CN112279952B - Hydrophilic lithium sulfonate terpolymer and preparation method thereof - Google Patents
Hydrophilic lithium sulfonate terpolymer and preparation method thereof Download PDFInfo
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- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
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Abstract
A hydrophilic lithium sulfonate terpolymer and a preparation method thereof, wherein the hydrophilic lithium sulfonate terpolymer is a copolymer containing a polyvinylidene fluoride structural unit consisting of vinylidene fluoride monomers, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomers and a perfluoro vinyl ether lithium sulfonate structural unit; the preparation method comprises the following steps: and respectively adding vinylidene fluoride monomer, vinyl pyrrolidone monomer, lithium perfluorovinyl ether sulfonate and initiator into a reaction device, and carrying out one-step copolymerization by adopting a polymerization reaction method to prepare the composite material. The invention keeps the structural advantages of polyvinylidene fluoride, overcomes the defects and improves the chemical stability; by introducing the ion high-efficiency transmission structural unit, the transmission efficiency of lithium ions is optimized, the ionic conductivity of the lithium battery is improved, the polarization in the charging process of the battery can be reduced, and the charge and discharge performance is improved; hydrophilic groups are introduced to improve hydrophilicity, so that the adsorption capacity of the electrolyte and the migration rate of lithium ions are increased.
Description
Technical Field
The invention relates to a lithium ion polymer and a preparation method thereof, in particular to a hydrophilic lithium sulfonate terpolymer and a preparation method thereof, belonging to the technical field of production and manufacturing of lithium ion polymer batteries.
Background
Lithium polymer batteries are the most advanced rechargeable batteries nowadays, and currently, major scientific and technological countries in the world are actively researching and developing.
The polymer lithium ion battery has the characteristics of small volume, light weight, high energy density, small self-discharge, no memory effect, good safety performance, capability of being made into any shape and the like, and meanwhile, the existing lithium ion rechargeable battery has more electrolyte and high flammability and is difficult to ensure in the aspect of safety, and the lithium ion high polymer rechargeable battery uses a porous high polymer material as the electrolyte, so that the electrolyte is reduced, the leakage is difficult to occur, and the safety of the lithium ion high polymer rechargeable battery can be ensured.
Lithium polymer batteries are mainly composed of a positive electrode, a negative electrode, and separator paper, and in the currently developed lithium polymer batteries, polymer materials are mainly applied to the positive electrode and an electrolyte, the material of the positive electrode includes a conductive polymer, an organic sulfur compound, or an inorganic compound used in a general lithium ion secondary battery, and the electrolyte may be a solid or colloidal polymer electrolyte, or an organic electrolyte.
Polyvinylidene fluoride (PVDF) is a homopolymer of VDF and is a thermoplastic fluoropolymer, the repeating unit of the molecular chain of which is-CH2-CF2The PVDF fluororesin has the characteristics of both fluorine-containing resin and general resin due to the special molecular structure, has the characteristics of chemical corrosion resistance, heat resistance and cold resistance, has excellent weather resistance, hydrophobic and oleophobic properties, has the characteristics of low surface energy, melt processability and the like, can be processed to form products with different shapes, and can be widely applied to lithium battery anode materials, binders, cathode materials and battery diaphragms.
The operation process of the lithium battery can be regarded as the reciprocating motion of lithium ions between two poles along with the cyclic intercalation and deintercalation of the lithium ions, so that the polymer used as the lithium battery has higher requirements on the aspects of the electrical conductivity, the lithium ion mobility and the electrochemical stability of the material.
However, because polyvinylidene fluoride is a crystalline polymer, the crystallinity is between 60% and 80%, the dielectric constant and the ohmic resistance are high, and the crystal melting temperature is about 140 ℃, under the normal use temperature of the battery, the PVDF polymer is purely used as a battery material, and the crystalline unit of the PVDF polymer can obstruct the transmission of ions in the electrolytic liquid, thereby greatly reducing the transmission efficiency of the ions and seriously influencing the charge and discharge performance of the lithium battery.
In addition, the hydrophobic property of PVDF can weaken the adsorption capacity of electrolyte and reduce the mobility of lithium ions in reciprocating motion, so that the chemical structure of PVDF homopolymer is optimized to prepare the polyvinylidene fluoride multipolymer with excellent performance, and the method has very important significance in effectively improving the lithium ion mobility of PVDF.
At present, for the defects of PVDF in lithium batteries, the ion transport performance of the material is improved by mostly adopting a mode of introducing a conductive agent containing a lithium sulfonate component by blending, for example:
the invention patent application (application number: 201611173765.0) provides a single ion gel polymer electrolyte and a preparation method thereof;
the invention patent application (application number: 201611145093.2) provides a lithium single-ion conductive solid polymer electrolyte, and the like.
However, although the addition of a conductive agent is effective in improving the electrochemical performance of the material, it reduces the compatibility of PVDF with other materials, weakens the adhesive force of the polymer material itself and the durability of the adhesive force, and causes problems such as easy partial or complete peeling of the electrode binder layer from the current collector, deterioration of load characteristics, and capacity deterioration.
In addition, there is also a related art that introduces a lithium sulfonate structure into a PVDF structure by way of copolymerization to improve ion conductivity, such as:
the invention provides a manufacturing process of an electrolyte membrane special for a solid lithium ion battery (application number: 02138204.2).
However, a large number of carbon-hydrogen bonds (C-H) are introduced in the copolymerization process, the stability of the copolymer is not higher than that of a carbon-fluorine bond (C-F) in the PVDF structure, and the chemical stability of the copolymer obtained in the mode is lower than the original performance of the PVDF homopolymer.
Disclosure of Invention
In order to overcome the defects of the related technology, the invention provides a hydrophilic lithium sulfonate terpolymer and a preparation method thereof, aiming at:
the structural advantages of the existing PVDF are retained and the defects of the PVDF are overcome; meanwhile, a high-efficiency transmission structural unit of lithium ions is introduced, a high-speed transmission channel of the lithium ions is constructed, the transmission efficiency of the lithium ions is optimized, the ionic conductivity of the lithium battery is improved, the polarization of the battery in the charging process is reduced, and the charging and discharging performance of the battery is improved; in addition, by introducing hydrophilic groups, the hydrophilic performance of the PVDF copolymer is improved, and the adsorption capacity of the electrolyte and the migration rate of lithium ions are effectively increased; in addition, a large number of ultrastable structural units are introduced, so that the chemical stability of the lithium battery is greatly improved, and an important polymer material is provided for further research and application of the lithium battery.
In order to achieve the above object, the present invention first provides a hydrophilic lithium sulfonate terpolymer.
A hydrophilic lithium sulfonate terpolymer comprising:
a copolymer consisting of three compound structural units, namely a polyvinylidene fluoride structural unit (A) consisting of x molar parts of vinylidene fluoride monomers, a vinyl pyrrolidone structural unit (B) consisting of y molar parts of vinyl pyrrolidone monomers and a perfluoro vinyl ether lithium sulfonate structural unit (C) consisting of z molar parts of perfluoro vinyl ether lithium sulfonate; and is
The copolymer has the following structural general formula:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the perfluorinated vinyl ether lithium sulfonate structural unit are respectively as follows:
x/(x + y + z) is 0.55-0.85, y/(x + y + z) is 0.05-0.35, and z/(x + y + z) is 0.10-0.40; and is
Among the lithium perfluorovinyl ether sulfonate structural units:
m is an integer of 0 to 10, and n is an integer of 0 to 6.
Further, the method comprises the following steps:
the mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the lithium perfluorovinyl ether sulfonate structural unit are respectively as follows:
x/(x + y + z) is 0.60-0.80, y/(x + y + z) is 0.10-0.30, and z/(x + y + z) is 0.10-0.30; and is
Among the lithium perfluorovinyl ether sulfonate structural units:
m is an integer of 1 to 3, and n is an integer of 0 to 2.
Further, the invention also provides a preparation method of the hydrophilic lithium sulfonate terpolymer, which comprises the following steps:
respectively adding a vinylidene fluoride monomer, a vinyl pyrrolidone monomer, lithium perfluorovinyl ether sulfonate and an initiator into a reaction device, and copolymerizing by adopting a polymerization reaction method to prepare the hydrophilic lithium sulfonate terpolymer;
the reaction formula is as follows:
further, in the above preparation method:
the reaction device is a high-pressure reaction kettle;
the step of respectively adding the vinylidene fluoride monomer, the vinyl pyrrolidone monomer, the lithium perfluorovinyl ether sulfonate and the initiator specifically comprises the following steps:
firstly, adding a vinyl pyrrolidone monomer, lithium perfluorovinyl ether sulfonate and an initiator into the high-pressure reaction kettle, repeatedly evacuating to remove oxygen, then filling vinylidene fluoride monomer gas into the high-pressure reaction kettle in a nitrogen atmosphere, and keeping the pressure in the high-pressure reaction kettle between 1.25 and 1.85 MPa;
the step of preparing the hydrophilic lithium sulfonate terpolymer by copolymerization through a polymerization reaction method specifically comprises the following steps:
slowly heating the materials in the high-pressure reaction kettle to 75-135 ℃, reacting for 24 hours by a polymerization reaction method under mechanical stirring, cooling to room temperature, releasing unreacted gas to obtain a hydrophilic lithium sulfonate terpolymer emulsion, demulsifying the emulsion by an ethanol solution to obtain a broken emulsion, washing the broken emulsion to remove an emulsifier and unreacted vinylidene fluoride monomer, vinylpyrrolidone monomer and lithium perfluorovinyl ether sulfonate, and drying to obtain the hydrophilic lithium sulfonate terpolymer.
Further:
the initiator is one of benzoyl peroxide, azo compounds or persulfate;
the polymerization reaction method is any one of emulsion polymerization, suspension polymerization or aqueous solution polymerization.
And further:
the emulsion polymerization method further comprises an emulsifier, wherein the emulsifier is ammonium perfluorooctanoate.
And further:
the aqueous phase solution polymerization method further comprises a dispersion medium, wherein the dispersion medium is trifluorotrichloroethane.
Further:
after the emulsion is demulsified by an ethanol solution to obtain a broken emulsion, the method also comprises an operation step of dissolving the broken emulsion in an organic solvent, and the broken emulsion dissolved in the organic solvent is subjected to subsequent washing and drying operation steps as required;
the organic solvent is one or a mixture of N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, ethanol, isopropanol, dimethyl sulfoxide or ethyl acetate.
Compared with the prior art, the invention has the beneficial effects and remarkable progresses that:
1) the invention provides a hydrophilic lithium sulfonate terpolymer which comprises three compound structural units, namely a polyvinylidene fluoride structural unit consisting of a vinylidene fluoride monomer, a vinyl pyrrolidone structural unit consisting of a vinyl pyrrolidone monomer and a perfluoro vinyl ether lithium sulfonate structural unit, and not only retains the advantageous skeleton structure (-CH) of polyvinylidene fluoride (PVDF for short in English)2CF2-) ensures that the copolymer has sufficient mechanical strength and thermal stability, and simultaneously can regulate and control the crystallinity and the ion conductivity of the hydrophilic lithium sulfonate terpolymer by regulating and controlling the proportion of an ion structural unit, namely a perfluorinated vinyl ether lithium sulfonate structural unit;
2) the hydrophilic lithium sulfonate terpolymer provided by the invention utilizes the copolymerization of a perfluorinated vinyl ether lithium sulfonate structural unit and a vinylidene fluoride monomer, and introduces a functional ionic group into the terpolymer, and the perfluorinated vinyl ether lithium sulfonate structural unit comprises an ionic group-SO3Li+The perfluoro-linking unit can effectively regulate and control the migration rate of lithium ions in the copolymer;
3) according to the hydrophilic lithium sulfonate terpolymer provided by the invention, the hydrophilic group vinyl pyrrolidone structural unit is introduced into the copolymer structure, so that the hydrophilic performance of the copolymer is improved, and the adsorption capacity of electrolyte and the migration rate of lithium ions can be more effectively increased;
4) the invention provides a hydrophilic lithium sulfonate terpolymer, which is prepared by introducing a large amount of perfluoro structural units (-CF) into the copolymer2CF2-) so that its chemical stability is much higher than that of the structural unit (-CH) of polyvinylidene fluoride2CF2-) thereby further improving chemical stability;
5) the length of the functional ionic group chain segment is adjusted by adopting the perfluoro connecting unit, so that the ionic conductivity of the copolymer is further improved, and the aim of optimizing the ionic transmission efficiency is fulfilled;
6) the preparation method of the hydrophilic lithium sulfonate terpolymer provided by the invention is prepared by copolymerizing three compound monomers including vinylidene fluoride, vinyl pyrrolidone and lithium perfluorovinyl ether sulfonate in one step by adopting a polymerization reaction method, and a subsequent alkali treatment process is not needed as in the prior art, so that an advantageous skeleton structure (-CH) in a polyvinylidene fluoride structural unit is avoided2CF2-) chemical degradation;
7) according to the preparation method of the hydrophilic lithium sulfonate terpolymer, the perfluoro vinyl ether lithium sulfonate in the comonomer has a self-emulsifying function, so that an emulsifier is not needed or is not needed in the polymerization reaction process, the production can be ensured, the production cost can be reduced, and the waste discharge is reduced, so that the preparation method has great popularization and application values.
Detailed Description
In order to make the objects, technical solutions, beneficial effects and significant progress of the embodiments of the present invention clearer, the following describes the technical solutions of the embodiments and cases clearly and completely, and it is obvious that all the described embodiments and cases are only some embodiments and cases of the present invention, but not all embodiments and cases;
based on the embodiments and examples of the present invention, all other embodiments and examples that can be obtained by a person of ordinary skill in the art without any creative effort belong to the protection scope of the present invention.
It should be noted that:
the terms "first," "second," and the like in the description and in the claims, are used for distinguishing between different elements and not necessarily for describing a particular sequential or chronological order;
furthermore, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to the listed steps or elements, but may alternatively include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus;
in addition, in the description and claims of the present invention:
the polyvinylidene fluoride structure unit composed of x mole parts of vinylidene fluoride monomer, the vinyl pyrrolidone structure unit composed of y mole parts of vinyl pyrrolidone monomer and the perfluoro vinyl ether lithium sulfonate structure unit composed of z mole parts of perfluoro vinyl ether lithium sulfonate are respectively the structure units in the dotted line frame marked by A, B and C in the following structural general formula;
the general structural formula is as follows:
in the above structural general formula:
x, y and z are respectively the respective mole fractions of a polyvinylidene fluoride structural unit, a vinyl pyrrolidone structural unit and a lithium perfluorovinyl ether sulfonate structural unit; and is
The polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the perfluoro vinyl ether lithium sulfonate structural unit respectively have the following molar parts:
x/(x + y + z), y/(x + y + z) and z/(x + y + z).
It should be further noted that the following specific embodiments and cases may be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments and cases.
The technical means of the present invention will be described in detail below with specific examples.
Example one
This example provides a hydrophilic lithium sulfonate terpolymer.
It should be noted that:
the monomer compounds mentioned in the examples are commercially available.
The present embodiment provides a hydrophilic lithium sulfonate terpolymer, which includes:
a copolymer consisting of three compound structural units, namely a polyvinylidene fluoride structural unit (A) consisting of x molar parts of vinylidene fluoride monomers, a vinyl pyrrolidone structural unit (B) consisting of y molar parts of vinyl pyrrolidone monomers and a perfluoro vinyl ether lithium sulfonate structural unit (C) consisting of z molar parts of perfluoro vinyl ether lithium sulfonate;
and the copolymer has the following structural general formula:
wherein:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the perfluoro vinyl ether lithium sulfonate structural unit are respectively as follows:
x/(x + y + z) is 0.55 to 0.85, y/(x + y + z) is 0.05 to 0.35, and z/(x + y + z) is 0.10 to 0.40; and is
In the lithium perfluorovinyl ether sulfonate structural unit:
m is an integer of 0 to 10, and n is an integer of 0 to 6.
As a preferred technical solution, further:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the perfluoro vinyl ether lithium sulfonate structural unit are respectively as follows:
x/(x + y + z) is 0.60-0.80, y/(x + y + z) is 0.10-0.30, and z/(x + y + z) is 0.10-0.30; and is
In the lithium perfluorovinyl ether sulfonate structural unit:
m is an integer of 1 to 3, and n is an integer of 0 to 2.
From the above description and the general structural formulae, it can be found that:
first, the hydrophilic lithium sulfonate terpolymer provided in this embodiment includes three compound structural units, i.e., a polyvinylidene fluoride structural unit composed of a vinylidene fluoride monomer, a vinyl pyrrolidone structural unit composed of a vinyl pyrrolidone monomer, and a perfluoro vinyl ether lithium sulfonate structural unit composed of a perfluoro vinyl ether lithium sulfonate, so that the dominant framework structure (-CH) of polyvinylidene fluoride (PVDF for short in english) is retained2CF2-) ensures that the copolymer has sufficient mechanical strength and thermal stability, and simultaneously can regulate and control the crystallinity and the ion conductivity of the hydrophilic lithium sulfonate terpolymer by regulating and controlling the proportion of an ion structural unit, namely a perfluorinated vinyl ether lithium sulfonate structural unit;
secondly, in the hydrophilic lithium sulfonate terpolymer provided by this embodiment, a perfluoro vinyl ether lithium sulfonate structural unit is copolymerized with a vinylidene fluoride monomer, SO that a functional ionic group is introduced into the copolymer, and the perfluoro vinyl ether lithium sulfonate structural unit includes an ionic group-SO3Li+The perfluoro-linking unit can effectively regulate and control the migration rate of lithium ions in the copolymer;
thirdly, in the hydrophilic lithium sulfonate terpolymer provided by the embodiment, the hydrophilic group vinyl pyrrolidone is introduced into the copolymer structure, so that the hydrophilic performance of the copolymer is improved, and the adsorption capacity of the electrolyte and the migration rate of lithium ions can be effectively increased;
in addition, this example provides a hydrophilic lithium sulfonate terpolymer, which is prepared by introducing a large amount of perfluoro structural units (-CF) into the copolymer2CF2-) so that its chemical stability is much higher than that of the structural unit (-CH) of polyvinylidene fluoride2CF2-) thereby further improving chemical stability;
in addition, the length of the functional ionic group chain segment is adjusted by adopting the perfluoro coupling unit, so that the ionic conductivity of the copolymer is further improved, and the purpose of optimizing the ionic transmission efficiency is achieved.
Example two
This example provides a method for preparing a hydrophilic lithium sulfonate terpolymer.
It should be noted that:
the reaction apparatus, monomer compound, initiator, emulsifier, demulsifier, and organic solvent referred to in this example are commercially available.
A preparation method of a hydrophilic lithium sulfonate terpolymer comprises the following steps:
respectively adding vinylidene fluoride monomer, vinyl pyrrolidone monomer, lithium perfluorovinyl ether sulfonate and initiator into a reaction device, and copolymerizing by adopting a polymerization reaction method to prepare a hydrophilic lithium sulfonate terpolymer;
the reaction formula is as follows:
further, in the above preparation method:
the reaction device is a high-pressure reaction kettle;
the step of respectively adding the vinylidene fluoride monomer, the vinyl pyrrolidone monomer, the lithium perfluorovinyl ether sulfonate and the initiator specifically comprises the following steps:
firstly, adding a vinyl pyrrolidone monomer, lithium perfluorovinyl ether sulfonate and an initiator into a high-pressure reaction kettle, repeatedly evacuating to remove oxygen, then filling vinylidene fluoride monomer gas into the high-pressure reaction kettle in a nitrogen atmosphere, and keeping the pressure in the high-pressure reaction kettle between 1.25 and 1.85 MPa;
the step of preparing the hydrophilic lithium sulfonate terpolymer by copolymerization with a polymerization reaction method specifically comprises the following steps:
slowly heating the materials in the high-pressure reaction kettle to 75-135 ℃, reacting for 24 hours by a polymerization reaction method under mechanical stirring, cooling to room temperature, releasing unreacted gas to obtain a hydrophilic lithium sulfonate terpolymer emulsion, performing emulsion breaking on the emulsion by using an ethanol solution to obtain a broken emulsion, washing the broken emulsion to remove an emulsifier, unreacted vinylidene fluoride monomer, vinyl pyrrolidone monomer and lithium perfluorovinyl ether sulfonate, and drying to obtain the hydrophilic lithium sulfonate terpolymer.
In this embodiment:
the initiator can be one of benzoyl peroxide, azo compounds or persulfate;
the polymerization method may be any of emulsion polymerization, suspension polymerization, or aqueous solution polymerization.
During the preparation process by using an emulsion polymerization method, the emulsion can also comprise an emulsifier, wherein the emulsifier is ammonium perfluorooctanoate;
in the preparation process by using the aqueous phase solution polymerization method, the aqueous phase solution polymerization method also comprises a dispersion medium, and the dispersion medium can be trifluorotrichloroethane.
In addition, after the emulsion is demulsified by the ethanol solution to obtain the demulsifying agent, the demulsifying agent can be dissolved in the organic solvent, and the subsequent washing and drying operation steps can be carried out on the demulsifying agent dissolved in the organic solvent at any time according to the requirement;
the organic solvent may be one or more of N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, ethanol, isopropanol, dimethylsulfoxide, or ethyl acetate.
From the above description, it can be found that:
first, the preparation method of the hydrophilic lithium sulfonate terpolymer provided in this embodiment adoptsThe polyvinylidene fluoride monomer, the vinyl pyrrolidone monomer and the lithium perfluorovinyl ether sulfonate are copolymerized in one step by a polymerization reaction method, and a subsequent alkali treatment process is not needed as in the prior art, so that the dominant framework structure (-CH) in the polyvinylidene fluoride structural unit is avoided2CF2-) chemical degradation;
secondly, in the preparation method of the hydrophilic lithium sulfonate terpolymer provided by the embodiment, because the perfluorinated vinyl ether lithium sulfonate in the terpolymer has a self-emulsifying function, an emulsifier is not needed or is less needed in the polymerization reaction process, so that the production can be ensured, the production cost can be reduced, and the waste discharge can be reduced;
in addition, according to the preparation method of the hydrophilic lithium sulfonate terpolymer provided by the embodiment, the molecular weight, the hydrophilicity, the molecular weight distribution and the crystallinity of the terpolymer can be controlled by adjusting the feeding molar ratio of the three monomers;
in addition, according to the preparation method of the hydrophilic lithium sulfonate terpolymer provided by the embodiment, the crystallinity of the terpolymer can be further regulated and controlled by regulating the length of the linking group in the structural unit of the lithium perfluorovinyl ether sulfonate, the crystal melting temperature of the PVDF is reduced, and the problems of low ion transmission efficiency, poor charge and discharge capacity, poor load characteristics and the like when the PVDF is used alone as a binder in the prior art are solved.
According to the above description, it can be seen that the hydrophilic lithium sulfonate terpolymer and the preparation method thereof provided by the invention have at least the following advantages:
1) the hydrophilic lithium sulfonate terpolymer provided by the invention reserves the dominant unit- (CH) of PVDF2CF2) x-, thereby ensuring that the copolymer has enough mechanical strength and thermal stability, and simultaneously, the crystallinity and the ionic conductivity of the terpolymer can be regulated and controlled by regulating and controlling the proportion of the ionic structural units;
2) the hydrophilic lithium sulfonate terpolymer provided by the invention introduces functional ions by copolymerization of perfluoro vinyl ether lithium sulfonate and vinylidene fluoride monomerA group comprising an ionic group-SO3Li+The perfluoro-linking unit can effectively regulate and control the migration rate of the lithium ions of the terpolymer;
3) the vinyl pyrrolidine unit in the structure of the hydrophilic lithium sulfonate terpolymer provided by the invention can improve the hydrophilic property of the copolymer and effectively increase the adsorption capacity of electrolyte and the migration rate of lithium ions;
4) the hydrophilic lithium sulfonate terpolymer provided by the invention is prepared by one-step copolymerization, and a subsequent alkali treatment process is not needed, so that the chemical degradation of a PVDF structure is avoided;
5) in the hydrophilic lithium sulfonate terpolymer provided by the invention, the copolymerization monomer of the perfluorinated vinyl ether lithium sulfonate has a self-emulsifying function, and the use of an emulsifier can be avoided in the polymerization process, so that the emission of discarded materials is reduced, and the environment is protected;
6) in the hydrophilic lithium sulfonate terpolymer provided by the invention, a large amount of perfluoro structural units (-CF) are introduced2CF2-) with chemical stability much higher than that of PVDF structural unit (-CH)2CF2-) to make the terpolymer more chemically stable;
7) the hydrophilic lithium sulfonate terpolymer provided by the invention adopts the perfluoro coupling unit to adjust the length of the functional ionic group chain segment, so that the ionic conductivity of the terpolymer can be further adjusted, and the purpose of optimizing the ionic transmission efficiency is achieved.
In summary, it can be seen that:
the hydrophilic lithium sulfonate terpolymer and the preparation method thereof provided by the invention have high popularization and application values.
To further assist understanding of the technical solutions of the present invention, the technical solutions of the present invention are described in more detail below by providing several specific embodiments.
Cases 1,
Adding a vinyl pyrrolidone monomer, lithium perfluorovinyl ether sulfonate and a benzoyl peroxide initiator into a high-pressure reaction kettle with the pressure resistance of 10MPa, repeatedly evacuating to remove oxygen, and then filling vinylidene fluoride gas in a nitrogen atmosphere;
wherein:
the mole fraction ratio of a polyvinylidene fluoride structural unit consisting of vinylidene fluoride gas, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomer and a perfluoro vinyl ether lithium sulfonate structural unit consisting of perfluoro vinyl ether lithium sulfonate is as follows:
vinylidene fluoride structural units, vinyl pyrrolidone structural units and perfluoro vinyl ether sulfonic acid lithium structural units are 0.80: 0.10; and is
In the lithium perfluorovinyl ether sulfonate structural unit: m is 1, n is 1;
keeping the pressure of the reaction kettle between 1.25MPa, slowly heating to 100 ℃, adding ammonium perfluorooctanoate as an emulsifier under mechanical stirring, and carrying out polymerization reaction for 24 hours by adopting an emulsion polymerization method;
after the reaction is finished, cooling the feed liquid to room temperature, releasing unreacted gas to obtain uniform terpolymer emulsion, demulsifying the emulsion by using an ethanol solution, washing, removing an emulsifier, unreacted vinylidene fluoride gas, vinyl pyrrolidone and lithium perfluorovinyl ether sulfonate, and drying to obtain the target product, namely the hydrophilic lithium sulfonate terpolymer.
Case 2,
The operation process and method of the present case are basically the same as those of case 1, and the differences are only that:
the mole fraction ratio of a polyvinylidene fluoride structural unit consisting of vinylidene fluoride gas, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomer and a perfluoro vinyl ether lithium sulfonate structural unit consisting of perfluoro vinyl ether lithium sulfonate is as follows:
vinylidene fluoride structural units, vinyl pyrrolidone structural units, and perfluoro vinyl ether sulfonic acid lithium structural units are 0.75:0.11: 0.14; and is
In the lithium perfluorovinyl ether sulfonate structural unit: m is 1, n is 1;
the pressure of the reaction kettle is kept at 1.50MPa, and the materials are slowly heated and kept at about 95 ℃;
further:
the polymerization reaction still adopts emulsion polymerization method without adding emulsifier, and takes the perfluoro vinyl ether sulfonic acid lithium as the emulsifier to carry out the polymerization reaction.
Cases 3,
The operation process and method of the present case are basically the same as those of case 1, and the differences are only that:
the initiator adopts azo compound;
the mole fraction ratio of a polyvinylidene fluoride structural unit consisting of vinylidene fluoride gas, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomer and a perfluoro vinyl ether lithium sulfonate structural unit consisting of perfluoro vinyl ether lithium sulfonate is as follows:
vinylidene fluoride structural units, vinyl pyrrolidone structural units, and perfluoro vinyl ether sulfonic acid lithium structural units are 0.80:0.10: 0.10; and is
In the lithium perfluorovinyl ether sulfonate structural unit: m is 3 and n is 2;
the pressure of the reaction kettle is kept at 1.85MPa, and the materials are slowly heated and kept at about 75 ℃;
in addition, the polymerization reaction adopts a suspension polymerization method and does not add an emulsifier.
Case 4,
The operation process and method of the present case are basically the same as those of case 3, and the differences are only that:
the mole fraction ratio of a polyvinylidene fluoride structural unit consisting of vinylidene fluoride gas, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomer and a perfluoro vinyl ether lithium sulfonate structural unit consisting of perfluoro vinyl ether lithium sulfonate is as follows:
vinylidene fluoride structural units, vinyl pyrrolidone structural units, and perfluoro vinyl ether sulfonic acid lithium structural units are 0.74:0.15: 0.11; and is
The pressure of the reaction kettle is kept at 1.60MPa, and the materials are slowly heated and kept at about 135 ℃;
in the lithium perfluorovinyl ether sulfonate structural unit: m is 2 and n is 2.
Cases 5,
The operation process and method of the present case are basically the same as those of case 1, and the differences are only that:
the initiator adopts sulfate;
the mole fraction ratio of a polyvinylidene fluoride structural unit consisting of vinylidene fluoride gas, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomer and a perfluoro vinyl ether lithium sulfonate structural unit consisting of perfluoro vinyl ether lithium sulfonate is as follows:
vinylidene fluoride structural units, vinyl pyrrolidone structural units and perfluoro vinyl ether sulfonic acid lithium structural units are 0.60: 0.30: 0.10; and is
In the lithium perfluorovinyl ether sulfonate structural unit: m is 1, n is 1;
the pressure of the reaction kettle is kept at 1.75MPa, and the materials are slowly heated and kept at about 85 ℃;
further:
the polymerization reaction adopts an aqueous solution polymerization method, and adopts trifluorotrichloroethane as a dispersion medium without adding an emulsifier to carry out polymerization reaction to obtain a terpolymer emulsion of polyvinylidene fluoride, vinyl pyrrolidone and perfluoro vinyl ether lithium sulfonate;
and demulsifying the emulsion by using an ethanol solution, dissolving the emulsion in one or more of N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, ethanol, isopropanol, dimethyl sulfoxide and ethyl acetate for storage, washing when necessary, removing an emulsifier, an organic solvent, unreacted vinylidene fluoride gas, vinylpyrrolidone and lithium perfluorovinyl ether sulfonate, and drying to obtain the target product, namely the hydrophilic lithium sulfonate terpolymer.
Cases 6,
The operation process and method of the present case are basically the same as those of case 5, and the differences are only that:
the mole fraction ratio of a polyvinylidene fluoride structural unit consisting of vinylidene fluoride gas, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomer and a perfluoro vinyl ether lithium sulfonate structural unit consisting of perfluoro vinyl ether lithium sulfonate is as follows:
vinylidene fluoride structural units, vinyl pyrrolidone structural units and perfluoro vinyl ether sulfonic acid lithium structural units are 0.85: 0.15: 0.05; and is
In the lithium perfluorovinyl ether sulfonate structural unit: m is 1, n is 2;
in addition, the pressure of the reaction kettle is kept at 1.55MPa, and the materials are slowly heated and maintained at about 105 ℃.
The following are specifically mentioned:
the above cases are only provided for illustrating the technical scheme of the present invention, and for the structural unit of lithium perfluorovinyl ether sulfonate, besides the structural units of the specific structural formula listed in the above cases, the structural unit formula is as follows:
the structural units marked with m being an integer of 0 to 10 and n being an integer of 0 to 6, especially the structural units marked with m being an integer of 1 to 3 and n being an integer of 0 to 2, have the same or similar functions and effects as the products obtained in the above cases, and the copolymerization method and control conditions are the same or similar to the methods and conditions listed in the above cases and included in the ranges listed in the above embodiments.
To further illustrate the embodiments of the present invention and the advantages achieved by the various cases, the following description will be made with reference to specific effect embodiments.
It should be noted that:
the detection instrument and the detection reagent according to the following effect examples are commercially available, and the detection method used is a conventional technique that can be searched.
Effect embodiment:
1) determination of the average molecular weight of the copolymer
The average molecular weight was measured by a high temperature gel permeation chromatograph model PL-220, and the average molecular weight was obtained by measuring the weight average molecular weight of each copolymer.
In the detection process, N-dimethylformamide is taken as a solvent, the detection is carried out at 160 ℃, and relevant data are processed by taking narrow-distribution vinylidene fluoride as a standard sample and adopting a universal correction method.
The average molecular weight values of the copolymers of cases 1 to 6 obtained by the test are shown in Table 1.
2) Determination of copolymer crystallinity
The crystallinity of the copolymer was measured by DSC2910 Differential Scanning Calorimeter (British name: Differential Scanning Calorimeter) manufactured by TA of America, and the copolymer was tested under nitrogen protection according to the method specified in GB/T19466.3-2004.
During detection, the sample is heated from room temperature to 150 ℃ at the speed of 10 ℃/min, is kept warm for 5min, is naturally cooled to room temperature, is subjected to temperature rise scanning at the speed of 10 ℃/min (from room temperature to 150 ℃), and is recorded with a corresponding DSC curve to obtain the corresponding melting enthalpy delta HfThen, the percent crystallinity of each copolymer was calculated according to the following formula:
Xi＝(ΔHf÷293)×100％
in the formula:
ΔHfis the enthalpy of fusion of the sample polymer, given in units of J.g-1；
293 is the enthalpy of fusion at 100% crystallinity of polyethylene, in J.g-1。
The percent crystallinity of the copolymers obtained in cases 1 to 6 was examined and is shown in Table 1.
3) Determination of the free volume of the copolymer
The free volume of the copolymer is measured by soaking the copolymer in 80 ℃ propylene carbonate serving as an electrolyte of a lithium battery for 10 hours, measuring the volume of the copolymer before and after soaking, and determining the difference value of the volume before and after soaking as the free volume of the copolymer, namely:
Vf＝V－Vo
in the formula:
Vois the volume of the initial copolymer sample;
v is the volume of the copolymer sample after soaking.
The free volume of each copolymer of cases 1 to 6 obtained by the examination is shown in Table 1.
3) Determination of the Ionic conductivity of the copolymer
The determination of the ionic conductivity of the copolymer is to thermally press each copolymer into a membrane at 150 ℃, then test the membrane resistance R of the membrane after swelling of propylene carbonate on the membrane by adopting a two-electrode method, the adopted detection instrument is an electrochemical workstation Autolab PGSTA302, the frequency interval is 106-10 Hz, and the conductivity is calculated by the following calculation formula:
σ＝L/RS
in the formula:
σ is the conductivity (s/cm) of the sample after swelling;
l is the thickness (cm) of the swollen membrane;
r is the resistance (omega) of the membrane after swelling;
s is the area (cm) of the test portion of the sample after swelling2)。
The ionic conductivity of the copolymers of cases 1 to 6 was measured as shown in Table 1.
TABLE 1
From the data listed in table 1, it can be seen that:
the average molecular weight, the crystallinity percentage, the free volume percentage and the ionic conductivity index of the copolymer obtained in cases 1-6 can meet the expected requirements, a high-speed transmission channel of lithium ions can be constructed in the copolymer structure, the transmission efficiency of the lithium ions is optimized, the ionic conductivity of a lithium battery is improved, the polarization of the battery in the charging process is reduced, and the charge and discharge performance of the battery is improved; by regulating and controlling the physical properties such as the free volume, the crystallinity and the like in the copolymer, the adsorption capacity to the electrolyte and the migration rate of lithium ions can be effectively increased, and a new important polymer material is provided for the further development and application of the lithium battery.
During the description of the above description:
the description of the terms "this embodiment," "an embodiment of the invention," "as shown at … …," "further," "as an alternative solution," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or case is included in at least one embodiment or case of the invention;
in this specification, the schematic representations of the terms used above are not necessarily for the same embodiment or case, and the particular features, structures, materials, or characteristics described, etc., may be combined or matched in any suitable manner in any one or more embodiments or cases;
furthermore, one of ordinary skill in the art may combine or combine various embodiments or cases and features of various embodiments or cases described herein without creating inconsistencies.
Finally, it should be noted that:
although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made on the technical solutions described in the foregoing embodiments, or some or all of the technical features of the embodiments can be equivalently replaced, and the corresponding technical solutions do not depart from the technical solutions of the embodiments of the present invention.
Claims (9)
1. A hydrophilic lithium sulfonate terpolymer comprising:
a copolymer consisting of three compound structural units, namely a polyvinylidene fluoride structural unit (A) consisting of x molar parts of vinylidene fluoride monomers, a vinyl pyrrolidone structural unit (B) consisting of y molar parts of vinyl pyrrolidone monomers and a perfluoro vinyl ether lithium sulfonate structural unit (C) consisting of z molar parts of perfluoro vinyl ether lithium sulfonate; and is
The copolymer has the following structural general formula:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the perfluorinated vinyl ether lithium sulfonate structural unit are respectively as follows:
x/(x + y + z) is 0.55-0.85, y/(x + y + z) is 0.05-0.35, and z/(x + y + z) is 0.10-0.40; and is
Among the lithium perfluorovinyl ether sulfonate structural units:
m is an integer of 0 to 10, and n is an integer of 0 to 6.
2. The hydrophilic lithium sulfonate terpolymer of claim 1, wherein:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the perfluorinated vinyl ether lithium sulfonate structural unit are respectively as follows:
x/(x + y + z) is 0.60-0.80, y/(x + y + z) is 0.10-0.30, and z/(x + y + z) is 0.10-0.30; and is
Among the lithium perfluorovinyl ether sulfonate structural units:
m is an integer of 1 to 3, and n is an integer of 0 to 2.
3. A method for preparing the hydrophilic lithium sulfonate terpolymer of claim 1 or 2, comprising the steps of:
respectively adding a vinylidene fluoride monomer, a vinyl pyrrolidone monomer, lithium perfluorovinyl ether sulfonate and an initiator into a reaction device, and copolymerizing by adopting a polymerization reaction method to prepare the hydrophilic lithium sulfonate terpolymer;
the reaction formula is as follows:
4. the method of claim 3, wherein the step of preparing the hydrophilic lithium sulfonate terpolymer comprises:
the reaction device is a high-pressure reaction kettle;
the step of respectively adding the vinylidene fluoride monomer, the vinyl pyrrolidone monomer, the lithium perfluorovinyl ether sulfonate and the initiator specifically comprises the following steps:
firstly, adding a vinyl pyrrolidone monomer, lithium perfluorovinyl ether sulfonate and an initiator into the high-pressure reaction kettle, repeatedly evacuating to remove oxygen, then filling vinylidene fluoride monomer gas into the high-pressure reaction kettle in a nitrogen atmosphere, and keeping the pressure in the high-pressure reaction kettle between 1.25 and 1.85 MPa;
the step of preparing the hydrophilic lithium sulfonate terpolymer by copolymerization through a polymerization reaction method specifically comprises the following steps:
slowly heating the materials in the high-pressure reaction kettle to 75-135 ℃, reacting for 24 hours by a polymerization reaction method under mechanical stirring, cooling to room temperature, releasing unreacted gas to obtain a hydrophilic lithium sulfonate terpolymer emulsion, demulsifying the emulsion by an ethanol solution to obtain a demulsified emulsion, washing the demulsified emulsion to remove an emulsifier, unreacted vinylidene fluoride monomer, vinyl pyrrolidone monomer and lithium perfluorovinyl ether sulfonate, and drying to obtain the hydrophilic lithium sulfonate terpolymer.
5. The method of preparing the hydrophilic lithium sulfonate terpolymer of claim 4, wherein: the initiator is one of benzoyl peroxide, azo compounds or persulfate.
6. The method of preparing the hydrophilic lithium sulfonate terpolymer of claim 4, wherein: the polymerization reaction method is any one of emulsion polymerization, suspension polymerization or aqueous solution polymerization.
7. The method of preparing a hydrophilic lithium sulfonate terpolymer according to claim 6, wherein: the emulsion polymerization method further comprises an emulsifier, wherein the emulsifier is ammonium perfluorooctanoate.
8. The method of preparing a hydrophilic lithium sulfonate terpolymer according to claim 6, wherein: the aqueous phase solution polymerization method further comprises a dispersion medium, wherein the dispersion medium is trifluorotrichloroethane.
9. The method of preparing the hydrophilic lithium sulfonate terpolymer of claim 4, wherein:
after the emulsion is demulsified by an ethanol solution to obtain a broken emulsion, the method also comprises an operation step of dissolving the broken emulsion in an organic solvent, and the broken emulsion dissolved in the organic solvent is subjected to subsequent washing and drying operation steps as required;
the organic solvent is one or a mixture of N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, ethanol, isopropanol, dimethyl sulfoxide or ethyl acetate.
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