Electrolyte lithium salt and application thereof

Abstract

The invention provides an electrolyte lithium salt and application thereof, the structural formula of the electrolyte lithium salt comprises a naphthalene ring, R2 and R2, R1 is selected from any one of P, N, S, B, BF2, PF3, O = S = O, B-O, P = O, S = O, N = O or O = P-OH, and R2 is selected from N or C. The electrolyte lithium salt has a polycyclic structure, contains functional groups, can form a relatively strong coordination effect with lithium ions, has good solubility and ionic conductivity in the electrolyte, and is beneficial to rapid transmission of the lithium ions between electrodes, so that the rate capability of the battery can be improved, and the service life of the battery is prolonged. In addition, formation of a firm SEI film rich in inorganic matter is facilitated, an electrode interface is stabilized, the good effect of prolonging the cycle life of the battery is achieved, decomposition of an electrolyte under the severe conditions of high voltage, high temperature and the like can be resisted to a certain degree, and the effect of improving the stability of the battery is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to an electrolyte lithium salt and its application. Background Art

[0002] Lithium-ion batteries are widely used in many fields such as electric vehicles, smart phones, energy storage power stations, etc. due to their advantages of high energy density, long cycle life, etc., and have become an indispensable energy storage device in modern life and industrial production. As a key component of lithium-ion batteries, electrolyte lithium salts have a significant impact on battery performance. Currently, the mainstream lithium salt is lithium hexafluorophosphate. Although it has high ionic conductivity and good electrochemical performance, it has disadvantages such as poor thermal stability and sensitivity to moisture, which will corrode the positive and negative electrode materials of the battery, reduce the cycle life and safety, and increase the production and application costs and difficulties. However, other lithium salts such as lithium tetrafluoroborate have a large gap with lithium hexafluorophosphate in terms of ionic conductivity, electrochemical stability, etc., and it is difficult to completely replace lithium hexafluorophosphate as the mainstream lithium salt.

[0003] In order to improve the performance of lithium-ion batteries, the research on electrolyte additives has become an important direction. Additives can improve the performance of the electrolyte by adding a small amount without changing the main lithium salt, such as improving the high and low temperature performance, flame retardancy, film-forming performance, etc. of the battery. However, the existing electrolyte additives have limited effects on improving battery performance and are difficult to fundamentally solve the problems existing in the current lithium salts.

[0004] The problems existing in the current electrolyte lithium salts are as follows: First, the thermal stability is less than satisfactory. For example, the commonly used lithium hexafluorophosphate is easily decomposed in a high-temperature environment, generating harmful substances such as hydrofluoric acid, which will not only corrode the positive and negative electrode materials of the battery, reduce the battery cycle life, but also may cause safety hazards; some new lithium salts also have poor stability at high temperatures, restricting the application of the battery in high-temperature scenarios and the performance of high-power charge and discharge. Second, it is sensitive to moisture. Many lithium salts are prone to react with water, which puts extremely high requirements on the control of moisture in the production and use environments, increasing the production difficulty and cost; if the battery encounters a humid environment during use, the reaction between the lithium salt and water will affect the performance of the electrolyte and the performance and life of the battery. Third, the conductivity needs to be improved. The ionic conductivity of some lithium salts is relatively low, which cannot meet the requirements of high-performance batteries for fast charge and discharge, affecting the rate performance of the battery; and in a low-temperature environment, the conductivity of some lithium salts will decrease significantly, the viscosity of the electrolyte increases, and the internal resistance of the battery increases, affecting the low-temperature discharge performance and endurance of the battery.

[0005] In addition, some of the current lithium salts have poor compatibility with electrode materials. These lithium salts may have adverse reactions with electrode materials during charge and discharge processes. For example, an uneven solid electrolyte interface film may form on the electrode surface, leading to the destruction of the electrode structure and capacity attenuation. At the same time, some lithium salts will corrode the current collector of the battery at a specific voltage, reducing the conductivity and mechanical strength of the current collector, and affecting the overall performance and safety of the battery. These technical defects limit the wide application and further development of lithium-ion batteries. Therefore, it is necessary to develop new lithium salts with high conductivity, good stability, and the ability to improve the electrochemical performance of lithium ions. Summary of the Invention

[0006] The purpose of the present invention is to provide an electrolyte lithium salt and its application. The electrolyte lithium salt has a multi-cyclic structure and contains multiple functional groups. This multi-cyclic structure containing functional groups can form a strong coordination effect with lithium ions, has good solubility and ion conductivity in the electrolyte, is conducive to the rapid transmission of lithium ions between electrodes, thereby improving the rate performance of the battery, and is also conducive to promoting the formation of a strong SEI film rich in inorganic substances, stabilizing the electrode interface, achieving a good effect of improving the battery cycle life, being able to resist the decomposition of the electrolyte to a certain extent under harsh conditions such as high voltage and high temperature, and having the effect of enhancing the battery stability.

[0007] To achieve the purpose of this invention, the following technical solutions are adopted:

[0008] In the first aspect, the present invention provides an electrolyte lithium salt, and the structural formula of the electrolyte lithium salt is as follows:

[0009]

[0010] Among them, R 1 is selected from any one of P, N, S, B, BF 2 , PF 3 , O=S=O, B-O, P=O, S=O, N=O or O=P-OH, and R 2 is selected from N or C.

[0011] The lithium salt with a specific naphthalene ring structure of the present invention has a high ionic conductivity, which is conducive to the rapid migration of lithium ions, reduces the internal resistance of the battery, improves the charge and discharge performance. Especially during high-rate charge and discharge, it can better maintain the capacity and power output, and has a wide electrochemical window, can be stable in a wide potential range, can match high-voltage cathode materials, and can also reduce side reactions, playing a good role in extending the cycle life of lithium-ion batteries.

[0012] In terms of thermal stability, since the electrolyte lithium salt contains elements such as B, P, S, N or F, it has good high-temperature resistance and is not easily decomposed or volatilized in a high-temperature environment, which can effectively stabilize the operation of the battery under high-temperature conditions. For example, it can reduce performance degradation and safety hazards caused by temperature rise during high-power output of electric vehicle batteries. In addition, the O=S=O, B-O, P=O, S=O, N=O or O=P-OH substituents contained in the electrolyte lithium salt can improve its solubility in organic solvents, help improve the uniform dispersion of the lithium salt in the electrolyte, form a stable system, ensure uniform lithium-ion transport, and improve the overall performance and consistency of the battery.

[0013] The electrolyte lithium salt of the present invention is 1,8-substituted-naphthalene lithium, which is substituted at the 1,8 positions. Compared with other positions, it can more effectively stabilize the molecular structure of the lithium salt, reduce the decomposition reaction in the electrolyte, improve the chemical stability of the electrolyte, and thus better adapt to the charge and discharge cycle process of the battery. And R 1 and R 2 are connected through a carbon atom to form a six-membered ring structure, which can enhance the steric hindrance effect of the molecule, effectively inhibit side reactions between the lithium salt and other components in the electrolyte, and at the same time optimize the lithium-ion transport channel and improve the migration rate of lithium ions in the electrolyte. In addition, the electrolyte lithium salt contains a naphthalene ring. Compared with only containing one benzene ring, it can increase the conjugated system of the molecule, enhance its electron delocalization ability, further enhance the solubility of the lithium salt in the electrolyte, and help improve the charge and discharge performance of the battery, enabling the battery to obtain higher energy density and better cycle life.

[0014] Preferably, the R 1 is selected from any one of BF 2 , B-O, PF 3 , O=S=O, P=O, O=P-OH or N.

[0015] Preferably, the R 2 is selected from N.

[0016] In the electrolyte lithium salt of the present invention, R 2 is preferably N, which can further improve the high-temperature and high-pressure performance of the electrolyte, etc.

[0017] Preferably, the electrolyte lithium salt includes any one or a combination of at least two of the following compounds 1 - compound 8:

[0018] (One B-F bond in compound 1 is connected by a coordination bond),

[0019]

[0020] In a second aspect, the present invention provides an electrolyte, wherein the electrolyte comprises the electrolyte lithium salt as described in the first aspect.

[0021] Preferably, in the electrolyte, the content of the electrolyte lithium salt is 5wt%-19wt%, for example, it can be 5wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt% or 19wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] The specific electrolyte lithium salt described in the present invention is preferably added in a specific content. If the amount of electrolyte lithium salt added is too little, the ionic conductivity of the electrolyte is reduced, and the effect of the electrolyte lithium salt is reduced. If the amount of electrolyte lithium salt added is too much, the viscosity of the electrolyte is significantly increased, which hinders the migration of lithium ions and causes the ion migration rate to slow down, thereby affecting the charge and discharge performance of the battery. At the same time, too high a lithium salt concentration may also cause the lithium salt to agglomerate or crystallize itself, destroying the uniformity of the electrolyte, and easily causing the side reaction at the interface between the electrode and the electrolyte to intensify, shortening the cycle life of the battery, and being not conducive to the stable performance of the overall performance of the battery.

[0023] Preferably, the electrolyte further comprises an organic solvent and an electrolyte additive.

[0024] Preferably, the content of the organic solvent is 80wt%-90wt%, for example, it can be 80wt%, 82wt%, 84wt%, 86wt%, 88wt% or 90wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the organic solvent comprises linear carbonate and / or cyclic carbonate.

[0026] Preferably, the volume ratio of the linear carbonate to the cyclic carbonate is (15-30):(70-85), for example, 15:85, 20:80, 25:75 or 30:70, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the linear carbonate comprises any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate or propyl acetate, or a combination of both.

[0028] Preferably, the cyclic carbonate includes any one of propylene carbonate, caprolactone or γ-butyrolactone, or a combination of both.

[0029] Preferably, in the electrolyte, the content of the electrolyte additive is 1wt%-5wt%, for example, it can be 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the electrolyte additive includes any one or a combination of at least two of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound or a borate compound.

[0031] In a third aspect, the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the electrolyte lithium salt as described in the first aspect, or comprises the electrolyte as described in the second aspect.

[0032] Preferably, the lithium-ion battery further comprises a positive electrode sheet and a negative electrode sheet.

[0033] Preferably, the positive electrode plate includes lithium transition metal oxide and / or lithium transition metal phosphate compound.

[0034] Preferably, the positive electrode sheet includes LiCoO 2 、LiNi x Co y Mn z O 2 、LiNi x Mn y O 2 、LiMn 2 O 4 、LiMnO 2 , Li 2 MnO 4 、LiFePO 4 、LiMnPO 4 or LiCoPO 4 Any one or a combination of at least two of the following, wherein 0≤x≤1, for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, 0≤y≤1, for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, 0≤z≤1, for example, it can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the negative electrode sheet includes any one or a combination of at least two of carbonaceous materials, alloy materials, metal composite materials containing lithium, or metallic lithium.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The 1,8-substituted naphthyllithium of the present invention has excellent electrochemical and thermal stability, is not easily decomposed under high temperature or high pressure, and can well broaden the operating temperature and voltage ranges of lithium-ion batteries. In addition, this lithium salt with a specific structure has a high ionic conductivity in terms of electrochemical performance, which is conducive to the rapid migration of lithium ions, reduces the internal resistance of the battery, and improves the charge and discharge performance. Especially during high-rate charge and discharge, it can better maintain the capacity and power output, and has a wide electrochemical window, can be stable in a relatively wide potential range, can match high-voltage cathode materials, reduce side reactions, and play a good role in extending the cycle life of lithium-ion batteries. Therefore, the lithium-ion battery containing the 1,8-substituted naphthyllithium compound as the lithium salt of the present invention can be used at a relatively wide temperature range and high voltage. The lithium-ion battery has excellent high-temperature cycle stability and capacity retention rate, breaking through the technical barriers of limited operating temperature and voltage of lithium-ion electrolytes while achieving stable long cycling of lithium-ion batteries. Detailed Embodiments

[0038] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0039] Example 1

[0040] This example provides an electrolyte lithium salt, and the electrolyte lithium salt is Compound 1. The structural formula of Compound 1 is shown as follows:

[0041]

[0042] The synthesis method of Compound 1 includes the following steps:

[0043] (1) Preparation of a boron-containing aromatic intermediate: Using 1-(3-bromopropenyl)naphthalene as the starting material, reacting it with boron trifluoride-ether complex in a tetrahydrofuran solution at -78°C. Under argon protection, boron trifluoride attacks the double bond of 1-(3-bromopropenyl)naphthalene to undergo an electrophilic addition reaction to generate a boron-containing aromatic intermediate, and the reaction time is 4 hours.

[0044] The reaction equation is:

[0045] (2) Preparation of the lithium salt: The boron-containing aromatic intermediate C obtained in the first step 13 H10 BF 2 Reacts with metallic lithium (lithium sand) in anhydrous diethyl ether. The reaction is carried out at room temperature (about 25 °C) under an argon protective atmosphere to prevent the oxidation of metallic lithium. The reaction lasts for 6 hours, and the lithiation reaction occurs between metallic lithium and the boron-containing intermediate, where lithium atoms replace some groups, thus obtaining the target product [C 13 H 10 BF 2 - Li + .

[0046] The reaction equation is as follows:

[0047] The infrared characteristic peaks of the prepared compound 1 are: 3000 - 3100 cm -1 (aromatic ring C-H stretching vibration), 1200 - 1400 cm -1 (B-F stretching vibration), 1450 - 1600 cm -1 (aromatic ring skeletal vibration), and the alkenyl group is at 1620 - 1680 cm -1 (alkenyl C=C stretching vibration); 1 H-NMR: 7 - 8 ppm (naphthalene ring hydrogen), and the alkenyl hydrogen is at 4.5 - 6.5 ppm; 11 B-NMR: -10 - 20 ppm; 19 F-NMR: -100 - 150 ppm; 13 C-NMR: 120 - 140 ppm (naphthalene ring carbon), and the alkenyl carbon is at 110 - 150 ppm.

[0048] This example also provides an electrolyte, which includes 90 wt% of an organic solvent, 4 wt% of an additive, and 6 wt% of the electrolyte lithium salt described in this example;

[0049] The organic solvent includes dimethyl carbonate and ethylene carbonate with a volume ratio of 30:70, and the additive includes ethylene carbonate.

[0050] Example 2

[0051] This example provides an electrolyte lithium salt, and the electrolyte lithium salt is compound 6. The structural formula of compound 6 is shown as follows:

[0052]

[0053] The synthesis method of the compound 6 includes the following steps:

[0054] ​(1) Preparation of 1-(3-haloallyl)naphthalene: Using 1-naphthol as the starting material, under alkaline conditions (aqueous sodium hydroxide solution), a nucleophilic substitution reaction occurs with 3-bromopropene in acetone. The reaction temperature is controlled at 70 °C, and the reaction time is about 4 hours to produce 1-(3-haloallyl)naphthalene. The reaction equation is:

[0055]

[0056] (2) Preparation of lithium salt: React 1-(3-haloallyl)naphthalene with sodium sulfite (Na 2 SO 3 ) in a polar aprotic solvent (N,N-dimethylformamide, DMF). Heat to 100 °C and react for 8 hours. The halogen atom is replaced by the sulfite group to produce [C 13 H 10 SO 3 - Na + . The reaction equation is:

[0057]

[0058] (3) Lithiation reaction: React [C 13 H 10 SO 3 - Na + with metallic lithium in anhydrous tetrahydrofuran under argon protection. The reaction temperature is room temperature (about 25 °C), and the reaction time is 5 hours. The lithium ion replaces the sodium ion to obtain the target product [C 13 H 10 SO 2 - Li + . Side reactions such as redox reactions occur during the reaction, causing changes in the apparent oxidation state of sulfur.

[0059] The reaction equation is:

[0060] The infrared characteristic peaks of the prepared compound 6 are: 3000 - 3100 cm -1 (C-H stretching vibration), 1300 - 1380 cm -1 and 1150 - 1250 cm -1 (S=O stretching vibration), 1450 - 1600 cm -1 (aromatic ring skeletal vibration), and the alkenyl group is at 1620 - 1680 cm -1 (alkenyl C-C stretching vibration). 1 H-NMR: 7 - 8 ppm (naphthalene ring hydrogen), and the alkenyl hydrogen is at 4.5 - 6.5 ppm; 13 ​​​13C-NMR: 120 - 140 ppm (naphthalene ring carbon), vinylic carbon at 110 - 150 ppm.

[0061] This example also provides an electrolyte, which is the same as that in Example 1 except that the electrolyte lithium salt described in this example is used.

[0062] Example 3

[0063] This example provides an electrolyte lithium salt, which is Compound 7. The structural formula of Compound 7 is shown as follows:

[0064]

[0065] The synthesis method of Compound 7 includes the following steps:

[0066] (1) Synthesis of 2-(2-chlorovinyl)naphthalene: React naphthalene (C 10 H 8 ) with 2-chloroacetaldehyde in an ethanol solution of sodium hydroxide. Heat under reflux at 80 °C for 4 hours; first, naphthalene undergoes alkylation, and then elimination occurs under the action of a base to form 2-(2-chlorovinyl)naphthalene (C 12 H 9 Cl).

[0067] Reaction equation:

[0068] (2) Construction of a nitrogen-containing heterocyclic intermediate: React 2-(2-chlorovinyl)naphthalene (C 12 H 9 Cl) with 2-aminopyridine (C 5 H 6 N 2 ) in an N,N-dimethylformamide solvent of potassium carbonate, add cuprous iodide as a catalyst, heat to 120 °C, and react for 8 hours to undergo a nucleophilic substitution reaction to form a nitrogen-containing heterocyclic intermediate (C 12 H 10 N 2 ).

[0069] Chemical reaction equation:

[0070] (3) Lithiation reaction: Under anhydrous, oxygen-free, and argon-protected conditions, react the nitrogen-containing heterocyclic intermediate (C 12 H 10 N 2 ) with n-butyllithium (C 4 H 9 Li) in an anhydrous diethyl ether solvent at -78 °C for 3 hours to obtain the target product [C 12 H 9 N2 - Li + 。

[0071] Reaction equation:

[0072] The infrared characteristic peaks of the obtained compound 7 are: 3000 - 3100 cm -1 (C-H stretching vibration), 1600 - 1650 cm -1 (C=N stretching vibration), 1450 - 1600 cm -1 (Aromatic ring skeleton vibration); 1 H-NMR: 7 - 8 ppm (naphthalene ring hydrogen), 6 - 9 ppm (heterocyclic ring hydrogen); 13 C-NMR: 120 - 140 ppm (naphthalene ring carbon), 110 - 160 ppm (heterocyclic ring carbon).

[0073] This example also provides an electrolyte, which is the same as that in Example 1 except that the electrolyte lithium salt described in this example is used.

[0074] Example 4

[0075] This example provides an electrolyte lithium salt, and the electrolyte lithium salt is compound 8. The structural formula of compound 8 is shown as follows:

[0076]

[0077] The synthesis method of the compound 8 includes the following steps:

[0078] (1) Prepare 1-(2-chlorovinyl)naphthalene: React naphthalene (C 10 H 8 ) with paraformaldehyde and hydrogen chloride in the presence of anhydrous ZnCl 2 as a catalyst in 1,2-dichloroethane solvent. Heat to 100 °C and react for 4 hours to carry out chloromethylation reaction to generate 1-(chloromethyl)naphthalene; then under the action of the ethanol solution of strong base KOH, heat to 80 °C to carry out an elimination reaction to generate 1-(2-chlorovinyl)naphthalene (C 12 H 9 Cl).

[0079] Chloromethylation reaction equation: Elimination reaction equation:

[0080] (2) Construct a nitrogen-containing heterocyclic intermediate: React 1-(2-chlorovinyl)naphthalene (C 12 H 9 Cl) with 2-vinylpyridine (C 7 H​7 N) in bis(triphenylphosphine)palladium dichloride (PdCl 2 (PPh 3 ) 2 ) catalyzed by copper iodide as a co-catalyst and triethylamine as a base, the reaction was carried out in N,N-dimethylformamide solvent. The reaction was heated to 120°C and allowed to react for 8 hours to generate a nitrogen-containing heterocyclic intermediate (C 13 H 10 NCl); reaction equation:

[0081]

[0082] (3) Lithiation reaction: In anhydrous, oxygen-free and argon-protected conditions, the nitrogen-containing heterocyclic intermediate (C 13 H 10 NCl) reacts with metallic lithium in anhydrous ether solvent. The reaction temperature is controlled at 25°C and the reaction is carried out for 3 hours. Li replaces Cl and deprotonates the intermediate to obtain the target product [C 13 H 10 N] - Li + .

[0083] Chemical reaction equation:

[0084] The infrared characteristic peaks of the prepared compound 8 are: 3000~3100cm -1 (aromatic ring CH stretching vibration), 2900~3000cm -1 (unsaturated CH stretching vibration), 1450~1600cm -1 (naphthalene ring C=C skeleton vibration), 1600-1650cm -1 (nitrogen-containing heterocyclic CC stretching vibration), 1000-1300cm -1 (CN stretching vibration); 1H-NMR: 7-8 ppm (naphthalene ring hydrogen), 6-8 ppm (heterocyclic hydrogen), 4.5-6.5 ppm (alkenyl hydrogen). 13C-NMR: 120-140 ppm (naphthalene ring carbon), 110-160 ppm (heterocyclic carbon), 110-150 ppm (alkenyl carbon).

[0085] This embodiment further provides an electrolyte, which is the same as that of Embodiment 1 except that the electrolyte lithium salt described in this embodiment is used.

[0086] Example 5

[0087] This embodiment provides an electrolyte lithium salt, and the electrolyte lithium salt is the same as that in Embodiment 1;

[0088] This embodiment also provides an electrolyte. Except for including 88 wt% of organic solvent, 4 wt% of additive, and 8 wt% of the electrolyte lithium salt described in this embodiment, the rest are the same as those in Embodiment 1.

[0089] Embodiment 6

[0090] This embodiment provides an electrolyte lithium salt, which is the same as that in Embodiment 1;

[0091] This embodiment also provides an electrolyte. Except for including 84 wt% of organic solvent, 4 wt% of additive, and 12 wt% of the electrolyte lithium salt described in this embodiment, the rest are the same as those in Embodiment 1.

[0092] Embodiment 7

[0093] This embodiment provides an electrolyte lithium salt, which is the same as that in Embodiment 1;

[0094] This embodiment also provides an electrolyte. Except for including 80 wt% of organic solvent, 4 wt% of additive, and 16 wt% of the electrolyte lithium salt described in this embodiment, the rest are the same as those in Embodiment 1.

[0095] Embodiment 8

[0096] This embodiment provides an electrolyte lithium salt, which is the same as that in Embodiment 1;

[0097] This embodiment also provides an electrolyte. Except for including 93 wt% of organic solvent, 4 wt% of additive, and 3 wt% of the electrolyte lithium salt described in this embodiment, the rest are the same as those in Embodiment 1.

[0098] Embodiment 9

[0099] This embodiment provides an electrolyte lithium salt, which is the same as that in Embodiment 1;

[0100] This embodiment also provides an electrolyte. Except for including 80 wt% of organic solvent, 1 wt% of additive, and 19 wt% of the electrolyte lithium salt described in this embodiment, the rest are the same as those in Embodiment 1.

[0101] Embodiment 10

[0102] This embodiment provides an electrolyte lithium salt, which is the same as that in Embodiment 1;

[0103] This embodiment also provides an electrolyte. Except for including 74 wt% of organic solvent, 4 wt% of additive, and 22 wt% of the electrolyte lithium salt described in this embodiment, the rest is the same as that in Embodiment 1.

[0104] Comparative Example 1

[0105] This comparative example provides an electrolyte lithium salt, and the electrolyte lithium salt is lithium hexafluorophosphate;

[0106] This comparative example also provides an electrolyte. Except for using the electrolyte lithium salt described in this comparative example, the rest is the same as that in Embodiment 1.

[0107] Comparative Example 2

[0108] This comparative example provides an electrolyte lithium salt, and the electrolyte lithium salt is lithium naphthalide;

[0109] This comparative example also provides an electrolyte. Except for using the electrolyte lithium salt described in this comparative example, the rest is the same as that in Embodiment 1.

[0110] Assemble the electrolytes obtained in the above embodiments and comparative examples into lithium-ion batteries. The preparation method of the lithium-ion battery includes the following steps:

[0111] (1) Preparation of the positive electrode sheet:

[0112] Dissolve the positive electrode active material lithium nickel cobalt manganate (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ), Super-P, and PVDF in N-methylpyrrolidone in a mass ratio of 95.8:2.2:2.0 and mix them evenly to make a positive electrode slurry. Then, evenly coat the positive electrode slurry on the current collector aluminum foil, and the coating amount is 18 mg / cm 2 . Subsequently, dry it at 90 °C, then perform cold pressing, edge cutting, slicing, and slitting. After that, dry it in a vacuum at 90 °C for 4 h, and weld the tab to obtain the positive electrode sheet.

[0113] (2) Preparation of the negative electrode sheet:

[0114] Dissolve the negative electrode active material artificial graphite, Super-P, CMC, and SBR in deionized water in a mass ratio of 96.5:1.0:1.0:1.5 and mix them evenly to make a negative electrode slurry. Then, evenly coat the negative electrode slurry on the current collector copper foil, and the coating amount is 8.0 mg / cm 2 . Subsequently, dry it at 90 °C, then perform cold pressing, edge cutting, slicing, and slitting. After that, dry it in a vacuum at 110 °C for 4 h, and weld the tab to obtain the negative electrode sheet.

[0115] (3) Preparation of lithium-ion battery:

[0116] The positive electrode sheet, negative electrode sheet and separator (PE film) obtained above are made into a battery with a thickness of 8 mm, a width of 60 mm and a length of 130 mm through a stacking process, and vacuum baked at 90 °C for 10 h, the electrolytes of the above examples and comparative examples are injected, and then the lithium-ion battery is obtained after standing, pre-charging formation, degassing and sealing.

[0117] Ion conductivity tests are carried out on the electrolytes of the above examples and comparative examples, and high-temperature cycle performance and high-temperature capacity retention rate tests are carried out on the lithium-ion batteries prepared corresponding to the above examples and comparative examples. The test methods include:

[0118] (1) Test of electrolyte room temperature ion conductivity: The electrolyte is injected into the test cell with a pipette in an anhydrous and oxygen-free environment in the glove box to ensure that the electrodes are immersed and there are no bubbles, and then sealed and connected to an AC impedance spectrometer; set the parameters of the AC impedance spectrometer, where the starting frequency is 100 kHz, the ending frequency is 0.1 Hz, and the amplitude of the AC signal is 5 - 10 mV, and the test is carried out in an environment with a constant temperature of 25 °C, and the impedance data at different frequencies are automatically collected; after the test, the data is exported to obtain a complex impedance spectrum diagram, the intersection point of the fitted semicircle and the real axis is used to obtain the electrolyte resistance value, and at the same time the electrode area and spacing are measured. Finally, the ion conductivity of the electrolyte is calculated according to the formula κ = L / (R×A), where κ is the ion conductivity, L is the electrode spacing, R is the electrolyte resistance value, and A is the electrode area.

[0119] (2) Tests of the high-temperature storage capacity retention rate and capacity recovery rate of the battery at 55 °C: Initial capacity tests are carried out on the lithium-ion batteries obtained in the above examples and comparative examples, and the initial capacity value C of each battery is recorded. 0 The battery is placed in a high-temperature test chamber, and the temperature is set to 55 °C and stored for 30 days. Capacity tests are carried out on the battery under the same charge and discharge conditions, and the capacity value C after storage is recorded. 1 . Calculate the capacity retention rate: Capacity retention rate = (C 1 / C 0 )×100%; A complete charge and discharge cycle is carried out on the battery that has undergone high-temperature storage and capacity retention rate tests to activate the battery performance. The battery charge and discharge test equipment is used again, and capacity tests are carried out on the battery under the same charge and discharge conditions, and the recovered capacity value C 2 is recorded. Calculate the capacity recovery rate: Capacity recovery rate = (C 2 / C 0 )×100%;

[0120] High-temperature (45°C, 55°C) cycling performance test: Adjust the temperature of the test chamber to 45°C and 55°C respectively. Charge the battery to 4.3V at a constant current of 0.1C, then maintain a voltage of 4.3V until the charging current drops below 0.05C. Discharge the battery to 2.8V at a constant current of 0.1C. Repeat the above charging and discharging steps for 1000 cycles. Calculate the capacity retention rate of the battery after the 1000th cycle. Capacity retention rate = Discharge capacity after the 1000th cycle / Discharge capacity of the first cycle.

[0121] The test results are shown in Table 1 as follows:

[0122] Table 1

[0123]

[0124] It can be seen from Table 1 above that:

[0125] (1) From Examples 1-4 and Comparative Example 1, it can be known that the electrolyte lithium salt of the present invention has high ionic conductivity and can improve the high-temperature storage performance and high-temperature cycling performance of the battery. For the conventional lithium salt in Comparative Example 1, the capacity retention rate and recovery rate after storing at 55°C for 30 days are only 74.6% and 78.5% respectively. After adding the lithium salt in Examples 1-4 to the electrolyte, the battery performance is greatly improved. For example, in Example 3, they reach 97.5% and 99.0% respectively. In terms of high-temperature cycling stability, the capacity retention rates of Comparative Example 1 after 1000 cycles at 45°C and 1000 cycles at 55°C are 75.7% and 77.5% respectively, while in Example 3, they can reach 97.2% and 98.8% respectively; From Examples 1-4 and Comparative Example 2, it can be known that even if naphthalene lithium is used as the lithium salt, but it does not contain the functional groups of the present invention and cannot achieve the technical effects of the present invention, and its ionic conductivity and high-temperature performance are inferior to those of the present invention.

[0126] (2) Therefore, after adding the electrolyte lithium salt of the present invention to the electrolyte, on the one hand, it will form a stable and ion-conductive solid electrolyte interface film on the electrode surface. This film can prevent the further reaction between the electrolyte and the electrode material, reduce the corrosion of the electrode material and the decomposition of the electrolyte, thereby improving the stability of the battery at high temperature and ensuring the retention and recovery of the battery capacity during high-temperature storage and cycling; on the other hand, the lithium salt of the present invention may improve the ionic conduction ability of the electrolyte, enabling lithium ions to transfer more smoothly between the positive and negative electrodes during the charge and discharge process of the battery, which helps to improve the cycling stability and cycling life of the battery. As the mass percentage of the electrolyte lithium salt of the present invention increases within a certain range (as can be seen from Examples 1 and 5-10), the battery performance shows a further upward trend, which also indicates that at an appropriate addition amount, it can better play its positive role.

[0127] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. An electrolyte lithium salt, characterized in that The structural formula of the electrolyte lithium salt is as follows: Among them, R1 is selected from any one of P, N, S, B, BF2, PF3, O=S=O, BO, P=O, S=O, N=O or O=P-OH, and R2 is selected from N or C.

2. The electrolyte lithium salt according to claim 1, characterized in that The R1 is selected from any one of BF2, BO, PF3, O=S=O, P=O, O=P-OH or N; Preferably, R2 is selected from N.

3. The electrolyte lithium salt according to claim 1 or 2, characterized in that The electrolyte lithium salt includes any one or a combination of at least two of the following compounds 1 to 8:

4. An electrolyte, characterized in that: The electrolyte comprises the electrolyte lithium salt according to any one of claims 1 to 3.

5. The electrolyte according to claim 4, characterized in that In the electrolyte, the content of the electrolyte lithium salt is 5wt%-19wt%; Preferably, the electrolyte further comprises an organic solvent and an electrolyte additive.

6. The electrolyte according to claim 5, characterized in that In the electrolyte, the content of the organic solvent is 80wt%-90wt%; Preferably, the organic solvent comprises linear carbonate and / or cyclic carbonate; Preferably, the volume ratio of the linear carbonate to the cyclic carbonate is (15-30):(70-85).

7. The electrolyte according to claim 6, characterized in that The linear carbonate includes any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate or propyl acetate, or a combination of the two; Preferably, the cyclic carbonate includes any one of propylene carbonate, caprolactone or γ-butyrolactone, or a combination of both.

8. The electrolyte according to any one of claims 5 to 7, characterized in that: In the electrolyte, the content of the electrolyte additive is 1wt%-5wt%; Preferably, the electrolyte additive includes any one or a combination of at least two of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound or a borate compound.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte lithium salt as described in any one of claims 1 to 3, or comprises the electrolyte as described in any one of claims 4 to 7.

10. The lithium ion battery according to claim 9, characterized in that: The lithium-ion battery also includes a positive electrode sheet and a negative electrode sheet; Preferably, the positive electrode plate includes lithium transition metal oxide and / or lithium transition metal phosphate compound; Preferably, the negative electrode plate includes any one or a combination of at least two of a carbonaceous material, an alloy material, a metal composite material containing lithium, or metallic lithium.

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