A method for preparing solid polymer electrolyte by initiating cyclic ether ring-opening polymerization

Abstract

The present invention belongs to the technical field of energy storage battery materials, and specifically relates to a method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization. The in-situ polymerization method adopted by the present invention to prepare the polymer solid electrolyte selects a specific initiator. Compared with currently commonly used initiators, without the need for inhibitors, it can not only improve the interfacial wettability and interfacial contact and create a stable SEI layer to inhibit dendrites, but also react with lithium metal to generate an interfacial layer in situ, thereby homogenizing the interfacial electric field and lithium ion flux. The polymer solid electrolyte prepared by the present invention has good compatibility with electrodes, low internal resistance, fewer internal side reactions in the battery, and excellent cycle life.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage battery materials, and particularly relates to a method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization. Background Art

[0002] The development of high-performance electrochemical energy storage devices is crucial for my country to achieve a low-carbon economy and sustainable energy supply. With the shortcomings of liquid electrolytes, such as leakage, flammability, and poor thermal stability, and the increasing demand for high-energy-density and high-safety energy storage devices in recent years, solid-state electrolytes have attracted attention. Solid-state electrolyte battery systems avoid the leakage problems of traditional organic liquid electrolytes, have relatively good thermal stability, and can fundamentally solve the safety issues of organic liquid batteries. They have become a key research focus and hot topic in industry and academia, and may be for some time to come.

[0003] According to the differences in composition, solid electrolytes can be divided into inorganic solid electrolytes, polymer solid electrolytes and polymer-inorganic composite solid electrolytes. The shortcomings of inorganic solid electrolytes such as high brittleness, poor processability and high interfacial impedance have seriously restricted their further development in large-scale industrialization and the preparation of high-energy-density and high-safety batteries. On the contrary, polymer solid electrolytes obtained by complexing polar polymer matrices with metal salts have better interfacial compatibility, flexibility and processability, and are highly promising next-generation solid electrolyte materials. Compared with traditional solid electrolyte membranes, a huge challenge is the solid-solid interface. Due to the weak wettability of solid electrolytes on the interface, the interfacial impedance is large, and the lithium ion transmission is hindered.

[0004] It is very necessary to prepare polymer solid electrolytes by in situ polymerization. The in situ prepared polymer solid electrolyte improves the compatibility of electrolyte / electrode to a certain extent, but the existing initiators are usually Lewis acids, such as aluminum trifluoromethanesulfonate (Al(oTf)3)), lithium hexafluorophosphate (LiPF6), etc. Although the polymer electrolytes prepared by their catalysis have good conductivity and good cycle stability, their polymerization rate is uncontrollable, and the introduced initiator will affect the battery performance. At the same time, the catalyst is highly corrosive to aluminum foil, which has a greater impact on the subsequent battery performance. The current conventional idea for the in situ preparation of polymer solid electrolytes is to add inhibitors to the polymerization reaction to regulate the initiator activity, such as the in situ preparation method of polymer solid electrolytes disclosed in patent 202111524087.9. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing a solid polymer electrolyte by initiating ring-opening polymerization of a cyclic ether.

[0006] The technical solution adopted by the present invention is as follows: a method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization, wherein the raw materials for preparing the solid polymer electrolyte are composed of a cyclic ether monomer, a conductive salt and an initiator;

[0007] The method comprises the following steps:

[0008] (1) Under the protection of an inert gas, the cyclic ether monomer and the conductive salt are uniformly mixed to obtain a mixed solution;

[0009] (2) adding the initiator to the mixed solution of (1), stirring and mixing uniformly to obtain a solid polymer electrolyte precursor;

[0010] (3) taking a certain volume of the solid polymer electrolyte precursor obtained in step (2) to assemble a battery in situ, and then placing it in a sealed manner to allow the gel polymer electrolyte precursor to gradually undergo a polymerization reaction under the catalysis of the initiator;

[0011] Wherein, the initiator is one of zirconium phosphate, sulfonated zirconium phosphate, lithiated zirconium phosphate, molybdenum sulfide, and tungsten phosphate.

[0012] Preferably, the initiator is zirconium phosphate.

[0013] Preferably, the cyclic ether monomer is one or a mixture of 1,3-dioxolane (DOL), tetrahydrofuran (THF), vinylene carbonate (VC), polyethylene glycol diformaldehyde (PEGDE), and fluorinated ethylene carbonate (FEC).

[0014] Preferably, the cyclic ether monomer is 1,3-dioxolane (DOL).

[0015] Preferably, the conductive salt is a conductive lithium salt or a conductive sodium salt; the conductive lithium salt is at least one of LiPF6, LiBF4, LiClO4, LiFSI, LiTFSI, LiBOB, LiODFB, LiODFP, and LiPO2F2; the conductive sodium salt is at least one of NaPF6, NaBF4, NaAsF6, NaClO4, NaTf, NaFSI, NaTFSI, NaBOB, NaODFB, and NaODFP.

[0016] Preferably, the conductive salt is LiTFSI.

[0017] Preferably, the concentration of the conductive salt in the mixed solution of the cyclic ether monomer and the conductive salt is 1 to 5 mol L -1 .

[0018] Preferably, the temperature of the polymerization reaction is controlled at 0-60°C.

[0019] Preferably, the conductive salt and the cyclic ether monomer are mixed by heating and stirring, with a stirring temperature of -20 to 60° C., a stirring speed of 50 to 1000 r / min, and a time of 5 to 24 hours.

[0020] Preferably, the polymerization reaction time is controlled to be 1 to 7 days.

[0021] In step (3), the polymerization reaction is carried out with the aid of a macroporous membrane as a skeleton.

[0022] The macroporous separator is one of glass fiber, polyethylene, polypropylene (PP), and non-woven fabric.

[0023] The present invention has the following beneficial effects: The in-situ polymerization method employed in the present invention prepares a polymer solid electrolyte. By selecting a specific initiator, compared to currently commonly used initiators, without the need for inhibitors, the polymer solid electrolyte not only improves interfacial wettability and contact, but also creates a stable SEI layer to inhibit dendrite formation. Furthermore, the polymer solid electrolyte reacts with lithium metal in situ to form an interfacial layer, thereby homogenizing the interfacial electric field and lithium ion flux. The polymer solid electrolyte prepared by the present invention exhibits good compatibility with electrodes, low internal resistance, minimal internal battery side reactions, and excellent cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0025] Figure 1 This is a graph showing the rate performance of a solid polymer electrolyte membrane prepared by ring-opening polymerization of a cyclic ether according to Example 1 of the present application and a lithium iron phosphate (LFP) positive electrode assembly according to Comparative Example 1 using LFP / electrolyte membrane / Li half-cell;

[0026] Figure 2 This is a graph showing the rate performance of a solid polymer electrolyte membrane prepared by ring-opening polymerization of a cyclic ether according to Example 1 of the present application and a lithium iron phosphate (LFP) positive electrode assembly according to Comparative Example 2 using LFP / electrolyte membrane / Li half-cell;

[0027] Figure 3 This is a charge and discharge curve diagram of an LFP / electrolyte membrane / Li half-cell assembled with a solid polymer electrolyte membrane matched with a lithium iron phosphate (LFP) positive electrode prepared by ring-opening polymerization of a cyclic ether according to Example 1 of the present application;

[0028] Figure 4This is a graph of the rate performance of the solid polymer electrolyte membrane prepared by the ring-opening polymerization of cyclic ether according to Example 1 of the present application and the nickel-cobalt-manganese ternary positive electrode (NCM) positive electrode assembly NCM / electrolyte membrane / Li half-cell. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0030] In the embodiment, the positive electrode sheet, negative electrode sheet and separator for secondary lithium battery are prepared by the following method:

[0031] (1) Preparation of positive electrode sheet

[0032] In the embodiment, the positive electrode sheet and the negative electrode sheet for secondary lithium battery are prepared by the following method:

[0033] 80 wt% active material (LFP / NCM), 10 wt% PVDF binder, and 10 wt% conductive additive were uniformly dispersed in an NMP solution and stirred at a constant speed for 12 hours. The resulting slurry was cast onto aluminum foil using a doctor blade and vacuum-dried at 80-100°C for 12 hours to obtain a thin film. This film was then punched into a disc with a diameter of 12-14 mm to obtain the positive electrode. Commercial lithium / sodium metal sheets were used as the negative electrode for the secondary battery.

[0034] Example 1:

[0035] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization comprises the following steps:

[0036] Step 1: Under inert gas protection, dissolve 2 mol of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in 1 ml of 1,3-dioxolane (DOL) to obtain a liquid electrolyte;

[0037] Step 2: Add 1 wt% zirconium phosphate (α-ZrP) as an initiator to the liquid electrolyte to initiate a polymerization reaction, and stir to mix evenly;

[0038] Step 3: Take a certain volume of the solid polymer electrolyte precursor obtained in step 2, use a macroporous diaphragm glass fiber as a skeleton, and then place it in a sealed manner to allow the gel polymer electrolyte precursor to gradually undergo a polymerization reaction under the catalysis of the initiator, and conduct relevant electrochemical performance tests of the polymer membrane.

[0039] Example 2:

[0040] The preparation process of this embodiment is basically similar to the preparation process of a solid polymer electrolyte prepared by initiating cyclic ether ring-opening polymerization described in Example 1, except that the 2 mol of LiTFSI is replaced with 1 mol; the rest remains unchanged, and the solid polymer electrolyte prepared by initiating cyclic ether ring-opening polymerization is obtained according to the method of Example 1.

[0041] Example 3:

[0042] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is as described in Example 1, except that the 2 mol of LiTFSI is replaced by 2 mol of LiPF6; the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0043] Example 4:

[0044] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is as described in Example 1, except that the α-ZrP as the initiator is replaced with sulfonated zirconium phosphate; the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0045] Example 5:

[0046] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is as described in Example 1, except that the α-ZrP as the initiator is replaced with lithiated zirconium phosphate; the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0047] Example 6:

[0048] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is as described in Example 1, except that the α-ZrP as the initiator is replaced with molybdenum sulfide; the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0049] Example 7:

[0050] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is as described in Example 1, except that the α-ZrP as the initiator is replaced with tungsten phosphate; the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0051] Example 8:

[0052] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is as described in Example 1, except that the DOL is replaced with tetrahydrofuran (THF); the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0053] Example 9:

[0054] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is as described in Example 1, except that the DOL is replaced by tetrahydrofuran (THF) and 2 mol of LiTFSI is replaced by 1 mol; the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0055] Example 10:

[0056] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is as described in Example 1, except that the DOL is replaced by tetrahydrofuran (THF) and the α-ZrP initiator is replaced by tungsten phosphate; the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0057] Example 11:

[0058] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is as described in Example 1, except that the α-ZrP as the initiator is replaced with sulfonated zirconium phosphate; the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0059] Comparative Example 1:

[0060] Under the protection of inert gas, 2 mol of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was dissolved in 1 ml of 1,3-dioxolane (DOL) to obtain a liquid electrolyte named DOL.

[0061] Comparative Example 2:

[0062] A process for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization is described in Example 1, except that the 1 wt % α-ZrP used as an initiator is replaced with 1 wt % aluminum trifluoromethanesulfonate; the rest remains unchanged, and the solid polymer electrolyte is prepared by initiating cyclic ether ring-opening polymerization according to the method of Example 1.

[0063] Table 1. Cyclic performance test of lithium iron phosphate / Li battery assembled with composite solid electrolyte membrane prepared in some embodiments and comparative examples.

[0064]

[0065]

[0066] Table 2. Battery performance test of NCM811 battery after 100 cycles

[0067]

[0068] From Table 1-2 and Figure 1-4 It can be seen that the lithium iron phosphate and NCM811 solid-state full batteries assembled with the solid polymer electrolyte prepared by ring-opening polymerization of the cyclic ether synthesized in the present invention have higher capacity, better capacity retention and higher coulombic efficiency than the comparative electrolyte.

[0069] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a solid polymer electrolyte by initiating ring-opening polymerization of a cyclic ether, characterized in that: The raw materials for preparing the solid polymer electrolyte are composed of cyclic ether monomers, conductive salts and initiators; The method comprises the following steps: (1) Under the protection of an inert gas, the cyclic ether monomer and the conductive salt are uniformly mixed to obtain a mixed solution; (2) adding the initiator to the mixed solution of (1), stirring and mixing uniformly to obtain a solid polymer electrolyte precursor; (3) taking a certain volume of the solid polymer electrolyte precursor obtained in step (2) to assemble a battery in situ, and then placing it in a sealed manner to allow the solid polymer electrolyte precursor to gradually undergo a polymerization reaction under the catalysis of an initiator; Wherein, the initiator is one of zirconium phosphate, sulfonated zirconium phosphate, lithiated zirconium phosphate, molybdenum sulfide, and tungsten phosphate.

2. The method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization according to claim 1, characterized in that: The initiator is zirconium phosphate.

3. The method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization according to claim 1, characterized in that: The cyclic ether monomer is one or a mixture of 1,3-dioxolane (DOL), tetrahydrofuran (THF), vinylene carbonate (VC), polyethylene glycol diformaldehyde (PEGDE), and fluorinated ethylene carbonate (FEC).

4. The method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization according to claim 1, characterized in that: The cyclic ether monomer is 1,3-dioxolane (DOL).

5. The method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization according to claim 1, characterized in that: The conductive salt is a conductive lithium salt or a conductive sodium salt; the conductive lithium salt is at least one of LiPF6, LiBF4, LiClO4, LiFSI, LiTFSI, LiBOB, LiODFB, LiODFP, and LiPO2F2; the conductive sodium salt is at least one of NaPF6, NaBF4, NaAsF6, NaClO4, NaTf, NaFSI, NaTFSI, NaBOB, NaODFB, and NaODFP.

6. The method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization according to claim 3, characterized in that: The conductive salt is LiTFSI.

7. The method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization according to claim 1, characterized in that: The concentration of the conductive salt in the mixed solution of the cyclic ether monomer and the conductive salt is 1 to 5 mol L -1 .

8. The method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization according to claim 1, characterized in that: The conductive salt and the cyclic ether monomer are mixed by heating and stirring, the stirring temperature is -20 to 60° C., the stirring speed is 50 to 1000 r / min, and the time is 5 to 24 hours.

9. The method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization according to claim 1, characterized in that: The temperature of the polymerization reaction is controlled to be 0-60° C., and the time of the polymerization reaction is controlled to be 1-7 days.

10. The method for preparing a solid polymer electrolyte by initiating cyclic ether ring-opening polymerization according to claim 1, characterized in that: In step (3), the polymerization reaction is carried out with the aid of a macroporous membrane as a skeleton; the macroporous membrane is one of glass fiber, polyethylene, polypropylene (PP), and non-woven fabric.

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