Sodium ion battery monomer and power utilization device

Abstract

The invention provides a sodium-ion battery monomer and a power utilization device, and belongs to the field of batteries, the sodium-ion battery monomer comprises a negative pole piece, a positive pole piece and an electrolyte, the negative pole piece comprises a negative current collector and a negative film layer arranged on at least one side of the negative current collector, the negative film layer comprises a carbon-based material, and the carbon-based material is arranged on the positive pole piece. The carbon-based material comprises graphite-like lamellas and a pore structure, wherein the space volume H1 of the space between every two adjacent graphite-like lamellas is 0.35-0.4 nm, and the total space volume H between every two adjacent graphite-like lamellas is greater than or equal to 30% and less than or equal to 65%; the pore volume V1 of the pore structure with the pore diameter of 5-10 nm in the carbon-based material measured based on a nitrogen adsorption method and the total pore volume V in the pore structure meet the condition that V1 / V is greater than or equal to 2% and less than or equal to 13%; the electrolyte further comprises a solvent, and the solvent comprises cyclic carbonate.

Description

[0001] Cross-references This application incorporates, in its entirety, patent application number PCT / CN2025 / 110447, filed on July 24, 2025, entitled “A Sodium-ion Battery Cell and Related Device Thereof”, which is hereby incorporated by reference. Technical Field

[0002] This application relates to the field of battery technology, and in particular to a sodium-ion battery cell and an electrical device thereof. Background Technology

[0003] Energy conservation and emission reduction are key to sustainable social development. Rechargeable batteries, with their ability to store and release energy as needed, are widely used in various electrical devices and energy storage systems, and are an important component in promoting energy transition and sustainable development. For the new energy industry, battery technology is a crucial factor in its development.

[0004] Sodium-ion batteries typically use carbon-based materials as the negative electrode active material. However, carbon-based materials cannot achieve both good kinetic performance and good cycle life when used as negative electrode active materials. Summary of the Invention

[0005] This application aims to at least address one of the technical problems existing in the background art. Therefore, one objective of this application is to provide a sodium-ion battery cell that balances its kinetic performance and cycle life.

[0006] This application provides a sodium-ion battery cell, including an electrolyte, a positive electrode, and a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a carbon-based material, which includes graphite-like sheets and a porous structure. The spacing between adjacent layers of the graphite-like sheets satisfies a spatial volume H1 of 0.35 nm to 0.4 nm, and the total spatial volume H between all layers of the graphite-like sheets satisfies: 30% ≤ H1 / H ≤ 65%. Based on nitrogen adsorption method, the pore volume V1 of the pore structure with a pore size of 5nm-10nm in the carbon-based material and the total pore volume V in the pore structure are satisfied with: 2%≤V1 / V≤13%; The electrolyte further includes a solvent, which includes cyclic carbonates, including one or more of propylene carbonate, ethylene carbonate, and butene carbonate.

[0007] This application, by controlling the spatial volume ratio of interlayer spacing to 0.35nm-0.4nm and the pore volume ratio of pore size to 5nm-10nm, and by adding a low-reduction-potential cyclic carbonate to the electrolyte, enables the electrolyte salt to preferentially form a better electrolyte interface film (SEI film) on the negative electrode surface. This improves the integrity of the initially formed SEI film, reduces the probability that sodium ions will not have enough time to form a film due to entering large pores, and ensures the kinetic performance of sodium ion insertion and extraction from the carbon-based negative electrode material by controlling the spatial volume ratio of interlayer spacing to 0.35nm-0.4nm. This improves the structural stability of the carbon-based material, enhances the stability of the SEI film during cycling, reduces sodium consumption caused by SEI film repair, and thus improves the cycle performance of the battery cell.

[0008] According to some embodiments of this application, the spatial volume H2 between adjacent layers of the graphite-like sheet is greater than or equal to 0.4 nm, and the total spatial volume H between the layers in the graphite-like sheet satisfies: 25% ≤ H2 / H ≤ 60%. Therefore, while improving the kinetic performance of carbon-based materials, side reactions between carbon-based materials and electrolytes are reduced, sodium consumption is decreased, and the cycle life of battery cells is improved.

[0009] According to some embodiments of this application, the spatial volume H3 between adjacent layers of the graphite-like sheet is less than 0.35 nm, and the total spatial volume H between the layers in the graphite-like sheet satisfies: H3 / H≤18%. Therefore, the high proportion of small interlayer spacing in the carbon-based material reduces the expansion of the carbon-based material, reduces sodium consumption, and improves the cycle life of the battery cell.

[0010] According to some embodiments of this application, 2% ≤ V1 / V ≤ 10%. This improves the kinetic performance of carbon-based materials while reducing side reactions between the negative electrode active material and the electrolyte, thereby reducing sodium consumption and increasing lifespan.

[0011] According to some embodiments of this application, the pore volume V2 of the pore structure with a pore size of less than or equal to 2 nm in the carbon-based material, measured by nitrogen adsorption, satisfies the following condition: 10% ≤ V2 / V ≤ 30%. This improves the capacity of the carbon-based material.

[0012] According to some embodiments of this application, the pore volume V3 of the pore structure with a pore size of 1nm-2nm in the carbon-based material, measured by nitrogen adsorption, satisfies the following condition: 5% ≤ V3 / V ≤ 15%. This improves the kinetic performance of the carbon-based material.

[0013] According to some embodiments of this application, the pore volume V4 of the pore structure with a pore size greater than 2 nm and less than 5 nm in the carbon-based material, measured by nitrogen adsorption, satisfies the following condition: 8% ≤ V4 / V ≤ 27%. This improves the kinetic performance of the carbon-based material.

[0014] According to some embodiments of this application, the conductivity C of the electrolyte at 25±1°C satisfies: 7mS / cm≤C≤13mS / cm. This improves the migration rate of sodium ions while reducing side reactions in the electrolyte, thus maintaining the cycle performance of the battery cells.

[0015] According to some embodiments of this application, the electrolyte further includes chain esters, which include chain carbonates and / or chain carboxylic acid esters. The chain carbonates include one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and dibutyl carbonate. The chain carboxylic acid esters include one or more of methyl acetate, ethyl acetate, ethyl propionate, methyl formate, ethyl formate, methyl propionate, propyl propionate, ethyl butyrate, and propyl acetate. This improves the migration rate of sodium ions in the electrolyte and enhances the kinetic performance of the battery cell.

[0016] According to some embodiments of this application, the mass ratio of the cyclic carbonate to the chain ester is 0.25-1.5. This balances the kinetic and cycle performance of the battery cell.

[0017] According to some embodiments of this application, the cyclic carbonate accounts for 15%-55% of the total mass of the electrolyte.

[0018] According to some embodiments of this application, the mass percentage of the chain ester is 30%-70% based on the total mass of the electrolyte.

[0019] When the content of cyclic carbonates is within the above range, sodium salts can be better dissociated, improving the stability of the negative electrode SEI film and increasing the cycle life of the battery cell.

[0020] When the content of chain esters is within the above range, the migration rate of sodium ions can be increased, thereby improving the kinetic performance of the battery cell.

[0021] According to some embodiments of this application, the cyclic carbonate includes one or more of propylene carbonate and ethylene carbonate.

[0022] Propylene carbonate has a low reduction potential and good stability, which can reduce side reactions caused by its own decomposition.

[0023] Ethylene carbonate has a high reduction potential, which allows it to preferentially form a dense and stable SEI film at the negative electrode, thereby reducing electrolyte decomposition and gas production and improving the cycle performance of the battery cell.

[0024] According to some embodiments of this application, the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0025] The aforementioned types of chain carbonates have low reduction potentials, which can reduce side reactions caused by their own decomposition, thereby improving the stability of the electrolyte and the cycle performance of the battery cells.

[0026] According to some embodiments of this application, the chain carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, and ethyl propionate.

[0027] The aforementioned types of chain carboxylic esters have low viscosity and excellent wettability, which can improve the wetting effect of the electrolyte on the positive and negative electrodes. They also have good fluidity at low temperatures, can maintain good ion transport at low temperatures, reduce capacity decay, and improve the cycle life of battery cells.

[0028] According to some embodiments of this application, the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and the chain carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, and ethyl propionate.

[0029] The electrolyte contains both chain carbonates and chain carboxylic esters, which can synergistically reduce the viscosity of the electrolyte, reduce electrolyte decomposition and gas production, and improve the cycle performance and safety performance of the battery cells.

[0030] According to some embodiments of this application, the cyclic carbonate includes propylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass ratios of the cyclic carbonate and the chain carbonate is 60%-90%.

[0031] Propylene carbonate has a low reduction potential and good stability. When combined with the above-mentioned chain carbonates with low reduction potential, it can further improve the chemical stability of the electrolyte, reduce side reactions in the electrolyte, and improve the cycle performance of the battery cells.

[0032] According to some embodiments of this application, the cyclic carbonate includes propylene carbonate, the chain carbonate includes methyl ethyl carbonate, and the total mass percentage of the cyclic carbonate and the chain carbonate is 60%-90% based on the total mass of the electrolyte.

[0033] The combination of propylene carbonate and ethyl methyl carbonate can further improve the chemical stability of the electrolyte, reduce the probability of solvent intercalation into the negative electrode, thereby reducing side reactions in the electrolyte, improving the structural stability of the negative electrode, and ultimately improving the cycle performance of the battery cell.

[0034] According to some embodiments of this application, the cyclic carbonate includes ethylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass ratios of the cyclic carbonate and the chain carbonate is 60%-90%.

[0035] Ethylene carbonate has a slightly larger molecular volume and its cyclic structure has better rigidity, which can reduce the risk of solvent embedding into graphite. It can form a dense and stable SEI film on the surface of the negative electrode active material. Furthermore, when combined with chain carbonates with low reduction potential, it can improve the chemical stability of the electrolyte, reduce side reactions of the electrolyte, and improve the cycle performance of the battery cell.

[0036] According to some embodiments of this application, the cyclic carbonate includes ethylene carbonate, and the chain carbonate includes dimethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonate and the chain carbonate is 60%-90%. This further improves the chemical stability of the electrolyte and enhances the cycle performance of the battery cell.

[0037] According to some embodiments of this application, the cyclic carbonate includes propylene carbonate and ethylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass ratios of the cyclic carbonate and the chain carbonate is 60%-90%.

[0038] Propylene carbonate exhibits good stability at high temperatures and is not prone to solidification at low temperatures. When combined with chain carbonates that have good film-forming properties, it can further improve the cycle life of battery cells.

[0039] According to some embodiments of this application, the cyclic carbonate includes propylene carbonate and ethylene carbonate, and the chain carbonate includes diethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonate and the chain carbonate is 60%-90%. This further improves the cycle life of the battery cell.

[0040] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes one or more of sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium perchlorate. This improves the ionic conductivity of the electrolyte.

[0041] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes sodium hexafluorophosphate and sodium difluorosulfonamide.

[0042] Sodium hexafluorophosphate has good thermal stability, while sodium difluorosulfonamide has high ionic conductivity and excellent film-forming properties. When used together, they can reduce side reactions in the electrolyte and improve the cycle performance of the battery cells.

[0043] According to some embodiments of this application, the electrolyte further includes a first additive, which includes one or more compounds represented by Formula I and Formula II: Formula I Formula II, R1, R2, R3, R4, R5, and R6 each independently include one or more of the following: hydrogen atom, C1-C6 alkyl group, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, ester group, cyano group, and sulfonic acid group.

[0044] Therefore, the aforementioned first additives can form a protective film containing organic components on the positive and negative electrode surfaces, reducing interfacial side reactions and improving the cycle life of the battery cells.

[0045] According to some embodiments of this application, the first additive includes one or more of the following compounds: Formula I-1 Formula I-2 Formula I-3 Formula II-1 Formula II-2 Formula II-3. Thus, the first additives of the above types can form a protective film containing organic components on the positive and negative electrode surfaces, reducing interfacial side reactions and improving the cycle life of the battery cells.

[0046] According to some embodiments of this application, the mass percentage of the first additive is 0.005%-2% based on the total mass of the electrolyte. This improves the stability of the interfacial film, reduces interfacial side reactions, and increases the cycle life of the battery cell.

[0047] According to some embodiments of this application, the electrolyte further includes a second additive, which comprises one or more of tris(trimethylsilane)phosphate, tris(trimethylsilyl)phosphite, and triphenyl phosphite. Therefore, the aforementioned type of second additive has a slightly higher reduction potential, can preferentially form a film on the positive and negative electrode surfaces, reduces the dissolution of transition metals in the positive electrode active material, reduces HF corrosion, and improves the cycle life of the battery cell.

[0048] According to some embodiments of this application, the mass percentage of the second additive is 0.005%-1% based on the total mass of the electrolyte. A mass percentage of the second additive within the above range can improve the cycle life of the battery cell.

[0049] According to some embodiments of this application, the conductivity C of the electrolyte at 25±1°C satisfies: 7 mS / cm ≤ C ≤ 15 mS / cm. This increases the migration rate of sodium ions and reduces side reactions between the negative electrode active material and the electrolyte.

[0050] According to some embodiments of this application, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds.

[0051] According to some embodiments of this application, the transition metal element in the sodium transition metal oxide includes one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.

[0052] According to some embodiments of this application, the sodium transition metal oxide includes compounds represented by Formula III: Na x M1O2 type III, M1 includes one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, where 0 < x ≤ 1.

[0053] According to some embodiments of this application, the sodium transition metal oxide includes one or more of copper-iron-manganese-based oxides and nickel-iron-manganese-based oxides.

[0054] According to some embodiments of this application, the polyanionic compound includes one or more of polyanionic phosphates, polyanionic sulfates, polyanionic silicates, polyanionic borates, and polyanionic fluorophosphates.

[0055] According to some embodiments of this application, the polyanionic phosphate includes: Na a Fe b M2 c M3 d (Condensed polyanions) e (Anion) f , M2 includes one or more transition metal elements, M3 includes one or more non-transition metal elements, a>b, c>0, d≥0, e≥1, f>0, and the condensed polyanion includes P2O7. 4-P3O9 5- P4O 11 6- One or more of the following anions are included: aluminate ion, silicate ion, phosphate ion, sulfate ion, titanate ion, vanadate ion, and tungstate ion.

[0056] According to some embodiments of this application, the polyanionic phosphate includes: Na x Fe a-y M4 y (M5O4) z (P2O7) w , Wherein, 2≤x≤4, 1≤a≤4, 1≤y≤4, 0≤z≤4, 0≤w≤1, at least one of z and w is greater than or equal to 1, M4 includes one or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, and M5 includes one or more of Al, Si, P, S, Ti, V, and W.

[0057] According to some embodiments of this application, the Prussian blue compounds include one or more of iron-based Prussian blue and manganese-based Prussian blue.

[0058] According to some embodiments of this application, at least a portion of the surface of the polyanionic phosphate has a carbon material. This improves the electronic conductivity of the positive electrode active material and enhances the cycle stability of the battery cell.

[0059] According to some embodiments of this application, the positive electrode film layer further includes a binder, which includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. Thus, the structural stability of the positive electrode film layer is maintained during battery cell cycling, a stable conductive network is constructed, and the cycle performance of the battery cell is improved.

[0060] According to some embodiments of this application, the positive electrode film layer further includes dot-shaped conductive agents and / or linear conductive agents. The dot-shaped conductive agents include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, and graphite-like materials. The linear conductive agents include one or more of carbon nanotubes, carbon nanofibers, and carbon nanorods.

[0061] The combined use of dot-shaped and linear conductive agents can construct a three-dimensional conductive network, thereby improving the transport effect of sodium ions and reducing the DC internal resistance of the battery cell during cycling to meet the requirements of high-power discharge, while also improving the cycle performance of the battery cell.

[0062] According to some embodiments of this application, the length of the linear conductive agent is 5μm-20μm.

[0063] By controlling the length of the linear conductive agent within the aforementioned range, it is beneficial to achieve effective connection between the linear conductive agent and the positive electrode active material particles, which is conducive to constructing a long-range conductive network.

[0064] According to some embodiments of this application, the mass percentage of the linear conductive agent is 0.7%-1.5% based on the total mass of the positive electrode film. By controlling the mass percentage of the linear conductive agent to be greater than 0.7% and within a suitable range, it is beneficial for the particles of the positive electrode active material to be effectively connected by the linear conductive agent without affecting the content of the positive electrode active material in the positive electrode film, and it is also beneficial to reduce costs.

[0065] According to some embodiments of this application, the positive electrode film layer includes sodium iron phosphate pyrophosphate, and the average pore width between the sodium iron phosphate pyrophosphate particles in the positive electrode film layer is 1μm-5μm.

[0066] By ensuring that the average pore width between sodium iron phosphate pyrophosphate particles is within the aforementioned range, it is beneficial for the filling of dot-like conductive agents within the pores and for the connection of linear conductive agents between particles. This facilitates the construction of a three-dimensional conductive network, further improving the transport effect of sodium ions and reducing the DC internal resistance of sodium-ion battery cells during cycling, while also improving the cycle performance of the battery cells.

[0067] According to some embodiments of this application, the pore width between the sodium iron phosphate pyrophosphate particles in the positive electrode film is 300 nm-10 μm.

[0068] By selecting the appropriate pore width between particles of sodium iron pyrophosphate, it is beneficial to effectively fill the voids with dot-like conductive agents and effectively connect linear conductive agents between particles.

[0069] According to some embodiments of this application, the average particle size of the dotted conductive agent in the positive electrode film is smaller than the average pore width between the particles of sodium iron phosphate pyrophosphate.

[0070] By controlling the average particle size of the dotted conductive agent to be smaller than the average pore width of the sodium iron phosphate pyrophosphate particles, the dotted conductive agent can more effectively fill the gaps between particles, thereby shortening the ion transport distance and improving short-range conductivity.

[0071] According to some embodiments of this application, the mass percentage of the dotted conductive agent is 2%-4% based on the total mass of the positive electrode film.

[0072] By controlling the mass percentage of the dotted conductive agent to be greater than 2% and within a suitable range, it is beneficial for the gaps between the sodium iron phosphate pyrophosphate particles to be better filled, and it does not significantly affect the content of the positive electrode active material in the positive electrode film.

[0073] The second aspect of this application provides an electrical device including a sodium-ion battery cell provided in the first aspect of this application, the sodium-ion battery cell being used to provide electrical energy.

[0074] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0075] 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: Figure 1 This is a schematic diagram of a sodium-ion battery cell according to one embodiment of this application.

[0076] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0077] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0078] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0079] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0080] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application.

[0081] Figure 7 This is a scanning electron microscope (SEM) cross-sectional view of the positive electrode sheet in Examples 1-13 of this application.

[0082] Figure 8 This is a pore width distribution curve of the positive electrode sheet obtained in Examples 1-13 of this application.

[0083] Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Sodium-ion battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0084] 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.

[0085] 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.

[0086] 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.

[0087] In this document, the term "embodiment" means that a specific 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 in 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. In the description of the embodiments of 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.

[0088] 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).

[0089] 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.

[0090] 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.

[0091] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0092] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0093] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0094] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0095] Currently, the application of rechargeable batteries is becoming increasingly widespread, judging from market trends. They are not only used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, but also extensively in various electronic devices, such as electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. As the application areas of rechargeable batteries continue to expand, the market demand is also constantly increasing.

[0096] Sodium-ion batteries, as a potential low-cost alternative to lithium-ion batteries, are limited in their commercialization process by the inherent contradiction between kinetic performance and cycle life—the optimization paths for the two have an essential "inverse relationship." The applicant has realized that the electrolyte interface film (SEI film) on the surface of the negative electrode active material has a significant impact on the kinetic and cycle performance of sodium-ion batteries.

[0097] Based on this, the first aspect of this application provides a sodium-ion battery cell, including an electrolyte, a negative electrode sheet, and a positive electrode sheet. The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a carbon-based material, which includes graphite-like sheets and a porous structure. The spacing between adjacent layers of the graphite-like sheets satisfies a spatial volume H1 of 0.35nm-0.4nm and the total spatial volume H between all layers of the graphite-like sheets satisfies: 30%≤H1 / H≤65%. Based on nitrogen adsorption method, the pore volume V1 of the pore structure with a pore size of 5nm-10nm in the carbon-based material and the total pore volume V in the pore structure are satisfied with: 2%≤V1 / V≤13%; The electrolyte further includes a solvent, which includes cyclic carbonates, including one or more of propylene carbonate, ethylene carbonate, and butene carbonate.

[0098] For long-life battery systems, existing technologies mainly improve the stability of the SEI film by modifying electrolyte additives. The applicant recognizes that the design of the insertion / extraction channels in the negative electrode active material, in conjunction with the electrolyte film-forming characteristics, can also significantly impact the improvement of individual battery cell lifespan. Specifically, if the pores of carbon-based materials collapse during cycling, it hinders the insertion and extraction of sodium ions, resulting in higher sodium consumption and deteriorating the battery cell lifespan. For carbon-based materials, which contain stacked graphene sheets with varying interlayer spacings, the spaces between adjacent graphene sheets serve as crucial channels for sodium ion insertion / extraction. Different anode materials exhibit significant performance differences during cycling. Furthermore, the pore size affects the transport path of sodium ions from the interior to the surface of the carbon-based material. Pores with a diameter of 5nm-10nm (also known as mesopores) have fewer active sites, but these pores can connect to micropores and ultramicropores. Micropores and ultramicropores have more active sites, so ions typically migrate to sites with active sites through macroporous structures. When pores with a diameter of 5nm-10nm are connected to internal micropores and ultramicropores, small molecules in the electrolyte are easily adsorbed into the internal pores, reducing the integrity of the film formation.

[0099] The applicant discovered that several conditions must be met simultaneously to ensure that the negative electrode selection is compatible with the electrolyte design in order to reduce sodium ion loss during each cycle, thereby improving the battery's cycle life: (a) By controlling the pore volume ratio of 5nm-10nm within a suitable range, the transport path of sodium ions from the interior to the surface of carbon materials can be shortened. At the same time, the electrolyte is prevented from entering the pores of carbon-based materials before it has a chance to form a film, thus preventing the formation of a stable SEI film on the surface of the insertion / extraction channels of carbon materials. As a result, since the initial SEI film is not fully formed and stable, more sodium ions are needed for subsequent repair. (b) Adding cyclic carbonates with low reduction potential to the electrolyte can make the electrolyte salts in the electrolyte preferentially form a film on the surface of the negative electrode active material, thereby forming a more stable SEI film containing more inorganic matter, so that the SEI film remains stable in subsequent cycling processes. (c) Appropriately increasing the spatial volume ratio of graphite-like sheets with larger interlayer spacing can make it easier for sodium ions to be inserted into and extracted from carbon-based materials. Furthermore, graphite-like sheets with large interlayer spacing are less likely to damage the insertion / extraction channels during ion insertion / extraction, further reducing sodium consumption caused by the repair of the SEI film during cycling.

[0100] In summary, this application, by controlling the spatial volume ratio of interlayer spacing to 0.35nm-0.4nm and the pore volume ratio of pore size to 5nm-10nm, and by adding a low-reduction-potential cyclic carbonate to the electrolyte, enables the electrolyte salt to preferentially form a stable SEI film at the negative electrode, improving the stability of the initially formed SEI film and reducing the probability that sodium ions will not have enough time to form a film due to entering macropores. Furthermore, by controlling the spatial volume ratio of interlayer spacing to 0.35nm-0.4nm, the overall performance of sodium ion insertion and extraction from carbon-based materials is improved, the structural stability of carbon-based materials is enhanced, the stability of the SEI film during cycling is improved, sodium consumption is reduced, and the cycle performance of the battery is improved.

[0101] As an example, H1 / H can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 65%, etc., or a range of any of the above values.

[0102] According to some embodiments of this application, the spatial volume H2 between adjacent layers of the graphite-like sheet is greater than or equal to 0.4 nm, and the total spatial volume H between all layers in the graphite-like sheet satisfies: 25% ≤ H2 / H ≤ 60%. The larger interlayer spacing of the graphite-like sheet allows sodium ions to be more easily embedded in the carbon-based material. This improves the kinetic performance of the carbon-based material while reducing side reactions between the carbon-based material and the electrolyte, lowering sodium consumption, and increasing the cycle life of the battery cell.

[0103] As an example, H2 / H can be 25%, 30%, 35%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, etc., or can be a range of any of the above values.

[0104] According to some embodiments of this application, the spatial volume H3 between adjacent layers of the graphite-like sheet is less than 0.35 nm, and the total spatial volume H between all layers in the graphite-like sheet satisfies: H3 / H≤18%. Therefore, the proportion of small interlayer spacing in the carbon-based material is moderate, which can reduce the expansion of the carbon-based material, reduce sodium consumption, and improve the cycle life of the battery cell.

[0105] As an example, H3 / H can be 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, etc., or a range of any of the above values.

[0106] The above H1 / H, H2 / H, and H3 / H can be obtained by peak fitting of the XRD pattern of carbon-based materials.

[0107] Specifically, the XRD diffraction pattern of the carbon-based material was first tested using the following method: The XRD diffraction pattern of the carbon-based material can be tested using an X-ray diffractometer according to JIS K 0131-1996. The test conditions were as follows: the carbon-based material and silicon powder were uniformly mixed at a mass ratio of 5:1, and the sample was prepared using the plate sample preparation method. CuKα rays were used as the radiation source, and a copper target was used as the anode target. The wavelength λ of the copper target was 1.5406 Å, the scanning 2θ angle range was 10º-40º, and the scanning rate was 1º / min. A Bruker D8 Discover X-ray diffractometer could be used as the testing instrument.

[0108] Next, the XRD diffraction pattern of the carbon-based material was fitted using XPS peak software. The XRD pattern of the carbon-based material was fitted into three small peaks, namely the first fitted peak A, the second fitted peak B, and the third fitted peak C. The fitting criteria were: the 2θ angle of the first fitted peak A was 22.2º~24.7º, the 2θ angle of the second fitted peak B was less than 22.2º, and the 2θ angle of the third fitted peak C was greater than 24.7º.

[0109] The interlayer spacing and the 2θ angle satisfy Bragg's law: Where d is the interlayer spacing of the (002) crystal plane of the carbon-based material. Let be the diffraction angle, and k be the reflection order. The wavelength of the copper target is denoted as k. In this disclosure, k is 1. The value is 1.5406 Å. According to Bragg's formula, the 2θ angle corresponding to graphite-like sheets with an interlayer spacing of 0.35 nm to 0.4 nm is 22.2° to 24.7°. The 2θ angle corresponding to graphite-like sheets with an interlayer spacing greater than 0.4 nm is less than 22.2°, and the 2θ angle corresponding to graphite-like sheets with an interlayer spacing less than 0.35 nm is greater than 24.7°.

[0110] Finally, the ratio of the area of ​​the first fitting peak to the total area of ​​the three fitting peaks is equal to the ratio of the spatial volume H1 between graphite-like sheets with an interlayer spacing of 0.35 nm to 0.4 nm to the total spatial volume H between the layers in the graphite-like sheets (H1 / H); the ratio of the area of ​​the second fitting peak to the total area of ​​the three fitting peaks is equal to the ratio of the spatial volume H2 between graphite-like sheets with an interlayer spacing greater than 0.4 nm to the total spatial volume H between the layers in the graphite-like sheets (H2 / H); and the ratio of the area of ​​the third fitting peak to the total area of ​​the three fitting peaks is equal to the ratio of the spatial volume H3 between graphite-like sheets with an interlayer spacing less than 0.35 nm to the total spatial volume H between the layers in the graphite-like sheets (H3 / H).

[0111] As an example, V1 / V can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, etc., or it can be a range of any of the above values.

[0112] According to some embodiments of this application, 2% ≤ V1 / V ≤ 10%. This improves the kinetic performance of carbon-based materials while reducing side reactions between the negative electrode active material and the electrolyte, thereby reducing sodium consumption and increasing lifespan.

[0113] According to some embodiments of this application, the pore volume V2 of the pore structure with a pore size of less than or equal to 2 nm in the carbon-based material, measured by nitrogen adsorption, satisfies the following condition: 10% ≤ V2 / V ≤ 30%. This improves the capacity of the carbon-based material.

[0114] As an example, V2 / V can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, etc., or a range of any of the above values.

[0115] According to some embodiments of this application, the pore volume V3 of the pore structure with a pore size of 1nm-2nm in the carbon-based material, measured by nitrogen adsorption, satisfies the following condition: 5% ≤ V3 / V ≤ 15%. This allows sodium ions to rapidly insert and extract into the negative electrode film, improving the kinetic performance of the carbon-based material.

[0116] As an example, V3 / V can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc., or a range of any of the above values.

[0117] According to some embodiments of this application, the pore volume V4 of the pore structure with a pore size greater than 2 nm and less than 5 nm in the carbon-based material, measured by nitrogen adsorption, satisfies the following condition: 8% ≤ V4 / V ≤ 27%. This facilitates the rapid insertion and extraction of sodium ions into the negative electrode film, while providing more adsorbent sodium storage active sites and improving the kinetic performance of the carbon-based material.

[0118] As an example, V4 / V can be 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 27%, etc., or a range of any of the above values.

[0119] The pore volumes V1, V2, V3, V4, and total pore volume Vtotal of the aforementioned carbon-based materials can be determined with reference to GB / T 19587-2017. For example, referring to GB / T 19587-2017, the nitrogen adsorption method can be used to test the adsorption and desorption isotherms, and a DFT model can be used to fit the distribution curve of the cumulative pore volume relative to the pore size, thus obtaining the pore volume for a specific pore size range.

[0120] 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.).

[0121] In some embodiments, the negative electrode film layer may optionally include an adhesive. As an example, the adhesive 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).

[0122] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite-like materials, and carbon nanofibers.

[0123] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0124] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode film, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0125] According to some embodiments of this application, the electrolyte further includes chain esters, which include one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, dibutyl carbonate, methyl acetate, ethyl acetate, ethyl propionate, methyl formate, ethyl formate, methyl propionate, propyl propionate, ethyl butyrate, and propyl acetate. This can increase the migration rate of sodium ions in the electrolyte and improve the kinetic performance of the battery cell.

[0126] According to some embodiments of this application, the mass ratio of the cyclic carbonate to the linear ester is 0.25-1.5. This balances the kinetic and cycle performance of the battery cell. Furthermore, by maintaining the relative mass of the cyclic carbonate and linear ester within the aforementioned range, the uniformity and stability of the SEI film can be improved, thereby increasing the cycle life of the battery cell.

[0127] As an example, the mass ratio of the cyclic carbonate to the chain ester can be 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.1, 1.2, 1.3, 1.4, 1.5, etc., or can be a range of any of the above values.

[0128] According to some embodiments of this application, the cyclic carbonate accounts for 15%-55% of the total mass of the electrolyte.

[0129] As an example, the mass percentage of the cyclic carbonate can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, etc., or can be a range of any of the above values.

[0130] Cyclic carbonates have a higher dielectric constant, which can increase the degree of dissociation of sodium salts. By keeping the content of cyclic carbonates within the above range, the uniformity and stability of the SEI film can be improved, thereby increasing the cycle life of the battery cell.

[0131] According to some embodiments of this application, the mass percentage of the chain ester can be 30%-70% based on the total mass of the electrolyte.

[0132] Chain esters have lower viscosity. By keeping the content of chain esters within the above range, the viscosity of the electrolyte can be reduced, the migration rate of sodium ions can be increased, and the kinetic performance of the battery cell can be improved.

[0133] As an example, the mass percentage of the chain ester can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc., or can be a range of any of the above values.

[0134] According to some embodiments of this application, the cyclic carbonate includes one or more of propylene carbonate and ethylene carbonate.

[0135] Propylene carbonate has a low reduction potential and good stability, which can reduce side reactions caused by its own decomposition.

[0136] Ethylene carbonate has a high reduction potential, which allows it to preferentially form a dense and stable SEI film at the negative electrode, thereby reducing electrolyte decomposition and gas production and improving the cycle performance of the battery cell.

[0137] According to some embodiments of this application, the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0138] The aforementioned types of chain carbonates have low reduction potentials, which can reduce side reactions caused by their own decomposition, thereby improving the stability of the electrolyte and the cycle performance of the battery cells.

[0139] According to some embodiments of this application, the chain carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, and ethyl propionate.

[0140] The aforementioned types of chain carboxylic esters have low viscosity and excellent wettability, which can improve the wetting effect of the electrolyte on the positive and negative electrodes. They also have good fluidity at low temperatures, can maintain good ion transport at low temperatures, reduce capacity decay, and improve the cycle life of battery cells.

[0141] According to some embodiments of this application, the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and the chain carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, and ethyl propionate.

[0142] The electrolyte contains both chain carbonates and chain carboxylic esters, which can synergistically reduce the viscosity of the electrolyte, reduce electrolyte decomposition and gas production, and improve the cycle performance and safety performance of the battery cells.

[0143] According to some embodiments of this application, the cyclic carbonate includes propylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass ratios of the cyclic carbonate and the chain carbonate is 60%-90%.

[0144] As an example, the sum of the mass percentages of the cyclic carbonate and the chain carbonate can be 60%, 70%, 80%, 90%, etc., or can be any range of the above values.

[0145] Propylene carbonate has a low reduction potential and good stability. When combined with the above-mentioned chain carbonates with low reduction potential, it can further improve the chemical stability of the electrolyte, reduce side reactions in the electrolyte, and improve the cycle performance of the battery cells.

[0146] According to some embodiments of this application, the cyclic carbonate includes propylene carbonate, the chain carbonate includes methyl ethyl carbonate, and the total mass percentage of the cyclic carbonate and the chain carbonate is 60%-90% based on the total mass of the electrolyte.

[0147] As an example, the sum of the mass percentages of methyl ethyl carbonate and propylene carbonate can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc., or can be any range of the above values.

[0148] The combination of propylene carbonate and ethyl methyl carbonate can further improve the chemical stability of the electrolyte, reduce the probability of solvent intercalation into the negative electrode, thereby reducing side reactions in the electrolyte, improving the structural stability of the negative electrode, and ultimately improving the cycle performance of the battery cell.

[0149] According to some embodiments of this application, the cyclic carbonate includes ethylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonate and the chain carbonate is 60%-90%. For example, it can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc., or it can be any range of the above values.

[0150] Ethylene carbonate has a slightly larger molecular volume and its cyclic structure has better rigidity, which can reduce the risk of solvent embedding into graphite. It can form a dense and stable SEI film on the surface of the negative electrode active material. Furthermore, when combined with chain carbonates with low reduction potential, it can improve the chemical stability of the electrolyte, reduce side reactions of the electrolyte, and improve the cycle performance of the battery cell.

[0151] According to some embodiments of this application, the cyclic carbonate includes ethylene carbonate, and the chain carbonate includes dimethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonate and the chain carbonate is 60%-90%. For example, it can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc., or any range of the above values. This further improves the chemical stability of the electrolyte and enhances the cycle performance of the battery cell.

[0152] According to some embodiments of this application, the cyclic carbonate includes propylene carbonate and ethylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonate and the chain carbonate is 60%-90%. For example, it can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc., or it can be any range of the above values.

[0153] Propylene carbonate exhibits good stability at high temperatures and is not prone to solidification at low temperatures. When combined with chain carbonates that have good film-forming properties, it can further improve the cycle life of battery cells.

[0154] According to some embodiments of this application, the cyclic carbonate includes propylene carbonate and ethylene carbonate, and the chain carbonate includes diethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonate and the chain carbonate is 60%-90%. For example, it can be 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc., or any range of the above values. This further improves the cycle life of the battery cell.

[0155] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes one or more of sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium perchlorate. This improves the ionic conductivity of the electrolyte.

[0156] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes sodium hexafluorophosphate and sodium difluorosulfonamide.

[0157] Sodium hexafluorophosphate has good thermal stability, while sodium difluorosulfonamide has high ionic conductivity and excellent film-forming properties. When used together, they can reduce side reactions in the electrolyte and improve the cycle performance of the battery cells.

[0158] According to some embodiments of this application, the electrolyte further includes a first additive, which includes one or more compounds represented by Formula I and Formula II: Formula I Formula II, R1, R2, R3, R4, R5, and R6 each independently include one or more of the following: hydrogen atom, C1-C6 alkyl group, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, ester group, cyano group, and sulfonic acid group. Therefore, the above-mentioned first additives can form a protective film containing organic components on the positive and negative electrode surfaces, reducing interfacial side reactions and improving the cycle life of the battery cells.

[0159] According to some embodiments of this application, the first additive includes one or more of the following compounds: Formula I-1 Formula I-2 Formula I-3 Formula II-1 Formula II-2 Formula II-3. Thus, the first additives of the above types can form a protective film containing organic components on the positive and negative electrode surfaces, reducing interfacial side reactions and improving the cycle life of the battery cells.

[0160] According to some embodiments of this application, the mass percentage of the first additive is 0.005%-2% based on the total mass of the electrolyte. This improves the stability of the interfacial film, reduces interfacial side reactions, and increases the cycle life of the battery cell.

[0161] As an example, the mass percentage of the first additive may be 0.005%, 0.01%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2%, etc., or may be a range of any of the above values.

[0162] In this application, after disassembling the battery cell to obtain the electrolyte, the types and contents of organic components in the electrolyte are known in the art and can be detected using equipment and methods known in the art. For example, GB / T9722-2023 "Chemical Reagents - General Rules for Gas Chromatography" can be referred to to perform qualitative and quantitative analysis of organic components in the electrolyte by gas chromatography.

[0163] According to some embodiments of this application, the conductivity C of the electrolyte at 25±1°C satisfies: 7 mS / cm ≤ C ≤ 15 mS / cm. This increases the migration rate of sodium ions and reduces side reactions between the negative electrode active material and the electrolyte.

[0164] As an example, the conductivity C can be 5 mS / cm, 6 mS / cm, 7 mS / cm, 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 19 mS / cm, 20 mS / cm, etc., or can be any range of the above values.

[0165] According to some specific embodiments of this application, the conductivity C of the electrolyte at 25±1°C satisfies: 7mS / cm≤C≤13mS / cm.

[0166] In this application, the conductivity of the electrolyte at room temperature can be tested using any method known in the art. As an example, refer to HG... T 4067 The 2015 standard for "Lithium Hexafluorophosphate Electrolyte" requires the following steps: Disassemble the battery cell to obtain the electrolyte. Take approximately 100 mL of the electrolyte sample in a dry, clean, corrosion-resistant sample bottle, seal it, and place it in a constant-temperature water bath. Shake the sample occasionally and maintain the temperature at 25°C (with a deviation of ±5°C). After the sample temperature stabilizes, use a commercially available conductivity meter to test its conductivity. Clean and dry the conductivity meter with calibration solution, then vertically immerse it in the liquid to be tested. Start the test and wait for the data to stabilize for more than 10 seconds before recording the test results. Take the average of three test results.

[0167] According to some embodiments of this application, the electrolyte further includes a second additive, which comprises one or more of tris(trimethylsilane)phosphate, tris(trimethylsilyl)phosphite, and triphenyl phosphite. Therefore, the second additive has a slightly higher reduction potential, allowing it to preferentially form a film on the positive and negative electrode surfaces, reducing the dissolution of transition metals in the positive electrode active material, reducing HF corrosion, and improving the cycle life of the battery cell.

[0168] According to some embodiments of this application, the mass percentage of the second additive is 0.005%-1% based on the total mass of the electrolyte. A mass percentage of the second additive within the above range can improve the cycle life of the battery cell.

[0169] As an example, the mass percentage of the second additive can be 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, etc., or can be a range of any of the above values.

[0170] According to some embodiments of this application, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds.

[0171] According to some embodiments of this application, the transition metal element in the sodium transition metal oxide includes one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.

[0172] According to some embodiments of this application, the sodium transition metal oxide includes compounds represented by Formula III: Na x M1O2 type III, M1 includes one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, where 0 < x ≤ 1.

[0173] According to some embodiments of this application, the sodium transition metal oxide includes one or more of copper-iron-manganese-based oxides and nickel-iron-manganese-based oxides.

[0174] According to some embodiments of this application, the polyanionic compound includes one or more of polyanionic phosphates, polyanionic sulfates, polyanionic silicates, polyanionic borates, and polyanionic fluorophosphates.

[0175] According to some embodiments of this application, the polyanionic phosphate includes: Na a Fe b M2 c M3 d (Condensed polyanions) e (Anion) f , M2 includes one or more transition metal elements, M3 includes one or more non-transition metal elements, a>b, c>0, d≥0, e≥1, f>0, and the condensed polyanion includes P2O7. 4- P3O9 5- P4O 11 6- One or more of the following anions are included: aluminate ion, silicate ion, phosphate ion, sulfate ion, titanate ion, vanadate ion, and tungstate ion.

[0176] According to some embodiments of this application, the polyanionic phosphate includes: Na x Fe a-y M4 y (M5O4) z (P2O7) w , Wherein, 2≤x≤4, 1≤a≤4, 1≤y≤4, 0≤z≤4, 0≤w≤1, at least one of z and w is greater than or equal to 1, M4 includes one or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, and M5 includes one or more of Al, Si, P, S, Ti, V, and W.

[0177] According to some embodiments of this application, the Prussian blue compounds include one or more of iron-based Prussian blue and manganese-based Prussian blue.

[0178] According to some embodiments of this application, at least a portion of the surface of the polyanionic phosphate has a carbon material. This improves the electronic conductivity of the positive electrode active material and enhances the cycle stability of the battery cell.

[0179] According to some embodiments of this application, the positive electrode film layer further includes a binder, which includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. Thus, the structural stability of the positive electrode film layer is maintained during battery cell cycling, a stable conductive network is constructed, and the cycle performance of the battery cell is improved.

[0180] According to some embodiments of this application, the positive electrode film layer further includes dot-shaped conductive agents and / or linear conductive agents. The dot-shaped conductive agents include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, and graphite-like materials. The linear conductive agents include one or more of carbon nanotubes, carbon nanofibers, and carbon nanorods.

[0181] The combined use of dot-shaped and linear conductive agents can construct a three-dimensional conductive network, thereby improving the transport effect of sodium ions and reducing the DC internal resistance of the battery cell during cycling to meet the requirements of high-power discharge, while also improving the cycle performance of the battery cell.

[0182] In this article, dot-shaped conductive agents refer to conductive materials with dot-shaped structures, also known as zero-dimensional conductive agents. These conductive agents mainly improve conductivity through point contact between particles, with conductive carbon black being a prime example.

[0183] In this article, linear conductive agents refer to conductive materials with a one-dimensional structure, also known as one-dimensional conductive agents. These conductive agents mainly improve conductivity through line contact between particles, and carbon nanotubes (CNTs) are a prime example.

[0184] According to some embodiments of this application, the length of the linear conductive agent is 5μm-20μm.

[0185] By controlling the length of the linear conductive agent within the aforementioned range, it is beneficial to achieve effective connection between the linear conductive agent and the positive electrode active material particles, which is conducive to constructing a long-range conductive network.

[0186] As an example, the length of the linear conductive agent is 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 14μm, 16μm, 20μm, etc., or can be any range of the above values.

[0187] The length of the aforementioned linear conductive agent can be tested using methods and equipment known in the art. As an example, the following steps can be followed: discharge the battery cell to 0% SOC, disassemble the battery cell to remove the positive electrode sheet, scrape off powder using a blade to obtain a sample of the positive electrode film layer, photograph the sample using a scanning electron microscope (e.g., ZEISS Sigma 300), and perform statistical analysis on the length of the linear conductive agent using ImageJ software.

[0188] According to some embodiments of this application, the mass percentage of the linear conductive agent is 0.7%-1.5% based on the total mass of the positive electrode film. By controlling the mass percentage of the linear conductive agent to be greater than 0.7% and within a suitable range, it is beneficial for the particles of the positive electrode active material to be effectively connected by the linear conductive agent without affecting the content of the positive electrode active material in the positive electrode film, and it is also beneficial to reduce costs.

[0189] As an example, the mass percentage of the linear conductive agent can be 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc., or can be a range of any of the above values.

[0190] According to some embodiments of this application, the positive electrode film layer includes sodium iron phosphate pyrophosphate, and the average pore width between the sodium iron phosphate pyrophosphate particles in the positive electrode film layer is 1μm-5μm.

[0191] By ensuring that the average pore width between sodium iron phosphate pyrophosphate particles is within the aforementioned range, it is beneficial for the filling of dot-like conductive agents within the pores and for the connection of linear conductive agents between particles. This facilitates the construction of a three-dimensional conductive network, further improving the transport effect of sodium ions and reducing the DC internal resistance of sodium-ion batteries after cycling, while also improving the cycle performance of the battery.

[0192] In this article, the average pore width refers to the average value of the pore width between sodium iron phosphate pyrophosphate particles in the positive electrode sheet in the scanning electron microscope image.

[0193] As an example, the average pore width between the particles of sodium iron phosphate pyrophosphate in the positive electrode film can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc., or can be any range of the above values.

[0194] Corresponding to the average particle size range of sodium iron phosphate pyrophosphate particles, further controlling the average pore width between particles within a suitable range (e.g., by controlling it through the pressure of the electrode roller) is beneficial for the filling of dot-shaped conductive agents in the pores and for the connection of linear conductive agents between particles. This, in turn, is beneficial for constructing a complete three-dimensional conductive network, further improving the transport effect of sodium ions, reducing the DC internal resistance of sodium-ion battery cells during cycling, and improving the cycle performance of battery cells.

[0195] In this paper, the chemical composition of sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7, abbreviated as NFPP, and its morphology is spherical particles.

[0196] According to some embodiments of this application, the pore width between the sodium ferric pyrophosphate particles is 300 nm to 10 μm. By selecting a suitable range for the pore width between the sodium ferric pyrophosphate particles, it is beneficial for the effective filling of dot-like conductive agents within the pores and the effective connection of linear conductive agents between the particles.

[0197] The aforementioned pore width and average pore width can be observed using methods and equipment known in the art. For example, they can be observed under a scanning electron microscope (e.g., ZEISS Sigma 300). As an example, the following steps can be followed: cut the positive electrode sheet into a sample of a certain size (e.g., 3 mm × 3 mm), clamp the sample between two conductive and thermally conductive sheets (e.g., copper foil), fix the sample to the copper foil with adhesive (e.g., double-sided tape), press it with a flat iron block of a certain mass (e.g., 400 g) for a certain time (e.g., 1 h), trim the edges with scissors, and stick it onto a sample stage with conductive adhesive. The sample stage is then mounted and fixed on the sample holder. The argon ion cross-section polisher (e.g., IB-19500 CP) is powered on and a vacuum is drawn (e.g., 10 Pa to 4 Pa). The argon flow rate (e.g., 0.15 MPa), voltage (e.g., 8 kV), and polishing time (e.g., 2 h) are set. The sample stage is adjusted to swing mode to begin polishing. After polishing, the ion-polished cross-sectional morphology image of the sample is obtained using a scanning electron microscope (e.g., ZEISS Sigma 300). Then, the pore width between particles is statistically analyzed using ImageJ software. This analysis is performed 100 times, and the statistical data is fitted with a normal distribution curve to obtain the pore width distribution curve. Based on this distribution curve, the pore width and average pore width can be obtained.

[0198] According to some embodiments of this application, the average particle size of the dotted conductive agent in the positive electrode film is smaller than the average pore width between the particles of sodium iron phosphate pyrophosphate.

[0199] By controlling the average particle size of the dotted conductive agent to be smaller than the average pore width of the sodium iron phosphate pyrophosphate particles, the dotted conductive agent can more effectively fill the gaps between particles, thereby shortening the ion transport distance and ensuring short-range conductivity.

[0200] As an example, the pore width between the particles of the sodium iron pyrophosphate is 300nm, 500nm, 800nm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc., or can be any range of the above values.

[0201] According to some embodiments of this application, the mass percentage of the dotted conductive agent is 2%-4% based on the total mass of the positive electrode film.

[0202] By controlling the mass percentage of the dotted conductive agent to be greater than 2% and within a suitable range, it is beneficial for the gaps between the sodium iron phosphate pyrophosphate particles to be better filled, and it does not significantly affect the content of the positive electrode active material in the positive electrode film.

[0203] As an example, the mass percentage of the dotted conductive agent can be 2%, 2.5%, 2.7%, 3%, 3.5%, 3.7%, 4%, etc., or can be any range of the above values.

[0204] 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.).

[0205] In some embodiments, the positive electrode sheet can be prepared by dispersing the 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 current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0206] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0207] 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.

[0208] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0209] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0210] In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0211] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured sodium-ion battery cell 5.

[0212] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The sodium-ion battery cell 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0213] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0214] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple sodium-ion battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple sodium-ion battery cells 5 can be secured using fasteners.

[0215] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple sodium-ion battery cells 5 are received.

[0216] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0217] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0218] In addition, this application also provides an electrical device, which includes at least one of the battery, battery module, or battery pack provided in this application. The battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0219] As the electrical device, a battery, battery module, or battery pack can be selected according to its usage requirements.

[0220] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0221] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0222] Example 1-1 Preparation of carbon-based materials (1) Pre-carbonization step and doping step: Under the condition of introducing carrier gas nitrogen and doping gas oxygen, the biomass carbon precursor coconut shell is placed in a box furnace and heated to 300℃ at a heating rate of 5℃ / min and held for 3h for pre-carbonization treatment, wherein the volume ratio of oxygen and nitrogen introduced is 0.05:1; the flow rate of the mixed gas of nitrogen and oxygen is 10mL / min; (2) Carbonization step: Under the condition of nitrogen gas, heat to 1100℃ and hold for 2 hours, then cool to room temperature; (3) The sample obtained by the above carbonization step is crushed, graded, sieved, demagnetized and other processes are carried out to finally obtain carbon-based materials.

[0223] Preparation of button cells The carbon-based material prepared in Example 1-1 was mixed with styrene-butadiene rubber (SBR) as a binder, sodium carboxymethyl cellulose (CCMC-Na) as a thickener, and Superp as a conductive agent in a mass ratio of 96:2.5:0.8:0.7 in an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the surface of a copper foil current collector and dried under vacuum at 80°C for 12 hours in an oven. The resulting sheets were then sliced ​​to form the negative electrode plate. Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1 to obtain an organic solvent. NaPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.4 mol / L. Subsequently, using a sodium metal sheet as the counter electrode and a polyethylene (PE) film as the separator, a CR2430 coin cell was assembled in a glove box.

[0224] Preparation method of battery cell Preparation of negative electrode sheet: The carbon-based material, conductive carbon black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber latex (SBR) obtained above are thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 96.5:1.0:1.0:1.5 to form a uniform negative electrode slurry. The negative electrode slurry is coated on both sides of the negative electrode current collector, and after drying and other processes, a double-sided negative electrode sheet is obtained.

[0225] Preparation of the positive electrode sheet: The positive electrode active material Na3V2(PO4)3F, conductive agent carbon black (Super P), and binder polyvinylidene fluoride were mixed at a mass ratio of 96:2:2. An appropriate amount of solvent N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0226] Electrolyte preparation: In an argon-atmospheric glove box (H2O content <0.1ppm, O2 content <0.1ppm), the components of each organic solvent were mixed, and an electrolyte sodium salt and additives were added to prepare the electrolyte. Based on the total mass of the electrolyte, 13% NaPF6 was added to 42% propylene carbonate and 42% methyl ethyl carbonate solvents, along with 1% 1,3-propanesulfonyl lactone, 1% fluoroethylene carbonate, and 1% tris(trimethylsilane)phosphate additives to prepare the electrolyte.

[0227] A polyethylene film is used as a separator and is placed in sequence with the positive and negative electrode sheets prepared above, so that the separator is placed between the positive and negative electrode sheets to play a separating role. Then, the electrode assembly is wound to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, shaping and other processes, the battery cell is obtained.

[0228] The battery preparation methods in Examples 1-2-1-5 and Examples 2-1-2-4 are the same as in Example 1-1, except that the final carbonization temperature in the material preparation process is different. Specifically, the final carbonization temperature in Example 1-2 is 1100℃ and the time is 5h; the final carbonization temperature in Example 1-3 is 1200℃ and the time is 2h; the final carbonization temperature in Example 1-4 is 1050℃ and the time is 3h; the final carbonization temperature in Example 1-5 is 1050℃ and the time is 1h; the final carbonization temperature in Example 2-1 is 1400℃ and the time is 3h; the final carbonization temperature in Example 2-2 is 1300℃ and the time is 3h; the final carbonization temperature in Example 2-3 is 1300℃ and the time is 5h; and the final carbonization temperature in Example 2-4 is 1050℃ and the time is 1.5h.

[0229] The battery preparation methods in Examples 1-6 are the same as those in Examples 1-1, except that the final carbonization temperature is 1200℃ and the time is extended to 4 hours during the preparation of carbon-based materials.

[0230] The preparation methods of the batteries in Examples 1-7 are the same as those in Examples 1-1. The difference is that in the process of preparing carbon-based materials, FeCl3, potassium permanganate and hydrogen peroxide are added to the pre-carbonized product and then heated to 1100℃ and kept at that temperature for 2 hours.

[0231] The relevant parameters of the carbon-based materials in Examples 1-1-1-7 and Examples 2-1-2-5 are shown in Table 1. The preparation method of the battery in Examples 2-5 is the same as that in Example 1-1, except that the electrolyte does not contain cyclic carbonates. The test results of the coin cell and the battery cell are shown in Table 2.

[0232] The preparation methods of the battery cells in Examples 1-8-1-12 and Examples 2-5 are the same as those in Example 1-1, except that the composition of the electrolyte is different, as detailed in Table 3.

[0233] Examples 1-13 Preparation of the positive electrode sheet: Sodium iron phosphate pyrophosphate (NFPP, average particle size 5.6 μm, phase purity greater than 96.5%), Super P (SP, average particle size 1 μm), carbon nanotubes (length 15 μm), and polyvinylidene fluoride (PVDF) were dissolved and mixed in N-methylpyrrolidone (NMP) at a mass ratio of 95.1:2:0.9:2 to prepare a positive electrode slurry. The positive electrode slurry was coated onto a current collector aluminum foil, dried, and cold-pressed to form the positive electrode sheet.

[0234] The assembly method of the remaining components and batteries is the same as in Example 1-1.

[0235] Examples 2-6 The preparation method of the positive electrode sheet is the same as in Examples 1-13, except that NFPP, SP, and PVDF are mixed in a ratio of 95.1:2.9:2.

[0236] Examples 2-7 The preparation method of the positive electrode sheet is the same as in Examples 1-13, except that NFPP, carbon nanotubes and PVDF are mixed in a ratio of 95.1:2.9:2.

[0237] Tests related to carbon-based materials: 1) XRD Test The carbon-based material and silicon powder prepared in the above examples were uniformly mixed at a mass ratio of 5:1, and the sample was prepared using the plate preparation method. A Bruker D8 Discover X-ray diffractometer was used for testing. CuKα rays were used as the radiation source, and a copper target was used as the anode target. The 2θ angle range was scanned from 10º to 40º, and the scan rate was 1º / min. The XRD diffraction pattern of the carbon-based material was obtained.

[0238] 2) Pore diameter and pore volume test For carbon-based materials, adsorption and desorption isotherms were tested using nitrogen and carbon dioxide adsorption methods, respectively, in accordance with GB / T 19587-2017. The nitrogen adsorption method employed a specific surface area and porosity analyzer (Micromeritics ASAP-2460, USA), and the carbon dioxide adsorption method also employed a specific surface area and porosity analyzer (Micromeritics ASAP-2460, USA). For the adsorption and desorption isotherms obtained by the nitrogen adsorption method, a DFT model was used to fit the pore size distribution curves, yielding the pore volume and total specific surface area for specific pore size ranges (1.0nm-1.5nm, 1nm-2nm, and above 2nm). For the adsorption and desorption isotherms obtained by the carbon dioxide adsorption method, a DFT model was used to fit the pore size distribution curves, and the pore volume for pores smaller than 1nm was calculated mathematically. These methods provide the pore size and pore volume parameters V1, V2, and Vtotal.

[0239] Positive electrode plate test (1) Average pore width The positive electrode sheet was cut into 6 mm × 6 mm samples. Two conductive and thermally conductive copper foils were used to clamp the sample, and double-sided tape was used to secure it to the copper foils. A 400 g flat iron block was used to press the sample for 1 hour. The edges were trimmed with scissors, and the sample was then attached to a sample stage with conductive adhesive. The sample stage was then mounted on a sample holder. The argon ion cross-section polisher (IB-19500 CP) was powered on and a vacuum (10 Pa ~ 4 Pa) was created. The argon flow rate (0.15 MPa), voltage (8 KV), and polishing time (2 h) were set. The sample stage was adjusted to swing mode to begin polishing. After polishing, an ion-polished cross-sectional morphology image of the sample was obtained using a scanning electron microscope (ZEISS Sigma 300). Then, ImageJ software was used to statistically analyze the pore width between particles. A normal distribution curve was fitted to obtain the pore width distribution curve, from which the average pore width could be obtained.

[0240] (2) Diaphragm resistance Cut the dried electrode sheet into small round pieces with a diameter of 10 mm from the left, center, and right sides of the positive electrode sheet. Turn on the Yuaneng Technology electrode resistance meter, place it at the appropriate position of the "probe" of the electrode resistance meter, click the "start" button, and wait for the reading to stabilize before taking the reading. Test two positions for each small round piece, and finally calculate the average of the six measurements, which is the film resistance of the positive electrode sheet.

[0241] Performance testing (1) Dynamic performance of button cells At 25°C, the prepared coin cell was first discharged at a constant current density of 0.1C to 0.1V, and the capacity above 0.1V of the coin cell was recorded. Then, it was discharged at a constant current density of 0.1C to 0V, and the first discharge capacity (i.e., the first sodium insertion capacity) of the coin cell was recorded. After that, it was charged at a constant current density of 0.1C to 2.0V, and the first charge capacity (i.e., the first sodium removal capacity) of the coin cell was recorded.

[0242] Capacity percentage above 0.1V (%) = Capacity above 0.1V / Initial sodium insertion capacity × 100%; The 0.1V capacity ratio can reflect the kinetic performance of a secondary battery. The larger the 0.1V capacity ratio, the better the kinetic performance of the battery, indicating that it is easier for ions to be inserted and extracted in the material.

[0243] (2) DC internal resistance (DCR) At 25 °C, the battery cells prepared in each embodiment were charged at a constant current of 0.33 C to 3.65 V, and then charged at a constant voltage to a current of 0.05 C, and the voltage V1 was recorded. After resting for 5 min, they were discharged at a constant current of 1 C to the discharge cutoff voltage of 1.5 V, and the voltage V2 was recorded. Then, 3 × (V2 - V1) / C was used to obtain the DC internal resistance DCR1 of the battery cell after the first charge-discharge cycle. After resting for 5 min (stabilization time), the above steps were repeated for the battery 300 times to obtain the DC internal resistance DCR300 of the battery cell after the 300th cycle.

[0244] (3) Cycle performance of individual battery cells At 25℃, the prepared battery cell was charged at a constant current of 0.3C to the upper limit cutoff voltage of 3.65V, then charged at a constant voltage of 3.65V until the current ≤0.05C, rested for 5 minutes, and then discharged at 0.5C to 2.0V. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle was recorded. The battery capacity retention rate after each cycle was Pn = Cn / C0 × 100%. The battery capacity retention rate was plotted on the ordinate and the corresponding number of cycles was plotted on the abscissa to obtain a curve of battery capacity retention rate versus number of cycles.

[0245] Table 1

[0246] Table 2

[0247] As can be seen from Table 2, by ensuring that the spatial proportion of interlayer spacing and the proportion of pores with specific diameters are within the above range, and by adapting cyclic carbonates in the electrolyte, the capacity ratio of the battery cell can be increased by 0.1V, thereby improving the dynamic performance of the battery cell while also taking into account the cycle performance.

[0248] The preparation methods of the battery cells in Examples 1-8-1-12 and Examples 2-5 are the same as those in Example 1-1, except that the composition of the electrolyte is different, as detailed in Table 3.

[0249]

[0250] As shown in Table 3, within a suitable range, the content of cyclic carbonate solvent can reduce side reactions between the negative electrode active material and the electrolyte, lower sodium consumption, and improve the cycle performance of sodium-ion batteries while meeting kinetic requirements. When the ratio of cyclic carbonate solvent to chain ester is within a suitable range, the cycle performance of sodium-ion batteries is significantly improved. When the electrolyte does not contain cyclic carbonate solvent, sodium salts are difficult to dissociate, resulting in more side reactions between the solvent and the negative electrode active material, high sodium consumption, and impact on SEI film stability, ultimately leading to deterioration of the cycle performance of individual battery cells.

[0251] Table 4

[0252] Table 5

[0253] As can be seen from Table 5, by using NFPP as the positive electrode active material and adding dot-shaped and linear conductive agents, the DC internal resistance of the battery cell after 300 cycles can be as low as about 4Ω, and the capacity retention rate of the battery cell after 300 cycles can be as high as 99.20%.

[0254] Figure 7 This is a scanning electron microscope (SEM) cross-sectional view of the positive electrode sheet in Examples 1-13 of this application. Figure 8 This is a pore width distribution curve of the positive electrode sheet obtained in Examples 1-13. From... Figure 7 and Figure 8 It can be seen that the pore width between particles in the positive electrode sheets of Examples 1-13 is 300 nm to 10 μm, and the average pore width is about 5 μm.

[0255] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A sodium-ion battery cell, characterized in that, The device includes an electrolyte, a negative electrode, and a positive electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a carbon-based material, which includes graphite-like layers and a porous structure. The spatial volume H1 between adjacent layers of the graphite-like layers (0.35 nm - 0.4 nm) and the total spatial volume H between all adjacent layers of the graphite-like layers satisfy: 30% ≤ H1 / H ≤ 65%. Based on nitrogen adsorption method, the pore volume V1 of the pore structure with a pore size of 5nm-10nm in the carbon-based material and the total pore volume V in the pore structure are satisfied with: 2%≤V1 / V≤13%; The electrolyte further includes a solvent, which includes cyclic carbonates, including one or more of propylene carbonate, ethylene carbonate, and butene carbonate.

2. The sodium-ion battery cell according to claim 1, characterized in that, The spatial volume H2 between adjacent layers of the graphite-like sheet is greater than or equal to 0.4 nm, and the total spatial volume H between all layers in the graphite-like sheet satisfies: 25% ≤ H2 / H ≤ 60%.

3. The sodium-ion battery cell according to claim 2, characterized in that, The spatial volume H3 between adjacent layers of the graphite-like sheet is less than 0.35 nm, and the total spatial volume H between all layers in the graphite-like sheet satisfies: H3 / H≤18%.

4. The sodium-ion battery cell according to claim 1, characterized in that, 2%≤V1 / V≤10%.

5. The sodium-ion battery cell according to claim 4, characterized in that, The pore volume V2 of the carbon-based material with a pore size of less than or equal to 2 nm, as measured by nitrogen adsorption, and the total pore volume V in the pore structure satisfy the following condition: 10% ≤ V2 / V ≤ 30%.

6. The sodium-ion battery cell according to claim 5, characterized in that, The pore volume V3 of the carbon-based material with a pore size of 1nm-2nm, as measured by nitrogen adsorption, and the total pore volume V in the pore structure satisfy the following condition: 5%≤V3 / V≤15%.

7. The sodium-ion battery cell according to claim 6, characterized in that, The pore volume V4 of the carbon-based material with a pore size greater than 2 nm and less than 5 nm, as measured by nitrogen adsorption, satisfies the following condition: 8% ≤ V4 / V ≤ 27%.

8. The sodium-ion battery cell according to claim 1, characterized in that, The conductivity C of the electrolyte at 25±1°C satisfies: 7mS / cm≤C≤13mS / cm.

9. The sodium-ion battery cell according to claim 8, characterized in that, The electrolyte further includes chain esters, which include chain carbonates and / or chain carboxylic acid esters. The chain carbonates include one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and dibutyl carbonate. The chain carboxylic acid esters include one or more of methyl acetate, ethyl acetate, ethyl propionate, methyl formate, ethyl formate, methyl propionate, propyl propionate, ethyl butyrate, and propyl acetate.

10. The sodium-ion battery cell according to claim 9, characterized in that, The mass ratio of the cyclic carbonate to the chain ester is 0.25-1.

5.

11. The sodium-ion battery cell according to claim 10, characterized in that, Based on the total mass of the electrolyte, the cyclic carbonate accounts for 15%-55% of the mass; and / or Based on the total mass of the electrolyte, the mass percentage of the chain ester is 30%-70%.

12. The sodium-ion battery cell according to claim 1, characterized in that, The cyclic carbonates include one or more of propylene carbonate and ethylene carbonate.

13. The sodium-ion battery cell according to claim 9, characterized in that, The chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

14. The sodium-ion battery cell according to claim 9, characterized in that, The chain carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, and ethyl propionate.

15. The sodium-ion battery cell according to claim 9, characterized in that, The chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and the chain carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, and ethyl propionate.

16. The sodium-ion battery cell according to claim 9, characterized in that, The cyclic carbonate includes propylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass ratios of the cyclic carbonate and the chain carbonate is 60%-90%.

17. The sodium-ion battery cell according to claim 9, characterized in that, The cyclic carbonate includes propylene carbonate, and the chain carbonate includes methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonate and the chain carbonate is 60%-90%.

18. The sodium-ion battery cell according to claim 9, characterized in that, The cyclic carbonate includes ethylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonate and the chain carbonate is 60%-90%.

19. The sodium-ion battery cell according to claim 9, characterized in that, The cyclic carbonate includes ethylene carbonate, and the chain carbonate includes dimethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonate and the chain carbonate is 60%-90%.

20. The sodium-ion battery cell according to claim 9, characterized in that, The cyclic carbonates include propylene carbonate and ethylene carbonate, and the chain carbonates include one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonates and the chain carbonates is 60%-90%.

21. The sodium-ion battery cell according to claim 9, characterized in that, The cyclic carbonates include propylene carbonate and ethylene carbonate, and the chain carbonates include diethyl carbonate. Based on the total mass of the electrolyte, the sum of the mass percentages of the cyclic carbonates and the chain carbonates is 60%-90%.

22. The sodium-ion battery cell according to claim 1, characterized in that, The electrolyte also includes an electrolyte salt, which includes one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium perchlorate.

23. The sodium-ion battery cell according to claim 1, characterized in that, The electrolyte also includes electrolyte salts, including sodium hexafluorophosphate and sodium difluorosulfonamide.

24. The sodium-ion battery cell according to claim 22, characterized in that, The electrolyte further includes a first additive, which comprises one or more compounds of Formula I and Formula II: Formula I Formula II, R1, R2, R3, R4, R5, and R6 each independently include one or more of the following: hydrogen atom, C1-C6 alkyl group, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, ester group, cyano group, and sulfonic acid group.

25. The sodium-ion battery cell according to claim 24, characterized in that, The first additive includes one or more of the following compounds: Formula I-1 Formula I-2 Formula I-3 Formula II-1 Formula II-2 Formula II-3.

26. The sodium-ion battery cell according to claim 24, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the first additive is 0.005%-2%.

27. The sodium-ion battery cell according to claim 24, characterized in that, The electrolyte also includes a second additive, which includes one or more of tris(trimethylsilane) phosphate, tris(trimethylsilyl) phosphite, and triphenyl phosphite.

28. The sodium-ion battery cell according to claim 27, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the second additive is 0.005%-1%.

29. The sodium-ion battery cell according to claim 1, characterized in that, The conductivity C of the electrolyte at 25±1°C satisfies: 7mS / cm≤C≤15mS / cm.

30. The sodium-ion battery cell according to claim 1, characterized in that, The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds.

31. The sodium-ion battery cell according to claim 30, characterized in that, The transition metal element in the sodium transition metal oxide includes one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.

32. The sodium-ion battery cell according to claim 30, characterized in that, The sodium transition metal oxide includes compounds represented by Formula III: Na x M1O2 type III, M1 includes one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, where 0 < x ≤ 1.

33. The sodium-ion battery cell according to claim 32, characterized in that, The sodium transition metal oxide includes one or more of copper-iron-manganese-based oxides and nickel-iron-manganese-based oxides.

34. The sodium-ion battery cell according to claim 30, characterized in that, The polyanionic compound includes one or more of polyanionic phosphates, polyanionic sulfates, polyanionic silicates, polyanionic borates, and polyanionic fluorophosphates.

35. The sodium-ion battery cell according to claim 34, characterized in that, The polyanionic phosphate includes: Na a Fe b M2 c M3 d (Condensed polyanions) e (Anion) f , M2 includes one or more transition metal elements, M3 includes one or more non-transition metal elements, a>b, c>0, d≥0, e≥1, f>0, and the condensed polyanion includes P2O7. 4- P3O9 5- P4O 11 6- One or more of the following anions are included: aluminate ion, silicate ion, phosphate ion, sulfate ion, titanate ion, vanadate ion, and tungstate ion.

36. The sodium-ion battery cell according to claim 34, characterized in that, The polyanionic phosphate includes: Na x Fe a-y M4 y (M5O4) z (P2O7) w , Wherein, 2≤x≤4, 1≤a≤4, 1≤y≤4, 0≤z≤4, 0≤w≤1, at least one of z and w is greater than or equal to 1, M4 includes one or more of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, and M5 includes one or more of Al, Si, P, S, Ti, V, and W.

37. The sodium-ion battery cell according to claim 30, characterized in that, The Prussian blue compounds include one or more of iron-based Prussian blue and manganese-based Prussian blue.

38. The sodium-ion battery cell according to claim 34, characterized in that, The polyanionic phosphate has at least a portion of its surface covered with carbon material.

39. The sodium-ion battery cell according to claim 30, characterized in that, The positive electrode film layer further includes a binder, which includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

40. The sodium-ion battery cell according to claim 39, characterized in that, The positive electrode film layer further includes dot-shaped conductive agents and / or linear conductive agents. The dot-shaped conductive agents include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, and graphite-like materials. The linear conductive agents include one or more of carbon nanotubes, carbon nanofibers, and carbon nanorods.

41. The sodium-ion battery cell according to claim 40, characterized in that, The length of the linear conductive agent is 5μm-20μm.

42. The sodium-ion battery cell according to claim 40, characterized in that, Based on the total mass of the positive electrode film, the mass percentage of the linear conductive agent is 0.7%-1.5%.

43. The sodium-ion battery cell according to claim 40, characterized in that, The positive electrode film layer includes sodium iron phosphate pyrophosphate, and the average pore width between the sodium iron phosphate pyrophosphate particles in the positive electrode film layer is 1μm-5μm.

44. The sodium-ion battery cell according to claim 43, characterized in that, The pore width between the sodium iron phosphate pyrophosphate particles in the positive electrode film is 300 nm-10 μm.

45. The sodium-ion battery cell according to claim 43, characterized in that, The average particle size of the dot-shaped conductive agent in the positive electrode film is smaller than the average pore width between the particles of sodium iron phosphate pyrophosphate.

46. ​​The sodium-ion battery cell according to claim 45, characterized in that, Based on the total mass of the positive electrode film, the mass percentage of the dotted conductive agent is 2%-4%.

47. An electrical appliance, characterized in that, Includes a sodium-ion battery cell as described in any one of claims 1-46, wherein the sodium-ion battery cell is used to provide electrical energy.

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