A sodium-ion fast ion conductor as a coating layer for a sodium-ion battery cathode material, its preparation method and application

Abstract

The present invention provides a sodium-ion battery positive electrode material with a sodium fast-ion conductor as a coating layer, a preparation method thereof, and an application thereof. The chemical formula of the sodium fast-ion conductor is: Na4MP2O9; wherein, M is Ti or V; the crystal structure is: PO4 tetrahedrons and MO6 octahedrons are connected by sharing vertices to form a one-dimensional chain structure, and Na ions are distributed between the chains and can freely diffuse in at least three directions. The positive electrode material has a core-shell structure and includes a core and a coating layer; the material of the core includes a sodium nickel iron manganese oxide positive electrode material; the mass ratio of the coating layer to the core is 0.1-0.3 wt%. The sodium fast-ion conductor enriches the diffusion path of sodium ions, improves the sodium ion content and ionic conductivity, reduces the impedance of the coating layer as a positive electrode material, and realizes the fast charge and discharge and high-temperature cycling performance of sodium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and relates to a sodium-ion battery cathode material, in particular to a sodium-ion battery cathode material with a sodium fast ion conductor as a coating layer, and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries have broad application prospects due to their cost advantages. Their working principle is similar to that of lithium-ion batteries, and they use the reversible insertion and extraction of sodium ions between the positive and negative electrodes to achieve energy storage and release. Currently, the cathode materials used for sodium-ion batteries mainly include three categories: transition metal oxide systems, polyanion compounds (phosphate systems, fluorophosphate systems, and NASICON structures), and Prussian blue systems. Among them, transition metal oxide cathode materials with high specific capacity have attracted extensive attention and research from those skilled in the art. However, with the increase in the number of charge and discharge cycles, the problem of electrochemical performance decay caused by their high surface activity and poor structural stability is becoming more and more serious. In this regard, by using a surface coating technology to construct a protective barrier on the surface of the cathode material, it is possible to avoid direct contact between the active substance and the electrolyte and prevent erosion, inhibit the dissolution of transition metals, and thus significantly improve the stability of the surface structure.

[0003] Sodium fast ion conductors have both high ionic conductivity and excellent thermal stability. After being coated on the surface of the cathode material, they can significantly improve the conductivity of the material, reduce the internal resistance, and enhance the rate performance and high-temperature cycle performance of sodium-ion batteries. The sodium fast ion conductor coating materials reported currently include sodium metaaluminate, sodium niobate, sodium titanate, sodium borate, sodium metaborate, sodium zirconate, lithium lanthanum zirconium sodium, lithium lanthanum titanium sodium, sodium aluminum titanium phosphate, sodium germanium aluminum phosphate, etc. Their crystal structures are mostly three-dimensional framework structures or two-dimensional layered structures, with a single sodium ion diffusion path and low ionic conductivity, and thus unable to fully exert the specific capacity and rate performance of the cathode material.

[0004] CN 114709404A discloses a NASICON sodium titanium phosphate-coated sodium iron phosphate cathode material and a preparation method thereof. The preparation method includes the preparation of a sodium titanium phosphate precursor slurry, the uniform coating of sodium titanium phosphate on sodium iron phosphate, the drying of the precursor, and the solid-phase synthesis of the NASICON sodium titanium phosphate-coated sodium iron phosphate cathode material. However, the crystal structure of the NASICON-type sodium fast ion conductor prepared by the invention is a three-dimensional framework structure formed by the connection of the vertices of TiO 6 octahedrons and PO 4 tetrahedrons, which has problems such as low sodium ion content, insufficiently wide sodium ion diffusion channels, and low ionic conductivity, and still has great room for improvement.

[0005] It can be seen that how to provide a sodium fast ion conductor to further enrich the diffusion path of sodium ions, increase the sodium ion content and ionic conductivity, reduce its impedance as the coating layer of the positive electrode material, and thus achieve the fast charge and discharge and high-temperature cycling performance of sodium ion batteries has become an urgent problem to be solved by those skilled in the art at present. Summary of the Invention

[0006] The purpose of the present invention is to provide a sodium ion battery positive electrode material with a sodium fast ion conductor as the coating layer, its preparation method and application. The sodium fast ion conductor enriches the diffusion path of sodium ions, increases the sodium ion content and ionic conductivity, reduces its impedance as the coating layer of the positive electrode material, and thus realizes the fast charge and discharge and high-temperature cycling performance of sodium ion batteries.

[0007] To achieve the purpose of this invention, the following technical solutions are adopted:

[0008] In the first aspect, the present invention provides a sodium fast ion conductor, and the chemical formula of the sodium fast ion conductor is: Na 4 MP 2 O 9 ; wherein, M is Ti or V.

[0009] The crystal structure of the sodium fast ion conductor is: PO 4 tetrahedrons and MO 6 octahedrons are connected by sharing vertices to form a one-dimensional chain structure, and Na ions are evenly distributed between the chains and can diffuse freely in at least 3 directions.

[0010] The sodium fast ion conductor provided by the present invention presents a one-dimensional chain structure in the crystal structure, and the free sodium ions can diffuse freely in multiple directions in three-dimensional space, further enriching the diffusion path of sodium ions, increasing the sodium ion content and ionic conductivity, reducing its impedance as the coating layer of the positive electrode material, and thus realizing the fast charge and discharge and high-temperature cycling performance of sodium ion batteries.

[0011] Preferably, the MO 6 octahedrons are connected by sharing vertices in sequence, and each of the PO 4 tetrahedrons independently shares 1 vertex with 2 adjacent MO 6 octahedrons respectively.

[0012] In the second aspect, the present invention provides a preparation method of the sodium fast ion conductor as described in the first aspect, and the preparation method includes the following steps:

[0013] (1) Mix a titanium source or a vanadium source, a sodium source, a phosphorus source, a template agent, an organic solvent and deionized water according to the stoichiometric ratio for hydrothermal synthesis to obtain Na 4 MP 2 O 9 crystals;

[0014] (2) The Na 4 MP 2 O 9 crystals are successively washed, dried, and ground to obtain Na 4 MP 2 O 9 sodium fast ion conductor.

[0015] The present invention prepares the Na 4 MP 2 O 9 sodium fast ion conductor by combining a series of post-treatment processes on the basis of the hydrothermal synthesis method. The raw materials are simple and easily available, the preparation process is simple, the preparation efficiency is improved, and the preparation cost is reduced at the same time, which is beneficial to large-scale popularization and application.

[0016] Preferably, the titanium source in step (1) includes titanium dioxide.

[0017] Preferably, the vanadium source in step (1) includes vanadium sesquioxide.

[0018] Preferably, the sodium source in step (1) includes sodium chloride.

[0019] Preferably, the phosphorus source in step (1) includes a phosphoric acid solution, and the concentration of the phosphoric acid solution is 80 - 90 wt%, for example, it can be 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, or 90 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0020] Preferably, the template agent in step (1) includes any one or a combination of at least two of ethylenediamine, triethylamine, tetraethylenepentamine, or pentaethylene tetramine. Typical but non-limiting combinations include the combination of ethylenediamine and tetraethylenepentamine, the combination of ethylenediamine and pentaethylene tetramine, the combination of triethylamine and tetraethylenepentamine, or the combination of triethylamine and pentaethylene tetramine. Further preferably, it is the combination of ethylenediamine and pentaethylene tetramine, or the combination of triethylamine and tetraethylenepentamine.

[0021] Preferably, the organic solvent in step (1) includes sec-butanol.

[0022] Preferably, the method of mixing in step (1) includes: first adding the titanium source or vanadium source and the sodium source into deionized water, then successively adding the organic solvent and the template agent, and finally adding the phosphoric acid solution and stirring evenly.

[0023] Preferably, the temperature of the hydrothermal synthesis in step (1) is 200 - 210 °C. For example, it can be 200 °C, 201 °C, 202 °C, 203 °C, 204 °C, 205 °C, 206 °C, 207 °C, 208 °C, 209 °C or 210 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0024] Preferably, the time of the hydrothermal synthesis in step (1) is 45 - 50 h. For example, it can be 45 h, 46 h, 47 h, 48 h, 49 h or 50 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0025] Preferably, the washing in step (2) is carried out with deionized water until the Na 4 MP 2 O 9 crystal is translucent and free of impurity adhesion.

[0026] Preferably, between the washing and drying in step (2), filtration is also included.

[0027] Preferably, the drying in step (2) is carried out in an oven, and the set temperature of the oven is 80 - 120 °C. For example, it can be 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C or 120 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0028] Preferably, the grinding in step (2) is carried out until the Na 4 MP 2 O 9 sodium fast ion conductor satisfies D50 ≤ 0.1 μm. For example, it can be D50 = 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm or 0.1 μm. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0029] In the present invention, the D50 specifically refers to the particle size corresponding to when the cumulative particle size distribution percentage of the sodium fast ion conductor reaches 50%. Its physical meaning is that 50% of the particles have a particle size greater than it, and 50% of the particles have a particle size less than it.

[0030] As a preferred technical solution of the second aspect of the present invention, the preparation method includes the following steps:

[0031] (1) First, add titanium dioxide or vanadium trioxide and sodium chloride into deionized water according to the stoichiometric ratio, then successively add sec-butanol and the template agent, and finally add a phosphoric acid solution with a concentration of 80-90 wt% and stir evenly. Perform hydrothermal synthesis at 200-210 °C for 45-50 h to obtain Na 4 MP 2 O 9 crystals; the template agent includes any one or a combination of at least two of ethylenediamine, triethylamine, tetraethylenepentamine, or pentaethylene tetramine;

[0032] (2) Wash the Na 4 MP 2 O 9 crystals obtained in step (1) successively until they are transparent and free of impurity adhesion, perform suction filtration, dry at 80-120 °C, and grind to D50 ≤ 0.1 μm to obtain Na 4 MP 2 O 9 sodium fast ion conductor.

[0033] Thirdly, the present invention provides a positive electrode material with the sodium fast ion conductor described in the first aspect as a coating layer. The positive electrode material has a core-shell structure and includes a core and a coating layer.

[0034] Preferably, the material of the core includes a sodium nickel iron manganese oxide positive electrode material.

[0035] Preferably, the mass ratio of the coating layer to the core is 0.1-0.3 wt%. For example, it can be 0.1 wt%, 0.12 wt%, 0.14 wt%, 0.16 wt%, 0.18 wt%, 0.2 wt%, 0.22 wt%, 0.24 wt%, 0.26 wt%, 0.28 wt%, or 0.3 wt%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0036] The present invention coats the sodium fast ion conductor with high ionic conductivity on the sodium nickel iron manganese oxide positive electrode material, reducing the contact area between the electrolyte and the positive electrode material, thereby suppressing the side reactions between the electrode materials and improving the cycle stability of the battery.

[0037] Fourthly, the present invention provides a preparation method of the positive electrode material described in the third aspect. The preparation method includes the following steps:

[0038] (1) Prepare a sodium nickel iron manganese oxide positive electrode material;

[0039] (2) Mix the sodium fast ion conductor, nano-carbon particles, and the sodium nickel iron manganese oxide positive electrode material obtained in step (1) for fusion coating, and obtain a positive electrode material with a sodium fast ion conductor as the coating layer after annealing treatment.

[0040] Preferably, the preparation method of the sodium nickel iron manganese oxide cathode material in step (1) includes dry sintering, crushing and sieving.

[0041] Preferably, the temperature of the annealing treatment in step (2) is 300 - 340 °C, for example, it can be 300 °C, 305 °C, 310 °C, 315 °C, 320 °C, 325 °C, 330 °C, 335 °C or 340 °C, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] In a fifth aspect, the present invention provides an application of the cathode material as described in the third aspect in a sodium-ion battery.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The sodium fast ion conductor provided by the present invention presents a one-dimensional chain structure in the crystal structure. The free sodium ions can freely diffuse in multiple directions in three-dimensional space, further enriching the diffusion path of sodium ions, improving the sodium ion content and ionic conductivity, reducing the impedance of its coating layer as a cathode material, and thus realizing the fast charge and discharge and high-temperature cycle performance of sodium-ion batteries;

[0045] (2) Based on the hydrothermal synthesis method, the present invention combines a series of post-treatment processes to prepare Na 4 MP 2 O 9 sodium fast ion conductor. The raw materials are simple and easy to obtain, the preparation process is simple, the preparation efficiency is improved, and the preparation cost is reduced at the same time, which is conducive to large-scale popularization and application;

[0046] (3) The present invention coats the sodium fast ion conductor with high ionic conductivity on the sodium nickel iron manganese oxide cathode material, reducing the contact area between the electrolyte and the cathode material, thereby inhibiting the side reaction between the electrode materials and improving the cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic diagram of the crystal structure of the sodium fast ion conductor provided by the present invention;

[0048] Figure 2 is a graph showing the change in capacity retention rate after 50 cycles of a sodium-ion battery prepared from the sodium-ion battery cathode materials obtained in Application Examples 3 - 4 and Comparative Application Examples 1 - 2;

[0049] Figure 3 is a graph showing the rate performance of a sodium-ion battery prepared from the sodium-ion battery cathode materials obtained in Application Examples 3 - 4 and Comparative Application Examples 1 - 2;

[0050] Figure 4It is the rate performance graph of the sodium-ion battery prepared using the sodium-ion battery cathode materials obtained from Application Examples 1, 3, 5 and Comparative Application Example 1;

[0051] Figure 5 It is the rate performance graph of the sodium-ion battery prepared using the sodium-ion battery cathode materials obtained from Application Examples 2, 4, 6 and Comparative Application Example 1.

[0052] Among them: 1 - PO 4 tetrahedron; 2 - MO 6 octahedron (M is Ti or V); 3 - Na ion. Specific implementation mode

[0053] The technical solution of the present invention will be further described below through specific implementation modes. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0054] Example 1

[0055] This example provides a sodium fast ion conductor and its preparation method. The preparation method includes the following steps:

[0056] (1) First, add titanium dioxide (22.80 g) and sodium chloride (46.80 g) into a 500 mL polytetrafluoroethylene inner liner containing 50 mL of deionized water. Then, successively add sec-butanol (100 mL), triethylamine (50 mL) and tetraethylenepentamine (150 mL). Finally, add a phosphoric acid solution with a concentration of 85 wt% (25 mL) into the inner liner and stir evenly with a glass rod; encapsulate the polytetrafluoroethylene inner liner in a stainless steel sleeve and place it in an oven at 205 °C for static reaction for 48 h for hydrothermal synthesis. After the reaction is completed, take out the reaction kettle, cool it to room temperature to obtain Na 4 TiP 2 O 9 crystals;

[0057] (2) Wash the Na 4 TiP 2 O 9 crystals obtained in step (1) successively with deionized water until they are transparent and free of impurity adhesion, and then filter by suction. After drying in an oven at 100 °C for 6 h, obtain Na 4 TiP 2 O 9 grains; grind the obtained grains until D50 ≤ 0.1 μm to obtain Na 4 TiP 2 O 9 sodium fast ion conductor.

[0058] The Na 4 TiP 2 O 9The crystal structure of the sodium fast ion conductor is as follows Figure 1 shown, PO 4 tetrahedron 1 and TiO 6 octahedron 2 are connected by sharing vertices to form a one-dimensional chain structure. Specifically: TiO 6 octahedrons 2 are connected by sharing vertices in sequence. Each 1 PO 4 tetrahedron 1 is independently connected to 2 adjacent TiO 6 octahedrons 2 by sharing 1 vertex. The free Na ions 3 can diffuse freely in multiple directions in three-dimensional space.

[0059] Example 2

[0060] This example provides a sodium fast ion conductor and its preparation method. The preparation method includes the following steps:

[0061] (1) First, add vanadium trioxide (21.38 g) and sodium chloride (46.80 g) into a 500 mL polytetrafluoroethylene inner liner containing 50 mL of deionized water. Then, add sec-butanol (100 mL), triethylamine (50 mL), and tetraethylenepentamine (150 mL) in sequence. Finally, add a phosphoric acid solution with a concentration of 85 wt% (25 mL) into the inner liner and stir evenly with a glass rod; encapsulate the polytetrafluoroethylene inner liner in a stainless steel sleeve and place it in an oven at 205 °C for static reaction for 48 h for hydrothermal synthesis. After the reaction is completed, take out the reaction kettle, cool it to room temperature to obtain Na 4 VP 2 O 9 crystals;

[0062] (2) Wash the Na 4 VP 2 O 9 crystals obtained in step (1) with deionized water until they are transparent and free of impurity adhesion, and then perform suction filtration. After drying in an oven at 100 °C for 6 h, obtain Na 4 VP 2 O 9 grains; Grind the obtained grains until D50 ≤ 0.1 μm to obtain Na 4 VP 2 O 9 sodium fast ion conductor.

[0063] The crystal structure of the Na 4 VP 2 O 9 sodium fast ion conductor obtained in this example is as follows Figure 1 shown, PO 4 tetrahedron 1 and VO 6 octahedron 2 are connected by sharing vertices to form a one-dimensional chain structure. Specifically: VO 6 octahedrons 2 are connected by sharing vertices in sequence. Each 1 PO 4The tetrahedron 1 is independently connected to two adjacent VO 6 The octahedron 2 shares one vertex, and the free Na ions 3 can freely diffuse in multiple directions in three-dimensional space.

[0064] Example 3

[0065] This example provides a sodium fast ion conductor and a preparation method thereof. The preparation method includes the following steps:

[0066] (1) First, add titanium dioxide (22.80 g) and sodium chloride (46.80 g) into a 500 mL polytetrafluoroethylene inner liner containing 50 mL of deionized water. Then, successively add sec-butanol (100 mL), ethylenediamine (50 mL), and pentaethylene tetramine (150 mL). Finally, add a phosphoric acid solution with a concentration of 80 wt% (25 mL) into the inner liner and stir evenly with a glass rod. Seal the polytetrafluoroethylene inner liner in a stainless steel sleeve and place it in an oven at 200 °C for static reaction for 50 h for hydrothermal synthesis. After the reaction, take out the reaction kettle, cool it to room temperature to obtain Na 4 TiP 2 O 9 crystals;

[0067] (2) Wash the Na 4 TiP 2 O 9 crystals obtained in step (1) successively with deionized water until they are transparent and free of impurity adhesion, and then filter by suction. After drying in an oven at 80 °C for 8 h, obtain Na 4 TiP 2 O 9 grains; Grind the obtained grains to D50 ≤ 0.1 μm to obtain Na 4 TiP 2 O 9 sodium fast ion conductor.

[0068] The Na 4 TiP 2 O 9 sodium fast ion conductor obtained in this example has a crystal structure as Figure 1 shown. The PO 4 tetrahedron 1 and the TiO 6 octahedron 2 are connected by sharing vertices to form a one-dimensional chain structure. Specifically, the TiO 6 octahedrons 2 are connected by sharing vertices in sequence. Each PO 4 tetrahedron 1 is independently connected to two adjacent TiO 6 octahedrons 2 by sharing one vertex, and the free Na ions 3 can freely diffuse in multiple directions in three-dimensional space.

[0069] Example 4

[0070] This embodiment provides a sodium fast ion conductor and a preparation method thereof. The preparation method includes the following steps:

[0071] (1) First, add vanadium trioxide (21.38 g) and sodium chloride (46.80 g) into a 500 mL polytetrafluoroethylene liner containing 50 mL of deionized water. Then, successively add sec-butanol (100 mL), ethylenediamine (50 mL), and pentaethylene tetramine (150 mL). Finally, add a 90 wt% phosphoric acid solution (25 mL) into the liner and stir evenly with a glass rod. Seal the polytetrafluoroethylene liner in a stainless steel sleeve and place it in an oven at 210 °C for 45 h for hydrothermal synthesis. After the reaction, take out the reaction kettle, cool it to room temperature to obtain Na 4 VP 2 O 9 crystals;

[0072] (2) Wash the Na 4 VP 2 O 9 crystals obtained in step (1) successively with deionized water until they are transparent and free of impurity adhesion, and then filter by suction. After drying in an oven at 120 °C for 4 h, obtain Na 4 VP 2 O 9 grains; Grind the obtained grains until D50 ≤ 0.1 μm to obtain Na 4 VP 2 O 9 sodium fast ion conductor.

[0073] The crystal structure of the Na 4 VP 2 O 9 sodium fast ion conductor obtained in this embodiment is as Figure 1 shown. The PO 4 tetrahedron 1 and the VO 6 octahedron 2 are connected by sharing vertices to form a one-dimensional chain structure. Specifically, the VO 6 octahedrons 2 are connected by sharing vertices in sequence. Each 1 PO 4 tetrahedron 1 independently shares 1 vertex with 2 adjacent VO 6 octahedrons 2. The free Na ions 3 can diffuse freely in multiple directions in three-dimensional space.

[0074] Application Example 1

[0075] This application example provides a cathode material using the sodium fast ion conductor obtained in Example 1 as a coating layer and a preparation method thereof. The preparation method includes the following steps:

[0076] (1) Add 5 kg of Ni 0.25 Fe 0.37 Mn 0.38 (OH)2 The ternary precursor is mixed with 2.99 kg of sodium carbonate in a high-speed mixer, and then subjected to dry sintering at 980 °C in an air atmosphere (5 m 3 / h) for 12 h. Finally, after pulverization and sieving, the O3-type sodium-ion battery cathode material is obtained;

[0077] (2) Add the sodium fast ion conductor (7.22 g) obtained in Example 1, the ultra-fine nano-carbon particles (5 g), and the sodium-ion battery cathode material (500 g) obtained in step (1) into a high-speed mixer for dry mixing, and put the mixed raw materials into a fusion coating machine. Under the action of the blade shear force, the interface between the cathode material and the coating material reaches the fusion effect; the coated cathode material is subjected to low-temperature annealing (320 °C), and finally the Na 4 TiP 2 O 9 coated sodium-ion battery cathode material NFM-0.1 wt% Na 4 TiP 2 O 9 .

[0078] Application Example 2

[0079] This application example provides a cathode material using the sodium fast ion conductor obtained in Example 2 as a coating layer and a preparation method thereof. The preparation method includes the following steps:

[0080] (1) Mix 5 kg of Ni 0.25 Fe 0.37 Mn 0.38 (OH) 2 The ternary precursor is mixed with 2.99 kg of sodium carbonate in a high-speed mixer, and then subjected to dry sintering at 980 °C in an air atmosphere (5 m 3 / h) for 12 h. Finally, after pulverization and sieving, the O3-type sodium-ion battery cathode material is obtained;

[0081] (2) Add the sodium fast ion conductor (7.28 g) obtained in Example 2, the ultra-fine nano-carbon particles (5 g), and the sodium-ion battery cathode material (500 g) obtained in step (1) into a high-speed mixer for dry mixing, and put the mixed raw materials into a fusion coating machine. Under the action of the blade shear force, the interface between the cathode material and the coating material reaches the fusion effect; the coated cathode material is subjected to low-temperature annealing (320 °C), and finally the Na 4 VP 2 O 9 coated sodium-ion battery cathode material NFM-0.1 wt% Na 4 VP 2 O 9 .

[0082] Application Example 3

[0083] This application example provides a cathode material with the sodium fast ion conductor obtained in Example 1 as the coating layer and its preparation method. The preparation method includes the following steps:

[0084] (1) Mix 5 kg of Ni 0.25 Fe 0.37 Mn 0.38 (OH) 2 ternary precursor with 2.99 kg of sodium carbonate in a high-speed mixer, and then carry out dry sintering at 980 °C in an air atmosphere (5 m 3 / h) for 12 h. Finally, after pulverization and sieving, an O3-type sodium battery cathode material is obtained;

[0085] (2) Add the sodium fast ion conductor obtained in Example 1 (14.44 g), ultra-fine nano-carbon particles (5 g), and the sodium battery cathode material obtained in step (1) (500 g) to a high-speed mixer for dry mixing, and put the mixed raw materials into a fusion coating machine. Under the action of the blade shear force, the interface between the cathode material and the coating material reaches the fusion effect; carry out low-temperature annealing (320 °C) on the coated cathode material, and finally obtain Na 4 TiP 2 O 9 -coated sodium battery cathode material NFM-0.2 wt% Na 4 TiP 2 O 9 .

[0086] Application Example 4

[0087] This application example provides a cathode material with the sodium fast ion conductor obtained in Example 2 as the coating layer and its preparation method. The preparation method includes the following steps:

[0088] (1) Mix 5 kg of Ni 0.25 Fe 0.37 Mn 0.38 (OH) 2 ternary precursor with 2.99 kg of sodium carbonate in a high-speed mixer, and then carry out dry sintering at 980 °C in an air atmosphere (5 m 3 / h) for 12 h. Finally, after pulverization and sieving, an O3-type sodium battery cathode material is obtained;

[0089] (2) Add the sodium fast ion conductor obtained in Example 2 (14.56 g), ultra-fine nano-carbon particles (5 g), and the sodium battery cathode material obtained in step (1) (500 g) to a high-speed mixer for dry mixing, and put the mixed raw materials into a fusion coating machine. Under the action of the blade shear force, the interface between the cathode material and the coating material reaches the fusion effect; carry out low-temperature annealing (320 °C) on the coated cathode material, and finally obtain Na 4 VP2 O 9 Coated sodium-based cathode material NFM - 0.2 wt% Na 4 VP 2 O 9 。

[0090] Application Example 5

[0091] This application example provides a cathode material with the sodium fast ion conductor obtained in Example 1 as the coating layer and its preparation method. The preparation method includes the following steps:

[0092] (1) Mix 5 kg of Ni 0.25 Fe 0.37 Mn 0.38 (OH) 2 ternary precursor with 2.99 kg of sodium carbonate in a high-speed mixer, and then carry out dry sintering at 980 °C in an air atmosphere (5 m 3 / h) for 12 h. Finally, after pulverization and sieving, an O3-type sodium-based cathode material is obtained;

[0093] (2) Add the sodium fast ion conductor obtained in Example 1 (21.66 g), ultra-fine nano-carbon particles (5 g), and the sodium-based cathode material obtained in step (1) (500 g) into a high-speed mixer for dry mixing, and put the mixed raw materials into a fusion coating machine. Under the action of the blade shear force, the interface between the cathode material and the coating material reaches the fusion effect; perform low-temperature annealing (320 °C) on the coated cathode material, and finally obtain Na 4 TiP 2 O 9 coated sodium-based cathode material NFM - 0.3 wt% Na 4 TiP 2 O 9 。

[0094] Application Example 6

[0095] This application example provides a cathode material with the sodium fast ion conductor obtained in Example 2 as the coating layer and its preparation method. The preparation method includes the following steps:

[0096] (1) Mix 5 kg of Ni 0.25 Fe 0.37 Mn 0.38 (OH) 2 ternary precursor with 2.99 kg of sodium carbonate in a high-speed mixer, and then carry out dry sintering at 980 °C in an air atmosphere (5 m 3 / h) for 12 h. Finally, after pulverization and sieving, an O3-type sodium-based cathode material is obtained;

[0097] (2) Add the sodium fast ion conductor obtained in Example 2 (21.84 g), ultra-fine nano-carbon particles (5 g), and the sodium battery cathode material obtained in step (1) (500 g) into a high-speed mixer for dry mixing, and then put the mixed raw materials into a fusion coating machine. Under the action of the blade shear force, the interface between the cathode material and the coating material reaches a fusion effect; perform low-temperature annealing (320 °C) on the coated cathode material to finally obtain Na 4 VP 2 O 9 coated sodium battery cathode material NFM - 0.3 wt% Na 4 VP 2 O 9 .

[0098] Comparative Application Example 1

[0099] This comparative application example provides a cathode material and a preparation method thereof. The preparation method is as follows: Mix 5 kg of Ni 0.25 Fe 0.37 Mn 0.38 (OH) 2 ternary precursor with 2.99 kg of sodium carbonate in a high-speed mixer, and then perform dry sintering at 980 °C in an air atmosphere (5 m 3 / h) for 12 h. Finally, after pulverizing and sieving, obtain the O3-type sodium battery cathode material NFM.

[0100] Comparative Application Example 2

[0101] This comparative application example provides a cathode material with NaAlO 2 as the coating layer and a preparation method thereof. The preparation method includes the following steps:

[0102] (1) Mix 5 kg of Ni 0.25 Fe 0.37 Mn 0.38 (OH) 2 ternary precursor with 2.99 kg of sodium carbonate in a high-speed mixer, and then perform dry sintering at 980 °C in an air atmosphere (5 m 3 / h) for 12 h. Finally, after pulverizing and sieving, obtain the O3-type sodium battery cathode material;

[0103] (2) Add NaAlO 2 powder (3.03 g), ultra-fine nano-carbon particles (5 g), and the sodium battery cathode material obtained in step (1) (500 g) into a high-speed mixer for dry mixing, and then put the mixed raw materials into a fusion coating machine. Under the action of the blade shear force, the interface between the cathode material and the coating material reaches a fusion effect; perform low-temperature annealing (320 °C) on the coated cathode material to finally obtain NaAlO 2Coated sodium-ion battery cathode material NFM-0.1wt% NaAlO 2 .

[0104] Sodium-ion batteries were independently prepared using the sodium-ion battery cathode materials obtained in Application Examples 1-6 and Comparative Application Examples 1-2, and the preparation method specifically included the following steps:

[0105] (1) Preparation of the positive electrode sheet: The prepared sodium-ion battery cathode material, polyvinylidene fluoride (PVDF), and acetylene black were placed in a weighing bottle in a mass ratio of 80:10:10, and an appropriate amount of dispersant N-methyl-2-pyrrolidone (NMP) was added and continuously stirred with a magnetic stirrer for 3 h; the stirred slurry was coated on a clean carbon-coated aluminum foil with a 250-μm coater, and the aluminum foil coated with the slurry was transferred to a 65°C forced-air drying oven to dry NMP, and then placed in a 100°C vacuum drying oven for thorough drying; the completely dried aluminum foil was cut into circular electrode sheets with a 10-mm cutter to obtain the required positive electrode sheets.

[0106] (2) Battery assembly: The positive electrode sheet, glass fiber separator, and sodium metal block prepared in the above steps were placed in an ultra-pure glove box under an argon atmosphere, and 1 mol / L NaClO 4 / PC+FEC (95:5) was the electrolyte pre-stored in the glove box; in the glove box, the battery was assembled in the order of the positive electrode case, positive electrode sheet, separator, sodium sheet, spring piece, and negative electrode case, and sealed with an MSK-110 battery sealer to obtain a 2025-type button half-cell; the battery was taken out of the glove box and left to stand for about 10 h for relevant tests.

[0107] Figure 2 It is a graph showing the change in capacity retention rate after 50 cycles of a sodium-ion battery prepared using the sodium-ion battery cathode materials obtained in Application Examples 3-4 and Comparative Application Examples 1-2.

[0108] It can be seen from Figure 2 that: In Application Examples 3 and 4, after coating nickel-iron-manganese sodium oxide with Na 4 MP 2 O 9 fast ion conductor, the 0.5C / 50-cycle capacity retention rate of the battery prepared with the obtained positive electrode material was significantly improved, and the highest reached 77%, which was about 26 percentage points higher than that of Comparative Application Example 1; compared with Comparative Application Example 2, the capacity retention rate of Application Examples 3 and 4 was slightly lower in the first 40 cycles, but after 40 cycles, the capacity retention rate of Application Examples 3 and 4 was more advantageous.

[0109] Thus, it can be seen that the present invention uses Na 4 MP 2 O 9The fast ion conductor uniformly coats sodium nickel iron manganese oxide, preventing direct contact between the electrolyte and sodium nickel iron manganese oxide, reducing side reactions, and improving the cycle stability of the battery.

[0110] Figure 3 It is the rate performance graph of sodium ion batteries prepared from the sodium ion battery cathode materials obtained in Application Examples 3 - 4 and Comparative Application Examples 1 - 2.

[0111] From Figure 3 it can be seen that: through Na 4 MP 2 O 9 the fast ion conductor uniformly coats sodium nickel iron manganese oxide, reducing the interfacial impedance and improving the rate performance of the battery. It can be seen from the performance test that for Application Examples 3 and 4 using Na 4 MP 2 O 9 after coating sodium nickel iron manganese oxide with the fast ion conductor, when the batteries prepared with this cathode material are discharged at 0.5C and 1C rates, the discharge capacities are slightly higher than those of Comparative Application Examples 1 and 2; when the discharge rate is further increased to 2C and 4C, the advantages of Application Examples 3 and 4 can be clearly demonstrated.

[0112] Figure 4 It is the rate performance graph of sodium ion batteries prepared from the sodium ion battery cathode materials obtained in Application Examples 1, 3, 5 and Comparative Application Example 1.

[0113] From Figure 4 it can be seen that: through Na 4 TiP 2 O 9 the fast ion conductor uniformly coats sodium nickel iron manganese oxide, reducing the interfacial impedance and improving the rate performance of the battery. It can be seen from the performance test that for Application Examples 1, 3 and 5 using Na 4 TiP 2 O 9 after coating sodium nickel iron manganese oxide with the fast ion conductor, when the batteries prepared with this cathode material are discharged at 0.5C and 1C rates, the discharge capacities are slightly higher than that of Comparative Application Example 1; when the discharge rate is further increased to 2C and 4C, the advantages of Application Examples 1, 3 and 5 are more obvious. Comparing Application Examples 1, 3 and 5, among them, Application Example 3 (coated with 0.2% Na 4 TiP 2 O 9 ) has the best rate performance, Application Example 1 (coated with 0.1% Na 4 TiP 2 O 9 ) comes second, and Application Example 5 (coated with 0.3% Na 4 TiP 2 O 9 ) comes third. It can be seen that coating with Na 4 TiP2 O 9 The amount of the fast ion conductor has an important influence on the rate performance of the sodium nickel iron manganese oxide cathode material. Too high or too low amount will both lead to a decrease in the rate performance. Therefore, in the present invention, 0.2% Na 4 TiP 2 O 9 is used for coating.

[0114] Figure 5 It is the rate performance graph of the sodium ion battery prepared from the sodium ion battery cathode materials obtained in Application Examples 2, 4, 6 and Comparative Application Example 1.

[0115] From Figure 5 it can be seen that: through the uniform coating of the sodium nickel iron manganese oxide with the fast ion conductor Na 4 VP 2 O 9 the interfacial impedance is reduced and the rate performance of the battery is improved. It can be seen from the performance test that when the sodium nickel iron manganese oxide is coated with the fast ion conductor Na 4 VP 2 O 9 in Application Examples 2, 4 and 6, the discharge capacity of the battery prepared from this cathode material is slightly higher than that in Comparative Application Example 1 when discharging at 0.5C and 1C rates; when the discharge rate is further increased to 2C and 4C, the advantages of Application Examples 2, 4 and 6 become more obvious. Among Application Examples 2, 4 and 6, Application Example 4 (coated with 0.2% Na 4 VP 2 O 9 ) has the best rate performance, followed by Application Example 2 (coated with 0.1% Na 4 VP 2 O 9 ), and Application Example 6 (coated with 0.3% Na 4 VP 2 O 9 ) comes next. It can be seen that the amount of the coated Na 4 VP 2 O 9 fast ion conductor has an important influence on the rate performance of the sodium nickel iron manganese oxide cathode material. Too high or too low amount will both lead to a decrease in the rate performance. Therefore, in the present invention, 0.2% Na 4 VP 2 O 9 is used for coating.

[0116] Thus, it can be seen that the sodium fast ion conductor provided by the present invention presents a one-dimensional chain structure in the crystal structure, and the free sodium ions can freely diffuse in multiple directions in the three-dimensional space, further enriching the diffusion path of the sodium ions, improving the sodium ion content and ionic conductivity, reducing the impedance of its coating layer as the cathode material, and thus realizing the fast charge and discharge and high-temperature cycle performance of the sodium ion battery.

[0117] In addition, based on the hydrothermal synthesis method, the present invention combines a series of post-treatment processes to prepare Na 4 MP 2 O 9 sodium fast ion conductor. The raw materials are simple and easy to obtain, the preparation process is simple, the preparation efficiency is improved, and the preparation cost is reduced, which is conducive to large-scale popularization and application.

[0118] Furthermore, the present invention coats the sodium fast ion conductor with high ionic conductivity on the sodium nickel iron manganese oxide cathode material, reducing the contact area between the electrolyte and the cathode material, thereby inhibiting the side reactions between the electrode materials and improving the cycle stability of the battery.

[0119] The applicant declares that the above description is only a specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived within the technical scope disclosed by the present invention by those skilled in the art all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A sodium fast ion conductor, characterized in that, The chemical formula of the sodium fast ion conductor is: Na 4 MP 2 O 9 ; wherein, M is Ti or V; The crystal structure of the sodium fast ion conductor is: PO 4 tetrahedrons and MO 6 octahedrons are connected by sharing vertices to form a one-dimensional chain structure, and Na ions are distributed between the chains and can diffuse freely in at least three directions; The said MO 6 The octahedrons are connected in sequence with a common vertex. Each of the said PO 4 tetrahedrons is independently connected to two adjacent said MO 6 octahedrons and shares one vertex.

2. A preparation method of the sodium fast ion conductor according to claim 1, characterized in that, the preparation method comprises the following steps: (1) Hydrothermal synthesis is carried out by mixing a titanium source or a vanadium source, a sodium source, a phosphorus source, a template agent, an organic solvent and deionized water according to a stoichiometric ratio to obtain a Na 4 MP 2 O 9 crystal; (2) The obtained Na 4 MP 2 O 9 crystals are successively washed, dried, and ground to obtain Na 4 MP 2 O 9 sodium fast ion conductor.

3. According to the preparation method described in claim 2, characterized in that, the titanium source in step (1) includes titanium dioxide.

4. According to the preparation method described in claim 2, characterized in that, the vanadium source in step (1) includes vanadium sesquioxide.

5. According to the preparation method described in claim 2, characterized in that, the sodium source in step (1) includes sodium chloride.

6. According to the preparation method described in claim 2, characterized in that, the phosphorus source in step (1) includes a phosphoric acid solution, and the concentration of the phosphoric acid solution is 80 - 90 wt%.

7. According to the preparation method described in claim 2, characterized in that, the template agent in step (1) includes any one or a combination of at least two of ethylenediamine, triethylamine, tetraethylenepentamine or pentaethylene tetramine.

8. According to the preparation method described in claim 2, characterized in that, the organic solvent in step (1) includes sec-butanol.

9. According to the preparation method described in claim 2, characterized in that, the method of mixing in step (1) includes: first adding the titanium source or vanadium source, sodium source into deionized water, then successively adding the organic solvent and the template agent, and finally adding the phosphoric acid solution and stirring evenly.

10. According to the preparation method described in claim 2, characterized in that, the temperature of the hydrothermal synthesis in step (1) is 200 - 210 °C.

11. According to the preparation method described in claim 2, characterized in that, the time of the hydrothermal synthesis in step (1) is 45 - 50 h.

12. According to the preparation method described in claim 2, characterized in that, The washing described in step (2) is carried out with deionized water and is washed until Na 4 MP 2 O 9 crystals are translucent and free of impurity adhesion.

13. According to the preparation method described in claim 2, characterized in that, between step (2) of washing and drying, there is also suction filtration.

14. According to the preparation method described in claim 2, characterized in that, the drying in step (2) is carried out in an oven, and the set temperature of the oven is 80 - 120 °C.

15. According to the preparation method described in claim 2, characterized in that, The grinding in step (2) until Na 4 MP 2 O 9 The sodium fast ion conductor satisfies D50 ≤ 0.1 μm.

16. According to the preparation method described in claim 2, characterized in that, the preparation method comprises the following steps: (1) First, add titanium dioxide or vanadium trioxide and sodium chloride into deionized water according to the stoichiometric ratio, then successively add sec-butanol and the template agent, and finally add a phosphoric acid solution with a concentration of 80-90 wt% and stir evenly. Perform hydrothermal synthesis at 200-210 °C for 45-50 h to obtain Na 4 MP 2 O 9 crystals; the template agent includes any one or a combination of at least two of ethylenediamine, triethylamine, tetraethylenepentamine, or pentaethylene tetramine; (2) The obtained Na 4 MP 2 O 9 crystals are successively washed until transparent and free of impurity adhesion, filtered by suction, dried at 80 - 120 °C, and ground to D50 ≤ 0.1 μm to obtain Na 4 MP 2 O 9 sodium fast ion conductor.

17. A positive electrode material with the sodium fast ion conductor according to claim 1 as a coating layer, characterized in that, the positive electrode material has a core-shell structure, including a core and a coating layer; the material of the core includes a sodium nickel iron manganese oxide positive electrode material; the mass ratio of the coating layer to the core is 0.1 - 0.3 wt%.

18. A preparation method of the positive electrode material according to claim 17, characterized in that, the preparation method comprises the following steps: (1) Prepare a sodium nickel iron manganese oxide positive electrode material; (2) Mix the sodium fast ion conductor, nano-carbon particles and the sodium nickel iron manganese oxide positive electrode material obtained in step (1) for fusion coating, and after annealing treatment, obtain a positive electrode material with the sodium fast ion conductor as the coating layer.

19. According to the preparation method described in claim 18, characterized in that, the preparation method of the sodium nickel iron manganese oxide positive electrode material in step (1) includes dry sintering and crushing and sieving.

20. The preparation method according to claim 18, characterized in that, the temperature of the annealing treatment in step (2) is 300-340 °C.

21. An application of the cathode material according to claim 17 in a sodium-ion battery.

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