Electrolyte, secondary battery, and electric device

Abstract

The application relates to the technical field of batteries, and relates to an electrolyte, a secondary battery and a power utilization device. The secondary battery comprises an electrolyte, and the electrolyte comprises an organic solvent, wherein the organic solvent comprises a chain ether compound shown in formula I: R1-O-(R2-O) n -R3 (I); wherein n is an integer greater than or equal to 2, R1 and R3 are each independently selected from branched C3-C6 alkyl, and R2 is selected from linear or branched C1-C4 alkylene. The technical scheme of the application can improve the safety performance of the secondary battery.

Description

Technical Field

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

[0002] Electrolytes, as a crucial component of secondary batteries, play a vital role as ion carriers in electrochemical reactions. However, during the storage of secondary batteries, a common problem is severe gas generation, which can lead to poor safety performance. Summary of the Invention

[0003] The main objective of this application is to provide an electrolyte, a secondary battery, and an electrical device, which aim to improve the safety performance of the secondary battery.

[0004] To achieve the above objectives, a first aspect of this application provides a secondary battery comprising an electrolyte, wherein the electrolyte comprises an organic solvent, and the organic solvent comprises a chain ether compound represented by Formula I:

[0005] R1-O-(R2-O) n -R3(I);

[0006] Where n is an integer ≥2, R1 and R3 are each independently selected from branched C3 to C6 alkyl groups, and R2 is selected from straight-chain or branched C1 to C4 alkylene groups.

[0007] In the secondary battery provided in this application, the organic solvent of the electrolyte includes chain-like ether compounds, wherein the terminal chains of the chain-like ether compounds are branched C3-C6 alkyl groups. On the one hand, this extends the length of the terminal chain, increases the volume effect of the solvent molecules, thereby weakening the coordination between the solvent molecules and the metal cations, resulting in a higher proportion of inorganic components in the generated SEI film, making the SEI film more stable, and reducing gas generation during secondary battery storage. On the other hand, it increases the substituents on α-C and reduces the number of α-H, thereby inhibiting the gas generation from the reaction between the active metal and α-H in the electrolyte. Thus, it can effectively suppress gas generation during secondary battery storage, thereby improving the safety performance of the secondary battery.

[0008] In one embodiment, the content of the chain ether compound in the organic solvent is 50wt%-100wt%.

[0009] This application limits the content of chain ether compounds to the range of 50wt%-100wt%, which can more effectively suppress gas generation during the storage of secondary batteries, thereby more effectively improving the safety performance of secondary batteries.

[0010] In one embodiment, the chain ether compound includes at least one of diethylene glycol diisopropyl ether, 2,11-dimethyl-3,6,10-trioxadodecane, dipropylene glycol diisopropyl ether, and dipropylene glycol ditert-butyl ether.

[0011] The end chains of the chain ether compounds in the embodiments of this application are all isopropyl or tert-butyl, which can effectively suppress gas generation during storage in secondary batteries, thereby improving the safety performance of secondary batteries.

[0012] In one embodiment, the organic solvent further includes a basic ether compound, which includes at least one of dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, and 1,3-dioxane.

[0013] In this application, the organic solvent used is a mixed ether compound consisting of chain ether compounds with isopropyl or tert-butyl end groups and basic ether compounds. This can more effectively suppress gas generation during secondary battery storage, thereby more effectively improving the safety performance of the secondary battery.

[0014] In one embodiment, the electrolyte further includes a metal salt, the concentration of which is 0.2 mol / L to 1.5 mol / L.

[0015] This application uses metal salts of appropriate concentrations to effectively suppress gas generation during secondary battery storage. If the concentration of the metal salt is too low, the ion transport inside the secondary battery will be relatively slow, limiting the electrode reaction kinetics and potentially leading to local charge accumulation during storage, triggering side reactions and generating gas. If the concentration of the metal salt is too high, it will exacerbate the side reactions on the electrode surface, especially at the interface between the electrode and the electrolyte, which may accelerate the gas generation reaction.

[0016] In one embodiment, the metal salt includes a sodium salt.

[0017] In this embodiment, the secondary battery is a sodium metal battery. The organic solvent of the electrolyte includes chain ether compounds with isopropyl or tert-butyl end chains. On the one hand, this extends the end chain length, increases the volume effect of solvent molecules, thereby weakening the coordination between solvent molecules and sodium ions. This results in a higher proportion of inorganic components in the generated SEI film, making the SEI film more stable and reducing gas generation during storage in the sodium metal battery. On the other hand, it increases the substituents on α-C and reduces the number of α-H, thereby inhibiting the gas generation from the reaction between metallic sodium and α-H in the electrolyte. This effectively suppresses gas generation during storage in the sodium metal battery, thus improving its safety performance.

[0018] In one embodiment, the secondary battery further includes a negative electrode sheet, which includes a negative current collector and a conductive coating disposed on at least one side surface of the negative current collector.

[0019] In some embodiments, the secondary battery is a negative electrode-free sodium-ion battery. The negative electrode includes a negative electrode current collector and a conductive carbon coating disposed on at least one side of the surface of the negative electrode current collector. The organic solvent of the electrolyte includes chain ether compounds with branched C3-C6 alkyl groups at the end groups. On the one hand, this extends the length of the end groups, increases the volume effect of the solvent molecules, thereby weakening the coordination between the solvent molecules and sodium ions. This results in a higher proportion of inorganic components in the generated SEI film, making the SEI film more stable and reducing gas generation during storage in the secondary battery. On the other hand, it increases the substituents on α-C and reduces the number of α-H groups, thereby suppressing the gas generation from the reaction of metallic sodium with α-H in the electrolyte. This effectively suppresses gas generation during storage in the negative electrode-free sodium-ion battery, thereby improving the safety performance of the negative electrode-free sodium-ion battery.

[0020] In one embodiment, the electrolyte further includes an additive, which includes a lithium salt.

[0021] The lithium salt used in this application as an additive to the electrolyte can form a stable SEI film and inhibit the decomposition of the electrolyte, thereby reducing gas generation during secondary battery storage and improving the safety performance of the secondary battery. At the same time, reducing gas generation can also improve the cycle performance of the secondary battery.

[0022] A second aspect of this application also provides an electrolyte comprising an organic solvent, the organic solvent comprising a chain ether compound of formula I:

[0023] R1-O-(R2-O) n -R3(I);

[0024] Where n is an integer ≥2, R1 and R3 are each independently selected from branched C3 to C6 alkyl groups, and R2 is selected from straight-chain or branched C1 to C4 alkylene groups.

[0025] In one embodiment, the content of the chain ether compound in the organic solvent is 50wt%-100wt%; and / or, the organic solvent further includes a basic ether compound; and / or, the electrolyte further includes a metal salt, the concentration of which is 0.2mol / L-1.5mol / L. 。

[0026] A third aspect of this application also provides an electrical device, which includes the secondary battery provided in the first aspect of this application.

[0027] In the secondary battery provided in this application, the organic solvent of the electrolyte includes chain-like ether compounds, wherein the terminal chains of the chain-like ether compounds are branched C3-C6 alkyl groups. On the one hand, this extends the length of the terminal chain, increases the volume effect of the solvent molecules, thereby weakening the coordination between the solvent molecules and the metal cations, resulting in a higher proportion of inorganic components in the generated SEI film, making the SEI film more stable, and reducing gas generation during secondary battery storage. On the other hand, it increases the substituents on α-C and reduces the number of α-H, thereby inhibiting the gas generation from the reaction between the active metal and α-H in the electrolyte. Thus, it can effectively suppress gas generation during secondary battery storage, thereby improving the safety performance of the secondary battery. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of a secondary battery in some embodiments of this application;

[0030] Figure 2 This is an exploded view of the secondary battery in some embodiments of this application.

[0031] Explanation of icon numbers:

[0032] 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. End cap assembly.

[0033] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0035] The electrolyte, secondary battery, and power supply device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0036] 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.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0038] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0039] 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.

[0040] A secondary battery typically consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte, as a crucial component, plays a vital role as an ion carrier in the electrochemical reactions. In related technologies, during the storage of secondary batteries, the electrolyte solvent can react with active metals (such as sodium), leading to severe gas generation during storage and consequently, poor safety performance.

[0041] To address the aforementioned technical problems, the first aspect of this application provides a secondary battery designed to suppress gas generation during storage, thereby improving the safety performance of the secondary battery.

[0042] In the secondary battery provided in this application, the organic solvent of the electrolyte includes chain-like ether compounds, wherein the terminal chains of the chain-like ether compounds are branched C3-C6 alkyl groups. On the one hand, this extends the length of the terminal chain, increases the volume effect of the solvent molecules, thereby weakening the coordination between the solvent molecules and the metal cations, resulting in a higher proportion of inorganic components in the generated SEI film, making the SEI film more stable, and reducing gas generation during secondary battery storage. On the other hand, it increases the substituents on α-C and reduces the number of α-H, thereby inhibiting the gas generation from the reaction between the active metal and α-H in the electrolyte. Thus, it can effectively suppress gas generation during secondary battery storage, thereby improving the safety performance of the secondary battery.

[0043] Normally, during the charging and discharging process of a secondary battery, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through.

[0044] Electrolyte

[0045] In this embodiment of the application, the secondary battery includes an electrolyte, which includes an organic solvent, and the organic solvent includes a chain ether compound represented by Formula I:

[0046] R1-O-(R2-O) n -R3(I);

[0047] Where n is an integer ≥2, R1 and R3 are each independently selected from branched C3 to C6 alkyl groups, and R2 is selected from straight-chain or branched C1 to C4 alkylene groups.

[0048] Chain ether compounds are a class of organic compounds containing ether bonds (C—O—C) and whose hydrocarbon moiety is a chain structure. The terminal group refers to the group attached to the terminal oxygen (O), α-C refers to the C directly attached to the oxygen (O), and α-H refers to the H directly attached to the α-C. In the embodiments of this application, the terminal groups R1 and R3 are each independently selected from branched C3-C6 alkyl groups. Branched C3-C6 alkyl groups are C3-C6 alkyl groups with branches. The number of α-H groups can be 0, 1, or 2. Branched C3-C6 alkyl groups include isopropyl, tert-butyl, isopentyl, neopentyl, isohexyl, and tert-hexyl. Compared to existing solvents like DME (with methyl end groups), the chain ether compounds in this application use branched C3-C6 alkyl end groups. This extends the end group chain length, increases the volume effect of solvent molecules, and weakens the coordination between solvent molecules and metal cations, resulting in a higher proportion of inorganic components in the generated SEI film, making the SEI film more stable and reducing gas generation during secondary battery storage. Furthermore, the addition of substituents on α-C reduces the number of α-H groups, thereby inhibiting the gas generation from the reaction of active metals with α-H groups in the electrolyte. This effectively suppresses gas generation during secondary battery storage, thus improving the safety performance of the secondary battery.

[0049] Extending the chain length of ether compounds and increasing the number of substituents on the α-C chain has the side effect of increased steric hindrance, leading to a decrease in the degree of dissociation of metal salts (such as sodium salts). In the embodiments of this application, n is an integer ≥2, that is, the number of oxygen atoms in the chain ether compound molecule is ≥3. Compared with the existing solvent DME (two oxygen atoms), the number of oxygen atoms in the solvent is increased, which can effectively improve the degree of dissociation of metal salts (such as sodium salts), giving the metal salts (such as sodium salts) better dissolution effects, thereby improving the ionic conductivity of the electrolyte. At the same time, it is beneficial for the metal salt to form a stable interface film (SEI film) on the electrode surface, preventing further reaction between the electrolyte and the electrode, reducing the loss of active materials and the damage to the electrode structure, and improving the cycle life of the secondary battery.

[0050] In some embodiments, the content of the chain ether compound in the organic solvent is 50wt%-100wt% (e.g., 50wt%, 60wt%, 70wt%, 80wt%, 90wt%, 100wt%, and any range between the two endpoints). Limiting the content of the chain ether compound to the range of 50wt%-100wt% in this application can more effectively suppress gas generation during secondary battery storage, thereby more effectively improving the safety performance of the secondary battery.

[0051] In some embodiments, the chain ether compound includes at least one of diethylene glycol diisopropyl ether, 2,11-dimethyl-3,6,10-trioxadodecane, dipropylene glycol diisopropyl ether, and dipropylene glycol ditert-butyl ether.

[0052] The end chains of the chain ether compounds in the embodiments of this application are all isopropyl or tert-butyl, which can effectively suppress gas generation during storage in secondary batteries, thereby improving the safety performance of secondary batteries.

[0053] In some embodiments, the organic solvent also includes a basic ether compound.

[0054] Basic ether compounds are organic compounds containing ether bonds (C—O—C). They can be chain ether compounds, either linear or cyclic, and are not limited here.

[0055] In this application, the organic solvent used is a mixed ether compound consisting of chain ether compounds with isopropyl or tert-butyl end groups and basic ether compounds. This can more effectively suppress gas generation during secondary battery storage, thereby more effectively improving the safety performance of the secondary battery.

[0056] In some embodiments, the base ether compound includes at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, 2,11-dimethyl-3,6,10-trioxadodecane, and 1,3-dioxane.

[0057] In some embodiments, the electrolyte further includes a metal salt, which may be a sodium salt or a lithium salt.

[0058] In some embodiments, the secondary battery is a lithium metal battery, and the electrolyte includes lithium salts, including but not limited to lithium hexafluorophosphate or a mixture of lithium hexafluorophosphate and other lithium salts. Other lithium salts may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0059] In some embodiments, the secondary battery is a sodium metal battery, and the electrolyte includes sodium salts, including but not limited to at least one of NaPF6, NaFSI, NaClO4, NaTFSI, NaDFOB, and NaBF4.

[0060] In this embodiment, the secondary battery is a sodium metal battery. The organic solvent of the electrolyte includes chain ether compounds with branched C3-C6 alkyl end groups. On the one hand, this extends the length of the end group chain, increases the volume effect of the solvent molecules, thereby weakening the coordination between the solvent molecules and sodium ions. This results in a higher proportion of inorganic components in the generated SEI film, making the SEI film more stable and reducing gas generation during storage in the sodium metal battery. On the other hand, it increases the substituents on α-C and reduces the number of α-H, thereby inhibiting the gas generation from the reaction between metallic sodium and α-H in the electrolyte. This effectively suppresses gas generation during storage in the sodium metal battery, thus improving its safety performance.

[0061] In some embodiments, the concentration of the metal salt is 0.2 mol / L to 1.5 mol / L (e.g., 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, and any interval between two endpoints).

[0062] This application uses metal salts of appropriate concentrations to effectively suppress gas generation during secondary battery storage. If the concentration of the metal salt is too low, the ion transport inside the secondary battery will be relatively slow, limiting the electrode reaction kinetics and potentially leading to local charge accumulation during storage, triggering side reactions and generating gas. If the concentration of the metal salt is too high, it will exacerbate the side reactions on the electrode surface, especially at the interface between the electrode and the electrolyte, which may accelerate the gas generation reaction.

[0063] In some embodiments, the electrolyte further includes additives, including lithium salts. Lithium salts, as additives to the electrolyte, can form a stable SEI film and inhibit the decomposition of the electrolyte, thereby reducing gas generation during secondary battery storage and improving the safety performance of the secondary battery. At the same time, reducing gas generation can also improve the cycle performance of the secondary battery.

[0064] In some embodiments, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, and lithium trifluoromethanesulfonate.

[0065] In some embodiments, the concentration of lithium salt is 0.01 mol / L-0.5 mol / L. This application selects lithium salt of appropriate concentration as an additive for the electrolyte, which can effectively form a stable SEI film and inhibit the decomposition of the electrolyte, thereby reducing gas generation during the storage of the secondary battery and improving the safety performance of the secondary battery.

[0066] [Positive electrode plate]

[0067] The positive electrode 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 a positive electrode material.

[0068] 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.

[0069] 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.).

[0070] In some embodiments, the secondary battery is a lithium-ion battery, and the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0071] In some embodiments, the secondary battery is a sodium-ion battery, and the positive electrode active material in the positive electrode slurry can be a positive electrode active material known in the art for sodium-ion batteries.

[0072] In an optional embodiment of the present invention, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and the sodium transition metal oxide is, for example, Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0073] In an optional embodiment of the present invention, the polyanionic compound may be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0074] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0075] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, tetrahedral unit (ZO) y ) m+ And a class of compounds with optional halide anions, where Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO)y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0076] Prussian blue compounds can contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0077] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0078] In some embodiments, the positive electrode active material layer 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.

[0079] 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.

[0080] [Negative electrode plate]

[0081] The negative electrode of a conventional secondary battery includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0082] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0083] 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 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 (copper, copper 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.).

[0084] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0085] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder 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).

[0086] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0088] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0089] In some embodiments, the secondary battery is a negative electrode-less battery. A negative electrode-less battery eliminates the traditional pre-prepared negative electrode film. Initially, its negative electrode side consists only of a current collector, such as copper foil. During charging, active ions released from the positive electrode (sodium ions in a sodium-ion battery, for example) migrate to the negative electrode under the influence of an electric field and directly deposit metallic sodium (or other corresponding metals) on the surface of the negative electrode current collector. During discharge, the metallic sodium previously deposited on the surface of the negative electrode current collector releases sodium ions again. These sodium ions migrate back to the positive electrode through the electrolyte and react with the positive electrode material, thus enabling the battery to discharge.

[0090] Because negative electrode-less batteries eliminate the volume and weight occupied by the traditional negative electrode film, they can theoretically accommodate more positive electrode material and electrolyte within the same battery volume or weight constraints, potentially significantly increasing the battery's energy density. Furthermore, taking sodium batteries as an example, the sodium metal layer formed during charging acts as the negative electrode, possessing a large theoretical capacity, which can improve the battery's energy density and power.

[0091] However, the nucleation and growth of active ions (such as sodium ions) are significantly limited by the thermodynamics of the negative electrode current collector (heterogeneous substrates such as copper and aluminum): for example, there is a large lattice mismatch between the current collector surface and the metal; the miscibility between the current collector surface and the metal is extremely small; the metal on the current collector surface has low adsorption free energy and high surface diffusion energy, resulting in a high direct nucleation energy barrier; and the randomly distributed structural defects such as grain boundaries and dislocations on the current collector surface preferentially become nucleation sites for metal deposition, leading to a random and uneven distribution of metal nuclei deposited on the current collector surface. This, in turn, causes the growth of porous moss-like morphology, i.e., the metal deposition layer has uneven deposition problems, which will aggravate the side reactions with the electrolyte, resulting in the generation of a large amount of dead lithium / sodium and low coulombic efficiency, thus affecting the cycle life of the battery.

[0092] To address the aforementioned issues, in some embodiments, the negative electrode includes a negative current collector and a conductive coating disposed on at least one surface of the negative current collector. This conductive coating increases the affinity between the metal deposition layer and the surface of the negative current collector, thereby improving the uniformity of the metal deposition layer. The thickness of the conductive coating is not limited herein.

[0093] In some embodiments, the conductive coating includes a conductive agent and a binder, and the ratio of the conductive agent and the binder is not limited. As an example, the conductive coating is a conductive carbon layer, which includes a conductive carbon material and a binder. The conductive carbon material includes, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binder includes, but is not limited to, at least one of sodium carboxymethyl cellulose, sodium polyacrylate, and sodium alginate.

[0094] In some embodiments, the secondary battery is a negative electrode-free sodium-ion battery. The negative electrode includes a negative electrode current collector and a conductive carbon coating disposed on at least one side of the surface of the negative electrode current collector. The organic solvent of the electrolyte includes chain ether compounds with branched C3-C6 alkyl groups at the end groups. On the one hand, this extends the length of the end groups, increases the volume effect of the solvent molecules, thereby weakening the coordination between the solvent molecules and sodium ions. This results in a higher proportion of inorganic components in the generated SEI film, making the SEI film more stable and reducing gas generation during storage in the secondary battery. On the other hand, it increases the substituents on α-C and reduces the number of α-H groups, thereby suppressing the gas generation from the reaction of metallic sodium with α-H in the electrolyte. This effectively suppresses gas generation during storage in the negative electrode-free sodium-ion battery, thereby improving the safety performance of the negative electrode-free sodium-ion battery.

[0095] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0096] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0097] [Isolation membrane]

[0098] A separator is a membrane material placed between the positive electrode and the negative current collector to prevent short circuits between the positive and negative electrodes and to allow the passage of active ions. 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.

[0099] 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. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0100] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0101] In some implementations, refer again Figure 2The outer packaging may include a housing 51 and an end cap 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 end cap assembly 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 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The 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.

[0102] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary 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.

[0103] The second aspect of this application also provides an electrolyte, which is the electrolyte described in the secondary battery provided in the first aspect of this application. Its specific composition can be referred to the above embodiments, and will not be repeated here.

[0104] A third aspect of this application also provides an electrical device comprising the secondary battery provided in the first aspect of this application. The electrical device of this application possesses at least all the beneficial effects of the aforementioned secondary battery, which will not be elaborated further here. The secondary battery 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.

[0105] As an example, the electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, a mobile phone, a tablet computer, a laptop computer, etc.

[0106] Example

[0107] 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.

[0108] Example 1

[0109] [Positive electrode plate]

[0110] A mixture of 95 wt% of the first positive electrode active material (sodium iron pyrophosphate with a particle size D50 of 2 μm), 2 wt% of the conductive agent Super P, 2.5 wt% of the binder PVDF, and 0.5 wt% of the cathode additive carbon nanotubes was prepared. N-methylpyrrolidone was then added and the mixture was stirred and dispersed to form a positive electrode slurry. After stirring, the viscosity of the prepared positive electrode slurry was adjusted to 40000 mPa·s. The slurry did not separate into layers. The positive electrode slurry was then coated onto both sides of an Al foil using a double-sided coating device, with a single-sided coating weight of 200 mg / 1540.25 cm⁻¹. 2 The single-sided coating thickness is 72μm. After double-sided coating, the positive electrode sheet with a thickness of 157μm is obtained after drying, cold pressing and slitting.

[0111] [Negative electrode plate]

[0112] 5g of sodium carboxymethyl cellulose was weighed and dissolved in 1000mL of water. Then, 5g of single-walled carbon nanotubes were added and dispersed by ultrasonication to prepare a negative electrode slurry. The negative electrode slurry was then coated on both surfaces of a copper foil with a single-sided coating thickness of 1μm. The coating was then transferred to a vacuum drying oven for complete drying to obtain a negative electrode sheet with a thickness of 10μm.

[0113] [Septum]

[0114] Polypropylene film is used as the separator.

[0115] Electrolyte

[0116] The electrolyte consists of a sodium salt and an organic solvent, wherein the sodium salt is NaPF6 with a concentration of 0.5 mol / L, and the organic solvent includes 50 wt% ethylene glycol diisopropyl ether (S4) and 50 wt% ethylene glycol dimethyl ether (DME).

[0117] In an argon-atmospheric glove box, a certain amount of sodium salt is dissolved in the above-mentioned organic solvent, and the electrolyte is obtained after stirring evenly.

[0118] [Non-anode sodium metal battery]

[0119] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The cells are then wound to obtain a bare cell. The bare cell is placed in outer packaging, injected with prepared electrolyte, and undergoes processes such as encapsulation, electrolyte injection, formation, and venting to obtain a sodium metal battery without a negative electrode.

[0120] Example 2

[0121] The difference between Example 2 and Example 1 is that the organic solvents include 70 wt% ethylene glycol diisopropyl ether (S4) and 30 wt% ethylene glycol dimethyl ether (DME), while all other aspects are the same as in Example 1.

[0122] Example 3

[0123] The difference between Example 3 and Example 1 is that the organic solvent includes 90 wt% ethylene glycol diisopropyl ether (S4) and 10 wt% ethylene glycol dimethyl ether (DME), while all other aspects are the same as in Example 1.

[0124] Example 4

[0125] The difference between Example 4 and Example 1 is that the organic solvents include 50 wt% 2,11-dimethyl-3,6,10-trioxadodecane (S5) and 50 wt% dimethyl ethylene glycol (DME), while all other aspects are the same as in Example 1.

[0126] Example 5

[0127] The difference between Example 5 and Example 1 is that the organic solvents include 50 wt% dipropylene glycol diisopropyl ether (S6) and 50 wt% diethylene glycol dimethyl ether (DME), while all other aspects are the same as in Example 1.

[0128] Example 6

[0129] The difference between Example 6 and Example 1 is that the organic solvents include 50 wt% dipropylene glycol ditert-butyl ether (S7) and 50 wt% ethylene glycol dimethyl ether (DME), while all other aspects are the same as in Example 1.

[0130] Example 7

[0131] The difference between Example 7 and Example 1 is that the organic solvents include 50 wt% ethylene glycol diisopropyl ether (S4) and 50 wt% ethylene glycol diethyl ether (S1), while all other aspects are the same as in Example 1.

[0132] Example 8

[0133] The difference between Example 8 and Example 1 is that the organic solvents include 50 wt% ethylene glycol diisopropyl ether (S4) and 50 wt% ethylene glycol dipropyl ether (S2), while all other aspects are the same as in Example 1.

[0134] Example 9

[0135] The difference between Example 9 and Example 1 is that the organic solvents include 50 wt% ethylene glycol diisopropyl ether (S4) and 50 wt% ethylene glycol dibutyl ether (S3), while all other aspects are the same as in Example 1.

[0136] Example 10

[0137] The difference between Example 10 and Example 1 is that the concentration of sodium salt is 0.2 mol / L, while all other aspects are the same as in Example 1.

[0138] Example 11

[0139] The difference between Example 11 and Example 1 is that the concentration of sodium salt is 1.5 mol / L, while all other aspects are the same as in Example 1.

[0140] Example 12

[0141] The difference between Example 12 and Example 1 is that a lithium salt additive, lithium hexafluorophosphate (LiPF6), was added to the electrolyte at a concentration of 0.05 mol / L. All other aspects are the same as in Example 1.

[0142] Example 13

[0143] The difference between Example 13 and Example 1 is that a lithium salt additive, lithium tetrafluoroborate (LiBF4), was added to the electrolyte at a concentration of 0.05 mol / L. All other aspects are the same as in Example 1.

[0144] Example 14

[0145] The difference between Example 14 and Example 1 is that a lithium salt additive, lithium bis(fluorosulfonyl)imide (LiFSI), was added to the electrolyte at a concentration of 0.05 mol / L. All other aspects are the same as in Example 1.

[0146] Comparative Example 1

[0147] The difference between Comparative Example 1 and Example 1 is that the organic solvent only includes dimethyl ethylene glycol (DME), while everything else is the same as in Example 1.

[0148] Comparative Example 2

[0149] The difference between Comparative Example 2 and Example 1 is that the organic solvent only includes ethylene glycol diethyl ether (S1), while all other components are the same as in Example 1.

[0150] Performance testing

[0151] Gas production test after 30 days of storage at 45℃ and 100% SOC (where SOC refers to the state of charge of the battery, which is the ratio of the remaining charge of the battery to its rated capacity under certain conditions):

[0152] Step 1, capacity testing, includes the following steps:

[0153] 1. The battery cell is left to stand at 25℃ for 120 minutes;

[0154] 2. Discharge at a constant current of 0.33C to 1.5V;

[0155] 3. Let stand at 25℃ for 5 minutes;

[0156] 4. Charge at a constant current of 0.33C to 3.65V, then charge at a constant voltage with a cutoff current of 0.05C;

[0157] 5. Let stand at 25℃ for 5 minutes;

[0158] 6. Discharge the battery at a constant current of 0.33C to 1.5V. The battery discharge capacity obtained in this step is defined as the battery capacity C0, and its value is recorded in Table 1.

[0159] 7. Let stand at 25℃ for 30 minutes;

[0160] Step 2, recharge to 100% SOC, including the following steps:

[0161] 1. Let stand for 5 minutes at 25℃;

[0162] 2. Charge at a constant current of 0.33C to 3.65V, then charge at a constant voltage with a cutoff current of 0.05C;

[0163] 3. Let stand at 25℃ for 5 minutes;

[0164] Step 3: Test the initial volume V0 of the battery using the water displacement method;

[0165] Step 4: Store the battery in a 45°C constant temperature chamber for 30 days;

[0166] Step 5: Remove the battery and test its volume V1 after storage using the water displacement method.

[0167] The battery gas production is calculated according to the formula: Battery gas production = (V1-V0) / C0, and the calculation results are recorded in Table 1.

[0168] Table 1. Parameters and test data for each embodiment and comparative example.

[0169]

[0170]

[0171] As can be seen from the data in Table 1, compared with Comparative Example 1 and Comparative Example 2, the organic solvent of the electrolyte in this application embodiment uses a combination of chain ether compounds with isopropyl or tert-butyl terminal groups and basic ether compounds. By reasonably adjusting the content and type of chain ether compounds with isopropyl or tert-butyl terminal groups, the type of basic ether compounds, the concentration of sodium salt in the electrolyte, and the type of additives in the electrolyte, the assembled negative electrode-free sodium metal batteries can maintain a relatively low storage gas generation while maintaining a considerable capacity.

[0172] The above description is merely an exemplary embodiment of this application and does not limit the patent scope of this application. Any equivalent structural transformations made based on the technical concept of this application and the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A secondary battery, characterized in that, The electrolyte includes an organic solvent, which includes a chain ether compound of Formula I: R1-O-(R2-O) n -R3(I); Where n is an integer ≥2, R1 and R3 are each independently selected from branched C3 to C6 alkyl groups, and R2 is selected from straight-chain or branched C1 to C4 alkylene groups.

2. The secondary battery as described in claim 1, characterized in that, The content of the chain ether compound in the organic solvent is 50wt%-100wt%; and / or, The chain ether compounds include at least one of diethylene glycol diisopropyl ether, 2,11-dimethyl-3,6,10-trioxadodecane, dipropylene glycol diisopropyl ether, and dipropylene glycol ditert-butyl ether.

3. The secondary battery as described in claim 1, characterized in that, The organic solvent also includes basic ether compounds, which include at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, and 1,3-dioxane.

4. The secondary battery as described in any one of claims 1 to 3, characterized in that, The electrolyte also includes a metal salt, the concentration of which is 0.2 mol / L to 1.5 mol / L.

5. The secondary battery as described in claim 4, characterized in that, The metal salt includes sodium salt.

6. The secondary battery as described in claim 5, characterized in that, The secondary battery also includes a negative electrode sheet, which includes a negative current collector and a conductive coating disposed on at least one side surface of the negative current collector.

7. The secondary battery as described in claim 4, characterized in that, The electrolyte also includes additives, including lithium salts.

8. An electrolyte, characterized in that, The electrolyte includes an organic solvent, which includes a chain ether compound of Formula I: R1-O-(R2-O) n -R3(I); Where n is an integer ≥2, R1 and R3 are each independently selected from branched C3 to C6 alkyl groups, and R2 is selected from straight-chain or branched C1 to C4 alkylene groups.

9. The electrolyte as described in claim 8, characterized in that, The content of the chain ether compound in the organic solvent is 50wt%-100wt%; and / or, The organic solvent also includes basic ether compounds; and / or, The electrolyte further includes a metal salt with a concentration of 0.2 mol / L to 1.5 mol / L; and / or, The electrolyte also includes additives, including lithium-containing salts.

10. An electrical device, characterized in that, The electrical device includes a secondary battery as described in any one of claims 1 to 7.

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