Application of linear triblock copolymer in thermoplastic elastomer type solid polymer electrolyte and electrolyte thereof

Abstract

The invention discloses an application of a linear triblock copolymer synthesized by an organic catalytic living free radical polymerization method in a thermoplastic elastomer type solid polymer electrolyte, and belongs to the technical field of high-molecular compounds. The preparation method comprises the following steps: (1) mixing a monomer containing a polyethylene glycol structural unit, an organic diiodide, a catalyst and an azo initiator, and carrying out polymerization reaction to obtain a macromolecular initiator containing an iodide at the tail end; and (2) carrying out catalytic reaction on the macroinitiator containing the iodide at the tail end and a comonomer to obtain the linear triblock copolymer. According to the invention, the influence of heavy metal residues on electrochemical performance can be avoided by adopting an organic catalytic active free radical polymerization method, and the volume fraction of soft and hard chain segments can be accurately regulated and controlled by active polymerization, so that the mechanical properties such as mechanical strength, elastic modulus and impact strength of the thermoplastic elastomer are regulated; and electrochemical properties such as lithium ion conduction number and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer compounds, and in particular relates to application of a linear triblock copolymer in a thermoplastic elastomer-type solid polymer electrolyte and an electrolyte thereof. Background Art

[0002] Thermoplastic elastomers (TPEs) are a class of materials that combine the elasticity of rubber and the plasticity of plastic. They can be processed and formed at high temperatures, retain their shape after cooling, and also have a certain degree of elasticity. Solid polymer electrolytes (SPEs) are electrolytes used in batteries, replacing liquid electrolytes to improve safety and energy density. Thermoplastic elastomer-based solid polymer electrolytes (TPE-SPEs) are solid electrolyte materials that use thermoplastic elastomers as a matrix. They are a type of polymer material that combines thermoplasticity, elasticity, and conductivity, and are primarily used in the electrolyte layer of solid-state batteries.

[0003] The structural features of TPE-SPEs include the choice of polymer matrix, such as the common SEBS (styrene-ethylene-butylene-styrene block copolymer), TPU (thermoplastic polyurethane) or SBS (styrene-butadiene-styrene block copolymer). These materials themselves have a microphase separation structure with alternating hard and soft segments, which may be conducive to ion conduction. In addition, conductive lithium salts, such as lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) and lithium hexafluorophosphate (LiPF6), need to be dissolved in the polymer matrix to form ion transport channels. Plasticizers or other additives may also be used to improve ionic conductivity.

[0004] TPE-SPEs have good processing performance and can be prepared through injection molding, extrusion and other processes, which is conducive to large-scale production and preparation. The mechanical properties of TPE-SPEs are also better than those of ordinary solid electrolytes, such as flexibility and impact resistance, which can adapt to the volume changes during battery charging and discharging. In terms of safety, solid electrolytes are not easy to leak and have better thermal stability, which may reduce the risk of thermal runaway. In addition, TPE-SPEs also have better interface contact because the elastomer has a certain deformation ability and can be in closer contact with the electrode material, reducing the interface impedance. However, the current field of solid electrolytes mainly faces the following challenges, such as whether the microphase separation structure of thermoplastic elastomers is conducive to ion conduction, the problem of interface impedance, the ionic conductivity at room temperature may be lower than that of liquid electrolytes, the long-term cycle stability of the battery, and whether the interface will degrade over time, resulting in a decrease in battery performance.

[0005] Therefore, being able to provide a thermoplastic elastomer-type solid polymer electrolyte with excellent performance is a problem that those skilled in the art urgently need to solve. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides an application of a linear triblock copolymer in a thermoplastic elastomer-type solid polymer electrolyte and an electrolyte thereof.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A linear triblock copolymer is used in a thermoplastic elastomer solid polymer electrolyte. The linear triblock copolymer has the following structural formula:

[0009]

[0010] The BAB type linear triblock copolymer of the present invention has high glass transition temperature (T g ), the middle segment has a lower T g , with adjustable soft and hard segment lengths, adjustable mechanical strength and elastic modulus, good flexibility, and strong impact resistance. It utilizes the microphase separation structure between different blocks to provide Li + conductive channels, thereby serving as a thermoplastic elastomer-type solid polymer electrolyte.

[0011] Preferably, the preparation method of the triblock copolymer comprises the following specific steps:

[0012] (1) mixing a monomer containing a polyethylene glycol (PEG) structural unit, an organic diiodide, a catalyst, and an azo initiator, and performing a polymerization reaction under an inert gas atmosphere to obtain a macromolecular initiator containing an iodide at the end;

[0013] (2) The macromolecular initiator containing an iodide at the end and the comonomer are reacted by a catalyst under an inert gas atmosphere to obtain the linear triblock copolymer.

[0014] The present invention uses an organic catalytic living radical polymerization technology to prepare a macromolecular initiator containing a PEG structural unit, and further initiates a block copolymerization reaction of a comonomer to obtain a BAB type linear triblock copolymer, which can be used to prepare a thermoplastic elastomer type solid polymer electrolyte; wherein the organic catalytic living radical polymerization technology can effectively control the volume fraction of each block, thereby regulating the mechanical strength, elastic modulus, elongation at break and impact resistance of the solid electrolyte film; at the same time, L i+ The conduction number and energy density can meet the requirements of Li + Battery usage requirements.

[0015] Preferably, in step (1), the mass ratio of the monomer containing polyethylene glycol structural units, the organic diiodide, the catalyst and the azo initiator is 40-60:1-2:0.3-0.8:0.4-1.5;

[0016] The polymerization reaction conditions are: reaction at 60° C. for 0.5-2 h.

[0017] Preferably, the monomer containing polyethylene glycol structural unit in step (1) includes polyethylene glycol monomethyl ether methacrylate PEGMA (M n =300,500), polyethylene glycol monomethyl ether acrylate PEGA (M n =480) and at least one of 2-methoxyethyl methacrylate MEMA;

[0018] The catalyst comprises at least one of tetrabutylammonium iodide (BNI), tetra-n-octylammonium iodide (ONI) and S-iodinated butyrylthiocholine (BChI);

[0019] The azo thermal initiator includes at least one of azobisisobutyronitrile (AIBN) and azobisisovaleronitrile (V65).

[0020] The present invention adopts organic catalytic active polymerization technology to avoid the influence of heavy metal ions or sulfur-containing groups on the purity of the resin, thereby affecting the subsequent electrochemical performance.

[0021] Preferably, in step (2), the mass ratio of the macroinitiator containing an iodide at the end, the comonomer and the catalyst is: 1-4:10-40:0.1-0.5;

[0022] The conditions of the catalytic reaction are: reaction at 60-80° C. for 0.5-8 h.

[0023] Preferably, the comonomer in step (2) comprises at least one of methyl methacrylate (MMA), benzyl methacrylate (BzMA) and dimethyl itaconate (DMI);

[0024] The catalyst in the catalytic reaction is at least one of BNI and ONI.

[0025] An electrolyte is a thermoplastic elastomer-type solid polymer electrolyte, wherein the thermoplastic elastomer is prepared by using the triblock copolymer described above.

[0026] Preferably, the preparation steps are iodine removal, film formation by solution method and thermal annealing treatment.

[0027] Preferably, specifically:

[0028] 1) mixing the linear triblock copolymer with 2-aminoethanol and reacting them in a dark environment to remove iodine;

[0029] 2) preparing a solution of the linear triblock copolymer after iodine removal, adding an electrolyte salt and mixing evenly, and then pouring the solution onto a substrate and waiting for the solvent to evaporate completely;

[0030] 3) performing thermal annealing on the substrate to obtain the thermoplastic elastomer-type solid polymer electrolyte.

[0031] Preferably, the electrolyte salt is a lithium salt.

[0032] Since the carbon-iodine bond (CI) at the end of the copolymer will undergo side reactions under white light at room temperature, generating free radicals that affect the electrochemical properties of the elastomer, 2-aminoethanol is used to remove the iodine atoms at the end of the polymer under light-proof conditions. The amount of 2-aminoethanol is determined according to the terminal iodine content, and the amount of initiator used affects the terminal iodine content.

[0033] Preferably, in step 1), the mixing ratio of the triblock copolymer and 2-aminoethanol is 1 g: (0.5-1) mL; and the reaction time is 12-48 h;

[0034] Preferably, in step 2), the solvent is THF, and the solution concentration is 0.1-0.5 g / mL. The thickness of the thermoplastic elastomer can be adjusted by the solution concentration;

[0035] Preferably, a glass sheet is placed on the substrate in step 2) to control the volatilization rate of the solvent THF by the sealing degree of the glass sheet, thereby ensuring the uniformity of the thermoplastic elastomer and preventing the generation of bubbles.

[0036] Preferably, the thermal annealing temperature in step 3) is 50-80°C and the time is 12-24h. During the thermal annealing process, the soft and hard segments have a strong microphase separation tendency and microphase separation occurs. The thermal annealing temperature is higher than the T of the soft segment. g , and lower than the T of the hard segment g value.

[0037] Application of electrolytes as described above in solid-state batteries in the fields of new energy, portable devices and energy storage.

[0038] The main application areas are solid-state lithium batteries, including electric vehicles, portable electronic devices and energy storage systems. They can also be used in flexible electronic devices because the elastomer itself has good flexibility. Others such as sensors and supercapacitors may also be used.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention synthesizes a linear BAB-type linear triblock copolymer by adopting organic catalytic living free radical polymerization technology, and uses it as a thermoplastic elastomer-type solid polymer electrolyte. The organic catalysis can avoid the influence of residual heavy metal ions on electrochemical performance, and the living polymerization can accurately control the volume fraction of soft and hard segments, thereby adjusting the mechanical properties of the thermoplastic elastomer, such as mechanical strength, elastic modulus and impact strength. The prepared thermoplastic elastomer-type solid polymer electrolyte can effectively avoid the risk of battery short circuit caused by the growth of lithium dendrites, which may cause combustion and explosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] 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 merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0042] Figure 1 Schematic diagram of the synthetic route of the polymer resin of the present invention;

[0043] Figure 2 : is the H NMR spectrum of the BAB-type linear triblock copolymer in Example 1 of the present invention;

[0044] Figure 3 This is a gel permeation chromatogram of a BAB-type linear triblock copolymer composed of different soft and hard segments in Example 1 of the present invention;

[0045] Figure 4 IR spectrum of the BAB linear triblock copolymer in Example 1 of the present invention;

[0046] Figure 5 Thermogravimetry (upper left), differential scanning calorimetry (upper right), wide-angle X-ray diffraction (lower left), and tensile curve (lower right) of the thermoplastic elastomer solid polymer electrolyte in Example 1 of the present invention;

[0047] Figure 6 is a scanning electron microscope image of the thermoplastic elastomer solid polymer electrolyte film in Example 1 of the present invention;

[0048] Figure 7 This is an atomic force microscope image of the thermoplastic elastomer solid polymer electrolyte film in Example 1 of the present invention;

[0049] Figure 8 Li is the thermoplastic elastomer solid polymer electrolyte in Example 1 of the present invention + Conductivity performance diagram. DETAILED DESCRIPTION

[0050] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0051] Example 1

[0052] like Figure 1 The present invention provides a method for using a BAB-type linear triblock copolymer as a thermoplastic elastomer-type solid polymer electrolyte, comprising the following specific steps:

[0053] (1) The monomer PEGMA (M n =300), initiator EPh-II, catalyst ONI and azo initiator V65 were charged into a Shrek test tube in a mass ratio of 100:2:2:1, the top was sealed with a three-way joint, argon was passed through for 20 minutes to eliminate residual air in the system, and then the temperature was raised to 60°C for reaction for 1 hour; after the reaction was completed, the temperature was returned to room temperature, ethanol was added to dilute, and then precipitated in a mixed solvent of n-hexane / diethyl ether (v / v=1:1) to obtain a yellow viscous oily liquid, which was vacuum dried to remove the solvent to obtain a macroinitiator PPEGMA-II, which was used as the middle soft segment of a BAB-type linear triblock copolymer;

[0054] (2) In a Shrek test tube, 3 parts by mass of the macroinitiator PPEGMA-II was dissolved in 10 parts by mass of the MMA monomer, and then 0.2 parts by mass of the BNI catalyst was added. The top was sealed with a three-way joint, and argon was passed through for 20 minutes to remove the residual air in the system. Then, the temperature was raised to 60°C and the reaction was carried out for 3 hours. After the reaction, the crude product was diluted with THF and then precipitated in ether to obtain a yellow semi-solid product. After vacuum drying, a BAB linear triblock copolymer (PMMA-b-PPEGMA-b-PMMA) was obtained, in which the mass fraction of the A segment was 61.9% and the total mass fraction of the B segment was 38.1%.

[0055] (3) Dissolve 2.0 g of BAB linear triblock copolymer in 10 mL of acetone, add 1.5 mL of 2-aminoethanol, and stir at room temperature in the dark for 24 h. The solution gradually changes from yellow to colorless.

[0056] (4) The BAB linear triblock copolymer after deiodination of the polymer chain ends was dissolved in THF to a concentration of approximately 0.1 g / mL, 0.2 g of LiTFSI was added, and then poured into the groove of a polytetrafluoroethylene plate, covered with a glass plate, and the solid polymer electrolyte film was obtained after the THF evaporated completely;

[0057] (5) placing the polytetrafluoroethylene plate of the solid polymer electrolyte film in a constant temperature and humidity chamber at 60°C for thermal annealing for 12 hours, causing microphase separation of the copolymer film. After cooling to room temperature, the copolymer film was peeled off from the polytetrafluoroethylene plate to obtain a thermoplastic elastomer-type solid polymer electrolyte;

[0058] like Figure 2 is the H NMR spectrum of BAB type linear triblock copolymer. Figure 3 This is a gel permeation chromatogram of products composed of different soft and hard segments, among which the upper left is PMMA 30 -PPEGMA 19 -PMMA 30 and PMMA 39 -PPEGMA 19 -PMMA 39 , upper right PMMA 55 -PPEGMA 31.5 -PMMA 55 and PMMA 59 -PPEGMA 31.5 -PMMA 59 , below is PMMA 68 -PPEGMA 49 -PMMA 68 、PMMA 87 -PPEGMA 49 -PMMA 87 and PMMA 98 -PPEGMA 49 -PMMA 98 ,for Figure 4 The infrared spectrum of the BAB-type linear triblock copolymer shows that each component in the triblock copolymer has a corresponding NMR signal peak. The molar ratio of the monomer units in the A and B segments can be calculated by the integrated area ratio of signals a and b, and then the volume or mass fraction of the soft and hard segments can be calculated. Compared with PPEGMA-II, the gel permeation chromatography curve of the triblock copolymer shifts toward the direction of low elution time and exhibits a symmetrical single peak, indicating the successful preparation of the BAB-type linear triblock copolymer.

[0059] Figure 5 The thermogravimetric, differential scanning calorimetry, wide-angle X-ray diffraction, and tensile curves of the thermoplastic elastomer-type solid polymer electrolyte in Example 1 are shown. As can be seen from the figure, the temperature corresponding to 5% weight loss is above 250°C, indicating that the polymer electrolyte synthesized in this example has good thermal stability and there is no need to worry about the risk of thermal degradation or combustion within the battery operating temperature range; it shows two glass transition temperatures (T g), one of which is between -31 and -52 °C, corresponding to the T of the soft segment PPEGMA g value; the other is between 60 and 75 ° C, corresponding to the T of hard segment PMMA g Value; T with large difference g The value can ensure that the electrolyte can operate in a wide temperature range. In addition, the electrolyte film has a weak crystallization ability, which is consistent with the characteristics of this type of polymer. The tensile strength of the solid polymer electrolyte film can reach 38MPa, and the elongation at break can reach 150%, showing good elastomeric properties.

[0060] Figure 6 and 7 They are scanning electron microscope and atomic force microscope images of the thermoplastic elastomer solid polymer electrolyte film in Example 1, wherein: Figure 7 The left image in the middle is a surface morphology image, and the right image is a three-dimensional morphology image. As can be seen from the images, the surface of the electrolyte film sample is relatively smooth and has low roughness, which facilitates the contact between the solid electrolyte film and the electrode, thereby facilitating lithium ion conduction and minimizing the interfacial impedance effect.

[0061] Figure 8 Lithium-ion battery with thermoplastic elastomer-based solid polymer electrolyte + Conductivity performance diagram, as shown in the figure, the lithium ion conduction number is 10 -5 -10 -6 S·m -1 .

[0062] Example 2

[0063] The preparation method was similar to that in Example 1, except that the BAB-type linear triblock copolymer was [(PDMI)-b-PPEGMA-b-(PDMI)], and in step (2), 3 parts by mass of the macroinitiator PPEGMA-II was dissolved in 12 parts by mass of the DMI monomer, and then 0.2 parts by mass of the catalyst BNI was added. The reaction time in step (2) was 4 h.

[0064] Example 3

[0065] The preparation method is similar to that of Example 1, except that the macroinitiator prepared in the first step is PMEMA-II, and the BAB-type linear triblock copolymer obtained in the second step is [(PDMI)-b-PMEGMA-b-(PDMI)]. In step (2), 2.8 parts by mass of the macroinitiator PMEGMA-II is dissolved in 12 parts by mass of the mixed monomer of DMI, and then 0.2 parts by mass of the catalyst BNI is added. The reaction time of step (2) is 6 h.

[0066] Example 4

[0067] The preparation method is similar to that of Example 1, except that the BAB-type linear triblock copolymer is (PDMI-b-PPEGA-b-PDMI), and in step (2), 3 parts by mass of the macroinitiator PPEGA-II is dissolved in 16 parts by mass of the DMI monomer, and then 0.2 parts by mass of the catalyst BNI is added. The reaction time of step (2) is 6 h.

[0068] The various embodiments are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to in detail.

[0069] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Application of a linear triblock copolymer in a thermoplastic elastomer solid polymer electrolyte, characterized in that: The structural formula of the linear triblock copolymer is as follows:

2. The use of a linear triblock copolymer in a thermoplastic elastomer solid polymer electrolyte according to claim 1, characterized in that: The preparation method of the linear triblock copolymer comprises the following specific steps: (1) mixing a monomer containing a polyethylene glycol structural unit, an organic diiodide, a catalyst, and an azo initiator, and performing a polymerization reaction under an inert gas atmosphere to obtain a macromolecular initiator containing an iodide at the end; (2) The macromolecular initiator containing an iodide at the end and the comonomer are reacted by a catalyst under an inert gas atmosphere to obtain the linear triblock copolymer.

3. The use of a linear triblock copolymer in a thermoplastic elastomer solid polymer electrolyte according to claim 2, characterized in that: The mass ratio of the monomer containing polyethylene glycol structural units, the organic diiodide, the catalyst and the azo initiator in step (1) is 40-60:1-2:0.3-0.8:0.4-1.5; The polymerization reaction conditions are: reaction at 60° C. for 0.5-2 h.

4. The use of a linear triblock copolymer in a thermoplastic elastomer solid polymer electrolyte according to claim 2, characterized in that: The monomer containing polyethylene glycol structural units in step (1) includes at least one of polyethylene glycol monomethyl ether methacrylate, polyethylene glycol monomethyl ether acrylate and 2-methoxyethyl methacrylate; The catalyst comprises at least one of tetrabutylammonium iodide, tetra-n-octylammonium iodide and S-iodinated butyrylthiocholine; The azo thermal initiator includes at least one of azobisisobutyronitrile and azobisisovaleronitrile.

5. The use of a linear triblock copolymer in a thermoplastic elastomer solid polymer electrolyte according to claim 2, characterized in that: The mass ratio of the macroinitiator containing an iodide at the end, the comonomer and the catalyst in step (2) is: 1-4:10-40:0.1-0.5; The conditions of the catalytic reaction are: reaction at 60-80° C. for 0.5-8 h.

6. The use of a linear triblock copolymer in a thermoplastic elastomer solid polymer electrolyte according to claim 2, characterized in that: The comonomer in step (2) comprises at least one of methyl methacrylate, benzyl methacrylate and dimethyl itaconate; The catalyst in the catalytic reaction is at least one of tetrabutylammonium iodide and tetra-n-octylammonium iodide.

7. An electrolyte, characterized in that The electrolyte is a thermoplastic elastomer-type solid polymer electrolyte, wherein the thermoplastic elastomer is prepared by the linear triblock copolymer described in claim 1.

8. An electrolyte according to claim 7, characterized in that The preparation steps are iodine removal, film formation by solution method and thermal annealing treatment.

9. Use of the electrolyte according to any one of claims 7 to 8 in a solid-state lithium battery.

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