Negative plate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a negative plate and a preparation method and application thereof. The negative electrode plate comprises a negative electrode current collector and a negative electrode material layer arranged on at least one side surface of the negative electrode current collector, the negative electrode material layer comprises a negative electrode active substance, a negative electrode conductive agent and a composite binder, and the composite binder comprises carboxymethyl cellulose lithium and siloxane. The negative electrode plate has relatively high stripping force or crack resistance, and the first coulombic efficiency or cycle stability of the battery can be effectively improved when the negative electrode plate is applied to the battery.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to negative electrode sheets and their preparation methods and applications, and more specifically, to negative electrode sheets and their preparation methods, battery cells, lithium-ion batteries, and electrical devices. Background Technology

[0002] The relevant technology employs a dry process to prepare the negative electrode, avoiding the health hazards to operators and the environment caused by N-methylpyrrolidone solvent in the wet process, and reducing energy consumption. However, the dry process currently commonly uses polytetrafluoroethylene (PTFE) as a binder. On the one hand, commercially available PTFE powder is prone to agglomeration during dry mixing, making it difficult to disperse uniformly. Furthermore, excessive PTFE addition can lead to excessive battery polarization, resulting in severe cycle degradation. On the other hand, PTFE is prone to side reactions at low potentials in the negative electrode, consuming active lithium and thus reducing the battery's initial coulombic efficiency and capacity. These defects in the binder ultimately reduce the electrochemical performance of the negative electrode, making it difficult to achieve both high energy density and long cycle life. Therefore, the negative electrode still requires further improvement. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention proposes a negative electrode sheet with high peel strength or crack resistance, and a method for preparing the same. Applying this negative electrode sheet to a battery can effectively improve the battery's initial coulombic efficiency or cycle stability.

[0004] In a first aspect, this application provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, a negative electrode conductive agent and a composite binder, the composite binder comprising lithium carboxymethyl cellulose and siloxane.

[0005] This application improves the peeling force and crack resistance of the negative electrode by synergistic effect of lithium carboxymethyl cellulose (CMC-Li) and siloxane, thereby improving the first coulombic efficiency and cycle stability of the battery.

[0006] According to embodiments of this application, the composite binder further includes modified polytetrafluoroethylene (PTFE), wherein the modified PTFE comprises PTFE particles and a polymer coating the surface of the PTFE particles, and the polymer contains carbonyl groups. This avoids or reduces direct contact between PTFE and active lithium, thus reducing side reactions; furthermore, the presence of carbonyl groups enables the formation of covalent bonds with the negative electrode active material, enhancing the adhesion within the negative electrode coating and significantly improving the peel strength of the negative electrode sheet.

[0007] According to embodiments of this application, the polymer comprises at least one of polymethyl methacrylate and polybutyl acrylate. Therefore, the polymer contains carbonyl groups, which can form covalent bonds with the negative electrode active material, thereby improving the peel strength of the negative electrode sheet.

[0008] According to embodiments of this application, the siloxane includes at least one of chain siloxanes, cyclic siloxanes, and cage-like siloxanes. Thus, all of the above siloxanes contain a -Si-O-Si- backbone, which can undergo a cross-linking reaction with the hydroxyl groups on CMC-Li to form a cross-linked network structure, thereby improving the mechanical strength of the negative electrode.

[0009] According to embodiments of this application, the chain siloxane includes at least one of polymethylsiloxane and methylphenyl silicone oil.

[0010] According to embodiments of this application, the cyclic siloxane includes at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane.

[0011] According to embodiments of this application, the cage-like silsesquioxane comprises an octameric cage-like silsesquioxane.

[0012] According to embodiments of this application, the mass ratio of the negative electrode active material, the negative electrode conductive agent, the lithium carboxymethyl cellulose, the siloxane, and the modified polytetrafluoroethylene is (90-93): (0.5-1.2): (2-3): (0.8-6.5): (1-2). Therefore, within the above range, the synergistic effect among lithium carboxymethyl cellulose, siloxane, and modified polytetrafluoroethylene can be utilized to jointly improve the mechanical strength, peel strength, and battery performance of the negative electrode sheet.

[0013] According to embodiments of this application, the above-mentioned negative electrode sheet satisfies at least one of the following conditions: The negative electrode active material is at least one of natural graphite, artificial graphite, silicon-based materials, and silicon-carbon materials; The negative electrode conductive agent includes at least one selected from carbon nanotubes, acetylene black, conductive carbon black, Ketjen black, superconducting carbon black, and graphene. A second aspect of this application provides a method for preparing the aforementioned negative electrode sheet, comprising: The negative electrode active material and the negative electrode conductive agent are first mixed to obtain a first mixture. The first mixture and the composite binder are mixed a second time to obtain a second mixture; The second mixture is sequentially subjected to air jet milling and fiberization to obtain a fibrous material. The fibrous material is subjected to differential speed hot roll forming and constant speed multi-stage hot roll forming to obtain the negative electrode material layer; The negative electrode material layer and the negative electrode current collector are hot rolled together to obtain a negative electrode sheet.

[0014] Therefore, this method is simple to operate and easy to scale up; the preparation process adopts a dry process, and no solvent is used throughout the process, so there is no need for drying, which reduces cracking, significantly reduces energy consumption, and also reduces waste liquid discharge, making it green and environmentally friendly. At the same time, it can also avoid the problem of binder floating during conventional drying, thereby improving the performance consistency of lithium-ion batteries. The above characteristics indicate that this method is suitable for manufacturing thick electrodes.

[0015] According to embodiments of this application, the above method satisfies at least one of the following conditions: The rotational speeds of the first and second mixtures are each independent, ranging from 500 rpm to 1200 rpm; The mixing times for the first and second mixing are each 10 min to 40 min independently; The airflow pressure for the airflow pulverizer is 0.5 MPa - 1.0 MPa; The feeding air pressure of the air jet mill is greater than the grinding air pressure; The feed rate during the fiberization process shall not exceed 45 kg / h; The fiberization temperature is 60℃-100℃; The fiberization time is 10-20 hours; The speed ratio of roller A and roller B in the differential hot roll forming is 1:(8-12). The speed ratio of roller A to roller B during the constant speed multi-stage hot rolling is 1:1. The temperatures for differential hot roll forming and constant speed multi-stage hot roll forming are each independently 150℃-180℃. The temperature of the hot roller pressing is 150℃-250℃.

[0016] A third aspect of this application provides a battery cell comprising a positive electrode and the aforementioned negative electrode. The features and advantages of this battery cell are consistent with those of the aforementioned negative electrode, and will not be repeated here.

[0017] In a fourth aspect, this application provides a lithium-ion battery comprising the aforementioned negative electrode or the aforementioned battery cell. The features and advantages of this lithium-ion battery are consistent with those of the aforementioned negative electrode or battery cell, and will not be repeated here.

[0018] A fifth aspect of this application provides an electrical device comprising the aforementioned negative electrode, the aforementioned battery cell, or the aforementioned lithium-ion battery. The features and advantages of this electrical device are consistent with those of the aforementioned negative electrode, the aforementioned battery cell, or the aforementioned lithium-ion battery, and will not be repeated here. Detailed Implementation

[0019] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0020] In a first aspect, this application provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, a negative electrode conductive agent and a composite binder, the composite binder comprising lithium carboxymethyl cellulose and siloxane.

[0021] This application achieves a negative electrode structure with high initial efficiency, high mechanical strength, and crack suppression through the synergistic effect of lithium carboxymethyl cellulose (CMC-Li) and siloxane. Specifically, on the one hand, CMC-Li can release active lithium ions during the first charge-discharge stage, replenishing the lithium lost due to the formation of the solid electrolyte interphase (SEI), thereby improving the battery's initial coulombic efficiency. Its abundant lithium carboxylate and hydroxyl functional groups form a dense hydrogen bond network with the surface of the negative electrode active material, significantly enhancing the dispersion among the active materials. This reduces stress concentration and improves the electrode peel strength. On the other hand, the siloxane, with its -Si-O-Si- main chain, can crosslink with the hydroxyl groups on the CMC-Li surface, forming an in-situ CMC-Li molecular chain-covalent bond-siloxane crosslink network. This crosslink network can buffer stress during charge-discharge volume changes, improving the mechanical properties of the negative electrode and suppressing microcrack formation. In summary, the synergistic effect of CMC-Li and siloxane jointly improves the peel strength of the negative electrode, thereby enhancing the battery's initial coulombic efficiency and cycle stability.

[0022] In this article, the initial coulombic efficiency refers to the percentage of electricity released during the first discharge relative to the initial charge input. The formula is: Initial Coulombic Efficiency = (First Discharge Amount / First Charge Amount) × 100%. A higher initial coulombic efficiency means more active lithium is available for subsequent cycles, resulting in higher battery energy utilization. Specifically, it can be tested using the following method: the cell is charged at 0.5C constant current and constant voltage to 3.65V, and then discharged at 0.5C constant current to 2.5V, with a charging capacity of Q1 and a discharging capacity of Q2. The initial coulombic efficiency n = Q2 / Q1 × 100%.

[0023] According to embodiments of this application, the composite binder further includes modified polytetrafluoroethylene (PTFE), which comprises PTFE particles and a polymer coating the surface of the PTFE particles, the polymer containing carbonyl groups. Thus, the material has a PTFE core and is coated with a carbonyl-containing polymer. This core-shell structure avoids or reduces direct contact between PTFE and active lithium, reducing side reactions; furthermore, the presence of carbonyl groups in the shell allows for covalent bonding with the negative electrode active material, enhancing the adhesion within the negative electrode coating and significantly improving the peel strength of the negative electrode sheet.

[0024] According to embodiments of this application, the polymer comprises at least one of polymethyl methacrylate and polybutyl acrylate. Therefore, the polymer contains carbonyl groups, which can form covalent bonds with the negative electrode active material, thereby improving the peel strength of the negative electrode sheet.

[0025] According to embodiments of this application, the siloxane includes at least one of chain siloxanes, cyclic siloxanes, and cage-like siloxanes. Thus, all of the above siloxanes contain a -Si-O-Si- backbone, which can undergo a cross-linking reaction with the hydroxyl groups on CMC-Li to form a three-dimensional network structure, thereby improving the mechanical strength of the negative electrode.

[0026] According to embodiments of this application, the chain siloxane includes at least one of polymethylsiloxane and methylphenyl silicone oil.

[0027] According to embodiments of this application, cyclic siloxanes include at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane.

[0028] According to embodiments of this application, cage-like silsesquioxanes include octameric cage-like silsesquioxanes.

[0029] According to embodiments of this application, the mass ratio of the negative electrode active material, the negative electrode conductive agent, the lithium carboxymethyl cellulose, the siloxane, and the modified polytetrafluoroethylene is (90-93):(0.5-1.2):(2-3):(0.8-6.5):(1-2), specifically such as 90:0.5:2:6.5:2, 91:0.8:2.5:3.5:1.5, 92:1.0:2.8:2.0:1.8, 93:1.2:3:0.8:1, or any two of these ranges. Therefore, within the above range, the synergistic effect between lithium carboxymethyl cellulose, siloxane, and modified polytetrafluoroethylene can be utilized to jointly improve the mechanical strength, peel strength, and battery performance of the negative electrode sheet.

[0030] According to embodiments of this application, the negative electrode active material is at least one of natural graphite, artificial graphite, silicon-based materials, and silicon-carbon materials. Therefore, the aforementioned negative electrode active material possesses high capacity, excellent cycle stability, excellent low-temperature performance, and good safety. These advantages contribute to improving battery energy density and battery lifespan.

[0031] According to embodiments of this application, the negative electrode conductive agent includes at least one selected from carbon nanotubes, acetylene black, conductive carbon black, Ketjen black, superconducting carbon black, and graphene. Therefore, the aforementioned negative electrode conductive agent can construct a conductive network, reduce electrode resistance, and thereby improve the battery's charge / discharge efficiency and rate performance.

[0032] According to embodiments of this application, the negative electrode current collector includes at least one of copper foil, carbon-coated copper foil, and composite copper foil. Therefore, the current collector has high conductivity, and the process is mature and cost-effective.

[0033] A second aspect of this application provides a method for producing a negative electrode as described in the first aspect, comprising: S10: The negative electrode active material and the negative electrode conductive agent are mixed in the first mixture to obtain the first mixture.

[0034] According to embodiments of this application, the rotation speed of the first mixing is 500 rpm to 1200 rpm, specifically 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, or any two of these ranges. Within this range, it is beneficial to uniformly mix the negative electrode active material and the negative electrode conductive agent. If the rotation speed is too high, a large amount of air may be introduced, forming small bubbles, which can create defects in the negative electrode material layer and affect the performance of the negative electrode sheet. If the rotation speed is too low, the negative electrode active material and the negative electrode conductive agent may not be uniformly mixed, causing some material to settle and affecting the uniformity of the negative electrode material layer.

[0035] According to embodiments of this application, the first mixing time is 10-40 minutes, specifically 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, or any two of these ranges. Within this range, it helps to ensure thorough mixing of the negative electrode active material and the negative electrode conductive agent. If the time is too long, agglomeration of the materials may occur, affecting the uniformity of the negative electrode material layer; if the time is too short, a uniformly mixed first mixture may not be obtained, thus affecting the uniformity of the negative electrode material layer.

[0036] S20: The first mixture and the composite binder are mixed a second time to obtain a second mixture; According to embodiments of this application, the rotational speed of the second mixing is 500 rpm to 1200 rpm, specifically 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, or any two of these ranges. Therefore, within this range, it is beneficial to uniformly mix the first mixture and the composite binder. If the rotational speed is too high, a large amount of air may be introduced, forming small bubbles, which can create defects in the negative electrode material layer and affect the performance of the negative electrode sheet. If the rotational speed is too low, the first mixture and the composite binder may not be uniformly mixed, causing some material to settle and affecting the uniformity of the negative electrode material layer.

[0037] According to embodiments of this application, the second mixing time is 10-40 minutes, specifically 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, or any two of these ranges. Within this range, it helps to ensure thorough mixing of the first mixture and the composite binder. If the time is too long, agglomeration may occur between the materials, affecting the uniformity of the negative electrode material layer; if the time is too short, a uniformly mixed second mixture may not be obtained, thus affecting the uniformity of the negative electrode material layer.

[0038] According to an embodiment of this application, the apparatus used for the first mixing and the second mixing includes a dual planetary high-speed mixer.

[0039] According to embodiments of this application, the method for preparing the modified polytetrafluoroethylene in the composite adhesive includes: For example, taking polymethyl methacrylate (PMMA) as the carbonyl polymer in the composite adhesive, the preparation method of the composite adhesive is as follows: polytetrafluoroethylene (PTFE) and PMMA are mixed evenly at a mass ratio of 5:5, and then 0.5% ammonium persulfate initiator is added. The mixture is reacted at 90°C for 40 minutes to obtain a core-shell structured PTFE-PMMA, with the core being polytetrafluoroethylene (PTFE) and the coating layer being PMMA.

[0040] S30: The second mixture is sequentially subjected to air jet milling and fiberization to obtain fiberized material.

[0041] In this step, the materials in the second mixture, as well as any agglomerates that may be present, are further crushed into powder. The composite binder is pulled into a network of tiny fibers during the fiberization process. These fiber networks uniformly wrap the powder together, which gives the fiberized material strong cohesive force and improves the peeling force of the negative electrode sheet.

[0042] According to embodiments of this application, the airflow pressure for the air jet milling is 0.5 MPa to 1.0 MPa, specifically within the range of 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, or any two thereof. Within this range, it helps to pulverize the second mixture into fine particles, resulting in a powder of uniform size without hard agglomerates. If the airflow pressure is too high, too many finer powders may be generated, which have an excessively large specific surface area, thereby increasing the contact area with the electrolyte and easily triggering side reactions; if the airflow pressure is too low, the second mixture may not be effectively and fully broken down, thus affecting the uniformity of the negative electrode material layer.

[0043] According to an embodiment of this application, the feed air pressure of the air jet mill is greater than the grinding air pressure. Therefore, the higher feed air pressure allows the fibrous material to be conveyed into the grinding chamber at a stable and uniform speed.

[0044] According to embodiments of this application, the fiberization method includes shear mixing. Therefore, the above method facilitates the fiberization of the composite adhesive.

[0045] According to embodiments of this application, the feed rate during the fiberization process is no more than 45 kg / h. This provides sufficient shear force, which helps the composite binder to fully fiberize.

[0046] According to embodiments of this application, the fibrillation temperature is 60℃-100℃, specifically within the ranges of 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, or any two of these ranges. Within this range, fibrillation of the molecular chains in the composite adhesive is facilitated, making it easier to stretch and thus more readily forming a fiber network structure. If the temperature is too high, the composite adhesive may melt, making it difficult to form a fiber network; if the temperature is too low, the degree of fibrillation may be low, resulting in poor mechanical strength of the fiber network structure.

[0047] According to embodiments of this application, the fiberization time is 10-20 hours, specifically 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, or any range between two of these. Within this time range, the composite adhesive is facilitated to fully fiberize, forming a fiber network structure. If the time is too long, the molecular chains of the composite adhesive may break, reducing the structural strength of the fiber network structure; if the time is too short, the degree of fiberization of the composite adhesive may be low, resulting in poor mechanical strength of the fiber network structure.

[0048] S40: The fibrous material is subjected to differential hot rolling and constant speed multi-stage hot rolling to obtain the negative electrode material layer.

[0049] "Differential hot roll forming" refers to the process where two hot rollers of a roll press rotate at different linear speeds. The powerful shearing force generated by this speed difference strongly extends the fiber network structure in the fibrous material, further fiberizing it and more tightly encapsulating the active material particles. It also further thins the negative electrode active layer. This significantly improves the peel strength (the bonding force between the negative electrode and the negative electrode current collector) and cohesion (the bonding force within the negative electrode material layer).

[0050] "Equal speed multi-stage hot roller pressing" refers to multi-stage hot rollers rotating synchronously at the same speed, which can improve electrode density and uniformity, and reduce electrode internal stress and cracking risk.

[0051] According to an embodiment of this application, the speed ratio of roller A and roller B in the differential hot roll forming is 1:(8-12), specifically 1:8, 1:9, 1:10, 1:11, 1:12, or any range between two of these. Thus, within the above range, the strong shear force can further extend the fiber network structure, causing it to become further fibrillated and more tightly encapsulate the active material particles.

[0052] According to embodiments of this application, the temperature for differential hot roll forming is 150℃-180℃, specifically 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, or any combination thereof. Within this range, the fiber network structure can be maintained, allowing it to be further effectively and fully extended. If the temperature is too high, the fiber network structure may soften or melt, making production impossible; if the temperature is too low, the fiber network structure may be in a hard and brittle state, leading to bonding failure.

[0053] According to an embodiment of this application, the speed ratio of roller A to roller B during the constant-speed multi-stage hot rolling is 1:1. This helps to improve electrode density and uniformity, and reduces internal stress and cracking risk in the electrode.

[0054] According to embodiments of this application, the temperature of the constant-speed multi-stage hot rolling is 150℃-180℃, specifically 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, or any combination thereof. Within this range, the binder bonding network can be precisely activated, while simultaneously achieving real-time stress release within the electrode, thereby significantly optimizing the electrode's processing performance. If the temperature is too high, it may cause thermal degradation of the binder, damaging the integrity of the bonding network; if the temperature is too low, it may lead to insufficient binder activation, making it difficult to form a stable bond and reducing the electrode's mechanical properties.

[0055] S50: The negative electrode material layer and the negative electrode current collector are hot rolled to obtain a negative electrode sheet.

[0056] According to embodiments of this application, the temperature of the hot roller pressing is 150℃-250℃, specifically 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, or any two of these ranges. Within this range, the composite adhesive can be more evenly distributed and connected between the active material and the negative electrode conductive agent particles, forming a stronger three-dimensional network. If the temperature is too high, the composite adhesive may undergo thermal decomposition, leading to adhesive failure; if the temperature is too low, the adhesive strength may not be effectively improved, resulting in reduced peel strength.

[0057] A third aspect of this application provides a battery cell comprising a positive electrode and the aforementioned negative electrode. The features and advantages of this battery cell are consistent with those of the aforementioned negative electrode, and will not be repeated here.

[0058] In some embodiments, the positive electrode may include a positive current collector and a positive active layer disposed on at least one side of the positive current collector.

[0059] In some embodiments, the positive current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, aluminum foil current collectors; composite current collectors may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. Composite current collectors 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.).

[0060] In some embodiments, the positive electrode active layer may include a positive electrode binder, a positive electrode conductive agent, and a positive electrode active material. Additives with specific functions and effects, such as thickeners, sodium supplements, film-forming additives, flame retardants, and high / low temperature stabilizers, may also be added as needed.

[0061] As an example, the positive electrode active material of a lithium-ion battery may include lithium nickel cobalt manganese oxide (including but not limited to NCM811, NCM613, NCM523, etc.), lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, or positive electrode active materials commonly used in the art.

[0062] As an example, the positive electrode binder in the positive electrode active layer may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0063] As an example, the positive electrode conductive agent in the positive electrode active layer may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0064] The aforementioned battery cell mainly consists of a positive electrode, a negative electrode (mentioned earlier), a separator, an electrolyte, and a packaging shell (metal shell or aluminum-plastic film). Specifically, a battery cell is a single-cell battery formed by assembling the positive electrode, negative electrode, and separator into a core pack through winding or stacking, injecting electrolyte, and then encapsulating it in a metal shell or aluminum-plastic film. Depending on the internal structure, battery cells include wound or stacked types, etc.

[0065] In some embodiments, the electrolyte in the battery cell can be a liquid electrolyte (i.e., an electrolyte solution) or a solid electrolyte.

[0066] In some embodiments, the electrolyte is a liquid electrolyte. In this case, the positive electrode, negative electrode, and separator can be fabricated into a battery cell using a winding or stacking process, and the battery cell and electrolyte can be contained in an outer packaging. During the charging and discharging process of the battery cell, lithium ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor of ions between the positive and negative electrode plates.

[0067] In some embodiments, the electrolyte is a solid electrolyte. In this case, the positive electrode, negative electrode, and electrolyte can be manufactured into a battery cell through winding or stacking processes, and the battery cell can be housed in an outer package. The positive and negative electrodes are alternately stacked, and the electrolyte and battery separator are disposed between adjacent positive and negative electrodes.

[0068] In a fourth aspect, this application provides a lithium-ion battery comprising the aforementioned negative electrode or the aforementioned battery cell. The features and advantages of this lithium-ion battery are consistent with those of the aforementioned negative electrode or battery cell, and will not be repeated here.

[0069] It is understood that there are no particular restrictions on the specific types and structures of the lithium-ion batteries mentioned above, as long as a lithium-ion battery requires a negative electrode. For example, classified by application, lithium-ion batteries can include, but are not limited to, primary batteries, secondary batteries, etc. Classified by shape, lithium-ion batteries can include, but are not limited to, prismatic batteries, cylindrical batteries, etc.; classified by packaging, lithium-ion batteries can include, but are not limited to, pouch batteries, hard-case batteries, etc.

[0070] A fifth aspect of this application provides an electrical device comprising the aforementioned negative electrode, the aforementioned battery cell, or the aforementioned lithium-ion battery. The features and advantages of this electrical device are consistent with those of the aforementioned negative electrode, the aforementioned battery cell, or the aforementioned lithium-ion battery, and will not be repeated here.

[0071] It is understood that there are no particular restrictions on the specific type of electrical device; it can be any device that uses a lithium-ion battery as a power source or energy storage unit. For example, electrical devices include, but are not limited to, 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.), mobile terminals (such as mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, and so on.

[0072] It is understandable that, in addition to the battery mentioned above, the electrical device also includes necessary structures and components, all of which can be made with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.

[0073] The embodiments of this application are described in detail below.

[0074] Example 1 1. Preparation of negative electrode sheet (1) Artificial graphite and conductive carbon black SP are first mixed in a double planetary high-speed mixer to obtain a first mixture, wherein the speed of the mixer is 800 rpm and the mixing time is 30 min; the first mixture is then mixed with composite binder (CMC-Li (binder A), polymethylsiloxane (binder B) and PTFE-polymethyl methacrylate (binder C)) at the above speed for a second time of 30 min to obtain a second mixture, wherein the mass ratio of artificial graphite: conductive carbon black SP: CMC-Li: polymethylsiloxane: PTFE-polymethyl methacrylate is 93:1:2:2:2; (2) The second mixture obtained in step (1) is subjected to air jet milling, the feeding air pressure is 0.8 MPa and the air jet milling air pressure is 0.5 MPa; the material after air jet milling in step (2) is subjected to fiberization, the feed rate is 10 kg / h, the temperature is 70℃ and the heat preservation time is 10 h to obtain fiberized material; (3) The fibrous material obtained in step (2) is subjected to differential hot rolling and constant speed multi-stage hot rolling to obtain a negative electrode material layer. The temperature of the rolling is 160°C. During the differential hot rolling process, the speed ratio of the two hot rolling rollers, roller A and roller B, is 1:8; the speed ratio of the constant speed multi-stage hot rolling is 1:1. (4) The negative electrode material layer obtained in step (3) is composited onto the negative electrode current collector copper foil by hot rolling to obtain a negative electrode sheet. The temperature of the hot rolling roller is 200°C. 2. Preparation of positive electrode sheet Lithium iron phosphate, conductive carbon black, carbon nanotubes, and polyvinylidene fluoride, the positive electrode active materials, are uniformly mixed in a mass ratio of 97.5:1.0:0.5:1.0. N-methylpyrrolidone is added to obtain a solid content of 60% to obtain a positive electrode active slurry. The positive electrode active slurry is coated on both sides of carbon-coated aluminum foil and dried at 110°C for 10 min to obtain a positive electrode sheet.

[0075] 3. Preparation of the diaphragm The diaphragm is a single-sided ceramic diaphragm with a 7μm polyethylene (PE) base membrane and a 2μm alumina inorganic layer.

[0076] 4. Preparation of electrolyte Ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed evenly in a mass ratio of 30:5:30:35. Then, 2.5% vinylene carbonate is added, and finally, 12% lithium hexafluorophosphate is added. The mixture is then thoroughly mixed to obtain the electrolyte.

[0077] 5. Battery fabrication The above-mentioned positive electrode, separator, and negative electrode are stacked in sequence and then wound to obtain a bare cell without electrolyte filling. The bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, standing, formation, shaping, and sorting, the battery is obtained.

[0078] Examples 2-9 The specific parameters for Examples 2-9 are shown in Table 1, and the other parameters are the same as those for Example 1.

[0079] Comparative Example 1 Same as Example 1, except that CMC-Li in step (1) is replaced with carboxymethyl cellulose CMC.

[0080] Comparative Example 2 Same as Example 1, except that CMC-Li in step (1) is replaced with carboxymethyl cellulose CMC and PTFE-polymethyl acrylate is replaced with PTFE.

[0081] Comparative Example 3 Same as Example 1, except that the composite adhesive in step (1) is replaced with CMC-Li and PTFE-polymethyl methacrylate.

[0082] Comparative Example 4 Same as Example 1, except that the composite adhesive in step (1) is replaced with polymethylsiloxane and PTFE-polymethyl methacrylate.

[0083] Comparative Example 5 Same as Example 1, except that only CMC-Li is used as the adhesive.

[0084] Comparative Example 6 Same as Example 1, except that the adhesive used is only polymethylsiloxane.

[0085] Comparative Example 7 Same as Example 1, except that the adhesive used is only PTFE-polymethyl methacrylate.

[0086] Performance testing (1) Electrode peeling force test The negative electrode obtained above was cold-pressed and then subjected to a peel force test using a universal tensile testing machine.

[0087] (2) First Coulomb efficiency test The negative electrode sheet obtained above is used to make a battery cell. The cell is charged to 3.65V at 0.5C constant current and constant voltage and discharged to 2.5V at 0.5C constant current. The charging capacity is Q1 and the discharging capacity is Q2. The initial coulombic efficiency is n=Q2 / Q1×100%.

[0088] (3) Room temperature cycling test: The negative electrode obtained above is made into a cell and charged at 25℃ with constant current and constant voltage at 0.5C to 3.65V and discharged at 0.5C with constant current to 2.5V for 1000 cycles. The discharge capacity of the first cycle is C1 and the discharge capacity of the 1000th cycle is C2. The capacity retention rate t = C2 / C1 × 100% is calculated.

[0089]

[0090] Conclusion: Examples 1-9 demonstrate that the composite binder of this application effectively improves the peel strength of the negative electrode sheet, while simultaneously increasing the initial coulombic efficiency and cycle performance of the battery, thus improving the overall performance of the battery. Comparative Examples 1-7 show a decrease in the peel strength of the negative electrode sheet, and a reduction in both the initial coulombic efficiency and cycle performance of the battery, further demonstrating the synergistic effect of the composite binder of this application.

[0091] 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 technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0092] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example 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, without contradiction, 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.

[0093] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A negative electrode sheet characterized by comprising: The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode material layer including a negative electrode active material, a negative electrode conductive agent, and a composite binder, the composite binder including lithium carboxymethyl cellulose and a siloxane.

2. The negative electrode sheet according to claim 1, characterized by The composite binder further includes: Modified polytetrafluoroethylene including polytetrafluoroethylene particles and a high molecular polymer coated on surfaces of the polytetrafluoroethylene particles, the high molecular polymer containing a carbonyl group.

3. The negative electrode sheet according to claim 2, characterized by The high molecular polymer includes at least one of polymethyl methacrylate and polybutyl acrylate.

4. The negative electrode sheet according to claim 1, characterized by The siloxane includes at least one of a chain siloxane, a cyclic siloxane, and a cage siloxane.

5. The negative electrode sheet of claim 4, wherein The chain siloxane includes at least one of polymethylsiloxane and methylphenyl silicone oil; and / or The cyclic siloxane includes at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane; and / or The cage siloxane includes octasilicane.

6. The negative electrode sheet according to claim 2, characterized by A mass ratio of the negative electrode active material, the negative electrode conductive agent, the lithium carboxymethyl cellulose, the siloxane, and the modified polytetrafluoroethylene is (90-93):(0.5-1.2):(2-3):(0.8-6.5):(1-2).

7. The negative electrode sheet according to claim 1, wherein At least one of the following conditions is satisfied: The negative electrode active material includes at least one of natural graphite, artificial graphite, a silicon-based material, and a silicon-carbon material; The negative electrode conductive agent includes at least one of a carbon nanotube, acetylene black, conductive carbon black, Ketjen black, super conductive carbon black, and graphene.

8. A method for producing the negative electrode sheet according to any one of claims 1 to 7, characterized by, The method includes: First mixing the negative electrode active material and the negative electrode conductive agent to obtain a first mixture; Second mixing the first mixture and the composite binder to obtain a second mixture; Sequentially performing airflow pulverization and fiberization on the second mixture to obtain a fiberized material; Performing differential speed hot roller molding and constant speed multi-stage hot roller molding on the fiberized material to obtain the negative electrode material layer; Performing hot roller molding on the negative electrode material layer and the negative electrode current collector to obtain the negative electrode sheet.

9. The method of claim 8, wherein, At least one of the following conditions is satisfied: A rotation speed of the first mixing and the second mixing is independently 500 rpm-1200 rpm; A time of the first mixing and the second mixing is independently 10 min-40 min; An airflow pressure of the airflow pulverization is 0.5 Mpa-1.0 Mpa; A feeding airflow pressure of the airflow pulverization is greater than a pulverization airflow pressure; A feeding amount during the fiberization is not greater than 45 kg / h; A temperature of the fiberization is 60℃-100℃; A time of the fiberization is 10 h-20 h; A speed ratio of a roller A and a roller B of the differential speed hot roller molding is 1:(8-12); A speed ratio of the roller A and the roller B of the constant speed multi-stage hot roller molding is 1:1; Temperatures of the differential speed hot roller molding and the constant speed multi-stage hot roller molding are independently 150℃-180℃; A temperature of the hot roller molding is 150℃-250℃.

10. An electric cell characterized by The battery cell includes the positive electrode sheet and the negative electrode sheet of claims 1-7.

11. A lithium-ion battery, characterized by The lithium ion battery includes the battery cell of claim 10.

12. An electrical device, comprising: The electric device includes the battery cell of claim 10, or the lithium ion battery of claim 11.

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