Sodium secondary battery and electric device

Abstract

Disclosed in the present application are a sodium secondary battery and an electric device. The sodium secondary battery comprises: a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, and the positive electrode active material comprising a polyanionic positive electrode active material; a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector, and sodium metal being formed by means of in situ deposition on the negative electrode current collector upon charging of the sodium secondary battery; a separator, the separator being located between the positive electrode sheet and the negative electrode sheet; and an electrolyte, the electrolyte comprising a solvent, the solvent comprising an ether solvent, and the volume proportion of the ether solvent being 50-100% on the basis of the total volume of the electrolyte. Therefore, the reaction degree of a sodium metal layer on a negative electrode is reduced during the cycling process, thereby improving the safety of the battery.

Description

Sodium secondary batteries and electrical equipment Technical Field

[0001] This application relates to the field of batteries, specifically to sodium secondary batteries and electrical equipment. Background Technology

[0002] Secondary batteries are not only used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. Using metallic sodium as the negative electrode can increase the energy density of secondary batteries (sodium has a high theoretical capacity); however, the reactions during battery cycling are more vigorous, which can reduce battery safety. Summary of the Invention

[0003] The first aspect of this application provides a sodium secondary battery, comprising a positive electrode sheet including a positive active material, the positive active material including a polyanionic positive active material; a negative electrode sheet including a negative current collector, wherein metallic sodium is deposited in situ on the negative current collector during charging; a separator membrane located between the positive and negative electrode sheets; and an electrolyte comprising a solvent, the solvent including an ether solvent, the ether solvent including a first ether solvent and a second ether solvent, wherein the first ether solvent has 2-4 carbon atoms, and the second ether solvent includes R1-(O-R3). n -O-R2, wherein R1 and R2 each independently comprise a straight-chain or branched alkyl group having 1-6 carbon atoms, and R3 comprises a straight-chain or branched alkylene group having 1-5 carbon atoms, where 1 ≤ n ≤ 5. Based on the total volume of the electrolyte, the volume percentage of the ether solvent is 50%-100%. Therefore, while increasing the energy density of the sodium secondary battery, it reduces side reactions in the sodium metal layer of the negative electrode during cycling, lowers the degree of reaction at the negative electrode, and improves battery safety.

[0004] According to some embodiments of this application, the volume percentage of the ether solvent is 80%-100% based on the total volume of the electrolyte. This reduces the specific surface area of ​​the sodium metal layer at the negative electrode, decreases the reactivity of the sodium metal layer, and improves the safety of the secondary battery.

[0005] According to some embodiments of this application, based on the total volume of the electrolyte, the volume percentages of the first ether solvent and the second ether solvent are independently 20%-80%. This reduces the specific surface area of ​​the sodium metal layer at the negative electrode while improving the stability of the electrolyte and decreasing the probability of a reaction between the electrolyte and the negative electrode metal layer.

[0006] According to some embodiments of this application, the first ether solvent includes ethylene glycol dimethyl ether; and / or the second ether solvent includes one or more of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, pentaethylene glycol diethyl ether, or ethylene glycol dibutyl ether. Thus, long-chain ether solvents can improve the stability of the electrolyte, reduce the probability of the electrolyte reacting with the negative electrode, and improve the interfacial stability of the negative electrode.

[0007] According to some embodiments of this application, the polyanionic positive electrode active material includes Na x M y1 N y2 (X a O b ) z Z w Wherein, M includes one or more of Ti, V, Cr, Mn, Fe, Ca, Mg, Al, Nb, Co, and Zr; N includes Ni; X includes one or more of Si, S, P, As, B, Mo, W, and Ge; Z includes one or more of F, O, and OH; 2≤x≤7, 1≤y1≤4, 0≤y2≤0.05, 0.2≤a / b≤0.3, 1≤z≤4, and 0≤w≤3. This reduces oxygen release from the positive electrode active material and the dissolution of transition metals, lowering the probability of ether solvent decomposition.

[0008] According to some embodiments of this application, the polyanionic positive electrode active material includes one or more of Na4Fe3(PO4)2(P2O7), Na3V2(PO4)3, and Na3V2(PO4)2F3. This reduces oxygen release and transition metal dissolution from the positive electrode active material, and lowers the probability of ether solvent decomposition.

[0009] According to some embodiments of this application, the compaction density of the positive electrode sheet is greater than or equal to 1.8 g / cm³. 3 This reduces the contact between the electrolyte and the positive electrode active material, lowering the probability of transition metal dissolution catalyzing the decomposition of ether solvents in the positive electrode active material.

[0010] According to some embodiments of this application, the compaction density of the positive electrode sheet is 1.9 g / cm³. 3 -2.2g / cm 3 This further reduces the contact between the electrolyte and the positive electrode active material, lowering the probability of transition metal dissolution catalyzing the decomposition of ether solvents in the positive electrode active material.

[0011] The second aspect of this application provides an electrical device, including the sodium secondary battery provided in the first aspect of this application.

[0012] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0013] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0014] Figure 1 is a schematic diagram of a sodium secondary battery according to an embodiment of this application.

[0015] Figure 2 is an exploded view of a sodium secondary battery according to an embodiment of this application, as shown in Figure 1.

[0016] Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

[0017] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0018] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0019] Figure 6 is a schematic diagram of an electrical device using a sodium secondary battery as a power source according to an embodiment of this application.

[0020] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Sodium secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0021] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0025] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates 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.

[0026] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing.

[0027] Electrodeless sodium batteries use metallic sodium as the negative electrode active material, offering advantages such as high energy density, but also posing certain safety risks. The type of electrolyte solvent in electrodeless sodium batteries affects the morphology of the deposited sodium metal layer. When the electrolyte solvent is an ester-based solvent, the specific surface area of ​​the sodium metal in the formed metal layer is larger, resulting in a porous sodium metal layer. This leads to more vigorous reactions during cycling, reducing battery safety.

[0028] The sodium secondary battery proposed in this application uses an ether-based solvent as the electrolyte. After charging, the sodium metal in the metal layer formed on the negative electrode current collector has a smaller specific surface area, reducing the degree of reaction at the negative electrode during cycling and thus improving the safety of the sodium secondary battery. Simultaneously, the positive electrode active material uses a polyanionic positive electrode active material, which can reduce the probability of oxygen release or transition metal dissolution catalyzing the decomposition of the ether solvent, thereby improving the stability of the electrolyte.

[0029] The sodium secondary battery proposed in this application can be used in electrical devices that use sodium secondary batteries as a power source or in various energy storage systems that use sodium secondary batteries as energy storage elements. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0030] This application provides a sodium secondary battery, comprising a positive electrode sheet including a positive active material, the positive active material including a polyanionic positive active material; a negative electrode sheet including a negative current collector, wherein metallic sodium is deposited in situ on the negative current collector during charging; a separator membrane located between the positive and negative electrode sheets; and an electrolyte comprising a solvent, the solvent including an ether solvent, the ether solvent including a first ether solvent and a second ether solvent, wherein the first ether solvent has 2-4 carbon atoms, and the second ether solvent includes R1-(O-R3). n -O-R2, wherein R1 and R2 each independently comprise a straight-chain or branched alkyl group having 1-6 carbon atoms, and R3 comprises a straight-chain or branched alkylene group having 1-5 carbon atoms, 1≤n≤5, and the volume percentage of the ether solvent is 50%-100% based on the total volume of the electrolyte.

[0031] The sodium secondary battery proposed in this application improves the safety of the secondary battery by increasing the content of ether solvents in the electrolyte. Ether solvents have good reduction resistance and better compatibility with sodium metal. By increasing the content of ether solvents, the specific surface area of ​​sodium metal in the negative electrode metal layer is reduced, which can reduce the degree of reaction of the negative electrode during cycling. The ether solvents include both short-chain and long-chain ethers. Short-chain ethylene glycol dimethyl ether can reduce the specific surface area of ​​the sodium metal layer of the negative electrode while increasing the transport rate of sodium ions in the electrolyte. Long-chain ethers have a certain degree of chemical inertness, which can improve the stability of the electrolyte, reduce the probability of electrolyte reaction with the negative electrode, improve the interfacial stability of the negative electrode, and thus improve the cycle performance of the sodium secondary battery. At the same time, the positive electrode uses a polyanionic positive electrode active material, which reduces the probability of ether solvent decomposition caused by oxygen release and transition metal dissolution, and improves the stability of the electrolyte.

[0032] As an example, a sodium secondary battery can be a sodium secondary battery without a negative electrode. A sodium secondary battery without a negative electrode means that no negative electrode active material layer is set on the negative electrode plate. Instead, a metal layer is formed on the negative electrode current collector as the negative electrode active material layer through the charging of the secondary battery.

[0033] In this application, the test method for the content of ether solvents is as follows: quantitative analysis of organic components in the electrolyte is performed by gas chromatography, referring to the standard GB / T 9722-2006.

[0034] As an example, the volume percentage of the ether solvent can be 50%, 60%, 70%, 80%, 82%, 84%, 86%, 88%, or 90%, or a range of any of the above values.

[0035] According to some specific embodiments of this application, the volume percentage of the ether solvent is 80%-100% based on the total volume of the electrolyte. This increases the content of the ether solvent in the electrolyte, further reducing the specific surface area of ​​sodium metal in the negative electrode metal layer, decreasing the degree of reaction at the negative electrode, and improving the safety of the secondary battery.

[0036] As an example, the first ether solvent includes dimethyl ethylene glycol (DME).

[0037] As an example, the second ether solvent may include one or more of diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether (TEGDME), pentaethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, pentaethylene glycol diethyl ether, or ethylene glycol dibutyl ether.

[0038] According to some embodiments of this application, the volume percentage of the first ether solvent and the volume percentage of the second ether solvent in the electrolyte are the same.

[0039] According to some embodiments of this application, when the electrolyte simultaneously contains a first ether solvent and a second ether solvent, the volume percentage of the first ether solvent is 20%-80% and the volume percentage of the second ether solvent is 20%-80% based on the total volume of the electrolyte. For example, when the volume percentage of the first ether solvent is 20%, the volume percentage of the second ether solvent is 80%; when the volume percentage of the first ether solvent is 80%, the volume percentage of the second ether solvent is 20%; when the volume percentage of the first ether solvent is 40%, the volume percentage of the second ether solvent is 60%.

[0040] As an example, the volume percentage of the first ether solvent can be 20%, 30%, 40%, 50%, 60%, 70%, or 80%, or a range of any of the above values.

[0041] As an example, the volume percentage of the second ether solvent can be 20%, 30%, 40%, 50%, 60%, 70%, or 80%, or a range of any of the above values.

[0042] According to some embodiments of this application, when the electrolyte contains both a first ether solvent and a second ether solvent, the electrolyte may also contain other solvents. For example, based on the total volume of the electrolyte, the volume percentage of the first ether solvent is 40%, the volume percentage of the second ether solvent is 40%, the volume percentage of propylene carbonate (PC) is 10%, and the volume percentage of fluoroethylene carbonate (FEC) is 10%.

[0043] According to some embodiments of this application, the polyanionic positive electrode active material includes Na xM y1 N y2 (X a O b ) z Z w Wherein, M includes one or more of Ti, V, Cr, Mn, Fe, Ca, Mg, Al, Nb, Co, and Zr, N includes Ni, X includes one or more of Si, S, P, As, B, Mo, W, and Ge, Z includes one or more of F, O, and OH, 2≤x≤7, 1≤y1≤4, 0≤y2≤0.05, 0.2≤a / b≤0.3, 1≤z≤4, and 0≤w≤3.

[0044] As an example, polyanionic cathode active materials may include one or more of Na4Fe3(PO4)2(P2O7)(NFPP), Na3V2(PO4)3, and Na3V2(PO4)2F3.

[0045] Therefore, selecting the above-mentioned positive electrode active materials can reduce the probability of ether solvent decomposition caused by oxygen release and transition metal dissolution, and improve the stability of the electrolyte.

[0046] According to some embodiments of this application, the compaction density of the positive electrode sheet is greater than or equal to 1.8 g / cm³. 3 For example, it could be 1.8 g / cm³. 3 1.9g / cm 3 2g / cm 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 Or 2.4g / cm 3 The values ​​can be any range of the aforementioned values. This increases the compaction density of the positive electrode sheet, reduces its porosity, decreases the contact between the electrolyte and the positive electrode active material, and lowers the probability of transition metal dissolution catalyzing the decomposition of ether solvents in the positive electrode active material. According to some specific embodiments of this application, the compaction density of the positive electrode sheet can be 1.9 g / cm³. 3 -2.2g / cm 3 .

[0047] In this application, the compaction density of the positive electrode sheet is determined by measuring the mass of the positive electrode sheet per unit area (g / cm³). 2 The compaction density PD of the positive electrode sheet is determined by the positive electrode sheet thickness (cm) (number of sampling points > 14). The compaction density PD of the positive electrode sheet is equal to the mass of the positive electrode sheet per unit area (g / cm³). 2 ) / Thickness of positive electrode (cm).

[0048] Typically, a sodium secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0049] [Positive electrode plate]

[0050] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes the positive active material.

[0051] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0052] 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.).

[0053] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0054] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0055] 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.

[0056] [Negative electrode plate]

[0057] 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.

[0058] [Electrolytes]

[0059] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0060] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0061] In some embodiments of this application, the electrolyte sodium salt may include at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, or sodium bis(trifluoromethanesulfonyl)imide.

[0062] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives 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.

[0063] [Isolation membrane]

[0064] In some embodiments, the battery 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.

[0065] In some embodiments, the material of the separator can be selected from one or more 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.

[0066] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0067] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0068] In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0069] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured sodium secondary battery 5 as an example.

[0070] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can 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 sodium secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0071] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module 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 module.

[0072] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple sodium secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple sodium secondary batteries 5 can be fixed in place using fasteners.

[0073] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of sodium secondary batteries 5 are received.

[0074] 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.

[0075] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 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 box 2 and a lower box 3, with the upper box 2 covering the lower box 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.

[0076] In addition, this application also provides an electrical device, which includes one or more of the sodium secondary battery, battery module, or battery pack provided in this application. The sodium secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for 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.

[0077] As the electrical equipment, sodium secondary batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0078] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0079] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use sodium-ion batteries as their power source.

[0080] 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 this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0081] Example 1

[0082] 1. Preparation of positive electrode sheet

[0083] The positive electrode active material Na4Fe3(PO4)2(P2O7) (NFPP), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone (NMP) solvent system at a weight ratio of 95:2.5:2.5 to obtain a positive electrode slurry. This slurry was then uniformly coated onto both surfaces of the positive electrode current collector aluminum foil. After drying, cold pressing, and slitting, the positive electrode sheet was obtained, with a compaction density of 2.0 g / cm³. 3 .

[0084] 2. Preparation of negative electrode sheet

[0085] Carbon nanotubes and sodium carboxymethyl cellulose were thoroughly mixed in deionized water at a weight ratio of 50:50 to form a porous slurry. This porous slurry was then coated onto the surface of a copper foil used as the negative electrode current collector, with a coating thickness of 5 μm. After coating, the material was dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0086] 3. Preparation of electrolyte

[0087] NaPF6 was dissolved in a mixed solvent of DME, DEGDME, PC, and FEC to prepare an electrolyte with a concentration of 1 mol / L. Based on the total volume of the electrolyte, the volume percentages of DME, DEGDME, PC, and FEC were 25%.

[0088] 4. Separating membrane

[0089] Polyethylene film.

[0090] 5. Preparation of a sodium metal battery without a negative electrode

[0091] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell, which is placed in a casing, dried, and then injected with electrolyte. After formation and settling processes, a sodium metal battery without a negative electrode is obtained.

[0092] The preparation methods of sodium secondary batteries in Examples 2-11, Comparative Examples 1 and 2 are the same as those in Example 1, with the differences detailed in Table 1.

[0093] Table 1

[0094] Performance testing

[0095] First comparison of coulomb efficiency:

[0096] After assembling the battery and letting it stand for 10 hours at 25°C, the first charge-discharge test was conducted. First, the secondary battery was charged to 3.65V with a constant current of 0.33C. Then, it was charged to a current of 0.05C with a constant voltage of 3.65V, and the charging capacity was recorded as C1. Next, it was discharged to the lower cutoff voltage (1.5V in this invention) with a constant current of 0.33C, and the charging capacity was recorded as C2. The initial stock efficiency FCE = C2 / C1 × 100%.

[0097] The specific capacity data corresponding to the charging and discharging steps can be extracted and read (if only the capacity value can be read, the capacity needs to be divided by the mass of the corresponding positive electrode active material that provides all the activity).

[0098] Security test

[0099] In this application, the safety capability is demonstrated by comparing the heat release through differential scanning calorimetry (DSC) testing of the electrode layers at the fully charged negative electrode of the battery.

[0100] The DSC exothermic peak value of a unit mass fully charged negative electrode sheet under nitrogen atmosphere at 50℃~500℃ can be determined using methods known in the art. As an example, the measurement can be performed with reference to the national standard document GB / T 13464-2008, where:

[0101] 1) Test conditions: Test equipment model: NETZSCH STA 449F3; Sample: The positive electrode sheet is punched into a small circular sheet with a diameter of 5mm (including the current collector, the mass of the current collector needs to be deducted when calculating the heat release per unit mass) and 2μL of electrolyte is dropped onto the electrode sheet; Test start temperature: room temperature; Heating rate: 10K / min; Test atmosphere: nitrogen; Sample preparation environment: glove box sample preparation;

[0102] 2) Post-test data standardization: In the DSC test results, the vertical axis represents heat flux in mW / mg, and the horizontal axis represents temperature in °C. The baseline for the empty crucible test results needs to be subtracted from the test data; the range from 50 °C to the final temperature is adjusted horizontally. Through fitting calculations, the DSC exothermic peaks of the test sample in a nitrogen atmosphere within the range of 50 °C to 500 °C, and the heat percentage corresponding to the first exothermic peak, are obtained.

[0103] The test results of sodium secondary batteries in Examples 1-11, Comparative Example 1, and Comparative Example 2 are shown in Table 2.

[0104] Table 2

[0105] Conclusion: Comparing Examples 1-11 with Comparative Examples 1 and 2, it can be seen that the initial coulombic efficiency of the sodium secondary batteries in Examples 1-11 is higher than that in Comparative Examples 1 and 2. The thermal decomposition temperature of the negative electrode in Examples 1-11 is higher than that in Comparative Examples 1 and 2, and the heat ratio during the first thermal decomposition is lower than that in Comparative Examples 1 and 2. This indicates that by using mixed ether solvents with different molecular chain lengths, this application can improve the initial coulombic efficiency and safety performance of sodium secondary batteries.

[0106] As can be seen from the comparison of Examples 1-5, the first coulombic efficiency and safety performance of the battery can be improved by adjusting the volume ratio of ether solvents in the electrolyte.

[0107] As can be seen from the comparison of Examples 5, 7 and 8, the first coulombic efficiency and safety performance of the battery can be improved by adjusting the compaction density of the positive electrode sheet.

[0108] As can be seen from the comparison of Examples 5, 9 and 10, the first coulombic efficiency and safety performance of the battery can be improved by adjusting the volume ratio of the first ether solvent and the second ether solvent in the electrolyte.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium secondary battery, wherein, Comprising: a positive electrode tab comprising a positive electrode active material, the positive electrode active material comprising a polyanion-based positive electrode active material; a negative electrode tab comprising a negative electrode current collector, the sodium secondary battery depositing metallic sodium in situ on the negative electrode current collector upon charging; a separator film between the positive electrode tab and the negative electrode tab; An electrolyte solution, the electrolyte solution including a solvent, the solvent including an ether-based solvent, the ether-based solvent including a first ether-based solvent and a second ether-based solvent, the first ether-based solvent including 2-4 carbon atoms, the second ether-based solvent including R1-(O-R3) n -O-R2, wherein R1 and R2 each independently include a linear or branched alkyl group having 1-6 carbon atoms, R3 includes a linear or branched alkylene group having 1-5 carbon atoms, 1≤n≤5, and the volume ratio of the ether-based solvent is 50-100% based on the total volume of the electrolyte solution.

2. The sodium secondary battery according to claim 1, wherein a volume percentage of the ether-based solvent is 80-100% based on a total volume of the electrolyte.

3. The sodium secondary battery according to claim 1 or 2, wherein, a volume percentage of the first ether-based solvent and the second ether-based solvent is independently 20-80% based on a total volume of the electrolyte.

4. The sodium secondary battery according to any one of claims 1 to 3, wherein the first ether-based solvent comprises ethylene glycol dimethyl ether; and / or the second ether-based solvent comprises one or more of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, pentaethylene glycol diethyl ether, ethylene glycol dibutyl ether.

5. The sodium secondary battery according to any one of claims 1 to 4, wherein The polyanion-based positive electrode active material includes Na x M y1 N y2 (X a O b ) z Z w , wherein M includes one or more of Ti, V, Cr, Mn, Fe, Ca, Mg, Al, Nb, Co, Zr, N includes Ni, X includes one or more of Si, S, P, As, B, Mo, W, Ge, Z includes one or more of F, O, OH, 2≤x≤7, 1≤y1≤4, 0≤y2≤0.05, 0.2≤a / b≤0.3, 1≤z≤4, 0≤w≤3.

6. The sodium secondary battery according to claim 5, wherein the polyanion-based positive electrode active material comprises one or more of Na4Fe3(PO4)2(P2O7), Na3V2(PO4)3, Na3V2(PO4)2F3.

7. The sodium secondary battery according to any one of claims 1 to 6, wherein The positive electrode plate has a compacted density greater than or equal to 1.8 g / cm 3 .

8. The sodium secondary battery according to any one of claims 1 to 7, wherein The compacted density of the positive electrode plate is 1.9 g / cm 3 - 2.2 g / cm 3 .

9. An electrical device, comprising: The sodium secondary battery of any one of claims 1-8.

Images