A method of crosslinking a uiO-66-nh2 bacterial cellulose lithium ion battery separator

Abstract

The application is a method for preparing a UIO-66-NH2 cross-linked bacterial cellulose lithium ion battery diaphragm. The method comprises the following steps: stirring a bacterial cellulose solution with epichlorohydrin at 60-80 DEG C for 3-5 h, then adding a UIO-66-NH2 solution, continuing to stir for 3-5 h, and then vacuum drying at 80 DEG C for 12-18 h to obtain a BC / UIO-66-NH2 composite diaphragm. The uniform and porous BC / UIO-66-NH2 composite diaphragm obtained by the method has both thermal stability and good wettability to electrolyte due to the combination of the two materials, and the use of the composite porous diaphragm as a lithium ion battery diaphragm improves the electrochemical performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the material of lithium ion battery separator, belongs to the technical field of polymer material preparation;The present application simultaneously relates to the research of the electrochemical performance of the battery in the lithium ion battery of the separator material, belongs to the technical field of electrochemical detection. BACKGROUND

[0002] Lithium ion battery has the advantages of high energy density, long life, good safety, etc., and is widely used in vehicles, aerospace, artificial satellites, digital products and large-scale energy storage devices. As one of the core materials of lithium ion battery, the separator is located between the positive and negative electrodes, which can not only avoid the short circuit of the two electrodes due to contact, but also can transport lithium ions to ensure the safety of lithium ion battery. The separator is a kind of microporous membrane, from the safety and high performance, it not only has excellent thermal stability, chemical stability, high ionic conductivity and mechanical properties, but also has appropriate pore size and porosity, and does not react with electrode material and electrolyte.

[0003] Bacterial cellulose (BC) is a porous network nanoscale biopolymer synthesized by microbial fermentation, named bacterial cellulose because it is synthesized by bacteria. It is composed of unique filamentous fibers with diameters between 0.01 and 0.10 μm, which are 2-3 orders of magnitude smaller than plant cellulose (10 μm). Each filamentous fiber is composed of a certain number of ultra-fine fibers in a network structure, and the main difference from plant cellulose is that it does not contain hemicellulose, lignin, etc. Hu and Kan (A flame-retardant, high ionic-conductivity and eco-friendly separator prepared by papermaking method for high-performance and superior safety lithium-ion batteries [J]. Energy Storage Materials, 2022, 48: 123-132.) added attapulgite and ammonium polyphosphate (APP) with flame retardant properties to bacterial cellulose, and designed a low-cost, high-performance and environmentally friendly bacterial cellulose-attapulgite composite separator (BA@ATP) using traditional papermaking process. Sun and Zhang (Safety and cycling stability enhancement of cellulose paper-based lithium-ion battery separator by aramid nanofibers [J]. 2022: 171: 111222.) combined cellulose nanofiber and aramid nanofiber with high thermal stability to prepare CFs / ANF composite separator using papermaking process; but due to the existence of a large number of hydrogen bonds in bacterial cellulose, this material has the limitations of uneven pore size distribution after film formation and long degradation period. SUMMARY

[0004] The application aims at the problems of poor electrolyte wettability of the current polyolefin separator, serious size shrinkage at high temperature, low lithium ion migration number, and influence on the safety and performance of LIBs, and develops a preparation method of a BC and UIO-66-NH2 composite separator. The method crosslinks bacterial cellulose and UIO-66-NH2 through epoxy chloropropane, introduces UIO-66-NH2 while destroying the hydrogen bond of bacterial cellulose, so that the pore size of the separator is uniform, and the -NH2 in UIO-66-NH2 provides a nitrogen source for microorganisms in the degradation process of the separator, and accelerates the degradation of the separator. The uniform and porous BC / UIO-66-NH2 composite separator obtained by the method has both thermal stability and good wettability to electrolyte, and the composite porous membrane is used as a lithium ion battery separator, and the electrochemical performance of the battery is improved.

[0005] The application is implemented by the following technical solutions:

[0006] A method for preparing a UIO-66-NH2 crosslinked bacterial cellulose lithium ion battery separator, which comprises the following steps:

[0007] (1) UIO-66-NH2 is added to H2O, stirred, and then ultrasonically treated at room temperature for 0.5-4h to obtain a UIO-66-NH2 solution;

[0008] The mass ratio of UIO-66-NH2:H2O is 1:50-100.

[0009] (2) The bacterial cellulose solution is stirred with epoxy chloropropane at 60-80℃ for 3-5h, then the UIO-66-NH2 solution is added, and the stirring is continued for 3-5h, and then the BC / UIO-66-NH2 composite separator is obtained by drying at 80℃ under vacuum for 12-18h.

[0010] The mass ratio of UIO-66-NH2:bacterial cellulose is 1:2-5, and 40-60ml of the bacterial cellulose solution is added per 5ml of epoxy chloropropane.

[0011] The mass percentage concentration of the bacterial cellulose solution is 0.1-0.5%.

[0012] The application of the battery separator prepared by the method is used in a lithium ion battery.

[0013] 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 sheet, graphite and lithium titanate, the solute of the electrolyte is one or more of LiPF6, LiClO4 and LiAsF6 lithium salt, and the solvent is one or more of EC, PC, DMC and DEC mixed solvents.

[0014] The present application has the following advantages:

[0015] (1) The UIO-66-NH2:BC composite separator prepared by the method of the present application has simple process and is degradable, thereby greatly reducing the harm to the environment

[0016] (2) The addition of UIO-66-NH2 improves the wettability of the battery separator, and compared with the commercial PP film, the number of lithium ion migration is increased from 0.45 to 0.62, thereby improving the electrochemical performance of the lithium ion battery (after 50 cycles at 0.2C, the discharge specific capacity is increased from 118.5 mAh / g to 150.2 mAh / g). BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 SEM images of the BC separator and the BC / UIO-66-NH2 composite separator prepared in Example 2;

[0018] Figure 2 Cycle performance test chart of the lithium ion battery assembled by the BC separator and the BC / UIO-66-NH2 composite separator prepared in Example 3.

[0019] Figure 3 Interface impedance spectrum chart of the lithium ion battery assembled by the BC separator and the BC / UIO-66-NH2 composite separator prepared in Example 4, respectively;

[0020] Figure 4 Bulk impedance spectrum chart of the lithium ion battery assembled by the BC separator and the BC / UIO-66-NH2 composite separator prepared in Example 5, respectively. DETAILED DESCRIPTION

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

[0022] The BC (bacterial cellulose) film used in the following Comparative Example 1 is a known material, which is a porous film with a thickness of 15-20 μm, a liquid absorption rate of 185%, and a porosity of 56%. The preparation thereof adopts a vacuum suction filtration method, wherein the uniformly dispersed BC solution is poured into a sand core funnel and subjected to vacuum suction filtration. However, the present application is not limited thereto.

[0023] Comparative Example 1

[0024] The BC separator was dried and then pressed into 19 mm round sheets using a puncher, assembled into CR2032 button cells (positive electrode selected LiCoO2, negative electrode lithium sheet, electrolyte 1M LiPF6 ternary carbonate solution), and the constant current charge-discharge cycle and rate performance of the lithium battery were tested using a LAND system; assembled into stainless steel sheet / separator / stainless steel sheet, and the electrochemical workstation with model Parstat2273 was used for EIS impedance test to calculate the ionic conductivity of the separator. The experimental results show that the capacity retention rate of the battery assembled by the PMIA separator is 89% after 50 cycles of charge-discharge cycle, the interface impedance is 125Ω, and the bulk impedance is 2.4Ω.

[0025] The UIO-66-NH2 involved in the present application is a known material, and the preparation method is as follows, but is not limited thereto:

[0026] ZrCl4(1.170g), diaminoterephthalic acid (1.27g), DMF (60.0ml) and HCl (10ml) were mixed and ultrasonicated for 15-30 minutes. The suspension was placed in a polytetrafluoroethylene-lined autoclave in an oven at 120°C for 18-24 hours. After synthesis, the UIO-66-NH2 solid was separated from water by centrifuge (10-30 minutes) and washed with water, methanol and acetone. The acetone suspension was separated by centrifugation. The obtained solid was separated by centrifugation and then dried in a vacuum environment at 75 degrees Celsius for 2 days.

[0027] Example 1

[0028] UIO-66-NH2 0.05 g was weighed into 5ml of H2O, stirred for 4h until uniform, and then ultrasonicated for 0.5h to obtain a UIO-66-NH2 suspension.

[0029] Example 2

[0030] First, 50ml of bacterial cellulose solution was stirred with 5ml of epichlorohydrin at 70°C for 3h, then the UIO-66-NH2 suspension prepared in Example 1 was mechanically stirred with the BC solution (mass fraction 0.2%) (i.e. the mass ratio of UIO-66-NH2 to BC was 1:2) for 4h, then it was poured into a sand core funnel, and a UIO-66-NH2 / BC composite separator was obtained by vacuum filtration, then it was placed for 0.5h, and dried in a vacuum oven at 80°C for 12h to obtain a BC / UIO-66-NH2 composite membrane.

[0031] Figure 1For scanning electron microscope graph, in the figure, a is the surface morphology of BC membrane, b is the surface morphology of BC / UIO-66-NH2 composite diaphragm, c is the cross-section morphology of BC membrane, d is the cross-section morphology of BC / UIO-66-NH2 composite diaphragm; through the figure, we can see that UIO-66-NH2 is uniformly crosslinked on the bacterial cellulose, and the pore size of BC / UIO-66-NH2 composite diaphragm is more uniform, which shows that UIO-66-NH2 plays a role in destroying hydrogen bond and adjusting pore size on the bacterial cellulose diaphragm.

[0032] Example 3

[0033] The lithium ion battery was assembled in an argon glove box, and was assembled into CR2032 type in the order of positive shell-LiCoO2 positive plate-membrane-lithium sheet-electrolyte-negative shell. The electrolyte was selected as 1M LiPF6 ternary carbonate (ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate = 1:1:1) solution. The assembled battery was tested by constant current charge and discharge in a LAND system, and the voltage range was 2.5-4.2V. After 50 cycles at 0.2C, the capacity retention rate was 95%, and the performance was better than that of the same type of battery assembled by BC membrane, as shown in Figure 2 .

[0034] Example 4

[0035] The lithium ion battery was assembled in an argon glove box in the order of positive shell-lithium sheet-membrane-lithium sheet-electrolyte (same composition as example 3)-negative shell. The assembled battery was tested by alternating current impedance method on an electrochemical workstation, and the frequency and amplitude were 0.01Hz-10 5 Hz and 5mV, respectively.

[0036] The results are shown in Figure 3 , and the interfacial impedance of the lithium ion battery assembled by BC / UIO-66-NH2 composite membrane is 61Ω, indicating that the lithium ion between the diaphragm and the lithium sheet is more easily passed.

[0037] Example 5

[0038] The lithium ion battery was assembled in an argon glove box in the order of positive shell-stainless steel sheet-membrane-stainless steel sheet-electrolyte (same composition as example 3)-negative shell. The assembled battery was tested by alternating current impedance method on an electrochemical workstation, and the frequency and amplitude were 0.01Hz-10 5 Hz and 5mV, respectively.

[0039] The results are shown in Figure 4 , and the bulk impedance of BC / UIO-66-NH2 composite porous membrane is 1.85Ω, indicating that the impedance of the diaphragm itself is small, and the loss is small when the battery is powered on.

[0040] Example 6

[0041] Other steps are the same as example 1, except that the UIO-66-NH2 and H2O mixed solution is replaced by stirring 0.5h instead of stirring 4h.

[0042] Example 7

[0043] Other steps are the same as example 1, except that the amount of H2O is replaced by 5ml instead of 3ml.

[0044] Example 8

[0045] Other steps are the same as example 2, except that the amount of epichlorohydrin is replaced by 5ml instead of 6ml.

[0046] As can be seen from the above examples, the application selects BC (with excellent electrolyte wettability) as a commercial polyolefin separator replacement material, and compensates for the instability of the electrospinning process by vacuum suction filtration. UIO-66-NH2 is stable under the treatment of ordinary organic solvents and aqueous inorganic acid solutions, and the crystal structure will not be destroyed when heated to 300℃. Therefore, in the field of new energy, the combination of BC and UIO-66-NH2 can make up for the shortcomings of polyolefin materials, achieve the effect of double increase of safety and electrochemical performance, and has a relatively ideal research prospect.

[0047] The above examples are only for illustrating the technical concept and characteristics of the application, and the purpose is to enable those skilled in the art to understand the content of the application and implement it, and cannot limit the protection scope of the application. Any equivalent changes or modifications made according to the spirit and essence of the application should be covered within the protection scope of the application.

[0048] The unfinished matters of the application are the known technology.

Claims

1. A method for preparing a UIO-66-NH2 cross-linked bacterial cellulose lithium ion battery separator, characterized in that the method comprises the following steps: (1) UIO-66-NH2 is added to H2O, stirred, and then ultrasonicated at room temperature for 0.5-4 h to obtain a UIO-66-NH2 solution; wherein mass ratio, UIO-66-NH2: H2O = 1: 50-100; (2) the bacterial cellulose solution is stirred with epichlorohydrin at 60-80℃ for 3-5 h, then the UIO-66-NH2 solution is added, and stirring is continued for 3-5 h, and then the mixture is dried at 80℃ under vacuum for 12-18 h to obtain a BC / UIO-66-NH2 composite separator; wherein the mass ratio of UIO-66-NH2 to bacterial cellulose is 1:2-5, and 40-60 ml of the bacterial cellulose solution is added per 5 ml of epichlorohydrin.

2. The method for preparing a UIO-66-NH2 cross-linked bacterial cellulose lithium ion battery separator according to claim 1, characterized in that the mass percentage concentration of the bacterial cellulose solution is 0.1-0.5%.

3. The application of the battery separator prepared by the method according to claim 1, characterized in that the battery separator is used in a lithium ion battery.

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 and LiMn2O4, the negative electrode material is one or more of lithium sheet, graphite and lithium titanate, the solute of the electrolyte is one or more of LiPF6, LiClO4 and LiAsF6 lithium salt, and the solvent is one or more of EC, PC, DMC and DEC.

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