Electrolyte additive for preventing positive electrode from being overcharged and improving thermal stability of negative electrode

Abstract

The invention discloses an electrolyte additive for preventing positive electrode overcharge and improving negative electrode thermal stability as shown in a formula 1 or a formula 2 as well as a preparation method and application of the electrolyte additive. The electrolyte additive has relatively high oxidation potential at 3.8-4.2 V and is applied to electrolyte of a lithium ion battery or other electrochemical energy storage devices; and when the overcharge potential is greater than the oxidation potential of the electrolyte additive, an oxidation reaction is generated on the positive electrode, so that the overcharge behavior of the battery is inhibited, and the battery is protected. Meanwhile, the thermal stability of the negative electrode can be improved, and the electrolyte additive has small influence on the cycle performance of the whole battery and basically does not influence the cycle performance of the battery. The preparation process is simple and pollution-free. # imgabs0 #

Description

Technical Field:

[0001] The present invention relates to the technical field of electrochemical energy storage, and particularly relates to an electrolyte additive for preventing overcharging of the positive electrode and improving the thermal stability of the negative electrode. Background Art:

[0002] Lithium-ion batteries are widely used in industries such as mobile electronic devices, electric vehicles, and energy storage due to their high specific energy, low cost, high power density, and long cycle life. Currently, the safety of lithium-ion batteries is an important factor restricting their large-scale application, and overcharging is one of the main safety problems. When lithium-ion batteries are overcharged or otherwise abused, it will cause the electrolyte to decompose to produce gas, release toxic substances, and even trigger fires or explosions. Currently, lithium-ion batteries often use external systems such as additional dedicated protection circuits, gas release valves, or PTC components to achieve overcharge protection of the battery. However, the addition of external systems will also increase the weight, volume, and manufacturing cost of the battery pack module. Achieving overcharge protection of the battery by adding overcharge prevention additives and simultaneously improving the thermal stability of the negative electrode material is of great significance for reducing the production and manufacturing cost of the battery and improving the overall safety performance of the lithium battery.

[0003] Therefore, it is a long-term and urgent technical need to research and develop new overcharge prevention electrolyte materials for preventing overcharging of the positive electrode and improving the thermal stability of the negative electrode to meet and improve the safety applications of electrochemical energy storage devices such as lithium-ion batteries. Summary of the Invention:

[0004] The object of the present invention is to provide an electrolyte additive for preventing overcharging of the positive electrode and improving the thermal stability of the negative electrode, as well as its preparation and application.

[0005] The present invention is achieved by the following technical solutions:

[0006] An electrolyte additive for preventing overcharging of the positive electrode and improving the thermal stability of the negative electrode shown in Formula 1 or Formula 2:

[0007]

[0008] The preparation method of the electrolyte additive includes the following steps: Under the protection of an inert gas, naphthol or biphenol and acrylonitrile are respectively subjected to a Michael addition reaction under the catalysis of Triton A, the reaction temperature is 50–100 °C, the reaction time is 5–24 h; the molar ratio of naphthol and biphenol to acrylonitrile is 1–2.2; the catalyst is selected from Triton A, and the amount of Triton A added is 0.1 wt%–5 wt% of naphthol or biphenol.

[0009] The specific synthesis route includes the following route:

[0010]

[0011] The present invention also protects the use of the electrolyte additive for preventing overcharging of the positive electrode and improving the thermal stability of the negative electrode shown in Formula 1 or Formula 2 in a lithium-ion battery or other electrochemical energy storage devices (such as sodium-ion batteries, potassium-ion batteries, lithium-sulfur batteries, supercapacitors, etc.). The electrolyte additive for preventing overcharging of the positive electrode and improving the thermal stability of the negative electrode shown in Formula 1 or Formula 2 is added to a conventional electrolyte. The usage amount of the electrolyte additive is 0.1 wt% - 2 wt%, preferably 0.5 wt% - 1.5 wt%.

[0012] The present invention also protects a battery electrolyte, to which the electrolyte additive for preventing overcharging of the positive electrode and improving the thermal stability of the negative electrode is added. The electrolyte includes a lithium salt and a solvent; the usage amount of the electrolyte additive is 0.1% - 2% of the total mass of the lithium salt and the solvent, preferably 0.5 wt% - 1.5 wt%. Among them, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide, and the solvent is selected from two or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate.

[0013] The present invention also protects the use of the battery electrolyte in electrochemical energy storage devices such as lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, lithium-sulfur batteries, and supercapacitors.

[0014] The positive electrode material of the lithium-ion battery can use a lithium iron phosphate or lithium manganese iron phosphate positive electrode material system; the negative electrode material of the lithium-ion battery uses one of metallic lithium, graphite, lithium titanate, or a silicon-based system.

[0015] The beneficial effects of the present invention are as follows: The electrolyte additive for preventing overcharging of the positive electrode and improving the thermal stability of the negative electrode of the present invention has a relatively high oxidation potential at 3.8 - 4.2 V. When applied to the electrolyte of a lithium-ion battery or other electrochemical energy storage devices (such as sodium-ion batteries, potassium-ion batteries, lithium-sulfur batteries, supercapacitors, etc.), when the overcharge potential is greater than the oxidation potential of the electrolyte additive, the electrolyte additive will undergo an oxidation reaction on the positive electrode, thereby inhibiting the overcharging behavior of the battery, inhibiting the decomposition of the electrolyte itself, effectively preventing the thermal runaway of the battery, and playing a protective role. The addition of the electrolyte additive can simultaneously improve the thermal stability of the negative electrode, and the electrolyte additive has little influence on the cycle performance of the overall battery and basically does not affect the cycle performance of the battery. The preparation process is simple and pollution-free. Description of the Drawings:

[0016] Figure 1 1H NMR spectrum of the compound of Example 1 of the present invention;

[0017] Figure 2 13C NMR spectrum of the compound of Example 1 of the present invention;

[0018] Figure 3 1H NMR spectrum of the compound of Example 2 of the present invention;

[0019] Figure 4 13C NMR spectrum of the compound of Example 2 of the present invention;

[0020] Figure 5 5V overcharge test curves of the electrolytes of Example 3 and Example 4 of the present invention;

[0021] Figure 6 100% overcharge test curve of the electrolyte of Example 3 of the present invention;

[0022] Figure 7 Comparison of the impedance of the electrolytes before overcharge of the electrolytes of Example 3 and Example 4 of the present invention;

[0023] Figure 8 Cycling test curve of the electrolyte of Example 4 of the present invention;

[0024] Figure 9 Overcharge test during cycling of the electrolyte of Example 4 of the present invention;

[0025] Figure 10 Normal temperature cycling test curves of SiC / Li batteries with the electrolytes of Example 5 and Example 6 of the present invention;

[0026] Figure 11 High temperature 45°C cycling test curves of SiC / Li batteries with the electrolytes of Example 5 and Example 6 of the present invention. Specific embodiments:

[0027] The following is a further description of the present invention, rather than a limitation of the present invention.

[0028] Example 1: Synthesis of cyano-functionalized 3-(naphthalen-2-yloxy)propanenitrile (NPCN)

[0029]

[0030] Under Ar gas protection, naphthol (10 g, 69.4 mmol), acrylonitrile (18.8 g, 0.354 mol), and 1.2 mL of a methanol solution of 40 wt% benzyltrimethylammonium hydroxide (Triton A) were successively added to a three-necked flask and reacted at 85°C for 10 h. After stopping the reaction, the reaction solution was diluted with dichloromethane and washed successively with 10 mL of 5 wt% aqueous NaOH solution and saturated NaCl aqueous solution to obtain the crude product NPCN, which was recrystallized from acetone to obtain 6.3 g of NPCN with a yield of 46%.

[0031] 1H-NMR(400MHz, CDCl3): δ 7.87 - 7.76 (m, 2H), 7.73 (d, J = 8.4 Hz, 1H), 7.51 - 7.43 (m, 1H), 7.42 - 7.32 (m, 1H), 7.17 (dd, J = 8.8, 2.8 Hz, 1H), 7.13 (d, J = 2.8 Hz, 1H), 4.32 (t, J = 6.4 Hz, 2H), 2.92 (t, J = 7.6 Hz, 2H); 13 C-NMR(100MHz, CDCl3): δ 155.55, 134.16, 129.65, 129.26, 127.61, 126.72, 126.53, 124.06, 118.43, 117.16, 106.99, 62.55, 18.40.

[0032] Example 2: Synthesis of 3,3’([1,1’-Biphenyl]-4,4’-diylbis(oxy))dipropionitrile (BPDCN)

[0033]

[0034] Under Ar gas protection, biphenol (10 g, 53.7 mmol), acrylonitrile (28.5 g, 0.537 mol), and 1.1 mL of a methanol solution of 40 wt% benzyltrimethylammonium hydroxide (Triton A) were successively added to a three-necked flask. The reaction was carried out at 85 °C for 10 h. After the reaction was stopped, the reaction solution was diluted with dichloromethane and washed successively with 10 mL of 5 wt% aqueous NaOH solution and saturated NaCl aqueous solution to obtain the crude product BPDCN. BPDCN was recrystallized from dichloromethane to obtain 8.5 g of BPDCN, with a yield of 66%.

[0035] 1 H-NMR(400MHz, DMSO-d 6 ): δ 7.57 (d, J = 4.4 Hz, 4H), 7.04 (d, J = 4.4 Hz, 4H), 3.02 (t, J = 6.0 Hz, 4H), 2.51 (t, J = 6.0 Hz, 4H); 13 C-NMR(100MHz, DMSO-d 6 ): δ 157.39, 133.32, 127.86, 119.36, 115.53, 63.35, 18.43.

[0036] Example 3:

[0037] The required basic electrolyte LB301 = 1M LiPF 6Ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) (1:1:1) was from Shanghai Xiaoyuan Energy Technology Co., Ltd. 1.5 wt.% of the overcharge additive NPCN synthesized in Example 1 was added to the electrolyte, and after stirring evenly, it was reserved for use.

[0038] Example 4:

[0039] The required basic electrolyte LB301 = 1M LiPF 6 EC / DMC / EMC (1:1:1) was from Shanghai Xiaoyuan Energy Technology Co., Ltd. 1 wt.% of the overcharge additive BPDCN synthesized in Example 2 was added to the electrolyte, and after stirring evenly, it was reserved for use.

[0040] Example 5

[0041] The required basic electrolyte was LB301 = 1M LiPF 6 EC / DMC / EMC (1:1:1). On this basis, 10 wt.% of fluoroethylene carbonate and 0.5 wt.% of the overcharge additive NPCN synthesized in Example 1 were added, and after stirring evenly, it was reserved for use.

[0042] Example 6:

[0043] The required basic electrolyte was LB301 = 1M LiPF 6 EC / DMC / EMC (1:1:1). On this basis, 10 wt.% of fluoroethylene carbonate and 0.5 wt.% of the overcharge additive BPDCN synthesized in Example 2 were added, and after stirring evenly, it was reserved for use. Comparative Example 1:

[0044] Basic electrolyte LB301 = 1M LiPF 6 EC / DMC / EMC (1:1:1). No other additives were added to this basic electrolyte.

[0045] Comparative Example 2:

[0046] Basic electrolyte LB301 = 1M LiPF 6 EC / DMC / EMC (1:1:1). 10% of fluoroethylene carbonate was added to this basic electrolyte.

[0047] Example 7: Electrode fabrication

[0048] The positive electrode material, conductive agent, binder, and solvent were mixed in a certain proportion. After mixing, it was coated on the aluminum foil and dried to prepare the positive electrode sheet. Similarly, the negative electrode material, conductive agent, binder, and solvent were mixed in a certain proportion, and then coated on the copper foil and dried to prepare the negative electrode sheet.

[0049] The positive electrode material is any one of lithium iron phosphate and lithium iron manganese phosphate; the negative electrode material is one of metallic lithium, graphite, and lithium titanate.

[0050] Acetylene black and Super P are conductive agents; the binder can be selected from one or more of vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), styrene-butadiene rubber, and sodium carboxymethyl cellulose; the solvent can be selected from one of N-methylpyrrolidone (NMP), acetone, and water.

[0051] The button cell separator is generally selected from separators that can better infiltrate the electrolyte, such as polyethylene, polypropylene, or a separator mixed with both.

[0052] Example 8: Battery Assembly and Performance Testing

[0053] Assemble a CR2025 button cell in a glove box. Prepare the positive electrode and negative electrode according to Example 7, and sequentially use the electrolytes of Example 3 and Example 4 as the battery test electrolytes. Assemble in the order of negative electrode case, negative electrode sheet, electrolyte, separator, electrolyte, positive electrode sheet, and positive electrode case. After assembly, leave it for 12 h to obtain a lithium iron phosphate button cell.

[0054] Assemble a CR2025 button cell in a glove box. Prepare the positive electrode and negative electrode according to Example 7, and sequentially use the electrolytes of Example 5 and Example 6 as the battery test electrolytes. Assemble in the order of negative electrode case, negative electrode sheet, electrolyte, separator, electrolyte, positive electrode sheet, and positive electrode case. After assembly, leave it for 12 h to obtain a silicon-carbon button cell.

[0055] Battery impedance test method: After the battery cycle ends, test the alternating current impedance EIS on a Shanghai Chenhua electrochemical workstation, with an amplitude of 5 mV and a frequency range of 0.01 Hz - 100 kHz.

[0056] Figure 5 This is the 5V overcharge test curve graph of the electrolytes of Examples 3 and 4 of the present invention. It is found that the voltage of the electrolyte of Comparative Example 1 rises sharply to 5V, the voltage of the electrolyte of Example 4 rises to 5V in about 20 h, and the voltage of the battery of the electrolyte of Example 3 rises to 5V after 132 h. It shows that the compounds of Examples 3 and 4 can both play the role of overcharge protection.

[0057] Figure 6 This is the 100% overcharge test curve graph of the electrolyte of Example 3 of the present invention. It is found that the battery of the electrolyte of Example 3 is still in normal circulation after 5 100% overcharge cycles.

[0058] Figure 7For the comparison of the impedance of the electrolytes before overcharging in Example 3 and Example 4 of the present invention, it was found that the surface film impedance values of the batteries with the electrolytes in Example 3 and Comparative Example 1 were close, and the surface film impedance of the battery with the electrolyte in Example 4 increased slightly, indicating that the addition of the compounds in Example 1 and 2 had little effect on the impedance performance of the battery.

[0059] As Figure 8 , a 2025 button cell was assembled using lithium iron phosphate and lithium sheet as the positive and negative electrodes respectively, and charged / discharged on a Shenzhen Neware charger / discharger with a charge / discharge voltage of 2.5 - 3.8V. The batteries with the electrolytes in Example 3 and Example 4 were charged / discharged at a constant current of 0.5C. It was found that the cycling performance of the lithium iron phosphate / Li half-cell assembled with the electrolyte in Example 4 increased slightly, and the cycling life of the battery was not deteriorated.

[0060] Figure 9 For the battery with the electrolyte in Example 4 of the present invention, after overcharge protection was carried out during the 8th and 14th cycles respectively, the battery could still cycle normally, indicating that the compound in Example 2 did not deteriorate the cycling performance of the battery.

[0061] As Figure 10 , a 2025 button cell was assembled using a silicon-carbon negative electrode and a lithium sheet for room-temperature cycling test. The charge / discharge voltage for the test was 0.01–2V, the test temperature was 25°C, and the batteries with the electrolytes in Example 5 and Example 6 were tested at a constant current of 800 mA / g. By comparing the performance of the SiC / Li half-cells with the electrolytes in Example 5, Example 6 and Comparative Example 2, the capacity retention rates of the batteries after 42 cycles were 99.9%, 100.4% and 99.7% respectively, indicating that the addition of the compounds in Example 1 and 2 did not deteriorate the cycling performance of the silicon-carbon negative electrode battery.

[0062] As Figure 11 , a 2025 button cell was assembled using a silicon-carbon negative electrode and a lithium sheet for high-temperature cycling test. The charge / discharge voltage for the test was 0.01–2V, the test temperature was 45°C, and the batteries with the electrolytes in Example 5 and Example 6 were tested at a constant current of 500 mA / g. By comparing the performance of the SiC / Li half-cells with the electrolytes in Example 5, Example 6 and Comparative Example 2, the capacity retention rates of the batteries after 35 cycles were 80.5%, 80.5% and 82.6% respectively, indicating that the addition of the compound in Example 1 did not deteriorate the high-temperature cycling performance of the silicon-carbon negative electrode battery, and the compound in Example 2 could improve the high-temperature cycling performance of the silicon-carbon negative electrode battery.

Claims

1. An electrolyte additive for preventing positive electrode overcharge and improving negative electrode thermal stability as shown in Formula 1 or Formula 2:

2. The method for preparing the electrolyte additive according to claim 1, characterized in that: The method comprises the following steps: under the protection of inert gas, naphthol or biphenyl diphenol and acrylonitrile are respectively subjected to Michael addition reaction under the catalysis of Triton A, the reaction temperature is 50-100°C, and the reaction time is 5-24 hours; the molar ratio of naphthol and biphenyl diphenol to acrylonitrile is 1-2.2; the catalyst is selected from Triton A, and the amount of Triton A added is 0.1wt%-5wt% of naphthol or biphenyl diphenol.

3. The use of the electrolyte additive according to claim 1 in lithium ion batteries, sodium ion batteries, potassium ion batteries, lithium sulfur batteries, and supercapacitors, characterized in that: The electrolyte additive is added into a conventional electrolyte, and the electrolyte additive is used in an amount of 0.1 wt%-2 wt%.

4. The use according to claim 3, characterized in that: The electrolyte additive is used in an amount of 0.5wt%-1.5wt%.

5. The use according to claim 3, characterized in that: The electrolyte comprises a lithium salt and a solvent; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide; and the solvent is selected from at least two of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate.

6. A battery electrolyte, characterized in that: Adding the electrolyte additive for preventing positive electrode overcharge and improving negative electrode thermal stability as described in claim 1, the electrolyte comprises a lithium salt and a solvent; the electrolyte additive is used in an amount of 0.1%-2% of the total mass of the lithium salt and the solvent, wherein the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium perchlorate, lithium bistrifluoromethanesulfonyl imide, and lithium bisfluorosulfonyl imide, and the solvent is selected from two or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate.

7. The battery electrolyte according to claim 6, characterized in that: The electrolyte additive is used in an amount of 0.5wt%-1.5wt%.

8. Use of the battery electrolyte according to claim 6 in electrochemical energy storage devices such as lithium ion batteries, sodium ion batteries, potassium ion batteries, lithium sulfur batteries, and supercapacitors.

9. The use according to claim 8, characterized in that: The positive electrode material of lithium-ion batteries uses lithium iron phosphate and lithium iron manganese phosphate positive electrode material systems; the negative electrode material of lithium-ion batteries uses one of metallic lithium, graphite, lithium titanate or silicon-based systems.

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