CN112968254A - Diaphragm for lithium ion battery, preparation method of diaphragm and lithium ion battery - Google Patents

Diaphragm for lithium ion battery, preparation method of diaphragm and lithium ion battery Download PDF

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Publication number
CN112968254A
CN112968254A CN202110134547.0A CN202110134547A CN112968254A CN 112968254 A CN112968254 A CN 112968254A CN 202110134547 A CN202110134547 A CN 202110134547A CN 112968254 A CN112968254 A CN 112968254A
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ion conductor
diaphragm
fast ion
conductor additive
composite coating
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占克军
王恒
张燕萍
楚英
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Dongguan Weike Battery Co ltd
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Dongguan Weike Battery Co ltd
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Priority to CN202110134547.0A priority Critical patent/CN112968254A/en
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    • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
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    • 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
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Abstract

The invention provides a diaphragm for a lithium ion battery, which comprises a base film and a composite coating; the composite coating is coated on at least one surface of the base film; the composite coating comprises a fast ion conductor additive, a thickening agent and a binder. Compared with the prior art, the diaphragm provided by the invention adopts the fast ion conductor additive which is a novel compound obtained from various oxides, the fast ion conductor additive is used as the main body of the composite coating, the fast ion conductor additive has the advantages of high ion conductivity and no electron conductivity, and the discharge multiplying power, the low-temperature performance and the cycle performance of the lithium ion battery are effectively improved due to the improvement of the ion conducting capacity of the diaphragm. In addition, the diaphragm of the invention also has the advantages of high thermal stability, strong liquid absorption capacity and good safety performance.

Description

Diaphragm for lithium ion battery, preparation method of diaphragm and lithium ion battery
Technical Field
The invention relates to the field of lithium batteries, in particular to a diaphragm for a lithium ion battery, a preparation method of the diaphragm and the lithium ion battery.
Background
The lithium ion battery has the advantages of high energy density, high working voltage, long cycle life and the like, is widely applied to portable electronic equipment, and is also popularized in the fields of electric automobiles and the like. With the widening of the application field of the lithium ion battery, the price cost, the safety performance, the cycle life and the like of the lithium ion battery are more and more concerned.
The main components of a lithium ion battery include a positive electrode, a negative electrode, a separator, and an electrolyte. The diaphragm inserts in proper order between the positive negative pole, and its function mainly is: 1) the positive electrode and the negative electrode are physically isolated, so that internal short circuit is prevented; 2) the lithium ions are ensured to uniformly and freely move back and forth between the anode and the cathode through the electrolyte; 3) at too high a temperature, the diaphragm should have the capacity of self-closing micropores, so as to cut off the lithium ion path and prevent the battery from further thermal runaway. Because the diaphragm plays a role in isolating the positive electrode and the negative electrode, the improvement of the safety performance of the diaphragm is an important research direction on the basis of ensuring the electrical performance and the cycle life of the diaphragm.
At present, most of commercial lithium ion battery separators are polyolefin separators, but when the temperature of a battery rises, the separators shrink thermally and even melt, so that potential safety hazards are caused. In view of the above problems, a common solution in the art is to coat a layer of ceramic layer material on the separator to reduce thermal shrinkage and prevent short circuit between the positive and negative electrodes. Meanwhile, the adhesive of the pole pieces can be improved by coating polymers such as polyvinylidene fluoride and acrylic, and the safety and the electrical property of the battery can be improved. However, it should be noted that the existing ceramic-coated separators can be rarely done in improving the rate and low temperature performance of lithium ion batteries.
In view of the above, it is necessary to provide a technical solution to the above problems.
Disclosure of Invention
One of the objects of the present invention is: the diaphragm has the advantages of improving the rate capability and the low-temperature performance of the lithium ion battery, and is particularly suitable for a high-capacity and high-energy-density battery system.
In order to achieve the purpose, the invention adopts the following technical scheme:
a separator for a lithium ion battery, comprising:
a base film;
the composite coating is coated on at least one surface of the base film; comprises a fast ion conductor additive (FIC), a thickening agent and a binder, wherein the fast ion conductor additive is Li2O-Al2O3-TiO2-SiO2-P2O5、Li2O-Al2O3-GeO2-SiO2-P2O5、Li2O-Al2O3-GeO2-TiO2-SiO2-P2O5、Li2O-Al2O3-TiO2-P2O5、Li2O-Al2O3-GeO2-P2O5、Li2O-Cr2O3-GeO2-P2O5、Li2O-La2O3-ZrO2At least one of (1).
The diaphragm provided by the invention adopts the fast ion conductor additive which is a novel compound obtained from various oxides, the fast ion conductor additive is used as the main body of the composite coating, the fast ion conductor additive has the advantages of high ion conductivity and no electron conductivity, and the discharge multiplying power, the low-temperature performance and the cycle performance of the lithium ion battery are effectively improved due to the improvement of the ion conductivity of the diaphragm. In addition, the diaphragm of the invention also has the advantages of high thermal stability, strong liquid absorption capacity and good safety performance. For example, for some of the fast ion conductors, silicon dioxide is used as a main crystal phase, in the crystal structure of the fast ion conductors, 4 covalent bonds are formed between 4 valence electrons of a silicon atom and 4 oxygen atoms, a Si atom is located at the center of a regular tetrahedron, an O atom is located at the vertex of the tetrahedron, the formed atomic crystal framework is stable, other oxides are easier to crystallize, and the obtained novel compound is stable in structure and is not easy to collapse. The introduced phosphorus (P) element can reduce the melting point of the oxide, and the microcrystalline formation capability is stronger; the introduced lithium oxide can enhance the compatibility with active material materials on one hand, and provides a lithium source to further enhance the energy density of the battery on the other hand; the introduced alumina has the function of stabilizing crystal lattices, and further promotes the formation of microcrystals under the combined action of the alumina and P; in addition, Ti and/or Ge are introduced into the invention, and both can form a smaller ion channel, and the ion channel has a smaller aperture, so that the crystal structure of the fast ion conductor additive is ensured on one hand, and the aperture of the ion channel is matched with the radius of Li ions on the other hand, so that the ion channel is suitable for migration of the Li ions and can play a role in improving the conductivity of the Li ions.
In addition, even if SiO is not added in several fast ion conductor additives2As the main crystal phase, other oxides can still be crystallized at high temperature to obtain the fast ion conductor additive with high ion conductivity and no electron conductivity, thereby improving the performance of the diaphragm.
Preferably, the fast ion conductor additive is Li2O-Al2O3-TiO2-SiO2-P2O5、Li2O-Al2O3-GeO2-SiO2-P2O5、Li2O-Al2O3-GeO2-TiO2-SiO2-P2O5、Li2O-Al2O3-TiO2-P2O5、Li2O-Al2O3-GeO2-P2O5At least one of (1).
Preferably, the thickness of the composite coating is 0.2-5 μm. If the thickness of the composite coating is too small, the effects of reducing diaphragm shrinkage and cutting off lithium ion channels when the battery is overheated cannot be achieved; if the thickness of the coating is too large, the migration of lithium ions in normal use is influenced to a certain extent, and the cycle performance and the rate performance of the battery are further influenced.
Preferably, the thickness of the base film is 3-40 μm, and the porosity is 20-80%; the base film is any one of a polyethylene film, a polypropylene/polyethylene/polypropylene composite film, a polyvinylidene fluoride film, a polyethylene/polyvinylidene fluoride composite film, a polypropylene/polyvinylidene fluoride composite film, an aramid film and a polyimide film.
Preferably, the content of the thickening agent is 0.5-10 wt%; the thickening agent is at least one of sodium carboxymethyl cellulose, carboxyethyl cellulose, sodium alginate, polyacrylamide and polyvinyl alcohol.
Preferably, the content of the binder is 4-30 wt%; the binder is at least one of styrene-acrylic latex, pure acrylic latex, styrene-butadiene latex, polyvinylidene fluoride and ethylene-vinyl acetate copolymer.
Preferably, the composite coating further comprises ceramic powder, and the total content of the fast ion conductor additive and the ceramic powder is 60-95.5 wt%.
Preferably, the mass ratio of the ceramic powder to the fast ion conductor additive is (0-1): 1.
Preferably, the particle size of the fast ion conductor additive and the particle size of the ceramic powder are both larger than the aperture of the base film; the particle size of the fast ion conductor additive and the particle size of the ceramic powder are both 0.1-5.0 mu m, and the particle size refers to the average particle size. Generally, the aperture of base film is 10 ~ 100nm, guarantees that the particle diameter of fast ion conductor additive and ceramic powder is greater than the aperture of base film, and the micropore of base film can be blockked up with fast ion conductor additive granule when normal use to the ceramic powder that can avoid dropping, and then guarantees that the business turn over of lithium ion is unobstructed, guarantees the normal use of battery.
Another object of the present invention is to provide a method for preparing a separator, comprising the steps of:
s1, adding the fast ion conductor additive into a dispersion solvent to obtain conductive slurry;
s2, adding the conductive slurry into an aqueous solution of a thickening agent, and mixing to obtain primary slurry;
s3, adding the primary slurry into a binder, stirring and mixing, and filtering to obtain composite coating slurry;
and S4, coating the composite coating slurry on at least one surface of the base film, and drying to obtain the diaphragm.
Preferably, the contact angle of the composite coating slurry when coated is less than 90 ° to obtain a separator having a uniform coating thickness.
The invention also provides a lithium ion battery, which comprises a positive plate, a negative plate and a diaphragm arranged between the adjacent positive plate and the negative plate, wherein the diaphragm is any one of the diaphragms.
Preferably, the positive plate comprises lithium fast ion conductorThe additive of the lithium fast ion conductor is Li2O-Al2O3-MaOb-SiO2-P2O5Wherein M is Ti and/or Ge, 0<a≤2，0<b is less than or equal to 3. Specifically, the lithium fast ion conductor additive is Li2O-Al2O3-TiO2-SiO2-P2O5(LATP)、Li2O-Al2O3-GeO2-SiO2-P2O5(LAGP)、Li2O-Al2O3-GeO2-TiO2-SiO2-P2O5(LAGTP).
Compared with the prior art, the invention has the beneficial effects that:
1) the diaphragm provided by the invention adopts the fast ion conductor additive which is a novel compound obtained from various oxides, the fast ion conductor additive is used as the main body of the composite coating, the fast ion conductor additive has the advantages of high ion conductivity and no electron conductivity, and the discharge multiplying power, the low-temperature performance and the cycle performance of the lithium ion battery are effectively improved due to the improvement of the ion conductivity of the diaphragm. In addition, the diaphragm of the invention also has the advantages of high thermal stability, strong liquid absorption capacity and good safety performance.
2) In addition, the fast ion conductor additive introduced by the diaphragm also has the advantages of high thermal stability, strong liquid absorption capability, good safety performance and the like, has good compatibility with other materials on the pole piece such as a current collector and the like, and provides more possibilities for the application of the lithium ion battery in the military fields of mobile phones, notebook computers, digital cameras and other civil electronic products in low-temperature areas, unmanned planes and the like.
3) Compared with the existing ceramic coating technologies such as oxidation rate and boehmite, the composite coating preparation method provided by the invention can be consistent with the ceramic coating, is realized by the same coating method such as micro-gravure, and has the advantages of safety, environmental protection, simplicity, easiness in implementation and easiness in realizing industrial production.
Drawings
FIG. 1 is a graph showing discharge rate curves of batteries of examples 1 to 2 and comparative example of the present invention.
FIG. 2 is a bar graph showing low-temperature discharge of the batteries of examples 1 to 2 and comparative example of the present invention.
FIG. 3 is a graph showing cycle performance of batteries of examples 1 to 2 and comparative example of the present invention.
Detailed Description
In order to make the technical solutions and advantages of the present invention clearer, the present invention and its advantages will be described in further detail below with reference to the following detailed description and the accompanying drawings, but the embodiments of the present invention are not limited thereto.
Example 1
A diaphragm for a lithium ion battery comprises a base film and a composite coating; the composite coating is coated on at least one surface of the base film; the composite coating comprises a fast ion conductor additive (FIC), a thickening agent and a binder; the fast ion conductor additive is Li2O-Al2O3-TiO2-SiO2-P2O5(LATP)、Li2O-Al2O3-GeO2-SiO2-P2O5(LAGP)、Li2O-Al2O3-GeO2-TiO2-SiO2-P2O5(LAGTP)、Li2O-Al2O3-TiO2-P2O5(LAT)、Li2O-Al2O3-GeO2-P2O5(LAG)、Li2O-Cr2O3-GeO2-P2O5(LCG)、Li2O-La2O3-ZrO2(Li7La3Zr2O12LLZO).
Further, the fast ion conductor additive is Li2O-Al2O3-TiO2-SiO2-P2O5、Li2O-Al2O3-GeO2-SiO2-P2O5、Li2O-Al2O3-GeO2-TiO2-SiO2-P2O5、Li2O-Al2O3-TiO2-P2O5、Li2O-Al2O3-GeO2-P2O5At least one of (1). The content of the fast ion conductor additive is 60-95.5 wt%; the particle size of the fast ion conductor additive is 0.1-5.0 μm.
Furthermore, the thickness of the composite coating is 0.2-5 μm. If the thickness of the composite coating is too small, the effects of reducing diaphragm shrinkage and cutting off lithium ion channels when the battery is overheated cannot be achieved; if the thickness of the coating is too large, the migration of lithium ions in normal use is influenced to a certain extent, and the cycle performance and the rate performance of the battery are further influenced.
Further, the thickness of the base film is 3-40 μm, and the porosity is 20-80%; the base film is any one of a polyethylene film, a polypropylene/polyethylene/polypropylene composite film, a polyvinylidene fluoride film, a polyethylene/polyvinylidene fluoride composite film, a polypropylene/polyvinylidene fluoride composite film, an aramid film and a polyimide film.
Further, the content of the thickening agent is 0.5-10 wt%; the thickener is at least one of sodium carboxymethylcellulose, carboxyethyl cellulose, sodium alginate, polyacrylamide and polyvinyl alcohol.
Further, the content of the binder is 4-30 wt%; the binder is at least one of styrene-acrylic latex, pure acrylic latex, styrene-butadiene latex, polyvinylidene fluoride and ethylene-vinyl acetate copolymer.
The preparation method of the diaphragm comprises the following steps:
s1, adding the fast ion conductor additive into a dispersion solvent to obtain conductive slurry;
s2, adding the conductive slurry into an aqueous solution of a thickening agent, and mixing to obtain primary slurry;
s3, adding the primary slurry into the binder, stirring and mixing, and filtering to obtain composite coating slurry;
and S4, coating the composite coating slurry on at least one surface of the base film, and drying to obtain the diaphragm.
Further, the contact angle of the composite coating slurry is less than 90 DEG when the composite coating slurry is coated, so that the diaphragm with uniform coating thickness is obtained.
The specific preparation method of the embodiment comprises the following steps:
s1, adding a fast ion conductor additive LATP with the average diameter of 0.5 mu m into a dispersion solvent, and stirring for 60min to obtain conductive slurry;
s2, adding water and water-soluble carboxymethyl cellulose into a stirring and grinding machine according to the mass ratio of 98.5:1.5 to completely dissolve the carboxymethyl cellulose to obtain an aqueous solution of the carboxymethyl cellulose;
s3, adding the conductive slurry into the aqueous solution of the carboxymethyl cellulose according to the proportion, and stirring and mixing to obtain primary slurry;
s3, adding the primary slurry into styrene-acrylic emulsion, stirring and mixing uniformly, and filtering through a filter screen of 150 meshes to obtain composite coating slurry; wherein the mass ratio of the fast ion conductor additive, the styrene-acrylic latex and the sodium carboxymethyl cellulose in the composite coating slurry is 85:10: 5;
and S4, coating the composite coating slurry on one surface of a base film with the thickness of 12 microns in a gravure printing or extrusion coating mode, wherein the thickness of single-side coating is 3 microns, and drying to obtain the diaphragm.
The obtained diaphragm is applied to a lithium ion battery, and the lithium ion battery also comprises a positive plate and a negative plate; the positive plate is prepared by mixing a positive active material, a conductive agent and a binder; the negative plate is prepared by mixing a negative active material, a conductive agent and a binder.
The preparation method of the positive plate comprises the following steps: mixing a positive electrode active material, Carbon Nanotubes (CNTs), conductive carbon black (SP) and polyvinylidene fluoride according to a mass ratio of 98.0: 0.5: 0.5: 1.0, uniformly mixing and pulping to obtain anode plate slurry; and uniformly coating the slurry of the negative plate on two surfaces of the copper foil, rolling and cutting to obtain the negative plate, and finally baking and vacuum drying for later use.
The active material of the positive plate is at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese rich base or lithium manganese oxide, and also can be at least one of lithium iron phosphate, lithium nickelate, lithium nickel cobalt aluminate, lithium nickel manganese oxide, sulfur compound, lithium iron sulfate, lithium fluorophosphate, lithium vanadium fluorophosphate and lithium iron fluorophosphate. Lithium cobaltate was used as the positive electrode active material in this example.
The preparation method of the negative plate comprises the following steps: negative electrode active material (purchased from jiang violet light in technologies ltd), conductive carbon black (SP), carboxymethyl cellulose (CMC), Styrene Butadiene Rubber (SBR)/acrylic acid (PAA) were mixed in a mass ratio of 95.0: 1.5: 1.5: 2.0, uniformly mixing, and then dispersing in deionized water to obtain cathode plate slurry; and uniformly coating the slurry of the negative plate on two surfaces of the copper foil, rolling and cutting to obtain the negative plate, and finally baking and vacuum drying for later use.
Example 2
Different from the embodiment 1, the composite coating layer of the separator of the present embodiment further includes ceramic powder. The total content of the fast ion conductor additive and the ceramic powder is 60-95.5 wt%.
Furthermore, the mass ratio of the ceramic powder to the fast ion conductor additive is (0-1): 1.
Furthermore, the grain diameter of the fast ion conductor additive and the grain diameter of the ceramic powder are both larger than the aperture of the basement membrane; the particle sizes of the fast ion conductor additive and the ceramic powder are both 0.1-5.0 mu m, and the particle sizes refer to average particle sizes. Generally, the aperture of base film is 10 ~ 100nm, guarantees that the particle diameter of fast ion conductor additive and ceramic powder is greater than the aperture of base film, and the micropore of base film can be blockked up with fast ion conductor additive granule when normal use to the ceramic powder that can avoid dropping, and then guarantees that the business turn over of lithium ion is unobstructed, guarantees the normal use of battery.
The specific preparation method of the embodiment comprises the following steps:
s1, adding alumina ceramic powder with the average diameter of 0.5 mu m and a fast ion conductor additive LATP into a dispersion solvent according to the mass ratio of 1:1, and stirring for 60min to obtain conductive ceramic slurry;
s2, adding water and water-soluble carboxymethyl cellulose into a stirring and grinding machine according to the mass ratio of 98.5:1.5 to completely dissolve the carboxymethyl cellulose to obtain an aqueous solution of the carboxymethyl cellulose;
s3, adding the conductive ceramic slurry into the aqueous solution of the carboxymethyl cellulose in proportion, and stirring and mixing to obtain primary slurry;
s3, adding the primary slurry into styrene-acrylic emulsion, stirring and mixing uniformly, and filtering through a filter screen of 150 meshes to obtain composite coating slurry; wherein the mass ratio of the alumina, the fast ion conductor additive, the styrene-acrylic latex and the sodium carboxymethyl cellulose in the composite coating slurry is 42.5:42.5:10: 5;
and S4, coating the composite coating slurry on one surface of a base film with the thickness of 12 microns in a gravure printing or extrusion coating mode, wherein the thickness of single-side coating is 3 microns, and drying to obtain the diaphragm.
The rest is the same as embodiment 1, and the description is omitted here.
Example 3
Different from the embodiment 1, the positive plate of the lithium ion battery also comprises a lithium fast ion conductor additive, and the lithium fast ion conductor additive is Li2O-Al2O3-MaOb-SiO2-P2O5Wherein M is Ti and/or Ge, 0<a≤2，0<b is less than or equal to 3. Specifically, the lithium fast ion conductor additive is Li2O-Al2O3-TiO2-SiO2-P2O5(LATP)、Li2O-Al2O3-GeO2-SiO2-P2O5(LAGP)、Li2O-Al2O3-GeO2-TiO2-SiO2-P2O5(LAGTP) of at least one, predominantly Li2CO3、Al2O3、MaOb、NH4H2PO4And SiO2Is crystallized by Li2CO3、Al2O3、MaOb、NH4H2PO4And SiO2Several substances are used as reaction raw materials, the obtained lithium fast ion conductor additive is simple and efficient to operate and low in price, and the lithium fast ion conductor additive can be effectively enhanced when being applied to an electrode materialThe transmission ability of the ions in the pole piece also has the advantages of reducing DCR and improving low-temperature discharge without influencing the high-temperature circulation of the battery, and the whole electrochemical performance of the battery is improved.
Preferably, if the positive electrode sheet also contains a lithium fast ion conductor additive, the active material is preferably lithium cobaltate. Because the positive plate and the diaphragm both contain the fast ion conductor additive, the compatibility and the associativity of the two are better, and the obtained lithium ion battery can be more suitable for working under the low temperature condition and has the performances of low impedance and high temperature resistance.
The mass of the lithium fast ion conductor additive in the positive plate is 0.1-10% of the mass of the positive plate; the particle size of the lithium fast ion conductor additive is 0.05-50 μm. The DCR is gradually reduced along with the increase of the addition amount of the fast ion conductor additive, but the DCR is not obviously reduced when the addition amount reaches a certain value, which is because the lithium fast ion conductor additive is uniformly dispersed on the electrode under the appropriate addition amount, a relatively perfect ion conducting path is formed, and even if the addition amount of the FIC is further increased, the contribution to further improving the migration rate of lithium ions is small, so that the reduction of the DCR impedance is more facilitated by controlling the addition amount of the lithium fast ion conductor additive within a certain range. However, the grain size of FIC is reduced to some extent, which makes it easier to form a microcrystalline structure, and the ion channel formed by Ti and Ge is more abundant, which can further increase the conductivity of lithium ions, thereby further reducing the DCR value of the lithium ion battery. Preferably, the mass of the fast ion conductor additive is 0.5-5% of that of the positive plate; the particle size of the fast ion conductor additive is 0.1-10 μm.
One specific preparation method of the positive plate comprises the following steps:
s1, dissolving the lithium fast ion conductor additive in a solvent according to the mass ratio, and stirring and dispersing to obtain an additive dispersion liquid; wherein the solvent is N-N-dimethyl pyrrolidone (NMP), and the mass ratio of FIC/NMP is 1/100-1/10;
s2, dissolving the adhesive in NMP, adding the additive dispersion liquid, and mixing to obtain a mixed glue solution; the adhesive is polyvinylidene fluoride, the molecular weight is between 50 and 200 ten thousand, and the addition amount is 0.5 to 10 percent;
s3, adding a positive active material lithium cobaltate (4.45V) and a conductive agent into the mixed glue solution to obtain positive plate slurry; the conductive agent comprises at least one of conductive acetylene black, Ketjen black, conductive carbon black (SP), Carbon Nanotubes (CNTs), VGCF and graphene, wherein the SP and the CNTs are adopted in the embodiment, and the addition amount is 0.1-10%; the additive amount of the positive active material is 50-99.5%;
and S4, coating the slurry of the positive plate on two sides of the aluminum foil, rolling and cutting to obtain the positive plate, baking and vacuum drying the positive plate for later use, wherein the specific baking and vacuum drying conditions can refer to the existing setting and are not described herein again.
The second specific preparation method of the positive plate comprises the following steps:
s1, dry-mixing a positive electrode active material lithium cobaltate (4.45V), conductive carbon black (SP), a polyvinylidene fluoride adhesive and a lithium fast ion conductor additive to obtain a powder mixture;
s2, adding conductive slurry Carbon Nanotubes (CNTs) and an organic solvent (NMP) into the powder mixture, stirring and dispersing with high viscosity to obtain viscous slurry, and adding a proper amount of NMP to adjust the viscosity to obtain anode plate slurry;
and S3, uniformly coating the slurry of the positive plate on two sides of the aluminum foil, rolling and cutting to obtain the positive plate, baking and vacuum drying the positive plate for later use, wherein the specific baking and vacuum drying conditions can refer to the existing setting and are not described herein again.
In the two methods, lithium cobaltate, CNTs, SP and PVDF (polyvinylidene fluoride) are mixed according to the mass ratio of 98.0: 0.5: 0.5: 1.0, stirring and pulping, wherein the mass ratio of the lithium fast ion conductor additive to the lithium cobaltate is 1: 100.
The rest is the same as embodiment 1, and the description is omitted here.
Example 4
Different from the embodiment 2, the positive plate of the lithium ion battery of the present invention further includes a lithium fast ion conductor additive, and the lithium fast ion conductor refers to the lithium fast ion conductor of the embodiment 3, and is not described herein again.
The rest is the same as embodiment 2, and the description is omitted here.
The specific arrangement of the separator and the positive electrode plate in the lithium ion batteries according to the preparation methods of the embodiment 1, the embodiments 5 to 14 and the comparative example is shown in table 1, and the rest are the same as the embodiment 1, and are not repeated herein.
TABLE 1
Figure BDA0002923565470000111
The specific arrangement of the separator and the positive plate of the lithium ion batteries according to the preparation methods of the above embodiment 3 and embodiments 15 to 24 is shown in table 2, and the rest are the same as those of the above embodiment 3, and are not repeated herein.
TABLE 2
Figure BDA0002923565470000121
The separators of examples 1 to 2, 5 to 14 and comparative example described above were subjected to relevant performance tests including a heat shrinkage test and a puncture strength test.
1) Thermal shrinkage test: the test conditions were that the separator samples 1H were baked at 110 c, and the heat shrinkage rates of the respective groups of separator samples were calculated, and the results are shown in table 3.
2) And (3) testing puncture strength: during testing, the diaphragm sample is fixed on a universal testing machine, a needle head device with the diameter of 2mm is used for pricking the diaphragm sample at the speed of 50mm/min, a stress-strain curve is recorded, the puncture strength value of the diaphragm sample is obtained, each group of samples are tested repeatedly for 5 times, and the results are listed in table 3.
TABLE 3
Figure BDA0002923565470000131
As can be seen from table 3: the separators of examples 1 to 2 and 5 to 14 of the present invention were compared in heat shrinkage performance with the separator of the present invention having a fast ion conductor in the composite coating layerComparative example Al2O3The ceramic coating is basically consistent, and the short circuit risk of the battery caused by thermal shrinkage under the high-temperature condition can be effectively reduced. The puncture strength of the diaphragm of the invention is in the same level as that of the comparative example, so that the capability of resisting the puncture of impurities, burrs and the like in the processes of winding and the like is also ensured, and the safety performance of the battery is favorably improved.
In addition, from the above test results, it can be seen that different types, different particle sizes, and different addition amounts of FIC all have certain effects on the heat shrinkage performance and puncture strength of the separator. Generally, as FIC content increases, the thermal shrinkage of the diaphragm generally shows a tendency to decrease first and then increase; the smaller the particle size of FIC, the smaller the thermal shrinkage of the separator, but the smaller the puncture strength value, and conversely, the larger the particle size, the larger the thermal shrinkage of the separator, and the larger the puncture strength value, mainly because the smaller the particle size, the more uniform the fast ion conductor additive is mixed in the composite coating slurry, and the more uniform the fast ion conductor additive is coated on the base film, the thermal shrinkage of the separator as a whole can be reduced.
And then, carrying out related performance tests on the lithium ion batteries prepared in the embodiments 1-24 and the comparative example, wherein the related performance tests comprise rate capability and low-temperature performance.
1. The results of the rate capability test are shown in tables 4-5 and FIG. 1. Wherein Table 4 shows the test results of examples 1 to 2, 5 to 14 and comparative example; table 5 shows the test results of examples 3 to 4 and 15 to 24.
TABLE 4
Figure BDA0002923565470000141
TABLE 5
Figure BDA0002923565470000142
Figure BDA0002923565470000151
By the above-mentioned measurementAs a result of the examination, it was found that under the high rate conditions of 2.0C and 1.5C, conventional Al2O3The discharge rate of the ceramic coating is relatively poor, because the FIC contained in the diaphragm of the lithium ion battery prepared by the diaphragm of the invention has the characteristic of leading lithium ions, the speed of the diaphragm for transmitting the lithium ions can be improved, and the advantage can be more obviously reflected under the heavy current, thereby providing the rate discharge performance of the battery.
The ratio of FIC to ceramic powder added by mass, and the particle size and type of FIC also affect the rate performance of the lithium ion battery. As can be seen from the comparison of examples 1 to 2 and 5 to 7, the discharge performance of the lithium ion battery at high rate is more excellent as the amount of FIC added is increased. If the grain size of the FIC is reduced, the FIC is dispersed in the diaphragm more uniformly, and the high-rate discharge performance is further improved. In addition, from the comparison of the above examples 2, 9 to 10 and 14, the lithium ion battery obtained by using LATP as the fast ion conductor additive has better high-rate discharge performance, mainly because the LATP type fast ion conductor additive has the highest conductivity, so the advantage of the LATP type fast ion conductor additive under high current is more obvious.
In addition, when the lithium fast ion conductor additive is also added into the positive plate, the performance is improved more obviously under high multiplying power, and the FIC is dispersed on the positive plate to form an ion conductive path, so that the purpose of further improving the lithium ion transmission rate is achieved. However, it should be noted that the addition amount of FIC in the positive electrode sheet should be controlled, and when the FIC forms a more perfect ion conduction path, even if the FIC content is further increased, the FIC content contributes less to further increase the migration rate of lithium ions, and relatively speaking, the addition amount of FIC of 1% is more suitable.
2. The test results of the low-temperature discharge performance are shown in tables 6 to 7 and FIG. 2. Wherein Table 6 shows the test results of examples 1 to 2, 5 to 14 and comparative example; table 7 shows the test results of examples 3 to 4 and 15 to 24.
TABLE 6
Figure BDA0002923565470000161
TABLE 7
Figure BDA0002923565470000162
Figure BDA0002923565470000171
The results of the low-temperature discharge test also prove that the added FIC is favorable for improving the discharge ratio of the lithium ion battery under the low-temperature conditions of-20 ℃ and-10 ℃, because the mobility difficulty of lithium ions is increased sharply due to the fact that the viscosity of electrolyte is increased and the conductivity of the battery is reduced and negative pole adhesive is vitrified under the low-temperature conditions, but the FIC has the characteristic of guiding the lithium ions, and the added FIC can play a role in transmitting the lithium ions in both a diaphragm and an electrode and is slightly influenced by the low-temperature environment.
In addition, the invention also aims at the examples 1-2 and the comparative example to carry out the cycle performance test under the conditions of 0.7C charging/0.7C discharging, CV0.02C, and the test result is shown in figure 3. The experimental results also show that the cycle performance of examples 1-2 is also significantly better than that of comparative example Al due to the presence of FIC2O3A ceramic coated membrane.
In conclusion, the test results show that the diaphragm provided by the invention uses the fast ion conductor additive as the main body of the composite coating, and has the advantages of high ion conductivity and no electron conductivity, so that the ion conductivity of the diaphragm can be improved, and further, the discharge multiplying power, the low-temperature performance and the cycle performance of the lithium ion battery are effectively improved.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (10)

1. A separator for a lithium ion battery, comprising:
a base film;
the composite coating is coated on at least one surface of the base film; comprises a fast ion conductor additive, a thickening agent and a binder; the fast ion conductor additive is Li2O-Al2O3-TiO2-SiO2-P2O5、Li2O-Al2O3-GeO2-SiO2-P2O5、Li2O-Al2O3-GeO2-TiO2-SiO2-P2O5、Li2O-Al2O3-TiO2-P2O5、Li2O-Al2O3-GeO2-P2O5、Li2O-Cr2O3-GeO2-P2O5、Li2O-La2O3-ZrO2At least one of (1).
2. The separator of claim 1, wherein the fast ion conductor additive is Li2O-Al2O3-TiO2-SiO2-P2O5、Li2O-Al2O3-GeO2-SiO2-P2O5、Li2O-Al2O3-GeO2-TiO2-SiO2-P2O5、Li2O-Al2O3-TiO2-P2O5、Li2O-Al2O3-GeO2-P2O5At least one of (1).
3. The separator according to claim 1, wherein the thickness of the composite coating layer is 0.2 to 5 μm.
4. The separator according to claim 1, wherein the thickener is contained in an amount of 0.5 to 10 wt%; the thickening agent is at least one of sodium carboxymethyl cellulose, carboxyethyl cellulose, sodium alginate, polyacrylamide and polyvinyl alcohol.
5. The separator according to claim 1, wherein the binder is present in an amount of 4 to 30 wt%; the binder is at least one of styrene-acrylic latex, pure acrylic latex, styrene-butadiene latex, polyvinylidene fluoride and ethylene-vinyl acetate copolymer.
6. The separator according to any one of claims 1 to 5, wherein the composite coating further comprises ceramic powder, and the total content of the fast ion conductor additive and the ceramic powder is 60 to 95.5 wt%.
7. The separator according to claim 6, wherein the mass ratio of the ceramic powder to the fast ion conductor additive is (0-1): 1.
8. The separator of claim 7, wherein the particle size of the fast ion conductor additive and the particle size of the ceramic powder are both larger than the pore size of the base film; the particle size of the fast ion conductor additive and the particle size of the ceramic powder are both 0.1-5.0 mu m.
9. A method for preparing a separator, comprising the steps of:
s1, adding the fast ion conductor additive into a dispersion solvent to obtain conductive slurry;
s2, adding the conductive slurry into an aqueous solution of a thickening agent, and mixing to obtain primary slurry;
s3, adding the primary slurry into a binder, stirring and mixing, and filtering to obtain composite coating slurry;
and S4, coating the composite coating slurry on at least one surface of the base film, and drying to obtain the diaphragm.
10. A lithium ion battery, comprising a positive plate, a negative plate and a diaphragm which is arranged between the adjacent positive plate and the negative plate, wherein the diaphragm is the diaphragm of any one of claims 1 to 8.
CN202110134547.0A 2021-01-29 2021-01-29 Diaphragm for lithium ion battery, preparation method of diaphragm and lithium ion battery Pending CN112968254A (en)

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CN114188668A (en) * 2021-12-17 2022-03-15 蜂巢能源科技股份有限公司 Coating slurry, preparation method thereof, composite diaphragm and lithium ion battery
CN114292552A (en) * 2021-12-31 2022-04-08 蜂巢能源科技(无锡)有限公司 Polyolefin diaphragm modification liquid, modified polyolefin diaphragm and preparation method and application thereof
CN114335902A (en) * 2021-12-23 2022-04-12 上海瑞浦青创新能源有限公司 Composite diaphragm and preparation method and application thereof
CN114335898A (en) * 2021-12-31 2022-04-12 北京卫蓝新能源科技有限公司 Diaphragm for metal lithium battery, preparation method of diaphragm and corresponding metal lithium battery
CN114361711A (en) * 2021-12-31 2022-04-15 北京卫蓝新能源科技有限公司 Composite coating diaphragm of metal lithium battery, preparation method of composite coating diaphragm and corresponding lithium battery
CN115275521A (en) * 2022-09-08 2022-11-01 珠海冠宇电池股份有限公司 Diaphragm, roll up core and battery

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CN114188668A (en) * 2021-12-17 2022-03-15 蜂巢能源科技股份有限公司 Coating slurry, preparation method thereof, composite diaphragm and lithium ion battery
CN114188668B (en) * 2021-12-17 2024-02-13 蜂巢能源科技股份有限公司 Coating slurry, preparation method thereof, composite diaphragm and lithium ion battery
CN114335902A (en) * 2021-12-23 2022-04-12 上海瑞浦青创新能源有限公司 Composite diaphragm and preparation method and application thereof
CN114292552A (en) * 2021-12-31 2022-04-08 蜂巢能源科技(无锡)有限公司 Polyolefin diaphragm modification liquid, modified polyolefin diaphragm and preparation method and application thereof
CN114335898A (en) * 2021-12-31 2022-04-12 北京卫蓝新能源科技有限公司 Diaphragm for metal lithium battery, preparation method of diaphragm and corresponding metal lithium battery
CN114361711A (en) * 2021-12-31 2022-04-15 北京卫蓝新能源科技有限公司 Composite coating diaphragm of metal lithium battery, preparation method of composite coating diaphragm and corresponding lithium battery
CN114335898B (en) * 2021-12-31 2024-02-23 北京卫蓝新能源科技有限公司 Diaphragm for metal lithium battery, preparation method of diaphragm and corresponding metal lithium battery
CN115275521A (en) * 2022-09-08 2022-11-01 珠海冠宇电池股份有限公司 Diaphragm, roll up core and battery

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Application publication date: 20210615