Mesoporous carbon paper-based flexible electrode material and preparation method and application thereof

Abstract

The invention discloses a mesopore-rich carbon paper-based flexible electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) carrying out fibrillation treatment on PAN fibers, and screening out the PAN fibers with 200 meshes or more; (2) mixing the PAN fibers obtained in the step (1) with CFs, making paper with pulp, drying, pre-oxidizing, carbonizing, and dipping in a CNTs dispersion liquid to obtain flexible carbon paper; the pre-oxidation is performed at the temperature of 100-400 DEG C, and heat preservation is performed for 0.5-3 (3) dipping the carbon paper obtained in the step (2) in a ZnCl2 solution, drying, and activating to obtain a mesopore-rich carbon paper-based flexible electrode material (ECNFP); the mass ratio of the carbon paper to the ZnCl2 is 1: (3-5). The ECNFP can be applied to the negative electrode of the lithium ion battery, and has the advantages of excellent flexibility, high specific capacity, cycle performance, rate performance and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of self-supporting flexible carbon paper electrode materials for lithium-ion batteries and new energy battery energy storage devices, and specifically to a mesoporous flexible carbon paper-based lithium-ion battery negative electrode material and a preparation method and application thereof. Background Art

[0002] Carbon paper with light weight, plasticity, high strength, high flexibility and high conductivity has been proven to be an excellent matrix for preparing flexible lithium-ion battery negative electrode materials. At present, flexible lithium-ion batteries often pursue high power density and energy density. The development of carbon paper-based flexible electrode materials with better performance is the prerequisite for the industrialization of carbon paper in the battery field. Constructing pores in carbon materials is a simple and effective method to obtain higher specific capacity and rate performance. The pores not only provide a good source of Li + The storage of Li provides abundant active sites and accelerates the + and electron transfer, making Li + Most researchers agree that the volume expansion caused by the embedding / extraction process in the carbon anode acts as an "ion buffer reservoir", effectively extending the service life of lithium-ion batteries. However, it is difficult for existing carbon paper to have both high flexibility and high conductivity. Summary of the invention

[0003] The object of the present invention is to provide a mesoporous carbon paper-based flexible electrode material and a preparation method and application thereof.

[0004] The present invention performs fibrillation and screening treatment on PAN (polyacrylonitrile) fibers through pulping equipment, and then prepares CFs (carbon fiber) mixed with PAN nano-scale fiber paper sheets through papermaking equipment fast Kaiser sheeter, and then pre-oxidizes and carbonizes them and impregnates them with CNTs (carbon nanotubes), and then activates them to obtain mesoporous-dominated carbon nanofiber paper (ECNFP).

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

[0006] A method for preparing a mesoporous carbon paper-based flexible carbon paper electrode material comprises the following steps:

[0007] (1) After PAN fibers are subjected to fibrillation treatment, PAN fibers with a mesh size of 200 or more are screened out;

[0008] (2) mixing the PAN fiber obtained in step (1) with CFs, forming paper, drying, pre-oxidizing and carbonizing, and then immersing in a CNTs dispersion to obtain a flexible carbon paper; the pre-oxidation is at 100 to 400° C. for 0.5 to 3 h; the carbonization temperature is 600 to 800° C. for 0.5 to 2 h;

[0009] (3) Immersing the carbon paper obtained in step (2) in a ZnCl2 solution, and activating it after drying, the activation temperature is 600-800°C, and the temperature is kept for 0.5-2h to obtain a mesoporous carbon paper-based flexible carbon paper electrode material; the mass ratio of the carbon paper to ZnCl2 is 1:(3-5).

[0010] Preferably, the mass ratio of the carbon paper to ZnCl2 in step (3) is: 1:(4±0.5).

[0011] Preferably, the concentration of the impregnated CNTs in step (2) is 0.01-0.1%.

[0012] Preferably, the amount of CFs added in step (2) accounts for (20±5) wt% of the total weight of the paper.

[0013] Preferably, the heating rate of the pre-oxidation in step (2) is 1 to 5°C / min; the heating rate of the carbonization is 1 to 10°C / min.

[0014] Preferably, the basis weight of the paper produced in step (2) is 40 to 100 g / m 2 .

[0015] Preferably, the activation heating rate in step (3) is 1 to 10° C. / min.

[0016] Preferably, the beating degree of the fibrillated PAN fibers in step (1) is (75±5) o SR.

[0017] The application of the mesoporous carbon paper-based flexible carbon paper electrode material prepared by the above method in the negative electrode of lithium ion batteries.

[0018] Compared with the prior art, the present invention has the following advantages and effects:

[0019] (1) Excellent flexibility and electrochemical performance: The carbon paper prepared by the present invention has a rich mesoporous structure and excellent flexible conductivity. It can still maintain its original shape after being bent, folded, and curled, and the highest conductivity is 4527S / m.

[0020] (2) The present invention uses cheap PAN fiber as raw material, obtains nano-scale PAN fiber through traditional pulping and papermaking methods, and then combines CFs and CNTs and undergoes low-temperature carbonization and activation to prepare a highly flexible special paper-based lithium-ion battery negative electrode material. The process is simple, the performance is excellent, and it is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 is the XRD diagram of ICNFP and ECNFP of the present invention.

[0022] Figure 2 The diagram is a preparation diagram of the ECNFP electrode material of the present invention and a lithium storage mechanism diagram.

[0023] Figure 3 The conductivity diagram of carbon paper with different weights after carbonization in Example 1.

[0024] Figure 4 The conductivity diagram of the ECNFP electrode prepared in Examples 1 to 5.

[0025] Figure 5 The test results of the ECNFP electrode material in Example 1 are shown in Figures 1 and 2, (a) and (b) are scanning electron microscopy (SEM) at different magnifications, (c) is transmission electron microscopy (TEM), (d) is HRTEM, (e) is SAED, (f) is the selected area of ​​Mapping, (g)-(j) are mapping diagrams and C, N, and O element distribution diagrams, respectively, and (k)-(m) are flexibility test diagrams in different bending states.

[0026] FIG. 6 is a graph showing the specific surface area (a) and pore size distribution (b) of the ECNFP electrode material in Example 1.

[0027] FIG. 7 is a graph showing the cycle performance of the ICNFP (a) and ECNFP (b) electrodes of the present invention.

[0028] FIG8 is a cycle performance diagram (a) and a rate performance test diagram (b) of the ECNFP flexible electrode prepared in Example 1.

[0029] Fig. 9 Figure 1 is a diagram of the lithium storage mechanism of the ECNFP electrode materials prepared in Examples 1 to 5; (a) and (b), (c) and (d), (e) and (f), (g) and (h), (i) and (j) represent the lithium storage mechanism of ECNFP-1, ECNFP-2, ECNFP-3, ECNFP-4, and ECNFP-5 in the range of 0.2 to 1 mV·S -1 CV curve and log(i)-log(v) graph under scanning rate, (k) is V me / V T- b R picture.

[0030] Fig.10 The reaction kinetics of the ECNFP electrode materials prepared in Examples 1 to 5 are shown in Figures 1 to 5. (a) and (b), (c) and (d), (e) and (f), (g) and (h), (i) and (j) represent the capacitance control contribution rate of ECNFP-1, ECNFP-2, ECNFP-3, ECNFP-4, and ECNFP-5 at a scan rate of 1 mV·S-1, and at a scan rate of 0.2 mV·S-1, respectively. -1 To 1mV·S -1Plots of capacitance-controlled contribution and diffusion-controlled contribution at scan rate.

[0031] Figure 11 shows the Nyquist plot (a) and ω before the ECNFP cycle -1 / 2 -Z Re Relationship curve (b). DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific embodiments.

[0033] Example 1

[0034] A mesoporous carbon paper-based flexible lithium-ion battery negative electrode material and a preparation method thereof, the specific steps are as follows: first, PAN is fibrillated with a PFI pulping machine until the fiber beating degree is 75°SR, and then taken out and sieved with a ball grading screen, and the fibers after 200 mesh are collected and stored in a sealed bag for later use. PAN fiber: CFs = 8:2 is weighed and mixed with PAN fiber and CFs, and then the fiber is made into 40g / m 2 The paper sheets were dried and transferred to an oven and heated to 250℃ at a heating rate of 1℃ / min for pre-oxidation and maintained for 1h. The pre-oxidized paper sheets were carbonized in a tube furnace at a carbonization temperature of 600℃, a heating rate of 5℃ / min, and a holding time of 1h. The obtained paper sheets were then immersed in a 0.2% CNTs aqueous dispersion for 24h. Finally, the obtained carbon paper (CNFP) was mixed with a ZnCl2 solution (concentration of 10wt%) and immersed for 12h and then dried, and activated at 800℃ for 2h in a tube furnace at a heating rate of 5℃ / min. The mass ratio of CNFP to ZnCl2 solid was 1:4, and it was marked as ECNFP-4.

[0035] Embodiment 2-5

[0036] The difference from Example 1 is that CNFP:ZnCl2=1:1, 1:2, 1:3 and 1:5, and the obtained ECNFPs are marked as ECNFP-1, ECNFP-2, ECNFP-3 and ECNFP-5, respectively. In order to compare the performance, CNFP was heated at 800°C for 2h in N2 atmosphere without adding ZnCl2 or CO2.

[0037] Comparative Examples 1-5

[0038] For the preparation of micropore-dominated porous carbon nanofiber paper (ICNFP), CNFP was placed in a CO2-filled tube furnace and heated at 5 °C min –1 The heating rates were heated to 800 °C and maintained for 0.5, 1, 1.5, 2 and 3 h, respectively, and were marked as ICNFP-0.5, ICNFP-1, ICNFP-1.5, ICNFP-2 and ICNFP-3.

[0039] 40g·m -2 The pores with different structures were fabricated in CNFP to study the relationship between the pore size and electrochemical performance of porous CNFP as anode materials for LIBs. Table 1 shows that when the CO2 activation time is prolonged, the micropore volume (V mi ) ratio first increases and then decreases. This may be due to the change of pore structure and collapse of carbon skeleton structure caused by long-term exposure to activation conditions, and some micropores will be effectively transformed into mesopores through the growth of original micropores or the merging of smaller micropores.

[0040] Table 1 Data of N2-adsorption / desorption fitting

[0041]

[0042] The increase in the ZnCl2 / CNFP ratio causes the SSA of ECNFP to increase first and then decrease. When the mass ratio of ZnCl2 / CNFP is 4:1, V mi and mesopore volume (V me ) were 41.78% and 65.01%, respectively, while the specific surface area (SSA) and total pore volume (V T ) reached a maximum value of 653m 2 ·g -1 and 0.383cm 3 ·g -1 With the increase of ZnCl2 activator dosage, V mi decreases, while V T The volume of mesopores increases due to the collapse of the micropore structure caused by the increase in temperature and the increase in the amount of ZnCl2 added. Determining the optimal ratio of micropores to mesopores is crucial to maximize the performance of the ECNFP anode for LIBs. While it is important to retain a sufficient number of micropores to ensure high specific capacity, a larger proportion of mesopores can improve the kinetic performance.

[0043] XRD revealed the crystal structures of ICNFP and ECNFP electrode materials, such as Figure 1(a) and (b). All samples showed two obvious peaks at around 25° and 43°, corresponding to the (002) and (100) crystal planes of the carbon material, respectively, representing the disordered and partially graphitized structure of the material. According to the Bragg equation (2dsinθ=nλ), the interlayer spacings of ECNFP-1, ECNFP-2, ECNFP-3, ECNFP-4 and ECNFP-5 were measured to be 0.353, 0.354, 0.355, 0.360 and 0.354 nm, respectively. The interlayer spacing of ECNFP is larger than that of graphite (0.335 nm). According to the calculation results, ECNFP-4 with the largest SSA has the largest interlayer spacing. The reason for the increase in the interlayer gap may be that ZnCl2 etching causes the collapse of the graphite crystal structure and the formation of micropores and mesopores.

[0044] The preparation process and material characterization of the mesoporous carbon paper-based flexible lithium-ion battery negative electrode material of the present invention are analyzed:

[0045] Figure 2 The preparation and lithium storage mechanism diagram of mesoporous carbon paper-based flexible lithium-ion battery negative electrode materials. After PFI fibrillation and Ball grading sieve screening, PAN fibers are treated to obtain smaller and more uniform nanofibers. After carbonization and activation, a large number of mesopores appear on the PAN fibers, which are Li + The storage of lithium ions provides a large number of active sites, thereby improving the specific capacity of lithium-ion batteries.

[0046] Figure 3 This is the conductivity graph of carbon paper with different weights after carbonization. It can be seen that as the weight increases, the thickness increases, but the conductivity decreases. 2 The quantitative carbon paper has the highest conductivity, which is 4527S / m.

[0047] Figure 4 The prepared ECNFP (carbon paper weight is 40g / m 2 ) Electrode conductivity diagram. It can be seen from the figure that from ECNFP-1 to ECNFP-5, the conductivity of the electrode gradually decreases from 4260S / m to 3057S / m. This is because with the addition of ZnCl2, the electrode material produces more defects, the amorphous carbon increases, the degree of graphitization decreases, and the conductivity is reduced, but ECNFP-4 still maintains a high conductivity of 33398 3057S / m.

[0048] Figure 5 These are the electron microscope images and flexibility test images of ECNFP prepared after carbonization and activation. Figure 5(a) and (b) show the surface morphology of ECNFP. After being impregnated with CNTs aqueous dispersion, some pores on the electrode surface are filled. The CNTs on the surface can make good contact with the electrolyte, thereby enhancing the rapid transport of ions. In addition, filling the gaps can also reduce the consumption of electrolyte. Figure 5 As shown in TEM in (c), fibrous CNTs are injected into the carbon material and connected into a complete carbon network. HRTEM observed that the crystalline regions of CNTs are highly ordered. Figure 5 The disordered structure and pore size of the PAN fiber region (marked by yellow circles) are the result of ZnCl2 activation. According to the SAED characterization of ECNFP, Figure 5 Several concentric halos are shown in (e), indicating that the prepared carbon electrode material has a disordered structure and that the etching of ZnCl2 produces a large amount of amorphous carbon. TEM-EDS element mapping shows the presence and uniform distribution of C, N, and O elements. It is worth noting that Figure 5 As shown in (k)-(m), the prepared ECNFP electrode material has good flexibility and can withstand bending, folding and winding.

[0049] Figure 6 is an analysis of the specific surface area and pore size structure of the ECNFP electrode. As can be seen from Figure 6(a), ECNFP-4 has the highest adsorption-desorption curve, suggesting that this electrode material has the largest specific surface area, which is 653 m 2 / g, and the BJH pore size analysis method showed that the pore size was mainly mesopores, which accounted for 65.01% of the total pore volume.

[0050] Figure 7 is the cycling performance diagram of ICNFP and ECNFP electrodes. As can be seen from Figure 7(a), the capacity of the ICNFP electrode after 100 cycles at a rate of 0.1C remains at 296, 291, 307, 310, and 311 mAh / g, respectively, and the corresponding specific surface areas are 181, 243, 252, 269, and 385 m 2 / g, indicating that the microporous ICNFP does not improve the specific capacity of LIBs much. As for the ECNFP electrode, the cycle performance of the mesoporous negative electrode of ECNFP-1, ECNFP-2, ECNFP-3, ECNFP-4 and ECNFP-5 is better. me 18.75m from ECNFP-1 3 / g increased to 65.01m / g for ECNFP-4 3 / g, and the corresponding specific capacities are maintained at 186 mAh / g and 440 mAh / g after 100 cycles at 0.1C, indicating that the presence of mesopores effectively improves the specific capacity. The excellent lithium storage performance of ECNFP-4 can be attributed to the high V me, and a large interlayer spacing of 0.360nm.

[0051] FIG8 is a study of the electrochemical performance of a button-type lithium-ion battery equipped with the electrode material prepared in Example 1. FIG8(a) shows the cycle life diagram of the Li / / ECNFP half-cell at a rate of 0.1C. It can be seen that after 100 cycles, ECNFP-4 has the highest specific capacity retention rate, which is 440 mAh / g, far exceeding ICNFP-3 and unactivated CNFP. In addition, FIG8(b) shows the test of ECNFP-4 under different rate conditions. After 10 cycles at rates of 0.05, 0.1, 0.2, 0.5, 1 and 3C, its capacity is 507, 445, 359, 253, 178 and 102 mAh / g, respectively. When the rate returns to 0.1C and is recycled for 10 cycles, it can still maintain a specific capacity of 389 mAh / g. This result shows that the electrode material prepared by this method has good cycle stability and rate performance, can adapt to work at different rates of charge and discharge, and provides guidance for the application of lithium-ion batteries in different environments.

[0052] As shown in Figure 9, in the range of 0.2 to 1 mV·S -1 CV tests were performed at different scan rates to study the lithium storage mechanism in ECNFP. All peak areas increased with increasing scan rate, which means that the electrode material has good rate performance. The relationship between peak current (i) and scan rate (v) is shown in Formula 3-5:

[0053] i=av b (1)

[0054] log(i)=blog(a)+log(a) (2)

[0055] Where a and b are constants, and Formula 2 is the logarithmic function of Formula 1. If the value of b is close to 0.5, then Li + The storage of is mainly dominated by diffusion control, whereas if the b value exceeds 0.5 and approaches 1, capacitance control is the main mechanism. Fitting with Eq. 2 Fig. 9 The b values ​​of the reduction peaks of (a) ECNFP-1, (c) ECNFP-2, (e) ECNFP-3, (g) ECNFP-4 and (i) ECNFP-5 are calculated to be 0.63, 0.56, 0.70, 0.92 and 0.78, respectively, which are generally greater than 0.5. The b value of ECNFP-4 is closest to 1, suggesting that its contribution to Li is mainly controlled by capacitance. + storage. Fig. 9 (k) shows the V values ​​of ECNFP-1, ECNFP-2, ECNFP-3, ECNFP-4 and ECNFP-5 me / V TWith b R From the relationship between , it can be seen that the presence of mesopores helps to enhance capacitance control, thereby improving the b-specific capacity and rate performance of the negative electrode material.

[0056] At the same time, the contribution rates of capacitance control and diffusion control are calculated according to Formula 3:

[0057]

[0058] Among them, k1v and k2v are the contribution rates of capacitance control and diffusion control respectively; i and V represent current and potential respectively. Fig.10 The contribution rates of capacitance control and diffusion control of ECNFP-1, ECNFP-2, ECNFP-3, ECNFP-4 and ECNFP-5 were calculated. Fig.10 (b) The calculated results of the ECNFP-1 electrode show that as the scan rate increases from 0.2 mV·S –1 Increase to 1mV·S –1 , the contribution of capacitance control is 40%, 58%, 66%, 74% and 80% respectively. The capacitance control and diffusion control contribution rates were calculated for all samples, showing the same trend. With the increase of scan rate, the capacitance control contribution rate increases rapidly. In addition, the ECNFP-1, ECNFP-2, ECNFP-3, ECNFP-4 and ECNFP-5 were compared at 1mV·S –1 The capacitance control contribution rate under the scanning speed is as follows Fig.10 (a), (c), (e), (g) and (i), as V me As the capacitance increases, the contribution rate of capacitance control increases positively. The contribution rate of capacitance control of ECNFP-4 is 1mV·S –1 90% when SSA was increased. This result indicates that lithium can be rapidly adsorbed / desorbed on the electrode surface, which greatly improves the storage kinetics of lithium. Capacitance control is very important for improving specific capacity and rate performance, which can be achieved by increasing SSA and adjusting pore size.

[0059] EIS was used to study the charge and discharge reaction kinetics when ECNFP was used as the negative electrode of LIBs. Figure 11(a) and (b) show the Nyquist plot and ω of the EIS measured for the new battery. -1 / 2 -Z Re By fitting the data in Figure 11(a), the R s and R ct Due to the presence of abundant mesopores, the R ct The linear part of the low-frequency region of EIS is fitted into ω -1 / 2 -Z Re The slope of the curve can further reveal the Li+ As shown in Figure 11(b), the slope of ECNFP-4 is lower, indicating that it has a higher Li + Migration capabilities.

[0060] The above is a preferred embodiment of the present invention, but the present invention should not be limited to the contents disclosed in the embodiment and the drawings, so any equivalent or modification completed without departing from the spirit disclosed in the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a mesoporous carbon paper-based flexible electrode material, characterized in that: The following steps are involved: (1) After PAN fibers are subjected to fibrillation treatment, PAN fibers with a mesh size of 200 or more are screened out; (2) mixing the PAN fiber obtained in step (1) with CFs, forming paper, drying, pre-oxidizing and carbonizing, and then immersing in a CNTs dispersion to obtain a flexible carbon paper; the pre-oxidation is performed at 100 to 400° C. and the temperature is kept at 0.5 to 3 h; (3) impregnating the carbon paper obtained in step (2) in a ZnCl2 solution, drying and activating the solution to obtain a mesoporous carbon paper-based flexible electrode material; the mass ratio of the carbon paper to the ZnCl2 is 1:(3-5); The temperature of the carbonization and activation is 600-800° C., and the temperature is kept for 0.5-2 hours.

2. The preparation method according to claim 1, characterized in that: The mass ratio of carbon paper to ZnCl2 in step (3) is: 1:(4±0.5).

3. The preparation method according to claim 1 or 2, characterized in that: The concentration of the CNTs impregnated in step (2) is 0.01-0.1%, and the impregnation time is 24±12h.

4. The preparation method according to claim 3, characterized in that: The amount of CFs added in step (2) accounts for (20±5) wt% of the total weight of the paper.

5. The preparation method according to claim 4, characterized in that: The heating rate of the pre-oxidation in step (2) is 1 to 5°C / min; the heating rate of the carbonization and activation is 1 to 10°C / min.

6. The preparation method according to claim 5, characterized in that: The heating rate of the carbonization and activation is 5°C / min.

7. The preparation method according to claim 6, characterized in that: The paper weight of the paper produced in step (2) is 40 to 100 g / m 2 .

8. The preparation method according to claim 7, characterized in that: The beating degree of the fibrillated PAN fibers in step (1) is (75±5) o SR.

9. A mesoporous carbon paper-based flexible electrode material prepared by the method according to any one of claims 1 to 8.

10. Use of the mesoporous carbon paper-based flexible electrode material according to claim 9 in the negative electrode of a lithium ion battery.

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