CN109461938B - Microcapsule, preparation method thereof and lithium ion battery - Google Patents
Microcapsule, preparation method thereof and lithium ion battery Download PDFInfo
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- CN109461938B CN109461938B CN201811324501.XA CN201811324501A CN109461938B CN 109461938 B CN109461938 B CN 109461938B CN 201811324501 A CN201811324501 A CN 201811324501A CN 109461938 B CN109461938 B CN 109461938B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
- A62C—FIRE-FIGHTING
- A62C37/00—Control of fire-fighting equipment
- A62C37/08—Control of fire-fighting equipment comprising an outlet device containing a sensor, or itself being the sensor, i.e. self-contained sprinklers
- A62C37/10—Releasing means, e.g. electrically released
- A62C37/11—Releasing means, e.g. electrically released heat-sensitive
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/627—Expanders for lead-acid accumulators
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Abstract
The invention provides a microcapsule, which comprises a capsule shell part and a capsule core part, wherein the capsule core part is selected from one or two of an organic flame retardant and an inorganic flame retardant, the outer surface of the capsule shell part is provided with a villus structure, and the capsule shell part is made of a high polymer material. The application also provides a preparation method of the microcapsule. The application also provides a lithium ion battery. The microcapsule provided by the application is applied to the lithium ion battery, so that the safety of the lithium ion battery can be improved, and the electrochemical performance of the lithium ion battery is not influenced.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a microcapsule, a preparation method thereof and a lithium ion battery.
Background
In recent years, the fields of portable electronic products, electric automobiles, energy storage power stations and the like are rapidly developed, and lithium ion batteries become the preferred chemical power source due to the advantages of high energy density, high working voltage, small self-discharge, long cycle life and the like. Along with the upgrading of products, people have higher and higher requirements on the energy density of the lithium ion battery, but the safety performance is not synchronously upgraded, and safety accidents occur in the actual use process, mainly because the lithium ion battery is subjected to thermal runaway caused by contact short circuit of a cathode and an anode due to contraction and embrittlement of a diaphragm in the processes of high temperature, falling and the like, so that the battery is ignited and even explodes, and the life and property safety of users is seriously influenced. For a power battery with larger capacity, the safety performance is more important.
In order to improve the safety performance of the lithium ion battery, in the prior art, the safety performance is often improved by adjusting the electrolyte formula, for example, adding a flame retardant, an overcharge additive, and the like into the electrolyte. However, this method usually sacrifices the electrochemical performance of the battery and cannot solve the problem fundamentally.
In view of this, chinese patent publication No. CN 104466186a employs a microcapsule technology, in which a reducing substance and/or a flame retardant is encapsulated in a microcapsule and dispersed on the surface of a positive electrode material or in the positive electrode material. When the battery is in thermal runaway, the microcapsules can be melted and covered on the surface of the positive electrode material, and simultaneously, reducing substances and/or flame retardants are released to prevent the battery from burning or exploding. However, because the conductivity of the anode material is poor, the resistance of the anode plate is increased after the non-conductive microcapsule is added, so that the internal resistance of the battery is increased, which is extremely unfavorable for the power battery. And as shown in the Chinese patent with the publication number of CN 105742733A, the fire retardant is wrapped in the microcapsule by adopting a microcapsule technology, and then the fire retardant is mixed with a solution containing a protective agent of the isolating membrane and coated on the surface of the isolating membrane, and finally the microcapsule is fixed on the surface of the isolating membrane. When the battery is out of control by heat, the flame retardant can be released to protect the battery. However, this method increases the internal resistance of the separator, affects lithium ion transport, and adversely affects the rate capability and low temperature performance of the battery.
In view of the above, it is desirable to provide a method for improving the safety of lithium ion batteries without affecting the electrochemical performance of the batteries.
Disclosure of Invention
The invention aims to provide a microcapsule and a preparation method thereof, and the microcapsule provided by the application is applied to a lithium ion battery, so that the safety of the lithium ion battery can be improved, and the electrochemical performance of the lithium ion battery is not influenced.
In view of the above, the present application provides a microcapsule, comprising a shell portion and a core portion, wherein the core portion is selected from one or two of an organic flame retardant and an inorganic flame retardant, the outer surface of the shell portion has a villus structure, and the shell portion is a polymer material.
Preferably, the microcapsule D50 is a microcapsule with a single core as the main when the size of the microcapsule D50 is less than 5 μm, the microcapsule D50 is a microcapsule with a double core as the main when the size of the microcapsule D50 is 5 μm to 10 μm, and the microcapsule D50 is a microcapsule with a multi core as the main when the size of the microcapsule D50 is more than 10 μm.
Preferably, the organic flame retardant is selected from one or more of high-fluorocarbon acid ester, phosphate ester flame retardant, hexaphenoxycyclotriphosphazene, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and phosphonate flame retardant, the inorganic flame retardant is selected from one or two of enveloped red phosphorus and ammonium polyphosphate, and the high polymer material is selected from homopolymer, copolymer, modified homopolymer or modified copolymer of one of low-density polyethylene, nitrocellulose plastic, polycaprolactone, ethylene-vinyl acetate copolymer and polyurethane.
Preferably, the length of the villus structure of the shell portion is less than 0.1 μm.
The application also provides a preparation method of the microcapsule, which comprises the following steps:
A) mixing a high polymer material, a flame retardant and an organic solvent to obtain an emulsion;
B) carrying out centrifugal spray drying on the emulsion in a centrifugal spray dryer to obtain microcapsules;
the flame retardant is selected from one or two of organic flame retardant and inorganic flame retardant;
including centrifugal disc, porous rail and powder collector in the centrifugal spray dryer, porous rail set up in the centrifugal disc with between the powder collector, porous rail surface is equipped with has fine hair structure through-hole.
Preferably, the pore diameter of the porous enclosure is smaller than the diameter of the spray liquid drop in the centrifugal spray drying process, and the density of the through holes of the porous enclosure is 50/mm2。
Preferably, the organic solvent is selected from one or more of acetone, ethanol, dimethyl carbonate, tetrahydrofuran and tetralin.
The application also provides a lithium ion battery, which comprises a positive pole piece, a diaphragm and a negative pole piece, and is characterized in that the periphery of the current collector active substance coating of the positive pole piece is coated with a safe coating; the safe coating is prepared from the microcapsule described in the scheme or the microcapsule prepared by the preparation method described in the scheme, ceramic powder, acrylic emulsion, a binder, a surfactant and a solvent, and the flame retardant of the safe coating is an organic flame retardant and an inorganic flame retardant.
Preferably, the safe coating is used as a base, the content of the microcapsule is 30-80 wt%, the content of the ceramic powder is 20-60 wt%, the content of the acrylic emulsion is 0-5 wt%, the content of the binder is 0-5 wt%, and the content of the surfactant is 0.5-3 wt%.
Preferably, the width pole ear area of the safety coating formed by the safety coating is 0.5-2 mm, the non-pole ear area is 2-10 mm, the thickness of the safety coating is less than or equal to that of the positive pole piece, and the overlapping width of the safety coating and the current collector active material coating is less than 0.2 mm.
The application provides a microcapsule, which comprises a capsule shell part and a capsule core part, wherein the capsule core part is selected from one or two of organic flame retardant and inorganic flame retardant, the outer surface of the capsule shell part has a villus structure, and the capsule shell part is made of high polymer material. The microcapsule provided by the application is applied to the positive pole piece, when the temperature in the battery core reaches above 120 ℃, the capsule shell with a low melting point is melted and releases the flame retardant, so that thermal runaway of the battery can be prevented, the surface of the capsule shell has a villus structure, the bonding force between the microcapsule and a current collector, ceramic powder and the like can be improved, the specific gravity in a safety coating of the microcapsule can be improved, the content of the flame retardant is increased, and the safety performance of the battery is improved; the safety coating is coated around the active substance coating of the current collector on the positive pole piece, so that the safety performance of the battery cell can be improved, and the energy density of the battery cell cannot be reduced; compared with the method that the microcapsule is mixed in the electrolyte, the active substance or fixed on the isolating membrane, the microcapsule is fixed around the active substance coating of the positive plate current collector, so that the short circuit caused by the contraction of the diaphragm and the contact of the positive electrode and the negative electrode can be prevented, the safety performance of the lithium ion battery is improved, and the electrochemical performance of the battery is not influenced.
Drawings
FIG. 1 is a schematic diagram of the microcapsule structure of example 1;
FIG. 2 is a schematic cross-sectional view of the coating of the positive electrode of example 1;
FIG. 3 is a schematic cross-sectional view of a stacked core of example 1;
FIG. 4 is a schematic view of the multi-well fence of example 3;
FIG. 5 is a schematic diagram of the microcapsule structure of example 3;
FIG. 6 is a schematic diagram of the microcapsule structure of example 5;
FIG. 7 is a schematic diagram of the microcapsule structure of example 6;
FIG. 8 is a schematic cross-sectional view of the coating of the positive electrode of comparative example 1;
FIG. 9 is a schematic cross-sectional view of a stacked core of comparative example 1;
FIG. 10 is an electron micrograph of microcapsules (with fluff);
FIG. 11 is a sectional electron micrograph of a microcapsule (with villus) core-shell structure;
fig. 12 is an electron micrograph of microcapsules (without fluff).
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
In view of the problem that the safety performance of the lithium ion battery and the electrochemical performance of the battery cannot be considered at the same time at present, the embodiment of the invention discloses a microcapsule which is used as an important component of a safety coating and is coated around a current collector active substance of a positive pole piece, so that the lithium ion battery has higher safety and simultaneously has the electrochemical performance which is not influenced. Specifically, the microcapsule described herein specifically includes: the capsule shell comprises a capsule shell part and a capsule core part, wherein the capsule core part is selected from one or two of organic flame retardant and inorganic flame retardant, the outer surface of the capsule shell part is provided with a villus structure, and the capsule shell part is made of high polymer material.
The microcapsule provided by the application comprises a shell part and a core part, wherein the core part is selected from one or more of organic flame retardants and inorganic flame retardants; specifically, when the capsule core part is selected from organic flame retardants, the microcapsules are organic flame retardant microcapsules, when the capsule core part is selected from inorganic flame retardants, the microcapsules are inorganic flame retardant microcapsules, and when the capsule core part is selected from inorganic flame retardants and organic flame retardants, the microcapsules are organic flame retardants and inorganic flame retardant microcapsules. The inorganic flame retardant is specifically selected from one or more of coated red phosphorus, ammonium polyphosphate, intumescent flame retardants formed by compounding ammonium polyphosphate and other substances, and compound inorganic flame retardants formed by compounding ammonium polyphosphate and other substances. The organic flame retardant is selected from one or more of high fluorocarbon ester, phosphate ester flame retardant, hexaphenoxycyclotriphosphazene, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and phosphonate flame retardant, in a specific embodiment, the organic flame retardant is selected from hexaphenoxycyclotriphosphazene; in particular embodiments, the core structure is selected from ammonium polyphosphate and hexaphenoxycyclotriphosphazene.
The capsule shell part is coated on the surface of the capsule core part, and the surface has a villus structure, and the specific structure is shown in fig. 5 and fig. 6. The capsule shell part is made of high polymer material, more specifically homopolymer, copolymer, modified homopolymer or modified copolymer of one of low density polyethylene, nitrocellulose plastic, polycaprolactone, ethylene-vinyl acetate copolymer and polyurethane; the capsule shell part is made of ethylene-vinyl acetate copolymer. The length of the villus structure of the shell part is less than 0.1 μm.
The microcapsule is divided into single-core, double-core or multi-core-based microcapsule particles according to the specific core number of the capsule core part in the microcapsule. When the proportion of one of the mononuclear, the binuclear or the polynuclear is larger than that of the other two, the particles are called as uniform particles mainly based on the same, and the D50 value of the flame retardant particles and the D50 value of the corresponding batch of microcapsule particles are judged. The D50 value of the microcapsule is, for example, a flame retardant with D50 of 3-5 μm, the microcapsule is mainly mononuclear when the D50 of the microcapsule is less than or equal to 5 μm, the microcapsule is mainly binuclear when the D50 of the microcapsule is less than or equal to 5 μm and less than or equal to 10 μm, and the microcapsule is mainly polynuclear when the D50 of the microcapsule is more than or equal to 10 μm.
The application also provides a preparation method of the microcapsule, which comprises the following steps:
A) mixing a high polymer material, a flame retardant and an organic solvent to obtain an emulsion;
B) carrying out centrifugal spray drying on the emulsion in a centrifugal spray dryer to obtain microcapsules;
the flame retardant is selected from one or more of organic flame retardant and inorganic flame retardant;
including centrifugal disc, porous rail and powder collector in the centrifugal spray dryer, porous rail set up in the centrifugal disc with between the powder collector, porous rail surface is equipped with has fine hair structure through-hole.
In the process of preparing the microcapsule, firstly, a high polymer material, a flame retardant and an organic solvent are mixed to form emulsion; in this process, the organic solvent is selected from one or more of acetone, ethanol, dimethyl carbonate, tetrahydrofuran and tetralin. The solid content of the emulsion is 20-75 wt%, and in a specific embodiment, the solid content of the emulsion is 40-65 wt%.
The application then centrifugally spray-drying the emulsion in a centrifugal spray-dryer to obtain microcapsules; including centrifugal disc, porous rail and powder collector in the centrifugal spray dryer, porous rail set up in the centrifugal disc with between the powder collector, porous rail surface is equipped with has fine hair structure through-hole.
In the centrifugal spray drying process, the vibration frequency, the temperature, the amount of the emulsion entering the disc in unit time and the rotating speed of the disc during rotation are adjusted, so that emulsion droplets thrown out at high speed bear different air tearing effects, and uniform microcapsule particles mainly comprising single core, double core or multiple core are respectively formed. The specific parameters are shown in table 0 below,
TABLE 0 data sheet of relevant parameters for centrifugal spray drying
In the centrifugal spray drying process, a porous fence with a fluff shape is arranged between the centrifugal disc and the powder collector, and the aperture is smaller than the diameter of spray liquid drops; the liquid drops which are not completely dried and formed by centrifugal spraying fly into the fluff structure through holes of the porous fence to form a fluff structure, and finally fly out of the porous fence, and are dried, cured and molded. The invention has villus shape on the surface of the porous fenceThe through-hole of form distributes and has the requirement, and it needs to be located the lateral wall of rail, just right with centrifugal disc discharge gate to be favorable to reducing the distance of microcapsule from centrifugal disc to spray drying district, can make the microcapsule of high temperature get into drying district from centrifugal disc fast, thereby better design. The density of the fence holes used in the present invention is about 50 holes/mm2。
The application also provides a lithium ion battery, which comprises a positive pole piece, a diaphragm and a negative pole piece, wherein a safe coating is coated around the current collector active substance coating of the positive pole piece; the safe coating is prepared from the microcapsules, ceramic powder, acrylic emulsion, a binder, a surfactant and a solvent, and the flame retardant of the safe coating is an organic flame retardant and an inorganic flame retardant.
In the safety coating, both an inorganic flame retardant and an organic flame retardant need to be included, in which case, the safety coating includes inorganic flame retardant microcapsules and organic flame retardant microcapsules or the safety coating includes organic flame retardant microcapsules and inorganic flame retardant microcapsules to improve the flame retardant efficiency, because the organic flame retardant is easy to volatilize, loses the flame retardant effect after volatilization, and the inorganic flame retardant is not easy to volatilize, and can continue to exert the flame retardant effect after the organic flame retardant is volatilized.
In the lithium ion battery, the safe coating is used as a base, the content of the microcapsule is 30-80 wt%, the content of the ceramic powder is 20-60 wt%, the content of the acrylic emulsion is 0-5 wt%, the content of the binder is 0-5 wt%, and the content of the surfactant is 0.5-3 wt%. The acrylic emulsion, binder and surfactant are well known materials to those skilled in the art, and the present application is not particularly limited thereto; the ceramic powder is selected from the ceramic powders of the berm stone, the aluminum oxide, the magnesium hydroxide and the like, preferably the berm stone, and the berm stone has insulating effect and relatively low hardness, so that the service life of the coating roller can be prolonged, and the microcapsules can be prevented from being broken and damaged in the rolling process.
The safe coating is coated around the coating of the active substance of the positive current collector, and the negative plate is not coated with the safe coating; because assemble into naked electric core after, the negative plate can surpass positive plate, if coating safety coating on the negative plate, not only play the safety action, still can reduce the energy density of battery.
The height of the positive pole piece can be smaller than, equal to or larger than that of the negative pole piece; in order to ensure the energy density and safety performance of the battery core, preferably, the height of the positive pole piece is equal to that of the negative pole piece, and the width of the active material coating of the positive pole piece is smaller than that of the negative pole piece.
The width of the safe coating layer is 0.5-2 mm in the pole ear area, the width of the non-pole ear area is 2-10 mm, the thickness of the coating layer is less than or equal to the thickness of the pole piece, and the overlapping width of the safe coating layer and the active substance coating layer is less than 0.2 mm.
The preparation method of the lithium ion battery provided by the application can be carried out according to a scheme well known to a person skilled in the art, and specifically comprises the following steps:
stirring the microcapsule, ceramic powder, acrylic emulsion, a binder, a surfactant and a solvent according to a certain proportion, and uniformly mixing to obtain a safe coating;
uniformly coating the active material slurry on a current collector of the positive pole piece by transfer coating or extrusion coating; coating the safety coating for a circle along the periphery of the current collector active substance coating, and drying to obtain the pole piece with the safety coating;
and assembling the pole piece and the diaphragm in a winding or laminating manner, and performing conventional procedures such as packaging, liquid injection, infiltration, formation and the like to obtain the finished battery.
The invention takes inorganic and organic fire retardant as capsule core, high molecular material as capsule shell, adopts centrifugal spray drying method, and adjusts the rotating speed of the disc, so that the emulsion liquid drop thrown out by the disc at high speed passes through the porous fence with hair follicle shape, finally flies out of the fence, and is molded and solidified into the multinuclear through-hole microcapsule with villus structure. On one hand, when the internal temperature of the battery core reaches above 120 ℃, the capsule shell with low melting point is melted and releases the flame retardant, so that thermal runaway of the battery can be prevented, and the safety performance of the battery is improved; on the other hand, the multi-core structure of the microcapsule with the same volume and weight can contain more flame retardant than the single-core structure, so that the flame retardant efficiency can be improved; in addition, the surface of the capsule shell has a villus structure, so that the adhesive force between the microcapsule and a current collector, ceramic powder and the like can be improved, the specific gravity of the microcapsule in the safety coating can be improved, and the content of the flame retardant can be increased.
The safe coating simultaneously contains inorganic flame retardant microcapsules and organic flame retardant microcapsules, so that the flame retardant efficiency can be improved; because the organic flame retardant is easy to volatilize and loses the flame retardant effect after volatilization, the inorganic flame retardant is difficult to volatilize and can continuously exert the flame retardant effect after the organic flame retardant volatilizes.
The ceramic powder (preferably the berm stone) is added into the safety coating, so that the microcapsules can be effectively protected from being extruded and broken to cause the failure of the microcapsules.
The invention can utilize the space that the negative pole exceeds the positive pole in the length direction of the battery cell, and coat the safe coating around the active substance coating of the current collector on the positive pole piece, thereby not only improving the safety performance of the battery cell, but also not reducing the energy density of the battery cell.
Compared with the method that the microcapsule is mixed in the electrolyte, the active substance or fixed on the isolating membrane, the microcapsule is fixed around the active substance coating of the current collector of the positive plate, so that the short circuit caused by the contraction of the diaphragm and the contact of the positive electrode and the negative electrode can be prevented, the safety performance of the lithium ion battery is improved, and the electrochemical performance of the battery is not influenced.
For further understanding of the present invention, the microcapsules provided by the present invention, the preparation method and the application thereof are described in detail below with reference to the following examples, and the scope of the present invention is not limited by the following examples.
Example 1
1) Preparing microcapsules: adding ammonium polyphosphate or hexaphenoxycyclotriphosphazene powder particles into an ethylene-vinyl acetate copolymer emulsion according to a mass ratio of 4:6, uniformly stirring in a dispersion machine to obtain an emulsion with a solid content of 60-65%, and finally performing centrifugal spray drying on the emulsion to obtain a dual-core-based microcapsule with ammonium polyphosphate and hexaphenoxycyclotriphosphazene as capsule cores and an ethylene-vinyl acetate copolymer as capsule shells (as shown in a schematic diagram 1, 1 is a capsule shell part and 2 is a capsule core part in the diagram 1, and as shown in the diagram 12, fig. 12 is an electron microscope photograph of the microcapsule prepared in the embodiment);
2) preparation of the safe coating: uniformly stirring and mixing the microcapsules containing the inorganic flame retardant and the organic flame retardant, the ceramic powder, the acrylic emulsion, the binder, the surfactant and the solvent according to the weight ratio of 40%, 53.1%, 5%, 1% and 0.9% with water to obtain the required safe coating slurry;
3) preparing a pole piece: uniformly coating the positive active material slurry on an aluminum foil by adopting extrusion coating, synchronously uniformly coating the safe coating on the periphery of a current collector active material coating, and drying to obtain a positive pole piece with a safe coating (as shown in a schematic diagram 2, 01 in figure 2 is a positive current collector aluminum foil, 02 is a positive active material coating, and 03 is a safe coating); the width of the safe coating is 0.5-0.7 mm in the extreme ear area, the width of the non-extreme ear area is 3-5 mm, the coating thickness is 80% -90% of the thickness of the active substance coating, and the overlapping area of the safe coating and the active substance coating is 0.1-0.2 mm;
uniformly coating the negative active material slurry on a copper foil by adopting extrusion coating, and drying to obtain a negative pole piece; the coating width of the positive plate (including the active material coating width and the safety coating width) is consistent with that of the negative plate (only including the active material coating width);
4) the pole pieces and the diaphragm are assembled into a laminated core according to a lamination process (as shown in a schematic diagram 3, 01 in fig. 3 is an aluminum foil of a positive current collector, 02 is a positive active material coating, 03 is a safe coating, 04 is a copper foil of a negative current collector, 05 is a negative active material coating, and 06 is the diaphragm), and the finished battery is prepared through conventional procedures of packaging, liquid injection, infiltration, formation and the like.
Example 2
The difference from the embodiment 1 is that: the weight ratio of the microcapsule, the burm stone, the acrylic emulsion, the binder and the surfactant in the safety coating is 55%, 42.1%, 1% and 0.9%.
Example 3
The difference from the embodiment 2 is that: the preparation method of the microcapsule and the shape of the microcapsule are different:
the preparation method of the microcapsule comprises the following steps: adding ammonium polyphosphate or hexaphenoxycyclotriphosphazene into ethylene-vinyl acetate copolymer emulsion, uniformly stirring in a dispersion machine to obtain emulsion, finally sending the emulsion to a centrifugal atomizer at the top of a centrifugal spray dryer to spray the emulsion into tiny fog-like liquid drops, wherein the vibration frequency of a centrifugal disc is 1850HZ, the temperature is 150 ℃, the feeding amount per unit time is 10.1Kg/min, the rotating speed is 1600rpm, the fog-like liquid drops pass through a porous fence with a villus shape (shown as figure 4, 07 is the porous fence, 08 is a through hole with a villus structure in figure 4), forming and curing to obtain the dinuclear through hole microcapsule (shown as a schematic diagram 5, 1 is a capsule shell part, 2 is a capsule core part, and 3 is a villus structure on the surface of the capsule shell part in figure 5) with the ammonium polyphosphate or hexaphenoxycyclotriphosphazene as the core and the ethylene-vinyl acetate capsule shell part as the fine hair structure in figure 10 and figure 11, FIG. 10 is an electron micrograph of the microcapsule prepared in this example; fig. 11 is a cross-sectional electron micrograph of the core-shell structure of the microcapsule prepared in this example).
Example 4
The difference from the embodiment 3 is that: in the second step, the weight ratio of the microcapsule, the berm stone, the acrylic emulsion, the binder and the surfactant is 70%, 27.1%, 1% and 0.9%.
Example 5
The difference from the embodiment 3 is that: in the microcapsule preparation process, the solid content of the emulsion is 70-75%, the microcapsule is of a multi-core through-hole structure, and the outside of the capsule shell has a villus structure (as shown in a schematic diagram 6, 1 in fig. 6 is a capsule shell part, 2 is a capsule core part, and 3 is a villus structure on the surface of the capsule shell part).
Example 6
The difference from the embodiment 1 is that: in the microcapsule preparation process, the solid content of the emulsion is 25-30%, the microcapsule is of a single-core structure, and the shell does not have a villus structure (as shown in a schematic diagram 7, 1 in fig. 7 is a shell part, and 2 is a core part).
Comparative example 1
The difference from the embodiment 1 is that: there is no safety coating coated around the active material coating of the current collector of the positive electrode sheet (as shown in schematic diagram 8, 01 in fig. 8 is an aluminum foil of the positive electrode current collector, 02 is a coating of the positive electrode active material), the prepared stack core is shown in schematic diagram 9, 01 in fig. 9 is an aluminum foil of the positive electrode current collector, 02 is a coating of the positive electrode active material, 04 is a copper foil of the negative electrode current collector, 05 is a coating of the negative electrode active material, and 06 is a diaphragm. It is to be noted that the widths of the cathode and anode active material coating were the same as in example 1, but the anode coating width was 6 to 10mm larger than the cathode coating width.
Comparative example 2
The difference from the embodiment 3 is that: the microcapsule containing the inorganic flame retardant and the microcapsule containing the organic flame retardant are added into the positive electrode slurry, and after coating and drying, the microcapsules are in the positive electrode active material coating. It is to be noted that the coating widths of the positive and negative electrode active materials were the same as in example 3, but the negative electrode coating width was 6 to 10mm larger than the positive electrode coating width, and the weight of the microcapsules of comparative example 2 was the same as that of example 3 per unit volume of the positive electrode sheet.
Comparative example 3
The difference from the embodiment 3 is that: the safe paint only contains organic flame retardant microcapsules, wherein the weight ratio of the organic flame retardant microcapsules to the berm stone to the acrylic emulsion to the binder to the surfactant is 55%, 42.1%, 1% and 0.9%.
Comparative example 4
The difference from the embodiment 3 is that: no burm stone was added to the security paint and the remaining materials were added in the same proportions and weights as in example 3.
The battery cells prepared by the methods of the above examples 1 to 6 and comparative examples 1 to 4 were fully charged with 0.7C at room temperature, and then left to stand for 3 hours, and then subjected to a 140 ℃ hot box test, and the test results are shown in table 1.
TABLE 1 resistance Properties data sheet of cells prepared in examples and comparative examples
From the examples 1 to 6, compared with the comparative example 1 (the battery cell prepared by the prior art), the method disclosed by the invention can greatly improve the safety performance of the battery cell, and can effectively prevent the battery cell from losing efficacy under the condition of thermal abuse when the proportion of the microcapsule in the safety coating reaches more than 55%.
It can be seen from examples 3 and 6 that the binuclear microcapsules have a better flame retardant effect than the mononuclear microcapsules due to the fact that the binuclear microcapsules contain more flame retardant under the same added weight.
It can be seen from example 3 and comparative example 3 that the inclusion of both inorganic flame retardant microcapsules and organic flame retardant microcapsules in the safety coating can improve the flame retardant efficiency. Because the organic flame retardant is easy to volatilize and loses the flame retardant effect after volatilization, the inorganic flame retardant is difficult to volatilize and can continuously exert the flame retardant effect after the organic flame retardant volatilizes.
It can be seen from examples 1 and 6 that the addition of berm to the safety coating effectively protects the microcapsules from the microcapsules failing due to crushing and breaking during the preparation process.
From the internal resistances of the embodiment 3 and the comparative example 2, and the embodiments 1 to 6 and the comparative example 1, the method of the invention can not obviously increase the internal resistance of the battery cell, thereby ensuring the rate capability and the cycle performance of the battery cell.
The cells prepared in examples 1 to 5 and comparative examples 1 to 2 were subjected to low-temperature, normal-temperature discharge rate performance and normal-temperature cycle performance tests, and the capacity retention rate was recorded, with the results shown in table 2.
TABLE 2 data table of cycle performance and capacity retention rate of cells prepared in examples and comparative examples
From the test results, the rate performance and the cycle performance of the examples 1 to 5 are equivalent to those of the comparative example 1 of the conventional battery, while the rate performance and the cycle performance of the comparative example 2 are deteriorated to different degrees.
In summary, as can be seen from the safety performance test results in table 1 and the electrochemical performance test results in table 2, the embodiment of the present invention can improve the safety performance of the battery without affecting the internal resistance and the electrochemical performance of the battery cell.
The pole pieces prepared in examples 1 to 5 were cut into the safety coating by an automatic slitting machine, and then the powder dropping condition of the cut edges was observed by a CCD, and the larger the exposed width of the substrate was, the more serious the powder dropping condition was, and the results are shown in table 3.
TABLE 3 dust falling condition table of pole pieces prepared in examples and comparative examples
From the experimental results, the content of the microcapsule (the outer surface of the capsule shell has no fluff) in example 1 is relatively low, the content of the binder is relatively high, and the powder falling condition is very slight; in example 2, when the content of the microcapsule (the outer surface of the capsule shell has no fluff) is increased and the content of the binder is reduced, obvious powder falling occurs; after the surface of the shell of the microcapsule of example 3 is added with fluff, the powder dropping condition is obviously improved, and after the content of the microcapsule of example 4 is increased and the structure of the microcapsule of example 5 is changed, no obvious powder dropping occurs. The results show that the fluff structure added on the surface of the microcapsule shell is beneficial to increasing the adhesive force between the microcapsule shell and the base material, the berm stone, the binder and the like, and the effect of avoiding powder falling, reducing and improving the safety performance is achieved.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A microcapsule comprising a shell portion and a core portion, wherein the core portion is selected from organic flame retardants and inorganic flame retardants, the outer surface of the shell portion has a villus structure, and the shell portion is a polymeric material;
the high polymer material is selected from one of low-density polyethylene, nitrocellulose plastic, polycaprolactone, ethylene-vinyl acetate copolymer and polyurethane.
2. The microcapsule according to claim 1, wherein the microcapsule D50 is a predominantly mononuclear microcapsule when the particle size is less than 5 μm, the microcapsule D50 is a predominantly binuclear microcapsule when the particle size is 5 μm to 10 μm, and the microcapsule D50 is a predominantly polynuclear microcapsule when the particle size is more than 10 μm.
3. A microcapsule according to claim 1, wherein the organic flame retardant is selected from one or more of a phosphate flame retardant, hexaphenoxycyclotriphosphazene, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and a phosphonate flame retardant, and the inorganic flame retardant is selected from one or both of coated red phosphorus and ammonium polyphosphate.
4. A microcapsule according to claim 1, characterized in that the length of the villous structure of the shell portion is less than 0.1 μm.
5. A process for the preparation of microcapsules according to claim 1 comprising the steps of:
A) mixing a high polymer material, a flame retardant and an organic solvent to obtain an emulsion;
B) carrying out centrifugal spray drying on the emulsion in a centrifugal spray dryer to obtain microcapsules;
the flame retardant is selected from organic flame retardants and inorganic flame retardants;
including centrifugal disc, porous rail and powder collector in the centrifugal spray dryer, porous rail set up in the centrifugal disc with between the powder collector, porous rail surface is equipped with has fine hair structure through-hole.
6. The method of claim 5, wherein the porous enclosure has a pore size smaller than the diameter of the spray droplets during the centrifugal spray drying process, and the density of the through holes of the porous enclosure is 50/mm2。
7. The method according to claim 5, wherein the organic solvent is one or more selected from the group consisting of acetone, ethanol, dimethyl carbonate, tetrahydrofuran, and tetralin.
8. A lithium ion battery comprises a positive pole piece, a diaphragm and a negative pole piece, and is characterized in that a safe coating is coated around an active material coating on a current collector of the positive pole piece; the safe coating is prepared from the microcapsule, ceramic powder, acrylic emulsion, binder, surfactant and solvent according to any one of claims 1-4, wherein the flame retardant of the microcapsule is organic flame retardant and inorganic flame retardant.
9. The lithium ion battery of claim 8, wherein the microcapsule is 30 to 80wt%, the ceramic powder is 20 to 60wt%, the acrylic emulsion is 0 to 5wt%, the binder is 0 to 5wt%, and the surfactant is 0.5 to 3wt% based on the safety coating; the content of the acrylic emulsion and the binder is not 0; the total of the microcapsule, the ceramic powder, the acrylic emulsion, the binder and the surfactant is 100%.
10. The lithium ion battery of claim 8, wherein the width of the safety coating formed by the safety coating is 0.5-2 mm in the tab area, 2-10 mm in the non-tab area, the thickness of the safety coating is less than or equal to that of the positive electrode piece, and the overlapping width of the safety coating and the active material coating on the current collector is less than 0.2 mm.
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| CN110010830A (en) * | 2019-04-23 | 2019-07-12 | 雒乙橙 | A kind of lithium battery diaphragm |
| CN110212201B (en) * | 2019-06-13 | 2021-05-18 | 桑顿新能源科技(长沙)有限公司 | Battery core, battery pole piece, preparation methods of battery pole piece and battery |
| CN110433419B (en) * | 2019-06-28 | 2021-09-07 | 浙江南都电源动力股份有限公司 | Lithium battery thermal runaway fire suppression capsule and lithium ion battery |
| CN113078412B (en) * | 2019-12-17 | 2022-08-19 | 山东海科创新研究院有限公司 | Flame-retardant composite diaphragm, preparation method thereof and lithium ion battery |
| CN112973591B (en) * | 2019-12-17 | 2023-01-17 | 山东海科创新研究院有限公司 | Flame-retardant microcapsule and preparation method and application thereof |
| CN113451664B (en) * | 2020-03-24 | 2023-01-24 | 东营市海科新源化工有限责任公司 | Thermally-excited active safety mechanism flame-retardant microcapsule, preparation method thereof and lithium ion battery |
| CN111803856A (en) * | 2020-07-21 | 2020-10-23 | 中国矿业大学 | Temperature-controlled injection release fire retardant for preventing and treating field fire and preparation method thereof |
| CN112382816B (en) * | 2021-01-15 | 2021-04-09 | 司诺瓦(北京)科技有限公司 | Fire extinguishing agent composition and battery |
| CN116918168A (en) * | 2021-10-29 | 2023-10-20 | 宁德时代新能源科技股份有限公司 | Sustained release device for battery and secondary battery comprising same |
| CN116271675A (en) * | 2023-03-22 | 2023-06-23 | 湖北火控安防科技有限公司 | Perfluoro-hexanone microcapsule fire extinguishing medium and preparation method thereof |
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