Electrolytes containing novel lithium salt additives and lithium-ion batteries containing such electrolytes

Abstract

This invention discloses an electrolyte containing a novel lithium salt additive and a lithium-ion battery containing the electrolyte. The electrolyte comprises a novel lithium salt additive, a lithium salt, an organic solvent, and an additive. The novel lithium salt additive has the structural formula (I): where R₂ is a cyano or nitro group, and R₁ and R₃ are independently selected from hydrogen or fluorine atoms. This additive preferentially decomposes under high potential, prior to solvent oxidation, to form a dense CEI film rich in inorganic components. This film effectively passivates surface defects on the positive electrode, inhibits electrolyte oxidation and transition metal dissolution under high voltage, and simultaneously consumes HF and water, mitigating interfacial corrosion. This invention also provides a method for synthesizing the additive. The lithium salt concentration in the electrolyte is 1~3 mol / L, and the additive concentration is 0.1~0.3 mol / L. The lithium-ion battery using this electrolyte exhibits excellent cycle stability and safety.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, and more particularly to an electrolyte containing a novel lithium salt additive and a lithium-ion battery containing the electrolyte. Background Technology

[0002] In recent years, lithium-ion batteries have become the most promising candidate for energy storage systems due to their high theoretical energy density. Currently, lithium batteries are widely used in home appliances, electric vehicles, energy storage power stations, aerospace and other fields. However, with the continuous development of science and technology, higher requirements are being placed on the cycle performance, energy density and safety performance of batteries.

[0003] Current research in electrolyte engineering includes high-concentration electrolytes (HCE), locally high-concentration electrolytes (LHCE), weakly solvated solvent electrolyte additives, and mixed salt / solvent electrolytes. Most strategies focus on constructing a good solid-electrolyte interface (SEI) at the negative electrode, as well as the modification of the positive electrode material and the study of lattice defects. Research on positive electrode interface modification and positive electrode stability still needs improvement. This application modifies the cathode-electrolyte interface (CEI) by adding a novel lithium salt additive to the electrolyte, forming a CEI film with good mechanical stability that is not easily broken during cycling, effectively protecting the positive electrode and improving the battery's cycle performance and safety. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, an interfacial film, the CEI film, is formed during the charging and discharging process of a battery by the oxidation reaction between the positive electrode material and the electrolyte at a high potential. The CEI film prevents direct contact between the electrolyte and the positive electrode material, reducing the dissolution of the positive electrode material and maintaining structural stability. Simultaneously, the CEI film provides ion channels, promoting lithium-ion transport. It is generally believed that the crystal structure of the positive electrode material changes under high voltage, enhancing surface reactivity. Substances in the electrolyte then react and deposit on the positive electrode surface. The order and density of deposition significantly affect the CEI film. A loose and unstable CEI film is prone to rupture during cycling, causing the electrolyte to continuously decompose and repeatedly form films at the rupture sites, increasing the battery's internal resistance and reducing coulombic efficiency.

[0005] To improve the structure of the CEI film, one approach is to add additives for regulation. This relies on the preferential oxidation and decomposition of lithium salt functional anions at high potentials over the solvent, generating a composite interfacial film rich in inorganic components. This effectively passivates surface defects on the cathode, inhibits continuous oxidation of the high-voltage electrolyte and dissolution of transition metals, and simultaneously consumes harmful impurities such as HF and trace amounts of moisture in the electrolyte, mitigating interfacial corrosion and side reactions. Furthermore, the synergistic effect of multiple lithium salts can enhance lithium-ion conductivity and reduce interfacial impedance while ensuring interfacial oxidation stability, making it suitable for high-voltage and wide-temperature operating environments.

[0006] Based on this, the present invention provides a novel lithium salt additive and its synthesis method, an electrolyte, and a battery. By adding the lithium salt additive to the electrolyte, the assembled lithium metal battery can form a CEI film with good mechanical stability during cycling, providing more effective protection for the positive electrode and improving cycle life and stability.

[0007] An electrolyte containing a novel lithium salt additive, the electrolyte being composed of the novel lithium salt additive, lithium salt, organic solvent, and additives, wherein the novel lithium salt additive is a compound having the structure shown in (I):

[0008] R2 is either a cyano group or a nitro group, and R1 and R3 are either hydrogen atoms or fluorine atoms, respectively.

[0009] The compounds with preferred structural formula (I) include the following compounds:

[0010] As a preferred embodiment, the method for synthesizing the lithium salt additive is as follows: First, 1.0 mol of trifluoromethanesulfonamide and 2.0 mol of potassium carbonate are mixed in anhydrous acetonitrile. After thorough stirring, 1.0 mol of one of the compounds of structural formula (III) is added. After the reaction is completed at room temperature, the insoluble solid is removed by filtration, and the solid obtained by rotary evaporation is dried under vacuum. The dried solid and lithium tetrafluoroborate are then subjected to a cation exchange reaction in anhydrous acetonitrile to synthesize the product. The supernatant is taken and the excess solvent is removed by rotary evaporation. Finally, the product is washed and dried under vacuum to obtain the lithium salt additive.

[0011]

[0012] As a preferred option, the concentration of lithium salt additive is 0.1~0.3 mol / L.

[0013] As a preferred embodiment, the lithium salt includes one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium dioxalate borate, lithium difluorooxalate borate, and lithium difluorodioxalate borate.

[0014] Furthermore, the concentration range of lithium salt in the electrolyte is 1~3 mol / L.

[0015] As a preferred embodiment, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethylene glycol dimethyl ether, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0016] As a preferred option, the additive includes one of fluoroethylene carbonate and vinylene carbonate.

[0017] Furthermore, the additives account for 2% to 5% of the total mass of the electrolyte.

[0018] The present invention also provides a lithium-ion battery that uses the electrolyte containing novel lithium salt additives described above.

[0019] This invention, by employing the above technical solutions, offers the following advantages compared to existing technologies: The lithium salt additive of this invention relies on the functional anions of lithium salts preferentially undergoing oxidative decomposition over the solvent at high potentials, generating a composite interface film rich in inorganic components. This effectively passivates surface defects on the positive electrode, inhibits continuous oxidation of the high-voltage electrolyte and dissolution of transition metals, and simultaneously consumes harmful impurities such as HF and trace amounts of moisture in the electrolyte, mitigating interface corrosion and side reactions. Furthermore, through the synergistic effect of multiple lithium salts, it enhances lithium-ion conductivity and reduces interface impedance while ensuring interfacial oxidation stability, adapting to high-voltage and wide-temperature operating environments. This improves battery stability and cycle performance.

[0020] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a synthetic route diagram for the lithium salt additive of the present invention. Detailed Implementation

[0022] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0024] The following is combined with Figure 1 The electrolyte containing novel lithium salt additives and the lithium-ion battery containing the electrolyte of the present invention will be described in detail below.

[0025] An electrolyte containing a novel lithium salt additive, the electrolyte being composed of the novel lithium salt additive, lithium salt, organic solvent, and additives, wherein the novel lithium salt additive is a compound having the structure shown in (I):

[0026] In this configuration, R2 represents either a cyano group or a nitro group, while R1 and R3 represent either a hydrogen atom or a fluorine atom. For example, R1 can be a hydrogen atom, R2 a nitro group, and R3 a hydrogen atom; R1 a fluorine atom, R2 a nitro group, and R3 a hydrogen atom; R1 a fluorine atom, R2 a nitro group, and R3 a fluorine atom; R1 a hydrogen atom, R2 a cyano group, and R3 a hydrogen atom; R1 a fluorine atom, R2 a cyano group, and R3 a fluorine atom. The specific structures are shown in Figures I-1 to I-6.

[0027] During cycling, lithium salt additives undergo an oxidation reaction at the positive electrode of the battery, generating a denser CEI film, reducing damage to the positive electrode material and improving the battery's cycle performance. At the same time, lithium salt additives can inhibit the corrosion of the aluminum current collector by the electrolyte, improving battery stability.

[0028] like Figure 1 As shown, the synthesis method of the lithium salt additive of the present invention is as follows: First, 1.0 mol of trifluoromethanesulfonamide and 2.0 mol of potassium carbonate are mixed in anhydrous acetonitrile. After thorough stirring, 1.0 mol of one of the compounds of structural formula (III) is added. After the reaction is completed at room temperature, the insoluble solid is removed by filtration, and the solid obtained by rotary evaporation of the filtrate is dried under vacuum. The dried solid and lithium tetrafluoroborate are subjected to a cation exchange reaction in anhydrous acetonitrile to synthesize the product. The supernatant is taken and the excess solvent is removed by rotary evaporation. Finally, the product is washed and dried under vacuum to obtain the lithium salt additive.

[0029]

[0030] The lithium salt in the electrolyte containing novel lithium salt additives includes one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium dioxalate borate, lithium difluorooxalate borate, and lithium difluorodioxalate borate.

[0031] The concentration of lithium salt in the electrolyte ranges from 1 to 3 mol / L, for example: 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, etc. Controlling the concentration of lithium salt in the electrolyte within this range facilitates lithium ion diffusion, resulting in an electrolyte with high ionic conductivity. If the lithium ion concentration is too low, the electrolyte conductivity is low, and the battery internal resistance increases; if the concentration is too high, the electrolyte viscosity increases significantly, increasing the resistance to lithium ion migration and reducing the diffusion rate, both of which degrade battery performance.

[0032] The concentration of lithium salt additive is 0.1~0.3 mol / L. A lower concentration can effectively protect the positive electrode while avoiding excessively high electrolyte viscosity, which would lead to a decrease in ion transport number.

[0033] The organic solvents in the electrolyte containing novel lithium salt additives include at least one of the commonly used solvents in the field, such as ethylene carbonate, propylene carbonate, ethylene glycol dimethyl ether, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0034] The electrolyte containing novel lithium salt additives includes fluoroethylene carbonate and vinylene carbonate; based on the total mass of the electrolyte, the additives account for 2% to 5% by mass, and can be selected according to actual conditions. The negative electrode film-forming additive undergoes reduction and decomposition at the negative electrode during cycling, forming a stable SEI film to protect the negative electrode. In addition, other additives that can improve certain battery performance can also be added.

[0035] This invention also provides a lithium-ion battery that uses the electrolyte containing the novel lithium salt additive described above. Typically, a battery also includes a positive electrode, a negative electrode, and a separator. During charging and discharging, active ions travel back and forth between the positive and negative electrodes, embedding and extracting within them. The electrolyte plays a role in ion transport between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0036] The positive electrode includes a positive current collector and a positive active material disposed on the current collector. The positive current collector can be a metal foil such as aluminum foil, or a composite current collector can be used. The composite current collector is formed by depositing metal materials (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on both sides of a polymer material (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0037] The cathode material can be any cathode active material known in the art for use in lithium-ion batteries. As examples, the cathode active material can be a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, or their respective modified compounds, such as lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, or ternary materials. However, this disclosure is not limited to these materials, and other conventional materials that can be used as cathode active materials for batteries can also be used. These cathode active materials can be used alone or in combination of two or more.

[0038] The positive electrode active material layer may optionally include a binder. The binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The positive electrode active material layer may also optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained.

[0039] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on the current collector. The negative current collector can be a metal foil such as copper foil, or a composite current collector can be used. A composite current collector is formed by depositing a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on both sides of a polymer material (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). The negative electrode film layer includes elemental lithium or graphite. The negative electrode sheet can be prepared by rolling lithium foil or graphite onto the negative current collector to obtain the negative electrode sheet.

[0040] The main function of an electrolyte is to conduct ions between the positive and negative electrodes while preventing electrons from passing directly through. In the embodiments of this application, the electrolyte disclosed in this invention is used.

[0041] This application does not impose any particular restrictions on the type of diaphragm. A porous diaphragm with good chemical and mechanical stability can be selected, and materials commonly used in the field, such as polyethylene, polypropylene, glass fiber, and non-woven fabric, can be selected.

[0042] The embodiments of this application are described in detail below. These embodiments are exemplary and are only used to explain this application, and should not be construed as limiting this application. The instruments and reagents used in the following embodiments are all commercially available conventional products. The rest are carried out in accordance with the description herein. Unless specific conditions and techniques are specified, they are carried out in accordance with common methods known in the art. Example

[0043] Preparation of positive electrode sheet The positive electrode active material LiFePO4, conductive agent conductive carbon black, and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare a positive electrode slurry. The positive electrode slurry is coated on the surface of carbon-coated aluminum foil, dried, and then cold-pressed. After trimming, cutting, and slitting, the positive electrode sheet is made.

[0044] Preparation of negative electrode sheet A negative electrode slurry is prepared by adding graphite (a negative electrode active material), conductive carbon black (a conductive agent), and polyvinylidene fluoride (PVDF) (a binder) to N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1. Graphite is then coated onto copper foil by rolling, and finally cut into sheets to form negative electrode plates.

[0045] Preparation of electrolyte In an argon-filled glove box, 1.0 mol of lithium hexafluorophosphate (LiPF6) or lithium bisfluorosulfonylimide (LiFSI) and 0.2 mol of lithium salt additives of formula I-1 to I-6 are added to 1 L of ethylene carbonate / ethyl methyl carbonate (EC / EMC) (3:7) or dimethyl ethylene glycol (DME), and then 5% of fluoroethylene carbonate (FEC) is added. After mixing evenly, the electrolyte is obtained.

[0046] Separating membrane A microporous three-layer membrane with a 25μm PP / PE / PP structure was used as the separator.

[0047] Lithium-ion battery manufacturing The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain a bare cell. The tabs are welded on, and the bare cell is placed in an outer package. The electrolyte prepared above is injected into the dried cell. The cells are then encapsulated, left to stand, formed, and shaped to complete the preparation of the lithium-ion battery.

[0048] ambient temperature cycling performance test Room temperature cell cycling: The ambient temperature for cell cycling is set at 25 ℃, and a charge-discharge rate of 1 C is used for charging and discharging. The cut-off voltages for charging and discharging are set at 2.5 V and 3.8 V, respectively. The battery life is considered to end when the discharge capacity decays to 80% of the first discharge capacity.

[0049] The test results are shown in Table 1 below: Table 1: Electrolyte composition and battery cycle performance

[0050] In the description of this invention, the term "a plurality of" refers to two or more. Unless otherwise explicitly defined, the terms "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. The terms "connection," "installation," "fixing," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0051] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0052] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrolyte containing a novel lithium salt additive, characterized in that... The electrolyte is composed of a novel lithium salt additive, a lithium salt, an organic solvent, and other additives. The novel lithium salt additive is a compound having the structural formula (I). ； R2 is either a cyano group or a nitro group, and R1 and R3 are either hydrogen atoms or fluorine atoms, respectively.

2. The electrolyte containing a novel lithium salt additive according to claim 1, characterized in that... The compounds of structural formula (I) include the following compounds: 。 3. The electrolyte containing a novel lithium salt additive according to claim 1, characterized in that... The method for synthesizing the lithium salt additive is as follows: First, 1.0 mol of trifluoromethanesulfonamide and 2.0 mol of potassium carbonate are mixed in anhydrous acetonitrile. After thorough stirring, 1.0 mol of one of the compounds of structural formula (III) is added. After the reaction is completed at room temperature, the insoluble solid is removed by filtration, and the solid obtained by rotary evaporation of the filtrate is dried under vacuum. The dried solid and lithium tetrafluoroborate are subjected to a cation exchange reaction in anhydrous acetonitrile to synthesize the product. The supernatant is taken and the excess solvent is removed by rotary evaporation. Finally, the product is washed and dried under vacuum to obtain the lithium salt additive. 。 4. The electrolyte containing a novel lithium salt additive according to claim 1, characterized in that... The concentration of the lithium salt additive is 0.1~0.3 mol / L.

5. The electrolyte containing a novel lithium salt additive according to claim 1, characterized in that... The lithium salt includes one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium dioxalate borate, lithium difluorooxalate borate, and lithium difluorodioxalate borate.

6. The electrolyte containing a novel lithium salt additive according to claim 5, characterized in that... The concentration of the lithium salt in the electrolyte ranges from 1 to 3 mol / L.

7. The electrolyte containing a novel lithium salt additive according to claim 1, characterized in that... The organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethylene glycol dimethyl ether, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

8. The electrolyte containing a novel lithium salt additive according to claim 1, characterized in that... The additives include one of fluoroethylene carbonate and vinylene carbonate.

9. The electrolyte containing a novel lithium salt additive according to claim 8, characterized in that... The additives account for 2% to 5% of the total mass of the electrolyte.

10. A lithium-ion battery, characterized in that... The lithium-ion battery uses the electrolyte containing novel lithium salt additives as described in claims 1-9.

Images