Positive electrode composite material, positive electrode sheet, battery, battery pack, and electric device

Abstract

A positive electrode composite material, a positive electrode sheet, a battery, a battery pack, and an electric device. The positive electrode composite material comprises a positive electrode active material and a shell layer present on at least part of the surface of the positive electrode active material. The shell layer comprises carbon nanotubes. The average tube diameter of the carbon nanotubes is less than or equal to 100 nm.

Description

Positive electrode composite materials, positive electrode sheets, batteries, battery packs and electrical equipment

[0001] This application claims priority to Chinese Patent Application No. 202510496427.3, filed on April 18, 2025, entitled "Positive Electrode Composite Material, Positive Electrode Sheet, Battery, Battery Pack and Electrical Equipment", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of batteries, specifically to a positive electrode composite material and its preparation method, a positive electrode sheet, a battery, a battery pack, and an electrical device. Background Technology

[0003] Batteries are common electrochemical devices with wide applications. The cathode material is a crucial component of a battery and a significant factor affecting its capacity and other performance characteristics. However, existing batteries generally suffer from low capacity and poor rate performance, problems that urgently need to be addressed. Summary of the Invention

[0004] This application provides a positive electrode composite material and its preparation method, a positive electrode sheet, a battery, a battery pack, and an electrical device, which can improve battery capacity and rate performance and effectively solve the defects of the prior art.

[0005] In one aspect, this application provides a positive electrode composite material, comprising a positive electrode active material and a shell layer present on at least a portion of the surface of the positive electrode active material, the shell layer comprising carbon nanotubes having an average diameter of less than or equal to 100 nm.

[0006] According to one embodiment of this application, the average diameter of the carbon nanotube is less than or equal to 40 nm; and / or, the average diameter of the carbon nanotube is greater than or equal to 5 nm.

[0007] According to one embodiment of this application, the shell layer further includes at least one of bulk carbon material and sheet carbon material.

[0008] According to one embodiment of this application, in the Raman spectrum of the positive electrode composite material, I D / I G ≤1.4, where I D The Raman spectrum is 1350±20cm. -1 The intensity of peak D at 1580 ± 20 cm⁻¹, IG represents the Raman spectrum at 1580 ± 20 cm⁻¹. -1 The intensity of the G peak at that location.

[0009] According to one embodiment of this application, in the Raman spectrum of the positive electrode composite material, 1.14 ≤ I D / I G ≤1.3.

[0010] According to one embodiment of this application, the carbon element in the positive electrode composite material accounts for 1% to 10% of the mass ratio of the positive electrode composite material.

[0011] According to one embodiment of this application, the shell contains heteroatoms, which include one or more of nitrogen, boron, sulfur and fluorine, and the atomic ratio of the heteroatoms to carbon atoms in the shell is 0 to 10%.

[0012] According to one embodiment of this application, the positive electrode active material includes a polyanionic positive electrode material.

[0013] According to one embodiment of this application, the polyanionic cathode material includes a phosphate-based polyanionic cathode material.

[0014] According to one embodiment of this application, the phosphate-based polyanionic cathode material includes sodium iron phosphate pyrophosphate materials.

[0015] Another aspect of this application provides a method for preparing the above-mentioned positive electrode composite material, comprising the following steps: calcining a mixture containing a first raw material and a second raw material to obtain a positive electrode composite material; wherein the first raw material is a raw material for forming the positive electrode active material, and the second raw material is a raw material for forming the shell layer.

[0016] According to one embodiment of this application, the second raw material includes carbon nanotube raw material and / or organic carbon source.

[0017] According to one embodiment of this application, the organic carbon source includes one or more of ascorbic acid, glucose, citric acid, cellulose, and oxalic acid.

[0018] According to one embodiment of this application, the second raw material includes carbon nanotube raw material, wherein the mass of the carbon nanotube raw material accounts for 1% to 50% of the total mass of the second raw material.

[0019] According to one embodiment of this application, the carbon nanotube raw material accounts for 1% to 30% of the total mass of the second raw material.

[0020] According to one embodiment of this application, the second raw material includes carbon nanotube raw material, wherein the diameter of the carbon nanotube raw material is distributed in the range of 2 to 100 nm.

[0021] According to one embodiment of this application, the calcination conditions are: calcination temperature of 500-600°C and calcination time of 2-12 hours.

[0022] Another aspect of this application provides a positive electrode sheet, comprising the above-described positive electrode composite material or a positive electrode composite material prepared according to the above-described method for preparing the positive electrode composite material.

[0023] Another aspect of this application provides a battery including the aforementioned positive electrode.

[0024] According to one embodiment of this application, the battery is a sodium-ion battery.

[0025] In another aspect of this application, a battery pack is provided, including the aforementioned battery.

[0026] Another aspect of this application provides an electrical device including the aforementioned battery or battery pack.

[0027] This application provides a positive electrode composite material and its preparation method, a positive electrode sheet, a battery, a battery pack, and an electrical device. A shell layer is formed on the surface of the positive electrode active material, and carbon nanotubes with an average diameter of no more than 100 nm are introduced into the shell layer. This can improve the structural stability of the positive electrode composite material, improve its conductivity, promote electron transfer between positive electrode composite material particles and the capacity utilization of the positive electrode active material, thereby increasing the battery capacity. At the same time, it can also improve the electrochemical properties of the positive electrode composite material, such as ionic conductivity, and enhance the rate performance of the battery. Attached Figure Description

[0028] Figure 1 is a schematic diagram of the structure of a positive electrode composite material according to an embodiment of this application. Detailed Implementation

[0029] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. When the following description relates to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0030] In related technologies, due to the limitations of the poor electronic conductivity, ionic conductivity, and structural stability of the cathode material (or cathode active material), batteries generally suffer from problems such as low capacity and poor rate performance, which urgently need to be solved.

[0031] For example, polyanionic materials are a common type of cathode material. For example, polyanionic sodium-ion battery cathode materials, such as sodium iron phosphate pyrophosphate (NFPP), have good long cycle life and thermal stability, which is conducive to achieving a long-life and safe battery system. However, these materials have poor conductivity, limited capacity, and poor rate performance.

[0032] According to the inventor's long-term research, coating the surface of the cathode material with carbon material can improve the conductivity of the cathode material to a certain extent. However, the structural characteristics of the coated carbon material are important factors affecting the conductivity and other properties of the cathode material (such as polyanionic materials). Therefore, optimizing the coated carbon material can be a feasible direction for improving the conductivity and other properties of the cathode material.

[0033] The inventors discovered that carbon nanotubes have good electrical conductivity and can be used as carbon coating materials for cathode materials. However, carbon nanotubes of different sizes can affect the electrical conductivity and ionic conductivity of the coated cathode material (cathode composite material), which in turn affects the battery's capacity and rate performance.

[0034] In view of this, the present application provides a positive electrode composite material, as shown in FIG1, including a positive electrode active material and a shell layer existing on at least a portion of the surface of the positive electrode active material, the shell layer including carbon nanotubes, the average diameter of the carbon nanotubes being less than or equal to 100 nm.

[0035] In this embodiment, by introducing carbon nanotubes into the shell, the electronic conductivity, ionic conductivity, and structural stability of the cathode composite material can be improved simultaneously, thereby enhancing the battery's capacity and rate performance. The reasons are as follows: (1) Introducing carbon nanotubes of the aforementioned size (average diameter less than or equal to 100 nm) into the shell can improve the electronic conductivity of the cathode composite material based on the excellent conductivity of the carbon nanotubes themselves, promoting electron transfer between cathode composite material particles, thus promoting the utilization of the cathode active material's bulk capacity, increasing the discharge capacity of the cathode composite material, and ultimately improving the battery capacity; (2) Introducing carbon nanotubes of the aforementioned size into the shell can utilize their tubular structure to promote electron transfer and ion transport between cathode composite material particles, improving the conductivity and kinetic performance of the cathode composite material, and enhancing the battery's capacity and rate performance; (3) Introducing carbon nanotubes of the aforementioned size into the shell has… It has a good graphitized structure, which is conducive to giving full play to the protective role of the shell on the positive electrode active material, as well as the conductivity and ion transport capability of the shell, thereby improving the electronic conductivity, ionic conductivity and structural stability of the positive electrode composite material, and improving the capacity and rate performance of the battery; (4) Using carbon nanotubes with a diameter of less than or equal to 100nm is conducive to more comprehensive coating of the positive electrode active material, improving the coating uniformity and density of the shell, while improving the protective role of the shell on the positive electrode active material, it can also form a good conductive network and ion transport network in the shell, improving the electronic conductivity, ionic conductivity and structural stability of the positive electrode composite material, and improving the capacity and rate performance of the battery.

[0036] For example, the diameter of the carbon nanotubes in the shell can be less than or equal to 100 nm, less than or equal to 90 nm, less than or equal to 80 nm, less than or equal to 70 nm, less than or equal to 60 nm, less than or equal to 50 nm, less than or equal to 40 nm, less than or equal to 30 nm, less than or equal to 20 nm, less than or equal to 15 nm, less than or equal to 10 nm, less than or equal to 5 nm, or between any two of the above values.

[0037] Further research revealed that the average diameter of carbon nanotubes can be less than or equal to 40 nm, which is beneficial for further improving the electronic conductivity, ionic conductivity, and structural stability of the cathode composite material, thereby enhancing the battery's capacity and rate performance.

[0038] In some embodiments, the average diameter of the carbon nanotubes can be greater than or equal to 5 nm, that is, the diameter of the carbon nanotubes can be 5 nm to 100 nm, for example, 5 nm to 40 nm. An average diameter of carbon nanotubes greater than or equal to 5 nm is beneficial for improving the electronic conductivity, ionic conductivity and structural stability of the cathode composite material, while also facilitating the preparation of carbon nanotubes and reducing their cost.

[0039] In this application, the diameter of carbon nanotubes refers to the outer diameter (or diameter) of the carbon nanotubes, which can be measured by conventional methods. For example, carbon nanotubes in the cathode composite material can be detected by scanning electron microscopy (SEM), the diameter of at least 30 carbon nanotubes can be measured, and then the average value can be calculated to obtain the average diameter of the carbon nanotubes.

[0040] Specifically, the aforementioned cathode composite material has a core-shell structure, meaning it includes a core layer (inner core) and a shell layer. The core layer includes the cathode active material, and the shell layer includes carbon material (or coated carbon), which includes carbon nanotubes. The shell layer can exist on part of the surface of the cathode active material or on the entire surface of the cathode active material, and the shell layer can be a carbon coating layer mainly composed of carbon material.

[0041] Specifically, the core and shell materials of the cathode composite material are different, and there is a clear interface between the core and shell. The core and shell structure of the cathode composite material can be determined by conventional methods. For example, the cathode composite material can be cut by focusing ion beam (FIB) cutting, and then the cross-section of the cathode composite material (which basically passes through the center (center of the sphere) of the cathode composite material particle) can be observed by electron microscopy (e.g., scanning electron microscopy (SEM)) to determine its shell structure.

[0042] According to further research by the inventors, the shell layer can also include non-tubular carbon materials. That is, the carbon materials in the shell layer include carbon nanotubes (tubular carbon materials) and non-tubular carbon materials. Using both carbon nanotubes and non-tubular carbon materials is beneficial to further improve the coating effect of the shell layer on the positive electrode active material, thereby further improving the electronic conductivity, ionic conductivity and structural stability of the positive electrode composite material, and enhancing the capacity and rate performance of the battery.

[0043] Specifically, non-tubular carbon materials do not have tubular structures and generally do not have regular shapes. They usually exist in block and / or sheet form in the shell, covering the surface of the core (positive electrode active material). The shell includes at least one of block carbon materials and sheet carbon materials.

[0044] The aforementioned non-tubular carbon materials can be conventional non-tubular carbon materials, which may include crystalline carbon (e.g., graphitized carbon materials) and / or amorphous carbon. Generally, non-tubular carbon materials may include carbon materials formed by sintering and carbonizing organic carbon sources.

[0045] In some embodiments, in the Raman spectrum of the shell of the cathode composite material, I D / I G ≤1.4, which is beneficial for further improving the conductivity and other properties of the positive electrode composite material. The reason for this is that I D / I GInfluenced by factors such as the diameter of carbon nanotubes and the content of carbon nanotubes in the shell, by controlling I D / I G ≤1.4, which is equivalent to synergistically regulating these factors, resulting in a better ion-conducting and conductive network in the shell, while also improving the uniformity and appropriate density of the shell's coating on the cathode composite material. Meanwhile, I D / I G ≤1.4, which makes the shell layer more crystallizable and less defective, is more conducive to the electron transfer performance of the shell layer, further promoting the capacity of the cathode composite material. This further improves the ionic conductivity, electronic conductivity and structural stability of the cathode composite material, thereby enhancing the capacity and rate performance of the battery.

[0046] Generally, in the Raman spectrum of the shell of the cathode composite material, 1.1≤I D / I G ≤1.4, I D / I G For example, a range consisting of 1.1, 1.14, 1.16, 1.18, 1.21, 1.25, 1.28, 1.3, 1.34, 1.37, 1.4, or any two of them.

[0047] In some embodiments, 1.14 ≤ I D / I G ≤1.3, I of the positive electrode composite material D / I G No greater than 1.3, smaller I D / I G This is beneficial for further improving the conductivity and other properties of the cathode composite material. At the same time, the Ig of the cathode composite material... D / I G A value of not less than 1.14 is more conducive to the preparation of cathode composite materials.

[0048] In Raman spectroscopy, I D The spectral peak attributable to the defective carbon structure (1350 cm⁻¹) -1 The intensity of the D peak (±20) is I G The spectral peak attributable to the graphitized carbon structure (1580 cm⁻¹) -1 The intensity of the G peak (±20) is I D / I G For I D with I G The ratio of .

[0049] This application allows for Raman spectroscopy testing of the cathode composite material using conventional methods in the art, to determine the Io of the cathode composite material. D / I GBecause the outer shell of the cathode composite material includes carbon materials such as carbon nanotubes, while its core is a non-carbon material (its core is the cathode active material), the I of the cathode composite material... D / I G This generally refers to the I layer (coated carbon). D / I G In practical implementation, Raman spectroscopy at wavenumbers of 800–2500 (800 cm⁻¹) can be used. -1 ~2500cm -1 To test the crystallinity of the shell material of the cathode composite material within a certain range, Raman spectra of n regions (n≥30, i.e., 30 or more different regions) of the cathode composite material can be tested. The Raman spectral data (Raman spectral lines) obtained from each region are normalized with the maximum intensity value being 1 and the minimum intensity value being 0 (i.e., the Raman spectral lines are standardized), resulting in normalized spectral lines. Thus, n normalized spectral lines are obtained. The average intensity at the same wavenumber of the n normalized Raman spectra is then taken. (That is, for the characteristic peak intensity at each wavenumber on a Raman spectrum, the average value of the characteristic peak intensities at that wavenumber across n spectral lines is taken) to average the Raman spectrum (for the characteristic peak intensity at each wavenumber, there are n intensity values ​​across n spectral lines; the average of these n intensity values ​​is the mean intensity at that wavenumber. The characteristic peak intensity at each wavenumber is averaged using this method to average the n spectral lines), thus obtaining the average Raman spectrum; from the obtained average Raman spectrum, the intensity of the peaks attributable to the defective carbon structure is selected (I... D ) and the intensity of the spectral peaks attributable to the graphitized carbon structure (I G ), calculate I D with I G and I D / I G .

[0050] In some embodiments, the mass ratio of carbon in the cathode composite material (i.e., the carbon content of the cathode composite material) can be 1% to 10%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination thereof. Thus, a carbon content of not less than 1% is beneficial for improving the coating effect of the shell on the cathode material and the conductivity of the cathode composite material. Simultaneously, a carbon content of not more than 10% helps maintain a higher concentration of active cathode material, maximizing capacity. Therefore, in the cathode composite material system with carbon nanotubes having an average diameter of no more than 100 nm introduced into the shell, further controlling the carbon content of the cathode composite material within the range of 1% to 10% helps to further improve the conductivity, ion conductivity, and structural stability of the cathode composite material, thereby enhancing the battery's capacity and rate performance.

[0051] It is understandable that the carbon content of the cathode composite material refers to the mass percentage of carbon in the cathode composite material (i.e., the proportion of carbon mass to the total mass of the cathode composite material). The carbon in the cathode composite material mainly exists in the shell. For example, when the shell is composed of carbon nanotubes and non-tubular carbon materials, the carbon in the cathode composite material mainly comes from carbon nanotubes and non-tubular carbon materials.

[0052] The carbon content of the cathode composite material can be determined by conventional methods in the art, such as using a carbon-sulfur analyzer (e.g., the HCS series infrared carbon-sulfur analyzer from Shanghai Dekai) to test the cathode composite material and thus determine its carbon content.

[0053] In addition, the shell of the cathode composite material may also contain heteroatoms, which may include one or more of nitrogen (N), boron (B), sulfur (S) and fluorine (F). The introduction of heteroatoms helps to provide conductivity to the shell (surface carbon layer), thereby further improving the conductivity and other properties of the cathode composite material, promoting its capacity utilization, and improving the capacity and rate performance of the battery.

[0054] It is understandable that the main element of the shell of the positive electrode composite material is carbon, and the content of heteroatoms in the shell is much smaller than the content of carbon in the shell. The atomic ratio of heteroatoms to carbon atoms in the shell is 0 to 10%.

[0055] This application allows the introduction of heteroatoms into the shell of a cathode composite material using conventional methods, such as using carbon nanotubes containing heteroatoms or adding compounds containing heteroatoms to the raw materials forming the shell. Both carbon nanotubes containing heteroatoms (such as nitrogen-doped carbon nanotubes) and compounds containing heteroatoms can be obtained through conventional methods, such as commercial purchases or self-made using conventional methods in the field, and there are no particular limitations on this.

[0056] This application allows for testing, using conventional methods, whether the shell (the surface region of the cathode composite material) contains heteroatoms and the types of heteroatoms, etc. For example, energy dispersive X-ray spectroscopy (EDS) and X-ray electron spectroscopy (XPS) can be used to test the cathode composite material to determine the types of heteroatoms in the shell of the cathode composite material.

[0057] In this embodiment, the positive electrode active material may include a polyanionic positive electrode material. Polyanionic positive electrode materials possess excellent long cycle life and thermal stability, which is beneficial for further improving the cycle life and safety of the battery. Simultaneously, the surface of the polyanionic positive electrode material contains carbon nanotubes with an average diameter of no more than 100 nm, effectively overcoming the poor conductivity problem of polyanionic positive electrode materials, thereby promoting the capacity utilization of the polyanionic positive electrode material. It also helps to improve the ionic conductivity and structural stability of the polyanionic positive electrode material, thus further improving the electronic conductivity, ionic conductivity, and structural stability of the positive electrode composite material. Therefore, in this embodiment, introducing carbon nanotubes with an average diameter of no more than 100 nm into the carbon coating layer of the polyanionic positive electrode material facilitates the formation of a low-defect carbon coating layer (shell), improving the conductivity and other properties of the polyanionic positive electrode material, and enhancing the battery's capacity and rate performance.

[0058] Specifically, polyanionic cathode materials can include phosphate-based polyanionic cathode materials.

[0059] In some embodiments, phosphate-based polyanionic cathode materials may include sodium iron phosphate pyrophosphate materials, which may include sodium iron phosphate pyrophosphate (NFPP) and / or doped sodium iron phosphate pyrophosphate (i.e., NFPP doped with dopants).

[0060] In the embodiments of this application, unless otherwise specified, NFPP, doped NFPP and other materials can be obtained by conventional methods in the art, such as commercial purchase or self-made by conventional methods in the art, and there are no special restrictions on this.

[0061] In this embodiment, the cathode composite material possesses both high capacity and high rate capability. The 0.1C discharge specific capacity of the cathode composite material can be greater than or equal to 105 mAh / g, specifically between 105 and 115 mAh / g, for example, 105 mAh / g, 108 mAh / g, 110 mAh / g, 113 mAh / g, 115 mAh / g, or any combination thereof. In some embodiments, the cathode active material is NFPP, and the discharge specific capacity of the cathode composite material can be greater than or equal to 105 mAh / g.

[0062] The 0.1C discharge specific capacity of the positive electrode composite material refers to the electrical capacity that a unit mass of the positive electrode composite material can release at a 0.1C rate. It can be measured by the conventional coin cell method, that is, by assembling a coin cell using the positive electrode composite material as the positive electrode and a metal sheet as the negative electrode, charging and discharging the coin cell at a current density (rate) of 0.1C, and recording the discharge capacity Q. Then, the discharge specific capacity of the positive electrode composite material = discharge capacity Q / mass of the positive electrode composite material.

[0063] In practice, the positive electrode composite material, PVDF, and conductive carbon black are mixed in a mass ratio of 8:1:1 and dispersed evenly in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry is then coated onto one side of an aluminum foil, dried, and rolled to form an areal density of 10 ± 0.2 mg / cm³ on the aluminum foil surface. 2 A positive electrode active layer was formed to prepare the positive electrode sheet. Then, the positive electrode sheet, metal sheet, and glass fiber separator were assembled into a coin cell. The coin cell was charged and discharged at a current density of 0.1C to obtain the discharge capacity Q. The electrolyte used in the assembled coin cell consisted of EC, DEC, and sodium hexafluorophosphate, with a volume ratio of EC to DEC of 1:1 and a sodium hexafluorophosphate concentration of 1M.

[0064] Furthermore, during the charge-discharge test, the coin cell is fully charged at 0.1C (i.e., charged until the battery reaches approximately 100% SOC), and then fully discharged (i.e., discharged until the battery reaches approximately 0% SOC) to obtain the discharge capacity Q. Specifically, the coin cell can be charged at a 0.1C rate to the upper cutoff voltage, then charged at a constant voltage until the current reaches 0.05C (i.e., the coin cell is approximately fully charged), and then discharged to the lower cutoff voltage (i.e., the coin cell is approximately fully discharged). The upper and lower cutoff voltages of the battery can be determined based on the type of positive electrode active material using conventional methods in the art. For example, when the positive electrode active material in the positive electrode composite material is NFPP, the coin cell can be charged and discharged within a voltage range of 2V to 4V (i.e., the lower cutoff voltage of the coin cell during the charge-discharge test is 2V, and the upper cutoff voltage is 4V) to obtain the discharge capacity Q.

[0065] Generally, the metal in the metal sheet and the active metal ions in the positive electrode active material are the same metal element. The active metal ions refer to metal ions that can be inserted / extracted from the positive and negative electrodes during battery charging and discharging. For example, when the positive electrode active material is a sodium-ion battery positive electrode material, the active metal ion is sodium ion, and the metal sheet is a sodium sheet; when the positive electrode active material is a lithium-ion battery positive electrode material, the active metal ion is lithium ion, and the metal sheet is a lithium sheet.

[0066] This application embodiment also provides a method for preparing the above-mentioned positive electrode composite material, including the following steps: calcining a mixture containing a first raw material and a second raw material to obtain a positive electrode composite material; the first raw material is a raw material used to form a positive electrode active material, and the second raw material is a raw material used to form a shell layer.

[0067] In this embodiment of the application, the first raw material is used to form the positive electrode active material, which contains and provides the elements required for the positive electrode active material. The first raw material may include compounds of these elements, such as oxides and / or salts of these elements. Specifically, the first raw material may be a mixture of compounds containing these elements respectively.

[0068] For example, the first raw material can be a raw material used to form NFPP, that is, in the positive electrode composite material obtained by the above preparation process, the positive electrode active material is NFPP. The first raw material may include a sodium source, an iron source, and a phosphorus source. The sodium source may include one or more of sodium pyrophosphate, sodium bicarbonate, sodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, or other sodium sources. The iron source may include one or more of iron oxide, ferrous oxalate, ferrous phosphate, iron phosphate, or other iron sources. The phosphorus source may include one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium pyrophosphate, or other phosphorus sources.

[0069] In this embodiment, the second raw material may include a carbon source, which may include carbon nanotubes and / or organic carbon sources, forming a carbon coating layer (shell) on the surface of the positive electrode active material in the obtained positive electrode composite material.

[0070] Specifically, the aforementioned carbon source (second raw material) includes a carbon source for forming carbon nanotubes. The carbon source for forming carbon nanotubes may include carbon nanotube raw materials and / or carbon source materials that can generate carbon nanotubes in situ during calcination. That is, the carbon nanotubes in the shell of the cathode composite material can be directly introduced during the synthesis feeding (i.e., the second raw material includes carbon nanotube raw materials), or they can be formed in situ through sintering (i.e., the second raw material includes carbon source materials that can generate carbon nanotubes in situ during calcination).

[0071] Generally, when the second raw material includes a carbon source material capable of generating carbon nanotubes in situ during calcination, the first and second raw materials can be mixed with a catalyst before calcination. During calcination, the carbon source material grows into carbon nanotubes in situ under the action of the catalyst, resulting in a cathode composite material containing carbon nanotubes in its shell. In the embodiments of this application, conventional carbon source materials and catalysts used in carbon nanotube synthesis processes can be employed. The catalysts used for synthesizing carbon nanotubes include, for example, metal catalysts, and are not particularly limited thereto.

[0072] In addition, when the second raw material includes an organic carbon source, the resulting shell may also contain non-tubular carbon materials.

[0073] In some embodiments, the organic carbon source may include one or more of ascorbic acid, glucose, citric acid, cellulose, oxalic acid, etc. Through the above-described calcination process, the organic carbon source is carbonized to form a carbon material, which is then coated on the surface of the positive electrode active material to obtain a positive electrode composite material.

[0074] According to the inventors' research, if only organic carbon sources are used for sintering and carbonization to coat the positive electrode active material, the structure of the coated carbon formed by sintering and carbonization with organic carbon sources is difficult to control. It has a high degree of amorphization and low crystallinity, and its conductivity is generally worse than that of inorganic carbon. Meanwhile, compared to carbon materials formed by sintering and carbonization with organic carbon sources, carbon nanotubes have better conductivity. Therefore, when the second raw material includes carbon nanotubes, it is beneficial to introduce carbon nanotubes into the shell layer of the prepared positive electrode composite material, thereby improving the electronic and ionic conductivity of the positive electrode composite material. Furthermore, based on the good conductivity of carbon nanotubes, it is also beneficial to reduce the amount of conductive agent used in the positive electrode active layer during the subsequent preparation of the positive electrode sheet. In addition, key parameters affecting conductivity, such as the crystallinity and morphology (e.g., tubular characteristics) of carbon nanotubes, are easier to control than carbon materials formed by sintering and carbonization with organic carbon, which is beneficial for the preparation of positive electrode composite materials.

[0075] Specifically, the mass of carbon nanotube raw material accounts for 1% to 100% of the total mass of the second raw material, for example, 1%, 5%, 9%, 10%, 20%, 22%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or any combination thereof. That is, carbon nanotube raw material can be used entirely as the second raw material, or carbon nanotube raw material and other carbon sources such as organic carbon sources can be used simultaneously as the second raw material. The mass of carbon nanotubes accounts for no less than 1% of the total mass of the second raw material. This is beneficial for introducing more carbon nanotubes into the formed shell, which is beneficial for improving the structural stability of the cathode composite material. At the same time, it forms a better conductive network and ion-conducting network on the surface of the cathode active material, which is beneficial for electron transfer and ion transport between cathode composite material particles, thereby improving the discharge capacity and rate performance of the cathode composite material.

[0076] According to further research by the inventors, by introducing an appropriate amount of organic carbon source into the second raw material, the organic carbon source can form non-tubular carbon material. While improving the electronic conductivity and ionic conductivity of the obtained positive electrode composite material, it is also beneficial to more comprehensively coat the positive electrode active material, improve the coating uniformity of the shell, and further optimize the comprehensive performance of the positive electrode composite material. Therefore, it is preferred that the mass of carbon nanotubes accounts for 1% to 50% of the total mass of the second raw material, and it is even more preferred that the mass of carbon nanotubes accounts for 1% to 30% of the total mass of the second raw material.

[0077] Furthermore, in the second raw material, the diameter (outer diameter) of the carbon nanotube material can be distributed in the range of 2–100 nm, for example, within any combination of 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and 100 nm. For example, the particle size of the carbon nanotubes can be distributed in the range of 2–10 nm, 10–30 nm, 30–100 nm, 50–120 nm, or 80–150 nm, etc.

[0078] In this application, when preparing the cathode composite material, the diameter distribution range of the carbon nanotubes used (carbon nanotubes as carbon source) can be measured by scanning electron microscopy (SEM). That is, carbon nanotubes are observed by scanning electron microscopy and photographs are taken. The diameter (outer diameter) of the carbon nanotubes is measured. At least 100 carbon nanotubes are tested. Among the obtained diameter data, the minimum value is a and the maximum value is b. Then the diameter distribution range of the carbon nanotubes is a~b (that is, the diameter distribution of the carbon nanotubes is within the range of a~b).

[0079] In some embodiments, the preparation process of a mixture containing a first raw material and a second raw material may include: mixing the first raw material and the second raw material in a liquid dispersion medium, and then drying (removing the solvent) to obtain a mixture containing the first raw material and the second raw material (or a precursor). For example, the preparation process of a mixture containing the first raw material and the second raw material may include: mixing a sodium source, an iron source, a phosphorus source, and an iron source in a liquid dispersion medium, and then drying to obtain a mixture containing the first raw material and the second raw material.

[0080] In practice, the first and second raw materials can be ball-milled together in a liquid dispersion medium. This involves dispersing the first and second raw materials in a solvent and then ball-milling them to ensure uniform mixing. The mixture is then dried, either by spray drying or evaporation, to obtain a mixture containing the first and second raw materials. When evaporation is used, the resulting solid product can be ground into powder and then calcined.

[0081] In the above preparation process, the calcination conditions can be: calcination temperature of 500-600℃, such as 500℃, 520℃, 540℃, 560℃, 580℃, 600℃ or any combination thereof, and calcination time of 2-12 hours (h), such as 2h, 4h, 6h, 8h, 10h, 12h or any combination thereof.

[0082] In practice, the above-mentioned mixture can be calcined in a protective atmosphere to obtain a positive electrode composite material. The protective atmosphere can be a conventional protective atmosphere, such as a nitrogen atmosphere or an argon atmosphere, and there are no special restrictions on it.

[0083] This application also provides a positive electrode sheet, comprising the above-mentioned positive electrode composite material or a positive electrode composite material prepared according to the above-mentioned method for preparing the positive electrode composite material. This positive electrode sheet has advantages corresponding to the above-mentioned positive electrode composite material, which will not be elaborated further.

[0084] Specifically, the positive electrode sheet includes a positive current collector and a positive active layer located on at least one surface of the positive current collector. Specifically, the positive active layer can be disposed on one surface in the thickness direction of the positive current collector, or positive active layers can be disposed on both opposite surfaces in the thickness direction of the positive current collector. The aforementioned positive electrode composite material is present in the positive active layer.

[0085] Generally, the positive electrode active layer may include a positive electrode composite material, a conductive agent, and a binder. In the positive electrode active layer, the mass percentage of the positive electrode composite material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof. The mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof. The mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0086] In the embodiments of this application, the conductive agent in the positive electrode active layer can be a conventional conductive material in the art. For example, the conductive agent in the positive electrode coating may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0087] In this embodiment, the binder in the positive electrode active layer can be a conventional adhesive material in the art. For example, the binder in the positive electrode active layer may include one or more of the following: polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0088] The embodiments of this application may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0089] In this embodiment, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder, and other components used to form the positive electrode active layer can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0090] This application also provides a battery including the above-described positive electrode sheet, which has advantages corresponding to the above-described positive electrode material, and will not be described in detail here.

[0091] In some embodiments, the battery can be a sodium-ion battery, and the positive electrode active material in the positive electrode composite material can specifically be a polyanion-type sodium-ion battery positive electrode material, such as NFPP.

[0092] Generally, a battery includes an electrolyte, a battery cell, and a casing that encapsulates the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of stacked positive electrode, separator, and negative electrode, which are then wound together.

[0093] In this embodiment, a conventional negative electrode sheet can be used, such as a sodium sheet. Alternatively, the negative electrode sheet may include a negative current collector and a negative active layer present on at least one surface of the negative current collector. Specifically, the negative active layer may be disposed on one surface of the negative current collector, or negative active layers may be disposed on both the negative and positive surfaces of the negative current collector. The negative current collector can be a conventional negative current collector, such as a copper foil.

[0094] In addition, the negative electrode active layer may include negative electrode active materials, conductive agents, and binders, all of which can be conventional materials in the art. For example, the negative electrode active material may include soft carbon and / or hard carbon, the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber, and the binder may include one or more of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0095] Generally, in the negative electrode active layer, the mass percentage of the negative electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof; the mass fraction of the conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof; and the mass fraction of the binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any combination thereof.

[0096] The electrolyte in this application embodiment can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include an organic solvent and an electrolyte salt (solute). The organic solvent may include one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC). The electrolyte salt may include a sodium salt, such as sodium hexafluorophosphate (NaPF6), but is not limited thereto.

[0097] In this embodiment, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. The separator in this embodiment can be a conventional separator in the art, such as a polypropylene separator and / or a glass fiber separator.

[0098] In this embodiment, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited to these.

[0099] The embodiments of this application can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in an alternating manner to obtain a stacked cell, or wound into a wound cell; then the cell is placed in a casing, and after conventional processes such as liquid injection (i.e., injection of electrolyte), encapsulation, standing, formation, aging and capacity testing, the battery is obtained.

[0100] The battery in this application embodiment can be a single cell or a battery pack composed of multiple single cells, and there is no particular limitation in this regard. When the battery is a battery pack composed of multiple single cells, at least one single cell in the battery pack includes the aforementioned positive electrode plate, specifically, each single cell may include the aforementioned positive electrode plate.

[0101] Specifically, these individual cells in the battery pack can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a hybrid connection including both of these connection methods, to form a battery pack, without any particular limitation.

[0102] This application also provides an electrical device, including the battery or battery pack described above. This electrical device has advantages corresponding to the positive electrode material described above, which will not be elaborated further.

[0103] The electrical equipment used in the embodiments of this application can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no special limitations on this.

[0104] The present application will be further described below through specific embodiments. In the following embodiments and comparative examples, unless otherwise specified, the diameter of the carbon nanotubes (carbon nanotubes as carbon source) used in the preparation of the cathode composite material was measured by scanning electron microscopy (SEM). That is, the carbon nanotubes were observed by scanning electron microscopy and photographed, and the diameter (outer diameter) of the carbon nanotubes was measured. At least 100 carbon nanotubes in at least 3 SEM photographs were tested. The minimum diameter value was a and the maximum diameter value was b. The diameter distribution range of the carbon nanotubes was a to b (for example, the diameter of the carbon nanotubes used in Example 1 was 30 to 100 nm).

[0105] Unless otherwise specified, in the following examples and comparative examples, the average diameter of carbon nanotubes in the carbon coating layer (shell) of the cathode composite material was measured by SEM. The testing process is as follows: The morphology of the cathode composite material was observed by SEM, and a photo of the carbon coating layer of the cathode composite material was taken. Thirty carbon nanotubes were randomly selected, and their diameter (outer diameter) was measured. The average value was then calculated, and the result is the average diameter of carbon nanotubes in the shell of the cathode composite material.

[0106] In the following examples and comparative examples, unless otherwise specified, the I in the Raman spectrum of the shell of the prepared positive electrode composite material is... D / I GThe following process was used to measure the crystallinity of the coated carbon in the cathode composite material within the wavenumber range of 800-2500 using Raman spectroscopy. Samples were taken from 30 regions of the cathode composite powder, and the Raman spectra of these 30 samples were measured, resulting in 30 Raman spectral lines. The Raman spectral data (each spectral line) of each sample was normalized with a maximum intensity of 1 and a minimum intensity of 0, resulting in 30 normalized spectral lines. The intensities at the same wavenumber of these 30 normalized Raman spectral lines were averaged to obtain an average Raman spectrum. The intensity of the peak at the defective carbon structure (I0) was selected from the average spectrum. D ) and the intensity of the spectral peaks attributable to the graphitized carbon structure (I G ), calculate its ratio (I) D / I G ).

[0107] Unless otherwise specified, the carbon content (mass percentage of carbon) of the cathode composite material in the following examples and comparative examples was measured by a carbon-sulfur analyzer (HCS series infrared carbon-sulfur analyzer from Shanghai Dekai).

[0108] Example 1

[0109] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and carbon nanotubes with a diameter of 30–100 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.5:0.05. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 °C for 4 hours under a nitrogen protective atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0110] The cathode composite material in this embodiment 1 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0111] Example 2

[0112] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and carbon nanotubes with a diameter of 10–30 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.5:0.05. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 °C for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0113] The cathode composite material in Example 2 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0114] Example 3

[0115] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and carbon nanotubes with a diameter of 2–10 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.5:0.05. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 °C for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0116] The cathode composite material in Example 3 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0117] Example 4

[0118] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and carbon nanotubes with a diameter of 2–10 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.36:0.1. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 °C for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0119] The cathode composite material in Example 4 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0120] Example 5

[0121] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, glucose, and carbon nanotubes with a diameter of 2–10 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.5:0.05. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 °C for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0122] The cathode composite material in Example 5 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0123] Example 6

[0124] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and carbon nanotubes with a diameter of 50–120 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.5:0.05. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550°C for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0125] The cathode composite material in Example 6 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0126] Example 7

[0127] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and carbon nanotubes with a diameter of 80–150 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.5:0.05. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 °C for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0128] The cathode composite material in Example 7 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0129] Example 8

[0130] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and carbon nanotubes with a diameter of 2–10 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.15:0.015. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 °C for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0131] The cathode composite material in Example 8 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0132] Example 9

[0133] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and carbon nanotubes with a diameter of 2–10 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:1:0.1, then evaporated to dryness. The evaporated solid was ground into powder, and the resulting powder (mixture) was calcined at 550 degrees Celsius for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0134] The cathode composite material in Example 9 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0135] Example 10

[0136] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and nitrogen-doped carbon nanotubes with a diameter of 30–100 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.5:0.05. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 °C for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., the positive electrode composite material).

[0137] The cathode composite material in Example 10 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0138] Example 11

[0139] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, and carbon nanotubes with a diameter of 50–120 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.25. The mixture was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550°C for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0140] The cathode composite material in this embodiment 11 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer is mainly composed of carbon nanotubes. The average diameter of the carbon nanotubes in the shell layer and the I in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0141] Comparative Example 1: Sodium dihydrogen phosphate, ferric nitrate nonahydrate, ascorbic acid, and carbon nanotubes with a diameter of 100-300 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.5:0.05, then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 degrees Celsius for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0142] The cathode composite material of Comparative Example 1 includes an NFPP (core layer) and a shell layer (carbon coating layer) covering the NFPP. The shell layer includes carbon nanotubes and non-tubular carbon materials (formed from an organic carbon source). The average diameter of the carbon nanotubes in the shell layer and the I0 in the Raman spectrum of the shell layer are specified. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0143] Comparative Example 2: Sodium dihydrogen phosphate, ferric nitrate nonahydrate, and carbon nanotubes with a diameter of 100-300 nm were dissolved and dispersed in water at a mass ratio of 1:2.4:0.25, then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 degrees Celsius for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0144] The cathode composite material of Comparative Example 2 includes an NFPP (core layer) and an NFPP-coated shell (carbon coating layer). The shell is mainly composed of carbon nanotubes. The average diameter of the carbon nanotubes in the shell and the I0 in the Raman spectrum of the shell are shown in the figure. D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0145] Comparative Example 3: Sodium dihydrogen phosphate, ferric nitrate nonahydrate, and ascorbic acid were dissolved and dispersed in water at a mass ratio of 1:2.4:0.75. The liquid was then evaporated to dryness, and the evaporated solid was ground into powder. The resulting powder (mixture) was then calcined at 550 degrees Celsius for 4 hours under an inert atmosphere to obtain carbon-coated sodium iron pyrophosphate (i.e., positive electrode composite material).

[0146] The cathode composite material of Comparative Example 3 includes an NFPP (core layer) and a shell coating the NFPP (coated carbon layer). The shell is mainly composed of non-tubular carbon material formed from an organic carbon source (SEM observation of the shell shows no tubular carbon material). The Raman spectrum of the shell shows I... D / I G The characteristics of the positive electrode composite material, such as carbon content, are shown in Table 1.

[0147] The average diameter of carbon nanotubes in the shell of the positive electrode composite materials prepared in each embodiment and comparative example, and the I of the shell are compared. D / I G The carbon content of the cathode composite material and the raw material composition during the preparation of the cathode composite material are summarized in Table 1.

[0148] The discharge specific capacity and rate performance of the cathode composite materials of each embodiment and comparative example were tested through the following process.

[0149] 1. Discharge specific capacity test of positive electrode composite material:

[0150] (1) Preparation of positive electrode

[0151] The positive electrode composite material, PVDF and conductive agent carbon black were uniformly dispersed in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain the positive electrode slurry.

[0152] The positive electrode slurry is coated onto one side of an aluminum foil (i.e., single-sided coating), then dried and rolled to form a positive electrode active layer (area density of 10 ± 0.2 mg / cm³) on the surface of the aluminum foil. 2 Then, cut the positive electrode sheet into the preset shape;

[0153] (2) Assembly and testing of sodium-ion button half-cells

[0154] A coin cell half-cell was assembled with a positive electrode, a sodium electrode (negative electrode), and a glass fiber separator. The electrolyte used was a 1:1 volume ratio of EC and DEC as the solvent, with a sodium hexafluorophosphate concentration of 1M (1 mol / L). The coin cell half-cell was charged and discharged at a current density of 0.1C within a voltage range of 2V to 4V to determine its discharge capacity Q. 0.1c Then the 0.1C discharge specific capacity of the positive electrode composite material = discharge capacity Q 0.1c The quality of the positive electrode composite material and the test results are shown in Table 1.

[0155] Then, the coin cell was charged and discharged at a current density of 3C within a voltage range of 2V to 4V, and the discharge specific capacity Q at the 3C rate was measured. 3c Calculate the discharge specific capacity Q at 3C rate. 3c Discharge specific capacity Q at 0.1C rate 0.1c The ratio (i.e. Q) 3c / Q 0.1c As a rate performance indicator, see Table 1.

[0156] Table 1

[0157] As can be seen from Table 1, the NFPP surface of Comparative Example 3 has a carbon coating layer (shell) formed by organic carbon, without the introduction of carbon nanotubes, and the shell has a high degree of defect (I). D / I G The discharge specific capacity and rate performance of the cathode composite material are poor (up to 1.53). Although carbon nanotubes were introduced into the carbon coating layer of NFPP in Comparative Examples 1 and 2, the average diameter of the carbon nanotubes is too large (>100nm), and the degree of defect in the carbon coating layer is still high, which cannot effectively improve the discharge specific capacity and rate performance of the cathode composite material.

[0158] In contrast to Comparative Examples 1 to 3, in Examples 1 to 11, a shell including carbon nanotubes is formed on the surface of NFPP, and the average diameter of the carbon nanotubes is no greater than 100 nm. This can significantly reduce the degree of defects in the shell and improve the discharge specific capacity and rate performance of the cathode composite material.

[0159] Further, as can be seen from Examples 1 to 7, compared with Examples 6 and 7, Examples 1 to 5 further control the average diameter of carbon nanotubes in the shell within the range of 5 to 40 nm, which helps to further reduce the degree of defects in the shell and improve the discharge specific capacity and rate performance of the cathode composite material.

[0160] As can be seen from Examples 6 and 11, compared to Example 11, Example 6, by further introducing non-tubular carbon materials into the shell, can further improve the discharge specific capacity and rate performance of the cathode composite material while maintaining a low degree of shell defects.

[0161] Comparative Examples 2 and 3, or Examples 6 and 11, show that when carbon nanotubes are used exclusively as the carbon source without an organic carbon source (Comparative Examples 2 and 11), the discharge capacity of the obtained cathode composite material is lower than that of the cathode composite material with non-tubular carbon material formed by introducing organic carbon source into the shell (Comparative Examples 3 and 6). The reason for this is that, on the one hand, the presence of non-tubular carbon material is beneficial to further improve the coating effect of the shell on positive active materials such as NFPP. On the other hand, compared with carbon nanotubes, organic carbon source has better reducibility, which helps to reduce high-valence Fe source during sintering and generate NFPP. Therefore, by using carbon nanotubes and organic carbon source as shell material at the same time, a shell containing both carbon nanotubes and non-tubular carbon material is formed. The two types of carbon source work together to further improve the electronic conductivity, ionic conductivity and structural stability of the cathode composite material, thereby improving the capacity and rate performance of the battery.

[0162] Finally, it should be noted that other embodiments of this application will readily conceive of by those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and alterations may be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A positive electrode composite material, characterized in that, It includes a positive electrode active material and a shell present on at least a portion of the surface of the positive electrode active material, the shell comprising carbon nanotubes having an average diameter of less than or equal to 100 nm.

2. The positive electrode composite material according to claim 1, characterized in that, The average diameter of the carbon nanotubes is less than or equal to 40 nm; And / or, the average diameter of the carbon nanotubes is greater than or equal to 5 nm.

3. The positive electrode composite material according to claim 1 or 2, characterized in that, The shell also includes at least one of bulk carbon material and sheet carbon material.

4. The positive electrode composite material according to any one of claims 1-3, characterized in that, In the Raman spectrum of the positive electrode composite material, I D / I G ≤1.4, where I D The Raman spectrum is 1350±20 cm⁻¹ -1 D peak intensity at I G This indicates that the Raman spectrum is at 1580±20 cm⁻¹. -1 The intensity of the G peak at that location.

5. The positive electrode composite material according to claim 4, characterized in that, In the Raman spectrum of the cathode composite material, 1.14 ≤ I D / I G ≤1.

3.

6. The positive electrode composite material according to any one of claims 1-5, characterized in that, The carbon element in the cathode composite material accounts for 1% to 10% of the mass of the cathode composite material.

7. The positive electrode composite material according to any one of claims 1-6, characterized in that, The shell contains heteroatoms, including one or more of nitrogen, boron, sulfur, and fluorine, and the atomic ratio of the heteroatoms to carbon atoms in the shell is 0 to 10%.

8. The positive electrode composite material according to any one of claims 1-7, characterized in that, The positive electrode active material includes a polyanionic positive electrode material.

9. The positive electrode composite material according to claim 8, characterized in that, The polyanionic cathode material includes phosphate-based polyanionic cathode materials.

10. The positive electrode composite material according to claim 9, characterized in that, The phosphate-based polyanionic cathode material includes sodium iron phosphate pyrophosphate materials.

11. A method for preparing the positive electrode composite material according to any one of claims 1-10, characterized in that, The process includes the following steps: calcining a mixture containing a first raw material and a second raw material to obtain the positive electrode composite material; the first raw material is a raw material used to form the positive electrode active material, and the second raw material is a raw material used to form the shell layer.

12. The method for preparing the positive electrode composite material according to claim 11, characterized in that, The second raw material includes carbon nanotube raw materials and / or organic carbon sources.

13. The method for preparing the positive electrode composite material according to claim 11, characterized in that, The second raw material includes an organic carbon source, which includes one or more of ascorbic acid, glucose, citric acid, cellulose, and oxalic acid.

14. The method for preparing the positive electrode composite material according to claim 11, characterized in that, The second raw material includes carbon nanotube raw material, wherein the mass of the carbon nanotube raw material accounts for 1% to 50% of the total mass of the second raw material.

15. The method for preparing the positive electrode composite material according to claim 14, characterized in that, The carbon nanotube raw material accounts for 1% to 30% of the total mass of the second raw material.

16. The method for preparing the positive electrode composite material according to any one of claims 11-15, characterized in that, The second raw material includes carbon nanotube raw material, wherein the diameter of the carbon nanotube raw material is distributed in the range of 2 to 100 nm.

17. The method for preparing the positive electrode composite material according to any one of claims 11-16, characterized in that, The calcination conditions are as follows: calcination temperature is 500-600℃, and calcination time is 2-12 hours.

18. A positive electrode plate, characterized in that, This includes the positive electrode composite material according to any one of claims 1-10 or the positive electrode composite material prepared according to the preparation method of the positive electrode composite material according to any one of claims 11-17.

19. A battery, characterized in that, Includes the positive electrode sheet as described in claim 18.

20. The battery according to claim 19, characterized in that, The battery is a sodium-ion battery.

21. A battery pack, characterized in that, Includes the battery as described in claim 19 or 20.

22. An electrical appliance, characterized in that, Includes the battery as described in claim 19 or 20, or the battery pack as described in claim 21.

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