A battery monomer, a preparation method thereof, a sodium ion battery and an electric device

Abstract

The application relates to a battery monomer, a preparation method thereof, a sodium ion battery and a power utilization device, and belongs to the technical field of secondary batteries. The battery monomer comprises a positive pole piece, the positive pole piece comprises a positive pole current collector, a positive pole active material layer and a sodium supplement layer which are sequentially stacked, and the sodium supplement layer comprises a sodium supplement agent, a linear conductive agent and a punctate conductive agent. When the battery monomer is prepared by using the positive pole piece, the sodium supplement agent is not directly mixed into the inside of the positive pole active material layer, the holes generated by the decomposition of the sodium supplement agent during formation are located in the sodium supplement layer, the stability of the structure of the positive pole active material layer is basically not affected, the punctate conductive agent and the linear conductive agent are added in the sodium supplement layer, good conductivity can be maintained during formation, the decomposition amount of the sodium supplement agent during formation can be improved, the content of the sodium supplement agent in the sodium supplement layer after formation can be reduced, the gram capacity and the capacity retention rate of the battery monomer can be improved, and the direct current internal resistance of the battery monomer during the cycle process can be reduced.

Description

Technical Field

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

[0002] Sodium-ion batteries have broad application prospects in the field of energy storage. Their working principle is similar to that of lithium-ion batteries, utilizing the reversible insertion and extraction of sodium ions between the positive and negative electrodes to achieve energy storage and release. However, during the first charge and discharge process, a solid electrolyte membrane (SEI membrane) forms at the negative electrode, consuming some sodium ions and causing a loss of sodium ions in the positive electrode active material, thus reducing the energy density of the sodium-ion battery.

[0003] To improve the energy density of sodium-ion batteries, a common current method is to add a small amount of high-capacity sodium-replenishing agent to the positive electrode active material. Its irreversible release during the first charge can compensate for the active sodium ions lost during the formation of the SEI film, thereby improving the energy density of the sodium-ion battery.

[0004] However, sodium-ion batteries prepared by the above methods often suffer from insufficient decomposition of the sodium additive in the positive electrode, thus failing to further improve the specific capacity of the sodium-ion battery. Furthermore, adding sodium additive to the positive electrode can easily lead to a decrease in the capacity retention rate of the sodium-ion battery and a deterioration in the DC internal resistance of the battery during cycling. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell and a method for preparing the same, a sodium-ion battery and an electrical device, so as to improve the problems of low specific capacity, reduced capacity retention and easy deterioration of battery internal resistance.

[0006] To achieve the above objectives, a first aspect of this application provides a battery cell including a positive electrode sheet. The positive electrode sheet includes a positive current collector, a positive active material layer, and a sodium replenishment layer; the positive active material layer is disposed on at least a portion of the surface of the positive current collector, and the sodium replenishment layer is disposed on at least a portion of the surface of the positive active material layer opposite to the positive current collector; the sodium replenishment layer includes a sodium replenishing agent, a linear conductive agent, and a dotted conductive agent.

[0007] Therefore, this application places the sodium-supplementing layer on top of the positive electrode active material layer. The pores generated after the sodium-supplementing agent decomposes are located within the sodium-supplementing layer, and these pores have virtually no impact on the structural stability of the positive electrode active material layer. Furthermore, the sodium-supplementing agent is not directly mixed into the positive electrode active material layer, which reduces the impact of adding the sodium-supplementing agent on the film resistance of the positive electrode sheet. In addition, this application adds linear and dot-shaped conductive agents to the sodium-supplementing layer. The combination of linear and dot-shaped conductive agents can form a good conductive network, which can maintain good conductivity during formation. This can increase the amount of sodium-supplementing agent decomposed during formation, reduce the amount of sodium-supplementing agent in the sodium-supplementing layer after formation, improve the specific capacity and capacity retention of the battery cell, and reduce the DC internal resistance of the battery cell during cycling.

[0008] In some embodiments, the sodium supplement agent accounts for 3.2% to 12.3% of the total mass of the sodium supplement layer. After formation, the mass content of the sodium supplement agent in the sodium supplement layer decreases to 3.2% to 12.3%, indicating that the amount of sodium supplement agent decomposed is relatively high, the sodium supplementation effect is good, and it can further improve the specific capacity and capacity retention of the battery cells, and reduce the DC internal resistance of the battery cells during cycling.

[0009] In some embodiments, the sodium supplement agent includes a gas-generating sodium supplement agent and / or a non-gas-generating sodium supplement agent; and / or, the gas-generating sodium supplement agent includes at least one of Na₂CO₃, Na₂SO₃, or NaNO₂; and / or, the non-gas-generating sodium supplement agent includes at least one of EDTA-4Na, DPTA-5Na, Na₆PS₅Cl, or Na₂C₆H₂O₆. Using at least one of these gas-generating or non-gas-generating sodium supplement agents to supplement sodium at the positive electrode of a battery cell can improve the capacity of the battery cell and reduce its DC internal resistance during cycling.

[0010] In some embodiments, the sodium replenishing agent includes a gas-generating sodium replenishing agent, which accounts for 3.2% to 5.7% of the total mass of the sodium replenishing layer. After formation, the mass content of the gas-generating sodium replenishing agent is reduced to 3.2% to 5.7%, resulting in better decomposition of the sodium replenishing agent and better sodium replenishment effect. This can further improve the capacity of the battery cells and reduce the DC internal resistance of the battery cells during cycling.

[0011] In some embodiments, the sodium replenishing agent includes a non-gas-generating sodium replenishing agent, which accounts for 7.1% to 12.3% of the total mass of the sodium replenishing layer. Using a non-gas-generating sodium replenishing agent as the sodium replenishing agent for the positive electrode sheet reduces the mass content of the non-gas-generating sodium replenishing agent to 7.1% to 12.3% after formation, which can increase the capacity of the battery cell while reducing the DC internal resistance of the battery cell during cycling.

[0012] In some embodiments, the linear conductive agent accounts for 12.9% to 19.4% of the total mass of the sodium-supplementing layer; and / or, the dot-shaped conductive agent accounts for 28.8% to 40.3% of the total mass of the sodium-supplementing layer. When the sodium-supplementing layer contains 12.9% to 19.4% by mass of linear conductive agent and 28.8% to 40.3% by mass of dot-shaped conductive agent, a three-dimensional network-like conductive structure can be formed in the sodium-supplementing layer. This can improve the problem of low sodium-supplementing agent decomposition due to incomplete conductive network caused by pores generated by sodium-supplementing agent decomposition, reduce the sodium-supplementing agent content in the sodium-supplementing layer after formation, further improve the specific capacity and capacity retention of the battery cells, and reduce the DC internal resistance of the battery cells during cycling.

[0013] In some embodiments, the sodium replenishing agent includes a gas-generating sodium replenishing agent, with dot-shaped conductive agents accounting for 37.1% to 40.3% of the total mass of the sodium replenishing layer, and linear conductive agents accounting for 12.9% to 15.5% of the total mass of the sodium replenishing layer. In the sodium replenishing layer, the combination of 37.1% to 40.3% by mass of dot-shaped conductive agents and 12.9% to 15.5% by mass of linear conductive agents can form a three-dimensional network conductive structure. Even if the gas-generating sodium replenishing agent produces a large number of pores during decomposition, a good conductive network can be maintained. This increases the amount of gas-generating sodium replenishing agent decomposed, reduces the content of gas-generating sodium replenishing agent in the sodium replenishing layer, and can improve the capacity of individual battery cells and reduce the DC internal resistance of individual battery cells during cycling.

[0014] In some embodiments, the sodium replenishing agent includes a non-gas-generating sodium replenishing agent, with dot-shaped conductive agents accounting for 28.8% to 30.2% of the total mass of the sodium replenishing layer and linear conductive agents accounting for 18.1% to 19.4% of the total mass of the sodium replenishing layer. In the sodium replenishing layer, the combination of 28.8% to 30.2% by mass of dot-shaped conductive agents and 18.1% to 19.4% by mass of linear conductive agents can form a three-dimensional network conductive structure, which can increase the decomposition amount of the non-gas-generating sodium replenishing agent, reduce the content of the non-gas-generating sodium replenishing agent in the sodium replenishing layer, increase the capacity of the battery cells, and reduce the DC internal resistance of the battery cells during cycling.

[0015] In some embodiments, the sodium-supplementing layer further contains a binder, which accounts for 35.4% to 50% of the total mass of the sodium-supplementing layer. The presence of 35.4% to 50% binder in the sodium-supplementing layer can improve the adhesion of the sodium-supplementing layer, help the dot-shaped conductive agent and the linear conductive agent to combine to form a stable conductive structure, improve the structural stability of the sodium-supplementing layer, and also reduce the resistance of the positive electrode.

[0016] In some embodiments, the dotted conductive agent includes at least one of acetylene black, conductive carbon black, Ketjen black, or hollow carbon black; and / or, the linear conductive agent includes at least one of carbon nanotubes, carbon nanowires, or carbon fibers.

[0017] In some embodiments, the thickness of the sodium supplement layer is 60–130 μm.

[0018] In some embodiments, the porosity of the positive electrode active material layer is less than that of the sodium-supplemented layer. In the positive electrode sheet of a battery cell, the porosity of the positive electrode active material layer is less than that of the sodium-supplemented layer, making the positive electrode active material layer less prone to collapse. This improves the structural stability of the positive electrode sheet and enhances the capacity retention rate of the battery cell.

[0019] A second aspect of this application also provides a method for preparing a battery cell, comprising:

[0020] Preparation of the positive electrode sheet: A positive active material layer is formed on at least a portion of the surface of the positive current collector, and a sodium-supplementing slurry is coated on at least a portion of the surface of the positive active material layer facing away from the positive current collector, and cured to form a sodium-supplementing coating; wherein, the sodium-supplementing slurry contains a sodium-supplementing agent, a dotted conductive agent and a linear conductive agent.

[0021] Battery assembly: Assembling the positive electrode, separator, electrolyte and negative electrode into a battery cell, which is then formed.

[0022] Therefore, this application involves coating a sodium-supplementing slurry containing a sodium-supplementing agent onto at least a portion of the surface of the positive electrode active material layer facing away from the positive electrode current collector. During the formation of the assembled cell after the slurry dries, the sodium-supplementing agent in the coating decomposes, transforming the coating into a sodium-supplementing layer. The decomposition of the sodium-supplementing agent creates pores within this layer, which have minimal impact on the structural stability of the positive electrode active material layer and the electrode resistance. Furthermore, by adding dot-shaped and linear conductive agents to the sodium-supplementing slurry, even with the formation of numerous pores due to sodium-supplementing agent decomposition, the interaction between the dot-shaped and linear conductive agents maintains a good conductive network. This increases the amount of sodium-supplementing agent decomposed during formation, reduces the sodium-supplementing agent content in the resulting sodium-supplementing layer, improves the charge / discharge specific capacity and capacity retention of the battery cell, and reduces the DC internal resistance of the battery cell during cycling.

[0023] In some embodiments, the sodium-replenishing slurry includes a solvent and raw materials for forming the sodium-replenishing coating. By weight percentage, the raw materials include 86%–89% sodium-replenishing agent, 4%–5.8% dot-like conductive agent, and 1.2%–3% linear conductive agent, with the balance being additives. Adding 86%–89% sodium-replenishing agent, 4%–5.8% dot-like conductive agent, and 1.2%–3% linear conductive agent to the raw materials of the sodium-replenishing slurry can increase the amount of sodium dissolved, improve the charge / discharge specific capacity and capacity retention of the battery cells, and reduce the DC internal resistance of the battery cells during cycling.

[0024] In some embodiments, the additive includes 5% to 7% binder. Adding 5% to 7% binder to the raw materials of the sodium-supplement slurry allows for the formation of a sodium-supplement coating with strong adhesion after drying the coated slurry layer. This improves the bonding strength between the sodium-supplement layer obtained after formation and the positive electrode active material layer, facilitates the combination of dot-like and linear conductive agents to form a stable conductive structure, and also reduces the internal resistance of the positive electrode sheet.

[0025] In some embodiments, the sodium supplement agent includes a gas-generating sodium supplement agent, the raw material of which contains 4.6% to 5% of a dot-like conductive agent and 2% to 2.4% of a linear conductive agent. The gas-generating sodium supplement agent produces relatively many pores during decomposition, which can affect the conductivity of the sodium supplement layer. This application adds 4.6% to 5% of a dot-like conductive agent and 2% to 2.4% of a linear conductive agent to the raw material of the sodium supplement slurry. These dot-like and linear conductive agents can work together to form a three-dimensional network-like conductive structure. Even when the sodium supplement layer contains a large number of pores, this three-dimensional network-like conductive structure can still meet the requirements for the decomposition of the gas-generating sodium supplement agent.

[0026] In some embodiments, the sodium replenishing agent includes a non-gas-generating sodium replenishing agent, and the raw material contains 4.0%–4.2% of a dot-like conductive agent and 2.8%–3.0% of a linear conductive agent. Adding a non-gas-generating sodium replenishing agent to the raw material of the sodium replenishing slurry allows for decomposition, which can increase energy density and reduce the internal resistance of the positive electrode. Adding 4.0%–4.2% of the dot-like conductive agent and 2.8%–3.0% of the linear conductive agent to the raw material of the sodium replenishing slurry can improve the conductivity of the sodium replenishing layer, meet the requirements for the decomposition of the non-gas-generating sodium replenishing agent, further increase the capacity of the battery cell, and reduce the DC internal resistance of the battery cell during cycling.

[0027] In some embodiments, the formation method includes: charging to 3.0V to 3.3V at a current rate of 0.1C to 0.2C, then charging to 3.5V to 3.6V at a current rate of 0.3C to 0.4C, and then charging to 3.8V to 4.0V at a current rate of 0.01C to 0.05C, which can further increase the decomposition amount of sodium supplement and reduce the sodium supplement content in the sodium supplement layer.

[0028] The third aspect of this application provides a sodium-ion battery, including the battery cell provided in the first aspect of this application, or the battery cell prepared according to the preparation method provided in the second aspect of this application.

[0029] A fourth aspect of this application provides an electrical device, including the sodium-ion battery provided in the third aspect of this application.

[0030] Using the above-mentioned sodium-ion battery to make an electrical device, since the sodium-ion battery cell utilizes the combination of linear and dot-shaped conductive agents, the amount of sodium supplementation agent decomposed can be increased. Moreover, the pores generated after the sodium supplementation agent decomposes are located in the sodium supplementation layer outside the positive electrode active material layer. These pore structures do not significantly affect the structural stability and internal resistance of the positive electrode active material layer. Therefore, the capacity of the sodium-ion battery can be increased and the DC internal resistance of the sodium-ion battery during cycling can be reduced, which can meet the power consumption requirements of the electrical device. Attached Figure Description

[0031] Figure 1 A schematic diagram of the preparation process of the battery cell provided in this application;

[0032] Figure 2 A schematic cross-sectional view of the positive electrode sheet before formation provided in this application;

[0033] Figure 3 A schematic cross-sectional view of the positive electrode sheet after formation provided in this application;

[0034] Figure 4 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0035] Figure 5 yes Figure 4 An exploded view of a battery cell according to one embodiment of this application is shown.

[0036] Figure 6 This is a schematic diagram of a battery module according to one embodiment of this application;

[0037] Figure 7 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0038] Figure 8 yes Figure 7 An exploded view of a battery pack according to an embodiment of this application is shown;

[0039] Figure 9 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application;

[0040] Figure 10 SEM images of the powder at 500x magnification provided for the test examples in this application;

[0041] Figure 11 SEM images of the powder at 5000x magnification provided for the test examples in this application;

[0042] Figure 12 The SEM image of the powder provided for the test example in this application is at 3000x magnification.

[0043] Explanation of reference numerals in the attached figures:

[0044] 1-Battery pack; 2-Upper casing; 3-Lower casing; 4-Battery module; 5-Battery cell; 51-Housing shell; 52-Electrode assembly; 521-Positive electrode sheet; 5211-Positive current collector; 5212-Positive active material layer; 5213-Sodium replenishing coating; 5214-Sodium replenishing layer; 53-Cover plate. Detailed Implementation

[0045] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell and its preparation method, sodium-ion battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0046] 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 understood that ranges of 60–110 and 80–120 are also expected. 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 "a–b" 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" and "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.

[0047] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0048] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0049] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0050] During the first charge and discharge process, sodium-ion batteries consume some sodium ions as a solid electrolyte membrane (SEI membrane) forms at the negative electrode, resulting in the loss of sodium ions in the positive electrode active material and thus reducing the energy density of the sodium-ion battery.

[0051] To improve the energy density of sodium-ion batteries, a small amount of high-capacity sodium-replenishing agent is usually added to the positive electrode active material. The irreversible release of this agent during the first charge compensates for the active sodium ions lost by the positive electrode during the formation of the SEI film, thereby improving the energy density of the sodium-ion battery.

[0052] However, the current method of mixing sodium supplementation agent into the positive electrode active material often results in a low amount of sodium supplementation agent decomposition, which cannot further improve the energy density and can easily lead to a deterioration in the capacity retention rate and internal resistance of sodium-ion batteries.

[0053] For example, currently, sodium-replenishing agents are typically mixed with raw materials such as positive electrode active materials to form a positive electrode slurry. This slurry is then coated onto a positive electrode current collector, dried, and assembled into a sodium-ion battery, which undergoes formation. During the formation of the sodium-ion battery, the sodium-replenishing agent decomposes to compensate for the active sodium ions lost by the positive electrode during SEI film formation, thereby increasing the energy density of the sodium-ion battery.

[0054] However, directly mixing the sodium-adding agent into the positive electrode slurry can lead to physical gelation of the slurry, making it prone to coating cracking. Furthermore, large-particle-size sodium-adding agents mixed into the active material layer of the positive electrode often form pores during decomposition. These pores can damage the electrode structure and worsen the film resistance of the positive electrode. During formation, the amount of sodium-adding agent incorporated into the active material layer is relatively low, ultimately preventing further optimization of battery performance such as specific capacity and DC internal resistance.

[0055] Based on this, the first aspect of this application provides a method for preparing a battery cell. Please refer to... Figures 1-3 The preparation methods of battery cells include:

[0056] S1. Preparation of the positive electrode sheet:

[0057] S11. A positive electrode active material layer 5212 is formed on at least a portion of the surface of the positive electrode current collector 5211.

[0058] S12. A sodium-supplementing slurry is coated on at least a portion of the surface of the positive electrode active material layer 5212 that is away from the positive electrode current collector 5211, and cured to form a sodium-supplementing coating 5213; wherein the sodium-supplementing slurry contains a sodium-supplementing agent, a dotted conductive agent, and a linear conductive agent.

[0059] S2. Battery assembly: Assemble the positive electrode 521, separator, electrolyte and negative electrode into a battery cell, and form it.

[0060] This application involves coating a sodium-supplementing slurry containing a sodium-supplementing agent onto at least a portion of the surface of the positive electrode active material layer 5212 facing away from the positive electrode current collector 5211, and forming a sodium-supplementing coating 5213 after the slurry coating has cured (e.g., ...). Figure 2 During the formation of the battery cell, most of the sodium-replenishing agent in the sodium-replenishing coating 5213 can be decomposed to form a sodium-replenishing layer 5214 containing a small amount of residual sodium-replenishing agent, dotted conductive agent, and linear conductive agent (e.g., Figure 3 ).

[0061] Since the sodium-supplementing slurry is applied to at least a portion of the surface of the positive electrode active material layer 5212, most of the sodium-supplementing agent is on top of the positive electrode active material layer 5212, thus reducing the impact of the sodium-supplementing agent on the electrode resistance. Furthermore, since the pores generated during the decomposition of the sodium-supplementing agent are located within the sodium-supplementing layer 5214, these pores have virtually no impact on the structural stability of the positive electrode active material layer 5212.

[0062] If a large amount of sodium supplement is mixed into the positive electrode active material layer 5212, for example, by adding the sodium supplement to the positive electrode slurry and coating it onto the surface of the positive electrode current collector 5211, and solidifying to form the positive electrode active material layer 5212, the sodium supplement in the positive electrode active material layer 5212 will decompose during formation, forming pores in situ within the positive electrode active material layer 5212. These pores will affect the internal resistance of the positive electrode active material layer 5212 and may cause the structure of the positive electrode active material layer 5212 to collapse, affecting the structural stability of the positive electrode sheet 521.

[0063] Furthermore, if the sodium supplement is added to the positive electrode slurry and coated on the surface of the positive electrode current collector 5211, and solidified to form the positive electrode active material layer 5212, the sodium supplement is located inside the positive electrode active material layer 5212. During formation, the amount of sodium supplement decomposed is low, resulting in the positive electrode active material layer 5212 containing more residual sodium supplement, which will reduce the specific capacity of the battery cell.

[0064] It should be noted that this application does not mean that sodium supplementation agents cannot be added to the positive electrode active material layer 5212, nor does it mean that positive electrode active materials cannot be added to the sodium supplementation layer 5214. Any solution that adds a small amount of sodium supplementation agent (e.g., less than 5% by mass) to the positive electrode active material layer 5212, or / and a small amount of positive electrode active material (e.g., less than 5% by mass) to the sodium supplementation layer 5214, but does not significantly affect the structure of the positive electrode sheet 521, is within the scope of protection of this application.

[0065] In addition, by adding dot-shaped and linear conductive agents to the sodium-supplementing slurry, the synergistic effect of the dot-shaped and linear conductive agents can improve the conductivity of the sodium-supplementing coating 5213. Even when the sodium-supplementing agent decomposes and produces a large number of pores, a good conductive network can be maintained. This can also increase the amount of sodium-supplementing agent decomposed and reduce the sodium-supplementing agent content in the sodium-supplementing layer 5214 of the positive electrode sheet 521 after formation. The battery cells prepared using the above method can improve the charge / discharge specific capacity and capacity retention rate of the battery cells, and reduce the DC internal resistance of the battery cells during cycling.

[0066] In step S11, forming a positive electrode active material layer 5212 on at least a portion of the surface of the positive electrode current collector 5211 means that the positive electrode current collector 5211 has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer 5212 is disposed on either or both of the two opposite surfaces of the positive electrode current collector 5211.

[0067] As an example, please continue reading Figure 2 The positive electrode active material layer 5212 is disposed on either of the two opposing surfaces of the positive electrode current collector 5211.

[0068] In some embodiments, the positive current collector 5211 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.).

[0069] The positive electrode active material layer 5212 includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material for a battery cell known in the art. As an example, the positive electrode active material can include at least one of the following materials: polyanion compounds, sodium transition metal oxides, Prussian blue compounds, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more.

[0070] As an optional technical solution of the present application, the polyanion-type compound can be Na 4+x R 3-y P 4-m O 15 / C; wherein, 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0071] As an optional technical solution of the present application, the polyanion-type compound can be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d , wherein the A element represents an alkali metal element that dopes and replaces the Na element, the M element represents a metal element that replaces the V element, the D element represents a doping element that replaces the P element, the Q element represents a doping element that replaces the F element, the D element includes at least one of Si and S, the Q element includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ 0.3y, 0 ≤ c ≤ 0.15, 0.8 ≤ z ≤ 1.1, 0 ≤ d ≤ 0.2z. Optionally, the A element includes at least one of K and Li; the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0072] In the sodium transition metal compound, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, and V, and 0 < x ≤ 1.

[0073] Prussian blue compounds can contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Mn, Fe, Ni, Co, Cu and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0074] In some embodiments, the positive electrode active material layer 5212 may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0075] In some embodiments, the positive electrode active material layer 5212 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.

[0076] In some embodiments, the positive electrode active material layer 5212 can be formed on at least a portion of the surface of the positive electrode current collector 5211 by dispersing the components used to prepare the positive electrode active material layer 5212, such as positive electrode 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 5211, and after drying, cold pressing and other processes, a positive electrode intermediate structure with the positive electrode active material layer 5212 located on at least a portion of the surface of the positive electrode current collector 5211 can be obtained.

[0077] In step S12, coating at least a portion of the surface of the positive electrode active material layer 5212 away from the positive electrode current collector 5211 with sodium supplement slurry means that the positive electrode active material layer 5212 has two surfaces opposite to each other in its own thickness direction, one of the surfaces of the positive electrode active material layer 5212 is in contact with the positive electrode current collector 5211, and the sodium supplement slurry is applied to the other surface of the positive electrode active material layer 5212.

[0078] The sodium-replenishing slurry includes a solvent and raw materials dispersed in the solvent for forming the sodium-replenishing coating 5213. These raw materials include a sodium-replenishing agent, a dotted conductive agent, and a linear conductive agent.

[0079] "Linear conductive agent" refers to a conductive agent material that resembles a line in shape, with its axial dimension being larger than its radial dimension, and it has a high aspect ratio of ≥5.

[0080] As an example, the aspect ratio of linear conductive agents can be 5 to 200.

[0081] In some embodiments, the linear conductive agent may include at least one of carbon nanotubes, carbon fibers, or carbon nanowires.

[0082] As an example, linear conductive agents may include at least one of whisker carbon nanotubes, multi-walled carbon nanotubes, or single-walled carbon nanotubes.

[0083] "Dot-like conductive agent" refers to a conductive agent material whose shape is similar to granules, with little difference between its axial and radial dimensions, resembling granules, and with an aspect ratio of 1 ≤ 5.

[0084] In some embodiments, the dotted conductive agent may include at least one of acetylene black, conductive carbon black, Ketjen black, or hollow carbon black.

[0085] As an example, the dotted conductive agent can be conductive carbon black.

[0086] As an example, the dotted conductive agent can be acetylene black.

[0087] In some embodiments, the sodium supplement may include at least one of a gas-producing sodium supplement and a non-gas-producing sodium supplement.

[0088] "Gas-producing sodium supplements" refer to sodium supplements that produce gas upon decomposition. "Non-gas-producing sodium supplements" are the opposite of "gas-producing sodium supplements."

[0089] As an optional technical approach in this application, the gas-generating sodium supplement may include at least one of Na2CO3, Na2SO3, or NaNO2.

[0090] As an optional technical approach in this application, the non-gas-producing sodium supplement may include at least one of EDTA-4Na (also known as tetrasodium ethylenediaminetetraacetate), DPTA-5Na (also known as pentasodium diethylenetriaminepentaacetate), Na6PS5Cl, or Na2C6H2O6.

[0091] In some embodiments, the raw materials of the sodium-supplementing slurry, by weight percentage, include 86% to 89% sodium supplement, 4% to 5.8% dot-like conductive agent, and 1.2% to 3% linear conductive agent, with the remainder being additives.

[0092] Adding the above-mentioned mass content of dot-shaped and linear conductive agents to the sodium-supplementing slurry can form a three-dimensional network-like conductive structure in the sodium-supplementing coating 5213 after coating and curing. During the subsequent formation of the battery cell, it can promote the decomposition of the sodium-supplementing agent, reduce the content of sodium-supplementing agent in the sodium-supplementing layer 5214 after formation, improve the capacity of the battery cell, and reduce the DC internal resistance of the battery cell during cycling.

[0093] As an example, the mass percentage of sodium supplement in the raw materials of sodium-supplementing slurry can be 86.0%, 86.5%, 87.0%, 87.5%, 88.0%, 88.5%, 89.0%, or any two of the above values.

[0094] As an example, the mass percentage of dot-shaped conductive agent in the raw materials of the sodium-supplementing slurry can be 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, or any value within the range formed by any two of the above points.

[0095] As an example, the mass percentage of linear conductive agent in the raw materials of the sodium-supplementing slurry can be 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, or any value within the range formed by any two of the above points.

[0096] In some embodiments, the sodium supplement is a gas-generating sodium supplement, and the sodium supplement slurry raw material contains 4.6% to 5% of dot-shaped conductive agent and 2% to 2.4% of linear conductive agent.

[0097] When the gas-generating sodium supplement agent decomposes during the formation stage, it creates pores in situ within the sodium supplement coating 5213. These pores affect the conductivity of the sodium supplement coating 5213, which in turn affects the further decomposition of the sodium supplement agent, resulting in a higher content of sodium supplement agent in the sodium supplement layer 5214 formed after formation. Therefore, when the sodium supplement agent in the sodium supplement slurry is a gas-generating sodium supplement agent, adding 4.6%–5% of dot-shaped conductive agent and 2%–2.4% of linear conductive agent to the raw materials of the sodium supplement slurry can form a three-dimensional network conductive structure after subsequent coating and curing. This can increase the amount of sodium supplement agent decomposed during formation and reduce the residual amount of sodium supplement agent in the sodium supplement layer 5214.

[0098] In some embodiments, the sodium supplement is a non-gas-generating sodium supplement, and the raw materials of the sodium supplement slurry contain 4.0% to 4.2% of dot-shaped conductive agent and 2.8% to 3.0% of linear conductive agent.

[0099] Compared to gas-generating sodium supplements, non-gas-generating sodium supplements produce less in-situ porosity during decomposition, thus having a smaller impact on the conductivity of the sodium supplement coating 5213. Therefore, when the sodium supplement is a non-gas-generating sodium supplement, adding 4.0%–4.2% of dot-shaped conductive agent and 2.8%–3.0% of linear conductive agent to the sodium supplement slurry raw material can meet the requirement for decomposition of the non-gas-generating sodium supplement during formation.

[0100] In some embodiments, the particle size of the sodium supplement can be 20–30 μm.

[0101] The above particle size range can further improve the decomposition rate of sodium supplement and reduce the impact of sodium supplement on the resistance of the 521 positive electrode film.

[0102] As an example, the particle size of the sodium supplement can be 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, or a value within the range formed by any two of the above points.

[0103] In some embodiments, the additives in the sodium-supplemented slurry may optionally include binders.

[0104] In some embodiments, the binder may be polyvinylidene fluoride (PVDF). Using PVDF as a binder for the sodium-supplementing coating 5213 not only improves the processability of the sodium-supplementing slurry, but also has good adhesion, which can improve the bonding strength between the sodium-supplementing coating 5213 and the positive electrode active material layer 5212, as well as improve the bonding stability of the linear and dotted conductive agents in the sodium-supplementing coating 5213.

[0105] As an example, the adhesive can be PVDF of type 5130.

[0106] In some embodiments, the sodium-supplementing slurry raw material may also include 5% to 7% binder. Adding 5% to 7% binder to the sodium-supplementing slurry raw material can reduce diaphragm resistance while ensuring adhesion.

[0107] As an example, the mass content of binder in the sodium-supplemented slurry raw material may include 5%, 5.5%, 6%, 6.5%, 7%, or any two of the above values.

[0108] In some embodiments, the solvent may include at least one of NMP and water.

[0109] As an example, the solvent could be N-methylpyrrolidone.

[0110] In some embodiments, the mass ratio of raw materials to solvent in the sodium-supplementing slurry can be 50% to 65%.

[0111] In some embodiments, in step S12, a sodium-supplementing slurry of 60 μm to 130 μm is coated on at least a portion of the surface of the positive electrode active material layer 5212 facing away from the positive electrode current collector 5211, so as to obtain a sodium-supplementing coating 5213 of appropriate thickness after subsequent curing of the coating. As an example, according to the above preparation method, the thickness of the sodium-supplementing coating 5213 in the obtained positive electrode sheet 521 may include 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, or a value within the range formed by any two of the above points.

[0112] In some implementations, the curing method in step S12 may include drying.

[0113] During the curing of the sodium-replenishing coating formed after the sodium-replenishing slurry is applied, the solvent in the sodium-replenishing slurry is removed. Therefore, the cured sodium-replenishing coating 5213 is mainly formed from the raw materials in the sodium-replenishing slurry. As an example, the cured sodium-replenishing coating 5213 mainly includes 86% to 89% sodium-replenishing agent, 4% to 5.8% dot-like conductive agent, 1.2% to 3% linear conductive agent, and 5% to 7% binder.

[0114] In step S2, the positive electrode 521, negative electrode, electrolyte, and separator are assembled into a battery cell. During the charging and discharging process of the battery cell, active sodium ions repeatedly insert and extract between the positive and negative electrode 521. The electrolyte acts as a conductor of ions between the positive and negative electrode 521. The separator is placed between the positive and negative electrode 521, mainly to prevent short circuits between the positive and negative electrodes, while allowing ions to pass through.

[0115] [Negative electrode plate]

[0116] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0117] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0118] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, and tin-based materials, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0120] In some embodiments, the negative electrode film layer may optionally include a binder. The binder includes at least one selected from 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).

[0121] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent includes at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0123] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0124] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and an undercoating layer. The undercoating layer can be disposed on at least one side of the current collector body. The undercoating layer essentially does not contain negative electrode active material, but may include a small amount of carbon material, with the carbon material forming a thin coating. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain an undercoating layer, the film layer can be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode sheet includes an undercoating layer, the film layer can be disposed on the surface of the undercoating layer away from the current collector.

[0125] In some embodiments, the membrane layer may also include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0126] [Electrolytes]

[0127] The electrolyte acts as a conductor of ions between the positive electrode 521 and the negative electrode. 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, or completely solid.

[0128] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0129] In some embodiments, the electrolyte salt includes at least one of sodium hexafluorophosphate and sodium perchlorate.

[0130] In some embodiments, the solvent includes at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0131] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0132] [Isolation membrane]

[0133] In some embodiments, the battery cell 5 also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0134] In some embodiments, the material of the separator includes at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0135] In some implementations, the positive electrode 521, the negative electrode, and the separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0136] In some embodiments, the battery cell 5 may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0137] In some embodiments, the outer packaging of the battery cell 5 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 5 can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0138] In step S2, after assembling the positive electrode 521, separator, electrolyte and negative electrode into a cell, formation is carried out, which can decompose the sodium replenishing agent in the sodium replenishing coating 5213 and improve the capacity of the battery cell 5.

[0139] "Formation" refers to the process of activating the positive and negative electrode materials inside the battery through a certain charging and discharging method, with the aim of forming a good solid electrolyte interphase (SEI) film.

[0140] In some embodiments, step S2 may include: charging to 3.0V to 3.3V at a current rate of 0.1C to 0.2C, then charging to 3.5V to 3.6V at a current rate of 0.3C to 0.4C, and then charging to 3.8V to 4.0V at a current rate of 0.01C to 0.05C.

[0141] For example, the voltage can be initially charged at 0.1C, 0.11C, 0.12C, 0.13C, 0.14C, 0.15C, 0.16C, 0.17C, 0.18C, 0.19C, 0.2C, or any two of the above values, to 3.0V, 3.05V, 3.10V, 3.15V, 3.20V, 3.25V, 3.30V, or any two of the above values; then charged at 0.3C, 0.31C, 0.32C, 0.33C, 0.34C, 0.35C, 0.36C, 0.37C, 0.38C, ... Charge at 0.39C, 0.40C, or any two of the above values ​​to 3.5V, 3.51V, 3.52V, 3.53V, 3.54V, 3.55V, 3.56V, 3.57V, 3.58V, 3.59V, 3.6V, or any two of the above values; finally charge at 0.01C, 0.02C, 0.03C, 0.04C, 0.05C, or any two of the above values ​​to 3.8V, 3.85V, 3.9V, 3.95V, 4.0V, or any two of the above values.

[0142] In some embodiments, the voltage is charged to 3.1V at a current rate of 0.1C, then to 3.5V at a current rate of 0.33C, and then to 3.9V at a current rate of 0.05C.

[0143] As an example, the positive electrode 521, separator, and negative electrode are stacked sequentially, and electrolyte is injected to form a battery cell. The battery cell is charged to 3.0V at a current rate of 0.33C, and then charged to 3.8V at a current rate of 0.1C to 0.2C. The sodium-replenishing agent is decomposed through low-current formation to obtain a single battery cell. The sodium-replenishing agent in the sodium-replenishing coating 5213 decomposes to form a sodium-replenishing layer 5214 with a porous structure. A cross-sectional schematic diagram of the formed positive electrode 521 is shown below. Figure 3 As shown ( Figure 3 This is a cross-sectional schematic diagram and does not represent the actual morphology of the positive electrode 521 after formation.

[0144] Most of the sodium-replenishing agent in the sodium-replenishing coating 5213 is decomposed and removed during formation, leaving a small amount of undecomposed residual sodium-replenishing agent in the sodium-replenishing layer 5214 formed after formation. In some embodiments, the sodium-replenishing agent accounts for 3.2% to 12.3% of the total mass of the sodium-replenishing layer 5214 in the positive electrode sheet 521 obtained after formation.

[0145] After formation, the mass content of sodium replenishing agent in the sodium replenishing layer 5214 decreased to 3.2% to 12.3%, indicating that the decomposition amount of sodium replenishing agent was relatively high and the sodium replenishment effect was good. This can further improve the specific capacity and capacity retention of the battery cells and reduce the DC internal resistance of the battery cells during cycling.

[0146] As an example, the percentage of sodium supplementation agent in the total mass of sodium supplementation layer 5214 may include 3.2%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.5%, 13.0%, 13.1%, 13.2%, or a value within the range formed by any two of the above points.

[0147] In some embodiments, the linear conductive agent accounts for 12.9% to 19.4% of the total mass of the sodium supplement layer 5214, and the dotted conductive agent accounts for 28.8% to 40.3% of the total mass of the sodium supplement layer 5214.

[0148] The sodium-supplementing layer 5214 contains 12.9% to 19.4% by mass of linear conductive agent and 28.8% to 40.3% by mass of dot conductive agent, which can form a conductive structure similar to a three-dimensional network. This can improve the problem of low sodium-supplementing agent decomposition due to incomplete conductive network caused by pores generated by sodium-supplementing agent decomposition. It can reduce the sodium-supplementing agent content in the sodium-supplementing layer 5214 after formation, and further improve the specific capacity and capacity retention of the battery cells, and reduce the DC internal resistance of the battery cells during cycling.

[0149] As an example, in the sodium-supplement layer 5214, the percentage content of the linear conductive agent in the total mass of the sodium-supplement layer 5214 may include 12.9%, 13.0%, 13.5%, 14.0%, 14.5%, 15.0%, 15.5%, 16.0%, 16.5%, 17.0%, 17.5%, 18.0%, 18.5%, 19.0%, 19.1%, 19.2%, 19.3%, 19.4%, or a value within the range formed by any two of the above points.

[0150] As an example, in the sodium supplement layer 5214, the percentage content of the dotted conductive agent in the total mass of the sodium supplement layer 5214 may include 28.8%, 28.9%, 30.0%, 31.0%, 32.0%, 33.0%, 34.0%, 35.0%, 36.0%, 37.0%, 38.0%, 39.0%, 40.0%, 40.1%, 40.2%, 40.3%, or a value within the range formed by any two of the above points.

[0151] In some embodiments, the sodium supplementer includes a gas-generating sodium supplementer, which accounts for 3.2% to 5.7% of the total mass of the sodium supplement layer. When the sodium supplementer in the sodium supplement slurry raw material is a gas-generating sodium supplementer, according to the preparation method of this application, after formation, the percentage of the gas-generating sodium supplementer in the total mass of the sodium supplement layer 5214 can be reduced to 3.2% to 5.7%, resulting in better decomposition effect of the sodium supplementer and better sodium supplementation effect, which can further improve the capacity of the battery cells and reduce the DC internal resistance of the battery cells during cycling.

[0152] As an example, in the sodium replenishment layer 5214, the percentage content of the gas-generating sodium replenishing agent in the total mass of the sodium replenishment layer 5214 may include 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, or a value within the range formed by any two of the above points.

[0153] In some embodiments, the sodium supplementing agent includes a gas-generating sodium supplementing agent, with dot-shaped conductive agents accounting for 37.1% to 40.3% of the total mass of the sodium supplementing layer 5214, and linear conductive agents accounting for 12.9% to 15.5% of the total mass of the sodium supplementing layer 5214.

[0154] In the sodium replenishment layer 5214, by combining 37.1% to 40.3% by mass of dot-shaped conductive agent with 12.9% to 15.5% by mass of linear conductive agent, a three-dimensional network conductive structure can be formed. Even if the gas-generating sodium replenishment agent produces a large number of pores during decomposition, a good conductive network can still be maintained. This increases the amount of gas-generating sodium replenishment agent decomposed and reduces the content of gas-generating sodium replenishment agent in the sodium replenishment layer 5214, thereby increasing the capacity of the battery cell and reducing the DC internal resistance of the battery cell during cycling.

[0155] As an example, when the sodium supplement is a gas-generating sodium supplement, the dot-shaped conductive agent accounts for 37.1%, 37.5%, 38.0%, 38.5%, 39.0%, 39.5%, 40.0%, 40.1%, 40.2%, 40.3% of the total mass of the sodium supplement layer 5214, or any two of the above values. The linear conductive agent accounts for 12.9%, 13.0%, 13.5%, 14.0%, 14.5%, 15.0%, 15.1%, 15.2%, 15.3%, 15.4%, 15.5% of the total mass of the sodium supplement layer 5214, or any two of the above values.

[0156] In some embodiments, the sodium supplementer includes a non-gas-generating sodium supplementer, which accounts for 7.1% to 12.3% of the total mass of the sodium supplement layer 5214. When the sodium supplementer in the sodium supplement slurry raw material is a non-gas-generating sodium supplementer, according to the preparation method of this application, after formation, the percentage of the non-gas-generating sodium supplementer in the total mass of the sodium supplement layer 5214 can be reduced to 7.1% to 12.3%, which can improve the capacity of the battery cell while reducing the DC internal resistance of the battery cell during cycling.

[0157] As an example, in the sodium replenishment layer 5214, the percentage of non-gas-producing sodium replenishing agent in the total mass of the sodium replenishment layer 5214 may include 7.1%, 7.3%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.1%, 12.2%, 12.3%, or a value within the range formed by any two of the above points.

[0158] In some embodiments, the sodium replenishing agent includes a non-gas-generating sodium replenishing agent, with dot-shaped conductive agents accounting for 28.8% to 30.2% of the total mass of the sodium replenishing layer 5214, and linear conductive agents accounting for 18.1% to 19.4% of the total mass of the sodium replenishing layer 5214.

[0159] In the sodium replenishment layer 5214, by combining 28.8% to 30.2% by mass of dot-shaped conductive agent with 18.1% to 19.4% by mass of linear conductive agent, a three-dimensional network conductive structure can be formed. This can increase the decomposition amount of non-gas-generating sodium replenishment agent, reduce the content of non-gas-generating sodium replenishment agent in the sodium replenishment layer 5214, increase the capacity of the battery cell, and reduce the DC internal resistance of the battery cell during cycling.

[0160] As an example, when the sodium supplement is a non-gas-generating sodium supplement, the dot-shaped conductive agent accounts for 28.8%, 28.9%, 29.0%, 29.1%, 29.2%, 29.3%, 29.4%, 29.5%, 29.6%, 29.7%, 29.8%, 29.9%, 30.0%, 30.1%, 30.2% of the total mass of the sodium supplement layer 5214, or any two of the above values; the linear conductive agent accounts for 18.1%, 18.2%, 18.3%, 18.4%, 18.5%, 18.6%, 18.7%, 18.8%, 18.9%, 19.0%, 19.1%, 19.2%, 19.3%, 19.4% of the total mass of the sodium supplement layer 5214, or any two of the above values.

[0161] In some embodiments, the sodium-supplementing layer 5214 also contains a binder, which accounts for 35.4% to 50% of the total mass of the sodium-supplementing layer 5214. The presence of 35.4% to 50% binder in the sodium-supplementing layer improves its adhesion, facilitates the bonding of dot-like and linear conductive agents to form a stable conductive structure, enhances the structural stability of the sodium-supplementing layer 5214, and also reduces the resistance of the positive electrode 521.

[0162] As an example, the adhesive accounts for 35.4%, 36.0%, 37.0%, 38.0%, 39.0%, 40.0%, 41.0%, 42.0%, 43.0%, 44.0%, 45.0%, 46.0%, 47.0%, 48.0%, 49.0%, 50.0% of the total mass of the sodium-filled layer 5214, or a value within the range formed by any two of the above points.

[0163] Since most of the sodium supplement is applied to the surface of the positive electrode active material layer 5212 through sodium supplement slurry, and most of the sodium supplement does not directly mix into the interior of the positive electrode active material layer 5212, the number and size of pores in the positive electrode sheet 521 formed after subsequent formation are smaller than the number and size of pores in the sodium supplement layer 5214, and the positive electrode active material layer 5212 has good structural stability.

[0164] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 The example shown is a square-structured battery cell 5.

[0165] In some implementations, refer to Figure 5 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0166] In some embodiments, the battery cells 5 can be assembled into a battery module, and the number of battery cells 5 contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0167] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 7In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0168] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0169] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0170] Figure 7 and Figure 8 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0171] A second aspect of this application also provides a sodium-ion battery, comprising a battery cell 5 prepared according to the method described above.

[0172] In addition, this application also provides an electrical device, which includes at least one of the battery cell 5, battery module, sodium-ion battery, or battery pack provided in this application. The battery cell 5, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0173] As an electrical device, you can choose from single battery cells, sodium-ion batteries, battery modules, or battery packs depending on your usage requirements.

[0174] Figure 9 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery cells 5, a battery pack or battery module can be used.

[0175] Another example device could be a mobile phone, tablet, laptop, etc. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0176] Example

[0177] 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.

[0178] Example 1

[0179] Example 1 provides a battery cell, the preparation method of which is as follows:

[0180] (1) Preparation of the positive electrode sheet: A positive electrode active material layer is formed on one surface of the positive electrode current collector. A sodium-supplementing slurry is coated on the surface of the positive electrode active material layer facing away from the positive electrode current collector, and then cured to form a sodium-supplementing coating. The positive electrode current collector is selected from aluminum foil. By mass percentage, the positive electrode active material layer comprises 90% positive electrode active material Na4Fe3(PO4)2P2O7, 5% binder polyvinylidene fluoride (PVDF), and 5% conductive carbon black (SP), with a thickness of 100 μm. The sodium-supplementing slurry comprises a solvent and raw materials dispersed in the solvent. By mass percentage, the raw materials comprise 86% sodium-supplementing agent NaNO2 (gas-generating type), 2% linear conductive agent carbon nanotubes (CNTs), 5% dotted conductive agent SP, and 7% binder PVDF (model 5130), with a thickness of 2 μm. The specific composition of the raw materials in the sodium-supplementing slurry is shown in Table 1.

[0181] (2) Battery assembly: The positive electrode, separator, and negative electrode obtained in step (1) are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes to obtain the battery cell; the battery cell is placed in the outer packaging foil, the electrolyte is injected into the dried battery cell, vacuum sealed, left to stand, and formed to obtain a battery cell. The negative electrode includes a copper foil negative current collector and a negative active material layer disposed on one surface of the negative current collector. By mass percentage, the negative active material layer includes 95% hard carbon, 5% binder SBR and 5% conductive carbon black (SP), and the thickness of the negative active material layer is 100um; the separator is 7um PE, and the electrolyte is NEL-C003; the formation method includes: charging to 3.1V at a current rate of 0.1C, then charging to 3.5V at a current rate of 0.33C, and then charging to 3.9V at a current rate of 0.05C.

[0182] Example 2

[0183] Example 2 provides a battery cell, which differs from Example 1 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 87% sodium-supplementing agent NaNO2, 2% linear conductive agent CNT, 5% dot conductive agent SP and 6% binder PVDF (model 5130).

[0184] Example 3

[0185] Example 3 provides a battery cell, which differs from Example 1 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 88% sodium-supplementing agent NaNO2, 2% linear conductive agent CNT, 5% dot conductive agent SP and 5% binder PVDF (model 5130).

[0186] Example 4

[0187] Example 4 provides a battery cell, which differs from Example 1 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 89% sodium-supplementing agent NaNO2, 2% linear conductive agent CNT, 5% dot conductive agent SP and 4% binder PVDF (model 5130).

[0188] Example 5

[0189] Example 5 provides a battery cell, which differs from Example 1 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 86% sodium-supplementing agent NaNO2, 1.2% linear conductive agent CNT, 5.8% dot conductive agent SP and 7% binder PVDF (model 5130).

[0190] Example 6

[0191] Example 6 provides a battery cell, which differs from Example 1 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 86% sodium-supplementing agent NaNO2, 1.6% linear conductive agent CNT, 5.4% dot conductive agent SP and 7.0% binder PVDF (model 5130).

[0192] Example 7

[0193] Example 7 provides a battery cell, which differs from Example 1 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 86% sodium-supplementing agent NaNO2, 2.4% linear conductive agent CNT, 4.6% dot conductive agent SP and 7.0% binder PVDF (model 5130).

[0194] Example 8

[0195] Example 8 provides a battery cell, which differs from Example 1 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 86% sodium-supplementing agent Na6PS5Cl (non-gas-generating type), 3.0% linear conductive agent CNT, 4.0% dot conductive agent SP and 7.0% binder PVDF (model 5130).

[0196] Example 9

[0197] Example 9 provides a battery cell, which differs from Example 8 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 86% sodium-supplementing agent Na6PS5Cl, 2.8% linear conductive agent CNT, 4.2% dot conductive agent SP and 7.0% binder PVDF (model 5130).

[0198] Example 10

[0199] Example 10 provides a battery cell, which differs from Example 8 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 86% sodium-supplementing agent Na6PS5Cl, 2.0% linear conductive agent CNT, 5.0% dot conductive agent SP and 7.0% binder PVDF (model 5130).

[0200] Example 11

[0201] Example 11 provides a single battery cell, which differs from Example 1 in that:

[0202] In step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 86% sodium supplement NaNO2, 1% linear conductive agent CNT, 6% dot conductive agent SP and 7.0% binder PVDF (model 5130).

[0203] Example 12

[0204] Example 12 provides a battery cell, which differs from Example 1 in that the formation method includes charging to a voltage of 3.1V at a current rate of 0.1C.

[0205] Comparative Example 1

[0206] Comparative Example 1 provides a battery cell that differs from Example 1 in that: in step (1), no sodium replenishment layer is provided on the surface of the positive electrode active material layer away from the positive electrode current collector.

[0207] Comparative Example 2

[0208] Comparative Example 2 provides a single battery cell, which differs from Example 1 in that:

[0209] The sodium supplement, dotted conductive agent, and linear conductive agent from step (1) are mixed together in the active material layer.

[0210] Comparative Example 3

[0211] Comparative Example 3 provides a battery cell that differs from Example 1 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 86% sodium-supplementing agent NaNO2, 7.0% linear conductive agent CNT and 7.0% binder PVDF (model 5130).

[0212] Comparative Example 4

[0213] Comparative Example 4 provides a battery cell that differs from Example 1 in that: in step (1), as shown in Table 1, the raw materials in the sodium-supplementing slurry include 86% sodium-supplementing agent NaNO2, 7.0% dot-shaped conductive agent SP and 7.0% binder PVDF (model 5130).

[0214] Test case

[0215] The battery cells provided in Examples 1-12 and Comparative Examples 1-4 were subjected to battery performance tests to determine the content of sodium supplementing agent in the sodium supplementing layer of the positive electrode after formation.

[0216] (1) DCR test (DC internal resistance):

[0217] Capacity testing was conducted: The lower cell (with clamp) was calibrated at room temperature (25°C), followed by pulse discharge to obtain the DC impedance diagram during the discharge process. The DCR values ​​at 50% SOC and 10% SOC were then plotted on the DC impedance diagram during the discharge process, yielding the DCR values ​​at 50% SOC and 10% SOC. The test results are shown in Table 1.

[0218] (2) Initial charge-discharge capacity test:

[0219] At 25℃, the cell was charged at a constant current of 0.33C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V to a current of 0.05C. This charging capacity is the first-cycle charging capacity of the battery cell. After resting for 30 minutes, the cell was discharged at a constant current of 0.33C to a voltage of 1.5V. This discharge capacity is the first-cycle discharge capacity of the lithium-ion battery. Dividing these charging and discharging capacities by the mass of the positive electrode active material in the battery gives the initial charging specific capacity and the initial discharging specific capacity, respectively. The test results are shown in Table 1.

[0220] (3) Capacity retention rate:

[0221] Under a constant temperature environment of 25℃, the battery was charged at a rate of 0.33C to 4.43V at a voltage range of 2.5V to 4.43V. Then, it was charged at a constant voltage of 4.43V until the current ≤0.05mA, allowed to stand for 5 minutes, and then discharged at a rate of 0.2C to 2.5V. The discharge capacity was recorded. This process was repeated to obtain the capacity retention rate after 100 cycles. The capacity retention rate = initial discharge capacity / discharge capacity at the specified number of cycles × 100%, which is the cycle retention rate (%) of the individual battery cell. The test results are shown in Table 1.

[0222] (4) Sodium supplement content test in the sodium supplementation layer:

[0223] The formed positive electrode sheet was removed from the battery cell, and the sodium replenishment layer was peeled off from the surface of the positive electrode active material layer. The mass content of sodium replenishing agent in the sodium replenishment layer was tested by ICP (inductively coupled plasma) test. The test results are shown in Table 1.

[0224] (5) Test of the content of conductive agent in sodium-supplemented coating:

[0225] The positive electrode sheet before formation in Example 1 was removed from the battery cell. The positive electrode sheet was then immersed in dimethyl carbonate (DMC) solvent for cleaning and dried. The sodium-added layer was scraped off from the surface of the positive electrode active material layer and dried. The morphology of the scraped powder was observed using a scanning electron microscope, and the test results are as follows: Figures 10-12 As shown in Table 2, the principal element analysis of the scraped powder was performed.

[0226] Table 1

[0227]

[0228]

[0229] Table 2

[0230]

[0231] Results analysis:

[0232] from Figure 10 It can be seen that among the scraped-off powder, the sodium supplement particles are irregular and small. Figure 10 In this context, particles with a linear structure are considered linear conductive agents. Similarly, from... Figure 12 It can also be seen that the linear structure connecting the particles is a linear conductive agent. From Figure 11 It can be seen that the large particles in the center are sodium supplement particles, while the smaller particles attached to the sodium supplement particles are dot-shaped conductive agent particles.

[0233] As can be seen from Table 1, compared with Comparative Example 1, which did not add sodium supplementation agent to the positive electrode sheet, when preparing battery cells according to the preparation methods provided in Examples 1 to 12 of this application, the sodium supplementation slurry is applied to the surface of the positive electrode active material layer, cured, and formed, which can improve the charge and discharge capacity of the battery cells. Even with the addition of sodium supplementation agent, the battery cells can still maintain a good capacity retention rate.

[0234] As can be seen from Table 1, compared to Comparative Example 2, which mixes sodium supplementer, linear conductive agent and dot conductive agent together in the positive electrode active material layer, the preparation method provided in Examples 1 to 12 of this application, when preparing the battery cell, coats the sodium supplement slurry on the surface of the positive electrode active material layer, cures and forms the sodium supplementer in the sodium supplement coating, thereby decomposing the sodium supplementer in the sodium supplement coating. This can improve the capacity retention rate of the battery cell and reduce the influence of the sodium supplementer on the internal resistance of the battery cell.

[0235] Table 1 shows that, compared with Comparative Examples 1 and 3-4, compared with Comparative Example 3 which only added linear conductive agent and not dot conductive agent, and Comparative Example 4 which only added dot conductive agent and not linear conductive agent, Example 1 of this application, by combining linear conductive agent and dot conductive agent, can increase the decomposition amount of sodium replenishing agent, reduce the sodium replenishing agent content in the sodium replenishing layer, and enable the battery cell to have a high charge and discharge specific capacity while having a low degree of deterioration in capacity retention rate, and reduce the DC internal resistance of the battery cell during cycling.

[0236] Table 1 shows that, compared with Examples 1 to 4, compared with Example 4 which added 4% PVDF binder to the raw materials of the sodium-supplementing slurry, Examples 1 to 3 which added 5% to 7% PVDF binder to the raw materials of the sodium-supplementing slurry can further improve the specific capacity and capacity retention of the battery cells and reduce the DC internal resistance of the battery cells during cycling.

[0237] Table 1 shows that, compared with Examples 1, 5-7 and Example 11, compared with Example 11 which added 1.0% linear conductive agent and 6.0% dot conductive agent to the sodium-supplementing slurry raw material, Examples 1 and 5-7 which added 1.2%-3.0% linear conductive agent and 4.0%-5.8% dot conductive agent to the sodium-supplementing slurry raw material can further increase the amount of sodium-supplementing agent decomposed, improve the charge and discharge specific capacity and capacity retention rate of the battery cells, and reduce the DC internal resistance of the battery cells during cycling.

[0238] Table 1 shows that, compared with Examples 1 and 5-7, when the sodium supplementer is a gas-generating sodium supplementer, compared with Examples 5 and 6 which added 1.2-1.6% linear conductive agent and 5.4-5.8% dot conductive agent to the sodium supplementer slurry raw material, Examples 1 and 7 which added 2.0-2.4% linear conductive agent and 4.6-5.0% dot conductive agent to the sodium supplementer slurry raw material can further improve the charge and discharge specific capacity and capacity retention rate of the battery cells and reduce the DC internal resistance of the battery cells during cycling.

[0239] In Table 1, comparing Examples 8-10, when the sodium replenishing agent is a non-gas-generating sodium replenishing agent, compared to Example 10 which added 2.0% linear conductive agent and 5.0% dot conductive agent to the sodium replenishing slurry raw material, Examples 8 and 9, which added 2.8%-3.0% linear conductive agent and 4.0%-4.2% dot conductive agent to the sodium replenishing slurry raw material, can further improve the charge-discharge specific capacity and capacity retention rate of the battery cells and reduce the DC internal resistance of the battery cells during cycling.

[0240] Table 1 shows that, compared with Example 1 and Example 12, compared with Example 12 which uses a conventional formation method to form the battery cell, Example 1 of this application, during formation, first charges to 3.0V at a current rate of 0.33C and then charges to 3.8V at a current rate of 0.1C to 0.2C. This can further increase the amount of sodium supplement decomposition, reduce the sodium supplement content in the sodium supplement layer after formation, further improve the charge and discharge specific capacity and capacity retention of the battery cell, and reduce the internal resistance of the battery cell.

[0241] In Table 2, the mass fraction of C is approximately 7.33%, which is close to the designed content (7%); combined with the content of each element in the sodium supplement, the NaNO2 content is approximately 86%.

[0242] 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 battery cell, characterized in that, The device includes a positive electrode sheet; the positive electrode sheet includes a positive current collector, a positive active material layer, and a sodium replenishing layer; the positive active material layer is disposed on at least a portion of the surface of the positive current collector, and the sodium replenishing layer is disposed on at least a portion of the surface of the positive active material layer opposite to the positive current collector; the sodium replenishing layer includes a sodium replenishing agent, a linear conductive agent, and a dotted conductive agent.

2. The battery cell according to claim 1, characterized in that, The sodium supplement agent accounts for 3.2% to 12.3% of the total mass of the sodium supplement layer.

3. The battery cell according to claim 2, characterized in that, The sodium supplement includes a gas-producing sodium supplement and / or a non-gas-producing sodium supplement; and / or, the gas-producing sodium supplement includes at least one of Na2CO3, Na2SO3 or NaNO2; and / or, the non-gas-producing sodium supplement includes at least one of EDTA-4Na, DPTA-5Na, Na6PS5Cl or Na2C6H2O6.

4. The battery cell according to claim 3, characterized in that, The sodium supplement agent includes a gas-generating sodium supplement agent, which accounts for 3.2% to 5.7% of the total mass of the sodium supplement layer.

5. The battery cell according to claim 3, characterized in that, The sodium supplement agent includes a non-gas-producing sodium supplement agent, which accounts for 7.1% to 12.3% of the total mass of the sodium supplement layer.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The linear conductive agent accounts for 12.9% to 19.4% of the total mass of the sodium replenishment layer; and / or, the dotted conductive agent accounts for 28.8% to 40.3% of the total mass of the sodium replenishment layer.

7. The battery cell according to claim 3 or 4, characterized in that, The sodium supplement agent includes a gas-generating sodium supplement agent, the dot-shaped conductive agent accounts for 37.1% to 40.3% of the total mass of the sodium supplement layer, and the linear conductive agent accounts for 12.9% to 15.5% of the total mass of the sodium supplement layer.

8. The battery cell according to claim 3 or 5, characterized in that, The sodium supplement agent includes a non-gas-generating sodium supplement agent, the dot-shaped conductive agent accounts for 28.8% to 30.2% of the total mass of the sodium supplement layer, and the linear conductive agent accounts for 18.1% to 19.4% of the total mass of the sodium supplement layer.

9. The battery cell according to any one of claims 1 to 8, characterized in that, The sodium replenishment layer also contains a binder, which accounts for 35.4% to 50% of the total mass of the sodium replenishment layer.

10. The battery cell according to any one of claims 1 to 9, characterized in that, The dotted conductive agent includes at least one of acetylene black, conductive carbon black, Ketjen black, or hollow carbon black; and / or, the linear conductive agent includes at least one of carbon nanotubes, carbon nanowires, or carbon fibers.

11. The battery cell according to claim 1, characterized in that, The thickness of the sodium-supplementing layer is 60µm to 130µm.

12. The battery cell according to claim 1, characterized in that, The porosity of the positive electrode active material layer is less than that of the sodium-supplementing layer.

13. A method for preparing a single battery cell, characterized in that, include: Preparation of the positive electrode: A positive active material layer is formed on at least a portion of the surface of the positive current collector, and a sodium-supplementing slurry is coated on at least a portion of the surface of the positive active material layer opposite to the positive current collector, and cured to form a sodium-supplementing coating; wherein, the sodium-supplementing slurry contains a sodium-supplementing agent, a dotted conductive agent, and a linear conductive agent; Battery assembly: The positive electrode, separator, electrolyte, and negative electrode are assembled into a battery cell, and the cell is formed.

14. The preparation method according to claim 13, characterized in that, The sodium-supplementing slurry includes a solvent and raw materials for forming the sodium-supplementing coating. By mass percentage, the raw materials include 86% to 89% of the sodium-supplementing agent, 4% to 5.8% of the dotted conductive agent, and 1.2% to 3% of the linear conductive agent, with the balance being additives.

15. The preparation method according to claim 14, characterized in that, The additives include 5% to 7% binder.

16. The preparation method according to claim 14 or 15, characterized in that, The sodium supplement agent includes a gas-generating sodium supplement agent, and the raw material contains 4.6% to 5% of the dot-shaped conductive agent and 2% to 2.4% of the linear conductive agent.

17. The preparation method according to claim 14 or 15, characterized in that, The sodium supplement includes a non-gas-producing sodium supplement, and the raw material contains 4.0% to 4.2% of the dot-shaped conductive agent and 2.8% to 3.0% of the linear conductive agent.

18. The preparation method according to any one of claims 13 to 17, characterized in that, The formation method includes: charging to 3.0V to 3.3V at a current rate of 0.1C to 0.2C, then charging to 3.5V to 3.6V at a current rate of 0.3C to 0.4C, and then charging to 3.8V to 4.0V at a current rate of 0.01C to 0.05C.

19. A sodium-ion battery, characterized in that, Includes the battery cell according to any one of claims 1 to 12, or the battery cell prepared by the preparation method according to any one of claims 13 to 18.

20. An electrical device, characterized in that, Including the sodium-ion battery as described in claim 19.

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