LATP coating diaphragm as well as preparation method and application thereof

Abstract

The invention provides an LATP coating diaphragm and a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials, the LATP coating diaphragm disclosed by the invention comprises a base membrane, at least one side of the base membrane is provided with a mixed coating comprising LATP and PVDF-HFP, and the LATP accounts for 10%-60% of the mass of the PVDF-HFP; the chemical formula of the LATP is Li1. 3Al0. 3Ti1. 7( PO4) 3, and the thickness of the mixed coating is 3 to 20 microns. The composite diaphragm disclosed by the invention has the characteristic of no combustion under a high-temperature condition, is high in mechanical strength, and can inhibit further growth of lithium dendrites and improve the safety performance and the stability of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery materials, in particular to a LATP coating diaphragm and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are one of the most widely used battery types in today's market, playing an important role in consumer electronics, electric vehicles and energy storage systems.

[0003] In lithium ion batteries, the diaphragm is a crucial component. The diaphragm isolates the positive and negative electrodes of the battery, preventing direct contact between them, thereby avoiding short circuits. At the same time, the diaphragm allows lithium ions to shuttle freely, ensuring the normal operation of the battery. Currently, the main diaphragm materials used in lithium ion batteries include polyolefins (PP), polypropylene (PE), etc. These materials have good mechanical strength, chemical stability and thermal stability, and can meet the needs of the battery under various working conditions.

[0004] However, diaphragm failure is a serious problem in lithium ion batteries. When the diaphragm has defects or is damaged, the positive and negative electrodes of the battery may come into direct contact, causing internal short circuits. Short circuits can generate a large amount of heat and gas, triggering thermal runaway of the battery. During thermal runaway, the temperature of the battery rises rapidly, easily causing a fire or explosion.

[0005] Optimizing and modifying the diaphragm to reduce the risk of combustion when the battery short circuits and improve the safety of lithium batteries is a technical problem that needs to be solved by those skilled in the art. SUMMARY

[0006] The purpose of the present application is to provide a LATP coating diaphragm to solve the problem of battery fire or explosion caused by diaphragm combustion during thermal failure of the battery.

[0007] The present application provides a method for preparing a LATP coating diaphragm, which can prepare a LATP coating diaphragm with good flame retardance.

[0008] The present application provides a lithium ion battery comprising the LATP coating diaphragm prepared by the present application, which has good safety performance and stability.

[0009] The technical solution adopted by the present application to solve the above technical problems is:

[0010] The present application provides a LATP coating diaphragm, which comprises a base film, at least one side of the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP, the mass fraction of LATP in PVDF-HFP is 10%-60%; the chemical formula of LATP is Li 1.3 Al0.3 Ti 1.7 (PO4)3, the thickness of the mixed coating is 3-20 microns;

[0011] The base film is a PP film or a PE film.

[0012] The LATP coating diaphragm as described above, wherein the LATP accounts for 20%-40% of the mass of the PVDF-HFP; the thickness of the mixed coating is 3-14 microns.

[0013] The LATP coating diaphragm as described above, wherein the thickness of the mixed coating is 8-14 microns.

[0014] The LATP coating diaphragm as described above, wherein Li 1.3 Al 0.3 Ti 1.7 The particle size of (PO4)3 is 0.5-1 micron.

[0015] The LATP coating diaphragm as described above, wherein the molecular weight of the PVDF-HFP is 35000-45000.

[0016] The LATP coating diaphragm as described above, wherein the molecular weight of the PVDF-HFP is 40000.

[0017] The LATP coating diaphragm as described above, wherein the ratio of the thickness of the base film to the thickness of the mixed coating is 1:(0.05-0.5).

[0018] The present application also provides a method for preparing a LATP coating diaphragm, wherein the steps of the method are:

[0019] The LATP powder is mixed with the PVDF-HFP, the LATP accounts for 10%-60% of the mass of the PVDF-HFP, and is dissolved in an organic solvent, stirred for 9-13 hours, and the obtained mixed solution is brushed on the surface of the base film, and the coating thickness is 3-20 microns.

[0020] The method for preparing a LATP coating diaphragm as described above, wherein the organic solvent is a mixed solvent of DMAC and acetone, and the volume ratio of DMAC to acetone is 1.5-2.5:1.

[0021] The present application also provides a lithium ion battery, which comprises a battery main body, a positive electrode shell, a negative electrode shell, a positive electrode sheet, a negative electrode sheet, an electrolyte, a gasket, a spring sheet and the LATP coating diaphragm of any one of the above.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] The application obtains a LATP coating diaphragm by setting the mixed coating layer of LATP and PVDF-HFP on the base film, which has the advantages of not burning under high temperature conditions; in addition, the LATP coating diaphragm prepared by the application also has the characteristics of high mechanical strength, significantly improves the tensile properties of the coating diaphragm, is not easy to be pierced when encountering lithium dendrites, and can inhibit the further growth of lithium dendrites, and the lithium ion battery containing the LATP coating diaphragm has good safety performance and stability. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0025] Figure 1 The cross-sectional structure schematic diagram of the LATP coating diaphragm prepared by the application;

[0026] Figure 2 The tensile strength comparison diagram of the LATP coating diaphragm prepared by Example 1 and the comparative example PP film;

[0027] Figure 3 The comparison diagram of the LATP coating diaphragm prepared by Example 1 before and after burning; wherein, figure a is before burning, and figure b is after burning;

[0028] Figure 4 The cycle performance test diagram of the lithium battery prepared by Example 1.

[0029] BRIEF DESCRIPTION OF DRAWINGS

[0030] 1-base film, 2-mixed coating layer of LATP and PVDF-HFP. DETAILED DESCRIPTION

[0031] In order for those skilled in the art to better understand the scheme of the application, the application will be further described in detail below. The following specific embodiments are only used to describe the principles and characteristics of the application, and the examples are only used to explain the application, and do not limit the scope of the application. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0032] In one aspect, the application provides a LATP coating diaphragm, which comprises a base film, and the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP on at least one side, and the mass fraction of LATP in PVDF-HFP is 10%-60%; the chemical formula of LATP is Li 1.3 Al 0.3 Ti 1.7 (PO4)3, and the thickness of the mixed coating layer is 3-20 μm.

[0033] The base film is a PP film or a PE film.

[0034] The cross-sectional structure of the LATP-coated diaphragm prepared by the present application is shown in the schematic diagram Figure 1

[0035] PVDF-HFP, as a polymer electrolyte, has shown its unique advantages in the application of battery field. First, PVDF-HFP is insoluble in the common electrolyte of lithium ion battery, such as EC / DEC, so the polymer protective shell will not dissolve when the battery is working normally, thereby maintaining the stability of the electrolyte. Second, PVDF-HFP has a relatively low melting point of about 160℃, which makes it melt before or before burning, further preventing the spread of the flame. In addition, PVDF-HFP is inert and stable in the reduction / oxidation electrochemical environment inside the battery, which means that it can maintain its flame-retardant performance during the long-term use of the battery and will not be degraded due to the chemical reaction inside the battery.

[0036] The coating uses the common electrolyte of PVDF-HFP-based lithium ion battery, which also has mechanical strength in the battery, and the PVDF-HFP composite LATP active filler does not affect the ionic conductivity thereof.

[0037] If the thickness of the LATP coating is too thick, it will affect the transmission of lithium ions in the battery and reduce the rate performance of the battery, and if the thickness of the LATP coating is too thin, the mechanical performance will not be obviously improved.

[0038] The PP diaphragm has excellent chemical resistance and high temperature resistance, while the PE diaphragm has the advantages of good mechanical strength, chemical stability and relatively low cost.

[0039] The LATP-coated diaphragm prepared by the present application is a composite diaphragm that does not burn under high temperature conditions and has high mechanical strength, and the coating uses the common electrolyte of PVDF-HFP-based lithium ion battery, which also has mechanical strength in the battery and inhibits the further growth of lithium dendrites, thereby improving the safety performance and stability of the lithium ion battery.

[0040] Specifically, the mass fraction of LATP in PVDF-HFP is 20%-40%, and the thickness of the mixed coating is 3-14μm.

[0041] Specifically, the thickness of the mixed coating is 8-14μm. The fire resistance of the battery is obviously improved, the ion transmission capacity is improved, the tensile performance of the diaphragm is improved, and thus the cycle life and rate performance of the battery are improved.

[0042] Specifically, the mass fraction of LATP in PVDF-HFP is 30%.

[0043] ​Specifically, Li 1.3 Al 0.3 Ti 1.7 The particle size of (PO4)3 is 0.5-1 um.

[0044] Small particle size can reduce the plasticity of the polymer, improve the ion, and be beneficial to the ion conductivity.

[0045] Specifically, the molecular weight of PVDF-HFP is 35000-45000.

[0046] Specifically, the molecular weight of PVDF-HFP is 40000.

[0047] Specifically, the ratio of the thickness of the base film to the thickness of the mixed coating is 1: (0.05-0.5).

[0048] Specifically, the ratio of the thickness of the base film to the thickness of the mixed coating is 1:0.3.

[0049] The thickness of the commercial base film is generally 10-50 um, and the thinner the base film, the more obvious the performance improvement of the coating on the mixed separator.

[0050] Specifically, the base film is one of single-layer PP, single-layer PE, double-layer PP / PE, double-layer PP / PP and three-layer PP / PE / PP.

[0051] Specifically, the base film can also be one of polyimide film, PP+ceramic coating, and PE+ceramic coating.

[0052] On the other hand, the application also provides a method for preparing a LATP coating separator, and the steps of the method are:

[0053] The LATP powder is mixed with PVDF-HFP, and the mass fraction of LATP in PVDF-HFP is 10%-60%, which is dissolved in an organic solvent, stirred for 9-13h, and the obtained mixed solution is brushed on the surface of the base film, and the coating thickness is 3-20 um.

[0054] Specifically, the organic solvent is a mixed solvent of DMAC and acetone, and the volume ratio of DMAC to acetone is 1.5-2.5:1.

[0055] The solvent obtained by mixing DMAC and acetone can fully dissolve PVDF-HFP, and the organic solvent will volatilize in the later stage, and the coating is easier to dry because the acetone content is relatively high.

[0056] Specifically, the total weight percentage of the LATP powder and PVDF-HFP in the mixed solution is 5%-20%.

[0057] Specifically, the obtained mixed solution is coated on the base film by using an adjustable doctor blade, and after drying in an air environment at room temperature for 2-3 hours, the composite coating film is transferred into a vacuum oven, and dried at 55-70°C under vacuum condition for 10-15 hours, so as to remove the mixed solvent.

[0058] The application further provides a lithium ion battery, which comprises a battery body, a positive electrode shell, a negative electrode shell, a positive electrode sheet, a negative electrode sheet, an electrolyte, a gasket, an elastic sheet and the LATP coating diaphragm.

[0059] The application is further described below by means of specific examples and comparative examples. Unless otherwise specified, the reagents, materials and instruments used in the following are conventional reagents, conventional materials and conventional instruments, which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthesis methods.

[0060] Example 1

[0061] The example provides a LATP coating diaphragm, which comprises a PP base film, and a mixed coating layer comprising LATP and PVDF-HFP is arranged on at least one side of the base film, the mass fraction of the LATP in the PVDF-HFP is 10%, and the chemical formula of the LATP is Li 1.3 Al 0.3 Ti 1.7 (PO4)3, the particle size is 0.6 μm, and the molecular weight of the PVDF-HFP is 40000; the thickness of the mixed coating layer is 10 μm, and the ratio of the thickness of the base film to the thickness of the mixed coating layer is 1:0.3.

[0062] The example provides a method for preparing the LATP coating diaphragm, which comprises the following steps:

[0063] The LATP powder and the PVDF-HFP are mixed, and then dissolved in a mixed solvent of DMAC and acetone, the volume ratio of the DMAC to the acetone is 2:1, the total weight percentage of the LATP powder and the PVDF-HFP in the mixed solution is 10%, and the stirring time is 9-13 hours; the obtained mixed solution is coated on the base film by using an adjustable doctor blade, and after drying in an air environment at room temperature for 2-3 hours, the composite coating film is transferred into a vacuum oven, and dried at 55-70°C under vacuum condition for 10-15 hours, so as to remove the mixed solvent, and obtain the LATP coating diaphragm.

[0064] Example 2

[0065] The example provides a LATP coating diaphragm, which comprises a PP base film, and a mixed coating layer comprising LATP and PVDF-HFP is arranged on at least one side of the base film, the mass fraction of the LATP in the PVDF-HFP is 20%, and the chemical formula of the LATP is Li 1.3 Al 0.3 Ti 1.7Li1.3Al0.3Ti1.7(PO4)3, the particle size is 0.6 μm, and the molecular weight of the PVDF-HFP is 40000; the thickness of the mixed coating is 10 μm, and the ratio of the thickness of the base film to the thickness of the mixed coating is 1:0.3.

[0066] Example 3

[0067] The example provides a LATP-coated diaphragm, which comprises a PP base film, and at least one side of the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP, the mass fraction of the LATP in the PVDF-HFP is 30%, and the chemical formula of the LATP is Li 1.3 Al 0.3 Ti 1.7 Li1.3Al0.3Ti1.7(PO4)3, the particle size is 0.6 μm, and the molecular weight of the PVDF-HFP is 40000; the thickness of the mixed coating is 10 μm, and the ratio of the thickness of the base film to the thickness of the mixed coating is 1:0.3.

[0068] Example 4

[0069] The example provides a LATP-coated diaphragm, which comprises a PP base film, and at least one side of the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP, the mass fraction of the LATP in the PVDF-HFP is 40%, and the chemical formula of the LATP is Li 1.3 Al 0.3 Ti 1.7 Li1.3Al0.3Ti1.7(PO4)3, the particle size is 0.6 μm, and the molecular weight of the PVDF-HFP is 40000; the thickness of the mixed coating is 10 μm, and the ratio of the thickness of the base film to the thickness of the mixed coating is 1:0.3.

[0070] Example 5

[0071] The example provides a LATP-coated diaphragm, which comprises a PP base film, and at least one side of the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP, the mass fraction of the LATP in the PVDF-HFP is 50%, and the chemical formula of the LATP is Li 1.3 Al 0.3 Ti 1.7 Li1.3Al0.3Ti1.7(PO4)3, the particle size is 0.6 μm, and the molecular weight of the PVDF-HFP is 40000; the thickness of the mixed coating is 10 μm, and the ratio of the thickness of the base film to the thickness of the mixed coating is 1:0.3.

[0072] Example 6

[0073] The example provides a LATP-coated diaphragm, which comprises a PP base film, and at least one side of the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP, the mass fraction of the LATP in the PVDF-HFP is 60%, and the chemical formula of the LATP is Li 1.3 Al 0.3Ti 1.7 The thickness of the mixed coating layer is 10 μm, and the ratio of the thickness of the base film to the thickness of the mixed coating layer is 1:0.3.

[0074] Example 7

[0075] The present example provides a LATP-coated separator, which comprises a PE base film, and at least one side of the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP, the mass fraction of LATP in PVDF-HFP being 30%, and the chemical formula of the LATP is Li 1.3 Al 0.3 Ti 1.7 The thickness of the mixed coating layer is 10 μm, and the ratio of the thickness of the base film to the thickness of the mixed coating layer is 1:0.3.

[0076] Example 8

[0077] The present example provides a LATP-coated separator, which comprises a PP base film, and at least one side of the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP, the mass fraction of LATP in PVDF-HFP being 30%, and the chemical formula of the LATP is Li 1.3 Al 0.3 Ti 1.7 The thickness of the mixed coating layer is 10 μm, and the ratio of the thickness of the base film to the thickness of the mixed coating layer is 1:0.3.

[0078] Example 9

[0079] The present example provides a LATP-coated separator, which comprises a PP base film, and at least one side of the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP, the mass fraction of LATP in PVDF-HFP being 30%, and the chemical formula of the LATP is Li 1.3 Al 0.3 Ti 1.7 The thickness of the mixed coating layer is 10 μm, and the ratio of the thickness of the base film to the thickness of the mixed coating layer is 1:0.3.

[0080] Example 10

[0081] The present example provides a LATP-coated separator, which comprises a PP base film, and at least one side of the base film is provided with a mixed coating layer comprising LATP and PVDF-HFP, the mass fraction of LATP in PVDF-HFP being 30%, and the chemical formula of the LATP is Li 1.3Al 0.3 Ti 1.7 (P04)3, the particle size is 0.6 μm, the molecular weight of PVDF-HFP is 40000; the thickness of the mixed coating is 3 μm, the ratio of the thickness of the base film to the thickness of the mixed coating is 1:0.2.

[0082] Example 11

[0083] The example provides a LATP coating diaphragm, including a PP base film, the base film is provided with a mixed coating including LATP and PVDF-HFP on at least one side, the mass of LATP accounts for 30% of the mass of PVDF-HFP, the chemical formula of LATP is Li 1.3 Al 0.3 Ti 1.7 (P04)3, the particle size is 0.6 μm, the molecular weight of PVDF-HFP is 40000; the thickness of the mixed coating is 3 μm, the ratio of the thickness of the base film to the thickness of the mixed coating is 1:0.2.

[0084] Comparative Example

[0085] The PP diaphragm is purchased on the market.

[0086] Test Example

[0087] 1, the mechanical properties of the diaphragm of examples 1-6 and comparative examples are detected, and the results are shown in table 1.

[0088] Among them, the electronic universal testing machine is used to test the tensile test of the base film and the composite film after adding the coating.

[0089] The influence of examples 1-6 and comparative examples on the mechanical properties of the diaphragm is shown in table 1.

[0090] Table 1

[0091]

[0092] From the data of examples 1-6 in table 1, the mass of LATP accounts for 10%, 20%, 30%, 40%, 50% and 60% of the mass of PVDF-HFP respectively. The tensile strength is improved, and with the increase of the mass of LATP accounts for the mass of PVDF-HFP, the tensile strength is first increased and then decreased, and when the mass of LATP accounts for 30% of the mass of PVDF-HFP, the tensile properties of the diaphragm are optimal.

[0093] Examples 3 and 7 are compared, and there is no difference in the change of tensile strength of PP film and PE film.

[0094] The thickness of the composite coating is changed when the thickness ratio of the base film and the coating layer is changed in Example 3 and Examples 8-11. Too thick coating will prolong the ion transmission distance, affecting the rate performance. Too thin coating will not have the effect of improving safety and prolonging service life.

[0095] Figure 2 The tensile strength of the LATP coating separator prepared in Example 1 is compared with that of the comparative example PP film. The LATP coating separator prepared in the application has better tensile strength than the pure PP film.

[0096] The tensile strength of the LATP coating separator prepared in Example 1 is compared with that of the comparative example PP film. The LATP coating separator prepared in the application has better tensile strength than the pure PP film.

[0097] 2、 Figure 3 The LATP coating separator prepared in Example 1 is compared before and after burning. The LATP coating separator is burned with an alcohol lamp. The state before burning is Figure a, and the state after burning is Figure b. During the burning process, the coating separator shrinks, and does not burn in a high temperature environment. It can be confirmed that the LATP coating separator contained in the lithium battery will not cause combustion when the lithium battery catches fire, avoiding further expansion of the fire.

[0098] 3, the LATP coating separator of the example and the comparative example is assembled into a lithium ion battery, and the cycle performance of the lithium ion battery is detected. The lithium ion battery used for detection is composed of a battery shell with a model of CR2032, a positive shell, a negative shell, a positive sheet, a negative sheet, an electrolyte, a gasket, a spring and the above-mentioned LATP coating separator.

[0099] The preparation method of the positive sheet of the lithium ion battery comprises: dispersing LFP 80wt%, Super P conductive carbon black 10wt%, binder PVDF 10wt% in NMP, coating the obtained paste on aluminum foil, drying in a vacuum oven at 100-120℃ for 8-12h, and transferring all to an argon-filled glove box, wherein the content of oxygen and water is <0.1ppm.

[0100] The test is carried out using a blue electric battery test system (CT3001A). The test current is calculated according to the mass of active substance LiFePO4. The cut-off voltage is charged to 3.6V, and the discharge voltage is cut-off voltage 2.0V. Cycle test is carried out.

[0101] The cycle performance test chart of the lithium battery prepared in Example 1 is shown in Figure 4

[0102] As can be seen from the figure, the lithium battery containing the LATP coating separator prepared in the application has a capacity retention rate of 96.9% after 500 cycles, and the cycle performance is stable. ​

[0103] Using the above method for preparing lithium batteries, the LATP layer separators of Examples 2-11 were placed in the batteries, respectively, and the half cells were tested for cycle performance at room temperature. The testing process was as follows: first, 3C constant current charging to 4.2V, then constant voltage charging with a cutoff current of 0.05C, and finally 1C constant current discharging to 2.5V. This cycle test was repeated until the capacity decayed to 80%. After 500 cycles, the average capacity retention rate of Examples 2-11 was 95.7%, and the cycle performance was stable.

[0104] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limiting; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art will understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solution to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An LATP-coated diaphragm, characterized in that, The base film includes a coating of LATP and PVDF-HFP on at least one side, wherein LATP comprises 10%-60% of the PVDF-HFP by mass; the chemical formula of LATP is Li 1.3 Al 0.3 Ti 1.7 (PO4)3, wherein the thickness of the hybrid coating is 3-20 μm; The base film is a PP film or a PE film.

2. The LATP-coated diaphragm according to claim 1, characterized in that, LATP accounts for 20%-40% of the mass of PVDF-HFP; the thickness of the hybrid coating is 3-14 μm.

3. The LATP-coated diaphragm according to claim 1, characterized in that, The thickness of the hybrid coating is 8-14 μm.

4. The LATP-coated diaphragm according to claim 1, characterized in that, Li 1.3 Al 0.3 Ti 1.7 The particle size of (PO4)3 is 0.5-1 μm.

5. The LATP-coated diaphragm according to claim 1, characterized in that, The molecular weight of PVDF-HFP is 35,000-45,000.

6. The LATP-coated diaphragm according to claim 1, characterized in that, The molecular weight of PVDF-HFP is 40,000.

7. The LATP-coated diaphragm according to claim 1, characterized in that, The ratio of the base film thickness to the mixed coating thickness is 1:(0.05-0.5).

8. A method for preparing an LATP-coated diaphragm, characterized in that, The method steps are as follows: LATP powder is mixed with PVDF-HFP, with LATP accounting for 10%-60% of the mass of PVDF-HFP. The mixture is dissolved in an organic solvent and stirred for 9-13 hours. The resulting mixture is then brushed onto the surface of the base film, with a coating thickness of 3-20 μm.

9. The method for preparing an LATP-coated diaphragm according to claim 8, characterized in that, The organic solvent is a mixture of DMAC and acetone, with a volume ratio of DMAC to acetone of 1.5-2.5:

1.

10. A lithium-ion battery, characterized in that, It includes a battery body, a positive electrode shell, a negative electrode shell, a positive electrode sheet, a negative electrode sheet, an electrolyte, a gasket, a spring sheet, and the LATP-coated separator as described in any one of claims 1-7.

Images