Positive electrode slurry, lithium-ion battery, and electric device

Abstract

The present application provides a positive electrode slurry, a lithium-ion battery, and an electric device. The positive electrode slurry in the present application comprises a lithium iron phosphate main material, a binder, a conductive agent, and a porous additive, wherein the conductive agent comprises conductive carbon black having a high specific surface area, and the specific surface area of the conductive carbon black is greater than or equal to 130 m2 / g. The porous additive having a medium pore size and the conductive carbon black having a small pore size and a high specific surface area fill the spaces between the lithium iron phosphate particles in the positive electrode slurry provided in the present application, so that a positive electrode sheet which uses the positive electrode slurry not only has a small pore spacing inside, but also forms a gradient pore structure that can reduce the tortuosity of lithium ion transport, thereby achieving the technical effects of improving the electrolyte wettability of an electrode and improving the properties such as a fast charge capability, cycle life, and low-temperature discharge capability of the battery.

Description

Positive electrode slurry, lithium-ion battery, electrical device

[0001] This application claims priority to Chinese Patent Application No. 202411812753.2, filed on December 10, 2024, entitled "Positive Electrode Slurry, Positive Electrode Sheet, Lithium-ion Battery, Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to, but is not limited to, the field of batteries, specifically to a positive electrode slurry, a lithium-ion battery, and an electrical device. Background Technology

[0003] With the rapid development of the lithium battery industry, the demand for batteries with high fast charging capabilities and long cycle life is becoming increasingly urgent. To meet market demand, battery performance is typically improved by adjusting the positive electrode slurry formulation and changing the electrode structure.

[0004] In existing technologies, the ability of the battery electrode to retain liquid locally, the ability to charge quickly, and the ability to cycle are often improved by increasing the amount of conductive agent in the positive electrode slurry formulation.

[0005] However, as the proportion of conductive agent increases, the content of lithium iron phosphate in the formulation will decrease, which in turn leads to a decrease in battery energy density and thus damages the overall performance of the battery. Summary of the Invention

[0006] This application provides a positive electrode slurry, a lithium-ion battery, and an electrical device, which can effectively improve the battery's local liquid retention capacity, fast charging capability, cycle life, and low-temperature discharge capability, effectively overcoming the defects in the prior art.

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] A first aspect of this application provides a positive electrode slurry, comprising: lithium iron phosphate as the main material, a binder, a conductive agent, and a porous additive, wherein the conductive agent comprises high specific surface area conductive carbon black, the specific surface area of ​​which is ≥130m². 2 / g.

[0009] According to one embodiment of this application, the conductive agent further includes carbon nanotubes compounded with conductive carbon black.

[0010] According to one embodiment of this application, the carbon nanotubes are multi-walled carbon nanotubes, wherein the specific surface area of ​​the multi-walled carbon nanotubes is 230–420 m². 2 / g, with a tube diameter of 7-11nm.

[0011] According to one embodiment of this application, the tap density of the conductive carbon black is ≤0.05 g / cm³. 3 .

[0012] According to one embodiment of this application, the average particle size of the primary structure of conductive carbon black is 20 to 30 nm.

[0013] According to one embodiment of this application, the porous additive is porous alumina.

[0014] According to one embodiment of this application, the specific surface area of ​​porous alumina is 320–360 m². 2 / g, wherein the porous alumina has a pore size distribution of 30-150nm.

[0015] According to one embodiment of this application, the primary particle size of porous alumina is 80 nm ≤ D. 50 ≤120nm.

[0016] According to one embodiment of this application, the average particle size of the primary particles in porous alumina is 60 nm.

[0017] According to one embodiment of this application, the primary particle size range of the lithium iron phosphate main material is 280–340 nm, and the particle size of the lithium iron phosphate main material satisfies 2.8 ≤ (D 90 -D 10 ) / D 50 ≤3.2.

[0018] According to one embodiment of this application, polyvinylidene fluoride (PVDF) is used.

[0019] According to one embodiment of this application, the conductive carbon black has a pore size of 5 to 30 nm, and the average pore size of the conductive carbon black is 5 to 9 nm.

[0020] According to one embodiment of this application, the primary structure particle size of the conductive carbon black is 60≤D. 50 ≤82nm.

[0021] A second aspect of this application provides a positive electrode sheet, comprising: a positive current collector and a positive electrode coating coated on the surface of the positive current collector, the positive electrode coating comprising the positive electrode slurry described in the first aspect and / or various possible embodiments of the first aspect.

[0022] A third aspect of this application provides a lithium-ion battery, including the positive electrode sheet described in the second aspect above.

[0023] A fourth aspect of this application provides an electrical device including the lithium-ion battery described in the third aspect above.

[0024] The implementation of this application has at least the following beneficial effects:

[0025] The lithium iron phosphate particles in the cathode slurry are filled with porous additives with medium pore size and high specific surface area conductive carbon black with small pore size. The cathode electrode using this cathode slurry not only has small pore spacing, but also forms a gradient pore structure that can reduce the tortuosity of lithium ion transport. This achieves the technical effect of improving the electrolyte wettability of the electrode, and improving the battery's fast charging capability, cycle life and low temperature discharge capability.

[0026] The above is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims. Other aspects will become clear upon reading and understanding the accompanying drawings and detailed description. Detailed Implementation

[0027] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0028] Based on the above technical background, the first aspect of this application provides a battery slurry, comprising lithium iron phosphate as the main material, a binder, a conductive agent, and a porous additive, wherein the conductive agent comprises high specific surface area conductive carbon black, and the specific surface area of ​​the conductive carbon black is ≥130m². 2 / g.

[0029] For example, the specific surface area of ​​conductive carbon black is, for instance, 130 m². 2 / g, 140m 2 / g, 150m 2 / g, 160m 2 / g、170m 2 / g is greater than or equal to 130m 2 The value of / g is not limited to the listed values; other unlisted values ​​within the given range also apply.

[0030] According to the inventors' research, lithium iron phosphate, porous additives, and high-specific-surface-area carbon black correspond to large, medium, and small pore size distributions, respectively. Because the lithium iron phosphate particles are filled with medium-pore porous additives and small-pore high-specific-surface-area carbon black, a multi-level gradient pore structure can be formed inside the electrode. This multi-level gradient pore structure can reduce the tortuosity of lithium-ion transport within the electrode, accelerate the transport speed of lithium ions in the pore structure, and shorten the pore path length, thereby improving the battery's fast-charging performance. Correspondingly, the battery's cycle life and low-temperature discharge capability will also be improved.

[0031] Furthermore, according to the inventors' research, the use of lithium iron phosphate, porous additives, and high specific surface area carbon black can effectively improve the electrolyte wettability of the electrode.

[0032] Specifically, the known formula for the permeability coefficient model is: K∝gL / χ 2

[0033] In the formula, K is the electrolyte permeability coefficient, g is the connectivity of each component of the electrode, L is the distance between pores on the critical path inside the electrode, and χ is the length of the critical path of the electrode, which is positively correlated with the thickness and compaction density of the electrode.

[0034] Based on the permeability coefficient model formula, it is known that the key to improving the electrolyte wettability of the electrode lies in increasing the porosity of the electrode and the distance between the pores. This application effectively reduces the distance L between the pores of the electrode by filling the spaces between lithium iron phosphate particles with porous additives of medium and small pore size and high specific surface area carbon black, thereby improving the electrolyte's wettability of the electrode. It is worth noting that the pore size between the primary aggregates of high specific surface area carbon black is larger than that of conventional conductive agents, which can further enhance the electrode's liquid absorption and retention capacity, thus improving the electrolyte wettability of the electrode.

[0035] Furthermore, according to the inventors' research, high specific surface area conductive carbon black, compared to conventional conductive agents, such as those with a specific surface area of ​​60m², exhibits superior performance. 2 High-specific-surface-area conductive carbon black has a small particle size and a large specific surface area. This makes it easier for the conductive network formed inside the electrode using high-specific-surface-area conductive carbon black to reach the permeation threshold. Therefore, using a small amount of high-specific-surface-area carbon black can effectively improve the electrode conductivity, and correspondingly, adding a larger amount of lithium iron phosphate can effectively improve the energy density of the battery.

[0036] Therefore, based on the above description, the combined use of lithium iron phosphate, porous additives, and high specific surface area carbon black can effectively improve the overall performance of the battery.

[0037] In some embodiments, the conductive agent further includes carbon nanotubes compounded with conductive carbon black. The particulate structure of the conductive carbon black and the tubular structure of the carbon nanotubes can form more conductive channels in the material, further accelerating lithium-ion transport, thereby improving the conductivity of the electrode and enhancing battery performance. For example, the carbon nanotubes can be single-walled carbon nanotubes, multi-walled carbon nanotubes, etc.

[0038] In some embodiments, the conductive agent is a composite of high specific surface area conductive carbon black and multi-walled carbon nanotubes, wherein the specific surface area of ​​the multi-walled carbon nanotubes is 230–420 m². 2 / g, tube diameter of 7-11nm. The specific surface area of ​​multi-walled carbon nanotubes is, for example, 230m². 2 / g、270m 2 / g、320m 2 / g、390m 2 / g、420m 2 / g, or select any two of the aforementioned values ​​to form a new range, and the value taken within the new range; the diameter of the multi-walled carbon nanotube is, for example, 7nm, 8nm, 9nm, 10nm, 11nm, or select any two of the aforementioned values ​​to form a new range, and the value taken within the new range.

[0039] In some embodiments, the high specific surface area conductive carbon black satisfies the following condition: tap density ≤ 0.05 g / cm³. 3 Generally, tap density reflects the porosity of particles during vibration. A low tap density in carbon black indicates better particle dispersion. Therefore, limiting the tap density of conductive carbon black helps form a more uniform conductive network within the electrode, further improving battery performance.

[0040] For example, the tap density of conductive carbon black is 0.05 g / cm³. 3 0.04g / cm 3 0.03g / cm 3 0.02g / cm 3 0.01g / cm 3 ≤0.05g / cm 3 The values ​​are not limited to those listed; other unlisted values ​​within the given range also apply. Conductive carbon black that meets the above conditions is considered high-specific-dimensional conductive carbon black.

[0041] In some embodiments, the average particle size of the primary structure of the high specific surface area conductive carbon black is 20–30 nm. The average particle size of the primary structure of the high specific surface area conductive carbon black is, for example, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, or 30 nm, or any two of the aforementioned values ​​can be selected to form a new range, and the values ​​taken within the new range.

[0042] In some embodiments, the pore size of the high specific surface area conductive carbon black is 5–30 nm, and the average pore size is 5–9 nm. The pore size of the high specific surface area conductive carbon black can be, for example, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, or 30 nm, or any two of the aforementioned values ​​can be selected to form a new range, with the value taken within that new range. Correspondingly, the average pore size of the high specific surface area conductive carbon black can be, for example, 5 nm, 6 nm, 7 nm, 8 nm, or 9 nm, or any two of the aforementioned values ​​can be selected to form a new range, with the value taken within that new range.

[0043] In some embodiments, the primary structure particle size of the high specific surface area conductive carbon black satisfies 60 ≤ D 50Further screening of carbon black particle size was conducted, with a particle size ≤82nm. High specific surface area conductive carbon black particle size D... 50 For example, 60nm, 64nm, 68nm, 72nm, 76nm, 80nm, 82nm, or any two of the aforementioned values ​​can be selected to form a new range, and the values ​​taken within the new range can be selected.

[0044] In some specific embodiments, the high specific surface area conductive carbon black used in this application, as measured by nitrogen desorption, has a pore volume of 0.4–1.2 cm³ with a size of 5–30 nm. 3 / g.

[0045] In some specific embodiments, the high specific surface area conductive carbon black used in this application has pores with a size of 5 to 30 nm accounting for 88% to 94% of the total pore volume.

[0046] In some embodiments, the porous additive is porous alumina. Lithium iron phosphate, porous alumina, and high specific surface area carbon work together to form a multi-level gradient pore structure inside the electrode, reducing the tortuosity of lithium-ion transport inside the electrode, accelerating the transport speed of lithium ions in the pore structure, and shortening the pore path length, thereby improving the fast charging performance of the battery.

[0047] In some embodiments, the porous additive is porous alumina, wherein the specific surface area of ​​the porous alumina is 320–360 m². 2 / g, and has a pore size distribution of 30–150 nm. The specific surface area of ​​porous alumina is, for example, 320 m² / g. 2 / g、330m 2 / g、340m 2 / g, 350m 2 / g、360m 2 / g, or select any two of the aforementioned values ​​to form a new range, and the values ​​taken within the new range; the pore size distribution of porous alumina is, for example, 30nm, 50nm, 70nm, 90nm, 110nm, 130nm, 150nm, or select any two of the aforementioned values ​​to form a new range, and the values ​​taken within the new range.

[0048] In some implementations, the primary particle size of porous alumina is 80 nm ≤ D. 50 ≤120nm. Primary particle size D of porous alumina. 50 For example, 80nm, 90nm, 100nm, 110nm, 120nm, or any two of the aforementioned values ​​can be selected to form a new range, and the values ​​taken within the new range can be selected.

[0049] In some implementations, the average primary particle size of porous alumina is 60 nm.

[0050] In a specific implementation, the adhesive is polyvinylidene fluoride (PVDF).

[0051] In some embodiments, the primary particle size range of the lithium iron phosphate main material is 280–340 nm, and the particle size of the lithium iron phosphate main material satisfies 2.8 ≤ (D 90 -D 10 ) / D 50 ≤3.2. The primary particle size of the lithium iron phosphate main material is, for example, 280nm, 290nm, 300nm, 310nm, 320nm, 330nm, 340nm, or any two of the aforementioned values ​​can be selected to form a new range, and the values ​​taken within the new range are specified; simultaneously, the primary particle size of the lithium iron phosphate main material (D... 90 -D 10 ) / D 50 For example, 2.8, 2.9, 3.0, 3.1, 3.2, or any two of the aforementioned values ​​can be selected to form a new range, and the values ​​taken within the new range can be selected.

[0052] Among them, D 10 Defined as the particle size distribution corresponding to 10% of the volume distribution of lithium iron phosphate, D 50 Defined as the volume median particle size of the lithium iron phosphate, D 90 Defined as the particle size distribution corresponding to a volume distribution ratio of 90% for lithium iron phosphate, where D 10 D 50 D 90 The unit is μm.

[0053] According to the inventor's research, D 50 The average size of lithium iron phosphate (LFP) particles determines the diffusion path of lithium ions within the particles and influences their specific surface area. Therefore, it directly affects the fast-charging and cycle performance of LFP. Under the same mass, the D of lithium iron phosphate... 50 The lower the specific surface area, the shorter the lithium-ion diffusion path, resulting in lower diffusion resistance and a larger specific surface area for lithium iron phosphate. Low diffusion resistance is beneficial for rapid charge-discharge of lithium iron phosphate, but a large specific surface area leads to increased side reactions with the electrolyte and decreased cycle performance. Therefore, selecting the appropriate lithium iron phosphate particle size is crucial for further optimizing electrode performance.

[0054] In this embodiment, considering the influence of lithium iron phosphate particle size on electrode performance, the lithium iron phosphate particles are sieved to achieve a suitable density. This allows for close packing of the lithium iron phosphate particles while ensuring good porosity distribution within the electrode, resulting in an electrode with high energy density, good electrolyte wettability, and excellent fast-charging performance.

[0055] A second aspect of this application provides a positive electrode sheet, including a positive current collector and a positive electrode coating coated on the surface of the positive current collector, wherein the positive electrode coating includes any of the positive electrode slurries described in the above embodiments.

[0056] The positive electrode sheet provided in this application may use conventional positive electrode current collectors in the art, such as carbon-coated aluminum foil.

[0057] In the specific preparation of the positive electrode sheet, for example, the positive electrode active material (lithium iron phosphate) of this application, the conductive agent (high specific surface area conductive carbon black), the porous additive and the binder can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by mass percentage, 70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent, 0.1-0.5 wt% of porous additive, and 0.5-15 wt% of binder; optionally, it comprises 80-98 wt% of positive electrode active material, 0.1-0.3 wt% of porous additive, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0058] A third aspect of this application provides a lithium-ion battery in which the positive electrode active material is lithium iron phosphate. It is conceivable that, in addition to the aforementioned positive electrode, the lithium-ion battery of this application also includes a positive electrode, an electrolyte, and a separator.

[0059] Generally, a battery includes an electrolyte, a battery cell, and a casing that encapsulates the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked battery cell, meaning it is composed of a positive electrode, a separator, and a negative electrode stacked together.

[0060] Specifically, the negative electrode sheet includes a negative current collector and a negative electrode coating located on at least one side surface of the negative current collector. Specifically, the negative electrode coating may be provided on one side surface of the negative current collector, or negative electrode coatings may be provided on both opposite sides of the negative current collector in the thickness direction.

[0061] Specifically, the negative electrode coating (negative electrode active material layer) may include a negative electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the negative electrode active material may include at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), and tin-based negative electrode materials (mainly including tin and tin alloys); the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0062] The battery provided in this application may use a conventional negative electrode current collector, such as copper foil.

[0063] In the battery provided in this application, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode coating, such as negative electrode active material, conductive agent, and binder, can be dispersed in a second solvent, such as water, to prepare a negative electrode slurry. Then, the slurry is coated on the surface of the negative electrode current collector and the negative electrode sheet is obtained after drying, rolling and other processes.

[0064] In the battery provided in this application, the electrolyte can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC). Additives include fluoroethylene carbonate (FEC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0065] In the battery provided in this application, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from contacting and short-circuiting. The embodiments of this application can use a conventional separator in the art, such as a polypropylene separator (PP), a polyethylene separator (PE), a polypropylene / polyethylene double-layer composite membrane (PP / PE), a polyimide electrospun separator (PI), a polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), a cellulose non-woven fabric separator, or a separator with a ceramic coating. This application does not limit the use of such separators.

[0066] In this embodiment, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited to these.

[0067] This application allows for the assembly of components such as positive electrode, separator, and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator, and negative electrode can be stacked to produce a stacked cell; then the cell is placed in a casing (outer packaging) and subjected to conventional processes such as electrolyte injection and encapsulation to obtain the battery.

[0068] The fourth aspect of this application provides an electrical device including the battery provided in this application. This application does not specifically limit the type of electrical device; it can be any electrical device including the battery, including but not limited to mobile phones, portable devices, laptops, electric bicycles, electric vehicles, electric toys, energy storage devices, etc.

[0069] Furthermore, in some embodiments, the improvement of battery electrolyte wettability by this application can be evaluated by the pre-formation voltage of the cell, as follows:

[0070] The positive electrode sheet obtained in this application is combined with a graphite negative electrode to prepare a soft-pack laminated battery cell. When the battery is not being charged or discharged, Li... x For FePO4, x is close to 1, and φc(V vs Li+ / Li) = 3.1V; while for graphite without lithium intercalation, φa(V vs H+ / H) = 0V, i.e., φa(V vs Li+ / Li) = 3.04V. Therefore, the voltage E of the LiFePO4 / graphite battery before formation is E = φc(V vs Li+ / Li) - φa(V vs Li+ / Li) = 0.06V. Due to the influence of process, materials, electrolyte, temperature, etc., the standard for evaluating the good electrolyte wetting of LiFePO4 / graphite pouch cells before formation is a voltage of not less than 100mV before formation. Based on this, this application has the technical effect of improving the electrolyte wettability of the electrodes.

[0071] The present application will be further described below through specific embodiments.

[0072] To ensure battery energy density and fast charging performance, the average particle size of the primary lithium iron phosphate particles in the comparative and examples is 300 nm. 90 -D 10 ) / D 50 =3.0. The porous additive used in the comparative examples and embodiments is porous alumina; the binder is polyvinylidene fluoride (PVDF); the conductive agent is a mixture of conductive carbon black and carbon nanotubes; the carbon black conductive agents are conventional carbon black SP-1, and high specific surface area conductive carbon blacks SP-2 and SP-3, respectively. The specific carbon black parameters are shown in Table 1.

[0073] Table 1

[0074] In the table above, the pore size parameters, specific surface area, and tap density of carbon black were tested in the following manner (the test method for porous alumina is the same as that for carbon black): (1) The specific surface area and pore parameters of carbon black in different examples and comparative examples were tested according to the method of GB / T19587-2004. Specifically, the specific surface area and pore size distribution of carbon black were determined by nitrogen adsorption method. The sample was degassed under vacuum at 250℃ for 2h. Then, the adsorption and desorption performance of the sample for N2 was measured in the range of p / p0 0~1 at liquid nitrogen (77K). The specific surface area of ​​carbon black was determined by Brunauer-Emmett-Teller (BET) method. The micropore area and micropore volume of the sample were analyzed by t-plot method. The pore size distribution of carbon black was calculated by density functional theory (DFT) method (N2@77K in carbon slit pore QSDFT adsorption branch model).

[0075] (2) Test of tapped density. The weighed powder is loaded into the measuring cylinder of the tapping device, and the cylinder is fixed to the support. The cam is rotated, causing the guide rod to slide up and down the support, impacting the anvil. The device vibrates 250±15 times per minute for 12 minutes. The volume of powder in the measuring cylinder is measured; the ratio of powder mass to volume is the tapped density of the powder.

[0076] Example 1

[0077] 1. Preparation of positive electrode sheet:

[0078] The cathode formulation of lithium iron phosphate, high specific surface area conductive carbon black SP-2, carbon nanotubes, porous alumina, and PVDF is in a mass ratio of 96.9:0.5:0.5:0.1:2. First, lithium iron phosphate, high specific surface area conductive carbon black SP-2, porous alumina, and PVDF powder are added to a mixing tank and stirred at low speed for 30 minutes to initially form a uniformly dispersed mixture.

[0079] Add N-methylpyrrolidone solution (NMP), set the slurry solid content to 72%, knead for 4 hours without dispersing, to form the first mixture;

[0080] Carbon nanotubes and NMP were added to the first mixed solution, and the slurry solid content was set to 60%. The mixture was dispersed at high speed for 2 hours to obtain the positive electrode slurry.

[0081] The positive electrode slurry is evenly coated on both sides of the carbon-coated aluminum foil, baked and dried, and then hot-pressed and slit to obtain the positive electrode sheet.

[0082] The cathode slurry formulation, by mass percentage, is: lithium iron phosphate: high specific surface area carbon black SP-2: carbon nanotubes: porous alumina: PVDF = 96.9: 0.5: 0.5: 0.1: 2.

[0083] 2. Preparation of negative electrode sheet:

[0084] The negative electrode slurry formulation, by mass percentage, is as follows: active material: conductive agent SP-1: CMC: SBR = 95.3: 1.5: 1.4: 1.8, with a slurry solid content of 48%. The prepared negative electrode slurry is coated on the surface of copper foil, baked and dried to form a negative electrode material coating, and the prepared negative electrode sheet is rolled and slit.

[0085] 3. Preparation of electrolyte:

[0086] The electrolyte used in the soft-pack battery is a mixed carbonate solution with a lithium hexafluorophosphate concentration of 1 mol / L (solvents: ethylene carbonate (EC): diethyl carbonate (DEC), dimethyl carbonate (DMC) = 1:1:1).

[0087] 4. Diaphragm:

[0088] It uses a commercially available 12μm porous polyethylene membrane.

[0089] 5. Preparation of lithium secondary batteries:

[0090] The die-cut positive electrode sheet, negative electrode sheet, and separator are stacked in sequence using a stacking process to obtain a core. The core is then packaged in an aluminum-plastic bag, dried, and injected with electrolyte. After processes such as impregnation, formation, and capacity testing, a lithium secondary battery is obtained.

[0091] Examples 2-12 and Comparative Examples 1-3 were the same as in Example 1 except for the change in the positive electrode formulation. The specific differences are shown in Table 2.

[0092] Table 2

[0093] The following performance tests were performed on the positive electrode or battery of each embodiment and comparative example, and the results are shown in Table 3. (1) Film resistance test:

[0094] Take 10 negative electrode sheets (30mm*50mm) from each batch prepared in the examples and comparative examples, and use a 2-probe film resistance meter to test the film resistance. Test 6 values ​​for each electrode sheet and take the average value.

[0095] (2) Electrolyte wetting test:

[0096] The soft-pack batteries prepared in the examples and comparative examples were subjected to high-temperature immersion after electrolyte injection. Ten batteries from each group were immersed at 45°C for 24 hours, and the cell voltage of each group was recorded. The average voltage of the ten cells was then taken. In addition, ten batteries from each group were immersed at 45°C for 48 hours, and the cell voltage of each group was recorded. The average voltage of the ten cells was then taken.

[0097] (3) Loop testing:

[0098] In both the example and comparative examples, three pouch cells with their capacities determined were taken from each group. Under room temperature (25°C) and voltage range of 2.0-3.75V, the cells were charged and discharged for 2000 cycles at a current of 1C. The average capacity retention rate of each group of cells after 2000 cycles was taken.

[0099] (4) Low-temperature discharge test:

[0100] In both the example and comparative examples, three pouch cells were taken from each group after capacity testing. They were fully charged to 3.75V at room temperature using a constant current and constant voltage of 1C. The fully charged cells were then transferred to a -20℃ environment and placed for 4 hours. Finally, they were discharged to 2.0V at a constant current of 0.33C in a -20℃ environment. The discharge capacity was recorded and the low-temperature discharge capacity retention rate at -20℃ was calculated. The average value of the three cells was taken.

[0101] (5) Dynamic performance DCR test

[0102] After the soft-pack cells prepared in the examples and comparative examples were tested for K-value after capacity grading, three cells from each were taken for DCR testing. The main steps of DCR testing were: (1) Capacitance was set at 0.33C for three weeks in the voltage range of 2.0-3.75V, and the average capacity C1 was taken; (2) Charged at 0.33C to 50% SOC, rested for 1 hour, and the voltage was recorded as V1; (3) Charged at 4C for 10s and rested for 40s, and the voltage was recorded as V2; (4) Charged at 0.33C to the cutoff voltage of 3.75V at room temperature. The DCR of charging at 50% SOC at 4C rate was finally obtained, and DCR = (V2-V1) / 4 / C1.

[0103] Table 3

[0104] As shown in Table 3, in Examples 1-5, with the increase in the proportion of high specific surface area carbon black SP-2 (from 0.5 to 0.9), the negative electrode film resistance gradually decreased, the battery voltage under high-temperature wetting at 45℃ / 24h continuously increased, the cycle capacity retention rate and low-temperature discharge performance continuously improved, and the DCR continuously decreased. It is evident that increasing the proportion of high specific surface area conductive carbon black gradually improves the electrolyte wettability of the electrode, the battery's fast-charging capability, cycle life, and low-temperature discharge capability, and further enhances the battery's rate performance.

[0105] As shown in Example 6, when the amount of SP-2 added increases to 1.0, the electrical performance of the battery is not further improved. SP-2 has high porosity and excellent conductivity, but when the amount of SP-2 added is >0.9, its effect reaches the upper limit of the threshold and no longer has a further improvement effect on the battery performance.

[0106] Examples 5 (with a porous alumina addition of 0.1%) and Examples 7-8 show that in Example 7, when the amount of porous alumina added is increased to 0.2%, the battery's 45℃ / 24h immersion voltage increases, the cycle capacity retention rate and low-temperature discharge performance are further improved, and the DCR decreases. However, in Example 8, when the amount of porous alumina added is 0.3%, the membrane resistance, cycle capacity retention rate, and low-temperature discharge performance all begin to deteriorate, and the DCR shows no significant improvement. It is evident that appropriately increasing the amount of porous alumina can further improve the battery's electrical performance, but when the amount of porous alumina added is excessive, its effect will worsen. Specifically, because porous alumina has a high specific surface area of ​​350 m² / g and a porous size distribution of 30-150 nm, it is difficult to disperse in slurry. Excessive addition will affect the dispersion consistency and stability of the slurry, leading to uneven dispersion of the various components in the formulation, low electrode consistency, and consequently, poor battery electrical performance.

[0107] As demonstrated in Examples 9-12 (using SP-2) and Examples 1-4 (using SP-3), using SP-3, a carbon black with a higher specific surface area, can further improve the battery's fast-charging capability, cycle capacity retention, and low-temperature performance. Specifically, in Examples 9-11, battery performance further improved with increasing proportions of electrolytic carbon black; however, in Example 12, when the SP-3 addition was 0.8%, the electrical performance deteriorated to some extent. It is evident that high specific surface area carbon black, with its smaller particle size, higher specific surface area, and higher porosity, helps improve the conductivity and wettability of the electrode. However, an excessively large specific surface area can prevent dispersion in existing slurry processes, thus failing to fully realize its potential and potentially leading to electrical performance degradation due to uneven dispersion. Therefore, high specific surface area carbon black should be selected only while meeting the requirements of existing process technologies to achieve improved electrical performance.

[0108] As shown in Examples 11 (with a porous alumina addition of 0.1%) and 13-14, high specific surface area carbon black combined with porous alumina can effectively improve the wettability, cycle capacity retention, and low-temperature performance of the positive electrode sheet, resulting in higher rate performance. In Example 13, the addition amount of porous alumina was 0.2%, and the increased proportion further improved the performance. However, when the addition amount of porous alumina reached 0.3% in Example 14, the high specific surface area of ​​the porous alumina also affected the dispersion consistency and stability of the slurry, leading to uneven dispersion of the various components in the formulation, low electrode sheet consistency, and consequently, poor battery electrical performance.

[0109] In Comparative Example 1, the carbon black used was SP-1; in Comparative Example 2, SP-1 was combined with 0.2g of porous alumina. The addition of porous alumina to Comparative Example 2 significantly improved the battery's performance compared to Comparative Example 1, further demonstrating the positive effects of porous alumina on electrolyte wettability, fast-charging capability, cycle capacity retention, and low-temperature performance. Furthermore, compared to Example 7 (SP-2 combined with 0.2g of porous alumina), Comparative Example 2 exhibited higher negative electrode film resistance, lower battery voltage under 45°C / 24h high-temperature electrolyte wettability, lower cycle capacity retention, lower low-temperature discharge performance, and higher DCR. This indicates that high-specific-surface-area conductive carbon black can significantly improve the overall performance of the battery, including electrolyte wettability, fast-charging capability, cycle life, and low-temperature discharge capability.

[0110] Furthermore, Comparative Example 3 and Example 1, and Comparative Example 4 and Example 9 also demonstrate the effect of porous alumina on improving the electrolyte wettability of electrodes, battery fast charging capability, cycle capacity retention, and low-temperature performance.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A positive electrode slurry, comprising: Lithium iron phosphate main material, binder, conductive agent and porous additive: The conductive agent includes high specific surface area conductive carbon black, wherein the specific surface area of ​​the conductive carbon black is ≥130m². 2 / g.

2. The positive electrode slurry according to claim 1, wherein, The conductive agent also includes carbon nanotubes compounded with the conductive carbon black.

3. The positive electrode slurry according to claim 2, wherein, The carbon nanotubes are multi-walled carbon nanotubes, and the specific surface area of ​​the multi-walled carbon nanotubes is 230–420 m². 2 / g, with a tube diameter of 7-11nm.

4. The positive electrode slurry according to any one of claims 1 to 3, wherein, The tap density of the conductive carbon black is ≤0.05 g / cm³. 3 .

5. The positive electrode slurry according to any one of claims 1 to 4, wherein, The average particle size of the primary structure of the conductive carbon black is 20–30 nm.

6. The positive electrode slurry according to any one of claims 1 to 5, wherein, The porous additive is porous alumina.

7. The positive electrode slurry according to claim 6, wherein, The specific surface area of ​​the porous alumina is 320–360 m². 2 / g, wherein the porous alumina has a pore size distribution of 30-150nm.

8. The positive electrode slurry according to claim 6 or 7, wherein, The primary particle size of the porous alumina is 80 nm ≤ D 50 ≤120nm.

9. The positive electrode slurry according to any one of claims 6 to 8, wherein, The average particle size of the primary particles in the porous alumina is 60 nm.

10. The positive electrode slurry according to any one of claims 1 to 9, wherein, The primary particle size range of the lithium iron phosphate main material is 280–340 nm, and the particle size of the lithium iron phosphate main material satisfies 2.8 ≤ (D 90 -D 10 ) / D 50 ≤3.

2.

11. The positive electrode slurry according to any one of claims 1 to 9, wherein, The adhesive is polyvinylidene fluoride.

12. The positive electrode slurry according to any one of claims 1 to 9, wherein, The conductive carbon black has a pore size of 5–30 nm, and the average pore size of the conductive carbon black is 5–9 nm.

13. The positive electrode slurry according to any one of claims 1 to 9, wherein, The primary structure particle size of the conductive carbon black is 60≤D 50 ≤82nm.

14. A lithium-ion battery, comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode coating coated on the surface of the positive current collector, the positive electrode coating comprising the positive electrode slurry according to any one of claims 1 to 13.

15. An electrical device comprising the lithium-ion battery of claim 14.

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