Preparation method of binder, binder, pole piece and battery

Abstract

The invention relates to a preparation method of a binder, the binder, a pole piece and a battery, and the preparation method of the binder comprises the following steps: S1, adding xanthan gum into a solvent, and stirring to obtain a xanthan gum solution; s2, adding a basic catalyst into the xanthan gum solution, stirring, adding isocapryloyl chloride, and carrying out a polymerization reaction under a reflux condition to obtain a copolymer; and S3, neutralizing the copolymer by using an acid solution, filtering, washing and drying to obtain the binder. Therefore, when the prepared binder is applied to positive and negative slurry, the suspension stability and uniformity of the slurry can be remarkably improved, so that the resistance of a pole piece prepared from the slurry can be reduced, the peel strength of the pole piece can be improved, and the dynamic performance of a finally prepared battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a preparation method of a binder, the binder, a pole piece and a battery. BACKGROUND

[0002] In the construction system of lithium ion batteries, the positive pole piece and the negative pole piece are core components, and the performance thereof plays a decisive role in the overall performance of the battery. The performance of the positive pole piece and the negative pole piece is determined by the preparation process and quality level of the positive pole slurry and the negative pole slurry to a great extent.

[0003] Taking the preparation process of the lithium iron phosphate positive pole slurry widely used in the field of lithium ion batteries as an example, there are mainly two processing methods of oily system and aqueous system. In the oily system process, N-methyl pyrrolidone (NMP) is usually selected as a solvent, and polyvinylidene fluoride (PVDF) is selected as a binder. PVDF has certain advantages of electrochemical stability, but its adhesion is relatively weak, and the mechanical tensile strength is also low, which limits the further improvement of the performance of the finally prepared pole piece to a certain extent. In addition, the use of the solvent NMP brings a series of problems, such as difficulty in recycling the organic solvent, environmental pollution risk, certain toxicity and high cost, etc. In comparison, the aqueous system process meets the development trend of green industry and is friendly to production personnel and environment.

[0004] However, the aqueous system positive and negative pole slurry has poor stability, and during the transfer and storage of the slurry, the solute is prone to sedimentation and stratification, resulting in poor consistency of the slurry. In the subsequent slurry coating and drying process, the pole piece surface is prone to enrichment, so that the consistency of the prepared pole piece is difficult to guarantee, thereby affecting the electronic transmission performance and the peeling strength of the pole piece, and finally leading to the decline of the kinetic performance of the battery. SUMMARY

[0005] Therefore, the present application provides a preparation method of a binder, the binder, a pole piece and a battery to solve at least one problem in the background art.

[0006] In a first aspect, the present application provides a preparation method of a binder, which comprises the following steps:

[0007] S1, xanthan gum is added to a solvent, and after stirring, a xanthan gum solution is obtained;

[0008] S2, an alkaline catalyst is added to the xanthan gum solution, and after stirring, isooctanoyl chloride is added, and a polymerization reaction is carried out under reflux conditions to obtain a copolymer;

[0009] S3, the copolymer is subjected to neutralization treatment with an acid solution, and after filtration, washing and drying, the binder is obtained.

[0010] In an optional implementation of the first aspect of the present application, the solvent in step S1 comprises at least one of ethanol, glycerol, and dimethyl sulfoxide.

[0011] In an optional implementation of the first aspect of the present application, before step S1, the method further comprises: performing vacuum drying treatment on the xanthan gum; optionally, the temperature of the vacuum drying treatment is 30-45°C, and the time of the vacuum drying treatment is 12-24h.

[0012] In an optional implementation of the first aspect of the present application, step S2 satisfies at least one of the following features:

[0013] (1) the molar ratio of the xanthan gum to the basic catalyst is 0.1-0.3;

[0014] (2) the molar ratio of the xanthan gum to the isooctanoyl chloride is 0.05-0.75;

[0015] (3) the basic catalyst comprises at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium methoxide, and sodium ethoxide;

[0016] (4) the stirring is performed at a temperature of 20-25°C;

[0017] (5) the temperature of the refluxing condition is 80-90°C;

[0018] (6) the time of the polymerization reaction is 6-8h.

[0019] In an optional implementation of the first aspect of the present application, step S3 satisfies at least one of the following features:

[0020] (1) after the neutralization treatment, the pH of the copolymer is 7-8;

[0021] (2) the temperature of the drying treatment is 70-80°C;

[0022] (3) the time of the drying treatment is 24-48h.

[0023] In a second aspect, the embodiments of the present application provide a binder comprising a copolymer of xanthan gum and isooctanoyl chloride; the copolymer comprises ester groups generated by the reaction between the hydroxyl groups in the xanthan gum and the acyl chloride groups in the isooctanoyl chloride.

[0024] In an optional implementation of the second aspect of the present application, the molar ratio of the xanthan gum to the isooctanoyl chloride is 0.05-0.75.

[0025] In a third aspect, the embodiments of the present application provide a pole piece, comprising a current collector and an active material layer on at least one surface of the current collector; the active material layer comprises the binder prepared by the method for preparing a binder according to any one of the first aspect or the binder according to any one of the second aspect.

[0026] In combination with the third aspect of the present application, in an optional embodiment, the active material layer further comprises an active material and a conductive agent, and the mass ratio of the active material, the conductive agent and the binder is 100:(1-20):(1-20).

[0027] In a fourth aspect, the embodiments of the present application provide a battery comprising the pole piece according to any one of the third aspect.

[0028] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0029] In the method for preparing a negative electrode material provided by the embodiments of the present application, the isooctyl chains are grafted on the xanthan gum main chain through the polymerization reaction of isooctanoyl chloride and xanthan gum, the hydrophobic groups are introduced, and the deacetylation degree of xanthan gum is improved, so that more hydroxyl groups are exposed, thereby the hydrogen bond interaction between the xanthan gum molecular chains can be enhanced, and the rigid structure of the xanthan gum molecular chains itself can make the xanthan gum form a good associated structure in the solution, thereby the stability and support of the three-dimensional network structure of the xanthan gum molecules are improved, that is, the mechanical properties and stability of the xanthan gum associated structure are improved. Therefore, when the prepared binder is applied to the positive and negative slurries, the suspension stability and uniformity of the slurry can be significantly improved, thereby the resistance of the pole piece prepared by using the slurry can be reduced and the peeling strength of the pole piece can be improved, and further the kinetic performance of the finally prepared battery can be improved. In addition, the binder prepared in the embodiments of the present application is suitable for the aqueous system, can reduce the pollution to the environment, reduce the damage to the health of the production personnel, and reduce the production and waste liquid disposal costs.

[0030] Additional aspects and advantages of the present application will be made apparent by the following description and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings, which are included to provide a further understanding of the present application, constitute a part of the present application and illustrate the illustrative embodiments of the present application and their description serve to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0032] Figure 1 A flowchart of the method for preparing a binder provided by the embodiments of the present application is shown. DETAILED DESCRIPTION

[0033] In order to make the technical solutions and beneficial effects of the present application more obvious and easy to understand, the following will be described in detail by combining the drawings and listing specific examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application. The experimental methods not specified in the following examples are generally carried out according to the conventional experimental conditions. The reagents and raw materials used in the present application are commercially available unless otherwise specified.

[0034] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without one or more of these specific details. In other instances, well-known features have not been described in detail in order to avoid obscuring the present application. In the following description, the terms "couple" and "coupled" refer to an operational coupling, whether mechanical, electrical, or magnetic, between two components, and does not require that the two components are in direct contact with each other.

[0035] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0036] For a thorough understanding of the present application, detailed steps and detailed structures will be set forth in the following description, so as to explain the technical solutions of the present application. The preferred embodiments of the present application are described in detail as follows, however, in addition to these detailed descriptions, the present application can also have other implementation manners.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0038] The experimental methods not specified in the following examples are generally carried out according to the conventional techniques described in the literature or according to the product instructions and manufacturer's recommended conditions. The numerical ranges in the following examples include the end point values.

[0039] Xanthan gum aqueous solution has the characteristics of low concentration and high viscosity, and is a high-efficiency thickening agent. Xanthan gum molecules can form super combined belt-shaped spiral copolymer, and form a three-dimensional network structure through double helix conformation and intermolecular association, so as to support the morphology of solid particles, liquid droplets and bubbles, and exhibit strong emulsification stability and high suspension capacity. However, the gel (three-dimensional network structure) of ordinary xanthan gum has low strength and poor stability. Meanwhile, due to the limitation of the molecular structure and properties, the compatibility of ordinary xanthan gum with other ingredients is not high, and problems such as delamination and precipitation are prone to occur.

[0040] Based on this, the application embodiment provides a preparation method of a binder, please refer to Figure 1 The preparation method of the binder provided in the application embodiment comprises the following steps:

[0041] S1, xanthan gum is added to a solvent, and after stirring, a xanthan gum solution is obtained;

[0042] S2, an alkaline catalyst is added to the xanthan gum solution, and after stirring, isooctanoyl chloride is added, and a polymerization reaction is carried out under reflux conditions to obtain a copolymer;

[0043] S3, the copolymer is subjected to neutralization treatment with an acid solution, and after filtration, washing and drying, a binder is obtained.

[0044] In the application embodiment, through the polymerization reaction of isooctanoyl chloride and xanthan gum (ester groups generated by the reaction of hydroxyl groups in xanthan gum and acyl chloride groups in isooctanoyl chloride), isooctyl chains are grafted on the xanthan gum main chain, hydrophobic groups are introduced, and the degree of deacetylation of xanthan gum is improved, so that more hydroxyl groups are exposed, thereby the hydrogen bond interaction between xanthan gum molecular chains can be enhanced, and in addition to the rigid structure of the xanthan gum molecular chain itself, the xanthan gum can form a good associated structure in the solution, and the stability and supporting effect of the three-dimensional network structure of the xanthan gum molecules are improved, that is, the mechanical properties and stability of the xanthan gum associated structure are improved. Therefore, when the prepared binder is applied to the positive and negative slurries, the suspension stability and uniformity of the slurry can be significantly improved, thereby the resistance of the pole piece prepared by using the slurry can be reduced and the peeling strength of the pole piece can be improved, and further the kinetic performance of the finally prepared battery can be improved. In addition, the binder prepared in the application embodiment is suitable for water-based systems, which can reduce the pollution to the environment, reduce the harm to the health of production personnel, and reduce the production and waste liquid disposal costs.

[0045] In some embodiments, before step S1, the preparation method of the binder can further comprise: subjecting the xanthan gum to vacuum drying treatment.

[0046] Optionally, the temperature of the vacuum drying treatment is 30-45℃, and the time of the vacuum drying treatment is 12-24h.

[0047] In step S1, xanthan gum is added into solvent, after stirring, xanthan gum solution is obtained.

[0048] In actual preparation process, after vacuum drying, xanthan gum powder can be added into solvent under magnetic stirring, and continuous stirring is performed to obtain xanthan gum solution. Exemplarily, the solvent can include at least one of ethanol, glycerol, and dimethyl sulfoxide.

[0049] In step S2, a basic catalyst is added into the xanthan gum solution, after stirring, isooctanoyl chloride is added, and a polymerization reaction is performed under refluxing condition to obtain a copolymer.

[0050] In actual preparation process, first, a basic catalyst is added into the xanthan gum solution, and stirring (magnetic stirring) is performed to obtain a xanthan gum basic solution, which provides a suitable basic environment for subsequent polymerization reaction of xanthan gum and isooctanoyl chloride, and accelerates the reaction rate; next, isooctanoyl chloride with a molar fraction of 1 is added dropwise into the xanthan gum basic solution, and under refluxing condition, the acyl chloride group (-COCl) in isooctanoyl chloride reacts with the hydroxyl group (-OH) in the xanthan gum molecule to form an ester bond (-COO-), thereby introducing isooctanoyl group into the xanthan gum molecule, and a xanthan gum / isooctanoyl chloride copolymer is obtained, that is, a xanthan gum modified derivative with amphiphilic properties (hydrophilic and lipophilic) is obtained.

[0051] In some embodiments, the molar ratio of xanthan gum to basic catalyst can be 0.1-0.3, for example, it can be 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, or any value within any two of the above-mentioned value ranges. In this way, it is beneficial to provide a suitable basic environment, promote sufficient and complete crosslinking reaction between xanthan gum and isooctanoyl chloride, and improve the quality of the obtained copolymer, thereby improving the performance of the finally obtained adhesive.

[0052] Exemplarily, the basic catalyst includes at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium methoxide, and sodium ethoxide. In a specific example, the basic catalyst includes NaOH solution. The addition rate of NaOH solution can be 0.05 ml / min-0.07 ml / min.

[0053] In some embodiments, the molar ratio of xanthan gum to isooctanoyl chloride can be 0.05-0.75, for example, can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.75, or any value between any two of the above-mentioned numerical ranges. In this way, it is beneficial to promote the cross-linking reaction between xanthan gum and isooctanoyl chloride to be sufficient and complete, improve the quality of the copolymer prepared, and thus improve the performance of the adhesive ultimately prepared.

[0054] In step S2, when the alkaline catalyst is added to the xanthan gum solution, stirring can be carried out at a temperature of 20-25°C.

[0055] In step S2, the temperature of the refluxing condition can be 80-90°C, for example, can be 80°C, 85°C, 90°C, or any value between any two of the above-mentioned numerical ranges. In this way, it is beneficial to promote the cross-linking reaction between xanthan gum and isooctanoyl chloride to be more sufficient and complete, improve the quality of the copolymer prepared, and thus improve the performance of the adhesive ultimately prepared.

[0056] Further, the time of the polymerization reaction can be 6-8h, for example, can be 6h, 7h, 8h, or any value between any two of the above-mentioned numerical ranges.

[0057] In step S3, the copolymer is treated with an acid solution for neutralization, and after filtration, washing, and drying, the adhesive is obtained.

[0058] In the actual preparation process, the copolymer prepared in step S2 can be first washed with an ethanol solution (volume concentration of 80-90%), and then treated with an acid solution (for example, acetic acid) for neutralization to a pH of 7-8, followed by vacuum filtration, repeated washing (for example, 5-10 times), and drying (for example, baking), to obtain the adhesive (which can also be referred to as modified xanthan gum powder).

[0059] After the neutralization treatment, the pH of the copolymer is 7-8. It can be understood that after the neutralization treatment, the pH of the solution containing the copolymer is 7-8.

[0060] Alternatively, the temperature of the drying treatment is 70-80°C. The time of the drying treatment is 24-48h.

[0061] The embodiments of the present application also provide an adhesive, which comprises a copolymer of xanthan gum and isooctanoyl chloride; and the copolymer comprises ester groups generated by the reaction between the hydroxyl groups in the xanthan gum and the acyl chloride groups in the isooctanoyl chloride.

[0062] The ester group generated by the reaction between the hydroxyl group in the xanthan gum and the acyl chloride group in the isooctanoyl chloride grafts the isooctyl chain on the main chain of the xanthan gum, introduces the hydrophobic group, and increases the deacetylation degree of the xanthan gum, exposes more hydroxyl groups, so that the hydrogen bond interaction between the xanthan gum molecular chains can be enhanced, and the rigid structure of the xanthan gum molecular chain itself can make the xanthan gum form a good associated structure in the solution, improve the stability and support of the three-dimensional network structure of the xanthan gum molecular, and improve the mechanical properties and stability of the associated structure of the xanthan gum. Therefore, when the prepared binder is applied to the positive and negative slurries, the suspension stability and uniformity of the slurry can be significantly improved, thereby reducing the resistance of the pole piece prepared by using the slurry and improving the peeling strength of the pole piece, and further improving the kinetic performance of the finally prepared battery. In addition, the binder prepared in the embodiment of the present application is suitable for water-based system, which can reduce the pollution to the environment, reduce the harm to the health of the production personnel, and reduce the production and waste liquid disposal cost.

[0063] In some embodiments, the molar ratio of the xanthan gum to the isooctanoyl chloride is 0.05-0.75, for example, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.75, or any value within any two of the above-mentioned value ranges. In this way, the performance of the binder can be improved.

[0064] The embodiment of the present application also provides a pole piece, which comprises a current collector and an active material layer on at least one surface of the current collector; the active material layer comprises the binder prepared by the preparation method of the binder described in any of the above-mentioned embodiments or comprises the binder described in any of the above-mentioned embodiments.

[0065] It can be understood that the beneficial effects of the binder described in any of the above-mentioned embodiments are applicable to the pole piece in the embodiment of the present application. Therefore, the pole piece in the embodiment of the present application has low resistance and high peeling strength.

[0066] In some embodiments, the pole piece can comprise a positive pole piece and / or a negative pole piece. In a specific embodiment, the pole piece is a positive pole piece.

[0067] In some embodiments, the active material layer further comprises an active material and a conductive agent, and the mass ratio of the active material, the conductive agent and the binder can be 100:(1-20):(1-20).

[0068] It can be understood that, when the pole piece is a positive pole piece, the active material is a positive active material, which may, for example, include at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese phosphate, lithium nickel cobalt manganese aluminate; when the pole piece is a negative pole piece, the active material is a negative active material, which may, for example, include at least one of graphite, silicon-based material, hard carbon. The conductive agent may, for example, include at least one of acetylene black, ketjen black, conductive carbon black (Super-P), carbon fiber, carbon nanotube. The binder may, for example, include polyvinylidene fluoride.

[0069] The embodiments of the present application also provide a battery, which includes the pole piece described in the above embodiments.

[0070] In some embodiments, the battery can be a secondary battery, which may, for example, be a lithium ion battery or a sodium ion battery. In a specific embodiment, the secondary battery is a lithium ion battery. Generally, the secondary battery includes a positive pole piece, a negative pole piece, an electrolyte and a separator. During the charging and discharging of the battery, active ions are embedded and extracted between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting active ions between the positive pole piece and the negative pole piece. The separator is arranged between the positive pole piece and the negative pole piece, mainly playing a role in preventing the short circuit of the positive and negative poles, while allowing the active ions to pass through.

[0071] In the actual preparation process of the battery, first, the positive pole piece, the separator, the negative pole piece and the separator can be stacked in sequence to obtain a bare cell after assembly, and the assembly mode may, for example, be selected as a laminated or wound mode; then, the electrolyte is injected into the dry bare cell, and a secondary battery is obtained after formation and aging. One or both of the positive pole piece and the negative pole piece is the pole piece described in the above embodiments. The separator may, for example, be a polyethylene film, a polypropylene film, a polyvinylidene fluoride film or a non-woven fabric, etc. The electrolyte may, for example, include lithium salt and solvent or sodium salt and solvent, wherein the lithium salt, the sodium salt and the type of solvent are not specifically limited and can be selected according to actual needs.

[0072] The technical solutions of the present application will be further described below in combination with a plurality of embodiments and comparative examples.

[0073] Embodiment 1

[0074] The preparation method of the binder in this embodiment includes the following steps:

[0075] Step S101: 5g of xanthan gum powder is taken and added to 200ml of ethanol (solvent) under magnetic stirring, and stirred for 4h to obtain a xanthan gum solution;

[0076] Step S102: 7.5 ml of NaOH solution (concentration of 15 mol / l) was added to the xanthan gum solution prepared above at a rate of 0.06 ml / min, and the solution was stirred at room temperature for 150 min. Then, 4 ml of isooctanoyl chloride with a molar fraction of 1 was added dropwise, and the solution was reacted at a reflux temperature of 85 °C for 8 h to obtain a xanthan gum / isooctanoyl chloride copolymer.

[0077] Step S103: The copolymer obtained in the above step was washed 5 times with an ethanol solution with a volume fraction of 85%, and then neutralized to a pH of 7.0 with acetic acid. Next, the copolymer was baked in an oven at 80 °C for 48 h to obtain a modified xanthan gum (binder).

[0078] Example 2

[0079] The preparation method of the binder in this example is basically the same as that in Example 1, except that:

[0080] 1) In step S101, the solvent was replaced with glycerol, and the amount of glycerol added was 100 ml;

[0081] 2) In step S102, the amount of NaOH solution added was adjusted to 10 ml, and the rate of addition was adjusted to 0.05 ml / min; the amount of isooctanoyl chloride added was adjusted to 8 ml.

[0082] Example 3

[0083] The preparation method of the binder in this example is basically the same as that in Example 1, except that:

[0084] 1) In step S101, the solvent was replaced with dimethyl sulfoxide, and the amount of dimethyl sulfoxide added was 100 ml;

[0085] 2) In step S102, the amount of NaOH solution added was adjusted to 5 ml, and the rate of addition was adjusted to 0.07 ml / min; the reaction time under reflux conditions was 6 h.

[0086] Comparative Example 1

[0087] In this comparative example, xanthan gum powder (the same as the xanthan gum powder in step S101 of Example 1) was used as a binder, and the performance of the binder was compared with the binders prepared in Examples 1 to 3.

[0088] Comparative Example 2

[0089] In this comparative example, polyvinylidene fluoride was used as a binder, and the performance of the binder was compared with the binders prepared in Examples 1 to 3.

[0090] The binders in each of the above examples and comparative examples were used in the preparation of positive electrode slurry and positive electrode sheets to verify the performance of the binders.

[0091] The positive electrode active material lithium iron phosphate, the binder of each of the above examples and comparative examples, and the conductive agent Super-P were added to deionized water in a mass ratio of 100:10:10, and after stirring to be uniform, a positive electrode slurry was obtained. The resistivity of the upper layer slurry, the middle layer slurry, and the lower layer slurry in the prepared positive electrode slurry was tested by a slurry resistance meter. The test conduit of the slurry resistance meter has three probes of upper, middle, and lower, which can simultaneously measure the resistivity of the upper layer slurry, the middle layer slurry, and the lower layer slurry after being vertically inserted into the slurry.

[0092] The positive electrode slurry prepared above was coated on the current collector aluminum foil, and after drying in an oven, a positive electrode sheet was obtained. The film surface resistance of the positive electrode sheet was tested by a four-probe method, and the peeling strength of the positive electrode sheet was tested by a 90° glass test method.

[0093] The test results above are shown in Table 1.

[0094] The positive electrode sheet prepared above was assembled into a battery, and the kinetic performance of the battery was tested.

[0095] The steps of assembling the battery were as follows: the positive electrode sheet, the separator, the graphite negative electrode, the spring sheet, and the gasket were sequentially stacked, and an electrolyte (a solution of LiPF6 dissolved in ethylene carbonate) was added, and a button cell was assembled.

[0096] The kinetic performance of the battery was tested as follows:

[0097] 1) Rate capacity: at 25°C, the discharge current density was 0.5 A / g and discharging was performed, and the discharge capacity was recorded as the first discharge capacity when discharging to 2.0 V; the charging current density was XA / g and charging was performed, and the charging capacity was recorded as the charging capacity at X rate when charging to 3.65 V; the discharge current density was XA / g and discharging was performed, and the discharge capacity was recorded as the discharge capacity at X rate when discharging to 2.0 V. Wherein X was 0.1 A / g, 0.5 A / g, 1 A / g, 2 A / g, 5 A / g, and 10 A / g.

[0098] 2) Cycle capacity retention rate: at 25°C, the current density was 1 A / g, and constant current discharging was performed to 2.0 V, and the discharge capacity was recorded as the first discharge capacity; the current density was 1 A / g, and constant current charging was performed to 3.65 V, and the charging capacity was recorded as the first charging capacity, which was one cycle and was recorded as the first cycle. The cycle was repeated for 1000 cycles, and the test was ended. Then, the cycle capacity retention rate of 1000 cycles = (the discharge capacity of the 1000th cycle / the discharge capacity of the 2nd cycle) * 100%. The test results above are shown in Table 2.

[0099] Table 1

[0100]

[0101] Table 2

[0102]

[0103]

[0104] As can be seen from the test data of the slurry resistivity in Table 1, the overall resistivity of the positive electrode slurry containing the binder prepared in Examples 1 to 3 is significantly reduced, and the resistivity difference of the upper layer, middle layer and lower layer slurry is small, i.e. the uniformity of the upper layer, middle layer and lower layer slurry is good, relative to Comparative Examples 1 and 2. Correspondingly, the film surface resistance of the positive electrode sheet prepared by using the positive electrode slurry containing the binder prepared in Examples 1 to 3 is significantly reduced, relative to Comparative Examples 1 and 2. This is consistent with the test results of the slurry resistivity. In addition, as can be seen from the peel strength data of the electrode sheet in Table 1, the peel strength of the positive electrode sheet prepared by using the positive electrode slurry containing the binder prepared in Examples 1 to 3 is improved, relative to Comparative Examples 1 and 2. This shows that, in the present application, by the polymerization reaction of isooctanoyl chloride and xanthan gum (ester groups generated by the reaction of hydroxyl groups in xanthan gum and acyl chloride groups in isooctanoyl chloride), isooctyl chains are grafted on the xanthan gum main chain, hydrophobic groups are introduced, and the rigid structure of the xanthan gum molecular chain itself makes the xanthan gum form a good associated structure in solution, while the degree of deacetylation of the xanthan gum is improved, more hydroxyl groups are exposed, the hydrogen bonding between xanthan gum molecular chains is enhanced, and thus the stability and support of the three-dimensional network structure of the xanthan gum molecular are improved, and the mechanical properties and thermal stability of the xanthan gum structure are improved. Therefore, when the prepared binder is applied to the positive and negative slurries, the suspension stability and uniformity of the slurry can be significantly improved, thereby reducing the resistance of the prepared electrode sheet and improving the peel strength of the electrode sheet.

[0105] As can be seen from the rate performance and cycle performance test data of the battery in Table 2, the capacity at different rates and the capacity retention rate after 1000 cycles of the battery using the positive electrode sheet containing the binder prepared in Examples 1 to 3 are obviously improved, relative to Comparative Examples 1 and 2, which shows that the corresponding battery has excellent rate performance and cycle performance. This shows that, since the binder prepared in the present application is applied to the positive and negative slurries, the suspension stability and uniformity of the slurry can be significantly improved, thereby reducing the resistance of the prepared electrode sheet and improving the peel strength of the electrode sheet, and thus the dynamics performance of the finally prepared battery is significantly improved.

[0106] In the step of preparing the binder in Example 1, the xanthan gum powder is dissolved in ethanol to obtain a xanthan gum solution, while in Example 2 and Example 3, the xanthan gum powder is dissolved in glycerol and dimethyl sulfoxide respectively to obtain a xanthan gum solution. As can be seen from the data of Example 1 to Example 3 in Table 1 and Table 2, when the binder obtained by using ethanol as the solvent and then modifying the xanthan gum through the polymerization reaction of xanthan gum and isooctanoyl chloride is applied to the slurry, the corresponding slurry has a relatively lower resistivity, i.e. the conductive performance of the slurry is better, the film surface resistance of the corresponding pole piece is also lower, and the peeling strength of the pole piece is also at a higher level; at the same time, the rate performance and cycle performance of the corresponding battery are also better. Therefore, it can be known that in the step of preparing the binder, using ethanol as the solvent to dissolve the xanthan gum powder is a more optimal technical solution.

[0107] It should be noted that the binder embodiments, the preparation method embodiments of the binder, the pole piece embodiments and the battery embodiments provided in the present application belong to the same concept; the technical features in the technical solutions recorded in each embodiment can be combined arbitrarily without conflict.

[0108] It should be understood that the above embodiments are all exemplary and are not intended to include all possible implementations. Various modifications and changes can also be made to the above embodiments without departing from the scope of the present disclosure. Similarly, each technical feature of the above embodiments can also be combined arbitrarily to form additional embodiments of the present application that have not been explicitly described. Therefore, the above embodiments only express several implementation manners of the present application and do not limit the protection scope of the patent of the present application.

Claims

1. A method for preparing an adhesive, characterized in that, The method includes the following steps: S1. Add xanthan gum to the solvent and stir to obtain a xanthan gum solution; S2. Add an alkaline catalyst to the xanthan gum solution, stir, add isooctanoyl chloride, and carry out a polymerization reaction under reflux conditions to obtain a copolymer; S3. The copolymer is neutralized with an acid solution, and after filtration, washing and drying, the binder is obtained.

2. The method for preparing the adhesive according to claim 1, characterized in that, The solvent in step S1 includes at least one of ethanol, glycerol, and dimethyl sulfoxide.

3. The method for preparing the adhesive according to claim 1, characterized in that, Before step S1, the method further includes: vacuum drying the xanthan gum; optionally, the temperature of the vacuum drying treatment is 30℃~45℃, and the time of the vacuum drying treatment is 12h~24h.

4. The method for preparing the adhesive according to claim 1, characterized in that, Step S2 satisfies at least one of the following characteristics: (1) The molar ratio of xanthan gum to alkaline catalyst is 0.1 to 0.3; (2) The molar ratio of xanthan gum to isooctanoyl chloride is 0.05 to 0.75; (3) The alkaline catalyst includes at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium methoxide, and sodium ethoxide; (4) The stirring is carried out at a temperature of 20℃~25℃; (5) The temperature of the reflux condition is 80℃~90℃; (6) The polymerization reaction takes 6 to 8 hours.

5. The method for preparing the adhesive according to claim 1, characterized in that, Step S3 satisfies at least one of the following characteristics: (1) After the neutralization treatment, the pH of the copolymer is 7-8; (2) The drying temperature is 70℃~80℃; (3) The drying time is 24h to 48h.

6. An adhesive, characterized in that, The copolymer includes xanthan gum and isooctanoyl chloride; the copolymer includes ester groups formed by the reaction of hydroxyl groups in xanthan gum and acyl chloride groups in isooctanoyl chloride.

7. The adhesive according to claim 6, characterized in that, The molar ratio of xanthan gum to isooctanoyl chloride is 0.05 to 0.

75.

8. An electrode sheet, characterized in that, The electrode includes a current collector and an active material layer located on at least one surface of the current collector; the active material layer includes an adhesive prepared by the method of preparing the adhesive according to any one of claims 1 to 5 or includes the adhesive according to claim 6 or 7.

9. The electrode sheet according to claim 8, characterized in that, The active material layer further includes an active material and a conductive agent, wherein the mass ratio of the active material, the conductive agent and the binder is 100:(1-20):(1-20).

10. A battery, characterized in that, Includes the electrode as described in claim 8 or 9.

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