Simple flexible three-dimensional thick electrode preparation method

Abstract

The invention relates to a preparation method of a simple flexible three-dimensional thick electrode, and belongs to the technical field of electrochemistry. The method comprises the following steps: preparing a mixed binder for preparing a flexible three-dimensional thick electrode; mixing and pulping the mixed binder, a conductive agent and an active material according to a certain proportion to prepare active material slurry; coating a glass plate with the slurry, then transferring the glass plate into a CNT aqueous solution for liquid phase transformation, constructing a three-dimensional conductive network and a CNT-based external conductive network at the same time, and finally taking out a sample for freeze drying to obtain the flexible three-dimensional thick electrode.

Description

Technical Field

[0001] The invention discloses a method for preparing a simple flexible three-dimensional thick electrode, belonging to the field of electrochemistry. Background Art

[0002] With the popularity of new energy vehicles and wearable devices, lithium-ion batteries have become the most popular secondary batteries due to their long cycle life and low maintenance. As a current research hotspot, improving its energy density is also the most popular research direction. There are currently several methods to improve the energy density of lithium-ion batteries: developing high-capacity batteries, developing high-voltage positive electrodes, and thick electrode design. Among them, thick electrode design is one of the most promising methods. However, in the process of increasing energy density with thick electrodes, two problems are exposed: low transfer rate due to poor charge transfer dynamics, and electrode fracture and delamination due to poor mechanical properties.

[0003] At present, low tortuosity thick electrodes are considered to be an effective solution to help thick electrodes achieve both high energy density and high power density. The main methods include laser etching, 3D printing and template method. Increasing the loading amount of active materials by thickening the battery electrode coating can increase the energy density of lithium-ion batteries, but the trade-off is the greatly reduced Li + To achieve the best energy and power density in thick electrodes, Li + The effective chemical diffusion coefficient of Li is maximized. + Diffusion within the electrode is a complex process involving both microscopic and macroscopic processes. The focus of charge transport in thick electrode architectures is to increase the rate of ion and electron transfer, thereby increasing the battery charge and discharge rate, and further improving the electrochemical performance. In response to the problem of thick electrodes having their own electrode thickness, which leads to the obstruction of ion and electron movement and transmission, patent CN 117317133 A discloses a thick electrode with a three-dimensional pore structure and its preparation method and application. This method constructs a three-dimensional pore structure inside the thick electrode, so that the thick electrode has the advantages of both high surface capacity and high rate performance. It should be noted that the preparation methods of thick electrodes developed previously need to be used in combination with metal current collectors and do not have flexible structures.

[0004] Therefore, it is urgent to develop a method for preparing flexible thick electrodes with excellent ion / electron transport performance, low cost and high scalability. Summary of the invention

[0005] In view of the problems existing in the existing preparation technology, the purpose of the present invention is to propose a simple flexible three-dimensional thick electrode preparation method, which is simple and easy to prepare.

[0006] Here, the present invention provides a simple method for preparing a flexible three-dimensional thick electrode, including: using a new mixed binder to mix with a conductive agent and an active material in a certain proportion and distributing them in a solvent; adjusting the proportion of each component and the solid content of the slurry, and fully stirring to ensure the uniformity of the slurry; uniformly coating the prepared slurry on a glass plate according to a certain thickness; then transferring it to a CNT aqueous solution for liquid phase transition, constructing a CNT-based external conductive network while constructing a three-dimensional conductive network, and finally taking out the sample for freeze-drying to obtain a flexible three-dimensional thick electrode.

[0007] Preferably, the novel mixed binder is a mixed binder such as PAN / TPU, PAN / PVDF, PAN / PEO, etc., and the ratio between the mixed binders is 10:0-0:10.

[0008] Preferably, the solvent used for the dispersion is an organic solvent such as DMF, NMP, hydrazine hydrate, etc.

[0009] Preferably, the active material is a positive electrode powder that can be used in a lithium ion battery, and a negative electrode powder material that can be used in a lithium ion battery.

[0010] Preferably, the method of thermal drying of the sample includes vacuum thermal drying, forced air drying, natural drying and the like.

[0011] Preferably, the conductive agent material includes highly active conductive materials such as super p, carbon black, KB, CNT, CNF, etc.

[0012] Preferably, the mass ratio of the electrode active material to the conductive agent and the mixed binder is 1:1 to 9:1.

[0013] Preferably, the electrolyte solvent may include organic solvents such as DME, DMC, EMC, EC, etc.

[0014] Preferably, the aqueous solution of CNTs is a CNT dispersion uniformly dispersed in a certain proportion;

[0015] Preferably, before freeze drying, the phase transition must be fully carried out and the cold trap temperature is required to be less than -50°C.

[0016] Preferably, the coating thickness can be adjusted by controlling the solid content of the slurry and the thickness of the scraper used for coating, and the thickness ranges from 100 to 500 μm.

[0017] The method of the present invention is simple and easy to implement. According to the preparation method of the present invention, the method for preparing a flexible self-supporting electrode does not require the use of an additional current collector material. The mixed binder is cross-linked and polymerized into a three-dimensional network structure under the action of phase transformation. The conductive agent will be compounded in the three-dimensional network during the phase transformation process to form an internal three-dimensional conductive network. The CNTs in the CNT aqueous solution used for phase transformation will be dispersed in the middle of the three-dimensional conductive network under the action of surface tension to form an external conductive network. At the same time, the porous structure is conducive to the infiltration of the electrolyte and improves the electrode reaction kinetics. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings, in which:

[0019] Figure 1 This is a digital photo of a three-dimensional thick electrode.

[0020] Figure 2 This is the surface porous structure of the three-dimensional thick electrode

[0021] Figure 3 This is a cross-sectional view of the porous structure inside a three-dimensional thick electrode.

[0022] Figure 4 This is the cycling performance diagram of the three-dimensional thick electrode at a current density of 0.1C.

[0023] Figure 5 This is a model diagram of a three-dimensional thick electrode. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings and the following specific embodiments. It should be understood that the following embodiments and / or drawings are only used to illustrate the present invention rather than to limit the present invention.

[0025] The above-mentioned invention object of the present invention is preferably achieved through the following technical solutions:

[0026] a) Active materials, conductive agents and novel mixed binders are mixed and distributed in a DMF solvent in a certain proportion to prepare electrode slurry for coating.

[0027] b) The prepared slurry is evenly coated on a glass plate at a certain thickness.

[0028] c) transferring the coated glass plate into a CNT aqueous solution for liquid phase transformation, thereby constructing a CNT-based external conductive network while constructing a three-dimensional conductive network.

[0029] d) Finally, the sample is taken out and freeze-dried to obtain a flexible three-dimensional thick electrode.

[0030] Preferably, the novel mixed binder in step a) can be a mixed binder such as PAN / TPU, PAN / PVDF, PAN / PEO, etc., and the ratio between the mixed binders is 10:1-1:1, and a more preferred ratio is greater than 7:3.

[0031] Preferably, the solvent used for the dispersion in step a) is an organic solvent such as DMF, NMP, hydrazine hydrate, etc.

[0032] Preferably, the active material in step a) is a positive electrode powder that can be used in a lithium ion battery, or a negative electrode powder material that can be used in a lithium ion battery.

[0033] Preferably, in step a), the mass ratio of the electrode active material to the conductive agent and the mixed binder is 1:1 to 9:1, and more preferably, the active material used in the positive three-dimensional flexible thick electrode is: KB:CNF:mixed binder=80:5:5:10.

[0034] Preferably, in step a), the mass ratio of the electrode active material to the conductive agent and the mixed binder is 1:1 to 9:1, and more preferably, the active material used in the negative three-dimensional flexible thick electrode is: KB:CNF:mixed binder=75:5:5:15.

[0035] Preferably, the conductive agent material in step a) includes highly active conductive materials such as super p, carbon black, KB, CNT, CNF, etc., and chain KB and one-dimensional CNF are more preferably selected as the internal conductive medium.

[0036] Preferably, the coating thickness in step b) can be adjusted by controlling the solid content of the slurry and the thickness of the scraper used for coating, and the thickness ranges from 100 to 500 μm. A thickness of 400 μm is more preferably selected for testing to show a more complete three-dimensional conductive network structure.

[0037] Preferably, the phase transition process in step c) uses a solvent system that can cause the mixed binder to undergo cross-linking polymerization, and more preferably uses a CNT aqueous solution to perform liquid phase transition, thereby constructing a CNT-based external conductive network while constructing a three-dimensional conductive network.

[0038] Preferably, the freeze-drying process in step d) requires that the sample be placed flat as a whole, the cold trap temperature be less than -50°C, and the drying time be more than 24 hours.

[0039] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The following examples of specific active materials, conductive agents, types of mixed binders, solid content of slurry, coating thickness, and solutions used for phase transition are also only examples within a suitable range, that is, those skilled in the art can choose within a suitable range according to the description of this article, and are not limited to the specific values ​​​​exemplified below.

[0040] Example 1

[0041] 1) PAN / TPU was used as a mixed binder with a ratio of PAN:TPU=8:2 and a solvent of DMF. The mixture was magnetically stirred at room temperature for 12 hours to obtain a 10 wt% P8T2 binder.

[0042] 2) Commercial lithium cobalt oxide (LCO) electrode material was mixed as active material (AM). The material was dispersed in DMF solution at a mass ratio of AM: P8T2: KB: CNF = 80: 10: 5: 5, and magnetic stirring was performed for 24 hours to prepare electrode slurry.

[0043] 3) The active material slurry is coated on ordinary glass, and the coating thickness is controlled at 400 μm.

[0044] 4) Placing the glass plate coated with the active material in a CNT dispersion for phase transition until the solvent exchange is completed.

[0045] 5) Take out the electrode after phase transformation, freeze it from bottom to top with liquid nitrogen, and freeze-dry it in vacuum. Figure 1 As shown in the model diagram Figure 5 As shown, its internal structure is as follows Figure 2 and 3 shown.

[0046] The obtained electrode film was cut into discs with a diameter of 10 mm, and button cells were assembled with the cut electrode pieces as the positive electrode, the metal lithium sheet as the negative electrode, the polypropylene microporous membrane (Celgard 2400) as the separator, and 1M LiPF6 EC / DEC / DMC (volume ratio of 1:1:1) solution as the electrolyte. The electrochemical properties of the cells were tested, and the charge and discharge cycle performance was shown in Figure 2. Figure 4 The first reversible specific capacity is 157.57 mAh g -1 After 200 cycles, the discharge capacity is 150.24 mAh g -1 The reversible capacity retention rate is 95.35%, which has good cycle stability.

[0047] Example 2

[0048] 1) PAN / TPU was used as a mixed binder with a ratio of PAN:TPU=8:2 and a solvent of DMF. The mixture was magnetically stirred at room temperature for 12 hours to obtain a 10 wt% P8T2 binder.

[0049] 2) Commercial lithium cobalt oxide (LCO) electrode material was mixed as active material (AM). The material was dispersed in DMF solution at a mass ratio of AM: P8T2: KB: CNF = 80: 10: 5: 5, and magnetic stirring was performed for 24 hours to prepare electrode slurry.

[0050] 3) The active material slurry is coated on ordinary glass, and the coating thickness is controlled at 400 μm.

[0051] 4) Placing the glass plate coated with the active material in an aqueous solution for phase transition until the solvent exchange is completed.

[0052] 5) Take out the electrode after phase transformation, freeze it from bottom to top with liquid nitrogen, and freeze-dry it in vacuum.

[0053] Example 3

[0054] 1) PAN / PVDF was used as a mixed binder with a ratio of PAN:PVDF=8:2 and a solvent of DMF. The mixture was magnetically stirred at room temperature for 12 hours to obtain a 10 wt% P8T2 binder.

[0055] 2) Commercial lithium cobalt oxide (LCO) electrode material was mixed as active material (AM). The material was dispersed in DMF solution at a mass ratio of AM: P8T2: KB: CNF = 80: 10: 5: 5, and magnetic stirring was performed for 24 hours to prepare electrode slurry.

[0056] 3) The active material slurry is coated on ordinary glass, and the coating thickness is controlled at 400 μm.

[0057] 4) Placing the glass plate coated with the active material in an aqueous solution for phase transition until the solvent exchange is completed.

[0058] 5) Take out the electrode after phase transformation, freeze it from bottom to top with liquid nitrogen, and freeze-dry it in vacuum.

[0059] Finally, it should be noted that the above embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above contents of the present invention all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a simple flexible three-dimensional thick electrode, characterized in that: include: A new type of mixed binder, a conductive agent and an active material are mixed and distributed in a solvent in a certain proportion; Adjust the proportion of each component and the solid content of the slurry, and stir it thoroughly to ensure the uniformity of the slurry; The prepared slurry is evenly coated on the glass plate according to a certain thickness; The glass plate coated with the slurry was transferred to an aqueous solution of CNTs for aqueous phase transition; The electrodes after phase transformation were finally dried using freeze drying technology. The novel mixed binder is a mixed binder such as PAN / TPU, PAN / PVDF, PAN / PEO, etc., and the ratio between the mixed binders is 10:1-1:1; The solvent used for the dispersion is an organic solvent such as DMF, NMP, hydrazine hydrate, etc. The active material is a positive electrode powder that can be used in lithium-ion batteries, and a negative electrode powder material that can be used in lithium-ion batteries; The aqueous solution of CNT is a CNT dispersion uniformly dispersed in a certain proportion; Before freeze drying, it is necessary to ensure that the phase transition is fully carried out and the cold trap temperature is required to be less than -50°C.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the electrode active material to the conductive agent and the mixed binder is 1:1 to 9:

1.

3. The preparation method according to claim 1, characterized in that: The conductive agent material includes highly active conductive materials such as super p, carbon black, KB, CNT, CNF, etc.

4. The preparation method according to claim 1, characterized in that: The prepared mixed adhesive comprises various hard segment polymers with supporting structures and polymers with flexible segment structures, and the ratio between the two is 10:0-0:

10.

5. The preparation method according to claim 1, characterized in that: The coating thickness can be adjusted by controlling the solid content of the slurry and the thickness of the scraper used for coating, and the thickness range is 100-500 μm.

6. The preparation method according to claim 1, characterized in that: The phase transition solution is a CNT aqueous dispersion, wherein the concentration of CNT is less than 0.001 wt %.

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