A polymer electrolyte composition, a method for preparing the same, and an application thereof

Abstract

The present application relates to a kind of polymer electrolyte composition and its preparation method and application, belong to the technical field for directly converting chemical energy into electrical energy method or device field.The polymer electrolyte composition of the present application includes polymer monomer, initiator I, initiator II and lithium salt;The polymer monomer is composed of 1,3-dioxolane and fluoroethylene carbonate;The initiator I is the initiator of 1,3-dioxolane, and the initiator II is the initiator of fluoroethylene carbonate.The polymer electrolyte composition polymerized into polymer electrolyte has good self-repairing performance and flame retardancy, and the battery prepared using the polymer electrolyte has excellent cycle performance and high safety.

Description

Technical Field

[0001] The present invention relates to the technical field of methods or devices for directly converting chemical energy into electrical energy, and in particular to a polymer electrolyte composition, a preparation method and an application thereof. Background Art

[0002] Compared with electrolytes, solid electrolytes have high mechanical strength, good electrochemical stability and thermal stability, and good compatibility with lithium metal negative electrodes or high-voltage positive electrodes, which can significantly improve the safety and energy density of lithium batteries. Solid electrolytes are mainly divided into inorganic electrolytes and polymer electrolytes. Among them, polymer electrolytes are mainly made into self-supporting membranes first and then assembled in the battery. However, polymer electrolytes cannot flow like liquid electrolytes and have difficulty penetrating into the internal pores of porous electrodes, resulting in a decrease in the utilization rate of active materials and energy density.

[0003] To address this problem, people began to adopt an in-situ polymerization process, injecting the liquid precursor solution of the polymer electrolyte directly into the battery, and then inducing in-situ polymerization under certain conditions to form a polymer electrolyte. Since the liquid precursor solution can maintain good fluidity, it can well infiltrate the electrode and form a closer interface contact after polymerization, thereby effectively improving the ionic conductivity of the battery. For example, the prior art (CN 113839096A) discloses a method for preparing a polymer electrolyte by in-situ polymerization, a lithium-ion battery and a preparation method thereof, using fluoroethylene carbonate and lithium salt as plasticizers and initiators, and combining with monomers such as vinylene carbonate, methyl methacrylate, 1,3-dioxolane and trioxymethylene to form a polymer electrolyte by in-situ polymerization; although the ionic conductivity of the polymer electrolyte can reach 10 -3 S / cm level, but its cycle performance is poor. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a polymer electrolyte composition and a preparation method and application thereof.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] In a first aspect, the present invention provides a polymer electrolyte composition comprising a polymer monomer, an initiator I, an initiator II, and a lithium salt; the polymer monomer is composed of 1,3-dioxolane (CAS No. 646-06-0) and fluoroethylene carbonate (CAS No. 114435-02-8); the initiator I is an initiator of 1,3-dioxolane, and the initiator II is an initiator of fluoroethylene carbonate.

[0007] The present invention combines 1,3-dioxolane and fluoroethylene carbonate, using in-situ ring-opening polymerization of 1,3-dioxolane and fluoroethylene carbonate under thermal initiation conditions to form a polyelectrolyte with an interpenetrating network structure. This not only improves the ionic conductivity and interfacial compatibility of the polymer electrolyte, but also inhibits the growth of lithium dendrites while enhancing flame retardancy, thereby significantly improving the battery's cycling performance and safety. Furthermore, the resulting polymer electrolyte has a certain degree of fluidity and can automatically repair itself to its original state after being damaged by external forces, thereby ensuring the battery's cycling performance and safety.

[0008] In addition, the mass proportion of the polymerized monomer in the above-mentioned polymer electrolyte composition is preferably ≥60%, more preferably 65% ​​to 85%; specifically, it can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85%.

[0009] Preferably, the mass fraction of 1,3-dioxolane in the polymerized monomer is ≤70%. Optionally, the mass fraction of 1,3-dioxolane in the polymerized monomer can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or 65%. Studies have found that when the mass fraction of 1,3-dioxolane in the polymerized monomer is ≤70%, the resulting polymer electrolyte not only maintains excellent cycling performance but also significantly increases its electrochemical window.

[0010] As a preferred embodiment of the polymer electrolyte composition of the present invention, the mass fraction of 1,3-dioxolane in the polymerized monomer is 30% to 50%. Optionally, the mass fraction of 1,3-dioxolane in the polymerized monomer can be 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, or 48%. Studies have found that when the mass fraction of 1,3-dioxolane in the polymerized monomer is 30% to 50%, it not only better broadens the electrochemical window of the polymer electrolyte but also significantly reduces gassing during battery cycling, thereby effectively improving the battery's cycling performance.

[0011] As a preferred embodiment of the polymer electrolyte composition of the present invention, the initiator I includes at least one of LiPF6, LiODFB, Mg(TFSI)2, Mg(CF3SO3)2, and R-BF3-Li; R in the R-BF3-Li is an alkyl group.

[0012] As a preferred embodiment of the polymer electrolyte composition of the present invention, the initiator II includes at least one of stannous octoate, dibutyltin dilaurate, dibutyltin didodecylsulfide, dibutyltin diacetate, and tin tert-butoxide.

[0013] As a preferred embodiment of the polymer electrolyte composition of the present invention, the polymer electrolyte composition also includes a solvent, and the solvent includes at least one of methyl trifluoroethyl carbonate, methyl difluoroacetate, ethyl 2,2,2-trifluoroacetate, 3,3,3-trifluoropropylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0014] In a second aspect, the present invention provides a method for preparing the above-mentioned polymer electrolyte composition, comprising the following steps: uniformly mixing the components to obtain the polymer electrolyte composition.

[0015] Preferably, in the above preparation method, the components are mixed uniformly in a water-proof and oxygen-proof environment.

[0016] In a third aspect, the present invention provides use of the above polymer electrolyte composition in preparing an electrolyte by in-situ polymerization.

[0017] In a fourth aspect, the present invention provides a gel polymer electrolyte, which is obtained by polymerizing the above-mentioned polymer electrolyte composition at 25-50°C for 5-48 hours (primary polymerization) and then polymerizing at 60-85°C for 48-96 hours (secondary polymerization). Optionally, the temperature of the primary polymerization can be 30°C, 35°C, 40°C, or 45°C, and the time can be 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, or 45 hours; the temperature of the secondary polymerization can be 65°C, 70°C, 75°C, or 80°C, and the time can be 50 hours, 55 hours, 60 hours, 65 hours, 70 hours, 75 hours, 80 hours, 85 hours, 90 hours, or 95 hours.

[0018] In a fifth aspect, the present invention provides a secondary battery comprising a positive electrode plate, a negative electrode plate and an electrolyte, wherein the electrolyte is the above-mentioned gel polymer electrolyte.

[0019] In a sixth aspect, the present invention provides an electrical device comprising the aforementioned secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention combines 1,3-dioxolane and fluoroethylene carbonate, and utilizes 1,3-dioxolane and fluoroethylene carbonate to form a polyelectrolyte with an interpenetrating network structure through in-situ ring-opening polymerization under thermal initiation conditions. This not only improves the ionic conductivity and interfacial compatibility of the polymer electrolyte, but also inhibits the growth of lithium dendrites while enhancing the flame retardant performance, thereby significantly improving the cycle performance and safety performance of the lithium battery. Moreover, the polymerized polymer electrolyte has a certain fluidity and can automatically repair to its original state after being damaged by external force, thereby ensuring the cycle performance and safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 1,3-dioxolane, fluoroethylene carbonate, and the infrared spectra of the polymer electrolyte prepared using the polymer electrolyte composition in Example 1;

[0023] Figure 2 is an LSV curve of a polymer electrolyte prepared using the polymer electrolyte composition in Comparative Example 1;

[0024] Figure 3 is an LSV curve of a polymer electrolyte prepared using the polymer electrolyte composition in Example 1;

[0025] Figure 4 Graph showing the cycling performance of an in-situ polymer electrolyte lithium battery prepared using the polymer electrolyte composition of Example 1;

[0026] Figure 5 The following is a photograph of the self-repair test of the polymer electrolyte prepared using the polymer electrolyte composition in Example 3.

[0027] Figure 6 This is a photograph of the flame retardancy test of the polymer electrolyte prepared using the polymer electrolyte composition in Example 1. DETAILED DESCRIPTION

[0028] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0029] Unless otherwise specified, other materials and reagents used in the examples can be obtained from commercial sources.

[0030] Example 1

[0031] An embodiment of the polymer electrolyte composition of the present invention comprises the following components, in parts by weight: 6.592 parts of a polymer monomer (composed of 1,3-dioxolane + fluoroethylene carbonate, wherein the mass fraction of 1,3-dioxolane is 37.5%), 1.648 parts of a solvent (ethyl methyl carbonate, EMC), 0.44 parts of an initiator I (LiDFOB), 1.319 parts of a lithium salt (LiTFSI), and 0.0412 parts of an initiator II (stannous octoate, Sn(Oct)2).

[0032] The preparation method of the polymer electrolyte composition described in this embodiment is as follows: in anhydrous and oxygen-free conditions, polymerizable monomers, initiator I, initiator II, lithium salt and solvent are uniformly mixed to obtain the polymer electrolyte composition.

[0033] Example 2

[0034] An embodiment of the polymer electrolyte composition of the present invention is substantially the same as that of embodiment 1, except that the mass fraction of 1,3-dioxolane in the polymerized monomer is 40%.

[0035] The preparation method of the polymer electrolyte composition in this embodiment is the same as that in Example 1.

[0036] Example 3

[0037] An embodiment of the polymer electrolyte composition of the present invention is substantially the same as that of embodiment 1, except that the mass fraction of 1,3-dioxolane in the polymerized monomer is 50%.

[0038] The preparation method of the polymer electrolyte composition in this embodiment is the same as that in Example 1.

[0039] Example 4

[0040] An embodiment of the polymer electrolyte composition of the present invention is substantially the same as that of embodiment 1, except that the mass fraction of 1,3-dioxolane in the polymerized monomer is 70%.

[0041] The preparation method of the polymer electrolyte composition in this embodiment is the same as that in Example 1.

[0042] Example 5

[0043] An embodiment of the polymer electrolyte composition of the present invention comprises the following components, in parts by weight: 8.256 parts of a polymer monomer (1,3-dioxolane + fluoroethylene carbonate, wherein the mass fraction of 1,3-dioxolane is 50%), 0.427 parts of initiator I (LiDFOB), 1.308 parts of a lithium salt (LiTFSI), and 0.0412 parts of initiator II (stannous octoate (Sn(Oct)2)).

[0044] The preparation method of the polymer electrolyte composition in this embodiment is the same as that in Example 1.

[0045] Example 6

[0046] An embodiment of the polymer electrolyte composition of the present invention comprises the following components, in parts by weight: 8.026 parts of a polymer monomer (consisting of 1,3-dioxolane and fluoroethylene carbonate, wherein the mass fraction of 1,3-dioxolane is 50%), 0.231 parts of initiator I (LiPF6), 1.744 parts of a lithium salt (LiTFSI), and 0.0401 parts of initiator II (stannous octoate (Sn(Oct)2)).

[0047] The preparation method of the polymer electrolyte composition in this embodiment is the same as that in Example 1.

[0048] Comparative Example 1

[0049] A comparative example of the polymer electrolyte composition of the present invention is substantially the same as that of Example 1, except that the polymerizable monomer is 1,3-dioxolane.

[0050] The preparation method of the polymer electrolyte composition in this comparative example is the same as that in Example 1.

[0051] Comparative Example 2

[0052] A comparative example of the polymer electrolyte composition of the present invention is substantially the same as that of Example 1, except that the polymerizable monomer is fluoroethylene carbonate.

[0053] The preparation method of the polymer electrolyte composition in this comparative example is the same as that in Example 1.

[0054] Comparative Example 3

[0055] A comparative example of the polymer electrolyte composition of the present invention is substantially the same as Example 1, except that it does not contain initiator II (ie, fluoroethylene carbonate cannot undergo ring-opening polymerization).

[0056] The preparation method of the polymer electrolyte composition in this comparative example is the same as that in Example 1.

[0057] Comparative Example 4

[0058] A comparative example of the polymer electrolyte composition of the present invention is substantially the same as Example 1, except that: the polymerized monomers consist of 1,3-dioxolane and vinyl ethylene carbonate, wherein the mass fraction of 1,3-dioxolane is 37.5%; and the initiator II is azobisisobutyronitrile.

[0059] The preparation method of the polymer electrolyte composition in this comparative example is the same as that in Example 1.

[0060] Performance Testing

[0061] 1. Infrared spectrum test

[0062] The polymer electrolyte composition in Example 1 was first polymerized at 45°C for 24 hours, then heated to 80°C and polymerized for 72 hours to obtain a polymer electrolyte. The polymer electrolyte was tested by Fourier transform infrared spectroscopy. The test results are as follows: Figure 1 As shown. Figure 1 It can be seen that 1,3-dioxolane is located at 1000-1200 cm -1 The characteristic peak at 1800 cm-1 disappeared after the copolymerization of 1,3-dioxolane and fluoroethylene carbonate, while the characteristic peak of fluoroethylene carbonate at 1800 cm-1 disappeared after the copolymerization of 1,3-dioxolane and fluoroethylene carbonate. -1 The characteristic peak at 1,3-dioxolane and fluoroethylene carbonate is significantly reduced after copolymerization, indicating that 1,3-dioxolane undergoes ring-opening polymerization to form poly-1,3-dioxolane and fluoroethylene carbonate undergoes ring-opening polymerization to form polyfluoroethylene carbonate, which proves that the polymer electrolyte composition of the present invention can be in situ polymerized to form a polymer electrolyte under the action of thermal initiation.

[0063] 2. Electrochemical window test

[0064] The test method is as follows: the polymer electrolyte compositions in Comparative Example 1 and Example 1 are respectively assembled together with the diaphragm to form a steel sheet / diaphragm (PP diaphragm with a thickness of 12 μm) + polymer electrolyte composition / steel sheet blocked battery, placed at 45°C for in-situ polymerization for 24 hours, then heated to 80°C and continued in-situ polymerization for 72 hours, and then the LSV curve is tested using an electrochemical workstation, with a test voltage range of 3 to 5 V and a voltage step of 1 mV / s.

[0065] The test results are as follows Figure 2 and Figure 3 As shown, according to Figure 2It can be seen that when the polymer monomer in the polymer electrolyte composition is 1,3-dioxolane, the electrochemical window of the electrolyte formed by in situ polymerization is only 4.1V; when the polymer monomer in the polymer electrolyte composition is a mixture of 1,3-dioxolane and fluoroethylene carbonate, the electrochemical window of the electrolyte formed by in situ polymerization is greater than 4.4V, which shows that the combination of 1,3-dioxolane and fluoroethylene carbonate can effectively improve the electrochemical window of the polymer electrolyte.

[0066] 3. Cycle performance test

[0067] The polymer electrolyte compositions in the examples and comparative examples were prepared into in-situ polymer electrolyte lithium batteries, and the preparation method included the following steps:

[0068] A positive electrode sheet, a separator (a PP separator with a thickness of 12 μm) and a negative electrode sheet were laminated to form a dry cell. After the cell was baked, 10 g (10 Ah cell) of the polymer electrolyte composition in each embodiment and comparative example was injected into the dry cell under anhydrous and oxygen-isolated conditions and allowed to stand for 24 hours. The cell was then placed at 45° C. for in-situ polymerization for 24 hours, and then heated to 80° C. for further in-situ polymerization for 72 hours to obtain an in-situ polymerized electrolyte lithium battery.

[0069] The negative electrode sheet in the above preparation method is a lithium-copper composite strip (a lithium metal layer is pressed on the copper surface); the positive electrode sheet is composed of aluminum foil and a positive electrode material coated on the aluminum foil. The positive electrode material is composed of commercial high-nickel ternary (NCM811), polyvinylidene fluoride (PVDF) and single-walled carbon nanotubes in a mass ratio of 9:0.5:0.5.

[0070] The above-mentioned in-situ polymer electrolyte lithium battery was subjected to a cycle performance test, with 100 charge and discharge cycles at 0.33C in the range of 2.5 to 4.2V at 25°C.

[0071] First cycle efficiency (%) = discharge capacity of the first cycle / charge capacity of the first cycle × 100%;

[0072] Capacity retention rate (%) = discharge capacity at the 100th cycle / discharge capacity at the 1st cycle × 100%. Table 1 First cycle capacity, first cycle efficiency and capacity retention rate of in-situ polymer electrolyte lithium batteries prepared using the polymer battery compositions of various examples and comparative examples

[0073]

[0074] According to the data in Table 1 and Figure 4It can be seen that the first cycle capacity and first cycle efficiency of the polymer electrolyte formed by in-situ polymerization of the polymer electrolyte composition in Examples 1 to 6 reached 5Ah and 87% or more, respectively, and the capacity retention rate after 100 cycles was greater than or equal to 92.78%, indicating that the polymer electrolyte prepared by in-situ polymerization of the polymer electrolyte composition of the present invention can not only give the battery good first cycle capacity and first cycle efficiency, but also significantly improve its cycle performance. At the same time, according to Comparative Examples 1 and 2, it can be seen that the polymer electrolyte formed by in-situ polymerization using 1,3-dioxolane or fluoroethylene carbonate as the polymerization monomer alone is difficult to effectively improve the cycle performance of the battery; according to Comparative Example 3, it can be found that using fluoroethylene carbonate as an additive and acting together with poly-1,3-dioxolane can improve the cycle performance of the battery to a certain extent, but the degree of improvement is limited; according to Comparative Example 4, it can be found that when fluoroethylene carbonate is replaced by ethylene carbonate and used together with 1,3-dioxolane as the polymerization monomer, the polymer electrolyte formed by in-situ polymerization is not only difficult to improve the first cycle capacity and first cycle efficiency of the battery, but also cannot effectively improve the cycle performance of the battery.

[0075] 4. Self-repair performance test

[0076] The polymer electrolyte composition in Example 3 was first polymerized at 45°C for 24 hours, then heated to 80°C and continued to polymerize for 72 hours to form a polymer electrolyte; then two portions of the polymer electrolyte were placed on the surface of weighing paper and a certain distance (such as Figure 5 A), and after standing for 30 minutes, the two polymer electrolytes were found to be completely fused together (as shown in Figure 5 B), indicating that the polymer solid electrolyte formed after the polymer electrolyte composition of the present invention is cured has a certain fluidity and can achieve self-repair; the polymer electrolytes formed by polymerization of the polymer electrolyte compositions in Examples 1 to 2 and Examples 4 to 6 are similar to those in Example 3 and have good self-repairing properties.

[0077] 5. Flame retardant performance test

[0078] The polymer electrolyte composition in Example 1 was first polymerized at 45°C for 24 hours, then heated to 80°C and continued to polymerize for 72 hours to form a polymer electrolyte. The polymer electrolyte was then placed in the outer flame of an electronic lighter and burned for 2 to 3 seconds (e.g. Figure 6 A), the polymer electrolyte immediately extinguishes itself after the burning stops (as Figure 6 B), indicating that the polymer electrolyte has good flame retardant properties; the polymer electrolytes polymerized from the polymer electrolyte compositions in Examples 2 to 6 are similar to those in Example 1, and all have good flame retardant properties.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A gel polymer electrolyte, characterized in that The polymer electrolyte composition is first polymerized at 25-50° C. for 5-48 hours, and then polymerized at 60-85° C. for 48-96 hours to obtain; The polymer electrolyte composition is composed of a polymer monomer, an initiator I, an initiator II, a lithium salt, and a solvent; the polymer monomer is composed of 1,3-dioxolane and fluoroethylene carbonate; the initiator I is an initiator of 1,3-dioxolane, and the initiator II is an initiator of fluoroethylene carbonate; The mass fraction of the polymerized monomer in the polymer electrolyte composition is 65% to 85%, and the mass fraction of 1,3-dioxolane in the polymerized monomer is 30% to 40%.

2. The gel polymer electrolyte according to claim 1, wherein The initiator I includes at least one of LiPF6, LiODFB, Mg(TFSI)2, Mg(CF3SO3)2, and R-BF3-Li; R in the R-BF3-Li is an alkyl group.

3. The gel polymer electrolyte according to claim 1, wherein The initiator II includes at least one of stannous octoate, dibutyltin dilaurate, dibutyltin didodecylsulfide, dibutyltin diacetate, and tin tert-butoxide.

4. The gel polymer electrolyte according to claim 1, wherein The solvent includes at least one of methyl trifluoroethyl carbonate, methyl difluoroacetate, ethyl 2,2,2-trifluoroacetate, 3,3,3-trifluoropropylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

5. A secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, characterized in that: The electrolyte is the gel polymer electrolyte according to any one of claims 1 to 4.

6. An electrical device, characterized in that: The secondary battery according to claim 5 is included, and the secondary battery serves as a power supply for the electrical device.

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