CN113659211B

CN113659211B - Nitrile diluted high-concentration quick-charging electrolyte for lithium battery and application of nitrile diluted high-concentration quick-charging electrolyte

Info

Publication number: CN113659211B
Application number: CN202110476974.7A
Authority: CN
Inventors: 谢佳; 曾子琪; 雷盛
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2021-04-29
Filing date: 2021-04-29
Publication date: 2023-05-30
Anticipated expiration: 2041-04-29
Also published as: CN113659211A

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a nitrile diluted high-concentration quick-charging electrolyte for a lithium battery and application thereof. The electrolyte comprises a nitrile organic solvent, lithium salt and a diluent. The nitrile has high dielectric constant, can well dissolve lithium salt, ensures that the nitrile can work under high voltage, and improves the reduction stability of electrolyte after the concentration of the lithium salt is increased; the diluent is fluorine-containing aromatic and fluorine-containing ether, and the density and viscosity of the electrolyte are effectively reduced under the condition that the reduction stability of the diluent is not affected by the diluent. When the current density of the battery assembled by the electrolyte is increased from 0.2C to 8C, the capacity retention rate is as high as 80 percent, and the rate capability of the battery assembled by the electrolyte is far better than that of the battery assembled by the commercial carbonate electrolyte. The nitrile diluted high-concentration quick-charging electrolyte for the lithium battery has wide application prospect.

Description

Nitrile diluted high-concentration quick-charging electrolyte for lithium battery and application of nitrile diluted high-concentration quick-charging electrolyte

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a nitrile diluted high-concentration quick-charging electrolyte for a lithium battery and application thereof.

Background

Lithium ion batteries have been widely used in the fields of electric automobiles and the like. However, the current electric vehicle has generally shorter endurance mileage, the charging frequency of the user is very frequent, and the electric vehicle is charged more time than the fuel vehicle, so the consumer acceptance is low, and the charging time is crucial to the consumption experience of the user.

However, when a lithium ion battery is charged at a high rate, ohmic polarization and concentration polarization are generated, and an increase in battery polarization causes a lithium precipitation phenomenon, a capacity drop, excessive heat generation, and other harmful effects, thereby affecting the charging time and safety of the battery. The electrolyte is an important component throughout the battery and is critical to the performance of the battery. The conventional electrolytic solution system is mainly composed of lithium hexafluorophosphate (LiPF) ₆ ) Dissolved in a carbonate-based mixed solvent. Such electrolytes cannot be supported without affecting performance and lifetimeThe dynamic performance is not high enough after the rapid charge, and the rapid charge can aggravate a series of side reactions of electrolyte solvents and structural degradation of the lithium layered transition metal oxide positive electrode material.

To improve the fast fill performance of conventional electrolytes, researchers have typically increased the fast fill performance of conventional electrolytes by way of additives (Journal of Power Sources 429 (2019) 67-74, journal of Power Sources 446 (2020) 227366). However, this approach has limited improvement and has developed to a degree of bottleneck. The development of a new fast-charging electrolyte solution system has important significance.

Acetonitrile solvent has high dielectric constant, good oxidation stability and high ionic conductivity, and is a potential fast-charging electrolyte solvent. However, acetonitrile has poor reduction stability, and the reduction stability of the electrolyte can be improved by increasing the lithium salt concentration, so that the electrolyte can be used normally in a battery. The attuo Yamada professor in japan developed a new 4.2M high-concentration acetonitrile quick-charge electrolyte (j.am. Chem. Soc.2014,136, 5039-5046), but the high-concentration electrolyte had problems of large density, high viscosity, high cost, and the like. Therefore, the existing fast-charge electrolyte needs to be optimized so as to have wide application prospect.

The main solvents reported in the literature about diluting high-concentration electrolyte are mainly ethers (adv. Funct. Mater.2020,2005991, adv. Mater.2020, 2004898), the working voltage window of the ethers electrolyte is limited, the performance improvement in quick charge is not obvious, and the diluted high-concentration electrolyte taking nitriles as the main solvents is not reported yet. There is also a related patent application (CN 110994031A, CN111146500A, CN111244546 a) for an electrolyte for quick charge, but the quick charge performance of the battery is improved by adding additives, the improvement degree is limited, and the additives are added in various types.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide the nitrile dilution high-concentration quick-charging electrolyte for the lithium battery with low viscosity, low cost and high conductivity, wherein the electrolyte comprises a nitrile organic solvent, lithium salt and a diluent, the diluent is fluorine-containing aromatic and fluorine-containing ether, the nitrile dilution high-concentration electrolyte not only maintains the ion coordination structure of the high-concentration electrolyte, maintains the excellent performance of the high-concentration electrolyte, reduces the viscosity and the cost, but also has excellent quick-charging performance, thereby solving the technical problems of high cost, multiple additive types, to-be-improved quick-charging performance and the like of the quick-charging electrolyte of the lithium battery in the prior art.

In order to achieve the above purpose, the invention provides a nitrile diluted high-concentration quick-charging electrolyte for a lithium battery, which comprises lithium salt, a nitrile organic solvent and a diluent; wherein, the liquid crystal display device comprises a liquid crystal display device,

the nitrile organic solvent has a general formula shown in a formula (I):

n is more than or equal to 0 and less than or equal to 10 in the formula (I); r is H atom or alkyl with 1-10 carbon atoms;

the diluent is at least one of fluorine-containing aromatic diluent and fluorine-containing ether diluent.

In a preferred scheme, n is more than or equal to 0 and less than or equal to 4 in the formula (I); r is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

Preferably, the lithium salt is selected from any one or two or more of phosphate, borate, boron cluster compound, imine salt, aluminate, heterocyclic anion salt, halogenate, sulfonate and derivatives thereof of lithium, which are mixed in any proportion.

Further preferably, the lithium salt is at least one of lithium bistrifluoromethylsulfonyl imide, lithium bistrifluorosulfonyl imide, lithium tetrafluoroborate and lithium perchlorate.

Preferably, the fluorine-containing aromatic diluent is selected from the group consisting of fluorobenzene, methyl fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene and hexafluorobenzene.

Preferably, the method comprises the steps of, the fluorine-containing ether diluent is selected from the group consisting of a fluoroether, an isoflurane, a sevoflurane, a 2, 2-trifluoroethyl ether 1, 2-tetrafluoroethyl 2, 3-tetrafluoropropyl ethers and 1, 2-tetrafluoroethyl difluoromethyl ether.

Preferably, the concentration of the lithium salt in the electrolyte is 0.5mol/L to 5mol/L.

Further preferably, the concentration of the lithium salt in the electrolyte is 0.8 to 2.5mol/L.

Preferably, the ratio of the amount of the nitrile organic solvent to the amount of the substance of the lithium salt is (1-7): 1; the ratio of the amount of the diluent to the amount of the lithium salt is (1-10): 1.

Further preferably, the ratio of the amount of the nitrile organic solvent to the amount of the substance of the lithium salt is (1.5 to 3.5): 1; the ratio of the amount of the diluent to the amount of the substance of the lithium salt is preferably (2 to 5): 1.

For lithium batteries with lithium metal as the negative electrode, preferably, the electrolyte further comprises an additive selected from Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), lithium nitrate (LiNO) ₃ )。

According to another aspect of the invention, there is provided the use of said electrolyte for the preparation of a fast-charging electrolyte for lithium ion batteries.

According to another aspect of the invention, a quick-charge lithium battery is provided, which comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte, wherein the electrolyte is the nitrile diluted high-concentration quick-charge electrolyte.

The quick-charging lithium battery can be a lithium ion battery, a lithium metal battery, a lithium sulfur battery and the like; the positive and negative electrodes of the lithium battery can be various common positive and negative electrode materials, such as lithium iron phosphate, lithium cobalt oxide, lithium manganate and ternary material LiCo _x Ni _y Mn _1-x-y O ₂ 、LiCo _x Ni _y Al _1-x-y O ₂ Ternary material lithium-rich material xLiMnO _3(1-x) LiMO ₂ Wherein x is greater than 0, y is greater than 0, and x+y is less than or equal to 1; the negative electrode may be one of artificial graphite, natural graphite, hard carbon, soft carbon, and lithium titanate.

In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

(1) The invention adopts the nitrile organic solvent as the only lithium salt solvent, and the nitrile organic solvent has high oxidation stability, high dielectric constant, good desolvation capacity, high ion conductivity, excellent ion transmission property and quick charge performance, and higher working voltage. The concentration of the nitrile organic solvent is increased, then the nitrile organic solvent is diluted, so that the ionic coordination of the lithium salt and the nitrile organic solvent is kept, the lithium salt and the diluent are not coordinated, and the electrolyte does not contain free nitrile solvent molecules, so that the problem of poor reduction stability of the nitrile organic solvent is solved. The adoption of the fluorine-containing aromatic and fluorine-containing ether diluents not only solves the problems of high viscosity, high cost, high density and the like caused by the increase of the concentration, but also maintains high ion conductivity and shows more excellent battery quick-charge performance. Compared with the reported ether local high-concentration electrolyte, the nitrile diluted high-concentration quick-charging electrolyte for the lithium battery has good oxidation stability, can be applied at higher voltage, and has wider application prospect than the ether local high-concentration electrolyte.

(2) The nitrile-based diluted high-concentration quick-charging electrolyte for the lithium battery provided by the invention has the advantages of high oxidation stability, high dielectric constant and high ion conductivity, and can well dissolve lithium salt, and the system electrolyte can work under high voltage and high multiplying power due to excellent ion transmission property. The nitrile diluted high-concentration electrolyte maintains the ion coordination structure of the high-concentration electrolyte, maintains the excellent performance of the high-concentration electrolyte, and reduces the viscosity and the cost.

(3) The nitrile diluted high-concentration quick-charging electrolyte for the lithium battery provided by the invention has the advantages of simple preparation method, low cost and convenience for practical popularization and application.

(4) The nitrile diluted high-concentration quick-charging electrolyte for the lithium battery is focused on the performance of the battery, and researches show that the electrolyte has good oxidation stability, still has higher conductivity (1.15 mS/cm at minus 40 ℃) at low temperature, and can be applied to a higher voltage system and a low-temperature environment.

Drawings

Fig. 1 is a graph showing the cycle capacity of the nitrile-based diluted high-concentration fast-charge electrolyte for lithium batteries and the basic electrolyte battery prepared in example 1 at a 1C rate.

Fig. 2 is a graph showing the comparison of the multiplying power performance of the nitrile diluted high-concentration quick-charge electrolyte and the basic electrolyte assembled lithium-graphite battery for the lithium battery prepared in example 1.

Fig. 3 is a first charge-discharge curve diagram of the lithium-iron phosphate full battery assembled by nitrile diluted high-concentration fast-charge electrolyte prepared in example 1 at 0.1C rate.

Fig. 4 is a ratio performance chart of a lithium iron phosphate full battery assembled by nitrile diluted high-concentration quick-charge electrolyte for a lithium battery prepared in example 1.

Fig. 5 is a first charge-discharge curve diagram of the lithium-nickel-cobalt-manganese ternary full battery assembled by nitrile diluted high-concentration fast-charge electrolyte for a lithium battery prepared in example 1 at 0.1C magnification.

Fig. 6 is a graph showing the cycle capacity of the nitrile-diluted high-concentration fast-charge electrolyte-assembled lithium-nickel-cobalt-manganese ternary full battery prepared in example 1 at a rate of 0.1C.

Fig. 7 is a graph showing the circulation capacity of the nitrile-based diluted high-concentration fast-charge electrolyte for lithium batteries and the basic electrolyte battery prepared in example 2 at a 5C rate.

Fig. 8 is a graph showing the comparison of the multiplying power performance of the nitrile diluted high-concentration quick-charge electrolyte and the basic electrolyte assembled lithium-graphite battery for the lithium battery prepared in example 2.

Fig. 9 is a graph showing the comparison of the multiplying power performance of the nitrile diluted high-concentration quick-charge electrolyte and the basic electrolyte assembled lithium-graphite battery for the lithium battery prepared in example 3.

Fig. 10 is a graph showing the comparison of the multiplying power performance of the nitrile diluted high-concentration fast-charging electrolyte and the basic electrolyte assembled lithium-graphite battery for the lithium battery prepared in example 4.

Detailed Description

The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

The invention discloses a nitrile diluted high-concentration quick-charging electrolyte for a lithium battery. The nitrile has high dielectric constant, can well dissolve lithium salt, and has good oxidation stability, so that the nitrile can work under high voltage, and the reduction stability of the electrolyte is improved after the concentration of the lithium salt is increased; the diluent is fluorine-containing aromatic and fluorine-containing ether, and the addition of the diluent changes the outer solvation structure of the lithium salt and acetonitrile under the condition that the reduction stability of the diluent is not affected, and effectively reduces the density and viscosity of the electrolyte. When the current density of the battery assembled by the electrolyte is increased from 0.2C to 8C, the capacity retention rate is as high as 80 percent, and the rate capability of the battery assembled by the electrolyte is far better than that of the battery assembled by the commercial carbonate electrolyte. The nitrile diluted high-concentration quick-charging electrolyte for the lithium battery has wide application prospect.

The following are examples:

comparative example 1

Electrolyte preparation: in a glove box filled with argon, mixing ethylene carbonate and dimethyl carbonate solvent according to a volume ratio of 1:1, then adding lithium hexafluorophosphate, uniformly stirring, and preparing a final concentration of the lithium hexafluorophosphate which is 1mol/L, marking as a basic electrolyte, wherein the water content in the glove box is less than 0.1ppm, and the oxygen content is less than 0.1ppm.

Example 1

Electrolyte preparation: lithium bis-fluorosulfonyl imide (LiSSI), acetonitrile (AN), fluorobenzene (FB) was formulated as a homogeneous solution in a molar ratio of 1:2:3 in a glove box filled with argon. Wherein, the molar concentration of the lithium salt is 2moL/L, and the quick-charging electrolyte for the lithium ion battery is obtained.

The above electrolyte was used to assemble a battery with lithium sheets, graphite, and separator, and cycle performance test was performed at a current density of 1C, as shown in fig. 1, at a current density of 1C, the nitrile-diluted high-concentration electrolyte had cycle stability comparable to that of the base electrolyte and a higher capacity than that of the base electrolyte. And the rate performance test is carried out under different current densities, as shown in fig. 2, when the current density is increased from 0.2 to 4C, the capacity retention rate of the nitrile diluted high-concentration quick-charging electrolyte for the lithium battery is 67%, and the capacity retention rate of the basic electrolyte is only 21%. The electrolyte, the lithium sheet, the lithium iron phosphate (LFP) and the diaphragm are assembled into a full battery, and the cycle performance test is carried out at the rate of 0.1C, as shown in figures 3 and 4, the electrolyte is friendly to the positive electrode lithium iron phosphate, and the feasibility of assembling the full battery by adopting the electrolyte in the embodiment is demonstrated. The electrolyte, the lithium sheet, the nickel cobalt manganese ternary (NCM 622) and the diaphragm are assembled into a full battery, and the cycle performance test is carried out at the rate of 0.1C, as shown in fig. 5 and 6, according to the cycle performance test chart, the electrolyte can be applied to a ternary higher voltage system. The electrolyte was subjected to conductivity testing and found to remain at 1.15mS/cm at-40 ℃.

Example 2

Electrolyte preparation: in a glove box filled with argon, lithium bis (fluorosulfonyl) imide (LiWSI), acetonitrile (AN) and Fluorobenzene (FB) are prepared into a uniform solution according to a molar ratio of 1:2:3, and in order to reduce the influence of a metallic lithium anode, proper additives can be added into AN electrolyte. In this example, vinylene Carbonate (VC) was added in an amount of 2wt% based on the mixed solution.

The above electrolyte was used together with a lithium sheet, graphite, and a separator to assemble a battery, and a cycle performance test was performed at a current density of 5C, as shown in fig. 7, and at a current density of 5C, the nitrile-based diluted high-concentration electrolyte had a cycle stability comparable to that of the base electrolyte and a higher capacity than that of the base electrolyte. And the rate performance test is carried out under different current densities, as shown in fig. 8, when the current density is increased from 0.2 to 8C, the capacity retention rate of the nitrile diluted high-concentration quick-charging electrolyte for the lithium battery is 80%, and the capacity retention rate of the basic electrolyte is only 18%.

Example 3

The lithium salt used was lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), the remainder being as in example 1.

The electrolyte, the lithium sheets, the graphite and the separator are used for assembling the battery, and the rate performance test is carried out under different current densities, as shown in fig. 9, when the current density is increased from 0.2 to 4C, the capacity retention rate of the nitrile diluted high-concentration quick-charging electrolyte for the lithium battery in the embodiment is 33%, and the capacity retention rate of the basic electrolyte is only 21%.

Example 4

The diluent used was 1, 2-tetrafluoroethyl 2, 3-tetrafluoropropyl ether (TTE) and the remainder was the same as in example 1.

The electrolyte, the lithium sheet, the graphite and the diaphragm are assembled into a battery, and the rate performance test is carried out under different current densities, as shown in fig. 10, when the current density is increased from 0.2C to 2C, the capacity retention rate of the nitrile diluted high-concentration quick-charging electrolyte for the lithium battery is 80%. And the sample still has good cycle stability under the current density of 0.2C after the multiplying power is measured. Experiments show that when the diluent is replaced by the fluorine-containing aromatic diluent and the fluorine-containing ether diluent is adopted, the capacity retention rate of the battery is obviously reduced under the same conditions, and the selection of the fluorine-substituted C-H structure fluorine-containing aromatic diluent is more beneficial to improving the quick charge performance of the lithium battery adopting the electrolyte.

Example 5

The diluent used was 1, 2-Tetrafluoroethyl Difluoromethyl Ether (TDE) and the remainder was the same as in example 1.

Example 6

The diluent used was 2, 2-trifluoroethyl ether (BTFE) and the remainder was the same as in example 1.

Example 7

The nitrile organic solvent is butyronitrile. The procedure is as in example 1.

Example 8

Lithium bis (fluorosulfonyl imide) (LiSSI), acetonitrile (AN), fluorobenzene (FB) in a molar ratio of 1:3:3 are the same as in example 1.

Example 9

Electrolyte preparation: in a glove box filled with argon, lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), acetonitrile (AN), 1, 2-tetrafluoroethyl 2, 3-tetrafluoropropyl ether (TTE) in a 1:2 ratio: 3 in a molar ratio to prepare a homogeneous solution.

Example 10

The diluent used was 1, 2-Tetrafluoroethyl Difluoromethyl Ether (TDE) and the rest was the same as in example 9.

Example 11

The diluent used was 2, 2-trifluoroethyl ether (BTFE) and the remainder was the same as in example 9.

Example 12

The nitrile organic solvent is butyronitrile. The procedure is as in example 9.

Experiments show that the electrolyte can be used as a fast charging electrolyte of a lithium ion battery, the half battery assembled into graphite and metal lithium has good multiplying power performance, and the full battery assembled into nickel-cobalt-manganese ternary and metal lithium is applicable to a ternary high-voltage system and has high capacity retention rate.

It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims

1. The nitrile diluted high-concentration quick-charging electrolyte for the lithium ion battery is characterized by comprising lithium salt, nitrile organic solvent and diluent; wherein, the liquid crystal display device comprises a liquid crystal display device,

the lithium salt is lithium bis (fluorosulfonyl) imide;

the nitrile organic solvent has a general formula shown in a formula (I):

n is more than or equal to 0 and less than or equal to 4 in the formula (I); r is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms;

the diluent is fluorine-containing aromatic diluent; the fluorine-containing aromatic diluent is selected from fluorobenzene, methyl fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene and hexafluorobenzene;

the concentration of the lithium salt in the electrolyte is 0.5mol/L to 5mol/L, and the ratio of the nitrile organic solvent to the mass of the lithium salt is (1 to 7) 1; the ratio of the amount of the diluent to the amount of the lithium salt is (1-10): 1.

2. The electrolyte of claim 1, wherein the concentration of the lithium salt in the electrolyte is 0.8 to 2.5mol/L.

3. The electrolyte according to claim 1, wherein the ratio of the amount of the nitrile organic solvent to the amount of the substance of the lithium salt is (1.5 to 3.5): 1; the ratio of the amount of the diluent to the amount of the lithium salt is (2-5): 1.

4. The electrolyte of claim 1 further comprising an additive selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, and lithium nitrate.

5. Use of the electrolyte according to any one of claims 1 to 4 for the preparation of a fast-charging electrolyte for lithium-ion batteries.

6. A fast-charging lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the electrolyte of any one of claims 1 to 4.