Secondary battery and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a secondary battery and a power utilization device, and the secondary battery comprises a positive pole piece, a negative pole piece and electrolyte; the electrolyte comprises electrolyte salt and a salt additive; the electrolyte salt comprises sodium hexafluorophosphate and sodium tetrafluoroborate; the salt additive comprises sodium trifluoroacetate and / or sodium nitrate. The secondary battery disclosed by the invention is excellent in cycle performance under high voltage.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a secondary battery and an electrical device. Background Technology

[0002] Secondary batteries, such as sodium secondary batteries, have broad application prospects due to their excellent performance. However, in actual use, especially under high voltage, the electrolyte's poor electrochemical stability can cause a decline in the cycle performance of secondary batteries.

[0003] Therefore, it is crucial to develop a secondary battery that can overcome the above-mentioned defects. Summary of the Invention

[0004] In view of the above problems, this application provides a secondary battery and an electrical device, wherein the secondary battery has excellent cycle performance under high voltage.

[0005] In a first aspect, this application provides a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte;

[0006] The electrolyte includes electrolyte salts and salt additives;

[0007] The electrolyte salts include sodium hexafluorophosphate (NaPF6) and sodium tetrafluoroborate (NaBF4);

[0008] The salt additives include sodium trifluoroacetate (NaTFA) and / or sodium nitrate (NaNO3).

[0009] In the technical solution of this application, sodium hexafluorophosphate and sodium tetrafluoroborate are used together in the electrolyte salt, and the resulting electrolyte has good electrochemical stability under high voltage, which makes the secondary battery have excellent cycle performance. At the same time, sodium trifluoroacetate and / or sodium nitrate, as salt additives, can adjust the solvation configuration of the electrolyte, making it more electrochemically stable under high voltage, and further improving the cycle performance of the secondary battery.

[0010] Specifically, among electrolyte salts, sodium hexafluorophosphate exhibits excellent overall performance in terms of ionic conductivity and electrolyte viscosity, but it has certain limitations in electrochemical stability under high voltage; while sodium tetrafluoroborate contains BF4... - Anions can participate in Na+ +The solvation layer forms a boron-containing positive electrolyte interphase (CEI) film and a solid electrolyte interphase (SEI) film at the interface between the positive and negative electrodes. The SEI film can effectively suppress the formation of dead sodium and sodium dendrites, and improve the reversibility of sodium deposition and stripping processes. The CEI film can protect the structural integrity of the positive electrode and hinder the dissolution of transition metal ions. Therefore, the combined use of sodium hexafluorophosphate and sodium tetrafluoroborate improves the cycle performance of the secondary battery under high voltage.

[0011] Furthermore, among salt additives, TFA - and NO3 - with Na + It has strong binding ability and can more easily enter Na+ in the electrolyte. + Solvated inner layer, and TFA - and NO3 - Oxidation and reduction reactions can preferentially occur on the surfaces of the positive and negative electrodes, which is conducive to the formation of anion-derived inorganic-rich positive and negative electrode interfaces, thereby accelerating the oxidation of Na. + The interfacial reaction kinetics. In addition, TFA... - and NO3 - When used in conjunction with other electrolytes, TFA can be effective in the presence of water molecules. - It can also preferentially bind to and inhibit NO3. - Hydrolysis reduces the generation of harmful gases such as hydrofluoric acid, thus improving the water resistance of the electrolyte. Furthermore, compared to other anions, the optimized electrolyte contains less NO3-. - It exhibits a faster voltage response, accumulates at the positive electrode during charging, and simultaneously reacts with Na in this region. + The good coordination greatly improves the oxidation stability of the electrolyte; therefore, the salt additive further improves the cycle performance of the secondary battery under high voltage.

[0012] In summary, this application utilizes the electrolyte salt and salt additives in combination to improve the cycle performance of secondary batteries under high voltage, and can also improve the high-temperature storage performance of secondary batteries and reduce gas production to a certain extent.

[0013] In some embodiments, the molar concentration ratio of sodium hexafluorophosphate to sodium tetrafluoroborate is 1:(0.01-0.3).

[0014] In the technical solution of this application, the electrolyte salt is mainly sodium hexafluorophosphate, combined with sodium tetrafluoroborate, which is suitable for sodium secondary batteries, especially negative electrode-free sodium metal secondary batteries. Specifically, the electrolyte salt has good compatibility with sodium metal and good solubility in the electrolyte, which can increase the concentration of the electrolyte and reduce uncoordinated free solvents, thereby increasing the potential window of the electrolyte and enabling the negative electrode-free sodium metal secondary battery to have excellent cycle performance.

[0015] In some embodiments, the molar concentration ratio of the sodium hexafluorophosphate to the salt additive is 1:(0.001-0.04).

[0016] In the technical solution of this application, the molar concentration ratio of the salt additive to sodium hexafluorophosphate is within the above-mentioned range, which is suitable for sodium secondary batteries, especially sodium metal secondary batteries without a negative electrode. Specifically, the salt additive within the above range can simultaneously improve the reaction kinetics of the secondary battery and the high-voltage stability of the electrolyte. The secondary battery forms a stable CEI film and SEI film at the interface of the positive electrode and the negative electrode, which improves the solvation structure of the electrolyte and enhances the cycle performance of the secondary battery. It can also reduce the continuous consumption of sodium metal and reduce the side reactions of the electrolyte. Therefore, the formed secondary battery has excellent storage performance and gas generation performance in addition to excellent cycle performance.

[0017] In some embodiments, the molar concentration ratio of sodium trifluoroacetate to sodium nitrate is 1:(0.1-10).

[0018] In the technical solution of this application, the molar concentration ratio of sodium trifluoroacetate and sodium nitrate is within the above-mentioned range, which is beneficial to further improve the cycle performance, storage performance and gas generation performance of the secondary battery.

[0019] In some embodiments, the electrolyte further includes ether solvents.

[0020] In the technical solution of this application, the ether solvent has good compatibility with sodium metal and good solubility for electrolyte salts and salt additives. The resulting electrolyte can form a uniform, stable, and highly protective CEI film and SEI film at the interface of the positive and negative electrodes. Combined with the electrolyte salts and salt additives described in this application, the irreversible consumption of sodium metal in the electrolyte can be reduced, the high-voltage stability of the electrolyte can be improved, and the resulting secondary battery has excellent high-voltage cycle performance.

[0021] In some embodiments, the ether solvent includes linear ethers and / or cyclic ethers; and / or;

[0022] The ether solvents include linear ethers and cyclic ethers in a volume ratio of (50-85):(15-50).

[0023] In the technical solution of this application, linear ethers are used as the main component, which can achieve full dissolution of electrolyte salts. Combined with cyclic ethers, the stability of the electrolyte can be improved, so that the secondary battery has excellent cycle performance, storage performance and gas generation performance.

[0024] In some embodiments, the linear ether comprises any one or a combination of at least two of ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), ethylene glycol dibutyl ether (DBE), diethylene glycol dimethyl ether (DEGDME), tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol diethyl ether (DEGDEE), and diethylene glycol dibutyl ether (DEGDBE); and / or;

[0025] The cyclic ether includes any one or a combination of at least two of tetrahydrofuran (THF), methyltetrahydrofuran (MeTHF), or dioxane.

[0026] In the technical solution of this application, the electrolyte formed by the combined use of linear ether and cyclic ether has better stability, which is beneficial to improving the cycle performance of the secondary battery.

[0027] In some embodiments, 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; and / or;

[0028] The positive electrode film layer includes a positive electrode active material; and / or;

[0029] The positive electrode active material includes layered oxides and / or polyanionic phosphates.

[0030] In the technical solution of this application, the positive electrode active material within the above-mentioned range can better cooperate with the electrolyte to form a high-performance secondary battery, especially a sodium metal secondary battery without a negative electrode.

[0031] In some embodiments, the secondary battery includes any one of a sodium metal secondary battery, a sodium-air secondary battery, or a sodium-sulfur secondary battery; and / or;

[0032] The sodium metal secondary battery includes a sodium metal secondary battery without a negative electrode.

[0033] Secondly, this application provides an electrical device, which includes the secondary battery described in the first aspect.

[0034] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Detailed Implementation

[0035] The embodiments of the technical solution of this application will be 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.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0037] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0038] 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.

[0039] 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 also 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 "2-10" indicates that all real numbers between "2-10" have been listed in this article; "2-10" 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.

[0040] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0041] Existing secondary batteries, especially sodium secondary batteries, suffer from poor electrochemical stability in their electrolytes during actual use, particularly under high voltage, leading to a decline in battery cycle performance.

[0042] This application provides a secondary battery and an electrical device, wherein the secondary battery exhibits excellent cycle performance under high voltage.

[0043] [Rechargeable Battery]

[0044] This application provides a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte.

[0045] The electrolyte includes electrolyte salts and salt additives;

[0046] The electrolyte salts include sodium hexafluorophosphate (NaPF6) and sodium tetrafluoroborate (NaBF4);

[0047] The salt additives include sodium trifluoroacetate (NaTFA) and / or sodium nitrate (NaNO3).

[0048] In the technical solution of this application embodiment, sodium hexafluorophosphate and sodium tetrafluoroborate are used together in the electrolyte salt, and the resulting electrolyte has good electrochemical stability under high voltage, giving the secondary battery excellent cycle performance. At the same time, sodium trifluoroacetate and / or sodium nitrate are used as salt additives in conjunction with the electrolyte salt, which can adjust the solvation configuration of the electrolyte, making it more electrochemically stable under high voltage (e.g., ≥4V, such as 4V, 4.2V, etc.), further improving the cycle performance of the secondary battery.

[0049] Specifically, among electrolyte salts, sodium hexafluorophosphate exhibits excellent overall performance in terms of ionic conductivity and electrolyte viscosity, but it has certain limitations in electrochemical stability under high voltage; while sodium tetrafluoroborate contains BF4... - Anions can participate in Na+ +The solvation layer forms a boron-containing positive electrolyte interphase (CEI) film and a solid electrolyte interphase (SEI) film at the interface between the positive and negative electrodes. The SEI film can effectively suppress the formation of dead sodium and sodium dendrites, and improve the reversibility of sodium deposition and stripping processes. The CEI film can protect the structural integrity of the positive electrode and hinder the dissolution of transition metal ions. Therefore, the combined use of sodium hexafluorophosphate and sodium tetrafluoroborate improves the cycle performance of the secondary battery under high voltage.

[0050] Furthermore, among salt additives, TFA - and NO3 - with Na + It has strong binding ability and can more easily enter Na+ in the electrolyte. + Solvated inner layer, and TFA - and NO3 - Oxidation and reduction reactions can preferentially occur on the surfaces of the positive and negative electrodes, which is conducive to the formation of anion-derived inorganic-rich positive and negative electrode interfaces, thereby accelerating the oxidation of Na. + The interfacial reaction kinetics. In addition, TFA... - and NO3 - When used in conjunction with other electrolytes, TFA can be effective in the presence of water molecules. - It can also preferentially bind to and inhibit NO3. - Hydrolysis reduces the generation of harmful gases such as hydrofluoric acid, thus improving the water resistance of the electrolyte. Furthermore, compared to other anions, the optimized electrolyte contains less NO3-. - It exhibits a faster voltage response, accumulates at the positive electrode during charging, and simultaneously reacts with Na in this region. + The good coordination greatly improves the oxidation stability of the electrolyte; therefore, the salt additive further improves the cycle performance of the secondary battery under high voltage.

[0051] In summary, this application utilizes the electrolyte salt and salt additives in combination to improve the cycle performance of secondary batteries under high voltage, and can also improve the high-temperature storage performance of secondary batteries and reduce gas production to a certain extent.

[0052] Regarding improving the high-voltage cycle performance of secondary batteries, taking a sodium-metal-free secondary battery as an example, the electrolyte salt described in this application has good compatibility with sodium metal. The electrolyte salt can alter the solvation structure of the electrolyte, forming anion and cation coordination. Therefore, during the formation of the negative electrode SEI and positive electrode CEI, its composition mainly comes from the decomposition of anions. This inorganic-rich SEI and CEI have good chemical and mechanical stability interfaces, inhibiting the consumption of sodium metal at the negative electrode and the decomposition of the cathode electrolyte, thereby enhancing the long-term cycle stability of the secondary battery. Based on this, salt additives are introduced, among which TFA... -and NO3 - Anions all have high donor values, TFA - and NO3 - with Na + With stronger binding ability and shorter binding distance, it is easier for it to enter the sodium ion solvation inner layer in the electrolyte and participate in subsequent reactions. At the same time, it reduces the coordination number of the solvent, thereby accelerating the reaction of Na+. + The desolvation energy is reduced, thus further improving the cycle stability of the secondary battery under high voltage.

[0053] In some embodiments, the molar concentration ratio of sodium hexafluorophosphate and sodium tetrafluoroborate is 1:(0.01-0.3), wherein 0.01-0.3 can be 0.05, 0.1, 0.15, 0.2, 0.25, etc.

[0054] In the technical solution of this application embodiment, the electrolyte salt is mainly sodium hexafluorophosphate, combined with sodium tetrafluoroborate, which is suitable for sodium secondary batteries, especially negative electrode-free sodium metal secondary batteries. Specifically, the electrolyte salt has good compatibility with sodium metal and good solubility in the electrolyte, which can increase the concentration of the electrolyte and reduce uncoordinated free solvents, thereby increasing the potential window of the electrolyte and enabling the negative electrode-free sodium metal secondary battery to have excellent cycle performance.

[0055] As an example, the molar concentration of sodium hexafluorophosphate in the electrolyte is 0.5-1.2 mol / L, such as 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.1 mol / L, etc.

[0056] It should be noted that after the electrolyte is assembled into a secondary battery, some electrolyte salts or salt additives will form an SEI film or CEI film, and the molar concentration will decrease to a certain extent compared with before assembly.

[0057] In some embodiments, the molar concentration ratio of sodium hexafluorophosphate to salt additives is 1:(0.001-0.04), wherein 0.001-0.04 can be 0.01, 0.02, 0.03, etc.

[0058] In the technical solution of this application embodiment, the molar concentration ratio of the salt additive to sodium hexafluorophosphate is within the above-mentioned range, which is suitable for sodium secondary batteries, especially sodium metal secondary batteries without a negative electrode. Specifically, the salt additive within the above range can simultaneously improve the reaction kinetics of the secondary battery and the high-voltage stability of the electrolyte. The secondary battery forms a stable CEI film and SEI film at the interface of the positive electrode and the negative electrode, which improves the solvation structure of the electrolyte and enhances the cycle performance of the secondary battery. It can also reduce the continuous consumption of sodium metal and reduce the side reactions of the electrolyte. Therefore, the formed secondary battery has excellent storage performance and gas generation performance in addition to excellent cycle performance.

[0059] In some embodiments, the molar concentration ratio of sodium trifluoroacetate to sodium nitrate is 1:(0.1-10), wherein 0.1-10 can be 0.2, 0.4, 0.6, 0.8, 1, 2, 4, 6, 8, etc.

[0060] In the technical solution of this application, the molar concentration ratio of sodium trifluoroacetate and sodium nitrate is within the above-mentioned range, which is beneficial to further improve the cycle performance, storage performance and gas generation performance of the secondary battery.

[0061] In some embodiments, the electrolyte further includes an ether solvent.

[0062] In the technical solution of this application embodiment, ether solvents have good compatibility with sodium metal and good solubility for electrolyte salts and salt additives. The formed electrolyte can form a uniform, stable and highly protective CEI film and SEI film at the interface of the positive electrode and the negative electrode. With the electrolyte salt and salt additives described in this application, the irreversible consumption of sodium metal and electrolyte can be reduced, the high-voltage stability of the electrolyte can be improved, and the formed secondary battery has excellent high-voltage cycle performance.

[0063] In some embodiments, the ether solvent includes linear ethers and / or cyclic ethers; and / or;

[0064] The ether solvents include linear ethers and cyclic ethers in a volume ratio of (50-85):(15-50), wherein 50-85 can be 55, 60, 65, 70, 75, 80, etc., and 15-50 can be 20, 25, 30, 35, 40, 45, etc.

[0065] In the technical solution of this application embodiment, linear ethers are used as the main component, which can achieve full dissolution of electrolyte salts. Combined with cyclic ethers, the stability of the electrolyte can be improved, so that the secondary battery has excellent cycle performance, storage performance and gas generation performance.

[0066] Taking a negative electrode-less sodium metal secondary battery as an example, the combined use of linear ethers and cyclic ethers can not only improve the stability of the electrolyte, but also improve the sodium ion desolvation kinetics, resulting in excellent cycle performance, storage performance and gas generation performance of the secondary battery.

[0067] In some embodiments, the linear ether comprises any one or a combination of at least two of ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), ethylene glycol dibutyl ether (DBE), diethylene glycol dimethyl ether (DEGDME), tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol diethyl ether (DEGDEE), and diethylene glycol dibutyl ether (DEGDBE); and / or;

[0068] The cyclic ether includes any one or a combination of at least two of tetrahydrofuran, methyltetrahydrofuran, or dioxapentane.

[0069] In the technical solution of this application embodiment, the electrolyte formed by the combined use of linear ether and cyclic ether has better stability, which is beneficial to improving the cycle performance of the secondary battery.

[0070] In some embodiments, the secondary battery includes any one of a sodium metal secondary battery, a sodium-air secondary battery, or a sodium-sulfur secondary battery; and / or;

[0071] The sodium metal secondary battery includes a sodium metal secondary battery without a negative electrode.

[0072] In this application, the negative electrode-free sodium metal secondary battery is a novel battery technology. Unlike traditional sodium metal batteries, it does not use traditional negative electrode active materials; instead, sodium metal is directly deposited on the negative electrode current collector.

[0073] In the technical solutions of this application embodiment, the secondary battery, especially the negative electrode-free sodium metal secondary battery, has excellent cycle performance under high voltage (such as ≥4.0V, such as 4.0 and 4.2V, etc.), and at the same time, its high temperature storage performance and gas generation performance are also significantly improved.

[0074] [Positive electrode plate]

[0075] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; and / or;

[0076] The positive electrode film layer includes a positive electrode active material; and / or;

[0077] The positive electrode active material includes layered oxides and / or polyanionic phosphates.

[0078] In the technical solutions of this application embodiment, the positive electrode active material within the above-mentioned range can better cooperate with the electrolyte to form a high-performance secondary battery, especially a sodium metal secondary battery without a negative electrode.

[0079] As an example, the chemical formula of the layered oxide is NaMO2, where M is a transition metal atom, including combinations of elements such as Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The layered oxide includes, but is not limited to, NaNi. 0.20 Fe 0.22 Cu 0.13 Mn 0.45 O2, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 or NaNi 0.68 Mn 0.22 Co 0.1 Any one or at least two of O2.

[0080] As an example, the chemical formula of the polyanionic phosphate is Na. x R y P m O n Wherein, 2.5≤x≤4.5, 1.5≤y≤3.5, 2.5<m<4.5, 11.5≤n≤15.5, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb, such as Na4Fe3(PO4)2(P2O7).

[0081] In some embodiments, the method for preparing the positive electrode sheet includes: dissolving a positive electrode material, such as a positive electrode active material, a conductive agent (such as carbon black), a binder (such as polyvinylidene fluoride), and other arbitrary components in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector (such as aluminum foil); and then drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0082] As an example, the compaction density of the positive electrode sheet is 2.5-3.5 g / cm³. 3 For example, 2.6 g / cm³ 3 2.8g / cm 3 3g / cm 3 3.2g / cm 3 3.4g / cm 3 wait.

[0083] In this application, the compaction density refers to the mass of the positive electrode active material per unit volume under a certain pressure, and the unit is g / cm³. 3 The density was measured using a compaction density meter; the calculation formula is: mass of positive electrode active material / (area of ​​positive electrode sheet × (thickness of positive electrode sheet after compaction - thickness of positive electrode current collector)).

[0084] As an example, the coating weight is 5-15 mg / cm³. 2 For example, 6mg / cm 2 8mg / cm 2 10mg / cm 2 12mg / cm 2 14mg / cm 2 wait.

[0085] [Negative electrode plate]

[0086] In some embodiments, the method for preparing the negative electrode sheet includes: dissolving a negative electrode material, such as a conductive agent (e.g., carbon nanotubes) and other arbitrary components (e.g., thickeners, such as sodium carboxymethyl cellulose) in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector (e.g., copper foil); and then drying, cold pressing, and slitting to obtain the negative electrode sheet, i.e., the negative electrode sheet of a sodium metal secondary battery without a negative electrode.

[0087] As an example, the coating thickness is 0.8-1.2 μm, such as 0.9 μm, 1 μm, 1.1 μm, etc.

[0088] As an example, the coating weight is 0.05-0.2 mg / cm³. 2 For example, 0.1 mg / cm 2 0.15 mg / cm 2 wait.

[0089] In some embodiments, the negative electrode material further includes a negative electrode active material (e.g., graphite) and / or a binder (e.g., styrene-butadiene rubber).

[0090] In some embodiments, the method for preparing the negative electrode sheet includes: dissolving a negative electrode material, such as a negative electrode active material (e.g., graphite), a binder (e.g., styrene-butadiene rubber), a conductive agent (e.g., carbon nanotubes), and other arbitrary components (e.g., thickeners, such as sodium carboxymethyl cellulose) in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector (e.g., copper foil); and then drying, cold pressing, and slitting to obtain the negative electrode sheet.

[0091] [Isolation membrane]

[0092] As for the separator, this application does not have any particular limitations, and any known porous structure separator with electrochemical and mechanical stability can be selected according to actual needs. For example, the separator can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0093] In some embodiments, the secondary battery can be prepared by the following method: stacking and winding the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence to obtain a battery cell; placing the battery cell in an outer packaging, adding electrolyte, and then performing processes such as encapsulation, standing, formation, and aging to obtain a secondary battery.

[0094] [Battery module, battery pack]

[0095] In some embodiments, the batteries can be assembled into a battery module, and the number of batteries contained in the 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.

[0096] In some embodiments, the batteries can also be assembled into a battery pack.

[0097] In some embodiments, the battery modules 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.

[0098] [Electrical appliances]

[0099] This application provides an electrical device, which includes the aforementioned secondary battery.

[0100] In some embodiments, the electrical device includes at least one of the battery modules or battery packs provided in any embodiment of this application.

[0101] The secondary battery, battery module, or battery pack described in this application 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 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., including but not limited to these.

[0102] Example 1

[0103] Electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), linear ether and cyclic ether solvents are mixed, and electrolyte salts NaPF6 and NaBF4 are added according to the formula. After mixing evenly, salt additives NaTFA and NaNO3 are added to obtain the electrolyte. The amount of each component added is shown in Table 1.

[0104] Positive electrode sheet

[0105] (1) Dissolve 10 wt% polyvinylidene fluoride binder in N-methylpyrrolidone, add 10 wt% carbon black conductive agent and 80 wt% positive electrode active material (such as NaNi). 0.20 Fe 0.22 Cu 0.13 Mn 0.45 Prepare a uniformly dispersed positive electrode slurry.

[0106] (2) The positive electrode slurry is coated onto the surface of the positive electrode current collector aluminum foil, and then transferred to a vacuum drying oven for complete drying. The resulting electrode sheet is rolled and then punched to obtain the positive electrode sheet. The compaction density of the positive electrode sheet is 2.8 g / cm³. 3 The coating weight is 10 mg / cm³. 2 .

[0107] Negative electrode sheet

[0108] (1) Weigh 5g of carboxymethyl cellulose and stir to dissolve in 1000mL of water, then add 5g of single-walled carbon nanotubes and prepare a negative electrode slurry by ultrasonic dispersion;

[0109] (2) The negative electrode slurry is then coated onto the surface of the negative electrode current collector copper foil, and then transferred to a vacuum drying oven for complete drying. After drying, it is slit and die-cut to prepare a negative electrode sheet without a negative electrode structure. The coating weight of the negative electrode sheet is 0.1 mg / cm³. 2 The coating thickness is approximately 1 μm.

[0110] Separator membrane: Polypropylene membrane is used as the separator membrane.

[0111] Assembly: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. Tabs are welded to the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. The electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. The non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a sodium-free negative electrode secondary battery.

[0112] Examples 2-12 and Comparative Examples 1-3

[0113] Except for the formulation design of each component in Table 1, a sodium-free secondary battery was obtained according to the method of Example 1.

[0114] Table 1

[0115]

[0116] In the table, " / " indicates content that is not involved; the percentage in the solvent refers to the volume percentage.

[0117] Performance testing

[0118] (1) Storage performance: The secondary battery was charged to 4.0V at a constant current of 0.2C at 25℃, then charged at a constant voltage of 4.0V 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.

[0119] Then, the secondary battery was charged again with a constant current of 0.2C to 4.0V, followed by constant voltage charging at 4.0V until the current dropped to 0.05C. The secondary battery was then stored in a 60℃ constant temperature chamber for 30 days. After removal, the secondary battery was placed at 25℃ and charged with a constant current of 0.2C to 4.0V, followed by constant voltage charging at 4.0V until the current dropped to 0.05C, and then discharged with a constant current of 0.2C to 1.5V. The discharge capacity (Cd2) after storage was obtained, and the capacity retention rate of the secondary battery was calculated using the following formula:

[0120] Capacity retention rate = Cd2 / Cd1 × 100%.

[0121] (2) Cycling performance: The prepared battery was left to stand for 30 minutes at 25°C, then charged to 4.0 / 4.2V with a constant current of 0.33C, and then charged to 0.05C with a constant voltage of 4.0 / 4.2V. After standing for 1 hour, it was discharged to 1.5V with a constant current of 0.33C to obtain the initial capacity (C0). After standing for 1 hour, it was charged to 4.0 / 4.2V with a constant current of 0.33C, and then charged to 0.05C with a constant voltage of 4.0 / 4.2V. After standing for 1 hour, it was discharged to 1.5V with a constant current of 0.33C to obtain the process capacity (C1). The above steps were repeated for the same secondary battery, and the number of cycles N when the cycle capacity decayed to 80% was recorded at the same time.

[0122] (3) Cyclic Gas Generation Performance: Before capacity testing, the cell volume (V1) was measured at 25°C using the water displacement method. The secondary battery was charged to 4.0V at a constant current of 0.2C at 25°C, then charged at a constant voltage of 4.0V 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 before storage (Cd1). The battery was then charged again to 4.0V at a constant current of 0.2C, and then charged at a constant voltage of 4.0V until the current dropped to 0.05C. The battery was then stored in a 60°C constant temperature chamber for 30 days. After removal, the cell volume (V2) was measured at 25°C, and the gas generation of the secondary battery was calculated using the following formula:

[0123] Gas production = [Volume of cell after storage (V2) - Volume of cell before storage (V1)] / Discharge capacity Cd1 before storage.

[0124] The test results are summarized in Table 2.

[0125] Table 2

[0126]

[0127] Analysis of the data in Table 2 shows that the secondary battery described in this application retains a capacity of over 85.5% after 30 days of storage at 60°C. After being charged to 4.0V with constant current or constant voltage for more than 256 cycles, the capacity decays to 80%. After being charged to 4.2V with constant current or constant voltage for more than 126 cycles, the capacity decays to 80%. The gas production rate after 30 days of storage at 60°C is less than 30.8 mL / Ah. The secondary battery described in this application has excellent cycle performance, storage performance, and gas production performance.

[0128] Analysis of Comparative Examples 1-3 and Example 1 shows that the performance of Comparative Examples 1-3 is not as good as that of Example 1, proving that the secondary battery described in this application has better performance.

[0129] Analysis of Example 6 and Example 1 shows that the performance of Example 6 is not as good as that of Example 1, proving that the secondary battery formed by the electrolyte salt or salt additive of this application within the specified range has better performance.

[0130] Analysis of Examples 7-8 and Example 1 shows that the performance of Examples 7-8 is not as good as that of Example 1, proving that the secondary battery formed by the combination of cyclic ether and linear ether has better performance.

[0131] Analysis of Examples 11-12 and Example 1 shows that the performance of Examples 11-12 is not as good as that of Example 1, proving that the secondary battery formed by the combined use of the two salt additives has better performance.

[0132] 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 secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, and an electrolyte; The electrolyte includes electrolyte salts and salt additives; The electrolyte salts include sodium hexafluorophosphate and sodium tetrafluoroborate; The salt additives include sodium trifluoroacetate and / or sodium nitrate.

2. The secondary battery according to claim 1, characterized in that, The molar concentration ratio of sodium hexafluorophosphate and sodium tetrafluoroborate is 1:(0.01-0.3).

3. The secondary battery according to claim 1 or 2, characterized in that, The molar concentration ratio of sodium hexafluorophosphate to salt additives is 1:(0.001-0.04).

4. The secondary battery according to any one of claims 1-3, characterized in that, The molar concentration ratio of sodium trifluoroacetate to sodium nitrate is 1:(0.1-10).

5. The secondary battery according to any one of claims 1-4, characterized in that, The electrolyte also includes ether solvents.

6. The secondary battery according to claim 5, characterized in that, The ether solvents include linear ethers and / or cyclic ethers; and / or; The ether solvents include linear ethers and cyclic ethers in a volume ratio of (50-85):(15-50).

7. The secondary battery according to claim 6, characterized in that, The linear ether comprises any one or a combination of at least two of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, or diethylene glycol dibutyl ether; and / or; The cyclic ether includes any one or a combination of at least two of tetrahydrofuran, methyltetrahydrofuran, or dioxapentane.

8. The secondary battery according to any one of claims 1-7, characterized in that, 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; and / or; The positive electrode film layer includes a positive electrode active material; and / or; The positive electrode active material includes layered oxides and / or polyanionic phosphates.

9. The secondary battery according to any one of claims 1-8, characterized in that, The secondary battery includes any one of a sodium metal secondary battery, a sodium-air secondary battery, or a sodium-sulfur secondary battery; and / or; The sodium metal secondary battery includes a sodium metal secondary battery without a negative electrode.

10. An electrical device, characterized in that, The electrical device includes the secondary battery as described in any one of claims 1-9.

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