Foamed lithium negative electrode, foamed lithium composite material, preparation method of foamed lithium composite material, battery, electric device and application of foamed lithium negative electrode and foamed lithium composite material

Abstract

The invention discloses a foamed lithium negative electrode, a foamed lithium composite material, a preparation method of the foamed lithium composite material, a battery, a power utilization device and application of the foamed lithium negative electrode, and the preparation method of the foamed lithium negative electrode comprises the following steps: adding MXene into molten metal lithium or lithium alloy, and mixing to obtain a mixed lithium solution; carrying out gas-liquid mixing on the mixed lithium liquid and inert gas to form foamed molten lithium; and coating the foamed molten lithium on a substrate, cooling and curing to form the foamed lithium layer. In the preparation method disclosed by the invention, MXene is used as a surfactant, so that the surface performance of molten lithium liquid is obviously improved, the obtained foamed lithium negative electrode has abundant pore structures and a large amount of unoccupied space, and enough space is given to cope with volume expansion of metal lithium in a battery cycle process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium metal batteries, in particular to a foamed lithium negative electrode, a foamed lithium composite material, a preparation method thereof, a battery, an electrical device and a use. BACKGROUND

[0002] Metal lithium negative electrode has the outstanding advantages of high capacity (3860 mAh / g), low potential (-3.040 V vs. SHE) and low density (0.53 g / cm 3 ), and is expected to obtain several times the theoretical energy density of existing lithium-ion batteries in the secondary battery system matching lithium-free high-capacity positive electrode materials (such as oxides, sulfur, etc.). However, there are obvious technical problems in the commercial application of metal lithium negative electrode, which include:

[0003] (1) Lithium dendrite growth: uncontrollable dendrite growth of lithium negative electrode during charging and discharging is one of the main challenges faced by metal lithium negative electrode, and lithium dendrite not only causes internal short circuit of the battery, but also can pierce the separator to cause battery thermal runaway and other safety problems;

[0004] (2) Volume expansion effect: metal lithium will undergo a huge volume change during deposition / dissolution, which will cause the destruction of the internal structure of the electrode, and then affect the stability and life of the battery;

[0005] (3) Interface instability: when metal lithium is directly used as a battery negative electrode, it is easy to react with the electrolyte, and a solid-state electrolyte interface layer (SEI) is repeatedly generated on the surface, resulting in the generation of a large amount of dead lithium, which will reduce the coulombic efficiency and stability of the battery, resulting in a significant gap between the theoretical capacity and the actual capacity;

[0006] (4) Incompatibility of negative electrode and positive electrode capacity: the capacity ratio (N / P ratio) of the existing lithium metal battery negative electrode and positive electrode far exceeds 1.05, resulting in the existence of excess metal lithium in the negative electrode, which further aggravates the above (1) ~ (3) technical problems.

[0007] For the problems of dendrite growth and unlimited volume change of metal lithium negative electrode, the solutions can be summarized into two categories: controlling the electrodeposition process of metal lithium and constructing a new type of three-dimensional composite negative electrode. (1) Controlling the electrodeposition process of metal lithium: the electrodeposition process of metal lithium negative electrode mainly includes nucleation, growth and SEI film formation of lithium, and controlling one or more stages is an effective measure to control the dendrite-free electrodeposition of metal lithium. The nucleation of metal lithium usually occurs in the initial stage of deposition, and once it is deposited unevenly at some active sites, it will further exacerbate this unevenness, leading to lithium dendrites, so regulating the uniform nucleation of metal lithium can achieve dendrite-free growth of lithium. Professor Zhang Qiang of Tsinghua University et al. added nano-diamonds to the electrolyte, and under the action of the electric field, a large number of diamond particles migrated to the electrode surface to form the initial nucleation points of lithium, thereby obtaining uniform lithium deposition. Professor Cui Yi's research group at Stanford University also constructed hollow carbon spheres containing gold particles. Lithium can form a solid solution alloy with gold, and the nucleation and growth of metal lithium in the hollow carbon sphere are controlled. After the nucleation of metal lithium, the accumulation of lithium ions and electrons at the tip of the lithium growth site produces a tip discharge effect, prompting lithium to continue to deposit along the tip and eventually grow into thick lithium dendrites. Therefore, controlling the growth direction of lithium is as important as controlling the nucleation of lithium. (2) Construction of a new type of three-dimensional composite lithium electrode: according to Sand's time theory The nucleation time of lithium during the deposition process is inversely proportional to the square of the actual current density, so in order to prolong the nucleation time of lithium, the specific surface area of the electrode can be increased to avoid uneven nucleation of lithium. However, the construction of a three-dimensional composite lithium electrode requires three-dimensional substrate construction, addition of lithium-friendly noble metals, lithium compounding and other steps, and the synthesis process is complex, costly and difficult to apply to industrial mass production.

[0008] For the technical problem of mismatch between the capacity of the negative electrode and the positive electrode, there is an excess of metal lithium, which is mainly prepared by reducing the thickness of metal lithium to reduce the content of metal lithium in the negative electrode. However, the mechanical strength of metal lithium is not good, and it is difficult to process ultra-thin thickness metal lithium. SUMMARY

[0009] The present application provides a three-dimensional composite lithium electrode construction technical scheme with simple preparation method, obtains a metal lithium / MXene composite foam lithium composite material with foam pore structure, and uses the foam lithium composite material for lithium metal battery negative electrode, to solve the technical problems of dendrite growth and volume change of metal lithium negative electrode.

[0010] The first aspect of the present application provides a preparation method of a foamed lithium negative electrode, wherein the foamed lithium negative electrode comprises a foamed lithium layer, and the preparation method of the foamed lithium layer comprises the following steps: adding MXene into molten metallic lithium or lithium alloy to obtain a mixed lithium liquid; mixing the mixed lithium liquid with inert gas to form foamed molten lithium; and coating the foamed molten lithium on a substrate to form the foamed lithium layer.

[0011] In an embodiment, the preparation method further comprises, after cooling and solidification, peeling the foamed lithium layer from the substrate to obtain the foamed lithium negative electrode.

[0012] In an embodiment, the substrate is a current collector, and the foamed lithium negative electrode comprises the foamed lithium layer and the current collector; preferably, the current collector is a metal foil, more preferably, a copper foil or a titanium foil.

[0013] In an embodiment, the method of gas-liquid mixing is a blowing bubble method, and the steps comprise: introducing the inert gas into the mixed lithium liquid.

[0014] In an embodiment, the method of gas-liquid mixing is a foaming method, and the steps comprise: under the inert gas environment, mixing the inert gas and the mixed lithium liquid by a foaming device to form a foam.

[0015] In an embodiment, the foaming device comprises at least one rotating shaft, and a dispersion head is arranged at one end of the rotating shaft; in use, the dispersion head is immersed in the mixed lithium liquid, and the rotating shaft drives the dispersion head to rotate to realize the gas-liquid mixing of the mixed lithium liquid and the inert gas.

[0016] In an embodiment, the mass fraction of the MXene is 1% to 45%; preferably, 10% to 30%; more preferably, 10% to 20%; and more preferably, 10% to 15%.

[0017] In an embodiment, the alloy element in the lithium alloy is selected from one or more of Na, Mg, Al, Zn, Sn, V, In, Ag, Au, B, Si, and Ge.

[0018] In an embodiment, the MXene contains a fluorine functional group.

[0019] In an embodiment, the MXene has a general chemical formula of M n+1 X n T x , wherein M is selected from one or more of Ti, V, Cr, Nb, Ta, W, Zr, Sc, Y, and Hf; X is selected from one or more of carbon, nitrogen, and boron, 1≤n≤4, and T xThe meaning is that the surface contains functional groups; preferably, the MXene is Ti3C2T x .

[0020] In one embodiment, in the above preparation method, the step further includes: adding an additive to the mixed lithium solution to adjust the surface tension of the mixed lithium solution.

[0021] In one embodiment, the additive is selected from one or more of transition metal sulfides, transition metal selenides, transition metal fluorides, and transition metal oxides; more preferably, the transition metal sulfide is molybdenum sulfide.

[0022] A second aspect of the present invention provides a foamed lithium negative electrode obtained by the above-mentioned preparation method.

[0023] In one embodiment, the density of the lithium foam layer in the lithium foam negative electrode is ≤0.3 g / cm 3 .

[0024] In one embodiment, the porosity of the foam lithium layer in the foam lithium negative electrode is ≥50%.

[0025] In one embodiment, the pore size of the foamed lithium negative electrode is ≤1000 μm.

[0026] In one embodiment, the density of the lithium foam layer in the lithium foam negative electrode is between 0.1 g / cm 3 to 0.3g / cm 3 .

[0027] In one embodiment, the porosity of the foam lithium layer in the foam lithium negative electrode is between 50% and 80%.

[0028] In one embodiment, the pore size of the lithium foam negative electrode is between 1 μm and 500 μm.

[0029] A third aspect of the present invention provides a battery comprising the above-mentioned foamed lithium negative electrode.

[0030] In one embodiment, the battery is a solid-state battery.

[0031] A fourth aspect of the present invention provides an electrical device comprising the above-mentioned battery or solid-state battery.

[0032] A fifth aspect of the present invention provides an energy storage device comprising the above-mentioned battery or solid-state battery.

[0033] A sixth aspect of the present invention provides a method for preparing a foamed lithium composite material, comprising the steps of: adding MXene to molten metallic lithium or lithium alloy to obtain a mixed lithium liquid; mixing the mixed lithium liquid with an inert gas to form foamed molten lithium, and obtaining the foamed lithium composite material after cooling and solidification.

[0034] In an embodiment, the method of mixing gas and liquid is a bubble blowing method, and the steps include: introducing the inert gas into the mixed lithium liquid;

[0035] In an embodiment, the method of mixing gas and liquid is a foaming method, and the steps include: under the inert gas environment, the inert gas is mixed with the mixed lithium liquid by a foaming device to form a foam.

[0036] In an embodiment, the foaming device includes at least one rotating shaft, and one end of the rotating shaft is provided with a dispersion head. In use, the dispersion head is immersed in the mixed lithium liquid, and the dispersion head is rotated by the rotating shaft to realize the gas-liquid mixing of the mixed lithium liquid and the inert gas.

[0037] In an embodiment, the mass fraction of MXene is 1% to 45%; preferably, 10% to 30%; more preferably, 10% to 20%; and more preferably, 10% to 15%.

[0038] In an embodiment, the alloying element in the lithium alloy is selected from one or more of Na, Mg, Al, Zn, Sn, V, In, Ag, Au, B, Si, and Ge.

[0039] In an embodiment, the general chemical formula of MXene is M n+1 X n T x , wherein M is selected from one or more of Ti, V, Cr, Nb, Ta, W, Zr, Sc, Y, and Hf; X is selected from one or more of carbon, nitrogen, or boron, 1≤n≤4, and T x , preferably, the MXene is Ti3C2T x .

[0040] In an embodiment, the steps further include: adding an additive to the mixed lithium liquid to adjust the surface tension of the mixed lithium liquid.

[0041] In an embodiment, the additive is selected from one or more of a transition metal sulfide, a transition metal selenide, a transition metal fluoride, and a transition metal oxide; more preferably, the transition metal sulfide is molybdenum sulfide.

[0042] The seventh aspect of the present application provides a foam lithium composite material, which includes MXene, metallic lithium or a lithium alloy, and has a foam-like pore structure. The foam lithium composite material can be obtained by the above-mentioned preparation method.

[0043] In an embodiment, the density of the foam lithium composite material is ≤0.3 g / cm 3.

[0044] In an embodiment, the porosity of the above-mentioned foam lithium composite material is ≥ 50%.

[0045] In an embodiment, the pore size in the above-mentioned foam lithium negative electrode is ≤ 1000 μm.

[0046] In an embodiment, the density of the above-mentioned foam lithium composite material is between 0.1 g / cm 3 and 0.3 g / cm 3 .

[0047] In an embodiment, the density of the above-mentioned foam lithium composite material is between 50% and 80%.

[0048] In an embodiment, the pore size in the above-mentioned foam lithium negative electrode is 1 μm to 500 μm.

[0049] In an embodiment, the mass fraction of the above-mentioned MXene is between 1% and 45%; preferably, between 10% and 30%; more preferably, between 10% and 20%; and even more preferably, between 10% and 15%.

[0050] In an embodiment, the alloying element in the above-mentioned lithium alloy is selected from one or more of Na, Mg, Al, Zn, Sn, V, In, Ag, Au, B, Si, Ge.

[0051] In an embodiment, the chemical general formula of the above-mentioned MXene is M n+1 X n T x , wherein M is selected from one or more of Ti, V, Cr, Nb, Ta, W, Zr, Sc, Y, Hf; X is selected from one or more of carbon, nitrogen or boron, 1 ≤ n ≤ 4, T x means that the surface contains a functional group; preferably, the MXene is Ti3C2T x .

[0052] The eighth aspect of the present application provides a use of the above-mentioned foam lithium composite material as a catalyst in the fields of medicine, petrochemicals, fine chemicals, as an electrode material or lithium supplement material in lithium batteries, and for manufacturing light alloys in the field of metallurgy. For example, in the field of medicine, the foam lithium composite material can be used as a catalyst for synthesizing antitumor drugs, anti-AIDS drugs, and drugs for treating hypertension and hyperlipidemia; in the field of petrochemicals, the foam lithium composite material can be used for synthesizing lithium bases; in the field of fine chemicals, the foam lithium composite material can be used as a catalyst for synthesizing rubber and fragrances.

[0053] The beneficial technical effects of the present application are as follows:

[0054] The preparation method of the foamed lithium negative electrode of the present application, MXene as a surfactant, significantly improves the surface performance of the molten lithium liquid, and then through the foaming device or the air device, a stable foamed molten lithium can be formed therein, and the characteristics of the foamed lithium negative electrode obtained after cooling and solidification are:

[0055] I. With rich pore structure

[0056] The foamed lithium negative electrode of the present application has rich pore structure and a large amount of free space, which provides sufficient space to cope with the volume expansion of metal lithium during the battery cycle process, so that the volume change value of the foamed lithium negative electrode as a whole is very small.

[0057] The high porosity inside the foamed lithium significantly reduces the density of the metal lithium negative electrode, and by controlling the thickness of the foamed lithium through a simple film forming method (such as coating, doctor blading, pulling, etc.), the content of metal lithium in the negative electrode can be easily adjusted, avoiding the problem of difficult processing of ultra-thin lithium caused by the soft texture and poor mechanical strength of metal lithium.

[0058] II. Contains MXene component

[0059] The MXene nanosheet added in the present application has the effect of reducing the surface tension of molten lithium, which is beneficial to improve the stability of metal lithium foam; at the same time, the MXene nanosheet is uniformly dispersed in the molten metal lithium, which can significantly improve the viscosity of the molten lithium, and also reduce the difficulty of metal lithium foaming. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 It is a structure schematic diagram of using a foaming device in the embodiment 1 of the present application.

[0061] Figure 2 It is a photo of the foamed lithium with MXene mass content of 15% prepared by using a foaming device in the embodiment 2 of the present application, SEM photos under different magnifications (e and f), and the obvious pore structure can be seen, and the corresponding element mapping diagram (g-j) of the SEM diagram. Figure 3 is according to an embodiment of the present application;

[0062] Figure 3 It is a photo of the foamed lithium electrode with different MXene contents prepared by using a blowing method in the embodiment 3 of the present application.

[0063] Figure 4 It is the density (a) and porosity (b) results of the foamed lithium negative electrode with different MXene contents tested in the embodiment 3 of the present application; the surface photo (c) and the SEM photo (d) of the foamed lithium negative electrode with MXene content of 15%.

[0064] Figure 5 It is a half-cell assembled in the embodiment 4 of the present application at 0.5mA cm-2 Current density of 2 mAh cm-2 -2 Afterwards, SEM images of different negative electrode surfaces to show the deposition behavior of lithium ions on different negative electrodes.

[0065] Figure 6 are cross-sectional SEM images of MXene-foam lithium negative electrode after lithium deposition in Example 4 of the present application, showing the deposition state of lithium in ~20 pm cavity (a1 and a2) and 50-200 pm cavity (b1 and b2).

[0066] Figure 7 are the results of full-cell electrochemical performance test of different negative electrodes in Example 4 of the present application, including: time-voltage curves under different current densities (a), 300 cycle performance test at 1C rate (b), 800 cycle performance test at 5C rate (c).

[0067] Main figure mark explanation:

[0068] 10-rotary motor, 20-rotary shaft, 30-dispersion head. DETAILED DESCRIPTION

[0069] The technical solutions of the present application are illustrated below by specific examples. It should be understood that the one or more steps mentioned in the present application do not exclude the existence of other methods and steps before and after the combination steps, or other methods and steps can be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. Unless otherwise specified, the numbering of each method step is only for the purpose of identifying each method step, and is not limited to the arrangement order of each method or the scope of the implementation of the present application. Changes or adjustments of the relative relationship can also be considered as the implementation scope of the present application without substantial technical content changes.

[0070] The raw materials and instruments used in the examples are not specifically limited in source, and can be purchased on the market or prepared according to the conventional methods well known to those skilled in the art. The MXene nanosheet used in the present application uses the MXene powder product produced by Jinan Sanchuan New Material Technology Co., Ltd.

[0071] The density of the foam lithium composite material in the present application is tested by specific gravity method, i.e. cutting a fixed volume V1 (in the present application, a cylinder with a diameter of 16 mm and a thickness of 2 mm is cut), then weighing m1, and then according to the density calculation formula The density p1 of MXene-foam lithium is calculated. Then the porosity P of MXene-foam lithium negative electrode is obtained according to the porosity calculation formula P=(1-p1 / p Li ) x 100%.

[0072] Example 1

[0073] The present embodiment provides a metal lithium negative electrode and a preparation method thereof. The metal lithium negative electrode comprises a foam lithium layer with abundant pore structure, wherein the foam lithium layer contains MXene nanosheets, and the MXene is obtained by etching a MAX phase. The preparation method of the metal lithium negative electrode comprises the following steps:

[0074] (1) In an argon atmosphere in a glove box, the prepared MXene nanosheets are dispersed in molten metal lithium or lithium alloy, and a metal stirrer is used for stirring to make the dispersion uniform, to obtain a mixed lithium liquid (or referred to as molten lithium slurry); preferably, the temperature of the molten lithium or lithium alloy is 200-380°C, and the mass fraction of the added MXene nanosheets is 1-45%;

[0075] (2) The argon in the environment is fully mixed with the mixed lithium liquid by a gas-liquid mixing device to form a foamed molten lithium (foamed molten lithium); in the present embodiment, the gas-liquid mixing can be performed in two ways. One is a foaming method: a foaming device (or referred to as a foaming machine, the structure is shown in Figure 1 ), which comprises a rotating shaft 20, one end of the rotating shaft 20 is a dispersion head 30, and the dispersion head 30 is immersed in the mixed lithium liquid during use. The other end of the rotating shaft 20 is connected to a rotating motor 10. The rotating motor 10 is turned on, the rotating shaft 20 rotates rapidly, and the dispersion head 30 rotates, so that the argon is fully mixed with the mixed lithium liquid to form abundant and dense foamed lithium. The process is similar to the process of whipping cream. In the present embodiment, the dispersion head 30 is a metal ring formed by winding a metal wire. In other embodiments, the dispersion head can also have other structures, and the purpose is to fully mix the inert gas in the atmosphere with the mixed lithium liquid to form foam. The other way is to blow bubbles. A gas pipe is inserted into the mixed lithium liquid, and gas is continuously blown into the mixed lithium liquid, which is similar to the process of blowing bubbles. Due to the surfactant effect of the added MXene, both methods can produce foamed lithium.

[0076] (3) The foamed lithium produced is transferred to the substrate with a preheated stainless steel spoon, and is scraped with a preheated scraper. After scraping, it is cooled and solidified in argon to form a foam lithium layer.

[0077] In some embodiments, the foam lithium layer formed is peeled off from the substrate, and the obtained foam lithium layer is directly used as a negative electrode, such as a negative electrode for a button cell.

[0078] In some embodiments, the substrate is a current collector, and after the foam lithium layer is solidified on the current collector, the obtained metal lithium negative electrode (including the foam lithium layer and the current collector layer) can be used as a negative electrode in a soft package, square or other battery. The current collector is a metal foil, preferably a copper foil or a titanium foil.

[0079] Example 2

[0080] The embodiment provides a specific foamed lithium negative electrode and a preparation method thereof, wherein MXene is Ti3C2T x nanosheet, which is produced by Jinan Sanchuan New Material Technology Co., Ltd. x nanosheet powder product, and the preparation method of the foamed lithium negative electrode, the steps comprising:

[0081] (1) dispersing Ti3C2T x nanosheet in molten metal lithium and stirring it uniformly by using a metal stirrer for 10 min. The temperature of the molten lithium is 300 DEG C, and the mass fraction of the added Ti3C2T x nanosheet is 0-30%, and the added amount is 15% in the embodiment;

[0082] (2) the gas-liquid mixing device is selected as a foam maker in the embodiment, and in the specific implementation, the foam maker is immersed into the molten lithium uniformly dispersed for 1-2 min, and then the foam maker is started to make the rotating speed reach 6000 r / min, and the foaming is continuously carried out until the foamed lithium fills the container;

[0083] (3) the foamed lithium is taken out by using a preheated stainless steel spoon, placed on a titanium foil, and scraped by using a preheated scraper, and the specific thickness can be adjusted according to the actual requirement, and after the scraping is completed, the foamed lithium is placed in argon for cooling and solidification;

[0084] (4) the foamed lithium is peeled off from the titanium foil to obtain a sheet-shaped foamed lithium negative electrode, or is not peeled off from the titanium foil and directly used as a composite negative electrode.

[0085] As shown in Figure 2 a, the foamed lithium foamed by using the foam maker can be foamed to fill the cup, which proves that the MXene improves the viscosity of the molten lithium and is beneficial to foaming. Then the foamed lithium is taken out by using a spoon Figure 2 b), coated on a titanium foil Figure 2 c), after the foamed lithium is cooled to room temperature, the foamed lithium is peeled off from the titanium foil Figure 2 d), and finally a macroscopically visible porous structure can be seen. The foamed lithium is characterized by using a scanning electron microscope (SEM), and the obtained results are as shown in Figure 2 e and f, it can be seen that the foamed lithium is a porous structure, the pores are uniformly distributed, and most of the pore diameters are 200-500 mu m, and a small number of pore diameters can be greater than 1000 mu m. As can be seen from the element mapping Figure 2 h-j corresponding to the SEM image, the elements C, O, F and Ti are uniformly distributed, and the nanosheet of the MXene can be obviously seen on the surface of the pore, which proves that the nanosheet of the MXene wraps the pore, and indicates that the three-dimensional skeleton of the MXene nanosheet is constructed in the molten metal lithium in the foaming process.

[0086] Embodiment 3

[0087] The embodiment provides another foamed lithium negative electrode prepared by the blowing method, and the specific operation steps include:

[0088] (1) MXene Ti3C2T x nanosheets are dispersed in molten lithium metal, and a metal stirrer is used for stirring for 10 min to make the nanosheets uniformly dispersed, the temperature of the molten lithium is 300 DEG C, and the mass fraction of the added Ti3C2T x nanosheets is 5%.

[0089] (2) In the embodiment, a blowing bubble device is selected as the gas-liquid mixing device, which includes a gas outlet needle (equivalent to a gas pipe) and a gas inlet system. In specific implementation, the gas outlet needle of the blowing bubble device is immersed in the uniformly dispersed mixed lithium liquid for 1-2 min, then the gas inlet system is started, the gas flow is controlled to be 60-100 ml / min, and the foaming is continuously carried out until the foamed lithium fills the container;

[0090] (3) The foamed lithium is taken out by using a preheated stainless steel spoon and placed on a titanium foil, and a preheated scraper is used for scraping, and the thickness can be adjusted according to actual requirements. After scraping is completed, the foamed lithium layer is placed in argon for cooling and solidification to form a foamed lithium layer;

[0091] (4) The foamed lithium layer is peeled off from the titanium foil to obtain a sheet-shaped foamed lithium negative electrode; or without being peeled off from the titanium foil, the foamed lithium layer is directly used as a negative electrode;

[0092] (5) The proportion of MXene (0%-30%) is changed, gradient experiments are carried out, a series of foamed lithium negative electrodes are prepared by using the blowing bubble method, and the density and porosity of the electrodes are further characterized.

[0093] The blowing bubble method is used to blow bubbles in the mixed lithium liquid with the MXene content of 0%-30%, and the gradient experiment results are shown in Figure 3 . No bubbles are generated in the molten pure lithium; when the MXene content is increased to 5%, some lithium bubbles are generated; when the MXene content is increased to 10%, the amount of bubbles is obviously increased; when the MXene content is continuously increased to 15%, the content of the foamed lithium is obviously increased, and the foamed lithium can be maintained in a foamed state for about 10 min and can be taken out by a spoon; when the MXene content is increased to 20% and 30%, the foamed lithium is also generated, and the effect is slightly worse than that of the foamed lithium with the MXene content of 15%. The above results show that the MXene content of 10%-20% is most beneficial to the generation of the foamed lithium, and a large amount of stable foamed lithium can be obtained, and the foaming effect is best when the MXene content is about 15%.

[0094] After solidification, the titanium foil is peeled off to obtain foamed lithium negative electrodes with different MXene contents, and then the density and porosity of the foamed lithium negative electrodes are tested, as shown in Figure 4As shown in FIGS. 4a and 4b, the 15%-MXene-foam lithium negative electrode has the lowest density (0.117 g cm -3 ) and the highest porosity (78.2%), and also has optimized space. As shown in FIGS. 4c and 4d, the 15%-MXene-foam lithium negative electrode obtained by scraping has a relatively flat surface and a spherical cavity structure inside, which is similar to the structure of the foam lithium prepared by the foam maker. Figure 4

[0095] Example 4

[0096] This example provides a lithium metal battery with the foam lithium as the negative electrode, specifically a button cell, to test the electrochemical performance of the foam lithium negative electrode. The assembly method of the button cell is as follows:

[0097] Negative electrode sheet: pure lithium negative electrode, MXene-lithium negative electrode (not foamed), and MXene-foam lithium negative electrode. The MXene-lithium negative electrode (not foamed) is obtained by mechanical stirring, rolling, and punching into a round sheet; the MXene-foam lithium negative electrode is obtained by punching the foam lithium layer obtained in Example 2 above into a round sheet with a diameter of 12 mm in an argon environment; the content of MXene in the MXene-lithium negative electrode (not foamed) and the MXene-foam lithium negative electrode is 15%;

[0098] Positive electrode sheet: lithium iron phosphate (LFP) is used as the positive electrode material, Super P is used as the conductive agent, and polyvinylidene fluoride (PVDF) is used as the binder, and the mass ratio of the three is 8:1:1.

[0099] First, half-cells with the three negative electrodes are assembled to study the lithium deposition behavior; then, the three negative electrodes are assembled into a pair of batteries to test the rate performance of the pair of batteries; finally, the three negative electrode sheets, positive electrode sheets, and separators (polypropylene PP separators) are assembled into full cells to test the cycle performance and rate performance. The electrolyte is LS-009 (1M LiTFSI in DME:DOL = 1:1 Vol% with 2% LiNO3). The test conditions are room temperature 25-28°C.

[0100] To study the lithium deposition behavior on the three negative electrodes, we assembled half-cells to deposit lithium at a current density of 0.5 mA cm -2 for 2 mAh cm -2 . As shown in FIGS. 5a, 5b, and 5c, the lithium deposition on the pure lithium negative electrode is uniform and smooth, while the lithium deposition on the MXene-lithium negative electrode (not foamed) is uneven and has a large number of small holes. The lithium deposition on the MXene-foam lithium negative electrode is uniform and smooth, and the foam lithium layer is not damaged. Figure 5 ​As shown, the lithium on the pure lithium surface is dendritic, the lithium on the MXene-lithium negative electrode surface is goose-warm stone, the gap between lithium and lithium particles is large, and the lithium deposited on the MXene-foam lithium negative electrode surface is uniform and smooth without obvious crystal grains. This is mainly because the MXene-foam lithium composite negative electrode has a micron-level spherical array structure, which can greatly reduce the tortuosity of the electrode, improve the transport rate of lithium ions in the electrode, and effectively reduce the local current density of the electrode; on the other hand, the functional groups on the MXene nanosheet can react with metal lithium and form a lithium fluoride-rich solid electrolyte (SEI) interface on the surface, which can prevent the continuous side reaction of foam lithium with electrolyte, enhance the conduction of lithium ions, and uniformize the lithium ion flow; combined with sand's time formula, it can be concluded that the MXene-foam lithium composite negative electrode can effectively prolong the formation time of dendrites, i.e. inhibit the growth of lithium dendrites, and is expected to obtain excellent rate performance and long cycle stability.

[0101] The MXene-foam lithium negative electrode was cut open to observe the deposition of lithium in the interface foam lithium. The cross section of the deposited lithium is shown in Figure 6 a, when the diameter of the cavity in the foam lithium is ~20 μm, the deposited metal lithium will fill it; when the diameter of the cavity in the foam lithium reaches 50-200 μm, lithium particles grow on the inner surface of the cavity, and due to the too large internal volume, it cannot be filled in time, which proves that the cavity inside can be filled with lithium and is most likely to solve the problem of unlimited volume change of lithium metal negative electrode (see Figure 6 b).

[0102] To further verify the volume change behavior of the composite lithium negative electrode, we tested the volume change of the three kinds of lithium negative electrodes at 0.5 mA cm -2 at 3 mAh cm -2 . As shown in Table 1, there is no significant difference in the volume growth rate of the three kinds of negative electrodes in the first charge-discharge cycle; after the three kinds of negative electrodes complete 100 cycles, the volume change rates of the three kinds of electrodes are very different, the volume of the pure lithium negative electrode increases from the initial 200 μm to 384 μm, the volume growth rate is 92%, and the volume growth rates of the MXene-lithium and MXene-foam lithium are 31% and 6% respectively. As can be seen, the MXene-foam lithium has obvious volume delay effect, the main reason is that the internal cavity can effectively store lithium and thus alleviate the volume change of the electrode.

[0103] Table 1 Volume growth rate of pure lithium, MXene-lithium, and MXene-foam lithium negative electrodes after 100 cycles

[0104]

[0105] To investigate the electrochemical performance of MXene-lithium foam, we assembled a symmetric cell. Figure 7 As shown in a, pure lithium anode, MXene-lithium anode (no foaming) and MXene-foam lithium anode are at 1mAcm -2 At a current density of 10 mA cm, the overpotential of MXene-foam lithium is the lowest (18 mV), which is lower than that of pure lithium anode (76 mV) and MXene-lithium anode (43 mV). -2 When the overpotential of MXene-foam lithium is only 82mV, which is slightly lower than that of MXene-lithium negative electrode (108mV) and much lower than that of pure lithium negative electrode (322mV). The above research results on battery rate performance test show that MXene-foam lithium negative electrode can effectively reduce electrode polarization and is expected to extend the cycle life of MXene-foam lithium composite negative electrode. In order to further verify the electrochemical performance of long MXene-foam lithium composite negative electrode in full battery, we matched the MXene-foam lithium composite negative electrode with LFP positive electrode and assembled a full battery. Figure 7 As shown in b, there is no significant difference in the initial capacity of the three composite anodes, which is about 148 mAh g -1 As the cycling process continues, the capacity of the MXene-lithium foam composite anode is 143.1 mAh g after 300 cycles. -1 , the capacity retention rate is as high as 96.6%, far exceeding the MXene-lithium negative electrode (85.3%) and pure lithium negative electrode (73.0%). This result shows that the MXene-foam lithium composite negative electrode has excellent cycle stability. In addition, the capacity retention rate of the MXene-foam lithium composite negative electrode is as high as 95% after 800 cycles at an ultra-high rate of 5C, showing excellent rate performance and long cycle life (see Figure 7 c).

[0106] In some embodiments, in order to optimize the foaming process, additives may be added to the molten lithium or lithium alloy (mixed lithium liquid) containing MXene to adjust the surface tension of the mixed lithium liquid; preferably, the additives are selected from one or more of transition metal sulfides, transition metal selenides, transition metal fluorides, and transition metal oxides; in a specific embodiment, molybdenum sulfide (MoS2) with a mass fraction of 1 to 2% is added to the mixed lithium liquid.

[0107] It should be noted that MXene is a family of two-dimensional materials with similar structures and properties. The general chemical formula can be expressed as M n+1 X n T x , wherein M is selected from one or more of Ti, V, Cr, Nb, Ta, W, Zr, Sc, Y, and Hf; X is selected from one or more of carbon, nitrogen, and boron, 1≤n≤4, and Tx The meaning is that the surface contains functional groups (such as -F, -Cl, -OH, etc.). The specific embodiments in the present application can also select MXene nanosheets of other element compositions, such as Nb3C2T x , V2CT x , Ti2CT x , Ti4C3T x , and the like. These MXene nanosheets have similar two-dimensional sheet structures and surface functional groups, and are used to prepare foam lithium composite materials or foam lithium layers by compounding with metal lithium or lithium alloy, which produce the same or similar effects as the method of the present application, and are all included in the technical solutions of the present application.

[0108] When the foam lithium composite material or the foam lithium layer of the present application is used as a lithium negative electrode, MXene containing fluorine (F) functional groups is preferred, because the functional groups carried by the MXene nanosheet can react with metal lithium and form a layer of fluorine-rich lithium solid electrolyte (SEI) interface on the surface. The fluorine-rich SEI film can prevent continuous side reactions between the foam lithium and the electrolyte, enhance the conduction of lithium ions, homogenize the flow of lithium ions, reduce the generation of lithium dendrites, and improve the safety performance and cycle life of the battery. From the ease of raw material preparation and cost, MXene is preferably Ti3C2T x .

[0109] In addition, the MXene material has excellent mechanical strength and flexibility, which can improve the mechanical properties of the foam lithium and play a reinforcing and toughening effect; the MXene material has excellent electrical conductivity and lithium affinity, which can effectively reduce the nucleation overpotential of lithium in the foam lithium negative electrode, avoid the generation of sharp lithium dendrites, and improve the safety performance and cycle life of the lithium battery. The high porosity inside the foam lithium can also reduce the heat generated by the reaction between the high-activity metal lithium and the electrolyte during the battery production liquid injection process, and reduce the reaction rate and safety risk.

[0110] In some embodiments, the mixed lithium liquid of the present application is obtained by adding MXene to a molten lithium alloy, such as an alloy of Li and Na, Mg, Al, Zn, Sn, V, In, Ag, Au, B, Si, Ge, etc. The foam-like structure is produced by the method of the present application, or the same or similar technical effects as the present application are obtained, which are all within the technical solutions of the present application.

[0111] Example 5

[0112] This embodiment provides a magnesium-lithium foam alloy and a method for preparing the same, comprising the following steps: adding MXene nanosheet powder to a molten magnesium-lithium alloy and dispersing it to obtain a mixed magnesium-lithium slurry; mixing the mixed magnesium-lithium slurry with an inert gas-liquid mixture by a bubble blowing method or foaming method similar to those in Examples 1 to 3 to form a foam, and then cooling and solidifying to obtain a magnesium-lithium foam alloy material. By introducing foam into the lithium-magnesium alloy, an ultra-light alloy material is obtained, and at the same time, MXene nanosheets can be dispersed into the alloy to form a skeleton, thereby changing the mechanical properties of the foam metal alloy. Preferably, in terms of mass fraction, the metal magnesium is 55-90%, the metal lithium is 10-30%, and the MXene nanosheets are 0.1-15%.

[0113] In a specific implementation step, the Ti3C2T x The nanosheets were dispersed in molten lithium and stirred for 10 minutes using a metal stirrer to achieve uniform dispersion. The molten lithium was heated to 300°C. Small pieces of magnesium flakes were then added and heated to 650°C to gradually melt the magnesium flakes, forming a molten magnesium-lithium alloy. In this example, the MXene nanosheets were added at a concentration of 5%; the magnesium content was 80% by weight, and the lithium content was 15%. Argon gas was then mixed with the molten magnesium-lithium alloy using the bubbler and gas outlet needle of Examples 2 or 3 to form a foamed magnesium-lithium alloy.

[0114] Example 6

[0115] This embodiment provides a foamed aluminum-lithium alloy and a method for preparing the same. This method is similar to that of Example 5, except that MXene nanosheet powder is added to a molten aluminum-lithium alloy for dispersion to obtain a mixed aluminum-lithium slurry. The mixed aluminum-lithium slurry is then mixed with an inert gas-liquid mixture using a bubble blowing or foaming method to form a foam, which is then cooled and solidified to obtain a foamed aluminum-lithium alloy material. The introduction of foam into an aluminum-magnesium alloy yields an ultralight alloy material. Preferably, the composition, by mass, comprises 90-99% aluminum, 1-4% lithium, and 0.1-2% MXene nanosheets.

[0116] In a specific implementation step, the Ti3C2T x The nanosheets were dispersed in molten lithium and stirred for 10 minutes using a metal stirrer to achieve uniform dispersion. The molten lithium was heated to 300°C. Small pieces of aluminum flakes were then added and heated to 680°C to gradually melt the aluminum flakes, forming a molten aluminum-lithium alloy. In this example, the MXene nanosheets were added at a concentration of 2%; the aluminum content was 94% by weight, and the lithium content was 4%. Argon gas was then mixed with the molten magnesium-lithium alloy using the bubbler and gas outlet needle of Example 2 or 3 to form a foamed aluminum-lithium alloy foam.

[0117] In other embodiments, some metal or non-metal elements for improving the performance of metal lithium or alloy can also be included in the foamed lithium alloy material of the present application, as long as the alloy contains metal lithium and MXene, and a foamed structure is formed by gas-liquid mixing, which is within the technical concept of the present application.

[0118] The foregoing description of specific exemplary embodiments of the application has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the application to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the application be limited not with this detailed description, but rather by the claims appended hereto.

Claims

1. A method for preparing a foamed lithium negative electrode, characterized in that: The foam lithium negative electrode comprises a foam lithium layer, and the steps of preparing the foam lithium layer include: Adding MXene to molten metallic lithium or lithium alloy to obtain a mixed lithium solution; Mixing the mixed lithium liquid with an inert gas to form foamed molten lithium; The foamed molten lithium is coated on a substrate and cooled and solidified to form the foamed lithium layer.

2. The preparation method according to claim 1, wherein The preparation method further comprises: after cooling and solidification, peeling the foam lithium layer from the substrate to obtain the foam lithium negative electrode; Alternatively, the substrate is a current collector, and the foamed lithium negative electrode comprises a foamed lithium layer and a current collector; preferably, the current collector is a metal foil, more preferably, a copper foil or a titanium foil.

3. The preparation method according to claim 1 or 2, wherein The gas-liquid mixing method is a bubble blowing method, which includes the following steps: introducing the inert gas into the mixed lithium liquid; Alternatively, the gas-liquid mixing method is a foaming method, comprising the steps of: in an inert gas environment, using a foaming device to mix the inert gas with the mixed lithium liquid to form a foam; preferably, the foaming device includes at least one rotating shaft, and a dispersing head is provided at one end of the rotating shaft. When in use, the dispersing head is immersed in the mixed lithium liquid, and the dispersing head is driven to rotate by the rotating shaft to achieve gas-liquid mixing of the mixed lithium liquid and the inert gas.

4. The preparation method according to any one of claims 1 to 3, characterized in that The added mass fraction of the MXene is between 1% and 45%; preferably, between 10% and 30%; more preferably, between 10% and 20%; and even more preferably, between 10% and 15%; And / or, the alloying elements in the lithium alloy are selected from one or more of Na, Mg, Al, Zn, Sn, V, In, Ag, Au, B, Si, and Ge; And / or, the MXene contains a fluorine functional group.

5. The preparation method according to any one of claims 1 to 4, wherein the step further comprises: Additives are added to the mixed lithium solution to adjust the surface tension of the mixed lithium solution; preferably, the additives are selected from one or more of transition metal sulfides, transition metal selenides, transition metal fluorides, and transition metal oxides; more preferably, the transition metal sulfide is molybdenum sulfide; And / or, the chemical formula of the MXene is M n+1 X n T x , wherein M is selected from one or more of Ti, V, Cr, Nb, Ta, W, Zr, Sc, Y, and Hf; X is selected from one or more of carbon, nitrogen, and boron, 1≤n≤4, and T x The meaning is that the surface contains functional groups; preferably, the MXene is Ti3C2T x .

6. A foamed lithium negative electrode obtained by the preparation method according to any one of claims 1 to 5; preferably, the density of the foamed lithium layer in the foamed lithium negative electrode is ≤0.3 g / cm 3 ; and / or, the porosity of the lithium foam layer is ≥50%; and / or, the pore size of the lithium foam layer is ≤1000 μm; More preferably, the density of the foam lithium layer in the foam lithium negative electrode is between 0.1 g / cm 3 to 0.3g / cm 3 ; and / or, the porosity of the lithium foam layer is between 50% and 80%; and / or, the pore size of the lithium foam layer is between 1 μm and 500 μm.

7. A battery, characterized in that: The battery contains the foamed lithium negative electrode as claimed in claim 6; preferably, the battery is a solid-state battery.

8. An electrical device or energy storage device, characterized in that: Contains the battery according to claim 7.

9. A method for preparing a foamed lithium composite material, characterized in that the steps include: Adding MXene to molten metallic lithium or lithium alloy to obtain a mixed lithium solution; The mixed lithium liquid is mixed with an inert gas to form foamed molten lithium, which is then cooled and solidified to obtain the foamed lithium composite material.

10. The preparation method according to claim 1, wherein The gas-liquid mixing method is a bubble blowing method, which includes the following steps: introducing the inert gas into the mixed lithium liquid; Alternatively, the gas-liquid mixing method is a foaming method, which includes the following steps: in an inert gas environment, through a foaming device, mixing the inert gas and the mixed lithium liquid to form a foam; preferably, the foaming device includes at least one rotating shaft, and a dispersing head is provided at one end of the rotating shaft. When in use, the dispersing head is immersed in the mixed lithium liquid, and the dispersing head is driven to rotate by the rotating shaft to achieve gas-liquid mixing of the mixed lithium liquid and the inert gas.

11. The preparation method according to any one of claims 9 or 10, characterized in that The added mass fraction of the MXene is between 1% and 45%; preferably, between 10% and 30%; more preferably, between 10% and 20%; and even more preferably, between 10% and 15%; And / or, the alloying elements in the lithium alloy are selected from one or more of Na, Mg, Al, Zn, Sn, V, In, Ag, Au, B, Si, and Ge; And / or, the step further comprises: adding an additive to the mixed lithium solution to adjust the surface tension of the mixed lithium solution; preferably, the additive is selected from one or more of transition metal sulfides, transition metal selenides, transition metal fluorides, and transition metal oxides; more preferably, the transition metal sulfide is molybdenum sulfide; and / or, the MXene contains a fluorine functional group; And / or, the chemical formula of the MXene is M n+1 X n T x , wherein M is selected from one or more of Ti, V, Cr, Nb, Ta, W, Zr, Sc, Y, and Hf; X is selected from one or more of carbon, nitrogen, and boron, 1≤n≤4, and T x The meaning is that the surface contains functional groups; preferably, the MXene is Ti3C2T x .

12. A foamed lithium composite material obtained by the preparation method according to any one of claims 9 to 11; preferably, the density of the foamed lithium composite material is ≤0.3 g / cm 3 ; and / or, the porosity of the lithium foam composite material is ≥50%; and / or, the pore size of the lithium foam composite material is ≤1000 μm; More preferably, the density of the foamed lithium composite material is between 0.1 g / cm 3 to 0.3g / cm 3 ; and / or, the porosity of the foam lithium composite material is between 50% and 80%; and / or, the pore size in the foam lithium composite material is between 1 μm and 500 μm.

13. A foam lithium composite material, characterized in that: The foam lithium composite material comprises components of MXene, metallic lithium or lithium alloy and has a foam-like pore structure.

14. The foamed lithium composite material according to claim 13, wherein: The density of the foam lithium composite material is ≤0.3g / cm 3 ; and / or, the porosity of the foamed lithium composite material is ≥50%; and / or, the pore size of the foamed lithium composite material is ≤1000μm. More preferably, the density of the foamed lithium composite material is between 0.1 g / cm 3 to 0.3g / cm 3 ; and / or, the porosity of the foam lithium composite material is between 50% and 80%; and / or, the pore size in the foam lithium composite material is between 1 μm and 500 μm.

15. The foamed lithium composite material according to claim 13 or 14, wherein: The mass fraction of the MXene is between 1% and 45%; preferably, between 10% and 30%; more preferably, between 10% and 20%; and even more preferably, between 10% and 15%; And / or, the alloying elements in the lithium alloy are selected from one or more of Na, Mg, Al, Zn, Sn, V, In, Ag, Au, B, Si, and Ge; And / or, the chemical formula of the MXene is M n+1 X n T x , wherein M is selected from one or more of Ti, V, Cr, Nb, Ta, W, Zr, Sc, Y, and Hf; X is selected from one or more of carbon, nitrogen, and boron, 1≤n≤4, and T x The meaning is that the surface contains functional groups; preferably, the MXene is Ti3C2T x .

16. Use of the foamed lithium composite material according to any one of claims 12 to 15 as a catalyst in the fields of medicine, petrochemicals, and fine chemicals, as an electrode material or lithium supplement material in lithium batteries, or for manufacturing lightweight alloys in the field of metallurgy.

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