Positive electrode slurry and preparation method thereof, positive plate, battery and electric equipment

Abstract

The invention provides positive electrode slurry and a preparation method thereof, a positive plate, a battery and electric equipment. The positive electrode slurry comprises a positive electrode active material, a first conductive agent, a second conductive agent and a binder, the positive electrode active material, the first conductive agent and the second conductive agent meet the relational expression: 3.7 < = aX + bY + cZ < = 4.2; wherein X is the mass ratio of the positive electrode active material in the positive electrode slurry, a is the specific surface area of the positive electrode active material, Y is the mass ratio of the first conductive agent in the positive electrode slurry, b is the specific surface area of the first conductive agent, Z is the mass ratio of the second conductive agent in the positive electrode slurry, and c is the specific surface area of the second conductive agent. According to the invention, the positive electrode slurry is subjected to formula model design, so that the produced positive electrode slurry is stable, the pole piece processing performance is excellent, and the produced sodium ion battery is stable in long-term circulation.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a positive electrode slurry and a preparation method thereof, a positive electrode sheet, a battery and an electrical device. Background Art

[0002] Sodium-ion batteries have broad application prospects as a complement to lithium-ion batteries and lead-acid batteries in the fields of new energy storage and small power due to their advantages such as extensive sodium resources, excellent rate performance, wide operating temperature range, and safety and stability.

[0003] However, due to the material characteristics of sodium-ion batteries, energy density is an obvious performance shortcoming. In order to improve this defect, the industry has carried out corresponding improvement work from the material end to the battery cell end. Among them, the improvement on the material end is to achieve the purpose of improving energy density by optimizing the raw material structure channel and carrying out specific design of doping elements and high entropy. The improvement on the battery cell end is to achieve the effect of improving energy density by mixing organic solvents on the positive electrode side and using high-capacity phosphorus electrodes on the negative electrode side.

[0004] However, doping raw materials with elements may introduce high voltage conditions to meet high capacity requirements, thereby sacrificing a certain degree of stability. This method also introduces unconventional production steps such as multi-step quenching that are difficult to industrialize, making it difficult to implement rapid mass industrial use. Sodium supplementation on the positive electrode side will increase battery impedance, reduce energy density, and reduce cycle capacity. Summary of the invention

[0005] The embodiments of the present application provide a positive electrode slurry and a preparation method thereof, a positive electrode sheet, a battery and an electrical device. The present invention designs a formula model for the positive electrode slurry, thereby making the output positive electrode slurry stable, the electrode sheet processing performance excellent, and the prepared sodium ion battery stable in long-term cycle.

[0006] A first aspect of the present invention provides a positive electrode slurry, the positive electrode slurry comprising a positive electrode active material, a first conductive agent, a second conductive agent, and a binder;

[0007] The positive electrode active material, the first conductive agent, and the second conductive agent satisfy the relationship: 3.7≤aX+bY+cZ≤4.2;

[0008] Among them, X is the mass proportion of the positive electrode active material in the positive electrode slurry, a is the specific surface area of ​​the positive electrode active material, Y is the mass proportion of the first conductive agent in the positive electrode slurry, b is the specific surface area of ​​the first conductive agent, Z is the mass proportion of the second conductive agent in the positive electrode slurry, and c is the specific surface area of ​​the second conductive agent.

[0009] The positive electrode slurry as described above, wherein the mass proportion of the positive electrode active material in the positive electrode slurry is 90%-98%, the mass proportion of the first conductive agent in the positive electrode slurry is 0%-5%, and the mass proportion of the second conductive agent in the positive electrode slurry is 0%-5%.

[0010] In the positive electrode slurry as described above, the positive electrode active material comprises at least one of a layered metal oxide, a polyanion compound and a Prussian blue compound.

[0011] In the positive electrode slurry as described above, the first conductive agent includes at least one of carbon black, Ketjen black, acetylene black and carbon fiber.

[0012] In the positive electrode slurry as described above, the second conductive agent includes at least one of graphene, carbon nanotubes, and carbon black.

[0013] In the positive electrode slurry as described above, the binder includes at least one of polyacrylic acid, styrene-butadiene rubber emulsion, styrene-acrylic emulsion, polyamide and sodium alginate.

[0014] A second aspect of the present invention provides a method for preparing the positive electrode slurry as described above, comprising the following steps:

[0015] Mixing the positive electrode active material, the binder, and the first conductive agent in solid dry powder according to their respective mass proportions to obtain a solid dry powder;

[0016] According to a preset first mass ratio, adding a preset solvent to the solid dry powder material, stirring and kneading the mixture, to obtain a slurry with a high solid content;

[0017] The second conductive agent is added into the high solid content slurry according to its own mass proportion and a preset second mass ratio, and the positive electrode slurry is obtained after stirring.

[0018] In the preparation method as described above, the preset first mass ratio is the solid content in the high-solid content slurry, and the preset first mass ratio is 75% to 90%.

[0019] In the preparation method as described above, the preset second mass ratio is the solid content in the positive electrode slurry, and the preset second mass ratio is 55%-65%.

[0020] The third aspect of the present invention provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 6, a first conductive agent, a second conductive agent, and a binder. The positive electrode active material layer comprises the positive electrode slurry provided in the first aspect of the present invention.

[0021] A fourth aspect of the present invention provides a method for preparing the positive electrode sheet as described above, comprising the following steps:

[0022] The positive electrode active material layer is coated on the surface of the positive electrode current collector to form a positive electrode coating, and the positive electrode coating is dried, cold pressed and die-cut to obtain the positive electrode sheet.

[0023] The preparation method as described above, wherein the coating surface density of the positive electrode coating is 360g / cm 2 -460g / cm 2 Between, compacted density is 2.0g / cm 3 -3.4g / cm 3 between.

[0024] A fifth aspect of the present invention provides a battery, comprising the positive electrode sheet provided by the third aspect of the present invention.

[0025] A sixth aspect of the present invention provides an electrical device, comprising the battery provided by the fourth aspect of the present invention.

[0026] The implementation of the present invention has at least the following beneficial effects: the positive electrode slurry of the present invention includes a positive electrode active material, a first conductive agent, a second conductive agent, and a binder; the positive electrode active material, the first conductive agent, and the second conductive agent satisfy the relationship: 3.7≤aX+bY+cZ≤4.2; wherein X is the mass proportion of the positive electrode active material in the positive electrode slurry, a is the specific surface area of ​​the positive electrode active material, Y is the mass proportion of the first conductive agent in the positive electrode slurry, b is the specific surface area of ​​the first conductive agent, Z is the mass proportion of the second conductive agent in the positive electrode slurry, and c is the specific surface area of ​​the second conductive agent. The present invention designs a formula model for the positive electrode slurry so that the positive electrode active material, the first conductive agent, and the second conductive agent satisfy a certain range relationship, so that the output positive electrode slurry is stable, without gel and sedimentation abnormalities, and the positive electrode sheet prepared by the slurry produced by the present invention has excellent processing performance and high conductivity, thereby achieving the long-term cycle stability requirements of the sodium ion battery. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Due to the material properties of sodium-ion batteries, energy density is an obvious performance shortcoming. To improve this defect, traditional methods mainly use optimization methods such as charge compensation on the material side, element doping, or mixing organic solvents on the positive electrode side of the cell to supplement sodium. However, additives may introduce hidden dangers that affect battery performance, and the process of doping elements is complicated, making it difficult to implement rapid mass industrial use.

[0029] Based on this, the first aspect of the present invention provides a positive electrode slurry, including a positive electrode active material, a first conductive agent, a second conductive agent, and a binder; the positive electrode active material, the first conductive agent, and the second conductive agent satisfy the relationship: 3.7≤aX+bY+cZ≤4.2; wherein X is the mass proportion of the positive electrode active material in the positive electrode slurry, a is the specific surface area of ​​the positive electrode active material, Y is the mass proportion of the first conductive agent in the positive electrode slurry, b is the specific surface area of ​​the first conductive agent, Z is the mass proportion of the second conductive agent in the positive electrode slurry, and c is the specific surface area of ​​the second conductive agent.

[0030] In order to improve the energy density of sodium-ion batteries, the formulation on the positive electrode side needs to pursue a high proportion of main powder by mass, which will inevitably reduce the content of binder and conductive agent, and may have a related impact on the stability of the slurry, the adhesion of the electrode, the conductivity of the electrode, and the internal resistance of the finished battery.

[0031] The present invention designs a formula model at the cell level, and proposes a range relationship based on the intrinsic specific surface area of ​​the sodium ion positive electrode material and the conductive agent and the corresponding mass proportion. By controlling it within this range, it can ensure that the positive electrode slurry produced is stable, the electrode sheet processing performance is excellent, and the sodium ion battery produced is stable in long-term cycle. The mass proportion and specific surface area of ​​the positive electrode active material, the first conductive agent, and the second conductive agent are all listed in Table 1, and the specific relationship is described as follows:

[0032] Table 1

[0033]

[0034] As shown in Table 1, X is the mass proportion of the positive electrode active material in the positive electrode slurry, a is the specific surface area of ​​the positive electrode active material, Y is the mass proportion of the first conductive agent in the positive electrode slurry, b is the specific surface area of ​​the first conductive agent, Z is the mass proportion of the second conductive agent in the positive electrode slurry, and c is the specific surface area of ​​the second conductive agent. Among them, the positive electrode active material, the first conductive agent, and the second conductive agent satisfy the relationship 3.7≤aX+bY+cZ≤4.2. By controlling the positive electrode active material, the first conductive agent, and the second conductive agent within this range, it can be ensured that the output positive electrode slurry is stable, the pole piece processing performance is excellent, and the prepared sodium ion battery has long-term cycle stability.

[0035] In a preferred embodiment, the mass proportion of the positive electrode active material in the positive electrode slurry is 90%-98%, the mass proportion of the first conductive agent in the positive electrode slurry is 0%-5%, and the mass proportion of the second conductive agent in the positive electrode slurry is 0%-5%. The inventors have found that the positive electrode slurry prepared by this mass proportion distribution method has better stability than other mass proportion distribution methods.

[0036] In a preferred embodiment, the positive electrode active material of the present application includes at least one of a layered metal oxide, a polyanion compound and a Prussian blue compound. The positive electrode active material can be detected by specific table parameters or specific table parameters provided by the manufacturer, based on the relationship satisfied by the positive electrode active material, the first conductive agent, and the second conductive agent. If the obtained specific table parameters conform to the relationship satisfied by the positive electrode active material, the first conductive agent, and the second conductive agent, it is determined to be a positive electrode active material.

[0037] In a preferred embodiment, the first conductive agent includes at least one of carbon black, Ketjen black, acetylene black, and carbon fiber. The first conductive agent can be obtained by specific table parameter detection or specific table parameters provided by the manufacturer, based on the relationship satisfied by the positive electrode active material, the first conductive agent, and the second conductive agent, if the obtained specific table parameters meet the relationship satisfied by the positive electrode active material, the first conductive agent, and the second conductive agent, it is determined to be the first conductive agent.

[0038] In a preferred embodiment, the second conductive agent includes at least one of graphene, carbon nanotubes, and carbon black. The second conductive agent can be obtained by specific table parameter detection or specific table parameters provided by the manufacturer, based on the relationship between the positive electrode active material, the first conductive agent, and the second conductive agent, if the obtained specific table parameters meet the relationship between the positive electrode active material, the first conductive agent, and the second conductive agent, it is determined to be the second conductive agent, wherein the second conductive agent is a mixed slurry form of a substance, which can contain one or more of graphene, carbon nanotubes, carbon black, etc.

[0039] In a preferred embodiment, the binder includes at least one of polyacrylic acid, styrene-butadiene rubber emulsion, styrene-acrylic emulsion, polyamide, and sodium alginate.

[0040] Based on this, the second aspect of the present application provides a method for preparing the positive electrode material as described above, comprising the following steps:

[0041] 1) mixing the positive electrode active material, the binder, and the first conductive agent in solid dry powder according to their respective mass proportions to obtain a solid dry powder;

[0042] 2) adding a preset solvent to the solid dry powder according to a preset first mass ratio, stirring and kneading the mixture to obtain a high solid content slurry;

[0043] 3) adding the second conductive agent into the high solid content slurry according to its own mass proportion and a preset second mass ratio, and stirring to obtain the positive electrode slurry.

[0044] In the above method, the positive electrode active material, the binder, and the first conductive agent are first mixed in solid dry powder according to their respective mass proportions, and stirred at 12rpm / min for 20min to form a uniformly mixed solid dry powder. During the dry powder mixing stage, the material particles are in contact with each other in the form of points, points and surfaces, and points and lines. The contact form varies depending on the type of material. At this stage, the internal porosity of the material is high and the friction of the powder surface is small, so most of the materials can be mixed and contacted in a short time.

[0045] Then take the corresponding mass of the solid dry powder obtained in step 1 and N-methylpyrrolidone solvent, add the solvent to the solid dry powder and pre-knead at 12 rpm / min for 20 minutes, stop stirring and scraping, and then knead at 15 rpm / min for 60 minutes to obtain a high solid content slurry. At this stage, after the dry powder is evenly mixed, N-methylpyrrolidone solvent is added, and the raw materials are moistened and muddy. After strong stirring by the mixer, the material is subjected to mechanical shear and friction, and there is also internal friction between the particles. Under various forces, the raw material particles tend to be highly dispersed.

[0046] Finally, the second conductive agent is added according to the mass ratio, N-methylpyrrolidone solvent is added, and the positive electrode slurry is obtained after stirring again. This stage is carried out after the second stage is completed. The solvent is slowly added to adjust the slurry viscosity and solid content for further dispersion. In this stage, dispersion and agglomeration coexist and finally reach a stable suspension state.

[0047] In a specific embodiment, the preset first mass ratio is the solid content in the high-solid content slurry, and the preset first mass ratio is 75% to 90%.

[0048] The high solid content slurry prepared by the above steps can fully wet and mix the materials, making it easier to disperse the raw material particles.

[0049] In a specific embodiment, the preset second mass ratio is the solid content in the positive electrode slurry, and the preset second mass ratio is 55%-65%.

[0050] The above process is to adjust the viscosity and solid content of the slurry to further disperse the slurry. In this stage, dispersion and agglomeration coexist and finally reach a stable suspension state, ensuring that the prepared slurry is stable without gel or sedimentation abnormalities.

[0051] A third aspect of the present invention provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode slurry provided by the first aspect of the present invention.

[0052] The positive electrode current collector of the present invention can be selected from positive electrode current collectors commonly used in the art, such as aluminum foil.

[0053] A fourth aspect of the present invention provides a method for preparing a positive electrode sheet as described above, comprising coating a positive electrode active material layer on the surface of a positive electrode current collector to form a positive electrode coating, and drying, cold pressing and die-cutting the positive electrode coating to obtain a positive electrode sheet.

[0054] In a specific embodiment, the positive electrode sheet can be prepared by the following method: the prepared positive electrode slurry is evenly coated on the front and back sides of the aluminum foil at a certain coating surface density, and after drying, it is rolled according to a certain compaction, and the positive electrode sheet is obtained by slitting and die-cutting.

[0055] Furthermore, the positive electrode active material layer includes 90% to 98% of positive electrode active material, 0 to 5% of a first conductive agent, 0 to 5% of a second conductive agent, and 1 to 10% of a binder in terms of mass percentage. The present invention does not strictly limit the positive electrode active material in the positive electrode sheet, and can be a positive electrode active material commonly used in sodium ion batteries, wherein the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinyl pyrrolidone, and polyurethane.

[0056] Preferably, the positive electrode active material in the present invention includes at least one of layered metal oxides, polyanion compounds and Prussian blue compounds, the first conductive agent includes one or more of carbon black (SP), Ketjen black, acetylene black, VGCF, the second conductive agent includes one or more composite slurries of graphene, carbon nanotubes, carbon black, etc., and the binder includes polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN).

[0057] In a specific embodiment, the coating surface density of the positive electrode coating is 360 g / cm 2 -460 g / cm 2 Between, compacted density is 2.0g / cm 3 -3.4g / cm 3 between.

[0058] The fifth aspect of the present invention provides a battery, comprising the positive electrode slurry provided in the first aspect and / or the positive electrode sheet provided in the third aspect. Since the battery comprises the positive electrode sheet having the positive electrode slurry, the battery has better stability, more excellent cycle performance and energy density during use.

[0059] The battery of the present invention comprises, in addition to the positive electrode sheet, a negative electrode sheet, a separator arranged between the positive electrode sheet and the negative electrode sheet, and an electrolyte.

[0060] Among them, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. Among them, the negative electrode current collector can be selected from the negative electrode current collectors conventionally used in the art, such as aluminum foil. The negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder. The present invention does not strictly limit the negative electrode active material in the negative electrode sheet. For example, the negative electrode active material can be selected from the negative electrode active materials conventionally used in the art, including but not limited to natural graphite, artificial graphite, silicon-carbon material, silicon-oxygen material, and one or more of hard carbon. The binder can be selected from carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. The composition of the conductive agent can refer to the type of conductive agent in the positive electrode sheet, which will not be repeated here.

[0061] Preferably, the negative electrode active material in the present invention is hard carbon, and the binder in the present invention includes one or more of polyacrylic acid, styrene-butadiene rubber emulsion, styrene-acrylic emulsion, polyamide, and sodium alginate.

[0062] Furthermore, when preparing the negative electrode sheet, the hard carbon, the first conductive agent, the dispersant, and the binder are uniformly mixed in a ratio of 90.0-97.0% by weight: 0.5-2.0%: 0.0-2.0%: 1.0-3.5% to obtain a negative electrode slurry, wherein the dispersant is sodium carboxymethyl cellulose or sodium hydroxypropyl methyl cellulose, and then uniformly coated on the front and back sides of the aluminum foil with a certain coating surface density, and after drying, the negative electrode sheet is obtained by slitting and die-cutting, wherein the coating surface density is 195-255g / cm 2 , compaction 0.95-1.05g / cm 3 .

[0063] The function of the diaphragm is to separate the positive electrode sheet from the negative electrode sheet to prevent the two from contacting and short-circuiting, and to allow sodium ions to pass freely. The present invention does not strictly limit the material selection of the diaphragm, and the diaphragm can also be a diaphragm conventionally used in the art, such as a polypropylene diaphragm, a polyethylene diaphragm, a polypropylene / polyethylene double-layer composite film, a polyimide electrospinning diaphragm, a polypropylene / polyethylene / polypropylene three-layer composite film, a cellulose non-woven fabric diaphragm, and a diaphragm with a ceramic coating.

[0064] Preferably, the diaphragm in the present invention is one of a polyethylene-based film, a polypropylene-based film, a polyethylene ceramic-coated diaphragm, and a polyethylene composite-coated diaphragm.

[0065] The present invention does not strictly limit the selection of the electrolyte, and may include one or more of the solvents commonly used in the current sodium ion battery electrolyte, and the electrolyte sodium salts commonly used in the current sodium ion electrolyte, for example: the solvent may be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, ethyl methyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be, for example, one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0066] Preferably, the electrolyte includes sodium salt, carbonate solvent and additive. The sodium salt includes at least one of NaPF6, NaClO4, NaBF4, NaFSI, NaTFSI, NaSO3CF3 and Na(CH3)C6H4SO3; the carbonate solvent includes cyclic organic solvent and chain organic solvent; the cyclic organic solvent is at least one of ethylene carbonate, propylene carbonate and butylene carbonate, and the chain organic solvent is at least one of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; the additive includes at least one of ethylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, propylene sulfite and 4-methyl ethylene sulfate.

[0067] The battery of the present invention can be manufactured by the following method: stacking the positive electrode sheet, the separator and the negative electrode sheet in sequence, obtaining a battery core through a winding process, baking the battery, performing electrolyte injection, aging and formation, and finally performing secondary injection, sealing and capacity separation to obtain the battery.

[0068] The sixth aspect of the present invention provides an electrical device, comprising the battery as described above. The present invention does not specifically limit the type of electrical device, and it can be any electrical device comprising the battery, including but not limited to mobile phones, portable devices, laptop computers, electric bicycles, electric cars, electric toys, energy storage devices, etc.

[0069] The positive electrode slurry provided by the present invention and its preparation method and application will be specifically introduced through specific embodiments below.

[0070] Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0071] Example 1

[0072] This embodiment provides a positive electrode slurry, including a positive electrode active material, a first conductive agent, a second conductive agent, and a binder, and a preparation method thereof includes the following steps:

[0073] 1) The positive electrode active material, the binder, and the first conductive agent are mixed in solid dry powder according to the mass proportion of 95.50%, 2.00%, and 1.50%, respectively, and stirred at 12 rpm / min for 20 minutes to form a uniformly mixed solid dry powder, wherein the specific surface areas of the positive electrode active material and the first conductive agent are 0.25 (m 2 / g)、65(m 2 / g).

[0074] 2) According to the solid content of 80.5%, take the corresponding mass of the solid dry powder obtained in step 1) and N-methylpyrrolidone solvent, add the solvent to the solid dry powder, pre-knead at 12 rpm / min for 20 min, stop stirring and scrape the material, and then stir and knead at 15 rpm / min for 60 min to obtain a high solid content slurry.

[0075] 3) Add the second conductive agent and N-methylpyrrolidone solvent, stir at 25 rpm / min revolution and 1800 rpm / min rotation for 60 min, and stir again at a solid content (mass ratio) of 65% to obtain a positive electrode slurry, wherein the mass ratio of the second conductive agent is 1.00% and the specific surface area is 220 (m 2 / g).

[0076] Example 2

[0077] The present embodiment provides a positive electrode slurry, including a positive electrode active material, a first conductive agent, a second conductive agent, and a binder. The preparation method thereof is basically the same as that of Example 1, except that: in step 1), the mass proportions of the positive electrode active material, the binder, and the first conductive agent are replaced with 95.20%, 2.00%, and 1.70%; in step 3), the mass proportion of the second conductive agent is replaced with 1.10%, as shown in Tables 2 and 3 for details.

[0078] Example 3

[0079] The present embodiment provides a positive electrode slurry, including a positive electrode active material, a first conductive agent, a second conductive agent, and a binder. The preparation method thereof is basically the same as that of Example 1, except that: in step 1), the mass proportions of the positive electrode active material, the binder, and the first conductive agent are replaced with 94.70%, 2.00%, and 2.00%; in step 3), the mass proportion of the second conductive agent is replaced with 1.30%, as shown in Tables 2 and 3 for details.

[0080] Example 4

[0081] The present embodiment provides a positive electrode slurry, including a positive electrode active material, a first conductive agent, a second conductive agent, and a binder. The preparation method thereof is substantially the same as that of the embodiment 1, except that: in step 1), the mass proportions of the positive electrode active material, the binder, and the first conductive agent are replaced with 97.40%, 1.50%, and 0.80%, respectively, and the specific surface area of ​​the first conductive agent is replaced with 250 (m 2 / g); in step 3), the mass proportion of the second conductive agent is replaced with 0.30%, and the specific surface area of ​​the second conductive agent is replaced with 290 (m 2 / g), see Table 2 and Table 3 for details.

[0082] Example 5

[0083] The present embodiment provides a positive electrode slurry, including a positive electrode active material, a first conductive agent, a second conductive agent, and a binder. The preparation method thereof is basically the same as that of Example 4, except that: in step 1), the mass proportions of the positive electrode active material, the binder, and the first conductive agent are replaced with 97.00%, 1.50%, and 1.00%; in step 3), the mass proportion of the second conductive agent is replaced with 0.50%, as shown in Tables 2 and 3 for details.

[0084] Example 6

[0085] The present embodiment provides a positive electrode slurry, including a positive electrode active material, a first conductive agent, a second conductive agent, and a binder. The preparation method thereof is basically the same as that of Example 4, except that: in step 1), the mass proportions of the positive electrode active material, the binder, and the first conductive agent are replaced with 97.40%, 1.50%, and 0.80%; in step 3), the mass proportion of the second conductive agent is replaced with 0.30%, as shown in Tables 2 and 3 for details.

[0086] Comparative Example 1

[0087] This embodiment provides a positive electrode slurry, including a positive electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass ratio and specific surface area of ​​the positive electrode active material, the first conductive agent, the second conductive agent, and the binder are consistent with those in Example 2, as shown in Table 2 and Table 3. The preparation method thereof includes the following steps:

[0088] 1) The positive electrode active material, the binder, the first conductive agent, the second conductive agent, and a certain proportion of the solvent were mixed at a mass ratio of 95.20%, 2.00%, 1.70%, and 1.10% respectively at a solid content of 65%, and the mixture was stirred at 12 rpm / min for 20 min, and then at 15 rpm / min for 20 min, and then the stirring was stopped and the material was scraped;

[0089] 2) N-methylpyrrolidone solvent was added, and the mixture was stirred at 25 rpm / min orbital speed and 1800 rpm / min autorotation speed for 60 min, and stirred again at a solid content of 60% to obtain a positive electrode slurry.

[0090] Comparative Example 2

[0091] The present embodiment provides a positive electrode slurry, including a positive electrode active material, a first conductive agent, a second conductive agent, and a binder. The mass proportions and specific surface areas of the positive electrode active material, the first conductive agent, the second conductive agent, and the binder are consistent with those in Example 5, as shown in Table 2 and Table 3. The preparation method is basically the same as that in Comparative Example 1.

[0092] The positive electrode slurries of the above embodiments and comparative examples were tested for the following properties:

[0093] 1. Screening condition

[0094] Test method:

[0095] The prepared positive electrode slurry was filtered through a sieve to obtain the positive electrode slurry passing through the sieve. The test results are shown in Table 4.

[0096] 2. Slurry fineness

[0097] Test method: 1) Take an appropriate amount of bubble-free slurry to the deepest part of the groove of the fineness plate, so that the slurry fills the groove and there is a little excess. Hold the scraper with both hands, place the scraper at the edge of the slurry, make the scraper contact vertically with the surface of the fineness plate, and within 3S, pull the scraper from the deepest part of the groove to the shallowest part (scrape only once) to fill the groove with slurry.

[0098] 2) After the scraper passes, immediately (no more than 5 seconds) make the line of sight at an angle of 15-30° with the scraper, observe the light where the particles are evenly and densely exposed in the groove, or where there are scratches on the particles, and record the value (accurate to the minimum scale value). Perform the experiment three times in parallel, take the arithmetic mean of two similar readings, and the error of the two readings should not be greater than the minimum scale value. In the dense particle area, observe where the particles are densely appearing on the fineness plate, including 5-10 particle points within the range of 3mm, and record the reading; in the particle scratch area, observe where the fineness plate is scratched and record the reading. The test results are shown in Table 4.

[0099] 3. Settlement

[0100] Test method: 1) When testing the solid content of the upper layer of sedimentation, use a medicine spoon to sample, and use a disposable plastic dropper to sample the solid content of the lower layer. For slurries with higher viscosity, use a combination of a dropper and a syringe. The sampling mass range is 1 to 4g.

[0101] 2) Before drying, first weigh the slurry before drying and record it. During drying, set the drying oven temperature to 120°C to dry the slurry. The drying time can be adjusted according to the sampling amount to ensure that the slurry is completely dried.

[0102] 3) The dried slurry was weighed and recorded, and the solid content of the slurry was calculated according to the formula, wherein the formula is solid content = mass of slurry after drying / mass of slurry before drying. The test results are shown in Table 4.

[0103] The positive electrode slurry prepared according to the above method was heated to 425 g / cm 2 The surface density is evenly coated on the front and back of the aluminum foil. After drying, it is rolled using the maximum compaction that can be continuously circulated, and then the positive electrode sheet is obtained through processes such as die cutting and slitting.

[0104] The compaction state and surface resistance state of the positive electrode plates of the above different implementation schemes are evaluated.

[0105] 1. Compacted state of positive electrode

[0106] Test method: The positive electrode sheet prepared according to the above method was tested in a compacted state. The test results are shown in Table 4.

[0107] 2. Surface resistance

[0108] Test method: 1) Use a micrometer to measure the thickness of the electrode to be tested and calculate the thickness of a single layer of dressing, calculate the correction factor, and input the correction factor into the test equipment.

[0109] 2) Place the sample to be tested on the test bench, start the test equipment and start the test, and record the test data after the data stabilizes. The test results are shown in Table 4.

[0110] After the positive electrode active materials in all the embodiments and comparative examples are made into positive electrode sheets, they are assembled with negative electrode sheets, electrolytes and separators according to the following method to obtain a sodium ion battery. The method includes:

[0111] 1) The positive electrode active material, the first conductive agent, the second conductive agent, and the binder are mixed according to the mass ratios in the examples and comparative examples, and a positive electrode slurry is obtained by dispersion. The slurry is prepared at a surface density of 425 g / cm 2 g / cm 3 Coating on an aluminum foil current collector and rolling to prepare a positive electrode sheet;

[0112] 2) The hard carbon material, the first conductive agent, carboxymethyl cellulose and styrene-butadiene rubber are pulped, coated and dried in a mass ratio of 95:1.5:1.5:2, and the coating surface density is 233 g / cm 2 , rolling according to the compaction density of 0.98g / m3, and manufacturing the negative electrode sheet through die cutting, slitting and other processes;

[0113] 3) The positive electrode sheet, the diaphragm (the diaphragm is a polyethylene coated composite ceramic diaphragm), and the negative electrode sheet are assembled into a bare battery cell by winding, and then assembled, welded, shelled, baked, injected with water, formed, injected with liquid once, sealed, and divided into different volumes to obtain a sodium ion battery.

[0114] The energy density and cycle performance of the sodium ion battery prepared above were evaluated.

[0115] 1. Energy density

[0116] Test method: At room temperature (25°C), take the battery prepared above, use a battery charge and discharge tester, use 0.5C constant current and constant voltage to charge to 4.0V, after standing for 15 minutes, discharge the battery to 1.5V at 0.5C constant current, and take the average discharge capacity of 3 cycles as the discharge capacity. Energy density = discharge capacity * working voltage / battery cell weight. The test results are shown in Table 4.

[0117] 2. Cycle performance

[0118] Test method: The battery prepared above was subjected to a cycle performance test at room temperature of 25°C. The test process was as follows: first, 0.5C constant current charging to 4.0V, standing for 15 minutes, and finally 1C constant current discharge to 1.5V. This process was repeated until the capacity retention rate was ≤80%, and the number of cycles was recorded. The test results are shown in Table 4.

[0119] Table 2

[0120]

[0121] Table 3

[0122] Group aX Y cZ ax+bY+cZ Slurry preparation method Example 1 0.239 0.975 2.200 3.414 This patented method Example 2 0.238 1.105 2.420 3.763 This patented method Example 3 0.237 1.300 2.860 4.397 This patented method Comparative Example 1 0.238 1.105 2.420 3.763 Non-patented method Example 4 0.244 2.000 0.870 3.114 This patented method Example 5 0.243 2.500 1.450 4.193 This patented method Example 6 0.238 5.000 3.770 9.008 This patented method Comparative Example 2 0.243 2.500 1.450 4.193 Non-patented method

[0123] Table 4

[0124]

[0125] The following conclusions can be drawn from Table 4:

[0126] 1) By comparing Example 2 with Example 1, and Example 5 with Example 4, it can be seen that the conductive agent with high specific surface area in Example 1 and Example 4 is less. Under the condition of the same amount of glue added, the slurry produced by the pulping process provided by the present invention has good dispersion state and stability, and the produced pole piece can also withstand high compaction state, but compared with Example 2 and Example 5, there is a significant gap in the monitored surface resistance data of Example 1 and Example 4. This is mainly due to the small amount of conductive agent. There is not enough conductive agent between the main powder particles to fill and form a complete conductive network, which affects the capacity of the positive electrode material and ultimately affects the energy density of the battery. At the same time, due to the lack of conductivity, the cycle stability will also be affected.

[0127] 2) By comparing Example 2 with Example 3, and Example 5 with Example 6, it can be seen that Example 3 and Example 6 have sufficient high specific surface area conductive agent, and theoretically can form a relatively complete conductive network. However, under the condition of the same binder mass ratio, the same batching process state cannot form a complete dispersion state, and the prepared slurry shows a large fineness and poor stability; at the same time, the produced pole piece is not well dispersed due to the poor slurry dispersion, and the continuous flow compaction state is affected, requiring more electrolyte to fill the gap; in addition, the amount of conductive agent added also affects the mass ratio of the positive electrode main powder. The above-mentioned conditions are combined, which seriously affects the energy density of the battery.

[0128] 3) By comparing Example 2 with Comparative Example 1, and Example 5 with Comparative Example 2, it can be seen that by adopting the positive electrode slurry preparation process provided by the present invention, the slurry can form a good dispersion effect, the compaction density of the positive electrode sheet is larger, and the surface resistance is smaller, which is beneficial to optimize the state of the output electrode sheet, the battery has a higher energy density and better cycle performance, and ultimately the output battery has better conductivity and cycle stability.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention 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 invention.

Claims

1. A positive electrode slurry, characterized in that: The positive electrode slurry includes a positive electrode active material, a first conductive agent, a second conductive agent, and a binder; The positive electrode active material, the first conductive agent, and the second conductive agent satisfy the relationship: 3.7≤aX+bY+cZ≤4.2; Among them, X is the mass proportion of the positive electrode active material in the positive electrode slurry, a is the specific surface area of ​​the positive electrode active material, Y is the mass proportion of the first conductive agent in the positive electrode slurry, b is the specific surface area of ​​the first conductive agent, Z is the mass proportion of the second conductive agent in the positive electrode slurry, and c is the specific surface area of ​​the second conductive agent.

2. The positive electrode slurry according to claim 1, characterized in that The mass proportion of the positive electrode active material in the positive electrode slurry is 90%-98%, the mass proportion of the first conductive agent in the positive electrode slurry is 0%-5%, and the mass proportion of the second conductive agent in the positive electrode slurry is 0%-5%.

3. The positive electrode slurry according to claim 1, characterized in that The positive electrode active material includes at least one of a layered metal oxide, a polyanion compound and a Prussian blue compound.

4. The positive electrode slurry according to claim 1, characterized in that: The first conductive agent includes at least one of carbon black, Ketjen black, acetylene black, and carbon fiber.

5. The positive electrode slurry according to claim 1, characterized in that: The second conductive agent includes at least one of graphene, carbon nanotubes, and carbon black.

6. The positive electrode slurry according to claim 1, characterized in that: The binder includes at least one of polyacrylic acid, styrene-butadiene rubber emulsion, styrene-acrylic emulsion, polyamide and sodium alginate.

7. A method for preparing a positive electrode slurry according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: Mixing the positive electrode active material, the binder, and the first conductive agent in solid dry powder according to their respective mass proportions to obtain a solid dry powder; According to a preset first mass ratio, adding a preset solvent to the solid dry powder material, stirring and kneading the mixture, to obtain a slurry with a high solid content; The second conductive agent is added into the high solid content slurry according to its own mass proportion and a preset second mass ratio, and the positive electrode slurry is obtained after stirring.

8. The method for preparing the positive electrode slurry according to claim 7, characterized in that: The preset first mass ratio is the solid content in the high-solid content slurry, and the preset first mass ratio is 75% to 90%.

9. The method for preparing positive electrode slurry according to claim 7, characterized in that: The preset second mass ratio is the solid content in the positive electrode slurry, and the preset second mass ratio is 55%-65%.

10. A positive electrode sheet, characterized in that: The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 6, a first conductive agent, a second conductive agent, and a binder.

11. A method for preparing a positive electrode sheet as claimed in claim 10, characterized in that: The positive electrode active material layer is coated on the surface of the positive electrode current collector to form a positive electrode coating, and the positive electrode coating is dried, cold pressed and die-cut to obtain the positive electrode sheet.

12. The method for preparing a positive electrode sheet according to claim 11, characterized in that: The coating surface density of the positive electrode coating is 360g / cm 2 -460 g / cm 2 Between, compacted density is 2.0g / cm 3 -3.4g / cm 3 between.

13. A battery, characterized in that: The battery comprises a negative electrode sheet, a separator, an electrolyte and the positive electrode sheet according to claim 10.

14. The battery according to claim 13, characterized in that The electrolyte includes sodium salt, carbonate solvent and additives.

15. The battery according to claim 14, characterized in that The sodium salt includes at least one of NaPF6, NaClO4, NaBF4, NaFSI, NaTFSI, NaSO3CF3 and Na(CH3)C6H4SO3.

16. The battery according to claim 14, characterized in that The carbonate solvent includes a cyclic organic solvent and a chain organic solvent; the cyclic organic solvent is at least one of ethylene carbonate, propylene carbonate and butylene carbonate, and the chain organic solvent is at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

17. The battery according to claim 14, characterized in that The additive includes at least one of ethylene carbonate, fluoroethylene carbonate, vinylethylene carbonate, propylene sulfite and 4-methylethylene sulfate.

18. An electrical equipment, characterized in that: A battery comprising the battery of any one of claims 13 to 17.

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