Multilayer negative pole piece and preparation method thereof, sodium ion battery and electric equipment

Abstract

The invention provides a multi-layer negative pole piece and a preparation method thereof, a sodium ion battery and electric equipment, and relates to the field of sodium ion batteries. The multi-layer negative pole piece comprises a current collector, a first coating and a second coating, the first coating is arranged between the current collector and the second coating; the raw materials of the first coating comprise hard carbon, a first conductive agent, a first dispersant and a first binder; and the raw materials of the second coating comprise a phosphorus-containing negative electrode material, a second conductive agent, a second dispersing agent and a second binder. The surface of the first coating is coated with the second coating, so that more sodium storage sites are close to the positive electrode direction, sodium ions can be rapidly stored during charging and can be rapidly released during discharging, and the charging and discharging efficiency is improved.

Description

Technical Field

[0001] The present application relates to the field of sodium ion batteries, and in particular to a multilayer negative electrode sheet and a preparation method thereof, a sodium ion battery and an electrical device. Background Art

[0002] As a new type of energy storage technology, sodium-ion batteries have attracted widespread attention due to their advantages such as abundant raw material reserves, low cost and high safety. They are also expected to alleviate the limited development of energy storage batteries caused by the shortage of lithium resources to a certain extent.

[0003] Research on negative electrode materials for sodium-ion batteries is focusing on improving their capacity and rapid charge and discharge performance. In terms of improving negative electrode capacity, high-capacity hard carbon negative electrodes are currently mainly used. However, the capacity increase of hard carbon negative electrodes is generally accompanied by a certain loss of kinetic performance, which is not conducive to high-rate discharge.

[0004] Among the many negative electrode material systems, phosphorus-based negative electrodes have high theoretical specific capacity and excellent rate performance, and their cost is relatively low. They are one of the research directions that are expected to further achieve high energy density and high rate performance in the future. However, phosphorus-based materials have poor conductivity and are prone to volume expansion during the cycle. If used alone in a sodium ion system, it will cause great internal stress due to expansion, affecting battery life and safety. Summary of the invention

[0005] The purpose of this application is to provide a multilayer negative electrode sheet and a preparation method thereof, a sodium ion battery and an electrical device to solve the above-mentioned problems.

[0006] To achieve the above objectives, the present application provides a multilayer negative electrode sheet in a first aspect, wherein the multilayer negative electrode sheet comprises a current collector, a first coating layer and a second coating layer;

[0007] The first coating is disposed between the current collector and the second coating;

[0008] The raw materials of the first coating layer include hard carbon, a first conductive agent, a first dispersant and a first binder;

[0009] The raw materials of the second coating layer include a phosphorus-containing negative electrode material, a second conductive agent, a second dispersant and a second binder.

[0010] Optionally, the thickness of the first coating is 30um-200um;

[0011] The thickness of the second coating layer is 3%-20% of the thickness of the first coating layer.

[0012] Optionally, the multilayer negative electrode sheet satisfies at least one of the following conditions:

[0013] A. The raw materials of the first coating layer, calculated by total mass as 100%, include:

[0014] The hard carbon is 80%-97%, the first conductive agent is 0.5%-10%, the first dispersant is 0.5%-10%, and the first binder is 0.5%-10%;

[0015] B. The raw materials of the second coating layer, based on the total mass as 100%, include:

[0016] The phosphorus-containing negative electrode material accounts for 80%-95%, the second conductive agent accounts for 0.5%-10%, the second dispersant accounts for 0.5%-10%, and the second binder accounts for 0.5%-10%.

[0017] Optionally, the multilayer negative electrode sheet satisfies at least one of the following conditions:

[0018] A. The hard carbon includes one or more of biomass hard carbon, resin hard carbon, coal-based hard carbon, and asphalt-based hard carbon;

[0019] B. The particle size of the hard carbon is 3um-7um;

[0020] C. The first conductive agent and the second conductive agent independently include one or more of SP, acetylene black, Ketjen black, carbon nanotubes, graphene, and conductive graphite;

[0021] D. the first dispersant and the second dispersant each independently comprise CMC;

[0022] E. the first binder and the second binder each independently comprise SBR and / or PAA;

[0023] F. The phosphorus-containing negative electrode material includes one or more of red phosphorus, black phosphorus, and phosphorus-carbon composites;

[0024] G. The phosphorus content in the phosphorus-containing negative electrode material is 80%-99%;

[0025] H. The current collector includes aluminum foil and / or copper foil.

[0026] Optionally, the multilayer negative electrode sheet satisfies at least one of the following conditions:

[0027] A. The surface density of the first coating is 10 mg / cm 2 -20mg / cm 2 ;

[0028] B. The surface density of the second coating is 1 mg / cm 2 -5mg / cm 2 .

[0029] The second aspect of the present application provides a method for preparing the multi-layer negative electrode sheet, including:

[0030] Mix the raw materials of the first coating to prepare the first slurry;

[0031] Under a protective atmosphere, mix the raw materials of the second coating to prepare the second slurry;

[0032] Coat the two sides of the current collector with the first slurry and perform the first drying to form the first coating;

[0033] Coat the surface of the first coating with the second slurry and perform the second drying to obtain the multi-layer negative electrode sheet.

[0034] Optionally, the method for preparing the multi-layer negative electrode sheet satisfies at least one of the following conditions:

[0035] A. The temperature of the first drying is 80°C - 120°C, and the time is 4h - 12h;

[0036] B. The temperature of the second drying is 80°C - 120°C, and the time is 4h - 12h;

[0037] C. The protective gas in the protective atmosphere includes nitrogen.

[0038] The third aspect of the present application provides a sodium-ion battery, including the multi-layer negative electrode sheet or the multi-layer negative electrode sheet prepared by the method for preparing the multi-layer negative electrode sheet.

[0039] Optionally, the sodium-ion battery further includes a positive electrode sheet;

[0040] The positive active material in the positive electrode sheet includes one or more of layered oxides, polyanion compounds, Prussian blue, and Prussian white.

[0041] The fourth aspect of the present application provides an electrical device, including the sodium-ion battery.

[0042] Compared with the prior art, the beneficial effects of the present application include:

[0043] The multilayer negative electrode plate provided by the present application, firstly, the second coating layer can greatly improve the average sodium storage capacity of the negative electrode and improve the mass energy density of the battery cell; secondly, the second coating layer is coated on the surface of the first coating layer, so that more sodium storage sites are close to the positive electrode direction, which can quickly store sodium ions during charging and release sodium ions faster during discharging, thereby improving the charging and discharging efficiency; then, more sodium ions can be stored in the second coating layer, avoiding sodium precipitation caused by larger polarization, thereby improving the safety of the battery cell; finally, the first coating layer and the second coating layer are respectively arranged, and when the negative electrode active material in the second coating layer changes due to expansion, less stress is generated on the first coating layer, so the structural stability of the first coating layer will not be destroyed, thereby improving the cycle life.

[0044] The method for preparing the multi-layer negative electrode sheet provided in the present application separately configures the first slurry and the second slurry, thereby reducing the consumption of the inert system and lowering the cost.

[0045] The sodium ion battery and electrical equipment provided in the present application have high energy density, long service life, and excellent kinetic performance and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0047] Figure 1 The multi-layer negative electrode sheet prepared in Example 1;

[0048] Figure 2 This is a comparison chart of the cycle capacity retention rate curves of the lithium ion battery prepared in Comparative Example 1 and the lithium ion battery prepared in Example 1.

[0049] Component Symbols:

[0050] 100 - current collector; 200 - first coating layer; 300 - second coating layer. DETAILED DESCRIPTION

[0051] As used herein:

[0052] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0053] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0054] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described in this article, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0055] In these examples, parts and percentages are by mass unless otherwise indicated.

[0056] "Parts by mass" refers to the basic unit of measurement for expressing the mass ratio of multiple components. 1 part can represent any unit mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that, unlike the mass parts, the sum of the mass of all components is not limited to 100 parts.

[0057] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0058] In a first aspect, the present application provides a multilayer negative electrode sheet, the multilayer negative electrode sheet comprising a current collector, a first coating layer and a second coating layer;

[0059] The first coating is disposed between the current collector and the second coating;

[0060] The raw materials of the first coating layer include hard carbon, a first conductive agent, a first dispersant and a first binder;

[0061] The raw materials of the second coating layer include a phosphorus-containing negative electrode material, a second conductive agent, a second dispersant and a second binder.

[0062] In some embodiments, the thickness of the first coating is 30um-200um;

[0063] Optionally, the thickness of the first coating layer may be 30um, 60um, 90um, 120um, 150um, 180um, 200um or any value between 30um and 200um;

[0064] The thickness of the second coating layer is 3%-20% of the thickness of the first coating layer.

[0065] Optionally, the thickness of the second coating layer may be 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20% or any value between 3% and 20% of the thickness of the first coating layer.

[0066] It should be noted that the phosphorus-containing negative electrode material in the second coating has a higher sodium storage capacity, which can be 6-10 times that of the hard carbon negative electrode. A small amount of application can greatly increase the average sodium storage capacity of the negative electrode and improve the mass energy density of the battery cell. Therefore, due to the high gram capacity of the phosphorus-containing negative electrode material, under the same capacity, a thinner negative electrode can be designed to match the positive electrode to improve the mass energy density of the battery cell; when the thickness of the second coating is 3%-20% of the thickness of the first coating, it is more appropriate. When it is greater than 20%, it will be greatly affected by expansion; when it is less than 3%, the capacity improvement effect is not obvious.

[0067] In some embodiments, the multilayer negative electrode sheet satisfies at least one of the following conditions:

[0068] A. The raw materials of the first coating layer, calculated by total mass as 100%, include:

[0069] The hard carbon is 80%-97%, the first conductive agent is 0.5%-10%, the first dispersant is 0.5%-10%, and the first binder is 0.5%-10%;

[0070] Optionally, the raw materials of the first coating layer are calculated based on the total mass of 100%, the hard carbon can be 80%, 85%, 90%, 95%, 97% or any value between 80% and 97%, the first conductive agent can be 0.5%, 1%, 2%, 4%, 6%, 8%, 10% or any value between 0.5% and 10%, the first dispersant can be 0.5%, 1%, 2%, 4%, 6%, 8%, 10% or any value between 0.5% and 10%, and the first binder can be 0.5%, 1%, 2%, 4%, 6%, 8%, 10% or any value between 0.5% and 10%;

[0071] It should be noted that when the raw materials of the first coating are in the above mass ratio, adhesion, conductivity and energy density can be taken into account;

[0072] B. The raw materials of the second coating layer, based on the total mass as 100%, include:

[0073] The phosphorus-containing negative electrode material accounts for 80%-95%, the second conductive agent accounts for 0.5%-10%, the second dispersant accounts for 0.5%-10%, and the second binder accounts for 0.5%-10%.

[0074] Optionally, based on the total mass of the raw materials for the second coating being 100%, the phosphorus-containing negative electrode material may be 80%, 85%, 90%, 95% or any value between 80% and 95%, the second conductive agent may be 0.5%, 1%, 2%, 4%, 6%, 8%, 10% or any value between 0.5% and 10%, the second dispersant may be 0.5%, 1%, 2%, 4%, 6%, 8%, 10% or any value between 0.5% and 10%, and the second binder may be 0.5%, 1%, 2%, 4%, 6%, 8%, 10% or any value between 0.5% and 10%.

[0075] In some embodiments, the multilayer negative electrode sheet satisfies at least one of the following conditions:

[0076] A. The hard carbon includes one or more of biomass hard carbon, resin hard carbon, coal-based hard carbon, and asphalt-based hard carbon;

[0077] B. The particle size of the hard carbon is 3um-7um;

[0078] Optionally, the particle size of the hard carbon may be 3um, 4um, 5um, 6um, 7um or any value between 3um and 7um;

[0079] C. The first conductive agent and the second conductive agent independently include one or more of SP, acetylene black, Ketjen black, carbon nanotubes, graphene, and conductive graphite;

[0080] D. the first dispersant and the second dispersant each independently comprise CMC;

[0081] E. the first binder and the second binder each independently comprise SBR and / or PAA;

[0082] F. The phosphorus-containing negative electrode material includes one or more of red phosphorus, black phosphorus, and phosphorus-carbon composites;

[0083] G. The phosphorus content in the phosphorus-containing negative electrode material is 80%-99%;

[0084] Optionally, the phosphorus content in the phosphorus-containing negative electrode material may be 80%, 85%, 90%, 95%, 99% or any value between 80% and 99%;

[0085] H. The current collector includes aluminum foil and / or copper foil.

[0086] In some embodiments, the multilayer negative electrode sheet satisfies at least one of the following conditions:

[0087] A. The surface density of the first coating is 10 mg / cm 2 -20mg / cm 2 ;

[0088] Optionally, the surface density of the first coating can be 10 mg / cm 2 , 12mg / cm 2 、14mg / cm 2 、16mg / cm 2 、18mg / cm 2 , 20mg / cm 2 Or 10mg / cm 2 -20mg / cm 2 Any value between

[0089] B. The surface density of the second coating is 1 mg / cm 2 -5mg / cm 2 .

[0090] Optionally, the surface density of the second coating can be 1 mg / cm 2 , 2mg / cm 2 、3mg / cm 2 , 4mg / cm 2 , 5mg / cm 2 Or 1mg / cm 2 -5mg / cm 2 Any value in between.

[0091] The second aspect of the present application provides a method for preparing the multi-layer negative electrode sheet, comprising:

[0092] Mixing the raw materials of the first coating layer to prepare a first slurry;

[0093] Under a protective atmosphere, mixing the raw materials of the second coating to prepare a second slurry;

[0094] Applying the first slurry on both sides of the current collector and performing a first drying to form a first coating;

[0095] The second slurry is coated on the surface of the first coating layer, and a second drying is performed to obtain a multi-layer negative electrode sheet.

[0096] In some embodiments, the method for preparing the multilayer negative electrode sheet satisfies at least one of the following conditions:

[0097] In some embodiments, the relevant parameters of the first drying and the second drying can be set according to the actual situation to achieve the purpose of drying without damaging the material;

[0098] A. The first drying temperature is 80°C-120°C and the time is 4h-12h;

[0099] Optionally, the temperature of the first drying can be 80°C, 90°C, 100°C, 110°C, 120°C or any value between 80°C and 120°C, and the time can be 4h, 6h, 8h, 10h, 12h or any value between 4h and 12h;

[0100] B. The second drying temperature is 80°C-120°C and the time is 4h-12h;

[0101] Optionally, the temperature of the second drying can be 80°C, 90°C, 100°C, 110°C, 120°C or any value between 80°C and 120°C, and the time can be 4h, 6h, 8h, 10h, 12h or any value between 4h and 12h;

[0102] C. The protective gas in the protective atmosphere includes nitrogen.

[0103] It should be noted that, in a nitrogen atmosphere, oxidation caused by temperature rise during the second slurry manufacturing process can be avoided.

[0104] A third aspect of the present application provides a sodium ion battery, comprising the multi-layer negative electrode sheet or the multi-layer negative electrode sheet prepared by the method for preparing the multi-layer negative electrode sheet.

[0105] In some embodiments, the sodium ion battery further comprises a positive electrode sheet;

[0106] The positive electrode active material in the positive electrode plate includes one or more of layered oxides, polyanion compounds, Prussian blue or Prussian white.

[0107] A fourth aspect of the present application provides an electrical device, comprising the sodium ion battery.

[0108] It should be noted that electrical equipment may be but is not limited to mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.; among them, mobile devices may include but are not limited to at least one of mobile phones, laptop computers, etc.; electric vehicles may include but are not limited to at least one of pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0109] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If specific conditions are not specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0110] Example 1

[0111] This embodiment provides a multi-layer negative electrode sheet, including a current collector 100, a first coating layer 200 and a second coating layer 300;

[0112] The first coating layer 200 is disposed between the current collector 100 and the second coating layer 300;

[0113] The current collector is aluminum foil;

[0114] The raw materials of the first coating 200 include: 1.9 kg of biomass hard carbon, 0.5 kg of carbon nanotubes, 0.05 kg of conductive agent SP, 0.2 kg of dispersant CMC, and 0.15 kg of binder SBR, wherein the particle size of the hard carbon is 5.5 um;

[0115] The total solid content of the first coating is 2kg, of which biomass hard carbon accounts for 92%, carbon nanotubes 0.5%, conductive agent SP 2.5%, dispersant CMC 2%, and binder SBR 3%;

[0116] The raw materials of the second coating layer 300 include: 0.2 kg of phosphorus-carbon composite, 0.05 kg of carbon nanotubes, 0.005 kg of conductive agent SP, 0.02 kg of dispersant CMC, 0.5 kg of binder PAA and 0.1 kg of SBR;

[0117] The total solid content of the second coating is 0.2 kg, of which the phosphorus negative electrode material accounts for 87%, carbon nanotubes 1%, conductive agent SP4%, dispersant CMC 3%, binder SBR 3% and PAA 2%;

[0118] The surface density of the first coating 200 is 15 mg / cm 2 The total surface density of the second coating 300 is 3 mg / cm 2 .

[0119] A second aspect of the present embodiment provides a method for preparing a multi-layer negative electrode sheet, comprising:

[0120] Mixing the raw materials of the first coating layer 200 to obtain a first slurry;

[0121] In a nitrogen atmosphere, the raw materials of the second coating layer 300 are mixed to obtain a second slurry;

[0122] The first slurry was applied to both sides of the aluminum foil and dried at a temperature of 100°C for 8 hours to obtain a first coating of 200;

[0123] The second slurry was applied to both sides of the first coating layer and dried at a temperature of 100° C. for 8 hours to obtain a multi-layer negative electrode sheet.

[0124] The schematic diagram of the multi-layer negative electrode sheet is as follows Figure 1 shown.

[0125] The third aspect of the present application provides a sodium ion battery, which is assembled into a battery by assembling the above-mentioned multi-layer negative electrode sheet and positive electrode sheet, a separator, an electrolyte, and a shell.

[0126] Example 2

[0127] The difference from Example 1 is that the surface density of the second coating is 5.

[0128] Example 3

[0129] The difference from Example 1 is that the surface density of the first coating is 20.

[0130] Example 4

[0131] The difference from the first embodiment is that the raw material of the first coating layer 200 does not include carbon nanotubes, and the proportion of the conductive agent SP is 3%.

[0132] Comparative Example 1

[0133] The difference from Example 1 is that no second coating layer is provided.

[0134] Comparison of the cycle capacity retention rate curves of the lithium ion battery prepared in Comparative Example 1 and the lithium ion battery prepared in Example 1 Figure 2 As shown (the solid line is Example 1, and the dotted line is Comparative Example 1).

[0135] Comparative Example 2

[0136] The difference from Example 1 is that the first coating layer is not provided.

[0137] Comparative Example 3

[0138] The difference from Example 1 is that the second slurry is firstly coated on both sides of the aluminum foil, and then the first slurry is coated after drying.

[0139] Comparative Example 4

[0140] The difference from Example 1 is that the formula of the second coating is adjusted, PAA is not used, the total solid content of the second coating is 0.2 kg, of which the phosphorus negative electrode material accounts for 87%, carbon nanotubes 1%, conductive agent SP 4%, dispersant CMC 3%, and binder SBR 5%.

[0141] The multilayer negative electrode sheets prepared in the above embodiments and comparative examples were subjected to surface density tests, and the specific results are shown in Table 1.

[0142] Surface density test: Use the weighing method and an electronic balance. The surface density is the weight divided by the surface area.

[0143] Table 1 Surface density test

[0144] sample <![CDATA[First coating (mg / cm 2 )]]> <![CDATA[Second coating (mg / cm 2 )]]> Example 1 15 3 Example 2 15 5 Example 3 20 3 Example 4 15 3 Comparative Example 1 18 0 Comparative Example 2 0 18 Comparative Example 3 10 10 Comparative Example 4 15 3

[0145] The sodium ion batteries prepared in the above examples and comparative examples were subjected to performance tests, and the specific test results are shown in Table 2.

[0146] Table 2 Performance test

[0147]

[0148] From Table 2, we can see that:

[0149] Although comparative example 1 has good stability, its capacity is relatively low. Comparative examples 2 and 3 have high initial capacity but low retention rate, which is caused by the expansion of the phosphorus negative electrode. Comparative example 4 has slightly poor cycle performance due to the lack of PAA bonding. The embodiment takes into account both high capacity and cycle stability and performs better. Therefore, the battery prepared by this scheme not only has a higher gram capacity and first efficiency, but also has good cycle stability.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0151] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present application and form different embodiments. For example, in the above claims, any one of the claimed embodiments may be used in any combination. The information disclosed in this background technology section is intended only to deepen the understanding of the overall background technology of the present application and should not be regarded as an admission or in any form of implication that the information constitutes prior art known to those skilled in the art.

Claims

1. A multi-layer negative electrode sheet, characterized in that: The multilayer negative electrode sheet comprises a current collector, a first coating layer and a second coating layer; The first coating is disposed between the current collector and the second coating; The raw materials of the first coating layer include hard carbon, a first conductive agent, a first dispersant and a first binder; The raw materials of the second coating layer include a phosphorus-containing negative electrode material, a second conductive agent, a second dispersant and a second binder.

2. The multi-layer negative electrode sheet according to claim 1, characterized in that: The thickness of the first coating is 30um-200um; The thickness of the second coating layer is 3%-20% of the thickness of the first coating layer.

3. The multi-layer negative electrode sheet according to claim 1, characterized in that: At least one of the following conditions is met: A. The raw materials of the first coating layer, calculated by total mass as 100%, include: The hard carbon is 80%-97%, the first conductive agent is 0.5%-10%, the first dispersant is 0.5%-10%, and the first binder is 0.5%-10%; B. The raw materials of the second coating layer, based on the total mass as 100%, include: The phosphorus-containing negative electrode material accounts for 80%-95%, the second conductive agent accounts for 0.5%-10%, the second dispersant accounts for 0.5%-10%, and the second binder accounts for 0.5%-10%.

4. The multi-layer negative electrode sheet according to claim 1, characterized in that: At least one of the following conditions is met: A. The hard carbon includes one or more of biomass hard carbon, resin hard carbon, coal-based hard carbon, and asphalt-based hard carbon; B. The particle size of the hard carbon is 3um-7um; C. The first conductive agent and the second conductive agent independently include one or more of SP, acetylene black, Ketjen black, carbon nanotubes, graphene, and conductive graphite; D. the first dispersant and the second dispersant each independently comprise CMC; E. the first binder and the second binder each independently comprise SBR and / or PAA; F. The phosphorus-containing negative electrode material includes one or more of red phosphorus, black phosphorus, and phosphorus-carbon composites; G. The phosphorus content in the phosphorus-containing negative electrode material is 80%-99%; H. The current collector includes aluminum foil and / or copper foil.

5. The multilayer negative electrode sheet according to any one of claims 1 to 4, characterized in that: At least one of the following conditions is met: A. The surface density of the first coating is 10 mg / cm 2 -20mg / cm 2 ; B. The surface density of the second coating is 1 mg / cm 2 -5mg / cm 2 .

6. A method for preparing a multilayer negative electrode sheet according to any one of claims 1 to 5, characterized in that: include: Mixing the raw materials of the first coating layer to prepare a first slurry; Under a protective atmosphere, mixing the raw materials of the second coating to prepare a second slurry; Applying the first slurry on both sides of the current collector and performing a first drying to form a first coating; The second slurry is coated on the surface of the first coating layer, and a second drying is performed to obtain a multi-layer negative electrode sheet.

7. The method for preparing a multi-layer negative electrode sheet according to claim 6, characterized in that: At least one of the following conditions is met: A. The first drying temperature is 80°C-120°C and the time is 4h-12h; B. The second drying temperature is 80°C-120°C and the time is 4h-12h; C. The protective gas in the protective atmosphere includes nitrogen.

8. A sodium ion battery, characterized in that: A multilayer negative electrode sheet comprising the multilayer negative electrode sheet according to any one of claims 1 to 5 or prepared by the method for preparing the multilayer negative electrode sheet according to claim 6 or 7.

9. The sodium ion battery according to claim 8, characterized in that: The sodium ion battery also includes a positive electrode plate; The positive electrode active material in the positive electrode sheet includes one or more of layered oxides, polyanion compounds, Prussian blue and Prussian white.

10. An electrical device, characterized in that: Including the sodium ion battery according to claim 8 or 9.

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