阅读说明：本技术 一种用于正极定向补锂的复合隔膜及其制备方法 (Composite diaphragm for directionally supplementing lithium to positive electrode and preparation method thereof ) 是由 杨鹏 郭盼 于 2021-08-26 设计创作，主要内容包括：本发明提出的一种用于正极定向补锂的复合隔膜,包括基膜、以及分别设置在所述基膜相对两侧的陶瓷涂层；所述陶瓷涂层朝向正极的一侧还设置有补锂涂层；所述补锂涂层为含锂化合物与含卤素高分子聚合物按质量比为(80％-98％):(2％-20％)复合形成的混合物层。通过采用设置有陶瓷涂层的基膜作为补锂涂层的涂覆基膜,可以有效地解决涂覆的所述补锂涂层堵塞所述基膜上的锂离子通道的问题,从而保证锂离子的传输率。通过采用含卤素高分子聚合物可使复合隔膜与正极材料粘结在一起,代替了传统的贴合,缩短了锂离子穿越隔膜路径,降低了两者之间的界面极化效应。本发明可以有效实现锂离子电池的补锂效果,提高锂离子电池的首次库伦效率及电池克容量。(The invention provides a composite diaphragm for directionally supplementing lithium to a positive electrode, which comprises a base film and ceramic coatings respectively arranged on two opposite sides of the base film; a lithium supplement coating is further arranged on one side, facing the anode, of the ceramic coating; the lithium-supplementing coating is a mixture layer formed by compounding a lithium-containing compound and a halogen-containing high polymer according to the mass ratio of (80% -98%) to (2% -20%). By adopting the base film provided with the ceramic coating as the coating base film of the lithium supplementing coating, the problem that the lithium supplementing coating blocks a lithium ion channel on the base film can be effectively solved, so that the transmission rate of lithium ions is ensured. By adopting the halogen-containing high molecular polymer, the composite diaphragm and the anode material can be bonded together, the traditional attachment is replaced, the path of lithium ions passing through the diaphragm is shortened, and the interface polarization effect between the lithium ions and the anode material is reduced. The invention can effectively realize the lithium supplementing effect of the lithium ion battery and improve the first coulombic efficiency and the gram capacity of the lithium ion battery.)

1. The composite diaphragm for directionally supplementing lithium to the positive electrode is characterized by comprising a base film and ceramic coatings respectively arranged on two opposite sides of the base film; a lithium supplement coating is further arranged on one side, facing the anode, of the ceramic coating; the lithium-supplementing coating is a mixture layer formed by compounding a lithium-containing compound and a halogen-containing high polymer according to the mass ratio of (80% -98%) to (2% -20%).

2. The composite separator for the directional lithium supplementation of the positive electrode according to claim 1, wherein the thickness of the lithium supplementation coating is 0.5 μm to 10 μm.

3. The composite separator for the directional lithium supplementation of a positive electrode according to claim 1, wherein the lithium-containing compound has an average particle size of 10nm to 5 μm; the lithium-containing compound is a lithium binary metal oxide or a lithium salt;

the halogen-containing high polymer is one or more of polytetrafluoroethylene, vinylidene fluoride, fluorinated ethylene propylene copolymer, polyvinyl fluoride, polyvinyl chloride, polyvinylidene chloride, brominated butadiene copolymer, brominated polybutadiene polymer and brominated polystyrene copolymer.

4. The composite separator for the directional lithium supplementation of a positive electrode according to claim 3, wherein the lithium binary metal oxide is Li₂O₂、Li₂O、Li₃One or more of N.

5. The composite separator for the directional lithium supplementation of a positive electrode according to claim 3, characterized in that the lithium salt is Li₂ZrO₃、Li₂TiO₃、Li₂CrO₄、Li₂Cr₂O₇、Li₄SiO₄、Li₂SiO₃、Li₃AsO₄、Li₂SeO₄、Li₂SeO₃、LiVO₃、LiAlO₂、Li₃PO₄、Li₂B₈O₁₃、Li₂B₄O₇、LiBO₂、LiPF₆、Li₃AlF₆、Li₂SnF₆Or LiAsF₆One or more of (a).

6. The composite separator for lithium aligned anode supplement according to claim 1, wherein the thickness of the base film is 5 μm to 30 μm; the selected basement membrane is one or more of polyethylene, polypropylene, polyamide, polyvinyl chloride, polyvinylidene fluoride and polytetrafluoroethylene.

7. The composite separator for the directional lithium supplementation of a positive electrode according to claim 1, characterized in that the ratio of the thickness of the ceramic coating layer to the thickness of the base film is less than or equal to 3: 10.

8. The composite separator for directional lithium supplementation of a positive electrode according to claim 1, wherein the ceramic coating is a mixture layer formed by compounding one or more of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, aluminum nitride, magnesium nitride, barium carbonate, barium sulfate, barium titanate and calcium sulfate.

9. The method for preparing the composite separator for the directional lithium supplement of the positive electrode according to any one of claims 1 to 8, characterized by comprising the following steps:

s1: coating the ceramic coating slurry on two opposite sides of a base film, and drying to obtain the base film containing the ceramic coating;

s2, adding the lithium-containing compound and the halogen-containing high polymer into a solvent according to the mass ratio of (80% -98%) (2% -20%) to be uniformly mixed to obtain a lithium supplement slurry;

and S3, coating the lithium supplementing slurry on the side, facing the positive electrode, of the base film containing the ceramic coating, wherein the coating thickness is 0.5-10 mu m, and then drying at 50-120 ℃ to obtain the lithium supplementing composite diaphragm.

10. The composite separator for positive electrode directional lithium supplement according to claim 9, wherein the solvent is any one of water or N-methylpyrrolidone.

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a composite diaphragm for directionally supplementing lithium to a positive electrode and a preparation method thereof.

Background

In the first charging process of the lithium ion battery, the organic electrolyte can be reduced and decomposed on the surface of the carbon negative electrode to form a solid electrolyte phase interface film (SEI film), a large amount of lithium from the positive electrode is permanently consumed, the coulombic efficiency of the first cycle is low, and the capacity and the energy density of the lithium ion battery are reduced. In order to solve this problem, researchers have begun to research lithium supplementation techniques. The irreversible lithium loss caused by the SEI film formation is offset by lithium supplement of the electrode material, so that the battery capacity and the energy density are improved.

At present, lithium is supplemented in a positive electrode, a negative electrode and a diaphragm in a lithium supplementing mode. The lithium supplement of the positive electrode is realized by adding a lithium-containing compound when the positive electrode material is homogenized, so that the safety and the stability are high, and the compatibility with the existing battery production process is good; the disadvantages are the decrease of the active material of the positive electrode and the decrease of the energy density of the battery. The lithium is supplemented to the negative electrode mostly by lithium metal, so that the capacity is high, but the operation is complex and the requirement on the environment is high. The lithium supplement of the diaphragm is also divided into two modes of anode directional lithium supplement and cathode directional lithium supplement, wherein the cathode directional lithium supplement also adopts metal lithium as a lithium supplement agent, and the phenomenon of lithium precipitation of the cathode is easy to occur; the positive electrode directional lithium supplement is to coat a lithium compound on the side facing the positive plate. For example, chinese patent application No. CN2020111080804 discloses a lithium-supplementing composite film prepared by adding a lithium-supplementing active material and a binder into a solvent, coating a lithium-supplementing slurry on a side of a base film facing a positive electrode, and drying at 35-100 ℃. The patent only coats a lithium compound on a common base film, the lithium compound coated in the lithium supplementing process easily blocks a lithium ion passing path of the base film, the lithium ion transmission rate of the diaphragm is reduced, the base film adopted by the patent is the common diaphragm, a coating material easily blocks a lithium ion channel of the common base film, and the thermoplasticity and the acid resistance are poor. For another example, chinese patent application No. CN2018102450932 discloses coating a common base film with a lithium-supplement material and a first binder, wherein the lithium-supplement material includes a lithium ion compound core, a first coating layer of carbon and metal carbide, and a second coating layer of a selected carbon material, and the second coating layer is between the core and the first coating layer, and the lithium-supplement coating layer further includes first inorganic particles. The selected basement membrane is a common membrane or a ceramic membrane. The patent needs to adopt high temperature of 500-700 ℃ in advance to fire the lithium supplement material under the protection of inert gas, and the subsequent preparation process is very complicated and high in cost.

Disclosure of Invention

Based on the above, the invention provides a composite diaphragm for directionally supplementing lithium to a positive electrode and a preparation method thereof, and aims to solve the problems that the lithium compound is coated on a common base membrane only in the conventional directional lithium supplementation of the positive electrode, and the lithium compound coated in the lithium supplementation process easily blocks a lithium ion passing path of the base membrane, so that the lithium ion transmission rate of the diaphragm is reduced.

In order to achieve the purpose, the invention provides the following technical scheme:

a composite diaphragm for directionally supplementing lithium to a positive electrode comprises a base film and ceramic coatings respectively arranged on two opposite sides of the base film; a lithium supplement coating is further arranged on one side, facing the anode, of the ceramic coating; the lithium-supplementing coating is a mixture layer formed by compounding a lithium-containing compound and a halogen-containing high polymer according to the mass ratio of (80% -98%) to (2% -20%).

In the present application, the lithium-containing compound in the lithium supplement coating is used for supplementing lithium; the halogen-containing high molecular polymer is used as a binder and mainly used for binding the lithium-containing compound on the ceramic coating; meanwhile, the halogen-containing high molecular polymer can bond the lithium supplement coating and the anode material together, so that the traditional bonding is replaced, the path of lithium ions passing through the diaphragm is shortened, and the interface polarization effect between the lithium supplement coating and the anode material is reduced. In the process of preparing the lithium ion battery, the lithium supplement coating is opposite to and tightly attached to the anode of the lithium ion battery. The invention adopts the base film provided with the ceramic coating as the coating base film of the lithium supplementing coating, and can effectively solve the problem that the lithium supplementing coating blocks the lithium ion channel on the base film, thereby ensuring the transmission rate of lithium ions in the lithium supplementing process.

Further, the thickness of the lithium supplement coating is 0.5-10 μm.

Further, the lithium-containing compound has an average particle size of 10nm to 5 μm; the lithium-containing compound is a lithium binary metal oxide or a lithium salt;

the halogen-containing high polymer is one or more of polytetrafluoroethylene, vinylidene fluoride, fluorinated ethylene propylene copolymer, polyvinyl fluoride, polyvinyl chloride, polyvinylidene chloride, brominated butadiene copolymer, brominated polybutadiene polymer and brominated polystyrene copolymer.

Further, the lithium binary metal oxide is Li₂O₂、Li₂O、Li₃One or more of N.

Further, the lithium salt is Li₂ZrO₃、Li₂TiO₃、Li₂CrO₄、Li₂Cr₂O₇、Li₄SiO₄、Li₂SiO₃、Li₃AsO₄、Li₂SeO₄、Li₂SeO₃、LiVO₃、LiAlO₂、Li₃PO₄、Li₂B₈O₁₃、Li₂B₄O₇、LiBO₂、LiPF₆、Li₃AlF₆、Li₂SnF₆Or LiAsF₆One or more of (a).

Further, the thickness of the base film is 5 μm to 30 μm; the selected basement membrane is one or more of polyethylene, polypropylene, polyamide, polyvinyl chloride, polyvinylidene fluoride and polytetrafluoroethylene.

Further, a ratio of a thickness of the ceramic coating to a thickness of the base film is less than or equal to 3: 10; the ceramic coating is a mixture layer formed by compounding one or more of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, aluminum nitride, magnesium nitride, barium carbonate, barium sulfate, barium titanate and calcium sulfate.

The invention also provides a preparation method of the composite diaphragm for directionally supplementing lithium to the anode, which comprises the following steps:

s1: coating the ceramic coating slurry on two opposite sides of a base film, and drying to obtain the base film containing the ceramic coating;

s2, adding the lithium-containing compound and the halogen-containing high polymer into a solvent according to the mass ratio of (80% -98%) (2% -20%) to be uniformly mixed to obtain a lithium supplement slurry;

and S3, coating the lithium supplementing slurry on the side, facing the positive electrode, of the base film containing the ceramic coating, wherein the coating thickness is 0.5-10 mu m, and then drying at 50-120 ℃ to obtain the lithium supplementing composite diaphragm.

Further, the solvent is any one of water or N-methylpyrrolidone.

According to the composite diaphragm for directionally supplementing lithium to the anode and the preparation method thereof, the base film provided with the ceramic coating is used as the coating base film of the lithium supplementing coating, so that the problem that the lithium ion channel on the base film is blocked by the coated lithium supplementing coating can be effectively solved, and the transmission rate of lithium ions is ensured; meanwhile, the existing manufacturing process of the lithium ion battery is not required to be changed, and compared with the common base film, the base film containing the ceramic coating has better thermoplasticity and acid resistance. The lithium ion battery has the advantages that a mixture layer formed by compounding a lithium-containing compound and a halogen-containing high polymer serves as a lithium supplement coating, and if the lithium-containing compound is a binary lithium compound, the coating thickness can be reduced, so that the volumetric energy density of the lithium ion battery is higher; if the lithium-containing compound is selected as the lithium salt, the oxide negative ions after lithium supplement can effectively enhance the mechanical toughness of the composite diaphragm and improve the heat resistance of the composite diaphragm; the halogen-containing high molecular polymer can bond the composite diaphragm and the anode material together, replaces the traditional bonding, shortens the path of lithium ions passing through the diaphragm, and reduces the interfacial polarization effect between the two. The invention can effectively realize the lithium supplementing effect of the lithium ion battery and improve the first coulombic efficiency and the gram capacity of the lithium ion battery.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.

Fig. 1 is an expanded schematic view of a structure of a composite separator for directional lithium supplement of a positive electrode according to an embodiment of the invention;

fig. 2 is a cross-sectional view of fig. 1.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that, if directional indications (such as up, down, left, right, front, back, top and bottom … …) are involved in the embodiment of the present invention, the directional indications are only used to explain the relative position relationship between the components, the motion situation, etc. in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indications are changed accordingly.

In this application, unless expressly stated or limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can include, for example, fixed connections, removable connections, or integral parts; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present.

In addition, if there is a description of "first", "second", etc. in an embodiment of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.

The existing positive electrode directional lithium supplement only coats a lithium compound on a common base film, and the lithium compound coated in the lithium supplement process easily blocks a lithium ion passing path of the base film, so that the lithium ion transmission rate of a diaphragm is reduced. In order to solve the technical problems, the invention provides a composite diaphragm for directionally supplementing lithium to a positive electrode and a preparation method thereof.

As shown in fig. 1 and 2, the composite separator for directionally supplementing lithium to a positive electrode according to the embodiment of the present invention includes a base film 1, and ceramic coatings 2 respectively disposed on two opposite sides of the base film 1; a lithium supplement coating 3 is also arranged on one side of the ceramic coating 2 facing the anode; the lithium-supplementing coating 3 is a mixture layer formed by compounding a lithium-containing compound and a halogen-containing high polymer according to the mass ratio of (80% -98%) to (2% -20%).

In the embodiment of the application, the lithium-containing compound in the lithium supplement coating 3 is used for supplementing lithium; the halogen-containing high molecular polymer is used as a binder and mainly used for binding the lithium-containing compound on the ceramic coating 2; meanwhile, the halogen-containing high molecular polymer can bond the lithium supplement coating and the anode material together, so that the traditional bonding is replaced, the path of lithium ions passing through the diaphragm is shortened, and the interface polarization effect between the lithium supplement coating and the anode material is reduced. In the process of preparing the lithium ion battery, the lithium supplement coating 3 is opposite to and tightly attached to the anode of the lithium ion battery. The invention adopts the base film 1 provided with the ceramic coating layer 2 as the coating base film of the lithium supplementing coating layer 3, and can effectively solve the problem that the lithium supplementing coating layer 3 blocks a lithium ion channel on the base film 1, thereby ensuring the transmission rate of lithium ions in the lithium supplementing process.

Further, the thickness of the lithium supplement coating 3 is 0.5-10 μm.

Further, the lithium-containing compound has an average particle size of 10nm to 5 μm; the lithium-containing compound is a lithium binary metal oxide or a lithium salt;

the halogen-containing high polymer is one or more of polytetrafluoroethylene, vinylidene fluoride, fluorinated ethylene propylene copolymer, polyvinyl fluoride, polyvinyl chloride, polyvinylidene chloride, brominated butadiene copolymer, brominated polybutadiene polymer and brominated polystyrene copolymer.

Further, the lithium binary metal oxide is Li₂O₂、Li₂O、Li₃One or more of N.

Further, the lithium salt is Li₂ZrO₃、Li₂TiO₃、Li₂CrO₄、Li₂Cr₂O₇、Li₄SiO₄、Li₂SiO₃、Li₃AsO₄、Li₂SeO₄、Li₂SeO₃、LiVO₃、LiAlO₂、Li₃PO₄、Li₂B₈O₁₃、Li₂B₄O₇、LiBO₂、LiPF₆、Li₃AlF₆、Li₂SnF₆Or LiAsF₆One or more of (a).

Further, the thickness of the base film 1 is 5 μm to 30 μm; the selected basement membrane 1 is one or more of polyethylene, polypropylene, polyamide, polyvinyl chloride, polyvinylidene fluoride and polytetrafluoroethylene. In the embodiment, the thickness of the base film 1 is preferably 20 μm to 30 μm, which can enhance the ability of bearing the lithium supplement coating 3, thereby improving the efficiency of lithium supplement; meanwhile, the transmission capability of the base film 1 to lithium ions can be effectively improved.

Further, the ratio of the thickness of the ceramic coating layer 2 to the thickness of the base film 1 is less than or equal to 3: 10; the ceramic coating 2 is a mixture layer formed by compounding one or more of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, aluminum nitride, magnesium nitride, barium carbonate, barium sulfate, barium titanate and calcium sulfate.

In the application, the ratio of the thickness of the ceramic coating 2 to the thickness of the base film 1 is less than or equal to 3:10, so that the ceramic coating 2 can play a role in isolating the base film 1 from the lithium supplement coating 3 and prevent the lithium supplement coating 3 from blocking a lithium ion channel on the base film 1; meanwhile, the higher lithium ion transmission efficiency can be ensured.

The invention also provides a preparation method of the composite diaphragm for directionally supplementing lithium to the anode, which comprises the following steps:

s1: coating the ceramic coating slurry on two opposite sides of a base film, and drying to obtain the base film containing the ceramic coating;

s2, adding the lithium-containing compound and the halogen-containing high polymer into a solvent according to the mass ratio of (80% -98%) (2% -20%) to be uniformly mixed to obtain a lithium supplement slurry;

and S3, coating the lithium supplementing slurry on the side, facing the positive electrode, of the base film containing the ceramic coating, wherein the coating thickness is 0.5-10 mu m, and then drying at 50-120 ℃ to obtain the lithium supplementing composite diaphragm.

Further, the solvent is any one of water or N-methylpyrrolidone.

In the examples of the present application, the ceramic coating slurry is a ceramic slurry prepared by a general method.

According to the composite diaphragm for directionally supplementing lithium to the anode and the preparation method thereof, the base film 1 provided with the ceramic coating layer 2 is used as the coating base film of the lithium supplementing coating layer, so that the problem that the lithium supplementing coating layer 3 blocks a lithium ion channel on the base film 1 can be effectively solved, and the transmission rate of lithium ions in the lithium supplementing process is ensured; meanwhile, the existing battery manufacturing process is not required to be changed, and compared with the common base film, the base film containing the ceramic coating 2 has better thermoplasticity and acid resistance. A mixture layer formed by compounding a lithium-containing compound and a halogen-containing high polymer is used as the lithium supplement coating 3, wherein if the lithium-containing compound is a binary lithiated compound, the coating thickness can be reduced, so that the volume energy density of the lithium ion battery is higher; if the lithium-containing compound is selected as the lithium salt, the oxide negative ions after lithium supplement can effectively enhance the mechanical toughness of the composite diaphragm and improve the heat resistance of the composite diaphragm; the halogen-containing high molecular polymer can bond the composite diaphragm and the anode material together, replaces the traditional bonding, shortens the path of lithium ions passing through the diaphragm, and reduces the interfacial polarization effect between the two. The invention can effectively realize the lithium supplementing effect of the lithium ion battery and improve the first coulombic efficiency and the gram capacity of the lithium ion battery.

In order to better understand the technical solutions, the technical solutions will be described in detail with reference to specific examples, which are only preferred embodiments of the present invention and are not intended to limit the present invention.

Example 1

A composite diaphragm for directionally supplementing lithium to a positive electrode comprises a polyethylene-based diaphragm; the opposite sides of the polyethylene base film are coated with ceramic coatings; one side of the ceramic coating facing the positive electrode is coated with a lithium supplement coating; the thickness of the polyethylene base film is 5 mu m; the lithium supplementing coating comprises a lithium-containing compound and a halogen-containing high polymer; the thickness of the lithium supplement coating is 0.5 mu m.

The preparation method of the composite diaphragm comprises the following steps:

s11: coating the ceramic coating slurry on two opposite sides of a polyethylene base film, wherein the coating thickness is 0.5 mu m, and drying to obtain the polyethylene base film containing the ceramic coating;

s12 preparation of 400g of Li₂O₂Adding 100g of polytetrafluoroethylene into a water solvent, and uniformly mixing at normal temperature to obtain lithium supplement slurry;

and S13, coating the lithium supplementing slurry on the side, facing the positive electrode, of the polyethylene base film containing the ceramic coating, wherein the coating thickness is 0.5 mu m, and then drying at 50 ℃ to obtain the lithium supplementing composite diaphragm.

Example 2

A composite diaphragm for directionally supplementing lithium to a positive electrode comprises a polyethylene-based diaphragm; the opposite sides of the polyethylene base film are coated with ceramic coatings; one side of the ceramic coating facing the positive electrode is coated with a lithium supplement coating; the thickness of the polyethylene base film is 5 mu m; the lithium supplementing coating comprises a lithium-containing compound and a halogen-containing high polymer; the thickness of the lithium supplement coating is 0.5 mu m.

The preparation method of the composite diaphragm comprises the following steps:

s21: coating the ceramic coating slurry on two opposite sides of a polyethylene base film, wherein the coating thickness is 0.5 mu m, and drying to obtain the polyethylene base film containing the ceramic coating;

s22 preparation of 400g of Li₂ZrO₃Adding 100g of polytetrafluoroethylene into a water solvent, and uniformly mixing at normal temperature to obtain lithium supplement slurry;

and S23, coating the lithium supplementing slurry on the side, facing the positive electrode, of the polyethylene base film containing the ceramic coating, wherein the coating thickness is 0.5 mu m, and then drying at 50 ℃ to obtain the lithium supplementing composite diaphragm.

Example 3

A composite diaphragm for directionally supplementing lithium to a positive electrode comprises a polyethylene-based diaphragm; the opposite sides of the polyethylene base film are coated with ceramic coatings; one side of the ceramic coating facing the positive electrode is coated with a lithium supplement coating; the thickness of the polyethylene base film is 5 mu m; the lithium supplementing coating comprises a lithium-containing compound and a halogen-containing high polymer; the thickness of the lithium supplement coating is 0.5 mu m.

The preparation method of the composite diaphragm comprises the following steps:

s31: coating the ceramic coating slurry on two opposite sides of a polyethylene base film, wherein the coating thickness is 0.5 mu m, and drying to obtain the polyethylene base film containing the ceramic coating;

s32 preparation of 490g of Li₂O₂Adding 10g of polytetrafluoroethylene into a water solvent, and uniformly mixing at normal temperature to obtain lithium supplement slurry;

and S33, coating the lithium supplementing slurry on the side, facing the positive electrode, of the polyethylene base film containing the ceramic coating, wherein the coating thickness is 0.5 mu m, and then drying at 50 ℃ to obtain the lithium supplementing composite diaphragm.

Example 4

A composite diaphragm for directionally supplementing lithium to a positive electrode comprises a polyethylene-based diaphragm; the opposite sides of the polyethylene base film are coated with ceramic coatings; one side of the ceramic coating facing the positive electrode is coated with a lithium supplement coating; the thickness of the polyethylene base film is 5 mu m; the lithium supplementing coating comprises a lithium-containing compound and a halogen-containing high polymer; the thickness of the lithium supplement coating is 0.5 mu m.

The preparation method of the composite diaphragm comprises the following steps:

s41: coating the ceramic coating slurry on two opposite sides of a polyethylene base film, wherein the coating thickness is 0.5 mu m, and drying to obtain the polyethylene base film containing the ceramic coating;

s42 preparation of 400g of Li₂O₂Adding 100g of polytetrafluoroethylene into a water solvent, and uniformly mixing at normal temperature to obtain lithium supplement slurry;

and S43, coating the lithium supplementing slurry on the side, facing the positive electrode, of the polyethylene base film containing the ceramic coating, wherein the coating thickness is 0.5 mu m, and then drying at 90 ℃ to obtain the lithium supplementing composite diaphragm.

Example 5

A composite diaphragm for directionally supplementing lithium to a positive electrode comprises a polyethylene-based diaphragm; the opposite sides of the polyethylene base film are coated with ceramic coatings; one side of the ceramic coating facing the positive electrode is coated with a lithium supplement coating; the thickness of the polyethylene base film is 5 mu m; the lithium supplementing coating comprises a lithium-containing compound and a halogen-containing high polymer; the thickness of the lithium supplement coating is 0.5 mu m.

The preparation method of the composite diaphragm comprises the following steps:

s51: coating the ceramic coating slurry on two opposite sides of a polyethylene base film, wherein the coating thickness is 0.5 mu m, and drying to obtain the polyethylene base film containing the ceramic coating;

s52 preparation of 400g of Li₂O₂Adding 100g of polytetrafluoroethylene into a water solvent, and uniformly mixing at normal temperature to obtain lithium supplement slurry;

and S53, coating the lithium supplementing slurry on the side, facing the positive electrode, of the polyethylene base film containing the ceramic coating, wherein the coating thickness is 0.5 mu m, and then drying at 120 ℃ to obtain the lithium supplementing composite diaphragm.

Example 6

A composite diaphragm for directionally supplementing lithium to a positive electrode comprises a polyethylene-based diaphragm; the opposite sides of the polyethylene base film are coated with ceramic coatings; one side of the ceramic coating facing the positive electrode is coated with a lithium supplement coating; the thickness of the polyethylene base film is 5 mu m; the lithium supplementing coating comprises a lithium-containing compound and a halogen-containing high polymer; the thickness of the lithium supplement coating is 0.5 mu m.

The preparation method of the composite diaphragm comprises the following steps:

s61: coating the ceramic coating slurry on two opposite sides of a polyethylene base film, wherein the coating thickness is 0.5 mu m, and drying to obtain the polyethylene base film containing the ceramic coating;

s62 preparation of 400g of Li₂O₂Adding 100g of polytetrafluoroethylene into a water solvent, and uniformly mixing at normal temperature to obtain lithium supplement slurry;

and S63, coating the lithium supplementing slurry on the side, facing the positive electrode, of the polyethylene base film containing the ceramic coating, wherein the coating thickness is 0.5 mu m, and then drying at 80 ℃ to obtain the lithium supplementing composite diaphragm.

Comparative example 1

Based on example 1, except that the polyethylene-based film was not coated with ceramic coating on both sides.

Comparative example 2

Based on example 1, except that the lithium supplement coating does not contain a halogen-containing high molecular polymer.

Comparative example 3

Based on example 1, the difference is that the ratio of the lithium-containing compound and the halogen-containing high molecular polymer in the lithium supplement coating is 30% to 70% by mass.

Comparative example 4

Based on example 1, except that the ratio of the lithium-containing compound to the halogen-containing high molecular polymer in the lithium supplement coating is 50% to 50% by mass.

Comparative example 5

Based on example 1, except that the ceramic coating was applied at a thickness of 2 μm.

Effects of the embodiment

In order to verify the performance of the lithium iron phosphate battery, lithium iron phosphate batteries were prepared from the composite diaphragms prepared in examples 1 to 6 and comparative examples 1 to 5, and relevant performance tests were performed, with the test results shown in table 1.

Table 1 results of performance test of composite separators of examples 1 to 6 and comparative examples 1 to 5 with respect to lithium iron phosphate batteries

And (3) testing results:

compared with the comparative examples 1 and 2, the test performance of the lithium iron phosphate battery prepared by the composite diaphragm coated with the ceramic coating and the composite diaphragm containing the halogen high molecular polymer is superior to that of the lithium iron phosphate battery prepared by the composite diaphragm without the ceramic coating or the halogen high molecular polymer.

Compared with the comparative examples 3 to 4, the lithium iron phosphate batteries prepared by the composite diaphragm containing the lithium compound in the mass ratio of the lithium supplement coating have better test performance than the lithium iron phosphate batteries prepared by the composite diaphragms containing other lithium compounds in the mass ratio of the lithium supplement coating.

Compared with the comparative example 5, the test performance of the lithium iron phosphate battery prepared by the composite diaphragm with the ceramic coating thickness accounting for 30% or less of the thickness of the base film is better than that of the lithium iron phosphate battery prepared by the composite diaphragm with the ceramic coating thickness accounting for 30% or more of the thickness of the base film, and the gram capacity of the battery is obviously improved.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.