Crosslinked polymers and methods of making, electrolyte compositions, polymer electrolytes and methods of making, lithium ion batteries and electrical devices

Abstract

The application discloses the technical field of lithium ion batteries, and discloses a cross-linked polymer and a preparation method thereof, an electrolyte composition, a polymer electrolyte and a preparation method thereof, a lithium ion battery and an electric device. 10 The cross-linked polymer comprises structural unit A shown in formula (1), structural unit B shown in formula (2) and connecting group C connecting the structural unit A and the structural unit B shown in formula (3); wherein R is selected from isomeric alkyl with C4-C The polymer matrix of the polymer electrolyte has a hyperbranched structure, the structural unit B and the connecting group C greatly improve the mechanical strength of the polymer electrolyte, and the polymer electrolyte has the advantages of high mechanical strength, high toughness, high elasticity, high ion conductivity, good thermal stability, high interface stability, simple preparation condition and easy industrialization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a cross-linked polymer and a preparation method, an electrolyte composition, a polymer electrolyte and a preparation method, a lithium ion battery and an electrical equipment. BACKGROUND

[0002] Solid polymer electrolyte (SPE) is composed of lithium salt and polymer, compared with electrolyte, polymer electrolyte has high safety, stability and easy forming processing characteristics, polymer electrolyte has strong plasticity, which is convenient for battery shape design and assembly.

[0003] The most commonly used polymer electrolyte matrix is polyether, which can provide high enough electron donor group density and has flexible polyether chain segment, so it can effectively dissolve cations by cage effect. However, due to the high crystallinity (70-85%) of the commonly used polyether polymer electrolyte (such as polyethylene oxide, PEO), its room temperature conductivity is only 10 -8 -10 - 6 S / cm, and the elasticity of the system is reduced, which is difficult to commercialize.

[0004] Current research and technology mainly focus on changing the structure of polyether to improve the ionic conductivity of lithium battery. For example, grafting polymer is used, the main chain is polymethyl methacrylate (MMA), and the side chain is polyether chain segment with different chain lengths, and it is found that the ionic conductivity can be improved to 10 -4 -10 -5 S / cm. MMA monomer as internal plasticizer improves the flexibility of the chain and the movement of the free segment in the amorphous region of polyether, increases the interchain distance of polyether chain, and is beneficial to the migration of lithium ions. However, the improvement of ionic conductivity is achieved by reducing the glass transition temperature (T g ) of the polymer to reduce the crystallinity of the polymer, thereby inevitably reducing the mechanical properties of the polymer electrolyte.

[0005] With the increasing demand for the capacity of energy storage devices, the mechanical properties of the electrolyte have also been improved, because the electrode material will continuously change in volume during the charge and discharge cycle, and the electrolyte needs high enough mechanical strength to resist the volume change of the electrode. The problem of polymer electrolyte is that the mechanical properties and ionic conductivity cannot be compatible, and the ionic conductivity of some solid polymer electrolyte is only 10 -5 S / cm even if the mechanical strength is ideal, in order to improve the ionic conductivity, small molecule additives and electrolyte are usually added to the polymer electrolyte, but this will cause deformation and fracture of the solid polymer electrolyte, so new technology of preparing electrolyte material with strong mechanical strength and high ionic conductivity is needed. SUMMARY

[0006] The present application aims to overcome the problem of low mechanical strength and ionic conductivity of polymer electrolyte in the prior art, and provides a cross-linked polymer and a preparation method, an electrolyte composition, a polymer electrolyte and a preparation method, a lithium ion battery and an electrical equipment.

[0007] To achieve the above-mentioned purpose, the first aspect of the present application provides a cross-linked polymer, wherein the cross-linked polymer comprises: a structural unit A represented by formula (1), a structural unit B represented by formula (2), and a connecting group C connecting the structural unit A and the structural unit B represented by formula (3).

[0008]

[0009]

[0010] wherein R is selected from a C4-C 10 isomeric alkyl residue, R1, R2 are each independently selected from H or C1-C6 alkyl; m is an integer of 1-100, and n is an integer of 1-100.

[0011] The second aspect of the present application provides a preparation method of the cross-linked polymer, wherein the preparation method comprises: performing a cross-linking reaction on a compound a represented by formula (4) and a compound b represented by formula (5) to obtain the cross-linked polymer.

[0012]

[0013] wherein R is selected from a C4-C 10 isomeric alkyl residue, R1, R2 are each independently selected from H or C1-C6 alkyl; m is an integer of 1-100, and n is an integer of 1-100.

[0014] The third aspect of the present application provides a cross-linked polymer prepared by the preparation method.

[0015] The fourth aspect of the present application provides a composition for preparing a polymer electrolyte, wherein the composition comprises: a lithium salt, a filler, a plasticizer and the cross-linked polymer.

[0016] The fifth aspect of the present application provides a preparation method of a polymer electrolyte, wherein the preparation method comprises:

[0017] (1) reacting the filler and the cross-linked polymer to form a film to obtain a film-forming material;

[0018] (2) mixing the film-forming material with a lithium salt solution and a plasticizer to obtain the polymer electrolyte.

[0019] The sixth aspect of the present application provides a polymer electrolyte prepared by the preparation method.

[0020] The seventh aspect of the present application provides a lithium ion battery, wherein the polymer lithium ion battery comprises the polymer electrolyte.

[0021] The eighth aspect of the present application provides an electrical equipment, wherein the electrical equipment comprises the lithium ion battery.

[0022] According to the technical scheme, the cross-linked polymer has a structure different from that of a conventional polymer. The polymer matrix of the polymer electrolyte has a hyperbranched structure. The structure unit A has three end connecting bonds. The structure unit B has two end connecting bonds. The connecting group C has two end connecting bonds. The hyperbranched structure of the cross-linked polymer is formed by multiple bonding of the structure unit A, the structure unit B and the connecting group C. The branched structure is distributed with polyether segments to dissolve lithium ions. Since the polyether segments are uniformly and widely distributed in the hyperbranched structure, the flexibility of the hyperbranched structure and the ability to dissolve lithium ions are improved. The ionic conductivity is greatly increased. The length of the polyether segment is controllable. The chain flexibility increases with the increase of the length, and the chain rigidity increases with the decrease of the length. The structure unit B and the connecting group C greatly improve the mechanical strength of the polymer electrolyte. The polymer electrolyte has high mechanical strength, high toughness, high elasticity, high ionic conductivity, good thermal stability, high interface stability, simple preparation conditions and easy industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structure diagram of the cross-linked polymer in the present application. DETAILED DESCRIPTION

[0024] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and the values are approximate values which are understood to encompass values approximating these ranges and values. For ranges, the endpoints are included between the various ranges, the endpoints are included with the individual points, and the individual points are included between the various ranges. These ranges are understood to be approximate.

[0025] The first aspect of the present application provides a cross-linked polymer, wherein the cross-linked polymer comprises: a structure unit A shown in formula (1), a structure unit B shown in formula (2), and a connecting group C connecting the structure unit A and the structure unit B shown in formula (3).

[0026]

[0027] wherein R is selected from C4-C 10isomeric alkyl residue having at least three branches, R1, R2 are each independently selected from H or C1-C6 alkyl; m is an integer from 1 to 100, n is an integer from 1 to 100.

[0028] In the present application, the cross-linked polymer is a hyperbranched structure, the structural unit A has three end linking groups, the structural unit B has two end linking groups, the linking group C has two end linking groups, and the hyperbranched structure of the cross-linked polymer is formed by multiple linking of the structural unit A, the structural unit B and the linking group C. The branched structure is distributed with polyether chain segments to dissolve lithium ions. Since the polyether chain segments are uniformly and widely distributed in the hyperbranched structure, the flexibility of the hyperbranched structure and the ability to dissolve lithium ions are improved, the ionic conductivity is greatly increased, the length of the polyether chain segment is controllable, the chain flexibility increases with the increase of the length, the chain rigidity increases with the decrease of the length, and the structural unit B and the linking group C greatly improve the mechanical strength of the polymer electrolyte. A polymer electrolyte with high mechanical strength, high toughness, high elasticity, high ionic conductivity, good thermal stability, high interface stability and simple preparation conditions is provided, which is easy to realize industrialization.

[0029] In the present application, the structural diagram of the cross-linked polymer is as shown in Figure 1 In the present application, the structural diagram of the cross-linked polymer is as shown in

[0030] In some specific embodiments of the present application, R is selected from C4-C 10 isomeric alkyl residue having at least three branches, R1, R2 are each independently selected from H or C1-C6 alkyl; m is an integer from 1 to 100, n is an integer from 1 to 100. or formula (b) R is selected from any of the above structures, which is beneficial to increase the flexibility and structural stability of the cross-linked polymer, and increase the mechanical strength of the cross-linked polymer.

[0031] Preferably, R1, R2 are each independently selected from H or methyl, which is beneficial to increase the stability of the cross-linked polymer.

[0032] Preferably, m is an integer from 3 to 60, and n is an integer from 3 to 60, more preferably, m is an integer from 9 to 15, and n is an integer from 9 to 15. The length of the polyether segment is controllable, and the chain flexibility increases with the increase of the length, and the chain rigidity increases with the decrease of the length. When m and n are limited in the preferred range, the length of the polyether segment is optimal for the performance of the cross-linked polymer, and the cross-linked polymer formed can maximize the ionic conductivity and mechanical strength of the polymer electrolyte.

[0033] In some embodiments of the present application, the molar ratio of the structural unit A: the structural unit B: the linking group C in the cross-linked polymer is 1-5: 3-15: 9-45; preferably 2-3: 6-9: 18-27. The structural unit A: the structural unit B: the linking group C in the above ratio range is beneficial to the distribution of the polyether segment and the distribution of the branched structure, and a polymer electrolyte with high mechanical strength, high toughness and high ionic conductivity is obtained.

[0034] In some embodiments of the present application, the weight average molecular weight of the cross-linked polymer is 6×10 5 -2×10 6 g / mol, which can make the room temperature ionic conductivity and the transference number of lithium ions in the polymer electrolyte reach a higher level.

[0035] The second aspect of the present application provides a preparation method of a cross-linked polymer, wherein the preparation method comprises: performing a cross-linking reaction on a compound a represented by formula (4) and a compound b represented by formula (5) to obtain the cross-linked polymer.

[0036]

[0037] wherein R is selected from C4-C 10 is an isomeric alkyl group containing a branched alkyl group, R1 and R2 are each independently selected from H or C1-C6 alkyl; m is an integer from 1 to 100, and n is an integer from 1 to 100.

[0038] In the present application, the compound a represented by formula (4) and the compound b represented by formula (5) perform a cross-linking reaction, wherein the carbon atom of the carbon-carbon triple bond of the compound a reacts with the terminal nitrogen atom and the meta nitrogen atom of the compound b to form a triazole nitrogen-containing heterocyclic ring (i.e. the linking group C). Each of the compound a contains three carbon-carbon triple bonds, and can react with three molecules of the compound b. The compound b contains two terminal nitrogen atoms, and can react with two molecules of the compound a respectively. Through the continuous cross-linking reaction of the compound a and the compound b, a macromolecular cross-linked polymer is formed.

[0039] In some embodiments of the present application, R is selected from formula (a) or formula (b) shown Preferably, R1, R2 are each independently selected from H or methyl; preferably, m is an integer from 3 to 60, n is an integer from 3 to 60, more preferably, m is an integer from 9 to 15, n is an integer from 9 to 15.

[0040] In some embodiments of the present application, the crosslinking reaction temperature is 60-100℃, and the crosslinking reaction time is 20-30h.

[0041] In some embodiments of the present application, the molar ratio of the compound a: compound b is 1-20:1-20.

[0042] In the present application, the composition and structure of the crosslinked polymer can be determined by nuclear magnetic resonance, infrared, GPC, elemental analysis, etc., or by preparation of the feed.

[0043] The third aspect of the present application provides a crosslinked polymer prepared by the preparation method of the present application.

[0044] The fourth aspect of the present application provides a polymer electrolyte raw material composition, wherein the composition comprises: a lithium salt, a filler, a plasticizer, and a crosslinked polymer provided by the present application.

[0045] The polymer electrolyte provided by the present application contains, in addition to the crosslinked polymer and the lithium salt, other doping agents disclosed in the art to improve performance, such as SiO2 nanoparticles and small molecule liquid plasticizers, to reduce the crystalline region content of the polymer matrix and improve the ionic conductivity.

[0046] In some embodiments of the present application, the lithium salt is selected from one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorosilicate, lithium tetraphenylborate, lithium chloride, lithium bromide, lithium chloroaluminate, lithium fluorocarbylsulfonate, LiCH3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, preferably lithium bis(trifluoromethylsulfonyl)imide.

[0047] In some embodiments of the present application, the filler is selected from one or more of TiO2, Al2O3, SiO2, MgO, ZrO2, LiNbO3, BaTiO3, PbTiO3, montmorillonite, molecular sieve.

[0048] In some embodiments of the present application, the plasticizer is selected from one or more of ethylene carbonate, propylene carbonate, and vinylene carbonate.

[0049] In some embodiments of the present application, the cross-linked polymer is 25-50 parts by weight, the lithium salt is 20-40 parts by weight, the filler is 1-4 parts by weight, and the plasticizer is 20-40 parts by weight.

[0050] The fifth aspect of the present application provides a preparation method of the polymer electrolyte, wherein the preparation method comprises:

[0051] (1) forming a film with the cross-linked polymer and the filler to obtain a film-forming material;

[0052] (2) mixing the film-forming material with the lithium salt solution and the plasticizer to obtain the polymer electrolyte.

[0053] In some embodiments of the present application, the preparation method comprises:

[0054] (1) forming a film with the cross-linked polymer and the filler to obtain a film-forming material;

[0055] (2) adding the film-forming material into the lithium salt solution, adsorbing and drying to form a film, adding the plasticizer, swelling and film-forming to obtain the polymer electrolyte.

[0056] The sixth aspect of the present application provides the polymer electrolyte obtained by the preparation method of the present application.

[0057] In some embodiments of the present application, the molar ratio of the number of oxygen atoms in the cross-linked polymer to the lithium ions in the lithium salt is 6-40:1, preferably 8-10:1.

[0058] In some embodiments of the present application, the polymer electrolyte has a room temperature ionic conductivity of 1x10 -4 -90x10 -4 S / cm, a tensile strength of 8-25 MPa, and a crystallinity of 6-35%.

[0059] The seventh aspect of the present application provides a lithium ion battery, wherein the polymer lithium ion battery comprises the polymer electrolyte. The lithium ion battery comprises a positive electrode, a negative electrode, and the polymer electrolyte provided by the present application, and the polymer electrolyte is located between the positive electrode and the negative electrode.

[0060] The positive electrode comprises a positive electrode current collector and a positive electrode active material loaded thereon. The positive electrode current collector can be an aluminum foil. The present application does not have a special limitation on the positive electrode material. The positive electrode material generally comprises a positive electrode active material, a binder, and a conductive agent. The positive electrode active material can use all the positive electrode materials that can be commercially available so far, such as LiFePO4, LiMnO2, LiNiO2, LiCoO2, LiVPO4F, LiFeO2, or a ternary system.

[0061] The negative electrode includes a negative electrode current collector, which can be a copper foil, and a negative electrode active material loaded thereon. The negative electrode material is not particularly limited, and generally includes a negative electrode active material, a binder, and a conductive agent. The negative electrode active material can be any of the negative electrode materials that have been commercially available so far, such as natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, or a mixture of one or more thereof.

[0062] The binder can be any of the binders known in the art, such as one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, and polyacrylate. The conductive agent can be any of the conductive agents known in the art, such as one or more of graphite, carbon fiber, carbon black, metal powder, metal oxide, and fiber.

[0063] The method for preparing the lithium ion battery including the polymer electrolyte is not particularly limited, and can be any of the methods known in the art, such as: coating a solution of the polymer electrolyte on the surface of a positive electrode sheet and a negative electrode sheet, removing the solvent by drying to form the polymer electrolyte, then winding or stacking the positive electrode sheet and the negative electrode sheet coated with the polymer electrolyte to prepare a core, placing the core in a battery case, sealing, formation, sealing, packaging; or first preparing the polymer electrolyte, then attaching a thin film of the polymer electrolyte on the surface of a positive electrode sheet or a negative electrode sheet, then winding or stacking the positive electrode sheet and the negative electrode sheet to prepare a core, placing the core in a battery case, sealing, formation, sealing, packaging; or adding a prepared polymer electrolyte between the positive electrode sheet and the negative electrode sheet to which the polymer electrolyte provided by the present application is attached, then winding or stacking the positive electrode sheet and the negative electrode sheet to prepare a core, placing the core in a battery case, sealing, formation, sealing, packaging, wherein the added polymer includes the polymer electrolyte provided by the present application, and also includes other polymer electrolytes and separator materials. The sealing and formation are performed by any of the methods known in the art.

[0064] The eighth aspect of the present application provides an electrical device, which includes the lithium ion battery provided by the present application.

[0065] The present application will be described in detail below by way of examples.

[0066] In the following examples and comparative examples, the specific conditions not specified are performed according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained by market purchase. The composition and structure of the crosslinked polymers described in the following examples and comparative examples can be determined by nuclear magnetic resonance, infrared, GPC, elemental analysis, etc., or by the preparation feedstock.

[0067] Example 1

[0068] (1) Preparation of cross-linked polymer

[0069] Compound a (where R is selected from formula (b)) and compound b (R1= R2= CH3, n = 12, m = 12) were mixed in a 1 :3 molar ratio and dimethylformamide (DMF) was added and heated to 80 °C for 24 hours. The product was reacted in solvent tetrahydrofuran (THF) for 24 hours to produce cross-linked polymer P10, wherein the weight average molecular weight of the cross-linked polymer was 1.2 million g / mol.

[0070] (2) Preparation of polymer electrolyte

[0071] To the cross-linked polymer, an appropriate amount of SiO2 with a particle size of 14 nm was added and heated to 120 °C with stirring until well mixed. The prepolymer melt was poured onto a glass sheet and heated to 120 °C in a vacuum box overnight. The resulting film was removed from the glass sheet and weighed, immersed in a solution of lithium salt in ethyl acetate for 24 hours, and swelled. After swelling, the film was dried in a vacuum box at 60 °C overnight, weighed, and the amount of lithium salt was calculated. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added and the film was swelled for at least two hours and reached equilibrium to produce the final polymer electrolyte S1.

[0072] (3) Preparation of polymer electrolyte composite electrode

[0073] An appropriate amount of lithium iron phosphate (LiFePO4) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S1 (45 wt%), and N-methyl pyrrolidone (NMP) were mixed well, and the mixture was poured onto a block of polytetrafluoroethylene, vacuumed, and heated to 150 °C overnight to obtain a composite cathode sheet C1.

[0074] Example 2

[0075] (1) Preparation of cross-linked polymer

[0076] Compound a (where R is selected from formula (a)) and compound b (R1= R2= CH3, n = 9, m = 15) were mixed in a 1 :3 molar ratio and dimethylformamide (DMF) was added and heated to 80 °C for 24 hours. The product was reacted in solvent tetrahydrofuran (THF) for 24 hours to produce cross-linked polymer P6, wherein the weight average molecular weight of the cross-linked polymer was 1 million g / mol.

[0077] (2) Preparation of polymer electrolyte

[0078] To the cross-linked polymer, an appropriate amount of SiO2with a particle size of 14 nm was added, heated to 120°C, and stirred until mixed uniformly. The prepolymer melt was poured onto a glass sheet, heated to 120°C in a vacuum chamber overnight, and the resulting film was removed from the glass sheet, weighed, and immersed in an ethyl acetate solution of lithium salt for 24 hours to swell. After swelling, the film was dried in a vacuum chamber at 60°C overnight, weighed, and the amount of lithium salt was calculated. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added, the film was swelled for at least two hours and reached equilibrium, and the final polymer electrolyte S2was prepared.

[0079] (3) Preparation of a polymer electrolyte composite electrode

[0080] An appropriate amount of lithium iron phosphate (LiFePO4) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S2(45 wt%), N-methyl pyrrolidone (NMP) were mixed uniformly, and the mixture was poured onto a block of polytetrafluoroethylene, vacuumed, and heated to 150°C overnight to obtain a composite cathode sheet C2.

[0081] Example 3

[0082] (1) Preparation of a cross-linked polymer

[0083] Compounds a (where R is selected from formula (a)) and b (R1= R2= CH3, n = 15, m = 9) were mixed in a molar ratio of 3:10, dimethylformamide (DMF) was added, and heated to 80°C for 24 hours. The product was reacted in the solvent tetrahydrofuran (THF) for 24 hours to form a cross-linked polymer P7, wherein the weight average molecular weight of the cross-linked polymer was 1.05 million g / mol.

[0084] (2) Preparation of a polymer electrolyte

[0085] To the cross-linked polymer, an appropriate amount of SiO2with a particle size of 14 nm was added, heated to 120°C, and stirred until mixed uniformly. The prepolymer melt was poured onto a glass sheet, heated to 120°C in a vacuum chamber overnight, and the resulting film was removed from the glass sheet, weighed, and immersed in an ethyl acetate solution of lithium salt for 24 hours to swell. After swelling, the film was dried in a vacuum chamber at 60°C overnight, weighed, and the amount of lithium salt was calculated. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added, the film was swelled for at least two hours and reached equilibrium, and the final polymer electrolyte S3was prepared.

[0086] (3) Preparation of a polymer electrolyte composite electrode

[0087] An appropriate amount of lithium iron phosphate (LiFeP04) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S3 (45 wt%), N-methyl pyrrolidone (NMP) were mixed uniformly, the mixture was poured onto a block of polytetrafluoroethylene, vacuum, heated to 150°C, overnight to obtain a composite cathode sheet C3.

[0088] Example 4

[0089] (1) Preparation of cross-linked polymer

[0090] Compound a (wherein R is selected from formula (b)) and compound b (R1= R2= CH3, n = 9, m = 15) were mixed in a molar ratio of 3:10, dimethylformamide (DMF) was added, heated to 80°C for 24 hours, the product was reacted in solvent tetrahydrofuran (THF) for 24 hours to form a cross-linked polymer P9, wherein the weight average molecular weight of the cross-linked polymer is 1 million g / mol.

[0091] (2) Preparation of polymer electrolyte

[0092] An appropriate amount of Si02with a particle size of 14 nm was added to the cross-linked polymer, heated to 120°C, stirred until mixed uniformly. The prepolymer melt was poured onto a glass sheet, heated to 120°C in a vacuum box overnight, the generated film was removed from the glass sheet, weighed, soaked in a lithium salt ethyl acetate solution for 24 hours, and swelled. After swelling, the film was dried in a vacuum box at 60°C overnight, weighed to calculate the amount of lithium salt. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added, the film was swelled for at least two hours and reached equilibrium, and the final polymer electrolyte S4 was prepared.

[0093] (3) Preparation of polymer electrolyte composite electrode

[0094] An appropriate amount of lithium iron phosphate (LiFeP04) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S4 (45 wt%), N-methyl pyrrolidone (NMP) were mixed uniformly, the mixture was poured onto a block of polytetrafluoroethylene, vacuum, heated to 150°C, overnight to obtain a composite cathode sheet C4.

[0095] Example 5

[0096] (1) Preparation of cross-linked polymer

[0097] Compound a (wherein R is selected from formula (a)) and compound b (R1= R2= H, m = n = 1) are mixed in a molar ratio of 1 :4 and dimethylformamide (DMF) is added and heated to 80°C for 24 hours and the product is reacted in solvent tetrahydrofuran (THF) for 24 hours to produce cross-linked polymer P1, wherein the weight average molecular weight of the cross-linked polymer is 600,000 g / mol.

[0098] (2) Preparation of polymer electrolyte

[0099] To the cross-linked polymer, an appropriate amount of SiO2 with a particle size of 14 nm is added and heated to 120°C with stirring until well mixed. The prepolymer melt is poured onto a glass sheet and heated to 120°C in a vacuum box overnight and the resulting film is removed from the glass sheet, weighed, and immersed in an ethyl acetate solution of lithium salt for 24 hours to swell. After swelling, the film is dried in a vacuum box at 60°C overnight and weighed to calculate the amount of lithium salt. The prepared polymer electrolyte film is immediately transferred to an argon-filled glove box to avoid water absorption from the air. In the glove box, propylene carbonate is added and the film is swelled for at least two hours and reaches equilibrium to prepare the final polymer electrolyte S5.

[0100] (3) Preparation of polymer electrolyte composite electrode

[0101] An appropriate amount of lithium iron phosphate (LiFePO4) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S5 (45 wt%), and N-methyl pyrrolidone (NMP) are mixed well and the mixture is poured onto a block of polytetrafluoroethylene, vacuumed, and heated to 150°C overnight to obtain a polymer electrolyte composite cathode sheet C5.

[0102] Example 6

[0103] (1) Preparation of cross-linked polymer

[0104] Compound a (wherein R is selected from formula (a)) and compound b (R1= R2= H, n = 9, m = 9) are mixed in a molar ratio of 1 :4 and dimethylformamide (DMF) is added and heated to 80°C for 24 hours and the product is reacted in solvent tetrahydrofuran (THF) for 24 hours to produce cross-linked polymer P2, wherein the weight average molecular weight of the cross-linked polymer is 800,000 g / mol.

[0105] (2) Preparation of polymer electrolyte

[0106] To the cross-linked polymer, an appropriate amount of SiO2with a particle size of 14 nm was added, heated to 120 °C, and stirred until mixed uniformly. The prepolymer melt was poured onto a glass sheet, heated to 120 °C in a vacuum chamber overnight, and the resulting film was removed from the glass sheet, weighed, and immersed in an ethyl acetate solution of lithium salt for 24 hours, swelled. After swelling, the film was dried in a vacuum chamber at 60 °C overnight, weighed, and the amount of lithium salt was calculated. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added, the film was swelled for at least two hours and reached equilibrium, and the final polymer electrolyte S6 was prepared.

[0107] (3) Preparation of a polymer electrolyte composite electrode

[0108] An appropriate amount of lithium iron phosphate (LiFePO4) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S6 (45 wt%), N-methyl pyrrolidone (NMP) were mixed uniformly, and the mixture was poured onto a block of polytetrafluoroethylene, vacuumed, heated to 150 °C overnight, and a composite cathode sheet C6 was obtained.

[0109] Example 7

[0110] (1) Preparation of a cross-linked polymer

[0111] Compounds a (where R is selected from formula (a)) and b (R1= R2= H, n = 15, m = 15) were mixed in a molar ratio of 3:10, and dimethylformamide (DMF) was added, heated to 80 °C for 24 hours, and the product was reacted in the solvent tetrahydrofuran (THF) for 24 hours to form a cross-linked polymer P3, wherein the weight average molecular weight of the cross-linked polymer is 1 million g / mol.

[0112] (2) Preparation of a polymer electrolyte

[0113] To the cross-linked polymer, an appropriate amount of SiO2with a particle size of 14 nm was added, heated to 120 °C, and stirred until mixed uniformly. The prepolymer melt was poured onto a glass sheet, heated to 120 °C in a vacuum chamber overnight, and the resulting film was removed from the glass sheet, weighed, and immersed in an ethyl acetate solution of lithium salt for 24 hours, swelled. After swelling, the film was dried in a vacuum chamber at 60 °C overnight, weighed, and the amount of lithium salt was calculated. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added, the film was swelled for at least two hours and reached equilibrium, and the final polymer electrolyte S7 was prepared.

[0114] (3) Preparation of a polymer electrolyte composite electrode

[0115] An appropriate amount of lithium iron phosphate (LiFeP04) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S7 (45 wt%), N-methyl pyrrolidone (NMP) were mixed uniformly, the mixture was poured onto a block of polytetrafluoroethylene, vacuum, heated to 150°C, overnight to obtain a composite cathode sheet C7.

[0116] Example 8

[0117] (1) Preparation of cross-linked polymer

[0118] Compound a (wherein R is selected from formula (a)) and compound b (R1= R2= H, n = 90, m = 90) were mixed in a molar ratio of 3:10, dimethylformamide (DMF) was added, heated to 80°C for 24 hours, the product was reacted in solvent tetrahydrofuran (THF) for 24 hours to form a cross-linked polymer P4, wherein the weight average molecular weight of the cross-linked polymer is 1.8 million g / mol.

[0119] (2) Preparation of polymer electrolyte

[0120] An appropriate amount of Si02 with a particle size of 14 nm was added to the cross-linked polymer, heated to 120°C, stirred until mixed uniformly. The prepolymer melt was poured onto a glass sheet, heated to 120°C in a vacuum box overnight, the generated film was removed from the glass sheet, weighed, soaked in a lithium salt ethyl acetate solution for 24 hours, and swelled. After swelling, the film was dried in a vacuum box at 60°C overnight, weighed to calculate the amount of lithium salt. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added, the film was swelled for at least two hours and reached equilibrium, and the final polymer electrolyte S8 was prepared.

[0121] (3) Preparation of polymer electrolyte composite electrode

[0122] An appropriate amount of lithium iron phosphate (LiFeP04) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S8 (45 wt%), N-methyl pyrrolidone (NMP) were mixed uniformly, the mixture was poured onto a block of polytetrafluoroethylene, vacuum, heated to 150°C, overnight to obtain a composite cathode sheet C8.

[0123] Example 9

[0124] (1) Preparation of cross-linked polymer

[0125] Compound a (where R is selected from formula (a)) and compound b (R1= R2= CH3, n = 3, m = 1) are mixed in a 1 :3 molar ratio and dimethylformamide (DMF) is added and heated to 80°C for 24 hours. The product is reacted in solvent tetrahydrofuran (THF) for 24 hours to produce cross-linked polymer P5, wherein the weight average molecular weight of the cross-linked polymer is 650,000 g / mol.

[0126] (2) Preparation of polymer electrolyte

[0127] To the cross-linked polymer, an appropriate amount of SiO2with a particle size of 14 nm is added and heated to 120°C with stirring until well mixed. The prepolymer melt is poured onto a glass sheet and heated to 120°C in a vacuum box overnight. The resulting film is removed from the glass sheet, weighed, and immersed in an ethyl acetate solution of lithium salt for 24 hours to swell. After swelling, the film is dried in a vacuum box at 60°C overnight, weighed, and the amount of lithium salt is calculated. The prepared polymer electrolyte film is immediately transferred to an argon-filled glove box to avoid water absorption from the air. In the glove box, propylene carbonate is added and the film is swelled for at least two hours and reaches equilibrium to prepare the final polymer electrolyte S9.

[0128] (3) Preparation of polymer electrolyte composite electrode

[0129] An appropriate amount of lithium iron phosphate (LiFePO4) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S9 (45 wt%), and N-methyl pyrrolidone (NMP) are mixed well, and the mixture is poured onto a block of polytetrafluoroethylene, vacuumed, and heated to 150°C overnight to obtain a composite cathode sheet C9.

[0130] Example 10

[0131] (1) Preparation of cross-linked polymer

[0132] Compound a (where R is selected from formula (a)) and compound b (R1= R2= CH3, n = 20, m = 55) are mixed in a 1 :3 molar ratio and dimethylformamide (DMF) is added and heated to 80°C for 24 hours. The product is reacted in solvent tetrahydrofuran (THF) for 24 hours to produce cross-linked polymer P8, wherein the weight average molecular weight of the cross-linked polymer is 1,550,000 g / mol.

[0133] (2) Preparation of polymer electrolyte

[0134] To the cross-linked polymer, an appropriate amount of SiO2with a particle size of 14 nm was added, heated to 120°C, and stirred until mixed uniformly. The prepolymer melt was poured onto a glass sheet, heated to 120°C in a vacuum chamber overnight, and the resulting film was removed from the glass sheet, weighed, and immersed in an ethyl acetate solution of lithium salt for 24 hours to swell. After swelling, the film was dried in a vacuum chamber at 60°C overnight, weighed, and the amount of lithium salt was calculated. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added, the film was swelled for at least two hours and reached equilibrium, and the final polymer electrolyte S10 was prepared.

[0135] (3) Preparation of a polymer electrolyte composite electrode

[0136] An appropriate amount of lithium iron phosphate (LiFePO4) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S10 (45 wt%), and N-methyl pyrrolidone (NMP) were mixed uniformly, the mixture was poured onto a block of polytetrafluoroethylene, vacuumed, heated to 150°C overnight, and a composite cathode sheet C10 was obtained.

[0137] Example 11

[0138] (1) Preparation of a cross-linked polymer

[0139] Compounds a (where R is selected from formula (b)) and b (R1= R2= CH3, n = 15, m = 80) were mixed in a molar ratio of 1:4, dimethylformamide (DMF) was added, heated to 80°C for 24 hours, and the product was reacted in a solvent tetrahydrofuran (THF) for 24 hours to form a cross-linked polymer P11, wherein the weight average molecular weight of the cross-linked polymer was 750,000 g / mol.

[0140] (2) Preparation of a polymer electrolyte

[0141] To the cross-linked polymer, an appropriate amount of SiO2with a particle size of 14 nm was added, heated to 120°C, and stirred until mixed uniformly. The prepolymer melt was poured onto a glass sheet, heated to 120°C in a vacuum chamber overnight, and the resulting film was removed from the glass sheet, weighed, and immersed in an ethyl acetate solution of lithium salt for 24 hours to swell. After swelling, the film was dried in a vacuum chamber at 60°C overnight, weighed, and the amount of lithium salt was calculated. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added, the film was swelled for at least two hours and reached equilibrium, and the final polymer electrolyte S11 was prepared.

[0142] (3) Preparation of a polymer electrolyte composite electrode

[0143] An appropriate amount of lithium iron phosphate (LiFeP04) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film Sll (45 wt%), N-methyl pyrrolidone (NMP) were mixed uniformly, the mixture was poured onto a block of polytetrafluoroethylene, vacuum, heated to 150°C, overnight to obtain a composite cathode sheet Cll.

[0144] Example 12

[0145] (1) Preparation of cross-linked polymer

[0146] Compound a (wherein R is selected from formula (b)) and compound b (R1= R2= CH3, n = 20, m = 88) were mixed in a molar ratio of 2:9, dimethylformamide (DMF) was added, heated to 80°C for 24 hours, the product was reacted in solvent tetrahydrofuran (THF) for 24 hours to form a cross-linked polymer P12, wherein the weight average molecular weight of the cross-linked polymer is 1.95 million g / mol.

[0147] (2) Preparation of polymer electrolyte

[0148] An appropriate amount of Si02 with a particle size of 14 nm was added to the cross-linked polymer, heated to 120°C, stirred until mixed uniformly. The prepolymer melt was poured onto a glass sheet, heated to 120°C in a vacuum box overnight, the generated film was removed from the glass sheet, weighed, soaked in a lithium salt ethyl acetate solution for 24 hours, and swelled. After swelling, the film was dried in a vacuum box at 60°C overnight, weighed to calculate the amount of lithium salt. The prepared polymer electrolyte film was immediately transferred to an argon-filled glove box to avoid absorbing moisture from the air. In the glove box, propylene carbonate was added, the film was swelled for at least two hours and reached equilibrium to prepare the final polymer electrolyte S12.

[0149] (3) Preparation of polymer electrolyte composite electrode

[0150] An appropriate amount of lithium iron phosphate (LiFeP04) (35 wt%), single-walled carbon nanotubes (5 wt%), the prepared polymer electrolyte film S12 (45 wt%), N-methyl pyrrolidone (NMP) were mixed uniformly, the mixture was poured onto a block of polytetrafluoroethylene, vacuum, heated to 150°C, overnight to obtain a composite cathode sheet C12.

[0151] Comparative Example 1

[0152] 0.683 g of lithium salt (LiTFSI) and 1 g of polyethylene oxide (PEO) (molecular weight of 400000 g / mol) were added to an appropriate amount of anhydrous acetonitrile, stirred at room temperature for 24 h, then cast into a film in polytetrafluoroethylene, and vacuum dried at 50°C for 48 h to obtain a polymer electrolyte RS1.

[0153] Test Example

[0154] Crystallinity: Differential scanning calorimeter (DSC-Q2000) was used, with indium standard calibration, sample weight was 8-10 mg, temperature range was -70°C to 150°C, heating and cooling rate was 10°C / min. The crystallinity of polymer electrolyte film samples S1-S12 and RS1 was recorded.

[0155] Tensile strength: Tensile testing equipment Instron 5565 was used, the strain rate of the instrument was 100% / min.

[0156] Ionic conductivity: The polymer electrolytes S1-S12 prepared in Examples 1-12 and RS1 of the comparative example were cut into thin films with an area of 2 cm 2 Thickness was 0.4 mm, in the glove, these polymer electrolytes were sandwiched between two parallel stainless steel sheets to assemble a 2032 button cell, the cell model was "stainless steel sheet | polymer electrolyte film | stainless steel sheet", CHI660B type electrochemical workstation of Shanghai Chenhua Instrument Co., Ltd. was used, the test frequency range was 1-100 kHz, the temperature was -20°C, -15°C, 20°C, 50°C, 80°C, 110°C, the bulk resistance (Rh) of the polymer electrolyte was the intersection of the Nyquist curve and the real axis, the ionic conductivity was calculated according to the formula σ = I / (A·Rh), where σ was the ionic conductivity, I was the thickness of the elastic polymer electrolyte, A was the contact area of the elastic polymer electrolyte and the electrode.

[0157] The crystallinity, tensile strength and room temperature ionic conductivity of the polymer electrolytes S1-S12 prepared in Examples 1-12 and RS1 of the comparative example were tested, and the results are shown in Table 1.

[0158] Table 1

[0159]

[0160]

[0161] It can be seen from the test results in Table 1 that, compared with the conventional electrolyte, the electrolyte prepared by using the polymer matrix provided by the application has higher ionic conductivity and lower crystallinity, and the mechanical property of tensile strength is not only not reduced but also better than that of the conventional electrolyte, which can effectively improve the safety performance of the lithium ion battery. When the PEO segment length in the hyperbranched structure is too small (n = 3), the solubility of lithium ions is limited, so the ionic conductivity is limited. With the increase of the PEO segment length, the solubility of lithium ions is improved due to the increase of flexibility, which significantly improves the ionic conductivity. However, with the continuous increase of the PEO segment length, the crystallinity will increase, which will hinder the ion migration rate. Therefore, only when the PEO segment length is at a suitable length (9-15), the ionic conductivity and the mechanical strength can be maximized.

[0162] The above describes the preferred embodiments of the application, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the application and fall within the protection scope of the application.

Claims

1. A cross-linked polymer, characterized in that The cross-linked polymer comprises: a structural unit A represented by formula (1), a structural unit B represented by formula (2), and a connecting group C represented by formula (3) connecting the structural unit A and the structural unit B; （1）， （2）， （3）， Wherein, R is selected from C4-C 10 wherein R1 and R2 are each independently selected from H or a C1-C6 alkyl group; m is an integer from 1 to 100, and n is an integer from 1 to 100.

2. The cross-linked polymer according to claim 1, wherein R is selected from C4-C 10 An isomeric alkyl residue containing three branches or an isomeric alkyl residue containing four branches.

3. The cross-linked polymer according to claim 2, wherein R is selected from the group represented by formula (a) (a) or (b) (b).

4. The cross-linked polymer according to claim 1, wherein R1 and R2 are each independently selected from H or methyl.

5. The cross-linked polymer according to claim 1, wherein m is an integer of 3-60, and n is an integer of 3-60. The cross-linked polymer according to claim 5, wherein m is an integer of 9-15, and n is an integer of 9-15.

7. The cross-linked polymer according to claim 1, wherein In the cross-linked polymer, the molar ratio of the structural unit A: the structural unit B: the connecting group C is 1-5: 3-15: 9-45.

8. The cross-linked polymer according to claim 7, wherein In the cross-linked polymer, the molar ratio of the structural unit A: the structural unit B: the connecting group C is 2-3: 6-9: 18-27.

9. The cross-linked polymer according to any one of claims 1 to 8, wherein The weight average molecular weight of the cross-linked polymer is 6×10 5 -2×10 6 g / mol.

10. A method for preparing a cross-linked polymer, characterized in that: The preparation method comprises: performing a cross-linking reaction on the compound a represented by formula (4) and the compound b represented by formula (5) to obtain the cross-linked polymer; （4）， （5）； Wherein, R is selected from C4-C 10 R1 and R2 are each independently selected from H or a C1-C6 alkyl group; m is an integer from 1 to 100, and n is an integer from 1 to 100.

11. The preparation method according to claim 10, wherein R is selected from the group represented by formula (a) (a) or (b) (b).

12. The preparation method according to claim 10, wherein R1 and R2 are each independently selected from H or methyl.

13. The preparation method according to claim 10, wherein m is an integer of 3-60, and n is an integer of 3-60.

14. The preparation method according to claim 10, wherein m is an integer of 9-15, and n is an integer of 9-15.

15. The preparation method according to any one of claims 10 to 14, wherein: The cross-linking reaction temperature is 60-100°C, and the cross-linking reaction time is 20-30h; And / or, the molar ratio of compound a:compound b is 1-20:1-20.

16. A cross-linked polymer obtained by the preparation method according to any one of claims 10 to 15.

17. A polymer electrolyte raw material composition, characterized in that: The composition comprises: a lithium salt, a filler, a plasticizer and the cross-linked polymer according to any one of claims 1 to 9 and 16.

18. The polymer electrolyte raw material composition according to claim 17, wherein The lithium salt is selected from one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorosilicate, lithium tetraphenylborate, lithium chloride, lithium bromide, lithium chloroaluminate, lithium fluoroalkylsulfonate, LiCH3SO3, LiN(SO2CF3)2, and LiN(SO2C2F5)2; and / or, the filler is selected from one or more of TiO2, Al2O3, SiO2, MgO, ZrO2, LiNbO3, BaTiO3, PbTiO3, montmorillonite, and molecular sieve; And / or, the plasticizer is selected from one or more of ethylene carbonate, propylene carbonate, and vinylene carbonate.

19. The polymer electrolyte raw material composition according to claim 17, wherein The lithium salt is selected from lithium bis(trifluoromethanesulfonyl)imide.

20. The polymer electrolyte raw material composition according to any one of claims 17 to 19, wherein: The cross-linked polymer is 25-50 parts by weight, the lithium salt is 20-40 parts by weight, the filler is 1-4 parts by weight, and the plasticizer is 20-40 parts by weight.

21. A method for preparing a polymer electrolyte, characterized in that: The preparation method comprises: (1) forming a film from a filler and the cross-linked polymer according to any one of claims 1 to 9 and 16 to obtain a film-forming substance; (2) The film-forming substance is mixed with a lithium salt solution and a plasticizer to obtain the polymer electrolyte.

22. A polymer electrolyte obtained by the preparation method according to claim 21.

23. The polymer electrolyte according to claim 22, wherein The molar ratio of the number of oxygen atoms contained in the cross-linked polymer to the number of lithium ions in the lithium salt is 6-40:1; And / or, the room temperature ionic conductivity of the polymer electrolyte is 1×10 -4 -90×10 -4 S / cm, tensile strength is 8-25MPa, and crystallinity is 6-35%.

24. The polymer electrolyte according to claim 23, wherein The molar ratio of the number of oxygen atoms contained in the cross-linked polymer to the number of lithium ions in the lithium salt is 8-10:

1.

25. A lithium ion battery, characterized in that: The polymer lithium-ion battery comprises the polymer electrolyte according to any one of claims 22 to 24.

26. An electrical device, characterized in that: Including the lithium ion battery according to claim 25.

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