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 battery monomer comprises a positive pole piece, the positive pole piece comprises a positive active material, the positive active material comprises a phosphate material and a carbon material, and the phosphate material comprises ferric sodium pyrophosphate; at least part of the surface of the phosphate material is coated with the carbon material, the graphitization degree R of the carbon material is larger than or equal to 0.8 and smaller than or equal to 1.1, R is equal to IG / ID, IG is the maximum wave crest intensity within the range of 1480 cm <-1 >-1680 cm <-1 > in a Raman spectrum of the positive electrode active material and is the intensity of a G peak, and ID is the maximum wave crest intensity within the range of 1250 cm <-1 >-1450 cm <-1 > in the Raman spectrum of the positive electrode active material and is the intensity of a D peak; the molar ratio of the sodium element to the iron element in the phosphate material is 1.33-1.45. According to the technical scheme, the low-temperature performance and the discharge rate of the sodium-ion battery can be improved.

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, improving the low-temperature performance and discharge rate of sodium-ion batteries is a pressing technical challenge. 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 a high discharge rate to improve the low-temperature 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 comprising a positive electrode active material, the positive electrode active material comprising a phosphate material and a carbon material, the phosphate material comprising sodium iron pyrophosphate; the carbon material coating at least a portion of the surface of the phosphate material, the degree of graphitization R of the carbon material satisfying: 0.8 ≤ R ≤ 1.1, where R = I G / I D I G The Raman spectrum of the positive electrode active material at 1480 cm⁻¹ -1 ~1680cm -1 The maximum peak intensity within the range is the intensity of peak G, I D The Raman spectrum of the positive electrode active material at 1250 cm⁻¹ -1 ~1450cm -1 The maximum peak intensity within the range is the intensity of peak D; the molar ratio of sodium to iron in the phosphate material is 1.33 to 1.45.

[0008] In this embodiment, the positive electrode film layer includes a phosphate material and a carbon material, wherein the phosphate material includes sodium iron pyrophosphate. The carbon material coats at least a portion of the surface of the phosphate material, which is beneficial for improving the surface conductivity of the phosphate material and promoting sodium ion migration. When the graphitization degree of the carbon material is greater than or equal to 0.8, the increased graphitization degree helps reduce charge transfer impedance, improves the electronic conductivity of the positive electrode, and thus reduces the initial voltage drop of the battery cell. When the graphitization degree of the carbon material is less than or equal to 1.1, it helps maintain the openness of the sodium ion diffusion channels, improves sodium ion transport efficiency, and thus improves the rate performance of the battery cell. Meanwhile, when the molar ratio of sodium to iron in phosphate materials is less than 1.33, the number of sodium ion transport channels is insufficient, the effective carrier concentration is reduced, and the inactive phase sodium ferrous pyrophosphate is easily formed, which restricts ion diffusion kinetics. On the other hand, when the molar ratio of sodium to iron is greater than 1.45, iron vacancies or lattice distortion are likely to occur, which will disrupt the periodic arrangement of the crystal and hinder the continuity of the sodium ion migration path. At the same time, the impurity phase sodium ferrous phosphate may be introduced, which will reduce the ionic conductivity. Therefore, controlling the molar ratio of sodium to iron within the above range is beneficial to further improve the conductivity of the positive electrode active material and increase the low-temperature discharge power of the battery cell.

[0009] In one possible implementation, 0.85 ≤ R ≤ 0.95.

[0010] In the embodiments of this application, when the graphitization degree of the carbon material is 0.85 to 0.95, the electronic conductivity of the positive electrode active material and the sodium ion diffusion efficiency can be balanced, thereby improving the rate performance and low-temperature performance of the sodium ion battery cell.

[0011] In one possible implementation, based on the total mass of the positive electrode active material, the mass content ratio A between phosphate material and carbon material satisfies: 49 ≤ A ≤ 70.

[0012] In this embodiment, the mass content of carbon material is controlled within the above-mentioned range. On the one hand, this can effectively improve the electronic conductivity of the positive electrode active material. On the other hand, it can avoid the content of the positive electrode active material being reduced due to excessive carbon material content. Thus, while improving the cycle stability of the battery cell, the energy density of the battery cell is guaranteed.

[0013] In one possible implementation, the carbon material includes at least one of glucose, sucrose, polyethylene glycol, polyacrylonitrile, and cellulose.

[0014] In this embodiment, selecting the above-mentioned types of carbon materials can improve the electronic conductivity of the positive electrode active material, which is beneficial to improving the cycle stability of the battery cell.

[0015] In one possible implementation, based on the total mass of the phosphate material, the mass percentage of sodium iron pyrophosphate is 98 wt% to 98.6 wt%.

[0016] In the embodiments of this application, the mass ratio of sodium iron pyrophosphate in the phosphate material is within the above range, which can improve the specific capacity of the positive electrode active material and increase the energy density of the battery cell.

[0017] In one possible implementation, the phosphate-based material also includes sodium ferrous pyrophosphate; the mass ratio of sodium ferric pyrophosphate to sodium ferrous pyrophosphate is 39–99 based on the total mass of the phosphate-based material.

[0018] In this embodiment, the proportion of sodium ferrous pyrophosphate in the phase composition design of the cathode phosphate material affects the polarization process of the cathode surface reaction and the stability of the material structure. By controlling the proportion of the heterogeneous phase sodium ferrous pyrophosphate in the phosphate material, the diffusion ability of sodium ions from the interior to the surface of the phosphate material is significantly improved, thereby reducing charge transfer impedance and improving the power performance and early cycle performance of sodium-ion battery cells.

[0019] In one possible implementation, the compaction density ρ of the positive electrode sheet satisfies: 1.9 g / cm³ 3 ≤ρ≤2.3g / cm 3 .

[0020] 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, wherein the mass ratio of sodium source to iron source is 0.25–0.27 based on the total mass of the intermediate particles; performing initial sintering on the intermediate particles followed by heated sintering, wherein the initial sintering temperature T1 is 300℃–400℃ and the initial sintering time t1 is 5h–10h; and the heated sintering temperature T2 is 500℃–550℃ and the heated sintering time t2 is 5h–15h to obtain a positive electrode active material, wherein the positive electrode active material includes a phosphate material and a carbon material, wherein the phosphate material includes sodium iron pyrophosphate, and the carbon material coats at least a portion of the surface of the phosphate material, wherein the degree of graphitization R of the carbon material satisfies: 0.8 ≤ R ≤ 1.1, where R = I. G / I D I G The Raman spectrum of the positive electrode active material at 1480 cm⁻¹ -1 ~1680cm -1 The maximum peak intensity within the range is the intensity of peak G, I D The Raman spectrum of the positive electrode active material at 1250 cm⁻¹ -1 ~1450cm -1The maximum peak intensity within the range is the intensity of peak D; positive electrode sheets are prepared using positive electrode active materials to prepare sodium-ion battery cells.

[0021] In this embodiment, the initial sintering temperature is relatively low, which helps maintain the phase composition of the phosphate material, ensuring that the proportions of sodium iron pyrophosphate and sodium ferrous pyrophosphate phases in the phosphate material are within a suitable range, thereby improving the energy density and power performance of the battery cell. Heating up the sintering temperature can increase the graphitization degree of the carbon material, improve the electronic conductivity of the positive electrode active material, and enhance the low-temperature discharge power of the battery cell. Using a segmented sintering method can balance the phase composition of the phosphate material and the graphitization degree of the carbon material, improving the low-temperature initial voltage drop of the battery cell. Simultaneously, controlling the mass ratio of sodium and iron sources allows for the regulation of the molar ratio of sodium and iron elements in the phosphate material within a suitable range, which is beneficial for improving sodium ion transport efficiency and further enhancing the discharge performance of the battery cell.

[0022] In one possible implementation, the mass content of the carbon source is 1.4 wt% to 2 wt%, based on the total mass of the carbon source, phosphorus source, iron source and sodium source.

[0023] In this embodiment, by controlling the mass content ratio of the carbon source, the mass ratio of phosphate material to carbon material in the generated positive electrode active material can be controlled. When the mass content ratio of the carbon source is within the above-mentioned range, it is beneficial to balance the electronic conductivity and sodium ion transport efficiency of the positive electrode active material, thereby improving the discharge performance of the battery cell.

[0024] In one possible implementation, the intermediate particles are obtained by mixing carbon source, phosphorus source, iron source and sodium source, including: mixing phosphorus source, iron source and carbon 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.

[0025] In this embodiment, carbon, phosphorus, and iron sources are first mixed to obtain a spray precursor forming a sodium-free framework, which avoids Na volatilization or excessive generation of the byproduct sodium ferrous phosphate during the high-temperature stage. Then, a sodium source is mixed in to complete solid-phase diffusion at a lower temperature, reducing Na loss and suppressing excessive Fe ion oxidation. This facilitates control over the proportion of each phase in the phosphate material, thereby improving the energy density and fast-charging performance of the battery cell.

[0026] In one possible implementation, the solid content of the first slurry is 30% to 40%.

[0027] In one possible implementation, the rotational speed v at which the carbon source, phosphorus source and iron source are mixed satisfies: 10 r / min ≤ v ≤ 100 r / min, and optionally, 40 r / min ≤ v ≤ 60 r / min.

[0028] In one possible implementation, the time t3 for mixing the carbon source, phosphorus source and iron source satisfies: 1h≤t3≤10h.

[0029] In one possible implementation, the inlet air temperature T3 for spray drying of the first slurry satisfies 180℃≤T3≤220℃; and the outlet air temperature T4 for spray drying of the first slurry satisfies 80℃≤T4≤120℃.

[0030] In one possible implementation, the sintering atmosphere is argon or nitrogen.

[0031] 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 phosphoric acid, sodium pyrophosphate, and disodium hydrogen phosphate; and the iron source includes at least one of ferrous sulfate, ferric nitrate, ferrous sulfate, and ferric phosphate.

[0032] Thirdly, a battery device is provided, comprising a battery cell according to the first aspect and any possible implementation thereof, and / or comprising a battery cell prepared according to the second aspect and any possible implementation thereof. The battery device includes at least one of a battery module and a battery pack.

[0033] Fourthly, an electrical device is provided, including the battery device of the third aspect. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application.

[0035] Figure 2 This is a schematic diagram of a battery cell preparation method according to an embodiment of this application.

[0036] Figure 3 This is a schematic diagram of the structure of a secondary battery according to an embodiment of this application.

[0037] Figure 4 This is a schematic diagram of the structure of a battery device according to an embodiment of this application.

[0038] Figure 5 This is a schematic diagram of an electrical device according to an embodiment of this application.

[0039] Figure 6 This is a discharge curve diagram of an embodiment of this application.

[0040] 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

[0041] 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.

[0042] 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.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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 low-temperature 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.

[0051] In related technologies, carbon materials are coated onto the surface of sodium ferric pyrophosphate to improve surface conductivity and promote the migration of sodium ions. However, due to the low synthesis temperature of sodium ferric pyrophosphate, the synthesized carbon materials have a low degree of graphitization and poor electronic conductivity.

[0052] 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 comprising a positive electrode active material, the positive electrode active material comprising a phosphate material and a carbon material, the phosphate material comprising sodium iron pyrophosphate; the carbon material coating at least a portion of the surface of the phosphate material, the degree of graphitization R of the carbon material satisfying: 0.8 ≤ R ≤ 1.1, where R = 1 G / I D I G The Raman spectrum of the positive electrode active material at 1480 cm⁻¹ -1 ~1680cm -1 The maximum peak intensity within the range is the intensity of peak G, I D The Raman spectrum of the positive electrode active material at 1250 cm⁻¹ -1 ~1450cm -1 The maximum peak intensity within the range is the intensity of peak D; the molar ratio of sodium to iron in the phosphate material is 1.33 to 1.45.

[0053] In this application, by adjusting the graphitization degree of the carbon material in the phosphate coating layer, the electron transfer rate on the phosphate material surface can be accelerated, the electronic conductivity of the phosphate material surface can be improved, the charge transfer impedance can be reduced, and the polarization and voltage drop at the low-temperature discharge first point of the phosphate material can be further reduced, thereby improving the discharge capability of the positive electrode active material. Simultaneously, since both the graphitization degree of the carbon material and the phase composition of the phosphate material are affected by the sintering temperature, it is necessary to control the graphitization degree of the carbon material within a certain range to maintain a balance between the specific capacity and electronic conductivity of the positive electrode active material. When the graphitization degree of the carbon material is less than 0.8, the electronic conductivity of the carbon material is poor, which is not conducive to improving the conductivity of the positive electrode active material; when the graphitization degree of the carbon material is greater than or equal to 1.1, impurity phases are easily generated, leading to a decrease in the mass proportion of the sodium iron pyrophosphate phase and a reduction in the specific capacity of the positive electrode active material. Therefore, a graphitization degree within the range of 0.8 to 1.1 is beneficial for balancing the specific capacity and electronic conductivity of the positive electrode active material, reducing the low-temperature first-point voltage drop, and improving the energy density of the battery cell. On the other hand, by controlling the molar ratio of sodium and iron within the above range, it is beneficial to maintain the openness of sodium ion diffusion channels, improve sodium ion transport efficiency, further enhance the conductivity of the positive electrode active material, and improve low-temperature discharge performance.

[0054] Next, the sodium-ion battery cell and its components provided in this application will be described.

[0055] Sodium-ion battery cell

[0056] In one embodiment of this application, a sodium-ion battery cell is provided, including a positive electrode.

[0057] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet according to an embodiment of this application.

[0058] 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.

[0059] 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.

[0060] The positive electrode film layer 11 includes a positive electrode active material, which includes a phosphate material;

[0061] Phosphate materials include sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7, NFPP).

[0062] NFPP is one of the commonly used phosphate cathode active materials in sodium-ion batteries. However, it has poor intrinsic conductivity and is prone to generating inactive impurity phases such as sodium ferrous phosphate (NaFePO4, NFP) and sodium ferrous pyrophosphate (Na2FeP2O7, NFPO). The NFP phase is an impurity phase that can limit the actual electrochemical performance of the NFPP phase, while the NFPO phase is an inactive phase that can limit ion diffusion.

[0063] In some embodiments, the positive electrode active material further includes a carbon material coated on at least a portion of the surface of the phosphate material, wherein the degree of graphitization R of the carbon material satisfies: 0.8 ≤ R ≤ 1.1, where R = 1. G / I D I G The Raman spectrum of the positive electrode active material at 1480 cm⁻¹ -1 ~1680cm -1 The maximum peak intensity within the range is the intensity of peak G, I D The Raman spectrum of the positive electrode active material at 1250 cm⁻¹ -1 ~1450cm -1 The maximum peak intensity within the range is the intensity of peak D.

[0064] The degree of graphitization, R, of carbon materials can be measured using a laser confocal Raman spectroscopy (LCS). By disassembling a single battery cell and obtaining the positive electrode active material from the surface of the positive electrode sheet, a laser wavelength of 532 nm is selected, and the degree of graphitization, R, is obtained as I under the surface scanning mode of the LCS.G / I D , where I G This indicates that the Raman spectrum is at 1480 cm⁻¹ -1 ~1580cm -1 The intensity of peak G at I D This indicates that the Raman spectrum is at 1250 cm⁻¹ -1 ~1450cm -1 The intensity of the D peak at that location. A higher R value indicates a higher degree of graphitization in the carbon material, and a higher concentration of sp in the carbon material. 2 The higher the proportion of hybrid carbon, the more π electrons are delocalized, which is conducive to the formation of a more complete conductive network and significantly reduces the charge transfer impedance at the interface between the electrode and the electrolyte; the lower the corresponding R value, the lower the degree of graphitization of the carbon material.

[0065] Specifically, in the embodiments of this application, the degree of graphitization of the carbon material can be 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1 or any value within the above range.

[0066] In some embodiments, the degree of graphitization R of the carbon material satisfies: 0.85≤R≤0.95.

[0067] Specifically, the degree of graphitization R of the carbon material can be 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95 or any value within the above range.

[0068] The positive electrode active material includes phosphate materials, among which NFPP has a high specific capacity, which is beneficial to improving the energy density of the battery cell. Simultaneously, coating the surface of the phosphate material with carbon material can improve the conductivity of the positive electrode active material. By controlling the graphitization degree R-value of the carbon material to be greater than or equal to 0.8, it is beneficial to further improve the electronic conductivity of the positive electrode active material, reduce the initial voltage drop of the battery cell, and improve the discharge power of the battery cell at low temperatures. At the same time, controlling the graphitization degree R-value of the carbon material to be less than or equal to 1.1 can ensure that the phase composition of the phosphate material in the positive electrode active material is within a suitable range, avoiding excessively low NFPP content or the generation of excessive byproducts such as NFPO and NFP, thereby improving the energy density of the battery cell.

[0069] When the graphitization degree R of carbon materials is in the range of 0.85 to 0.95, it is also beneficial to further improve the discharge power and energy density of battery cells.

[0070] In some embodiments, the molar ratio of sodium to iron in the phosphate material is 1.33 to 1.45.

[0071] Specifically, the molar ratio of sodium to iron in phosphate materials can be 1.33, 1.34, 1.35, 1.36, 1.37, 1.38, 1.39, 1.40, 1.41, 1.42, 1.43, 1.44, 1.45, or any value within the above range.

[0072] When the molar ratio of sodium to iron in phosphate materials is less than 1.33, the sodium content is too low, resulting in insufficient sodium ion transport channels and a tendency to form the inactive phase NFPO, which is detrimental to sodium ion diffusion. Conversely, when the molar ratio is greater than 1.45, the iron content is too low, easily leading to iron vacancies or lattice distortion in the phosphate material, hindering sodium ion migration, and also easily introducing the impurity phase NFP, reducing the conductivity of the positive electrode active material. Therefore, by improving the graphitization degree of the carbon coating layer and controlling the molar ratio of sodium to iron in the phosphate material within the range of 1.33–1.45, it is beneficial to further improve the low-temperature discharge performance of sodium-ion battery cells.

[0073] In some embodiments, based on the total mass of the positive electrode active material, the mass content ratio A between the phosphate material and the carbon material satisfies: 49 ≤ A ≤ 70.

[0074] The mass content ratio A between phosphate materials and carbon materials can be 49, 52, 55, 57, 60, 62, 65, 67, 70 or any value within the above range.

[0075] When the mass ratio of phosphate material to carbon material is greater than or equal to 49, the excessive carbon material content can be avoided, which would reduce the content of positive electrode active material. This ensures the energy density of the battery cell while improving its cycle stability. When the mass ratio of phosphate material to carbon material is less than or equal to 70, the electronic conductivity of the positive electrode active material can be effectively improved, thereby improving the discharge power of the battery cell.

[0076] In some embodiments, the carbon material includes at least one of glucose, sucrose, polyethylene glycol, polyacrylonitrile, and cellulose.

[0077] The above-mentioned materials are all beneficial to improving the conductivity of positive electrode active materials and improving the electronic conductivity of phosphate materials.

[0078] In some embodiments, based on the total mass of phosphate materials, the mass content B of NFPP satisfies: 98wt% ≤ B ≤ 98.6wt%.

[0079] Specifically, the mass content B of NFPP can be 98wt%, 98.1wt%, 98.2wt%, 98.3wt%, 98.4wt%, 98.5wt%, 98.6wt%, or any value within the above range.

[0080] Within the above-mentioned range, the mass content of NFPP is beneficial to control the proportion of NFPP, NFPO and NFP phases in phosphate materials, thereby improving the power performance of the battery cell and taking into account the high energy density of the battery cell.

[0081] In some embodiments, the phosphate material further includes NFPO; based on the total mass of the phosphate material, the mass ratio of NFPP to NFPO is 39 to 99.

[0082] The mass content ratio of NFPP to NFPO can be measured as follows: Disassemble the battery cell, remove the positive electrode sheet, place the positive electrode active material powder in the sample cell, put it in an XRD analyzer, select the Cu target, the scanning range is 5-60°, the step size is 0.02° / min, and the obtained XRD spectrum is refined by Fullprof to obtain the mass content ratio of NFPP phase and NFPO phase in the phosphate material.

[0083] Specifically, the mass ratio of NFPP to NFPO can be 39, 42, 45, 50, 56, 60, 65, 70, 75, 80, 85, 90, 95, 99 or any value within the above range.

[0084] The NFPO phase significantly enhances the diffusion ability of sodium ions from the interior to the surface of phosphate materials, thereby reducing charge transfer resistance. By maintaining the mass ratio of NFPO to NFPP in the phosphate material within the above range, it is beneficial to improve the power performance and cycle performance of sodium-ion battery cells.

[0085] In some embodiments, the compaction density ρ of the positive electrode sheet satisfies: 1.9 g / cm³ 3 ≤ρ≤2.3g / cm 3 .

[0086] Specifically, the compaction density ρ of the positive electrode sheet can be 1.9 g / cm³. 3 2.0g / cm 3 2.05g / cm 3 2.1g / cm 3 2.15g / cm 3 2.2g / cm 3 2.25g / cm 3 2.3g / cm 3 Or any value within the above range.

[0087] [Preparation methods for battery cells]

[0088] 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:

[0089] S21, intermediate particles are obtained by mixing carbon source, phosphorus source, iron source and sodium source. Based on the total mass of the intermediate particles, the mass content ratio of sodium source to iron source is 0.25 to 0.27.

[0090] S22, after the initial sintering of the intermediate particles, a heating sintering is performed. The initial sintering temperature T1 is 300-400℃, the initial sintering time t1 is 5-10h, the heating sintering temperature T2 is 500-550℃, and the heating sintering time t2 is 5-15h, so as to obtain the positive electrode active material.

[0091] S23, using positive electrode active materials to prepare positive electrode sheets in order to prepare sodium-ion battery cells.

[0092] The positive electrode active material obtained in S21 includes a phosphate material and a carbon material. The phosphate material includes sodium iron pyrophosphate, and the carbon material coats at least a portion of the surface of the phosphate material. The degree of graphitization R of the carbon material satisfies: 0.8 ≤ R ≤ 1.1, where R = 1. G / I D I G The Raman spectrum of the positive electrode active material at 1480 cm⁻¹ -1 ~1680cm -1 The maximum peak intensity within the range is the intensity of peak G, I D The 1250 cm⁻¹ value in the Raman spectrum of the positive electrode active material -1 ~1450cm -1 The maximum peak intensity within the range is the intensity of peak D.

[0093] Therefore, by adopting a segmented sintering method, the phase composition of the phosphate material can be controlled to avoid the formation of impurity phases due to excessively high temperatures, thereby maintaining the specific capacity of the positive electrode active material and improving the energy density of the battery cell. At the same time, the high temperature during the heating sintering process can increase the graphitization degree of the coating carbon material, thereby improving the problem of insufficient electronic conductivity of the phosphate material, increasing the discharge power of the battery cell, and improving low-temperature performance.

[0094] In some embodiments, the mass content of the carbon source is 1.4 wt% to 2 wt% based on the total mass of the carbon source, phosphorus source, iron source and sodium source.

[0095] Specifically, the mass content of the carbon source can be 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, or any value within the above range.

[0096] Therefore, controlling the mass content of the carbon source can regulate the mass ratio of carbon materials to phosphate materials in the cathode active material. When the mass content of the carbon source is within the aforementioned range, it is beneficial to improve the electronic conductivity of the cathode active material, while also considering the energy density and discharge power of the battery cell.

[0097] 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.

[0098] In some embodiments, the solid content of the first slurry is 30% to 40%.

[0099] In some embodiments, the rotational speed v at which the carbon source, phosphorus source and iron source are mixed satisfies: 10 r / min ≤ v ≤ 100 r / min, and optionally, 40 r / min ≤ v ≤ 60 r / min.

[0100] In some embodiments, the mixing time t3 of the carbon source, phosphorus source and iron source satisfies: 1h≤t3≤10h.

[0101] In some embodiments, the inlet air temperature T3 for spray drying of the first slurry satisfies 180℃≤T3≤220℃; the outlet air temperature T4 for spray drying of the first slurry satisfies 80℃≤T4≤120℃.

[0102] In some embodiments, the sintering atmosphere is argon or nitrogen.

[0103] 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 phosphoric acid, sodium pyrophosphate, and disodium hydrogen phosphate; and the iron source includes at least one of ferrous sulfate, ferric nitrate, ferrous sulfate, and ferric phosphate.

[0104] [Positive electrode plate]

[0105] 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.

[0106] 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.

[0107] 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.).

[0108] In some embodiments, the positive electrode active material comprises a phosphate material, wherein the phosphate material comprises NFPP, and a carbon material is coated on at least a portion of the surface of the phosphate material, wherein the degree of graphitization R of the carbon material satisfies: 0.8 ≤ R ≤ 1.1, where R = 1. G / I D I G The Raman spectrum of the positive electrode active material at 1480 cm⁻¹ -1 ~1680cm -1 The maximum peak intensity within the range is the intensity of peak G, I D The Raman spectrum of the positive electrode active material at 1250 cm⁻¹ -1 ~1450cm -1 The maximum peak intensity within the range is the intensity of peak D; the molar ratio of sodium to iron in the phosphate material is 1.33 to 1.45.

[0109] 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。

[0110] 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).

[0111] 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, where 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, and 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.

[0112] As an optional technical solution of the present application, the polyanionic compound may be Na x R 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.

[0113] 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.

[0114] The Prussian blue compound may be a type of compound 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.

[0115] 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.

[0116] In some embodiments, the sodium-containing layered oxide is an iron-manganese layered oxide, specifically including at least one of nickel-iron-manganese layered oxide and copper-iron-manganese layered oxide.

[0117] During the charging and discharging process, the battery will produce active ions (Na+). + The molar content of sodium varies depending on the insertion / extraction and consumption of sodium (Na) as it is discharged to different states. In the examples of positive electrode active materials in this application, the molar content of Na refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar content of Na changes after charge-discharge cycles.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] [Negative electrode plate]

[0122] 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.

[0123] 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.).

[0124] 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.

[0125] 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).

[0126] 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.

[0127] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0128] 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.

[0129] [Electrolytes]

[0130] 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.

[0131] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] [Isolation membrane]

[0136] 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.

[0137] 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.

[0138] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0139] [Battery cell]

[0140] In some embodiments, the secondary battery is a single battery cell, which can be the smallest structural unit of the battery.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] [Battery Device]

[0150] 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 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.

[0151] It should be understood that, such as Figure 4 As 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.

[0152] 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.

[0153] 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.

[0154] [Electrical appliances]

[0155] This application provides an electrical device including the battery device described in the above embodiments.

[0156] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use battery devices.

[0157] 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.

[0158] For ease of explanation, the following embodiments use a vehicle as an example of electrical equipment.

[0159] 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.

[0160] 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.

[0161] Example 1

[0162] (1) Preparation of positive electrode sheet

[0163] A first slurry was prepared by mixing glucose (carbon source), sodium pyrophosphate (phosphorus source), and ferrous sulfate heptahydrate (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 was 500 rpm, and the mixing time was 4 hours. The first slurry was then sprayed in a spray drying tower with an inlet air temperature of 200℃ and an outlet air temperature 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 T1 was 300℃, and the initial sintering time t1 was 10 hours. Subsequent sintering was carried out at a higher temperature T2 of 510℃ for 6 hours. The sintering atmosphere was nitrogen. After sintering, the positive electrode active material was obtained. The positive electrode active material includes phosphate material and carbon material. The phosphate material includes NFPP. The carbon material is coated on at least part of the surface of the phosphate material, and the degree of graphitization R of the carbon material is 0.872. The mass content of NFPP in the phosphate material is 98.5%. The mass proportion of carbon source in the intermediate particles is 1.6%. The mass ratio of sodium source to iron source is 0.257. The molar ratio of Na to Fe in the phosphate material is 1.35. Based on the total mass of the positive electrode active material, the mass content ratio of phosphate material to carbon material is 61.5.

[0164] 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 2.2 g / cm³. 3 The positive electrode sheet.

[0165] (2) Preparation of negative electrode sheet

[0166] 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. 3 .

[0167] (3) Separating membrane

[0168] Porous polyethylene film is used as the separator.

[0169] (4) Preparation of electrolyte

[0170] 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.

[0171] (5) Preparation of secondary batteries

[0172] 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.

[0173] Example 2

[0174] Compared with Example 1, the heating and sintering time in Example 2 was 8 hours, resulting in a graphitization degree R of 0.893 for the carbon material and an NFPP mass content of 98.2 wt% in the phosphate material.

[0175] Example 3

[0176] Compared with Example 1, the heating and sintering time in Example 3 was 10 hours, resulting in a graphitization degree R of 0.91 for the carbon material and an NFPP mass content of 98.1 wt% in the phosphate material.

[0177] Example 4

[0178] Compared with Example 1, the heating and sintering time in Example 4 was 5 hours, resulting in a graphitization degree R of 0.85 for the carbon material and an NFPP mass content of 98.6 wt% in the phosphate material.

[0179] Example 5

[0180] Compared with Example 1, the sintering temperature in Example 5 was 530°C, resulting in a graphitization degree R of 1.1 for the carbon material and an NFPP content of 98.0 wt% in the phosphate material.

[0181] Example 6

[0182] Compared with Example 1, the mass ratio of sodium source to iron source in Example 6 was 0.27, the molar ratio of Na to Fe in the phosphate material was 1.45, and the mass content of NFPP in the phosphate material was 98.5 wt%.

[0183] Example 7

[0184] Compared with Example 1, the mass ratio of sodium source to iron source in Example 7 was 0.25, the molar ratio of Na to Fe in the phosphate material was 1.33, and the mass content of NFPP in the phosphate material was 98.1 wt%.

[0185] Example 8

[0186] Compared with Example 1, the carbon source in the intermediate particles of Example 8 accounts for 1.4 wt% by mass; based on the total mass of the positive electrode active material, the mass content of phosphate material to the mass content of carbon material is 70.

[0187] Example 9

[0188] Compared with Example 1, the carbon source in the intermediate particles of Example 9 accounts for 2.0 wt% by mass; based on the total mass of the positive electrode active material, the mass content of phosphate material to the mass content of carbon material is 49.

[0189] Comparative Example 1

[0190] Compared to Example 1, Comparative Example 1 did not employ a segmented sintering method. Instead, the sprayed precursor and sodium source Na2CO3 were mixed at a mass ratio of 9:50 to obtain intermediate particles. These intermediate particles were then sintered in a kiln at a temperature of 510°C for 6 hours. The sintering atmosphere was nitrogen.

[0191] Comparative Example 2

[0192] Compared with Example 1, in Comparative Example 2, the heating and sintering temperature was 560°C and the heating and sintering time was 8h, resulting in a graphitization degree R of 1.15 for the carbon material and a NFPP mass content of 97.2wt% in the phosphate material.

[0193] Comparative Example 3

[0194] Compared with Example 1, the mass ratio of sodium source to iron source in Comparative Example 3 was 0.24, and the molar ratio of Na to Fe in the phosphate material was 1.31.

[0195] Comparative Example 4

[0196] Compared with Example 1, the mass ratio of sodium source to iron source in Comparative Example 4 was 0.28, and the molar ratio of Na to Fe in the phosphate material was 1.47.

[0197] Comparative Example 5

[0198] Compared with Example 1, the carbon source in the intermediate particles of Comparative Example 5 accounted for 2.2 wt% of the total mass of the positive electrode active material; the mass content of phosphate material to carbon material was 45 based on the total mass of the positive electrode active material.

[0199] Comparative Example 6

[0200] Compared with Example 1, the carbon source in the intermediate particles of Comparative Example 6 accounted for 1.35 wt%; based on the total mass of the positive electrode active material, the mass content of phosphate material to the mass content of carbon material was 75.

[0201] The secondary batteries obtained in Examples 1-9 and Comparative Examples 1-6 were subjected to parameter and performance tests.

[0202] (1) Method for testing gram capacity

[0203] Under constant temperature conditions of 25℃, the voltage was charged at 0.33C to 3.65V within the range of 2.0 to 3.65V. Then, it was charged at a constant voltage of 3.65V until the current was ≤0.05C. After resting for 5 minutes, it was discharged at 0.33C to 2.0V, and the discharge capacity was recorded.

[0204] (2) Graphitization degree test method

[0205] Disassemble the battery cell, remove the positive electrode sheet, and obtain the positive electrode film powder on the surface; obtain the graphitization degree R value of the powder in laser microscopy confocal Raman spectroscopy surface scanning mode, where R value is I. G / I D A laser wavelength of 532nm was selected, where I G This indicates that the Raman spectrum is at 1580±100 cm⁻¹ -1 The intensity of peak G at I D This indicates that the Raman spectrum is at 1350±100 cm⁻¹ -1 The intensity of peak D at that location.

[0206] (3) Method for measuring the composition of positive electrode active materials

[0207] X-ray diffraction (XRD) was used to analyze the composition of the positive electrode active material. Specifically, the crystal structure of the sample was characterized using an XRD diffractometer (Rigaku Ultima IV). The testing range was 2θ = 5°–80°. Fourier transform infrared spectroscopy (Nicoleti S50) was used to analyze the molecular structure and chemical composition of the sample. Raman spectroscopy (LabRAM HR Evolution) was used to analyze the physical properties of the sample, with an excitation wavelength of 532 nm. X-ray photoelectron spectroscopy (VGEscalab250xi) was used to analyze the chemical valence states of the elements on the sample surface. Scanning electron microscopy (FEI-Nova NanoSEM230) and transmission electron microscopy (FEI Titan G260–300) were used to observe the morphology and microstructure of the sample. Thermogravimetric analysis (Thermogravimetric analysis) was used to analyze the thermal stability and carbon content of the sample.

[0208] (4) Method for testing discharge power

[0209] Under constant temperature conditions of 25℃, charge at 0.33C to 3.65V within the range of 2.25 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 0.4C0, let stand for 5 minutes, adjust the temperature to -20℃, let stand for 2 hours, and then discharge at 1.33C for 1200 seconds. Record the final discharge voltage (in V).

[0210] (5) Test method for initial voltage drop

[0211] Under constant temperature of 25℃, charge at 0.33C to 3.65V, then charge at 3.65V at constant voltage until the current is less than or equal to 0.05C, let stand for 5 minutes, then discharge at 0.33C to 0.4C0, let stand for 5 minutes, adjust the temperature to -20℃, let stand for 2 hours, then discharge at 1.33C for 20 minutes, and record the voltage drop at the first point of discharge in V.

[0212] The specific parameters and test results are shown in Table 1-2.

[0213] Table 1: Specific parameters and test results of Examples 1-7 and Comparative Examples 1-4

[0214]

[0215] Table 2: Specific parameters and test results of Examples 1, 8-9, and Comparative Examples 5-6

[0216]

[0217] Figure 6 These are discharge curves for Examples 1-3 and Comparative Example 1 of this application. Figure 6 As shown, segmented sintering can improve the graphitization degree of the carbon coating layer, which is beneficial to improving the low-temperature discharge power.

[0218] As shown in Examples 1-7 and Comparative Example 1, the segmented sintering method is beneficial to improve the graphitization degree of the carbon coating layer and control the mass content of NFPP within a suitable range. This can balance the specific capacity and first-point voltage drop of the positive electrode active material and improve the low-temperature discharge power.

[0219] As shown in Examples 1-5 and Comparative Example 2, with the extension of heating and sintering time, the degree of graphitization of the carbon coating layer increases, but the content of NFPP decreases. Similarly, with the increase of heating and sintering temperature, the degree of graphitization also increases, while the mass content of NFPP decreases. Therefore, it is necessary to control the heating and sintering time and sintering temperature within a suitable range to balance the initial voltage drop and specific capacity, thereby improving the discharge performance of the battery cell.

[0220] As shown in Examples 1, 6-7 and Comparative Examples 3-4, adjusting the molar ratio of Na to Fe in the phosphate material within a suitable range is beneficial to further reduce the initial voltage drop and improve the discharge power.

[0221] As shown in Examples 1-9 and Comparative Examples 5-6, as the mass ratio of carbon material increases, the initial voltage drop decreases and the specific capacity also decreases. Therefore, it is necessary to control the mass ratio of carbon material within a suitable range to balance the specific capacity and conductivity of the positive electrode active material, thereby improving the energy density and cycle performance of the battery cell.

[0222] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A sodium-ion battery cell, characterized in that, include: A positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material, wherein the positive electrode active material comprises a phosphate material and a carbon material, wherein the phosphate material comprises sodium iron pyrophosphate; The carbon material coats at least a portion of the surface of the phosphate material, and the degree of graphitization R of the carbon material satisfies: 0.8 ≤ R ≤ 1.1, where R = 1. G / I D I G The Raman spectrum of the positive electrode active material at 1480 cm⁻¹ -1 ~1680cm -1 The maximum peak intensity within the range is the intensity of peak G, I D The 1250 cm⁻¹ value in the Raman spectrum of the positive electrode active material -1 ~1450cm -1 The maximum peak intensity within the range is the intensity of peak D; The molar ratio of sodium to iron in the phosphate material is 1.33 to 1.

45.

2. The sodium-ion battery cell according to claim 1, characterized in that, 0.85≤R≤0.95。 3. The sodium-ion battery cell according to claim 1 or 2, characterized in that, Based on the total mass of the positive electrode active material, the mass content ratio A between the phosphate material and the carbon material satisfies: 49 ≤ A ≤ 70.

4. The sodium-ion battery cell according to any one of claims 1 to 3, characterized in that, The carbon material includes at least one of glucose, sucrose, polyethylene glycol, polyacrylonitrile, and cellulose.

5. The sodium-ion battery cell according to any one of claims 1 to 4, characterized in that, Based on the total mass of the phosphate material, the mass content B of sodium iron pyrophosphate satisfies: 98wt% ≤ B ≤ 98.6wt%.

6. The sodium-ion battery cell according to any one of claims 1 to 5, characterized in that, Phosphate materials also include sodium ferrous pyrophosphate; Based on the total mass of the phosphate material, the mass ratio of sodium iron pyrophosphate to sodium ferrous pyrophosphate is 39 to 99.

7. The sodium-ion battery cell according to any one of claims 1 to 6, characterized in that, The compaction density ρ of the positive electrode sheet satisfies: 1.9 g / cm³ 3 ≤ρ≤2.3g / cm 3 .

8. A method for preparing a sodium-ion battery cell, characterized in that, An intermediate particle is obtained by mixing a carbon source, a phosphorus source, an iron source, and a sodium source. Based on the total mass of the intermediate particle, the mass ratio of the sodium source to the iron source is 0.25 to 0.

27. The intermediate particles are initially sintered and then subjected to further heating sintering. The initial sintering temperature T1 is 300℃~400℃, and the initial sintering time t1 is 5h~10h. The heating sintering temperature T2 is 500℃~550℃, and the heating sintering time t2 is 5h~15h, to obtain a positive electrode active material. The positive electrode active material includes a phosphate material and a carbon material. The phosphate material includes sodium iron pyrophosphate. The carbon material coats at least a portion of the surface of the phosphate material. The degree of graphitization R of the carbon material satisfies: 0.8≤R≤1.1, where R=1. G / I D I G The Raman spectrum of the positive electrode active material at 1480 cm⁻¹ -1 ~1680cm -1 The maximum peak intensity within the range is the intensity of peak G, I D The 1250 cm⁻¹ value in the Raman spectrum of the positive electrode active material -1 ~1450cm -1 The maximum peak intensity within the range is the intensity of peak D; The positive electrode sheet is prepared using the positive electrode active material to prepare a sodium-ion battery cell.

9. The method according to claim 8, characterized in that, Based on the total mass of the carbon source, the phosphorus source, the iron source and the sodium source, the mass content of the carbon source is 1.4 wt% to 2 wt%.

10. The method according to claim 8 or 9, characterized in that, The step of mixing carbon source, phosphorus source, iron source and sodium source to obtain intermediate particles includes: mixing the phosphorus source, the iron source and the carbon source to obtain a first slurry, spray drying the first slurry to obtain a spray precursor, and mixing the spray precursor with the sodium source to obtain the intermediate particles.

11. The method according to claim 10, characterized in that, The solid content of the first slurry is 30% to 40%.

12. The method according to claim 10 or 11, characterized in that, The rotational speed v at which the phosphorus source, the iron source and the carbon source are mixed satisfies: 10 r / min ≤ v ≤ 100 r / min, and optionally, 40 r / min ≤ v ≤ 60 r / min.

13. The method according to any one of claims 10 to 12, characterized in that, The time t3 for mixing the phosphorus source, the iron source and the carbon source satisfies: 1h≤t3≤10h.

14. The method according to any one of claims 10 to 13, characterized in that, The inlet air temperature T3 for spray drying the first slurry satisfies 180℃≤T3≤220℃; The outlet air temperature T4 for spray drying the first slurry satisfies 80℃≤T4≤120℃.

15. The method according to any one of claims 8 to 14, characterized in that, The sintering atmosphere is argon or nitrogen.

16. The method according to any one of claims 8 to 15, characterized in that, 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 phosphoric acid, sodium pyrophosphate, and disodium hydrogen phosphate. The iron source includes at least one of ferrous sulfate, ferric nitrate, ferrous sulfate, and ferric phosphate.

17. A battery device, characterized in that, Includes sodium-ion battery cells as described in any one of claims 1-7, and / or sodium-ion battery cells prepared by the method as described in any one of claims 8-16.

18. An electrical appliance, characterized in that, Includes the battery device as described in claim 17.

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