Negative pole piece and electrochemical device and electronic equipment comprising same

Abstract

The invention relates to a negative pole piece and an electrochemical device and electronic equipment comprising the same, and belongs to the technical field of electrochemical energy storage. The negative pole piece comprises a negative current collector and a negative active layer arranged on at least one surface of the negative current collector, wherein the negative active layer comprises a negative active material, a lithium salt, a functional additive and a dry binder; the lithium salt comprises at least one of lithium bis (trifluoromethanesulfonyl) imide, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate, lithium difluorosulfonyl imide, lithium tetrafluoroborate, lithium difluorophosphate and lithium trifluoromethanesulfonate. The negative pole piece provided by the invention can avoid the risk of lithium salt hydrolysis in a traditional scheme, after the battery is packaged, the solid lithium salt is directionally released and high ion conduction SEI is formed in situ through a controllable heat-pressure activation program, the first efficiency, the cycling stability and the system reliability are improved, and the liquid injection time is remarkably shortened.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to negative electrode sheets and electrochemical devices and electronic devices containing them. Background Technology

[0002] Existing electrochemical devices (such as lithium-ion batteries) generally employ a wet coating process to prepare the negative electrode, relying on the Li in the electrolyte. + After the initial lithium intercalation film is formed, if additional lithium is needed, sacrificial additives (such as Li2S, Li5FeO4), lithium metal powder dispersion, or external lithium foil are often used. However, these methods all have significant drawbacks: sacrificial additives are prone to failure due to oxidation or hydrolysis in the drying stage; lithium powder is flammable, explosive, and difficult to handle; and lithium foil has stringent requirements for roll forming precision and has high interfacial contact resistance.

[0003] Research has found that if conventional lithium salts are directly mixed into aqueous systems or NMP anode slurries, they may decompose violently upon contact with water and release HF gas at high temperatures (>60 °C), leading to coating blistering, adhesion failure, and incompatibility with standard electrode production lines. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a negative electrode and an electrochemical device and electronic device comprising the same. The negative electrode provided by this application has excellent interfacial performance, which can significantly improve cycle performance.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: The first aspect of this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material, a lithium salt, a functional additive and a dry binder. The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium dioxarate borate, lithium difluorooxarate borate, lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorophosphate, and lithium trifluoromethanesulfonate.

[0006] As an embodiment of this application, the functional additive includes at least one of lithium fluoride, lithium nitride, and fluoroethylene carbonate.

[0007] As an embodiment of this application, the functional additives include lithium fluoride and lithium nitride.

[0008] As an embodiment of this application, in the negative electrode active layer, the mass percentage of lithium fluoride is w1, the mass percentage of lithium nitride is w2, and 0.25≤w1 / w2≤3.

[0009] As an embodiment of this application, in the negative electrode active layer, the mass percentage of lithium fluoride is w1, the mass percentage of lithium nitride is w2, and 0.6≤w1 / w2≤1.5.

[0010] As an embodiment of this application, the Dv50 particle size of the lithium fluoride is 50-200 nm.

[0011] As an embodiment of this application, the lithium nitride has a Dv50 particle size of 50-200 nm.

[0012] As an embodiment of this application, the total mass percentage of functional additives in the negative electrode active layer is 2-8%.

[0013] As an embodiment of this application, the dry adhesive comprises polytetrafluoroethylene fibers.

[0014] As an embodiment of this application, the diameter of the polytetrafluoroethylene fiber is 200-1 μm.

[0015] As an embodiment of this application, the negative electrode active layer contains 70-88% by mass of the negative electrode active material.

[0016] As an embodiment of this application, the lithium salt content in the negative electrode active layer is 3-15% by mass.

[0017] As an embodiment of this application, the dry binder in the negative electrode active layer has a mass percentage content of 5-12%.

[0018] As an embodiment of this application, the method for preparing the electrode sheet described in this application includes the following steps: S1. The negative electrode active material, lithium salt and functional additives are ball-milled and mixed, and then a dry binder is added and mixed by dry mixing to obtain the negative electrode precursor powder. S2. The negative electrode precursor powder is used to prepare a negative electrode active film by screw extrusion process; S3. The negative electrode active film and the negative electrode current collector are formed by calendering, dried and cut to obtain the negative electrode sheet.

[0019] As an embodiment of this application, the ball-to-material ratio of the ball mill is (20-40):1, and the ball milling time is 20-40 min.

[0020] As an embodiment of this application, the shearing rate of the dry mixing is 450-550 rpm, and the processing time is 8-12 min.

[0021] As an embodiment of this application, the temperature of the screw extrusion process is 110-130 ℃ and the screw speed is 50-70 rpm.

[0022] As an embodiment of this application, the thickness of the negative electrode active film is 50-120 μm.

[0023] A second aspect of this application provides an electrochemical device comprising a negative electrode as described above.

[0024] As an embodiment of this application, the electrochemical device further includes an electrolyte, which includes an ether solvent.

[0025] As an embodiment of this application, the ether solvent includes a first ether solvent and a second ether solvent. The first ether solvent includes at least one of tetraethylene glycol dimethyl ether, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether. The second ether solvent includes at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hydrofluoroether, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0026] As an embodiment of this application, the mass ratio of the first ether solvent and the second ether solvent in the electrolyte is (6-9):(1-4).

[0027] A third aspect of this application provides an electronic device, including the electrochemical device described above.

[0028] Compared with the prior art, the beneficial effects of this application are as follows: The negative electrode sheet described in this application can achieve stable lithium salt loading. The lithium salt can effectively maintain chemical inertness, with zero decomposition and zero risk of dust explosion. Moreover, the lithium salt loss rate is low, and the mass production yield is high, which is far superior to the existing technology. At the same time, it has excellent interface performance, generates SEI in situ, is electronically insulating and highly ionicly conductive, has a low negative electrode expansion rate, no lithium plating, and can also improve first efficiency and cycle stability, effectively suppress dendrites and reduce interface impedance, and effectively improve cycle performance. Detailed Implementation

[0029] To better illustrate the purpose, technical solution, and advantages of this application, the following detailed description will be provided in conjunction with specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; and unless otherwise specified, the materials and reagents used are commercially available.

[0030] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0031] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0032] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this application are commercially available, and the components and raw materials used in each parallel experiment are the same.

[0033] In the following description, all figures disclosed herein are approximate values, regardless of whether the terms "about" or "approximately" are used in conjunction. They may vary by 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a range of values ​​with a lower limit RL and an upper limit RU is disclosed, any values ​​falling within that range are specifically disclosed. Specifically, the following values ​​within this range are specifically disclosed: R = RL + k * (RU - RL), where k is a variable with a 1% increment from 1% to 100%, i.e., k is 1%, 2%, 3%, 4%, 5%, ..., 50%, 51%, 52%, ..., 95%, 96%, 97%, 98%, 99%, or 100%. Furthermore, any range of values ​​defined by the two R values ​​as defined above are also specifically disclosed.

[0034] General definition The term "negative electrode active layer" refers to a functional thin film layer located on the negative electrode side of the battery, loaded on the surface of the current collector, or formed by self-support. It is mainly composed of negative electrode active material and is prepared through specific processes. This layer can achieve charge storage and transfer through reversible lithium ion insertion / extraction, alloying reaction, or lithium metal deposition / stripping. It is the core functional layer for the negative electrode to realize electrochemical functions.

[0035] The term "functional additive" refers to a substance introduced in small amounts (usually accounting for 0.01-10% of the corresponding system mass fraction) that does not change the main composition and basic properties of the system, but can specifically improve one or more key performance characteristics of the battery.

[0036] The term "polytetrafluoroethylene fiber" refers to fiber made of polytetrafluoroethylene (PTFE, chemical formula -(CF2-CF2)). n -) A polymer material with continuous filament or discrete short fiber morphology, prepared from resin as raw material through processes such as paste extrusion, stretching, heat setting, cutting (short fiber) or continuous spinning; its diameter is usually in the range of 100 nm-10 mm.

[0037] The term “Dv50 particle size”, as used herein and in the claims, is defined as “volume median particle size”, which is a core characteristic parameter of particle size distribution in a particle system. It refers to the particle size value corresponding to the cumulative volume of the particles when the cumulative volume accounts for 50% of the total particle volume in the cumulative volume distribution curve of the particles.

[0038] I. Negative electrode plate To address the shortcomings of existing negative electrode lithium replenishment solutions, this application provides a negative electrode sheet: The negative electrode sheet provided in this application includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. The negative active layer includes a negative active material, a lithium salt, a functional additive, and a dry binder. The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium dioxaborate (LiBOB), lithium difluorooxaborate (LiDFOB), lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorophosphate, and lithium trifluoromethanesulfonate.

[0039] The negative electrode sheet provided in this application is itself a lithium source carrier, and the selected lithium salts all have melting points >200 °C and vapor pressures <10. -5 High stability with a mass change of ≤0.3% over 7 days in air at 120 °C; By selecting specific solid lithium salts that are completely stable, do not decompose, do not lose weight, and do not react under air, moisture, mechanical shear, and calendering temperature conditions, and do not decompose to produce combustion-supporting gases during the use of electrochemical devices, combined with functional additives and dry binders, it can be safely incorporated into the colloidal network of the negative electrode without the risk of explosion, and the yield of mass production is high.

[0040] The negative electrode provided in this application has a lithium salt that releases Li in a directional manner. + It also forms a high ion conductivity SEI in situ, which has excellent interface properties, is electronically insulating and highly ion-conductive, improves the first efficiency and cycle stability of electrochemical devices, and effectively improves lithium plating.

[0041] In some embodiments, the lithium salt includes at least one selected from lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium dioxolaneborate (LiBOB), and lithium difluorooxolaneborate (LiDFOB). In some embodiments, the negative electrode active material includes at least one selected from natural graphite, artificial graphite, and silicon-carbon composite materials.

[0042] In some embodiments, the functional additive includes at least one of lithium fluoride (LiF), lithium nitride (Li3N), and fluoroethylene carbonate (FEC).

[0043] In some embodiments, the functional additives include lithium fluoride and lithium nitride.

[0044] In some embodiments, the mass percentage of lithium fluoride in the negative electrode active layer is w1, the mass percentage of lithium nitride is w2, and 0.25 ≤ w1 / w2 ≤ 3. For example, it can be 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, or a range of any two of these values.

[0045] In some embodiments, the negative electrode active layer contains lithium fluoride at a mass percentage of w1 and lithium nitride at a mass percentage of w2, and 0.6 ≤ w1 / w2 ≤ 1.5.

[0046] In some embodiments, the Dv50 particle size of the lithium fluoride is 50-200 nm, for example, it can be a range of 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm or any two of these values.

[0047] In some embodiments, the Dv50 particle size of the lithium nitride is 50-200 nm, for example, it can be a range of 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm or any two of these values.

[0048] LiF is beneficial for SEI densification, while Li3N has ultra-high Li content. + Electrical conductivity; by selecting specific functional additives and controlling their ratio and particle size, the pulsed thermal activation mechanism can be better realized, achieving a process from thermally softened matrix to low-current induced Li + The three-stage activation path of insertion / extraction followed by preferential film formation ensures that the molar ratio of LiF in the formed SEI is ≥50% and Li3N is ≥20%, effectively suppressing dendrites, reducing interfacial impedance, and improving the cyclic expansion rate of the negative electrode.

[0049] In some embodiments, the total mass percentage of functional additives in the negative electrode active layer is 2-8%, for example, it can be 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, or any two of these values.

[0050] In some embodiments, the dry adhesive comprises polytetrafluoroethylene (PTFE) fibers.

[0051] In some embodiments, the average diameter of the polytetrafluoroethylene fiber is 200 nm to 1 μm, for example, it can be a range of 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1 μm or any two of these values. By controlling the average diameter of the polytetrafluoroethylene fiber within this range, a three-dimensional coating structure can be formed on the surface of the negative electrode active material, effectively improving the structural stability of the negative electrode active material, effectively mitigating the volume expansion and contraction of the negative electrode active material, avoiding the pulverization of the negative electrode active material, and further improving the cycle performance of the electrochemical device.

[0052] In some embodiments, the negative electrode active material in the negative electrode active layer has a mass percentage content of 70-88%, for example, it can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, or any two of these values.

[0053] In some embodiments, the lithium salt content in the negative electrode active layer is 3-15% by mass, for example, it can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, or a range of any two of these values.

[0054] In some embodiments, the dry binder in the negative electrode active layer has a mass percentage content of 5-12%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, or any two of these values.

[0055] In this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be at least one of copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, and composite current collector.

[0056] In some embodiments, the negative current collector includes at least one of copper foil, copper alloy foil, and copper foam.

[0057] II. Preparation method of negative electrode sheet This application provides a method for preparing the above-mentioned negative electrode sheet, including the following steps: S1. The negative electrode active material, lithium salt and functional additives are ball-milled and mixed, and then a dry binder is added and mixed by dry mixing to obtain the negative electrode precursor powder. S2. The negative electrode precursor powder is used to prepare a negative electrode active film by screw extrusion process; S3. The negative electrode active film and the negative electrode current collector are formed by calendering, dried and cut to obtain the negative electrode sheet.

[0058] In some embodiments, the ball-to-material ratio of the ball mill is (20-40):1, and the milling time is 20-40 minutes.

[0059] In some embodiments, the dry mixing shear rate is 450-550 rpm and the processing time is 8-12 min.

[0060] In some embodiments, the temperature of the screw extrusion process is 110-130 °C and the screw speed is 50-70 rpm.

[0061] In some embodiments, the thickness of the negative electrode active film is 50-120 μm.

[0062] The negative electrode preparation process provided in this application is compatible with existing dry electrode production lines, requiring no modification to the drying and coating systems; at the same time, it eliminates the need for NMP or H2O solvent systems, completely avoiding the risk of lithium salt hydrolysis, avoiding any side reactions induced by liquid media, and producing no VOC emissions from the workshop. It also simplifies the factory's VOC and wastewater treatment process, eliminating the need for NMP recovery towers or HF corrosion-resistant workshop designs.

[0063] III. Electrochemical Device This application provides an electrochemical device including a negative electrode as described above. In some embodiments, the electrochemical device further includes a positive electrode, a separator, and an electrolyte.

[0064] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0065] positive electrode The electrochemical device of this application includes a positive electrode, wherein the positive electrode includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector.

[0066] In some of these embodiments, the type of positive current collector is not particularly limited, and it may be any material known to be suitable for use as a positive current collector.

[0067] In some embodiments, the positive current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0068] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0069] In some embodiments, the positive electrode active layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0070] diaphragm The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures.

[0071] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.

[0072] electrolyte The electrolyte in this application includes ether solvents.

[0073] In some embodiments, the ether solvent includes a first ether solvent and a second ether solvent. The first ether solvent includes at least one of tetraethylene glycol dimethyl ether, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether. The second ether solvent includes at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hydrofluoroether, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0074] As an embodiment of this application, the mass ratio of the first ether solvent and the second ether solvent in the electrolyte is (6-9):(1-4).

[0075] In some embodiments, the electrolyte comprises tetraethylene glycol dimethyl ether (TEGDME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a mass ratio of (6-9):(1-4).

[0076] The electrochemical device provided in this application does not require lithium supply via electrolyte. Therefore, the electrolyte may not contain any dissociable lithium salts or other solutes, but only low-viscosity ethers or fluorinated solvents, which allows the viscosity of the electrolyte to be controlled at 0.2-0.35 mPa·s at 25 °C.

[0077] IV. Electronic Equipment This application provides an electronic device, including the electrochemical device described above.

[0078] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art.

[0079] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. According to some embodiments of this application, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, android robots, etc.

[0080] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0081] In the following examples and comparative examples, the battery disassembly and pretreatment methods are as follows: the battery is frozen at -20 ℃ for 12 hours, then dissected at room temperature, and the electrode sheets are dried in a vacuum drying oven for 12 hours to remove residual electrolyte; In the following examples and comparative examples, the test method for the Dv50 particle size of lithium fluoride and lithium nitride is as follows: using a laser particle size analyzer, the powder is dispersed in anhydrous ethanol to form a suspension. When the laser beam passes through the suspension, particles of different sizes will generate scattered light at different angles. The scattered light signal is collected by a detector and fitted by an algorithm to obtain the Dv50 particle size.

[0082] In the following examples and comparative examples, the method for testing the vapor pressure of lithium salts is as follows: lithium salts are placed in a Knudsen cell with tiny openings, and the vapor pressure is calculated by measuring the rate at which gas molecules escape from the openings under vacuum at 120 °C. In the following examples and comparative examples, the method for testing the thermal decomposition temperature of lithium salts is as follows: under an inert atmosphere, the lithium salt is linearly heated, and the change in sample mass with temperature is monitored in real time. The starting temperature at which the sample shows significant mass loss is the thermal decomposition temperature.

[0083] The sources of raw materials and parameters used in the following examples and comparative examples are shown in Table 1 below.

[0084] Table 1 Example 1 This application discloses a method for preparing a lithium-ion battery, comprising the following steps: (I) Preparation of the negative electrode S1. Premixing: The negative electrode active material artificial graphite (82.5 g), lithium salt LiTFSI (5.0 g), functional additive LiF (3.0 g, Dv50 particle size 100 nm) and Li3N (2.0 g, Dv50 particle size 100 nm) are mixed and placed in a ball mill jar. Zirconia balls are added and the mixture is ball-milled for 30 minutes at a ball-to-material ratio of 30:1 to ensure no local enrichment. Then, the mixture is transferred to a high-speed mixer and dry binder PTFE fiber (7.5 g) is added. The mixture is then mixed at a shear rate of 500 rpm for 10 minutes to obtain the negative electrode precursor powder. S2. Fiber stretching to form a film: The prepared negative electrode precursor powder was stretched into a self-supporting negative electrode active film with a thickness of 65 μm by a twin-screw extruder at 125℃ and a screw speed of 60 rpm. During the preparation process, TGA, ICP-OES, XPS and SEM tests showed that there was no decomposition of lithium salt, no loss of lithium element, no oxidation hydrolysis, no cracks in the cross section, and the fiber encapsulation was complete, indicating excellent film quality. S3. The negative electrode active film and a copper foil current collector with a thickness of 6 μm are formed by calendering, vacuum dried at 80 ℃ for 2 hours, and cut to obtain a negative electrode sheet of 100×80 mm.

[0085] (II) Preparation of the positive electrode: The positive electrode active material NCM811 (91.5 g), conductive agent Super P (3.0 g), and binder PVDF (5.5 g) were added to NMP (60 g). After stirring and mixing, the mixture was milled using a three-roll mill and degassed under vacuum to obtain a uniform slurry with a solid content of 72 wt%. The slurry was then coated onto a 12 μm aluminum foil using a slot coater, resulting in an areal capacity of 3.2 mAh / cm². 2 After drying, cold pressing is performed to achieve a compaction density of 3.62 g / cm³. 3 Finally, it is cut into positive electrode sheets of a specified size.

[0086] (iii) Separator: A ceramic-coated PE separator with a thickness of 7 μm.

[0087] (iv) Preparation of electrolyte: At room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), TEGDME and TTE are mixed evenly at a mass ratio of 7:3 to obtain electrolyte. The viscosity of the electrolyte (25 °C) measured by Ubbelohde viscometer is 0.28 mPa·s, and the moisture content measured by KF moisture meter is ≤15 ppm.

[0088] (V) Assembly of lithium-ion batteries: The positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, Hi-pot testing, and tab welding, bare cells are obtained. The bare cells are packaged in an outer aluminum-plastic film and baked in an oven at 100±5 ℃ for 48h. The electrolyte prepared above (injection coefficient of 4.0g / Ah) is injected into the dried battery. After standing, hot pressing, formation and capacity testing, lithium-ion batteries are obtained.

[0089] The hot-pressing parameters are as follows: under nitrogen protection, the temperature is 80 ℃, the pressure is 1.8 MPa, and the time is 10 min. The formation parameters are as follows: charge to 0.2 V at 0.05 C; charge to 0.8 V at 0.1 C; discharge to 0.01 V at 0.1 C; discharge to 1.2 V in the second cycle; and then charge to 1.5 V at 0.5 C for the subsequent conventional formation.

[0090] Example 2-11 The only difference between Examples 2-11 and Example 1 is that the negative electrode active layer in the prepared negative electrode sheet uses different components, specifically: Example 2: Lithium salt LiTFSI was replaced with an equal mass of LiBOB; Example 3: Lithium salt LiTFSI was replaced with an equal mass of LiDFOB; Example 4: The Li3N in the functional additive was replaced with an equal mass of FEC; Example 5: The LiF in the functional additive was replaced with an equal mass of FEC; In Examples 6-7, LiF was replaced with equal amounts of Dv50 LiF with particle sizes of 50 nm and 150 nm, respectively. In Examples 8-9, Li3N was replaced with equal amounts of Dv50 Li3N with particle sizes of 50 nm and 150 nm, respectively.

[0091] Example 10 replaces LiF and Li3N with equal amounts of LiF and Li3N with a Dv50 particle size of 200 nm; Example 11 replaces the dry adhesive with an equal amount of PVDF-HFP.

[0092] The comparison between Examples 2-11 and Example 1 is shown in Table 2 below.

[0093] Table 2 Examples 12-23 The only difference between Examples 12-23 and Example 1 is that the negative electrode active layer in the prepared negative electrode sheet has different component ratios, with the addition of negative electrode active material, lithium salt, functional additives and dry binder adjusted, as shown in Table 3 below.

[0094] Table 3 Comparative Examples 1-4 The specific differences between Comparative Examples 1-4 and Example 1 are as follows: In the negative electrode active layer prepared in Comparative Example 1, an equal amount of LiClO4 was used to replace the lithium salt LiTFSI; In Comparative Example 2, no lithium salt was added to the negative electrode active layer, while LiPF6 was added to the electrolyte to make its concentration 1 M. In the preparation of Comparative Example 3 battery, hot pressing was not performed; formation was carried out only at room temperature. The negative electrode active layer prepared in Comparative Example 4 did not contain functional additives LiF and Li3N.

[0095] Example of effect To investigate the performance of the negative electrode and lithium-ion battery provided in this application, the following tests were conducted: (1) Cycling performance: The Xinwei BTS4000 test system was used to perform 500 cycles at a 0.5C rate with limited voltage, and the ambient temperature was 25±2℃. The first charge capacity (Qc1) and discharge capacity (Qd1) were recorded and the first efficiency was calculated. The discharge capacity (Qd500) of the 500th cycle was recorded and the capacity retention rate was calculated as (Qd500 / Qd1)×100%.

[0096] (2) Interface impedance: The interface impedance was tested using a Solartron 1260 EIS system with a frequency range of 10 mHz to 100 kHz and an AC amplitude of 5 mV at 25±1℃. The SEI film resistance value was analyzed using ZView software combined with the Randle model.

[0097] (3) Moisture tolerance: The coulombic efficiency method was used for evaluation. The prepared and dried battery samples and electrolyte were placed in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm); deionized water was added to the electrolyte storage container using a micro-syringe, and the water concentration of the electrolyte was measured using a Karl Fischer moisture analyzer (Metrohm 831 KF) and adjusted to 120 ppm. Then the prepared electrolyte was injected into the dried battery and the encapsulation was completed; after the battery was left to stand at 25±2℃ for 12 h, a 0.1 C voltage-limited cycle test was performed (voltage range: 0.01-1.5 V), and the first-cycle charging capacity (Qc1) and discharging capacity (Qd1) were recorded. The first-cycle coulombic efficiency (CE = Qd1 / Qc1×100%) was calculated; the higher the CE value, the stronger the battery system's tolerance to moisture interference.

[0098] (4) Injection time: During the test, a high-precision stopwatch was used to manually record the time. The battery was placed in a constant temperature environment of 25±2℃. The battery was connected to the graduated injection cup. After the liquid was injected, the timer was started and the changes in the liquid level in the injection cup were observed. The timer was stopped when the changes in the liquid level were no longer visible to the naked eye and the bubbles had completely disappeared.

[0099] The test results are shown in Table 4 below.

[0100] Table 4 As shown in Table 4: Compared to the comparative example, the negative electrode sheet provided by this invention can impart superior electrochemical and cycle performance to the battery. By using specific lithium salts such as lithium bis(trifluoromethanesulfonyl)imide as the lithium source, selecting appropriate types and proportions of functional additives, and matching the particle size of the additives within the 50-200 nm range, coupled with PTFE fiber dry bonding, a rapid liquid injection time of less than 45 seconds can be achieved. Simultaneously, after 500 cycles, the capacity retention rate is not less than 81%, the moisture tolerance (120 ppm) is maintained above 85%, and the interfacial impedance is 14 Ω·cm. 2 The results are significantly superior to traditional lithium replenishment systems. Comparative Example 2, which lacks salt loading, exhibits rapid capacity decay, a thick SEI, and high impedance, while Comparative Example 1 shows an ignition reaction, fully demonstrating the irreplaceable nature of the lithium salt and functional additives used in this invention.

[0101] Further XPS analysis was used to analyze the SEI composition of the negative electrode surface after cycling in Example 1. The molar percentage of LiF was ≥55%, and the molar percentage of Li3N was ≥20%.

[0102] In summary, this application provides a negative electrode sheet that serves as a lithium source carrier. The selected lithium salt exhibits high stability, allowing for safe incorporation into the colloidal network of the negative electrode without the risk of explosion, and achieving high yield in mass production. By optimizing functional additives, a three-stage activation path can be achieved, forming an SEI film in situ, effectively suppressing dendrites and reducing interfacial impedance. After encapsulation, a controllable thermal-pressure activation process enables the directional release of Li from the solid lithium salt in the negative electrode sheet. + It forms a high-ion-conductivity SEI in situ, which has excellent interface performance, electronic insulation and high ion conductivity, improves the battery's first efficiency and cycle stability, improves the lithium plating suppression rate, solves the defects of traditional external lithium foil and other technologies, and further improves battery performance.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material, a lithium salt, a functional additive and a dry binder. The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium dioxarate borate, lithium difluorooxarate borate, lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorophosphate, and lithium trifluoromethanesulfonate.

2. The negative electrode sheet as described in claim 1, characterized in that, The functional additives include at least one of lithium fluoride, lithium nitride, and fluoroethylene carbonate.

3. The negative electrode sheet as described in claim 2, characterized in that, The functional additives include lithium fluoride and lithium nitride.

4. The negative electrode sheet as described in claim 3, characterized in that, In the negative electrode active layer, the mass percentage of lithium fluoride is w1, the mass percentage of lithium nitride is w2, and 0.25≤w1 / w2≤3.

5. The negative electrode sheet as described in claim 3, characterized in that, The Dv50 particle size of the lithium fluoride is 50-200 nm; And / or, the Dv50 particle size of the lithium nitride is 50-200 nm.

6. The negative electrode sheet as described in claim 1, characterized in that, The total mass percentage of functional additives in the negative electrode active layer is 2-8%.

7. The negative electrode sheet as described in claim 1, characterized in that, The dry adhesive includes polytetrafluoroethylene fibers.

8. The negative electrode sheet as described in claim 1, characterized in that, The negative electrode active layer contains 70-88% by mass of the negative electrode active material. And / or, in the negative electrode active layer, the mass percentage content of lithium salt is 3-15%; And / or, in the negative electrode active layer, the dry binder has a mass percentage content of 5-12%.

9. An electrochemical device, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-8.

10. The electrochemical device as claimed in claim 9, characterized in that, The electrochemical device further includes an electrolyte, which includes an ether solvent.

11. The electrochemical device as claimed in claim 10, characterized in that, The ether solvents include at least one of tetraethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hydrofluoroether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.

12. An electronic device, characterized in that, Includes the electrochemical device as described in any one of claims 9-11.

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