Solid electrolyte based on graphene oxide and preparation method thereof

Abstract

The invention relates to the technical field of solid electrolyte materials, and discloses a solid electrolyte based on graphene oxide and a preparation method thereof. According to the solid electrolyte, multi-layer graphene oxide (mGO), an oxide (LLZO) and a polymer (PEO) are taken as core components, and a nano confinement ion channel is constructed, so that the technical problems of low room-temperature ionic conductivity, insufficient electronic insulativity, poor mechanical strength and poor interface contact of the existing solid electrolyte are solved. The preparation process comprises the steps of preparation of a multi-layer graphene oxide film, preparation of mGO-LLZO mixed slurry, compounding with a PEO solution, film forming and the like, and the obtained solid electrolyte film has excellent electronic insulativity, mechanical strength and interface stability while keeping high ionic conductivity. The electrolyte is suitable for the field of solid-state batteries, can remarkably improve the rate charge-discharge performance and the cycle stability of the batteries, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte materials technology, specifically to a solid electrolyte based on multilayer graphene oxide (mGO) constructing nano-confined channels and its preparation method, applicable to fields such as solid-state batteries. Background Technology

[0002] With the development of new energy technologies, the electric vehicle and renewable energy industries have rapidly emerged. Solid-state batteries, with their higher energy density, superior safety, and longer cycle life, have become an important alternative to lithium batteries. As the core component of solid-state batteries, the solid electrolyte's ionic conductivity and electronic insulation directly determine the overall performance of the battery.

[0003] Currently, mainstream solid electrolyte materials include polymers (such as PEO) and oxides (such as LLZO), but these materials have significant drawbacks: their room temperature ionic conductivity is generally below 10. -4 S cm -1 Furthermore, their mechanical strength is insufficient, making it difficult to meet the practical application requirements of solid-state batteries. Multilayer graphene oxide (mGO) has a unique two-dimensional layered structure, abundant oxygen-containing functional groups (epoxy, hydroxyl, and carboxyl groups), and excellent mechanical properties (elastic modulus of approximately 250 GPa), making it an ideal candidate material for improving the performance of solid-state electrolytes.

[0004] However, graphene oxide itself has a certain degree of electronic conductivity, which can easily lead to battery short circuits or reduced efficiency when used alone as a solid electrolyte. How to rationally apply graphene oxide in solid electrolytes, balancing its electronic conductivity and ionic conductivity while simultaneously improving mechanical strength and interfacial contact performance, has become a current research challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of existing solid electrolytes and provide a solid electrolyte based on graphene oxide and its preparation method, so as to improve the ionic conductivity and electronic insulation of solid electrolytes, improve the interfacial contact effect, increase mechanical strength and rate performance, and thus optimize the rate charge and discharge performance and cycle stability of solid batteries.

[0006] To achieve the above objectives, the present invention provides a solid electrolyte based on graphene oxide, characterized in that it is made by combining an mGO-LLZO mixed slurry with a PEO solution, wherein the mass ratio of multilayer graphene oxide film (mGO) to oxide (LLZO) in the mGO-LLZO mixed slurry is 7-26:40-95, and the amount of PEO added accounts for 30-40% of the total mass of the solid electrolyte.

[0007] Furthermore, the fragment diameter D50 of the multilayer graphene oxide is 0.5-50 μm, preferably 10-15 μm.

[0008] Furthermore, the solvent of the PEO solution is N-methylpyrrolidone or acetonitrile, and the solid content of the PEO solution is 5%.

[0009] On the other hand, the present invention also provides a method for preparing the above-mentioned solid electrolyte based on graphene oxide, comprising the following steps: S1. Graphene oxide is coated on a substrate material, dried, and peeled to obtain a multilayer graphene oxide film. S2. After breaking the multilayer graphene oxide film, dissolve it in an organic solvent, stir and disperse it evenly, add LLZO powder and dissolve it to obtain mGO-LLZO mixed slurry; S3. Mix the PEO solution and mGO-LLZO slurry evenly, apply the mixture to the base membrane, and dry it under vacuum to obtain a solid electrolyte membrane.

[0010] Furthermore, in step S1, the coating process is blade coating, the coating thickness is 100-300μm, the coating speed is 30-50mm / s; the drying conditions are drying at 50-85℃ for 8-24h.

[0011] Furthermore, in step S1, the thickness of the doctor blade coating is preferably 150-200 μm, the coating speed is preferably 35-45 mm / s, and the drying conditions are preferably drying at 55-65℃ for 12-24 h.

[0012] Furthermore, in step S2, the organic solvent is at least one of N-methylpyrrolidone, dimethylformamide, ethylene glycol, butanol, and acetonitrile; and after the multilayer graphene oxide film is broken, it needs to be sieved through a 500-mesh sieve.

[0013] Furthermore, in step S3, the base film is a PE base film or a PP base film, and the thickness of the PE base film is 5μm; the coating process is one or more of the following: scraping coating, spin coating, casting, and casting, and the coating thickness is 7-20μm.

[0014] Furthermore, in step S3, when the coating process is scraping, the coating thickness is preferably 7-10 μm; the vacuum drying conditions are drying at 60°C for 48 hours.

[0015] Furthermore, in step S3, the thickness of the obtained solid electrolyte membrane is 12-15 μm; and during the preparation process, the concentration of the graphene oxide dispersion is 2-3 wt%.

[0016] The beneficial effects of this invention are: High ion conduction efficiency: The oxygen-containing functional groups on the surface of graphene oxide form a multilayer structure with increased interlayer spacing with LLZO. Combined with the PEO polymer skeleton, a highly efficient nano-confined ion channel is constructed, which significantly improves the lithium-ion conduction rate and solves the problems of slow ion migration and insufficient kinetics inside solid-state batteries.

[0017] Excellent electronic insulation: Graphene oxide has lower electronic conductivity than graphite, which can effectively isolate electrons and reduce the risk of short circuits at the positive and negative electrodes of the battery. Combined with a polymer substrate that does not conduct electrons but allows ions to pass through, it further ensures battery safety.

[0018] Good mechanical properties and interface stability: The polymer substrate material improves the mechanical strength of the solid electrolyte membrane, enabling it to maintain good flexibility during cyclic charging and discharging. At the same time, it optimizes the interface contact effect, avoiding accelerated cycle decay caused by poor interface contact after long-term cycling. Attached Figure Description

[0019] Figure 1 This is a SEM image of the mGO-LLZO mixed slurry provided in Example 1 of this application after coating and drying; Figure 2 This describes the morphological distribution of graphene oxide inside the solid electrolyte prepared in this application. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments, but these embodiments do not limit the scope of protection of the present invention.

[0021] Preparation Example 1 This preparation example provides a method for preparing mGO-LLZO slurry, which includes: (1) Weigh 6g of 5wt% graphene oxide dispersion and add it to 4g of deionized water to obtain 3wt% graphene oxide dispersion. (2) The graphene oxide dispersion was coated on the polymer base film with a thickness of 300 μm and then placed in a vacuum oven (60℃ / 18h) for drying to obtain a multilayer graphene oxide film.

[0022] (3) The dried multilayer graphene oxide film was added to the NMP solution and then crushed to control the particle size D50 to 15 μm. The film was then fully dispersed and stirred.

[0023] (4) The dispersed solution is sieved and filtered using a 500-mesh sieve; the residue on the sieve after filtration is weighed and the weight is recorded.

[0024] (5) Add 5g of LLZO electrolyte powder to the multilayer graphene oxide dispersion and stir thoroughly to obtain a multilayer graphene oxide-oxide solid electrolyte (mGO-LLZO) mixed slurry. Wherein mGO:LLZO=15:85.

[0025] Preparation Example 2 The difference between this preparation example and Preparation Example 1 is that the 5 wt% graphene oxide dispersion was diluted to a 2 wt% graphene oxide dispersion.

[0026] Preparation Example 3 The difference between this preparation example and Preparation Example 1 is that the thickness of the scraper is 150 μm, and then it is placed in a vacuum oven (60℃ / 18h) for drying to obtain a multilayer graphene oxide film.

[0027] Preparation Example 4 The difference between this preparation example and Preparation Example 1 is that the dried multilayer graphene oxide film is added to an acetonitrile solution.

[0028] Preparation Example 5 The difference between this preparation example and Preparation Example 1 is that the dispersed solution is not sieved.

[0029] Preparation Example 6 The difference between this preparation example and Preparation Example 1 is that the mGO:LLZO ratio in the graphene oxide mixture slurry is 10:90.

[0030] Preparation Example 7 The difference between this preparation example and Preparation Example 1 is that the mGO:LLZO ratio in the graphene oxide mixture slurry is 20:80.

[0031] Example 1 This embodiment provides a graphene-based solid electrolyte membrane, the preparation method of which includes: (1) Dissolve PEO in NMP solution and stir thoroughly to obtain an organic solvent containing PEO polymer (solid content 5%). (2) PEO organic solvent was added to the mGO-LLZO mixed slurry of Preparation Example 1. After mixing and stirring, the slurry was coated on a 5µm PE base film. The coating thickness was controlled at 7-10µm to ensure the consistency and continuity of the coating. (3) Transfer the coated film to a vacuum oven for drying at 60°C for 48 hours. The thickness of the solid electrolyte film is 12-15 μm.

[0032] Example 2 The difference between this embodiment and Embodiment 1 is that the organic solvent obtained by dissolving PEO in acetonitrile solution is as follows:

[0033] Example 3 The difference between this embodiment and Embodiment 1 is that the slurry is coated on the PE base film, and the coating thickness is controlled at 10-20μm.

[0034] Example 4 The difference between this embodiment and Embodiment 1 is that the slurry is coated on a polypropylene (PP) base film, and the coating thickness is controlled at 7-10 μm.

[0035] Example 5 The difference between this embodiment and Example 1 is that PEO organic solvent is added to the unsieved mGO-LLZO mixed slurry prepared in Example 1.

[0036] Example 6 The difference between this comparative example and Example 1 is that 5 wt% graphene oxide was diluted to a 2 wt% graphene oxide dispersion.

[0037] Comparative Example 1 The difference between this comparative example and Example 1 is that mGO-LLZO is replaced with a polymer slurry containing only LLZO, that is, the addition of multilayer graphene oxide is cancelled.

[0038] Comparative Example 2 The difference between this comparative example and Example 1 is that the slurry is coated onto the PE base film using a spin coating method, and the coating thickness is controlled at 5-10 μm.

[0039] Comparative Example 3 The difference between this comparative example and Example 1 is that the temperature in step (3) is set to 80°C for 12 hours.

[0040] Comparative Example 4 The difference between this comparative example and Example 1 is that the graphene oxide used is commercial graphene oxide powder, without the steps in the preparation example.

[0041] Performance testing I. Electrochemical performance testing of assembled half-cells: (1) Assemble a button cell The electrochemical performance of the solid electrolyte membranes provided in the above embodiments and comparative examples was tested: Preparation of the positive electrode sheet: Nickel-cobalt-manganese (NCM811) material was used as the active material, Super P as the conductive agent, and PVDF as the binder. The mass ratio of active material, Super P, and PVDF was 94:3:3. The active material, Super P, and 5% solid content PVDF@NMP solution were thoroughly mixed and stirred in the specified proportions to obtain the positive electrode slurry. Finally, the positive electrode slurry was uniformly coated onto aluminum foil, and the positive electrode sheet was obtained after drying and cold pressing. Negative electrode sheet: The active material (93% graphite + 7% silicon carbide), conductive agent Super P, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in a deionized water solvent system at a weight ratio of 95.5:1.5:1.2:1.8. The mixture is then coated onto Cu foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0042] (2) Assembling lithium-ion batteries: The above-mentioned positive electrode, solid electrolyte (provided by the examples and comparative examples), and negative electrode are stacked in sequence, and then heated and pressurized to ensure that the positive and negative electrodes can be in close contact with the electrolyte membrane. Then, an aluminum-plastic film is wrapped around the battery, and the battery is transferred to a vacuum oven for drying (60°C, 48h), electrolyte is injected (adding a small amount of 5% electrolyte), and the battery is sealed. After formation, the battery is made into a soft-pack battery. The assembled lithium-ion battery is subjected to electrochemical performance tests at different current densities within the voltage range of 2.5-4.4V. The results are shown in Table 1 (material properties and electrochemical performance) (test temperature is 25°C): Table 1

[0043] As shown in Table 1: The solid-state electrolytes prepared based on graphene oxide as described in Examples 1-5 all exhibited high capacity retention and constant current charge-to-discharge ratios at different rates, indicating that the ion-conducting channels constructed internally by the multilayer graphene oxide play a crucial role. This effectively solves the problems of slow ion migration rate and insufficient kinetics within solid-state batteries. It can achieve 85% capacity retention under 1C charge-discharge conditions; and over 80% capacity retention under 2C charge-discharge conditions, with a capacity retention greater than 80% after 500 cycles.

[0044] As shown in Example 1 and Comparative Example 1, adding graphene oxide to the solid electrolyte membrane to construct internal lithium-ion transport channels can effectively improve the rate performance of the battery and reduce internal polarization. At the same time, the hydroxyl and carboxyl groups in graphene oxide combine with the oxide to form a more stable structure, avoiding accelerated cycle decay due to deterioration of contact with the interface after long-term cycling.

[0045] As shown in Examples 3, 5, and 6, the thickness of the slurry coating, the concentration of the graphene oxide dispersion, and the particle size of the dispersed graphene oxide have a significant impact on the rate performance of the battery cell. Appropriate concentration and interlayer spacing have a beneficial effect on the internally constructed lithium-ion channels, while the particle size directly affects the continuity and consistency of the internal ion channels; conversely, inappropriate particle size may hinder lithium-ion transfer, leading to impaired kinetic performance and reduced rate capability.

[0046] As demonstrated in Examples 2 and 4, the type of solvent, the material of the base film, and the coating process can all affect the performance of the battery cell to varying degrees. The solvent affects the distribution of graphene oxide within the coating and the bonding between the slurry and the foil, thus impacting the rate performance of the battery cell. Simultaneously, the coating process (compared to Example 1) affects the uniformity and continuity of the solid electrolyte membrane, leading to poorer interfacial contact during charging and discharging, thereby affecting rate performance.

[0047] As shown in Comparative Example 3, drying temperature and time affect the formation of internal lithium-ion channels. Although increasing the baking temperature can achieve the drying purpose more quickly, it leads to rapid evaporation of the internal solvent, preventing uniform formation of ion channels and thus affecting rate performance and cycle life. As shown in Comparative Example 4, the multilayer graphene oxide (mGO) film prepared in this application provides more ion migration channels compared to commercial graphene materials, which helps to improve the ion conduction rate inside the electrolyte membrane. Simultaneously, its multilayer structure effectively suppresses agglomeration, ensuring the uniformity and continuity of the solid electrolyte membrane. This structural stability results in tighter interfacial contact between the electrode and electrolyte during charging and discharging, significantly reducing interfacial impedance and improving the reversibility of the electrochemical reaction.

[0048] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention. This specific embodiment is merely an explanation of this application and is not a limitation thereof. Those skilled in the art... After reading this specification, technicians may make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A solid-state electrolyte based on graphene oxide, characterized in that, It is made by combining mGO-LLZO mixed slurry with PEO solution. The mass ratio of multilayer graphene oxide film (mGO) to oxide (LLZO) in the mGO-LLZO mixed slurry is 7-26:40-95, and the amount of PEO added accounts for 30-40% of the total mass of solid electrolyte.

2. The solid-state electrolyte based on graphene oxide according to claim 1, characterized in that, The fragment diameter D50 of the multilayer graphene oxide is 0.5-50 μm, preferably 10-15 μm.

3. The solid-state electrolyte based on graphene oxide according to claim 1, characterized in that, The solvent of the PEO solution is N-methylpyrrolidone or acetonitrile, and the solid content of the PEO solution is 5%.

4. A method for preparing a solid electrolyte based on graphene oxide according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Graphene oxide is coated on a substrate material, dried, and peeled to obtain a multilayer graphene oxide film. S2. After breaking the multilayer graphene oxide film, dissolve it in an organic solvent, stir and disperse it evenly, add LLZO powder and dissolve it to obtain mGO-LLZO mixed slurry; S3. Mix the PEO solution and mGO-LLZO slurry evenly, apply the mixture to the base membrane, and dry it under vacuum to obtain a solid electrolyte membrane.

5. The preparation method according to claim 4, characterized in that, In step S1, the coating process is blade coating, the coating thickness is 100-300μm, and the coating speed is 30-50mm / s; the drying conditions are drying at 50-85℃ for 8-24h.

6. The preparation method according to claim 5, characterized in that, In step S1, the thickness of the blade coating is preferably 150-200 μm, the coating speed is preferably 35-45 mm / s, and the drying conditions are preferably drying at 55-65℃ for 12-24 h.

7. The preparation method according to claim 4, characterized in that, In step S2, the organic solvent is at least one of N-methylpyrrolidone, dimethylformamide, ethylene glycol, butanol, and acetonitrile; and the multilayer graphene oxide film, after being broken, needs to be sieved through a 500-mesh sieve.

8. The preparation method according to claim 4, characterized in that, In step S3, the base film is a PE base film or a PP base film, and the thickness of the PE base film is 5μm; the coating process is one or more of the following: scraping coating, spin coating, casting, and casting, and the coating thickness is 7-20μm.

9. The preparation method according to claim 8, characterized in that, In step S3, when the coating process is scraping, the coating thickness is preferably 7-10 μm; the vacuum drying conditions are drying at 60°C for 48 hours.

10. The preparation method according to claim 4, characterized in that, In step S3, the thickness of the obtained solid electrolyte membrane is 12-15 μm; and during the preparation process, the concentration of the graphene oxide dispersion is 2-3 wt%.

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