Secondary battery and electric equipment

Abstract

The embodiment of the invention provides a secondary battery and electric equipment, the secondary battery provided by the embodiment of the invention comprises a positive pole piece and an electrolyte, the positive pole piece comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, the positive electrode active material layer comprises a positive electrode active material and a dispersant, the dispersant comprises a solvation chain segment, a first functional chain segment, a second functional chain segment and a third functional chain segment, the first functional chain segment has an amino group, the second functional chain segment has a Si-containing group, and the third functional chain segment has a P-containing group. According to the secondary battery provided by the embodiment of the invention, the problem that an existing thick electrode is easy to crack can be relieved.

Description

Technical Field

[0001] This application relates to the field of battery manufacturing technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0002] Currently, in order to meet the demand for high capacity, lithium-ion batteries such as lithium iron phosphate often use thick electrodes, which can load more active materials per unit area, thereby seeking higher energy density.

[0003] However, thick electrodes are prone to cracking during processing, which not only damages the integrity of the electrode structure and interrupts the electron transport path, reducing the battery's charging and discharging efficiency, but also causes poor contact between the active material and the current collector, accelerating the battery's capacity decay and thus seriously affecting battery performance. Summary of the Invention

[0004] The technical problem to be solved by this application is to provide a secondary battery and electrical device to solve the problem that existing thick electrodes are prone to cracking.

[0005] To solve the above problems, this application provides the following technical solution: This application proposes a secondary battery, comprising a positive electrode and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active substance and a dispersant. The dispersant includes a solvation segment, a first functional segment, a second functional segment, and a third functional segment. The first functional segment has an amino group, the second functional segment has a Si group, and the third functional segment has a P group.

[0006] Furthermore, the secondary battery satisfies at least one of the following conditions: a. The solvation segment includes at least one of methoxy polyethylene glycol acrylate, polyethylene glycol monomethyl ether methacrylate, and polypropylene glycol monomethyl ether acrylate; b. The first functional segment includes at least one of 3-(dimethylamino)acrylate, N,N-dimethylacrylamide, and 2-methoxyethyl methacrylate; c. The second functional segment includes at least one of diethylmethylvinylsilane, vinyltrimethoxysilane, and 3-methacryloyloxypropyltrimethoxysilane; d. The third functional segment includes at least one of vinyl phosphate, dioxypropyl phosphate, and dimethyl vinylphosphonate.

[0007] Furthermore, in the secondary battery, the electrolyte includes an organic solvent, which includes a linear carboxylic acid ester.

[0008] Furthermore, in the secondary battery, the linear carboxylic acid ester includes at least one selected from ethyl acetate, ethyl propionate, methyl butyrate, propyl acetate, butyl acetate, ethyl butyrate, and methyl acetate.

[0009] Furthermore, in the secondary battery, the viscosity of the electrolyte at 25±5℃ is less than 2.2 mPa·s.

[0010] Furthermore, in the secondary battery, the linear carboxylic acid ester has a content of 5wt% to 30wt% in the organic solvent.

[0011] Furthermore, in the secondary battery, the positive electrode active material layer includes a first active material layer and a second active material layer. The first active material layer is disposed on at least one side of the positive electrode current collector, and the second active material layer is disposed on the surface of the first active material layer. Both the first active material layer and the second active material layer include the dispersant, and the content of the dispersant in the second active material layer is greater than the content of the dispersant in the first active material layer.

[0012] Furthermore, in the secondary battery, the content of the dispersant in the second active material layer is 0.3wt%~1wt%; and / or the content of the dispersant in the first active material layer is 0.1wt%~0.5wt%.

[0013] Furthermore, in the secondary battery, the first active material layer includes a first lithium iron phosphate, the second active material layer includes a second lithium iron phosphate, and the particle size Dv50 of the first lithium iron phosphate is smaller than the particle size Dv50 of the second lithium iron phosphate.

[0014] Furthermore, the secondary battery satisfies the following condition: 0.615 < particle size Dv50 of the second lithium iron phosphate / particle size Dv50 of the first lithium iron phosphate < 0.905.

[0015] Furthermore, in the secondary battery, the thickness of the first active material layer is 60μm~135μm, and the thickness of the second active material layer is 10μm~40μm.

[0016] This application also proposes an electrical device, which includes the aforementioned secondary battery, serving as the power supply for the electrical device.

[0017] Compared with the prior art, the embodiments of this application have the following advantages: In this embodiment, the secondary battery includes a positive electrode sheet and an electrolyte. The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active substance and a dispersant. The dispersant includes a solvation segment, a first functional segment, a second functional segment, and a third functional segment. The first functional segment has an amino group, the second functional segment has a P-containing group, and the third functional segment has a Si-containing group. The solvation segment serves as the core framework of the dispersant, enabling the dispersant to be compatible with the solvent and forming a steric hindrance effect to prevent particle agglomeration. The first functional segment with an amino group... The dispersant is able to uniformly cover the surface of the positive electrode active material and react chemically with the surface of the positive electrode active material to form strong chemical bonds, which acts as a bonding agent. This enhances the bonding force between the dispersant and the positive electrode active material, as well as between the positive electrode active material and the positive electrode current collector, making the positive electrode active material more uniformly dispersed in the slurry and improving the structural stability of the electrode. At the same time, the second functional segment containing Si groups and the third functional segment containing P groups endow the dispersant with good flexibility and steric hindrance effect, which can effectively alleviate the shrinkage stress inside the positive electrode active material layer during the coating and drying process, thereby improving the coating cracking problem as a whole.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0019] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to specific embodiments.

[0020] To address the aforementioned problems, this application provides a secondary battery comprising a positive electrode and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active substance and a dispersant. The dispersant includes a solvation segment, a first functional segment, a second functional segment, and a third functional segment. The first functional segment has an amino group, the second functional segment has a Si group, and the third functional segment has a P group.

[0021] The dispersant in the positive electrode active material layer includes solvated segments, which serve as the core framework of the dispersant, enabling it to be compatible with the medium and forming a steric hindrance effect to prevent particle agglomeration. The dispersant also includes a first functional segment with a strong nucleophilic amino group, allowing it to uniformly cover the surface of the positive electrode active material and react chemically with it to form strong chemical bonds, enhancing the bonding force between the dispersant and the positive electrode active material, as well as between the positive electrode active material and the positive electrode current collector. This results in more uniform dispersion of the positive electrode active material in the slurry and improves the structural stability of the electrode. Furthermore, the dispersant includes a second functional segment containing Si groups and a third functional segment containing P groups, which impart good flexibility and steric hindrance effect, effectively alleviating shrinkage stress within the positive electrode active material layer during drying, thereby improving the overall coating cracking problem.

[0022] Optionally, the positive electrode active material in this application is not limited and can be a sodium ion compound, which may be a sodium ion transition metal oxide, sodium ion transition metal phosphate, sodium ion transition metal sulfate, or Prussian blue compound. It can also be a lithium ion compound, which may be a lithium ion transition metal oxide, lithium ion transition metal phosphate, etc.

[0023] Optionally, in one embodiment, the solvation segment includes at least one of methoxy polyethylene glycol acrylate, polyethylene glycol monomethyl ether methacrylate, and polypropylene glycol monomethyl ether acrylate; the solvation segment serves as the core framework, achieving miscibility with the medium, thereby forming a steric hindrance effect and preventing particle agglomeration.

[0024] Optionally, in one embodiment, the first functional segment includes at least one of 3-(dimethylamino)acrylate, N,N-dimethylacrylamide, and N-(2-methoxyethyl)acrylamide, wherein the first functional segment can effectively provide an amino group that anchors to the surface of the positive electrode active material.

[0025] Optionally, in one embodiment, the second functional segment includes at least one of diethylmethylvinylsilane, vinyltrimethoxysilane, and 3-methacryloyloxypropyltrimethoxysilane; the weak polarity of the siloxane segment of the second functional segment can improve the compatibility of the dispersant with the non-polar conductive agent and the binder, avoid the dispersant from “competing for adsorption” with other components, and reduce the stratification, agglomeration or sedimentation of the slurry during storage.

[0026] Optionally, in one embodiment, the third functional segment includes at least one of vinyl phosphate, dioxypropyl phosphate, and dimethyl vinylphosphonate, which serves as an auxiliary functional modification segment. Its phosphate group is a polar group that can assist the amino group in binding with the particles, thereby effectively improving the oil compatibility of the dispersant and enhancing the anchoring strength.

[0027] In this embodiment, the dispersant is obtained by polymerizing copolymer monomers under the action of an initiator. The copolymer monomers include amino-containing compounds, ether-containing (or alcohol-containing) compounds, siloxy-containing compounds, and phosphate-containing compounds. During the polymerization process, the mass ratio of the above-mentioned amino-containing compounds, ether-containing (or alcohol-containing) compounds, siloxy-containing compounds, and phosphate-containing compounds is controlled to be (15~25):(60~70):(5~8):(3~5). The initiator can be azobisisobutyronitrile and the amount added is 1~3% of the total mass of the monomers. The reaction is carried out at a temperature of 80~100℃ for 8~12 hours under nitrogen deoxygenation conditions.

[0028] Optionally, in one embodiment, the electrolyte includes an active material salt and an organic solvent, the organic solvent including a linear carboxylic acid ester. The linear carboxylic acid ester in the electrolyte not only gives the electrolyte lower viscosity and surface tension, enabling rapid penetration into the thick electrode and increasing the wetting rate, but also allows the carboxyl groups in the linear carboxylic acid ester to interact with the amino groups in the dispersant through hydrogen bonds, enhancing the adsorption and spreading ability of the electrolyte on the electrode surface, shortening the wetting time, improving the wetting effect, alleviating the problem of difficult wetting of thick electrodes, and providing excellent lithium-ion diffusion channels, effectively reducing the polarization resistance of the thick electrode.

[0029] Optionally, in one embodiment, the linear carboxylic acid ester includes at least one of ethyl acetate, ethyl propionate, methyl butyrate, propyl acetate, butyl acetate, ethyl butyrate, and methyl acetate. These substances have low viscosity and surface tension, enabling them to quickly penetrate into the interior of the thick electrode and improve the wetting speed of the electrolyte.

[0030] Optionally, in one embodiment, the linear carboxylic acid ester has a mass content of 5 wt% to 30 wt% in the organic solvent, for example, it can be one or any two of the following: 5 wt%, 6 wt%, 8 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, and 30 wt%. When the mass content of the linear carboxylic acid ester in the organic solvent is within the above range, it can effectively exert the synergistic effect of the amino groups in the dispersant and the carboxyl groups in the linear carboxylic acid ester electrolyte, while maintaining the stability of the electrode-electrolyte interface and the uniformity of mass transfer, thereby enhancing the adsorption and spreading ability of the electrolyte on the electrode surface and effectively shortening the wetting time.

[0031] Optionally, in one embodiment, the content W1 of the linear carboxylic acid ester in the organic solvent and the content W2 of the dispersant in the positive electrode active material layer satisfy the following: W1 ≥ 30W2 + 5%.

[0032] In this embodiment, controlling the content of linear carboxylic acid ester in the organic solvent to conform to the above-mentioned relationship with the content of the dispersant can ensure that the amino groups in the dispersant and the carboxyl groups in the carboxylic acid ester electrolyte can effectively enhance the adsorption and spreading ability of the electrolyte on the electrode surface through hydrogen bonding or other weak interactions, thereby effectively shortening the wetting time.

[0033] Optionally, in one embodiment, the viscosity of the electrolyte at 25±5°C is less than 2.5 mPa·s. The addition of the linear carboxylic acid ester enables the electrolyte to achieve the aforementioned low viscosity and surface tension, which is beneficial for electrolyte wetting and allows for rapid penetration into the thick electrode, thus increasing the wetting rate. In some embodiments, the viscosity of the electrolyte at 25±5°C is greater than or equal to 1.5 mPa·s and less than 2.5 mPa·s; for example, the viscosity of the electrolyte at 25±5°C can be 1.5 mPa·s, 1.8 mPa·s, 2.0 mPa·s, or 2.15 mPa·s.

[0034] In one embodiment, the viscosity of the electrolyte can be tested using an LVDV-2T (BROOKFIELD) rotary viscometer. The specific steps may include: after stabilizing the system temperature to 25°C using a ULA-40Y constant temperature water bath system, connecting the ULA sample cup to the ULA-40Y water bath jacket, selecting rotor No. 0, setting the rotation speed to 50 rpm, placing rotor No. 0 into the sample cup, adding 16 mL of electrolyte, and starting the test after the entire system is kept at a constant temperature for 15 minutes. The readings are repeated three times, and the average value is taken as the viscosity value of the electrolyte.

[0035] Optionally, in one embodiment, the positive electrode active material layer includes a first active material layer and a second active material layer. The first active material layer is disposed on at least one side of the positive electrode current collector, and the second active material layer is disposed on the surface of the first active material layer. The content of dispersant in the second active material layer is greater than the content of dispersant in the first active material layer.

[0036] In this embodiment, the second active material layer located on the surface is controlled to have a high dispersant content, so as to effectively improve the dispersibility of the positive electrode active material in the second active material layer, thereby improving the overall adhesion. Meanwhile, the first active material layer located in the inner layer is controlled to have a low dispersant content, which can effectively reduce the anchoring of the dispersant on the surface of the active particles, so that the first active material layer has high kinetics, which is conducive to the rapid diffusion of active ions in the first active material layer.

[0037] Optionally, in one embodiment, the content of dispersant in the second active material layer is 0.3wt%~1%wt%, which can effectively enhance the dispersibility of particles in the second active material layer and alleviate shrinkage stress, thereby stabilizing the electrode structure and effectively alleviating the problem of coating cracking.

[0038] Optionally, in one embodiment, the content of dispersant in the first active material layer is 0.1wt%~0.5wt%, which can enhance the active ion migration ability of the positive electrode and the kinetics of the battery, especially in thick electrodes, where it has a significant kinetic enhancement effect.

[0039] In this embodiment, the mass percentage of dispersant in the positive electrode sheet can be tested using thermogravimetric-mass spectrometry (TG / MS), and the mass percentage of dispersant in the first and second active material layers can be determined by the melt endothermic reaction peak area. Specifically, the mass percentage of dispersant in each active material layer = melt endothermic reaction peak area of ​​the active material layer powder / melt endothermic reaction peak area of ​​the pure additive.

[0040] Optionally, in one embodiment, the first active material layer includes a first lithium iron phosphate, the second active material layer includes a second lithium iron phosphate, and the particle size Dv50 of the first lithium iron phosphate is smaller than the particle size Dv50 of the second lithium iron phosphate.

[0041] In this embodiment, the particle size Dv50 of the second lithium iron phosphate located on the surface is controlled to be larger, resulting in a smaller specific surface area and lower surface energy of the second lithium iron phosphate particles. This ensures that the pores are conducive to wetting and processing, and provides better resistance to shrinkage stress, which can reduce stress changes during the drying process. Meanwhile, the particle size Dv50 of the first lithium iron phosphate located in the inner layer is smaller, resulting in a larger specific surface area of ​​the first lithium iron phosphate, which in turn provides higher surface energy, enabling rapid diffusion of lithium ions and ensuring better kinetic performance.

[0042] Optionally, in one embodiment, the first lithium iron phosphate and the second lithium iron phosphate satisfy the following: 0.615 < particle size Dv50 of the first lithium iron phosphate / particle size Dv50 of the second lithium iron phosphate < 0.905, which can ensure that the pores are easy to wet and process, and also make the overall positive electrode active material layer have better kinetic performance.

[0043] Optionally, in one embodiment, the particle size Dv50 of the first lithium iron phosphate is 0.5μm to 1μm, for example, it can be one or any two of the following: 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm. This enables the first lithium iron phosphate to have a large specific surface area, thereby having a high surface energy, realizing rapid lithium ion transport and diffusion, and ensuring better kinetic performance.

[0044] Optionally, in one embodiment, the particle size Dv50 of the second lithium iron phosphate is 1μm to 2μm, for example, it can be one or any two of the following values: 1μm, 1.1μm, 1.2μm, 1.5μm, 1.8μm, 2μm. This can effectively ensure the porosity for easy wetting and processing, and can reduce stress changes during the drying process.

[0045] Optionally, in one embodiment, the porosity of the first active material layer is less than or equal to the porosity of the second active material layer. For example, the porosity of the first active material layer is in the range of 24-27%, while the porosity of the second active material layer is 28-33%. This allows the larger porosity of the outer layer to guide the electrolyte to wet quickly, while the smaller porosity of the inner layer can achieve better kinetic performance.

[0046] In this embodiment of the application, the Dv50 of the first active material layer and the second active material layer in the positive electrode sheet can be tested by LPS (Laser Particle Size Distribution) after the first active material layer and the second active material layer in the first active material layer are scraped and sintered.

[0047] Optionally, in one specific embodiment, the thickness of the first active material layer is 60μm~135μm, and the thickness of the second active material layer is 10μm~40μm, which can effectively balance the energy density and better dynamic performance of the battery while ensuring electrode wetting, low polarization resistance and resistance to cracking.

[0048] Optionally, the thickness of the first active material layer can be a value within the range of one or any two of 60μm, 65μm, 75μm, 90μm, 100μm, 125μm, and 135μm, and the thickness of the second active material layer can be a value within the range of one or any two of 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, and 40μm.

[0049] Optionally, in one embodiment, the positive electrode sheet further includes a first binder and a first conductive agent. The first binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. The first conductive agent may be acetylene black, carbon fiber, carbon nanotubes, carbon black, graphene, etc.

[0050] In some embodiments, the positive electrode sheet is prepared as follows: the components used to prepare the positive electrode sheet, such as the positive active material, the first binder and any other components, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is uniformly coated on both sides of a positive electrode current collector such as an aluminum foil; after baking, rolling, cutting and other processes, the positive electrode sheet can be obtained.

[0051] The secondary battery provided in this application is composed of a positive electrode, a negative electrode, and a separator, which are stacked and then wound together.

[0052] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer can be a negative active material used in batteries, such as a metal negative electrode material or a non-metal negative electrode material. When the secondary battery is a sodium-ion secondary battery, the metal negative electrode material is preferably a metal foil or alloy compound such as sodium, sodium alloy, tin, or antimony. The non-metal negative electrode material is preferably any one or a combination of at least two of hard carbon, soft carbon, graphite, and silicon suboxide.

[0053] In some embodiments, the negative electrode sheet further includes a second conductive agent and a second binder; optionally, the second conductive agent includes one or more of conductive carbon black, acetylene black, carbon nanotubes, and graphene, and the second binder includes carboxymethyl cellulose-based binders and resin-based binders.

[0054] Optionally, in one embodiment, the carboxymethyl cellulose-based adhesive includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and / or the resin-based adhesive includes one or more of styrene rubber, polyacrylic acid, and polyacrylonitrile.

[0055] In some embodiments, the negative electrode sheet is prepared as follows: the components used to prepare the negative electrode sheet, such as the negative electrode active material, the second binder and the second conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as a copper foil; after baking, rolling, cutting and other processes, the negative electrode sheet can be obtained.

[0056] In practical applications, the negative electrode, separator and positive electrode are stacked in sequence and wound to obtain a cell assembly. The cell assembly is then packaged to obtain a bare cell. After baking, the bare cell is injected with electrolyte, formed, resealed and sorted to obtain the above-mentioned secondary battery.

[0057] This application also proposes an electrical device, which includes the aforementioned secondary battery, serving as the power supply for the electrical device.

[0058] The above-described electrical equipment embodiment includes the aforementioned secondary battery and achieves the same technical effect. To avoid repetition, it will not be described again here. For relevant details, please refer to the description of the secondary battery embodiment.

[0059] To make the inventive objectives, technical solutions, and beneficial effects of this application clearer, the application is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application.

[0060] The present application will be described in detail below through embodiments.

[0061] Test methods (1) Capacity retention test: At 25°C, the battery was charged and discharged at 0.25P / 0.25P within a voltage range of 2.5~3.65V until the battery capacity was cycled 2000 times. The capacity retention rate of the battery after 2000 cycles was then calculated.

[0062] (2) DCR test: At 25℃±5℃, the battery was discharged to 2.5V at 0.25C, then charged to 50% SOC at 0.25C with a cutoff current of 0.05C. After that, it was placed at 25℃±5℃ for 2 hours. Then, the battery at 50% SOC was subjected to a constant current discharge pulse test at a rate of 0.5C. The discharge pulse lasted for 30 seconds. During the test, the battery's terminal voltage and discharge current were monitored at each moment. The terminal voltage V1 and discharge current I1 at 30 seconds were obtained. Based on this, the DC internal resistance DCR at 30 seconds was calculated as (V0-V1) / I1, where V0 is the battery open circuit voltage at the instant before the start of the discharge pulse test.

[0063] (3) Energy efficiency test: After placing the battery in a constant temperature chamber at 25±2℃ for 5 hours, repeat the following steps three times: Charge the lithium-ion battery at a constant power of 0.25P until its terminal voltage reaches 3.65V, then let it rest for 30 minutes; Discharge the lithium-ion battery at 0.25P until its terminal voltage drops to 2.5V, then let it rest for 30 minutes. Collect the discharge energy and charging energy for each cycle, and calculate the energy efficiency for each cycle = (discharge energy / charging energy) × 100%. Finally, calculate the average energy efficiency of the three cycles as the battery's energy efficiency.

[0064] (4) Test on the degree of cracking of the positive electrode sheet: Observe the surface condition of the electrode after continuous coating and drying, and judge the severity based on the crack phenomenon: 1) No cracks: The electrode surface is smooth and flat, without any surface cracks or internal cracks. 2) Minor cracks: Obvious cracks on the electrode surface or internal cracks, with cracks <10mm in length and <1mm in width, appearing irregularly during continuous coating. 3) Severe cracks: Continuous obvious cracks or regular internal cracks with a length >10mm and a width >1mm at the same location on the electrode surface in the conveying direction. Among them, surface cracks refer to obvious cracks on the electrode surface that cause material shortage in that area; internal cracks refer to obvious material shortage on the surface but with obvious strip-shaped protrusions.

[0065] Example 1 (1) Preparation of dispersant 3-(dimethylamino)acrylate, methoxy polyethylene glycol acrylate, diethylmethyl vinylsilane, and vinyl phosphate were mixed in a mass ratio of 22:68:6:4, and 1.5% of the total mass of the monomers was added as an initiator. The mixture was polymerized at 80°C for 10 hours under nitrogen deoxygenation conditions to obtain a dispersant.

[0066] (2) Preparation of positive electrode slurry The first lithium iron phosphate (Dv50=0.9μm), conductive carbon black, polyvinylidene fluoride, and the dispersant prepared in step (1) were mixed evenly in a mass ratio of 97.2:0.5:2:0.3 and stirred with NMP solvent to obtain the first positive electrode slurry. The second lithium iron phosphate (Dv50=1.2μm), CNT, conductive carbon black, polyvinylidene fluoride, and the dispersant prepared in step (1) were mixed evenly in a mass ratio of 96:0.7:0.5:2:0.8 and stirred with NMP solvent to obtain the second positive electrode slurry.

[0067] (3) Preparation of positive electrode sheet The first positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil to form the first active material layer. Then, the second positive electrode slurry is coated on the first active material layer. After baking, rolling, and die cutting, the positive electrode sheet is obtained. The thickness of the first active material layer on one side is controlled to be 120 μm and the thickness of the second active material layer on one side is controlled to be 30 μm.

[0068] (4) Preparation of negative electrode sheet Artificial graphite (anode active material), conductive carbon black (SP) (conductive agent), and sodium carboxymethyl cellulose (CMC) (binder) were dry-mixed at a mass ratio of 96.7:0.5:1:1.8. After uniform mixing, a certain amount of deionized water was added for kneading, followed by high-speed dispersion and dilution with another certain amount of deionized water. Finally, the mixture was mixed evenly with styrene-butadiene rubber (SBR) to form a uniform black slurry. The slurry was then coated on both sides of a copper foil, baked, rolled, and die-cut to obtain the anode sheet.

[0069] (5) Preparation of electrolyte Ethyl carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1 as the base solvent. Then, ethyl acetate was added, and 1 mol / L LiPF6 was dissolved in the mixed organic solvent. The mixture was stirred evenly to prepare the electrolyte. The content of ethyl acetate in the organic solvent was controlled to be 20 wt%.

[0070] (6) Preparation of secondary batteries The positive electrode, the separator (composed of a PE base film, a ceramic layer and a PVDF coating layer, with thicknesses of 7μm, 2μm and 5μm respectively), and the negative electrode are stacked in sequence, then wound into a bare cell and installed in an aluminum shell. After processes such as encapsulation, liquid injection, formation and sorting, a lithium-ion battery is obtained.

[0071] Example 2 The only difference from Example 1 is that in step (1), N,N-dimethylacrylamide, polyethylene glycol monomethyl ether methacrylate, vinyltrimethoxysilane, and dioxyallyl phosphate are polymerized in a mass ratio of 15:70:5:25 to obtain a dispersant.

[0072] Example 3 The only difference from Example 1 is that in step (1), N,N-dimethylacrylamide, N-(2-methoxyethyl)acrylamide, methoxy polyethylene glycol acrylate, polypropylene glycol monomethyl ether methacrylate, vinyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, dioxypropyl phosphate, and dimethyl vinylphosphonate are polymerized in a mass ratio of 12:13:30:30:2:3:1:2 to obtain a dispersant.

[0073] Example 4 The only difference from Example 1 is that in step (2), the mass ratio of lithium iron phosphate, conductive carbon black, polyvinylidene fluoride and dispersant in the first positive electrode slurry is adjusted to 97.4:0.5:2:0.1 and mixed evenly; the mass ratio of lithium iron phosphate, CNT, conductive carbon black, polyvinylidene fluoride and dispersant in the second positive electrode slurry is 96.5:0.7:0.5:2:0.3.

[0074] Example 5 The only difference from Example 1 is that in step (2), the mass ratio of lithium iron phosphate, conductive carbon black, polyvinylidene fluoride and dispersant in the first positive electrode slurry is adjusted to 97:0.5:2:0.5 and mixed evenly; the mass ratio of lithium iron phosphate, CNT, conductive carbon black, polyvinylidene fluoride and dispersant in the second positive electrode slurry is 95.8:0.7:0.5:2:1.

[0075] Examples 6-7 The only difference from Example 1 is that in step (2), the first lithium iron phosphate Dv50 is adjusted to 0.8 μm and the second lithium iron phosphate Dv50 is adjusted to 1.3 μm, and the first lithium iron phosphate Dv50 is adjusted to 0.99 μm and the second lithium iron phosphate Dv50 is adjusted to 1.1 μm.

[0076] Examples 8-11 The only difference from Example 1 is that in step (5), ethyl acetate is adjusted to ethyl propionate, ethyl acetate is adjusted to methyl butyrate and propyl acetate with the same content, the content of ethyl acetate in the organic solvent is adjusted to 5 wt%, and the content of ethyl acetate in the organic solvent is adjusted to 30 wt%.

[0077] Examples 12-14 The only difference from Example 1 is that in step (3), the thickness of the first active material layer is controlled to be 60 μm and the thickness of the second active material layer is 40 μm, the thickness of the first active material layer is 135 μm and the thickness of the second active material layer is 10 μm, and the thickness of the first active material layer is 90 μm and the thickness of the second active material layer is 20 μm.

[0078] Example 15 The only difference from Example 1 is that in step (2), lithium iron phosphate, conductive carbon black, polyvinylidene fluoride and dispersant are mixed evenly in a mass ratio of 97:0.5:2:0.5 to obtain a positive electrode slurry; the positive electrode slurry coating is coated on both sides of the positive electrode current collector aluminum foil to form an active material layer, and then baked, rolled and cut to obtain a positive electrode sheet, wherein the thickness of the active material layer is controlled to be 150μm.

[0079] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that step (1) is omitted, and in step (2), the first lithium iron phosphate, conductive carbon black and polyvinylidene fluoride are mixed evenly in a mass ratio of 97.2:0.5:2.3, and NMP solvent is used to stir and mix to obtain the first positive electrode slurry; The second positive electrode slurry was obtained by mixing lithium iron phosphate, CNT, conductive carbon black and polyvinylidene fluoride in a mass ratio of 96:0.7:0.5:2.8 and stirring with NMP solvent.

[0080] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that step (1) is omitted, and polyvinylpyrrolidone (PVP) is used as a dispersant in step (2).

[0081] The process parameters and test data for each embodiment and comparative example are shown in Table 1.

[0082] Table 1

[0083] DCR, energy efficiency and capacity retention tests were conducted on Examples 1-15 and Comparative Examples 1-2, respectively, and the results are shown in Table 2.

[0084] Table 2

[0085] As can be seen from the above data, the technical solution of this application can alleviate the problem of easy cracking of existing thick electrodes, reduce the DCR of secondary batteries, improve the energy efficiency of secondary batteries, and improve the cycle performance of secondary batteries.

[0086] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0087] The above provides a detailed description of a secondary battery and electrical device provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A secondary battery, characterized in that, The device includes a positive electrode sheet and an electrolyte. The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active substance and a dispersant. The dispersant includes a solvation segment, a first functional segment, a second functional segment, and a third functional segment. The first functional segment has an amino group, the second functional segment has a Si group, and the third functional segment has a P group.

2. The secondary battery according to claim 1, characterized in that, At least one of the following conditions must be met: a. The solvation segment includes at least one of methoxy polyethylene glycol acrylate, polyethylene glycol monomethyl ether methacrylate, and polypropylene glycol monomethyl ether acrylate; b. The first functional segment includes at least one of 3-(dimethylamino)acrylate, N,N-dimethylacrylamide, and N-(2-methoxyethyl)acrylamide; c. The second functional segment includes at least one of diethylmethylvinylsilane, vinyltrimethoxysilane, and 3-methacryloyloxypropyltrimethoxysilane; d. The third functional segment includes at least one of vinyl phosphate, dioxypropyl phosphate, and dimethyl vinylphosphonate.

3. The secondary battery according to claim 1, characterized in that, The electrolyte includes an organic solvent, which includes linear carboxylic acid esters.

4. The secondary battery according to claim 3, characterized in that, The linear carboxylic acid ester includes at least one of ethyl acetate, ethyl propionate, methyl butyrate, propyl acetate, butyl acetate, ethyl butyrate, and methyl acetate.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The electrolyte has a viscosity of less than 2.2 mPa·s at 25±5℃.

6. The secondary battery according to claim 3, characterized in that, The linear carboxylic acid ester has a mass content of 5 wt% to 30 wt% in the organic solvent.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The positive electrode active material layer includes a first active material layer and a second active material layer. The first active material layer is disposed on at least one side of the positive electrode current collector, and the second active material layer is disposed on the surface of the first active material layer. Both the first active material layer and the second active material layer include the dispersant, and the content of the dispersant in the second active material layer is greater than the content of the dispersant in the first active material layer.

8. The secondary battery according to claim 7, characterized in that, The content of the dispersant in the second active material layer is 0.3wt%~1wt%; and / or the content of the dispersant in the first active material layer is 0.1wt%~0.5wt%.

9. The secondary battery according to claim 7, characterized in that, The first active material layer includes a first lithium iron phosphate, and the second active material layer includes a second lithium iron phosphate. The particle size Dv50 of the first lithium iron phosphate is smaller than the particle size Dv50 of the second lithium iron phosphate.

10. The secondary battery according to claim 9, characterized in that, The following condition must be met: 0.615 < particle size Dv50 of the first lithium iron phosphate / particle size Dv50 of the second lithium iron phosphate < 0.

905.

11. The secondary battery according to claim 1, characterized in that, The thickness of the first active material layer is 60μm~135μm, and the thickness of the second active material layer is 10μm~40μm.

12. An electrical appliance, characterized in that, The device includes the secondary battery as described in any one of claims 1 to 11, wherein the secondary battery serves as the power supply for the electrical equipment.

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