WO2018103563A1

WO2018103563A1 - Lithium metal negative electrode utilized in lithium battery

Info

Publication number: WO2018103563A1
Application number: PCT/CN2017/113586
Authority: WO
Inventors: 张强; 程新兵; 闫崇
Original assignee: 清华大学
Priority date: 2016-12-09
Filing date: 2017-11-29
Publication date: 2018-06-14
Also published as: CN107068971A

Abstract

The invention discloses a lithium metal negative electrode utilized in a lithium battery. A solid electrolyte protective layer is disposed at a surface of the lithium metal negative electrode. The invention provides, by performing an electrochemical process on a lithium negative electrode, an efficient and stable solid electrolyte interface at a surface of a lithium plate. In a process of repeated deposition and deintercalation of lithium ions, the solid electrolyte protective layer can inhibit formation of a crystal dendrite to enhance safety performance of the battery, and isolate an electrolyte solution from metal lithium to protect the metal lithium from being corroded by the electrolyte solution. By selecting an electroplating method and a type of an electrolyte solution, the embodiment can be employed to implement effective protection of the lithium metal negative electrode, increasing a cycle life of the lithium battery. In comparison to an unprocessed lithium negative electrode, the lithium metal negative electrode protected by the solid electrolyte layer can effectively inhibit formation of crystal dendrite-like lithium deposition, reducing side effects of the electrolyte solution and the metal lithium, and increasing cycle efficiency and cycle stability of the battery, thereby extending the cycle life of the lithium battery employing metal lithium as the negative electrode.

Description

Metal lithium negative electrode of lithium battery

Technical field

The invention relates to a metal lithium negative electrode, belonging to the technical field of metal lithium batteries using metal lithium as a negative electrode.

Background technique

Energy is closely related to people's lives, and the emergence of batteries makes energy use more convenient and faster. In the 1990s, Sony developed a graphite anode that can be safely utilized, bringing the scale of lithium-ion batteries in the field of personal electronic devices. However, with the increasing demand for high-end electronic equipment and electric vehicles, lithium-ion batteries based on conventional oxide cathodes and graphite anodes are gradually difficult to meet demand, and it is urgent to develop energy storage systems with higher energy density. Among the known electrode materials, the lithium metal anode has become the "Holy Grail" of the energy storage industry with a high capacity of 3860 mAh·g ^-1 and a negative potential (-3.040 V vs. standard hydrogen electrode), which has attracted the attention of researchers ( Energy Environ. Sci. 2014, 7, 513). Lithium-sulfur batteries (2600Wh/kg) and lithium-air batteries (3500Wh/kg) with lithium metal as the negative electrode are regarded as an important choice for next-generation energy storage batteries due to their extremely high energy density.

The metal lithium battery has obvious advantages, but in practical applications, it has encountered the problem of dendritic growth of the negative electrode. When metallic lithium is used as a negative electrode of a secondary battery, metallic lithium is reversibly deposited, causing dendrite growth. The dendrite pierces the diaphragm, causing a short circuit in the battery, which is likely to cause a safety accident. Inhibiting dendrite growth is the key to achieving high-energy-density lithium metal batteries (such as lithium-sulfur batteries, lithium-oxygen batteries, etc.). In order to suppress dendrite growth and improve the safety, utilization and cycle life of lithium metal batteries, scientists have proposed various solutions in the past half century. Professor Lynden A. Archer uses LiF as an electrolyte additive (Nature Materials 2014, 13, 961). The surface energy of lithium ions on the surface of LiF is large and the diffusion energy is small, so that lithium ions are more easily diffused into uniform lithium ions around LiF, thereby achieving uniform distribution of lithium ions. Lu et al. used copper nanowires as a current collector of metallic lithium to reduce the current density of the negative electrode, thereby extending the sand's time and inhibiting dendrite growth (Nano Letters 2016, 16, 4431). Zhao Chenxi et al. used a composite electrolyte additive of polysulfide and lithium nitrate to achieve the stability of the solid electrolyte interface film on the surface of the negative electrode, thereby inhibiting the growth of dendrites and improving the safety performance of the battery (publication number: CN 201610252402). These methods provide many new ideas for inhibiting dendrites, but they are limited by many conditions in the application process. For example, an additive can only be applied to a specific solvent, and the three-dimensional nano-framework will bring more side reactions. Wait. How to directionalally modify metallic lithium to obtain a lithium metal negative electrode that can inhibit dendrite growth and can be applied to various electrolytes and battery systems will be of great significance. Therefore, the current lithium sheet is processed to enable it to inhibit the growth of dendrites, and the application of the same lithium sheet in different battery and electrolyte systems can be realized, and the practical application of the metal lithium battery with lithium metal as the negative electrode is realized. .

Summary of the invention

The object of the invention is to change the current low cycle life of the negative electrode of the metal lithium battery, and to introduce a high-efficiency solid electrolyte interface film on the surface of the lithium plate by electrochemical pretreatment of the conventional lithium plate negative electrode, thereby suppressing the metal lithium negative electrode. Dendritic growth reduces side reactions of electrolyte and lithium metal, improving battery utilization and cycle life.

The technical solution of the present invention is: a lithium metal negative electrode of a lithium battery, characterized in that: the surface of the metal lithium negative electrode comprises a solid electrolyte protective layer, and the solid electrolyte protective layer is prepared by the following electroplating method:

1) preparing a mixed solution of a lithium salt and an organic solvent as an electrolyte solution, the molar concentration of the lithium salt is 0.1 to 10 mol / L;

2) immersing the lithium sheet into the electrolyte solution for electroplating, the current of the electroplating process is 1 μA cm ^-2 to 100 mA cm ^-2 , and after the surface of the lithium sheet is plated with a solid electrolyte protective film, the lithium sheet is taken out, that is, as a metal Lithium negative electrode.

In the above technical solution, the electrolyte solution further contains an additive, which is lithium nitrate, lithium polysulfide, lithium carbonate, fluoroethylene carbonate, vinylene carbonate, propylene sulfite, vinyl sulfite, lithium halide. One or more of sulfur dioxide and carbon dioxide, the concentration of the additive is 0.001 to 1 mol L ^-1 .

In the above technical solution, the lithium salt is lithium hexafluorophosphate, lithium hexafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium difluoroxaluminate and two (three) One or a combination of lithium fluoromethylsulfonyl).

In the above technical solution, the organic solvent is ethylene carbonate, propylene carbonate, dimethyl sulfoxide, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dimethoxyethane, acetic acid. One or more of ethyl ester, acrylonitrile, methyl formate, methacrylate, tetrahydrofuran, sulfolane, 1,3-dioxolane and tetraethylene glycol dimethyl ether.

The plating treatment time is 1 s to 1000 h, and the number of treatments is 1-1000 times. The thickness of the solid electrolyte protective film on the surface of the lithium sheet obtained by electroplating is 2 nm to 200 μm.

Compared with the prior art, the invention has the following advantages and outstanding effects: the invention adopts a plating method to compact chemical pretreatment of the lithium sheet, and the surface of the lithium electrode contains a stable solid electrolyte protective layer, which is not only simple and feasible, but also It can effectively inhibit the dendrite growth of the lithium metal anode, reduce the side reaction of the electrolyte and the metal lithium, and significantly improve the utilization rate and cycle life of the battery; experimental research shows that the metal lithium anode has no branches in the 10 to 8000 battery cycle. The crystal appears; the metal lithium negative electrode can increase the utilization rate of the lithium battery negative electrode to 80 to 99.9999%.

detailed description:

The invention provides a metal lithium negative electrode of a lithium battery, wherein the metal lithium negative electrode surface comprises a solid electrolyte protective layer, and the solid electrolyte protective layer is prepared by an electroplating method. The electrolyte solution used for electroplating contains a certain concentration of a lithium salt and an organic solvent. The lithium salt is lithium hexafluorophosphate, lithium hexafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium difluoroxaluminate and lithium bis(trifluoromethylsulfonyl) One or more of them, the lithium salt molar concentration is generally between 0.1 and 10 mol L ^-1 . The organic solvent is ethylene carbonate, propylene carbonate, dimethyl sulfoxide, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dimethoxyethane, ethyl acetate, acrylonitrile, formic acid One or more of ester, methacrylate, tetrahydrofuran, sulfolane, 1,3-dioxolane and tetraethylene glycol dimethyl ether. The electrolyte solution may further contain an additive, and the additive is lithium nitrate, lithium polysulfide, lithium carbonate, fluoroethylene carbonate, vinylene carbonate, propylene sulfite, vinyl sulfite, lithium halide, sulfur dioxide, carbon dioxide, and the like. One or more of them have a molar concentration of 0.001 to 1 mol L ^-1 . The current in the electroplating process is generally 1 μA cm ^-2 to 100 mA cm ^-2 , the treatment time is 1 s to 1000 h, and the number of treatments is 1-1000 times. The thickness of the solid electrolyte protective film on the surface of the lithium sheet obtained by electroplating is preferably 2 nm to 200 um.

The invention will be further understood from the following examples, but the invention is not limited to the following examples.

Example 1: A lithium sheet was placed in an electrolytic bath using an electrolyte of lithium bis(trifluoromethylsulfonyl) (2 mol L ^-1 ) - lithium nitrate (0.001 mol L ^-1 ) - 1,3- Oxolane/dimethoxyethane, electroplating once, current density is 1μA cm ^-2 , time is 1000h, the thickness of the protective film obtained on the surface of the lithium sheet is 200um, the lithium sheet is taken out, and assembled with the sulfur positive electrode Lithium-sulfur battery, after testing, found that the lithium-sulfur battery can achieve a coulombic efficiency of 99% and a cycle life of 5,000 cycles.

Example 2: A lithium sheet was placed in an electrolytic bath using an electrolyte of lithium bis(dicarboxylate) (0.1 mol L ^-1 )-fluoroethylene carbonate (0.01 mol L ^-1 ) - ethylene carbonate / two Ethyl carbonate, electroplating 50 times, current density is 4mA cm ^-2 , time is 10h, the thickness of the protective film obtained on the surface of the lithium sheet is 100um, the lithium sheet is taken out, assembled into a lithium empty battery, after testing, it is found that lithium The battery has a Coulomb efficiency of 92% and a cycle life of 500 laps.

Example 3: A lithium sheet was placed in an electrolytic bath using an electrolyte of lithium bisfluoroxaluminate (5 mol L ^-1 ) - vinylene carbonate (0.1 mol L ^-1 ) - dimethyl sulfoxide, electroplating 100 The current density is 100 mA cm ^-2 for 1 s. The thickness of the protective film obtained on the surface of the lithium sheet is 50 um. The lithium sheet is taken out and assembled into a battery together with the ternary material. After testing, the coulombic efficiency of the battery can be found. Up to 80%, the cycle life can reach 100 laps.

Example 4: A lithium sheet was placed in an electrolytic cell, and the electrolyte used was lithium hexafluorophosphate (1 mol L ^-1 ) - lithium polysulfide (0.5 mol L ^-1 ) - tetraethylene glycol dimethyl ether, electroplated 20 times, current The density is 0.5 mA cm ^-2 , the time is 0.5 h, the thickness of the protective film obtained on the surface of the lithium sheet is 10 um, the lithium sheet is taken out, and assembled into a battery together with lithium cobaltate. After testing, the coulombic efficiency of the battery can be achieved. 99.9999%, cycle life can reach 2000 laps.

Example 5: A lithium sheet was placed in an electrolytic cell, and the electrolyte used was lithium perchlorate (0.1 mol L ^-1 )-propylene carbonate, electroplated 800 times, current density was 0.2 mA cm ^-2 , time was 1 h The protective film obtained on the surface of the lithium sheet has a thickness of 5 um, and the lithium sheet is taken out and assembled into a battery together with lithium iron phosphate. After testing, the battery has a Coulomb efficiency of 90% and a cycle life of 5,000 cycles.

Example 6: A lithium sheet was placed in an electrolytic cell, and the electrolyte used was lithium hexafluoroarsenate (2.5 mol L ^-1 )-tetrahydrofuran, electroplated 10 times, current density was 8 mA cm ^-2 , time was 30 s, The thickness of the protective film obtained on the surface of the lithium sheet is 1 um. The lithium sheet is taken out and assembled into a battery together with sulfur dioxide. After testing, the battery has a coulombic efficiency of 82% and a cycle life of 150 laps.

Example 7: A lithium sheet was placed in an electrolytic cell using an electrolyte of lithium difluorooxalate borate (2.5 mol L ^-1 ) - propylene sulfite (1 mol L ^-1 ) - ethylene carbonate / diethyl carbonate Ester/methyl ethyl carbonate, electroplated 400 times, current density is 100μA cm ^-2 , time is 30s, the thickness of the protective film obtained on the surface of the lithium sheet is 20um, the lithium sheet is taken out, and assembled into a battery together with lithium manganate. The test found that the battery has a Coulomb efficiency of 99.5% and a cycle life of 1500 cycles.

Example 8: A lithium sheet was placed in an electrolytic cell using an electrolyte of lithium bis(dicarboxylate) (0.1 mol L ^-1 )-fluoroethylene carbonate (0.5 mol L ^-1 )-dimethyl carbonate /Diethyl carbonate, electroplating 50 times, current density is 40mA cm ^-2 , time is 10h, the thickness of the protective film obtained on the surface of the lithium sheet is 500nm, the lithium sheet is taken out, assembled into a lithium battery, after testing, Lithium batteries have a Coulombic efficiency of 92% and a cycle life of 500 laps.

Example 9: A lithium sheet was placed in an electrolytic cell using an electrolyte of lithium bis(dicarboxylate) (0.1 mol L ^-1 )-ethylene carbonate/ethyl acetate, electroplated 50 times, and a current density of 0.1 mA cm. ^-2 , the time is 10h, the thickness of the protective film obtained on the surface of the lithium sheet is 100nm, the lithium sheet is taken out and assembled into a lithium empty battery. After testing, the coulombic efficiency of the lithium empty battery can reach 97%, and the cycle life can reach 500. ring.

Example 10: A lithium sheet was placed in an electrolytic cell, and the electrolyte used was lithium perchlorate (0.1 mol L ^-1 )-acrylonitrile, electroplated 800 times, current density was 5 mA cm ^-2 , time was 1 h, The protective film obtained on the surface of the lithium sheet has a thickness of 50 nm. The lithium sheet is taken out and assembled into a battery together with lithium iron phosphate. After testing, the battery has a coulombic efficiency of 85% and a cycle life of 5,000 cycles.

Example 11: A lithium sheet was placed in an electrolytic cell, and the electrolyte used was lithium hexafluorophosphate (2.5 mol L ^-1 )-methyl formate, electroplated 10 times, current density was 8 A cm ^-2 , time was 30 s, in lithium tablets The surface of the protective film has a thickness of 10 nm. The lithium sheet is taken out and assembled into a battery together with sulfur dioxide. After testing, the battery has a coulombic efficiency of 82% and a cycle life of 150 cycles.

Example 12: A lithium sheet was placed in an electrolytic cell, and the electrolyte used was lithium hexafluorophosphate (1 mol L ^-1 ) - methacrylate, electroplated 20 times, current density was 0.5 A cm ^-2 , time was 0.5 h, The thickness of the protective film obtained on the surface of the lithium sheet is 5 nm. The lithium sheet is taken out and assembled into a battery together with lithium cobaltate. After testing, the battery has a Coulomb efficiency of 99.996% and a cycle life of 2000 cycles.

Example 13: A lithium sheet was placed in an electrolytic cell, and the electrolyte used was lithium bis(dicarboxylate) borate (2.5 mol L ^-1 )-sulfolane, electroplated 10 times, current density was 3 mA cm ^-2 , time was 30 s, The protective film obtained on the surface of the lithium sheet has a thickness of 2 nm. The lithium sheet is taken out and assembled into a battery together with sulfur dioxide. After testing, the battery has a coulombic efficiency of 82% and a cycle life of 150 cycles.

Example 14: A lithium sheet was placed in an electrolytic cell using an electrolyte of lithium hexafluoroborate (0.1 mol L ^-1 ) - fluoroethylene carbonate (0.005 mol L ^-1 ) - dimethyl carbonate / two Ethyl carbonate, electroplating 50 times, current density 4 mA cm ^-2 , time 10 h, the thickness of the protective film obtained on the surface of the lithium sheet is 20 nm, the lithium sheet is taken out, assembled into a lithium empty battery, after testing, it is found that lithium empty The battery has a Coulomb efficiency of 92% and a cycle life of 500 laps.

Example 15: A lithium sheet was placed in an electrolytic cell using an electrolyte of lithium bis(trifluoromethylsulfonyl) (2 mol L ^-1 ) - lithium carbonate (0.05 mol L ^-1 ) - 1,3- Oxolane/dimethoxyethane, electroplated 1000 times, current density is 40μA cm ^-2 , time is 1h, the thickness of the protective film obtained on the surface of the lithium sheet is 60nm, the lithium sheet is taken out, and assembled with the sulfur positive electrode Lithium-sulfur battery, after testing, found that the lithium-sulfur battery can achieve a coulombic efficiency of 99% and a cycle life of 5,000 cycles.

Example 16: A lithium sheet was placed in an electrolytic cell using an electrolyte of lithium difluorooxalate borate (2.5 mol L ^-1 ) - vinyl sulfite (0.5 mol L ^-1 ) - ethylene carbonate, electroplating 400 times The current density is 10 mA cm ^-2 for 15 min. The thickness of the protective film obtained on the surface of the lithium sheet is 200 nm. The lithium sheet is taken out and assembled into a battery together with lithium manganate. After testing, the coulombic efficiency of the battery can be achieved. 99.9%, cycle life can reach 1500 laps.

Example 17: A lithium sheet was placed in an electrolytic cell using an electrolyte of lithium bis(trifluoromethylsulfonyl) (2 mol L ^-1 ) - lithium fluoride (0.8 mol L ^-1 ) - 1,3- Dioxolane/dimethoxyethane, electroplating 300 times, current density 300μA cm ^-2 , time 10h, protective film thickness on the surface of lithium sheet is 800nm, lithium sheet is taken out, assembled with sulfur positive electrode Lithium-sulfur battery has been tested and found that the lithium-sulfur battery can achieve a coulombic efficiency of 99.91% and a cycle life of 5000 cycles.

Example 18: A lithium sheet was placed in an electrolytic cell, and the electrolyte used was lithium bisfluoroxaluminate (5 mol L ^-1 )-vinylene carbonate, and sulfur dioxide was flushed into the electrolytic cell, electroplating 10 times, current density is a 0.1mA cm ^-2, time was 5h, the film thickness of the protective sheet on the surface of the lithium obtained was 50 nm, the lithium sheet removed, together with the ternary material is assembled into a battery, tested and found coulombic efficiency of the battery can reach 80% The cycle life can reach 100 laps.

Example 19: A lithium sheet was placed in an electrolytic cell using an electrolyte of lithium bis(trifluoromethylsulfonyl) (1 mol L ^-1 )-ethylene carbonate/ethyl acetate and flushed into an electrolytic cell. Sulfur dioxide, electroplating 50 times, current density is 40mA cm ^-2 , time is 10s, the thickness of the protective film obtained on the surface of the lithium sheet is 40μm, the lithium sheet is taken out, and assembled with the sulfur positive electrode into a battery, after testing, the battery is found Coulomb efficiency can reach 99.95%, cycle life can reach 10 laps.

Example 20: A lithium sheet was placed in an electrolytic cell using an electrolyte of lithium difluoroxaluminate (4 mol L ^-1 )-1,3-dioxolane/dimethoxyethane and directed to an electrolytic cell. The carbon dioxide is poured into the carbon dioxide, electroplated twice, the current density is 0.8 mA cm ^-2 , the time is 4.5 h, and the thickness of the protective film obtained on the surface of the lithium sheet is 15 μm. The lithium sheet is taken out and assembled into a battery together with lithium iron phosphate. The test found that the battery can achieve a coulombic efficiency of 89.9% and a cycle life of 8,000 cycles.

Claims

A lithium metal negative electrode of a lithium battery, characterized in that: the surface of the metal lithium negative electrode comprises a solid electrolyte protective layer, and the solid electrolyte protective layer is prepared by the following electroplating method:

1) preparing a mixed solution of a lithium salt and an organic solvent as an electrolyte solution, the molar concentration of the lithium salt is 0.1 to 10 mol / L;

2) immersing the lithium sheet into the electrolyte solution for electroplating, the current of the electroplating process is 1 μA cm -2 to 100 mA cm -2 , and after the surface of the lithium sheet is plated with a solid electrolyte protective film, the lithium sheet is taken out, that is, as a metal Lithium negative electrode.
The lithium metal negative electrode of a lithium battery according to claim 1, wherein the electrolyte solution contains an additive, and the additive is lithium nitrate, lithium polysulfide, lithium carbonate, fluoroethylene carbonate, vinylene carbonate. One or more of ester, propylene sulfite, vinyl sulfite, lithium halide, sulfur dioxide and carbon dioxide, the molar concentration of the additive is from 0.001 to 1 mol L -1 .
The lithium metal negative electrode of a lithium battery according to claim 1, wherein the lithium salt is lithium hexafluorophosphate, lithium hexafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate) borate, A combination of one or more of lithium difluorooxalate borate, lithium difluoroxaluminate, and lithium bis(trifluoromethylsulfonyl).
The lithium metal negative electrode of a lithium battery according to claim 1, wherein the organic solvent is ethylene carbonate, propylene carbonate, dimethyl sulfoxide, dimethyl carbonate, diethyl carbonate. Ester, methyl ethyl carbonate, dimethoxyethane, ethyl acetate, acrylonitrile, methyl formate, methacrylate, tetrahydrofuran, sulfolane, 1,3-dioxolane and tetraethylene glycol dimethyl ether One or a combination of several.
A metal lithium negative electrode for a lithium battery according to any one of claims 1 to 4, characterized in that the plating treatment time is from 1 s to 1000 h, and the number of treatments is from 1 to 1000 times.
The lithium metal negative electrode of a lithium battery according to any one of claims 1 to 4, wherein the solid electrolyte protective film on the surface of the lithium sheet obtained by electroplating has a thickness of 2 nm to 200 μm.