CN114976235B - Solid polymer electrolyte and preparation method and application thereof - Google Patents

Abstract

The invention relates to the technical field of electrolytes, in particular to a solid polymer electrolyte, a preparation method and application thereof. The solid polymer electrolyte of the present invention includes: maleic anhydride modified cyclodextrin, pentaerythritol tetrakis (3-mercaptopropionate), polymers containing ester groups and alkenyl groups, lithium salts and plasticizers; the mass ratio of the maleic anhydride modified cyclodextrin, the pentaerythritol tetra (3-mercaptopropionic acid) ester, the polymer containing ester groups and alkenyl groups and the plasticizer is (30-40): (10-25): (25-45): 10; the ratio of the mass of the lithium salt to the total mass of the maleic anhydride modified cyclodextrin, pentaerythritol tetrakis (3-mercaptopropionate), the polymer containing ester groups and alkenyl groups and the plasticizer is (20-40): 100; the preparation raw materials also comprise azodiisobutyronitrile and/or dibenzoyl peroxide. The solid polymer electrolyte has both high lithium ion migration number and mechanical properties at room temperature.

Description

A solid polymer electrolyte and its preparation method and application

Technical Field

The present invention relates to the technical field of electrolytes, and in particular to a solid polymer electrolyte and a preparation method and application thereof.

Background Art

Solid electrolytes can be divided into three categories: inorganic solid electrolytes, solid polymer electrolytes, and organic-inorganic solid electrolytes. Compared with inorganic solid electrolytes (oxides, sulfides, and halides), solid polymer electrolytes have broad prospects due to their superior interfacial adhesion, easy processability, and flexibility. At present, polyethylene oxide (PEO) electrolyte is one of the most widely used organic solid Li ⁺ conductors, which has excellent properties such as low cost, high dielectric constant, and strong processability. However, as a semi-crystalline polymer, PEO usually needs to work at a temperature above its melting point. PEO-based polymer electrolytes usually have low ionic conductivity and a narrow electrochemical stability window at room temperature, which limits their practical application. Therefore, improving the room temperature conductivity of polymer electrolytes while maintaining sufficient mechanical strength is crucial for the development of solid polymer electrolytes.

The ion conduction mechanism of solid polymer electrolytes can be summarized as a process in which lithium ions continuously complex and decomplex with polar groups in polymer segments, and then migrate under the action of an electric field. The faster the lithium ions migrate, the higher the ionic conductivity. The ionic conductivity of polymer electrolytes is usually controlled by the Vogel-Tamman-Fulcher (VTF) model, in which the parameter related to the movement of polymer segments is the glass transition temperature Tg, and a low glass transition temperature (Tg) represents high molecular chain fluidity. Therefore, research on solid polymer electrolytes has always focused on lowering the glass transition temperature to improve its ion conductivity, such as adding inorganic fillers, and polymer blending, copolymerization, grafting and cross-linking modification, etc. The Chinese patent with publication number CN111542961A discloses that linear polymers can form polyrotaxanes with cyclic molecules (cyclodextrins, cucurbiturils), thereby forming ion channels to improve the ionic conductivity of polymer electrolytes. However, its mechanical properties are poor. For solid polymer electrolytes, it is difficult to obtain both high ion migration numbers and high mechanical properties. In addition, polymer electrolytes can usually only be used at high temperatures (≥60°C).

Summary of the invention

The object of the present invention is to provide a solid polymer electrolyte and a preparation method and application thereof. The solid polymer electrolyte has high lithium ion transference number and mechanical properties at room temperature.

In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

The present invention provides a solid polymer electrolyte, comprising the following preparation raw materials: maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionic acid) ester, a polymer containing an ester group and an olefin group, a lithium salt and a plasticizer;

The mass ratio of the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionic acid), the polymer containing an ester group and an olefin group, and the plasticizer is (30-40):(10-25):(25-45):10;

The ratio of the mass of the lithium salt to the total mass of the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionic acid), the polymer containing ester groups and olefin groups, and the plasticizer is (20-40):100;

The preparation raw materials also include an initiator, and the initiator is azobisisobutyronitrile and/or dibenzoyl peroxide.

Preferably, the maleic anhydride-modified cyclodextrin includes one or more of maleic anhydride-modified α-cyclodextrin, maleic anhydride-modified β-cyclodextrin and maleic anhydride-modified γ-cyclodextrin.

Preferably, the preparation method of the maleic anhydride modified cyclodextrin comprises the following steps:

Cyclodextrin, maleic anhydride and an organic solvent are mixed and modified to obtain the maleic anhydride-modified cyclodextrin.

Preferably, the molar ratio of cyclodextrin to maleic anhydride is 1:(1-15); the modification temperature is 60-120° C., and the modification time is 6-24 hours.

Preferably, the polymer containing ester groups and alkenyl groups includes one or more of polyethylene glycol diacrylate, tripropylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, triethylene glycol diacrylate and polyethylene glycol methyl ether methacrylate.

Preferably, the plasticizer includes one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, ethylene glycol dimethyl ether and 1,3-dioxolane.

Preferably, the lithium salt includes one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate) and lithium difluorooxalatoborate.

The present invention also provides a method for preparing the solid polymer electrolyte described in the above technical solution, comprising the following steps:

Cyclodextrin modified with maleic anhydride, pentaerythritol tetrakis(3-mercaptopropionic acid), polymer containing ester group and olefin group, lithium salt, plasticizer and organic solvent are mixed, and then an initiator is added to form a film to obtain the solid polymer electrolyte film.

Preferably, the film forming method includes photopolymerization or thermal polymerization.

The present invention also provides the use of the solid polymer electrolyte described in the above technical solution or the solid polymer electrolyte prepared by the preparation method described in the above technical solution in a lithium ion battery.

The invention provides a solid polymer electrolyte, comprising the following preparation raw materials: maleic anhydride-modified cyclodextrin, tetrakis(3-mercaptopropionic acid) pentaerythritol ester, a polymer containing an ester group and an alkenyl group, a lithium salt and a plasticizer; the mass ratio of the maleic anhydride-modified cyclodextrin, tetrakis(3-mercaptopropionic acid) pentaerythritol ester, the polymer containing an ester group and an alkenyl group and the plasticizer is (30-40):(10-25):(25-45):10; the mass ratio of the lithium salt to the total mass of the maleic anhydride-modified cyclodextrin, tetrakis(3-mercaptopropionic acid) pentaerythritol ester, the polymer containing an ester group and an alkenyl group and the plasticizer is (20-40):100; the preparation raw materials also include an initiator, and the initiator is azobisisobutyronitrile and/or dibenzoyl peroxide. In the present invention, the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionic acid), polymer containing ester group and olefin group, lithium salt and plasticizer can undergo thiol-olefin click reaction in a polymerization manner to obtain a solid polymer electrolyte with an interpenetrating network structure. The solid polymer electrolyte has a high ion migration number, ion conductivity and excellent mechanical properties at room temperature, and has good interface stability to the positive and negative electrodes.

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

1) The present invention modifies the hydroxyl groups on the surface of cyclodextrin with maleic anhydride to add more reaction sites. The modified cyclodextrin can be used as both an inorganic filler and a crosslinking agent, and is applied to solid polymer electrolytes, which reduces the crystallinity of the electrolyte and also reduces the glass transition temperature. A low glass transition temperature means high segment movement, which is beneficial to promote the transmission of lithium ions. The prepared solid polymer electrolyte has a high ionic conductivity (1 to 1.27×10 ^-4 S·cm ^-1 ) at room temperature, thereby increasing the cycle life of the battery at high rates;

2) The tetrakis(3-mercaptopropionic acid) pentaerythritol ester can undergo a thiol-ene click chemical reaction with a polymer containing an ester group and an olefin group and a modified cyclodextrin via a C-S-C bond, thereby improving the mechanical properties of the polymer electrolyte at room temperature, wherein the stress can reach up to 3.2 MPa and the strain can reach 210%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a physical picture of the solid polymer electrolyte described in Comparative Example 1;

FIG2 is a SEM image and element distribution diagram of the solid polymer electrolyte described in Example 1;

FIG3 is a graph showing the lithium ion migration number of the solid polymer electrolyte described in Example 2;

FIG4 shows the mechanical properties of the solid polymer electrolyte described in Example 2;

FIG5 is an infrared spectrum and a hydrogen spectrum of β-cyclodextrin, MAH-β-CD and maleic anhydride in Example 3;

FIG6 is an electrochemical stability window of the solid polymer electrolyte described in Example 4;

FIG7 is a curve showing the change of ionic conductivity of the solid electrolyte-free material as a function of temperature in Example 5;

FIG8 is a cycle stability curve of a lithium iron ferrite full battery prepared using the solid polymer electrolyte described in Example 2.

DETAILED DESCRIPTION

The present invention provides a solid polymer electrolyte, comprising the following preparation raw materials: maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionic acid) ester (PETMP), a polymer containing an ester group and an olefin group, a lithium salt and a plasticizer;

The mass ratio of the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionic acid), the polymer containing an ester group and an olefin group, and the plasticizer is (30-40):(10-25):(25-45):10;

The ratio of the mass of the lithium salt to the total mass of the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionic acid), the polymer containing ester groups and olefin groups, and the plasticizer is (20-40):100;

The preparation raw materials also include an initiator, and the initiator is azobisisobutyronitrile and/or dibenzoyl peroxide.

In the present invention, the maleic anhydride-modified cyclodextrin preferably includes one or more of maleic anhydride-modified α-cyclodextrin, maleic anhydride-modified β-cyclodextrin and maleic anhydride-modified γ-cyclodextrin; when the maleic anhydride-modified cyclodextrin is two or more of the above-mentioned specific selections, the present invention has no special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

In the present invention, the method for preparing the maleic anhydride-modified cyclodextrin preferably comprises the following steps:

Cyclodextrin, maleic anhydride and an organic solvent are mixed and modified to obtain the maleic anhydride-modified cyclodextrin.

In the present invention, the cyclodextrin is preferably one or more of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin; when the cyclodextrin is two or more of the above-mentioned specific selections, the present invention has no special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

The present invention does not have any special limitation on the type of the organic solvent, and any type known to those skilled in the art can be used. In a specific embodiment of the present invention, the organic solvent is N,N-dimethylformamide.

In the present invention, the molar ratio of cyclodextrin to maleic anhydride is preferably 1:(1-15), more preferably 1:(1-10), and most preferably 1:10.

In the present invention, the mixing is preferably carried out under stirring conditions. The present invention does not have any special limitation on the stirring conditions. The conditions well known to those skilled in the art can be used to fully disperse the cyclodextrin and maleic anhydride in the organic solvent.

In the present invention, the modification temperature is preferably 60-120°C, more preferably 80-100°C, and most preferably 90°C; the modification time is preferably 6-24h, more preferably 8-10h, and most preferably 8h.

After the modification is completed, the present invention also preferably includes post-treatment of the obtained product; the post-treatment preferably includes cooling, precipitation, filtration, washing, drying and recrystallization performed in sequence; the present invention has no special limitation on the cooling process, and the process well known to those skilled in the art can be used. In the present invention, the precipitation is preferably to mix the reaction solution obtained after cooling with chloroform for precipitation; the present invention has no special limitation on the amount of chloroform, and the amount well known to those skilled in the art can be used to ensure that all target products are precipitated; the present invention has no special limitation on the filtering process, and the process well known to those skilled in the art can be used. In the present invention, the washing is preferably washed three times with acetone and distilled water in sequence. In the present invention, the drying is preferably vacuum drying; the temperature of the vacuum drying is preferably 50°C, and the time is preferably 24h. The present invention has no special limitation on the recrystallization process, and the process well known to those skilled in the art can be used.

In the present invention, the molar ratio of maleic anhydride to cyclodextrin in the obtained maleic anhydride-modified cyclodextrin is preferably 1:5.

In the present invention, the polymer containing ester groups and alkenyl groups preferably includes one or more of polyethylene glycol diacrylate (PEGDA), tripropylene glycol diacrylate (TPGDA), ethylene glycol dimethacrylate (EGDMA), polyethylene glycol dimethacrylate (PEGDMA), triethylene glycol diacrylate (TEGDA) and polyethylene glycol methyl ether methacrylate (PEGMEM), more preferably PEGDA, further preferably PEGDA with a molecular weight of 400 to 6000, and most preferably PEGDA with a molecular weight of 1000 (PEGDA1000); when the polymer containing ester groups and alkenyl groups is two or more of the above-mentioned specific selections, the present invention has no special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

In the present invention, the plasticizer preferably includes one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL), and more preferably PC; when the plasticizer is two or more of the above-mentioned specific selections, the present invention has no special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

In the present invention, the lithium salt preferably includes one or more of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalatoborate) (LiBOB) and lithium difluorooxalatoborate (LiFOB), and more preferably includes LiTFSI; when the lithium salt is two or more of the above-mentioned specific selections, the present invention has no special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

In the present invention, the mass ratio of the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionate), the polymer containing ester groups and olefin groups and the plasticizer is preferably (30-40):(10-25):(25-45):10, more preferably (32-38):(15-20):(30-40):10, and most preferably 35:20:35:10.

In the present invention, the ratio of the mass of the lithium salt to the total mass of the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionate), the polymer containing ester groups and olefin groups and the plasticizer is preferably (20-40):100, more preferably (25-35):100, and most preferably 30:100.

In the present invention, the initiator is preferably azobisisobutyronitrile (AIBN) and/or dibenzoyl peroxide (BPO), more preferably AIBN; when the initiator is azobisisobutyronitrile (AIBN) and dibenzoyl peroxide (BPO), the present invention has no special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio.

In the present invention, the mass ratio of the total mass of the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionate), the polymer containing ester groups and olefin groups and the plasticizer to the initiator is preferably 100:(0.3-0.8), more preferably 100:0.5.

In the present invention, the preparation raw materials also preferably include an organic solvent; the organic solvent preferably includes N,N-dimethylformamide and/or N-methylpyrrolidone, more preferably N,N-dimethylformamide; when the organic solvent is N,N-dimethylformamide and N-methylpyrrolidone, the present invention has no special limitation on the ratio of N,N-dimethylformamide and N-methylpyrrolidone, and they can be mixed in any ratio.

In the present invention, the volume ratio of the total mass of the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionate), the polymer containing ester groups and olefin groups and the plasticizer to the organic solvent is preferably 2g:(4-10)mL, more preferably 2g:5mL.

The present invention also provides a method for preparing the solid polymer electrolyte described in the above technical solution, comprising the following steps:

Cyclodextrin modified with maleic anhydride, pentaerythritol tetrakis(3-mercaptopropionic acid), polymer containing ester group and olefin group, lithium salt, plasticizer and organic solvent are mixed, and then an initiator is added to form a film to obtain the solid polymer electrolyte film.

In the present invention, the mixing is preferably carried out under stirring conditions. The present invention does not have any special limitation on the stirring process. A process well known to those skilled in the art is adopted to uniformly disperse the maleic anhydride-modified cyclodextrin, pentaerythritol tetrakis(3-mercaptopropionic acid), polymer containing ester groups and olefin groups, lithium salt and plasticizer in an organic solvent.

The present invention has no special limitation on the method of adding the initiator, and any method familiar to those skilled in the art may be used.

In the present invention, the film forming process preferably includes: ultrasonically dispersing the obtained precursor solution, spreading it on a polytetrafluoroethylene plate, and performing photopolymerization or thermal polymerization.

In the present invention, the wavelength of light for the photopolymerization is preferably 254 to 400 nm, more preferably 395 nm, and the time is preferably 0.5 to 4 h, more preferably 1 h; the photopolymerization is preferably carried out in a glove box.

In the present invention, the temperature of the thermal polymerization is preferably 40 to 80° C., more preferably 50 to 60° C.; the time is preferably 6 to 24 hours, more preferably 12 hours; and the thermal polymerization is preferably carried out in a vacuum drying oven.

In the present invention, after the polymerization reaction is completed, the thiol group at the end of the PETMP reacts with the double bond in the polymer containing ester groups and alkenyl groups to generate S-C bonds to form a hyperbranched structure; the double bonds of the polymer containing ester groups and alkenyl groups themselves can also undergo polymerization reaction to generate C-C bonds, extending the chain length of the polymer containing ester groups and alkenyl groups and increasing its molecular weight; the thiol group at the end of the PETMP can also react with the double bond next to the carboxyl group in the maleic anhydride-modified cyclodextrin to generate a small amount of S-C bonds; the double bond next to the carboxyl group in the maleic anhydride-modified cyclodextrin may react with the terminal double bond of the polymer containing ester groups and alkenyl groups (very small amount); and finally, with PETMP as the core of the molecule, it expands outward to form a hyperbranched star structure, a small amount of unreacted maleic anhydride-modified cyclodextrin is dispersed in the polymer matrix as an inorganic filler, and the polymer (small molecular weight) obtained by the polymerization reaction of the double bonds of the polymer containing ester groups and alkenyl groups itself is also dispersed in the matrix as a polymer to form an interpenetrating network structure.

The present invention also provides the use of the solid polymer electrolyte described in the above technical solution or the solid polymer electrolyte prepared by the preparation method described in the above technical solution in a lithium ion battery. The present invention does not have any special limitation on the method of the application, and the method well known to those skilled in the art can be used.

The solid polymer electrolyte provided by the present invention and its preparation method and application are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

Comparative Example 1

0.01 mol of β-cyclodextrin and 0.1 mol of maleic anhydride were mixed with 80 mL of dimethylformamide, stirred for 30 min, heated to 90°C for 8 h, cooled to room temperature, precipitated the obtained reaction solution with chloroform, filtered, and the obtained filter residue was washed and purified three times with acetone and distilled water respectively, dried under vacuum at 50°C for 24 h, and recrystallized to obtain maleic anhydride-modified β-cyclodextrin (MAH-β-CD);

0.7 g of MAH-β-CD, 0.4 g of PETMP, 0.7 g of PEGDA1000, 0.6 g of LiTFSI and 0.2 g of plasticizer PC were mixed with 5 mL of N-methylpyrrolidone and stirred until clear and transparent, 0.01 g of phenylbis(2,4,5-trimethylbenzoyl)phosphine oxide was added, and stirred again for 1 h to obtain a precursor solution;

The precursor solution was ultrasonicated for 20 minutes to make it evenly dispersed, and then moved into a glove box. The precursor solution was spread on a polytetrafluoroethylene plate and irradiated with an ultraviolet lamp (395 nm) for 1 hour to obtain a solid polymer electrolyte (denoted as A).

FIG. 1 is a physical picture of the solid polymer electrolyte. As can be seen from FIG. 1 , the solid polymer electrolyte has an uneven thickness and an uneven reaction, and has insufficient toughness.

Example 1

0.01 mol of β-cyclodextrin and 0.1 mol of maleic anhydride were mixed with 80 mL of dimethylformamide, stirred for 30 min, heated to 90 ° C for 8 h, cooled to room temperature, precipitated the obtained reaction solution with chloroform, filtered, and the obtained filter residue was washed and purified three times with acetone and distilled water respectively, dried under vacuum at 50 ° C for 24 h, and recrystallized to obtain maleic anhydride-modified β-cyclodextrin (MAH-β-CD, the molar ratio of maleic anhydride to β-cyclodextrin is 1:5);

0.6 g of MAH-β-CD, 0.6 g of PETMP, 0.6 g of PEGDA1000, 0.6 g of LiTFSI and 0.2 g of plasticizer PC were mixed with 5 mL of N-methylpyrrolidone and stirred until clear and transparent, 0.01 g of AIBN was added, and stirred again for 1 h to obtain a precursor solution;

After the precursor solution was ultrasonically dispersed for 20 minutes, the precursor solution was spread on a polytetrafluoroethylene plate and thermally polymerized at 60° C. for 12 hours to obtain a solid polymer electrolyte (denoted as B);

Figure 2 is the SEM image and element distribution diagram of the solid polymer electrolyte, wherein a is the SEM image, b is the element distribution diagram of the nitrogen element, c is the element distribution diagram of the fluorine element, and d is the element distribution diagram of the sulfur element. As can be seen from Figure 2, the solid polymer electrolyte is light yellow and transparent, and is flat and uniform when observed with the naked eye. Even under SEM, the surface is still flat and smooth, without cracks or protrusions. It can be seen from the element distribution diagram that each element is evenly distributed.

Example 2

Referring to Example 1, the difference is that the mass ratio of MAH-β-CD, PETMP, PEGDA1000 and plasticizer PC is 35:20:35:10, and a solid polymer electrolyte (denoted as C) is prepared;

The solid polymer electrolyte C was assembled into a lithium-lithium symmetric battery, and the lithium ion migration number was calculated to be 0.46 by combining constant voltage polarization and AC impedance (as shown in Figure 3), which is much higher than that of pure PEGDA electrolyte (0.1-0.2); cyclodextrin acts as an inorganic filler and a cross-linking agent at the same time, promoting the dissociation of lithium salts;

The solid state without electrolyte was subjected to a tensile test, and the test results are shown in FIG4 . As can be seen from FIG4 , the strain reached 210% and the stress was 3.2 MPa. This may be because the C-S-C bonds generated by the thiol-ene click reaction increase the cross-linking sites while increasing the flexibility of the polymer chain, thereby increasing its mechanical properties. Good stress can alleviate the formation of lithium dendrites to a certain extent.

Example 3

Referring to Example 1, except that the molar ratio of β-cyclodextrin (β-CD) to maleic anhydride is 1:1, a solid polymer electrolyte (denoted as D) is prepared;

FIG5 is the infrared spectra and hydrogen spectra of β-cyclodextrin, MAH-β-CD and maleic anhydride, wherein a is the infrared spectra of β-cyclodextrin and MAH-β-CD, and b is the hydrogen spectra of β-cyclodextrin, MAH-β-CD and maleic anhydride. From a, it can be seen that the characteristic peaks at 1727 cm ^-1 , 1216 cm ^-1 , and 1644 cm ^-1 correspond to the stretching vibrations of the carbonyl group, ester group and carbon-carbon double bond in C＝CC(＝O)-O, respectively, which can be judged that maleic anhydride and cyclodextrin have reacted; from b, it can be seen that the absorption peaks at 6.57 ppm and 6.26 ppm in MAH-β-CD correspond to the protons in the carbon-carbon double bond, while there is no C＝C proton in pure β-CD, which can indicate that a chemical reaction has occurred between maleic anhydride and β-CD, that is, the hydroxyl groups on the surface of cyclodextrin have been successfully modified.

Example 4

Referring to Example 1, the difference is that the plasticizer PC is replaced by DOL to prepare a solid polymer electrolyte (denoted as E);

FIG. 6 shows the electrochemical stability window of the solid polymer electrolyte. As can be seen from FIG. 6 , the solid polymer electrolyte will not decompose until the voltage is greater than 4.2V.

Example 5

Referring to Example 1, the difference is that N-methylpyrrolidone is replaced by N,N-dimethylformamide to prepare a solid polymer electrolyte (denoted as F);

FIG. 7 is a curve showing the change of ionic conductivity of the solid electrolyte-free material with temperature. As shown in FIG. 7 , at 25° C., the ionic conductivity can reach 1×10 ⁻⁴ S·cm ⁻¹ , which can meet the normal use of the electrolyte.

Test Case

The prepared solid polymer electrolyte C and lithium iron phosphate positive electrode material were used to construct a lithium metal battery, and the battery was assembled to test its electrochemical performance; the test results are shown in Figure 8, which is a cycle stability curve of the lithium iron ferrite full battery. As shown in Figure 8, at 60°C and 0.7C, the first cycle released a specific capacity of 142.8mAh g ^-1 , and after 450 cycles, the capacity retention rate was 82.1%, and the average coulomb efficiency was greater than 99.1%. The solid polymer electrolyte C exhibits good interface stability to the lithium metal negative electrode and the lithium iron phosphate positive electrode.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (8)

1. A solid polymer electrolyte characterized by comprising the following preparation raw materials: maleic anhydride modified cyclodextrin, pentaerythritol tetrakis (3-mercaptopropionate), polymers containing ester groups and alkenyl groups, lithium salts and plasticizers;

The mass ratio of the maleic anhydride modified cyclodextrin to the pentaerythritol tetra (3-mercaptopropionic acid) ester to the polymer containing ester groups and alkenyl groups to the plasticizer is (30-40): (25-45): 10;

the mass of the lithium salt is equal to that of the maleic anhydride modified cyclodextrin, pentaerythritol tetra (3-mercaptopropionate) the ratio of the total mass of the polymer containing ester groups and alkenyl groups to the plasticizer is (20-40): 100;

the preparation raw materials also comprise an initiator, wherein the initiator is azodiisobutyronitrile and/or dibenzoyl peroxide;

The preparation method of the maleic anhydride modified cyclodextrin comprises the following steps:

Mixing cyclodextrin, maleic anhydride and an organic solvent, and modifying to obtain maleic anhydride modified cyclodextrin;

The molar ratio of the cyclodextrin to the maleic anhydride is 1: (1-15); the temperature of the modification is 60-120 ℃ and the time is 6-24 h.

2. The solid polymer electrolyte of claim 1 wherein the maleic anhydride modified cyclodextrin comprises one or more of maleic anhydride modified alpha-cyclodextrin, maleic anhydride modified beta-cyclodextrin, and maleic anhydride modified gamma-cyclodextrin.

3. The solid polymer electrolyte of claim 1 wherein said polymer containing ester groups and alkenyl groups comprises one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate and polyethylene glycol methyl ether methacrylate.

4. The solid polymer electrolyte of claim 1 wherein said plasticizer comprises one or more of ethylene carbonate, propylene carbonate, ethylmethyl carbonate, diethyl carbonate, dimethyl carbonate, ethylene glycol dimethyl ether and 1, 3-dioxolane.

5. The solid polymer electrolyte of claim 1 wherein said lithium salt comprises one or more of lithium bis (trifluoromethylsulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium bis (oxalato) borate, and lithium bis (oxalato) borate.

6. The method for producing a solid polymer electrolyte according to any one of claims 1 to 5, comprising the steps of:

Mixing maleic anhydride modified cyclodextrin, pentaerythritol tetra (3-mercaptopropionate), polymer containing ester groups and alkenyl groups, lithium salt, plasticizer and organic solvent, adding initiator, and forming film to obtain the solid polymer electrolyte film.

7. The method of claim 6, wherein the film forming means comprises photopolymerization or thermal polymerization.

8. Use of the solid polymer electrolyte according to any one of claims 1 to 5 or the solid polymer electrolyte prepared by the preparation method according to claim 6 or 7 in lithium ion batteries.