Electrolyte additive based on natural product rosin ester compound and high-voltage electrolyte containing additive

Abstract

The invention relates to a natural product rosin ester compound electrolyte additive and an electrolyte containing the electrolyte additive. Belongs to the field of lithium ion batteries. The abietate compound is used in the lithium battery electrolyte to obtain the electrolyte; the electrolyte comprises a lithium salt, an organic solvent and a rosin ester compound, wherein the mass of the rosin ester compound is 0.1-10% of the mass of the lithium battery electrolyte. The abietate compound provided by the invention is beneficial to formation of stable and compact interfacial films on the surfaces of a positive electrode and a negative electrode under high voltage, inhibition of oxygenolysis of an electrolyte, uniform deposition of lithium dendrites and reduction of formation of dead lithium, so that the safety performance and the cycle performance of high specific capacity of the lithium ion battery are improved.

Description

Technical Field

[0001] The present invention relates to an electrolyte additive of natural product rosin ester compounds and a high-voltage electrolyte containing the electrolyte additive; it belongs to the field of lithium-ion batteries. Background Art

[0002] Due to the rapid development of new energy vehicles, the requirements for energy storage and battery capacity in the era are gradually increasing. Compared with lead-acid batteries, nickel-cadmium batteries, and nickel-metal hydride batteries, lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in fields such as postal and telecommunications, power tools, electric bicycles, electric motorcycles, electric vehicles, special equipment, and special aerospace due to their characteristics of large energy density, high working voltage, long life, and environmental friendliness. With the progress of technology and the continuous development of the market, it has become increasingly important and urgent to improve the energy density of lithium batteries. In addition to improving the existing materials and battery manufacturing processes, high-voltage cathode materials are one of the popular research directions, which achieve high energy density of the battery by increasing the charging depth of the cathode active material. So far, a variety of high-voltage cathode materials such as binary material LiNiMn0 4 , ternary material LiNixCoyMn 2 O 2 (x + y + z = 1), vanadium-based oxides LiMxV 2 -x0 4 and phosphate materials LiMPO 4 have been successfully developed. However, the ester-based electrolytes of conventional lithium-ion batteries are prone to decomposition under high voltage, and lithium ions are likely to migrate to the negative electrode side and be reduced and deposited on the negative electrode surface, damaging the SEI film, accelerating side reactions, resulting in the consumption of a large amount of active lithium, leading to relatively low charge-discharge efficiency and poor cycle performance of lithium-ion batteries, restricting the further development of high-voltage lithium-ion batteries.

[0003] Based on the above defects of existing lithium-ion batteries, it is necessary to optimize the electrolyte by reducing the free amount of lithium ions in the electrolyte, inhibiting lithium deposition on the negative electrode, and preventing a large amount of lithium metal deposition on the negative electrode. The current solution is to add additives with a stabilizing effect to the electrolyte to inhibit the reaction between the electrode and the electrolyte, such as fluorobenzene, cyclohexylbenzene, cyclohexylfluorobenzene, etc. However, these additives have disadvantages such as high viscosity, environmental unfriendliness, and low commercial value, significantly reducing the fluidity of the electrolyte, thus affecting the transfer rate of ions in the electrolyte and reducing the performance of the battery. Therefore, developing an electrolyte additive that is inexpensive, environmentally friendly and can keep lithium-ion batteries with good cycle performance has become an urgent problem to be solved. Summary of the Invention

[0004] Aiming at the defects existing in the existing lithium-ion battery electrolytes, the purpose of the present invention is to provide an electrolyte additive of a natural product rosin ester compound and the application of this electrolyte additive; this rosin ester compound forms a stable and dense interfacial film on the surfaces 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 cycling performance at a voltage of 4.5 - 5.0V.

[0005] Aiming at the defects existing in the existing lithium-ion battery electrolytes, the purpose of the present invention is to provide an electrolyte additive of a natural product rosin ester compound and the application of this electrolyte additive; this rosin ester compound forms a stable and dense interfacial film on the surfaces 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 cycling performance at a voltage of 4.5 - 5.0V. dygg

[0006] The present invention relates to an electrolyte additive containing a rosin ester compound; its structural formula is

[0007]

[0008] In the said rosin ester compound; when R is a hydrogen atom, its rosin product is a rosin acid compound;

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

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

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

[0012] In the said rosin ester compound; when R is a glycidyl p-toluenesulfonate group, its rosin product is a glycidyl p-toluenesulfonate rosin ester;

[0013] An electrolyte additive of a rosin ester compound in the present invention, its preparation method is a conventional esterification and ring-opening reaction; that is, reacting a rosin acid compound with an alcohol compound at 140 - 160°C can obtain a rosin alcohol ester compound, and reacting with a glycidyl ester compound at 100 - 120°C can obtain a rosin glycerol ester compound;

[0014] A high-voltage electrolyte containing an electrolyte additive of a rosin ester compound in the present invention; the said electrolyte is a lithium battery electrolyte.

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

[0016] An electrolyte of the present invention containing a rosin ester compound as an electrolyte additive; in the electrolyte, the concentration of the lithium salt is 0.5 M to 1.5 M.

[0017] An electrolyte of the present invention containing a rosin ester compound as an electrolyte additive; in the electrolyte, the lithium salt is selected from lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), lithium tetrafluoroborate (LiBF 4 ), lithium methanesulfonate (LiCH 3 SO 3 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 ) 2 ), and at least one of lithium bis(oxalato)borate (LiBOB).

[0018] An electrolyte of the present invention containing a rosin ester compound as an electrolyte additive; in the electrolyte, the organic solvent accounts for 65% to 85% of the total mass of the lithium battery electrolyte.

[0019] An electrolyte of the present invention containing a rosin ester compound as an 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), ethyl methyl 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 γ-butyrolactone (BL).

[0020] An electrolyte of the present invention containing a rosin ester compound as an electrolyte additive; the oxidation potential of the high-voltage electrolyte is 4.6 V.

[0021] The beneficial effects of the present invention: It contains 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 +The plasma forms coordination complexes, which can better prevent the solvation of lithium ions from damaging the anode structure, and form stable and dense SEI films on the surfaces of the cathode and anode respectively, inhibit the generation of lithium dendrites, reduce the consumption of the electrolyte and the generation of parasitic product "dead lithium". In addition, rosin ester has a relatively high oxidation potential, which increases the transport of lithium ions, enables lithium to deposit uniformly on the interface, thereby reducing the electrochemical impedance, and has good compatibility with ester-based electrolytes and does not affect the physical properties of the electrolyte itself. Therefore, the natural product rosin ester can effectively improve the capacity of lithium-ion batteries and the cycling performance at high voltages (4.6V), reduce the risk of battery short circuit caused by lithium dendrites piercing the diaphragm, and improve the cycling performance and safety performance of LMBs. Description of the Drawings

[0022] Description of the Drawings for Going to Jiangxi

[0023] Figure 1 、 2 It is a schematic diagram of the 5C rate cycling performance test results at room temperature of a lithium-ion battery composed of a carbon-based material and a lithium metal sheet using the electrolytes prepared in Example 2 and the comparative example of the present invention.

[0024] Figure 3 、 4 、5 is a schematic diagram of the AC impedance test results of a lithium-ion battery composed of a carbon-based material and a lithium metal sheet using the electrolyte prepared by the present invention. (a) Schematic diagram of the impedance of the test battery; (b) Schematic diagram of the impedance of the test battery after 1 cycle; (c) Schematic diagram of the impedance of the test battery after 25 cycles. Detailed Description of the Invention

[0025] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0026] Example 1 In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) were mixed as organic solvents in a weight ratio of 1:1:1, and lithium salt LiPF 6 was added to this solvent with a final concentration of 1.0 mol / L to obtain a conventional electrolyte; then pentaerythritol rosin ester was added to the prepared conventional electrolyte in an amount of 0.5%; a high-voltage electrolyte for lithium secondary batteries was obtained. The structural formula of the electrolyte additive is as follows:

[0027] Preparation of Lithium-Ion Battery: Cathode: A lithium sheet with a diameter of 15.6 mm is selected; Anode: It includes lithium iron phosphate, acetylene black, and the solvent N-methylpyrrolidone (NMP) mixed evenly; In the anode active coating, the mass ratio of lithium iron phosphate, acetylene black, and the solvent N-methylpyrrolidone (NMP) is 8:1:1, and the solid content of the anode binder is 1.0%. Stack the cathode, Celgard 2500 separator, and anode in sequence, obtain an electrode core through the stacking process, place the electrode core in an outer packaging shell, dry it, inject electrolyte, and obtain a lithium-ion battery after vacuum packaging, standing, formation, and grading processes.

[0028] Example 2

[0029] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed as an organic solvent in a weight ratio of 1:1:1. Lithium salt LiPF 6 is added to this solvent with a final concentration of 1.0 mol / L to obtain a conventional electrolyte; Then, pentaerythritol ester of rosin is added to the prepared conventional electrolyte with an addition amount of 0.5%; A high-voltage electrolyte for lithium secondary batteries is obtained. The structural formula of the electrolyte additive is as follows:

[0030]

[0031] Preparation of Lithium-Ion Battery: Cathode: A lithium sheet with a diameter of 15.6 mm is selected; Anode: It includes lithium iron phosphate, acetylene black, and the solvent N-methylpyrrolidone (NMP) mixed evenly; In the anode active coating, the mass ratio of lithium iron phosphate, acetylene black, and the solvent N-methylpyrrolidone (NMP) is 8:1:1, and the solid content of the anode binder is 1.0%. Stack the cathode, Celgard 2500 separator, and anode in sequence, obtain an electrode core through the stacking process, place the electrode core in an outer packaging shell, dry it, inject electrolyte, and obtain a lithium-ion battery after vacuum packaging, standing, formation, and grading processes.

[0032] Example 3

[0033] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed as an organic solvent in a weight ratio of 1:1:1. Lithium salt LiPF 6, with a final concentration of 1.0 mol / L, a conventional electrolyte was obtained; then pentaerythritol ester of rosin was added to the prepared conventional electrolyte, and the addition amount was 0.5%; a high-voltage electrolyte for lithium secondary batteries was obtained. The structural formula of the electrolyte additive is as follows:

[0034]

[0035] Preparation of lithium-ion batteries: Cathode: A lithium sheet with a diameter of 15.6 mm was selected; Anode: Lithium iron phosphate, acetylene black, and the solvent N-methylpyrrolidone (NMP) were mixed evenly; In the anode active coating, the mass ratio of lithium iron phosphate, acetylene black, and the solvent N-methylpyrrolidone (NMP) was 8:1:1, and the solid content of the anode binder was 1.0%. The cathode, Celgard 2500 separator, and anode were stacked in sequence, and a battery cell was obtained through the stacking process. The battery cell was placed in an outer packaging case, dried, injected with the electrolyte, and after vacuum packaging, standing, formation, and grading processes, a lithium-ion battery was obtained.

[0036] Comparative Example 1

[0037] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed as organic solvents in a weight ratio of 1:1:1. Lithium salt LiPF 6 , with a final concentration of 1.0 mol / L, a conventional electrolyte was obtained;

[0038] The assembled lithium-ion batteries were tested for discharge rate performance, and the test results are shown in Table 1 below

[0039] Table 1 Discharge rate performance test results of examples and comparative examples

[0040] Number 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%

[0041] After standing at room temperature for one day, the above-mentioned example and comparative example batteries were tested for electrochemical performance. The example and comparative example were cycled at 4.6 V at 1C, 2C, and 5C rates for 300 cycles, and the cycle performance results are shown in Table 2.

[0042] Table 2 Cycle test results of examples and comparative examples

[0043] Number 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

[0044] As can be seen from the table, the addition of the novel substituted rosin additive significantly improves the cycling performance of the lithium-ion battery at high voltages, and the Coulombic efficiency and the battery capacity retention rate are greatly improved. From Table 2, the initial Coulombic efficiency of the battery containing pentaerythritol ester of rosin in the negative half-cell is close to that of the battery without pentaerythritol ester of rosin, and the different contents also have different effects on the battery performance. In Example 2 and Example 3, the battery capacity retention rate is higher than that of the battery without pentaerythritol ester of rosin. The lower capacity retention rate of Example 1 compared to the battery without pentaerythritol ester of rosin may be due to the relatively low content of pentaerythritol ester of rosin. Figure 1 , Figure 2 They are the blank electrolyte and Example 2 respectively. It can be seen that the battery with 2% pentaerythritol ester of rosin has a very stable cycle at a high current (5C), ensuring the long cycle life and capacity performance of the battery, achieving the purpose of the present invention.

[0045] After standing at room temperature for 4 h, the above-mentioned example and comparative example batteries were subjected to AC impedance tests. After the batteries were subjected to constant current charge and discharge cycles for 1 week and 25 weeks, AC impedance tests were respectively carried out using an electrochemical workstation. The test frequency range was 10 mHz to 100 mHz, the oscillating voltage was 5 mV, and the scan was from high frequency to low frequency.

[0046] Table 3 Impedance test results of examples and comparative examples

[0047] Number Z' / ohm Z' / ohm (1 cycle) Z' / ohm (25 cycles) Example 1 260 241 90 Example 2 185 143 45 Example 3 210 179 64 Comparative Example 1 238 190 72

[0048] The impedance of the test battery after two weeks of charge and discharge is shown in Table 3. The impedance of the example battery is smaller than that of the comparative example. This is because pentaerythritol ester of rosin, as an electrolyte additive, undergoes an oxidation reaction on the surface of the negative electrode prior to the electrolyte solvent, forming a dense SEI film, reducing the generation of lithium dendrites, and making the lithium deposition uniform. The impedance increase values of the test batteries with 2.0% and 3.0% pentaerythritol ester of rosin added to the electrolyte are much smaller than those of the comparative example. The SEI film optimizes the interfacial performance between the electrode and the electrolyte, preventing the continuous decomposition of the electrolyte and the deterioration of the negative electrode structure, thereby improving the cycle stability of the battery. At the same time, it can be found from Example 1 that the performance of the test battery with 0.5% pentaerythritol ester of rosin added to the electrolyte is reduced, indicating that the content of the additive in the electrolyte should be strictly controlled to improve the comprehensive performance of the battery.

[0049] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An electrolyte containing a natural product rosin ester compound electrolyte additive; characterized in that: The components of the electrolyte include lithium salt, organic solvent, and rosin ester compound, and the mass of the rosin ester compound used is 0.5% to 5% of the mass of the electrolyte; The structural formula of the rosin ester compound is: ; wherein R is selected from the group consisting of an H atom, a metal atom, an alkyl group, an alcohol group, an alkenyl group, an ester group, an acetyl group, a haloalcohol group, a haloacetyl group, a glycidyl ester group, a benzene ring, and a halogenated benzene ring; In the electrolyte, the concentration of lithium salt is 0.5M to 1.5M; In the high-voltage electrolyte, the organic solvent accounts for 75% to 85% of the total mass of the high-voltage electrolyte; The organic solvent includes propylene carbonate, diethyl carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl propyl carbonate, γ-butyrolactone, methyl propionate, fluorinated ethylene carbonate, trifluoropropylene carbonate, ethyl difluoroacetate, ethyl trifluoroacetate and other carbonates and a combination of two or more of the fluorinated carbonates; The lithium salt includes at least one of inorganic anion lithium salts and organic anion lithium salts such as lithium hexafluorophosphate, lithium tetrafluoroborate, bis(oxalatoborate), lithium difluorooxalatoborate, lithium perchlorate, lithium bis(difluorosulfonylimide), lithium bis(trifluoromethylsulfonylimide), and lithium difluorophosphate; The oxidation potential of the high voltage electrolyte is 4.5-5V.

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

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

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

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

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

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