Electrolyte, secondary battery, battery module, battery pack, and power consuming device

Abstract

The present application provides an electrolyte, a secondary battery, a battery module, a battery pack and a power consumption device. The electrolyte of the present application includes a first additive, the first additive being a sulfur-containing compound with a boiling point not exceeding 70°C under standard atmospheric pressure, and the mass content of the first additive in the electrolyte is 0.05%-6%. The electrolyte of the present application can form a stable interface film on the surface of the negative electrode plate, inhibit the occurrence of side reactions between the electrolyte and the negative electrode plate, reduce the interface impedance of the negative electrode, reduce sodium precipitation, and improve the cycle performance and safety performance of the secondary battery.

Description

[Technical field]

[0001] The present application relates to the field of secondary battery technology, in particular to electrolytes, secondary batteries, battery modules, battery packs and power consuming devices. [Background technology]

[0002] In recent years, as the application range of secondary batteries becomes wider and wider, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. As secondary batteries have made great strides in development, higher requirements are being placed on their energy density, cycle performance and safety performance.

[0003] At present, the negative electrode interfacial film of sodium-ion secondary batteries is unstable and prone to side reactions with the electrolyte, and additives in the electrolyte are prone to form by-products that increase the interface impedance at the negative electrode, causing sodium precipitation problems and significantly reducing the cycle performance and safety performance of the battery. Therefore, this situation needs to be improved as soon as possible. Summary of the Invention

[0004] The present application has been made in view of the above problems, and an object of the application is to provide an electrolyte, a secondary battery, a battery module, a battery pack, and a power consumption device. By adopting the above electrolyte, the present application is able to obtain a stable negative electrode interfacial film, making it difficult for side reactions to occur between the negative electrode plate and the electrolyte, reducing the interfacial impedance of the negative electrode, reducing sodium precipitation, and improving the cycle performance and safety performance of the secondary battery.

[0005] In order to achieve the above object, according to a first aspect of the present application, there is provided an electrolyte, the electrolyte comprising a first additive, the first additive being a sulfur-containing compound having a boiling point not exceeding 70°C under standard atmospheric pressure, the mass content of the first additive in the electrolyte being 0.05%-6%, optionally the mass content of the first additive in the electrolyte being 0.05%-5%, further optionally the mass content of the first additive in the electrolyte being 0.1%-2%.

[0006] As a result, the electrolyte of the present application forms a stable negative electrode interfacial film on the surface of the negative electrode plate, and can suppress the occurrence of side reactions between the electrolyte and the negative electrode, thereby reducing the interface impedance of the negative electrode, reducing sodium precipitation, and improving the cycle performance and safety performance of the secondary battery. The electrolyte of the present application has a low viscosity and a fast diffusion speed of the first additive in the electrolyte, allowing it to quickly form a film on the negative electrode surface, and the migration speed of sodium ions on the negative electrode surface after film formation is good, thereby further reducing the interface impedance of the negative electrode.

[0007] In an optional embodiment, the first additive is one or more selected from the group consisting of fluorides of sulfur, oxides of sulfur, sulfur carbon compounds, thioethers, sulfuryl compounds (optionally fluorine-containing sulfuryl compounds), and sulfinyl compounds (optionally fluorine-containing sulfinyl compounds); Optionally, the first additive is one or more selected from SF6, SF4, SO2F2, SO2, SO3, CS2, dimethyl sulfide, methyl ethyl sulfide, S2F2, SF2, SOF2, and SOF4.

[0008] The selected first additive has a low viscosity after being dissolved in a solvent, a fast diffusion rate, and can react on the negative electrode surface faster than the solvent to form a sulfur-containing inorganic salt. This inorganic salt has a good sodium ion migration rate and is less likely to undergo side reactions with the electrolyte, improves the stability of the negative electrode interfacial film, reduces the interface impedance of the negative electrode, reduces sodium precipitation, and improves the cycle performance and safety performance of the secondary battery.

[0009] In an optional embodiment, the electrolyte further comprises a second additive, the second additive being one or more selected from fluorinated carbonate esters and fluorinated carboxylate esters, the mass content of the second additive in the electrolyte being 0.005%-12%, optionally 0.01%-10%; Optionally, the second additive is fluorinated ethylene carbonate and / or ethyl 2,2-difluoroacetate; Optionally, the mass content of the second additive in the electrolyte is 0.1%-5%.

[0010] The first and second additives can form an interfacial film with good toughness and high strength on the negative electrode, which makes the interfacial film less likely to break due to the expansion and contraction of the volume of the negative electrode active material, further improves the stability of the interfacial film, reduces the interfacial impedance of the negative electrode, reduces sodium precipitation, and improves the cycle performance and safety performance of the secondary battery. At the same time, the reduction potential of the first additive is higher than that of the second additive, which can suppress the side reaction of the second additive in the negative electrode, thereby improving the cycle performance of the secondary battery.

[0011] The mass content of the second additive in the electrolyte is 0.01%-10%, which can form a negative electrode interfacial film with appropriate thickness and good toughness and strength, further inhibit the occurrence of side reactions between the negative electrode and the electrolyte, further improve the stability of the interfacial film, further reduce the interfacial impedance of the negative electrode, reduce sodium precipitation, and improve the cycle performance and safety performance of the secondary battery.

[0012] In any embodiment, the mass content of the first additive in the electrolyte is W1%, the mass content of the second additive in the electrolyte is W2%, and the product of W1 and W2 is any number in the range of 0.01-24, optionally any number selected from the range of 0.05-16, and further optionally any number selected from the range of 0.05-10.

[0013] The first additive and the second additive form a film containing a large amount of inorganic material with high strength and a film containing a large amount of organic material with high toughness, respectively. Therefore, when the mass content of the first additive and the mass content of the second additive satisfy the above relationship, the toughness and strength of the negative electrode interfacial film can be ensured and the stability of the negative electrode interfacial film can be improved, thereby improving the service life of the battery core, while reducing the thickness of the interfacial film, reducing the interfacial impedance of the negative electrode, and improving the power performance of the battery core.

[0014] In any embodiment, the electrolyte further comprises a solvent and / or an electrolyte salt, optionally, the solvent is a carbonate-based solvent.

[0015] According to a second aspect of the present application, there is further provided a secondary battery, the secondary battery including a positive plate, a negative plate, a separator, and the electrolyte of the first aspect of the present application.

[0016] As a result, the secondary battery of the present application can form a stable negative electrode interfacial film using the above electrolyte, making it less likely that side reactions will occur between the negative electrode and the electrolyte, thereby reducing the interfacial impedance of the negative electrode and reducing sodium precipitation, thereby improving the cycle performance and safety performance of the secondary battery.

[0017] In any embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the mass content of elemental sulfur in the negative electrode film layer is 0.01%-1.14%, optionally 0.01%-1%, and further optionally 0.05%-0.5%.

[0018] This further improves the stability of the negative electrode interfacial film, further reduces the negative electrode interfacial impedance, improves the transport rate of sodium ions in the electrode plate, and further reduces sodium precipitation, thereby further improving the cycle performance and safety performance of the secondary battery.

[0019] According to a third aspect of the present application, there is provided a battery module including the secondary battery according to the second aspect of the present application.

[0020] According to a fourth aspect of the present application, there is provided a battery pack including the battery module of the third aspect of the present application.

[0021] According to a fifth aspect of the present application, there is provided a power consumption device, the power consumption device including at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, and the battery pack of the fourth aspect of the present application. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application. [Diagram 2] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. [Diagram 3] FIG. 1 is a schematic diagram of a battery module according to an embodiment of the present application. [Figure 4] FIG. 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Diagram 5] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application. [Figure 6] 1 is a schematic diagram of a power consuming device in which a secondary battery according to an embodiment of the present application is used as a power source; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing an electrolyte used in a sodium ion secondary battery, a sodium ion secondary battery, a battery module, a battery pack, and a power consumption device of the present application will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and duplicated description of structures that are actually the same may be omitted. This is to avoid the following description becoming unnecessarily long and to allow those skilled in the art to easily understand. Note that the drawings and the following description are provided to allow those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0024] The "ranges" disclosed in this application are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also envisaged. It is noted that if 1 and 2 are listed as the minimum range values, and 3, 4, and 5 are listed as the maximum range values, the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all envisaged. In this application, unless otherwise specified, a numerical range "a-b" represents a shorthand representation of any combination of real numbers a-b, where a and b are both real numbers. For example, the numerical range "0-5" represents a list of all real numbers between "0-5" already listed in this specification, and "0-5" is only a shorthand representation of combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0025] Unless otherwise stated, all the embodiments and optional embodiments in the present application can be combined with each other to form a new technical solution.

[0026] Unless otherwise stated, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0027] Unless otherwise stated, all steps in this application may be performed in sequence, randomly, and preferably in sequence. For example, a method includes steps (a) and (b) means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), etc.

[0028] Unless otherwise stated, the terms "comprise" and "comprises" referred to in this application may be open ended or closed ended. For example, "comprise" and "comprises" may further include or include other components not listed, or may include or include only the listed components.

[0029] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied in the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) but B is true (or exists); and A and B are both true (or exist).

[0030] [Secondary battery] A secondary battery is also called a rechargeable battery or a storage battery, and refers to a battery that can be continuously used by activating the active material through a charging method after the battery is discharged.

[0031] A secondary battery generally includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During charging and discharging of the battery, active ions (e.g., sodium ions) move between the positive electrode plate and the negative electrode plate to absorb and release. The separator is provided between the positive electrode plate and the negative electrode plate, and mainly serves to prevent short-circuiting between the positive and negative electrodes, while allowing the active ions to pass through. The electrolyte mainly serves to conduct the active ions between the positive and negative electrode plates.

[0032] In some embodiments, the secondary battery is a sodium ion secondary battery.

[0033] [Electrolytes] The electrolyte serves to conduct ions between the positive and negative plates. The electrolyte of the present application may be in the form of a liquid or a gel.

[0034] An embodiment of the present application provides an electrolyte, the electrolyte comprising a first additive, the first additive being a sulfur-containing compound having a boiling point not exceeding 70°C under standard atmospheric pressure, the mass content of the first additive in the electrolyte being 0.05%-6%, optionally the mass content of the first additive in the electrolyte being 0.05%-5%, further optionally 0.1%-2%, for example 1%, 2%.

[0035] Thus, although the mechanism is not yet fully understood, the applicant unexpectedly discovered that the first additive reacts on the surface of the negative electrode in the electrolyte rather than in the solvent to form an inorganic salt product containing sulfur, and such a product can suppress the occurrence of side reactions between the electrolyte and the negative electrode, thereby improving the stability of the negative electrode interfacial film, reducing sodium precipitation, reducing the interface impedance of the negative electrode, and improving the cycle performance and safety performance of the secondary battery. And, the first additive has a low viscosity after dissolving in the electrolyte, a fast diffusion rate, and is easy to rapidly form a film on the surface of the negative electrode, and the inorganic salt product formed by the first additive on the surface of the negative electrode has a good sodium ion migration rate, further reducing the interface impedance of the negative electrode.

[0036] In some embodiments, the first additive is one or more selected from fluorides of sulfur, oxides of sulfur, sulfur carbon compounds, thioethers, sulfuryl compounds (optionally fluorine-containing sulfuryl compounds) and sulfinyl compounds (optionally fluorine-containing sulfinyl compounds); Optionally, the first additive is one or more selected from SF6, SF4, SO2F2, SO2, SO3, CS2, dimethyl sulfide, methyl ethyl sulfide, S2F2, SF2, SOF2, and SOF4.

[0037] The selected first additive has a low viscosity after being dissolved in a solvent, a fast diffusion rate, and can react on the negative electrode surface faster than the solvent to form a sulfur-containing inorganic salt. This inorganic salt has a good sodium ion migration rate and is less likely to undergo side reactions with the electrolyte, improves the stability of the negative electrode interfacial film, reduces the interface impedance of the negative electrode, reduces sodium precipitation, and improves the cycle performance and safety performance of the secondary battery.

[0038] In some embodiments, the electrolyte further comprises a second additive, the second additive being one or more selected from fluorinated carbonate esters and fluorinated carboxylate esters, the mass content of the second additive in the electrolyte being 0.005%-12%, optionally 0.01%-10%, and optionally the second additive being fluorinated ethylene carbonate (also called fluoroethylene carbonate) and / or ethyl 2,2-difluoroacetate, where the structural formula of fluorinated ethylene carbonate (also called fluoroethylene carbonate) is: JPEG2025511543000002.jpg19170, Optionally, the mass content of the second additive in the electrolyte is 0.1%-5%.

[0039] The first and second additives can form an interfacial film with good toughness and high strength on the negative electrode interface, which makes the interfacial film less likely to break due to the expansion and contraction of the volume of the negative electrode active material, further improves the stability of the negative electrode interfacial film, reduces the interfacial impedance of the negative electrode, reduces sodium precipitation, and improves the cycle performance and safety performance of the secondary battery. At the same time, the reduction potential of the first additive is higher than that of the second additive, which can suppress the side reaction of the second additive at the negative electrode, thereby improving the cycle performance of the secondary battery.

[0040] The mass content of the second additive in the electrolyte is 0.01%-10%, which can form a negative electrode interfacial film with appropriate thickness and good toughness and strength, further inhibit the occurrence of side reactions between the negative electrode and the electrolyte, further improve the stability of the negative electrode interfacial film, further reduce the interface impedance of the negative electrode, reduce sodium precipitation, and improve the cycle performance and safety performance of the secondary battery.

[0041] In some embodiments, the mass content of the first additive in the electrolyte is W1%, the mass content of the second additive in the electrolyte is W2%, and the product of W1 and W2 is any number selected from the range of 0.01-24, optionally any number selected from the range of 0.05-16, and further optionally any number selected from the range of 0.05-10.

[0042] The first additive and the second additive form a film containing a large amount of inorganic material with high strength and a film containing a large amount of organic material with high toughness, respectively. Therefore, when the mass content of the first additive and the mass content of the second additive satisfy the above relationship, the toughness and strength of the negative electrode interfacial film can be ensured and the stability of the negative electrode interfacial film can be improved, thereby improving the service life of the battery core, while reducing the thickness of the interfacial film, reducing the interfacial impedance of the negative electrode, and improving the power performance of the battery core.

[0043] In some embodiments, the electrolyte further comprises a solvent and / or an electrolyte salt, optionally, the solvent is a carbonate-based solvent.

[0044] In some embodiments, the electrolyte salt is NaPF, NaBF, NaN(SOF) (abbreviated as NaFSI), NaClO, NaAsF, NaB(C0) (abbreviated as NaBOB), NaBF(C0) (abbreviated as NaDFOB), NaN(SOR F )2 and NaN(SO2F)(SO2R F ), where R F is C b F 2b+1 where b is an integer in the range of 1-10, optionally an integer in the range of 1-3, and optionally R F is -CF3, -C2F5 or -CF2CF2CF3, Optionally, the electrolyte salt is one or more selected from NaPF6, NaN(SO2F)2, NaN(CF3SO2)2, NaB(C2O4)2, and NaBF2(C2O4); Further optionally, the electrolyte salt is one or more selected from NaPF6, NaN(SO2F)2, and NaBF2(C2O4).

[0045] In some embodiments, the solvent may be at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluorinated ethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, 1,3-dioxolane, tetrahydrofuran, ethylene glycol dimethyl ether, and acetonitrile.

[0046] In some embodiments, the electrolyte optionally further comprises other additives other than the first additive and the second additive, such as vinyl sulfate, maleic anhydride, propylene sultone, succinonitrile, adiponitrile, vinylene carbonate, succinic anhydride, 1,3-propane sultone, triethanolamine borate, triphenyl borate, triallyl phosphate, tris(trimethylsilane) phosphate, and the like.

[0047] In some embodiments, the electrolyte is an electrolyte used in sodium ion secondary batteries.

[0048] [Negative plate] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0049] For example, the negative electrode current collector has two opposing surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0050] In some embodiments, the mass content of elemental sulfur in the negative electrode film layer is 0.01%-1.14%, optionally 0.01%-1%, and further optionally, the mass content of elemental sulfur in the negative electrode film layer is 0.05%-0.5%. The above negative electrode film layer is a negative electrode film layer on a negative electrode plate after formation of a secondary battery.

[0051] This further improves the stability of the negative electrode interfacial film, further reduces the negative electrode interfacial impedance, improves the transport rate of sodium ions in the electrode plate, and further reduces sodium precipitation, thereby further improving the cycle performance and safety performance of the secondary battery.

[0052] In some embodiments, the negative electrode current collector may employ a metal foil sheet or a composite current collector. For example, a copper foil may be employed as the metal foil sheet. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0053] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries well known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. The silicon-based material may be selected from at least one of silicon alone, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy. The tin-based material may be selected from at least one of tin alone, tin oxide, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery may be used. These negative electrode active materials may be used alone or in combination of two or more.

[0054] In some embodiments, the negative electrode membrane layer optionally further comprises a binder. For example, 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).

[0055] In some embodiments, the negative electrode membrane layer optionally further comprises a conductive agent. By way of example, 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.

[0056] In some embodiments, the negative electrode membrane layer optionally further comprises other auxiliary agents, such as a thickening agent (eg, sodium carboxymethylcellulose (CMC-Na)).

[0057] In some embodiments, the negative electrode plate may be manufactured by the following method: The above-mentioned components for manufacturing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, which is then coated onto a negative electrode current collector, and the negative electrode plate is obtained through processes such as drying and cold pressing.

[0058] [Positive plate] A positive electrode plate generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0059] For example, the positive electrode current collector has two opposing surfaces in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0060] In some embodiments, the positive electrode current collector may employ a metal foil sheet or a composite current collector. For example, as the metal foil sheet, aluminum foil may be employed. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0061] In some embodiments, the positive electrode active material may employ a positive electrode active material for batteries well known in the art. As an example, the positive electrode active material may include at least one material among Prussian blue analogs, sodium-containing phosphates, sodium-containing 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 the positive electrode active material of the battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Here, the Prussian blue analog is Na x P[R(CN)6] δ ·zH2O, where P and R are each independently at least one selected from transition metal elements, 0 < x ≦ 2, 0 < δ ≦ 1, and 0 ≦ z ≦ 10. The sodium-containing phosphate is Na b Me c (PO4) d O2X, where Me is one or more selected from Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, X is one or more selected from F, Cl, and Br, 0 < b ≦ 4, 0 < c ≦ 2, 1 ≦ d ≦ 3. The sodium-containing transition metal oxide is Na a M b Fe c O2, where M is a transition metal ion, 0.67 < a < 1.1, 0.5 < b < 1, 0 < c < 0.5.

[0062] In some embodiments, the positive electrode membrane layer optionally further includes a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester resin.

[0063] In some embodiments, the positive electrode membrane layer optionally further comprises a conductive agent. By way of example, the conductive agent may comprise at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0064] In some embodiments, the positive electrode plate may be manufactured by the following method: The above-mentioned components for manufacturing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, and the positive electrode slurry is coated on a positive electrode current collector, followed by drying, cold pressing, and other processes to obtain a positive electrode plate.

[0065] [Separator] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any well-known separator with a porous structure having good chemical stability and mechanical stability may be selected.

[0066] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer thin film or a multi-layer composite thin film, and there is no particular limitation. When the separator is a multi-layer composite thin film, the materials of each layer may be the same or different, and there is no particular limitation.

[0067] In some embodiments, the positive and negative plates and the separator may be fabricated into an electrode assembly by a winding or lamination process.

[0068] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and the electrolyte.

[0069] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a pouch, such as a bag-shaped pouch. The material of the pouch may be plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0070] The present application is not particularly limited to the shape of the secondary battery, which may be cylindrical, rectangular or any other shape. For example, FIG. 1 shows a secondary battery 5 having a rectangular structure as an example.

[0071] In some embodiments, referring to FIG. 2, the exterior body may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and a side plate connected on the bottom plate, and the bottom plate and the side plate surround the case 51 to form a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided to cover the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate and the separator can form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte permeates the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can select according to actual specific needs.

[0072] In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, with the specific number being selectable by one skilled in the art based on the application and capacity of the battery module.

[0073] Fig. 3 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, the secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the secondary batteries 5 may be fixed by fasteners.

[0074] Optionally, the battery module 4 may further include a housing having an accommodating space, and the multiple secondary batteries 5 are accommodated in the accommodating space.

[0075] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and the specific number can be selected by one skilled in the art based on the application and capacity of the battery pack.

[0076] 4 and 5 show an example of a battery pack 1. Referring to FIG. 4 and FIG. 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 is provided to cover the lower housing 3 to form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box according to any manner.

[0077] The present application further provides a power consuming device including at least one of the secondary battery, battery module, or battery pack according to the present application. The secondary battery, battery module, or battery pack may be used as a power source for the power consuming device, or may be used as an energy storage unit for the power consuming device. The power consuming 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.), trains, ships, and satellites, energy storage systems, etc.

[0078] As the power consuming device, a secondary battery, a battery module, or a battery pack can be selected according to the demands of the usage.

[0079] 6 shows an example of a power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A battery pack or a battery module can be adopted to meet the power consuming device's demand for high power and high energy density of secondary batteries.

[0080] [Example] The following describes the examples of the present application. The examples described below are illustrative and are only for interpreting the present application, and should not be understood as limitations on the present application. If no specific techniques or conditions are specified in the examples, they will be performed according to the techniques or conditions described in the literature in the field or the product instructions. For reagents or instruments used, those without the manufacturer's name are all common products that can be purchased commercially.

[0081] Example 1 1. Preparation of positive electrode plate: The positive electrode active material sodium vanadium phosphate Na3V2(PO4)3, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 90:5:5 in an N-methylpyrrolidone solvent system with sufficient stirring to prepare a positive electrode slurry. The positive electrode slurry was then uniformly applied to a positive electrode current collector aluminum foil, which was then dried, cold pressed, and cut to obtain a positive electrode plate.

[0082] 2. Manufacturing of negative electrode plate: A negative electrode active material, hard carbon, a conductive agent, acetylene black, a binder, styrene butadiene rubber (SBR), and a thickener, sodium carboxymethyl cellulose (CMC-Na), were mixed thoroughly and uniformly in a weight ratio of 90:4:4:2 in a deionized water solvent system to manufacture a negative electrode slurry. The negative electrode slurry was then applied to an aluminum foil negative electrode current collector, which was then dried, cold pressed, and cut to obtain a negative electrode plate.

[0083] 3. Separator: A thin PE porous polymer film is used.

[0084] 4. Preparation of electrolyte: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:70, NaPF6 sodium salt was dissolved in the above solution, and the molar concentration of NaPF6 sodium salt in the electrolyte was 1M. Then, SO2 gas was flowed into the electrolyte and stirred to dissolve, and the mass content of the first additive SO2 in the electrolyte was 1%.

[0085] 5. Manufacturing of secondary battery: The positive electrode plate, separator, and negative electrode plate are stacked and wound in this order to obtain an electrode assembly, the electrode assembly is placed in an outer casing, the electrolyte prepared above is added, and a secondary battery is obtained through processes such as sealing, standing, chemical formation, and aging.

[0086] Examples 2-27 and Comparative Examples 1-11 In Examples 2-27 and Comparative Examples 1-11, the manufacturing method of the secondary battery is similar to that of Example 1, but the parameters were adjusted. The details of the different parameters are as shown in Table 1.

[0087] JPEG2025511543000003.jpg250146JPEG2025511543000004.jpg250160JPEG2025511543000005.jpg250160JPEG2025511543000006.jpg250160

[0088] Battery Testing (1) Measurement of the mass content of sulfur element in the negative electrode film layer of a secondary battery: At 25°C, the new sodium ion secondary batteries manufactured in the examples and comparative examples were left for 5 minutes, then charged at a constant current of 1C to 4.2V, and then charged at a constant voltage until the current was 0.05C or less, and then left for 5 minutes, and then discharged at a constant current of 1C to 2.0V to obtain a fully discharged battery core. The fully discharged battery core was disassembled, the negative plate was taken out, and the negative electrode film layer on the negative plate was scraped off with a blade, and the mass content of sulfur element in the scraped material, i.e., the mass content of sulfur element in the negative electrode film layer, was measured using an inductively coupled plasma atomic emission spectrometer according to the EPA 6010D-2014 test standard.

[0089] (2) Room temperature cycle performance test for secondary batteries: After leaving the sodium ion secondary battery for 5 minutes at 25°C, it was charged at a constant current of 1C to 4.2V, then charged at a constant voltage until the current became 0.05C or less, left for 5 minutes, and then discharged at a constant current of 1C to 2.0V, which was regarded as one charge / discharge cycle, and the discharge capacity at this time was recorded as the discharge capacity of the first cycle of the sodium ion secondary battery. The sodium ion secondary battery was subjected to 800 cycle charge / discharge tests using the above method, the discharge capacity of each cycle was recorded, and the capacity retention rate of the secondary battery was calculated using the following formula.

[0090] Capacity retention rate (%) of secondary battery = 100% × discharge capacity at 800th cycle / discharge capacity at 1st cycle.

[0091] (3) DC impedance test for secondary batteries: At 25°C, the sodium ion secondary battery was left for 5 minutes, charged at a constant current of 1C to 4.2V, and then charged at a constant voltage until the current was 0.05C or less. At this time, the state of charge (SOC) of the battery was 100%. After that, the battery was left for 5 minutes, and discharged at a constant current of 1C to adjust the state of charge (SOC) of the sodium ion secondary battery to 50%. The sodium ion secondary battery with 50% SOC was then left for 10 minutes, and the voltage U1 for the last second of the left-standing period was recorded, and then discharged at a constant current of 4C for 30 seconds. The constant current discharge current I and the voltage U2 for the last second of the constant current discharge were recorded, and the DC impedance of the secondary battery was calculated using the following formula.

[0092] DC impedance of secondary battery = (U2-U1) / I.

[0093] The test results are shown in Table 1 above.

[0094] As can be seen from Table 1, Comparing the results of Examples 1-6 and Comparative Examples 1-3, and comparing the results of Example 9 and Comparative Examples 10-11, it is clear that when the mass content of the first additive in the electrolyte of the present application is 0.05%-5%, the DC internal resistance of the secondary battery is lower, and when the mass content of the first additive in the electrolyte of the present application is 1%-6%, the cycle capacity retention rate of the secondary battery is higher. When the mass content of the first additive in the electrolyte is less than 0.05% (Comparative Examples 2 and 11), the amount of sulfur-containing inorganic salt product formed is relatively small, which is insufficient to suppress the occurrence of side reactions in the electrolyte, causing the secondary battery to have poor cycle performance and a slightly high DC internal resistance. When the mass content of the first additive in the electrolyte is greater than 6% (Comparative Examples 3 and 10), the excess first additive causes a clear increase in the internal resistance of the secondary battery, and the cycle performance is slightly poor.

[0095] Comparing the results of Examples 1, 7-17 with Comparative Examples 4-5, and comparing the results of Example 20 with Comparative Example 9, it is clear that the present application employs a sulfur-containing compound having a boiling point not exceeding 70°C as a first additive to be added to the electrolyte, thereby producing a secondary battery with a lower DC internal resistance and a higher cycle capacity retention rate.

[0096] When Examples 20, 21, and 23 are compared with the results of Comparative Examples 6-8, it is clear that, compared with the case where only the second additive is added to the electrolyte, the present application simultaneously adds a sulfur-containing compound having a boiling point not exceeding 70°C as a first additive to the electrolyte, thereby significantly reducing the DC internal resistance of the secondary battery and significantly improving the cycle capacity retention rate of the secondary battery.

[0097] Comparing the results of Example 1 with those of Examples 20-23 and 25, and comparing the results of Example 5 with those of Example 18 and Example 26, it is clear that when the mass content of the second additive of the present application in the electrolyte is 0.01%-10%, the negative electrode film formation quality is better, and therefore the cycle capacity retention rate of the secondary battery is further improved.

[0098] Comparing Examples 18-23, 25 with Examples 24, 26, and 27, it is clear that in the present application, when the product of W1 and W2 is any value between 0.05 and 10, the negative electrode interfacial film of the secondary battery produced is stable, the DC internal resistance is at an appropriate level, and the cycle capacity retention rate is further improved.

[0099] Comparing Examples 1-5 with Example 6 and Comparative Examples 2-3, and comparing Example 9 with Comparative Examples 10-11, it is clear that when the mass content of sulfur element in the negative electrode film layer of the present application is 0.01%-1%, the secondary battery produced has a stable negative electrode interfacial film, and the DC internal resistance is also at an appropriate level, and the cycle capacity retention rate is further improved.

[0100] In summary, the electrolyte of the present application can obtain a stable negative electrode interfacial film, making it difficult for the negative electrode plate to undergo side reactions with the electrolyte, reducing sodium precipitation, reducing the DC internal resistance of the secondary battery, and improving the cycle performance and safety performance of the secondary battery.

[0101] It should be noted that the present application is not limited to the above-mentioned embodiment. The above-mentioned embodiment is an example, and any embodiment having substantially the same configuration as the technical idea and the same effect within the scope of the technical proposal of the present application is included in the technical scope of the present application. In addition, various modifications that a person skilled in the art can make to the embodiment and other forms constructed by combining some of the components in the embodiment are also included in the scope of the present application, within the scope of the purpose of the present application. [Explanation of symbols]

[0102] 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 case, 52 electrode assembly, 53 top cover assembly.

Claims

1. An electrolyte comprising a first additive, the first additive being a sulfur-containing compound having a boiling point not exceeding 70°C at standard atmospheric pressure, the mass content of the first additive in the electrolyte being 0.05%-6%.

2. 2. The electrolyte of claim 1, wherein the mass content of the first additive in the electrolyte is 0.05%-5%, optionally 0.1%-2%.

3. The first additive is one or more selected from the group consisting of sulfur fluorides, sulfur oxides, sulfur carbon compounds, thioethers, sulfuryl compounds, and sulfinyl compounds; Optionally, the first additive is SF ６ , S.F. ４ , S.O. ２ F ２ , S.O. ２ , S.O. ３ , C.S. ２ , dimethyl sulfide, methyl ethyl sulfide, S ２ F ２ , S.F. ２ , SOF ２ and SOF ４ 2. The electrolyte of claim 1, wherein the electrolyte is one or more selected from the following:

4. Further comprising a second additive, the second additive being one or more selected from fluorinated carbonate esters and fluorinated carboxylate esters, the mass content of the second additive in the electrolyte being 0.005%-12%, optionally 0.01%-10%; Optionally, the second additive is fluorinated ethylene carbonate and / or ethyl 2,2-difluoroacetate.

5. The electrolyte of claim 4 , wherein the mass content of the second additive in the electrolyte is 0.1%-5%.

6. The electrolyte according to claim 4 or 5, wherein the mass content of the first additive in the electrolyte is W1%, the mass content of the second additive in the electrolyte is W2%, and the product of W1 and W2 is any number selected from the range of 0.01-24, optionally any number selected from the range of 0.05-16, and further optionally any number selected from the range of 0.05-10.

7. Further comprising a solvent and / or an electrolyte salt; 7. The electrolyte of claim 1, wherein optionally the solvent is a carbonate-based solvent.

8. A secondary battery comprising a positive electrode plate, a negative electrode plate, a separator, and the electrolyte according to claim 1 .

9. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, and the mass content of sulfur element in the negative electrode film layer is 0.01%-1.14%, optionally 0.01%-1%. The secondary battery according to claim 8.

10. 10. The secondary battery according to claim 9, wherein the mass content of sulfur element in the negative electrode film layer is 0.05%-0.5%.

11. A battery module comprising the secondary battery according to claim 8 .

12. A battery pack comprising the battery module according to claim 11.

13. A power consuming device comprising at least one selected from the group consisting of the secondary battery according to any one of claims 8 to 10, the battery module according to claim 11, and the battery pack according to claim 12.

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