CN108807916B - Application of carbon nanotube film in lithium ion battery cathode, symmetric battery, half battery and preparation method - Google Patents

Abstract

The invention provides an application of a carbon nanotube film in a lithium ion battery cathode, belonging to the field of lithium ion batteries. In the invention, the carbon nanotube film is in contact with the lithium sheet. The invention introduces the carbon nanotube film as an interlayer to realize the lithium metal cathode with long service life and no dendrite, and the prepared electrode has ultra-long cycle stability and high capacity retention rate at 1mA/cm²Current density of 1mAh/cm²Can stably circulate for 1000 hours under the capacity limit, and is more than 10 times of pure Li metal. At 3mA/cm²、5mA/cm²The stability of the CNT film under high current density is far higher than that of pure Li metal, and the application design of the CNT film in the lithium ion battery cathode provides a new way for future high energy density Li metal batteries.

Description

Application of carbon nanotube film in lithium ion battery cathode, symmetric battery, half battery and preparation method

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to application of a carbon nanotube film in a lithium ion battery cathode, a symmetric battery, a half battery and a preparation method.

Background

Lithium metal (Li) batteries have been widely used in portable electronic devices, electric vehicles, and large energy storage stations for the past several decades. The next generation of lithium-based batteries, such as Li-S, Li-air and solid-state lithium batteries, have received much attention. Lithium metal is considered as one of the most promising negative electrode material candidates for the next generation of lithium metal batteries because of its high specific capacity, low potential and light weight. However, lithium metal is easy to form lithium dendrite during electrochemical plating/stripping, the cycle life is reduced, the potential safety hazard is increased, and the further application in commercial batteries is not facilitated, and the following three main challenges are provided: (1) li dendrite growth during electrochemical plating/stripping; (2) an unstable solid electrolyte interface layer is formed between the Li metal and the organic electrolyte; (3) infinite volume variation of Li metal electrodes.

At present, researchers have used carbon nanotube films as interlayers between the positive plate and the diaphragm of the Li-S battery to inhibit the dissolution and diffusion of polysulfides, prevent shuttling effects, and improve the capacity and cycle performance of the lithium-sulfur battery. But there is no report on the use of carbon nanotube films in the negative electrodes of lithium ion batteries.

Disclosure of Invention

In view of this, the present invention provides an application of a carbon nanotube film in a negative electrode of a lithium ion battery, a symmetric battery, a half-cell and a preparation method thereof. The carbon nanotube film is applied to the negative electrode of the lithium ion battery, so that the growth of lithium dendrites is inhibited, and the cycle service life of the negative electrode of the lithium ion battery is prolonged.

In order to achieve the above object, the present invention provides the following technical solutions:

the carbon nanotube film is applied to the cathode of the lithium ion battery, and the carbon nanotube film is in contact with a lithium sheet.

The invention also provides a symmetrical battery which sequentially comprises a negative battery shell, an elastic sheet, a gasket, a first lithium sheet, a first CNT film, a Celgard film, an electrolyte, a second CNT film, a second lithium sheet and a positive battery shell, wherein the areas of the first lithium sheet and the first CNT film are the same, and the areas of the second lithium sheet and the second CNT film are the same.

Preferably, the first CNT thin film and the second CNT thin film independently have an areal density of 1.5 to 2mg/cm²The thickness is 40 to 50 μm independently.

Preferably, the electrolyte comprises LiTFSI and an organic solvent, the organic solvent is a mixed solution of 1, 3-dioxolane and ethylene glycol dimethyl ether, and the concentration of the LiTFSI in the electrolyte is 1 mol/L.

The invention also provides a preparation method of the symmetrical battery in the technical scheme, which comprises the following steps:

and in the glove box, assembling the negative electrode battery shell, the elastic sheet, the gasket, the first lithium sheet, the first CNT film, the Celgard film, the electrolyte, the second CNT film, the second lithium sheet and the positive electrode battery shell in sequence to obtain the symmetrical battery.

The invention also provides a half cell, which sequentially comprises a negative electrode cell shell, a lithium sheet, a CNT film, a Celgard film, an electrolyte and LiFePO₄Electrode slice and positive battery shell.

Preferably, the surface density of the CNT film is 1.5-2 mg/cm²The thickness is 40 to 50 μm.

Preferably, the electrolyte comprises LiTFSI, an organic solvent and LiNO₃The organic solvent is a mixed solution of 1, 3-dioxolane and ethylene glycol dimethyl ether, the concentration of LiTFSI in the electrolyte is 1mol/L, and the LiNO is₃Is 1% by mass.

Preferably, the LiFePO₄LiFePO in electrode slice₄The content of (a) is 10-12 mg/cm²。

The invention also provides a preparation method of the half cell in the technical scheme, which comprises the following steps:

in a glove box, sequentially arranging a negative electrode battery shell, a lithium sheet, a CNT film, a Celgard film, an electrolyte and LiFePO₄And assembling the electrode plate and the positive battery shell to obtain the half battery.

The invention provides an application of a carbon nanotube film in a lithium ion battery cathode, wherein the carbon nanotube film is in contact with a lithium sheet. The invention introduces the carbon nanotube film as an interlayer to realize the lithium metal cathode with long service life and no dendrite, and the prepared electrode has ultra-long cycle stability and high capacity retention rate at 1mA/cm²Current density, 1mAh/cm²Can stably circulate for 1000 hours under the capacity limit, and is more than 10 times of pure Li metal. In that3mA/cm²、5mA/cm²The stability of the CNT film under high current density is far higher than that of pure Li metal, and the application design of the CNT film in the lithium ion battery cathode provides a new way for future high energy density Li metal batteries.

Furthermore, the battery containing the carbon nanotube film is easy to prepare and can be applied to large-scale electronic device equipment.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 shows that the current invention is at 1mA/cm²Voltage change curves for pure lithium and the symmetrical cell prepared in example 1 under constant current conditions;

FIG. 2 shows that the current invention is at 5mA/cm²Voltage change curves for pure lithium and the symmetrical cell prepared in example 1 under constant current conditions;

FIG. 3 shows the results of example 1 at 1mA/cm for pure Li metal symmetric cells and Li-CNT symmetric cells²Current density of 1mAh/cm²A rate characteristic curve at capacity limit;

FIG. 4 shows the 3mA/cm pure Li metal symmetric cell and Li-CNT symmetric cell of example 1²Current density of 3mAh/cm²Cycling stability and voltage curves at capacity limits;

FIG. 5 is a surface SEM image of a pure Li electrode of example 1 before cycling;

FIG. 6 is a cross-sectional SEM spectrum of a pure Li electrode of example 1 before cycling;

FIG. 7 is a surface SEM spectrum of a pure Li electrode of example 1 after 1 cycle;

FIG. 8 is a surface SEM spectrum of a Li-CNT electrode in a Li-CNT symmetric cell in example 1;

FIG. 9 is a surface SEM spectrum of a pure Li electrode of example 1 after 50 cycles;

FIG. 10 is a surface SEM spectrum of a Li-CNT electrode of a Li-CNT symmetric cell of example 1 after 50 cycles;

FIG. 11 is a cross-sectional SEM spectrum of a pure Li electrode of example 1 after 50 cycles;

FIG. 12 is a cross-sectional SEM spectrum of a Li-CNT electrode of a Li-CNT symmetric cell of example 1 after 50 cycles;

FIG. 13 is a charge-discharge cycle test curve for the pure Li metal half-cell and the LFP/Li-CNT half-cell of example 2;

FIG. 14 is an EIS spectrum of LFP/Li and LFP/Li-CNT at 1C current density prior to half-cell cycling;

FIG. 15 is an EIS spectrum of LFP/Li and LFP/Li-CNT after 10 half-cell cycles at 1C current density.

Detailed Description

The invention provides an application of a carbon nanotube film in a lithium ion battery cathode, wherein the carbon nanotube film is in contact with a lithium sheet. The invention introduces the carbon nanotube film as an interlayer, realizes long service life and a lithium metal cathode without dendrites, and the prepared electrode has ultra-long cycle stability and high capacity retention rate.

The invention also provides a symmetric battery, which sequentially comprises a negative battery shell, an elastic sheet, a gasket, a first lithium sheet, a first CNT (carbon nano tube) film, a Celgard film, an electrolyte, a second CNT film, a second lithium sheet and a positive battery shell, wherein the first lithium sheet and the first CNT film have the same area, and the second lithium sheet and the second CNT film have the same area.

In the present invention, the first CNT thin film and the second CNT thin film independently have an areal density of preferably 1.5 to 2mg/cm²More preferably 1.65 to 1.95mg/cm²The thickness is preferably 40 to 50 μm, and more preferably 42 to 48 μm. The source of the CNT thin film is not particularly limited in the present invention, and commercially available products known to those skilled in the art may be used.

In the invention, the CNT film is preferably in a shape of a disk, and the diameter of the disk-shaped CNT film is preferably 15.5-16 cm. In the present invention, the mass of the disk-shaped CNT film with a diameter of 16cm is preferably 3 to 4mg, and more preferably 3.5 to 3.8 mg. In the present invention, when the CNT thin film is preferably in a disk shape, it is preferably used for preparing a button-shaped lithium ion battery.

In the present invention, the thickness of the first lithium sheet and the second lithium sheet is independently preferably 0.45 mm.

The sources of the negative electrode battery case, the spring plate, the gasket, the Celgard membrane, the electrolyte and the positive electrode battery case are not particularly limited in the present invention, and commercially available products well known to those skilled in the art can be used.

In the present invention, the electrolyte preferably includes LiTFSI (lithium bistrifluoromethylsulfonylamide) and an organic solvent, which is preferably a mixed solution of 1, 3-Dioxolane (DOL) and ethylene glycol dimethyl ether (DME). In the present invention, the concentration of LiTFSI in the electrolyte is preferably 1 mol/L.

The invention also provides a preparation method of the symmetrical battery in the technical scheme, which comprises the following steps:

and in the glove box, assembling the negative electrode battery shell, the elastic sheet, the gasket, the first lithium sheet, the first CNT film, the Celgard film, the electrolyte, the second CNT film, the second lithium sheet and the positive electrode battery shell in sequence to obtain the symmetrical battery.

The assembly method is not particularly limited, and the assembly method known to those skilled in the art can be adopted, specifically, when the disk-shaped CNT film and the lithium sheet are used for preparing the button cell, the CNT film and the lithium sheet are combined together by using the pressure of a sealing machine during the assembly process.

In the present invention, O in the glove box₂Preferably in an amount of<0.01ppm，H₂The content of O is preferably<0.01ppm。

The invention also provides a half cell, which sequentially comprises a negative electrode cell shell, a lithium sheet, a CNT film, a Celgard film, an electrolyte and LiFePO₄Electrode slice and positive battery shell.

In the present invention, the surface density of the CNT film is preferably 1.5 to 2mg/cm²More preferably 1.45 to 1.95mg/cm²The thickness is preferably 40 to 50 μm, and more preferably 42 to 48 μm. The source of the CNT thin film is not particularly limited in the present invention, and commercially available products known to those skilled in the art may be used.

In the invention, the CNT film is preferably in a shape of a disk, and the diameter of the disk-shaped CNT film is preferably 15.5-16 cm. In the present invention, the mass of the disk-shaped CNT film with a diameter of 16cm is preferably 3 to 4mg, more preferably 3.2 to 3.8 mg. In the present invention, when the CNT thin film is preferably in a disk shape, it is preferably used for preparing a button-shaped lithium ion battery.

In the present invention, the thickness of the lithium sheet is independently preferably 0.45 mm.

The invention is applied to the negative electrode battery shell, the CNT film, the lithium sheet, the Celgard film, the electrolyte and the LiFePO₄The source of the electrode plate and the positive electrode battery case is not particularly limited, and commercially available products known to those skilled in the art can be adopted, specifically, the CNT film is purchased from flexible power (wuhan) science and technology limited, the lithium foil is purchased from shenzhen science and technology limited, and the CR2032 battery case is adopted for assembling the battery.

In the present invention, the electrolyte preferably includes LiTFSI, an organic solvent and LiNO₃The organic solvent is preferably a mixed solution of 1, 3-dioxolane and ethylene glycol dimethyl ether, the concentration of LiTFSI in the electrolyte is preferably 1mol/L, and the LiNO is preferably₃The mass fraction of (b) is preferably 1%.

In the present invention, the LiFePO₄LiFePO in electrode slice₄The content of (b) is preferably 10-12 mg/cm²More preferably 10.5 to 11.5mg/cm²。

The invention is to the LiFePO₄The preparation method of the electrode sheet is not particularly limited, and the preparation method known to those skilled in the art can be adopted, specifically, for example, the LiFePO with the mass ratio of 8:1:1₄Mixing the powder, conductive carbon black (SuperP), a binder polyvinylidene fluoride (PVDF) and Dimethylformamide (DMF) to obtain a mixed material, coating the mixed material on an aluminum sheet, and performing vacuum drying for 12 hours at 110 ℃ to obtain LiFePO₄An electrode sheet. The invention has no special limit on the dosage and the coating amount of the dimethylformamide, and can ensure LiFePO₄LiFePO in electrode slice₄The content of (b) may be within the above-mentioned range.

The invention also provides a preparation method of the half cell in the technical scheme, which comprises the following steps:

in the glove box, a negative electrode battery shell, a lithium sheet and a CNT film are arranged in sequenceCelgard film, electrolyte, LiFePO₄And assembling the electrode plate and the positive battery shell to obtain the half battery.

In the present invention, the atmosphere in the glove box is preferably identical to the above-described protocol, and will not be described herein.

The method of assembling the present invention is not particularly limited, and the assembling method known to those skilled in the art may be used.

The following will describe the anode electrode sheet of the air fuel cell, the preparation method and application thereof, and an air fuel cell in detail with reference to the examples, but they should not be construed as limiting the scope of the invention.

In this example, the CNT film was purchased from flexible power (wuhan) technologies ltd, and the lithium foil was purchased from shenzhen, kojizhida technologies ltd, and the assembly of the battery was performed using a CR2032 battery case.

Example 1

The thin surface density of the carbon nano tube is 2mg/cm²And a thickness of 50 μm. The carbon nanotube film was cut into a 16cm diameter wafer with a microtome, and one 16cm diameter CNT film wafer weighed 4 mg. The lithium foil with a thickness of 0.45mm was also cut to the same size as the CNT thin film.

The battery assembly was performed using a CR2032 battery case. Battery Assembly Process in glove Box (O)₂<0.01ppm，H₂O<0.01ppm) was completed.

The symmetric cells were assembled in the order of negative cell can-shrapnel-gasket-first lithium sheet-first CNT film-Celgard film-electrolyte (DOL/DME solution of 1M LiTFSI) -second CNT film-second lithium sheet-positive cell can (Li-CNT symmetric cells).

Symmetric batteries were prepared with pure lithium metal and assembled in the order of negative battery case-shrapnel-gasket-first lithium sheet-Celgard membrane-electrolyte (1M DOL/DME solution of LiTFSI) -second lithium sheet-positive battery case.

Electrochemical testing

At 1mA/cm²The voltage change curves (FIG. 1) obtained by charging and discharging pure lithium and the symmetrical battery obtained in example 1 under the constant current condition for 1 hour were 5mA/cm²OfAs can be seen from FIG. 1, the voltage of the pure Li metal symmetric battery suddenly drops to-0.04 to-0.05V in the first discharge process, which is 2 times that of the Li-CNT symmetric battery, when the pure Li and the symmetric battery prepared in example 1 are charged and discharged for 0.2h respectively under the current condition (FIG. 2). The voltage of the Li-CNT symmetric cell gradually stabilized, about-0.02V, as the cycling proceeded. Li⁺Deposit on CNT in cycle process, form stable SEI film on CNT surface, and make Li⁺Can be deposited uniformly. However, the voltage of the pure Li metal symmetrical battery is gradually reduced, the voltage is reduced to-0.10V after about 200h, the polarization is serious, and on the contrary, the polarization of the Li-CNT symmetrical battery is lower after 1000h (500 cycles) of circulation. The symmetric battery is at 5mA/cm²The same characteristics are exhibited at high current densities.

FIG. 3 shows a pure Li metal symmetric cell and a Li-CNT symmetric cell at 1mA/cm²Current density of 1mAh/cm²The rate characteristic curve at capacity limit, Li-CNT symmetric cell shows more stable and lower polarization, while pure Li metal symmetric cell is more polarized at all current densities, especially 10mA/cm²At high current densities, the polarization is very severe. Indicating that the CNT thin film can provide a more efficient lithium ion transport path.

FIG. 4 shows a 3mA cm pure Li metal symmetric cell and a Li-CNT symmetric cell^-2Current density of 3mAh/cm²Cycling stability and voltage curves at capacity limits, it can be seen from fig. 4 that the pure Li metal symmetric cell is severely polarized at a voltage of less than 100h, but the Li-CNT symmetric cell is still able to stably cycle for 450h and polarization is very low.

The cell after the charge-discharge cycle was opened in a glove box, and the lithium sheet and CNT film were taken out. And (3) putting the lithium sheet and the thin film into ethylene glycol dimethyl ether (DME) to be carefully washed for three times, washing away redundant electrolyte and impurities on the surface, and then carrying out vacuum drying. And then observed with a scanning electron microscope.

To further understand the effect of CNT films during lithium dendrite growth, the symmetric cell was cycled before and at 5mA/cm²Current density of 1mAh/cm²Pure L after 1 and 50 cycles at capacity limiti metal and lithium metal in the Li-CNT electrode were observed under a scanning electron microscope. The results are shown in FIGS. 5 to 12. The surface was substantially flat with slight bumps and pits (fig. 5) and a cross-sectional thickness of 400 μm (fig. 6) before cycling of the pure Li metal. After 1 cycle, brush-bushy lithium dendrites appeared on the surface of the pure Li metal electrode (fig. 7), while substantially no dendrites appeared on the surface of the lithium metal in the Li-CNT electrode (fig. 8), due to the non-uniform nucleation and growth of lithium on the surface of the pure Li metal electrode. As the deposition/exfoliation process increased, a large number of lithium dendrites appeared on the surface of the pure Li metal electrode after 50 cycles (fig. 9), much more than the lithium metal surface in the Li-CNT electrode (fig. 10). The thick and coarse lithium dendrites form a dead lithium layer, which affects the conductive effect, resulting in a decrease in coulombic efficiency and an increase in polarization. The pure Li metal electrode thickness increased to 445 μm after 50 cycles (fig. 11) and the lithium metal thickness increased to 420 μm in the Li-CNT electrode (fig. 12), which also indicates that the pure Li metal electrode had a large amount of dendrite formation and severe volume expansion.

Example 2

LiFePO₄Electrode sheet: cutting the aluminum foil into the same size as the CNT film, and mixing LiFePO with the mass ratio of 8:1:1₄Pouring the powder, conductive carbon black (SuperP) and polyvinylidene fluoride (PVDF) as a binder into dimethyl formamide (DMF), uniformly stirring, uniformly coating the stirred slurry on a cut aluminum sheet, and vacuum-drying at 110 ℃ for 12 h. LiFePO₄The active substance mass of the electrode slice is 12mg/cm²。

Half cell was made according to the negative cell casing-lithium plate-CNT film-Celgard film-electrolyte (DOL/DME solution of 1M LiTFSI, 1% LiNO)₃)-LiFePO₄Electrode tab-positive battery can sequential assembly (LFP/Li-CNT).

Half cells were prepared from pure lithium metal according to the negative cell casing-lithium plate-Celgard membrane-electrolyte (DOL/DME solution from 1MLiTFSI, 1% LiNO)₃)-LiFePO₄Electrode tab-positive battery can sequential assembly (LFP/Li).

Circulating between 2.4V and 4.2V, activating twice with 0.1C current, and performing charge-discharge cycle test with 1C current (1.5 mAh/cm)²Capacity limit), the results are shown in fig. 13, and can be seen from fig. 13And a coulomb efficiency change curve circulating 100 times. The coulombic efficiency dropped to 0 after 100 cycles of pure Li metal half-cells, indicating that dendrite formation and active lithium loss were almost exhausted, which is related to uneven charge distribution on the surface of metallic lithium, and unstable SEI film formation. As the carbon nanotubes are porous, and the CNT film is formed by overlapping a plurality of layers of the carbon nanotubes, the surface of the Li-CNT electrode has more active sites, lithium can be uniformly deposited, and a stable SEI film is formed.

Fig. 14 is an EIS diagram of LFP/Li and LFP/Li-CNT at 1C current density before half-cell cycling, fig. 15 is an EIS diagram of LFP/Li and LFP/Li-CNT at 1C current density after half-cell cycling 10 times, the interface resistance and the negative electrode surface charge transfer resistance are related to the high frequency region semicircle, and it can be seen from fig. 14 and 15 that the interface resistance before pure Li metal half-cell cycling is large, being 238ohm, because of the passivation film formed on the electrode surface. After 10 cycles, the interfacial resistance dropped to 146ohm, since the passivation film decomposed and lithium dendrite formation caused an increase in surface area. The interface impedance of the Li-CNT half-cell is only 78ohm before circulation, and the interface impedance is 47ohm after 10 times of circulation, which shows that the Li-CNT electrode is beneficial to oxidation-reduction reaction and accelerates the charge transmission process. This also explains well that Li-CNT symmetric cells have lower voltage polarization than pure Li metal symmetric cells.

The invention uses CNT film as interlayer, can realize high stable Li metal anode, and has the following advantages: Li-CNT is easy to prepare and can be applied to large electronic device equipment; the prepared Li-CP battery has ultra-long circulation stability and high capacity retention rate at 1mA/cm²Current density of 1mAh/cm²Can stably circulate for 1000 hours under the capacity limit, and is 10 times of pure Li; the lithium dendrite number is less during Li deposition and the design of CNT thin film interlayers provides a new avenue for future high energy density Li metal batteries.

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 (7)

1. A symmetric battery sequentially comprises a negative battery shell, an elastic sheet, a gasket, a first lithium sheet, a first CNT film, a Celgard film, an electrolyte, a second CNT film, a second lithium sheet and a positive battery shell, wherein the first lithium sheet and the first CNT film have the same area, and the second lithium sheet and the second CNT film have the same area; the first CNT film and the second CNT film independently have an areal density of 1.5 to 2mg/cm²The thickness is 40 to 50 μm independently.

2. The symmetrical battery of claim 1, wherein the electrolyte comprises LiTFSI and an organic solvent, the organic solvent is a mixed solution of 1, 3-dioxolane and ethylene glycol dimethyl ether, and the concentration of LiTFSI in the electrolyte is 1 mol/L.

3. A method of making a symmetrical battery according to claim 1 or 2, comprising the steps of:

and in the glove box, assembling the negative electrode battery shell, the elastic sheet, the gasket, the first lithium sheet, the first CNT film, the Celgard film, the electrolyte, the second CNT film, the second lithium sheet and the positive electrode battery shell in sequence to obtain the symmetrical battery.

4. A half-cell sequentially comprises a negative electrode cell shell, a lithium sheet, a CNT film, a Celgard film, an electrolyte and LiFePO₄The surface density of the CNT film is 1.5-2 mg/cm²The thickness is 40 to 50 μm.

5. The half-cell of claim 4, wherein the electrolyte comprises LiTFSI, an organic solvent, and LiNO₃The organic solvent is a mixed solution of 1, 3-dioxolane and ethylene glycol dimethyl ether, the concentration of LiTFSI in the electrolyte is 1mol/L, and the LiNO is₃Is 1% by mass.

6. The half-cell according to claim 4, wherein said LiFePO₄In the electrode plateLiFePO₄The content of (a) is 10-12 mg/cm²。

7. A method of manufacturing a half-cell according to any one of claims 4 to 6, comprising the steps of:

in a glove box, sequentially arranging a negative electrode battery shell, a lithium sheet, a CNT film, a Celgard film, an electrolyte and LiFePO₄And assembling the electrode plate and the positive battery shell to obtain the half battery.

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