm, 920μm, 930μm, 940μm, 950μm, 960μm, 970μm, 980μm, 990μm, 1000μm, 1100μm, 1200μm, 1300μm, 1400μm, 1500μm or any value between these; and / or

[0288] The hole formation rate of the blind hole is 0.1%-10% or 2%-4%, for example, it can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value between these values.

[0289] In some embodiments, the blind holes are evenly distributed.

[0290] There are no particular limitations on the thickness of the first negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the first negative electrode active material layer is 10-100 μm or 60-100 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or any value between these values.

[0291] There are no particular limitations on the thickness of the second negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the second negative electrode active material layer is 10-200 μm or 60-100 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm or any value between these values.

[0292] There are no particular limitations on the thickness of the third negative electrode active material layer, and those commonly used in the art can be used. Typically, the thickness of the third negative electrode active material layer is 10-100 μm or 20-40 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or any value between these values.

[0293] There are no particular limitations on the particle size of the natural and artificial graphite; those commonly used in the art can be used. Typically, the median particle size of the artificial graphite in the negative electrode active material of the first negative electrode active material layer is 5-20 μm, for example, it can be 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 or any value between these values; and / or

[0294] The median particle size of the natural graphite in the negative electrode active material of the second negative electrode active material layer is 5-20 μm, for example, it can be 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 or any value between these values; and / or

[0295] The median particle size of the artificial graphite in the negative electrode active material of the third negative electrode active material layer is 5-20 μm, for example, it can be 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 or any value between these values.

[0296] Lithium-ion batteries

[0297] To at least partially address one or more of the aforementioned problems and other potential issues, a third exemplary embodiment of this disclosure provides a lithium-ion battery comprising a negative electrode sheet prepared according to the first exemplary embodiment described above or by the method described in the second exemplary embodiment. Typically, the lithium-ion battery can be a single cell, a battery module, or a battery pack.

[0298] The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0299] Example 1 (Preparation of negative electrode sheet using physical pore-forming method, three-layer structure)

[0300] refer to Figure 1 The negative electrode sheet is prepared by: firstly, forming a system consisting of a first negative electrode active material layer 102 and a second negative electrode active material layer 105 on a current collector 101; then, creating pores in this system to form blind pores 107; finally, forming a third negative electrode active material layer 108 on the second negative electrode active material layer 105. The specific method is as follows:

[0301] A first negative electrode slurry was prepared by mixing 95.5 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose thickener, and 1000 parts by weight of deionized water. The first negative electrode slurry was then uniformly coated onto a copper foil current collector and dried at 60°C to form a first negative electrode active material layer with a thickness of 50 μm.

[0302] A second negative electrode slurry was prepared by mixing 95.5 parts by weight of natural graphite (median particle size of 18 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The second negative electrode slurry was then uniformly coated onto the first negative electrode active material layer. After drying at 60°C, a second negative electrode active material layer was formed with a thickness of 60 μm.

[0303] A drilling device (i.e., the electrode drilling device disclosed in patent CN216084936U) is used to physically create pores in the system composed of the first negative electrode active material layer and the second negative electrode active material layer to form multiple uniformly distributed blind holes (pore creation rate of 4%). The opening of the blind hole is located on the outside of the second negative electrode active material layer. The depth of the blind hole is 90 μm, the diameter of the blind hole is 200 μm, and the spacing between the blind holes is 400 μm.

[0304] A third negative electrode slurry was prepared by mixing 95.5 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The prepared third negative electrode slurry was then uniformly coated onto the second negative electrode active material layer. After drying at 60°C, a third negative electrode active material layer with a thickness of 30 μm was formed.

[0305] Then, cold pressing and slitting are performed to obtain the negative electrode sheet.

[0306] Example 2 (Preparation of negative electrode sheet by chemical pore-forming method, three-layer structure)

[0307] The method for preparing the negative electrode sheet is as follows:

[0308] A first negative electrode slurry was prepared by mixing 90 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 2 parts by weight of sodium carboxymethyl cellulose thickener and 5 parts by weight of ammonium bicarbonate pore-forming agent with 1000 parts by weight of deionized water. The first negative electrode slurry was then uniformly coated onto copper foil current collector and semi-dried at 50°C to form a semi-dried first negative electrode active material layer with a thickness of 50 μm.

[0309] A second negative electrode slurry was prepared by mixing 95.5 parts by weight of natural graphite (median particle size of 18 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The second negative electrode slurry was then uniformly coated onto the semi-dry first negative electrode active material layer. After high-temperature drying at 60°C and pore formation, a second negative electrode active material layer was formed. One or more uniformly distributed blind pores (pore formation rate of 4%) were formed in the system composed of the first negative electrode active material layer and the second negative electrode active material layer. The thickness of the second negative electrode active material layer was 60 μm, the depth of the blind pores was 90 μm, the pore size of the blind pores was 200 μm, and the spacing between the blind pores was 400 μm.

[0310] A third negative electrode slurry was prepared by mixing 95.5 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The prepared third negative electrode slurry was then uniformly coated onto the second negative electrode active material layer. After drying at 60°C, a third negative electrode active material layer with a thickness of 30 μm was formed.

[0311] Then, cold pressing and slitting are performed to obtain the negative electrode sheet.

[0312] Example 3 (No holes, three-layer structure)

[0313] The method for preparing the negative electrode sheet is as follows:

[0314] A first negative electrode slurry was prepared by mixing 95.5 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose thickener, and 1000 parts by weight of deionized water. The first negative electrode slurry was then uniformly coated onto a copper foil current collector and dried at 60°C to form a first negative electrode active material layer with a thickness of 50 μm.

[0315] A second negative electrode slurry was prepared by mixing 95.5 parts by weight of natural graphite (median particle size of 18 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The second negative electrode slurry was then uniformly coated onto the first negative electrode active material layer. After drying at 60°C, a second negative electrode active material layer was formed with a thickness of 60 μm.

[0316] A third negative electrode slurry was prepared by mixing 95.5 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The prepared third negative electrode slurry was then uniformly coated onto the second negative electrode active material layer. After drying at 60°C, a third negative electrode active material layer with a thickness of 30 μm was formed.

[0317] Then, cold pressing and slitting are performed to obtain the negative electrode sheet.

[0318] Example 4 (Preparation of negative electrode sheet using physical pore-forming method, two-layer structure)

[0319] refer to Figure 2 The negative electrode sheet is prepared by: firstly, forming a first negative electrode active material layer 102 on the current collector 101, and then creating pores in the first negative electrode active material layer 102 to form blind holes 103 (containing channels 104). The specific method is as follows:

[0320] A first negative electrode slurry was prepared by mixing 95.5 parts by weight of natural graphite (median particle size of 18 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The first negative electrode slurry was then uniformly coated onto a copper foil current collector and dried at 60°C to form a first negative electrode active material layer with a thickness of 60 μm.

[0321] Physical pores are formed in the first negative electrode active material layer to create multiple uniformly distributed blind holes (pore formation rate 4%). The opening of the blind hole is located on the outside of the first negative electrode active material layer. The depth of the blind hole is 90 μm, the diameter of the blind hole is 200 μm, and the spacing between the blind holes is 400 μm.

[0322] A second negative electrode slurry was prepared by mixing 95.5 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The second negative electrode slurry was then uniformly coated onto the first negative electrode active material layer. After drying at 60°C, a second negative electrode active material layer was formed with a thickness of 50 μm.

[0323] Then, cold pressing and slitting are performed to obtain the negative electrode sheet.

[0324] Example 5 (Preparation of negative electrode sheet by chemical pore-forming method, two-layer structure)

[0325] The method for preparing the negative electrode sheet is as follows:

[0326] A first negative electrode slurry was prepared by mixing 90 parts by weight of natural graphite (median particle size of 18 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 2 parts by weight of sodium carboxymethyl cellulose thickener and 5 parts by weight of ammonium bicarbonate pore-forming agent with 1000 parts by weight of deionized water. The first negative electrode slurry was then uniformly coated onto a copper foil current collector. After high-temperature drying at 60°C and pore-forming, a first negative electrode active material layer containing multiple uniformly distributed blind holes (pore-forming rate of 4%) was formed. The opening of the blind holes was located on the outside of the first negative electrode active material layer. The depth of the blind holes was 90 μm, the pore size was 200 μm, the spacing between the blind holes was 400 μm, and the thickness of the first negative electrode active material layer was 60 μm.

[0327] A second negative electrode slurry was prepared by mixing 95.5 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The second negative electrode slurry was then uniformly coated onto the first negative electrode active material layer. After drying at 60°C, a second negative electrode active material layer was formed with a thickness of 50 μm.

[0328] Then, cold pressing and slitting are performed to obtain the negative electrode sheet.

[0329] Example 6 (No holes, two-layer structure)

[0330] A first negative electrode slurry was prepared by mixing 95.5 parts by weight of natural graphite (median particle size of 18 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The first negative electrode slurry was then uniformly coated onto a copper foil current collector and dried at 60°C to form a first negative electrode active material layer with a thickness of 60 μm.

[0331] A second negative electrode slurry was prepared by mixing 95.5 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The second negative electrode slurry was then uniformly coated onto the first negative electrode active material layer. After drying at 60°C, a second negative electrode active material layer was formed with a thickness of 80 μm.

[0332] Then, cold pressing and slitting are performed to obtain the negative electrode sheet.

[0333] Example 7

[0334] It is basically the same as Example 1, except that the depth of the blind hole is 70 μm.

[0335] Example 8

[0336] It is basically the same as Example 1, except that the depth of the blind hole is 108 μm.

[0337] Example 9

[0338] It is basically the same as Example 1, except that the diameter of the blind hole is 100μm.

[0339] Example 10

[0340] It is basically the same as Example 1, except that the diameter of the blind hole is 500 μm.

[0341] Example 11

[0342] It is basically the same as Example 1, except that the spacing of the blind holes is 100μm.

[0343] Example 12

[0344] It is basically the same as Example 1, except that the spacing of the blind holes is 1500μm.

[0345] Example 13

[0346] It is basically the same as Example 1, except that the hole formation rate of the blind hole is 0.1%.

[0347] Example 14

[0348] It is basically the same as Example 1, except that the hole formation rate of the blind hole is 10%.

[0349] Example 15

[0350] It is basically the same as Example 1, except that the thickness of the first negative electrode active material layer is 10 μm.

[0351] Example 16

[0352] It is basically the same as Example 1, except that the thickness of the first negative electrode active material layer is 70 μm.

[0353] Example 17

[0354] It is basically the same as Example 1, except that the thickness of the second negative electrode active material layer is 10 μm.

[0355] Example 18

[0356] It is basically the same as Example 1, except that the thickness of the second negative electrode active material layer is 70 μm.

[0357] Example 19

[0358] It is basically the same as Example 1, except that the thickness of the third negative electrode active material layer is 10 μm.

[0359] Example 20

[0360] It is basically the same as Example 1, except that the thickness of the third negative electrode active material layer is 50 μm.

[0361] Example 21

[0362] The method is basically the same as in Example 1, except that the median particle size of artificial graphite in the negative electrode active material of the first negative electrode active material layer is 10 μm, the median particle size of natural graphite in the negative electrode active material of the second negative electrode active material layer is 10 μm, and the median particle size of artificial graphite in the negative electrode active material of the third negative electrode active material layer is 10 μm.

[0363] Example 22

[0364] The method is basically the same as in Example 1, except that the median particle size of artificial graphite in the negative electrode active material of the first negative electrode active material layer is 20 μm, the median particle size of natural graphite in the negative electrode active material of the second negative electrode active material layer is 25 μm, and the median particle size of artificial graphite in the negative electrode active material of the third negative electrode active material layer is 20 μm.

[0365] Comparative Example 1 (One-layer structure)

[0366] A negative electrode slurry was prepared by mixing 95.5 parts by weight of natural graphite (median particle size of 18 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose, and 1000 parts by weight of deionized water. The prepared negative electrode slurry was then uniformly coated onto a copper foil current collector and dried at 60°C to form a first negative electrode active material layer with a thickness of 140 μm.

[0367] Then, cold pressing and slitting are performed to obtain the negative electrode sheet.

[0368] Comparative Example 2 (One-layer structure)

[0369] A negative electrode slurry was prepared by mixing 95.5 parts by weight of artificial graphite (median particle size of 12 μm), 1 part by weight of carbon nanotubes, 2 parts by weight of a mixture of styrene-butadiene rubber and lithium polyacrylate (mass ratio of 1:1), 1.5 parts by weight of sodium carboxymethyl cellulose thickener, and 1000 parts by weight of deionized water. The prepared negative electrode slurry was then uniformly coated onto a copper foil current collector and dried at 60°C to form a first negative electrode active material layer with a thickness of 140 μm.

[0370] Then, cold pressing and slitting are performed to obtain the negative electrode sheet.

[0371] test

[0372] Test Standards

[0373] The diameter of the blind hole is obtained by SEM observation. The method for determining the diameter of the blind hole is the longest distance between the edges on the opening side of the hole. That is, select two points on the edge of the opening side of the hole, measure the distance between the two points, and the longest distance is the diameter of the blind hole.

[0374] The spacing between blind holes was obtained by SEM observation. The spacing between blind holes refers to the shortest distance between the edges of the opening sides of two holes. That is, a point on the edge of the opening side of one hole and a point on the edge of the opening side of another hole are selected, and the distance between the two points is measured. The shortest distance is the spacing between blind holes.

[0375] The hole formation rate of blind holes was measured using the following method:

[0376] For regular cylindrical holes, the hole-forming rate of blind holes per unit area (e.g., 1 mm) is... 2 (Electrode sheet), the hole area divided by the unit area, and then multiplied by the ratio of hole depth to total thickness.

[0377] For conical holes, the hole-forming rate of blind holes per unit area (e.g., 1 mm) 2 (Electrode sheet), divide the hole area by the unit area, multiply by the ratio of hole depth to total thickness, and then multiply by 1 / 3.

[0378] Test Results

[0379] For specific test results, please refer to Table 1 below.

[0380]

[0381]

[0382]

[0383] As can be clearly seen from the data in Examples 3 and 6 in Table 1, this disclosure, by employing a method of stacking artificial graphite layers and natural graphite layers, balances the advantages of high energy density of artificial graphite and low cost of natural graphite, thereby achieving a compromise performance balance. That is, maintaining high energy density and short fast charging time while keeping costs low. Furthermore, the data from the other examples in Table 1 also clearly show that by creating pores in the negative electrode active material layer, highly efficient lithium intercalation channels can be formed, thereby improving the overall lithium intercalation capability compared to Examples 3 and 6, and achieving a better technical effect of achieving a good balance between maintaining high energy density, high fast charging capability, and cost control.

[0384] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. Negative electrode plate, which includes: current collector; and A layer of negative electrode active material is formed on the current collector; in, The negative electrode active material layer comprises, from the inside out, a first negative electrode active material layer, a second negative electrode active material layer, and a third negative electrode active material layer. The negative electrode active material in the first negative electrode active material layer includes artificial graphite, the negative electrode active material in the second negative electrode active material layer includes natural graphite, and the negative electrode active material in the third negative electrode active material layer includes artificial graphite. The system consisting of the first negative electrode active material layer and the second negative electrode active material layer is provided with one or more blind holes, and the opening of the blind hole is located on the outside of the second negative electrode active material layer; The hole formation rate of the blind hole is 0.1%-10%; The artificial graphite in the third negative electrode active layer penetrates into the first and second negative electrode active material layers.

2. The negative electrode sheet according to claim 1, wherein the depth of the blind hole is 1-80% of the thickness of the second negative electrode active material layer plus the thickness of the first negative electrode active material layer.

3. The negative electrode sheet according to claim 2, wherein the depth of the blind hole is 10-70% of the thickness of the second negative electrode active material layer plus the thickness of the first negative electrode active material layer.

4. The negative electrode sheet according to claim 2, wherein the depth of the blind hole is 30-60% of the thickness of the second negative electrode active material layer plus the thickness of the first negative electrode active material layer.

5. The negative electrode sheet according to claim 1, wherein the diameter of the blind hole is 20-500 μm.

6. The negative electrode sheet according to claim 5, wherein the diameter of the blind hole is 100-150 μm.

7. The negative electrode sheet according to claim 1, wherein the spacing between the blind holes is 100-1500 μm.

8. The negative electrode sheet according to claim 7, wherein the spacing between the blind holes is 400-500 μm.

9. The negative electrode sheet according to claim 1, wherein the perforation rate of the blind hole is 2%-4%.

10. The negative electrode sheet according to claim 1, wherein the thickness of the first negative electrode active material layer is 10-100 μm.

11. The negative electrode sheet according to claim 10, wherein the thickness of the first negative electrode active material layer is 60-100 μm.

12. The negative electrode sheet according to claim 1, wherein the thickness of the second negative electrode active material layer is 10-200 μm.

13. The negative electrode sheet according to claim 12, wherein the thickness of the second negative electrode active material layer is 60-100 μm.

14. The negative electrode sheet according to claim 1, wherein the thickness of the third negative electrode active material layer is 10-100 μm.

15. The negative electrode sheet according to claim 14, wherein the thickness of the third negative electrode active material layer is 20-40 μm.

16. The negative electrode sheet according to claim 1, wherein the thickness of the second negative electrode active material layer is greater than the thickness of the first negative electrode active material layer and / or the third negative electrode active material layer.

17. The negative electrode sheet according to claim 1, wherein the median particle size of the artificial graphite in the negative electrode active material of the first negative electrode active material layer is 5-20 μm; and / or The median particle size of the natural graphite in the negative electrode active material of the second negative electrode active material layer is 5-20 μm; and / or The median particle size of the artificial graphite in the negative electrode active material of the third negative electrode active material layer is 5-20 μm.

18. A lithium-ion battery comprising a negative electrode sheet according to any one of claims 1-17.

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