Patent Application
20240368070
The present disclosure relates to the technical field of batteries, and in particular, to an electrolyte additive and a preparation method therefor, an electrolyte and a lithium ion battery.
An electrolyte, as an important constituent part of a lithium ion battery, directly affects the overall performance of the battery, such as cycle life, rate, cell internal resistance, capacity, and safety. A liquid electrolyte is generally composed of components such as a lithium salt, an organic solvent and an additive. The existing electrolyte has defects, resulting in that lithium dendrites easily precipitate on an electrode sheet, and the battery has poor cycle performance.
In view of this, the present disclosure is specially proposed.
An object of some embodiments of the present disclosure is to provide an electrolyte additive and a preparation method therefor, an electrolyte and a lithium ion battery, in which an electrolyte added with the electrolyte additive can effectively inhibit precipitation of lithium dendrites, and improve the battery cycle performance.
Some embodiments of the present disclosure are implemented as follows:
According to a first aspect, some embodiments of the present disclosure provide a preparation method for an electrolyte additive, the electrolyte additive being used for being added to an electrolyte of a lithium ion battery, and the preparation method for an electrolyte additive comprising:
Dissolving a picric acid in an organic solvent to obtain an additive solution, the organic solvent comprising at least one element of B, F and N; and
In optional embodiments, the organic solvent comprises at least one of an alcohol solvent, an ether solvent, and a ketone solvent.
In optional embodiments, the alcohol solvent comprises one or more of tetrafluoro p-methoxymethyl methanol, β-sitosterol, 2-bromo-9-methyl-9H-fluoren-9-ol, (1S,4R)-1-methyl-4-(1-methylvinyl)-2-cyclohexen-1-ol, 4-trifluoromethylbenzylboronic acid pinacol ester, tetramethylpiperidinol, triisopropanolamine and 2-(5-methylfuran-2-yl)ethanol;
The ether solvent comprises one or more of diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, boron trifluoride diethyl ether, tetrafluoroborate diethyl ether, tetrafluoromethyl ether and tetrahydrofuran; and
The ketone solvent comprises one or more of 2-phenylchromone, flavonol, 2-hydroxychalcone, N-ethyl-2-pyrrolidone, isophorone and 2,4-pentanedione.
In optional embodiments, the step of dissolving the picric acid in the organic solvent comprises:
In optional embodiments, the stirring temperature is 20-30° C. and the duration is 6-8 h.
In optional embodiments, the temperature in the vacuum oven is 60-80° C.
In optional embodiments, the step of performing crystallization from the additive solution, to precipitate the electrolyte additive, comprises:
In optional embodiments, the step of performing crystallization from the additive solution, to precipitate the electrolyte additive, comprises:
And/or, vacuumizing at −5 to −20° C., to remove a solvent from the additive solution.
According to a second aspect, some embodiments of the present disclosure provide an electrolyte additive, which is prepared by the preparation method for an electrolyte additive according to any one of the embodiments above.
According to a third aspect, some embodiments of the present disclosure provide an electrolyte, the preparation raw material thereof comprising the electrolyte additive of the embodiments above.
According to a fourth aspect, some embodiments of the present disclosure provide a lithium ion battery, comprising the electrolyte of the embodiments above.
Some embodiments of the present disclosure have the following beneficial effects:
The lithium ion battery provided in some embodiments of the present disclosure comprises the electrolyte added with the electrolyte additive, and therefore has a lower resistance and better cycle performance.
In order to illustrate the technical solutions of the embodiments of the present disclosure more clearly, hereinafter, accompanying drawings requiring to be used in the embodiments will be briefly introduced. It should be understood that the following accompanying drawings only illustrate certain embodiments of the present disclosure, and therefore shall not be considered as limiting the scope. For a person of ordinary skill in the art, other related accompanying drawings may also be obtained according to these accompany drawings without any inventive effort.
To make the object, technical solutions and advantages of the embodiments of the present disclosure clearer, hereinafter, the technical solutions in the embodiments of the present disclosure will be clearly and completely described. If no specific conditions are noted in the embodiments, the experiments are performed according to conventional conditions or conditions suggested by a manufacturer. If manufacturers for reagents or instruments used are not noted, the reagents or instruments can be conventional products that can be commercially-available.
The features and performance in some embodiments of the present disclosure will be further described in detail below in combination with embodiments.
The preparation method for an electrolyte additive provided in embodiments of the present disclosure comprises:
Step S100, dissolving a picric acid in an organic solvent to obtain an additive solution, the organic solvent comprising at least one element of B, F and N.
In embodiments of the present disclosure, the organic solvent comprises at least one of an alcohol solvent, an ether solvent, and a ketone solvent.
Optionally, the alcohol solvent may be one or more of tetrafluoro p-methoxymethyl methanol, β-sitosterol, 2-bromo-9-methyl-9H-fluoren-9-ol, (1S,4R)-1-methyl-4-(1-methylvinyl)-2-cyclohexen-1-ol, 4-trifluoromethylbenzylboronic acid pinacol ester, tetramethylpiperidinol, triisopropanolamine and 2-(5-methylfuran-2-yl)ethanol;
The ether solvent may be one or more of diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, boron trifluoride diethyl ether, tetrafluoroborate diethyl ether, tetrafluoromethyl ether and tetrahydrofuran; and
The ketone solvent may be one or more of 2-phenylchromone, flavonol, 2-hydroxychalcone, N-ethyl-2-pyrrolidone, isophorone and 2,4-pentanedione, etc.
The picric acid additive molecule comprises a C atom and an H atom, the C atom and the H atom are dissolved in an ether-based electrolyte, and may undergo redox, spontaneous reaction, catalytic induction, and similar compatibility, etc. The alcohol, ether and ketone solvents contain fluorine, oxygen, nitrogen, boron and metal ions, or are a mixture thereof; these components can be grafted in the structure of the picric acid, and finally can improve the protection of the electrolyte additive against an anode. Specifically, these components can make an electropolymerization layer more stable and uniform, or participate in an SEI film formation process, thereby generating higher contents of LiF, Li2O, Li3N, etc.
Further, the step of dissolving the picric acid in the organic solvent may specifically comprise:
Adding the picric acid to the organic solvent and stirring same; and performing vacuumizing in a vacuum oven for performing a reaction.
Optionally, the stirring temperature is 20-30° C. and the duration is 6-8 h. Optionally, the temperature in the vacuum oven is 60-80° C. By a suitable stirring temperature, stirring duration and reaction temperature, the solubility and functionality of the picric acid in the organic solvent can be improved, which can assist some functional groups and chemical bonds to react.
The obtained additive solution is equivalent to a modified picric acid solution, as the additive solution contains a B element, an F element, metal ions or other various functional groups, the substance will undergo electropolymerization during charging and discharging of a battery, and BxOy (x=n, y=n+1) will be generated in the polymerization layer; the F element is bound with lithium ions in the electrolyte to generate LiF, and metal ions can be preferentially adsorbed on the tips of lithium dendrites, which helps to make a polymer layer and the SEI film more rigid and stable, and helps to suppress the growth of the lithium dendrites.
Step S200: performing crystallization from the additive solution, to precipitate the electrolyte additive.
In embodiments of the present disclosure, the step S200 may comprise: performing crystallization by at least one method of rotary evaporator drying, oven drying, vacuum drying under reduced pressure, slow drying in an oil bath pan, and vacuum drying in a cryogenic vessel, to precipitate the electrolyte additive. Optionally, the crystallinity is controlled at 50%-65%.
For example, the electrolyte additive may be crystallized and precipitated in the following several manners:
Hereinafter, in combination with various embodiments, the effect after the electrolyte additive prepared by using the preparation method for an electrolyte additive provided in some embodiments of the present disclosure is applied to a lithium ion battery will be described in detail.
20 mg of picric acid was dissolved in 40 mL of 2-(5-methylfuran-2-yl)ethanol by stirring, and after drying by using a rotary evaporator, an electrolyte additive (about 50% of crystallinity) was obtained.
0.5 wt % of the electrolyte additive was used in an electrolyte base solution (not added with the electrolyte additive). A lithium salt in the electrolyte base solution is lithium bis(trifluoromethanesulfonyl)imide, the concentration of the lithium salt was 1.0 mol−1, the solvent is 1,3-dioxolane and ethylene glycol dimethyl ether, and contained 0.5 wt % of lithium nitrate.
10 mg of picric acid was dissolved in 20 mL of boron trifluoride diethyl ether by stirring, and the mixture was dried in an oven to raise the temperature from 25° C. to 90° C. at 5° C. per minute, and the temperature was maintained for 6 h to obtain an electrolyte additive in a powder form.
1 wt % of the electrolyte additive was used in an electrolyte base solution. The electrolyte base solution was the same as the electrolyte base solution in Embodiment 1.
10 mg of picric acid was dissolved in 20 m L of N-ethyl-2-pyrrolidone by stirring, the mixture was vacuum-dried and vacuumized under reduced pressure, then the temperature was increased from an initial temperature of 25° C. to 60-70° C. at 5° C. per minute, and the temperature was maintained for 6 h to obtain an electrolyte additive in a powder form.
1.2 wt % of the electrolyte additive was used in an electrolyte base solution. The electrolyte base solution was the same as the electrolyte base solution in Embodiment 1.
10 mg of picric acid was dissolved in 20 mL of 2-bromo-9-methyl-9H-fluoren-9-ol by stirring, the mixture was slowly dried by using an oil bath pan, and then transferred to a rotary evaporator for further drying, and the temperature was increased from an initial temperature of 25° C. to 100° C. at 5° C. per minute, and then the heating was stopped; the whole oil bath pan was wrapped with an aluminum foil so that the temperature thereof was slowly reduced, the temperature thereof was reduced to room temperature after 6-8 h, and the temperature was maintained for 24-48 h, and then an electrolyte additive (with a crystallinity of 55-60%) was crystallized and precipitated.
1.5 wt % of the electrolyte additive was used in an electrolyte base solution. The electrolyte base solution was the same as the electrolyte base solution in Embodiment 1.
10 mg of picric acid was dissolved in 30 mL of a 4-trifluoromethylbenzylboronic acid pinacol ester solution by stirring, the mixture was vacuum-dried in a cryogenic vessel, and maintained at a low temperature of −10° C. In this method, it is necessary to add an appropriate amount of liquid nitrogen and dry ice, to ensure uniform formation of crystals in the solution (about 65% of crystallinity). Then, the solvent was slowly removed by suction by a small amount of vacuum for 3-5 times and left for 24-48 h, to obtain the electrolyte additive.
2 wt % of the electrolyte additive was used in an electrolyte base solution. The electrolyte base solution was the same as the electrolyte base solution in Embodiment 1.
No electrolyte additive was added to an electrolyte, that is, the electrolyte is the same as the electrolyte base solution in Embodiments 1-5.
The difference from the embodiment 1 lied in that, picric acid was not pre-dissolved in an organic solvent containing at least one element of B, F and N and was not modified, but 0.5 wt % of picric acid was directly added to an electrolyte.
The electrolytes of the embodiments and comparative embodiments were applied to a battery, and the performance thereof was tested. The specific manner is as follows.
A battery impedance test was performed on batteries after cycling under a condition of 100 Hz.
At 25±2° C., a battery was charged to 3.65 V under a 1 C constant current and a constant voltage, with a cut-off current being 0.05 C; and the battery stood still for 60 min, then was discharged to 2.5V at 1 C, the process continued until the capacity decayed to 80% of the initial capacity, and the number of cycles was recorded.
Table 1 was the parameters and test results of various embodiments and comparative embodiments.
It could be determined from Table 1 that, after the electrolytes of Embodiments 1-5 in the present disclosure were applied to a battery, the deposition thickness of the lithium anode was thinner than that of the comparative embodiments; and the impedance value of the battery was lower than that of the comparative embodiments, and had better conductivity. Furthermore, compared with the comparative embodiments, the number of cycles was obviously improved, and therefore using the electrolyte additive provided in embodiments of the present disclosure could improve the cycle performance of a lithium ion battery.
Preparation raw materials of the electrolyte provided in embodiments of the present disclosure comprises the electrolyte additive prepared by the preparation method. In addition to having an electropolymerization function, the electrolyte additive provided in embodiments of the present disclosure could also participate in an electropolymerization reaction on the surface of an anode to generate a polymerization layer with stronger performance, thereby reducing adverse reactions between the electrolyte and lithium ions, reducing the thickness of a deposition layer on the surface of the anode, and reducing the internal impedance of the battery. Some functional groups and chemical bonds contained in the electrolyte additive could participate in the reaction of an anode SEI film, so that there were more inorganic substances such as Li2O, LiF and Li3N in the SEI film layer, which rendered the anode SEI film to be more robust, and could well inhibit the growth of lithium dendrites; moreover, the chemical bonds and functional groups carried a certain electrostatic force field, so that ion channels could be formed, facilitating uniform transmission of lithium ions, and being beneficial to improving the cycle performance and safety performance of the lithium battery. Furthermore, the electrolyte additive provided in the embodiments of the present disclosure has a simple preparation process and was easy to implement industrial production.
In addition, embodiments of the present disclosure further provide a lithium ion battery, which comprises the electrolyte provided by the embodiments of the present disclosure.
The content above merely relates to preferred embodiments of the present disclosure and is not intended to limit some embodiments of the present disclosure. For a person skilled in the art, some embodiments of the present disclosure may have various modifications and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of some embodiments of the present disclosure shall all belong to the scope of protection of some embodiments of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202310498087.9 | May 2023 | CN | national |
