Sodium-ion battery monomer, preparation method thereof, battery device and power utilization device

Abstract

The invention provides a sodium ion battery monomer, a preparation method thereof, a battery device and a power utilization device. The sodium ion battery monomer comprises: a positive pole piece, the positive pole piece comprises a positive current collector and a positive film layer, the positive film layer is arranged on at least one side surface of the positive current collector, the positive film layer comprises a phosphate material, and the phosphate material comprises ferric sodium pyrophosphate, sodium ferrous pyrophosphate and sodium ferrous phosphate; the molar ratio A of the sodium element to the phosphorus element in the phosphate material is more than or equal to 0.95 and less than or equal to 1.05; based on the total mass of the positive electrode film layer, the mass content C of the ferric sodium pyrophosphate is greater than or equal to 92.1 wt% and less than or equal to 95.8 wt%, the mass content D of the ferrous sodium pyrophosphate is greater than or equal to 0.6 wt% and less than or equal to 4.3 wt%, and the mass content E of the ferrous sodium phosphate is greater than or equal to 0.5 wt% and less than or equal to 1.9 wt%. According to the technical scheme, the energy density of the sodium ion battery monomer can be improved, and the discharge performance is considered.

Description

Technical Field

[0001] This application relates to the field of batteries, and more specifically, to a sodium-ion battery cell and its preparation method, battery device, and power-consuming device. Background Technology

[0002] The new energy industry is attracting increasing attention. Within this industry, battery technology is a crucial factor in its development.

[0003] Sodium-ion batteries are gradually gaining attention due to their advantages such as low cost, good low-temperature performance, and abundant sodium resources, showing great application potential in markets such as large-scale energy storage and passenger vehicles. Sodium-ion batteries demonstrate their potential to replace lead-acid batteries with their excellent low-temperature performance, higher safety, higher discharge rate, and longer lifespan.

[0004] The development of battery technology requires consideration of various design factors, such as the high power discharge performance, high energy density, cycle performance, and lifespan of sodium-ion batteries. Therefore, how to provide a sodium-ion battery that combines high power discharge performance with high energy density is a pressing technical problem that needs to be solved. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a sodium-ion battery cell with high power discharge performance to improve the fast charging performance of the battery cell.

[0006] To achieve the above objectives, this application provides a sodium-ion battery cell, its preparation method, battery device, and power-consuming device.

[0007] In a first aspect, a sodium-ion battery cell is provided, comprising: a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one side surface of the positive current collector, the positive electrode film layer including a phosphate material, the phosphate material including sodium iron pyrophosphate, sodium ferrous pyrophosphate, and sodium ferrous phosphate; the molar ratio A of sodium to phosphorus in the phosphate material satisfies: 0.95≤A≤1.05; based on the total mass of the positive electrode film layer, the mass content C of sodium iron pyrophosphate satisfies: 92.1wt%≤C≤95.8wt%, the mass content D of sodium ferrous pyrophosphate satisfies: 0.6wt%≤D≤4.3wt%, and the mass content E of sodium ferrous phosphate satisfies: 0.5wt%≤E≤1.9wt%.

[0008] In the embodiments of this application, the positive electrode film layer includes phosphate materials, wherein the phosphate materials include sodium iron pyrophosphate, sodium ferrous pyrophosphate, and sodium ferrous phosphate. This application has found that sodium ferrous pyrophosphate, a byproduct generated during the preparation of sodium iron pyrophosphate, has high electronic conductivity. Therefore, unlike the prior art which minimizes the byproducts generated during the preparation of sodium iron pyrophosphate, this application controls the molar ratio of sodium to phosphorus in the phosphate material to be greater than or equal to 0.95, which can increase the content of sodium iron pyrophosphate, thereby increasing the specific capacity of the positive electrode and improving the energy density of the battery cell. When the molar ratio of sodium to phosphorus in the phosphate material is less than or equal to 1.05, it is beneficial to increase the content of sodium ferrous pyrophosphate in the phosphate material, thereby improving the electronic conductivity of the phosphate material, increasing the discharge power of the battery cell, and improving the fast-charging performance of the battery cell. Simultaneously, sodium ferrous phosphate is easily generated during the preparation of the phosphate material. Sodium ferrous phosphate is inert and affects the conductivity of the phosphate material. Controlling the mass percentage of sodium ferrous phosphate in phosphate materials to between 0.5 wt% and 1.9 wt% is beneficial to improving the electronic conductivity of phosphate materials and further enhancing the discharge power of battery cells.

[0009] In one possible implementation, 0.97 ≤ A ≤ 1.01.

[0010] In the embodiments of this application, by controlling the molar ratio of sodium and phosphorus within the above-mentioned range, it is beneficial to further improve the energy density and fast charging performance of the battery cell.

[0011] In one possible implementation, based on the total mass of the positive electrode film, the mass content ratio F between sodium iron pyrophosphate and sodium ferrous pyrophosphate satisfies: 21≤F≤142.

[0012] In the embodiments of this application, when the mass content ratio of sodium iron pyrophosphate phase to sodium ferrous pyrophosphate phase in the positive electrode film layer is within the above-mentioned range, it is beneficial to balance the energy density and discharge power of the battery cell, so as to improve the fast charging performance of the battery cell.

[0013] In one possible implementation, the phosphate material is at least partially coated with carbon material.

[0014] In this embodiment, coating the surface of the phosphate material with carbon material improves the conductivity of the phosphate material surface, promotes the migration process of sodium ions on the surface, and improves the fast charging performance of the battery cell.

[0015] In one possible implementation, based on the total mass of phosphate materials and carbon materials, the mass content W of carbon materials satisfies: 1.4wt% ≤ W ≤ 1.6wt%.

[0016] In this embodiment, setting the carbon material content within the above-mentioned range can effectively improve the electronic conductivity of the phosphate material, while avoiding excessive carbon material content that would reduce the phosphate material content. This ensures both the increase in the discharge power of the battery cell and the maintenance of its energy density.

[0017] Secondly, a method for preparing a sodium-ion battery cell is provided, comprising: mixing a carbon source, a phosphorus source, an iron source and a sodium source to obtain intermediate particles; sintering the intermediate particles to obtain a phosphate material, wherein the phosphate material includes sodium iron pyrophosphate and sodium ferrous pyrophosphate, and the mass ratio of sodium source to phosphorus source is 0.17 to 0.2; and using the phosphate material to prepare a positive electrode sheet to prepare a sodium-ion battery cell.

[0018] In the embodiments of this application, by controlling the mass ratio of sodium source to phosphorus source within the above-mentioned range, the mass proportion of sodium iron pyrophosphate and sodium ferrous pyrophosphate in the phosphate material can be within a suitable range, which is beneficial to improving the energy density and discharge power of the battery cell.

[0019] In one possible implementation, the mass ratio of iron source to phosphorus source is 0.17 to 0.19.

[0020] In this embodiment, by controlling the mass ratio of iron source to phosphorus source, the mass ratio of sodium ferrous phosphate phase in the generated phosphate material can be controlled. When the mass ratio of iron source to phosphorus source is within the above-mentioned range, it is beneficial to reduce the formation of sodium ferrous phosphate phase and improve the discharge power of the battery cell.

[0021] In one possible implementation, the intermediate particles are obtained by mixing carbon source, phosphorus source, iron source and sodium source, including: mixing carbon source, phosphorus source and iron source to obtain a first slurry, spray drying the first slurry to obtain a spray precursor, and mixing the spray precursor with sodium source to obtain intermediate particles.

[0022] In this embodiment, the carbon source, phosphorus source, and iron source are first mixed to obtain a spray precursor forming a sodium-free framework, which can avoid Na volatilization or excessive generation of the byproduct sodium ferrous phosphate during the high-temperature stage; then, the sodium source is mixed to complete solid-phase diffusion at a lower temperature, reducing Na loss and suppressing Fe3+. + Excessive oxidation is beneficial for controlling the proportion of each phase in phosphate materials, thereby improving the energy density and fast-charging performance of individual battery cells.

[0023] In one possible implementation, the solid content of the first slurry is 30%–40%; the mixing speed v of the carbon source, phosphorus source and iron source satisfies: 10 r / min ≤ v ≤ 100 r / min, optionally, 40 r / min ≤ v ≤ 60 r / min; the mixing time t1 of the carbon source, phosphorus source and iron source satisfies: 1 h ≤ t1 ≤ 10 h; the inlet air temperature T1 for spray drying the first slurry satisfies 180℃ ≤ T ≤ 220℃; and the outlet air temperature T2 for spray drying the first slurry satisfies 80℃ ≤ T ≤ 120℃.

[0024] In one possible implementation, sintering the intermediate particles includes: initial sintering of the intermediate particles followed by heated sintering, wherein the initial sintering temperature T3 is 300℃~400℃, the initial sintering time t2 is 5h~10h, the heated sintering temperature T4 is 500℃~600℃, and the heated sintering time t3 is 5h~15h.

[0025] In this embodiment, by adopting a segmented sintering method, it is beneficial to improve the graphitization degree of the carbon material coating on the surface of the phosphate material, improve the electronic conductivity of the positive electrode surface, maintain the proportion of each phase of the phosphate material, avoid excessively high sintering temperature from affecting the preparation of the phosphate material, and improve the discharge power of the battery cell.

[0026] In one possible implementation, the carbon source includes at least one of glucose, polyethylene glycol, sucrose, urea, and polyvinyl alcohol; the sodium source includes at least one of sodium carbonate, sodium hydroxide, sodium acetate, and sodium nitrate; the phosphorus source includes at least one of ferric phosphate, disodium hydrogen phosphate, phosphoric acid, and sodium pyrophosphate; and the iron source includes at least one of ferrous sulfate, ferric nitrate, ferrous sulfate, and ferric phosphate.

[0027] Thirdly, a battery device is provided, comprising a sodium-ion battery cell as described in the first aspect and any possible implementation thereof, and / or, comprising a sodium-ion battery cell prepared as described in the second aspect and any possible implementation thereof. The battery device includes at least one of a battery module and a battery pack.

[0028] Fourthly, an electrical device is provided, including the battery device of the third aspect. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application.

[0030] Figure 2 This is a schematic diagram of a battery cell preparation method according to an embodiment of this application.

[0031] Figure 3 This is a schematic diagram of the structure of a secondary battery according to an embodiment of this application.

[0032] Figure 4 This is a schematic diagram of the structure of a battery device according to an embodiment of this application.

[0033] Figure 5 This is a schematic diagram of an electrical device according to an embodiment of this application.

[0034] Figure 6 This is a discharge curve diagram of an embodiment of this application.

[0035] Explanation of reference numerals in the attached drawings: 1 Positive electrode sheet; 10 Positive current collector; 11 Positive electrode film; 3 Battery cell; 31 Housing; 32 End cap assembly; 33 Electrode assembly; 34 Connecting member; 322 Electrode terminal; 331 Electrode assembly body; 332 Tab; 4 Motor; 5 Battery device; 51 Housing; 511 First housing section; 512 Second housing section; 6 Controller; 7 Vehicle. Detailed Implementation

[0036] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, its manufacturing method, the battery, and the 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.

[0037] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0038] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0040] 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.

[0041] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through; for example, the separator can be a membrane or a separator. In some embodiments, the battery cell is also referred to as a secondary battery, and the battery cell can be the smallest possible battery unit.

[0042] During the charging process of a sodium-ion battery, sodium ions are released from the positive electrode active material, move and embed into the negative electrode material; while during the discharging process, sodium ions are released from the negative electrode material, move and embed into the positive electrode active material.

[0043] It should be understood that the “intercalation” process described in this application refers to the process in which sodium ions are intercalated in the positive electrode active material and the negative electrode material due to an electrochemical reaction, and the “deintercalation” and “deintercalation” processes described in this application refer to the process in which sodium ions are deintercalated in the positive electrode active material and the negative electrode active material due to an electrochemical reaction.

[0044] Sodium-ion batteries are gradually gaining attention due to their advantages such as low cost, good low-temperature performance, and abundant sodium resources, showing great application potential in markets such as large-scale energy storage and passenger vehicles. For example, in the start-stop battery market, sodium-ion batteries demonstrate their potential to replace lead-acid batteries due to their excellent low-temperature performance, higher safety, higher discharge rate, and longer lifespan.

[0045] The development of sodium start-stop battery technology requires consideration of multiple design factors, such as balancing high-power discharge performance, high energy density, cycle performance, and lifespan. Therefore, the requirements for energy density and discharge performance of sodium-ion batteries are gradually increasing. Among positive electrode active materials, sodium iron pyrophosphate has a high theoretical capacity, but it also suffers from low electronic conductivity, which can easily affect the discharge power of individual battery cells.

[0046] In related technologies, carbon materials are coated onto the surface of sodium iron pyrophosphate to improve surface conductivity and promote sodium ion migration. Simultaneously, the introduction of non-d-orbital elements can lower its Fermi level and enhance the material's electronic conductivity. However, carbon coating only improves the surface conductivity of sodium iron pyrophosphate but does not affect its electronic conductivity, thus the improvement effect is limited. Furthermore, non-d-orbital elements are generally inactive elements, and excessive introduction can lead to a significant decrease in the capacity of sodium iron pyrophosphate.

[0047] In view of this, in one embodiment of this application, a sodium-ion battery cell is provided, comprising: a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one side surface of the positive current collector, the positive electrode film layer including a phosphate material, the phosphate material including sodium iron pyrophosphate, sodium ferrous pyrophosphate, and sodium ferrous phosphate; the molar ratio A of sodium to phosphorus in the phosphate material satisfies: 0.95≤A≤1.05; based on the total mass of the positive electrode film layer, the mass content C of sodium iron pyrophosphate satisfies: 92.1wt%≤C≤95.8wt%, the mass content D of sodium ferrous pyrophosphate satisfies: 0.6wt%≤D≤4.3wt%, and the mass content E of sodium ferrous phosphate satisfies: 0.5wt%≤E≤1.9wt%.

[0048] In this application, the preparation of sodium iron pyrophosphate is accompanied by the formation of sodium ferrous pyrophosphate and sodium ferrous phosphate. Therefore, the phosphate material in the positive electrode film includes sodium iron pyrophosphate, sodium ferrous pyrophosphate, and sodium ferrous phosphate. Existing technologies typically aim to minimize the generation of byproducts and increase the mass content of sodium iron pyrophosphate in the phosphate material to improve the energy density of the battery cell. However, this application finds that although the byproduct sodium ferrous pyrophosphate has a lower specific capacity, its electronic conductivity is superior to that of sodium iron pyrophosphate. Increasing the proportion of sodium ferrous pyrophosphate in the phosphate material promotes electron conduction, thereby improving the power performance of the battery cell. Simultaneously, sodium ferrous phosphate is an inert phase, thus requiring a reduction in its content. Therefore, this application improves the conductivity of the positive electrode film by controlling the mass content of sodium iron pyrophosphate, sodium ferrous pyrophosphate, and sodium ferrous phosphate, thereby addressing the poor charge-discharge performance of phosphate materials and improving the discharge performance of the battery cell.

[0049] When the molar ratio A of sodium to phosphorus in phosphate materials is greater than 1.05, the content of sodium iron pyrophosphate in the phosphate material is too high, which reduces the conductivity of the positive electrode film and thus affects the discharge performance of the battery cell. When the value of A is less than 0.95, the content of sodium ferrous pyrophosphate in the phosphate material is reduced, resulting in a decrease in the specific capacity of the positive electrode film and affecting the energy density of the battery cell. Therefore, controlling the molar ratio A of sodium to phosphorus in the phosphate material to be within the range of 0.95 ≤ A ≤ 1.05 can balance the mass proportions of sodium iron pyrophosphate, sodium ferrous pyrophosphate, and sodium ferrous phosphate in the phosphate material, thereby improving the energy density and high-power discharge performance of the battery cell.

[0050] Next, the sodium-ion battery cell and its components provided in this application will be described.

[0051] Sodium-ion battery cell

[0052] In one embodiment of this application, a sodium-ion battery cell is provided, including a positive electrode.

[0053] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet according to an embodiment of this application.

[0054] The positive electrode 1 includes a positive current collector 10 and a positive electrode film layer 11 disposed on at least one side of the positive current collector 10.

[0055] The positive current collector 10 has two opposite sides along its own thickness direction, wherein the positive electrode film layer 11 can be disposed on one side of the positive current collector 10 or on both sides of the positive current collector 10.

[0056] The positive electrode film layer 11 includes a positive electrode active material, which includes a phosphate material;

[0057] Phosphate materials include sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7, NFPP), sodium ferrous pyrophosphate (Na2FeP2O7, NFPO), and sodium ferrous phosphate (NaFePO4, NFP).

[0058] NFPP is one of the commonly used phosphate cathode active materials in sodium-ion batteries, but its intrinsic conductivity is poor and it is easy to generate inactive impurities NFP and NFPO. Among them, NFP is an inert phase, which can limit the actual electrochemical performance of NFPP. This application found that although NFPO has a lower specific capacity, its electronic conductivity is better than that of NFPP.

[0059] In some embodiments, the molar ratio A of sodium to phosphorus in the phosphate material satisfies: 0.95 ≤ A ≤ 1.05.

[0060] Specifically, the molar ratio A of sodium to phosphorus in the phosphate material can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05 or any value within the above range.

[0061] In some embodiments, the molar ratio A of sodium to phosphorus in the phosphate material satisfies: 0.97 ≤ A ≤ 1.01.

[0062] Specifically, the molar ratio A of sodium to phosphorus in the phosphate material can be 0.97, 0.98, 0.99, 1.0, 1.01 or any value within the above range.

[0063] When the molar ratio of sodium to phosphorus is greater than or equal to 0.95, it is beneficial to ensure the specific capacity of the positive electrode active material and improve the energy density of the battery cell. When the molar ratio of sodium to phosphorus is less than or equal to 1.05, it is beneficial to improve the electronic conductivity of the positive electrode film, thereby improving the power performance of the positive electrode active material and improving the fast charging performance of the battery cell.

[0064] In some embodiments, based on the total mass of the positive electrode film 11, the mass content C of NFPP satisfies: 92.1wt% ≤ C ≤ 95.8wt%, and the mass content D of NFPO satisfies: 0.6wt% ≤ D ≤ 4.3wt%.

[0065] Specifically, the mass content C of NFPP can be 92.1 wt%, 92.5 wt%, 93 wt%, 93.5 wt%, 94 wt%, 94.5 wt%, 95 wt%, 95.5 wt%, 95.8 wt%, or any value within the above range.

[0066] The NFPO mass content D can be 0.6wt%, 0.7wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.3wt%, or any value within the above range.

[0067] During the preparation of NFPP, NFPO and NFP are easily generated. Existing technologies typically aim to minimize the generation of byproducts and increase the NFPP content in the phosphate material to improve the energy density of the battery cell. However, this application discovers that although the byproduct NFPO has a low specific capacity, its electronic conductivity is superior to that of NFPP. Increasing the NFPO proportion in the phosphate material promotes electron conduction, thereby improving the power performance of the battery cell. Therefore, this application addresses the poor charge-discharge performance of NFPP by controlling the mass content of NFPP and NFPO to improve the conductivity of the positive electrode film, thus enhancing the discharge performance of the battery cell.

[0068] In some embodiments, based on the total mass of the positive electrode film 11, the mass content ratio F between NFPP and NFPO satisfies 21≤F≤142.

[0069] Specifically, the mass ratio F of NFPP to NFPO can be 21, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 142 or any value within the above range.

[0070] Maintaining the mass ratio of NFPO to NFPP within the above range in phosphate materials is beneficial for balancing the energy density and discharge power of individual battery cells.

[0071] In some embodiments, the molar ratio B of iron to phosphorus in the phosphate material satisfies: 0.72 ≤ B ≤ 0.75; the phosphate material also includes NFP, and based on the total mass of the positive electrode film 11, the mass content E of NFP satisfies: 0.5 wt% ≤ E ≤ 1.9 wt%.

[0072] Specifically, the molar ratio B of iron to phosphorus in the phosphate material can be 0.72, 0.725, 0.73, 0.735, 0.74, 0.745, 0.75 or any value within the above range.

[0073] The mass content E of NFP can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 1.9wt%, or any value within the above range.

[0074] During the preparation of phosphate materials, impurity phases NFP are easily generated, which affect the conductivity of the NFPP main phase. When the molar ratio B of iron to phosphorus in the phosphate material meets the above range, it is beneficial to generate NFPP while avoiding the generation of too much NFP, which limits the electronic conductivity of NFPP. This ensures that the phosphate material contains a large amount of NFPP and NFPO, thereby increasing the discharge power of the battery cell and improving fast charging performance.

[0075] In some embodiments, the phosphate material is at least partially coated with carbon material.

[0076] Coating phosphate materials with carbon materials can improve surface conductivity, enhance the electronic conductivity of the positive electrode active material, and thus improve the power performance of the battery cell.

[0077] In some embodiments, based on the total mass of phosphate materials and carbon materials, the mass content W of carbon materials satisfies: 1.4wt% ≤ W ≤ 1.6wt%.

[0078] Specifically, the mass content W of the carbon material can be 1.4wt%, 1.45wt%, 1.5wt%, 1.55wt%, 1.6wt%, or any value within the above range.

[0079] When the mass content W of carbon material is greater than or equal to 1.4 wt%, it is beneficial to improve the power performance of the battery cell. When the mass content W of carbon material is less than or equal to 1.6 wt%, the proportion of phosphate material can be guaranteed, the specific capacity of the positive electrode active material can be increased, and the energy density of the battery cell can be improved.

[0080] [Preparation methods for battery cells]

[0081] Figure 2 This is a schematic diagram of a battery cell preparation method according to an embodiment of this application. Figure 2 As shown, in some embodiments, the method for preparing a single battery cell may include the following steps:

[0082] S20 is prepared by mixing carbon source, phosphorus source, iron source and sodium source to obtain intermediate particles, and sintering the intermediate particles to obtain phosphate material. The phosphate material includes NFPP and NFPO, and the mass ratio of sodium source to phosphorus source is 0.17 to 0.2.

[0083] S21, using phosphate materials to prepare positive electrode sheets in order to prepare sodium-ion battery cells.

[0084] Specifically, the mass ratio of sodium source to phosphorus source can be 0.17, 0.175, 0.18, 0.185, 0.19, 0.195, 0.2 or any value within the above range.

[0085] Therefore, by controlling the mass ratio of sodium and phosphorus sources, the molar ratio of sodium and phosphorus in phosphate materials can be controlled, and NFPO and NFPP phases with appropriate proportions can be obtained, which is beneficial to balancing the power performance and energy density of battery cells.

[0086] In some embodiments, the mass ratio of iron source to phosphorus source is 0.17 to 0.19.

[0087] Specifically, the mass ratio of iron source to phosphorus source can be 0.17, 0.175, 0.18, 0.185, 0.19 or any value within the above range.

[0088] Therefore, by controlling the mass ratio of sodium source to phosphorus source within the above range, the molar ratio of iron and phosphorus in the phosphate material can be controlled to avoid the formation of NFP in the phosphate material, which would affect the electronic conductivity of the positive electrode active material and improve the energy density and discharge power of the battery cell.

[0089] In some embodiments, mixing a carbon source, a phosphorus source, an iron source, and a sodium source to obtain intermediate particles includes: mixing a carbon source, a phosphorus source, and an iron source to obtain a first slurry; spray drying the first slurry to obtain a spray precursor; and mixing the spray precursor with a sodium source to obtain intermediate particles.

[0090] First, a spray precursor is obtained, then mixed with a sodium source to obtain intermediate particles. This allows for precise control of the amount of sodium source added and adjustment of the sodium-to-phosphorus ratio. Furthermore, this method can first form a sodium-free framework, avoiding excessive Na volatilization or the formation of the byproduct NFP at high temperatures. Subsequent mixing with the sodium source allows solid-phase diffusion to be completed at lower temperatures, reducing Na loss and simultaneously suppressing Fe3+. + Excessive oxidation.

[0091] In some embodiments, the solid content of the first slurry is 30% to 40%; the mixing speed v of the carbon source, phosphorus source and iron source satisfies: 10 r / min ≤ v ≤ 100 r / min, optionally, 40 r / min ≤ v ≤ 60 r / min; the mixing time t1 of the carbon source, phosphorus source and iron source satisfies: 1 h ≤ t1 ≤ 10 h; the inlet air temperature T1 for spray drying the first slurry satisfies 180 °C ≤ T1 ≤ 220 °C; the outlet air temperature T2 for spray drying the first slurry satisfies 80 °C ≤ T2 ≤ 120 °C.

[0092] In some embodiments, sintering the intermediate particles includes: sintering the intermediate particles in the initial stage followed by a heated sintering process, wherein the initial sintering temperature T3 is 300℃~400℃, the initial sintering time t2 is 5h~10h, the heated sintering temperature T4 is 500℃~600℃, and the heated sintering time t3 is 5h~15h.

[0093] By gradually heating the intermediate particles through segmented sintering, it is beneficial to control the proportion of NFPP and NFPO phases and to improve the graphitization degree of the carbon material coating layer, thereby improving the conductivity of the positive electrode sheet.

[0094] In some embodiments, the sintering atmosphere is argon or nitrogen.

[0095] In some embodiments, the carbon source includes at least one of glucose, polyethylene glycol, sucrose, urea, and polyvinyl alcohol; the sodium source includes at least one of sodium carbonate, sodium hydroxide, sodium acetate, and sodium nitrate; the phosphorus source includes at least one of ferric phosphate, disodium hydrogen phosphate, phosphoric acid, and sodium pyrophosphate; and the iron source includes at least one of ferrous sulfate, ferric nitrate, ferrous sulfate, and ferric phosphate.

[0096] [Positive electrode plate]

[0097] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0098] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0099] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0100] In some embodiments, the positive electrode active material includes a phosphate material, wherein the phosphate material includes sodium iron pyrophosphate and sodium ferrous pyrophosphate, and the molar ratio A of sodium to phosphorus in the phosphate material satisfies: 0.95≤A≤1.05.

[0101] In some embodiments, the positive electrode active material may include, in addition to the aforementioned phosphate materials, positive electrode active materials known in the art for use in sodium-ion batteries. As examples, the positive electrode active material may include sodium transition metal oxides, polyanionic compounds, Prussian blue compounds, etc., and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used. For example, as an optional technical solution in this application, the transition metal in the sodium transition metal oxide may be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide may be, for example, Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0102] As an optional technical approach in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state. Polyanionic compounds can also have sodium ions, transition metal ions, or tetrahedral (YO4) ions. n-A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl, and Br. Polyanionic compounds can also have sodium ions, tetrahedral (YO4) valence states. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl, and Br. Examples of polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn, and Ni), and Na3(VO4)2. y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0103] As an optional technical approach in this application, the polyanionic compound can be Na... x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z-d Q d Wherein, element A represents an alkali metal element that substitutes for element Na, element M represents a metal element that substitutes for element V, element D represents a dopant element that substitutes for element P, and element Q represents a dopant element that substitutes for element F. Element D includes at least one of Si and S, and element Q 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, element A includes at least one of K and Li; element M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0104] As an optional technical approach in this application, the polyanionic compound can be Na... xR y (PO4)2P2O7, where x = 3.5 - 4.5, y = 2.75 - 3.25, 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.

[0105] As an optional technical solution of the present application, the polyanionic compound may be Na 4+x R 3-y P 4-m O 15 / C; where 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.

[0106] The Prussian blue compound may be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue compound is, for example, Na a Me b Me’ c (CN)6, where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0107] In some embodiments, the positive electrode active material includes at least one of a sodium-containing layered oxide, a polyanionic sodium compound, and a Prussian blue sodium compound.

[0108] In some embodiments, the sodium-containing layered oxide is an iron-manganese-based layered oxide, specifically including at least one of a nickel-iron-manganese-based layered oxide and a copper-iron-manganese-based layered oxide.

[0109] During the charge and discharge process of the battery, the insertion and extraction and consumption of active ions (Na + ) will occur. Therefore, the molar content of sodium is different when discharging to different states. In the listing of the positive electrode active material in the present application, the molar content of Na is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Na will change.

[0110] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0111] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0113] [Negative electrode plate]

[0114] As described above, the negative electrode current collector has two opposing surfaces along its thickness direction. The negative electrode film layer can be disposed on one surface of the negative electrode current collector or on both surfaces.

[0115] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0116] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. 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.

[0117] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0118] As described above, in some embodiments, the negative electrode film may optionally include conductive carbon. The conductive carbon may be selected from at least one of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0120] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive carbon, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0121] [Electrolytes]

[0122] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0123] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0124] The electrolyte salt includes, but is not limited to, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. One of the above electrolyte salts may be used alone, or two or more may be used simultaneously.

[0125] Solvents include carbonate or ether solvents. Carbonate solvents include cyclic ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and chain-like dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), etc.; ether solvents include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxane, etc.

[0126] 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.

[0127] [Isolation membrane]

[0128] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0129] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0130] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0131] [Battery cell]

[0132] In some embodiments, the secondary battery is a single battery cell, which can be the smallest structural unit of the battery.

[0133] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0134] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery 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.

[0135] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is a square-structured battery cell 3, used as an example.

[0136] In some implementations, refer to Figure 3 The battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33 disposed in the housing 31. The housing 31 may include a bottom plate and a side plate connected to the bottom plate, the bottom plate and the side plate forming a receiving cavity.

[0137] The housing 31 has an opening communicating with a receiving cavity, and an end cap assembly 32 is capable of covering the opening to close the receiving cavity. The end cap assembly 32 includes electrode terminals 322, such as... Figure 3 As shown, the end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0138] The electrode assembly 33 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 33. The positive electrode, negative electrode, and separator can be formed into the electrode assembly 33 via a winding or stacking process. The electrode assembly 33 includes an electrode assembly body 331 and tabs 332 extending from the electrode assembly body 331.

[0139] The battery cell 3 also includes a connecting member 34, which is used to connect the tabs 332 and the electrode terminals 322 of the electrode assembly 33. The battery cell 3 may contain one or more electrode assemblies 33, which can be selected by those skilled in the art according to specific practical needs.

[0140] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries 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.

[0141] [Battery Device]

[0142] This application provides a battery device, including the battery cell described in the above embodiments. Figure 4 This is a schematic diagram of the structure of a battery device according to an embodiment of this application. Figure 4 As shown, the battery device 5 may include multiple battery cells 3 to meet different power usage requirements. The shape of the battery cell 3 in this embodiment can be set according to actual application. For example, the battery cell 3 may be as follows: Figure 3 The cuboid shown can also be different. Figure 3 The embodiments shown are cylindrical or other shapes, but are not limited to these.

[0143] It should be understood that, such as Figure 4As shown, the battery device 5 in this embodiment may further include a housing 51, which can be used to accommodate multiple battery cells 3. The housing 51 in this embodiment has a hollow interior, and the multiple battery cells 3 are accommodated within the housing 51. The housing 51 may include two parts, referred to herein as a first housing portion 511 and a second housing portion 512, which are fastened together. The shapes of the first housing portion 511 and the second housing portion 512 can be determined according to the shape of the components housed inside, for example, according to the shape of the combination of the multiple battery cells 3 housed inside. At least one of the first housing portion 511 and the second housing portion 512 has an opening. For example, as... Figure 4 As shown, the first housing portion 511 and the second housing portion 512 can both be hollow cuboids with one open side. The openings of the first housing portion 511 and the second housing portion 512 are opposite to each other, and the first housing portion 511 and the second housing portion 512 are interlocked to form a housing 51 with a closed cavity, which can be used to accommodate multiple battery cells 3. The multiple battery cells 3 are connected in parallel, series, or mixed and placed inside the housing 51 formed by the interlocking of the first housing portion 511 and the second housing portion 512.

[0144] For example, unlike Figure 4 As shown, either the first housing portion 511 or the second housing portion 512 may have only one hollow cuboid with an opening, while the other is plate-shaped to cover the opening. Taking the second housing portion 512 as a hollow cuboid with one opening, and the first housing portion 511 as a plate-shaped example, then the first housing portion 511 covers the opening of the second housing portion 512 to form a housing 51 with a closed chamber, which can be used to accommodate multiple battery cells 3.

[0145] The battery cells 3 can be directly assembled into the battery device 5, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into the battery device 5.

[0146] [Electrical appliances]

[0147] This application provides an electrical device including the battery device described in the above embodiments.

[0148] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use battery devices.

[0149] Electrical equipment can include vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-mentioned electrical equipment.

[0150] For ease of explanation, the following embodiments use a vehicle as an example of electrical equipment.

[0151] For example, such as Figure 5 The diagram shown is a structural schematic of a vehicle 7 according to one embodiment of this application. The vehicle 7 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. The vehicle 7 can have a motor 4, a controller 6, and a battery device 5 installed inside. The controller 6 controls the battery device 5 to supply power to the motor 4. For example, the battery device 5 can be installed at the bottom, front, or rear of the vehicle 7. The battery device 5 can be used to power the vehicle 7; for example, it can serve as the operating power source for the vehicle 7's electrical system, such as meeting the power requirements for starting, navigation, and operation. In another embodiment of this application, the battery device 5 can not only serve as the operating power source for the vehicle 7 but also as the driving power source, replacing or partially replacing gasoline or natural gas to provide driving power to the vehicle 7.

[0152] 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.

[0153] Example 1

[0154] (1) Preparation of positive electrode sheet

[0155] A first slurry was prepared by mixing glucose (carbon source), sodium pyrophosphate (phosphorus source), and ferrous sulfate (iron source) in a buffer tank at a mass ratio of 70:50:0.31. The solid content of the first slurry was 30%. The mixing speed (v) was 50 r / min, and the mixing time (t1) was 4 h. The first slurry was then sprayed in a spray drying tower with an inlet air temperature (T1) of 200℃ and an outlet air temperature (T2) of 110℃ to obtain a dried spray precursor. The spray precursor was mixed with sodium source Na2CO3 at a mass ratio of 9:50 to obtain intermediate particles. The intermediate particles were then sintered in a kiln using a staged heating method. The initial sintering temperature (T3) was 300℃, and the initial sintering time (t2) was 10 h. Subsequent sintering was carried out at a higher temperature (T4) of 510℃ for a further sintering time (t3) of 6 h. The sintering atmosphere was nitrogen. After sintering, the positive electrode active material was obtained. The positive electrode active material includes phosphate materials, which include sodium iron pyrophosphate and sodium ferrous pyrophosphate. The molar ratio A of sodium to phosphorus in the phosphate materials is 1.0.

[0156] The positive electrode active material, nano-scale conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were dissolved in N-methylpyrrolidone solvent at a mass ratio of 94:3:3 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto one side of a 13 μm thick aluminum foil current collector. After drying and cold pressing, a coating surface density of 0.02 g / cm³ was obtained. 2 The compacted density is 2.0 g / cm³. 3 The positive electrode sheet.

[0157] (2) Preparation of negative electrode sheet

[0158] Hard carbon (negative electrode active material), acetylene black (nano-scale conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed in a weight ratio of 95:2:2:1, and deionized water was added to obtain a negative electrode slurry. The negative electrode slurry was coated onto one side of a 6 μm thick copper foil. After drying and cold pressing, a negative electrode sheet was obtained. The areal density of the coating on one side of the negative electrode sheet was 0.012 g / cm³. 2 The compaction density of the negative electrode sheet is 0.97 g / cm3.

[0159] (3) Separating membrane

[0160] Porous polyethylene film is used as the separator.

[0161] (4) Preparation of electrolyte

[0162] The organic solvents ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Then, fully dried NaPF6 was dissolved in the above mixed solvent at a ratio of 1 mol / L to obtain the electrolyte.

[0163] (5) Preparation of secondary batteries

[0164] The positive electrode, separator, and negative electrode are prepared in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound, hot-pressed, shaped, and welded to obtain the electrode assembly. The electrode assembly is placed in a square aluminum shell, vacuum-dried, and then injected with electrolyte. It is then left to stand, undergoes formation testing, aging, and capacity testing to finally obtain the battery cell.

[0165] Example 2

[0166] Compared with Example 1, the mass ratio of sodium source to phosphorus source in Example 2 is 0.177, and the molar ratio of sodium element to phosphorus element in phosphate material is 0.985.

[0167] Example 3

[0168] Compared with Example 1, the mass ratio of sodium source to phosphorus source in Example 3 is 0.174, and the molar ratio of sodium element to phosphorus element in phosphate material is 0.97.

[0169] Example 4

[0170] Compared with Example 1, the mass ratio of sodium source to phosphorus source in Example 4 is 0.171, and the molar ratio of sodium element to phosphorus element in phosphate material is 0.95.

[0171] Example 5

[0172] Compared with Example 1, the mass ratio of sodium source to phosphorus source in Example 5 is 0.189, and the molar ratio of sodium element to phosphorus element in phosphate material is 1.05.

[0173] Example 6

[0174] Compared with Example 1, the mass ratio of iron source to phosphorus source in Example 6 is 0.19.

[0175] Example 7

[0176] Compared with Example 1, the mass ratio of iron source to phosphorus source in Example 7 is 0.17.

[0177] Example 8

[0178] Compared to Example 1, in Example 8, the carbon material content is 1.45 wt% based on the total mass of phosphate and carbon materials.

[0179] Example 9

[0180] Compared to Example 1, in Example 9, the mass content of carbon material is 1.4 wt% based on the total mass of phosphate material and carbon material.

[0181] Comparative Example 1

[0182] Compared with Example 1, the mass ratio of sodium source to phosphorus source in Comparative Example 1 was 0.22, and the molar ratio of sodium to phosphorus in the phosphate material was 1.07.

[0183] Comparative Example 2

[0184] Compared with Example 1, the mass ratio of sodium source to phosphorus source in Comparative Example 2 was 0.167, and the molar ratio of sodium to phosphorus in the phosphate material was 0.93.

[0185] The secondary batteries obtained in Examples 1-9 and Comparative Examples 1-2 were subjected to parameter and performance tests. The test results are shown in Table 1 below.

[0186] Table 1: Specific parameters of Examples 1-9 and Comparative Examples 1-2

[0187]

[0188] (1) Methods for measuring the mass content of NFPP and NFPO

[0189] Disassemble the battery cell, remove the positive electrode sheet, place the positive electrode powder in the sample cell, put it into the XRD analyzer, select Cu target, scan range 5°-60°, step size 0.02° / min, and the obtained XRD spectrum is refined by Fullpro to obtain the mass content of NFPP and NFPO in the positive electrode film.

[0190] (2) Test method for discharge final voltage

[0191] Under constant temperature conditions of 25℃, charge at 0.33C to 3.65V at a voltage of 2.0V to 3.65V, then charge at 3.65V at a constant voltage until the current is ≤0.05C, let stand for 5 minutes, then discharge at 0.33C to 0.4C, let stand for 5 minutes, adjust the temperature to -20℃, let stand for 2 hours, then discharge at 4C for 120 seconds, then discharge at 2.33C for 120 seconds, and record the final discharge voltage (in V).

[0192] (3) Methods for testing specific capacity

[0193] Under constant temperature conditions of 25℃, the battery was charged to 3.65V at 0.33C and discharged to 2.0V at 0.33C. The discharge capacity (in mAh) was recorded. The battery cells were disassembled, and the mass of the positive electrode active material in the electrode sheet was weighed and recorded (in g). The specific capacity was calculated using the following formula: Specific capacity (mAh / g) = Discharge capacity (mAh) / Mass of positive electrode active material (g).

[0194] The test results for the above parameters are shown in Table 2.

[0195] Table 2: Test results of Examples 1-9 and Comparative Examples 1-2

[0196]

[0197] Figure 6 These are discharge curves for Examples 1-3 and Comparative Example 1 of this application. Figure 6 As shown, as the molar ratio of sodium to phosphorus decreases, the final discharge voltage increases, which is beneficial to improving the discharge power of the battery cell.

[0198] Based on Examples 1-9 and Comparative Examples 1-2, it can be seen that the specific capacity of the positive electrode film in Examples 1-9 is higher than that in Comparative Examples 1-2, and the final discharge voltage is also higher than that in Comparative Examples 1-2. This indicates that when the molar ratio of sodium to phosphorus is in the range of 0.95 to 1.05, it is beneficial to balance the specific capacity of the positive electrode film and the discharge power of the battery cell.

[0199] As shown in Examples 1-5, with the increase of the molar ratio of sodium to phosphorus, the proportion of NFPO decreases while the proportion of NFPP increases. By controlling the molar ratio of sodium to phosphorus within the range of 0.95 to 1.05, the mass content of NFPP can be controlled within the range of 92.1 wt% to 95.8 wt%, and the mass content of NFPO can be controlled within the range of 0.6 wt% to 4.3 wt%, thereby improving the discharge power and energy density of the battery cell.

[0200] As can be seen from Examples 1 and 6-7, as the mass ratio of iron and phosphorus sources increases, the mass content of NFP also increases, leading to a decrease in specific capacity and discharge final voltage. Therefore, controlling the mass ratio of iron and phosphorus sources within the range of 0.17 to 0.19 is beneficial to improving the specific capacity and discharge power of the battery cells.

[0201] As can be seen from Examples 1 and 8-9, coating the surface of the phosphate material with carbon material is beneficial to improving the conductivity of the positive electrode film, thereby increasing the discharge power of the battery cell.

[0202] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A sodium-ion battery cell, characterized in that, The application relates to a positive electrode sheet, a preparation method of the positive electrode sheet, and a sodium-ion battery cell. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side surface of the positive electrode current collector, wherein the positive electrode film layer comprises a phosphate material, and the phosphate material comprises sodium iron pyrophosphate, sodium ferrous pyrophosphate and sodium ferrous phosphate. The molar ratio A of sodium and phosphorus in the phosphate material satisfies 0.95<=A<=1.

05. The mass content C of the sodium iron pyrophosphate satisfies 92.1wt%<=C<=95.8wt% based on the total mass of the positive electrode film layer, the mass content D of the sodium ferrous pyrophosphate satisfies 0.6wt%<=D<=4.3wt%, and the mass content E of the sodium ferrous phosphate satisfies 0.5wt%<=E<=1.9wt%.

2. The sodium-ion battery cell of claim 1, wherein, 0.97≤A≤1.01。 3. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The mass content ratio F between the sodium iron pyrophosphate and the sodium ferrous pyrophosphate satisfies 21<=F<=142 based on the total mass of the positive electrode film layer.

4. The sodium-ion battery cell according to any one of claims 1 to 3, characterized in that, The phosphate material is at least partially coated with a carbon material.

5. The sodium-ion battery cell of claim 4, wherein, The mass content W of the carbon material satisfies 1.4wt%<=W<=1.6wt% based on the total mass of the phosphate material and the carbon material.

6. A method of producing a sodium-ion battery cell, characterized by, The carbon source, the phosphorus source, the iron source and the sodium source are mixed to obtain intermediate particles, and the intermediate particles are sintered to obtain the phosphate material, wherein the phosphate material comprises sodium iron pyrophosphate and sodium ferrous pyrophosphate, the mass content ratio of the sodium source to the phosphorus source is 0.17-0.2, and the phosphate material is used to prepare the positive electrode sheet to prepare the sodium-ion battery cell. The mass content ratio of the iron source to the phosphorus source is 0.17-0.

19.

7. The method of claim 6, wherein, The mixing of the carbon source, the phosphorus source and the iron source comprises the following steps: the carbon source, the phosphorus source and the iron source are mixed to obtain a first slurry, the first slurry is spray-dried to obtain a spray precursor, and the spray precursor is mixed with the sodium source to obtain the intermediate particles.

8. The method of claim 6, wherein, The solid content of the first slurry is 30%-40%.

9. The method of claim 8, wherein, The rotating speed v of the mixing of the carbon source, the phosphorus source and the iron source satisfies 10r / min<=v<=100r / min, and the rotating speed v of the mixing of the carbon source, the phosphorus source and the iron source optionally satisfies 40r / min<=v<=60r / min. The mixing time t1 of the carbon source, the phosphorus source and the iron source satisfies 1h<=t1<=10h. The inlet air temperature T1 of the spray-drying of the first slurry satisfies 180℃<=T1<=220℃. The outlet air temperature T2 of the spray-drying of the first slurry satisfies 80℃<=T2<=120℃. The sintering of the intermediate particles comprises the following steps: the intermediate particles are sintered at a first temperature T3 for a first time t2, and then the intermediate particles are sintered at a second temperature T4 for a second time t3, wherein the first temperature T3 is 300-400℃, the first time t2 is 5-10h, the second temperature T4 is 500-600℃, and the second time t3 is 5-15h.

10. The method according to any one of claims 6 to 9, characterized in that, The carbon source comprises at least one of glucose, polyethylene glycol, sucrose, urea and polyvinyl alcohol.

11. The method according to any one of claims 6 to 10, characterized in that, The sodium source comprises at least one of sodium carbonate, sodium hydroxide, sodium acetate and sodium nitrate. ​ The phosphorus source includes at least one of ferric phosphate, disodium hydrogen phosphate, phosphoric acid, sodium pyrophosphate; The iron source includes at least one of ferrous sulfate, ferric nitrate, ferrous sulfate, ferric phosphate.

12. A battery device characterized by comprising: A sodium-ion battery cell comprising the sodium-ion battery cell as claimed in any one of claims 1-5, and / or a sodium-ion battery cell prepared by the method as claimed in any one of claims 6-11.

13. An electrical device, characterized by A battery device comprising the battery device as claimed in claim 12.

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