High-voltage-resistant electrolyte as well as preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a high-voltage-resistant electrolyte and a preparation method and application thereof. The high-voltage-resistant electrolyte comprises an organic solvent, an electrolyte and an additive; the additive is bromo ether 1, 2-bis (2-bromoethoxy) ethane; the mass fraction of the additive in the electrolyte is 0.5 to 3.0 percent; the concentration of the electrolyte in the electrolyte solution is 0.5 to 1.5 mol / L; the organic solvent comprises a first organic solvent, a second organic solvent and a third organic solvent; the first organic solvent is dimethyl carbonate, diethyl carbonate or methyl propyl carbonate; the second organic solvent is ethylene carbonate or propylene carbonate; the third organic solvent is methyl ethyl carbonate or diethyl sulfite. The preparation method has the advantages of simple operation, low cost, easily available raw materials and the like. The high-voltage-resistant electrolyte can be used for preparing a lithium ion / lithium metal battery, and the lithium ion / lithium metal battery has high energy density, excellent cycle life and rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a high voltage resistant electrolyte and a preparation method and application thereof. Background Art

[0002] In order to solve the range anxiety of new energy electric vehicles, it is urgent to develop the next generation of high energy density lithium-ion batteries with long life and high safety characteristics. In recent years, one of the important directions to improve the energy density of lithium-ion batteries is to use layered high nickel (Ni) positive electrode materials (such as LiNi) with high theoretical specific capacity and high operating voltage. x Co y Mn z O2, x+y+z=1, x≥0.5). However, when the Ni content in the high-nickel cathode material is increased to a higher level (Ni≥0.8), the cycle life and safety of ultra-high nickel lithium-ion batteries will be significantly reduced due to the aggravation of problems such as HF corrosion, electrolyte oxidation, transition metal dissolution, surface phase change, particle cracking and poor thermal stability, especially under high temperature and higher charge cut-off voltage conditions.

[0003] Developing electrolyte functional additives is one of the most cost-effective strategies to improve the cycle life and safety of lithium-ion batteries. However, because the chemical / electrochemical environment of ultra-high nickel lithium-ion battery systems is more complex, some additives suitable for medium and low nickel lithium-ion batteries have a general improvement effect on ultra-high nickel lithium-ion batteries. Therefore, it is urgent to design and develop electrolyte functional additives that can significantly improve the performance of ultra-high nickel lithium-ion batteries. Summary of the invention

[0004] In view of the deficiencies in the prior art, a first object of the present invention is to provide a high voltage resistant electrolyte.

[0005] The second object of the present invention is to provide a method for preparing the above-mentioned high-voltage resistant electrolyte, which has the advantages of simple operation, low cost and easy availability of raw materials.

[0006] The third object of the present invention is to provide an application of the above-mentioned high-voltage resistant electrolyte, which can be used to prepare lithium ion / lithium metal batteries with high energy density, excellent cycle life and rate performance.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A high voltage resistant electrolyte, comprising the following components: an organic solvent, an electrolyte and an additive;

[0009] Wherein, the additive is brominated ether 1,2-bis(2-bromoethoxy)ethane (BBAE), and the structural formula of the brominated ether 1,2-bis(2-bromoethoxy)ethane is shown as follows:

[0010]

[0011] Furthermore, the mass fraction of the additive in the electrolyte is 0.5-3.0%. The strong electronegativity of bromine atoms reduces the HOMO energy level of solvent molecules and improves the antioxidant capacity of the electrolyte.

[0012] Further, the concentration of the electrolyte in the electrolyte is 0.5-1.5 mol / L;

[0013] Preferably, the concentration of the electrolyte in the electrolyte solution is 1.0 mol / L.

[0014] Furthermore, the electrolyte is a lithium salt.

[0015] Further, the lithium salt is at least one of lithium hexafluorophosphate (LiPF6), lithium difluorooxalatoborate (LiODFB), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4) and lithium tetrafluoroborate (LiBF4);

[0016] Preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium perchlorate and lithium tetrafluoroborate.

[0017] Furthermore, the organic solvent includes a first organic solvent, a second organic solvent and a third organic solvent.

[0018] Furthermore, the first organic solvent is dimethyl carbonate (DMC), diethyl carbonate

[0019] (DEC) or methyl propyl carbonate (MPC); the second organic solvent is ethylene carbonate (EC) or propylene carbonate (PC); the third organic solvent is ethyl methyl carbonate (EMC) or diethyl sulfite (DES);

[0020] Preferably, the first organic solvent is dimethyl carbonate, the second organic solvent is ethylene carbonate, and the third organic solvent is ethyl methyl carbonate.

[0021] Furthermore, the volume ratio of the first organic solvent, the second organic solvent and the third organic solvent is 1:(1-2):(0.5-1.5).

[0022] The preparation method of the high voltage resistant electrolyte adopts the following steps: under inert gas conditions, electrolyte is added to an organic solvent, dissolved, and additives are added to obtain the high voltage resistant electrolyte.

[0023] Furthermore, the conditions also include a moisture content of less than 0.01 ppm and an oxygen content of less than 0.01 ppm.

[0024] The application of the high voltage resistant electrolyte is that the high voltage resistant electrolyte can be used to prepare lithium ion / lithium metal batteries. The lithium ion / lithium metal batteries have high energy density, excellent cycle life and rate performance.

[0025] Beneficial effects:

[0026] 1. The present invention provides a novel high-voltage resistant ester solvent electrolyte for lithium ion / lithium metal batteries. The additive of the electrolyte is bromoether 1,2-bis(2-bromoethoxy)ethane. The bromine atom of the bromoether 1,2-bis(2-bromoethoxy)ethane has a higher HOMO and a lower LUMO energy level, and can be preferentially oxidized and reduced. Its strong electronegativity reduces the HOMO energy level of the solvent molecule and improves the antioxidant capacity of the electrolyte. The bromoether 1,2-bis(2-bromoethoxy)ethane can effectively improve SEI cracking, help inhibit the side reaction between Li and the electrolyte, and reduce Li + The irreversible consumption of dead Li is reduced, thereby reducing the accumulation of dead Li, which is beneficial to improving the coulombic efficiency of lithium ion / lithium metal batteries. The electrolyte provided by the present invention is a long-chain bromate flame-retardant electrolyte that can be used for lithium batteries. On the basis of ensuring the electrochemical performance of lithium ion batteries, the high-voltage performance of lithium ion / lithium metal batteries is improved, and the problems of significantly reduced cycle life and safety of ultra-high nickel lithium ion batteries caused by HF corrosion, electrolyte oxidation, transition metal dissolution, surface phase change, particle cracking and poor thermal stability are solved.

[0027] 2. The preparation method of the high-voltage resistant electrolyte provided by the present invention is simple, low in cost and the raw materials are readily available. The prepared high-voltage resistant electrolyte can improve the ultra-high nickel positive electrode material LiNi 0.9 Co 0.05 Mn 0.05 The interface properties of the positive and negative electrodes of the O2 (NCM90) battery; the prepared high-voltage resistant electrolyte has good stability and an electrochemical window of up to 4.6V.

[0028] 3. The high-voltage resistant electrolyte provided by the present invention can be used to prepare high-voltage lithium-ion batteries. The prepared lithium-ion symmetrical battery can stably cycle for 700 hours. The prepared lithium-ion / lithium metal battery has high energy density, excellent cycle life and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A comparison chart of the first cycle coulombic efficiency of batteries assembled with the electrolytes prepared in Examples 1-3 and Comparative Example 1;

[0030] Figure 2 A comparison chart of the reversible discharge specific capacities of batteries assembled from the electrolytes prepared in Examples 1-3 and Comparative Example 1;

[0031] Figure 3 It is a comparison chart of the rate performance of batteries assembled with the electrolytes prepared in Examples 1-3 and Comparative Example 1;

[0032] Figure 4 The figure is a comparison of the coulombic efficiency of batteries assembled with the electrolytes prepared in Example 2 and Comparative Example 1;

[0033] Figure 5 It is a comparison diagram of SEI of symmetrical batteries assembled with electrolytes prepared in Example 2 and Comparative Example 1;

[0034] Figure 6 CV comparison diagram of symmetrical batteries assembled with electrolytes prepared in Example 2 and Comparative Example 1;

[0035] Figure 7 A comparison diagram of nucleation overpotentials of batteries assembled from the electrolytes prepared in Example 2 and Comparative Example 1;

[0036] Figure 8 Analyze molecular orbital energy maps of solvent and additive molecules for density functional theory (DFT) calculations;

[0037] Fig. 9 CEI performance test diagram of batteries assembled with the electrolytes prepared in Example 2 and Comparative Example 1; Fig. 9 a is a CEI performance test diagram of a battery assembled with the electrolyte prepared in Example 2; Fig. 9 b is a CEI performance test diagram of the battery assembled with the electrolyte prepared in Comparative Example 1. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] Example 1

[0040] In a glove box filled with argon, with a moisture content of less than 0.01ppm and an oxygen content of less than 0.01ppm, DMC, EC and EMC in a volume ratio of 1:1:1 were mixed to form an electrolyte solvent system, and then LiPF6 was added and stirred until completely dissolved. The concentration of LiPF6 in the electrolyte was 1.0mol / L. BBAE was then added, with the mass of BBAE accounting for 0.5% of the total mass of the electrolyte. After stirring evenly, a high-voltage electrolyte for lithium-ion / lithium metal batteries was obtained, which was recorded as EED-BBAE0.5.

[0041] Example 2

[0042] In a glove box filled with argon, with a moisture content of less than 0.01ppm and an oxygen content of less than 0.01ppm, DMC, EC and EMC in a volume ratio of 1:1:1 were mixed to form an electrolyte solvent system, and then LiPF6 was added and stirred until completely dissolved. The concentration of LiPF6 in the electrolyte was 1.0mol / L. BBAE was then added, with the mass of BBAE accounting for 1.0% of the total mass of the electrolyte. After stirring evenly, a high-voltage electrolyte for lithium-ion / lithium metal batteries was obtained, which was recorded as EED-BBAE1.0.

[0043] Example 3

[0044] In a glove box filled with argon, with a moisture content of less than 0.01ppm and an oxygen content of less than 0.01ppm, DMC, EC and EMC in a volume ratio of 1:1:1 were mixed to form an electrolyte solvent system, and then LiPF6 was added and stirred until completely dissolved. The concentration of LiPF6 in the electrolyte was 1.0mol / L. BBAE was then added, with the mass of BBAE accounting for 1.5% of the total mass of the electrolyte. After stirring evenly, a high-voltage electrolyte for lithium-ion / lithium metal batteries was obtained, which was recorded as EED-BBAE1.5.

[0045] Example 4

[0046] In a glove box filled with argon, with a moisture content of less than 0.01ppm and an oxygen content of less than 0.01ppm, DEC, PC and DES in a volume ratio of 1:1.5:1.5 were mixed to form an electrolyte solvent system, and then LiClO4 was added thereto and stirred until completely dissolved. The concentration of LiClO4 in the electrolyte was 0.5mol / L. BBAE was then added, with the mass of BBAE accounting for 2.5% of the total mass of the electrolyte. After stirring evenly, a high-voltage electrolyte for lithium-ion / lithium metal batteries was obtained, which was recorded as EED-BBAE2.5.

[0047] Example 5

[0048] In a glove box filled with argon, with a moisture content of less than 0.01ppm and an oxygen content of less than 0.01ppm, MPC, PC and DES in a volume ratio of 1:2:0.5 were mixed to form an electrolyte solvent system, and then LiBF4 was added and stirred until completely dissolved. The concentration of LiBF4 in the electrolyte was 1.5mol / L. BBAE was then added, with the mass of BBAE accounting for 3.0% of the total mass of the electrolyte. After stirring evenly, a high-voltage electrolyte for lithium-ion / lithium metal batteries was obtained, which was recorded as EED-BBAE3.0.

[0049] Comparative Example 1

[0050] In a glove box filled with argon, with a moisture content of less than 0.01ppm and an oxygen content of less than 0.01ppm, DMC, EMC and EC in a volume ratio of 1:1:1 were mixed to form an electrolyte solvent system, and then LiPF6 was added thereto and stirred until completely dissolved. The concentration of LiPF6 in the electrolyte was 1.0mol / L. After stirring evenly, a lithium ion / lithium metal battery electrolyte was obtained, which was recorded as EED.

[0051] Performance Testing

[0052] In order to evaluate the stability of ester-based electrolytes with BBAE as additives under high voltage, we assembled Li||NMC90 batteries for electrochemical testing. Electrochemical performance tests were performed on lithium-ion / lithium metal batteries assembled using the EED-BBAE0.5 electrolyte prepared in Example 1, the EED-BBAE1.0 electrolyte prepared in Example 2, the EED-BBAE1.5 electrolyte prepared in Example 3, and the EED electrolyte prepared in Comparative Example 1.

[0053] The first effect and cycle performance were measured, and the results were as follows Figure 1 , Figure 2 As shown. Figure 1 and Figure 2 It can be seen that compared with the battery assembled with EED electrolyte, the electrochemical performance of Li||NMC90 battery with EED-BBAE1.0 (BBAE addition amount is 1.0%) electrolyte at 4.6V cutoff voltage has been significantly improved. The battery assembled with EED-BBAE1.0 electrolyte has higher coulombic efficiency (87%) and reversible discharge specific capacity (222.7mAh g -1 ).

[0054] The charge and discharge characteristics of the battery assembled with EED-BBAE1.0 electrolyte and EED electrolyte were tested at different current densities. The results are as follows Figure 3 As shown, the results show that the battery assembled using EED-BBAE1.0 electrolyte exhibits better rate performance.

[0055] Increasing or decreasing the BBAE content will reduce the coulombic efficiency, reversible discharge specific capacity and cycle performance of Li||NMC90 batteries.

[0056] CE performance test results such as Figure 4 As shown in the figure, CE performance is related to SEI, and the decrease of CE indicates the cracking of SEI, which causes Li + Irreversible consumption. EED: CE 81-84%; EED-BBAE1.0: CE 84-93%. Experiments show that the additive BBAE can effectively improve SEI cracking and reduce Li + irreversible consumption.

[0057] SEI stability test results are as follows Figure 5 As shown in the figure, the stability of SEI in the non-conductive dielectric was further verified by a Li||Li symmetric battery. The Li||Li symmetric battery using EED electrolyte showed obvious voltage fluctuation after cycling for 450 hours, which put the battery at serious short circuit risk. The Li||Li symmetric battery using EED-BBAE1.0 electrolyte cycled stably for 700 hours. The good stability confirmed the formation of a good SEI, which helped to inhibit the side reactions between Li and electrolyte, thereby reducing the accumulation of dead Li.

[0058] The CV test results and the nucleation overpotential test results are as follows: Figure 6 , Figure 7 As shown, Figure 6 The results show that a new peak appears at 1.5 V in the Li||Li symmetric cell using EED-BBAE1.0 electrolyte, indicating that BBAE is reduced earlier than other solvents; Figure 7 The results show that according to the classical equation of uniform nucleation, the lower the overpotential, the larger the grain size. Increasing the grain size is beneficial to maintaining the overall conductivity, which can reduce the formation of dead lithium during lithium plating / stripping and is beneficial to improving the coulombic efficiency of lithium-ion / lithium metal batteries.

[0059] The redox stability test was carried out and the molecular orbital energy of solvent EC, EMC, DMC and additive BBAE molecules were analyzed using density functional theory (DFT) calculations. Figure 8 As shown, the redox stability of the material is evaluated by molecular orbital energy levels. BBAE has the highest HOMO (-1.70ev) and the lowest LUMO (-7.77ev) energy levels, is preferentially oxidized and reduced, and participates in the formation of CEI and SEI.

[0060] The CEI performance test of the battery assembled with the electrolyte prepared in Example 2 and Comparative Example 1 was carried out. The results are as follows: Fig. 9 As shown, the CEI performance test results of the battery assembled using EED-BBAE1.0 electrolyte are as follows Fig. 9 As shown in a, the thickness of the electrolyte interface film is 3.01nm; the CEI performance test results of the battery assembled using EED electrolyte are shown in Fig. 9 As shown in b, the thickness of the electrolyte interface film reaches 12.8nm.

Claims

1. A high voltage resistant electrolyte, characterized in that: The high voltage resistant electrolyte comprises the following components: an organic solvent, an electrolyte and an additive; The additive is bromoether 1,2-bis(2-bromoethoxy)ethane, and the structural formula of the bromoether 1,2-bis(2-bromoethoxy)ethane is shown below:

2. The high voltage resistant electrolyte according to claim 1, characterized in that: The mass fraction of the additive in the electrolyte is 0.5-3.0%; the concentration of the electrolyte in the electrolyte is 0.5-1.5 mol / L.

3. The high voltage resistant electrolyte according to claim 1, characterized in that: The electrolyte is at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium hexafluoroarsenate, lithium perchlorate and lithium tetrafluoroborate.

4. The high voltage resistant electrolyte according to claim 1, characterized in that: The organic solvent includes a first organic solvent, a second organic solvent and a third organic solvent; the first organic solvent is dimethyl carbonate, diethyl carbonate or methyl propyl carbonate; the second organic solvent is ethylene carbonate or propylene carbonate; the third organic solvent is ethyl methyl carbonate or diethyl sulfite.

5. The high voltage resistant electrolyte according to claim 4, characterized in that: The volume ratio of the first organic solvent, the second organic solvent and the third organic solvent is 1:(1-2):(0.5-1.5).

6. A method for preparing a high voltage resistant electrolyte according to any one of claims 1 to 5, characterized in that: The preparation method adopts the following steps: under inert gas conditions, electrolyte is added to an organic solvent, dissolved, and additives are added to obtain the high voltage resistant electrolyte.

7. Use of the high voltage resistant electrolyte according to any one of claims 1 to 5 and / or the high voltage resistant electrolyte prepared by the method according to claim 6, characterized in that: The high voltage resistant electrolyte can be used to prepare lithium ion / lithium metal batteries.

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