Secondary battery and electric device

Abstract

A secondary battery and an electric device, relating to the technical field of secondary batteries. When a positive electrode active material is a nickel-iron-manganese layered metal oxide, a cyclic sulfate ester compound is capable of forming films on both a positive electrode sheet and a negative electrode sheet, and a CEI film formed on the positive electrode sheet suppresses a side reaction between the nickel-iron-manganese layered metal oxide and a non-aqueous electrolyte, thereby improving the cycle performance of the secondary battery and reducing gas generation during high-SOC storage. Moreover, a difluorooxalatoborate salt compound, which has a higher reduction potential than the cyclic sulfate ester compound, is selected, the difluorooxalatoborate salt compound is capable of preferentially forming an inorganic SEI film on the surface of a negative electrode sheet prior to the cyclic sulfate ester compound, and the inorganic SEI film is distributed in a dot-like manner to occupy some of surface active sites of a negative electrode active material, thereby reducing extensive formation of an organic polymer-type SEI film by the cyclic sulfate ester compound on the negative electrode sheet, so that the overall impedance of the SEI film is low, reducing the DCR of the secondary battery, and isolating the electrolyte from a negative electrode to suppress gas generation caused by reduction at the negative electrode.

Description

Secondary batteries and electrical equipment

[0001] Cross-referencing

[0002] This application claims priority to Chinese Patent Application No. 202411813002.2, filed on December 10, 2024, entitled “A Secondary Battery and Electrical Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of secondary battery technology, and more specifically, to a secondary battery and an electrical device. Background Technology

[0004] During the charge / discharge cycle of a secondary battery, the layered structure of sodium-based layered oxide cathode materials is prone to reconstruction, accompanied by the formation of surface cracks. This results in the exposure of fresh interfaces created by the cracks to the non-aqueous electrolyte. Due to its high activity, this leads to a continuous oxidative decomposition of the non-aqueous electrolyte, ultimately deteriorating the cycle performance of the secondary battery and causing gas generation during high SOC storage.

[0005] To improve this problem, additives are usually added to form a CEI film on the positive electrode to suppress the occurrence of side reactions. However, for nickel-iron-manganese layered metal oxides, the addition of additives will seriously worsen the impedance of the negative electrode of the secondary battery, resulting in a high DCR of the secondary battery. Summary of the Invention

[0006] In view of the above problems, this application provides a secondary battery and an electrical device to improve the cycle performance and high SOC storage gas generation of a secondary battery with nickel-iron-manganese layered metal oxide as the positive electrode active material, while maintaining a low DCR of the secondary battery.

[0007] In a first aspect, this application provides a secondary battery, comprising a positive electrode sheet and a non-aqueous electrolyte, with the positive electrode sheet and non-aqueous electrolyte in contact. The positive electrode sheet includes a positive active material layer, the positive active material layer includes a positive active material, and the positive active material includes Na. a M b Ni c Fe d Mn e O2, wherein M is selected from at least one of Sc, Ti, V, Cr, Co, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 0 < a ≤ 4, 0 ≤ b ≤ 0.2, 0.23 < c ≤ 0.35, 0 < d ≤ 0.35, 0 < e ≤ 0.4;

[0008] The non-aqueous electrolyte includes a first additive and a second additive. The first additive includes cyclic sulfate compounds, and the second additive includes difluorooxalate borate compounds.

[0009] In the technical solution of this application embodiment, the secondary battery uses cyclic sulfate ester compounds and difluorooxalate borate compounds as electrolyte additives, which can improve the performance of the electrolyte when using Na... a M b Ni c Fe d Mn e The secondary battery using O2 as the positive electrode active material maintains low DCR while achieving high SOC storage and gas generation.

[0010] The inventive mechanism by which this application can solve the above-mentioned technical problems may be as follows: the secondary battery uses Na... a M b N c Fe d Mn e O2 is used as the positive electrode active material. Because this material does not contain highly oxidizing metal elements, the oxidation of cyclic sulfate compounds on the positive electrode side is weak. This means that besides forming the CEI film, most of the cyclic sulfate compounds are reduced to the negative electrode side to form an organic polymer SEI film. Since it is difficult to control the polymerization rate and degree in the battery system, the polymer SEI film is usually relatively thick, significantly affecting the negative electrode impedance and consequently impacting Na+. + Therefore, for this secondary battery, difluorooxalate borate compounds are selected as the second additive in combination with cyclic sulfate compounds. Difluorooxalate borate compounds have a higher reduction potential than cyclic sulfate compounds, and can preferentially form an inorganic SEI film containing F and B elements on the negative electrode sheet. Moreover, the inorganic SEI film generally exhibits a dotted distribution, occupying some of the surface active sites of the negative electrode active material, thereby reducing the large-scale formation of organic polymer SEI films on the negative electrode sheet by cyclic sulfate compounds. This composite SEI film not only makes the SEI film of the entire negative electrode sheet have a lower impedance, thus maintaining a low DCR of the secondary battery, but also effectively isolates the non-aqueous electrolyte from the negative electrode, suppressing the gas generation caused by the reduction of active hydrogen generated by the side reaction between the positive electrode sheet and the non-aqueous electrolyte on the negative electrode sheet.

[0011] In some embodiments, difluorooxalate borate compounds include: N y M, where N is (F₂C₂O₄B). y- M is Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ and Ni 3+ At least one of them, where y is 1, 2 or 3.

[0012] In the above implementation process, N is selected as (F2C2O4B). y- M is Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ and Ni 3+ N y M-type difluorooxalate borate compounds, as a second additive, can form a better low-impedance SEI film, thereby enabling the secondary battery to have a lower DCR.

[0013] In some embodiments, the difluorooxalate borate compounds include at least one of sodium difluorooxalate borate, lithium difluorooxalate borate, and calcium difluorooxalate borate. These three difluorooxalate borate compounds, as second additives, can all form a good low-impedance SEI film, thereby enabling the secondary battery to have a low DCR.

[0014] In some embodiments, the mass content of difluorooxalate borate compounds in the non-aqueous electrolyte is 0.005% to 3%.

[0015] In the above implementation process, the higher the mass content of difluorooxalate borate compounds, the more beneficial it is to maintain a low DCR of the secondary battery. The lower the mass content of difluorooxalate borate compounds, the less residue in the non-aqueous electrolyte, which is more beneficial to avoid interfacial impedance and gas generation deterioration. By controlling the mass content of difluorooxalate borate compounds to 0.005%~3%, the secondary electrode can have a low DCR and less gas generation.

[0016] In some embodiments, the mass content of difluorooxalate borate compounds in the non-aqueous electrolyte is 0.2% to 3%.

[0017] In the above implementation process, by controlling the mass content of difluorooxalate borate compounds to be 0.2%~3%, the secondary electrode can have a lower DCR and less gas production.

[0018] In some embodiments, cyclic sulfate compounds include at least one of monocyclic cyclic sulfate compounds and polycyclic cyclic sulfate compounds.

[0019] The aforementioned cyclic sulfate compounds can all form a CEI film on the positive electrode, suppressing the side reactions of sodium layered oxides with non-aqueous electrolytes, improving the cycle performance of secondary batteries and gas generation during high SOC storage.

[0020] In some embodiments, polycyclic cyclic sulfate compounds include R1, R2, R3, and R4 each independently include R5 and R6 each independently include hydrogen atoms, C1-C6 alkyl groups, halogen atoms, C1-C3 haloalkyl groups, C1-C3 alkoxy groups, C1-C3 haloalkoxy groups, alkenyl groups, ester groups, cyano groups, or sulfonic acid groups. Hydrogen atom, C1-C6 alkyl group, halogen atom, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, alkenyl group, ester group, cyano group or sulfonic acid group.

[0021] In the above-mentioned process, the polycyclic cyclic sulfate can better form a CEI film at the positive electrode, thereby suppressing the side reactions between the layered oxides of sodium and the non-aqueous electrolyte.

[0022] In some embodiments, polycyclic cyclic sulfate compounds include at least one of Formulas 1-16:

[0023] , , , , , , , ,

[0024] , , , ,

[0025] , , , .

[0026] In the above implementation process, the polycyclic cyclic sulfate compounds of Formulas 1 to 16 can form a better CEI film at the positive electrode, and can better suppress the side reactions of sodium layered oxides and non-aqueous electrolytes.

[0027] In some embodiments, the cyclic sulfate ester compound accounts for 0.005% to 4% of the mass of the non-aqueous electrolyte.

[0028] In the above implementation process, the higher the mass proportion of cyclic sulfate compounds in the non-aqueous electrolyte, the more beneficial it is to reducing the side reactions of the secondary battery. Conversely, the lower the mass proportion of cyclic sulfate compounds in the non-aqueous electrolyte, the more beneficial it is to control the DCR of the secondary battery. By controlling the mass proportion of cyclic sulfate compounds in the non-aqueous electrolyte to 0.005%~4%, it is beneficial to balance the reduction of side reactions and the control of DCR in the secondary battery.

[0029] In some embodiments, the cyclic sulfate ester compound accounts for 0.2% to 2% of the mass of the non-aqueous electrolyte.

[0030] In the above implementation process, by controlling the mass ratio of cyclic sulfate compounds in the non-aqueous electrolyte to 0.2%~2%, it is more beneficial to balance the reduction of secondary battery side reactions and the control of DCR.

[0031] In some embodiments, the non-aqueous electrolyte further includes a third additive, which is a negative electrode film-forming additive.

[0032] In the above implementation process, by adding a negative electrode film-forming additive to the non-aqueous electrolyte, a better SEI film can be formed on the negative electrode, which can better suppress the gas generation caused by the reduction of active hydrogen generated by the side reaction between the positive electrode and the non-aqueous electrolyte on the negative electrode.

[0033] In some embodiments, the mass content of the third additive in the non-aqueous electrolyte is 0.05% to 4%.

[0034] In the above implementation process, the higher the mass percentage of the third additive in the non-aqueous electrolyte, the more beneficial it is to reducing gas production in the secondary battery. The lower the mass percentage of the third additive in the non-aqueous electrolyte, the more beneficial it is to control the DCR of the secondary battery. By controlling the mass percentage of the third additive in the non-aqueous electrolyte to 0.05%~4%, it is beneficial to balance low gas production and DCR of the secondary battery.

[0035] In some embodiments, the third additive includes at least one selected from fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, maleic anhydride, succinic anhydride, and triallyl phosphate.

[0036] In the above implementation process, by adding third additives such as fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, maleic anhydride, succinic anhydride, and triallyl phosphate to the non-aqueous electrolyte in combination with difluorooxalate borate compounds, a better SEI film can be formed at the negative electrode. This can better suppress the gas generation caused by the reduction of active hydrogen generated by the side reaction between the positive electrode and the non-aqueous electrolyte at the negative electrode.

[0037] Secondly, this application provides an electrical device that includes the secondary battery provided in the first aspect. Attached Figure Description

[0038] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0039] Figure 1 is a structural schematic diagram of a vehicle provided in some embodiments of this application;

[0040] Figure 2 is an exploded structural diagram of a secondary battery provided in some embodiments of this application;

[0041] Figure 3 is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0042] Figure 4 is an exploded view of a battery cell provided in some embodiments of this application.

[0043] The reference numerals in the detailed embodiments are as follows:

[0044] 1000 - Vehicle; 100 - Secondary battery; 200 - Motor; 300 - Controller; 10 - Housing; 11 - Accommodation space; 12 - First part; 13 - Second part; 20 - Battery cell; 21 - Housing; 211 - Opening; 22 - End cap assembly; 221 - End cap; 222 - Electrode terminal; 23 - Electrode assembly; 24 - Current collector; 25 - Insulation protection component. Embodiments of the present invention

[0045] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0047] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0048] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0049] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0050] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0051] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0052] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0053] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0054] The power battery can be a sodium-ion secondary battery. During the charge / discharge cycle of the secondary battery, the layered structure of the sodium layered oxide cathode material is prone to reconstruction, accompanied by the formation of surface cracks. This causes the fresh interface of the material to be exposed to the electrolyte due to the cracks. Because of its high activity, it will cause side reactions of continuous oxidation and decomposition of electrolyte, which will eventually deteriorate the cycle performance of the secondary battery and produce gas during high SOC storage.

[0055] To improve this problem, additives, such as sulfates, are usually added to form a CEI film on the positive electrode to suppress side reactions. However, for nickel-iron-manganese layered metal oxides, the oxidation performance of the positive electrode active material is relatively weak, which leads to weak oxidation of the sulfate additive on the positive electrode side. As a result, in addition to forming a CEI film, most of the sulfate additive also needs to be reduced to form a film on the negative electrode side, which worsens the impedance of the negative electrode of the secondary battery, resulting in a higher DCR of the secondary battery and thus affecting battery performance.

[0056] Based on the above considerations, in order to improve the cycle performance of secondary batteries and maintain a low DCR while achieving high SOC storage and gas generation, this application proposes a secondary battery. The secondary battery includes a positive electrode sheet and a non-aqueous electrolyte, with the positive electrode sheet and non-aqueous electrolyte in contact. The positive electrode sheet includes a positive active material layer, which includes a positive active material, and the positive active material includes Na. a M b Ni c Fe d Mn eO2, wherein M is selected from at least one of Sc, Ti, V, Cr, Co, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 0 < a ≤ 4, 0 ≤ b ≤ 0.2, 0.23 < c ≤ 0.35, 0 < d ≤ 0.35, 0 < e ≤ 0.4;

[0057] The non-aqueous electrolyte includes a first additive and a second additive. The first additive includes cyclic sulfate compounds, and the second additive includes difluorooxalate borate compounds.

[0058] This secondary battery uses cyclic sulfate compounds and difluorooxalate borate compounds as electrolyte additives, which can improve the performance of batteries using Na+ electrolytes. a M b Ni c Fe d Mn e The secondary battery using O2 as the positive electrode active material maintains low DCR while achieving high SOC storage and gas generation.

[0059] The inventive mechanism by which this application can solve the above-mentioned technical problems may be as follows: the secondary battery uses Na... a M b N c Fe d Mn e O2 is used as the positive electrode active material. Because this material does not contain highly oxidizing metal elements, the oxidation of cyclic sulfate compounds on the positive electrode side is relatively weak. This results in most of the cyclic sulfate compounds, besides forming the CEI film, being reduced to an organic polymer-type SEI film on the negative electrode side. Since the polymerization rate and degree are difficult to control in the battery system, the polymer-type SEI film is usually quite thick, significantly impacting the negative electrode impedance and consequently affecting the Na+. + Therefore, for this secondary battery, difluorooxalate borate compounds are selected as the second additive in combination with cyclic sulfate compounds. Difluorooxalate borate compounds have a higher reduction potential than cyclic sulfate compounds, and can preferentially form an inorganic SEI film containing F and B elements on the negative electrode sheet. Moreover, the inorganic SEI film generally exhibits a dotted distribution, occupying some of the surface active sites of the negative electrode active material, thereby reducing the large-scale formation of organic polymer SEI films on the negative electrode sheet by cyclic sulfate compounds. This composite SEI film not only makes the SEI film of the entire negative electrode sheet have a lower impedance, thus maintaining a low DCR of the secondary battery, but also effectively isolates the non-aqueous electrolyte from the negative electrode, suppressing the gas generation caused by the reduction of active hydrogen generated by the side reaction between the positive electrode sheet and the non-aqueous electrolyte on the negative electrode sheet.

[0060] This secondary battery can be used, but is not limited to, in electrical equipment such as vehicles, ships, or aircraft. The power system of such electrical equipment can be composed of a secondary battery disclosed in this application.

[0061] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0062] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device according to an embodiment of this application.

[0063] Please refer to Figure 1, which is a structural schematic diagram of a vehicle provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. A secondary battery 100 is installed inside the vehicle 1000, and the secondary battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The secondary battery 100 can be used to power the vehicle 1000; for example, the secondary battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 300 and a motor 200. The controller 300 is used to control the secondary battery 100 to supply power to the motor 200, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0064] In some embodiments of this application, the secondary battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0065] In this application, the secondary battery 100 can refer to a single battery cell 20, or it can refer to a single physical module comprising multiple battery cells 20 to provide higher voltage and capacity, which can be in the form of a battery pack, battery module, etc. The secondary battery 100 may include a housing 10 for encapsulating multiple battery cells 20, and the housing 10 can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells 20.

[0066] Figure 2 is an exploded structural diagram of a secondary battery 100 provided in some embodiments of this application. Referring to Figure 2, the secondary battery 100 includes a housing 10 and battery cells 20, with the battery cells 20 housed within the housing 10.

[0067] The housing 10 provides a receiving space 11 for the battery cell 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap each other to define the receiving space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealant (not shown), such as a sealing ring, sealant, etc.

[0068] The first part 12 and the second part 13 can be of various shapes, such as cuboids, cylinders, etc. The first part 12 can be a hollow structure with one side open to form a cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with one side open to form a cavity for accommodating the battery cell 20. The opening side of the second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11. Of course, as shown in Figure 2, the first part 12 can also be a hollow structure with one side open, and the second part 13 can be a plate-like structure. The second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11.

[0069] In the secondary battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they can be connected in series, in parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed configuration, and then the whole assembly of multiple battery cells 20 is housed in the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, in parallel, or in a mixed configuration to form a battery module, and then multiple battery modules can be connected in series, in parallel, or in a mixed configuration to form a whole, which is then housed in the housing 10. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes. Figure 2 illustrates an example of a square battery cell 20.

[0070] In some embodiments, the secondary battery 100 may further include a busbar (not shown), through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of multiple battery cells 20.

[0071] Figure 3 is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of this application, and Figure 4 is an exploded view of a battery cell 20 provided in some embodiments of this application. Referring to Figures 3 and 4, the battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, the electrode assembly 23 is accommodated within the housing 21, and the end cap assembly 22 is used to seal the opening 211.

[0072] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a cuboid structure, the housing 21 can also be a cuboid structure. Figures 3 and 4 exemplarily show the case where the housing 21 and the electrode assembly 23 are square.

[0073] The outer shell 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. This application embodiment does not impose any special restrictions on this.

[0074] The end cap assembly 22 includes an end cap 221 and electrode terminals 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed mounting space (not shown), which is used to accommodate the electrode assembly 23. The mounting space is also used to accommodate an electrolyte, such as an electrolyte solution. As a component that outputs electrical energy to the electrode assembly 23, the end cap assembly 22 has electrode terminals 222 that are electrically connected to the electrode assembly 23, i.e., the electrode terminals 222 are electrically connected to the tabs of the electrode assembly 23. For example, the electrode terminals 222 and the tabs are connected via a current collector 24 to achieve the electrical connection between the electrode terminals 222 and the tabs.

[0075] It should be noted that the opening 211 of the outer casing 21 can be one or two. If the outer casing 21 has one opening 211, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are used to electrically connect to the positive electrode tab and the negative electrode tab of the electrode assembly 23, respectively. If the outer casing 21 has two openings 211, for example, the two openings 211 are located on opposite sides of the outer casing 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 respectively cover the two openings 211 of the outer casing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, used to electrically connect to the positive electrode tab of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, used to electrically connect to the negative electrode plate of the electrode assembly 23.

[0076] In some embodiments, as shown in FIG4, the battery cell 20 may further include an insulating protective member 25 fixed to the outer periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is an adhesive tape bonded to the outer periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 surrounds the outer periphery of multiple electrode assemblies 23, forming multiple electrode assemblies 23 into an integral structure to maintain the structural stability of the electrode assembly 23.

[0077] The electrode assembly 23 includes a positive electrode, a negative electrode, and a separator. The electrode assembly 23 can be a wound electrode assembly 23 or a stacked electrode assembly 23, and the embodiments of this application are not limited thereto.

[0078] The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector. The positive current collector without the positive active material layer protrudes from the positive current collector with the positive active material layer. The positive current collector without the positive active material layer serves as the positive electrode tab.

[0079] 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.).

[0080] The positive electrode active material layer includes a binder positive electrode active material.

[0081] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0082] 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.

[0083] 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.

[0084] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode current collector. The negative electrode current collector without the negative electrode active material layer protrudes from the negative electrode current collector with the negative electrode active material layer. The negative electrode current collector without the negative electrode active material layer serves as the negative electrode tab.

[0085] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0086] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which 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. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials 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.

[0087] 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).

[0088] 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.

[0089] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0090] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as 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 a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0091] In other embodiments, the current collector of the negative electrode sheet may also include a current collector body and a base coating. The base coating may be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, but may contain a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer of the negative electrode sheet can be disposed on the surface of at least one side of the current collector body; when the current collector of the negative electrode sheet includes a base coating, the film layer of the negative electrode sheet can be disposed on the surface of the base coating away from the current collector body.

[0092] In some implementations, in order to ensure that a large current can pass through without melting, there are multiple positive electrode tabs stacked together, and multiple negative electrode tabs stacked together.

[0093] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0094] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0095] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0096] In some embodiments, the electrolyte is a non-aqueous electrolyte. Non-aqueous electrolytes include electrolyte salts and organic solvents.

[0097] Electrolyte salts include sodium salts, which include, but are not limited to, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, or Na(CH3)C6H4SO3.

[0098] In some embodiments, the organic solvent may be selected from at least one of ester solvents, ether solvents, and sulfone solvents. Exemplarily, the solvent includes, but is not limited to, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene 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, methyl ethyl sulfone, and diethyl sulfone.

[0099] In some embodiments, the non-aqueous electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0100] This application provides a secondary battery, which includes a positive electrode sheet and a non-aqueous electrolyte. The positive electrode sheet and the non-aqueous electrolyte are in contact. The positive electrode sheet includes a positive active material layer, and the positive active material layer includes a positive active material, which includes Na. a M b Ni c Fe d Mn e O2, wherein M is selected from at least one of Sc, Ti, V, Cr, Co, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 0 < a ≤ 4, 0 ≤ b ≤ 0.2, 0.23 < c ≤ 0.35, 0 < d ≤ 0.35, 0 < e ≤ 0.4;

[0101] The non-aqueous electrolyte includes a first additive and a second additive. The first additive includes cyclic sulfate compounds, and the second additive includes difluorooxalate borate compounds.

[0102] It should be noted that in the list of positive electrode active materials in this application, the molar content of Na refers to the initial state of the material, that is, the state before feeding. When the positive electrode material is applied to the battery system, the molar content of Na will change after charge and discharge cycles.

[0103] Furthermore, due to differences in the preparation processes and conditions of materials, the molar content of oxygen is usually not strictly the same as the coefficient of oxygen in the chemical formula, and fluctuations may occur. For example, in the layered oxide of sodium, Na... a M b Ni c Fe d Mn e The molar content of O in O2 is not strictly 2.

[0104] The type of the first or second additive in the non-aqueous electrolyte can be determined using the following method: In a nitrogen-filled glove box, add 500 μl of deuterated reagent to an NMR tube, then add 100 μl of the non-aqueous electrolyte sample to the NMR tube. Shake the NMR tube to dissolve the non-aqueous electrolyte in the deuterated reagent. The test is performed using an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because the non-aqueous electrolyte is highly sensitive to moisture, both the NMR test and sample preparation are conducted in a nitrogen atmosphere (H₂O content less than 0.1 ppm, O₂ content less than 0.1 ppm). Simultaneously, all instruments used in the test must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours. The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831 KF coulometric moisture analyzer was used for moisture testing. Then, in a nitrogen-filled glove box, 10 ml of dried DMSO-d6 and 300 μl of dried internal standard trifluoromethylbenzene were mixed thoroughly to obtain the first solution. 10 ml of dried deuterated acetonitrile and 300 μl of dried internal standard trifluoromethylbenzene were then mixed thoroughly to obtain the second solution. The first and second solutions were then mixed thoroughly to obtain the deuterated reagent.

[0105] In summary, this secondary battery, by using cyclic sulfate compounds and difluorooxalate borate compounds as electrolyte additives, can improve the performance of batteries using Na+. a M b Ni c Fe d Mn e The secondary battery using O2 as the positive electrode active material maintains low DCR while achieving high SOC storage and gas generation.

[0106] The inventive mechanism by which this application can solve the above-mentioned technical problems may be as follows: the secondary battery uses Na... a M b N c Fe d Mn e O2 is used as the positive electrode active material. Because this material does not contain highly oxidizing metal elements, the oxidation of cyclic sulfate compounds on the positive electrode side is relatively weak. This results in most of the cyclic sulfate compounds, besides forming the CEI film, being reduced to an organic polymer-type SEI film on the negative electrode side. Since the polymerization rate and degree are difficult to control in the battery system, the polymer-type SEI film is usually quite thick, significantly impacting the negative electrode impedance and consequently affecting the Na+. +Therefore, for this secondary battery, difluorooxalate borate compounds are selected as the second additive in combination with cyclic sulfate compounds. Difluorooxalate borate compounds have a higher reduction potential than cyclic sulfate compounds, and can preferentially form an inorganic SEI film containing F and B elements on the negative electrode sheet. Moreover, the inorganic SEI film generally exhibits a dotted distribution, occupying some of the surface active sites of the negative electrode active material, thereby reducing the large-scale formation of organic polymer SEI films on the negative electrode sheet by cyclic sulfate compounds. This composite SEI film not only makes the SEI film of the entire negative electrode sheet have a lower impedance, thus maintaining a low DCR of the secondary battery, but also effectively isolates the non-aqueous electrolyte from the negative electrode, suppressing the gas generation caused by the reduction of active hydrogen generated by the side reaction between the positive electrode sheet and the non-aqueous electrolyte on the negative electrode sheet.

[0107] In the technical solution of this application embodiment, the difluorooxalate borate compound includes: N y M, where N is (F₂C₂O₄B). y- M is Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ and Ni 3+ At least one of them, where y is 1, 2 or 3.

[0108] Choose N as (F2C2O4B) y- M is Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ and Ni 3+ N y M-type difluorooxalate borate compounds, as a second additive, can not only preferentially form a film on the negative electrode side compared to cyclic sulfate compounds, but also cooperate with cyclic sulfate compounds to form a low-impedance SEI film with better stability, thereby enabling the secondary battery to have a lower DCR.

[0109] For example, difluorooxalate borate compounds may be selected from at least one of (F2C2O4B)Li, (F2C2O4B)Na, (F2C2O4B)K, (F2C2O4B)Rb, (F2C2O4B)Cs, (F2C2O4B)2Mg, (F2C2O4B)2Ca, (F2C2O4B)2Ba, (F2C2O4B)2Fe, (F2C2O4B)2Ni, (F2C2O4B)3Al, (F2C2O4B)3Fe, (F2C2O4B)3Ni, etc.

[0110] In the technical solutions of this application embodiment, the difluorooxalate borate compounds include at least one of sodium difluorooxalate borate, lithium difluorooxalate borate, and calcium difluorooxalate borate.

[0111] All three difluorooxalate borate compounds mentioned above can combine with cyclic sulfate compounds to form a stable, low-impedance SEI film, thereby enabling the secondary battery to have a low DCR.

[0112] In the technical solution of this application embodiment, the mass content of difluorooxalate borate compounds in the non-aqueous electrolyte is 0.005%~3%.

[0113] The content of difluorooxalate borate compounds in non-aqueous electrolytes can be determined using the following method: 500 μl of deuterated reagent is added to an NMR tube in a nitrogen-filled glove box. 100 μl of the non-aqueous electrolyte sample is then added to the NMR tube. The tube is shaken to dissolve the non-aqueous substance in the deuterated reagent. The test is performed using an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because non-aqueous electrolytes are highly sensitive to moisture, both the NMR test and sample preparation are conducted under a nitrogen atmosphere (H₂O content less than 0.1 ppm, O₂ content less than 0.1 ppm). Simultaneously, all instruments used in the test must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours. The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831 KF coulometric moisture analyzer was used for moisture testing. Then, in a nitrogen-filled glove box, 10 ml of dried DMSO-d6 and 300 μl of dried internal standard trifluoromethylbenzene were mixed thoroughly to obtain the first solution. 10 ml of dried deuterated acetonitrile and 300 μl of dried internal standard trifluoromethylbenzene were then mixed thoroughly to obtain the second solution. The first and second solutions were then mixed thoroughly to obtain the deuterated reagent.

[0114] The higher the mass content of difluorooxalate borate compounds, the better it is to maintain a low DCR of the secondary battery. The lower the mass content of difluorooxalate borate compounds, the less residue in the non-aqueous electrolyte, which is more conducive to avoiding interfacial impedance and gas generation deterioration. By controlling the mass content of difluorooxalate borate compounds to 0.005%~3%, the secondary electrode can have a lower DCR and less gas generation.

[0115] For example, the mass content of difluorooxalate borate compounds can be any value among 0.005%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, and 3%, or between any two values.

[0116] Furthermore, in the non-aqueous electrolyte, the mass content of difluorooxalate borate compounds is 0.2% to 3%. By controlling the mass content of difluorooxalate borate compounds to 0.2% to 3%, the secondary electrode can have a lower DCR and less gas production.

[0117] In the technical solutions of this application embodiment, cyclic sulfate compounds include at least one of monocyclic cyclic sulfate compounds and polycyclic cyclic sulfate compounds.

[0118] It is understandable that monocyclic cyclic sulfates refer to cyclic sulfate compounds that contain only one cyclic structure with a sulfate group.

[0119] Polycyclic cyclic sulfate compounds refer to cyclic sulfate compounds that have at least two cyclic structures with sulfate groups. Here, "at least two" includes, but is not limited to, two, three, four, etc.

[0120] The aforementioned cyclic sulfate compounds can all form a CEI film on the positive electrode, suppressing the side reactions of sodium layered oxides with non-aqueous electrolytes, improving the cycle performance of secondary batteries and gas generation during high SOC storage.

[0121] In the technical solutions of this application embodiment, polycyclic cyclic sulfate compounds include R1, R2, R3, and R4 each independently include R5 and R6 each independently include hydrogen atoms, C1-C6 alkyl groups, halogen atoms, C1-C3 haloalkyl groups, C1-C3 alkoxy groups, C1-C3 haloalkoxy groups, alkenyl groups, ester groups, cyano groups, or sulfonic acid groups. Hydrogen atom, C1-C6 alkyl group, halogen atom, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, alkenyl group, ester group, cyano group or sulfonic acid group.

[0122] This polycyclic sulfate compound has at least two cyclic structures with sulfate groups, which is beneficial for forming a network polymer structure (three-dimensional network structure, which is not easy to break) after oxidation and decomposition, resulting in better coating effect. It is also beneficial for forming a stable and unbreakable CEI film on the positive electrode, suppressing the side reaction between sodium layered oxide and non-aqueous electrolyte, improving the cycle performance of secondary battery and high SOC storage gas generation.

[0123] Understandably, when R1, R2, R3, and R4 include R5 and R6 include hour, The structure is not an infinite cycle, meaning the last replacement... R5 and R6 on the form independently include a hydrogen atom, a C1-C6 alkyl group, a halogen atom, a C1-C3 haloalkyl group, a C1-C3 alkoxy group, a C1-C3 haloalkoxy group, an alkenyl group, an ester group, a cyano group, or a sulfonic acid group.

[0124] It should be noted that the above Bending key in the structure "Refers to the connection sites on the molecular structure, i.e., substitutions" In the structure, R1 and R2 、 Connection sites of R3 or R4.

[0125] As an example, C1-C6 alkyl groups can be understood as alkyl groups with 1-6 carbon atoms, such as methyl (-CH3), ethyl (-CH2CH3), n-propyl (-CH2CH2CH3), isopropyl (-CH(CH3)2), n-butyl (-CH2CH2CH2CH3), tert-butyl (-C(CH3)3), n-pentyl (-CH2CH2CH2CH2CH3), n-hexyl (-CH2CH2CH2CH2CH2CH3), etc.; halogen atoms can include F, Cl, Br or I.

[0126] As an example, C1-C3 haloalkyl groups can be understood as groups in which at least one hydrogen atom on an alkyl group with 1-3 carbon atoms is replaced by a halogen atom, such as -CH2Cl, -CH2CH2Cl, -CH2CH2CH2Cl, etc.

[0127] As an example, C1-C3 alkoxy groups can be understood as alkoxy groups with 1-3 carbon atoms, such as methoxy (CH3O-), ethoxy (CH3CH2O-), propoxy (CH3CH2CH2O-), etc.

[0128] As an example, C1-C3 haloalkoxy groups can be understood as groups in which at least one hydrogen atom on an alkoxy group with 1-3 carbon atoms is replaced by a halogen atom, such as ClCH2O-, ClCH2CH2O-, ClCH2CH2CH2O-, etc.

[0129] As an example, alkenyl can be understood as a group formed by removing one or more hydrogen atoms from the olefin molecule, such as vinyl CH2=CH-, propenyl -CH=CH-CH3, etc.

[0130] Furthermore, the polycyclic cyclic sulfate compounds include at least one of formulas 1-16:

[0131] , , , , , , , ,

[0132] , , , ,

[0133] , , , .

[0134] Polycyclic sulfate compounds of Formulas 1 to 16 can be reduced and opened, interconnected to form a polymer network structure, which can form a CEI film with good stability at the positive electrode and better suppress the side reactions of sodium layered oxides and non-aqueous electrolytes.

[0135] In the technical solutions of this application, monocyclic cyclic sulfate compounds include vinyl sulfate.

[0136] Vinyl sulfate can form a CEI film at the positive electrode, inhibiting the side reactions of sodium layered oxides with non-aqueous electrolytes.

[0137] In the technical solution of this application embodiment, the mass percentage of cyclic sulfate ester compounds in the non-aqueous electrolyte is 0.005%~4%.

[0138] The content of cyclic sulfate compounds in non-aqueous electrolytes can be determined using the following method: 500 μl of deuterated reagent is added to an NMR tube in a nitrogen-filled glove box. 100 μl of the non-aqueous electrolyte sample is then added to the NMR tube. The tube is shaken to dissolve the non-aqueous electrolyte in the deuterated reagent. The NMR is then performed using an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because non-aqueous electrolytes are highly sensitive to moisture, both the NMR test and sample preparation are conducted under a nitrogen atmosphere (H₂O content less than 0.1 ppm, O₂ content less than 0.1 ppm). Simultaneously, all instruments used in the test must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours. The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831 KF coulometric moisture analyzer was used for moisture testing. Then, in a nitrogen-filled glove box, 10 ml of dried DMSO-d6 and 300 μl of dried internal standard trifluoromethylbenzene were mixed thoroughly to obtain the first solution. 10 ml of dried deuterated acetonitrile and 300 μl of dried internal standard trifluoromethylbenzene were then mixed thoroughly to obtain the second solution. The first and second solutions were then mixed thoroughly to obtain the deuterated reagent.

[0139] The higher the mass percentage of cyclic sulfate compounds in the non-aqueous electrolyte, the better it is for reducing side reactions in the secondary battery. Conversely, the lower the mass percentage of cyclic sulfate compounds in the non-aqueous electrolyte, the better it is for controlling the DCR (discharge rate) of the secondary battery. By controlling the mass percentage of cyclic sulfate compounds in the non-aqueous electrolyte to 0.005%~4%, it is beneficial to balance the reduction of side reactions and the control of DCR in the secondary battery.

[0140] Furthermore, the mass percentage of cyclic sulfate compounds in the non-aqueous electrolyte is 0.2% to 2%. By controlling the mass percentage of cyclic sulfate compounds in the non-aqueous electrolyte to 0.2% to 2%, it is more beneficial to balance the reduction of secondary battery side reactions and the control of DCR.

[0141] For example, the mass percentage of cyclic sulfate compounds in the non-aqueous electrolyte can be any value or between any two of the following: 0.005%, 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%.

[0142] In the technical solution of this application embodiment, the non-aqueous electrolyte also includes a third additive, which is a negative electrode film-forming additive.

[0143] By adding a negative electrode film-forming additive to the non-aqueous electrolyte, a better SEI film can be formed on the negative electrode, which can better suppress the gas generation caused by the reduction of active hydrogen generated by the side reaction between the positive electrode and the non-aqueous electrolyte on the negative electrode.

[0144] In the technical solution of this application embodiment, the mass content of the third additive in the non-aqueous electrolyte is 0.05%~4%.

[0145] The content of the third additive in the non-aqueous electrolyte can be tested using the following method: 500 μl of deuterated reagent is added to an NMR tube in a nitrogen-filled glove box. 100 μl of the non-aqueous electrolyte sample is then added to the NMR tube. The NMR tube is shaken to dissolve the non-aqueous electrolyte in the deuterated reagent. The test is performed using an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because the non-aqueous electrolyte is highly sensitive to moisture, both the NMR test and sample preparation are conducted in a nitrogen atmosphere (H₂O content less than 0.1 ppm, O₂ content less than 0.1 ppm). Simultaneously, all instruments used in the test must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours. The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831 KF coulometric moisture analyzer was used for moisture testing. Then, in a nitrogen-filled glove box, 10 ml of dried DMSO-d6 and 300 μl of dried internal standard trifluoromethylbenzene were mixed thoroughly to obtain the first solution. 10 ml of dried deuterated acetonitrile and 300 μl of dried internal standard trifluoromethylbenzene were then mixed thoroughly to obtain the second solution. The first and second solutions were then mixed thoroughly to obtain the deuterated reagent.

[0146] The higher the mass percentage of the third additive in the electrolyte, the better it is for reducing gas production in the secondary battery. The lower the mass percentage of the third additive in the non-aqueous electrolyte, the better it is for controlling the DCR of the secondary battery. By controlling the mass percentage of the third additive in the non-aqueous electrolyte to 0.05%~4%, it is beneficial to balance low gas production and DCR of the secondary battery.

[0147] In the technical solutions of this application embodiment, the negative electrode film-forming additive includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, maleic anhydride, succinic anhydride, and triallyl phosphate.

[0148] The type of the third additive in the non-aqueous electrolyte can be determined using the following method: 500 μl of deuterated reagent is added to an NMR tube in a nitrogen-filled glove box. 100 μl of the non-aqueous electrolyte sample is then added to the NMR tube. The tube is shaken to dissolve the non-aqueous electrolyte in the deuterated reagent. The test is performed using an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because the non-aqueous electrolyte is highly sensitive to moisture, both the NMR test and sample preparation are conducted in a nitrogen atmosphere (H₂O content less than 0.1 ppm, O₂ content less than 0.1 ppm). Simultaneously, all instruments used in the test must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours. The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831 KF coulometric moisture analyzer was used for moisture testing. Then, in a nitrogen-filled glove box, 10 ml of dried DMSO-d6 and 300 μl of dried internal standard trifluoromethylbenzene were mixed thoroughly to obtain the first solution. 10 ml of dried deuterated acetonitrile and 300 μl of dried internal standard trifluoromethylbenzene were then mixed thoroughly to obtain the second solution. The first and second solutions were then mixed thoroughly to obtain the deuterated reagent.

[0149] The aforementioned negative electrode film-forming additives can work in conjunction with the first and second additives to form a better SEI film on the negative electrode, thereby better suppressing the gas generation caused by the reduction of active hydrogen generated by the side reaction between the positive electrode and the electrolyte on the negative electrode.

[0150] In the technical solution of this application embodiment, the secondary battery includes a negative electrode sheet, which includes a negative electrode active material, and the negative electrode active material includes hard carbon. Hard carbon material has many sodium storage active sites, high specific capacity, small volume expansion after sodium intercalation, good safety, and stable structure, which is beneficial to improving the performance of the secondary battery.

[0151] Having described the structure and components of a secondary battery, the following section details its preparation method. This includes the following steps:

[0152] S101. Preparation of the positive electrode sheet: The positive electrode active material, conductive agent, and binder are mixed to obtain a mixture. The mixture is then added to N-methylpyrrolidone (NMP) and stirred until homogeneous to obtain a positive electrode active slurry. The positive electrode active slurry is then uniformly coated onto the positive electrode current collector, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0153] Leveling agents, dispersants, etc. can also be added to the positive electrode active slurry.

[0154] The coating method can be: scraping, roller coating, slot coating, etc., and this application does not limit it.

[0155] S102. Dissolve the negative electrode active material, conductive agent, binder and thickener in a solvent, mix them evenly to prepare a negative electrode active slurry; coat the negative electrode active slurry evenly on the negative electrode current collector once or multiple times, and obtain the negative electrode sheet after drying, cold pressing and slitting.

[0156] S103. The prepared positive electrode sheet, negative electrode sheet, and separator are fabricated into corresponding electrode assemblies according to a winding or stacking structure. The electrode assemblies are then installed into a suitable-sized shell for top and side sealing, followed by the injection of electrolyte and sealing to obtain a non-charged battery. The non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, aging, shaping, and capacity testing to obtain a single battery cell.

[0157] Because additives participate in the formation of CEI and SEI films during the secondary battery preparation process, such as formation and aging, their usage will be reduced to some extent. According to the test, after applying the above-mentioned non-aqueous electrolyte (i.e., the mass content of the first additive in the non-aqueous electrolyte is 0.005%~4%, referred to as fresh electrolyte) to the secondary battery and completing the formation and aging steps, the mass content of the first additive in the non-aqueous electrolyte is 0%-2%, and it is positively correlated with the amount of the first additive in the fresh electrolyte to a certain extent.

[0158] Similarly, if the original non-aqueous electrolyte contains a second additive, and the mass content of the second additive in the non-aqueous electrolyte is 0.005% to 3%, after it is applied to a secondary battery and undergoes formation, aging, and other steps, the mass content of the second additive in the electrolyte at this time is 0% to 1.5%, and it is positively correlated to some extent with the amount of the second additive used in the fresh electrolyte.

[0159] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0160] In the following examples and comparative examples, the components of the first additive, according to Formula 1, are: Equation 4 is Equation 9 is Equation 15 is Equation A is (Ethylene sulfate).

[0161] Example 1

[0162] Preparation of the positive electrode sheet

[0163] NaNi, the positive electrode active material0.33 Fe 0.33 Mn 0.33 O2, polyvinylidene fluoride binder, and acetylene black conductive agent are mixed in a weight ratio of 90:5:5 and dissolved in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The slurry is then coated on both surfaces of the current collector aluminum foil, dried, and then cold-pressed, trimmed, cut, and slit to produce the positive electrode sheet of the secondary battery.

[0164] Preparation of the negative electrode sheet

[0165] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) are mixed in a weight ratio of 90:4:4:2 and dissolved in deionized water to prepare a negative electrode slurry. The slurry is then coated onto a current collector copper foil, dried, and then cold-pressed, trimmed, cut, and slit to produce the negative electrode sheet of the secondary battery.

[0166] Preparation of non-aqueous electrolytes

[0167] The preparation of the non-aqueous electrolyte was carried out in an argon-atmospheric glove box with a water content of <10 ppm. First, sodium salt NaPF6 was added to the solvent, followed by the addition of a first additive (a cyclic sulfate compound of formula 15), a second additive (sodium difluorooxalate borate), and a third additive (fluoroethylene carbonate, FEC), thus completing the preparation of the non-aqueous electrolyte. The molar concentration of the sodium salt was 1 mol / L, and the solvents were propylene carbonate (PC) and ethyl methyl carbonate (EMC), with a mass ratio of PC to EMC of 3:7.

[0168] 【Isolation Film】

[0169] Polyethylene film is used as the separation membrane.

[0170] [Preparation of Secondary Batteries]

[0171] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode. The electrode assembly is then wound up to obtain an electrode assembly. The electrode assembly is placed in a housing, dried, and then injected with electrolyte for sodium-ion batteries. After vacuum sealing, settling, formation, and shaping, the sodium secondary battery product of Example 1 is obtained.

[0172] Examples 2-17 and Comparative Examples 1-2

[0173] The only difference between Comparative Example 1 and Example 1 is that the electrolyte does not contain cyclic sulfate compounds or sodium difluorooxalate borate.

[0174] The only difference between Comparative Example 2 and Example 1 is that the electrolyte does not contain cyclic sulfate compounds.

[0175] The differences between the various embodiments and comparative examples are shown in Table 1:

[0176] Table 1. Differences between the various embodiments and comparative examples

[0177]

[0178] The mass content in Table 1 is the mass percentage of each additive in the non-aqueous electrolyte. For example, in Example 1, the mass content of the first additive in the non-aqueous electrolyte is 1%.

[0179] The secondary batteries provided in each embodiment and comparative example were tested, including:

[0180] High-temperature and high-pressure secondary battery volume change rate test: At 25℃, the freshly prepared secondary battery was left to stand for 5 minutes, then charged at a constant current rate of 0.33C to 4.0V, and then charged at a constant voltage until the current is less than or equal to 0.05C. After that, it was left to stand for 5 minutes, and the volume V1 of the battery was tested by the water displacement method. Then the secondary battery was placed in a 60℃ oven and stored for 2 months. After that, the secondary battery was taken out and the volume was tested as V2. The volume change rate of the secondary battery = (V2-V1) / V1*100%.

[0181] Secondary battery cycle retention test: At 25℃, the newly prepared secondary battery was charged to 4.0V with a constant current of 0.33C, then charged to 0.05C with a constant voltage of 4.0V until the current dropped to 0.05C. After standing for 5 minutes, it was discharged to 1.5V with a constant current of 1C. This is the first charge / discharge cycle of the battery, and the discharge capacity of this cycle is recorded as the discharge capacity of the battery in the first cycle (C0). The above steps were repeated for the same battery. The discharge capacity of the battery after 500 cycles (C1) was recorded. The capacity retention rate after 500 cycles = C1 / C0 × 100%.

[0182] DC Impedance (DCR) Test: At -25℃, adjust the secondary battery's state of charge to 50% SOC, let it stand for 30 minutes, and record the battery voltage at this time as U1 (V). Discharge at 0.36C for 10 seconds, and record the battery voltage at this time as U2 (V). The corresponding battery discharge current I (mA) is 0.36 × battery design capacity (mAh). DC Impedance DCR (mΩ) = (U1 - U2) / I.

[0183] The test results are shown in Table 2 below:

[0184] Table 2 Test Results

[0185]

[0186] As can be seen from the table above, the secondary battery provided in this application embodiment has high cycle performance and low DCR, while suppressing gas generation during high SOC storage and reducing the volume change rate of the high temperature and high pressure storage cell.

[0187] As shown in Examples 1-5 and Comparative Examples 1-2, the combination of cyclic sulfate compounds and difluorooxalate borate compounds can improve the cycle performance of secondary batteries with nickel-iron-manganese layered metal oxides as the positive electrode active material, and maintain a low DCR while storing gas at high SOC. Examples 1-5 also show that different cyclic sulfate compounds affect the performance of the secondary battery. In Examples 1-4, due to the polycyclic nature of the cyclic sulfate compounds, the battery performance containing them was significantly improved compared to the battery containing ethylene sulfate of formula A, at the same addition amount.

[0188] As can be seen from Examples 1 and 6-8, in non-aqueous electrolytes, when the mass content of cyclic sulfate compounds is less than or equal to 4%, especially when the mass content of cyclic sulfate compounds is greater than 0.2% and less than or equal to 2%, the secondary battery achieves both lower DCR and better cycle performance.

[0189] As can be seen from Examples 1 and 9-11, when the mass content of difluorooxalate borate compounds in the non-aqueous electrolyte is less than or equal to 3%, the secondary battery achieves both low DCR and good cycle performance.

[0190] As can be seen from Examples 1 and 12-13, difluorooxalate borate compounds of different compositions can be compounded with cyclic sulfate compounds to improve the cycle performance of secondary batteries with nickel-iron-manganese layered metal oxides as the positive electrode active material and maintain a low DCR of the secondary battery while storing gas at high SOC. Among them, sodium difluorooxalate borate has a better improvement effect than calcium difluorooxalate borate and lithium difluorooxalate borate.

[0191] As can be seen from Examples 1 and 14-15, by controlling the mass percentage of the third additive in the electrolyte to be less than or equal to 4%, it is beneficial for it to work in combination with the first and second additives, so that the secondary battery can achieve both high cycle performance and low DCR.

[0192] As can be seen from Examples 1 and 16, the negative electrode film-forming agent FEC and succinic anhydride can both work in combination with the first additive and the second additive to enable the secondary battery to achieve both high cycle performance and low DCR.

[0193] As can be seen from Examples 1 and 17, the nickel-iron-manganese layered metal oxide Na... a M b Ni c Fe d Mn eO2 (M is selected from at least one of Sc, Ti, V, Cr, Co, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 0 < a ≤ 4, 0 ≤ b ≤ 0.2, 0.23 < c ≤ 0.35, 0 < d ≤ 0.35, 0 < e ≤ 0.4) can be used in the non-aqueous electrolyte of this application, regardless of whether M is doped. The non-aqueous electrolyte provided by this application can improve the cycle performance of the secondary battery containing the nickel-iron-manganese layered metal oxide and maintain a low DCR of the secondary battery while storing gas at high SOC.

[0194] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery, wherein, The secondary battery includes a positive electrode sheet and a non-aqueous electrolyte. The positive electrode sheet is in contact with the non-aqueous electrolyte. The positive electrode sheet includes a positive active material layer, which includes a positive active material, namely Na. a M b Ni c Fe d Mn e O2, wherein M is selected from at least one of Sc, Ti, V, Cr, Co, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb, 0 < a ≤ 4, 0 ≤ b ≤ 0.2, 0.23 < c ≤ 0.35, 0 < d ≤ 0.35, 0 < e ≤ 0.4; The non-aqueous electrolyte includes a first additive and a second additive. The first additive includes cyclic sulfate compounds, and the second additive includes difluorooxalate borate compounds.

2. The secondary battery according to claim 1, wherein, The difluorooxalate borate compounds include: N y M, where N is (F₂C₂O₄B). y- M is Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ and Ni 3+ At least one of them, where y is 1, 2 or 3.

3. The secondary battery according to claim 1, wherein, The difluorooxalate borate compounds include at least one of sodium difluorooxalate borate, lithium difluorooxalate borate, and calcium difluorooxalate borate.

4. The secondary battery according to any one of claims 1 to 3, wherein, In the non-aqueous electrolyte, the mass content of the difluorooxalate borate compound is 0.005% to 3%.

5. The secondary battery according to claim 4, wherein, In the non-aqueous electrolyte, the mass content of the difluorooxalate borate compound is 0.2% to 3%.

6. The secondary battery according to any one of claims 1 to 5, wherein, The cyclic sulfate compounds include at least one of monocyclic cyclic sulfate compounds and polycyclic cyclic sulfate compounds.

7. The secondary battery according to claim 6, wherein, The polycyclic cyclic sulfate compounds include R1, R2, R3, and R4 each independently include R5 and R6 each independently include hydrogen atoms, C1-C6 alkyl groups, halogen atoms, C1-C3 haloalkyl groups, C1-C3 alkoxy groups, C1-C3 haloalkoxy groups, alkenyl groups, ester groups, cyano groups, or sulfonic acid groups. Hydrogen atom, C1-C6 alkyl group, halogen atom, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, alkenyl group, ester group, cyano group or sulfonic acid group.

8. The secondary battery according to claim 6, wherein, The polycyclic cyclic sulfate compounds include at least one of Formulas 1-16: 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 。 9. The secondary battery according to claim 6, wherein, The monocyclic cyclic sulfate compounds include vinyl sulfate.

10. The secondary battery according to any one of claims 1 to 9, wherein, In the non-aqueous electrolyte, the mass content of the cyclic sulfate ester compound is 0.005% to 4%.

11. The secondary battery according to claim 10, wherein, In the non-aqueous electrolyte, the mass content of the cyclic sulfate ester compound is 0.2% to 2%.

12. The secondary battery according to any one of claims 1 to 11, wherein, The non-aqueous electrolyte also includes a third additive, which is a negative electrode film-forming additive.

13. The secondary battery according to claim 12, wherein, In the non-aqueous electrolyte, the mass content of the third additive is 0.05% to 4%.

14. The secondary battery according to claim 11 or 12, wherein, The negative electrode film-forming additive includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, maleic anhydride, succinic anhydride, and triallyl phosphate.

15. An electrical appliance, wherein, The electrical equipment includes the secondary battery as described in any one of claims 1 to 14.

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