WO2025156897A1 - Electrolyte, lithium ion battery, and electric device - Google Patents

Abstract

The present application provides an electrolyte, a lithium ion battery, and an electric device. The electrolyte comprises a lithium salt, an organic solvent, and an additive as shown in formula (I): formula (I), wherein Ar is selected from substituted or unsubstituted aryl groups. The additive represented by formula (I) in the electrolyte can respectively generate a stable cathode-electrolyte interface film and a stable solid electrolyte interface film on the surfaces of the positive and negative electrodes of the battery, so that the battery has good high-voltage resistance and high-voltage cycle performance.

Description

Electrolyte, lithium-ion battery and electrical equipment

This application claims priority to the Chinese patent application filed with the China Patent Office on January 27, 2024, with application number 202410125059.7 and application name “Electrolyte, lithium-ion battery and electrical equipment”, the entire contents of which are incorporated by reference into this application.

Technical Field

The present application relates to the technical field of lithium-ion batteries, and in particular to an electrolyte, a lithium-ion battery, and an electrical device.

Background Art

Conventional commercial lithium-ion battery electrolytes are susceptible to oxidative decomposition under high voltage conditions, leading to rapid electrolyte consumption, accelerated metal ion dissolution from the cathode material, increased cathode surface impedance, and severely reduced battery cycle performance and safety. Therefore, it is necessary to develop lithium-ion battery electrolytes that can withstand high voltages without compromising battery performance.

Summary of the Invention

In view of this, the present application provides an electrolyte, a lithium-ion battery and an electrical device. The fluoroaromatic amide additive contained in the electrolyte can generate a stable cathode electrolyte interface (cathode–electrolyte interface, CEI) film and a solid electrolyte interface (solid electrolyte interface, SEI) film on the positive and negative electrode surfaces of the battery, respectively. The battery using the electrolyte has good high-voltage stability and high-voltage cycle performance.

Specifically, the first aspect of the present application provides an electrolyte, which includes a lithium salt, an organic solvent, and an additive as shown in formula (I):

In formula (I), Ar is selected from substituted or unsubstituted aryl groups.

The electrolyte introduces a fluoroaromatic amide additive represented by formula (I). This additive can be reduced on the negative electrode surface before the solvent to form a dense and stable SEI film, and oxidized on the positive electrode surface before the solvent to form a stable CEI film, which can reduce solvent consumption and improve the high-voltage resistance of the electrolyte. In addition, the SEI film and the CEI film also contain nitrogen-containing inorganic components with high ionic conductivity generated by the decomposition of this additive. This enables the CEI film and the SEI film to more effectively improve the interface between the positive/negative electrode and the electrolyte and reduce the interfacial impedance, thereby effectively improving the high-voltage stability, high-voltage cycle performance and coulombic efficiency of the battery, and reducing battery gas expansion.

A second aspect of the present application provides a lithium-ion battery comprising the electrolyte provided in the first aspect of the present application. Specifically, the battery comprises a battery housing, a battery cell housed within the battery housing, and an electrolyte. The battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator positioned between the positive and negative electrode sheets.

The battery has good high-voltage resistance, excellent high-temperature storage and high-voltage cycle performance, and good high-temperature expansion characteristics, so the battery has high safety performance and a long service life.

The third aspect of the present application provides an electric device, wherein the electric device comprises the lithium-ion battery provided in the second aspect of the present application. The lithium-ion battery can supply power to the electric device.

DETAILED DESCRIPTION

To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

The charging cutoff voltage of high-nickel ternary positive electrode materials is generally above 4.5V (vs. Li/Li+), and when charged to 4.5V, it will produce a large amount of highly oxidizing Ni ⁴⁺ . Traditional commercial lithium-ion electrolytes are mainly composed of carbonate solvents and lithium salts (such as lithium hexafluorophosphate). When the voltage exceeds 4.5V, the Ni ⁴⁺ dissolved from the positive electrode will oxidize the carbonate solvent, consuming active lithium and electrolyte. The byproducts generated by the rapid consumption of the electrolyte (such as proton products such as water) will accelerate the degradation of the electrolyte performance and accelerate the dissolution of metal ions in the high-nickel ternary positive electrode material, and even cause the collapse of the positive electrode material structure, destroying the interface film generated by the electrolyte on the positive and negative electrode surfaces, increasing the impedance of the positive electrode surface, and ultimately leading to battery gas expansion and rapid capacity decay. In addition, high-nickel ternary positive electrode materials are more prone to oxygen evolution at high potentials, further accelerating the oxidative decomposition and gas production of the electrolyte, and ultimately leading to poor stability of the electrode interface film, increased impedance and reduced battery performance.

Replacing the electrolyte solvent with a strong antioxidant, or replacing the lithium salt that produces less or no hydrofluoric acid can improve the high-voltage resistance of the electrolyte, but it will lose the ionic conductivity of the electrolyte or cause the viscosity of the electrolyte to be too large, affecting the performance of the battery. The introduction of high-voltage additives (such as nitriles, fluoroesters, etc.) into conventional electrolytes can also improve the high-voltage resistance of the electrolyte to a certain extent, but it is difficult to generate a stable interface film on the surface of the positive electrode, and the improvement of the cycle performance of the battery in a high-voltage environment is limited. In view of this, the present application provides an electrolyte with good high-voltage resistance that does not affect the performance of the battery, as well as a lithium-ion battery and electrical equipment using the electrolyte.

The electrolyte provided in the embodiment of the present application includes: a lithium salt, an organic solvent, and a fluoroaromatic amide additive as shown in formula (I):

In formula (I), Ar is selected from substituted or unsubstituted aryl groups.

The above electrolyte introduces a fluoroaromatic amide additive represented by formula (I). The conjugation effect formed between the tertiary amino nitrogen atom and the aromatic group Ar and the carbonyl group -C(=O)- in the structure of this type of additive can reduce the lowest unoccupied molecular orbital (LUMO) energy of the additive. According to the frontier orbital theory, the reduction potential of the additive is relatively high, and it can be reduced on the negative electrode surface before the solvent to form a dense and stable SEI film, thereby reducing the consumption of the electrolyte solvent and improving the interface between the negative electrode and the electrolyte (such as preventing side reactions between the electrolyte and the negative electrode), thereby reducing the high-temperature storage expansion rate and battery gas production of the battery, and improving the high-voltage stability, cycle performance and safety performance of the battery. At the same time, the above-mentioned conjugation effect can also increase the highest occupied molecular orbital (HOMO) energy of the additive, so that the additive can be oxidized on the positive electrode surface before the solvent to form a stable CEI film. The CEI film can prevent the dissolution of nickel elements in the nickel-containing ternary positive electrode material, the contact of the highly oxidizing Ni ⁴⁺ with the solvent to cause the oxidative decomposition of the solvent, and reduce the damage of Ni ⁴⁺ to the SEI film, thereby improving the high-voltage stability and cycle performance of the battery (especially the cycle performance under high temperature and high voltage).

Moreover, the above-mentioned additives will decompose during the electrochemical reaction to form nitrogen-containing inorganic components with high ionic conductivity, such as methyl lithium ( _CH3Li ) and lithium nitride ( _Li3N ). These nitrogen-containing inorganic components can reduce the interfacial impedance of the SEI film and the CEI film, better improve the battery cycle performance, and help reduce the degree of battery polarization and improve the battery rate performance. In addition, the SEI film containing the above-mentioned nitrogen-containing inorganic components has a more stable structure and good ion conductivity, which is also conducive to the uniform deposition of lithium ions on the negative electrode surface, reducing lithium dendrites and porous lithium morphology, inhibiting the irreversible reaction caused by the growth of lithium dendrites, and improving the coulombic efficiency of the battery.

Therefore, the above-mentioned electrolyte has good high-voltage resistance, consumes less organic solvent at high voltage, and has fewer side reactions between the electrolyte and the positive/negative electrodes. Using this electrolyte can reduce battery gas production and volume expansion, thereby improving the battery's cycle performance, safety, and coulombic efficiency. Furthermore, the above-mentioned fluoroaromatic amides are highly soluble in electrolyte solvents (particularly carbonate solvents), and their addition to the electrolyte has a minimal effect on electrolyte viscosity. They also provide a more effective approach for introducing nitrogen-containing inorganic components with high ionic conductivity into SEI and CEI membranes.

In the present application, the substituted or unsubstituted aryl group may be either an aryl group without ring heteroatoms or a heteroaryl group containing ring heteroatoms. The ring heteroatoms may be one or more of a nitrogen atom, an oxygen atom, a sulfur atom, a selenium atom, a boron atom, a phosphorus atom, and the like. In some embodiments of the present application, the substituted or unsubstituted aryl group may include a substituted or unsubstituted phenyl group or a substituted or unsubstituted fused ring aryl group. It is understood that the fused ring aryl group may or may not contain ring heteroatoms.

The substituted or unsubstituted fused ring aromatic group may include one or more of a substituted or unsubstituted benzothiophenyl group, a substituted or unsubstituted benzofuranyl group, a substituted or unsubstituted benzopyrrolyl group, a substituted or unsubstituted dibenzofuranyl group, a substituted or unsubstituted dibenzothiophenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted anthracenyl group, a substituted or unsubstituted fluorenyl group, and a substituted or unsubstituted spirofluorenyl group, but is not limited thereto.

In some embodiments of the present application, Ar is a substituted or unsubstituted phenyl group. In this case, the additive represented by formula (I) is easier to synthesize and is more easily reduced at the negative electrode to form a stable SEI film with high ionic conductivity, thereby ensuring better battery cycle performance in the electrolyte containing it.

When Ar is a substituted or unsubstituted phenyl group, the additive represented by formula (I) can be represented as:

wherein R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are independently selected from hydrogen atoms or substituents on phenyl groups. When R ₁ to R ₅ are all hydrogen atoms, Ar is an unsubstituted phenyl group.

In an embodiment of the present application, the substituent in the substituted aryl group includes at least one of a halogen atom, a cyano group (-CN), an isothiocyano group (-NCS), an isocyanate group (-NCO), a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, and a substituted or unsubstituted aryl group. Corresponding to the above formula (Ia), R ₁ , R ₂ , R ₃ , R ₄ , and R ₅ are independently selected from at least one of a hydrogen atom, a halogen atom, a cyano group (-CN), an isothiocyano group (-NCS), an isocyanate group (-NCO), a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, and a substituted or unsubstituted aryl group. The halogen atom may include one or more of a fluorine atom (F), a chlorine atom (Cl), a bromine atom (Br), and an iodine atom (I). Cycloalkyl groups may or may not contain ring heteroatoms.

The introduction of different substituents in the aryl group can obtain more additives of the above formula (I) with different structures, thereby adjusting their reduction potential/oxidation potential to meet the needs of different scenarios. In the embodiment of the present application, the substituents in the substituted aryl group do not include an ester group. Because the additive of formula (I) does not contain an ester group, it will not decompose to form inorganic components with poor ion conductivity (such as _Li2O and _Li2CO3 ) during the electrochemical reaction. Instead, it will decompose to form nitrogen-containing inorganic components with high ionic conductivity such as methyllithium ( _CH3Li ) and lithium nitride ( _{Li3N )} , which are more conducive to reducing the impedance of the SEI film and the CEI film.

In the embodiment of the present application, the substituents in the substituted alkyl, substituted alkoxy, substituted alkenyl and substituted alkynyl are independently selected from at least one of a halogen atom, a cyano group (-CN), an isothiocyano group (-NCS), an isocyanate group (-NCO), a substituted or unsubstituted alkoxy group, and a substituted or unsubstituted aryl group; the substituents in the substituted cycloalkyl and substituted aryl groups are independently selected from at least one of a halogen atom, a cyano group (-CN), an isothiocyano group (-NCS), an isocyanate group (-NCO), a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, and a substituted or unsubstituted aryl group.

In the embodiments of the present application, the substituted or unsubstituted alkyl group is a substituted or unsubstituted _C1 - _C10 alkyl group, and may further be a substituted or unsubstituted _C1 - _C6 alkyl group, a substituted or unsubstituted _C1 - _C4 alkyl group, etc. The substituted or unsubstituted alkoxy group is a substituted or unsubstituted _C1 - _C10 alkoxy group, and may further be a substituted or unsubstituted _C1 - _C6 alkoxy group, a substituted or unsubstituted _C1 - _C4 alkoxy group, etc. The substituted or unsubstituted cycloalkyl group is a substituted or unsubstituted _C3 - _C10 cycloalkyl group, for example, a substituted or unsubstituted cyclopentyl group, a substituted or unsubstituted cyclohexyl group, etc. The substituted or unsubstituted alkenyl group is a substituted or unsubstituted _C2 - _C10 alkenyl group, and may further be a substituted or unsubstituted _C2 - _C6 alkenyl group, a substituted or unsubstituted _C2 - _C4 alkenyl group, etc. Wherein, the substituted or unsubstituted alkynyl group is a substituted or unsubstituted C ₂ to C ₁₀ alkynyl group, and may further be a substituted or unsubstituted C ₂ to C ₆ alkynyl group, a substituted or unsubstituted C ₂ to C ₄ alkynyl group, etc. Wherein, the substituted or unsubstituted aryl group is a substituted or unsubstituted C ₆ to C ₃₀ aryl group, which may be a monocyclic aryl group or a polycyclic aryl group; the polycyclic aryl group may be a fused ring type or a non-fused ring type (such as biphenyls). In some embodiments, the substituted or unsubstituted aryl group may be a substituted or unsubstituted C ₆ to C ₂₀ aryl group, a substituted or unsubstituted C ₆ to C ₁₂ aryl group, etc. Limiting the number of carbon atoms of the above-mentioned substituted or unsubstituted alkyl, alkoxy, cycloalkyl, alkenyl, alkynyl, and aryl groups to a certain range can ensure that the solubility of the additive of formula (I) in the organic solvent is appropriate and the viscosity of the electrolyte is within a suitable range, thereby ensuring that the wetting properties of the electrolyte containing the additive are not significantly affected.

In some embodiments of the present application, the fluoroaromatic amide additive represented by formula (I) is selected from one or more of the following compounds:

Among them, the additive represented by formula (i-1) can be called 2,2,2-fluoro-N-methyl-N-acetanilide. The additive represented by formula (i-2) can be called 2,2,2-trifluoro-N-(4-isocyanatophenyl)-N-methylacetamide. The additive represented by formula (i-3) can be called 2,2,2-trifluoro-N-(4-cyanophenyl)-N-methylacetamide. The additive represented by formula (i-4) can be called 2,2,2-trifluoro-N-(3-fluorophenyl)-N-methylacetamide. The additive represented by formula (i-5) can be called 2,2,2-trifluoro-N-(4-isothiocyanatophenyl)-N-methylacetamide. The additive represented by formula (i-6) can be called N-(3,5-difluoro-4-allylphenyl)-2,2,2-trifluoro-N-methylacetamide. The additive represented by formula (i-7) can be called N-(2-benzothienyl)-2,2,2-trifluoro-N-methylacetamide.

In an embodiment of the present application, the total mass percentage of the additive represented by formula (I) in the electrolyte is 0.1-10%. By controlling the concentration of the additive represented by formula (I) in the electrolyte within an appropriate range, it is possible to ensure the formation of SEI films and CEI films of appropriate thickness. For example, the total mass percentage of the additive represented by formula (I) in the electrolyte is 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. In some embodiments, the total mass percentage of the additive represented by formula (I) in the electrolyte is 3-8%. This ensures that there is enough of the additive to form the SEI film and CEI film, thereby more effectively improving the capacity retention rate of the battery during high-voltage cycling, reducing the amount of nickel element dissolution from the positive electrode, improving high-temperature storage stability, etc., while also avoiding the thickness of the SEI film and CEI film being too thick, thereby affecting the battery performance.

In some embodiments of the present application, the electrolyte further comprises conventional film-forming additives. Conventional film-forming additives are mainly used to form a solid electrolyte interface film on the surface of the electrode to prevent side reactions between electrolysis and the electrolyte. Among them, the conventional film-forming additives may include one or more of fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), vinyl carbonate (VC), vinyl sulfite (ES), diethylene sulfate (DTD), and methylene disulfonate (MMDS). In an electrolyte system containing conventional film-forming additives, the additive shown in formula (I) of the embodiment of the present application is added, and the two additives have a good coordination effect on the SEI film formed at the negative electrode. In some embodiments, the conventional film-forming additive is FEC. FEC can form a thin but stable low-impedance SEI film on the surface of the negative electrode.

In the embodiments of the present application, the mass percentage of the conventional film-forming additive in the electrolyte is 0.1%-10%. For example, the mass percentage may be 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. In some specific embodiments, the mass percentage of the conventional film-forming additive is preferably 3%. An appropriate amount of conventional film-forming additive can effectively improve the interfacial stability between the battery electrode and the electrolyte.

In some embodiments of the present application, the mass of the additive shown in formula (I) is 0.03-3.33 times the mass of the conventional film-forming additive. The two additives are used in combination in an appropriate proportion to produce a synergistic effect. They can generate a more stable and dense SEI film on the surface of the negative electrode of the battery better than the solvent, thereby being more conducive to improving the electrochemical performance of the battery, especially the cycle performance. Specifically, the additive shown in formula (I) is 0.03 times, 0.05 times, 0.17 times, 0.33 times, 0.67 times, 1 times, 1.33 times, 1.67 times, 2 times, 2.33 times, 2.67 times, 3 times, 3.2 times, 3.33 times, etc. of the mass of the conventional film-forming additive. In some embodiments, the additive shown in formula (I) is 1-3 times the mass of the conventional film-forming additive, and can further be 1-2.67 times.

The most significant effect of the additive represented by the aforementioned formula (I) in the embodiments of the present application is that it can improve the tolerance of the electrolyte to high voltage (i.e., as a high-voltage additive), and it also has the effect of improving the film-forming effect of the electrode interface film. In some embodiments of the present application, the electrolyte also includes other high-voltage additives. Among them, the other high-voltage additives include one or more of propylene sulfite (1,3-Propylene Sulfite, PS), tripropynyl phosphate (TPP), and tris(trimethylsilyl) phosphite (TMSP). The introduction of these additives also contributes to the stability of the above-mentioned electrolyte under high voltage.

In an embodiment of the present application, the organic solvent in the electrolyte includes a cyclic carbonate and a linear carbonate. The cyclic carbonate has a high dielectric constant and the linear carbonate has a low viscosity. The use of the two together is conducive to improving the overall ionic conductivity of the electrolyte. In addition, the cyclic carbonate can also participate in the formation of the SEI film, thereby effectively preventing the occurrence of negative electrode side reactions. In some embodiments of the present application, the mass of the linear carbonate is 1-2.5 times the mass of the cyclic carbonate. In this case, it is more helpful for the electrolyte to take into account both viscosity and good ionic conductivity.

The cyclic carbonate may include one or more of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate, and the linear carbonate may include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). In some embodiments, the organic solvent is a mixture of EC and DEC in a mass ratio of 3:7, or 1:2.3.

In the embodiment of the present application, the lithium salt in the above-mentioned electrolyte includes lithium hexafluorophosphate (LiPF ₆ ). Lithium hexafluorophosphate has a large LUMO-HOMO energy band, has strong chemical stability and oxidation resistance, and is low in price and most widely used. Among them, the molar concentration of lithium hexafluorophosphate in the electrolyte can be 0.1mol/L-1.2mol/L, for example, specifically 0.1mol/L, 0.2mol/L, 0.5mol/L, 0.6mol/L, 0.8mol/L, 1.0mol/L, 1.1mol/L, 1.2mol/L, etc. An appropriate concentration of LiPF ₆ is conducive to the performance of the battery. In some embodiments, the molar concentration of LiPF ₆ can be 1.0mol/L.

In some embodiments of the present application, the lithium salt further comprises one or both of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). These two lithium salts have low fluorine content and are not easily decomposed to produce hydrofluoric acid. Using them as a further supplement to _LiPF6 can reduce the amount of hydrofluoric acid produced by the decomposition of the overall lithium salt and help improve the high-temperature resistance of the electrolyte.

A second aspect of the present application further provides a lithium-ion battery comprising the electrolyte described above in the embodiments of the present application. The lithium-ion battery comprising the electrolyte described above not only exhibits excellent high-voltage resistance, but also exhibits excellent high-temperature storage stability (low battery expansion at high temperatures), good room-temperature cycling performance, and good high-voltage cycling performance.

The lithium-ion battery may include a battery housing, a battery cell contained within the battery housing, and the aforementioned electrolyte of the embodiments of the present application. The battery cell includes a positive electrode sheet, a negative electrode sheet, and a separator positioned between the positive and negative electrode sheets. The battery preparation method includes stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence to form a battery cell, placing the battery cell in a battery housing, injecting the aforementioned electrolyte, and then sealing the battery housing to produce the battery.

In this application, the negative electrode sheet, the positive electrode sheet, and the separator are all conventional choices in the battery field. Among them, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, and the negative electrode material layer may include a negative electrode active material, a binder, and an optional conductive agent. Exemplarily, the negative electrode active material includes but is not limited to artificial graphite, natural graphite, mesophase carbon microbeads (MCMB), silicon-carbon materials, etc. Similarly, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer includes a positive electrode active material, a binder, and an optional conductive agent.

In some embodiments of the present application, the positive electrode active material may include a nickel-containing ternary material. The general structural formula of the nickel-containing ternary material can be expressed as LiNi _x Co _y M _z O ₂ , where 0.33 ≤ x ≤ 0.98, 0 < y < 1, 0 < z < 1, and x + y + z = 1; M is at least one metal element from Group III to Group V, for example, M is selected from at least one of Mn, Al, Zr, Ti, Y, Sr, and W. When x is relatively high, such as 0.50 ≤ x ≤ 0.98, the nickel-containing ternary material can be referred to as a high-nickel ternary material, which has a higher specific capacity. Furthermore, the value range of x can be 0.70 ≤ x ≤ 0.98, 0.70 ≤ x ≤ 0.90, 0.80 ≤ x ≤ 0.90, or 0.83 ≤ x ≤ 0.88, among others. In some embodiments, the nickel-containing ternary material is a nickel-cobalt-manganese ternary material (i.e., M is Mn). Illustratively, the nickel-manganese-cobalt ternary material includes LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (referred to as NCM111), LNi _0.4 Co _0.2 Mn _0.4 O ₂ (referred to as NCM424), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (referred to as NCM523), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (referred to as NCM622), LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (referred to as NCM811), LiNi _0.85 Co _0.075 Mn _0.075 O ₂ and other materials.

It should be noted that the above-mentioned electrolyte provided in the embodiments of the present application is not limited to battery systems whose positive electrodes are nickel-containing ternary materials, but can also be applied to lithium phosphate systems (such as lithium iron phosphate, lithium manganese iron phosphate, etc.), lithium cobalt oxide ( _LiCoO2 , LCO) systems, lithium nickel manganese oxide (LMNO) systems, lithium-rich manganese-based material systems, etc.

The present application also provides an electric device, which includes the lithium-ion battery of the present application. The lithium-ion battery can supply power to the electric device.

In the embodiments of the present application, the electrical device may be a 3C product (such as a mobile phone, laptop computer, tablet computer, pen-type computer, e-book player, wearable device, etc.), or an electric vehicle (such as an electric car, electric motorcycle, electric bicycle, etc.). In addition, the lithium-ion battery of the embodiments of the present application may also be used in an energy storage system.

The embodiments of the present application are further described below with reference to a number of embodiments.

Example 1

A method for preparing a lithium ion battery comprises the following steps:

(1) Preparation of an electrolyte: 120 g of ethylene carbonate (EC) and 280 g of diethyl carbonate (DEC) were mixed to obtain a mixed solvent. 60 g of lithium hexafluorophosphate (LiPF ₆ ) was added to the mixed solvent to adjust the molar concentration of LiPF ₆ to 1.0 mol/L. 13.8 g of a film-forming additive, fluoroethylene carbonate (FEC), and 23 g of the additive represented by formula (i-1) were then added. The mixture was stirred until all solid matter was dissolved to obtain the desired electrolyte. The types and contents of the additives in the electrolyte are shown in Table 1. The concentration of FEC in the electrolyte of Example 1 was 3 wt %, and the concentration of the additive represented by formula (i-1) was 5 wt %.

(2) Preparation of negative electrode sheet: 100 parts of graphite material, 1 part of conductive agent Super-p, 1.5 parts of thickener sodium carboxymethyl cellulose (CMC) and 2.5 parts of binder styrene-butadiene rubber (SBR) were mixed into a uniform paste, and evenly coated on the negative electrode current collector copper foil, and vacuum dried at 80°C for 24 hours to obtain the negative electrode sheet.

(3) Preparation of positive electrode sheet: 100 parts by weight of ternary nickel-manganese-cobalt material LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM523) was mixed with 2 parts of carbon nanotubes, 1 part of conductive agent Super-p and 2 parts of binder polyvinylidene fluoride (PVDF) to form a uniform paste, and the paste was evenly coated on the positive electrode current collector aluminum foil and vacuum dried at 80°C for 24 h to obtain the positive electrode sheet.

(4) Assembly and formation of batteries: In an argon glove box with a water content of less than 5 ppm, the positive electrode sheets, separators, and negative electrode sheets were stacked in order and wound into a bare cell. The bare cell was placed in a battery case and welded. Subsequently, 1.6 g of the above electrolyte was injected into the battery case, and the battery case was sealed to produce a soft-pack lithium-ion battery with a model number of SL582736.

The above-mentioned soft-pack battery was formed using the following process: The battery was first charged to 1.5V at a current of 40mA (0.05C) and held at 1.5V for 10 hours to fully wet the battery electrode sheets. After the constant voltage was completed, the battery was initially charged at a lower current of 8mA (C/100) for 10 hours to form a stable and dense SEI film. It was then charged to 4.35V at a current of 40mA (0.05C) and then discharged to 3.0V.

Example 2-11

Referring to the method of Example 1, the electrolytes and lithium-ion batteries of Examples 2-11 were prepared according to the ratios in Table 1.

Comparative Example 1

An electrolyte, which differs from Example 1 in that the electrolyte does not contain the film-forming additive FEC and the fluoroaromatic amide additive provided by the present application.

Referring to the method of Example 1, the electrolyte of Comparative Example 1 was prepared into a lithium ion battery.

Comparative Example 2

An electrolyte, which differs from Example 1 in that the electrolyte does not contain the fluoroaromatic amide additive provided by the present application.

Referring to the method of Example 1, the electrolyte of Comparative Example 2 was prepared into a lithium ion battery.

Table 1 Composition of additives in each electrolyte

The lithium ion batteries prepared in Examples 1-11 and Comparative Examples 1-2 were subjected to the following performance tests:

(1) High-temperature storage expansion rate test: Each battery after formation was charged at 0.5C with a cut-off voltage of 4.5V, and then charged at a constant voltage of 4.5V until the current was less than 0.02C, to obtain a fully charged battery. Each fully charged battery was placed in a 60°C constant temperature oven for 5 days. The battery thickness before and after storage was measured with a vernier caliper. The battery thickness after storage was subtracted from the battery thickness before storage. The percentage obtained by dividing the thickness difference by the battery thickness before storage was recorded as the battery expansion rate.

(2) Nickel dissolution test: After the high-temperature expansion rate test, the battery was disassembled, the negative electrode was taken out, and it was immersed in the solvent DMC. The negative electrode was dried and the powder was scraped off. The collected powder was sent to the Inductively Coupled Plasma Emission Spectrometer (ICP) produced by Thermo Fisher for testing to obtain the nickel content dissolved from the positive electrode to the negative electrode.

(3) Battery high-voltage cycle performance test: The airbag of each battery was removed and the battery was vacuum-sealed. The battery was then placed in a constant temperature chamber at 25°C and subjected to 300 charge and discharge cycles at a current of 1C between 2.75V and 4.5V. The percentage obtained by dividing the discharge capacity of each battery at the 300th cycle by the initial discharge capacity of the first cycle was recorded as the capacity retention rate. The ratio of the discharge capacity to the charge capacity of each battery at the first cycle was recorded as the first coulombic efficiency.

(4) Battery DC internal resistance test: After 300 cycles in (3) above, each battery was charged to 4.5 V, then discharged to 50% SOC and allowed to stand for 2 h. The instantaneous voltage U ₁ of the battery was measured at the last 1 second of the 2 h. The battery was then discharged at a constant current I ₀ of 1.5 C for 30 seconds, and the instantaneous voltage U ₂ at the 30th second of discharge was measured. The direct current internal resistance (DCIR) of the battery was then calculated using the following formula: DCIR = (U ₁ - _{U 2} )/I ₀ .

Ten batteries of each embodiment or comparative example were taken to perform the above tests. The average value of the 10 batteries was taken for each group of test results. The test results of each group of batteries are summarized in Table 2.

Table 2 Performance test results of each battery

Comparison of Examples 1-14 with Comparative Examples 1-2 demonstrates that the introduction of the fluoroaromatic amide additive represented by formula (I) provided in the examples of this application into the electrolyte can reduce the expansion rate of fully-charged batteries during high-temperature storage, thereby improving the safety of the batteries in high-temperature environments. Furthermore, it can effectively reduce nickel dissolution from the positive electrode of fully-charged batteries during high-temperature storage and improve the battery's capacity retention during cycling at a high voltage of 4.5V. In particular, the batteries of Examples 1-10 exhibit higher room-temperature initial coulombic efficiency and lower DCIR values than the batteries of Comparative Examples 1-2.

Furthermore, a comparison between Examples 1 and 8-11 reveals that when the weight percentage of the additive represented by formula (I) in the electrolyte is greater than 0.05%, for example, in the range of 1-10%, the improvement in the aforementioned battery properties is more pronounced. In particular, when the additive content is in the range of 3%-8%, the battery can better balance low high-temperature storage expansion, low positive electrode nickel dissolution, and high room-temperature cycle capacity retention.

The above is an exemplary embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims (14)

An electrolyte, wherein the electrolyte comprises a lithium salt, an organic solvent, and an additive represented by formula (I):
In formula (I), Ar is selected from substituted or unsubstituted aryl groups. The electrolyte according to claim 1, wherein the substituted or unsubstituted aryl group is selected from a substituted or unsubstituted phenyl group, or a substituted or unsubstituted fused ring aryl group; The substituted or unsubstituted fused ring aromatic group includes one or more of a substituted or unsubstituted benzothiophenyl group, a substituted or unsubstituted benzofuranyl group, a substituted or unsubstituted benzopyrrolyl group, a substituted or unsubstituted dibenzofuranyl group, a substituted or unsubstituted dibenzothiophenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted anthracenyl group, a substituted or unsubstituted fluorenyl group, and a substituted or unsubstituted spirofluorenyl group. The electrolyte according to claim 1 or 2, wherein the substituent in the substituted aryl group includes at least one of a halogen atom, a cyano group, an isothiocyano group, an isocyanate group, a substituted or unsubstituted C ₁ to C ₁₀ alkyl group, a substituted or unsubstituted C ₁ to C ₁₀ alkoxy group, a substituted or unsubstituted C ₃ to C ₁₀ cycloalkyl group, a substituted or unsubstituted C ₂ to C ₁₀ alkenyl group, a substituted or unsubstituted C ₂ to C ₁₀ alkynyl group, and a substituted or unsubstituted C ₆ to C ₃₀ aryl group. The electrolyte according to any one of claims 1 to 3, wherein the additive represented by formula (I) is selected from one or more of the following compounds:

The electrolyte according to any one of claims 1 to 4, wherein the mass percentage of the additive represented by formula (I) in the electrolyte is 0.1-10%. The electrolyte according to any one of claims 1 to 5, wherein the electrolyte further comprises a conventional film-forming additive; wherein the conventional film-forming additive comprises one or more of fluoroethylene carbonate, vinyl ethylene carbonate, vinyl carbonate, vinyl sulfite, vinyl sulfate, and methylene methanedisulfonate. The electrolyte according to claim 6, wherein the mass percentage of the conventional film-forming additive in the electrolyte is 0.1%-10%. The electrolyte according to claim 6, wherein the mass of the additive represented by formula (I) is 0.03-3.33 times the mass of the conventional film-forming additive. The electrolyte according to any one of claims 1 to 8, wherein the electrolyte further comprises a high-voltage additive; wherein the high-voltage additive comprises one or more of propylene sulfite, tripropynyl phosphate, and tris(trimethylsilyl)phosphite. The electrolyte according to claim 1, wherein the organic solvent comprises a cyclic carbonate and a linear carbonate; wherein the mass of the linear carbonate is 1-2.5 times the mass of the cyclic carbonate. The electrolyte of claim 1, wherein the lithium salt comprises lithium hexafluorophosphate. The electrolyte according to claim 11, wherein the lithium salt further comprises one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. A lithium-ion battery, wherein the lithium-ion battery comprises the electrolyte according to any one of claims 1 to 12. An electrical device, wherein the electrical device comprises the lithium-ion battery according to claim 13.