CN112341562A - Hydrophilic lithium carbonate terpolymer and preparation method thereof - Google Patents
Hydrophilic lithium carbonate terpolymer and preparation method thereof Download PDFInfo
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Abstract
A hydrophilic lithium carbonate terpolymer and a preparation method thereof, wherein the hydrophilic lithium carbonate terpolymer comprises a polyvinylidene fluoride structural unit consisting of vinylidene fluoride monomers, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomers and a vinyl-alkyl lithium carbonate structural unit; the preparation method is that vinylidene fluoride monomer, vinyl pyrrolidone monomer, vinyl-alkyl lithium carbonate monomer and initiator are respectively added into a reaction device, and copolymerization is carried out by adopting a polymerization reaction method. The invention keeps the structural advantages of the polyvinylidene fluoride, overcomes the defects of the polyvinylidene fluoride and improves the thermal stability; the crystallinity, the ionic conductivity and the ionic migration rate of the copolymer can be effectively regulated and controlled by regulating and controlling the proportion of the ionic structural units, so that the aim of optimizing the ionic transmission is fulfilled; hydrophilic groups are introduced to improve hydrophilicity, and the adsorption capacity of the electrolyte and the migration rate of lithium ions are increased; the physical and chemical properties of the copolymer can be effectively regulated and controlled.
Description
Technical Field
The invention relates to a lithium ion polymer and a preparation method thereof, in particular to a hydrophilic lithium carbonate terpolymer and a preparation method thereof, belonging to the technical field of production and manufacture of lithium ion polymer batteries.
Background
The lithium ion polymer 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.
The existing lithium ion rechargeable battery has more electrolyte, high flammability and difficult guarantee in safety, while the lithium ion polymer rechargeable battery uses porous polymer material as electrolyte, so that the electrolyte is reduced, the leakage is not easy to occur, and the safety of the lithium ion polymer rechargeable battery can be guaranteed, so that the lithium ion polymer rechargeable battery becomes the most advanced rechargeable battery at present, and the major science and technology strong countries in the world are researched and developed vigorously at present.
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.
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.
Polyvinylidene fluoride (PVDF) is a homopolymer of VDF (VDF), a thermoplastic fluoropolymer with a repeating unit of the molecular chain of-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, and has excellent weather resistance, hydrophobic and oleophobic properties and low surface energyAnd the lithium ion battery can be processed into products with different shapes by virtue of the characteristics of melt processing and the like, and can be widely applied to lithium battery anode materials, binders, cathode materials and battery separators.
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, blending and introducing a conductive agent such as lithium carbonate are mostly used to improve the ion transmission performance of materials, for example:
the invention provides a high-safety lithium ion battery anode slurry and a preparation method thereof (application number: 201610061070.7);
the invention patent application (application number: 201811642119.3) provides a foamed graphite sheet for a negative electrode of a lithium battery and a preparation method thereof;
the invention provides a lithium battery anode with high capacity and high safety performance and a preparation method thereof, and the like, which are provided by the invention patent (application number: 201610887432.8).
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.
Disclosure of Invention
In order to overcome the defects of the related technology, the invention particularly provides a hydrophilic lithium carbonate 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, by introducing a large amount of polar groups, the physical properties such as viscosity, solubility, crystallinity and the like of the copolymer are effectively regulated and controlled, and an important polymer material is provided for further research and application of the lithium battery.
To achieve the above object, the present invention provides a hydrophilic lithium carbonate terpolymer.
A hydrophilic lithium carbonate 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 vinyl-alkyl lithium carbonate structural unit (C) consisting of z molar parts of vinyl-alkyl lithium carbonate monomers;
and the copolymer has the following structural general formula:
further:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the vinyl-alkyl lithium carbonate 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 vinyl-alkyl lithium carbonate monomers:
n is an integer of 1 or more.
Further, the method comprises the following steps:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the vinyl-alkyl lithium carbonate 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 vinyl-alkyl lithium carbonate monomers:
n is an integer of 2 to 6.
Further, the invention also provides a preparation method of the hydrophilic lithium carbonate terpolymer, which comprises the following steps:
respectively adding a vinylidene fluoride monomer, a vinyl pyrrolidone monomer, a vinyl-alkyl lithium carbonate monomer and an initiator into a reaction device, and copolymerizing by adopting a polymerization reaction method to prepare the hydrophilic lithium carbonate terpolymer;
the reaction formula is as follows:
further, in the above preparation method:
the reaction device is a high-pressure reaction kettle;
in the step of respectively adding the vinylidene fluoride monomer, the vinyl pyrrolidone monomer, the vinyl-alkyl lithium carbonate monomer and the initiator, the method specifically comprises the following steps:
firstly, adding a vinyl pyrrolidone monomer, a vinyl-alkyl lithium carbonate monomer and an initiator into the high-pressure reaction kettle, repeatedly evacuating to remove oxygen, then filling a vinylidene fluoride monomer gas 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 carbonate 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 carbonate 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, vinyl pyrrolidone monomer and vinyl-alkyl lithium carbonate monomer, and drying to obtain the hydrophilic lithium carbonate 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 also comprises an emulsifier, wherein the emulsifier is ammonium perfluorooctanoate;
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 carbonate terpolymer, which comprises three compound structural units, namely a polyvinylidene fluoride structural unit consisting of vinylidene fluoride monomers, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomers and a vinyl-alkyl lithium carbonate structural unit, and is a novel polymer material for lithium battery research and application;
2) the hydrophilic lithium carbonate terpolymer provided by the invention not only retains the advantageous structural unit- (CH) of the existing PVDF material2CF2)xSo as to ensure that the copolymer has enough mechanical strength and thermal stability, and simultaneously, the crystallinity and the ionic conductivity of PVDF in the terpolymer can be regulated and controlled by regulating and controlling the proportion of ionic structural units;
3) the hydrophilic lithium carbonate terpolymer provided by the invention introduces functional ionic group-COOLi through a copolymerized vinyl-alkyl lithium carbonate structural unit+And an alkyl linking group- (CH)2)nThe migration rate of lithium ions in the terpolymer can be effectively regulated and controlled;
4) the invention provides a hydrophilic lithium carbonate terpolymer, which adopts alkyl linking group- (CH)2)nThe length of the functional ionic group chain segment is adjusted, so that the crystallinity of the terpolymer is further adjusted, and the aim of optimizing the ion transmission efficiency is fulfilled;
5) in the hydrophilic lithium carbonate terpolymer provided by the invention, the hydrophilicity of the terpolymer is improved through a copolymerized vinyl pyrrolidone structural unit, so that the adsorption capacity of electrolyte and the migration rate of lithium ions are effectively increased;
6) according to the hydrophilic lithium carbonate terpolymer provided by the invention, by introducing a large number of polar groups such as ester bonds and carbonate bonds, the physical properties such as viscosity, solubility and crystallinity of the terpolymer can be effectively regulated and controlled;
7) the hydrophilic lithium carbonate terpolymer provided by the invention is prepared by one-step copolymerization of a polymerization reaction method, and the hydrophilic lithium carbonate terpolymer comprises a polyvinylidene fluoride structural unit consisting of vinylidene fluoride monomers, a vinyl pyrrolidone structural unit consisting of vinyl pyrrolidone monomers and a vinyl-alkyl lithium carbonate structural unit, does not need a subsequent alkali treatment process, and avoids- (CH) in the copolymer2CF2)xChemical degradation of the structure, which guarantees the structural strength of the copolymer;
8) the preparation method of the hydrophilic lithium carbonate terpolymer has a certain self-emulsifying function of the vinyl-alkyl lithium carbonate structural unit in the copolymer, 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, thereby having great popularization and application values.
Detailed Description
In order to make the objects, technical solutions, advantages and significant progress of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments and cases of the present invention, 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;
all other embodiments and examples which can be obtained by a person skilled in the art without any inventive step based on the embodiments and examples of the present invention are within the scope of the present invention.
It should be noted that:
the terms "first," "second," and the like in the description and in the claims of the present invention are used for distinguishing between different objects and not necessarily for describing a particular sequential 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 consisting of x mole parts of vinylidene fluoride monomer, the vinyl pyrrolidone structure unit consisting of y mole parts of vinyl pyrrolidone monomer and the vinyl-lithium alkyl carbonate structure unit consisting of z mole parts of vinyl-lithium alkyl carbonate monomer are respectively structure units in a 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 general structural formula:
x, y and z are respectively the respective mole fractions of a polyvinylidene fluoride structural unit, a vinyl pyrrolidone structural unit and a vinyl-alkyl lithium carbonate structural unit; and is
The polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the vinyl-alkyl lithium carbonate structural unit respectively have the following mole fraction:
x/(x + y + z), y/(x + y + z) and z/(x + y + z).
It should also be noted that:
the following embodiments and examples may be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments and examples.
The technical means of the present invention will be described in detail below with specific examples.
Example one
This example provides a hydrophilic lithium carbonate terpolymer.
It should be noted that:
the monomer compounds mentioned in the examples are commercially available.
The present embodiment provides a hydrophilic lithium carbonate 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 vinyl-alkyl lithium carbonate structural unit (C) consisting of z molar parts of vinyl-alkyl lithium carbonate monomers; and is
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 vinyl-alkyl lithium carbonate 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
Vinyl-alkyl lithium carbonate monomer:
n is an integer of 1 or more.
As a preferred technical solution, further:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the vinyl-alkyl lithium carbonate 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
Vinyl-alkyl lithium carbonate monomer:
n is an integer of 2 to 6.
From the above description and the general structural formulae, it can be found that:
first, the hydrophilic lithium carbonate terpolymer provided in this embodiment includes three compound structural units, namely a polyvinylidene fluoride structural unit composed of vinylidene fluoride monomers, a vinyl pyrrolidone structural unit composed of vinyl pyrrolidone monomers, and a vinyl-alkyl lithium carbonate structural unit composed of vinyl-alkyl lithium carbonate monomers, and is a novel polymer material for lithium battery research and application, which not only retains the advantageous skeleton structure (-CH) of polyvinylidene fluoride (PVDF for english short)2CF2-) to ensure that the copolymer has sufficient mechanical strength and thermal stability, and simultaneously, the crystallinity and the ionic conductivity of the hydrophilic lithium carbonate terpolymer can be regulated and controlled by regulating and controlling the proportion of an ionic structural unit, namely a vinyl-alkyl lithium carbonate structural unit;
secondly, the present embodiment provides a methodThe hydrophilic lithium carbonate terpolymer utilizes vinyl-alkyl lithium carbonate structural unit to copolymerize with vinylidene fluoride monomer, so that functional ionic group is introduced into the copolymer, and the vinyl-alkyl lithium carbonate structural unit comprises ionic group-COOLi+And an alkyl linking group- (CH)2)nThe migration rate of lithium ions in the terpolymer can be effectively regulated and controlled;
thirdly, in the hydrophilic lithium carbonate terpolymer provided by this embodiment, a 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 more effectively increased;
in addition, according to the hydrophilic lithium carbonate terpolymer provided by this embodiment, by introducing a large amount of polar groups such as ester bonds and carbonate bonds into the terpolymer, physical properties such as viscosity, solubility, and crystallinity of the terpolymer can be effectively controlled.
Example two
This example provides a method for preparing a hydrophilic lithium carbonate terpolymer.
It should be noted that:
the reaction apparatus, monomer compound, vinyl-alkyl lithium carbonate structural unit, initiator, emulsifier, demulsifier, and organic solvent referred to in this example were all commercially available.
A preparation method of a hydrophilic lithium carbonate terpolymer comprises the following steps:
respectively adding a vinylidene fluoride monomer, a vinyl pyrrolidone monomer, a vinyl-alkyl lithium carbonate monomer and an initiator into a reaction device, and copolymerizing by adopting a polymerization reaction method to prepare a hydrophilic lithium carbonate terpolymer;
the reaction formula is as follows:
further, in the above preparation method:
the reaction device is a high-pressure reaction kettle;
in the step of respectively adding the vinylidene fluoride monomer, the vinyl pyrrolidone monomer, the vinyl-alkyl lithium carbonate monomer and the initiator, the method specifically comprises the following steps:
firstly, adding a vinyl pyrrolidone monomer, a vinyl-alkyl lithium carbonate monomer and an initiator into a high-pressure reaction kettle, repeatedly evacuating to remove oxygen, then filling a vinylidene fluoride monomer gas 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 carbonate 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 carbonate 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 vinyl-alkyl lithium carbonate monomer, and drying to obtain the hydrophilic lithium carbonate 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 liquid, the demulsifying liquid can be dissolved in the organic solvent, and the demulsifying liquid dissolved in the organic solvent can be subjected to subsequent washing and drying operation steps 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, in the preparation method of the hydrophilic lithium carbonate terpolymer provided in this embodiment, a polymerization reaction method is adopted to copolymerize three compounds including a vinylidene fluoride monomer, a vinyl pyrrolidone monomer, and a vinyl-alkyl lithium carbonate monomer in one step, and a subsequent alkali treatment process is not required as in the prior art, so that a dominant skeleton structure (-CH) in a polyvinylidene fluoride structural unit is avoided2CF2-) chemical degradation;
secondly, in the preparation method of the hydrophilic lithium carbonate terpolymer provided by the embodiment, because the vinyl-lithium alkyl carbonate in the terpolymer has a self-emulsifying function, an emulsifier is not needed or is not needed in the polymerization 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 carbonate terpolymer, 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 carbonate terpolymer provided by this embodiment, the crystallinity of the terpolymer can be further controlled by controlling the length of the linking group in the vinyl-lithium alkyl carbonate structural unit, and the crystal melting temperature of PVDF is reduced, so that the problems in the prior art, such as low ion transmission efficiency, poor charge and discharge capacity, poor load characteristics and the like when PVDF is used alone as a binder, are solved.
According to the above description, it can be seen that the hydrophilic lithium carbonate terpolymer and the preparation method thereof provided by the invention have at least the following advantages:
1) the hydrophilic lithium carbonate terpolymer provided by the invention reserves the dominant unit- (CH) of PVDF2CF2)xThe copolymer can be ensured to have sufficient mechanical strength and thermal stability, and meanwhile, 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, so that a new method is provided for applying the PVDF material to the field of lithium batteries;
2) in the structure of the hydrophilic lithium carbonate terpolymer provided by the invention, a hydrophilic vinyl pyrrolidine unit is introduced, so that the hydrophilic performance of the copolymer can be improved, and the adsorption capacity of electrolyte and the migration rate of lithium ions can be effectively increased;
3) the hydrophilic lithium carbonate terpolymer provided by the invention has the advantages of a PVDF structure, and simultaneously, a great amount of polar groups such as ester bonds and carbonate bonds are introduced through a copolymerized vinyl-alkyl lithium carbonate structural unit, so that the physical and chemical properties of the copolymer, such as viscosity, solubility, crystallinity and the like, can be effectively regulated and controlled;
4) in the hydrophilic lithium carbonate terpolymer provided by the invention, the lithium carbonate structural unit is connected with the controllable chain segment, so that the crystallinity and the ionic conductivity of the copolymer can be effectively controlled;
5) the hydrophilic lithium carbonate terpolymer provided by the invention is prepared by one-step copolymerization, a subsequent alkali treatment process is not needed, and chemical degradation of a PVDF structure is avoided;
6) in the hydrophilic lithium carbonate terpolymer provided by the invention, the comonomer vinyl-alkyl lithium carbonate has a self-emulsifying function, and the use of an emulsifier can be avoided in the polymerization process, so that the emission of discarded matters is reduced, and the environment is protected.
In summary, it can be seen that:
the hydrophilic lithium carbonate terpolymer and the preparation method thereof provided by the invention have great popularization and application values.
To further aid in understanding the technical aspects of the present invention, the technical aspects of the present invention are described in more detail below by providing several specific preparation examples.
The following specific preparation embodiment mainly comprises the following steps:
s1) adding a vinyl pyrrolidone monomer, a vinyl-alkyl lithium carbonate monomer and an initiator into a high-pressure reaction kettle with the pressure resistance of 10MPa, and repeatedly vacuumizing to remove oxygen;
s2) making the inside of the high-pressure reaction kettle in a nitrogen atmosphere, and filling CH in one or more times2＝CF2Feeding a gas monomer, keeping the reaction kettle under a certain pressure, slowly heating to the polymerization reaction temperature, and reacting for 24 hours under mechanical stirring after feeding is finished;
s3), cooling to room temperature after the reaction is finished, and releasing unreacted gas to obtain uniform terpolymer emulsion;
s4), demulsifying the emulsion by using an ethanol solution, washing for multiple times to remove an emulsifier and unreacted monomers, and drying to obtain a target product.
In the preparation process, the polymerization reaction is any one of emulsion polymerization reaction, suspension polymerization reaction or aqueous phase solution polymerization reaction;
when the aqueous solution polymerization reaction is adopted for copolymerization, trichlorotrifluoroethane is taken as a dispersion medium.
In the preparation process:
the terpolymer emulsion obtained from the step S3) can also be directly used as a binder material of a lithium battery without demulsification treatment; in addition to this, the present invention is,
s4), the emulsion may be dissolved in a conventional organic solvent, such as N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, ethanol, isopropanol, dimethylsulfoxide or ethyl acetate, for subsequent operations.
The following are some specific embodiments.
Cases 1,
Vinyl pyrrolidone monomer and CH are added into a high-pressure reaction kettle with the pressure resistance of 10MPa2＝CH-CH2-COOLi+Repeatedly evacuating the monomer and the benzoyl peroxide initiator to remove oxygen, and then filling vinylidene fluoride gas in a nitrogen atmosphere;
wherein:
poly (vinylidene fluoride) gasVinylidene fluoride structural unit, vinylpyrrolidone structural unit comprising vinylpyrrolidone monomer, and CH2＝CH-CH2-COOLi+The mole fraction ratio of the structural units is as follows:
vinylidene fluoride structural unit, vinyl pyrrolidone and CH2＝CH-CH2-COOLi+The structural unit is 0.55: 0.35: 0.10;
keeping the pressure of the reaction kettle at 1.25MPa, slowly heating to about 135 ℃, adding ammonium perfluorooctanoate serving 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 to remove an emulsifier, unreacted vinylidene fluoride gas, vinyl pyrrolidone and CH2＝CH-CH2-COOLi+And drying to obtain the target product hydrophilic lithium carbonate 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 copolymers and the molar fraction ratios thereof vary, wherein:
the vinyl-lithium alkyl carbonate is specifically: CH (CH)2＝CH-C2H4-COOLi+；
Polyvinylidene fluoride structural unit composed of vinylidene fluoride gas, vinylpyrrolidone structural unit composed of vinylpyrrolidone monomer, and CH2＝CH-C2H4-COOLi+The mole fraction ratio of the structural units is as follows:
vinylidene fluoride structural unit, vinyl pyrrolidone structural unit and CH2＝CH-C2H4-COOLi+Structural units are 0.60:0.10: 0.30;
in addition, the polymerization reaction still adopts emulsion polymerization method without adding emulsifier, and uses CH2＝CH-C2H4-COOLi+The structural units themselves act as emulsifiers for the polymerizationAnd (4) carrying out a synthesis 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 copolymers and the molar fraction ratios thereof vary, wherein:
the vinyl-lithium alkyl carbonate is specifically: CH (CH)2＝CH-C3H6-COOLi+；
Polyvinylidene fluoride structural unit composed of vinylidene fluoride gas, vinylpyrrolidone structural unit composed of vinylpyrrolidone monomer, and CH2＝CH-C3H6-COOLi+The mole fraction ratio of the structural units is as follows:
vinylidene fluoride structural unit, vinyl pyrrolidone structural unit and CH2＝CH-C3H6-COOLi+Structural units are 0.70:0.10: 0.20;
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 copolymers and the molar fraction ratios thereof vary, wherein:
the vinyl-lithium alkyl carbonate is specifically: CH (CH)2＝CH-C4H8-COOLi+；
Polyvinylidene fluoride structural unit composed of vinylidene fluoride gas, vinylpyrrolidone structural unit composed of vinylpyrrolidone monomer, and CH2＝CH-C4H8-COOLi+The mole fraction ratio of the structural units is as follows:
vinylidene fluoride structural unit, vinyl pyrrolidone structural unit and CH2＝CH-C4H8-COOLi+The structural unit is 0.70:0.20: 0.10.
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 copolymers and the molar fraction ratios thereof vary, wherein:
the vinyl-lithium alkyl carbonate is specifically:
CH2＝CH-C5H10-COOLi+；
polyvinylidene fluoride structural unit composed of vinylidene fluoride gas, vinylpyrrolidone structural unit composed of vinylpyrrolidone monomer, and CH2＝CH-C5H10-COOLi+The mole fraction ratio of the structural units is as follows:
vinylidene fluoride structural unit, vinyl pyrrolidone structural unit and CH2＝CH-C5H10-COOLi+The structural unit is 0.85: 0.05: 0.10;
in addition, the polymerization reaction adopts an aqueous phase solution polymerization method, and trifluorotrichloroethane is added as a dispersion medium without adding an emulsifier to carry out polymerization reaction to obtain a terpolymer emulsion of polyvinylidene fluoride, vinyl pyrrolidone and vinyl-lithium alkyl carbonate;
demulsifying the emulsion with ethanol solution, dissolving in one or more of N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, ethanol, isopropanol, dimethyl sulfoxide and ethyl acetate, storing, washing when necessary, removing emulsifier, organic solvent and unreacted vinylidene fluoride gas, vinylpyrrolidone and CH2＝CH-C5H10-COOLi+And drying the monomer to obtain the target product hydrophilic lithium carbonate 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 copolymers and the molar fraction ratios thereof vary, wherein:
the vinyl-lithium alkyl carbonate is specifically: CH (CH)2＝CH-C6H12-COOLi+；
Polyvinylidene fluoride structural unit composed of vinylidene fluoride gas, vinylpyrrolidone structural unit composed of vinylpyrrolidone monomer, and CH2＝CH-C6H12-COOLi+The mole fraction ratio of the structural units is as follows:
vinylidene fluoride structural unit, vinyl pyrrolidone structural unit and CH2＝CH-C6H12-COOLi+The structural unit is 0.80:0.10: 0.10.
The following are specifically mentioned:
the above cases are only provided to illustrate some embodiments of the present invention, and the structural formula of the monomer for the vinyl-alkyl lithium carbonate structural unit is shown in the following general formula, in addition to the monomers of the specific structural formula listed in the above cases:
CH2＝CH-(CH2)n-COOLi+
the various monomers marked with n as an integer of not less than 1, especially when n is an integer of 2 to 6, and the related products obtained after copolymerization of the monomers also have the same or similar functions and effects as the products obtained in the above cases, and the copolymerization method and control conditions are also the same or similar to the methods and conditions listed in the above cases and are included in the ranges listed in the above embodiments, so the related processes and control methods are not repeated and only the summary description is made.
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 is measured by a PL-220 type high temperature gel permeation chromatograph, and the average molecular weight is 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 obtained in cases 1 to 6 was measured and is shown in Table 1.
TABLE 1
In the above specific case, it can be seen that:
1) vinylidene fluoride-vinyl pyrrolidone-vinyl-lithium alkyl carbonate terpolymers with different chain lengths and different molecular weights can be obtained by regulating the feed ratio of the comonomer, so as to meet different requirements;
2) the crystallinity of the terpolymer can be further regulated and controlled by regulating and controlling the chain segment length of an alkyl linking group in the vinyl-alkyl lithium carbonate, the crystallization 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 singly used as a binder at present are solved;
3) when the emulsion polymerization method is adopted for copolymerization, the ammonium perfluorooctanoate can be used as an emulsifier of a reaction system; of course, since the lithium vinyl-alkylcarbonate monomer itself has a self-emulsifying function, it is also possible to carry out emulsion polymerization without adding an emulsifier.
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 in this specification without undue contradiction.
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 (10)
1. A hydrophilic lithium carbonate 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 vinyl-alkyl lithium carbonate structural unit (C) consisting of z molar parts of vinyl-alkyl lithium carbonate monomers; and is
The copolymer has the following structural general formula:
2. the hydrophilic lithium carbonate terpolymer according to claim 1, wherein:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the vinyl-alkyl lithium carbonate 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 vinyl-alkyl lithium carbonate monomers:
n is an integer of 1 or more.
3. The hydrophilic lithium carbonate terpolymer according to claim 1, wherein:
the respective mole fractions of the polyvinylidene fluoride structural unit, the vinyl pyrrolidone structural unit and the vinyl-alkyl lithium carbonate 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 vinyl-alkyl lithium carbonate monomers:
n is an integer of 2 to 6.
4. A method for preparing the hydrophilic lithium carbonate terpolymer according to any one of claims 1-3, comprising the steps of:
respectively adding a vinylidene fluoride monomer, a vinyl pyrrolidone monomer, a vinyl-alkyl lithium carbonate monomer and an initiator into a reaction device, and copolymerizing by adopting a polymerization reaction method to prepare the hydrophilic lithium carbonate terpolymer;
the reaction formula is as follows:
5. the method of claim 4, wherein the method comprises the steps of:
the reaction device is a high-pressure reaction kettle;
in the step of respectively adding the vinylidene fluoride monomer, the vinyl pyrrolidone monomer, the vinyl-alkyl lithium carbonate monomer and the initiator, the method specifically comprises the following steps:
firstly, adding a vinyl pyrrolidone monomer, a vinyl-alkyl lithium carbonate monomer and an initiator into the high-pressure reaction kettle, repeatedly evacuating to remove oxygen, then filling a vinylidene fluoride monomer gas 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 carbonate 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 carbonate 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, vinyl pyrrolidone monomer and vinyl-alkyl lithium carbonate monomer, and drying to obtain the hydrophilic lithium carbonate terpolymer.
6. The method of claim 5, wherein the method comprises the steps of: the initiator is one of benzoyl peroxide, azo compounds or persulfate.
7. The method of claim 5, wherein the method comprises the steps of: the polymerization reaction method is any one of emulsion polymerization, suspension polymerization or aqueous solution polymerization.
8. The method of claim 7, wherein the method comprises the steps of: the emulsion polymerization method further comprises an emulsifier, wherein the emulsifier is ammonium perfluorooctanoate.
9. The method of claim 7, wherein the method comprises the steps of: the aqueous phase solution polymerization method further comprises a dispersion medium, wherein the dispersion medium is trifluorotrichloroethane.
10. The method of claim 5, wherein the method comprises the steps of:
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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| WO2018092675A1 (en) * | 2016-11-15 | 2018-05-24 | 株式会社クレハ | Vinylidene fluoride copolymer, binder composition, electrode mix, electrode, and nonaqueous-electrolyte secondary battery |
| CN110698586A (en) * | 2019-10-14 | 2020-01-17 | 北京卫蓝新能源科技有限公司 | Lithium battery positive electrode additive and preparation method thereof |
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| CN1342172A (en) * | 1999-03-02 | 2002-03-27 | 纳幕尔杜邦公司 | Free radical polymerization method for fluorinated copolymers |
| WO2018092675A1 (en) * | 2016-11-15 | 2018-05-24 | 株式会社クレハ | Vinylidene fluoride copolymer, binder composition, electrode mix, electrode, and nonaqueous-electrolyte secondary battery |
| CN110698586A (en) * | 2019-10-14 | 2020-01-17 | 北京卫蓝新能源科技有限公司 | Lithium battery positive electrode additive and preparation method thereof |
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