Preparation method of clay mineral nanocomposite / polymer composite solid electrolyte with high room temperature ionic conductivity

Abstract

The invention discloses a preparation method of a clay mineral nanocomposite / polymer composite solid electrolyte with high room-temperature ionic conductivity. First, at 60 °C, a lithium salt is dissolved in a mixed solvent of succinonitrile and fluoroethylene carbonate; then, pretreated clay mineral nanoparticles are added thereto, and a clay mineral nanocomposite with high lithium ion conductivity is obtained through vacuum ultrasonic treatment. Second, the clay mineral nanocomposite is dispersed in anhydrous acetonitrile, a polymer is added and stirred under vacuum to obtain a uniform slurry, and then a composite solid electrolyte is prepared by using a coating technique. The invention improves the lithium ion transfer ability of the clay mineral nanomaterial in the solid electrolyte and improves the interfacial chemical environment and continuity between the clay mineral nanomaterial and the polymer through the microscopic interfacial interaction between different components, thereby significantly improving the room-temperature ionic conductivity of the polymer composite solid electrolyte and finally effectively improving the cycle stability of the lithium metal battery.

Description

Technical Field

[0001] The present invention relates to the technical field of nanocomposite materials, and particularly relates to a clay mineral nanocomposite / polymer composite solid electrolyte with high room temperature ionic conductivity and a preparation method thereof. Background Art

[0002] Lithium metal batteries are one of the most promising high specific energy electrochemical energy storage systems. However, the existing liquid lithium metal batteries are restricted in their commercial development due to problems such as lithium dendrites and leakage. Solid electrolytes can not only effectively solve the above problems but also increase the energy density of the battery. Therefore, developing solid electrolytes to gradually replace liquid electrolytes is an inevitable choice for the development of current electrochemical energy storage technologies, which has attracted great attention from enterprises such as CATL and BYD; it is expected that by 2030, the global demand for solid-state batteries will be close to 500 GWh, and the market space will reach about 152 billion yuan.

[0003] Among various types of solid electrolytes, polymer solid electrolytes have developed rapidly due to their advantages such as good flexibility, easy processing, and low cost. However, the low room-temperature ionic conductivity of polymer solid electrolytes greatly limits their application in solid-state lithium metal batteries. Currently, methods such as polymer chain modification, addition of plasticizers, and introduction of ceramic fillers can all improve the room-temperature ionic conductivity of polymer solid electrolytes. Among them, the inorganic / polymer composite solid electrolyte prepared by introducing ceramic fillers not only improves the ionic conductivity but also retains the flexibility and easy processing of polymer components, which is the most practical solid electrolyte (Nat. Rev. Mater. 2021, 6, 1003). Commonly used ceramic fillers include lithium-ion conductor fillers (CN202211516554.8, CN202011495087.6, CN202110896051.) and non-lithium-ion conductor fillers (CN201611225335.9, CN202211302169.3, CN202310009942.5). Lithium-ion conductor fillers are more effective in enhancing ion transport; however, due to the unstable chemical properties of lithium-ion conductor fillers (such as sulfides being prone to water absorption and decomposition), they require harsh processing techniques. Non-lithium-ion conductor fillers mainly inhibit the crystallization of polymers through physical interactions and simultaneously form ion transport channels through Lewis acid-base interactions in the interfacial layer between polymers and particles to improve ionic conductivity. However, the ionic conductivity of polymer composite solid electrolytes based on non-lithium-ion conductor fillers is still relatively low. Therefore, researchers directly added succinonitrile to the polymer composite solid electrolyte, effectively improving the ionic conductivity of the composite electrolyte (Adv.Energy Mater. 2023, 13, 2204036, Electrochim. Acta 2023, 437, 141504, CN202010889688.9, CN201910802415.3). However, the introduction of succinonitrile not only accelerates the corrosion of the lithium metal anode but also limits the charge-discharge rate of solid-state lithium metal batteries.

[0004] As natural nanomaterials, clay minerals have the advantages of large reserves, wide distribution, low cost, and diverse types. The rich elemental composition, diverse morphologies (such as nanorods, nanotubes, nanosheets, etc.) and crystal structures (1:1 type, 1:2 type) of clay minerals endow them with unique physical and chemical properties (such as surface charge, strong adsorption, cation exchange capacity, chemical / thermal stability), and have received great attention in the energy storage field, such as functionalized electrode materials (CN202210702260.8, CN202110749766.X), composite battery separators (CNZL201710856895.2, CN202110651748.8, CN202110651753.9, CN202011626485.7) and inorganic / polymer composite solid electrolytes (CN201910406415.1, CN202011596279.6, CN201610153789.3, CN202110261409.9, CN202210583711.0, CN201810382451.4, CN201910223172.8, CN202110855463.6, CN202110025374.9, CN202010804810.8, CN202111568055.9), etc. For example: Patent CN200710144760.X dispersed lithium salt and polyethylene oxide in a solvent, and then added ultrafine powders such as nanoclay to obtain a solid-state electrolyte; Patent CN202310047074.X first modified hectorite with ionic liquid, and then dispersed it with a polymer substrate and lithium salt in an organic solvent to prepare a solid-state electrolyte with high ion transference number and good interfacial compatibility. In addition to the above technological developments, a large number of theoretical studies have also focused on the influence of clay minerals on the performance of solid electrolytes (Adv. Funct. Mater. 2019, 29, 1900648, ACS Appl. Mater. Interfaces 2019, 11, 8954, Nano Energy 2021, 90, 106490, Adv. Mater. 2022, 34, 2202063). For example: Jan D. Miller et al. directly dispersed halloysite, lithium salt and polyethylene oxide in acetonitrile, and obtained a solid-state electrolyte by doctor blading, revealing the influence of halloysite on the ionic conductivity of the composite solid electrolyte (Nano Energy 2017, 31, 478); Yuan Yang et al. directly used attapulgite as a new type of ceramic filler to enhance the mechanical and electrochemical properties of PVDF-based composite solid electrolytes (Nano Lett. 2018, 18, 6113).However, existing technologies and research mainly focus on the effects of clay mineral nanoparticles as novel ceramic fillers on the ionic conductivity and mechanical properties of polymer composite solid electrolytes. However, the low lithium-ion conductivity of clay minerals limits their further application in composite solid electrolytes. Therefore, how to develop clay mineral nanocomposites with high lithium-ion conductivity is the key to realizing the large-scale application of clay minerals in composite solid electrolytes. Based on this, this application proposes to construct clay mineral nanocomposites with high lithium-ion conductivity through the interaction between multiple components, and then regulate the interfacial environment between them and polymers to prepare composite solid electrolytes with high room-temperature ionic conductivity, which is expected to solve the key problem of low room-temperature ionic conductivity of existing solid electrolytes, significantly improve the comprehensive performance of solid-state lithium-metal batteries such as capacity, rate performance, and cycle stability, and promote the rapid development of solid-state batteries. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a clay mineral nanocomposite / polymer composite solid electrolyte with high room-temperature ionic conductivity to solve the problem of low room-temperature ionic conductivity of existing polymer composite solid electrolytes and promote the development of solid-state lithium-metal batteries.

[0006] I. Preparation of Clay Mineral Nanocomposite / Polymer Composite Solid Electrolyte with High Room-Temperature Ionic Conductivity

[0007] 1) Preparation of clay mineral nanocomposites with high lithium-ion conductivity: At 60 °C, dissolve a lithium salt in a mixed solvent of succinonitrile and fluoroethylene carbonate, and then add pretreated clay mineral nanoparticles thereto. After vacuum ultrasonic treatment, clay mineral nanocomposites with high lithium-ion conductivity are obtained; wherein, the pretreatment of the clay mineral is achieved by vacuum ultrasonic and high-pressure homogenization processes to exfoliate the clay mineral aggregates.

[0008] The lithium salt is at least one of lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, and lithium bis(fluorosulfonyl)imide; the mass ratio of the lithium salt in the mixed solvent is 3-55 wt%; the clay mineral is at least one of attapulgite, montmorillonite, lithium saponite, halloysite, mica, and kaolinite; the mass ratio of the clay mineral in the mixed solvent is 10-60 wt%; the volume ratio of succinonitrile and fluoroethylene carbonate in the mixed solvent is 9.8:0.2-6.8:3.2.

[0009] The vacuum ultrasonic treatment means that the vacuum degree is controlled at -0.65×100 KPa ~ -0.85×100 Kpa, the ultrasonic time is controlled at 0.5-6 h, and the temperature is controlled at 60 °C.

[0010] 2) Preparation of clay mineral nanocomposite / polymer composite solid electrolyte: The clay mineral nanocomposite with high lithium ion conductivity obtained in step 1) is dispersed in anhydrous acetonitrile, and then a polymer is added for vacuum stirring to obtain a uniform slurry. Finally, a clay mineral nanocomposite / polymer composite solid electrolyte is prepared by a coating technique.

[0011] The polymer is at least one of polyethylene oxide, polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropylene), and polyacrylonitrile.

[0012] The mass ratio of the clay mineral nanocomposite to the polymer is 7.5:2.5 to 3.5:6.5.

[0013] The vacuum stirring means that the vacuum degree is controlled at -0.35×100 KPa to -0.8×100 Kpa, the stirring time is controlled at 1 to 24 h, and the ambient temperature is controlled at 20 to 55 °C.

[0014] The synthesis mechanism of the present invention is as follows: First, based on the surface and interface chemistry of clay minerals, a mixture of succinonitrile / fluoroethylene carbonate of a lithium salt is compounded with it, which can effectively improve the lithium ion transfer ability of clay minerals while maximizing the exfoliation of clay minerals to reduce their aggregation in the polymer. At the same time, by compounding succinonitrile with clay minerals, the free succinonitrile small molecules in the polymer composite solid electrolyte can be effectively reduced, avoiding the corrosion of the lithium metal electrode by succinonitrile. In addition, using fluoroethylene carbonate as a co-solvent can effectively promote the interfacial stability between the composite solid electrolyte and the lithium metal negative electrode, thereby improving the cycle stability of the lithium metal battery.

[0015] II. Performance of clay mineral nanocomposite / polymer composite solid electrolyte

[0016] 1. Ionic conductivity

[0017] Figure 1 It is a comparison chart of the ionic conductivities of the composite solid electrolytes of the comparative example, Example 1 and 3 of the present invention at different temperatures. The experimental results show that the ionic conductivity of the composite solid electrolyte prepared by the present invention can reach 0.25×10 −3 S cm −1 -1, which is 13 times higher than the ionic conductivity of the composite solid electrolyte of the comparative example of the present invention.

[0018] 2. Electrochemical stability

[0019] Figure 2Figure for comparing the electrochemical stabilities of different composite solid electrolytes prepared in Comparative Example, Example 1, and Example 3. Through the comparative study of the electrochemical stabilities of different composite solid electrolytes, it was found that the electrochemical stability voltages of the composite solid electrolytes invented in Example 1 and Example 3 can reach 5.3 V and 3.8 V respectively, which are higher than that of the composite solid electrolyte invented in the Comparative Example (3.5 V). This indicates that the composite solid electrolyte invented in this application has excellent electrochemical stability.

[0020] 3. Cycling stability of lithium metal batteries

[0021] Using NCM811 as the positive electrode and lithium metal as the negative electrode, high-voltage lithium metal batteries were assembled with the composite solid electrolytes invented in the Comparative Example and Example 1 respectively; after activation, their charge-discharge performance at 1.0 C was investigated, and the results are as Figure 3 shown. It was found that the composite solid electrolyte invented in this application can effectively improve the cycling stability of lithium metal batteries. In addition, even after being bent 180° and cut and damaged, the lithium metal battery soft pack can still light up a light-emitting diode.

[0022] In summary, in this invention, a clay mineral nanocomposite with high lithium ion conductivity was first constructed through the interaction between multiple components, and then the interface environment between the clay mineral nanocomposite and the polymer was regulated to prepare a composite solid electrolyte with high room temperature ionic conductivity, solving the key problem of low room temperature ionic conductivity of existing solid electrolytes, significantly improving the comprehensive performance such as the capacity, rate performance, and cycling stability of solid-state lithium metal batteries, and promoting the rapid development of solid-state batteries. Brief Description of the Drawings

[0023] Figure 1 Curve showing the effect of temperature on the ionic conductivity of the composite solid electrolyte.

[0024] Figure 2 Figure for comparing the electrochemical stabilities of different composite solid electrolytes.

[0025] Figure 3 Figure for comparing the cycling stabilities of lithium metal batteries assembled with different composite solid electrolytes.

[0026] Figure 4 Photos showing the lighting of a light-emitting diode by the lithium metal battery assembled with the composite solid electrolyte invented in Example 1 in different states. Detailed Description of the Invention

[0027] The following further explains and illustrates the present invention with specific examples.

[0028] Example 1

[0029] (1)Preparation of clay mineral nanocomposites with high lithium ion conductivity: At 60 °C, 0.08 g of lithium perchlorate was dissolved in a mixed solvent of 0.32 g of succinonitrile and fluoroethylene carbonate (v:v = 8:2), and stirred for 30 min; then 0.32 g of pretreated attapulgite nanoparticles were added thereto, and vacuum ultrasonic treatment (vacuum degree controlled at -0.76×100 KPa) was carried out at 60 °C for 1 h to obtain attapulgite nanocomposites with high lithium ion conductivity.

[0030] (2)Preparation of clay mineral nanocomposite / polymer composite solid electrolyte: The attapulgite nanocomposites (0.8 g) prepared in (1) were dispersed in 5 mL of anhydrous acetonitrile, 0.343 g of polyethylene oxide was added, and a uniform slurry was obtained by vacuum stirring (vacuum degree controlled at -0.55×100 KPa, stirring time controlled at 6 h, and ambient temperature controlled at 50 °C), and then an attapulgite / polyethylene oxide composite solid electrolyte was prepared by a coating technique.

[0031] After testing, the ionic conductivity of the attapulgite / polyethylene oxide composite solid electrolyte at room temperature can reach 0.25×10 −3 S cm −1 ; the electrochemical stable voltage reaches 5.3 V.

[0032] Example 2

[0033] (1)Preparation of clay mineral nanocomposites with high lithium ion conductivity: At 60 °C, 0.04 g of lithium trifluoromethanesulfonate was dissolved in a mixed solvent of 0.16 g of succinonitrile and fluoroethylene carbonate (v:v = 6.8:3.2), and stirred for 40 min; then 0.3 g of pretreated montmorillonite nanoparticles were added thereto, and vacuum ultrasonic treatment (vacuum degree controlled at -0.82×100 KPa) was carried out at 60 °C for 5 h to obtain montmorillonite nanocomposites with high lithium ion conductivity.

[0034] (2)Preparation of clay mineral nanocomposite / polymer composite solid electrolyte: The montmorillonite nanocomposites (0.9 g) prepared in (1) were dispersed in 50 mL of anhydrous acetonitrile, 0.6 polyacrylonitrile was added, and a uniform slurry was obtained by vacuum stirring (vacuum degree controlled at -0.7×100 KPa, stirring time controlled at 18 h, and ambient temperature controlled at 25 °C), and then a montmorillonite / polyacrylonitrile composite solid electrolyte was prepared by a coating technique.

[0035] After testing, the ionic conductivity of the montmorillonite / polyacrylonitrile composite solid electrolyte at room temperature can reach 0.5×10 −3 Scm −1 ; the electrochemical stable voltage reaches 4.8 V.

[0036] Example 3

[0037] (1) Preparation of clay mineral nanocomposites with high lithium ion conductivity: At 60 °C, 0.18 lithium bis(fluorosulfonyl)imide was dissolved in a mixed solvent of 0.27 g of succinonitrile and fluoroethylene carbonate (v:v = 7.5:2.5), and stirred for 45 min; then 0.25 g of pretreated hectorite nanoparticles were added thereto, and vacuum ultrasonic treatment (vacuum degree controlled at -0.66×100 KPa) was carried out at 60 °C for 2 h to obtain hectorite nanocomposites with high lithium ion conductivity.

[0038] (2) Preparation of clay mineral nanocomposite / polymer composite solid electrolyte: The hectorite nanocomposites (0.7 g) prepared in (1) were dispersed in 13 mL of anhydrous acetonitrile, 0.6 g of polyethylene oxide was added, and a uniform slurry was obtained by vacuum stirring (vacuum degree controlled at -0.4×100 KPa, stirring time controlled at 24 h, and ambient temperature controlled at 30 °C), and then a hectorite / polyethylene oxide composite solid electrolyte was prepared by a coating technique.

[0039] After testing, the ionic conductivity of the hectorite / polyethylene oxide composite solid electrolyte at room temperature can reach 0.20×10 −3 S cm −1 ; the electrochemical stable voltage reaches 3.8 V.

[0040] Example 4

[0041] (1) Preparation of clay mineral nanocomposites with high lithium ion conductivity: At 60 °C, 0.5 g of bis(trifluoromethanesulfonyl)imide lithium was dissolved in a mixed solvent of 0.24 g of succinonitrile and fluoroethylene carbonate (v:v = 9:1), and stirred for 60 min; then 0.26 g of pretreated halloysite nanoparticles were added thereto, and vacuum ultrasonic treatment (vacuum degree controlled at -0.8×100 KPa) was carried out at 60 °C for 0.5 h to obtain halloysite nanocomposites with high lithium ion conductivity.

[0042] (2) Preparation of clay mineral nanocomposite / polymer composite solid electrolyte: The halloysite nanocomposites (1.0 g) prepared in (1) were dispersed in 42 mL of anhydrous acetonitrile, 2.3 g of poly(vinylidene fluoride - co - hexafluoropropylene) was added, and a uniform slurry was obtained by vacuum stirring (vacuum degree controlled at -0.5×100 KPa, stirring time controlled at 12 h, and ambient temperature controlled at 45 °C), and then a halloysite / poly(vinylidene fluoride - co - hexafluoropropylene) composite solid electrolyte was prepared by a coating technique.

[0043] After testing, the ionic conductivity of the halloysite / poly(vinylidene fluoride-co-hexafluoropropylene) composite solid electrolyte can reach 0.63×10 −3 S cm −1 ; the electrochemical stable voltage reaches 5.3 V.

[0044] Comparative example

[0045] Using polyethylene oxide as the polymer, it was dispersed in anhydrous acetonitrile; subsequently, lithium bis(trifluoromethanesulfonyl)imide (10 wt%) and succinonitrile (5 wt%) were added respectively, and a uniform slurry was obtained by stirring and ultrasonic treatment. Subsequently, a polyethylene oxide polymer electrolyte was prepared by a coating technique.

Claims

1. A preparation method of a clay mineral nanocomposite / polymer composite solid electrolyte with high room-temperature ionic conductivity, characterized in that, It includes the following steps: 1) Preparation of clay mineral nanocomposites with high lithium ion conductivity: At 60 °C, dissolve a lithium salt in a mixed solvent of succinonitrile and fluoroethylene carbonate, and then add pretreated clay mineral nanoparticles thereto. After vacuum ultrasonic treatment, clay mineral nanocomposites with high lithium ion conductivity are obtained; wherein, the pretreatment of the clay mineral is to achieve the exfoliation of clay mineral aggregates through a vacuum ultrasonic and high-pressure homogenization process; The lithium salt is at least one of lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, and lithium bis(fluorosulfonyl)imide; the mass ratio of the lithium salt in the mixed solvent is 3-55 wt%; The volume ratio of succinonitrile to fluoroethylene carbonate in the mixed solvent is 9.8:0.2-6.8:3.2; The clay mineral is at least one of attapulgite, montmorillonite, lithium saponite, halloysite, mica, and kaolinite; the mass ratio of the clay mineral in the mixed solvent is 10-60 wt%; The vacuum ultrasonic treatment means that the vacuum degree is controlled at -0.65×100 KPa to -0.85×100 Kpa, the ultrasonic time is controlled at 0.5-6 h, and the temperature is controlled at 60 °C; 2) Preparation of clay mineral nanocomposite / polymer composite solid electrolyte: Disperse the clay mineral nanocomposites with high lithium ion conductivity obtained in step 1) in anhydrous acetonitrile, then add a polymer and perform vacuum stirring to obtain a uniform slurry, and finally use a coating technique to prepare a clay mineral nanocomposite / polymer composite solid electrolyte; The polymer is at least one of polyethylene oxide, polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropylene), and polyacrylonitrile; The mass ratio of the clay mineral nanocomposites to the polymer is 7.5:2.5-3.5:6.5; The vacuum stirring means that the vacuum degree is controlled at -0.35×100 KPa to -0.8×100 Kpa, the stirring time is controlled at 1-24 h, and the ambient temperature is controlled at 20-55 °C.

2. Application of a clay mineral nanocomposite / polymer composite solid electrolyte with high room temperature ionic conductivity prepared by the method according to claim 1 in a solid-state lithium metal battery.

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