High-liquid-retention self-repairing diaphragm, preparation method thereof and lithium ion battery
阅读说明：本技术 一种高保液自修复隔膜及其制备方法、锂离子电池 (High-liquid-retention self-repairing diaphragm, preparation method thereof and lithium ion battery ) 是由 符宽 赖旭伦 孙先维 陈杰 杨山 郑明清 于 2020-12-08 设计创作，主要内容包括：本发明属于电池材料技术领域,尤其涉及一种高保液自修复隔膜,包括基膜以及设置于所述基膜至少一面的功能涂层,所述功能涂层由混合浆料涂覆干燥形成,所述混合浆料包括陶瓷浆料和PEO-PAA络合物溶液。另外,本发明还涉及一种高保液自修复隔膜的制备方法及一种锂离子电池。相比于现有技术,本发明的隔膜具有良好的吸电解液能力,同时对隔膜的损坏具有一定的修复能力,能提高电池的循环稳定性和安全性。(The invention belongs to the technical field of battery materials, and particularly relates to a high-liquid-retention self-repairing diaphragm which comprises a base film and a functional coating arranged on at least one surface of the base film, wherein the functional coating is formed by coating and drying mixed slurry, and the mixed slurry comprises ceramic slurry and a PEO-PAA complex solution. In addition, the invention also relates to a preparation method of the high liquid retention self-repairing diaphragm and a lithium ion battery. Compared with the prior art, the diaphragm provided by the invention has good electrolyte absorption capacity, has certain repair capacity for damage of the diaphragm, and can improve the cycle stability and safety of the battery.)
1. The high-liquid-retention self-repairing diaphragm is characterized by comprising a base film and a functional coating arranged on at least one surface of the base film, wherein the functional coating is formed by coating and drying mixed slurry, and the mixed slurry comprises ceramic slurry and PEO-PAA complex solution.
2. The high liquid retention and self-repair membrane of claim 1, wherein the solid content of the PEO-PAA complex solution is 10-15% of the solid content of the ceramic slurry.
3. The high liquid retention and self-repair membrane of claim 1, wherein the ceramic slurry comprises ceramic powder, a thickening agent, a wetting agent and a glue solution.
4. The high liquid retention and self-repair membrane of claim 1, wherein the PEO-PAA complex solution is prepared by separately dissolving PEO and PAA in deionized water and blending.
5. The high liquid retention and self-repair membrane of claim 4, wherein the mass ratio of the PEO to the PAA in the PEO-PAA complex solution is 1 (0.4-0.8).
6. The high liquid retention and self-repair membrane of claim 5, wherein the PEO has a molecular weight of 650 to 750 ten thousand, and the PAA has a molecular weight of 90 to 110 ten thousand.
7. The high liquid retention and self-repair membrane as claimed in claim 1, wherein the thickness of the base membrane is 1-20 μm, and the base membrane is at least one of a polyethylene film, a polypropylene film, a polyimide film and a non-woven fabric.
8. The high liquid retention and self-repair membrane as claimed in claim 1, wherein the thickness of the functional coating is 0.5-10 μm.
9. The preparation method of the high liquid retention self-repairing diaphragm as claimed in any one of claims 1 to 8, characterized by comprising the following steps:
1) respectively and independently dissolving PEO and PAA in deionized water to form a solution A and a solution B with the concentration of 15-25 mg/mL;
2) according to the following steps of 1: (0.4-0.8) taking the solution A and the solution B according to the proportion, and carrying out rapid stirring and blending reaction to prepare a PEO-PAA complex solution;
3) adding the PEO-PAA complex solution into the ceramic slurry, and uniformly mixing to obtain mixed slurry;
4) and coating the mixed slurry on at least one surface of the base film, and drying to form a functional coating, thereby obtaining the high-liquid-retention self-repairing diaphragm.
10. A lithium ion battery, characterized by comprising the high liquid retention self-repair separator as claimed in any one of claims 1 to 8.
Technical Field
The invention belongs to the technical field of battery materials, and particularly relates to a high-liquid-retention self-repairing diaphragm, a preparation method of the diaphragm, and a lithium ion battery.
Background
Lithium ion batteries have attracted attention because of their high energy density, high volume density, and reusability. The separator is an extremely critical part of a lithium ion battery. Currently, polyolefin separators are most widely used in lithium ion batteries because of their excellent mechanical strength, uniform and stable pore structure, and low cost characteristics. However, the polyolefin separator still has obvious disadvantages such as poor wettability to liquid electrolyte, low liquid retention rate, poor heat resistance and the like.
In order to solve the above disadvantages of the polyolefin separator, the polyolefin separator may be modified to improve the electrode/electrolyte interface performance, thereby further improving the electrochemical performance of the battery. Most of the commercial separators at present are coated with a ceramic layer on the surface of the separator to increase the heat resistance and strength of the separator to improve the safety performance of the battery. However, the absorption and diffusion rate of the electrolyte of the separator coated with the ceramic layer is not obviously improved.
As is known, a lithium battery continuously consumes electrolyte during charging and discharging, and the liquid retention of the battery determines the charging and discharging performance and the service life of the battery. In view of the above, it is necessary to provide a new separator to improve the liquid retention of the battery, and further improve the charging and discharging performance and the service life of the battery.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, the high liquid retention self-repairing diaphragm is provided, has good electrolyte absorption capacity, and has certain repair capacity on the damage of the diaphragm.
In order to achieve the purpose, the invention adopts the following technical scheme:
the high liquid retention self-repairing diaphragm comprises a base film and a functional coating arranged on at least one surface of the base film, wherein the functional coating is formed by coating and drying mixed slurry, and the mixed slurry comprises ceramic slurry and PEO-PAA complex solution.
As an improvement of the high liquid retention self-repairing diaphragm, the solid content of the PEO-PAA complex solution is 10-15% of that of the ceramic slurry.
As an improvement of the high liquid retention self-repairing diaphragm, the ceramic slurry comprises ceramic powder, a thickening agent, a wetting agent and glue solution.
As an improvement of the high liquid retention self-repair diaphragm, the PEO-PAA complex solution is prepared by respectively dissolving PEO and PAA in deionized water and then blending.
As an improvement of the high liquid retention self-repair diaphragm, the mass ratio of the PEO to the PAA in the PEO-PAA complex solution is 1 (0.4-0.8).
As an improvement of the high liquid retention self-repairing diaphragm, the molecular weight of the PEO is 650-750 ten thousand, and the molecular weight of the PAA is 90-110 ten thousand.
As an improvement of the high liquid retention self-repairing diaphragm, the thickness of the base film is 1-20 microns, and the base film is at least one of a polyethylene film, a polypropylene film, a polyimide film and a non-woven fabric.
As an improvement of the high liquid retention self-repairing diaphragm, the thickness of the functional coating is 0.5-10 μm.
The second purpose of the invention is: the preparation method of the high liquid retention self-repairing diaphragm comprises the following steps:
1) respectively and independently dissolving PEO and PAA in deionized water to form a solution A and a solution B with the concentration of 15-25 mg/mL;
2) according to the following steps of 1: (0.4-0.8) taking the solution A and the solution B according to the proportion, and carrying out rapid stirring and blending reaction to prepare a PEO-PAA complex solution;
3) adding the PEO-PAA complex solution into the ceramic slurry, and uniformly mixing to obtain mixed slurry;
4) and coating the mixed slurry on at least one surface of the base film, and drying to form a functional coating, thereby obtaining the high-liquid-retention self-repairing diaphragm.
The third purpose of the invention is that: the lithium ion battery comprises the high liquid retention self-repairing diaphragm.
Compared with the prior art, the beneficial effects of the invention include but are not limited to:
1) according to the invention, the PEO-PAA complex is added into the functional coating of the diaphragm, the complex has good film forming property, and a large number of hydrogen bonds are contained in the three substances of the PEO/PAA/PEO-PAA complex, and the three substances are combined through the hydrogen bonds in the drying process to form a stable film structure, so that the functional coating can be kept integral by mixing the stable film structure with the ceramic slurry, and the subsequent cutting process is facilitated.
2) According to the invention, the PEO-PAA complex is added into the functional coating of the diaphragm, and the complex has good electrophilic electrolyte performance, can absorb electrolyte to form tiny gel particles, and has good liquid retention. Specifically, because hydroxyl groups in polyethylene oxide can be combined with ether bonds in the electrolyte, the dissolution of PEO in the electrolyte is a process of swelling and then dissolving, and the existence of PAA and PEO form a complex so as to weaken the dissolution of PEO, namely when PEO and ether bonds in the electrolyte start to act, carboxyl groups of PAA replace ether bonds, so that PEO is in a liquid-absorbing swelling state, namely a gel state, and the absorption and infiltration of the electrolyte are improved. In addition, PAA and PEO are bonded to reduce crystallization of PEO, and the formed amorphous region is favorable for Li+To be transmitted.
3) According to the invention, the PEO-PAA complex is added into the functional coating of the diaphragm, and the complex has certain adhesive property after absorbing electrolyte, so that the interface stability can be further increased.
4) The invention adds PEO-PAA complex in the functional coating of the diaphragm, the complex is a substance which conducts ions and blocks electrons, the addition does not affect the performance of the diaphragm, and when the diaphragm is punctured by lithium dendrite, the PEO-PAA complex can flow to block the pores, and has a repairing function, thereby increasing the safety performance.
Drawings
FIG. 1 is a graph showing the melting point change of PEO and a PEO-PAA complex in the present invention.
Fig. 2 is a graph comparing the cycle stability of the batteries of example 1 and comparative example 1 in the present invention.
Fig. 3 is a comparative plot of the polarization voltage of the cells of example 1 and comparative example 1 of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below. The examples of the invention should not be construed as limiting the invention.
1. High liquid retention self-repairing diaphragm
The invention provides a high-liquid-retention self-repairing diaphragm which comprises a base film and a functional coating arranged on at least one surface of the base film, wherein the functional coating is formed by coating and drying mixed slurry, and the mixed slurry comprises ceramic slurry and PEO-PAA complex solution. The structural formulas of the PEO, the PAA and the PEO-PAA complex are respectively shown in formulas I to III.
Among them, polyethylene oxide (PEO) has an unshared electron pair of ether oxygen, has a strong affinity for hydrogen bonds, and can form complexes with many organic low-molecular compounds, polymers, and some inorganic electrolytes. Polyacrylic acid (PAA) is a water-soluble high-molecular polymer, and is often used as a binder in the lithium battery industry. The inventor finds that: 1) the melting point of the complex formed by hydrogen bonding PEO and PAA to each other is greatly changed, and the complex does not see melting peak at 100 ℃, which means that the addition of the complex does not cause the battery to be at 100 DEG CThe inside has an adverse effect. The melting point profiles of PEO and PEO-PAA complexes are shown in figure 1. 2) The PEO-PAA complex has good film forming property, can keep the integrity of the functional coating by mixing the PEO-PAA complex with the ceramic slurry, and is beneficial to the subsequent slitting process. Specifically, three substances, i.e., PEO/PAA/PEO-PAA complex, have a large number of hydrogen bonds, and they are combined by hydrogen bonds during drying to form a stable film structure. 3) The PEO-PAA complex has good electrophilic electrolyte performance, can absorb electrolyte to form tiny gel particles, and has good liquid retention. Specifically, because hydroxyl in polyethylene oxide can be combined with ether bonds in the electrolyte, PEO is dissolved in the electrolyte in a process of swelling and dissolving, and the existence of PAA and PEO form a complex to weaken the dissolution of PEO, namely when PEO and ether bonds in the electrolyte begin to act, carboxyl of PAA replaces ether bonds, PEO is in a liquid-absorbing swelling state, namely a gel state, so that the absorption and infiltration of the electrolyte are improved, and the PAA and PEO are bonded to reduce the crystallization of PEO, and the formed amorphous region is favorable for Li+To be transmitted. 4) The PEO-PAA complex has certain adhesive property after absorbing the electrolyte, thereby further increasing the interface stability. 5) The PEO-PAA complex is a substance that conducts ions and blocks electrons, so its addition does not affect the performance of the separator, and when the separator is punctured by lithium dendrite, the PEO-PAA complex flows to block the pores, having a repairing function, thereby increasing the safety performance.
In some embodiments, the PEO-PAA complex solution has a solid content of 10-15% of the solid content of the ceramic slurry. When the content of the PEO-PAA complex is too high, the cell is easy to soften, and when the content of the PEO-PAA complex is too low, the liquid retention and self-repairing effects are not obvious.
In some embodiments, the ceramic slurry includes a ceramic powder, a thickener, a wetting agent, and a glue solution. Specifically, the ceramic powder may be at least one of calcium oxide, zinc oxide, magnesium oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, cerium dioxide, aluminum oxide, boehmite, calcium carbonate, and barium titanate. Preferably, the ceramic powder is alumina ceramic powder.
In some embodiments, the PEO-PAA complex solution is prepared by separately dissolving PEO and PAA in deionized water and blending. The two solutions are respectively prepared and then mixed, so that the mixing is more uniform.
In some embodiments, the mass ratio of PEO to PAA in the PEO-PAA complex solution is 1 (0.4-0.8). Preferably, the mass ratio of PEO to PAA is 1: 0.6. Because the melting point of the PEO is low (about 60 ℃), if the proportion of the PEO is too high, the use temperature range of the battery core is limited, and the PEO swells and dissolves in the electrolyte, and if the proportion of the PEO is too high, the integrity of the diaphragm is affected after liquid injection; in addition, because of strong hydrogen bonding force between PEO and PAA, if the content of PAA is too high, individual PEO-PAA agglomerated particles are formed in the slurry, which affects the coating process and the surface uniformity of the separator.
In some embodiments, the PEO has a molecular weight of 650 to 750 ten thousand and the PAA has a molecular weight of 90 to 110 ten thousand. Preferably, the PEO has a molecular weight of 700 million and the PAA has a molecular weight of 100 million. PEO with a molecular weight of 700 million is selected because the higher the molecular weight of the polymer, the higher the viscosity of the polymer, and thus the PEO solution can act as a thickener and dispersion in the mixed slurry.
In some embodiments, the base film has a thickness of 1 to 20 μm, and the base film is at least one of a polyethylene film, a polypropylene film, a polyimide film, and a non-woven fabric. Of course, the base film may be a composite of at least two of the films listed above.
In some embodiments, the functional coating has a thickness of 0.5 to 10 μm. Too thin a functional coating layer does not provide a corresponding improvement, and too thick a functional coating layer may reduce the energy density of the battery.
2. Preparation method
The second aspect of the invention provides a preparation method of the high liquid retention self-repairing diaphragm, which comprises the following steps:
1) respectively and independently dissolving PEO and PAA in deionized water to form a solution A and a solution B with the concentration of 15-25 mg/mL;
2) according to the following steps of 1: (0.4-0.8) taking the solution A and the solution B according to the proportion, and carrying out rapid stirring and blending reaction to prepare a PEO-PAA complex solution;
3) adding the PEO-PAA complex solution into the ceramic slurry, and uniformly mixing to obtain mixed slurry;
4) and coating the mixed slurry on at least one surface of the base film, and drying to form a functional coating, thereby obtaining the high-liquid-retention self-repairing diaphragm.
In some embodiments, the ceramic slurry includes a ceramic powder, a thickener, a wetting agent, and a glue solution. The solid content of the ceramic slurry is 28-35%.
In some embodiments, the mixed slurry comprises ceramic powder, thickener, wetting agent, gum solution, and PEO-PAA complex, wherein the dry weight ratio of the ceramic powder, the thickener, the wetting agent, the gum solution, and the PEO-PAA complex is 82%, 0.3%, 0.5%, 6.5%, and 10.7%, respectively.
3. Lithium ion battery
The third aspect of the invention provides a lithium ion battery, which comprises the high liquid retention self-repairing diaphragm.
In some embodiments, the lithium ion battery of the present invention includes a positive electrode sheet, a negative electrode sheet, and a separator.
Positive electrode
The positive plate comprises a positive current collector and a positive active material layer coated on at least one surface of the positive current collector. The material of the positive electrode current collector includes, but is not limited to, aluminum foil, and the specific type of the positive electrode active material layer is not particularly limited and may be selected as desired.
In some embodiments, the positive electrode active material layer includes a positive electrode active material including LiCoO2、LiNiO2、LiMnO4、LiCo1-yMyO2、LiNi1-yMyO4And LiNixCoyMnzM1-x-y-zO2Wherein M is at least one of Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, and y is more than or equal to 0 and less than or equal to 1, x is more than or equal to 0 and less than or equal to 1<1，0≤z≤1，x+y+z≤1。
In some embodiments, the positive electrode further comprises a binder that improves the binding of the positive active material particles to each other and also improves the binding of the positive active material to the body of the pole piece. Non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like.
In some embodiments, the positive electrode further comprises a conductive material, thereby imparting conductivity to the electrode. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.
Negative electrode
The negative plate comprises a negative current collector and a negative active material layer coated on at least one surface of the negative current collector. The material of the negative electrode current collector includes, but is not limited to, copper foil, and the specific kind of the negative electrode active material layer is not particularly limited and may be selected as desired.
In some embodiments, the negative electrode active material layer includes a negative electrode active material including carbon, graphite, and SiO2One or a combination of two of (1).
In some embodiments, the negative active material layer may include a binder that improves the binding of the negative active material particles to each other and to the current collector. Non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon, and the like.
In some embodiments, the negative electrode active material layer further includes a conductive material, thereby imparting conductivity to the electrode. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.
Embodiments of the present invention are illustrated below with reference to examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the claimed invention.
Example 1
Preparing a positive plate:
lithium cobaltate (positive electrode active material), conductive agent superconducting carbon (Super-P), and binder polyvinylidene fluoride (PVDF) according to a mass ratio of 96: 2.0: 2.0, evenly mixing to prepare anode slurry, coating the slurry on a current collector aluminum foil, drying at 110 ℃, and then carrying out cold pressing, slitting, edge cutting and tab welding to prepare the lithium ion battery anode plate.
Preparing a negative plate:
graphite, conductive agent superconducting carbon (Super-P), thickening agent carboxymethyl cellulose sodium (CMC) and binder Styrene Butadiene Rubber (SBR) are mixed according to a mass ratio of 96: 1.5: 1.0: 1.5 preparing negative electrode slurry, coating the slurry on a current collector copper foil, drying at 85 ℃, and then carrying out cold pressing, slitting, edge cutting and tab welding to prepare the lithium ion battery negative electrode plate.
Preparing a high liquid retention self-repairing diaphragm:
1) respectively dissolving PEO with the molecular weight of 700 million and PAA with the molecular weight of 100 million into deionized water to form a solution A and a solution B with the concentration of 20 mg/mL;
2) according to the following steps of 1: taking the solution A and the solution B according to the proportion of 0.6, and carrying out rapid stirring and blending reaction to prepare a PEO-PAA complex solution;
3) adding the PEO-PAA complex solution into the ceramic slurry, and uniformly mixing to obtain mixed slurry; in this embodiment, the mixed slurry includes alumina ceramic powder, a thickener, a wetting agent, a glue solution and a PEO-PAA complex, and the dry weights of the above substances are 82%, 0.3%, 0.5%, 6.5% and 10.7%, respectively.
4) And coating the mixed slurry on at least one surface of a base film (polypropylene film) with the thickness of 9 mu m, and drying to form a functional coating with the thickness of 4 mu m, thus obtaining the high-liquid-retention self-repairing diaphragm.
Preparing an electrolyte: mixing lithium hexafluorophosphate (LiPF)6) Dissolving the components in a solvent with the mass ratio of 1: 2: 1 Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) to obtain an electrolyte.
Preparing a lithium ion battery: winding the positive plate, the diaphragm and the negative plate into a battery cell, wherein the isolating film is positioned between the adjacent positive plate and the negative plate, the positive electrode is led out by spot welding of an aluminum tab, and the negative electrode is led out by spot welding of a nickel tab; and then placing the battery core in an aluminum-plastic packaging bag, injecting the electrolyte, and carrying out processes such as packaging, formation, capacity and the like to prepare the lithium ion battery.
Example 2
Different from the embodiment 1, the preparation of the high liquid retention self-repairing diaphragm comprises the following steps:
1) respectively dissolving PEO with the molecular weight of 700 million and PAA with the molecular weight of 100 million into deionized water to form a solution A and a solution B with the concentration of 20 mg/mL;
2) according to the following steps of 1: taking the solution A and the solution B according to the proportion of 0.6, and carrying out rapid stirring and blending reaction to prepare a PEO-PAA complex solution;
3) adding the PEO-PAA complex solution into the ceramic slurry, and uniformly mixing to obtain mixed slurry; in this embodiment, the mixed slurry includes alumina ceramic powder, a thickener, a wetting agent, a glue solution and a PEO-PAA complex, and the dry weights of the above substances are 82%, 0.3%, 0.5%, 6.5% and 10.7%, respectively.
4) And coating the mixed slurry on at least one surface of a base film (polypropylene film) with the thickness of 9 mu m, and drying to form a functional coating with the thickness of 4 mu m, thus obtaining the high-liquid-retention self-repairing diaphragm.
The rest is the same as embodiment 1, and the description is omitted here.
Example 3
Different from the embodiment 1, the preparation of the high liquid retention self-repairing diaphragm comprises the following steps:
1) respectively dissolving PEO with the molecular weight of 700 million and PAA with the molecular weight of 100 million into deionized water to form a solution A and a solution B with the concentration of 20 mg/mL;
2) according to the following steps of 1: taking the solution A and the solution B according to the proportion of 0.6, and carrying out rapid stirring and blending reaction to prepare a PEO-PAA complex solution;
3) adding the PEO-PAA complex solution into the ceramic slurry, and uniformly mixing to obtain mixed slurry; in this embodiment, the mixed slurry includes alumina ceramic powder, a thickener, a wetting agent, a glue solution and a PEO-PAA complex, and the dry weights of the above substances are 82%, 0.3%, 0.5%, 6.5% and 10.7%, respectively.
4) And coating the mixed slurry on at least one surface of a base film (polypropylene film) with the thickness of 9 mu m, and drying to form a functional coating with the thickness of 4 mu m, thus obtaining the high-liquid-retention self-repairing diaphragm.
The rest is the same as embodiment 1, and the description is omitted here.
Example 4
Different from the embodiment 1, the preparation of the high liquid retention self-repairing diaphragm comprises the following steps:
1) respectively dissolving PEO with the molecular weight of 700 million and PAA with the molecular weight of 100 million into deionized water to form a solution A and a solution B with the concentration of 20 mg/mL;
2) according to the following steps of 1: taking the solution A and the solution B according to the proportion of 0.4, and carrying out rapid stirring and blending reaction to prepare a PEO-PAA complex solution;
3) adding the PEO-PAA complex solution into the ceramic slurry, and uniformly mixing to obtain mixed slurry; in this embodiment, the mixed slurry includes alumina ceramic powder, a thickener, a wetting agent, a glue solution and a PEO-PAA complex, and the dry weights of the above substances are 82%, 0.3%, 0.5%, 6.5% and 10.7%, respectively.
4) And coating the mixed slurry on at least one surface of a base film (polypropylene film) with the thickness of 9 mu m, and drying to form a functional coating with the thickness of 4 mu m, thus obtaining the high-liquid-retention self-repairing diaphragm.
The rest is the same as embodiment 1, and the description is omitted here.
Example 5
Different from the embodiment 1, the preparation of the high liquid retention self-repairing diaphragm comprises the following steps:
1) respectively dissolving PEO with the molecular weight of 700 million and PAA with the molecular weight of 100 million into deionized water to form a solution A and a solution B with the concentration of 20 mg/mL;
2) according to the following steps of 1: taking the solution A and the solution B according to the proportion of 0.8, and carrying out rapid stirring and blending reaction to prepare a PEO-PAA complex solution;
3) adding the PEO-PAA complex solution into the ceramic slurry, and uniformly mixing to obtain mixed slurry; in this embodiment, the mixed slurry includes alumina ceramic powder, a thickener, a wetting agent, a glue solution and a PEO-PAA complex, and the dry weights of the above substances are 82%, 0.3%, 0.5%, 6.5% and 10.7%, respectively.
4) And coating the mixed slurry on at least one surface of a base film (polypropylene film) with the thickness of 9 mu m, and drying to form a functional coating with the thickness of 4 mu m, thus obtaining the high-liquid-retention self-repairing diaphragm.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 1
The difference from example 1 is the preparation of the barrier film:
a polypropylene film having a thickness of 9 μm was used as a separator.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 2
The difference from example 1 is the preparation of the barrier film:
1) taking a polypropylene film with the thickness of 9 mu m as a base film;
2) and coating the ceramic slurry on at least one surface of the base film, and drying to form a functional coating with the thickness of 4 mu m, thereby obtaining the diaphragm. In this embodiment, the mixed slurry includes alumina ceramic powder, a thickener, a wetting agent and a glue solution, and the dry weight ratios of the above substances are 92%, 0.34%, 0.56% and 7.1%, respectively.
The rest is the same as embodiment 1, and the description is omitted here.
Performance testing
1) The separators prepared in the examples and comparative examples were immersed in the electrolyte for 1 hour, and then left at 25 ℃ for various times, and the liquid retention rate was calculated, and the results are shown in table 1.
2) The cycle stability at 1C rate of the batteries manufactured in example 1 and comparative example 1 was taken, and the results are shown in fig. 2.
3) The batteries obtained in example 1 and comparative example 1 were used at a current density of 2mA/cm2Then, the polarization voltage was observed, and the results are shown in FIG. 3.
TABLE 1 liquid retention test results
As can be seen from table 1, the separator of example has a higher liquid retention rate than the separator of comparative example, with the liquid retention rate being the highest with the separator of example 1. It is thus demonstrated that the separator of the present invention has high liquid retention capacity because the separator of the present invention forms a functional layer having excellent liquid absorption and retention capacity by coating and drying a mixed slurry made of a PEO/PAA complex and a ceramic slurry on a base film.
As can be seen from fig. 2, the specific capacity of the battery of comparative example 1 (with a PP thin film as a separator) at 1C rate was about 132mAh/g, whereas the specific capacity of the battery of example 1 (with a PP thin film coated with a functional layer made of PEO/PAA complex-ceramic slurry as a separator) at 1C rate was about 141mAh/g, which was higher by about 10mAh/g in comparison. And the coulombic efficiency of the high-liquid-retention self-repairing diaphragm and the high-liquid-retention self-repairing diaphragm is about 99% under 100-circle circulation, so that the battery prepared by the high-liquid-retention self-repairing diaphragm has higher specific capacity.
As can be seen from FIG. 3, the current density was 2mA/cm2When the cell of comparative example 1 (with PP film as separator) reached a polarization voltage of 0.4V or more at around 78h, indicating that the separator had been pierced by dendrites. While the polarization voltage of the battery of example 1 (with a PP film coated with a functional layer made of PEO/PAA complex-ceramic slurry as the separator) was consistently in the 0.004mV loitering range at 1200h cycles without much change, thus demonstrating that the separator of the present invention can repair the problem of the separator being pierced by lithium dendrites.
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.