Flame-retardant electrolyte for lithium ion battery and preparation method thereof

Abstract

The application belongs to the field of lithium ion batteries, and particularly relates to a kind of flame-retardant electrolyte for lithium ion batteries and its preparation method. A kind of flame-retardant electrolyte for lithium ion batteries, characterized in that it comprises the following components: organic solvent, electrolyte and additive, the concentration of the electrolyte in the electrolyte is 0.5-1.5 mol / L, the mass of the additive accounts for 0.5-13% of the total mass of the electrolyte, and the additive is bromoether 1,2-bis(2-bromoethoxy)ethane. The application uses bromoether 1,2-bis(2-bromoethoxy)ethane (Br-DEE) which is a bromoether molecule with single substitution of bromine atom. By introducing the additive bromoether 1,2-bis(2-bromoethoxy)ethane (Br-DEE), the flame-retardant electrolyte for lithium ion batteries prepared has excellent flame-retardant effect when used in lithium ion batteries, and does not affect the electrochemical performance of lithium ion batteries. At the same time, the electrolyte preparation process is simple and low in cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion batteries, and particularly relates to a flame-retardant electrolyte for lithium ion batteries and a preparation method thereof. BACKGROUND

[0002] As a new type of green battery, lithium ion batteries have the advantages of high energy density and no memory effect, and their application is rapidly expanding from consumer electronics to electric vehicles and new energy storage. However, in recent years, with the large-scale application of lithium ion batteries, a large number of safety accidents related to the misuse of thermal runaway of lithium ion batteries occur every year worldwide, and the academic and industrial communities are also paying increasing attention to and strengthening the exploration and improvement of the safety of lithium ion batteries. Therefore, the electrolyte is bearing more and more stringent tasks.

[0003] Commercial lithium ion batteries usually use carbonate-based electrolytes, which include lithium salts (such as lithium hexafluorophosphate LiPF6) and carbonate solvents (such as ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, diethyl carbonate DEC, and methyl ethyl carbonate EMC) with low flash point, high flammability, and poor electrochemical stability. At present, from the perspective of materials, there are many safety improvement strategies to prevent lithium ion batteries from catching fire and exploding due to thermal runaway, such as using flame-retardant electrolytes, flame-retardant heat-resistant shrinkable separators, solid electrolytes, and electrode materials with high structural stability (such as lithium iron phosphate LFP). Among them, developing high-safety flame-retardant electrolytes is the most economical and simple strategy, which can effectively reduce the risk of lithium ion battery thermal runaway, combustion, and explosion. The commonly used additives for flame-retardant electrolytes are mainly phosphite and phosphazene, which can improve the safety performance of lithium ion batteries, but to some extent, they will reduce the electrochemical performance of lithium ion batteries, and have the defects of high cost and complex preparation process.

[0004] Therefore, it is of great significance to develop an intrinsically safe electrolyte with flame-retardant properties suitable for lithium batteries for the further promotion and application of lithium batteries. SUMMARY

[0005] The present application aims at the deficiencies of the prior art, and provides a flame-retardant electrolyte for lithium ion batteries and a preparation method thereof, so as to improve the safety performance of lithium ion batteries on the basis of ensuring the electrochemical performance of lithium ion batteries, and solve the problem that the electrolyte provided by the prior art is prone to cause battery combustion or thermal runaway under extreme conditions.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The application provides a novel high-voltage-resistant non-flammable ether solvent electrolyte for a lithium battery, which comprises an organic solvent, an electrolyte and an additive, the concentration of the electrolyte in the electrolyte is 0.5-1.5 mol / L, the mass of the additive accounts for 0.5-13% of the total mass of the electrolyte, and the additive is bromoether 1,2-bis(2-bromoethoxy)ethane (Br-DEE) with a structural formula as shown in formula I.

[0008]

[0009] Formula I

[0010] Preferably, the organic solvent comprises a first organic solvent and a second organic solvent, the first organic solvent is dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) or methyl propyl carbonate (MPC), and the second organic solvent is ethylene carbonate (EC) or propylene carbonate (PC).

[0011] Further preferably, the volume of the first organic solvent accounts for 40-70% of the total volume of the organic solvent, and the rest is the second organic solvent.

[0012] Preferably, the electrolyte is one or more of lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium bis-trifluorosulfonimide, lithium bis-oxalato borate, lithium difluoro-oxalato borate and lithium nitrate.

[0013] More preferably, the electrolyte is lithium hexafluorophosphate.

[0014] Preferably, in the above-mentioned non-flammable electrolyte for a lithium battery, the concentration of the lithium salt in the non-flammable electrolyte is 0.1-5 mol / L.

[0015] The application further provides a preparation method of the non-flammable electrolyte for a lithium ion battery, which comprises the following steps:

[0016] The organic solvent is mixed and stirred in an argon-filled glove box, then the formula amount of the electrolyte is added and stirred until completely dissolved, then the formula amount of the additive is added and stirred uniformly, and the non-flammable electrolyte for the lithium ion battery is obtained.

[0017] Preferably, the moisture content in the glove box is less than 0.01 ppm, and the oxygen content is less than 0.01 ppm.

[0018] The application has the following beneficial effects:

[0019] The present application utilizes the ether molecule bromine atom single-substituted bromo ether 1,2-bis(2-bromoethoxy)ethane (Br-DEE), by introducing the additive bromo ether 1,2-bis(2-bromoethoxy)ethane (Br-DEE), so that the prepared lithium ion battery with flame-retardant electrolyte has excellent flame-retardant effect when used in lithium ion battery, and will not affect the electrochemical performance of lithium ion battery. At the same time, the electrolyte preparation process is simple, low cost.

[0020] The present application utilizes the ether molecule bromine atom single-substituted bromo ether 1,2-bis(2-bromoethoxy)ethane (Br-DEE), by introducing the additive bromo ether 1,2-bis(2-bromoethoxy)ethane (Br-DEE), so that the prepared lithium ion battery with flame-retardant electrolyte has excellent flame-retardant effect when used in lithium ion battery, and will not affect the electrochemical performance of lithium ion battery. At the same time, the electrolyte preparation process is simple, low cost. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The ignition experiment diagram of the electrolyte prepared for Comparative Example 2 is, Figure 1 a is before combustion, Figure 1 b is during combustion, Figure 1 c is after combustion;

[0022] Figure 2 The ignition experiment diagram of the electrolyte prepared for Comparative Example 1 is, Figure 2 a is before combustion, Figure 2 b is during combustion, Figure 2 c is after combustion;

[0023] Figure 3 The ignition experiment diagram of the electrolyte prepared for Example 1 is, Figure 3 a is before combustion, Figure 3 b is during combustion, Figure 3 c is after combustion. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0025] Example 1

[0026] In a glove box filled with argon, moisture content less than 0.01 ppm, oxygen content less than 0.01 ppm, methyl ethyl carbonate (EMC) and propylene carbonate (EC) in a volume ratio of 7:3 are mixed to form an electrolyte solvent system, then LiPF6 is added thereto and stirred until completely dissolved, the concentration of LiPF6 in the electrolyte is 1 mol / L, then DEE is added, the mass of DEE accounts for 5% of the total mass of the electrolyte, and stirring is uniform, thereby obtaining a lithium ion battery electrolyte.

[0027] Comparative Example 1

[0028] In a glove box filled with argon, moisture content less than 0.01 ppm, oxygen content less than 0.01 ppm, EMC and EC in a volume ratio of 7:3 are mixed to form an electrolyte solvent system, then LiPF6 is added thereto and stirred until completely dissolved, the concentration of LiPF6 in the electrolyte is 1 mol / L, then DEE is added, the mass of DEE accounts for 5% of the total mass of the electrolyte, and stirring is uniform, thereby obtaining a lithium ion battery electrolyte.

[0029] Comparative Example 2

[0030] This comparative example provides a commercial electrolyte, specifically 1 mol / L LiPF6 / EC:EMC (volume ratio 3:7).

[0031] Example 2

[0032] In a glove box filled with argon, moisture content less than 0.01 ppm, oxygen content less than 0.01 ppm, diethyl carbonate (DEC) and propylene carbonate (PC) in a volume ratio of 4:6 are mixed to form an electrolyte solvent system, then lithium bisfluorosulfonylimide is added thereto and stirred until completely dissolved, the concentration of lithium bisfluorosulfonylimide in the electrolyte is 0.5 mol / L, then Br-DEE is added, the mass of Br-DEE accounts for 0.5% of the total mass of the electrolyte, and stirring is uniform, thereby obtaining a lithium ion battery electrolyte.

[0033] Example 3

[0034] In a glove box filled with argon, moisture content less than 0.01 ppm, oxygen content less than 0.01 ppm, methyl propyl carbonate (MPC) and ethylene carbonate (EC) in a volume ratio of 5:5 are mixed to form an electrolyte solvent system, then lithium bisoxalate borate is added thereto and stirred until completely dissolved, the concentration of lithium bisoxalate borate in the electrolyte is 1.5 mol / L, then Br-DEE is added, the mass of Br-DEE accounts for 13% of the total mass of the electrolyte, and stirring is uniform, thereby obtaining a lithium ion battery electrolyte.

[0035] Ignition experiments were performed on the electrolytes of Example 1 and Comparative Example 1 and Comparative Example 2 (200 μL of electrolyte was injected into a glass fiber), and the flame retardant properties were measured, and the results are shown in Figures 1 to 3

[0036] Figure 1 Figure 2 Figure 3 The pictures before ignition, during combustion and after combustion of the commercial electrolyte, the electrolyte of Comparative Example 2 and the electrolyte prepared in Example 1, respectively, are shown in Figures 1 to 3 It can be seen from the pictures that the commercial electrolyte continues to burn after ignition, the glass fiber used in the test is completely burned, the electrolyte of Comparative Example 2 also burns violently after ignition, most of the glass fiber used in the test is burned, while the electrolyte of Example 1 is not easy to burn, and the glass fiber used in the test remains basically unchanged after burning, and has good flame retardant properties.

[0037] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered within the scope of protection of the present application.​​​

Claims

1. A flame retardant electrolyte for lithium ion batteries, characterized in that: The invention comprises the following components: an organic solvent, an electrolyte and an additive. The concentration of the electrolyte in the electrolyte is 0.5-1.5 mol / L, the mass of the additive accounts for 0.5-13% of the total mass of the electrolyte, and the additive is 1,2-bis(2-bromoacetoxy)ethane, and its structural formula is as shown in Formula I: Formula I.

2. The flame-retardant electrolyte for batteries according to claim 1, characterized in that: The organic solvent includes a first organic solvent and a second organic solvent, the first organic solvent is dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate or methyl propyl carbonate, and the second organic solvent is ethylene carbonate or propylene carbonate.

3. The flame-retardant electrolyte for batteries according to claim 2, characterized in that: The volume of the first organic solvent accounts for 40-70% of the total volume of the organic solvent, and the remainder is the second organic solvent.

4. The flame-retardant electrolyte for batteries according to claim 1, characterized in that: The electrolyte is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate and lithium nitrate.

5. The flame-retardant electrolyte for batteries according to claim 1, characterized in that: The concentration of the lithium salt in the flame retardant electrolyte is 0.1-5 mol / L.

6. A method for preparing a flame-retardant electrolyte for a battery according to any one of claims 1 to 5, characterized in that: The following steps are adopted: mixing and stirring an organic solvent in an environment filled with argon, then adding an electrolyte thereto and stirring until completely dissolved, then adding an additive and stirring evenly to obtain the flame retardant electrolyte for lithium ion batteries.

7. The preparation method according to claim 6, characterized in that The solvents are mixed and stirred in a glove box; wherein the moisture content in the glove box is less than 0.01 ppm, and the oxygen content is less than 0.01 ppm.

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