A method for preparing a modified dual-ion battery

Abstract

The present invention relates to a method for preparing a modified dual-ion battery, which belongs to the technical field of dual-ion battery preparation. In an ultrasonic environment, superhard nanodiamonds are used to peel off the graphite layer and form a few-layer curled graphene, which serves as the positive or negative electrode of the dual-ion battery to improve the storage capacity of anions and cations. Surface-fluorinated nanodiamonds are used as electrolyte additives to form a uniform and dense solid electrolyte interface on the surface of the graphite electrode, thereby improving the long-cycle stability and ion transmission efficiency of the battery. Nanodiamonds are simultaneously applied to the modification of dual-ion battery electrodes and electrolytes, and the capacity and long-cycle performance of the assembled dual-carbon full battery are significantly improved. The dual-ion battery of the present invention utilizes the modification of the component structure by diamond and the strong adsorption of anions and cations to improve the capacity of the dual-ion battery, and has good cost-effectiveness and industrial prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of dual-ion battery preparation, and relates to a nanodiamond (NDs)-assisted preparation of a curled graphene electrode and an electrolyte, which improves the capacity, long-cycle stability and rate performance of DIBs. Background Art

[0002] Dual-ion batteries (DIBs) are a new type of energy storage system. They use electrolytes as active materials to provide anions and cations, carbonaceous materials as positive electrode materials, and conventional carbonaceous negative electrodes used in lithium-ion batteries as negative electrode materials. Compared with traditional lithium-ion batteries, DIBs have many advantages, such as higher energy density, long cycle stability, fast charging speed, lower cost, and environmental friendliness. However, at a high working potential voltage close to 5.0V, the DIBs positive electrode undergoes long-term high-rate redox reactions of anion insertion / deinsertion, which can cause serious side reactions such as irreversible decomposition of the electrolyte, electrode structure shedding, and low Coulombic efficiency, which directly reduce the performance and service life of the battery. To overcome these problems, the configuration of DIBs needs to be further optimized.

[0003] Research on DIBs negative electrode materials mainly focuses on new materials and structural design modification technologies to improve the capacity, safety and reaction kinetics of DIBs. The positive electrode material and electrolyte are more critical factors in determining the performance of DIBs. The most commonly used positive electrode material for DIBs is graphite. However, when large-sized anions are embedded in the graphite positive electrode, some inevitable structural collapse and capacity loss will occur. In addition, the graphite positive electrode is not very resistant to anions (PF6 - )’s actual capacity is only ~100mAh g -1 . Therefore, structural modification of traditional graphite electrodes and increasing their interlayer spacing to provide more channels and binding sites for the transport and storage of anions are effective means of modifying graphite-based positive electrodes. In addition, modification of electrolyte composition can optimize the internal reactions of the battery, such as the oxidation / reduction of anions and cations, the formation and stability of the solid electrolyte interface (SEI) on the cathode or anode surface, and the solvation / desolvation ability of electrolyte ions. At present, many electrolyte optimization strategies have been proposed to achieve high performance of DIBs, including the regulation of electrolyte concentration and the use of additives, but the current cost of electrolyte modification is quite high. Implementing cost-effective optimization strategies related to electrode structure and electrolyte modification is crucial to improving the overall performance of DIBs.

[0004] This patent design synthesizes a nanodiamond (ND) modified curly graphene (DCG) as a dual carbon electrode for DIBs, and introduces fluorinated NDs (FNDs) into the electrolyte to achieve efficient storage and transport of large-sized anions. Based on these strategies, the performance of the battery is significantly improved. The DCG electrode modification and FND electrolyte modification strategy provides a method for designing DIB all-carbon electrode battery systems. Summary of the Invention

[0005] This invention overcomes the shortcomings of prior art by using ultrasonic treatment to mechanically exfoliate graphite with NDs and form curly graphene, providing more active sites for the binding of anions and cations. Modification of the electrolyte with FNDs enhances the electrode structure stability and anion-cation redox reversibility during cycling. This invention provides a component modification and preparation method for a dual-ion battery with high capacity, high rate performance, and long-cycle stability.

[0006] The main contents of the present invention include: (1) proposing to ultrasonically treat commercial graphite with ND ultra-dispersed colloidal solution, realizing the exfoliation and curling of graphite layers by controlling the ultrasonic power and time, and using the ND-modified curled graphite as the positive and negative electrodes of a dual-ion battery, thereby achieving a significant increase in the capacity of a dual-graphite-based dual-ion battery; (2) proposing a new method of introducing FNDs to modify the electrolyte of a dual-ion battery, obtaining an ND-stabilized electrode structure, and improving the battery cycle stability.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for preparing a modified dual-ion battery comprises the following steps:

[0009] 1) annealing ND powder at 300-500°C in air for 2 hours to remove non-diamond phases on the ND surface; then heating the purified ND to 500°C in a vacuum tube furnace under a 50 sccm atmosphere of hydrogen purified to 99.99% and naturally cooling to room temperature to obtain surface H-terminated ND (i.e., surface-modified hydrogen nanodiamonds), denoted as HND;

[0010] 2) Disperse HND powder in ethanol by adding 0.001-0.01 g HND per 50 mL of ethanol, sonicate for 4 h, and centrifuge at 5000-10000 rpm for 5 min. Collect the supernatant to obtain an ultra-dispersed ND colloidal solution.

[0011] 3) The ultra-dispersed ND colloidal solution was mixed with commercial graphite powder, ultrasonicated for 5-15 hours, and dried in a forced air drying oven at 60°C to obtain ND-modified curly graphene, denoted as DCG;

[0012] 4) Immerse the ND powder in a perfluoroiodobutane solution and fluorinate under a xenon lamp for 4-12 hours. Wash by centrifugation until the solution is transparent. Dry the solution to obtain a surface-fluorinated ND sample, designated as FND.

[0013] 5) LiPF6 was dissolved in ethyl methyl carbonate (EMC) to obtain a 3M solution, and 1% tris(trimethylsilyl) phosphate (TMSP) was added to the solution to obtain a base electrolyte; FND powder was placed in the base electrolyte and ultrasonicated under vacuum for 30 minutes to obtain a uniformly dispersed FND electrolyte;

[0014] 6) Assembling a dual-ion half-cell or a dual-carbon-dual-ion full battery, wherein the assembled dual-ion half-cell refers to assembling a button half-cell in an Ar-protected glove box using the DCG as the positive electrode or negative electrode, lithium as the counter electrode, FND electrolyte, and a commercial glass fiber separator; the assembled dual-carbon-dual-ion full battery refers to assembling a button full cell in an Ar-protected glove box using the DCG as the positive and negative electrodes, FND electrolyte, and a commercial glass fiber separator.

[0015] The ND powders described in step 1) and step 4) can be selected from nanodiamonds produced by pulverization method or nanodiamonds produced by detonation method, and the particle size is preferably 3-20 nm.

[0016] The ultrasonic power in step 3) is preferably 200-400 W, and the ultrasonic time is preferably 10 h.

[0017] The fluorination time in step 4) is preferably 7 h.

[0018] Beneficial effects of the present invention:

[0019] The dual-ion battery prepared by the present invention, which is assembled with ND-modified curled graphene electrodes and FND electrolyte, has good electrochemical performance. -1 At a current density of 1.5 GHz, after 200 cycles, the specific capacity of the half-cell assembled with DCG as the positive and negative electrodes was 150 mAh g -1 and 1100mA hg -1 , which is significantly higher than the actual capacity of conventional graphite positive and negative electrodes. The DCG / / DCG full battery assembled with FND electrolyte has a high capacity of 1Ag -1 After more than 2000 cycles at high rates, it still maintains a current of more than 140 mA hg -1 The capacity is 1.5 times that of conventional dual-graphite electrode DIBs. The DCG electrode modification and electrolyte engineering proposed in this paper provide guidance for further design of all-carbon electrode DIBs battery systems with compatible high performance and cost-effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope (SEM) image of the original graphite in Example 1;

[0021] Figure 2 This is a scanning electron microscope image of the DCG sample prepared in Example 1;

[0022] Figure 3 Transmission electron microscopy (TEM) image of the DCG sample prepared in Example 1;

[0023] Figure 4 XRD and Raman patterns of DCG and pristine graphite prepared in Example 1;

[0024] Figure 5 The batteries S1 and S2 prepared in Example 3 were -1 The charge-discharge cycle capacity curve at low current density;

[0025] Figure 6 The batteries S1 and S2 prepared in Example 3 were -1 The charge-discharge cycle capacity curve at high current density;

[0026] Figure 7 The batteries S3 and S4 prepared in Example 3 were -1 Charge and discharge capacity curves under current density;

[0027] Figure 8 The batteries S3 and S4 prepared in Example 3 were -1 The charge and discharge capacity curve at high current density;

[0028] Figure 9 Batteries S3, S4, and S5 prepared in Example 3 were tested at 50, 100, 200, 500, 1000, and 2000 mA g -1 The charge and discharge capacity curves under variable current density;

[0029] Figure 10 The battery S5 prepared in Example 3 was -1 and 1A g -1 Charge and discharge capacity curves at current density of ;

[0030] Figure 11 The full cells S6 and S7 prepared in Example 4 were -1 Charge and discharge capacity curves at current density of ; DETAILED DESCRIPTION

[0031] The present application is further described in detail below in conjunction with the accompanying drawings and examples. It should be noted that the examples described below are intended to facilitate understanding of the present application and do not have any limiting effect on it.

[0032] Example 1 Preparation of Nanodiamond Modified Curled Graphene

[0033] Commercial NDs were annealed at 425°C in air for 2 h to remove the non-diamond phase on the ND surface. The purified NDs were placed in a vacuum tube furnace and heated to 500-700°C in a 50 sccm hydrogen atmosphere and naturally cooled to room temperature to obtain surface H-terminated NDs (HNDs).

[0034] 0.01 g of HND powder was dispersed in 50 mL of ethanol solution, sonicated for 4 h, and centrifuged for 5 min to obtain the supernatant to obtain an ultra-dispersed ND colloidal solution;

[0035] 50 ml of ultra-dispersed ND was mixed with 0.5 g of commercial graphite powder, ultrasonically treated at 300 W power for 10 h, and then dried in a forced air drying oven at 60°C to obtain ND-modified curly graphene (DCG), which was recorded as sample 1#, and the original graphite was recorded as comparison sample 1#.

[0036] The SEM images of sample 1# and comparison sample 1# are shown in Figure 2 and Figure 1 ; Transmission electron microscope (TEM) image of sample 1# is shown in Figure 3 ; XRD and Raman spectra of sample 1# and comparative sample 1# are shown in Figure 4 .

[0037] Depend on Figure 1 The scanning electron microscope image shows that the original graphite of the comparative sample 1# presents a typical block structure. After ultrasonic treatment in the ND colloidal solution, the sample 1# ( Figure 2 The main manifestation is the exfoliation of the graphite surface under the impact of ND. With extended treatment time, the exfoliated graphite flakes further curl, ultimately producing few-layer graphene with branch-like and tubular structures. Transmission electron microscopy of sample 1 further demonstrated that the ND nanoparticles were evenly distributed between the graphene layers.

[0038] XRD and Raman spectroscopy were used to characterize sample 1#DCG and comparative sample 1#graphite. Figure 4 ). In the XRD spectrum, the strongest diffraction peak (002) of sample 1#DCG has a red shift compared to the original graphite, and the other weaker diffraction peaks have a blue shift, indicating that the lattice expansion of DCG occurs along the (0001) orientation of bulk graphite. In the Raman spectrum, the G and 2D peaks of sample 1# have a large red shift compared to the original graphite, confirming the formation of few-layer graphene. In addition, at ~1620cm -1A new D' peak appears at the center, which corresponds to the disordered vibration peak and defects in DCG. The 2D and G peak intensity ratio of DCG and graphite (I 2D / I G ) are 0.530 and 0.285, respectively, indicating that the number of DCG layers is reduced compared to the initial graphite, which is consistent with the observations of TEM and XRD. Under ultrasonic treatment, the impact of ND on the initial graphite can change the nanostructure of the graphite electrode.

[0039] Example 2: Preparation of fluorinated ND modified electrolyte

[0040] ND powder was immersed in perfluoroiodobutane solution and fluorinated under a xenon lamp for 7 hours. After fluorination, the solution was repeatedly centrifuged and washed until the color of the solution was completely transparent. After drying, a surface fluorinated ND (FND) sample was obtained.

[0041] LiPF6 was dissolved in ethyl methyl carbonate (EMC; ≥99.9%, Aladdin) to prepare a 3M solution, and 1% of the solution volume of TMSP (≥99.9%, DoDoChem) was added as the base electrolyte, which was recorded as comparative sample 2#;

[0042] 0.001 g of FND powder was placed in 5 ml of the basic electrolyte and ultrasonically treated for 30 min to obtain a uniformly dispersed FND electrolyte, which was recorded as sample 2#.

[0043] Example 3: Fabrication and performance testing of dual-ion half-cells

[0044] The positive or negative electrode of the lithium-ion battery is composed of a mixture of 80wt% graphite or DCG material (active material), 10wt% binder (polyvinylidene fluoride, PVDF) and 10wt% carbon black as a conductive agent. The three are mixed and ground for 0.5h and then placed in a container. A certain amount of 1-methyl-2-pyrrolidone (NMP, solvent) is added to the container and then placed on a magnetic stirrer and stirred at a constant speed for 6h until the mixture becomes a viscous fluid. Copper foil or aluminum foil is used as the current collector, and the above-mentioned mixed viscous material is applied on it. The coating density must be uniform, and they are used as negative and positive electrode sheets respectively. The temperature of the vacuum drying oven is set at 110℃, and the above-mentioned copper foil coating is placed in the drying oven. After 12h, it is taken out for use. The prepared copper foil or aluminum foil coating is cut into several electrode discs using a special cutting die, and then the active material on the electrode sheet is compacted with a tablet press to ensure full contact with the current collector to prevent material peeling. Weigh the mass of the electrode sheet for calculation of specific capacity parameters, etc.

[0045] The lithium-ion battery assembled during the test was a CR-2025 button cell. The prepared nanocomposite electrode and the supporting battery positive and negative electrode shells, gaskets, shrapnel, diaphragm, and basic electrolyte or FND electrolyte, electrode sheet, lithium sheet counter electrode, etc. were operated according to the manufacturing regulations of the lithium-ion battery, and operated safely and orderly in a glove box filled with argon. The battery was packaged and then its performance was tested. The electrode sheet mass was weighed before assembly to prepare for the calculation of subsequent specific capacity parameters, etc. The batteries prepared with comparative sample 2# electrolyte, sample 1# or comparative sample 1# as the battery negative electrode material were marked as S1 and S2 respectively, the batteries prepared with comparative sample 2# electrolyte, sample 1# or comparative sample 1# as the battery positive electrode material were marked as S3 and S4 respectively, and the batteries prepared with sample 2# electrolyte and sample 1# as the battery positive electrode material were marked as S5 respectively.

[0046] 1) Negative electrode electrochemical performance test and structural characterization

[0047] The batteries S1 and S2 prepared in Example 3 were tested in a blue-electric test system. They were discharged to 0.01V at a certain current density. After the discharge, the batteries were left to stand for 3 minutes. Then, they were charged to 3V at a certain rate. After the charge, the batteries were left to stand for 3 minutes and then discharged to 0.01V at the same constant rate. After the discharge, the batteries were left to stand for 3 minutes and then charged under the same conditions. Figure 5 , 6, at 0.1A g -1 Low current and 1A -1 At a high current density of 1121 mA hg after 200 cycles, the DCG negative electrode has a high current density of 1121 mA hg -1 and 958mA hg -1 The reversible capacity of the conventional graphite anode is only 420 mA hg -1 and 345mA hg -1 capacity.

[0048] 2) Positive electrode electrochemical performance test and structural characterization

[0049] The batteries S3, S4 and S5 prepared in Example 3 were tested in a blue electric test system, and were repeatedly charged and discharged at a certain current density between 3-5V. Figure 7 As shown, battery S3 is at 0.1A g -1 After 200 cycles, the current density of 149mA hg -1 The reversible capacity is 1.4 times that of the battery S4 under the same test conditions (106mAh g -1 ). In 1Ag -1 After 600 cycles at a high current density ( Figure 8 ), battery S3 still has a reversible capacity of 130 mAh g-1 In contrast, the capacity of the battery S4 drops to 90mAh g after 500 cycles. -1 , and the battery has a low coulombic efficiency (90%) during the overall cycle

[0050] The introduction of sample 2#FND electrolyte is beneficial to further improve the long-term cycle stability of DCG cathode, such as Figure 9 As shown, by comparing 50, 100, 200, 500, 1000, and 2000mA g -1 The capacities of batteries S3, S4, and S5 at the variable rate are shown in Table 1. It is found that battery S5 has 181, 174, 171, 168, and 164 mAh g -1 The capacity is significantly higher than that of battery S3 (157, 144, 139, 135, and 97 mAh g -1 ) and S4 (105, 102, 101, 99, 97, and 75mAh g -1 ) corresponding data. -1 and 1Ag -1 At a current density of ( Figure 10 ), battery S5 still maintains 176 and 146mA hg after 1000 cycles -1 The capacity of the double-ion battery is further improved on the basis of electrode S3. Therefore, the combination of sample 2#FND electrolyte and sample 1#DCG positive electrode can significantly improve the overall performance of the double-ion battery.

[0051] Example 4: Fabrication and performance testing of dual-ion full battery

[0052] The battery's positive and negative electrodes are composed of a mixture of 80wt% graphite or DCG material (active material), 10wt% binder (polyvinylidene fluoride, PVDF), and 10wt% carbon black as a conductive additive. The three components are ground together for 0.5 hours and then placed in a container. A certain amount of 1-methyl-2-pyrrolidone (NMP, solvent) is added to the container, and the mixture is stirred uniformly on a magnetic stirrer for 6 hours until it becomes a viscous fluid. Copper or aluminum foil is used as the current collector, and the viscous mixture is applied to it with a uniform coating density. These serve as the negative and positive electrode sheets, respectively. A vacuum drying oven is set to 110°C, and the copper foil smear is placed in the drying oven for 12 hours before removal. The prepared copper or aluminum foil smear is cut into several electrode discs using a special cutting die. A tablet press is then used to compact the active material on the electrode sheet, ensuring full contact with the current collector and preventing material loss. The electrode sheets are weighed for calculation of specific capacity parameters and other parameters.

[0053] The lithium-ion battery assembled during the test was a CR-2025 button cell. The prepared nanocomposite positive and negative electrodes were combined with the matching battery positive and negative electrode shells, gaskets, shrapnel, diaphragms, and basic electrolytes or FND electrolytes in accordance with the manufacturing regulations of lithium-ion batteries. The operation was carried out safely and orderly in an argon-filled glove box, the batteries were packaged, and then their performance was tested. The mass of the electrode sheets was weighed before assembly in preparation for the calculation of subsequent specific capacity parameters. The battery prepared with the comparison sample 2# basic electrolyte and the comparison sample 1# graphite as the positive and negative electrodes was marked as battery S6, and the battery prepared with the sample 2# FND electrolyte and the sample 1# DCG as the positive and negative electrodes was marked as S7.

[0054] The batteries S6 and S7 prepared in Example 4 were tested in an electrochemical test system, and were repeatedly charged and discharged at a certain current density between 3 and 5 V. Figure 11 As shown, at 0.1Ag -1 At a current density of 1.5 GHz, the capacity of battery S7 showed an upward trend in 1000 cycles, and the final capacity increased to 230 mA hg -1 , while in comparison, the capacity of the battery S6 decreases to 36mA hg -1 At 1A g -1 At a higher current density, the battery S7 has good long-cycle performance and still maintains 143mAh g after 3300 cycles. -1 The capacity of battery S6 is lower and short circuit occurs after 2000 cycles.

Claims

1. A method for preparing a modified dual-ion battery, comprising the following steps: 1) annealing the nanodiamond powder in air at 300-500° C. for 2 hours to remove the non-diamond phase on the nanodiamond surface; heating the purified nanodiamond to 500° C. in a vacuum tube furnace under a 50 sccm atmosphere of hydrogen purified to 99.99% and naturally cooling to room temperature to obtain surface H-terminated nanodiamonds, denoted as HND; 2) Dispersing HND powder in ethanol by adding 0.001-0.01 g HND per 50 mL of ethanol, sonicating for 4 hours, and then centrifuging at 5000-10000 rpm for 5 minutes to obtain the supernatant to obtain an ultra-dispersed nanodiamond colloidal solution; 3) Mixing the ultra-dispersed nanodiamond colloidal solution with commercial graphite powder, ultrasonicating for 5-15 hours, and drying in a forced air drying oven at 60°C to obtain ND-modified curly graphene, denoted as DCG; 4) immersing the nanodiamond powder in a perfluoroiodobutane solution, irradiating the solution under a xenon lamp for fluorination for 4-12 hours, washing the solution by centrifugation until the solution is transparent, and drying the solution to obtain a surface-fluorinated nanodiamond sample, which is designated as FND; 5) LiPF6 was dissolved in ethyl methyl carbonate to obtain a 3M solution, and tris(trimethylsilyl)phosphate was added at 1% by volume of the solution to obtain a base electrolyte; FND powder was placed in the base electrolyte and ultrasonicated under vacuum for 30 minutes to obtain a uniformly dispersed FND electrolyte; 6) Assembling a dual-ion half-cell or a dual-carbon-dual-ion full battery, wherein the assembled dual-ion half-cell refers to assembling a button half-cell in an Ar-protected glove box using the DCG as the positive electrode or negative electrode, lithium as the counter electrode, FND electrolyte, and a commercial glass fiber separator; the assembled dual-carbon-dual-ion full battery refers to assembling a button full cell in an Ar-protected glove box using the DCG as the positive and negative electrodes, FND electrolyte, and a commercial glass fiber separator.

2. The method for preparing a modified dual-ion battery according to claim 1, wherein: The nano-diamond powder in step 1) and step 4) is nano-diamond obtained by a pulverization method or a detonation method, and has a particle size of 3-20 nm.

3. The method for preparing a modified dual-ion battery according to claim 1, wherein: The ultrasonic power in step 3) is 200-400 W, and the ultrasonic time is 10 hours.

4. The method for preparing a modified dual-ion battery according to claim 1, wherein: The fluorination time in step 4) is 7 hours.

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