A method for blending MIL-101 with meta-aramid for lithium-ion battery separators

Abstract

The present invention relates to a method for blending MIL-101(Cr) with meta-aramid for a lithium-ion battery separator. The method comprises the following steps: adding MIL-101(Cr) into DMAC and stirring at room temperature for 0.5 - 4 h to obtain a MIL-101(Cr) solution; stirring the MIL-101(Cr) solution and the PMIA solution at room temperature for 3 - 5 h, then preparing a PMIA / MIL-101 composite separator, and further drying it in vacuum at 80 °C for 12 - 18 h to obtain the PMIA / MIL-101 composite separator. The sponge-like and uniformly porous PMIA / MIL-101 composite separator obtained by the present invention has the combination of the two materials, endowing the separator with both thermal stability and good wettability to the electrolyte. Using this composite porous membrane as a lithium-ion battery separator improves the electrochemical performance of the battery.

Description

Technical Field

[0001] The present invention relates to a material for a lithium-ion battery separator, belonging to the technical field of polymer material preparation; the present invention also relates to the research on the electrochemical performance of the battery by using this separator material in a lithium-ion battery, belonging to the field of electrochemical detection technology. Background Art

[0002] With the depletion of fossil fuels and the aggravation of environmental pollution, the demand for high-performance lithium-ion batteries is increasing day by day, and they are widely used in rechargeable electronic devices and new energy vehicle fields. The separator is a core component of a lithium-ion battery (in addition to the positive and negative electrodes and the electrolyte). Commercial polyolefin separators have excellent mechanical properties and an appropriate thermal closure temperature. However, the commonly used polyolefin separator materials at present have poor electrolyte wettability, which is not conducive to lithium-ion transport and thus causes the generation of lithium dendrites, affecting the safety and electrochemical performance of lithium-ion batteries.

[0003] During the actual operation of LIBs, the separator not only needs to have thermal stability and maintain dimensional stability at high temperatures, but also needs to improve the wettability of the electrolyte and increase the lithium-ion transference number. The PMIA-modified PE separator prepared by Wang through the vapor-induced phase inversion method forms a PMIA porous layer on both sides of the PE separator, improving the thermal stability of the PE separator. At the same time, the composite separator shows excellent electrolyte affinity and anti-lithium dendrite performance (Vapor-induced phase inversion of poly(m-phenylene isophthalamide)modified polyethylene separator for high-performancelithium-ion batteries.doi.org / 10.1016 / j.cej). The PAN / Co-MOF composite separator prepared by Cao through the electrospinning method suppresses the movement of anions through the strong electrostatic interaction between MOF and PF6 - and increases the lithium-ion transference number to 0.74, which is 64.4% higher than that of the PAN separator. (Electrospun MOF / PAN composite separator withsuperior electrochemical performances forhigh energy density lithiumbatteries.doi.org / 10.1016 / j.electacta). However, when using polyolefin as the base film for modification, the improvement of thermal stability performance is limited, and it is difficult to inhibit the growth of lithium dendrites. Summary of the Invention

[0004] In view of the problems that the current polyolefin separator has poor thermal stability, serious dimensional shrinkage at high temperature, low lithium ion transference number, and affects the safety and performance of LIBs, a preparation method of a PMIA and MIL-101(Cr) composite porous separator is developed. This method blends PMIA and MIL-101(Cr), and through the nonsolvent phase inversion method, unsaturated metal sites are formed during the vacuum drying process of MIL-101 and chemically complex with anions in the electrolyte, preparing a composite separator with high thermal stability and excellent electrochemical performance. The sponge-like and uniformly porous PMIA / MIL-101 composite separator obtained by the present invention combines the two materials, endowing the separator with both thermal stability and good wettability to the electrolyte. Using this composite porous membrane as the lithium ion battery separator improves the electrochemical performance of the battery.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing a MIL-101(Cr) blended meta-aramid lithium ion battery separator, the method comprising the following steps:

[0007] (1) Add MIL-101(Cr) to DMAC and stir at room temperature for 0.5 - 4 h to obtain a MIL-101(Cr) solution;

[0008] Wherein, the mass ratio of MIL-101(Cr) to DMAC is 1:1 - 3;

[0009] (2) Stir the MIL-101(Cr) solution and the PMIA solution at room temperature for 3 - 5 h, then prepare a PMIA / MIL-101 composite separator, and then vacuum dry at 80 °C for 12 - 18 h to obtain the PMIA / MIL-101 composite separator.

[0010] Wherein, the mass ratio of MIL-101(Cr) to PMIA is 1:10 - 20;

[0011] The application of the MIL-101 blended meta-aramid lithium ion battery separator prepared by the method in a lithium ion battery.

[0012] The positive electrode material of the lithium ion battery is one or more of LiCoO2, LiFePO4, and LiMn2O4, the negative electrode material is one or more of lithium foil, graphite, and lithium titanate, the solute of the electrolyte is one or more of lithium salts such as LiPF6, LiClO4, and LiAsF6, and the solvent is one or a multi-component mixed solvent of EC, PC, DMC, and DEC.

[0013] The beneficial effects of the present invention are as follows:

[0014] (1) The PMIA / MIL-101 composite separator prepared by the method of the present invention has a simple process and can maintain dimensional integrity at a high temperature of 300 °C, greatly reducing the risk of thermal runaway explosion of LIBs.

[0015] (2) The addition of MIL-101(Cr) improves the wettability of the battery separator. Compared with the pure PMIA membrane, the ionic conductivity of the lithium-ion battery increases from 0.58 mS cm -1 to 1.32 mS cm -1 , and the lithium-ion transference number increases from 0.23 to 0.65, improving the electrochemical performance of the lithium-ion battery (after 50 cycles at 0.2C, the discharge specific capacity increases from 85.6 mAh / g to 120.4 mAh / g). Description of the Drawings

[0016] Figure 1 SEM images of the PMIA / MIL-101 composite separator prepared in Example 2 of the present invention; among them, Figure 1 a is the surface morphology image of the PMIA membrane, Figure 1 b is the surface morphology image of the PMIA / MIL-101 composite separator, Figure 1 c is the cross-sectional morphology image of the PMIA membrane, Figure 1 d is the cross-sectional morphology image of the PMIA / MIL-101 composite separator;

[0017] Figure 2 shows the dimensional change diagrams of the PMIA separator and the PMIA / MIL-101 composite separator prepared in Example 2 of the present invention before and after heat treatment.

[0018] Figure 3 shows the cycle performance test diagrams of the lithium-ion batteries assembled with the PMIA separator and the PMIA / MIL-101 composite separator prepared in Example 3 of the present invention.

[0019] Figure 4 shows the interfacial impedance spectra diagrams of the lithium-ion batteries assembled with the PMIA separator and the PMIA / MIL-101 composite separator prepared in Example 4 of the present invention respectively;

[0020] Figure 5 shows the bulk impedance spectra diagrams of the lithium-ion batteries assembled with the PMIA separator and the PMIA / MIL-101 composite separator prepared in Example 5 of the present invention respectively. Specific Embodiment Methods

[0021] The positive electrode material used in the following examples of the present invention is LiCoO2.

[0022] The PMIA (poly(m-phenylene isophthalamide)) membrane used in Comparative Example 1 is a well-known material, which is an asymmetric sponge-like porous membrane with a thickness of 30 - 35 μm, a liquid absorption rate of 166%, and a porosity of 58%. Its preparation adopts the non-solvent phase inversion method. By means of stepwise coagulation bath forming, the PMIA casting solution coated well is placed in the first-stage coagulation bath DMAc / Gl (v:v = 7 / 3) for 10 s and then taken out immediately and put into the second-stage coagulation bath DMAc / H2O (v:v = 3 / 7) for 20 s and then formed and taken out, and washed several times. But it is not limited to this.

[0023] Comparative Example 1

[0024] After the PMIA separator is dried, it is pressed into a 19 mm round piece with a punching machine and assembled into a CR2032 button battery (the positive electrode selects LiCoO2, the negative electrode is a lithium sheet, and the electrolyte is a ternary carbonate solution of 1M LiPF6). The LAND system is used to test the constant current charge and discharge cycle and rate performance of the lithium battery; it is assembled into a stainless steel sheet / separator / stainless steel sheet, and an electrochemical workstation of model Parstat 2273 is used to perform EIS impedance test to calculate the ionic conductivity of the separator. The experimental results show that after 50 charge and discharge cycles of the battery assembled with the PMIA separator, the capacity retention rate is 75%, the interfacial impedance is 123 Ω, and the bulk impedance is 3.23 Ω.

[0025] MIL-101(Cr) involved in the present invention is a well-known material, and the preparation method is as follows, but it is not limited to this:

[0026] Cr(NO3)3·9H2O (2.00 g, 5 mmol), terephthalic acid (0.83 g, 5 mmol) and deionized water (20.0 mL) are mixed and ultrasonicated for 15 - 30 minutes to obtain a dark blue suspension with a pH of 2.58. The suspension is placed in a high-pressure autoclave with a polytetrafluoroethylene lining and placed in an oven at 200 °C for 18 - 24 hours. After synthesis, a centrifuge (10 - 30 minutes) separates the MIL-101 solid from water, and it is washed with water, methanol and acetone. The acetone suspension is centrifuged. The obtained solid is centrifuged and then dried in a vacuum environment at 75 °C for 2 days.

[0027] Example 1

[0028] Weigh 1.875 g of MIL-101(Cr) and add it to 5 ml of N,N-dimethylacetamide (DMAC), stir for 4 h until uniform, and then ultrasonicate for 0.5 h to obtain a MIL-101(Cr) suspension.

[0029] Example 2

[0030] By the non-solvent phase inversion method, the MIL-101(Cr) suspension prepared in Example 1 was mechanically stirred with the casting solution PMIA (the mass ratio of MIL-101(Cr) to PMIA was 1:10) for 4 h, and then it was blade-coated on a glass plate. The thickness of the blade was set to 30 μm. After blade-coating, it was left standing for 4 h and dried in a vacuum oven at 80 °C for 12 h to obtain a PMIA / MIL-101 composite membrane.

[0031] The diaphragm was subjected to heat treatment experiments at different temperatures. The diaphragm was heated in an oven at 50 °C, 100 °C, 150 °C, 200 °C, 250 °C, and 300 °C for 0.5 h respectively. The results showed that the composite membrane could maintain dimensional integrity at 300 °C, as Figure 2 shown. It indicates that the composite membrane has better thermal stability than polyolefins and can improve the safety of the battery.

[0032] Example 3

[0033] The lithium-ion battery was assembled in an argon glove box and assembled into a CR2032 type in the order of positive electrode case - LiCoO2 positive electrode sheet - membrane - lithium sheet - electrolyte - negative electrode case. The electrolyte was a ternary carbonate (ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate = 1:1:1) solution of 1 M LiPF6. The assembled battery was subjected to constant current charge and discharge tests on a LAND system. The test voltage range was 2.5 - 4.2 V. After cycling 50 times at 0.2 C, the capacity retention rate was 84.3%. The performance was superior to that of the same type of battery assembled with PMIA membrane, as Figure 3 shown.

[0034] Example 4

[0035] The lithium-ion battery was assembled in an argon glove box in the order of positive electrode case - lithium sheet - membrane - lithium sheet - electrolyte - negative electrode case. The assembled battery was tested by the AC impedance method on an electrochemical workstation. The test frequencies and amplitudes were 0.01 Hz - 10 5 Hz and 5 mV respectively.

[0036] The results showed that the interfacial impedance of the lithium-ion battery assembled with the PMIA / MIL-101 composite membrane was 78 Ω, as Figure 4 shown.

[0037] Example 5

[0038] The lithium-ion battery was assembled in an argon glove box in the order of positive electrode case - stainless steel sheet - membrane - stainless steel sheet - electrolyte - negative electrode case. The assembled battery was tested by the AC impedance method on an electrochemical workstation. The test frequencies and amplitudes were 0.01 Hz - 10 5 Hz and 5 mV respectively.

[0039] The results show that the bulk impedance of the PMIA / MIL-101 composite porous membrane is 1.87 Ω, as Figure 5 shown.

[0040] Example 6

[0041] Other steps are the same as those in Example 1, except that the stirring time of the MIL-101(Cr) and DMAC mixed solution is changed from 4 h to 0.5 h.

[0042] Example 7

[0043] Other steps are the same as those in Example 1, except that the dosage of DMAC is changed from 5 ml to 3 ml.

[0044] It can be seen from the above examples that the present invention selects the high heat-resistant material PMIA (with a thermal decomposition temperature of 400 °C, excellent self-extinguishing property and chemical corrosion resistance) as a replacement material for commercial polyolefin diaphragms, and makes up for the instability of the electrospinning process by forming through the non-solvent phase inversion method. MIL-101(Cr) is stable under the treatment of common organic solvents and inorganic acid aqueous solutions, and its crystal structure will not be damaged even when heated to 300 °C. Therefore, in the new energy field, the combination of PMIA and MIL-101(Cr) can make up for the shortcomings of polyolefin materials, achieving the effect of doubling both safety and electrochemical performance, and having an ideal research prospect.

[0045] The above examples are only for explaining the technical concept and characteristics of the present invention, and their purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and shall not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention shall be covered within the protection scope of the present invention.

[0046] Matters not covered in the present invention are well-known technologies.

Claims

1. A method for blending MIL-101(Cr) with meta-aramid for lithium-ion battery separator, characterized in that the method comprises the following steps: (1) Add MIL-101(Cr) to DMAC and stir at room temperature for 0.5 - 4 h to obtain a MIL-101(Cr) solution; Among them, The mass ratio of MIL-101(Cr) to DMAC is 1:1 - 3; (2) Stir the MIL-101(Cr) solution and the PMIA solution at room temperature for 3 - 5 h, then prepare a PMIA / MIL-101 composite separator, and then dry it in vacuum for 12 - 18 h to obtain the PMIA / MIL-101 composite separator; Among them, the mass ratio of MIL-101(Cr) to PMIA is 1:10 - 20.

2. The method for preparing the MIL-101(Cr) blended meta-aramid lithium-ion battery separator according to claim 1, characterized in that The vacuum drying temperature in step (2) is 75 - 85 °C.

3. The application of the MIL-101(Cr) blended meta-aramid lithium-ion battery separator prepared by the method according to claim 1, characterized in that it is used for lithium-ion batteries.

4. The application according to claim 3, characterized in that the positive electrode material of the lithium-ion battery is one or more of LiCoO2, LiFePO4, LiMn2O4, the negative electrode material is one or more of lithium flakes, graphite, and lithium titanate, and the solute of the electrolyte is one or more of lithium salts such as LiPF6, LiClO4, and LiAsF6, and the solvent is one or more of EC, PC, DMC, and DEC.

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