Dry-method electrode material, preparation method thereof and secondary battery

Abstract

The invention discloses a dry-method electrode material, a preparation method thereof and a secondary battery. The dry-method electrode material comprises a current collector and a dry-method diaphragm arranged on the surface of the current collector, the dry-method diaphragm comprises an active material and a fluorine-containing binder, the active material comprises one or two of spongy porous carbon and honeycomb porous carbon, a silicon group is formed on the active material, and the silicon group is also bonded with the fluorine-containing binder. Wherein the spongy porous carbon or the honeycomb porous carbon is used as an electrode active material, so that ion transmission and reaction sites are increased, and the conductivity of the electrode is enhanced. The silicon group on the active material is bridged with the active material and the fluorine-containing binder, so that the binding force between the active material and the fluorine-containing binder is improved, the falling of the active material in the use process of the dry-method electrode material is reduced, and the cycle performance of the obtained secondary battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of battery preparation, and particularly relates to a dry electrode material, a preparation method thereof, and a secondary battery. Background Art

[0002] As an efficient energy storage device, secondary batteries (such as lithium-ion batteries) have been widely used in fields such as mobile electronic devices and electric vehicles. Electrode materials are the core components of lithium-ion batteries. The dry electrode material preparation technology utilizes the fibrillation effect of fluorine-containing polymer binders to integrate active materials, conductive agents, and binders into one body. While reducing the use of solvents, it can prepare electrode materials with good electrochemical performance. Therefore, dry electrode materials have the advantages of being more environmentally friendly and having lower costs, and have received extensive attention in recent years. However, during the use of dry electrode materials, the dry film formed by the integration of active materials, conductive agents, and binders has the phenomena of pulverization and powder shedding, which affects the electrochemical performance of the electrode materials. Summary of the Invention

[0003] In view of this, the present application provides a dry electrode material and a preparation method thereof to solve at least one of the above technical problems. In addition, the present application also provides a secondary battery based on the above dry electrode material.

[0004] To achieve the above object, in a first aspect, the present application provides a dry electrode material, including a current collector and a dry film disposed on the surface of the current collector. The dry film includes an active material and a fluorine-containing binder. The active material includes one or both of spongy porous carbon and honeycomb porous carbon. A silicon group is formed on the active material, and the silicon group is also bonded to the fluorine-containing binder.

[0005] In some possible implementation manners, the fluorine-containing binder includes one or more of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinylidene fluoride.

[0006] In a second aspect, the present application provides a preparation method of a dry electrode material, including: performing pretreatment on a porous carbon material, where the porous carbon material includes one or both of spongy porous carbon and honeycomb porous carbon, and the pretreatment includes activation treatment to obtain an activation product; hydrolyzing a silane coupling agent, where the general formula of the silane coupling agent is R-Si-(OR’)3, where R includes one or both of an amino group and an epoxy group, and R’ includes an alkoxy group, to obtain a hydrolyzed silane coupling agent, mixing the activation product with the hydrolyzed silane coupling agent to form a bond between the hydrolyzed silane coupling agent and the activation product to obtain an active material; mixing the active material, a fluorine-containing binder, and a conductive agent to obtain a mixture, and subjecting the mixture to fibrillation under the action of shear force to obtain a dry film; and fixing the dry film on the surface of the current collector to obtain a dry electrode material.

[0007] In some possible implementation manners, the activation treatment of the porous carbon material includes: mixing the porous carbon material and an activator, where the activator includes an alkali solution, and causing the porous carbon material to react with the alkali solution.

[0008] In some possible implementation manners, the pretreatment further includes carbonization treatment. The carbonization treatment of the porous carbon material includes: maintaining the activated porous carbon material in an inert gas atmosphere at a temperature of 600 °C to 900 °C for 2 h to 4 h.

[0009] In some possible implementation manners, after the pretreatment of the porous carbon material, the preparation method further includes: grinding the pretreated porous carbon material to obtain an activated product, and the average particle size of the activated product is 50 μm to 100 μm.

[0010] In some possible implementation manners, the silane coupling agent includes one or both of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

[0011] In some possible implementation manners, the activated product is mixed with the hydrolyzed silane coupling agent, and the mass ratio of the activated product to the hydrolyzed silane coupling agent is greater than 90:10 and less than 99:1.

[0012] In some possible implementation manners, mixing the activated product with the hydrolyzed silane coupling agent includes: spraying the hydrolyzed silane coupling agent on the surface of the activated product through a spraying device to mix the activated product with the hydrolyzed silane coupling agent.

[0013] In some possible implementation manners, after obtaining the active material, the preparation method further includes: performing heat treatment on the active material, where the temperature of the heat treatment is 100 °C to 200 °C and the time of the heat treatment is 1 h to 2 h.

[0014] In some possible implementation manners, after obtaining the active material, the preparation method further includes: washing and drying the active material.

[0015] In some possible implementation manners, before mixing the active material, the fluorine-containing binder and the conductive agent, the preparation method further includes: placing the active material in a mixing device and dispersing it at a rotation speed of 100 r / min to 200 r / min.

[0016] In some possible implementation manners, causing the mixture to fibrillate under the action of shear force includes: placing the mixture in a mixing device and providing a shear force at a rotation speed of 500 r / min to 1500 r / min to cause the mixture to fibrillate.

[0017] In a third aspect, the present application provides a secondary battery, which includes the above-mentioned dry electrode material, or a dry electrode material prepared by the above-mentioned preparation method.

[0018] In the dry electrode material of the present application, the sponge-like porous carbon or honeycomb-like porous carbon has a relatively rich pore structure and a relatively high specific surface area, and also has relatively high structural stability. Being used as an electrode active material is beneficial to increasing ion transport and reaction sites, and is beneficial to improving the reaction rate in the battery and enhancing the conductivity of the electrode. At the same time, the silicon groups on the active material bridge the active material and the fluorine-containing binder, enhancing the binding force between the active material and the fluorine-containing binder, which helps to reduce the shedding of the active material during the use of the dry electrode material, and thus is beneficial to improving the cycling performance of the obtained secondary battery.

[0019] In the preparation method of the dry electrode material of the present application, by activating the porous carbon material (sponge-like porous carbon or honeycomb-like porous carbon), hydroxyl groups are formed on its surface, which is beneficial to further improving the porosity and specific surface area of the porous carbon, and thus is beneficial to improving the storage performance of active ions. Then, a specific silane coupling agent is hydrolyzed, and the hydrolyzed silane coupling agent is reacted with the activation product according to a preset mass ratio. Through the bonding of the silanol structure (Si-OH) in the hydrolyzed silane coupling agent with the hydroxyl groups (-OH) on the surface of the active material, a relatively large amount of the hydrolyzed silane coupling agent is anchored inside the porous structure of the activation product. At the same time, the R groups in the hydrolyzed silane coupling agent are intertwined with the long-chain structure of the fluorine-containing binder to form a physical interpenetrating network, which helps to promote the filling of the fluorine-containing binder in the pores or gaps of the active material to form a stable three-dimensional network structure, thereby enhancing the binding force between the active material and the fluorine-containing binder, and thus helping to reduce the shedding of the active material during the use of the dry electrode material. Description of the Drawings

[0020] Figure 1 It is a scanning electron microscope image of the active material provided in Example 1 of the present application. Detailed Description of the Embodiments

[0021] The embodiments of the present application will be described in detail below. The embodiments described below by combining with the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation to the present application; it should be noted that unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs; without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other; many specific details are set forth in the following description in order to fully understand the present application, and the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments.

[0022] Spongy porous carbon (also known as space bamboo) or honeycomb porous carbon is a natural biomass resource with a relatively rich pore structure, a high specific surface area, and a high stability of the spongy structure. Therefore, in this application, the research focuses on applying spongy porous carbon or honeycomb porous carbon to dry electrode materials (such as active materials). During this research process, the preparation method of the dry electrode material is also improved to enhance the binding between the active material and the fluorine-containing binder, thereby achieving the purpose of reducing the shedding of the active material during the use of the dry electrode material.

[0023] Based on this, an embodiment of this application provides a method for preparing a dry electrode material, including: Step 1: Pretreat the porous carbon material. The porous carbon material includes one or both of spongy porous carbon and honeycomb porous carbon. The pretreatment includes activation treatment to obtain an activated product.

[0024] The activation treatment of the porous carbon material forms hydroxyl groups on the surface of the porous carbon, which is beneficial to further increase the porosity and specific surface area of the porous carbon, thereby facilitating the improvement of the storage performance of active ions.

[0025] In some embodiments, the activation treatment of the porous carbon material includes: mixing the porous carbon material and an activator. The activator includes an alkali solution, and the porous carbon material reacts with the alkali solution. For example, the alkali solution includes one or both of sodium hydroxide and potassium hydroxide. It can be understood that through the activation treatment of the porous carbon material with the above-mentioned activator, the components in the porous carbon material react with the alkali solution in the activator, forming hydroxyl groups on the surface of the porous carbon, which is beneficial to further increase the porosity and specific surface area of the porous carbon.

[0026] In some embodiments, the concentration of the alkali solution is 1 mol / L to 5 mol / L, and the reaction time after mixing is 6 h to 24 h. For example, the concentration of the alkali solution can be 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or any value within the range composed of any two of the above values. The reaction time can be 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, or any value within the range composed of any two of the above values.

[0027] In some embodiments, the pretreatment further includes carbonization. Carbonizing the porous carbon material includes: maintaining the activated porous carbon material in an inert gas atmosphere at 600 °C to 900 °C for 2 h to 4 h. For example, the temperature of the carbonization treatment can be 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, or any value within the range formed by any two of the above values. The time of the carbonization treatment can be 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, 3.0 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h, 4 h, or any value within the range formed by any two of the above values.

[0028] In some embodiments, after the pretreatment of the porous carbon material, the preparation method further includes: washing and drying the pretreated porous carbon material. Washing is beneficial for removing residual activators and impurities, while drying is beneficial for removing moisture.

[0029] In some embodiments, the pretreated porous carbon material is immersed in deionized water and an appropriate amount of dilute hydrochloric acid with a low concentration (0.1 M to 0.5 M), and gently stirred for washing. In some embodiments, the immersion is carried out at room temperature. In some embodiments, the immersion time does not exceed 30 min. Until the washing liquid is neutral, which is beneficial for removing residual activators and impurities while maintaining the hydroxyl structure on the surface of the porous carbon material.

[0030] In some embodiments, drying includes vacuum drying at 60 °C to 80 °C for 4 h to 6 h. This is beneficial for ensuring the removal of moisture while maintaining the density of hydroxyl groups.

[0031] In some embodiments, after the pretreatment of the porous carbon material, the preparation method further includes: grinding the pretreated porous carbon material to obtain an activated product, and the average particle size of the activated product is 50 μm to 100 μm. For example, the average particle size of the activated product can be 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, or any value within the range formed by any two of the above values. It is found in the research of this application that the activated product with an average particle size within the above range can be more uniformly dispersed when mixed with the fluorine-containing binder powder subsequently, which is beneficial for improving the bonding force with the fluorine-containing binder powder in the follow-up.

[0032] Step 2: Hydrolyze the silane coupling agent. The general formula of the silane coupling agent is R-Si-(OR’)3, where R includes one or both of an amino group and an epoxy group, and R’ includes an alkoxy group, to obtain the hydrolyzed silane coupling agent. Mix the activated product with the hydrolyzed silane coupling agent to form a bond between the hydrolyzed silane coupling agent and the activated product, thereby obtaining the active material.

[0033] After hydrolysis, the Si-OR’ structure in the above silane coupling agent can form a silanol structure (Si-OH). React the hydrolyzed silane coupling agent with the activated product according to a preset mass ratio, and bond the silanol structure (Si-OH) in the hydrolyzed silane coupling agent with the hydroxyl group (-OH) on the surface of the activated product, such as forming a hydrogen bond or dehydrating and condensing to form a Si-O-C bond, so that a large amount of the hydrolyzed silane coupling agent is anchored inside the porous structure of the activated product, obtaining the active material. This active material has a reduced surface energy and improved wettability. At the same time, the hydrolyzed silane coupling agent retains the R group, and this R group (such as an amino group or an epoxy group) can entangle with the long-chain structure of the fluorine-containing binder in the subsequent process to form a physical interpenetrating network, which helps to promote the filling of the fluorine-containing binder in the pores or gaps of the active material to form a stable three-dimensional network structure, thereby enhancing the binding force between the active material and the fluorine-containing binder, and thus helping to reduce the shedding of the active material during the use of the dry electrode material. It can be understood that in this way, the hydrolyzed silane coupling agent bridges the active material bonded to it and the fluorine-containing binder entangled with it through a silicon group.

[0034] In some embodiments, the silane coupling agent includes one or both of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane. When the silane coupling agent includes the above substances, they both have a Si-OR’ structure that can be hydrolyzed to form a silanol structure. Moreover, γ-aminopropyltriethoxysilane (KH550) contains an amino group (corresponding to the above R group), which can form a polar interaction with the fluorine atoms in the fluorine-containing binder (such as PTFE), so that it can entangle with the fluorine-containing binder to form a physical interpenetrating network; γ-glycidoxypropyltrimethoxysilane (KH560) contains an epoxy group (corresponding to the above R group), which can undergo partial cross-linking with the fluorine-containing binder (such as PTFE) at high temperature, so that it can entangle with the fluorine-containing binder to form a physical interpenetrating network.

[0035] In some embodiments, hydrolyzing the silane coupling agent includes: mixing the silane coupling agent with water to cause the silane coupling agent to hydrolyze.

[0036] In some embodiments, to promote the hydrolysis of the silane coupling agent, the hydrolysis of the silane coupling agent further includes: adjusting the pH of the solution during hydrolysis to acidic. For example, the pH of the solution during hydrolysis can be adjusted to 3.5, 4, 4.5, 5, 5.5 or any value within the range formed by any two of the above values.

[0037] In some embodiments, to promote the hydrolysis of the silane coupling agent, before mixing the silane coupling agent with water, it further includes: mixing the silane coupling agent and an organic solvent to obtain a silane coupling agent solution, and then mixing the silane coupling agent solution with water. For example, the organic solvent includes one or both of ethanol and toluene.

[0038] In some embodiments, to promote the hydrolysis of the silane coupling agent, after mixing the silane coupling agent with water, it further includes: reacting at room temperature for 0.5 h to 2 h. For example, it can react at room temperature for 0.5 h, 0.7 h, 0.9 h, 1.1 h, 1.3 h, 1.5 h, 1.7 h, 1.9 h, 2 h or any value within the range formed by any two of the above values.

[0039] In some embodiments, the mass ratio of the activation product to the hydrolyzed silane coupling agent is greater than 90:10 and less than 99:1. For example, the mass ratio of the activation product to the hydrolyzed silane coupling agent can be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 98 or any value within the range formed by any two of the above values. Controlling the mass ratio of the activation product to the hydrolyzed silane coupling agent within the above range is beneficial for the hydrolyzed silane coupling agent to form a relatively uniform distribution on the surface of the activation product, thereby forming relatively sufficient bonding, improving the stability of the bonding, and increasing the subsequent entanglement with the fluorine-containing binder. It can be understood that when the mass ratio of the activation product to the hydrolyzed silane coupling agent is too low, the possible distribution of the hydrolyzed silane coupling agent on the surface of the activation product may be insufficient, the formed bonding may be less and the stability may be insufficient, and the subsequent entanglement with the fluorine-containing binder is also reduced, resulting in limited improvement in the binding force between the active material and the fluorine-containing binder. When the mass ratio of the activation product to the hydrolyzed silane coupling agent is too high, the silane coupling agent may easily self-polymerize to form an inactive film layer, blocking the pores of the porous carbon and affecting the active material loading.

[0040] In some embodiments, mixing the activation product with the hydrolyzed silane coupling agent includes: spraying the hydrolyzed silane coupling agent on the surface of the activation product through a spraying device, and stirring to cause the hydrolyzed silane coupling agent to react with the activation product to form a bond. Such mixing is beneficial for the hydrolyzed silane coupling agent to more fully contact the surface of the activation product and form sufficient wetting.

[0041] In some embodiments, after obtaining the active material, the preparation method further includes: performing heat treatment on the active material, where the temperature of the heat treatment is 100 °C to 200 °C, and the time of the heat treatment is 1 h to 2 h. For example, the temperature of the heat treatment can be 100 °C, 120 °C, 140 °C, 160 °C, 180 °C, 200 °C, or any value within the range formed by any two of the above values. The time of the heat treatment can be 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2 h, or any value within the range formed by any two of the above values. Performing heat treatment on the active material is beneficial to further promoting bonding and improving the stability of the bonding.

[0042] In some embodiments, after obtaining the active material, the preparation method further includes: washing and drying the active material. Washing and drying are beneficial to removing the residual silane coupling agent and moisture in the active material. At the same time, the dried active material can be better dispersed in subsequent steps and can be better mixed uniformly with the fluorine-containing binder and the conductive agent.

[0043] Step three: Mix the active material, the fluorine-containing binder, and the conductive agent to obtain a mixture, and fibrillate the mixture under the action of shear force to obtain a dry film sheet.

[0044] According to the principle of the dry electrode preparation technology, the fluorine-containing binder (such as PTFE) will fibrillate under the action of shear force. While bonding the mixed active material and conductive agent, etc., the fibrillation forms a dry film sheet with a certain mechanical strength. In the above process, the shear force can further improve the uniformity of the mixture, which is beneficial to promoting the formation of a good combination between the active material and the fluorine-containing binder, and thus is beneficial to improving the bonding strength between the active material and the fluorine-containing binder.

[0045] In some embodiments, the fluorine-containing binder includes one or more of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinylidene fluoride.

[0046] In some embodiments, before mixing the active material, the fluorine-containing binder, and the conductive agent, the preparation method further includes: placing the active material in a mixing device and dispersing it at a rotation speed of 100 r / min to 200 r / min. For example, the rotation speed for this dispersion can be 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, 200 r / min, or any value within the range formed by any two of the above values. Mixing at a low rotation speed is beneficial to dispersing the active material evenly in advance and is beneficial to promoting the uniformity of subsequent mixing.

[0047] In some embodiments, fibrillating the mixture under shear force includes: placing the mixture in a mixing device and providing a shear force at a rotational speed of 500 r / min to 1500 r / min to fibrillate the mixture. For example, the rotational speed for providing the shear force can be 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min, 1000 r / min, 1100 r / min, 1200 r / min, 1300 r / min, 1400 r / min, 1500 r / min or any value within the range formed by any two of the above values. While providing the shear force through a high rotational speed, it is possible to promote the mixing uniformity of the components in the mixture, prompt the fluorine-containing binder to come into more sufficient contact with the R group, and thus promote a better combination between the active material and the fluorine-containing binder.

[0048] Step Four: Fix the dry film on the surface of the current collector to obtain the dry electrode material.

[0049] In some embodiments, it includes pressing the dry film into a suitable thickness by hot roll pressing and fixing it on the surface of the current collector. Through the hot roll pressing process, the dry film can be well compounded with the surface of the current collector, and it can also promote the crosslinking of the hydrolyzed silane coupling agent (such as KH560) with the fluorine-containing binder (such as PTFE) at high temperature, thereby strengthening the binding force between the active material and the fluorine-containing binder in the dry film.

[0050] Another embodiment of the present application provides a dry electrode material, including a current collector and a dry film disposed on the surface of the current collector. The dry film includes an active material and a fluorine-containing binder. The active material includes one or both of spongy porous carbon and honeycomb porous carbon. A silicon group is formed on the active material, and the silicon group is also bonded to the fluorine-containing binder.

[0051] In the dry electrode material of the present application, the spongy porous carbon or honeycomb porous carbon has a relatively rich pore structure and a high specific surface area, and also has high structural stability. Being used as the electrode active material is beneficial to increasing ion transport and reaction sites, beneficial to improving the reaction rate in the battery, and enhancing the conductivity of the electrode. At the same time, the silicon group on the active material bridges the active material and the fluorine-containing binder, enhancing the binding force between the active material and the fluorine-containing binder, helping to reduce the shedding of the active material during the use of the dry electrode material, and thus being beneficial to improving the cycle performance of the obtained secondary battery.

[0052] In some embodiments, the fluorine-containing binder includes one or more of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinylidene fluoride.

[0053] In some embodiments, the above dry electrode material is prepared by the preparation method of the dry electrode material provided by an embodiment of the present application.

[0054] Another embodiment of the present application further provides a secondary battery, including the above dry electrode material. In the secondary battery of the present application, the above dry electrode material is used as the negative electrode. The positive electrode can be a positive electrode sheet obtained by a dry preparation process or a positive electrode sheet obtained by a wet process, which is not limited herein. The separator and electrolyte can be the separators and electrolytes known in the art, which are not limited herein.

[0055] The solution of the present application will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are only for explaining the present application and cannot be construed as a limitation of the present application. Unless otherwise stated, the reagents, software and instruments involved in the following examples that are not specifically stated are all commercially available products or open source.

[0056] Example 1: (1) A dry electrode material, the preparation method of which includes: The first step: Mix the space bamboo powder (i.e., sponge-like porous carbon, porous carbon material) with an activator. The activator includes NaOH with a concentration of 3 mol / L, and the activator fully infiltrates the space bamboo powder and is soaked for 12 h to obtain an activated product.

[0057] The second step: Under a nitrogen atmosphere, the activated product is heated to 800 °C at a heating rate of 4 °C / min and maintained at this temperature for 3 h for carbonization treatment. The carbonized product is cooled to room temperature and washed with deionized water and dilute hydrochloric acid until the washing liquid is neutral to remove the residual activator and impurities, obtaining a carbonized product; The third step: The carbonized product is vacuum dried at 90 °C for 10 h, and the dried product is ground with a grinding device (vibrating grinding or air grinding) to obtain a powder material with an average particle size of 80 μm, obtaining an activated product.

[0058] The fourth step: The silane coupling agent is added to an appropriate organic solvent for dissolution to obtain a silane coupling agent solution; an appropriate amount of water is added to the silane coupling agent solution, and the pH is adjusted to 4.5, and stirred evenly. The silane coupling agent is hydrolyzed at room temperature for 1 h to obtain the hydrolyzed silane coupling agent.

[0059] Step 5: Spray 5 parts of the hydrolyzed silane coupling agent evenly on the surface of 95 parts of the activated product under continuous stirring, that is, the mass ratio of the activated product to the hydrolyzed silane coupling agent is 95:5. After spraying, continue stirring for 1 h to allow the hydrolyzed silane coupling agent to fully react with the activated product to form bonds; wash the reaction product to remove residual solvents and moisture, and heat it appropriately to 150 °C and maintain for 1.5 h to further strengthen the bonding, obtaining the active material.

[0060] Step 6: Dry the active material in an oven at 100 °C for 10 h, then transfer it to a mixing device and premix it at a relatively low rotation speed of 150 r / min for 1 min; then add an appropriate amount of PTFE powder (particle size 50 μm - 200 μm) and conductive agent (active material:PTFE:conductive agent = 94:4:2) to obtain a mixture, increase the rotation speed to 1000 r / min to uniformly mix the mixture, and at the same time, under the action of shear force, fibrillate the PTFE in the mixture and bond the active material and the conductive agent to form a dry film.

[0061] Step 7: Hot press the above dry film into a 150-μm dry film using a roll press, and then perform double-sided lamination with the current collector to obtain the dry electrode material.

[0062] (2) A secondary battery, the preparation method of which includes: using the dry electrode material prepared above as the negative electrode, assembling it with the positive electrode and the separator into a 2032 button cell and injecting an electrolyte containing a lithium salt.

[0063] Example 2: The difference from Example 1 is that in Step 5, 8 parts of the hydrolyzed silane coupling agent are evenly sprayed on the surface of 92 parts of the activated product under continuous stirring, that is, the mass ratio of the activated product to the hydrolyzed silane coupling agent is 92:8.

[0064] Assemble the obtained dry electrode material into a lithium-ion battery according to the secondary battery preparation method of Example 1.

[0065] Example 3: The difference from Example 1 is that in Step 5, 3 parts of the hydrolyzed silane coupling agent are evenly sprayed on the surface of 97 parts of the activated product under continuous stirring, that is, the mass ratio of the activated product to the hydrolyzed silane coupling agent is 97:3.

[0066] Assemble the obtained dry electrode material into a lithium-ion battery according to the secondary battery preparation method of Example 1.

[0067] Example 4: The difference from Example 1 is that in the fifth step, 10 parts of the hydrolyzed silane coupling agent are evenly sprayed on the surface of 90 parts of the activated product under continuous stirring through a spraying device, that is, the mass ratio of the activated product to the hydrolyzed silane coupling agent is 90:10.

[0068] The obtained dry electrode material is assembled into a lithium-ion battery according to the secondary battery preparation method of Example 1.

[0069] Example 5: The difference from Example 1 is that in the fifth step, 1 part of the hydrolyzed silane coupling agent is evenly sprayed on the surface of 99 parts of the activated product under continuous stirring through a spraying device, that is, the mass ratio of the activated product to the hydrolyzed silane coupling agent is 99:1.

[0070] The obtained dry electrode material is assembled into a lithium-ion battery according to the secondary battery preparation method of Example 1.

[0071] Comparative Example 1: A dry electrode material, the preparation method of which includes: homogeneously mixing hard carbon (manufacturer: Kuraray) with PTFE and a conductive agent in a conventional ratio (hard carbon:PTFE:conductive agent = 94:4:2), hot pressing into a 150 μm dry film with a roll press, and then double-sidedly laminating with a current collector to form a double-sided dry electrode sheet, obtaining the dry electrode material.

[0072] The obtained dry electrode material is assembled into a lithium-ion battery according to the secondary battery preparation method of Example 1.

[0073] In this application, a scanning electron microscope was used to perform a morphology test on the active material in Example 1. Please refer to Figure 1 , the treated active material has a highly porous structure, the pore size distribution is relatively uniform, and the overall morphology presents a sponge-like or foamy shape, providing a large specific surface area, which is beneficial to the penetration of the electrolyte and the transmission of electrons / ions.

[0074] In this application, a cutting machine was used to cut 5 test samples with a size of 5*5 at 5 different positions of the dry electrode materials of Examples 1-5 and Comparative Example 1 respectively. Powder resistivity testing was adopted, and the four-probe testing method was selected. A gasket was installed in the mold, and the probe round hole part was completely covered by the electrode sheet to test the through resistance of the dry electrode material. Each dry electrode material was tested 5 times. The test results are shown in Table 1.

[0075] The present application also conducts a cycling performance test on the secondary batteries of Examples 1-5 and Comparative Example 1. The test method includes: at room temperature, charging at a constant current of 0.5 C to 4.3 V, charging at a constant voltage of 4.3 V until the current ≤ 0.02 C, discharging at a constant current of 1 C to 3.0 V, cycling for 50 weeks, recording the discharge capacity at different cycle numbers, calculating the capacity retention rate of the battery after 50 weeks of cycling. The test results are shown in Table 2.

[0076] Table 1. Test results of the through-plane resistance of the dry electrode materials of Examples 1-5 and Comparative Example 1 of the present application Table 2. Test results of the cycling performance of the secondary batteries of Examples 1-5 and Comparative Example 1 of the present application The dry film sheets in the dry electrode materials prepared in Examples 1-5 of the present application include active materials and fluorine-containing binders. The active materials include one or both of sponge-like porous carbon and honeycomb-like porous carbon. Silicon groups are formed on the active materials, and the silicon groups are also bonded to the fluorine-containing binders. The active materials have a relatively rich pore structure and a relatively high specific surface area, and the structural stability is relatively high. Using them as electrode active materials is beneficial to increasing ion transport and reaction sites, improving the reaction rate in the battery, and enhancing the conductivity of the electrode. Therefore, the through-plane resistance of the dry electrode materials of Examples 1-5 is relatively low. At the same time, the silicon groups on the active materials bridge the active materials and the fluorine-containing binders, improving the binding force between the active materials and the fluorine-containing binders, helping to reduce the shedding of the active materials during the use of the dry electrode materials, and thus being beneficial to improving the cycling performance of the obtained secondary batteries. Therefore, the capacity retention rate of the secondary batteries of Examples 1-5 is relatively high.

[0077] Among them, in the preparation process of the dry electrode materials of Examples 1-3, further controlling the mass ratio of the activation product to the hydrolyzed silane coupling agent to fall within a preset range (greater than 90:10 and less than 99:1) is beneficial to forming a relatively uniform distribution of the hydrolyzed silane coupling agent on the surface of the activation product, thereby forming relatively sufficient bonding, improving the stability of the bonding, and increasing the entanglement with the fluorine-containing binder in the subsequent process, thereby further improving the conductivity of the dry electrode materials and the cycling performance of the obtained secondary batteries.

[0078] Compared with Examples 1-5, in the preparation of the dry electrode material of Comparative Example 1, ordinary hard carbon is used and no special treatment is carried out on the hard carbon. During the use of this dry electrode material, the dry film sheets formed by the active materials, conductive agents, and binders may experience powdering and powder shedding, resulting in poor conductivity of the obtained dry electrode material and poor cycling performance of the secondary battery. Therefore, the through-plane resistance of the dry electrode material is significantly higher, and the capacity retention of the secondary battery is significantly lower.

[0079] The above embodiments are only used to illustrate the technical solutions of the present application rather than to limit it. Although the present application has been described in detail with reference to the above preferred embodiments, those of ordinary skill in the art should understand that modifications or equivalent replacements of the technical solutions of the present application should not depart from the spirit and scope of the technical solutions of the present application.

Claims

1. A dry electrode material, comprising a current collector and a dry membrane disposed on the surface of the current collector, characterized in that: The dry process membrane comprises an active material and a fluorine-containing binder. The active material comprises one or both of sponge-like porous carbon and honeycomb-like porous carbon. Silicon groups are formed on the active material, and the silicon groups are also bonded to the fluorine-containing binder.

2. The dry electrode material according to claim 1, characterized in that: The fluorine-containing binder includes one or more of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer and polyvinylidene fluoride.

3. A method for preparing a dry electrode material, characterized in that: include: Pre-treating a porous carbon material, wherein the porous carbon material comprises one or both of sponge-like porous carbon and honeycomb-like porous carbon, wherein the pre-treatment comprises activation treatment to obtain an activated product; Hydrolyzing a silane coupling agent, wherein the general formula of the silane coupling agent is R-Si-(OR')3, wherein R includes one or both of an amino group and an epoxy group, and R' includes an alkoxy group, to obtain a hydrolyzed silane coupling agent, and mixing the activated product with the hydrolyzed silane coupling agent to form a bond between the hydrolyzed silane coupling agent and the activated product, to obtain an active material; The active material, the fluorine-containing binder and the conductive agent are mixed to obtain a mixture, and the mixture is fiberized under the action of shear force to obtain a dry film; The dry process membrane is arranged on the surface of a current collector to obtain the dry process electrode material.

4. The preparation method according to claim 3, characterized in that: The pretreatment of the porous carbon material satisfies at least one of the following conditions: (1) performing the activation treatment on the porous carbon material comprises: mixing the porous carbon material and an activator, wherein the activator comprises an alkaline solution, and causing the porous carbon material to react with the alkaline solution; (2) The pretreatment further includes carbonization treatment, and the carbonization treatment of the porous carbon material includes: keeping the porous carbon material after the activation treatment in an inert gas atmosphere at 600°C to 900°C for 2 h to 4 h; (3) After the porous carbon material is pretreated, the preparation method further comprises: grinding the porous carbon material after the pretreatment to obtain an activated product, wherein the average particle size of the activated product is 50 μm to 100 μm.

5. The preparation method according to claim 3, characterized in that: The silane coupling agent includes one or both of γ-aminopropyltriethoxysilane and γ-glycidyloxypropyltrimethoxysilane.

6. The preparation method according to claim 3, characterized in that: Mixing the activated product with the hydrolyzed silane coupling agent satisfies at least one of the following conditions: (1) The mass ratio of the activated product to the hydrolyzed silane coupling agent is greater than 90:10 and less than 99:1; (2) Spraying the hydrolyzed silane coupling agent on the surface of the activated product by a spray device to mix the activated product with the hydrolyzed silane coupling agent.

7. The preparation method according to claim 3, characterized in that: After obtaining the active material, the preparation method further comprises at least one of the following steps: (1) heat treating the active material at a temperature of 100°C to 200°C for a time of 1 hour to 2 hours; (2) Washing and drying the active material.

8. The preparation method according to claim 3, characterized in that: Before mixing the active material, the fluorine-containing binder and the conductive agent, the preparation method further comprises at least one of the following steps: (1) drying the active material; (2) The active material is placed in a mixing device and dispersed at a rotation speed of 100 to 200 r / min.

9. The preparation method according to claim 3, characterized in that: The step of causing the mixture to undergo fiberization under the action of shear force comprises: The mixture is placed in a mixing device, and the shear force is provided at a rotation speed of 500 r / min to 1500 r / min to fiberize the mixture.

10. A secondary battery, characterized in that: The invention comprises the dry electrode material as described in claim 1 or 2, or comprises the dry electrode material prepared by the preparation method as described in any one of claims 3 to 9.

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