Sodium-ion battery cell, battery device, and electric device

Abstract

This application relates to the field of battery technology, and provides a sodium-ion battery cell, a battery device, and an electrical device. The sodium-ion battery cell includes a positive electrode and an electrolyte; the thickness L of the positive electrode film layer satisfies: 50 μm ≤ L ≤ 90 μm; the general structural formula of the layered oxide material in the positive electrode film layer is Na. x Ni b Fe c Mn d Cu e N f O g N includes active and / or inert doped metal elements, including at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca; the electrolyte includes cyclic carbonates and chain esters, the freezing point T of the cyclic carbonates satisfies: -60℃≤T≤-10℃, the viscosity η of the chain esters at 25℃±1℃ satisfies: 0.2mPa·s≤η≤3mPa·s, and the mass ratio E of cyclic carbonates to chain esters satisfies: 0.11≤E≤1.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a sodium-ion battery cell, battery device, and electrical equipment. Background Technology

[0002] Sodium-ion batteries are gaining popularity due to their low cost, good low-temperature performance, and abundant sodium resources. Particularly in the high-power sector, their cost advantage and low-temperature discharge performance make them competitive. They have wide applications in new energy vehicles, drones and robots, smart grids, data centers, renewable energy storage, large-scale energy storage systems, power starters, and power tools.

[0003] With the development of battery technology, the application of sodium-ion batteries in the high-power field is no longer solely focused on their high-power performance, but also on their overall performance while maintaining high power output. Therefore, how to provide a sodium-ion battery with good overall performance is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a sodium-ion battery cell that combines high power discharge and long service life.

[0005] To achieve the above objectives, this application provides a sodium-ion battery cell, a battery device, and an electrical device.

[0006] In a first aspect, a sodium-ion battery cell is provided, comprising: a positive electrode sheet and an electrolyte; the positive electrode sheet includes a positive current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one surface of the positive current collector, and the thickness L of the positive electrode film layer satisfying: 50 μm ≤ L ≤ 90 μm; the positive electrode film layer includes a layered oxide material, the general structural formula of the layered oxide material being Na x Ni b Fe c Mn d Cu e N f O gWhere 0.80≤x≤1, 0≤b≤0.35, 0.2≤c≤0.4, 0.28≤d≤0.55, 0.04≤e≤0.12, 0.02≤f≤0.08, 1.8≤g≤2, and b+c+d>0.85, b+c+d+e+f=1; N includes active and / or inert doped metal elements, wherein the doped metal elements include Zn, V, Cr, Al, Sc, Sn, At least one of Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca; the electrolyte comprises cyclic carbonate and chain ester, wherein the freezing point T of the cyclic carbonate satisfies: -60℃ ≤ T ≤ -10℃, the viscosity η of the chain ester at a temperature of 25℃ ± 1℃ satisfies: 0.2 mPa·s ≤ η ≤ 3 mPa·s, and the mass ratio E of the cyclic carbonate to the chain ester satisfies: 0.11 ≤ E ≤ 1.

[0007] In the embodiments of this application, the positive electrode film layer includes a layered oxide material, which is doped with a variable valence metal element Cu, and may also be doped with a variable valence metal element Ti. That is, in a layered oxide system (NFM system) containing Na, Ni, Fe, and Mn, Cu and Ti are doped with metal elements. Compared with other metal elements in the NFM system, Cu and Ti have larger ionic radii and stronger binding energies, which can effectively improve the problems of migration, structural distortion and irreversible phase transition of iron and nickel transition metals in the layered oxide material during sodium insertion / extraction. This makes the positive electrode layered oxide material have better structural stability, which is beneficial to improving the cycle stability of sodium-ion battery cells at high discharge rates and increasing cycle life. Meanwhile, layered oxide materials can also be doped with non-variable valence metal elements such as Al, Zn, Mg, Ca, or Zr. These non-variable valence metal elements can work together with variable valence metal elements such as Cu and Ti to regulate the disordered arrangement of metal elements in the transition metal layers of the layered oxide material. This helps to improve the cell stability of the cathode layered oxide material, enhance the cycle performance of sodium-ion battery cells, increase the interlayer spacing, widen sodium ion channels, improve the rate performance of sodium-ion battery cells, and increase discharge power. Furthermore, when the electrolyte contains low-freezing-point cyclic carbonates, it can improve the liquid phase transport rate of sodium ions in the electrolyte at low temperatures, while also improving the stability of the electrode / electrolyte interface film. Simultaneously, introducing low-viscosity chain esters into the electrolyte can improve the migration kinetics of sodium ions while ensuring sodium salt dissociation. This can increase the migration rate of ions at the electrolyte-cathode interface, reduce ion accumulation at the interface, improve charge distribution uniformity, reduce diffusion resistance, and thus improve electron conduction, thereby improving the power performance and cycle performance of the battery cell. Within the aforementioned ratio range of cyclic carbonates and chain esters in the electrolyte, a better balance can be struck between sodium salt dissociation and improved sodium ion migration kinetics, allowing sodium ions in the electrolyte to reach the positive electrode interface more quickly and participate in the reaction. Combined with the above technical solution, under low-temperature conditions, the transport rate of sodium ions between the positive and negative electrode plates is increased, resulting in improved power performance. During the discharge of a sodium-ion battery cell, sodium ions released from the negative electrode material can reach the positive electrode interface more quickly to participate in the reaction, achieving high-rate discharge of the sodium-ion battery cell and improving discharge power performance. Simultaneously, during the migration of sodium ions between the positive and negative electrode plates, charge transfer impedance and liquid phase diffusion impedance are reduced, improving the power performance and cycle performance of the sodium-ion battery cell. The technical solution of this application embodiment can achieve high-power discharge of sodium-ion battery cells while also considering the cycle life of sodium-ion battery cells, providing a sodium-ion battery cell with excellent overall performance.

[0008] In one possible implementation, the volume average particle size Dv50 of the layered oxide material satisfies: 4μm≤Dv50≤9μm.

[0009] The Dv50 of layered oxide materials affects the ion diffusion capability of the positive electrode. By setting the Dv50 of the layered oxide materials within the above range, the ion diffusion capability of the positive electrode can be improved, thereby enhancing the power performance of sodium-ion battery cells.

[0010] In one possible implementation, based on the total mass of the electrolyte, the mass content P1 of the cyclic carbonate satisfies: 10% ≤ P1 ≤ 50%.

[0011] In the embodiments of this application, when the mass percentage of cyclic carbonate in the electrolyte is within the above-mentioned range, the sodium salt can be better dissociated, thereby improving the stability of the negative electrode / electrolyte interface film.

[0012] In one possible implementation, based on the total mass of the electrolyte, the mass content P2 of the chain ester satisfies: 40% ≤ P2 ≤ 90%.

[0013] In the embodiments of this application, when the mass percentage of the chain ester in the electrolyte is within the above-mentioned range, the migration kinetics of sodium ions can be further improved, thereby increasing the discharge power of the sodium-ion battery cell.

[0014] In one possible implementation, the cyclic carbonate includes at least one of propylene carbonate and ethylene carbonate.

[0015] In the embodiments of this application, the relevant components of the cyclic carbonate can also be decomposed into a film to a certain extent to improve the interfacial stability of the electrode / electrolyte, thereby further taking into account the life performance of the sodium-ion battery cell.

[0016] In one possible implementation, the chain ester includes at least one of chain carbonates and chain carboxylic acid esters.

[0017] In one possible implementation, the chain carbonate includes at least one 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.

[0018] In one possible implementation, the chain carboxylic acid ester includes at least one of methyl acetate, ethyl acetate, ethyl propionate, methyl formate, ethyl formate, methyl propionate, propyl propionate, ethyl butyrate, and propyl acetate.

[0019] In the embodiments of this application, the relevant components of the chain ester can further enhance the sodium ion migration kinetics under low temperature conditions, thereby improving the low-temperature discharge power of sodium ion battery cells.

[0020] In one possible implementation, the electrolyte further includes a first additive comprising a difluorooxalate borate compound.

[0021] In one possible implementation, based on the total mass of the electrolyte, the mass content P3 of the first additive satisfies: 0.05% ≤ P3 ≤ 2%.

[0022] In the embodiments of this application, during the charge and discharge process of a sodium-ion battery cell, difluorooxalate borate compound, as an electrolyte additive, can decompose to form a thin and stable CEI film on the surface of the positive electrode and a thin and stable SEI film on the surface of the negative electrode. This further reduces the side reactions at the electrode / electrolyte interface, which in turn facilitates the charge transfer process at the electrode interface and further improves the discharge power performance, cycle performance, and storage life of the sodium-ion battery under low-temperature conditions.

[0023] In one possible implementation, the sodium-ion battery cell further includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer. The negative electrode film layer is disposed on at least one side surface of the negative current collector, and the negative electrode film layer includes a carbon-based material or a tin-based alloy.

[0024] In one possible implementation, the carbon-based material comprises multiple pore structures, and the pore volume V1 of the pore structures with a pore size greater than 10 nm in the carbon-based material, measured by nitrogen adsorption, satisfies the following condition: 20% ≤ V1 / V ≤ 40%.

[0025] By controlling the volume ratio of large-pore structures (greater than 10 nm) in carbon-based materials, the proportion of large pores is reduced, thereby shortening the migration path of sodium ions from the interior to the surface of the negative electrode active material and enabling them to escape more quickly, thus improving the discharge power of the battery cell. Furthermore, reducing the proportion of large pores in the negative electrode carbon-based material can reduce side reactions at the interface between the negative electrode sheet and the electrolyte, reduce the consumption of electrolyte and active ions, and thus improve the service life of the battery cell.

[0026] In one possible implementation, the carbon-based material comprises a plurality of graphite-like sheets, with at least a portion of the graphite-like sheets having an interlayer spacing between two of the graphite-like sheets, wherein the interlayer spacing satisfies that the volume H1 of the space of 0.35 nm to 0.4 nm and the total volume H of the space formed by the plurality of graphite-like sheets satisfy: 20% ≤ H1 / H ≤ 60%.

[0027] Sodium ions can be rapidly extracted between graphite-like layers with an interlayer spacing of 0.35 nm to 0.4 nm. By setting the spatial volume ratio of graphite-like layers with an interlayer spacing of 0.35 nm to 0.4 nm within the above range, increasing the spatial proportion of graphite-like layers with larger interlayer spacing is beneficial for sodium ions to be rapidly extracted from the interior of carbon-based materials, thereby improving the discharge power of the battery cell.

[0028] In one possible implementation, the sodium-ion battery cell further includes: a housing, which is a hollow structure with an opening, wherein the positive electrode and the electrolyte are housed within the housing; and a top cover that closes the opening.

[0029] In a second aspect, a battery device is provided, comprising a sodium-ion battery cell as described in the first aspect and any possible implementation thereof.

[0030] Thirdly, an electrical device is provided, comprising a sodium-ion battery cell as described in the first aspect and any possible implementation thereof, or a battery device as described in the second aspect.

[0031] In one possible implementation, the sodium-ion battery cell or the battery device is used as the start-stop power source for the electrical equipment. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application;

[0034] Figure 2 This is a schematic diagram of the structure of a negative electrode sheet according to an embodiment of this application;

[0035] Figure 3 This is a schematic diagram of a battery cell according to an embodiment of this application;

[0036] Figure 4 This is a schematic diagram of a battery device according to an embodiment of this application;

[0037] Figure 5 This is a schematic diagram of a vehicle according to an embodiment of this application. Detailed Implementation

[0038] Embodiments of the sodium-ion battery cell, battery device, and power supply of this application have been described in detail with reference to the accompanying drawings, but unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0039] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is 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.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0042] 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 method may also include step (c), indicating 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.

[0043] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process of the battery cell, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing active ions to pass through; for example, the separator can be a membrane. In some embodiments, the above-described battery cell is also referred to as a secondary battery, and the battery cell can be the smallest possible battery unit.

[0044] During the charging process of a sodium-ion battery, sodium ions are released from the positive electrode active material, move and embed into the negative electrode material; while during the discharging process, sodium ions are released from the negative electrode material, move and embed into the positive electrode active material.

[0045] It should be understood that the “intercalation” process described in this application refers to the process in which sodium ions are intercalated in the positive electrode active material and the negative electrode material due to an electrochemical reaction, and the “deintercalation” and “deintercalation” processes described in this application refer to the process in which sodium ions are deintercalated in the positive electrode active material and the negative electrode active material due to an electrochemical reaction.

[0046] If mentioned, "graphite-like sheets" can refer to local layered structures composed of carbon atoms in carbon-based materials, or "graphite-like microcrystals," or "pseudo-graphitic domains," or disordered stacked carbon sheets, or symbiotic large-area graphite-like crystals, or "amorphous carbon" and / or "difficult-to-graphitize carbon" as defined in current national standards (such as GB / T 43114-2023 Hard Carbon).

[0047] Sodium-ion batteries have gradually come into view due to their advantages such as low cost, good low-temperature performance, and abundant sodium resources. Especially in the high-power field, the cost advantage and low-temperature discharge performance of sodium-ion batteries make them competitive in the high-power market.

[0048] In specific applications, such as new energy vehicles, drones and robots, smart grids, data centers, renewable energy storage, large-scale energy storage systems, power start-up, and power tools, the development of high-power sodium-ion battery technology requires consideration of multiple design factors. For example, it's necessary to balance high-power discharge performance with high energy density, cycle performance, and lifespan. Furthermore, depending on the vehicle application scenario, the performance requirements of sodium-ion batteries at low temperatures, such as low-temperature high-power discharge performance, also need to be considered.

[0049] The design of the positive electrode, negative electrode, and electrolyte in a battery cell is crucial to its performance. For example, the power performance of a battery cell is related to the migration rate of sodium ions between the positive and negative electrodes. This involves the migration of sodium ions in the positive electrode, the negative electrode, the electrolyte, and at the solid-liquid interface. With the development of battery technology, many solutions have emerged to improve the power performance of battery cells by modifying the positive electrode, negative electrode, or electrolyte. However, battery cells with high-power discharge often have a shorter lifespan. This is because high-current discharge generates Joule heat, causing the battery temperature to rise, accelerating electrode deformation and active material shedding, shortening cycle life, and also accelerating electrode corrosion and electrolyte decomposition, which also shortens cycle life.

[0050] Current technologies primarily focus on the interface between the electrode and the electrolyte, aiming to improve battery life by mitigating side reactions between them. However, the applicant recognizes that the main bottleneck in solving these problems lies in the excessive charge transfer resistance during the solid-phase diffusion of the positive electrode active material and the structural stability of sodium ions during long-term rapid intercalation in sodium-ion battery cells. Simultaneously, the applicant has also found that the electrolyte's liquid-phase diffusion resistance affects the high-power discharge of sodium-ion battery cells. Especially under prolonged discharge conditions, the liquid-phase diffusion resistance accumulates during discharge, further exacerbating polarization within the battery and impacting the discharge power and lifespan of the sodium-ion battery cell. In summary, the bottleneck to the repeated high-rate discharge performance of sodium-ion battery cells lies in simultaneously reducing both the positive electrode charge transfer resistance and the liquid-phase diffusion resistance. Only by addressing these bottlenecks can repeated high-rate discharge of sodium-ion battery cells be achieved.

[0051] In view of this, this application provides a sodium-ion battery cell, including a positive electrode and an electrolyte; wherein the positive electrode includes a positive current collector and a positive electrode film, and the positive electrode film is disposed on at least one surface of the positive current collector. Specifically, the thickness L of the positive electrode film satisfies: 50 μm ≤ L ≤ 90 μm. The positive electrode film includes a layered oxide material, and the general structural formula of the layered oxide material is Na. x Ni b Fe c Mn d Cu e N f O gThe following conditions apply: 0.80≤x≤1, 0≤b≤0.35, 0.2≤c≤0.4, 0.28≤d≤0.55, 0.04≤e≤0.12, 0.02≤f≤0.08, 1.8≤g≤2, and b+c+d>0.85, b+c+d+e+f=1; N includes active and / or inert doped metal elements, wherein the doped metal elements include at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca. The electrolyte includes cyclic carbonates and chain esters. The freezing point T of the cyclic carbonates satisfies: -60℃≤T≤-10℃, the viscosity η of the chain esters at a temperature of 25℃±1℃ satisfies: 0.2mPa·s≤η≤3mPa·s, and the mass ratio E of the cyclic carbonates to the chain esters satisfies: 0.11≤E≤1. The sodium-ion battery cell provided in the application embodiment can balance high power discharge performance and long service life.

[0052] Based on the above understanding, the applicant, in designing the positive electrode, has a relatively thin positive electrode film layer while maintaining the energy density of the battery cell, which can improve the transport rate of sodium ions in the positive electrode. Furthermore, the positive electrode layered oxide material is doped with metals, including variable-valence metals such as Cu and Ti. Cu and Ti have stronger binding energies and larger ionic radii. Their doping in the positive electrode layered oxide material can effectively improve the problems of migration, structural distortion, and irreversible phase transitions of iron and nickel transition metals during sodium insertion / extraction in the layered oxide material, enhancing the structural stability of the layered oxide material and enabling the sodium-ion battery cell to exhibit good cycle stability during repeated high-rate discharge. Meanwhile, non-variable valence metal elements Al, Zn, Mg, Ca, or Zr are also doped into the positive electrode layered oxide material. These non-variable valence metal elements can work together with variable valence metal elements Cu and Ti to regulate the disordered arrangement of metal elements in the transition metal layer contained in the layered oxide material. This is beneficial to improving the cell stability of the positive electrode layered oxide material, improving the cycle performance of sodium-ion battery cells, increasing the interlayer spacing of the layered oxide material, widening the sodium ion channels, improving the rate performance of sodium-ion battery cells, and improving the discharge power performance.

[0053] Meanwhile, in the electrolyte design for use with the aforementioned positive electrode, the cyclic carbonate in the electrolyte can dissociate from the sodium salt and has a lower freezing point, thereby improving the liquid-phase transport rate of sodium ions in the electrolyte at low temperatures. Simultaneously, the cyclic carbonate can be decomposed into a film, optimizing the electrode / electrolyte interface, thus further improving the stability of the positive electrode / electrolyte interface film without affecting the sodium ion migration rate in the electrolyte. Furthermore, the introduction of low-viscosity chain esters into the electrolyte can improve the migration kinetics of sodium ions while simultaneously ensuring sodium salt dissociation. This enhances the ion migration rate at the electrolyte-positive electrode interface, reduces ion accumulation at the interface, improves charge distribution uniformity, reduces diffusion resistance, and thus improves electron conduction, thereby improving the power performance and cycle performance of the battery cell. Within the aforementioned ratio range of cyclic carbonate and chain esters in the electrolyte, a better balance between sodium salt dissociation and improved sodium ion migration kinetics can be achieved, allowing sodium ions in the electrolyte to reach the positive electrode interface more quickly to participate in the reaction under low-temperature conditions.

[0054] In summary, the above-described technical solution combining the positive electrode and electrolyte improves the transport rate of sodium ions between the positive and negative electrodes, thereby enhancing power performance. During the discharge of a sodium-ion battery cell, sodium ions released from the negative electrode material can reach the positive electrode interface more quickly to participate in the reaction, achieving high-rate discharge and improving discharge power performance. Simultaneously, during the migration of sodium ions between the positive and negative electrodes, the charge transfer impedance and liquid phase diffusion impedance decrease, improving the power performance and cycle life of the sodium-ion battery cell. Therefore, the sodium-ion battery cell provided in this application embodiment can maintain good cycle life performance even during high-rate discharge at room temperature or low temperature.

[0055] As an example, the sodium-ion battery cell provided in this application can be used in automotive high-power discharge systems as a high-power discharge battery. Furthermore, the sodium-ion battery cell provided in this application combines high-power discharge and long service life. When used in automotive high-power discharge systems, it can repeatedly discharge at high rates, meeting automotive usage requirements and reducing the frequency of battery replacements.

[0056] The sodium-ion battery cell, battery device, and electrical device of this application will be described below with appropriate reference to the accompanying drawings.

[0057] Sodium-ion battery cell

[0058] This application provides a sodium-ion battery cell, including a positive electrode and an electrolyte.

[0059] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application. For example, as shown... Figure 1As shown, the positive electrode 1 includes a positive current collector 10 and a positive electrode film layer 11 disposed on at least one side surface of the positive current collector 10.

[0060] The positive current collector 10 has two opposing surfaces along its thickness direction. The positive electrode film layer 11 can be disposed on one surface of the positive current collector 10 or on both surfaces of the positive current collector 10. As an example, such as... Figure 1 As shown, the positive electrode film layer 11 is disposed on both sides of the positive electrode current collector 10.

[0061] In this embodiment, the thickness L of the positive electrode film 11 satisfies: 50μm≤L≤90μm.

[0062] As an example, L can be 50μm, 55μm, 60μm, 65μm, 70μm, 80μm, 90μm, or a value within the range obtained by any combination of the above two values.

[0063] It should be noted that when positive electrode films are disposed on both sides of the positive electrode current collector, the thicknesses of the positive electrode films on both sides may be equal or unequal. Here, "equal" can be considered as approximately equal. For example, within a certain error range known to those skilled in the art, the thicknesses of two positive electrode films with different thickness values ​​are considered to be approximately equal.

[0064] Setting the thickness of the positive electrode film 11 within the above-mentioned range, i.e., the positive electrode sheet is thinly coated, can improve the sodium ion transport rate in the positive electrode film, so that the sodium ions removed from the negative electrode can quickly migrate from the surface of the positive electrode to the interior of the positive electrode to participate in the reaction, which is beneficial to improving the discharge power of the battery cell.

[0065] The positive electrode film layer comprises a layered oxide material, the general structural formula of which is Na. x Ni b Fe c Mn d Cu e N f O g Where 0.80≤x≤1, 0≤b≤0.35, 0.2≤c≤0.4, 0.28≤d≤0.55, 0.04≤e≤0.12, 0.02≤f≤0.08, 1.8≤g≤2, and b+c+d>0.85, b+c+d+e+f=1; N includes active and / or inert doped metal elements, and the doped metal elements include at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca.

[0066] For example, x can be 0.80, 0.85, 0.88, 0.90, 0.95, 0.97, 1, or a value within the range obtained by any two combinations of the above values. b can be 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or a value within the range obtained by any two combinations of the above values. c can be 0.2, 0.25, 0.3, 0.35, 0.37, 0.4, or a value within the range obtained by any two combinations of the above values. d can be 0.28, 0.3, 0.32, 0.35, 0.4, 0.45, 0.5, 0.55, or a value within the range obtained by any two combinations of the above values. e can be 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, or 0.12, or a value within the range obtained by any two combinations of the above values. f can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, or 0.08, or a value within the range obtained by any two combinations of the above values. g can be 1.8, 1.85, 1.87, 1.9, 1.93, 1.95, 1.97, or 2, or a value within the range obtained by any two combinations of the above values.

[0067] It should be understood that during the charging and discharging process of a battery, there is a process of Na insertion / extraction and consumption, and the molar content of Na varies when the battery is discharged to different states. In the examples of cathode materials in this application, the molar content of Na refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar content of Na will change after charge-discharge cycles.

[0068] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0069] In positive electrode layered oxide materials, the presence of variable-valence metal elements such as Cu and Ti can be beneficial. Cu and Ti possess stronger binding energies and larger ionic radii. Their doping effectively mitigates the migration, structural distortion, and irreversible phase transitions of iron and nickel transition metals during sodium insertion / extraction in layered oxide materials, enhancing structural stability and resulting in good cycle stability for sodium-ion battery cells during repeated high-rate discharges. Simultaneously, non-variable-valence metal elements such as Al, Zn, Mg, Ca, or Zr can also be doped into the positive electrode layered oxide materials. These non-variable-valence metal elements can interact with Cu and Ti to regulate the disordered arrangement of metal elements within the transition metal layers of the layered oxide material. This improves the cell stability of the positive electrode layered oxide material, enhances the cycle performance of sodium-ion battery cells, increases interlayer spacing, widens sodium-ion channels, improves rate performance, and increases discharge power.

[0070] The electrolyte includes cyclic carbonates and chain esters. The freezing point T of the cyclic carbonates satisfies: -60℃≤T≤-10℃. The viscosity η of the chain esters at a temperature of 25℃±1℃ satisfies: 0.2mPa·s≤η≤3mPa·s. The mass ratio E of cyclic carbonates to chain esters satisfies: 0.11≤E≤1.

[0071] As an example, T can be -60℃, -55℃, -50℃, -45℃, -40℃, -35℃, -30℃, -20℃, -15℃, -10℃, or a value within the range obtained by any combination of the above two values.

[0072] As an example, η can be 0.2 mPa·s, 0.5 mPa·s, 0.7 mPa·s, 1 mPa·s, 1.5 mPa·s, 2 mPa·s, 2.5 mPa·s, 3 mPa·s, or a value within the range obtained by any combination of the above two values.

[0073] As an example, E can be 0.11, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a value within the range obtained by any combination of the above two values.

[0074] In electrolyte design, cyclic carbonates in the electrolyte can dissociate sodium salts and have lower freezing points, thereby improving the liquid-phase transport rate of sodium ions in the electrolyte at low temperatures. Simultaneously, cyclic carbonates can be decomposed into films to optimize the interfacial stability of the electrode / electrolyte interface, thus further improving the stability of the positive electrode / electrolyte interface film without affecting the sodium ion migration rate in the electrolyte. Furthermore, the introduction of low-viscosity chain esters into the electrolyte can improve sodium ion migration kinetics while simultaneously ensuring sodium salt dissociation. This enhances the ion migration rate at the electrolyte-positive electrode interface, reduces ion accumulation at the interface, improves charge distribution uniformity, lowers diffusion resistance, and ultimately improves electron conduction, thereby improving the power performance and cycle performance of the battery cell. Within the aforementioned ratio range of cyclic carbonates and chain esters in the electrolyte, a better balance between sodium salt dissociation and improved sodium ion migration kinetics can be achieved, allowing sodium ions in the electrolyte to reach the positive electrode interface more quickly to participate in the reaction.

[0075] Combining the above technical solutions, under low-temperature conditions, the transport rate of sodium ions between the positive and negative electrode plates is increased, thus improving power performance. During the discharge of a sodium-ion battery cell, sodium ions released from the negative electrode material can reach the positive electrode interface more quickly to participate in the reaction, achieving high-rate discharge of the sodium-ion battery cell and improving discharge power performance. Simultaneously, during the migration of sodium ions between the positive and negative electrode plates, the charge transfer impedance and liquid phase diffusion impedance are reduced, improving the power performance and cycle performance of the sodium-ion battery cell. The technical solution of this application embodiment can achieve high-power discharge of sodium-ion battery cells while also considering the cycle life of sodium-ion battery cells, providing a sodium-ion battery cell with excellent overall performance.

[0076] The content of organic components (such as solvents or organic additives) in the above electrolyte can be tested qualitatively and quantitatively by gas chromatography, referring to the methods in GB / T6041-2002 and GB / T 9722-2006. The content of salts and salt-type additives in the above electrolyte can be tested by referring to the General Rules for Ion Chromatography in Modern Analytical Instrumentation (JY / T 020-1996, issued on January 23, 1997, and implemented on April 1, 1997).

[0077] It should be noted that an electrolyte sample needs to be obtained before analyzing the components in the electrolyte. The sample preparation steps are as follows: Discharge the battery cell at any stage of use. Specifically, at 25°C, discharge the battery cell at a constant current of 1C to 1.5V, then let it stand for 20 minutes, and then discharge it at a constant voltage of 1.5V until the current is 0%, ending the discharge. Define the state of the battery cell at this point as 0% SOC. Then, in an argon atmosphere (H2O content <10ppm, O2 content <1ppm) glove box, disassemble the battery cell to obtain the electrolyte (if the electrolyte content in the battery cell is low, the electrolyte can be separated from the positive and negative electrode plates by centrifugation). After sample preparation, vacuum seal and transfer it out of the glove box for subsequent testing.

[0078] In some embodiments, based on the total mass of the electrolyte, the mass content P1 of the cyclic carbonate satisfies: 10% ≤ P1 ≤ 50%.

[0079] As an example, P1 can be 10%, 20%, 30%, 40%, 50%, or its value can be within the range obtained by any combination of the two values ​​mentioned above.

[0080] In the embodiments of this application, when the mass percentage of cyclic carbonate in the electrolyte is within the above-mentioned range, the sodium salt can be better dissociated, thereby improving the stability of the negative electrode / electrolyte interface film.

[0081] In some embodiments, based on the total mass of the electrolyte, the mass content P2 of the chain ester satisfies: 40% ≤ P2 ≤ 90%.

[0082] As an example, P2 can be 40%, 50%, 60%, 70%, 80%, 90%, or a value within the range obtained by any combination of the two values ​​mentioned above.

[0083] In the embodiments of this application, when the mass percentage of the chain ester in the electrolyte is within the above-mentioned range, the migration kinetics of sodium ions can be further improved, thereby increasing the discharge power of the sodium-ion battery cell.

[0084] In some embodiments, the dielectric constant D of the cyclic carbonate satisfies: 50 ≤ D ≤ 98.

[0085] As an example, D can be 50, 55, 60, 65, 70, 72, 77, 80, 85, 90, 96, 98, or a value within the range obtained by any combination of the above two values.

[0086] In the embodiments of this application, cyclic carbonates with high dielectric constants are more likely to dissociate from sodium salts, thereby enabling the electrolyte to have higher ionic conductivity and higher sodium ion migration kinetics, thus improving the discharge power of sodium-ion battery cells.

[0087] In some embodiments, cyclic carbonates include at least one of propylene carbonate and ethylene carbonate.

[0088] Specifically, cyclic carbonates may include only propylene carbonate, only ethylene carbonate, or both propylene carbonate and ethylene carbonate.

[0089] Propylene carbonate has a lower risk of solidification at low temperatures. In addition, it has a lower reduction potential, is less prone to reduction and decomposition, and has stronger chemical stability.

[0090] In the embodiments of this application, the relevant components of the cyclic carbonate can also be decomposed into a film to a certain extent to improve the interfacial stability of the electrode / electrolyte, thereby further taking into account the life performance of the sodium-ion battery cell.

[0091] In some embodiments, the molecular weight M of the chain ester satisfies: 50 ≤ M ≤ 150.

[0092] As an example, M can be 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or a value within the range obtained by any combination of the above two values.

[0093] In the embodiments of this application, when the molecular weight of the chain ester is within the above range, the chain ester can have a lower viscosity, thereby improving the migration kinetics of sodium ions and increasing the discharge power of sodium-ion battery cells.

[0094] In some embodiments, the chain ester includes at least one of chain carbonates and chain carboxylic acid esters.

[0095] Specifically, a chain ester may include only chain carbonates, only chain carboxylic esters, or both chain carbonates and chain carboxylic esters.

[0096] In some embodiments, the chain carbonate includes at least one 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.

[0097] In some embodiments, the chain carboxylic acid ester includes at least one of methyl acetate, ethyl acetate, ethyl propionate, methyl formate, ethyl formate, methyl propionate, propyl propionate, ethyl butyrate, and propyl acetate.

[0098] In the embodiments of this application, the relevant components of the chain ester can further enhance the sodium ion migration kinetics under low temperature conditions, thereby improving the low-temperature discharge power of sodium ion battery cells.

[0099] In some embodiments, the electrolyte further includes a first additive, which includes a difluorooxalate borate compound.

[0100] In some embodiments, based on the total mass of the electrolyte, the mass content P3 of the first additive satisfies: 0.05% ≤ P3 ≤ 2%.

[0101] As an example, P3 can be 0.05%, 0.06%, 0.07%, 0.1%, 0.5%, 0.7%, 1%, 1.2%, 1.5%, 2%, or a value within the range obtained by any combination of the above two values.

[0102] In the embodiments of this application, during the charge and discharge process of a sodium-ion battery cell, difluorooxalate borate compound, as an electrolyte additive, can decompose to form a thin and stable CEI film on the surface of the positive electrode and a thin and stable SEI film on the surface of the negative electrode. This further reduces the side reactions at the electrode / electrolyte interface, which in turn facilitates the charge transfer process at the electrode interface and further improves the discharge power performance, cycle performance, and storage life of the sodium-ion battery under low-temperature conditions.

[0103] In some embodiments, the general formula of the difluorooxalate borate compound is (F₂C₂O₄B). y M y+ , of which M y+ Including Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Fe 2+ Ni 2+ Al 3+ Fe 3+ Ni 3+ One or more of the following, where y = 1, 2, or 3.

[0104] In some embodiments, the volume average particle size Dv50 of the layered oxide material satisfies: 4μm≤Dv50≤9μm.

[0105] Dv50 refers to the particle size at which the cumulative volume distribution percentage of a material reaches 50%.

[0106] As an example, Dv50 can be 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or a value within the range obtained by any combination of the above two values.

[0107] As an example, the volume average particle size Dv50 of layered oxide materials can be determined using laser diffraction particle size analysis. Specifically, the Dv50 of layered oxide materials can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) in accordance with standard GB / T 19077-2016.

[0108] The Dv50 of layered oxide materials affects the ion diffusion capability of the positive electrode. By setting the Dv50 of the layered oxide materials within the above range, the ion diffusion capability of the positive electrode can be improved, thereby enhancing the power performance of sodium-ion battery cells.

[0109] In some embodiments, a sodium-ion battery cell may further include a negative electrode sheet.

[0110] Figure 2 This is a schematic diagram of the structure of a negative electrode sheet according to an embodiment of this application. For example, as shown... Figure 2 As shown, the negative electrode 2 includes a negative current collector 20 and a negative electrode film layer 21 disposed on at least one side surface of the negative current collector 20.

[0111] The negative electrode current collector 20 has two opposing surfaces along its thickness direction. The negative electrode film layer 21 can be disposed on one surface of the negative electrode current collector 20 or on both surfaces. As an example, such as... Figure 2 As shown, the negative electrode film layer 21 is disposed on both sides of the negative electrode current collector 20. The negative electrode film layer 21 may include a carbon-based material or a tin-based alloy.

[0112] In some embodiments, the carbon-based material includes at least one of the following materials: hard carbon, a mixture of hard carbon and soft carbon, and a mixture of hard carbon and graphite.

[0113] In some embodiments, tin-based alloys may include alloys of tin with at least one of the following metals: bismuth, zirconium.

[0114] In some embodiments, the carbon-based material includes multiple pore structures, and the pore volume V1 of the pore structures with a pore size greater than 10 nm in the carbon-based material, measured by nitrogen adsorption method, satisfies the following condition: 20% ≤ V1 / V ≤ 40%.

[0115] For example, V1 / V can be 20%, 22%, 25%, 27%, 30%, 33%, 35%, 38%, 40%, or a value within the range obtained by any combination of the above two values.

[0116] By controlling the volume ratio of large-pore structures (greater than 10 nm) in carbon-based materials, the proportion of large pores is reduced, thereby shortening the migration path of sodium ions from the interior to the surface of the negative electrode active material and enabling them to escape more quickly, thus improving the discharge power of the battery cell. Furthermore, reducing the proportion of large pores in the negative electrode carbon-based material can reduce side reactions at the interface between the negative electrode sheet and the electrolyte, reduce the consumption of electrolyte and active ions, and thus improve the service life of the battery cell.

[0117] In some embodiments, the pore volume V2 of the pore structure with a pore size of 5nm~10nm in the carbon-based material, measured by nitrogen adsorption method, and the total pore volume V of the carbon-based material satisfy the following: 5%≤V2 / V≤15%.

[0118] For example, V2 / V can be 5%, 6%, 8%, 10%, 12%, 14%, 15%, or a value within the range obtained by any combination of the above two values.

[0119] In some embodiments, the pore volume V3 of the pore structure with a pore size of 2nm~5nm in the carbon-based material, measured by nitrogen adsorption method, and the total pore volume V of hard carbon satisfy the following condition: 20%≤V3 / V≤40%.

[0120] Specifically, V3 / V can be 20%, 25%, 27%, 30%, 32%, 35%, 38%, 40%, or its value can be within the range obtained by any combination of the above two values.

[0121] Sodium ions diffuse rapidly in pore structures with a pore size of 2nm to 5nm. Setting the pore volume ratio of pore structures with a pore size of 2nm to 5nm in carbon-based materials within this range is beneficial for increasing the diffusion rate of sodium ions in the negative electrode active material, leading to faster insertion and thus improving the charging power of the battery cell. Furthermore, setting the pore volume ratio of pore structures with a pore size of 2nm to 5nm within this range also improves the wettability of the electrolyte on the negative electrode sheet, thereby enhancing the battery's rate performance and cycle stability.

[0122] In some embodiments, the pore volume V4 of the pore structure with a pore size of less than 2 nm in the carbon-based material, measured by nitrogen adsorption method, and the total pore volume V of hard carbon satisfy the following condition: 5% ≤ V4 / V ≤ 15%.

[0123] Specifically, V4 / V can be 5%, 6%, 8%, 10%, 12%, 14%, 15%, or its value can be within the range obtained by any combination of the above two values.

[0124] Sodium ions have a shorter migration path in pore structures with a pore size of less than 2 nm. By setting the pore volume ratio of pore structures with a pore size of less than 2 nm in carbon-based materials within the above range, the proportion of micropores (pore structures with a pore size of less than 2 nm) in carbon-based materials can be increased to shorten the migration path of sodium ions from the interior to the surface of the negative electrode active material, allowing them to escape more quickly and thus improve the discharge power of the battery cell.

[0125] The following provides a method for testing the pore volume of pore structures with different pore sizes in carbon-based materials.

[0126] Sample Preparation: Sodium-ion battery cells at any stage of use were discharged. Specifically, at 25°C, the cell was discharged at a constant current of 1C to 1.5V, then allowed to stand for 20 minutes, followed by a constant voltage discharge of 1.5V until the current reached zero. This state of the cell was defined as 0% SOC. The cell was then disassembled in an argon atmosphere (H2O <10ppm, O2 <1ppm) glove box to obtain the negative electrode. The surface of the electrode was cleaned with dimethyl carbonate (DMC) or acetone to remove residual electrolyte, and then allowed to air dry for 24 hours. The negative electrode surface was then powdered for sample preparation. The powder sample needed to be ground uniformly to avoid interference from large particles. The negative electrode powder was mixed with deionized water, stirred, filtered, and dried to obtain the sample to be tested.

[0127] Detection: (1) First, the sample is pretreated to remove moisture, impurities and other substances adsorbed on the surface of the hard carbon sample, so as to ensure that nitrogen adsorption only occurs on the clean material surface.

[0128] Specifically, first weigh an appropriate amount of hard carbon sample and perform vacuum degassing. Place the weighed sample into a sample tube and put it into a vacuum degassing device. The degassing temperature needs to be strictly controlled. Since hard carbon may oxidize at temperatures above 300℃ in air, the degassing temperature should be set between 120~300℃, with 150~250℃ being recommended, which can effectively degas the sample while avoiding damage to the material structure. The degassing time should be 6~12 hours to ensure that impurities on the sample surface are fully removed.

[0129] (2) Then, isotherm tests are performed to obtain adsorption-desorption data of nitrogen on hard carbon materials, providing the original basis for subsequent pore structure analysis.

[0130] Specifically, the pretreated sample tube is first placed in the test position of the adsorption instrument and then placed in a liquid nitrogen bath at 77K to stabilize the test environment temperature at the liquid nitrogen temperature. The adsorption process is then tested. Nitrogen gas is introduced, and the relative pressure P / P0 (P refers to the partial pressure of nitrogen, and P0 refers to the saturated vapor pressure of the adsorbate gas at the adsorption temperature) is gradually increased from 0.01 to 0.995. The amount of nitrogen adsorbed by the hard carbon material is recorded at each pressure point. At low relative pressures (P / P0), nitrogen molecules first form a monolayer adsorption on the pore walls, gradually forming a multilayer as the pressure increases. When the pressure reaches a certain value, capillary condensation occurs in the mesopores, resulting in a sharp increase in adsorption. Micropores, due to their extremely small pore size, can be filled with nitrogen molecules even at very low P / P0, without a significant condensation step. After the adsorption process is complete, the desorption process is tested. The relative pressure is gradually decreased, and the amount of desorption at different pressures is recorded to obtain desorption branch data. The shape of the isotherms formed during the adsorption-desorption process (such as the hysteresis loop type) can reflect the structural characteristics of the pores.

[0131] (3) Data calculation

[0132] The adsorption-desorption isotherm data obtained from the test were processed using specialized software to calculate the relevant parameters of the pore structure.

[0133] Calculate the total pore volume: Usually, the adsorption amount is taken when the relative pressure (P / P0) ≈ 0.99, and it is converted into the volume of liquid nitrogen. This volume is the total pore volume of the material, which represents the total volume of nitrogen that the material can hold.

[0134] Calculating micropore volume: For micropores with a diameter <2 nm, the t-plot method or the DR (Dubinin-Radushkevich) equation can be used for calculation. The t-plot method requires the selection of a suitable t-curve (such as the t-curve of standard carbon materials) to avoid baseline errors; the DR equation is suitable for hard carbon with relatively weak polarity.

[0135] Calculating mesopore volume: For hard carbon materials containing only micropores and mesopores, the mesopore volume is equal to the difference between the total pore volume and the micropore volume.

[0136] Analysis of pore size distribution: Pore size distribution reflects the proportion of pore volume within different pore size ranges and can be calculated using corresponding models. For mesopores (pore size of 2nm~50nm), the BJH (Barret-Joyner-Halenda) model is used, and calculations are performed based on desorption branch data; the pore size distribution of micropores needs to be analyzed in conjunction with their corresponding calculation models.

[0137] (4) Results Analysis

[0138] Based on the obtained parameters such as total pore volume, micropore volume, mesopore volume, and pore size distribution, analysis is performed in conjunction with the shape of the adsorption-desorption isotherm. For example, the mesoporous structure can be determined by the type of hysteresis ring: H1 type hysteresis rings correspond to cylindrical pores with uniform pore size, while H2 type hysteresis rings correspond to pores with uneven pore size or "ink bottle" pores.

[0139] In some embodiments, the carbon-based material includes a plurality of graphite-like sheets, and at least some of the graphite-like sheets form an interlayer spacing between two of the graphite-like sheets. The interlayer spacing satisfies that the volume H1 of the space of 0.35nm to 0.4nm and the total volume H of the space formed by the plurality of graphite-like sheets satisfy: 20%≤H1 / H≤60%.

[0140] For example, H1 / H can be 20%, 22%, 25%, 27%, 30%, 33%, 35%, 38%, 40%, 45%, 50%, 55%, 59%, 60%, or a value within the range obtained by any combination of the above two values.

[0141] Sodium ions can be rapidly extracted between graphite-like layers with an interlayer spacing of 0.35 nm to 0.4 nm. By setting the spatial volume ratio of graphite-like layers with an interlayer spacing of 0.35 nm to 0.4 nm within the above range, increasing the spatial proportion of graphite-like layers with larger interlayer spacing is beneficial for sodium ions to be rapidly extracted from the interior of carbon-based materials, thereby improving the discharge power of the battery cell.

[0142] In some embodiments, the spatial volume H2 between graphite-like sheets with an interlayer spacing greater than 0.4 nm and the total spatial volume H between all layers in the graphite-like sheets satisfy the following: 20% ≤ H2 / H ≤ 50%.

[0143] Specifically, H2 / H can be 20%, 25%, 27%, 30%, 32%, 35%, 38%, 40%, 45%, 50%, or its value can be within the range obtained by any combination of the two values ​​mentioned above.

[0144] Graphite-like sheets with an interlayer spacing greater than 0.4 nm have a large space volume between the sheets, which makes it easier for active ions to embed and adsorb onto the surface of the graphite-like sheets for energy storage. However, if the proportion of their space volume is too large, it will lead to an excessively high capacity in the slope section of the carbon-based material, thereby affecting the first-cycle coulombic efficiency of the sodium-ion battery cell. Therefore, the proportion of the space volume between graphite-like sheets with an interlayer spacing greater than 0.4 nm is set within the above range to achieve both the kinetic performance and the first-cycle coulombic efficiency of the sodium-ion battery cell.

[0145] In some embodiments, the spatial volume H3 between graphite-like sheets with an interlayer spacing of less than 0.35 nm and the total spatial volume H between all layers in the graphite-like sheet satisfy: 0 ≤ H3 / H ≤ 5%.

[0146] Specifically, H3 / H can be 0, 2%, 4%, 5%, or its value can be within the range obtained by any combination of the two values ​​mentioned above.

[0147] Setting the proportion of the space volume between graphite-like sheets with an interlayer spacing of less than 0.35 nm within the above range can reduce the risk of sodium deposition on the negative electrode, which is conducive to improving the capacity of the negative electrode and thus increasing the energy density of the battery cell.

[0148] In this embodiment of the application, H1 / H, H2 / H, and H3 / H can be obtained by peak fitting of the XRD pattern of carbon-based materials.

[0149] 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.

[0150] 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 less than 22.2º, the 2θ angle of the second fitted peak B was 22.2º~24.7º, and the 2θ angle of the third fitted peak C was greater than 24.7º.

[0151] 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 greater than 0.4 nm is less than 22.2º, the 2θ angle corresponding to graphite-like sheets with an interlayer spacing of 0.35 nm to 0.4 nm is 22.2º to 24.7º, and the 2θ angle corresponding to graphite-like sheets with an interlayer spacing less than 0.35 nm is greater than 24.7º.

[0152] 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 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); 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 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); 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).

[0153] For example, H1 / H, H2 / H, and H3 / H can be calculated as follows: the area of ​​the graphite-like sheet is 15.24 mm². 2 In this case, H2 / H = 15.24 mm 2 *Sum of interlayer spacings greater than 0.4 nm in carbon-based materials / 15.24 mm 2 * The total interlayer spacing in carbon-based materials is 15.24 mm. 2 *Area of ​​the first fitted peak / 15.24 mm 2 *(Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the first fitted peak / (Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the first fitted peak / Total area of ​​the three fitted peaks. H1 / H = 15.24 mm 2 *Sum of interlayer spacings from 0.35nm to 0.4nm in carbon-based materials / 15.24mm 2 * The total interlayer spacing in carbon-based materials is 15.24 mm. 2 *Area of ​​the second fitted peak / 15.24 mm 2 *(Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the second fitted peak / (Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the second fitted peak / Total area of ​​the three fitted peaks. H3 / H = 15.24 mm 2 *Sum of interlayer spacings smaller than 0.35 nm in carbon-based materials / 15.24 mm 2 * The total interlayer spacing in carbon-based materials is 15.24 mm. 2 *Area of ​​the third fitted peak / 15.24 mm 2 *(Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the third fitted peak / (Area of ​​the first fitted peak + Area of ​​the second fitted peak + Area of ​​the third fitted peak) = Area of ​​the third fitted peak / Total area of ​​the three fitted peaks.

[0154] In some embodiments, the sodium-ion battery cell further includes a housing and a top cover. The housing is a hollow structure with an opening, and the positive electrode and electrolyte are contained within the housing. The top cover is used to close the opening.

[0155] The embodiments of this application do not impose any particular restrictions on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape.

[0156] Figure 3 This is a schematic diagram of a battery cell according to an embodiment of this application. For example, as shown... Figure 3 As shown, the battery cell 3 is a square battery cell. The battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33 disposed in the housing 31.

[0157] The electrode assembly 33 can be made from a positive electrode 1, a negative electrode 2 and a separator through a winding process or a stacking process.

[0158] End cap assembly 32 includes electrode terminals 322, such as Figure 3 As shown, the end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0159] The battery cell 3 also includes a current collector 34, which is used to connect the tab 332 and the electrode terminal 322 of the electrode assembly 33. For example, in the case of a negative electrode in this embodiment, one current collector 34 is used to connect the tab and the negative electrode terminal of the negative electrode, and another current collector 34 is used to connect the tab and the positive electrode terminal of the positive electrode.

[0160] In some embodiments, the battery cell 3 includes an electrode assembly 33, which includes an electrode assembly body 331 and a tab 332 extending from the electrode assembly body 331.

[0161] In some embodiments, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0162] [Positive electrode plate]

[0163] 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.).

[0164] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0165] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0166] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0167] [Negative electrode plate]

[0168] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0169] In some embodiments, the negative electrode film layer may optionally include an adhesive. 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).

[0170] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0171] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li)).

[0172] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0173] [Electrolytes]

[0174] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0175] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0176] The electrolyte salt includes, but is not limited to, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. One of the above electrolyte salts may be used alone, or two or more may be used simultaneously.

[0177] Solvents include carbonate or ether solvents. Carbonate solvents include cyclic ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and chain-like dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), etc.; ether solvents include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxane, etc.

[0178] The electrolyte may also optionally include electrolyte additives. For example, electrolyte additives may include negative electrode film-forming additives, positive electrode film-forming additives, and performance additives that can improve certain battery performance, such as performance additives that improve battery overcharge performance, or improve battery high-temperature or low-temperature performance.

[0179] [Isolation Component]

[0180] The separator is used to isolate the positive electrode and the negative electrode. 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.

[0181] The material of the separator can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film; there are no particular restrictions. When the separator is a multi-layer composite film, the materials of each layer can be the same or different; there are no particular restrictions.

[0182] Positive electrode, negative electrode and separator can be made into electrode assembly by winding process or stacking process.

[0183] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0184] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0185] [Battery Device]

[0186] This application provides a battery device, including the battery cell described in the above embodiments. Figure 4 This is a schematic diagram of the structure of a battery device according to an embodiment of this application. Figure 4 As shown, the battery device 5 may include multiple battery cells 3 to meet different power usage requirements. The shape of the battery cell 3 in this embodiment can be set according to actual application. For example, the battery cell 3 may be as follows: Figure 3 The cuboid shown can also be different. Figure 3 The embodiments shown are cylindrical or other shapes, but are not limited to these.

[0187] It should be understood that, such as Figure 4As shown, the battery device 5 in this embodiment may further include a housing 51, which can be used to accommodate multiple battery cells 3. The housing 51 in this embodiment has a hollow interior, and the multiple battery cells 3 are accommodated within the housing 51. The housing 51 may include two parts, referred to herein as a first housing portion 511 and a second housing portion 512, which are fastened together. The shapes of the first housing portion 511 and the second housing portion 512 can be determined according to the shape of the components housed inside, for example, according to the shape of the combination of the multiple battery cells 3 housed inside. At least one of the first housing portion 511 and the second housing portion 512 has an opening. For example, as... Figure 4 As shown, the first housing portion 511 and the second housing portion 512 can both be hollow cuboids with one open side. The openings of the first housing portion 511 and the second housing portion 512 are opposite to each other, and the first housing portion 511 and the second housing portion 512 are interlocked to form a housing 51 with a closed cavity, which can be used to accommodate multiple battery cells 3. The multiple battery cells 3 are connected in parallel, series, or mixed and placed inside the housing 51 formed by the interlocking of the first housing portion 511 and the second housing portion 512.

[0188] For example, unlike Figure 4 As shown, either the first housing portion 511 or the second housing portion 512 may have only one hollow cuboid with an opening, while the other is plate-shaped to cover the opening. Taking the second housing portion 512 as a hollow cuboid with one opening, and the first housing portion 511 as a plate-shaped example, then the first housing portion 511 covers the opening of the second housing portion 512 to form a housing 51 with a closed chamber, which can be used to accommodate multiple battery cells 3.

[0189] The battery cells 3 can be directly assembled into the battery device 5, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into the battery device 5.

[0190] [Electrical Equipment]

[0191] This application provides an electrical device including a sodium-ion battery cell or battery device as described in the above embodiments. The sodium-ion battery cell or battery device can be used as the start-stop power supply for the electrical device.

[0192] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use battery devices. For example, electrical devices can be used in fields such as new energy vehicles, drones and robots, smart grids, data centers, renewable energy storage, large-scale energy storage systems, power starters, and power tools.

[0193] Electrical equipment can include vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-mentioned electrical equipment.

[0194] For ease of explanation, the following embodiments use a vehicle as an example of electrical equipment.

[0195] For example, such as Figure 5 The diagram shown is a structural schematic of a vehicle 7 according to one embodiment of this application. The vehicle 7 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. The vehicle 7 can have a motor 4, a controller 6, and a battery device 5 installed inside. The controller 6 controls the battery device 5 to supply power to the motor 4. For example, the battery device 5 can be installed at the bottom, front, or rear of the vehicle 7. The battery device 5 can be used to power the vehicle 7; for example, it can serve as the operating power source for the vehicle 7's electrical system, such as meeting the power requirements for starting, navigation, and operation. In another embodiment of this application, the battery device 5 can not only serve as the operating power source for the vehicle 7 but also as the driving power source, replacing or partially replacing gasoline or natural gas to provide driving power to the vehicle 7.

[0196] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0197] [Examples and Comparative Examples]

[0198] 1. Preparation of positive electrode sheet

[0199] Preparation of the positive electrode active material: NiO, Al2O3, Mn2O3, Fe2O3, and CuO were mixed in a specific molar ratio and ball-milled at 800 r / min for 5 hours. Sodium carbonate was then added in a specific ratio for further mixing to obtain the precursor of the positive electrode active material. This precursor was then sintered in a muffle furnace under an oxygen atmosphere and pulverized to obtain the layered oxide material for the positive electrode. The sintering conditions were: temperature: 800℃; time: 8 h; heating rate: 10℃ / min.

[0200] It should be noted that during the preparation of positive electrode active materials, the proportion of each metal element in the positive electrode layered oxide material can be controlled by adjusting the molar ratio of NiO, Al2O3, Mn2O3, Fe2O3, and CuO in the raw materials.

[0201] The above-prepared layered oxide material for the positive electrode, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 94:3:3. After thorough mixing, a positive electrode slurry was prepared. The positive electrode slurry was then uniformly coated on both sides of a 13 μm thick aluminum foil for the positive electrode current collector, with a single-side coating areal density of 286 mg / 1540.25 mm. 2 After drying, cold pressing, and slitting, positive electrode 1 is obtained. In positive electrode 1, the thickness L of the positive electrode film is 70 μm, and the positive electrode layered oxide material is Na. 0.91 Ni 0.26 Fe 0.24 Mn 0.4 Cu 0.06 Al 0.04 O2.

[0202] Positive electrode 2-3

[0203] The preparation process of positive electrode 2-3 is similar to that of positive electrode 1, except that the positive electrode layered oxide material in positive electrode 2-3 is Na. 0.88 Ni 0.3 Fe 0.3 Mn 0.3 Cu 0.04 Zr 0.06 O2 and N a0.94 N i0.22 Fe 0.3 Mn 0.38 Cu 0.06 Mg 0.04 O2.

[0204] Positive electrode plate 4-5

[0205] The preparation process of positive electrode 4-5 is similar to that of positive electrode 1, except that the thickness L of the positive electrode film layer of positive electrode 4-5 is 50 μm and 90 μm, respectively.

[0206] The preparation process of positive electrode 6 is similar to that of positive electrode 1, except that the layered oxide material in positive electrode 6 is Na. 0.95 Ni 0.4 Fe 0.2 Mn 0.4 O2.

[0207] 2. Preparation of negative electrode sheet

[0208] Hard carbon (negative electrode active material), acetylene black (conductive agent), SBR (binder), and CMC-Na (thickener) were mixed uniformly in a mass ratio of 95:2:2:1, dissolved in deionized water, and thoroughly stirred to obtain a negative electrode slurry. This slurry was then uniformly coated onto both sides of a 13 μm thick aluminum foil used as a negative electrode current collector, with a single-side coating density of 123 mg / 1540.25 mm. 2 After drying, cold pressing, and slitting, negative electrode sheets are formed.

[0209] 3. Preparation of electrolyte

[0210] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 25:75. Then, 1 mol / L NaPF6 sodium salt was added and dispersed evenly to obtain electrolyte 1. In electrolyte 1, the mass ratio E of the cyclic carbonate PC to the chain ester EMC was 0.2.

[0211] Electrolyte 2-3: The preparation process of electrolyte 2-3 is similar to that of electrolyte 1, except that the mass ratio E of cyclic carbonate PC to chain ester EMC in electrolyte 2-3 is 0.11 and 1, respectively.

[0212] Electrolyte 4: The preparation process of electrolyte 4 is similar to that of electrolyte 3, except that the cyclic carbonate in electrolyte 4 is ethylene carbonate (EC).

[0213] Electrolyte 5: The preparation process of electrolyte 5 is similar to that of electrolyte 2, except that the chain esters in electrolyte 5 include EMC and dimethyl carbonate (DMC), and the mass ratio of EMC to DMC is 1:1.

[0214] Electrolyte 6: The preparation process of electrolyte 6 is similar to that of electrolyte 1, except that the organic solvent in electrolyte 6 includes EMC but does not include PC.

[0215] 4. Preparation of the separator membrane: The separator membrane is a conventional polyethylene membrane with a thickness of 7μm.

[0216] 5. Assembly of sodium-ion batteries

[0217] The positive electrode, separator, and negative electrode are stacked in sequence and then wound to obtain an electrode assembly. The electrode assembly is placed in a shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a sodium-ion battery is obtained.

[0218] [Examples 1-5]

[0219] In Examples 1-5, the same separator, negative electrode, and electrolyte 1 were used. The difference was that different positive electrode was used, namely positive electrode 1-5, as detailed in Table 1.

[0220] [Examples 6-9]

[0221] In Examples 6-9, the same separator, negative electrode, and positive electrode 1 were used. The difference was that different electrolytes were used, namely electrolytes 2-5, as detailed in Table 2.

[0222] [Comparative Example 1]

[0223] In Comparative Example 1, the same separator, negative electrode, and electrolyte 1 as in Example 1 were used. The difference was that a different positive electrode was used. Comparative Example 1 used a positive electrode 6, as detailed in Table 1.

[0224] [Comparative Example 2]

[0225] In Comparative Example 2, the same separator, negative electrode, and positive electrode 1 as in Example 6 were used. The difference was that a different electrolyte was used. Comparative Example 2 used electrolyte 6, as detailed in Table 2.

[0226] In Table 1-2 below, L represents the thickness of the positive electrode film; E represents the mass ratio of cyclic carbonate to chain ester; and U1 represents the final voltage of the sodium-ion battery after discharging at a 5C0 current for 30 seconds at a temperature of -20℃ and a lower cutoff voltage of 1.8V.

[0227] Table 1. Product parameters and performance parameters of Examples 1-5 and Comparative Example 1

[0228]

[0229] Combining the results of Examples 1-3 and Comparative Example 1, it is evident that doping the layered oxide material with the variable-valence metal element Cu and the non-variable-valence metal elements Al, Mg, or Zr results in better discharge power performance and cycle performance for sodium-ion battery cells. In contrast, the layered oxide material in Comparative Example 1 lacked both the variable-valence metal element Cu and the non-variable-valence metal elements Al, Mg, or Zr, leading to poorer discharge power performance and cycle performance for the sodium-ion battery cell. This is because the variable-valence metal element Cu has a larger ionic radius and stronger binding energy, which can effectively mitigate the migration, structural distortion, and irreversible phase transitions of iron and nickel transition metals during sodium insertion / extraction in the layered oxide material. This results in better structural stability of the cathode layered oxide material, which is beneficial for improving the cycle stability of sodium-ion battery cells at high discharge rates and increasing cycle life. Non-variable valence metal elements Al, Mg, or Zr can work together with variable valence metal elements Cu to regulate the disordered arrangement of metal elements in the transition metal layers of layered oxide materials. This helps to improve the cell stability of the cathode layered oxide material, enhance the cycle performance of sodium-ion battery cells, increase the interlayer spacing of the layered oxide material, widen the sodium-ion channels, improve the rate performance of sodium-ion battery cells, and increase the discharge power performance.

[0230] Table 2 Product parameters and performance parameters of Examples 6-9 and Comparative Example 2

[0231]

[0232] The results from Examples 6-7 and Comparative Example 2 show that, with the same positive and negative electrode configurations, setting the mass ratio of cyclic carbonates to chain esters in the electrolyte within the range specified in this application results in better discharge power performance and cycle performance for the sodium-ion battery cell. In Comparative Example 1, the organic solvent contained only chain esters and no cyclic carbonates, resulting in poorer discharge power performance and cycle performance for the sodium-ion battery cell. This is because Examples 6-7 contain low-freezing-point cyclic carbonates, which can dissociate more sodium salts and improve the liquid phase transport rate of sodium ions in the electrolyte at low temperatures, while also enhancing the stability of the electrode / electrolyte interface film, thus giving the sodium-ion battery cell better discharge power performance and cycle performance.

[0233] Combining the results of Examples 7 and 8, it is evident that when the cyclic carbonate in the electrolyte is propylene carbonate (PC), the sodium-ion battery cell exhibits better discharge power performance and better cycle performance under low temperature and low SOC conditions. It is speculated that this is because the use of ethylene carbonate (EC) in Example 8 makes the desolvation process more difficult, leading to a deterioration in the discharge power performance of the sodium-ion battery. Furthermore, the ethylene carbonate in Example 8 is more prone to reduction side reactions than the propylene carbonate in Example 7, which may also worsen the cycle life of the sodium-ion battery.

[0234] Combining the results of Examples 6 and 9, it is evident that when dimethyl carbonate (DMC), a chain ester, is added to the electrolyte, the sodium-ion battery cell exhibits better discharge power performance and better cycle performance under low-temperature, low-SOC conditions. The reason for these results is presumably that the addition of dimethyl carbonate in Example 9, due to its high reduction stability and resistance to reduction, reduces the consumption of active sodium, thus improving the cycle performance of the sodium-ion battery cell. Compared to ethyl methyl carbonate (EMC), dimethyl carbonate also has a higher ability to dissociate sodium salts and maintains good conductivity and fluidity at low temperatures, which is beneficial for improving the high-power discharge performance of the sodium-ion battery cell at low temperatures.

[0235] The following is a brief description of the testing methods for the physicochemical and performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0236] 1. Testing the discharge power of sodium-ion battery cells under low temperature and low SOC conditions

[0237] Under a constant temperature environment of 25℃, the sodium-ion battery was charged to 3.65V at 0.33C, then charged at 3.65V with a constant voltage until the current was less than or equal to 0.05mA. It was then left to stand for 2 hours, followed by discharge at 0.33C to 2.0V. The discharge capacity at this point was recorded as C0, and the battery was left to stand for 10 minutes. The sodium-ion battery was then charged again at 0.33C to 0.5C0 (i.e., adjusted to 50% SOC), and then placed in a constant temperature environment of -20℃ for 2 hours. Finally, it was discharged at a current of 5C0 for 30 seconds, with a lower cutoff voltage of 1.8V. The final voltage U1 and time were recorded.

[0238] 2. Test methods for the cycle performance of sodium-ion batteries

[0239] Under a constant temperature environment of 25℃, the lithium-ion battery was charged to 3.65V at 0.33C, and then charged at 3.65V at a constant voltage until the current equals 0.05mA. After resting for 5 minutes, it was discharged to 1.5V at 1C, and the discharge capacity at this point was recorded as D0. This charge-discharge cycle was repeated until the discharge capacity decreased to 80% of D0. The number of cycles the battery underwent was recorded; a higher number of cycles indicates a better cycle life.

[0240] 3. Method for measuring the thickness of the positive electrode film

[0241] Sample Preparation: Sodium-ion battery cells at any stage of use were subjected to discharge treatment. Specifically, at 25°C, the battery cells were discharged at a constant current of 1C to 1.5V, then allowed to stand for 20 minutes, and then discharged at a constant voltage of 1.5V until the current reached 0%, ending the discharge. The state of the battery cell at this point was defined as 0% SOC. The battery cells were then disassembled in an argon atmosphere (H2O content <10ppm, O2 content <1ppm) glove box to obtain the positive electrode. The residual electrolyte on the electrode surface was cleaned with dimethyl carbonate (DMC) or acetone, and then allowed to air dry for 24 hours.

[0242] The thickness of the positive electrode film can be obtained by directly testing the positive electrode sheet using a spiral side-mount instrument.

[0243] 4. Determination of Cathode Layered Oxide Materials

[0244] Sample Preparation: Sodium-ion battery cells at any stage of use were discharged. Specifically, at 25°C, the cell was discharged at a constant current of 1C to 1.5V, then allowed to stand for 20 minutes, followed by a constant voltage discharge of 1.5V until the current reached zero. This state of the cell was defined as 0% SOC. The cell was then disassembled in an argon atmosphere (H2O <10ppm, O2 <1ppm) glove box to obtain the positive electrode. The surface of the electrode was cleaned with dimethyl carbonate (DMC) or acetone to remove residual electrolyte, and then allowed to air dry for 24 hours. The positive electrode surface was then powdered for sample preparation. The powder sample needed to be ground uniformly to avoid interference from large particles. The positive electrode powder was mixed with N-methylpyrrolidone (NMP), stirred, filtered, and dried to obtain the sample to be tested.

[0245] Detection: The composition of the positive electrode active material was analyzed using X-ray diffraction (XRD). Specifically, the crystal structure of the sample was characterized using an XRD diffractometer (Rigaku Ultima IV). The testing range was 2θ = 5° to 80°. The molecular structure and chemical composition of the sample were analyzed using Fourier transform infrared spectroscopy (Nicolet iS50). The physical properties of the sample were analyzed using Raman spectroscopy (LabRAM HR Evolution) at an excitation wavelength of 532 nm. The chemical valence states of the elements on the sample surface were analyzed using X-ray photoelectron spectroscopy (VGEscalab250xi). The morphology and microstructure of the sample were observed using scanning electron microscopy (FEI-Nova NanoSEM230) and transmission electron microscopy (FEI Titan G260–300). The thermal stability of the sample was analyzed using thermogravimetric analysis (Netzsch STA449C).

[0246] 5. Determination of the types and mass content of substances in the electrolyte.

[0247] Sample Preparation: Battery cells at any stage of use are discharged. Specifically, at 25°C, the battery cell is discharged at a constant current of 1C to 1.5V, then allowed to stand for 20 minutes, and then discharged at a constant voltage of 1.5V until the current reaches zero. The state of the battery cell at this point is defined as 0% SOC. Then, in an argon atmosphere (H2O content <10ppm, O2 content <1ppm) glove box, the battery cell is disassembled to obtain the electrolyte. (If the electrolyte content in the battery cell is low, the electrolyte can be separated from the positive and negative electrode plates by centrifugation). After sample preparation, the sample is vacuum-sealed and transferred out of the glove box for subsequent testing.

[0248] Detection: A variety of analytical techniques, such as gas chromatography / mass spectrometry (GC / MS), liquid chromatography / mass spectrometry (LC / MS), and inductively coupled plasma mass spectrometry (ICP-MS), can be used to perform comprehensive qualitative and quantitative analysis of components such as organic solvents, sodium salts, and additives in the electrolyte.

[0249] For example, when using GC / MS to identify high levels of volatile components in the electrolyte, the sample is diluted 1000-fold with dichloromethane and analyzed in split mode. For the analysis of trace volatile organic additives, the electrolyte sample is directly injected into the GC / MS without split mode and dilution is not required.

[0250] 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, include: Positive electrode and electrolyte; The positive electrode includes a positive current collector and a positive electrode film layer. The positive electrode film layer is disposed on at least one surface of the positive current collector, and the thickness L of the positive electrode film layer satisfies: 50μm≤L≤90μm. The positive electrode film layer comprises a layered oxide material, the general structural formula of which is Na. x Ni b Fe c Mn d Cu e N f O g Where 0.80≤x≤1, 0≤b≤0.35, 0.2≤c≤0.4, 0.28≤d≤0.55, 0.04≤e≤0.12, 0.02≤f≤0.08, 1.8≤g≤2, and b+c+d>0.85, b+c+d+e+f=1; N includes active and / or inert doped metal elements, wherein the doped metal elements include at least one of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca; The electrolyte comprises cyclic carbonates and chain esters. The freezing point T of the cyclic carbonates satisfies: -60℃≤T≤-10℃. The viscosity η of the chain esters at a temperature of 25℃±1℃ satisfies: 0.2mPa·s≤η≤3mPa·s. The mass ratio E of the cyclic carbonates to the chain esters satisfies: 0.11≤E≤1. The sodium-ion battery cell further includes a negative electrode sheet, which includes a negative current collector and a negative electrode film. The negative electrode film is disposed on at least one side surface of the negative current collector, and the negative electrode film includes a carbon-based material or a tin-based alloy. The carbon-based material includes multiple pore structures. Based on nitrogen adsorption, the pore volume V1 of the pore structures with a pore size greater than 10 nm in the carbon-based material and the total pore volume V of the carbon-based material are found to satisfy: 20% ≤ V1 / V ≤ 40%.

2. The sodium-ion battery cell according to claim 1, characterized in that, The volume average particle size Dv50 of the layered oxide material satisfies: 4μm≤Dv50≤9μm.

3. The sodium-ion battery cell according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass content P1 of the cyclic carbonate satisfies: 10% ≤ P1 ≤ 50%.

4. The sodium-ion battery cell according to any one of claims 1 to 3, characterized in that, Based on the total mass of the electrolyte, the mass content P2 of the chain ester satisfies: 40% ≤ P2 ≤ 90%.

5. The sodium-ion battery cell according to any one of claims 1 to 3, characterized in that, The cyclic carbonates include at least one of propylene carbonate and ethylene carbonate.

6. The sodium-ion battery cell according to any one of claims 1 to 3, characterized in that, The chain ester includes at least one of chain carbonates and chain carboxylic acid esters.

7. The sodium-ion battery cell according to claim 6, characterized in that, The chain carbonate includes at least one 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.

8. The sodium-ion battery cell according to claim 6, characterized in that, The chain carboxylic acid ester includes at least one of methyl acetate, ethyl acetate, ethyl propionate, methyl formate, ethyl formate, methyl propionate, propyl propionate, ethyl butyrate, and propyl acetate.

9. The sodium-ion battery cell according to any one of claims 1 to 3, characterized in that, The electrolyte also includes a first additive, which comprises a difluorooxalate borate compound.

10. The sodium-ion battery cell according to claim 9, characterized in that, Based on the total mass of the electrolyte, the mass content P3 of the first additive satisfies: 0.05% ≤ P3 ≤ 2%.

11. The sodium-ion battery cell according to any one of claims 1 to 3, characterized in that, The carbon-based material comprises multiple graphite-like sheets, and at least some of the graphite-like sheets form an interlayer spacing between two of the graphite-like sheets. The interlayer spacing satisfies that the volume H1 of the space of 0.35nm~0.4nm and the volume H of the total space formed by the multiple graphite-like sheets satisfy: 20%≤H1 / H≤60%.

12. The sodium-ion battery cell according to any one of claims 1 to 3, characterized in that, The sodium-ion battery cell also includes: The housing is a hollow structure with an opening, and the positive electrode and the electrolyte are housed within the housing; A top cover that closes the opening.

13. A battery device, characterized in that, Includes sodium-ion battery cells according to any one of claims 1 to 12.

14. An electrical appliance, characterized in that, Includes the sodium-ion battery cell according to claim 1, and / or the battery device according to claim 13.

15. The electrical equipment according to claim 14, characterized in that, The sodium-ion battery cell or the battery device serves as the start-stop power source for the electrical equipment.

Images