Dispersion agent for electrode slurry and application, and method for preparing dispersion agent

Abstract

The application provides a dispersant for electrode slurry and application and a preparation method of the dispersant. The dispersant for electrode slurry provided by the application has a specific end-capping group, can be stably adsorbed on the surface of electrode active material particles, achieves a better dispersion and viscosity reduction effect, and can be used to provide a uniform and stable electrode slurry.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dispersants, in particular to a dispersant for electrode slurry and application, and a preparation method of the dispersant. BACKGROUND

[0002] The dispersant for electrode slurry is a kind of substance that can disperse electrode active material particles in a dispersion medium and form a stable electrode slurry. A uniform and stable electrode slurry has a positive influence on the preparation of a battery and the performance of the battery. At present, the types of dispersants for electrode slurry mainly include cationic and anionic types, nonionic types, amphoteric types, and high molecular types. In recent years, new high molecular dispersants containing anchoring groups have gradually attracted attention. In particular, in the preparation of electrode slurry, the industry currently mostly uses polyurethane dispersants with carboxyl anchoring groups, but such dispersants generally have the shortcomings of poor viscosity reduction effect and easy desorption, which causes the electrode slurry to flocculate. SUMMARY

[0003] In view of this, the present application provides a dispersant for electrode slurry with a specific end-capping group. The dispersant can be stably adsorbed on the surface of electrode active material particles, achieve a good dispersion and viscosity reduction effect, and thus be used to provide a uniform and stable electrode slurry.

[0004] The first aspect of the present application provides a dispersant for electrode slurry, comprising a polyurethane polymer; the end-capping group at at least one end of the polyurethane polymer is a substituted or unsubstituted hydrocarbon group, and the end-capping group at at least part of the end portions of the polyurethane polymer away from the hydrocarbon group is an isocyanate group.

[0005] The end-capping group in the above dispersant includes both isocyanate and a substituted or unsubstituted hydrocarbon group. The isocyanate group can act as an anchoring group to enable the dispersant to be stably adsorbed on the surface of electrode active material particles and form an adsorption layer. At the same time, the hydrocarbon group has good compatibility with the solvent, which can promote the wetting of the electrode active material particles by the solvent, and thus enable the electrode active material particles to be stably dispersed in the dispersion medium, achieve a good dispersion and viscosity reduction effect, and obtain a uniform and stable slurry.

[0006] Optionally, in the polyurethane polymer with 1 molecular structure, the number of isocyanate groups is greater than or equal to 2.

[0007] Optionally, the substituted or unsubstituted hydrocarbon group is a branched C3-C24 hydrocarbon group.

[0008] Optionally, the number average relative molecular mass of the polyurethane polymer is 100-5000.

[0009] Optionally, the molecular structure of the polyurethane polymer is as shown in formula (I),

[0010] wherein, the R2 is the hydrocarbon group, the n is a value that makes the relative molecular mass of the polyurethane polymer in the range of 100-5000;

[0011] wherein, the R1 includes the R3 includes a segment of a polymer of a small molecule polyol and a segment of a polymer of a macromolecular diol and diisocyanate.

[0012] Further, the small molecule polyol is selected from a small molecule diol and a small molecule triol; the small molecule diol includes at least one of 1,4-butanediol, ethylene glycol, propylene glycol, octanediol and neopentyl glycol; the small molecule triol includes at least one of glycerol and trimethylolpropane.

[0013] Optionally, the macromolecular diol includes a polyether diol and / or a polyester diol; wherein, the polyether diol includes at least one of polypropylene glycol, polyethylene oxide / propylene oxide block copolymer diol, polytetrahydrofuran diol, tetrahydrofuran / ethylene oxide copolymer diol and tetrahydrofuran / propylene oxide copolymer diol.

[0014] Optionally, the polyester diol includes at least one of adipic acid / butanediol copolymer diol, adipic acid / diethylene glycol copolymer diol, polycarbonate diol and polycaprolactone diol.

[0015] The second aspect of the present application provides a preparation method of a dispersant, including the following steps:

[0016] (1) providing a first raw material, the first raw material including diisocyanate, macromolecular diol and catalyst, and in the first raw material, the molar ratio of isocyanate group to hydroxyl group is greater than or equal to 1.055:1;

[0017] heating the first raw material to a first temperature and keeping for a first time, so that the diisocyanate reacts with the macromolecular polyol to obtain a first prepolymer; wherein, the end groups of at least part of the first prepolymer are isocyanate groups;

[0018] (2) adding a small molecule polyol to the first prepolymer to obtain a second raw material; wherein, in the second raw material, the molar ratio of isocyanate group to hydroxyl group is greater than or equal to 1.055:1; wherein, the small molecule polyol is selected from a small molecule diol, or a small molecule diol and a small molecule triol;

[0019] The second raw material is heated to a second temperature and kept for a second time, so that the first prepolymer reacts with the second raw material to obtain a second prepolymer; wherein the second prepolymer comprises an isocyanate group terminated polyurethane polymer;

[0020] (3) adding a monohydric alcohol to the second prepolymer to obtain a third raw material; wherein the molar ratio of isocyanate groups to hydroxyl groups in the third raw material is greater than or equal to 1.055:1;

[0021] The third raw material is kept at a third temperature for a third time, so that the monohydric alcohol reacts with part of the isocyanate groups in the second prepolymer, so that part of the end-capping groups in the second prepolymer are converted into substituted or unsubstituted hydrocarbon groups, to obtain a dispersant.

[0022] The above preparation method has simple steps, strong controllability, and high production efficiency, and can realize large-scale industrial production.

[0023] Optionally, in the first raw material, the second raw material, and the third raw material, the molar ratio of isocyanate groups to hydroxyl groups is independently in the range of (1.05-1.55):1.

[0024] Optionally, in step (1), the keeping time for the first time is the time required when the amount of substance of isocyanate groups in the reaction system is 40%-60% of the isocyanate groups in the first raw material;

[0025] In step (2), the keeping time for the second time is the time required when the amount of substance of isocyanate groups in the reaction system is 15%-35% of the isocyanate groups in the first raw material;

[0026] In step (3), the keeping time for the third time is the time required when the amount of substance of isocyanate groups in the reaction system is 10%-16% of the isocyanate groups in the first raw material.

[0027] Optionally, the first temperature is in the range of 60-100°C; and the second temperature and the third temperature are independently in the range of 70-110°C.

[0028] The third aspect of the present application provides an electrode slurry, comprising an electrode active material, a solvent, and the dispersant for electrode slurry provided in the first aspect of the present application.

[0029] Due to the use of the dispersant provided in the present application, in the case that the above electrode slurry and the electrode slurry in the prior art have the same viscosity, the electrode slurry of the present application has higher solid content and good stability.

[0030] The fourth aspect of the present application provides an electrode tab, comprising a current collector and an electrode active material layer arranged on at least one side surface of the current collector, wherein the electrode active material layer comprises the dispersant for electrode slurry provided in the first aspect of the present application, or the electrode active material layer is prepared by using the electrode slurry.

[0031] It can be understood that the electrode slurry is finally coated on the surface of the current collector, and then dried, rolled and cut to obtain the electrode tab. However, due to the process limitation, the thickness of the coating obtained by coating on the surface of the current collector is limited. Therefore, by using the electrode slurry provided in the embodiments of the present application, the amount of substance of the electrode active material in the electrode active material layer obtained after drying is larger under the same coating thickness, so that the electrode tab can improve the capacity of the battery.

[0032] Optionally, the electrode active material comprises a phosphate-based positive electrode active material.

[0033] The fifth aspect of the present application provides a battery comprising the electrode tab provided in the fourth aspect of the present application. Since the above electrode tab is used, the battery has good market competitiveness. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The viscosity curves of the slurries with different dispersant contents of Example 1 and the viscosity curves of the slurries of Comparative Examples are collected in Table 1.

[0035] Figure 2 The viscosity curves of the slurries with different dispersant contents of Comparative Example 1 and the viscosity curves of the slurries of Comparative Examples are collected in Table 2.

[0036] Figure 3 The infrared spectrum of the dispersant of Example 1 is shown in Figure 1. DETAILED DESCRIPTION

[0037] The high molecular dispersant for electrode slurry usually uses carboxyl group as anchoring group. The dispersant is adsorbed on the surface of electrode active material particles through the anchoring group to promote the dispersion of solid particles. However, the binding force between carboxyl group and electrode active material is weak, especially the binding force between carboxyl group and lithium iron phosphate material is weak, which often leads to limited dispersion and viscosity reduction effect of the dispersant. In addition, due to the high safety of phosphate-based positive active material (for example, modified or unmodified lithium iron phosphate material), phosphate-based positive active material is still favored in the market. Based on the preparation method and application of lithium iron phosphate material, the surface of phosphate-based positive active material used in the market is coated with a carbon material layer, and the surface of the carbon material layer on the surface of the material generally has H atoms. These H atoms may be directly connected to C atoms, or may exist in some functional groups (for example, phenolic hydroxyl, carboxyl, etc.). Therefore, when the anchoring group of the dispersant is a carboxyl group, it is difficult to form a stable chemical bond with the above-mentioned material, the adsorption is poor, and the uniformity and stability of the prepared slurry are insufficient. During the storage of the slurry and when contaminated by impurities, the dispersant is easily desorbed, leading to slurry flocculation, which seriously affects the application of the slurry.

[0038] To solve the above problems, the application provides a kind of dispersant, including polyurethane polymer;The end-capping group of at least one end of the polyurethane polymer is modified or unmodified hydrocarbon group, and the end-capping group of at least some ends away from the hydrocarbon group is isocyanate group. In the present application, for a single polyurethane polymer molecule, the above-mentioned polyurethane polymer can be linear or claw-shaped. For a linear single polyurethane polymer molecule, the end-capping group at one end of the molecular chain is isocyanate group, and the end-capping group at the other end of the molecular chain is modified or unmodified hydrocarbon group. For a single claw-shaped polyurethane polymer molecule, the end-capping group of at least one end is the above-mentioned hydrocarbon group, and the end-capping group of at least some ends away from the above-mentioned hydrocarbon group on the molecular chain is isocyanate group. In the present application, the above-mentioned substituted hydrocarbon group includes but is not limited to at least one group of alcohol group, carboxylic acid group, ether group, ester group and urethane group.

[0039] After the above dispersant is added to the system to be dispersed (including the system of the dispersion medium and the electrode active material particles), the isocyanate end-capped group can be stably adsorbed on the surface of the solid particles as an anchoring group, so that the polyurethane-based polymer (the dispersant molecule) forms an adsorption layer on the surface of the electrode active material particles, and the other end-capped group (i.e., the substituted or unsubstituted hydrocarbon group) has good compatibility with the dispersion medium (for example, an organic solvent), which can enhance the wettability of the dispersion medium to the electrode active material particles, and therefore, the presence of the above dispersant can reduce the viscosity of the system and obtain a uniform and stable slurry. Specifically, two electrode slurries with the same composition are prepared, one is prepared by using the above dispersant, and the other is prepared by using the dispersant in the prior art. When the solid content of the two electrode slurries is the same, the viscosity of the electrode slurry containing the dispersant of the present application is lower; when the viscosity of the two electrode slurries is the same, the solid content of the electrode slurry containing the dispersant of the present application is higher.

[0040] In particular, for phosphate-based active materials (for example, modified or unmodified lithium iron phosphate), the isocyanate group can form a chemical bond (for example, a urethane bond, etc.) with the H atoms on the surface of the lithium iron phosphate-based material, so that the dispersant can be stably and durably adsorbed on the surface of the material. Not only can a uniform, stable and low-viscosity (or high-solid-content) electrode slurry be obtained, but also the dispersant is less likely to desorb when the electrode slurry is stored for a long time and contaminated with impurities, thereby reducing the risk of slurry flocculation.

[0041] In the embodiments of the present application, the presence of the isocyanate group end-capped group in the dispersant can be proved by the following method:

[0042] (1) Preparation of bromocresol green indicator: 0.1 g of bromocresol green is dissolved in 100 ml of 20% volume fraction ethanol;

[0043] (2) 0.1 mol / L di-n-butylamine-toluene solution: 12.9 g of di-n-butylamine is dissolved in toluene and transferred to a 1000 ml volumetric flask, diluted to the calibration line with toluene, and shaken well to obtain a di-n-butylamine-toluene solution;

[0044] (3) About 1 g of the dispersant to be tested is placed in a dry conical flask, 25 ml of toluene is added, and it is dissolved by shaking well. Then, 25 mL of the above di-n-butylamine-toluene solution is added, the bottle opening is covered, and it is shaken well. After standing for 30 min, 100 mL of isopropyl alcohol and 5 drops of bromocresol green indicator are added, and titration is performed with 0.1 mol / L hydrochloric acid solution until the end point (when the titration end point is reached, the color of the solution changes from blue to yellow).

[0045] In some embodiments of this application, the number of carbon atoms in the substituted or unsubstituted hydrocarbon groups is 1 to 24. Exemplarily, the number of carbon atoms in the substituted or unsubstituted hydrocarbon groups can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, etc. In this way, the chain length and steric hindrance of the substituted or unsubstituted hydrocarbon groups can be controlled within a suitable range, which is beneficial to the dispersibility of polyurethane polymers and their wettability to solid particles.

[0046] In some embodiments of this application, the substituted or unsubstituted hydrocarbon group is a C3-C24 branched hydrocarbon group. Thus, the substituted or unsubstituted hydrocarbon group also possesses more suitable steric hindrance, enabling the polyurethane polymer molecular chains to form a more stable steric barrier, thereby more stably dispersing solid particles. Therefore, the dispersant molecule can possess both good wetting properties and good barrier properties. Exemplarily, the aforementioned substituted or unsubstituted branched hydrocarbon group includes, but is not limited to, carbon-carbon branches, branches with ether oxygen atoms, and branches with ester groups.

[0047] In some embodiments of this application, the number-average molecular weight of the polyurethane polymer is 100 to 5000. Exemplarily, the number-average molecular weight of the polyurethane polymer can be 100, 200, 500, 800, 1000, 1200, 1500, 1800, 2000, 2200, 2500, 2800, 3000, 3200, 3500, 3800, 4000, 4200, 4500, 4800, etc. Controlling the number-average molecular weight of the polyurethane polymer within the above range means controlling the length of the polyurethane polymer molecular chains within a suitable range, which can reduce entanglement between polyurethane polymers or entanglement of individual molecules; simultaneously, the polyurethane polymer molecules have suitable steric hindrance; therefore, the dispersion effect of the polyurethane polymer (i.e., the dispersant) can be improved.

[0048] In some embodiments of this application, the polyurethane polymer with a 1-molecule structure has two or more isocyanate groups. It should be noted that the isocyanate groups here specifically refer to end-capped isocyanate groups. In this case, a single polyurethane polymer molecule has at least two isocyanate anchoring (end-capping) groups, thus further enhancing the binding force between the polyurethane polymer (i.e., the dispersant) and the electrode active material particles, allowing the dispersant to be adsorbed onto the material surface more persistently and stably, thereby further improving the stability of the electrode slurry. Further, in some specific embodiments, the polyurethane polymer is a claw-shaped polymer, and the 1-molecule polyurethane polymer has one or more polyurethane branches, with at least some of the polyurethane branches having isocyanate groups as end-capping groups; understandably, when it has only one polyurethane branch, the end-capping group of that branch is an isocyanate group. Further, in some specific embodiments, in the 1-molecule claw-shaped polyurethane polymer, the ratio of isocyanate end-capping groups to substituted or unsubstituted hydrocarbon end-capping groups is in the range of 1:(1-9). In this way, while further enhancing the bonding force between the dispersant and the electrode active material particles, it can also achieve suitable steric hindrance and good wetting properties. For example, the ratio of isocyanate end-capping groups to hydrocarbon end-capping groups can be 1:1, 1:2, 1:3, 1:5, 1:6, 1:8, etc.

[0049] In some embodiments of this application, the molecular structure of the polyurethane polymer is shown in formula (Ⅰ).

[0050] Wherein, R2 is the hydrocarbon group, and the value of n is such that the relative molecular mass of the polyurethane polymer is in the range of 100 to 5000;

[0051] Wherein, R1 includes R3 includes small molecule polyols and The polymer segments; R4 comprises polymer segments of macromolecular diols and diisocyanates. R3 comprises small molecule polyols and... The polymer segment specifically refers to the residues at the end of the polymer that undergo amino esterification with NCO and / or OH groups; the following explanation uses the simplest case, where R3 is one glycerol molecule and one... Taking a polymer chain segment as an example, in this case, R3 is... In some embodiments of this application, the aforementioned small-molecule polyols are selected from small-molecule triols and small-molecule diols. The small-molecule diols include, but are not limited to, 1,4-butanediol and ethylene glycol, while the small-molecule triols include, but are not limited to, glycerol. The aforementioned large-molecule diols include, but are not limited to, polyether diols and / or polyester diols. The polyether diols and polyester diols can be any polyether diols known in the art. In some embodiments, the polyether diols include, but are not limited to, at least one of polypropylene glycol, polyethylene oxide / propylene oxide block copolymer diol, polytetrahydrofuran diol, tetrahydrofuran / ethylene oxide copolymer diol, and tetrahydrofuran / propylene oxide copolymer diol; the polyester diols include, but are not limited to, at least one of adipic acid / butanediol copolymer diol, adipic acid / diethylene glycol copolymer diol, polycarbonate diol, and polycaprolactone diol. In this application, the aforementioned diisocyanate can be any diisocyanate known in the art.

[0052] It should be noted that in the embodiments of this application, small molecule polyols are polyols with an index-average molecular weight of 32-500, and large molecule polyols are polyols with an index-average molecular weight greater than 500. In some specific embodiments, the number-average molecular weight of the large molecule polyol is less than or equal to 2000.

[0053] In some embodiments of this application, the polyurethane polymer with a single molecular structure is linear. That is, the end-capping group at one end of the polyurethane polymer molecular chain is an isocyanate group, and the end-capping group at the other end of the molecular chain is a substituted or unsubstituted hydrocarbon group. In some embodiments of this application, the molecular structure of the above-mentioned polyurethane polymer is shown in formula (II).

[0054] Wherein, R2 is the hydrocarbon group, and the value of n is such that the relative molecular mass of the polyurethane polymer is in the range of 100 to 5000;

[0055] Wherein, R'1 includes The R'3 includes small molecule diols and The block copolymer; R4 comprises a copolymer of a macromolecular diol and a diisocyanate. In some embodiments of this application, the aforementioned small-molecule diol includes, but is not limited to, 1,4-butanediol, ethanol, etc. The aforementioned macromolecular diol includes, but is not limited to, polyether diols and / or polyester diols. The polyether diol and polyester diol can be any polyether diol known in the art. In some embodiments, the polyether diol includes, but is not limited to, at least one of polypropylene glycol, polyethylene oxide / propylene oxide block copolymer diol, polytetrahydrofuran diol, tetrahydrofuran / ethylene oxide copolymer diol, and tetrahydrofuran / propylene oxide copolymer diol; the polyester diol includes, but is not limited to, at least one of adipic acid / butanediol copolymer diol, adipic acid / diethylene glycol copolymer diol, polycarbonate diol, and polycaprolactone diol. In this application, the aforementioned diisocyanate can be any diisocyanate known in the art.

[0056] In some embodiments of this application, the diisocyanate includes, but is not limited to, at least one of isophorone diisocyanate, hexamethyl diisocyanate, toluene diisocyanate, hydrogenated 4,4-diphenylmethane diisocyanate, and diphenylmethane 4,4'-diisocyanate.

[0057] This application also provides a method for preparing a dispersant, which can be used to prepare the aforementioned dispersant for electrode slurry. The preparation method includes the following steps:

[0058] S01. Provide a first raw material, the first raw material comprising diisocyanate, macromolecular diol and catalyst, wherein the molar ratio of isocyanate group to hydroxyl group in the first raw material is greater than or equal to 1.055:1;

[0059] The first raw material is heated to a first temperature and held at that temperature for a first time to allow the diisocyanate to react with the macromolecular polyol to obtain a first prepolymer; wherein at least a portion of the first prepolymer has isocyanate groups as end groups;

[0060] S02. Add a small molecule polyol to the first prepolymer to obtain a second raw material; wherein, in the second raw material, the molar ratio of isocyanate groups to hydroxyl groups is greater than or equal to 1.055:1; wherein, the small molecule polyol is selected from small molecule diols, or small molecule triols and small molecule diols.

[0061] The second raw material is heated to a second temperature and held at that temperature for a second time, so that the first prepolymer reacts with the second raw material to obtain a second prepolymer; wherein, the second prepolymer comprises an isocyanate-terminated polyurethane polymer;

[0062] S03. Add a monohydric alcohol to the second prepolymer to obtain a third raw material; wherein, in the third raw material, the molar ratio of isocyanate groups to hydroxyl groups is greater than or equal to 1.055:1;

[0063] The third raw material is kept at a third temperature for a third time to allow the monohydric alcohol to react with some of the isocyanate groups in the second prepolymer, causing some of the end-capped groups in the second prepolymer to transform into substituted or unsubstituted hydrocarbon groups, thus obtaining a dispersant. Understandably, the dispersant at this time is a polyurethane polymer, wherein in a single-molecule dispersant, at least one end group is a hydrocarbon group and at least one end group is an isocyanate group.

[0064] In the above preparation method, by controlling the molar ratio of isocyanate groups to hydroxyl groups in each raw material to be greater than or equal to 1.055, at least some of the first and second prepolymers can have isocyanate groups as end groups. This provides a material basis for the preparation of dispersant molecules with both hydrocarbon and isocyanate end groups in step S03, thus successfully obtaining a dispersant with special end groups. The above preparation method is simple, reliable, and efficient, and can be used for large-scale industrial production.

[0065] The following example, using one type of change in the molecular structure of the dispersant, illustrates the synthetic route in conjunction with the above preparation method:

[0066]

[0067] In the above synthetic route, OCN-R a -NCO is selected from one or more of toluene diisocyanate (TDI), isophoric diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and dicyclohexylmethane diisocyanate (HMDI). OH-R b -OH is selected from macromolecular diols with both main and branched chains between C2 and C8. OH-R c -OH is selected from small molecule diols with a relative molecular mass between 100 and 2000. OH-R d -OH is selected as C1 for both the main chain and branches. ～ Triols between C8 atoms.

[0068] In some embodiments of this application, the monohydric alcohol includes, but is not limited to, at least one of dodecanol, octadecyl alcohol, and hexadecyl alcohol. The residues of the monohydric alcohol after reacting with the second prepolymer serve as end groups in the final dispersant molecule. The residues of the monohydric alcohol after reaction have both suitable steric hindrance and good compatibility with organic solvents, thus the final dispersant has both good dispersibility and viscosity reduction properties.

[0069] In some embodiments of this application, the molar ratio of isocyanate groups to hydroxyl groups in the first raw material, the second raw material, and the third raw material is independently within the range of (1.05 to 1.55):1. Exemplarily, the molar ratio of isocyanate groups to hydroxyl groups in the first raw material, the second raw material, and the third raw material can be independently 1.05:1, 1.1:1, 1.15:1, 1.20:1, 1.25:1, 1.30:1, 1.35:1, 1.40:1, 1.45:1, 1.50:1, 1.55:1, etc. Controlling the molar ratio of isocyanate groups to hydroxyl groups within the above range not only allows control over the end-capping groups of the dispersant molecular chain to include both isocyanate groups and substituted or unsubstituted hydrocarbon groups, but also, when the dispersant is a claw-type polymer, allows adjustment of the ratio of isocyanate end-capping groups to hydrocarbon end-capping groups in a single-molecule dispersant to a suitable range. Consequently, the dispersant can simultaneously possess both good dispersing performance and good binding force with solid particles.

[0070] In some embodiments of this application, in step S01, the initial heat preservation time is the time required for the amount of isocyanate groups in the reaction system to reach 40% to 60% of the isocyanate groups in the first raw material (i.e., 40% to 60% of the amount of isocyanate groups initially added to the first raw material). Although the reaction time has little effect on the monomer conversion rate in the polycondensation reaction, given the special design of the synthetic route in this application, the above condition can be simply understood as stopping the reaction in step S01 when the conversion rate of isocyanate groups in the system reaches 40% to 60%, thus obtaining the first prepolymer.

[0071] In step S02, the second heat preservation time is the time required for the amount of isocyanate groups in the reaction system to reach 15% to 35% of the isocyanate groups in the first raw material (that is, 15% to 35% of the amount of isocyanate groups initially added to the first raw material). Simply put, in the reaction system of step S02, based on the amount of isocyanate groups in the first raw material, when the conversion rate of the isocyanate groups reaches 65% to 85%, the reaction in step S02 is stopped, and the second prepolymer is obtained.

[0072] Similarly, in S03, the third heat preservation time is the time required for the amount of isocyanate groups in the reaction system to reach 10% to 16% of the isocyanate groups in the first raw material (that is, 10% to 16% of the amount of isocyanate groups initially added to the first raw material). Simply put, in the reaction system of step S03, when the conversion rate of isocyanate groups reaches 84% ​​to 90% based on the amount of isocyanate groups in the first raw material, the reaction in step S03 is stopped, and a dispersant is obtained.

[0073] All of the reactions in the above steps are condensation reactions. By controlling the conversion rate of isocyanate groups in the reaction system in steps S01, S02, and S03 within the above-mentioned ranges, production efficiency can be improved.

[0074] In the embodiments of this application, the conversion rate of isocyanate groups can be determined by the following method: (1) Preparation of bromocresol green indicator: 0.1 g of bromocresol green is dissolved in 100 ml of 20% ethanol;

[0075] (2) 0.1 mol / L di-n-butylamine-toluene solution: Dissolve 12.9 g of di-n-butylamine in toluene, transfer to a 1000 ml volumetric flask, dilute to the mark with toluene, and shake well to obtain di-n-butylamine-toluene solution;

[0076] (3) Take about 1g of the sample to be tested and place it in a dry conical flask. Add 25ml of toluene and shake well to dissolve. Add 25mL of the above di-n-butylamine-toluene solution, cover the mouth of the flask and shake well. Let it stand for 30min. Then add 100mL of isopropanol and 5 drops of bromocresol green indicator and titrate with 0.1mol / L hydrochloric acid solution to the endpoint (the solution color changes from blue to yellow at the titration endpoint). At the same time, perform a blank experiment. No sample is added to the blank group experiment.

[0077]

[0078] In the formula:

[0079] V1 represents the volume of hydrochloric acid consumed in the blank experiment of the sample to be tested, in mL;

[0080] V2 represents the volume of hydrochloric acid consumed by the sample to be tested, in mL;

[0081] V 10 The volume of hydrochloric acid consumed in the blank experiment representing the diisocyanate raw material in the first raw material is expressed in mL.

[0082] V 20 The volume of hydrochloric acid consumed in the test experiment of diisocyanate raw material in the first raw material is represented in mL;

[0083] m 01 This represents the total weight of the sample to be tested, in grams.

[0084] m1 represents the weight of the sample during the NCO test, in grams;

[0085] m 02 This represents the total mass of diisocyanate in the first raw material, expressed in grams.

[0086] m2 represents the weight of the sample of diisocyanate raw material in the first raw material when the NCO test is performed, in grams.

[0087] Correspondingly, when testing the conversion rate of NCO in step S01, the sample to be tested in (3) is the material obtained after the first raw material is kept warm for a first time;

[0088] When testing the conversion rate of NCO in step S02, the sample to be tested in (3) is the material obtained after the second raw material is kept at a constant temperature for a second time;

[0089] When testing the conversion rate of NCO in step S03, the sample to be tested in (3) is the material obtained after the third raw material is kept at a constant temperature for a third time. That is, the final sample to be tested in (3) is the dispersant that has been prepared.

[0090] In some embodiments of this application, in step S01, the first temperature is within the range of 60°C to 100°C. For example, the first temperature can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, etc. Controlling the first temperature within the above range ensures the reaction proceeds and also helps to increase the reaction rate.

[0091] In some embodiments of this application, in steps S02 and S03, the second temperature and the third temperature are each independently within the range of 70°C to 110°C. For example, the second temperature and the third temperature can each be independently 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, etc. Similarly, this ensures the reaction proceeds, facilitates an increased reaction rate, and reduces the risk of side reactions.

[0092] In some embodiments of this application, after step S03, step S04 is also included: after the third heat preservation is completed, the system is cooled to 10℃~45℃, the material is discharged, and the dispersant is obtained.

[0093] This application also provides an electrode slurry, including an electrode active material, a solvent, and the aforementioned dispersant for electrode slurry. Because it uses the dispersant provided in this application, the resulting electrode slurry, while having the same viscosity as electrode slurries in the prior art, has a higher solids content, is more stable over time, and is less prone to flocculation during long-term storage or contamination. Therefore, the electrode slurry provided in this application has high market competitiveness.

[0094] In this application, the electrode slurry can be either a positive electrode slurry or a negative electrode slurry. Correspondingly, the electrode active material can be either a positive electrode active material or a negative electrode active material. The positive and negative electrode active materials are commonly used positive and negative electrode active materials in batteries such as lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, and aluminum-ion batteries. In some embodiments of this application, the electrode slurry is a positive electrode slurry. In some specific embodiments, the electrode active material is a phosphate-based positive electrode active material. In some specific embodiments, the electrode active material is modified or unmodified lithium iron phosphate, preferably modified or unmodified lithium iron phosphate with a carbon coating layer on the surface. Isocyanate groups can form chemical bonds (e.g., urethane bonds, etc.) with the H atoms on the surface of lithium iron phosphate materials, so that the dispersant can be persistently and stably adsorbed on the material surface. This not only yields a uniform, stable electrode slurry with low viscosity (or high solid content), but also prevents the dispersant from desorbing during long-term storage and contamination by impurities, further reducing the risk of slurry flocculation. The modified lithium iron phosphate mentioned above includes, but is not limited to, doped lithium iron phosphate.

[0095] This application also provides an electrode sheet, which includes a current collector and an electrode active material layer disposed on at least one side surface of the current collector. The electrode active material layer includes the dispersant for electrode slurry provided in this application, or the electrode active material layer is obtained by the electrode slurry.

[0096] The aforementioned electrode plates can be either positive or negative electrodes. The aforementioned current collector can be any known current collector for negative or positive electrodes within the field.

[0097] This application provides a battery including the electrode plates provided in this application. Due to the use of the aforementioned electrode plates, this battery has good market competitiveness.

[0098] The aforementioned batteries can be either liquid batteries or solid-state batteries. Among them, solid-state batteries can be either all-solid-state batteries or semi-solid-state batteries.

[0099] The technical solution of this application is further described below with reference to several embodiments.

[0100] Example 1

[0101] (1) Provide the first raw material: 50 parts by weight of diisocyanate (specifically isophorone diisocyanate), 20 parts by weight of macromolecular diol (specifically polyether diol with a molecular weight of 1000) and 0.5 parts by weight of catalyst, wherein the molar ratio of isocyanate groups to hydroxyl groups in the first raw material is 12:1. Place the first raw material in a reaction apparatus, heat it to a first holding temperature (specifically 80°C), hold it at this temperature for a first time, and monitor the amount of isocyanate groups in real time during the reaction. When the amount of isocyanate groups drops to 91% of the initial amount of isocyanate groups in the first raw material, the first prepolymer is obtained, and step (2) is carried out.

[0102] (2) Add 13 parts by weight of small molecule polyol (specifically 3 parts by weight of glycerol and 10 parts by weight of 1,4-butanediol) to the reaction apparatus to obtain the second raw material; wherein the molar ratio of isocyanate groups to hydroxyl groups in the second raw material is 1.42:1. Continue to heat to the second holding temperature (specifically 85°C) and hold for a second time. Monitor the amount of isocyanate groups in real time during the reaction. When the amount of isocyanate groups drops to 21% of the initial amount of isocyanate groups in the first raw material, the second prepolymer is obtained, and proceed to step (3).

[0103] (3) Add 6 parts by weight of monohydric alcohol (specifically 3 parts by weight of dodecanol and 3 parts by weight of octadecyl alcohol) to the reaction apparatus to obtain a third raw material; wherein the molar ratio of isocyanate groups to hydroxyl groups in the third raw material is 17:1. Maintain the reaction at a third holding temperature (specifically 85°C) for a third holding time, monitoring the amount of isocyanate groups in real time during the reaction. When the amount of isocyanate groups decreases to 14.95% of the initial amount of isocyanate groups in the first raw material, cool the reaction to 45°C to obtain a dispersant. The number-average molecular weight of this dispersant is 2780.

[0104] Example 2

[0105] (1) Provide the first raw material: 60 parts by weight of diisocyanate (specifically toluene diisocyanate), 8 parts by weight of macromolecular diol (specifically polyether diol with a molecular weight of 1200) and 0.5 parts by weight of catalyst, wherein the molar ratio of isocyanate groups to hydroxyl groups in the first raw material is 37:1. Place the first raw material in a reaction apparatus, heat it to a first holding temperature (specifically 70°C), hold it at this temperature for a first time, and monitor the amount of isocyanate groups in real time during the reaction. When the amount of isocyanate groups drops to 97% of the initial amount of isocyanate groups in the first raw material, the first prepolymer is obtained, and step (2) is carried out.

[0106] (2) 29 parts by weight of small molecule polyol (specifically 4 parts by weight of glycerol and 10 parts by weight of ethylene glycol) are added to the reaction apparatus to obtain the second raw material; wherein the molar ratio of isocyanate groups to hydroxyl groups in the second raw material is 1.3:1. The temperature is raised to the second holding temperature (specifically 75°C) and held for a second time. The amount of isocyanate groups is monitored in real time during the reaction. When the amount of isocyanate groups drops to 21% of the initial amount of isocyanate groups in the first raw material, the second prepolymer is obtained, and step (3) is carried out.

[0107] (3) Add 9 parts by weight of a monohydric alcohol (specifically 5 parts by weight of dodecanol acrylate and 4 parts by weight of octadecyl acrylate) to the reaction apparatus to obtain a third raw material; wherein the molar ratio of isocyanate groups to hydroxyl groups in the third raw material is 11:1. Maintain the reaction at a third holding temperature (specifically 75°C) for a third holding time, monitoring the amount of isocyanate groups in real time during the reaction. When the amount of isocyanate groups drops to 12.03% of the initial amount of isocyanate groups in the first raw material, cool the temperature to 30°C to obtain a dispersant. The number-average molecular weight of this dispersant is 5640.

[0108] Example 3

[0109] The difference from Example 1 is that in step (2), 13 parts by weight of 1,4-butanediol are added to the reaction apparatus. The number-average relative molecular mass of the dispersant is 3130, and after the third time of heat preservation, the amount of isocyanate groups is 12.00% of the amount of isocyanate groups initially present in the first raw material.

[0110] To highlight the beneficial effects of the embodiments of this application, the following comparative examples are provided.

[0111] Comparative Example 1

[0112] Commercially available dispersants are specifically carboxylic acid ester dispersants.

[0113] Performance testing:

[0114] 1. Viscosity test of electrode slurry: The viscosity was tested using a rotational rheometer at 25℃ and a shear rate of 1s. -1 50s -1 100s -1 The viscosity of each positive electrode slurry was tested. The preparation method of the positive electrode slurry samples to be tested is as follows:

[0115] (1) Preparation of electrode slurry: 100g of lithium iron phosphate, 70g of solvent (specifically N-methylpyrrolidone), 5g of binder (specifically polyvinylidene fluoride PVDF), and 2g of conductive agent were used to form a dispersion system. 1.0g of the dispersant from each of the above examples and comparative examples was added to the dispersion system to obtain the positive electrode slurry. The viscosity test results are summarized in Table 1.

[0116] Specifically, a comparative slurry is provided, which contains no dispersant.

[0117] (2) Viscosity tests were conducted on slurries containing different concentrations of dispersant from Example 1 and Comparative Example 1. 0.2, 0.4, 0.6, 0.8, and 1.0 g of dispersant from Example 1 were added to the five dispersion systems described above, respectively. The positive electrode slurries were designated as S1-1, S1-2, S1-3, S1-4, and S1-5. The viscosity test curves for these samples can be found in [reference needed]. Figure 1 Please refer to Table 2 for specific test results; 0.2, 0.4, 0.6, 0.8, and 1.0 g of the dispersant from Comparative Example 1 were added to the five dispersion systems mentioned above, respectively. The positive electrode slurries are designated as DS1-1, DS1-2, DS1-3, DS1-4, and DS1-5. Please refer to Table 2 for the viscosity test curves of the above samples. Figure 2 Please refer to Table 2 for the specific test results.

[0118] 2. Stability test of electrode paste: The stability was tested using a rotational rheometer at 25℃ and a shear rate of 50s. -1 The initial viscosity of each positive electrode slurry and the comparative slurry was tested and denoted as viscosity a; each slurry was allowed to stand in a dew point environment for 24 hours, and then the upper layer of slurry was tested at 25°C and a shear rate of 50 s. -1 The viscosity was tested and denoted as viscosity b. The viscosity rebound rate was calculated as (viscosity b - viscosity a) * 100% / viscosity a. The viscosity rebound rate characterizes the stability of the slurry; a higher viscosity rebound rate indicates poorer slurry stability. The results are summarized in Table 3. In chemical engineering, dew point is defined as the temperature at which unsaturated air is cooled to saturation. Specifically, the dew point environment refers to controlling the ambient humidity during slurry settling to be low or close to saturation humidity (i.e., high dryness).

[0119] 3. Infrared testing: The dispersant in Example 1 was subjected to infrared testing at a resolution of 15 cm⁻¹. -1 For the infrared spectrum of the dispersant in Example 1, please refer to [link / reference needed]. Figure 3 .

[0120] Table 1

[0121]

[0122] Table 2

[0123]

[0124] Table 3

[0125]

[0126]

[0127] Based on the data in Tables 1-3, it can be seen that the dispersant provided in the embodiments of this application can not only significantly reduce the viscosity of the slurry, but also significantly improve the stability of the slurry.

[0128] Furthermore, it should be noted that in the comparative slurry (slurry without dispersant), at a shear rate of 1 s... -1 The viscosity of the slurry in Comparative Example 1 is lower than that in Comparative Example 1, indicating that the dispersant in Comparative Example 1 increases the viscosity of the slurry upon addition, exhibiting a viscosity-reducing effect at high shear rates and thickening at low shear rates. However, for slurries DS1-3 to DS1-5, there is a situation where "the slurry viscosity increases with the increase of dispersant dosage." This is because as the dosage of the dispersant in Comparative Example 1 increases, its role in the slurry changes from "dispersion" to "bridging." At this point, this type of dispersant acts as a connector for lithium iron phosphate particles, and this effect is more pronounced, especially at lower shear rates, leading to an increase in slurry viscosity. The dispersant provided in this application does not have the above-mentioned problem; therefore, the advantages of the dispersant provided in this application can be further explained.

[0129] The above description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A dispersant for electrode paste, characterized in that, The electrode slurry includes a polyurethane polymer, wherein the electrode slurry is a positive electrode slurry; at least one end of the polyurethane polymer has a capping group that is a substituted or unsubstituted hydrocarbon group, and at least a portion of the end of the polyurethane polymer away from the hydrocarbon group has a capping group that is an isocyanate group; the substituted or unsubstituted hydrocarbon group has an integer number of carbon atoms from 6 to 24, and the substituents in the substituted hydrocarbon group include carboxylic acid groups.

2. The dispersant according to claim 1, characterized in that, In the polyurethane polymer with a molecular structure of 1, the number of isocyanate groups is greater than or equal to 2.

3. The dispersant according to claim 1, characterized in that, The substituted or unsubstituted hydrocarbon group is a branched hydrocarbon group of C6 to C24.

4. The dispersant according to any one of claims 1 to 3, characterized in that, The number-average relative molecular mass of the polyurethane polymer is 200-5000.

5. The dispersant according to claim 1, characterized in that, The molecular structure of the polyurethane polymer is shown in formula (Ⅰ). Formula (I), wherein R2 is the hydrocarbon group, and the value of n is such that the relative molecular mass of the polyurethane polymer is in the range of 800 to 5000; Wherein, R1 includes R3 comprises small molecule polyols and The polymer segments; R4 comprises polymer segments of macromolecular diols and diisocyanates.

6. The dispersant according to claim 5, characterized in that, The small molecule polyol is selected from small molecule diols and small molecule triols; the small molecule diol includes at least one of 1,4-butanediol, ethylene glycol, propylene glycol, octanediol, and neopentyl glycol; the small molecule triol includes at least one of glycerol and trimethylolpropane. The macromolecular diols include polyether diols and / or polyester diols; wherein the polyether diols include at least one of polypropylene glycol, polyethylene oxide / propylene oxide block copolymer diol, polytetrahydrofuran diol, tetrahydrofuran / ethylene oxide copolymer diol, and tetrahydrofuran / propylene oxide copolymer diol. Polyester diols include at least one of adipic acid / butanediol copolyol, adipic acid / diethylene glycol copolyol, polycarbonate diol, and polycaprolactone diol.

7. A method for preparing a dispersant, characterized in that, Includes the following steps: (1) Provide a first raw material, the first raw material comprising diisocyanate, macromolecular diol and catalyst, wherein the molar ratio of isocyanate group to hydroxyl group in the first raw material is greater than or equal to 1.055:1; The first raw material is heated to a first temperature and held at that temperature for a first time to allow the diisocyanate to react with the macromolecular diol to obtain a first prepolymer; wherein at least a portion of the first prepolymer has isocyanate groups as end groups; (2) Add a small molecule polyol to the first prepolymer to obtain a second raw material; wherein, in the second raw material, the molar ratio of isocyanate group to hydroxyl group is greater than or equal to 1.055:1; wherein, the small molecule polyol is selected from small molecule diols, or small molecule diols and small molecule triols; The second raw material is heated to a second temperature and held at that temperature for a second time, so that the first prepolymer reacts with the second raw material to obtain a second prepolymer; wherein, the second prepolymer comprises an isocyanate-terminated polyurethane polymer; (3) Add a monohydric alcohol to the second prepolymer to obtain a third raw material; wherein, in the third raw material, the molar ratio of isocyanate groups to hydroxyl groups is greater than or equal to 1.055:1; The third raw material is kept at a third temperature for a third time so that the monohydric alcohol reacts with some of the isocyanate groups in the second prepolymer, thereby converting some of the end-capped groups in the second prepolymer into substituted or unsubstituted hydrocarbon groups, to obtain a dispersant.

8. The preparation method according to claim 7, characterized in that, In the first raw material, the second raw material, and the third raw material, the molar ratio of isocyanate groups to hydroxyl groups is independently in the range of (1.055~1.55):

1.

9. The preparation method according to claim 8, characterized in that, In step (1), the first heat preservation time is the time required when the amount of isocyanate groups in the reaction system is 40% to 60% of the isocyanate groups in the first raw material; In step (2), the second heat preservation time is the time required when the amount of isocyanate groups in the reaction system is 15% to 35% of the isocyanate groups in the first raw material; In step (3), the third heat preservation time is the time required when the amount of isocyanate groups in the reaction system is 10% to 16% of the isocyanate groups in the first raw material.

10. The preparation method according to claim 8, characterized in that, The first temperature is in the range of 60℃ to 100℃; the second temperature and the third temperature are each independently in the range of 70℃ to 110℃.

11. An electrode paste, characterized in that, The electrode slurry includes an electrode active material, a solvent, and a dispersant for electrode slurry as described in any one of claims 1 to 6.

12. The electrode paste according to claim 11, characterized in that, The electrode active material includes phosphate-based positive electrode active materials.

13. An electrode sheet, characterized in that, The present invention includes a current collector and an electrode active material layer disposed on at least one side of the current collector, wherein the electrode active material layer includes a dispersant for electrode slurry as described in any one of claims 1 to 6, or the electrode active material layer is prepared by electrode slurry as described in claim 11 or 12.

14. A battery, characterized in that, The battery includes the electrode plates as described in claim 13.

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