A simple flexible three-dimensional thick electrode preparation method

Abstract

The present application relates to a simple flexible three-dimensional thick electrode preparation method, and belongs to the technical field of electrochemistry. The method comprises the following steps: preparing a mixed binder for flexible three-dimensional thick electrode preparation; mixing the mixed binder with a conductive agent and an active material in a certain proportion to prepare an active material slurry; coating the slurry on a glass plate, and then transferring it to a CNT aqueous solution for liquid phase conversion, thereby 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.

Description

TECHNICAL FIELD

[0001] A simple flexible three-dimensional thick electrode preparation method belongs to the field of electrochemistry. BACKGROUND

[0002] With the environment of new energy vehicle and wearable device epidemic, lithium ion battery has become the most popular secondary battery due to its long cycle life and low maintenance. As the current research hotspot, the improvement of its energy density is also the most popular research direction. In order to improve the energy density of lithium ion battery, there are currently various methods: developing high specific capacity battery, developing high voltage positive electrode, thick electrode design, etc. Among them, thick electrode design is one of the most promising methods. However, in the process of improving the energy density of thick electrode, two problems are exposed: low transmission rate caused by poor charge transfer dynamics, and electrode fracture and delamination caused by poor mechanical properties.

[0003] At present, low tortuosity thick electrode is considered to be an effective solution to help thick electrode have high energy density and high power density, and the main methods include laser etching, 3D printing and template method, etc. Thickening the electrode coating of the battery can increase the loading capacity of the active material to improve the energy density of the lithium ion battery, but the trade-off is the greatly reduced Li + transport dynamics. In order to achieve the best energy and power density of thick electrode, the effective chemical diffusion coefficient of Li + must be maximized. However, the diffusion of Li + in the electrode is a complex process involving micro and macro processes. Thick electrode architecture focuses on improving ion and electron transport rates to improve battery charge and discharge rates and thus improve electrochemical performance. In view of the problem of thick electrode caused by its 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 channel structure and its preparation method and application. This method constructs a three-dimensional channel structure inside the thick electrode, so that the thick electrode has the advantages of high surface capacity and high rate performance. It should be noted that the preparation methods of the thick electrode developed before all need to be used in combination with metal current collectors and do not have flexible structure.

[0004] Therefore, it is urgent to develop a flexible thick electrode preparation method with excellent ion / electron transport performance, low cost and high scalability. SUMMARY

[0005] In view of the problems existing in the prior art preparation technology, the purpose of the present application is to provide a simple flexible three-dimensional thick electrode preparation method. This flexible electrode preparation method is simple and easy to operate.

[0006] The application provides a simple flexible three-dimensional thick electrode preparation method, which comprises the following steps: mixing a new type of mixed binder with a conductive agent and an active material in a solvent in a certain proportion; 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 to a CNT aqueous solution for liquid phase transformation, 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 new type of mixed binder is a PAN / TPU, PAN / PVDF, PAN / PEO or the like mixed binder, and the proportion of the mixed binders is 10:0-0:10.

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

[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 sample heat drying mode comprises vacuum heat drying, air blowing drying, natural drying and the like.

[0011] Preferably, the conductive agent material comprises super p, carbon black, KB, CNT, CNF and the like high-activity conductive material.

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

[0013] Preferably, the electrolyte solvent can comprise an organic solvent such as DME, DMC, EMC, EC and the like.

[0014] Preferably, the CNT aqueous solution is a CNT dispersion liquid uniformly dispersed in a certain proportion.

[0015] Preferably, before freeze-drying, it is required to ensure that the phase inversion is fully performed, and the cold trap temperature is required to be less than-50℃.

[0016] Preferably, the coating thickness can be controlled by controlling the solid content of the slurry and the thickness of the scraper used for coating, and the thickness range is 100-500μm.

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

[0018] The preferred embodiments of the present application will be described below with reference to the accompanying drawings, in which:

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

[0020] Figure 2 is a surface porous structure diagram of a three-dimensional thick electrode

[0021] Figure 3 is a cross-sectional internal porous structure diagram of a three-dimensional thick electrode

[0022] Figure 4 is a cycle performance diagram of a three-dimensional thick electrode under a current density of 0.1C

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

[0024] The present application will be 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 application, but not to limit the present application.

[0025] The above application objectives of the present application are preferably achieved by the following technical solutions:

[0026] a) mixing and distributing the active material, the conductive agent and the novel mixed binder in a certain proportion in DMF solvent to prepare a coating electrode slurry.

[0027] b) uniformly coating the prepared slurry on a glass plate according to a certain thickness.

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

[0029] d) finally taking out the sample for freeze-drying to obtain a flexible three-dimensional thick electrode.

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

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

[0032] As preferred, the active material in step a) 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.

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

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

[0035] As preferred, the conductive agent material in step a) includes super p, carbon black, KB, CNT, CNF, etc. high-activity conductive material, and the more preferred chain KB and one-dimensional CNF are selected as the internal conductive medium.

[0036] As preferred, the coating thickness in step b) can be controlled by controlling the solid content of the slurry and the thickness of the coating using a doctor blade, and the thickness range is 100-500 μm, and the more preferred thickness of 400 μm is selected for testing, which shows a more complete three-dimensional conductive network structure.

[0037] As preferred, the phase transition process in step c) uses a solvent system that can cross-link and polymerize the mixed binder, and the more preferred liquid phase transition is carried out in a CNT aqueous solution, which constructs a CNT-based external conductive network while constructing a three-dimensional conductive network.

[0038] As preferred, the freeze-drying process in step d) requires the sample to be placed flat, the cold trap temperature is less than -50℃, and the drying time is more than 24h.

[0039] The following examples are further illustrated in detail to explain the present application. It should also be understood that the following examples are only used to further illustrate the present application, and cannot be understood as limiting the scope of protection of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present application are within the scope of protection of the present application. The specific active material, conductive agent, type of mixed binder, solid content of the slurry, coating thickness, and solution used for phase inversion, etc. described in the following examples are only one example in the appropriate range, i.e. those skilled in the art can select within the appropriate range described herein, and are not limited to the specific values of the following examples.

[0040] Example 1

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

[0042] 2) Commercial lithium cobalt oxide (LCO) electrode material was mixed as an active material (AM). The materials were dispersed into a DMF solution with a mass ratio of AM: P8T2: KB: CNF = 80:10:5:5, and stirred magnetically for 24 hours to prepare an electrode slurry.

[0043] 3) The active material slurry was coated on a common glass with a coating thickness of 400μm.

[0044] 4) The glass plate coated with the active material was placed in a CNT dispersion liquid for phase inversion until the solvent exchange was completed.

[0045] 5) The phase-inverted electrode was taken out, frozen from bottom to top with liquid nitrogen, and vacuum freeze-dried to prepare an electrode as shown in Figure 1 , a model diagram thereof is shown in Figure 5 , and the internal structure thereof is shown in Figure 2 and 3 .

[0046] The obtained electrode film was cut into a circular piece with a diameter of 10mm. The cut electrode was used as a positive electrode, a lithium metal sheet was used as a negative electrode, a polypropylene microporous membrane (Celgard 2400) was used as a separator, and a 1M LiPF6 EC / DEC / DMC (volume ratio of 1:1:1) solution was used as an electrolyte to assemble a coin cell battery. The electrochemical performance of the coin cell battery was tested, and the charge-discharge cycle performance is shown in Figure 4 . The first reversible specific capacity was 157.57mAh g -1 , the discharge specific capacity after 200 cycles was 150.24mAh g -1 , and the reversible capacity retention rate was 95.35%, which had good cycle stability.

[0047] Example 2

[0048] 1) PAN / TPU as mixed binder, ratio of PAN:TPU = 8:2, solvent DMF, magnetic stirring at room temperature for 12 hours, 10wt% P8T2 binder was obtained.

[0049] 2) Commercial lithium cobalt oxide (LCO) electrode material as active material (AM) was mixed. AM: P8T2: KB: CNF = 80:10:5:5 by mass ratio, the material was dispersed into DMF solution, magnetic stirring for 24 hours, and electrode slurry was prepared.

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

[0051] 4) The glass plate coated with active material was placed in an aqueous solution for phase inversion until the solvent exchange was completed.

[0052] 5) The phase-inverted electrode was taken out, frozen from bottom to top with liquid nitrogen, and vacuum freeze-dried.

[0053] Example 3

[0054] 1) PAN / PVDF as mixed binder, ratio of PAN:PVDF = 8:2, solvent DMF, magnetic stirring at room temperature for 12 hours, 10wt% P8T2 binder was obtained.

[0055] 2) Commercial lithium cobalt oxide (LCO) electrode material as active material (AM) was mixed. AM: P8T2: KB: CNF = 80:10:5:5 by mass ratio, the material was dispersed into DMF solution, magnetic stirring for 24 hours, and electrode slurry was prepared.

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

[0057] 4) The glass plate coated with active material was placed in an aqueous solution for phase inversion until the solvent exchange was completed.

[0058] 5) The phase-inverted electrode was taken out, frozen from bottom to top with liquid nitrogen, and vacuum freeze-dried.

[0059] Finally, it should be pointed out that the above examples are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present application are within the protection scope of the present application.

Claims

1. A simple method for fabricating a flexible three-dimensional thick electrode, characterized in that, include: A slurry is formed by mixing a hybrid binder, a conductive agent, and an active material in a certain proportion and distributing them in a solvent. Adjust the proportions of each component in the slurry and the solid content of the slurry, and stir thoroughly to ensure the homogeneity of the slurry; The prepared slurry is uniformly coated onto a glass plate to a certain thickness. The glass plate coated with the slurry is transferred to a CNT aqueous solution for an aqueous phase transition; The electrode after the phase transformation is completed is finally dried using freeze-drying technology; The mixed adhesive is any one of PAN / TPU, PAN / PVDF, and PAN / PEO, and the ratio of PAN to the other adhesive in the mixed adhesive is 10:1 to 1:

1. The solvent is any one of DMF, NMP, and hydrazine hydrate organic solvents; The active material is a positive electrode powder material used in lithium-ion batteries, or a negative electrode powder material used in lithium-ion batteries. The CNT aqueous solution is a CNT dispersion that is uniformly dispersed in a certain proportion; Before performing the freeze-drying, it is necessary to ensure that the phase transformation is fully carried out, and the cold trap temperature is required to be less than -50°C; The mixed binder crosslinks and polymerizes into a three-dimensional network structure under the action of the phase transition. The conductive agent will be composited in the three-dimensional network structure during the phase transition to form an internal three-dimensional conductive network structure. The CNTs in the CNT aqueous solution used for the phase transition will be dispersed in the middle of the three-dimensional conductive network structure under the action of surface tension to form an external conductive network.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the 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 includes one or more of the highly active conductive materials selected from super p, KB, CNT, and CNF.

4. The preparation method according to claim 1, characterized in that, The conductive agent includes carbon black.

5. The preparation method according to claim 1, characterized in that, The coating thickness is controlled by adjusting the solid content of the slurry and the thickness of the doctor blade used for coating, and the coating thickness ranges from 100 to 500 μm.

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

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