Sodium metal secondary battery and electric device

Abstract

The application provides a sodium metal secondary battery and an electric device, which comprises an electrolyte, the electrolyte comprises an ether solvent and an additive, the additive is selected from a compound shown in general formula I and / or general formula II, A is selected from *-R or *-R3; R is selected from *-O-R3, *-CH2-R3, *-CH(R3)2, *-C(R3)2 or at least one of R1, R2 and R3 is an independent group or forms a ring group together with the atom connected therewith; R4, R5 and R6 are independent groups respectively; R1 to R6 are each independently selected from at least one of a substituted or unsubstituted C1-C10 saturated alkyl group, a substituted or unsubstituted C2-C10 unsaturated alkyl group and a substituted or unsubstituted phenyl group; the substituent group comprises at least one of F, a thio phenyl group, an oxo phenyl group and a heteroaryl group. The sodium metal secondary battery in the application has improved storage performance and safety performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a sodium metal secondary battery and an electrical device thereof. Background Technology

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, and aerospace.

[0003] Sodium metal secondary batteries, as a typical type of secondary battery, have gained increasing attention due to their advantages such as abundant raw material resources and low cost compared to other types of batteries. The design of anode-free sodium metal secondary batteries (Advanced Flexible Sodium Metal Batteries, AFSMBs) theoretically significantly improves the mass and volumetric energy density of AFSMBs by omitting traditional anode active materials.

[0004] However, in these AFSMBs, the interfacial chemical stability between the sodium metal layer and the electrolyte is poor, leading to continuous rupture of the solid electrolyte interphase (SEI) film on the surface of the sodium metal layer. On the one hand, the rupture of the SEI film causes the loss of sodium ions, affecting the storage performance of AFSMBs; on the other hand, the rupture of the SEI film causes the sodium metal layer to come into contact with the electrolyte, generating a large amount of gas, which affects the safety performance of AFSMBs. Summary of the Invention

[0005] This application was made in view of the above-mentioned problems, and its object is to provide a sodium metal secondary battery and an electrical device thereof. The sodium metal secondary battery of this application has improved storage performance and safety performance.

[0006] To achieve the above objectives, the first aspect of this application provides a sodium metal secondary battery, comprising an electrolyte, the electrolyte comprising an ether solvent and an additive, the additive being selected from compounds represented by general formula I and / or general formula II: A is selected from *-R or *-R3; R is selected from *-O-R3, *-CH2-R3, *-CH(R3)2, *-C(R3)2 or *-B(O R3)2, at least one of R1, R2, and R3 is an independent functional group or forms a cyclic functional group together with the atoms to which it is attached; R4, R5, and R6 are each an independent functional group;

[0007] R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C2-C10 unsaturated alkyl groups, and substituted or unsubstituted phenyl groups; substituents include F, thiophenyl, oxophenyl, etc. At least one of them.

[0008]

[0009] In this application, the additives used contain boron atoms (B) with empty orbitals, which are capable of reacting with anions in sodium salts (such as PF6). - Boron atoms coordinate with oxygen atoms in ether solvents, effectively inhibiting the hydrolysis of anions and reducing the damage of hydrolysis products to the SEI. Furthermore, boron atoms can coordinate with the lone pair electrons on oxygen atoms in ether solvents, helping to bind the ether solvent and reduce its contact with sodium metal, thereby reducing the amount of gas produced in sodium metal secondary batteries. Moreover, boron atoms can participate in the formation of the SEI film, increasing the inorganic components in the SEI film and thus improving its stability.

[0010] Further additives utilize groups (R1 to R6) with low reactivity, which helps reduce side reactions between the additives and metallic sodium, thereby lowering gas production. Simultaneously, these groups have appropriate sizes, ensuring effective coordination of boron atoms with anions and ether solvents. Furthermore, they limit the binding of coordinated ether solvent molecules to anions through steric hindrance, reducing the deposition of ether solvents (organic components) within the SEI film, thus decreasing the organic content of the SEI film and improving its stability.

[0011] The stability of the SEI film is improved, which helps to reduce sodium ion consumption and reduce side reactions of the sodium metal layer, thereby improving the battery's storage performance and reducing the battery's gas production.

[0012] In some embodiments, the additive is selected from compounds represented by general formula III:

[0013]

[0014] At least one of R7 and R8 is an independent group or forms a cyclic group together with the atoms to which it is attached.

[0015] In this implementation, an additive molecule contains at least two B atoms, which helps to enhance the coordination of the additive with anionic / ether solvents, thereby further improving the battery's storage performance and further reducing the battery's gas production.

[0016] In some embodiments, in general formula I, R1, R2 and the oxygen atoms to which they are attached together form cyclic groups.

[0017] In this implementation, the molecular structure of the additive includes cyclic groups, which helps to increase the steric hindrance of the additive molecules. This increased steric hindrance can effectively prevent the anions from approaching and combining with the ether solvent molecules, thereby further reducing the deposition of organic components in the SEI film, improving the stability of the SEI film, reducing the risk of SEI film rupture, and thus further improving the storage performance of the battery and further reducing the gas production of the battery.

[0018] In some embodiments, in general formula I, R1, R2, and the oxygen atoms they are attached to form five- to eight-membered cyclic groups. Five- to eight-membered cyclic groups have high structural stability and are less prone to ring-opening reactions. Additives containing five- to eight-membered cyclic groups release a low amount of active hydrogen inside the battery, which helps reduce side reactions of sodium metal, thereby further improving the battery's storage performance and reducing gas production.

[0019] In some embodiments, in general formula I, R1, R2, and the oxygen atoms they are attached to form five- or six-membered cyclic groups. Five- or six-membered cyclic groups have lower ring strain, further reducing the probability of ring-opening, which helps to further reduce the amount of active hydrogen released by the additive and further reduce side reactions of sodium metal.

[0020] In some embodiments, in general formulas I and II, R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C3-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, and substituted or unsubstituted phenyl groups.

[0021] The aforementioned groups have significant steric hindrance. When R1 to R6 are selected from these groups, it is beneficial to further hinder the approach / combination of anions with ether solvent molecules, reduce the deposition of organic components in the SEI film, improve the stability of the SEI, reduce the risk of SEI rupture, and thus reduce the consumption of sodium ions. This is beneficial to further improve the storage performance of the battery and further reduce the gas production of the battery.

[0022] In some embodiments, in general formulas I and II, R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C3-C10 saturated alkyl groups and substituted or unsubstituted C3-C10 unsaturated alkyl groups. The aforementioned alkyl groups do not contain π bonds and have a weaker attraction for electrons. When R1 to R6 are selected from these alkyl groups, the additive is less likely to participate in redox reactions during battery charging and discharging. This helps the additive maintain its original chemical structure within the battery for a longer period, thus allowing it to continuously exert its coordination effect over a longer time, thereby improving the battery's storage performance and safety performance.

[0023] In some embodiments, in general formulas I and II, the substituents include at least one of F and thiophenyl. The inorganic atoms (F, S) contained in the above substituents can participate in the formation of the SEI film, which helps to increase the proportion of inorganic components in the SEI film, thereby improving the toughness of the SEI film and the stability of the SEI film during the charge and discharge process of the secondary battery. This is beneficial to further improve the storage performance of the battery and further reduce the gas production of the battery.

[0024] In some embodiments, the additives include 4-(trifluoromethoxy)phenylborane pinacol ester, trimethylol borate, triethyl borate, tripropyl borate, isopropyl borate, tri-n-butyl borate, triisobutyl borate, tri-tert-butyl borate, trihexyl borate, trioctyl borate, tri(hexafluoroisopropyl) borate, tri(2,2,2-trifluoroethyl) borate, triphenyl borate, (4,4,5,5-tetramethyl-1,3-ethylhexafluoro) borate, and (4,4,5,5-tetramethyl-1,3-ethylhexafluoro) borate. At least one of the following: (2-dioxaborane-2-yl)benzene, 2-phenyl-1,3,2-dioxaborane, propanol pinacol ester, borate cycloethanol pinacol ester, diboronol ester, bis(2,4-dimethyl-2,4-pentanediol)boron ester, trimethylcyclotriboroxane, 4,4,5,5,-tetramethyl-2-phenylthioalkylmethyl-1,3,2-dioxaborane, and propyl borate o-ditert-ol ester. Using the above additives is beneficial for improving the battery's storage performance and reducing gas production.

[0025] In some embodiments, the molar concentration of the additive relative to the electrolyte is from 0.01 mol / L to 0.5 mol / L. A molar concentration within this range allows for strong coordination between the additive and the anionic / ether solvent, reducing sodium metal side reactions and improving the stability of the SEI film. This, in turn, helps to further improve the battery's storage performance and further reduce gas production. Optionally, the molar concentration of the additive is from 0.05 mol / L to 0.3 mol / L.

[0026] In some embodiments, the ether solvent includes chain ethers. Chain ethers have good solubility for sodium salts, and the selection of chain ethers helps to maintain a stable sodium ion concentration in the electrolyte, thereby contributing to an improved lifespan of the sodium metal secondary battery.

[0027] In some embodiments, the ether solvent also includes cyclic ethers. Cyclic ethers typically have good ion transport properties, thereby improving the ionic conductivity of the electrolyte, which in turn helps to achieve improved fast-charging performance in sodium metal secondary batteries.

[0028] In some embodiments, the chain ether includes at least one selected from ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, and diethylene glycol dibutyl ether. By selecting the above-mentioned chain ethers, it is beneficial to reduce the dissolution of the sodium metal layer, thereby reducing the gas production of the battery and improving the battery's safety performance.

[0029] In some embodiments, the cyclic ether includes at least one selected from tetrahydrofuran, methyltetrahydrofuran, 1,3-dioxopentane, and 1,3-dioxane. By selecting the aforementioned chain ether, it is beneficial to reduce the dissolution of the sodium metal layer, thereby reducing the amount of gas produced by the battery and improving its safety performance.

[0030] In some embodiments, the volume ratio of chain ethers to cyclic ethers is (100-50):(0-50). This is beneficial for further balancing the solubility of sodium salts in ether solvents and the ionic conductivity of the electrolyte.

[0031] In some embodiments, the electrolyte further includes a sodium salt, with a molar concentration of 0.5 mol / L to 2 mol / L relative to the electrolyte. When the molar concentration of the sodium salt falls within the above concentration range, it is beneficial for the electrolyte to maintain excellent ionic conductivity, and the secondary battery using this electrolyte can achieve improved cycle life.

[0032] In some embodiments, a negative electrode sheet is also included, which consists of a negative current collector and a sodium metal layer or sodium alloy layer disposed on at least one side of the negative current collector. The sodium metal layer and sodium alloy have very high theoretical specific capacity, which allows the sodium metal secondary battery to store more charge and achieve high energy density. Optionally, the thickness of the sodium metal layer or sodium alloy layer is 1 μm-15 μm.

[0033] In some embodiments, the negative electrode further includes a conductive layer disposed between the current collector and the sodium metal layer or sodium alloy layer. The conductive layer provides a good electron transport path, thereby improving the electron transport efficiency of the negative electrode, which in turn helps to improve the charge and discharge efficiency of the battery and reduce its internal resistance. Optionally, the thickness of the conductive layer is 1 μm-5 μm.

[0034] In some embodiments, a positive electrode sheet is also included, comprising a positive current collector and a positive electrode film layer disposed on the positive current collector. The positive electrode film layer comprises at least one of sodium transition metal oxide, polyanionic compound, and Prussian blue compound. This sodium metal secondary battery has improved storage performance and safety performance.

[0035] In some implementations, the secondary battery is a sodium metal secondary battery without a negative electrode. This is advantageous for achieving high energy density.

[0036] A second aspect of this application provides an electrical device, including the sodium metal secondary battery provided in the first aspect. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0038] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0039] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0040] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0041] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0042] Figure 6 This is a schematic diagram of an electrical device using a sodium metal secondary battery as a power source according to an embodiment of this application.

[0043] Explanation of reference numerals in the attached figures:

[0044] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0045] The embodiments of the sodium metal secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0046] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0048] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0049] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0050] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0051] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0052] In this application, the term "saturated alkyl" refers to a hydrocarbon group composed of carbon and hydrogen atoms, where the carbon atoms in the molecule are connected only by single bonds, and each carbon atom is bonded to as many hydrogen atoms as possible, achieving maximum saturation. In this application, saturated alkyl includes chain-like saturated alkyl and cyclic saturated alkyl.

[0053] In this application, "chain-like saturated alkyl" refers to a molecule in which carbon atoms are linked by single bonds to form a linear or branched chain structure, and each carbon atom is bonded to as many hydrogen atoms as possible to achieve a saturated state.

[0054] In this application, "cyclic saturated alkyl" refers to a molecule in which carbon atoms are linked by single bonds to form one or more closed cyclic structures, and each carbon atom is also bonded to as many hydrogen atoms as possible to achieve a saturated state.

[0055] In this application, "unsaturated alkyl" refers to a hydrocarbon substituent containing at least one carbon-carbon double or triple bond. Compared to saturated alkyl (i.e., alkyl groups), in unsaturated alkyl groups, the carbon atoms are not all connected by single bonds, but rather have one or more unsaturated bonds (double or triple bonds), preventing them from being bonded to the maximum number of hydrogen atoms. In this application, unsaturated alkyl groups include chain-like and cyclic unsaturated alkyl groups.

[0056] In this application, "chain-like unsaturated alkyl" refers to a hydrocarbon group in which carbon atoms are linked in a chain structure and contain at least one carbon-carbon double bond or carbon-carbon triple bond.

[0057] In this application, "cyclic unsaturated alkyl" refers to a hydrocarbon group in which carbon atoms are linked in a cyclic structure and contain at least one carbon-carbon double bond or carbon-carbon triple bond.

[0058] In this application, the term "phenyl" is an aromatic substituent consisting of six carbon atoms, five of which form a benzene ring and the sixth carbon atom serves as the linking point of the substituent.

[0059] In this application, "thiophenyl" refers to a functional group in a class of compounds, which is a group formed when a hydrogen atom on a benzene ring is replaced by a sulfur atom. Thiophenyl can be represented as...

[0060] In this application, "oxophenyl" refers to a functional group in a class of compounds, which is a group formed when a hydrogen atom on a benzene ring is replaced by an oxygen atom. Oxophenyl can be represented as...

[0061] In sodium metal secondary batteries, during the first charge, anions in the sodium salt (such as NaPF6) decompose with sodium ions to form an SEI film. The SEI film exists between the negative electrode and the electrolyte, which can reduce internal side reactions of the battery and thus improve the battery's safety performance.

[0062] Compared to traditional sodium metal secondary batteries, the negative electrode of a negative electrodeless sodium battery does not contain traditional negative electrode active materials. Therefore, the sodium ions consumed during the formation of the SEI film cannot be replenished, potentially leading to a decrease in the battery's storage performance. Furthermore, during the charging process of a negative electrodeless sodium battery, sodium ions are reduced on the surface of the negative electrode current collector and deposit to form a sodium metal layer. Due to the poor interfacial chemical stability between the sodium metal layer and the SEI film, the SEI film may continuously rupture, causing the sodium metal layer to come into direct contact with the electrolyte and potentially generating a large amount of gas, thus affecting the battery's safety performance.

[0063] To address the aforementioned technical problems, this application discloses a sodium metal secondary battery and an electrical device. The invention and its optional embodiments are described in more detail below.

[0064] The first aspect of this application provides a sodium metal secondary battery, which includes an electrolyte. The electrolyte includes an ether solvent and an additive, the additive being selected from compounds represented by general formula I and / or general formula II. A is selected from *-R or *-R3; R is selected from *-O-R3, *-CH2-R3, *-CH(R3)2, *-C(R3)2 or *-B(O R3)2; at least one of R1, R2, and R3 is an independent functional group or forms a cyclic group together with the atoms to which it is attached.

[0065] R4, R5, and R6 are each independent functional groups; R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C2-C10 unsaturated alkyl groups, and substituted or unsubstituted phenyl groups; substituents include F, thiophenyl, oxophenyl, etc. At least one of the following. The sodium metal secondary battery of this application has improved storage performance and safety performance.

[0066]

[0067] In this application, the additives used contain boron atoms (B) with empty orbitals, which are capable of reacting with anions in sodium salts (such as PF6). -Boron atoms coordinate with oxygen atoms in ether solvents, effectively inhibiting the hydrolysis of anions and reducing the damage of hydrolysis products to the SEI. Furthermore, boron atoms can coordinate with the lone pair electrons on oxygen atoms in ether solvents, helping to bind the ether solvent and reduce its contact with sodium metal, thereby reducing the amount of gas produced in sodium metal secondary batteries. Moreover, boron atoms can participate in the formation of the SEI film, increasing the inorganic components in the SEI film and thus improving its stability.

[0068] Further additives utilize groups (R1 to R6) with low reactivity, which helps reduce side reactions between the additives and metallic sodium, thereby lowering gas production. Simultaneously, these groups have appropriate sizes, ensuring effective coordination of boron atoms with anions and ether solvents. Furthermore, they limit the binding of coordinated ether solvent molecules to anions through steric hindrance, reducing the deposition of ether solvents (organic components) within the SEI film, thus decreasing the organic content of the SEI film and improving its stability.

[0069] The stability of the SEI film is improved, which helps to reduce sodium ion consumption and reduce side reactions of the sodium metal layer, thereby improving the battery's storage performance and reducing the battery's gas production.

[0070] The term "sodium metal secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0071] Typically, a single secondary battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through. The following provides further explanation of the components of a sodium metal secondary battery.

[0072] electrolyte

[0073] In this application, the electrolyte serves to conduct ions between the positive and negative electrode plates. The components of the electrolyte disclosed in this application will be further described below.

[0074] In this application, the electrolyte includes an ether solvent and an additive, the additive being selected from compounds represented by general formula I and / or general formula II.

[0075] In some embodiments, A in general formula I is selected from *-R3. Exemplarily, additives include, but are not limited to, 4-(trifluoromethoxy)phenylboronic acid pinacol ester.

[0076] The structural formula of 4-(trifluoromethoxy)phenylboronic acid pinacol ester is as follows:

[0077]

[0078] In some embodiments, A in general formula I is selected from R, and R is selected from *-O-R3. Exemplarily, additives include, but are not limited to, trimethylolpropane borate, triethyl borate, tripropyl borate, isopropyl borate, tri-n-butyl borate, triisobutyl borate, tri-tert-butyl borate, trihexyl borate, trioctyl borate, tri(hexafluoroisopropyl) borate, tri(2,2,2-trifluoroethyl) borate, triphenyl borate, (4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzene, 2-phenyl-1,3,2-dioxaborane heterocyclic, propanol pinacol ester, and borate cycloethanol pinacol ester.

[0079] The structural formula of methyl borate is as follows:

[0080]

[0081] The structural formula of (4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzene is as follows:

[0082]

[0083] The structural formula of the 2-phenyl-1,3,2-dioxoboron heterocycle is as follows:

[0084]

[0085] The structural formula of propanol pinacol borate ester is as follows:

[0086]

[0087] The structural formula of borate cycloethanol pinacol ester is as follows:

[0088]

[0089] In some embodiments, A is selected from *-R, and R is selected from *-B(OR3)2. Exemplary additives include, but are not limited to, pinacol diborate and bis(2,4-dimethyl-2,4-pentanediol)borate.

[0090] The structural formula of pinacol diboronate is as follows:

[0091]

[0092] The structural formula of bis(2,4-dimethyl-2,4-pentanediol)boronic acid ester is as follows:

[0093]

[0094] In some embodiments, A is selected from *-R, and R is selected from *-CH2-R3. Exemplary additives include, but are not limited to, o-ditert-ol propylene borate and 4,4,5,5,-tetramethyl-2-phenylthioalkylmethyl-1,3,2-dioxoborane.

[0095] The structural formula of 1,4-di-tert-ol propylene borate is as follows:

[0096]

[0097] The structural formula of 4,4,5,5,-tetramethyl-2-phenylthioalkylmethyl-1,3,2-dioxoboronyl ring is as follows:

[0098]

[0099] It should be noted that the embodiments in this application are merely illustrative examples of R being selected from *-CH2-R3. In some embodiments, R may be selected from *-CH(R3)2 or *-C(R3)2. Exemplary additives include, but are not limited to, the following compounds:

[0100] At least one of them.

[0101] In some embodiments, in general formula I, R1, R2, and R3 can be the same group. Exemplary additives include, but are not limited to, triethyl borate, tripropyl borate, isopropyl borate, tri-n-butyl borate, triisobutyl borate, tri-tert-butyl borate, trihexyl borate, trioctyl borate, and triphenyl borate.

[0102] In some embodiments, R1, R2, and R3 in general formula I can be different functional groups. Exemplarily, additives include, but are not limited to, 2-phenyl-1,3,2-dioxoborocyclic, (4,4,5,5-tetramethyl-1,3,2-dioxoboro-2-yl)benzene, propanol pinacol ester, and borate cycloethanol pinacol ester.

[0103] In some embodiments, in general formula I, R1, R2, and R3 are all independent functional groups. Exemplary examples include, but are not limited to, triethyl borate, triethyl borate, and tripropyl borate.

[0104] In some embodiments, R3 in general formula I is an independent group, and R1, R2, and the oxygen atoms they are attached to form cyclic groups. Exemplarily, additives include, but are not limited to: methyl borate, (4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzene, 2-phenyl-1,3,2-dioxaborane heterocycle, propanol pinacol ester, borate cycloethanol pinacol ester, 4,4,5,5-tetramethyl-2-phenylthioalkylmethyl-1,3,2-dioxaborane pentane.

[0105] In some embodiments, in general formula I, R3 and the atoms it is attached to form a cyclic group, and R1 and R2, together with the oxygen atoms they are attached to and the B atom, form a cyclic group. Exemplarily, the additive includes pinacol diborate and bis(2,4-dimethyl-2,4-pentanediol)borate.

[0106] In some embodiments, R1, R2, and R3 are each independently selected from substituted or unsubstituted C1-C10 saturated alkyl groups. Exemplarily, the additives include, but are not limited to, at least one of the following: trimethylolpropene borate, triethyl borate, tripropyl borate, isopropyl borate, tri-n-butyl borate, triisobutyl borate, tri-tert-butyl borate, trihexyl borate, trioctyl borate, tri(hexafluoroisopropyl) borate, and tri(2,2,2-trifluoroethyl) borate.

[0107] It should be noted that tris(hexafluoroisopropyl) borate and tris(2,2,2-trifluoroethyl) borate are only examples illustrating the case where the hydrogen atom in an alkyl group is replaced by F. The implementation of the substitution of the hydrogen atom in an alkyl group by the substituents defined in this application is included within the scope of protection of this application.

[0108] In some implementations, in general formula I, at least one of R1, R2, and R3 is a straight-chain structure (straight-chain alkyl). Exemplarily, the additives include, but are not limited to, tripropyl borate and tri-n-butyl borate.

[0109] In some implementations, in general formula I, at least one of R1, R2, and R3 is a branched structure (branched alkyl group). Exemplarily, the additive includes isopropyl borate, triisobutyl borate, and tri-tert-butylborate.

[0110] In some implementations, in general formula I, at least one of R1, R2, and R3 is a cyclic structure (cyclic alkyl group). For example, the additive includes borate cycloethanol pinacol ester.

[0111] It should be noted that this application is merely an example illustrating that R3 includes cyclohexyl (C6 saturated alkyl), and the above example does not constitute a specific limitation.

[0112] In some embodiments, in general formula I, two of R1, R2, and R3 are independently ring structures. In some embodiments, all three of R1, R2, and R3 are independently ring structures. Furthermore, this application only illustrates one scenario where the ring structure is not replaced; it should be noted that all implementations where the ring structure is replaced by the substituents defined in this application are included within the scope of protection of this application.

[0113] In some embodiments, in general formula I, at least one of R1, R2, and R3 comprises a substituted or unsubstituted C2-C10 unsaturated alkyl group. An example is 1,4-ditertiary propylene borate.

[0114] It should be noted that this application merely illustrates, by way of example, that R3 includes a propenyl group (C3 unsaturated alkyl group). The above example does not constitute a specific limitation. In some embodiments, both of R1, R2, and R3 are C2-C10 unsaturated alkyl groups. In some embodiments, all three of R1, R2, and R3 are C2-C10 unsaturated alkyl groups. Furthermore, this application only illustrates, by way of example, a case where the unsaturated alkyl group (propenyl group) is not substituted. It should be noted that all implementations of substituting the unsaturated alkyl group with the substituents defined in this application are included within the scope of protection of this application.

[0115] In some embodiments, in general formula I, at least one of R1, R2, and R3 comprises a phenyl group. Exemplarily, the additive includes triphenyl borate, (4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzene, 2-phenyl-1,3,2-dioxaborane heterocyclic ring, and 4-(trifluoromethoxy)phenylboronic acid pinacol ester.

[0116] It should be noted that this application only illustrates the case where the phenyl group is not substituted. It should be pointed out that all implementations in which the phenyl group is substituted with the substituents defined in this application are included within the scope of protection of this application.

[0117] In some embodiments, in general formula II, R4, R5, and R6 are independent functional groups. For example, the additive includes trimethylcyclotriboroxane.

[0118] The structural formula of trimethylcyclotriboroxane is as follows:

[0119]

[0120] This application is merely an illustrative example showing that R4, R5, and R6 are selected from methyl. The above examples do not constitute specific limitations. In some embodiments, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C2-C10 unsaturated alkyl groups, and substituted or unsubstituted phenyl groups.

[0121] In some embodiments, the additive is selected from compounds represented by general formula III. In general formula III, at least one of R7 and R8 is an independent group or forms a cyclic group together with the atoms to which it is attached.

[0122]

[0123] In this implementation, an additive molecule contains at least two B atoms, which enhances the coordination of the additive with anionic / ether solvents, thereby further improving the battery's storage performance and reducing gas production. Examples of additives include pinacol diborate and bis(2,4-dimethyl-2,4-pentanediol)borate.

[0124] In some embodiments, in general formula I, R1, R2 and the oxygen atoms to which they are attached together form cyclic groups.

[0125] In this implementation, the molecular structure of the additive includes cyclic groups, which helps to increase the steric hindrance of the additive molecules. This increased steric hindrance can effectively prevent the anions from approaching and combining with the ether solvent molecules, thereby further reducing the deposition of organic components in the SEI film, improving the stability of the SEI film, reducing the risk of SEI film rupture, and thus further improving the storage performance of the battery and further reducing the gas production of the battery.

[0126] For example, the additives include 4-(trifluoromethoxy)phenylboronic acid pinacol ester, methyl borate, (4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzene, 2-phenyl-1,3,2-dioxaborane heterocycle, propanol pinacol ester, borate cycloethanol pinacol ester, pinacol diboronic acid ester, bis(2,4-dimethyl-2,4-pentanediol) borate ester, 1-di-tert-ol propenylboronic acid ester, and 4,4,5,5-tetramethyl-2-phenylthioalkylmethyl-1,3,2-dioxaborane pentane.

[0127] In some embodiments, in general formula I, R1, R2, and the oxygen atoms to which they are attached together form five- to eight-membered cyclic groups.

[0128] Five- to eight-membered ring groups have high structural stability and are not prone to ring-opening reactions. Additives containing five- to eight-membered ring groups release a low amount of active hydrogen inside the battery, which helps to reduce the side reactions of sodium metal, thereby further improving the battery's storage performance and reducing the amount of gas produced by the battery.

[0129] In some embodiments, in general formula III, R1 and R2 together with the oxygen atoms they are attached to form five- to eight-membered cyclic groups, and R7 and R8 together with the oxygen atoms they are attached to form five- to eight-membered cyclic groups. Exemplarily, additives include, but are not limited to, pinacol diborate and bis(2,4-dimethyl-2,4-pentanediol)borate.

[0130] In some embodiments, in general formula III, R1 and R2 together with the oxygen atoms they are attached to form five- or six-membered cyclic groups, and R7 and R8 together with the oxygen atoms they are attached to form five- or six-membered cyclic groups. The ring strain of the five- or six-membered cyclic groups is relatively small, further reducing the probability of ring-opening, thereby facilitating a further reduction in the release of active hydrogen from the cyclic groups and minimizing side reactions of sodium metal.

[0131] For example, R1 and R2 together with the oxygen atoms they are attached to form five-membered ring groups, and R7 and R8 together with the oxygen atoms they are attached to form five-membered ring groups. For example, the additives include, but are not limited to, pinacol diboronate.

[0132] Exemplarily, R1 and R2 together with the oxygen atoms they are attached to form a six-membered ring group, and R7 and R8 together with the oxygen atoms they are attached to form a six-membered ring group. Exemplarily, the additives include, but are not limited to, bis(2,4-dimethyl-2,4-pentanediol)borate.

[0133] In some embodiments, in general formulas I and II, R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C3-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, and substituted or unsubstituted phenyl groups.

[0134] The aforementioned groups have significant steric hindrance. When R1 to R6 are selected from these groups, it is beneficial to further hinder the approach / combination of anions with ether solvent molecules, reduce the deposition of organic components in the SEI film, improve the stability of the SEI, reduce the risk of SEI rupture, and thus reduce the consumption of sodium ions. This is beneficial to further improve the storage performance of the battery and further reduce the gas production of the battery.

[0135] For example, the additives include, but are not limited to, tripropyl borate, isopropyl borate, tri-n-butyl borate, triisobutyl borate, tri-tert-butyl borate, trihexyl borate, trioctyl borate, tri(hexafluoroisopropyl) borate, tri(2,2,2-trifluoroethyl) borate, triphenyl borate, and (4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)benzene.

[0136] In some embodiments, in general formulas I and II, R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C3-C10 saturated alkyl groups and substituted or unsubstituted C3-C10 unsaturated alkyl groups. The aforementioned alkyl groups do not contain π bonds and have a weaker attraction for electrons. When R1 to R6 are selected from these alkyl groups, the additive is less likely to participate in redox reactions during battery charging and discharging. This helps the additive maintain its original chemical structure within the battery for a longer period, thus allowing it to continuously exert its coordination effect over a longer time, thereby improving the battery's storage performance and safety performance.

[0137] For example, the additives include, but are not limited to, tripropyl borate, isopropyl borate, tri-n-butyl borate, triisobutyl borate, tri-tert-butyl borate, trihexyl borate, trioctyl borate, tri(hexafluoroisopropyl) borate, and tri(2,2,2-trifluoroethyl) borate.

[0138] In some embodiments, in general formulas I and II, the substituents include at least one of F and thiophenyl. The inorganic atoms (F, S) contained in the aforementioned substituents can participate in the formation of the SEI film, which helps to increase the proportion of inorganic components in the SEI film, thereby improving the toughness of the SEI film and its stability during the charge and discharge process of the secondary battery. This is beneficial for further improving the battery's storage performance and further reducing the battery's gas production.

[0139] For example, the additives include, but are not limited to, tris(hexafluoroisopropyl) borate, tris(2,2,2-trifluoroethyl) borate, and 4,4,5,5,-tetramethyl-2-phenylthioalkylmethyl-1,3,2-dioxoborane.

[0140] In some embodiments, the additives include 4-(trifluoromethoxy)phenylborane pinacol ester, trimethylol borate, triethyl borate, tripropyl borate, isopropyl borate, tri-n-butyl borate, triisobutyl borate, tri-tert-butyl borate, trihexyl borate, trioctyl borate, tri(hexafluoroisopropyl) borate, tri(2,2,2-trifluoroethyl) borate, triphenyl borate, (4,4,5,5-tetramethyl-1,3-ethylhexafluoro) borate, and (4,4,5,5-tetramethyl-1,3-ethylhexafluoro) borate. At least one of the following: (2-dioxaborane-2-yl)benzene, 2-phenyl-1,3,2-dioxaborane, propanol pinacol ester, borate cycloethanol pinacol ester, pinacol diboron ester, bis(2,4-dimethyl-2,4-pentanediol)boron ester, trimethylcyclotriboroxane, 4,4,5,5,-tetramethyl-2-phenylthioalkylmethyl-1,3,2-dioxaborane, and propyl borate o-ditert-ol ester. Using the above additives is beneficial for improving the battery's storage performance and further reducing the battery's gas production.

[0141] In some embodiments, the molar concentration of the additive relative to the electrolyte is from 0.01 mol / L to 0.5 mol / L. A molar concentration within this range allows for strong coordination between the additive and the anionic / ether solvent, reducing sodium metal side reactions and improving the stability of the SEI film. This, in turn, helps to further improve the battery's storage performance and further reduce gas production. Exemplarily, the molar concentration of the additive is a value between 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, or any two of these values, but is not limited thereto. Optionally, the molar concentration of the additive is from 0.05 mol / L to 0.3 mol / L.

[0142] In some embodiments, the ether solvent includes chain ethers. Chain ethers have good solubility for sodium salts, and the selection of chain ethers helps to maintain a stable sodium ion concentration in the electrolyte, thereby contributing to an improved lifespan of the sodium metal secondary battery.

[0143] In this application, "chain ether" refers to a molecular structure in which one or more oxygen atoms connect two carbon atoms to form a COC bonding mode, and the carbon chain formed by these carbon atoms is a straight chain or branched chain structure, rather than a cyclic structure.

[0144] In some embodiments, the ether solvent also includes cyclic ethers. Cyclic ethers typically have good ion transport properties, thereby improving the ionic conductivity of the electrolyte, which in turn helps to achieve improved fast-charging performance in sodium metal secondary batteries.

[0145] In this application, "cyclic ether" refers to a molecular structure containing one or more cyclic structures formed by carbon atoms linked by oxygen atoms.

[0146] In some embodiments, the chain ether includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, and diethylene glycol dibutyl ether. By selecting the above-mentioned chain ether, it is beneficial to reduce the dissolution of the sodium metal layer, thereby reducing the gas production of the battery and improving the safety performance of the battery.

[0147] In some embodiments, the cyclic ether includes at least one selected from tetrahydrofuran, methyltetrahydrofuran, 1,3-dioxopentane, and 1,3-dioxane. By selecting the aforementioned cyclic ether, it is beneficial to reduce the dissolution of the sodium metal layer, thereby reducing the gas production of the battery and improving its safety performance.

[0148] In some embodiments, the volume ratio of the chain ether to the cyclic ether is (100-50):(0-50). This is advantageous for further balancing the solubility of the sodium salt in the ether solvent and the ionic conductivity of the electrolyte. Exemplarily, the volume ratio of the chain ether to the cyclic ether is 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, or any range of two such values, but is not limited thereto.

[0149] In some embodiments, the electrolyte further includes a sodium salt, comprising at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate. Optionally, the sodium salt comprises sodium hexafluorophosphate.

[0150] In some embodiments, the molar concentration of the sodium salt relative to the electrolyte is 0.5 mol / L to 2 mol / L. When the molar concentration of the sodium salt falls within the above concentration range, it is beneficial for the electrolyte to maintain excellent ionic conductivity (electrical conductivity), and the secondary battery using this electrolyte can achieve improved cycle life. Exemplarily, the molar concentration of the sodium salt is a value between: 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, or any two of these values, but is not limited thereto.

[0151] In some embodiments, the electrolyte may optionally include other additives. For example, additives may include those that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0152] Negative electrode sheet

[0153] The negative electrode typically includes a negative current collector and a sodium metal layer or sodium alloy layer disposed on at least one side of the negative current collector. Sodium metal layers and sodium alloys have very high theoretical specific capacity, which allows sodium metal secondary batteries to store more charge and achieve high energy density.

[0154] The sodium metal layer or sodium alloy layer can be prepared using methods known in the art. When the sodium metal layer or sodium alloy layer is formed by the deposition of sodium ions on the negative electrode current collector during the charging and discharging process of the battery, it is also called a negative electrode-free alkali metal battery.

[0155] In some implementations, the secondary battery is a sodium metal secondary battery without a negative electrode. This is advantageous for achieving high energy density.

[0156] In some embodiments, the thickness of the sodium metal layer or sodium alloy layer is 1 μm-15 μm.

[0157] In some embodiments, the negative electrode sheet further includes a conductive layer disposed between the negative electrode current collector and the sodium metal layer or sodium alloy layer.

[0158] In some implementations, the thickness of the conductive layer is 1 μm-5 μm.

[0159] The conductive layer provides a good electron transport path, thereby improving the electron transport efficiency of the negative electrode, which in turn helps to improve the charge and discharge efficiency of the battery and reduce its internal resistance. The conductive layer includes a conductive agent, which, as an example, may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0160] In some embodiments, the conductive layer further includes an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0161] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0162] Positive electrode sheet

[0163] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0164] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0165] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0166] In some embodiments, the positive electrode active material may be a known positive electrode active material for sodium metal secondary batteries. As an example, the positive electrode active material may include at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. The positive electrode active material may include, but is not limited to, NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and Na... 0.67 MO2 (M includes at least two of Fe, Co, Cr, Mn, Ni, V, Ti, and Mo), NaMO2 (M includes at least two of Fe, Co, Ni, V, Ti, and Mo), NaFePO4, NaMnPO4, NaCoPO4, Na4Fe3(PO4)2O7, Na3V2(PO4)2F3, Na3V2(PO4)3, Prussian blue, Prussian white, sodium iron pyrophosphate, and one or more of their respective modified compounds. In some embodiments, a carbon coating layer is provided on the surface of the positive electrode active material.

[0167] During the charging and discharging process of a battery, sodium (Na) undergoes insertion / extraction and consumption, resulting in varying molar Na content at different discharge states. In the examples of positive electrode active materials in this application, the molar Na content refers to the initial state of the material, i.e., before feeding. When the positive electrode active material is applied to the battery system, the molar Na content changes after charge-discharge cycles.

[0168] In the examples of positive electrode active materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0169] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0170] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0171] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0172] Separating membrane

[0173] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0174] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0175] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0176] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0177] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0178] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0179] In some implementations, refer to Figure 2The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0180] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0181] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0182] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0183] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0184] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0185] Electrical appliances

[0186] In addition, a second aspect of this application provides an electrical device, which includes the sodium metal secondary battery provided in the first aspect of this application. The sodium metal secondary battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0187] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0188] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of sodium metal secondary batteries for this device, a battery pack or battery module can be used.

[0189] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0190] Example

[0191] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0192] Example 1

[0193] Preparation of sodium metal secondary batteries

[0194] (1) Preparation of positive electrode sheet

[0195] The positive electrode slurry was obtained by stirring and dispersing sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) coated with carbon as the positive electrode active material, polyvinylidene fluoride as the binder, and conductive carbon black (Super-P) as the conductive agent in an N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1.

[0196] The positive electrode slurry was coated on both sides of an aluminum foil with a thickness of 13 μm. After drying, cold pressing, and die cutting, a positive electrode sheet with a thickness of 160 μm was obtained. The coating weight of the positive active material on the positive electrode sheet was 200 mg / 1540.25 mm. 2 .

[0197] (2) Preparation of negative electrode sheet

[0198] Conductive agent single-walled carbon nanotubes and binder sodium carboxymethyl cellulose were dispersed in an aqueous solution at a mass ratio of 1:1, wherein the mass ratio of conductive agent to water was 1:200. The conductive slurry was prepared by ultrasonic dispersion.

[0199] A conductive paste is coated onto a copper foil that serves as the negative electrode current collector, and then transferred to a vacuum drying oven for complete drying to prepare a negative electrode sheet, wherein the thickness of the conductive layer formed is 1 μm.

[0200] (3) Separating membrane

[0201] A 20μm thick polypropylene membrane was used as the separator.

[0202] (4) Preparation of electrolyte

[0203] Equal volumes of ethylene glycol dimethyl ether (DME) and 1,3-dioxane were mixed to obtain an organic solvent. Then, NaPF6 and triethyl borate were dissolved in the organic solvent, with a molar concentration of 1 mol / L for NaPF6 and a molar concentration of 1 mol / L for triethyl borate, forming an electrolyte.

[0204] (5) Preparation of sodium metal secondary batteries

[0205] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the anode and cathode for isolation. This arrangement is then wound to obtain a sodium metal secondary battery. The sodium metal secondary battery is placed in outer packaging, filled with prepared electrolyte, and then sealed, injected, formed, and vented to obtain the final sodium metal secondary battery.

[0206] Battery performance testing

[0207] (1) Storage capacity retention rate test:

[0208] The following test procedure was conducted at a test temperature of 25℃, and the test steps are as follows:

[0209] ① Charge the capacitor to 3.65V with a constant current of 0.2C, then charge it to 0.05C with a constant voltage of 3.65V. Discharge it to 1.5V with a constant current of 0.2C, and record the discharge capacity (Cd1) before storage.

[0210] ② Charge at a constant current of 0.2C to 3.65V, then charge at a constant voltage of 3.65V to a current of 0.05C.

[0211] ③ Store the battery in a 60℃ constant temperature chamber for 30 days.

[0212] ④ Charge at a constant current of 0.2C to 3.65V, then charge at a constant voltage of 3.65V to a current of 0.05C. Discharge at a constant current of 0.2C to 1.5V, and record the discharge capacity (Cd2) after storage.

[0213] The storage capacity retention rate of sodium metal secondary batteries is calculated using the following formula:

[0214] Storage capacity retention rate = Cd2 / Cd1 × 100%.

[0215] (2) Testing of the volume of gas produced during storage:

[0216] ① Before testing the capacity, the volume (V1) of the sodium metal secondary battery was tested at 25°C using the water displacement method.

[0217] ② The sodium metal secondary battery was charged to 3.65V at a constant current of 0.2C at 25℃, then charged at a constant voltage of 3.65V until the current dropped to 0.05C, and then discharged to 1.5V at a constant current of 0.2C to obtain the discharge capacity (Cd1) before storage.

[0218] ③Then the sodium metal secondary battery is charged again with a constant current of 0.2C to 3.65V, and then charged with a constant voltage of 3.65V until the current drops to 0.05C.

[0219] ④ Store the battery in a 60℃ constant temperature chamber for 30 days.

[0220] ⑤ After removing the sodium metal secondary battery, place it at 25°C and test the volume (V2) of the stored sodium metal secondary battery.

[0221] The gas production of a sodium metal secondary battery is calculated using the following formula:

[0222] Gas production = [Volume of sodium metal secondary battery after storage (V2) - Volume of sodium metal secondary battery before storage (V1)] / Capacity of sodium metal secondary battery Cd1.

[0223] Examples 2 to 12

[0224] Examples 2 to 12 were prepared using the same method as Example 1, with the only difference being that the types of additives were adjusted according to Table 1-1.

[0225] Comparative Example 1

[0226] Comparative Example 1 and Example 1 were prepared using the same method, except that no additives were added to the electrolyte.

[0227] Comparative Example 2

[0228] Comparative Example 2 and Example 1 were prepared using the same method to prepare sodium metal secondary batteries, the only difference being that the additive was triethyl phosphite, the structural formula of which can be represented by general formula IV.

[0229]

[0230] Comparative Example 3

[0231] Comparative Example 3 and Example 1 were prepared using the same method, with the only difference being that the additive was tris(trifluoroacetic acid)borane. The structural formula of tris(trifluoroacetic acid)borane is as follows;

[0232]

[0233] The battery performance of sodium metal secondary batteries prepared in Examples 2 to 12 and Comparative Examples 1 to 3 was tested in the same manner as in Example 1, and the test results are recorded in Tables 1-2.

[0234] Table 1-1

[0235]

[0236]

[0237] Table 1-2

[0238]

[0239] The data in Tables 1-1 and 1-2 show that, compared with Comparative Example 1 (no additives), Comparative Example 2 (additives do not contain B), and Comparative Example 3 (the substituents (ester groups) in the additives have high reactivity with sodium metal), the sodium metal secondary batteries of Examples 1 to 12 have improved storage performance and safety performance.

[0240] Examples 13 to 16

[0241] Examples 13 to 16 were prepared in the same manner as Example 8, with the only difference being that the molar concentration of the additives was adjusted according to Table 2.

[0242] The battery performance of the sodium metal secondary batteries prepared in Examples 13 to 16 was tested in the same manner as in Example 8, and the test results are recorded in Table 2.

[0243] Table 2

[0244]

[0245] The data in Table 2 show that sodium metal secondary batteries exhibit improved storage and safety performance when the molar concentration of the additive is between 0.01 mol / L and 0.5 mol / L. In particular, when the molar concentration of the additive is between 0.05 mol / L and 0.3 mol / L, it is beneficial to further balance the storage and safety performance of sodium metal secondary batteries.

[0246] Examples 17 to 19

[0247] Examples 17 to 19 were prepared in the same manner as Example 8, with the only difference being that the type or amount of ether solvent was adjusted according to Table 3.

[0248] The battery performance of the sodium metal secondary batteries prepared in Examples 17 to 19 was tested in the same manner as in Example 8, and the test results are recorded in Table 3.

[0249] Table 3

[0250]

[0251] The data in Table 3 shows that sodium metal secondary batteries exhibit improved storage and safety performance when the ether solvent includes chain ethers, or when the ether solvent includes both chain ethers and cyclic ethers.

[0252] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, without departing from the spirit of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this application.

Claims

1. A sodium metal secondary battery, characterized in that, Including electrolyte, The electrolyte comprises an ether solvent and an additive, wherein the additive is selected from compounds represented by general formula I and / or general formula II: A is selected from *-R or *-R3; R is selected from *-O-R3, *-CH2-R3, *-CH(R3)2, *-C(R3)2 or *-B(OR3)2; At least one of R1, R2, and R3 is an independent radical or forms a cyclic radical together with the atoms to which it is attached; R4, R5, and R6 are independent radicals. R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C2-C10 unsaturated alkyl groups, and substituted or unsubstituted phenyl groups; substituents include F, thiophenyl, oxophenyl, etc. At least one of them.

2. The sodium metal secondary battery according to claim 1, characterized in that, The additive is selected from compounds represented by general formula III: Among them, at least one of R7 and R8 is an independent group or forms a cyclic group together with the atoms it is attached to.

3. The sodium metal secondary battery according to claim 1 or 2, characterized in that, In the general formula I, R1, R2 and the oxygen atoms they are attached to together form cyclic groups.

4. The sodium metal secondary battery according to any one of claims 1 to 3, characterized in that, In the general formula I, R1, R2, and the oxygen atoms they are attached to together form five- to eight-membered cyclic groups.

5. The sodium metal secondary battery according to any one of claims 1 to 4, characterized in that, In the general formula I, R1, R2, and the oxygen atoms they are attached to together form five- or six-membered cyclic groups.

6. The sodium metal secondary battery according to any one of claims 1 to 5, characterized in that, In both general formula I and general formula II, R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C3-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, and substituted or unsubstituted phenyl groups.

7. The sodium metal secondary battery according to any one of claims 1 to 6, characterized in that, In both general formula I and general formula II, R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of substituted or unsubstituted C3-C10 saturated alkyl groups and substituted or unsubstituted C3-C10 unsaturated alkyl groups.

8. The sodium metal secondary battery according to any one of claims 1 to 7, characterized in that, In both general formulas I and II, the substituents include at least one of F and thiophenyl.

9. The sodium metal secondary battery according to claim 1, characterized in that, The additives include 4-(trifluoromethoxy)phenylborane pinacol ester, trimethylol borate, triethyl borate, tripropyl borate, isopropyl borate, tri-n-butyl borate, triisobutyl borate, tri-tert-butyl borate, trihexyl borate, trioctyl borate, tri(hexafluoroisopropyl) borate, tri(2,2,2-trifluoroethyl) borate, triphenyl borate, and (4,4,5,5-tetramethyl-1,3,2-diphenyl)-2-diphenyl borate. At least one of the following: oxaborane-2-yl)benzene, 2-phenyl-1,3,2-dioxoborane, propanol pinacol ester, borate cycloethanol pinacol ester, pinacol diboron ester, bis(2,4-dimethyl-2,4-pentanediol)boron ester, trimethylcyclotriboroxane, 4,4,5,5,-tetramethyl-2-phenylthioalkylmethyl-1,3,2-dioxoboronylcyclohexane, and 0.5-ditert-diol ester of propenylboronate.

10. The sodium metal secondary battery according to any one of claims 1 to 9, characterized in that, The molar concentration of the additive relative to the electrolyte is from 0.01 mol / L to 0.5 mol / L.

11. The sodium metal secondary battery according to any one of claims 1 to 10, characterized in that, The molar concentration of the additive relative to the electrolyte is from 0.05 mol / L to 0.3 mol / L.

12. The sodium metal secondary battery according to any one of claims 1 to 11, characterized in that, The ether solvents include chain ethers.

13. The sodium metal secondary battery according to claim 12, characterized in that, The ether solvents also include cyclic ethers.

14. The sodium metal secondary battery according to claim 13, characterized in that, The chain ether comprises at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, and diethylene glycol dibutyl ether, and / or, The cyclic ethers include at least one of tetrahydrofuran, methyltetrahydrofuran, 1,3-dioxopentane, and 1,3-dioxane.

15. The sodium metal secondary battery according to claim 13 or 14, characterized in that, The volume ratio of chain ethers to cyclic ethers is (100-50):(0-50).

16. The sodium metal secondary battery according to any one of claims 1 to 15, characterized in that, The electrolyte also includes a sodium salt, wherein the molar concentration of the sodium salt is 0.5 mol / L to 2 mol / L relative to the electrolyte.

17. The sodium metal secondary battery according to any one of claims 1 to 16, characterized in that, It also includes a negative electrode sheet, which includes a negative current collector and a sodium metal layer or sodium alloy layer disposed on at least one side of the negative current collector.

18. The sodium metal secondary battery according to claim 17, characterized in that, The thickness of the sodium metal layer or sodium alloy layer is 1μm-15μm.

19. The sodium metal secondary battery according to claim 17 or 18, characterized in that, The negative electrode also includes a conductive layer, which is disposed between the current collector and the sodium metal layer or sodium alloy layer.

20. The sodium metal secondary battery according to claim 19, characterized in that, The thickness of the conductive layer is 1μm-5μm.

21. The sodium metal secondary battery according to any one of claims 1 to 20, characterized in that, It also includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on the positive current collector, wherein the positive electrode film layer includes at least one of sodium transition metal oxide, polyanionic compound, and Prussian blue compound.

22. The sodium metal secondary battery according to any one of claims 1 to 21, characterized in that, The secondary battery is a sodium metal secondary battery without a negative electrode.

23. An electrical appliance, characterized in that, The sodium metal secondary battery includes any one of claims 1 to 22.

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