Lithium ion battery and electric equipment thereof

Abstract

The invention relates to the technical field of batteries, and discloses a lithium ion battery and electric equipment thereof, the lithium ion battery comprises a positive plate, a negative plate, a diaphragm and an electrolyte; the electrolyte comprises phosphorus-containing trinitrile of which the addition amount is 0.1 wt%-5wt%; the diaphragm comprises a base membrane and a coating located on at least one surface of the base membrane, the coating comprises nitrogen-containing organic particles, and the content of nitrogen in the coating accounts for 5wt%-60wt%. Through optimization of the electrolyte and the diaphragm in the lithium ion battery and mutual cooperation of the electrolyte and the diaphragm, the high-temperature cycle performance of the battery is improved, the thermal runaway risk is reduced, and meanwhile, the lithium ion battery has the advantage of low-temperature performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium-ion battery and electrical equipment thereof. Background Art

[0002] The growing demand for high-energy-density lithium-ion batteries poses a greater challenge to their electrical performance. Increasing the battery's operating voltage can effectively increase its energy density, but it can lead to structural instability in the cathode active material, significantly affecting the battery's high-temperature cycling performance and thermal safety.

[0003] Therefore, there is an urgent need to improve the high-temperature cycling performance and thermal safety performance of batteries under high voltage. Summary of the Invention

[0004] In view of this, the present invention provides a lithium-ion battery to solve the problems of poor high-temperature cycle performance caused by the high voltage of the battery system, large thickness expansion, and thermal safety hazards caused by the generation of gas by-products; thereby improving high-temperature cycle performance, reducing the generation of gas by-products and reducing the risk of thermal runaway.

[0005] In a first aspect, the present invention provides a lithium-ion battery comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte;

[0006] The electrolyte includes a phosphorus-containing trinitrile added in an amount of 0.1 wt% to 5 wt%; the phosphorus-containing trinitrile includes a structure shown in Formula 1;

[0007] Formula 1: wherein R1, R2, and R3 are each independently selected from O, substituted or unsubstituted C0-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, or substituted or unsubstituted C2-C10 alkenyl, and the substituent is halogen;

[0008] The diaphragm includes a base film and a coating located on at least one surface of the base film. The coating includes nitrogen-containing organic particles, and the content of nitrogen in the coating is 5wt% to 60wt%.

[0009] In an optional embodiment, the phosphorus-containing trinitrile comprises at least one of the following structures:

[0010] Formula 1-1:

[0011] Formula 1-2:

[0012] Formula 1-3:

[0013] In an optional embodiment, the nitrogen-containing organic particles include at least one of melamine cyanurate, melamine polyphosphate, melamine thiocyanate, piperazine pyrophosphate, urea-formaldehyde resin, melamine formal resin, polyacrylonitrile, 1,3,5-triazine-2,4,6-triamine, polyacrylamide, polyamide, polyimide, polyaniline, polypyrrole, polyurethane, and polyurea.

[0014] In an optional embodiment, the particle size D1 of the nitrogen-containing organic particles is 0.2 μm to 5 μm, preferably, D1 is 0.2 μm to 3 μm.

[0015] In an optional embodiment, the diaphragm further comprises a glue layer, the glue layer is arranged on a side of the coating layer away from the base film, and the glue layer comprises polymer particles;

[0016] Preferably, the polymer particles include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polystyrene, polyacrylate, polyacrylic acid, polyacrylonitrile, polymethyl methacrylate, polyvinyl pyrrolidone, polyvinyl acetate, an ethylene-vinyl acetate copolymer, polyimide, polyphenylene phthalate, an acrylonitrile-styrene-butadiene copolymer, polyvinyl alcohol, and a styrene-butadiene copolymer.

[0017] In an optional embodiment, the coverage of the adhesive layer on the base film is 10% to 90%, preferably 20% to 75%;

[0018] And / or, the particle size D2 of the polymer particles is 0.1 μm to 10 μm, preferably 0.1 to 5 μm.

[0019] In an optional embodiment, the thickness T of the coating is 0.2 μm to 5 μm.

[0020] In an optional embodiment, the electrolyte includes a carbonate solvent, and when the carbonate solvent includes ethylene carbonate (EC), the content of ethylene carbonate in the electrolyte is less than or equal to 15 wt %.

[0021] In an optional embodiment, the electrolyte includes ethyl difluoroacetate (DFEA), preferably, the ethyl difluoroacetate includes at least one of 2,2-difluoroethyl acetate and ethyl 2,2-difluoroacetate;

[0022] Preferably, the content S2 of ethyl difluoroacetate satisfies 3wt% <S2<50wt%。

[0023] In a second aspect, the present invention provides an electrical device comprising the above-mentioned lithium-ion battery.

[0024] Beneficial effects:

[0025] The lithium-ion battery provided by the present invention comprises: a positive electrode, a negative electrode, a separator, and an electrolyte; the electrolyte includes a phosphorus-containing trinitrile added in an amount of 0.1wt% to 5wt%; the separator comprises a base membrane and a coating located on at least one surface of the base membrane, the coating including nitrogen-containing organic particles, wherein the nitrogen content of the coating is 5wt% to 60wt%. The present invention uses a coating-modified separator with nitrogen-containing organic particles. The nitrogen-containing organic particles can significantly enhance the battery's flame retardancy, improve the battery's high-temperature performance, and suppress thermal runaway. However, the nitrogen-containing organic particles in the separator are prone to react with acidic substances generated in the electrolyte, causing partial failure, which can significantly reduce the separator's improvements in high-temperature cycling performance and thermal safety performance. After adding the phosphorus-containing trinitrile to the electrolyte of the present invention, the P-containing and cyano (-CN) functional groups in the phosphorus-containing trinitrile compound have strong coordination ability, which can capture Lewis acidic substances in the electrolyte, such as phosphorus pentafluoride (PF5). By capturing PF5, the generation of HF is further effectively reduced, thereby reducing the consumption of nitrogen-containing organic particles by acid, maintaining the long-term flame retardant effect of the diaphragm, improving high-temperature cycle performance, and reducing the risk of thermal runaway. DETAILED DESCRIPTION

[0026] 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 those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0027] The following describes an embodiment of the present invention in conjunction with the following schemes.

[0028] According to an embodiment of the present invention, on the one hand, a lithium-ion battery is provided, comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the electrolyte comprises a phosphorus-containing trinitrile added in an amount of 0.1 wt% to 5 wt%; the separator comprises a base film and a coating located on at least one surface of the base film, the coating comprising nitrogen-containing organic particles, and the content of nitrogen in the coating is 5 wt% to 60 wt%.

[0029] The present invention provides a lithium-ion battery that uses a modified diaphragm with a coating containing nitrogen-containing organic particles. The nitrogen-containing organic particles significantly improve the flame retardancy of the battery and suppress the thermal runaway problem of the battery. However, the nitrogen-containing organic particles in the diaphragm easily react with acidic substances generated in the electrolyte, causing partial failure, which greatly reduces the improvement of the diaphragm's high-temperature cycle performance and thermal safety performance. After adding phosphorus-containing trinitrile to the electrolyte of the present invention, the P-containing and cyano (-CN) functional groups in the phosphorus-containing trinitrile compound have strong coordination ability and can capture Lewis acidic substances in the electrolyte, such as phosphorus pentafluoride (PF5). By capturing PF5, the generation of HF is further effectively reduced, thereby reducing the consumption of nitrogen-containing organic particles by acid, maintaining the long-term flame retardant effect of the diaphragm, improving high-temperature cycle performance, and reducing the risk of thermal runaway.

[0030] If the amount of phosphorus-containing trinitrile added to the electrolyte of the present invention is too small, a continuous SEI film cannot be formed, and the Lewis acidic substances are insufficiently captured, affecting the high-temperature cycle performance; if the amount of phosphorus-containing trinitrile added is too large, its impedance increases, resulting in an increase in the desolvation energy barrier of the electrolyte and an aggravation of side reactions; at the same time, if the content of nitrogen in the coating of the present invention is too large, the mechanical properties of the diaphragm will be reduced; if the content of nitrogen in the coating is too small, the effect of inhibiting high-temperature heat generation reactions is weak.

[0031] As an example, the amount of phosphorus-containing trinitrile added to the electrolyte can be 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt% or within the range of any two of the above values; the nitrogen content in the coating can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 60wt% or within the range of any two of the above values.

[0032] In summary, the present invention achieves the advantages of improving the high-temperature performance of the battery while taking into account the thermal safety performance through the optimization of the above-mentioned electrolyte and separator, which cooperate with each other.

[0033] In an optional embodiment, the phosphorus-containing trinitrile comprises a structure shown in Formula 1;

[0034] Formula 1: Wherein, R1, R2, and R3 are each independently selected from O, substituted or unsubstituted C0-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, or substituted or unsubstituted C2-C10 alkenyl, and the substituent is halogen; when R1, R2, and R3 are selected from C0 alkyl, the structure of Formula 1 is

[0035] Preferably, the phosphorus-containing trinitrile comprises at least one of the following structures:

[0036] Formula 1-1:

[0037] Formula 1-2:

[0038] Formula 1-3:

[0039] The phosphorus-containing trinitrile of the structure added to the electrolyte of the present invention can form a CEI film containing P=O bonds on the surface of the positive electrode, thereby inhibiting the transition metal (such as Co) in the positive electrode. 3+ ) dissolution; the use of phosphorus-containing trinitrile can also inhibit the surge in SEI impedance of the negative electrode after cycling, thereby reducing the aggravated expansion of the negative electrode, further improving the high-temperature cycle performance and flame retardancy of the battery, and inhibiting the thermal runaway of the battery.

[0040] In an optional embodiment, the nitrogen-containing organic particles include at least one of melamine cyanurate, melamine polyphosphate, melamine thiocyanate, piperazine pyrophosphate, urea-formaldehyde resin, melamine formal resin, polyacrylonitrile, 1,3,5-triazine-2,4,6-triamine, polyacrylamide, polyamide, polyimide, polyaniline, polypyrrole, polyurethane, and polyurea.

[0041] The present invention achieves the goal of improving the high-temperature performance and thermal safety of the battery through the mutual cooperation of the above-mentioned electrolyte and separator, while also having the advantage of taking into account the low-temperature performance.

[0042] In an optional embodiment, the particle size D1 of the nitrogen-containing organic particles is 0.2μm to 5μm, preferably, D1 is 0.2μm to 3μm; in the present invention, the smaller the particle size of the nitrogen-containing organic particles, the larger their specific surface area, which is more conducive to accelerating electrolyte infiltration, but correspondingly, the mechanical strength is weak, affecting the cycle performance; the larger the particle size, the better its mechanical strength, but the smaller the specific surface area, which affects the wettability. Therefore, the particle size D1 of the nitrogen-containing organic particles in the present invention is set to 0.2μm to 5μm, preferably, D1 is 0.2μm to 3μm. By limiting the particle size of the nitrogen-containing organic particles, the adsorption capacity, electrolyte infiltration and thermal stability are effectively improved.

[0043] As an example, the particle size D1 of the nitrogen-containing organic particles can be set to 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or within the range of any two of the above values.

[0044] The particle size of the nitrogen-containing organic particles is the particle size at which 50% of the volume is accumulated, starting from the smallest particle size in a volume-based particle size distribution. For example, the following method can be used for testing: a sample on the coating is scraped off the substrate, dispersed in a solvent (such as water or ethanol), and ultrasonically treated to prevent agglomeration; and then measured using a laser particle size analyzer (such as a Malvern Mastersizer).

[0045] In an optional embodiment, the diaphragm further comprises an adhesive layer, wherein the adhesive layer is arranged on a side of the coating away from the base film, and the adhesive layer comprises polymer particles, and the polymer particles comprise at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polystyrene, polyacrylate, polyacrylic acid, polyacrylonitrile, polymethyl methacrylate, polyvinyl pyrrolidone, polyvinyl acetate, a copolymer of ethylene and vinyl acetate, polyimide, polyphenylene phthalate, a copolymer of acrylonitrile, styrene and butadiene, polyvinyl alcohol, and a copolymer of styrene and butadiene.

[0046] In an optional embodiment, the coverage of the adhesive layer on the base film is 10% to 90%, preferably 20% to 75%. This coverage can improve the wettability of the electrolyte to the separator and electrode, ion transport performance, and ensure the bonding strength of the electrodes, thereby increasing the migration speed of lithium ions, reducing the internal resistance of the battery, and improving high-temperature cycling stability.

[0047] In the present invention, when the coverage is too low, for example, when the coverage is less than 10%, it may lead to insufficient bonding between the separator and the positive and negative electrodes. When the coverage is too high, for example, when the coverage is greater than 90%, the excessively high coverage may increase the resistance to ion transport and increase the impedance. Therefore, the coverage of the coating on the base film in the present invention is set to 10% to 90%, preferably 20% to 75%.

[0048] As an example, the coverage of the coating on the base film can be set to 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or within a range consisting of any two of the above values.

[0049] The coverage of the adhesive layer on the base film is tested using the following method:

[0050] 1) Sampling: Cut a sample of 10 mm × 10 mm from the diaphragm material;

[0051] 2) Cleaning: Place the sample in an ultrasonic cleaner and clean it with anhydrous ethanol for 5 minutes to remove surface contaminants;

[0052] 3) Drying: Place the sample in an oven at 50°C for 30 minutes to ensure that there is no residual solvent on the surface;

[0053] 4) Place the sample: Fix the sample on the microscope stage and ensure the surface is flat;

[0054] 5) Adjust parameters: Set the microscope magnification to 200× and adjust the focus until the adhesive layer is clearly visible;

[0055] 6) Image capture: randomly select five areas on the sample surface and capture high-resolution images (e.g., 1024×1024 pixels) of each area;

[0056] 7) Image import: Import the captured images into image analysis software (such as ImageJ);

[0057] 8) Threshold segmentation: Set the threshold by grayscale value to distinguish the adhesive layer area from the substrate area;

[0058] 9) Area calculation: Click the software menu option Per Areas to directly output the coverage result;

[0059] 10) Multiple measurements: Calculate the coverage of 5 areas of each sample separately, take the average value and record the final result.

[0060] The particle size D2 of the polymer particles is 0.1 μm to 10 μm, preferably 0.1 to 5 μm. The present invention limits the particle size D2 of the polymer particles to ensure the cycle stability of the battery while further improving the safety of the battery.

[0061] Controlling the particle size of the polymer particles in the adhesive layer of the present invention within the aforementioned range not only increases the specific surface area of ​​the material, increasing the contact area between the electrolyte and the electrode, facilitating charge transfer, reducing electrode resistance, and helping to mitigate side reactions, but also forms an effective heat conduction channel, dissipating heat promptly and reducing heat and gas production during the battery's charge and discharge processes. Therefore, by controlling the particle size of the polymer particles within the range of 0.1 ≤ D2 ≤ 10 μm, the present invention further enhances the thermal stability of the battery while maintaining mechanical strength.

[0062] As an example, the particle size D2 of the polymer particles can be set to 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or within a range formed by any two of the above values.

[0063] In an optional embodiment, the thickness T of the coating is 0.2 μm to 5 μm. By limiting the thickness of the coating, electrolyte infiltration and thermal stability are effectively enhanced.

[0064] As an example, the thickness T of the coating can be set to 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or within the range composed of any two of the above values.

[0065] In an optional embodiment, the electrolyte includes a carbonate solvent. When ethylene carbonate (EC) is included in the carbonate solvent, the content of ethylene carbonate in the electrolyte is less than or equal to 15 wt%.

[0066] When the EC content in the electrolyte of the present invention is too high, since EC has a low oxidation resistance potential, gas is easily generated. By controlling the EC content in the electrolyte to be less than or equal to 15%, side reactions can be further reduced and gas generation can be decreased.

[0067] As an example, the EC content in the electrolyte can be set to 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or within the range composed of any two of the above values.

[0068] In an optional embodiment, the electrolyte includes ethyl difluoroacetate (DFEA). Preferably, the ethyl difluoroacetate includes at least one of 2,2-difluoroethyl acetate and ethyl 2,2-difluoroacetate; the content of the ethyl difluoroacetate is S2, satisfying 3 wt% < S2 < 50 wt%. The present invention improves the low-temperature performance through DFEA.

[0069] The fluorine atoms in DFEA can effectively weaken the interaction between Li+ and the solvent, promoting the desolvation process at low temperatures. This solvation effect helps to improve the performance of the battery under low-temperature conditions, enabling the battery to maintain a high discharge efficiency at lower temperatures.

[0070] As an example, the DFEA content in the electrolyte can be set to 3%, 5%, 7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50% or within the range composed of any two of the above values.

[0071]

Electrolyte

[0072] The electrolyte of the present invention is a non-aqueous electrolyte, and the electrolyte further includes other organic solvents, lithium salts, and other functional additives.

[0073] Among them, other organic solvents can be selected from carbonate solvents and / or carboxylate solvents. Carbonate solvents can be selected from propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and one or more fluorinated compounds of the above solvents; carboxylate solvents can be selected from ethyl acetate (EA), propyl acetate, n-butyl acetate, isobutyl acetate, methyl propionate (MP), propyl propionate (PP), ethyl butyrate (EB), ethyl propionate (EP), methyl butyrate, ethyl butyrate and one or more fluorinated compounds of the above solvents.

[0074] Other functional additives include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), fluoroethylene carbonate (FEC), tetravinylsilane (TVS), tris(trimethylsilyl)borate (TMSB), hexamethyldisilazane (HMDS), fluorobenzene (FB), triphenyl phosphite (TPPi) or sulfur-containing polyheterocyclic compounds.

[0075] Sulfur-containing polyheterocyclic compounds:

[0076] Other functional additives may also include nitrile additives.

[0077] The nitrile additives include one or more of benzonitrile, p-toluonitrile, 3,5-difluorobenzonitrile, adiponitrile (AND), succinonitrile (SN), glutaronitrile, suberonitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrinitrile (HTCN), glycerol trinitrile, tris(2-cyanoethyl) phosphate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, ethoxy(pentafluoro)cyclotriphosphazene (PFPN), pentafluoro(phenoxy)cyclotriphosphazene, etc.

[0078] In the present application, the lithium salt or lithium salt additive may be selected from the electrolyte lithium salts conventionally used in the art, including but not limited to lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI) and lithium 4,5-dicyano-2-trifluoromethylimidazole (LiDTI), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate), lithium difluorobis(oxalatoborate), lithium hexafluorozirconate (LiZrF6), and lithium trifluoromethylsulfinate (LiCFSO).

[0079] [Diaphragm]

[0080] The coating of the diaphragm of the present invention is provided on a base film; the base film can be selected from base film materials commonly used in the art, including but not limited to one of polyethylene (PE), polypropylene (PP) and PE composite diaphragm.

[0081] The coating of the present invention includes not only nitrogen-containing organic particles but also a binder, and the binder includes at least one of polyacrylic acid, polyvinylidene fluoride, polyacrylate, lithium polyacrylate, styrene-butadiene rubber or sodium carboxymethyl cellulose.

[0082] The diaphragm of the present invention can be coated on one side or both sides by any coating process including gravure coating, transfer coating, dip coating and spray coating.

[0083]

Positive electrode

[0084] The positive electrode sheet of the present invention includes a current collector, a positive electrode active material, a conductive agent, and a binder. The positive electrode sheet includes a current collector and a positive electrode active material layer disposed on the surface of the current collector. The positive electrode active material layer includes, by weight, 80% to 99.8% of the positive electrode active material, 0.1% to 10% of the conductive agent, and 0.1% to 10% of the binder. Preferably, the positive electrode active material layer includes, by weight, 90% to 99.6% of the positive electrode active material, 0.2% to 5% of the conductive agent, and 0.2% to 5% of the binder.

[0085] The positive electrode active material of the present invention may include at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary material, lithium iron phosphate, lithium manganese oxide, etc.

[0086] In the present invention, the positive electrode active material preferably includes lithium cobalt oxide, which can adapt to a higher voltage platform.

[0087] The present invention does not particularly limit the conductive agent in the positive electrode sheet, which can be selected from conductive agents commonly used in the art, including but not limited to one or more of acetylene black, conductive carbon black, Ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers, and graphene.

[0088] The present invention does not particularly limit the binder in the positive electrode sheet, which can be selected from binders commonly used in the art, including but not limited to one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene oxide.

[0089]

Negative electrode

[0090] The negative electrode sheet of the present invention includes a current collector, a negative electrode active material, a conductive agent, and a binder. The negative electrode sheet includes a current collector and a negative electrode active material layer arranged on the surface of the current collector; in the negative electrode active material layer, the negative electrode active material accounts for 80wt% to 98.5wt% of the mass of the negative electrode active material layer, the conductive agent accounts for 0.1wt% to 10wt% of the mass of the negative electrode active material layer, and the binder accounts for 0.1wt% to 10wt% of the mass of the negative electrode active material layer.

[0091] According to the battery of the present invention, the negative electrode active material includes at least one of graphite, silicon-based materials, and the like.

[0092] According to the battery of the present invention, the conductive agent is selected from at least one of acetylene black, conductive carbon black, Ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers, and graphene.

[0093] According to the battery of the present invention, the binder is at least one selected from polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene oxide.

[0094] The present invention does not impose any particular limitation on the types of the conductive agent and the binder in the negative electrode sheet. The selection range thereof can refer to the types of the conductive agent and the binder in the positive electrode sheet, and will not be further described here.

[0095] The lithium-ion battery provided by the present invention will be further described in detail below through specific examples.

[0096] Unless otherwise specified, the reagents, materials, and instruments used in the following examples are conventional reagents, conventional materials, and conventional instruments in the art and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0097] According to an embodiment of the present invention, in another aspect, the present invention further provides an electrical device comprising the above-mentioned lithium-ion battery.

[0098] Examples and Comparative Examples

[0099] A lithium-ion battery, the specific preparation process is as follows:

[0100] 1. Preparation of positive electrode sheet: The positive electrode active material LiCoO2, the conductive agent carbon black, and the binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a mass ratio of 97.8:1.1:1.1, and fully stirred to form a uniform positive electrode slurry with a solid content of 75%. The positive electrode slurry is coated on the current collector of the positive electrode sheet, and the positive electrode sheet is obtained after drying, rolling, and cutting.

[0101] 2. Preparation of negative electrode sheet: artificial graphite, silicon-carbon material (silicon content of silicon-carbon material is 60%), conductive agent carbon black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are dispersed in an appropriate amount of deionized water in a weight ratio of 90.3:7:0.8:1.1:0.8, and stirred thoroughly to form a uniform negative electrode slurry with a solid content of 75%. The negative electrode slurry is coated on the negative electrode current collector copper foil, and then dried, rolled, and cut to obtain the negative electrode sheet.

[0102] 3. Preparation of electrolyte: In an argon-filled glove box (H2O <0.1ppm, O2 <0.1ppm), PC / EP / PP were mixed in a mass ratio of 1 / 1 / 4, and then 14% of fully dried lithium hexafluorophosphate (LiPF6) and 5% LiTFSI based on the total mass of the electrolyte were added. After dissolution, 14wt% of FEC, 1wt% SN, 1.5wt% HTCN, 1wt% of phosphorus-containing trinitrile with the structure shown in Formula 1-1, 2wt% PS, 0.2wt% PST, 0.3wt% LiODFB, 6.1wt% 2,2-difluoroethyl acetate (DFEA), and 7.3wt% EC were added and stirred evenly. After passing the moisture and free acid tests, the required non-aqueous electrolyte was obtained.

[0103] 4. Preparation of a diaphragm containing a coating: The coating slurry is coated on a PE diaphragm substrate using a gravure coating process. After drying, a diaphragm containing a coating (thickness 1 μm) is obtained, and then a glue layer is coated on the surface of the coating; the coating slurry includes nitrogen-containing organic particles and a binder (the ratio of the content of nitrogen-containing organic particles to the binder is 95:5), the nitrogen-containing organic particles are melamine cyanurate particles (particle size D1 is 0.5 μm), the binder is polyacrylic acid, and the polymer particles included in the glue layer are polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA), with a particle size D2 of about 0.6 μm. The content of nitrogen in the coating is controlled by adjusting the mass ratio of the nitrogen-containing organic particles and the binder in the coating. The content of nitrogen in the coating of Example 1 is 46.9 wt%; the coverage of the glue layer on the base film is 60%.

[0104] 5. Preparation of lithium-ion batteries: Place the above-mentioned positive electrode, negative electrode and separator in order, so that the separator is between the positive and negative electrodes, and then weld the tabs and wind to obtain a core. Then place the core in an aluminum-plastic film packaging bag, and then carry out the processes of liquid injection, formation, secondary sealing, and sorting to prepare a lithium-ion battery. Finally, the electrical performance of the battery is tested.

[0105] The prepared examples and comparative examples were subjected to 0°C low-temperature cycle performance, 45°C high-temperature cycle performance, and 128°C thermal shock test tests. The specific test process is as follows:

[0106] 1. Test of low temperature cycle performance at 0℃

[0107] After standing at 0°C for 4 hours, discharge the battery at 0.2C to 3.0V at a temperature of 0±2°C. Let it stand for 10 minutes. Charge at a constant current of 0.34C to the upper limit voltage (4.53V). Then charge at a constant voltage of 4.53V to 0.05C. Discharge at a constant current of 0.5C to 3.0V and let it stand for 10 minutes. This constitutes one charge-discharge cycle, and the charge-discharge cycle is repeated 150 times. The highest discharge capacity of the first three cycles is recorded as the initial capacity Q1, and the discharge capacity at the 150th cycle is recorded as Q2. Calculate the battery's capacity retention rate = Q2 / Q1 × 100%.

[0108] 2. High temperature cycle performance at 45°C

[0109] After standing at 45°C for 2 hours, when the battery temperature is 45±2°C, discharge at 0.2C to 3.0V; let it stand for 10 minutes; charge at 2C to 4.25V (current cutoff at 1.5C), then transfer to 1.5C to fully charge (cutoff at 0.05C) to the upper limit voltage (4.53V), then charge at 4.53V constant voltage to 0.05C, then discharge at 1C to 3.5V, then transfer to 0.7C to 3V, and let it stand for 5 minutes. This is one charge and discharge cycle, and the charge and discharge cycles are 500 times. The highest discharge capacity of the first three cycles is recorded as the initial capacity Q3 and thickness H1, and the discharge capacity of the 500th cycle is recorded as Q4 and thickness H2. Calculate the battery capacity retention rate = Q4 / Q3×100%, and the expansion rate % = 1-H2 / H1.

[0110] 3. 128℃ thermal shock test

[0111] First, the battery is charged at a constant current and constant voltage of 0.7C to the upper voltage limit, with a cutoff current of 0.05C. The initial state of the battery, including voltage, internal resistance, and thickness, is tested. The battery is then placed in a convection or circulating hot air oven and heated at an initial temperature of 25±3°C at a rate of 5±2°C. The temperature is raised to 128±2°C and held for 60 minutes before the test is concluded. The passing standard for the 128°C thermal shock test is that the battery cell does not ignite or explode.

[0112] In conjunction with Table 1 below, through several groups of test examples, the low-temperature capacity retention rate / %, high-temperature capacity retention rate / % and 128°C thermal shock test of the lithium-ion batteries provided by the embodiments of the present invention and the comparative examples were verified for different amounts of phosphorus-containing trinitrile added to the electrolyte and different nitrogen content ratios in the coating. Among them, the different nitrogen content ratios in the coating were obtained by adjusting the content ratio of nitrogen-containing organic particles and binder. Specifically, the nitrogen-containing organic particles were melamine cyanurate particles, and the nitrogen content ratio in the melamine cyanurate particles was 49.4%. Converted to the nitrogen content ratio in the coating in Table 1, the content ratio of nitrogen-containing organic particles to binder in Examples 1-4 was 95:5, the content ratio of nitrogen-containing organic particles to binder in Example 5 was 10:90, and the content ratio of nitrogen-containing organic particles to binder in Example 6 was 61:39.

[0113] Table 1

[0114]

[0115]

[0116] In Comparative Example 1, the nitrogen content of the coating is 0%, that is, the coating is entirely a binder; in Comparative Example 3, ordinary ceramic particles of the same particle size are used to replace the nitrogen-containing organic particles, so that the nitrogen content of the coating is 0%.

[0117] It can be seen from Table 1 above that by optimizing the electrolyte and the diaphragm, they work together to improve the high-temperature cycle performance of the lithium cobalt oxide battery, inhibit thickness expansion and improve safety, while also having the advantage of taking into account low-temperature performance.

[0118] In conjunction with Table 2 below, through several groups of test examples, the low-temperature capacity retention rate / %, high-temperature capacity retention rate / % and 128°C thermal shock test of the lithium-ion batteries provided in the embodiments of the present invention and the comparative examples were verified for different DFEA contents and EC contents in the electrolyte, and different coating thicknesses T, coating coverage on the base film, and types of nitrogen-containing organic particles in the coating.

[0119] Table 2

[0120]

[0121]

[0122] In the embodiments of Table 2 above, in addition to the variables listed in the table, in Example 19, the content ratio of the nitrogen-containing organic particles and the binder is controlled to be 90:10 so that the content of nitrogen in the coating accounts for 60%, in Example 18, the content ratio of the nitrogen-containing organic particles and the binder is controlled to be 95:5 so that the content of nitrogen in the coating accounts for 22.2%, and in Example 20, the content ratio of the nitrogen-containing organic particles and the binder is controlled to be 95:5 so that the content of nitrogen in the coating accounts for 15.4%. Other parameter conditions are the same as in Example 1.

[0123] As can be seen from Table 2 above, controlling the DFEA content, EC content, coating thickness, coating coverage on the base film, and the type of nitrogen-containing organic particles within the scope of this application has no significant effect on performance, and can all achieve the advantages of improving the high-temperature cycle performance of lithium cobalt oxide system batteries, inhibiting thickness expansion, and improving safety, while also having the advantage of taking into account low-temperature performance.

[0124] In conjunction with Table 3 below, through several groups of test examples, different particle sizes D1 of nitrogen-containing organic particles and particle sizes D2 of polymer particles in the coating were used to verify the low-temperature capacity retention rate / %, high-temperature capacity retention rate / % and 128°C thermal shock test of the lithium-ion batteries provided in the embodiments of the present invention and the comparative examples.

[0125] Table 3

[0126]

[0127] In the embodiment of Table 3 above, except for the variables listed in the table, other parameter conditions are the same as those in Example 1.

[0128] As can be seen from Table 3 above, controlling the particle size D1 of the nitrogen-containing organic particles and the particle size D2 of the polymer particles within the scope of this application has no significant effect on the performance, and both can achieve the advantages of improving the high-temperature cycle performance of the lithium cobalt oxide system battery, inhibiting thickness expansion and improving safety, while also having the advantage of taking into account low-temperature performance.

[0129] The embodiments of the present invention are described above. However, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A lithium-ion battery comprising: A positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; wherein the electrolyte comprises a phosphorus-containing trinitrile added in an amount of 0.1 wt% to 5 wt%, and the phosphorus-containing trinitrile comprises a structure shown in Formula 1; Formula 1: wherein R1, R2, and R3 are each independently selected from O, substituted or unsubstituted C0-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, or substituted or unsubstituted C2-C10 alkenyl, and the substituent is halogen; The diaphragm includes a base film and a coating located on at least one surface of the base film. The coating includes nitrogen-containing organic particles, and the content of nitrogen in the coating is 5wt% to 60wt%.

2. The lithium-ion battery according to claim 1, wherein The phosphorus-containing trinitrile comprises at least one of the following structures: Formula 1-1: Formula 1-2: Formula 1-3:

3. The lithium-ion battery according to claim 1, wherein The nitrogen-containing organic particles include at least one of melamine cyanurate, melamine polyphosphate, melamine thiocyanate, piperazine pyrophosphate, urea-formaldehyde resin, melamine formal resin, polyacrylonitrile, 1,3,5-triazine-2,4,6-triamine, polyacrylamide, polyamide, polyimide, polyaniline, polypyrrole, polyurethane, and polyurea.

4. The lithium-ion battery according to any one of claims 1 to 3, wherein: The average particle size D1 of the nitrogen-containing organic particles is 0.2 μm to 5 μm, preferably, D1 is 0.2 μm to 3 μm.

5. The lithium-ion battery according to any one of claims 1 to 4, characterized in that: The diaphragm further comprises a glue layer, which is arranged on a side of the coating layer away from the base film, and the glue layer comprises polymer particles; Preferably, the polymer particles include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trichloroethylene copolymer, polystyrene, polyacrylate, polyacrylic acid, polyacrylonitrile, polymethyl methacrylate, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyimide, polyphenylene phthalate, acrylonitrile-styrene-butadiene copolymer, polyvinyl alcohol and styrene-butadiene copolymer.

6. The lithium-ion battery according to claim 5, characterized in that The coverage of the adhesive layer on the base film is 10% to 90%, preferably 20% to 75%; And / or, the average particle size D2 of the polymer particles is 0.1 μm to 10 μm, preferably 0.1 to 5 μm.

7. The lithium-ion battery according to any one of claims 1 to 6, characterized in that: The thickness T of the coating is 0.2 μm to 5 μm.

8. The lithium-ion battery according to any one of claims 1 to 7, wherein: The electrolyte includes a carbonate solvent. When the carbonate solvent includes ethylene carbonate, the content of the ethylene carbonate in the electrolyte is less than or equal to 15 wt %.

9. The lithium-ion battery according to any one of claims 1 to 8, characterized in that: The electrolyte includes ethyl difluoroacetate; Preferably, the ethyl difluoroacetate includes at least one of 2,2-difluoroethyl acetate and ethyl 2,2-difluoroacetate; Preferably, the content S2 of ethyl difluoroacetate satisfies 3wt% <S2<50wt%。 10. An electrical device, characterized in that: A lithium-ion battery comprising the lithium-ion battery according to any one of claims 1 to 9.

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