A pretreatment method for the lithium metal anode of a lithium-air battery

Abstract

The present invention relates to a pretreatment method for a lithium metal anode of a lithium-air battery, which is characterized in that the method involves three steps: dropping an aluminum chloride / nitrobenzene solution on the surface of the lithium metal, pressing the lithium metal with a battery separator containing an organic solvent, and finally forming a stable alloy protective layer through cyclic charge and discharge activation of a lithium|lithium symmetric battery. The implementation of this method can significantly improve the stability of the lithium metal. The pretreated lithium metal as the anode of the lithium-air battery can significantly improve its cycle life.

Description

Technical Field

[0001] The present invention relates to a pretreatment method for a lithium metal anode of a lithium-air battery Technical Background

[0002] Lithium metal is considered to be the most promising anode material in the field of lithium batteries due to its low density (0.534 g cm -3 ), high theoretical specific capacity (3861 mAh g -1 ), etc., and is also known as the "Holy Grail" in the lithium battery industry. The electrode potential of lithium metal is the lowest (-3.040V vs SHE), which can spontaneously react with the organic electrolyte to form a solid electrolyte interface (SEI) composed of various organic and / or inorganic substances, etc., which can protect lithium metal.

[0003] However, during the lithium metal electrodeposition process, dendrites are easily formed, continuously damaging the SEI film, and the electrode volume constantly changes. When the dendrites pierce the separator, it will cause the battery to short-circuit, and in severe cases, it may trigger a battery explosion. When the root of the dendrite breaks, it is separated from the lithium metal by the newly formed SEI film, forming "dead lithium". In addition, lithium metal may also be corroded by trace amounts of moisture in the electrolyte. Dendrites and corrosion seriously affect the cycle stability of the battery.

[0004] Therefore, constructing a strong SEI and improving the stability of the lithium metal anode are crucial for improving the lifespan of lithium batteries. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a pretreatment method for a lithium metal anode of a lithium-air battery to improve the stability of the lithium metal anode.

[0006] The specific steps are as follows:

[0007] (1) First, place lithium metal in tetrahydrofuran for etching. After taking it out and drying, then dropwise add an aluminum chloride / nitrobenzene solution with a concentration of 100-140 mg / mL, so that its content on the lithium metal is 10-15 μL / cm², and let it stand for 18-36 hours;

[0008] (2) After dropping 50-80 μL / cm² of an organic solvent on the battery separator, spread it on the lithium metal in step (1). After pressing for a period of time, remove the battery separator;

[0009] (3) Assemble the lithium metal obtained in step (2) into a lithium|lithium symmetric battery, use a 1 mol / L lithium bis(trifluoromethanesulfonyl)imide-ethylene glycol dimethyl ether / 1,3-dipentylheptane as the electrolyte, and perform activation by cyclic charge and discharge. The charge and discharge current is 0.05-2 mA / cm², the charge and discharge time is 1-1.5 hours, and the number of cycles is 1-30 times.

[0010] (4) Using the metallic lithium obtained in step (3) as the anode of a lithium-air battery, assembling a lithium-air battery with a cathode and an organic electrolyte can improve the cycle life of the lithium-air battery.

[0011] The organic solvent is one or more of ethers such as tetrahydrofuran and ethylene glycol dimethyl ether, or esters such as diethyl carbonate and ethylene carbonate.

[0012] The cathode of the lithium-air battery is one or more of carbon materials such as graphene, carbon nanotubes, and acetylene black, or carbon-supported noble metals and carbon-supported transition metal compounds. The solvent of the electrolyte is one or more of sulfones such as dimethyl sulfoxide, ethers such as ethylene glycol dimethyl ether, and esters such as propylene carbonate. The solute is one or more of common solutes such as lithium hexafluorophosphate, lithium perchlorate, and lithium tetrafluoroborate, and the concentration is 0.1 to 4 mol / L.

[0013] The present invention has no special requirement for the etching time of metallic lithium in tetrahydrofuran, as long as the impurities on the surface of metallic lithium can be removed.

[0014] The present invention has no requirement for the size of the battery spread on metallic lithium, as long as it can cover the metallic lithium. There is no special requirement for the pressing force and time, as long as the aluminum chloride / nitrobenzene layer can be homogenized, the unreacted aluminum chloride / nitrobenzene can be removed, and the metallic lithium will not be bent.

[0015] The present invention has no special requirement for the assembly of the lithium|lithium symmetric battery and the addition amount of the electrolyte, as long as the symmetric battery can operate normally.

[0016] The present invention has no special requirement for the assembly of the lithium-air battery, the loading amount of the cathode material, and the addition amount of the electrolyte, as long as the lithium-air battery can operate normally. Description of the Drawings

[0017] Figure 1 Surface morphologies of as-received (a) and pretreated (b) metallic lithium

[0018] Figure 2 Deposition and precipitation polarization curves of as-received and pretreated lithium metal (a), cycling details from 0 - 4 h (b), 300 - 204 h (c), and 800 - 804 h (d)

[0019] Figure 3 Performance of lithium-air batteries with as-received and pretreated lithium metal Detailed Description of the Invention

[0020] Example 1

[0021] (1) First, place metallic lithium in tetrahydrofuran for etching. After taking it out and drying, then dropwise add a solution of aluminum chloride / nitrobenzene at 130 mg / mL so that its content on the metallic lithium is 10 μL / cm², and let it stand for 18 hours;

[0022] (2) After dropping 70 μL / cm² of ethylene glycol dimethyl ether on the battery separator, spread it onto the metallic lithium in step (1). After pressing for a period of time, remove the battery separator;

[0023] (3) Assemble the metallic lithium obtained in step (2) into a lithium|lithium symmetric battery, use 1 mol / L lithium bis(trifluoromethanesulfonyl)imide - ethylene glycol dimethyl ether / dipentylheptane as the electrolyte, and perform activation by cyclic charge and discharge. The charge and discharge current is 1 mA / cm², the charge and discharge time is 1 hour, and the number of cycles is 10 times.

[0024] Conduct morphological characterization on the unpretreated and pretreated metallic lithium, Figure 1 It can be seen that the surface of the unpretreated metallic lithium has obvious undulations, which is not conducive to the deposition of lithium. The pretreated metallic lithium forms a dense and flat protective layer on the surface, which is not only conducive to the uniform deposition of lithium, but also has a certain inhibitory effect on the growth of lithium dendrites.

[0025] Example 2

[0026] (1) First, place metallic lithium in tetrahydrofuran for etching. After taking it out and drying, then dropwise add a solution of aluminum chloride / nitrobenzene at 100 mg / mL so that its content on the metallic lithium is 12 μL / cm², and let it stand for 24 hours;

[0027] (2) After dropping 60 μL / cm² of ethylene glycol dimethyl ether on the battery separator, spread it onto the metallic lithium in step (1). After pressing for a period of time, remove the battery separator;

[0028] (3) Assemble the metallic lithium obtained in step (2) into a lithium|lithium symmetric battery, and perform activation by cyclic charge and discharge. The charge and discharge current is 0.1 mA / cm², the charge and discharge time is 1.5 hours, and the number of cycles is 30 times.

[0029] As Figure 2 shown, the deposition and precipitation polarization curve of the unpretreated metallic lithium shows that at a current of 0.1 mA / cm², the potential of deposition and precipitation fluctuates sharply around 800 hours, indicating the formation of lithium dendrites. While the pretreated lithium metal can stably deposit and precipitate for at least 2100 hours. It can be seen that using the method of the present invention to pretreat metallic lithium can inhibit the formation of lithium dendrites.

[0030] Example 3

[0031] (1) First, place metallic lithium in tetrahydrofuran for etching. After taking it out and drying, then dropwise add an aluminum chloride / nitrobenzene solution with a concentration of 120 mg / mL, such that its content on the metallic lithium is 14 μL / cm², and let it stand for 36 hours.

[0032] (2) After dropping 50 μL / cm² of tetrahydrofuran on the battery separator, spread it onto the metallic lithium obtained in step (1). After pressing for a period of time, remove the battery separator.

[0033] (3) Assemble a lithium symmetric battery with the metallic lithium obtained in step (2). Using lithium bis(trifluoromethanesulfonyl)imide - ethylene glycol dimethyl ether / 1 - 3 - dipentylheptane with a concentration of 1 mol / L as the electrolyte, perform activation by cyclic charge and discharge. The charge and discharge current is 0.5 mA / cm², the charge and discharge time is 1 hour, and the number of cycles is 15 times.

[0034] (4) Use the metallic lithium obtained in step (3) as the anode of a lithium - air battery, and assemble a lithium - air battery with a carbon nanotube cathode and a 1 mol / L lithium bis(trifluoromethanesulfonyl)imide - tetraethylene glycol dimethyl ether organic electrolyte. The charge and discharge current is 0.1 mA / cm², and the charge and discharge time is 1 hour.

[0035] As Figure 3 , for a lithium - air battery with untreated metallic lithium as the anode, it can only cycle 20 times and then fails at a current of 0.1 mA / cm². While for a lithium - air battery with pretreated metallic lithium as the anode, it can cycle up to 374 times. It can be seen that using pretreated metallic lithium as the anode of a lithium - air battery can significantly improve the cycle stability of the lithium - air battery.

Claims

1. A pretreatment method for the lithium metal anode of a lithium-air battery, comprising the following steps: (1) First, etch lithium metal in tetrahydrofuran, take it out and dry it, then dropwise add an aluminum chloride / nitrobenzene solution, and then let it stand for a period of time; the content of the aluminum chloride / nitrobenzene solution on the lithium metal anode is 10 - 15 μL / cm², the content of aluminum chloride in the nitrobenzene solution is 100 - 140 mg / mL, and the standing time is 18 - 36 hours; (2) After dropping an organic solvent on the battery separator, spread it onto the lithium metal in step (1), press for a period of time and then remove the battery separator; the organic solvent dropped on the battery separator is one or more of tetrahydrofuran, ethylene glycol dimethyl ether, diethyl carbonate, and ethylene carbonate, and the content of the organic solvent is 50 - 80 μL / cm²; (3) Assemble the lithium metal obtained in step (2) into a lithium|lithium symmetric battery, use 1 mol / L lithium bis(trifluoromethanesulfonyl)imide - ethylene glycol dimethyl ether / 1,3-dipentylheptane as the electrolyte, and carry out activation by cyclic charge and discharge; the charge and discharge current during the activation process of the lithium|lithium symmetric battery in step (3) is 0.05 - 2 mA / cm², the charge and discharge time is 1 - 1.5 hours, and the number of cycles is 1 - 30 times.

2. A lithium-air battery, characterized in that: The lithium metal obtained by the method according to claim 1 is used as the anode of the lithium-air battery, the cathode of the lithium-air battery is one or more of graphene, carbon nanotubes, acetylene black, carbon-supported noble metals, and carbon-supported transition metal compounds, the electrolyte solvent is one or more of dimethyl sulfoxide, ethylene glycol dimethyl ether, and propylene carbonate, the solute is one or more of lithium hexafluorophosphate, lithium perchlorate, and lithium tetrafluoroborate, and the concentration is 0.1 - 4 mol / L.

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