A hyperbranched polymer electrolyte and a preparation method thereof

Abstract

The application discloses a kind of hyperbranched polymer electrolyte and preparation method thereof, belong to electrolyte material technical field.The hyperbranched polymer electrolyte includes comonomer A, comonomer B and catalyst;The comonomer A is polyhydric alcohol comonomer, and the comonomer B is acrylic ester comonomer;Wherein, the molar ratio of comonomer A and comonomer B is comonomer A:comonomer B=1-3:1-3, and the catalyst accounts for 15%-55% of the total mass of hyperbranched polymer electrolyte.The polymer electrolyte system described in the application has hyperbranched structure, can effectively inhibit the crystallization of PEO-based polymer electrolyte, and improve the ion transport performance of electrolyte;The catalyst is the electrolyte salt required for secondary battery, without additional initiator, the system is more pure, can reduce the side reaction caused by initiator use, and preparation process is simple.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrolyte materials, in particular to a hyperbranched polymer electrolyte and a preparation method thereof. BACKGROUND

[0002] Lithium batteries are considered as a strong candidate for the next generation of energy storage devices due to their low redox potential and high theoretical specific capacity. However, the use of lithium metal batteries has been limited due to safety concerns such as lithium dendrite growth, flammability and leakage of liquid electrolytes. Among them, solid-state polymer electrolytes based on polyethylene oxide are of great concern due to their high flexibility, good interface compatibility and strong scalability. However, the solid-solid interface contact between the solid-state polymer electrolyte and the electrode leads to an increase in the interfacial impedance of the electrolyte, which is an important obstacle to the development of solid-state batteries.

[0003] The in-situ curing method for preparing polymer electrolyte is an effective strategy to improve the interface performance of solid-state electrolyte. At present, many in-situ curing systems use AIBN, BPO and other initiators to initiate, and the addition of initiators may cause side reactions, affecting the performance of the battery. Michael addition reaction has become an advantageous reaction system for constructing and preparing in-situ curing electrolyte due to its mild reaction conditions; at present, the polymers prepared by Michael addition polymerization are mainly based on the polymerization of amino or mercapto groups with unsaturated bond monomers, however, amino and sulfur monomers have potential toxicity and unpleasant irritating odor, in addition, the types of mercapto monomers are few and the stability is poor, which limits the application of Michael addition polymerization. The nucleophilic alcohol (phenol) monomers have many types and good stability, but the nucleophilicity of alcohol (phenol) is weaker than that of amine and mercapto monomer, and the reactivity is poor, which leads to low yield and molecular weight of the product of Michael polymerization of hydroxyl and electron-deficient double bond, so it is of great significance to develop Michael addition polymerization based on hydroxyl and double bond to prepare polymers. In recent years, the application of small organic molecule catalysts in the field of Michael addition polymerization of hydroxyl and double bond has been reported. For example, Phosphazene-catalyzed oxa-Michael addition click polymerization, Polym. Chem, 2018, 9, 4716-4723 reports that under normal temperature conditions, primary or secondary alcohol and double bond monomer are polymerized by Michael addition polymerization catalyzed by organic phosphazene base t-BuP2, and the polymerization exhibits the characteristics of click reaction, but the molecular weight of the polymer synthesized by the method is still low, and there is an ester exchange side reaction, and Jiang Qimin et al. (Jiang Qimin, Han Chaoran, Tang Mao Tong, Yang Hongjun, Huang Wenyang, Xue Xiaoqiang, Jiang Li, Jiang Bibiao. Michael addition polymerization of hydroxyl and double bond catalyzed by phosphazene base [J]. Journal of Changzhou University (Natural Science Edition), 2020, 32 (06): 8-14.) further studied the influencing factors of Michael addition polymerization of primary alcohol and double acrylate monomers catalyzed by phosphazene base in a reaction bottle with water removal at high temperature and argon replacement under argon protection. However, the organic phosphazene base used in the above reaction is expensive, and the polymerization reaction needs to be carried out under strict water-free and oxygen-free conditions, which is difficult to implement.

[0004] In view of the above problems of the polymer electrolyte, it is the focus of the current research to develop a polymer electrolyte with hyperbranched structure that can improve the ion transport performance of the electrolyte. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a polymer electrolyte with hyperbranched structure that can improve the ion transport performance of the electrolyte and a preparation method thereof.

[0006] To achieve the above object, the technical scheme adopted by the present application is:

[0007] In the first aspect, the present application provides a hyperbranched polymer electrolyte, which comprises a comonomer A, a comonomer B and a catalyst.

[0008] The comonomer A is a polyol comonomer, and the comonomer B is an acrylic ester comonomer.

[0009] The molar ratio of the comonomer A to the comonomer B is comonomer A: comonomer B = 1-4:1-4, and the catalyst accounts for 15%-55% of the total mass of the hyperbranched polymer electrolyte.

[0010] There are few existing catalytic systems that can catalyze the copolymerization of polyols and acrylic ester monomers, and some existing catalysts for catalyzing the addition polymerization of hydroxyl groups and double bonds, such as organophosphazene bases, are relatively expensive.

[0011] In view of the above problems, the present application provides a new hyperbranched polymer electrolyte, and the inventors have found in experiments that a fluorinated alkyl sulfonimide compound, such as lithium bistrifluoromethylsulfonimide, can catalyze the addition reaction of hydroxyl groups and double bonds, and the catalyst provided by the present application has a lower cost compared with existing catalysts.

[0012] The polymer electrolyte is constructed in situ, which can effectively reduce the interface impedance of the solid-state electrolyte; the catalyst is an alkali metal salt required for a secondary battery, which can not only play a catalytic role but also serve as an ion source for the polymer electrolyte, so that an external initiator is not needed, the reaction system is more pure, and the side reactions are less; the polymer electrolyte synthesized by the present application has a hyperbranched structure, which can effectively inhibit the crystallization of PEO-based polymer electrolytes and improve the ionic conductivity of the electrolyte.

[0013] The inventors have found through a large number of experiments that when the catalyst accounts for 15%-55% of the total mass of the hyperbranched polymer electrolyte, the ionic conductivity of the final polymer electrolyte is higher; if the amount of the catalyst is too small, the catalytic efficiency is low and the solidification time is too long; and if the amount of the catalyst is too large, the catalyst is difficult to completely dissolve, crystallization occurs, the catalytic efficiency is reduced, and the crystallization of the catalyst itself as an electrolyte salt also leads to a decrease in the ionic conductivity of the polymer electrolyte.

[0014] The inventors have also found that when the molar ratio of the comonomer A to the comonomer B is comonomer A: comonomer B = 1-3:3-1, the polymerization product can be successfully formed.

[0015] As a preferred embodiment of the hyperbranched polymer electrolyte of the present application, the molar ratio of the co-monomer A to the co-monomer B is co-monomer A: co-monomer B = 1-2: 2-1, and the catalyst accounts for 25-40% of the total mass of the hyperbranched polymer electrolyte; the inventors have found through a large number of experiments that the polymer electrolyte obtained under this condition has the highest ionic conductivity.

[0016] As a preferred embodiment of the hyperbranched polymer electrolyte of the present application, the polyol co-monomer includes at least one of polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol block copolymer, polyvinyl alcohol, and polyether polyol.

[0017] As a more preferred embodiment of the hyperbranched polymer electrolyte of the present application, the polyol co-monomer includes polyethylene glycol, polypropylene glycol, and polyether polyol.

[0018] As a preferred embodiment of the hyperbranched polymer electrolyte of the present application, the acrylate co-monomer includes at least one of glycerol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, pentaerythritol tetraacrylate, and ditrimethylolpropane tetra(meth)acrylate.

[0019] As a more preferred embodiment of the hyperbranched polymer electrolyte of the present application, the acrylate co-monomer includes glycerol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate.

[0020] As a preferred embodiment of the hyperbranched polymer electrolyte of the present application, the catalyst is selected from at least one of a fluorinated alkylsulfonylimide alkali metal salt and a fluorinated alkylsulfonylimide ionic liquid.

[0021] As a more preferred embodiment of the hyperbranched polymer electrolyte of the present application, the catalyst is lithium bis(trifluoromethylsulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and sodium bis(fluorosulfonyl)imide.

[0022] In a second aspect, the present application also provides a preparation method of the hyperbranched polymer electrolyte of the first aspect, which comprises the following steps: uniformly mixing the co-monomer A, the co-monomer B, and the catalyst to obtain a homogeneous solution, and then reacting at 0-100°C for 2-148h to obtain the hyperbranched polymer electrolyte.

[0023] As a preferred embodiment of the preparation method of the hyperbranched polymer electrolyte of the present application, the reaction temperature is 20-60℃, and the reaction time is 2-72h.

[0024] Compared with the prior art, the present application has the beneficial effects that:

[0025] The present application provides a hyperbranched polymer electrolyte, which has a hyperbranched structure, can effectively inhibit the crystallization of a PEO-based polymer electrolyte, and improve the ion transmission performance of the electrolyte; the catalyst is an electrolyte salt required for a secondary battery, and no initiator needs to be additionally added, so that the system is more pure, and the side reactions caused by the use of the initiator can be reduced; the polymerization can be initiated under the condition of no strict water removal and oxygen removal, and the polymerization can be applicable to solution polymerization in the presence of a solvent or bulk polymerization without the addition of a solvent, so that the application range is wide, and the preparation process is simple. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a linear sweep voltammetry curve of Example 1;

[0027] Figure 2 is an electrochemical impedance spectrum of Example 3; DETAILED DESCRIPTION

[0028] The technical solutions of the present application are further described below in combination with examples. Obviously, the described examples are only a part of the examples of the present application, rather than all the examples. Based on the examples in the present application, all the other examples obtained by a person of ordinary skill in the art without making creative efforts fall within the protection scope of the present application. The methods or operations used in the examples are all conventional methods or conventional operations in the art, unless otherwise specified.

[0029] Example 1

[0030] Example 1 is a hyperbranched polymer electrolyte of the present application, which comprises a comonomer A, a comonomer B and a catalyst.

[0031] The comonomer A is a polyol comonomer, and the comonomer B is an acrylic ester comonomer.

[0032] The polyol comonomer is polyethylene glycol, the acrylic ester comonomer is pentaerythritol triacrylate, and the catalyst is lithium bistrifluoromethanesulfonimide.

[0033] The molar ratio of the comonomer A to the comonomer B is comonomer A:comonomer B=1:1, and the catalyst accounts for 25% of the total mass of the hyperbranched polymer electrolyte.

[0034] The preparation method of the embodiment comprises the following steps: mixing the comonomer A, the comonomer B and the catalyst uniformly to obtain a homogeneous solution, and then reacting at 60°C for 2h to obtain the hyperbranched polymer electrolyte. The preparation process of the hyperbranched polymer electrolyte of the embodiment is shown in the following formula.

[0035]

[0036] Example 2

[0037] The difference between Example 2 and Example 1 is only that the molar ratio of the comonomer A to the comonomer B is comonomer A: comonomer B = 1:3.

[0038] Example 3

[0039] The difference between Example 3 and Example 1 is only that the molar ratio of the comonomer A to the comonomer B is comonomer A: comonomer B = 3:1, and the catalyst accounts for 50% of the total mass of the hyperbranched polymer electrolyte.

[0040] Example 4

[0041] The difference between Example 4 and Example 1 is only that the polyhydric alcohol comonomer is polypropylene glycol, the acrylic ester comonomer is pentaerythritol tetraacrylate, and the catalyst is sodium bistrifluoromethanesulfonimide.

[0042] Example 5

[0043] The difference between Example 5 and Example 1 is only that the polyhydric alcohol comonomer is polyether polyol, the acrylic ester comonomer is polyethylene glycol diacrylate, and the catalyst is lithium bistrifluoromethanesulfonimide.

[0044] Comparative Example 1

[0045] The difference between Comparative Example 1 and Example 1 is only that the molar ratio of the comonomer A to the comonomer B is comonomer A: comonomer B = 1:4.

[0046] Comparative Example 2

[0047] The difference between Comparative Example 2 and Example 1 is only that the molar ratio of the comonomer A to the comonomer B is comonomer A: comonomer B = 4:1.

[0048] Comparative Example 3

[0049] The difference between Comparative Example 3 and Example 3 is only that the catalyst accounts for 60% of the total mass of the hyperbranched polymer electrolyte.

[0050] Comparative Example 4

[0051] Comparative Example 4 differs from Example 1 only in that the catalyst accounts for 5% of the total mass of the hyperbranched polymer electrolyte.

[0052] Performance test

[0053] The conductivity of the hyperbranched polymer electrolytes of Examples 1-5 and Comparative Examples 1-3 above was tested, and lithium ion batteries were assembled, and electrochemical impedance spectroscopy was tested at 60°C, with an alternating current perturbation of 10 mV, and a test frequency range of 0.1 Hz-1 MHz. The bulk resistance and interface resistance of the polymer electrolyte can be calculated from the alternating current impedance spectrogram, and the ionic conductivity thereof is calculated according to the following formula:

[0054]

[0055] wherein σ, R b , d and S are the conductivity (S cm -1 ), bulk resistance (Ω), thickness (cm) and area (cm 2 ) of the electrolyte membrane, respectively. Lithium-stainless steel half-batteries were assembled, and the electrochemical window of the polymer electrolyte was tested using linear sweep voltammetry, with a test cut-off voltage of 6.0 V, and a scan rate of 2.0 mV s -1 .

[0056] The test results are shown in Table 1 below.

[0057] Table 1

[0058]

[0059] As can be seen from Table 1, when the technical solution of the present application is used, the hyperbranched polymer obtained has a hyperbranched structure, which can effectively inhibit the crystallization of PEO-based polymer electrolytes, and improve the ion transport performance of the electrolyte; the catalyst is an electrolyte salt required for secondary batteries, and no initiator needs to be added additionally, so the system is purer, and side reactions caused by the use of an initiator can be reduced; the polymerization can be initiated without strict water and oxygen removal, and the system can be applied to solution polymerization in the presence of a solvent or bulk polymerization without the addition of a solvent, so the scope of application is wide, and the preparation process is simple.

[0060] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A hyperbranched polymer electrolyte, characterized by, The hyperbranched polymer electrolyte comprises the following raw materials: comonomer A, comonomer B and catalyst; The comonomer A is a polyol comonomer, which comprises at least one of polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol block copolymer, polyvinyl alcohol, and polyether polyol; the comonomer B is an acrylate comonomer; the acrylate comonomer comprises at least one of glycerol di(meth)acrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, pentaerythritol tetraacrylate, and ditrimethylolpropane tetra(meth)acrylate; and the catalyst is selected from at least one of a fluorosulfonimide alkali metal salt and a fluorinated alkylsulfonimide alkali metal salt. The molar ratio of the comonomer A to the comonomer B is comonomer A: comonomer B = 1-3:1-3, and the catalyst accounts for 15%-60% of the total mass of the hyperbranched polymer electrolyte.

2. The hyperbranched polymer electrolyte according to claim 1, wherein The molar ratio of the comonomer A to the comonomer B is comonomer A: comonomer B = 1-2:2-1, and the catalyst accounts for 20%-40% of the total mass of the hyperbranched polymer electrolyte.

3. The hyperbranched polymer electrolyte according to claim 1, wherein The polyol comonomer comprises polyethylene glycol, polypropylene glycol, and polyether polyol.

4. The hyperbranched polymer electrolyte according to claim 1, wherein The acrylate comonomer comprises glycerol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate.

5. The hyperbranched polymer electrolyte according to claim 1, wherein The catalyst is lithium bis(trifluoromethylsulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, or sodium bis(fluorosulfonyl)imide.

6. The method of claim 1-5, wherein the method is characterized by, The preparation method comprises the following steps: uniformly mixing the comonomer A, the comonomer B and the catalyst to obtain a homogeneous solution, and then reacting at 0-100 ℃ for 2-148 h to obtain the hyperbranched polymer electrolyte.

7. The method of claim 6, wherein the hyperbranched polymer electrolyte is prepared by the reaction of the hyperbranched polymer and the ionic liquid. The reaction temperature is 20-60 ℃, and the reaction time is 2-72 h.

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