A composite conductive agent, positive electrode sheet, and preparation method and application thereof

Abstract

This proposal discloses a method for preparing a composite conductive agent, comprising the following steps: dissolving a chitosan oligosaccharide base in deionized water, adding SP and CNTs after complete dissolution, ultrasonicating the mixture for 15-30 minutes, drying the mixture at 80-120°C to obtain an SP / CNTs / COS composite, and curing the dried SP / CNTs / COS composite at 800-1000°C to obtain a composite conductive agent. The composite conductive agent of this application exhibits a well-developed conductive network.

Description

Technical Field

[0001] The present invention belongs to the field of chemical energy storage batteries, and in particular relates to a composite conductive agent, a positive electrode sheet, and a preparation method and application thereof. Background Art

[0002] With the development of related new energy power battery technologies, high-performance energy and power storage devices have attracted much attention due to their advantages such as low self-discharge rate, good cycle life, high energy density and high power. Currently, the widely used positive electrode materials for energy storage devices include lithium cobalt oxide (LiCoO2, LCO), lithium manganese oxide (LiMn2O4, LMO), lithium iron phosphate (LiFePO4, LFP) and ternary materials (LiNi x Co y Mn 1-x-y O2, NCM), etc., due to their corresponding structural reasons, their electrical conductivity is often poor, which seriously limits their electrochemical performance, especially the charge and discharge performance at high rates. To solve this problem, it is necessary to add a conductive agent to the electrode material or use a mixture of multiple conductive agents to improve the conductivity of the electrode, reduce the internal polarization resistance of the battery, and thus improve the electrochemical performance of the battery. The ideal distribution of the conductive agent should meet the following three points: (1) The conductive agent is evenly dispersed to form a conductive thin layer on the surface of the active material particles; (2) The conductive agent is in close contact with the surface of the active material particles, so that electrons can effectively participate in the lithium extraction / insertion reaction; (3) The conductive agents are interconnected and conductive, forming an electron path from the current collector to each active material particle.

[0003] There are two main types of conductive agents commonly used in energy storage devices: granular conductive agents, including acetylene black, conductive carbon black Super P (SP), artificial graphite, and natural graphite; and fibrous and linear conductive agents, including metal fibers, vapor-grown carbon fibers (VGCF), and carbon nanotubes (CNTs). SP, due to its small particle size, is a point-like conductive agent; CNTs, due to their linear structure, are a linear conductive agent; and conductive graphite, due to its lamellar structure, is a planar conductive agent. Therefore, the advantages of each conductive agent can be combined to fully utilize the synergistic coupling effect to construct a conductive network. However, the conductivity is not ideal. Research has found that nitrogen atoms, due to their similar atomic radius, can easily replace lattice carbon atoms. By conjugating with lone pairs of electrons, they provide additional free electrons, imparting positive charge density to adjacent carbon atoms. Therefore, incorporating nitrogen atoms into composite conductive materials can effectively improve ionic and electronic conductivity, reducing internal resistance, and ultimately achieving and optimizing high-rate charge and discharge performance.

[0004] In the prior art, in order to further improve the performance of the conductive agent, a common method is to prepare lithium-ion batteries by simply composite coating the conductive agent (such as patents CN108258245A and CN105449155B). However, the lithium-ion batteries prepared by this method do not have a good conductive network and cannot meet the requirements of high power and high energy. Summary of the Invention

[0005] The present invention aims to provide a composite conductive agent with a good conductive network.

[0006] A preparation method of a composite conductive agent in this scheme includes the following steps: dissolving chitosan oligosaccharide in deionized water, adding SP and CNTs respectively after complete dissolution, ultrasonicating for 15 to 30 minutes, taking out and drying at 80 to 120°C to obtain an SP / CNTs / COS composite, and curing the dried SP / CNTs / COS composite at a high temperature of 800 to 1000°C to obtain a composite conductive agent.

[0007] Beneficial effects of this scheme: This scheme adopts the method of doping chitosan oligosaccharide-based COS into conductive carbon black SP and carbon nanotubes CNTs, and then utilizing the cavitation effect of ultrasound to cure the SP / CNTs / COS composite material at high temperature to obtain a composite conductive agent SCN. The composite conductive agent SCN has a good conductive network and can meet excellent power density and other performance requirements under ultra-high rate constant current discharge conditions.

[0008] Furthermore, when preparing the composite conductive agent, the addition ratio of chitosan oligosaccharide to deionized water, SP, and CNTs is 10-30 g: 20-60 mL: 5-15 g: 5-15 g.

[0009] A composite conductive agent is prepared by the above-mentioned preparation method of the composite conductive agent.

[0010] A positive electrode sheet, wherein the raw materials contain the composite conductive agent.

[0011] The method for preparing the positive electrode sheet comprises the following steps:

[0012] Step 1: Evenly mix the positive electrode material, the binder and the composite conductive agent to obtain a mixture, and then add an organic solvent and mix evenly to obtain a viscous mixed slurry;

[0013] Step 2: The mixed slurry is evenly coated on one side of the aluminum foil according to a coating thickness of 20 to 30 μm to obtain a positive electrode coating; the positive electrode coating coated on the first side is placed in a vacuum drying oven at 80 to 120 ° C and dried for 30 to 60 minutes, then taken out and coated on the second side, with a coating thickness of 20 to 30 μm, and the positive electrode coating coated on the second side is dried in a vacuum drying oven at 80 to 120 ° C for 30 to 60 minutes, and then the positive electrode coating is transferred to a vacuum drying oven at 100 to 120 ° C and dried for 8 to 12 hours and taken out;

[0014] Step 3: Roll-press the dried positive electrode coating and then cut it into positive electrode sheets.

[0015] Furthermore, during the preparation of the positive electrode sheet, the positive electrode material is lithium cobalt oxide.

[0016] Furthermore, during the preparation of the positive electrode sheet, the adhesive is polyvinylidene fluoride.

[0017] Furthermore, during the preparation of the positive electrode sheet, the organic solvent is 1-methyl-2-pyrrolidone.

[0018] Furthermore, during the preparation of the positive electrode sheet, the mass ratio of the positive electrode material, the adhesive and the composite conductive agent is 90-95:6-3:4-2.

[0019] Application of the composite conductive agent and / or positive electrode sheet in the preparation of energy storage devices.

[0020] The energy storage device is a lithium ion capacitor or a lithium ion battery.

[0021] The lithium-ion capacitor prepared using this scheme has a discharge capacity of 566.9 mAh at a high rate of 100C, and has high rate performance and capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM images of SP, CNTs and SCN;

[0023] Figure 2 SEM images of SP, CNTs, SC and SCN pole pieces;

[0024] Figure 3 The resistivity diagrams of SP, CNTs, SC and SCN electrodes;

[0025] Figure 4 AC impedance test diagrams of SP, CNTs, SC and SCN electrodes;

[0026] Figure 5 The charge and discharge capacity diagram of SP, CNTs, SC and SCN ionic capacitors at 1C rate;

[0027] Figure 6 The discharge curves of rate performance of SP, CNTs, SC and SCN ionic capacitors are shown;

[0028] Figure 7 This is the SCN ion capacitor's 1600A pulse discharge curve. DETAILED DESCRIPTION

[0029] The following is further described in detail through specific implementation methods:

[0030] Preparation of lithium ion capacitors:

[0031] Example 1:

[0032] (1) Ultrasonic-assisted technology was used to dissolve 20 g of COS (molecular weight ~50W) in 40 mL of deionized water. After complete dissolution, 8 g of SP and CNTs were added respectively. The mixture was ultrasonically treated for 20 min and then dried at 100 °C to obtain an SP / CNTs / COS composite. The dried SP / CNTs / COS composite was cured at 900 °C to obtain a composite conductive agent SCN.

[0033] (2) Lithium cobalt oxide (LiCoO2) positive electrode material, polyvinylidene fluoride (PVDF) and the composite conductive agent (SCN) prepared in (1) were weighed in a planetary stirring tank at a mass ratio of 92.5:4:3.5. The mixture was mixed and ground in a planetary stirring tank at a certain rotation and revolution speed and with ultrasonic assistance for about 45 minutes to obtain a uniform mixture. An appropriate amount of 1-methyl-2-pyrrolidone (NMP) organic solvent was then added and stirred to obtain a viscous mixed slurry with moderate viscosity. The prepared mixed slurry was evenly coated on an aluminum foil (12 μm) with a designed coating thickness of 25 μm using a small coating machine to obtain a positive electrode coating. Place the positive electrode coating in a vacuum drying oven at 100°C for 45 minutes to fully volatilize the NMP, then take it out and coat the second side. After drying the positive electrode coating on the second side in a vacuum drying oven at 100°C for 45 minutes, transfer the positive electrode coating to a vacuum drying oven at 110°C for 10 hours and take it out. The drying time does not need to be too long to avoid oxidation. Use a roller machine to roll the dried positive electrode coating to 45μm (excluding the thickness of the current collector), and then use a slitting machine to cut the rolled double-sided electrode sheet into the designed SCN electrode sheet (SCN electrode).

[0034] (3) Assemble the SCN electrode prepared in (2) and the corresponding negative electrode into a soft-pack SCN lithium-ion capacitor. The entire assembly process is carried out in a dry room and the humidity is strictly controlled. After assembly, it is encapsulated with an aluminum-plastic mold and placed in a vacuum oven and baked at 45°C for 10 hours before being removed and injected with liquid. During the assembly of the lithium-ion capacitor, it is necessary to ensure that there are no operational errors, that the positive and negative electrodes do not contact to cause a short circuit, and that there are no bubbles between the diaphragm and the electrode. The seal is tight and air is isolated to avoid affecting the performance of the lithium-ion capacitor.

[0035] Example 2:

[0036] (1) 55.054 g of lithium cobalt oxide (LiCoO2) cathode material, polyvinylidene fluoride (PVDF), and SP were weighed in a planetary agitator at a mass ratio of 92.5:4:3.5. The mixture was mixed and ground in a planetary agitator at a certain rotation and revolution speed with ultrasonic assistance for about 45 minutes to obtain a uniform mixture. An appropriate amount of 1-methyl-2-pyrrolidone (NMP) organic solvent was then added and stirred to obtain a viscous mixed slurry with moderate viscosity. The prepared mixed slurry was evenly coated on aluminum foil (12 μm) using a small coating machine according to the designed coating thickness of 25 μm. Place the first side coated electrode in a vacuum drying oven at 100°C for 45 minutes to fully volatilize the NMP, then take it out and proceed with the second side coating. After drying the coated electrode in a vacuum drying oven at 100°C for 45 minutes, transfer the electrode to a 110°C vacuum drying oven and dry it for 10 hours. The drying time does not need to be too long to avoid oxidation. Use a roller machine to roll the dried positive electrode coating to 45μm (excluding the thickness of the current collector), and then use a slitting machine to cut the rolled double-sided electrode into the designed SP electrode (SP electrode).

[0037] (2) Assemble the SP electrode prepared in (1) and the corresponding negative electrode into a soft-pack SP lithium-ion capacitor. The entire assembly process is carried out in a dry room and the humidity is strictly controlled. After assembly, it is encapsulated with an aluminum-plastic mold and placed in a vacuum oven and baked at 45°C for 10 hours. Remove and inject liquid. During the assembly of the lithium-ion capacitor, it is necessary to ensure that there are no operational errors, the positive and negative electrodes do not contact to cause a short circuit, and there are no bubbles between the diaphragm and the electrode. The seal is tight and air is isolated to avoid affecting the performance of the lithium-ion capacitor.

[0038] Example 3:

[0039] (1) 55.054 g of lithium cobalt oxide (LiCoO2) cathode material, polyvinylidene fluoride (PVDF), and CNTs were weighed in a planetary agitator at a mass ratio of 92.5:4:3.5. The mixture was mixed and ground in a planetary agitator at a certain rotation and revolution speed with ultrasonic assistance for approximately 45 minutes to obtain a uniform mixture. An appropriate amount of 1-methyl-2-pyrrolidone (NMP) organic solvent was then added and stirred to obtain a viscous mixed slurry with moderate viscosity. The prepared mixed slurry was evenly coated on aluminum foil (12 μm) using a small coating machine according to the designed coating thickness of 25 μm. Place the first side coated electrode in a vacuum drying oven at 100°C for 45 minutes to fully volatilize the NMP, then take it out and proceed with the second side coating. After drying the coated electrode in a vacuum drying oven at 100°C for 45 minutes, transfer the electrode to a 110°C vacuum drying oven and dry it for 10 hours before taking it out. The drying time does not need to be too long to avoid oxidation. Use a roller machine to roll the dried positive electrode coating to 45μm (excluding the thickness of the current collector), and then use a slitting machine to cut the rolled double-sided electrode into the designed CNTs electrode (CNTs electrode).

[0040] (2) Assemble the CNTs electrode prepared in (1) and the corresponding negative electrode into a soft-package CNTs lithium-ion capacitor. The entire assembly process is carried out in a dry room and the humidity is strictly controlled. After assembly, it is encapsulated with an aluminum-plastic mold and placed in a vacuum oven and baked at 45°C for 10 hours before being removed and injected with liquid. During the assembly of the lithium-ion capacitor, it is necessary to ensure that there are no operational errors, that the positive and negative electrodes do not contact to cause a short circuit, and that there are no bubbles between the diaphragm and the electrode. The seal is tight and air is isolated to avoid affecting the performance of the lithium-ion capacitor.

[0041] Example 4:

[0042] (1) 55.054 g of lithium cobalt oxide (LiCoO2) cathode material, polyvinylidene fluoride (PVDF), SP, and CNTs were weighed in a planetary agitator at a mass ratio of 92.5:4:1.75:1.75. The mixture was mixed and ground in a planetary agitator at a certain rotation and revolution speed with ultrasonic assistance for about 45 minutes to obtain a uniform mixture. An appropriate amount of 1-methyl-2-pyrrolidone (NMP) organic solvent was then added and stirred to obtain a viscous mixed slurry with moderate viscosity. The prepared mixed slurry was evenly coated on aluminum foil (12 μm) using a small coating machine according to the designed coating thickness of 25 μm. Place the first side coated electrode in a vacuum drying oven at 100°C for 45 minutes to fully volatilize the NMP, then take it out and proceed with the second side coating. After drying the coated electrode in a vacuum drying oven at 100°C for 45 minutes, transfer the electrode to a 110°C vacuum drying oven and dry it for 10 hours before taking it out. The drying time does not need to be too long to avoid oxidation. Use a roller machine to roll the dried positive electrode coating to 45μm (excluding the thickness of the current collector), and then use a slitting machine to cut the rolled double-sided electrode into the designed SC electrode (SC electrode).

[0043] (2) Assemble the SC electrode prepared in (1) and the corresponding negative electrode into a soft-pack SC lithium-ion capacitor. The entire assembly process is carried out in a dry room and the humidity is strictly controlled. After assembly, it is encapsulated with an aluminum-plastic mold and placed in a vacuum oven and baked at 45°C for 10 hours. Remove and inject liquid. During the assembly of the lithium-ion capacitor, it is necessary to ensure that there are no operational errors, the positive and negative electrodes do not contact to cause a short circuit, and there are no bubbles between the diaphragm and the electrode. The seal is tight and air is isolated to avoid affecting the performance of the lithium-ion capacitor.

[0044] The composite conductive agent SCN is a fast ion conductor material with a point-line structure and positive cloud density. It can form a three-dimensional conductive network structure with lithium cobalt oxide positive electrode material and has higher electrical conductivity. The formed composite conductive agent material has a higher lithium ion diffusion coefficient and excellent electrochemical properties as the positive electrode of lithium ion capacitors.

[0045] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a composite conductive agent, characterized in that: The following steps are involved: Chitosan oligosaccharide COS is dissolved in deionized water, and SP and CNTs are added respectively after complete dissolution. The mixture is ultrasonicated for 15 to 30 minutes, taken out and dried at 80 to 120°C to obtain an SP / CNTs / COS composite. The dried SP / CNTs / COS composite is cured at a high temperature of 800 to 1000°C to obtain a composite conductive agent. When preparing the composite conductive agent, the addition ratio of chitosan oligosaccharide COS to deionized water, SP, and CNTs is 10 to 30 g: 20 to 60 mL: 5 to 15 g: 5 to 15 g.

2. A composite conductive agent, characterized in that: Prepared by the preparation method according to claim 1.

3. A positive electrode sheet, characterized in that: The raw materials include the composite conductive agent according to claim 2.

4. The method for preparing the positive electrode sheet according to claim 3, characterized in that: The following steps are involved: Step 1: Evenly mix the positive electrode material, the binder and the composite conductive agent to obtain a mixture, and then add an organic solvent and mix evenly to obtain a viscous mixed slurry; Step 2: The mixed slurry is evenly coated on one side of the aluminum foil at a coating thickness of 20 to 30 μm to obtain a positive electrode coating; the positive electrode coating coated on the first side is placed in a vacuum drying oven at 80 to 120 ° C and dried for 30 to 60 minutes, then taken out and coated on the second side, with a coating thickness of 20 to 30 μm, and the positive electrode coating coated on the second side is dried in a vacuum drying oven at 80 to 120 ° C for 30 to 60 minutes, and then the positive electrode coating is transferred to a vacuum drying oven at 100 to 120 ° C and dried for 8 to 12 hours before being taken out; Step 3: Roll-press the dried positive electrode coating and then cut it into positive electrode sheets.

5. The method for preparing the positive electrode sheet according to claim 4, wherein: The positive electrode material is lithium cobalt oxide.

6. The method for preparing the positive electrode sheet according to claim 4, wherein: The adhesive is polyvinylidene fluoride.

7. The method for preparing a positive electrode sheet according to claim 4, wherein: The organic solvent is 1-methyl-2-pyrrolidone.

8. The method for preparing a pole piece according to claim 4, characterized in that: The mass ratio of the positive electrode material, the adhesive and the composite conductive agent is 90-95:6-3:4-2.

9. Use of the composite conductive agent according to claim 2 or the positive electrode sheet according to claim 3 in the preparation of an energy storage device.

10. Use of the composite conductive agent or positive electrode sheet according to claim 9 in preparing an energy storage device, characterized in that: The energy storage device is a lithium ion capacitor or a lithium ion battery.

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