阅读说明：本技术 一种电解液及双离子电池 (Electrolyte and double-ion battery ) 是由 王宏宇 陈聪聪 于 2021-08-25 设计创作，主要内容包括：本发明涉及一种电解液及双离子电池,属于电化学技术领域。解决了现有技术中双离子电池的容量和循环性能有待提高的技术问题。本发明的电解液包括电解质和有机溶剂；电解质为二氟草酸硼酸锂和六氟磷酸锂的混合物；有机溶剂为碳酸乙烯酯。本发明提供的电解液以六氟磷酸锂和二氟草酸硼酸锂两种锂盐作为电解质盐,原料不仅制备简单,易于获取,而且成本低廉；通过二者的协同作用,能够削弱溶剂分子对于阴离子储能的抑制作用,大幅度提升电池的容量。(The invention relates to an electrolyte and a dual-ion battery, and belongs to the technical field of electrochemistry. The technical problem that the capacity and the cycle performance of the double-ion battery in the prior art need to be improved is solved. The electrolyte of the invention comprises an electrolyte and an organic solvent; the electrolyte is a mixture of lithium difluoro-oxalato-borate and lithium hexafluorophosphate; the organic solvent is ethylene carbonate. The electrolyte provided by the invention takes two lithium salts, namely lithium hexafluorophosphate and lithium difluoroborate, as electrolyte salts, and the raw materials are simple to prepare, easy to obtain and low in cost; through the synergistic effect of the two components, the inhibition effect of solvent molecules on anion energy storage can be weakened, and the capacity of the battery can be greatly improved.)

1. An electrolytic solution, characterized by comprising an electrolyte and an organic solvent;

the electrolyte is a mixture of lithium difluorooxalato borate and lithium hexafluorophosphate.

2. The electrolyte of claim 1, wherein the electrolyte comprises 0.1 to 99.9 mole percent lithium difluorooxalato borate and 99.9 to 0.1 mole percent lithium hexafluorophosphate.

3. The electrolyte of claim 2, wherein the electrolyte comprises 65 to 95 mole percent lithium difluorooxalato borate and 5 to 35 mole percent lithium hexafluorophosphate.

4. The electrolyte according to claim 3, wherein the molar percentage of lithium difluorooxalato borate in the electrolyte is 70-90%, and the molar percentage of lithium hexafluorophosphate in the electrolyte is 10-30%.

5. The electrolyte of claim 4, wherein the electrolyte comprises 80 mole percent lithium difluorooxalato borate and 20 mole percent lithium hexafluorophosphate.

6. The electrolyte of claim 1, wherein the organic solvent is ethylene carbonate.

7. The electrolyte solution of claim 1, wherein the molar concentration of the electrolyte in the organic solvent is 0.5mol/L to 2 mol/L.

8. The electrolyte of claim 7, wherein the organic solvent has a molar concentration of electrolyte of 1 mol/L.

9. A bi-ion battery comprising the electrolyte of any of claims 1 to 8, further comprising a graphite positive electrode, a negative electrode, a separator interposed between the graphite positive electrode and the negative electrode;

the material of the negative electrode is a material capable of performing reversible electrochemical reaction with an electrolyte;

the material of the separator is a material capable of separating the graphite positive electrode and negative electrode and allowing electrolyte ions to pass therethrough.

10. The bi-ion battery of claim 9,

the negative electrode is a lithium sheet;

the diaphragm is made of glass fiber.

Technical Field

The invention belongs to the technical field of a double-ion battery, and particularly relates to an electrolyte and a double-ion battery.

Background

The bi-ion battery is an energy storage device based on reversible electrochemical reactions of anions and cations on a positive electrode and a negative electrode respectively, is a novel secondary battery with an anion-inserted graphite positive electrode, and has the advantages that with the adjustment of modern social energy structures and the development and utilization of new energy, electrode materials are easy to obtain, the environment is friendly, and the bi-ion battery can be applied to large-scale energy storage and becomes the focus of research in recent years.

The electrodes of the bi-ion battery are classified into carbon materials, metal compounds, organic small molecules, polymers and the like. The double-ion battery using graphite as the positive electrode has the advantages of stable electrode structure and high reversible potential. During the charging process, anions are embedded into the graphite anode, meanwhile, the cations are subjected to electrochemical reaction at the cathode, and during the discharging process, the anions and the cations are separated from the anode and the cathode and return to the electrolyte, so that the anions and the cations in the electrolyte are required to be completely dissociated. Therefore, the electrolyte affects the capacity and the cyclicity of the battery and even determines whether the battery has significance in practical application. In the prior art, electrolytes for a dual-ion battery mainly include: quaternary ammonium salt organic electrolyte, ionic liquid and lithium salt organic electrolyte.

For a dual-ion battery system taking anion intercalation graphite as a positive electrode, the capacity is increased along with the rise of the charging potential, and the highest reversible intercalation potential is about 5.2V. However, when the voltage is charged to about 5V, the conventional organic solvent is oxidized and decomposed, and thus the capacity and cycle performance of the battery are poor. Some researchers introduce ionic liquid to solve the problem, but the ionic liquid has high viscosity and low conductivity, so that the ionic liquid is poor in wetting with the surface of an electrode at room temperature, and the rate characteristic is poor, so that the ionic liquid is difficult to popularize in practical application.

An organic solvent with a wide electrochemical window, high anode stability and high dielectric constant becomes a hot spot solvent for researching an anion-intercalated graphite electrode under high voltage in recent years. However, in the electrolyte solution composed of LiDFOB (lithium difluoroborate) and EC (ethylene carbonate), the intercalation capacity of the graphite/Li positive electrode half cell was only 5.5mAh/g at the maximum, and the intercalation capacity was very low.

Therefore, how to obtain a more suitable electrolyte solution capable of improving the capacity and cycle performance of the dual-ion battery has become a problem to be solved by leading researchers in the field.

Disclosure of Invention

In view of the above, the present invention provides an electrolyte and a bi-ion battery, and the bi-ion battery containing the electrolyte has high capacity and good cycle performance.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides an electrolyte, which comprises an electrolyte and an organic solvent;

the electrolyte is lithium hexafluorophosphate (LiPF)₆) And lithium difluorooxalato borate (LiDFOB).

Preferably, in the electrolyte, the molar percentage of the lithium difluorooxalato borate is 0.1-99.9%, and the molar percentage of the lithium hexafluorophosphate is 99.9-0.1%.

More preferably, in the electrolyte, the molar percentage of the lithium difluoroborate is 50 to 99.9 percent, and the molar percentage of the lithium hexafluorophosphate is 0.1 to 50 percent.

More preferably, the molar percentage of the lithium difluorooxalato borate in the electrolyte is 65-95%, and the molar percentage of the lithium hexafluorophosphate in the electrolyte is 5-35%.

More preferably, the molar percentage of the lithium difluorooxalato borate in the electrolyte is 70-90%, and the molar percentage of the lithium hexafluorophosphate in the electrolyte is 10-30%.

It is particularly preferred that the electrolyte has a molar percentage of lithium difluoroborate of 80% and a molar percentage of lithium hexafluorophosphate of 20%.

Preferably, the organic solvent is ethylene carbonate.

Preferably, the molar concentration of the electrolyte in the organic solvent is 0.5mol/L to 2 mol/L.

More preferably, the molar concentration of the electrolyte in the organic solvent is 1 mol/L.

The invention also provides a bi-ion battery containing the electrolyte, which also comprises a graphite anode, a graphite cathode and a diaphragm between the graphite anode and the graphite cathode;

the material of the negative electrode is a material capable of performing reversible electrochemical reaction with an electrolyte;

the material of the separator is a material capable of separating the graphite positive electrode and negative electrode and allowing electrolyte ions to pass therethrough.

Preferably, the negative electrode is a lithium sheet.

Preferably, the material of the separator is glass fiber.

Compared with the prior art, the invention has the beneficial effects that:

the electrolyte provided by the invention takes lithium hexafluorophosphate and lithium difluoroborate as electrolyte salts, and the raw materials are simple to prepare, easy to obtain and low in cost. The lithium hexafluorophosphate is used as a common lithium salt, and has higher solubility and conductivity, a wide electrochemical window and good electrochemical stability; lithium difluoro (oxalato) borate also has the advantages of good thermal stability and good anode matching property. But the two can be inhibited in the organic solvent Ethylene Carbonate (EC) alone, the capacity is only 2.2mAh/g and 5.5mAh/g, the capacity is very low, and the inhibition effect of solvent molecules on anion energy storage can be weakened through the synergistic effect of the two, so that the capacity of the battery is greatly improved. The experimental result shows that when the molar ratio of the two in the electrolyte is 2:8 (LiPF)₆LiDFOB), the battery capacity can be increased to 21.2mAh g^-1。

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings used in the detailed description will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive labor.

FIG. 1 shows specific capacity versus LiPF of the bi-ion batteries prepared in comparative examples 1-2 and examples 1-9 of the present invention₆A trend graph of the proportion of the electrolyte;

FIG. 2 is a first-turn charge-discharge curve of the diionic batteries prepared in comparative examples 1-2, examples 1-3 and example 5 of the present invention;

fig. 3 is a cyclic voltammogram of the diionic cells prepared in comparative example 3 and example 10 of the present invention.

Detailed Description

For a further understanding of the invention, preferred embodiments of the invention are described below in conjunction with the detailed description, but it is to be understood that the description is intended to further illustrate the features and advantages of the invention and not to limit the claims to the invention.

The electrolyte of the invention comprises electrolyte and organic solvent, and can also consist of electrolyte and organic solvent.

The electrolyte of the present invention is lithium hexafluorophosphate (LiPF)₆) And lithium difluorooxalato borate (LiDFOB). Lithium hexafluorophosphate (LiPF) of the present invention₆) The proportion of lithium difluoroborate (LiDFOB) is not particularly limited, and can be selected and adjusted by the skilled in the art according to the actual situation, the product performance and the quality requirement, and the invention preferably selects the molar percentage of lithium difluoroborate in the electrolyte to be 0.1-99.9 percent, and the molar percentage of lithium hexafluorophosphate to be 99.9-0.1 percent; more preferably, the molar percentage of the lithium difluoro-oxalato-borate in the electrolyte is 50-99.9%, and the molar percentage of the lithium hexafluorophosphate is 0.1-50%; preferably, the molar percentage of the lithium difluoro oxalate borate in the electrolyte is 65-95 percent, and the molar percentage of the lithium hexafluorophosphate is 5-35 percent; preferably, the molar percentage of the lithium difluoro oxalate borate in the electrolyte is 70-90%, and the molar percentage of the lithium hexafluorophosphate is 10-30%; particularly preferably, the molar percentage of lithium difluorooxalato borate in the electrolyte is 80% and the molar percentage of lithium hexafluorophosphate is 20%.

The organic solvent used in the present invention is not particularly limited, and may be any organic solvent known to those skilled in the art that can be used for such batteries and electrolytes. The preferred organic solvent of the present invention is ethylene carbonate. The ratio of the electrolyte in the organic solvent is not particularly limited, and can be selected and adjusted by those skilled in the art according to the actual situation, the product performance and the quality requirement. In the present invention, the molar concentration of the electrolyte in the organic solvent is preferably 0.5mol/L to 2mol/L, and the molar concentration of the electrolyte in the organic solvent is more preferably 1 mol/L.

The double-ion battery comprises a graphite positive electrode, a graphite negative electrode, a diaphragm between the graphite positive electrode and the graphite negative electrode, and the electrolyte.

The present invention is not particularly limited to the bi-ion battery, and the bi-ion battery known to those skilled in the art may be used. The graphite positive electrode of the present invention is not particularly limited, and may be a graphite positive electrode for a bi-ion battery known to those skilled in the art. The graphite anode has the advantages of easily obtained electrode materials, stable structure, high reversible potential, environmental friendliness and suitability for large-scale energy storage. The negative electrode material is not particularly limited, and can be selected and adjusted by a person skilled in the art according to the actual situation, the product performance and the quality requirement, and is a material capable of performing reversible electrochemical reaction with lithium ions, such as a lithium sheet. The material of the separator is not particularly limited, and those skilled in the art can select and adjust the material according to the actual situation, the product performance and the quality requirement, and the material is a material which can separate the graphite positive electrode from the graphite negative electrode and can allow electrolyte ions to pass through, and the material is preferably glass fiber.

The method for preparing the diionic battery is not particularly limited, and the method for preparing the diionic battery, which is well known to those skilled in the art, can be adopted. The specific steps are preferably as follows: and (3) preparing the high-rate cold-resistant electrolyte in a glove box, and assembling the graphite positive electrode, the graphite negative electrode, the graphite diaphragm and the high-rate cold-resistant electrolyte into the dual-ion battery.

The capacity performance of the double-ion battery is represented by performing charge and discharge tests on the double-ion battery at normal temperature. Under the condition of room temperature (27 ℃), 1mol/L LiPF is used₆The battery capacity of the EC electrolyte is only 2.2mAh g^-1The capacity of the battery using 1mol/LLIDFOB/EC electrolyte was also only 5.5mAh g^-1. When the mixed electrolyte of the two is configured, the battery capacity shows a trend of increasing and then decreasing, and when the molar ratio of the two is 2:8 (LiPF)₆LiDFOB), the battery capacity can be increased to 21.2mAh g^-1And the capacity is greatly improved.

All of the starting materials of the present invention, without particular limitation as to their source, are either commercially available or prepared according to conventional methods well known to those skilled in the art.

All the raw materials of the present invention are not particularly limited in purity, and analytical purity is preferably used in the present invention.

The terms used in the present invention generally have meanings commonly understood by those of ordinary skill in the art, unless otherwise specified. In order to make those skilled in the art better understand the technical solution of the present invention, the present invention will be further described in detail with reference to the following embodiments.

In the following examples and comparative examples, various procedures and methods not described in detail are conventional methods well known in the art. Materials, reagents, apparatuses, instruments, equipment and the like used in the following examples and comparative examples are commercially available unless otherwise specified.

Comparative example 1

Preparing 1mol/L (M) lithium hexafluorophosphate solution in a glove box, wherein the solvent of the solution is ethylene carbonate, and standing the prepared solution for 12 h. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Comparative example 2

Preparing 1mol/L (M) lithium difluoro-oxalato-borate solution in a glove box, wherein the solvent of the solution is ethylene carbonate, and standing the prepared solution for 12 hours. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Comparative example 3

Preparing 1mol/L (M) lithium difluoro-oxalato-borate solution in a glove box, wherein the solvent is ethylene carbonate, and standing the prepared solution for 12 hours. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) for cyclic voltammetry.

Example 1

1mol/L (M) of lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution is prepared in a glove box, wherein the molar ratio of the lithium hexafluorophosphate to the lithium difluorooxalato borate is 1:9 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. Using the above-mentioned solution as electrolyte, placing it in glove boxManufacturing a double-ion battery, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Example 2

1mol/L (M) of lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution is prepared in a glove box, wherein the molar ratio of the lithium hexafluorophosphate to the lithium difluorooxalato borate is 2:8 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Example 3

1mol/L (M) of lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution is prepared in a glove box, wherein the molar ratio of the lithium hexafluorophosphate to the lithium difluorooxalato borate is 3:7 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Example 4

1mol/L (M) of lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution is prepared in a glove box, wherein the molar ratio of the lithium hexafluorophosphate to the lithium difluorooxalato borate is 4:6 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Example 5

Respectively preparing 1mol/L (M) lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution in a glove box, wherein the molar ratio of the two solutions is 5:5 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. The solution is used as electrolyte to manufacture a double-ion battery in a glove box, wherein the positive electrode is graphite, and the negative electrode is graphiteThe lithium sheet is adopted, and the diaphragm is made of glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Example 6

Respectively preparing 1mol/L (M) lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution in a glove box, wherein the molar ratio of the two solutions is 6:4 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Example 7

Respectively preparing 1mol/L (M) lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution in a glove box, wherein the molar ratio of the two solutions is 3:7 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Example 8

Respectively preparing 1mol/L (M) lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution in a glove box, wherein the molar ratio of the two solutions is 2:8 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Example 9

Respectively preparing 1mol/L (M) lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution in a glove box, wherein the molar ratio of the two solutions is 1:9 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. The solution is used as electrolyte to manufacture a double-ion battery in a glove box, wherein the anode is graphite, the cathode is a lithium sheet, and the diaphragm isGlass fibers; the cell was left at room temperature (27 ℃) to undergo a charge-discharge long cycle test.

Example 10

1mol/L (M) of lithium hexafluorophosphate and lithium difluorooxalato borate mixed solution is prepared in a glove box, wherein the molar ratio of the lithium hexafluorophosphate to the lithium difluorooxalato borate is 2:8 (LiPF)₆LiDFOB) and ethylene carbonate as a solvent, and the prepared solution was allowed to stand for 12 hours. Taking the solution as electrolyte, and manufacturing a double-ion battery in a glove box, wherein the positive electrode is graphite, the negative electrode is a lithium sheet, and the diaphragm is glass fiber; the cell was left at room temperature (27 ℃) for cyclic voltammetry.

The charge and discharge tests were performed on the above comparative examples and the prepared bi-ion batteries of the present invention, and the current density: 100mA g^-1The voltage range is as follows: 3V to 5V, and the testing temperature is 27 ℃; the test results are shown in FIGS. 1 to 3.

FIG. 1 shows specific capacity versus LiPF of the bi-ion batteries prepared in comparative examples 1-2 and examples 1-9 of the present invention₆A trend graph of the ratio of the mixed electrolyte salt to the mixed electrolyte salt; as can be seen from fig. 1, as the molar ratio of lithium hexafluorophosphate in the mixed electrolyte salt increases, the capacity of the bi-ion battery using the corresponding electrolyte solution shows a tendency to increase first and then decrease when lithium difluoroborate (liddob) and lithium hexafluorophosphate (LiPF) are used₆) When the molar ratio of (a) to (b) is 8:2, the specific capacity of the corresponding bi-ion battery is the largest, which shows that the specific capacity of the battery can be greatly improved by using the battery containing the dual-electrolyte.

FIG. 2 is a first-turn charge-discharge curve of the diionic batteries prepared in comparative examples 1-2, examples 1-3 and example 5 of the present invention; as can be seen from FIG. 2, LiDFOB: LiPF is present in the electrolyte₆When the ratio is 8:2, the first-turn charge-discharge capacity of the double-ion battery is larger than that of the single electrolyte salt, and the efficiency is high.

Fig. 3 is a cyclic voltammogram of the diionic cells prepared in comparative example 3 and example 10 of the present invention. As can be seen from FIG. 3, LiDFOB: LiPF is present in the electrolyte₆The higher capacity is also confirmed by the larger peak area of the diionic cell at 8: 2.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.