Preparation methods of dispersing agent, positive electrode slurry, positive electrode plate and lithium ion battery

Abstract

The invention provides a preparation method of a dispersing agent, positive electrode slurry, a positive plate and a lithium ion battery, and relates to the technical field of lithium ion batteries. The molecular structure of the dispersing agent comprises an anchoring group, a dispersing group and a safety group, the anchoring group comprises a first anchoring group and a second anchoring group, the first anchoring group is used for anchoring iron-lithium particles, and the second anchoring group is used for anchoring carbon particles; the dispersing groups are used for preventing particle aggregation; the safety group is used for decomposing and polymerizing under overcharge high pressure to generate an insulating high-molecular polymer. The internal resistance of the pole piece and the battery is rapidly improved through the dispersing agent, so that the charging voltage rapidly reaches the cut-off voltage, and the overcharge time of the battery is reduced, thereby avoiding the chained temperature rise, reducing the thermal runaway probability, reducing the production cost and improving the production efficiency.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a method for preparing a dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. Background Technology

[0002] With the rapid development of electric vehicles and energy storage power stations, lithium iron phosphate (LiFePO4, LFP) has become one of the mainstream cathode materials due to its advantages such as high safety, long cycle life, and low cost. To further enhance the market competitiveness of lithium iron phosphate batteries, improving their energy density has become a key research direction. At the cathode material level, the main approaches to improving energy density include increasing compaction density. Optimizing particle morphology and size distribution to increase the compaction density of the electrode coating has become the primary means of improving energy density.

[0003] Currently, the mainstream method to improve compaction density is to employ particle size distribution technology, which uses large particles to provide high packing density and small particles to fill voids and improve electrochemical performance. However, the synthesis of large particles usually requires high-temperature sintering (>800℃), and under reducing atmospheres (such as H2 or CO), some lithium iron phosphate may be reduced to iron phosphide (Fe2P). Although a small amount of Fe2P can improve the electronic conductivity of the material, excessive Fe2P can trigger the Fe / Li shuttle effect during battery overcharging, leading to battery endothermic and thermal runaway risks, seriously threatening battery safety.

[0004] To balance high compaction density and safety, the industry generally adopts a two-sintering process, which optimizes the particle structure through two sintering operations. This process can improve the material's density and crystallinity, lower the sintering temperature, and enable the Fe2P reaction to occur reversibly, thereby reducing or even eliminating its negative impacts. However, the two-sintering process has problems such as complex procedures, high energy consumption, and increased costs (more than 10% per ton), which are not conducive to further cost reduction and market promotion of lithium iron phosphate products.

[0005] Therefore, there is an urgent need to provide a method for preparing dispersants, positive electrode slurries, positive electrode sheets, or lithium-ion batteries that can ensure battery safety while reducing manufacturing costs. Summary of the Invention

[0006] This application provides a method for preparing a dispersant, a positive electrode slurry, a positive electrode sheet, or a lithium-ion battery, which can ensure battery safety while reducing manufacturing costs, thus solving the current problem that manufacturing costs and battery safety cannot be guaranteed simultaneously.

[0007] In a first aspect, this application provides a dispersant whose molecular structure includes: an anchoring group, a dispersing group, and a safety group. The anchoring group includes a first anchoring group and a second anchoring group. The first anchoring group is used to anchor lithium iron phosphate particles, and the second anchoring group is used to anchor carbon particles. The dispersing group is used to prevent particle agglomeration. The safety group is used to decompose and polymerize under overcharge and high voltage to generate an insulating polymer.

[0008] Through the above scheme, the first and second anchoring groups anchor lithium iron phosphate particles and carbon particles respectively. This targeted anchoring method enhances the bonding force between the electrode active material and the electrode matrix, making the electrode structure more stable. During battery charging and discharging, a stable electrode structure helps maintain battery performance, reduces electrode material shedding and active material loss, thereby extending battery cycle life and improving long-term battery performance. Carbon particles typically act as conductive agents in lithium-ion batteries. Their good dispersibility allows carbon particles to better contact lithium iron phosphate particles, forming a more efficient conductive network. Simultaneously, the dispersing groups prevent particle aggregation and help maintain the electrode's porous structure, facilitating lithium-ion transport and diffusion, thereby improving the battery's charge / discharge efficiency and rate performance. This enables the battery to charge and discharge rapidly under different operating conditions, meeting the needs of various application scenarios.

[0009] Under overcharge high voltage (e.g., >4.5V), the safety group triggers a decomposition-polymerization reaction, generating an insulating polymer. The electrode resistance jumps by 2-3 orders of magnitude within seconds. This dynamic insulating layer causes a sharp drop in charging current, rapidly bringing the voltage close to the cutoff voltage (e.g., 4.2V), and shortening overcharge time by more than 80%. In traditional overcharge, side reactions (such as electrolyte oxidation and Fe2P formation) continuously release heat. This design, however, quickly terminates overcharge, directly cutting off the energy input of side reactions, significantly reducing heat absorption, preventing a chain reaction of temperature increases, and lowering the probability of thermal runaway.

[0010] The dispersing group prevents particle agglomeration, ensuring uniform dispersion of lithium iron phosphate and carbon particles. This excellent dispersibility helps improve the stability of the battery's electrode structure, avoiding problems such as excessively high local current density and intensified electrode polarization caused by particle agglomeration. This, in turn, enhances battery safety at the microstructural level, making the battery more stable and reliable during charging and discharging. Using a single-sintering process with this dispersant reduces the number of sintering steps and the use of related equipment compared to traditional multi-step sintering processes, lowering energy consumption and equipment wear during production. Simultaneously, the simplified process also reduces potential errors and quality control difficulties in production, improving production efficiency and thus lowering overall manufacturing costs. Furthermore, the formation of iron phosphide (Fe2P) during lithium-ion battery manufacturing can adversely affect battery performance and safety. This dispersant, through its unique molecular structure, effectively reduces iron phosphide formation with just a single-sintering process, improving safety.

[0011] In one possible design, the safety group is one or a combination of one or more of the following: ethylene carbonate (VC) molecules, ethylene sulfate (DTD) molecules, fluoroethylene carbonate (FEC) molecules, biphenyl (BP) molecules, terephthalonitrile (PTMN) molecules, or p-dimethylbenzoic acid (DMTB) molecules.

[0012] By using the above method, when ethylene carbonate (VC) molecules, ethylene sulfate (DTD) molecules, fluoroethylene carbonate (FEC) molecules, biphenyl (BP) molecules, terephthalonitrile (PTMN) molecules, or p-dimethylbenzoic acid (DMTB) molecules are added to the dispersant, a decomposition-polymerization reaction is triggered under overcharge high voltage, which can generate insulating polymer molecules. This causes the electrode resistance to increase within seconds, allowing the charging voltage to quickly reach the cutoff voltage, reducing battery overcharge time, reducing heat absorption, and preventing thermal runaway.

[0013] In one possible design, the first anchoring group is a phosphate ester molecule; the second anchoring group is a molecule containing a benzene ring.

[0014] Through the above-described scheme, the strong anchoring force (Fe-P bond) of phosphate ester to lithium iron phosphate inhibits particle agglomeration, and the sedimentation rate of the slurry decreases after a period of settling. The π-π stacking effect of benzene ring molecules on carbon particles improves the uniformity of the conductive agent network and reduces the electrode resistivity. The dual-anchoring system maintains the relative positions of lithium iron phosphate and carbon particles during charge and discharge, and the electrode pulverization rate can also be effectively reduced after multiple cycles. Furthermore, the flame-retardant properties of phosphate ester and the high-temperature stability of benzene rings synergistically suppress electrode thermal shrinkage.

[0015] In one possible design, the dispersing group is attached to the main chain, which is a long chain structure with repeating units that can provide attachment sites for the functional groups. The dispersing group includes steric hindrance segments and electrostatic repulsion units. The steric hindrance segments are branched polyethers or polyesters, and the electrostatic repulsion units are sulfonic acid groups or quaternary ammonium salt groups, which are used to inhibit particle agglomeration through steric hindrance and Coulomb forces.

[0016] Through the above scheme, the main chain is a long-chain structure with repeating units, providing attachment sites for various functional groups (such as functional groups). Anchoring groups, dispersing groups, safety groups, and solvation chains can all attach to the main chain. The dispersing groups include steric hindrance segments and electrostatic repulsion units. The steric hindrance segments are branched polyethers or polyesters with a molecular weight of 800-3000 Da, and the electrostatic repulsion units are sulfonic acid groups or quaternary ammonium salt groups, used to inhibit particle aggregation through steric hindrance and Coulomb forces. Increasing the distance between particles significantly reduces the likelihood of particle aggregation. The sulfonic acid groups or quaternary ammonium salt units form charged surfaces in the solvent, further preventing particles from approaching each other through electrostatic repulsion. This electrostatic repulsion can further enhance the repulsive force between particles, preventing particle aggregation. The electrostatic repulsion between particles makes them more spatially dispersed, further reducing aggregation. Through the dual effects of steric hindrance and electrostatic repulsion, the particle dispersion stability is significantly improved. The particles exhibit better dispersibility in the solvent, and the sedimentation rate is significantly reduced. By combining steric hindrance segments (branched polyethers or polyesters) and electrostatic repulsion units (sulfonic acid groups or quaternary ammonium salt groups), this dispersing group design achieves a dual synergistic effect of steric hindrance and electrostatic repulsion, significantly improving particle dispersion stability, electrode uniformity, slurry process window, and long-term cycling stability.

[0017] Secondly, this application provides a lithium-ion battery positive electrode slurry, comprising a positive electrode active material, a conductive agent, a binder, a solvent, and a dispersant of any one of the above.

[0018] The beneficial effects of the positive electrode slurry provided by the above-described scheme, the second aspect, and the various possible designs of the second aspect can be found in the beneficial effects of the first aspect and the various possible implementations of the first aspect, and will not be repeated here.

[0019] In one possible design, the dispersant accounts for 0.01% to 3% by mass.

[0020] The above-described method addresses the potential adverse effects of iron phosphide (Fe2P) formation on battery performance and safety during lithium-ion battery manufacturing. A dispersant concentration of 0.01% to 3% can effectively reduce Fe2P formation and improve safety. A dispersant concentration less than 0.01% may weaken the Fe2P inhibition effect, worsen the dispersion, and decrease electrochemical performance. A dispersant concentration greater than 3% increases cost, raises slurry viscosity, may negatively impact electrochemical performance, and increases process complexity.

[0021] In one possible design, the dispersant has a safety group, the amount of which is 0.5% to 3% of the mass of the dispersant, and the insulating film generated by electropolymerization has a coverage of ≥90%.

[0022] Using the above method, an addition of 0.5%–3% safety groups can achieve an insulation film coverage of ≥90%, effectively preventing overcharging and thermal runaway, and improving battery safety and performance. At an addition level of 0.5%–3%, the insulation film formed by the electrolytic polymerization of safety groups significantly improves battery safety, extends cycle life, and enhances rate performance, while maintaining low cost and process compatibility. An insulation film coverage of ≥90% effectively prevents direct contact between the electrolyte and the electrodes, reducing side reactions and heat generation, and lowering the risk of thermal runaway. A coverage below 0.5% may result in an insulation film coverage below 90%, failing to effectively prevent overcharging and thermal runaway. A coverage above 3% significantly increases material costs, and excessive safety groups may introduce other side reactions, affecting the battery's electrochemical performance, such as increasing internal resistance and reducing capacity retention.

[0023] Thirdly, this application provides a positive electrode sheet, which includes a current collector and a positive electrode material layer disposed on the current collector, wherein the positive electrode material layer includes a positive electrode active material, a conductive agent, a binder, and a dispersant as described above.

[0024] The beneficial effects of the positive electrode provided by the above-described solution, the third aspect, and the various possible designs of the third aspect can be found in the beneficial effects of the first aspect and the various possible implementations of the first aspect, and will not be repeated here.

[0025] Fourthly, this application provides a method for preparing a lithium-ion battery, comprising: mixing iron phosphate (FePO4), a lithium source, a carbon source and a dispersant as described above to obtain a precursor mixture; subjecting the precursor mixture to a single sintering process to synthesize carbon-coated LiFePO4, wherein the sintering process comprises: a sintering temperature greater than 750°C and a sintering time greater than 10 h.

[0026] The beneficial effects of the lithium-ion battery preparation method provided by the above-described scheme, the fourth aspect, and the various possible designs of the fourth aspect can be found in the beneficial effects of the first aspect and the various possible implementations of the first aspect, and will not be repeated here.

[0027] In one possible design, the amount of dispersant added is 0.01% to 3% by mass percentage.

[0028] The above-described method addresses the potential adverse effects of iron phosphide (Fe2P) formation on battery performance and safety during lithium-ion battery manufacturing. A dispersant concentration of 0.01% to 3% can effectively reduce Fe2P formation and improve safety. A dispersant concentration less than 0.01% may weaken the Fe2P inhibition effect, worsen the dispersion, and decrease electrochemical performance. A dispersant concentration greater than 3% increases cost, raises slurry viscosity, may negatively impact electrochemical performance, and increases process complexity.

[0029] The above description is merely an overview of the technical solutions of the embodiments of this application. In order to better understand the technical means of the embodiments of this application and to implement them in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the embodiments of this application more obvious and understandable, specific implementation methods of this application are described below. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of a dispersant molecule provided in one embodiment of this application.

[0032] Figure 2 This is a schematic diagram comparing the voltage-time relationship curves during overcharging of the first-burning process and the second-burning process provided in one embodiment of this application. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims and drawings of this application are intended to cover non-exclusive inclusion.

[0035] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of the phrase "embodiment" in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists, A and B exist simultaneously, or B exists. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0037] Furthermore, the terms "first," "second," etc., in the specification and claims of this application or in the aforementioned drawings are used to distinguish different objects rather than to describe a specific order, and may explicitly or implicitly include one or more of the features.

[0038] In the description of this application, unless otherwise stated, "multiple" means two or more (including two), and similarly, "multiple groups" means two or more (including two groups).

[0039] As can be seen from the background technology, current lithium-ion battery manufacturing methods suffer from either high production costs or poor safety, and there is no production process that can simultaneously reduce production costs and improve safety.

[0040] Analysis shows that high-temperature sintering can synthesize large particles to provide high packing density. However, during high-temperature sintering (>800℃) in a reducing atmosphere (such as H2 or CO), some lithium iron phosphate may be reduced to iron phosphide (Fe2P). Excess Fe2P can trigger the Fe / Li shuttle effect during battery overcharging, leading to heat absorption and thermal runaway risks, seriously threatening battery safety. Therefore, a single-stage high-temperature sintering process (one-stage sintering) cannot meet safety requirements.

[0041] Among related technologies, a two-stage sintering process is employed, which optimizes the particle structure through two sintering operations. This process can improve the density and crystallinity of the material, lower the sintering temperature, and enable the Fe2P reaction to occur reversibly, thereby reducing or even eliminating its negative impacts. However, the two-stage sintering process suffers from problems such as complex procedures, high energy consumption, and increased costs (more than 10% per ton), which are detrimental to further cost reduction and market promotion of lithium iron phosphate products.

[0042] In view of this, embodiments of this application provide a method for preparing a dispersant, a positive electrode slurry, a positive electrode sheet, or a lithium-ion battery, which can solve the problem that current manufacturing costs and battery safety cannot be guaranteed simultaneously by reducing the overcharge cutoff time.

[0043] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0044] Figure 1 This is a schematic diagram of the dispersant molecule provided in this embodiment. Please refer to... Figure 1 This application provides a dispersant whose molecular structure includes: an anchoring group, a dispersing group, and a safety group. The anchoring group includes a first anchoring group and a second anchoring group. The first anchoring group is used to anchor lithium iron phosphate particles, and the second anchoring group is used to anchor carbon particles. The dispersing group is used to prevent particle agglomeration. The safety group is used to decompose and polymerize under overcharge and high voltage to generate an insulating polymer.

[0045] The first and second anchoring groups anchor lithium iron phosphate (LFP) particles and carbon particles, respectively. This targeted anchoring method enhances the bonding force between the electrode active material and the electrode matrix, making the electrode structure more stable. During battery charging and discharging, a stable electrode structure helps maintain battery performance, reduces electrode material shedding and active material loss, thereby extending battery cycle life and improving long-term battery performance. Carbon particles typically act as conductive agents in lithium-ion batteries. Their good dispersibility allows them to better contact LFP particles, forming a more efficient conductive network. Simultaneously, the dispersing groups prevent particle aggregation and help maintain the electrode's porous structure, facilitating lithium-ion transport and diffusion, thus improving charge / discharge efficiency and rate performance. This enables the battery to charge and discharge rapidly under various operating conditions, meeting the needs of different application scenarios.

[0046] In this embodiment, the first anchoring group is a phosphate ester molecule; the second anchoring group is a molecule containing a benzene ring. The strong anchoring force (Fe-P bond) of the phosphate ester to lithium iron phosphate inhibits particle agglomeration, and the sedimentation rate of the slurry decreases after standing for a period of time. The π-π stacking effect of the benzene ring molecule on the carbon particles improves the uniformity of the conductive agent network and reduces the electrode resistivity. The dual anchoring system maintains the relative position of lithium iron phosphate / carbon particles during charge and discharge, and the electrode pulverization rate can also be effectively reduced after multiple cycles. Furthermore, the flame-retardant properties of the phosphate ester and the high-temperature stability of the benzene ring synergistically suppress electrode thermal shrinkage.

[0047] Under overcharge high voltage (e.g., >4.5V), the safety group triggers a decomposition-polymerization reaction, generating an insulating polymer. The electrode resistance jumps by 2-3 orders of magnitude within seconds. This dynamic insulating layer is equivalent to forming an "electronic circuit breaker" on the electrode surface, forcing a sharp drop in charging current and rapidly bringing the voltage close to the cutoff voltage (e.g., 4.2V), shortening the overcharge time by more than 80%. In traditional overcharge, side reactions (such as electrolyte oxidation and Fe2P formation) continuously release heat. This design, however, rapidly terminates overcharge, directly cutting off the energy input of side reactions, reducing heat absorption by 60-70%, avoiding a chain reaction of temperature increases, and reducing the probability of thermal runaway by more than 90%.

[0048] Figure 2 This is a schematic diagram comparing the voltage-time relationship curves during overcharge for the first-firing and second-firing processes provided in this embodiment. Please refer to... Figure 2 The blue line represents the time required for the lithium-ion battery obtained through the two-stage firing process to reach the overcharge voltage, while the red line represents the time required for the lithium-ion battery obtained through the one-stage firing process in this embodiment to reach the overcharge voltage. The comparison shows that the lithium-ion battery obtained through the one-stage firing process using the dispersant in this embodiment can shorten the charging voltage to reach the cutoff voltage more quickly, thus reducing the battery overcharge time. Because the battery overcharge time is short, it can reduce the side reaction time, reduce heat absorption, and prevent thermal runaway.

[0049] The dispersing group prevents particle agglomeration, ensuring uniform dispersion of lithium iron phosphate and carbon particles. This excellent dispersibility helps improve the stability of the battery's electrode structure, avoiding problems such as excessively high local current density and intensified electrode polarization caused by particle agglomeration. This, in turn, enhances battery safety at the microstructural level, making the battery more stable and reliable during charging and discharging. Using a single-sintering process with this dispersant reduces the number of sintering steps and the use of related equipment compared to traditional multi-step sintering processes, lowering energy consumption and equipment wear during production. Simultaneously, the simplified process also reduces potential errors and quality control difficulties in production, improving production efficiency and thus lowering overall manufacturing costs. Furthermore, the formation of iron phosphide (Fe2P) during lithium-ion battery manufacturing can adversely affect battery performance and safety. This dispersant, through its unique molecular structure, effectively reduces iron phosphide formation with just a single-sintering process, improving safety.

[0050] In this embodiment, the dispersing group includes a steric hindrance segment and an electrostatic repulsion unit. The steric hindrance segment is a branched polyether or polyester, and the electrostatic repulsion unit is a sulfonic acid group or a quaternary ammonium salt group, which are used to inhibit particle agglomeration through steric hindrance and Coulomb force.

[0051] The dispersing group comprises steric hindrance segments and electrostatic repulsion units. The steric hindrance segments are branched polyethers or polyesters with molecular weights ranging from 800 to 3000 Da, while the electrostatic repulsion units are sulfonic acid groups or quaternary ammonium salt groups. These units inhibit particle agglomeration through steric hindrance and Coulombic forces. Increasing the distance between particles significantly reduces the likelihood of agglomeration. The sulfonic acid or quaternary ammonium salt units form charged surfaces in the solvent, further preventing particles from approaching each other through electrostatic repulsion. This electrostatic repulsion further enhances the repulsive force between particles, preventing agglomeration. The electrostatic repulsion between particles makes them more spatially dispersed, further reducing agglomeration. Through the dual effects of steric hindrance and electrostatic repulsion, particle dispersion stability is significantly improved. Particles exhibit better dispersibility in the solvent, and sedimentation rates are significantly reduced. By combining steric hindrance segments (branched polyethers or polyesters) and electrostatic repulsion units (sulfonic acid or quaternary ammonium salt groups), this dispersing group design achieves a synergistic effect of steric hindrance and electrostatic repulsion, significantly improving particle dispersion stability, electrode uniformity, slurry process window, and long-term cycling stability.

[0052] In this embodiment, the safety group is one or more of the following: ethylene carbonate (VC) molecules, ethylene sulfate (DTD) molecules, fluoroethylene carbonate (FEC) molecules, biphenyl (BP) molecules, terephthalonitrile (PTMN) molecules, or p-dimethylbenzoic acid (DMTB) molecules.

[0053] The molecular formula of ethylene carbonates (VC) is:

[0054]

[0055] The molecular formula of vinyl sulfate (DTD) is:

[0056]

[0057] The molecular formula of fluoroethylene carbonate (FEC) is:

[0058]

[0059] The molecular formula of biphenyl (BP) is:

[0060]

[0061] The molecular formula of terephthalonitrile (PTMN) is:

[0062]

[0063] The molecular formula of p-dimethylbenzoic acid (DMTB) is:

[0064]

[0065] Compounds containing ethylene carbonate (VC), ethylene sulfate (DTD), fluoroethylene carbonate (FEC), biphenyl (BP), terephthalonitrile (PTMN), or p-dimethylbenzoic acid (DMTB) can decompose under high voltage and electropolymerize into LEDC macromolecules. This process can rapidly increase the internal resistance of the electrode and battery, raise the overcharge voltage, reduce overcharge time and heat absorption, thereby improving the battery's safety performance.

[0066] In this embodiment, as Figure 1 As shown, the main chain is connected to anchoring groups, dispersing groups, safety groups, and solvation chains, including short and long solvation chains. The main chain is a long chain structure with repeating units, providing attachment sites for various functional groups (such as functional groups). For example, the main chain can be a repeating unit composed of carbon atoms. The solvation chains provide steric hindrance segments and electrostatic repulsion units in the dispersing groups.

[0067] Based on the above embodiments, this application also provides a lithium-ion battery positive electrode slurry, comprising a positive electrode active material, a conductive agent, a binder, a solvent, and the dispersant in the above embodiments.

[0068] Since the components of the dispersant and their beneficial effects have been described in detail in the previous embodiments, they will not be repeated here.

[0069] In this embodiment, the dispersant accounts for 0.01% to 3% by mass percentage.

[0070] The above-described method addresses the potential adverse effects of iron phosphide (Fe2P) formation on battery performance and safety during lithium-ion battery manufacturing. A dispersant concentration of 0.01% to 3% can effectively reduce Fe2P formation and improve safety. A dispersant concentration less than 0.01% may weaken the Fe2P inhibition effect, worsen the dispersion, and decrease electrochemical performance. A dispersant concentration greater than 3% increases cost, raises slurry viscosity, may negatively impact electrochemical performance, and increases process complexity.

[0071] In this embodiment, the dispersant contains a safety group, the amount of which is 0.5% to 3% of the mass of the dispersant, and the insulating film generated by electropolymerization has a coverage of ≥90%.

[0072] It is understandable that the safety group takes effect when the battery is overcharged and does not react at other times. The safety group can also be added directly to the positive electrode slurry, but this may result in the safety group not being evenly dispersed, thus failing to achieve sufficient insulation film coverage.

[0073] In this embodiment, the safety group is added to the dispersant and then to the positive electrode slurry. This allows the safety group to be more evenly dispersed in the electrode, effectively enhancing its function. Safety groups are generally molecular compounds, and adding them directly to the dispersant can effectively improve their activity and prevent them from reacting with battery components during certain battery processes. Furthermore, the addition of the safety group along with the additives simplifies the process and eliminates the need for additional processing steps.

[0074] In this embodiment, an addition of 0.5% to 3% safety groups achieves an insulation film coverage of ≥90%, effectively preventing overcharging and thermal runaway, and improving battery safety and performance. At an addition level of 0.5% to 3%, the insulation film generated by the electrolytic polymerization of the safety groups significantly improves battery safety, extends cycle life, and enhances rate performance, while maintaining low cost and process compatibility. An insulation film coverage of ≥90% effectively prevents direct contact between the electrolyte and the electrodes, reducing side reactions and heat generation, and lowering the risk of thermal runaway. A coverage below 0.5% may result in an insulation film coverage below 90%, failing to effectively prevent overcharging and thermal runaway. A coverage above 3% significantly increases material costs, and excessive safety groups may introduce other side reactions, affecting the battery's electrochemical performance, such as increasing internal resistance and reducing capacity retention.

[0075] Based on the above embodiments, this application also provides a positive electrode sheet, which includes a current collector and a positive electrode material layer disposed on the current collector, wherein the positive electrode material layer includes a positive electrode active material, a conductive agent, a binder, and a dispersant as described above.

[0076] Since the components of the dispersant and their beneficial effects have been described in detail in the previous embodiments, they will not be repeated here.

[0077] Based on the above embodiments, this application also provides a method for preparing a lithium-ion battery, comprising: mixing iron phosphate (FePO4), a lithium source, a carbon source and a dispersant as described above to obtain a precursor mixture; subjecting the precursor mixture to a sintering process to synthesize carbon-coated LiFePO4, wherein the sintering process comprises: a sintering temperature greater than 750°C and a sintering time greater than 10 h.

[0078] In this embodiment, the sintering temperature of the single-pass sintering process can be 750℃, 760℃, 780℃, or 800℃, and the sintering time can be 10h, 11h, or 12h. Compared with the sintering problems required in the prior art, this reduces the energy consumption and lowers the cost.

[0079] This embodiment presents a method for preparing a lithium iron phosphate battery. By combining a single sintering process with a dispersant, the process flow is simplified, which also means reducing potential errors and quality control difficulties in the production process, improving production efficiency, and thus reducing overall manufacturing costs. Furthermore, the decomposition-polymerization reaction triggered under overcharge high voltage generates an insulating polymer, causing the electrode resistance to increase within seconds, allowing the charging voltage to quickly reach the cutoff voltage, reducing battery overcharge time, reducing heat absorption, and preventing thermal runaway.

[0080] In this embodiment, the amount of dispersant added is 0.01% to 3% by mass percentage. During the preparation of lithium-ion batteries, the formation of iron phosphide (Fe2P) can adversely affect battery performance and safety. A dispersant content of 0.01% to 1% can effectively reduce iron phosphide formation and improve safety by reaching the cutoff voltage within a short time, thereby cutting off the energy input of side reactions. A dispersant content of less than 0.01% may weaken the Fe2P inhibition effect, worsen the dispersion effect, and decrease electrochemical performance. A dispersant content greater than 3% increases cost, raises slurry viscosity, may affect electrochemical performance, and increases process complexity.

[0081] Example 1

[0082] This embodiment provides a lithium-ion battery, which is manufactured using a dispersant-based sintering process. The dispersant molecule has a first anchoring group of a phosphate ester molecule, a second anchoring group of a molecule containing a benzene ring, and a safety group of an ethylene carbonate (VC) molecule. During manufacturing, the dispersant is added to the positive electrode slurry and stirred to obtain a precursor mixture. This mixture undergoes a sintering process, followed by coating, rolling, slitting, assembly, and testing to obtain the lithium-ion battery.

[0083] In this embodiment, the amount of dispersant added is 0.01% of the precursor mixture.

[0084] The obtained lithium-ion batteries were subjected to overcharge tests, and the test results are shown in Table 1.

[0085] Example 2

[0086] Example 2 was prepared in the same way as Example 1, except that the amount of dispersant added was 0.05% of the precursor mixture.

[0087] Example 3

[0088] Example 3 was prepared in the same way as Example 1, except that the amount of dispersant added was 0.1% of the precursor mixture.

[0089] Example 4

[0090] Example 4 was prepared in the same way as Example 1, except that the amount of dispersant added was 0.15% of the precursor mixture.

[0091] Example 5

[0092] Example 5 was prepared in the same way as Example 1, except that the amount of dispersant added was 0.2% of the precursor mixture.

[0093] Example 6

[0094] Example 6 was prepared in the same way as Example 1, except that the amount of dispersant added was 0.25% of the precursor mixture.

[0095] Example 7

[0096] Example 7 was prepared in the same way as Example 1, except that the amount of dispersant added was 0.3% of the precursor mixture.

[0097] Example 8

[0098] Example 8 was prepared in the same way as Example 1, except that the safety group in the dispersant molecule was vinyl sulfate (DTD) molecule, and the amount of dispersant added was 0.1% of the precursor mixture.

[0099] Example 9

[0100] Example 9 was prepared in the same way as Example 1, except that the safety group in the dispersant molecule was vinyl sulfate (DTD) molecule, and the amount of dispersant added was 0.2% of the precursor mixture.

[0101] Example 10

[0102] Example 10 was prepared in the same way as Example 1, except that the safety group in the dispersant molecule was vinyl sulfate (DTD) molecule, and the amount of dispersant added was 0.3% of the precursor mixture.

[0103] Example 11

[0104] Example 11 was prepared in the same way as Example 1, except that the safety group in the dispersant molecule was fluoroethylene carbonate (FEC) molecule, and the amount of dispersant added was 0.1% of the precursor mixture.

[0105] Example 12

[0106] Example 12 was prepared in the same way as Example 1, except that the safety group in the dispersant molecule was fluoroethylene carbonate (FEC) molecule, and the amount of dispersant added was 0.2% of the precursor mixture.

[0107] Example 13

[0108] Example 13 was prepared in the same way as Example 1, except that the safety group in the dispersant molecule was fluoroethylene carbonate (FEC) molecule, and the amount of dispersant added was 0.3% of the precursor mixture.

[0109] Example 14

[0110] Example 14 was prepared in the same way as Example 1, except that the safety group in the dispersant molecule was biphenyl (BP) molecule, and the amount of dispersant added was 0.2% of the precursor mixture.

[0111] Example 15

[0112] Example 15 was prepared in the same way as Example 1, except that the safety group in the dispersant molecule was terephthalonitrile (PTMN) molecule, and the amount of dispersant added was 0.2% of the precursor mixture.

[0113] Example 16

[0114] Example 16 was prepared in the same way as Example 1, except that the safety group in the dispersant molecule was p-dimethylbenzoic acid (DMTB) molecule, and the amount of dispersant added was 0.2% of the precursor mixture.

[0115] Comparative Example 1

[0116] The difference between Comparative Example 1 and Example 1 is that no dispersant was added, but the other preparation methods were the same.

[0117] Comparative Example 2

[0118] The difference between Comparative Example 2 and Example 1 is that the dispersant molecule added has only a first anchoring group and a second anchoring group. The first anchoring group is a phosphate ester molecule, and the second anchoring group is a molecule containing a benzene ring. No other groups are present.

[0119] Comparative Example 3

[0120] The difference between Comparative Example 3 and Example 1 is that the dispersant molecules added have only a first anchoring group and a second anchoring group. The first anchoring group is a phosphate ester molecule, the second anchoring group is a molecule containing a benzene ring, and the safety group is other phosphate ester / amide / ether groups, etc.

[0121] Performance testing:

[0122] The lithium-ion battery was subjected to an overcharge test, which included constant current discharge-constant current charging, constant current charging to 5.475V (overcharge potential), and the overcharge potential cutoff time was measured.

[0123] The lithium-ion batteries obtained in Examples 1 to 16 and Comparative Examples 1 to 3 were tested for the above-mentioned performance indicators, and the results are shown in Table 1.

[0124] Table 1:

[0125] Added amount Overcharge cutoff voltage Overcharge cutoff time / s Comparative Example 1 / 5.475V 1688 Comparative Example 2 0.1％ 5.475V 1597 Comparative Example 3 0.1％ 5.475V 1604 Example 1 0.01％ 5.475V 1375 Example 2 0.05％ 5.475V 1085 Example 3 0.1％ 5.475V 943 Example 4 0.15％ 5.475V 836 Example 5 0.2％ 5.475V 683 Example 6 0.25％ 5.475V 657 Example 7 0.3％ 5.475V 672 Example 8 0.1％ 5.475V 826 Example 9 0.2％ 5.475V 596 Example 10 0.3％ 5.475V 573 Example 11 0.1％ 5.475V 663 Example 12 0.2％ 5.475V 604 Example 13 0.3％ 5.475V 587 Example 14 0.2％ 5.475V 635 Example 15 0.2％ 5.475V 763 Example 16 0.2％ 5.475V 617

[0126] As can be seen from Table 1:

[0127] The results from Examples 1 to 16 indicate that the lithium-ion battery obtained using the dispersant described in this application takes significantly less time to charge to the overcharge cutoff voltage compared to the lithium-ion batteries obtained using the dispersants in Comparative Examples 1 to 3. Because the overcharge time is shorter, side reaction time is reduced, heat absorption is decreased, and thermal runaway is prevented. Furthermore, the preparation process is simple and the cost is greatly reduced, thus improving the production efficiency of lithium-ion batteries. Therefore, compounds containing ethylene carbonate (VC), ethylene sulfate (DTD), fluoroethylene carbonate (FEC), biphenyl (BP), terephthalonitrile (PTMN), or p-dimethylbenzoic acid (DMTB) have better effects.

[0128] Examples 5, 9, 12, 14, 15, and 16 show that when the amount of dispersant added is 0.2% of the precursor mixture, it can have a better effect on reducing overcharge time.

[0129] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A dispersant, characterized in that, The molecular structure of the dispersant includes: an anchoring group, a dispersing group, and a safety group. The anchoring group includes a first anchoring group and a second anchoring group. The first anchoring group is used to anchor lithium iron phosphate particles, and the second anchoring group is used to anchor carbon particles. The dispersing group is used to prevent particle agglomeration. The safety group is used to decompose and polymerize under overcharge and high voltage to generate an insulating polymer.

2. The dispersant according to claim 1, characterized in that, The safety group is one or more of the following: ethylene carbonate (VC) molecules, ethylene sulfate (DTD) molecules, fluoroethylene carbonate (FEC) molecules, biphenyl (BP) molecules, terephthalonitrile (PTMN) molecules, or p-dimethylbenzoic acid (DMTB) molecules.

3. The dispersant according to claim 1, characterized in that, The first anchoring group is a phosphate ester molecule; the second anchoring group is a molecule containing a benzene ring.

4. The dispersant according to claim 1, characterized in that, The dispersed groups are attached to the main chain, which is a long chain structure with repeating units, providing attachment sites for functional groups. The dispersing group comprises a steric hindrance segment and an electrostatic repulsion unit. The steric hindrance segment is a branched polyether or polyester, and the electrostatic repulsion unit is a sulfonic acid group or a quaternary ammonium salt group, which are used to inhibit particle agglomeration through steric hindrance and Coulomb force.

5. A positive electrode slurry, characterized in that, It comprises a positive electrode active material, a conductive agent, a binder, a solvent, and a dispersant as described in any one of claims 1 to 4.

6. The positive electrode slurry according to claim 5, characterized in that, The dispersant accounts for 0.01% to 3% by mass percentage.

7. The positive electrode slurry according to claim 6, characterized in that, In the dispersant, the amount of the safety group added is 0.5% to 3% of the mass of the dispersant, and the insulating film generated by electropolymerization has a coverage of ≥90%.

8. A positive electrode plate, characterized in that, The positive electrode sheet includes a current collector and a positive electrode material layer disposed on the current collector, wherein the positive electrode material layer includes a positive electrode active material, a conductive agent, a binder, and a dispersant as described in any one of claims 1 to 4.

9. A method for preparing a lithium-ion battery, characterized in that, include: Iron phosphate (FePO4), a lithium source, a carbon source, and a dispersant as described in any one of claims 1 to 4 are mixed to obtain a precursor mixture; The precursor mixture is subjected to a single sintering process to synthesize carbon-coated LiFePO4, wherein the sintering process includes: a sintering temperature greater than 750°C and a sintering time greater than 10 hours.

10. The preparation method according to claim 9, characterized in that, The amount of the dispersant added is 0.01% to 3% by mass percentage.

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