CN112786835B - A lithium metal negative electrode and its preparation and application - Google Patents

Abstract

This patent proposes a lithium metal negative electrode with an oxide layer to prepare and use. The extruded lithium metal is soaked in organic ester, and is subjected to ex-situ hydrolysis and polycondensation to form a stable porous oxide layer, so that the continuous reaction and consumption of the electrolyte and the lithium metal are effectively inhibited, and the cycling stability of the battery is improved.

Description

A lithium metal negative electrode and its preparation and application

technical field

The invention relates to the preparation and application of a lithium metal negative electrode with an oxide layer.

Background technique

Currently, the world market for electric vehicles and portable electronic devices including passenger cars, buses and passenger cars is growing rapidly. Lithium-ion batteries with high charge-discharge voltage and long cycle life are widely used as power sources for portable electronic devices and electric vehicles, but due to the limitation of their theoretical energy density, new electrode materials with higher energy density need to be developed. Among them, lithium metal as an anode material has the advantages of high theoretical energy density (3860mAh g ^-1 ) and low electrochemical potential (-3.040V vs. SHE), which has attracted great attention of researchers in recent years.

However, there are still two problems to be solved in the application of lithium metal anodes. One is the lithium dendrite problem. Due to the non-uniformity of lithium deposition, moss/dendritic lithium is formed during charge-discharge cycles, which can easily pierce the separator and cause internal short circuits or even fires in the battery. Another problem is the instability of the electrode/electrolyte interface. Metal lithium reacts spontaneously with the electrolyte to form a solid electrolyte interface film (SEI), which is continuously damaged and repaired with the volume expansion of the negative electrode during the charge-discharge cycle, resulting in continuous consumption of lithium metal and electrolyte, reducing the Coulombic efficiency of lithium metal batteries and cycle life.

At present, related solutions have been proposed, which can suppress the growth of dendrites by designing 3D framework structures and using solid electrolytes, but there are still some problems to be solved. The 3D skeleton structure can slow down the dendrite growth by reducing the current density, but it cannot isolate the direct contact between lithium metal and the electrolyte to inhibit the occurrence of side reactions; while the inorganic solid-state electrolysis has high mechanical strength, but the interface impedance is large, and the contact with lithium metal is poor. ; Although the polymer electrolyte has good flexibility and elasticity, the room temperature ionic conductivity is relatively low (about 10 ^-7 S cm ^-1 ). Ex-situ coating of a passivation film to improve the interfacial uniformity and stability is an important strategy to effectively inhibit the growth of lithium dendrites and improve the cycling stability and safety performance of lithium anodes. The use of organic esters to treat lithium metal ex situ and construct a porous oxide layer on the surface of the lithium metal negative electrode can effectively improve the uniformity of lithium deposition, block side reactions between the electrolyte and lithium metal, and improve the battery cycle stability and Coulomb efficiency. It has been reported in the literature that silicon oxide films can be directly sputtered on lithium surfaces to suppress dendrite growth. However, the method using sputtering treatment is relatively complicated, and the dense silicon oxide layer will reduce the ionic conductivity and increase the interface resistance. Therefore, it is necessary to further simplify the method for handling lithium, realize practical application, and further improve the ion transport capability of the interface layer.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a lithium metal negative electrode with good application effect.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

A lithium metal anode with an oxide layer,

The oxide layer is formed by ex-situ hydrolysis and condensation of organic esters on the extruded lithium surface.

The organic esters are one or more of tetramethyl silicate, tetraethyl silicate, isopropyl silicate, tetrabutyl titanate, isopropyl titanate, and tetrabutyl zirconate;

The preparation method of the above-mentioned lithium metal negative electrode with oxide layer, the method adopts the following steps to prepare:

(1) Extruding the lithium sheet with a glass plate padded with a polyolefin film to obtain a bright lithium sheet PLi;

(2) Immerse PLi in organic esters for ex-situ reaction for 10s-5min, take out PLi and use non-woven fabric to wipe off the organic ester liquid on the lithium surface, and dry it in a glove box for 2-60min to obtain an oxide layer with an oxide layer. the lithium metal anode.

The polyolefin film is one or more of polyethylene film, polypropylene film and polyethylene/polypropylene composite film, and its thickness is 10-200 μm;

The pressure range is 0.15-0.5MPa, and the time range is 10s-5min.

The beneficial results of the present invention are:

The invention relates to a lithium metal negative electrode with an oxide layer, which is formed by ex-situ hydrolysis and condensation of organic esters on the extruded lithium surface.

(1) The extrusion pretreatment can flatten the lithium surface and expose fresh lithium, which is conducive to the formation of a uniform oxide layer on the lithium surface by organic esters, and the flat lithium surface can improve the uniformity of lithium deposition.

(2) The porous oxide layer is conducive to the transport of lithium ions at the interface, improves the ionic conductivity of the interface, reduces the interface impedance, and improves the deposition uniformity.

(3) Lithophilic silicon oxide is conducive to the adsorption of lithium ions on the lithium surface and promotes the uniform nucleation of lithium ions.

(4) The oxide layer with high mechanical strength is conducive to inhibiting dendrites, and has good stability, which can effectively inhibit the continuous reaction and consumption of the lithium anode and the electrolyte, and prolong the cycle life of the battery.

Description of drawings

Figure 1: Lithium metal anode with porous oxide layer;

Figure 2: Infrared spectra of lithium metal before and after immersion in tetraethyl silicate (TEOS);

Figure 3: Cycling performance of lithium metal symmetrical batteries of Comparative Example 1 and Example 2;

Figure 4: Cycling performance of lithium metal symmetrical batteries of Comparative Example 1 and Example 4;

Figure 5: Cycling performance of lithium metal symmetrical batteries of Comparative Example 1 and Examples 1-3;

Figure 6: Surface morphologies of the lithium metal electrodes of Comparative Example 1 and Example 1 after 10 deposition cycles with a deposition-dissolution capacity of ¹ mAh/cm at a current density of ¹ mA/cm.

Detailed ways

The following examples are intended to further illustrate the present invention, but not to limit the scope of the present invention.

Comparative Example 1

Lithium sheets with a diameter of 1.6 mm were used, celgard 2325 was used as the separator, 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was used as the supporting electrolyte, and the solvents were 1,3-dioxolane (DOL) and ethyl acetate. A mixture of glycol dimethyl ether (DME) (with a volume ratio of 1:1) was used as the electrolyte to assemble a lithium|lithium symmetrical battery. Charge-discharge cycles were performed at a current density of 1 mA/cm ² with a deposition dissolution capacity of 1 mAh/cm ² .

Example 1

Glass plates are placed on both sides of the lithium sheet to form a laminated structure, and a polyethylene film (thickness 25μm) is placed between the lithium sheet and the glass plate, and then the lithium sheet is pressed on the side of the glass plate away from the lithium sheet , the pressure is 0.2MPa, and the time is 20s; the lithium sheet with a diameter of 1.6mm and a thickness of 700μm is extruded with a glass plate padded with a polyethylene film to obtain a bright lithium sheet PLi (PLi means the extruded lithium sheet); Soak in tetrabutyl titanate for ex-situ reaction for 10 s, take out PLi and wipe off the tetrabutyl titanate liquid on the lithium surface with a non-woven fabric, dry for 15 min, and obtain an oxide layer (titanium oxide) with a thickness of about 500 nm. Lithium metal anode. A symmetrical battery was assembled using the treated lithium sheet as the electrode, celgard2325 as the separator, 1M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as the supporting electrolyte, and 1,3-dioxolane (DOL) as the solvent. ) and ethylene glycol dimethyl ether (DME) mixture (volume ratio of 1:1) was used as the electrolyte to assemble a lithium|lithium symmetrical battery. Charge-discharge cycles were performed at a current density of 1 mA/cm ² with a deposition dissolution capacity of 1 mAh/cm ² .

Example 2

According to the process of Example 1, a glass plate with a diameter of 1.6 mm and a thickness of 700 μm was used to extrude a lithium sheet with a thickness of 700 μm to obtain a bright lithium sheet PLi; the PLi was immersed in tetrabutyl titanate for ex-situ reaction After 1 min, the PLi was taken out and the tetrabutyl titanate liquid on the lithium surface was wiped off with a non-woven fabric, and dried for 15 min to obtain a lithium metal negative electrode with an oxide layer (titanium oxide) with a thickness of about 800 nm. A symmetric battery was assembled using the treated lithium sheet as an electrode, and a lithium|lithium symmetric battery was assembled according to the method and conditions of Example 1. Charge-discharge cycles were performed at a current density of 1 mA/cm ² with a deposition dissolution capacity of 1 mAh/cm ² .

Example 3

According to the process of Example 1, a glass plate with a diameter of 1.6 mm and a thickness of 700 μm was used to extrude a lithium sheet with a thickness of 700 μm to obtain a bright lithium sheet PLi; the PLi was immersed in tetrabutyl titanate for ex-situ reaction After 5 minutes, the PLi was taken out and the tetrabutyl titanate liquid on the lithium surface was wiped off with a non-woven fabric, and dried for 15 minutes to obtain a lithium metal negative electrode with an oxide layer (titanium oxide) with a thickness of about 1 μm. A symmetric battery was assembled using the treated lithium sheet as an electrode, and a lithium|lithium symmetric battery was assembled according to the method and conditions of Example 1. Charge-discharge cycles were performed at a current density of 1 mA/cm ² with a deposition dissolution capacity of 1 mAh/cm ² .

Example 4

According to the process of Example 1, a glass plate with a diameter of 1.6 mm and a thickness of 700 μm was used to extrude a lithium sheet with a thickness of 700 μm to obtain a bright lithium sheet PLi; the PLi was immersed in tetraethyl silicate for ex-situ reaction After 1 min, the PLi was taken out and the tetraethyl silicate liquid on the lithium surface was wiped off with a non-woven fabric, and dried for 15 min to obtain a lithium metal negative electrode with an oxide layer (silicon oxide) with a thickness of about 500 nm. A symmetric battery was assembled using the treated lithium sheet as an electrode, and a lithium|lithium symmetric battery was assembled according to the method and conditions of Example 1. Charge-discharge cycles were performed at a current density of 1 mA/cm ² with a deposition dissolution capacity of 1 mAh/cm ² .

Example 5

According to the process of Example 1, a glass plate with a diameter of 1.6 mm and a thickness of 700 μm was used to extrude a lithium sheet with a thickness of 700 μm to obtain a bright lithium sheet PLi; the PLi was immersed in tetrabutyl zirconate for ex-situ reaction After 1 min, the PLi was taken out and the tetrabutyl zirconate liquid on the lithium surface was wiped off with a non-woven fabric, and dried for 15 min to obtain a lithium metal negative electrode with an oxide layer (zirconia) with a thickness of about 600 nm. A symmetric battery was assembled using the treated lithium sheet as an electrode, and a lithium|lithium symmetric battery was assembled according to the method and conditions of Example 1. Charge-discharge cycles were performed at a current density of 1 mA/cm ² with a deposition dissolution capacity of 1 mAh/cm ² .

Example 6

According to the process of Example 1, a lithium sheet with a diameter of 1.6 mm and a thickness of 700 μm was extruded with a glass plate padded with a polyethylene film to obtain a bright lithium sheet PLi; PLi was soaked in tetraethyl silicate and tetrabutyl titanate The ester mixed solution (volume ratio of 1:1) was reacted ex-situ for 1 min, the PLi was taken out and the tetraethyl silicate and tetrabutyl titanate liquids on the lithium surface were wiped off with a non-woven fabric, and dried for 15 min to obtain a product with a thickness of Lithium metal anode with about 700nm oxide layer (silicon oxide). A symmetric battery was assembled using the treated lithium sheet as an electrode, and a lithium|lithium symmetric battery was assembled according to the method and conditions of Example 1. Charge-discharge cycles were performed at a current density of 1 mA/cm ² with a deposition dissolution capacity of 1 mAh/cm ² .

The tetraethyl silicate (TEOS)-treated lithium surface was characterized by infrared spectroscopy. It can be seen from Figure 2 that there are obvious Si-O-Si peaks on the lithium surface after TEOS treatment, which proves that TEOS is hydrolyzed and condensed on the lithium surface to form a Si-O-Si layer. It can be seen from Figures 3, 4, and 5 that organic esters can significantly improve the cycling stability of lithium deposition and dissolution. It can be seen from Figure 3 that under the conditions of a current density of 1 mA/cm ² and a specific capacity of 1 mAh/cm ² , the polarization voltage of the untreated lithium symmetric battery increased to 130 mV after 160 h of cycling, and decreased after 170 h. After 400h of cycling, the polarization voltage of the lithium symmetric battery treated with tetrabutyl titanate increased to 130mV, and the polarization voltage of the lithium symmetric battery treated with tetraethyl silicate only increased to 110mV, and no short circuit occurred. The titanium oxide and silicon oxide films on the lithium surface can not only improve the cycling stability, but also their high porosity can accelerate the interfacial lithium ion transport, improve the uniformity of lithium deposition, and reduce the polarization voltage. The experiment also further explored the effect of tetrabutyl titanate treatment time on the cycle stability of lithium metal. It can be seen from Figure 4 that the cycle stability of the battery is the best after treatment for 1min. This is because the treatment time of 10s is not enough for lithium metal. The surface reacts completely to form a uniform oxide layer; if the treatment time is too long (5min), the surface film will be too thick and the interface resistance will be increased.

The morphology of lithium deposition was investigated by SEM. It can be seen from Figure 6 that in the ether electrolyte, under the conditions of a current density of 1 mA/cm ² and a specific capacity of 1 mAh/cm ² for 10 charge-discharge cycles, the surface of the untreated lithium metal electrode is uneven, and the lithium battery The electrode has a large specific surface area, and the electrolyte is continuously consumed, thereby increasing the polarization voltage of the lithium symmetric battery. The surface morphology of lithium treated with tetraethyl silicate is stable, which can inhibit the continuous reaction and consumption of the electrolyte and lithium metal and inhibit the growth of dendrites; and the high-porosity interface film accelerates the interfacial lithium ion transport and improves the uniformity of lithium deposition properties, thereby improving the battery cycle stability.

Claims (7)

1. a preparation method of lithium metal negative electrode, is characterized in that: described lithium metal negative electrode is that the surface has oxide layer lithium electrode; The oxide layer is formed by ex-situ hydrolysis and condensation of organic esters on the extruded lithium surface; the preparation includes the following steps: (1) Use a glass plate with a polyolefin film to extrude the lithium sheet, that is, set glass plates on both sides of the lithium sheet to form a laminated structure, and set a polyolefin film between the lithium sheet and the glass plate, and then Apply pressure to the lithium sheet on the side of the glass plate away from the lithium sheet for a certain period of time to obtain a lithium sheet PLi with a bright surface, where PLi represents the extruded lithium sheet; the pressure range is 0.15-0.5MPa, and the time range is 10 s-5 min; (2) Immerse the PLi in the organic ester solution for 10 s-5 min, take out the PLi and wipe off the organic ester liquid on the lithium surface with a non-woven fabric, and dry it in the glove box for 2-60 min to obtain an oxide layer. the lithium metal anode. 2 . The preparation method according to claim 1 , wherein the lithium electrode is a lithium sheet electrode, and both outer surfaces of the lithium sheet are provided with oxide layers. 3 . 3. according to the described preparation method of claim 1, it is characterized in that: The thickness of the oxide layer is 500 nm to 80 μm. 4. preparation method according to claim 1, is characterized in that, The organic esters are one or more of tetramethyl silicate, tetraethyl silicate, isopropyl silicate, tetrabutyl titanate, isopropyl titanate, and tetrabutyl zirconate, The corresponding oxide layer oxide is one or more of silicon oxide, titanium oxide and zirconium oxide. 5. preparation method according to claim 1, is characterized in that: The polyolefin film is one or more of polyethylene film, polypropylene film and polyethylene/polypropylene composite film, and its thickness is 10-200 μm. 6. preparation method according to claim 1, is characterized in that: The organic esters are one or more of tetramethyl silicate, tetraethyl silicate, isopropyl silicate, tetrabutyl titanate, isopropyl titanate, and tetrabutyl zirconate. 7. An application of preparing a lithium metal negative electrode by the preparation method according to any one of claims 1-6, characterized in that: the prepared lithium metal negative electrode is applied to the negative electrode side of a lithium metal battery.

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