High-performance lithium-rich manganese-based lithium ion battery electrolyte with flame-retardant function and preparation method thereof

Abstract

The invention relates to a high-performance lithium-rich manganese-based lithium ion battery electrolyte with a flame-retardant function and a preparation method thereof, the high-performance lithium-rich manganese-based lithium ion battery electrolyte comprises a lithium salt and an electrolyte organic solvent, the lithium salt is a composite lithium salt, the composite lithium salt comprises lithium hexafluorophosphate and lithium salt additive lithium difluoro (oxalato) borate, and the electrolyte solvent comprises the electrolyte organic solvent and an additive, the additive comprises a positive electrode film-forming additive tris (trimethylsilane) phosphate and a flame-retardant additive ethyoxyl (pentafluoro) cyclotriphosphazene. The electrolyte has the advantages that the electrolyte not only has excellent cycle performance, but also has a flame-retardant function.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a high-performance lithium-rich manganese-based lithium ion battery electrolyte with flame retardant function and a preparation method thereof. Background Art

[0002] As the world pays more attention to sustainable development and energy conservation and emission reduction, the application of lithium-ion batteries, as key components for clean energy storage and conversion, continues to expand and deepen. From the initial portable electronic devices, such as smartphones and laptops, to electric vehicles and hybrid vehicles in recent years, and even large-scale energy storage systems and aerospace fields, lithium-ion batteries have become an important force in promoting the new energy revolution with their advantages such as high energy density, long cycle life, low self-discharge rate and environmental friendliness. Especially driven by the strong development of the new energy vehicle industry, the market demand for higher energy density, safer and more reliable lithium-ion batteries is growing, which poses unprecedented challenges to the innovation and optimization of battery materials.

[0003] Among the many cathode materials, lithium-rich manganese-based materials are regarded as ideal cathode materials for the next generation of high-energy-density lithium-ion batteries due to their significantly high specific capacity (>280mAh g-1) and high energy density (>1000Wh kg-1), which are much higher than the currently widely used traditional materials such as lithium cobalt oxide and lithium iron phosphate. In addition, they are cost-effective and environmentally friendly. However, the high operating voltage characteristics of lithium-rich manganese-based materials (usually exceeding 4.5V) cause the electrolyte to decompose easily during the charge and discharge process, accompanied by the release of oxygen, which not only accelerates the consumption of the electrolyte, but also may trigger thermal runaway reactions inside the battery, seriously threatening the safety performance of the battery.

[0004] In view of the safety challenges brought by lithium-rich manganese-based cathode materials, the development of flame-retardant electrolytes has become an important way to improve the overall safety of lithium-ion batteries. Flame-retardant electrolytes effectively slow down or prevent the spread of fire by inhibiting the chain reaction during thermal runaway of batteries, providing an additional safety barrier for batteries. However, the research and development of flame-retardant electrolytes faces the problem of how to ensure high flame retardancy without sacrificing the electrochemical performance of lithium-ion batteries. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function and a preparation method thereof. The electrolyte not only has excellent cycle performance but also has flame retardant function.

[0006] The technical solution of the present invention is:

[0007] A high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function, comprising a lithium salt and an electrolyte organic solvent, and having the following special features:

[0008] The lithium salt is a composite lithium salt, which includes lithium hexafluorophosphate and a lithium salt additive, lithium difluorooxalate borate. The electrolyte solvent includes an electrolyte organic solvent and additives, and the additives include a positive electrode film-forming additive, tris(trimethylsilane) phosphate, and a flame retardant additive, ethoxy(pentafluoro)cyclotriphosphazene.

[0009] The molar concentration of the composite lithium salt in the electrolyte is 1 mol / L, wherein the molar concentration of the lithium salt is 0.8-0.9 mol / L, and the molar concentration of the lithium salt additive is 0.1-0.2 mol / L.

[0010] The added mass of the positive electrode film-forming additive tris(trimethylsilyl)phosphate accounts for 0.5-2wt.% of the total mass of the composite lithium salt and the organic solvent of the electrolyte, and the added mass of the flame retardant additive ethoxy(pentafluoro)cyclotriphosphazene accounts for 6-8wt.% of the total mass of the composite lithium salt and the organic solvent of the electrolyte.

[0011] Preferably, the organic solvent of the electrolyte consists of cyclic carbonate and linear carbonate.

[0012] Further preferably, the cyclic carbonate is ethylene carbonate, and the chain carbonate includes ethyl methyl carbonate and diethyl carbonate, wherein the volume ratio of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate is 1:1:1.

[0013] More preferably, the molar concentration of lithium salt lithium hexafluorophosphate in the electrolyte is 0.9 mol / L.

[0014] Further preferably, the molar concentration of the lithium salt additive lithium difluorooxalate borate in the electrolyte is 0.1 mol / L.

[0015] Further preferably, the added mass of the positive electrode film-forming additive tris(trimethylsilyl)phosphate accounts for 1.0 wt.% of the total mass of the composite lithium salt and the organic solvent of the electrolyte.

[0016] Further preferably, the added mass of the flame retardant additive ethoxy (pentafluoro) cyclotriphosphazene accounts for 7.0 wt.% of the total mass of the composite lithium salt and the organic solvent of the electrolyte.

[0017] A high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function, the specific process is as follows:

[0018] At room temperature, lithium hexafluorophosphate and lithium difluorooxalatoborate are dissolved in an electrolyte organic solvent and stirred evenly, and then tri(trimethylsilyl) phosphate and ethoxy(pentafluoro)cyclotriphosphazene are added and stirred evenly to obtain a high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function.

[0019] The beneficial effects of the present invention are:

[0020] By using the composite lithium salts of lithium hexafluorophosphate and lithium difluorooxalatoborate and the cathode film-forming additive tri(trimethylsilyl) phosphate, the electrolyte can form a stable and complete CEI film, effectively preventing further decomposition of the electrolyte and improving the cycle life of the lithium-rich manganese-based cathode. At the same time, the electrolyte uses ethoxy (pentafluoro) cyclotriphosphazene as a flame retardant additive. At high temperatures, the flame retardant additive can produce fluorine and phosphorus free radicals, interrupt the combustion chain reaction, and has a significant flame retardant effect. And the electrolyte can improve the flame retardant properties of the electrolyte and enhance the safety performance of lithium-ion batteries without sacrificing the cycle performance of lithium-rich manganese-based batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a comparison diagram of LSV curves of Li / / Pt batteries assembled using the electrolytes prepared in Comparative Example 1 and Example 2;

[0022] Figure 2 This is a comparison diagram of electrochemical impedance of lithium-rich manganese-based batteries assembled with the electrolytes prepared in Comparative Example 1 and Example 2 after 100 cycles at 1C;

[0023] Figure 3 This is a comparison chart of the cycle performance of lithium-rich manganese-based batteries assembled using the electrolytes prepared in Comparative Example 1 and Example 2 at 1C;

[0024] Figure 4 The figure is a comparison of the cycle performance of lithium-rich manganese-based batteries assembled with the electrolytes prepared in Comparative Example 2 and Example 2 at 1C;

[0025] Figure 5 This is a comparison chart of the cycle performance of lithium-rich manganese-based batteries assembled using the electrolytes prepared in Comparative Example 3 and Example 2 at 1C;

[0026] Figure 6 Ignition test of glass fibers soaked in electrolyte prepared in Comparative Example 1 and Example 2 and the corresponding photo comparison charts. DETAILED DESCRIPTION

[0027] Example 1

[0028] At room temperature, cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of EC:EMC:DEC=1:1:1 to obtain an organic solvent for the electrolyte; lithium hexafluorophosphate (LiPF 6 ) and lithium difluorooxalatoborate (LiDFOB) are dissolved in the electrolyte organic solvent and stirred evenly to obtain a lithium hexafluorophosphate concentration of 0.9 mol·L -1 , lithium difluorooxalate borate concentration is 0.1 mol·L -1A mixed solution is prepared, and then 0.5 wt.% of tris(trimethylsilyl) phosphate (TMSP) and 8.0 wt.% of ethoxy(pentafluoro)cyclotriphosphazene (PFPN) are added to the mixed solution, and after stirring evenly, a high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function is obtained.

[0029] Example 2

[0030] At room temperature, cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of EC:EMC:DEC=1:1:1 to obtain an organic solvent for the electrolyte; lithium hexafluorophosphate (LiPF 6 ) and lithium difluorooxalatoborate (LiDFOB) are dissolved in the electrolyte organic solvent and stirred evenly to obtain a lithium hexafluorophosphate concentration of 0.9 mol·L -1 , lithium difluorooxalate borate concentration is 0.1 mol·L -1 A mixed solution is prepared, and then 1.0 wt.% of tris(trimethylsilyl) phosphate (TMSP) and 7.0 wt.% of ethoxy(pentafluoro)cyclotriphosphazene (PFPN) are added to the mixed solution, and after stirring evenly, a high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function is obtained.

[0031] Example 3

[0032] At room temperature, cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed uniformly at a volume ratio of EC:EMC:DEC=1:1:1 to obtain an electrolyte organic solvent; 0.8 mol·L -1 LiPF 6 ) and 0.2 mol·L -1 LiDFOB is dissolved in the electrolyte organic solvent and stirred evenly to obtain a lithium hexafluorophosphate concentration of 0.8 mol·L -1 , lithium difluorooxalate borate concentration is 0.2 mol·L -1 A mixed solution is prepared, and then 1.0 wt.% of tris(trimethylsilyl) phosphate (TMSP) and 6.0 wt.% of ethoxy(pentafluoro)cyclotriphosphazene (PFPN) are added to the mixed solution, and after stirring evenly, a high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function is obtained.

[0033] Comparative Example 1

[0034] At room temperature, cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of EC:EMC:DEC=1:1:1 to obtain an organic solvent for the electrolyte; lithium hexafluorophosphate (LiPF 6 ) is dissolved in the organic solvent of the electrolyte and stirred evenly to obtain a lithium hexafluorophosphate concentration of 1.0 molL -1 Lithium-rich manganese-based lithium-ion battery electrolyte.

[0035] Comparative Example 2

[0036] At room temperature, cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of EC:EMC:DEC=1:1:1 to obtain an organic solvent for the electrolyte; lithium hexafluorophosphate (LiPF 6 ) and lithium difluorooxalatoborate (LiDFOB) are dissolved in the electrolyte organic solvent and stirred evenly to obtain a lithium hexafluorophosphate concentration of 0.9 mol·L -1 , lithium difluorooxalate borate concentration is 0.1 mol·L -1 A mixed solution is prepared, and then 1.0 wt. % of tris(trimethylsilyl) phosphate (TMSP) is added to the mixed solution, and the mixture is stirred evenly to obtain the lithium-rich manganese-based lithium ion battery electrolyte of Comparative Example 2.

[0037] Comparative Example 3

[0038] At room temperature, cyclic carbonate solvent ethylene carbonate (EC) and linear carbonate solvent ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed uniformly at a volume ratio of EC:EMC:DEC=1:1:1 to obtain an electrolyte organic solvent; 0.9 mol·L -1 LiPF 6 ) and 0.1 mol·L -1 LiDFOB is dissolved in the electrolyte organic solvent and stirred evenly to obtain a lithium hexafluorophosphate concentration of 0.9 mol·L -1 , lithium difluorooxalate borate concentration is 0.1 mol·L -1 Lithium-rich manganese-based lithium-ion battery electrolyte.

[0039] 1. Comparison of the electrolyte performance of Example 2 of the present invention and Comparative Examples 1-3, wherein Comparative Examples 1-3 are parallel tests of Example 2

[0040] (1) A lithium metal sheet was used as the negative electrode and a Pt sheet was used as the positive electrode. The electrolyte of Example 2 / Comparative Example 1 was dripped into the electrolyte. A CR2025 stainless steel button cell (referred to as a Li / / Pt cell) was assembled in a glove box filled with argon gas and having a moisture content of less than 0.01 ppm.

[0041] The LSV curve comparison of Li / / Pt batteries assembled with the electrolytes prepared in Comparative Example 1 and Example 2 is shown in the figure below: Figure 1 As shown, the oxidation potential of the base electrolyte of Comparative Example 1 is 4.81 V, and the addition of lithium difluorooxalatoborate (LiDFOB), tris(trimethylsilyl) phosphate (TMSP) and ethoxy(pentafluoro)cyclotriphosphazene (PFPN) additives in Example 2 can broaden the electrochemical window to 5.64 V. After adding the above three additives, the oxidation current of the electrolyte increases, indicating that the three additives are preferentially oxidized.

[0042] (2) Using a metallic lithium sheet as the negative electrode and a lithium-rich manganese-based material as the positive electrode, the electrolyte of Example 2 / Comparative Example 1 / Comparative Example 2 / Comparative Example 3 was dripped into the electrolyte, and CR2025 stainless steel button cells (referred to as lithium-rich manganese-based cells) were assembled in a glove box filled with argon gas and with a moisture content of less than 0.01 ppm.

[0043] The electrochemical impedance comparison diagram of the lithium-rich manganese-based battery assembled with the electrolyte prepared in Comparative Example 1 and Example 2 after 100 cycles at 1C is as follows: Figure 2 As shown, the lithium-rich manganese-based battery assembled using the electrolyte containing lithium difluorooxalatoborate (LiDFOB), tris(trimethylsilyl) phosphate (TMSP) and ethoxy(pentafluoro)cyclotriphosphazene (PFPN) additives prepared in Example 2 has lower interfacial impedance.

[0044] The cycle performance comparison of lithium-rich manganese-based batteries assembled using the electrolytes prepared in Comparative Example 1 and Example 2 at 1C is shown in the figure Figure 3 As shown, the capacity retention rate of the lithium-rich manganese-based battery assembled using the electrolyte prepared in Comparative Example 1 after 600 cycles at 1C is only 55%, while the capacity retention rate of the lithium-rich manganese-based battery assembled using the electrolyte containing lithium difluorooxalatoborate (LiDFOB), tris(trimethylsilyl) phosphate (TMSP) and ethoxy(pentafluoro)cyclotriphosphazene (PFPN) additives prepared in Example 2 is 82% after 600 cycles at a high voltage of 4.8V, and the cycle stability is significantly improved.

[0045] The cycle performance comparison of lithium-rich manganese-based batteries assembled using the electrolytes prepared in Comparative Example 2 and Example 2 at 1C is shown in the figure Figure 4As shown, the lithium-rich manganese-based battery assembled using the electrolyte containing lithium difluorooxalatoborate (LiDFOB) and tris(trimethylsilyl) phosphate (TMSP) additives prepared in Comparative Example 2 has a capacity retention rate of 82% after 600 cycles at 4.8V. On this basis, after adding ethoxy(pentafluoro)cyclotriphosphazene (PFPN) additive (Example 2), the specific capacity of the lithium-rich manganese-based battery is slightly reduced, but it still has a capacity retention rate of 82% after 600 cycles at 4.8V, indicating that the introduction of ethoxy(pentafluoro)cyclotriphosphazene (PFPN) flame retardant additive does not significantly reduce the electrochemical performance of the lithium-rich manganese electrode.

[0046] The cycle performance comparison of lithium-rich manganese-based batteries assembled using the electrolytes prepared in Comparative Example 3 and Example 2 at 1C is shown in the figure Figure 5 As shown, the battery assembled using the electrolyte containing lithium difluorooxalate borate (LiDFOB) additive prepared in Comparative Example 3 has a capacity retention rate of only 69% after 600 cycles at 4.8V, while the battery assembled using the electrolyte containing lithium difluorooxalate borate (LiDFOB), tris(trimethylsilyl) phosphate (TMSP) and ethoxy(pentafluoro)cyclotriphosphazene (PFPN) additives prepared in Example 2 has higher cycle stability, and the capacity retention rate reaches 82% after 600 cycles at 4.8V. II. Flame retardancy comparison experiment of Example 2 of the present invention and Comparative Example 1

[0047] The glass fibers impregnated with the same amount of electrolyte prepared in Example 1 and Example 2 were subjected to parallel ignition tests. The test results are shown in the photo. Figure 6 As shown. The glass fiber soaked with the electrolyte prepared in Comparative Example 1 was easily ignited when it touched the flame, and continued to burn for 16.6 seconds, with a SET value of up to 67.9 s / g. The electrolyte prepared in Example 2 was completely non-flammable under the contact of the flame, and its self-extinguishing time was 0 s / g, indicating that the electrolyte prepared in Example 2 has excellent flame retardant properties.

[0048] The above are only specific embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function, comprising a lithium salt and an electrolyte solvent, characterized in that: The lithium salt is a composite lithium salt, which includes lithium hexafluorophosphate and a lithium salt additive, lithium difluorooxalate borate. The electrolyte solvent includes an electrolyte organic solvent and additives, and the additives include a positive electrode film-forming additive, tris(trimethylsilane) phosphate, and a flame retardant additive, ethoxy(pentafluoro)cyclotriphosphazene.

2. The high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function according to claim 1 is characterized in that: The molar concentration of the composite lithium salt in the electrolyte is 1 mol / L, wherein the molar concentration of the lithium salt is 0.8-0.9 mol / L, and the molar concentration of the lithium salt additive is 0.1-0.2 mol / L.

3. The high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function according to claim 1 is characterized in that: The added mass of the positive electrode film-forming additive tris(trimethylsilyl)phosphate accounts for 0.5-2wt.% of the total mass of the composite lithium salt and the organic solvent of the electrolyte, and the added mass of the flame retardant additive ethoxy(pentafluoro)cyclotriphosphazene accounts for 6-8wt.% of the total mass of the composite lithium salt and the organic solvent of the electrolyte.

4. The high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function according to claim 1 is characterized in that: The organic solvent of the electrolyte consists of cyclic carbonate and linear carbonate.

5. The high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function according to claim 4 is characterized in that: The cyclic carbonate is ethylene carbonate, and the chain carbonate includes ethyl methyl carbonate and diethyl carbonate, wherein the volume ratio of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate is 1:1:

1.

6. The high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function according to claim 2 is characterized in that: The molar concentration of lithium salt lithium hexafluorophosphate in the electrolyte is 0.9 mol / L.

7. The high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function according to claim 2 is characterized in that: The molar concentration of lithium salt additive lithium difluorooxalate borate in the electrolyte is 0.1 mol / L.

8. The high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function according to claim 3 is characterized by: The added mass of the positive electrode film-forming additive tris(trimethylsilyl)phosphate accounts for 1.0 wt.% of the total mass of the composite lithium salt and the organic solvent of the electrolyte.

9. The high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function according to claim 3 is characterized in that: The added mass of the flame retardant additive ethoxy (pentafluoro) cyclotriphosphazene accounts for 7.0 wt.% of the total mass of the composite lithium salt and the organic solvent of the electrolyte.

10. A high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function as claimed in claim 1, characterized in that: The specific process is as follows: At room temperature, lithium hexafluorophosphate and lithium difluorooxalatoborate are dissolved in an electrolyte organic solvent and stirred evenly, and then tri(trimethylsilyl) phosphate and ethoxy(pentafluoro)cyclotriphosphazene are added and stirred evenly to obtain a high-performance lithium-rich manganese-based lithium-ion battery electrolyte with flame retardant function.

Images