A polymer electrolyte membrane and a preparation method thereof

Abstract

The present invention belongs to the field of electrolyte membranes, and particularly relates to a polymer electrolyte membrane and a preparation method thereof. The method includes: 1) uniformly mixing a heterocyclic compound and a diol A, subjecting them to a thermal reaction, successively adding a diol B and a catalyst and mixing uniformly, subjecting them to an esterification reaction, and cooling to obtain a substrate; 2) mixing a linear polyether compound and an organic lithium salt into the substrate under an inert gas atmosphere, adding a dispersant and mixing uniformly, injecting into a film mold and standing for reaction, and drying to obtain the polymer electrolyte membrane. The polymer electrolyte membrane prepared by the present invention has a short lithium ion transport path, high transport efficiency, exhibits good ionic conductivity, and at the same time has an array structure on its surface, can be quickly wetted, exhibits excellent liquid absorption rate, and maintains good dimensional stability and performance stability under high temperature and pressure conditions.

Description

Technical Field

[0001] The present invention belongs to the field of electrolyte membranes, and particularly relates to a polymer electrolyte membrane and a preparation method thereof. Background Art

[0002] With the development of technology, lithium batteries have been gradually widely used in various fields. A lithium battery includes a positive electrode, a negative electrode, an electrolyte, etc. Among them, the liquid electrolyte is widely used due to its excellent ionic conductivity. Since the liquid electrolyte is prone to leakage, a polymer electrolyte membrane is often prepared to separate the two electrodes.

[0003] On traditional polyether and polycarbonate-based polymer electrolyte membranes, a continuous reduced lithium substance often cannot be formed, which will cause a significant degradation in battery performance. Moreover, the commercially available polymer electrolyte membranes mainly have the following problems: 1) The membrane pore size is too large, resulting in easy direct contact between the two electrodes and short circuit, but a membrane with too small pore size leads to a long lithium ion transport path, thus making it difficult for lithium ions to diffuse; 2) The wettability of the electrolyte to the membrane is poor, and the absorption effect of the membrane on the electrolyte is poor. Electrostatic breakdown occurs due to lithium dendrites and dry liquid regions in the membrane, significantly affecting the performance of the battery; 3) At a higher temperature, the polymer chain movement ability is enhanced, and the structural binding points are damaged, resulting in poor dimensional stability. The diaphragm shrinks, causing the two electrodes to come into direct contact and fail. Further, at a continuous high temperature, the polymer electrolyte membrane is prone to water loss, which destroys the hydrogen bond network in the membrane, reduces the proton transport path, and leads to a decrease in proton conductivity.

[0004] Most importantly, the shrinkage of the membrane will cause the lithium ion transport to be blocked, resulting in a change in resistance, leading to poor ionic conductivity of the battery, a further decrease in the active electrode area, and a decrease in the charge and discharge efficiency of the battery. A continuous high temperature environment will cause irreversible damage to the electrolyte membrane. The stress formed by the membrane shrinkage will also cause electrons to be squeezed, resulting in an increase in battery resistance and deterioration of performance.

[0005] Therefore, it is necessary to develop a polymer electrolyte membrane that can solve the above problems. Summary of the Invention

[0006] Based on the above, in order to solve the problems that the membrane is easily damaged by lithium dendrites, the membrane has poor absorption effect on the electrolyte, and the membrane has poor stability, the present invention proposes a polymer electrolyte membrane and a preparation method thereof.

[0007] The object of the present invention is as follows:

[0008] First, ensure that a large amount of lithium ions can pass through the polymer electrolyte membrane;

[0009] Second, improve the wettability of the polymer electrolyte membrane to the electrolyte and enhance its liquid absorption capacity;

[0010] III. Enhance the dimensional stability of the polymer electrolyte membrane at high temperatures.

[0011] To achieve the above object, the present invention adopts the following technical solutions.

[0012] A preparation method of a polymer electrolyte membrane,

[0013] The method includes:

[0014] 1) Take a heterocyclic compound and diol A, mix them evenly, carry out a thermal reaction, then add diol B and a catalyst in sequence and mix them evenly, carry out an esterification reaction, and cool to obtain a substrate;

[0015] 2) Under an inert gas atmosphere, mix a linear polyether compound and an organic lithium salt into the substrate, add a dispersant and mix evenly, inject into a thin film mold and let it stand for reaction, and dry to obtain a polymer electrolyte membrane.

[0016] Preferably,

[0017] In step 1), the heterocyclic compound is 2-methyl-1,2-oxaphospholan-5-one 2-oxide;

[0018] The 2-methyl-1,2-oxaphospholan-5-one 2-oxide is 2-Methyl-1,2-oxaphospholan-5-one 2-oxide, and its CAS number is 15171-48-9;

[0019] In step 1), the diol A is ethylene glycol, and its dosage is 0.5 - 0.6 mL / mL of the heterocyclic compound.

[0020] Preferably,

[0021] The thermal reaction process in step 1) is as follows:

[0022] Under an inert gas atmosphere, heat to 120 - 140 °C and keep the temperature constant for 3.5 - 4.5 h.

[0023] Preferably,

[0024] In step 1), the diol B is 1,4-butanediol, and its dosage is 0.81 - 0.94 mL / mL of the heterocyclic compound;

[0025] In step 1), the catalyst is molecular sieve, its pore diameter is less than or equal to 0.5 nm, and its dosage is 0.02 - 0.06 g / mL of the heterocyclic compound.

[0026] Preferably,

[0027] The esterification reaction process in step 1) is as follows:

[0028] Under an inert gas atmosphere, heat to 150 - 170 °C and keep the temperature constant for 5.5 - 6.5 h.

[0029] Preferably,

[0030] The linear polyether compound described in step 2) is polyethylene oxide, and 3 - 3.5 mL of the linear polyether compound is added per gram of the substrate.

[0031] The organolithium salt described in step 2) is a 0.5 - 0.8 mol / L n - butyllithium solution, and 0.1 - 0.3 mL of the organolithium salt is added per gram of the substrate.

[0032] The n - butyllithium solution referred to in the present invention is a commercially available n - butyllithium n - pentane solution.

[0033] The dispersant described in step 2) is dichloromethane, and 100 - 150 mL of the dispersant is added per gram of the substrate.

[0034] Preferably,

[0035] The drying in step 2) is carried out by constant - temperature vacuum drying.

[0036] The temperature in the drying process described in step 2) is controlled ≤25 °C.

[0037] Preferably,

[0038] The temperature in the drying process described in step 2) is controlled at 15 - 25 °C.

[0039] A polymer electrolyte membrane.

[0040] During the transmission of lithium ions, lithium ions form a path through the potential barrier. The polyethylene oxide skeleton inevitably shrinks due to high temperature, resulting in changes in the path of the path, and the lithium - ion conductivity decreases. The mobility of the polyethylene oxide molecular chain is enhanced, and cracks are likely to occur. The penetration of cracks will cause the two electrodes to be in direct contact, leading to battery deterioration. At the same time, the contraction stress causes electrons to be squeezed, resulting in an increase in battery resistance. To solve this problem, the technical solution of the present invention first prepares a substrate with an asymmetric structure of adjacent carbon atoms, performs diol treatment with ethylene glycol and 1,4 - butanediol. First, ethylene glycol is used for chain breaking, which is the premise for introducing an alcohol - ester structure into the material, and then catalytic esterification is carried out to form an alcohol - ester compound.

[0041] During the preparation process, temperature can significantly affect lithium-ion coordination clusters and porosity, thereby influencing lithium-ion transport. High temperature helps increase the size of lithium-ion coordination clusters and reduce the number of through holes and lattice defects. However, excessively high temperature will cause the material resistance to increase and the piezoresistive coefficient to increase. Therefore, the preparation temperature should be controlled to retain appropriate lattice defects. After treatment with diol, a 1,4-butanediol segment is introduced into the main chain of the heterocyclic compound, effectively increasing the solution viscosity. After forming, it is beneficial to enhance the mechanical properties of the material to avoid shrinkage and internal structure collapse of the membrane material during the subsequent forming process, resulting in a decline in its electrochemical performance. In this alcohol ester compound, the phosphorus-oxygen single bond and phosphorus-oxygen double bond are thermally transformed, which can inhibit the release of hydrogen free radicals and oxygen free radicals during the thermal decomposition process, improve the piezoresistive effect of the polymer electrolyte membrane, and enhance the high-temperature dimensional stability of the material.

[0042] There are multiple -CH2CH2O- segments in the structure of polyethylene oxide, and the segment movement can promote the movement of lithium ions. However, due to the regular lithium-ion transport channels and high crystallinity, lithium ions are prone to migrate in the amorphous region, resulting in low ionic conductivity of the polymer electrolyte membrane. In the technical solution of the present invention, the hydrogen bond between the hydroxyl group of the substrate and the polymer and the asymmetric active hydroxyl group structure in the substrate are beneficial to constructing lithium-ion transport channels and overcoming the problem of lithium-ion migration in the amorphous region. By synergistically combining various bonding effects, the rapid migration of lithium ions is promoted. At the same time, the hydrogen bond weakens the coordination between lithium ions and oxygen and enhances the interfacial stability. This structure enables the density to decrease while the mechanical properties of the membrane do not decline significantly, avoiding cracks in the polymer skeleton caused by external stress stimulation.

[0043] On this basis, the present invention further adds and uses a specific organic lithium salt. The organic lithium salt used is a strong base and an organic reagent with strong nucleophilic ability. It can react with the formed alcohol ester compound and polyethylene oxide to form and construct and stabilize the lithium ion transport channel. In addition, the introduction of an appropriate amount of lithium ions in the preparation process of the electrolyte membrane can generally improve the conductivity of the electrolyte membrane to a certain extent, improve the mechanical properties of the electrolyte membrane, and enhance the electrochemical stability of the electrolyte membrane. However, for the technical solution of the present invention, a certain degree of controllable assembly is actually achieved. In the drying process of step 2), due to the gradual volatilization of dichloromethane, the hydrogen bonds between the substrate hydroxyl group and the polymer and the asymmetric active hydroxyl structure in the substrate will be affected, and may shrink and collapse. In particular, for the hydrogen bonds between the substrate hydroxyl group and the polymer, it will cause the rearrangement of the substrate and the polymer. In this case, the present invention can form a bond or connect and fix with the alcohol ester compound substrate and polyethylene oxide to a certain extent by introducing a strong base and a strong nucleophilic ability organic lithium salt. At the same time, the introduced lithium ions are also conducive to avoiding hydrogen bond rearrangement, thereby effectively maintaining the formed lithium ion channel, ensuring that the electrolyte membrane of the present invention has good stability and electrochemical properties. However, organic lithium salts with strong base and strong nucleophilicity are usually very active. In terms of selection, the present invention has only found that n-butyl lithium has a relatively good preparation effect, but n-butyl lithium is still relatively active, and common drying processes such as heat drying and freeze drying will generally cause irreversible effects on film material forming. For example, heat drying may cause the remaining n-butyl lithium to burn during the static curing molding process, while freeze drying will have a more significant impact on the hydrogen bond between the substrate hydroxyl group and the polymer, and the asymmetric active hydroxyl structure in the substrate, and at the same time cause the pre-product before complete curing molding to produce physical shrinkage, resulting in a decrease in thickness but also a simultaneous decrease in ion conductivity, because the lithium ion channel collapses and decreases, and the present invention specifically uses vacuum drying under room temperature conditions, and removes the solvent under mild conditions to increase the concentration of n-butyl lithium in disguise, thereby activating its reaction activity to a certain extent, achieving the fixation of the channel and enhancing the conductivity of the electrolyte membrane, significantly optimizing the various properties of the electrolyte membrane and ensuring the safety of industrial production and processing.

[0044] Furthermore, the copolymer forms an array structure on the outer surface of the membrane, which increases the contact area between the liquid and the membrane, reduces the mass transfer resistance, and promotes the electrode reaction. The synergistic hydrophilic phosphonic acid group can enhance the material's liquid absorption capacity, can be completely wetted, and promote Li + OH - transmission.

[0045] The material prepared by the present invention has a special structure, which is different from the product obtained by directly adding monomers with good thermal stability and copolymerizing. The electrolyte membrane of the present invention constructs a stable lithium ion channel through an organic polymer and an organic lithium salt. When under pressure, lithium ions can still migrate orderly, and there is no obvious relaxation process at the interface, which can significantly improve the piezoresistive effect. However, the method of increasing the density of the polymer network and reducing the segmental movement at high temperature by chemical or physical crosslinking will cause the hindrance of lithium ion migration. At the same time, the material has a long chain length and overlaps with each other, which instead reduces the structural stability of the material at high temperature. Adding heat-stable fillers may lead to the appearance and expansion of cracks due to stiffness mismatch, resulting in a more serious piezoresistive effect.

[0046] The beneficial effects of the present invention are as follows:

[0047] (1) The lithium ion transport path of the polymer electrolyte membrane prepared by the present invention is short, the transport efficiency is high, and it shows good ionic conductivity;

[0048] (2) The surface of the polymer electrolyte membrane prepared by the present invention has an array structure, can be quickly wetted, and shows excellent liquid absorption rate;

[0049] (3) The polymer electrolyte membrane prepared by the present invention can maintain good dimensional stability and performance stability under high temperature and pressure conditions. Description of the Drawings

[0050] Figure 1 It is the SEM characterization diagram of the polymer electrolyte membrane prepared in Example 1 of the present invention. Detailed Embodiments

[0051] The following further clearly and detailedly describes the present invention in combination with specific embodiments and the drawings of the specification. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are usually only a part of the embodiments of the present invention, rather than all the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the scope of protection of the present invention.

[0052] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available or raw materials that can be obtained by those skilled in the art; unless otherwise specified, the methods used in the embodiments of the present invention are all methods mastered by those skilled in the art.

[0053] Example 1: A method for preparing a polymer electrolyte membrane, the method comprising:

[0054] 1) Take 10 mL of 2-methyl-1,2-oxaphospholane-5-oxide and 5 mL of ethylene glycol, mix them evenly, heat to 120 °C under a nitrogen atmosphere, keep the temperature constant for 4 h, successively add 8.1 mL of 1,4-butanediol and 0.2 g of molecular sieve with a pore size of 0.4 nm, mix them evenly, heat to 150 °C under a nitrogen atmosphere, keep the temperature constant for 6 h, and cool to obtain the substrate;

[0055] 2) Under a nitrogen atmosphere, mix polyethylene oxide into the substrate. Mix 3 mL of polyethylene oxide per gram of the substrate, add 0.2 mL of a 0.5 mol / L n-butyllithium n-pentane solution per gram of the substrate, add 100 mL of dichloromethane per gram of the substrate, mix them evenly, inject into a film mold, let it stand and react for 3 h, and then vacuum dry at 20 °C to obtain the polymer electrolyte membrane.

[0056] Perform SEM characterization on the polymer electrolyte membrane prepared in this example. The characterization results are as Figure 1 shown. It can be clearly seen from Figure 1 the characterization results that the polymer electrolyte membrane prepared by the present invention has a very high porosity, with a rich pore structure distributed on the surface, thus having rich ion channels and a large liquid absorption space. On the other hand, the pores show a hierarchical distribution and have a larger specific surface area, and there are a small number of sheet-like nanostructures distributed.

[0057] Perform performance testing on the polymer electrolyte membrane of this example. The testing method is as follows.

[0058] 1. Liquid absorption test

[0059] Immerse the polymer electrolyte membrane prepared in this example in deionized water for 4 h, weigh the membrane before and after immersion to calculate the mass difference, and calculate the liquid absorption rate of the membrane according to the mass difference The formula is:

[0060] . .

[0061] 2. Electrochemical performance test

[0062] Lithium sheets and germanium graphene with the same diameter are used as the two electrodes, and are assembled with the electrolyte membrane prepared in this example into a battery, and detected using an SC28-CHI660E electrochemical workstation. Under the condition of introducing H2 on the anode side and N2 on the cathode side, cyclic voltammetry tests are carried out. The gas flow rate is 1000 mL / min for both. In an environment of 40 °C, the scanning voltage range is set to 0.01 - 1.5 V, the scanning speed is 20 mV / s. After multiple scans, according to the cyclic voltammetry test results, it is detected whether there is an obvious voltage shift in the oxidation-reduction process. Cycle 50 times at 0.5 C, and the battery capacity retention rate is detected and recorded as DCR1. The commercially available all-polymer solid electrolyte membrane A (purchased from Ampcera, PER / PPC@LLZTO composite solid electrolyte) and the commercially available polymer all-solid electrolyte membrane B (purchased from NEI Corporation, PEO / PPC / nano TiO2-PMMA composite solid polymer electrolyte membrane) are respectively subjected to the same test characterization, and the battery capacity retention rates are respectively recorded as DCR2 and DCR3. The characterization results show that DCR2 > DCR3. Therefore, the improvement rate of the battery capacity retention rate of the polymer electrolyte membrane prepared in this example compared with the commercially available high-quality polymer solid electrolyte membrane A is calculated using the recorded DCR1 and DCR2. The calculation process is as follows:

[0063] The improvement rate of the battery capacity retention rate △DCR = (DCR1 - DCR2) / DCR2 × 100%.

[0064] 3. Ion conductivity test

[0065] The ion conductivity of the polymer electrolyte membrane prepared in this example is characterized and recorded by the alternating current impedance spectroscopy method.

[0066] The results are as follows.

[0067]

[0068] According to the results in the table, due to the conical array structure on the material surface effectively promoting liquid absorption, the polymer electrolyte membrane in this example has excellent liquid absorption effect. Because the polymer electrolyte membrane has a tight network structure, the entanglement of each component reduces the phenomena of cracking and separation, and the uniform dispersion of particulate matter during molding reduces the excess stress, so that the material will not have obvious curling, shrinkage and other phenomena at high temperatures. This indicates that the polymer electrolyte membrane has strong high-temperature dimensional stability. In addition, after applying a dynamic pressure of 3 - 30 MPa to clamp the front and back sides of the polymer electrolyte membrane of the present invention, the ion conductivity characterization test is carried out. When starting to apply pressure, the ion conductivity first slightly increases and then decreases with the increase of pressure. When the dynamic external pressure reaches 22 - 30 MPa, the ion conductivity tends to be stable, reaching about 2.01 mS·cm-1 , still exhibits excellent ionic conductivity. Since there is no obvious interface in the material of this example, the lithium ions near the interface do not have an obvious relaxation process, showing a relatively small change trend in the piezoresistive coefficient.

[0069] Example 2: A method for preparing a polymer electrolyte membrane, the method comprising:

[0070] 1) Take 10 mL of 2-methyl-1,2-oxaphospholane-5-oxide and 5 mL of ethylene glycol, mix them evenly, under a nitrogen atmosphere, heat to 130 °C, keep the temperature constant for 4 h, and successively add 8.1 mL of 1,4-butanediol and 0.2 g of molecular sieve with a pore size of 0.4 nm, mix them evenly, under a nitrogen atmosphere, heat to 160 °C, keep the temperature constant for 6 h, and cool to obtain a substrate;

[0071] 2) Under a nitrogen atmosphere, mix polyethylene oxide into the substrate. Mix 3 mL of polyethylene oxide per gram of the substrate, add 0.2 mL of a 0.5 mol / L n-butyllithium n-pentane solution per gram of the substrate, and add 100 mL of dichloromethane per gram of the substrate, mix them evenly, inject into a thin film mold and let it stand for reaction for 3 h, and then obtain a polymer electrolyte membrane after vacuum drying at 20 °C.

[0072] Perform the performance test on the polymer electrolyte membrane of this example as in Example 1, and the results are as follows.

[0073]

[0074] Preparing the substrate by heating in this example is beneficial to constructing a lithium ion transport channel. Microscopically, the size of the ionic coordination clusters increases and the growth orientation is consistent, which is beneficial to the orderly migration of lithium ions and avoids relaxation at the material interface. Similarly, the ionic conductivity test is carried out under the dynamic pressure condition of 3 - 30 MPa. Since the lattice defects in the material are reduced, the change rate of the ionic conductivity is smaller, and when it reaches equilibrium, the ionic conductivity remains at about 2.05 mS·cm -1 . The influence of the shrinkage stress on the battery at high temperature becomes smaller. The ionic conductivity of the assembled battery hardly changes, which is beneficial to lithium ion transport, and the battery capacity retention rate is relatively high.

[0075] Example 3: A method for preparing a polymer electrolyte membrane, the method comprising:

[0076] 1) Take 10 mL of 2-methyl-1,2-oxaphospholane-5-oxide and 5 mL of ethylene glycol, mix them evenly, under a nitrogen atmosphere, heat to 140 °C, keep the temperature constant for 4 h, and successively add 8.1 mL of 1,4-butanediol and 0.2 g of molecular sieve with a pore size of 0.4 nm, mix them evenly, under a nitrogen atmosphere, heat to 170 °C, keep the temperature constant for 6 h, and cool to obtain a substrate;

[0077] 2) Under a nitrogen atmosphere, polyethylene oxide was mixed into the substrate at a rate of 3 mL of polyethylene oxide per gram of the substrate. 0.2 mL of a 0.5 mol / L n-butyllithium n-pentane solution was added per gram of the substrate, and 100 mL of dichloromethane was added per gram of the substrate and mixed evenly. The mixture was injected into a film mold and allowed to stand and react for 3 h, and then vacuum-dried at 20 °C to obtain a polymer electrolyte membrane.

[0078] The performance of the polymer electrolyte membrane in this example was tested in the same manner as in Example 1, and the results are as follows.

[0079]

[0080] Although in this example, the ionic conductivity of the material decreased. This is because the higher temperature made the material gradually become compact, and the porosity decreased accordingly. Moreover, due to the decrease in porosity, its liquid absorption rate also decreased significantly.

[0081] Comparative Example 1: A method for preparing a polymer electrolyte membrane, the method comprising:

[0082] 1) Take 10 mL of 2-methyl-1,2-oxaphospholane-5-oxide and 5 mL of ethylene glycol and mix them evenly. Under a nitrogen atmosphere, heat to 130 °C and keep the temperature constant for 4 h. Then, add 8.1 mL of 1,4-butanediol and 0.2 g of molecular sieve with a pore size of 0.4 nm and mix them evenly. Under a nitrogen atmosphere, heat to 160 °C and keep the temperature constant for 6 h, and then cool to obtain the substrate.

[0083] 2) Under a nitrogen atmosphere, polyethylene was mixed into the substrate at a rate of 3 g of polyethylene per gram of the substrate. 0.2 mL of a 0.5 mol / L n-butyllithium n-pentane solution was added per gram of the substrate, and 100 mL of dichloromethane was added per gram of the substrate and mixed evenly. The mixture was injected into a film mold and allowed to stand and react for 3 h, and then vacuum-dried at 20 °C to obtain a polymer electrolyte membrane.

[0084] The performance of the polymer electrolyte membrane in this example was tested in the same manner as in Example 1, and the results are as follows.

[0085]

[0086] In this example, the polymer electrolyte is prepared based on a polyethylene backbone. After heating, the material undergoes a deformation - recovery process. The thermal shrinkage phenomenon of this material is severe, and it is very likely to cause the direct contact between the positive and negative electrodes of the battery, leading to battery short - circuit. At the same time, although it is somewhat difficult for lithium ions to migrate in the amorphous region, due to the poor charge migration ability and loose structure inside the non - polar material, the migration rate of lithium ions in the transport channels is also very low, resulting in low ionic conductivity. This leads to the attenuation of battery capacity and makes it difficult to meet the actual requirements.

[0087] Comparative Example 2: A method for preparing a polymer electrolyte membrane, the method comprising:

[0088] 1) Take 10 mL of 2 - methyl - 1,2 - oxaphospholane - 5 - oxide and 5 mL of ethylene glycol, mix them evenly, under a nitrogen atmosphere, heat to 130 °C, keep the temperature constant for 4 h, successively add 8.1 mL of 1,4 - butanediol and 0.2 g of molecular sieve with a pore size of 0.4 nm, mix them evenly, under a nitrogen atmosphere, heat to 160 °C, keep the temperature constant for 6 h, and cool to obtain the substrate;

[0089] 2) Under a nitrogen atmosphere, mix polystyrene into the substrate, at a ratio of 3 g of polystyrene per gram of substrate, add 0.2 mL of a 0.5 mol / L n - butyllithium in n - pentane solution per gram of substrate, add 100 mL of dichloromethane per gram of substrate, mix them evenly, inject into a thin - film mold, let it stand and react for 3 h, and then vacuum - dry at 20 °C to obtain the polymer electrolyte membrane.

[0090] Perform the same performance tests on the polymer electrolyte membrane of this example as in Example 1, and the results are as follows.

[0091]

[0092] In this example, a polymer containing an aromatic structure is used to synthesize a polymer backbone with stronger heat resistance, significantly improving the stability at high temperatures. However, first, the liquid absorption rate of the membrane prepared based on polystyrene decreases. Second, the polymer density increases, the stiffness increases, and under the influence of shrinkage stress, its skeleton is prone to cracking and it is difficult to maintain structural stability; moreover, the movement of chain segments hinders the migration of lithium ions, and the battery capacity attenuation is obvious. There is an obvious relaxation process of lithium ions at the material interface, and the piezoresistive effect is obvious.

[0093] Comparative Example 3: A method for preparing a polymer electrolyte membrane, the method comprising:

[0094] 1) Take 10 mL of 2-methyl-1,2-oxaphospholane-5-oxide and 5 mL of ethylene glycol, mix them evenly, heat to 130 °C under a nitrogen atmosphere, keep the temperature constant for 4 h, add 8.1 mL of 1,4-butanediol and 0.2 g of molecular sieve with a pore size of 0.4 nm in sequence, mix them evenly, heat to 160 °C under a nitrogen atmosphere, keep the temperature constant for 6 h, and cool to obtain the substrate;

[0095] 2) Under a nitrogen atmosphere, mix polyethylene oxide into the substrate. Mix 3 mL of polyethylene oxide and 0.05 g of calcium carbonate per gram of the substrate. Add 0.2 mL of a 0.5 mol / L n-butyllithium in n-pentane solution per gram of the substrate. Add 100 mL of dichloromethane per gram of the substrate, mix them evenly, inject into a film mold, let it stand and react for 3 h, and then vacuum dry at 20 °C to obtain the polymer electrolyte membrane.

[0096] Perform the performance test on the polymer electrolyte membrane in this example as in Example 1, and the results are as follows.

[0097]

[0098] In this example, a small amount of heat-stable filler is added, and the stability of the battery is good at 40 °C. Moreover, the interaction between the C=O polar bond of the material and calcium carbonate can enhance the liquid absorption of calcium carbonate. However, under pressure conditions, due to the mismatch between calcium carbonate and the molecular chain backbone stiffness, crack formation and expansion occur, resulting in a more serious piezoresistive effect, and the ionic conductivity never reaches equilibrium. When the applied pressure reaches 30 MPa, its ionic conductivity drops to about 1.07, showing a very obvious decrease.

[0099] Comparative Example 4: A method for preparing a polymer electrolyte membrane, the method comprising:

[0100] 1) Take 10 mL of 2-methyl-1,2-oxaphospholane-5-oxide and 5 mL of ethylene glycol, mix them evenly, heat to 130 °C under a nitrogen atmosphere, keep the temperature constant for 4 h, add 8.1 mL of 1,4-butanediol and 0.2 g of molecular sieve with a pore size of 0.4 nm in sequence, mix them evenly, heat to 160 °C under a nitrogen atmosphere, keep the temperature constant for 6 h, and cool to obtain the substrate;

[0101] 2) Under a nitrogen atmosphere, mix polyethylene oxide into the substrate. Mix 3 mL of polyethylene oxide per gram of the substrate. Add 0.2 mL of a 0.5 mol / L n-butyllithium in n-pentane solution per gram of the substrate. Add 100 mL of dichloromethane per gram of the substrate, mix them evenly, inject into a film mold, let it stand and react for 3 h, and then freeze-dry at -20 °C to obtain the polymer electrolyte membrane.

[0102] The performance of the polymer electrolyte membrane in this example was detected in the same way as in Example 1, and the results are as follows.

[0103]

[0104] In this example, freeze-drying was used to achieve the final solidification of the product. Under the condition of the same mold and material quantity, the thickness of the solidified product was significantly smaller than that of the products prepared in Examples 1-3. Moreover, in view of the above characterization results, the performance of the product prepared in this example was much inferior to that of Example 2. This was mainly because during the freeze-drying process, the internal microstructure was damaged due to the collapse of lithium-ion channels and the macroscopic shrinkage of the polymer electrolyte membrane, resulting in a very significant performance decline. When vacuum drying was carried out at 5 °C, a significant performance decline also occurred, mainly in terms of the performance decline of ionic conductivity, only maintaining about 1.36 mS·cm -1 , which was mainly because although the organolithium salt gradually showed reactivity as its concentration increased in the solvent system during the drying process, too low a temperature would inhibit the reaction and even be easily removed during the drying process, resulting in poor actual preparation effects.

[0105] Comparative Example 5: A method for preparing a polymer electrolyte membrane, the method comprising:

[0106] 1) Take 10 mL of 2-methyl-1,2-oxaphospholane-5-oxide and 5 mL of ethylene glycol, mix them evenly, heat to 130 °C under a nitrogen atmosphere, keep the temperature constant for 4 h, add 8.1 mL of 1,4-butanediol and 0.2 g of molecular sieve with a pore size of 0.4 nm in sequence, mix them evenly, heat to 160 °C under a nitrogen atmosphere, keep the temperature constant for 6 h, and cool to obtain a substrate;

[0107] 2) Mix polyethylene oxide into the substrate under a nitrogen atmosphere. Mix 3 mL of polyethylene oxide per gram of the substrate, add 100 mL of dichloromethane per gram of the substrate, mix them evenly, inject into a thin film mold, let it stand and react for 3 h, and then obtain a polymer electrolyte membrane through vacuum drying at 20 °C.

[0108] The performance of the polymer electrolyte membrane in this example was detected in the same way as in Example 1, and the results are as follows.

[0109]

[0110] During the preparation process of this example, no organolithium salt was added, which directly led to a significant decrease in the ionic conductivity of the electrolyte membrane. At the same time, from the changes in the liquid absorption rate and △DCR, it was also proved that it had a direct impact on improving the performance and structural stability of the electrolyte membrane. The decrease in the liquid absorption rate indicates that during the drying process, due to the failure of hydrogen bonds and structural rearrangement, the internal space was compressed and reduced. Although the drying conditions were mild, an obvious decrease still inevitably occurred. With the shrinkage and collapse of the microstructure, and the loss of the effect of the organolithium salt itself on improving the ionic conductivity, the ionic conductivity of the electrolyte membrane also deteriorated very significantly.

Claims

1. A method for preparing a polymer electrolyte membrane, characterized in that: The method includes: 1) Mix a heterocyclic compound and diol A evenly, conduct a thermal reaction, then sequentially add diol B and a catalyst and mix evenly, conduct an esterification reaction, and cool to obtain a substrate; 2) Under an inert gas atmosphere, mix a linear polyether compound and an organic lithium salt into the substrate, add a dispersant and mix evenly, inject into a film mold and let it stand for reaction, and obtain the polymer electrolyte membrane after drying; The heterocyclic compound in step 1) is 2-methyl-1,2-oxaphospholane-5-oxide; The diol A in step 1) is ethylene glycol, and its dosage is 0.5 - 0.6 mL / mL of the heterocyclic compound; The thermal reaction process in step 1) is: Under an inert gas atmosphere, heat to 120 - 140 °C and keep the temperature constant for 3.5 - 4.5 h; The diol B in step 1) is 1,4-butanediol, and its dosage is 0.81 - 0.94 mL / mL of the heterocyclic compound; The catalyst in step 1) is molecular sieve, its pore diameter is less than or equal to 0.5 nm, and its dosage is 0.02 - 0.06 g / mL of the heterocyclic compound; The esterification reaction process in step 1) is: Under an inert gas atmosphere, heat to 150 - 170 °C and keep the temperature constant for 5.5 - 6.5 h; The linear polyether compound in step 2) is polyethylene oxide, and 3 - 3.5 mL of the linear polyether compound is added per gram of the substrate; The organic lithium salt in step 2) is a 0.5 - 0.8 mol / L n-butyllithium solution, and 0.1 - 0.3 mL of the organic lithium salt is added per gram of the substrate; The dispersant in step 2) is dichloromethane, and 100 - 150 mL of the dispersant is added per gram of the substrate; The drying in step 2) adopts constant temperature vacuum drying; The temperature in the drying process in step 2) is controlled at 15 - 25 °C.

2. A polymer electrolyte membrane prepared by the method according to claim 1.

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