Framework type nanocellulose positive electrode binder and preparation method and application thereof

Abstract

The invention belongs to the field of lithium ion batteries, and discloses a lithium ion battery skeleton type nanocellulose positive electrode binder and a preparation method and application thereof. The skeleton type nanocellulose positive electrode binder comprises nanocellulose, a cross-linking agent and a lithium salt, the mass fraction of the nanocellulose accounts for 70-95 wt% of the total amount of the binder, the mass fraction of the cross-linking agent accounts for 2-10 wt% of the total amount of the binder, and the mass fraction of the lithium salt accounts for 5-20 wt% of the total amount of the binder. After the binder is cured, a continuous three-dimensional ion transmission channel skeleton structure is formed, and a good and smooth conduction path is provided for intercalation-deintercalation of lithium ions while a positive electrode active material is fixed, so that the cycle performance and the rate capability of the battery are improved. The binder is rich in raw material source and low in price, and large-scale commercial production can be achieved easily.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and more specifically, relates to a framework-type nanocellulose cathode binder, its preparation method, and its application. Background Technology

[0002] In the manufacturing and use of lithium-ion batteries, binders, as key materials connecting electrode active materials, conductive agents, and current collectors, not only ensure the integrity of the electrode and the continuity of the conductive channels, but also directly affect the cycle life of the battery. Traditional binders such as polyvinylidene fluoride (PVDF) and sodium carboxymethyl cellulose (CMC), while providing a certain level of bonding strength, struggle to achieve ideal electrochemical performance during long-term cycling of lithium-ion batteries, especially exhibiting significant limitations in high-rate charge-discharge cycles and complex operating environments. In recent years, high-performance binders with three-dimensional cross-linked structures have become a research hotspot. Compared to traditional linear structures, three-dimensional cross-linked structures possess higher mechanical strength, making the electrode less prone to cracking or detachment due to volume changes caused by repeated charge-discharge cycles, thereby extending the battery's lifespan.

[0003] Cellulose-based materials, as a novel type of green binder, offer advantages such as being environmentally friendly, non-toxic, widely available, and inexpensive. The polar functional groups in the cellulose structure, such as hydroxyl and carboxyl groups, can form hydrogen bonds or other chemical bonds with the surface of active materials, thereby enhancing the adhesion between the binder and the active material and further improving the structural stability of the electrode. Furthermore, these binders can form a stable, continuous support structure between active material particles, providing a three-dimensional ion channel framework for the electrode. Summary of the Invention

[0004] In order to overcome the shortcomings and disadvantages of the existing technology, the present invention aims to provide a framework-type nanocellulose cathode binder, which can solve the problems of poor mechanical properties, low conductivity and environmental unfriendliness of binders in lithium-ion batteries.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned skeletonized nanocellulose positive electrode binder.

[0006] Another object of the present invention is to provide the application of the above-mentioned skeletonized nanocellulose positive electrode binder.

[0007] The objective of this invention is achieved through the following technical solution: The first aspect of this invention provides a framework-type nanocellulose cathode binder, the framework-type nanocellulose cathode binder comprising nanocellulose, a crosslinking agent, and a lithium salt; the nanocellulose is a product of long-chain cellulose after sulfuric acid hydrolysis, and its mass fraction is 70-95 wt% of the total binder; the crosslinking agent is one of phytic acid, citric acid, and phthalic acid, and its mass fraction is 2-10 wt% of the total binder; the lithium salt is one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrate, and its mass fraction is 5-20 wt% of the total binder.

[0008] Preferably, the molecular weight of the nanocellulose is 500~1,000 Da.

[0009] Preferably, the crosslinking agent is phytic acid and the lithium salt is lithium nitrate.

[0010] A second aspect of this invention provides a method for preparing a framework-type nanocellulose positive electrode binder, comprising the following steps: S1. Break the slurry plate into flakes and disperse it in sulfuric acid solution, and stir thoroughly at 45°C for 60 minutes; S2. Add 10 times the volume of deionized water to the mixed liquid after the above reaction to stop the reaction. Then let it stand for 6 hours to allow the nanocellulose to settle to the bottom. Pour off the supernatant to obtain the nanocellulose dispersion. S3. Wash and homogenize the above dispersion, then remove residual acid by dialysis with deionized water until the pH of the sample is close to neutral.

[0011] S4. Add crosslinking agent and lithium salt to the above sample, stir evenly, and obtain a framework nanocellulose cathode binder.

[0012] A third aspect of the present invention provides an application of a framework-type nanocellulose cathode binder in lithium-ion batteries.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The nanocellulose material used in this invention has abundant ion conduction sites, which is beneficial for the transport of lithium ions inside the electrode, thereby improving the cycle performance and rate performance of the battery.

[0014] This invention utilizes a crosslinking agent to bind nanocellulose molecules together. After the electrode is dried, a solidified skeleton structure is formed, which improves the mechanical properties of the binder and enables it to cope with the volume changes that occur during the charging and discharging process.

[0015] The raw material used in this invention is paper pulp board, which is inexpensive and widely available, effectively reducing the production cost of binders. Furthermore, water is used as a dispersant in the preparation process, making it environmentally friendly. Attached Figure Description

[0016] Figure 1 The image shows the battery cycle performance of the binder prepared in one example applied to the lithium iron phosphate cathode.

[0017] Figure 2 This is a comparison graph showing the battery cycle performance of the lithium iron phosphate cathodes prepared in Application Example 1 and Comparative Example 1. Detailed Implementation

[0018] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field. Example

[0019] A framework-type nanocellulose cathode binder comprises nanocellulose, a crosslinking agent, and a lithium salt. The nanocellulose (molecular weight 100-10,000 Da) is obtained by acid hydrolysis of long-chain cellulose and contains abundant polar functional groups.

[0020] Preparation of framework-type nanocellulose cathode binder: The raw material slurry was crushed into flakes and dispersed in sulfuric acid solution. The mixture was stirred thoroughly at 45°C for 60 minutes. Ten times the volume of deionized water was added to the mixture after the reaction to stop the reaction. The mixture was then allowed to stand for 6 hours to allow the nanocellulose to settle to the bottom. The supernatant was then poured off to obtain a nanocellulose dispersion. The dispersion was washed and homogenized. Residual acid was then removed by dialysis with deionized water until the pH of the sample was close to neutral. A crosslinking agent and lithium salt were added to the sample and stirred until homogeneous to obtain the framework-type nanocellulose cathode binder.

[0021] The aforementioned framework-type nanocellulose cathode binder is used in lithium-ion batteries, which include a lithium iron phosphate cathode and a lithium metal anode. The lithium iron phosphate cathode comprises lithium iron phosphate active material (LFP), a conductive agent (Super P), and a binder (framework-type nanocellulose). The lithium iron phosphate cathode is prepared by mixing and stirring the lithium iron phosphate active material, conductive agent, and binder in water until homogeneous, coating the mixture onto carbon-coated aluminum foil, and then drying and curing it.

[0022] Application Example 1 1. Crush the raw material slurry into flakes and disperse them in a 60% sulfuric acid solution. Stir at 45°C for 60 minutes to carry out acid hydrolysis.

[0023] 2. Add 10 times the volume of deionized water to the mixed liquid after the above reaction is completed to stop the reaction. Then let it stand for 6 hours to allow the nanocellulose to settle to the bottom. Pour off the supernatant to obtain the nanocellulose dispersion.

[0024] 3. Wash and homogenize the above dispersion, then remove residual acid by dialysis with deionized water until the pH of the sample is close to neutral. Finally, add the crosslinking agent and lithium salt to the above sample, stir evenly, and obtain the framework-type nanocellulose positive electrode binder.

[0025] 4. Lithium iron phosphate active material (LFP), conductive agent (Super P), and binder (skeletal nanocellulose) are mixed evenly in water at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The above positive electrode slurry is coated onto a carbon-coated aluminum foil current collector, dried and cured, and then cut into circular electrode sheets with a diameter of 12 mm to obtain the lithium iron phosphate positive electrode sheet.

[0026] 4. The lithium-ion battery is assembled in a glove box. The assembly sequence is: positive electrode casing, lithium iron phosphate positive electrode sheet, electrolyte, lithium sheet, and negative electrode casing. After encapsulation, a lithium-ion battery is obtained. The electrolyte consists of 1 M LiPF6 as the solute and EC, DMC, and EMC as solvents (volume ratio of 1:1:1).

[0027] Comparative Example 1 1. Dissolve PVDF in NMP (N-methylpyrrolidone) to prepare a 3% PVDF solution.

[0028] 2. Lithium iron phosphate active material (LFP), conductive agent (Super P), and binder (PVDF) are mixed evenly in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. The above positive electrode slurry is coated onto a carbon-coated aluminum foil current collector, dried, and then cut into circular electrode sheets with a diameter of 12 mm to obtain the lithium iron phosphate positive electrode sheet.

[0029] 3. The lithium-ion battery is assembled in a glove box. The assembly sequence is: positive electrode casing, lithium iron phosphate positive electrode sheet, electrolyte, lithium sheet, and negative electrode casing. After encapsulation, a lithium-ion battery is obtained. The electrolyte consists of 1 M LiPF6 as the solute and EC, DMC, and EMC as solvents (volume ratio 1:1:1).

[0030] Charge and discharge test: The lithium-ion batteries assembled in Application Example 1 and Comparative Example 1 were subjected to constant current charge-discharge tests after being left to stand at 27 °C for 2 h.

[0031] Figure 1 The image shows the cycle performance of the lithium-ion battery prepared in Application Example 1. Based on... Figure 1 It can be seen that, at the first-cycle current density of 0.1C, the lithium-ion battery using the framework nanocellulose cathode binder has an initial discharge specific capacity of 171 mAh / g and a discharge specific capacity of 157 mAh / g after 100 cycles, demonstrating excellent cycle stability.

[0032] Figure 2 This is a comparison graph showing the cycle performance of lithium-ion batteries prepared in Application Example 1 and Comparative Example 1. According to... Figure 2 It can be seen that the lithium-ion battery prepared using Example 1 has a higher discharge specific capacity and capacity retention rate during the charging and discharging process.

[0033] Test results show that the skeletonized nanocellulose cathode binder of the present invention is beneficial to enhancing the mechanical properties of the electrode and improving the transport of lithium ions inside the cathode, thereby improving the cycle stability of the lithium battery.

[0034] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery skeleton-type nanocellulose positive electrode binder, characterized in that, The framework-type nanocellulose cathode binder comprises nanocellulose, a crosslinking agent, and a lithium salt; the nanocellulose is a product of long-chain cellulose after sulfuric acid hydrolysis, and its mass fraction is 70-95 wt% of the total binder; the mass fraction of the crosslinking agent is 2-10 wt% of the total binder; and the mass fraction of the lithium salt is 5-20 wt% of the total binder.

2. The framework-type nanocellulose positive electrode binder according to claim 1, characterized in that, The nanocellulose has a molecular weight of 100 to 10,000 Da and is obtained by hydrolyzing pulp with sulfuric acid.

3. The framework-type nanocellulose positive electrode binder according to claim 1, characterized in that, The crosslinking agent is one of phytic acid, citric acid, and phthalic acid.

4. The framework-type nanocellulose positive electrode binder according to claim 1, characterized in that, The lithium salt is one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrate.

5. A method for preparing a framework-type nanocellulose positive electrode binder, characterized in that, Includes the following steps: S1. Break the slurry plate into flakes and disperse it in sulfuric acid solution, and stir thoroughly at 45°C for 60 minutes; S2. Add 10 times the volume of deionized water to the mixed liquid after the above reaction to stop the reaction. Then let it stand for 6 hours to allow the nanocellulose to settle to the bottom. Pour off the supernatant to obtain the nanocellulose dispersion. S3. Wash and homogenize the above dispersion, then remove residual acid by dialysis with deionized water until the pH of the sample is close to neutral; S4. Add crosslinking agent and lithium salt to the above sample, stir evenly, and obtain a framework nanocellulose cathode binder.

6. Application of a framework-type nanocellulose cathode binder in lithium-ion batteries.

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