Battery electrolyte, secondary battery, and electric device

Abstract

The embodiment of the application provides a battery electrolyte, a secondary battery and a power utilization device, the battery electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive comprises fluoroethylene carbonate, a first additive shown in formula (I) and a second additive shown in formula (II), in formula (I), R1 is selected from alkenylene, alkynylene and the like; R2 and R3 are selected from alkyl, haloalkyl and the like; in formula (II), each X1, X2 and X3 are selected from O or S; n1, m n2 and n3 are 1 or 2; m is 0, 1 or 2; y and z are 0 or 1; R4 and R5 are selected from a hydrogen atom, alkyl and haloalkyl; the mass ratio of the first additive to the second additive is (0.3-5):1. The battery electrolyte is matched with fluoroethylene carbonate by simultaneously adding the first additive and the second additive with specific structures and specific proportions, so that the first coulomb efficiency of the battery, the fast charging performance and the cycle stability can be simultaneously improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a battery electrolyte, a secondary battery, and an electrical device. Background Technology

[0002] Secondary batteries have been widely used in portable electronic devices and new energy vehicles due to their high energy density, long cycle life and good environmental adaptability. However, with the continuous development of equipment and devices, higher requirements have been placed on the energy density of batteries.

[0003] Currently, to improve battery energy density, high-capacity anode materials such as silicon-carbon anodes are commonly used. However, these anode materials suffer from low initial coulombic efficiency and poor fast-charging performance. To address this, the industry has further explored solutions such as optimizing electrolyte solvents or introducing anode additives to compensate for the low initial efficiency and poor fast-charging performance of silicon-carbon anodes by using electrolytes with higher conductivity, better wettability, and superior film-forming properties. Taking lithium-ion batteries with lithium cobalt oxide as the positive electrode and silicon-carbon materials as the anode as an example, fluoroethylene carbonate (FEC) is commonly used as a consumable solvent for anode film formation. This solvent continuously repairs the SEI (Solid Electrolyte Interphase) film on the anode surface during battery operation, thereby improving the stability of the anode-electrolyte interface. However, in practical applications, it has been found that increasing the FEC content leads to increased electrolyte viscosity and reduced battery fast-charging performance. Furthermore, increasing the FEC content does not effectively improve the initial coulombic efficiency, thus inhibiting battery performance. Therefore, it is necessary to provide a specific electrolyte formulation to simultaneously address the issues of low initial coulombic efficiency and poor fast-charging performance of batteries. Summary of the Invention

[0004] In view of this, embodiments of this application provide a battery electrolyte, a secondary battery, and an electrical device. The battery electrolyte, by simultaneously adding a first additive and a second additive with a specific structure and a specific ratio, in combination with fluoroethylene carbonate, can simultaneously improve the battery's initial coulombic efficiency, fast charging performance, and cycle stability.

[0005] In a first aspect, embodiments of this application provide a battery electrolyte, which includes an electrolyte salt, an organic solvent, and additives, wherein the additives include fluoroethylene carbonate, a first additive represented by formula (I), and a second additive represented by formula (II).

[0006]

[0007] In formula (I), R1 is selected from one of alkenyl, haloalkenyl, alkyneyl, and haloalkyneyl; R2 and R3 are independently selected from one of alkyl, haloalkyl, alkenyl, substituted alkenyl, alkyne, and haloalkyne.

[0008] In formula (II), each X1, X2, X3 is independently selected from O or S; n1, m n2, n3 are independently 1 or 2; m is 0, 1 or 2; y is 0 or 1; z is 0 or 1; R4 and R5 are independently selected from one of hydrogen atoms, alkyl groups, and haloalkyl groups;

[0009] In the battery electrolyte, the mass ratio of the first additive to the second additive is (0.3-5):1.

[0010] The battery electrolyte provided in this application addresses the problem that the viscosity of the commonly used film-forming agent FEC in existing electrolytes is too high, and that it is excessively consumed at the negative electrode during battery formation and capacity testing, resulting in low initial efficiency and limited fast-charging cycle capability. By adding a specific proportion of first and second additives to the battery electrolyte to work synergistically with FEC, the initial coulombic efficiency, fast-charging performance, and cycle performance of the battery can be improved. The first additive is a sulfonate ester containing unsaturated double or triple bonds, and the second additive is a cyclic ester with a polycyclic structure. These two types of additives can preferentially undergo reduction reactions on the negative electrode surface to form a film, thus synergistically avoiding excessive consumption of FEC during battery formation and improving the battery's initial coulombic efficiency. At the same time, under appropriate ratios, these two types of additives can generate an organic oligomeric negative electrode electrolyte interface film on the negative electrode surface, which is rich in high-valence (+4, +6) sulfur, with alternating structures of specific sulfonates and specific cyclic esters. This structure is stable, robust, highly ion-conducting, and mechanically elastic, thus achieving a balance between low impedance and stability at the negative electrode interface, thereby improving the battery's initial coulombic efficiency, fast-charging performance, and cycle stability.

[0011] In this embodiment, the alkenyl group, haloalkenyl group, and alkyne group have 2-10 carbon atoms; the haloalkyne group has 3-10 carbon atoms; the alkyl group and haloalkyl group have 1-10 carbon atoms; and the alkenyl group, substituted alkenyl group, alkyne group, and haloalkyne group have 2-10 carbon atoms. A suitable lower number of carbon atoms is beneficial for obtaining a first additive with a suitable chain length, effectively reducing the negative electrode interface impedance, and also improving its dispersibility in the battery electrolyte system, avoiding the negative effects of uneven dispersion.

[0012] In this embodiment of the application, the mass ratio of the first additive to the second additive in the battery electrolyte is (0.5-2):1. This is beneficial for improving the initial coulombic efficiency and fast charge cycle performance.

[0013] In this embodiment, the mass percentage of the first additive in the battery electrolyte is 0.1%-2%. A suitable proportion of the first additive is beneficial to improve battery performance while avoiding excessive inhibition of FEC and other film formation on the negative electrode, and also avoids the formation of an excessively thick interfacial film.

[0014] In this embodiment, the second additive is present in the battery electrolyte at a mass percentage of 0.2%-2.5%. A suitable proportion of the second additive is beneficial for improving battery performance while avoiding excessive inhibition of FEC and other film formation on the negative electrode, and also avoids the formation of an excessively thick interfacial film.

[0015] In this embodiment of the application, the first additive includes one or more compounds of formula (I-1) to (I-9):

[0016] (I-1): (I-2):

[0017] (I-3): (I-4):

[0018] (I-5): (I-6):

[0019] (I-7): (I-8):

[0020] (I-9):

[0021] In this application embodiment, the second additive includes one or more compounds of formula (II-1) to (II-6):

[0022] (II-1): (II-2): (II-3):

[0023] (II-4): (II-5): (II-6):

[0024] In this embodiment, the fluoroethylene carbonate ester is present in the battery electrolyte at a mass percentage of 5%-50%. The addition of a suitable amount of fluoroethylene carbonate ester can effectively generate a passivation interface film on the negative electrode, suppressing continuous side reactions of the electrolyte at the negative electrode.

[0025] In this embodiment of the application, the mass ratio of the first additive to the fluoroethylene carbonate in the battery electrolyte is (0.0025-0.2):1.

[0026] In this embodiment of the application, the mass ratio of the second additive to the fluoroethylene carbonate in the battery electrolyte is (0.005-0.25):1.

[0027] In this embodiment, the additive further includes other additives, including one or more of the following: difluoroethylene carbonate, biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl ethylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, vinyl sulfite, methanedisulfonate, 1,2-bis(2-cyanoethoxy)ethane, and nitrile compounds. The addition of these other additives is beneficial for further improving battery performance.

[0028] In this embodiment, the electrolyte salt includes at least one selected from lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt. The selection of the electrolyte salt is specifically determined according to the battery type. For example, if the battery electrolyte is used for a lithium-ion battery, the electrolyte salt includes lithium salt; if the battery electrolyte is used for a sodium-ion battery, the electrolyte salt includes sodium salt.

[0029] In this embodiment, the molar concentration of the electrolyte salt in the battery electrolyte is 0.01 mol / L to 2.0 mol / L. A suitable electrolyte salt concentration can achieve suitable ion migration rates and electrode reaction rates, thereby improving battery performance.

[0030] In the embodiments of this application, the organic solvent includes one or more of carbonate solvents, ether solvents, and carboxylic acid ester solvents.

[0031] A second aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, a separator and an electrolyte located between the positive and negative electrodes, wherein the electrolyte includes the battery electrolyte described in the first aspect of this application. The secondary battery provided by this application, due to the use of the battery electrolyte described in the first aspect of this application, can achieve higher initial coulombic efficiency, better fast-charging performance, and better cycle stability.

[0032] In this embodiment of the application, the secondary battery includes a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a magnesium secondary battery, a zinc secondary battery, or an aluminum secondary battery.

[0033] In this application embodiment, the negative electrode includes one or more of the following: carbon-based negative electrode, silicon-based negative electrode, tin-based negative electrode, phosphorus-based negative electrode, lithium titanium oxide negative electrode, lithium negative electrode, sodium negative electrode, potassium negative electrode, magnesium negative electrode, zinc negative electrode, and aluminum negative electrode.

[0034] A third aspect of this application provides a battery module including a plurality of secondary batteries, wherein the plurality of secondary batteries are connected in series, in parallel or in series-parallel connection, and at least a portion of the plurality of secondary batteries include the secondary batteries described in the first aspect.

[0035] A fourth aspect of this application provides a battery pack including a plurality of battery modules and a support structure for carrying the plurality of battery modules, wherein at least a portion of the plurality of battery modules includes the battery modules described in the third aspect.

[0036] This application also provides an electrical device, characterized in that the electrical device includes a receiving cavity and a battery housed within the receiving cavity, the battery including a secondary battery as described in the second aspect, a battery module as described in the third aspect, or a battery pack as described in the fourth aspect. By employing the secondary battery, battery module, or battery pack provided in this application, the electrical device of this application can improve product fast-charging performance and long-term reliability, thereby enhancing product competitiveness. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the secondary battery 100 provided in the embodiments of this application;

[0038] Figure 2 This is a schematic diagram of the structure of the electrical equipment 200 provided in the embodiments of this application;

[0039] Figure 3 This is a graph showing the cycle capacity retention results of the batteries in Embodiments 1, 4, 7 and Comparative Example 3 of this application;

[0040] Figure 4 This is a graph showing the first coulombic efficiency results of the batteries in Examples 1, 4, 7 and Comparative Example 3 of this application;

[0041] Figure 5 These are photographs of the negative electrode interface after the batteries of Embodiment 4, Comparative Example 2, and Comparative Example 3 of this application have been disassembled after 800 cycles. Detailed Implementation

[0042] The embodiments of this application will now be described in conjunction with the accompanying drawings.

[0043] Currently, fluoroethylene carbonate (FEC) is commonly used as a consumable solvent for negative electrode film formation and is added to the electrolyte to continuously repair the SEI film on the negative electrode surface during battery operation, thereby improving the interfacial stability between the negative electrode and the electrolyte. However, in practical use, it has been found that increasing the FEC content leads to increased electrolyte viscosity and reduced battery fast-charging performance. Furthermore, increasing the FEC content cannot effectively improve the initial coulombic efficiency, thus inhibiting battery performance. To address the problem of excessively high viscosity of FEC, a commonly used film-forming agent in electrolytes, and its excessive consumption at the negative electrode during battery formation and capacity testing, resulting in low initial efficiency and limited fast-charging cycle capability, this application provides a battery electrolyte, a secondary battery, and an electrical device. This battery electrolyte, by simultaneously adding a first additive and a second additive with specific structures and proportions to fluoroethylene carbonate, can simultaneously improve the battery's initial coulombic efficiency, fast-charging performance, and cycle stability.

[0044] The battery electrolyte provided in this application includes an electrolyte salt, an organic solvent, and additives. The additives include fluoroethylene carbonate, a first additive shown in formula (I), and a second additive shown in formula (II).

[0045]

[0046] In formula (I), R1 is selected from one of alkenyl, haloalkenyl, alkyneyl, and haloalkyneyl; R2 and R3 are independently selected from one of alkyl, haloalkyl, alkenyl, substituted alkenyl, alkyne, and haloalkyne.

[0047] In formula (II), each X1, X2, X3 is independently selected from O or S; n1, m n2, n3 are independently 1 or 2; m is 0, 1 or 2; y is 0 or 1; z is 0 or 1; R4 and R5 are independently selected from one of hydrogen atoms, alkyl groups, and haloalkyl groups;

[0048] In the battery electrolyte, the mass ratio of the first additive to the second additive is (0.3-5):1.

[0049] The battery electrolyte provided in this application addresses the problem that the viscosity of the commonly used film-forming agent FEC in existing electrolytes is too high, and that it is excessively consumed at the negative electrode during battery formation and capacity testing, resulting in low initial efficiency and limited fast-charging cycle capability. By adding a specific proportion of first and second additives to the battery electrolyte to work synergistically with FEC, the initial coulombic efficiency, fast-charging performance, and cycle performance of the battery can be improved. The first additive is a sulfonate ester containing unsaturated double or triple bonds, and the second additive is a cyclic ester with a polycyclic structure. These two types of additives can preferentially undergo reduction reactions on the negative electrode surface to form a film, thus synergistically avoiding excessive consumption of FEC during battery formation and improving the battery's initial coulombic efficiency. At the same time, under appropriate ratios, these two types of additives can generate an organic oligomeric negative electrode electrolyte interface film on the negative electrode surface, which is rich in high-valence (+4, +6) sulfur, with alternating structures of specific sulfonates and specific cyclic esters. This structure is stable, robust, highly ion-conducting, and mechanically elastic, thus achieving a balance between low impedance and stability at the negative electrode interface, thereby improving the battery's initial coulombic efficiency, fast-charging performance, and cycle stability.

[0050] In the embodiments of this application, the first additive shown in formula (I) is a sulfonate additive containing unsaturated double or triple bonds. Specifically, when R1 is an alkenyl or haloalkenyl, the first additive is a sulfonate additive containing unsaturated double bonds; when R1 is an alkyne or haloalkyne, the first additive is a sulfonate additive containing unsaturated triple bonds.

[0051] In R1, the number of carbon atoms of the alkenyl group, haloalkenyl group, and alkyne group can be 2-10, and the number of carbon atoms of the haloalkyne group can be 3-10. A suitable lower number of carbon atoms is beneficial for obtaining a first additive with a suitable chain length, effectively reducing the negative electrode interface impedance, and also improving its dispersibility in the battery electrolyte system, avoiding the negative impact of uneven dispersion. For example, the number of carbon atoms of the alkenyl group, haloalkenyl group, and alkyne group can be 2, 3, 4, 5, 6, 7, 8, 9, or 10, and the number of carbon atoms of the haloalkyne group can be 3, 4, 5, 6, 7, 8, 9, or 10. In some embodiments, the number of carbon atoms of the alkenyl group, haloalkenyl group, and alkyne group can be 2-5, and the number of carbon atoms of the haloalkyne group can be 3-5. The halogenated alkenyl and halogenated ynyl groups can be partially or fully halogenated, meaning that the hydrogen atoms in the alkenyl and ynyl groups are partially or completely replaced by a halogen, which can be one or more selected from fluorine, chlorine, bromine, and iodine. Exemplarily, the alkenyl group can be, but is not limited to, vinylene, propynene, butenyl, or pentenyl. Exemplarily, the ynyl group can be, but is not limited to, ethynene, propynene, butynene, or pentyyn. The alkenyl, halogenated alkenyl, ynyl, and halogenated ynyl groups can have straight-chain or branched structures.

[0052] In formula (I), R2 and R3 are independently selected from alkyl, haloalkyl, alkenyl, substituted alkenyl, alkynyl, and haloalkynyl groups. R2 and R3 can be the same group or different groups. In some embodiments, the number of carbon atoms in alkyl and haloalkyl groups can be 1-10; the number of carbon atoms in alkenyl, substituted alkenyl, alkynyl, and haloalkynyl groups can be 2-10. A suitable number of fewer carbon atoms is beneficial for obtaining a first additive with a suitable chain length, effectively reducing the negative electrode interface impedance, and also improving its dispersibility in the battery electrolyte system, avoiding the negative impact of uneven dispersion. Haloalkyl, haloalkenyl, and haloalkynyl groups can be partially or fully halogenated, that is, the hydrogen atoms in alkyl, alkenyl, and alkynyl groups are partially or completely replaced by a halogen, which can be one or more selected from fluorine, chlorine, bromine, and iodine.

[0053] Exemplarily, the alkyl or haloalkyl group may have 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms. In some embodiments, the alkyl or haloalkyl group may have 1-5 carbon atoms. Exemplarily, the alkyl group may be, but is not limited to, methyl, ethyl, propyl, butyl, etc. Propyl may be n-propyl or isopropyl. Exemplarily, the haloalkyl group may be, but is not limited to, trifluoromethyl or pentafluoroethyl.

[0054] Exemplarily, the number of carbon atoms in the alkenyl, haloalkenyl, ynyl, and haloynyl groups can be 2, 3, 4, 5, 6, 7, 8, 9, or 10. In some embodiments, the number of carbon atoms in the alkenyl, haloalkenyl, ynyl, and haloynyl groups can be 2-5. Exemplarily, the alkenyl group can be, but is not limited to, vinyl, propenyl, butenyl, or pentenyl. Exemplarily, the ynyl group can be, but is not limited to, ethynyl, propynyl, butynyl, or pentynyl.

[0055] When R2 and R3 are haloalkyl, haloalkenyl, or haloalkynyl groups, it is beneficial for the first additive to form a film better at the negative electrode.

[0056] In some embodiments of this application, in formula (I), R1 is butylene-based or butylene-based, and R2 and R3 are independently selected from methyl, trifluoromethyl, ethyl, or propyl. R1, R2, and R3 all have a small number of carbon atoms, which is beneficial for the first additive to be better dispersed in the battery electrolyte system and to give fuller play to the performance advantages of the first additive.

[0057] In some embodiments of this application, the first additive comprises one or more compounds of formulas (I-1) to (I-9):

[0058] (I-1): (I-2):

[0059] (I-3): (I-4):

[0060] (I-5): (I-6):

[0061] (I-7): (I-8):

[0062] (I-9):

[0063] In this embodiment, the second additive represented by formula (II) is a cyclic ester additive having multiple (m+2) cyclic ester ring structures. The cyclic ester ring structure is a sulfur-containing cyclic ester ring structure. In formula (II), m can be 0, 1, or 2; when m is 0, the second additive represented by formula (II) includes 2 cyclic ester ring structures; when m is 1, the second additive represented by formula (II) includes 3 cyclic ester ring structures; when m is 2, the second additive represented by formula (II) includes 4 cyclic ester ring structures. The multiple cyclic ester ring structures can have the same structure or different structures.

[0064] In equation (II), n1, m n2s, and n3 can be independently 1 or 2. In some embodiments, n1, m n2s, and n3 are all 1. In some embodiments, n1, m n2s, and n3 are all 2. In other embodiments, n1, m n2s, and n3 can also be partially 1 and partially 2.

[0065] In formula (II), each X1, X2, and X3 can be independently selected from O or S. That is, n1 X1 atoms on the same sulfur atom (i.e., sulfur atoms within the ring), multiple X2 atoms on the same sulfur atom and on different sulfur atoms, and n3 X3 atoms on the same sulfur atom can be independently selected from O or S. In some embodiments, X1 atoms on the same sulfur atom are the same, X2 atoms on the same sulfur atom are the same, and X3 atoms on the same sulfur atom are the same. In formula (II), the atoms connected to the double bonds on the sulfur atoms (i.e., sulfur atoms within the ring) in multiple (m+2) cyclic ester ring structures can be the same, all O or all S, or they can be different. That is, the atoms connected to the double bonds on the sulfur atoms in some cyclic ester ring structures are O, and the atoms connected to the double bonds on the sulfur atoms in other cyclic ester ring structures are S.

[0066] In some embodiments, the structure of the second additive shown in formula (II) is as shown in formula (II-a), where the double bonds on the sulfur atoms in the plurality of (m+2) cyclic ester ring structures are all connected to the same atom, O.

[0067] Formula (II-a):

[0068] In formula (II-a), when n1, m n2, and n3 are all 1, that is, when multiple cyclic ester ring structures are cyclic sulfite structures, the second additive is a bisulfite additive.

[0069] In formula (II-a), when n1, m n2, and n3 are all 2, that is, when multiple cyclic ester ring structures are cyclic sulfate ester structures, the second additive is a bisulfate ester additive.

[0070] In formula (II-a), when n1, m n2, and n3 are part 1 and the other part is 2, that is, when multiple cyclic ester ring structures are cyclic sulfate structures and the other part is cyclic sulfate structures, then the second additive is a bisulfate-sulfite additive.

[0071] In this embodiment, the multiple cyclic ester ring structures include cyclic sulfate ester structures, and the interface film formed by the reduction of the second additive has better stability and better suppression effect on battery gas generation.

[0072] In other embodiments, the structure of the second additive shown in formula (II) is as shown in formula (II-b), where the double bonds on the sulfur atoms in the plurality of (m+2) cyclic ester ring structures are all S atoms;

[0073] Equation (II-b):

[0074] In equation (II), y and z can both be 0 or both be 1, or one of them can be 0 and the other can be 1.

[0075] In formula (II), R4 and R5 are independently selected from hydrogen atoms, alkyl groups, and haloalkyl groups. The selection of alkyl groups and haloalkyl groups can refer to the selection of R2 and R3 in formula (I) above. R4 and R5 can be the same group or different groups. In some embodiments, R4 and R5 are both hydrogen atoms, in which case the structure of the second additive is simpler and easier to prepare.

[0076] Understandably, the meanings of the same groups and letter parameters in formulas (II-a) and (II-b) are consistent with those in formula (II), and the selection range is consistent.

[0077] In some embodiments of this application, the second additive comprises one or more compounds of formulas (II-1) to (II-6):

[0078] (II-1): (II-2): (II-3):

[0079] (II-4): (II-5): (II-6):

[0080] To better utilize the synergistic effect of the first and second additives to improve the battery's initial coulombic efficiency, fast-charging performance, and cycle performance, in this embodiment, the mass ratio of the first additive to the second additive in the battery electrolyte is controlled within the range of (0.3-5):1. Specifically, when the mass ratio of the first additive to the second additive is too high, it easily leads to an excessive amount of organic long-chain sulfonate additives in the interfacial film, resulting in increased impedance and easy lithium plating during high-rate fast charging. When the mass ratio of the first additive to the second additive is too low, it easily leads to an excessive amount of cyclic ester additives with polycyclic structures in the interfacial film, resulting in insufficient interfacial stability and increased battery cycle degradation. For example, the mass ratio of the first additive to the second additive may be, but is not limited to, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 1.0:1, 1.2:1, 1.5:1, 1.8:1, 2.0:1, 2.2:1, 2.5:1, 2.7:1, 3.0:1, 3.2:1, 3.5:1, 4.0:1, 4.3:1, 4.5:1, 4.8:1, 5.0:1, and any number between any two of the above values. For example, it may be a value between 0.3 and 1.0, or a value between 1.0 and 2.5, or a value between 0.5 and 3.0, or a value between 2.0 and 5.0, or any other number between any two values. To better control the film-forming reaction at the negative electrode interface and further improve performance, while taking into account the initial coulombic efficiency, fast-charging performance and cycle performance, in some embodiments of this application, the mass ratio of the first additive to the second additive in the battery electrolyte is controlled within the range of (0.5-2):1.

[0081] In this embodiment, the mass percentage of the first additive in the battery electrolyte is 0.1%-2%. A suitable proportion of the first additive is beneficial for improving battery performance while avoiding excessive inhibition of FEC film formation on the negative electrode and the formation of an excessively thick interfacial film. Exemplarily, the mass percentage of the first additive in the battery electrolyte can be, but is not limited to, 0.1%, 0.2%, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.5%, 1.6%, 1.8%, and 2%. To better avoid excessive inhibition of FEC film formation that may result from increased first additive concentration, and to better avoid increased battery impedance and deterioration of cycle stability due to the formation of a thicker interfacial film, in some embodiments, the mass percentage of the first additive in the battery electrolyte is controlled to be 0.2%-1.5%.

[0082] In this embodiment, the second additive has a mass percentage of 0.2%-2.5% in the battery electrolyte. A suitable proportion of the second additive is beneficial for improving battery performance without excessively inhibiting the formation of FEC and other substances on the negative electrode, nor for generating an excessively thick interfacial film. Exemplarily, the mass percentage of the second additive in the battery electrolyte can be, but is not limited to, 0.2%, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, and 2.5%. This is to better avoid excessive inhibition of FEC formation that may result from increased concentration of the first additive, and to better avoid increased battery impedance and deterioration of cycle stability due to the formation of a thicker sulfur-containing organic interfacial film. In some embodiments, the mass percentage of the second additive in the battery electrolyte is 0.3%-2%.

[0083] In this embodiment, the mass percentage of fluoroethylene carbonate in the battery electrolyte is 5%-50%. Exemplarily, the mass percentage of fluoroethylene carbonate in the battery electrolyte can be, but is not limited to, 5%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%. The addition of a suitable amount of fluoroethylene carbonate can effectively generate a passivation interface film on the negative electrode, suppressing continuous side reactions of the electrolyte at the negative electrode.

[0084] In this embodiment, the mass ratio of the first additive to fluoroethylene carbonate in the battery electrolyte is (0.0025-0.2):1. Controlling the mass ratio of the first additive to fluoroethylene carbonate within a suitable range helps to suppress excessive consumption of fluoroethylene carbonate during battery formation while avoiding excessive inhibition of its film-forming effect. This allows for better utilization of the beneficial effects of fluoroethylene carbonate, thereby better balancing initial coulombic efficiency, generating an excellent sulfur-rich SEI film, and improving the stability of the negative electrode. For example, the mass ratio of the first additive to fluoroethylene carbonate can be 0.0025, 0.01, 0.03, 0.05, 0.07, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, or any number between any two of the above values. For instance, the mass ratio of the first additive to fluoroethylene carbonate can be a value between 0.0025 and 0.05, a value between 0.03 and 0.1, a value between 0.07 and 0.15, a value between 0.12 and 0.2, or any other number between any two values.

[0085] In this embodiment of the application, the mass ratio of the second additive to the fluoroethylene carbonate in the battery electrolyte is (0.005-0.25):1. Controlling the mass ratio of the second additive to the fluoroethylene carbonate within a suitable range helps to suppress excessive consumption of the fluoroethylene carbonate during battery formation while avoiding excessive inhibition of its film-forming effect. This allows for a better balance between initial coulombic efficiency, the formation of an excellent sulfur-rich SEI film, and improved negative electrode stability. For example, the mass ratio of the second additive to fluoroethylene carbonate can be 0.005, 0.01, 0.03, 0.05, 0.07, 0.1, 0.13, 0.15, 0.17, 0.19, 0.21, 0.23, 0.25, or any number between any two of the above values. For instance, the mass ratio of the second additive to fluoroethylene carbonate can be a value between 0.005 and 0.05, a value between 0.03 and 0.1, a value between 0.05 and 0.15, a value between 0.15 and 0.25, or any other number between any two values.

[0086] It is understood that the mass percentages of the first additive, the second additive, the mass ratio of fluoroethylene carbonate, and the mass ratio of the first additive, the second additive, and the fluoroethylene carbonate mentioned above may have certain measurement and testing system errors during actual testing operations. Values ​​within the range of system errors can be understood as the ranges defined by the embodiments of this application.

[0087] In this embodiment, the additives further include other additives, including one or more of the following: difluoroethylene carbonate, biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl ethylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, vinyl sulfite, methanedisulfonate, 1,2-bis(2-cyanoethoxy)ethane, and nitrile compounds. The addition of these other additives is beneficial for further improving battery performance. The mass percentage of each other additive in the battery electrolyte may, for example, be 2%-6%, exemplarily, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, or 6%. Nitrile compounds may include mononitrile compounds and / or polynitrile compounds. Polynitrile compounds include, but are not limited to, butadienenitrile, glutaronitrile, adiponitrile, and 1,3,6-hexanetrionitrile. Nitrile compounds can stabilize the positive electrode through adsorption and inhibit the oxidative decomposition of the electrolyte on the positive electrode side.

[0088] It is understood that after actual battery formation, capacity testing, or cycling, the consumption of additives will have a certain impact on the additive content and ratio, and a certain measurement and testing error is permissible. Values ​​within the error range can be understood as the range defined by the embodiments of this application; or the additive content and ratio tested after battery formation, capacity testing, or cycling are still within the above range, which can be understood as the range defined by the embodiments of this application.

[0089] In this embodiment of the application, the electrolyte salt includes at least one of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt. Specifically, the lithium salt, sodium salt, and potassium salt can be MClO4, MBF4, MPF6, MAsF6, MPF2O2, MCF3SO3, MTDI, MB(C2O4)2(MBOB), MBF2C2O4(MDFOB), M[(CF3SO2)2N], M[(FSO2)2N], and M[(C m F 2m+1 SO2)(C n F 2n+1 Lithium salts can be one or more of the following: [(C(SO2)N], where M is Li, Na, or K, and m and n are natural numbers. For example, lithium salts can be, but are not limited to, LiClO4, LiBF4, LiPF6, LiAsF6, LiPF2O2, LiCF3SO3, LiTDI, Li[(CF3SO2)2N], Li[(FSO2)2N], and Li[(C(C(SO2)N)N]]. m F 2m+1 SO2)(C n F 2n+1 Sodium salts can be one or more of the following: Na[(CF3SO2)2N], where m and n are natural numbers. For example, sodium salts can be, but are not limited to, NaClO4, NaBF4, NaPF6, NaAsF6, NaPF2O2, NaCF3SO3, NaTDI, Na[(CF3SO2)2N], Na[(FSO2)2N], and Na[(C m F 2m+ 1SO2)(C n F 2n+1 One or more of [SO2)N], where m and n are natural numbers. Similarly, magnesium salts, zinc salts, and aluminum salts can also be salts formed by magnesium ions, zinc ions, aluminum ions, and anions from the lithium salts, sodium salts, and potassium salts mentioned above.

[0090] In this embodiment, the molar concentration of the electrolyte salt in the battery electrolyte is 0.01 mol / L to 2.0 mol / L. In some embodiments, the molar concentration of the electrolyte salt in the battery electrolyte can be, for example, 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, or 2.0 mol / L.

[0091] In this application, the organic solvent may be one or more of carbonate solvents, ether solvents, and carboxylic acid ester solvents. In this application, the carbonate solvent includes cyclic carbonates or chain carbonates. Specifically, cyclic carbonates may be, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), butylene carbonate (BC), trifluoromethyl ethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, and (2,2,2-trifluoroethyl)methyl carbonate. Chain carbonates may be, but are not limited to, one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). Ether solvents include cyclic ethers or chain ethers. Cyclic ethers may be, but are not limited to, one or more of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). Chain ethers may be, but are not limited to, one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (TEGDME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether. Carboxylic acid ester solvents may be, but are not limited to, one or more of methyl formate, ethyl formate, methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), butyl propionate, methyl difluoroacetate, and methyl trifluoroacetate.

[0092] Accordingly, embodiments of this application also provide a method for preparing the above-mentioned battery electrolyte, including the following steps:

[0093] In an inert or sealed environment (such as a glove box filled with argon), the additives are added to an organic solvent, and the fully dried electrolyte salt is dissolved in the organic solvent. After stirring and mixing evenly, a battery electrolyte is obtained, wherein the additives include the first additive, the second additive and fluoroethylene carbonate mentioned above.

[0094] Each operation in the above preparation method can be implemented according to existing conventional electrolyte preparation processes. The specific selection of organic solvents, electrolyte salts, first additives, second additives, and other additives is as described above and will not be repeated here.

[0095] See Figure 1 , Figure 1 This is a schematic diagram of the structure of the secondary battery 100 provided in this application embodiment. The secondary battery 100 also provided in this application embodiment includes a positive electrode 10, a negative electrode 20, a separator 30 located between the positive electrode 10 and the negative electrode 20, and an electrolyte 40. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20, and the electrolyte 40 fills the space between the positive electrode 10 and the negative electrode 20 and wets the separator 30. During charging, metal ions (e.g., lithium ions) are extracted from the positive electrode active material 102 of the positive electrode 10, pass through the electrolyte 40, and then embed into the negative electrode active material 202 of the negative electrode 20. During discharging, metal ions (e.g., lithium ions) are extracted from the negative electrode active material 202, pass through the electrolyte 40, and then insert into the positive electrode active material 102. The electrolyte 40 is the battery electrolyte provided in the above-described embodiment of this application. In the secondary battery 100, the electrolyte 40 is the transport medium for metal ions during transport between the positive electrode 10 and the negative electrode 20. The secondary battery provided in this application, due to the use of the aforementioned battery electrolyte, can achieve high initial coulombic efficiency, good fast-charging performance, and cycle stability. In this application's embodiments, the secondary battery can be a lithium secondary battery, potassium secondary battery, sodium secondary battery, magnesium secondary battery, zinc secondary battery, aluminum secondary battery, etc.

[0096] In this embodiment, the positive electrode 10 includes a positive electrode current collector 101 and a positive electrode material layer disposed on the surface of the positive electrode current collector 101. The positive electrode current collector 101 can be a metal foil, such as aluminum, gold, platinum, titanium, tantalum, or their alloy foil. The positive electrode material layer includes a positive electrode active material 102 capable of reversibly inserting / de-inserting metal ions (lithium ions, sodium ions, potassium ions, magnesium ions, zinc ions, aluminum ions, etc.). This application does not have a specific limitation on the selection of the positive electrode active material; it can be any positive electrode active material conventionally used in existing secondary batteries. To facilitate the preparation of high-voltage secondary batteries, high-voltage positive electrode materials can be used. Taking a lithium secondary battery as an example, the positive electrode active material can be lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), or lithium nickel cobalt manganese ternary materials (LiNi...). a Co b Mn c (abbreviated as NCM, a+b+c=1), polyanionic lithium compound LiM x (PO4) y(M represents materials such as Ni, Co, Mn, Fe, Ti, V, 0≤x≤5, 0≤y≤5, etc.). Taking a sodium secondary battery as an example, the positive electrode active material can be one or more of the following: layered sodium transition metal oxides, Prussian blue (white) compounds, and sodium polyanionic compounds. For example, layered sodium transition metal oxides can be sodium-nickel-iron-manganese (NaNi). 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (abbreviated as NFM), Prussian blue (white) compounds such as Prussian white (Na2Mn[Fe(CN)6], abbreviated as PBA), and sodium polyanionic compounds such as sodium iron phosphate (NaFePO4, abbreviated as NFP).

[0097] In this embodiment, the aforementioned positive electrode material layer may further include a certain amount of binder, conductive agent, and other components. The binder may be, for example, polyvinylidene fluoride (PVDF). The conductive agent may be, for example, amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. The binder and conductive agent described above are merely illustrative examples and are not intended to limit the scope of the invention.

[0098] In this embodiment, the negative electrode 20 can be one or more of the following: carbon-based negative electrode, silicon-based negative electrode, tin-based negative electrode, phosphorus-based negative electrode, lithium titanium oxide negative electrode, lithium negative electrode, sodium negative electrode, potassium negative electrode, magnesium negative electrode, zinc negative electrode, and aluminum negative electrode. The carbon-based negative electrode can include, but is not limited to, one or more carbon-based negative electrode materials selected from graphite (e.g., artificial graphite), mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, porous carbon, and graphene; the silicon-based negative electrode can include, but is not limited to, one or more silicon-based negative electrode materials selected from silicon, silicon carbide, silicon oxide, and silicon metal compound; the tin-based negative electrode can include, but is not limited to, one or more tin-based negative electrode materials selected from tin, tin carbide, tin oxide, and tin metal compound; the phosphorus-based negative electrode can include, but is not limited to, one or more phosphorus-based negative electrode materials selected from red phosphorus, black phosphorus, and phosphorus compounds; and the lithium titanium oxide negative electrode can include, but is not limited to, lithium titanate (Li4Ti5O4). 12 Lithium titanium oxide anode materials; lithium anodes, sodium anodes, potassium anodes, magnesium anodes, zinc anodes, and aluminum anodes can be elemental lithium, sodium, potassium, magnesium, zinc, or aluminum, or alloys thereof, or the aforementioned metals or alloys thereof with a current collector. For example, lithium anodes may include metallic lithium or lithium alloys. Specifically, lithium alloys may be at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys. The electrolyte in the embodiments of this application also exhibits good compatibility with the metal anodes, while also possessing oxidation resistance and meeting high-voltage characteristics.

[0099] In some embodiments of this application, the negative electrode 20 includes a negative electrode current collector 201 and a negative electrode material layer disposed on the surface of the negative electrode current collector 201. The negative electrode current collector 201 can be a metal foil, such as copper foil, aluminum foil, gold foil, platinum foil, nickel foil, stainless steel foil, etc. The negative electrode material layer includes a negative electrode active material 202, which can accept and release metal ions (lithium ions, sodium ions, potassium ions, magnesium ions, zinc ions, aluminum ions, etc.). In embodiments of this application, the negative electrode active material 202 can be one of the following: carbon-based negative electrode materials, silicon-based negative electrode materials, tin-based negative electrode materials, phosphorus-based negative electrode materials, lithium titanium oxide negative electrode materials, elemental lithium metal or its alloys, elemental sodium metal or its alloys, elemental potassium metal or its alloys, elemental magnesium metal or its alloys, elemental zinc metal or its alloys, elemental aluminum metal or its alloys.

[0100] In this embodiment, the negative electrode material layer may further include a certain amount of binder, conductive agent, and other components. The binder may be, for example, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (NaPAA), etc., and the conductive agent may be, for example, amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. The above-mentioned binders and conductive agents are merely illustrative examples and are not limited thereto.

[0101] In other embodiments of this application, the negative electrode 20 is a metal negative electrode that does not include a current collector. For example, the negative electrode 20 is a lithium metal elemental or alloy negative electrode, sodium metal elemental or alloy negative electrode, potassium metal elemental or alloy negative electrode, magnesium metal elemental or alloy negative electrode, zinc metal elemental or alloy negative electrode, or aluminum metal elemental or alloy negative electrode without a current collector.

[0102] In the secondary battery 100, the separator 30 blocks electrons from passing through while allowing metal ions to pass through. In the embodiments of this application, the separator 30 can be a conventional separator, such as a polymer separator, non-woven fabric, etc., including but not limited to single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, and ceramic-coated PE separators.

[0103] The specific shape or type of the secondary battery in this application embodiment is not limited, and it can be a square battery, button battery, cylindrical battery, pouch battery, etc.; it can be a wound battery or a stacked battery. The secondary battery can be in rigid packaging, such as a hard plastic shell, aluminum shell, steel shell, etc., or in flexible packaging, such as a pouch-type flexible packaging. The material of the flexible packaging can be plastic, such as polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0104] The secondary battery provided in this application embodiment can be used in terminal devices, such as consumer electronic products, such as mobile phones, tablets, power banks, laptops, and other wearable or mobile electronic devices, as well as equipment products such as vehicles, drones, energy storage devices, and base stations, to improve the fast charging performance and long-term reliability of the products.

[0105] This application also provides a battery module including multiple secondary batteries. These secondary batteries can be connected in series, in parallel, or in a series-parallel configuration (i.e., series plus parallel). At least a portion of the multiple secondary batteries includes the secondary battery 100 described in this application embodiment. Specifically, in the battery module, all multiple secondary batteries may be the secondary batteries provided in this application embodiment, or a portion may consist of the secondary batteries provided in this application embodiment, with the remaining portion being other secondary batteries.

[0106] This application also provides a battery pack, including multiple battery modules and a support structure for supporting the multiple battery modules. At least a portion of the multiple battery modules include the battery modules described above in this application embodiment. Specifically, the battery pack may contain multiple battery modules that are all the battery modules provided in this application embodiment, or it may contain a portion of the battery modules provided in this application embodiment and another portion of other battery modules.

[0107] See Figure 2 , Figure 2 This is a schematic diagram of the structure of the electrical device 200 provided in this application embodiment. The electrical device 200 provided in this application embodiment includes a housing 211, and electronic components and a battery 212 housed within the housing 211. The battery 212 is electrically connected to the electronic components, and the battery 212 includes the secondary battery 100 described above in this application embodiment. In this application, the electrical device 200 can be a consumer electronic product, such as a mobile phone, tablet computer, desktop computer, laptop computer, power bank, portable computer, smart screen, monitor, audio equipment, in-vehicle products, and other wearable or portable electronic devices (e.g., glasses, watches, bracelets, headphones, etc.), or it can be a drone, vehicle (e.g., all-electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, electric bicycle, electric scooter, electric golf cart, electric truck, electric train, etc.), ship, satellite, energy storage equipment or system, base station, and other equipment products.

[0108] In this embodiment, the electrical device 200 may include one or more of the secondary battery 100, battery module, and battery pack provided in this embodiment, depending on actual needs. The secondary battery, battery module, or battery pack can be used as the power source for the electrical device or as the energy storage unit of the electrical device.

[0109] The embodiments of this application will be further described below through multiple examples.

[0110] Unless otherwise specified, all materials used in the following embodiments are commercially available products.

[0111] Example 1

[0112] Preparation of battery electrolyte:

[0113] In an argon-filled glove box, propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and fluoroethylene carbonate (FEC) are mixed to form an organic solvent. Fully dried lithium hexafluorophosphate (LiPF6) is then dissolved in this solvent and stirred to form a homogeneous solution. The mass percentages of PC, DEC, PP, FEC, and LiPF6 are 10%, 22.5%, 15%, 40%, and 12.5%, respectively. Then, the first additive shown in formula (I-1), the second additive shown in formula (II-1), and succinic anionylene are added to the solution at mass percentages of 1.5%, 0.3%, and 2%, respectively, and mixed thoroughly to obtain the lithium secondary battery electrolyte.

[0114] (I-1): (II-1):

[0115] Manufacturing of lithium-ion secondary batteries:

[0116] Weigh out 2% polyvinylidene fluoride (PVDF), 2% conductive agent Super P and 96% positive electrode active material (LiCoO2, abbreviated LCO, commercially available), and add them sequentially to N-methylpyrrolidone (NMP). Stir and mix thoroughly. Coat the slurry onto an aluminum foil current collector, dry, cold press and cut to obtain the positive electrode sheet, thus obtaining the positive electrode.

[0117] Weigh out 1.5% CMC, 2.5% SBR, 1% Super P and 95% negative electrode active material (50% silicon carbon material and 50% graphite material by mass), add them to deionized water in sequence, stir and mix thoroughly, coat the slurry on copper foil current collector, dry, cold press and cut to obtain negative electrode sheet, thus obtaining negative electrode.

[0118] The positive electrode, negative electrode, and commercial PE separator prepared above are used to make a battery cell, which is then packaged with polymer, filled with the lithium secondary battery electrolyte prepared above, and processed through formation and other processes to produce a 4Ah soft-pack lithium-ion secondary battery.

[0119] Example 2

[0120] Preparation of battery electrolyte:

[0121] In an argon-filled glove box, propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and fluoroethylene carbonate (FEC) are mixed to form an organic solvent. Fully dried lithium hexafluorophosphate (LiPF6) is then dissolved in this solvent and stirred to form a homogeneous solution. The mass percentages of PC, DEC, PP, FEC, and LiPF6 are 10%, 22.5%, 15%, 40%, and 12.5%, respectively. Then, the first additive shown in formula (I-2), the second additive shown in formula (II-1), and succinic anionylene are added to the solution at mass percentages of 0.6%, 2%, and 2%, respectively, and the mixture is stirred until homogeneous to obtain the lithium secondary battery electrolyte.

[0122] (I-2): (II-1):

[0123] Manufacturing of lithium-ion secondary batteries:

[0124] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Example 2.

[0125] Example 3

[0126] Preparation of battery electrolyte:

[0127] The method is the same as in Example 1, except that the first additive shown in formula (I-1), the second additive shown in formula (II-1), and succinic anion are added at a mass percentage of 0.5%, 1%, and 2%, respectively.

[0128] Manufacturing of lithium-ion secondary batteries:

[0129] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Example 3.

[0130] Example 4

[0131] Preparation of battery electrolyte:

[0132] The method is the same as in Example 1, except that the first additive shown in formula (I-1), the second additive shown in formula (II-1), and succinic anion are added at mass percentages of 1%, 0.5%, and 2%, respectively.

[0133] Manufacturing of lithium-ion secondary batteries:

[0134] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Example 4.

[0135] Example 5

[0136] Preparation of battery electrolyte:

[0137] The method is the same as in Example 1, except that the first additive shown in formula (I-1), the second additive shown in formula (II-1), and succinic anion are added at a mass percentage of 0.2%, 0.3%, and 2%, respectively.

[0138] Manufacturing of lithium-ion secondary batteries:

[0139] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Example 5.

[0140] Example 6

[0141] Preparation of battery electrolyte:

[0142] The method is the same as in Example 1, except that the first additive shown in formula (I-1), the second additive shown in formula (II-1), and succinic anion are added at a mass percentage of 1.5%, 2%, and 2%, respectively.

[0143] Manufacturing of lithium-ion secondary batteries:

[0144] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Example 6.

[0145] Example 7

[0146] Preparation of battery electrolyte:

[0147] The method is the same as in Example 1, except that the first additive shown in formula (I-1), the second additive shown in formula (II-1), and succinic anion are added at a mass percentage of 2%, 2.5%, and 2%, respectively.

[0148] Manufacturing of lithium-ion secondary batteries:

[0149] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Example 7.

[0150] Example 8

[0151] Preparation of battery electrolyte:

[0152] In an argon-filled glove box, propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and fluoroethylene carbonate (FEC) are mixed to form an organic solvent. Fully dried lithium hexafluorophosphate (LiPF6) is then dissolved in this solvent and stirred to form a homogeneous solution. The mass percentages of PC, DEC, PP, FEC, and LiPF6 are 10%, 22.5%, 15%, 40%, and 12.5%, respectively. Then, the first additive shown in formula (I-2), the second additive shown in formula (II-2), and succinic anionylene are added to the solution at mass percentages of 0.1%, 0.2%, and 2%, respectively. The mixture is then thoroughly mixed to obtain the lithium secondary battery electrolyte.

[0153] (I-2): (II-2):

[0154] Manufacturing of lithium-ion secondary batteries:

[0155] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Example 8.

[0156] Example 9

[0157] Preparation of battery electrolyte:

[0158] In an argon-filled glove box, propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and fluoroethylene carbonate (FEC) are mixed to form an organic solvent. Fully dried lithium hexafluorophosphate (LiPF6) is then dissolved in this solvent and stirred to form a homogeneous solution. The mass percentages of PC, DEC, PP, FEC, and LiPF6 are 20%, 22.5%, 30%, 15%, and 12.5%, respectively. Then, the first additive shown in formula (I-1), the second additive shown in formula (II-1), and succinic anionylene are added to the solution at mass percentages of 1.5%, 2%, and 2%, respectively, and the mixture is stirred until homogeneous to obtain the lithium secondary battery electrolyte.

[0159] Manufacturing of lithium-ion secondary batteries:

[0160] The method is the same as in Example 1, except that the mass ratio of silicon-carbon material in the negative electrode active material is 15%, the mass ratio of graphite material is 85%, and the lithium secondary battery electrolyte of Example 9 is used.

[0161] Example 10

[0162] Preparation of battery electrolyte:

[0163] The difference from Example 9 is that the first additive shown in Formula (I-1), the second additive shown in Formula (II-1), and succinic anion are added at a mass percentage of 3%, 2%, and 2%, respectively.

[0164] Manufacturing of lithium-ion secondary batteries:

[0165] The preparation method of the lithium-ion secondary battery is the same as that in Example 9, except that the battery uses the lithium secondary battery electrolyte of Example 10.

[0166] Example 11

[0167] Preparation of battery electrolyte:

[0168] The difference from Example 9 is that the first additive shown in Formula (I-1), the second additive shown in Formula (II-1), and succinic anion are added at a mass percentage of 1.5%, 3.5%, and 2%, respectively.

[0169] Manufacturing of lithium-ion secondary batteries:

[0170] The preparation method of the lithium-ion secondary battery is the same as that in Example 9, except that the battery uses the lithium secondary battery electrolyte of Example 11.

[0171] Example 12

[0172] Preparation of battery electrolyte:

[0173] In an argon-filled glove box, propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and fluoroethylene carbonate (FEC) are mixed to form an organic solvent. Fully dried lithium hexafluorophosphate (LiPF6) is then dissolved in this solvent and stirred to form a homogeneous solution. The mass percentages of PC, DEC, PP, FEC, and LiPF6 are 25%, 27.5%, 30%, 5%, and 12.5%, respectively. Then, the first additive shown in formula (I-1), the second additive shown in formula (II-1), and succinic anionylene are added to the solution at mass percentages of 0.75%, 1%, and 2%, respectively, and the mixture is stirred until homogeneous to obtain the lithium secondary battery electrolyte.

[0174] (I-1): (II-1):

[0175] Manufacturing of lithium-ion secondary batteries:

[0176] The preparation method of the lithium-ion secondary battery is the same as that in Example 9, except that the battery uses the lithium secondary battery electrolyte of Example 12.

[0177] Example 13

[0178] Preparation of battery electrolyte:

[0179] The difference from Example 12 is that the first additive shown in Formula (I-1), the second additive shown in Formula (II-1), and succinic anion are added at a mass percentage of 1.5%, 1%, and 2%, respectively.

[0180] Manufacturing of lithium-ion secondary batteries:

[0181] The difference from Example 12 is that the battery uses the lithium secondary battery electrolyte of Example 13.

[0182] Example 14

[0183] Preparation of battery electrolyte:

[0184] The difference from Example 12 is that the first additive shown in Formula (I-1), the second additive shown in Formula (II-1), and succinic anionylene are added at a mass percentage of 0.75%, 2%, and 2%, respectively.

[0185] Manufacturing of lithium-ion secondary batteries:

[0186] The difference from Example 12 is that the battery uses the lithium secondary battery electrolyte of Example 14.

[0187] Comparative Example 1

[0188] Preparation of battery electrolyte:

[0189] The difference from Example 4 is that the second additive shown in Formula (II-1) is not added.

[0190] Manufacturing of lithium-ion secondary batteries:

[0191] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the lithium secondary battery electrolyte of Comparative Example 1 is used.

[0192] Comparative Example 2

[0193] Preparation of battery electrolyte:

[0194] The difference from Example 3 is that the first additive shown in Formula (I-1) is not added.

[0195] Manufacturing of lithium-ion secondary batteries:

[0196] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Comparative Example 2.

[0197] Comparative Example 3

[0198] Preparation of battery electrolyte:

[0199] The difference from Example 1 is that the first additive shown in Formula (I-1), the second additive shown in Formula (II-1), and succinic anion are added at a mass percentage of 2%, 0.2%, and 2%, respectively.

[0200] Manufacturing of lithium-ion secondary batteries:

[0201] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Comparative Example 3.

[0202] Comparative Example 4

[0203] Preparation of battery electrolyte:

[0204] The difference from Example 1 is that the first additive shown in Formula (I-1), the second additive shown in Formula (II-1), and succinic anion are added at a mass percentage of 0.2%, 2%, and 2%, respectively.

[0205] Manufacturing of lithium-ion secondary batteries:

[0206] The preparation method of the lithium-ion secondary battery is the same as that in Example 1, except that the battery uses the lithium secondary battery electrolyte of Comparative Example 4.

[0207] To better illustrate the beneficial effects of the embodiments of this application, the lithium-ion secondary batteries prepared in the above embodiments and comparative examples of this application were subjected to the following tests:

[0208] 1. Room temperature cycling performance test:

[0209] The lithium-ion secondary batteries prepared in the above examples and comparative examples were placed in an oven at a constant temperature of 25±3℃ and charged at a constant current of 4C to 4.2V, then charged at a constant current of 1C to 4.53V, and then charged at a constant voltage until the current dropped to 0.025C. After standing for 10 minutes, they were discharged at a constant current of 1C to 3.0V. This cycle was repeated 800 times. The discharge capacity of the 1st and 800th cycles was recorded, and the capacity retention rate after 800 cycles was calculated using the following formula:

[0210] Capacity retention (%) = Discharge capacity of the 800th cycle / Discharge capacity of the 1st cycle × 100%.

[0211] In addition, the cycled battery was disassembled to observe the condition of the negative electrode interface.

[0212] 2. Initial Coulomb efficiency (first-effect) test:

[0213] The lithium-ion secondary batteries prepared in the above examples and comparative examples were charged at 45°C to 3.2V using hot pressing at 0.05C, and the charging capacity C1 was recorded. After standing for 5 minutes, they were charged at a constant current of 0.5C to 4.53V, and then charged at a constant voltage until the current dropped to 0.025C. The charging capacity C2 was recorded. After standing for 5 minutes, they were discharged at a constant current of 0.5C to 3V, and the discharge capacity C3 was recorded.

[0214] First coulomb efficiency (%) = C3 / (C1+C2)×100%.

[0215] Table 1 shows the mass content of each additive, the mass ratio of each additive, the mass ratio of silicon-carbon material in the negative electrode active material, the first efficiency of the battery, the capacity retention rate after 800 cycles, and the condition of the negative electrode interface after disassembly of the battery after cycling in Examples 1 to 14 and Comparative Examples 1 to 4.

[0216] Table 1. Parameters and battery performance results of Examples 1 to 14 and Comparative Examples 1 to 4.

[0217]

[0218]

[0219] Comparing Examples 1 to 8 with Comparative Examples 1 to 4, it can be seen that when the mass ratio of silicon-carbon material in the negative electrode active material and the mass content of FEC in the electrolyte are fixed, Examples 1 to 8, by simultaneously adding the first additive and the second additive to the battery electrolyte and controlling the mass ratio of the first additive and the second additive within the range of (0.3-5), can effectively improve the battery's initial efficiency and fast-charge cycle capacity retention rate, and suppress lithium plating during battery cycles. The initial efficiency of the batteries in Examples 1 to 8 is above 83%, the capacity retention rate after 800 cycles is above 84%, and no lithium plating occurs at the negative electrode interface. In contrast, Comparative Examples 1-2 did not simultaneously add the first additive and the second additive to the battery electrolyte, and although Comparative Examples 3 to 4 simultaneously added the first additive and the second additive, the mass ratio of the first additive and the second additive was not within the suitable range of (0.3-5). The initial efficiency of the batteries in Comparative Examples 1 to 4 is below 82%, the capacity retention rate after 800 cycles is below 79%, and slight or even severe lithium plating occurs at the negative electrode interface. This is because the first and second additives preferentially undergo reduction reactions on the negative electrode surface to form a film, thus synergistically preventing excessive consumption of FEC during battery formation and improving the battery's initial coulombic efficiency. Simultaneously, under suitable ratios, these two types of additives can form an organic oligomeric electrolyte interface film with alternating high-valence sulfur-rich sulfonates and cyclic esters through electrochemical reduction and transesterification reactions. This structure is stable, robust, highly ionic, and mechanically elastic, achieving a balance between low impedance and stability at the negative electrode interface, thereby improving the battery's initial coulombic efficiency, fast-charging performance, and cycle stability. When the mass ratio of the first and second additives is too high, it easily leads to an excessive amount of long-chain organic sulfonates in the interface film, resulting in increased impedance and easy lithium plating during high-rate charging. When the mass ratio of the first and second additives is too low, it easily leads to an excessive amount of sulfur-containing cyclic esters in the interface film, resulting in interface instability and increased battery cycle degradation.

[0220] Figure 3 This is a graph showing the cycle capacity retention results of the batteries in Embodiments 1, 4, 7 and Comparative Example 3 of this application; Figure 4 This is a graph showing the initial coulombic efficiency results of the batteries used in Examples 1, 4, 7, and Comparative Example 3 of this application. Figure 3 and Figure 4 It can be seen that the batteries of Examples 1, 4 and 7 exhibit higher 800-cycle capacity retention and first efficiency than the battery of Comparative Example 3.

[0221] Figure 5 These are photographs of the negative electrode interface after disassembly of the batteries in Embodiment 4, Comparative Example 2, and Comparative Example 3 of this application, following 800 battery cycles. Figure 5It can be seen that the battery of Example 4 exhibits better fast charging cycle performance compared to the batteries of Comparative Example 2 and Comparative Example 3. After 800 cycles of 4C fast charging, no lithium was deposited at the negative electrode interface of the battery of Example 4, while lithium was deposited at the negative electrode interface of the batteries of Comparative Example 2 and Comparative Example 3.

[0222] Comparing Examples 9 and 10 and 11, it can be found that having the mass content of the first additive in the range of 0.1%-2% and the mass content of the second additive in the range of 0.2%-2.5% is more conducive to improving the battery's first efficiency and fast charging cycle capacity retention rate.

[0223] Comparing Examples 12, 13, and 14, it can be found that the mass ratio of the first additive to FEC is 0.0025-0.2, and the mass ratio of the second additive to FEC is 0.005-0.25. The combination of the first and second additives has a more significant improvement effect. This is because the film formation of FEC on the negative electrode side is affected by the first and second additives. A more suitable mass ratio of the first additive to FEC and the second additive to FEC can be more conducive to the effective film formation of FEC or avoid excessive consumption of FEC.

[0224] Comparing Examples 3-6 with Examples 1-2, it can be seen that controlling the mass ratio of the first additive and the second additive within the range of (0.5-2) can better improve the battery's first efficiency and fast charging cycle capacity retention rate.

[0225] Comparing Examples 3-6 and Examples 7-8 reveals that a first additive with a mass content in the range of 0.2%-1.5% and a second additive with a mass content in the range of 0.3%-2% are more conducive to improving the battery's first efficiency and fast charging cycle capacity retention rate.

[0226] Comparing Examples 6 and 9, it can be seen that the battery electrolyte system of this application can be effective for anode materials with different proportions of silicon-carbon materials, and the improvement effect is more significant for systems with high silicon content.

[0227] It should be understood that the use of the terms "first," "second," and various numerical designations in this document is merely for descriptive convenience and is not intended to limit the scope of this application.

[0228] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone, where A and B can be singular or plural. The character " / " generally indicates that the related objects before and after it are in an "or" relationship.

[0229] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0230] In this application, "-" indicates a range value, including the endpoint values ​​at both ends. For example, the value of a can be 0.5-15, meaning that the value of a can be between 0.5 and 15, and includes the endpoint values ​​of 0.5 and 15.

[0231] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

Claims

1. A battery electrolyte, characterized in that, The battery electrolyte comprises an electrolyte salt, an organic solvent, and additives, wherein the additives include fluoroethylene carbonate, a first additive represented by formula (I), and a second additive represented by formula (II). In formula (I), R1 is selected from one of alkenyl, haloalkenyl, alkyneyl, and haloalkyneyl; R2 and R3 are independently selected from one of alkyl, haloalkyl, alkenyl, substituted alkenyl, alkyne, and haloalkyne. In formula (II), each X1, X2, X3 is independently selected from O or S; n1, m n2, n3 are independently 1 or 2; m is 0, 1 or 2; y is 0 or 1; z is 0 or 1; R4 and R5 are independently selected from one of hydrogen atoms, alkyl groups, and haloalkyl groups; In the battery electrolyte, the mass ratio of the first additive to the second additive is (0.3-5):

1.

2. The battery electrolyte as described in claim 1, characterized in that, The number of carbon atoms in the alkenyl group, haloalkenyl group, and alkyne group is 2-10; the number of carbon atoms in the haloalkyne group is 3-10; the number of carbon atoms in the alkyl group and haloalkyl group is 1-10; and the number of carbon atoms in the alkenyl group, substituted alkenyl group, alkyne group, and haloalkyne group is 2-10.

3. The battery electrolyte as described in claim 1 or 2, characterized in that, In the battery electrolyte, the mass ratio of the first additive to the second additive is (0.5-2):

1.

4. The battery electrolyte according to any one of claims 1-3, characterized in that, The first additive has a mass percentage of 0.1%-2% in the battery electrolyte.

5. The battery electrolyte according to any one of claims 1-4, characterized in that, The second additive has a mass percentage of 0.2%-2.5% in the battery electrolyte.

6. The battery electrolyte according to any one of claims 1-5, characterized in that, The first additive comprises one or more compounds of formula (I-1) to (I-9): (I-1): (I-2): (I-3): (I-4): (I-5): (I-6): (I-7): (I-8): (I-9)： 7. The battery electrolyte according to any one of claims 1-6, characterized in that, The second additive comprises one or more compounds of formulas (II-1) to (II-6): (II-1): (II-2): (II-3): (II-4): (II-5): (II-6):

8. The battery electrolyte according to any one of claims 1-7, characterized in that, The fluoroethylene carbonate ester constitutes 5%-50% of the mass percentage in the battery electrolyte.

9. The battery electrolyte according to any one of claims 1-8, characterized in that, In the battery electrolyte, the mass ratio of the first additive to the fluoroethylene carbonate is (0.0025-0.2):

1.

10. The battery electrolyte according to any one of claims 1-9, characterized in that, In the battery electrolyte, the mass ratio of the second additive to the fluoroethylene carbonate is (0.005-0.25):

1.

11. The battery electrolyte according to any one of claims 1-10, characterized in that, The additives also include other additives, including one or more of the following: difluoroethylene carbonate, biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl ethylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, vinyl sulfite, methane disulfonate, 1,2-bis(2-cyanoethoxy)ethane, and nitrile compounds.

12. The battery electrolyte according to any one of claims 1-11, characterized in that, The electrolyte salt includes at least one of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt.

13. The battery electrolyte according to any one of claims 1-12, characterized in that, The molar concentration of the electrolyte salt in the battery electrolyte is 0.01 mol / L to 2.0 mol / L.

14. The battery electrolyte according to any one of claims 1-13, characterized in that, The organic solvent includes one or more of carbonate solvents, ether solvents, and carboxylic acid ester solvents.

15. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte includes the battery electrolyte according to any one of claims 1-14.

16. The secondary battery as described in claim 15, characterized in that, The secondary battery includes lithium secondary batteries, potassium secondary batteries, sodium secondary batteries, magnesium secondary batteries, zinc secondary batteries, or aluminum secondary batteries.

17. The secondary battery as described in claim 15 or 16, characterized in that, The negative electrode includes one or more of the following: carbon-based negative electrode, silicon-based negative electrode, tin-based negative electrode, phosphorus-based negative electrode, lithium titanium oxide negative electrode, lithium negative electrode, sodium negative electrode, potassium negative electrode, magnesium negative electrode, zinc negative electrode, and aluminum negative electrode.

18. A battery module, characterized in that, It includes multiple secondary batteries, which are connected in series, in parallel, or in a series-parallel configuration, and at least some of the multiple secondary batteries include the secondary batteries as described in any one of claims 15-17.

19. A battery pack, characterized in that, It includes a plurality of battery modules and a support structure for carrying the plurality of battery modules, wherein at least a portion of the plurality of battery modules includes the battery module of claim 18.

20. An electrical appliance, characterized in that, The electrical device includes a receiving cavity and a battery housed within the receiving cavity, the battery including a secondary battery as described in any one of claims 15-17, a battery module as described in claim 18, or a battery pack as described in claim 19.

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