Water-soluble polyionic liquid binder

Abstract

The application provides a water-soluble polyionic liquid binder, a polar group is introduced into a polyionic liquid through molecular design, and a water-soluble polyionic liquid is formed by polymerization, so that the polarity of the polyionic liquid is increased, and the polyionic liquid can be dissolved in a water solution with greater polarity. The polyionic liquid has good bonding performance and good conductivity, when used as a binder, can effectively reduce the resistance between the conductive agent and the active material, and improve the cycle capacity of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, and particularly relates to a water-soluble polyionic liquid and application of the water-soluble polyionic liquid as a binder. BACKGROUND

[0002] Since the birth of lithium battery, its development has undergone many changes. However, no matter when, the binder in its composition, although the proportion is very small, plays an important role, and some characteristics of the binder polymer will also bring unexpected influence to the battery. With the increasingly high requirements of the application end on the battery, it is particularly important to develop an advanced battery binder.

[0003] At present, in the large-scale production of pole pieces, oil phase coating technology is still generally used. The binder used is mainly a fluorine-containing polymer binder, such as polyvinylidene fluoride (PVDF), and the commonly used solvent is N-methyl pyrrolidone. The volatilization of the solvent in the preparation process not only pollutes the environment, but also harms the health of the operators. In addition, the solvent cost is also relatively high, which increases the production cost of lithium ion batteries.

[0004] Polyionic liquid has excellent thermal stability, non-combustion, wide electrochemical stability window and other advantages, and also has excellent processability and flexibility advantages, and is a very promising material. SUMMARY

[0005] The present application provides a water-soluble polyionic liquid. By molecular design, a polar group is introduced into the polyionic liquid, and a water-soluble polyionic liquid is formed by polymerization, so that the polarity of the polyionic liquid is increased, and the polyionic liquid can be dissolved in a water solution with larger polarity.

[0006] The present application first provides a water-soluble polyionic liquid binder, which has the structure of formula I:

[0007]

[0008] In the formula, A is an imidazole group or a pyridine group; B is a polar group containing a nitrile group, an amino group, a carboxyl group, a hydroxyl group, or a sulfonic group; X is halogen, specifically Cl, Br, or I; n is an integer greater than 1; B and X are both connected to the same N atom on the imidazole ring or the pyridine ring of A. - -

[0009] ​​Further, the B is a substituent having formula II, wherein m is M / 2, M is a positive integer, preferably 2-6; R1 is nitrile group, amino group, carboxyl group, hydroxyl group, or sulfonic group. Suitable carbon chain length can reduce steric hindrance to promote polymerization of the polyionic liquid, and on the other hand, can maintain strong polarity of the polar group, improve electron-withdrawing effect on the imidazole ring or pyridine ring, thereby promoting ionization of the N atom and improving water solubility.

[0010]

[0011] Further, the N atom on the imidazole ring or pyridine ring, which is connected with the B and X - is located on a non-adjacent position of the atom connected with the main chain.

[0012] For the need of more suitable adhesion performance, the molecular weight of the water-soluble polyionic liquid binder is controlled to be 1000-1000000, preferably 5000-50000. In addition, the viscosity of the water-soluble polyionic liquid binder can be controlled to be 1000-500000 mPa·s, preferably 6000-10000 mPa·s. Suitable molecular weight indicates that the polyionic liquid has suitable polymerization degree, suitable molecular strength, and suitable flexibility and rigidity between particles during adhesion; suitable viscosity is more conducive to adhesion and mutual connection between particles. The access of the polar group is more conducive to the affinity of the polyionic liquid with water, and more easily wets the particles to be adhered when a slurry is prepared with water as a solvent, thereby promoting adhesion effect.

[0013] The preparation method of the above-mentioned water-soluble polyionic liquid binder of the present application comprises the following steps:

[0014] S1: quaternary ammonium reaction of vinyl imidazole or vinyl pyridine with an alkane containing halogen and a polar group to obtain vinyl imidazole or vinyl pyridine with a substituent of formula II and a halogen ion simultaneously connected to the same N atom on the imidazole ring or pyridine ring;

[0015] wherein the alkane containing halogen and a polar group has a structure of formula III, m is M / 2, M is a positive integer, preferably 2-6; R1 is nitrile group, amino group, carboxyl group, hydroxyl group, or sulfonic group; X is halogen, specifically Cl, Br, I;

[0016]

[0017] The reaction route of this step is as follows:

[0018]

[0019] S2: addition polymerization reaction of the product obtained in step S1 to obtain the target water-soluble polyionic liquid;

[0020] The reaction route of the step is as follows:

[0021]

[0022] In the above steps:

[0023] The step S1 is reacted at 40-80℃ for 24-48h, and the reaction solution is preferably ethyl acetate.

[0024] The specific operation method of the step S2 is that the initiator is added to the product obtained in the step S2, and the polymerization reaction is carried out under heating or light irradiation conditions to obtain the water-soluble polyionic liquid product.

[0025] Further, in the step S1, after the reaction is completed, a purification operation is further included, which specifically includes the process of distillation at 80℃ and 10mbar for 40min, and washing with ethyl acetate after the distillation is completed;

[0026] Further, in the step S2, the polymerization temperature of the thermal polymerization is 40-80℃, and is preferably 50-60℃, and the polymerization time is 3-12h, and is preferably 4-6h; the light polymerization adopts 365nm ultraviolet light, and the light irradiation time is 5s-10min; the initiator is one or more of thermal initiators such as azobisisobutyronitrile, azobisisoheptyl nitrile, dibenzoyl peroxide, dialkyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, and photoinitiators such as 2-hydroxy-methyl phenylpropane-1-ketone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone, and bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide.

[0027] Further, in the step S2, the initiator is 0.1-5wt% of the mass of the water-soluble polyionic liquid monomer.

[0028] The application further provides a water-based slurry comprising the above water-soluble polyionic liquid adhesive.

[0029] The mass ratio of the water-soluble polyionic liquid adhesive in the slurry is 1-10wt%.

[0030] Further, the slurry comprises the following components by weight: water-soluble polyionic liquid adhesive: conductive agent: active substance = (1-10):(1-20):(70-98).

[0031] Further, the active material includes one of positive electrode materials such as lithium iron phosphate, lithium cobaltate, lithium manganate, lithium nickelate, nickel cobalt aluminum ternary, nickel cobalt manganese ternary, sulfur, sulfur-carbon composite material, sulfide, etc., or a mixture or composite of two or more; one of negative electrode materials such as graphite, soft carbon, hard carbon, carbon fiber, porous carbon, carbon black, graphene, carbon nanotube, lithium titanate, nano-silicon, silicon-carbon composite, silicon oxide, elemental tin, tin oxide, tin cobalt carbon, metallic lithium, metallic sodium, metallic magnesium, etc., or a mixture or composite of two or more. The conductive agent includes one of graphite, soft carbon, hard carbon, carbon fiber, porous carbon, carbon black, graphene, carbon nanotube, etc., or a mixture or composite of two or more.

[0032] The present application has the following advantages: 1. The polyionic liquid binder is soluble in water, and can be used to prepare slurry with water as solvent, which is environmentally friendly. 2. The polyionic liquid binder has the advantages of high temperature resistance and non-combustion. 3. The polyionic liquid has good bonding performance and good conductivity, which can effectively reduce the resistance between the conductive agent and the active material when used as a binder, and improve the cycle capacity of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0033] The technical solutions of the embodiments of the present application will be further described in detail below with reference to the drawings and examples.

[0034] Figures 1-5 The molecular weight results of Examples 1-5 are shown in the following figures, respectively.

[0035] Figures 6-11 The first week discharge specific capacity and capacity retention results of Examples 1-5 and Comparative Examples are shown in the following figures, respectively. DETAILED DESCRIPTION

[0036] The present application will be further described below with reference to the drawings and specific examples, but it should be understood that these examples are only used for more detailed description, and should not be understood as limiting the present application in any form, i.e. not intended to limit the protection scope of the present application.

[0037] Dissolve the vinyl imidazole or vinyl pyridine and the alkane containing halogen and polar group and the alkane containing polar group in ethyl acetate, according to the stoichiometric ratio, the alkane containing halogen and polar group can be slightly excessive, for example, 1.05-1.5 times of the molar amount of the vinyl imidazole or vinyl pyridine, and react at 40-80℃ for 24-48h. After the reaction is completed, distill at 80℃ and 10mbar for 40min. After the distillation is completed, wash three times (separate liquid) with ethyl acetate, and distill at 80℃ and 10mbar for 40min to obtain the vinyl imidazole or vinyl pyridine with the same N atom on the imidazole ring or pyridine ring simultaneously connected with the polar group substituent and the halogen ion;

[0038] The product obtained in the previous step is mixed with an initiator, and a polymerization reaction is initiated by heating or light to obtain a water-soluble polyionic liquid binder. The initiator is 0.1-5 wt% of the mass of the water-soluble polyionic liquid monomer.

[0039] As an example, the reaction route for preparing a water-soluble polyionic liquid from chloropropionitrile and 1-vinylimidazole is as follows:

[0040]

[0041] To further verify the application performance of the water-soluble polyionic liquid binder of the present application, the following examples and comparative examples are prepared for detailed performance evaluation.

[0042] Example 1:

[0043] (1) Preparation of water-soluble ionic liquid monomer

[0044] Take 25.0 g of 3-chloropropionitrile and 50.0 g of 1-vinylimidazole and dissolve them in ethyl acetate at 70°C for 48 h. After the reaction is completed, distill at 80°C and 10 mbar for 40 min. After distillation, wash three times with ethyl acetate (separate), distill at 80°C and 10 mbar for 40 min to obtain the ionic liquid monomer.

[0045] (2) Preparation of water-soluble polyionic liquid

[0046] Take 10 g of water-soluble ionic liquid monomer, initiator azobisisobutyronitrile 0.05 g (0.5 wt%), and polymerize at 60°C for 4 h to obtain a water-soluble polyionic liquid. The molecular weight is 17358 and the viscosity is 7251 mPa·s.

[0047] (3) Preparation of sulfur-carbon batteries

[0048] Take 0.2 g of polyionic liquid and dissolve it in 10 g of deionized water, stir for 1 h until it is completely dissolved, then add 0.2 g of conductive carbon black (super-p), stir for 1 h, then add 1.6 g of sulfur-carbon material (sulfur:carbon = 3:1) and stir for 8 h. The obtained slurry is uniformly scraped on an aluminum foil with a thickness of 300 μm, then placed in an 80°C air oven for 4 h, weighed, transferred to a glove box, and assembled into a button lithium metal battery. After standing for 5 h, test the voltage range of 1.8-2.5 V and the charge-discharge rate of 0.2C.

[0049] Example 2:

[0050] (1) Preparation of water-soluble ionic liquid monomer

[0051] Take 25.0g 3-chloropropionitrile and 50.0g 1-vinylimidazole dissolved in ethyl acetate, 70°C for 48h. After the reaction, 80°C and 10mbar for 40min. After distillation, washed with ethyl acetate three times (separated), 80°C and 10mbar for 40min to get ionic liquid monomer.

[0052] (2) Preparation of water-soluble polyionic liquid

[0053] Take 10g water-soluble ionic liquid monomer, initiator azobisisobutyronitrile 0.05g (0.5wt%), 60°C for 6h to get water-soluble polyionic liquid. Test its molecular weight is 24024, viscosity is 7785mPa·s.

[0054] (3) Preparation of sulfur-carbon battery

[0055] Take 0.2g polyionic liquid dissolved in 10g deionized water, stir for 1h to completely dissolve, then add 0.2g conductive carbon black (super-p), stir for 1h, then add 1.6g sulfur-carbon material (sulfur: carbon = 3:1) and stir for 8h. The obtained slurry is uniformly scraped on aluminum foil. The thickness is 300μm, then placed in 80°C air oven for 4h, weighed in a punch, transferred to a glove box to assemble a button lithium metal battery. After standing for 5h, test the voltage range of 1.8~2.5V, and the charge-discharge rate is 0.2C.

[0056] Example 3:

[0057] (1) Preparation of water-soluble ionic liquid monomer

[0058] Take 25.0g 3-chloropropionitrile and 50.0g 1-vinylimidazole dissolved in ethyl acetate, 70°C for 48h. After the reaction, 80°C and 10mbar for 40min. After distillation, washed with ethyl acetate three times (separated), 80°C and 10mbar for 40min to get ionic liquid monomer.

[0059] (2) Preparation of water-soluble polyionic liquid

[0060] Take 10g water-soluble ionic liquid monomer, initiator azobisisobutyronitrile 0.1g (1wt%), 50°C for 4h to get water-soluble polyionic liquid. Test its molecular weight is 20272, viscosity is 7526mPa·s.

[0061] (3) Preparation of sulfur-carbon battery

[0062] Take 0.2 g of polyionic liquid to dissolve in 10 g of deionized water, stir for 1 h to completely dissolved, then add 0.2 g of conductive carbon black (super-p), stir for 1 h, then add 1.6 g of sulfur-carbon material (sulfur: carbon = 3:1) and stir for 8 h. The obtained slurry is uniformly scraped on aluminum foil. The thickness is 300 μm, then placed in 80 ℃ air oven for 4 h, weighed on punch, transferred to the glove box to assemble the button lithium metal battery. After standing for 5 h, test the voltage range of 1.8-2.5 V, and the charge-discharge rate is 0.2 C.

[0063] Example 4:

[0064] (1) Preparation of water-soluble ionic liquid monomer

[0065] Take 25.0 g of 3-chloropropionitrile and 50.0 g of 1-vinylimidazole to dissolve in ethyl acetate, react at 70 ℃ for 48 h. After the reaction is completed, distill at 80 ℃ and 10 mbar for 40 min. After distillation, wash three times with ethyl acetate (separated), distill at 80 ℃ and 10 mbar for 40 min to obtain the ionic liquid monomer.

[0066] (2) Preparation of water-soluble polyionic liquid

[0067] Take 10 g of water-soluble ionic liquid monomer, initiator azobisisobutyronitrile 0.2 g (2 wt%), polymerize at 60 ℃ for 4 h to obtain water-soluble polyionic liquid. The molecular weight is 15620, and the viscosity is 7162 mPa·s.

[0068] (3) Preparation of sulfur-carbon battery

[0069] Take 0.2 g of polyionic liquid to dissolve in 10 g of deionized water, stir for 1 h to completely dissolved, then add 0.2 g of conductive carbon black (super-p), stir for 1 h, then add 1.6 g of sulfur-carbon material (sulfur: carbon = 3:1) and stir for 8 h. The obtained slurry is uniformly scraped on aluminum foil. The thickness is 300 μm, then placed in 80 ℃ air oven for 4 h, weighed on punch, transferred to the glove box to assemble the button lithium metal battery. After standing for 5 h, test the voltage range of 1.8-2.5 V, and the charge-discharge rate is 0.2 C.

[0070] Example 5:

[0071] (1) Preparation of water-soluble ionic liquid monomer

[0072] Take 25.0 g of 3-chloropropionitrile and 50.0 g of 1-vinylimidazole to dissolve in ethyl acetate, react at 70 ℃ for 48 h. After the reaction is completed, distill at 80 ℃ and 10 mbar for 40 min. After distillation, wash three times with ethyl acetate (separated), distill at 80 ℃ and 10 mbar for 40 min to obtain the ionic liquid monomer.

[0073] (2) Preparation of water-soluble polyionic liquid

[0074] Take 10 g of water-soluble ionic liquid monomer, initiator azobisisobutyronitrile 0.2 g (2 wt%), polymerize at 60°C for 6 h to obtain water-soluble polyionic liquid. The molecular weight is 19752 and the viscosity is 7327 mPa·s.

[0075] (3) Preparation of sulfur-carbon battery

[0076] Take 0.2 g of polyionic liquid and dissolve it in 10 g of deionized water, stir for 1 h until completely dissolved, then add 0.2 g of conductive carbon black (super-p), stir for 1 h, then add 1.6 g of sulfur-carbon material (sulfur: carbon = 3:1) and stir for 8 h. The obtained slurry is uniformly scraped on an aluminum foil with a thickness of 300 μm, then placed in an 80°C air oven for 4 h, weighed on a punch, transferred to a glove box to assemble a button lithium metal battery. After standing for 5 h, test the voltage range of 1.8-2.5 V and the charge-discharge rate of 0.2C.

[0077] Comparative Example 1

[0078] Preparation of sulfur-carbon battery

[0079] Take 0.2 g of polyvinylidene fluoride (PVDF) and dissolve it in 10 g of N-methyl pyrrolidone (NMP), stir for 1 h until completely dissolved, then add 0.2 g of conductive carbon black (super-p), stir for 1 h, then add 1.6 g of sulfur-carbon material (sulfur: carbon = 3:1) and stir for 8 h. The obtained slurry is uniformly scraped on an aluminum foil with a thickness of 300 μm, then placed in an 80°C air oven for 4 h, weighed on a punch, transferred to a glove box to assemble a button lithium metal battery. After standing for 5 h, test the voltage range of 1.8-2.5 V and the charge-discharge rate of 0.2C.

[0080] The conditions of the products prepared in the above examples are shown in Table 1, and the viscosity and molecular weight of each product are controlled in a suitable range. Figures 1-5 It can be seen that by adjusting the amount of initiator and the synthesis conditions such as polymerization temperature and time, the target molecular weight and viscosity of the product can be adjusted and optimized.

[0081] Table 1 Molecular weight and viscosity of each product in the examples

[0082]

[0083] The sulfur-carbon batteries prepared in the above examples and comparative examples were tested for the first week discharge specific capacity and capacity retention rate (50 weeks), and the results are shown in Table 2 and Table 3, respectively. Figures 6-11Compared with general adhesive products, the water-soluble polyionic liquid adhesive can significantly improve the first-week discharge specific capacity and cycle performance of the assembled battery.

[0084] Table 2: Evaluation of the electrical properties of each example and the comparative example

[0085] Initial discharge specific capacity Capacity retention (50 weeks) Example 1 1221 91％ Example 2 1200 95％ Example 3 1264 93％ Example 4 1152 88％ Example 5 1120 90％ Comparative Example 1 1087 85％

[0086] The above description is merely preferred embodiments of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A water-based slurry, characterized in that, The aqueous slurry comprises the following components by weight: water-soluble polyionic liquid binder: conductive agent: active substance = (1~10): (1~20): (70~98); The preparation method of the water-soluble polyionic liquid binder includes the following steps: S1: A quaternization reaction is carried out between vinylimidazolium or vinylpyridine and an alkane containing halogens and polar groups to obtain vinylimidazolium or vinylpyridine with a substituent of Formula II and a halide ion attached to the same N atom on the imidazolium ring or pyridine ring. In Formula II, m is M / 2, where M is 2, 4, or 6; R1 is a nitrile, amino, carboxyl, hydroxyl, or sulfonyl group. ； Wherein, the alkane containing halogen and polar group has the structure of formula III, m is M / 2, M is 2, 4 or 6; R1 is nitrile, amino, carboxyl, hydroxyl or sulfonyl; X is halogen, specifically Cl, Br or I; ； S2: The product obtained in step S1 undergoes an addition polymerization reaction of olefin bonds to obtain the target water-soluble polyionic liquid; The step S1 is carried out at 40~80℃ for 24~48h; The specific operation method of step S2 is to add an initiator to the product obtained in step S1, and carry out a polymerization reaction under heating or light conditions to obtain a water-soluble polyionic liquid product. The water-soluble polyionic liquid binder has the structure of Formula I: ； Where A is an imidazole group or a pyridinyl group; B is a polar group containing a nitrile group, an amino group, a carboxyl group, a hydroxyl group, or a sulfonyl group; X - The halogens are Cl, Br, and I; n is an integer greater than 1; B and X - All are attached to the same N atom on the imidazole or pyridine ring of A; On the imidazole ring or pyridine ring, with B and X - The N atom in the connection is located in a non-adjacent position to the atom connected to the main chain; The molecular weight of the water-soluble polyionic liquid binder is controlled at 5000~50000, and the viscosity is controlled at 6000~10000 mPa·s. The reaction solution of S1 is ethyl acetate; In S2, the initiator is one or more of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dialkyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide thermal initiator, or 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide photoinitiator; The initiator is 0.1-5 wt% of the water-soluble polyionic liquid monomer.

2. The aqueous slurry according to claim 1, characterized in that, In step S1, after the reaction is completed, a purification operation is also included, specifically including distillation at 80°C and 10 mbar for 40 min, followed by washing with ethyl acetate after distillation. In step S2, the thermal polymerization temperature is 40~80 ℃ and the polymerization time is 3~12 h; the photopolymerization uses 365 nm ultraviolet light and the irradiation time is 5 s-10 min.

3. The aqueous slurry according to claim 2, characterized in that, In step S2, the thermal polymerization temperature is 50~60 ℃ and the polymerization time is 4~6 h.

4. The aqueous slurry according to claim 1, characterized in that, The positive electrode material in the active material includes one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, nickel cobalt aluminum ternary, nickel cobalt manganese ternary, sulfur, sulfur-carbon composite material, and sulfides; the negative electrode material in the active material includes one or more of graphite, soft carbon, hard carbon, carbon fiber, carbon black, graphene, carbon nanotubes, lithium titanate, nano-silicon, silicon-carbon composite, silicon oxide, elemental tin, tin oxide, tin cobalt carbon, metallic lithium, metallic sodium, and metallic magnesium; the conductive agent includes one or more of graphite, soft carbon, hard carbon, carbon fiber, carbon black, graphene, and carbon nanotubes.

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