Binder, secondary battery, and electric device

Abstract

The application discloses a kind of binder, secondary battery and electric device, belong to battery technical field, the binder comprising carboxyl-containing polymer binder, ionic liquid and metal ion, the infrared absorption spectrum of the binder has absorption peak at 1250~1650cm ‑1 Place.This binder can improve the problem of traditional carboxyl-containing polymer binder causing fragile pole piece;And improve the thermal stability and low temperature performance of pole piece, while it can improve the problem of traditional carboxyl-containing polymer binder poor kinetics, thereby effectively reducing the DCR of secondary battery, improve the energy efficiency and cycle life of secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to an adhesive, a secondary battery, and an electrical device. Background Technology

[0002] Secondary batteries, especially lithium-ion batteries, have high capacity, long cycle life, no memory effect, low self-discharge, wide operating temperature range, and high rate capability, and have been widely used in mobile phones, computers, electric bicycles, and electric vehicles.

[0003] With the rapid development of the new energy industry, the demand for high-performance energy storage devices is increasing. The electrochemical performance of secondary batteries is closely related to the stability of the electrode structure (positive electrode and / or negative electrode) and the interfacial adhesion between the electrode and the current collector.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide an adhesive, a secondary battery and an electrical device. The adhesive can effectively improve the cycle life and energy efficiency of the secondary battery and reduce the DCR of the secondary battery.

[0006] To achieve the above objectives, a first aspect of this application provides an adhesive comprising a carboxyl-containing polymer adhesive, an ionic liquid, and metal ions, wherein the infrared absorption spectrum of the adhesive is in the range of 1250–1650 cm⁻¹. -1 It has an absorption peak.

[0007] As an implementation scheme of this application, at least one of the following (a) to (d) is satisfied: (a) The infrared absorption spectrum of the adhesive is in the range of 1280~1320 cm⁻¹ -1 It has an absorption peak; (b) The infrared absorption spectrum of the adhesive is in the range of 1380~1420 cm⁻¹. -1 It has an absorption peak; (c) The infrared absorption spectrum of the adhesive is in the range of 1500~1550 cm⁻¹ -1 It has an absorption peak; (d) The infrared absorption spectrum of the adhesive is in the range of 1620~1650 cm⁻¹. -1 It has an absorption peak.

[0008] As an implementation scheme of this application, at least one of the following (e) to (g) is satisfied: (e) The carboxyl-containing polymer binder includes at least one of polyacrylic acid, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose; (f) The ionic liquid comprises at least one of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt, and N,N-dimethyl-N-ethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide salt; (g) The metal ions include at least one of zinc ions, magnesium ions, and calcium ions.

[0009] As an implementation scheme of this application, at least one of the following (h) to (j) is satisfied: (h) The carboxyl-containing polymer adhesive has a mass percentage content of 20-60% in the adhesive; (i) The ionic liquid has a mass percentage of 2-8% in the binder; (j) The mass percentage of the metal ions in the adhesive is 2-8%.

[0010] As an embodiment of this application, the adhesive further includes sulfur-containing anions, wherein the sulfur-containing anions include SO4. 2- TFSI - At least one of them.

[0011] As an embodiment of this application, the sulfur-containing anion in the adhesive has a mass percentage content of 20-68%.

[0012] A second aspect of this application provides a secondary battery including an electrode, the electrode including a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer including the aforementioned binder.

[0013] As an embodiment of this application, the active material layer includes a first active material layer and a second active material layer, wherein the first active material layer is located on at least one surface of the current collector, and the second active material layer is located on the surface of the first active material layer away from the current collector; The porosity of the first active material layer is P1, and the porosity of the second active material layer is P2, satisfying P1 < P2.

[0014] As an embodiment of this application, the mass percentage of the adhesive in the first active material layer is a, and the mass percentage of the adhesive in the second active material layer is b, satisfying that a > b.

[0015] As an implementation scheme of this application, at least one of the following (1) to (4) is satisfied: (1) 20%≤P1≤35%; (2) 35%≤P2≤50%; (3) 0.8% ≤ a ≤ 1.8%; (4) 0.2%≤b≤0.8%.

[0016] As an embodiment of this application, the first active material layer includes a pore-forming agent, and the second active material layer includes a pore-forming agent; the pore-forming agent includes a core and a carbon coating layer covering the outer surface of the core, the core includes porous carbon spheres, and the average pore size of the porous carbon spheres is larger than the average pore size of the carbon coating layer.

[0017] As an embodiment of this application, the thickness of the carbon coating layer is 5~15 nm; and / or The carbon coating layer also includes a conductive agent, and the conductive agent has a mass percentage content of 4.8~16.7% in the carbon coating layer.

[0018] As an embodiment of this application, the pore-forming agent has a mass percentage content of 0.1~0.3% in the first active material layer; and / or The pore-forming agent has a mass percentage content of 0.4-0.6% in the second active material layer.

[0019] A third aspect of this application provides an electrical device including the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0020] The beneficial effects of this application are as follows: the adhesive described in this application includes carboxyl-containing polymer adhesives, ionic liquids, and metal ions, and the infrared absorption spectrum of the adhesive is in the range of 1250~1650 cm⁻¹. -1 The metal ions exhibit an absorption peak at a specific location, where they coordinate with the carboxyl-containing polymer binder to form reversible metal-polymer coordination bonds. Simultaneously, an ionic liquid is introduced, incorporating the ionic liquid additive into the carboxyl-containing polymer binder. The metal ions enhance mechanical properties and provide some ion transport sites, ultimately increasing the electrode's flexibility and mitigating the brittleness issue caused by traditional carboxyl-containing polymer binders. The ionic liquid, acting as a powerful ion-conducting medium, effectively reduces the ion migration resistance of the entire system and improves the electrode's thermal stability and low-temperature performance, thereby effectively increasing the cycle life and energy efficiency of the secondary battery and reducing its drain-cement ratio (DCR). Attached Figure Description

[0021] Figure 1 Example 1 ( Figure 1 (Black lines in the middle), Comparison 1 ( Figure 1 The infrared absorption spectrum of the adhesive prepared by the medium gray lines. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] 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.

[0024] 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.

[0025] The inventors of this application have discovered that carboxyl-containing polymer binders can effectively improve the structural stability of electrode sheets and alleviate the cracking problem after coating and drying of thick active material layers (thickness ≥ 160 μm). However, carboxyl-containing polymer binders can make the electrode sheets brittle, resulting in severe powder shedding at the corners of the electrode sheet winding. Furthermore, carboxyl-containing polymer binders can increase DCR (Direct Current Resistance), thus deteriorating energy efficiency.

[0026] Therefore, based on the above-mentioned problems, embodiments of this application provide an adhesive comprising a carboxyl-containing polymer adhesive, an ionic liquid, and metal ions, wherein the infrared absorption spectrum of the adhesive is in the range of 1250~1650 cm⁻¹. -1 It has an absorption peak at, for example, at 1250 cm⁻¹. -1 1300cm -1 1350cm -1 1400cm -1 1450cm -1 1500cm -1 1550cm -1 1600cm -1 1650cm -1 Or the range formed by any two of these values.

[0027] The adhesives described in this application include carboxyl-containing polymer adhesives, ionic liquids, and metal ions, and the infrared absorption spectrum of the adhesives is in the range of 1250~1650 cm⁻¹. -1 The metal ions exhibit an absorption peak at a specific location, where they coordinate with the carboxyl-containing polymer binder to form reversible metal-polymer coordination bonds. Simultaneously, an ionic liquid is introduced, incorporating ionic liquid additives into the carboxyl-containing polymer binder. The metal ions enhance mechanical properties and provide some ion transport sites, ultimately increasing the electrode's flexibility and mitigating the brittleness issue caused by traditional carboxyl-containing polymer binders. The ionic liquid, acting as a powerful ion-conducting medium, effectively reduces the ion migration resistance of the entire system and improves the electrode's thermal stability and low-temperature performance, thereby effectively increasing the cycle life and energy efficiency of the secondary battery and reducing its drain-ceiling ratio (DCR).

[0028] The infrared absorption spectrum of the adhesive is in the range of 1250~1650 cm⁻¹. -1 The presence of an absorption peak indicates that at least some of the metal ions form coordination bonds with the carboxyl-containing polymer binder.

[0029] In some embodiments, the infrared absorption spectrum of the adhesive is in the range of 1280~1320 cm⁻¹. -1 It has an absorption peak, for example, at 1280 cm⁻¹. -1 1285cm -1 1290cm -1 1295m -1 1297cm -1 1300cm -1 1305cm -1 1310cm -1 1315cm -1 1320 cm -1 Or the range formed by any two of these values.

[0030] In some embodiments, the infrared absorption spectrum of the adhesive is in the range of 1380~1420 cm⁻¹. -1 It has an absorption peak at, for example, at 1380 cm⁻¹. -1 1385cm -1 1390cm -1 1395m -1 1396cm -1 1400cm -1 1405cm -1 1410cm -1 1415cm -1 1420 cm -1 Or the range formed by any two of these values.

[0031] In some embodiments, the infrared absorption spectrum of the adhesive is in the range of 1500~1550 cm⁻¹. -1 It has an absorption peak at, for example, at 1500 cm⁻¹. -1 1510cm -1 1520cm -1 1525m -1 1526cm -1 1530cm -1 1540cm -1 1545cm -1 1550cm -1 Or the range formed by any two of these values.

[0032] In some embodiments, the infrared absorption spectrum of the adhesive is in the range of 1620~1650 cm⁻¹. -1 It has an absorption peak at, for example, 1620 cm⁻¹. -1 1630cm -1 1633cm -1 1635m -1 1640cm -1 1645cm -1 1650cm -1 Or the range formed by any two of these values.

[0033] The diffraction peaks mentioned above indicate that at least some of the metal ions form reversible metal-polymer coordination bonds with the carboxyl-containing polymer binder.

[0034] In some embodiments, the carboxyl-containing polymer binder includes at least one of polyacrylic acid, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose. When such a carboxyl-containing polymer binder is used, it can better coordinate with metal ions and promote the filling of ionic liquids in the pores and interchain spaces of the carboxyl-containing polymer binder network, effectively improving the ion migration rate, enhancing the stability of the electrode structure, reducing pulverization, further improving the cycle life and energy efficiency of the secondary battery, and reducing the DCR of the secondary battery.

[0035] In some embodiments, the ionic liquid comprises at least one of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide, and N,N-dimethyl-N-ethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide. In particular, when such ionic liquids are used, the ionic liquids and the carboxyl-containing polymer binders are combined through physical interactions such as hydrogen bonding, electrostatics, and van der Waals forces, which effectively improves the ionic conductivity and reduces the interfacial impedance, further improving the cycle life and energy efficiency of the secondary battery and reducing the DCR of the secondary battery.

[0036] In some embodiments, the metal ions include at least one of zinc ions, magnesium ions, and calcium ions.

[0037] In some embodiments, the metal ions include zinc ions.

[0038] In some embodiments, the mass percentage of the carboxyl-containing polymer binder in the binder is 20-60%, for example, it can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any two of these values. By controlling the mass percentage of the carboxyl-containing polymer binder in the binder within this range, a continuous and complete three-dimensional network is ensured to be formed, effectively improving cohesive strength, improving the toughness of the electrode, improving the adhesion between the electrode and the active material, and reducing polymer agglomeration.

[0039] In some embodiments, the ionic liquid has a mass percentage content of 2-8% in the binder; for example, it can be 2%, 3%, 4%, 5%, 7%, 8%, or any two of these values. By controlling the mass percentage content of the ionic liquid in the binder within this range, it can help the ionic liquid penetrate between polymer segments. On the one hand, it can directly improve the ionic conductivity of the binder layer and reduce the internal resistance of the battery through its own ion migration; on the other hand, it can lower the glass transition temperature of the polymer and increase the chain segment mobility, thereby improving the flexibility of the electrode.

[0040] In some embodiments, the mass percentage of the metal ions in the binder is 2-8%; for example, it can be 2%, 3%, 4%, 5%, 7%, 8%, or any two of these values. By controlling the mass percentage of the metal ions in the binder within this range, the metal ions undergo ionic coordination with the carboxyl groups on the polymer chain, promoting the formation of a suitable number of dynamic ionic crosslinking points, further enhancing the mechanical strength (modulus) and elasticity of the binder network. At the same time, due to its dynamic reversible characteristics, it can dissipate energy through bond breaking and recombination when the volume of the active material changes, thereby reducing the risk of electrode cracking and effectively improving the cycle life of the secondary battery.

[0041] In some embodiments, the binder further includes sulfur-containing anions, including SO4. 2- TFSI - At least one of them.

[0042] In some embodiments, the mass percentage of sulfur-containing anions in the adhesive is 20-68%, for example, it can be 20%, 25%, 30%, 40%, 50%, 60%, 65%, 68%, or any two of these values. By controlling the mass percentage of sulfur-containing anions in the adhesive within this range, it is ensured that the sulfur-containing anions can effectively construct continuous ion transport channels, significantly improve the ionic conductivity of the adhesive layer, and at the same time, the main structure and mechanical integrity of the polymer crosslinking network will not be damaged due to excessive content.

[0043] The content of each component in the adhesive was determined by testing using the following method: I. Sample Pretreatment: From Secondary Cell to Sample Secondary battery disassembly and electrode acquisition: In a glove box protected by inert gas, the discharged secondary battery is disassembled and the target electrode is removed.

[0044] Effective separation of binder - solvent dissolution and stripping method: Using a highly polar solvent (N-methylpyrrolidone and / or dimethyl sulfoxide), the coating on the electrode is completely dissolved under heating or ultrasonic assistance. The supernatant containing the binder is then collected by centrifugation.

[0045] Sample purification and enrichment: The collected solution is purified by removing the solvent through methods such as rotary evaporation to obtain a concentrated mixture containing all binder components, which serves as the initial sample for subsequent analyses.

[0046] II. Quantitative Analysis Procedure and Calculation After obtaining the initial sample, the analysis and data calculation can be performed according to the following procedure: Quantitative analysis of polymers and ionic liquids: Thermogravimetric analysis (TGA) is performed on the initial sample. Under a nitrogen atmosphere, the polymers and ionic liquids decompose sequentially, and their total organic content can be estimated by observing the weight loss steps. For further differentiation, proton nuclear magnetic resonance (NMR) spectroscopy can be used. By identifying and integrating the characteristic peaks of ionic liquids (such as the proton peak on the imidazole ring) and polymers, their respective mass fractions can be calculated using the internal standard method or absolute quantification method.

[0047] Quantitative analysis of metal ions and sulfur-containing anions: Accurately weigh an initial sample, completely digest it with a strong acid (such as nitric acid), and then bring it to a final volume. Use ion chromatography or ICP-OES to plot zinc ions (Zn) using the external standard method. 2+ The standard curve can be used to quantify the total zinc content in a sample. Another initial sample, diluted with a suitable solvent, is directly injected into an ion chromatograph to analyze TFSI⁻ or SO₄²⁻. 2- The peak area is used to calculate its content using the corresponding standard curve.

[0048] Data calculation and cross-validation: Mass fraction (%) of each component = (quantitative mass of the component / total mass of the initial sample) × 100%.

[0049] In some embodiments, the adhesive is prepared by: Sodium salt solution is added to carboxyl-containing polymer binder solution and stirred until homogeneous. Metal salt solution is added and stirred until homogeneous. Ionic liquid is added and stirred until homogeneous. The mixture is then dried to obtain the binder.

[0050] In some embodiments, the sodium salt solution includes at least one of sodium hydroxide solution, sodium acetate solution, sodium carbonate solution, and sodium bicarbonate solution.

[0051] In some embodiments, the molar concentration of the sodium salt solution is 0.1 to 5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or any two of these values.

[0052] In some embodiments, the carboxyl-containing polymer binder solution includes at least one of a carboxyl-containing polymer binder aqueous solution and a carboxyl-containing polymer binder ethanol solution.

[0053] In some embodiments, the concentration of the carboxyl-containing polymer binder solution is 2 to 20 wt%, for example, it can be 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, 15 wt%, 16 wt%, 18 wt%, 20 wt%, or any two of these values.

[0054] In some embodiments, the sodium salt solution adjusts the neutralization degree in the carboxyl-containing polymer binder solution to 60-80% (i.e., 60-80% of the carboxyl groups are neutralized).

[0055] In some embodiments, the metal salt solution includes at least one of an aqueous solution of a metal salt and an ethanol solution of a metal salt.

[0056] In some embodiments, the concentration of the metal salt solution is 10 to 70 wt%, for example, it can be 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, or any two of these values.

[0057] In some embodiments, the molar ratio of the metal salt in the metal salt solution to the carboxyl group in the carboxyl-containing polymer binder is (0.1~0.5):1, for example, it can be 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1 or any two of these values.

[0058] In some embodiments, the mass ratio of the ionic liquid to the carboxyl-containing polymer binder is (5~30):100, for example, it can be 5:100, 10:100, 15:100, 20:100, 25:100, 30:100 or any two of these values.

[0059] In some embodiments, the process of drying includes adding the resulting material into a mold (which may be a polytetrafluoroethylene mold).

[0060] One embodiment of this application provides a secondary battery, including an electrode, the electrode including a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer including the aforementioned binder.

[0061] This application does not limit the type of electrode sheet. The electrode sheet can be a positive electrode sheet or a negative electrode sheet. That is, the binder can be used as a negative electrode binder, as a positive electrode binder, or as both a positive and negative electrode binder.

[0062] When the binder is used as a negative electrode binder, the corresponding active material layer is a negative electrode active material layer, the corresponding current collector is a negative electrode current collector, and the corresponding electrode sheet is a negative electrode sheet.

[0063] When the binder is used as a positive electrode binder, the corresponding active material layer is a positive electrode active material layer, the corresponding current collector is a positive electrode current collector, and the corresponding electrode sheet is a positive electrode sheet.

[0064] The binder described in this application can effectively improve the flexibility and mechanical properties of the electrode, effectively improve the structural stability of the electrode, reduce the phenomenon of powder shedding, and the introduction of metal ions and ionic liquids synergistically improve the ionic conductivity of the electrode, effectively promote ion transport, increase the ion transport rate, improve the wettability of the electrolyte to the electrode, improve the electrolyte retention of the electrode, reduce the impedance of the secondary battery, improve the safety performance and operating temperature range of the secondary battery, improve the high and low temperature resistance of the secondary battery, and effectively improve the cycle life of the secondary battery.

[0065] In some embodiments, the active material layer includes a first active material layer and a second active material layer, wherein the first active material layer is located on at least one surface of the current collector, and the second active material layer is located on the surface of the first active material layer away from the current collector. The porosity of the first active material layer is P1, and the porosity of the second active material layer is P2, satisfying P1 < P2.

[0066] This application controls the active material layer to include a first active material layer and a second active material layer. With the first and second active material layers containing the aforementioned binder, the porosity of the first active material layer is further controlled to be less than that of the second active material layer. This achieves a higher porosity in the active layer farther from the current collector and a lower porosity in the active layer closer to the copper foil. This gradient porosity distribution is beneficial for electrolyte wetting and lithium-ion liquid-phase transport. Simultaneously, the lower porosity of the lower layer allows for better electron transport, effectively improving the cycle life and energy efficiency of the secondary battery and reducing its DCR.

[0067] In some embodiments, the mass percentage of the binder in the first active material layer is 'a', and the mass percentage of the binder in the second active material layer is 'b', satisfying that 'a > b'. By controlling the mass percentage of the binder in the first active material layer to be greater than that in the second active material layer, the adhesion between the binder and the current collector can be improved, while reducing excessive floating of the binder and its excessive migration to the surface of the electrode away from the current collector. This improves the structural stability of the electrode, effectively increases the cycle life of the secondary battery, and reduces the DCR of the secondary battery.

[0068] In some embodiments, 20%≤P1≤35%, for example, can be a range consisting of 20%, 22%, 25%, 28%, 30%, 32%, 34%, 35%, or any two of these values. By controlling P1 within this range, the first active material layer is close to the current collector, ensuring that the secondary battery has excellent energy density, conductivity, and structural stability, and promoting ion and electron transport, effectively extending the cycle life of the secondary battery and reducing the DCR of the secondary battery.

[0069] In some embodiments, 35%≤P2≤50%, for example, can be a range consisting of 35%, 36%, 38%, 40%, 42%, 44%, 45%, 46%, 50%, or any two of these values. By controlling P2 within this range, the second active material layer directly contacts the separator and the electrolyte, forming a gradient pore design that is dense at the bottom and sparse at the top. This provides effective buffering and improves the wettability of the electrolyte to the electrode, effectively improving the kinetic performance of the secondary battery, extending the cycle life of the secondary battery, and reducing the DCR of the secondary battery.

[0070] In some embodiments, 0.8%≤a≤1.8%, for example, can be 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8% or any two of these values. By controlling a within this range, the internal stress of the first active material layer can be effectively increased, ensuring that the first active material layer has sufficient mechanical strength and interfacial adhesion, effectively extending the cycle life of the secondary battery, and reducing the DCR of the secondary battery.

[0071] In some implementations, 0.2% ≤ b ≤ 0.8%, for example, it can be a range consisting of 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or any two of these values. By controlling b within this range, the energy density and ionic conductivity of the electrode can be effectively improved, the cycle life of the secondary battery can be effectively extended, and the DCR of the secondary battery can be reduced.

[0072] The testing methods for P1 and P2 are as follows: porosity is the ratio of the total volume of the tiny voids inside the electrode to the total volume of the electrode coating. The apparent volume of the electrode can be measured using tools such as a micrometer, while the true volume can be measured using a true density meter. The pore volume of the electrode is the difference between the apparent volume and the true volume. The formula is: Sample porosity = [(Vapparent - Vfoil) - (Vtrue - Vfoil)] / (Vapparent – ​​Vfoil) * 100%. The specific operation involves punching 40 small round pieces (Φ = 16mm) into the negative electrode to be tested using a punching machine, and then placing them in a true density meter to determine their porosity.

[0073] In some embodiments, the first active material layer includes a pore-forming agent, and the second active material layer includes a pore-forming agent; the pore-forming agent includes a core and a carbon coating layer covering the outer surface of the core, the core includes porous carbon spheres, and the average pore size of the porous carbon spheres is larger than the average pore size of the carbon coating layer. By using a core-shell structured pore-forming agent, the pore-forming agent can effectively improve the ion transport rate and further improve the structural stability of the electrode, effectively improve the electrolyte wettability and the electrolyte retention of the electrode, further improve the cycle life and energy efficiency of the secondary battery, and reduce the DCR of the secondary battery.

[0074] In some embodiments, the thickness of the carbon coating layer is 5 to 15 nm, for example, it can be 5 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 15 nm or any two of these values.

[0075] In some embodiments, the carbon coating layer further includes a conductive agent, the conductive agent having a mass percentage content of 4.8% to 16.7% in the carbon coating layer, for example, 4.8%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 16.5%, 16.7%, or any two of these values. By incorporating a conductive agent into the carbon coating layer, the structural stability and conductivity of the pore-forming agent can be effectively improved, further enhancing the cycle life and energy efficiency of the secondary battery and reducing the DCR of the secondary battery.

[0076] In some embodiments, the pore-forming agent has a mass percentage content of 0.1-0.3% in the first active material layer, for example, it may be 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, or any two of these values.

[0077] In some embodiments, the Dv50 particle size of the pore-forming agent is 2~10μm, for example, it can be 2μm, 3μm, 4μm, 5μm, 6μm, 8μm, 10μm or any two of these values.

[0078] In some embodiments, the pore-forming agent has a mass percentage content of 0.4-0.6% in the second active material layer, for example, it can be 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.52%, 0.55%, 0.58%, 0.6%, or any two of these values.

[0079] In some embodiments, the pore-forming agent is prepared by: To prepare gel microspheres, acrylamide monomers, acrylic monomers, sulfonic acid acrylamide monomers, and quaternary ammonium acrylate monomers were dissolved in water, a crosslinking agent was added, and the mixture was reacted to obtain gel microspheres. Gel microspheres, a phenolic resin precursor, and a conductive agent are mixed uniformly and then heat-treated. During this heat treatment, the phenolic resin precursor cross-links and carbonizes on the surface of the gel microspheres, forming a dense carbon coating layer. Simultaneously, the internal gel microspheres undergo partial carbonization and activation, transforming into porous carbon cores rich in micropores and polar functional groups. After cleaning and drying, the O / N co-doped porous carbon sphere pore-forming agent is obtained.

[0080] In some embodiments, the gel microspheres comprise copolymers of acrylamide monomers, acrylic monomers, sulfonic acid acrylamide monomers, and quaternary ammonium acrylate monomers.

[0081] In some embodiments, the molar ratio of the acrylamide monomer, acrylic monomer, sulfonic acid acrylamide monomer, and quaternary ammonium acrylate monomer is (50~80):(10~30):(5~15):(3~10).

[0082] The acrylamide monomers include acrylate, methacrylamide, N-isopropylacrylamide, N-hydroxymethylacrylamide, and diacetone acrylamide; The acrylic monomers include acrylic acid, methacrylic acid, itaconic acid, and hydroxyethyl acrylate; The sulfonic acid acrylamide monomers include at least one of 2-acrylamido-2-methylpropanesulfonic acid, vinyl sulfonic acid, and sodium styrene sulfonate; The quaternary ammonium acrylate monomers include methacryloyloxyethyltrimethylammonium chloride.

[0083] In some embodiments, the mass ratio of the acrylamide monomer to water is 1:(2~20), for example, it can be 1:2, 1:4, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20 or any two of these values.

[0084] In some embodiments, the crosslinking agent includes N,N'-methylenebisacrylamide.

[0085] In some embodiments, the crosslinking agent is 0.05 to 0.2% of the total molar amount of acrylamide monomers, acrylic monomers, sulfonic acid acrylamide monomers, and quaternary ammonium acrylate monomers, for example, it can be 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, or any two of these values.

[0086] In some embodiments, the reaction temperature is 50~70°C, for example, it can be 50°C, 52°C, 55°C, 58°C, 60°C, 65°C, 70°C or any two of these values.

[0087] In some embodiments, the reaction time is 0.5 to 10 hours, for example, it can be 0.5 hours, 1 hour, 2 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours or any two of these values.

[0088] In some embodiments, the mass ratio of the precursor to the phenolic resin precursor is (1~10):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 8:1, 10:1 or any two of these values.

[0089] In some embodiments, the phenolic resin precursor includes at least one of phenol and formaldehyde.

[0090] In some embodiments, the mass ratio of the conductive agent to the phenolic resin precursor is 1:(5~20), for example, it can be 1:5, 1:6, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20 or any two of these values.

[0091] In some embodiments, the carbonization temperature is 600~1000°C, for example, it can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 1000°C or any two of these values.

[0092] In some embodiments, the carbonization time is 1 to 4 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours or any two of these values.

[0093] In some embodiments, the activation includes at least one of steam activation, carbon dioxide activation, and alkaline immersion activation.

[0094] In some embodiments, the water vapor activation time is 10 to 60 minutes, for example, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes or any two of these values.

[0095] In some embodiments, the carbon dioxide activation time is 10 to 60 minutes, for example, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes or any two of these values.

[0096] In some embodiments, alkaline activation includes immersion in a potassium hydroxide solution.

[0097] In some embodiments, the molar concentration of the potassium hydroxide solution is 0.1~5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or any two of these values.

[0098] In some embodiments, the solid-liquid ratio during soaking is 1g:(2~10)mL, for example, it can be 1g:2mL, 1g:4mL, 1g:5mL, 1g:6mL, 1g:8mL, 1g:10mL or any two of these values.

[0099] In some embodiments, the soaking time is 0.5 to 10 hours, for example, it can be 0.5 hours, 1 hour, 2 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours or any two of these values.

[0100] In some embodiments, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0101] In some embodiments, the thickness of the first active material layer is 50~70μm, for example, it can be 50μm, 52μm, 55μm, 58μm, 60μm, 62μm, 65μm, 68μm, 70μm or any two of these values.

[0102] In some embodiments, the thickness of the second active material layer is 110~180μm, for example, it can be 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm or any two of these values.

[0103] In some embodiments, the positive electrode active material may include lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials or substances, and other conventional materials or substances that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Non-limiting examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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 copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc.

[0108] In some embodiments, the negative electrode active material includes graphite, silicon-based materials, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, and spinel-structured lithium titanate Li4Ti5O. 12At least one of Li-Al alloys and metallic lithium.

[0109] In some of these embodiments, the secondary battery may include an outer packaging.

[0110] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0111] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or other shapes.

[0112] One embodiment of this application provides an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0113] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, 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, etc., but are not limited thereto.

[0114] The present application is further illustrated below with specific embodiments: Example 1 A method for preparing a secondary battery includes the following steps: (1) Preparation of adhesive: S1. Weigh 10.0 g of polyacrylic acid (PAA, solid, molecular weight 500,000) into a 250 mL three-necked flask. Add 60.0 g of deionized water and stir at 300 rpm for 4 hours at room temperature to form a homogeneous and clear PAA aqueous solution.

[0115] S2, according to Zn 2+ Calculate the required mass of zinc salt based on the molar ratio of PAA to the carboxyl group (-COOH) on the PAA chain being 0.3:1. For example, using Zn(TFSI)₂, 10.0 g PAA (138.9 mmol carboxyl group) requires 41.67 mmol of Zn. 2+ Coordination.

[0116] Weigh 25.5 g of Zn(TFSI)2 and dissolve it in 20.0 g of ethanol solution to prepare a clear zinc salt crosslinking solution.

[0117] S3. Keep the PAA solution obtained in S1 at room temperature and stir it with a mechanical stirring speed of 500 rpm. Using a constant pressure dropping funnel, add the zinc salt ethanol solution prepared in step S2 dropwise to the PAA solution. After the addition is complete, continue to react at a stirring speed of 500 rpm for 2 hours. Finally, a uniform, non-flowing elastic hydrogel is formed.

[0118] S4. Based on the mass ratio of ionic liquid to PAA of 20:100, calculate and weigh 2.0 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM][TFSI]). Add the weighed [EMIM][TFSI] directly to the elastic hydrogel obtained in step S3. Increase the stirring speed to 1500 rpm and perform high-speed shear mixing for 3 hours until the ionic liquid is completely and uniformly dispersed in the gel network, forming a uniform, milky-white paste-like composite. Pour the mixture into a polytetrafluoroethylene (PTFE) mold and smooth the surface. Place the mold in a vacuum drying oven and dry at 70°C and a vacuum of -0.1 MPa for 36 hours. After drying, pulverize to obtain the binder. The infrared absorption spectrum of the binder is shown below (…). Figure 1 (The black pattern in the middle) Figure 1 As shown, at 1633cm -1 1526cm -1 1396cm -1 1297cm -1 Zn appears 2+ The mixed PAA coordination exhibits a strong diffraction peak, while pure PAA shows a peak at 1710 cm⁻¹. -1 There are strong peaks, and the shift in the position of the peaks indicates the formation of coordinate bonds.

[0119] (2) Preparation of pore-forming agent: S21. Acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and methacryloyloxyethyltrimethylammonium chloride are dissolved in water, and N,N'-methylenebisacrylamide is added. The mixture is reacted at 60°C for 4 hours to obtain a precursor (gel microspheres). The molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and methacryloyloxyethyltrimethylammonium chloride is 65:15:12:8. The solid-liquid ratio of acrylamide to water is 1:10.

[0120] Wherein, N,N'-methylenebisacrylamide is 0.1% of the total molar amount of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and methacryloyloxyethyltrimethylammonium chloride; S22. Mix 10g of precursor, 5g of phenol, 6.5g of 37% formaldehyde aqueous solution, 0.1g of sodium hydroxide as a catalyst, and 0.05g of carbon nanotubes evenly. Stir and react at 80℃ for 2-4 hours to allow for complete polycondensation to generate phenolic resin, which then coats the precursor surface. Dry the resulting solid product, then carbonize it at 800℃ for 2 hours under an inert atmosphere (such as argon), activate it with carbon dioxide gas for 20 minutes, wash, and dry to obtain the pore-forming agent.

[0121] The pore-forming agent includes porous carbon spheres and a carbon coating layer covering the outer surface of the porous carbon spheres. The carbon coating layer contains carbon nanotubes, the carbon nanotubes in the carbon coating layer are 12.5 wt%, and the thickness of the carbon coating layer is 20 nm.

[0122] (3) Preparation of negative electrode sheet: Graphite, conductive carbon black SP, binder prepared in step (1), and pore-forming agent prepared in step (1) are mixed evenly in a mass ratio of 98:0.5:1.3:0.2. Deionized water is added and stirred evenly to obtain a first negative electrode active material layer slurry with a solid content of 55%. Graphite, conductive carbon black SP, binder prepared in step (1), and pore-forming agent prepared in step (1) are mixed evenly in a mass ratio of 98.6:0.5:0.5:0.4. Deionized water is added and the mixture is stirred evenly to obtain a second negative electrode active material layer slurry with a solid content of 52%.

[0123] The first and second negative electrode active material layers are simultaneously coated onto a 6μm thick current collector copper foil using a double-layer coating equipment. The coated foil is then dried, rolled, and slit to obtain the negative electrode sheet. The first negative electrode active material layer has a thickness of 60μm, and the second negative electrode active material layer has a thickness of 160μm.

[0124] (4) Preparation of positive electrode sheet: Lithium iron phosphate (LiFePO4), conductive agent (conductive carbon black SP) and binder (polyvinylidene fluoride) are added to NMP solvent in a mass ratio of 97:1:2 and stirred thoroughly to form a positive electrode slurry with a solid content of 68%. The positive electrode slurry is then coated on an aluminum foil with a thickness of 17μm, dried, rolled and cut to obtain the positive electrode sheet. (5) Separator: 7μm PE base film + 2μm ceramic coating (boehmite) + 5μm PVDF (polyvinylidene fluoride), total thickness 14μm.

[0125] (6) Preparation of electrolyte: At room temperature (25°C), in an argon-filled glove box (H₂O < 1 ppm, O₂ < 1 ppm), ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed uniformly at a mass ratio of 3:2:5. Water was removed using a 4Å molecular sieve to obtain a mixed solvent. Lithium salts and film-forming additives were added sequentially to the mixed solvent. The lithium salts were lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, with the concentration of lithium hexafluorophosphate at 0.8 mol / L and the concentration of lithium bis(fluorosulfonyl)imide at 0.4 mol / L. The film-forming additives were vinylene carbonate and fluoroethylene carbonate, with the amount of vinylene carbonate added being 4% of the total electrolyte mass and the amount of fluoroethylene carbonate added being 1.3% of the total electrolyte mass. During the addition process, continuous stirring was maintained, and a dry ice bath was used to control the temperature, ensuring that the system temperature did not rise by more than 2°C. The electrolyte was obtained when all components were completely dissolved to form a homogeneous, colorless, and transparent liquid.

[0126] (7) Assembly of secondary battery: The positive electrode, separator and negative electrode are wound by a winding machine to obtain bare cell without liquid injection; the bare cell is placed in aluminum shell, the prepared electrolyte is injected into the dried aluminum shell, and after standing, formation, aging and capacity testing, a secondary battery is obtained.

[0127] The parameters of the binder and negative electrode sheet are shown in Table 1 and Table 2.

[0128] Examples 2-4 The difference between Examples 2-4 and Example 1 is that Zn 2+ The mass ratio of ionic liquid to PAA differs from that of the molar ratio of carboxyl groups (-COO⁻) on the PAA chain.

[0129] Zn in Example 2 2+ The molar ratio of the ionic liquid to the carboxyl group (-COO⁻) on the PAA chain is 0.2:1, and the mass ratio of the ionic liquid to PAA is 20:100.

[0130] In Example 3, Zn 2+ The molar ratio of the ionic liquid to the carboxyl group (-COO⁻) on the PAA chain is 0.5:1, and the mass ratio of the ionic liquid to PAA is 30:100.

[0131] In Example 4, Zn 2+ The molar ratio of the ionic liquid to the carboxyl group (-COO⁻) on the PAA chain is 0.1:1, and the mass ratio of the ionic liquid to PAA is 5:100.

[0132] Example 5 Example 5 differs from Example 1 in that an equal amount of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM] BF4) is used instead of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]).

[0133] Example 6 The difference between Example 6 and Example 1 is that Example 6 uses an equimolar amount of zinc sulfate to replace Zn(TFSI)2.

[0134] Examples 7-15 The difference between Examples 7-15 and Example 1 is that the compositions of the first negative electrode active material layer and the second negative electrode active material layer are different.

[0135] In Example 7, graphite, conductive carbon black SP, binder, and pore-forming agent in the first negative electrode active material layer slurry are mixed evenly in a mass ratio of 97.5:0.5:1.8:0.2; graphite, conductive carbon black SP, binder, and pore-forming agent in the second negative electrode active material layer slurry are mixed evenly in a mass ratio of 98.3:0.5:0.8:0.4.

[0136] In Example 8, graphite, conductive carbon black SP, binder, and pore-forming agent in the first negative electrode active material layer slurry are mixed evenly in a mass ratio of 98.5:0.5:0.8:0.2; graphite, conductive carbon black SP, binder, and pore-forming agent in the second negative electrode active material layer slurry are mixed evenly in a mass ratio of 98.9:0.5:0.2:0.4.

[0137] In Example 9, graphite, conductive carbon black SP, binder, and pore-forming agent in the first negative electrode active material layer slurry are mixed evenly in a mass ratio of 98.5:0.5:0.8:0.2; graphite, conductive carbon black SP, binder, and pore-forming agent in the second negative electrode active material layer slurry are mixed evenly in a mass ratio of 98.3:0.5:0.8:0.4.

[0138] In Example 10, graphite, conductive carbon black SP, binder, and pore-forming agent in the first negative electrode active material layer slurry are mixed evenly in a mass ratio of 98.7:0.5:0.6:0.2; graphite, conductive carbon black SP, binder, and pore-forming agent in the second negative electrode active material layer slurry are mixed evenly in a mass ratio of 99:0.5:0.1:0.4.

[0139] In Example 11, graphite, conductive carbon black SP, binder, and pore-forming agent in the first negative electrode active material layer slurry are mixed evenly in a mass ratio of 97.3:0.5:2:0.2; in the second negative electrode active material layer slurry, graphite, conductive carbon black SP, binder, and pore-forming agent are mixed evenly in a mass ratio of 98.1:0.5:1:0.4.

[0140] In Example 12, graphite, conductive carbon black SP, binder, and pore-forming agent in the first negative electrode active material layer slurry are mixed evenly in a mass ratio of 98.1:0.5:1.3:0.1; graphite, conductive carbon black SP, binder, and pore-forming agent in the second negative electrode active material layer slurry are mixed evenly in a mass ratio of 98.7:0.5:0.5:0.3.

[0141] In Example 13, graphite, conductive carbon black SP, binder, and pore-forming agent in the first negative electrode active material layer slurry are mixed evenly in a mass ratio of 97.9:0.5:1.3:0.3; and graphite, conductive carbon black SP, binder, and pore-forming agent in the second negative electrode active material layer slurry are mixed evenly in a mass ratio of 98.4:0.5:0.5:0.6.

[0142] In Example 14, graphite, conductive carbon black SP, binder, and pore-forming agent in the first negative electrode active material layer slurry are mixed evenly in a mass ratio of 97.7:0.5:1.3:0.5; and graphite, conductive carbon black SP, binder, and pore-forming agent in the second negative electrode active material layer slurry are mixed evenly in a mass ratio of 98:0.5:0.5:1.

[0143] In Example 15, graphite, conductive carbon black SP, and binder were mixed uniformly in the first negative electrode active material layer slurry at a mass ratio of 98.2:0.5:1.3; graphite, conductive carbon black SP, binder, and pore-forming agent were mixed uniformly in the second negative electrode active material layer slurry at a mass ratio of 99:0.5:0.5.

[0144] Example 16 The difference between Example 16 and Example 1 is that Example 16 does not contain a second negative electrode active material layer, and the total thickness of the negative electrode sheet is the same, that is, the second negative electrode active material layer in the original Example 1 is replaced by the first negative electrode active material layer.

[0145] Example 17 The difference between Example 17 and Example 1 is that Example 17 does not contain a first negative electrode active material layer, and the total thickness of the negative electrode sheet is the same, that is, the first negative electrode active material layer in the original Example 1 is replaced by a second negative electrode active material layer.

[0146] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the adhesive in Comparative Example 1 is a single PAA, which has not been treated in any way.

[0147] Among them, the infrared absorption spectrum of Comparative Example 1 ( Figure 1 (Medium gray spectrum) such as Figure 1 As shown.

[0148] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses an equal amount of styrene-butadiene rubber to replace PAA.

[0149] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that no ionic liquid was added to Comparative Example 3.

[0150] Preparation of the adhesive in Comparative Example 3: S1. Weigh 10.0 g of polyacrylic acid (PAA, solid, molecular weight 500,000) into a 250 mL three-necked flask. Add 60.0 g of deionized water and stir at 300 rpm for 4 hours at room temperature to form a homogeneous and clear PAA aqueous solution.

[0151] S2, according to Zn 2+ Calculate the required mass of zinc salt based on the molar ratio of PAA to the carboxyl group (-COOH) on the PAA chain being 0.3:1. For example, using Zn(TFSI)₂, 10.0 g PAA (138.9 mmol carboxyl group) requires 41.67 mmol of Zn. 2+ Coordination.

[0152] Weigh 25.5 g of Zn(TFSI)2 and dissolve it in 20.0 g of ethanol solution to prepare a clear zinc salt crosslinking solution.

[0153] S3. The PAA solution obtained in S1 was kept at room temperature and stirred at a mechanical stirring speed of 500 rpm. Using a constant pressure dropping funnel, the zinc salt ethanol solution prepared in step S2 was added dropwise to the PAA solution. After the addition was complete, the stirring speed was maintained at 500 rpm for 2 hours. The mixture was then dried at 70°C and a vacuum of -0.1 MPa for 36 hours. After drying, the mixture was pulverized to obtain the binder.

[0154] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that no metal salt was added to Comparative Example 4.

[0155] Preparation of the adhesive in Comparative Example 4: S1. Weigh 10.0 g of polyacrylic acid (PAA, solid, molecular weight 500,000) into a 250 mL three-necked flask. Add 60.0 g of deionized water and stir at 300 rpm for 4 hours at room temperature to form a homogeneous and clear PAA aqueous solution.

[0156] S2. Based on the mass ratio of ionic liquid to PAA of 20:100, calculate and weigh 2.0 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM][TFSI]). Add the weighed [EMIM][TFSI] directly to the PAA aqueous solution from step S1. Increase the stirring speed to 1500 rpm and perform high-speed shear blending for 3 hours. Pour the mixture into a polytetrafluoroethylene (PTFE) mold and smooth the surface. Place the mold in a vacuum drying oven and dry at 70°C and a vacuum of -0.1 MPa for 36 hours. After drying, pulverize to obtain the binder.

[0157] Table 1 Adhesive Parameter Table Table 2 Parameters of Negative Electrode Sheet Performance testing (1) DCR: In an incubator at 25±2℃, 1C = 314A; The test is conducted using a high-precision Newway or Arbin machine, and the test procedure is as follows: The capacity of the secondary battery was tested at a rate of 0.2C, and the tested capacity was C0. Discharge the battery at a rate of 0.2C for 30 minutes to reduce the secondary battery charge to 50% SOC, and let it stand for 30 minutes. Discharge at a rate of 1C for 10 seconds; Read the voltage V0 at the start of the secondary battery discharge and the voltage V10 at the end of the discharge; DCR = (V0 - V10) / discharge current.

[0158] (2) Energy efficiency at 25℃ / 0.5P: In an incubator at 25±2℃, 1P = 1004.8W. 1. Let stand for 2 hours; 2. Charge to 3.65V at 0.5P; 3. Let stand for 10 minutes; 4. Discharge to 2.5V at 0.5P; 5. Let stand for 10 minutes; 6. Repeat steps 2-5 once, take the capacity and energy of the second test, and calculate the 0.5P energy efficiency (energy efficiency = discharge energy / charging energy * 100%). (3) Capacity retention rate during 25℃ cycling: The secondary battery was charged to 3.65V at a constant power of 0.5P at 25℃, and then discharged to 2.5V at a constant power of 0.5P. This constitutes one cycle. The cycle was repeated 2000 times. The discharge capacity C1 of the first cycle and the discharge capacity C2000 of the 2000th cycle were recorded. The capacity retention rate was calculated as C2000 / C1 × 100%.

[0159] Table 3 Performance Test Results As can be seen from Table 3, the binder described in this application can improve the problem of brittle electrodes caused by traditional carboxyl-containing polymer binders; and improve the thermal stability and low-temperature performance of the electrodes. At the same time, it can improve the problem of poor kinetics of traditional carboxyl-containing polymer binders, thereby effectively reducing the DCR of the secondary battery and improving the energy efficiency and cycle life of the secondary battery.

[0160] 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. An adhesive, characterized in that, The binder includes carboxyl-containing polymer binders, ionic liquids, and metal ions, and the infrared absorption spectrum of the binder is in the range of 1250–1650 cm⁻¹. -1 It has an absorption peak.

2. The adhesive according to claim 1, characterized in that, Satisfy at least one of the following (a) to (d): (a) The infrared absorption spectrum of the adhesive is in the range of 1280~1320 cm⁻¹ -1 It has an absorption peak; (b) The infrared absorption spectrum of the adhesive is in the range of 1380~1420 cm⁻¹. -1 It has an absorption peak; (c) The infrared absorption spectrum of the adhesive is in the range of 1500~1550 cm⁻¹. -1 It has an absorption peak; (d) The infrared absorption spectrum of the adhesive is in the range of 1620~1650 cm⁻¹. -1 It has an absorption peak.

3. The adhesive according to claim 1, characterized in that, Satisfy at least one of the following (e) to (g): (e) The carboxyl-containing polymer binder includes at least one of polyacrylic acid, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose; (f) The ionic liquid comprises at least one of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt, and N,N-dimethyl-N-ethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide salt; (g) The metal ions include at least one of zinc ions, magnesium ions, and calcium ions.

4. The adhesive according to claim 1, characterized in that, Satisfy at least one of the following (h)~(j): (h) The carboxyl-containing polymer adhesive has a mass percentage content of 20-60% in the adhesive; (i) The ionic liquid has a mass percentage of 2-8% in the binder; (j) The mass percentage of the metal ions in the adhesive is 2-8%.

5. The adhesive according to claim 1, characterized in that, The adhesive also includes sulfur-containing anions, including SO4. 2- TFSI - At least one of them.

6. The adhesive according to claim 5, characterized in that, The sulfur-containing anion in the adhesive has a mass percentage of 20-68%.

7. A secondary battery, characterized in that, The electrode includes a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer including the binder according to any one of claims 1 to 6.

8. The secondary battery according to claim 7, characterized in that, The active material layer includes a first active material layer and a second active material layer, wherein the first active material layer is located on at least one surface of the current collector, and the second active material layer is located on the surface of the first active material layer away from the current collector. The porosity of the first active material layer is P1, and the porosity of the second active material layer is P2, satisfying P1 < P2.

9. The secondary battery according to claim 8, characterized in that, The adhesive has a mass percentage content of a in the first active material layer and a mass percentage content of b in the second active material layer, satisfying that a > b.

10. The secondary battery according to any one of claims 8 to 9, characterized in that, Satisfy at least one of the following (1) to (4): （1）20%≤P1≤35%； （2）35%≤P2≤50%； （3）0.8%≤a≤1.8%； （4）0.2%≤b≤0.8%。 11. The secondary battery according to claim 8, characterized in that, The first active material layer includes a pore-forming agent, and the second active material layer includes a pore-forming agent; the pore-forming agent includes a core and a carbon coating layer covering the outer surface of the core, the core includes porous carbon spheres, and the average pore size of the porous carbon spheres is larger than the average pore size of the carbon coating layer.

12. The secondary battery according to claim 11, characterized in that, The thickness of the carbon coating layer is 5~15 nm; and / or The carbon coating layer also includes a conductive agent, and the conductive agent has a mass percentage content of 4.8~16.7% in the carbon coating layer.

13. The secondary battery according to claim 11, characterized in that, The pore-forming agent has a mass percentage content of 0.1~0.3% in the first active material layer; and / or The pore-forming agent has a mass percentage content of 0.4-0.6% in the second active material layer.

14. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 7 to 13, wherein the secondary battery serves as the power supply for the electrical device.

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