CN115275341A

CN115275341A - Low-temperature electrolyte suitable for silicon-based lithium ion battery, and preparation method and application thereof

Info

Publication number: CN115275341A
Application number: CN202211049629.6A
Authority: CN
Inventors: 唐伟; 舒程勇; 陈慧鑫
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2022-08-30
Filing date: 2022-08-30
Publication date: 2022-11-01

Abstract

The invention discloses a low-temperature electrolyte suitable for a silicon-based lithium ion battery, and a preparation method and application thereof. The electrolyte can establish a high-performance and stable solid electrolyte interface film on the surface of a silicon-based negative electrode, still shows higher ionic conductivity at lower temperature (-30 ℃), and due to the addition of the fluorinated solvent, solvent molecules and cations have lower desolvation energy, so that the low-temperature ion desorption is facilitated. The carboxylate negative electrode film-forming additive can effectively form an elastic SEI protective layer on the outer side in a long circulation process so as to relieve volume change of a silicon electrode in a lithiation process and keep battery performance unaffected by side reactions for a long time. The electrolyte provided by the invention is suitable for lithium ion batteries, particularly silicon-based negative electrode batteries, and can show good electrochemical performance at low temperature.

Description

Low-temperature electrolyte suitable for silicon-based lithium ion battery, and preparation method and application thereof

Technical Field

The invention belongs to the technical field of preparation of lithium ion battery electrolyte, and particularly relates to a low-temperature electrolyte suitable for a silicon-based lithium ion battery, and a preparation method and application thereof.

Background

The lithium ion battery has the advantages of long service life, large specific capacity, no memory effect and the like, and the application range is gradually widened. However, early research into external influencing factors of lithium ion battery performance focused mainly on safety and cycle performance issues under high temperature conditions. With the continuous expansion of the application field, the low-temperature performance of the lithium ion battery has become a main influence factor of the development and application of the lithium ion battery in some fields. The working temperature of the lithium ion battery using the traditional lithium ion battery electrolyte is between-20 and +55 ℃, however, the discharge capacity of the lithium ion battery at the temperature of-20 ℃ is only about 31.5 percent of that at the room temperature. However, in the fields of aerospace, war industry, electric vehicles and the like, the battery is required to work normally at the temperature of minus 40 ℃. Therefore, from the viewpoints of military use, aviation, environmental protection, energy conservation and the like, the significance of improving the low-temperature performance of the lithium ion battery is great, but the research on the low-temperature characteristics of the lithium ion battery is obviously lagged at present.

The silicon negative electrode material has higher theoretical specific capacity and is one of the most promising negative electrode materials of the lithium ion battery. However, the silicon negative electrode material has a large volume expansion during lithiation, which causes mechanical breakage or pulverization of the material, resulting in loss of active material and exposure of a highly active surface to an electrolyte. This results in a sustained increase in Solid Electrolyte Interface (SEI) at the surface of the negative electrode, rapid consumption of electrolyte, resulting in low cycle Coulombic Efficiency (CE) and poor cycle life of the battery. The organic-inorganic SEI formed in conventional carbonate electrolytes is not sufficient to accommodate the volume expansion of silicon negative electrodes. Therefore, silicon negative electrode batteries exhibit a rapid capacity drop, typically to below 60% over 20 charge-discharge cycles.

Therefore, for silicon-based negative electrode lithium ion batteries, it is necessary to design an electrolyte solution that can construct a strong solid electrolyte interface and improve the low-temperature performance of the solid electrolyte interface.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a low-temperature electrolyte suitable for a silicon-based lithium ion battery, a preparation method and application, and can solve the technical problems that a solid electrolyte interface cannot be constructed for the electrolyte of the silicon-based negative electrode lithium ion battery in the prior art and the cycle performance is poor at low temperature.

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

the invention discloses a low-temperature electrolyte suitable for a silicon-based lithium ion battery, which comprises a lithium salt, a non-aqueous solvent and a negative electrode film-forming additive; wherein the nonaqueous solvent is composed of one of fluorinated cyclic carbonates represented by the following formula I and one of fluorinated cyclic carboxylates represented by the following formula II;

preferably, the low-temperature electrolyte contains 10-30% of lithium salt, 60-90% of non-aqueous solvent and 10-30% of negative electrode film-forming additive by mass percentage.

Preferably, the lithium salt is selected from one or more of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide and lithium hexafluoroarsenate.

Further preferably, the lithium salt is selected from lithium bis-fluorosulfonylimide.

Preferably, the nonaqueous solvent is a solution prepared by mixing fluoroethylene carbonate and fluorocyclic carboxylic ester according to a mass ratio of 2.

Preferably, the negative film-forming additive is ethylene glycol sulfate.

The invention also discloses a preparation method of the low-temperature electrolyte suitable for the silicon-based lithium ion battery, which is characterized in that under the argon environment, lithium salt and a negative electrode film-forming additive are added into a non-aqueous solvent, so that the concentration of the lithium salt reaches 1.0mol/L, and the lithium salt and the negative electrode film-forming additive are fully and uniformly stirred to prepare the low-temperature electrolyte suitable for the silicon-based lithium ion battery.

The invention also discloses application of the low-temperature electrolyte suitable for the silicon-based lithium ion battery in preparing the lithium ion battery taking silicon or silicon carbon as a negative electrode.

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

the invention discloses a low-temperature electrolyte suitable for a silicon-based lithium ion battery, which comprises lithium salt, a non-aqueous solvent and a negative electrode film-forming additive, wherein the non-aqueous solvent comprises fluorinated cyclic carbonate and fluorinated cyclic carboxylate. The carboxylate negative electrode film-forming additive can effectively form an elastic SEI protective layer on the outer side in a long circulation process so as to relieve volume change of a silicon electrode in a lithiation process and keep battery performance unaffected by side reactions for a long time. The electrolyte provided by the invention is suitable for lithium ion batteries, particularly silicon-based negative electrode batteries, and can show good electrochemical performance at low temperature.

Drawings

FIG. 1 is a graph of the cycling performance of example 1 at different temperatures.

FIG. 2 is a graph comparing the cycle performance at low temperature-30 ℃ of example 1 and comparative example 2.

FIG. 3 is a graph showing a comparison of specific capacities of example 1 and comparative examples 1 and 2 when cycled at room temperature.

FIG. 4 is a graph comparing the AC impedance of example 1 with that of comparative examples 1 and 2 at-30 ℃.

FIG. 5 is a plot of dQ/dV at different temperatures for example 1;

in the figure, code LX419 (example 1) code LD120 (comparative example 1) code LX463 (comparative example 2).

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Moreover, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

The invention is described in further detail below with reference to the accompanying drawings:

example 1

A lithium ion battery electrolyte is prepared by filling high-purity argon (water, oxygen content is less than or equal to 1 ppm) in a standard glove box, taking fluoroethylene carbonate and fluorinated cyclic carboxylate (MTFA) as non-aqueous solvents, taking lithium bis (fluorosulfonyl) imide (LiFSI) as lithium salt and taking ethylene glycol sulfate as a negative film-forming additive. The preparation method comprises the following steps: 6.88g of fluoroethylene carbonate and 27.5g of fluorinated cyclic carboxylate (MTFA) are mixed, then 1.24g of ethylene glycol sulfate and 3.74g of lithium bis (fluorosulfonyl) imide (LiFSI) are added into the solution, so that the concentration of the lithium salt reaches 1.0mol/L, and the mixture is fully stirred uniformly, and a low-temperature electrolyte LX419 is obtained.

And (3) configuring a button cell by taking the configured LX419 as an electrolyte, nano silicon powder as a positive electrode and metal lithium as a negative electrode for electrochemical test. FIG. 1 compares the capacity performance of the electrolyte at different temperatures, and the maximum capacity is 3264mAh/g when the electrolyte is charged and discharged at the normal temperature of 25 ℃ at 0.36A/g. The low-temperature charge and discharge performance is shown in figure 2, the LX419 electrolyte can still reach 2490mAh/g at the low temperature of minus 30 ℃ by charging and discharging at 100 mA/g. FIG. 3 shows the cycle performance of the LX419 electrolyte, wherein the LX419 electrolyte is charged and discharged at 0.72A/g at the normal temperature of 25 ℃, the capacity is reduced from 3264mAh/g to 2460mAh/g after 100 cycles, and the capacity retention rate is 75%. Fig. 4 shows the low charge transfer resistance of LX419 electrolyte at low temperature-30 ℃. FIG. 5 shows that the peak dQ/dV potential of LX419 electrolyte is increased by about 0.05V to 0.46V at-30 deg.C compared to room temperature.

Comparative example 1

A lithium ion battery electrolyte prepared under the same experimental conditions as in example 1, using two carbonates, namely Ethylene Carbonate (EC) and dimethyl carbonate (DMC), as solvents, and lithium hexafluorophosphate (LiPF) ₆ ) Is a lithium salt. The preparation method comprises the following steps: ethylene carbonate and dimethyl carbonate (DMC) were mixed in a mass ratio of 2 ₆ ) The concentration of the electrolyte is 1mol/L, and the electrolyte is fully and uniformly stirred to obtain the electrolyte LD120.

And (3) taking the prepared LD120 as electrolyte, nano silicon powder as a positive electrode and metal lithium as a negative electrode, and configuring a button cell for electrochemical test. The electrolyte is charged and discharged at 0.36A/g at the normal temperature of 25 ℃, the capacity is 2980mAh/g, the circulation performance of the electrolyte is 0.72A/g at the normal temperature of 25 ℃, the capacity is reduced to 580mAh/g from 2400mAh/g after 100 times of circulation, and the capacity retention rate is 24%. The material can not work normally at the low temperature of minus 30 ℃ when charged and discharged at 100 mA/g.

Comparative example 2

A lithium ion battery electrolyte is prepared by using two carbonates, namely Ethylene Carbonate (EC) and dimethyl carbonate (DMC), as solvents and lithium salt of bis (fluorosulfonyl) imide (LiFSI) as a lithium salt under the same experimental conditions as in example 1. The preparation method comprises the following steps: mixing ethylene carbonate and dimethyl carbonate (DMC) according to a mass ratio of 2.

And (3) configuring a button cell for electrochemical test by taking the prepared LX463 as an electrolyte, nano silicon powder as a positive electrode and metal lithium as a negative electrode. The capacity is 2965mAh/g at the normal temperature of 25 ℃, the cycle performance of the electrolyte is 0.72A/g at the normal temperature of 25 ℃, the capacity is reduced from 2630mAh/g to 1180mAh/g after 100 cycles, and the capacity retention rate is 49%. The material can not work normally at the low temperature of minus 30 ℃ when charged and discharged at 100 mA/g.

In conclusion, the LX419 electrolyte disclosed in the embodiment 1 is used for realizing the highest capacity of 3264mAh/g at room temperature and the highest capacity retention rate of 75% after 100 times of circulation, and can realize normal circulation operation at-30 ℃ and the capacity of 2490mAh/g. In contrast, the capacity, capacity retention rate and low-temperature performance of comparative example 1 and comparative example 2 cannot exceed those of example 1, which shows that the electrolyte of example 1 has excellent electrochemical performance and low-temperature performance.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims

1. The low-temperature electrolyte suitable for the silicon-based lithium ion battery is characterized by comprising a lithium salt, a non-aqueous solvent and a negative electrode film-forming additive; wherein the nonaqueous solvent consists of one of fluorinated cyclic carbonates shown in the following formula I and one of fluorinated cyclic carboxylates shown in the following formula II;

2. the low-temperature electrolyte for the silicon-based lithium ion battery according to claim 1, wherein the low-temperature electrolyte comprises, by mass, 10% to 30% of a lithium salt, 60% to 90% of a non-aqueous solvent, and 10% to 30% of a negative electrode film-forming additive.

3. The low-temperature electrolyte suitable for the silicon-based lithium ion battery according to claim 1, wherein the lithium salt is one or more selected from lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide and lithium hexafluoroarsenate.

4. The low-temperature electrolyte suitable for silicon-based lithium ion batteries according to claim 3, wherein the lithium salt is selected from lithium bis-fluorosulfonylimide.

5. The low-temperature electrolyte suitable for the silicon-based lithium ion battery according to claim 1, wherein the non-aqueous solvent is a mixture of fluoroethylene carbonate and fluorocyclic carboxylic ester in a mass ratio of 2.

6. The low-temperature electrolyte suitable for the silicon-based lithium ion battery as claimed in claim 1, wherein the negative film-forming additive is ethylene glycol sulfate.

7. The method for preparing the low-temperature electrolyte suitable for the silicon-based lithium ion battery as claimed in any one of claims 1 to 6, wherein the low-temperature electrolyte suitable for the silicon-based lithium ion battery is prepared by adding lithium salt and a negative film-forming additive into a non-aqueous solvent under an argon environment to enable the concentration of the lithium salt to reach 1.0mol/L and fully and uniformly stirring.

8. The use of the low-temperature electrolyte suitable for silicon-based lithium ion batteries according to any one of claims 1 to 6 for the preparation of lithium ion batteries with silicon or silicon carbon as the negative electrode.