Long-life sodium ion battery electrolyte, sodium ion battery and electric device

Abstract

The invention provides a long-life sodium ion battery electrolyte, a sodium ion battery and an electric device. The long-life sodium-ion battery electrolyte comprises sodium salt, an organic solvent and a single-component additive, the sodium salt is sodium hexafluorophosphate; the organic solvent is an ester solvent; the additive is a sulfur unsaturated ester additive; based on the mass of the electrolyte, the use amount of the additive is 0.1-5wt%; based on the volume of the electrolyte, the amount-of-substance concentration of the sodium salt is 0.5-3 mol / L; the conductivity of the electrolyte solution at 25 DEG C is 5-15 mS / cm. The long-life sodium-ion battery electrolyte provided by the invention can effectively inhibit the gas production behavior of the sodium-ion battery in the cycle process, reduce the occurrence of side reactions, and improve the coulombic efficiency and cycle performance of the battery.

Description

Technical Field

[0001] This application belongs to battery energy storage, and particularly relates to a long-life sodium-ion battery electrolyte, a sodium-ion battery, and an electrical device. Background Art

[0002] Due to the higher terrestrial abundance of its metal ore, lower cost, and the potential for fast charging and discharging and low-temperature performance brought about by a smaller Stokes radius, sodium-ion batteries can be a favorable competitor to lithium-ion batteries in fields such as electric two-wheelers and energy storage where the energy density requirement is not high, and have a wide market.

[0003] Currently, the mainstream anode of sodium-ion batteries still uses hard carbon. Due to its unique pore structure, it can achieve stable storage of sodium ions in carbon materials. At the same time, there is a stable low-voltage platform that can effectively increase the working voltage of the device to achieve the purpose of increasing the energy density. However, due to the complex structure of the hard carbon material itself, a large number of defects exist at the edges of the internal graphite microcrystals, which can serve as active sites for reactions. Therefore, a large number of side reactions will occur on the surface of the hard carbon anode during the cycling process, resulting in excessive consumption of the electrolyte and ultimately capacity decay.

[0004] To improve the cycling performance of sodium-ion batteries, improvements are currently mainly made in two aspects: the material bulk phase and the electrolyte. Among them, the modification of the electrolyte is mainly through the screening of solvents and additives. Therefore, how to select suitable additives and solvents for the sodium-ion battery system and design an electrolyte that meets the usage requirements of the sodium-ion battery system has always been a research hotspot and difficulty in this field. Summary of the Invention

[0005] The embodiments of this application provide a long-life sodium-ion battery electrolyte, a sodium-ion battery, and an electrical device, which can effectively inhibit the gas generation behavior during the cycling of sodium-ion batteries, reduce the occurrence of side reactions, and improve the Coulomb efficiency and cycling performance of the battery.

[0006] In a first aspect, the embodiments of this application provide a long-life sodium-ion battery electrolyte. The electrolyte includes a sodium salt, an organic solvent, and an additive of a single component; the sodium salt is sodium hexafluorophosphate; the additive is a sulfur-based unsaturated ester additive; the organic solvent is an ester solvent; based on the mass of the electrolyte, the dosage of the additive is 0.2 - 5 wt%; based on the volume of the electrolyte, the molar concentration of the sodium salt is 0.5 - 3 mol / L, and the physical parameters of the electrolyte include that the conductivity of the electrolyte at 25°C is 5 - 15 mS / cm.

[0007] According to the embodiments of the first aspect of this application, the mass ratio of the dosage of the additive to the sodium salt is 1:5 - 1:50.

[0008] According to the embodiments of the first aspect of this application, the additive is selected from one of ethylene sulfate and propylene sulfite.

[0009] According to an embodiment of the first aspect of the present application, the additive is a sulfur-based unsaturated ester additive.

[0010] According to an embodiment of the first aspect of the present application, the additive is ethylene sulfate, and based on the mass of the electrolyte, the dosage of ethylene sulfate is 1.5 - 2.5 wt%.

[0011] According to an embodiment of the first aspect of the present application, the dosage of the sodium salt in the sodium-ion battery electrolyte is 0.6 - 1.4 mol / L.

[0012] According to an embodiment of the first aspect of the present application, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, and diethyl carbonate.

[0013] According to an embodiment of the first aspect of the present application, based on the volume of the organic solvent, the dosage of ethylene carbonate in the organic solvent is 10 - 60 vol%; the dosage of propylene carbonate is 30 - 60 vol%; the dosage of diethyl carbonate is 10 - 40 vol%.

[0014] According to an embodiment of the first aspect of the present application, based on the volume of the organic solvent, the ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate is 1:(1 - 2):(1 - 2).

[0015] In a second aspect, an embodiment of the present application provides a sodium-ion battery, including the above-mentioned long-life sodium-ion battery electrolyte.

[0016] According to an embodiment of the second aspect of the present application, the sodium-ion battery can stably cycle more than 2000 times at a charge-discharge rate of 1.0C, and there is no obvious gas generation phenomenon during the cycling process.

[0017] In a third aspect, an embodiment of the present application provides an electrical device, characterized by including the above-mentioned sodium-ion battery.

[0018] Compared with the prior art, the present application has at least the following beneficial effects:

[0019] The long-life sodium-ion battery electrolyte of the embodiment of the present application realizes the regulation of the SEI film by optimizing the ratio of each component in the electrolyte and the type and physical and chemical properties of the additive, uses sodium hexafluorophosphate as the sodium salt, and cooperates with a single-component sulfur-based unsaturated ester additive to improve the stability of the electrode and ensure the cycling performance of the battery. At the same time, the formula of the long-life sodium-ion battery electrolyte in the present application is simple, and excellent charge-discharge cycling performance can be achieved under the conditions of using a single sodium salt and a single additive, saving costs. Description of the Drawings

[0020] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required in the embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is the XPS diagram of the SEI film in Embodiment 1 of the present application;

[0022] Figure 2 It is the battery cycle life curve diagram in Embodiment 1 of the present application;

[0023] Figure 3 It is the battery cycle life curve diagram in Embodiment 2 of the present application;

[0024] Figure 4 It is the battery cycle life curve diagram in Embodiment 3 of the present application. Detailed implementation manners

[0025] In order to more clearly understand the above-mentioned objects, features and advantages of the present application, the following will further describe the solutions of the present application. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0026] In the following description, many specific details are set forth in order to fully understand the present disclosure, but the present application can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present application, rather than all the embodiments.

[0027] Hereinafter, the embodiments of the long-life sodium-ion battery electrolyte, sodium-ion battery and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0028] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0030] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0031] Unless otherwise specified, the raw materials in the embodiments of this application are all purchased through commercial channels.

[0032] Unless otherwise specified, this application adopts conventional test methods or test methods recommended by the instruments.

[0033] As the "blood" of the battery, the electrolyte plays a role in transporting ions. At the same time, the electrolyte will form an interfacial passivation layer at the interface during the first charge and discharge process, and the stable passivation layer can effectively improve the cycle performance of the battery.

[0034] At present, the modification of electrolytes mainly focuses on the screening of additives and solvents. However, the inventors of this application noticed that since the electrode potential of Na / Na+ is about 0.3V higher than that of Li / Li+, the decomposition path of the electrolyte on the electrode surface is also different from that of lithium-ion batteries, and the components of the formed interface layer also have some differences. At the same time, the larger ionic radius of Na+ makes its diffusion in the interface components more difficult. Therefore, how to select suitable additives and solvents for sodium-ion battery systems and design electrolytes that meet the usage requirements of sodium-ion battery systems has always been a research hotspot and difficulty in this field.

[0035] The embodiments of this application provide a long-life sodium-ion battery electrolyte, its preparation method, a sodium-ion battery, and an electrical device, which can effectively inhibit the gas generation behavior of sodium-ion batteries during cycling, reduce the occurrence of side reactions, and improve the Coulomb efficiency and cycling performance of the batteries.

[0036]

Long-life Sodium-ion Battery Electrolyte

[0037] In a first aspect, the embodiments of this application provide a long-life sodium-ion battery electrolyte. The electrolyte includes a sodium salt, an organic solvent, and a single-component additive; the sodium salt is sodium hexafluorophosphate; the additive is a sulfur-based unsaturated ester additive; the organic solvent is an ester solvent; based on the mass of the electrolyte, the dosage of the additive is 0.2 - 5 wt%; based on the volume of the electrolyte, the molar concentration of the sodium salt is 0.5 - 3 mol / L, and the physical parameters of the electrolyte include that the conductivity of the electrolyte at 25°C is 5 - 15 mS / cm.

[0038] The long-life sodium-ion battery electrolyte of the embodiments of this application contains specific sodium salts, organic solvents, and single-component additives. Among them, sodium hexafluorophosphate is selected as the sodium salt. Sodium hexafluorophosphate has good dissociation effect, is easily completely dissociated in organic solvents, forms a solution with low viscosity, and has high ionic conductivity, which can meet the ion migration rate required during charge and discharge.

[0039] The process of battery charge and discharge is essentially the migration process of ions between the positive and negative electrodes. In the electrolyte of the embodiments of the present application, sodium hexafluorophosphate is selected as the single sodium salt. The chemical structure of sodium hexafluorophosphate is relatively stable, and it can stably dissociate sodium ions in the electrolyte. Compared with the system of mixing multiple sodium salts, the single sodium salt can avoid the complex side reactions that may occur between different sodium salts. If there are multiple sodium salts, in the high-potential or low-potential environment of battery charge and discharge, the ions of different sodium salts may compete to participate in the reaction, resulting in a complex and uncontrollable reaction path. This will not only consume the active substances, but also may form unstable intermediate products on the electrode surface, and these intermediate products may further decompose to produce gases such as carbon dioxide and methane, thereby reducing the cycle life of the battery. However, in the process of cycling, the single sodium hexafluorophosphate can ensure the consistency and stability of the sodium ion migration path. It stably dissociates sodium ions in the electrolyte, provides a stable ion source for battery charge and discharge, reduces the generation of by-products caused by complex reactions, and fundamentally reduces the possibility of gas generation. At the same time, the interface formed by sodium hexafluorophosphate on the electrode surface is relatively uniform and stable, and will not cause abnormal decomposition and gas generation of the electrolyte due to the instability of the interface, which also helps to improve the life of the battery.

[0040] In the embodiments of the present application, the use of a single thio unsaturated ester additive can accurately construct a uniform and stable solid electrolyte interface (SEI) film on the electrode surface. This film has good ion conductivity, allowing sodium ions to pass through smoothly, and at the same time can effectively block the direct contact between the electrolyte and the electrode, preventing further reaction between the electrolyte and the electrode, greatly reducing the loss of active sodium ions in the system, and thus helping to improve the energy density and cycle life of the battery. In the case of mixing multiple additives, there may be interactions between different additives, affecting their film-forming reactions on the electrode surface. For example, some additives may compete for adsorption sites on the electrode surface, resulting in an uneven and unstable film formation.

[0041] When the battery is charged for the first time, due to its cyclic structure, the thio unsaturated ester additive will react on the electrode surface first. On the negative electrode surface, under the reduction of external electrons, its cyclic structure opens to form a radical anion, and then through a series of polymerization reactions, a solid electrolyte interface (SEI) film rich in thio components is constructed. This film not only protects the electrode, but also can effectively regulate the mass transfer between the electrode and the electrolyte. During the battery cycling process, due to the good compactness and chemical stability of the SEI film formed by the thio unsaturated ester additive, it can prevent the solvent molecules in the electrolyte from further reacting deeply with the electrode. When the solvent molecules cannot easily contact the active sites on the electrode surface, the situation of the solvent molecules being reduced to produce gases on the electrode surface is reduced.

[0042] In the embodiments of the present application, an ester solvent is used as the organic solvent. The ester solvent has a suitable dielectric constant and low viscosity, and can effectively dissolve sodium hexafluorophosphate to form a homogeneous and stable solution system. The suitable dielectric constant is beneficial to the dissociation of sodium salts and increases the ion concentration in the solution, while the low viscosity can reduce the resistance of ion migration, thereby improving the overall conductivity of the electrolyte.

[0043] A higher conductivity means that the ion migration in the electrolyte is smoother. In the embodiments of the present application, when the conductivity of the long-life sodium-ion battery electrolyte is 5-15 mS / cm at 25 °C, the charge and discharge process of the battery can proceed more efficiently. In this case, the electrode reaction is closer to the ideal state, reducing the local potential anomaly caused by slow reaction. For example, if the conductivity is too low, the ion transport is slow, and local charge accumulation may occur on the electrode surface, triggering side reactions of the electrolyte and generating gas. In some battery systems with poor conductivity, solvent molecules may accumulate on the electrode surface, bringing overpotential, causing excessive battery polarization, resulting in battery capacity loss or sodium deposition behavior, and ultimately leading to poor cycle performance of the battery failure.

[0044] During the charge and discharge cycle of the battery, the conductivity affects the migration efficiency of sodium ions between the positive and negative electrodes. If the conductivity is high, sodium ions can shuttle quickly and stably in the electrolyte, ensuring efficient and stable charge and discharge processes of the battery. This helps to maintain the structural stability of the electrode material and reduce the structural damage of the electrode material caused by increased polarization due to poor ion transport. For example, when ion transport is blocked, the electrode reaction kinetics slows down, and a higher overpotential is required to drive the reaction, resulting in local voltage anomalies on the surface of the electrode material and accelerating material failure. On the contrary, the electrolyte with a suitable conductivity in the embodiments of the present application can ensure that the electrode always maintains good reaction activity and structural stability during multiple cycles of the battery, thereby significantly improving the cycle life of the battery.

[0045] In summary, in the long-life sodium-ion battery electrolyte of the present application, by optimizing the ratio of each component in the electrolyte and the type and physical and chemical properties of the additives, sodium hexafluorophosphate is selected as the sodium salt, and a single-component sulfur-based unsaturated ester additive is used to realize the regulation of the SEI film. By constructing an excellent SEI to improve the sodium deposition morphology on the electrode surface and effectively inhibit the gas generation behavior during the cycling of sodium-ion batteries, reduce the occurrence of side reactions, and have a suitable conductivity, so that it has excellent charge and discharge cycle performance at high and low temperatures. Thus, after the first charge of the sodium-ion battery using this long-life sodium-ion battery electrolyte, an SEI film rich in sulfur-based components can be formed. At the same time, the formula of the long-life sodium-ion battery electrolyte in the present application is simple, and excellent charge and discharge cycle performance can be achieved under the conditions of using a single sodium salt and a single additive, saving costs.

[0046] Optionally, based on the volume of the electrolyte, the molar concentration of the sodium salt is 0.5 to 3 mol / L, independently selected from any value of 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L or the range value between any two of them.

[0047] Optionally, based on the mass of the electrolyte, the dosage of the additive is 0.1 to 5 wt%, independently selected from any value of 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt% or the range value between any two of them.

[0048] According to the embodiment of the first aspect of the present application, the mass ratio of the dosage of the additive to the sodium salt is 1:5 to 1:50.

[0049] During the charge and discharge process of the battery, improper reactions will generate gases such as hydrogen and carbon dioxide, which will reduce the battery performance and even cause safety problems. In the present application, the ratio of the additive to the sodium salt of 1:5 - 1:50 can effectively inhibit the gas generation phenomenon. The SEI film formed by the additive at an appropriate ratio has good barrier performance. It can prevent the solvent molecules in the electrolyte from undergoing excessive oxidation or reduction reactions on the electrode surface, thereby reducing the gases generated by the solvent decomposition. On the negative electrode surface, the SEI film at this ratio can prevent the solvent from reacting with the electrode because the additive preferentially decomposes and forms a stable interfacial layer on the surface, preventing further reaction of the solvent, and thus inhibiting the generation of gases such as hydrogen and carbon dioxide, improving the safety and stability of the battery.

[0050] In addition, within the range of 1:5 - 1:50, the SEI film formed by the additive not only has good ion conductivity but also can reduce the interfacial resistance between the electrode and the electrolyte. On the one hand, an appropriate amount of the additive ensures that the content of the sulfur-based component in the SEI film is appropriate, without increasing the resistance of ions passing through the film due to excessive sulfur-based components and at the same time can improve the low sodium ion flux caused by the rich sodium fluoride in the SEI; on the other hand, the additive improves the solvation structure around the sodium ion. When the sulfur-based additive enters the solvation structure, due to its large steric hindrance, it forms a weakly solvated structure, which has a lower desolvation energy when desolvating at the SEI.

[0051] Exemplarily, the mass ratio of the dosage of the additive to the sodium salt is 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50.

[0052] According to the embodiment of the first aspect of the present application, the additive is selected from one of vinylene sulfate and propylene sulfite.

[0053] The above-mentioned single chalcogen-based unsaturated ester additive can form a SEI film with excellent performance on the electrode surface, and the properties of the SEI film will indirectly affect the charge transfer and reaction inside the battery. In the embodiments of the present application, the SEI film rich in chalcogen-based components, such as sodium alkyl sulfate, has good ionic conductivity, which can ensure the smooth passage of sodium ions through the film between the electrode and the electrolyte, maintain the normal ionic transport inside the battery, and contribute to maintaining the high efficiency of the overall battery reaction, thereby ensuring the positive impact of conductivity on battery performance from the side.

[0054] According to an embodiment of the first aspect of the present application, the additive is a chalcogen-based unsaturated ester additive.

[0055] Without being bound by any theory or explanation, the inventors of the present application have noticed that when the chalcogen-based unsaturated ester additive is combined with a carbonate solvent, the electrolyte of the long-life sodium-ion battery can have excellent film-forming performance, and can form a SEI film with excellent performance during the first cycle, thereby achieving the long life and high Coulomb efficiency of the sodium-ion battery.

[0056] According to an embodiment of the first aspect of the present application, the additive is vinylene sulfate, and based on the mass of the electrolyte, the dosage of vinylene sulfate is 1.5 - 2.5 wt%.

[0057] Without being bound by any theory or explanation, the inventors of the present application have noticed in the experiment that when the content of vinylene sulfate is within the above range, the electrolyte can form a SEI with a suitable sulfur content during decomposition, thereby effectively improving the cycle life of the sodium-ion battery. Too high will significantly increase the internal resistance of the battery, and too low will cause the battery to be unable to achieve a significant improvement in cycle life due to the too low content of beneficial components in the SEI.

[0058] According to an embodiment of the first aspect of the present application, the dosage of the sodium salt in the sodium-ion battery electrolyte is 0.6 - 1.4 mol / L.

[0059] In the embodiments of the present application, a single sodium hexafluorophosphate is used as the sodium salt, and its stability and dissociation degree in the electrolyte will affect the conductivity. Sodium hexafluorophosphate can be completely dissociated to provide a sufficient amount of sodium ions, providing a carrier for ion migration and contributing to maintaining a suitable conductivity. Different sodium salts, due to their different chemical structures and ionic characteristics, have different dissociation constants in the electrolyte, which will lead to different ion concentrations and thus affect the conductivity.

[0060] Without being bound by any theory or explanation, the inventors of the present application have noticed that when the content of the sodium salt is within the above range and the conventional electrolyte concentration is selected, the requirements of the battery system for the ionic conductivity of the electrolyte can be met. At the same time, due to the low desolvation energy of sodium ions, the requirement of achieving a high ionic conductivity can also be met at a lower concentration.

[0061] According to an embodiment of the first aspect of the present application, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, and diethyl carbonate.

[0062] The above ester solvents used in the embodiments of the present application have appropriate dielectric constants and low viscosities, which have a significant impact on conductivity. An appropriate dielectric constant is beneficial to the dissociation of sodium salts, increasing the concentration of ions in the solution, thereby increasing conductivity. The low viscosity can reduce the resistance to ion migration, making the ions move more smoothly in the solution, further enhancing the conductivity. If the dielectric constant of the organic solvent is too low, the sodium salt is not easily dissociated and the ion concentration is low; if the viscosity is too high, the ion migration is hindered, both of which will lead to a decrease in conductivity.

[0063] According to an embodiment of the first aspect of the present application, based on the volume of the organic solvent, the dosage of ethylene carbonate in the organic solvent is 10-60 vol%; the dosage of diethyl carbonate is 10-40 vol%; the dosage of propylene carbonate is 30-60 vol%. Without being limited by any theory or explanation, the inventors of the present application noticed in the experiment that when ethylene carbonate, propylene carbonate, and diethyl carbonate in the organic solvent are compounded and within the above range, the long-life sodium-ion battery electrolyte can have an appropriate viscosity, so that the battery has certain rate performance. Dimethyl carbonate itself has a high melting point and a low boiling point compared with diethyl carbonate, which is not conducive to the performance of the battery in a wide temperature range. At the same time, ethylene carbonate has excellent film-forming properties but too high a melting point. Therefore, too high a content will affect the operating temperature range of the battery, and too low a content will not be conducive to forming a good SEI to improve the cycle performance of the battery. Among the three, ethylene carbonate has good sodium salt dissolution and film-forming properties, propylene carbonate has good film-forming and anti-solidification properties, and diethyl carbonate can reduce the viscosity of the electrolyte and increase the conductivity of the electrolyte. The compounding of the three can achieve the effect of long battery life.

[0064] According to an embodiment of the first aspect of the present application, based on the volume of the organic solvent, the ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate is 1:(1-2):(1-2).

[0065] Exemplarily, the ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate is 1:1:2, which can balance the viscosity of the electrolyte while ensuring that the electrolyte has good film-forming properties, is beneficial to reducing the ion transport resistance, reducing the side reaction between the electrode and the electrolyte, and improving the cycle life of the battery.

[0066]

Preparation Method

[0067] Under the conditions that the concentration of H2O ≤ 0.1 ppm and the concentration of O2 ≤ 0.1 ppm, the sodium salt, the organic solvent, and the additive are mixed in a preset ratio to obtain a long-life sodium-ion battery electrolyte.

[0068] Without intending to be limited by any theory or explanation, the preparation method of the present application is simple, facilitating large-scale production and quantitative control.

[0069] The preparation device of the present application is not specifically limited, and those skilled in the art can adjust it according to needs. As an example, it can be carried out in a glove box.

[0070]

Sodium-ion battery

[0071] In a second aspect, an embodiment of the present application provides a sodium-ion battery, including the above-mentioned long-life sodium-ion battery electrolyte.

[0072] Without intending to be limited by any theory or explanation, in the long-life sodium-ion battery electrolyte of the present application, by optimizing the ratio of each component in the electrolyte and the types and physical and chemical properties of the additives, sodium hexafluorophosphate is selected as the sodium salt, and combined with a single-component sulfur-based unsaturated ester additive, the viscosity of the electrolyte is within the above suitable range, realizing the regulation of the SEI film. By constructing an excellent SEI to improve the desolvation and cross-SEI transport behavior of sodium on the electrode surface, and being able to inhibit the side reactions at the electrode-electrolyte interface, it can achieve a desirable cycle life at room temperature. Thus, after the first charge of the sodium-ion battery using this long-life sodium-ion battery electrolyte, an SEI film with excellent mechanical stability and ion transport performance can be formed. At the same time, the formula of the long-life sodium-ion battery electrolyte in the present application is simple, and excellent charge-discharge cycle performance can be achieved under the condition of using a single sodium salt and a single additive, saving costs.

[0073] The sodium-ion battery of the present application using the above electrolyte can enable the battery to achieve more than 2000 cycles at room temperature, with a capacity retention greater than 80%, meeting the requirements for long-life stable cycling of the battery.

[0074] According to the embodiment of the second aspect of the present application, the SEI film is rich in sulfur-based components such as sodium alkyl sulfate or sodium alkyl sulfite.

[0075] Sulfur-based components such as sodium alkyl sulfate and sodium alkyl sulfite can form stable chemical bonds on the electrode surface, have good chemical stability, and can form a tough and dense protective film on the electrode surface. During the charge and discharge process of the battery, the electrode will withstand high potential differences and the frequent insertion and extraction of ions. Ordinary SEI films may be gradually damaged during long-term cycling. However, the SEI film rich in these sulfur-based components, due to the relatively high bond energy of the chemical bonds formed by sulfur atoms with other atoms, can effectively resist the erosion of the electrode by external factors. The SEI film can prevent the direct contact between the electrolyte and the electrode, prevent other components in the electrolyte from further reacting with the electrode, reduce the possibility of electrolyte decomposition, inhibit the occurrence of side reactions, and thus extend the service life of the electrode.

[0076] Under normal circumstances, a sodium-ion battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly functioning to prevent short circuit between the positive and negative electrodes, and at the same time allowing active ions to pass through.

[0077] In some embodiments, the sodium-ion battery further includes a positive electrode sheet.

[0078] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector.

[0079] As an example, the positive electrode current collector has two opposite sides in its own thickness direction, and the positive electrode active material layer is disposed on either one or both of the two opposite sides of the positive electrode current collector.

[0080] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector and containing a positive electrode active material.

[0081] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one side of the polymer material base layer. As an example, the metal material can include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0082] In some embodiments, the sodium-ion battery further includes a negative electrode sheet.

[0083] In some embodiments, the negative electrode sheet includes a negative electrode current collector. During the charging process, sodium ions gain electrons on the surface of the negative electrode current collector to form a sodium metal layer.

[0084] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil or copper foil can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one side of the polymer material base layer. As an example, the metal material can include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0085] Further, the negative electrode sheet further includes a conductive layer provided on the negative electrode current collector, and the conductive layer includes a negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] In some other embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0087] In some embodiments, the sodium ion battery further includes a separator. There is no particular limitation on the type of the separator in the embodiments of the present application, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0088] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0089] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0090] In some embodiments, the sodium ion battery may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0091] In some embodiments, the outer package of the sodium ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the sodium ion battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0092] There is no particular limitation on the shape of the sodium ion battery in the embodiments of the present application, and it can be cylindrical, square, or any other shape.

[0093]

Electric device

[0094] In a third aspect, an embodiment of the present application provides an electric device, including the above sodium ion battery.

[0095] The electrical device includes one or more of the sodium-ion battery, battery module or battery pack according to the second aspect of the present application. The sodium-ion battery, battery module or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device.

[0096] In the present application, the electrical device can be, but is not limited to, mobile phones, tablets, laptop computers, electric toys, electric tools, battery cars, electric vehicles, ships, spacecrafts, energy storage systems, etc. Among them, the electric toy can include fixed or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys and electric aircraft toys, etc., and the spacecraft can include airplanes, rockets, space shuttles and spaceships, etc.

[0097] In addition, the electrical device can select the sodium-ion battery, battery module or battery pack according to its usage requirements.

[0098] The following embodiments more specifically describe the content disclosed in the present application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the present application are obvious to those skilled in the art. All reagents used in the embodiments are commercially available or synthesized according to conventional methods, and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0099] Example 1

[0100] (1) Electrolyte: Under the conditions that the concentration of H2O ≤ 0.1 ppm and the concentration of O2 ≤ 0.1 ppm, the sodium salt is sodium hexafluorophosphate with a concentration of 1 mol / L. The organic solvents are ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed in a volume ratio of 1:1. The additive is vinylene sulfate (DTD) with a dosage of 2 wt%. After mixing the sodium salt, organic solvents and additives in a preset ratio, a long-life sodium-ion battery electrolyte is obtained.

[0101] The conductivity of the electrolyte is 3 - 8 mS / cm.

[0102] Positive electrode plate: Layered oxide positive electrode; Negative electrode: Hard carbon.

[0103] The positive electrode plate, separator and negative electrode plate are formed into an electrode assembly through a stacking process. The electrode assembly is placed in an outer package, dried and then injected with the electrolyte. After vacuum packaging, standing, forming, shaping and other processes, a sodium-ion battery is obtained.

[0104] Example 2

[0105] A sodium-ion battery was prepared using a method similar to that of Example 1. Different from Example 1, the organic solvents were selected as ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) in a volume ratio of 1:1:2, and the conductivity of the electrolyte was 8 - 15 mS / cm.

[0106] Example 3

[0107] A sodium-ion battery was prepared using a method similar to that of Example 1. Different from Example 1, the organic solvents were selected as ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) in a volume ratio of 1:2:2, and the conductivity of the electrolyte was 8 - 13 mS / cm.

[0108] Example 4

[0109] A sodium-ion battery was prepared using a method similar to that of Example 1. Different from Example 1, in this example, the sodium salt was selected as sodium hexafluorophosphate with a concentration of 2 mol / L, and the conductivity of the electrolyte was 8 - 10 mS / cm.

[0110] Example 5

[0111] A sodium-ion battery was prepared using a method similar to that of Example 1. Different from Example 1, in this example, the sodium salt was selected as sodium hexafluorophosphate with a concentration of 0.5 mol / L, and the conductivity of the electrolyte was 5 - 10 mS / cm.

[0112] Comparative Example 1

[0113] A sodium-ion battery was prepared using a method similar to that of Example 1. Different from Example 1, the organic solvents were selected as ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 1:1, and the conductivity of the electrolyte was 2 - 5 mS / cm.

[0114] Comparative Example 2

[0115] A sodium-ion battery was prepared using a method similar to that of Example 1. Different from Example 1, the organic solvents were selected as ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) in a volume ratio of 4:1:5, and the conductivity of the electrolyte was 2 - 8 mS / cm.

[0116] Comparative Example 3

[0117] A sodium-ion battery was prepared using a method similar to that of Example 1. Different from Example 1, in this example, the sodium salt was selected as sodium bis(fluorosulfonyl)imide with a concentration of 1 mol / L, and the conductivity of the electrolyte was 8 - 12 mS / cm.

[0118] Comparative Example 4

[0119] A sodium-ion battery was prepared by a method similar to that of Example 1. Different from Example 1, in this example, sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide were selected as the sodium salts, with a concentration of 1 mol / L, and the conductivity of the electrolyte was 8 - 15 mS / cm.

[0120] Comparative Example 5

[0121] A sodium-ion battery was prepared by a method similar to that of Example 1. Different from Example 1, in this example, vinylene carbonate (VC) was selected as the additive, and the conductivity of the electrolyte was 8 - 13 mS / cm.

[0122] Testing Part

[0123] 1. Cycling performance of the sodium-ion battery

[0124] At 25°C, the sodium-ion battery was charged at a constant current of 1C to 3.8V, then charged at a constant voltage of 3.8V until the current reached 0.05C, and then discharged at a constant current of 1C to 2V. This was one charge-discharge cycle. Taking the capacity of the second discharge as 100%, the capacity retention rate of the battery after 1500 cycles was calculated. The capacity retention rate (%) after 1500 cycles of the battery = discharge capacity of the 1500th cycle / discharge capacity of the second cycle × 100%.

[0125] 2. SEI film performance

[0126] Test Results

[0127] The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] Combined with the data in Table 1, it can be seen that in the long-life sodium-ion battery electrolyte of this application, by optimizing the ratio of each component in the electrolyte and the type and physical and chemical properties of the additive, sodium hexafluorophosphate was selected as the sodium salt, combined with a single-component unsaturated ester additive, to realize the regulation of the SEI film. By constructing an excellent SEI, the ease of sodium passing through the SEI was improved, and the gas generation behavior of the sodium-ion battery during cycling was effectively inhibited, reducing the occurrence of side reactions, with a suitable conductivity, making it have excellent charge-discharge cycling performance at both high and low temperatures.

[0132] At the same time, combined with Figures 1 to 4 , through Figure 2 , Figure 3 and Figure 4As can be seen from the results, the battery has excellent cycling performance. The sodium-ion battery can stably cycle more than 2000 times at a charge-discharge rate of 1.0C, and there is no obvious gas generation phenomenon during the cycling process. Through Figure 1 It can be seen that a SEI film rich in chalcogen components can be formed.

[0133] As described above, this is only the specific implementation manner of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the above-described systems, modules, and units can refer to the corresponding processes in the foregoing method embodiments, which will not be repeated here. It should be understood that the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present application.

Claims

1. A long-life sodium ion battery electrolyte, characterized in that: The electrolyte comprises a sodium salt, an organic solvent and a single-component additive; The sodium salt is sodium hexafluorophosphate; The additive is a sulfur-based unsaturated ester additive; The organic solvent is an ester solvent; Based on the mass of the electrolyte, the amount of the additive is 0.2 to 5 wt%; Based on the volume of the electrolyte, the molar concentration of the sodium salt is 0.5 to 3 mol / L; The conductivity of the long-life sodium ion battery electrolyte at 25° C. is 5 to 15 mS / cm.

2. The long-life sodium ion battery electrolyte according to claim 1, characterized in that The ratio of the amount of the additive to the mass of the sodium salt is 1:5 to 1:

50.

3. The long-life sodium ion battery electrolyte according to claim 1, characterized in that: The additive is selected from vinyl sulfate and propylene sulfite.

4. The long-life sodium ion battery electrolyte according to claim 1 or 3, characterized in that: The additive is vinyl sulfate, and based on the mass of the electrolyte, the amount of the vinyl sulfate is 1.5-2.5wt%.

5. The long-life sodium ion battery electrolyte according to claim 1, characterized in that: The dosage of the sodium salt in the sodium ion battery electrolyte is 0.6-1.4 mol / L.

6. The long-life sodium ion battery electrolyte according to claim 1, characterized in that: The organic solvent includes one or more of ethylene carbonate, propylene carbonate, and diethyl carbonate.

7. The long-life sodium ion battery electrolyte according to claim 1, characterized in that: Based on the volume of the organic solvent, the amount of ethylene carbonate in the organic solvent is 10-60 vol%; the amount of propylene carbonate is 30-60 vol%; and the amount of diethyl carbonate is 10-40 vol%.

8. The long-life sodium ion battery electrolyte according to claim 1, characterized in that: Based on the volume of the organic solvent, the ratio of ethylene carbonate, propylene carbonate and diethyl carbonate is 1:(1-2):(1-2).

9. A sodium ion battery, characterized in that: Comprising the long-life sodium ion battery electrolyte as described in any one of claims 1 to 8, the sodium ion battery is stably cycled for more than 2000 times at a charge and discharge rate of 1.0C, and there is no obvious gas production during the cycle.

10. An electrical device, characterized in that: Comprising the sodium ion battery as claimed in claim 9.

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