High-safety flame-retardant composite diaphragm

Abstract

The utility model discloses a high-safety flame-retardant composite diaphragm which comprises a base diaphragm, nano cellulose coatings are arranged on two opposite side surfaces of the base diaphragm, the nano cellulose coatings are bonded and connected with the base diaphragm through PVDF (Polyvinylidene Fluoride), composite ceramic particles which are uniformly distributed are embedded in the nano cellulose coatings, and the composite ceramic particles are uniformly distributed on the base diaphragm. The composite ceramic particle is of a core-shell structure with ammonium polyphosphate as a core and an MOF base material as a shell. The nano cellulose coating is arranged on the surface of the base membrane, and the composite ceramic particles with the core-shell structure are embedded into the nano cellulose coating, so that the nano cellulose is used as a framework to support the base membrane, the diaphragm can be prevented from thermal shrinkage at high temperature even when the coating thickness is low, and the safety of the battery is improved; ammonium polyphosphate in the composite ceramic particles is heated and decomposed to release ammonia gas to play a flame-retardant role, ammonium polyphosphate can promote decomposition of the MOP base material, a compact carbon layer is formed to be attached to the nanocellulose skeleton, and the stability and the thermal decomposition resistance are improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of battery separator, specifically relates to a high safety flame -retardant composite separator. BACKGROUND

[0002] As an important component of lithium battery, the performance of the separator has a decisive influence on the performance of the battery. Lithium ion battery is prone to heat release during charging and discharging, so the temperature of the lithium battery will rise, and when the lithium ion battery temperature is high when overcharging occurs, the separator is easy to melt and shrink under heat, causing the lithium battery to short circuit and catch fire, poor safety. In order to improve the heat resistance of the separator, ceramic coating is usually coated on the surface of the separator, however, the existing ceramic coated separator needs a large coating thickness to effectively prevent the thermal shrinkage of the separator under high temperature, which does not meet the current requirements of miniaturization and high safety of the battery. SUMMARY

[0003] The utility model provides a high safety flame -retardant composite separator in view of the deficiency of prior art, it can improve the heat resistance of the separator under the condition of reducing the coating thickness of the separator, improve the safety of lithium ion battery.

[0004] To achieve the above object, the utility model adopts the following technical scheme:

[0005] A kind of high safety flame -retardant composite separator, including base film, the opposite two side surfaces of the base film are equipped with nanocellulose coating, the nanocellulose coating is connected by PVDF and base film adhesion, the nanocellulose coating is inlaid with the composite ceramic particles of uniform distribution, the composite ceramic particle is the core-shell structure with polyammonium phosphate as core, MOF base material as shell. By setting nanocellulose coating on the surface of base film, and embedding the composite ceramic particles of core-shell structure in nanocellulose coating, the base film is supported using nanocellulose as framework, even at low coating thickness, it can avoid the thermal shrinkage of the separator under high temperature, improve battery safety;When battery temperature is further increased or burns, polyammonium phosphate in composite ceramic particles is decomposed to release ammonia gas to play a flame -retardant role, at the same time, polyammonium phosphate can promote the decomposition of MOP base material, so as to form dense carbon layer attached to nanocellulose framework, thereby improving the stability and heat decomposition resistance of nanocellulose framework.

[0006] As a preferred technical scheme, the outer surface of one layer of nanocellulose coating is coated with electrolyte storage layer, and the electrolyte storage layer is a styrene-acrylate emulsion copolymer coating. By coating the electrolyte storage layer, a large amount of electrolyte can be absorbed to form a gel layer inside the battery, and the lithium ions in the electrolyte storage layer can be uniformly diffused to the negative electrode during battery charging, which is conducive to relieving the formation of lithium dendrites.

[0007] Preferably, the nanocellulose coating has a coating thickness of 0.5-3 microns.

[0008] Preferably, the base film is one of a PP film, a PE film, or a PP / PE composite film.

[0009] Preferably, the base film has a thickness of 4-12 microns.

[0010] Preferably, the nanocellulose in the nanocellulose coating has a diameter of 4-30 nanometers, a length of 300-1000 nanometers, and a thermal decomposition temperature of 265-335 degrees Celsius.

[0011] Preferably, the nanocellulose in the nanocellulose coating is a plant-based cellulose nanocrystal.

[0012] Preferably, the MOF substrate is one of ZIF-8, ZIF-67, MOF-199, MOF-74, or UIO-66.

[0013] Preferably, the electrolyte storage layer has a coating thickness of 0.5-3 microns.

[0014] Preferably, the composite ceramic particles have a particle size D50 of 0.3-2 microns.

[0015] The present application has obvious advantages and beneficial effects compared to the prior art. Specifically, by providing a nanocellulose coating on the surface of the base film and embedding composite ceramic particles with a core-shell structure in the nanocellulose coating, the nanocellulose is used as a framework to support the base film, which can prevent the diaphragm from thermal contraction at high temperatures even at a low coating thickness, thereby improving battery safety. When the battery temperature further increases or burns, the ammonium polyphosphate in the composite ceramic particles decomposes and releases ammonia gas to play a flame-retardant role. At the same time, the ammonium polyphosphate can also promote the decomposition of the MOP substrate, thereby forming a dense carbon layer attached to the nanocellulose framework, thereby improving the stability and thermal decomposition resistance of the nanocellulose framework. By coating the electrolyte storage layer, a large amount of electrolyte can be absorbed inside the battery cell to form a gel layer. During the battery charging process, lithium ions in the electrolyte storage layer will uniformly diffuse to the negative electrode, which is conducive to relieving the formation of lithium dendrites.

[0016] To make the structure, technical means, and specific purposes and functions of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1is a cross-sectional structure schematic view of the embodiment one of the utility model.

[0018] Figure 2 is a cross-sectional structure schematic view of the embodiment two of the utility model.

[0019] Explanation of the drawing mark:

[0020] 10, base film; 20, nanocellulose coating;

[0021] 21, composite ceramic particle; 30, electrolyte storage layer. Specific implementation

[0022] In the description of the utility model, it is necessary to explain that the orientation or position relation indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like is the orientation or position relation based on the drawing shown, and is only for the convenience of describing the utility model and simplifying the description, and is not indicative or suggestive of the position or element indicated must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the utility model.

[0023] In the description of the utility model, it is necessary to explain that, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, can be fixed connection, can also be detachable connection, or integrally connected;Can be mechanical connection, can also be electrical connection;Can be directly connected, can also be indirectly connected through an intermediate medium, can be the communication inside two elements. For ordinary skilled in the art, the specific meaning of the above terms in the utility model can be understood according to the specific circumstances.

[0024] As Figure 1As shown in Embodiment 1 of this utility model, a high-safety flame-retardant composite separator includes a base film 10. Both opposite surfaces of the base film 10 are provided with a nano-cellulose coating 20. The nano-cellulose coating 20 is bonded to the base film 10 via PVDF. Uniformly distributed composite ceramic particles 21 are embedded in the nano-cellulose coating 20. The composite ceramic particles 21 have a core-shell structure with ammonium polyphosphate as the core and MOF substrate as the shell. By setting the nano-cellulose coating 20 on the surface of the base film 10 and embedding the core-shell structured composite ceramic particles 21 within the nano-cellulose coating 20, nano-cellulose is used as a framework to support the base film 10. Even at low coating thicknesses and high temperatures, thermal shrinkage of the separator can be avoided, improving battery safety. When the battery temperature further increases or combustion occurs, the ammonium polyphosphate in the composite ceramic particles 21 decomposes upon heating, releasing ammonia gas, which can dilute flammable gases and play a flame-retardant role. Simultaneously, ammonium polyphosphate can also promote the decomposition of the MOP substrate, thereby forming a dense carbon layer attached to the nano-cellulose framework, thus improving the stability and thermal decomposition resistance of the nano-cellulose framework.

[0025] In this invention, the coating thickness of the nanocellulose coating 20 is 0.5–3 μm, preferably 1–2 μm. The base film 10 is one of PP film, PE film, or PP / PE composite film, and the thickness of the base film 10 is 4–12 μm. The nanocellulose in the nanocellulose coating 20 has a diameter of 4–30 nm, a length of 300–1000 nm, and a thermal decomposition temperature of 265℃–335℃. The nanocellulose in the nanocellulose coating 20 is selected from plant-based cellulose nanocrystals. The MOF substrate is one of ZIF-8, ZIF-67, MOF-199, MOF-74, or UIO-66. The particle size D50 of the composite ceramic particles 21 is 0.3–2 μm, preferably 0.5–0.8 μm.

[0026] like Figure 2 As shown in Embodiment 2 of this utility model, the difference from Embodiment 1 is that an electrolyte storage layer 30 is coated on the outer surface of the nanocellulose coating 20. The electrolyte storage layer 30 is a styrene-acrylate emulsion copolymer coating, and the coating thickness of the electrolyte storage layer 30 is 0.5–3 μm. By coating the electrolyte storage layer 30, a large amount of electrolyte can be absorbed inside the battery cell to form a gel layer. During battery charging, lithium ions in the electrolyte storage layer 30 will diffuse evenly to the negative electrode, which helps to alleviate the formation of lithium dendrites.

[0027] In summary, the utility model discloses a base film 10 surface is provided with nanocellulose coating 20, and the nanocellulose coating 20 is embedded in the composite ceramic particle 21 of core-shell structure, to utilize nanocellulose as the skeleton to support base film 10, even in low coating thickness at high temperature can avoid diaphragm heat shrinkage, improve battery safety, when battery temperature is further raised or burns, ammonium polyphosphate in composite ceramic particle 21 is heated and decomposed and releases ammonia gas and plays the role of flame retardant, simultaneously, ammonium polyphosphate can promote the decomposition of MOP base material, to form the compact carbon layer and attach on nanocellulose skeleton, thereby improve the stability and heat decomposition performance of nanocellulose skeleton, through coating electrolyte storage layer 30, to can absorb a large amount of electrolyte and form gel layer in the inside of electric core, in the battery charging process, the lithium ion of electrolyte storage layer 30 will evenly diffuse to the negative pole, be favorable to the formation of lithium dendrite relief.

[0028] The above is only the preferred embodiment of the utility model, and does not limit the utility model, so any modification, equivalent replacement, improvement, etc. of the above embodiment according to the technical actuality of the utility model still belongs to the range of the technical scheme of the utility model.

Claims

1. A high safety flame retardant composite separator comprising a base film, characterized in that, The two opposite side surfaces of the base film are provided with nanocellulose coatings, the nanocellulose coatings are bonded and connected with the base film through PVDF, the nanocellulose coatings are inlaid with uniformly distributed composite ceramic particles, and the composite ceramic particles are core-shell structures with ammonium polyphosphate as the core and MOF base material as the shell.

2. A high safety flame retardant composite separator according to claim 1, wherein, The outer surface of one layer of the nanocellulose coating is coated with an electrolyte storage layer, and the electrolyte storage layer is a styrene-acrylate emulsion copolymer coating.

3. A high safety flame retardant composite separator according to claim 1, wherein The coating thickness of the nanocellulose coating is 0.5-3 microns.

4. The high safety flame retardant composite separator according to claim 1, wherein, The base film is one of a PP film, a PE film or a PP / PE composite film.

5. The high safety flame retardant composite separator according to claim 1 or 4, wherein The thickness of the base film is 4-12 microns.

6. A high safety flame retardant composite separator according to any one of claims 1 to 3, wherein The diameter of the nanocellulose in the nanocellulose coating is 4-30 nm, the length is 300-1000 nm, and the thermal decomposition temperature is 265-335 DEG C.

7. A high safety flame retardant composite separator according to claim 6, wherein The nanocellulose in the nanocellulose coating is selected from plant cellulose nanocrystals.

8. A high safety flame retardant composite separator according to claim 1, wherein The MOF base material is selected from one of ZIF-8, ZIF-67, MOF-199, MOF-74 or UIO-66.

9. A high safety flame retardant composite separator according to claim 2, wherein The coating thickness of the electrolyte storage layer is 0.5-3 microns.

10. The high safety flame retardant composite separator according to claim 1, wherein The particle size D50 of the composite ceramic particles is 0.3-2 microns.

Images