Electrolyte for sodium secondary battery and sodium secondary battery

Abstract

The invention belongs to the technical field of sodium secondary batteries, and discloses an electrolyte for a sodium secondary battery and the sodium secondary battery, the electrolyte for the sodium secondary battery comprises the following components: a sodium salt and a solvent; the sodium salt comprises halide sodium salt; the general molecular formula of the halide sodium salt is NaX; wherein X is F <->, Cl <->, Br <-> or I <->; when X is F <->, Cl <-> or Br <->, an anion acceptor is further included; wherein the anion acceptor is one of BF3, tris (pentafluorophenyl) borane and 4-aminophenylboronic acid pieatinol ester; according to the invention, the halide sodium salt is introduced as the sodium salt of the electrolyte, so that the ionic conductivity of the electrolyte can be remarkably improved, the polarization linearity in the battery charging and discharging process is avoided, and the energy density of the sodium secondary battery is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sodium secondary batteries, and particularly relates to an electrolyte for a sodium secondary battery and a sodium secondary battery. BACKGROUND

[0002] A sodium secondary battery is a kind of secondary battery with metal sodium or sodium-containing compounds as active materials, and its working principle relies on the reversible intercalation and deintercalation process of sodium ions between the positive and negative electrode materials. Compared with lithium, sodium has abundant resources and low acquisition cost, making the sodium secondary battery show great potential application prospect in many fields such as energy storage and electric vehicles. As an important part of the sodium secondary battery, the electrolyte not only provides a channel for the migration of sodium ions as the medium for the transmission of sodium ions between the positive and negative electrodes, but also participates in the formation and stability of the electrode / electrolyte interface, which has a decisive influence on the charge-discharge performance, cycle life, safety and other properties of the battery.

[0003] However, the current electrolyte technology for sodium secondary batteries still faces many challenges. Among them, the selection and performance of sodium salt in the electrolyte is one of the key factors restricting the development of sodium secondary batteries. Currently, sodium hexafluorophosphate is the main sodium salt commonly used in the electrolyte of sodium secondary batteries. In theory, sodium hexafluorophosphate has certain advantages, such as its certain solubility in organic solvents, which can meet the basic requirements of the electrolyte to a certain extent.

[0004] However, in practical applications, due to the single positive charge of sodium ions and the relatively large ionic radius, the Coulomb interaction between sodium ions and hexafluorophosphate ions is strong, making it difficult for sodium hexafluorophosphate to fully dissociate into free sodium ions and hexafluorophosphate ions in the electrolyte. This limits the number of freely movable ions in the electrolyte, which in turn leads to a significant decrease in the ionic conductivity of the electrolyte. Low ionic conductivity increases the internal resistance of the battery, making the migration resistance of sodium ions between the positive and negative electrode materials increase, and the polarization phenomenon during the charge and discharge process intensify. At the same time, low ionic conductivity has an adverse effect on the energy density of the battery, limiting the actual energy output of the battery, resulting in the energy density of the sodium secondary battery generally lower than that of the lithium ion battery, which seriously restricts the popularization and application of the sodium secondary battery. SUMMARY

[0005] In view of the technical problems existing in the prior art, the present application provides an electrolyte for a sodium secondary battery and a sodium secondary battery to solve the technical problem that sodium hexafluorophosphate in the electrolyte for the sodium secondary battery cannot be fully dissociated, resulting in a significant decrease in the ionic conductivity of the electrolyte.

[0006] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0007] The application provides an electrolyte for a sodium secondary battery, which comprises the following components: a sodium salt and a solvent; the sodium salt comprises a halide sodium salt;

[0008] The molecular general formula of the halide sodium salt is NaX; wherein X=F - , Cl - , Br - or I - ;

[0009] When X=F - , Cl - or Br - , an anion receptor is further included.

[0010] The anion receptor is one of BF3, tris (pentafluorophenyl) borane and 4-aminobenzene boronic acid pinacol ester.

[0011] Further, the concentration of the halide sodium salt is 0.1-1.5M.

[0012] Further, the addition amount of the anion receptor is 0.1%-10% of the total mass of the electrolyte.

[0013] Further, the sodium salt further comprises a conventional sodium salt; the conventional sodium salt is one of NaPF6, NaClO4, NaCF3SO3, Na (CF3SO2) 2N, Na (FSO2) 2N, NaBF4, NaC2BF2O4, NaPF2O2 and NaC4BO8.

[0014] Further, the total concentration of the sodium salt is 0.1-3.0M.

[0015] Further, the solvent is an ether solvent, a carbonate solvent or a chain carbonate solvent.

[0016] Further, the ether solvent is one of ethylene glycol dimethyl ether, 1, 3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0017] Further, the carbonate solvent is one of vinyl carbonate, propylene carbonate and fluorinated vinyl carbonate.

[0018] Further, the chain carbonate is one of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

[0019] The application further provides a sodium secondary battery, which comprises a positive electrode sheet, a negative electrode sheet, a diaphragm arranged between the positive electrode sheet and the negative electrode sheet and the electrolyte for the sodium secondary battery.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] The electrolyte for sodium secondary batteries provided by the application can significantly improve the ionic conductivity of the electrolyte by introducing halide sodium salt as the sodium salt used in the electrolyte, avoids the polarization linear in the charging and discharging process of the battery, and effectively improves the energy density of the sodium secondary battery; specifically, when the anion of the halide sodium salt is fluoride ion, chloride ion or bromide ion, by introducing anion acceptor as an additive, the combination of the anion acceptor and the fluoride ion, chloride ion or bromide ion greatly promotes the dissociation degree of the halide sodium salt in the electrolyte; when the anion of the halide sodium salt is iodine ion, the volume of the iodine ion is large enough to greatly reduce the negative charge density on the unit anion surface, so that the interaction between sodium ion and iodine ion is sufficiently weakened, and therefore sodium iodide can be fully dissociated when used as a sodium salt; due to the full dissociation of the halide sodium salt, the number of freely movable ions in the electrolyte is significantly improved, thereby effectively improving the ionic conductivity of the electrolyte, avoiding the polarization phenomenon in the charging and discharging process of the battery, and improving the energy density of the battery, thereby ensuring the actual energy output of the battery; in addition, the halide sodium salt can be used as a basic component of the electrode-electrolyte film, which is in a thermodynamic stable state with respect to sodium metal, has good compatibility with sodium metal, negative electrode-free and tin and other conversion type negative electrodes, and also has good compatibility with hard carbon and other insertion type negative electrodes; secondly, when NaCl or NaI is used as the sodium salt of the electrolyte, the positive electrode of the battery can match Cl2 and I2 as the positive electrode in addition to the commonly used positive electrode materials, thereby greatly improving the energy density of the sodium battery.

[0022] The sodium secondary battery provided by the application has all the advantages of the above-mentioned electrolyte for sodium secondary batteries. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely; obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0024] The present application provides an electrolyte for sodium secondary batteries, comprising the following components: sodium salt and solvent.

[0025] The total concentration of the sodium salt is 0.1-3.0M; the sodium salt includes halide sodium salt, and the concentration of the halide sodium salt is 0.1-1.5M; wherein the general formula of the halide sodium salt is: NaX; wherein X=F - , Cl - , Br - or I- .

[0026] when X=F - , Cl - or Br - , also includes an anion receptor; wherein the anion receptor is added in an amount of 0.1%-10% of the total mass of the electrolyte; the anion receptor is one of BF3, tris(pentafluorophenyl)borane (TPFPB) and 4-aminophenylboronic acid pinacol ester (ABAPE).

[0027] Optionally, the sodium salt also includes a conventional sodium salt; preferably, the conventional sodium salt is one of NaPF6, NaClO4, NaCF3SO3, Na(CF3SO2)2N, Na(FSO2)2N, NaBF4, NaC2BF2O4 (sodium difluoro oxalate borate, NaDFOB), NaPF2O2 and NaC4BO8 (sodium bisoxalate borate, NaBOB).

[0028] Optionally, the solvent is an ether solvent, a carbonate solvent or a chain carbonate solvent; preferably, the ether solvent is one of ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MTHF), diethylene glycol dimethyl ether (G2) and tetraethylene glycol dimethyl ether (G4); the carbonate solvent is one of ethylene carbonate (EC), propylene carbonate (PC) and fluoroethylene carbonate (FEC); the chain carbonate is one of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0029] Design principle of the electrolyte:

[0030] The sodium secondary battery electrolyte provided by the application uses a halide sodium salt as the sodium salt in the electrolyte, which has the advantages of simple molecular structure and low cost, can significantly reduce the cost of the sodium secondary battery and effectively improve the energy density thereof; specifically, when sodium fluoride (NaF), sodium chloride (NaCl) or sodium bromide (NaBr) is used as the sodium salt, an anion receptor is added as an additive; under the action of the anion receptor, halide anions such as fluoride ions (F - ), chloride ions (Cl - ) or bromide ions (Br - ) can be combined with the anion receptor, thereby greatly promoting the complete dissociation of NaF, NaCl or NaBr in the solvent; when sodium iodide (NaI) is used as the sodium salt, the volume of iodide ions (I - ) is large enough, so that the negative charge density on the unit anion surface is greatly reduced, resulting in Na + and I -The force between them is sufficiently weakened, so that NaI can be fully dissociated by solvent without the effect of additives; due to the full dissociation of the halide sodium salt in the solvent, the number of free moving ions in the electrolyte is significantly improved, effectively improving the ionic conductivity of the electrolyte, thereby avoiding the polarization phenomenon in the charging and discharging process, improving the energy density of the battery, reducing the actual energy output influence of the battery, and promoting the popularization and application of sodium secondary batteries.

[0031] Secondly, the halide sodium salt itself can be used as a basic component of the electrode-electrolyte film (Solid-Electrolyte Interphase, SEI), which is almost in a thermodynamic stable state with sodium metal, that is, it is very stable to sodium metal, and has good compatibility with sodium metal, negative electrode and tin conversion type negative electrode, and also has good compatibility with hard carbon and other embedded type negative electrodes.

[0032] In addition, when NaCl or NaI is used as the sodium salt of the electrolyte, the positive electrode of the battery can match Cl2 and I2 as the positive electrode in addition to the commonly used positive electrode material, and a high specific energy and long life Na||I2 or Na||Cl2 secondary battery can be formed, thereby greatly improving the energy density of the sodium battery.

[0033] The application also provides a sodium secondary battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the positive electrode sheet comprises a positive electrode current collector and a positive electrode body containing a positive electrode active material adhered to the positive electrode current collector; wherein the positive electrode active material is one or two or more of sodium layered transition metal oxide, polyanion, prussian blue and iron sulfide; the negative electrode sheet is a negative electrode current collector, or the negative electrode sheet comprises a negative electrode current collector and sodium metal loaded on the negative electrode current collector; the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the separator is a polypropylene, polyethylene, PP / PE composite film or ceramic coated separator; and the electrolyte uses the electrolyte for sodium secondary batteries according to the application.

[0034] The electrolyte for sodium secondary batteries and the sodium secondary battery according to the application introduce halide sodium salt as the sodium salt of the electrolyte of the sodium secondary battery, significantly improve the ionic conductivity of the electrolyte, avoid the polarization phenomenon of the battery during charging and discharging, and effectively improve the energy density and actual energy output of the battery; when the anion is F - , Cl - or Br - , the introduction of anion acceptor promotes dissociation, and iodine ions can be fully dissociated due to their large volume, thereby increasing the number of free moving ions; and the halide sodium salt has good compatibility with various negative electrodes, and when NaCl or NaI is used as the sodium salt, the positive electrode has more matching options, which can greatly improve the energy density of the sodium battery.

[0035] Example 1-32

[0036] In the example 1, the electrolyte for sodium secondary battery is provided, which comprises sodium salt, solvent and anion acceptor; the concentration of the sodium salt is 0.5M, the sodium salt is NaF; the solvent is diethylene glycol dimethyl ether (G2); and the anion acceptor is BF3.

[0037] The preparation process of the electrolyte for sodium secondary battery comprises:

[0038] In the glove box under argon protection, the weighed BF3 is dissolved in diethylene glycol dimethyl ether to form a BF3-G2 mixture; the weighed diethylene glycol dimethyl ether is mixed with NaF, and then the BF3-G2 mixture is added; and the mixture is shaken and dissolved to obtain the electrolyte for sodium secondary battery; wherein, in the glove box under argon protection, the oxygen concentration is less than 1ppm, and the water content is less than 1ppm; since BF3 is a gas, the BF3 is mixed with diethylene glycol dimethyl ether to form a mixture for use in the preparation of the electrolyte

[0039] The example 1 further provides a sodium secondary battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the positive electrode sheet comprises a positive electrode current collector and a positive electrode body comprising a positive electrode active material adhered to the positive electrode current collector; wherein the positive electrode active material is one or two or more of sodium layered transition metal oxide, polyanion, Prussian blue and iron sulfide; the negative electrode sheet is a negative electrode current collector, or the negative electrode sheet comprises a negative electrode current collector and sodium metal loaded on the negative electrode current collector; the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the separator is polypropylene, polyethylene, PP / PE composite film or ceramic coated separator; and the electrolyte is the electrolyte for sodium secondary battery provided in the example 1.

[0040] In order to study the performance of the electrolyte for sodium secondary battery, different sodium secondary batteries are prepared by adding the electrolyte in the example 1- and the comparative examples 1-3, and the cycle performance and results of all the sodium secondary batteries are evaluated.

[0041] The component characteristics and battery performance test results of the electrolyte for sodium secondary battery in the example 1-32 and the comparative examples 1-3 are specifically described as shown in the following table 1.

[0042] Table 1 Component characteristics and battery performance test results of the electrolyte for sodium secondary battery

[0043]

[0044]

[0045]

[0046] As can be seen from Table 1, compared with the sodium salt of the conventional sodium salt (NaPF6) used as the electrolyte in Comparative Example 1, the halide sodium salt NaF or NaCl is added as the sodium salt of the electrolyte in Examples 1-23; wherein the sodium secondary battery constructed based on the electrolyte for the sodium secondary battery described in Examples 1-23 can normally discharge, the discharge capacity is maintained at 68.5-89.5 mAh / g, and the capacity retention rate after 100 cycles is maintained at 78.2%-100%; wherein the capacity retention rate of the sodium secondary battery constructed based on the electrolyte for the sodium secondary battery described in Examples 1-23 is equivalent to, or even higher than, the capacity retention rate of the sodium secondary battery constructed based on the electrolyte containing the conventional sodium salt; thus, it can be seen that the feasibility of using the halide sodium salt as the sodium salt of the electrolyte is proved, and there is a significant cost advantage.

[0047] In addition, as can be seen from the above Table 1, in Comparative Example 2, NaF is used as the sodium salt of the electrolyte, and no anion acceptor is added; at this time, NaF cannot be dissolved in the electrolyte solvent; therefore, the sodium secondary battery constructed based on the electrolyte provided in Comparative Example 2 cannot work; compared with Comparative Example 2, in Examples 1-22, in addition to using the halide sodium salt NaF or NaCl as the sodium salt of the electrolyte, an anion acceptor is also introduced; the halide sodium salt NaF or NaCl can obviously have normal solubility under the action of the anion acceptor; therefore, the sodium secondary battery constructed based on the electrolyte for the sodium secondary battery described in Examples 1-22 can normally work; secondly, as can be seen from Example 23, in the sodium secondary battery constructed based on the electrolyte for the sodium secondary battery described in Example 22, Al is used as the current collector of the negative electrode, i.e. without pre-storing Na or without the negative electrode battery configuration, the capacity retention rate of the sodium secondary battery after 100 cycles is 95.3%, which still has a very high capacity retention rate, indicating that the halide sodium salt NaF can promote the efficient deposition and stripping of sodium metal on the negative electrode;

[0048] Secondly, as can be seen from the above Table 1, the sodium secondary battery constructed based on the electrolyte for the sodium secondary battery described in Examples 24-31 uses the Na / I2 battery configuration, i.e. uses NaI as the sodium salt of the electrolyte; at this time, the battery can normally discharge, and the capacity and the capacity retention rate of the battery are equivalent to, or even slightly higher than, the capacity retention rate of the sodium secondary battery constructed based on the electrolyte of Comparative Example 3; thus, it can be fully illustrated that the sodium secondary battery constructed based on the electrolyte for the sodium secondary battery described in Examples 24-31 and the feasibility of using NaI as the sodium salt of the electrolyte of the Na / I2 battery, and there is a significant cost advantage.

[0049] It is worth noting that by comparing Example 32 and Comparative Example 4 in Table 1 above, it can be found that the Na / Cl2 battery using conventional NaPF6 as the sodium salt in Comparative Example 4 has a discharge capacity of 250.0 mAh / g, while the Na / Cl2 battery using NaCl as the sodium salt in Example 32 has a capacity of 320.1 mAh / g and has a higher capacity retention rate; thus, it fully illustrates the feasibility of using NaCl as the sodium salt of the Na / Cl2 battery, which has a cost advantage and can obtain a more optimal choice of capacity improvement.

[0050] The sodium secondary battery electrolyte described in the present application significantly improves the ionic conductivity of the electrolyte by introducing a halide sodium salt as the sodium salt of the sodium secondary battery electrolyte, avoids the battery charge and discharge polarization phenomenon, and effectively improves the battery energy density and actual energy output; wherein by improving the ionic conductivity, the ions can move faster between the positive and negative electrodes during the charging and discharging process, reducing the internal resistance of the battery, and effectively avoiding the polarization phenomenon during the charging and discharging of the battery; and the reduction of the polarization phenomenon will further enable the battery to more fully undergo chemical reactions, thereby effectively improving the energy density and actual energy output of the battery, ensuring that the sodium secondary battery can provide more durable and stable power support in actual application.

[0051] When the anion in the halide sodium salt is F - , Cl- or Br - , because F-, Cl- or Br - has relatively strong interaction with the cation, there may be some degree of association phenomenon in the electrolyte, limiting the free movement of ions; at this time, by introducing anion receptors, specific interactions with F-, Cl- or Br - can occur, weakening the binding force between F-, Cl- or Br - and the cation, thereby promoting the dissociation of the halide sodium salt; in addition, I - has a relatively large volume and its interaction with the cation is relatively weak, and it can be fully dissociated in the electrolyte, thereby greatly increasing the number of free-moving ions in the electrolyte, thereby improving the ionic conductivity of the electrolyte and providing a strong guarantee for the high-performance operation of the battery.

[0052] In the present application, by introducing a halide sodium salt as the sodium salt of the sodium secondary battery electrolyte, the ionic conductivity can be improved, the ion dissociation can be promoted, the negative electrode compatibility can be enhanced, and the positive electrode matching selection can be widened, and the multiple aspects of synergistic effect, so that the energy density, the actual energy output and the application flexibility of the sodium secondary battery are significantly improved, laying a solid foundation for the wide application of the sodium secondary battery in the field of energy storage.

[0053] The above embodiment is only one of the implementation manners of the technical scheme of the present application, and the scope of the present application is not limited to the above embodiment, but also includes any changes, substitutions and other implementation manners that are easily thought of by those skilled in the art within the technical scope disclosed by the present application.

Claims

1. An electrolyte for a sodium secondary battery, characterized in that The method comprises the following components: a sodium salt and a solvent; the sodium salt comprises a halide sodium salt; The molecular formula of the sodium halide salt is: NaX; wherein X=F - 、Cl - Br - or I - ; When X=F - 、Cl - or Br - When, anion receptors are also included; Wherein, the anion receptor is one of BF3, tris(pentafluorophenyl)borane and 4-aminophenylboronic acid borane.

2. The electrolyte for sodium secondary battery according to claim 1, characterized in that: The concentration of the halide sodium salt is 0.1-1.5M.

3. The electrolyte for sodium secondary battery according to claim 1, characterized in that: The added amount of the anion receptor is 0.1%-10% of the total mass of the electrolyte.

4. The electrolyte for sodium secondary battery according to claim 1, characterized in that: The sodium salt also includes conventional sodium salt; the conventional sodium salt is one of NaPF6, NaClO4, NaCF3SO3, Na(CF3SO2)2N, Na(FSO2)2N, NaBF4, NaC2BF2O4, NaPF2O2 and NaC4BO8.

5. The electrolyte for sodium secondary battery according to claim 4, characterized in that: The total concentration of the sodium salt is 0.1-3.0M.

6. The electrolyte for sodium secondary battery according to claim 1, characterized in that: The solvent is an ether solvent, a carbonate solvent or a chain carbonate solvent.

7. The electrolyte for sodium secondary battery according to claim 6, characterized in that: The ether solvent is one of ethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

8. The electrolyte for sodium secondary battery according to claim 6, characterized in that: The carbonate solvent is one of ethylene carbonate, propylene carbonate and fluoroethylene carbonate.

9. The electrolyte for sodium secondary battery according to claim 6, characterized in that: The chain carbonate is one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

10. A sodium secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator arranged between the positive electrode sheet and the negative electrode sheet, and an electrolyte for a sodium secondary battery according to any one of claims 1 to 9.

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