Battery cell, lithium ion battery comprising same and electronic equipment

Abstract

The invention discloses a battery cell, a lithium ion battery containing the same and electronic equipment. Electrolyte is injected into the battery cell by adopting a one-two injection scheme, the electrolyte comprises a one-injection electrolyte and a two-injection electrolyte, the two-injection electrolyte comprises bis (trifluoromethylsulfonyl) lithium imide and / or difluorosulfamide lithium, the content of bis (trifluoromethylsulfonyl) lithium imide and / or difluorosulfamide lithium is 1-10%, and the content of bis (trifluoromethylsulfonyl) lithium imide and / or difluorosulfamide lithium is 1-10%. The percentage is the mass percentage of the secondary injection electrolyte; and the positive electrode material layer of the positive plate of the battery cell comprises lithium iron phosphate and an overcharge-proof material. The battery cell is relatively good in safety performance and excellent in cycle performance.

Description

Technical Field

[0001] The invention relates to an electric core and a lithium ion battery and electronic equipment containing the same. Background Art

[0002] As the market demand for energy storage cells grows, the capacity of lithium iron phosphate energy storage cells is gradually increasing, and the energy density is constantly improving, but the accompanying battery safety and long cycle life will be reduced accordingly, which is not conducive to the application of the battery cells in the market.

[0003] Existing technologies often improve battery safety by using safety diaphragms, using ceramic coatings on diaphragms, or by adjusting the electrolyte formula, especially during thermal runaway and overcharging, to reduce the total amount of heat generated by the battery, and ultimately obtain a safer battery. However, this method often has many disadvantages. For example, after using a diaphragm with a ceramic coating, the cost will increase significantly, and the performance will deteriorate slightly; while improving the electrolyte, while improving the safety performance, the electrochemical performance will deteriorate, especially the long-term performance of the battery, including the battery's cycle life and storage performance, which are difficult to take into account well. Summary of the invention

[0004] In order to solve the problem that existing battery cells cannot improve safety performance while taking into account excellent cycle performance, the present invention provides a battery cell and a lithium ion battery and electronic device containing the same. The battery cell has good safety performance and can take into account excellent cycle performance.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions.

[0006] In a first aspect, the present invention provides a battery cell, wherein the battery cell adopts a one-two injection scheme to inject an electrolyte, wherein the electrolyte comprises a one-injection electrolyte and a two-injection electrolyte, wherein the two-injection electrolyte comprises lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide, and the content of the lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide is 1%-10%, where the percentage is the mass percentage of the two-injection electrolyte;

[0007] The positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and anti-overcharge material; the anti-overcharge material meets the following requirements: when the test battery cell is overcharged according to the battery cell overcharge test method in GB / T 36276-2023, the maximum voltage after overcharge for 0.5 hours does not exceed 5V, wherein the content of lithium iron phosphate in the positive electrode material layer of the test battery cell is greater than or equal to 90%, and the content of the anti-overcharge material is 0.1%, and the percentage is the mass percentage of the positive electrode material layer.

[0008] In a second aspect, the present invention provides a lithium-ion battery comprising the battery cell as described above.

[0009] In a third aspect, the present invention provides an electronic device comprising the lithium-ion battery as described above.

[0010] The positive and progressive effects of the present invention are:

[0011] The present invention aims at the problem that lithium ion batteries using lithium iron phosphate as positive electrode active material have poor safety performance and cannot take into account excellent cycle performance. On the one hand, a one-two injection scheme is adopted to inject electrolyte, and lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide are added to the two injections of electrolyte; on the other hand, an anti-overcharge material is added to the positive electrode material layer of the battery cell, and the obtained battery cell has the following advantages:

[0012] (1) Good safety performance: The battery cell can pass the overcharge test and thermal runaway test, and the maximum temperature of the thermal runaway battery cell can be lower than 520°C;

[0013] (2) It can also provide excellent cycle performance: the capacity retention rate after 500 cycles at room temperature can reach over 96.8%. DETAILED DESCRIPTION

[0014] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0015] Battery Cell

[0016] In the battery cell provided in the first aspect of the present invention, the battery cell adopts a one-two injection scheme to inject electrolyte, and the electrolyte includes a one-injection electrolyte and a two-injection electrolyte, wherein the two-injection electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide, and the content of lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide is 1%-10%, and the percentage is the mass percentage of the two-injection electrolyte;

[0017] The positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and anti-overcharge material; the anti-overcharge material meets the following requirements: when the test battery cell is overcharged according to the battery cell overcharge test method in GB / T 36276-2023, the maximum voltage after overcharge for 0.5 hours does not exceed 5V, wherein the content of lithium iron phosphate in the positive electrode material layer of the test battery cell is greater than or equal to 90%, and the content of the anti-overcharge material is 0.1%, and the percentage is the mass percentage of the positive electrode material layer.

[0018] In some optional embodiments, the anti-overcharge material includes FeP, Fe2P, Fe3P, FeN4, Fe2N and Fe 16 One or more of N2.

[0019] In some optional embodiments, the ratio of the Dv50 particle size of the anti-overcharge material to the Dv50 particle size of the lithium iron phosphate is (0.4-0.9):1, preferably (0.5-0.7):1, for example, 0.41:1.

[0020] In some optional embodiments, the Dv50 of the anti-overcharge material is 0.2-5 μm, preferably 0.5-3 μm, for example 1.87 μm.

[0021] In some optional embodiments, the content of the overcharge prevention material is 0.01%-0.25%, preferably 0.02%-0.08%, for example 0.05%, where the percentage is the mass percentage of the positive electrode material layer.

[0022] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP; wherein the content of the FeP is, for example, 0.05%, and the content of the lithium iron phosphate is, for example, 97.25%.

[0023] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP; wherein the content of the FeP is, for example, 0.02%, and the content of the lithium iron phosphate is, for example, 97.28%.

[0024] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP; wherein the content of the FeP is, for example, 0.08%, and the content of the lithium iron phosphate is, for example, 97.22%.

[0025] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP; wherein the content of the FeP is, for example, 0.01%, and the content of the lithium iron phosphate is, for example, 97.29%.

[0026] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP; wherein the content of the FeP is, for example, 0.25%, and the content of the lithium iron phosphate is, for example, 97.05%.

[0027] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and Fe2P; wherein the content of the Fe2P is, for example, 0.05%, and the content of the lithium iron phosphate is, for example, 97.25%.

[0028] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeN4; wherein the content of the FeN4 is, for example, 0.05%, and the content of the lithium iron phosphate is, for example, 97.25%.

[0029] In some optional embodiments, the content of lithium iron phosphate is not less than 90%, for example, 97.05%, 97.22%, 97.25%, 97.28% or 97.29%, where the percentage is the mass percentage of the positive electrode material layer.

[0030] In some optional embodiments, the mass ratio of the anti-overcharge material to the lithium iron phosphate is 1:(320-9800), for example, 1:388, 1:1215, 1:1945, 1:4864 or 1:9729.

[0031] In some preferred embodiments, the content of lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide is 2%-5%.

[0032] In the present invention, the second electrolyte includes a second additive, a second lithium salt and a second solvent.

[0033] In some optional embodiments, the second additive includes vinylene carbonate, and the content of the vinylene carbonate is 5%-15%, preferably 7%-12%, for example 10%, where the percentage is the mass percentage of the second electrolyte.

[0034] In some optional embodiments, the second lithium salt includes lithium hexafluorophosphate.

[0035] In some preferred embodiments, the content of lithium hexafluorophosphate is 2%-11.5%, for example, 2.5%, 4.5%, 6.25%, 7.5%, 9.5% or 10.5%, where the percentage is the mass percentage of the second electrolyte.

[0036] In some optional embodiments, the second solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, propyl formate, propyl propionate and ethyl butyrate.

[0037] In the present invention, the electrolyte solution includes a first additive, a first lithium salt and a first solvent.

[0038] In some optional embodiments, the first lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0039] In a specific embodiment, the first lithium salt is lithium hexafluorophosphate.

[0040] In some optional embodiments, the first solvent includes one or more of ethylene carbonate (EC), propylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, propyl formate, propyl propionate and ethyl butyrate.

[0041] In some specific embodiments, the first solvent is ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate, and the mass ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate is, for example, 3:3:4.

[0042] In some optional embodiments, the first additive includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC) and diethylene sulfate (DTD); when the additive in the one injection of electrolyte includes vinylene carbonate, the content of vinylene carbonate may be 0.5%-4%, preferably 1%-3.5%, for example 2%, and the percentage is the mass percentage of the one injection of electrolyte.

[0043] In some specific embodiments, the first additive is vinylene carbonate, fluoroethylene carbonate and vinyl sulfate, and the mass ratio of vinylene carbonate, fluoroethylene carbonate and vinyl sulfate is 2:1:1.

[0044] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 6.25%, and the content of lithium hexafluorophosphate is, for example, 6.25%.

[0045] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and Fe2P, and the second injection electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of Fe2P is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 6.25%, and the content of lithium hexafluorophosphate is, for example, 6.25%.

[0046] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeN4, and the second injection electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeN4 is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 6.25%, and the content of lithium hexafluorophosphate is, for example, 6.25%.

[0047] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second injection electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.02%, the content of lithium iron phosphate is, for example, 97.28%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 6.25%, and the content of lithium hexafluorophosphate is, for example, 6.25%.

[0048] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.08%, the content of lithium iron phosphate is, for example, 97.22%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 6.25%, and the content of lithium hexafluorophosphate is, for example, 6.25%.

[0049] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.01%, the content of lithium iron phosphate is, for example, 97.29%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 6.25%, and the content of lithium hexafluorophosphate is, for example, 6.25%.

[0050] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.25%, the content of lithium iron phosphate is, for example, 97.05%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 6.25%, and the content of lithium hexafluorophosphate is, for example, 6.25%.

[0051] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 8%, and the content of lithium hexafluorophosphate is, for example, 4.5%.

[0052] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 3%, and the content of lithium hexafluorophosphate is, for example, 9.5%.

[0053] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 1%, and the content of lithium hexafluorophosphate is, for example, 11.5%.

[0054] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 10%, and the content of lithium hexafluorophosphate is, for example, 2.5%.

[0055] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 2%, and the content of lithium hexafluorophosphate is, for example, 10.5%.

[0056] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(trifluoromethylsulfonyl)imide is, for example, 5%, and the content of lithium hexafluorophosphate is, for example, 7.5%.

[0057] In some specific embodiments, the positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and FeP, and the second injection electrolyte includes lithium bis(fluorosulfonamide)imide and lithium hexafluorophosphate; wherein the content of FeP is, for example, 0.05%, the content of lithium iron phosphate is, for example, 97.25%, the content of lithium bis(fluorosulfonamide)imide is, for example, 6.25%, and the content of lithium hexafluorophosphate is, for example, 6.25%.

[0058] In some embodiments, the preparation method of the battery cell includes the following steps: winding the positive electrode sheet, separator and negative electrode sheet stacked in sequence, injecting a shot of electrolyte, performing formation and aging, injecting a second shot of electrolyte, and dividing the volume after heat sealing to obtain.

[0059] Positive electrode

[0060] In some optional embodiments, the positive electrode material layer further includes a binder.

[0061] The type of the binder is not particularly limited, and can be selected from polyvinylidene fluoride, polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonate, styrene-butadiene rubber (SBR), fluororubber and various copolymers, such as PVDF.

[0062] In some optional embodiments, the content of the binder is 1%-10%, for example, 1.8%, where the percentage is the percentage of the total mass of the positive electrode material layer.

[0063] In some optional embodiments, the positive electrode material layer further includes a conductive agent.

[0064] The type of the conductive agent is not particularly limited, and is a reagent used to ensure that the electrode has good charge and discharge performance. It can be selected from graphite materials such as natural graphite and artificial graphite, carbon black SP, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and other carbon black materials, carbon fibers, metal fibers and other conductive fibers, metal powders such as carbon fluoride powder, aluminum powder, nickel powder and other metal powders, zinc oxide, potassium titanate and other conductive whiskers, and titanium dioxide and other conductive metal oxides or polyphenylene derivatives.

[0065] In a specific embodiment, the conductive agent is conductive carbon SP.

[0066] In some optional embodiments, the content of the conductive agent is 0.2%-3%, for example, 0.9%, where the percentage is the percentage of the total mass of the positive electrode material layer.

[0067] In some specific embodiments, in the positive electrode material layer, the mass ratio of the lithium iron phosphate, the anti-overcharge material, the conductive agent and the binder is 97.25:0.05:0.9:1.8.

[0068] In the present invention, the positive electrode sheet of the battery cell includes a positive electrode current collector, and the positive electrode material layer is arranged on at least one surface of the positive electrode current collector.

[0069] Wherein, the positive electrode current collector may be a conventional positive electrode current collector in the art. The positive electrode current collector is a substrate supporting the positive electrode material layer, usually a metal foil with a thickness of 3-500 microns. There is no particular restriction on the material, as long as it has high conductivity and does not produce chemical reactions in the secondary battery system. For example, it can be a foil formed after surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The positive electrode current collector usually has a smooth surface, but fine lines can also be formed on its surface to increase the adhesion between the positive electrode material layer and the positive electrode current collector. In addition to the foil, the positive electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam or non-woven fabric. Generally, the positive electrode current collector is aluminum foil.

[0070] In some embodiments, the preparation method of the positive electrode sheet includes: fully stirring and mixing the components of the positive electrode material layer in a solvent to obtain a positive electrode slurry, coating it on at least one surface of the positive electrode collector, drying it, and rolling and compacting it.

[0071] In some optional embodiments, the solvent includes one or more of N-methylpyrrolidone (NMP), dimethyl carbonate, ethylene carbonate and diethylene carbonate, for example, NMP.

[0072] Negative plate

[0073] In the present invention, the negative electrode sheet in the battery cell comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector.

[0074] In the present invention, the negative electrode active material in the negative electrode material layer may be a conventional negative electrode active material of a lithium ion battery in the art. The negative electrode active material of the lithium ion battery may use a compound that can reversibly embed and deintercalate lithium. Specific examples include but are not limited to: carbon materials such as crystalline carbon (natural graphite and artificial graphite, etc.), amorphous carbon, carbon-coated graphite and resin-coated graphite, or oxide materials such as indium oxide, silicon oxide, tin oxide, lithium titanate, zinc oxide, lithium oxide, etc., or lithium metal or a metal material that can form an alloy with lithium; wherein the metal material that can form an alloy with lithium is, for example, Cu, Sn, Si, Co, Mn, Fe, Sb and Ag. Binary or ternary alloys containing these metals and lithium may also be used as negative electrode active materials. These negative electrode active materials may be used alone or in combination of two or more. From the perspective of high energy density, carbon materials such as graphite may also be used in combination with Si, Si alloys, Si oxides and other Si-based materials.

[0075] In some embodiments, the negative electrode active material includes any one of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxides, silicon carbon compounds, or lithium titanate, or a combination of at least two thereof.

[0076] In one specific embodiment, the negative electrode active material is artificial graphite.

[0077] In some embodiments, the negative electrode material layer further includes a thickener.

[0078] The addition of the thickener can increase the system viscosity of each component in the negative electrode slurry, and can be a thickener conventionally used in the art for preparing negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0079] In some embodiments, the negative electrode material layer further includes a conductive agent.

[0080] There are no particular restrictions on the conductive agent, as long as it has conductivity and does not cause chemical changes in the battery. For example, the conductive agent may be: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black (Super P), acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black or carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0081] In some embodiments, the negative electrode material layer further includes a binder.

[0082] The type of the binder is not particularly limited, and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonate, styrene-butadiene rubber (SBR), fluororubber and various copolymers, such as PAA and SBR.

[0083] In some specific embodiments, in the negative electrode material layer, the mass ratio of the negative electrode active material, the conductive agent, the binder and the thickener is 97.2:0.5:1.8:0.5.

[0084] In the present invention, the negative electrode current collector may be a conventional negative electrode current collector in the art. The negative electrode current collector is used as a substrate to support the negative electrode material layer, and is generally a metal foil having a thickness of 3-500 microns. There is no particular restriction on the material, as long as it has high conductivity and does not produce chemical reactions in the secondary battery system. For example, it can be a foil formed after surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The negative electrode current collector is generally a smooth surface, but fine lines may also be formed on its surface to increase the adhesion between the negative electrode material layer and the negative electrode current collector. In addition to the foil, the negative electrode current collector may also be used in any one or more combinations of various forms such as film, mesh, porous, foam or non-woven fabric. Generally, the negative electrode current collector is copper foil.

[0085] In some embodiments, the method for preparing the negative electrode sheet comprises the following steps: thoroughly stirring and mixing the components of the negative electrode material layer in a solvent to obtain a negative electrode slurry which is applied on at least one surface of the negative electrode current collector, dried, cold pressed, and cut.

[0086] Diaphragm

[0087] In the present invention, the separator in the battery cell may be a separator conventionally used in the art.

[0088] In some optional embodiments, the separator may be a polypropylene film or a polyethylene film.

[0089] Wherein, the air permeability of the diaphragm may be 180-380 s / 100mL.

[0090] Wherein, the porosity of the diaphragm may be 30%-50%.

[0091] Wherein, the thickness of the diaphragm may be 9-18 μm.

[0092] In a specific embodiment, the diaphragm is a polyethylene film; the thickness of the diaphragm is 11 μm; the air permeability of the diaphragm is 230 s / 100 mL; and the porosity of the diaphragm is 40%.

[0093] Lithium-ion battery

[0094] The lithium ion battery provided in the second aspect of the present invention comprises the battery cell as described above.

[0095] In the present invention, the lithium-ion battery is generally a square hard-shell battery, a soft-pack battery and a cylindrical battery.

[0096] In the present invention, the lithium ion battery can be prepared by conventional methods in the art.

[0097] Electronic devices

[0098] The electronic device provided in the third aspect of the present invention comprises the lithium-ion battery as described above.

[0099] Exemplarily, the electronic device described in the present invention may be, but is not limited to, mobile devices (such as mobile phones, tablet computers, laptop computers, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0100] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention. The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the embodiments described. The experimental methods in the following examples that do not specify specific conditions are selected according to conventional methods and conditions, or according to the product specifications. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.

[0101] Example 1

[0102] The preparation of the battery cell includes the following steps:

[0103] (1) Preparation of positive electrode sheet: The positive electrode active materials lithium iron phosphate (Dv50 particle size is 4.53 μm), polyvinylidene fluoride (PVDF), conductive carbon SP, and anti-overcharge material FeP (Dv50 particle size is 1.87 μm) are mixed evenly in a solvent N-methylpyrrolidone (NMP) (45 mass parts) in a mass ratio of lithium iron phosphate: PVDF: conductive carbon SP: anti-overcharge material FeP = 97.25:1.8:0.9:0.05 (a total of 100 mass parts). The resulting slurry is coated on an aluminum foil and dried to obtain a positive electrode sheet.

[0104] (2) Preparation of negative electrode sheet: The negative electrode active materials artificial graphite, polyacrylic acid (PAA), CMC, conductive carbon SP, and SBR were mixed evenly in a solvent deionized water (50 parts by mass) in a mass ratio of graphite: PAA: CMC: conductive carbon SP: SBR = 97.2:1.3:0.5:0.5:0.5 (a total of 100 parts by mass), and the resulting slurry was coated on a copper foil and dried to obtain a negative electrode sheet.

[0105] (3) Preparation of an electrolyte: In an argon atmosphere glove box with oxygen and water content less than 1 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 3:3:4 to obtain a mixed solvent. 1 mol / L lithium hexafluorophosphate was added as a conductive salt to the mixed solvent, and the mixture was dissolved and mixed evenly to obtain a salt solution without additives.

[0106] Additives were added to the salt solution obtained above, wherein the amount of vinylene carbonate (VC) added was 2%, the amount of fluoroethylene carbonate (FEC) added was 1%, and the amount of diethylene sulfate (DTD) added was 1%, and after mixing evenly, an electrolyte solution was obtained.

[0107] (4) Preparation of two injections of electrolyte: In an argon atmosphere glove box with oxygen and moisture content less than 1 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 3:3:4 to obtain a mixed solvent. A total of 62.5 g of lithium hexafluorophosphate and 62.5 g of lithium bis(trifluoromethylsulfonyl)imide were weighed and dissolved in the mixed solvent to mix evenly. The electrolyte additive VC was added to the mixed solution, and the solution was fixed to a volume of 1 L, wherein the mass content of lithium hexafluorophosphate was 6.25%, the mass content of lithium bis(trifluoromethylsulfonyl)imide was 6.25%, and the mass content of VC was 10%. Two injections of electrolyte were prepared.

[0108] (5) Preparation of battery cells: The positive electrode sheets, separators and negative electrode sheets stacked in sequence are wound into square shell battery cells. The battery cell capacity is designed to be 320Ah. A total of 950g of electrolyte is injected. After formation and aging, a second injection of electrolyte is injected, totaling 150g. After heat sealing, the capacity is divided to obtain a battery cell. Among them, the separator is a polyethylene film; the thickness of the separator is 11μm; the air permeability of the separator is 230s / 100mL; and the porosity of the separator is 40%.

[0109] Example 2-3

[0110] The anti-overcharge materials in the battery cells of Examples 2-3 are Fe2P and FeN4 (both with a Dv50 particle size of 1.87 μm), and the other conditions are the same as those of Example 1.

[0111] Example 4

[0112] The only difference between Example 4 and Example 1 is that the content of lithium iron phosphate is 97.28%, the content of the anti-overcharge material is 0.02%, and the other conditions are the same as those of Example 1.

[0113] Example 5

[0114] The only difference between Example 5 and Example 1 is that the content of lithium iron phosphate is 97.22%, the content of the anti-overcharge material is 0.08%, and the other conditions are the same as those of Example 1.

[0115] Example 6

[0116] The only difference between Example 6 and Example 1 is that the content of lithium iron phosphate is 97.29%, the content of the anti-overcharge material is 0.01%, and the other conditions are the same as those of Example 1.

[0117] Example 7

[0118] The only difference between Example 7 and Example 1 is that the content of lithium iron phosphate is 97.05%, the content of the anti-overcharge material is 0.25%, and the other conditions are the same as those of Example 1.

[0119] Example 8

[0120] The only difference between Example 8 and Example 1 is that the content of LiTFSI in the second injection of electrolyte is 8%, and the content of LiPF6 is 4.5%. The other conditions are the same as those in Example 1.

[0121] Example 9

[0122] The only difference between Example 9 and Example 1 is that the content of LiTFSI in the second injection of electrolyte is 3%, and the content of LiPF6 is 9.5%. The other conditions are the same as those in Example 1.

[0123] Example 10

[0124] The only difference between Example 10 and Example 1 is that the content of LiTFSI in the second injection of electrolyte is 1%, and the content of LiPF6 is 11.5%. The other conditions are the same as those in Example 1.

[0125] Embodiment 11

[0126] The only difference between Example 11 and Example 1 is that the content of LiTFSI in the second injection of electrolyte is 10%, and the content of LiPF6 is 2.5%. The other conditions are the same as those in Example 1.

[0127] Example 12

[0128] The only difference between Example 12 and Example 1 is that the content of LiTFSI in the second injection of electrolyte is 5%, and the content of LiPF6 is 7.5%. The other conditions are the same as those in Example 1.

[0129] Example 13

[0130] The only difference between Example 13 and Example 1 is that LiFSI is used to replace LiTFSI in the second injection of electrolyte, the content of LiFSI is 6.25%, and the other conditions are the same as those in Example 1.

[0131] Embodiment 14

[0132] The only difference between Example 14 and Example 1 is that the content of LiTFSI in the second injection of electrolyte is 2%, and the content of LiPF6 is 10.5%. The other conditions are the same as those in Example 1.

[0133] Comparative Example 1

[0134] The only difference between this comparative example and Example 1 is that the content of lithium iron phosphate is 97.3%, there is no overcharge prevention material, and the other conditions are the same as those of Example 1.

[0135] Comparative Example 2

[0136] The only difference between this comparative example and Example 1 is that the content of lithium iron phosphate is 97.3%, there is no overcharge protection material, the second injection electrolyte does not contain VC and LiTFSI, the content of LiPF6 is 12.5%, and the other conditions are the same as Example 1.

[0137] Comparative Example 3

[0138] The difference between this comparative example and Example 1 is that the anti-overcharge material uses lithium oxalate to replace FeP, and the content of lithium oxalate is 0.05%, and the other conditions are the same as those of Example 1. When lithium oxalate is used as the anti-overcharge material, lithium oxalate is easy to decompose, and does not meet the following conditions: when the test cell is overcharged according to the battery cell overcharge test method in GB / T 36276-2023, the maximum voltage after overcharging for 0.5 hours does not exceed 5V.

[0139] Comparative Example 4

[0140] The only difference between this comparative example and Example 1 is that the second electrolyte does not contain LiTFSI, the content of LiPF6 is 12.5%, and the other conditions are the same as those in Example 1.

[0141] Comparative Example 5

[0142] The only difference between this comparative example and Example 1 is that the content of LiTFSI in the second injection of electrolyte is 12.5%, and no LiPF6 is contained. The other conditions are the same as those in Example 1.

[0143] Comparative Example 6

[0144] The only difference between this comparative example and Example 1 is that the content of LiTFSI in the second injection of electrolyte is 0.5%, and the content of LiPF6 is 12%. The other conditions are the same as those in Example 1.

[0145] Effect Example 1

[0146] The battery cells obtained in Examples 1-14 and Comparative Examples 1-6 were subjected to overcharge tests and thermal runaway tests according to the national standard GB / T 36276-2023.

[0147] Effect Example 2

[0148] The battery cells prepared in Examples 1-14 and Comparative Examples 1-6 were tested for capacity retention after 500 cycles at room temperature. The test steps were as follows:

[0149] At 25°C, after 3 cycles of activation at 0.33C, charge to 80% SOC at 1C, charge 80%-100% SOC (3.65V) at 0.33C, and discharge to 2.5V at 1C. The capacity of the first cycle using this process is C 初 After 500 cycles of this process, the capacity is C n ; The capacity retention rate after 500 cycles at room temperature is C n / C 初 ×100%. The test results are shown in Table 1.

[0150]

[0151] As can be seen from Table 1, in Examples 1-14 of the present invention, on the basis of using lithium iron phosphate as the positive electrode active material, a specific type of anti-overcharge material is added to the positive electrode material layer of the battery cell, and the electrolyte is injected using a one-two injection scheme, and lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide is added to the two-injection electrolyte. The resulting battery cell has good overcharge performance and thermal runaway performance, and can take into account excellent cycle performance. Specifically, the battery cell can pass the overcharge test and thermal runaway test, the maximum temperature of the thermal runaway battery cell can be lower than 520°C, and the capacity retention rate of 500 cycles at room temperature can reach more than 96.8%.

[0152] Compared with Example 1, no anti-overcharge material is added to the battery cell of Comparative Example 1. Although the capacity retention rate after 500 cycles at room temperature is comparable and it can also pass the overcharge test and thermal runaway test, the maximum temperature of the thermal runaway battery cell increases significantly, and it is impossible to have both excellent safety performance and good performance.

[0153] Compared with Example 1, no anti-overcharge material is added to the battery cell of Comparative Example 2, and the second electrolyte does not contain LiTFSI. The capacity retention rate of the battery cell after 500 cycles at room temperature is significantly deteriorated, and it cannot pass the overcharge test and thermal runaway test. The maximum temperature of the thermal runaway battery cell is significantly increased, and it is impossible to take into account both excellent safety performance and cycle performance.

[0154] Compared with Example 1, the battery cell of Comparative Example 3 uses conventional lithium oxalate as an anti-overcharge material. The capacity retention rate of the battery cell after 500 cycles at room temperature is significantly deteriorated, and it cannot pass the overcharge test and thermal runaway test. The maximum temperature of the thermal runaway battery cell is significantly deteriorated, and it is impossible to take into account both excellent safety performance and cycle performance. This may be because when lithium oxalate is used as an anti-overcharge material, lithium oxalate is easy to decompose, and it cannot effectively play the role of anti-overcharge, and cannot improve the safety performance of the battery cell.

[0155] Compared with Example 1, LiTFSI is not added to the second injection of electrolyte in the battery cell of Comparative Example 4. Although the capacity retention rate after 500 cycles at room temperature is comparable and the overcharge test and thermal runaway test can be passed, the maximum temperature of the thermal runaway battery cell is significantly higher, and it is impossible to take into account both excellent safety performance and cycle performance.

[0156] Compared with Example 1, the content of LiTFSI in the second injection electrolyte in the battery cells of Comparative Examples 5-6 is not within the scope of the present invention, and is too high or too low. Although the capacity retention rate after 500 cycles at room temperature is comparable, and the overcharge test and thermal runaway test can also be passed, the maximum temperature of the thermal runaway battery cell is significantly increased, and it is impossible to ensure excellent safety performance while ensuring the cycle performance.

[0157] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A battery cell, characterized in that: The battery cell adopts a one-two injection scheme to inject electrolyte, and the electrolyte includes a one-injection electrolyte and a two-injection electrolyte, wherein the two-injection electrolyte includes lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide, and the content of lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide is 1%-10%, and the percentage is the mass percentage of the two-injection electrolyte; The positive electrode material layer of the positive electrode sheet of the battery cell includes lithium iron phosphate and anti-overcharge material; the anti-overcharge material meets the following requirements: when the test battery cell is overcharged according to the battery cell overcharge test method in GB / T 36276-2023, the maximum voltage after overcharge for 0.5 hours does not exceed 5V, wherein the content of lithium iron phosphate in the positive electrode material layer of the test battery cell is greater than or equal to 90%, and the content of the anti-overcharge material is 0.1%, and the percentage is the mass percentage of the positive electrode material layer.

2. The battery cell according to claim 1, characterized in that: The anti-overcharge material includes FeP, Fe2P, Fe3P, FeN4, Fe2N and Fe 16 One or more of N2.

3. The battery cell according to claim 1, characterized in that: The anti-overcharge material satisfies one or two of the following conditions ab: a. The ratio of the Dv50 particle size of the anti-overcharge material to the Dv50 particle size of the lithium iron phosphate is (0.4-0.9): 1; b. The Dv50 particle size of the anti-overcharge material is 0.2-5 μm.

4. The battery cell according to claim 1, characterized in that: The battery cell meets one or more of the following conditions ac: a. The content of the anti-overcharge material is 0.01%-0.25%, where the percentage is the mass percentage of the positive electrode material layer; b. The content of the lithium iron phosphate is not less than 90%, where the percentage is the mass percentage of the positive electrode material layer; c. The mass ratio of the anti-overcharge material to the lithium iron phosphate is 1:(320-9800).

5. The battery cell according to claim 1, characterized in that: The content of the lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide is 2%-5%.

6. The battery cell according to claim 1, characterized in that: The second electrolyte includes a second additive, the second additive includes vinylene carbonate, the content of the vinylene carbonate is 5%-15%, and the percentage is the mass percentage of the second electrolyte.

7. The battery cell according to claim 1, characterized in that: The second electrolyte includes a second lithium salt and a second solvent, and the second electrolyte satisfies one or two of the following conditions ab: a. The second lithium salt includes lithium hexafluorophosphate; b. The second solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, propyl formate, propyl propionate and ethyl butyrate.

8. The battery cell according to claim 1, characterized in that: The electrolyte comprises a first lithium salt, a first solvent and a first additive, and the electrolyte satisfies one or more of the following conditions ac: a. The first lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide; b. The first solvent comprises one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, propyl formate, propyl propionate and ethyl butyrate; c. The first additive includes one or more of vinylene carbonate, fluoroethylene carbonate and vinyl sulfate; when the additive in the one injection of electrolyte includes vinylene carbonate, the content of vinylene carbonate is 0.5%-4%, and the percentage is the mass percentage of the one injection of electrolyte.

9. A lithium ion battery, characterized in that: It comprises the battery cell as claimed in any one of claims 1 to 8.

10. An electronic device, characterized in that: It comprises the lithium ion battery as claimed in claim 9.

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