Boron-nitrogen heterocyclic compound and application thereof in electrolyte

Abstract

The invention discloses a boron-nitrogen heterocyclic compound and application thereof in electrolyte, and belongs to the technical field of batteries. The boron-nitrogen heterocyclic compound provided by the invention can effectively improve the solubility of lithium nitrate in an ester organic solvent, so that when the boron-nitrogen heterocyclic compound is applied to the preparation of the electrolyte, the dissolution of lithium nitrate in the ester organic solvent can be effectively promoted, and the lithium nitrate can be decomposed into Li3N prior to the ester organic solvent; therefore, a compact and firm SEI layer rich in inorganic Li3N is formed on the surface of the negative electrode, and side reaction between the negative electrode and electrolyte is inhibited; meanwhile, the formed inorganic SEI layer rich in Li3N has relatively high ionic conductivity, so that deposition of Li ions on the surface of the negative electrode can be induced, and growth of lithium dendrites is inhibited; and thus, the prepared secondary battery has excellent cycle performance and rate capability.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular to a boron-nitrogen heterocyclic compound and its application in an electrolyte. Background Art

[0002] Metal lithium has a very high theoretical specific capacity (3860 mAh g -1 ), the lowest electrode potential (-3.04V), is considered to be the most promising negative electrode material to replace graphite negative electrode. However, the uncontrollable dendrite growth of lithium metal negative electrode during the cycle process poses a safety hazard to the battery.

[0003] Electrolyte improvement is one of the effective ways to inhibit dendrite growth and improve the cycle life of lithium metal batteries. Among them, LiNO3 is widely considered to be an excellent ether electrolyte additive. However, the solubility of LiNO3 in ester electrolytes is very low, which limits the promotion and application of this excellent additive. Therefore, improving the solubility of LiNO3 in ester electrolytes is of great significance. Summary of the invention

[0004] The purpose of the present application is to solve the problem that the prior art cannot achieve effective solubilization of lithium nitrate, thus making it difficult to prepare a secondary battery with excellent rate performance and cycle performance, and to provide a boron-nitrogen heterocyclic compound that can significantly promote the dissolution of lithium nitrate in an ester organic solvent electrolyte and its application in the electrolyte.

[0005] To achieve the above-mentioned object, the first aspect of the present application provides a boron-nitrogen heterocyclic compound, the chemical structural formula of the boron-nitrogen heterocyclic compound is shown in (1) to (4):

[0006]

[0007] Among them, R1~R 12 Each is independently selected from any one of hydrogen, fluorine, chlorine, bromine, C1-C4 hydrocarbon group, phenyl, fluorophenyl, bromophenyl and chlorophenyl.

[0008] As an embodiment of the present application, the R1 to R2 are each independently selected from a methyl group.

[0009] As an embodiment of the present application, R3 to R4 are each independently selected from methyl.

[0010] As an embodiment of the present application, the R5 to R8 are each independently selected from any one of hydrogen, fluorine, chlorine, and vinyl, and at least one of R5 to R8 is not hydrogen.

[0011] As an embodiment of the present application, the R9 to R 12Each is independently selected from any one of hydrogen, fluorine, chlorine, and methyl, and R9 to R 12 At least one of them is not hydrogen.

[0012] In a second aspect of the present application, an electrolyte is provided, the electrolyte comprising a lithium salt, an additive, an ester organic solvent and the boron nitrogen heterocyclic compound described in the present application; the additive comprises lithium nitrate.

[0013] As an embodiment of the present application, the mass percentage of the boron nitrogen heterocyclic compound is 15 to 45% based on the mass of the electrolyte.

[0014] As an embodiment of the present application, the mass percentage of lithium nitrate is 1-5% based on the mass of the electrolyte.

[0015] As an embodiment of the present application, the mass ratio of the ester organic solvent to the boron nitrogen heterocyclic compound is (2-10):1.

[0016] As an embodiment of the present application, the molar concentration of the lithium salt in the electrolyte is 0.5 to 6 mol / L.

[0017] As an embodiment of the present application, the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalatoborate, lithium oxalatodifluoroborate, and lithium perchlorate.

[0018] As an embodiment of the present application, the ester organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propyl acetate, methyl acetate, vinylene carbonate, and fluoroethylene carbonate.

[0019] In a third aspect of the present application, a secondary battery is provided, comprising a positive electrode plate, a negative electrode plate and the electrolyte described in the present application.

[0020] In a fourth aspect of the present application, an electrical device is provided, comprising the secondary battery described in the present application.

[0021] Compared with the prior art, the beneficial effects of this application are:

[0022] The boron nitrogen heterocyclic compound provided in the present application can effectively improve the solubility of lithium nitrate in ester organic solvents. Therefore, when it is used in the preparation of electrolyte, it can not only effectively promote the dissolution of lithium nitrate in ester organic solvents, but also decompose into Li3N preferentially before ester organic solvents, thereby forming a dense and solid inorganic Li3N-rich SEI layer on the surface of the negative electrode, inhibiting the side reaction between the negative electrode and the electrolyte; at the same time, the formed Li3N-rich inorganic SEI layer has a high ionic conductivity, can induce the deposition of Li ions on the surface of the negative electrode, and inhibit the growth of lithium dendrites; thereby, the prepared secondary battery has a high capacity and excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the hydrogen spectrum of boron nitrogen heterocyclic compound A1;

[0024] Figure 2 is the hydrogen spectrum of the boron nitrogen heterocyclic compound A2;

[0025] Figure 3 is the hydrogen spectrum of the boron nitrogen heterocyclic compound A3;

[0026] Figure 4 is the hydrogen spectrum of the boron nitrogen heterocyclic compound A4;

[0027] Figure 5 is the hydrogen spectrum of the boron nitrogen heterocyclic compound A5;

[0028] Figure 6 This is the result of the solubility test:

[0029] a-Blank group, b-A1 group, c-A2 group, d-A3 group. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0031] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0032] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0033] The reagents or instruments used in this application without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0034] In one embodiment of the present application, the present application proposes a boron-nitrogen heterocyclic compound, the chemical structural formula of the boron-nitrogen heterocyclic compound is shown in (1) to (4):

[0035]

[0036] Among them, R1~R 12 Each is independently selected from any one of hydrogen, fluorine, chlorine, bromine, C1-C4 hydrocarbon group, phenyl, fluorophenyl, bromophenyl and chlorophenyl.

[0037] The present application has found that the boron nitrogen heterocyclic compound provided by the present application can effectively increase the solubility of lithium nitrate in ester organic solvents and promote the rapid migration of lithium ions in electrolytes containing ester organic solvents. Specifically, the nitrogen on the ring of the boron nitrogen heterocyclic compound can act as a nucleophilic site to coordinate with the lithium ions in lithium nitrate, thus having a higher DN (Gutmann donor number) value, which can significantly increase the solubility of lithium nitrate in ester organic solvents; at the same time, the electron-deficient boron on the boron nitrogen heterocyclic compound ring can serve as an electrophilic site, which can repel lithium ions from the first solvation shell, so that the coupling energy between the boron nitrogen heterocyclic compound and lithium ions is lower than the coupling energy between the ester organic solvent and lithium ions, so that the lithium ions can smoothly coordinate with the ester organic solvent molecules to achieve rapid migration in the electrolyte; in addition, when the boron nitrogen heterocyclic compound is used in a secondary battery, it will promote the decomposition of lithium nitrate into Li3N in the ester organic solvent in the electrochemical process, thereby forming a dense and solid inorganic Li3N-rich SEI layer on the surface of the negative electrode, inhibiting the side reaction between the negative electrode and the electrolyte; at the same time, the formed Li3N-rich inorganic SEI layer has a high ionic conductivity, which can induce the deposition of Li ions on the surface of the negative electrode and inhibit the growth of lithium dendrites; thereby, the prepared secondary battery has excellent cycle performance and rate performance.

[0038] In one embodiment, each of R1 to R2 is independently selected from a methyl group.

[0039] In one embodiment, each of R3 to R4 is independently selected from a methyl group.

[0040] In one embodiment, the R5-R8 are independently selected from any one of hydrogen, fluorine, chlorine, and vinyl, and at least one of R5-R8 is not hydrogen.

[0041] In one embodiment, the R9 to R 12 Each is independently selected from any one of hydrogen, fluorine, chlorine, and methyl, and R9 to R 12 At least one of them is not hydrogen.

[0042] The present application study found that when different substituent groups are selected for the boron nitrogen heterocyclic compound, the obtained compound has certain differences in the solubilization effect on lithium nitrate, and also has a certain influence on the migration ability of lithium ions in the electrolyte; when R1~R 12 When the boron nitrogen heterocyclic compound is independently selected from the above groups, when it is applied to an electrolyte or a secondary battery, the comprehensive performance of the secondary battery obtained is more excellent.

[0043] In one embodiment, the boron nitrogen heterocyclic compound includes at least one of 2,3-dimethyl-o-azaborane, 3,6-dimethyl-p-azaborane, 1-fluoro-4,6-vinyl-o-azaborane, 1-chloro-2,4-dimethyl-p-azaborane, 1-fluoro-2,4-dimethyl-p-azaborane, 1-bromo-3,6-dimethyl-p-azaborane, 1-chloro-3,6-dimethyl-p-azaborane, 1-chloro-2,3-dimethyl-o-azaborane, and 1,4-dichloro-2,3-dimethyl-o-azaborane.

[0044] In one embodiment, the boron nitrogen heterocyclic compound includes at least one of 2,3-dimethyl-o-azaborane, 3,6-dimethyl-p-azaborane, 1-fluoro-4,6-vinyl-o-azaborane, 1-chloro-2,4-dimethyl-p-azaborane, 1-fluoro-2,4-dimethyl-p-azaborane, 1-bromo-3,6-dimethyl-p-azaborane, 1-chloro-3,6-dimethyl-p-azaborane, and 1-chloro-2,3-dimethyl-o-azaborane.

[0045] In one embodiment, the boron nitrogen heterocyclic compound includes at least one of 2,3-dimethyl-o-azaborane, 3,6-dimethyl-p-azaborane, 1-fluoro-2,4-dimethyl-p-azaborane, 1-bromo-3,6-dimethyl-p-azaborane, and 1-chloro-3,6-dimethyl-p-azaborane.

[0046] In one embodiment, the method for preparing the boron nitrogen heterocyclic compound comprises the following steps:

[0047] (1) In an inert gas environment, N-allyl amide and 1,3-dicarbonyl compound are added to an anhydrous solvent, and then a catalyst is added and placed in an electrochemical workstation for electrochemical oxidation reaction; after the reaction is completed, extraction, washing, drying, and purification are performed to obtain methyl / phenyl / amino substituted benzamide;

[0048] (2) adding methyl / phenyl / amino substituted benzamide, a mediating agent and an alkali source into a three-necked flask containing a solvent and continuously introducing borane to react in an ice-salt bath. After the reaction is completed, extraction, washing, drying and purification are performed, and then a boron nitrogen heterocyclic compound is obtained with or without halogen substitution.

[0049] In one embodiment, in step (1), the molar ratio of N-allyl amide to 1,3-dicarbonyl compound is 1:1.

[0050] In one embodiment, in step (1), the anhydrous solvent includes at least one of methanol, isopropanol, acetonitrile, toluene, acetone, dichloromethane, pyridine, and dimethyl sulfoxide. The 1,3-dicarbonyl compound includes at least one of pyruvic acid, methyl ethyl ketone, ethyl acetoacetate, succinic acid, and α-ketoglutaric acid. The catalyst includes at least one of sulfuric acid, p-toluenesulfonic acid, sodium hydroxide, triethylamine, Wilkinson catalyst, Raney nickel, and crown ether.

[0051] In one embodiment, in the electrochemical oxidation reaction, the potential is 2 to 5 V, the current is 100 to 700 mA, and the reaction time is 0.5 to 12 h.

[0052] In one embodiment, in step (2), the mediating agent includes at least one of iodophenyl, N-heterocyclic carbene, trifluoromethylsilane, and acylsilane. The alkali source includes at least one of potassium hydroxide, sodium hydroxide, ammonia, triethylamine, potassium carbonate, and sodium tert-butoxide. The reaction solvent includes at least one of methanol, isopropanol, acetonitrile, toluene, acetone, dichloromethane, pyridine, and dimethyl sulfoxide.

[0053] In one embodiment, in step (2), the reaction time is 6 to 72 hours.

[0054] In one embodiment, when synthesizing the compounds represented by formula (1) and formula (3), the molar concentration of the alkali source in the reaction solvent of step (2) is greater than or equal to 0.2 mol / L and less than 0.4 mol / L; when synthesizing the compounds represented by formula (2) and formula (4), the molar concentration of the alkali source in the reaction solvent of step (2) is greater than or equal to 0.4 mol / L and less than 1 mol / L.

[0055] In one embodiment, in step (2), the halogen substitution reaction step is: reacting the purified substance in step (2) with a halogen to obtain a boron nitrogen heterocyclic compound. The number of halogen substitutions is controlled by controlling the reaction temperature. When the reaction temperature is 75 to 85°C, the number of halogen substitutions is 1; when the reaction temperature is 145 to 155°C, the number of halogen substitutions is 2.

[0056] In a second aspect of the present application, the present application provides an electrolyte, which includes a lithium salt, an additive, an ester organic solvent and the boron nitrogen heterocyclic compound described in the present application; the additive is lithium nitrate.

[0057] The present application has found that by selecting lithium nitrate as an additive in the electrolyte, and adding an ester organic solvent and a boron nitrogen heterocyclic compound at the same time, on the one hand, the boron nitrogen heterocyclic compound can effectively promote the dissolution of lithium nitrate in the ester organic solvent, and on the other hand, under the action of the boron nitrogen heterocyclic compound, lithium nitrate will be reduced by metallic lithium to produce Li3N in preference to the ester organic solvent. The produced Li3N has good lithium ion conduction efficiency, can accelerate the passage of lithium ions through the SEI film, and uniformly deposit on the negative electrode surface, avoiding the growth of lithium dendrites, thereby improving the rate performance and cycle performance of the secondary battery.

[0058] In one embodiment, the mass percentage of the boron nitrogen heterocyclic compound is 15-45% based on the mass of the electrolyte.

[0059] It should be noted that the mass percentage of the boron nitrogen heterocyclic compound is obtained by high performance liquid chromatography (HPLC) testing.

[0060] Exemplarily, based on the mass of the electrolyte, the mass percentage of the boron nitrogen heterocyclic compound can be any point value between 15 and 45% or any two points in the range, such as 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, etc.

[0061] In one embodiment, the mass percentage of the boron nitrogen heterocyclic compound is 25-35% based on the mass of the electrolyte.

[0062] The present application study found that the mass percentage of the boron nitrogen heterocyclic compound, calculated on the mass of the electrolyte, will have a certain influence on the solubility of lithium nitrate and its ability to decompose into Li3N after dissolution. When the mass percentage of the boron nitrogen heterocyclic compound calculated on the mass of the electrolyte is selected to be 15-45%, especially 25-35%, the resulting secondary battery has better cycle performance and higher capacity.

[0063] In one embodiment, the mass percentage of lithium nitrate is 1-5% based on the mass of the electrolyte.

[0064] It should be noted that the mass percentage of lithium nitrate, based on the mass of the electrolyte, is obtained by ion chromatography.

[0065] Illustratively, based on the mass of the electrolyte, the mass percentage of lithium nitrate can be any point value between 1% and 5% or any two points in the range, such as 1%, 2%, 3%, 4%, 5%, etc.

[0066] The present application study found that the mass percentage of lithium nitrate in the electrolyte affects the degree to which it decomposes into Li3N after dissolution in preference to ester organic solvents, thereby affecting the thickness of the dense and solid inorganic Li3N-rich SEI layer formed on the surface of the negative electrode, and further affecting the degree of side reactions between the negative electrode and the electrolyte, and also affecting the ionic conductivity of the inorganic Li3N-rich SEI layer, thereby affecting the deposition of lithium ions on the surface of the negative electrode; when the mass percentage of lithium nitrate in the electrolyte is further selected to be 1-5%, the rate performance and cycle performance of the secondary battery obtained are even better.

[0067] In one embodiment, the mass ratio of the ester organic solvent to the boron nitrogen heterocyclic compound is (2-10):1.

[0068] It should be noted that the mass ratio of the ester organic solvent to the boron nitrogen heterocyclic compound is obtained by: using liquid chromatography-mass spectrometry (HPLC-MS) to test the mass of the ester organic solvent and the mass of the boron nitrogen heterocyclic compound; and then calculating the ratio of the two.

[0069] Exemplarily, the mass ratio of the ester organic solvent to the boron nitrogen heterocyclic compound can be any point value or any two point range values ​​between (2-10):1, for example, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.

[0070] The present application study found that the mass ratio of ester organic solvents and boron nitrogen heterocyclic compounds affects the dissolution effect of lithium nitrate in ester organic solvents, and also affects the optimization effect of boron nitrogen heterocyclic compounds on the solvation structure of lithium ions in ester organic solvents and the generation effect of SEI layer rich in inorganic Li3N; when the mass ratio of ester organic solvents and boron nitrogen heterocyclic compounds is further selected to be (2 to 10): 1, while promoting the dissolution of lithium nitrate, it can also avoid the formation of lithium dendrites, thereby improving the comprehensive performance of secondary batteries.

[0071] In one embodiment, the molar concentration of the lithium salt in the electrolyte is 0.5-6 mol / L.

[0072] It should be noted that the molar concentration of the lithium salt in the electrolyte is obtained by ion chromatography testing.

[0073] Exemplarily, the molar concentration of the lithium salt in the electrolyte can be any point value or any two point range values ​​between 0.5 and 6 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, etc.

[0074] The present application study found that when the molar concentration of the lithium salt in the electrolyte is further selected to be 0.5 to 6 mol / L, the comprehensive performance of the secondary battery prepared subsequently is better.

[0075] In one embodiment, the lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate) (LiBOB), lithium oxalatodifluoroborate (LiDFOB), and lithium perchlorate (LiClO4).

[0076] In one embodiment, the ester organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propyl acetate (PA), methyl acetate (MA), vinylene carbonate (VC), and fluoroethylene carbonate (FEC).

[0077] In one embodiment, the purity of the lithium nitrate is ≥99%.

[0078] In one embodiment, the method for preparing the electrolyte comprises the following steps:

[0079] (1) under the protection of inert gas, adding lithium nitrate to the boron nitrogen heterocyclic compound and stirring to dissolve, to obtain a lithium nitrate solution;

[0080] (2) adding a lithium salt into an ester organic solvent and stirring to dissolve, thereby obtaining a lithium salt ester organic solution;

[0081] (3) Add the lithium nitrate solution into the lithium salt organic solution and stir evenly to obtain an electrolyte.

[0082] In one embodiment, the inert gas includes at least one of argon and helium.

[0083] In a third aspect of the present application, the present application provides a secondary battery, comprising a positive electrode plate, a negative electrode plate, a separator and the electrolyte described in the present application.

[0084] The secondary battery provided by the present application contains the electrolyte described in the present application, and a dense and solid inorganic Li3N-rich SEI layer can be formed on the surface of the negative electrode during the electrochemical process of the secondary battery, thereby inhibiting the side reaction between the negative electrode and the electrolyte; at the same time, the inorganic SEI layer rich in Li3N formed has a high ionic conductivity, which can induce the deposition of Li ions on the surface of the negative electrode and inhibit the growth of lithium dendrites; thereby making the prepared secondary battery have excellent cycle performance and rate performance. Specifically, the secondary battery of the present application can form an inorganic SEI layer rich in Li3N on the negative electrode sheet during the electrochemical process, wherein according to X-ray photoelectron spectroscopy analysis, Li3N accounts for 2 to 8% of the total mass of the SEI film; and the thickness of the SEI film characterized by TEM is 2 to 30 nm.

[0085] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. The present application has no limitation on the positive electrode active material, the conductive agent, and the binder, and any known positive electrode active material, conductive agent, and binder can be used.

[0086] For example, the positive electrode active material may be LiFePO4, LiCoO2, LiNi x Co y Mn z O2(x+y+z=1), LiNi x Co y Al z At least one of O2(x+y+z=1), LiMn2O4, Li3V2(PO4)3. The conductive agent may be at least one of SuperP, carbon nanotubes, and graphene. The binder may be at least one of PVDF, PTFE, PAANa, CMC, SBR, and sodium alginate.

[0087] In one embodiment, the positive electrode active material includes the following components in mass percentage: 70-95% positive electrode active material, 3-20% conductive agent, and 2-10% binder.

[0088] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material. The present application has no limitation on the negative electrode active material, and any known negative electrode active material can be used.

[0089] Illustratively, the negative electrode active material may be at least one of lithium metal, carbon-based materials, silicon-based materials, and metal oxide materials.

[0090] The present application has no limitation on the diaphragm, and the diaphragm conventionally used in the art can be selected; illustratively, the material of the diaphragm can be polypropylene, polyethylene, or a composite of polypropylene and polyethylene, etc.

[0091] In a fourth aspect of the present application, the present application provides an electrical device, comprising the secondary battery described in the present application.

[0092] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0093] Example 1

[0094] The embodiment of the present application provides a boron nitrogen heterocyclic compound A1, wherein the boron nitrogen heterocyclic compound is 2,3-dimethyl-o-nitrogen boroalkane, and the preparation method of the boron nitrogen heterocyclic compound comprises the following steps:

[0095] (1) In a mixed protective gas containing 80% argon and 20% nitrogen, 0.052 mol of N-allylamide and 0.12 mol of methyl ethyl ketone were mixed and added to a three-electrode electrolytic cell containing 300 mL of acetonitrile and stirred vigorously; then 0.013 mol of triethylamine was added under stirring conditions and stirring was maintained for 45 minutes, and then the electrolytic cell was connected to an electrochemical workstation, and the current of the electrochemical oxidation reaction was controlled to 15-25 mA, and the reaction time was 1 hour. After the reaction was completed, extraction, washing, drying, and passivation were performed to obtain 2-(methyl(phenyl)amino)benzamide;

[0096] (2) 0.01 mol of 2-(methyl(phenyl)amino)benzamide, 0.013 mol of iodophenyl and 0.2 mol of sodium hydroxide were added to a three-necked flask containing 500 mL of acetonitrile and borane was continuously introduced. The mixture was reacted for 18 h in an ice-salt bath. After the reaction, liquid-liquid extraction was performed. The two solvents selected were acetonitrile and dimethyl phosphate. During the extraction process, 1 mL of a 0.1 mol / L sodium chloride aqueous solution was added for demulsification. After the extraction, a mixed solution of acetonitrile / dimethyl sulfoxide with a molar ratio of 1:3 was used for washing, followed by drying in a vacuum oven at 160°C for 12 hours, and drying and passivation was performed in air at 45°C to finally obtain o-dimethylborane heterocycle A1;

[0097] The H NMR spectrum of the prepared boron nitrogen heterocyclic compound A1 is as follows Figure 1 shown.

[0098] Example 2

[0099] The embodiment of the present application provides a boron nitrogen heterocyclic compound A2, wherein the boron nitrogen heterocyclic compound is 3,6-dimethylparanitrogenborane, and the preparation method of the boron nitrogen heterocyclic compound comprises the following steps:

[0100] (1) In a mixed protective gas containing 80% argon and 20% nitrogen, 0.052 mol of N-allylamide and 0.12 mol of methyl ethyl ketone were mixed and added to a three-electrode electrolytic cell containing 300 mL of acetonitrile and stirred vigorously, and then 0.013 mol of triethylamine was added under stirring conditions and stirred for 45 minutes. Then, the electrolytic cell was connected to an electrochemical workstation, and the current of the electrochemical oxidation reaction was controlled to 15-25 mA, and the reaction time was 1 hour. After the reaction was completed, extraction, washing, drying, and passivation were performed to obtain 2-(methyl(phenyl)amino)benzamide;

[0101] (2) 0.01 mol of 2-(methyl(phenyl)amino)benzamide, 0.013 mol of iodophenyl and 0.6 mol of sodium hydroxide were added to a three-necked flask containing 500 mL of acetonitrile and borane was continuously introduced. The mixture was reacted for 48 hours in an ice-salt bath. After the reaction, liquid-liquid extraction was performed. The two solvents selected were acetonitrile and dimethyl phosphonate. During the extraction process, 1 mL of a 0.1 mol / L sodium chloride aqueous solution was added for demulsification. After the extraction, a mixed solution of acetonitrile / dimethyl sulfoxide with a molar ratio of 1:3 was used for washing, and then the mixture was dried in a vacuum oven at 160°C for 12 hours, and then dried and passivated in air at 45°C to finally obtain p-dimethylborane heterocycle A2;

[0102] The H NMR spectrum of the prepared boron nitrogen heterocyclic compound A2 is as follows Figure 2 shown.

[0103] Example 3

[0104] The embodiment of the present application provides a boron nitrogen heterocyclic compound A3, wherein the boron nitrogen heterocyclic compound is 1-bromo-3,6-dimethyl-p-nitrogen boroalkane, and the preparation method of the boron nitrogen heterocyclic compound comprises the following steps:

[0105] (1) In a mixed protective gas containing 80% argon and 20% nitrogen, 0.052 mol of N-allylamide and 0.12 mol of methyl ethyl ketone were mixed and added to a three-electrode electrolytic cell containing 300 mL of acetonitrile and stirred vigorously. Then, 0.013 mol of triethylamine was added under stirring conditions and stirring was maintained for 45 minutes. Then, the electrolytic cell was connected to an electrochemical workstation. The current of the electrochemical oxidation reaction was controlled to 15-25 mA, and the reaction time was 1 hour. After the reaction was completed, extraction, washing, drying, and passivation were performed to obtain 2-(methyl(phenyl)amino)benzamide.

[0106] (2) 0.01 mol of 2-(methyl(phenyl)amino)benzamide, 0.013 mol of iodobenzophenone and 0.6 mol of sodium hydroxide were added to a three-necked flask containing 500 mL of acetonitrile and borane was continuously introduced. The mixture was reacted for 48 h in an ice-salt bath. After the reaction, liquid-liquid extraction was performed. The two solvents selected were acetonitrile and dimethyl phosphate. During the extraction process, 1 mL of a 0.1 mol / L sodium chloride aqueous solution was added for demulsification. After the extraction, a mixed solution of acetonitrile / dimethyl sulfoxide with a molar ratio of 1:3 was used for washing. The mixture was then dried in a vacuum oven at 160°C for 12 hours and dried and passivated in air at 45°C. The obtained product was then dissolved in a three-necked flask containing 200 mL of dimethyl sulfoxide, bromopropane was introduced and the reaction was continued at 80°C for 8 h, and 1-bromo-3,6-dimethyl-para-nitrogen boroalkane A3 was finally obtained.

[0107] The H NMR spectrum of the prepared boron nitrogen heterocyclic compound A3 is as follows Figure 3 shown.

[0108] Example 4

[0109] The embodiment of the present application provides a boron nitrogen heterocyclic compound A4, wherein the boron nitrogen heterocyclic compound is 1-chloro-3,6-dimethyl-p-nitrogen boroalkane, and the preparation method of the boron nitrogen heterocyclic compound comprises the following steps:

[0110] (1) In a mixed protective gas containing 80% argon and 20% nitrogen, 0.052 mol of N-allylamide and 0.12 mol of methyl ethyl ketone were mixed and added to a three-electrode electrolytic cell containing 300 mL of acetonitrile and stirred vigorously. Then, 0.013 mol of triethylamine was added under stirring conditions and stirring was maintained for 45 minutes. Then, the electrolytic cell was connected to an electrochemical workstation. The current of the electrochemical oxidation reaction was controlled to 15-25 mA, and the reaction time was 1 hour. After the reaction was completed, extraction, washing, drying, and passivation were performed to obtain 2-(methyl(phenyl)amino)benzamide.

[0111] (2) 0.01 mol of 2-(methyl(phenyl)amino)benzamide, 0.013 mol of iodobenzophenone and 0.6 mol of sodium hydroxide were added to a three-necked flask containing 500 mL of acetonitrile and borane was continuously introduced. The mixture was reacted for 48 h in an ice-salt bath. After the reaction, liquid-liquid extraction was performed. The two solvents selected were acetonitrile and dimethyl phosphonate. During the extraction process, 1 mL of a 0.1 mol / L sodium chloride aqueous solution was added for demulsification. After the extraction, a mixed solution of acetonitrile / dimethyl sulfoxide with a molar ratio of 1:3 was used for washing. The mixture was then dried in a vacuum oven at 160°C for 12 hours and dried and passivated in air at 45°C. The obtained product was then dissolved in a three-necked flask containing 200 mL of dimethyl sulfoxide, dichloromethane was introduced and the reaction was continued at 80°C for 8 h, and 1-chloro-3,6-dimethyl-para-nitrogen boroalkane A4 was finally obtained.

[0112] The H NMR spectrum of the prepared boron nitrogen heterocyclic compound A4 is as follows Figure 4 shown.

[0113] Example 5

[0114] The embodiment of the present application provides a boron nitrogen heterocyclic compound A5, wherein the boron nitrogen heterocyclic compound is 1-chloro-2,3-dimethyl-o-nitrogen boroalkane, and the preparation method of the boron nitrogen heterocyclic compound comprises the following steps:

[0115] In a mixed protective gas containing 80% argon and 20% nitrogen, 0.052 mol of N-allylamide and 0.12 mol of methyl ethyl ketone were mixed and added into a three-electrode electrolytic cell containing 300 mL of acetonitrile and stirred vigorously. Subsequently, 0.013 mol of triethylamine was added under stirring conditions and stirring was maintained for 45 minutes. Subsequently, the electrolytic cell was connected to an electrochemical workstation. The current of the electrochemical oxidation reaction was controlled to 15-25 mA, and the reaction time was 1 hour. After the reaction, extraction, washing, drying and passivation were performed to obtain 2-(methyl(phenyl)amino)benzamide.

[0116] 0.01 mol of 2-(methyl(phenyl)amino)benzamide, 0.013 mol of iodobenzophenone and 0.2 mol of sodium hydroxide were added to a three-necked flask containing 500 mL of acetonitrile and borane was continuously introduced. The mixture was reacted for 18 h in an ice-salt bath. After the reaction, liquid-liquid extraction was performed. The two solvents selected were acetonitrile and dimethyl phosphate. During the extraction process, 1 mL of a 0.1 mol / L sodium chloride aqueous solution was added for demulsification. After the extraction, a mixed solution of acetonitrile / dimethyl sulfoxide with a molar ratio of 1:3 was used for washing. The mixture was then dried in a vacuum oven at 160°C for 12 hours and dried and passivated in air at 45°C. The obtained product was then dissolved in a three-necked flask containing 200 mL of dimethyl sulfoxide, dichloromethane was introduced and the reaction was continued at 80°C for 8 h, and 1-chloro-2,3-dimethyl-o-nitroborane A5 was finally obtained.

[0117] The NMR spectrum of the prepared boron nitrogen heterocyclic compound A5 is as follows Figure 5 shown.

[0118] Example 6

[0119] The embodiment of the present application provides a boron nitrogen heterocyclic compound A6, wherein the boron nitrogen heterocyclic compound is 1,4-dichloro-2,3-dimethyl-o-nitrogen boroalkane, and the preparation method of the boron nitrogen heterocyclic compound comprises the following steps:

[0120] In a mixed protective gas containing 80% argon and 20% nitrogen, 0.052 mol of N-allylamide and 0.12 mol of methyl ethyl ketone were mixed and added into a three-electrode electrolytic cell containing 300 mL of acetonitrile and stirred vigorously. Subsequently, 0.013 mol of triethylamine was added under stirring conditions and stirring was maintained for 45 minutes. Subsequently, the electrolytic cell was connected to an electrochemical workstation. The current of the electrochemical oxidation reaction was controlled to 15-25 mA, and the reaction time was 1 hour. After the reaction, extraction, washing, drying and passivation were performed to obtain 2-(methyl(phenyl)amino)benzamide.

[0121] 0.01 mol of 2-(methyl(phenyl)amino)benzamide, 0.013 mol of iodobenzophenone and 0.2 mol of sodium hydroxide were added to a three-necked flask containing 500 mL of acetonitrile and borane was continuously introduced. The mixture was reacted for 18 h in an ice-salt bath. After the reaction, liquid-liquid extraction was performed. The two solvents selected were acetonitrile and dimethyl phosphate. During the extraction process, 1 mL of a 0.1 mol / L sodium chloride aqueous solution was added for demulsification. After the extraction, a mixed solution of acetonitrile / dimethyl sulfoxide with a molar ratio of 1:3 was used for washing. The mixture was then dried in a vacuum oven at 160°C for 12 hours and dried and passivated in air at 45°C. The obtained product was then dissolved in a three-necked flask containing 200 mL of dimethyl sulfoxide, dichloromethane was introduced and the reaction was continued at 150°C for 8 h to finally obtain 1,4-dichloro-2,3-dimethyl-o-nitroborane A6.

[0122] The promoting effect of the boron nitrogen heterocyclic compounds A1-A5 prepared in Examples 1-5 on the dissolution of lithium nitrate in an ester organic solvent was investigated. Specifically, 4.14 g of lithium nitrate was added to 10 mL of the blank group and the A1-A5 groups, stirred at 45° C. for 24 h, then allowed to stand at room temperature for 12 h, and then the solubility of lithium nitrate was tested by ICP and recorded;

[0123] The solvent of the blank group is ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1 using an ester organic solvent, the lithium salt is lithium hexafluorophosphate, and the molar concentration of lithium hexafluorophosphate in the ester organic solvent is 1 mol / L; the difference between the A1-A5 groups and the blank group is that 25 wt% of A1-A5 boron nitrogen heterocyclic compounds are added to the solvent of the blank group respectively;

[0124] The obtained results are shown in Table 1;

[0125] Table 1 Solubility data record of lithium nitrate under different conditions

[0126] Blank Group Group A1 Group A2 Group A3 Group A4 Group A5 Solubility (g / L) 23.6 283.2 254.1 235.7 243.4 271.2

[0127] It can be seen from Table 1 that the boron nitrogen heterocyclic compound prepared in the present application can effectively promote the dissolution of lithium nitrate in ester organic solvents; the dissolution state photographs of the blank group and groups A1 to A3 are shown in FIG. Figure 6 As shown, from Figure 6 It can be seen that there are more solid insoluble lithium nitrate in the blank group, while the solutions of groups A1 to A3 are clear.

[0128] Application Example 1

[0129] The application example of the present application provides an electrolyte and a secondary battery, and the preparation method of the electrolyte and the secondary battery comprises the following steps:

[0130] (1) Preparation of electrolyte

[0131] In an argon-protected glove box, lithium nitrate was added to a solubilizing agent (boron nitrogen heterocyclic compound A1), and the mixture was stirred at a speed of 200 rpm until the lithium nitrate was dissolved to form a lithium nitrate solution, and then the lithium nitrate solution was added to an ester organic solvent (EC and DMC with a volume ratio of 1:1) containing a lithium salt (lithium hexafluorophosphate) and mixed evenly to obtain an electrolyte;

[0132] Wherein, based on the electrolyte, the mass percentage of the solubilizer is 25%, and the mass percentage of the lithium nitrate is 3%; the mass ratio of the ester organic solvent to the solubilizer is 6:1; in the ester organic solvent, the molar concentration of the lithium salt is 1 mol / L;

[0133] (2) Preparation of secondary batteries

[0134] The positive electrode active material, polyvinylidene fluoride (PVDF) and superconductive carbon black (Super P) were mixed in a mass ratio of 8:1:1, N-methylpyrrolidone (NMP) was added dropwise and ground until uniform, and then the resulting slurry was coated on a copper foil with a scraper. After drying at 80°C in a vacuum oven for 12 hours, a positive electrode sheet was obtained, and a secondary battery was assembled using a metal lithium sheet as the negative electrode and a polypropylene / polyethylene composite film as a separator.

[0135] Application Examples 2 to 5

[0136] The application example of the present application provides an electrolyte and a secondary battery. The difference between the electrolyte and the embodiment 1 is the choice of a solubilizing agent.

[0137] Application Examples 6 to 8

[0138] The application example of the present application provides an electrolyte and a secondary battery. The electrolyte is different from that of Example 1 in that the amount of the solubilizer added is different.

[0139] Application Examples 9-12

[0140] The application example of the present application provides an electrolyte and a secondary battery. The electrolyte is different from that of Example 1 in that the amount of lithium nitrate added is different.

[0141] Application Examples 13-16

[0142] The application example of the present application provides an electrolyte and a secondary battery. The electrolyte is different from that of Example 1 in that the mass ratio of the solubilizer and the ester organic solvent is changed by adjusting the added amounts of the solubilizer and the ester organic solvent.

[0143] Application Examples 17-20

[0144] The application example of the present application provides an electrolyte and a secondary battery. The electrolyte is different from that of Example 1 in that the amount of lithium salt added is changed.

[0145] Application Example 21

[0146] The application example of the present application provides an electrolyte and a secondary battery. The electrolyte is different from that of Example 1 in that the ester organic solvent is ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a volume ratio of 1:1:1.

[0147] Application Example 22

[0148] The application example of the present application provides an electrolyte and a secondary battery. The difference between the electrolyte and the embodiment 1 is that the lithium salt is lithium bis(oxalatoborate).

[0149] Application Example 23

[0150] The application example of the present application provides an electrolyte and a secondary battery. The difference between the electrolyte and the embodiment 1 is the choice of a solubilizing agent.

[0151] Comparative application example 1

[0152] The comparative application example of the present application provides an electrolyte and a secondary battery. The electrolyte is different from that of Example 1 in that lithium nitrate is not added.

[0153] Comparative Application Example 2

[0154] The comparative application example of the present application provides an electrolyte and a secondary battery. The electrolyte is different from that of Example 1 in that no solubilizing agent is added.

[0155] Comparative Application Example 3

[0156] The comparative application example of the present application provides an electrolyte and a secondary battery. The difference between the electrolyte and the embodiment 1 is that the solubilizing agent is pyridine.

[0157] Comparative Application Example 4

[0158] The comparative application example of the present application provides an electrolyte and a secondary battery. The difference between the electrolyte and the embodiment 1 is that the solubilizer is pyrimidone.

[0159] The types of solubilizers in the electrolytes of the application examples and comparative application examples and the contents of various substances in the electrolytes are shown in Table 2;

[0160] Table 2 Material and parameter selection results of application examples and comparative application examples

[0161]

[0162]

[0163] The secondary batteries prepared in Application Examples 1 to 24 and Comparative Application Examples 1 to 4 were charged and discharged at a voltage range of 4.3 to 2.8 V at a rate of 0.2C, and the test temperature was 25°C. The number of cycles at which the capacity decayed to 80% of the initial capacity at a rate of 0.2C was recorded; at the same time, the capacity retention rate at a current density of 2C compared to that at a current density of 0.1C was recorded;

[0164] The results obtained are shown in Table 3;

[0165] Table 3 Performance data of secondary batteries prepared by application examples and comparative application examples

[0166]

[0167] As can be seen from Table 3, when the boron nitrogen heterocyclic compound provided by the present application is used as a solubilizing agent in the preparation of an electrolyte containing lithium nitrate, and further used as an electrolyte of a secondary battery, the obtained secondary battery has excellent cycle performance and rate performance; specifically, the number of cycles when the capacity of the obtained secondary battery decays to 80% of the initial capacity at a rate of 0.2C is more than 293 cycles, and the capacity retention rate at a current density of 2C is more than 57% compared with that at a current density of 0.1C;

[0168] The results of application examples 1 to 22 of the present application and comparative application examples 1 to 2 also show that when none of lithium nitrate and boron nitrogen heterocyclic compounds are introduced, the cycle performance and rate performance of the obtained secondary battery are poor; the results of application examples 1 to 22 and comparative application examples 3 to 4 also show that currently available solubilizers cannot achieve the effect of the present application.

[0169] Finally, it should be noted that the above embodiments are intended to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A boron-nitrogen heterocyclic compound, characterized in that The chemical structural formula of the boron nitrogen heterocyclic compound is shown in formula (1) to (4): Among them, R1~R 12 Each is independently selected from any one of hydrogen, fluorine, chlorine, bromine, C1-C4 hydrocarbon group, phenyl, fluorophenyl, bromophenyl and chlorophenyl.

2. The boron nitrogen heterocyclic compound according to claim 1, characterized in that Satisfy at least one of the following: a. The R1 to R2 are each independently selected from a methyl group; b. the R3 to R4 are each independently selected from a methyl group; c. R5 to R8 are each independently selected from any one of hydrogen, fluorine, chlorine and vinyl, and at least one of R5 to R8 is not hydrogen; d. The R9~R 12 Each is independently selected from any one of hydrogen, fluorine, chlorine, and methyl, and R9 to R 12 At least one of them is not hydrogen.

3. An electrolyte, characterized in that: The electrolyte comprises a lithium salt, an additive, an ester organic solvent and the boron nitrogen heterocyclic compound as claimed in claim 1 or 2; The additive includes lithium nitrate.

4. The electrolyte according to claim 3, characterized in that Calculated by the mass of the electrolyte, the mass percentage of the boron nitrogen heterocyclic compound is 15-45%.

5. The electrolyte according to claim 3, characterized in that The mass percentage of lithium nitrate is 1 to 5% based on the mass of the electrolyte.

6. The electrolyte according to claim 3, characterized in that The mass ratio of the ester organic solvent to the boron nitrogen heterocyclic compound is (2-10):

1.

7. The electrolyte according to claim 3, characterized in that The molar concentration of the lithium salt in the electrolyte is 0.5-6 mol / L.

8. The electrolyte according to claim 3, characterized in that The lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium oxalatodifluoroborate, and lithium perchlorate; And / or, the ester organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propyl acetate, methyl acetate, vinylene carbonate, and fluoroethylene carbonate.

9. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and an electrolyte as claimed in any one of claims 3 to 8.

10. An electrical device, characterized in that: Comprising the secondary battery as claimed in claim 9.

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