CN114944489A - Thin film layer with accordion MXene array and preparation method thereof, current collector, electrode and battery - Google Patents

Abstract

The invention discloses a thin film layer with an accordion MXene array, a preparation method thereof, a current collector, an electrode and a battery. The thin film layer with the accordion MXene array contains accordion MXene materials, and the accordion MXene materials are arranged in an array. The invention provides a simple and effective method for preparing an ordered or vertically arranged structure matrix. The accordion MXene material itself has the characteristics of oriented arrangement and low curvature of the MXene sheet, and the effect of the interfacial surface tension of the liquid-liquid two-phase mixed liquid, The accordion MXene material is spread on the interface layer to obtain an ultra-thin thin film layer with an accordion MXene array structure with oriented MXene sheets. Due to the simple preparation method of the accordion MXene array structure of the present invention, the effect of being applied to metal electrodes is remarkable, and a technical path that can be applied is provided for the practical application of high-power and high-capacity lithium metal batteries, and has significant industrial utility. value.

Description

Thin film layers with accordion MXene arrays and methods for their preparation, current collectors, electrodes and batteries

technical field

The invention belongs to the technical field of new materials and batteries, and particularly relates to a thin film layer with accordion MXene arrays and a preparation method thereof, a current collector, an electrode and a battery.

Background technique

Lithium metal anode is considered as the most potential material to replace graphite anode (372mAh g ^-1 ) due to its highest theoretical specific capacity (3860mAh g ^-1 ) and lowest electrochemical potential (-3.04V relative to standard hydrogen electrode) . In recent decades, in order to develop high-performance lithium metal batteries (LMBs), lithium metal anodes have been used to pair with a variety of high-capacity cathodes, including layered nickel-rich cathodes, sulfur, and oxygen. Lithium-ion battery (LIB) 2 to 6 times. However, the slow ion diffusion and high charge transfer resistance in Li metal anodes, especially under high-rate charge-discharge conditions, greatly exacerbate the growth and volume change of Li dendrites, resulting in rapid consumption of electrolyte in Li metal batteries. Coulombic efficiency decreases and capacity decays significantly.

In order to improve the diffusion and electron transfer capabilities of lithium ions in lithium metal anodes, and thus improve the electrochemical performance of lithium metal anodes, researchers have developed various methods, such as: constructing three-dimensional matrix materials, designing artificial solid electrolyte interfaces (SEI) and modified electrolytes; among them, the reported three-dimensional matrix materials, including graphene aerogels, three-dimensional carbonaceous electrodes, three-dimensional porous metal structures, etc., have been widely studied. A three-dimensional matrix material with a porous structure can adsorb a large amount of electrolyte, thereby increasing the local ion concentration therein and reducing the ion concentration polarization at high current densities. In addition, the three-dimensional structure can also buffer the volume change of the electrode, localize the overall volume change of the electrode to improve the electrode stability, thereby improving the electrochemical performance of the lithium metal anode.

However, these three-dimensional matrix materials have been reported to be generally thick (over 100 μm) and structurally disordered and randomly arranged. According to the diffusion coefficient equation D _eff =D×ε/τ (where D _eff is the effective diffusion coefficient of ions, ε is the porosity, and τ is the tortuosity), the conduction path is determined by the ratio of the porosity to the tortuosity. The randomly arranged structure in the 3D matrix material has high tortuosity, resulting in low effective electron diffusivity, slow ion transport, and non-uniform distribution of electric field and lithium ion flux inside the electrode. In addition, the high tortuosity will cause the redox reaction of Li ⁺ /Li to only take place at the limited anode/electrolyte interface, resulting in extremely low rate capability (<1 mA cm ⁻² ). Based on the Sand'time Li-ion plating time model (t _Sand = πD _eff (z _c c ₀ F) ² /4(Jt _a ) ² ), the thicker 3D negative electrode also has high curvature, and it can be charged and discharged at a high rate. Under these conditions, the growth of lithium dendrites will be aggravated, resulting in a significant decrease in battery performance and safety hazards. It can be seen that tortuosity plays a very important role in ion diffusion and charge transfer in 3D electrodes.

The tortuosity (τ) is related to the porosity (ε) and the Bruggeman index (α) according to the Bruggeman relation: τ=ε ^α . In this case, when the tortuosity is 1, which corresponds to the electrode with the fastest ion transport, it can be seen that the ideal electrode should be continuous and vertically aligned, and a three-dimensional matrix with an ordered or vertically aligned structure is important for promoting ion transport , reducing the apparent resistance, and greatly improving the rate performance and practicality of lithium metal anodes are crucial.

SUMMARY OF THE INVENTION

The purpose of the present invention is for the existence of slow ion diffusion and high charge transfer resistance in the lithium metal negative electrode, especially under the condition of high rate charge and discharge, which will greatly intensify the growth and volume change of lithium dendrites, lithium metal batteries The electrolyte is rapidly consumed, the Coulombic efficiency is reduced and the capacity is obviously attenuated.

A first aspect of the present invention provides a thin film layer with an accordion MXene array, the thin film layer contains an accordion MXene material, and the accordion MXene material is arranged in an array.

In some embodiments, the chemical formula of the above accordion MXene material is represented as M _n+1 X _n T _x , wherein M is selected from one or more transition metal elements, and X is selected from one of carbon, nitrogen, and boron elements. one or more, T _x represents a surface functional group.

In some embodiments, M in the above-mentioned accordion MXene material is selected from one or more elements of Ti, Ta, Nb, Cr, V, and Mo.

In some embodiments, the above _- mentioned Tx includes at least one of -F, -Cl, -Br, -I, -S, -O, _-NH4 .

In some embodiments, M in the above accordion MXene material contains Nb element.

In some embodiments, X in the above-described accordion MXene material is a C and/or N element.

In some embodiments, the thickness of the thin film layer is between 1 μm and 100 μm.

A second aspect of the present invention provides a method for preparing the above-mentioned thin film layer, the steps comprising: adding an accordion MXene material into a liquid-liquid two-phase system, and dispersing the accordion MXene material in the liquid-liquid two-phase interface layer to form an accordion array film; transfer the accordion array film to the surface of a medium to obtain the above-mentioned thin film layer.

In some embodiments, a more specific embodiment of the above-mentioned preparation method includes: adding the above-mentioned dispersion of the accordion MXene material into a water-oil two-phase system.

In some embodiments, a more specific embodiment of the above-mentioned preparation method includes: disposing a dielectric layer on the above-mentioned interface layer, and by pulling the dielectric layer, the above-mentioned accordion array film is transferred to the surface of the dielectric layer to obtain the above-mentioned thin film layer .

In some embodiments, the oil phase in the above water-oil two-phase system is selected from the group consisting of dichloromethane, trichloromethane, and tetrachloromethane.

In some embodiments, the solvent in the dispersion of the above-described accordion MXene material is water.

In some embodiments, the above-mentioned dielectric layer is a metal foil.

In some embodiments, the material of the above-mentioned metal foil includes one or more of copper, nickel, and stainless steel.

A third aspect of the present invention provides a current collector, comprising a conductive layer, the surface of the conductive layer is the above-mentioned thin film layer having an accordion MXene array; or, the thin film layer obtained by the above-mentioned preparation method.

In some embodiments, the above-mentioned conductive layer is a metal foil.

In some embodiments, the material of the metal foil includes copper, nickel, and stainless steel.

A fourth aspect of the present invention provides an electrode comprising an electrochemically active metal and the above current collector;

In some embodiments, the above-mentioned electrochemically active metal is selected from at least one metal lithium, sodium, zinc, calcium, and potassium.

A fifth aspect of the present invention provides a method for preparing the above-mentioned electrode, the step comprising: electroplating the metal on the above-mentioned current collector.

A sixth aspect of the present invention provides another method for preparing the above-mentioned electrode, the step comprising: after the metal or the alloy of the metal is heated and melted, it is combined with the above-mentioned current collector.

A seventh aspect of the present invention provides a battery comprising the above-mentioned current collector; or, the above-mentioned electrode.

The beneficial technical effect of the present invention is:

1. The present invention provides a simple and effective method for preparing an ordered or vertically arranged structure matrix, utilizing the characteristics of the MXene sheet oriented arrangement and low curvature of the accordion MXene material itself, and the interfacial tension of the liquid-liquid two-phase mixed liquid. act to spread the accordion MXene material on the interface layer, and obtain an ultra-thin thin film layer with an accordion MXene array structure in which the MXene sheets are aligned;

2. When used in battery electrodes, the thin film layer of the accordion MXene array of the present invention is used as the matrix of metal lithium. First, due to the ultra-thin structure of the array and the low curvature of the MXene sheet, the electrolyte can be quickly immersed, promoting lithium The rapid diffusion of ions; secondly, the accordion MXene array structure can also provide a uniform electric field, so that the distribution of lithium ions is uniform; thirdly, the MXene material can also reduce the nucleation overpotential of lithium metal and inhibit the growth of lithium dendrites. A new type of dendrite-free lithium metal battery is obtained, and the stability and safety of the battery are improved; in the fourth aspect, the accordion MXene array structure of the present invention also has abundant space, which can provide for the volume change of lithium metal during charging and discharging. Buffer space to improve the stability of the entire electrode. Through experimental tests, the accordion MXene array structure of the present invention is applied to the negative electrode of the battery, and the electrochemical performance of the battery is effectively improved, including cycle performance, rate performance and Coulomb efficiency.

3. Due to the simple preparation method of the accordion MXene array structure of the present invention, the effect of being applied to metal electrodes is remarkable, providing a technical path that can be applied in high-power and high-capacity lithium metal batteries, and has significant industrial utility. value.

Description of drawings

Fig. 1 is the SEM photograph of accordion TiNbC-MXene (a) and two-dimensional TiNbC-MXene in Example 1 of the present invention;

2 is a schematic diagram (a) and a corresponding photo (b) of the preparation process of the thin film layer with an accordion TiNbC-MXene array structure in Example 1 of the present invention;

3 is a schematic diagram (a) of the rapid spreading of an accordion TiNbC-MXene dispersion in a water-oil two-phase interface layer in Example 1 of the present invention, a top view (b) and a side view (c) of the prepared MXene thin film layer, and The contact angle photograph (d) of dripping electrolyte solution on the thin film layer;

4 is a copper foil composite tape with a thin film layer of accordion MXene arrays on the surface prepared in Example 1 of the present invention;

Fig. 5 is a test photograph of the contact angle of the electrolyte on the MXene thin film layer of the accordion TiNbC-MXene array structure (a), the accordion Ti3C2 _{- MXene} array structure (b) and the copper foil surface (c) in Example 2 of the present invention ;

Fig. 6 is the voltage distribution (a) of the accordion TiNbC-MXene array under 1 mAcm ^-2 with a capacity of 0.1 to 5 mAhcm ^-2 for electroplating lithium in Example 4 of the present invention; SEM images of the accordion TiNbC-MXene array under different lithium plating capacities : 0mAhcm ^-2 (b), 0.1mAh cm ^-2 (c), 1mAh cm ^-2 (d) and 5mAh cm ^-2 (e); real-time monitoring of accordion TiNbC-MXene arrays by specific in situ optical microscopy (f) The lithium growth photos under different lithium plating times: 0min(g), 10min(h), 30min(i) and 60min(j), and the electroplating current density is 2mA cm ^-2 ;

Fig. 7 SEM images of the comparative copper foil in Example 4 of the present invention under different lithium plating capacities: 0.1mAh cm ^-2 (a), 1mAh cm ^-2 (b) and 5mAh cm ^-2 (c);

Fig. 8 is the nucleation overpotential test results (a) of the accordion TiNbC-MXene array, the accordion Ti3C2 _{- MXene} array and the lithium plating on the Cu foil in Example 4 of the present invention, the Nyquist curve (b) and the Coulomb of the symmetric cell Efficiency comparison diagram (c), and corresponding discharge voltage distribution diagrams (d~f);

Figure 9 shows the rate performance (a) of TiNbC-MXene-Li, Ti ₃ C ₂ -MXene-Li and Cu-Li electrodes at different current densities of 1 to 20 mAcm ^-2 in Example 4 of the present invention, TiNbC-MXene accordion Cycling performance of arrayed lithium electrodes at high current densities of 5 (b) and 20 mA cm ^-2 (c).

Figure 10 shows the cycle performance of TiNbC-MXene-Li//LFP, Ti3C2 _{- MXene} -Li//LFP and Cu-Li//LFP full cells at 0.2C in Example 5 of the present invention (a) and 0.1C Rate performance at ~4C (b), and cycling performance at 4C (c).

Detailed ways

The technical solutions of the present invention are described below through specific embodiments. It should be understood that one or more steps mentioned in the present invention do not exclude the existence of other methods and steps before and after the combination step, or other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are intended to illustrate the invention only and not to limit the scope of the invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, rather than limiting the arrangement order of each method or limiting the scope of implementation of the present invention, and the change or adjustment of the relative relationship shall not be changed without substantial technical content. Under the conditions of the present invention, it can also be regarded as the implementable scope of the present invention.

The raw materials and instruments used in the examples have no specific restrictions on their sources, and can be purchased in the market or prepared according to conventional methods well known to those skilled in the art.

The accordion MXene material in this application refers to the MXene material that maintains the accordion morphology obtained by etching the A component in the MAX phase material, and its morphology is different from the MXene material of the two-dimensional sheet (see Figure 1a and b) .

Example 1

This embodiment provides an MXene thin film layer with an accordion-like array arrangement and a preparation method thereof, wherein the accordion MXene material adopts TiNbC-MXene, and the preparation method of the accordion TiNbC-MXene includes: mixing Al in the MAX phase material TiNbAlC Obtained after etching; a more specific preparation method includes: adding 2 g of MAX phase (TiNbAlC) powder to a mixture of 4 g of lithium fluoride (LiF) and 40 mL of 12 mol mL ^-1 hydrochloric acid (HCl). Subsequently, the mixture was heated to 50 °C for 48 hours, then filtered and washed several times until the pH value reached about 7, and the filtered product was freeze-dried to obtain accordion TiNbC-MXene. Figure 1a shows the SEM image of the accordion TiNbC-MXene. It can be clearly seen that TiNbC-MXene has a layered morphology similar to that of an accordion. The lamella array is arranged in an orderly manner, and the lamellar spacing (void) is about 100 nm. The thickness of the lamella is about 1-3 nm, and the lateral dimension is several micrometers; Figure 1b shows a typical SEM image of 2D TiNbC-MXene. It can be seen that the 2D lamellae in the 2D morphology TiNbC-MXene are disordered. The alignment is usually supplemented by ultrasound during the etching of the A component of the MAX phase material, so that the lamellae are peeled off and peeled off.

The preparation method of the MXene thin film layer arranged in an accordion-shaped array in this embodiment includes the following steps: dispersing the accordion TiNbC-MXene into a water-oil two-phase system, and under the action of the surface tension of the water-oil two-phase interface layer, The accordion TiNbC-MXene is spread on the interface to form the TiNbC-MXene accordion array film, and then the accordion array film is transferred to the surface of the medium to obtain the MXene thin film layer arranged in the accordion-shaped array of the present invention.

A more specific implementation process, as shown in Figures 2a and b, includes:

1. The above-prepared accordion TiNbC-MXene and deionized water were prepared into a dispersion of 1.2 mg ml ^-1 ;

2. The above dispersion was added dropwise to the water-dichloromethane two-phase mixed solution. Under the action of gravity, the accordion TiNbC-MXene quickly sank until it spread rapidly at the water-dichloromethane interface layer, forming a TiNbC-MXene accordion array film; Figure 3a shows a schematic diagram of the rapid spreading of the accordion TiNbC-MXene dispersion at the water-oil two-phase interface, and the surface tension at the water-oil interface is the key driving force for the assembly process of the liquid-liquid interface , through experiments we observed that the accordion TiNbC-MXene spreads rapidly to the entire interface once it contacts the water-dichloromethane interface, which reduces the Gibbs free energy (Gγ) of the water-oil interface;

3. Place a copper tape on the water-dichloromethane two-phase interface, and slowly pull it along one direction. The above TiNbC-MXene accordion array film is then spread on the copper tape, and after drying, the copper tape has accordion-shaped arrays. Copper foil composite tape of cloth MXene film layer. Figure 3b presents a top-down SEM image of the composite ribbon, which shows a uniform distribution of accordion TiNbC-MXene arrays on the surface of the composite ribbon, with many nanoscale gaps in the vertical direction. From the side view (3c), it can be seen that the thickness of the array is approximately is 15 μm. Figures 4a-c show the photos of the prepared copper foil composite tape. It can be seen that the MXene film layer has good contact with the metal copper foil, and still exhibits excellent stability under the action of folding or twisting.

When the electrolyte is dropped on the surface of the MXene layer on the surface of the obtained copper foil composite tape, it can be seen that the contact angle between the electrolyte and the surface of the MXene layer is almost zero (Fig. 3d), which is because the accordion of the MXene film layer MXene array structure, the electrolyte can directly and quickly penetrate to the bottom of the substrate (copper tape). Using the composite tape as the current collector of the lithium battery electrode is beneficial to the uniform distribution of lithium ions in the electrode.

In this embodiment, the copper strip can also be replaced with a thin film material (equivalent to a dielectric layer) of other materials, including but not limited to metal materials. Since metal materials have excellent electrical conductivity, the current collectors in the electrodes are usually metal materials, such as copper Tape/foil, nickel tape/foil, stainless steel tape/foil, nickel plated copper tape/foil, etc. The MXene thin film layer of the accordion array structure of the present invention is arranged on the surface of these metal strips or metal foils to obtain a novel surface-modified current collector of the present invention. The current collector of the present invention can be applied to, including but not limited to, lithium metal batteries.

The liquid-liquid two-phase system of the present invention can also choose other liquid phase types. Since the MXene material is hydrophilic, considering the convenience and ease of implementation, the water-oil two-phase system is preferred; the oil phase can also be selected from other types. Types of liquids, such as chloroform, tetrachloromethane and other organic solvents, but as long as the array arrangement of the accordion MXene material is realized through the liquid-liquid two-phase or multi-phase interface, it is all within the technical concept of the present invention.

The thickness of the accordion MXene array of the present invention can be further controlled by adjusting the particle size of different MXene materials. In some embodiments, the thickness of the accordion MXene array can be adjusted between 1 μm and 100 μm.

Example 2

This embodiment provides another thin film layer with an accordion MXene array. The accordion MXene material is Ti ₃ C ₂ -MXene, and its preparation method is similar to that of TiNbC-MXene in Embodiment 1, except that the raw material MAX phase material is Ti ₃ AlC ₂ .

The preparation method of the MXene thin film layer in this example is similar to that in Example 1. Figures 5a-c show the contact angle test photos of the electrolyte on the MXene thin film layer of the accordion TiNbC-MXene array structure (a), the accordion Ti3C2 _{- MXene} array structure (b), and the copper foil surface (c), respectively. It can be seen that the contact angle on the MXene thin film layer is significantly smaller than that of the copper foil, which is related to the array structure of MXene, while the surface of the TiNbC-MXene array structure exhibits the smallest contact angle (~0°), which is lower than that of Ti ₃ C ₂ -MXene array structure (~22°), which may be related to the fact that TiNbC-MXene is easier to etch and has a more perfect accordion array structure.

Example 3

This embodiment provides another MXene thin film layer with an accordion-shaped array. The accordion MXene material is Ti ₂ C-MXene. The material is Ti ₂ AlC. The preparation method of the MXene thin film layer is similar to that of Example 1.

Similarly, in other embodiments, the accordion MXene material may alternatively be Ti ₃ CNT _x , Ti ₄ N ₃ T _x , TiNbC, TiNbCN, Ta ₄ C ₃ T _x and the like.

Example 4

This embodiment provides a lithium metal negative electrode and a preparation method thereof, wherein the preparation method steps include: electroplating lithium metal on the surface of the MXene thin film layer of the accordion-shaped array of the present invention. In this embodiment, the metal lithium is used as the plating layer on the composite copper tape obtained in Embodiment 1.

More specific implementation method steps include: cutting the composite copper tape in Example 1 into a disc, and assembling into a CR2032 type button-type symmetrical battery, wherein the electrolyte is 1M LiPF ₆ in EC, EMC, DEC (v:v: v=1:1:1) and 1% solution in VC. The specific deposition capacity of symmetric cells with accordion TiNbC- ^MXene arrays was tested at a constant current density of 1.0 mAcm-2 to study the growth of metallic lithium on TiNbC-MXene accordion arrays.

Figure 6a presents the voltage distribution of electroplated Li with a Li plating capacity ranging from 0.1 to 5 mAh cm ^-2 , and the evolution of Li plating on the accordion TiNbC-MXene array during this process was characterized by SEM tests (Figure 6b–e), which can be It is seen that in the initial nucleation stage, at a low plating level of 0.1 mAh cm ⁻² , Li metal nucleates uniformly on the MXene nanosheets of the accordion TiNbC-MXene array, which should be attributed to the uniform electric field and ion concentration distribution (Fig. 6c); in contrast, a large number of heterogeneous nucleation sites for lithium were observed on the copper foil (Fig. 7a). As the Li plating capacity increased to 1 mAh cm ⁻² , Li metal further grew in the voids between the accordion TiNbC-MXene arrays (Fig. 6d). At this time, a large number of Li dendrites were found on the copper foil (Fig. 7b), and a small amount of Li dendrites were also observed on the copper foil not covered by the accordion Ti3C2 _{- MXene} . Further increasing the Li plating capacity to 5 mAh cm ⁻² , it can be seen that the Li plating fills and covers the array, presenting a dendrite-free and smooth surface composed of dense and uniformly distributed Li with many grain boundaries (Fig. 6e). ). Under the same conditions, the surface of the copper foil was randomly plated with a large number of lithium dendrites, showing an uneven surface with a loose porous structure (Fig. 7c). When the lithium plating is completely stripped, the accordion TiNbC-MXene array structure maintains the intact array morphology without collapse.

Lithium on accordion TiNbC-MXene arrays was further monitored in real time by in situ optical microscopy using chronopotentiometry at a constant plating current density of 2 mA cm ^-2 and a cut-off potential of -2.0 V using a specially designed transparent quartz cell (Fig. 6f). Growth process (Fig. 6g~j). At the initial stage, the accordion TiNbC-MXene array is framed in white in the optical photograph, showing an accordion structure with uniform array spacing (Fig. 6g). After 10 min of electroplating, the plated Li can be seen to grow into the voids of the accordion TiNbC-MXene with bright color, and the border of the accordion is white (Fig. 6h). When plated for 30 min, bright and uniformly distributed plated lithium was observed within the accordion TiNbC-MXene arrays with no obvious protrusions on the surface (marked by purple shapes, Fig. 6i). Notably, the accordion TiNbC-MXene arrays maintained a flat surface without any Li dendrites even when electroplated at a current density of 2 mA cm ^-2 for 60 min (Fig. 6j). Even at high rates, the dendrite-free phenomenon after Li plating can be attributed to the low tortuosity of the arrays and the nanogap in the arrays, which favors a super-permeable electrolyte and a uniform electric field that promotes Li-ion/charge at high current densities Fast transfer.

To gain insight into the nucleation behavior of Li metal on accordion MXene arrays, the nucleation overpotential (μn) was calculated using the difference between tip voltage (μt) and mass transfer-controlled overpotential, and the results are shown in Fig. 8a, accordion TiNbC-MXene array The output μn (9.9mV) of the accordion is much lower than that of the accordion Ti3C2 _{- MXene} array (16.1mV) and copper foil (28.3mV), which indicates that the lithium plating barrier on the TiNbC-MXene accordion array is significantly reduced, which is attributed to Fast ion kinetics, low charge transfer resistance, and uniformly distributed high Li-ion conductor LiF ensure fast electron and Li-ion transfer into the low-bending accordion TiNbC-MXene array (Fig. 8b).

The Coulombic efficiency (CE) of the half-cell was investigated based on the good dendrite-free Li plating behavior achieved by fast ion diffusion and charge transfer in the accordion TiNbC-MXene array (Fig. 8c). All cells were cycled between 0 and 1.0 V with a lithium plating capacity of 1 mAh cm ^-2 and a current density of 1 mAh cm ^-2 . The average CE of the accordion TiNbC-MXene array was 98.2% in the first three cycles, and then stabilized at around 99.8% in the subsequent cycles (890 cycles), comparable to the accordion Ti3C2 _{- MXene} array (230 cycles) Compared with copper foil (170 cycles), the utilization rate of lithium metal is the highest, and the cycle life is increased by 300-400%. The corresponding voltage distributions for Li plating/stripping on TiNbC-MXene accordion MXene arrays are shown in Fig. 8d. Compared to the copper foil (overpotential of 48 mV), the accordion TiNbC-MXene array showed a small overpotential of 18 mV even after 800 cycles (Fig. 8d–f).

In addition, symmetric cells were further assembled to evaluate the cycling stability of the accordion TiNbC-MXene arrays, and the corresponding electrodes in the symmetric cells were assembled by plating Li metal electrodes with a capacity of 6 mAh cm ^-2 on the accordion MXene arrays (labeled as TiNbC-MXene- Li), the corresponding accordion Ti3C2 _{- MXene} array lithium metal electrodes and copper foil lithium metal electrodes are labeled (Ti3C2 _{- MXene} -Li and Cu-Li). Tests show that the symmetric cell with TiNbC-MXene-Li achieves excellent cycling stability within 1100h with a low overpotential of 16mV, superior to Ti3C2 _{- MXene} -Li (26mV) and Cu-Li (46mV) . In contrast, the symmetric cells of Ti3C2 _{- MXene} -Li and Cu-Li undergo a gradual increase in overpotential and fail abruptly at nearly 700 hours and 600 hours, respectively. Symmetrical cells with TiNbC-MXene-Li exhibit excellent deep stripping/plating behavior and operate stably for over 800 hours at high areal capacities up to 20 mAh cm ^{-2 at} a current density of 1 mAcm-2.

The rate capability of TiNbC-MXene-Li was further investigated at current densities ranging from 1 to 20 mA cm ^-2 . As shown in Figure 9a, when the current density is gradually increased to 5 mA cm ^-2 , the overpotential of TiNbC-MXene-Li remains at 35 mV, which is better than that of Ti3C2 _{- MXene} -Li (46mV) and Cu-Li ( 78mV). TiNbC-MXene-Li can provide a stable overpotential of 102mV without short-circuiting even at extremely high current densities of 10mA cm ^-2 and even as high as 20mAcm ^-2 . However, the overpotentials of the Ti3C2 _{- MXene} -Li (202 mV) and Cu-Li electrodes (560 mV) increased significantly (Fig. 9a). We also further investigated the cycling stability of the TiNbC-MXene-Li electrode at high rates. At 5 mA cm ^-2 , the TiNbC-MXene-Li symmetric cell can run stably for 28,000 minutes. Even operating at a high current density of 20 mA cm ^-2 , TiNbC-MXene-Li can maintain a stable overpotential (103mV) with long-term cycling stability (2500 cycles) with only a slight increase in overpotential (115mV) , paving the way for practical lithium metal anodes in high-power lithium metal batteries (Fig. 9b–c). These excellent rate performances of TiNbC-MXene-Li symmetric cells should be attributed to the fast transport paths of ions and electrons in the low-bend arrays, and the lithiophilic halogen functional group (-F) of TiNbC-MXene nanosheets, through the low-bend accordion The TiNbC-MXene array can effectively adjust the dendrite-free Li plating and buffer the volume change of Li metal.

Example 5

This embodiment provides a lithium metal full battery, in which LiFePO ₄ (LFP) is used as the positive electrode material to assemble the full battery (negative electrode, positive electrode capacity ratio=2.0); the lithium metal negative electrode is the accordion TiNbC-MXene array in the above-mentioned embodiment 4 and accordion Ti ₃ C ₂ -MXene arrays were plated with lithium metal electrodes with a capacity of 6 mAh cm ^-2 , and the assembled full cells were labeled as TiNbC-MXene-Li//LFP, Ti ₃ C ₂ -MXene-Li//LFP, The comparative example is a full cell assembled with a copper foil plated lithium electrode, marked as Cu-Li//LFP. The galvanostatic charge/discharge measurements were performed in the voltage range of 2.0 and 4.0 V, compared to Li/Li ⁺ , at different current densities from 0.2 to 4C (1C=172 mA g ⁻¹ ).

The test results are shown in Fig. 10. The TiNbC-MXene-Li//LFP full cell operates stably for 280 cycles at 0.2C with a capacity retention rate as high as 92%. In contrast, the capacity of the Cu-Li//LFP full cell starts to decrease significantly after 50 cycles (Fig. 10a). In addition, the TiNbC-MXene-Li//LFP full cell also exhibits high rate capability (Fig. 10b). When the discharge rate is increased to 4C, the discharge capacity of the TiNbC-MXene-Li//LFP full cell still remains at 130mAh g ^-1 , which is much higher than that of Cu-Li//LFP (97mAh g ^-1 ) and Ti ₃ C ₂ -Discharge capacity of MXene-Li//LFP (114mAh g ^-1 ) full cell. Not only that, the TiNbC-MXene-Li//LFP full cell also exhibits excellent durability, with a Coulombic efficiency of 99% after 1000 cycles, and a capacity retention rate of 86% even at a high rate of 4C ( Figure 10c). The long-cycle stability at high rates of this full cell further confirms that the accordion MXene array structure has fast ion and charge transfer kinetics in metallic batteries.

Example 6

The lithium metal battery of the present invention can also realize the composite of the accordion MXene array structure and lithium metal through other preparation methods. This embodiment provides another lithium metal negative electrode and a preparation method thereof, wherein the preparation method steps include: combining the accordion MXene array structure of the present invention with lithium metal. The thin film layer of the MXene-like array is contacted with molten lithium metal or its alloy, so that the molten lithium metal or its alloy infiltrates between the accordion MXene array structures, and after cooling, a lithium metal electrode containing the accordion MXene array is obtained.

The specific implementation steps include:

1. Heat the lithium metal or lithium metal alloy to 400℃～800℃, and melt it into a liquid state;

2. Coating liquid molten lithium or lithium alloy on the copper foil with an accordion MXene array thin film layer on the surface, and after cooling and solidifying, a lithium metal electrode is obtained.

In a specific embodiment, the steps include: after heating lithium metal to 400° C. to melt, coating the surface of the thin film layer of the accordion TiNbC-MXene array prepared in Example 1 of the present invention to obtain a lithium metal electrode.

It should be noted that, since MXene material is a kind of two-dimensional material, it is represented by the chemical formula M _n+1 X _n T _x , wherein M is selected from one or more transition metal elements; X is selected from carbon, nitrogen Or one or more of boron elements; T _x represents a functional group, including one or more of -F, -Cl, Br, I, -O, -S, -OH, -NH ₄ ; 1≤n≤4 . Under the inspiration of the present invention, other types of accordion MXene materials are selected for compounding with metals, and the metal compound materials are used for electrodes of batteries, which also belong to the technical concept of the present invention.

In the present invention, it is found that the binary accordion MXene material containing Nb element is applied to the lithium metal electrode compared with the single element accordion MXene material, which shows lower lithium metal nucleation overpotential, better cycle performance and rate performance, which is On the one hand, it can be attributed to the fact that Nb-containing binary accordion MXene is easier to prepare MXene materials with uniform particle size distribution and remarkable accordion structure; The migration of electrons in the electrodes makes the electric field distribution uniform. Therefore, the accordion MXene material containing Nb element is more preferable in the present invention.

It should also be noted that due to electrochemically active metals, including metals Na, Zn, K, Ca, and Mg, when used as negative electrode materials for metal batteries, there are the same problems as lithium metal (including metal dendrite growth, etc.) , therefore, the thin film layer of the accordion MXene array of the present invention can also be used for compounding with these metals to obtain compound metal electrodes, which can be used in corresponding metal battery systems.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise form disclosed, and obviously many changes and modifications are possible in light of the above teachings. The exemplary embodiments were chosen and described for the purpose of explaining certain principles of the invention and their practical applications, to thereby enable one skilled in the art to make and utilize various exemplary embodiments and various different aspects of the invention. Choose and change. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims (10)

1. A thin film layer with an accordion MXene array, wherein the thin film layer contains an accordion MXene material, and the accordion MXene material is arranged in an array. 2. The thin film layer according to claim 1, wherein the chemical formula of the accordion MXene material is represented as M _{n+ 1} X _n T _x , wherein M selects one or more of transition metal elements, and X selects From one or more of carbon, nitrogen and boron elements, T _x represents a surface functional group; Preferably, the M is selected from one or more of Ti, Ta, Nb, Cr, V, Mo elements; Preferably, the T _x includes at least one of -F, -Cl, -Br, -I, -S, -O, -NH ₄ . 3. The thin film layer according to claim 2, wherein the M contains Nb element; And/or, the X is a C and/or N element. And/or, the thickness of the thin film layer is between 1 μm and 100 μm. 4. The preparation method of the thin film layer according to any one of claims 1 to 3, wherein the step comprises: adding the accordion MXene material into the liquid-liquid two-phase system, so that the accordion MXene material is dispersed in the interface layer of the liquid-liquid two-phase to form an accordion array film; The film layer is obtained by transferring the accordion array film to the surface of a medium. 5. preparation method as claimed in claim 4 is characterized in that, the more specific embodiment of described preparation method comprises: adding the dispersion of the accordion MXene material to a water-oil two-phase system; And/or, a dielectric layer is provided on the interface layer, and the thin film layer is obtained by pulling the dielectric layer to transfer the accordion array film to the surface of the dielectric layer. 6. The preparation method of claim 5, wherein the oil phase in the water-oil two-phase system is selected from dichloromethane, trichloromethane, and tetrachloromethane; And/or, the solvent in the dispersion of the accordion MXene material is water; And/or, the dielectric layer is a metal foil; preferably, the material of the metal foil includes one or more of copper, nickel, and stainless steel. 7. A current collector, characterized by comprising a conductive layer, the surface of the conductive layer containing the thin film layer as claimed in any one of claims 1 to 3; or, as in any one of claims 4 to 6 The thin film layer obtained by the preparation method; Preferably, the conductive layer is a metal foil; more preferably, the material of the metal foil includes copper, nickel, and stainless steel. 8. An electrode comprising an electrochemically active metal, and a current collector as claimed in claim 7; Preferably, the metal is selected from at least one metal lithium, sodium, zinc, calcium and potassium. 9. A method for preparing an electrode as claimed in claim 8, wherein the step comprises: electroplating the metal onto the current collector; And/or, after heating and melting the metal or the metal alloy, it is combined with the current collector. 10. A battery, characterized in that it contains the current collector as claimed in claim 7; Or, the electrode of claim 8.

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