阅读说明：本技术 一种提高锂离子电池电解液保液量和安全性能的隔膜功能涂层材料 (Diaphragm functional coating material for improving liquid retention capacity and safety performance of lithium ion battery electrolyte ) 是由 田义军 申红光 李俊义 徐延铭 于 2019-10-16 设计创作，主要内容包括：本发明涉及锂离子电池技术领域,尤其涉及一种提高锂离子电池电解液保液量和安全性能的隔膜功能涂层材料。本发明的涂层材料中的氧化物陶瓷以多孔、比表面积较大的g-C-3N-4聚合物材料为载体实现了其在涂层中均匀分布,而且g-C-3N-4聚合物的引入使得涂层的机械性能和柔韧性增加,从而使得涂层中氧化物陶瓷的比重可以显著增加,可以提升含有该涂层的隔膜的耐热性能,防止所述隔膜受热收缩,进而提高了含有该隔膜的电池的过充、短路和炉温等等的安全性能。(The invention relates to the technical field of lithium ion batteries, in particular to a diaphragm functional coating material for improving the liquid retention capacity and safety performance of lithium ion battery electrolyte. The oxide ceramic in the coating material of the invention is porous and has g-C with large specific surface area 3 N 4 The polymer material is used as carrier to realize uniform distribution in the coating layer, and g-C 3 N 4 The introduction of the polymer increases the mechanical property and flexibility of the coating, so that the specific gravity of the oxide ceramic in the coating can be obviously increased, and the coating can be improvedThe heat resistance of the diaphragm prevents the diaphragm from being heated and shrunk, and the safety performance of overcharge, short circuit, furnace temperature and the like of the battery containing the diaphragm is further improved.)

1. The coating material is characterized by comprising graphite-phase carbon nitride and oxide ceramics, wherein the graphite-phase carbon nitride is used as a carrier, and the oxide ceramics are uniformly distributed on the surface of the graphite-phase carbon nitride carrier.

2. The coating material of claim 1, wherein the oxide ceramic is also uniformly distributed within the pores of the graphite phase carbon nitride;

preferably, the particle size of the oxide ceramic is nano-sized.

3. The coating material of claim 1 or 2, wherein the graphite phase carbon nitride is a modified graphite phase carbon nitride;

preferably, the graphite phase carbon nitride is carbonyl modified graphite phase carbon nitride;

preferably, the mass ratio of the graphite-phase carbon nitride to the oxide ceramic is 1: 19-19: 1.

4. A method for preparing a coating material, comprising the steps of:

(1) dissolving a carbon-nitrogen monomer in an organic solvent to prepare a carbon nitride precursor mixed system;

(2) dissolving a ceramic precursor in water to prepare a ceramic precursor mixed system;

(3) mixing the carbon nitride precursor mixed system obtained in the step (1) with the ceramic precursor mixed system obtained in the step (2), optionally adjusting the pH value to be alkaline, and then carrying out hydrothermal reaction to prepare a precursor of the ceramic coating material;

(4) and (4) roasting the precursor of the ceramic coating material obtained in the step (3) to prepare the coating material.

5. The method according to claim 4, wherein in the step (1), the organic solvent is a carboxyl group-containing organic solvent, such as one or more selected from formic acid, acetic acid, propionic acid, butyric acid, oxalic acid and benzoic acid.

Preferably, in step (2), the ceramic precursor is selected from TiO₂Ceramic precursors (e.g., tetrabutyl titanate (TBT), titanyl sulfate (TiOSO)₄) One or two of them), SiO₂Ceramic precursor (e.g., alkyl orthosilicate, specifically, for example, tetraethyl orthosilicate (TEOS)), Al₂O₃Ceramic precursors (e.g., sodium metaaluminate (NaAlO)₂)、Potassium metaaluminate (KAlO)₂) One or more of these soluble meta-aluminates), MgO ceramic precursors (e.g., magnesium chloride (MgCl)₂·H₂O), magnesium nitrate (Mg (NO)₃)₂) One or more of these soluble magnesium salts);

preferably, in the step (3), the carbon nitride precursor mixed system of the step (1) is added dropwise into the ceramic precursor mixed system of the step (2).

6. A separator coating layer comprising the coating material according to any one of claims 1 to 3, or a coating material produced by the production method according to claim 4 or 5.

7. Separator coating according to claim 6, wherein the coating material in the separator coating is 1-99 wt%, preferably 20-60 wt% of the total mass of the separator coating;

preferably, the thickness of the separator coating is 0.1 μm to 10 μm, preferably 1 μm to 5 μm.

8. A separator comprising a base layer and the separator coating of claim 6 or 7.

9. A method of making the separator of claim 8, comprising the steps of:

mixing the coating material according to any one of claims 1 to 3 or prepared by the preparation method according to claim 4 or 5, a binder and optionally a solvent to prepare a mixed slurry, coating the mixed slurry on at least one side surface of a base layer, drying and compacting to prepare the separator;

preferably, the solid content in the mixed slurry is 30-90 wt%, i.e. the mass percentage of the coating material is 30-90 wt%.

10. A battery comprising the separator of claim 8.

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a coating material based on graphite-phase carbon nitride/oxide ceramic, which can improve the liquid retention capacity of electrolyte of a lithium ion battery and can also improve the safety performances of overcharge, short circuit and the like of the lithium ion battery.

Background

The lithium ion battery has the advantages of high energy density, long cycle life, environmental friendliness and the like, and is widely applied to portable electronic products such as mobile phones and notebook computers and new energy automobiles. However, for lithium ion batteries, cycle life and safety are the two most important items, and particularly for power lithium ion batteries, the service life of the current new energy automobile is shortened, and safety accidents frequently occur. Therefore, it is important to improve the cycle life and safety performance of the lithium ion battery.

In the lithium ion battery, the adding amount (liquid retention amount) of the electrolyte is a key factor influencing the cycle life of the battery, and particularly for the soft package battery with lower space utilization rate, the improvement of the liquid retention amount is quite limited on the premise of ensuring that the liquid does not expand. Therefore, the phenomenon that the polarization is increased and the cycle performance is rapidly reduced due to the consumption of the electrolyte occurs in the long-term cycle of the lithium ion battery, so that the service life of the battery is greatly shortened. And the use of the ceramic coating of the diaphragm enhances the hardness of the diaphragm and reduces the thermal shrinkage of the diaphragm, and relieves the possibility that the lithium dendrite punctures the diaphragm, thereby greatly improving the safety performance of the battery.

The current ceramic diaphragm coating is usually prepared from ceramic particles, wherein alumina is usually used as the ceramic particles, and silica, magnesia, calcium oxide and the like can also be used as the ceramic particles. The ceramic powder on the market can be divided into two qualities of high purity (99.99 percent, the grain diameter is 0.3-1.0 μm) and refining (99.7 percent, the grain diameter is 0.3-2.5 μm), wherein the ceramic powder can be uniformly distributed in the slurry without further grinding; the latter is relatively poor in dispersibility and needs further grinding processing to be able to disperse uniformly in the slurry, which is high in process requirements of coating manufacturers, needs stable control and increases the cost.

For a slurry of a certain concentration, the higher the mass ratio of the ceramic particles, the higher the hardness of the coated separator, and the better the thermal properties, but the mechanical properties and cycle properties are degraded because too many ceramic particles reduce the coating uniformity and weaken the skeleton structure of the polymer binder. And the porosity of the ceramic material is low, the specific surface area is low, the liquid retention amount is low, and the pores of the diaphragm are easy to block, so that the lithium ion transmission channel of the battery is blocked, the internal resistance of the battery is increased, and the cycle performance of the battery is reduced.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a diaphragm functional coating material for improving the liquid retention capacity and safety performance of lithium ion battery electrolyte, a preparation method thereof and application thereof in a diaphragm. The invention prepares the graphite phase carbon nitride (g-C) by a hydrothermal method-solid phase reaction method two-step method₃N₄) As a support, the oxide ceramic is uniformly distributed based on g-C₃N₄Coating material for oxide ceramics.

Higher energy density is a continuously challenging goal of lithium ion batteries, but safety performance and cycle life also face greater and greater challenges, and finding ways to improve liquid retention and safety performance on separator coatings is the most straightforward and simple way. Through a large amount of researches, the applicant finds a coating material which is easy to disperse, easy to combine with oxide ceramic, good in mechanical property, large in porosity and specific surface area, low in price and easy to prepare, can promote the dispersion of the oxide ceramic in slurry, the oxide ceramic is uniformly distributed in a diaphragm coating, the mass ratio of the oxide ceramic is increased, the mechanical property is not very poor, and more importantly, the electrolyte retention capacity of a battery can be increased due to the large porosity and specific surface area, and the coating material has a great significance for improving the cycle performance and the safety performance of a lithium ion battery.

Graphite phase carbon nitride (g-C)₃N₄) Is a typical polymer semiconductor and has a planar two-dimensional lamellar structure similar to graphene. g-C₃N₄Has good thermal stability and chemical stability. g-C₃N₄The high-temperature-resistant high-strength steel can be stable in structural performance at high temperature, the thermal stability can begin to decline when the temperature exceeds 600 ℃, and the structural performance is kept stable under strong acid and strong alkali, so that the high-temperature-resistant high-strength steel is non-toxic, environment-friendly and free of secondary pollution. g-C₃N₄The preparation method is simple and low in cost. g-C₃N₄The conventional preparation methods are classified into a solid-phase reaction method, a solvothermal method, an electrochemical deposition method and a thermal polymerization method. The invention firstly uses the composite material prepared by compounding the graphite-phase carbon nitride and the oxide ceramic for the coating of the diaphragm, and improves various defects of the existing ceramic-based diaphragm. Further, the invention also provides modified graphite phase carbon nitride which is different from the conventional method and has the specific surface area larger than g-C prepared by the conventional method₃N₄Specific surface area (in the range of 40-50 m)²About/g) and the porosity is far larger than that of g-C prepared by the conventional method₃N₄The porosity is generally low, uniform combination with oxide ceramics is better realized, and the electrolyte retention of the lithium ion battery and the safety performances of overcharge, short circuit and the like of the lithium ion battery are better improved.

The specific technical scheme of the invention is as follows:

a coating material, wherein the coating material comprises graphite phase carbon nitride and oxide ceramic, wherein the graphite phase carbon nitride is used as a carrier, and the oxide ceramic is uniformly distributed on the surface of the graphite phase carbon nitride carrier.

According to the invention, the oxide ceramic is also uniformly distributed within the pores of the graphite phase carbon nitride.

According to the present invention, the particle size of the oxide ceramic is nano-sized.

According to the invention, the graphite phase carbon nitride is a modified graphite phase carbon nitride.

According to the invention, the graphite phase carbon nitride is carbonyl-modified graphite phase carbon nitride.

According to the invention, the mass ratio of the graphite-phase carbon nitride to the oxide ceramic is 1: 19-19: 1.

A method of preparing a coating material, the method comprising the steps of:

(1) dissolving a carbon-nitrogen monomer in an organic solvent to prepare a carbon nitride precursor mixed system;

(2) dissolving a ceramic precursor in water to prepare a ceramic precursor mixed system;

(3) mixing the carbon nitride precursor mixed system obtained in the step (1) with the ceramic precursor mixed system obtained in the step (2), optionally adjusting the pH value to be alkaline, and then carrying out hydrothermal reaction to prepare a precursor of the ceramic coating material;

(4) and (4) roasting the precursor of the ceramic coating material obtained in the step (3) to prepare the coating material.

According to the present invention, in the step (1), the organic solvent is an organic solvent containing a carboxyl group, for example, one or more selected from formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, and benzoic acid.

According to the invention, in step (2), the ceramic precursor is selected from TiO₂Ceramic precursors (e.g., tetrabutyl titanate (TBT), titanyl sulfate (TiOSO)₄) One or two of them), SiO₂Ceramic precursor (e.g., alkyl orthosilicate, specifically, for example, tetraethyl orthosilicate (TEOS)), Al₂O₃Ceramic precursors (e.g., sodium metaaluminate (NaAlO)₂) Potassium metaaluminate (KAlO)₂) One or more of these soluble meta-aluminates), MgO ceramic precursors (e.g., magnesium chloride (MgCl)₂·H₂O), magnesium nitrate (Mg (NO)₃)₂) One or more of these soluble magnesium salts).

According to the invention, in the step (3), the carbon nitride precursor mixed system in the step (1) is added dropwise into the ceramic precursor mixed system in the step (2).

A coating material is prepared by the preparation method.

A diaphragm coating comprises the coating material.

According to the invention, in the membrane coating layer, the coating material accounts for 1-99 wt%, preferably 20-60 wt% of the total mass of the membrane coating layer.

According to the invention, the thickness of the membrane coating is between 0.1 and 10 μm, preferably between 1 and 5 μm.

A separator includes a base layer and the above separator coating layer.

The preparation method of the diaphragm comprises the following steps:

mixing the coating material, the binder and an optional solvent to prepare mixed slurry, coating the mixed slurry on at least one side surface of a base layer, drying and compacting to prepare the diaphragm.

According to the invention, the solid content in the mixed slurry is 30-90 wt%, namely the mass percentage of the coating material is 30-90 wt%.

A battery comprises the separator.

The invention has the beneficial effects that:

(1) the coating materials described herein include graphite phase carbon nitride (i.e., g-C)₃N₄Polymeric materials) and oxide ceramics, wherein the oxide ceramics have a porous g-C with a large specific surface area₃N₄The polymer material is used as carrier to realize uniform distribution in the coating layer, and g-C₃N₄The introduction of the polymer increases the mechanical property and flexibility of the coating, so that the specific gravity of oxide ceramic in the coating can be obviously increased, the heat resistance of the diaphragm applying the coating can be improved, the diaphragm is prevented from being heated and shrunk, and the safety properties of overcharge, short circuit, furnace temperature and the like of the battery containing the diaphragm are further improved.

(2) The coating material has high porosity and large specific surface area. Therefore, the diaphragm containing the coating material can greatly improve the electrolyte retention of the lithium ion battery, thereby improving the cycle performance and the service life of the battery.

(3) The coating material is easy to prepare, low in cost, stable in structural performance under strong acid and strong alkali, resistant to corrosion of hydrofluoric acid generated by side reaction of electrolyte, non-toxic, environment-friendly, free of secondary pollution and easy to prepare and produce on a large scale.

Drawings

FIG. 1 is a graph of the performance of cells prepared in examples 1-5 and comparative examples 1-3 at room temperature for a 3C/1C 100% DOD cycle.

Detailed Description

As described above, the present invention provides a coating material comprising graphite phase carbon nitride and an oxide ceramic, wherein the graphite phase carbon nitride is a carrier, and the oxide ceramic is uniformly distributed on the surface of the graphite phase carbon nitride carrier.

Wherein, because the graphite phase carbon nitride has a porous structure, the oxide ceramic is also uniformly distributed in the pores of the graphite phase carbon nitride, such as the pores inside the graphene carbon nitride carrier.

Wherein the particle size of the oxide ceramic may be nano-sized.

Wherein the oxide ceramic is at least one selected from aluminum oxide, magnesium oxide, silicon oxide, titanium oxide and the like.

Wherein the mass ratio of the graphite-phase carbon nitride to the oxide ceramic is 1:19 to 19:1, for example 1:9 to 9:1, such as 1:4 to 4:1, such as 1: 1.

Wherein the graphite phase carbon nitride is a modified graphite phase carbon nitride, specifically, a carbonyl-modified graphite phase carbon nitride. Specifically, the pure graphite phase carbon nitride has a two-dimensional layered structure with a molecular formula shown in formula I, has a complete planar structure, is tightly combined with one another, has fewer defects, and has a low specific surface area (40-50 m)²(g), low porosity: (<15％)。

The molecular formula of the two-dimensional layered structure of the carbonyl modified graphite-phase carbon nitride is shown as the formula II, and carbonyl groups are introduced into the structure shown as the formula I(namely, in the hydrothermal process, carbonyl groups are introduced into the structure shown in the formula I) by adopting the hydrothermal method of the application), so that the defect appears in the plane structure, the specific surface area is increased, and CO is generated after high-temperature roasting₂Gas, causing the porosity to increase. Thus, the porosity and specific surface area of the graphite-phase carbon nitride support can be significantly increased.

Wherein, during the hydrothermal reaction, the oxide ceramic can be bonded with the graphite-phase carbon nitride through chemical bonds. Specifically, for example, in the case of carbonyl-modified graphite-phase carbon nitride, the electron-rich carbonyl group, C ═ O, is easily bonded to the electron-deficient oxide metal element or nonmetal element to form a coordinate bond (as shown in formula III below, where X is a metal element), so that the ceramic precursor is uniformly dispersed in g-C₃N₄The nano-scale oxide ceramics is formed on g-C with larger specific surface area and porosity after high-temperature roasting₃N₄At the pore space of (a).

Wherein the specific surface area of the coating material>500m²Per g, porosity>40％。

Illustratively, g-C₃N₄/Al₂O₃、g-C₃N₄/MgO、g-C₃N₄/SiO₂And g-C₃N₄/TiO₂The specific surface area of the coating material is 550-630m²/g、550-620m²/g、520-600m²G and 520-600m²The porosity is between 40% and 48%.

As mentioned above, the present invention also provides a method for preparing a coating material, the method comprising the steps of:

(1) dissolving a carbon-nitrogen monomer in an organic solvent to prepare a carbon nitride precursor mixed system;

(2) dissolving a ceramic precursor in water to prepare a ceramic precursor mixed system;

(3) mixing the carbon nitride precursor mixed system obtained in the step (1) with the ceramic precursor mixed system obtained in the step (2), optionally adjusting the pH value to be alkaline, and then carrying out hydrothermal reaction to prepare a precursor of the ceramic coating material;

(4) and (4) roasting the precursor of the ceramic coating material obtained in the step (3) to prepare the coating material.

In the step (1), the carbon nitrogen monomer is selected from melamine or urea.

In the step (1), the organic solvent is an organic solvent containing a carboxyl group, and is selected from formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, benzoic acid, and the like. The introduction of the carboxyl groups can increase the specific surface area of the carbon nitride material, as discussed above with respect to carbonyl-modified graphite-phase carbon nitride.

In the step (1), the mass fraction of the carbon-nitrogen monomer in the carbon nitride precursor mixed system is 1-50 wt%, for example, 1 wt%, 2 wt%, 5 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%.

In the step (1), when the organic solvent is selected from carboxylic acids, the organic solvent may be added in the form of an aqueous solution of the carboxylic acid, and the concentration of the solution of the carboxylic acid is 1% or more and less than 100%.

In the step (2), the ceramic precursor is selected from TiO₂Ceramic precursors (e.g., tetrabutyl titanate (TBT), titanyl sulfate (TiOSO)₄) Etc.), SiO₂Ceramic precursor (e.g., alkyl orthosilicate, specifically, tetraethyl orthosilicate (TEOS), etc.), Al₂O₃Ceramic precursors (e.g., sodium metaaluminate (NaAlO)₂) Potassium metaaluminate (KAlO)₂) Isosoluble meta-aluminate), MgO ceramic precursor (e.g., magnesium chloride (MgCl)₂·H₂O), magnesium nitrate (Mg (NO)₃)₂) Etc. soluble magnesium salt).

In the step (2), the mass fraction of the ceramic precursor in the ceramic precursor mixed system is 1-80 wt%, for example

In the step (3), the carbon nitride precursor mixed system in the step (1) is added dropwise to the ceramic precursor mixed system in the step (2), for example.

In the step (3), the volume ratio of the carbon nitride precursor mixed system in the step (1) to the ceramic precursor mixed system in the step (2) is 1: 19-19: 1.

In step (3), the pH of the mixed system is adjusted to be alkaline using sodium hydroxide, for example, to a pH > 8. Preferably, when the ceramic precursor is selected from MgO ceramic precursors, the pH of the mixed system is adjusted to be alkaline with sodium hydroxide.

In the step (3), the hydrothermal process is carried out in a sealed reaction kettle, and the volume space ratio of the mixed system is 20-90%.

In the step (3), the temperature of the hydrothermal reaction is 160-260 ℃, and the time of the hydrothermal reaction is 3-48 hours.

In the step (3), the method further comprises a post-processing step: and filtering and drying the product after the hydrothermal reaction to prepare a precursor of the ceramic coating material with uniform distribution.

In step (4), the calcination is performed under an inert atmosphere, which may be, for example, nitrogen.

In the step (4), the calcination is performed in a muffle furnace or a tube furnace.

In the step (4), the roasting temperature is 450-580 ℃, and the roasting time is 3-12 hours.

The invention also provides a coating material prepared by the method.

The invention also provides a diaphragm coating which comprises the coating material.

Wherein the separator coating further comprises a binder.

Wherein the binder is selected from an oily binder or a water-based binder, and the oily binder is selected from at least one of PVDF5130, HSV900 and Kynar 761A; the aqueous binder is at least one selected from PTFE emulsion, SBR emulsion and PAA emulsion aqueous binder.

In the diaphragm coating, the coating material accounts for 1-99 wt%, preferably 20-60 wt% of the total mass of the diaphragm coating.

Wherein the thickness of the diaphragm coating is 0.1-5 μm, preferably 1-2 μm.

The invention also provides a diaphragm which comprises a base layer and the diaphragm coating.

The base layer is a common base layer of the diaphragm for the lithium ion battery, and can be a PP diaphragm base layer, a PE diaphragm base layer or a PP layer and PE layer mixed diaphragm base layer.

The invention also provides a preparation method of the diaphragm, which comprises the following steps:

mixing the coating material, the binder and an optional solvent to prepare mixed slurry, coating the mixed slurry on at least one side surface of a base layer, drying and compacting to prepare the diaphragm.

Wherein the solid content in the mixed slurry is 30-90 wt%, namely the mass percentage of the coating material is 30-90 wt%.

Wherein the solvent is at least one selected from N-methylpyrrolidone (NMP), N-dimethyl amide (DMF) and dimethyl sulfoxide (DMSO).

Wherein, if the binder is selected from oily binders, the mixed slurry comprises a solvent.

The invention also provides a battery, which comprises the diaphragm.

The battery is a lithium ion battery, such as a wound lithium ion battery or a laminated lithium ion battery.

The preparation method of the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.

Example 1

(1)g-C₃N₄/Al₂O₃Preparation of ceramic-coated diaphragm S1

And dissolving melamine into an acetic acid solution by stirring to obtain a mixed system A with the mass fraction of the melamine being 30%. Sodium metaaluminate (NaAlO) is added by stirring₂) Dissolving in water solution to obtain a mixed system B with the mass fraction of sodium metaaluminate of 30%.

And dropwise adding the mixed system A into the mixed system B while stirring to obtain a mixed system C, wherein the volume ratio of the mixed system A to the mixed system B is 1: 1. And (3) placing the mixed system C in a sealed reaction kettle, wherein the volume space ratio of the mixed system C in the reaction kettle is 70%, the heating temperature is 180 ℃, and the heating time is 8 hours. After hydrothermal reaction, filtering, drying and collecting a sample.

g-C prepared above₃N₄/Al₂O₃Precursor is introduced into N₂Is placed in a 520 ℃ tube furnace to be sintered for 5 hours at high temperature in the gas environment to prepare the uniformly distributed g-C₃N₄/Al₂O₃Porous, large specific surface area ceramic coating materials.

g-C in the ceramic coating material₃N₄And Al₂O₃The mass ratio of (A) to (B) is 1: 1.

g-C prepared above₃N₄/Al₂O₃The ceramic coating material and the PVDF binder are stirred at high speed to obtain a uniformly dispersed mixture. In the mixture, g-C₃N₄/Al₂O₃The mass of the ceramic coating material accounts for 20 wt%. The mixture was made into a separator ceramic coating slurry using N-methylpyrrolidone (NMP) as a solvent, and the solid content in the slurry was 70 wt%. Uniformly coating the slurry on two sides of a PP diaphragm, drying and compacting to obtain the porous and large-specific-surface-area g-C coated membrane₃N₄/Al₂O₃The thickness of the single-side coating of the diaphragm made of the ceramic coating material is 1 mu m.

(2) Preparation of Positive electrode sheet P1

Mixing the ternary nickel-cobalt-manganese NCM serving as the positive electrode active substance, the PVDF serving as the binder and the conductive carbon black, and stirring at a high speed to obtain a uniformly dispersed mixture. In the mixture, the solid component contained 95% by weight of NCM, 2% by weight of PVDF as binder and 3% by weight of conductive carbon black. The mixture was made into positive electrode active material slurry using N-methylpyrrolidone as a solvent, and the solid content in the slurry was 70 wt%. The slurry was uniformly coated on both sides of the aluminum foil, dried and compacted by a roller press to give a positive plate P1.

(3) Preparation of negative electrode sheet N1

Mixing artificial graphite as an active substance, SBR binder, thickener carboxymethyl cellulose sodium and conductive agent conductive carbon black Super-P, and stirring at high speed to obtain a mixture containing a negative active substance. The solid content of the mixture contained 95 wt% of artificial graphite, 1.5 wt% of sodium carboxymethylcellulose, 1.5 wt% of conductive carbon black Super-P, and 2 wt% of SBR-based binder. Deionized water is used as a solvent to prepare cathode active substance slurry, and the solid content of the slurry is 50 wt%. The slurry was uniformly coated on both sides of copper foil, dried and compacted by a roll press to obtain a negative electrode sheet N1.

(4) Assembly of Battery C1

Punching a positive pole piece P1 and a negative pole piece N1, and then using g-C₃N₄/Al₂O₃And the ceramic coating diaphragm S1 adopts Z-shaped lamination to form a bare cell, and an aluminum tab and a copper nickel-plated tab are respectively rotated out. Clamping the bare cell by a glass clamp with a force of 100MPa/m²And vacuum baking at 85 deg.C for 24 hr, and packaging with aluminum plastic film. The electrolyte adopts 1M lithium hexafluorophosphate electrolyte, and the solvent is a mixed solvent of ethylene carbonate/dimethyl carbonate/1, 2-propylene carbonate-1: 1:1 (volume ratio). After packaging, the cells were subjected to formation and aging to obtain a rectangular flexibly packaged cell having a length, width and thickness of 160mm × 60mm × 10mm, and designated as C1.

Example 2

The other operations are the same as example 1, except that:

in the step (1)Magnesium chloride (MgCl) is added by stirring₂·H₂O) is dissolved in the water solution to obtain a mixed system B with the mass fraction of magnesium chloride of 30 percent, and g-C is prepared₃N₄MgO diaphragm ceramic coating. g-C in the ceramic coating material₃N₄And MgO in a mass ratio of 1: 1.

I.e. g-C₃N₄/Al₂O₃g-C for diaphragm ceramic coating₃N₄the/MgO diaphragm ceramic coating is replaced, and the prepared battery is C2.

Example 3

The other operations are the same as example 1, except that:

in the step (1), titanyl sulfate (TiOSO) is stirred₄) Dissolving in water solution to obtain mixed system B with 30% titanyl sulfate by mass fraction, and preparing to obtain g-C₃N₄/TiO₂And (3) a diaphragm ceramic coating. g-C in the ceramic coating material₃N₄And TiO₂The mass ratio of (A) to (B) is 1: 1.

I.e. g-C₃N₄/Al₂O₃g-C for diaphragm ceramic coating₃N₄/TiO₂The separator ceramic coating was replaced and the resulting cell was made C3.

Example 4

The other operations are the same as example 1, except that:

in the step (1), Tetraethoxysilane (TEOS) is dissolved in an aqueous solution by stirring to obtain a mixed system B with the mass fraction of 30% of tetraethoxysilane, and g-C is prepared₃N₄/SiO₂And (3) a diaphragm ceramic coating. g-C in the ceramic coating material₃N₄And SiO₂The mass ratio of (A) to (B) is 1: 1.

I.e. g-C₃N₄/Al₂O₃g-C for diaphragm ceramic coating₃N₄/SiO₂The separator ceramic coating was replaced and the resulting cell was made C4.

Example 5

The difference from the embodiment 1 is that:

g to C₃N₄/Al₂O₃The thickness of the single-sided diaphragm ceramic coating is changed from 1 mu m to 2 mu m, and the prepared battery is C5.

Example 6

The difference from the embodiment 1 is that:

the volume ratio of the mixed system A to the mixed system B is changed from 1:1 to 1:2, so that g-C in the ceramic coating material₃N₄And Al₂O₃The mass ratio of (a) to (b) was 1:2, and the battery obtained was C6.

Comparative example 1

The difference from the embodiment 1 is that:

mixing single side of 1 μm thick g-C₃N₄/Al₂O₃The ceramic coating diaphragm is changed into the traditional commercial Al with the thickness of 1 mu m on one side₂O₃The ceramic coating diaphragm, the battery prepared is C7.

Comparative example 2

The other operations are the same as example 1, except that:

and dissolving melamine into an acetic acid solution by stirring to obtain a mixed system A with the mass fraction of the melamine being 30%. The mixed system A is placed in a sealed reaction kettle, the volume space ratio of the mixed system A in the reaction kettle is 70%, the heating temperature is 180 ℃, and the heating time is 8 hours. After hydrothermal reaction, filtering, drying and collecting a sample. The cell thus prepared was C8.

Comparative example 3

The other operations are the same as example 1, except that:

sodium metaaluminate (NaAlO) is added by stirring₂) Dissolving in water solution to obtain a mixed system B with the mass fraction of sodium metaaluminate of 30%.

And placing the mixed system B in a sealed reaction kettle, wherein the volume space ratio of the mixed system B in the reaction kettle is 70%, the heating temperature is 180 ℃, and the heating time is 8 hours. After hydrothermal reaction, filtering, drying and collecting a sample. The cell thus prepared was C9.

Test example 1

The diaphragm porosity, tensile strength, heat shrinkage and HF acid corrosion of the diaphragm of the battery C1-C9 prepared in the above manner are tested, and the test procedures are as follows: eight separators of the C1-C9 batteries are respectively selected and are in a square shape with the side length of 15mm, the porosity is measured by using an analytical balance weighing method, the tensile strength of Transverse Direction (TD) and longitudinal direction (MD) is measured by using a tensile tester, the heat shrinkage of TD and MD is measured by using a measuring method of an oven and a straight steel ruler, the corrosion of the coating is verified by using an HF acid dipping method, and the test results are shown in Table 1.

Table 1 shows the results of characterization of the battery separators prepared in examples 1 to 6 and comparative examples 1 to 3

Test example 2

The batteries C1-C9 prepared above were tested for electrolyte retention, the procedure of which was as follows: respectively selecting 5 batteries of C1-C9, respectively injecting electrolyte with the same mass into each battery, then aging and infiltrating, forming and secondary sealing, weighing and calculating the mass of the electrolyte sealed in the aluminum-plastic film, namely the liquid retention amount, wherein the test results are shown in Table 2.

Table 2 shows the results of the amount of electrolyte remaining in the batteries prepared in examples 1 to 6 and comparative examples 1 to 3

Numbering	C1/g	C2/g	C3/g	C4/g	C5/g	C6/g	C7/g	C8/g	C9/g
										1#	22.3	22.8	22.7	22.2	24.8	21.8	19.5	21.5	20.4
2#	22.1	23.0	22.9	22.3	25.0	21.5	19.7	21.3	20.6
										3#	22.6	22.9	23.4	22.2	24.3	21.7	19.5	21.8	20.0
4#	22.5	22.9	22.9	22.4	24.6	21.4	19.6	21.9	20.2
										5#	22.5	23.1	22.8	22.2	24.2	21.7	19.7	21.4	20.5

Test example 3

The safety performance of the prepared batteries C1-C9 is tested, the test process is as follows, 5 batteries C1-C9 are respectively selected and placed in an oven, the batteries are heated to 150 ℃ at the heating rate of 5 ℃/min and kept for 3 hours, the batteries Pass the oven temperature test standard with no smoke and no fire, Pass is marked as Pass, otherwise, the batteries are marked as NG; the test results are shown in table 3.

Table 3 shows the results of safety tests of the batteries prepared in examples 1 to 6 and comparative examples 1 to 3 at an oven temperature of 150 ℃ for 3 hours

It can be seen from Table 1 that g-C₃N₄The oxide ceramic coating diaphragm is more traditional ceramic diaphragm and pure g-C₃N₄The porosity and tensile strength of the coating diaphragm and the oxide ceramic coating diaphragm are greatly improved, the heat shrinkage rate at 105 ℃ for 1h is much smaller, the high-temperature resistant ceramic battery also resists corrosion of HF acid, and the performance of the materials can obviously improve the liquid retention capacity, the cycle performance and the safety performance of the battery.

It can be seen from Table 2 that the use of g-C₃N₄The electrolyte retention capacity of the oxide ceramic coating diaphragm battery is more than that of the traditional ceramic diaphragm battery, especially the g-C₃N₄The largest retention capacity of the C5 cell with the ceramic oxide coating added, which demonstrates the porous, large specific surface area g-C₃N₄The introduction of the electrolyte can obviously improve the electrolyte retention of the lithium ion battery.

As can be seen from Table 3, g-C is used₃N₄The heat resistance of the oxide ceramic coating diaphragm is improved greatly compared with that of a battery adopting the traditional ceramic diaphragm, and the polymer g-C₃N₄The introduction of the composite material can improve the uniformity and the adding proportion of the ceramic oxide on the diaphragm coating, and enhance the hardness and the mechanical property of the diaphragm, thereby better preventing the diaphragm from shrinking and improving the safety performance of the lithium ion battery. To increase g-C₃N₄The ceramic oxide ratio in the oxide ceramic coating, such as C6 battery, can relatively reduce the porosity of the diaphragm and the liquid retention capacity of the battery, but the hardness and mechanical properties of the diaphragm are improved, the thermal shrinkage and heat resistance are improved, and the safety performance of the diaphragm is improved, which shows that the existence of graphite phase carbon nitride polymer in the diaphragm coating can enable the oxide ceramic to be preparedThe specific gravity is increased without affecting the mechanical properties of the diaphragm, so that the hardness and the heat resistance of the diaphragm are improved.

Test example 4

The battery C1-C9 prepared in the above manner is subjected to a 3C/1C 100% DOD cycle performance test at room temperature, and the test process is as follows, wherein 3C is subjected to constant current charging to 4.2V, then constant voltage charging is carried out, the current is cut off by 0.05C, and finally 1C is subjected to constant current discharging to 2.5V, the cycle test is carried out until the capacity is reduced to 80%, and the test result is shown in figure 1.

As can be seen from FIG. 1, g-C is used₃N₄Oxide ceramic coating diaphragm has a time delay compared with the cycle water-jumping time of a battery adopting a traditional ceramic diaphragm, especially g-C₃N₄The cycle number of the C5 battery with the oxide ceramic coating with the larger thickness can reach 1000 circles, which is improved by 800 circles compared with the cycle number of the traditional ceramic diaphragm battery, which shows that the electrolyte retention amount plays an important role in the cycle performance and the service life of the lithium ion battery, and the g-C battery with the porous and large specific surface area₃N₄The introduction of the oxide ceramic coating can improve the electrolyte retention capacity to the maximum extent, thereby improving the cycle performance and the service life of the lithium ion battery.

In order to accelerate the circulation speed of the battery cell, the battery cell circulation test method comprises the steps of charging the battery cell to 4.2V at room temperature under 3C, then discharging the battery cell to 3.0V under 1C, and recording the discharge capacity values of different circulation turns.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.