A sodium ion battery composite electrolyte and a sodium ion battery

Abstract

The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery composite electrolyte and a sodium ion battery. The composite electrolyte comprises electrolyte A and electrolyte B, wherein electrolyte A comprises sodium salt, ether solvent and ester solvent, and electrolyte B comprises sodium salt and ester solvent, wherein electrolyte A accounts for 70-95% of the total mass of the composite electrolyte, and electrolyte B accounts for 5-30% of the total mass of the composite electrolyte. Ether solvents are conducive to realizing the wetting effect of the composite electrolyte on the sodium ion battery, and the products completely decomposed in the first charge are used as part of the SEI film on the surface of the negative electrode, thereby improving the first effect of the negative electrode, and at the same time improving the battery cycle performance and the oxidation resistance of the electrolyte, reducing the cycle gas production, and further improving the oxidation resistance of the composite electrolyte and the working performance of the sodium ion battery. Ester solvents can provide high voltage stability, fully activate the sodium ion battery, and synergize with ether solvents to enhance the various working performances of the sodium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery composite electrolyte and a sodium ion battery. Background Art

[0002] In recent years, sodium-ion batteries have been widely studied for their long service life, high safety, low theoretical cost and abundant resources. In particular, the research on the material system and electrochemical mechanism of sodium-ion batteries has gradually become the research focus. However, due to the diversity of sodium-ion battery material systems, the electrochemical properties of each are also different.

[0003] In the prior art lithium-ion batteries, fluorine-containing compounds such as lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) are usually used as lithium salts, so that the solid electrolyte interface film (SEI film) formed subsequently contains relatively stable lithium fluoride (LiF) and has good ionic conductivity. In sodium-ion batteries, since the solubility of sodium fluoride (NaF) is higher than that of lithium fluoride (LiF), there is a risk of instability in the long-term use of sodium-ion batteries. In addition, the negative electrode active material of sodium-ion batteries is mainly hard carbon, and hard carbon also has the problem of poor film-forming stability. Therefore, it is necessary to provide an optimized sodium-ion battery material system to improve the working performance of sodium-ion batteries. Summary of the invention

[0004] The purpose of the present invention is to provide a sodium ion battery composite electrolyte and a sodium ion battery in view of the problem that sodium ion batteries prepared by the sodium ion battery material system in the prior art have the risk of instability during long-term use.

[0005] The specific technical solutions of the present invention are as follows:

[0006] The present invention provides a sodium ion battery composite electrolyte, characterized in that the composite electrolyte comprises an electrolyte A and an electrolyte B, the electrolyte A comprises a sodium salt, an ether solvent and an ester solvent, the electrolyte B comprises a sodium salt and an ester solvent, the electrolyte A accounts for 70-95% of the total mass of the composite electrolyte, and the electrolyte B accounts for 5-30% of the total mass of the composite electrolyte.

[0007] In a possible implementation manner, the electrolyte A is composed of sodium salt, ether solvent and ester solvent;

[0008] In a possible implementation manner, the electrolyte B is composed of sodium salt and ester solvent.

[0009] In a possible implementation manner, in the electrolyte A, the ether solvent accounts for 5-30% of the total volume of the solvent of the electrolyte A, and the ester solvent accounts for 70-95% of the total volume of the solvent of the electrolyte A.

[0010] In a possible implementation, the ether solvent is at least one of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane (4-MeDOL), dimethoxymethane (DMM), 1,2-dimethoxypropane (DMP), diethylene glycol dimethyl ether (DG), crown ether, cryptand, ethylene glycol dimethyl ether (DME) and derivatives thereof;

[0011] In a possible implementation manner, the ester solvent is one of propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0012] In a possible embodiment, the derivatives include diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME) and tetraethylene glycol dimethyl ether (TEGDME).

[0013] In a possible implementation manner, the ester solvent in the electrolyte B is at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl formate (MF), methyl acetate (MA), vinylene carbonate (VC), 1,3-propane sultone (PS), sodium dioxalatoborate (NaBOB), and sodium difluorooxalatoborate (NaODFB).

[0014] In a possible implementation, the sodium salt is at least one of sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0015] In a possible implementation manner, the concentration of the sodium salt is 0.7-1.4 mol / L.

[0016] In a possible implementation manner, the formation process of the sodium ion battery includes injecting the electrolyte A into the sodium ion battery, performing a first charging formation, and then injecting the electrolyte B into the sodium ion battery, and performing a second charging formation.

[0017] The present invention also provides a sodium ion battery, which comprises the composite electrolyte in any of the above embodiments.

[0018] In a possible implementation manner, the oxidation voltage of the electrolyte A is tested before the electrolyte A is injected, and during the first charging formation, the sodium ion battery is charged to a constant voltage of 0.1-0.3V higher than the oxidation voltage.

[0019] Based on the above technical solution, the present invention has at least the following beneficial effects:

[0020] 1. Two groups of electrolytes with different components are used as composite electrolytes for sodium ion batteries, one group includes sodium salt, ether solvent and ester solvent, and the other group includes sodium salt and ester solvent. Among them, adding ether solvent to one group of electrolytes and injecting it into the sodium ion battery can make the composite electrolyte have a certain viscosity, which is beneficial to improve the wetting effect of the composite electrolyte on the sodium ion battery. Furthermore, the ether solvent can match the negative electrode, and the product completely decomposed in the first charge is used as part of the solid electrolyte interface film (SEI film) on the surface of the negative electrode, thereby forming a dense and stable SEI film on the surface of the negative electrode, which can improve the first effect of the negative electrode, and prevent the solvent from continuously co-embedded into the negative electrode in the subsequent process, improve the cycle performance, and improve the oxidation resistance of the negative electrode, further improve the oxidation resistance of the composite electrolyte, and then improve the working performance of the sodium ion battery. At the same time, the ester solvent in this group of electrolytes can also play a wetting role, facilitate injection, and cooperate with the ether component to form an SEI film. In another group of electrolytes, ester solvents with high dielectric constants can provide high voltage stability, fully activate sodium-ion batteries, and improve the effect of rehydration and infiltration, enhance the charge and discharge cycle performance of sodium-ion batteries, and thus improve the various working performances of sodium-ion batteries. Not using ether solvents in this group of electrolytes can ensure that a dense and stable SEI film is formed in the final sodium-ion battery obtained by charging and formation, and there is no ether component residue, which greatly reduces the gas production caused by the ether component residue, which is conducive to the control of gas production.

[0021] 2. The sodium ion battery is injected with two groups of electrolytes with different components in two injections. Specifically, after a group of electrolytes including ether solvents are injected into the sodium ion battery, the first charging formation is carried out, and then another group of electrolytes not including ether solvents are injected, and the second charging formation is carried out. The ether solvent injected preferentially can be completely decomposed during the first charging process, and its decomposition product is used as a part of the solid electrolyte interface film (SEI film) on the negative electrode surface, thereby improving the film formation utilization rate of the ether solvent. After the ether component in the electrolyte is completely consumed during the subsequent charging process, another group of electrolytes is added for the second charging formation under the condition that there is no residual ether component. This is beneficial to greatly reduce the gas production caused by the residual ether component on the basis of forming a dense and stable SEI film, realize the control of gas production, and improve the rehydration and infiltration effect, thereby synergistically improving the working performance of the sodium ion battery.

[0022] 3. Before injecting the electrolyte including the ether solvent, the oxidation voltage of the electrolyte is tested, and during the first charging formation, the sodium ion battery is charged to a constant voltage after being charged to a voltage 0.1-0.3V higher than the oxidation voltage, so that the residual ether solvent in the electrolyte after the solid electrolyte interface film (SEI film) is formed can be completely oxidized and decomposed, so that there is no ether solvent residue in the sodium ion battery, so that on the basis of using the ether solvent to form the solid electrolyte interface film (SEI film), the influence of the residual ether solvent on the subsequent working performance of the sodium ion battery can be eliminated. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0024] For the following defined terms, these definitions shall apply unless a different definition is given elsewhere in the claims or specification. All numerical values, whether or not explicitly indicated, are defined herein as modified by the term "about". The term "about" generally refers to a numerical range that is considered by those skilled in the art to be equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A numerical range indicated by a lower value and a higher value is defined to cover all numerical values ​​included in this numerical range and all subranges included in this numerical range.

[0025] In addition, the terms "comprises", "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or equipment.

[0026] The embodiments of the present invention are described below in combination with the above technical solutions.

[0027] An embodiment of the present application provides a sodium ion battery composite electrolyte, characterized in that the composite electrolyte includes electrolyte A and electrolyte B, electrolyte A includes sodium salt, ether solvent and ester solvent, electrolyte B includes sodium salt and ester solvent, electrolyte A accounts for 70-95% of the total mass of the composite electrolyte, and electrolyte B accounts for 5-30% of the total mass of the composite electrolyte.

[0028] Specifically, it can be understood that electrolyte A is any point value between 70% and 95% of the total mass of the composite electrolyte, and illustratively, it can be 70%, 75%, 80%, 85%, 90%, 95%, etc.; Correspondingly, electrolyte B can be any point value between 5% and 30% of the total mass of the composite electrolyte, and illustratively, it can be 5%, 10%, 15%, 20%, 25%, 30%, etc.

[0029] In this way, two groups of electrolytes with different components are used as composite electrolytes for sodium ion batteries, one group includes sodium salt, ether solvent and ester solvent, and the other group includes sodium salt and ester solvent. Among them, introducing ether solvent into electrolyte and injecting it into sodium ion battery can make the composite electrolyte have a certain viscosity, which is conducive to the wetting effect of composite electrolyte on sodium ion battery. Furthermore, ether solvent can match with negative electrode, and the product generated by complete decomposition in the first charge is used as part of solid electrolyte interface film (SEI film) on the surface of negative electrode, so as to form a dense and stable SEI film on the surface of negative electrode, which can improve the first effect of negative electrode, and prevent the continuous co-embedding of solvent into negative electrode in subsequent process, improve cycle performance, and improve the oxidation resistance of negative electrode, further improve the oxidation resistance of composite electrolyte, and then improve the working performance of sodium ion battery. At the same time, the ester solvent in this group of electrolyte can also play a role of wetting, which is convenient for liquid injection, and cooperates with ether component to form SEI film. In another group of electrolytes, ester solvents with high dielectric constants can provide high voltage stability for the composite electrolyte, fully activate the sodium-ion battery, and improve the effect of rehydration and infiltration, thereby improving the various working performances of the sodium-ion battery. Not using ether solvents in this group of electrolytes can ensure that a dense and stable SEI film is formed in the final sodium-ion battery obtained by charging and formation, and there is no ether component residue, which greatly reduces the gas production caused by the ether component residue, which is conducive to the control of gas production. Controlling a group of electrolytes including ether solvents to 70-95% of the total mass of the composite electrolyte can provide sufficient viscosity for the composite electrolyte, so that the composite electrolyte can infiltrate the sodium ion battery, and can also achieve the product completely decomposed in the first charge as part of the solid electrolyte interface film (SEI film) on the surface of the negative electrode, and form a dense and stable SEI film on the surface of the negative electrode, which can improve the first effect of the negative electrode, and prevent the solvent from continuously co-embedded into the negative electrode in the subsequent process, improve the cycle performance, and improve the oxidation resistance of the negative electrode, further improve the oxidation resistance of the composite electrolyte, improve the effect of the sodium ion battery formation process, and thus improve the various working performances of the sodium ion battery. Further, controlling another group of electrolytes to 5-30% of the total mass of the composite electrolyte allows the group of electrolytes to fully activate the sodium ion battery under the action of the high voltage stability provided by the high dielectric constant ester solvent, synergistically enhance the charge and discharge cycle performance of the sodium ion battery, and thus improve the various working performances of the sodium ion battery. If the mass proportion of electrolyte A in the composite electrolyte is too low, the initial injection volume of the sodium ion battery will be insufficient, and the internal structure of the sodium ion battery will not be completely infiltrated, resulting in severe polarization during the subsequent charging process of the sodium ion battery, which greatly degrades the performance of the prepared sodium ion battery.

[0030] In some embodiments, the electrolyte A is composed of a sodium salt, an ether solvent, and an ester solvent;

[0031] Specifically, the electrolyte A contains only three components of sodium salt, ether solvent and ester solvent, and does not contain other components.

[0032] In some embodiments, electrolyte B is composed of sodium salt and ester solvent.

[0033] Specifically, the electrolyte B contains only two components, namely, sodium salt and ester solvent, and does not contain other components.

[0034] In this way, a composite electrolyte with the simplest components is provided for sodium ion batteries, wherein one group of electrolytes contains only three components, namely sodium salt, ether solvent and ester solvent, and the other group of electrolytes contains only two components, namely sodium salt and ester solvent. Adding ether solvents to one group of electrolytes and injecting them into sodium ion batteries can make the electrolyte have a certain viscosity, which is conducive to the wetting effect of the composite electrolyte on the sodium ion battery. Furthermore, the ether solvent can match the negative electrode, and the product generated by the complete decomposition in the first charge is used as part of the solid electrolyte interface film (SEI film) on the surface of the negative electrode, thereby forming a dense and stable SEI film on the surface of the negative electrode, which can improve the first effect of the negative electrode, and prevent the solvent from being continuously co-embedded into the negative electrode in the subsequent process, improve the cycle performance, and improve the oxidation resistance of the negative electrode, further improve the oxidation resistance of the composite electrolyte, and thus improve the working performance of the sodium ion battery. At the same time, the ester solvent in this group of electrolytes can also play a wetting role, facilitate liquid injection, and cooperate with the ether component to form an SEI film. In another group of electrolytes, ester solvents with high dielectric constants can provide high voltage stability for the composite electrolyte, fully activate the sodium-ion battery, and improve the effect of rehydration and infiltration, thereby improving the various working performances of the sodium-ion battery. Not using ether solvents in this group of electrolytes can ensure that a dense and stable SEI film is formed in the final sodium-ion battery obtained by charging and formation, and there is no ether component residue, which greatly reduces the gas production caused by the ether component residue, which is conducive to the control of gas production.

[0035] In some embodiments, in electrolyte A, the ether solvent accounts for 5-30% of the total volume of the solvent of electrolyte A, and the ester solvent accounts for 70-95% of the total volume of the solvent of electrolyte A.

[0036] Specifically, in electrolyte A, the ether solvent can be any point value between 5 and 30% of the total solvent volume of electrolyte A, and illustratively, it can be 5%, 10%, 15%, 20%, 25%, 30%, etc.; correspondingly, the ester solvent can be any point value between 70 and 95% of the total solvent volume of electrolyte A, and illustratively, it can be 70%, 75%, 80%, 85%, 90%, 95%, etc.

[0037] Thus, in the electrolyte, the ether solvent is controlled at 5-30% of the total volume of the solvent of electrolyte A, which can make the composite electrolyte have sufficient viscosity, which is conducive to the wetting effect of the composite electrolyte on the sodium ion battery. Furthermore, the ether solvent can match the negative electrode, and the product completely decomposed in the first charge is used as part of the solid electrolyte interface film (SEI film) on the surface of the negative electrode, thereby forming a dense and stable SEI film on the surface of the negative electrode, which can improve the first effect of the negative electrode, and prevent the solvent from continuously co-embedded into the negative electrode in the subsequent process, improve the cycle performance, and improve the oxidation resistance of the negative electrode, reduce the gas production during the cycle of the sodium ion battery, further improve the oxidation resistance of the composite electrolyte, and then improve the working performance of the sodium ion battery. Accordingly, the ester solvent is controlled at 70-95% of the total volume of the solvent of electrolyte A, so that the ester solvent can provide high voltage stability for the composite electrolyte, fully activate the sodium ion battery, and synergize with the ether solvent to enhance the charge and discharge cycle performance of the sodium ion battery, thereby improving the various working performances of the sodium ion battery. If the volume proportion of ether solvent in electrolyte A is too high, the ether solvent cannot be completely oxidized and decomposed during the first charge process, and the excess ether solvent will remain in the electrolyte of the sodium ion battery, thereby affecting the performance of the sodium ion battery prepared subsequently. At the same time, the excess ether solvent will prolong the time required for the formation process, thereby reducing the production efficiency of the sodium ion battery. If the volume proportion of ether solvent in electrolyte A is too low, the ether solvent decomposition products involved in the formation of the SEI film will be too few, and a dense and stable SEI film cannot be formed on the negative electrode surface, which greatly affects the performance of the prepared sodium ion battery.

[0038] In some embodiments, the ether solvent is at least one of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane (4-MeDOL), dimethoxymethane (DMM), 1,2-dimethoxypropane (DMP), diethylene glycol dimethyl ether (DG), crown ether, cryptand, ethylene glycol dimethyl ether (DME) and their derivatives;

[0039] In some embodiments, the ester solvent is one of propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0040] Specifically, a single-component ether can be used as an ether solvent to prepare a composite electrolyte, that is, one of tetrahydrofuran (THF), dimethoxymethane (DMM), ethylene glycol dimethyl ether (DME), and diethylene glycol dimethyl ether (DEGDME) can be used as an ether solvent to prepare a composite electrolyte. A multi-component ether can also be used as an ether solvent to prepare a composite electrolyte, for example, tetrahydrofuran (THF) and dimethoxymethane (DMM) are used as a two-component composite ether solvent to prepare a composite electrolyte. It should be noted that ether solvents and ester solvents are not limited to the several ethers and esters listed above, and other ethers and esters can also be used. As long as the ethers and esters can achieve the wetting of the sodium ion battery and the formation of the negative electrode SEI film, and provide voltage stability for the sodium ion battery, they are all within the protection scope of this specification.

[0041] In some embodiments, the derivatives include diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), and tetraethylene glycol dimethyl ether (TEGDME).

[0042] In some embodiments, the ester solvent in the electrolyte B is at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl formate (MF), methyl acetate (MA), vinylene carbonate (VC), 1,3-propane sultone (PS), sodium dioxalatoborate (NaBOB), and sodium difluorooxalatoborate (NaODFB).

[0043] Specifically, a single-component ester can be used as an ester solvent to prepare a composite electrolyte, that is, one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl formate (MF), methyl acetate (MA), vinylene carbonate (VC), 1,3-propane sultone (PS), sodium dioxalate borate (NaBOB), and sodium difluorooxalate borate (NaODFB) can be used as an ester solvent to prepare a composite electrolyte. A multi-component ester can also be used as an ester solvent to prepare a composite electrolyte, for example, ethylene carbonate (EC) and propylene carbonate (PC) are used as two-component composite ester solvents to prepare a composite electrolyte. It should be noted that the ester solvent is not limited to the above-mentioned esters, and other esters can also be used. As long as the ester can achieve the improvement of the voltage stability of the sodium ion battery, it is within the protection scope of this specification.

[0044] In some embodiments, the sodium salt is at least one of sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0045] Specifically, a single-component sodium salt may be used, i.e., one of sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI). A multi-component sodium salt may also be used, for example, sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI) may be used as a two-component sodium salt. It should be noted that the sodium salt is not limited to the several sodium salts listed above, and other salts may also be used. As long as the sodium salt has sufficient solubility and ion transport performance, it is within the protection scope of this specification.

[0046] In some embodiments, the concentration of the sodium salt is 0.7-1.4 mol / L.

[0047] Specifically, it can be understood that the concentration of sodium salt can be any point value between 0.7 and 1.4 mol / L. For example, it can be 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, etc.

[0048] In this way, controlling the concentration of sodium salt at 0.7~1.4mol / L can ensure that sodium ions can migrate safely and stably between the positive and negative electrodes in the sodium ion battery, providing the composite electrolyte with the ion transport performance required by the sodium ion battery, thereby realizing the cyclic working process of the sodium ion battery.

[0049] In some embodiments, the formation process of the sodium ion battery includes injecting electrolyte A into the sodium ion battery, performing a first charging formation, and then injecting electrolyte B into the sodium ion battery, and then performing a second charging formation.

[0050] Specifically, during the preparation process of the sodium ion battery, the composite electrolyte is injected into the sodium ion battery twice. First, the electrolyte A including the ether solvent is injected into the sodium ion battery, and then constant current charging and constant voltage charging are performed in sequence to complete the first charging formation of the sodium ion battery. After standing for a period of time, the electrolyte B is injected again for the second charging formation.

[0051] In this way, in the first charging formation, the ether solvent in the electrolyte A can completely decompose the generated products as part of the solid electrolyte interface film (SEI film) on the surface of the negative electrode, and form a dense and stable SEI film on the surface of the negative electrode, which can improve the initial effect of the negative electrode, and at the same time prevent the solvent from continuously co-embedded into the negative electrode in the subsequent process, thereby improving the cycle performance, and improving the oxidation resistance of the negative electrode, reducing the gas production during the cycle of the sodium ion battery, further improving the oxidation resistance of the composite electrolyte, and improving the effect of the sodium ion battery formation process, thereby improving the various working performances of the sodium ion battery.

[0052] The present application also provides a sodium ion battery, which includes the composite electrolyte in any of the above embodiments.

[0053] In this way, the sodium ion battery using the composite electrolyte in any of the above embodiments can use the product generated by the complete decomposition of the ether solvent as part of the solid electrolyte interface film (SEI film) on the surface of the negative electrode during the first charge, thereby forming a dense and stable SEI film on the surface of the negative electrode, improving the first effect of the negative electrode, and preventing the solvent from being continuously co-embedded into the negative electrode in the subsequent process, improving the cycle performance, and improving the oxidation resistance of the negative electrode, further improving the oxidation resistance of the composite electrolyte, and thus improving the working performance of the sodium ion battery. In another group of electrolytes, ester solvents with high dielectric constants can provide high voltage stability for the composite electrolyte, fully activate the sodium ion battery, and at the same time improve the effect of fluid replenishment and infiltration, thereby improving the various working performances of the sodium ion battery. Not using ether solvents in this group of electrolytes can ensure that a dense and stable SEI film is formed in the sodium ion battery obtained by the final charge formation, and there is no ether component residue, which greatly reduces the gas production caused by the residual ether component, which is conducive to the control of gas production.

[0054] In some embodiments, the oxidation voltage of electrolyte A is tested before injecting electrolyte A, and during the first charging formation, the sodium ion battery is charged to a voltage higher than the oxidation voltage by 0.1-0.3V and then constant voltage charging is performed.

[0055] Specifically, during the preparation of the sodium ion battery, the composite electrolyte is injected into the sodium ion battery twice, the oxidation voltage of electrolyte A is first measured by linear sweep voltammetry (LSV), and then electrolyte A including an ether solvent is injected into the sodium ion battery, and the battery is charged to 20% SOC at a current of 0.05~0.1C, and then the battery is constant-current charged to 0.1~0.3V higher than the oxidation voltage of electrolyte A at a current of 0.2~0.5C, and then constant-voltage charging is performed until the current is reduced to 0.01C and the charging is cut off, completing the first charging formation of the sodium ion battery. After standing for a period of time, electrolyte B is injected and the second charging formation is performed.

[0056] In this way, the voltage setting in the first charging formation is determined by the oxidation voltage of the electrolyte A, so that during low current charging, the ether solvent and the ester solvent can jointly participate in the reduction reaction at the initial stage of charging to form a dense and stable SEI film, and then in the constant voltage charging stage, it is ensured that the residual ether solvent in the electrolyte after the SEI film is formed is completely oxidized and decomposed, so that no matter whether it is a single-component ether solvent or a multi-component ether solvent, there is no ether solvent residue in the sodium ion battery, so that on the basis of using ether solvents to form the SEI film, the influence of residual ether solvents on the subsequent working performance of the finished sodium ion battery can be eliminated.

[0057] The present application also provides a series of examples for further verifying the implementation effects of the sodium ion battery composite electrolyte and the sodium ion battery in the technical solution of the present application. The implementation effects of the technical solution of the present application are described in detail below in combination with specific examples.

[0058] Example 1

[0059] This embodiment provides a sodium ion battery composite electrolyte, the specific components are as follows:

[0060] 1. The sodium ion battery composite electrolyte includes electrolyte A and electrolyte B, and the mass ratio of the two groups of electrolytes is electrolyte A: electrolyte B = 17:3.

[0061] 2. Electrolyte A includes sodium salt, ether solvent and ester solvent, wherein NaPF6 and NaFSI are used as composite sodium salt, the mass ratio of NaPF6 and NaFSI is 1:1, and the total concentration of the composite sodium salt is 1 mol / L; DEGDME is used as the ether solvent, DEC is used as the ester solvent, and the volume ratio of the solvent is DEGDME:DEC=3:17.

[0062] 3. Electrolyte B includes sodium salt and ester solvents, wherein NaPF6 is used as the sodium salt, and the concentration of the sodium salt is 1 mol / L; EC and DEC are used as the composite ester solvent, and the volume ratio of the solvent is EC:DEC=3:7.

[0063] This embodiment also provides a sodium ion battery, and the specific preparation method is as follows:

[0064] 1. The above-mentioned sodium ion composite electrolyte was prepared in a dry environment, and the oxidation voltage U1 of electrolyte A was measured by linear sweep voltammetry (LSV). Then, sodium iron sulfate was used as the positive electrode, hard carbon was used as the negative electrode, and polypropylene was used as the separator to assemble a sodium ion battery.

[0065] 2. The assembled sodium ion battery was placed in a dry environment and injected with electrolyte A. After sealing, the battery was charged to 20% SOC at a current of 0.05~0.1C, and then the battery was constant-current charged at a current of 0.2~0.5C to an oxidation voltage 0.1~0.3V higher than the electrolyte A. Then, constant-voltage charging was performed until the current dropped to 0.01C and the charging was cut off to complete the first charging formation. Then, electrolyte B was injected in a dry environment. After sealing, the second charging formation and subsequent sodium ion battery preparation processes were performed to obtain a sodium ion battery with a rate performance of 97.2% and a cycle performance of 96.0%.

[0066] Example 2

[0067] This embodiment provides a sodium ion battery composite electrolyte, the specific components are as follows:

[0068] 1. In electrolyte A, NaPF6 is used as the sodium salt, and the concentration of the sodium salt is 1 mol / L.

[0069] This embodiment also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 97.1%, and the cycle performance of the battery is 96.2%. The other specific steps and settings of this embodiment are the same as those of Example 1, and are not described in detail here.

[0070] Example 3

[0071] This embodiment provides a sodium ion battery composite electrolyte, the specific components are as follows:

[0072] 1. The mass ratio of electrolyte A to electrolyte B is electrolyte A: electrolyte B = 7:3.

[0073] This embodiment also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 96.1%, and the cycle performance of the battery is 95.3%. The other specific steps and settings of this embodiment are the same as those of Example 2, and are not described in detail here.

[0074] Example 4

[0075] This embodiment provides a sodium ion battery composite electrolyte, the specific components are as follows:

[0076] 1. The mass ratio of electrolyte A to electrolyte B is electrolyte A: electrolyte B = 19:1.

[0077] This embodiment also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 96.3%, and the cycle performance of the battery is 95.8%. The other specific steps and settings of this embodiment are the same as those of Example 2, and are not described here.

[0078] Example 5

[0079] This embodiment provides a sodium ion battery composite electrolyte, the specific components are as follows:

[0080] 1. In electrolyte A, the volume ratio of solvent is DEGDME:DEC=1:19.

[0081] This embodiment also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 96.1%, and the cycle performance of the battery is 95.9%. The other specific steps and settings of this embodiment are the same as those of Example 2, and are not described in detail here.

[0082] Example 6

[0083] This embodiment provides a sodium ion battery composite electrolyte, the specific components are as follows:

[0084] 1. In electrolyte A, the volume ratio of solvent is DEGDME:DEC=3:7.

[0085] This embodiment also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 96.6%, and the cycle performance of the battery is 95.5%. The other specific steps and settings of this embodiment are the same as those of Example 2, and are not described in detail here.

[0086] Example 7

[0087] This embodiment provides a sodium ion battery composite electrolyte, the specific components are as follows:

[0088] 1. In electrolyte A, the concentration of NaPF6 sodium salt is 0.7 mol / L.

[0089] This embodiment also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 95.8%, and the cycle performance of the battery is 94.1%. The other specific steps and settings of this embodiment are the same as those of Example 2, and are not described here.

[0090] Example 8

[0091] This embodiment provides a sodium ion battery composite electrolyte, the specific components are as follows:

[0092] 1. In electrolyte A, the concentration of NaPF6 sodium salt is 1.3 mol / L.

[0093] This embodiment also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 97.0%, and the cycle performance of the battery is 96.0%. The other specific steps and settings of this embodiment are the same as those of Example 2, and are not described in detail here.

[0094] Example 9

[0095] 1. In electrolyte B, NaPF6 is used as sodium salt, and the concentration of sodium salt is 1 mol / L; EC, PC and EMC are used as complex ester solvents, and the volume ratio of the solvent is EC:PC:EMC=3:2:5.

[0096] This embodiment also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 96.4%, and the cycle performance of the battery is 95.5%. The other specific steps and settings of this embodiment are the same as those of Example 2, and are not described in detail here.

[0097] Example 10

[0098] 1. In electrolyte A, DME is used as the ether solvent, EMC is used as the ester solvent, and the volume ratio of the solvents is DME:EMC=3:17.

[0099] This embodiment also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 96.5%, and the cycle performance of the battery is 95.8%. The other specific steps and settings of this embodiment are the same as those of Example 2, and are not described here.

[0100] Comparative Example 1

[0101] This comparative example provides a sodium ion battery composite electrolyte, the specific components of which are as follows:

[0102] 1. The mass ratio of electrolyte A to electrolyte B is electrolyte A: electrolyte B = 3:2.

[0103] This comparative example also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 70.2%, and the cycle performance of the battery is less than 80%. The other specific steps and settings of this comparative example are the same as those of Example 2, and are not described in detail here.

[0104] Comparative Example 2

[0105] This comparative example provides a sodium ion battery composite electrolyte, the specific components of which are as follows:

[0106] 1. The mass ratio of electrolyte A to electrolyte B is electrolyte A: electrolyte B = 99:1.

[0107] This comparative example also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 95.9%, and the cycle performance of the battery is 95.0%. The other specific steps and settings of this comparative example are the same as those of Example 2, and are not described in detail here.

[0108] Comparative Example 3

[0109] This comparative example provides a sodium ion battery composite electrolyte, the specific components of which are as follows:

[0110] 1. In electrolyte A, the volume ratio of solvent is DEGDME:DEC=1:49.

[0111] This comparative example also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 93.6%, and the cycle performance of the battery is 92.1%. The other specific steps and settings of this comparative example are the same as those of Example 2, and are not described in detail here.

[0112] Comparative Example 4

[0113] This comparative example provides a sodium ion battery composite electrolyte, the specific components of which are as follows:

[0114] 1. In electrolyte A, the volume ratio of solvent is DEGDME:DEC=7:13.

[0115] This comparative example also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 89.0%, and the cycle performance of the battery is 84.0%. The other specific steps and settings of this comparative example are the same as those of Example 2, and are not described in detail here.

[0116] Comparative Example 5

[0117] This comparative example provides a sodium ion battery electrolyte, the specific components of which are as follows:

[0118] 1. The sodium ion battery electrolyte only includes electrolyte B.

[0119] 2. In electrolyte B, NaPF6 is used as the sodium salt, the concentration of the sodium salt is 1 mol / L, EC and DEC are used as the complex ester solvents, and the volume ratio of the solvent is EC:DEC=3:17.

[0120] This comparative example also provides a sodium ion battery, which is prepared by the preparation method in Example 1, and the rate performance of the battery is 93.5%, and the cycle performance of the battery is 92.1%. The other specific steps and settings of this comparative example are the same as those of Example 2, and are not described in detail here.

[0121] The parameters of the composite electrolytes of the above-mentioned Examples 1-10 and Comparative Examples 1-5 and the performance of the sodium ion batteries are shown in Table 1 below.

[0122] Table 1 Parameters and performance comparison of the examples and comparative examples

[0123] Group Electrolyte A component Electrolyte B component Mass ratio of electrolyte A and B Rate performance / % Cycle performance / % Example 1 <![CDATA[NaPF6:NaFSI = 1:1, a total of 1 mol / L, DEGDME:DEC = 3:17]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 17:3 97.2 96.0 Example 2 <![CDATA[NaPF61mol / LDEGDME:DEC=3:17]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 17:3 97.1 96.2 Example 3 <![CDATA[NaPF61mol / LDEGDME:DEC=3:17]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 7:3 96.1 95.3 Example 4 <![CDATA[NaPF61mol / LDEGDME:DEC=3:17]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 19:1 96.3 95.8 Example 5 <![CDATA[NaPF61mol / LDEGDME:DEC=1:19]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 17:3 96.1 95.9 Example 6 <![CDATA[NaPF61mol / LDEGDME:DEC=3:7]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 17:3 96.6 95.5 Example 7 <![CDATA[NaPF60.7mol / LDEGDME:DEC=3:17]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 17:3 95.8 94.1 Example 8 <![CDATA[NaPF61.3mol / LDEGDME:DEC=3:17]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 17:3 97.0 96.0 Example 9 <![CDATA[NaPF61mol / LDEGDME:DEC=3:17]]> <![CDATA[NaPF61mol / LEC:PC:EMC=3:2:5]]> 17:3 96.4 95.5 Example 10 <![CDATA[NaPF61mol / LDME:EMC=3:17]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 17:3 96.5 95.8 Comparative Example 1 <![CDATA[NaPF61mol / LDEGDME:DEC=3:17]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 3:2 70.2 ＜80% Comparative Example 2 <![CDATA[NaPF61mol / LDEGDME:DEC=3:17]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 99:1 95.9 95.0 Comparative Example 3 <![CDATA[NaPF61mol / LDEGDME:DEC=1:49]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 17:3 93.6 92.1 Comparative Example 4 <![CDATA[NaPF61mol / LDEGDME:DEC=7:13]]> <![CDATA[NaPF61mol / LEC:DEC=3:7]]> 17:3 89 84 Comparative Example 5 / <![CDATA[NaPF61mol / LEC:DEC=3:17]]> / 93.5 92.1

[0124] Referring to Table 1, it can be seen from the comparison of Examples 1-10 and Comparative Example 5 that the sodium ion battery prepared by the composite electrolyte of the present invention is obviously better than the sodium ion battery using only ester solvents as electrolytes in terms of rate performance and cycle performance. Comparative Examples 1-10 and Comparative Examples 1-2 show that controlling the electrolyte A in the composite electrolyte to 70-95% of the total mass of the electrolyte can provide sufficient viscosity for the composite electrolyte to infiltrate the sodium ion battery, and form a dense and stable SEI film on the surface of the negative electrode, significantly improving the rate performance and cycle performance of the sodium ion battery. Comparative Examples 1-10 and Comparative Examples 3-4 show that controlling the volume of the ether solvent in the electrolyte A to 5-30% of the total volume of the electrolyte A can avoid the ether solvent volume ratio being too high, resulting in the inability to completely oxidize and decompose during the first charge process, and can also avoid the ether solvent decomposition products participating in the formation of the SEI film being too few and unable to form a dense and stable SEI film on the surface of the negative electrode, thereby achieving the performance improvement of the sodium ion battery. Furthermore, Examples 1-10 use different proportions of sodium salt, ether solvent and ester solvent components provided by the present invention, as well as electrolyte A and electrolyte B in different mass ratios, which can effectively form a dense and stable SEI film on the surface of the negative electrode, improve the initial effect of the negative electrode, prevent the solvent from continuously co-embedded into the negative electrode in the subsequent process, and replenish the sodium ion battery. At the same time, the proportion of ether solvent in electrolyte A is controlled to be completely consumed in the first charging formation to greatly reduce the gas production caused by the residual ether components, thereby achieving control of gas production and improving the working performance of the sodium ion battery.

[0125] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0126] It should be noted that all the features recorded in the present invention (including the technical features recorded in different embodiments) can be arbitrarily combined under reasonable circumstances, and new technical solutions formed by the combination are all within the protection scope of the present invention.

[0127] What is described above are only some embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art should understand that the present invention may be subject to various changes and improvements, and any modifications, equivalent substitutions and improvements made in accordance with the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A sodium ion battery composite electrolyte, characterized in that: The composite electrolyte comprises electrolyte A and electrolyte B, wherein electrolyte A is composed of sodium salt, ether solvent and ester solvent, and electrolyte B is composed of sodium salt and ester solvent; The electrolyte A accounts for 70-95% of the total mass of the composite electrolyte, the ether solvent in the electrolyte A accounts for 5-30% of the total volume of the solvent of the electrolyte A, and the ester solvent in the electrolyte A accounts for 70-95% of the total volume of the solvent of the electrolyte A; the electrolyte B accounts for 5-30% of the total mass of the composite electrolyte; The ether solvent is at least one of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane (4-MeDOL), dimethoxymethane (DMM), 1,2-dimethoxypropane (DMP), diethylene glycol dimethyl ether (DG), crown ether, cryptand, ethylene glycol dimethyl ether (DME) and ethylene glycol dimethyl ether derivatives; The formation process of the sodium ion battery includes injecting the electrolyte A into the sodium ion battery, performing a first charging formation, and then injecting the electrolyte B into the sodium ion battery, and performing a second charging formation.

2. The composite electrolyte according to claim 1, characterized in that The ester solvent in the electrolyte A is one of propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

3. The composite electrolyte according to claim 2, characterized in that: The glycol dimethyl ether derivatives include diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME) and tetraethylene glycol dimethyl ether (TEGDME).

4. The composite electrolyte according to claim 1, characterized in that: The ester solvent in the electrolyte B is at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl formate (MF), methyl acetate (MA), vinylene carbonate (VC), and 1,3-propane sultone (PS).

5. The composite electrolyte according to claim 1, characterized in that: The sodium salt is at least one of sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

6. The composite electrolyte according to claim 1, characterized in that: The concentration of the sodium salt in the electrolyte A and the concentration of the sodium salt in the electrolyte B are 0.7-1.4 mol / L.

7. A sodium ion battery, characterized in that: The sodium ion battery comprises the composite electrolyte according to any one of claims 1 to 6.

8. The sodium ion battery according to claim 7, characterized in that: Before injecting the electrolyte A, the oxidation voltage of the electrolyte A is tested. During the first charging formation, the sodium ion battery is charged to a voltage 0.1-0.3V higher than the oxidation voltage and then constant voltage charging is performed.