Binder material, preparation method thereof and dry-method pole piece

Abstract

The invention discloses a binder material and a preparation method thereof, and a dry-method pole piece, the binder material comprises a binder matrix and a sulfuric acid group arranged on at least part of the surface of the binder matrix, an EDS energy spectrum analysis chart of the binder material comprises a first zone and a second zone, in the first zone, the area ratio of sulfur element is x, the area ratio of sulfur element is x, and the area ratio of sulfur element is x; and in the second region, the area proportion of the sulfur element is y, x is greater than or equal to y, and x and y meet the following conditions: x-y is less than or equal to 20%, and y is greater than or equal to 20%. The binder material provided by the invention is helpful for improving the affinity of a dry-method electrode to an electrolyte and reducing the occurrence of side reactions.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and in particular to an adhesive material, a preparation method thereof, and a dry-process electrode. Background Art

[0002] The preparation of traditional electrode sheets is mainly a wet process. For example, a mixed slurry consisting of active materials, conductive agents, adhesives and solvents is coated on the current collector. However, since the wet molding process uses solvents, the solvent and the binder form a binder layer. Some conductive agent particles will be completely surrounded by the binder layer, which hinders the contact between the conductive agent particles and between the conductive agent particles and the active material, affecting the conductivity of the electrode. As an emerging electrode preparation method, the core advantage of dry electrode technology lies in simplifying the production process, reducing the solvent, making the binder exist in a fibrous state, and making the conductive agent and the active material particles in closer contact.

[0003] However, dry electrodes also face some challenges in practical applications, especially due to the relatively rough surface of the electrode sheet and the hydrophobicity of commonly used binders such as polytetrafluoroethylene (PTFE), which leads to poor wettability between the dry electrode and the electrolyte. Summary of the Invention

[0004] The present invention provides a binder material. On the one hand, the binder material helps to improve the affinity of dry-process electrodes for electrolytes, thereby significantly reducing the difficulty of Li ion transmission, thereby improving the rate performance of dry-process electrodes. On the other hand, the grafted groups at different points on the surface of the material are evenly distributed, which can avoid local volume changes and stress concentration in the electrode, reduce the risk of local overcharge or over-discharge, thereby reducing the occurrence of side reactions and helping to improve its cycle life.

[0005] The present invention also provides a method for preparing the above-mentioned adhesive material, which can prepare the above-mentioned adhesive material and has a relatively simple process.

[0006] The present invention also provides a dry-process electrode. Since the electrode comprises the above-mentioned adhesive material, the electrode has good affinity to the electrolyte.

[0007] In a first aspect, the present invention provides an adhesive material, wherein the EDS energy spectrum analysis diagram of the adhesive material includes a first zone and a second zone, wherein in the first zone, the area proportion of the sulfur element is x, and in the second zone, the area proportion of the sulfur element is y, x is greater than or equal to y, and x and y satisfy: xy≤20%, y≥20%.

[0008] Optionally, the binder matrix comprises polytetrafluoroethylene.

[0009] Optionally, the molar ratio of the sulfate groups to the binder material is not less than 10%.

[0010] Optionally, the number average molecular weight of the binder material is 50wDa-200wDa;

[0011] And / or, the binder material has a dispersion index of 1.8-2.2.

[0012] In a second aspect, the present invention provides a method for preparing the binder material according to the first aspect, comprising the following steps:

[0013] The adhesive matrix is ​​placed in a plasma containing oxygen as the plasma gas, and reacted at 40-50° C. for 1-5 hours to obtain the adhesive matrix containing oxygen groups; wherein the mass ratio of the sulfonating agent to the adhesive matrix containing oxygen groups is 0.05-0.3:1.

[0014] Optionally, the sulfonating agent includes at least one of sulfamic acid, sodium sulfite, sodium bisulfite, and p-toluenesulfonyl chloride;

[0015] And / or, the ball milling process is performed at a speed of 1500-3000 rpm for a time of 1-2 h.

[0016] In a third aspect, the present invention provides a dry-process electrode, comprising a current collector and the dry-process self-supporting film disposed on at least one side of the current collector, wherein the dry-process self-supporting film comprises the adhesive material described in the first aspect.

[0017] Optionally, the dry electrode further includes a conductive agent, the conductive agent includes a carbon material, and the molar ratio of the carbon element in the carbon material to the sulfur element in the binder material is (5-18):1.

[0018] Optionally, the contact angle of the dry self-supporting film to water is 0-20°, the dry self-supporting film includes a third region and a fourth region, the contact angle of the third region to water is m°, the contact angle of the fourth region to water is n°, and the difference between m and n is not greater than 15°.

[0019] On the one hand, the binder material provided by the present invention helps to improve the affinity of the dry electrode for the electrolyte, so as to significantly reduce the difficulty of Li ion transmission, thereby improving the rate performance of the dry electrode. On the other hand, the content of sulfate groups at different points on the surface of the binder material is relatively consistent, which can avoid local volume changes and stress concentration in the electrode sheet to a certain extent, reduce the risk of local overcharge or over-discharge, thereby reducing the occurrence of side reactions, and helping to improve the cycle stability of the dry electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0021] Figure 1 This is a picture showing the contact angle of the dry-process self-supporting film of Comparative Example 1 to water;

[0022] Figure 2 This is a picture showing the contact angle of the dry-process self-supporting film of Example 1 to water;

[0023] Figure 3 This is the S element distribution diagram of the first zone on the surface of the adhesive material of Example 1;

[0024] Figure 4 This is the S element distribution diagram of the second zone on the surface of the adhesive material of Example 1. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0026] In this application, the terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0027] Throughout this application, references to "one embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment, embodiment, or example is included in at least one embodiment of the present invention. Therefore, appearances of the phrases "one embodiment," "an embodiment," "an example," or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combinations and / or subcombinations in one or more embodiments or examples.

[0028] The electrode's affinity for the electrolyte is crucial to the performance of lithium-ion batteries, as it affects the efficient transport of lithium ions within the electrode material, the formation of interfacial stability, and the improvement of battery energy density. Poor affinity can hinder lithium ion transport within the electrode, affecting the battery's electrochemical properties, such as cycling stability and rate capability. Furthermore, poor affinity can lead to problems such as localized overheating within the battery, impacting battery safety and service life. Therefore, improving the wettability of dry-process electrodes with the electrolyte is a key step in enhancing the performance of batteries using dry-electrode technology.

[0029] Sulfuric acid modification of dry-process electrodes can improve their wettability, but the electrode modified with sulfuric acid cannot achieve uniformity in all regions. Some areas are over-sulfonated while others are not. This results in large differences in contact angles on the electrode surface, affecting the battery's cycle stability and rate performance. To address the above technical issues, the present invention provides the following solutions:

[0030] In a first aspect, the present invention provides a binder material, comprising a binder matrix and a sulfate group arranged on at least a portion of the surface of the binder matrix. The EDS energy spectrum analysis diagram of the binder material comprises a first zone and a second zone. In the first zone, the area proportion of the sulfur element is x, and in the second zone, the area proportion of the sulfur element is y, x is greater than or equal to y, and x and y satisfy: xy≤20%, y≥20%.

[0031] It should be noted that the above-mentioned first zone and second zone refer to any two different areas on the surface of the adhesive material. The areas of the two areas can be the same or different, and the present invention does not particularly limit this. In the first zone, the area ratio of sulfur element is x, in units of %, which is based on the total area of ​​the first zone as 100%. Similarly, in the second zone, the area ratio of sulfur element is y, in units of %, which is based on the total area of ​​the second zone as 100%.

[0032] In addition, the terms "x" and "y" are only used to distinguish the area proportions of sulfur elements in different regions. If x=y, x can also be called y, and y can also be called x.

[0033] In the present invention, by limiting the proportion of sulfate groups and sulfur elements contained in the binder material, the affinity of the electrode to the electrolyte can be effectively guaranteed, and the cycle stability and rate performance of the battery can be effectively improved. Specifically, the sulfate groups on at least part of the surface of the binder matrix and the sulfur content of any two regions are limited to meet the above relationship, indicating that the sulfate groups are evenly grafted on the surface of the binder matrix, which is conducive to the good and consistent wettability of the binder material surface. On the one hand, it means that the electrolyte can more evenly infiltrate the surface of the electrode, thereby improving the ion transfer efficiency. During high-rate discharge, the uniform distribution of the electrolyte helps to reduce polarization, thereby improving the rate performance of the battery. On the other hand, good wettability can ensure that the electrolyte fully contacts the active material, improve the utilization rate of the active material, and the uniform wettability makes the electrolyte evenly distributed on the surface of the electrode, avoiding local volume changes and stress concentration in the electrode, reducing the risk of local overcharge or over-discharge, and thus reducing the occurrence of side reactions, which is crucial for improving the safety and cycle life of the battery.

[0034] In some embodiments, the sulfur content can be obtained by energy dispersive X-ray spectroscopy (EDS) analysis, extracting characteristic peaks of the S element, and performing statistics and calculations.

[0035] In one embodiment, the binder matrix comprises polytetrafluoroethylene.

[0036] As a binder material, polytetrafluoroethylene (PTFE) exhibits excellent chemical stability and resistance to electrolyte corrosion, which helps further improve the long-term stability of the electrode and the cycle life of the battery. The sulfate groups on at least part of the surface of PTFE contribute to the dispersion index of the PTFE polymer, thereby increasing the degree of fiberization during the dry process and enhancing the mechanical properties of the electrode.

[0037] In one embodiment, the molar ratio of the sulfate groups to the binder material is not less than 10%.

[0038] The molar ratio of the sulfate groups to the binder material is within the above range, which can ensure that the binder material has a suitable water contact angle and basic adhesion of the binder material.

[0039] Illustratively, the mass / molar ratio of sulfate groups to the binder material is any value among 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc., or a range consisting of any two of them.

[0040] In one embodiment, the number average molecular weight of the binder material is 50 wDa-200 wDa.

[0041] The binder material described above can form a stronger fiber network structure, which helps to improve the structural integrity and durability of the pole piece and provide the pole piece with better mechanical strength and toughness.

[0042] Illustratively, the number average molecular weight of the binder material is any one of 50 wDa, 70 wDa, 90 wDa, 100 wDa, 120 wDa, 140 wDa, 160 wDa, 180 wDa, 200 wDa, etc., or a range consisting of any two of the values.

[0043] In one embodiment, the dispersion index of the binder material is 1.8-2.2.

[0044] The dispersion index of the binder material, also known as the polydispersity index (PDI), is a parameter that measures the width of the molecular weight distribution of the polymer. Its value is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), that is, PDI = Mw / Mn.

[0045] Among them, the dispersion index of the binder material is 1.8-2.2, which can provide a more uniform fiber network structure for the electrode, thereby making the mechanical properties of various parts of the electrode more consistent.

[0046] Illustratively, the dispersion index of the binder material is any value among 1.8, 1.9, 2.0, 2.1, 2.2, etc., or a range consisting of any two of them.

[0047] In a second aspect, the present invention provides a method for preparing the binder material according to the first aspect, comprising the following steps:

[0048] performing a pre-oxidation treatment on the adhesive matrix to obtain an adhesive matrix containing oxygen groups;

[0049] The binder matrix containing oxygen groups and the sulfonating agent are ball-milled to obtain the binder material; wherein the mass ratio of the sulfonating agent to the binder matrix containing oxygen groups is 0.05-0.3:1.

[0050] Among them, the above preparation method uses a two-step reaction of "pre-oxidation treatment" and "grafting sulfonic acid groups". Compared with direct grafting of sulfonic acid groups, the reaction is controllable and the sulfonate grafting is more uniform. The main reason is that if the sulfonic acid groups are directly grafted, the adhesive matrix needs to complete the two-step reaction of "surface oxidation" and "grafting sulfonic acid groups" at the same time. There is local competition between the sulfonic acid grafting and the oxidation reaction, resulting in a chaotic distribution of surface sulfonic acid groups, such as over-sulfonation in some areas and only oxidation without sulfonation in some areas. The preparation method provided by the present invention first performs a "pre-oxidation treatment" to obtain an oxygen-containing adhesive matrix, and then performs a "grafting sulfonic acid group" treatment. This can avoid the local competition between the sulfonic acid grafting and the oxidation reaction, making the sulfonic acid grafting more uniform.

[0051] In addition, the above preparation method ensures that the sulfonating agent is in full contact with the active sites of the binder matrix by regulating the ratio of the binder matrix and the sulfonating agent, so as to ensure that the area proportion of sulfur element in any area of ​​the binder material is not less than 20%. At the same time, it reduces the residue and raw material waste caused by excessive sulfonating agent, optimizes the reaction efficiency and cost, and avoids the breakage of the binder matrix molecular chain.

[0052] In one embodiment, the pre-oxidation treatment includes the following steps:

[0053] The adhesive matrix is ​​placed in a plasma whose plasma gas is oxygen, and reacted at 40-50° C. for 1-5 hours to obtain the adhesive matrix containing oxygen groups.

[0054] Among them, the above embodiment can further improve the grafting uniformity of sulfonate groups by pre-oxidation through plasma, thereby ensuring the consistent affinity of the electrode to the electrolyte at all parts, and further helping to improve the cycle stability and rate performance of the battery.

[0055] In a specific embodiment, the sulfonating agent includes at least one of sulfamic acid (H3NSO3), sodium sulfite (Na2SO3), sodium bisulfite (NaHSO3), and p-toluenesulfonyl chloride (C7H7ClO2S).

[0056] Among them, the above-mentioned sulfonating agents can directly participate in the ball milling reaction and release sulfonic acid groups (-SO3H) through mechanical activation. As for the specific type of sulfonating agent, it can be selected according to different preparation scenarios and needs. For example, aminosulfonic acid is a solid powder, and the reaction is highly controllable. Sodium sulfite and sodium bisulfite are both cheap industrial raw materials, non-corrosive, and environmentally friendly. The reaction produces water-soluble by-products such as sodium sulfate, which is compatible with the environmental characteristics of PTFE. Toluenesulfonyl chloride, as an acyl chloride sulfonating agent, has a sulfonation efficiency significantly higher than other solid sulfonating agents and can quickly graft sulfonic acid groups. Low temperature adaptability: It can be activated under ball milling friction heat (80-100°C) to avoid cold flow deformation of PTFE due to high temperature.

[0057] In one embodiment, the binder matrix is ​​polytetrafluoroethylene.

[0058] In a specific embodiment, the mass ratio of the binder matrix containing oxygen groups to the sulfonating agent is any ratio of 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, etc.

[0059] In one embodiment, the ball milling process is performed at a speed of 1500-3000 rpm for a time of 1-2 h.

[0060] Among them, the above ball milling treatment can further improve the grafting uniformity of the sulfonate group, thereby ensuring the consistent affinity of the electrode to the electrolyte at all parts, and is more conducive to improving the cycle stability and rate performance of the battery.

[0061] In a third aspect, the present invention provides a dry-process electrode, comprising a current collector and a dry-process self-supporting film disposed on at least one side of the current collector, wherein the dry-process self-supporting film comprises the adhesive material described in the first aspect.

[0062] Since the electrode comprises the aforementioned adhesive material, it has good and consistent affinity to the electrolyte.

[0063] In a specific embodiment, the dry electrode further includes a conductive agent and an active material, the conductive agent includes a carbon material, and the molar ratio of the carbon element in the carbon material to the sulfur element in the binder material is (5-18):1.

[0064] The carbon and sulfur elements in the above-mentioned ratio can simultaneously ensure the mechanical adhesion performance of the binder material to the active material, and can also enhance the sufficient affinity between the electrode and the electrolyte.

[0065] Illustratively, the molar ratio of carbon element in the carbon material to sulfur element in the binder material is any one of 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:17, 18:1, etc.

[0066] In a specific embodiment, the contact angle of the dry self-supporting film to water is 0-20°, and the dry self-supporting film includes a third region and a fourth region, the contact angle of the third region to water is m°, and the contact angle of the fourth region to water is n°, and the difference between m and n is not greater than 15°.

[0067] It should be noted that the third region and the fourth region refer to any two different regions on the surface of the dry-process self-supporting film, and the areas of the two regions may be the same or different, which is not particularly limited in the present invention.

[0068] In the present invention, by limiting the contact angle of the dry self-supporting film to water and the difference in contact angles between the third and fourth regions, the affinity of the electrode to the electrolyte can be effectively guaranteed, and the cycle stability and rate performance of the battery can be effectively improved. Specifically, the contact angle of the dry self-supporting film to water and the difference in contact angles between the third and fourth regions are limited to no more than 15°, indicating that the dry self-supporting film has a suitable and uniform contact angle. On the one hand, it means that the electrolyte can more evenly infiltrate the surface of the electrode, thereby improving the ion transfer efficiency. During high-rate discharge, the uniform electrolyte distribution helps to reduce polarization, thereby improving the rate performance of the battery. On the other hand, good wettability can ensure that the electrolyte fully contacts the active material, improving the utilization rate of the active material, and the uniform contact angle makes the electrolyte evenly distributed on the surface of the electrode, avoiding local volume changes and stress concentration in the electrode, reducing the risk of local overcharge or over-discharge, and thus reducing the occurrence of side reactions, which is crucial for improving the safety and cycle life of the battery.

[0069] Exemplarily, the contact angle of the electrode membrane to water is any value among 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, etc., or a range consisting of any two of them.

[0070] In one embodiment, the active material includes lithium manganese iron phosphate.

[0071] Lithium iron manganese phosphate (LFMP) is a high-energy-density, cost-effective cathode material for lithium-ion batteries, offering advantages such as increased safety, lower cost, and environmental friendliness. However, conventional dry-process LFMP electrodes have a relatively rough surface and low electrolyte compatibility. The present invention, by employing a special binder material, addresses this problem.

[0072] In some embodiments, the dry electrode is prepared by the following process:

[0073] 1) preparing a positive electrode active material, a conductive agent, and a binder material in a mass ratio of 85-99:1-3:1-32. After the preparation is completed, the positive electrode active material and the conductive agent are added to a dry mixer and mixed for 20 minutes, and then the binder material is added and mixed for 40 minutes to obtain a primary mixture;

[0074] 2) Place the primary mixture into an internal mixer to fiberize the material and mix for 1 hour to obtain a secondary mixture;

[0075] 3) hot rolling the obtained secondary mixture three times to obtain a self-supporting electrode film with uniform thickness;

[0076] 4) Two dry-process self-supporting films are placed on the upper and lower surfaces of the current collector respectively, and heated and cured using a hot roller press to ensure that the dry-process self-supporting films and the current collector are firmly adhered to obtain a dry-process electrode.

[0077] Among them, the above-mentioned conductive agent is selected from one or more of SuperP, Ketjen black, carbon nanotubes, carbon nanofibers, graphene, and conductive carbon; the above-mentioned current collector can be one or more of aluminum foil, titanium foil, nickel foil, and carbon-coated aluminum foil.

[0078] The present invention does not particularly limit the source of the positive electrode active material, which can be purchased from the market or prepared by conventional means.

[0079] The present invention will be further described below with reference to specific embodiments:

[0080] Example 1

[0081] This example provides a polytetrafluoroethylene binder material, comprising a polytetrafluoroethylene matrix and sulfonic acid groups grafted on the surface, with a number average molecular weight of 82 wDa and a dispersion index of 1.86.

[0082] The preparation method thereof comprises the following steps:

[0083] 1) Surface treatment using a high-temperature plasma reactor: a polytetrafluoroethylene substrate is placed in a plasma generator, the plasma gas is oxygen, the reaction temperature is 50° C., and the reaction is carried out for 1 hour. After the reaction is completed, polytetrafluoroethylene with oxygen-containing groups is obtained, which is recorded as NI;

[0084] 2) N1 and aminosulfonic acid were mixed in a mass ratio of 1:0.2; the mixture was placed in a high-energy ball mill and ball-milled at a speed of 2000 rpm for 2 hours to obtain a polytetrafluoroethylene binder material.

[0085] Example 2

[0086] This example provides a polytetrafluoroethylene binder material, comprising a polytetrafluoroethylene matrix and sulfonic acid groups grafted on the surface, with a number average molecular weight of 115 wDa and a dispersion index of 2.05.

[0087] The preparation method thereof differs from that of Example 1 in that: a polytetrafluoroethylene matrix is ​​placed in a plasma generator and reacted for 2 h; N1 and aminosulfonic acid are mixed in a mass ratio of 1:0.3 and ball milled for 3 h.

[0088] Example 3

[0089] This example provides a polytetrafluoroethylene binder material, comprising a polytetrafluoroethylene matrix and sulfonic acid groups grafted on the surface, with a number average molecular weight of 123 wDa and a dispersion index of 1.98.

[0090] The difference between the preparation method and Example 1 is that the polytetrafluoroethylene matrix is ​​placed in a plasma generator and reacted for 0.5 h.

[0091] Example 4

[0092] This example provides a polytetrafluoroethylene binder material, comprising a polytetrafluoroethylene matrix and sulfonic acid groups grafted on the surface, with a number average molecular weight of 124 wDa and a dispersion index of 2.00.

[0093] The preparation method thereof is different from that of Example 1 in that the ball milling time is 0.5 h.

[0094] Example 5

[0095] This example provides a polytetrafluoroethylene binder material, comprising a polytetrafluoroethylene matrix and sulfonic acid groups grafted on the surface, with a number average molecular weight of 103 wDa and a dispersion index of 2.10.

[0096] The preparation method thereof is different from that of Example 1 in that the mass ratio of polytetrafluoroethylene to the sulfonating agent is 1:0.1.

[0097] Example 6

[0098] This example provides a polytetrafluoroethylene binder material, comprising a polytetrafluoroethylene matrix and sulfonic acid groups grafted on the surface, with a number average molecular weight of 124 wDa and a dispersion index of 1.91.

[0099] The preparation method thereof is different from that of Example 1 in that the sulfonating agent is p-toluenesulfonyl chloride.

[0100] Comparative Example 1

[0101] This example provides a polytetrafluoroethylene binder material, which is composed of the polytetrafluoroethylene matrix of Example 1, and has a number average molecular weight of 128 wDa and a dispersion index of 1.78.

[0102] Comparative Example 2

[0103] This example provides a polytetrafluoroethylene binder material, comprising a polytetrafluoroethylene matrix and sulfonic acid groups grafted on the surface, with a number average molecular weight of 123 wDa and a dispersion index of 1.99.

[0104] The preparation method thereof is different from that of Example 1 in that N1 and aminosulfonic acid are mixed in a mass ratio of 1:0.02.

[0105] Comparative Example 3

[0106] This example provides a polytetrafluoroethylene binder material, comprising a polytetrafluoroethylene matrix and sulfonic acid groups grafted on the surface, with a number average molecular weight of 119 wDa and a dispersion index of 2.21.

[0107] The preparation method thereof differs from that of Example 1 in that the plasma gas is replaced with sulfur dioxide and step 2) is not performed. The other steps are the same as those of Example 1.

[0108] Comparative Example 4

[0109] This example provides a polytetrafluoroethylene material, comprising polytetrafluoroethylene and oxygen groups grafted on the surface, with a number average molecular weight of 118 wDa and a dispersion index of 1.76.

[0110] The preparation method thereof is different from that of Example 1 in that step 2) is not performed, and the other steps are the same as those of Example 1.

[0111] Test Example 1

[0112] The dry-process positive electrode sheet is prepared using the binder materials of the above-mentioned embodiment and comparative example, comprising the following steps:

[0113] 1) Synthesize lithium manganese iron phosphate positive electrode material, the molecular formula is LiMn 0.6 Fe 0.4 PO4 (LFMP): The manganese source is manganese dihydrogen phosphate; the lithium source is lithium hydroxide (LiOH); and the iron source is ferric phosphate. The molar ratio of Mn:Fe is controlled at 6:4. Water is then added to adjust the solids content of the slurry to 35%. Once the slurry is uniformly mixed, it is added to a coarse grinder at 1500 rpm for 1 hour. After coarse grinding, it is transferred to a sand mill for sand grinding at 1500 rpm for 2 hours. After sand grinding, the slurry is slowly transferred to a spray dryer for drying at an inlet temperature of 200°C, an outlet temperature of 100°C, a compressed air pressure of 0.4 MPa, and a drying time of 7 hours. The resulting powder particles are placed in a tube furnace and sintered under nitrogen at 280°C for 4 hours to obtain P1 material.

[0114] 2) The P1 material was subjected to secondary sintering, with the temperature controlled at 600° C. and the sintering time being 12 h. After the sintering was completed, it was naturally cooled to room temperature to obtain a lithium manganese iron phosphate positive electrode material, which was recorded as P2 material.

[0115] 3) Prepare P2 material, conductive agent SuperP and binder material in a mass ratio of LFMP: binder material: conductive agent = 90:3:7 (the molar ratio of carbon element in the conductive agent to sulfur element in the binder material is 11.7:1). After preparation, add P2 material and conductive agent to a dry mixer and mix for 20 minutes, then add binder material and mix for 40 minutes to obtain P3 material;

[0116] 4) Put the P3 material into an internal mixer and set the temperature to 180°C and the speed to 30 rpm / min to fiberize the material and internally mix for 1 hour to obtain the P4 material;

[0117] 5) The obtained P4 material was subjected to four hot roller pressings at 160° C.-220° C. to obtain a dry self-supporting film P5 with uniform thickness;

[0118] 6) Two self-supporting electrode films P5 are placed on the upper and lower surfaces of the carbon-coated aluminum foil respectively, and heated and cured using a hot roller press to ensure that the electrode film and the current collector are firmly adhered to obtain a dry-process positive electrode sheet.

[0119] Test Example 2

[0120] The difference from Experimental Example 1 is that the mass ratio of the binder material and the conductive agent is adjusted so that the molar ratio of the carbon element in the conductive agent to the sulfur element in the binder material is 17:1.

[0121] Test Example 3

[0122] The difference from Experimental Example 1 is that the mass ratio of the binder material and the conductive agent is adjusted so that the molar ratio of the carbon element in the conductive agent to the sulfur element in the binder material is 5:1.

[0123] Test Example 4

[0124] The difference from Experimental Example 1 is that the mass ratio of the binder material and the conductive agent is adjusted so that the molar ratio of the carbon element in the conductive agent to the sulfur element in the binder material is 1:1.

[0125] Test Example 5

[0126] Batteries were assembled using the positive electrode sheets of the test examples:

[0127] Electrolyte: Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1, LiPF6 was added to make the concentration 1M, and ethyl fluoroacetate was added to make its mass account for 2% of the total mass of the electrolyte;

[0128] Assembly: The positive electrode sheet, the counter electrode lithium sheet (15 mm in diameter) and the separator (PP / ceramic composite) of the experimental example were layered and 50 μL of electrolyte was added dropwise. The packaging pressure was 10 MPa to prevent the fiber structure from being damaged.

[0129] Static activation: After assembly, let it stand for 12 hours to ensure that the electrolyte is fully infiltrated (the ambient temperature and humidity must be controlled at 25℃±1℃ / 50%RH).

[0130] Test Case

[0131] 1. Contact angle test of dry self-supporting film:

[0132] 1) Prepare the instrument: SDC-280F fiber-type contact angle meter equipped with a micro-droplet system. Test mode: Sessile drop method, static contact angle measurement, drop volume: 3.0 ± 0.2 nL, precisely adjusted by software-controlled micro-injection pump;

[0133] 2) Sample pretreatment: ultrasonically clean the surface of the dry self-supporting film with anhydrous ethanol for 5 minutes and blow dry with nitrogen to eliminate surface contamination;

[0134] 3) Partition positioning: Use microscope to locate any different area, 500×500μm 2 ≥Single zone area≥25×25μm 2 ), mark the test coordinate points;

[0135] 4) Droplet deposition: 3 nL of deionized water was added to the target area, and the droplet release height was 1 mm from the sample surface;

[0136] 5) Stabilization time: let it stand for 10 seconds until the droplet reaches wetting equilibrium with the surface of the dry self-supporting film;

[0137] 6) Image acquisition: Use a high-resolution industrial camera (resolution ≥ 5 μm / pixel) to capture the droplet profile, capturing one frame of image every 0.5 seconds for 30 seconds;

[0138] 7) Contact angle fitting method: Young-Laplace method is preferred, and the droplet profile is automatically fitted by software;

[0139] 8) Perform three tests and calculate the average value as the final result.

[0140] 2. Mechanical properties test of dry self-supporting membrane:

[0141] 1) Sample preparation: Cut the membrane to be tested into rectangular samples (length 50-150mm, width 40-120mm) according to the standard. Make sure that the edges are free of burrs and the active coating is intact.

[0142] 2) Pretreatment: Place the sample in an environment of 23±2℃ and 50% humidity for 4 hours to eliminate the influence of ambient temperature and humidity on material properties;

[0143] 3) Equipment setting: Use a tensile testing machine, set the preload stress to 0.1N, control the stretching rate at 20-80mm / min (typical value 100mm / min), and set the clamp spacing according to the standard;

[0144] 4) Test execution: Clamp the sample vertically between the upper and lower fixtures, keep the longitudinal axis of the diaphragm consistent with the tensile direction, start the equipment until the sample breaks, and simultaneously record the stress-strain curve;

[0145] 5) Data analysis: The slope of the elastic stage is used to calculate the elastic modulus, the yield point corresponds to the yield strength, and the peak value of the fracture point is taken as the tensile strength.

[0146] 3. Test on the uniformity of sulfonic acid group distribution of binder materials:

[0147] 1) Sample pretreatment: Cut the adhesive material to be tested into 5×5mm 2 The thin slices were ultrasonically cleaned with ethanol for 10 minutes to remove surface contaminants, dried with nitrogen, and fixed to conductive tape. The sample surface was gold-sprayed (gold layer thickness 5-10nm) to eliminate the effect of non-conductivity on EDS analysis.

[0148] 2) EDS parameter settings: field emission scanning electron microscope equipped with silicon drift detector (SDD), accelerating voltage 10 kV;

[0149] 3) Analysis mode: Surface scanning mode, the scanning area includes the first and second areas (500×500μm 2 ≥Single zone area≥25×25μm 2 ), pixel resolution not less than 500×500, single point dwell time 50μs;

[0150] 4) Sulfur element identification: Through EDS spectrum analysis, the characteristic peak of the S element (Kα line energy 2.307keV) is extracted, and a threshold is set higher than 3 times the standard deviation of the background noise to determine it as a valid bright spot;

[0151] 5) Bright spot statistics: Binarize the EDS surface scan image and calculate the ratio of the number of bright spots (N_S) to the total number of pixels (N_total):

[0152] 6) x (or y) = (N_S / N_total) × 100%.

[0153] 4. Test the 1C / 0.33C capacity retention rate and 1C 500-cycle capacity retention rate of each battery:

[0154] 1) Initial capacity calibration: Charge each battery at 0.1C constant current to 4.1V → constant voltage to current ≤ 0.05C → let stand for 5 minutes → discharge at 0.1C to 2.5V, repeat 3 times and take the average value C0;

[0155] 2) 0.33C retention rate: discharge each battery at 0.33C constant current to 2.5V, capacity C1 / C0×100%; 1C retention rate: discharge at 1C constant current under the same conditions, capacity C2 / C0×100%;

[0156] 3) Cycle life test: Each battery is charged at 1C constant current to 4.1V and then discharged at 1C constant current to 2.5V for 1 cycle, and the cycle is 500 cycles; the capacity C is calibrated every 50 cycles.n , calculate C n / C0×100%, terminate when capacity ≤80% (internal resistance change needs to be monitored simultaneously);

[0157] The test results of the above binder materials and positive electrode sheets are summarized in Table 1, and the test results of the battery are summarized in Table 2.

[0158] Table 1:

[0159]

[0160]

[0161] As can be seen from Table 1, compared with the comparative example, the sulfur content in different regions of the binder material of the embodiment is relatively consistent, the prepared dry-process electrode has a lower contact angle to water, and the difference in contact angles at different points is smaller.

[0162] Table 2

[0163]

[0164] By comparing the data of Test Example 1 in Table 2, it can be seen that, compared with the comparative example, the binder material of the embodiment is more helpful in improving the rate capability and cycle stability of the battery when used in the battery.

[0165] By comparing the data of Test Examples 1-4 in Table 2, it can be seen that the molar ratio of the carbon element in the carbon material to the sulfur element in the binder material is (5-18):1, which can ensure that the contact angle of the dry self-supporting film to water is not higher than 20°, thereby further ensuring the rate capability and cycle stability of the battery.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A binder material, characterized in that: The binder material includes a binder matrix and a sulfate group arranged on at least a portion of the surface of the binder matrix. The EDS energy spectrum analysis diagram of the binder material includes a first zone and a second zone. In the first zone, the area proportion of the sulfur element is x, and in the second zone, the area proportion of the sulfur element is y, x is greater than or equal to y, and x and y satisfy: xy≤20%, y≥20%.

2. The adhesive material according to claim 1, characterized in that The binder matrix includes polytetrafluoroethylene.

3. The adhesive material according to claim 1 or 2, characterized in that The molar ratio of the sulfate groups to the binder material is not less than 10%.

4. The adhesive material according to any one of claims 1 to 3, characterized in that: The number average molecular weight of the binder material is 50wDa-200wDa; And / or, the dispersion index of the binder material is 1.8-2.

2.

5. A method for preparing the adhesive material according to any one of claims 1 to 4, characterized in that: The following steps are involved: performing a pre-oxidation treatment on the adhesive matrix to obtain an adhesive matrix containing oxygen groups; The binder matrix containing oxygen groups and the sulfonating agent are ball-milled to obtain the binder material; wherein the mass ratio of the sulfonating agent to the binder matrix containing oxygen groups is 0.05-0.3:

1.

6. The preparation method according to claim 5, characterized in that The pre-oxidation treatment includes the following processes: The adhesive matrix is ​​placed in a plasma containing oxygen as the plasma gas, and reacted at 40-50° C. for 1-5 hours to obtain the adhesive matrix containing oxygen groups.

7. The preparation method according to claim 5, characterized in that The sulfonating agent includes at least one of sulfamic acid, sodium sulfite, sodium bisulfite, and p-toluenesulfonyl chloride; And / or, the ball milling process is performed at a speed of 1500-3000 rpm for a time of 1-2 h.

8. A dry electrode, characterized in that: The invention comprises a current collector and a dry-process self-supporting film arranged on at least one side of the current collector, wherein the dry-process self-supporting film comprises the adhesive material according to any one of claims 1 to 4.

9. The dry electrode according to claim 8, characterized in that: The dry process self-supporting film further includes a conductive agent, which includes a carbon material. The molar ratio of the carbon element in the carbon material to the sulfur element in the binder material is (5-18):

1.

10. The dry electrode according to claim 9, characterized in that: The dry self-supporting film has a contact angle of 0-20° to water. The dry self-supporting film includes a third region and a fourth region. The contact angle of the third region to water is m°, and the contact angle of the fourth region to water is n°. The difference between m and n is not greater than 15°.

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