Inner salt type organic lithium salt and preparation method thereof, lithium battery electrolyte and lithium battery

Abstract

The invention provides an inner salt type organic lithium salt with a structural formula (III). The inner salt type organic lithium salt can be used for a lithium battery electrolyte, and can be used for obtaining a lithium battery with excellent fast charge-discharge performance and cycling stability. Moreover, the inner salt type organic lithium salt also has the advantages of higher conductivity, milder synthesis conditions and higher compatibility with an electrolyte additive. The invention also provides a lithium battery electrolyte containing the inner salt type organic lithium salt and a lithium battery. The invention also provides a preparation method of the inner salt type organic lithium salt, and the mild synthesis condition is more beneficial to large-scale production. And # imgabs0 # (III).

Description

[0001] This application is a divisional application of application No. 202310023056.8, with a filing date of January 5, 2023 and an invention name of “Inner salt type organic lithium salt and preparation method thereof, lithium battery electrolyte and lithium battery”. Technical Field

[0002] The present invention relates to the field of electrochemical technology, and in particular to an inner salt type organic lithium salt, a lithium battery electrolyte and a lithium battery. Background Art

[0003] In recent years, with people's attention to climate change, air pollution and concerns about the depletion of non-renewable energy, the application technology of renewable clean energy has shown a booming development. As an efficient clean energy storage and output device, lithium batteries have the characteristics of high specific capacity, long cycle life, low self-discharge rate, and environmental friendliness. They are widely used in consumer electronics, new energy vehicles and other power battery products. Although the new energy vehicle market is growing rapidly, the satisfaction of power vehicle users with electric vehicles is still very limited. Compared with gasoline vehicles, the poor endurance and long charging time of new energy electric vehicles greatly reduce the economic benefits and time utilization of electric vehicle users, and severely limit the scope and number of user groups. Therefore, fast charging performance has become the main pursuit of batteries and electric vehicles. However, in conventional commercial batteries, high-rate charging is limited by factors such as slow lithium ion transmission kinetics in electrodes and electrolytes, large resistance polarization, accelerated electrolyte decomposition, and heat generated by ion migration that accelerates electrolyte decomposition side reactions, thereby reducing energy utilization efficiency and accelerating battery capacity decay and power degradation.

[0004] Chinese patent application CN202110944035.0 discloses an inner salt type organic lithium salt, which comprises a segment with strong complexing effect on lithium ions and a segment with strong electron-withdrawing ability, so as to have a strong ability to coordinate with lithium ions and promote the dissociation of other lithium salts. The inner salt type organic lithium salt is easy to participate in the formation of solid electrolyte interface (SEI) film and cathode electrolyte interface (CEI) film, which is beneficial to lithium ion conduction and can improve the fast charging performance and cycle stability of lithium batteries. However, the compatibility of this lithium salt and some lithium battery additives such as fluoroethylene carbonate is general, and the requirements for synthesis conditions are high, which is not easy to mass produce.

[0005] There remains a need for improvements in lithium batteries and electrolyte materials used therein. Summary of the invention

[0006] In one aspect, the present invention provides an inner salt type organic lithium salt having the following general structural formula:

[0007] (I) or (II)

[0008] in,

[0009] R1 is ,

[0010] Where R 11 -(CH2) m CH3 or -(CH2) p (CF2) q CF3, m, p, q are integers between 0 and 10,

[0011] X is O, N, S, P or C,

[0012] Y 11 , Y 12 , Y 13 , Y 14 are independently selected from the group consisting of: H, F, Cl, Br, I, -CH[(CH2) a (CH2CH2O) b CH3]2 and -(CH2) c (CH2CH2O) d CH3, wherein a and c are integers between 0 and 10, and b and d are integers between 0 and 5;

[0013] n is an integer between 1 and 12.

[0014] R2 is -CN or -SO2(CH2) e (CF2) f F, e, and f are all integers between 0 and 10.

[0015] Preferably, R in R1 11 is -CH3 or -CH2CF2CF3, n is an integer from 1 to 5, X is O,

[0016] R2 is -CN, -SO2F or -SO2CF3.

[0017] Preferably, the inner salt type organic lithium salt is:

[0018] (III)

[0019] (IV),

[0020] (V),

[0021] (VI)

[0022] (VII)

[0023] (VIII), or

[0024] (IX).

[0025] In another aspect, the present invention provides a lithium battery electrolyte, which includes the above-mentioned inner salt type organic lithium salt.

[0026] Preferably, the mass percentage content of the inner salt type organic lithium salt in the lithium battery electrolyte is in the range of 0.01-80%.

[0027] Preferably, the lithium battery electrolyte further comprises an organic solvent and a lithium salt different from the inner salt type organic lithium salt.

[0028] Preferably, the lithium battery electrolyte further comprises an additive selected from the group consisting of fluoroethylene carbonate, lithium nitrate, lithium perchlorate, lithium sulfate, lithium difluorooxalatoborate, lithium carbonate, and combinations thereof.

[0029] Preferably, the lithium salt different from the inner salt type organic lithium salt is selected from the group consisting of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium tetrafluoroborate and lithium bis(oxalatoborate), and combinations thereof; and

[0030] The organic solvent is a mixture including at least two selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane.

[0031] Preferably, the lithium salt different from the inner salt type organic lithium salt is lithium hexafluorophosphate;

[0032] The organic solvent is a mixture of ethylene carbonate and diethyl carbonate;

[0033] The additive is a mixture of fluoroethylene carbonate and lithium nitrate.

[0034] In another aspect, the present invention provides a lithium battery, wherein the lithium battery comprises:

[0035] positive electrode;

[0036] negative electrode;

[0037] a separator between the positive electrode and the negative electrode; and

[0038] The above-mentioned lithium battery electrolyte is in contact with the positive electrode and the negative electrode.

[0039] In yet another aspect, the present invention provides a method for preparing the above-mentioned inner salt type organic lithium salt, wherein the method comprises the following steps:

[0040] The first step is to react sulfonyl chloride or an acyl chloride compound with a sulfonamide or a cyanoamine compound at room temperature in the presence of potassium carbonate to obtain a potassium salt intermediate;

[0041] In the second step, the potassium salt intermediate obtained in the first step is subjected to a salt exchange reaction with lithium perchlorate or lithium tetrafluoroborate at room temperature to obtain the inner salt type organic lithium salt. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The voltage-time diagram of the Li||Cu battery in Example 3 of the present invention is shown.

[0043] Figure 2 The voltage-time diagram of the Li||Cu battery in Comparative Example 3 of the present invention is shown.

[0044] Figure 3 The cycle diagrams of Example 3 of the present invention and Comparative Example 3 under 2C conditions in a Li||NCM811 full battery are shown. DETAILED DESCRIPTION

[0045] The present invention provides an inner salt type organic lithium salt and a preparation method thereof, a lithium battery electrolyte and a lithium battery. The inner salt type organic lithium salt of the present invention can be used in a lithium battery electrolyte, and can be used to obtain a lithium battery with excellent fast charge and discharge performance and cycle stability. Moreover, the inner salt type organic lithium salt of the present invention has the advantages of higher conductivity, milder synthesis conditions, and higher compatibility with electrolyte additives. The present invention also proposes a lithium battery electrolyte and a lithium battery containing the inner salt type organic lithium salt. The present invention also proposes a preparation method of the inner salt type organic lithium salt, and its mild synthesis conditions are more conducive to large-scale production.

[0046] The present invention provides an inner salt type organic lithium salt having the following general structural formula:

[0047] (I) or (II)

[0048] in,

[0049] R1 is ,

[0050] Where R 11 -(CH2) m CH3 or -(CH2) p (CF2) q CF3, m, p, q are integers between 0 and 10,

[0051] X is O, N, S, P or C,

[0052] Y 11 , Y 12 , Y 13 , Y 14 are independently selected from the group consisting of: H, F, Cl, Br, I, -CH[(CH2) a (CH2CH2O) b CH3]2 and -(CH2) c (CH2CH2O) d CH3, wherein a and c are integers between 0 and 10, and b and d are integers between 0 and 5;

[0053] n is an integer between 1 and 12.

[0054] R2 is -CN or -SO2(CH2) e (CF2) f F, e, and f are all integers between 0 and 10.

[0055] The present invention improves the performance of lithium batteries by improving the electrolyte in lithium batteries. The inner salt type organic lithium salt can be used as the electrolyte itself in the lithium battery electrolyte, and can also be used as an additive for other types of electrolytes. The inner salt type organic lithium salt is easy to participate in the formation of SEI film and CEI film, generating CEI and SEI that are conducive to lithium ion conduction, thereby improving the fast charging performance and cycle stability of lithium batteries.

[0056] The inner salt type organic lithium salt of the present invention is composed of lithium ions, nitrogen atoms, group R1, group R2, and a sulfone group or a carbonyl group connecting the nitrogen atom and the group R1.

[0057] The nitrogen atom, after being linked to the group R2, the sulfone group or the carbonyl group and the group R1, forms a negatively charged ligand which can form a lithium salt with a lithium ion.

[0058] The group R1 comprises a segment having n structural units and R as a terminal group. 11 , where the main chain of the structural unit contains an X atom and two Y 11 , Y 12 , Y 13 , Y 14 C atom as a substituent. Such a group R1 has a strong complexing effect on lithium ions.

[0059] Wherein, the X atom on the main chain of the structural unit is O, N, S, P or C. In particular, when the X atom is O, the group R1 has a stronger complexing effect on lithium ions. In the present invention, an appropriate number of hydrogen atoms are connected to the X atom in the structural formula. For example, when the X atom is a nitrogen atom, the nitrogen atom is also connected to a hydrogen atom; when the X atom is a carbon atom, the carbon atom is also connected to two hydrogen atoms.

[0060] Y is connected to the two C atoms of the main chain of the structural unit. 11 , Y 12 , Y 13 , Y 14 , which can be hydrogen, halogen or a specific branching group. The branching group is selected from -CH[(CH2) a (CH2CH2O) b CH3]2 and -(CH2) c (CH2CH2O) d CH3, wherein a and c are integers within the range of 0 to 10, and b and d are integers within the range of 0 to 5. The presence of a -CH2CH2O- segment in the branched group can further enhance the complexing effect on lithium ions.

[0061] X, Y in the n structural units in the group R1 11 , Y 12 , Y 13 , Y 14 The structural units may be different from each other, that is, the structural units may be similar to each other but not completely repeated.

[0062] The group R1 also has as a terminal group R 11 . R 11 -(CH2) m CH3 or -(CH2) p (CF2) q CF3, m, p, q are integers within the range of 0 to 10. Such an end group cooperates with the above-mentioned segment having n structural units to provide a strong complexing effect on lithium ions. When the end of the end group is CF3, it has a particularly strong complexing effect on lithium ions.

[0063] The groups R2 are all groups with strong electron-withdrawing ability, among which -SO2CF3 has a particularly strong electron-withdrawing ability.

[0064] The R1 group in the inner salt type organic lithium salt of the present invention has a strong complexing effect on lithium ions, and the R2 group has a strong electron-withdrawing ability. Therefore, having both R1 and R2 groups provides a strong coordination ability with lithium ions, and can also promote the dissociation of lithium salts such as lithium carbonate, alkyl lithium carbonate, and lithium nitrate. The organic lithium salt with such a structure can participate in the dissolution of organic lithium salts with poor mechanical strength and weaker lithium ion conductivity in SEI and CEI, thereby generating inorganic-rich CEI and SEI that are conducive to lithium ion conduction, thereby improving the fast charging performance and cycle stability of lithium batteries.

[0065] The inner salt type organic lithium salt of the present invention particularly comprises a sulfone group or a carbonyl group connecting the R1 group and the nitrogen atom. The inventors of the present invention have found that the introduction of an electron-withdrawing sulfone group or a carbonyl group between the nitrogen atom and the R1 group can help reduce the charge density around the nitrogen atom, achieve a better electron delocalization effect, thereby reducing the charge interaction between the anion and the lithium ion in the lithium salt, achieving better dissociation of the lithium salt in an organic solvent, and thus obtaining a higher conductivity.

[0066] Preferably, R in R1 11 is -CH3 or -CH2CF2CF3, n is an integer between 1 and 5, X is O, and R2 is -CN or -SO2CF3. The preferred reason is that R 11 When it is -CH3, the raw materials are easier to obtain, and when it is -CH2CF2CF3, it can help improve the pressure resistance of lithium salts. n is an integer between 1 and 5 to ensure the ability of the repeating unit to complex lithium ions while avoiding the problem of excessive viscosity and low conductivity of the electrolyte containing the lithium salt configured later. X is O because the ethoxy group has a stronger complexing ability for lithium ions, and R2 is -CN or -SO2CF3 electron-withdrawing groups, which can reduce the negative charge density of anions through the electron-withdrawing effect and improve the dissociation of lithium salts in organic electrolytes.

[0067] The inner salt type organic lithium salt of the present invention has the advantages of better dissociation and higher conductivity due to the introduction of sulfone group or carbonyl group, and also has the advantage of being prepared under milder synthesis conditions, which is more conducive to large-scale production. Mild synthesis conditions are very advantageous in terms of cost, environmental protection and process.

[0068] More preferably, the inner salt type organic lithium salt is:

[0069] (III)

[0070] (IV),

[0071] (V),

[0072] (VI)

[0073] (VII)

[0074] (VIII), or

[0075] (IX).

[0076] These preferred inner salt type organic lithium salts have excellent performance and are easier to synthesize in terms of raw material cost and process.

[0077] The present invention provides a method for preparing the inner salt type organic lithium salt, wherein the method comprises the following steps:

[0078] The first step is to react sulfonyl chloride or an acyl chloride compound with a sulfonamide or a cyanoamine compound at room temperature in the presence of potassium carbonate to obtain a potassium salt intermediate;

[0079] In the second step, the potassium salt intermediate obtained in the first step is subjected to a salt exchange reaction with lithium perchlorate or lithium tetrafluoroborate at room temperature to obtain the inner salt type organic lithium salt.

[0080] The reaction formula is as follows.

[0081] The first step is to form the following potassium salt intermediate in the presence of potassium carbonate.

[0082] Sulfonyl chloride compounds react with sulfonamide or cyanamide compounds:

[0083] R1S(O)2Cl+NH2R2—> R1S(O)2NR2 - K +

[0084] Among them, when R2 is -SO2(CH2) e (CF2) f When F is a sulfonamide compound, it reacts with a sulfonamide compound. When R2 is -CN, it reacts with a cyanamide compound.

[0085] Reaction of acyl chloride compounds with sulfonamide or cyanamide compounds:

[0086] R1C(O)Cl+NH2R2—> R1C(O)NR2 - K +

[0087] Among them, when R2 is -SO2(CH2) e (CF2) f When F is a sulfonamide compound, it reacts with a sulfonamide compound. When R2 is -CN, it reacts with a cyanamide compound.

[0088] Step 2: Salt exchange the potassium salt intermediate with LiClO4 or LiBF4 to obtain R1S(O)2NR2 - Li + or R1S(O)2NR2 - Li + .

[0089] The present invention prepares an inner salt type organic lithium salt by means of a potassium salt intermediate. The potassium salt intermediate can be obtained in the presence of potassium carbonate. The R1 group is provided by the above-mentioned sulfonyl chloride or acyl chloride compound, and the R2 group is provided by the above-mentioned sulfonamide or cyanoamine compound. The two react with potassium carbonate at room temperature, and the generated potassium salt intermediate can be converted into a lithium salt by a subsequent salt exchange reaction. Normal temperature can also be referred to as room temperature. The method of the present invention can be implemented without special heating.

[0090] In the method of the present invention, potassium carbonate is selected to form potassium salt because potassium carbonate and the product after neutralization with proton hydrogen have low solubility in organic solvents, which is conducive to subsequent purification.

[0091] The reaction can be carried out in a solvent such as acetonitrile, dichloromethane, tetrahydrofuran, etc. Preferred solvents include acetonitrile.

[0092] In one embodiment, the preparation method of the inner salt type organic lithium salt (III) comprises the following steps:

[0093] In the first step, in the presence of potassium carbonate, CH3(OCH2CH2)3SO2Cl reacts with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 12-24 hours.

[0094] In the second step, the potassium salt intermediate product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate or lithium tetrafluoroborate to obtain the target product. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 4-12 hours.

[0095] In one embodiment, the preparation method of the inner salt type organic lithium salt (IV) comprises the following steps:

[0096] In the first step, in the presence of potassium carbonate, CH3(OCH2CH2)3SO2Cl reacts with cyanamide to obtain the corresponding potassium salt intermediate. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 12-24 hours.

[0097] In the second step, the potassium salt intermediate product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate or lithium tetrafluoroborate to obtain the target product. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 4-12 hours.

[0098] In one embodiment, the preparation method of the inner salt type organic lithium salt (V) comprises the following steps:

[0099] In the first step, in the presence of potassium carbonate, CF3CF2CH2OCH2CH2SO2Cl reacts with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 12-24 hours.

[0100] In the second step, the potassium salt intermediate product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate or lithium tetrafluoroborate to obtain the target product. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 4-12 hours.

[0101] In one embodiment, the preparation method of the inner salt type organic lithium salt (VI) comprises the following steps:

[0102] In the first step, in the presence of potassium carbonate, CH3(OCH2CH2)3COCl reacts with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 12-24 hours.

[0103] In the second step, the potassium salt intermediate product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate or lithium tetrafluoroborate to obtain the target product. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 4-12 hours.

[0104] In one embodiment, the preparation method of the inner salt type organic lithium salt (VII) comprises the following steps:

[0105] In the first step, in the presence of potassium carbonate, CH3(SCH2CH2)3SO2Cl reacts with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 12-24 hours.

[0106] In the second step, the potassium salt intermediate product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate or lithium tetrafluoroborate to obtain the target product. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 4-12 hours.

[0107] In one embodiment, the preparation method of the inner salt type organic lithium salt (IX) comprises the following steps:

[0108] In the first step, in the presence of potassium carbonate, CH3(OCH2CH2) 12 SO2Cl reacts with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 12-24 hours.

[0109] In the second step, the potassium salt intermediate product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate or lithium tetrafluoroborate to obtain the target product. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 4-12 hours.

[0110] From the reaction conditions of the above embodiments, it can be seen that the lithium salt having a sulfone group or a carbonyl group between the nitrogen atom and the R1 group of the present invention has the following three main advantages in synthesis:

[0111] First, the first step in the synthesis of the lithium salt of the present invention is to react sulfonyl chloride or an acyl chloride compound with a sulfonamide or a cyanoamine compound at room temperature, which is mild and has few side reactions. In contrast, when a lithium salt is prepared without a sulfone group or a carbonyl group between the R1 group and the nitrogen atom, the reaction is violent and there are many by-products. For example, when R2 is -SO2CF3, if the R1 group and the nitrogen atom are directly connected, its preparation method requires the reaction of trifluoromethanesulfonic anhydride with an amine compound. The reaction is very violent at room temperature, so it needs to be carried out at a low temperature of, for example, -78°C, and the reaction conditions are harsh.

[0112] Secondly, the second step in the synthesis of the lithium salt of the present invention is to carry out a salt exchange reaction between the potassium salt obtained by the first step and LiBF4 or LiClO4, and the reaction conditions are also mild and can be carried out at room temperature. In contrast, when preparing a lithium salt that does not contain a sulfone group or a carbonyl group between the R1 group and the nitrogen atom, lithium hydride is required to dehydrogenate the imine compound to obtain the corresponding lithium salt. The reaction is relatively violent, involving the use of lithium hydride and the generation of hydrogen, and the safety is worse.

[0113] Third, in the preparation process of the lithium salt without sulfone group or carbonyl group between the R1 group and the nitrogen atom, if a reaction pathway similar to the present invention is adopted, the sulfonamide compound is reacted with a chlorine-containing terminal compound without sulfone group or carbonyl group in the first step. Since the reaction activity of the compound containing only chlorine terminal group is much lower than that of the acyl chloride or sulfonyl chloride compound, the reaction usually faces the problem of low yield or more stringent reaction conditions.

[0114] Therefore, the organic lithium salt of the present invention not only has excellent performance, but can also be prepared under mild reaction conditions, and has great advantages in process and cost.

[0115] The present invention also provides a lithium battery electrolyte, comprising the inner salt type organic lithium salt. The inner salt type organic lithium salt of the present invention can be used as a lithium salt electrolyte in the electrolyte, or as an additive other than the lithium salt electrolyte in the electrolyte. It should be noted that the inner salt type organic lithium salt is used as a lithium salt electrolyte or additive, and it does not exclude that the electrolyte also includes other components that can be used as lithium salt electrolytes or additives.

[0116] Further, the mass percentage of the inner salt type organic lithium salt is 0.01-80%. When the inner salt type organic lithium salt is used as the main salt, the preferred mass fraction is 30%-80%. When the inner salt type organic lithium salt is used as an additive, its preferred amount is within 20%, more preferably 1%-10%. The mass percentage mentioned here is based on the mass of the lithium battery electrolyte.

[0117] In a specific embodiment of the present invention, the lithium battery electrolyte further comprises an organic solvent and a lithium salt different from the inner salt type organic lithium salt. When the inner salt type organic lithium salt is used as an additive in the lithium battery electrolyte, the lithium salt different from the inner salt type organic lithium salt can be used as a lithium salt electrolyte.

[0118] Further, the lithium battery electrolyte also includes an additive, and the additive is selected from the group consisting of the following items: lithium nitrate, fluoroethylene carbonate, lithium difluorooxalate borate, lithium perchlorate, lithium sulfate, lithium carbonate, and combinations thereof. When the inner salt type organic lithium salt of the present invention is used as an additive or a first additive, these additives may be common additives or second additives. The present invention has found that when the inner salt type organic lithium salt provided by the present invention is used as an additive, it is used in combination with the above-mentioned common additive, and it is better in the fast charging performance of the whole battery. More preferred common additives include lithium nitrate, fluoroethylene carbonate, and lithium difluorooxalate borate. Lithium nitrate can generate an inorganic interface rich in nitrides to reduce the nucleation overpotential of lithium metal, fluoroethylene carbonate can synergistically generate an interface rich in lithium fluoride inorganic compounds, and lithium difluorooxalate borate can generate a boron-containing interface on the positive electrode surface to improve the stability of the positive electrode. When the inner salt type organic lithium salt of the present invention is used in common with lithium nitrate as an additive, it can increase the solubility of lithium nitrate in the electrolyte, and the two play a synergistic role to further improve the battery performance. Particularly unexpectedly, fluoroethylene carbonate has a higher compatibility with the inner salt type organic lithium salt of the present invention, and can form a stable and uniform electrolyte. The lithium battery electrolyte containing both fluoroethylene carbonate and the inner salt type organic lithium salt of the present invention can also exert a synergistic effect, thereby improving the fast charging performance and cycle stability of the lithium battery. The advantage of the inner salt type organic lithium salt of the present invention and lithium difluorooxalatoborate is that while maintaining the stability of the negative electrode, the cycle performance of the battery is further improved by constructing a stable interface of the positive electrode.

[0119] Further, when a lithium salt different from the inner salt type organic lithium salt is used as the lithium salt electrolyte, it is preferably selected from the group consisting of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium tetrafluoroborate, lithium nitrate and combinations thereof.

[0120] Further, the organic solvent is a mixture comprising at least two selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and 1,3-dioxolane.

[0121] In a preferred embodiment of the present invention, the lithium salt electrolyte is lithium hexafluorophosphate;

[0122] The organic solvent is a mixture of ethylene carbonate and diethyl carbonate;

[0123] The additives are fluoroethylene carbonate and lithium nitrate.

[0124] The advantage of this preferred embodiment is that the introduction of the inner salt type lithium salt of the present invention into the traditional carbonate electrolyte formula can promote the dissociation of lithium nitrate which is insoluble in the traditional carbonate electrolyte. Lithium nitrate can generate an inorganic interface rich in nitride, reducing the overpotential of lithium metal nucleation. Fluorinated ethylene carbonate can synergistically generate an interface rich in lithium fluoride inorganic compounds in a stable system, further improving the cycle performance of the battery.

[0125] The organic lithium salt of the present invention can participate in dissolving organic lithium salts with poor mechanical strength and weaker lithium ion conductivity in SEI and CEI, thereby generating inorganic-rich CEI and SEI that are conducive to lithium ion conduction, thereby improving the fast charging performance and cycle stability of lithium batteries.

[0126] The present invention also provides a lithium battery, comprising a positive electrode; a negative electrode; a separator between the positive electrode and the negative electrode; and the above-mentioned lithium battery electrolyte in contact with the positive electrode and the negative electrode. The lithium battery has good fast charging performance and cycle stability. The positive electrode is preferably a ternary positive electrode material (such as LiMn 1-x-y Ni x Co y O2, wherein 0<x<1, 0<y<1, and x+y<1) and lithium iron phosphate positive electrode material (LFP), etc., but not limited thereto. The negative electrode can be a carbonaceous negative electrode.

[0127] The shape of the battery of the present invention is not limited, and can be a cylinder, an aluminum shell, a plastic shell or a soft package shell.

[0128] The present invention provides an inner salt type organic lithium salt and a preparation method thereof, a lithium battery electrolyte and a lithium battery. The advantages of the inner salt type organic lithium salt include but are not limited to: due to the R1 group with strong complexing effect on lithium ions and the R2 group with strong electron-withdrawing ability, it has a strong ability to coordinate with lithium ions and promote the dissociation of other lithium salts; it is easy to participate in the formation of SEI film and CEI film, and generate CEI and SEI that are conducive to lithium ion conduction, thereby improving the fast charging performance and cycle stability of the lithium battery; the electron-withdrawing sulfone group or carbonyl group between the nitrogen atom and the R1 group can help lithium ions and nitrogen atoms to significantly dissociate, thereby significantly improving the conductivity; due to the presence of the sulfone group or carbonyl group, it can be synthesized in a milder route, which is more conducive to large-scale production; it has higher compatibility with fluoroethylene carbonate, and can exert a synergistic effect to further improve the fast charging performance and cycle stability of the lithium battery.

[0129] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0130] The organic solvents, lithium salt electrolytes and commercial additives used in the examples and comparative examples of the present invention are all of battery grade. The inner salt type organic lithium salt prepared by the present invention is subjected to multi-step purification and strict drying.

[0131] The electrolytes involved in the present invention are all prepared in a glove box with an argon atmosphere and a moisture content of less than 0.1 ppm. The positive electrode, negative electrode, diaphragm and other battery components are dried at a specific temperature. The solution preparation and battery assembly are all carried out at room temperature.

[0132] Synthesis Example 1

[0133] This embodiment provides an inner salt type organic lithium salt, and its structural formula is as follows:

[0134] ( )

[0135] The preparation method is as follows:

[0136] In the first step, in the presence of potassium carbonate, commercially available CH3(OCH2CH2)3SO2Cl is reacted with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate product. Acetonitrile can be used as the reaction solvent in this step, the reaction temperature is room temperature, and the reaction time is 12h. In the second step, the potassium salt product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate to obtain the target product. Acetonitrile can be used as the reaction solvent, the reaction temperature is room temperature, and the reaction time is 6h. The specific reaction formula is as follows:

[0137]

[0138] The obtained lithium salt H NMR spectrum:

[0139] 1 H-NMR (300 M, DMSO-d6, δ / ppm): 3.93 (2H); 3.58 (2H); 3.55-3.52 (8H); 3.40 (3H).

[0140] Synthesis Example 2

[0141] This embodiment provides an inner salt type organic lithium salt, and its structural formula is as follows: ( )

[0142] The preparation method is as follows:

[0143] In the first step, commercially available CH3(OCH2CH2)3SO2Cl is reacted with cyanamide in the presence of potassium carbonate to obtain a potassium salt intermediate. Acetonitrile can be used as the reaction solvent in this step, the reaction temperature is room temperature, and the reaction time is 12 hours. In the second step, the intermediate product prepared in the first step is reacted with lithium perchlorate at room temperature to obtain the target compound. Acetonitrile can be used as the reaction solvent, the reaction temperature is room temperature, and the reaction time is 6 hours.

[0144]

[0145] The obtained lithium salt H NMR spectrum:

[0146] 1 H-NMR (300 M, DMSO-d6, δ / ppm): 3.93 (2H); 3.58 (2H); 3.55-3.52 (8H); 3.40 (3H).

[0147] Synthesis Example 3

[0148] This embodiment provides an inner salt type organic lithium salt, and its structural formula is as follows:

[0149] ( )

[0150] The specific preparation method is as follows:

[0151] In the first step, commercially available CF3CF2CH2OCH2CH2SO2Cl is reacted with trifluoromethanesulfonamide in the presence of potassium carbonate to obtain the corresponding potassium salt intermediate. The reaction solvent in this step can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 12h. In the second step, the potassium salt intermediate prepared in the first step is reacted with lithium perchlorate to obtain the target compound. The reaction solvent can be acetonitrile, the reaction temperature is room temperature, and the reaction time is 6h:

[0152]

[0153] The obtained lithium salt H NMR spectrum:

[0154] 1 H-NMR (300 M, DMSO-d6, δ / ppm): 3.93 (2H); 3.67 (2H); 3.58 (2H).

[0155] Synthesis Example 4

[0156] This embodiment provides an inner salt type organic lithium salt, and its structural formula is as follows:

[0157] ( )

[0158] The specific preparation method is as follows:

[0159] In the first step, in the presence of potassium carbonate, commercially available CH3(OCH2CH2)3COCl is reacted with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate product. Acetonitrile can be used as the reaction solvent in this step, the reaction temperature is room temperature, and the reaction time is 12h. In the second step, the potassium salt product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate to obtain the target product. Acetonitrile can be used as the reaction solvent, the reaction temperature is room temperature, and the reaction time is 6h. The specific reaction formula is as follows:

[0160]

[0161] The obtained lithium salt H NMR spectrum:

[0162] 1 H-NMR (300 M, DMSO-d6, δ / ppm): 3.67 (2H); 3.55-3.52 (8H); 3.40 (3H); 2.57 (2H).

[0163] Synthesis Example 5

[0164] This embodiment provides an inner salt type organic lithium salt, and its structural formula is as follows:

[0165] ( )

[0166] The preparation method is as follows:

[0167] In the first step, in the presence of potassium carbonate, commercially available CH3(SCH2CH2)3SO2Cl is reacted with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate product. Acetonitrile can be used as the reaction solvent in this step, the reaction temperature is room temperature, and the reaction time is 12h. In the second step, the potassium salt product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate to obtain the target product. Acetonitrile can be used as the reaction solvent, the reaction temperature is room temperature, and the reaction time is 6h. The specific reaction formula is as follows:

[0168]

[0169] The obtained lithium salt H NMR spectrum:

[0170] 1 H-NMR (300 M, DMSO-d6, δ / ppm): 3.78 (2H); 3.00 (2H); 2.81 (8H); 2.07(3H).

[0171] Synthesis Example 6

[0172] This embodiment provides an inner salt type organic lithium salt, and its structural formula is as follows:

[0173] ( )

[0174] The preparation method is as follows:

[0175] In the first step, in the presence of potassium carbonate, commercially available CH3(OCH2CF2)3SO2Cl is reacted with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate product. Acetonitrile can be used as the reaction solvent in this step, the reaction temperature is room temperature, and the reaction time is 12h. In the second step, the potassium salt product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate to obtain the target product. Acetonitrile can be used as the reaction solvent, the reaction temperature is room temperature, and the reaction time is 6h. The specific reaction formula is as follows:

[0176]

[0177] The obtained lithium salt H NMR spectrum:

[0178] 1 H-NMR (300 M, DMSO-d6, δ / ppm): 4.25 (2H); 3.00 (2H); 3.86 (4H); 3.23(3H).

[0179] Synthesis Example 7

[0180] This embodiment provides an inner salt type organic lithium salt, and its structural formula is as follows:

[0181] (IX)

[0182] The preparation method is as follows:

[0183]

[0184] In the first step, commercially available CH3(OCH2CH2) 12 SO2Cl reacts with trifluoromethanesulfonamide to obtain the corresponding potassium salt intermediate product. Acetonitrile can be used as the reaction solvent in this step, the reaction temperature is room temperature, and the reaction time is 12h. In the second step, the potassium salt product prepared in the first step is subjected to salt exchange reaction with lithium perchlorate to obtain the target product. Acetonitrile can be used as the reaction solvent, the reaction temperature is room temperature, and the reaction time is 6h. The specific reaction formula is as follows:

[0185] The obtained lithium salt H NMR spectrum:

[0186] 1 H-NMR (300 M, DMSO-d6, δ / ppm): 3.93 (2H); 3.58 (2H); 3.55 (2H); 3.52(42H); 3.40 (3H)

[0187] Example 1

[0188] This embodiment provides a kind of organic lithium salt containing the above inner salt type ( ) of lithium battery electrolyte, which is prepared as follows:

[0189] Take 18.2g of the above organic lithium salt ( ) and 50 ml of a mixture of ethylene carbonate / diethyl carbonate (volume ratio = 1:1), and mixed thoroughly to obtain the electrolyte of Example 1.

[0190] Example 2

[0191] This embodiment provides a kind of organic lithium salt containing the above inner salt type ( ) of lithium battery electrolyte, which is prepared as follows:

[0192] Take 7.6g of lithium hexafluorophosphate, 50ml of ethylene carbonate / diethyl carbonate mixture (volume ratio = 1:1), 2.5ml of fluoroethylene carbonate and 1.82g of the above organic lithium salt ( ), and fully mixed to obtain the electrolyte of Example 2, which is in a uniform and stable state.

[0193] Example 3

[0194] This embodiment provides a kind of organic lithium salt containing the above inner salt type ( ) Lithium battery electrolyte combined with other additives is prepared as follows:

[0195] Take 7.6g lithium hexafluorophosphate, 0.35g lithium nitrate, 50ml ethylene carbonate / diethyl carbonate mixture (volume ratio = 1:1), 2.5ml fluoroethylene carbonate and 1.82g of the above organic lithium salt ( ), and mix thoroughly to obtain the electrolyte of Example 3.

[0196] Comparative Example 1

[0197] This comparative example provides a lithium battery electrolyte containing an inner salt type organic lithium salt disclosed in CN202110944035.0. The structure of the organic lithium salt is as follows:

[0198] (X).

[0199] The lithium battery electrolyte is prepared as follows:

[0200] 15.0 g of an organic lithium salt (X) and 50 ml of a mixture of ethylene carbonate and diethyl carbonate (volume ratio = 1:1) were taken and mixed thoroughly to obtain an electrolyte of Comparative Example 1.

[0201] Comparative Example 2

[0202] This comparative example provides a lithium battery electrolyte containing the inner salt type organic lithium salt (X), which is formulated as follows:

[0203] 7.6 g of lithium hexafluorophosphate, 50 ml of a mixture of ethylene carbonate / diethyl carbonate (volume ratio = 1:1), 2.5 ml of fluoroethylene carbonate and 1.5 g of the above-mentioned organic lithium salt (X) were mixed thoroughly to obtain an electrolyte of Comparative Example 2. As a result, it was observed that the solution gradually changed from a colorless state to a brown-yellow state.

[0204] Comparative Example 3

[0205] This comparative example provides a lithium battery electrolyte comprising the inner salt type organic lithium salt (X) and other additives, which is formulated as follows:

[0206] 7.6 g of lithium hexafluorophosphate, 0.35 g of lithium nitrate, 50 ml of a mixture of ethylene carbonate / diethyl carbonate (volume ratio = 1:1), and 1.5 g of the above-mentioned organic lithium salt (X) were mixed thoroughly to obtain an electrolyte of Comparative Example 3.

[0207] Battery cycle performance test

[0208] The lithium battery electrolytes obtained in the examples and comparative examples were used to assemble batteries, and the cycle performance was tested after standing overnight. In order to evaluate the conductivity, Celgard 2325 type diaphragm was used to assemble a stainless steel-to-stainless steel symmetrical battery, and the conductivity of the electrolyte in the presence of the diaphragm was calculated by measuring the battery impedance. In order to evaluate the performance of the lithium metal side, a lithium sheet was used as the negative electrode and copper as the positive electrode to assemble a lithium-copper half-cell. In terms of rate performance testing, the positive electrode of the battery is LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) powder is the active material, which is coated on the current collector after being mixed with a binder and conductive carbon powder. The negative electrode is lithium metal, and the separator model is Celgard 2325. The assembled full battery was charged and discharged at 0.1 C, 2.8 V to 4.3 V at room temperature, and then the cycle stability was tested at a constant rate of 2 C and 3 C; the test results are shown in Tables 1 to 3 and Figures 1 to 3 .

[0209] Table 1 Conductivity of electrolyte in Example 1 and Comparative Example 1 with diaphragm

[0210] Group Conductivity with diaphragm (mS / cm) Example 1 0.10 Comparative Example 1 0.03

[0211] Table 2 Solution states of Example 2 and Comparative Example 2

[0212] Group Solution state Example 2 Uniform and transparent Comparative Example 2 Transparent gradually turns to brown

[0213] Table 3 Coulombic efficiency of Li||Cu battery in Example 3 and Comparative Example 3

[0214] Group Coulombic efficiency of Li||Cu battery Example 3 99.0 % Comparative Example 3 96.5 %

[0215] Table 1 shows that the electrolyte prepared by the lithium salt of the present invention has a higher conductivity. Table 2 shows that the lithium salt of the present invention has a higher compatibility with the fluoroethylene carbonate additive. Table 3 shows that the battery prepared by the lithium salt of the present invention has a higher coulombic efficiency.

[0216] Figure 1 and Figure 2 The voltage-time diagrams of the Li||Cu battery in Example 3 of the present invention and Comparative Example 3 are shown respectively. Figure 1 and Figure 2 From the comparison, it can be seen that the deposition curve of the electrolyte in Example 3 is smoother, and its Coulomb efficiency is as high as 99.0%, which is higher than the 96.5% Coulomb efficiency in Comparative Example 3.

[0217] Figure 3 The cycle diagrams of Example 3 of the present invention and Comparative Example 3 under 2C conditions in a Li||NCM811 full battery are shown. Figure 3It shows that the battery prepared with the lithium salt of the present invention has much better cycle performance.

[0218] It can be seen from the above results that the organic lithium salt of the present invention has a strong ability to coordinate with lithium ions and promote the dissociation of other lithium salts due to the R1 group with strong complexing effect on lithium ions and the R2 group with strong electron-withdrawing ability; it is easy to participate in the formation of SEI film and CEI film to generate CEI and SEI that are conducive to lithium ion conduction, thereby improving the fast charging performance and cycle stability of lithium batteries; in particular, the electron-withdrawing sulfone group or carbonyl group between the nitrogen atom and the R1 group can help lithium ions and nitrogen atoms to dissociate significantly better, thereby significantly improving the conductivity; the synthesis conditions are milder and more conducive to large-scale production; it has higher compatibility with fluoroethylene carbonate, and can exert a synergistic effect, thereby further improving the fast charging performance and cycle stability of lithium batteries.

[0219] Electrolyte experiments were also conducted for the inner salt type organic lithium salts (IV)-(VIII) prepared in Synthesis Examples 2-6, and similar excellent results were obtained.

[0220] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An inner salt type organic lithium salt, characterized in that: It has the following structural formula (III): (III)。 2. A lithium battery electrolyte, characterized in that: Including the inner salt type organic lithium salt according to claim 1.

3. The lithium battery electrolyte according to claim 2, characterized in that: The mass percentage content of the inner salt type organic lithium salt in the lithium battery electrolyte is in the range of 0.01-80%.

4. The lithium battery electrolyte according to claim 3, characterized in that: The lithium battery electrolyte further includes an organic solvent and a lithium salt different from the inner salt type organic lithium salt.

5. The lithium battery electrolyte according to claim 4, characterized in that: The lithium battery electrolyte further includes an additive selected from the group consisting of fluoroethylene carbonate, lithium nitrate, lithium perchlorate, lithium sulfate, lithium difluorooxalatoborate, lithium carbonate, and combinations thereof.

6. The lithium battery electrolyte according to claim 4 or 5, characterized in that: The lithium salt different from the inner salt type organic lithium salt is selected from the group consisting of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylsulfonyl imide, lithium trifluoromethylsulfonate, lithium tetrafluoroborate and lithium bisoxalatoborate, and combinations thereof; and The organic solvent is a mixture including at least two selected from the group consisting of ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane.

7. The lithium battery electrolyte according to claim 6, characterized in that: The lithium salt different from the inner salt type organic lithium salt is lithium hexafluorophosphate; The organic solvent is a mixture of ethylene carbonate and diethyl carbonate; The additive is a mixture of fluoroethylene carbonate and lithium nitrate.

8. A lithium battery, characterized in that: The lithium battery comprises: positive electrode; negative electrode; a separator between the positive electrode and the negative electrode; and A lithium battery electrolyte according to any one of claims 2 to 7 in contact with the positive electrode and the negative electrode.

9. A method for preparing the inner salt type organic lithium salt according to claim 1, characterized in that: The method comprises the following steps: The first step is to react a sulfonyl chloride compound with a sulfonamide compound at room temperature in the presence of potassium carbonate to obtain a potassium salt intermediate; In the second step, the potassium salt intermediate obtained in the first step is subjected to a salt exchange reaction with lithium perchlorate or lithium tetrafluoroborate at room temperature to obtain the inner salt type organic lithium salt.

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