CN117577773A

CN117577773A - Negative plate, lithium ion battery and vehicle

Info

Publication number: CN117577773A
Application number: CN202210945458.9A
Authority: CN
Inventors: 杨勇
Original assignee: Weilai Automobile Technology Anhui Co Ltd
Current assignee: Weilai Automobile Technology Anhui Co Ltd
Priority date: 2022-08-08
Filing date: 2022-08-08
Publication date: 2024-02-20

Abstract

The invention relates to the technical field of batteries, in particular to a negative plate, a lithium ion battery and a vehicle, and aims to solve the problem that lithium is easy to separate out from the surface of the negative plate in the later life cycle of the lithium ion battery. Therefore, the negative electrode plate comprises a negative electrode current collector, the negative electrode current collector comprises a first surface and a second surface which are opposite to each other, at least one of the first surface and the second surface is provided with two layers of negative electrode active material layers, the first negative electrode active material layer is arranged on the surface of the negative electrode current collector, the second negative electrode active material layer is arranged on the surface of the first negative electrode active material layer, the lithium intercalation potential of the first negative electrode active material layer is lower than that of the second negative electrode active material layer, the lithium intercalation potential of the surface layer of the negative electrode plate is improved, the lithium precipitation potential of the surface layer of the negative electrode plate is ensured to be higher than that of the inside of the negative electrode plate, the negative electrode lithium precipitation of the lithium ion battery in the working process is effectively restrained, the performance attenuation speed of the battery core of the lithium ion battery is slowed down, and the cycle life of the lithium ion battery is prolonged.

Description

Negative plate, lithium ion battery and vehicle

Technical Field

The invention relates to the technical field of batteries, and particularly provides a negative plate, a lithium ion battery and a vehicle.

Background

Along with the continuous high-speed development of the fields of large-scale energy storage, electric automobiles, consumer electronics and the like, the demand for lithium ion batteries is continuously increased, and the performances of energy density, quick charge capacity, safety reliability and the like are gradually approaching the limit.

At present, the charging rate of a lithium ion battery is faster and faster, at the later stage of the life cycle of the lithium ion battery, an SEI (Solid Electrolyte Interface ) film on the surface of a negative electrode is gradually thickened, the internal resistance of the lithium ion battery is gradually increased, the internal polarization is larger and larger, the dynamic performance is attenuated, lithium is easy to separate out from the surface of a negative electrode plate, and the separated lithium can cause the performance of a battery core to further accelerate and attenuate, so that serious potential safety hazards exist.

Accordingly, there is a need in the art for a new negative electrode sheet, lithium ion battery, and vehicle to address the above-described problems.

Disclosure of Invention

The invention aims to solve the technical problems that the charging rate of the existing lithium ion battery is faster and faster, and lithium is easy to separate out from the surface of the negative electrode plate in the later life cycle of the lithium ion battery.

In a first aspect, the present invention provides a negative electrode sheet, where the negative electrode sheet includes a negative electrode current collector, the negative electrode current collector includes a first surface and a second surface opposite to each other, at least one of the first surface and the second surface is provided with two negative electrode active material layers, the first negative electrode active material layer is disposed on the surface of the negative electrode current collector, the second negative electrode active material layer is disposed on the surface of the first negative electrode active material layer, and a lithium intercalation potential of the first negative electrode active material layer is lower than a lithium intercalation potential of the second negative electrode active material layer.

In a preferred embodiment of the above negative electrode sheet, the difference between the lithium intercalation potential of the first negative electrode active material layer and the lithium intercalation potential of the second negative electrode active material layer is 0.05V to 1.5V, preferably 0.1V to 1.0V, and preferably 0.1V to 0.5V.

In the preferable technical scheme of the negative electrode sheet, the lithium intercalation potential of the first negative electrode active material layer is 0-0.5V; the second negative electrode active material layer has a lithium intercalation potential of 0.1 to 1.55V.

In a preferred embodiment of the above negative electrode sheet, the first negative electrode active material layer contains only the first negative electrode active material or contains both the first negative electrode active material and the second negative electrode active material, and the second negative electrode active material layer contains only the second negative electrode active material or contains both the first negative electrode active material and the second negative electrode active material; wherein the lithium intercalation potential of the first negative electrode active material is 0-0.5V, and the lithium intercalation potential of the second negative electrode active material is 0.1-1.55V.

In the above preferred technical solution of the negative electrode sheet, the proportion of the mass of the first negative electrode active material in the first negative electrode active material layer to the total mass of the active materials in the first negative electrode active material layer is 10 to 100wt%; the mass of the first negative electrode active material in the second negative electrode active material layer accounts for 0-90 wt% of the total mass of the active materials in the second negative electrode active material layer; wherein the content of the first anode active material in the first anode active material layer is greater than or equal to the content of the first anode active material in the second anode active layer.

In the preferable technical scheme of the negative electrode sheet, the proportion of the mass of the first negative electrode active material in the first negative electrode active material layer to the total mass of the active materials in the first negative electrode active material layer is 50-99 wt%; the mass of the first anode active material in the second anode active material layer is 2-88 wt% of the total mass of the active materials in the second anode active material layer.

In the preferable technical scheme of the negative electrode sheet, the mass of the first negative electrode active material in the first negative electrode active material layer accounts for 80-97wt% of the total mass of the active materials in the first negative electrode active material layer; the mass of the first anode active material in the second anode active material layer is 20 to 80wt% of the total mass of the active materials in the second anode active material layer.

In the above preferred technical solution of the negative electrode sheet, the first negative electrode active material is selected from one or more of a carbon-based material, a silicon-based material, a tin-based material, a lithium titanate material, a metal oxide material, and a lithium metal material.

In the preferable technical scheme of the negative plate, the carbon-based material is high-compaction artificial graphite, quick-filling artificial graphite, natural graphite, hard carbon, soft carbon or mesophase carbon microspheres; and/or the silicon-based material is a silicon-carbon material, a silicon oxygen material, a silicon alloy material or a pure silicon material; and/or the metal oxide material is titanium oxide, nickel oxide or manganese oxide.

In the above preferred technical solution of the negative electrode sheet, the first negative electrode active material is selected from one or more of fast-charging artificial graphite, natural graphite, hard carbon, soft carbon, mesophase carbon microspheres, and lithium metal materials.

In the above preferred technical solution of the negative electrode sheet, the second negative electrode active material is selected from one or more of a carbon-based material, a silicon-based material, a tin-based material, a lithium titanate material, a metal oxide material, and a lithium metal material.

In the above preferred technical solution of the negative electrode sheet, the second negative electrode active material is selected from one or more of highly compacted artificial graphite, a silicon-based material, a tin-based material, a lithium titanate material, and a metal oxide material.

In the preferable technical scheme of the negative electrode sheet, the second negative electrode active material is selected from one or more of high-compaction artificial graphite, silicon carbon material, silicon oxygen material, titanium oxide and lithium titanate material.

In the preferable technical scheme of the above-mentioned negative electrode sheet, when the type of the first negative electrode active material is the same as the type of the second negative electrode active material, the median diameter D of the first negative electrode active material ₅₀ A median particle diameter D of 4-15 μm, of the second anode active material ₅₀ Is 6 to 25 mu m, and the median diameter D of the first anode active material ₅₀ And said secondMedian particle diameter D of negative electrode active material ₅₀ The ratio of (2) is greater than or equal to 0.2 and less than or equal to 1.

In the preferable technical scheme of the negative electrode sheet, the first negative electrode active material has a median diameter D ₅₀ Median particle diameter D with the second anode active material ₅₀ The ratio of (2) is greater than or equal to 0.3 and less than or equal to 0.8.

In the above preferred technical solution of the negative electrode sheet, the thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is 9:1 to 1:9.

In the above preferred technical solution of the negative electrode sheet, the thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is 7: 3-3: 7.

in the preferable technical scheme of the negative plate, the negative current collector is a common copper foil or a carbon-coated copper foil.

In the above preferred technical solution of the negative electrode sheet, the first negative electrode active material layer includes the following raw materials by weight percent: 70 to 98.5wt% of a first negative electrode active material or a first negative electrode active material and a second negative electrode active material, 0.5 to 10wt% of a first thickener, 0.5 to 10wt% of a first conductive agent, and 0.5 to 10wt% of a first binder; and/or the second anode active material layer comprises the following raw materials in percentage by weight: 70 to 98.5wt% of a second anode active material or a first anode active material and a second anode active material, 0.5 to 10wt% of a second thickener, 0.5 to 10wt% of a second conductive agent, and 0.5 to 10wt% of a second binder.

In a second aspect, the present invention provides a lithium ion battery, which includes the negative electrode sheet according to any one of the above preferred technical solutions.

In a third aspect, the present invention provides a vehicle comprising a negative electrode sheet or a lithium ion battery according to any one of the above preferred embodiments.

In a preferred technical scheme of the negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector, the negative electrode current collector comprises a first surface and a second surface which are opposite to each other, at least one of the first surface and the second surface is provided with two layers of negative electrode active material layers, the first negative electrode active material layer is arranged on the surface of the negative electrode current collector, the second negative electrode active material layer is arranged on the surface of the first negative electrode active material layer, and the lithium intercalation potential of the first negative electrode active material layer is lower than that of the second negative electrode active material layer.

Compared with the condition that the surface layer lithium intercalation potential of the negative electrode plate is low in the prior art, the lithium intercalation potential of the second negative electrode active material layer far away from the negative electrode current collector is set to be higher than the lithium intercalation potential of the first negative electrode active material layer close to the negative electrode current collector, through the arrangement, the lithium intercalation potential of the surface layer of the negative electrode plate is improved, and is ensured to be higher than the lithium precipitation potential of the interior of the negative electrode plate, so that the problem that lithium is precipitated on the surface of the negative electrode of the lithium ion battery in the working process is effectively inhibited, and even under the condition of overcharging, the precipitation of lithium metal in the negative electrode plate can be started from the interior of the negative electrode plate preferentially, and the lithium precipitation cannot be started from the surface layer of the negative electrode plate, thereby slowing down the performance decay speed of the battery core of the lithium ion battery, prolonging the cycle life of the lithium ion battery, and maximally reducing the potential safety hazards such as combustion, explosion and the like.

Further, when the second anode active material layer only contains the second anode active material, that is, the anode sheet surface layer area only contains the second anode active material with relatively high lithium intercalation potential, so that the lithium intercalation potential of the anode sheet surface layer reaches the highest, the anode sheet surface chromatographic lithium of the lithium ion battery in the working process is further inhibited, the performance attenuation speed of the battery core of the lithium ion battery is further slowed down, and the cycle performance and reliability of the lithium ion battery are further improved.

Further, when the first anode active material layer only contains the first anode active material, that is, the anode current collector surface layer area only contains the first anode active material with relatively low lithium intercalation potential, so that the lithium intercalation potential of the anode current collector surface layer area reaches the minimum, the lithium intercalation potential of the anode sheet surface layer is ensured to be higher than the lithium intercalation potential of the anode current collector surface layer area, the anode sheet surface layer lithium chromatography of the lithium ion battery in the working process is further inhibited, the performance attenuation speed of the battery core of the lithium ion battery is further slowed down, and the cycle performance and reliability of the lithium ion battery are further improved.

Further, when the type of the first anode active material is the same as that of the second anode active material, the median diameter D of the first anode active material ₅₀ Median diameter D of the second anode active material is 4-15 μm ₅₀ Is 6 to 25 mu m, and the median diameter D of the first anode active material ₅₀ Median particle diameter D with second negative electrode active material ₅₀ A ratio of greater than or equal to 0.2 and less than or equal to 1, in particular the median diameter D of the first negative electrode active material ₅₀ The lithium intercalation potential of the corresponding anode active material is correspondingly increased along with the increase of the median particle diameter, so that the lithium intercalation potential of the first anode active material is ensured to be lower than that of the second anode active material layer, and the problem of lithium precipitation on the anode surface of the lithium ion battery in the working process can be inhibited even if the anode active materials with the same type are adopted.

Scheme 1, a negative plate, its characterized in that, the negative plate includes the negative current collector, the negative current collector includes opposite first surface and second surface, be provided with two-layer negative electrode active material layer on at least one of first surface and the second surface, first negative electrode active material layer sets up the surface of negative current collector, second negative electrode active material layer sets up the surface on first negative electrode active material layer, the lithium intercalation potential on first negative electrode active material layer is less than the lithium intercalation potential on second negative electrode active material layer.

The negative electrode sheet according to claim 2, wherein the difference between the lithium intercalation potential of the first negative electrode active material layer and the lithium intercalation potential of the second negative electrode active material layer is 0.05V to 1.5V, preferably 0.1V to 1.0V, and preferably 0.1V to 0.5V.

The negative electrode sheet according to claim 3, wherein the lithium intercalation potential of the first negative electrode active material layer is 0 to 0.5V;

the second negative electrode active material layer has a lithium intercalation potential of 0.1 to 1.55V.

The negative electrode sheet according to claim 4, wherein the first negative electrode active material layer contains only the first negative electrode active material or contains both the first negative electrode active material and the second negative electrode active material, and the second negative electrode active material layer contains only the second negative electrode active material or contains both the first negative electrode active material and the second negative electrode active material;

wherein the lithium intercalation potential of the first negative electrode active material is 0-0.5V, and the lithium intercalation potential of the second negative electrode active material is 0.1-1.55V.

The negative electrode sheet according to claim 5, characterized in that the mass of the first negative electrode active material in the first negative electrode active material layer is 10 to 100wt% of the total mass of the active materials in the first negative electrode active material layer;

The mass of the first negative electrode active material in the second negative electrode active material layer accounts for 0-90 wt% of the total mass of the active materials in the second negative electrode active material layer;

wherein the content of the first anode active material in the first anode active material layer is greater than or equal to the content of the first anode active material in the second anode active layer.

The negative electrode sheet according to claim 6, characterized in that the mass of the first negative electrode active material in the first negative electrode active material layer is 50 to 99wt% of the total mass of the active materials in the first negative electrode active material layer;

the mass of the first anode active material in the second anode active material layer is 2-88 wt% of the total mass of the active materials in the second anode active material layer.

The negative electrode sheet according to claim 7, characterized in that the mass of the first negative electrode active material in the first negative electrode active material layer is 80 to 97wt% of the total mass of the active materials in the first negative electrode active material layer;

the mass of the first anode active material in the second anode active material layer is 20 to 80wt% of the total mass of the active materials in the second anode active material layer.

The negative electrode sheet according to any one of aspects 8, 4 to 7, wherein the first negative electrode active material is selected from one or more of a carbon-based material, a silicon-based material, a tin-based material, a lithium titanate material, a metal oxide material, and a lithium metal material.

The negative plate according to scheme 9, wherein the carbon-based material is highly compacted artificial graphite, fast-charged artificial graphite, natural graphite, hard carbon, soft carbon, or mesophase carbon microspheres; and/or

The silicon-based material is a silicon-carbon material, a silicon oxygen material, a silicon alloy material or a pure silicon material; and/or

The metal oxide material is titanium oxide, nickel oxide or manganese oxide.

The negative electrode sheet according to claim 10, wherein the first negative electrode active material is one or more selected from the group consisting of fast-charged artificial graphite, natural graphite, hard carbon, soft carbon, mesophase carbon microspheres, and lithium metal materials.

The negative electrode sheet according to any one of aspects 11, 4 to 7, wherein the second negative electrode active material is selected from one or more of a carbon-based material, a silicon-based material, a tin-based material, a lithium titanate material, a metal oxide material, and a lithium metal material.

The negative electrode sheet according to claim 12, wherein the carbon-based material is highly compacted artificial graphite, quick-charge artificial graphite, natural graphite, hard carbon, soft carbon, or mesophase carbon microspheres; and/or

The metal oxide material is titanium oxide, nickel oxide or manganese oxide.

The negative electrode sheet according to claim 13, wherein the second negative electrode active material is one or more selected from the group consisting of highly compacted artificial graphite, a silicon-based material, a tin-based material, a lithium titanate material, and a metal oxide material.

The negative electrode sheet according to claim 14, wherein the second negative electrode active material is one or more selected from highly compacted artificial graphite, a silicon carbon material, a silicon oxygen material, titanium oxide, and a lithium titanate material.

The negative electrode sheet according to any one of aspects 15, 4 to 7, characterized in that, when the first negative electrode active material and the second negative electrode active material are of the same type, the median particle diameter D of the first negative electrode active material ₅₀ A median particle diameter D of 4-15 μm, of the second anode active material ₅₀ Is 6 to 25 mu m, and the median diameter D of the first anode active material ₅₀ Median particle diameter D with the second anode active material ₅₀ The ratio of (2) is greater than or equal to 0.2 and less than or equal to 1.

The negative electrode sheet according to claim 16, wherein the first negative electrode active material has a median diameter D ₅₀ Median particle diameter D with the second anode active material ₅₀ The ratio of (2) is greater than or equal to 0.3 and less than or equal to 0.8.

The negative electrode sheet according to any one of claims 17, 4 to 7, characterized in that a thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is 9:1 to 1:9.

the negative electrode sheet according to claim 18, wherein a thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is 7: 3-3: 7.

the negative electrode sheet according to claim 19, any one of claims 4 to 7, wherein the negative electrode current collector is a normal copper foil or a carbon-coated copper foil.

The negative electrode sheet according to any one of claims 20 to 7, wherein the first negative electrode active material layer contains the following raw materials in weight percent:

70 to 98.5wt% of a first negative electrode active material or a first negative electrode active material and a second negative electrode active material, 0.5 to 10wt% of a first thickener, 0.5 to 10wt% of a first conductive agent, and 0.5 to 10wt% of a first binder; and/or

The second negative electrode active material layer comprises the following raw materials in percentage by weight:

70 to 98.5wt% of a second anode active material or a first anode active material and a second anode active material, 0.5 to 10wt% of a second thickener, 0.5 to 10wt% of a second conductive agent, and 0.5 to 10wt% of a second binder.

A lithium ion battery according to claim 21, characterized in that the lithium ion battery includes the negative electrode sheet according to any one of claims 1 to 20.

A vehicle according to claim 22, characterized in that the vehicle includes the negative electrode sheet according to any one of claims 1 to 20 or the lithium ion battery according to claim 21.

Drawings

The negative electrode sheet of the present invention is described below with reference to the accompanying drawings, in which:

fig. 1 is a schematic structural view of a negative electrode sheet of the present invention;

fig. 2 is a schematic structural view of a negative electrode sheet according to the present invention.

List of reference numerals

1. A negative electrode current collector;

21. a first anode active material layer; 22. a second anode active material layer;

31. a first negative electrode active material; 32. a second negative electrode active material;

4. a diaphragm.

Detailed Description

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are merely for explaining the technical principles of the present invention, and are not intended to limit the scope of the present invention. For example, although the present application is described in connection with an electric vehicle, the technical solution of the present invention is not limited thereto, and the negative electrode sheet may obviously be applied to other vehicles such as a hybrid vehicle, without departing from the principle and scope of the present invention.

It should be noted that, in the description of the present invention, terms such as "upper", "lower", and the like, refer to directions or positional relationships based on those shown in the drawings, which are merely for convenience of description, and do not indicate or imply that the apparatus or elements must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

Based on the technical problems in the prior art, the invention provides a negative plate, which comprises a negative current collector, wherein at least one of a first surface and a second surface of the negative current collector, which are opposite, is provided with two negative active material layers, and the lithium intercalation potential of the second negative active material layer far away from the negative current collector is set to be higher than that of the first negative active material layer close to the negative current collector.

Referring first to fig. 1 and 2, the negative electrode sheet of the present invention will be described. Fig. 1 is a schematic structural diagram of a negative plate of the present invention; fig. 2 is a schematic structural view of a negative electrode sheet according to the present invention.

As shown in fig. 1 and 2, the negative electrode sheet of the present invention comprises a negative electrode current collector 1, the negative electrode current collector 1 comprises a first surface and a second surface opposite to each other along a thickness direction (i.e., a direction from bottom to top in fig. 1), two layers of negative electrode active material layers, namely a first negative electrode active material layer 21 and a second negative electrode active material layer 22, are arranged on the first surface (i.e., the surface shown in fig. 1) of the negative electrode current collector 1, wherein the first negative electrode active material layer 21 is arranged on the surface of the negative electrode current collector 1, the second negative electrode active material layer 22 is arranged on the surface of the first negative electrode active material layer 21, and the lithium intercalation potential of the first negative electrode active material layer is lower than the lithium intercalation potential of the second negative electrode active material layer, so that the lithium intercalation potential of the surface layer of the negative electrode sheet is higher, and lithium precipitation of a negative electrode in a working process of the lithium ion battery is effectively inhibited; further, since the lithium intercalation potential of the first anode active material layer 21 is low, the influence on the internal resistance of the lithium ion battery is small, and the resistance is low.

Preferably, the first anode active material layer 21 and the second anode active material layer 22 may be sequentially coated on the first surface of the anode current collector 1, or the first anode active material layer 21 and the second anode active material layer 22 may be simultaneously coated, i.e., the first anode active material layer 21 and the second anode active material layer 22 are simultaneously coated on the first surface of the anode current collector 1.

Further, one of gravure coating, transfer coating, extrusion coating, and spray coating may be selected to coat the first anode active material layer 21 and the second anode active material layer 22, and of course, any two of the above coating methods may be selected to coat the first anode active material layer 21 and the second anode active material layer 22, and a specific coating method may be determined by one skilled in the art according to actual process requirements, etc., which is not limited in the present invention.

In particular, the coating step of the two anode active material layers can be performed by a mode of coating one layer and then coating the other layer; the two layers are coated simultaneously, i.e., the two layers of active material slurry are coated on at least one surface of the negative electrode current collector simultaneously.

Further, a separator 4 may be provided on the surface of the second anode active material layer 22.

The negative electrode current collector 1 is a metal foil such as copper foil, aluminum foil, or nickel foil. Further, the negative electrode current collector 1 is a normal copper foil or a carbon-coated copper foil, wherein the normal copper foil is a copper foil which has not been subjected to other treatments such as carbon coating.

In addition, in practical applications, the first anode active material layer 21 and the second anode active material layer 22 may be disposed on both surfaces of the anode current collector 1 in the thickness direction, and those skilled in the art may flexibly adjust and set the disposition positions of the first anode active material layer 21 and the second anode active material layer 22 on the anode current collector 1 according to the actual requirements of lithium ion battery products, etc.

With continued reference to fig. 1 and 2, the first anode active material layer and the second anode active material layer of the present invention will be described taking as an example the first anode active material layer and the second anode active material layer provided on the first surface of the anode current collector.

First, the lithium intercalation potential LP of the first anode active material layer 21 is set ₁ Lithium intercalation potential LP with second anode active material layer 22 ₂ Is set to 0.05-1.5V, where Δlp=lp ₂ -LP ₁ . Preferably, the difference of the lithium intercalation potential Δlp is 0.1 to 1.0V; further, the difference in lithium intercalation potential Δlp is 0.1 to 0.5V, for example, 0.05V, 0.07V, 0.09V, 0.1V, 0.11V, 0.12V, 0.13V, 0.14V, 0.15V, 0.39V, 1.5V, or the like, and the difference in lithium intercalation potential may be selected so that the difference in lithium intercalation potential falls within the preset range listed above.

Further, the lithium intercalation potential of the first anode active material layer 21 is set to 0 to 0.5V, for example, 0.05V, 0.06V, 0.07V, 0.30V, 0.32V, 0.33V, 0.34V, 0.35V, 0.36V, 0.39V, 0.46V, or the like, and the lithium intercalation potential of the first anode active material layer 21 is selected so long as the lithium intercalation potential of the first anode active material layer 21 is lower than the lithium intercalation potential of the second anode active material layer 22.

Further, the lithium intercalation potential of the second anode active material layer 22 is set to 0.1 to 1.55V, for example, 0.11V, 0.14V, 0.16V, 0.42V, 0.43V, 0.44V, 0.47V, 0.49V, 0.5V, 0.52V, 0.6V, 1.55V, or the like, so long as the lithium intercalation potential of the second anode active material layer 22 is made higher than the lithium intercalation potential of the first anode active material layer 21, regardless of whether the lithium intercalation potential of the second anode active material layer 22 is selected.

As shown in fig. 1, the first anode active material layer 21 may be provided to contain only the first anode active material 31, and not contain the second anode active material 32; as shown in fig. 2, the first anode active material layer 21 may be provided to contain the first anode active material 31 and the second anode active material 32, and those skilled in the art can flexibly adjust and set the kind of anode active material contained in the first anode active material layer 21 according to the actual anode tab lithium intercalation potential and the like, as long as the lithium intercalation potential of the first anode active material layer 21 is made lower than the lithium intercalation potential of the second anode active material layer 22.

As shown in fig. 1, the second anode active material layer 22 may be provided to contain only the second anode active material 32, not the first anode active material 31; as shown in fig. 2, the second anode active material layer 22 may be provided to contain the first anode active material 31 and the second anode active material 32, and those skilled in the art can flexibly adjust and set the kind of anode active material contained in the second anode active material layer 22 according to the actual anode tab lithium intercalation potential and the like, as long as the lithium intercalation potential of the second anode active material layer 22 is made higher than the lithium intercalation potential of the first anode active material layer 21.

Next, the first anode active material 31 will be described.

First, the lithium intercalation potential of the first anode active material 31 is set to 0 to 0.5V, for example, other lithium intercalation potentials of 0.05V, 0.06V, 0.07V, 0.30V, 0.32V, 0.33V, 0.34V, 0.35V, 0.36V, 0.39V, 0.46V, etc., and the lithium intercalation potential of the first anode active material 31 is selected so that the lithium intercalation potential of the first anode active material 31 is lower than the lithium intercalation potential of the second anode active material 32.

Preferably, the mass of the first anode active material 31 in the first anode active material layer 21 is 10 to 100wt% of the total mass of the active materials in the first anode active material layer 21; further, 50-99wt%; further, 80 to 97wt%; for example, 80wt%, 95wt%, 97wt%, 100%, etc., the ratio may be selected in any way as long as the content of the first anode active material 31 in the first anode active material layer 21 is made greater than or equal to the content of the first anode active material 31 in the second anode active material layer 22.

The first negative electrode active material 31 is one, two, three or more of carbon-based materials with low lithium intercalation potential, such as fast-charging artificial graphite, soft carbon, hard carbon, etc., and the lithium intercalation potential of the above-listed carbon-based materials is close to 0.1V, or even lower, which is beneficial to reducing the lithium intercalation potential of the first negative electrode active material layer 21. Of course, other carbon-based materials may be selected from highly compacted artificial graphite, natural graphite, mesophase carbon microspheres, and the like.

Alternatively, the first negative electrode active material 31 may be one, two, three or more selected from silicon-based materials such as a silicon-carbon material, a silicon oxygen material, a silicon alloy material, and a pure silicon material, and the lithium intercalation potential of the above-listed silicon-based materials is 0.1 to 0.2V, which is also advantageous for reducing the lithium intercalation potential of the first negative electrode active material layer 21.

Of course, the first negative electrode active material 31 may be selected from one, two, three or more of lithium metal materials, lithium titanate materials, metal oxide materials such as titanium oxide, nickel oxide, and manganese oxide, and tin-based materials such as tin oxide and tin alloy.

In addition, in practical applications, the first negative electrode active material 31 may be selected from two, three or more of the above listed carbon-based materials, silicon-based materials, lithium metal materials, lithium titanate materials, metal oxide materials and tin-based materials, and a person skilled in the art may flexibly adjust the combination of the above listed first negative electrode active materials 31 according to the actual lithium ion battery product requirements or the like, so long as the lithium intercalation potential of the first negative electrode active material 31 is lower than the lithium intercalation potential of the second negative electrode active material 32.

Preferably, the first negative active material 31 is selected from one, two, three or more of fast-charging artificial graphite, natural graphite, hard carbon, soft carbon, mesophase carbon microspheres, lithium metal materials.

Next, the second anode active material 32 will be described.

First, the lithium intercalation potential of the second anode active material 32 is set to 0.1 to 1.55V, for example, other lithium intercalation potentials of 0.11V, 0.14V, 0.16V, 0.42V, 0.43V, 0.44V, 0.47V, 0.49V, 0.5V, 0.52V, 0.6V, 1.55V, etc., and the lithium intercalation potential of the second anode active material 32 is selected in any case so long as the lithium intercalation potential of the second anode active material 32 is higher than the lithium intercalation potential of the first anode active material 31.

Preferably, the mass of the first anode active material 31 in the second anode active material layer 22 is 0 to 90wt%, further, 2 to 88wt% of the total mass of the active materials in the second anode active material layer 22; further, 20 to 80wt%; for example, 0%, 20%, 50%, 80%, 85%, 88%, etc., and the ratio may be selected in any way as long as the content of the first anode active material 31 in the second anode active material layer 22 is less than or equal to the content of the first anode active material 31 in the first anode active material layer 21.

The second negative electrode active material 32 is selected from carbon-based materials having a high lithium intercalation potential, such as highly compacted artificial graphite. Of course, other carbon-based materials may be selected from the group consisting of fast-charging artificial graphite, natural graphite, hard carbon, soft carbon, mesophase carbon microspheres, and the like.

Alternatively, the second anode active material 32 may be one, two, three or more selected from silicon-based materials such as a silicon-carbon material, a silicon oxygen material, a silicon alloy material, a pure silicon material, and the like.

Of course, the second anode active material 32 may be selected from one, two, three or more of lithium metal materials, lithium titanate materials, metal oxide materials such as titanium oxide, nickel oxide, and manganese oxide, and tin-based materials such as tin oxide and tin alloy.

In addition, in practical applications, the second anode active material 32 may be selected from two, three or more of the above listed carbon-based materials, silicon-based materials, lithium metal materials, lithium titanate materials, metal oxide materials and tin-based materials, and a person skilled in the art may flexibly adjust the combination of the above listed second anode active materials 32 according to the actual lithium ion battery product requirements or the like, so long as the lithium intercalation potential of the second anode active material 32 is higher than that of the first anode active material 31.

Preferably, the second anode active material 32 is selected from one, two, three or more of highly compacted artificial graphite, silicon-based material, tin-based material, lithium titanate material, metal oxide material; further, the second anode active material 32 is selected from one, two, three or more of highly compacted artificial graphite, a silicon carbon material, a silicon oxygen material, titanium oxide, and a lithium titanate material.

For the first anode active material 31 and the second anode active material 32 listed above, when the types of the first anode active material 31 and the second anode active material 32 are selected to be the same, the median particle diameter D of the first anode active material 31 is determined ₅₀ Is set to 4-15 mu m, and the median diameter D of the second anode active material 32 is set to ₅₀ Is set to 6 to 25 mu m, and the first anode active material 31 has a median diameter D ₅₀ Median particle diameter D with second anode active material 32 ₅₀ A ratio of greater than or equal to 0.2 and less than or equal to 1, in particular the median diameter D of the first anode active material 31 ₅₀ Median particle diameter D with second anode active material 32 ₅₀ A ratio of greater than 0.2 and less than 1, such that the median diameter D of the first anode active material 31 ₅₀ Less than the median particle diameter D of the second anode active material 32 ₅₀ As the median particle diameter increases, the lithium intercalation potential of the corresponding anode active material increases accordingly, so that the lithium intercalation potential of the first anode active material 31 is lower than that of the second anode active material layer 22. Even if the content of the first anode active material 31 in the second anode active material layer 22 is equal to the content of the first anode active material 31 in the first anode active material layer 21, due to the median diameter D of the first anode active material 31 ₅₀ Less than the median particle diameter D of the second anode active material 32 ₅₀ The lithium intercalation potential of the first anode active material 31 can also be made lower than that of the second anode active material layer 22.

Preferably, the median diameter D of the first anode active material 31 ₅₀ The median particle diameter D of the first anode active material 31 is selected to be 4 μm, 5 μm, 6 μm, 8 μm, 15 μm, etc., regardless of the selection ₅₀ So long as the median diameter D of the first anode active material 31 is made ₅₀ Less than the median particle diameter D of the second anode active material 32 ₅₀ And (3) obtaining the product.

Preferably, the second anode active material 32Median particle diameter D ₅₀ The median particle diameter D of the second anode active material 32 is selected regardless of whether it is 6 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 17 μm, 18 μm, 20 μm, 25 μm, or the like ₅₀ So long as the median particle diameter D of the second anode active material 32 is made ₅₀ Larger than the median diameter D of the first anode active material 31 ₅₀ And (3) obtaining the product.

Further, the median diameter D of the first anode active material 31 ₅₀ Median particle diameter D with second anode active material 32 ₅₀ The ratio of (c) is 0.3 or more and 0.8 or less, for example, 0.2, 0.44, 0.5, 0.57, 0.6, 0.67, 0.8, etc., to control the difference between the lithium intercalation potential of the second anode active material layer 22 and the lithium intercalation potential of the first anode active material layer 21 to be in the range of 0.05 to 1.5V.

Wherein the thickness ratio of the first anode active material layer 21 to the second anode active material layer 22 is 9:1 to 1:9, preferably 7: 3-3: 7, for example 9: 1. 8: 2. 7: 3. 6: 4. 5: 5. 4: 6. 3: 7. 2: 8. 1:9, etc., can be made higher in energy density if the thickness of the first anode active material layer 21 is larger, and can be made faster in charging ability if the thickness of the second anode active material layer 22 is larger, based on which the thickness ratio of the first anode active material layer 21 to the second anode active material layer 22 can be flexibly adjusted and set by a person skilled in the art according to the performance requirements of the lithium ion battery, etc.

Next, other raw materials of the first anode active material layer 21 and the second anode active material layer 22 will be further described.

Preferably, the first anode active material layer 21 further includes a first thickener, a first conductive agent, a first binder, and a first solvent, wherein the raw materials are as follows by weight percent: 70 to 98.5wt% of the first anode active material 31 or the first and second anode active materials 31 and 32,0.5 to 10wt% of the first thickener, 0.5 to 10wt% of the first conductive agent, and 0.5 to 10wt% of the first binder.

Preferably, the second anode active material layer 22 further includes a second thickener, a second conductive agent, a second binder, and a second solvent, wherein the raw materials are as follows by weight percent: 70 to 98.5wt% of the second anode active material 32 or the first anode active material 31 and the second anode active material 32,0.5 to 10wt% of the second thickener, 0.5 to 10wt% of the second conductive agent, and 0.5 to 10wt% of the second binder.

The first thickener and the second thickener may be the same or different, and may be selected from other thickeners such as sodium carboxymethyl cellulose or lithium carboxymethyl cellulose, and the specific content is 1wt%, 3wt%, 5wt%, 7wt%, 9wt%, and the like.

The first conductive agent and the second conductive agent may be the same or different, and may be selected from conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, graphene, single-wall or multi-wall carbon nanotubes, metal powder, carbon fiber, and other conductive agents, and the specific content is 1wt%, 3wt%, 5wt%, 7wt%, 9wt%, and other contents, respectively.

The first binder and the second binder may be the same or different, and may be selected from styrene-butadiene rubber, polyacrylic acid, polytetrafluoroethylene, polyethylene oxide, and other binders, wherein the specific content is 1wt%, 3wt%, 5wt%, 7wt%, 9wt%, and other contents.

Wherein the first solvent and the second solvent are deionized water, ultrapure water, and the like.

The negative electrode sheet of the present invention will be described in further detail with reference to examples and comparative examples.

Comparative example 1: single layer high lithium precipitation potential material

Step 1: the negative electrode active material is quickly filled with artificial graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber and conductive carbon black according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5%, adding deionized water, and obtaining the negative electrode slurry under the action of a vacuum stirrer, wherein the solid content of the negative electrode slurry is 40-49%, the viscosity is 2000-6000 mPa.s, and coating the slurry on the common copper foil (optical foil, non-carbon coated) with the thickness of 5 mu m by using an extrusion coater according to an extrusion coating mode, thereby completing the coating process. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Wherein, the median diameter D of the quick-charging artificial graphite ₅₀ Is 8 μm.

Step 2: obtaining NCM622, PVDF and conductive carbon black, and mixing the NCM622, PVDF and conductive carbon black according to the weight ratio of 97.5%:1.4%:1.1% of the aluminum foil is mixed, NMP (N-methylpyrrolidone) is added, positive electrode slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the positive electrode slurry is 70-80%, the viscosity is 3500-6500 mPa.s, and the positive electrode slurry is coated on the aluminum foil with the thickness of 10 mu m by using an extrusion coater according to an extrusion coating mode, so that the coating process is completed. And then drying, cold pressing and slitting to finish the preparation of the positive plate.

Step 3: and (3) respectively die-cutting the negative electrode sheet obtained in the step (1) and the positive electrode sheet obtained in the step (2), then laminating the negative electrode sheet and the diaphragm to prepare a bare cell, putting the bare cell into a packaging bag, and performing procedures such as liquid injection, formation, capacity division, standing and the like to prepare the cell of the lithium ion battery.

Comparative example 2: single layer-low lithium precipitation potential material

Step 1: high-compaction artificial graphite of a cathode active material, sodium carboxymethyl cellulose as a thickener, styrene-butadiene rubber as a binder and conductive carbon black as a conductive agent in a weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5%, adding deionized water, and obtaining the negative electrode slurry under the action of a vacuum stirrer, wherein the solid content of the negative electrode slurry is 40-49%, the viscosity is 2000-6000 mPa.s, and coating the slurry on the common copper foil with the thickness of 5 mu m by using an extrusion coater according to an extrusion coating mode to complete a coating process. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Wherein the median diameter D of the highly compacted artificial graphite ₅₀ Is 14 μm.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Comparative example 3: monolayer-high&Low-precipitation lithium potential material mixing

Step 1: the negative electrode active material (namely quick-charge artificial graphite and high-compaction artificial graphite, the weight ratio of which is 1:1), thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber and conductive carbon black are mixed according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5%, adding deionized water, and obtaining the negative electrode slurry under the action of a vacuum stirrer, wherein the solid content of the negative electrode slurry is 40-49%, the viscosity is 2000-6000 mPa.s, and coating the slurry on the common copper foil with the thickness of 5 mu m by using an extrusion coater according to an extrusion coating mode to complete a coating process. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Wherein, the median diameter D of the quick-charging artificial graphite ₅₀ Median particle diameter D of highly compacted artificial graphite of 8. Mu.m ₅₀ Is 14 mu m, and the median diameter D of the quick-filling artificial graphite ₅₀ Median particle diameter D of high-compaction artificial graphite ₅₀ The ratio of (2) was 0.57.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Comparative example 4: monolayer-high&Low-precipitation lithium potential material mixing

Step 1: mixing a negative electrode active material (namely quick-charge artificial graphite and a silicon oxide material in a weight ratio of 90:10), a mixture of a thickener sodium carboxymethyl cellulose, a binder styrene-butadiene rubber and polyacrylic acid, and a conductive agent conductive carbon black in a weight ratio of 96.5 percent to 0.5 percent to 2.0 percent to 1.0 percent, adding deionized water, and obtaining negative electrode slurry under the action of a vacuum stirrer, wherein the solid content of the negative electrode slurry is 40-49 percent, the viscosity is 2000-6000 mPa.s, and coating the slurry on the common copper foil with the thickness of 5 mu m by using an extrusion coater according to an extrusion coating mode to complete a coating procedure. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Wherein, the median diameter D of the quick-charging artificial graphite ₅₀ Median particle diameter D of the silica material of 8. Mu.m ₅₀ 10 μm and a median particle diameter D of the quick-charging artificial graphite ₅₀ Median particle diameter D with silica material ₅₀ The ratio of (2) was 0.8.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 1: double-layer pure negative electrode active material

Step 1: the first negative electrode active material is quickly filled with artificial graphite, thickener sodium carboxymethyl cellulose, binder styrene butadiene rubber and conductive carbon black according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

the second negative electrode active material is highly compacted with artificial graphite, sodium carboxymethyl cellulose as a thickener, styrene-butadiene rubber as a binder and conductive carbon black as a conductive agent according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

the first anode active material layer slurry and the second anode active material layer slurry are coated on common copper foil with the thickness of 5 mu m by adopting a double-layer coating machine, the first anode active material layer slurry is coated near the common copper foil area, the second anode active material layer slurry is coated on the surface of the first anode active material layer, and the thickness ratio of the two slurries on the anode current collector is 5:5 (after rolling, the thickness of the first anode active material layer was 47 μm, and the thickness of the first anode active material layer was 45 μm), the coating process was completed. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ Median particle diameter D of highly compacted artificial graphite (i.e., second negative electrode active material) of 8 μm ₅₀ Is 14 mu m, and the median diameter D of the quick-filling artificial graphite ₅₀ Median particle diameter D of high-compaction artificial graphite ₅₀ The ratio of (2) was 0.57.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 2: double-layer pure negative electrode active material and mixed negative electrode active material

Step 1: the negative electrode active material is quickly filled with artificial graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber and conductive carbon black according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

the negative electrode active material (namely quick-charge artificial graphite and high-compaction artificial graphite, the weight ratio of which is 20:80), thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber and conductive carbon black are mixed according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 3: double-layer-all mixed cathode active material

Step 1: the negative electrode active material (namely soft carbon and silicon carbon materials with the weight ratio of 95:5), sodium carboxymethyl cellulose as a thickener, polyacrylic acid as a binder and conductive carbon black as a conductive agent with the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

The negative electrode active material (namely soft carbon and silicon carbon materials, the weight ratio of which is 80:20), sodium carboxymethyl cellulose serving as a thickener, polyacrylic acid serving as a binder and conductive carbon black serving as a conductive agent are mixed according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

Wherein the median diameter D of the soft carbon (i.e., the first anode active material) ₅₀ Median particle diameter D of 6 μm for the silicon carbon material (i.e., second negative electrode active material) ₅₀ Is 9 mu m, and the median diameter D of the soft carbon ₅₀ Median particle diameter D with silicon carbon Material ₅₀ The ratio of (2) was 0.67.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 4: double-layer-all mixed cathode active material

Step 1: the negative electrode active material (namely hard carbon and titanium oxide, the weight ratio of which is 95:5), sodium carboxymethyl cellulose as a thickener, polyacrylic acid as a binder and conductive carbon black as a conductive agent are mixed according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

the negative electrode active material (namely hard carbon and titanium oxide, the weight ratio of which is 80:20), sodium carboxymethyl cellulose as a thickener, polyacrylic acid as a binder and conductive carbon black as a conductive agent are mixed according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

Wherein the hard carbon (i.e., the first negative electrode active material) has a median diameter D ₅₀ Median particle diameter D of titanium oxide (i.e., second negative electrode active material) of 5 μm ₅₀ 17 μm, and a median particle diameter D of hard carbon ₅₀ Median particle diameter D with titanium oxide ₅₀ The ratio of (2) was 0.29.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 5: double-layer-all mixed cathode active material

Step 1: the negative electrode active material (namely quick-charge artificial graphite and silicon oxide material, the weight ratio of which is 95:5), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

The negative electrode active material (namely quick-charge artificial graphite and silicon oxide material, the weight ratio of which is 80:20), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ Median particle diameter D of the silica material (i.e., second negative electrode active material) of 8. Mu.m ₅₀ 10 μm and a median particle diameter D of the quick-charging artificial graphite ₅₀ Median particle diameter D with silica material ₅₀ The ratio of (2) was 0.8.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 6: double-layer pure negative electrode active material

Step 1: the first negative electrode active material is quickly filled with artificial graphite, sodium carboxymethyl cellulose as a thickener, polyacrylic acid as a binder and conductive carbon black as a conductive agent according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

the second negative electrode active material lithium titanate, thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ Median particle diameter D of 8 μm of lithium titanate (i.e., second negative electrode active material) ₅₀ Is 18 mu m, and the median diameter D of the quick-filling artificial graphite ₅₀ Median particle diameter D with lithium titanate ₅₀ The ratio of (2) was 0.44. The lithium intercalation potential of the first anode active material layer is 0.05V, the lithium intercalation potential of the second anode active material layer is 1.55V, and the lithium intercalation potential difference is 1.5V, so that the upper limit of the lithium intercalation potential difference is reached.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 7: double-layer-all mixed cathode active material

Step 1: the negative electrode active material (namely quick-charge artificial graphite and silicon oxide material, the weight ratio of which is 97:3), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

the negative electrode active material (namely quick-charging artificial graphite and silicon oxide material, the weight ratio of which is 88:12), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ Median particle diameter D of the silica material (i.e., second negative electrode active material) of 8. Mu.m ₅₀ 10 μm and a median particle diameter D of the quick-charging artificial graphite ₅₀ Median particle diameter D with silica material ₅₀ The ratio of (2) was 0.8. The first negative electrode active material layer intercalates lithiumThe potential was 0.32V, the lithium intercalation potential of the second anode active material layer was 0.42V, and the difference in lithium intercalation potential was 0.1V, which was the interval value of the difference in lithium intercalation potential.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 8: double-layer-all mixed cathode active material

Step 1: the negative electrode active material (namely quick-charge artificial graphite and high-compaction artificial graphite, the weight ratio of which is 95:5), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

the negative electrode active material (namely quick-charge artificial graphite and high-compaction artificial graphite, the weight ratio of which is 50:50), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ Is 8 μm, high-compaction artificial graphite (i.e. secondMedian particle diameter D of anode active material) ₅₀ Is 14 mu m, and the median diameter D of the quick-filling artificial graphite ₅₀ Median particle diameter D of high-compaction artificial graphite ₅₀ The ratio of (2) was 0.57. The lithium intercalation potential of the first anode active material layer is 0.06V, the lithium intercalation potential of the second anode active material layer is 0.11V, and the lithium intercalation potential difference value is 0.05V, so that the lower limit of the lithium intercalation potential difference value is reached.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 9: double-layer-all mixed cathode active material

Step 1: the negative electrode active material (namely quick-charge artificial graphite and high-compaction artificial graphite, the weight ratio of which is 80:20 and the interval value of the proportion of the active material), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

the negative electrode active material (namely quick-charge artificial graphite and high-compaction artificial graphite, the weight ratio of which is 20:80 and the interval value of the proportion of the active material), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98%:0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 10: double-layer-all mixed cathode active material

Step 1: the negative electrode active material (namely quick-charge artificial graphite and silicon oxide material, the weight ratio of which is 95:5 and is the interval value of the proportion of the active material), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

The negative electrode active material (namely quick-charge artificial graphite and silicon oxide material, the weight ratio of which is 85:15 and the interval value of the proportion of the active material), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 11: double-layer-all mixed cathode active material

Step 1: the negative electrode active material (namely quick-charging artificial graphite and silicon oxide material, the weight ratio of which is 95:5), thickener sodium carboxymethyl cellulose, binder styrene butadiene rubber and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining first anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the first anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

the negative electrode active material (namely quick-charging artificial graphite and silicon oxide material, the weight ratio of which is 85:15), thickener sodium carboxymethyl cellulose, binder polyacrylic acid and conductive carbon black are mixed according to the weight ratio of 98 percent: 0.7%:0.8%: mixing 0.5 percent, adding deionized water, and obtaining second anode active material layer slurry under the action of a vacuum stirrer, wherein the solid content of the second anode active material layer slurry is 40-49 percent, and the viscosity is 2000-6000 mPa.s;

The first anode active material layer slurry and the second anode active material layer slurry are coated on common copper foil with the thickness of 5 mu m by adopting a double-layer coating machine, the first anode active material layer slurry is coated near the common copper foil area, the second anode active material layer slurry is coated on the surface of the first anode active material layer, and the thickness ratio of the two slurries on the anode current collector is 9:1 (after rolling, the thickness of the first anode active material layer was 83 μm, and the thickness of the first anode active material layer was 8 μm), the upper limit of the thickness ratio was reached, and the coating process was completed. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 12: double-layer-all mixed cathode active material

the first anode active material layer slurry and the second anode active material layer slurry are coated on common copper foil with the thickness of 5 mu m by adopting a double-layer coating machine, the first anode active material layer slurry is coated near the common copper foil area, the second anode active material layer slurry is coated on the surface of the first anode active material layer, and the thickness ratio of the two slurries on the anode current collector is 3:7 (after rolling, the thickness of the first anode active material layer was 26 μm, and the thickness of the first anode active material layer was 65 μm), which is a range value of the thickness ratio, the coating process was completed. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 13: double-layer-all mixed cathode active material

The first anode active material layer slurry and the second anode active material layer slurry are coated on common copper foil with the thickness of 5 mu m by adopting a double-layer coating machine, the first anode active material layer slurry is coated near the common copper foil area, the second anode active material layer slurry is coated on the surface of the first anode active material layer, and the thickness ratio of the two slurries on the anode current collector is 1:9 (after rolling, the thickness of the first anode active material layer was 9 μm, and the thickness of the first anode active material layer was 84 μm), the lower limit of the thickness ratio was reached, and the coating process was completed. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 14: double-layer-all mixed cathode active material

the first negative electrode active material layer slurry and the second negative electrode active material layer slurry are simultaneously coated on a carbon-coated copper foil with the thickness of 5 mu m by adopting a double-layer coating machine, the first negative electrode active material layer slurry is coated near the carbon-coated copper foil area, the second negative electrode active material layer slurry is coated on the surface of the first negative electrode active material layer, and the thickness ratio of the two slurries on a negative electrode current collector is 3:7 (after rolling, the thickness of the first anode active material layer was 27 μm, and the thickness of the first anode active material layer was 64 μm), the coating process was completed. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 15: double-layer-all mixed cathode active material

The first anode active material layer slurry and the second anode active material layer slurry are coated on common copper foil with the thickness of 5 mu m by adopting a double-layer coating machine, the first anode active material layer slurry is coated near the common copper foil area, the second anode active material layer slurry is coated on the surface of the first anode active material layer, and the thickness ratio of the two slurries on the anode current collector is 3:7 (after rolling, the thickness of the first anode active material layer was 26 μm, and the thickness of the first anode active material layer was 65 μm), the coating process was completed. And then drying, cold pressing and slitting to finish the preparation of the negative plate.

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ At 4 μm, a minimum limit of the median particle diameter of the first negative electrode active material, the median particle diameter D of the silicon oxide material (i.e., the second negative electrode active material) was reached ₅₀ At 6 μm, a minimum limit value of the median particle diameter of the second anode active material was reached, and the median particle diameter D of the quick-charge artificial graphite ₅₀ Median particle diameter D with silica material ₅₀ The ratio of (2) is 0.67, and the lower limit value of the median particle diameter of the first negative electrode active material and the second negative electrode active material is reached.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 16: double-layer-all mixed cathode active material

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ At 15 μm, the maximum limit of the median particle diameter of the first negative electrode active material was reached, and the median particle diameter D of the silicon oxide material (i.e., the second negative electrode active material) ₅₀ 25 μm, the maximum limit of the median particle diameter of the second negative electrode active material was reached, and the median particle diameter D of the quick-charge artificial graphite ₅₀ Median particle diameter D with silica material ₅₀ The ratio of (2) is 0.6, and the upper limit value of the median particle diameter of the first negative electrode active material and the second negative electrode active material is reached.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 17: double-layer-all mixed cathode active material

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ At 4 μm, a minimum limit of the median particle diameter of the first negative electrode active material, the median particle diameter D of the silicon oxide material (i.e., the second negative electrode active material) was reached ₅₀ Is 20 mu m, and the median diameter D of the quick-filling artificial graphite ₅₀ Median particle diameter D with silica material ₅₀ Is 0.2, and a minimum limit value for this ratio is reached.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 18: double-layer-all mixed cathode active material

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ Median particle diameter D of the silica material (i.e., second negative electrode active material) of 8. Mu.m ₅₀ Is 8 mu m, and the median diameter D of the quick-filling artificial graphite ₅₀ Median particle diameter D with silica material ₅₀ Is 1.0, and reaches the maximum limit of the ratio.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

Example 19: double-layer-all mixed cathode active material

Wherein the median diameter D of the fast-charging artificial graphite (namely the first negative electrode active material) ₅₀ Median particle diameter D of the silicon oxide material (i.e., second negative electrode active material) of 6 μm ₅₀ Is 12 mu m, and the median diameter D of the quick-filling artificial graphite ₅₀ Median particle diameter D with silica material ₅₀ Is 0.5, is the interval value of the ratio.

Step 2: step 2 of comparative example 1.

Step 3: step 3 of comparative example 1.

For the above comparative examples 1 to 4, and examples 1 to 19, the lithium intercalation potential of the first anode active material layer, the lithium intercalation potential of the second anode active material layer were detected, respectively; and after 500 cycles of 0.7C charging/0.7C discharging in 45 ℃, the mass energy density average value, the capacity retention rate, the lithium precipitation condition on the surface of the negative electrode sheet, and the adhesion force between the negative electrode active material layer and the negative electrode current collector were detected, and the obtained test results are shown in Table 1.

The method for testing the lithium intercalation potential comprises the following steps: the negative plate, the positive plate and a reference electrode (lithium metal electrode) are assembled into a three-electrode battery, the three-electrode battery is placed in an environment with the temperature of (25+/-3) DEG C, the three-electrode battery is kept stand for 3 hours, when the battery core body reaches the temperature of (25+/-3) DEG C, the battery is charged to 4.45V according to 0.2C, then is charged to the cut-off current of 0.05C at a constant voltage, is discharged to 3V at 0.2C, the lithium intercalation potential of the negative electrode active material layer is determined according to a negative electrode charge-discharge curve, and the lithium intercalation potential of the negative electrode active material layer is obtained through testing.

The method for testing the mass energy density average value comprises the following steps: placing the battery cell in 45 ℃ environment, standing for 3h, discharging to 3V according to 0.7 ℃ when the battery cell reaches 45 ℃, and standing for 30min; charging to cut-off current according to constant voltage of 0.7C, and standing for 30min; repeating the steps for 3 times, measuring the discharge energy of each time, and calculating the average value E of the discharge energy E of 3 times _everage The method comprises the steps of carrying out a first treatment on the surface of the The mass M of the cell was measured with a weighing machine and the mass energy density mean PED was calculated, ped=e _everage /M。

The testing method for the capacity retention rate of 500 circles of 45 ℃ circulation comprises the following steps: placing the battery cell in 45 ℃ environment, standing for 3h, charging to 4.3V according to 1.5C, charging to 4.48V according to 0.7C, charging to cut-off current of 0.05C under constant voltage of 4.48V, discharging to 3V according to 0.5C when the battery cell reaches 45 ℃, and recording initial capacity Q ₁ When the cycle reaches the required number of times, the previous discharge capacity is taken as the capacity Q of the battery ₂ And calculates the capacity retention rate, capacity retention rate (%) =q ₂ /Q ₁ ×100％。

The lithium separation test method comprises the following steps: the battery is firstly charged to 4.3V according to 1.5C (or 2C, 1.2C or 1C), then charged to 4.48V by 0.7C, then charged to 0.05C by a constant voltage of 4.48V, and then charged and discharged for 20 times (namely 1.5C step charge) at 25 ℃ according to a charging system of discharging to 3V by 0.5C, so that the battery is fully charged and disassembled, and the interface condition of the negative plate is observed. If lithium is not separated, the negative plate is golden yellow, which indicates that the negative plate can support the charging with the system at the temperature; otherwise, the negative plate is partially or wholly gray, namely lithium is separated out, which indicates that the negative plate does not support the charging of the system.

The method for testing the binding force between the anode active material layer and the anode current collector comprises the following steps: quantitatively evaluated by 180 ° or 90 ° peeling, and tested with a tensile tester.

TABLE 1 Performance parameters of lithium ion batteries of examples and comparative examples

In the table, "-" indicates no presence.

As can be seen from table 1, comparing the double-layer anode active material layer structure defined in example 1 (i.e., the intercalation potential of the second anode active material layer far from the anode current collector is higher than that of the first anode active material layer near the anode current collector) with the single-layer anode active material layer structure with low intercalation potential, not only the rate of the lithium precipitation phenomenon on the surface of the anode sheet is significantly improved, but also the binding power is slightly improved, the mass energy density average is also significantly improved, the capacity retention rate is also significantly improved, and the purposes of avoiding lithium precipitation on the surface of the lithium ion battery and achieving better cycle capability can be achieved.

Further, in comparison of example 1 and comparative example 2, namely, the double-layer anode active material layer structure (as above) defined in example 1 was compared with the single-layer anode active material layer structure having a high lithium intercalation potential, the mass energy density average was lost and the binding power was lowered, but the capacity retention rate was significantly improved, the rate at which the lithium precipitation phenomenon did not occur on the anode sheet surface was significantly improved, and the purpose of achieving both the surface non-precipitation lithium and the better cycle ability of the lithium ion battery was achieved.

Further, in comparison of example 1 and comparative example 3, namely, the double-layer anode active material layer structure (same as above) defined in example 1 and the single-layer anode active material layer structure of the mixed active material having a high and low lithium intercalation potential, although the adhesion is slightly reduced, the mass energy density average value is slightly improved, the capacity retention rate is remarkably improved, the multiplying power of the anode sheet surface without occurrence of lithium precipitation phenomenon is greatly improved, and the purpose of achieving both the surface non-lithium precipitation and the better cycle ability of the lithium ion battery can be achieved.

Further, in comparison of example 1 and comparative example 4, namely, the double-layer anode active material layer structure (same as above) defined in example 1 was compared with the single-layer anode active material layer structure of the mixed active material having high and low lithium intercalation potential, although the mass energy density average value was significantly reduced and the binding force was slightly reduced, the capacity retention rate was significantly improved, the rate at which the lithium precipitation phenomenon did not occur on the anode sheet surface was significantly improved, and the purpose of achieving both the surface non-lithium precipitation and the better cycle ability of the lithium ion battery was achieved.

As can also be seen from table 1, comparing examples 2 to 6, the technical effects similar to example 1 can also be obtained by replacing the first negative electrode active material with a low lithium intercalation potential with hard carbon, soft carbon, and replacing the second negative electrode active material with a high lithium intercalation potential with a silicon carbon material, a silicon oxygen material, titanium oxide, or a lithium titanate material.

Further, by comparing examples 6 to 8, the lithium intercalation potentials of the first negative electrode active material and the second negative electrode active material are adjusted within a limited range, the improvement of the difference value of the lithium intercalation potentials is favorable for improving the capacity retention rate and the multiplying power of the negative electrode sheet surface without occurrence of the lithium precipitation phenomenon, the reduction of the difference value of the lithium intercalation potentials is favorable for improving the binding force, and the moderate difference value of the lithium intercalation potentials is favorable for the mass energy density average value, so that the lithium intercalation potential can be selected according to the actual demands of products, and the purpose of achieving both the surface non-precipitation lithium and the better cycle capability of the lithium ion battery is achieved.

Further, comparing examples 9 and 10, adjusting the content ratio of the first negative electrode active material and the second negative electrode active material within a limited range, improving the content ratio of the first negative electrode active material is beneficial to improving the mass energy density average value, improving the content ratio of the second negative electrode active material is beneficial to improving the capacity retention rate, the binding force and the multiplying power of the negative electrode sheet surface without lithium precipitation phenomenon, and the method can be selected according to the actual requirement of the product, so that the purpose of achieving both the surface non-lithium precipitation and the better cycle capability of the lithium ion battery is achieved.

Further, by comparing examples 11 to 13, the thickness ratio of the first negative electrode active material layer and the second negative electrode active material layer is adjusted within a limited range, the reduction of the thickness ratio is favorable for improving the mass energy density average value, the improvement of the thickness ratio is favorable for improving the capacity retention rate, the binding force and the multiplying power of the negative electrode sheet surface without lithium precipitation phenomenon, and the lithium ion battery can be selected according to the actual requirement of a product, so that the purpose of achieving both the surface non-lithium precipitation and better cycle capability of the lithium ion battery is achieved.

Further, comparing examples 1 and 14, replacing the common copper foil with the carbon-coated copper foil is beneficial to improving the average value of quality energy density, and can be selected according to the actual requirement of the product, so that the purpose of achieving both the surface non-precipitation lithium and the better circulation capability of the lithium ion battery is achieved.

Further, examples 15 to 19 were compared, and the median particle diameter D of the first anode active material, the second anode active material was adjusted within a defined range ₅₀ Reducing the median diameter D ₅₀ Is favorable for improving the multiplying power of the surface of the negative plate without lithium precipitation phenomenon and improving the median diameter D ₅₀ The method is favorable for improving the average value of the mass energy density, can be selected according to the actual demands of products, and achieves the aim of combining the surface non-precipitation lithium of the lithium ion battery with better circulation capability.

Those skilled in the art will appreciate that while some embodiments herein include some features but not others included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims of the present invention, any of the claimed embodiments may be used in any combination.

In addition, the invention also provides a lithium ion battery, which comprises the negative electrode plate of any one of the above embodiments.

In addition, the invention also provides an electric automobile, which comprises the negative electrode sheet or the lithium ion battery in any one of the above embodiments.

Thus far, the technical solution of the present invention has been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of protection of the present invention is not limited to these specific embodiments. Equivalent modifications and substitutions for related technical features may be made by those skilled in the art without departing from the principles of the present invention, and such modifications and substitutions will fall within the scope of the present invention.

Claims

1. The negative electrode plate is characterized by comprising a negative electrode current collector, wherein the negative electrode current collector comprises a first surface and a second surface which are opposite to each other, at least one of the first surface and the second surface is provided with two layers of negative electrode active material layers, the first negative electrode active material layer is arranged on the surface of the negative electrode current collector, the second negative electrode active material layer is arranged on the surface of the first negative electrode active material layer, and the lithium intercalation potential of the first negative electrode active material layer is lower than that of the second negative electrode active material layer.

2. The negative electrode sheet according to claim 1, wherein a difference between the lithium intercalation potential of the first negative electrode active material layer and the lithium intercalation potential of the second negative electrode active material layer is 0.05V to 1.5V, preferably 0.1V to 1.0V, preferably 0.1V to 0.5V.

3. The negative electrode sheet according to claim 2, wherein the lithium intercalation potential of the first negative electrode active material layer is 0 to 0.5V;

4. The negative electrode sheet according to claim 3, wherein the first negative electrode active material layer contains only a first negative electrode active material or contains both a first negative electrode active material and a second negative electrode active material, and the second negative electrode active material layer contains only a second negative electrode active material or contains both a first negative electrode active material and a second negative electrode active material;

5. The negative electrode sheet according to claim 4, wherein the proportion of the mass of the first negative electrode active material in the first negative electrode active material layer to the total mass of the active materials in the first negative electrode active material layer is 10 to 100wt%;

6. The negative electrode sheet according to claim 5, wherein a proportion of the mass of the first negative electrode active material in the first negative electrode active material layer to the total mass of the active materials in the first negative electrode active material layer is 50 to 99wt%;

7. The negative electrode sheet according to claim 6, wherein a proportion of the mass of the first negative electrode active material in the first negative electrode active material layer to the total mass of the active materials in the first negative electrode active material layer is 80 to 97wt%;

8. The negative electrode sheet according to any one of claims 4 to 7, wherein the first negative electrode active material is selected from one or more of a carbon-based material, a silicon-based material, a tin-based material, a lithium titanate material, a metal oxide material, and a lithium metal material.

9. The negative electrode sheet of claim 8, wherein the carbon-based material is highly compacted artificial graphite, fast-charged artificial graphite, natural graphite, hard carbon, soft carbon, or mesophase carbon microspheres; and/or

The metal oxide material is titanium oxide, nickel oxide or manganese oxide.

10. The negative electrode sheet of claim 9, wherein the first negative electrode active material is selected from one or more of fast-charging artificial graphite, natural graphite, hard carbon, soft carbon, mesophase carbon microspheres, lithium metal materials.