Sodium-ion battery and preparation method and application thereof

Abstract

Embodiments of the present application provide a kind of sodium ion battery and its preparation method and application.In the sodium ion battery, the surface of positive electrode and / or negative electrode has electrolyte interface film;The electrolyte interface film includes organic matter, sodium salt and M salt, wherein M is non-sodium metal element, and in the mixed solvent of equal volume ratio of ethylene carbonate and diethyl carbonate, the solubility of M salt is lower than that of sodium salt.By introducing non-sodium metal salt with low solubility in electrolyte into the electrolyte interface film on the surface of sodium battery electrode, the stability of the electrolyte interface film can be improved, thereby improving the stability of sodium battery under long cycle / high temperature working condition.

Description

Technical Field

[0001] This application relates to the field of sodium battery technology, specifically to a sodium-ion battery, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries are a type of battery with a similar energy storage mechanism to lithium-ion batteries. Due to the abundance and low cost of sodium resources on Earth, sodium-ion batteries have lower manufacturing costs and are more likely to meet the low-cost demand for large-scale energy storage devices. During the formation / cycling process, an electrolyte interface film forms on the electrode surface of a sodium-ion battery, which can block side reactions between the electrode material and the electrolyte, thus improving the battery's cycle stability.

[0003] However, due to differences in the composition and solubility of the electrolyte interface film between sodium-ion batteries and lithium-ion batteries, the stability of the electrolyte interface film of sodium-ion batteries is worse than that of lithium-ion batteries. Consequently, the long-cycle stability and high-temperature storage / float charging stability of sodium-ion batteries are significantly weaker than those of lithium-ion batteries. Summary of the Invention

[0004] Therefore, this application provides a sodium-ion battery with a highly stable electrolyte interface membrane, its preparation method, and its application, so that the sodium-ion battery has excellent stability under long-cycle or high-temperature conditions.

[0005] Specifically, the first aspect of this application provides a sodium-ion battery, which includes a positive electrode and a negative electrode, and the surfaces of the positive electrode and / or the negative electrode have an electrolyte interface film; wherein the electrolyte interface film includes an organic substance, a sodium salt and an M salt, wherein M is a non-sodium metal element, and the solubility of the M salt is lower than that of the sodium salt in a mixed solvent composed of ethylene carbonate and diethyl carbonate in equal volume ratios.

[0006] In addition to sodium salts and organic matter, the electrolyte interface film on the negative and / or positive electrode surfaces of the aforementioned sodium-ion batteries also includes non-sodium metal element salts—M salts. The solubility of M salts in typical electrolyte solvents is lower than that of sodium salts. Introducing such M salts can help reduce the solubility of the electrolyte interface film on the negative and / or positive electrode surfaces in the electrolyte, improve the stability of the electrolyte interface film of sodium-ion batteries, and thus improve the long-cycle stability, high-temperature storage / float charging stability, etc. of sodium-ion batteries.

[0007] In some embodiments of this application, the element M includes one or more of lithium, potassium, magnesium, and aluminum. When M is one of these elements, it is easier to achieve a lower solubility in the electrolyte in the M salt formed by the element M and anion commonly found in the electrolyte interface membrane compared to the sodium salt formed by sodium and that anion.

[0008] In some embodiments of this application, the anions in the M salt include one or more of fluoride ions, carbonate ions, nitrogen anions, fluorophosphate ions, and organic anions. These anions originate from the anionic products of electrochemical reactions of sodium salts, additives, etc., in the sodium battery electrolyte. The M salt composed of these anions has low solubility in the electrolyte.

[0009] In some embodiments of this application, the mass percentage of element M relative to the mass percentage of element M and sodium in the electrolyte interface membrane is greater than 0 and less than or equal to 0.12%. In this case, while ensuring that the above-mentioned M salt helps improve the solubility of the electrolyte interface membrane of the sodium battery electrode in the electrolyte, the transport of sodium ions will not be hindered due to excessive M element content, nor will the M salt dissolve in the electrolyte.

[0010] In some embodiments of this application, the mass percentage of the M salt in the electrolyte interface membrane is 0.002%-0.024%. This ensures that there is sufficient M salt to help improve the stability of the electrolyte interface membrane of the sodium battery in the electrolyte, while preventing excessive M salt content from interfering with sodium ion transport on the positive / negative electrode surfaces.

[0011] In some embodiments of this application, the electrolyte interface film on the negative electrode surface accounts for a mass ratio of greater than 0 and less than or equal to 5% relative to the electrolyte interface film and the negative active material in the negative electrode, and / or, the electrolyte interface film on the positive electrode surface accounts for a mass ratio of greater than 0 and less than or equal to 2% relative to the electrolyte interface film and the positive active material in the positive electrode. This avoids the electrolyte interface film on the positive / negative electrode surfaces from being too thick, which could interfere with the transport of sodium ions on the negative electrode surface and affect the rate performance of the sodium battery.

[0012] In this embodiment of the application, along the direction away from the positive or negative electrode, the electrolyte interface membrane includes a first membrane layer, a second membrane layer, and a third membrane layer stacked sequentially, wherein the first membrane layer includes the sodium salt, the second membrane layer includes the M salt, and the third membrane layer includes the organic matter.

[0013] The third membrane layer containing organic matter is located on the outermost layer of the electrolyte interface membrane, which facilitates the wetting of the electrolyte interface membrane by the electrolyte. The M salt is located between the sodium salt-containing membrane layer and the organic matter layer, and the M salt is located outside the first membrane layer containing sodium salt. This can reduce the dissolution of sodium salt, improve the stability of the electrolyte interface membrane, and reduce the side reactions between the battery active materials and the electrolyte.

[0014] In some embodiments of this application, a transition layer containing the sodium salt and the M salt is further included between the second film layer and the first film layer. The presence of the transition layer can help improve the bonding force between the first film layer and the second film layer.

[0015] In some embodiments of this application, along the direction from the first film layer to the second film layer, the content of the sodium salt in the transition layer gradually decreases, while the content of the M salt gradually increases. In this case, the bonding force between the transition layer and the first film layer or the second film layer is relatively high.

[0016] In some embodiments of this application, along the thickness direction perpendicular to the electrolyte interface membrane, the content of element M in the edge region of the second membrane layer is greater than the content of element M in other regions of the second membrane layer. The edge region of the second membrane layer is closer to the electrolyte in the sodium battery, and the content of element M in this edge region is higher than in other regions.

[0017] In some embodiments of this application, the thickness of the third film layer is in the range of 5nm-20nm. An appropriate thickness of the outer layer containing organic matter in the electrolyte interface film effectively hinders contact between the electrolyte and the inner sodium salt, reducing the probability of highly soluble sodium salt dissolving in the electrolyte. It also avoids hindering the transport of sodium ions in the electrolyte interface film and affecting the battery rate performance due to excessive thickness of the organic layer.

[0018] In some embodiments of this application, the thickness of the third membrane layer is greater than the sum of the thicknesses of the first and second membrane layers. The third membrane layer containing organic matter in the electrolyte interface membrane has a relatively loose structure, and its thickness is greater than the thickness of the total distribution area of ​​the sodium salt and M salt. This facilitates electrolyte wetting of the third membrane layer and allows sodium ions to shuttle and desolvate within it.

[0019] In some embodiments of this application, the sum of the thicknesses of the first film layer and the second film layer is in the range of greater than 0 to less than or equal to 15 nm. This avoids the situation where the sum of the thicknesses of these two relatively dense layers is too large, which could affect the transport of sodium ions and degrade the rate performance of the battery.

[0020] The second aspect of this application provides a method for preparing a sodium-ion battery, comprising the following steps:

[0021] A positive electrode, a negative electrode, and a separator are provided for sodium-ion batteries; wherein the positive electrode active material layer of the positive electrode and / or the negative electrode active material layer of the negative electrode contain a non-sodium metal element M salt or its precursor, and / or the M salt or its precursor is coated on the surface of the positive electrode and / or the negative electrode, and / or the separator is impregnated with a precursor solution of the M salt.

[0022] The positive electrode, the separator, and the negative electrode are assembled into a battery cell. The battery cell is then installed in a battery casing, an electrolyte is injected, and the casing is sealed. After formation, a sodium-ion battery as described in the first aspect of the present application is obtained.

[0023] By introducing element M into the electrode active material layer of a sodium battery through at least one method, such as mixing it into the electrode surface, coating it, or impregnating it with a separator, an electrolyte interface film containing element M salt can be formed on the positive and / or negative electrode surfaces of the formed sodium battery. This film exhibits high stability, thereby improving the cycle stability and high-temperature storage and high-temperature float charging stability of the sodium battery. The above-mentioned method for preparing sodium-ion batteries is simple and easy to operate.

[0024] In this embodiment of the application, the solubility of the precursor of the M salt in the electrolyte is greater than the solubility of the M salt in the electrolyte; wherein, the precursor of the M salt is the MY salt, and the anion Y in the MY salt is a common anion in the electrolyte.

[0025] In some embodiments of this application, the M element contained in the positive electrode active material layer is 0.01%-2% of the mass of the positive electrode active material, and / or, the M element contained in the negative electrode active material layer is 0.01%-3% of the mass of the negative electrode active material; and / or, the coating amount of the M element on the surface of the positive electrode and / or negative electrode is 0.01-0.2 mg / cm³. 2 ; and / or, the precursor solution of the M salt is a carbonate solution with a concentration of 0.01-1M for the M salt.

[0026] When introducing raw materials containing element M into sodium batteries in different ways, controlling the amount of each raw material within an appropriate range can ensure that the electrolyte interface film formed on the surface of the positive and / or negative electrodes contains an appropriate amount of M salt, thereby effectively improving the stability of the electrolyte interface film without affecting the transport of sodium ions within it.

[0027] A third aspect of this application provides an electrical device, which includes an electrical component and a power supply component. The power supply component supplies power to the electrical component and includes the sodium-ion battery described in the embodiments of this application, or a sodium-ion battery prepared using the preparation method described in the embodiments of this application. This electrical device can be an electronic device or a mobile device, etc.

[0028] Since the sodium-ion battery of this application embodiment has good performance under long cycle or high temperature conditions, by using the sodium-ion battery provided in this application embodiment to power the electrical components of the electrical device, the user experience and market competitiveness of the electrical device can be improved.

[0029] A fourth aspect of this application provides an energy storage device, which includes the sodium-ion battery described in the embodiments of this application, or a sodium-ion battery prepared using the preparation method described in the embodiments of this application. The sodium-ion battery of this application stores electrical energy in the energy storage device, thereby improving the performance of the energy storage device and enhancing its product competitiveness. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a sodium-ion battery provided in an embodiment of this application.

[0031] Figure 2 This is a schematic diagram of a sodium battery negative electrode with an electrolyte interface film on its surface, provided in an embodiment of this application.

[0032] Figure 3 This is another schematic diagram of the structure of a sodium battery negative electrode with an electrolyte interface film on its surface, provided in an embodiment of this application.

[0033] Figure 4 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0034] Figure 5 This is a schematic diagram of a mobile device provided in an embodiment of this application.

[0035] Figure 6 This is a schematic diagram of the structure of an energy storage device provided in an embodiment of this application.

[0036] Figure 7 A transmission electron microscope image of the negative electrode active material layer with an SEI film on the negative electrode surface of the sodium battery of Example 1 is shown.

[0037] Figure 8 The 25°C room temperature cycling performance curves of sodium batteries from Example 1 and Comparative Example 1 are summarized.

[0038] Figure 9 The high-temperature cycling performance curves of sodium batteries from Example 1 and Comparative Example 1 at 55°C are summarized.

[0039] Figure 10 The high-temperature storage capacity retention curves of sodium batteries in Example 1 and Comparative Example 1 at 45°C are summarized.

[0040] Figure 11 The capacity retention curves of sodium batteries in Example 1 and Comparative Example 1 at 45°C during float charging are summarized. Detailed Implementation

[0041] The embodiments of this application will now be described in conjunction with the accompanying drawings.

[0042] During the formation process of a sodium-ion battery (i.e., the initial charge before leaving the factory), sodium ions in the system react with components in the electrolyte to form an electrolyte interface film on the electrode surface. The film formed on the negative electrode is typically called a solid electrolyte interface (SEI) film, and the film formed on the positive electrode is typically called a cathode electrolyte interphase (CEI) film. The main components of the SEI or CEI film include sodium salts and organic matter. The organic matter is generally located on the side of the electrolyte interface film closer to the electrolyte, while the sodium salt is generally located on the side of the electrolyte interface film closer to the electrode active material layer. Although sodium-ion batteries and lithium-ion batteries share similar energy storage mechanisms, the solubility of their electrolyte interface membrane components in the electrolyte differs significantly. For example, the electrolyte interface membrane of sodium-ion batteries has a higher solubility in the electrolyte than that of lithium-ion batteries. This results in the SEI or CEI membrane of sodium-ion batteries having significantly lower stability than that of lithium-ion batteries. Consequently, the failure risk of the SEI or CEI membrane of sodium-ion batteries increases under long-cycle or high-temperature conditions, leading to significantly weaker long-cycle stability and high-temperature storage / float charge stability compared to lithium-ion batteries. Therefore, it is necessary to construct a highly stable electrolyte interface membrane on the electrode surface of sodium-ion batteries.

[0043] Figure 1 This is a schematic diagram of a sodium-ion battery provided in an embodiment of this application. Figure 1 The sodium-ion battery 100 shown is a sodium battery after formation. For example... Figure 1 As shown, the sodium-ion battery 100 includes a negative electrode 10 and a positive electrode 20, and the surfaces of the negative electrode 10 and / or the positive electrode 20 have an electrolyte interface film 30. The electrolyte interface film 30 includes an organic compound, a sodium salt, and an M salt, wherein M is a non-sodium metal element, and the solubility of the M salt is lower than that of the sodium salt in a mixed solvent composed of ethylene carbonate (EC) and diethyl carbonate (DEC) in equal volume ratios.

[0044] In addition to sodium salts and organic matter, the electrolyte interface film 30 on the surface of the negative electrode 10 and / or positive electrode 20 of the aforementioned sodium-ion battery also includes a non-sodium metal element salt (i.e., M salt). The solubility of this M salt in a typical electrolyte solvent (a mixed solvent composed of cyclic carbonate-ethylene carbonate and linear carbonate-diethyl carbonate in equal volume ratios) is lower than that of sodium salts. Introducing such an M salt helps reduce the solubility of the electrolyte interface film 30 on the surface of the negative electrode and / or positive electrode in the electrolyte, thereby improving the stability of the electrolyte interface film 30 of the sodium-ion battery. This, in turn, is beneficial to improving the long-cycle stability and high-temperature storage / float charge stability of the sodium-ion battery 100. The M salt in the electrolyte interface film 30 can be directly introduced during the preparation of the sodium battery or generated in situ during the formation / cycling process of the sodium battery.

[0045] In some possible embodiments of this application, the aforementioned element M may include one or more of lithium, potassium, magnesium, and aluminum, but is not limited thereto.

[0046] It should be noted that, in this application, the organic matter in the electrolyte interface membrane 30 refers to carbonaceous substances that cannot ionize into metal cations and acid anions. This organic matter typically originates from the decomposition of electrolyte components. For example, this organic matter may include polyethylene oxide (PEO). PEO can be formed through the electrochemical decomposition of ethylene carbonate, a solvent in the electrolyte.

[0047] The anions of sodium salt and M salt in the electrolyte interface membrane 30 mentioned above are common anions in the electrolyte interface membranes of sodium-ion batteries. The anions of sodium salt in this electrolyte interface membrane are generally different from those of sodium salt in the electrolyte of a sodium-ion battery. The anions of sodium salt and M salt in the electrolyte interface membrane usually originate from the anionic products of electrochemical reactions of sodium salt, additives, etc., in the electrolyte. These anions have low solubility in the electrolyte. If the anion of M salt is denoted as X, then this M salt can be called MX salt.

[0048] In some embodiments of this application, the anions in the M salt within the electrolyte interface membrane 30 include fluoride ions (F... - ), carbonate ions (CO3) 2- ), nitrogen anions (N 3- The anion may be one or more of fluorophosphate ions and organic anions, but is not limited thereto. Similarly, the anion of the sodium M salt in the electrolyte interface membrane 30 may also be selected from the above-mentioned anions. Among them, fluorophosphate ions can be represented as PF... y O z x- y and z are both integers greater than 0; the valence of element P is equal to y + 2z + x. The organic anion includes CH3O. - CH3CH2O - CH3CH2CO3 - CO3CH2CH2CO3 2- One or more of these, but not limited to them.

[0049] For example, PF6-, BF4-, and difluorophosphate anions (DFP) in the electrolyte - ) can be converted into fluoride ions (F) in the electrolyte interface membrane. - TFSI in the electrolyte - (bis(trifluoromethanesulfonyl)imide anion), FSI - (bisfluorosulfonyl imide anion), ODFB -(Difluorooxalate-boron anion) and other substances can be converted into CO3 in the electrolyte interface membrane. 2- and F - etc. BOB in the electrolyte - (Dioxabolate-boronate anion) can transform CO3 in the interfacial membrane. 2- .

[0050] In this embodiment, the mass ratio of element M relative to element M and sodium (i.e., M / (M+Na)) in the electrolyte interface membrane 30 is within the range of greater than 0 to less than or equal to 0.12%. By controlling the mass ratio of element M to total metal elements in the electrolyte interface membrane on the positive and / or negative electrode surfaces to be within an excessively high range, it is possible to ensure that the aforementioned M salt helps improve the solubility of the electrolyte interface membrane on the sodium battery electrode surface in the electrolyte, without hindering the transport of sodium ions due to excessively high concentrations of element M, or causing the M salt to begin dissolving in the electrolyte and reducing the stability of the sodium battery electrolyte interface membrane in the electrolyte.

[0051] In some embodiments, the mass percentage of element M relative to element M and sodium in the electrolyte interface membrane 30 is in the range of 0.01%-0.12%, specifically 0.02%, 0.05%, 0.08%, or 0.10%. In this case, it is more advantageous for the electrolyte interface membrane containing the M salt to achieve both good structural stability and low impedance.

[0052] It should be noted that the aforementioned mass ratio range of element M relative to element M and sodium applies not only to the electrolyte interphase (SEI) film on the negative electrode surface but also to the electrolyte interphase (CEI) film on the positive electrode surface. It can be understood that the amounts of element M and Na are relative to either the SEI film on the negative electrode surface or the CEI film on the positive electrode surface. The aforementioned mass ratio can be obtained through elemental analysis of the electrolyte interphase film on the electrode surface. Elemental analysis methods include, but are not limited to, inductively coupled plasma (ICP) atomic emission spectrometry, energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS).

[0053] In some embodiments of the present application, in the electrolyte interface film 30, the mass proportion of the M salt may be 0.002%-0.024%. Controlling the M salt in the electrolyte interface film 30 on the surface of the positive electrode and / or the negative electrode of the sodium battery to have an appropriate mass proportion not only ensures that sufficient M salt can help improve the stability of the electrolyte interface film 30 of the sodium battery in the electrolyte, but also does not interfere with the sodium ion transport on the surface of the positive electrode / negative electrode due to the excessively high content of the M salt.

[0054] As shown in Figure 1 , the negative electrode 10 includes a negative electrode current collector 11 and a negative electrode active material layer 12 disposed on the surface of the negative electrode current collector 11. The negative electrode active material layer 12 includes a negative electrode active material, a binder, and an optional conductive agent (not shown in the figure). The positive electrode 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22 disposed on the surface of the positive electrode current collector 21. The positive electrode active material layer 22 includes a positive electrode active material, a binder, and a conductive agent (not shown in the figure).

[0055] In some embodiments of the present application, the mass proportion of the electrolyte interface film on the surface of the negative electrode 10 relative to the total mass of the electrolyte interface film and the negative electrode active material in the negative electrode 10 is in the range of greater than 0 to less than or equal to 5%. If the mass of the electrolyte interface film on the surface of the negative electrode is denoted as m1, and the mass of the negative electrode active material contained in the negative electrode is denoted as m2, then 0<m1 / (m1+m2)≤5%. Controlling the mass proportion of the electrolyte interface film 30 on the surface of the negative electrode 10 relative to the total mass of itself and the negative electrode active material not to be in an excessively high range can prevent an excessively large / thick SEI film from interfering with sodium ion transport on the surface of the negative electrode and affecting the rate performance of the sodium battery. In some embodiments, this mass proportion is in the range of 0.01%-3%, for example, specifically 0.02%, 0.05%, 0.08%, 0.09%, 1%, 1.2%, 1.5%, 2%, 2.2%, 2.5%, etc.

[0056] In some embodiments of the present application, the mass proportion of the electrolyte interface film on the surface of the positive electrode 20 relative to the total mass of the electrolyte interface film and the positive electrode active material in the positive electrode 20 is in the range of greater than 0 to less than or equal to 2%. Exemplarily, this mass proportion may be 0.01%, 0.02%, 0.05%, 0.08%, 0.09%, 1%, 1.2%, 1.5%, 1.8%, etc. Similarly, controlling the mass proportion of the electrolyte interface film on the surface of the positive electrode 20 relative to the total mass of itself and the positive electrode active material not to be in an excessively high range can prevent an excessively large / thick SEI film from interfering with sodium ion transport on the surface of the positive electrode and affecting the rate performance of the sodium battery.

[0057] The structure of the electrolyte interface film 30 in the sodium battery of the present application will be introduced below by taking the electrolyte interface film 30 on the surface of the negative electrode of the sodium battery as an example. Please refer to Figure 2 , Figure 2This is a schematic diagram of a sodium battery negative electrode with an electrolyte interface film on its surface, provided in an embodiment of this application.

[0058] like Figure 2 As shown, along the direction of the electrolyte interface film 30 away from its negative electrode 10 (e.g.) Figure 2 (in the Z direction), the electrolyte interface membrane 30 includes a first membrane layer 31, a second membrane layer 32, and a third membrane layer 33 stacked sequentially. Specifically, the second membrane layer 32 is located on the side of the first membrane layer 31 facing away from the negative electrode 10, and the third membrane layer 33 is located on the side of the second membrane layer 32 facing away from the negative electrode 10. The first membrane layer 31 includes the aforementioned sodium salt, the second membrane layer 32 includes the aforementioned M salt, and the third membrane layer 33 includes the aforementioned organic matter.

[0059] The aforementioned organic matter is typically an electrochemical reaction product of solvents, additives, etc., in the electrolyte. Therefore, the third film layer 33 containing this organic matter is usually located on the outermost layer of the electrolyte interface film 30, away from its negative electrode 10. The third film layer 33 facilitates the wetting of the electrolyte interface film 30 of the negative electrode 10 by the electrolyte. The aforementioned sodium salt generally originates from the electrochemical reaction product of electrolyte components and sodium ions in the sodium battery system. This sodium salt is distributed in the inner layer of the electrolyte interface film 30 near its negative electrode 10. The film layer containing sodium salt has a higher density than the third film layer 33 containing organic matter, which facilitates the reduction of side reactions between the battery active materials and the electrolyte. The aforementioned M salt can be a product formed after the decomposition of raw materials containing element M introduced into the sodium battery and electrolyte components. When the sodium salt with high solubility in the inner layer of the electrolyte interface membrane 30 dissolves, the M salt can replace this part of the sodium salt to form a second membrane layer 32 containing the M salt. This can help increase the stability of the electrolyte interface membrane 30 of the sodium battery, reduce the dissolution of the first membrane layer 31 located inside the second membrane layer 32, and better block the side reactions between the battery active material and the electrolyte.

[0060] Generally, the second membrane layer 32 includes the aforementioned M salt, but does not include the aforementioned sodium salt. A second membrane layer 32 comprising only the aforementioned M salt can be obtained by completely replacing the sodium salt in the outer portion of the membrane layer containing the aforementioned sodium salt in the electrolyte interface membrane with the M salt. The presence of this second membrane layer 32 has a better effect on improving the stability of the electrolyte interface membrane 30 in the electrolyte.

[0061] For some embodiments of this application, please refer to [link / reference]. Figure 2 Along the second direction, the content of element M in the edge region of the second membrane layer 32 is greater than the content of element M in other regions (such as the middle region) of the second membrane layer 32. This second direction can be perpendicular to the thickness direction of the electrolyte interface membrane 30, for example, the length or width direction of the negative or positive electrode where the electrolyte interface membrane 30 is located. The edge region of the second membrane layer 32 can refer to the side region of the second membrane layer 32, close to the electrolyte. Other regions can refer to regions other than the edge region.

[0062] Since the edge region of the second membrane layer 32 is closer to the electrolyte and has more contact with the electrolyte, the content of element M in the second membrane layer 32 tends to be high at the edge and low in the middle. This can better prevent the dissolution of the electrolyte interface membrane edge that has more contact with the electrolyte.

[0063] In this embodiment, the thickness of the third film layer 33 is greater than the sum of the thicknesses of the first film layer 31 and the second film layer 32. The outermost layer containing organic matter in the electrolyte interface film 30 is generally a relatively loosely structured layer. Therefore, the thickness of the organic component layer containing the aforementioned organic matter in the electrolyte interface film 30 is generally greater than the thickness of the total distribution area of ​​the sodium salt and M salt. This facilitates the wetting of the third film layer 33 by the electrolyte and allows active sodium ions in the sodium battery to shuttle and desolvate within the third film layer 33.

[0064] In some possible embodiments of this application, the thickness of the third film layer 33 can be in the range of 5 nm to 20 nm. An appropriate thickness of the outer layer containing organic matter in the electrolyte interface film 30 effectively hinders the contact between the electrolyte and the inner sodium salt, reducing the probability of highly soluble sodium salt dissolving in the electrolyte. It also avoids hindering the transport of sodium ions in the electrolyte interface film 30 due to excessive thickness of the organic layer, thus preventing any impact on the battery rate performance. For example, the thickness of the third film layer 33 can specifically be 8 nm, 10 nm, 12 nm, 15 nm, or 18 nm, etc.

[0065] In some possible embodiments of this application, the sum of the thicknesses of the first film layer 31 and the second film layer 32 is greater than 0 and less than or equal to 15 nm. This avoids the possibility that the sum of the thicknesses of these two layers, which have high density, would be too large, thus affecting the transport of sodium ions and degrading the rate performance of the battery. In some embodiments, the sum of the thicknesses of the first film layer 31 and the second film layer 32 is in the range of 1 nm to 14 nm, specifically 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 12 nm, or 13 nm.

[0066] Among them, along the direction from the first film layer 31 to the second film layer 32 (that is...) Figure 2 In the Z-direction of the transition layer 34, the content of the sodium salt gradually decreases, while the content of the M salt gradually increases. In this case, the transition layer 34 is a composition gradient layer. Figure 3 In the diagram, the dashed arrows indicate M salts, and the solid arrows indicate sodium salts. Along the Z direction in the diagram, the sodium content in transition layer 34 gradually decreases, while the M content gradually increases.

[0067] Since the transition layer 34 can be formed by the distribution sites of sodium salt in the inner layer of the electrolyte interface membrane 30 from the outside to the inside by the above-mentioned M salt, the content of M salt and M element is greater and the content of sodium element / sodium salt is smaller closer to the transition layer 34 and farther away from the first membrane layer 31.

[0068] Figure 3 This is another schematic diagram of a sodium battery negative electrode with an electrolyte interface film on its surface, provided as an embodiment of this application. (See attached diagram.) Figure 3 As shown, in some embodiments of this application, a transition layer 34 containing both the aforementioned sodium salt and M salt is further included between the first film layer 31 and the second film layer 32.

[0069] In this case, along the direction away from the negative electrode 10, the electrolyte interface membrane 30 includes a first membrane layer 31, a transition layer 34, a second membrane layer 32, and a third membrane layer 33 stacked sequentially. That is, along this direction, the electrolyte interface membrane 30 gradually transitions from a sodium salt-rich membrane layer to an M salt layer, and the outermost layer is an organic layer rich in organic matter.

[0070] In some embodiments, the thickness of the second film layer 32 is less than the thickness of the transition layer 34.

[0071] When the electrolyte interface membrane 30 includes a transition layer 34, the thickness of the third membrane layer 33 can be greater than the sum of the thicknesses of the first membrane layer 31, the second membrane layer 32, and the transition layer 34. In some possible embodiments of this application, when the transition layer 34 is present, the sum of the thicknesses of the first membrane layer 31, the second membrane layer 32, and the transition layer 34 is also in the range of greater than 0 and less than 15 nm. The thickness of the third membrane layer 33 can be in the range of 5 nm to 20 nm. For a list of point values ​​for these parameters, please refer to the preceding section of this application. Figure 2 The description is as follows. Similarly, when the electrolyte interface membrane 30 includes a transition layer 34, along the aforementioned second direction (such as the direction perpendicular to the thickness of the electrolyte interface membrane 30), the content of element M in the edge region of the transition layer 34 is greater than the content of element M in other regions of the transition layer 34.

[0072] Figure 1 The sodium-ion battery 100 shown is a liquid battery. Both the negative electrode 10 and the positive electrode 20 are immersed in the electrolyte 50. The electrolyte 50 generally includes sodium electrolyte salt, organic solvent, and film-forming additives.

[0073] like Figure 1As shown, the sodium-ion battery 100 also includes a separator 40 located between the negative electrode 10 and the positive electrode 20. The separator 40 has ion conductivity and electronic insulation, separating the negative electrode 10 and the positive electrode 20 to prevent short circuits between them. Correspondingly, the electrolyte interface film 30 on the surface of the negative electrode 10 and the electrolyte interface film 30 on the surface of the positive electrode 20 are also separated by the separator 40. The separator 40 can be, but is not limited to, single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, etc.

[0074] Sodium-ion batteries 100 utilize active sodium ions (Na+) + Energy storage and release are achieved through deintercalation / deintercalation between the negative electrode 10 and the positive electrode 20. For example... Figure 1 As shown, during charging, under the action of an external circuit, Na + Electrons are extracted from the positive electrode active material layer 22 of the positive electrode 20, migrate through the electrolyte 50 and the separator 40 to the negative electrode 10, and simultaneously electrons (e) are released from the positive electrode. - As energy flows from the positive terminal 20 to the negative terminal 10 in the external circuit, the open-circuit voltage of the sodium-ion battery 100 increases, and electrical energy is stored. During discharge, Na... + Electrons are released from the negative electrode active material layer 12 in the negative electrode 10, pass through the electrolyte 50 and the separator 40, and migrate back to the positive electrode 20. Correspondingly, electrons migrate from the negative electrode 10 to the positive electrode active material layer 22 of the positive electrode 20 from the external circuit. The battery voltage decreases, electrical energy is released, and the battery performs work on the outside, such as releasing electrical energy to the electrical load that is electrically connected to the sodium-ion battery 100. Figure 1 In the diagram, the arrow pointing to the right indicates the charging process, and the arrow pointing to the left indicates the discharging process.

[0075] For the sodium-ion battery 100, the negative electrode active material in the negative electrode active material layer 12 may include, but is not limited to, one or more of hard carbon, soft carbon, sodium titanate, and metallic materials that can form alloys with sodium. The positive electrode active material in the positive electrode active material layer 22 may include, but is not limited to, one or more of layered sodium-based transition metal oxides (such as sodium cobaltate, manganese cobaltate, sodium oxides containing nickel iron manganese, etc.), polyanionic positive electrode materials (such as sodium vanadium phosphate (Na3V2(PO4)3), sodium iron phosphate (NaFePO4), sodium iron pyrophosphate (NFPP, chemical formula may be Na4Fe3(PO4)2P2O7), etc.), Prussian blue, Prussian white, etc.

[0076] The sodium-ion battery provided in this application embodiment can be used as a battery for consumer electronic devices, a power battery for mobile devices, and can also be applied to energy storage devices, base stations, etc. Consumer electronic devices may include, but are not limited to, mobile phones, tablets, laptops, and wearable electronic devices. Mobile devices may include, for example, electric vehicles, electric tricycles, electric motorcycles, and electric bicycles.

[0077] This application also provides a method for preparing a sodium-ion battery, including the following steps S01 and S02:

[0078] S01, providing a positive electrode, a negative electrode, and a separator for a sodium-ion battery; wherein the positive electrode active material layer of the positive electrode and / or the negative electrode active material layer of the negative electrode contain a non-sodium metal element M salt or its precursor, and / or, the M salt or its precursor is coated on the surface of the positive electrode and / or the negative electrode, and / or, the separator is impregnated with a precursor solution of the M salt;

[0079] S02, the positive electrode, the separator, and the negative electrode are assembled into a battery cell, the battery cell is installed in a battery casing, electrolyte is injected and sealed, and after formation, the sodium-ion battery of the present application embodiment is obtained.

[0080] This application achieves an electrolyte interface film formed on the positive and / or negative electrode surfaces of a sodium battery after formation. This film includes organic matter, sodium salt, and M salt with low solubility in the electrolyte. The M salt can be used to improve the stability of the electrolyte interface film, thereby improving the cycle stability, high-temperature storage stability, and high-temperature float charge stability of the sodium battery at room temperature or high temperature.

[0081] In this application, the precursor of the M salt refers to a substance that can be converted into the M salt during the formation or cycling process of a sodium-ion battery. In this embodiment, the solubility of the precursor of the M salt in the electrolyte is greater than the solubility of the M salt itself in the electrolyte. Specifically, the precursor of the M salt is a MY salt, and the anion Y in the MY salt is a common anion found in the electrolyte. This allows the M element to be introduced into the sodium battery in the form of an M salt precursor with high solubility in the electrolyte, facilitating a sufficient and uniform introduction of the M element raw material, especially when using a membrane impregnation method to introduce the M element in the form of an M salt precursor. The anion Y in the MY salt is generally different from the anion X in the aforementioned MX salt.

[0082] The methods for preparing the positive and negative electrodes are similar. Taking the preparation of the negative electrode as an example, the preparation method is as follows: A negative electrode slurry containing negative electrode active material, binder, and solvent is prepared; this negative electrode slurry is coated onto a current collector for the negative electrode; after drying, a negative electrode active material layer is formed, thus obtaining the negative electrode. In step S01, when the positive electrode active material layer of the positive electrode and / or the negative electrode active material layer contains M salt or its precursor, the M salt or its precursor can be introduced into the slurry used to prepare the positive and / or negative electrodes. For example, when preparing a slurry for a sodium battery negative electrode, the M salt or its precursor can be added directly in solid form or in solution form.

[0083] Generally, the solvents in the slurries for the negative or positive electrodes differ from those in the electrolytes of sodium-ion batteries. Therefore, although the M salt has low solubility in sodium-ion battery electrolytes, it can achieve good dissolution in the slurries for the negative or positive electrodes of sodium-ion batteries. For example, the solvent in the negative electrode slurry can be water, and the solvent in the positive electrode slurry can be N-methylpyrrolidone (NMP).

[0084] In some embodiments of this application, the mass of element M in the negative electrode active material layer can be 0.01%-3% of the mass of the negative electrode active material, and / or the mass of element M in the positive electrode active material layer is 0.01%-2% of the mass of the positive electrode active material. This facilitates the formation of a sufficient but not excessive amount of element M salt in the electrolyte interface film formed on the surfaces of the negative and / or positive electrodes during the sodium battery formation process. Exemplarily, the mass of element M in the negative electrode active material layer is 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, etc., of the negative electrode active material. For example, the mass of element M in the positive electrode active material layer is 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 1.8%, 2%, etc., of the positive electrode active material mass.

[0085] When coating the surface of the positive and / or negative electrodes with M salt or its precursor, the M salt or its precursor is added in the form of a solution. For example, the solvent in the solution of the M salt or its precursor can be one or more of water, NMP, tetrahydrofuran, dimethyl carbonate, diethyl carbonate, propylene carbonate, etc.

[0086] In some embodiments of this application, when coating the surface of the positive and / or negative electrode with M salt or its precursor, the coating amount of element M on the surface of the positive and / or negative electrode can be 0.01-0.2 mg / cm³. 2This facilitates the introduction of an appropriate amount of M salt or its precursor onto the surfaces of the positive and / or negative electrodes, thereby forming an electrolyte interface film containing an appropriate amount of M salt on the surfaces of the positive and / or negative electrodes during the formation of the sodium battery, effectively improving its stability. For example, the coating amount can be 0.02 mg / cm³. 2 0.05 mg / cm 2 0.08 mg / cm 2 0.1 mg / cm 2 0.15 mg / cm 2 0.2 mg / cm 2 wait.

[0087] When the membrane is impregnated with a solution containing the precursor of the M salt, the solvent in the solution can be a common solvent found in sodium battery electrolytes, such as a carbonate solvent. In some embodiments, the carbonate solvent is a mixed solvent composed of linear carbonates and cyclic carbonates. Exemplarily, linear carbonates may include one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Cyclic carbonates may include one or more of ethylene carbonate (EC) and propylene carbonate (PC).

[0088] In some embodiments of this application, the precursor solution of the M salt is a carbonate solution with an M salt precursor concentration of 0.01M-1M. Using an M salt precursor solution of appropriate molar concentration to impregnate the separator ensures that the impregnated separator contains an appropriate amount of M salt precursor, thereby enabling the in-situ generation of an electrolyte interface film containing M salt during the formation process of the sodium battery. Exemplarily, the molar concentration of the M salt precursor solution can be 0.02M, 0.05M, 0.08M, 0.1M, 0.2M, 0.5M, 0.8M, 0.9M, etc.

[0089] In this embodiment, the sodium-ion battery can be a stacked battery or a wound battery. If it is a stacked battery, the cell is obtained by stacking the positive electrode, separator, and negative electrode. If it is a wound battery, the positive electrode, separator, and negative electrode need to be stacked and then wound.

[0090] In this embodiment of the application, in step S02, the formation can be carried out in a stepped, graded manner, that is, the formation can include two or more charging stages. After the formation is completed, the battery reaches 100% SOC.

[0091] In some embodiments of this application, the room-temperature formation includes a two-step charging process. Specifically, the first step involves charging at a rate of 0.01C-0.2C to a State of Charge (SOC) of 5%-25%, followed by a resting period before the second step of charging. This second step involves constant current and constant voltage charging at a rate of 0.2C-0.5C to 100% SOC. Controlling the first charging rate to be relatively low and allowing the material to rest helps ensure a relatively high density in the inner layer of the electrolyte interface film, which is primarily composed of sodium salt, and the intermediate layer containing M salt, thus reducing side reactions between the electrode active material and the electrolyte. The second charging rate is higher than the first charging rate, which reduces charging time and facilitates the formation of a looser outer film structure, primarily composed of organic matter, which is beneficial for electrolyte wetting.

[0092] In some embodiments of this application, after the formation process, further steps such as venting, aging, or volume separation may be performed.

[0093] The sodium-ion battery preparation method provided in this application can produce a sodium-lithium-ion battery with a stable electrolyte interface film as described above. This preparation method is simple and easy to operate.

[0094] This application also provides an electrical device, which includes the sodium-ion battery described in the embodiments of this application, or a sodium-ion battery prepared using the preparation method described in the embodiments of this application. The electrical device is powered by the sodium-ion battery described above. The electrical device includes an electrical component and a power supply component, with the power supply component supplying power to the electrical component. The power supply component includes the sodium-ion battery described in the embodiments of this application. It is understood that the electrical component is electrically connected to the sodium-ion battery to enable the sodium-ion battery to supply power. In this application embodiment, the electrical device may be an electronic device or a mobile device (such as an electric vehicle).

[0095] In the embodiments of this application, the electronic device may be a mobile phone, tablet computer, laptop computer, wearable device (such as smartwatch, smart bracelet, smart glasses, smart headphones, etc.), augmented reality (AR) device, virtual reality (VR) device, television, digital camera, in-vehicle equipment, and other electronic products. This application does not limit the scope of the electronic device.

[0096] In some implementations, see Figure 4 , Figure 4 This is a schematic diagram of the structure of an electronic device 300 provided in an embodiment of this application. The electronic device 300 includes a housing 301 and a circuit board assembly housed within the housing 301. Figure 4(Not shown in the diagram) and battery 302. Battery 302 can power electronic device 300, and battery 302 includes the sodium-ion battery 200 described above in the embodiments of this application. Battery 302 is electrically connected to a circuit board and can power the circuit board assembly. The circuit board assembly can be one of the power-consuming components of electronic device 300. In some embodiments, housing 301 may include a front cover assembled on the front side of the electronic device and a rear cover assembled on the rear side, and battery 302 may be fixed inside the rear cover. Figure 4 The electronic device 300 shown may specifically be a mobile phone, etc.

[0097] In other implementations, see Figure 5 , Figure 5 This is a schematic diagram of a mobile device 400 provided in an embodiment of this application. The mobile device 400 can be various movable devices used for loading, transportation, assembly, disassembly, security, etc., such as various types of vehicles, including but not limited to electric vehicles, electric buses, electric trucks, electric tricycles, electric motorcycles, electric bicycles, etc. Of course, the mobile device 400 can also be a ship, aerospace equipment, drone, etc. In this embodiment, an electric vehicle is used as a specific example for illustration.

[0098] Specifically, the mobile device 400 may include a vehicle body 401, a moving component 402 (e.g., wheels), and a drive component. The drive component includes a motor 403 and a battery system 404. The battery system 404 includes the sodium-ion battery 200 described in the embodiments of this application. The battery system 404 is housed within the vehicle body 401 (e.g., located under the chassis) and electrically connected to the motor 403, providing power to the motor 403 to drive the moving component 402. The motor 403 is one of the electrical components of the mobile device 400. The battery system 404 may be a battery pack containing multiple sodium-ion batteries 200. These multiple sodium-ion batteries may be connected in series and parallel to form a battery pack, with at least one battery module and a battery management system packaged together to form the battery pack.

[0099] This application also provides an energy storage device, including a receiving cavity and a battery housed in the receiving cavity, wherein the battery stores electrical energy for the energy storage device. The energy storage device generally includes multiple sodium-ion batteries 100 as described above.

[0100] See Figure 6 , Figure 6This is a schematic diagram of a structure of an energy storage device 500 provided in an embodiment of this application. The energy storage device 500 includes a receiving cavity 51 and at least one battery pack 52. The battery pack 52 is housed within the receiving cavity 51. The battery pack 52 can be a module formed by connecting multiple sodium-ion batteries 100 in series, parallel, or a combination thereof. Any two sodium-ion batteries 100 are connected in series and / or in parallel. Figure 6 The energy storage device shown can specifically be a battery pack.

[0101] In some embodiments, the energy storage device 500 may further include a battery management system (BMS) 53, which may be electrically connected to the battery pack 52. The BMS 53 may be used to monitor the status information of each sodium-ion battery 100 in the battery pack 52, such as temperature, voltage, current, internal resistance, etc., and to control the charging / discharging status of each sodium-ion battery 100.

[0102] This application also provides an energy storage system, which includes an electrically connected power converter and at least one of the energy storage devices described in this application. The number of energy storage devices or power converters can be one or more. The power converter is used to convert the voltage and / or current output from the energy storage device and output it to the power grid or electrical load, and / or to convert the voltage and / or current output from an external power source and input it to the energy storage device.

[0103] The embodiments of this application will be further described below through multiple examples.

[0104] Example 1

[0105] A method for preparing a sodium-ion battery, comprising:

[0106] 1) Preparation of negative electrode sheet: Hard carbon as the negative electrode active material is mixed with binder (specifically polyacrylic acid) and conductive carbon black in a mass ratio of 50:40:6:4, and LiFSI (lithium bisfluorosulfonyl imide) is additionally introduced so that the mass ratio of LiFSI in the mixture is 0.2wt%. Then the mixture is dispersed in solvent water and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on copper foil current collector, dried at room temperature and then transferred to a 120°C forced-air oven for drying for 1 hour to form a negative electrode active material layer. After that, the negative electrode sheet is obtained by cold pressing and die cutting.

[0107] 2) Preparation of positive electrode sheet: Sodium iron pyrophosphate (NFPP), which is used as the positive electrode active material, is mixed with binder (specifically polyvinylidene fluoride PVDF) and conductive carbon black at a mass ratio of 98:1:1 and dispersed in solvent N-methylpyrrolidone (NMP). After stirring evenly, a positive electrode slurry is obtained. The positive electrode slurry is uniformly coated on a carbon-coated aluminum foil current collector with a thickness of 9μm. After drying at room temperature, it is transferred to a 120℃ forced-air oven for drying for 1 hour to form a positive electrode active material layer. Then, the positive electrode sheet is obtained by cold pressing and die cutting.

[0108] 3) Battery Assembly: The negative electrode sheet is stacked with the separator and positive electrode sheet in a stacked manner to obtain a battery cell. The battery cell is then placed in an aluminum-plastic film packaging shell, electrolyte is injected into the shell, and it is sealed. The process involves standing, formation, and capacity testing to produce a soft-pack sodium-ion battery. The electrolyte is prepared by dissolving NaPF6 in an organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a 1:1:1 volume ratio. After thorough mixing, the concentration of NaPF6 in the electrolyte is approximately 1.0 M. The formation process involves charging at a constant current of 0.05C to 10% SOC, allowing it to stand for 12 hours, and then charging at a constant current and voltage of 0.2C to 100% SOC. After formation, a lithium salt-containing electrolyte interface film forms on the surfaces of the negative and positive electrodes.

[0109] Example 2

[0110] A method for preparing a sodium-ion battery differs from Example 1 only in that: when preparing the negative electrode sheet, LiFSI is not introduced into the negative electrode slurry, and the separator is pretreated as follows: the separator is completely immersed in a 0.1M dimethyl carbonate (DMC) solution of LiFSI, left to stand for 12 hours, and then the immersed separator is taken out and placed in a vacuum oven and dried at 90°C for 12 hours.

[0111] In the case of a battery cell prepared using the pretreated diaphragm described above, after formation, an electrolyte interface film containing lithium salt will be formed on the surfaces of the negative and positive electrodes.

[0112] Comparative Example 1

[0113] A method for preparing a sodium-ion battery differs from Example 1 only in that LiFSI is not introduced into the negative electrode slurry during the preparation of the negative electrode sheet.

[0114] Characterization of the electrolyte interface film in sodium batteries:

[0115] After the sodium battery of Example 1 was fully discharged, it was disassembled in an inert gas environment. The negative electrode was removed and thoroughly immersed in DMC to wash away residual electrolyte and salt adhering to its surface. The cleaned negative electrode was then removed, and the negative electrode active material layer with the SEI film on its surface was scraped off and dispersed in ethanol. The image was observed under a transmission electron microscope equipped with a cryostat. The obtained transmission electron microscope image is shown below. Figure 7 As shown.

[0116] from Figure 7 It can be seen that, from the negative electrode surface of the sodium battery outward, the SEI film on the surface of the negative electrode active material layer successively includes a first film layer containing sodium carbonate (Na2CO3), a second film layer containing lithium fluoride (LiF), and the outermost organic layer. Figure 7 The circles in each region represent the crystal structures of Na₂CO₃ and LiF, respectively. Furthermore, from... Figure 7 Other areas in the transmission electron microscope image (not shown) show a compositional gradient layer containing both Na2CO3 and LiF between the Na2CO3-containing film and the LiF-containing film.

[0117] The following electrochemical performance tests were performed on each sodium-ion battery.

[0118] 25℃ ambient temperature cycling performance test: Charge and discharge tests were conducted on each sodium-ion battery at 25℃, with a voltage range of 1.5-3.3V and a charge / discharge rate of 1C. The discharge capacity of each battery in the first cycle and the percentage of discharge capacity in each subsequent cycle relative to its first cycle discharge capacity (i.e., capacity retention rate) were recorded to plot the ambient temperature cycling performance curve.

[0119] High-temperature cycling performance test at 55℃: The sodium-ion batteries mentioned above were placed in an oven at 55℃ for charge and discharge tests. The voltage range was 1.5-3.3V and the charge and discharge rate was 1C. The discharge capacity of each battery in the first cycle and the percentage of the discharge capacity in each subsequent cycle relative to its first cycle discharge capacity (i.e., capacity retention rate) were recorded to plot the high-temperature cycling performance curve.

[0120] 45℃ High Temperature Storage Performance Test: First, calibrate the room temperature discharge capacity of each sodium-ion battery: discharge each sodium-ion battery at 0.2C constant current to 1.5V at 25℃ and let it stand for 5 minutes; then fully charge it at 0.2C constant current and constant voltage to 3.3V / 0.05C cutoff at 25℃ and let it stand for 5 minutes; repeat the above discharge-charge cycle once, and take the discharge capacity of the second discharge as the initial discharge capacity C1.

[0121] Then, each sodium-ion battery that has been calibrated and fully charged (charged to 3.3V / 0.05C at 0.2C constant current and constant voltage at 25℃) is placed in an oven at 45℃ and left to stand. Every 14 days, the battery is discharged and charged (i.e., after the battery is taken out of the oven and cooled to 25℃, it is discharged first, and the discharge capacity C2 is recorded. Then it is fully charged to 3.3V / 0.05C at 25℃ at 0.2C constant current and constant voltage). The battery is then placed back in the oven at 45℃ and left to stand. The percentage of the room temperature discharge capacity C2 of the battery relative to the initial discharge capacity C1 after standing at 45℃ for different numbers of days is recorded as the high temperature storage capacity retention rate.

[0122] 45℃ High-Temperature Float Charge Performance Test: Each sodium-ion battery, calibrated to its room-temperature discharge capacity C1 and fully charged (charged at 25℃ using a constant current and voltage of 0.2C to 3.3V / 0.02C), was placed in a 45℃ oven and left to stand for 2 hours. It was then charged at a constant voltage of 3.3V for 15 days. At regular intervals, the batteries were removed and placed in a 25℃ environment for a complete discharge and charge cycle (specifically, at 25℃, discharged at a constant current of 0.2C to 1.5V, left to stand for 5 minutes, then fully charged at a constant current and voltage of 0.2C to 3.3V / 0.05C, and left to stand for 5 minutes). The discharge capacity C2 of this cycle was recorded. ’ Record C2 of this lap. ’ The remaining percentage relative to the initial discharge capacity C1 is used as the high-temperature float charge capacity retention rate. The fully charged battery is then placed in a 45°C oven for constant voltage charging and resting.

[0123] The relevant test results are summarized in Table 1 below. Furthermore, Figure 8 The 25°C room temperature cycling performance curves of sodium batteries from Example 1 and Comparative Example 1 are summarized. Figure 9 The high-temperature cycling performance curves of sodium batteries from Example 1 and Comparative Example 1 at 55°C are summarized. Figure 10 The high-temperature storage capacity retention curves of sodium batteries in Example 1 and Comparative Example 1 at 45°C are summarized. Figure 11 The capacity retention curves of sodium batteries in Example 1 and Comparative Example 1 at 45°C during float charging are summarized.

[0124] Table 1

[0125]

[0126] From the above Figures 8 to 11As shown in Table 1, when the sodium battery cathode material is a polyanionic cathode material, the capacity retention rate of the sodium battery of Example 1 of this application after 400 cycles at room temperature is 1.5% higher than that of the battery of Comparative Example 1; the capacity retention rate of the sodium battery of Example 1 of this application after 400 cycles at a high temperature of 55°C is about 0.5% higher than that of the battery of Comparative Example 1. These results indicate that the present application introduces a non-sodium metal salt (i.e., lithium salt) into the electrolyte interface film on the electrode surface of the sodium battery, which improves the stability of the electrolyte interface film, thereby optimizing the room temperature and high temperature cycle performance of the sodium battery. In addition, the sodium battery of Example 1 of this application showed improved discharge capacity retention rates in both the 45°C high-temperature storage test and the 45°C high-temperature float charge test, with an improvement of about 1.0%, which also demonstrates the excellent stability of the electrolyte interface film of the sodium battery of this application.

[0127] Similarly, the sodium battery in Example 2 also showed certain improvements in room temperature cycling, high temperature cycling, high temperature storage, and high temperature float charging test results compared to Comparative Example 1.

[0128] The above description merely illustrates exemplary embodiments of this application, and while the description is specific and detailed, it should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0129] The above description merely illustrates exemplary embodiments of this application, and while the description is specific and detailed, it should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0130] In the description of this application, unless otherwise stated, "multiple" means two or more. "At least one" means one or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0131] Furthermore, the numerical range indicated by "-" in this application refers to the range including the values ​​before and after "-", which are respectively taken as the minimum and maximum values. In this application, expressions regarding parameter ranges, such as "greater than or equal to (≥)", "less than or equal to (≤)", "above", and "below", all include the stated number. The numerical values ​​and ranges involved in the embodiments of this application are approximate values, and may have a certain range of errors due to the influence of manufacturing processes / testing methods, etc. These errors are negligible to those skilled in the art.

Claims

1. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode and a negative electrode, and the surface of the positive electrode and / or the negative electrode has an electrolyte interface film; wherein, the electrolyte interface film includes organic matter, sodium salt and M salt, wherein M is a non-sodium metal element, and in a mixed solvent composed of ethylene carbonate and diethyl carbonate in equal volume ratio, the solubility of the M salt is lower than that of the sodium salt.

2. The sodium-ion battery as described in claim 1, characterized in that, The element M includes one or more of lithium, potassium, magnesium, and aluminum.

3. The sodium-ion battery as described in claim 1 or 2, characterized in that, The anions in the M salt include one or more of fluoride ions, carbonate ions, nitrogen anions, fluorophosphate ions, and organic anions; wherein the organic anions include CH3O. - CH3CH2O - CH3CH2CO3 - CO3CH2CH2CO3 2- One or more of them.

4. The sodium-ion battery according to any one of claims 1-3, characterized in that, In the electrolyte interface membrane, the mass percentage of element M relative to the mass percentage of element M and sodium is greater than 0 and less than or equal to 0.12%.

5. The sodium-ion battery according to any one of claims 1-4, characterized in that, In the electrolyte interface membrane, the mass percentage of the M salt is 0.002%-0.024%.

6. The sodium-ion battery according to any one of claims 1-5, characterized in that, The electrolyte interface film on the negative electrode surface has a mass ratio of greater than 0 and less than or equal to 5% relative to the electrolyte interface film and the negative active material in the negative electrode, and / or the electrolyte interface film on the positive electrode surface has a mass ratio of greater than 0 and less than or equal to 2% relative to the electrolyte interface film and the positive active material in the positive electrode.

7. The sodium-ion battery according to any one of claims 1-6, characterized in that, Along the direction away from the positive or negative electrode, the electrolyte interface membrane includes a first membrane layer, a second membrane layer, and a third membrane layer stacked sequentially, wherein the first membrane layer includes the sodium salt, the second membrane layer includes the M salt, and the third membrane layer includes the organic matter.

8. The sodium-ion battery as described in claim 7, characterized in that, The second membrane layer further includes a transition layer containing the sodium salt and the M salt between the two membrane layers.

9. The sodium-ion battery as described in claim 8, characterized in that, Along the direction from the first film layer to the second film layer, in the transition layer, the content of the sodium salt gradually decreases, and the content of the M salt gradually increases.

10. The sodium-ion battery according to any one of claims 7-9, characterized in that, Along the thickness direction perpendicular to the electrolyte interface membrane, the content of element M in the edge region of the second membrane layer is greater than the content of element M in other regions of the second membrane layer.

11. The sodium-ion battery according to any one of claims 7-10, characterized in that, The thickness of the third film layer is in the range of 5nm-20nm.

12. The sodium-ion battery according to any one of claims 7-11, characterized in that, The thickness of the third film layer is greater than the sum of the thicknesses of the first film layer and the second film layer.

13. The sodium-ion battery according to any one of claims 7-12, characterized in that, The sum of the thicknesses of the first film and the second film is in the range of greater than 0 to less than or equal to 15 nm.

14. A method for preparing a sodium-ion battery, characterized in that, Includes the following steps: A positive electrode, a negative electrode, and a separator are provided for sodium-ion batteries; wherein the positive electrode active material layer of the positive electrode and / or the negative electrode active material layer of the negative electrode contain a non-sodium metal element M salt or its precursor, and / or the M salt or its precursor is coated on the surface of the positive electrode and / or the negative electrode, and / or the separator is impregnated with a precursor solution of the M salt. The positive electrode, the separator, and the negative electrode are assembled into a battery cell. The battery cell is then installed in a battery casing, an electrolyte is injected, and the casing is sealed. After formation, a sodium-ion battery as described in any one of claims 1-12 is obtained.

15. The preparation method according to claim 14, characterized in that, The precursor of the M salt has a higher solubility in the electrolyte than the M salt itself; wherein the precursor of the M salt is a MY salt, and the anion Y in the MY salt is a common anion in the electrolyte.

16. The preparation method according to claim 14, characterized in that, The negative electrode active material layer contains M element at a mass of 0.01%-3% of the negative electrode active material, and / or, the positive electrode active material layer contains M element at a mass of 0.01%-2% of the positive electrode active material; and / or, The amount of element M coated on the surface of the positive and / or negative electrodes is 0.01-0.2 mg / cm³. 2 ; and / or, The precursor solution of the M salt is a carbonate solution with a concentration of 0.01-1M for the M salt.

17. An electrical appliance, characterized in that, The electrical device includes an electrical component and a power supply component, wherein the power supply component supplies power to the electrical component, and the power supply component includes a sodium-ion battery as described in any one of claims 1-13.

18. An energy storage device, characterized in that, The energy storage device includes a sodium-ion battery as described in any one of claims 1-13, or a sodium-ion battery prepared by the preparation method described in any one of claims 14-16.

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