CN112151740B - Lithium metal battery cathode, preparation method thereof and lithium metal battery - Google Patents

Lithium metal battery cathode, preparation method thereof and lithium metal battery Download PDF

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CN112151740B
CN112151740B CN201910560194.3A CN201910560194A CN112151740B CN 112151740 B CN112151740 B CN 112151740B CN 201910560194 A CN201910560194 A CN 201910560194A CN 112151740 B CN112151740 B CN 112151740B
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lithium
lto
metal battery
lithium metal
mixing
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魏子栋
甘芮弋
陈四国
李存璞
董琴
付娜
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Chongqing University
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    • HELECTRICITY
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    • HELECTRICITY
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    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
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    • H01M4/13Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
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    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/13Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/13Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139Processes of manufacture
    • H01M4/1391Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/13Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/13Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139Processes of manufacture
    • H01M4/1397Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
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    • H01M4/38Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381Alkaline or alkaline earth metals elements
    • H01M4/382Lithium
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

The invention provides a lithium metal battery cathode, a preparation method thereof and a lithium metal battery, and belongs to the field of lithium batteries. The preparation method of the lithium metal battery cathode provided by the invention comprises the following steps: mixing Ti3C2Mixing with lithium hydroxide solution to react in Ti3C2Generating lithium titanium oxide LTO on the surface to obtain LTO/Ti3C2A composite material; mixing LTO/Ti3C2Mixing the composite material and polyvinylidene fluoride, and performing ball milling to obtain mixed powder; mixing the mixed powder with N-methyl pyrrolidone to obtain slurry; coating the slurry on a current collector, and performing vacuum drying treatment to obtain LTO/Ti3C2A cathode; using lithium sheet as anode, adding LTO/Ti3C2Assembling the cathode, the lithium sheet and the electrolyte into a button battery, then carrying out electrodeposition on the button battery, and disassembling the button battery to obtain Li/LTO/Ti3C2And a negative electrode. The lithium metal battery cathode provided by the invention has no lithium dendrite growth.

Description

Lithium metal battery cathode, preparation method thereof and lithium metal battery
Technical Field
The invention relates to the field of lithium metal batteries, in particular to a lithium metal battery cathode, a preparation method thereof and a lithium metal battery.
Background
Lithium dendrite can be formed by the uneven extraction and deposition of lithium on the surface of a lithium metal negative electrode in the charging and discharging processes, and the existence of the lithium dendrite causes the following problems of the lithium metal battery: (1) lithium dendrites which grow violently on the surface of the negative electrode are likely to pierce through the diaphragm to contact with a positive electrode material of the battery, so that electronic contact between the positive electrode and the negative electrode is caused, and a battery short circuit is formed; such short circuits are often accompanied by thermal runaway of the battery and can cause flammable electrolyte to catch fire and even the battery to explode; (2) the growth of lithium dendrites damages a fragile Solid Electrolyte Interface (SEI) film on the surface of the negative electrode, so that more lithium is exposed to the electrolyte and a new SEI film is formed; moreover, the dendritic morphology of the lithium dendrites enables the contact area of the metal lithium and the electrolyte to be increased rapidly, side reactions at the interface of the metal lithium and the electrolyte are aggravated, the side reactions irreversibly consume the metal lithium and the electrolyte but have no actual discharge capacity, so that the coulombic efficiency and the capacity of the battery are reduced, and irreversible loss is brought to a lithium metal cathode; (3) repeated disruptive re-establishment of the unstable interface between the lithium negative electrode and the electrolyte during charging and discharging is highly susceptible to the formation of "dead lithium" which can severely impede the transport paths for lithium ions and electrons in the negative electrode, leading to severe polarization and lower energy efficiency.
The safety problems caused by lithium dendrites make it difficult to implement lithium metal secondary batteries for large-scale commercial applications. Therefore, the growth of lithium dendrites is inhibited, and the method has important significance for lithium metal batteries.
Disclosure of Invention
The invention provides a lithium metal battery cathode, a preparation method thereof and a lithium metal battery.
The invention provides a preparation method of a lithium metal battery cathode, which comprises the following steps:
(1) mixing Ti3C2Mixing with lithium hydroxide aqueous solution for reaction to obtain LTO/Ti3C2A composite material;
(2) the LTO/Ti obtained in the step (1) is3C2Mixing the composite material and polyvinylidene fluoride, and performing ball milling to obtain mixed powder;
(3) mixing the mixed powder obtained in the step (2) with N-methyl pyrrolidone to obtain slurry;
(4) coating the slurry obtained in the step (3) on a current collector, and then carrying out vacuum drying treatment to obtain LTO/Ti3C2A cathode;
(5) taking a lithium sheet as an anode, and adding the LTO/Ti obtained in the step (4)3C2Assembling the cathode, the lithium sheet and the electrolyte into a button battery, then carrying out electrodeposition on the button battery, and disassembling the button battery to obtain Li/LTO/Ti3C2And a negative electrode.
Preferably, Ti in said step (1)3C2The mass ratio of the lithium hydroxide aqueous solution to the lithium hydroxide aqueous solution is 10-1000 m g: 10-1000 mL, and the concentration of the lithium hydroxide aqueous solution is 1-10 mol.L-1
Preferably, LTO/Ti in said step (2)3C2The mass ratio of the composite material to the polyvinylidene fluoride is 1-9: 1, and the rotating speed of the ball milling is 200-800 rmp.
Preferably, the concentration of the mixed powder in the slurry in the step (3) is 0.1-2 mg/mL-1
Preferably, the thickness of the coating layer of the slurry in the step (4) on the current collector is 100-1000 μm.
Preferably, the temperature of the heating treatment in the step (4) is 40-100 ℃, and the time is 5-24 hours.
Preferably, the electrolyte in the step (5) is a lithium bis (trifluoromethyl) sulfonate imide solution, and the solvent of the lithium bis (trifluoromethyl) sulfonate imide solution is a mixed solution of 1, 3-dioxolane, ethylene glycol dimethyl ether and lithium nitrate; the volume ratio of the 1, 3-dioxolane to the glycol dimethyl ether in the solvent is 1: 0.5-2; the mass fraction of lithium nitrate in the solvent is 0.1-5%.
Preferably, the current for electrodeposition in the step (5) comprises direct current or pulse current; when direct current is adopted, the current density is 0.1-10 mA-cm-2The duty cycle is 100%; when pulse current is adopted, the current density is 0.1-10 mA-cm-2The pulse frequency is 20-5000 Hz, the duty ratio is 20-100%,duty cycle does not include 100%; the time of the electrodeposition is 0.5-24 h.
The invention also provides the lithium metal battery cathode prepared by the method in the technical scheme, and the lithium metal battery cathode is prepared from Li, LTO and Ti3C2The LTO is lithium titanium oxide, and grows in two-dimensional layered Ti3C2The Li is deposited on the Ti surface by taking LTO as a seed crystal3C2Surface and interlayer.
The invention also provides a lithium metal battery, and the lithium metal battery cathode is the lithium metal battery cathode prepared by the method in the technical scheme or the lithium metal battery cathode in the technical scheme.
The invention provides a preparation method of a lithium metal battery cathode, which comprises the following steps: mixing Ti3C2Mixing with lithium hydroxide aqueous solution for reaction to obtain LTO/Ti3C2A composite material; mixing LTO/Ti3C2Mixing the composite material and polyvinylidene fluoride, and performing ball milling to obtain mixed powder; mixing the mixed powder with N-methyl pyrrolidone to obtain slurry; coating the slurry on a current collector, and then carrying out vacuum drying treatment to obtain LTO/Ti3C2A cathode; using lithium sheet as anode, adding LTO/Ti3C2Assembling the cathode, the lithium sheet and the electrolyte into a button battery, then carrying out electrodeposition on the button battery, and disassembling the button battery to obtain Li/LTO/Ti3C2And a negative electrode. In the present invention, Ti of the lamellar layer3C2Provides an interlayer framework for the intercalation and deintercalation of lithium ions, and Ti is arranged in the framework3C2The LTO on the surface of the layer can also induce lithium ions to be uniformly deposited, so that the lithium ions and electrons are uniformly distributed, a uniform additional electric field is formed, the growth of lithium dendrites and the formation of dead lithium are favorably inhibited, and the lithium metal battery cathode with high lithium utilization rate, stability, safety and long service life is obtained. The embodiment result shows that the lithium metal battery cathode provided by the invention has no lithium dendrite growth, so that the lithium metal battery cathode platform provided by the invention has the advantages of small and stable voltage difference, stable charge and discharge platform, high specific capacity, and deposition and lithium removal processesThe platform voltage difference is small and the coulombic efficiency is high.
Drawings
FIG. 1 shows Li/LTO/Ti as negative electrodes of lithium metal batteries prepared in example 1 of the present invention3C2Scanning electron microscopy images of (a);
FIG. 2 is a scanning electron microscope photograph of a Li/copper foil prepared in comparative example 1 of the present invention;
FIG. 3 is a graph of charge-discharge cycle voltage of 0-600 h for lithium-lithium symmetric batteries with negative electrodes prepared in example 1 and comparative example 1 of the present invention;
FIG. 4 is a graph of charge-discharge cycle voltage of 0-30 h for lithium-lithium symmetric batteries with negative electrodes prepared in example 1 and comparative example 1 of the present invention;
FIG. 5 is a graph of the cycling performance at 0.2C current density for half-cells assembled according to example 2 of the present invention and comparative example 2;
FIG. 6 is a constant current charge and discharge curve diagram of a half cell assembled according to example 2 and comparative example 2 of the present invention at a current density of 0.2C;
FIG. 7 shows the results of example 3 and comparative example 3 at 1mA cm-2Electrodeposition/delithiation curves at current density for the first and tenth weeks;
FIG. 8 shows the results of example 3 and comparative example 3 at 1mA cm-2The plateau voltage difference of electrodeposition and delithiation for ten weeks at current density;
FIG. 9 shows the results of example 3 and comparative example 3 at 1mA cm-2Coulombic efficiencies of electrodeposition and delithiation for ten weeks at current density.
Detailed Description
The invention provides a preparation method of a lithium metal battery cathode, which comprises the following steps:
(1) mixing Ti3C2Mixing with lithium hydroxide aqueous solution for reaction to obtain LTO/Ti3C2A composite material;
(2) the LTO/Ti obtained in the step (1) is3C2Mixing the composite material and polyvinylidene fluoride, and performing ball milling to obtain mixed powder;
(3) mixing the mixed powder obtained in the step (2) with N-methyl pyrrolidone to obtain slurry;
(4) coating the slurry obtained in the step (3) on a current collector, and then carrying out vacuum drying treatment to obtain LTO/Ti3C2A cathode;
(5) taking a lithium sheet as an anode, and adding the LTO/Ti obtained in the step (4)3C2Assembling the cathode, the lithium sheet and the electrolyte into a button battery, then carrying out electrodeposition on the button battery, and disassembling the button battery to obtain Li/LTO/Ti3C2And a negative electrode.
The invention is to mix Ti3C2Mixing with lithium hydroxide aqueous solution for reaction to obtain LTO/Ti3C2A composite material.
In the present invention, the Ti is3C2The production method of (2) preferably comprises: ti with hydrofluoric acid3AlC2Or Ti3SiC2Etching is carried out to obtain Ti3C2. In the present invention, Ti is preferably used3AlC2Or Ti3SiC2Mixing with hydrofluoric acid, wherein the mass fraction of the hydrofluoric acid is 40%; the Ti3AlC2Or Ti3SiC2The amount ratio of hydrofluoric acid to hydrofluoric acid is preferably 1-10 g: 10-100 mL, more preferably 1-5 g: 20-80 mL, and even more preferably 1g:40 mL. In the invention, the mixing is preferably stirring mixing, the mixing temperature is preferably room temperature, and the mixing time is preferably 12-48 h, more preferably 15-35 h, and even more preferably 24 h. The invention adopts hydrofluoric acid to Ti3AlC2Or Ti3SiC2Performing treatment to etch off Ti with hydrofluoric acid3AlC2Or Ti3SiC2Aluminum element or silicon element in the titanium alloy to obtain Ti3C2. According to the invention, preferably, after hydrofluoric acid treatment is finished, the obtained product is sequentially washed and dried to remove residual hydrofluoric acid; the washing is preferably carried out with ethanol and water in this order. In the present invention, the Ti is3C2Is a two-dimensional layered material.
To obtain Ti3C2Then, the invention mixes Ti3C2And an aqueous lithium hydroxide solution, the Ti3C2Quality and lithium hydroxideThe volume ratio of the aqueous solution is preferably 10-1000 mg: 10-1000 mL, more preferably 100-800 mg: 100-800 mL, and even more preferably 200-600 mg: 200-600 mL; the concentration of the lithium hydroxide aqueous solution is preferably 1-10 mol.L-1More preferably 2 to 8 mol.L-1More preferably 4 to 6 mol.L-1. In the invention, the mixing mode is preferably stirring mixing, and the stirring mixing time is preferably 90-500 h, more preferably 100-400 h, and even more preferably 200-300 h. The invention is to mix Ti3C2Mixing with an aqueous solution of lithium hydroxide, Ti3C2The surface molecules react with lithium hydroxide to form Lithium Titanium Oxide (LTO), which adheres to Ti3C2Surface to obtain LTO/Ti3C2A composite material. In the present invention, Ti is preferable3C2After the lithium hydroxide aqueous solution is mixed, the mixed material liquid is centrifuged and dried to obtain LTO/Ti3C2A composite material.
Obtaining LTO/Ti3C2After the composite material is compounded, LTO/Ti is mixed in the invention3C2And mixing the composite material and polyvinylidene fluoride, and performing ball milling to obtain mixed powder. In the present invention, the LTO/Ti3C2The mass ratio of the composite material to the polyvinylidene fluoride is preferably 1-9: 1, more preferably 2-8: 1, and even more preferably 4-6: 1. In the invention, the rotation speed of the ball mill is preferably 200-800 rmp, and more preferably 400-600 rmp; the ball milling time is preferably 0.1-2 h, and more preferably 0.5-1.5 h.
After the mixed powder is obtained, the mixed powder and the N-methyl pyrrolidone are mixed to obtain slurry. In the present invention, the concentration of the mixed powder in the slurry is preferably 0.1 to 2 mg/mL-1More preferably 0.5 to 1.5 mg/mL-1
After obtaining the slurry, the invention coats the slurry on a current collector, and then carries out vacuum drying treatment to obtain LTO/Ti3C2And a cathode. In the present invention, the current collector is preferably a copper foil; the thickness of the coating layer of the slurry on the current collector is preferably 100-1000 mu m, and more preferably 200-800 mu mμ m, more preferably 400 to 600 μm; the coating is preferably carried out by adopting an I-shaped scraper with the thickness of 100-1000 mu m. After coating, the current collector coated with the slurry is subjected to vacuum drying treatment, wherein the temperature of the vacuum drying treatment is preferably 40-100 ℃, more preferably 60-80 ℃, and the time is preferably 5-24 hours, more preferably 10-20 hours, and more preferably 13-17 hours. In the vacuum drying process, N-methyl pyrrolidone is volatilized, and LTO/Ti is converted by polyvinylidene fluoride3C2Bonding the composite material and the collector to obtain LTO/Ti3C2And a cathode. The LTO/Ti to be obtained is preferred in the present invention3C2The cathode was cut into 12mm diameter disks for subsequent use.
Obtaining LTO/Ti3C2After the cathode, the invention takes a lithium sheet as an anode, and the LTO/Ti is put into the anode3C2Assembling the cathode, the lithium sheet and the electrolyte into a button battery, then carrying out electrodeposition on the button battery, and disassembling the button battery to obtain Li/LTO/Ti3C2And a negative electrode. The present invention does not require any particular embodiment for assembling the button cell, and can be implemented by methods known to those skilled in the art. In the invention, the electrolyte is preferably a lithium bis (trifluoromethyl) sulfonate imide solution, and the concentration of the lithium bis (trifluoromethyl) sulfonate imide solution is preferably 0.1-5 mol/L, more preferably 0.5-4 mol/L, and more preferably 1-2 mol/L; the solvent of the lithium bis (trifluoromethyl) sulfonate imide solution is a mixed solution of 1, 3-dioxolane, ethylene glycol dimethyl ether and lithium nitrate; the volume ratio of the 1, 3-dioxolane to the ethylene glycol dimethyl ether in the solvent is preferably 1: 0.5-2, and more preferably 1: 1; the mass fraction of lithium nitrate in the solvent is preferably 0.1% to 5%, and more preferably 1%.
In the present invention, the current for electrodeposition preferably includes a direct current or a pulse current. In the present invention, when the current for electrodeposition is preferably a direct current, the current density is preferably 0.1 to 10mA cm-2More preferably 1 to 9mA cm-2More preferably 2 to 8mA · cm-2(ii) a The duty cycle is preferably 100%. In the present invention, when electrodeposition is carried outWhen the current is preferably pulse current, the current density is preferably 0.1-10 mA-cm-2More preferably 1 to 9mA cm-2More preferably 2 to 8mA · cm-2(ii) a The pulse frequency of the pulse current is preferably 20 to 5000Hz, more preferably 100 to 500 Hz, and still more preferably 100-200 Hz; the duty ratio of the pulse current is preferably 20-100%, and the duty ratio does not include 100%, more preferably 20-99%, even more preferably 40-80%, and most preferably 50-70%. In the invention, regardless of the electrodeposition is carried out by using direct current or pulse current, the electrodeposition time is independently preferably 0.5 to 24 hours, more preferably 1 to 20 hours, and even more preferably 5 to 15 hours. The invention preferably controls the parameters of the electrodeposition treatment within the above range, which is beneficial to uniformly depositing Li on LTO/Ti3C2And the cathode surface inhibits the growth of lithium dendrites and the formation of dead lithium.
After the electrodeposition is finished, the button cell is preferably disassembled in a glove box, and the button cell is dried in a transfer bin of the glove box in vacuum at room temperature to obtain Li/LTO/Ti3C2And a negative electrode.
The invention also provides the lithium metal battery cathode prepared by the method in the technical scheme, and the lithium metal battery cathode is prepared from Li, LTO and Ti3C2The LTO is lithium titanium oxide, and grows in two-dimensional layered Ti3C2The Li is deposited on the Ti surface by taking LTO as a seed crystal3C2Surface and interlayer.
The invention also provides a lithium metal battery, and the lithium metal battery cathode is the lithium metal battery cathode prepared by the method in the technical scheme or the lithium metal battery cathode in the technical scheme. The present invention does not particularly require other components in the lithium metal battery, and components well known to those skilled in the art may be used.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.
Example 1
(1)、LTO/Ti3C2Of composite materialsPreparation of
Separately, 1g of commercially available Ti was added to a polytetrafluoroethylene beaker3AlC2Powder and 40mL of hydrofluoric acid with the mass fraction of 40% sold in the market are stirred and reacted for 24 hours at room temperature, and then are centrifugally washed and dried by ethanol and water respectively to obtain Ti3C2(ii) a Mixing Ti3C2Adding the mixture to a concentration of 1 mol.L-1Stirring and reacting the lithium hydroxide aqueous solution for 90 hours at room temperature; then centrifugally washing the mixture obtained by the reaction for a plurality of times, and drying to obtain LTO/Ti3C2A composite material.
(2)、LTO/Ti3C2Preparation of the cathode
Polyvinylidene fluoride and LTO/Ti prepared in the step (1)3C2Mixing the composite materials according to the mass ratio of 1:9, and then carrying out ball milling for 1h under the condition of 500rmp to obtain mixed powder; using N-methyl pyrrolidone as solvent, and preparing the mixed powder into the powder with the concentration of 1 mg/mL-1The slurry of (a); uniformly coating the slurry on a copper foil by using an I-shaped scraper with the thickness of 500 mu m, finally treating for 12h at 60 ℃ under a vacuum condition, and cutting into a wafer with the diameter of 12mm to obtain LTO/Ti3C2And a cathode.
(3)Li/LTO/Ti3C2Preparation of the negative electrode
Taking a lithium sheet as an anode, and using the LTO/Ti obtained in the step (2)3C2The cathode, the lithium sheet and 60 mu L of electrolyte are assembled into a button cell for electrodeposition, and the electrodeposition current density is 1mA cm-2The duty ratio is 100 percent (namely direct current), the electrodeposition time is 4 hours, and the electrolyte is 1 mol.L-1Lithium bis (trifluoromethyl) sulfonate imide solution, wherein the solvent of the electrolyte is 1, 3-dioxolane and glycol dimethyl ether in a volume ratio of 1:1, and 1% by mass of lithium nitrate is added into the solvent; after electrodeposition, the battery is disassembled in a glove box, and vacuum drying is carried out for 5 hours at room temperature in a transfer bin of the glove box to obtain Li/LTO/Ti without dendritic crystal growth3C2And a negative electrode.
For Li/LTO/Ti prepared in example 13C2The negative electrode was subjected to a scanning electron microscope test, and the results are shown in FIG. 1. As can be seen from FIG. 1, Li/LTO/Ti3C2The surface forms a flat plate structure without generating lithium dendrites.
Example 2
(1)、LTO/Ti3C2Preparation of composite materials
Separately, 1g of commercially available Ti was added to a polytetrafluoroethylene beaker3AlC2Stirring the powder and 40mL of commercial hydrofluoric acid at room temperature for 24h, and then respectively centrifugally washing and drying the powder by using ethanol and water to obtain Ti3C2(ii) a Mixing Ti3C2Adding the mixture to a concentration of 5 mol.L-1Stirring and reacting the lithium hydroxide aqueous solution for 500 hours at room temperature; then centrifugally washing the mixture obtained by the reaction for a plurality of times, and drying to obtain LTO/Ti3C2A composite material.
(2)、LTO/Ti3C2Preparation of the cathode
Polyvinylidene fluoride and LTO/Ti prepared in the step (1)3C2Mixing the composite materials according to the mass ratio of 1:7, and then carrying out ball milling for 0.5h under the condition of 800rmp to obtain mixed powder; using N-methyl pyrrolidone as solvent, and preparing the mixed powder into 0.5 mg/mL-1The slurry of (a); uniformly coating the slurry on a copper foil by using an I-shaped scraper with the thickness of 200 mu m, finally processing for 6h at 80 ℃ under the vacuum condition, and cutting into a circular sheet with the diameter of 12mm to obtain LTO/Ti3C2And a cathode.
(3)Li/LTO/Ti3C2Preparation of the negative electrode
Taking a lithium sheet as an anode, and adding the LTO/Ti obtained in the step (2)3C2The cathode, the lithium sheet and 80 mu L of electrolyte are assembled into a button cell for electrodeposition, and the electrodeposition current density is 0.1 mA-cm-2The pulse frequency is 200 Hz, the duty ratio is 80 percent, the electrodeposition time is 12h, and the electrolyte is 1 mol.L-1Lithium bis (trifluoromethyl) sulfonate imide solution, wherein the solvent of the electrolyte is 1, 3-dioxolane and glycol dimethyl ether in a volume ratio of 1:1, and 1% by mass of lithium nitrate is added into the solvent; after electrodeposition, the battery is disassembled in a glove box, and vacuum drying is carried out for 5 hours at room temperature in a transfer bin of the glove box to obtain Li/LTO/Ti without dendritic crystal growth3C2And a negative electrode.
Example 3
(1)、LTO/Ti3C2Preparation of composite materials
Separately, 1g of commercially available Ti was added to a polytetrafluoroethylene beaker3SiC2Stirring the powder and 40mL of commercial hydrofluoric acid at room temperature for 24h, and then respectively centrifugally washing and drying the powder by using ethanol and water to obtain Ti3C2(ii) a Mixing Ti3C2Adding the mixture to a concentration of 5 mol.L-1Stirring and reacting the lithium hydroxide aqueous solution for 500 hours at room temperature; then centrifugally washing the mixture obtained by the reaction for a plurality of times, and drying to obtain LTO/Ti3C2A composite material.
(2)、LTO/Ti3C2Preparation of the cathode
Polyvinylidene fluoride and LTO/Ti prepared in the step (1)3C2Mixing the composite materials according to the mass ratio of 1:1, and then carrying out ball milling for 0.1h under the condition of 200rmp to obtain mixed powder; using N-methyl pyrrolidone as solvent, and preparing the mixed powder into the solution with the concentration of 0.1 mg/mL-1The slurry of (a); uniformly coating the slurry on a copper foil by using an I-shaped scraper with the thickness of 1000 mu m, finally processing for 24h at 50 ℃ under the vacuum condition, and cutting into a wafer with the diameter of 12mm to obtain LTO/Ti3C2And a cathode.
(3)Li/LTO/Ti3C2Preparation of the negative electrode
Taking a lithium sheet as an anode, and adding the LTO/Ti prepared in the step (2)3C2The cathode, the lithium sheet and 100 mu L of electrolyte are assembled into a button cell for electrodeposition, and the electrodeposition current density is 10mA cm-2The duty ratio is 100 percent (namely direct current), the electrodeposition time is 0.5h, and the electrolyte is 1 mol.L-1Lithium bis (trifluoromethyl) sulfonate imide solution, wherein the solvent of the electrolyte is 1, 3-dioxolane and glycol dimethyl ether in a volume ratio of 1:1, and 1% by mass of lithium nitrate is added into the solvent; after electrodeposition, the battery is disassembled in a glove box, and vacuum drying is carried out for 5 hours at room temperature in a transfer bin of the glove box to obtain Li/LTO/Ti without dendritic crystal growth3C2And a negative electrode.
Comparative example 1
Li/copper foil negative electrode
Preparation of Li/copper foil negative electrode: copper foil is used as a cathode, a lithium sheet is used as an anode, 60 mu L of electrolyte is added to assemble a button cell for electrodeposition, and the electrodeposition current density is 1 mA-cm-2And the electrodeposition time is 4h, and the Li/copper foil negative electrode is obtained.
The Li/copper foil negative electrode prepared in comparative example 1 was subjected to a scanning electron microscope test, and the test results are shown in fig. 2. As can be seen from fig. 2, lithium is electrodeposited on a smooth copper foil surface to form lithium dendrites.
Comparative example 2
Li/Ti3C2Negative electrode
Li/Ti3C2Preparation of a negative electrode: polyvinylidene fluoride and Ti3C2TxMixing according to the mass ratio of 1:7, and then carrying out ball milling for 0.5h under the condition of 800rmp to obtain mixed powder; using N-methyl pyrrolidone as solvent, and preparing the mixed powder into 0.5 mg/mL-1The slurry of (a); uniformly coating the slurry on a copper foil by using an I-shaped scraper with the thickness of 200 mu m, finally treating for 6h at 80 ℃ under a vacuum condition, and cutting into a wafer with the diameter of 12mm to obtain Ti3C2A cathode; then, a lithium sheet is taken as an anode, 80 mu L of electrolyte is added to assemble a button cell for electrodeposition, and the electrodeposition current density is 0.1 mA-cm-2The electrodeposition time is 12 hours; disassembling the battery in a glove box after electrodeposition, and carrying out vacuum drying for 5h at room temperature in a transfer bin of the glove box to obtain Li/Ti3C2And a negative electrode.
Comparative example 3
Li/LTO negative electrode
Preparation of Li/LTO negative electrode: mixing polyvinylidene fluoride and commercially available lithium titanate according to the mass ratio of 1:1, and then carrying out ball milling for 0.1h under the condition of 200rmp to obtain mixed powder; using N-methyl pyrrolidone as solvent, and preparing the mixed powder into the solution with the concentration of 0.1 mg/mL-1The slurry of (a); uniformly coating the slurry on a copper foil by using an I-shaped scraper with the thickness of 1000 mu m, finally treating for 24 hours at 50 ℃ under a vacuum condition, and cutting into a wafer with the diameter of 12mm to obtain a Li/LTO cathode; then, lithium plate is used as anode, 10 is added0 mu L of electrolyte is assembled into a button cell for electrodeposition, and the electrodeposition current density is 10mA cm-2The electrodeposition time is 0.5 h; and (4) disassembling the battery in a glove box after electrodeposition to obtain the Li/LTO negative electrode.
Electrochemical performance test
Symmetric battery cycle performance test
For Li/LTO/Ti prepared in example 13C2The Li/copper foil negative electrode prepared in the comparative example 1 and the negative electrode were subjected to lithium-lithium symmetric battery cycle test respectively with a tester model CT2001A from Wuhan blue electric company and a test current of 1mA cm-2The test period is 2h, and the test result is shown in fig. 3. As can be seen from fig. 3, the plateau voltage difference of the Li/copper foil symmetrical battery is increasing due to the high charge transfer resistance between the lithium electrode and the electrolyte and the growing lithium dendrites; when the test was run for 200h, the voltage dropped suddenly, which is a short circuit caused by lithium dendrites; and Li/LTO/Ti3C2The symmetrical cell has a smaller and more stable plateau voltage difference, and no short circuit occurs after 600h of cycling.
FIG. 4 is an enlarged view of the first 30h of FIG. 3. from FIG. 4, it can be seen that the voltage for lithium deposition by the copper foil is significantly greater than the de-lithiation voltage because Li/copper foil has grown lithium dendrites during the initial lithium deposition process, and Li/LTO/Ti3C2The voltage for depositing and delithiating of lithium is always symmetrically stable.
Half-cell constant current charge-discharge test
Li/LTO/Ti prepared in example 23C2And Li/Ti prepared in comparative example 23C2Respectively react with LiFePO4Half cells were assembled and subjected to cycle performance test at a current density of 0.2C, and the test results are shown in fig. 5.
The assembly method of the half cell comprises the following steps: polyvinylidene fluoride, acetylene black and LiFePO4Mixing and ball-milling according to the mass ratio of 1:1:8 to obtain mixed powder; using N-methyl pyrrolidone as solvent, and preparing the mixed powder into the powder with the concentration of 1 mg/mL-1The slurry is evenly coated on an aluminum foil, dried and cut into round pieces with the diameter of 12mm for standby(ii) a The anodes prepared in example 2 and comparative example 2 were respectively put in a glove box under argon atmosphere with the above-mentioned LiFePO4The positive electrode is assembled into a half cell, and the electrolyte is as follows: 1 mol. L-1The lithium bis (trifluoromethyl) sulfonate imide electrolyte is prepared by assembling a 2032 type button cell by using 1, 3-dioxolane and ethylene glycol dimethyl ether as solvents of electrolyte in a volume ratio of 1:1, adding 1 mass percent of lithium nitrate into the solvents and using a Celegard2400 type polypropylene membrane as a diaphragm.
As can be seen from FIG. 5, Li/Ti3C2The charging and discharging specific capacity of the alloy shows obvious fluctuation, and Li/LTO/Ti3C2The charging and discharging specific capacity of the lithium ion battery is stably maintained at 140 mAh.g-1In the above, Li/LTO/Ti is explained3C2The negative electrode does not form lithium dendrite, and can be safely charged and discharged.
For Li/LTO/Ti prepared in example 23C2And Li/Ti prepared in comparative example 23C2Respectively react with LiFePO4The half-cells were assembled and tested for constant current charge and discharge performance at 0.2C current density for 10 weeks of half-cell cycling. The constant current charge and discharge test is carried out on a CT2001A type tester of Wuhan blue-electricity company, the test voltage window is 2.5-3.8V, the test current density is 0.2C, wherein 1C is 170 mAh.g-1. The results of the tests are shown in FIG. 6, and it can be seen from FIG. 6 that Li/Ti was added in the tenth week3C2Both the charge and discharge curves of (A) are suddenly reduced, which is caused by a short circuit due to the growth of lithium dendrites, while Li/LTO/Ti3C2The charging and discharging platform is stable, and the specific capacity is 143.7 mAh.g-1The specific capacity is far greater than Li/Ti3C2The result shows that the cathode provided by the invention has no lithium dendrite growth and higher specific capacity.
Electrodeposition/delithiation test
For Li/LTO/Ti prepared in example 33C2The negative electrode and the Li/LTO negative electrode prepared in comparative example 3 were subjected to an electrodeposition/delithiation test using a CT2001A model test instrument manufactured by Wuhan blue electric company and a test current of 1mA cm-2The electrodeposition time was 1h, and the delithiation termination voltage was 0.5V. The test results are shown in fig. 7, 8 and 9. Wherein FIG. 7 shows the first week and tenth week of lithium deposition and delithiationWeekly electrodeposition/delithiation curves; FIG. 8 is a plateau voltage difference for ten weeks of lithium deposition and delithiation; fig. 9 is the coulombic efficiency for ten weeks of lithium deposition and delithiation.
As can be seen from FIG. 7, the plateau voltage difference during the first week of deposition and delithiation of Li/LTO reached 609mV, while Li/LTO/Ti3C2And only 177.9mV shows that the surface polarization of the Li/LTO electrode is serious and the charge distribution is not uniform.
As can be seen from FIG. 8, Li/LTO/Ti3C2The voltage difference of the deposition and lithium removal processes in ten periods gradually decreases to be close to zero, and each period of Li/LTO is larger than Li/LTO/Ti3C2And the tendency of the surface polarization of the Li/LTO electrode is larger, which indicates that the surface polarization of the Li/LTO electrode is more serious, the charge distribution is not uniform, and lithium dendrites have grown.
As can be seen from FIG. 9, Li/LTO/Ti3C2The coulombic efficiency of (A) is also more stable and close to 95%, because of Li/LTO/Ti3C2The electrode can form a more stable SEI film, a more flat and dendrite-free lithium deposition surface, and reversible lithium deposition and delithiation processes.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (10)

1. A preparation method of a lithium metal battery negative electrode comprises the following steps:
(1) mixing Ti3C2Mixing with lithium hydroxide aqueous solution for reaction to obtain LTO/Ti3C2A composite material;
(2) the LTO/Ti obtained in the step (1) is3C2Mixing the composite material and polyvinylidene fluoride, and performing ball milling to obtain mixed powder;
(3) mixing the mixed powder obtained in the step (2) with N-methyl pyrrolidone to obtain slurry;
(4) coating the slurry obtained in the step (3) on a current collector, and then carrying out vacuum dryingDrying to obtain LTO/Ti3C2A cathode;
(5) taking a lithium sheet as an anode, and adding the LTO/Ti obtained in the step (4)3C2Assembling the cathode, the lithium sheet and the electrolyte into a button battery, then carrying out electrodeposition on the button battery, and disassembling the button battery to obtain Li/LTO/Ti3C2And a negative electrode.
2. The method according to claim 1, wherein Ti in the step (1) is used3C2The ratio of the mass of the lithium hydroxide to the volume of the lithium hydroxide aqueous solution is 10-1000 mg: 10-1000 mL, and the concentration of the lithium hydroxide aqueous solution is 1-10 mol.L-1
3. The method according to claim 1, wherein LTO/Ti in the step (2)3C2The mass ratio of the composite material to the polyvinylidene fluoride is 1-9: 1, and the rotation speed of the ball milling is 200-800 rpm.
4. The method according to claim 1, wherein the concentration of the mixed powder in the slurry of step (3) is 0.1 to 2 mg-mL-1
5. The preparation method according to claim 1, wherein the thickness of the coating layer of the slurry in the step (4) on the current collector is 100-1000 μm.
6. The preparation method according to claim 1 or 5, wherein the temperature of the vacuum drying treatment in the step (4) is 40-100 ℃ and the time is 5-24 h.
7. The preparation method according to claim 1, wherein the electrolyte in the step (5) is a lithium bis (trifluoromethyl) sulfonate imide solution, and the solvent of the lithium bis (trifluoromethyl) sulfonate imide solution is a mixed solution of 1, 3-dioxolane, ethylene glycol dimethyl ether and lithium nitrate; the volume ratio of the 1, 3-dioxolane to the glycol dimethyl ether in the solvent is 1: 0.5-2; the mass fraction of lithium nitrate in the solvent is 0.1-5%.
8. The production method according to claim 1 or 7, wherein the electric current for electrodeposition in the step (5) includes a direct current or a pulse current; when the direct current is adopted for electrodeposition, the current density is 0.1-10 mA-cm-2The duty ratio is 100%; when pulse current is adopted for electrodeposition, the current density is 0.1-10 mA-cm-2The pulse frequency is 20-5000 Hz, the duty ratio is 20-100%, and the duty ratio does not include 100%; the time of the electrodeposition is 0.5-24 h.
9. The negative electrode of the lithium metal battery prepared by the method of any one of claims 1 to 8, wherein the negative electrode of the lithium metal battery is made of Li, LTO and Ti3C2The LTO is lithium titanium oxide, and grows in two-dimensional layered Ti3C2The Li is deposited on the Ti surface by taking LTO as a seed crystal3C2Surface and interlayer.
10. A lithium metal battery, characterized in that the lithium metal battery negative electrode is the lithium metal battery negative electrode prepared by the method of any one of claims 1 to 8 or the lithium metal battery negative electrode of claim 9.
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