A separator for lithium metal batteries and a method of making the same

Abstract

The application discloses a separator for a lithium metal battery and a preparation method thereof, wherein the separator comprises a base film and a coating layer on at least one side surface of the base film, and the coating layer comprises a coating material, and the coating material comprises one of a rare earth metal halide, a rare earth metal nitride, a rare earth metal sulfide, a rare earth metal nitrate and a rare earth metal phosphate. + The separator for the lithium metal battery has more uniform Li transmission channels and excellent cycle performance. Meanwhile, the separator has better cycle stability when used in combination with metal lithium, and provides a new idea for stable cycle of the lithium metal battery and surface functionalization of the separator.

Description

TECHNICAL FIELD

[0001] The present application relates to lithium battery technology, in particular to a separator for lithium metal battery and a preparation method thereof. BACKGROUND

[0002] As early as in the 1990s, rechargeable lithium-ion batteries have successfully realized commercialization in the energy storage field with the advantages of long service life and light weight, and are widely used in electronic devices and electric vehicles. However, the theoretical upper limit of energy density of the currently commercialized graphite negative electrode is only 372 mAh / g, which cannot meet the demand of energy density secondary battery applications such as increasing energy storage and electric vehicles. It has become urgent to develop alternative graphite negative electrode materials with low operating voltage, high capacity, high coulombic efficiency and high stability. Compared with traditional graphite negative electrode, metal lithium has ultra-high theoretical specific capacity (3860 mAh / g) and extremely low redox potential, and is considered to be a promising negative electrode material in high-energy-density rechargeable batteries. However, the lithium metal anode has serious dendrite problems and capacity decay during charging / discharging, which hinders the practical application of lithium metal anode. In order to overcome this challenge, the academic and industrial circles have proposed various modification methods to achieve uniform lithium deposition and improve the stability of lithium metal batteries.

[0003] From the modification strategy, it is mainly through the introduction of solid electrolyte, separator surface modification and artificial protective layer in lithium metal battery and the adjustment of solid-state electrolyte interface layer composition to realize uniform lithium deposition. Among them, due to the chemical stability and operability of the separator in the air, the separator modification strategy of coating a functional coating on the separator surface is a promising method to stabilize the lithium metal anode. Coating a layer of lithiumophilic inorganic material on the surface of the commercialized polypropylene or polyethylene separator can provide lithiumophilic sites, uniform Li + distribution of transmission channels, guide Li + nucleation, and then inhibit the formation of lithium dendrites to achieve uniform lithium deposition. Part of the functional material has a reversible first-order phase change in the process of lithium deposition and stripping, which helps to protect the lithium anode and inhibit the propagation of lithium dendrites, thereby realizing long-life plating / detaching lithium stable lithium metal anode [Yang Ruizhi, Journal of Power Sources, 2021, 484:229253].

[0004] Therefore, it is particularly crucial to develop a coated separator with lithium dendrite inhibition and uniform lithium deposition for the development of lithium metal batteries. The present application discloses a separator with lithiumophilic and rigidity and a preparation method thereof, and applies it to lithium metal batteries. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a separator for a lithium metal battery and a preparation method thereof, which solves the problems of serious dendrite and capacity attenuation of a lithium metal anode in the prior art during charging and discharging.

[0006] The technical solution adopted by the present application to solve the above technical problem is:

[0007] A separator for a lithium metal battery, comprising a base film and a coating layer on at least one side surface of the base film, wherein the coating layer comprises a coating material, and the coating material comprises one of a rare earth metal halide, a rare earth metal nitride, a rare earth metal sulfide, a rare earth metal nitrate, and a rare earth metal phosphate.

[0008] Preferably, the coating layer further comprises a binder and a dispersant, the coating material accounts for 75-95% of the total mass of the coating layer, the binder accounts for 5-20% of the total mass of the coating layer, and the dispersant accounts for 0.1-2% of the total mass of the coating layer.

[0009] Preferably, the particle size of the coating material ranges from 0.1 to 1.5 microns.

[0010] Preferably, the coating material comprises one of CeCl3, LaCl3, NdCl3, CeI3, LaI3, LaN, Ce2S3, Ce(NO3)3, and CePO4.

[0011] Preferably, the thickness of the coating layer is 3-8 microns, and the base film layer is one of PE and PP, with a thickness of 5-20 microns.

[0012] Preferably, the binder comprises one or more of PVDF, PVDF-HFP, PAN, PEO, and PTFE.

[0013] Preferably, the dispersant comprises one of triethylhexyl phosphate, sodium dodecyl sulfate, polyacrylamide, and methyl amyl alcohol.

[0014] A preparation method of a separator for a lithium metal battery, for preparing the above separator, comprising the following steps:

[0015] S1, the weighed coating material and the dispersant are respectively added to the solvent according to the determined solid content, ball milling or double planetary high-speed pre-dispersion is used, and the median particle size of the coating material is made to meet the preset requirements, to obtain a pre-dispersed slurry;

[0016] S2, the weighed binder is added to another portion of the solvent according to the determined solid content to prepare a binder solution;

[0017] S3, adding the binder solution prepared in step S2 to the pre-dispersed slurry prepared in step S1 for further dispersion to obtain a coating slurry;

[0018] S4, coating the coating slurry prepared in step S3 onto the surface of the base film by using a micro-concave coater or a flow coater, and drying in a coater oven.

[0019] Preferably, the solvent is one of dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

[0020] Preferably, the solid content of the coating material in the solvent in step S1 is 25%-50%, the solid content of the binder in the solvent in step S2 is 5%-15%, the pre-dispersion time in step S1 is 1h-20h, and the dispersion time in step S3 is 1h-3h.

[0021] Compared with the prior art, the separator for lithium metal batteries and the preparation method thereof have the following advantages:

[0022] (1) By forming a coating layer on the surface of the base film, compared with the traditional PE or PP separator, there are uniform Li+ transmission channels and excellent cycle performance, and better cycle stability when matched with metal lithium;

[0023] (2) By introducing one of rare earth metal halides, rare earth metal nitrides, rare earth metal sulfides, rare earth metal nitrates, and rare earth metal phosphates into the coating layer, a layer of lithium uniform deposition layer is formed on the surface of the base film, thereby improving the cycle performance of the lithium metal battery;

[0024] (3) According to the method in the present application, the coating material is mixed with the dispersant and the binder, which is beneficial to the good dispersion of the coating material, and a uniform spread separator is obtained to realize the uniform deposition of lithium in the charging and discharging process. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is an electron micrograph of the coated separator surface in the present embodiment;

[0026] Figure 2 It is a schematic diagram of the charge-discharge cycle performance at 1C (1C=180mA / g relative to NCM811) rate in the present embodiment. DETAILED DESCRIPTION

[0027] The present application will be further described in detail below in combination with the embodiments of the drawings.

[0028] EMBODIMENT

[0029] A kind of separator for lithium metal battery, including base film and coating layer located at the at least one side surface of base film, base film is PE or PP, thickness is 5 μm-20 μm, the thickness of coating layer is 3 μm-8 μm.

[0030] Coating layer includes coating material, binder and dispersant, wherein coating material includes one of rare earth metal halide, rare earth metal nitride, rare earth metal sulfide, rare earth metal nitrate and rare earth metal phosphate, specifically, one of CeCl3, LaCl3, NdCl3, CeI3, LaI3, LaN, Ce2S3, Ce (NO3) 3, CePO4, coating material accounts for 75%-95% of total mass of coating layer, and the particle size of coating material ranges from 0.1 μm to 1.5 μm. Binder includes one or more of PVDF, PVDF-HFP, PAN, PEO, PTFE, and binder accounts for 5%-20% of total mass of coating layer. Dispersant includes one of triethylhexyl phosphate, sodium dodecyl sulfate, polyacrylamide, methyl amyl alcohol, and dispersant accounts for 0.1%-2% of total mass of coating layer.

[0031] The preparation method of the above-mentioned separator for lithium metal battery includes the following steps:

[0032] S1, the weighed coating material and dispersant are respectively added to the solvent according to the determined solid content, the solid content of the coating material in the solvent is 25%-50%, ball milling or double planetary high-speed pre-dispersion is used, and the median particle size of the coating material reaches the preset requirement, to obtain a pre-dispersed slurry, the pre-dispersion time is 1h-20h, and the median particle size of the coating material is 3 μm-8 μm;

[0033] S2, the weighed binder is added to another portion of solvent to prepare a binder solution, and the solid content of the binder in the solvent is 5%-15%;

[0034] S3, the binder solution prepared in step S2 is added to the pre-dispersed slurry prepared in step S1 for further dispersion for 1h-3h to obtain a coating slurry;

[0035] S4, the coating slurry prepared in step S3 is coated onto the surface of the base film by using a micro-recess coater or a flow coating machine, and is dried in the oven of the coating machine.

[0036] The solvent in steps S1 and S2 is one of dimethylformamide, dimethylacetamide and N-methylpyrrolidone.

[0037] Example 1,

[0038] A kind of separator for lithium metal battery, prepared by the following steps:

[0039] S1, respectively, take the coating material LaCl3, binder PVDF, dispersant sodium dodecyl sulfate and solvent dimethylformamide, the coating material LaCl3 is dispersed in the solvent dimethylformamide with a solid content of 40%, the dispersant sodium dodecyl sulfate is added, and the coating material is pre-dispersed at 800 rpm for 1 h to make the median particle size of the coating material 0.3 μm, and a pre-dispersed slurry is obtained;

[0040] S2, the binder PVDF is dispersed in another portion of the solvent dimethylformamide to prepare a binder solution with a solid content of 8%;

[0041] S3, the binder solution prepared in step S2 is added to the pre-dispersed slurry prepared in step S1, and the mixture is dispersed at 600 rpm for 1.5 h to obtain a uniform coating slurry;

[0042] S4, the coating slurry obtained in step S3 is coated on the surface of the PE-based film after 12 μm using a micro-concave coater, and dried in a coater oven at 75°C to obtain a coating layer with a thickness of 5 μm on the surface of the PE-based film. The prepared separator for lithium metal battery, the mass ratio of LaCl3, PVDF and sodium dodecyl sulfate in the surface coating layer of the prepared separator is 80.5%, 18.3% and 1.2% respectively.

[0043] Example 2,

[0044] A separator for lithium metal battery is prepared by the following steps:

[0045] S1, respectively, take the coating material LaN, binder PTFE, dispersant triethylhexyl phosphate and solvent N-methyl pyrrolidone, the coating material LaN is dispersed in the solvent N-methyl pyrrolidone with a solid content of 35%, the dispersant triethylhexyl phosphate is added, and the coating material is pre-dispersed at 300 rpm for 5 h to make the median particle size of the coating material 0.5 μm, and a pre-dispersed slurry is obtained;

[0046] S2, the binder PTFE is dispersed in another portion of the solvent N-methyl pyrrolidone to prepare a binder solution with a solid content of 15%;

[0047] S3, the binder solution prepared in step S2 is added to the pre-dispersed slurry prepared in step S1, and the mixture is dispersed at 200 rpm for 2 h to obtain a uniform coating slurry;

[0048] S4, using a micro concave coating machine, the coating slurry obtained in step S3 is coated on the surface of the 8 pm PP base film, and dried in the coating machine oven at 75°C, obtaining a coating layer with a thickness of 5 pm on the surface of the PP base film, and a roll-to-roll winding is obtained for the separator for lithium metal batteries. The mass ratio of LaN, PTFE and triethylhexyl phosphoric acid in the surface coating layer of the prepared separator is 88%, 11.5% and 0.5% respectively.

[0049] Example 3,

[0050] A separator for lithium metal batteries is prepared by the following steps:

[0051] S1, respectively, the coating material Ce2S3, the binder PEO, the dispersant triethylhexyl phosphoric acid and the solvent N-methyl pyrrolidone are weighed, the weighed coating material LaN is dispersed in the solvent N-methyl pyrrolidone at a solid content of 30%, the dispersant triethylhexyl phosphoric acid is added, and the coating material is pre-dispersed at 300 rpm for 6 hours to obtain a pre-dispersed slurry with a median particle size of 0.8 pm;

[0052] S2, the binder PTFE is dispersed in another portion of the solvent N-methyl pyrrolidone to obtain a binder solution with a solid content of 8%;

[0053] S3, the binder solution prepared in step S2 is added to the pre-dispersed slurry prepared in step S1, and the mixture is dispersed at 300 rpm for 2 hours to obtain a uniform coating slurry;

[0054] S4, using a micro concave coating machine, the coating slurry obtained in step S3 is coated on the surface of the 8 pm PP base film, and dried in the coating machine oven at 75°C, obtaining a coating layer with a thickness of 5 pm on the surface of the PP base film, and a roll-to-roll winding is obtained for the separator for lithium metal batteries. The mass ratio of LaN, PTFE and triethylhexyl phosphoric acid in the surface coating layer of the prepared separator is 88%, 11.5% and 0.5% respectively.

[0055] Example 4,

[0056] A separator for lithium metal batteries is prepared by the following steps:

[0057] S1, respectively, the coating material Ce2S3, the binder PEO, the dispersant triethylhexyl phosphoric acid and the solvent N-methyl pyrrolidone are weighed, the weighed coating material LaN is dispersed in the solvent N-methyl pyrrolidone at a solid content of 30%, the dispersant triethylhexyl phosphoric acid is added, and the coating material is pre-dispersed at 300 rpm for 6 hours to obtain a pre-dispersed slurry with a median particle size of 0.8 pm;

[0058] S2, a binder PVDF was dispersed in another portion of solvent dimethylformamide to prepare a binder solution with solid content of 10%;

[0059] S3, the binder solution prepared in step S2 was added to the pre-dispersed slurry prepared in step S1, and after high-speed dispersion at 250 rpm for 2 h by double planetary, a uniform coating slurry was obtained;

[0060] S4, the coating slurry obtained in step S3 was coated on the surface of a PE base film with a thickness of 12 μm using a micro-concave coater, and dried in a coater oven at 75°C, obtaining a coating layer on the surface of the PE base film with a thickness of 8 μm. A separator for lithium metal batteries was obtained by roll-to-roll winding, and the mass ratio of CePO4, PVDF and sodium dodecyl sulfate in the coating layer on the surface of the prepared separator was 92%, 7% and 1%, respectively.

[0061] Lithium metal batteries were prepared using the separators for lithium metal batteries obtained in Examples 1-4, respectively, according to the following specific steps:

[0062] Preparation of positive electrode sheet: lithium nickel cobalt manganese oxide (NCM811), super conductive carbon black (SP) and binder (PVDF) were dispersed in N-methyl pyrrolidone solvent at a mass ratio of 97:2:1, with a solid content of 78%, and the obtained positive electrode slurry was coated on an aluminum foil, and after air drying, a positive electrode sheet was obtained, and its size was cut to 52 cm*90 cm;

[0063] Preparation of negative electrode sheet: an 80 μm thick lithium metal foil was used as the negative electrode, with a size of 56 cm*93 cm;

[0064] Preparation of lithium metal battery: the side of the coating layer was oriented towards the metal lithium negative electrode, and the soft-pack battery was prepared according to the lamination method, and the tab was welded, top-sealed, side-sealed, and baked at 60°C for 6 h; in a glove box under high-purity argon protection, an interfacial wetting agent (1M LiFSI dissolved in EC:DEC:DMC=1:1:1 organic solvent) was added, and sealed, and finally low-rate formation and two-sealing were performed to obtain a lithium metal battery.

[0065] Comparative Example 1,

[0066] A lithium metal battery was prepared using the above-prepared positive electrode sheet, negative electrode sheet and ordinary PE separator with a thickness of 12 μm.

[0067] Comparative Example 2,

[0068] A lithium metal battery was prepared using the above-prepared positive electrode sheet, negative electrode sheet and ordinary PP separator with a thickness of 10 μm.

[0069] Cycling stability test: the discharge specific capacity at 1C (1C = 180 mA / g vs. NCM811) rate is shown in Table 1, from the cycling results of examples and comparative examples, it can be seen that the lithium metal battery assembled after coating a layer of coating material on the surface of the base film has better cycling performance, the capacity retention rate of the example is still 90.42% after 150 cycles at 1C, while that of the comparative example is only 82.41%. Figure 2

[0070] Through the above cycling stability test, it can be proved that the coated separator prepared by the scheme has more excellent cycling performance in the lithium metal battery compared with the traditional PE / PP separator.

[0071] Although the preferred embodiments of the present application are described in detail above, it should be clearly understood that the present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.​

Claims

1. A separator for a lithium metal battery, characterized in that: The invention comprises a base film and a coating layer located on at least one side of the base film, wherein the coating layer comprises a coating material, and the coating material comprises one of CeCl3, LaCl3, NdCl3, CeI3, LaI3, LaN, Ce2S3, Ce(NO3)3, and CePO4, and is used to form an adjustable lithium uniform deposition layer on the surface of the base film; The coating layer further comprises a binder and a dispersant, wherein the coating material accounts for 75%-95% of the total mass of the coating layer, the binder accounts for 5%-20% of the total mass of the coating layer, and the dispersant accounts for 0.1%-2% of the total mass of the coating layer; The particle size of the coating material ranges from 0.1 μm to 1.5 μm.

2. The separator for lithium metal batteries according to claim 1, wherein: The coating layer has a thickness of 3 μm-8 μm; the base film layer is one of PE and PP, and has a thickness of 5 μm-20 μm.

3. The separator for lithium metal batteries according to claim 1, wherein: The binder includes one or more of PVDF, PVDF-HFP, PAN, PEO, and PTFE.

4. The separator for lithium metal batteries according to claim 1, wherein: The dispersant includes one of triethylhexyl phosphoric acid, sodium lauryl sulfate, polyacrylamide, and methyl amyl alcohol.

5. A method for preparing a separator for a lithium metal battery, characterized in that: The method for preparing the diaphragm according to any one of claims 1 to 4 comprises the following steps: S1. Add the weighed coating material and dispersant to the solvent according to the determined solid content, use a ball mill or a double planetary mill for high-speed pre-dispersion, and make the median particle size of the coating material reach the preset requirements to obtain a pre-dispersed slurry; S2. adding the weighed binder according to the determined solid content to another solvent to prepare a binder solution; S3, adding the binder solution prepared in step S2 to the pre-dispersed slurry prepared in step S1 and further dispersing to obtain a coating slurry; S4. The coating slurry prepared in step S3 is coated on the surface of the base film by using a micro-concave coater or a casting coater, and then dried in an oven of the coater.

6. The method for preparing a separator for a lithium metal battery according to claim 5, wherein: The solvent is one of dimethylformamide, dimethylacetamide and N-methylpyrrolidone.

7. The method for preparing a separator for a lithium metal battery according to claim 5, wherein: In step S1, the solid content of the coating material in the solvent is 25%-50%; in step S2, the solid content of the binder in the solvent is 5%-15%; the pre-dispersion time in step S1 is 1h-20h; and the dispersion time in step S3 is 1h-3h.

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