Method for preparing sodium electric positive electrode material

Abstract

The application belongs to the field of batteries, and specifically provides a preparation method of a sodium battery positive electrode material, which comprises the following steps: (1) providing sintered material and mixed material; the sintered material is a sintered product of a sodium source and a metal precursor, and the molar ratio of the amount of the sodium source to the amount of the metal precursor is a; the mixed material is a mixture of the sodium source and the metal precursor, and the molar ratio of the amount of the sodium source to the amount of the metal precursor is b; a = 0.4-0.7, and b = 0.9-1.1; (2) loading the sintered material and the mixed material into a sagger; a layer of the sintered material is laid on the bottom of the sagger, and then the mixed material is loaded on the sintered material; after being cut into pieces, a sagger loaded with the sintered material and the mixed material is obtained, wherein the thickness of the sintered material is h1, the thickness of the mixed material is h2, and h1 and h2 satisfy the following relationship: 5≤h2 / h1≤18; and (3) sintering the sagger loaded with the sintered material and the mixed material to form the sodium battery positive electrode material. The preparation method can effectively prolong the service life of the sagger while not affecting the electrical properties of the sodium battery positive electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of batteries, and in particular, a preparation method of a sodium battery cathode material is provided. BACKGROUND

[0002] Sodium-ion batteries, as a representative of secondary batteries, have been applied in many fields such as electric vehicles, energy storage power systems (such as hydroelectric, thermal, wind and solar power stations, etc.). Compared with lithium-ion batteries, sodium-ion batteries have a significant raw material cost advantage, especially for the cathode material which accounts for a large proportion of the cost, the sodium source, as the main raw material of the sodium battery cathode material, has more abundant reserves, which makes the sodium-ion battery have a good application prospect in large-scale energy storage fields such as energy storage power grids.

[0003] At present, the main preparation method of sodium battery cathode material includes high-temperature solid-phase sintering process. In the sintering process, the cathode precursor and sodium source are placed in the sagger, and after sintering, the sintered block is separated from the sagger, and the sagger is recycled for the production of cathode material. However, the sintering temperature used in this process is much higher than the melting point of sodium source, which makes the sodium source in a molten state and causes corrosion to the sagger, which is prone to react with the components in the sagger and affect the service life of the sagger, especially when high-sodium ratio raw materials are used to prepare sodium battery cathode materials. For example, in a ceramic sagger with aluminum oxide as the main component, the molten sodium source in the high-sodium ratio raw material is prone to react with aluminum oxide to form sodium feldspar, causing the sagger to expand in volume, which is prone to cause the sagger to crack and damage, and shorten the service life.

[0004] CN108649216A discloses a preparation method of a lithium nickel cobalt manganese oxide cathode material, which comprises: uniformly mixing raw materials including a lithium compound and a nickel cobalt manganese precursor, loading the raw materials into a sagger with at least one layer of filter paper laid at the bottom, and sintering and crushing to obtain a lithium nickel cobalt manganese oxide material. Although the introduction of filter paper can delay the damage of the sagger to some extent, the filter paper will burn at a high temperature of about 600℃, and the protective effect on the sagger is limited, which may introduce some impurities and seriously affect the performance of the cathode material. In addition, compared with the preparation of lithium battery cathode materials, the damage to the sagger is more serious in the preparation of sodium battery cathode materials. On the one hand, the larger radius and stronger alkalinity of sodium ions make the sodium source more severely erode the sagger; on the other hand, the sodium source has stronger permeability in the sintering process and is more likely to penetrate into the pores of the sagger.

[0005] CN117342629A discloses a method for preparing a sodium-ion battery cathode material with a low surface residual alkali content, comprising: mixing a sodium source, a precursor, and an M source (M is selected from Al, Ti, etc.) to obtain a mixture; and sintering the mixture in a coated sagger to obtain a cathode material, wherein the coating on the sagger includes oxides such as MgO, CaO, and TiO2. This method can reduce the loss of the sodium source, but the sagger is modified to coat its surface, resulting in a high cost, and the coating easily falls off after multiple sintering cycles, which has limited effect on improving the sagger.

[0006] Therefore, it is urgent to develop a new method for preparing sodium-ion cathode materials that can extend the service life of saggers. Summary of the Invention

[0007] The purpose of the present application is to provide a method for preparing a sodium battery cathode material, which can effectively extend the service life of a sagger without affecting the electrical properties of the sodium battery cathode material.

[0008] To achieve the above objectives, the present application provides a method for preparing a sodium cathode material, comprising:

[0009] (1) Provide sintering materials and mixed materials

[0010] The sintering material is a sintering product of a sodium source and a metal precursor, and the molar ratio of the sodium source to the metal precursor is calculated as Na / Me as a;

[0011] The mixed material is a mixture of a sodium source and a metal precursor, and the molar ratio of the sodium source to the metal precursor is calculated as b in terms of Na / Me;

[0012] a=0.4~0.7,b=0.9~1.1,Me represents the metal element in the metal precursor;

[0013] (2) Sagger loading

[0014] A layer of sintering material is laid on the bottom of the sagger, and then the mixed material is loaded on the sintering material, and cut into pieces to obtain a loading sagger;

[0015] In the charging sagger, the thickness of the sintered material is h1, the thickness of the mixed material is h2, and h1 and h2 satisfy the following relationship: 5≤h2 / h1≤18;

[0016] (3) sending the charging sagger to a sintering furnace for sintering to obtain the sodium positive electrode material.

[0017] In the preparation method of the application, a low-sodium-ratio positive electrode material (sintering material) is laid at the bottom of the sagger, which has sodium vacancies, so that part of the sodium ions in the high-sodium-ratio raw material (mixed material) located thereon can be accepted to generate the required sodium battery positive electrode material during sintering. In addition, due to the sodium deficiency characteristics of the low-sodium-ratio positive electrode material, it is basically not directly reacted with the sagger, so that the corrosion degree of the sagger can be significantly slowed down.

[0018] In some embodiments of the application, the thickness of the sintering material in the sagger is h1, which is 5-15 mm, the total thickness of the sagger is h = h1+h2, and h is 70-100 mm.

[0019] In some embodiments of the application, the metal element Me in the metal precursor is selected from one or more of Ni, Fe, Mn, Co, Al, Ti, Mg, Ca, Zn, Cu, W and La.

[0020] Further, the metal precursor is a nickel-containing ternary precursor.

[0021] Further, the chemical formula of the nickel-containing ternary precursor is Ni x M y A 1-x-y (OH)2, wherein M is Fe or Co, A is Mn or Ti, 0.2≤x≤0.6, 0.1

[0022] In some embodiments of the application, the sodium source is sodium carbonate and / or sodium hydroxide.

[0023] In some embodiments of the application, the sintering material is prepared by the following steps:

[0024] In the presence of an oxygen-containing atmosphere, the sodium source and the metal precursor are high-temperature calcined and crushed to powder; wherein the temperature of the high-temperature calcination is 800-900℃, and the time is 15-30h.

[0025] In some embodiments of the application, the sintering is carried out in an oxygen-containing atmosphere, the temperature of the sintering is 900-1000℃, and the sintering time is 15-30h.

[0026] In some embodiments of the application, the sintering furnace is a high-temperature roller furnace, and the high-temperature roller includes a sintering zone, and the temperature of the sintering zone is 900-1000℃.

[0027] In some embodiments of the application, the sagger is a ceramic sagger.

[0028] Further, the material of the ceramic sagger contains at least two of cordierite, mullite and spinel.

[0029] In some embodiments of the present application, a=0.45-0.7, b=0.95-1.05, and 6

[0030] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0032] Figure 1 This is a schematic diagram of sagger loading according to one embodiment of the present application;

[0033] Figure 2 These are the XRD patterns of the sodium-ion positive electrode materials prepared in Comparative Example 1, Comparative Example 3 and Example 2. DETAILED DESCRIPTION

[0034] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0035] The "range" disclosed in this application is defined in the form of a lower limit and / or an upper limit, and a given range is defined by selecting a lower limit and / or an upper limit. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range that is not clearly stated, and any lower limit can be combined with other lower limits to form a range that is not clearly stated, and similarly any upper limit can be combined with any other upper limit to form a range that is not clearly stated. In addition, each separately disclosed point or single value itself can be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form a range that is not clearly stated.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0037] The present application provides a method for preparing a sodium ion positive electrode material, the method comprising:

[0038] (1) Provide sintering materials and mixed materials

[0039] ​The sintered material is a low sodium ratio positive electrode material, specifically a sintered product of a sodium source and a metal precursor, and the molar ratio of the sodium source to the metal precursor is calculated as Na / Me, a=0.4-0.7,

[0040] The mixed material is a mixture of a sodium source and a metal precursor, and the molar ratio of the sodium source to the metal precursor is calculated as b, b=0.9-1.1,

[0041] Me represents the metal element in the metal precursor;

[0042] (2) Sagger loading

[0043] A layer of sintering material is laid on the bottom of the sagger, and then the mixed material is loaded on the sintering material, and cut into pieces to obtain a loading sagger;

[0044] (3) sending the charging sagger to a sintering furnace for sintering to form a sodium positive electrode material.

[0045] The inventors of the present application have found in their research that in the process of preparing sodium-based positive electrode materials using a high-temperature sintering process with a high sodium ratio as raw material, high-concentration sodium ions will inevitably diffuse into the pores of the sagger in contact with it and react with the sagger components to cause corrosion and cracking of the sagger. Accordingly, before the high-sodium ratio raw material (mixture) is loaded into the sagger for sintering, the present application first lays a layer of low-sodium ratio positive electrode material (sintering material) at the bottom of the sagger to provide more sodium vacancies. In this way, during the sintering process, some of the sodium ions in the high-sodium ratio raw material diffuse into the low-sodium ratio positive electrode material area at the bottom, and are received by the sodium vacancies to generate a positive electrode material with an increased sodium ratio. Moreover, due to its sodium-deficient characteristics, the low-sodium ratio positive electrode material at the bottom will not react with the sagger, effectively increasing the number of uses of the sagger.

[0046] In the present application, the sodium source can be an inorganic substance containing sodium, such as sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium chloride, etc. According to some embodiments, the sodium source is sodium hydroxide and / or sodium carbonate.

[0047] In the present application, the metal precursor may include one or more metal elements Me other than Na.

[0048] In some embodiments, the metal element Me in the metal precursor may be selected from one or more of Ni, Fe, Mn, Co, Al, Ti, Mg, Ca, Zn, Cu, W, and La.

[0049] In the present application, the metal precursor can be selected from various metal sources (i.e., Me sources), for example, one or more metal raw materials such as nickel source, manganese source, iron source, cobalt source, etc., or it can be a multi-element precursor containing multiple metal elements at the same time.

[0050] Preferably, the metal precursor is a nickel-containing ternary precursor, such as nickel-iron-manganese hydroxide, nickel-iron-cobalt hydroxide, or nickel-manganese-titanium hydroxide.

[0051] Preferably, the chemical formula of the nickel-containing ternary precursor is Ni x M y A 1-x-y (OH)2, wherein M is Fe or Co, A is Mn or Ti, 0.2≤x≤0.6, 0.1<y<0.4.

[0052] As some examples, the metal precursor is Ni 0.34 Fe 0.33 Mn 0.33 (OH)2 or Ni 0.34 Co 0.33 Mn 0.33 (OH)2.

[0053] In the present application, in the sintering material, the molar ratio of the sodium source to the metal precursor is Na / Me, and a=0.4-0.7, for example, 0.4, 0.45, 0.55, 0.57, 0.58, 0.60, 0.62, 0.65, 0.67, 0.7, etc. The sodium-deficient characteristic of the sintering material can, on the one hand, prevent the charging sagger from reacting with the charging sagger during the sintering process, and on the other hand, can provide sufficient sodium vacancies, so that the sodium ions in the mixed material flow to replenish the sodium vacancies.

[0054] In this application, it is understood that when the metal precursor contains one metal element, Me represents the metal element; when the metal precursor contains multiple metal elements, Me represents all of these metal elements. For example, when the metal precursor is Ni 0.34 Fe 0.33 Mn 0.33 In the case of (OH)2, Me represents Ni, Fe and Mn, and Na / Me refers to the molar ratio between Na provided by the sodium source and the sum of Ni, Fe and Mn provided by the metal precursor.

[0055] In some embodiments, the sintering material is prepared by a method including the following steps: high-temperature calcining and crushing a sodium source and a metal precursor in the presence of an oxygen-containing atmosphere; wherein the high-temperature calcination temperature is 800-900°C (for example, 800°C, 810°C, 820°C, 850°C, 870°C, 900°C, etc.), and the high-temperature calcination time is 15-30h (for example, 15h, 18h, 20h, 24h, 26h, 28h, 30h, etc.).

[0056] In the present application, the oxygen-containing atmosphere may be, for example, oxygen, high-concentration oxygen (concentration ≥ 70%), or carbon-free air (CO2 content ≤ 50 ppm).

[0057] In the present application, the sintering material is in powder form, and generally the smaller the particle size, the more uniform and the easier to compact, and the better to isolate the mixture from the saggar. Generally, the median particle size Dv 50 may be 5-10 μm, for example 5 μm, 6 μm, 7 μm, 8 μm, etc.

[0058] In the present application, in the mixture, the molar ratio of the amount of sodium source to the amount of metal precursor is b, b = 0.9-1.1, for example 0.9, 0.92, 0.95, 0.97, 0.98, 1, 1.02, 1.05, 1.06, 1.08, 1.1, etc. Preferably, the types of sodium source and metal precursor in the mixture are the same as those in the sintering material. In this way, the possibility of product delamination can be reduced.

[0059] In the present application, in the loaded saggar, the thickness of the sintering material is h1, the thickness of the mixture is h2, and h1 and h2 satisfy the following relationship: 5≤h2 / h1≤18. The sintering material laid in the saggar can act as an isolation layer between the mixture and the saggar, and the mixture, as the main raw material for preparing the sodium battery cathode material, can provide excellent electrical properties for the cathode material. Controlling the ratio of h2 / h1 in the above range can, on the one hand, avoid the use of too much sintering material, which can cause poor crystallinity and severe capacity loss of the cathode material, and on the other hand, avoid the use of too much mixture, which can shorten the service life of the saggar. As some examples, the ratio of h2 / h1 can be 5.5, 6.0, 6.5, 6.8, 7, 7.1, 7.2, 7.5, 7.7, 7.9, 8, 8.2, 8.5, 8.9, 9, 9.2, 9.5, 10, 11, 12, 13, 14, 16, etc.

[0060] In some embodiments, a = 0.45-0.7, b = 0.95-1.05, and 6

[0061] The present application does not have a particular limitation on the shape of the saggar used, which can be a square saggar, or a cylindrical saggar, or an oval saggar. In addition, the material of the saggar can include high-temperature-resistant ceramics, for example, a ceramic saggar selected to include at least two of cordierite, mullite, and spinel.

[0062] In some embodiments, the saggar is a ceramic saggar. Such a saggar is inexpensive, and the loading method of the present application is simple and easy to implement, which can effectively prolong the service life of such a saggar and inhibit the contamination of the saggar to the cathode material, achieving mass production of sodium battery cathode materials. Generally, the content of alumina in the chemical composition of the ceramic saggar is more than 25 wt%.

[0063] In some embodiments, as Figure 1 As shown, the sagger is a square opening sagger with the specifications of a×b×h t , a is 300~350mm, b is 300~350mm, h t The thickness of the sintered material is h1, which is 5-15 mm, the thickness of the mixed material is h2, and the total thickness of the charge is h, which is the value of the sagger h. t The difference from the opening height.

[0064] In the present application, the laying thickness of the sintering material can be selected according to the specifications of the sagger. According to some embodiments, in the charging sagger, the thickness of the sintering material is h1, which is 5 to 15 mm, such as 5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 10 mm, 12 mm, 13 mm, 15 mm, etc.; the total charging thickness h (h = h1 + h2) is 70 to 100 mm, such as 70 mm, 75 mm, 80 mm, 85 mm, 88 mm, 90 mm, 92 mm, 95 mm, 98 mm, 100 mm, etc. In addition, the total charging thickness h can be less than the height of the sagger, or it can be equal to the height of the sagger (i.e., the sagger is fully filled with material).

[0065] According to some specific implementations, in step (2), the method of loading the sagger includes the following process:

[0066] The sagger is loaded with powdered sintering material, spread evenly across the bottom of the sagger, and compacted to form an isolation layer with a thickness of h1. The sagger is then filled with powdered mixed material, spread evenly across the isolation layer, and compacted to form a raw material layer with a thickness of h2, thus completing the loaded sagger. The powdered material can be spread evenly across the bottom of the sagger by methods such as scraping, shaking, and vibrating.

[0067] According to the present application, in step (3), the sintering of the charging sagger can be carried out in an oxygen-containing atmosphere. According to some embodiments, the sintering temperature is 900-1000°C, for example, 900°C, 910°C, 950°C, 960°C, 970°C, 985°C, 1000°C, etc.; the sintering time is 15-30h, for example, 15h, 16h, 17h, 18h, 19h, 20h, 22h, 23h, 24h, 25h, 27h, 30h, etc.

[0068] In the present application, the sintering can be performed in various sintering furnaces, such as a box furnace or a roller hearth furnace. The sintering furnace can also be used to sinter multiple charging saggers at the same time to improve production efficiency.

[0069] In some embodiments, the sintering furnace is a high-temperature roller hearth furnace that can be used to sinter multiple charging saggers simultaneously. The high-temperature roller hearth furnace includes a sintering zone with a temperature of 900-1000°C.

[0070] In the present application, during the sintering process, the sodium source and the metal precursor in the mixture mainly react to form the positive electrode material, and a small amount of sodium ions diffuse into the sintered material at the bottom and are received by the sodium-deficient phase, which can also increase the sodium content of the material in this area, so that the prepared sodium positive electrode material has a higher capacity.

[0071] In some embodiments, the method further comprises: crushing and pulverizing the sintered product to obtain a median particle size Dv 50 It is a sodium battery positive electrode material with a thickness of 5 to 8 μm.

[0072] In some embodiments, the sodium-ion positive electrode material is an O3-type sodium-ion layered oxide.

[0073] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application.

[0074] In the following examples and comparative examples,

[0075] 1. Nickel iron manganese precursor (Ni 0.34 Fe 0.33 Mn 0.33 (OH)2) was synthesized according to the following method:

[0076] A nickel sulfate solution, a ferrous sulfate solution, and a manganese sulfate solution were prepared to prepare a nickel-iron-manganese metal salt solution with a Ni / Fe / Mn molar ratio of 0.34:0.33:0.33; and a 2 mol / L ammonia complexing agent solution and a 2 mol / L sodium hydroxide solution were prepared.

[0077] The nickel-iron-manganese metal salt solution, ammonia complexing agent solution and sodium hydroxide solution were added to the reactor at a uniform rate of 40 L / h, 4 L / h and 10 L / h respectively, and reacted at 50 ° C under stirring until particles with a particle size of Dv were formed. 50 The precipitate product is 5 μm, which is washed and dried to obtain Ni 0.34 Fe 0.33 Mn 0.33 (OH)2.

[0078] 2. Nickel-cobalt-manganese precursor (Ni 0.34 Co 0.33 Mn 0.33 (OH)2) was synthesized according to the following method:

[0079] A nickel sulfate solution, a cobalt sulfate solution, and a manganese sulfate solution were prepared to form a 2 mol / L nickel, cobalt, and manganese salt solution at a Ni / Co / Mn molar ratio of 0.34:0.33:0.33; a 2.3 mol / L sodium hydroxide solution was used as a precipitant, and a 0.1 mol / L ammonium dihydrogen phosphate solution was used as a complexing agent;

[0080] The nickel-cobalt-manganese metal salt solution, precipitant, and complexing agent were added to the reactor at a uniform rate of 40 L / h, 4 L / h, and 10 L / h, respectively, and reacted at 60 ° C under stirring until particles of size Dv were formed. 50 The precipitate product is 5 μm, and after washing and drying, Ni 0.34 Co 0.33 Mn 0.34 (OH)2.

[0081] In the synthesis of the above two precursors, the solutions used are all water-based.

[0082] 3. Sagger: Cordierite-mullite ceramic sagger; Specifications: 30mm long × 330mm wide × 100mm high, opening is 15mm.

[0083] 4. Performance test of sodium battery cathode materials

[0084] (1) Preparation of sodium button cells

[0085] The sodium battery positive electrode material, the conductive agent acetylene black, the binder polytetrafluoroethylene (PVDF) were mixed with an appropriate amount of NMP in a mass ratio of 7:2:1 and ground into a uniform slurry. The positive electrode slurry was evenly coated on the surface of aluminum foil (thickness of 15 μm), and then dried and punched to obtain a positive electrode sheet with a positive electrode film thickness of 120 μm.

[0086] Negative electrode: sodium sheet (thickness 600μm);

[0087] Diaphragm: glass fiber membrane (thickness 40 μm);

[0088] Electrolyte: NaClO4 electrolyte with a concentration of 1 mol / L, the solvent is composed of propylene carbonate (PC) and fluoroethylene carbonate (FEC) in a mass ratio of 19:1.

[0089] After cutting the positive electrode sheet, separator, and negative electrode sheet, they were assembled in a glove box, with the separator positioned between the positive and negative electrodes to act as a barrier. The separator was then soaked in electrolyte and compacted to create a button-type sodium battery.

[0090] (2) Capacity test

[0091] The sodium battery was charged to 4.05V at a constant current of 1C at 25°C, then charged at a constant voltage of 4.0V until the current dropped to 0.05C, and then discharged to 1.5V at a constant current of 1C to obtain the first cycle discharge capacity; this charging and discharging was repeated until the 50th cycle, and the discharge capacity of the sodium battery after 50 cycles was obtained.

[0092] Preparation Example 1

[0093] This preparation example is used to illustrate the preparation method of sintering materials and mixed materials.

[0094] Preparation of sintering materials: Na2CO3 and Ni 0.34 Fe 0.33 Mn 0.33 (OH)2 is prepared and mixed evenly, and loaded into different saggers respectively, and then vibrated and cut into blocks. The three saggers are sent together to a roller kiln for sintering. The kiln is an oxygen atmosphere, and the temperature of the sintering zone is controlled to 950℃. The kiln is sintered at 950℃ for 20 hours. The obtained sintered blocks are crushed and powdered to obtain low sodium ratio positive electrode materials, which are respectively recorded as material A, material B and material C.

[0095] Preparation of the mixture: Na2CO3 and Ni 0.34 Fe 0.33 Mn 0.33 (OH)2 was mixed evenly on a high-speed mixer to obtain mixed materials, which were respectively recorded as material D and material E.

[0096] Examples 1-2, Comparative Examples 1-2

[0097] Prepare 4 new saggers to be loaded, marked as No. 1, No. 2, No. 3, and No. 4 respectively.

[0098] S1: Load the four saggers separately. The loading conditions are as follows:

[0099] No. 1 sagger: filled with mixed material D (material layer thickness 85mm);

[0100] No. 2 sagger: Spread 10mm of material A on the bottom, scrape and compact it, and then fill it with mixed material D;

[0101] No. 3 sagger: Spread 10mm of material B on the bottom, scrape and compact it, and then fill it with mixed material D;

[0102] No. 4 sagger: Spread 10mm of material C on the bottom, scrape and compact it, and then fill it with mixed material D.

[0103] S2: Sintering to prepare sodium cathode materials

[0104] The sagger loaded in the above manner is vibrated and cut into pieces, and then simultaneously placed in a roller kiln for sintering. The temperature of the sintering zone is controlled at 950°C and sintered at 950°C for 20 hours in an oxygen atmosphere.

[0105] The sagger is turned over to separate the sintered material blocks, and the obtained sintered material blocks are subjected to roller coarse crushing and air flow crushing to obtain Dv 50 It is a 5.5μm sodium battery positive electrode material.

[0106] S3: Repeat steps S1 to S2

[0107] During S2, the bottom and four sides of the sagger are observed and analyzed for cracking. If any of the four saggers show obvious cracking (crack length > 10 mm, the same below), the verification is stopped; if no cracking occurs, steps S1 to S2 are repeated to cycle into the furnace for verification. Each time the sagger is entered into the furnace is counted as one time, and the number is accumulated in sequence.

[0108] The service life of the sagger is the number of times it is reused until it cracks minus 1.

[0109] The charging conditions, service life and electrical properties of the sodium cathode materials prepared in the first furnace of the four saggers are shown in Table 1.

[0110] Table 1

[0111]

[0112] It can be seen from Table 1 that sagger No. 1 (Comparative Example 1) without sintered material at the bottom cracked after one use, indicating that the direct use of a high sodium ratio mixture to prepare the sodium positive electrode material makes it easy for sodium ions to penetrate into the pores of the sagger and react with the sagger to cause the sagger to crack; and sagger No. 4 (Comparative Example 2) with a higher sodium ratio material laid on the bottom also cracked after two uses. The reason is that the sodium ratio of the bottom material is relatively high, and there is a lack of sodium vacancies, which cannot absorb the free sodium diffused from the mixture, causing the sodium ions to eventually penetrate into the No. 4 sagger to participate in the reaction and cause the sagger to crack; the number of uses of No. 2 and No. 3 saggers increased significantly, and the capacity performance was good, and was comparable to the capacity of the sodium positive electrode material prepared in Comparative Example 1, indicating that laying a certain thickness of low sodium ratio sintered material at the bottom can effectively improve the corrosion and cracking problem of the sagger without affecting the capacity.

[0113] Example 3 and Comparative Example 3

[0114] Prepare two new saggers to be loaded, marked as No. 5 and No. 6 respectively.

[0115] S1: Load the two saggers separately. The loading conditions are as follows:

[0116] No. 5 sagger: Spread 30mm of material B on the bottom, scrape and compact it, and then fill it with mixed material D;

[0117] No. 6 sagger: Spread 8mm material A on the bottom, scrape and compact it, and then fill it with mixed material D;

[0118] S2: Sintering to prepare sodium cathode materials

[0119] The sagger loaded in the above manner is vibrated and cut into pieces, and then simultaneously placed in a roller kiln for sintering. The temperature of the sintering zone is controlled at 950°C and sintered at 950°C for 20 hours in an oxygen atmosphere.

[0120] The sagger is turned over to separate the sintered material blocks, and the obtained sintered material blocks are subjected to roller coarse crushing and air flow crushing to obtain Dv 50 It is a 5.5μm sodium battery positive electrode material.

[0121] S3: Repeat steps S1 to S2

[0122] During S2, the bottom and four sides of the sagger are observed and analyzed for cracking. If any of the two saggers show obvious cracking, the verification is stopped; if no cracking occurs, steps S1 to S2 are repeated to cycle into the furnace for verification. Each time the sagger is entered into the furnace is counted as one time, and the number is accumulated in sequence.

[0123] The service life of the sagger is the number of times it is reused until it cracks minus 1.

[0124] The charging conditions, service life of the two saggers and the electrical properties of the sodium cathode materials prepared in the first furnace are shown in Table 2.

[0125] Table 2

[0126]

[0127] For ease of comparison, Table 2 also lists the effects of Comparative Example 1 and Example 2. It can be seen from Table 2 that cracking occurs after No. 1 sagger, which does not have a sintered material at the bottom, is used once, and the number of uses of No. 3 and No. 6 saggers (Example 3) increases. In addition, it is known that when No. 3 and No. 5 saggers (Comparative Example 3) are compared, under the condition of using the same sintered material (a has the same value), as the laying thickness of the sintered material increases, the service life of the sagger will increase, but it can be seen from Comparative Example 3 that when the laying thickness of the sintered material is too high, the capacity of the prepared sodium positive electrode material is significantly reduced. This is because the laying thickness of the sintered material in No. 5 sagger is too high, which causes the sodium ions diffused by the mixture on the upper layer to be unable to fully supplement the sodium vacancies, thereby affecting the performance of the sodium positive electrode material.

[0128] Figure 2The XRD spectra of the sodium cathode materials prepared in Comparative Example 1, Example 2, and Comparative Example 3 show the presence of a characteristic peak of 003 of the O3 phase at 16.8° and a characteristic peak of 104 of the O3 phase near 42°, indicating that O3 layered oxide compounds were synthesized. However, the 003 / 104 peak intensity ratio of the sintered material (Comparative Example 3) with a 30mm bottom layer is weaker than that of the other two groups, indicating poor crystallinity. This indicates that the sintered material of Comparative Example 3 did not fully react in the No. 5 sagger, resulting in severe capacity loss.

[0129] Examples 4 to 6 and Comparative Example 4

[0130] Prepare 4 new saggers to be loaded, marked as No. 7, No. 8, No. 9, and No. 10 respectively.

[0131] S1: Load the four saggers separately. The loading conditions are as follows:

[0132] No. 7 sagger: directly filled with mixed material E;

[0133] No. 8 sagger: Spread 5mm of material A on the bottom, scrape and compact it, and then fill it with mixed material E;

[0134] No. 9 sagger: Spread 10mm of material B on the bottom, scrape and compact it, and then fill it with mixed material E;

[0135] No. 10 sagger: Spread 8mm material B on the bottom, scrape and compact it, and then fill it with mixed material E.

[0136] S2: Sintering to prepare sodium cathode materials

[0137] The sagger loaded in the above manner is vibrated and cut into pieces, and then simultaneously placed in a roller kiln for sintering. The temperature of the sintering zone is controlled at 950°C and sintered at 950°C for 20 hours in an oxygen atmosphere.

[0138] The sagger is turned over to separate the sintered material blocks, and the obtained sintered material blocks are subjected to roller coarse crushing and air flow crushing to obtain Dv 50 It is a 6μm sodium battery positive electrode material.

[0139] S3: Repeat steps S1 to S2

[0140] During S2, the bottom and four sides of the sagger are observed and analyzed for cracking. If any of the four saggers show obvious cracking, the verification is stopped; if no cracking occurs, steps S1 to S2 are repeated to cycle into the furnace for verification. Each time the sagger is entered into the furnace is counted as one time, and the number is accumulated in sequence.

[0141] The service life of the sagger is the number of times it is reused until it cracks minus 1.

[0142] The charging conditions, service life and electrical properties of the sodium cathode materials prepared in the first furnace of the four saggers are shown in Table 3.

[0143] Table 3

[0144]

[0145] It can be seen from Table 3 that in order to prepare sodium battery cathode materials with the same target sodium ratio, after laying a sintered material of appropriate thickness on the bottom of the sagger, the service life of the sagger can be significantly improved while maintaining the electrical properties of the sodium battery cathode material.

[0146] Preparation Example 2

[0147] This preparation example is used to illustrate the preparation method of sintering materials and mixed materials.

[0148] Preparation of sintering material: Na2CO3 and Ni 0.34 Co 0.33 Mn 0.33 (OH)2 are mixed and loaded into different saggers respectively, then vibrated and cut, and the two saggers are sent together to a roller kiln for sintering. The kiln is an oxygen atmosphere, and the temperature of the sintering zone is controlled to 980℃, and sintered at 980℃ for 25h. The obtained sintered material blocks are crushed and powdered to obtain low sodium ratio positive electrode materials, which are respectively recorded as material F and material G.

[0149] Preparation of the mixture: Na2CO3 and Ni 0.34 Co 0.33 Mn 0.33 The (OH)2 ingredients are mixed evenly on a high-speed mixer to obtain a mixture, which is recorded as material H.

[0150] Examples 7 to 8 and Comparative Example 5

[0151] Prepare three new saggers to be loaded, marked as No. 11, No. 12, and No. 13 respectively.

[0152] S1: Load the three saggers separately. The loading conditions are as follows:

[0153] No. 11 sagger: directly filled with mixed material H;

[0154] No. 12 sagger: Spread 6mm material F on the bottom, scrape and compact it, and then fill it with mixed material H;

[0155] No. 13 sagger: Spread 12mm material G on the bottom, scrape and compact it, and then fill it with mixture H.

[0156] S2: Sintering to prepare sodium cathode materials

[0157] The sagger loaded in the above manner is vibrated and cut into pieces, and then simultaneously placed in a roller kiln for sintering. The temperature of the sintering zone is controlled at 950°C and sintered at 950°C for 24 hours in an oxygen atmosphere.

[0158] The sagger is turned over to separate the sintered material blocks, and the obtained sintered material blocks are subjected to roller coarse crushing and air flow crushing to obtain Dv 50 It is a 5.5μm sodium battery positive electrode material.

[0159] S3: Repeat steps S1 to S2

[0160] During S2, the bottom and four sides of the sagger are observed and analyzed for cracking. If any of the three saggers show obvious cracking, the verification is stopped; if no cracking occurs, steps S1 to S2 are repeated to cycle into the furnace for verification. Each time the sagger is entered into the furnace is counted as one time, and the number is accumulated in sequence.

[0161] The service life of the sagger is the number of times it is reused until it cracks minus 1.

[0162] The charging conditions, service life and electrical properties of the sodium cathode materials prepared in the first furnace of the three saggers are shown in Table 4.

[0163] Table 4

[0164]

[0165] It can be seen from Table 4 that for sodium-based cathode materials with the same target sodium ratio, after laying appropriate thicknesses of sintered materials with different low sodium ratios on the bottom, the service life of the sagger can be significantly improved while maintaining the electrical properties of the sodium-based cathode materials.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A method for preparing a sodium cathode material, characterized in that: include: (1) Provide sintering materials and mixed materials The sintering material is a sintering product of a sodium source and a metal precursor, and the molar ratio of the sodium source to the metal precursor is calculated as Na / Me as a; The mixed material is a mixture of a sodium source and a metal precursor, and the molar ratio of the sodium source to the metal precursor is calculated as b in terms of Na / Me; a=0.4~0.7,b=0.9~1.1,Me represents the metal element in the metal precursor; (2) Sagger loading A layer of sintering material is laid on the bottom of the sagger, and then the mixed material is loaded on the sintering material, and cut into pieces to obtain a loading sagger; In the charging sagger, the thickness of the sintered material is h1, the thickness of the mixed material is h2, and h1 and h2 satisfy the following relationship: 5≤h2 / h1≤18; (3) sending the charging sagger to a sintering furnace for sintering to form a sodium positive electrode material; The thickness h1 of the sintering material is 5-15 mm, the total thickness of the charge h=h1+h2, and h is 70-100 mm.

2. The preparation method according to claim 1, characterized in that The metal element Me in the metal precursor is selected from one or more of Ni, Fe, Mn, Co, Al, Ti, Mg, Ca, Zn, Cu, W and La.

3. The preparation method according to claim 1, characterized in that The metal precursor is a nickel-containing ternary precursor.

4. The preparation method according to claim 3, characterized in that The chemical formula of the nickel-containing ternary precursor is Ni x M y A 1-x-y (OH)2, wherein M is Fe or Co, A is Mn or Ti, 0.2≤x≤0.6, 0.1<y<0.

4.

5. The preparation method according to claim 1, characterized in that The sodium source is sodium carbonate and / or sodium hydroxide.

6. The preparation method according to claim 1, characterized in that The sintering material is prepared by a method comprising the following steps: In the presence of an oxygen-containing atmosphere, the sodium source and the metal precursor are subjected to high-temperature roasting and crushed into powder; wherein the high-temperature roasting temperature is 800-900° C. and the time is 15-30 hours.

7. The preparation method according to any one of claims 1 to 6, characterized in that The sintering is carried out in an oxygen-containing atmosphere, the sintering temperature is 900-1000° C., and the sintering time is 15-30 hours.

8. The preparation method according to any one of claims 1 to 6, characterized in that The sintering furnace is a high-temperature roller furnace, which includes a sintering zone. The temperature of the sintering zone is 900-1000°C.

9. The preparation method according to any one of claims 1 to 6, characterized in that The sagger is a ceramic sagger.

10. The preparation method according to claim 9, characterized in that The material of the ceramic sagger includes at least two of cordierite, mullite and spinel.

11. The preparation method according to any one of claims 1 to 6, characterized in that: a=0.45~0.7, b=0.95~1.05, 6<h2 / h1≤16.

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