Sodium-ion battery electrolyte, sodium-ion battery and electric device

Abstract

The application belongs to the technical field of batteries, and particularly discloses a sodium-ion battery electrolyte, a sodium-ion battery and an electric device. The sodium-ion battery electrolyte comprises a sodium salt, a solvent, an overcharge-preventing additive and a film-forming additive. The overcharge-preventing additive comprises at least one of cyclohexylbenzene, diphenyl, tert-amylbenzene, fluorocyclohexylbenzene, o-terphenyl and anisole. The addition of the overcharge-preventing additive in the sodium-ion battery electrolyte can make the sodium-ion battery electrolyte form a dense high-impedance film under the conditions of battery overcharge or high potential, effectively block the overcharge reaction, inhibit the oxidative decomposition and gas production of the electrolyte, improve the overcharge safety and high-temperature stability of the battery, and, in combination with the film-forming additive, optimize the interface film structure, reduce the interface impedance, widen the voltage window of the battery and improve the cycle life.

Description

Technical Field

[0001] This application belongs to the field of battery technology, and specifically discloses a sodium-ion battery electrolyte, a sodium-ion battery, and an electrical device. Background Technology

[0002] High-voltage sodium-ion batteries have broad application prospects in the fields of energy storage and power due to their high energy density and low cost.

[0003] However, the carbonate electrolytes in current sodium-ion batteries have poor antioxidant stability. They are prone to oxidation and decomposition at high potentials above 4.0V, which generates CO and CO2 gases, causing the battery to swell and increase internal pressure. At the same time, the oxidation and decomposition products form a loose, high-resistivity, and unstable CEI film on the surface of the positive electrode. This inferior film cannot block the continuous side reactions between the electrolyte and the positive electrode, which leads to continuous consumption of electrolyte, continuous loss of active sodium ions, and continuous increase in interfacial impedance. Ultimately, this results in a sharp decline in battery cycle performance and a narrow battery voltage window. Summary of the Invention

[0004] This application provides a sodium-ion battery electrolyte, a sodium-ion battery, and an electrical device. The sodium-ion battery electrolyte can improve the cycle performance and narrow the battery voltage window.

[0005] To solve the above-mentioned technical problems, this application provides a sodium-ion battery electrolyte, which includes: sodium salt, solvent, overcharge prevention additive, and film-forming additive; wherein the overcharge prevention additive includes at least one of the following: cyclohexylbenzene, biphenyl, tert-amylbenzene, fluorocyclohexylbenzene, o-terphenyl, and anethole.

[0006] In one embodiment, at least one of the following is satisfied: in the sodium-ion battery electrolyte, the mass fractions of the sodium salt, the solvent, the overcharge protection additive, and the film-forming additive are 13-17 wt%, 75-85 wt%, 1.3-3 wt%, and 4-8 wt%, respectively; the overcharge protection additive is a mixture of cyclohexylbenzene, biphenyl, and tert-amylbenzene, or a mixture of fluorocyclohexylbenzene, o-terphenyl, and anisole.

[0007] In one embodiment, the mass ratio of cyclohexylbenzene, biphenyl, and tert-amylbenzene in the overcharge prevention additive is (0.5~1):(0.5~1):(0.3~1).

[0008] In one embodiment, the mass ratio of fluorocyclohexylbenzene, o-terphenyl, and anethole in the overcharge prevention additive is (0.5~1):(0.5~1):(0.3~1).

[0009] In one embodiment, the sodium salt includes at least one of the following: NaBF4, NaPF6, NaFSI, and NaDFOB.

[0010] In one embodiment, the solvent includes at least one of the following: ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, and difluoromethyl ethylene carbonate.

[0011] In one embodiment, the film-forming additive includes at least one of the following: fluoroethylene carbonate, vinylene carbonate, sodium difluorophosphate, and ethylene sulfate.

[0012] In one embodiment, the sodium-ion battery electrolyte comprises, by mass fraction: 13-17 wt% sodium salt, 75-85 wt% solvent, 0.5-1 wt% cyclohexylbenzene, 0.5-1 wt% biphenyl, 0.3-1 wt% tert-amylbenzene, and 4-8 wt% film-forming additives.

[0013] This application also provides a sodium-ion battery, which includes the sodium-ion battery electrolyte described above, and the sodium-ion battery is any one of a single cell, a battery module, or a battery pack.

[0014] This application also provides an electrical device, which includes the aforementioned sodium-ion battery, the sodium-ion battery being used to supply power to the electrical device. This application provides a sodium-ion battery electrolyte, which includes: sodium salt, solvent, overcharge protection additive, and film-forming additive; wherein the overcharge protection additive includes at least one of the following: cyclohexylbenzene (CHB), biphenyl (BP), tert-amylbenzene (TAP), fluorocyclohexylbenzene, o-terphenyl, and anethole.

[0015] Adding anti-overcharge additives to sodium-ion battery electrolytes allows the electrolyte to undergo oxidative polymerization under overcharge or high-potential conditions, forming a dense, high-resistivity film. This effectively blocks overcharge reactions, inhibits electrolyte oxidation and decomposition, and gas generation, improving battery overcharge safety and high-temperature stability. Simultaneously, film-forming additives optimize the interfacial film structure, reduce interfacial impedance, widen the battery voltage window, and improve cycle life. Detailed Implementation

[0016] The present invention will be further described in detail below through specific embodiments. In the following embodiments, many details are described to facilitate a better understanding of this application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to this application are not shown or described in the specification. This is to avoid obscuring the core parts of this application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0017] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification are only for clearly describing a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0018] The serial numbers assigned to components in this document, such as "first" and "second," are used only to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages).

[0019] This application provides a sodium-ion battery electrolyte, which includes: sodium salt, solvent, overcharge protection additive, and film-forming additive; wherein the overcharge protection additive includes at least one of the following: cyclohexylbenzene (CHB), biphenyl (BP), tert-amylbenzene (TAP), fluorocyclohexylbenzene, o-terphenyl, and anethole.

[0020] Adding anti-overcharge additives to sodium-ion battery electrolytes allows the electrolyte to undergo oxidative polymerization under overcharge or high-potential conditions, forming a dense, high-resistivity film. This effectively blocks overcharge reactions, inhibits electrolyte oxidation and decomposition, and gas generation, improving battery overcharge safety and high-temperature stability. Simultaneously, film-forming additives optimize the interfacial film structure, reduce interfacial impedance, widen the battery voltage window, and improve cycle life.

[0021] In one embodiment, the overcharge prevention additive is a mixture of cyclohexylbenzene, biphenyl, and tert-amylbenzene.

[0022] Cyclohexylbenzene, biphenyl, and tert-amylbenzene are combined to form a synergistic system that promotes gradient oxidation, complementary film formation, and suppression of side reactions. Through their ordered interaction at different potentials, a comprehensive balance is achieved in the safety, cycle life, initial efficiency, and high-voltage performance of sodium-ion batteries. The core mechanism is as follows: the three components oxidize and polymerize sequentially from low to high oxidation potential, synergistically forming a dense and stable CEI film on the positive electrode surface. This effectively prevents oxidative decomposition of the electrolyte, thereby achieving stable high-voltage operation, widening the voltage window, and suppressing gas generation and side reactions, thus ensuring all key performance characteristics are met. Specifically: Cyclohexylbenzene has the lowest oxidation potential and is an overcharge-triggered additive. During overcharge, it undergoes oxidation polymerization on the positive electrode surface first, forming a dense, high-resistance cross-linked polymer film. This film can quickly block current and suppress voltage spikes, achieving first-level overcharge protection and laying the foundation for battery safety. Furthermore, its film formation process is mild and produces little gas, which can reduce the risk of battery gas expansion.

[0023] Biphenyl has a higher oxidation potential than cyclohexylbenzene, and plays a secondary overcharge protection role. It undergoes a polymerization reaction in the later stage of overcharge or under high voltage conditions, and further forms a thicker and more stable barrier layer on the basis of the cyclohexylbenzene film layer, which significantly improves the high voltage stability and high temperature cycle performance of the battery.

[0024] Tert-amylbenzene has the highest oxidation potential. Due to its large steric hindrance, the oxidation reaction is milder and there are fewer side reactions. It can form a thin and uniform CEI film on the positive electrode surface, which can improve the battery interface stability, extend cycle life, and optimize low-temperature performance. Moreover, it has the least impact on the battery's first efficiency. As an efficiency enhancer and stabilizer in the ternary composite system, it can make up for the performance defects of excessive addition of cyclohexylbenzene and biphenyl, and achieve a synergistic balance of various performances.

[0025] In one embodiment, the mass ratio of cyclohexylbenzene, biphenyl, and tert-amylbenzene is (0.5~1):(0.5~1):(0.3~1). Cyclohexylbenzene and biphenyl provide primary overcharge protection, while tert-amylbenzene regulates polymerization potential and solubility. This ratio of the three compounds allows for rapid polymerization to block current during overcharge without compromising electrolyte stability, thus balancing safety and normal cell performance.

[0026] Specifically, the mass ratio of cyclohexylbenzene, biphenyl, and tert-amylbenzene is 0.5:0.5:0.3, 0.8:0.7:0.6, 1:1:1, or any value within the above range.

[0027] In one embodiment, the overcharge prevention additive is a mixture of fluorocyclohexylbenzene, o-terphenyl, and anethole.

[0028] A synergistic system is formed by combining fluorocyclohexylbenzene, o-terphenyl, and anisole, which features gradient oxidation, complementary film formation, and suppression of side reactions. Through the orderly interaction of these three components at different potentials, a comprehensive balance is achieved in the safety, cycle life, first-efficiency performance, and high-voltage performance of sodium-ion batteries. The core mechanism is that the three components oxidize and polymerize sequentially from low to high oxidation potential, synergistically forming a dense and stable CEI film on the positive electrode surface. This effectively prevents the oxidative decomposition of the electrolyte, thereby achieving stable high-voltage operation of the battery, widening the voltage window, and simultaneously suppressing gas generation and side reactions, thus ensuring all key performance characteristics are met.

[0029] Anethole has the lowest oxidation potential and is an overcharge-triggered additive. In the early stage of overcharge, it undergoes oxidation and polymerization on the positive electrode surface first, quickly forming a dense polymer protective film. This rapidly blocks current transmission and suppresses abnormal voltage spikes, achieving first-level overcharge protection and laying a solid foundation for battery overcharge safety. Furthermore, its film-forming speed is fast and it produces less gas, which can effectively reduce the risk of battery gas expansion and increased internal pressure.

[0030] Fluorinated cyclohexylbenzene has a higher oxidation potential than anisole, and plays a role in secondary overcharge protection and high voltage adaptation. Thanks to the high antioxidant properties brought by fluorine substitution, it can exist stably at higher potentials. In the later stage of overcharge or under high voltage conditions, it undergoes a polymerization reaction, and a fluorine-containing stable barrier layer is further formed on the base film layer formed by anisole, which significantly improves the high voltage stability and antioxidant capacity of the battery and effectively widens the voltage window.

[0031] o-terphenyl has the highest oxidation potential. Due to the rigidity of the polyaromatic rings in its molecular structure, the oxidation reaction is milder and there are fewer side reactions. It can form a thin and tough CEI film on the positive electrode surface, which can improve the battery interface stability, extend cycle life, and improve high-temperature stability. Moreover, it has minimal impact on the battery's initial efficiency. As an efficiency enhancer and stabilizer in ternary composite systems, it can make up for the performance defects of excessive addition of anisole and fluorocyclohexylbenzene, and achieve a synergistic balance of various performances.

[0032] In one embodiment, the mass ratio of fluorocyclohexylbenzene, o-terphenyl, and anisole is (0.5~1):(0.5~1):(0.3~1). Fluorocyclohexylbenzene and o-terphenyl are the main protective components, which undergo sequential oxidative polymerization during overcharge to form a current-blocking layer. Anisole regulates the polymerization initiation potential and interfacial compatibility, thereby improving protection sensitivity. Therefore, this ratio ensures rapid activation during overcharge without affecting the normal cycling and interfacial stability of the battery cell.

[0033] Specifically, the mass ratio of fluorocyclohexylbenzene, o-terphenyl, and anisole is 0.5:0.5:0.3, 0.8:0.7:0.6, 1:1:1, or any value within the above range.

[0034] In one embodiment, the mass fractions of sodium salt, solvent, overcharge prevention additive, and film-forming additive in the sodium-ion battery electrolyte are 13-17 wt%, 75-85 wt%, 1.3-3 wt%, and 4-8 wt%, respectively. This ratio can form a stable interfacial film, suppress side reaction gas production, and ensure overcharge safety and high-voltage stability.

[0035] Specifically, in the sodium-ion battery electrolyte, the mass fraction of sodium salt is 13wt%, 15wt%, 17wt%, or any value within the above range; the mass fraction of solvent is 75wt%, 80wt%, 85wt%, or any value within the above range; the mass fraction of overcharge prevention additive is 1.3wt%, 2wt%, 3wt%, or any value within the above range; and the mass fraction of film-forming additive is 4wt%, 6wt%, 8wt%, or any value within the above range.

[0036] In one embodiment, the sodium salt includes at least one of the following: NaBF4, NaPF6, NaFSI, and NaDFOB, all of which can provide sodium ions to ensure the ionic conductivity of the electrolyte.

[0037] In one embodiment, the solvent includes at least one of the following: ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and difluoromethyl ethylene carbonate (DFEC), which are used to dissolve sodium salts, adjust the viscosity and dielectric constant of the electrolyte, and ensure ion transport.

[0038] In one embodiment, the film-forming additive includes at least one of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), sodium difluorophosphate, and ethylene sulfate. These additives form a stable SEI or CEI film on the electrode surface, which can suppress side reactions and improve the battery's initial efficiency and cycle life.

[0039] In one embodiment, the sodium-ion battery electrolyte comprises, by mass fraction: 13-17 wt% sodium salt, 75-85 wt% solvent, 0.5-1 wt% cyclohexylbenzene, 0.5-1 wt% biphenyl, 0.3-1 wt% tert-amylbenzene, and 4-8 wt% film-forming additives.

[0040] This application also provides a method for preparing a sodium-ion battery electrolyte, comprising: 1. Prepare sodium salt, solvent, overcharge prevention additive, and film-forming additive; 2. Sodium-ion battery electrolyte is obtained by mixing sodium salt, solvent, anti-overcharge additive, and film-forming additive.

[0041] This application also provides a sodium-ion battery, which includes the sodium-ion battery electrolyte described above.

[0042] The sodium-ion battery may be in the form of a single battery cell, a battery module, or a battery pack. In some embodiments, the single battery cells may be assembled into a battery module, and the number of single battery cells contained in a battery module may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, the battery modules may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0043] This application also provides an electrical device, which includes the aforementioned sodium-ion battery for powering the device. Specifically, the electrical device can be, but is not limited to, electric vehicles, electric bicycles, mobile phones, tablets, laptops, electric toys, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, etc.

[0044] To enable those skilled in the art to better understand this application, the following detailed description, in conjunction with specific embodiments, further illustrates the application. Obviously, the described embodiments are merely some, not all, of the embodiments described. It should be understood that the specific embodiments are only used to explain the application, and are not intended to limit the scope of the application.

[0045] Example 1 The preparation method of sodium-ion battery cells specifically includes: 1. Prepare the positive electrode sheet.

[0046] Sodium DFD, PVDF, CNTs and SP were mixed in a mass ratio of 96.6:1.5:0.6:1.3 and dissolved in a solvent to obtain a positive electrode slurry. The positive electrode slurry was coated on an aluminum foil current collector to form a positive electrode active material layer. After drying, rolling, slicing and vacuum drying, a positive electrode sheet was obtained.

[0047] The areal density of the positive electrode active material layer is 98 g / m². 2 The compacted density is 3 g / cm³. 3 .

[0048] 2. Prepare the negative electrode sheet.

[0049] Hard carbon, CMC, SP, and SBR are mixed in a mass ratio of 95.9:1.7:1:1.4 and dissolved in a solvent to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil current collector to form a negative electrode active material layer. After drying, rolling, slicing, and vacuum drying, a negative electrode sheet is obtained.

[0050] The areal density of the negative electrode active material layer is 82 g / m², and the negative real density is 1 g / cm³. 3. The diaphragm is a ceramic diaphragm.

[0051] 4. Prepare the electrolyte.

[0052] Sodium-ion battery electrolyte is obtained by mixing sodium salts (NaBF4, NaPF6), solvents (ethylene carbonate, methyl ethyl carbonate, difluoromethyl ethylene carbonate), overcharge prevention additives (cyclohexylbenzene), and film-forming additives (fluoroethylene carbonate, vinylene carbonate).

[0053] The mass fractions of each substance in the sodium-ion battery electrolyte are shown in Table 1.

[0054] 5. Manufacturing battery cells.

[0055] The positive electrode, separator, and negative electrode are stacked in sequence and placed into the battery case. Then, the battery case is injected with electrolyte, and after sealing, standing, formation, and aging, the battery cell is obtained.

[0056] Examples 2-9 The difference from Example 1 is that in step 4, the electrolyte contains only one anti-overcharge additive component, and the substance and content of this component are adjusted.

[0057] Examples 10-18 The difference from Example 1 is that in step 4, the electrolyte contains two anti-overcharge additive components, and the substances and contents of these two components are adjusted.

[0058] Examples 19-21 The difference from Example 1 is that in step 4, the electrolyte contains three anti-overcharge additive components, and the content of these three components is adjusted.

[0059] Comparative Example 1 The difference from Example 1 is that there is no overcharge prevention additive in the electrolyte in step 4.

[0060] Table 1. Parameters of the electrolytes in the examples and comparative examples.

[0061] The following performance tests were performed on the battery cells of the examples and comparative examples, and the performance data are shown in Table 2.

[0062] I. Conduct overcharge safety tests on the battery cells. The test methods include: 1. At room temperature, discharge the battery cell at a constant current of 1C to the lower cutoff voltage of 2.0V. After the discharge is complete, let it rest for 30 minutes. Then charge it at a constant current of 1C to the upper limit voltage of 4.2V. Then maintain a constant voltage of 4.2V until the current drops below 0.05C. After the charge is complete, let it rest for 30 minutes to allow the battery cell to reach a stable 100% SOC state.

[0063] 2. After pretreatment, continuously overcharge at a constant current of 1C at room temperature until the charging capacity reaches 200% SOC. After the test is stopped, observe whether the battery cell exhibits bulging, fire, thermal runaway, or other phenomena.

[0064] II. Conduct cycle performance tests on the battery cells. The test methods include: At 25℃, the cell is charged at 1C from 2.0V to 4.2V, left to stand for 30 minutes, discharged at 1C to 2.0V, left to stand for 60 minutes, and finally cycled for 500 cycles. The cycle capacity retention rate corresponding to 500 cycles is calculated as (discharge capacity at 500th cycle / initial discharge capacity × 100%).

[0065] III. Conduct the initial efficiency performance test on the battery cell. The test methods include: 1. First, discharge the cell at 1C to 2.0V and let it rest for 30 minutes to allow the cell to stabilize; then charge it at 1C at constant current and constant voltage to 4.2V, record the initial charge capacity, and let it rest for 30 minutes to eliminate polarization.

[0066] 2. Discharge the cell at a constant current of 1C to 2.0V, record the initial discharge capacity, and then calculate the initial efficiency (initial discharge capacity / initial charge capacity × 100%).

[0067] Table 2 Performance data test table for the examples and comparative sample cells

[0068] As can be seen from the data in Table 2, compared with Comparative Example 1, Examples 1-21 significantly improved overcharge safety performance and had better long-term cycle capacity retention and first-cycle efficiency.

[0069] Finally, it should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the aforementioned element.

[0070] The above description, in conjunction with specific embodiments, provides a further detailed explanation of this application and should not be construed as limiting the specific implementation of this application to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of this application.

Claims

1. A sodium-ion battery electrolyte, characterized in that, The sodium-ion battery electrolyte includes: sodium salt, solvent, overcharge protection additive, and film-forming additive; The overcharge prevention additive includes at least one of the following: cyclohexylbenzene, biphenyl, tert-amylbenzene, fluorocyclohexylbenzene, o-terphenyl, and anethole.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, Meet at least one of the following: In the sodium-ion battery electrolyte, the mass fractions of the sodium salt, the solvent, the overcharge protection additive, and the film-forming additive are 13-17 wt%, 75-85 wt%, 1.3-3 wt%, and 4-8 wt%, respectively. The overcharge prevention additive is a mixture of cyclohexylbenzene, biphenyl, and tert-amylbenzene, or a mixture of fluorocyclohexylbenzene, o-terphenyl, and anethole.

3. The sodium-ion battery electrolyte according to claim 2, characterized in that, In the overcharge prevention additive, the mass ratio of cyclohexylbenzene, biphenyl, and tert-amylbenzene is (0.5~1):(0.5~1):(0.3~1).

4. The sodium-ion battery electrolyte according to claim 2, characterized in that, In the overcharge prevention additive, the mass ratio of fluorocyclohexylbenzene, o-terphenyl, and anisole is (0.5~1):(0.5~1):(0.3~1).

5. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt includes at least one of the following: NaBF4, NaPF6, NaFSI, and NaDFOB.

6. The sodium-ion battery electrolyte according to claim 5, characterized in that, The solvent includes at least one of the following: ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, and difluoromethyl ethylene carbonate.

7. The sodium-ion battery electrolyte according to claim 6, characterized in that, The film-forming additive includes at least one of the following: fluoroethylene carbonate, vinylene carbonate, sodium difluorophosphate, and ethylene sulfate.

8. The sodium-ion battery electrolyte according to claim 7, characterized in that, The sodium-ion battery electrolyte comprises, by mass fraction: 13-17 wt% sodium salt, 75-85 wt% solvent, 0.5-1 wt% cyclohexylbenzene, 0.5-1 wt% biphenyl, 0.3-1 wt% tert-amylbenzene, and 4-8 wt% film-forming additives.

9. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion battery electrolyte according to any one of claims 1-8, and the sodium-ion battery is any one of a single cell, a battery module, or a battery pack.

10. An electrical appliance, characterized in that, The electrical device includes the sodium-ion battery of claim 9, which is used to power the electrical device.

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