Carboxymethyl cellulose derivative as well as preparation method and application thereof

Abstract

The invention discloses a carboxymethyl cellulose derivative as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing carboxymethyl cellulose salt, a bifunctional compound and a solvent; adding a first catalyst into the system, and carrying out a first reaction to obtain a carboxymethyl cellulose conductive substrate; adjusting the system to be neutral, adding a conductive monomer and a second catalyst, and carrying out a second reaction to obtain the carboxymethyl cellulose derivative, the bifunctional compound has a first reactive group for attachment to the carboxymethyl cellulose salt and a second reactive group for attachment to the conductive monomer. According to the preparation method of the carboxymethyl cellulose derivative, the conductive monomer for forming the delocalized pi molecular orbit is grafted on the carboxymethyl cellulose salt, and the conductive monomer and the carboxymethyl cellulose salt are combined through chemical bonds, so that the carboxymethyl cellulose is provided with a conductive channel and low in resistivity, and the non-conductive performance of a CMC material is fundamentally improved.

Description

Technical Field

[0001] The present invention relates to the technical field of carboxymethyl cellulose and polymer chemical modification, and in particular to a method for preparing a low-resistivity carboxymethyl cellulose derivative suitable for electrode slurry, the prepared carboxymethyl cellulose derivative, and the application of the carboxymethyl cellulose derivative in (lithium) batteries, electrodes, and slurry. Background Art

[0002] Carboxymethyl cellulose materials (including sodium carboxymethyl cellulose and lithium carboxymethyl cellulose) are often used as auxiliary materials for preparing battery materials. They are mainly added to the negative electrode graphite slurry of lithium batteries. Their function is to keep the slurry stable for a period of time, so that the graphite powder in the slurry can be stably suspended and dispersed in the solution without sedimentation and aggregation in a short time, so that the slurry has good processing and coating performance in the later stage.

[0003] However, as the battery preparation proceeds, the water in the battery slurry coated on the copper foil surface evaporates, and the carboxymethyl cellulose eventually exists in the battery graphite negative electrode material in a solid form. However, carboxymethyl cellulose is a natural poor conductor, and its presence has a negative effect on the battery's electrical performance. As the amount of carboxymethyl cellulose added increases, the internal resistance of the battery will also increase, thereby reducing the battery's electrical performance.

[0004] Regarding the above-mentioned problem of "carboxymethyl cellulose being a poor conductor". There are also some public solutions. For example, patent CN111875792A proposes adding pyrrole and ammonium persulfate solution to dissolved carboxymethyl cellulose to obtain a conductive composite. However, the problem with this method is that the conductive layer formed by this method is adsorbed on the surface of the carboxymethyl cellulose, and the mutual force is weak. In the preparation process of the battery slurry, it is necessary to dissolve sodium carboxymethyl cellulose and add graphite and continue to stir. The later dissolution and stirring will affect the distribution of the conductive layer material adsorbed on the surface of CMC. After dissolution and mechanical action, the conductive layer originally adsorbed on the surface of carboxymethyl cellulose is stripped off the carrier of carboxymethyl cellulose due to the dissolution of carboxymethyl cellulose, the centrifugal force of stirring, its own lipophilicity, etc., and gradually adsorbed on the surface of graphite powder. The carboxymethyl cellulose in the dried battery pole piece still exists in the form of no conductive layer, which will eventually affect the conductive performance of the battery negative electrode coating. The conductivity of the composite material simply tested (testing the conductivity of the material directly without dissolving it) does not match the actual conductivity in the battery coating, because the conductive layer on the surface of the carboxymethyl cellulose after the battery is prepared is transferred, adsorbed, and agglomerated due to the dissolution and precipitation of the carboxymethyl cellulose, the centrifugal force of stirring, and the polar attraction of the carboxymethyl cellulose itself. After coating and drying, the carboxymethyl cellulose still exists in the negative electrode of the battery as a poor conductor. The newly introduced conductive layer has little effect on reducing the poor conductor performance of carboxymethyl cellulose. Therefore, a relatively strong force is needed to maintain the connection between the conductive layer and the carboxymethyl cellulose.

[0005] For example, patent CN107663428A discloses a conductive composite water-based binder and its one-pot preparation method and application, which adds double-bond grafted monomers and conductive polymer monomers to the solution, and adds an initiator, and polymer grafting and chemical polymerization of the conductive polymer occur simultaneously. Finally, a two-component mixture of a water-soluble polymer with a non-conductive branch chain and a conductive polymer polymer material is generated. As a result, when preparing the slurry negative electrode later, after a lot of stirring, the highly lipophilic conductive polymer material will gradually adsorb on the graphite, and the water-soluble polymer with a non-conductive branch chain will be dispersed in the system, and the resistance of the CMC will be reduced to a limited extent.

[0006] The disclosure of the above background technology content is only used to assist in understanding the inventive concept and technical solution of the present invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above content has been disclosed before the filing date of this patent application, the above background technology should not be used to evaluate the novelty and creativity of this application. Summary of the invention

[0007] In view of this, in order to overcome the defects of the prior art, the present invention provides an improved method for preparing a conductive carboxymethyl cellulose derivative, and the prepared conductive carboxymethyl cellulose derivative has a continuously low resistivity.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing a carboxymethyl cellulose derivative comprises the following steps: mixing a carboxymethyl cellulose salt, a bifunctional compound, and a solvent; Adding a first catalyst into the system to carry out a first reaction to obtain a carboxymethyl cellulose conductive matrix; The system is adjusted to be neutral, a conductive monomer and a second catalyst are added, and a second reaction is performed to obtain the carboxymethyl cellulose derivative; The bifunctional compound has a first reactive group for connecting with the carboxymethyl cellulose salt and a second reactive group for connecting with the conductive monomer.

[0009] According to some preferred embodiments of the present invention, the mass ratio of the carboxymethyl cellulose salt, the bifunctional compound and the first catalyst is 100:0.5-1:0.05-0.2.

[0010] According to some preferred embodiments of the present invention, the mass ratio of the carboxymethyl cellulose salt, the conductive monomer and the second catalyst is 100:5-20:2-4.

[0011] According to some preferred embodiments of the present invention, the first reactive group is an epoxy group.

[0012] According to some preferred embodiments of the present invention, the epoxy group is an ethylene oxide group.

[0013] According to some preferred embodiments of the present invention, the conductive monomer contains a conductive group capable of forming a delocalized π orbital morphology.

[0014] According to some preferred embodiments of the present invention, the conductive group is a thiophene group.

[0015] According to some preferred implementation aspects of the present invention, the conductive monomer is a thiophene monomer.

[0016] According to some preferred embodiments of the present invention, the second reactive group is the same as the conductive group in the conductive monomer.

[0017] According to some preferred embodiments of the present invention, the bifunctional compound is 2-((thiophen-2-ylmethoxy)methyl)oxirane.

[0018] According to some preferred embodiments of the present invention, the second catalyst is one or more selected from ferric chloride, ammonium persulfate, potassium persulfate, sodium persulfate, and ferric p-toluenesulfonate, preferably ammonium persulfate.

[0019] According to some preferred implementation aspects of the present invention, the first catalyst is an alkaline substance such as sodium hydroxide, and the adjustment system is neutral by adding an acidic substance into the system.

[0020] According to some preferred implementation aspects of the present invention, the first catalyst is an acidic substance such as acetic acid or hydrochloric acid, and the regulating system is neutral by adding an alkaline substance into the system.

[0021] According to some preferred embodiments of the present invention, the carboxymethyl cellulose salt is sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

[0022] According to some preferred implementation aspects of the present invention, the first reaction is carried out at room temperature for 1-5 hours.

[0023] According to some preferred embodiments of the present invention, the second reaction is carried out at 45-65° C. for 1-5 hours.

[0024] According to some preferred embodiments of the present invention, the step further comprises post-treatment: washing the carboxymethyl cellulose derivative with ethanol, drying at 110°C-130°C for 1.5-2.5h, crushing and filtering through a 60-100 mesh filter to obtain a treated carboxymethyl cellulose derivative.

[0025] The present invention also provides a carboxymethyl cellulose derivative prepared according to the above preparation method.

[0026] The carboxymethyl cellulose derivative provided by the present invention has the following structural formula:

[0027] In the formula, 10≤n≤49, and n is an integer.

[0028] The present invention also provides a use of the above-mentioned carboxymethyl cellulose derivative in electrode slurry, battery electrode or (lithium) battery.

[0029] The present invention also provides an electrode slurry, which comprises the following raw material components in parts by weight: 40-50 parts water Ordinary graphite 45-55 parts Conductive graphite 0.2-0.5 parts CMC 0.5-1.0 parts SBR 1.8-2.5 parts; The CMC is the above-mentioned carboxymethyl cellulose derivative.

[0030] The present invention also provides a method for preparing the above electrode slurry, comprising the following steps: The carboxymethyl cellulose derivative is mixed with deionized water and stirred to obtain CMC glue solution after the carboxymethyl cellulose derivative is fully dissolved.

[0031] Ordinary graphite powder, conductive graphite powder and the above CMC glue are mixed to form the dispersed graphite powder into a dough-like state that is bonded to each other.

[0032] Add the above CMC glue solution again for mixing and dispersion. The mass of the CMC glue solution added at this time is 0.8-1 of the mass of the CMC glue solution added last time.

[0033] After adding deionized water and styrene-butadiene rubber (SBR), vacuum defoaming and stirring were performed to obtain electrode slurry.

[0034] The present invention also provides a method for preparing an electrode, comprising the following steps: The electrode slurry is coated on the copper foil and heated and dried; Cool to room temperature in a constant temperature and humidity space to obtain a (negative) electrode.

[0035] During the test, the copper foil was replaced with a plastic film, and the resistivity of the graphite layer on the plastic film was ≤0.75Ω•cm.

[0036] The principle of the present invention is: some conductive bases are grafted onto carboxymethyl cellulose salts through chemical bonds, and then some conductive monomers that can form delocalized π molecular orbitals are added, and conductive bases and conductive monomers are formed into conductive channels through polymerization reactions. Since there is a covalent bond between the conductive monomers of the conductive layer and the carboxymethyl cellulose salt, the conductive layer of the material will not peel off and agglomerate during the later dissolution and stirring process. The carboxymethyl cellulose derivative prepared by the present invention is applied to electrode slurry, which can not only provide viscosity and stable dispersion slurry, but also the dried carboxymethyl cellulose has its own conductive channel and low resistivity, so that it is no longer just a stumbling block to block the movement of electrons, and fundamentally improves the non-conductive properties of CMC materials.

[0037] In some embodiments of the present invention, the reaction principle is as shown below:

[0038] In the formula, 10≤n≤49, and n is an integer.

[0039] By adopting the above technical scheme, compared with the prior art, the advantages of the present invention are: the preparation method of the carboxymethyl cellulose derivative of the present invention forms a delocalized π molecular orbital conductive monomer by grafting the carboxymethyl cellulose salt, and the two are chemically bonded, so that the carboxymethyl cellulose has its own conductive channel and low resistivity, which fundamentally improves the non-conductive properties of the CMC material. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present invention.

[0041] In order to fundamentally solve the problem that "carboxymethyl cellulose is a poor conductor", the present invention provides a synthesis idea and preparation method for reducing the resistance of carboxymethyl cellulose, and the obtained carboxymethyl cellulose derivative has a grafted conductive polymer, which is a conductive group having a delocalized π orbital; grafting refers to forming a covalent bond with the carboxymethyl cellulose salt through an active cross-linking group. The mass proportion of the carboxymethyl cellulose salt in the carboxymethyl cellulose derivative is greater than the mass proportion of the conductive polymer.

[0042] The mass of the conductive polymer is 2-20% of the mass of the carboxymethyl cellulose salt; the conductive group forming the delocalized π orbital is the thiophene group; and the active cross-linking group is the ethylene oxide group.

[0043] The preparation method of a carboxymethyl cellulose derivative for an electrode comprises the following steps: (1) Preparation of carboxymethyl cellulose conductive base points. Carboxymethyl cellulose is grafted with a bifunctional compound. The first reactive group of the bifunctional compound is an ethylene oxide group; the second reactive group is a thiophene group that can form a delocalized π orbital morphology. The reaction is carried out under an acid or base catalyst to obtain a carboxymethyl cellulose conductive matrix.

[0044] (2) Linking conductive base points. Neutralize the above system, add thiophene monomer and catalyst, catalyze polymerization, and obtain a crude product of carboxymethyl cellulose derivative.

[0045] (3) The crude product after the above reaction is washed with ethanol several times, dried and crushed to obtain a purified carboxymethyl cellulose derivative.

[0046] Based on the above purpose and principle, the preparation method of the carboxymethyl cellulose derivative of the present invention specifically comprises the following steps: Step 1: Preparation of carboxymethyl cellulose conductive matrix Mix carboxymethyl cellulose salt, bifunctional compound and solvent; add the first catalyst to the system, carry out the first reaction, and obtain the carboxymethyl cellulose conductive matrix. The mass ratio of carboxymethyl cellulose salt, bifunctional compound and the first catalyst is 100:0.5-1:0.05-0.2. The first reaction is carried out at room temperature (25-35°C) for 1-5 hours.

[0047] The carboxymethyl cellulose salt is sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose, and the solvent is preferably ethanol. The first catalyst is an alkaline substance such as sodium hydroxide or an acidic substance such as acetic acid or hydrochloric acid, and the sodium hydroxide is preferably a 48% sodium hydroxide aqueous solution.

[0048] The bifunctional compound has a first reactive group for connecting to the carboxymethyl cellulose salt and a second reactive group for connecting to the conductive monomer. The first reactive group is an epoxy group, preferably an oxirane group. The second reactive group is a group capable of forming a delocalized π orbital morphology after polymerization, preferably a thiophene group. More preferably, the bifunctional compound is 2-((thiophen-2-ylmethoxy)methyl)oxirane.

[0049] The reaction principle of step 1 is shown below:

[0050] Step 2: Preparation of crude carboxymethyl cellulose derivatives The system is adjusted to be neutral, and a conductive monomer and a second catalyst are added to carry out a second reaction to obtain a carboxymethyl cellulose derivative. The mass ratio of the carboxymethyl cellulose salt, the conductive monomer and the second catalyst is 100:5-20:2-4. The second reaction is carried out at 45-65°C for 1-5 hours.

[0051] The conductive monomer contains a conductive group capable of forming a delocalized π orbital morphology, and is preferably the same as the conductive group in the bifunctional compound, that is, a thiophene monomer.

[0052] The second catalyst is one or more selected from ferric chloride, ammonium persulfate, potassium persulfate, sodium persulfate, and ferric p-toluenesulfonate, and the added amount is 10-50% of the mass of thiophene, preferably ammonium persulfate.

[0053] If the first catalyst is an alkaline substance, an acidic substance is added to the system to adjust the system to be neutral; if the first catalyst is an acidic substance, an alkaline substance is added to the system to adjust the system to be neutral.

[0054] The reaction principle of step 2 is shown below:

[0055] In the formula, 10≤n≤49, and n is an integer.

[0056] Step 3: Post-processing The crude product of the carboxymethyl cellulose derivative is washed with ethanol, dried and crushed in sequence to obtain a treated and purified carboxymethyl cellulose derivative.

[0057] The carboxymethyl cellulose derivative prepared according to the above preparation method has the following structural formula:

[0058] In the formula, 10≤n≤49, and n is an integer.

[0059] The present invention also provides a use of the above carboxymethyl cellulose derivative in electrode slurry, battery electrode or (lithium) battery. For example, an electrode slurry comprises the following raw material components by weight: 40-50 parts water Ordinary graphite 45-55 parts Conductive graphite 0.2-0.5 parts CMC 0.5-1.0 parts SBR 1.8-2.5 parts; The CMC is the above-mentioned carboxymethyl cellulose derivative.

[0060] The method for preparing the electrode slurry comprises the following steps: The carboxymethyl cellulose derivative is mixed with deionized water and stirred to obtain CMC glue solution after the carboxymethyl cellulose derivative is fully dissolved.

[0061] Ordinary graphite powder, conductive graphite powder and the above CMC glue are mixed to form the dispersed graphite powder into a dough-like state that is bonded to each other.

[0062] Add the above CMC glue solution again for mixing and dispersion.

[0063] After adding deionized water and styrene-butadiene rubber (SBR), vacuum defoaming and stirring were performed to obtain electrode slurry.

[0064] The method for preparing an electrode comprises the following steps: The electrode slurry is coated on the copper foil and heated and dried; Cool to room temperature in a constant temperature and humidity space to obtain a (negative) electrode.

[0065] During the test, the copper foil was replaced with a plastic film, and the resistivity of the graphite layer on the plastic film was ≤0.75Ω•cm.

[0066] Example 1 The preparation method of the carboxymethyl cellulose derivative of this embodiment specifically comprises the following steps: Step 1: Add sodium carboxymethyl cellulose, ethanol and 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide into a reaction kettle, add 48% sodium hydroxide aqueous solution dropwise under stirring at room temperature and continue stirring for 2 hours to obtain a carboxymethyl cellulose conductive matrix. The mass ratio of sodium carboxymethyl cellulose to 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide and 48% sodium hydroxide aqueous solution is 100:0.5:0.1.

[0067] Step 2: After adding acid to the above system for neutralization, add thiophene, disperse evenly, add ammonium persulfate, and stir at 50°C for 3 hours to obtain a crude product of low-resistance carboxymethyl cellulose. The mass ratio of sodium carboxymethyl cellulose, thiophene, and ammonium persulfate is 100:5:2.

[0068] Step 3: Wash the crude product several times with ethanol aqueous solution to remove unreacted monomers and catalysts, then dry, crush, and sieve for later use to obtain product 1.

[0069] Example 2 The preparation method of the carboxymethyl cellulose derivative of this embodiment specifically comprises the following steps: Step 1: Add lithium carboxymethyl cellulose, ethanol, and 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide to a reaction kettle, add 48% sodium hydroxide aqueous solution dropwise under stirring at room temperature and continue stirring for 5 hours to obtain a carboxymethyl cellulose conductive matrix. The mass ratio of lithium carboxymethyl cellulose to 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide and 48% sodium hydroxide is 100:0.5:0.2.

[0070] Step 2: After neutralizing with acid in the above system, add thiophene, disperse evenly, add ammonium persulfate, and react at 55°C with stirring for 5 hours to obtain a crude product of low-resistance carboxymethyl cellulose. The mass ratio of lithium carboxymethyl cellulose, thiophene, and ammonium persulfate is 100:10:2.

[0071] Step 3: Wash the crude product several times with ethanol aqueous solution to remove unreacted monomers and catalysts, then dry, crush, and sieve for later use to obtain Product 2.

[0072] Example 3 The preparation method of the carboxymethyl cellulose derivative of this embodiment specifically comprises the following steps: Step 1: Add sodium carboxymethyl cellulose, ethanol, and 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide into a reaction kettle, add acetic acid dropwise under stirring at room temperature and continue stirring for 3 hours to obtain a carboxymethyl cellulose conductive matrix. The mass ratio of sodium carboxymethyl cellulose to 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide and acetic acid is 100:1:0.1.

[0073] Step 2: After adding alkali to the above system for neutralization, add thiophene, disperse evenly, add ferric chloride, and stir at 55°C for 3 hours to obtain a crude product of low-resistance carboxymethyl cellulose. The mass ratio of sodium carboxymethyl cellulose, thiophene, and ferric chloride is 100:15:4.

[0074] Step 3: Wash the crude product several times with ethanol aqueous solution to remove unreacted monomers and catalysts, then dry, crush, and sieve for later use to obtain Product 3.

[0075] Example 4 The preparation method of the carboxymethyl cellulose derivative of this embodiment specifically comprises the following steps: Step 1: Add sodium carboxymethyl cellulose, ethanol, and 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide into a reaction kettle, add hydrochloric acid dropwise under stirring at room temperature and continue stirring for 4 hours to obtain a carboxymethyl cellulose conductive matrix. The mass ratio of sodium carboxymethyl cellulose to 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide and hydrochloric acid is 100:1:0.1.

[0076] Step 2: After adding alkali to the above system for neutralization, add thiophene, disperse evenly, add ferric chloride, and stir at 60°C for 5 hours to obtain a crude product of low-resistance carboxymethyl cellulose. The mass ratio of sodium carboxymethyl cellulose, thiophene, and ferric chloride is 100:20:4.

[0077] Step 3: Wash the crude product several times with ethanol aqueous solution to remove unreacted monomers and catalysts, then dry, crush, and sieve for later use to obtain product 4.

[0078] Comparative Example 1 does not contain active cross-linking groups The preparation method of the carboxymethyl cellulose derivative of this comparative example specifically comprises the following steps: Step 1: Add sodium carboxymethyl cellulose, ethanol and thiophene into a reaction kettle, add ammonium persulfate after uniform dispersion, and stir at 55° C. for 5 hours to obtain a crude product. The mass ratio of carboxymethyl cellulose, thiophene and ammonium persulfate is 100:10:3.

[0079] Step 2: Wash the crude product several times with ethanol aqueous solution to remove unreacted monomers and catalysts, then dry, crush, and sieve for later use to obtain product 5.

[0080] Comparative Example 2: Less thiophene added after crosslinking The preparation method of the carboxymethyl cellulose derivative of this comparative example specifically comprises the following steps: Step 1: Add sodium carboxymethyl cellulose, ethanol, and 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide to a reaction kettle, add sodium hydroxide aqueous solution dropwise under stirring at room temperature and continue stirring for 2 hours to obtain a carboxymethyl cellulose conductive matrix. The mass ratio of carboxymethyl cellulose to 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide and 48% sodium hydroxide aqueous solution is 100:0.2:0.1.

[0081] Step 2: After neutralizing with acid in the above system, add thiophene, disperse evenly, add ammonium persulfate, and stir at 55°C for 4 hours to obtain a crude product of low-resistance carboxymethyl cellulose. The mass ratio of carboxymethyl cellulose, thiophene, and ammonium persulfate is 100:1:0.3.

[0082] Step 3: Wash the crude product several times with ethanol aqueous solution to remove unreacted monomers and catalysts, then dry, crush, and sieve for later use to obtain product 6.

[0083] Comparative Example 3: Thiophene added after crosslinking The preparation method of the carboxymethyl cellulose derivative of this comparative example specifically comprises the following steps: Step 1: Add sodium carboxymethyl cellulose, ethanol, and 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide to a reaction kettle, add sodium hydroxide aqueous solution dropwise under stirring at room temperature and continue stirring for 2 hours to obtain a carboxymethyl cellulose conductive matrix. The mass ratio of carboxymethyl cellulose to 2-((thiophen-2-ylmethoxy)methyl)ethylene oxide and 48% sodium hydroxide aqueous solution is 100:1:0.1.

[0084] Step 2: After neutralizing with acid in the above system, add thiophene, disperse evenly, add ammonium persulfate, and react at 55°C with stirring for 5 hours to obtain a crude product of low-resistance carboxymethyl cellulose. The mass ratio of carboxymethyl cellulose, thiophene, and ammonium persulfate is 100:25:5.

[0085] Step 3: Wash the crude product several times with ethanol aqueous solution to remove unreacted monomers and catalysts, then dry, crush, and sieve for later use to obtain product 7.

[0086] Comparative Example 4 Ordinary CMC This comparative example is a common commercially available CMC purchased from Changshu Weiyi Technology Co., Ltd., model BH90-III.

[0087] Example 5 Electrode slurry and electrode and preparation method thereof The electrode slurry of this embodiment includes the following raw material components by weight: Water 45.44 parts Ordinary graphite 51.40 parts Conductive graphite 0.38 parts CMC 0.64 parts SBR 2.14 copies; The CMC is the above-mentioned carboxymethyl cellulose derivative.

[0088] The method for preparing the electrode slurry comprises the following steps: 1. Add 492.5 g of deionized water into a beaker, slowly add 7.5 g of the carboxymethyl cellulose derivative prepared above while stirring, and continue stirring for 3 hours to fully dissolve it to obtain CMC glue solution for later use.

[0089] 2. Add 300g of common graphite powder, 2.2g of conductive graphite powder and 137g of CMC glue into a 1L mixing and dispersing device, turn on the stirring and dispersing disks at the same time, and stir for 1 hour to make the dispersed graphite powder form a dough that sticks to each other.

[0090] 3. Add 112 g CMC glue and stir and disperse for 2 hours.

[0091] 4. After adding 20 g of deionized water and 12.5 g of styrene-butadiene rubber (SBR), vacuum defoaming was performed and stirring was performed for 1 hour to obtain electrode slurry.

[0092] The method for preparing the electrode of this embodiment comprises the following steps: 1. Set the coating thickness of the coater to 70 microns.

[0093] 2. Turn on the vacuum pump to absorb the copper foil, add electrode slurry and apply it.

[0094] 3. After coating, cover the lid of the coating machine, turn on the heating and bake for 30 minutes.

[0095] 4. Place the electrode (including the graphite layer) prepared above in a constant temperature and humidity room for 4 hours, and then roll it 5 times in one direction with a 10 kg roller to compact it to obtain a battery (negative) electrode.

[0096] Test and Results Discussion The carboxymethyl cellulose derivative product (CMC) in the above examples or comparative examples is respectively prepared into a conductive graphite layer, and the preparation steps are as follows: 1. Set the coating thickness of the coater to 70 microns.

[0097] 2. Turn on the vacuum pump to absorb the plastic film, add the electrode slurry and apply it.

[0098] 3. After coating, cover the coater, turn on the heating and bake for 30 minutes to dry.

[0099] 4. Place the plastic film (including the graphite layer) prepared above in a constant temperature and humidity room for 4 hours, and then roll it 5 times in one direction with a 10kg roller to compact it.

[0100] 5. The resistivity of the graphite layer was tested using a ST2258C four-probe tester (straight four-probe, needle distance 2.0 mm). The experimental results are as follows:

[0101] From the data in the above table, we can see that: 1. Compared with ordinary CMC, the CMC prepared by the embodiment can reduce the resistivity of the graphite layer. Its resistivity can be as low as 23.5%-28.7% of the resistivity of the negative electrode slurry prepared by using ordinary CMC.

[0102] 2. The test results of using the CMC product of Comparative Example 1 to prepare the negative electrode graphite layer are similar to the resistivity of ordinary CMC. The reason may be that the CMC prepared in Comparative Example 1, after being dissolved in the early stage, the conductive layer adsorbed on its surface loses its carrier, and because the polymer formed later has strong lipophilicity, it is adsorbed on the graphite surface, losing its significance in reducing the resistivity of CMC.

[0103] 3. The resistivity of the graphite negative electrode layer prepared using the CMC of Comparative Example 2 is close to that of ordinary CMC. The reason may be that the amount of thiophene added is small, resulting in fewer conductive channels formed by the reaction, so the resistivity increases.

[0104] 4. The CMC of Comparative Example 3 is used to prepare the graphite negative electrode layer, which has a relatively low resistivity. However, the conductive chain is oleophilic and not hydrophilic. Due to the increase in molecular weight, the molecular chain becomes longer, resulting in larger particles of insoluble matter, forming obvious insoluble matter. The insoluble matter is prone to sharp points during the preparation process, affecting the product quality and the application of the product in the battery.

[0105] The carboxymethyl cellulose derivative for electrode of the present invention comprises carboxymethyl cellulose and a conductive polymer grafted on the carboxymethyl cellulose, and the conductive groups are connected by chemical bonds so that the conductive groups become multiple branches of CMC. The conductive polymer contains a group forming a delocalized π orbital, preferably a thiophene group; the mass proportion of carboxymethyl cellulose in the derivative is greater than that of the conductive polymer. The preparation method is a two-step synthesis method, which specifically comprises the following steps: 1. Preparing a conductive base point of carboxymethyl cellulose. Covalently grafting conductive base points at different points of the carboxymethyl cellulose chain through a grafting chemical reaction; 2. Linking conductive base points through a polymerization reaction of monomers. Adding monomers and catalysts can extend or link the conductive points, thereby achieving the purpose of conductivity. The carboxymethyl cellulose derivative prepared by this method, in addition to retaining the dispersion, water retention, thickening and other properties of the original carboxymethyl cellulose, has a significantly reduced resistivity of the negative electrode graphite layer of the battery prepared by the carboxymethyl cellulose derivative.

[0106] The equipment and raw materials used in the above-mentioned embodiments can be purchased from the market or are commonly used in this field. The methods in the above-mentioned embodiments, if not otherwise specified, are conventional methods in this field. The raw materials not specifically specified in the embodiments are all obtained commercially. The operation without special mention of temperature is carried out at room temperature. The operating methods and conditions not specifically specified can adopt the known or conventional means and conditions in this field. The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise range or value, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0107] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a carboxymethyl cellulose derivative, characterized in that: The steps include: mixing a carboxymethyl cellulose salt, a bifunctional compound, and a solvent; Adding a first catalyst into the system to carry out a first reaction to obtain a carboxymethyl cellulose conductive matrix; The system is adjusted to be neutral, a conductive monomer and a second catalyst are added, and a second reaction is performed to obtain the carboxymethyl cellulose derivative; The bifunctional compound has a first reactive group for connecting with the carboxymethyl cellulose salt and a second reactive group for connecting with the conductive monomer.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the carboxymethyl cellulose salt, the bifunctional compound and the first catalyst is 100:0.5-1:0.05-0.

2.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the carboxymethyl cellulose salt, the conductive monomer and the second catalyst is 100:5-20:2-4.

4. The preparation method according to claim 1, characterized in that: The first reactive group is an epoxy group.

5. The preparation method according to claim 4, characterized in that: The epoxy group is an ethylene oxide group.

6. The preparation method according to claim 1, characterized in that: The conductive monomer contains a conductive group capable of forming a delocalized π orbital morphology.

7. The preparation method according to claim 6, characterized in that: The conductive group is a thiophene group.

8. The preparation method according to claim 6, characterized in that: The conductive monomer is a thiophene monomer.

9. The preparation method according to claim 6, characterized in that: The second reactive group is the same as the conductive group in the conductive monomer.

10. The preparation method according to claim 1, characterized in that: The bifunctional compound is 2-((thiophen-2-ylmethoxy)methyl)oxirane.

11. The preparation method according to claim 1, characterized in that: The second catalyst is one or more selected from ferric chloride, ammonium persulfate, potassium persulfate, sodium persulfate, and ferric p-toluenesulfonate.

12. The preparation method according to claim 1, characterized in that: The first catalyst is an alkaline substance, and the regulating system is neutral by adding an acidic substance into the system.

13. The preparation method according to claim 1, characterized in that: The first catalyst is an acidic substance, and the regulating system is neutral by adding an alkaline substance into the system.

14. The preparation method according to claim 1, characterized in that: The carboxymethyl cellulose salt is sodium carboxymethyl cellulose and / or lithium carboxymethyl cellulose.

15. The preparation method according to claim 1, characterized in that: The first reaction is carried out at room temperature for 1-5 hours.

16. The preparation method according to claim 1, characterized in that: The second reaction is carried out at 45-65°C for 1-5 hours.

17. The preparation method according to any one of claims 1 to 16, characterized in that: The step also includes post-processing: washing, drying and crushing the carboxymethyl cellulose derivative in sequence to obtain the treated carboxymethyl cellulose derivative.

18. A carboxymethyl cellulose derivative prepared according to the preparation method according to any one of claims 1 to 17.

19. A carboxymethyl cellulose derivative, characterized in that The structural formula of the derivative is as follows: ； In the formula, 10≤n≤49, and n is an integer.

20. Use of the carboxymethyl cellulose derivative according to claim 18 or 19 in a battery electrode.

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