An electrolyte additive based on natural product rosin ester compounds and a high-voltage electrolyte containing the additive

Abstract

The present application relates to a kind of natural product rosin ester compound electrolyte additive and the electrolyte containing the electrolyte additive;Belong to lithium ion battery field.The present application is used in lithium battery electrolyte of the rosin ester compound and obtains electrolyte;The electrolyte includes lithium salt, organic solvent, rosin ester compound, the mass of rosin ester compound used is 0.1%~10% of lithium battery electrolyte mass.Rosin ester compound of the present application is beneficial to form the interface film of stable, dense under high voltage on the surface of positive and negative, inhibit the oxidative decomposition of electrolyte, make lithium dendrite deposition uniform, reduce the formation of " dead lithium", thereby improve the safety performance and high specific capacity cycle performance of lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to a natural product rosin ester compound electrolyte additive and a high-voltage electrolyte containing the electrolyte additive; it belongs to the field of lithium ion batteries. BACKGROUND

[0002] With the rapid development of new energy vehicles, the requirements for energy storage and battery capacity are gradually increasing. Compared with lead-acid batteries, nickel-cadmium batteries and nickel-hydrogen batteries, lithium ion batteries have the characteristics of high energy density, high working voltage, long service life, green environmental protection and are widely used in water power, thermal power, wind power, solar power station and other energy storage power systems, postal and telecommunications, electric tools, electric bicycles, electric motorcycles, electric vehicles, special equipment, special aerospace and other fields. With the progress of science and technology and the continuous development of the market, it is increasingly important and urgent to improve the energy density of lithium batteries. In addition to the improvement of existing materials and battery manufacturing processes, high-voltage positive electrode materials are one of the more popular research directions. It is through improving the charging depth of the positive active material to achieve high energy density of the battery. So far, a variety of high-voltage positive electrode materials such as binary material LiNiMnO4, ternary material LiNixCoyMn2O2 (x+y+z=1), vanadium-based oxide LiMxV2-xO4 and phosphate material LiMPO4 have been successfully developed. However, the ester electrolyte of the conventional lithium ion battery is easy to decompose at high voltage, lithium ions are easy to migrate to the negative electrode side and reduce and deposit on the negative electrode surface, destroy the SEI film, accelerate the side reaction, and cause a large amount of active lithium to be consumed, resulting in low charge-discharge efficiency and poor cycle performance of the lithium ion battery, which restricts the further development of high-voltage lithium ion batteries.

[0003] Based on the above-mentioned defects of the existing lithium ion battery, it is necessary to optimize the electrolyte, reduce the free amount of lithium ions in the electrolyte, inhibit the lithium deposition on the negative electrode, and prevent a large amount of lithium metal from depositing on the negative electrode. The current solution is to add additives with stabilizing effect to the electrolyte to inhibit the reaction between the electrode and the electrolyte, such as fluorobenzene, cyclohexylbenzene, cyclohexylfluorobenzene, etc., but such additives have the disadvantages of high viscosity, environmental unfriendliness, low commercial value, etc., which significantly reduces the flowability of the electrolyte, thereby affecting the transfer rate of ions in the electrolyte and reducing the performance of the battery. Therefore, it is an urgent problem to develop an electrolyte additive that is low in price, friendly to the environment and can maintain good cycle performance of lithium ion batteries. SUMMARY

[0004] In view of the defects existing in the existing lithium ion battery electrolyte, the purpose of the present application is to provide a natural product rosin ester compound electrolyte additive and the application of the electrolyte additive; the rosin ester compound forms a stable and dense interface film on the surface of the positive electrode and the graphite negative electrode, and inhibits the oxidative decomposition of other components of the electrolyte, thereby improving the safety performance of the lithium ion battery and the cycle performance under 4.5-5.0V voltage.

[0005] In view of the defects existing in the existing lithium ion battery electrolyte, the purpose of the present application is to provide a natural product rosin ester compound electrolyte additive and the application of the electrolyte additive; the rosin ester compound forms a stable and dense interface film on the surface of the positive electrode and the graphite negative electrode, and inhibits the oxidative decomposition of other components of the electrolyte, thereby improving the safety performance of the lithium ion battery and the cycle performance under 4.5-5.0V voltage.

[0006] The present application is a rosin ester compound-containing electrolyte additive; the structural formula is

[0007]

[0008] In the rosin ester compound, when R is an H atom, the rosin product is a rosin acid compound;

[0009] In the rosin ester compound, when R is a Na atom, the rosin product is a sodium rosin acid compound;

[0010] In the rosin ester compound, when R is a pentaerythritol group, the rosin product is a rosin pentaerythritol ester;

[0011] In the rosin ester compound, when R is a glycidyl acrylate group, the rosin product is a rosin glycidyl acrylate;

[0012] In the rosin ester compound, when R is a glycidyl p-toluenesulfonic acid group, the rosin product is a rosin glycidyl p-toluenesulfonic acid ester;

[0013] The present application is a rosin ester compound electrolyte additive, and the preparation method is a conventional esterification and ring-opening reaction; that is, the rosin acid compound and the alcohol compound are subjected to esterification reaction at 140-160 DEG C to obtain the rosin alcohol ester compound, and the glycidyl ester compound is subjected to ring-opening reaction at 100-120 DEG C to obtain the rosin glycerol ester compound.

[0014] The present application is a high-voltage electrolyte containing a rosin ester compound electrolyte additive; the electrolyte is a lithium battery electrolyte.

[0015] The components of the electrolyte include lithium salt, organic solvent, rosin ester compound, and the mass of the rosin ester compound used is 0.5% to 3% of the mass of the lithium battery electrolyte, preferably 1-2%.

[0016] The electrolyte contains rosin ester compound electrolyte additive; the concentration of lithium salt in the electrolyte is 0.5M to 1.5M.

[0017] The electrolyte contains rosin ester compound electrolyte additive; the lithium salt in the electrolyte is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium methylsulfonate (LiCH3SO3), lithium trifluoromethylsulfonate (LiCF3SO3), lithium bis-trifluoromethylsulfonimide (LiN(CF3SO2)2), and lithium bisoxalate borate (LiBOB).

[0018] The electrolyte contains rosin ester compound electrolyte additive; the organic solvent accounts for 65% to 85% of the total mass of the lithium battery electrolyte.

[0019] The electrolyte contains rosin ester compound electrolyte additive; the organic solvent is a cyclic carbonate or a linear carbonate. The linear carbonate is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethyl acetate, and methyl propyl carbonate. The cyclic carbonate is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), and gamma-butyrolactone (BL).

[0020] The electrolyte contains rosin ester compound electrolyte additive; the oxidation potential of the high-voltage electrolyte is 4.6V.

[0021] The beneficial effects of the present application: containing a natural product rosin ester additive, due to the presence of organic ester groups and carbon-carbon double bond functional groups, it is easier to capture Li + Plasma forms coordination complex, can better prevent the destruction of the negative electrode structure by lithium ion solvation, and form stable and dense SEI film on the surface of the positive electrode and the negative electrode respectively, inhibit the generation of lithium dendrite, reduce the consumption of electrolyte and the generation of "dead lithium". In addition, rosin ester has a high oxidation potential, increases the transmission of lithium ions, makes the lithium deposit on the interface uniform deposition, thereby reduces the electrochemical impedance, and has good compatibility with ester electrolyte, does not affect the physical properties of the electrolyte itself. Therefore, the natural product rosin ester can effectively improve the capacity and cycle performance of lithium ion battery at high voltage (4.6V), reduce the risk of battery short circuit caused by lithium dendrite piercing the separator, and improve the cycle performance and safety performance of LMB. BRIEF DESCRIPTION OF DRAWINGS

[0022] Attached image description: Trip to Jiangxi

[0023] Figure 1 , 2 This diagram illustrates the results of a 5C rate cycling test at room temperature using the electrolyte prepared in Embodiment 2 and the comparative example of this invention, which is a lithium-ion battery composed of carbon-based materials and lithium metal sheets.

[0024] Figure 3 , 4 Figure 5 shows the AC impedance test results of a lithium-ion battery composed of carbon-based materials and lithium metal sheets using the electrolyte prepared according to the present invention. (a) Impedance diagram of the tested battery; (b) Impedance diagram of the tested battery after 1 cycle; (c) Impedance diagram of the tested battery after 25 cycles. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all examples. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0026] Example 1

[0027] In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a weight ratio of 1:1:1 as an organic solvent. Lithium salt LiPF6 was added to this solvent to a final concentration of 1.0 mol / L to obtain a conventional electrolyte. Then, 0.5% pentaerythritol rosin was added to the prepared conventional electrolyte to obtain a high-voltage electrolyte for lithium secondary batteries. The structural formula of the electrolyte additive is as follows:

[0028]

[0029] Preparation of lithium ion battery: positive electrode: lithium sheet with a diameter of 15.6 mm is selected; negative electrode: lithium iron phosphate, acetylene black, and solvent N-methyl pyrrolidone (NMP) are uniformly mixed; in the negative electrode active coating, the mass ratio of lithium iron phosphate, acetylene black, and solvent N-methyl pyrrolidone (NMP) is 8:1:1, wherein the solid content of the negative electrode binder is 1.0%. The positive electrode, Celgard2500 separator, and negative electrode are stacked in order, and an electric core is obtained through the lamination process. The electric core is placed in an outer packaging shell, dried, injected with electrolyte, and subjected to vacuum packaging, standing, formation, and capacity distribution processes to obtain a lithium ion battery.

[0030] Example 2

[0031] In an argon-filled glove box (moisture <0.1 ppm, oxygen <0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) are mixed as organic solvents in a weight ratio of 1:1:1, and lithium salt LiPF6 is added to the solvent to a final concentration of 1.0 mol / L to obtain a conventional electrolyte; then rosin pentaerythritol ester is added to the prepared conventional electrolyte in an amount of 0.5%; a high-voltage electrolyte for lithium secondary batteries is obtained. The structure of the electrolyte additive is as follows:

[0032]

[0033] Preparation of lithium ion battery: positive electrode: lithium sheet with a diameter of 15.6 mm is selected; negative electrode: lithium iron phosphate, acetylene black, and solvent N-methyl pyrrolidone (NMP) are uniformly mixed; in the negative electrode active coating, the mass ratio of lithium iron phosphate, acetylene black, and solvent N-methyl pyrrolidone (NMP) is 8:1:1, wherein the solid content of the negative electrode binder is 1.0%. The positive electrode, Celgard2500 separator, and negative electrode are stacked in order, and an electric core is obtained through the lamination process. The electric core is placed in an outer packaging shell, dried, injected with electrolyte, and subjected to vacuum packaging, standing, formation, and capacity distribution processes to obtain a lithium ion battery.

[0034] Example 3

[0035] In an argon-filled glove box (moisture <0.1 ppm, oxygen <0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) are mixed as organic solvents in a weight ratio of 1:1:1, and lithium salt LiPF6 is added to the solvent to a final concentration of 1.0 mol / L to obtain a conventional electrolyte; then rosin pentaerythritol ester is added to the prepared conventional electrolyte in an amount of 0.5%; a high-voltage electrolyte for lithium secondary batteries is obtained. The structure of the electrolyte additive is as follows:

[0036]

[0037] Preparation of lithium ion battery: positive electrode: lithium sheet with a diameter of 15.6 mm is selected; negative electrode: lithium iron phosphate, acetylene black, and solvent N-methyl pyrrolidone (NMP) are mixed uniformly; in the negative electrode active coating, the mass ratio of lithium iron phosphate, acetylene black, and solvent N-methyl pyrrolidone (NMP) is 8:1:1, wherein the solid content of the negative electrode binder is 1.0%. The positive electrode, Celgard 2500 separator, and negative electrode are stacked in order, and a cell is obtained through the lamination process. The cell is placed in an outer packaging shell, dried, injected with electrolyte, and subjected to vacuum packaging, standing, formation, and capacity distribution processes to obtain a lithium ion battery.

[0038] Comparative Example 1

[0039] In an argon-filled glove box (moisture <0.1 ppm, oxygen <0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) are mixed as organic solvents in a weight ratio of 1:1:1. Lithium salt LiPF6 is added to the solvent to a final concentration of 1.0 mol / L to obtain a conventional electrolyte.

[0040] The assembled lithium ion battery is subjected to discharge rate performance testing, and the test results are shown in Table 1 below

[0041] Table 1: Rate performance test results of examples and comparative examples

[0042] No. Cycling temperature (°C) 1C / 0.5C (%) 2C / 0.5C (%) 3C / 0.5C (%) 5C / 0.5C (%) Example 1 25 92.86% 90.11% 86.29% 85.16% Example 2 25 97.49% 94.64% 93.59% 91.67% Example 3 25 95.37% 92.56% 90.72% 88.78% Comparative Example 1 25 90.77% 89.65% 88.26% 86.54%

[0043] The above example and comparative example batteries are subjected to electrochemical performance testing after standing at room temperature for one day. The examples and comparative examples are cycled at 1C, 2C, and 5C rates at 4.6V for 300 cycles, and the cycle performance results are shown in Table 2.

[0044] Table 2: Cycle test results of examples and comparative examples

[0045] No. Cycling temperature (°C) Initial coulombic efficiency (%) Battery capacity retention rate after 300 cycles at 1C, 4.6V (%) Battery capacity retention rate after 300 cycles at 2C, 4.6V (%) Battery capacity retention rate after 300 cycles at 5C, 4.6V (%) Example 1 25 86.10 58.23 56.18 54.81 Example 2 25 97.56 71.26 71.89 70.58 Example 3 25 94.36 64.23 64.15 63.29 Comparative Example 1 25 95.23 65.26 65.13 64.29

[0046] As can be seen from the table, the addition of the new substituted rosin additive significantly improves the cycle performance of the lithium ion battery at high voltage, and the coulombic efficiency and battery capacity retention rate are greatly improved. As can be seen from Table 2, the first coulombic efficiency of the battery containing rosin pentaerythritol ester in the negative electrode half-cell is close to that of the battery without rosin pentaerythritol ester, and the content of rosin pentaerythritol ester has different effects on the battery performance. The battery capacity retention rate of Example 2 and Example 3 is higher than that of the battery without rosin pentaerythritol ester, and the capacity retention rate of Example 1 is lower than that of the battery without rosin pentaerythritol ester, which may be due to the lower content of rosin pentaerythritol ester. Figure 1 、 Figure 2As the blank electrolyte and the case 2, it can be seen that the battery with 2% rosin pentaerythritol ester added has very stable cycle at large current (5C), which ensures the long cycle life and capacity of the battery, and achieves the purpose of the application.

[0047] The above example and comparative example batteries were placed at room temperature for 4h, and then the AC impedance test was performed. The batteries were cycled for 1 week and 25 weeks, and then the AC impedance test was performed by using an electrochemical workstation. The frequency range was 10mHz-100mHz, the vibration voltage was 5mV, and the scanning was from high frequency to low frequency.

[0048] Table 3: Impedance test results of the example and comparative example batteries

[0049] No. Z' / ohm Z' / ohm (cycle 1) Z' / ohm (cycle 25) Example 1 260 241 90 Example 2 185 143 45 Example 3 210 179 64 Comparative Example 1 238 190 72

[0050] The impedance of the tested batteries after two weeks of charge and discharge is shown in Table 3. The impedance of the example batteries is smaller than that of the comparative example, because the rosin pentaerythritol ester as an electrolyte additive is oxidized on the surface of the negative electrode before the electrolyte solvent, forming a dense SEI film, reducing the generation of lithium dendrites, and making the lithium deposition uniform. The impedance increase of the tested batteries with 2.0% and 3.0% rosin pentaerythritol ester added in the electrolyte is much smaller than that of the comparative example. The SEI film optimizes the interface performance between the electrode and the electrolyte, prevents the continuous decomposition of the electrolyte and the deterioration of the negative electrode structure, and thus improves the cycle stability of the battery. At the same time, it can be found from example 1 that the performance of the tested battery with 0.5% rosin pentaerythritol ester added in the electrolyte is reduced, which shows that the content of the additive in the electrolyte should be strictly controlled to improve the comprehensive performance of the battery.

[0051] The above is only the preferred embodiment 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, which should also be considered within the scope of protection of the present application.

Claims

1. A high-voltage electrolyte containing rosin ester compound electrolyte additives; characterized in that: The electrolyte comprises lithium salt, organic solvent, and rosin ester compounds, wherein the mass of the rosin ester compounds used is 0.5% to 5% of the mass of the electrolyte. The structural formula of the rosin ester compound is: R is selected from H atoms, metal atoms, alkyl groups, alcohol groups, alkenyl groups, ester groups, acetyl groups, haloalcohol groups, haloacetyl groups, glycidyl ester groups, benzene rings, and halobenzene rings; The concentration of lithium salt in the high-voltage electrolyte is 0.5M to 1.5M; In the high-voltage electrolyte, organic solvents account for 75% to 85% of the total mass of the high-voltage electrolyte; The organic solvents include two or more of the following: propylene carbonate, diethyl carbonate, ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, methyl propyl carbonate, γ-butyrolactone, methyl propionate, fluorinated ethylene carbonate, trifluoropropylene carbonate, ethyl difluorocarbonate, ethyl trifluorocarbonate, and fluorocarbonates. The lithium salts include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, bis(oxalate)boronic acid, lithium difluorooxalateborate, lithium perchlorate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorophosphate. The oxidation potential of the high-voltage electrolyte is 4.5-5V.

2. The high-voltage electrolyte containing rosin ester compound electrolyte additive according to claim 1; characterized in that: In the rosin ester compounds, when R is an H atom, the rosin product is a rosin acid compound.

3. A high-voltage electrolyte containing rosin ester compound electrolyte additives according to claim 1; characterized in that: In the rosin ester compounds, when R is a Na atom, the rosin product is a sodium rosinate compound.

4. A high-voltage electrolyte containing rosin ester compound electrolyte additives according to claim 1; characterized in that: In the rosin ester compounds, when R is a pentaerythritol ester group, the rosin product is rosin pentaerythritol ester.

5. A high-voltage electrolyte containing rosin ester compound electrolyte additives according to claim 1; characterized in that: In the rosin ester compounds, when R is a glycidyl acrylate group, the rosin product is rosin glycidyl acrylate.

6. A high-voltage electrolyte containing rosin ester compound electrolyte additives according to claim 1; characterized in that: In the rosin ester compounds, when R is a glycidyl p-toluenesulfonate group, the rosin product is rosin glycidyl p-toluenesulfonate.

Images