CN112909222A

CN112909222A - Lithium metal negative electrode and preparation method and application thereof

Info

Publication number: CN112909222A
Application number: CN202011437477.8A
Authority: CN
Inventors: 胡志远; 邓伟; 周旭峰; 刘兆平
Original assignee: Ningbo Institute of Material Technology and Engineering of CAS
Current assignee: Ningbo Institute of Material Technology and Engineering of CAS
Priority date: 2020-12-07
Filing date: 2020-12-07
Publication date: 2021-06-04
Anticipated expiration: 2040-12-07
Also published as: CN112909222B

Abstract

The invention provides a preparation method of a lithium metal negative electrode, which comprises the following steps: mixing melamine foam and aniline solution, and standing to obtain a mixed solution; reacting the mixed solution with ammonium persulfate to obtain a reaction product; and rolling and compounding the reaction product and a lithium foil to obtain the lithium metal cathode. The in-situ buffer layer material prepared by the method provided by the invention has stronger mechanical modulus, the fiber layer with weak conductivity can disperse the high current density at the tip of the dendritic crystal when the dendritic crystal contacts the fiber, inhibit the growth of the dendritic crystal and homogenize the concentration of lithium ions, and meanwhile, the elastically expandable buffer layer material has larger reserved space, can restrict a large amount of accumulated dead lithium and is suitable for volume expansion. The invention also provides a lithium metal negative electrode and application thereof.

Description

Lithium metal negative electrode and preparation method and application thereof

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to a lithium metal negative electrode and a preparation method and application thereof.

Background

Along with the dependence of people on the use of energy storage equipment, the human life can not leave the benefits brought by the energy storage equipment, and meanwhile, the requirement on the energy density of the energy storage equipment is higher and higher, namely the energy storage equipment is small to small digital equipment and is large to a new energy automobile power battery. Because lithium metal has higher theoretical specific capacity, the lithium metal battery gradually enters the visual field of people in order to improve the energy density of the battery, but the cycle life and reversible capacity of the lithium metal battery can be reduced due to a series of side reactions caused by the growth of lithium dendrites in the lithium metal battery, including the consumption of electrolyte, and the generation of 'dead lithium', even if the growth of dendrites can pierce through a diaphragm to cause the short circuit of the battery, so that the safety problem is caused.

The lithium metal cathode buffer layer is prepared mainly by the following steps: the mode of coating the buffer layer to protect the lithium metal cathode is that firstly, the filler, the cross-linking agent and the like are mixed according to the mass proportion, the mixture is fully stirred to be uniformly mixed, then the mixed solution is coated on the cathode material, and the cathode material is dried in a vacuum oven to obtain the lithium metal cathode; the mode of growing the buffer layer on the cathode material in situ is to prepare the raw material and generate the buffer layer solution on the electrode plate in situ.

The buffer layer is coated to protect the lithium metal cathode and the buffer layer material grown in situ on the cathode material from having no elastic function, so that the buffer layer material cannot accommodate volume expansion caused by large cathode deformation such as accumulation of 'dead lithium' in the long-time circulation process, and further the buffer layer material cannot be continuously contacted with the lithium metal to play a functional role; the buffer layer material coated with the buffer layer and grown in situ is generally non-conductive high polymer, and can promote lithium ion transmission, play a role in enhancing the mechanical strength of the negative electrode by high elastic modulus, but cannot disperse the tip current of the lithium dendrite and inhibit the growth of the dendrite.

Disclosure of Invention

In view of this, the present invention aims to provide a lithium metal negative electrode, a preparation method and an application thereof.

The invention provides a preparation method of a lithium metal negative electrode, which comprises the following steps:

mixing melamine foam and aniline solution, and standing to obtain a mixed solution;

reacting the mixed solution with ammonium persulfate to obtain a reaction product;

and rolling and compounding the reaction product and a lithium foil to obtain the lithium metal cathode.

Preferably, the thickness of the melamine foam is 1.8-2.5 mm.

Preferably, the solvent in the aniline solution is a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.5-1.5 mol/L.

Preferably, the standing is performed under ice bath conditions.

Preferably, the standing time is 4-8 hours.

Preferably, the reaction is carried out in an ice bath.

Preferably, the reaction time is 10-12 hours.

Preferably, the mass ratio of the melamine foam to the aniline to the ammonium persulfate is 1: (3-7): (4-8).

The invention provides a lithium metal negative electrode prepared by the method in the technical scheme.

The invention provides application of the lithium metal negative electrode in the technical scheme in a battery.

The preparation method of the lithium cathode provided by the invention takes melamine foam as a framework, generates a buffer layer material after polyaniline grows in situ, and then rolls the buffer layer material and the lithium metal to obtain the buffer layer lithium metal cathode. The method provided by the invention can synthesize the buffer layer material in situ in a large area, has an elastic function, can expand and compress, adapts to larger volume expansion and weak conductivity, disperses dendritic crystal tip current, homogenizes the concentration of lithium ions, inhibits dendritic crystal growth, and prepares the lithium metal cathode of the buffer layer by rolling so that the buffer layer and the lithium metal are tightly combined. The in-situ buffer layer material prepared by the invention has stronger mechanical modulus, the fiber layer with weak conductivity can disperse the high current density at the tip of the dendritic crystal when the dendritic crystal contacts the fiber, inhibit the growth of the dendritic crystal and homogenize the concentration of lithium ions, and meanwhile, the elastically expandable buffer layer material has larger reserved space, can restrict a large amount of accumulated dead lithium and is suitable for volume expansion.

Drawings

FIG. 1 is a flow chart of a process for preparing a lithium metal anode according to an embodiment of the present invention;

FIG. 2 shows the performance test results of a battery prepared by using a lithium metal negative electrode prepared in example 1 of the present invention;

fig. 3 is an SEM picture of a lithium metal negative electrode prepared in example 2 of the present invention after rolling;

fig. 4 is an SEM picture of a lithium metal anode prepared in example 2 of the present invention after testing cycle performance;

fig. 5 shows the performance test results of the battery prepared by the lithium metal negative electrode prepared in example 2 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other examples, which may be modified or appreciated by those of ordinary skill in the art based on the examples given herein, are intended to be within the scope of the present invention. It should be understood that the embodiments of the present invention are only for illustrating the technical effects of the present invention, and are not intended to limit the scope of the present invention. In the examples, the methods used were all conventional methods unless otherwise specified.

The process flow for preparing the lithium metal negative electrode provided by the embodiment of the invention is shown in fig. 1.

In the present invention, the melamine foam is preferably a sheet. In the invention, the thickness of the melamine foam is preferably 1.8-2.5 mm, and more preferably 2-2.2 mm. In the present invention, the melamine foam is preferably a melamine formaldehyde resin, preferably formed by the reaction of formaldehyde and melamine, and the porosity is preferably more than 99.9%. In the invention, the melamine foam is preferably used in an amount of 15 to 35 pieces, more preferably 28 to 32 pieces, and most preferably 30 pieces.

In the present invention, it is preferable that the melamine foam is ultrasonically cleaned with acetone or alcohol and then used for the preparation of the lithium metal negative electrode. In the invention, the ultrasonic cleaning time is preferably 25 to 35 minutes, more preferably 28 to 32 minutes, and most preferably 30 minutes. In the invention, after the ultrasonic cleaning is completed, the cleaned melamine foam is preferably dried, and the drying temperature is preferably 55-65 ℃, more preferably 58-62 ℃, and most preferably 60 ℃.

In the invention, the solvent in the aniline solution is preferably hydrochloric acid solution, more preferably hydrochloric acid aqueous solution, and the concentration of the hydrochloric acid solution is preferably 0.5-1.5 mol/L, more preferably 0.8-1.2 mol/L, and most preferably 1 mol/L.

In the invention, the standing is preferably performed under the condition of ice bath, and the standing time is preferably 4 to 8 hours, more preferably 5 to 7 hours, and most preferably 6 hours.

In the invention, the reaction is preferably carried out in an ice bath, and the reaction time is preferably 10-12 hours.

In the present invention, the mass ratio of the melamine foam, aniline and ammonium persulfate is preferably 1: (3-7): (4-8), more preferably 1: (4-6): (5-7), most preferably 1: 5: 6.

in the present invention, the melamine foam and the hydrochloric acid solution are preferably used in a ratio of 1 g: (350-450) mL, more preferably 1 g: (380-420) mL, most preferably 1 g: 400 mL.

Polyaniline is a conductive polymer with a pi-electron single-double-bond alternate conjugated structure, is generated by standing and reacting aniline and ammonium persulfate under an acidic condition, and is preferably subjected to an ice bath condition in the whole reaction process.

In the present invention, after obtaining the reaction product, preferably, the reaction product is washed and then dried, and the washing reagent is preferably water, and more preferably deionized water; the drying is preferably carried out in a forced air oven; the drying temperature is preferably 55-65 ℃, more preferably 58-62 ℃, and most preferably 60 ℃.

In the invention, the thickness of the lithium foil is preferably 30-120 microns, more preferably 50-100 microns, and most preferably 60-80 microns.

In the invention, the rolling thickness in the rolling process is preferably 200-400 microns, more preferably 250-350 microns, and most preferably 300 microns. In the invention, the rolling can be single-side rolling or double-side rolling, the single-side rolling is to roll and compound one side surface of the lithium foil with a reaction product, the double-side rolling is to roll and compound two side surfaces of the lithium foil with the reaction product, and the thickness of the lithium foil during the single-side rolling is preferably 40-60 micrometers, more preferably 45-55 micrometers, and most preferably 50 micrometers; the thickness of the lithium foil during double-sided rolling is preferably 80-120 micrometers, more preferably 90-110 micrometers, and most preferably 100 micrometers. In the present invention, the method of double-side rolling preferably includes:

symmetrically placing the reaction product on two sides of the lithium foil to form a reaction product-lithium foil-reaction product structure;

adding an ET diaphragm on the outermost layer of the structure to form a PET-reaction product-lithium foil-reaction product-PET structure;

and adjusting the rolling thickness of the rolling machine to be 300-400 mu m, and tearing off the PET diaphragm after rolling.

In the invention, the thickness of the PET diaphragm is preferably 70-80 micrometers, and more preferably 75 micrometers; the rolling thickness is preferably 320-380 micrometers, more preferably 340-360 micrometers, and most preferably 350 micrometers.

In the present invention, the method of single-side rolling preferably includes:

placing the reaction product on one side of a lithium foil, and adding a PET diaphragm on the outer layers of the lithium foil and the reaction product to form a PET-lithium foil reaction product-PET structure;

adjusting the rolling thickness of the roller press to 200-300 mu m, and tearing off the PET diaphragm after rolling.

In the invention, the thickness of the PET diaphragm is consistent with that of the PET diaphragm in the technical scheme, and the rolling thickness is preferably 220-280 micrometers, more preferably 240-260 micrometers, and most preferably 250 micrometers.

The invention provides a lithium metal cathode prepared by the method in the technical scheme.

The invention provides an application of the metal lithium negative electrode in the technical scheme in a battery, wherein the metal lithium negative electrode is used as a negative electrode in the battery, for example, a copper foil can be matched to prepare a half battery.

The raw materials used in the following examples of the present invention are all commercially available products, and the melamine foam is melamine formaldehyde resin, provided by zhengzhou feng thai nano materials limited, which has a porosity of more than 99.9%.

Example 1

30 pieces of melamine foam with the thickness of about 1.8mm, the area of 3 x 4cm and the total mass of 0.69g are ultrasonically cleaned by acetone and alcohol for 30 minutes and then placed in a blast drying agent at 60 ℃ for drying for later use, 3.70g of aniline is weighed by an analytical balance and dispersed in 280mL of 1moL/mL hydrochloric acid solution, the melamine foam is added, and the mixture is kept stand for 4 hours under the ice bath condition; weighing 4.10g of ammonium persulfate by using an analytical balance, adding the ammonium persulfate into a hydrochloric acid solution mixed by melamine foam and aniline, fully dissolving, and standing for reaction for 8 hours under an ice bath condition; and taking the elastic buffer layer material prepared after the reaction out of hydrochloric acid, washing the elastic buffer layer material by using deionized water for multiple times, washing off excessive polyaniline particles except the surface of the melamine foam framework, and then drying the polyaniline particles in a 60 ℃ blast oven for later use.

Cutting the dried elastic buffer layer material into a round pole piece with the radius of 0.7cm and a lithium foil with the radius of 0.7cm and the thickness of 50 microns, rolling the round pole piece and the lithium foil on one side, assembling the round pole piece and the lithium foil into a PET (75 microns) -lithium foil-buffer layer-PET (75 microns) structure, adjusting the rolling thickness of a rolling machine to be 250 microns, and tearing off a PET diaphragm after rolling to obtain the lithium metal cathode of the single-side buffer layer.

The lithium metal negative electrode prepared in the embodiment 1 of the invention is matched with copper foil to prepare a half cell:

the lithium metal negative electrode prepared in example 1 of the present invention was used as a negative electrode, a copper foil 18 μm thick with a radius of 0.7cm as a positive electrode, a PP separator 1cm thick with a radius of 25 μm was assembled (assembly press pressure was 50 MPa); at 1mA/cm²、5mAh/cm²Cycling test under Current conditions (at 1 mA/cm)²Constant current is discharged to 5mAh/cm under the current density²The area capacity is then charged by constant current until the voltage reaches 1V, the step is repeatedly circulated for many times, and the test equipment: blue battery test equipment), the detection result is shown in fig. 2, and as can be seen from fig. 2, the half-cell with the buffer layer has good cycling stability and has more stable and higher cycling efficiency compared with the half-cell without the buffer layer.

Example 2

20 pieces of melamine foam with a thickness of about 1.8mm, an area of 5 x 6cm and a total mass of 1.38g were ultrasonically cleaned with acetone and alcohol for 30 minutes, then dried in a blowing drier at 60 ℃ for use, 7.45g of aniline was weighed by an analytical balance and dispersed in 550mL of 1moL/mL hydrochloric acid solution, melamine foam was added, and the mixture was allowed to stand for 5 hours under ice bath conditions. 8.28g of ammonium persulfate is weighed by an analytical balance and added into a hydrochloric acid solution mixed by melamine foam and aniline, the mixture is fully dissolved, and the mixture is kept stand and reacted for 10 hours under the ice bath condition. And taking the elastic buffer layer material prepared after the reaction out of hydrochloric acid, washing the elastic buffer layer material by using deionized water for multiple times, washing off excessive polyaniline particles except the surface of the melamine foam framework, and then drying the polyaniline particles in a 60 ℃ blast oven for later use.

Cutting the dried elastic buffer layer material into a lithium foil with the area of 4.7 x 5.7cm and the thickness of 100 microns, performing double-sided rolling, symmetrically placing buffer layers on two sides of the lithium foil to form a buffer layer-lithium foil-buffer layer structure, and adding a PET diaphragm with the thickness of 75 microns on the outermost layer to form a PET-buffer layer-lithium foil-buffer layer-PET structure; and adjusting the rolling thickness of a rolling machine to 350 mu m, and tearing off the PET diaphragm after rolling to obtain the lithium metal cathode with the double-sided buffer layer.

SEM examination was performed on the lithium metal negative electrode prepared after rolling in example 2 of the present invention, and the examination result is shown in fig. 3, and it can be seen from fig. 3 that the buffer layer and the lithium metal are completely roll-combined.

The lithium metal cathode prepared in embodiment 2 of the invention is prepared into a soft package battery with the capacity of 0.9Ah by matching with an NCM811 cathode material, and the cycle performance is detected, wherein the test method comprises the following steps: the soft package battery is cycled under the charge and discharge multiplying power of 0.2C, the charge cut-off voltage is 4.3V, the discharge cut-off voltage is 2.6V, the cycle is repeated for multiple times, the metal lithium cathode after the cycle performance detection is subjected to SEM detection, the detection result is shown in figure 4, and as can be seen from figure 4, the buffer layer still wraps the lithium metal after the multiple cycles, so that the buffer layer has the expanded elastic performance; as shown in fig. 5, a in fig. 5 is a cell without a buffer layer, and b is a cell with a buffer layer, it can be seen from fig. 5 that the lithium metal cell with a buffer layer has more cycle efficiency, and the lithium metal cell with a buffer layer has more discharge capacity under the condition of not much different cycle times.

The preparation method of the lithium metal cathode can synthesize the buffer layer material in situ in a large area, has an elastic function, can expand and compress, is suitable for larger volume expansion and weak conductivity, disperses dendritic crystal tip current, homogenizes lithium ion concentration, inhibits dendritic crystal growth, and prepares the lithium metal cathode of the buffer layer by rolling so that the buffer layer is tightly combined with lithium metal. The in-situ buffer layer material prepared by the invention has stronger mechanical modulus, the fiber layer with weak conductivity can disperse the high current density at the tip of the dendritic crystal when the dendritic crystal contacts the fiber, inhibit the growth of the dendritic crystal and homogenize the concentration of lithium ions, and meanwhile, the elastically expandable buffer layer material has larger reserved space, can restrict a large amount of accumulated dead lithium and is suitable for volume expansion.

While only the preferred embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. A method of making a lithium metal anode, comprising:

2. The method according to claim 1, characterized in that the melamine foam has a thickness of 1.8 to 2.5 mm.

3. The method according to claim 1, wherein the solvent in the aniline solution is a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.5-1.5 mol/L.

4. The method of claim 1, wherein the resting is performed under ice bath conditions.

5. The method according to claim 1, wherein the standing time is 4 to 8 hours.

6. The method of claim 1, wherein the reaction is carried out under ice bath conditions.

7. The method according to claim 1, wherein the reaction time is 10 to 12 hours.

8. The method according to claim 1, wherein the mass ratio of the melamine foam to the aniline to the ammonium persulfate is 1: (3-7): (4-8).

9. A lithium metal negative electrode prepared by the method of claim 1.

10. Use of the lithium metal anode of claim 9 in a battery.