CN115000410A - Carbon nano tube-titanium carbide composite porous microsphere, preparation thereof and application thereof in lithium-sulfur battery - Google Patents

Carbon nano tube-titanium carbide composite porous microsphere, preparation thereof and application thereof in lithium-sulfur battery Download PDF

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CN115000410A
CN115000410A CN202210847080.9A CN202210847080A CN115000410A CN 115000410 A CN115000410 A CN 115000410A CN 202210847080 A CN202210847080 A CN 202210847080A CN 115000410 A CN115000410 A CN 115000410A
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titanium carbide
composite porous
carbide composite
carbon nano
lithium
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CN115000410B (en
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郭容婷
李伟
刘峥
陈梦琦
郭雨婷
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Guilin University of Technology
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    • H—ELECTRICITY
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    • H01M4/00—Electrodes
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
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Abstract

The invention discloses a preparation method of a carbon nano tube-titanium carbide composite porous microsphere and application of the carbon nano tube-titanium carbide composite porous microsphere in a lithium-sulfur battery. The invention discloses a method for preparing carbon nano tube-titanium carbide composite porous microspheres, which mainly comprises the following steps: (1) ti 3 AlC 2 Etching; (2) porous titanium carbide p-Ti 3 C 2 T x Preparing; (3) preparing the carbon nano tube-titanium carbide composite porous microspheres. The preparation method is simple and feasible, and can realize large-scale synthesis.

Description

Carbon nano tube-titanium carbide composite porous microsphere, preparation thereof and application thereof in lithium-sulfur battery
Technical Field
The invention belongs to the technical field of electrode material preparation, and particularly relates to a carbon nano tube-titanium carbide composite porous microsphere, and preparation and application thereof in a lithium-sulfur battery.
Background
In a lithium ion secondary battery system, compared with a negative electrode material (such as artificial graphite and natural graphite negative electrode material), the positive electrode material (LiFePO) with low specific capacity 4 And LiCoO 2 Respectively theoretical specific capacity of 170mAh g -1 、274mAh·g -1 ) Has been a major factor restricting the development thereof. For this reason, attention has been directed to a novel secondary battery system in order to expect higher energyDensity. Among the currently known positive electrode materials, sulfur has a relatively high specific capacity (1675mAh · g) -1) Compared with common lithium ion battery anode materials (lithium cobaltate, lithium manganate, lithium iron phosphate and the like), the theoretical energy density of the Li/S battery formed by the lithium ion battery anode and the lithium metal cathode is 3-5 times that of the traditional lithium ion battery. The content of the elemental sulfur is very rich, and the theoretical energy density of the lithium-sulfur battery is 2600Wh kg -1 And is much higher than the common lithium ion battery. The lithium sulfur (Li-S) system is considered to be useful for next-generation secondary batteries.
In the sixties of the last century, Ulam and Herbet and the like put forward the concept of Li-S batteries, and the battery uses sulfur as a positive electrode material, and the theoretical specific capacity can reach 1675 mAh.g < -1 >. Li-S batteries have the main advantages of: (1) the elemental sulfur has rich reserves in the earth, low price and environmental protection; (2) the theoretical specific capacity of the anode material and the theoretical specific energy of the battery are higher and respectively reach 1675 mAh.g < -1 > and 2600 Wh.kg < -1 >, and the capacity of the anode material is far higher than that of a lithium cobaltate battery widely applied commercially; (3) the specific capacity of the negative electrode can reach 3860mAh g < -1 > by using lithium as the negative electrode. Large volume expansion (-80%) due to complete conversion of sulfur with lithium ions during discharge, and low conductivity (5 x 10) of elemental sulfur -30 S cm -1 ) Resulting in poor electrochemical performance. The most important problem to be solved is the shuttle effect, i.e. the lithium polysulphide (LPS, Li) generated in the elemental sulphur positive electrode on discharge 2 S x X is 4. ltoreq. x.ltoreq.8) is soluble in aprotic solvents used in lithium-sulfur batteries, and under the action of an applied electric field, negatively charged LPS readily moves toward the Li anode, so ions re-oxidized from LPS cannot return to the cathode, resulting in loss of active species, which in turn leads to severe capacity fade and poor rate performance. In order to overcome these disadvantages, many studies have been made, and there have been attempted methods of: (1) preparing a C @ S composite by a design using a mixing, impregnation and limiting method, (2) using a multifunctional binder; (3) improved membranes (interlayers); (4) a specially formulated electrolyte is used to inhibit the shuttling mechanism. The document reports that graphene, conductive polymer or metal oxide is used as a carrier to load elemental sulfur to obtain a compositeAlthough materials that trap dissolved LPS in the diffusion barrier of the support material by physical/chemical adsorption have some effect in suppressing the shuttling effect, these materials do not completely overcome the above-mentioned disadvantages of the lithium-sulfur battery.
MXene is a novel two-dimensional (2D) carbide and/or nitride discovered by Naguib et al in 2011. These 2D materials are called MXene because they are obtained by selectively etching a ( group 3 or 4 element) in a precursor MAX phase in an acid (HF acid) and an organic solvent. MXenes have the general formula Mn +1XnTx, where M represents an early transition metal, X represents C or N, and Tx represents some chemical group, e.g. in etching Ti 3 AlC 2 T x And surface groups such as-O, -OH and-F which are substituted for aluminum atoms. MXene has unique properties, such as high metal conductivity (>5000S·cm -1 ) And is environmentally friendly. In addition, MXene developed can be adjusted with various surface functional groups according to the application requirements, and the versatility of the MXene is increased.
Lithium-sulfur batteries (Li-S) are considered to be a promising energy storage system because of their high energy density and low cost, but they suffer from the most complex problems of shuttling effect of soluble polysulfides, resulting in fast capacity fade, severe self-discharge, low energy efficiency, and poor cycling stability. The use of nanostructured materials as sulfur carriers is a common method of mitigating polysulfide shuttling. The MXenes material has excellent electronic property, electrochemical property, optical property and mechanical property, so that the MXenes material can be widely applied to the fields of energy storage, flexible electronics, hydrogen storage and the like. Research also shows that MXenes materials are easy to stack among layers, so that the specific surface area and ion adsorption sites of the materials are reduced, the stacking can further hinder the migration of ions, and the specific capacity and rate performance of the MXenes as electrode materials are greatly influenced.
The invention prepares a novel CNT/p-Ti 3 C 2 T x MXene composite porous microsphere based on MXene materialAnd meanwhile, the CNT is added, the core forming effect of the carbon nano tube is utilized, the collapse and the stacking defect of the MXene material lamellar structure are prevented, and the electrical conductivity of the composite porous microsphere can be enhanced by the CNT. The present invention is directed to the use of CNT/p-Ti 3 C 2 T x The MXene composite porous microspheres are used for solving the problems existing in the lithium-sulfur battery cathode material at present, and the MXene composite porous microspheres have important significance for promoting the development of the lithium-sulfur battery cathode material.
Disclosure of Invention
The invention aims to provide a carbon nano tube-titanium carbide composite porous microsphere and a preparation method thereof. The invention discloses a method for preparing a carbon nano tube-titanium carbide composite porous micro-particle, which comprises the following steps:
(1)Ti 3 AlC 2 etching: in a fume hood, 120mL of HF and 6g of Ti were taken 3 AlC 2 Is prepared from Ti 3 AlC 2 Slowly adding the mixture into a plastic beaker filled with HF, continuously stirring the mixture in an oil bath at the temperature of 35 ℃ for 24 hours to obtain a mixture after reaction;
(2) porous titanium carbide p-Ti 3 C 2 Preparation of Tx: transferring the reacted mixture obtained in the step (1) into a centrifuge tube, centrifuging at the speed of 3500r min-1 for 8min, washing the obtained precipitate with deionized water until the pH of the supernatant is close to neutral, adding 15-25mL of deionized water into the washed precipitate, performing ultrasonic treatment for 6-8h, centrifuging at the speed of 4000r min-1 for 30min, and taking the upper dark green liquid to obtain a few layers of Ti 3 C 2 T x Suspending liquid, freezing and drying to obtain porous titanium carbide p-Ti 3 C 2 T x Powder;
(3) preparing the carbon nano tube-titanium carbide composite porous microspheres: weighing 2g of porous titanium carbide p-Ti obtained in the step (2) according to the mass ratio of 1:1 3 C 2 T x Respectively adding the powder and 2g of multi-walled carbon nanotube (MWCNT) into 40mL of ethanol, stirring for 1h, performing ultrasonic treatment for 2h, uniformly mixing, and spray-drying by using a spray dryer to obtain the CNT-titanium carbide composite porous microsphere powder CNT/p-Ti 3 C 2 T x 。
In the preparation method of the carbon nano tube-titanium carbide composite porous microsphere, the carbon nano tube CNT is moreThe wall carbon nanotube MWCNT has a diameter of 30-50nm and a length of 10-20 μm, and the titanium carbide is porous titanium carbide p-Ti 3 C 2 T X 。
Another object of the present invention is to provide the use of the carbon nanotube-titanium carbide composite porous membrane of the present invention.
A large number of electrochemical performance tests prove that the carbon nano tube-titanium carbide composite porous microspheres prepared by the method can be used as sulfur carriers and applied to the positive electrode material of the lithium-sulfur battery, and can improve the specific capacity, the rate capability and the cycle life of the positive electrode material.
Based on the previous research on the lithium-sulfur battery, the invention takes MXene material as a sulfur carrier of the lithium-sulfur battery, utilizes the lamellar structure of MXene, takes a carbon nano tube as a core, and obtains CNT/p-Ti through ultrasonic stripping, freeze drying, compounding with the carbon nano tube and spray drying 3 C 2 T x MXene composite porous microsphere can be used as the sulfur carrier, can enhance the physical barrier and chemical adsorption capacity to polysulfide compound, reduce the dissolution shuttle of lithium polysulfide and relieve the volume expansion effect of a sulfur positive electrode. Proposed CNT/p-Ti 3 C 2 T x The preparation method of the MXene composite porous microspheres is simple and feasible, and can realize large-scale synthesis.
Drawings
FIG. 1CNT/p-Ti 3 C 2 SEM image and EDS image of preparation process of TxMXene composite porous microsphere (wherein FIG. 1(a) untreated Ti 3 AlC 2 (ii) a (b) Etched Ti 3 C 2 T x (ii) a (c, d) less porous Ti 3 C 2 T x (ii) a (e) Less-layer porous Ti obtained after ultrasonic treatment 3 C 2 T x A dispersion liquid; (f) microspherical CNT/p-Ti 3 C 2 T x (ii) a (g) Sulfur-compounded CNT/p-Ti 3 C 2 T x /S)
FIG. 2 contains CNT/p-Ti 3 C 2 T x MXene (PMC) composite porous microsphere sulfur-carrying positive electrode material and Ti 3 C 2 T x Nyquist diagram of MXene (M) sulfur-carrying anode material
FIG. 3 CNT-containing/p-Ti 3 C 2 T x MXene (PMV) composite porous microsphere sulfur-carrying positive electrode material and Ti 3 C 2 T x Multiplying power performance comparison graph of MXene (M) sulfur-carrying cathode material under different multiplying powers
FIG. 4 contains CNT/p-Ti 3 C 2 T x MXene (PMC) composite porous microsphere sulfur-carrying positive electrode material and Ti 3 C 2 T x Comparative graph of cycle Performance of MXene (PMC) sulfur-carrying cathode material under different multiplying power
Detailed Description
The following examples are further illustrative of the present invention and are not intended to be limiting thereof.
Example 1 preparation of nanotube-titanium carbide composite porous microspheres.
(1)Ti 3 AlC 2 Etching of
In a fume hood, 120mL of HF and 6g of Ti were taken 3 AlC 2 Is prepared from Ti 3 AlC 2 Slowly adding the mixture into a plastic beaker filled with HF, continuously stirring the mixture under oil bath at the temperature of 35 ℃ for 24 hours to obtain a mixture after reaction.
(2) Porous titanium carbide p-Ti 3 C 2 Preparation of Tx
Transferring the mixture obtained in the step (1) after the reaction into a centrifugal tube, wherein the centrifugal speed is 3500rmin -1 Centrifuging for 8min, washing the obtained precipitate with deionized water until the pH of the supernatant is close to neutral, adding 20mL of deionized water into the washed precipitate, performing ultrasonic treatment for 7h, and performing ultrasonic treatment for 4000r min -1 Centrifuging for 30min, and collecting the upper dark green liquid to obtain Ti layer 3 C 2 T x Suspending liquid, freezing and drying to obtain porous titanium carbide p-Ti 3 C 2 T x And (3) powder.
(3) Preparation of carbon nano tube-titanium carbide composite porous microsphere
Weighing 2g of porous titanium carbide p-Ti obtained in the step (2) according to the mass ratio of 1:1 3 C 2 T x Respectively adding the powder and 2g of multi-walled carbon nanotube (MWCNT) into 40mL of ethanol, stirring for 1h, performing ultrasonic treatment for 2h, uniformly mixing, and spray-drying by using a spray dryer to obtain the CNT/p-Ti composite porous microsphere powder CNT/titanium carbide 3 C 2 T x 。
FIG. 1 is SEM image and EDS image of the preparation process of the carbon nano tube-titanium carbide composite porous microsphere and after sulfur loading. As can be seen from a comparison of FIG. 1(a) with FIG. 1(b), Ti at the beginning 3 AlC 2 Is stacked together in blocks, and is etched by HF to remove Ti 3 AlC 2 After Al is contained, Ti can be clearly seen 3 AlC 2 Changed to an accordion-like Ti as shown in FIG. 1(b) 3 C 2 T x 。Ti 3 C 2 T x Obtaining Ti through ultrasonic treatment 3 C 2 T x The dispersion (FIG. 1(e)), which was observed to have a Tyndall effect; after the dispersion is subjected to freeze drying, Ti with few layers and multiple pores is successfully obtained 3 C 2 T x (i.e., p-Ti) 3 C 2 T x ) As shown in fig. 1(c) and 1 (d). The porous structure can effectively relieve the volume expansion effect of the sulfur positive electrode. Fully mixing with alcohol solution of carbon nano tube and spray drying to finally obtain microspherical CNT/p-Ti 3 C 2 T x (FIG. 1 (f)). Elemental mapping of EDS showed (FIG. 1(g)), S and CNT/p-Ti 3 C 2 T x Good adhesion of the material, CNT/p-Ti 3 C 2 T x Ti, C and S in/S are uniformly distributed, which indicates that CNT/pTi 3 C 2 T x The material has strong sulfur loading capacity, can strengthen physical limitation and chemical adsorption on polysulfide, enhances the conductivity of S, and further improves the electrochemical performance of the battery.
Example 2CNT/p-Ti 3 C 2 T x MXene/S electrochemical performance test.
With Ti 3 C 2 T x MXene/S for comparison, the sulfur loading procedure was as follows: mixing Ti 3 C 2 T x MXene or CNT/p-Ti 3 C 2 T x Mixing MXene and sulfur powder according to the mass ratio of 1:4, dropwise adding alcohol in an infrared drying oven, and uniformly grinding with an agate mortar. Placing the obtained mixture in a tube furnace, and burning for 12h at 155 ℃ under Ar atmosphere to obtain Ti 3 C 2 T x MXene/S or CNT/p-Ti 3 C 2 T x MXene/S
The electrochemical performance test procedure is as follows:
(1)CNT/p-Ti 3 C 2 T x preparation of MXene/S positive plate
0.07g of the composite material (CNT/p-Ti) was weighed out 3 C 2 T x MXene) was mixed with 0.02g of acetylene black and 0.0.1g of polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP) was used as a solvent, and uniformly ground in an agate grinding bowl into slurry, and then an aluminum foil was used as a current collector, and the ground slurry was coated on the aluminum foil, and vacuum-dried at 80 ℃ for 12 hours.
(2) Assembling the prepared positive electrode material into a battery in a vacuum glove box (the volume fraction of oxygen is less than 0.1ppm, the volume fraction of water is less than 0.1ppm), taking a lithium sheet as a negative electrode, and sequentially placing a positive electrode sheet, a diaphragm, the lithium sheet, a gasket and a spring sheet into a battery shell; and (4) dropwise adding a proper amount of electrolyte, sealing by using a sealing machine, and assembling into the CR2032 button cell for later use.
(3) Electrochemical alternating current impedance spectroscopy (EIS) testing
FIG. 2 shows CNT/p-Ti 3 C 2 T x (hereinafter referred to as PMC) composite material and Ti 3 C 2 T x Nyquist plot for the/S (hereinafter M) material. As can be seen from fig. 2, two semicircles are shown in the high and medium frequency regions, and a diagonal line is shown in the low frequency region. The first half circle in the high frequency range represents the interface resistance of a solid electrolyte interface film (SEI) or the resistance (Rs) of lithium ions flowing through the SEI. The half circles at mid frequency represent the resistance to charge transfer (Rct) between the SEI and the electrolyte. The diagonal line (Warburg impedance) reflects the diffusion of lithium ions in the electrode. Analysis of FIG. 2 reveals that CNT/p-Ti 3 C 2 T x The AC impedance of the composite material of the/S (PMC) is 9.74 omega, which is far less than that of Ti 3 C 2 Tx (m), indicating faster kinetics for the charge transfer process. The addition of the multi-wall CNT can enhance the conductivity of the composite porous microsphere, is beneficial to charge transfer of an electrode, and can reduce the impedance value of a PMC anode material and improve the conductivity of the PMC anode material.
(4) Rate capability test
FIG. 3 shows CNT/p-Ti 3 C 2 T x (hereinafter referred to as PMC) composite material and Ti 3 C 2 T x The material/S (hereinafter referred to as M) is subjected to a rate capability test. As can be seen from fig. 3, the PMC positive electrode exhibited excellent rate performance against continuous change in current density, and when tested at current densities of 0.1, 0.2, 0.3, 0.5, 1, 2, 1, 0.5, 0.3, 0.2, 0.1C, the PMC electrode provided 889.06, 746.62, 656.28, 600.47, 519.45, 601.85, 673.75mA · g, respectively -1 Excellent specific discharge capacity. Moreover, the PMC electrode was still able to recover 673.75mAh g after cycling the current density back to 0.1C -1 Stable and high specific capacity. This is in sharp contrast to M-electrodes, where the specific discharge capacities of the M-electrode materials were only 615.37, 540.93, 476.90, 401.59, 181.77, 318.11, 407.03, 496.70, and 544.81 mAh-g, respectively, at the same test rate -1 And only shows lower specific capacity. These test data clearly show that CNT/p-Ti 3 C 2 T x (PMC) electrode materials have better rate performance and cycle stability, further illustrating the advantage and necessity of CNT addition.
(4) Cycle performance test
Fig. 4(a) is the result of constant current charge and discharge performance test of CNT/p-Ti3C2Tx (PMC) and Ti3C2Tx (M) at a current density of 0.1C, fig. 4(b) is the result of 200 cycles at a large current density of 1C, and fig. 4(C) is a graph comparing cycle performance of PMC and M at a current of 0.1C. As can be seen from the discharge curves in fig. 4(a), PMC starts to appear at 2.1 and 2.3V with two distinct discharge plateaus, which are the processes of sulfur reduction to polysulfide and polysulfide conversion to insoluble long-chain polysulfide, respectively. As can be seen from FIG. 4(b), the PMC composite material had a first discharge capacity of 631.51mA hg -1 The concentration of the active carbon can be maintained at 390.91mAh g after 200 cycles -1 The capacity attenuation rate is small. As can be seen from fig. 4(c), the discharge capacities of the PMC composite materials were 915.51, 913.65, 912.05, and 902.18mAh · g, respectively, in the first four cycles -1 Furthermore, the voltage difference between the charge and discharge plateaus of the PMC composite is stable during cycling, which in turn indicates a decrease in resistance in the active material during cycling, Li + Ion diffusionThe rate is enhanced. As can also be seen from fig. 4(C), the specific discharge capacity of the PMC material was maintained at 900mAh g after 20 cycles at a current density of 0.1C -1 Above and below, accounting for 90% of its initial specific capacity, PMC consistently exhibits higher and better coulombic efficiency during these 20 cycles.

Claims (3)

1. A carbon nano tube-titanium carbide composite porous microsphere is characterized in that: comprises multi-wall carbon nano-tube MWCNT with the diameter of 30-50nm and the length of 10-20 mu m and porous titanium carbide p-Ti 3 C 2 T X 。
2. The carbon nanotube-titanium carbide composite porous microsphere according to claim 1, wherein the preparation method comprises:
(1)Ti 3 AlC 2 etching: in a fume hood, 120mL of HF and 6g of Ti were taken 3 AlC 2 Is prepared from Ti 3 AlC 2 Slowly adding the mixture into a plastic beaker filled with HF, continuously stirring the mixture in an oil bath at the temperature of 35 ℃ for 24 hours to obtain a mixture after reaction;
(2) porous titanium carbide p-Ti 3 C 2 T x The preparation of (1): transferring the mixture obtained in the step (1) into a centrifuge tube, and centrifuging at 3500r min -1 Centrifuging for 8min, washing the obtained precipitate with deionized water until the pH of the supernatant is close to neutral, adding 15-25mL deionized water into the washed precipitate, performing ultrasonic treatment for 6-8h, and performing ultrasonic treatment at 4000r min -1 Centrifuging for 30min, and collecting the upper dark green liquid to obtain Ti layer 3 C 2 T x Suspending liquid, freezing and drying to obtain porous titanium carbide p-Ti 3 C 2 T x Powder;
(3) preparing the carbon nano tube-titanium carbide composite porous microspheres: weighing 2g of porous titanium carbide p-Ti obtained in the step (2) according to the mass ratio of 1:1 3 C 2 T x Respectively adding the powder and 2g of multi-walled carbon nanotube (MWCNT) into 40mL of ethanol, stirring for 1h, performing ultrasonic treatment for 2h, uniformly mixing, and spray-drying by using a spray dryer to obtain the CNT-titanium carbide composite porous microsphere powder CNT/p-Ti 3 C 2 T x 。
3. The carbon nanotube-titanium carbide composite porous microsphere according to claim 1, wherein the carbon nanotube-titanium carbide composite porous microsphere can be used as a sulfur carrier and applied to a lithium-sulfur battery positive electrode material, and can improve the specific capacity, rate capability and cycle life of the positive electrode material.
CN202210847080.9A 2022-07-07 2022-07-07 Positive electrode material of lithium-sulfur battery Active CN115000410B (en)

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