阅读说明：本技术 一种复合隔膜及其制备方法和应用 (Composite diaphragm and preparation method and application thereof ) 是由 易怀波 吕鑫 刘荣江 黄彬彬 刘金成 刘建华 于 2020-12-28 设计创作，主要内容包括：本发明提供了一种复合隔膜及其制备方法和应用,所述复合隔膜的制备方法包括：将陶瓷粉末、刻蚀剂与水混合,反应后固液分离,得到固体产物；将得到的固体产物、锂盐与氧化剂混合,反应后依次经过干燥和煅烧,得到改性陶瓷粉末；将得到的改性陶瓷粉末与分散剂、粘结剂和溶剂混合,得到改性陶瓷浆料,将所述改性陶瓷浆料涂覆到基膜上,经烘干后得到复合隔膜。本发明所述制备方法通过对陶瓷粉末进行改性,得到改性陶瓷浆料,将其涂覆在基膜之上,一方面提高了陶瓷粉末表面的不规则度,另一方面提高了复合隔膜的电导率；所述制备方法工艺流程简单,有利于工业化应用。(The invention provides a composite diaphragm and a preparation method and application thereof, wherein the preparation method of the composite diaphragm comprises the following steps: mixing ceramic powder, an etching agent and water, and carrying out solid-liquid separation after reaction to obtain a solid product; mixing the obtained solid product, lithium salt and an oxidant, and drying and calcining the mixture in sequence after reaction to obtain modified ceramic powder; mixing the obtained modified ceramic powder with a dispersant, a binder and a solvent to obtain modified ceramic slurry, coating the modified ceramic slurry on a base film, and drying to obtain the composite diaphragm. According to the preparation method, the ceramic powder is modified to obtain the modified ceramic slurry, and the modified ceramic slurry is coated on the base film, so that the irregularity of the surface of the ceramic powder is improved, and the conductivity of the composite diaphragm is improved; the preparation method has simple process flow and is beneficial to industrial application.)

1. A preparation method of a composite diaphragm is characterized by comprising the following steps:

(1) mixing ceramic powder, an etching agent and water, and carrying out solid-liquid separation after reaction to obtain a solid product;

(2) mixing the solid product obtained in the step (1), lithium salt and an oxidant, and drying and calcining the mixture in sequence after reaction to obtain modified ceramic powder;

(3) and (3) mixing the modified ceramic powder obtained in the step (2) with a dispersant, a binder and a solvent to obtain modified ceramic slurry, and coating the modified ceramic slurry on a base film to obtain the composite diaphragm.

2. The method according to claim 1, wherein the ceramic powder of step (1) comprises an alumina powder;

preferably, the purity of the ceramic powder in the step (1) is not less than 95%;

preferably, the ceramic powder in the step (1) has a particle size of 0.3-4 μm;

preferably, the etchant in step (1) comprises any one or a combination of at least two of oxalic acid, sulfurous acid, phosphoric acid, hydrofluoric acid, formic acid, benzoic acid, acetic acid, propionic acid, stearic acid, hydrosulfuric acid, hypochlorous acid, boric acid, silicic acid, or phenol.

3. The production method according to claim 1 or 2, characterized in that stirring is performed during the reaction of step (1);

preferably, the reaction time in the step (1) is 30-60 min;

preferably, the pH value is controlled to be 6-7 in the reaction process in the step (1); preferably, the solid-liquid separation of step (1) comprises filtration;

preferably, the solid-liquid separation in the step (1) is sequentially carried out with washing and drying;

preferably, the drying is vacuum drying;

preferably, the drying temperature is 150-250 ℃;

preferably, the drying time is 60-120 min;

preferably, the specific surface area of the solid product in the step (1) is 5-15 m²/g。

4. The production method according to any one of claims 1 to 3, wherein the lithium salt in step (2) comprises any one of lithium carbonate, lithium hydroxide or lithium hydrogencarbonate, or a combination of at least two thereof;

preferably, the purity of the lithium salt in the step (2) is not less than 99.9%;

preferably, the oxidizing agent of step (2) comprises a hydrogen peroxide solution;

preferably, the concentration of the hydrogen peroxide solution is 20-40 wt%;

preferably, the mass ratio of the solid product, the lithium salt and the oxidant in the step (2) is 1 (0.125-0.5) to (0.25-1).

5. The production method according to any one of claims 1 to 4, wherein the mixing in step (2) is followed by heating;

preferably, the heating temperature is 40-50 ℃;

preferably, the heating time is 3-6 min;

preferably, stirring is carried out during the reaction in step (2).

6. The method according to any one of claims 1 to 5, wherein the drying temperature in step (2) is 80 to 120 ℃;

preferably, the drying time in the step (2) is 2.5-4 h;

preferably, the calcining temperature in the step (2) is 800-1000 ℃;

preferably, the calcining time in the step (2) is 30-90 min.

7. The production method according to any one of claims 1 to 6, wherein the dispersant in step (3) comprises any one or a combination of at least two of sodium carboxymethylcellulose, ammonium carboxymethylcellulose, carboxyethylcellulose or carboxypropylmethylcellulose;

preferably, the molecular weight of the dispersant in the step (3) is 10-120 ten thousand;

preferably, the binder in step (3) comprises any one or a combination of at least two of polyacrylate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate, acrylonitrile copolymer, modified polymethyl methacrylate, polyvinylidene fluoride or polytetrafluoroethylene;

preferably, the solvent in step (3) comprises any one of water, absolute ethyl alcohol, acetone, N-methyl pyrrolidone, dimethylformamide or dimethylacetamide;

preferably, the mixing in step (3) is followed by stirring;

preferably, the base film of step (3) comprises any one of or a combination of at least two of a polyolefin separator, a non-woven fabric separator or a polyimide separator;

preferably, the porosity of the base film in the step (3) is 38-70%;

preferably, the thickness of the coating in the step (3) is 2-6 μm;

preferably, drying is also needed after the coating in the step (3).

8. The method of any one of claims 1 to 7, comprising the steps of:

(1) mixing and stirring ceramic powder with the purity of not less than 95% and the particle size of 0.3-4 mu m, an etching agent and water, reacting for 30-60 min, controlling the pH to be 6-7 in the reaction process, carrying out solid-liquid separation and washing after the reaction, and carrying out vacuum drying for 60-120 min at the temperature of 150-250 ℃ to obtain a solid product, wherein the specific surface area of the solid product is 5-15 m²/g；

(2) Mixing the solid product obtained in the step (1), lithium salt with the purity not less than 99.9% and hydrogen peroxide solution with the concentration of 20-40 wt% according to the mass ratio of 1 (0.125-0.5) to (0.25-1), heating for 3-6 min at 40-50 ℃, stirring in the reaction process, drying for 2.5-4 h at 80-120 ℃ after reaction, and then calcining for 30-90 min at 800-1000 ℃ to obtain modified ceramic powder;

(3) mixing the modified ceramic powder obtained in the step (2), a dispersing agent with the molecular weight of 10-120 ten thousand, a binder and a solvent, stirring to obtain modified ceramic slurry, coating the modified ceramic slurry on a base film with the porosity of 38-70% in a thickness of 2-6 microns, and drying to obtain the composite diaphragm.

9. A composite separator produced by the production method according to any one of claims 1 to 8.

10. A lithium ion battery comprising the composite separator of claim 9.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a composite diaphragm and a preparation method and application thereof.

Background

With the shortage of non-renewable energy and the control of environmental pollution in the whole society, the development of new energy is a non-blocking potential. Lithium ion batteries have been widely used in the electric vehicle field and the energy storage field because of their advantages of high specific energy, light weight, long cycle life, low self-discharge rate, no memory effect, and environmental friendliness. With the continuous expansion of the application range of lithium ion batteries, various industries have made more stringent requirements on the performance of lithium ion batteries, such as the improvement of battery capacity, the increase of battery cycle life, the improvement of battery safety performance, and the like.

The diaphragm is used as a main material consisting of the lithium ion battery, and plays an important role in the performance and safety of the battery. At present, ceramic coating diaphragms are widely applied to consumer and power batteries, particularly, the alumina ceramic coating diaphragms can improve the safety of lithium ion batteries, but the shapes of battery-grade alumina ceramics are mostly rectangular and elliptical, the surfaces are smooth, pores become small after ceramic particles are stacked, the air permeability of prepared ceramic coating layers becomes poor, the air permeability of the diaphragms becomes low, the impedance is increased, and the electrochemical performance of the batteries is weakened. Therefore, the development of a new alumina ceramic-coated separator, which can improve the air permeability, reduce the impedance and improve the battery performance, is a problem to be solved urgently.

CN109742298A discloses porous ceramic diaphragm slurry and a preparation method and application thereof, wherein the preparation method comprises the following steps: corroding the ceramic powder with hydrofluoric acid to obtain porous ceramic powder, wherein the ceramic powder is made of at least two ceramic materials; mixing the porous ceramic powder with hydrochloric acid or nitric acid for activation to obtain activated porous ceramic powder; coating the surface of the activated porous ceramic powder by using a silane coupling agent to obtain sensitized porous ceramic powder; and mixing the sensitized porous ceramic powder with a binder and an organic solvent, and uniformly stirring to obtain the porous ceramic diaphragm slurry. The method needs to adopt various ceramic powders as raw materials, and needs to be subjected to activation, sensitization and other treatments, so that the process flow is complex.

CN109686918A discloses a lithium ion battery pole piece, which comprises: the mass flow body and the thick liquids diaphragm of coating on the mass flow body, evenly seted up the micropore on the thick liquids diaphragm, the micropore runs through the both sides surface of thick liquids diaphragm. The battery pole piece improves the battery performance by punching the micropores on the slurry membrane, and the preparation process is not easy to control, is easy to damage the battery pole piece and is not beneficial to industrial application.

In summary, how to provide a new alumina ceramic coated separator, which improves the battery performance while improving the air permeability and reducing the resistance, is a problem to be solved at present.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a composite diaphragm and a preparation method and application thereof, wherein the preparation method of the composite diaphragm is characterized in that ceramic powder is modified to obtain modified ceramic slurry, and the modified ceramic slurry is coated on a base membrane, so that the irregularity degree of the surface of the ceramic powder is improved on one hand, and the conductivity of the composite diaphragm is improved on the other hand; the preparation method has simple process flow and is beneficial to industrial application.

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

in a first aspect, the present invention provides a method for preparing a composite separator, comprising the steps of:

(1) mixing ceramic powder, an etching agent and water, and carrying out solid-liquid separation after reaction to obtain a solid product;

(2) mixing the solid product obtained in the step (1), lithium salt and an oxidant, and drying and calcining the mixture in sequence after reaction to obtain modified ceramic powder;

(3) and (3) mixing the modified ceramic powder obtained in the step (2) with a dispersant, a binder and a solvent to obtain modified ceramic slurry, and coating the modified ceramic slurry on a base film to obtain the composite diaphragm.

According to the preparation method, on one hand, the ceramic powder is corroded by the etching agent to form porous ceramic powder, so that the heat resistance of the diaphragm is guaranteed, meanwhile, due to the fact that the porous structure improves the irregularity of the surface of the ceramic powder, the defects are increased, the porosity of the coating is increased, the liquid absorption and retention capacity of the battery cell and the binding force between the positive and negative pole pieces and the diaphragm are further improved, the impedance of the diaphragm is reduced, the conduction of lithium ions between the positive and negative pole pieces is facilitated, and the battery cell obtains good rate performance and cycle life; in addition, the porous ceramic powder has a porous structure, so that the specific surface area of the porous ceramic powder is greatly increased, and compared with a porous ceramic diaphragm made of conventional solid ceramic powder (the porous ceramic powder is only a gap formed when the solid ceramic powder is stacked on a base film), the porous ceramic powder has larger contact area with a binder and a dispersing agent, the adsorption capacity is enhanced, and the stripping force is improved; on the other hand, the lithium salt reacts with the oxidant to generate lithium peroxide, and the lithium peroxide is calcined with the ceramic powder at high temperature to form a lithium ion conductor which has an excellent ion conduction function and can improve the conductivity of the diaphragm; the preparation method has simple process flow and good industrial application prospect.

The following technical solutions are preferred technical solutions of the present invention, but not limited to the technical solutions provided by the present invention, and technical objects and advantageous effects of the present invention can be better achieved and achieved by the following technical solutions.

In a preferred embodiment of the present invention, the ceramic powder in step (1) comprises alumina powder.

Preferably, the purity of the ceramic powder in step (1) is not less than 95%, such as 95%, 96%, 97%, 98%, or 99%, but not limited to the recited values, and other values not recited in the range of values are also applicable.

Preferably, the ceramic powder of step (1) has a particle size of 0.3 to 4 μm, for example, 0.3 μm, 0.5 μm, 1 μm, 2 μm, 3 μm or 4 μm, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the etchant of step (1) comprises any one of oxalic acid, sulfurous acid, phosphoric acid, hydrofluoric acid, formic acid, benzoic acid, acetic acid, propionic acid, stearic acid, hydrosulfuric acid, hypochlorous acid, boric acid, silicic acid or phenol, or a combination of at least two thereof, as typical but non-limiting examples: combinations of formic acid and acetic acid, hydrofluoric acid and bisulfate acid, boric acid, silicic acid, and stearic acid, and the like.

As a preferred embodiment of the present invention, stirring is carried out during the reaction in step (1).

Preferably, the reaction time in step (1) is 30-60 min, such as 30min, 35min, 40min, 45min, 50min, 55min or 60min, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the pH during the reaction in step (1) is controlled to 6-7, such as 6, 6.2, 6.4, 6.6, 6.8 or 7, but not limited to the values listed, and other values not listed in the range of values are also applicable.

In the invention, the pH value in the reaction process has an important influence on the etching effect. Because the ceramic powder is alumina powder and alumina is an amphoteric compound, the alumina ceramic is excessively reacted due to the over-low or over-high pH value, so that ceramic particles are dissolved or cracked, and the subsequent operation is influenced.

Preferably, the solid-liquid separation of step (1) comprises filtration.

Preferably, the solid-liquid separation in step (1) is followed by washing and drying in sequence.

Preferably, the drying is vacuum drying.

Preferably, the drying temperature is 150 to 250 ℃, for example 150 ℃, 160 ℃, 170 ℃, 180 ℃, 190 ℃, 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃ or 250 ℃, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the drying time is 60 to 120min, such as 60min, 70min, 80min, 90min, 100min, 110min or 120min, but not limited to the recited values, and other values not recited in the range of values are also applicable.

Preferably, the specific surface area of the solid product in the step (1) is 5-15 m²In g, e.g. 5m²/g、7m²/g、9m²/g、11m²/g、13m²G or 15m²And/g, but are not limited to, the recited values, and other values not recited within the range of values are equally applicable.

In the invention, the solid product is etched ceramic powder, and the specific surface area of the etched ceramic powder needs to be controlled. If the specific surface area of the etched ceramic powder is too large, the particles of the ceramic powder are agglomerated, so that the air permeability is poor, the porosity is low, and the contact area between the adhesive and the ceramic particles and the peeling force are reduced; if the specific surface area of the etched ceramic powder is too small, the pores are reduced, resulting in a decrease in gas permeability.

As a preferred technical solution of the present invention, the lithium salt in step (2) includes any one or a combination of at least two of lithium carbonate, lithium hydroxide or lithium bicarbonate, and the combination is exemplified by, typically but not limited to: a combination of lithium carbonate and lithium bicarbonate, a combination of lithium carbonate and lithium hydroxide, a combination of lithium carbonate, lithium hydroxide and lithium bicarbonate, and the like.

Preferably, the lithium salt of step (2) has a purity of not less than 99.9%, such as 99.9%, 99.99%, 99.999%, etc., but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the oxidizing agent of step (2) comprises a hydrogen peroxide solution.

Preferably, the concentration of the hydrogen peroxide solution in step (2) is 20 to 40 wt%, such as 20 wt%, 25 wt%, 30 wt%, 35 wt% or 40 wt%, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the mass ratio of the solid product, the lithium salt and the oxidant in the step (2) is 1 (0.125-0.5): (0.25-1), such as 1:0.125:0.25, 1:0.25:0.5, 1:0.2:0.3, 1:0.4:0.7, 1:0.3:0.3, 1:0.35:0.8 or 1:0.5:1, but not limited to the enumerated values, and other non-enumerated values in the numerical range are also applicable.

In the present invention, the amounts of the solid product, the lithium salt and the oxidizing agent to be added are controlled. If the addition amount of the lithium salt is too large, the lithium salt which does not react becomes impurities; if the addition amount of the oxidant is too large, waste is caused, and the cost is increased; if the amount of the lithium salt or the oxidizing agent added is too small, the amount of lithium peroxide produced decreases, so that only a part of the alumina powder participates in the reaction, and the content of the lithium ion conductor decreases.

As a preferable embodiment of the present invention, the step (2) is performed by mixing and then heating.

In the invention, before the mixing in the step (2), the solid product obtained in the step (1), lithium salt and water can be mixed, so that the solid product and the lithium salt are mixed more uniformly.

Preferably, the heating temperature is 40 to 50 ℃, for example, 40 ℃, 41 ℃, 42 ℃, 43 ℃, 44 ℃, 45 ℃, 46 ℃, 47 ℃, 48 ℃, 49 ℃ or 50 ℃, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.

Preferably, the heating time is 3 to 6min, such as 3min, 3.5min, 4min, 4.5min, 5min, 5.5min or 6min, but not limited to the recited values, and other values not recited in the range of values are also applicable.

In the present invention, the reaction between the lithium salt and the oxidizing agent is exothermic, but the reaction is started by heating it appropriately, and the heating can be stopped after the reaction has occurred.

Preferably, stirring is carried out during the reaction in step (2).

In a preferred embodiment of the present invention, the drying temperature in the step (2) is 80 to 120 ℃, for example, 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃ or 120 ℃, but the temperature is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the drying time in step (2) is 2.5 to 4 hours, such as 2.5 hours, 3 hours, 3.5 hours or 4 hours but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the temperature of the calcination in step (2) is 800 to 1000 ℃, for example 800 ℃, 810 ℃, 830 ℃, 850 ℃, 900 ℃, 920 ℃, 950 ℃, 980 ℃ or 1000 ℃, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

In the present invention, the calcination temperature has a very important influence on the formation of the structure of the final modified ceramic material. If the calcination temperature is too high, the lithium salt can be evaporated and disappear; if the calcination temperature is too low, the lithium ion conductor is difficult to form.

Preferably, the calcination time in step (2) is 30-90 min, such as 30min, 35min, 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min, 80min, 85min or 90min, but not limited to the recited values, and other non-recited values in the range of the values are also applicable.

In the present invention, the calcination time is controlled. If the calcination time is too long, the lithium salt will be lost; if the calcination time is too short, the amount of the lithium ion conductor formed is too small.

As a preferred embodiment of the present invention, the dispersant in step (3) comprises any one or a combination of at least two of sodium carboxymethyl cellulose, ammonium carboxymethyl cellulose, carboxyethyl cellulose or carboxypropyl methyl cellulose, and typical but non-limiting examples of the combination are: sodium carboxymethylcellulose and ammonium carboxymethylcellulose, carboxyethylcellulose and carboxypropylmethylcellulose, sodium carboxymethylcellulose, ammonium carboxymethylcellulose and carboxyethylcellulose, and the like.

Preferably, the molecular weight of the dispersant in step (3) is 10 to 120 ten thousand, for example, 10 ten thousand, 20 ten thousand, 30 ten thousand, 40 ten thousand, 150 ten thousand, 60 ten thousand, 70 ten thousand, 80 ten thousand, 90 ten thousand, 100 ten thousand, 110 ten thousand or 120 ten thousand, etc., but it is not limited to the enumerated values, and other non-enumerated values within the range of the enumerated values are also applicable.

Preferably, the binder in step (3) comprises any one or a combination of at least two of polyacrylates, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate, acrylonitrile copolymer, modified polymethyl methacrylate, polyvinylidene fluoride, or polytetrafluoroethylene, and the combination is typically but not limited to: a combination of polyvinyl alcohol and an ethylene-vinyl acetate copolymer, a combination of a copolymer of polyvinyl acetate and acrylonitrile, a combination of modified polymethyl methacrylate, polyvinylidene fluoride and polytetrafluoroethylene, and the like.

Preferably, the solvent in step (3) comprises any one of water, absolute ethanol, acetone, N-methylpyrrolidone, dimethylformamide or dimethylacetamide.

Preferably, the mixing in step (3) is followed by stirring.

Preferably, the base film of step (3) comprises any one of a polyolefin separator, a non-woven fabric separator, or a polyimide separator, or a combination of at least two thereof, as typical but non-limiting examples: a combination of a polyolefin separator and a nonwoven fabric separator, a combination of a nonwoven fabric separator and a polyimide separator, a combination of a polyolefin separator and a polyimide separator, and the like.

Preferably, the porosity of the base film in step (3) is 38 to 70%, for example 38%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%, but is not limited to the recited values, and other values not recited in the range of values are also applicable.

Preferably, the thickness of the coating in step (3) is 2 to 6 μm, such as 2 μm, 3 μm, 4 μm, 5 μm or 6 μm, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, drying is also needed after the coating in the step (3).

As a preferred technical scheme of the invention, the preparation method comprises the following steps:

(1) mixing and stirring ceramic powder with the purity of not less than 95% and the particle size of 0.3-4 mu m, an etching agent and water, reacting for 30-60 min, controlling the pH to be 6-7 in the reaction process, carrying out solid-liquid separation and washing after the reaction, and carrying out vacuum drying at 150-250 ℃ for 60The reaction lasts for 120min to obtain a solid product, and the specific surface area of the solid product is 5-15 m²/g；

(2) Mixing the solid product obtained in the step (1), lithium salt with the purity not less than 99.9% and hydrogen peroxide solution with the concentration of 20-40 wt% according to the mass ratio of 1 (0.125-0.5) to (0.25-1), heating for 3-6 min at 40-50 ℃, stirring in the reaction process, drying for 2.5-4 h at 80-120 ℃ after reaction, and then calcining for 30-90 min at 800-1000 ℃ to obtain modified ceramic powder;

(3) mixing the modified ceramic powder obtained in the step (2), a dispersing agent with the molecular weight of 10-120 ten thousand, a binder and a solvent, stirring to obtain modified ceramic slurry, coating the modified ceramic slurry on a base film with the porosity of 38-70% in a thickness of 2-6 microns, and drying to obtain the composite diaphragm.

In a second aspect, the invention provides a composite diaphragm prepared by the preparation method.

The invention provides a lithium ion battery, which comprises the composite diaphragm.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the preparation method, on one hand, the ceramic powder is modified by the etching agent, so that the irregularity of the surface of the ceramic powder is improved, the porosity of a coating is increased, and the air permeability of the diaphragm is improved, so that the liquid absorption and retention capacity of the battery cell and the binding force between the positive and negative pole pieces and the diaphragm are improved, the impedance of the diaphragm is reduced, the conduction of lithium ions between the positive and negative pole pieces is facilitated, and the battery cell has good rate performance and cycle life; on the other hand, the lithium salt reacts with the oxidant, and then the lithium salt and the etched ceramic powder are calcined to generate the ion conductor, so that the conductivity of the diaphragm is improved; according to the preparation method, the air permeability of the prepared composite diaphragm is below 156s/100mL, the impedance is below 64m omega, the porosity is above 41.2%, the ionic conductivity is above 6mS/cm, and the stripping force is above 115N/m by controlling the etching conditions;

(2) according to the preparation method, the performance of the composite diaphragm can be further improved by further controlling the proportion among the raw materials and the calcining condition, so that the prepared composite diaphragm has the air permeability of less than 141s/100mL, the impedance of less than 40m omega, the porosity of more than 42%, the ionic conductivity of more than 7mS/cm and the stripping force of more than 101N/m;

(3) the preparation method has the advantages of simple process flow, easily obtained raw materials and good industrial application prospect.

Detailed Description

In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the present invention, which is defined by the claims.

The invention provides a composite diaphragm and a preparation method thereof, and the preparation method comprises the following steps:

(1) mixing ceramic powder, an etching agent and water, and carrying out solid-liquid separation after reaction to obtain a solid product;

(2) mixing the solid product obtained in the step (1), lithium salt and an oxidant, and drying and calcining the mixture in sequence after reaction to obtain modified ceramic powder;

(3) and (3) mixing the modified ceramic powder obtained in the step (2) with a dispersant, a binder and a solvent to obtain modified ceramic slurry, coating the modified ceramic slurry on a base film, and drying to obtain the composite diaphragm.

The following are typical but non-limiting examples of the invention:

example 1:

the embodiment provides a composite diaphragm and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) mixing and stirring aluminum oxide powder with the purity of 95% and the particle size of 2.5 mu m, hydrofluoric acid and water, reacting for 45min, controlling the pH to be 7 in the reaction process, filtering and washing after the reaction, and drying in vacuum for 90min at the temperature of 200 ℃ to obtain a solid product, wherein the ratio of the solid product to the hydrofluoric acid isSurface area of 15m²/g；

(2) Mixing the solid product obtained in the step (1), lithium carbonate with the purity of 99.9% and hydrogen peroxide with the concentration of 30 wt% according to the mass ratio of 1:0.125:0.25, heating for 3min at the temperature of 40 ℃, stirring in the reaction process, drying for 4h at the temperature of 80 ℃ after reaction, and then calcining for 90min at the temperature of 800 ℃ to obtain modified alumina powder;

(3) and (3) mixing 40 parts by weight of the modified alumina powder obtained in the step (2), 12 parts by weight of sodium carboxymethylcellulose with the molecular weight of 100 ten thousand and 12 parts by weight of polyvinyl alcohol with water, stirring to obtain modified ceramic slurry, coating the modified ceramic slurry on a polyolefin diaphragm with the porosity of 50% in a double-sided manner at the thickness of 2 microns, and drying to obtain the composite diaphragm.

Example 2:

the embodiment provides a composite diaphragm and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) mixing aluminum oxide powder with the purity of 96% and the particle size of 0.3 mu m, oxalic acid and water, stirring, reacting for 30min, controlling the pH to be 6 in the reaction process, filtering and washing after the reaction, and drying in vacuum for 60min at the temperature of 150 ℃ to obtain a solid product, wherein the specific surface area of the solid product is 5m²/g；

(2) Mixing the solid product obtained in the step (1), lithium carbonate with the purity of 99.99% and hydrogen peroxide with the concentration of 20 wt% according to the mass ratio of 1:0.2:0.3, heating for 6min at the temperature of 50 ℃, stirring in the reaction process, drying for 2.5h at the temperature of 120 ℃ after reaction, and then calcining for 30min at the temperature of 1000 ℃ to obtain modified alumina powder;

(3) and (3) mixing 40 parts by weight of the modified alumina powder obtained in the step (2), 12 parts by weight of carboxyethyl cellulose with the molecular weight of 100 ten thousand, 12 parts by weight of polyvinyl acetate and N-methyl pyrrolidone, stirring to obtain modified ceramic slurry, coating the modified ceramic slurry on a polyimide diaphragm with the porosity of 38% in a double-sided manner at the thickness of 6 microns, and drying to obtain the composite diaphragm.

Example 3:

the embodiment provides a composite diaphragm and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) mixing alumina powder with purity of 96% and particle size of 4 μm, phenol and water, stirring, reacting for 60min, controlling pH to 7 during reaction, filtering, washing, and vacuum drying at 250 deg.C for 120min to obtain solid product with specific surface area of 10m²/g；

(2) Mixing the solid product obtained in the step (1), lithium bicarbonate with the purity of 99.9 percent and hydrogen peroxide with the concentration of 40wt percent according to the mass ratio of 1:0.5:1, heating for 5min at the temperature of 45 ℃, stirring in the reaction process, drying for 3h at the temperature of 100 ℃ after reaction, and then calcining for 60min at the temperature of 900 ℃ to obtain modified alumina powder;

(3) and (3) mixing 40 parts by weight of the modified alumina powder obtained in the step (2), 15 parts by weight of carboxyethyl cellulose with the molecular weight of 120 ten thousand, 15 parts by weight of polyvinyl acetate and N-methyl pyrrolidone, stirring to obtain modified ceramic slurry, coating the modified ceramic slurry on a polyimide diaphragm with the porosity of 70% in a double-sided manner at the thickness of 4 microns, and drying to obtain the composite diaphragm.

Example 4:

the embodiment provides a composite diaphragm and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) mixing alumina powder with purity of 97% and particle size of 1 μm, formic acid, acetic acid and water, stirring, reacting for 50min, controlling pH to 6.5 during reaction, filtering, washing, and vacuum drying at 180 deg.C for 80min to obtain solid product with specific surface area of 7m²/g；

(2) Mixing the solid product obtained in the step (1), lithium hydroxide with the purity of 99.9 percent and hydrogen peroxide with the concentration of 35wt percent according to the mass ratio of 1:0.4:0.9, heating for 4min at the temperature of 43 ℃, stirring in the reaction process, drying for 3.5h at the temperature of 90 ℃ after reaction, and then calcining for 40min at the temperature of 950 ℃ to obtain modified alumina powder;

(3) and (3) mixing 40 parts by weight of the modified alumina powder obtained in the step (2), 13 parts by weight of carboxypropylmethyl cellulose with the molecular weight of 50 ten thousand, 13 parts by weight of polyvinylidene fluoride and acetone, stirring to obtain modified ceramic slurry, coating the two sides of the modified ceramic slurry with the thickness of 5 microns on a non-woven fabric diaphragm with the porosity of 60%, and drying to obtain the composite diaphragm.

Example 5:

this example provides a composite separator and a method of making the same, the method being referenced to the method of example 1, except that: in the step (2), the amount of lithium carbonate added is reduced by mixing the solid product obtained in the step (1), lithium carbonate having a purity of 99.9% and hydrogen peroxide having a concentration of 30 wt% in a mass ratio of 1:0.025: 0.25.

Example 6:

this example provides a composite separator and a method of making the same, with reference to the method of example 3, except that: and (3) increasing the adding amount of lithium bicarbonate in the step (2), namely mixing the solid product obtained in the step (1), lithium bicarbonate and 40 wt% of hydrogen peroxide according to the mass ratio of 1:1: 1.

Example 7:

this example provides a composite separator and a method of making the same, the method being referenced to the method of example 1, except that: in the step (2), the amount of hydrogen peroxide added was reduced by 30 wt%, that is, the solid product obtained in the step (1), lithium carbonate having a purity of 99.9% and hydrogen peroxide having a concentration of 30 wt% were mixed in a mass ratio of 1:0.125: 0.1.

Example 8:

this example provides a composite separator and a method of making the same, the method being referenced to the method of example 1, except that: the etchant selected in the step (1) is sodium hydroxide, and the pH is controlled to be 9 in the reaction process, so that the specific surface area of the obtained solid product is 24m²/g。

Example 9:

this example provides a composite separator and method of making the sameThe preparation is as described in example 2, with the only difference that: the etchant selected in the step (1) is dilute sulfuric acid, and the pH is controlled to be 5 in the reaction process, so that the specific surface area of the obtained solid product is 21m²/g。

Example 10:

this example provides a composite separator and a method of making the same, the method being referenced to the method of example 1, except that: the calcination temperature in step (2) was 750 ℃.

Example 11:

this example provides a composite separator and a method of making the same, the method being referenced to the method of example 2, except that: the calcination temperature in step (2) was 1100 ℃.

Comparative example 1:

this comparative example provides a composite separator and a method of making the same, the method of making being referenced to the method of example 1, except that: without adding hydrofluoric acid, that is, without carrying out step (1), alumina powder having a purity of 95% and a particle size of 2.5 μm, lithium carbonate having a purity of 99.9%, and hydrogen peroxide having a concentration of 30 wt% were directly mixed in a mass ratio of 1:0.125: 0.25.

The composite separators obtained in examples 1 to 11 and comparative example 1 were measured for air permeability, resistance, porosity, ionic conductivity, and peel force, and the measurement results are shown in table 1.

Table 1 examples 1 to 11 measurement results of air permeability, resistance, porosity, ionic conductivity, and peeling force of the composite separator obtained in comparative example 1

In the present invention, the air permeability is defined as the time for 100mL of gas to pass through the membrane under a certain pressure, and the smaller the value of the air permeability, the better the air permeability is, and vice versa.

As can be seen from table 1, the composite separators prepared in examples 1 to 4 all had an air permeability of less than 141s/100mL, an impedance of less than 40m Ω, a porosity of more than 42%, an ionic conductivity of more than 7mS/cm, and a peeling force of more than 115N/m by using an etching technique and controlling the addition amounts of the respective substances during the preparation process, the pH during the etching process, and the calcination temperature; the composite separators prepared in examples 5 to 11 were inferior in all aspects of performance due to improper control of the preparation conditions.

The composite separator obtained in example 5 had a reduced amount of lithium salt added during the preparation process, resulting in a reduction in the amount of lithium peroxide generated, a failure to react with a portion of the alumina powder, and a reduction in the content of the lithium ion conductor; the addition amount of lithium salt is increased in the preparation process of the composite diaphragm obtained in the embodiment 6, the lithium salt does not react completely, namely impurities are introduced, and the performance of the composite diaphragm is influenced finally; the composite separator obtained in example 7 had a reduced amount of oxidant added during the preparation process, resulting in a reduction in the amount of lithium peroxide produced and a partial failure of the alumina powder to react, and a reduction in the content of lithium ion conductor; the composite membrane obtained in the embodiment 8-9 has too large or too small pH value in the etching process, so that the ceramic powder is excessively etched to influence the performance of the composite membrane; the calcination temperature of the composite diaphragm obtained in the embodiment 10 is too low in the preparation process, and a lithium ion conductor is difficult to form, so that the ionic conductivity of the composite diaphragm is influenced; the composite separator obtained in example 11 has an excessively high calcination temperature during the preparation process, and a part of lithium salt evaporates and disappears, so that the content of the generated lithium ion conductor is reduced, and the performance of the composite separator is affected.

It can be seen from the above examples and comparative examples that, on one hand, the preparation method of the invention adopts the etching agent to modify the ceramic powder, which improves the irregularity of the surface of the ceramic powder, increases the porosity of the coating, improves the air permeability of the diaphragm, further improves the liquid absorption and retention capacity of the battery cell and the binding force between the positive and negative plates and the diaphragm, reduces the impedance of the diaphragm, is beneficial to the conduction of lithium ions between the positive and negative plates, and enables the battery cell to obtain good rate capability and cycle life; on the other hand, the lithium ion conductor is generated by the reaction of the lithium salt and the oxidant and the calcination of the etched ceramic powder, so that the conductivity of the diaphragm is improved; according to the preparation method, the air permeability of the prepared composite diaphragm is below 156s/100mL, the impedance is below 64m omega, the porosity is above 41.2%, the ionic conductivity is above 6mS/cm, and the stripping force is above 115N/m by controlling the etching conditions; moreover, the performance of the composite diaphragm can be further improved by further controlling the proportion among the raw materials and the calcining condition, so that the prepared composite diaphragm has the air permeability of less than 141s/100mL, the impedance of less than 40m omega, the porosity of more than 42 percent, the ionic conductivity of more than 7mS/cm and the stripping force of more than 115N/m; the preparation method has the advantages of simple process flow, easily obtained raw materials and good industrial application prospect.

The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It will be apparent to those skilled in the art that any modifications to the present invention, equivalents thereof, additions of additional operations, selection of specific ways, etc., are within the scope and disclosure of the present invention.