Sulfate-series sodium-ion battery positive electrode material, preparation method thereof and sodium-ion battery

Abstract

The invention discloses a sulfate-series sodium-ion battery positive electrode material with an expanded structure, a preparation method of the sulfate-series sodium-ion battery positive electrode material and a sodium-ion battery. The general formula of the sulfate-series sodium-ion battery positive electrode material is Na < 6-x > L < x > Fe < 5-y > M < y > (SO4) 8, wherein x is more than or equal to 0 and less than or equal to 0.5, y is more than 0 and less than or equal to 0.5, L is an alkali metal element with the same chemical valence as Na, and M is a transition metal element with the same chemical valence as Fe. According to the positive electrode material disclosed by the embodiment of the invention, the sodium ferric sulfate material with an expanded structure is taken as a main phase, and elements with variable radiuses are introduced into sodium sites and iron sites, so that the material further obtains a pore channel structure and defects with proper sizes, a three-dimensional diffusion channel of sodium ions is expanded, and the volume change in an electrochemical cycle process is inhibited; the structural stability of the material is ensured, so that the material shows relatively high gram volume and relatively good rate capability.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and in particular to a sulfate-based sodium cathode material with an expanded structure, a preparation method thereof, and a sodium ion battery. Background Art

[0002] With the increasing demand for new energy sources, sodium-ion batteries and their material systems have experienced explosive growth in recent years. Currently, the main cathode materials for sodium-ion batteries fall into three categories: transition metal oxides, polyanionic compounds (phosphates, fluorophosphates, and sulfates), and Prussian blue. Among these, sulfate-based sodium iron sulfate polyanionic cathode materials have attracted extensive attention and research due to their high voltage platform, wide availability of raw materials, extremely low cost, and excellent recyclability.

[0003] Traditional sulfate-based polyanion sodium cathode materials, Fe 2+ / Fe 3+ As a redox center, it can be described as an infinite link formed by alternating bridges of FeO6 octahedra and SO4 tetrahedra, formed by corner sharing, Na + Occupying the gaps between the long chains, it presents a framework stacking structure in which the sodium redox active sites and the iron redox active sites are interlaced. At the same time, the highly electronegative SO4 2- Anions and unique edge-sharing Fe2O 10 The dimer geometry gives sulfate-based polyanion cathode materials a three-dimensional sodium ion diffusion channel and a voltage-balanced platform of ≥3.6V. However, in this three-dimensional structure, some sodium ion sites are close to iron ion sites, and some sodium diffusion tunnels overlap during the three-dimensional diffusion process, resulting in capacity loss and reduced rate performance. Summary of the Invention

[0004] The present application provides a sulfate-based sodium cathode material with an expanded structure, a preparation method thereof, and a sodium ion battery. The cathode material of the embodiment of the present application is based on a sodium iron sulfate cathode material with an expanded structure. Compared with the traditional sulfate-based sodium cathode material, a potassium element (or rubidium element) that can expand the sodium site is introduced at the sodium site, and a divalent element (such as magnesium, copper, zinc, nickel, etc.) is introduced at the iron site. While expanding the distance between the sodium layers of the material, the introduction of the divalent element induces the intrinsic ordered dislocation of the iron site, so that the material further obtains a pore structure and defects of appropriate size, and also increases the SO4 2-The electronegativity and strong inductive effect near the anion further expand the three-dimensional diffusion channel of the sodium ion in the material, inhibiting the volume change during the electrochemical cycle, ensuring the structural stability of the material, and making the material exhibit a higher gram capacity and better rate performance. The positive electrode material of this application has an extremely high pressure area use range, high gram capacity, ultra-high cycle stability and excellent rate performance. The sodium ion battery prepared has the characteristics of high capacity, high rate, low cost and long cycle, providing a solution for the development of a new category of low-cost, high-rate and long-cycle sulfate polyanion sodium ion batteries.

[0005] In the first aspect, the present application provides a sulfate-based sodium cathode material with an expanded structure, wherein the sulfate-based sodium cathode material has the general formula Na 6-x L x Fe 5-y M y (SO4)8; wherein 0≤x≤0.5, 0<y≤0.5; L is an alkali metal element having the same chemical valence as Na, and M is a transition metal element having the same chemical valence as Fe.

[0006] In a second aspect, the present application provides a method for preparing a sodium sulfate cathode material having an expanded structure, comprising the following steps:

[0007] Sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, and sulfate containing transition metal M are mixed in a stoichiometric ratio and dissolved in water to obtain a sulfate aqueous solution. The pH value is controlled and the sulfate aqueous solution is spray-dried by a spray method to obtain a sodium ferric sulfate spray precursor. The sodium ferric sulfate spray precursor is mixed with a carbon material, ball-milled, dried, and sintered to obtain a sulfate-based sodium cathode material with an expanded structure.

[0008] In a third aspect, the present application provides a method for preparing another expanded structure sodium sulfate cathode material, comprising the following steps:

[0009] According to the stoichiometric ratio, sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, sulfate containing transition metal M and carbon material are mixed, ball-milled, dried and sintered to obtain a sulfate-based sodium cathode material with an expanded structure.

[0010] In a fourth aspect, the present application provides a sodium ion battery comprising a positive electrode material, wherein the positive electrode material comprises a sulfate-based sodium positive electrode material with an expanded structure as described in the first aspect above, or a sulfate-based sodium positive electrode material with an expanded structure prepared using the preparation method of a sulfate-based sodium positive electrode material with an expanded structure as described in the second or third aspect above.

[0011] Compared with the prior art, the expanded structure of the sulfate-based sodium cathode material provided in the embodiments of the present application has the following beneficial effects:

[0012] The expanded structure design replaces some traditional Fe sites with divalent transition metal elements (such as Mg, Ca, Cu, Zn, Sr, etc.), which is beneficial to the formation of an intrinsically ordered dislocation structure near the Fe site, optimizes the three-dimensional tunnel space for sodium ion migration, and increases the mobility of Na ions.

[0013] The preparation method of the expanded structure sodium sulfate cathode material provided in the embodiment of the present application can be obtained by spray drying combined with calcination, or by mixing, ball milling, drying, and sintering. It has the characteristics of cheap and readily available raw materials and a simple preparation process. The obtained expanded structure sodium sulfate cathode material has a complete crystal form and high purity.

[0014] In the embodiment of the present application, it is possible to adjust the sodium content and the content of monovalent doping elements (such as K, Rb, etc.), especially to control the total amount of monovalent elements (such as the sum of Na, K, Rb, etc.), while introducing a small amount of inert doping elements (such as divalent Mg, Ca, Cu, Zn, Sr, etc.) into the iron site structure to expand the support system and stabilize the structure; By element doping to regulate the cation potential as a whole, it is possible to effectively synthesize a purer sulfate-based sodium ion battery cathode material, so that the obtained positive electrode material has a higher sodium iron sulfate phase purity, thereby further increasing the structural stability, air stability, charge and discharge capacity, rate performance and long cycle capacity of the positive electrode material. At the same time, in the process of synthesis, by regulating the atmosphere (nitrogen atmosphere) and controlling the gas flow rate, the sintering atmosphere is maintained in the range of a higher nitrogen gas concentration, and the sulfate-based sodium electric material sodium ion battery cathode material with a purer support structure can be further effectively sintered.

[0015] The sodium ion battery provided in the embodiment of the present application provides a higher gram capacity, better structural stability and high rate performance for the sodium ion battery of the present application due to the use of a sulfate-based sodium cathode material with an expanded structure as the cathode material; compared with the traditional sulfate-based sodium ion battery cathode material, a potassium element (or rubidium element) with a larger atomic radius and capable of expanding the sodium site is introduced at the sodium site, and a divalent element with a variable radius (such as magnesium, copper, zinc, nickel, etc.) is introduced at the iron site. The introduction of dual-phase doping forms an inductive effect of intrinsic ordered dislocation, which enables the material to further obtain a pore structure and defects of appropriate size, and also increases SO4 2-The electronegativity and strong inductive effect near the anion further expand the three-dimensional diffusion channel of the sodium ion of the material, so that the material exhibits a higher gram capacity and stronger rate performance in a higher voltage range (2-4.5V), expanding the use scenarios of sulfate-based sodium cathode materials at low cost, high rate and long cycle. The positive electrode material of this application has an extremely high voltage area usage range, high gram capacity, ultra-high cycle stability and excellent rate performance. The sodium ion battery prepared has the characteristics of high capacity, high rate, low cost and long cycle.

[0016] In order to more clearly demonstrate the technical means of this application and ensure the smooth implementation of the contents of the specification, some typical embodiments of this application will be listed below together with drawings and detailed descriptions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 XRD patterns of the expanded-structure sulfate-based sodium cathode materials prepared in Examples 1 to 10 of the present application and the traditional sulfate-based sodium cathode material prepared in Comparative Example 1;

[0018] Figure 2 This is a SEM image of the sulfate-based sodium cathode material with an expanded structure prepared in Example 1 of the present application;

[0019] Figure 3 Schematic diagram comparing the first cycle charge and discharge curves of sodium ion half-cells assembled with the positive electrode materials of Example 1 and Comparative Example 1 of the present application at 2.0-4.5V and 0.1C;

[0020] Figure 4 Schematic diagram showing a rate comparison of sodium ion half-cells assembled using the positive electrode materials of Example 1 and Comparative Example 1 of the present application at 2.0-4.5V, 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C;

[0021] Figure 5 Schematic diagram of the long cycle of the sodium ion half-cell assembled in Example 1 of the present application at 2.0-4.5V and 0.5C. DETAILED DESCRIPTION

[0022] To make the invention objectives and technical solutions of this application more clear and understandable, the content of this application is further described in detail below with reference to the accompanying drawings and examples. However, it should be understood that the specific embodiments described herein are only intended to explain this application and are not intended to limit this application. Modifications and substitutions made to the methods, preparation steps, or conditions of this application without departing from the spirit and substance of this application are within the scope of this application.

[0023] Traditional sulfate-based polyanion sodium cathode materials, Fe 2+ / Fe 3+As a redox center, Na + Occupies the gaps between FeSO4 long chains, in Na + While entering and exiting the structure, Fe 2+ / Fe 3+ By changing the chemical bond valence to achieve chemical bond and charge balance, the sulfate-based polyanion cathode material possesses a three-dimensional sodium ion diffusion channel. However, within this three-dimensional structure, some sodium ion sites are close to iron ion sites, and during the three-dimensional diffusion process, some sodium diffusion tunnels overlap, resulting in capacity loss and reduced rate performance.

[0024] To solve the above problems, the present application provides a sulfate-based sodium cathode material with an expanded structure, a preparation method, and a sodium ion battery.

[0025] The present invention provides a sodium sulfate cathode material with an expanded structure. The sodium sulfate cathode material has the following general formula:

[0026] Na 6-x L x Fe 5-y M y (SO4)8;

[0027] Wherein, 0≤x≤0.5, 0<y≤0.5; L is an alkali metal element having the same chemical valence as Na, and M is a transition metal element having the same chemical valence as Fe.

[0028] For example: x is 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, etc.; y is 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, etc.

[0029] In order to induce the intrinsic ordered dislocation of iron sites and further expand the three-dimensional diffusion channel of sodium ions, the monovalent base element L and the divalent transition metal element M can only partially dope and replace the corresponding Na sites and Fe sites. If the value of x or y is greater than 0.5, it means that the monovalent base element L or the divalent transition metal element M has replaced the corresponding Na sites and Fe sites in large quantities, which may lead to phase separation, and the structural stability of the material cannot be guaranteed.

[0030] For example, x can be equal to 0, that is, the sulfate-based sodium cathode material can contain no L element. In this case, only divalent transition metal elements (such as Mg, Ca, Cu, Zn, Sr, etc.) can be doped to replace part of the traditional Fe sites, thereby forming a dislocation structure to increase the mobility of Na ions. In this case, the sulfate-based sodium cathode material has the following general formula:

[0031] Na6Fe 5-y M y(SO4)8; wherein, 0<y≤0.5.

[0032] Preferably, x is greater than 0, so that on the basis of being able to replace part of the traditional Fe sites with divalent transition metal elements (such as Mg, Ca, Cu, Zn, Sr, etc.), the traditional Na sites can also be doped with monovalent alkali metal elements (such as K, Rb, etc.), which is beneficial to further expand the structural space of the Na site and form a dislocation structure to increase the movement space of Na ions.

[0033] In the embodiments of the present application, it is also possible to use monovalent doping elements with larger atomic radius (such as K, Rb, etc.) to replace some of the traditional Na sites, so as to expand the Na sites and expand the channel space for sodium ions to enter and exit the three-dimensional structure, thereby increasing the ability of Na to quickly enter and exit, and improving the capacity and rate performance of the material.

[0034] In some embodiments, the atomic radius of L is greater than that of Na, and the atomic radius of M is different from that of Fe, i.e., the atomic radius of M can be greater or less than that of Fe. By controlling the atomic radii of L and M, more dislocation structures are formed to increase the mobility of Na ions.

[0035] For example, the atomic radius of L can be greater than the atomic radius of Na, and the atomic radius of M can be greater than or smaller than the atomic radius of Fe; divalent transition metal elements with different atomic radii (such as Mg, Ca, Cu, Zn, Sr, etc.) are doped to replace some traditional Fe sites, thereby forming a dislocation structure to increase the movement space of Na ions to activate the redox channel of iron. The expansion structure is designed to provide more movement space for the migration channel of Na in the staggered three-dimensional structure.

[0036] Specifically, the embodiment of the present application provides a sulfate-based sodium cathode material with an expanded structure. Compared with the prior art, a potassium element (or rubidium element) with a larger atomic radius and capable of expanding the sodium site is introduced into the sodium site, and a divalent element (such as magnesium, copper, zinc, nickel, etc.) with a variable radius is introduced into the iron site. While expanding the distance between the sodium layers of the material, the introduction of the divalent element induces the intrinsic ordered dislocation of the iron site, so that the material further obtains a pore structure and defects of appropriate size, and also increases SO4 2-The electronegativity and strong inductive effect near the anion further expand the three-dimensional diffusion channel of the sodium ion in the material, inhibiting the volume change during the electrochemical cycle, ensuring the structural stability of the material, and making the material exhibit a higher gram capacity and better rate performance. The positive electrode material of this application has an extremely high pressure area usage range, high gram capacity, ultra-high cycle stability and excellent rate performance. The sodium ion battery prepared has the characteristics of high capacity, high rate, low cost and long cycle, which provides a solution for the development of a new category of low-cost, high-rate and long-cycle sulfate polyanion sodium ion batteries.

[0037] In some embodiments, L is at least one element selected from K and Rb, and M is at least one element selected from Mg, Ca, Cu, Zn, Sr, and Ni.

[0038] Specifically, taking into comprehensive consideration factors such as cost-effectiveness, sintering difficulty, radiation resistance, and structural fusion, L generally selects at least one element from K and Rb, and M generally selects at least one element from Mg, Ca, Cu, Zn, Sr, and Ni.

[0039] In some embodiments, the sulfate sodium electrolyte material may be

[0040] Na 5.95 K 0.05 Fe 4.9 Mg 0.1 (SO4)8、Na 5.95 K 0.05 Fe 4.9 Ca 0.1 (SO4)8,

[0041] Na 5.95 K 0.05 Fe 4.9 Cu 0.1 (SO4)8、Na 5.95 K 0.05 Fe 4.9 Zn 0.1 (SO4)8,

[0042] Na 5.95 K 0.05 Fe 4.9 Sr 0.1 (SO4)8、Na 5.95 K 0.05 Fe 4.9 Ni 0.1 (SO4)8,

[0043] Na6Fe 4.9 Mg 0.1 (SO4)8、Na 5.8 K 0.2Fe 4.8 Mg 0.2 (SO4)8,

[0044] Na 5.7 K 0.3 Fe 4.7 Mg 0.3 (SO4)8、Na 5.5 K 0.5 Fe 4.5 Mg 0.5 (SO4)8

[0045] At least one of .

[0046] like Figure 1 As shown, Figure 1 Therefore

[0047] Na 5.95 K 0.05 Fe 4.9 Mg 0.1 (SO4)8 (Example 1), Na 5.95 K 0.05 Fe 4.9 Ca 0.1 (SO4)8 (Example 2),

[0048] Na 5.95 K 0.05 Fe 4.9 Cu 0.1 (SO4)8 (Example 3), Na 5.95 K 0.05 Fe 4.9 Zn 0.1 (SO4)8 (Example 4),

[0049] Na 5.95 K 0.05 Fe 4.9 Sr 0.1 (SO4)8 (Example 5), Na 5.95 K 0.05 Fe 4.9 Ni 0.1 (SO4)8 (Example 6),

[0050] Na6Fe 4.9 Mg 0.1 (SO4)8 (Example 7), Na 5.8 K 0.2 Fe 4.8 Mg 0.2 (SO4)8 (Example 8),

[0051] Na 5.7 K 0.3 Fe4.7 Mg 0.3 (SO4)8 (Example 9), Na 5.5 K 0.5 Fe 4.5 Mg 0.5 (SO4)8 (Example 10)

[0052] For example, in the XRD (X-ray diffraction) pattern, the horizontal axis is twice the incident angle (θ) of the X-ray (2θ, in degrees), and the vertical axis is the intensity after diffraction (intensity, au in the figure is the abbreviation of absorbance unit); according to Figure 1 It can be seen that this type of sulfate-based sodium electrolyte material has a crystal structure of sodium iron sulfate phase and is partially doped with elements. While maintaining a high capacity, it also maintains excellent structural stability.

[0053] In the embodiment of the present application, the sulfate-based sodium battery cathode material with an expanded structure refers to a sodium ion battery cathode material whose main phase is a sodium iron sulfate phase.

[0054] It should be noted that the main phase of the expanded sulfate-based sodium battery cathode material prepared in the examples of the present application is a sodium ferric sulfate phase. Alternatively, a mixed-phase sodium ion battery cathode material may be used, i.e., a sodium ferric sulfate phase as the main phase, but may also contain a partial ferrous sulfate phase, a partial sodium sulfate phase, or other mixed-phase materials, without specific limitation herein.

[0055] Preferably, the expanded structure sulfate-based sodium cathode material prepared in the embodiment of the present application contains only sodium ferric sulfate phase, thereby making the purity of the sodium ferric sulfate phase in the prepared cathode material higher, thereby further increasing the structural stability, air stability, charge and discharge capacity, rate performance and long cycle capacity of the cathode material.

[0056] The present invention provides a method for preparing the above-mentioned sulfate-based sodium cathode material with an expanded structure, which comprises the following steps:

[0057] Sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, and sulfate containing transition metal M are mixed in a stoichiometric ratio and dissolved in water to obtain a sulfate aqueous solution. The pH value is controlled and the sulfate aqueous solution is spray-dried by a spray method to obtain a sodium ferric sulfate spray precursor. The sodium ferric sulfate spray precursor is mixed with a carbon material, ball-milled, dried, and sintered to obtain a sulfate-based sodium cathode material with an expanded structure.

[0058] In the embodiment of the present application, the sulfate aqueous solution is a sulfate aqueous solution containing an alkali metal L and a transition metal M, and the sodium ferric sulfate spray precursor is a sodium ferric sulfate spray precursor containing an alkali metal L and a transition metal M. The carbon material may include carbon-containing materials such as carbon nanotubes, nanoscale carbon black, or carbon fibers.

[0059] An embodiment of the present application provides another method for preparing the above-mentioned sulfate-based sodium cathode material with an expanded structure, which includes the following steps: mixing sodium sulfate, ferrous sulfate, a sulfate containing an alkali metal L, a sulfate containing a transition metal M, and a carbon material according to a stoichiometric ratio, ball milling, drying, and sintering to obtain the sulfate-based sodium cathode material with the expanded structure.

[0060] In the embodiment of the present application, the carbon material may include carbon-containing materials such as carbon nanotubes, nanoscale carbon black or carbon fibers.

[0061] The above two preparation methods are explained in detail below.

[0062] The first preparation method:

[0063] (1) Sodium sulfate, ferrous sulfate, a sulfate containing an alkali metal L, and a sulfate containing a transition metal M are mixed in a stoichiometric ratio and dissolved in water to obtain a sulfate aqueous solution;

[0064] (2) spray drying the sulfate aqueous solution by spraying, controlling the pH value, and obtaining a sodium iron sulfate spray precursor after spray drying;

[0065] (3) According to the stoichiometric ratio, the sodium iron sulfate spray precursor is mixed with carbon materials (carbon nanotubes, nano-scale carbon black or carbon fibers and other carbon-containing materials), ball milled, dried, and sintered to obtain a sulfate-based sodium cathode material containing an expanded structure.

[0066] The corresponding conditions for the sintering treatment are: first sintering at a constant temperature of 150-220° C. for 5-10 hours, then heating to 340-380° C. and sintering at a constant temperature for 12-48 hours, and the sintering atmosphere is a nitrogen atmosphere.

[0067] In some embodiments, the sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, and sulfate containing transition metal M are mixed and fed in a ratio of (2.5-3):(3-5):(0-0.25):(0-0.5).

[0068] In some embodiments, before the spray drying reaction, sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, and sulfate containing transition metal M are prepared into corresponding aqueous solutions and uniformly mixed to improve the reaction efficiency of the spray drying.

[0069] In some embodiments, a dispersant needs to be added to the solution during the spray drying reaction. Preferably, the pH value of the reaction system can also be adjusted to a pH value that is conducive to the reaction.

[0070] In some embodiments, a sodium ferric sulfate spray precursor is mixed with a carbon material (carbon-containing materials such as carbon nanotubes, nanoscale carbon black or carbon fibers) according to a molar ratio, wherein the mass ratio of the sodium ferric sulfate spray precursor to the carbon material is 100:(0.5-5), and then ball milling, tableting and sintering are performed.

[0071] The second preparation method:

[0072] (1) Sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, sulfate containing transition metal M and carbon material (carbon nanotubes, nano-scale carbon black or carbon fiber and other carbon-containing materials) are mixed, ball-milled, dried and sintered according to the stoichiometric ratio to obtain a sulfate-based sodium cathode material with an expanded structure.

[0073] The corresponding conditions for the sintering treatment are: first sintering at a constant temperature of 150-220° C. for 5-10 hours, then heating to 340-380° C. and sintering at a constant temperature for 12-48 hours, and the sintering atmosphere is a nitrogen atmosphere.

[0074] In some embodiments, the sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, and sulfate containing transition metal M are added in a ratio of (2.5-3):(3-5):(0-0.25):(0-0.5) to obtain a mixture; the mass ratio of the above mixture to the carbon material = 100:(0.5-5).

[0075] In some embodiments, the mixing process can be performed by mechanical grinding or by preparing a solution. Specifically, the mixture can be mixed and ultrasonically shaken to form a slurry, or directly wet high-energy ball milling can be used to form a slurry. Finally, after drying and secondary ball milling, the expanded structure of the sulfate-based sodium cathode material can be obtained.

[0076] Among them, the purpose of mixing is to mix the sodium ferric sulfate spray precursor and the carbon material evenly, or to mix the sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, sulfate containing transition metal M and carbon material evenly, so as to facilitate sintering into a sulfate-based sodium cathode material with an expanded structure.

[0077] The preparation method of the sulfate-based sodium cathode material with an expanded structure provided in the embodiment of the present application adopts a spray drying combined with calcination method, or adopts mixing, ball milling, drying, and sintering treatment to obtain it. It has the characteristics of cheap and easy-to-obtain raw materials and a simple preparation process. The obtained sulfate-based sodium cathode material with an expanded structure has a complete crystal form and high purity. At the same time, during the synthesis process, by adjusting the airflow (nitrogen atmosphere) and controlling the air flow size, the sintering atmosphere is maintained in a range of relatively high air intake concentration, and a relatively pure expanded structure sulfate-based sodium cathode material can be effectively sintered, which is beneficial to improving the sodium iron sulfate phase purity of the cathode material.

[0078] The expanded structure of the sulfate-based sodium cathode material prepared in the embodiment of the present application introduces a potassium element (or rubidium element) with a large atomic radius and capable of expanding the sodium site at the sodium site, and introduces a divalent element with a variable radius (such as magnesium, copper, zinc, nickel, etc.) at the iron site. The introduction of dual-phase doping forms an inductive effect of intrinsic ordered dislocation, which enables the material to further obtain a pore structure and defects of appropriate size, and also increases SO4 2- The electronegativity and strong inductive effect near the anion further expand the three-dimensional diffusion channel of the sodium ion of the material, so that the material exhibits a higher gram capacity and stronger rate performance in a higher voltage range (2-4.5V), expanding the use scenarios of sulfate-based sodium cathode materials at low cost, high rate and long cycle. The positive electrode material of this application has an extremely high voltage area usage range, high gram capacity, ultra-high cycle stability and excellent rate performance. The sodium ion battery prepared has the characteristics of high capacity, high rate, low cost and long cycle.

[0079] The embodiments of the present application also provide a positive electrode sheet and a sodium ion battery using the sodium transition metal oxide positive electrode material with the above-mentioned expanded structure. Specifically, the sulfate-based sodium positive electrode material with the above-mentioned expanded structure is mixed with a conductive agent, a binder and a solvent to form a positive electrode slurry, which is applied to the surface of the positive electrode collector, and is dried, rolled and cut into pieces to form a positive electrode sheet. The mass ratio of the sulfate-based sodium positive electrode material with the expanded structure, the conductive agent and the binder in the positive electrode sheet is 8:1:1. When preparing the positive electrode slurry, the solvent can be N-methylpyrrolidone (NMP), the positive electrode binder is selected from PVDF, and the positive electrode conductive additive is selected from carbon black, acetylene black, SuperP, etc.

[0080] Based on the positive electrode sheet provided above, an embodiment of the present invention further provides a method for preparing a sodium ion battery. The sodium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0081] In some embodiments, the sodium ion battery provided in the embodiments of the present application uses metallic sodium as the negative electrode material, and the electrolyte is any one of 1M NaPF6 / (EC:DMC=1:1) electrolyte, 1M NaPF6 / PC electrolyte, and 1M NaClO4 / (EC:PC=1:1) electrolyte, wherein EC represents ethylene carbonate, DMC represents dimethyl carbonate, PC represents propylene carbonate, EC:DMC=1:1 represents a solvent formed by ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1, and EC:PC represents a solvent formed by ethylene carbonate and propylene carbonate in a volume ratio of 1:1.

[0082] In some embodiments, the sodium ion battery provided in the embodiments of the present application uses a diaphragm that is a polyolefin microporous membrane such as polyethylene, polypropylene, etc., such as a Celgard diaphragm.

[0083] The sodium ion battery provided in the embodiment of the present application provides a higher gram capacity, better structural stability and extremely high rate performance for the sodium ion battery of the present application due to the use of a sulfate-based sodium cathode material with an expanded structure as the positive electrode material; compared with the traditional sulfate-based sodium ion battery positive electrode material, the sulfate-based sodium cathode material with an expanded structure provided in the embodiment of the present application introduces a potassium element (or rubidium element) with a larger atomic radius and capable of expanding the sodium site at the sodium site, and introduces a divalent element with a variable radius (such as magnesium, copper, zinc, nickel, etc.) at the iron site. The introduction of dual-phase doping forms an inductive effect of intrinsic ordered dislocation, which enables the material to further obtain a pore structure and defects of appropriate size, while also increasing SO4 2- The electronegativity and strong inductive effect near the anion further expand the three-dimensional diffusion channel of the sodium ion in the material, allowing the material to exhibit higher gram capacity and stronger rate performance in a higher voltage range (2-4.5V). Compared with traditional sulfate-based sodium-ion battery positive electrode materials, the sulfate-based sodium cathode material with an expanded structure in this application exhibits higher gram capacity and more stable cycle performance, expanding the use scenarios of sulfate-based sodium cathode materials under low cost, high rate and long cycle conditions.

[0084] In order to more effectively illustrate the technical solution of the present invention, a number of specific embodiments are provided below.

[0085] Example 1

[0086] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0087] (a) Sodium sulfate, potassium sulfate, ferrous sulfate, and magnesium sulfate raw materials are mixed and dissolved in water at a molar ratio of 2.975:0.025:4.9:0.1 to prepare a 1.0 mol / L mixed transition metal salt solution, and the resulting sulfate aqueous solution is spray-dried by a spray method, and the pH value is controlled. After spray drying, a sodium ferric sulfate spray precursor is obtained.

[0088] (b) The sodium iron sulfate spray precursor obtained in step (a) was mixed with carbon nanotubes at a ratio of 96:4 in terms of the total weight of the raw materials to the weight of the carbon nanotubes, and added to a ball mill together with grinding beads of the same weight. An appropriate amount of ethanol was added, and the mixture was ball milled at a speed of 200 r / min for 2 h to obtain a uniformly mixed powder slurry.

[0089] (c) The powder slurry mixed uniformly in step (b) was dried in a drying device at a drying temperature of 120° C. for 24 h, and ball-milled twice to obtain a dry mixture powder precursor.

[0090] (d) The dry mixture powder precursor obtained in step (c) was placed in a tube furnace, heated to 150°C under a nitrogen atmosphere and sintered at a constant temperature for 10 hours, then heated to 360°C and sintered at a constant temperature for 20 hours, and naturally cooled to room temperature to obtain sample 1, whose molecular formula is Na 5.95 K 0.05 Fe 4.9 Mg 0.1 (SO4)8.

[0091] (e) XRD and SEM (Scanning Electron Microscope) tests were performed on the obtained sample 1. The specific test results are shown in Figure 1 and Figure 3 , the cycle performance is shown in Table 1.

[0092] Example 2

[0093] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0094] According to the molar ratio, sodium sulfate, potassium sulfate, ferrous sulfate, and calcium sulfate raw materials are mixed in a molar ratio of 2.975:0.025:4.9:0.1, and the weight ratio of the total weight of the above raw materials to the carbon nanotubes is controlled to be 96:4. The corresponding weight of the carbon nanotube material is added and mixed, and added to the ball mill jar together with the same weight of grinding beads. At the same time, some ethanol is added and high-energy ball milling is carried out at a speed of 400r / min for 8h to take out the mixed powder slurry. Then, referring to the treatment method (c)-(d) in Example 1, after ball milling, drying, and sintering, the expanded structure sulfate sodium positive electrode material Na is obtained. 5.95 K0.05 Fe 4.9 Ca 0.1 (SO4)8, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0095] Example 3

[0096] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0097] Referring to Example 1, sodium sulfate, potassium sulfate, ferrous sulfate, and copper sulfate raw materials were prepared in a molar ratio of 2.975:0.025:4.9:0.1 to prepare a sodium ferric sulfate spray precursor. The prepared sodium ferric sulfate spray precursor was mixed with carbon nanotubes in a ratio of 96:4 in terms of the total weight of the raw materials and the weight of the carbon nanotubes. Then, the treatment methods (b) to (d) in Example 1 were followed to obtain a sulfate-based sodium cathode material Na with an expanded structure. 5.95 K 0.05 Fe 4.9 Cu 0.1 (SO4)8, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0098] Example 4

[0099] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0100] Referring to Example 1, sodium sulfate, potassium sulfate, ferrous sulfate, and zinc sulfate raw materials were prepared in a molar ratio of 2.975:0.025:4.9:0.1 to prepare a sodium ferric sulfate spray precursor. The prepared sodium ferric sulfate spray precursor was mixed with carbon nanotubes in a ratio of 96:4 in terms of the total weight of the raw materials and the weight of the carbon nanotubes. Then, the treatment methods (b) to (d) in Example 1 were followed to obtain a sulfate-based sodium cathode material Na with an expanded structure. 5.95 K 0.05 Fe 4.9 Zn 0.1 (SO4)8, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0101] Example 5

[0102] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0103] Referring to Example 1, sodium sulfate, potassium sulfate, ferrous sulfate, and strontium sulfate raw materials were prepared in a molar ratio of 2.975:0.025:4.9:0.1 to prepare a sodium ferric sulfate spray precursor. The prepared sodium ferric sulfate spray precursor was mixed with carbon nanotubes in a ratio of 96:4 in terms of the total weight of the raw materials and the weight of the carbon nanotubes. Then, the treatment methods (b) to (d) in Example 1 were followed to obtain a sulfate-based sodium cathode material Na with an expanded structure. 5.95 K 0.05 Fe 4.9 Sr 0.1 (SO4)8, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0104] Example 6

[0105] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0106] Referring to Example 1, sodium sulfate, potassium sulfate, ferrous sulfate, and nickel sulfate raw materials were prepared in a molar ratio of 2.975:0.025:4.9:0.1 to prepare a sodium ferric sulfate spray precursor. The prepared sodium ferric sulfate spray precursor was mixed with carbon nanotubes in a ratio of 96:4 in terms of the total weight of the raw materials and the weight of the carbon nanotubes. Then, the treatment methods (b) to (d) in Example 1 were followed to obtain a sulfate-based sodium cathode material Na with an expanded structure. 5.95 K 0.05 Fe 4.9 Ni 0.1 (SO4)8, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0107] Example 7

[0108] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0109] Referring to Example 1, sodium sulfate, ferrous sulfate, and magnesium sulfate raw materials were prepared in a molar ratio of 3:4.9:0.1 to prepare a sodium ferric sulfate spray precursor. The prepared sodium ferric sulfate spray precursor was mixed with carbon nanotubes in a ratio of 96:4 in terms of the total weight of the raw materials and the weight of the carbon nanotubes. Then, the treatment methods (b) to (d) in Example 1 were followed to obtain a sulfate-based sodium cathode material Na6Fe 4.9 Mg 0.1 (SO4)8, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0110] Example 8

[0111] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0112] Referring to Example 1, sodium sulfate, potassium sulfate, ferrous sulfate, and magnesium sulfate raw materials were prepared in a molar ratio of 2.9:0.1:4.8:0.2 to prepare a sodium ferric sulfate spray precursor. The prepared sodium ferric sulfate spray precursor was mixed with carbon nanotubes in a ratio of 96:4 in terms of the total weight of the raw materials and the weight of the carbon nanotubes. Then, the treatment methods (b) to (d) in Example 1 were followed to obtain a sulfate-based sodium cathode material Na with an expanded structure. 5.8 K 0.2 Fe 4.8 Mg 0.2 (SO4)8, its XRD pattern is as follows Figure 1 The cycle performance is shown in Table 1.

[0113] Example 9

[0114] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0115] Referring to Example 1, sodium sulfate, potassium sulfate, ferrous sulfate, and magnesium sulfate raw materials were prepared in a molar ratio of 2.85:0.15:4.7:0.3 to prepare a sodium ferric sulfate spray precursor. The prepared sodium ferric sulfate spray precursor was mixed with carbon nanotubes in a ratio of 96:4 in terms of the total weight of the raw materials and the weight of the carbon nanotubes. Then, the treatment method (b)-(d) in Example 1 was followed to obtain a sulfate-based sodium cathode material Na with an expanded structure. 5.7 K 0.3 Fe 4.7 Mg 0.3 (SO4)8, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0116] Example 10

[0117] A method for preparing a sodium sulfate cathode material with an expanded structure comprises the following steps:

[0118] Referring to Example 1, sodium sulfate, potassium sulfate, ferrous sulfate, and magnesium sulfate raw materials were prepared in a molar ratio of 2.75:0.25:4.5:0.5 to prepare a sodium ferric sulfate spray precursor. The prepared sodium ferric sulfate spray precursor was mixed with carbon nanotubes in a ratio of 96:4 in terms of the total weight of the raw materials and the weight of the carbon nanotubes. Then, the treatment method (b)-(d) in Example 1 was followed to obtain a sulfate-based sodium cathode material Na with an expanded structure. 5.5 K 0.5 Fe 4.5 Mg 0.5 (SO4)8, its XRD pattern is as follows Figure 1 The cycle performance is shown in Table 1.

[0119] Comparative Example 1

[0120] A related technology provides a sulfate-based sodium cathode material:

[0121] (a) Sodium sulfate and ferrous sulfate raw materials are mixed and dissolved in water at a molar ratio of 3:5 to prepare a 1.0 mol / L sulfate aqueous solution, and the obtained sulfate aqueous solution is spray-dried by a spray method, and the pH value is controlled. After spray drying, a sodium ferric sulfate spray precursor is obtained.

[0122] (b) The sodium iron sulfate spray precursor obtained in step (a) was mixed with carbon nanotubes at a ratio of 96:4 in terms of the total weight of the raw materials to the mass of the carbon nanotubes. The mixture was added to a ball mill together with grinding beads of the same weight. An appropriate amount of ethanol was added and the mixture was ball milled at a speed of 200 r / min for 2 h. The uniformly mixed powder slurry was taken out.

[0123] (c) The powder slurry mixed uniformly in step (b) was dried in a drying device at a drying temperature of 120° C. for 24 h, and ball-milled twice to obtain a dry mixture powder precursor.

[0124] (d) The dry mixture powder precursor obtained in step (c) was placed in a tube furnace, heated to 150°C under a nitrogen atmosphere and sintered at a constant temperature for 10 hours, then heated to 360°C and sintered at a constant temperature for 20 hours, and naturally cooled to room temperature to obtain comparative example sample 1, whose molecular formula is Na6Fe5(SO4)8.

[0125] Application Example 1

[0126] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0127] (1) The sample obtained in Example 1 was used as the positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and then dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, which was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0128] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0129] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0130] Application Example 2

[0131] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0132] (1) The sample obtained in Example 2 was used as the positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and then dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The slurry was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0133] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0134] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0135] Application Example 3

[0136] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0137] (1) The sample obtained in Example 3 was used as the positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and then dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The slurry was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0138] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0139] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0140] Application Example 4

[0141] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0142] (1) The sample obtained in Example 4 was used as the positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, which was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0143] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0144] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0145] Application Example 5

[0146] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0147] (1) The sample obtained in Example 5 was used as the positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, which was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0148] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0149] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0150] Application Example 6

[0151] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0152] (1) The sample obtained in Example 6 was used as the positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The slurry was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0153] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0154] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0155] Application Example 7

[0156] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0157] (1) The sample obtained in Example 7 was used as the positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and then dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The slurry was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0158] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0159] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0160] Application Example 8

[0161] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0162] (1) The sample obtained in Example 8 was used as the positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and then dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The slurry was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0163] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0164] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0165] Application Example 9

[0166] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0167] (1) The sample obtained in Example 9 was used as the positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The slurry was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0168] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0169] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0170] Application Example 10

[0171] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0172] (1) The sample obtained in Example 10 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The slurry was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0173] (2) The positive electrode obtained in step (1) was assembled with sodium metal and a Celgard separator into a sodium ion battery. The electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (EC:DMC=1:1 by volume). After assembly, the battery was allowed to stand for 24 hours and then subjected to charge and discharge activation tests.

[0174] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0175] Application Example 11

[0176] A sodium ion battery comprising a sulfate-based sodium cathode material with an expanded support structure, wherein the preparation method comprises the following steps:

[0177] (1) The sample obtained in Comparative Example 1 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, and dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, which was then coated on aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0178] (2) Assemble the positive electrode obtained in step (1) with sodium metal and Celgard separator to form a sodium ion battery. The electrolyte of the sodium ion battery is a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, let it stand for 24 hours, and then perform charge and discharge activation test.

[0179] Specifically, the test method involved charging and discharging three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.5V. Rate performance was then tested at various rates, including 5C (1C = 100 mA / g). The results are shown in Table 1.

[0180] Figure 1 The main diffraction peaks of all samples from Example 1 to Example 10 show a sulfate-based sodium electrode material crystal structure, with a complete crystal structure and a low impurity content, proving that the obtained materials are sodium electrode positive electrode materials containing a sulfate-based crystal structure.

[0181] from Figure 2 The SEM results show that the sample 1 of Example 1 is spherical and partially coated with carbon nanotubes. Figure 2 The dimension in the lower right corner is 5 μm.

[0182] The expanded structure of the sulfate sodium cathode material Na 5.95 K 0.05 Fe 4.9 Mg 0.1 (SO4)8 and the traditional sulfate sodium cathode material Na6Fe5(SO4)8 of Comparative Example 1 were used as cathode materials, respectively, and assembled with sodium metal negative electrode to form sodium ion batteries and the electrochemical performance tests were carried out. Figure 3 As shown, the sodium ion battery assembled by the sample of Example 1 has a reversible initial capacity of about 105 mAh / g when cycled at a current density of 0.1C (10 mA / g) in the voltage range of 2.0 to 4.5 V, and the capacity is expressed in a higher voltage range (3.3 to 4.3 V). However, the sodium ion battery assembled by the sample of Comparative Example 1 has a reversible initial capacity of only about 80 mAh / g under the same conditions. In the subsequent rate test, as shown in FIG. Figure 4 As shown, the sodium ion batteries assembled with the materials of Example 1 and Comparative Example 1 were tested under current density cycling conditions of 0.1C (10mA / g), 0.2C (20mA / g), 0.5C (50mA / g), 1C (100mA / g), 2C (200mA / g) and 5C (500mA / g), respectively. The reversible initial capacities of Example 1 were approximately 105mAh / g, 103mAh / g, 99mAh / g, 95mAh / g, 91mAh / g and 85mAh / g, respectively, which were significantly higher than the rate retention rate of Comparative Example 1 (Comparative Example 1 was only about 49mAh / g at 5C); in the subsequent long cycle test, as shown in FIG. Figure 5As shown, when cycled at 0.5C (50mA / g), the material of Example 1 still retains a discharge specific capacity of about 99mAh / g, and after 100 long cycles, the capacity retention rate is still about 100%, showing super strong cycle stability. The reason is that in Example 1 of this application, an expanded structure of sodium iron sulfate positive electrode material is used as the active material. Compared with the traditional sulfate-based sodium positive electrode material, a potassium element (or rubidium element) with a larger atomic radius and capable of expanding the sodium site is introduced at the sodium site, and a divalent element with a radius change (such as magnesium, copper, zinc, nickel, etc.) is introduced at the iron site. While expanding the distance between the sodium layers of the material, the introduction of the divalent element induces the intrinsic ordered dislocation of the iron site, so that the material further obtains a pore structure and defects of suitable size, and also increases SO4 2- The electronegativity and strong inductive effect near the anion further expand the three-dimensional diffusion channel of sodium ions in the material, inhibiting the volume change during the electrochemical cycle, ensuring the structural stability of the material, and enabling the material to exhibit higher gram capacity, stable long-cycle capability and better rate performance.

[0183] In addition, Table 1 shows the materials of Examples 1-10, the charge and discharge capacity test results at 0.1C and 5C, and the rate test results at 5C. The results show that Examples 1-10 exhibit higher high-rate discharge specific capacity and rate retention rate (the energy retention rate at 5C high rate is 75-85%), showing stronger rate performance. In comparison, the material of Comparative Example 1 has poor discharge capacity and rate retention at high rate (the rate retention rate at 5C high rate is only about 60%). Therefore, the sulfate-based sodium positive electrode material with an expanded structure in the embodiment of the present application overcomes the problem of low rate performance of sulfate-based sodium positive electrode materials, relative to traditional sulfate-based sodium positive electrode materials, and exhibits higher gram capacity, stronger rate performance and super cycle stability (100 cycles ≈ 100%), expanding the use scenarios of sulfate-based sodium positive electrode materials under high capacity, high rate and long cycle.

[0184] The positive electrode material of the present application has an extremely high pressure area usage range, high gram capacity, ultra-high cycle stability and excellent rate performance. The sodium ion battery prepared has the characteristics of high capacity, large rate, low cost and long cycle, which provides a solution for the development of a new category of low-cost, high-rate and long-cycle sulfate-based polyanion sodium ion batteries.

[0185] Table 1

[0186]

[0187]

[0188] It should be understood that the terms used in the present specification are only used to describe specific embodiments and are not intended to limit the present application.

[0189] It will also be understood that the term "and / or" used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0190] The above descriptions are merely specific embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included within the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A sodium sulfate cathode material with an expanded structure, characterized in that: The sulfate-based sodium cathode material has the following general formula: Na 6-x L x Fe 5-y M y (SO4)8; Wherein, 0≤x≤0.5, 0<y≤0.5; L is an alkali metal element having the same chemical valence as Na, and M is a transition metal element having the same chemical valence as Fe.

2. The cathode material according to claim 1, wherein the atomic radius of L is greater than that of Na, and the atomic radius of M is different from that of Fe.

3. The positive electrode material according to claim 1, wherein L is at least one element selected from K and Rb, and M is at least one element selected from Mg, Ca, Cu, Zn, Sr, and Ni.

4. The positive electrode material according to claim 1, wherein The sulfate sodium electrode material is Na 5.95 K 0.05 Fe 4.9 Mg 0.1 (SO4)8、Na 5.95 K 0.05 Fe 4.9 Ca 0.1 (SO4)8、Na 5.95 K 0.05 Fe 4.9 Cu 0.1 (SO4)8、Na 5.95 K 0.05 Fe 4.9 Zn 0.1 (SO4)8、Na 5.95 K 0.05 Fe 4.9 Sr 0.1 (SO4)8、Na 5.95 K 0.05 Fe 4.9 Ni 0.1 (SO4)8、Na6Fe 4.9 Mg 0.1 (SO4)8、Na 5.8 K 0.2 Fe 4.8 Mg 0.2 (SO4)8、Na 5.7 K 0.3 Fe 4.7 Mg 0.3 (SO4)8、Na 5.5 K 0.5 Fe 4.5 Mg 0.5 At least one of (SO4)8.

5. The positive electrode material according to any one of claims 1 to 4, characterized in that The main phase of the positive electrode material is sodium iron sulfate positive electrode material.

6. A method for preparing a sulfate-based sodium cathode material with an expanded structure according to any one of claims 1 to 4, characterized in that: The preparation method comprises: Sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, and sulfate containing transition metal M are mixed in a stoichiometric ratio and dissolved in water to obtain a sulfate aqueous solution. The pH value is controlled and the sulfate aqueous solution is spray-dried by a spray method to obtain a sodium ferric sulfate spray precursor. The sodium ferric sulfate spray precursor is mixed with a carbon material, ball-milled, dried, and sintered to obtain a sulfate-based sodium cathode material with an expanded structure.

7. A method for preparing a sulfate-based sodium cathode material with an expanded structure according to any one of claims 1 to 4, characterized in that: The preparation method comprises: According to the stoichiometric ratio, sodium sulfate, ferrous sulfate, sulfate containing alkali metal L, sulfate containing transition metal M and carbon material are mixed, ball-milled, dried and sintered to obtain a sulfate-based sodium cathode material with an expanded structure.

8. The preparation method according to claim 6 or 7, wherein the sodium sulfate, the ferrous sulfate, the sulfate containing the alkali metal L, and the sulfate containing the transition metal M are mixed and fed in a ratio of (2.5-3):(3-5):(0-0.25):(0-0.5).

9. The preparation method according to claim 6 or 7, wherein the sintering conditions are: first sintering at a constant temperature of 150-220°C for 5-15 hours, then heating to 340-380°C and sintering at a constant temperature for 12-48 hours, and the sintering atmosphere is a nitrogen atmosphere.

10. A sodium ion battery comprising a positive electrode material, characterized in that: The positive electrode material comprises the sodium sulfate-based positive electrode material with an expanded structure according to any one of claims 1 to 4, or the sodium sulfate-based positive electrode material with an expanded structure prepared by the preparation method according to any one of claims 6 to 9.

Images