High-purity fiber for cellulose-based negative electrode of lithium battery and preparation method of high-purity fiber

Abstract

The invention discloses a high-purity fiber for a cellulose-based negative electrode of a lithium battery and a preparation method of the high-purity fiber, and belongs to the technical field of lithium battery negative electrode materials. In the preparation process of the high-purity fiber for the cellulose-based negative electrode of the lithium battery, cotton fibers are filled with alkali liquor, then the temperature is controlled to be the critical value of the freezing point of the alkali liquor, and the high-purity fiber for the cellulose-based negative electrode of the lithium battery is obtained at the temperature. The alkali liquor expands in volume, lignin in the cotton fibers is separated from a hemicellulose binding layer, so that impurities in the cotton fibers are effectively removed, the purity of the cellulose-based fibers is improved, the network structure of the fibers is not damaged, the method can be better suitable for the volume change of active substances in a negative electrode material, and the lithium storage capacity of the negative electrode is improved; and the cellulose-based fiber is further subjected to activating treatment, so that the number of active groups on the surface of the cellulose-based fiber is increased, interaction can be generated between the cellulose-based fiber, a lithium battery negative electrode active material and a current collector, and the stability of an electrode structure is protected.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery anode materials, and particularly relates to a high-purity fiber for a cellulose-based anode of a lithium battery and a preparation method thereof. Background Art

[0002] Compared with traditional fossil energy, lithium batteries are widely used in energy storage, electronics and electrical appliances, electric vehicles and other fields because of their advantages such as light weight, high energy density, high cycle life and environmental friendliness. The material properties of the anode of a lithium-ion battery also determine the energy density, electrochemical characteristics and safety reliability of the lithium battery.

[0003] The anode material of a lithium battery generally consists of an active material, a conductive agent and a binder. Currently, commonly used active materials include graphite materials, silicon-based materials, titanium-based materials, tin-based materials, etc. Among them, silicon-based materials have become the primary choice of active materials due to their high theoretical specific capacity, low reaction potential and abundant natural resources. However, as the active material of the anode of a lithium battery, during the reaction equilibrium process of lithiation and delithiation during the charge and discharge of the lithium battery, there is a huge volume change, resulting in problems such as particle cracking and pulverization under stress, damage to the electrode structure, and the generation of an unstable solid electrolyte interface film, which all limit the further popularization and application of lithium batteries.

[0004] Cellulose-based materials have good hydrophilicity and adaptability, as well as certain adhesiveness. When used as an anode modifier, they can significantly improve the voltage platform of a lithium battery, reduce the internal resistance of the battery, and thus improve the performance of the lithium battery. However, cellulose-based materials generally have low viscosity and high brittleness, and the electrode sheet is prone to cracking during the charge and discharge process, making it difficult to adapt to the volume effect of silicon-based materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-purity fiber for a cellulose-based anode of a lithium battery and a preparation method thereof, so as to solve the problem of damage to the structure of a lithium battery caused by the volume effect during the charge and discharge process of the anode material of the lithium battery.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] In the first aspect, the present invention provides a preparation method of a high-purity fiber for a cellulose-based anode of a lithium battery, including the following technological steps:

[0008] S1. Pretreatment: After washing, drying, pulverizing and sieving short-staple cotton, pretreated cotton fibers are obtained;

[0009] S2. Alkali treatment: Add the pretreated cotton fibers to an aqueous sodium hydroxide solution with a mass fraction of 8-12%, raise the temperature to 60-80°C, and impregnate for 60-90 minutes to obtain an alkali solution mixture;

[0010] S3. Low-temperature separation treatment: Stir and disperse the lye mixture at -6 to -4 °C for 4 to 5 h. After standing and returning to room temperature, centrifuge, wash, and dry to obtain cellulose-based fibers.

[0011] S4. Activation treatment: Add the cellulose-based fibers to an aqueous hydrogen peroxide solution, stir and disperse, add a polymer activator, raise the temperature to 30 to 50 °C, keep warm for 3 to 4 h, and finally filter, wash, and dry to obtain high-purity fibers for the negative electrode of lithium batteries made of cellulose.

[0012] The polymer activator is loaded with transition metal ions.

[0013] Preferably, the transition metal ions include Fe 3+ 、Fe 2+ 、Mn 2+ and Cu 2+ or a combination of one or more of them.

[0014] Preferably, the addition amount of the polymer activator is 2 to 5% of the mass of the cellulose-based fibers.

[0015] Preferably, the solid-liquid ratio of the pretreated cotton fibers to the sodium hydroxide aqueous solution is 1:(20 - 30).

[0016] Preferably, the mass fraction of the aqueous hydrogen peroxide solution is 5 to 10%; the solid-liquid ratio of the cellulose-based fibers to the aqueous hydrogen peroxide solution is 1:(15 - 25).

[0017] By adopting the above technical solutions, first, the short-staple cotton is pretreated to remove impurities therein, and then smaller particles are obtained by crushing and sieving. On the one hand, it can increase the specific surface area of the cotton fibers, increase the contact area between chemical reagents and cotton fibers in the following treatment process, and the small-particle cotton fibers are also more easily penetrated and acted upon by chemical reagents, accelerating the reaction rate and improving the uniformity of the reaction. On the other hand, it can improve the fluidity and operability of the fibers, and reduce the problems of caking and blockage that may occur to the cotton fibers during the post-treatment process.

[0018] Then, the pretreated cotton fibers are subjected to alkali treatment. At a certain temperature, the alkali solution can completely penetrate into the interior of the cotton fibers, causing the cotton fibers to swell. The interior of the cotton fibers is filled with the alkali solution. Then, the cotton fibers penetrated by the alkali solution are subjected to low-temperature separation treatment. The temperature is reduced to -20~-10°C, so that the alkali solution inside the cotton fibers is in a critical state at the freezing point. The density of the alkali solution decreases and the volume increases. The internal gaps of the fibers increase due to the increase in the volume of the alkali solution, which is conducive to the separation of various components inside the fibers, especially the separation of the lignin and hemicellulose binding layers. The separated lignin and hemicellulose will be degraded and destroyed by the alkali solution and enter the alkali solution, so that the impurities in the cotton fibers can be effectively removed, leaving the necessary cellulose components, and the content of cellulose is increased.

[0019] Moreover, compared with the purification of cellulose by the general alkali solution cooking method to remove impurities in cotton fibers, the low-temperature alkali solution treatment used in the present invention will not damage the network structure of the fibers and will not cause the loss of some cellulose. Furthermore, it is conducive to the formation of a cellulose-based fiber material with a complete structure and a high cellulose purity content. The cellulose-based fiber with a network structure can better adapt to the volume change of the active material of the lithium battery negative electrode material, provide enough accommodation space for the volume change during the charge and discharge process, and is also conducive to improving the lithium storage capacity of the lithium battery, thereby improving the rate performance of the lithium battery.

[0020] At the same time, in order to further improve and adapt to the application in the lithium battery negative electrode material, the cellulose-based fiber is further activated. On the one hand, the transition metal ions loaded on the polymer activator can react with hydrogen peroxide to generate free radicals. The formed free radicals can react with the hydroxyl groups and terminal aldehyde groups contained in the cellulose-based fiber to form active carboxyl groups, and can quickly terminate the reaction to avoid cellulose decomposition. The introduced carboxyl groups can have a strong interaction with the hydroxyl groups on the surface of the active material, thereby forming a stable connection, reducing the shedding of the active material particles, and further improving the cycle performance of the battery and adapting to the volume change.

[0021] On the other hand, the transition metal ions can also activate the hydroxyl groups contained in the cellulose-based fiber. While exposing more hydroxyl groups, the activity of the hydroxyl groups in the material is increased, so that the interaction force between the negative electrode material and the current collector can be improved, reducing the expansion and fracture caused by the volume effect and protecting the stability of the electrode structure.

[0022] Finally, the polymer activator can also accelerate the breakage of chemical bonds in lignin, promote the removal of residual lignin, thereby improving the cellulose purity. The improvement of fiber purity is also beneficial to the improvement of the electrochemical performance of the anode material, reducing the adverse effects of impurities on the lithiation and delithiation reactions during the charge and discharge processes. Moreover, after the activation treatment, the flexibility of the fiber is also increased, which can improve the structural stability of the lithium battery during the charge and discharge processes, not easily break, and improve the cycle performance of the lithium battery.

[0023] Preferably, the raw materials of the polymer activator include sodium polystyrene sulfonate and transition metal salts with a mass ratio of 1:(0.06 - 0.1).

[0024] Preferably, the transition metal salts include one or a combination of more of ferric sulfate, ferric nitrate nonahydrate, ferrous sulfate heptahydrate, ferrous chloride tetrahydrate, ferrous nitrate tetrahydrate, manganese sulfate, manganese chloride tetrahydrate, manganese nitrate hexahydrate, copper sulfate pentahydrate, copper chloride, and copper nitrate trihydrate.

[0025] Preferably, the molecular weight of sodium polystyrene sulfonate is 5×10 4 ~8×10 4 .

[0026] Preferably, the polymer activator is prepared by the following method:

[0027] Add sodium polystyrene sulfonate to water, stir to dissolve, then raise the temperature to 70 - 80°C, add an aqueous solution of transition metal salts in a nitrogen atmosphere, adjust the pH value of the solution to 5 - 7, stir and react for 2 - 3 h, and obtain the polymer activator after rotary evaporation.

[0028] By adopting the above technical solution, the polymer activator used in the present invention uses sodium polystyrene sulfonate as a carrier, loads transition metal ions on it, while introducing new active groups on the cellulose-based fiber, activates the cellulose-based fiber, and further improves the fiber purity, thereby improving the structural stability and electrochemical performance of the lithium battery anode material.

[0029] Among them, using sodium polystyrene sulfonate as a carrier, on the one hand, a large number of coordination active sites are contained on sodium polystyrene sulfonate, and ion exchange reactions occur with transition metal ions, and then stable complexes can be formed, and the catalytic activity of transition metal ions can also be improved, effectively catalyzing and activating the cellulose-based fiber; on the other hand, as a polymer compound, sodium polystyrene sulfonate can effectively disperse transition metal ions, prevent the aggregation of transition metal ions, provide a stable action environment for the activation of the activator, and is beneficial to the uniformity of the reaction of the cellulose-based fiber.

[0030] And sodium polystyrene sulfonate is a soluble polymer material. Loading transition metal ions within the scope provided by the present invention will not seriously affect the water solubility of sodium polystyrene sulfonate, and can maintain the water-soluble characteristics of sodium polystyrene sulfonate. Furthermore, after the cellulose-based fiber is activated by the polymer activator, it can be easily removed through filtration and washing, and will not be mixed with the cellulose-based fiber to introduce new impurities, thus affecting the electrochemical performance of the lithium battery.

[0031] In a second aspect, the present invention provides a high-purity fiber for a cellulose-based anode of a lithium battery, which is applied to the anode material of the lithium battery; it is prepared according to the preparation method of the high-purity fiber for the cellulose-based anode of the lithium battery described above.

[0032] Advantages of the present invention:

[0033] 1. The present invention provides a preparation method of a high-purity fiber for a cellulose-based anode of a lithium battery. After the cotton fiber swells in the alkali solution and is treated at a low temperature, in the critical state of the freezing point of the alkali solution, the volume of the alkali solution inside the cotton fiber increases, which is conducive to the separation of the impurity lignin and the hemicellulose binding layer in the fiber, effectively removing the impurities in the cotton fiber, and can also maintain the network structure of the fiber, thus better adapting to the volume change of the active material of the lithium battery anode, improving the lithium storage capacity, and thus improving the rate performance.

[0034] 2. In the preparation method of the high-purity fiber for the cellulose-based anode of the lithium battery of the present invention, a polymer activator is also used to activate the cellulose-based fiber, which can improve the activity of cellulose hydroxyl groups, introduce new active groups, improve the binding force with the active material, and protect the stability of the electrode structure; and it can also promote the separation and removal of residual impurities, and the improvement of fiber purity is also beneficial to improving the electrochemical performance of the anode material. Specific embodiments

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0036] Preparation example

[0037] Preparation example 1, a polymer activator, is prepared according to the following method:

[0038] Take 10 g of sodium polystyrene sulfonate (average molecular weight is 7×10 4) Add it to 500 mL of water, stir to dissolve, and then raise the temperature to 80 °C; take 0.8 g of ferrous nitrate hexahydrate and prepare an aqueous solution with a mass fraction of 10%. Add the aqueous solution of ferrous nitrate hexahydrate to the aqueous solution of sodium polystyrene sulfonate in a nitrogen atmosphere, adjust the pH value of the solution to 6, stir and react for 2 h, and obtain a polymer activator after rotary evaporation.

[0039] Preparation Example 2, a polymer activator, the difference from Preparation Example 1 is only that the addition amount of ferrous nitrate hexahydrate is 0.6 g.

[0040] Preparation Example 3, a polymer activator, the difference from Preparation Example 1 is only that the addition amount of ferrous nitrate hexahydrate is 1 g.

[0041] Preparation Example 4, a polymer activator, the difference from Preparation Example 1 is only that an equal amount of copper nitrate trihydrate is used to replace ferrous nitrate hexahydrate.

[0042] Preparation Example 5, a polymer activator, the difference from Preparation Example 1 is only that the addition amount of ferrous nitrate hexahydrate is 0.4 g.

[0043] Preparation Example 6, a polymer activator, the difference from Preparation Example 1 is only that the addition amount of ferrous nitrate hexahydrate is 1.2 g.

[0044] Example

[0045] Example 1, a high-purity fiber for the cellulose-based negative electrode of a lithium battery, is prepared according to the following process steps:

[0046] S1. Pretreatment: Wash, dry, pulverize and sieve short-staple cotton to obtain pretreated cotton fibers;

[0047] S2. Alkali treatment: Add the pretreated cotton fibers to an aqueous sodium hydroxide solution with a mass fraction of 10%, the solid-liquid ratio is 1:25, raise the temperature to 60 °C, and impregnate for 90 min to obtain an alkali solution mixture;

[0048] S3. Low-temperature separation treatment: Stir and disperse the alkali solution mixture at -5 °C for 5 h, let it stand and return to room temperature, and then obtain cellulose-based fibers after centrifugation, washing and drying;

[0049] S4. Activation treatment: Add the cellulose-based fibers to an aqueous hydrogen peroxide solution with a mass fraction of 8%, the solid-liquid ratio is 1:20, stir and disperse, add 3% of the polymer activator prepared in Preparation Example 1, raise the temperature to 40 °C, keep warm for 3 h, and finally obtain high-purity fibers for the cellulose-based negative electrode of a lithium battery after filtration, washing and drying.

[0050] Example 2. A high-purity fiber for a cellulose-based anode of a lithium battery. The difference from Example 1 is only that the mass fraction of the sodium hydroxide aqueous solution during the alkali treatment is 8%; the temperature during the low-temperature separation treatment is -4°C.

[0051] Example 3. A high-purity fiber for a cellulose-based anode of a lithium battery. The difference from Example 1 is only that the mass fraction of the sodium hydroxide aqueous solution during the alkali treatment is 12%; the temperature during the low-temperature separation treatment is -6°C.

[0052] Example 4. A high-purity fiber for a cellulose-based anode of a lithium battery. The difference from Example 1 is only that during the activation treatment, the solid-liquid ratio of the cellulose-based fiber to the hydrogen peroxide aqueous solution with a mass fraction of 8% is 1:15, and the addition amount of the polymer activator prepared in Preparation Example 1 is 2%.

[0053] Example 5. A high-purity fiber for a cellulose-based anode of a lithium battery. The difference from Example 1 is only that during the activation treatment, the solid-liquid ratio of the cellulose-based fiber to the hydrogen peroxide aqueous solution with a mass fraction of 8% is 1:25, and the addition amount of the polymer activator prepared in Preparation Example 1 is 5%.

[0054] Example 6. A high-purity fiber for a cellulose-based anode of a lithium battery. The difference from Example 1 is only that the polymer activator prepared in Preparation Example 1 is replaced with an equal amount of the polymer activator prepared in Preparation Example 2.

[0055] Example 7. A high-purity fiber for a cellulose-based anode of a lithium battery. The difference from Example 1 is only that the polymer activator prepared in Preparation Example 1 is replaced with an equal amount of the polymer activator prepared in Preparation Example 3.

[0056] Example 8. A high-purity fiber for a cellulose-based anode of a lithium battery. The difference from Example 1 is only that the polymer activator prepared in Preparation Example 1 is replaced with an equal amount of the polymer activator prepared in Preparation Example 4.

[0057] Example 9. A high-purity fiber for a cellulose-based anode of a lithium battery. The difference from Example 1 is only that the polymer activator prepared in Preparation Example 1 is replaced with an equal amount of the polymer activator prepared in Preparation Example 5.

[0058] Example 10. A high-purity fiber for a cellulose-based anode of a lithium battery. The difference from Example 1 is only that the polymer activator prepared in Preparation Example 1 is replaced with an equal amount of the polymer activator prepared in Preparation Example 6.

[0059] Comparative Example

[0060] Comparative Example 1, a high-purity fiber for a cellulose-based anode of a lithium battery, is different from Example 1 only in that the temperature is controlled at 0 °C during the low-temperature separation process.

[0061] Comparative Example 2, a high-purity fiber for a cellulose-based anode of a lithium battery, is different from Example 1 only in that the temperature is controlled at -10 °C during the low-temperature separation process.

[0062] Comparative Example 3, a high-purity fiber for a cellulose-based anode of a lithium battery, is prepared according to the following process steps:

[0063] S1. Pretreatment: The short-staple cotton is washed, dried, pulverized and sieved to obtain pretreated cotton fibers.

[0064] S2. Alkali treatment: The pretreated cotton fibers are added to an aqueous sodium hydroxide solution with a mass fraction of 10%, the solid-liquid ratio is 1:25, the temperature is raised to 60 °C, impregnated for 90 min, then the temperature is raised to 100 °C, and high-temperature cooking is carried out for 3 h. After cooling to room temperature, centrifugation, washing and drying are carried out to obtain cellulose-based fibers.

[0065] S3. Activation treatment: The cellulose-based fibers are added to an aqueous hydrogen peroxide solution with a mass fraction of 8%, the solid-liquid ratio is 1:20, stirred and dispersed, 3% of the high-molecular activator prepared in Preparation Example 1 is added, the temperature is raised to 40 °C, and kept warm for 3 h. Finally, filtration, washing and drying are carried out to obtain high-purity fibers for a cellulose-based anode of a lithium battery.

[0066] Comparative Example 4, a high-purity fiber for a cellulose-based anode of a lithium battery, is different from Example 1 only in that the aqueous hydrogen peroxide solution with a mass fraction of 8% is replaced with the same amount of deionized water during the activation treatment process.

[0067] Comparative Example 5, a high-purity fiber for a cellulose-based anode of a lithium battery, is different from Example 1 only in that the addition amount of the high-molecular activator prepared in Preparation Example 1 is 1%.

[0068] Comparative Example 6, a high-purity fiber for a cellulose-based anode of a lithium battery, is different from Example 1 only in that the addition amount of the high-molecular activator prepared in Preparation Example 1 is 7%.

[0069] Comparative Example 7, a high-purity fiber for a cellulose-based anode of a lithium battery, is different from Example 1 only in that the high-molecular activator prepared in Preparation Example 1 is replaced with an equal amount of ferrous nitrate hexahydrate.

[0070] Comparative Example 8, a high-purity fiber for a cellulose-based anode of a lithium battery, which is different from Example 1 only in that the polymer activator prepared in Preparation Example 1 is not added. The specific steps of the activation treatment process are as follows: Add the cellulose-based fiber to an aqueous hydrogen peroxide solution with a mass fraction of 8%, the solid-liquid ratio is 1:20, stir and disperse, raise the temperature to 40 °C, keep warm for 3 h, and finally obtain the high-purity fiber for a cellulose-based anode of a lithium battery through filtration, washing and drying.

[0071] Comparative Example 9, a high-purity fiber for a cellulose-based anode of a lithium battery, which is different from Example 1 only in that the obtained cellulose-based fiber is not subjected to activation treatment.

[0072] Performance detection test

[0073] 1. Cellulose purity test: The cellulose purity of the fibers obtained in the examples and comparative examples was tested according to the high-performance liquid chromatography method. The test results are shown in Table 1.

[0074] 2. Electrochemical performance test:

[0075] (1) Sample preparation: Mix silicon powder (average particle size of 80 nm), carbon black (Super-P) and the high-purity fibers obtained in the examples and comparative examples in a mass ratio of 5:3:2, and then uniformly coat them on a copper foil. After drying for 12 h, an electrode sheet is obtained. Using lithium iron phosphate as the positive electrode in an argon atmosphere and the prepared electrode sheet as the negative electrode, the electrolyte solvent is EC:DEC:DMC with a volume ratio of 1:1:1, the electrolyte solute is LiPF 6 with a concentration of 1 mol / L, the separator is a microporous polypropylene membrane, and a 2032 button battery is assembled;

[0076] (2) At a current density of 1 A / g and a temperature of 25 °C, the sample capacity was tested, and the sample capacity after 100 charge-discharge cycles was also tested. The test results are shown in Table 2.

[0077] 3. Peel strength test: Use a microcomputer-controlled electronic universal testing machine to test the peel strength between the electrode material of the sample electrode sheet obtained in Test 2 and the current collector. The test results are shown in Table 3.

[0078] Table 1 Cellulose purity test results

[0079]

[0080] Table 2 Electrochemical performance test results

[0081]

[0082] Table 3 Peel strength test results

[0083]

[0084]

[0085] According to Table 1, Table 2 and Table 3, combined with Example 1, Example 2 to Example 8, it can be seen that there are no obvious differences in the fiber cellulose purity, the capacity of the lithium battery after the first and 100th cycles, and the average peel force between Example 2 to Example 8 and Example 1, indicating that there are no obvious changes in the purity of the cellulose-based fibers obtained in Example 2 to Example 8, the electrochemical improvement ability for the negative electrode of the lithium battery, and the peel strength of the negative electrode compared with Example 1. The reason is that in Example 2 to Example 8, only the process parameters, polymer activator and ratio of the cellulose-based fibers in the preparation process are changed within the required range compared with Example 1, indicating that changing the process parameters within the required range has little effect on the obtained cellulose-based fibers.

[0086] Combined with Example 1, Example 9, Example 10 and Comparative Example 7, it can be seen that each performance of Example 9 has a slight decrease. The reason is that in Example 9, the loading amount of transition metal ions in the polymer activator is reduced. In addition to affecting the activation progress, resulting in a decrease in electrochemical performance and peel strength, it will also affect the removal of residual impurities, resulting in a slight decrease in purity; while in Comparative Example 7, no transition metal ions are loaded, and the ability to activate the groups on the surface of the cellulose-based fibers is significantly reduced, making it difficult to form active groups that can bind to the active substances, resulting in a significant decrease in performance; the purity in Example 10 has decreased. The reason is that in Example 10, the content of transition metal ions in the polymer activator is increased, resulting in a decrease in the solubility of the polymer activator in water. It is difficult to remove by simple filtration, increasing the separation difficulty. The residual polymer activator mixed with the cellulose-based fibers will affect the electrochemical performance and also cause excessive decomposition of cellulose, resulting in a decrease in performance.

[0087] Combined with Example 1 and Comparative Examples 1 to 3, it can be seen that the various performances of Comparative Examples 1 to 3 have significantly decreased compared to Example 1. In Comparative Examples 1 to 3, the temperature for separating cellulose impurities from the lye was changed compared to Example 1. In Comparative Example 1, the low-temperature separation temperature was slightly increased, and the lye did not reach the critical value of the freezing point. Although the volume slightly increased, the separation effect of lignin and hemicellulose in the fiber decreased, thus affecting the purity of the cellulose-based fiber and the material performance when applied to the negative electrode of a lithium battery. In Comparative Example 2, the low-temperature separation temperature was further decreased, and this temperature was below the freezing point of the lye, causing the lye to freeze and the separation effect to significantly decrease, and the purity of the cellulose-based fiber to significantly decrease. In Comparative Example 3, the cellulose-based fiber was treated by the form of conventional lye cooking. Under high-temperature cooking, the network structure of the cellulose-based fiber would be damaged to a certain extent. When used as the negative electrode material of a lithium battery, it was not only difficult to adapt to the volume change of the active material, but also the lithium storage capacity of the negative electrode material would be decreased, resulting in the decrease of the electrochemical performance of the lithium battery.

[0088] Combined with Example 1, Comparative Examples 4 to 6, and Comparative Examples 8 and 9, it can be seen that the various performances of Comparative Examples 5 and 6 have decreased compared to Example 1, and the performances of Comparative Examples 4, 8, and 9 have significantly decreased. The reason is that in Comparative Example 5, the addition amount of the polymer activator was reduced, the activity of the cellulose-based fiber decreased, and the number of active groups also decreased accordingly, resulting in a decrease in the modification effect on the negative electrode of the lithium battery. In Comparative Examples 8 and 9, no polymer activator was added, and the performance decreased more significantly. In Comparative Example 6, the addition amount of the polymer activator was increased, which would cause partial cellulose decomposition during the activation process, affecting the purity of the cellulose-based fiber while the cellulose content decreased, and the binding force between the active material and the negative electrode material and the current collector decreased, the peel strength decreased, and the cycle performance of the lithium battery decreased. In Comparative Example 4, hydrogen peroxide aqueous solution was not used as the solvent in the activation stage. It was difficult for transition metal ions to generate a large number of free radicals to initiate the conversion of hydroxyl groups on cellulose into active carboxyl groups with hydrogen peroxide as an intermediate, which would further reduce the binding between active substances and the stability. When used as the negative electrode material of a lithium battery, it was difficult to adapt to the volume change of the active material, resulting in a significant decrease in the capacity of the lithium battery during multiple charge and discharge cycles.

[0089] It should be noted that, in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variation thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0090] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-purity fiber for cellulose-based negative electrode of lithium battery, characterized in that: The process steps include: S1. Pretreatment: washing, drying, crushing and sieving the short-staple cotton to obtain pretreated cotton fibers; S2. Alkali treatment: adding the pretreated cotton fiber to an aqueous solution of sodium hydroxide having a mass fraction of 8 to 12%, raising the temperature to 60 to 80°C, and immersing for 60 to 90 minutes to obtain an alkali solution mixture; S3. Low temperature separation treatment: the alkali solution mixture is stirred and dispersed at -6 to -4°C for 4 to 5 hours, allowed to stand and return to room temperature, and then centrifuged, washed and dried to obtain cellulose-based fibers; S4. Activation treatment: adding cellulose-based fibers to an aqueous solution of hydrogen peroxide, stirring and dispersing, adding a polymer activator, raising the temperature to 30 to 50°C, keeping the temperature for 3 to 4 hours, and finally filtering, washing and drying to obtain a high-purity fiber for a cellulose-based negative electrode of a lithium battery; The polymer activator is loaded with transition metal ions.

2. The method for preparing high-purity fiber for cellulose-based negative electrode of lithium battery according to claim 1, characterized in that: The transition metal ions include Fe 3+ , Fe 2+ , Mn 2+ and Cu 2+ A combination of one or more of .

3. The method for preparing high-purity fiber for cellulose-based negative electrode of lithium battery according to claim 1, characterized in that: The added amount of the polymer activator is 2-5% of the mass of the cellulose-based fiber.

4. The method for preparing high-purity fiber for cellulose-based negative electrode of lithium battery according to claim 1, characterized in that: The raw materials of the polymer activator include sodium polystyrene sulfonate and transition metal salt in a mass ratio of 1: (0.06-0.1).

5. The method for preparing high-purity fiber for cellulose-based negative electrode of lithium battery according to claim 4, characterized in that: The transition metal salt includes one or more combinations of ferric sulfate, ferric nitrate nonahydrate, ferrous sulfate heptahydrate, ferrous chloride tetrahydrate, ferrous nitrate hexahydrate, manganese sulfate, manganese chloride tetrahydrate, manganese nitrate hexahydrate, copper sulfate pentahydrate, copper chloride and copper nitrate trihydrate.

6. The method for preparing high-purity fiber for cellulose-based negative electrode of lithium battery according to claim 4, characterized in that: The molecular weight of the sodium polystyrene sulfonate is 5×10 4 ~8×10 4 .

7. The method for preparing high-purity fiber for cellulose-based negative electrode of lithium battery according to claim 4, characterized in that: The polymer activator is prepared according to the following method: Sodium polystyrene sulfonate is added to water, stirred to dissolve, and then the temperature is raised to 70-80°C. An aqueous solution of a transition metal salt is added in a nitrogen atmosphere, and the pH value of the solution is adjusted to 5-7. The solution is stirred to react for 2-3 hours, and then the polymer activator is obtained after being spin-dried.

8. The method for preparing high-purity fiber for cellulose-based negative electrode of lithium battery according to claim 1, characterized in that: The solid-to-liquid ratio of the pretreated cotton fiber to the sodium hydroxide aqueous solution is 1:(20-30).

9. The method for preparing high-purity fiber for cellulose-based negative electrode of lithium battery according to claim 1, characterized in that: The mass fraction of the hydrogen peroxide aqueous solution is 5-10%; the solid-liquid ratio of the cellulose-based fiber to the hydrogen peroxide aqueous solution is 1:(15-25).

10. A high-purity fiber for a cellulose-based negative electrode of a lithium battery, characterized in that: The high-purity fiber is applied to negative electrode materials of lithium batteries; The cellulose-based negative electrode for a lithium battery is prepared by the method for preparing high-purity fibers according to any one of claims 1 to 9.

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