Positive electrode additive, preparation method thereof, battery containing positive electrode additive and electric device

Abstract

The invention provides a positive electrode additive, a preparation method thereof, a battery containing the positive electrode additive and an electric device, and relates to the technical field of batteries. The positive electrode additive comprises at least one of compounds shown as a formula I, L1 and L2 are respectively and independently C5-C20 alkylene, each R is respectively and independently C0-C5 alkyl, each a, each b and each c are respectively and independently an integer of 10-60, m is an integer of 5-20, and m + n is an integer of 5-30. The positive electrode additive not only can reduce the viscosity of the positive electrode slurry and improve the dispersion stability of the positive electrode slurry, but also can improve the resistance, the adhesive force, the flexibility and the cycling stability of the positive electrode plate, so that the battery containing the positive electrode plate is suitable for preparing the battery with high stability and high capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode additive, a preparation method thereof, and a battery and an electrical device containing the same. Background Art

[0002] Polyvinylidene fluoride (PVDF) is often used as a positive electrode binder. However, PVDF is a semi-crystalline polymer that shrinks significantly when drying, making the electrode hard and brittle, and prone to bending and powdering. These problems can be addressed by adding a softener. Softeners are typically polyether compounds, often containing polymer chains with ether bonds. These bonds can rotate freely, increasing steric hindrance and reducing the crystallinity of PVDF, thereby making PVDF more plastic and flexible, and reducing the risk of electrode cracking. However, polyether compounds themselves lack adhesive properties, and their addition can actually reduce the adhesion of the electrode, thus often requiring an increase in the amount of PVDF used. Lithium iron phosphate particles are typically small, ranging from a few hundred nanometers to 3 microns, making them more difficult to process than lithium cobalt oxide. Lithium iron phosphate has a low specific capacity, and thick coatings are usually required to increase battery capacity. When applied thickly, the electrode is prone to cracking and powdering, which is detrimental to subsequent processing steps. Therefore, an additive is needed to improve the flexibility of the electrode while ensuring adhesion. Summary of the Invention

[0003] The object of the present invention is to overcome the deficiencies of the above-mentioned prior art and to provide a positive electrode additive, a preparation method thereof, and a battery and an electrical device containing the same.

[0004] To achieve the above objectives, in a first aspect, the present invention provides a positive electrode additive comprising at least one compound of formula I,

[0005]

[0006] Among them, L 1 and L 2 Each independently is C5~C 20 Alkylene, each R is independently a C0-C5 alkyl group, each a, each b and each c is independently an integer of 5-30, m is an integer of 0-20, and m+n is an integer of 5-30.

[0007] In a second aspect, the present invention provides a method for preparing the positive electrode additive, comprising the following steps:

[0008] The long-chain terminal dibromopolyether compound is synthesized by combining an alkyl alcohol and a dihalogenated alkane to obtain compound A;

[0009] Compound A is reacted with a first borate to introduce a borate group into the polyether main chain, and then reacted with a second borate to introduce a borate group into the end of the polyether side chain to obtain compound B, that is, a positive electrode additive.

[0010] In a third aspect, the present invention provides a battery comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode material, the positive electrode material comprises the positive electrode additive, and the mass proportion of the positive electrode additive in the positive electrode material is 0.1% to 0.8%.

[0011] In a fourth aspect, the present invention provides an electrical device comprising the battery.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] (1) The positive electrode additive of the present invention is introduced into the polyether main chain and the polyether side chain The boron (B) element in the group has an empty orbital, which is easy to complex with highly electronegative ions, such as oxygen ions, fluoride ions, etc., and can be anchored on positive electrode materials such as PVDF and positive electrode active materials, which is beneficial to improve the adhesion of the positive electrode sheet and the stability of the slurry. At the same time, the complexation of the boron element in the above group with the oxygen ions also enables it to react with water first when it meets water to generate boric acid, thereby avoiding the gelation of PVDF due to the presence of water. At the same time, the ether bonds on the polyether main chain and the polyether side chain can rotate, synergistically The group improves the flexibility of the positive electrode sheet and the dispersibility of the positive electrode slurry.

[0014] (2) Adding the positive electrode additive of the present invention to the positive electrode material can reduce the viscosity of the positive electrode slurry, improve its fluidity, and enhance its coating performance; it can also improve the dispersibility and stability of the positive electrode slurry; improve the resistance, adhesion, flexibility and cycle stability of the positive electrode sheet, so that the battery containing the positive electrode sheet is suitable for preparing a high-stability and high-capacity battery. DETAILED DESCRIPTION

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0016] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0017] In the present invention, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0018] In the present invention, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0019] The reagents and instruments used in the present invention without indicating the manufacturer are all conventional products that can be purchased from the market.

[0020] According to the first aspect of the present application, there is provided a positive electrode additive comprising at least one compound of formula I,

[0021]

[0022] Among them, L 1 and L 2 Each independently is C5~C 20 Alkylene, each R is independently a C0-C5 alkyl group, each a, each b and each c is independently an integer of 5-30, m is an integer of 0-20, and m+n is an integer of 5-30.

[0023] The positive electrode additive is introduced into the polyether main chain and the polyether side chain The boron (B) element in this group has an empty orbital, which is easy to complex with highly electronegative ions, such as oxygen ions and fluoride ions. Therefore, it can form coordination bonds with the fluoride ions in PVDF and the oxygen ions in the positive electrode active material, which is beneficial to the formation of a whole positive electrode sheet and improve the bonding force. In addition, during the homogenization stage, The group can play an anchoring role, which can promote the connection between the positive electrode additives and the positive electrode active materials, PVDF and other substances, forming a reversible cross-linking system, increasing the stability of the slurry, and at the same time, The complexation between the boron (B) element in the group and the oxygen ion also enables it to react with water first when it comes into contact with water to generate boric acid, thus preventing PVDF from gelling due to the presence of water, making the positive electrode slurry low in viscosity, good in fluidity, and easy to coat on the current collector. At the same time, the ether bonds on the polyether main chain and the polyether side chain can rotate, and can act as flexible groups to coordinately anchor to the positive electrode active material, PVDF and other materials. The group improves the flexibility of the electrode, and the ether bond can also form a hydrogen bond with PVDF, which is beneficial to the stretching of the PVDF chain segment and increases flexibility; the polyether side chain can also stretch into the solvent by rotation, reducing the crystallinity of PVDF and improving the adhesion of the positive electrode.

[0024] L 1 C5~C 20 Alkylene, such as C 12 Alkylene, wherein C 12 The alkylene group may have either a linear structure or a branched structure.

[0025] L 2 is C0~C5 alkylene, for example C 12 Alkylene, wherein C 12 The alkylene group may have either a linear structure or a branched structure.

[0026] Each R is independently a C0-C5 alkyl group, such as at least one of a methyl group, an ethyl group, and a propyl group, wherein the propyl group can be either a straight-chain structure or a branched-chain structure.

[0027] a, b and c are independent of each other. Each a is independently an integer from 5 to 30, such as 5, 10, 15, 20, 25 or 30; each b is independently an integer from 5 to 30, such as 5, 10, 15, 20, 25 or 30; and each c is independently an integer from 5 to 30, such as 5, 10, 15, 20, 25 or 30.

[0028] m is an integer from 0 to 20, for example, 0, 2, 4, 6, 8, 10, 12, 14, 16, 18 or 20.

[0029] m+n is an integer from 5 to 30, for example, 5, 10, 15, 20, 25 or 30.

[0030] n can be selected as an integer from 0 to 20, for example, 0, 2, 4, 6, 8, 10, 12, 14, 16, 18 or 20.

[0031] In some embodiments, the mass percentage y of the boron element in the positive electrode additive satisfies: 0.28%≤y<1.28%.

[0032] The present invention does not limit the method for detecting the mass percentage of the boron element in the positive electrode additive. Those skilled in the art can detect it according to conventional technical means. Exemplarily, the method for detecting the mass percentage of the boron element in the positive electrode additive includes the following steps: using the ICP method for testing: 1. Sample treatment (digesting the solid with acid); 2. Calibration of the instrument (preparing a gradient concentration standard solution and internal standard correction); 3. Sample injection and analysis (plasma excitation, signal detection); 4. Data processing (subtracting background interference).

[0033] In some embodiments, the weight average molecular weight of the positive electrode additive is 10,000 g / mol to 500,000 g / mol, for example, 10,000 g / mol, 50,000 g / mol, 100,000 g / mol, 200,000 g / mol, 300,000 g / mol, 400,000 g / mol or 500,000 g / mol.

[0034] The present invention does not limit the method for determining the weight-average molecular weight of the cathode additive; those skilled in the art can perform such determinations using conventional techniques. Exemplarily, the method for determining the weight-average molecular weight of the cathode additive comprises the following steps: ultracentrifuge sedimentation velocity method: 1. Sample preparation (preparation of a homogeneous polymer solution); 2. High-speed centrifugation; 3. Recording interfacial movement (solute particles settle to form a clear interface, and measuring the change in interface position over time); 4. Calculation of the sedimentation coefficient to obtain the weight-average molecular weight.

[0035] In some embodiments, the PDI of the positive electrode additive is 1-5.

[0036] The present invention does not limit the method for detecting the PDI of the cathode additive, and those skilled in the art can detect it according to conventional technical means. Exemplary, the method for detecting the PDI of the cathode additive includes the following steps: gel permeation chromatography / GPC method: 1. GPC separation (polymer solution flows through the chromatographic column and is separated by molecular size); 2. Detection of concentration (differential refractive index detector (RI) records the concentration signal of each fraction); 3. Calculation of molecular weight (number average molecular weight and weight average molecular weight); 4. Obtaining the PDI value.

[0037] According to a second aspect of the present invention, there is provided a method for preparing the positive electrode additive comprising the following steps:

[0038] The long-chain terminal dibromopolyether compound is synthesized by combining an alkyl alcohol and a dihalogenated alkane to obtain compound A;

[0039] Compound A is reacted with a first borate to introduce a borate group into the polyether main chain, and then reacted with a second borate to introduce a borate group into the end of the polyether side chain to obtain compound B, that is, a positive electrode additive.

[0040] In some embodiments, the specific steps for preparing compound A include: dissolving an alkyl alcohol in a first solvent under anhydrous and anaerobic conditions to obtain an alkyl alcohol solution, dissolving a dihaloalkane in a second solvent to obtain a dihaloalkane solution, adding a base to the alkyl alcohol solution and dispersing at 0-5°C, adding the dihaloalkane solution at 0-5°C, performing a first reaction at 20-30°C, adding an acid to adjust the pH value to 6-7 at 0-5°C, and adding a first anti-solvent to precipitate a white substance, followed by solid-liquid separation to obtain compound A.

[0041] The specific steps for preparing compound B include: dissolving the compound A in a third solvent under anhydrous and anaerobic conditions to obtain solution A, adding a base to the solution A, adding a first borate after the base is completely dissolved, performing a second reaction at 40-60°C, cooling to 20-30°C, adding a second borate, performing a third reaction at 20-30°C, adding an acid to adjust the pH value to 6-7 at 0-5°C, and performing a fourth reaction at 20-30°C to obtain solution B; adding a second anti-solvent to the solution B to precipitate a white substance, followed by solid-liquid separation to obtain the positive electrode additive.

[0042] In some embodiments, the alkyl alcohol includes at least one of 1,12-dodecanediol, 1,16-hexadecanediol, and 1,6-hexanediol.

[0043] In some embodiments, the dihaloalkane includes at least one of 1,12-dibromododecane, 1,16-dibromohexadecane, and 1,6-dibromo-n-hexane.

[0044] In some embodiments, the molar ratio of the alkyl alcohol to the dihaloalkane is (1-1.1):1.

[0045] In some embodiments, the first reaction is performed at a rotation speed of 500-2000 rpm for 20-30 h.

[0046] In some embodiments, when the base is added to the alkyl alcohol solution, the molar ratio of the base to the alkyl alcohol is (1-1.1):1.

[0047] In some embodiments, when the base is added to the alkyl alcohol solution for dispersion, the dispersion rotation speed is 500-2000 rpm, and the dispersion time is 0.2-0.5 h.

[0048] In some embodiments, when the base is added to the alkyl alcohol solution, the base used includes at least one of NaOH and KOH.

[0049] In some embodiments, the concentration of the alkyl alcohol in the alkyl alcohol solution is 0.1 to 0.3 mol / L, and the first solvent includes at least one of dimethyl sulfoxide (DMSO), N,N-dimethylformamide, and N,N-dimethylacetamide.

[0050] In some embodiments, the concentration of dihalogenated alkane in the dihalogenated alkane solution is 1 to 3 mol / L, and the second solvent includes at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0051] In some embodiments, the first anti-solvent comprises at least one of toluene, diethyl ether, and n-hexane.

[0052] In some embodiments, the ratio of the first anti-solvent to the alkyl alcohol is (800-2000) mL:1 mol.

[0053] In some embodiments, during the process of preparing compound A using the first anti-solvent, the cleaning reagent includes at least one of ethanol, DMF, toluene, ethanol, diethyl ether, and n-hexane.

[0054] In some embodiments, during the preparation of the compound A, the acid used to adjust the pH includes at least one of acetic acid and formic acid.

[0055] In some embodiments, when a base is added to the solution A, the molar ratio of the base to the compound A is (5-8):1.

[0056] In some embodiments, when a base is added to the solution A for dispersion, the dispersion speed is 500 to 2000 rpm, and the dispersion time is 0.2 to 0.5 h.

[0057] In some embodiments, when a base is added to the solution A, the base used includes at least one of NaOH and KOH.

[0058] In some embodiments, the first borate ester and the second borate ester each independently include at least one of triethyl borate, trimethyl borate, and tripropyl borate.

[0059] In some embodiments, the molar ratio of the compound A to the first borate ester is (1-1.2):1.

[0060] In some embodiments, the second reaction is carried out for 2 to 5 hours. In one embodiment, the second reaction is carried out at a rotation speed of 500 to 2000 rpm.

[0061] In some embodiments, the molar ratio of the compound A to the second borate ester is 1:(2-4).

[0062] In some embodiments, the third reaction is carried out for 20 to 30 hours. In one embodiment, the third reaction is carried out at a rotation speed of 500 to 2000 rpm.

[0063] In some embodiments, the fourth reaction is carried out for 3 to 8 hours. In one embodiment, the fourth reaction is carried out at a rotation speed of 500 to 2000 rpm.

[0064] In some embodiments, the concentration of compound A in the solution A is 5 to 10 mmol / L, and the third solvent includes at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, and dimethyl sulfoxide.

[0065] In some embodiments, the second anti-solvent comprises at least one of toluene, diethyl ether, and n-hexane.

[0066] In some embodiments, the ratio of the second anti-solvent to the compound A is (2000-4000) mL:1 mol.

[0067] In some embodiments, the method further includes the following steps: recrystallizing the compound B, wherein the solvent used for the recrystallization includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, toluene, diethyl ether, and n-hexane, and the recrystallization is heated to dissolve at 80-100°C and cooled to crystallize at 20-30°C.

[0068] In some embodiments, when acid is added to adjust the pH value, the acid used is independently selected from at least one of formic acid and acetic acid.

[0069] In some embodiments, during the process of preparing the cathode additive using the solution B, the cleaning reagent includes at least one of ethanol, N,N-dimethylformamide, toluene, and ethanol.

[0070] According to a third aspect of the present invention, a battery is provided, comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode material, the positive electrode material comprises the positive electrode additive, and the mass proportion of the positive electrode additive in the positive electrode material is 0.1% to 0.8%.

[0071] In some embodiments, the positive electrode additive accounts for 0.2% to 0.8% by mass of the positive electrode material.

[0072] When the mass proportion of the positive electrode additive in the positive electrode material is in the range of 0.1% to 0.8%, especially in the range of 0.2% to 0.8%, it can better reduce the viscosity of the positive electrode slurry, improve the stability of the positive electrode slurry, and better improve the flexibility, adhesion, resistance and cycle performance of the positive electrode sheet.

[0073] In some embodiments, the positive electrode material further comprises polyvinylidene fluoride, and the mass proportion of the polyvinylidene fluoride is 1% to 4% based on the total weight of the positive electrode material.

[0074] In some embodiments, the positive electrode material further comprises a positive electrode active material, and the mass proportion of the positive electrode active material is 90% to 98% based on the total weight of the positive electrode material.

[0075] The positive electrode active material generally contains oxygen. Exemplarily, the positive electrode active material includes but is not limited to at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide.

[0076] In one embodiment, the positive electrode material further comprises a positive electrode active material, and the average particle size of the positive electrode active material particles is 0.3 to 2 μm, such as 0.3 μm, 0.5 μm, 0.8 μm, 1 μm or 2 μm.

[0077] The present invention does not limit the method for detecting the average diameter of the lithium iron phosphate particles, and those skilled in the art can detect it according to conventional technical means. Exemplary methods for detecting the average diameter of the lithium iron phosphate particles are: laser diffraction or dynamic light scattering (DLS).

[0078] In some embodiments, the positive electrode material further includes a conductive agent comprising carbon nanotubes (CNTs), with the mass of the CNTs accounting for 0.1% to 2% of the total weight of the positive electrode material. Carbon nanotubes often incorporate oxygen-containing groups on their surfaces to enhance their dispersibility. When the positive electrode material includes CNTs, the boron in the positive electrode additive can anchor the oxygen-containing groups on the surface of the CNTs, improving the dispersibility and stability of the positive electrode material.

[0079] In some embodiments, the conductive agent further comprises at least one of conductive graphite, carbon black (SP), carbon nanotubes, graphene, and carbon fibers.

[0080] In some embodiments, the conductive agent accounts for 2% to 5% by mass of the positive electrode material.

[0081] In some embodiments, the positive electrode sheet further comprises a positive electrode current collector. The positive electrode material is disposed on at least one side of the positive electrode current collector. Exemplarily, the positive electrode current collector comprises at least one of aluminum foil and primer-coated aluminum foil.

[0082] The present application does not impose any particular restrictions on the preparation method of the positive electrode sheet. Those skilled in the art can prepare the positive electrode sheet according to conventional technical means. Exemplarily, the preparation method of the positive electrode sheet includes the following steps:

[0083] The positive electrode active material, the conductive agent, the PVDF and the positive electrode additive are dissolved or dispersed in a solvent to prepare a positive electrode slurry;

[0084] The positive electrode slurry is coated on at least one side of the positive electrode current collector, rolled or dried to obtain a positive electrode sheet; or the positive electrode slurry is cast on a separate carrier, and then the film separated from the carrier is laminated on at least one side of the positive electrode current collector to obtain a positive electrode sheet.

[0085] In some embodiments, the battery further comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode material, and the negative electrode material comprises a negative electrode active material. The negative electrode active material includes, but is not limited to, at least one of graphite, silicon.

[0086] In some embodiments, the mass fraction of the negative electrode active material in the negative electrode material is 90% to 97%.

[0087] In some embodiments, the negative electrode material further comprises a conductive agent. The conductive agent includes, but is not limited to, at least one of carbon nanotubes, graphite, graphene.

[0088] In some embodiments, the mass fraction of the conductive agent in the negative electrode material is 0.01% to 1%.

[0089] In some embodiments, the negative electrode material comprises a binder. The binder includes, but is not limited to, at least one of polyacrylic acid, carboxymethyl cellulose, butadiene-styrene rubber.

[0090] In some embodiments, the negative electrode sheet further comprises a negative electrode current collector. The negative electrode material is arranged on at least one side of the negative electrode current collector. Illustratively, the negative electrode current collector includes at least one of copper foil, primer-coated copper foil.

[0091] The application does not make special limitations on the preparation method of the negative electrode sheet, and those skilled in the art can prepare the negative electrode sheet according to conventional technical means. Illustratively, the preparation method of the negative electrode sheet comprises the following steps:

[0092] The negative electrode active material, the conductive agent and the binder are dissolved or dispersed in a solvent to prepare a negative electrode slurry;

[0093] The negative electrode slurry is coated on at least one side of the negative electrode current collector, rolled or dried to obtain a negative electrode sheet; or the negative electrode slurry is cast on a separate carrier, and then the film separated from the carrier is laminated on at least one side of the negative electrode current collector to obtain a negative electrode sheet.

[0094] In some embodiments, the battery further comprises an electrolyte. The electrolyte can be selected from various electrolytes suitable for batteries in the art. The electrolyte comprises a lithium salt and a solvent.

[0095] For example, the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate, lithium perchlorate, and lithium bis(fluorosulfonyl)imide. The concentration of the lithium salt in the electrolyte can be selected to be 0.1 to 2 mol / L.

[0096] For example, the solvent in the electrolyte includes, but is not limited to, at least one of fluoroethylene carbonate (FEC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC). The mass percentage of the solvent in the electrolyte can be selected to be 80% to 90%.

[0097] The electrolyte may also contain additives. For example, these additives may include high-voltage, flame-retardant, and electrolyte-stabilizing additives. High-voltage additives may include at least one of vinyl sulfate, lithium bis(fluorosulfonyl)imide, and boron-containing additives. The weight percentage of high-voltage additives in the electrolyte may be 1% to 5%.

[0098] The battery may also include a separator positioned between the positive and negative electrodes to separate the positive and negative electrodes and prevent short circuits. The separator may be made of any suitable battery separator material known in the art. Exemplary separators include, but are not limited to, at least one of polypropylene and polyethylene.

[0099] According to a fourth aspect of the present application, an electrical device is provided, comprising the secondary battery. The electrical device is any device that can utilize electrical energy and convert it into one or more other energy forms, such as mechanical energy, thermal energy, light energy, etc., such as an electric lamp, an electric motor, an electric heat generator, etc.

[0100] The present invention is further described below with specific embodiments:

[0101] The lithium iron phosphate used is from the same batch of products, and lithium iron phosphate of different particle sizes is obtained through ball milling and screening.

[0102] Cathode Additive A

[0103] The preparation method of the positive electrode additive A comprises the following steps:

[0104] Under anhydrous and oxygen-free conditions, 1,12-dodecanediol (20.23 g, 100 mmol) was dissolved in DMSO (800 mL) to obtain an alkyl alcohol solution, and 1,12-dibromododecane (31.2 g, 95 mmol) was dissolved in DMSO (100 mL) to obtain a dihalogenated alkane solution. NaOH (4.2 g, 105 mmol) was added to the alkyl alcohol solution, and the mixture was stirred in an ice bath at 400 rpm for 30 min. The dihalogenated alkane solution was added at 0°C, and all of the mixture was stirred at 25°C and 600 rpm for 24 h. The pH value was adjusted to 6-7 with acetic acid at 0°C, and toluene was added. A large amount of white substance precipitated, which was filtered, washed, and dried to obtain compound A.

[0105] Compound A was dissolved in DMF (1000 mL) under anhydrous and oxygen-free conditions to obtain solution A. NaOH (0.8 g) was added to solution A. After the NaOH was completely dissolved, triethyl borate (0.7 g) was added, and the mixture was reacted at 50° C. for 3 h. The mixture was cooled to 25° C., triethyl borate (1.5 g) was added, and the mixture was reacted at 25° C. for 24 h. Acetic acid was added at 0° C. to adjust the pH to 6-7, and the mixture was reacted at 25° C. for 5 h to obtain solution B.

[0106] Toluene was added to solution B, and a large amount of white substance precipitated. The white substance was filtered and washed (using ethanol, DMF, toluene, and n-hexane in sequence), dried, and recrystallized to obtain positive electrode additive A.

[0107] The positive electrode additive A was detected by infrared spectrometer, and the following peaks were found: 1148 cm -1 (ether), 1136cm -1 and 1384cm -1 (corresponding to CO and BO in -COBOC- respectively);

[0108] The positive electrode additive A was detected by mass spectrometry, and it was found that there were multiple peaks between 5000 and 400000 g / mol. Its weight average molecular weight and PDI are shown in Table 1.

[0109] The mass percentage of boron element in the positive electrode additive A was measured using the ICP test method, and the results are shown in Table 1.

[0110] Cathode additive B

[0111] The preparation method of positive electrode additive B is different from that of positive electrode additive A in that compound A is synthesized as follows:

[0112] Under anhydrous and oxygen-free conditions, 1,6-hexanediol (11.82 g, 100 mmol) was dissolved in DMSO (800 ml), and NaOH (4.2 g, 105 mmol) was added. The mixture was stirred in an ice bath for 30 min. 1,6-dibromohexane (23.18 g, 95 mmol) was dissolved in DMSO (100 ml) and slowly added at 0°C. After complete addition, the mixture was stirred at room temperature for 24 h. Acetic acid was used to adjust the mixture to a weak acidity at 0°C. Toluene was added, resulting in the precipitation of a large amount of white material. This was filtered, washed, and then dried to obtain Compound A.

[0113] The positive electrode additive B was detected by infrared spectrometer, and the following peaks were found: 1148 cm -1 (ether), 1136cm -1 and 1384cm -1 (corresponding to CO and BO in -COBOC- respectively);

[0114] The positive electrode additive B was detected by mass spectrometry, and it was found that it had multiple peaks between 10,000 and 500,000 g / mol. Its weight average molecular weight and PDI are shown in Table 1.

[0115] The mass percentage of boron element in the positive electrode additive B was measured by ICP method, and the results are shown in Table 1.

[0116] Cathode additive C

[0117] The preparation method of positive electrode additive C is different from the preparation method of positive electrode additive A in that compound A is synthesized as follows:

[0118] Under anhydrous and oxygen-free conditions, 1,16-hexadecanediol (25.84 g, 100 mmol) was dissolved in DMSO (800 ml), and NaOH (4.2 g, 105 mmol) was added. The mixture was stirred in an ice bath for 30 min. 1,16-Dibromohexadecane (36.5 g, 95 mmol) was dissolved in DMSO (100 ml) and slowly added at 0°C. After complete addition, the mixture was stirred at room temperature for 24 h. Acetic acid was used to adjust the mixture to a weak acidity at 0°C. Toluene was added, resulting in the precipitation of a large amount of white material. This was filtered, washed, and then dried to obtain Compound A.

[0119] The positive electrode additive C was detected by infrared spectrometer, and the following peaks were found: 1148 cm -1 (ether), 1136cm -1 and 1384cm -1 (corresponding to CO and BO in -COBOC- respectively);

[0120] The positive electrode additive C was detected by mass spectrometry, and it was found that it had multiple peaks between 10,000 and 500,000 g / mol. Its weight-average molecular weight and PDI are shown in Table 1.

[0121] The mass percentage of boron element in the positive electrode additive C was measured by ICP method, and the results are shown in Table 1.

[0122] Cathode additive D

[0123] The preparation method of positive electrode additive D is different from the preparation method of positive electrode additive A in that compound A is synthesized as follows:

[0124] Under anhydrous and oxygen-free conditions, compound A was dissolved in DMF (1000 ml), and NaOH (0.8 g) was added. After dissolution, triethyl borate (0.7 g) was added and the mixture was allowed to react at 50°C for 3 hours. The reaction temperature was lowered to room temperature and allowed to react for 24 hours. At 0°C, acetic acid was added to adjust the pH to a weak alkaline level, followed by dilute hydrochloric acid to a weak acidic level. The reaction was continued at room temperature for 5 hours. This yielded mixed solution B. Toluene was added to mixed solution B, causing a large amount of white material to precipitate. This was filtered, washed (ethanol, DMF, toluene, ethanol), dried, and recrystallized to yield additive D.

[0125] Example 1

[0126] This embodiment provides a battery, and the preparation method thereof is as follows:

[0127] (1) Positive electrode

[0128] PVDF, a first conductive agent and a positive electrode additive were added to NMP (N-methylpyrrolidone), stirred and dispersed, and then the second conductive agent was added and stirred and dispersed. Then, half of the positive electrode active material was added and stirred and dispersed, and then the remaining positive electrode active material was added and stirred and dispersed to obtain a positive electrode slurry. The above positive electrode slurry was coated on both sides of the aluminum foil using a coating machine (the coating thickness was 250 μm), and dried to obtain a positive electrode sheet. The types of positive electrode active materials, first conductive agents, second conductive agents and positive electrode additives, as well as the mass proportions of positive electrode active materials, PVDF, first conductive agents, second conductive agents and positive electrode additives in the positive electrode materials of the obtained positive electrode sheet are shown in Table 1.

[0129] (2) Negative electrode

[0130] Graphite, PAA, and CNTs were added to deionized water and stirred to disperse. SBR and CMC were then added and stirred to obtain a negative electrode slurry. The positive electrode slurry was applied to both sides of a copper foil using a coating machine and dried to obtain a negative electrode sheet. The negative electrode material of the negative electrode sheet contained the following components by weight: 95% graphite, 2.5% PAA, 0.5% CNT, 1.2% SBR, and 0.8% CMC.

[0131] (3) Electrolyte

[0132] A solution of lithium salt LiPF6and non-aqueous organic solvent (component ratio: ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): vinylene carbonate (VC) = 20:30:20:28:2, mass ratio) prepared at a mass ratio of 12:88 was used as the electrolyte of the lithium ion secondary battery.

[0133] (4) Separator

[0134] The separator is not particularly limited and can be any material suitable for use as a separator in a lithium ion battery in the art, for example, can be a combination of one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers, etc.

[0135] (5) Battery

[0136] 486687 size battery.

[0137] Examples 2-14 and Comparative Examples 1-2

[0138] The examples and comparative examples all provide a battery, the difference between the preparation method and Example 1 is that:

[0139] The types of positive active material, first conductive agent, second conductive agent, and positive electrode additive, and the mass ratio of positive active material, PVDF, first conductive agent, second conductive agent, and positive electrode additive in the positive electrode material of the obtained positive electrode tab are shown in Table 1.

[0140] Table 1

[0141]

[0142]

[0143] The positive electrode slurry, positive electrode tab, or battery obtained in the above examples and comparative examples were tested as follows:

[0144] (1) Slurry viscosity test: The freshly prepared positive electrode slurry and the positive electrode slurry after being stored at 25°C for 24 h were tested for viscosity using a rotational viscometer, the rotational speed was set to 15 rpm, and the viscosity unit was cps.

[0145] (2) Adhesion test: Apply a 24mm wide double-sided tape about 10cm wide on one side of the positive electrode, leaving a 15cm free space on the other side. Use a roller to roll the double-sided tape 4 times to make the electrode and the double-sided tape fit tightly. Cut the electrode into 25cm long strips, with double-sided tape on one end and a blank electrode on the other end. Prepare 3 strips. Stick the electrode with double-sided tape (i.e. cut into 25cm long strips) on a clean glass plate, roll it 3 times with a roller, and then use a tensile testing machine to test the adhesion. Fix one end of the electrode on the glass plate facing up, and fix the other end with a clamp. Turn the free end of the electrode upward and fix it with the upper clamp. Keep the lower clamp stationary, stretch the upper clamp at a speed of 250mm / min, and test for about 20s. Repeat 3 times and take the average value. Unit: gf.

[0146] (3) After rolling the positive electrode, cut it into 10cm wide and 20cm long pieces, fold it in half, and roll it three times at the fold using a 3kg roller. Open the electrode and observe the light transmittance against a light source. If it is light transmittance, classify it according to the following grades:

[0147] Grade A light transmittance: ≤3 points; Grade B light transmittance: >3 points, ≤7 points, and the light transmittance points are discontinuous; Grade C light transmittance: >7 points, or the light transmittance points are continuously distributed.

[0148] (4) Resistance: Use a resistance meter to measure the resistance of the positive electrode and take the average value of the five measurements.

[0149] (5) 1000-cycle capacity retention rate: In a temperature environment of 25°C, the cycle test was carried out according to the following method: charging mode: charging at a constant current of 2C, with a cut-off voltage of 4V; then charging at a constant current of 1.5C, with a cut-off voltage of 4.3V; then charging at a constant current and constant voltage of 0.8C to 4.5V, with a cut-off rate of 0.05C; discharging mode: discharging at a constant current of 0.5C, with a cut-off voltage of 3.0V; the capacity retention rate after 1000 cycles of charge and discharge was calculated, and the 1000-cycle capacity retention rate = discharge capacity at the 1000th cycle / discharge capacity at the 1st cycle * 100%.

[0150] (6) Pole flexibility: Cut the rolled positive electrode into a square with a width of 10 cm and a length of 20 cm; fold the electrode in half and use a 1 kg roller to roll the electrode from the middle through the fold to the outside three times; open the electrode and observe whether there is powder falling from the fold.

[0151] (7) Slurry solid content test: Use the differential weight method to test the solid content of the positive electrode slurry just prepared and the lower slurry after the positive electrode slurry is placed at 25°C for 24 hours.

[0152] (8) Cohesion test: After removing the aluminum foil from the electrode for adhesion testing, stick the electrode part to the glass plate. Cut the transparent tape into a 25cm long strip with the same width as the double-sided tape, and stick it to the electrode on the glass plate, aligning the electrode part with the tape. Roll it three times with a roller. Then use a tensile testing machine to test the cohesion. The test is the same as the adhesion test step. The obtained data is the electrode cohesion.

[0153] The test results are shown in Table 2.

[0154] Table 2

[0155]

[0156]

[0157] Comparison of Examples 1-6 with Comparative Examples 1-2 shows that the addition of the present positive electrode additive helps reduce discharge viscosity, improve slurry stability, reduce positive electrode sheet resistance, increase adhesion and cohesion, and improve cycle performance. The improvement effect increases with increasing addition amount, but decreases when the addition amount of the positive electrode additive to the positive electrode material exceeds 0.8wt%.

[0158] From the comparison of Examples 7 to 11, it can be seen that as the particle size of lithium iron phosphate increases, the viscosity of the slurry decreases and the electrode resistance decreases. This is because large-sized particles are easier to disperse. The adhesion and cohesion of the electrode also increase with the increase of particle size, but begin to decrease when the particle size exceeds 1μm. This is because as the particle size increases, the dispersibility of the slurry increases, so the adhesion and cohesion increase accordingly. However, as the particle size increases, the specific surface area of ​​the main material decreases. The same content of additives can adsorb more on the surface of the main material, which is equivalent to using more additives than with small particle size. Therefore, both adhesion and cohesion begin to decrease.

[0159] Comparing Examples 12 and 13, it is clear that reducing the length of the additive's branched polyether segments improves dispersibility but degrades adhesion; increasing the length of the branched polyether segments improves adhesion but hinders dispersion. Example 14 demonstrates that too low a boron content degrades both the electrode's adhesion and cohesion, reducing its flexibility and battery cycle retention.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of this article may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of this article.

Claims

1. A positive electrode additive, characterized in that comprising at least one compound of formula I, Among them, L 1 and L 2 Each independently is C5~C 20 Alkylene, each R is independently a C0-C5 alkyl group, each a, each b and each c is independently an integer of 5-30, m is an integer of 0-20, and m+n is an integer of 5-30.

2. The positive electrode additive according to claim 1, wherein The mass percentage y of the boron element in the positive electrode additive satisfies: 0.28%≤y<1.28%.

3. The positive electrode additive according to claim 1, wherein The weight average molecular weight of the positive electrode additive is 10,000 g / mol to 500,000 g / mol.

4. The method for preparing a cathode additive according to any one of claims 1 to 3, wherein: The following steps are involved: The long-chain terminal dibromopolyether compound is synthesized by combining an alkyl alcohol and a dihalogenated alkane to obtain compound A; Compound A is reacted with a first borate to introduce a borate group into the polyether main chain, and then reacted with a second borate to introduce a borate group into the end of the polyether side chain to obtain compound B, that is, a positive electrode additive.

5. The method for preparing a cathode additive according to claim 4, wherein: The specific steps of preparing compound A include: dissolving an alkyl alcohol in a first solvent under anhydrous and oxygen-free conditions to obtain an alkyl alcohol solution, dissolving a dihalogenated alkane in a second solvent to obtain a dihalogenated alkane solution, adding a base to the alkyl alcohol solution at 0-5°C and dispersing, adding the dihalogenated alkane solution at 0-5°C, conducting a first reaction at 20-30°C, adding an acid at 0-5°C to adjust the pH to 6-7, then adding a first anti-solvent to precipitate a white substance, and performing solid-liquid separation to obtain compound A; The specific steps of preparing compound B include: dissolving the compound A in a third solvent under anhydrous and oxygen-free conditions to obtain solution A, adding a base to the solution A, adding a first borate after the base is completely dissolved, conducting a second reaction at 40-60° C., cooling to 20-30° C., adding a second borate, conducting a third reaction at 20-30° C., adding an acid at 0-5° C. to adjust the pH value to 6-7, and conducting a fourth reaction at 20-30° C. to obtain solution B; adding a second antisolvent to the solution B to precipitate a white substance, and performing solid-liquid separation to obtain compound B.

6. The method for preparing a cathode additive according to claim 4, wherein: At least one of the following conditions is met: S1. The alkyl alcohol includes at least one of 1,12-dodecanediol, 1,16-hexanediol, and 1,6-hexanediol; S2. The dihalogenated alkane includes at least one of 1,12-dibromododecane, 1,16-dibromohexadecane, and 1,6-dibromohexane; S3. The molar ratio of the alkyl alcohol to the dihalogenated alkane is (1-1.1):1; S4. The first reaction time is 20 to 30 hours; S5. When a base is added to the alkyl alcohol solution, the molar ratio of the base to the alkyl alcohol is (1 to 1.1): 1; S6. The concentration of the alkyl alcohol in the alkyl alcohol solution is 0.1 to 0.3 mol / L, and the first solvent comprises at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide; S7. The concentration of the dihalogenated alkane in the dihalogenated alkane solution is 1 to 3 mol / L, and the second solvent comprises at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide; S8. The first anti-solvent comprises at least one of toluene, diethyl ether, and n-hexane; S9. The ratio of the first anti-solvent to the alkyl alcohol is (800-2000) mL:1 mol; S10. When a base is added to the solution A, the molar ratio of the base to the compound A is (5 to 8):1; S11. The first borate ester and the second borate ester each independently include at least one of triethyl borate, trimethyl borate, and tripropyl borate; S12. The molar ratio of the compound A to the first borate ester is (1-1.2):1; S13. The second reaction time is 2 to 4 hours; S14. The molar ratio of the compound A to the second borate ester is 1:(2-4); S15. The third reaction time is 20 to 30 hours; S16. The fourth reaction time is 4 to 7 hours; S17. The concentration of compound A in the solution A is 5 to 10 mmol / L, and the third solvent comprises at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; S18. The second anti-solvent comprises at least one of toluene, diethyl ether, and n-hexane; S19. The ratio of the second anti-solvent to the compound A is (2000-4000) mL:1 mol.

7. A battery, characterized in that: The invention comprises a positive electrode plate, wherein the positive electrode plate comprises a positive electrode material, wherein the positive electrode material comprises the positive electrode additive according to any one of claims 1 to 3, and the mass proportion of the positive electrode additive in the positive electrode material is 0.1% to 0.8%.

8. The battery according to claim 6, wherein The positive electrode material further comprises polyvinylidene fluoride, and the mass proportion of the polyvinylidene fluoride is 1% to 4% based on the total weight of the positive electrode material; And / or, the positive electrode material further comprises a positive electrode active material, and the mass proportion of the positive electrode active material is 90% to 98% based on the total weight of the positive electrode material; And / or, the positive electrode material further comprises carbon nanotubes, and the mass proportion of the carbon nanotubes is 0.1% to 2% based on the total weight of the positive electrode material.

9. The battery according to claim 8, wherein The positive electrode material further comprises a positive electrode active material, and the average particle size of the positive electrode active material particles is 0.3 to 2 μm.

10. An electrical device, characterized in that: The method comprises the battery according to any one of claims 7 to 9.

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