Fluorinated polydioxolame solid electrolyte, preparation method thereof and battery prepared by using fluorinated polydioxolame solid electrolyte

Abstract

The invention belongs to the technical field of solid-state batteries, and particularly relates to a fluorinated polydioxolame solid-state electrolyte, a preparation method thereof and a battery prepared from the fluorinated polydioxolame solid-state electrolyte. Fluorinated polydioxolame is prepared by adopting a fluorine fluorination method and is applied to the solid-state electrolyte, so that on one hand, the oxidation resistance of the electrolyte is effectively improved, and the service life of the electrolyte is prolonged; a high-voltage and high-capacity positive electrode material can be matched, and the energy density of the battery is improved; on the other hand, the fluorinated polydioxolame electrolyte is decomposed to generate a LiF-rich SEI interface layer, so that the ionic conductivity is improved, the interface stability is enhanced, the battery keeps good cycling stability and safety under high voltage, in addition, the polymerization process of 1, 3-dioxolame can be carried out at room temperature, additional operation is not needed, the preparation process is simplified, and the production cost is reduced. The method has low requirements on equipment and can be used for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery technology, and particularly relates to a fluorinated polydioxolane, its preparation method, and a battery prepared using the same. Background Technology

[0002] Lithium-ion batteries, as high-energy-density rechargeable batteries, are widely used in electronic products and electric vehicles. However, traditional lithium-ion batteries have some pressing problems, mainly related to the organic electrolytes they use. Organic electrolytes are flammable and volatile, posing safety hazards such as leakage, combustion, and explosion, seriously affecting the safety and stability of lithium-ion batteries. Furthermore, the energy density of traditional lithium-ion batteries is insufficient to meet the demands of future high-performance applications.

[0003] To address these issues, solid-state lithium batteries were developed. By solidifying the electrolyte, solid-state lithium batteries effectively avoid the safety hazards of traditional liquid electrolytes, while also offering advantages such as high mechanical strength, high energy density, and non-flammability. Solid-state electrolytes are mainly divided into two categories: inorganic solid-state electrolytes and polymer solid-state electrolytes. Inorganic solid-state electrolytes have advantages such as high ionic conductivity and a wide electrochemical window, but suffer from insufficient mechanical strength and poor interfacial contact. While polymer solid-state electrolytes possess good flexibility and a wide electrochemical stability window, their low room-temperature ionic conductivity makes them unsuitable for high-power operation.

[0004] Polymer electrolyte materials possess advantages such as light weight, low cost, easy film formation, and good stability, playing a crucial role in the application of all-solid-state lithium-ion batteries. In particular, they have a low elastic modulus, can be designed into various shapes, and have a simple preparation process and wide applicability. Currently, there are various polymers available, including polyethylene oxide (PEG), polydioxanone (PDOL), polyacrylonitrile (PAC), and polyvinylidene fluoride (PVDF). Among them, PDOL is a polymer that readily polymerizes at room temperature, has low crystallinity, and exhibits high ionic conductivity, making it a common raw material for electrolytes. However, the ionic conductivity of current PDOL-based solid electrolytes still lags significantly behind that of liquid electrolytes, and their oxidation resistance under high pressure is poor. Therefore, developing a novel solid electrolyte material that can further reduce the regularity of PDOL polymers and improve their ionic conductivity, oxidation resistance, and cycle stability is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a fluorinated polydioxolane, a method for preparing the same, and a solid-state battery prepared using the same.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing fluorinated polydioxolane includes the following steps: S1. Add 1,3-dioxolane (DOL) monomer to the fluorination equipment, and add lithium hexafluorophosphate (LiPF6) as an initiator (the amount of initiator added accounts for 1wt%-5wt% of the total mass). Mix at room temperature to obtain a homogeneous mixed solution. Let it stand for 8~24h. The 1,3-dioxolane will complete the self-polymerization, thus obtaining polydioxolane that has been cured and has no flowability. The specific reaction process is as follows: S2. In the fluorination equipment, nitrogen gas is introduced at a flow rate of 0.5-5 mL / min for 0.5-2 h to remove air, and then a mixture of nitrogen and fluorine gas (fluorine content 10wt%-40wt%) is introduced at a flow rate of 3-7 mL / min. The reaction temperature is controlled at -30-0℃ for 72-168 h to obtain fluorinated polydioxolane. S3. The prepared fluorinated polydioxolane is mixed evenly with lithium salt and organic solvent at room temperature, and 8-15 μL is added dropwise to the surface of the battery separator per square centimeter. The mixture is then allowed to stand at room temperature to obtain the fluorinated polydioxolane solid electrolyte.

[0007] Furthermore, in step S3, the lithium salt is at least one of lithium perchlorate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium hexafluorophosphate; the amount of lithium salt is 10-30 wt% of the solid electrolyte.

[0008] Furthermore, the organic solvent is any one of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, and tetrahydrofuran; the mass ratio of the solid electrolyte to the organic solvent is 1~4:1.

[0009] Furthermore, in step S3, the battery separator can be any one of PE separator, PP separator, or glass fiber separator.

[0010] Another object of the present invention is to provide a fluorinated polydioxolane solid electrolyte prepared by the above-described preparation method.

[0011] Another object of the present invention is to provide a solid-state battery comprising the above-described fluorinated polydioxolane solid electrolyte.

[0012] This invention also provides a method for preparing a solid-state battery, comprising the following steps: a. Slurry preparation: The electrode material, conductive agent, and binder are mixed in a mass ratio of 8-9:0.5-1:0.5-1 to prepare the electrode slurry; b. Coating: The prepared electrode paste is uniformly coated on aluminum foil with a coating thickness of 80-180 μm, and then dried in a forced-air drying oven at 60-80℃ for 6-12 hours to obtain the electrode sheet. c. Battery assembly: The coin cell is assembled by using the electrode sheet as the positive electrode, the lithium sheet as the negative electrode, and the fluorinated polydioxolane solid electrolyte.

[0013] Furthermore, the electrode material is one of lithium nickel cobalt manganese, lithium nickel cobalt aluminum, lithium nickel cobalt manganese aluminum, lithium iron phosphate, lithium manganese oxide, or graphite.

[0014] Mechanism: The fluorination process of this invention introduces strongly polar CF bonds into PDOL. Their decomposition can form a LiF-rich SEI layer, which can improve ionic conductivity, effectively suppress side reactions, and reduce interfacial impedance, thereby significantly improving the cycle life of the battery. In addition, the ether bonds of PDOL are relatively unstable at high voltages and are easily oxidized and decomposed at high potentials (such as when paired with high-voltage cathode materials). Fluorinated polydioxolane rings are substituted with fluorine on the chain. Fluorine atoms attack and replace hydrogen atoms on the PDOL molecular chain to form a fluorinated PDOL network structure, which can improve oxidation resistance, widen the voltage window, and improve ionic conductivity. The fluorination treatment introduces strong CF bonds with high bond energy and good chemical stability, which effectively delays the oxidative decomposition of PDOL under high voltage.

[0015] The advantages of this invention are as follows: By using fluorination gas to prepare fluorinated polydioxolane and applying it to solid electrolytes, this invention effectively improves the oxidation resistance of the electrolyte, enabling it to match high-voltage, high-capacity cathode materials and increase battery energy density. On the other hand, the fluorinated polydioxolane electrolyte decomposes to generate a LiF-rich SEI interface layer, which improves ionic conductivity and enhances interface stability, allowing the battery to maintain good cycle stability and safety under high voltage. Furthermore, the polymerization process of 1,3-dioxolane can occur at room temperature without additional operations, simplifying the preparation process, reducing equipment requirements, and making it suitable for large-scale industrial production. Detailed Implementation

[0016] Example 1 Add 1,3-dioxolane (DOL) monomer to the container of the fluorination equipment, then add lithium hexafluorophosphate (LiPF6) as an initiator (addition amount is 2wt%), mix evenly at room temperature, and let stand for 1,3-dioxolane to complete self-polymerization to obtain polydioxolane (PDOL).

[0017] PDOL was added to the fluorination equipment, and nitrogen gas was introduced at a flow rate of 2 mL / min for 2 h to remove air. Then, a mixture of nitrogen and fluorine gas (fluorine content 10 wt%) was introduced at a flow rate of 4 mL / min. The reaction temperature was controlled at -10℃ and the reaction time was 154 h to obtain fluorinated polydioxolane (hereinafter abbreviated as F-PDOL).

[0018] The F-PDOL obtained above was mixed with LiFSI and acetonitrile at room temperature to form a mixture for use. The mass ratio of F-PDOL to acetonitrile was 1:1, and the amount of LiFSI added was 15 wt% of the total.

[0019] 30 μL of a well-mixed solution was added dropwise to the negative electrode side. After covering with a 19 mm diameter PP separator, another 30 μL of the mixture was added dropwise. The positive electrode was then placed on top, and the battery was encapsulated. The solid-state battery prepared in this invention uses lithium metal as the negative electrode and NCM613 as the positive electrode. The mass ratio of NCM613, SP, and binder is 90:5:5, and the areal density is 150 g / m³. 2 . Example 2 Lithium hexafluorophosphate (LiPF6) (2wt%) is added to 1,3-dioxolane (DOL) monomer as an initiator. The mixture is stirred evenly at room temperature and allowed to stand until the 1,3-dioxolane self-polymerizes to obtain polydioxolane (PDOL).

[0020] PDOL was added to the fluorination equipment, and nitrogen gas was introduced at a flow rate of 3 mL / min for 1 hour to remove air. Then, a mixture of nitrogen and fluorine gas (fluorine content 20 wt%) was introduced at a flow rate of 4 mL / min. The reaction temperature was controlled at -10℃ and the reaction was carried out for 128 hours to obtain fluorinated polydioxolane (hereinafter abbreviated as F-PDOL).

[0021] The F-PDOL obtained above was mixed with LiFSI and acetonitrile at room temperature to form a mixture. The mass ratio of F-PDOL to acetonitrile was 1:1, and the amount of LiFSI added was 15 wt% of the total.

[0022] 30 μL of a well-mixed solution was added dropwise to the negative electrode side. After covering with a 19 mm diameter PP separator, another 30 μL of the mixture was added dropwise. The positive electrode was then placed on top, and the battery was encapsulated. The solid-state battery prepared in this invention uses lithium metal as the negative electrode and NCM613 as the positive electrode. The mass ratio of NCM613, SP, and binder is 90:5:5, and the areal density is 150 g / m³. 2 . Example 3: Lithium hexafluorophosphate (LiPF6) (2wt%) is added to 1,3-dioxolane (DOL) monomer as an initiator. The mixture is stirred evenly at room temperature and allowed to stand until the 1,3-dioxolane self-polymerizes to obtain polydioxolane (PDOL).

[0023] PDOL was added to the fluorination device, and nitrogen gas was introduced at a flow rate of 3 mL / min for 1 hour to remove air. Then, a mixture of nitrogen and fluorine gas (fluorine content 20 wt%) was introduced at a flow rate of 6 mL / min. The reaction temperature was controlled at -20℃ and the reaction was carried out for 120 hours to obtain fluorinated polydioxolane (hereinafter abbreviated as F-PDOL).

[0024] The F-PDOL obtained above was mixed with LiFSI and acetonitrile at room temperature to form a mixture. The mass ratio of F-PDOL to acetonitrile was 1:1, and the amount of LiFSI added accounted for 15 wt% of the total.

[0025] 30 μL of a well-mixed solution was added dropwise to the negative electrode side. After covering with a 19 mm diameter PP separator, another 30 μL of the mixture was added dropwise. The positive electrode was then placed on top, and the battery was encapsulated. The solid-state battery prepared in this invention uses lithium metal as the negative electrode and NCM613 as the positive electrode. The mass ratio of NCM613, SP, and binder is 90:5:5, and the areal density is 150 g / m³. 2 . Example 4 Lithium hexafluorophosphate (LiPF6) (2wt%) is added to 1,3-dioxolane (DOL) monomer as an initiator. The mixture is stirred evenly at room temperature and allowed to stand until the 1,3-dioxolane self-polymerizes to obtain polydioxolane (PDOL).

[0026] PDOL was added to the fluorination device, and nitrogen gas was introduced at a flow rate of 3 mL / min for 1 hour to remove air. Then, a mixture of nitrogen and fluorine gas (fluorine content 40 wt%) was introduced at a flow rate of 6 mL / min. The reaction temperature was controlled at -20℃ and the reaction was carried out for 75 hours to obtain fluorinated polydioxolane (hereinafter abbreviated as F-PDOL).

[0027] The F-PDOL obtained above was mixed with LiFSI and acetonitrile at room temperature to form a mixture. The mass ratio of F-PDOL to acetonitrile was 3:1, and the amount of LiFSI added accounted for 15 wt% of the total.

[0028] 30 μL of a well-mixed solution was added dropwise to the negative electrode side. After covering with a 19 mm diameter PP separator, another 30 μL of the mixture was added dropwise. The positive electrode was then placed on top, and the battery was encapsulated. The solid-state battery prepared in this invention uses lithium metal as the negative electrode and NCM613 as the positive electrode. The mass ratio of NCM613, SP, and binder is 90:5:5, and the areal density is 150 g / m³. 2 . Example 5 Lithium hexafluorophosphate (LiPF6) (2wt%) is added to 1,3-dioxolane (DOL) monomer as an initiator. The mixture is stirred evenly at room temperature and allowed to stand until the 1,3-dioxolane self-polymerizes to obtain polydioxolane (PDOL).

[0029] PDOL was added to the fluorination device, and nitrogen gas was introduced at a flow rate of 3 mL / min for 1 hour to remove air. Then, a mixture of nitrogen and fluorine gas (fluorine content 30 wt%) was introduced at a flow rate of 6 mL / min. The reaction temperature was controlled at -20℃ and the reaction was carried out for 96 hours to obtain fluorinated polydioxolane (hereinafter abbreviated as F-PDOL).

[0030] The F-PDOL obtained above was mixed with LiFSI and acetonitrile at room temperature to form a mixture for use. The mass ratio of F-PDOL to acetonitrile was 4:1, and the amount of LiFSI added accounted for 20 wt% of the total.

[0031] 30 μL of a well-mixed solution was added dropwise to the negative electrode side. After covering with a 19 mm diameter PP separator, another 30 μL of the mixture was added dropwise. The positive electrode was then placed on top, and the battery was encapsulated. The solid-state battery prepared in this invention uses lithium metal as the negative electrode and NCM613 as the positive electrode. The mass ratio of NCM613, SP, and binder is 90:5:5, and the areal density is 150 g / m³. 2 . Comparative Example 1 Lithium hexafluorophosphate (LiPF6) was added as an initiator to 1,3-dioxolane (DOL) monomer (2wt%) and mixed thoroughly at room temperature. 30 μL of the homogeneous solution was then dropped onto the negative electrode side. After covering with a 19 mm diameter PP separator, another 30 μL of the mixture was dropped on, followed by the placement of the positive electrode and encapsulation of the battery. The solid-state battery prepared in this invention uses lithium metal as the negative electrode and NCM613 as the positive electrode. The mass ratio of NCM613, SP, and binder is 90:5:5, and the areal density is 150 g / m³. 2 . Comparative Example 2 Lithium hexafluorophosphate (LiPF6) was added as an initiator to 1,3-dioxolane (DOL) monomer (2 wt%), along with LiFSI and acetonitrile (DOL to acetonitrile mass ratio 3:1, LiFSI accounting for 15 wt%). The mixture was thoroughly mixed at room temperature and allowed to stand until the 1,3-dioxolane self-polymerized to obtain polydioxolane (PDOL). 30 μL of the thoroughly mixed solution was dropped onto the negative electrode side, and a 19 mm diameter PP separator was placed on top. Another 30 μL of the mixture was then dropped on, followed by the placement of the positive electrode to encapsulate the battery. The solid-state battery prepared in this invention uses lithium metal as the negative electrode and NCM613 as the positive electrode. The mass ratio of NCM613, SP, and binder is 90:5:5, and the areal density is 150 g / m³. 2 . The lithium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to performance tests. The batteries were tested at 25°C, first under constant current and constant voltage charging (0.1C) to 4.3V, with a cutoff current of 0.05C, followed by constant current discharging (0.1C) to 2.8V. After 100 cycles under these charge-discharge conditions, the capacity retention rates of the batteries are shown in Table 1. Additionally, the room temperature ionic conductivity and electrochemical window test results are also shown in Table 1.

[0032] Electrochemical window test conditions (V): The precursor solutions from each example and comparative example were assembled into batteries together with lithium sheets, PP separators, and steel sheets, and then cured at room temperature for 8-24 hours. The electrochemical window was tested using an electrochemical workstation with a test voltage range of 3-6V and a scan rate of 0.5mV / s.

[0033] Table 1. Battery cycle capacity retention, room temperature ionic conductivity, and electrochemical window test results. Battery number Cyclic performance (capacity retention after 100 cycles) Room temperature ionic conductivity (S / cm) Electrochemical window (V) Compare with Example 1 41% <![CDATA[1.03×10 -4 ]]> 4.3 Compare with Example 2 72% <![CDATA[1.64×10 -4 ]]> 4.5 Example 1 92% <![CDATA[3.8×10 -4 ]]> 5.3 Example 2 93% <![CDATA[4.2×10 -4 ]]> 5.3 Example 3 95% <![CDATA[6.5×10 -4 ]]> 5.4 Example 4 98% <![CDATA[8×10 -4 ]]> 5.5 Example 5 96% <![CDATA[7.3×10 -4 ]]> 5.4 Based on the detection data obtained from the application of the F-PDOL solid electrolyte in batteries according to the embodiments of the present invention, the F-PDOL solid electrolyte provided by the present invention has excellent electrochemical performance. When applied to batteries, it can significantly improve the room temperature ionic conductivity of the battery, broaden the electrochemical window, and improve cycle performance.

Claims

1. A method for preparing fluorinated polydioxolane, characterized in that, Includes the following steps: S1. Add 1,3-dioxolane monomer to a container, then add lithium hexafluorophosphate and mix at room temperature until the 1,3-dioxolane self-polymerization is complete, to obtain polydioxolane; S2. After removing the air from the container, a mixture of nitrogen and fluorine gas is introduced at a flow rate of 3-7 mL / min. The reaction temperature is -30-0℃ and the time is 72-168 h to obtain fluorinated polydioxolane. S3. The prepared fluorinated polydioxolane is mixed evenly with lithium salt and organic solvent at room temperature, and 8-15 μL is added dropwise to the surface of the battery separator per square centimeter. The mixture is then allowed to stand at room temperature to obtain the fluorinated polydioxolane solid electrolyte.

2. The method for preparing fluorinated polydioxolane as described in claim 1, characterized in that: In step S1, the amount of initiator used is 1-5% of the total reactant mass.

3. The method for preparing fluorinated polydioxolane as described in claim 1, characterized in that: The specific operation for removing air from the container in step S2 is as follows: nitrogen gas is introduced at a flow rate of 0.5-5 mL / min for 0.5-2 hours.

4. The method for preparing fluorinated polydioxolane as described in claim 1, characterized in that: In step S3, the lithium salt is at least one of lithium perchlorate, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium hexafluorophosphate; the amount of lithium salt is 10-30 wt% of the solid electrolyte.

5. The method for preparing fluorinated polydioxolane as described in claim 1, characterized in that: In step S3, the organic solvent is any one of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, and tetrahydrofuran; the mass ratio of the solid electrolyte to the organic solvent is 1~4:

1.

6. The method for preparing fluorinated polydioxolane as described in claim 1, characterized in that: In step S3, the battery separator can be any one of PE separator, PP separator, or glass fiber separator.

7. Fluorinated polydioxolane solid electrolyte prepared by the preparation method according to any one of claims 1-6.

8. A solid-state battery, characterized in that: Use the fluorinated polydioxolane solid electrolyte as described in claim 7.

9. The method for preparing a solid-state battery as described in claim 8, characterized in that, Includes the following steps: a. Slurry preparation: The electrode material, conductive agent, and binder are mixed in a mass ratio of 8-9:0.5-1:0.5-1 to prepare the electrode slurry; b. Coating: The prepared electrode paste is uniformly coated on aluminum foil with a coating thickness of 80-180 μm, and then dried in a forced-air drying oven at 60-80℃ for 6-12 hours to obtain the electrode sheet. c. Battery assembly: The coin cell is assembled by using the electrode sheet as the positive electrode, the lithium sheet as the negative electrode, and the fluorinated polydioxolane solid electrolyte.

10. The method for preparing the battery as described in claim 9, characterized in that: The electrode material is one of lithium nickel cobalt manganese, lithium nickel cobalt aluminum, lithium nickel cobalt manganese aluminum, lithium iron phosphate, lithium manganese oxide, or graphite.

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