CN108736056B - A lithium metal interface protection structure and its preparation and application - Google Patents

Abstract

The invention relates to a lithium metal interface protection structure and its preparation and application. Specifically, the present invention discloses an interface protection structure. The invention also discloses the preparation method and application of the interface protection structure. The battery including the interface protection structure has excellent cycle performance and service life. The preparation method has the characteristics of simple process, low cost, readily available raw materials and the like.

Description

A lithium metal interface protection structure and its preparation and application

technical field

The invention relates to the field of electrochemistry, in particular to a lithium metal interface protection structure and its preparation and application.

Background technique

Benefiting from the small volume change of ~10% of the graphite anode during cycling, lithium-ion batteries using it as the anode material can achieve stable cycling performance and long service life. However, the lithium storage capacity of graphite anode materials is relatively low (339mAh/g in the case of lithium intercalation, 372mAh/g in the case of lithium extraction), and in the process of continuously seeking higher energy density systems in the lithium battery market, it has been unable to meet the needs of the industry .

As a high energy density anode material (the theoretical capacity of lithium metal is 3860mAh/g and has the lowest electrode potential), the application prospects of lithium metal in emerging high energy storage battery systems such as lithium-air and lithium-sulfur are unanimously promising. However, the cycle efficiency Problems such as low safety and poor safety have always hindered its further promotion and application in the battery industry. Through a large number of studies, it has been found that in the process of battery charging, non-uniform lithium deposition will occur on the surface of lithium metal or other metal current collectors. With the continuous charging process, uneven Li deposition inevitably leads to huge volume expansion and local Li dendrite growth on the Li metal surface. Volume expansion and dendrite issues can lead to increased electrode interface impedance and battery capacity loss. The continuous dendrite growth can pierce the electrolyte separator and cause the battery to short-circuit, making the lithium metal negative electrode always accompanied by huge safety hazards during use, which also makes it difficult to be used in electric vehicles, portable electronic devices, etc. in a demanding work environment. In recent years, through various solutions proposed by the industry, the service life and efficiency of lithium metal anodes have been significantly improved, but the improved strength is still difficult to meet the needs of large-scale commercialization.

The existing protection methods are too single in the protection of lithium dendrites. Among them, the use of solid electrolyte can inhibit dendrite growth to a certain extent, but the lower ionic conductivity and the poor electrode/electrolyte interface will lead to a large increase in the internal resistance of the battery; The additive can accelerate the formation of a protective passivation layer on the surface of the electrode, but the passivation layer itself does not have the mechanical properties to inhibit the growth of dendrites. In the end, uneven dendrite growth will still occur on the surface of the electrode, and excessive dendrite growth will occur. The growth can pierce the passivation layer, so that the part of the lithium metal that is not covered by the passivation layer directly contacts the electrolyte and generates a new passivation layer again. Repeated cracking and regeneration of the passivation layer will continuously consume the lithium and lithium in the system. Electrolyte.

In summary, although there are alternative lithium metal protection methods in the art, the structural stability and cycle effect of the existing lithium metal anodes are still unsatisfactory.

Therefore, there is an urgent need in the art to develop a protection method that can effectively achieve high cycle efficiency of lithium metal and a preparation process thereof.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an interface protection structure capable of efficiently protecting lithium metal and its preparation and application.

In a first aspect of the present invention, an interface protection structure precursor material is provided, and the precursor material is prepared as follows:

1) Provide a mixed slurry, the mixed slurry includes: metal fluoride, carbon material, binder and solvent;

2) coating the mixed slurry on the surface of the metal substrate to obtain a metal substrate containing the first coating;

3) Baking the metal substrate containing the first coating to obtain a metal substrate containing a second coating, where the second coating is the precursor material of the interface protection structure.

In another preferred example, the metal base is a metal base material that does not alloy with lithium metal.

In another preferred embodiment, the metal substrate is selected from the group consisting of copper foil, nickel foil, and stainless steel foil.

In another preferred embodiment, the metal fluoride is selected from the group consisting of nickel fluoride, manganese fluoride, iron fluoride, titanium fluoride, copper fluoride, tin fluoride, or a combination thereof; and/or

The carbon material is selected from the group consisting of ultra-conductive carbon black, graphene, Ketjen black, acetylene black, carbon nanotubes, or a combination thereof; and/or

The binder is selected from the group consisting of polyvinylidene fluoride, polyimide, t-phenylbutyl rubber, polyacrylonitrile, polyacrylate, sodium alginate, or a combination thereof.

In another preferred embodiment, the solvent is selected from the group consisting of water, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, or its combination.

In another preferred example, in the mixed slurry, the mass ratio of the metal fluoride, the carbon material and the binder is 5-12:1-3:1-5, preferably 7 -10:1-2:1-3.

In another preferred embodiment, the thickness of the first coating is 10-100 microns, preferably 20-40 microns.

In another preferred embodiment, the treatment temperature of the baking treatment is 60-160°C, preferably 100-140°C; and/or

The treatment time of the baking treatment at the treatment temperature is 1-20h, preferably 6-16h, more preferably 8-14h.

In another preferred embodiment, the baking process is carried out under the protection of vacuum or inert gas.

In another preferred example, after step 3), the method further includes a step of: cutting the product obtained in step 3) to obtain a negative electrode material containing the interface protection structure precursor material.

In a second aspect of the present invention, an interface protection structure is provided, and the interface protection structure is prepared as follows:

i) providing a negative electrode material, an electrolyte, a separator, and a lithium electrode sheet containing the precursor material of the interface protection structure according to the first aspect of the present invention;

ii) assembling a battery with the negative electrode material, the electrolyte, the separator and the lithium electrode sheet;

iii) The battery obtained in the electrochemical reduction treatment step ii) is disassembled, and the interface protection structure can be obtained by peeling off the obtained negative electrode.

In another preferred example, the electrolyte, the separator and the lithium electrode sheet are not particularly limited, and can be prepared by using conventional materials in the art, or prepared by conventional methods in the art, or purchased from the market.

In another preferred example, the electrolyte is selected from the following group: 3011R (purchased from Zhangjiagang Guotai Huarong Chemical New Material Co., Ltd.), the electrolyte (wherein, the lithium salt is selected from the following group: lithium hexafluorophosphate, high Lithium chlorate, lithium bistrifluoromethanesulfonimide, lithium bisfluorosulfonimide, or a combination thereof; the solvent is selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate , propylene carbonate, ethylene glycol dimethyl ether, 1,3-dioxolane, or a combination thereof).

In another preferred embodiment, the separator is selected from the group consisting of polyethylene separator, polypropylene separator, propylene/ethylene copolymer separator, polyester film (PET, Polyethylene Terephthalate), cellulose film, polyimide film ( PI), polyamide film (PA), spandex or aramid film, or a combination thereof.

In another preferred embodiment, the thickness of the lithium electrode sheet is 50-200 microns, preferably 100-150 microns.

In another preferred example, the electrochemical reduction treatment refers to: discharging the battery to 0V.

According to a third aspect of the present invention, there is provided an article comprising the interface protection structure precursor material of the first aspect of the present invention or the interface protection structure of the second aspect of the present invention.

In another preferred embodiment, the product is preferably a battery.

A fourth aspect of the present invention provides a battery, which includes the interface protection structure described in the second aspect of the present invention.

In another preferred example, the battery is a lithium metal battery, preferably a lithium metal secondary battery.

In another preferred example, the battery further includes a positive electrode material, a negative electrode material, an electrolyte and a separator.

In another preferred embodiment, the interface protection structure in the second aspect of the present invention is arranged adjacent to the diaphragm.

In another preferred embodiment, the interface protection structure in the second aspect of the present invention is located between the negative electrode material and the separator material.

In another preferred example, the negative electrode material is the support material of the interface protection structure, preferably, the negative electrode material is selected from the following group: copper foil, copper mesh, lithium foil, nickel mesh, aluminum foil, aluminum mesh, or a combination thereof.

In another preferred embodiment, the coulombic efficiency of the battery after 100 cycles of lithium metal deposition/decomposition is greater than or equal to 60%, preferably greater than or equal to 70%, more preferably greater than or equal to 80%, preferably greater than or equal to 90%, and most preferably Good location ≥ 95%.

It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described in the following (eg, the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, it is not repeated here.

Description of drawings

FIG. 1 illustrates a method of using the interface protection structure of the present invention.

FIG. 2 shows the change in coulombic efficiency of the copper-lithium batteries 1-6 prepared in Examples 1-6 and the copper-lithium battery C1 prepared in Comparative Example 1 under the test conditions of the present invention for 100 cycles.

Detailed ways

After long-term and in-depth research, the inventors have unexpectedly prepared an interface protection structure that can efficiently protect lithium metal, and a battery comprising the interface protection structure can obtain excellent cycle performance and service life. The preparation method of the interface protection structure has the characteristics of simple process, low cost, easy availability of raw materials and the like. On this basis, the inventors have completed the present invention.

Interface protection structure and preparation method thereof

In the present invention, it should be understood that the interface protection structure obtained by the electrochemical reduction treatment has a lithium fluoride framework.

In the present invention, the interface protection structure precursor material includes metal fluoride/carbon material/binder.

Typically, the metal fluorides include (but are not limited to): conventional metal fluorides such as nickel fluoride, titanium fluoride, copper fluoride, iron fluoride, or manganese fluoride or combinations thereof, which can be selected in the art Conventional materials, either prepared by conventional methods, or purchased from the market.

Typically, the particle size of the metal fluoride is 10-100 nanometers.

Representatively, the carbon material includes (but is not limited to): Super-P, Ketjen black, acetylene black, graphene, carbon nanotube, or a combination thereof.

Typically, the binder includes (but is not limited to): tert-phenylene butyl rubber, polyimide, polyvinylidene fluoride, polyacrylonitrile, polyacrylate, sodium alginate, or a combination thereof.

In a preferred example, the weight ratio of the metal fluoride: the carbon material: the binder is 65-89%: 10-30%: 1-5%.

In the present invention, the loading amount of the metal fluoride is 1-5 mg/cm 2 .

Typically, the interface protection structure is prepared as follows:

(1) the binder is stirred and pre-dissolved in an organic solvent to obtain a binder solution, and the concentration of the binder solution does not exceed 30% by mass;

(2) mixing and stirring the metal fluoride, the carbon material and the binder solution in an organic solvent to obtain a precursor material slurry;

(3) Coating the precursor material slurry on one side of the current collector, preheating the volatilized organic solvent at a low temperature, and then baking in an inert atmosphere or a vacuum environment;

(4) Put the baked pole piece into the battery whose counter electrode is a lithium piece and discharge to 0V for reduction, disassemble the battery, and leave the electrochemically reduced pole piece in an air environment to obtain a peelable self-contained Support interface protection structure.

Typically, the organic solvent is different according to the binder, including (but not limited to): water, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or a combination thereof.

In another preferred embodiment, the solvent is N-methylpyrrolidone.

In another preferred embodiment, the stirring is magnetic stirring.

In another preferred example, the stirring time in the step (1) and/or (2) is 1-5 hours, preferably 2-3 hours.

In another preferred example, the concentration of the binder solution in the step (1) is 5-30%, preferably 10%.

In another preferred embodiment, the low temperature preheating temperature is 80-140°C, more preferably 100-120°C. In another preferred example, the baking time is 1-20h, more preferably 3-15h.

In another preferred embodiment, the baking is performed in a vacuum environment or under the protection of an inert gas.

The protection structure according to the present invention mainly forms a negative electrode with the support structure and acts in the lithium secondary battery. The support structure is selected from the group consisting of copper foil, copper mesh, lithium foil, nickel mesh.

More specifically, in the present invention, the inventors consist of metal fluoride/carbon material/binder by coating the surface of copper foil, nickel foil or stainless steel foil and other metal base current collectors that do not alloy with lithium metal. coating, it was found that a self-supporting structure with a lithium fluoride framework could be formed after it was electrochemically reduced by lithium ions. This structure is not only easy to peel off from the metal base current collector, but when it is placed on the surface of lithium metal or other negative current collectors, it can effectively protect the lithium metal deposited under the protective structure and on the side of the current collector during battery cycling. Its direct contact with the electrolyte avoids the occurrence of side reactions, prevents lithium metal dendrite growth and passivation and a series of characteristics to optimize the electrode cycle efficiency and service life (the usage method of the protective structure is shown in Figure 1). Cells incorporating the interface protection structure can achieve ~98% coulombic efficiency and cycle life over 100 weeks at a current density of 0.5 mA/cm2 and operating conditions of 1 mAh/cm2. At the same time, the preparation method of the interface protection structure described in the present invention is simple and effective, can be processed in large batches at one time, and has huge application potential.

Typically, the interfacial protection structure directly caps the copper current collector, protects the lithium metal deposited between the copper current collector and the protection structure, and characterizes the deposition/decomposition of lithium metal on the protected copper current collector. Coulomb efficiency. The lithium metal placed on the other side of the separator in this system only serves as the lithium source to provide the lithium metal deposited on the copper foil, not a protected object.

It should be understood that in practical applications, the protection structure can also be covered on the lithium metal negative electrode in the lithium metal battery to protect the lithium metal interface between the lithium metal and the protection structure, as shown in schematic diagram 1 .

application

The present invention also provides a battery including the interface protection structure.

In the present invention, the coulombic efficiency of the battery after 100 cycles of lithium metal deposition/decomposition is ≥ 60%, preferably ≥ 70%, more preferably ≥ 80%, preferably ≥ 90%, most preferably ≥95%.

Compared with the prior art, the present invention has the following main advantages:

(1) In the battery comprising the interface protection structure, during the cycle process, the interface protection structure can effectively protect the lithium metal, so that the lithium metal is isolated from the electrolyte during the deposition process, and no side reactions or only a small amount of side reactions occur. ;

(2) In a battery including the interface protection structure, the interface protection structure can effectively prevent the growth and passivation of lithium metal dendrites;

(3) The battery including the interface protection structure has extremely excellent cycle performance of lithium metal anode, and can reach ~98% coulomb under the current density of 0.5 mA/cm2 and the working condition of 1 mAh/cm2 Efficiency and cycle life of over 100 weeks;

(4) the preparation method of the interface protection structure has the characteristics of simple process, low cost, easy availability of raw materials and the like;

(5) After the protection structure is prepared, it can be directly peeled off from the metal substrate and implanted into other lithium metal batteries to protect the surface of the lithium metal negative electrode, which has strong applicability.

The present invention will be further described below in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In the following examples, the experimental methods without specific conditions are usually in accordance with conventional conditions or in accordance with the conditions suggested by the manufacturer. Percentages and parts are by weight unless otherwise indicated.

Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described can be used in the methods of the present invention. Methods and materials for preferred embodiments described herein are provided for illustrative purposes only.

Example 1 Copper-lithium battery 1 with interface protection structure 1

a. Pre-dissolve polyvinylidene fluoride (PVdF) with a mass ratio of 10% in N-methylpyrrolidone (NMP) solvent, and mix and stir in a magnetic stirrer for 3 hours to obtain a uniform solution;

b. Stir nickel fluoride, super conductive carbon black (Super-P) and polyvinylidene fluoride in a mass ratio of 7:1:2, add solvent N-methylpyrrolidone (NMP) to the mixture and place it under magnetic stirring Mixing and stirring in the vessel for 3 hours to obtain the precursor material slurry;

c. Coat the precursor material slurry on the surface of the copper foil (the thickness of the coating is about 20-60 μm), and bake it at 120 ° C for 12 hours in a vacuum environment;

d, cutting the pole piece after baking in step c into a circular piece with a diameter of 16 mm as a negative pole piece having an interface protection structure precursor;

e. Drop the electrolyte 3011R into a polyethylene separator with a thickness of 20 microns in an amount of 70 μL, and put it into a CR2032 button battery case together with the negative electrode piece and the counter electrode metal lithium piece obtained in d. The battery is assembled in the glove box.

f. The battery obtained in e is discharged to 0V for reduction, the battery is disassembled, and the electrochemically reduced negative electrode is allowed to stand in an air environment to obtain a peelable interface protection structure 1 .

g. Place the interface protection structure 1 obtained in f on the surface of the copper foil, drop the electrolyte 3011R into a polyethylene separator with a thickness of 20 microns in an amount of 70 μL, and load the CR2032 button battery with the metal lithium sheet as the counter electrode. shell to obtain a copper-lithium battery 1 with an interface protection structure 1 .

Example 2 Copper-lithium battery 2 with interface protection structure 2

Same as Example 1, the difference is: in step b, the metal fluoride is manganese fluoride.

Embodiment 3 Copper-lithium battery 3 with interface protection structure 3

With Embodiment 1, the difference is: in step b, the metal fluoride is iron fluoride.

Embodiment 4 Copper-lithium battery 4 with interface protection structure 4

Same as Example 1, the difference is: in step b, the ratio of nickel fluoride: super conductive carbon black (Super-P): polyvinylidene fluoride is 8:1:1.

Embodiment 5 Copper-lithium battery 5 with interface protection structure 5

Same as Example 1, the difference is: in step b, the carbon material is graphene.

Embodiment 6 Copper-lithium battery 6 with interface protection structure 6

Same as Example 1, the difference is: in step b, the binder is polyimide.

Comparative Example 1 Copper-lithium battery C1 without interface protection structure

a. Drop the electrolyte 3011R into a 20-micron-thick polyethylene separator in an amount of 70 μL, and use copper foil as the working electrode and metal lithium sheet as the counter electrode to put it into a CR2032 button battery case to obtain a CR2032 button battery case without an interface protection structure. Copper lithium battery C1.

Electrochemical performance test

At a current density of 0.5 mA/cm 2 , lithium metal deposition/decomposition cycles were performed on copper-lithium batteries 1-6 prepared in Examples 1-6 and copper-lithium battery C1 prepared in Comparative Example 1, respectively. The cycling conditions were to deposit 1 mAh/cm2 of lithium metal on the copper electrode every week, and then decompose it with a decomposition cut-off potential of 0.5 V. The lithium metal protection effect on the copper electrode side was characterized by the Coulomb efficiency, that is, the amount of decomposition/deposition.

The results are shown in Table 1 and Figure 2.

Table 1 Coulomb efficiency results

Week 10 Week 50 Week 100 Example 1 97.55% 97.60% 97.65% Example 2 94.39% 97.19% 81.95% Example 3 95.75% 97.25% 68.68% Example 4 92.36% 95.25% 90.35% Example 5 95.90% 97.65% 97.15% Example 6 94.4% 96.7% 90.35% Comparative Example 1 55.66% 25.22% --

It can be seen from Fig. 2 and Table 1 that during the 100-cycle cycle, the copper-lithium batteries 1-6 with the interface protection structure of the present invention can maintain a coulombic efficiency of more than 90% in the first 50 weeks, but do not have the interface of the present invention. The copper-lithium battery C1 with the protective structure was only 55.66% in the 10th week, attenuated to 25.22% in the 50th week, and could not be cycled to 100 weeks.

All documents mentioned herein are incorporated by reference in this application as if each document were individually incorporated by reference. In addition, it should be understood that after reading the above teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims (11)

1. A lithium metal battery, wherein the battery comprises an interface protection structure; The interface protection structure is prepared as follows: i) Anode materials, electrolytes, separators, and lithium electrode sheets that provide interface protection structure precursor materials; ii) assembling a battery with the negative electrode material, the electrolyte, the separator and the lithium electrode sheet; iii) The battery obtained in the electrochemical reduction treatment step ii) is disassembled, and the interface protection structure can be obtained by peeling off the obtained negative electrode; The interface protection structure precursor material is prepared as follows: 1) Provide a mixed slurry, the mixed slurry includes: metal fluoride, carbon material, binder and solvent; 2) coating the mixed slurry on the surface of the metal substrate to obtain a metal substrate containing the first coating; 3) baking the metal substrate containing the first coating to obtain a metal substrate containing a second coating, where the second coating is the precursor material of the interface protection structure; The electrochemical reduction treatment refers to: discharging the battery to 0V; The interface protection structure obtained by the electrochemical reduction treatment has a lithium fluoride framework; The battery also includes a positive electrode material, a negative electrode material, an electrolyte and a separator; The interface protection structure is located between the negative electrode material and the separator material. 2 . The battery of claim 1 , wherein the negative electrode material is a support material of the interface protection structure. 3 . 3. The battery of claim 1, wherein the negative electrode material is selected from the group consisting of copper foil, copper mesh, lithium foil, nickel mesh, aluminum foil, aluminum mesh, or a combination thereof. 4. The battery of claim 1, wherein the metal fluoride is selected from the group consisting of nickel fluoride, manganese fluoride, iron fluoride, titanium fluoride, copper fluoride, tin fluoride, or its combination; and/or The carbon material is selected from the group consisting of ultra-conductive carbon black, graphene, Ketjen black, acetylene black, carbon nanotubes, or a combination thereof; and/or The binder is selected from the group consisting of polyvinylidene fluoride, polyimide, t-phenylbutyl rubber, polyacrylonitrile, polyacrylate, sodium alginate, or a combination thereof. 5 . The battery of claim 1 , wherein in the mixed slurry, the mass ratio of the metal fluoride, the carbon material and the binder is 5-12:1-3:1 5 . -5. 6 . The battery according to claim 1 , wherein the processing temperature of the baking treatment is 60-160° C.; and/or The treatment time of the baking treatment at the treatment temperature is 1-20 h. 7. The battery of claim 1, wherein the battery has a coulombic efficiency of ≥60% after 100 cycles of lithium metal deposition/decomposition cycles. 8. The battery of claim 1, wherein the battery has a coulombic efficiency of ≥70% after 100 cycles of lithium metal deposition/decomposition cycles. 9 . The battery of claim 1 , wherein the battery has a coulombic efficiency of ≥80% after 100 cycles of lithium metal deposition/decomposition cycles. 10 . 10. The battery of claim 1, wherein the battery has a coulombic efficiency of ≥90% after 100 cycles of lithium metal deposition/decomposition cycles. 11. The battery of claim 1, wherein the battery has a coulombic efficiency > 95% after 100 cycles of lithium metal deposition/decomposition cycles.

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