Dispersing agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a dispersing agent and a preparation method and application thereof. Wherein the dispersant comprises a polyphosphate and a functionalized elastomer containing a nitrogen group; wherein the polyphosphate is prepared by carrying out phosphorylation reaction on polymer polyol, and the mass ratio of the polymer polyol to the functionalized elastomer containing the nitrogen group in the raw materials of the polyphosphate is 1: (0.8-1.2). The dispersing agent provided by the invention not only can effectively solve the problems of overhigh slurry viscosity and poor coating effect caused by difficult dispersion of the current main material, but also can remarkably improve the processing problem of easy belt breakage in the brittle processing of the pole piece at the same time. In addition, the dispersing agent provided by the invention is environment-friendly, environment humidity does not need to be controlled, and the production cost can be greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a dispersant, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium iron phosphate plays a crucial role in power batteries due to its excellent safety performance. The processing method of its positive electrode sheet is usually to mix the main material, conductive agent, binder, etc. in a solvent, and make a positive electrode slurry through stirring and kneading, etc. Subsequently, the slurry is coated on a conductive aluminum foil by using equipment such as extrusion or transfer coating, and finally a lithium iron phosphate positive electrode sheet is obtained through drying and rolling processes.

[0003] However, currently, nano-scale lithium iron phosphate materials are prone to agglomeration due to reasons such as large specific surface area and high surface energy. At the same time, in order to increase the conductivity of lithium iron phosphate, the surface of nano-scale particles will be further carbon-coated, resulting in difficulties in dispersing the positive electrode slurry. For the above reasons, the viscosity of the lithium iron phosphate positive electrode slurry is too high, causing problems such as uneven dispersion of the slurry and poor coating effect of the electrode sheet. To address this, the following two methods are mainly used to improve the above problems: 1) reducing the solid content of the slurry to adapt to the viscosity required for coating, which not only prolongs the drying time and increases the cost, but also greatly reduces the electrode sheet loading due to the reduction of the slurry solid content; 2) adding surfactants (such as polyvinylpyrrolidone) to assist in dispersing lithium iron phosphate, but the required addition amount of the surfactant is still relatively high, and the unsaturated bonds in the molecular structure are not suitable for the high-voltage environment of the positive electrode, and are prone to side reactions of the electrode sheet during cycling, thereby damaging the electrode sheet structure and causing rapid decline of battery performance. In addition, lithium iron phosphate also has poor flexibility and is prone to tape breakage under high tap density (≥2.5 g / cm 3 ) Therefore, there is an urgent need to provide a dispersant that can simultaneously solve the dispersion problem of the lithium iron phosphate positive electrode slurry and the problem of easy tape breakage of the electrode sheet. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of difficult dispersion of the existing lithium iron phosphate positive electrode slurry and easy tape breakage of the electrode sheet, so as to provide a dispersant, a preparation method thereof, and an application thereof to solve the above problems.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a dispersant, comprising: polyphosphate ester and a functionalized elastomer with a nitrogen-containing group; wherein, the polyphosphate ester is prepared by phosphorylating a polymer polyol, and the mass ratio of the polymer polyol to the functionalized elastomer with a nitrogen-containing group in the raw materials of the polyphosphate ester is 1:(0.8 - 1.2).

[0007] Preferably, the polyphosphate ester includes at least one of polypropylene glycol phosphate ester, polyethylene glycol phosphate ester, and polyvinyl alcohol phosphate ester;

[0008] and / or, the nitrogen-containing group functionalized elastomer includes at least one of hydrogenated nitrile rubber, nitrile rubber, and polyurethane;

[0009] and / or, the polymer polyol includes at least one of polypropylene glycol, polyethylene glycol, and polyvinyl alcohol;

[0010] and / or, the phosphorylation reagent used in the phosphorylation reaction process includes at least one of polyphosphoric acid, phosphorus pentoxide, and phosphorus trichloride;

[0011] and / or, the mass ratio of the polymer polyol to the phosphorylation reagent used in the phosphorylation reaction process is 1:(0.15 - 0.2), preferably, the mass ratio of the polymer polyol to the phosphorylation reagent used in the phosphorylation reaction process is 1:0.2;

[0012] and / or, the temperature of the phosphorylation reaction is 80 - 120 °C, and the duration is 2 - 5 h; preferably, the temperature of the phosphorylation reaction is 100 °C, and the duration is 3 h;

[0013] and / or, an acidic catalyst is further added in the phosphorylation reaction; preferably, the catalyst includes at least one of phosphoric acid, sulfuric acid, and p-toluenesulfonic acid, and the mass ratio of the polymer polyol to the acidic catalyst is 1:(0.005 - 0.01), more preferably, the mass ratio of the polymer polyol to the acidic catalyst is 1:0.01;

[0014] and / or, an organic solvent is further added to the dispersant; preferably, the organic solvent includes N-methylpyrrolidone (NMP), and the mass ratio of the polymer polyol to the organic solvent is 1:(5 - 10), more preferably, the mass ratio of the polymer polyol to the organic solvent is 1:7.

[0015] Preferably, the dispersant further includes an unsaturated amide compound; preferably, the unsaturated amide compound has the following structural formula: R1 is selected from C2 - C6 alkenyl, C2 - C6 alkenyl substituted by C1 - C3 alkyl, C5 - C10 aryl unsubstituted or substituted by C1 - C3 alkyl, and C1 - C6 alkyl substituted by C5 - C10 arylcarbonyl; R2 and R3 are independently selected from hydrogen, C1 - C6 alkyl, C1 - C6 alkyl substituted by hydroxyl, or C5 - C10 aryl unsubstituted or substituted by C1 - C3 alkyl;

[0016] More preferably, R1 is selected from alkenyl groups having 2 to 3 carbon atoms, alkenyl groups having 2 to 3 carbon atoms substituted with C1-C2 alkyl groups, phenyl groups, phenyl groups substituted with C1-C2 alkyl groups, or C1-C2 alkyl groups substituted with benzoyl groups;

[0017] More preferably, R2 and R3 are independently selected from hydrogen, C1-C3 alkyl groups, C1-C3 alkyl groups substituted with hydroxyl groups, or phenyl groups.

[0018] Preferably, the unsaturated amide compounds include at least one of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, N-phenylacetamide, p-toluamide (CAS: 619-55-6; molecular formula: C8H9NO);

[0019] And / or, the mass ratio of the unsaturated amide compound to the polymer polyol is (0.5-1):1.

[0020] In a second aspect, the present invention also provides a method for preparing the above dispersant, including: mixing the polyphosphate ester and the functionalized elastomer with a nitrogen-containing group to obtain the dispersant.

[0021] Preferably, the temperature for mixing is 40-80 °C, and the duration is 5-8 h;

[0022] And / or, an unsaturated amide compound is further added during the mixing process;

[0023] And / or, the preparation process of the polyphosphate ester includes: dissolving the polymer polyol in an organic solvent, and then adding a phosphorylation reagent and an acidic catalyst for reaction to obtain the polyphosphate ester. Since the phosphorylation reaction has relatively high requirements for water control, after dissolving the polyol polymer in the solvent, a dehydration treatment is also carried out. However, since conventional reagents all have water control, generally within 1 wt%, the water content is very low and has little impact on the weight of the reagent, so there is no need to deliberately calculate the mass loss of water in the reagent.

[0024] In a third aspect, the present invention also provides a positive electrode paste, which includes the above dispersant or the dispersant prepared by the above method for preparing the dispersant. Based on the mass of the dry matter (solvent-free) in the positive electrode paste being 100 wt%, the mass ratio of the dry matter (solvent-free) in the dispersant is 0.1-0.3 wt%.

[0025] Preferably, the dry matter in the positive electrode paste further includes an electrode active material, a conductive agent, and a binder;

[0026] And / or, the positive electrode paste further includes a solvent;

[0027] And / or, the solid content of the positive electrode paste is 55-65 wt%.

[0028] Preferably, based on the total mass of the dry matter of the electrode active material, conductive agent, binder, and dispersant in the positive electrode slurry being 100 wt%, the electrode active material accounts for 94.7 - 96.9 wt%, the conductive agent accounts for 1 - 2 wt%, the binder accounts for 2 - 3 wt%, and the dry matter in the dispersant accounts for 0.1 - 0.3 wt%;

[0029] and / or, the electrode active material includes at least one of lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP);

[0030] and / or, the conductive agent includes at least one of carbon black, super conducting carbon black, carbon nanotubes, and graphene;

[0031] and / or, the binder includes polyvinylidene fluoride (PVDF);

[0032] and / or, the solvent is an organic solvent. Optionally, the organic solvent includes N-methylpyrrolidone (NMP).

[0033] Fourthly, the present invention also provides a positive electrode plate, the raw material of which includes the above-mentioned positive electrode slurry.

[0034] Fifthly, the present invention also provides a lithium ion battery, including the above-mentioned positive electrode plate.

[0035] The technical solution of the present invention has the following advantages:

[0036] 1. The dispersant provided by the present invention includes: polyphosphate ester and a functionalized elastomer with a nitrogen-containing group; wherein, the polyphosphate ester is prepared by phosphorylating polymer polyol, and the mass ratio of the polymer polyol to the functionalized elastomer with a nitrogen-containing group in the raw material of the polyphosphate ester is 1:(0.8 - 1.2). The dispersant provided by the present invention can not only effectively solve the problems of high viscosity of the slurry and poor coating effect caused by difficult dispersion of the current main materials, but also significantly improve the processing problem of brittle processing and easy breakage of the electrode plate. In addition, the dispersant provided by the present invention is environmentally friendly, does not require controlling the environmental humidity, and can greatly reduce the production cost. In the dispersant provided by the present invention, the functionalized elastomer with a nitrogen-containing group has a nitrogen-containing polar functional group, and nitrogen contains lone pairs of electrons, which can form a large π bond with carbon atoms in the main material, thereby synergistically promoting dispersion and preventing agglomeration with the polyphosphate ester to achieve the effect of stable viscosity. At the same time, the glass transition temperature (T g ) of the functionalized elastomer with a nitrogen-containing group is relatively low and soft, which can significantly increase the areal density of the electrode plate.

[0037] 2. In the dispersant provided by the present invention, an unsaturated amide compound is also added. The unsaturated amide compound has strong polarity and can form a better coating on the conductive agent in the slurry, so that the wettability of the conductive agent is better and it is easier to disperse, further improving the dispersion effect of the slurry.

[0038] 3. In the positive electrode paste provided by the present invention, based on the total mass of the dry matter of the electrode active material, conductive agent, binder, and dispersant in the positive electrode paste being 100 wt%, by adding 0.1 - 0.3 wt% of the dry matter of the dispersant, the viscosity of the paste can be effectively reduced, the fluidity can be improved, and the battery performance can be effectively improved. Detailed implementation mode

[0039] The following embodiments are provided to better further understand the present invention. They are not limited to the best implementation mode, and do not constitute a limitation to the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0040] For those not indicating specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not indicating the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0041] Example 1

[0042] This example provides a dispersant, a preparation method of the dispersant, a positive electrode paste, a positive electrode sheet, and a lithium-ion battery. Among them, the dispersant includes 700 g of N-methylpyrrolidone (NMP) solvent, polypropylene glycol phosphate obtained by phosphorylating 100 g of polypropylene glycol with 20 g of polyphosphoric acid, 100 g of hydrogenated nitrile rubber, and 80 g of acrylamide;

[0043] The above dispersant is prepared through the following steps:

[0044] (1) Obtaining polypropylene glycol phosphate: First, add 100 g of polypropylene glycol (weight average molecular weight 4000) and 700 g of NMP solvent to the reaction kettle, heat to 80 °C under vacuum (the boiling point of NMP is 203 °C, which is a high-boiling solvent with a very low evaporation rate at 80 °C and is considered to have no loss), and dehydrate for 30 min; then gradually add 20 g of polyphosphoric acid and 1 g of phosphoric acid (phosphoric acid as a catalyst), and stir and react at 100 °C for 3 hours to obtain a polypropylene glycol phosphate solution;

[0045] (2) Then add 100 g of hydrogenated nitrile rubber and 80 g of acrylamide to the polypropylene glycol phosphate solution prepared in step (1), and stir at 50 °C for 6 hours to obtain the dispersant.

[0046] The preparation method of the positive electrode slurry is as follows: Weigh lithium iron phosphate (LFP), carbon black, polyvinylidene fluoride (PVDF), and the dry matter (solvent-free, the same below) of the above dispersant according to the mass ratio of 96.8:1:2:0.2. Add the above materials into a double planetary stirrer, and then add an appropriate amount of NMP solvent to adjust the solid content of the slurry (as shown in Table 1). Disperse at medium speed at room temperature (rotation speed is 3500 rpm, dispersion duration is 4 h) to obtain the positive electrode slurry.

[0047] The preparation method of the positive electrode plate is as follows: Coating the above-prepared positive electrode slurry on one side of the aluminum foil by transfer coating (single-sided surface density is 23 mg / cm 2 ), and finally baking in an oven at 120 °C for 3 min to obtain the positive electrode plate.

[0048] The preparation method of the lithium-ion battery is as follows: Specifically, roll press the negative electrode plate and the above positive electrode plate (the compaction density of the positive electrode is 2.55 g / cm 3 , and the compaction density of the negative electrode is 1.58 g / cm 3 ) and die cut. Stack the positive electrode plate, separator, and negative electrode plate in sequence, with the separator placed between the positive electrode plate and the negative electrode plate to play a role in isolation. After stacking and winding, a bare battery cell is obtained; Place the bare battery cell in an outer packaging shell, inject the electrolyte after drying, and go through processes such as vacuum packaging, standing, formation, and shaping to obtain the lithium-ion battery.

[0049] Among them, the negative electrode plate adopts an artificial graphite formula, and the negative electrode slurry includes: artificial graphite, carbon black, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) with a weight ratio of 95:1.5:1.6:1.9 。 Add the above materials into a double planetary stirrer, and then add ultrapure water as the solvent. Disperse at medium speed at room temperature (rotation speed is 2500 rpm, dispersion duration is 4 h) to obtain the negative electrode slurry.

[0050] The preparation method of the negative electrode plate is as follows: Coating the above-prepared negative electrode slurry on one side of the copper foil by transfer coating (single-sided surface density is 9 mg / cm 2 ), and finally baking in an oven at 80 °C for 3 min to obtain the negative electrode plate;

[0051] The electrolyte is an organic solution containing 15 wt% LiPF6 and the rest is the solvent (ethylene carbonate); the separator is a polyethylene film.

[0052] Example 2

[0053] This embodiment provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this embodiment and Embodiment 1 is that during the preparation of the dispersant, the mass of hydrogenated nitrile rubber is adjusted to 80 g, so that during the preparation of the dispersant, the mass ratio of NMP solvent: polypropylene glycol in the raw material of polyphosphate ester: hydrogenated nitrile rubber: acrylamide is 7:1:0.8:0.8, and other conditions are the same as those in Embodiment 1.

[0054] Embodiment 3

[0055] This embodiment provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this embodiment and Embodiment 1 is that during the preparation of the dispersant, the mass of hydrogenated nitrile rubber is adjusted to 120 g, so that during the preparation of the dispersant, the mass ratio of NMP solvent: polypropylene glycol in the raw material of polyphosphate ester: hydrogenated nitrile rubber: acrylamide is 7:1:1.2:0.8, and other conditions are the same as those in Embodiment 1.

[0056] Embodiment 4

[0057] This embodiment provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this embodiment and Embodiment 1 is that during the preparation of the dispersant, the mass of acrylamide is adjusted to 50 g, so that during the preparation of the dispersant, the mass ratio of NMP solvent: polypropylene glycol in the raw material of polyphosphate ester: hydrogenated nitrile rubber: acrylamide is 7:1:1:0.5, and other conditions are the same as those in Embodiment 1.

[0058] Embodiment 5

[0059] This embodiment provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this embodiment and Embodiment 1 is that during the preparation of the dispersant, the mass of acrylamide is adjusted to 100 g, so that during the preparation of the dispersant, the mass ratio of NMP solvent: polypropylene glycol in the raw material of polyphosphate ester: hydrogenated nitrile rubber: acrylamide is 7:1:1:1, and other conditions are the same as those in Embodiment 1.

[0060] Embodiment 6

[0061] This embodiment provides a dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this embodiment and Embodiment 1 is that during the preparation of the dispersant, polypropylene glycol is replaced with poly(ethylene glycol) of the same mass, hydrogenated nitrile rubber is replaced with nitrile rubber of the same mass, and acrylamide is replaced with N-phenylacetamide of the same mass, and other conditions are the same as those in Embodiment 1. In this embodiment, the preparation method of poly(ethylene glycol) phosphate ester is the same as that in Embodiment 1, and the weight-average molecular weight of the poly(ethylene glycol) used is 4000.

[0062] Example 7

[0063] This example provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this example and Example 1 is that during the preparation of the dispersant, polypropylene glycol is replaced with the same mass of polyethylene glycol (from the same batch as Example 6), hydrogenated nitrile rubber is replaced with the same mass of polyurethane, and acrylamide is replaced with the same mass of p-toluamide, and other conditions are the same as those in Example 1.

[0064] Example 8

[0065] This example provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this example and Example 1 is that during the preparation of the dispersant, acrylamide is not added in step (3), and other conditions are the same as those in Example 1.

[0066] Example 9

[0067] This example provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this example and Example 1 is that during the preparation of the positive electrode slurry, the dispersant of Example 1 is used. Based on the mass of the dry matter (solvent-free (NMP)) in the positive electrode slurry, LFP, carbon black, PVDF, and the dispersant are weighed in a mass ratio of 95:2:2.9:0.1. The above materials are added to a double planetary stirrer, and then an appropriate amount of NMP solvent is added to adjust the solid content of the slurry (as shown in Table 1). The slurry is dispersed at medium speed (rotation speed of 3500 rpm, dispersion duration of 4 h) at room temperature to obtain the positive electrode slurry. Other conditions are the same as those in Example 1.

[0068] Example 10

[0069] This example provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this example and Example 1 is that during the preparation of the positive electrode slurry, the dispersant of Example 1 is used. Based on the mass of the dry matter (solvent-free (NMP)) in the positive electrode slurry, LFP, carbon black, PVDF, and the dispersant are weighed in a mass ratio of 96.7:1:2:0.3. The above materials are added to a double planetary stirrer, and then an appropriate amount of NMP solvent is added to adjust the solid content of the slurry (as shown in Table 1). The slurry is dispersed at medium speed (rotation speed of 3500 rpm, dispersion duration of 4 h) at room temperature to obtain the positive electrode slurry. Other conditions are the same as those in Example 1.

[0070] Comparative Example 1

[0071] This comparative example provides a method for preparing a positive electrode paste, a positive electrode sheet, and a lithium-ion battery. The difference between this comparative example and Example 1 is that during the acquisition of the positive electrode paste, the dispersant is replaced with LFP. LFP, carbon black, and PVDF are weighed according to the ratio of 97:1:2 by mass of LFP, carbon black, and PVDF. The above materials are added to a double planetary stirrer, and then an appropriate amount of NMP solvent is added to adjust the solid content of the paste (as shown in Table 1). The positive electrode paste is obtained by medium-speed dispersion at room temperature (rotation speed is 3500 rpm, dispersion duration is 4 h), and other conditions are the same as those in Example 1.

[0072] Comparative Example 2

[0073] This comparative example provides a dispersant, a method for preparing the dispersant, a positive electrode paste, a positive electrode sheet, and a lithium-ion battery. The difference between this comparative example and Example 1 is that the dispersant consists of 700 g of NMP solvent and polypropylene glycol phosphate obtained by phosphorylation reaction of 300 g of polypropylene glycol and 60 g of polyphosphoric acid, and other conditions are the same as those in Example 1. The method for preparing the dispersant in this comparative example is as follows: 300 g of polypropylene glycol (weight average molecular weight 4000) and 700 g of NMP solvent are added to a reaction kettle, heated to 80 °C under vacuum, and dehydrated for 30 min; then 60 g of polyphosphoric acid and 1 g of phosphoric acid (phosphoric acid as a catalyst) are gradually added, and the reaction is stirred at 100 °C for 3 hours to obtain the dispersant.

[0074] Comparative Example 3

[0075] This comparative example provides a dispersant, a method for preparing the dispersant, a positive electrode paste, a positive electrode sheet, and a lithium-ion battery. The difference between this comparative example and Example 1 is that the composition of the dispersant is different. The dispersant in this comparative example consists of NMP and hydrogenated nitrile rubber with a mass ratio of 7:3.6, and other conditions are the same as those in Example 1.

[0076] Comparative Example 4

[0077] This comparative example provides a dispersant, a method for preparing the dispersant, a positive electrode paste, a positive electrode sheet, and a lithium-ion battery. The difference between this comparative example and Example 1 is that the composition of the dispersant is different. The dispersant in this comparative example consists of NMP and acrylamide with a mass ratio of 7:3.6, and other conditions are the same as those in Example 1.

[0078] Comparative Example 5

[0079] This comparative example provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this comparative example and Example 6 is that N-phenylacetamide is not added during the preparation of the dispersant, and at the same time, the mass of nitrile rubber is adjusted to 180 g, so that during the preparation of the dispersant, the mass ratio of NMP solvent: polyethylene glycol in the raw material of polyphosphate: nitrile rubber is 71:1:1.8, and other conditions are the same as those in Example 6.

[0080] Comparative Example 6

[0081] This comparative example provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this comparative example and Example 6 is that N-phenylacetamide is not added during the preparation of the dispersant, and at the same time, the masses of polyethylene glycol, polyphosphoric acid, and nitrile rubber are adjusted (the mass of polyethylene glycol is 170 g, the mass of polyphosphoric acid is 30 g, and the mass of nitrile rubber is 100 g), so that during the preparation of the dispersant, the mass ratio of NMP solvent: polyethylene glycol in the raw material of polyphosphate: nitrile rubber is 7:1.7:1, and other conditions are the same as those in Example 6.

[0082] Comparative Example 7

[0083] This comparative example provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this example and Example 1 is that, based on dry matter (solvent-free), the mass ratio of LFP:SP:PVDF:dispersant dry matter (without NMP) in the positive electrode slurry is 96.95:1:2:0.05, and other conditions are the same as those in Example 1.

[0084] Comparative Example 8

[0085] This comparative example provides a dispersant, a preparation method of the dispersant, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The difference between this example and Example 1 is that, based on dry matter (solvent-free), the mass ratio of LFP:SP:PVDF:dispersant dry matter (without NMP) in the positive electrode slurry is 96.6:1:2:0.4, and other conditions are the same as those in Example 1.

[0086] Test Example 1

[0087] Perform performance tests on the solid content, viscosity of the positive electrode slurries and the folding light transmittance, sheet resistivity, and breakage rate of the positive electrode sheets prepared in the above examples and comparative examples. The test results are shown in Table 1.

[0088] Among them, the steps for testing the solid content of the positive electrode slurry are as follows: dry it in an oven, weigh 2 g ± 0.5 g of the sample with an electronic balance accurate to 0.1 mg, record the mass as m2, put it into a weighing flat dish with a mass of m1, spread it out as flat as possible, then put it into a constant temperature oven and bake at 120 ± 2 °C for 2 h, and then put it into a desiccator to cool for 30 min and then weigh its mass as m3. Then the solid content is calculated as (m3 - m1) / m2 × 100%.

[0089] The steps for testing the viscosity of the positive electrode slurry are as follows: use a Brookfield viscometer to test, and obtain the viscosity of the sample by matching different rotors and rotation speeds.

[0090] The steps for testing the folding light transmittance of the positive electrode plate are as follows: fold the plate at 180° with the same force, and observe the light transmittance of the plate. By the size of the light transmittance of the plate, judge the softness of the plate under the same compaction density (2.55 g / cm 3 ). If the light transmittance of the plate is more than 60%, it proves that the plate is brittle and there is a risk of tape breakage during continuous high-speed roll pressing in the production line.

[0091] Resistivity of the electrode plate: Two-probe method. Place the terminals on both end faces of the sample, input an alternating voltage signal, collect the current at both ends of the sample, so as to obtain the sample resistance R, and obtain the sample resistivity ρ through the conversion formula; the conversion formula is: ρ = RS / l; where ρ is the sample resistivity (unit: Ω·m), R is the sample resistance (unit: Ω), S is the cross-sectional area of the sample (unit: m 2 ), and l is the length of the sample (unit: m).

[0092] Tape breakage rate: Under the same compaction density (2.55 g / cm 3 ), the number of tape breaks per 10,000 meters during the roll pressing of the electrode roll.

[0093] Table 1

[0094]

[0095] As can be seen from Table 1, when the solid content of the discharged material is controlled at about 60%, the discharged viscosities of Examples 1-7 and Examples 9-10 in which polyphosphate, a functionalized elastomer containing a nitrogen group, and an unsaturated amide compound are added to the dispersant at the same time are relatively stable, between 5500 and 6500 cP. However, the discharged viscosity of Comparative Example 1 is significantly higher than that of Examples 1-7 and Examples 9-10, which proves that the dispersants of these examples of the present invention have a good effect of increasing the solid content and reducing the viscosity. The dispersant in Example 8 does not add an unsaturated amide compound, which to a certain extent results in a worse actual viscosity reduction effect of the dispersant, and thus the initial viscosity of the slurry is higher, but the overall viscosity stability effect is still significantly better than that of Comparative Example 1.

[0096] Looking again at the 24-hour viscosity rebound data of Comparative Example 1 (without dispersant) and Examples 1 to 10, it is found that it is nearly 100 to 400% higher than the 24-hour viscosity rebound effect of Examples 1 to 10, which also confirms that the viscosity stabilization effect of the dispersant of the present invention is also very prominent; at the same time, at a high tap density of 2.55 g / cm 3 Under the condition, the folding light transmittance of the electrode sheet of Comparative Example 1 is as high as 80 to 100%, far exceeding that of Examples 1 to 10, which also confirms that the dispersant of the present invention has a good flexibility-increasing effect.

[0097] The dispersant in Comparative Example 2 only added polyphosphate ester, so its viscosity reduction effect and folding light transmittance are worse than those of Example 1.

[0098] The dispersant in Comparative Example 3 only added a functionalized elastomer containing a nitrogen group. Although its flexibility increased significantly, its viscosity reduction effect was average and the cost was high.

[0099] The dispersant in Comparative Example 4 only added unsaturated amide. Although its viscosity reduction was obvious, its viscosity stabilization effect was average and it had a certain influence on the resistivity of the electrode sheet.

[0100] In the preparation of the dispersant in Comparative Example 5 and Comparative Example 6, the mass ratio of polypropylene glycol in the raw material of polyphosphate ester to the functionalized elastomer containing a nitrogen group exceeded the range of 1:(0.8 to 1.2). Specifically, in the dispersant of Comparative Example 5, the polyphosphate ester was too little and the functionalized elastomer containing a nitrogen group was excessive. Although the flexibility increased significantly, its viscosity reduction effect was poor; in the dispersant of Comparative Example 6, the functionalized elastomer containing a nitrogen group was excessive and the polyphosphate ester was too little. Its flexibility and viscosity reduction effect increased significantly, but it had a greater influence on the resistivity of the electrode sheet.

[0101] In the positive electrode slurry of Comparative Example 7 and Comparative Example 8 under the condition of high solid content, the addition amount of the dispersant was too little or too much. Specifically, in Comparative Example 7, the dispersant was too little. Although the flexibility increased significantly, its viscosity reduction effect was poor; in Comparative Example 8, the dispersant was excessive. Although the flexibility and viscosity reduction effect increased significantly, it had a greater influence on the resistivity of the electrode sheet.

[0102] Test Example 2

[0103] The performance (basic electrical performance, kinetic performance and cycle performance) of the lithium-ion batteries prepared from the above-mentioned examples and comparative examples was tested, and the test results are shown in Table 2 below.

[0104] Among them, the test steps for the basic electrical performance are as follows: at 25°C, the lithium-ion battery is first pre-charged at a small current of 0.1C for 180 min, then charged at a constant current of 0.33C to 3.65V, constant voltage to 0.05C, and then discharged at 0.33C to 2.5V. The ratio of the discharge capacity to the charge capacity is calculated to obtain the first efficiency.

[0105] The test steps for kinetic performance are as follows: The lithium-ion battery is tested at 25°C and -20°C respectively using the standard HPPC test method (the test duration is 5 s, the charging test current is 3C, and the discharging test current is 9C), and the charge-discharge DCR at different states of charge (SOC) is measured. The charge-discharge DCR (constant current resistance CC DCR, direct current resistance DCDCR) at 50% SOC is mainly evaluated.

[0106] The test steps for cycle performance are as follows: At 25°C, the lithium-ion battery is charged at a rate of 2C to 100% SOC and discharged at a rate of 1C to 0% SOC, and a full charge and discharge cycle test is carried out until the capacity of the lithium-ion battery decays to 80% of the initial capacity, and the number of cycles is recorded.

[0107] Table 2

[0108]

[0109]

[0110] As can be seen from Table 2, the comprehensive performance of Examples 1 to 10 is significantly better than that of Comparative Examples 1 to 8. Compared with Comparative Examples 1 to 8, on the basis of maintaining a relatively high initial efficiency and a relatively low internal resistance, the cycle stability is significantly improved. Among them, the initial efficiency of the batteries in Examples 1 to 10 is equivalent to that of the non-dispersant positive electrode paste formulation (Comparative Example 1), but the internal resistance of the battery is reduced by about 5-15%, and the DCR at room temperature and low temperature is also reduced, and the number of cycles at 2C / 1C at room temperature is increased by about 8-11%. The reason for the analysis is that the addition of the dispersant in each embodiment of the present invention makes the paste more uniformly dispersed and reduces the agglomeration of substances such as carbon black, thereby improving the internal resistance, DCR and cycle of the battery.

[0111] When comparing Examples 1 to 10 with Comparative Example 7, the effective component addition in the dispersant of Comparative Example 7 is less, and the positive electrode paste is relatively unevenly dispersed, so the number of cycles is less than that of Examples 1 to 10.

[0112] When comparing Examples 1 to 10 with Comparative Example 8, the internal resistance, DCR and the number of cycles at room temperature of the batteries in Examples 1 to 10 are much higher than those of Comparative Example 8. The reason for the analysis is that this dispersant is a non-conductive component and the material is relatively brittle, so the excessive addition will affect the internal resistance and DCR of the battery; at the same time, at the end of the cycle, the interface of the positive electrode sheet is poor and it is easy to drop materials, thus affecting the number of cycles.

[0113] Obviously, the above examples are only for clear illustration and not a limitation of the implementation manner. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A dispersant, characterized in that: include: Polyphosphate ester and functionalized elastomer containing nitrogen groups; wherein the polyphosphate ester is prepared by phosphorylation reaction of polymer polyol, and the mass ratio of polymer polyol and functionalized elastomer containing nitrogen groups in the raw material of the polyphosphate ester is 1:(0.8-1.2).

2. The dispersant according to claim 1, characterized in that The polyphosphate ester includes at least one of polypropylene glycol phosphate, polyethylene glycol phosphate, and polyvinyl alcohol phosphate; And / or, the functionalized elastomer containing nitrogen groups comprises at least one of hydrogenated nitrile rubber, nitrile rubber, and polyurethane; And / or, the polymer polyol includes at least one of polypropylene glycol, polyethylene glycol, and polyvinyl alcohol; And / or, the phosphorylation reagent used in the phosphorylation reaction process includes at least one of polyphosphoric acid, phosphorus pentoxide, and phosphorus trichloride; And / or, the mass ratio of the polymer polyol to the phosphorylation reagent used in the phosphorylation reaction is 1:(0.15-0.2), preferably, the mass ratio of the polymer polyol to the phosphorylation reagent used in the phosphorylation reaction is 1:0.2; And / or, the temperature of the phosphorylation reaction is 80-120°C, and the duration is 2-5 hours; preferably, the temperature of the phosphorylation reaction is 100°C, and the duration is 3 hours; And / or, an acidic catalyst is further added to the phosphorylation reaction; preferably, the catalyst comprises at least one of phosphoric acid, sulfuric acid, and p-toluenesulfonic acid, and the mass ratio of the polymer polyol to the acidic catalyst is 1:(0.005-0.01), and more preferably, the mass ratio of the polymer polyol to the acidic catalyst is 1:0.01; And / or, an organic solvent is further added to the dispersant; preferably, the organic solvent includes N-methylpyrrolidone, and the mass ratio of the polymer polyol to the organic solvent is 1:(5-10), and more preferably, the mass ratio of the polymer polyol to the organic solvent is 1:

7.

3. The dispersant according to claim 1 or 2, characterized in that The dispersant further includes an unsaturated amide compound; preferably, the unsaturated amide compound has the following structural formula: R1 is selected from C2-C6 alkenyl, C2-C6 alkenyl substituted by C1-C3 alkyl, C5-C10 aryl unsubstituted or substituted by C1-C3 alkyl, C1-C6 alkyl substituted by C5-C10 aroyl, R2 and R3 are independently selected from hydrogen, C1-C6 alkyl, C1-C6 alkyl substituted by hydroxyl, or C5-C10 aryl unsubstituted or substituted by C1-C3 alkyl; More preferably, R1 is selected from C2-C3 alkenyl, C2-C3 alkenyl substituted by C1-C2 alkyl, phenyl, phenyl substituted by C1-C2 alkyl or C1-C2 alkyl substituted by benzoyl; More preferably, R2 and R3 are independently selected from hydrogen, C1-C3 alkyl, hydroxy-substituted C1-C3 alkyl or phenyl.

4. The dispersant according to claim 3, characterized in that The unsaturated amide compound includes at least one of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, N-phenylacetamide, and p-toluamide; And / or, the mass ratio of the unsaturated amide compound to the polymer polyol is (0.5-1):

1.

5. A method for preparing the dispersant according to any one of claims 1 to 4, characterized in that: include: The polyphosphate ester and the functionalized elastomer containing nitrogen groups are mixed evenly to obtain the product.

6. A positive electrode slurry, characterized in that: The positive electrode slurry comprises the dispersant according to any one of claims 1 to 4 or the dispersant prepared by the preparation method of the dispersant according to claim 5, and the mass proportion of the dry matter in the dispersant is 0.1 to 0.3 wt%, based on the mass of the dry matter in the positive electrode slurry being 100 wt%.

7. The positive electrode slurry according to claim 6, characterized in that: The dry matter in the positive electrode slurry also includes electrode active material, conductive agent and binder; And / or, the positive electrode slurry further includes a solvent.

8. The positive electrode slurry according to claim 7, characterized in that: Taking the total mass of the dry matter in the electrode active material, the conductive agent, the binder and the dispersant in the positive electrode slurry as 100wt%, the electrode active material accounts for 94.7-96.9wt%, the conductive agent accounts for 1-2wt%, the binder accounts for 2-3wt%, and the dry matter in the dispersant accounts for 0.1-0.3wt%; And / or, the electrode active material includes at least one of lithium iron phosphate and lithium iron manganese phosphate; And / or, the conductive agent includes at least one of carbon black, superconducting carbon black, carbon nanotubes, and graphene; and / or, the binder comprises polyvinylidene fluoride; And / or, the solvent is an organic solvent, optionally, the organic solvent includes N-methylpyrrolidone.

9. A positive electrode sheet, characterized in that: The raw material thereof includes the positive electrode slurry as described in any one of claims 6 to 8.

10. A lithium ion battery, characterized in that: Including the positive electrode sheet as described in claim 9.

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