Binder, positive electrode slurry, positive electrode plate, battery and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a binder, positive electrode slurry, a positive electrode plate, a battery and an electric device. The binder comprises a polyvinylidene fluoride main body structure and a modified group, wherein the modified group comprises a conductive conjugated polymer and a sulfonate group; the conductive conjugated polymer comprises one or more of poly (3, 4-ethylenedioxythiophene), poly (3-hexylthiophene) and poly (aniline). A conductive conjugated polymer fragment and a sulfonate group are introduced to a polyvinylidene fluoride main body structure, so that the conductivity, the adhesion and the interface wettability of the binder are remarkably improved, the interface resistance of a pole piece can be effectively reduced, the peel strength is improved, the viscosity resilience of slurry is inhibited, and the service life of the pole piece is prolonged. The positive pole piece still has excellent processability and electrochemical stability under a high compaction condition, the rate capability and the long cycle life are remarkably improved, and the positive pole piece is suitable for large-scale preparation of high-energy-density lithium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to binders, positive electrode slurries, positive electrode sheets, batteries, and electrical devices. Background Technology

[0002] With the rapid growth in demand from the new energy vehicle and energy storage sectors, the requirements for lithium-ion batteries with high energy density, high rate performance, long cycle life, and high safety are becoming increasingly stringent. As a key component determining battery capacity and power output, the binder used in the electrode fabrication process is crucial.

[0003] Polyvinylidene fluoride (PVDF) is the most commonly used binder in the positive electrode of commercial lithium-ion batteries due to its excellent chemical stability, mechanical adhesion, and corrosion resistance. However, PVDF is a non-conductive polymer and does not promote the migration of electrons and lithium ions. This leads to greater resistance inside the positive electrode and at the electrode-electrolyte interface under high-rate charge-discharge conditions, resulting in intensified polarization and significantly reducing the high-rate capacity and cycle stability of the battery. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a binder, a positive electrode slurry, a positive electrode sheet, a battery, and an electrical device. The binder provided by the present invention has both an electronic conductive network and provides coordinated adsorption sites for lithium ions, and has good durability and stability in common alkaline dispersion systems, which can meet the requirements of batteries with high energy density, high rate, and high cycle stability.

[0005] This invention provides an adhesive comprising a polyvinylidene fluoride (PVDF) main structure and modifying groups;

[0006] The modifying groups include conductive conjugated polymers grafted onto the main chain and / or side chains of the polyvinylidene fluoride host structure, and sulfonate groups introduced by functionalization onto the main chain and / or side chains of the polyvinylidene fluoride host structure.

[0007] The conductive conjugated polymer includes one or more of poly(3,4-ethylenedioxythiophene), poly(3-hexylthiophene), and poly(aniline).

[0008] Preferably, the Fourier transform infrared spectrum of the adhesive is in the range of 1400–1480 cm⁻¹. -1 The region exhibits characteristic peaks of C=C skeletal vibration, ranging from 1030 to 1080 cm⁻¹. -1 The region exhibits characteristic peaks of S=O symmetrical stretching vibration.

[0009] And / or, the Raman spectrum of the adhesive is in the range of 1420–1460 cm⁻¹. -1Characteristic peaks belonging to conjugated C=C double bonds appear in the range of 1040–1060 cm⁻¹. -1 The range shows characteristic peaks attributable to the S=O bonds in sulfonate groups.

[0010] Preferably, the grafting content of the conductive conjugated polymer is 1 wt% to 7.5 wt%.

[0011] And / or, the sulfonate group is introduced in a proportion of 1 wt% to 10 wt%.

[0012] Preferably, the molecular weight of the polyvinylidene fluoride main structure is 3 × 10⁻⁶. 5 g / mol~2×10 6 g / mol.

[0013] The present invention also provides a positive electrode slurry, comprising the binder described in the above technical solution.

[0014] Preferably, the positive electrode slurry further includes a positive electrode active material, a conductive agent, and a solvent;

[0015] And / or, the positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate;

[0016] And / or, the conductive agent includes carbon black and / or carbon nanotubes;

[0017] And / or, the solvent includes N-methylpyrrolidone;

[0018] And / or, the mass percentage of the positive electrode active material, conductive agent and binder is (94.5% to 98%): (1% to 3.5%): (1% to 2.5%).

[0019] The present invention also provides a positive electrode sheet, comprising a positive current collector and a positive active material layer, wherein the positive active material layer is formed by curing the positive electrode slurry described in the above technical solution.

[0020] Preferably, the curing temperature is 80℃~140℃;

[0021] And / or, the curing time is 1 hour to 2 hours;

[0022] And / or, the compaction density of the positive electrode sheet is >3.4 g / cm³. 3 ;

[0023] And / or, the interface resistance of the positive electrode is 1.0 × 10⁻⁶. -2 mΩ·cm 2 Up to 4.0×10 -2 mΩ·cm 2 between;

[0024] And / or, the peel strength of the positive electrode sheet is greater than or equal to 8.5 N / m and less than or equal to 20.0 N / m.

[0025] The present invention also provides a battery comprising the positive electrode sheet described in the above technical solution.

[0026] The present invention also provides an electrical device, including the battery described in the above technical solution.

[0027] This invention provides an adhesive, a positive electrode slurry, a positive electrode sheet, a battery, and an electrical device. The adhesive comprises a polyvinylidene fluoride (PVDF) main structure and modifying groups. The modifying groups include a conductive conjugated polymer grafted onto the main chain and / or side chains of the PVDF main structure, and sulfonate groups introduced through functionalization of the main chain and / or side chains of the PVDF main structure. The conductive conjugated polymer includes one or more of poly(3,4-ethylenedioxythiophene), poly(3-hexylthiophene), and poly(aniline). Compared with the prior art, this invention significantly improves the conductivity, adhesion, and interfacial wettability of the adhesive by introducing conductive conjugated polymer fragments and sulfonate groups into the PVDF main chain and / or side chains. This effectively reduces the interfacial resistance of the electrode sheet, improves peel strength, and suppresses slurry viscosity rebound, enabling the positive electrode sheet to maintain excellent processing performance and electrochemical stability under high compaction conditions. It also significantly improves rate performance and long cycle life, making it suitable for the large-scale preparation of high-energy-density lithium-ion batteries. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 The infrared spectrum of the modified PVDF binder provided in Example 1 of the present invention. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present application, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In the description of this application, it should be understood that the terms "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0032] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0033] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0034] Unless otherwise stated, all technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. All patents and publications referenced in this application are incorporated herein by reference in their entirety. The terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this application but do not exclude other contents.

[0035] Currently, polyvinylidene fluoride (PVDF), as the most commonly used binder in the positive electrode of commercial lithium-ion batteries, still faces the following technical challenges: PVDF is a non-conductive polymer and does not promote the migration of electrons and lithium ions. This leads to significant resistance within the positive electrode and at the electrode-electrolyte interface under high-rate charge-discharge conditions, exacerbating polarization and significantly reducing the high-rate capacity and cycle stability of the battery. Therefore, there is an urgent need to develop a modified PVDF binder that possesses both an electronically conductive network and provides coordinated adsorption sites for lithium ions, while exhibiting good durability and stability in common alkaline dispersion systems, to meet the demands of batteries with high energy density, high rate capability, and high cycle stability.

[0036] Based on this, the present invention provides an adhesive that, on the one hand, introduces conductive polymer fragments into the PVDF molecular structure, which helps to form an electron channel network, reduce the ohmic impedance of the positive electrode, and improve the electron transport rate; on the other hand, it introduces sulfonate groups (-SO3H / -SO3) into the PVDF main chain or side chain through functionalization. -This modified PVDF binder can form partial ion-conducting channels, thereby reducing interfacial impedance and increasing the diffusion rate of lithium ions within the electrode and at the electrode / electrolyte interface; it also maintains good dispersion and viscosity stability in common alkaline slurry environments. Furthermore, this invention provides an application scheme for this modified PVDF binder in the preparation of lithium-ion battery cathodes, which can significantly improve the rate performance, cycle performance, and interfacial alkali resistance of lithium batteries, providing guidance for the preparation of high-performance cathodes.

[0037] In this invention, the adhesive comprises a polyvinylidene fluoride main structure and modified groups;

[0038] The modifying groups include conductive conjugated polymers grafted onto the main chain and / or side chains of the polyvinylidene fluoride host structure, and sulfonate groups introduced by functionalization onto the main chain and / or side chains of the polyvinylidene fluoride host structure.

[0039] The conductive conjugated polymer includes one or more of poly(3,4-ethylenedioxythiophene), poly(3-hexylthiophene), and poly(aniline).

[0040] In this invention, the polyvinylidene fluoride main structure is polyvinylidene fluoride (PVDF), and the molecular weight of the polyvinylidene fluoride main structure is preferably 3 × 10⁻⁶. 5 g / mol~2×10 6 g / mol, more preferably 4×10 g / mol 5 g / mol~1.2×10 6 The present invention utilizes the above-mentioned PVDF molecular weight, enabling the electrode to exhibit lower interfacial resistance, higher peel strength, and better rate and cycle performance. This is because a suitable molecular weight is conducive to the orderly arrangement and crystallization of molecular chains, thereby improving electron / ion transport efficiency and electrode structural stability. Conversely, excessively low or high molecular weights can weaken overall performance. This phenomenon is attributed to the fact that the molecular weight of PVDF directly determines its chain length, crystallinity, and film-forming ability. At a medium molecular weight, its chain segments can be fully stretched and oriented during drying and rolling processes, forming a uniform and dense highly crystalline phase, which helps to establish stable interfacial contact and reduce interfacial resistance. At the same time, a suitable molecular weight can also balance the diffusion synergistic effect between molecular chains, improve the solution viscoelasticity of the system, and mitigate viscosity fluctuations caused by insufficient chain entanglement, thereby reducing viscosity rebound. A suitable molecular weight also helps to form a good pore structure, improve the uniformity of ion distribution and reaction equilibrium in the electrode, thereby improving 10C rate and long cycle performance. However, if the molecular weight is too high (>2.0×10), the performance will be significantly reduced. 6 Excessive chain entanglement and decreased solvent penetration will reduce the effective film-forming rate of the binder, leading to increased interfacial impedance, structural embrittlement, and decreased capacity.

[0041] In this invention, the polyvinylidene fluoride (PVDF) host structure is provided with modifying groups; the modifying groups include conductive conjugated polymers grafted onto the main chain and / or side chains of the PVDF host structure, and sulfonate groups (-SO3H / -SO3) introduced through functionalization (via fluorine atom substitution or copolymerization) onto the main chain and / or side chains of the PVDF host structure. - The conductive conjugated polymer comprises one or more of poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3-hexylthiophene) (P3HT), and poly(aniline) (PANI), preferably poly(3-hexylthiophene) (P3HT).

[0042] In this invention, the Fourier transform infrared spectrum of the adhesive is preferably in the range of 1400–1480 cm⁻¹. -1 The region exhibits characteristic peaks of C=C skeletal vibration (PEDOT, P3HT, or PANI at 1400–1480 cm⁻¹). -1 All exhibit strong characteristic absorption peaks of C=C double bonds, in the range of 1030–1080 cm⁻¹. -1 The region exhibits characteristic peaks of S=O symmetric stretching vibration; while pure PVDF lacks C=C double bonds, and peaks are observed in the 1400–1480 cm⁻¹ region. -1 No characteristic absorption peaks.

[0043] In this invention, the Raman spectrum of the adhesive is in the range of 1420–1460 cm⁻¹. -1 Characteristic peaks belonging to conjugated C=C double bonds appear in the range of 1040–1060 cm⁻¹. -1 The range shows characteristic peaks attributable to the S=O bonds in sulfonate groups.

[0044] Furthermore, the present invention combines the binder film with a glassy carbon electrode to assemble a three-electrode system. In a 1M LiPF6 / EC:DEC (1:1 v / v) electrolyte, cyclic voltammetry (CV) was used at a scan rate of 0.1 mV / s within a voltage window of 2.5–4.2 V, and no obvious redox peaks were observed.

[0045] In this invention, the grafting content of the conductive conjugated polymer is preferably 1 wt% to 7.5 wt%, more preferably 1 wt% to 5 wt%. By employing a suitable grafting content of the conductive conjugated polymer, this invention can construct stable and continuous π-conjugated electron conduction channels within the PVDF matrix, improving the electronic coupling and interfacial charge transfer efficiency of the electrode, thereby effectively reducing interfacial impedance. Simultaneously, the flexible structure and polar functional groups of the conjugated segments enhance the adhesion of the binder to the active particles and current collectors, improving the mechanical bonding strength of the electrode. Furthermore, a reasonable grafting content can improve the stability and wettability of the polymer solution, alleviate viscosity rebound in alkaline systems, and promote the self-assembly of segments into a three-dimensional conductive network during the drying process, which is beneficial for the coordinated migration of electrons and ions. Conversely, excessively high grafting content can easily lead to inter-chain entanglement, microphase separation, or uneven structural coating, resulting in interruption of conductive channels and destruction of the bonding network, ultimately increasing interfacial impedance and exacerbating electrochemical decay.

[0046] In this invention, the preferred proportion of the sulfonate group is 1 wt% to 10 wt%, more preferably 1 wt% to 7.5 wt%. This invention employs a suitable proportion of sulfonate group introduction. As a strongly polar ionophilic group, the sulfonate group can form uniformly distributed negatively charged sites on the PVDF molecular chain, which helps to enhance the migration efficiency of lithium ions within the electrode and at the interface, significantly reducing interfacial impedance; simultaneously, -SO3... - Ionic and hydrogen bonds can form between the sulfonic acid group and the metal oxides on the surface of the active particles, improving the bonding strength of the electrode structure. Furthermore, its high hydrophilicity can stabilize the PVDF dispersion and suppress viscosity rebound caused by the aggregation of hydrophobic segments in alkaline environments. The presence of sulfonic acid groups can also form local ion channels inside the electrode, enhancing the electrochemical reaction kinetics at high rates. However, if the proportion introduced is too high (>10wt%), it will cause abnormally high solution viscosity, free radical side chain aggregation, and even uneven dielectric stress, thereby affecting the overall stability of the electrode and leading to a decrease in rate capability and cycle life.

[0047] The adhesive provided by this invention is specifically a modified PVDF adhesive with conductivity and ion affinity, which is achieved by simultaneously introducing conductive conjugated polymer segments (such as PEDOT, P3HT, or PANI) and sulfonate groups (-SO3H / -SO3) into the PVDF molecular structure. - The ) group achieves synergistic enhancement of the binder in terms of conductivity, adhesion and interfacial stability. It has both an electronic conductive network and provides coordinated adsorption sites for lithium ions. It also has good durability and stability in common alkaline dispersion systems, which can meet the requirements of high energy density, high rate and high cycle stability batteries.

[0048] The present invention also provides a positive electrode slurry, comprising the binder described in the above technical solution.

[0049] In this invention, the positive electrode slurry, in addition to the binder described in the above-mentioned technical solution, preferably also includes a positive electrode active material, a conductive agent, and a solvent; wherein, the positive electrode active material preferably includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate, more preferably lithium nickel cobalt manganese oxide; the general formula of the lithium nickel cobalt manganese oxide is Li1Ni. x Co y Mn z M b O2, wherein 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0≤b≤0.25, x+y+z+b=1, and element M includes one or more of zirconium (Zr), tungsten (W), titanium (Ti), aluminum (Al), strontium (Sr), boron (B), and neodymium (Nd), preferably LiNi. 0.8 Co 0.1 Mn 0.1 O2; the conductive agent preferably includes carbon black and / or carbon nanotubes, more preferably carbon black and / or carbon nanotubes; the solvent preferably includes N-methylpyrrolidone (NMP); the present invention does not impose any special restrictions on the source of the above-mentioned positive electrode active material, conductive agent and solvent, and commercially available products well known to those skilled in the art can be used.

[0050] In this invention, the preferred mass percentage of the positive electrode active material, conductive agent, and binder is (94%–98%):(1%–3.5%):(1%–2.5%).

[0051] The present invention does not impose any special restrictions on the preparation method of the positive electrode slurry. It can be achieved by using a wet slurry preparation technique known to those skilled in the art, which involves mixing the above-mentioned raw materials with a solvent.

[0052] In this invention, the viscosity rebound rate of the positive electrode slurry (pH>12) within 12 hours at room temperature (15℃~35℃) is preferably less than 50%.

[0053] The present invention also provides a positive electrode sheet, comprising a positive current collector and a positive active material layer, wherein the positive active material layer is formed by curing the positive electrode slurry described in the above technical solution.

[0054] In this invention, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil; the composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate; the composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0055] The present invention involves coating the positive electrode slurry described in the above technical solution onto at least one surface of the positive electrode current collector, curing it, and then cold pressing it to form a positive electrode sheet.

[0056] In this invention, the curing method is drying, and the temperature is preferably 80℃~140℃, more preferably 80℃~120℃; the curing time is preferably 1h~2h.

[0057] In this invention, the compaction density of the positive electrode sheet is preferably >3.4 g / cm³. 3 .

[0058] In this invention, the interface resistance of the positive electrode is preferably 1.0 × 10⁻⁶. -2 mΩ·cm 2 Up to 4.0×10 -2 mΩ·cm 2 Between; the peel strength of the positive electrode sheet is preferably greater than or equal to 8.5 N / m and less than or equal to 20.0 N / m.

[0059] The present invention also provides a battery comprising the positive electrode sheet described in the above technical solution.

[0060] In this invention, in addition to the positive electrode sheet described in the above technical solution, the battery preferably also includes a negative electrode sheet, a separator, an electrolyte, and other necessary or non-essential functional components or packaging components, which can be arbitrarily selected and combined by those skilled in the art; when the battery includes the positive electrode sheet described in the above technical solution, regardless of whether other composite positive electrodes are used in the battery, it can be regarded as an embodiment of this invention.

[0061] In a preferred embodiment of the present invention, the battery is a 21700 cylindrical lithium-ion battery. Based on this, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being formed by curing a negative electrode slurry. The negative electrode slurry includes a negative electrode active material, a thickener, a binder, and a conductive agent. Preferably, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon, more preferably artificial graphite and / or natural graphite. The thickener preferably includes sodium carboxymethyl cellulose. The binder preferably includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber, more preferably styrene-butadiene rubber. The conductive agent preferably includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black, more preferably single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The present invention does not impose any special restrictions on the source of the above-mentioned negative electrode active material, thickener, binder, and conductive agent; commercially available products well known to those skilled in the art can be used.

[0062] In a preferred embodiment of the present invention, the mass percentages of the negative electrode active material, thickener, binder and conductive agent are (94%~98%): (0.5%~1.5%): (0.5%~2%): (1%~2.5%).

[0063] The present invention does not impose any particular limitation on the preparation method of the negative electrode slurry; it can be achieved by using a wet slurry preparation technique well known to those skilled in the art, which involves mixing the above-mentioned raw materials with water. After obtaining the negative electrode slurry, it is coated onto at least one surface of the negative electrode current collector, and then dried and cold-pressed to form a negative electrode sheet. In the present invention, the compaction density of the negative electrode sheet is preferably 1 g / cm³. 3 ~2g / cm 3 .

[0064] In this invention, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil; the composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate; the composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0065] In a preferred embodiment of the present invention, the diaphragm includes, but is not limited to, PP, PE, and composite diaphragms made of any combination of these materials. It can also be a composite diaphragm made of the above-mentioned materials as a base membrane with a ceramic coating and / or a polymer coating. Any material that can provide insulation and prevent direct contact between the positive and negative electrodes, and has certain mechanical strength, thermal stability, chemical stability and suitable porosity can be used as a diaphragm. The present invention does not have any special limitations on this.

[0066] In a preferred embodiment of the present invention, the electrolyte comprises a lithium salt, a solvent, and an additive; wherein the lithium salt preferably comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium difluorosulfonylimide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethanesulfonylimide), more preferably lithium hexafluorophosphate (LiPF6); the solvent preferably comprises one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate; and the additive preferably comprises one or more of fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfate, ethylene sulfite, ethylene carbonate, and vinyl carbonate.

[0067] The present invention does not impose any special restrictions on the assembly method of the battery, and can be implemented by battery assembly techniques known to those skilled in the art; for the above-mentioned 21700 cylindrical lithium-ion battery, the present invention first rolls and cuts the positive electrode sheet and the negative electrode sheet, and then winds them together with the separator to obtain the 21700 cylindrical battery core, and then welds the battery core to the connecting piece and puts it into the battery casing. After completing the liquid injection, sealing and formation processes, the battery is obtained; the casing of the battery is cylindrical.

[0068] In this invention, the battery is a lithium-ion battery, and its discharge characteristics are as follows: after a lithium-ion battery with 100% charge is left to stand at 25°C for 6 hours, it is discharged at a rate of 0.1C to 2.5V, and the corresponding discharge capacity is Q1; the discharge capacity at 10C to 2.5V is Q2; the discharge capacity retention rate Q2 / Q1 ≥ 72%.

[0069] In this invention, the lithium-ion battery exhibits a capacity decay rate of less than 25% after 1000 cycles at 25°C and a 1C rate.

[0070] The present invention also provides an electrical device, including the battery described in the above technical solution. Specifically, the battery can serve as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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, and energy storage systems.

[0071] This invention provides an adhesive, a positive electrode slurry, a positive electrode sheet, a battery, and an electrical device. The adhesive comprises a polyvinylidene fluoride (PVDF) main structure and modifying groups. The modifying groups include a conductive conjugated polymer grafted onto the main chain and / or side chains of the PVDF main structure, and sulfonate groups introduced through functionalization of the main chain and / or side chains of the PVDF main structure. The conductive conjugated polymer includes one or more of poly(3,4-ethylenedioxythiophene), poly(3-hexylthiophene), and poly(aniline). Compared with the prior art, this invention significantly improves the conductivity, adhesion, and interfacial wettability of the adhesive by introducing conductive conjugated polymer fragments and sulfonate groups into the PVDF main chain and / or side chains. This effectively reduces the interfacial resistance of the electrode sheet, improves peel strength, and suppresses slurry viscosity rebound, enabling the positive electrode sheet to maintain excellent processing performance and electrochemical stability under high compaction conditions. It also significantly improves rate performance and long cycle life, making it suitable for the large-scale preparation of high-energy-density lithium-ion batteries.

[0072] To further illustrate the present invention, the following embodiments provide a detailed description. In the following embodiments, unless specific techniques or conditions are specified, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions; reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0073] Example 1

[0074] (1) Preparation method of modified PVDF adhesive:

[0075] ① Conductive polymer grafting:

[0076] 1 kg of commercial PVDF powder (weight average molecular weight approximately 1.2 × 10⁻⁶) was used. 6 Under nitrogen protection, the product was dissolved in 7.5 L NMP and heated to 80 °C until fully dissolved. 200 g of ammonium persulfate (NH4)2S2O8 was added as a free radical initiator, and the reaction temperature was maintained at 80 °C. 50 g (equivalent to 5 wt%) of P3HT monomer (or P3HT solution) was slowly added to the reaction system, and the reaction was carried out for 4 h to obtain the graft polymerization product. After the reaction was completed, the product was precipitated with methanol, filtered, and repeatedly washed with deionized water until the filtrate was colorless. The product was placed in a vacuum oven and dried at 80 °C for 12 h to obtain the PVDF-P3HT precursor.

[0077] ②Sulfonate functionalization:

[0078] Dissolve 500g of PVDF-P3HT in 5000mL of tetrahydrofuran (THF); slowly add 25g of sodium styrene sulfonate (PSSNa) (equivalent to approximately 5wt% of the theoretical grafted sulfonate group) dropwise, while simultaneously adding 300mL of triethylamine (TEA) as a catalyst; under a nitrogen atmosphere, heat to 65℃ and react for 6h to introduce sulfonate groups into the PVDF backbone via nucleophilic substitution or free radical copolymerization; after the reaction is complete, pour the reaction solution into deionized water to precipitate, filter the precipitate, wash with hot water (60℃) until the pH of the filtrate is approximately 7; wash with methanol, and then dry the resulting dark solid in a vacuum oven at 80℃ for 12h to obtain PVDF-P3HT-SO3H (hereinafter referred to as modified PVDF). See the infrared spectrum for details. Figure 1 As shown.

[0079] Depend on Figure 1 It can be seen that the Fourier transform infrared (FT-IR) spectrum of the modified PVDF binder provided in Example 1 of this invention is in the range of 1400–1480 cm⁻¹. -1 The region exhibits characteristic peaks of C=C skeletal vibration, ranging from 1030 to 1080 cm⁻¹. -1 The region exhibits characteristic peaks of S=O symmetrical stretching vibration.

[0080] Methods for determining the molecular weight of modified PVDF:

[0081] The determination was performed using gel permeation chromatography (GPC): The sample was dissolved in anhydrous DMF containing 0.1 wt% LiBr, completely dissolved at 60 °C, filtered through a 0.22 μm filter membrane, and injected into the GPC system. The number-average molecular weight (Mn), weight-average molecular weight (Mw), and distribution coefficient (PDI) were obtained using a differential refractive index (RI) or multi-angle laser scattering (MALS) detector, through calibration curves or absolute methods.

[0082] (2) Preparation method of positive electrode slurry:

[0083] The preparation of the positive electrode slurry employs a combination of dry premixing and wet dispersion using a dual planetary mixer. The specific steps are as follows: First, each powder component is accurately weighed according to the mass percentage (NCM811: Super P: HCNT: modified PVDF = 96:1:1:2), and dry-mixed into a homogenate in a dual planetary mixer. The mixing speed is set to 40 rpm, and the mixture is stirred for 30 minutes to ensure that the conductive agent and binder are uniformly coated on the surface of the active material. Then, an appropriate amount of NMP solvent is slowly added to control the solid content at 68±2wt%. The mixture is then switched to a low-speed-high-speed alternating mode, and staged stirring is performed sequentially: low speed at 80 rpm for 30 minutes for initial wetting, followed by high-speed stirring at 3000 rpm for 2.5 hours to form a uniform slurry. During the stirring process, a negative pressure (-0.08MPa) is maintained inside the mixer to prevent the introduction of air bubbles, and the temperature is controlled at 25±2℃ through the jacket. After stirring, the slurry is allowed to stand to degas or vacuum degassed for 30 minutes to obtain a positive electrode slurry with stable viscosity, uniform dispersion, and suitable for coating.

[0084] (3) Method for manufacturing positive electrode sheets:

[0085] The above-mentioned positive electrode slurry was uniformly coated onto a 12.0 μm thick aluminum foil. After drying the electrode at 120°C for 1.5 hours, it was cold-pressed, slit, and cut to obtain the positive electrode sheet with a compacted density of 3.5 g / cm³. 3 .

[0086] (4) Preparation methods of negative electrode slurry and negative electrode sheet:

[0087] The negative electrode sheet comprises a copper foil as the negative current collector and a negative electrode coating material coated on both sides of the copper foil. By mass percentage, the negative electrode coating material comprises 96.0% graphite, 1.5% carbon nanotubes, 1.0% sodium carboxymethyl cellulose (CMC) thickener, and 1.5% styrene-butadiene rubber (SBR) binder. These substances are added to deionized water and stirred to form the negative electrode coating material, with a solid content of 40%. The negative electrode coating material is then coated onto both sides of the negative current collector (copper foil), dried, and cold-pressed to form the negative electrode sheet with a compacted density of 1.5 g / cm³. 3 .

[0088] (5) Preparation of electrolyte:

[0089] The electrolyte was prepared by mixing lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), and vinylene carbonate (VC) in a mass percentage ratio of 10.0:20.0:55.0:2.0:8.0:5.0.

[0090] (6) Diaphragm:

[0091] A high-porosity membrane is selected, in which the thickness of the PE base membrane is 9μm, the thickness of the ceramic coating on both sides of the base membrane is 1.0μm, and the thickness of the PVDF coating is 1.0μm.

[0092] (7) Assembly of lithium-ion batteries:

[0093] The positive and negative electrode sheets are rolled and slit respectively, and then wound together with the separator to obtain a 21700 cylindrical battery core. The battery core is then welded to the connecting piece and installed into the battery casing. After completing the liquid injection, sealing and formation processes, the lithium-ion battery of Example 1 is obtained. The casing of the lithium-ion battery is cylindrical with the following dimensions: diameter: 21.0 mm, length: 70.0 mm.

[0094] Example 2

[0095] The difference between this embodiment and Example 1 is that the mass of P3HT monomer added during the preparation of the modified PVDF binder is 10g (equivalent to 1wt%), while all other aspects are the same as in Example 1.

[0096] Example 3

[0097] The difference between this embodiment and Example 1 is that the mass of P3HT monomer added during the preparation of the modified PVDF binder is 25g (equivalent to 2.5wt%), while all other aspects are the same as in Example 1.

[0098] Example 4

[0099] The difference between this embodiment and Example 1 is that the mass of P3HT monomer added during the preparation of the modified PVDF binder is 75g (equivalent to 7.5wt%), while all other aspects are the same as in Example 1.

[0100] Example 5

[0101] The difference between this embodiment and Example 1 is that 5g of sodium styrene sulfonate (PSSNa) (equivalent to approximately 1wt% of the theoretical grafted sulfonate ratio) was added during the preparation of the modified PVDF binder; all other aspects are the same as in Example 1.

[0102] Example 6

[0103] The difference between this embodiment and Example 1 is that 12.5g of sodium styrene sulfonate (PSSNa) (equivalent to approximately 2.5wt% of the theoretical grafted sulfonate ratio) was added during the preparation of the modified PVDF binder. All other aspects are the same as in Example 1.

[0104] Example 7

[0105] The difference between this embodiment and Example 1 is that 37.5g of sodium styrene sulfonate (PSSNa) (equivalent to approximately 7.5wt% of the theoretical grafted sulfonate ratio) was added during the preparation of the modified PVDF binder. All other aspects are the same as in Example 1.

[0106] Example 8

[0107] The difference between this embodiment and Embodiment 1 is that the weight-average molecular weight of PVDF is 4 × 10⁻⁶. 5 Everything else is the same as in Example 1.

[0108] Example 9

[0109] The difference between this embodiment and Embodiment 1 is that the weight-average molecular weight of PVDF is 8 × 10⁻⁶. 5 Everything else is the same as in Example 1.

[0110] Example 10

[0111] The difference between this embodiment and Embodiment 1 is that the weight-average molecular weight of PVDF is 2.0 × 10⁻⁶. 6 Everything else is the same as in Example 1.

[0112] Example 11

[0113] The difference between this embodiment and Embodiment 1 is that the modified PVDF added during the preparation of the positive electrode slurry has a mass percentage of 1.0 wt%, while all other aspects are the same as in Embodiment 1.

[0114] Example 12

[0115] The difference between this embodiment and Embodiment 1 is that the modified PVDF added during the preparation of the positive electrode slurry is 1.5 wt% by mass, while all other aspects are the same as in Embodiment 1.

[0116] Example 13

[0117] The difference between this embodiment and Embodiment 1 is that the modified PVDF added during the preparation of the positive electrode slurry is 2.5 wt% by mass, while all other aspects are the same as in Embodiment 1.

[0118] Example 14

[0119] The difference between this embodiment and Embodiment 1 is that the drying temperature of the positive electrode sheet is 80°C, while all other aspects are the same as in Embodiment 1.

[0120] Example 15

[0121] The difference between this embodiment and Embodiment 1 is that the drying temperature of the positive electrode sheet is 100°C, while all other aspects are the same as in Embodiment 1.

[0122] Example 16

[0123] The difference between this embodiment and Embodiment 1 is that the drying temperature of the positive electrode is 140°C, while all other aspects are the same as in Embodiment 1.

[0124] Comparative Example 1

[0125] The difference between this embodiment and Embodiment 1 is that PVDF is not grafted with P3HT, while everything else is the same as in Embodiment 1.

[0126] Comparative Example 2

[0127] The difference between this embodiment and Embodiment 1 is that PVDF is not grafted with sulfonate groups; otherwise, they are the same as in Embodiment 1.

[0128] Performance testing:

[0129] Test method for viscosity rebound of positive electrode slurry:

[0130] First, immediately remove the prepared positive electrode slurry and measure its initial viscosity (η0) using a rotational viscometer (such as a Brookfield DV2T) at 25°C with a No. 5 rotor at a shear rate of 60 rpm. Then, seal the slurry and allow it to stand at 25°C for 24 hours, and measure the viscosity (η0) again under the same conditions. 24 Finally, the viscosity rebound rate is calculated using the following formula:

[0131] Viscosity rebound rate = (η) 24 -η0) / (η0)×100%;

[0132] Cylindrical battery pretreatment:

[0133] First, discharge the lithium-ion battery to a constant current of 2.5V to ensure it is in a safe state, reducing the risk of short circuits or thermal runaway during disassembly. Carefully disassemble the battery within a glove box (protected by argon or other inert atmosphere) and remove the positive electrode from the cylindrical cell. Use tweezers or a suitable tool to peel off the electrode, avoiding damage to the active material layer. Next, cut the removed positive electrode to an appropriate size and soak it in anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. After removing the electrode, gently wipe the surface with lint-free paper, then replace with fresh DMC solution, repeating the soaking-wiping process three times to ensure no residual contaminants remain on the electrode surface. Subsequently, rinse the electrode with anhydrous ethanol and wipe again to further remove solvent and impurities. After cleaning, place the electrode in a glove box and let it stand for 48 hours to ensure it is completely dry, preventing interference from residual solvent in subsequent testing.

[0134] Method for testing the interface resistance of the positive electrode:

[0135] The interfacial resistance of the negative electrode was measured using the 46-probe method (45 probes arranged in a square matrix, with one probe serving as a ground probe) of the RM2610 resistance testing system. First, the negative electrode, after being rinsed with dimethyl carbonate and vacuum dried, was divided into 40 square grids to ensure a flat sample surface. Next, the sample was placed on the testing apparatus, and the pressure applied to the probes was adjusted using a pressure gauge to ensure good contact between the probes and the sample, with a contact area of ​​0.01 cm². 2 During the test, a constant current was applied to the outer 20 probes, allowing the current to flow through the surface, interface, and current collector of the electrode. Simultaneously, the middle 25 probes measured the voltage change in real time. Since the surface, interface, and current collector of the electrode have significantly different resistances, the measured voltage reflects these differences. Finally, the membrane resistance R1 was calculated using Ohm's law and fitting analysis. Subsequently, the same method was used to randomly select another 9 square grids on the electrode for interface resistance measurement, and the obtained values ​​were recorded as R2, R3, R4, R5, R6, R7, R8, R9, and R... 10 Finally, the average interface resistance R is obtained by calculating the arithmetic mean of these values. α This is to facilitate a comprehensive evaluation of the conductivity and uniformity of the negative electrode.

[0136] Test method for compaction density of positive electrode sheet:

[0137] First, the positive electrode sheet, after being washed with dimethyl carbonate and vacuum dried, was cut into six standard-sized square samples (2.0cm × 2.0cm). Next, the active material on both sides of three of these square samples was removed, and they were rinsed with ethanol, dried, weighed, and their average mass M1 was calculated. Simultaneously, the average thickness L1 of the samples was measured using a micrometer. Then, the mass of the remaining three square samples was weighed, and their average mass M2 was calculated. The average thickness L2 of the samples was also measured. The electrode sheet thickness was calculated as: L2 - L1, in cm. The compacted density of the electrode sheet was calculated as: ρ = (M2 - M1) / [2 × 2 × (L2 - L1)], in g / cm³. 3 .

[0138] Test method for peel force of positive electrode sheet:

[0139] The positive electrode sheet, after being washed with dimethyl carbonate and dried under vacuum, was cut into standard-sized strips (2cm × 10cm). The samples were fixed to a flat steel plate using double-sided tape, ensuring the adhesive area was centered on the steel plate. The protective film of the double-sided tape was then removed, and the strip of electrode to be tested was adhered to the tape surface. A pressure roller was used to evenly press the strip, ensuring full contact and firm adhesion between the electrode and the steel plate surface. The unattached end of the electrode was folded naturally to 180° and fixed to the fixture on an electronic tensile testing machine. A 180° peel test was performed at a tensile speed of 100mm / min, and the peel force-displacement curve was recorded throughout the tensile process. Data was collected during the stable phase where the force fluctuation was less than ±10%, and the average tensile force for that segment was calculated. Finally, this average tensile force was divided by the electrode width to obtain the peel strength per unit width, expressed in N·m. -1 To improve the reliability of the test, at least three tests should be conducted at different sample locations, and the average value should be taken as the final peel strength.

[0140] 25℃ Rate Discharge Performance Test Method:

[0141] Place the battery in a 25°C constant temperature chamber for 4 hours and test it according to the following steps:

[0142] (1) Charge the battery to 4.2V under constant current and constant voltage conditions at 0.1C, with a cutoff current of 0.01C, and let it stand for 30 minutes.

[0143] (2) Discharge under constant current at 0.1C until 2.5V cutoff, with capacity meter reading Q1, and let stand for 30 minutes;

[0144] (3) Charge the battery to 4.2V under constant current and constant voltage conditions at 0.1C, with a cutoff current of 0.01C, and let it stand for 30 minutes.

[0145] (4) Discharge under constant current at 10C until 2.5V cutoff, the capacitance value is Q2, and let stand for 30 minutes;

[0146] The 10C capacity retention rate is calculated as: Q2 / Q1 × 100%.

[0147] Cyclic performance testing methods:

[0148] Place the battery in a 25°C constant temperature chamber for 4 hours and test it according to the following steps:

[0149] (1) First round of constant current and constant voltage charging: Charge at a constant current of 0.1C to 4.2V, then switch to constant voltage charging until the current drops to 0.01C.

[0150] (2) Let it stand for 10 minutes after charging is complete.

[0151] (3) Perform constant current discharge, and discharge to 2.5V at a rate of 0.1C.

[0152] (4) Repeat the above charging and discharging process: Charge at a constant current rate of 1C to 4.2V. Let it rest for 30 minutes again. Discharge at a constant current rate of 1C to 2.5V.

[0153] (5) Repeat the above charging and discharging process for a total of 1000 cycles.

[0154] Statistical analysis of the battery discharge capacity Q1 and Q after 1 cycle and 1000 cycles. 1000 Statistical analysis of battery capacity decay rate (Q1-Q) 1000 ) / Q1×100%.

[0155] The above embodiments and comparative examples underwent various performance tests, and the results are shown in Tables 1 to 6.

[0156] Table 1

[0157]

[0158] As shown in Table 1, comparing Examples 1-4, it can be seen that as the content of the conductive polymer grafting increases from 1 wt% to 5 wt%, the interfacial resistance of the electrode decreases significantly, while the peel strength, 10C rate discharge capacity, and cycle stability all improve significantly, and the viscosity rebound of the slurry is effectively suppressed. However, when the grafting amount is further increased to 7.5 wt%, the overall performance declines, showing a typical trend of "increasing first and then decreasing." This behavior is mainly attributed to the fact that an appropriate amount of grafted conductive conjugated polymer can construct a stable and continuous π-conjugated electron conduction channel in the PVDF matrix, improving the electronic coupling and interfacial charge transfer efficiency of the electrode, thereby effectively reducing the interfacial impedance. At the same time, the flexible structure and polar functional groups of the conjugated segments enhance the adhesion of the binder to the active particles and current collectors, improving the mechanical bonding strength of the electrode. In addition, a reasonable grafting amount can also improve the stability and wettability of the polymer solution, alleviate viscosity rebound in alkaline systems, and promote the self-assembly of segments into a three-dimensional conductive network during the drying process, which is beneficial for the coordinated migration of electrons and ions. Conversely, excessive grafting can easily lead to inter-chain entanglement, microphase separation, or uneven structural coating, resulting in interruption of conductive channels and destruction of the bonding network, which ultimately increases interfacial impedance and exacerbates electrochemical decay.

[0159] Table 2

[0160]

[0161] As shown in Table 2, comparing Examples 1 and 5-7, it can be seen that as the sulfonate group introduction ratio gradually increases from 1 wt% to 5 wt%, the electrode interface resistance decreases and the peel strength increases, the viscosity rebound gradually decreases, and the 10C rate discharge performance improves, while the capacity decay after 1000 cycles gradually decreases. However, performance declines at 7.5 wt%, indicating the existence of an optimal introduction window. This phenomenon is attributed to the sulfonate group, as a strongly polar ionic group, whose introduction can form uniformly distributed negative charge sites on the PVDF molecular chain, which helps to enhance the migration efficiency of lithium ions inside the electrode and at the interface, significantly reducing interface impedance. Simultaneously, -SO3... - Ionic and hydrogen bonds can form between the sulfonic acid group and the metal oxides on the surface of the active particles, improving the bonding strength of the electrode structure. Furthermore, its high hydrophilicity stabilizes the PVDF dispersion and suppresses viscosity rebound caused by hydrophobic segment aggregation in alkaline environments. The presence of sulfonic acid groups can also form local ion channels within the electrode, enhancing the electrochemical reaction kinetics at high rates. However, if the proportion introduced is too high (>10wt%), it can cause abnormally high solution viscosity, free radical side chain aggregation, and even uneven dielectric stress, thereby affecting the overall stability of the electrode and leading to a decrease in rate capability and cycle life.

[0162] Table 3

[0163]

[0164] As shown in Table 3, comparing Examples 1, 8-10, it can be seen that the molecular weight of PVDF is approximately 1.2 × 10⁻⁶. 6 At a molecular weight of g / mol, the electrode exhibits the lowest interfacial resistance, the highest peel strength, and the best rate and cycle performance, indicating that a suitable molecular weight is beneficial for the ordered arrangement and crystallization of molecular chains, thereby improving electron / ion transport efficiency and electrode structural stability. Conversely, excessively low or high molecular weights weaken overall performance. This phenomenon is attributed to the fact that the molecular weight of PVDF directly determines its chain length, crystallinity, and film-forming ability. At a medium molecular weight, its chain segments can be fully stretched and oriented during drying and rolling, forming a uniform and dense highly crystalline phase, which helps to establish stable interfacial contact and reduce interfacial resistance. At the same time, a suitable molecular weight can also balance the diffusion synergistic effect between molecular chains, improve the solution viscoelasticity of the system, and mitigate viscosity fluctuations caused by insufficient chain entanglement, thereby reducing viscosity rebound. A suitable molecular weight also helps to form a good pore structure, improve the uniformity of ion distribution and reaction equilibrium in the electrode, thereby improving 10C rate and long cycle performance. However, if the molecular weight is too high (>2.0×10), the performance will be compromised. 6 Excessive chain entanglement and decreased solvent penetration will reduce the effective film-forming rate of the binder, leading to increased interfacial impedance, structural embrittlement, and decreased capacity.

[0165] Table 4

[0166]

[0167] As shown in Table 4, comparing Examples 1 and 11-13, it can be seen that an optimal PVDF binder ratio of 2.0 wt% achieves the best conductive network. Too low a PVDF binder content leads to a loose structure and high interfacial resistance, while too high a content causes blockage of conductive channels and performance degradation. This phenomenon is attributed to the fact that appropriately increasing the mass ratio of modified PVDF binder helps to construct a continuous "bridging chain network" structure inside the electrode, enhancing the mechanical support and electronic coupling between active materials and reducing the interfacial resistance between the current collector and the material. Simultaneously, the binder's thorough coating of active particles enhances the overall toughness and structural integrity of the electrode, thereby improving peel strength. Good distribution uniformity and interchain miscibility also help improve the elasticity of the slurry's bonding network in alkaline environments, reducing the risk of viscosity rebound after long-term storage. Furthermore, under high-rate charge-discharge conditions, the binder helps to achieve rapid charge-discharge reactions in the electrode system by distributing and regulating ion pathways and pore structure. However, when the binder ratio is too high, excessive coating inhibits the contact of the conductive agent, dilutes the active material content, and causes blockage of electron and ion channels, thus affecting rate performance and accelerating capacity decay.

[0168] Table 5

[0169]

[0170] As shown in Table 5, comparing Examples 1 and 14-16, it is evident that the electrode exhibits optimal performance at a drying temperature of 120°C due to sufficient solvent evaporation and ordered chain rearrangement. Temperatures that are too low result in insufficient crystallization and poor conductivity, while temperatures that are too high may lead to pyrolysis of functional groups, impairing conductivity and structural integrity. This phenomenon is attributed to the fact that appropriately increasing the drying temperature (80-120°C) facilitates complete solvent evaporation and ordered crystallization of PVDF segments. Especially at 100-120°C, it promotes the directional rearrangement of conductive polymer segments and the fixation of sulfonate sites, thereby forming a continuous, dense, and highly conductive composite network structure, significantly reducing the interfacial resistance of the electrode. Simultaneously, the uniform film formation process enhances the overall bonding strength and shear resistance of the electrode, improving peel strength. The multi-scale porous structure and uniformly distributed conductive-ion channels formed at high temperatures also significantly improve the charge / discharge efficiency and structural buffering capacity at 10C rates. However, if the temperature exceeds 140°C, some sulfonate groups may undergo pyrolysis, and the conductive polymer may also fail due to thermal crosslinking or chain breakage, resulting in increased interfacial resistance, structural embrittlement, and decreased cycle stability.

[0171] Table 6

[0172]

[0173] As shown in Table 6, comparing Example 1 and Comparative Examples 1-2, it can be seen that the absence of conductive polymer grafting and sulfonate groups in PVDF both lead to a significant increase in interfacial resistance and a significant decrease in electrode peel strength, resulting in a significant reduction in rate discharge performance and cycle performance. The lack of conductive polymer grafting prevents the binder from constructing a continuous electron conduction network, limiting the efficient migration of electrons within the electrode. Simultaneously, the absence of sulfonate groups reduces the polar interaction force and wetting ability between binder molecules and active materials, leading to weakened interfacial bonding, a loose structure, and ultimately, increased interfacial impedance, weak adhesion, and uneven electrochemical reactions, resulting in a decline in overall performance. In summary, by systematically controlling five key parameters—conductive polymer grafting content, sulfonate group introduction ratio, binder addition amount, PVDF molecular weight, and electrode drying temperature—a continuous and uniform conductive-adhesive bifunctional network can be effectively constructed, optimizing the electrode interfacial contact quality and structural density, significantly reducing interfacial resistance, improving adhesion strength, alleviating slurry viscosity rebound, and achieving excellent rate discharge capability and cycle stability. This strategy provides a systematic control path and theoretical basis for the application of modified PVDF binders in high-performance lithium-ion battery cathodes.

[0174] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0175] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An adhesive, characterized in that, Includes the polyvinylidene fluoride main structure and modifying groups; The modifying groups include conductive conjugated polymers grafted onto the main chain and / or side chains of the polyvinylidene fluoride host structure, and sulfonate groups introduced by functionalization onto the main chain and / or side chains of the polyvinylidene fluoride host structure. The conductive conjugated polymer includes one or more of poly(3,4-ethylenedioxythiophene), poly(3-hexylthiophene), and poly(aniline).

2. The adhesive according to claim 1, characterized in that, The Fourier transform infrared spectrum of the adhesive is in the range of 1400–1480 cm⁻¹. -1 The region exhibits characteristic peaks of C=C skeletal vibration, ranging from 1030 to 1080 cm⁻¹. -1 The region exhibits characteristic peaks of S=O symmetrical stretching vibration. And / or, the Raman spectrum of the adhesive is in the range of 1420–1460 cm⁻¹. -1 Characteristic peaks belonging to conjugated C=C double bonds appear in the range of 1040–1060 cm⁻¹. -1 The range shows characteristic peaks attributable to the S=O bonds in sulfonate groups.

3. The adhesive according to claim 1, characterized in that, The grafting content of the conductive conjugated polymer is 1 wt% to 7.5 wt%. And / or, the sulfonate group is introduced in a proportion of 1 wt% to 10 wt%.

4. The adhesive according to claim 1, characterized in that, The molecular weight of the polyvinylidene fluoride main structure is 3×10. 5 g / mol~2×10 6 g / mol.

5. A positive electrode slurry, characterized in that, Includes the adhesive as described in any one of claims 1 to 4.

6. The positive electrode slurry according to claim 5, characterized in that, The positive electrode slurry also includes a positive electrode active material, a conductive agent, and a solvent; And / or, the positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate; And / or, the conductive agent includes carbon black and / or carbon nanotubes; And / or, the solvent includes N-methylpyrrolidone; And / or, the mass percentage of the positive electrode active material, conductive agent and binder is (94.5% to 98%): (1% to 3.5%): (1% to 2.5%).

7. A positive electrode sheet, characterized in that, It includes a positive current collector and a positive active material layer, wherein the positive active material layer is formed by curing the positive slurry according to any one of claims 5 to 6.

8. The positive electrode sheet according to claim 7, characterized in that, The curing temperature is 80℃~140℃; And / or, the curing time is 1 hour to 2 hours; And / or, the compaction density of the positive electrode sheet is >3.4 g / cm³. 3 ; And / or, the interface resistance of the positive electrode is 1.0 × 10⁻⁶. -2 mΩ·cm 2 Up to 4.0×10 -2 mΩ·cm 2 between; And / or, the peel strength of the positive electrode sheet is greater than or equal to 8.5 N / m and less than or equal to 20.0 N / m.

9. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 7 to 8.

10. An electrical device, characterized in that, Includes the battery as described in claim 9.

Images