CN114784423B - Lithium air battery and application - Google Patents

Abstract

The present invention provides a lithium-air battery, comprising an electrolyte, wherein the electrolyte comprises a pentamethylphenol additive. The lithium-air battery electrolyte additive provided by the present invention is pentamethylphenol, which can induce liquid phase discharge of the lithium-air battery, thereby greatly improving the discharge capacity of the lithium-air battery. The present invention avoids the high cost and long time required for the use of solid catalysts. In order to save material costs and production time and speed up battery production efficiency, the use of cheap liquid phase catalysts will be conducive to the promotion and popularization of lithium-air batteries. The present invention also provides the use of pentamethylphenol as an electrolyte additive in improving the discharge capacity of lithium-air batteries.

Description

A lithium-air battery and its application

Technical Field

The present invention belongs to the technical field of lithium-air batteries, and in particular relates to a lithium-air battery and its application.

Background Art

As a new generation of batteries with high theoretical energy density (3460Wh·g ^-1 ), lithium-air batteries have received widespread attention in recent years. The discharge capacity of non-aqueous lithium-air batteries is mainly determined by the reaction environment at the three-phase interface of the positive electrode region. In the past, a large number of studies have been conducted on complex designs of the positive electrode structure and components to increase the specific surface area of the positive electrode and the space for storing discharge products, and to regulate the adsorption energy of the products to increase the ORR reaction rate. For example, by carefully designing and regulating the structure of the positive electrode solid catalyst, the positive electrode oxygen reduction activity can be increased and the discharge capacity can be greatly increased. By adjusting the positive electrode catalyst components, electrode specific surface area and pore size, it will be beneficial to provide a good reaction environment for the discharge reaction from all aspects, such as oxygen diffusion and ion transport, increase in ORR reaction rate, and accumulation of discharge products, thereby promoting the realization of large capacity.

There are also many problems based on carefully designed positive solid catalysts; first, the complex design of the structure and components, especially when the production scale is expanded, will inevitably lead to a large amount of production costs. Second, due to the limitations of the solid catalyst synthesis method, it is impossible to achieve stable and uniform precise synthesis of the positive electrode structure, which will lead to obvious differences in the capacity of batteries dominated by the positive electrode structure and poor consistency. Third, due to structural limitations, the reaction occurs at the active sites of the electrode, which causes the solid discharge product lithium peroxide to accumulate at the active sites on the electrode surface and gradually block the oxygen transmission channels, etc., which makes it easy for the battery to die suddenly. Fourth, the complex material synthesis process and the long synthesis time required will greatly increase the production cost of the battery and greatly hinder the practical application of the battery.

Summary of the invention

The purpose of the present invention is to provide a lithium-air battery and its application. When pentamethylphenol is used as an electrolyte additive, the present invention can promote the liquid phase discharge of the lithium-air battery to generate large-sized _{Li2O2 particles} , thereby greatly improving the discharge capacity.

The present invention provides a lithium-air battery, characterized in that it comprises an electrolyte, wherein the electrolyte comprises a pentamethylphenol additive.

Preferably, the concentration of pentamethylphenol in the electrolyte is 10-200 mmol/L.

Preferably, the solvent used in the electrolyte includes one or more of ether solvents, sulfone solvents and amide solvents.

Preferably, the ether solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and 1,4-dioxolane; the sulfone solvent includes dimethyl sulfoxide and/or cyclopentane sulfone; and the amide solvent includes dimethylformamide and/or dimethylacetamide.

Preferably, the lithium-air battery comprises a lithium-oxygen battery.

Preferably, the electrolyte includes a lithium salt, and the lithium salt is one or more of LiNO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiCF ₃ SO ₃ , LiN(FSO ₂ ) ₃ and LiClO ₄ , and the concentration of the lithium salt in the electrolyte is 0.1-3 mol/L.

Preferably, it comprises a positive electrode and a negative electrode, wherein the positive electrode material in the positive electrode comprises a carbon material and/or a non-carbon positive electrode material; and the negative electrode comprises metallic lithium.

The invention provides application of pentamethylphenol as an electrolyte additive in improving the discharge capacity of a lithium-air battery.

The present invention provides a lithium-air battery, comprising an electrolyte, wherein the electrolyte comprises a pentamethylphenol additive. The lithium-air battery electrolyte additive provided by the present invention is pentamethylphenol, which can induce liquid phase discharge of the lithium-air battery, thereby greatly improving the discharge capacity of the lithium-air battery. The present invention avoids the high cost and long time required for using a solid catalyst. In order to save material costs and production time and speed up battery production efficiency, the use of a cheap liquid phase catalyst will be conducive to the promotion and popularization of lithium-air batteries.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

FIG1 is a constant current discharge capacity curve of a lithium oxygen battery at 200 mA/g in Example 1 of the present invention;

FIG2 is a SEM image of discharge products in the electrolyte containing pentamethylphenol in Example 1 of the present invention;

FIG. 3 is a SEM image of discharge products in a common electrolyte in Comparative Example 1 of the present invention.

DETAILED DESCRIPTION

The invention provides a lithium-air battery, comprising an electrolyte, wherein the electrolyte comprises a pentamethylphenol additive.

In the present invention, the concentration of pentamethylphenol in the electrolyte is preferably 10-200 mmol/L, more preferably 50-150 mmol/L, such as 10 mmol/L, 20 mmol/L, 30 mmol/L, 40 mmol/L, 50 mmol/L, 60 mmol/L, 70 mmol/L, 80 mmol/L, 90 mmol/L, 100 mmol/L, 110 mmol/L, 120 mmol/L, 130 mmol/L, 140 mmol/L, 150 mmol/L, 160 mmol/L, 170 mmol/L, 180 mmol/L, 190 mmol/L, 200 mmol/L, preferably a range value with any of the above values as the upper or lower limit.

In the present invention, the electrolyte includes a solvent, and the solvent includes one or more of an ether solvent, a sulfone solvent and an amide solvent; preferably, the ether solvent is preferably one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and 1,4-dioxolane; the sulfone solvent includes dimethyl sulfoxide and/or cyclopentane sulfone; the amide solvent includes dimethylformamide and/or dimethylacetamide. The solvent is preferably dried using an activated 4A molecular sieve for more than one month before use.

In the present invention, the electrolyte includes a lithium salt, and the lithium salt is preferably one or more of LiNO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiCF ₃ SO ₃ , LiN(FSO ₂ ) ₃ and LiClO _4. The concentration of the lithium salt in the electrolyte is preferably 0.1~3 mol/L, more preferably 0.5~2.5 mol/L, such as 0.1 mol/L, 0.5 mol/L, 0.8 mol/L, 1 mol/L, 1.2 mol/L, 1.5 mol/L, 2 mol/L, 2.5 mol/L, 3 mol/L, preferably a range value with any of the above values as the upper or lower limit.

In the present invention, the lithium-air battery comprises a positive electrode and a negative electrode, the positive electrode material in the positive electrode is preferably a carbon material and/or a non-carbon positive electrode material; the negative electrode comprises metallic lithium.

The present invention also provides the use of pentamethylphenol as a liquid electrolyte additive in improving the discharge capacity of a lithium-air battery. In the present invention, the pentamethylphenol can be added to the electrolyte of a lithium-air battery as a single additive or as a combined additive with other substances to improve its discharge capacity.

The pentamethylphenol used in the present invention is an inorganic additive for efficiently regulating liquid phase discharge, and has the advantages of low cost and stable structure. At the same time, pentamethylphenol, as a solvent with a high DN (Donor Number, Gutmann donor number) value, can comprehensively regulate various organic electrolyte environments and increase the solubility of Li ⁺ in the electrolyte. It promotes the dissolution of LiO ₂ in the solvent to increase the solubility of the intermediate LiO ₂ , and plays a comprehensive role in improving the discharge capacity by regulating the liquid phase discharge. In addition, pentamethylphenol has a high AN (Acceptor Number) value, which can stabilize the medium-intensity Lewis base discharge intermediate O ₂ ^- and increase the solubility of the intermediate LiO _2. On the other hand, whether using the soft and hard acid-base theory or based on the AN/DN value, pentamethylphenol can increase the solubility of Li ⁺ and O ₂ ^- respectively, thereby inducing the dissolution of the discharge intermediate LiO ₂ and realizing the liquid phase discharge of the lithium-air battery. Therefore, pentamethylphenol is a very ideal liquid phase additive for promoting the capacity improvement of lithium-air batteries.

The present invention provides a lithium-air battery, comprising an electrolyte, wherein the electrolyte comprises a pentamethylphenol additive. The electrolyte additive of the lithium-air battery provided by the present invention is pentamethylphenol, which can induce liquid phase discharge of the lithium-air battery, thereby greatly improving the discharge capacity of the lithium-air battery. The present invention avoids the high cost and long time required for using a solid catalyst. In order to save material costs and production time and speed up battery production efficiency, the use of a cheap liquid phase catalyst will be conducive to the promotion and popularization of lithium-air batteries.

In order to further illustrate the present invention, a lithium-air battery and applications provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

Example 1

165g of lithium trifluoromethanesulfonate was dissolved in 1L of tetraethylene glycol dimethyl ether solvent to prepare an electrolyte with a lithium salt concentration of 1M, and an electrolyte containing 50 mM pentamethylphenol was prepared. Super P was used as the positive electrode catalyst. The battery assembly was carried out in a glove box filled with argon atmosphere; a lithium sheet with a thickness of 0.4mm and a diameter of 14mm was used as the negative electrode, a polyethylene diaphragm, a polypropylene diaphragm, a glass fiber membrane or a polyimide membrane was used as a diaphragm, and the positive electrode was cut into a disc with a diameter of 12mm for testing. After the electrolyte was dripped, nickel foam was used as the current collector, and the battery was encapsulated in a CR2025 button cell with holes and sealed in a glass bottle filled with oxygen for testing. The test was carried out on a Blue Electric CT2001A tester at a test temperature of 30℃.

Four batteries are tested simultaneously in each test, and the battery data closest to the average value is used as a reference. If the battery deviation is too large, the test is repeated.

As shown in Figure 1, in the lithium-oxygen battery containing 50 mM pentamethylphenol additive, the full discharge capacity at 200 mA/g is as high as 7833 mAh/g, and the discharge products are large round particles (Figure 2), which fully proves that pentamethylphenol can promote liquid phase discharge to grow large particle discharge products and improve the discharge capacity.

Comparative Example 1

165 g of lithium trifluoromethanesulfonate was dissolved in 1 L of tetraethylene glycol dimethyl ether solvent to prepare an electrolyte with a lithium salt concentration of 1 M, thereby preparing an electrolyte without additives. Super P was used as a positive electrode catalyst. The battery was assembled according to the method in Example 1.

Four batteries are tested simultaneously in each test, and the battery data closest to the average value is used as a reference. If the battery deviation is too large, the test is repeated.

Comparative Example 2

165 g of lithium trifluoromethanesulfonate was dissolved in 1 L of tetraethylene glycol dimethyl ether solvent to prepare an electrolyte with a lithium salt concentration of 1 M, thereby preparing an electrolyte containing 50 mM phenol. Super P was used as a positive electrode catalyst. The battery was assembled according to the method in Example 1.

Four batteries are tested simultaneously in each test, and the battery data closest to the average value is used as a reference. If the battery deviation is too large, the test is repeated.

Comparative Example 3

165 g of lithium trifluoromethanesulfonate was dissolved in 1 L of tetraethylene glycol dimethyl ether solvent to prepare an electrolyte with a lithium salt concentration of 1 M, and an electrolyte containing 50 mM pentamethylbenzene was prepared. Super P was used as a positive electrode catalyst. The battery was assembled according to the method in Example 1.

Four batteries are tested simultaneously in each test, and the battery data closest to the average value is used as a reference. If the battery deviation is too large, the test is repeated.

As shown in Figure 1, in the lithium oxygen battery without pentamethylphenol additive, the discharge capacity is only 4057 mAh/g. When 50 mM phenol is added, the discharge capacity is increased to 5917 mAh/g, and when 50 mM pentamethylphenol is added, the discharge capacity is significantly increased to 7506 mAh/g. And from the discharge capacity curve of the battery with 50 mM pentamethylbenzene, it can be seen that pentamethylbenzene has an adverse effect on the discharge capacity, which is caused by the low DN and AN values of pentamethylbenzene. The battery containing pentamethylphenol has a significant improvement in discharge capacity compared with the battery containing phenol, which can be attributed to the methyl substitution of the benzene ring, which can prevent phenol from being oxidized to p-benzoquinone and further decomposition (as shown in Formula I). This strategy of methyl substitution of active hydrogen on the benzene ring can greatly improve the stability of the phenol structure, so that pentamethylphenol can be stable for a long time during discharge, thereby obtaining a longer-lasting catalytic effect.

Formula I.

As shown in Figures 2 and 3, in the electrolyte containing pentamethylphenol additives, the discharge reaction path is significantly changed, and cyclic lithium peroxide is generated, which is a typical product of the solution reaction path, indicating that liquid phase discharge is dominant. In the electrolyte without pentamethylphenol additives, the discharge reaction still follows the general reaction mechanism of ether electrolytes, that is, the surface-mediated reaction path, generating film/layer lithium peroxide. Under full discharge, lithium peroxide is stacked in the form of sheets, which is significantly smaller than the lithium peroxide generated by the solution reaction, corresponding to a lower discharge capacity.

In summary, by using pentamethylphenol as an electrolyte additive for lithium-air batteries, we have effectively promoted the liquid phase discharge of lithium-air batteries and greatly improved the discharge specific capacity of the batteries, which fully demonstrates the reliability of the present invention, overcomes the rapid passivation of the electrode caused by the surface discharge path in the absence of additives, and avoids the problem of phenol being oxidized by oxygen and other substances during discharge. This method of full substitution with methyl groups effectively improves the oxidation stability of phenol.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (3)

1. A lithium-air battery, characterized in that it comprises an electrolyte, and pentamethylphenol is used as an electrolyte additive to improve the discharge capacity of the lithium-air battery, The concentration of pentamethylphenol in the electrolyte is 10-200 mmol/L; The solvent used in the electrolyte includes one or more of ether solvents, sulfone solvents and amide solvents; The ether solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and 1,4-dioxolane; the sulfone solvent includes dimethyl sulfoxide and/or sulfolane; the amide solvent includes dimethylformamide and/or dimethylacetamide; The electrolyte includes a lithium salt, which is one or more of LiNO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiCF ₃ SO ₃ , LiN(FSO ₂ ) ₃ and LiClO ₄ , and the concentration of the lithium salt in the electrolyte is 0.1-3 mol/L. 2. The lithium-air battery according to claim 1, characterized in that the lithium-air battery comprises a lithium-oxygen battery. 3. The lithium-air battery according to claim 1, characterized in that it comprises a positive electrode and a negative electrode, the positive electrode material in the positive electrode comprises a carbon material and/or a non-carbon positive electrode material; and the negative electrode comprises metallic lithium.