A topologically processed polymer solid electrolyte, battery and preparation method thereof

Abstract

A topologically processed polymer solid-state electrolyte, a battery, and a method for preparing the same are disclosed. The solid-state electrolyte comprises a polymer PVDF-HFP, a lithium salt, and LiOH·H2O and phenylboronic acid (PhB) as grafting reactants to provide an alkaline environment. The mass ratio of PVDF-HFP to the lithium salt is configured to an effective amount that allows the lithium salt to fully dissolve and form a homogeneous mixture with the polymer. The molar ratio of LiOH·H2O to PVDF-HFP is configured to an effective amount that provides a sufficiently alkaline environment to promote polymer dehydrofluorination and grafting of -OH groups. The amount of phenylboronic acid (PhB) added is configured to react with the polymer grafting groups to form dynamic covalent bonds in borate esters and optimize the ionic conductivity of the electrolyte. By introducing lithium salt LiTFSI, alkaline environment provider LiOH·H2O, and phenylboronic acid (PhB) into the polymer PVDF-HFP, an enhanced topological structure is formed, improving the ionic conductivity and mechanical strength of the electrolyte. This solid-state electrolyte effectively inhibits lithium dendrite growth and improves battery cycle stability. The preparation method is simple and efficient.

Description

Technical Field

[0001] This invention relates to lithium-ion batteries, and more particularly to a topologically processed polymer solid electrolyte, a battery, and a method for preparing the same. Background Technology

[0002] With the rapid development of lithium-ion battery technologies and the emergence of diverse energy storage demands, people are placing higher requirements on future lithium-ion batteries. Limited by safety concerns, such as lithium dendrite growth and the flammability and leakage of liquid electrolytes, solid electrolytes, especially solid polymer electrolytes, have attracted attention due to their high flexibility, good interfacial compatibility, and scalability. However, polymer solid electrolytes still suffer from problems such as low ionic conductivity, low ion transport number, and weak mechanical strength, limiting their application in lithium batteries.

[0003] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] The main objective of this invention is to overcome the deficiencies in the above-mentioned background technology and provide a topologically processed polymer solid electrolyte, battery and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A topologically processed polymer solid electrolyte comprises a polymer PVDF-HFP, a lithium salt, and LiOH·H2O and a grafting reactant phenylboronic acid PhB to provide an alkaline environment. The mass ratio of the polymer PVDF-HFP to the lithium salt is configured to be an effective amount that allows the lithium salt to fully dissolve and form a homogeneous mixture with the polymer. The molar ratio of the LiOH·H2O to the polymer PVDF-HFP is configured to be an effective amount that provides a sufficiently alkaline environment to promote the dehydrofluorination of the polymer and the grafting of -OH groups. The amount of the grafting reactant phenylboronic acid PhB added is configured to be an effective amount that reacts with the polymer grafting groups to form dynamic covalent bonds of borate esters and optimize the ionic conductivity of the electrolyte.

[0007] Furthermore, the lithium salt is LiTFSI, and the organic solvent is N,N-dimethylformamide (DMF).

[0008] Further, the mass ratio of the polymer PVDF-HFP to the lithium salt is 1:(0.5-1); the molar ratio of the LiOH·H2O providing the alkaline environment to the polymer PVDF-HFP is (0.5-2):10; and the grafting reactant phenylboronic acid PhB is 5-25% of the mass of the polymer PVDF-HFP.

[0009] Furthermore, the grafting reactant phenylboronic acid PhB is 15% of the mass of the polymer PVDF-HFP.

[0010] A method for preparing a topologically processed polymer solid electrolyte includes the following steps:

[0011] S1. Obtain a homogeneous polymer solution by adding the polymer PVDF-HFP and lithium salt LiTFSI to an organic solvent and mixing and stirring to ensure that the lithium salt and polymer are mixed evenly.

[0012] S2. LiOH·H2O is added to a homogeneous polymer solution to prepare an alkaline topological grafting environment for polymer grafting -OH groups. Then, phenylboronic acid PhB, a grafting reactant, is added and mixed and stirred. The reaction with the polymer grafting groups forms a chemical crosslink to form a dynamic covalent bond of borate ester, thus obtaining a polymer solid electrolyte precursor solution with a topological structure.

[0013] S3: The polymer solid electrolyte precursor solution with the topological structure is poured and leveled, and then vacuum dried to obtain the topologically processed polymer solid electrolyte.

[0014] Furthermore, the lithium salt is LiTFSI, and the organic solvent is N,N-dimethylformamide (DMF).

[0015] Further, the mass ratio of the polymer PVDF-HFP to the lithium salt is 1:(0.5-1); the molar ratio of the LiOH·H2O providing the alkaline environment to the polymer PVDF-HFP is (0.5-2):10; and the grafting reactant phenylboronic acid PhB is 5-25% of the mass of the polymer PVDF-HFP, preferably 15%.

[0016] A battery comprising a positive electrode, a negative electrode, and a topologically processed polymer solid electrolyte.

[0017] Furthermore, the negative electrode is a lithium electrode.

[0018] Furthermore, the topologically processed polymer solid electrolyte is used after being soaked in a common electrolyte solution for 3-6 hours.

[0019] The present invention has the following beneficial effects:

[0020] This invention provides a topologically processed polymer solid-state electrolyte, a battery, and its preparation method. The method utilizes the polymer PVDF-HFP to generate C=C double bonds through dehydrofluorination in an alkaline environment provided by LiOH·H2O. After continuous grafting of (-OH) groups, it reacts with phenylboronic acid (PhB) to form a borate ester, creating a polymer topological structure that promotes polymer chain movement and increases the electrolyte's ionic conductivity. This preparation method is simple and efficient. In its application, a continuous SEI film composed of lithium borate, lithium fluoride, and some organic compounds forms on the lithium anode surface. This film possesses strong mechanical strength, effectively preventing unnecessary side reactions between lithium and the electrolyte and inhibiting lithium dendrite growth, thereby obtaining a solid-state lithium battery with excellent cycle performance and long-term stability.

[0021] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0022] Figure 1 The critical performance graphs are for Comparative Example 1 and Examples 1-5.

[0023] Figure 2 This is the XRD pattern of phenylboronic acid (PhB).

[0024] Figure 3 The images are XRD patterns of Comparative Example 1 and Examples 1-5.

[0025] Figure 4 The graph shows the cycle performance of Comparative Example 1 and Example 3 under 0.5C charge-discharge conditions.

[0026] Figure 5 Impedance diagrams for Comparative Example 1 and Example 3 at 25°C.

[0027] Figure 6 The ionic conductivity and fitting Arrhenius plots of Comparative Example 1 and Example 3 at different temperatures are shown.

[0028] Figure 7 For comparative examples 1 and 3, at 1 mA cm -2 Symmetric properties of lithium under cycling conditions. Detailed Implementation

[0029] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0030] Conventional polymer solid electrolytes still suffer from problems such as low ionic conductivity, low ion transference number, and weak mechanical strength, which limit their application in lithium batteries. This invention provides a topologically processed polymer solid electrolyte and its preparation method. Utilizing the characteristic that polymer PVDF-HFP readily undergoes dehydrofluorination and grafting of -OH groups under alkaline conditions, borate ester bonds are introduced to topologically process long-chain PVDF-HFP, promoting chain segment movement and enhancing electrolyte stability.

[0031] This invention provides a topologically processed polymer solid electrolyte, comprising a polymer PVDF-HFP, a lithium salt, and LiOH·H2O and a grafting reactant phenylboronic acid PhB to provide an alkaline environment. The mass ratio of the polymer PVDF-HFP to the lithium salt is configured to be an effective amount that allows the lithium salt to fully dissolve and form a homogeneous mixture with the polymer. The molar ratio of LiOH·H2O to the polymer PVDF-HFP is configured to be an effective amount that provides a sufficiently alkaline environment to promote the dehydrofluorination of the polymer and the grafting of -OH groups. The amount of the grafting reactant phenylboronic acid PhB added is configured to be an effective amount that reacts with the polymer grafting groups to form dynamic covalent bonds of borate esters and optimize the ionic conductivity of the electrolyte.

[0032] In a preferred embodiment, the lithium salt is LiTFSI and the organic solvent is N,N-dimethylformamide (DMF).

[0033] In a preferred embodiment, the mass ratio of the polymer PVDF-HFP to the lithium salt is 1:(0.5-1), more preferably 1:0.8; the molar ratio of the LiOH·H2O providing the alkaline environment to the polymer PVDF-HFP is (0.5-2):10, more preferably 1:10; and the grafting reactant phenylboronic acid PhB is 5-25% of the mass of the polymer PVDF-HFP, most preferably 15%.

[0034] This invention also provides a method for preparing the topologically processed polymer solid electrolyte, comprising the following steps:

[0035] S1. Obtain a homogeneous polymer solution by adding the polymer PVDF-HFP and lithium salt LiTFSI to an organic solvent and mixing and stirring to ensure that the lithium salt and polymer are mixed evenly.

[0036] S2. LiOH·H2O is added to a homogeneous polymer solution to prepare an alkaline topological grafting environment for polymer grafting -OH groups. Then, phenylboronic acid PhB, a grafting reactant, is added and mixed and stirred. The reaction with the polymer grafting groups forms a chemical crosslink to form a dynamic covalent bond of borate ester, thus obtaining a polymer solid electrolyte precursor solution with a topological structure.

[0037] S3: The polymer solid electrolyte precursor solution with the topological structure is poured and leveled, and then vacuum dried to obtain the topologically processed polymer solid electrolyte.

[0038] This invention also provides a battery comprising a positive electrode, a negative electrode, and a topologically processed polymer solid electrolyte. Preferably, the topologically processed polymer solid electrolyte is used after being soaked in a common electrolyte for 3-6 hours. Preferably, the negative electrode can be a lithium sheet.

[0039] The polymer PVDF-HFP, possessing high conductivity, readily undergoes dehydrofluorination in an alkaline environment to form C=C double bonds and continuously grafts -OH groups. This invention utilizes this characteristic, employing -OH groups and the alkaline environment to topologically modify the chain polymer, introducing borate ester bonds. This alters the polymer's properties, promoting chain segment movement and enhancing electrolyte stability. Compared to existing technologies, this invention leverages the polymer's properties to create an alkaline environment, allowing the grafted -OH groups to react with phenylboronic acid. After topological processing, this accelerates chain segment movement within the electrolyte, improving ionic conductivity. Furthermore, the dehydrofluorinated polymer and the topologically added phenylboronic acid provide a continuous SEI film composed of lithium borate, lithium fluoride, and some organic compounds for the lithium anode in lithium batteries, inhibiting lithium dendrite growth and resulting in an all-solid-state lithium metal battery with excellent cycle performance and long-term stability. Moreover, the preparation method of this invention is simple and efficient.

[0040] The following describes specific embodiments of the present invention.

[0041] In one embodiment, a method for preparing a polymer solid electrolyte with a specific topology includes the following steps:

[0042] (1) Obtain a homogeneous polymer solution. Add the polymer PVDF-HFP and lithium salt LiTFSI to the organic solvent DMF and mix and stir for 12 hours to make the lithium salt and polymer evenly mixed.

[0043] (2) Topological grafting: LiOH·H2O was added to the homogeneous polymer solution and stirred at room temperature for 6 hours to prepare an alkaline topological grafting environment for polymer grafting -OH groups. Then, phenylboronic acid PhB, a grafting reactant, was added and the mixture was stirred for another 6 hours to react with the polymer grafting groups to form a dynamic covalent bond of borate ester, thus obtaining a polymer solid electrolyte precursor solution with a topological structure.

[0044] (3) Vacuum drying: The polymer solid electrolyte precursor solution with the topological structure is poured into a petri dish or glass plate and automatically leveled. After being placed in a vacuum drying oven at 80°C for 12 hours, the topologically processed polymer solid electrolyte is obtained.

[0045] In one embodiment, in step (1), there are 0.9 g of polymer PVDF-HFP, 0.6 g of lithium salt LiTFSI, and 7.5 mL of solvent DMF.

[0046] In one embodiment, the molar ratio of LiOH·H2O to polymer PVDF-HFP in step (2) is 1:10. The amount of grafting reactant phenylboronic acid (PhB) added is 5-25% of the mass of polymer PVDF-HFP.

[0047] In one embodiment, a battery fabrication method using a topologically processed polymer solid electrolyte as a separator in place of a lithium-ion battery includes the following steps:

[0048] After the topologically processed polymer solid electrolyte is cut into sheets, it is assembled into a lithium symmetric battery in a glove box filled with Ar gas in the following order: positive electrode shell, lithium sheet, electrolyte membrane, lithium sheet, gasket, spring sheet, and negative electrode shell.

[0049] In one embodiment, the positive electrode is prepared by uniformly mixing LFP, PVDF, and Super P at a mass ratio of 8:1:1, adding them to NMP to form a slurry, coating it onto an Al foil, and drying it.

[0050] Examples 1-5

[0051] A method for preparing a topologically processed polymer solid electrolyte with PVDF-HFP as the polymer, LiTFSI as the lithium salt, phenylboronic acid (PhB) as the grafting reactant, DMF as the solvent, and LiOH·H2O as the alkaline environment, includes the following steps:

[0052] (1) Weigh 0.9g PVDF-HFP and 0.6g LiTFSI and add them to 7.5mL DMF solution. Stir for 12h to mix the lithium salt and polymer evenly.

[0053] (2) Weigh 0.0176g LiOH·H2O and add it to the solution in (1). Stir at room temperature for 6 hours to graft -OH groups onto the polymer PVDF-HFP. Then add the grafting reactant phenylboronic acid PhB and continue mixing and stirring for 6 hours. The amount of phenylboronic acid PhB in each example is 5%, 10%, 15%, 20%, and 25% of the mass of the polymer PVDF-HFP, respectively.

[0054] (3) The electrolyte precursor solution in (2) is poured into a petri dish or glass plate and automatically leveled. After being placed in a vacuum drying oven at 80°C for 12 hours, the topologically processed polymer solid electrolyte is obtained.

[0055] Comparative Example 1

[0056] A method for preparing a topology-free polymer solid electrolyte with PVDF-HFP as the polymer, LiTFSI as the lithium salt, and DMF as the solvent, comprising the following steps:

[0057] (1) Weigh 0.9g PVDF-HFP and 0.6g LiTFSI and add them to 7.5mL DMF solution. Stir for 12h to mix the lithium salt and polymer evenly.

[0058] (2) The electrolyte precursor solution in (1) is poured into a petri dish or glass plate and automatically leveled. After being placed in a vacuum drying oven at 80°C for 12 hours, a topology-free polymer solid electrolyte is obtained.

[0059] The polymer electrolyte membranes prepared in the above embodiments and comparative examples were subjected to critical current density tests to obtain the maximum current that the electrolyte could withstand under gradually increasing current conditions. The specific operation process is as follows: the polymer electrolyte membrane was sandwiched between two lithium sheets to assemble a button cell. Then, the maximum current that the button cell could withstand under gradually increasing current conditions was tested using a Blue Battery testing system to compare its performance. The test results are shown in Table 1.

[0060] Table 1

[0061]

[0062] Table 1 shows that the maximum current that can be withstood under gradually increasing current conditions varies significantly depending on the amount of phenylboronic acid (PhB) added in Examples 1-5. Example 3, with an addition of 15%, exhibits the best maximum current and critical performance. The addition of PhB leads to the in-situ formation of a LiF / Li-BO-rich SEI layer on the lithium anode surface, enhancing the mechanical strength of the SEI film and improving critical performance. Furthermore, an appropriate amount of PhB is required for optimal results.

[0063] Electrochemical performance tests were conducted on the polymer electrolyte membranes prepared in the preferred Example 3 and Comparative Example 1 to obtain the long-cycle performance of the electrolyte under 0.5C charge-discharge conditions. The specific operation process is as follows: The polymer electrolyte membrane was sandwiched between the positive electrode and the lithium sheet to assemble a button cell. Then, the discharge capacity of the button cell under 0.5C charge-discharge conditions was tested for 200 cycles using a Blue Battery testing system to compare its cycle performance. The test results are shown in Table 2.

[0064] Table 2

[0065]

[0066]

[0067] As shown in Table 2, the capacity retention rates of the electrolyte in Comparative Example 1 and Example 3 were significantly different after 200 cycles of constant current charge-discharge at 0.5C. Specifically, Example 3, with an added amount of 15%, still retained 147.5 mAh·g electrolyte after 200 cycles. -1 The cycle performance was the best. Compared with Comparative Example 1, Example 3, after topological processing, promoted the movement of polymer chain segments, accelerated the transport of lithium ions in the electrolyte, and greatly improved the electrochemical performance.

[0068] Figure 1 The critical performance diagrams are for Comparative Example 1 and Examples 1-5.

[0069] Figure 2 This is the XRD pattern of phenylboronic acid (PhB).

[0070] Figure 3 The XRD patterns of Comparative Example 1 and Examples 1-5 show that the PVDF-HFP crystallization peaks in Examples 1-5 all decreased, indicating that more amorphous regions were generated after topological grafting of phenylboronic acid PhB, which promoted polymer chain segment movement.

[0071] Figure 4 The graph shows the cycle performance of Comparative Example 1 and Example 3 under 0.5C charge-discharge conditions.

[0072] Figure 5 The impedance diagrams for Comparative Example 1 and Example 3 at 25°C are shown. The specific procedure is as follows: A polymer electrolyte membrane is sandwiched between two stainless steel sheets to assemble a button cell. An AC impedance test is performed using a CHI660E electrochemical workstation. During the test, the amplitude is set to 10mV, and the scan frequency range is 0.1Hz to 10Hz. 5 Hz. Calculations showed that at 25℃, the ionic conductivity of Comparative Example 1 was 0.89 × 10⁻⁶. -3 S cm -1 The polymer electrolyte after topological processing in Example 3 exhibits an ionic conductivity of 1.52 × 10⁻⁶. -3 S cm -1 .

[0073] Figure 6 The figures show the ionic conductivity and fitted Arrhenius plots of Comparative Example 1 and Example 3 at different temperatures. Example 3 exhibits a higher ionic conductivity than Comparative Example 1 at all temperatures, and the activation energy for ion migration in Example 3 is lower than that in Comparative Example 1, indicating that the topologically modified electrolyte enables rapid Li+ conduction within the electrolyte.

[0074] Figure 7 For comparative examples 1 and 3, at 1 mA cm -2The symmetric performance of lithium under cycling conditions is shown in the diagram. The specific operation process is as follows: A polymer electrolyte membrane is sandwiched between two lithium sheets to assemble a coin cell. Then, the coin cell is tested at 1 mA cm⁻¹ using the Blue Battery testing system. -2 Its performance was compared by cyclic charging and discharging under current conditions. Example 3 exhibited a lower polarization voltage, compared to... Figure 6 The results of the electrolyte activation energy Ea corroborate each other, showing that compared with Comparative Example 1, Example 3 can effectively suppress lithium dendrites.

[0075] In summary, the advantages of this invention compared to existing technologies are:

[0076] The topologically processed polymer solid electrolyte of this invention, compared with the prior art, utilizes the polymer properties to topologically process chain polymers, promoting chain segment movement and increasing ionic conductivity. Simultaneously, a more robust SEI is constructed through phenylboronic acid (PhB) bonds, effectively protecting the lithium anode. This results in an all-solid-state lithium metal battery with excellent cycle performance and long-term stability. The preparation process of this invention is simple and efficient.

[0077] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are 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. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for preparing a topologically processed polymer solid electrolyte, characterized in that, Includes the following steps: S1. Obtain a homogeneous polymer solution by adding the polymer PVDF-HFP and lithium salt LiTFSI to an organic solvent and mixing and stirring to ensure that the lithium salt and polymer are mixed evenly. S2. LiOH·H2O is added to a homogeneous polymer solution to prepare an alkaline topological grafting environment for polymer grafting -OH groups. Then, phenylboronic acid PhB, a grafting reactant, is added and mixed and stirred to react with the polymer grafting groups to form a dynamic covalent bond of borate ester to obtain a polymer solid electrolyte precursor solution with a topological structure. S3: The polymer solid electrolyte precursor solution with the topological structure is poured and leveled, and then vacuum dried to obtain the topologically processed polymer solid electrolyte. The mass ratio of the polymer PVDF-HFP to lithium salt is 1:(0.5~1); the molar ratio of LiOH·H2O, which provides an alkaline environment, to the polymer PVDF-HFP is (0.5~2):10; and the grafting reactant phenylboronic acid PhB is 5~25% of the mass of the polymer PVDF-HFP.

2. The method for preparing the topologically processed polymer solid electrolyte as described in claim 1, characterized in that, The lithium salt is LiTFSI, and the organic solvent is N,N-dimethylformamide (DMF).

3. The method for preparing the topologically processed polymer solid electrolyte as described in claim 1 or 2, characterized in that, The grafting reactant, phenylboronic acid PhB, accounts for 15% of the mass of the polymer PVDF-HFP.

4. A topologically processed polymer solid electrolyte, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 3.

5. A battery, characterized in that, It includes positive electrode plates, negative electrode plates, and polymer solid electrolytes with topological processing as described in claim 4.

6. The battery as described in claim 5, characterized in that, The negative electrode is a lithium electrode.

7. The battery as described in claim 5 or 6, characterized in that, The polymer solid electrolyte with the aforementioned topological processing is used after soaking in ordinary electrolyte for 3-6 hours.

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