A layered oxide cathode material and its preparation method in sodium-ion batteries

Abstract

This invention discloses a layered oxide cathode material, its preparation method, and a sodium-ion battery, belonging to the field of battery technology. The chemical formula of the layered oxide cathode material is Na. x Zn y Ni z Fe α Mn β C 1‑y‑z‑α‑β The cathode material consists of O2, 0 < x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ α ≤ 1, 0 ≤ β ≤ 1, 0 ≤ 1 − y − z − α − β ≤ 1, and C is any element other than Na, Zn, Ni, Fe, Mn, and O. This layered oxide cathode material possesses at least one of the following characteristics: it has a single-crystal particle structure; the single-crystal particles are complete and uniform, without aggregation; and the particle size is 1–20 μm. The preparation method of this cathode material is simple and inexpensive. Sodium-ion batteries prepared from this material exhibit high voltage, high first-cycle coulombic efficiency, good cycle performance, and good safety.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a layered oxide cathode material, its preparation method, and a sodium-ion battery. Background Technology

[0002] Currently, the main cathode materials for sodium-ion batteries include polyanionic, Prussian, and layered oxides. Generally, polyanionic materials have relatively low specific capacity due to their large molecular weight, while Prussian materials suffer from poor cycle life due to limitations in conductivity and the presence of water of crystallization. Layered oxide materials, on the other hand, exhibit high specific capacity and energy density, thus attracting widespread attention from researchers.

[0003] The general formula for layered oxides is Na x MO2, where M is mainly a transition metal element, but also contains some main group metal elements, including Li. + Ni 2+ Mg 2+ Zn 2+ Co 2+ Ca 2+ Ba 2+ 、Sr 2+ Al 3+ B 3+ Cr 3+ Co 3+ V 3+ Zr 4+ Ti 4+ Sn 4+ V 4+ Mo 5+ Mo 6+ Ru 4+ 、Nb 5+ Si 4+ Sb 5+ 、Nb 5+ Mo 6+ and Te 6+ One or more of the following. Among them, Na x Ni y Mn z Fe 1-y-z O2 has similar structural characteristics to lithium-ion ternary nickel-cobalt-manganese-based cathode materials and has the advantage of low cost. However, its actual discharge capacity is far lower than its theoretical capacity, which will severely limit the energy density of sodium-ion batteries.

[0004] Doping with multiple ions to modify the structure is currently the main technical approach. Reported Zn ion doping methods mainly focus on mono-component doping (such as Na₂O₃). x MnO2) or binary (such as Na) x Ni yMn 1-y The method involves ball milling with ethanol or ether as an additive to uniformly mix the precursor, or stirring the precursor in a volatile organic solvent (such as ethanol or ether) until the solvent is completely evaporated to obtain precursor powder, or spray drying the slurry obtained by mixing the above precursor with ethanol or water to obtain precursor powder. The precursor powder is then placed in a muffle furnace and heat-treated in an air atmosphere at 800-1000℃ for 10-24 hours to obtain Na. x A (1-y) Zn y O2 or Na x A y B z Zn 1-y-z O2, where A or B is a transition metal element or a part of the main group metal element.

[0005] However, the materials formed by the above methods exhibit severe agglomeration and can only form secondary particles. When used in sodium-ion batteries, their voltage, first-cycle coulombic efficiency, and cycle performance are all poor.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] One of the objectives of this invention is to provide a layered oxide cathode material having a complete and uniform single-crystal particle structure with no aggregation between the single-crystal particles.

[0008] The second objective of this invention is to provide a method for preparing the above-mentioned layered oxide cathode material.

[0009] The third objective of this invention is to provide a sodium-ion battery containing the above-mentioned layered oxide cathode material, which has high voltage, first-cycle coulombic efficiency and cycle performance, and good safety.

[0010] This application can be implemented as follows:

[0011] In a first aspect, this application provides a layered oxide cathode material with the chemical formula Na. x Zn y Ni z Fe α Mn β C 1-y-z-α-β O2, 0<x≤1, 0≤y≤1, 0≤z≤1, 0≤α≤1, 0≤β≤1, 0≤1-yz-α-β≤1, C is any element other than Na, Zn, Ni, Fe, Mn and O;

[0012] Layered oxide cathode materials have at least one of the following characteristics:

[0013] Feature 1: Layered oxide cathode materials have a single-crystal particle structure;

[0014] Feature 2: The single crystal particles of the layered oxide cathode material are complete and uniform, without aggregation;

[0015] Feature 3: The particle size of the layered oxide cathode material is 1-20 μm.

[0016] Secondly, this application provides a method for preparing the layered oxide cathode material as described in the foregoing embodiments, comprising the following steps: high-energy ball milling of a mixture of sodium source, zinc source, nickel source, iron source and manganese source mixed in a preset ratio with a solution containing surfactant.

[0017] In an optional embodiment, the sodium source includes at least one of sodium carbonate, sodium hydroxide, and sodium citrate;

[0018] And / or, the zinc source includes ZnO;

[0019] And / or, the nickel source includes NiO;

[0020] And / or, the iron source includes at least one of Fe2O3 and FeO;

[0021] And / or, the manganese source includes at least one of MnO2 and Mn2O3.

[0022] In an optional embodiment, the surfactant-containing solution includes a surfactant and a solvent; the surfactant includes at least one of cationic surfactants, anionic surfactants, amphoteric surfactants and nonionic surfactants; the solvent includes ethanol and water.

[0023] In an optional embodiment, the anionic surfactant includes at least one of stearic acid and sodium dodecylbenzenesulfonate;

[0024] And / or, cationic surfactants include quaternary ammonium compounds;

[0025] And / or, zwitterionic surfactants include at least one of lecithin, amino acid type and betaine type;

[0026] And / or, nonionic surfactants include at least one of alkyl glucosides, fatty acid glycerides, fatty acid sorbitan, polysorbates, and polyvinylpyrrolidone.

[0027] In some preferred embodiments, the surfactant includes at least one of polyvinylpyrrolidone and sodium dodecylbenzenesulfonate.

[0028] In an optional embodiment, the amount of surfactant used is 0.1-15 wt% of the mixture.

[0029] In an optional embodiment, the high-energy ball mill includes at least one of the following features:

[0030] Feature 1: The rotational speed of the high-energy ball mill is ≥1200 r / min; preferably 1200-2000 r / min;

[0031] Feature 2: The high-energy ball milling time is 3-7 hours;

[0032] Feature 3: Zirconium bead gradation ≥ 3;

[0033] Feature 4: In the upper and lower gradations, the diameter of the smaller diameter zirconium bead is 0.5-0.8 times the diameter of the larger diameter zirconium bead.

[0034] In an optional embodiment, the method further includes drying and pressing the ball-milled sample after high-energy ball milling into tablets, followed by heat treatment.

[0035] In an optional embodiment, drying is carried out at 60-120°C for 1-5 hours;

[0036] And / or, tableting is performed at a pressure of 10-20 MPa for 1-5 minutes.

[0037] In an optional implementation, the heat treatment includes at least one of the following features:

[0038] Feature 1: The heat treatment includes: first at 750-1200℃ for 12-24 hours, and then at 950-1200℃ for 12-20 hours;

[0039] Feature 2: The heating rate during the heat treatment process is 3-10℃ / min; preferably, the temperature is first raised to 750-1200℃ at a heating rate of 3-5℃ / min, and then raised to 950-1200℃ at a heating rate of 5-10℃ / min.

[0040] Feature 3: A grinding process occurs between the two heat treatment stages;

[0041] Feature 4: Heat treatment is carried out in an air or oxygen atmosphere;

[0042] Feature 5: After heat treatment, furnace cooling is also carried out. During furnace cooling, the dew point temperature of the surrounding environment is not higher than -25℃.

[0043] Thirdly, this application provides a sodium-ion battery having the layered oxide cathode material of the aforementioned embodiments.

[0044] The beneficial effects of this application include:

[0045] The layered oxide cathode material provided in this application has a complete and uniform single-crystal particle structure with no aggregation between the single-crystal particles.

[0046] This application involves high-energy ball milling of zinc, nickel, iron, manganese, and sodium sources with a surfactant-containing solution. This process alters the distribution of the sodium source and oxides. Under high-energy ball milling, the added oxides form chemically bonded ZnNiFeMnO2 particles, resulting in a uniform distribution of the sodium source on the ZnNiFeMnO2 particle surface after milling. Furthermore, the carbon chains of the surfactant undergo pyrolysis and volatilization, forming an interconnected microporous structure that hinders particle agglomeration and prevents the formation of secondary particles. The final material obtained exhibits high single-crystallinity and uniform particle size.

[0047] The corresponding sodium-ion batteries have high voltage, high first-cycle coulombic efficiency and cycle performance, and good safety. Attached Figure Description

[0048] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 The NaZn provided in Embodiment 1 of this application 0.05 Ni 0.317 Mn 0.317 Fe 0.317 XRD pattern of O2;

[0050] Figure 2 NaZn provided in Embodiment 2 of this application 0.05 Ni 0.317 Mn 0.317 Fe 0.317 SEM images of O2;

[0051] Figure 3 This is a charge-discharge curve of the sodium-ion half-cell provided in Example 3 of the test examples of this application. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0053] The layered oxide cathode material, its preparation method, and sodium-ion battery provided in this application are described in detail below.

[0054] This application proposes a layered oxide cathode material with the chemical formula Na. x Zn y Ni z Fe α Mn β C 1-y-z-α-β O2, 0<x≤1, 0≤y≤1, 0≤z≤1, 0≤α≤1, 0≤β≤1, 0≤1-yz-α-β≤1, C is any element other than Na, Zn, Ni, Fe, Mn and O.

[0055] The layered oxide cathode material is a single-crystal Zn-Ni-Fe-Mn sodium salt layered oxide.

[0056] This layered oxide cathode material has a complete and uniform single-crystal particle structure with no aggregation between the single-crystal particles.

[0057] For reference, the particle size of the above-mentioned layered oxide cathode material is 1-20 μm, such as 1 μm, 2 μm, 5 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, or any other value in the range of 1-20 μm.

[0058] This layered oxide cathode material exhibits high voltage, first-cycle coulombic efficiency, and cycle performance, as well as good safety.

[0059] Accordingly, this application also provides a method for preparing the above-mentioned layered oxide cathode material, including the following steps: mixing a mixture of sodium source, zinc source, nickel source, iron source and manganese source in a preset ratio with a solution containing surfactant and then performing high-energy ball milling.

[0060] For reference, the sodium source may include, for example, at least one of sodium carbonate (anhydrous sodium carbonate and / or hydrated sodium carbonate), sodium hydroxide, and sodium citrate. The zinc source may include ZnO. The iron source may include at least one of Fe₂O₃ and FeO. The nickel source may include NiO. The manganese source may include at least one of MnO₂ and Mn₂O₃.

[0061] In this application, the solution containing a surfactant includes a surfactant and a solvent. The surfactant may include at least one of cationic surfactants, anionic surfactants, amphoteric surfactants, and nonionic surfactants.

[0062] For example, anionic surfactants may include at least one of stearic acid and sodium dodecylbenzenesulfonate; cationic surfactants may include quaternary ammonium compounds; zwitterionic surfactants may include at least one of lecithin, amino acid type and betaine type; and nonionic surfactants may include at least one of alkyl glucoside (APG), fatty acid glycerides, fatty acid sorbitan (Span), polysorbate (Tween) and polyvinylpyrrolidone (PVP).

[0063] Solvents include ethanol and water. The volume ratio of ethanol to water can be from 1:1 to 25:1, such as 1:1, 5:1, 10:1, 15:1, 20:1, or 25:1. The ratio of surfactant to solvent can be from 1g:10mL to 1g:50mL, such as 1g:10mL, 1g:15mL, 1g:20mL, 1g:25mL, 1g:30mL, 1g:35mL, 1g:40mL, 1g:45mL, or 1g:50mL.

[0064] In some preferred embodiments, the surfactant includes at least one of polyvinylpyrrolidone (PVP) and sodium dodecylbenzenesulfonate (NDB). PPVP is suitable for solvents containing ethanol and water in any proportion, eliminating the need to adjust the amount added due to variations in solvent composition. NDB contains sodium (Na), and when pyrolyzed at high temperatures, the residual Na can chemically react with Na-deficient transition metal oxides, resulting in a more homogeneous phase composition in the final material.

[0065] The amount of the surfactant used can be 0.1-15 wt% of the mixture, such as 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, or 15 wt%, or any other value within the range of 0.1-15 wt%.

[0066] The surfactant at the aforementioned dosage can form a homogeneous and stable solution in the solvent. During high-energy ball milling, the surfactant binds various oxide particles to sodium ions, acting as a connecting bridge and solving the problem of uneven distribution of sodium source and oxides in traditional ball milling. Furthermore, during high-energy ball milling, various oxides can form ZnNiFeMnO2 precursors. In traditional methods, the synthesized precursors are ZnO / NiO / Fe2O3 / MnO2 with non-physical tight bonds. This application, through high-energy ball milling and the combination of surfactant, utilizes mechanical energy to induce chemical reactions and changes in material microstructure, structure, and properties, forming a sodium source tightly encapsulated in ZnNiFeMnO2. x Complex.

[0067] It should be noted that if the amount of surfactant used is too small, the above-mentioned effect will not be achieved; if the amount of surfactant used is too large, it will affect the material structure formation during the subsequent heat treatment process.

[0068] In this application, the rotational speed of the high-energy ball mill is ≥1200 r / min, preferably 1200-2000 r / min, such as 1200 r / min, 1300 r / min, 1400 r / min, 1500 r / min, 1600 r / min, 1700 r / min, 1800 r / min, 1900 r / min or 2000 r / min, etc., or any other value within the range of 1200-2000 r / min.

[0069] The high-energy ball milling time can be 3-7 hours, such as 3 hours, 4 hours, 5 hours, 6 hours or 7 hours, or any other value within the range of 3-7 hours.

[0070] If the ball mill speed is too low or the ball milling time is too short, it can only achieve the effect of conventional mixing, and may even cause uneven mixing of materials; if the ball mill speed is too high or the ball milling time is too long, it can easily damage the structure of the material.

[0071] In some implementations, during high-energy ball milling, the zirconium bead gradation ratio is ≥3, that is, at least three different diameter zirconium beads are used to obtain better high-energy ball milling results. Preferably, in the upper and lower gradations, the diameter of the smaller diameter zirconium bead is 0.5-0.8 times the diameter of the larger diameter zirconium bead.

[0072] For example, zirconium beads with diameters of 10mm, 8mm and 4mm can be used simultaneously.

[0073] Furthermore, the ball-milled sample after high-energy ball milling is dried, pressed into tablets, and then subjected to heat treatment.

[0074] For reference, drying can be carried out at 60-120℃ (such as 60℃, 70℃, 80℃, 90℃, 100℃, 110℃ or 120℃, etc.) for 1-5 hours (such as 1 hour, 2 hours, 3 hours, 4 hours or 5 hours, etc.).

[0075] Tableting can be performed at a pressure of 10-20 MPa (such as 10 MPa, 12 MPa, 15 MPa, 18 MPa or 20 MPa, etc.) for 1-5 minutes (such as 1 minute, 2 minutes, 3 minutes, 4 minutes or 5 minutes, etc.).

[0076] The heat treatment includes: first, 12-24 hours at 750-1200℃ (defined as the first heat treatment stage), and then 12-20 hours at 950-1200℃ (defined as the second heat treatment stage).

[0077] The temperature of the first heat treatment stage can be 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, or 1200℃, or any other value within the range of 750-1200℃. The duration of the first heat treatment stage can be 12h, 14h, 16h, 18h, or 20h, or any other value within the range of 12-20h.

[0078] The temperature of the second heat treatment stage can be 950℃, 1000℃, 1050℃, 1100℃, 1150℃, or 1200℃, or any other value within the range of 950-1200℃. The duration of the second heat treatment stage can be 12h, 14h, 16h, 18h, or 20h, or any other value within the range of 12-20h.

[0079] After the first heat treatment stage, the resulting material is further subjected to furnace cooling and grinding (e.g., the ground material particles can pass through a 500-mesh sieve), followed by a second heat treatment stage.

[0080] In this application, by performing grinding and a second heat treatment after the first heat treatment stage, the problem of uneven sintering that may exist in the first heat treatment stage can be improved. On the other hand, grinding can destroy the macroscopic pore structure (the scale of which is about several hundred micrometers to millimeters) formed in the material after the first heat treatment stage, release residual gas, and further promote the uniformity of material reaction, forming more uniform reaction products. In addition, the second heat treatment stage can promote the reaction between sodium source and transition metal, which is beneficial to reducing the residual alkali in the material.

[0081] The heating rate during the above heat treatment process can be 3-10℃ / min. In some preferred embodiments, the heating rate corresponding to the first heat treatment stage can be 3-5℃ / min, such as 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, or 5℃ / min, or any other value within the range of 3-5℃ / min. The heating rate corresponding to the second heat treatment stage can be 5-10℃ / min, such as 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min, or any other value within the range of 5-10℃ / min.

[0082] If the heating rate in the first heat treatment stage is below 3℃ / min, it can easily lead to abnormal grain growth, which is not conducive to the rapid transport of sodium ions in the bulk phase. If it is above 5℃ / min, the grown grains are prone to bipolarization, that is, the coexistence of large and small grains. If the heating rate in the second heat treatment stage is below 5℃ / min, it can easily lead to secondary aggregation of single crystal particles, forming secondary particles. If it is above 10℃ / min, it can easily lead to thermal stress in the material, causing grain fracture.

[0083] In this application, the heat treatment is carried out in an air or oxygen atmosphere.

[0084] The surfactant used in this application undergoes pyrolysis under high temperature and air conditions, forming an interconnected channel structure within the material. This allows the internal air concentration to be in equilibrium with the external concentration, which is more conducive to the chemical reaction between the solid material and the gaseous oxygen.

[0085] Furthermore, after heat treatment, the material is cooled in the furnace. During furnace cooling, the dew point temperature of the surrounding environment does not exceed -25°C.

[0086] By controlling the dew point temperature of the environment to no higher than -25°C, it is possible to ensure that the environment has a low moisture content, thus avoiding the impact and damage to the materials.

[0087] Continuing from the above, this application uses high-energy ball milling of zinc, nickel, iron, manganese, and sodium sources with a surfactant-containing solution to alter the distribution of the sodium source and oxides. Under high-energy ball milling, the added oxides form chemically bonded ZnNiFeMnO2 particles, and the milled sodium source is uniformly distributed on the surface of the ZnNiFeMnO2 particles. Existing technologies can only achieve aggregation of multiple oxides through physical bonding, resulting in severely agglomerated material morphology and the formation of secondary particles. In this application, by adding a surfactant, the precursor material after high-energy ball milling and drying contains a certain amount of surfactant. During high-temperature heat treatment, the carbon chains of the surfactant undergo pyrolysis and volatilization in an air or oxygen atmosphere, forming an interconnected microporous structure (with a scale of approximately a few micrometers), hindering particle aggregation and thus preventing the formation of secondary particles. Existing technologies typically involve directly sintering the precursor, ultimately resulting in severely agglomerated secondary particles. In this application, the surfactant remaining in the solid mixture inhibits particle aggregation in a physical and chemical manner. Simultaneously, the interconnected porous structure promotes air contact with the particle surface, reducing the oxygen concentration difference between the bulk phase and the material surface, thus preventing Na... x Zn y Ni z Fe α Mnβ C 1-y-z-α-β O2 materials react more fully with O2 in the air, resulting in materials with good single crystallinity and uniform particles.

[0088] Furthermore, this application also provides a sodium-ion battery having the aforementioned layered oxide cathode material. This sodium-ion battery exhibits superior electrochemical performance.

[0089] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0090] Example 1

[0091] This embodiment provides a layered oxide cathode material (Zn-Ni-Fe-Mn sodium salt layered oxide cathode material, with the molecular formula NaZn). 0.05 Ni 0.317 Mn 0.317 Fe 0.317 O2), which is prepared by the following method:

[0092] Step (1): Weigh and mix zinc oxide, nickel oxide, iron oxide, manganese dioxide and anhydrous sodium carbonate according to the preset molar ratio of 0.05:0.317:0.317:0.156:0.56, and put them into a ball mill jar (60mL) for later use;

[0093] Step (2): Weigh 0.1% of the total mass of surfactant (polyvinylpyrrolidone) from step (1), add it to a mixed solvent of ethanol and water (volume ratio of ethanol to water is 1:1) and stir. The ratio of the mixed solvent to the surfactant is 50 mL: 1 g.

[0094] Step (3): Transfer the solution obtained in step (2) to a ball mill jar and perform high-energy ball milling. Set the rotation speed to 1200 r / min and the ball milling time to 3 h.

[0095] The zirconium beads used in the high-energy ball milling process are graded in three stages, with diameters of 10 mm, 8 mm and 4 mm respectively.

[0096] Step (4): Dry the ball-milled sample in a forced-air drying oven at a temperature of 60°C for 5 hours. Then press it into tablets with a pressure setting of 10 MPa and a holding time of 1 minute.

[0097] Step (5): Place the tableted sample in a muffle furnace and heat it in an air atmosphere. The heating rate is 3℃ / min, the holding temperature is 750℃, and the holding time is 12h. Cool it with the furnace and then take it out for grinding.

[0098] Step (6): Place the powder sample from step (5) into a muffle furnace and heat treat it in an air atmosphere. The heating rate is 5℃ / min, the holding temperature is 950℃, and the holding time is 12h. Cool it with the furnace while controlling the dew point of the environment to be no higher than -25℃.

[0099] The Zn-Ni-Fe-Mn sodium salt layered oxide prepared in this embodiment has a single crystal structure, uniform particles, and a size of 1-5 μm. 50 =3μm. The XRD pattern of this cathode material is as follows: Figure 1 As shown, the results indicate that the diffraction peaks at 19.273°, 39.183°, 41.520°, 43.117°, 49.082°, 53.216°, 63.332°, 69.205°, and 74.624° are related to NaNi. 0.5 Mn 0.5 The (003), (006), (101), (012), (104), (015), (107), (018) and (110) crystal planes of O2 standard card 54-0887 are consistent, and some peak positions are shifted, indicating that Zn ions have been successfully doped into the crystal structure.

[0100] Example 2

[0101] This embodiment provides a layered oxide cathode material (Zn-Ni-Fe-Mn sodium salt layered oxide cathode material, with the molecular formula NaZn). 0.05 Ni 0.317 Mn 0.317 Fe 0.317 O2), which is prepared by the following method:

[0102] Step (1): Weigh and mix zinc oxide, nickel oxide, iron oxide, manganese dioxide and anhydrous sodium carbonate according to the preset ratio (0.05:0.317:0.158:0.317:0.56), and put them into a ball mill jar for later use;

[0103] Step (2): Weigh 7.5% of the total mass of surfactant (sodium dodecylbenzenesulfonate) from step (1), add it to a mixed solvent of ethanol and water (volume ratio of ethanol to water is 25:1) and stir. The ratio of mixed solvent to surfactant is 50mL:1g.

[0104] Step (3): Transfer the solution obtained in step (2) to a ball mill jar and perform high-energy ball milling. Set the rotation speed to 1500 r / min and the ball milling time to 5 h.

[0105] Step (4): The ball-milled sample is dried in a forced-air drying oven at 80°C for 8 hours; then it is pressed into tablets at a pressure of 15 MPa for 2 minutes.

[0106] Step (5): Place the tableted sample in a muffle furnace and heat treat it in an oxygen atmosphere. The heating rate is 3℃ / min, the holding temperature is 1050℃, and the holding time is 15h. Cool it with the furnace and take it out for grinding.

[0107] Step (6): Place the powder sample from step (5) in a muffle furnace and heat treat it in an oxygen atmosphere. The heating rate is 5℃ / min, the holding temperature is 950℃, and the holding time is 15h. At the same time, the dew point of the environment is controlled to be no higher than -25℃.

[0108] The Zn-Ni-Fe-Mn sodium salt layered oxide prepared in this embodiment has a single-crystal structure, uniform particles, and a size of 2-15 μm. 50 =8μm. The SEM image of this cathode material is shown below. Figure 2 As shown in the figure, the results indicate that the single crystal particles have smooth surfaces and uniform sizes.

[0109] Example 3

[0110] This embodiment provides a layered oxide cathode material (Zn-Ni-Fe-Mn sodium salt layered oxide cathode material, with the molecular formula NaZn). 0.1 Ni 0.317 Mn 0.317 Fe 0.317 O2), which is prepared by the following method:

[0111] Step (1): Weigh and mix zinc oxide, nickel oxide, iron oxide, manganese dioxide and anhydrous sodium carbonate in a preset ratio (0.1:0.317:0.156:0.317:0.56) and put them into a ball mill jar for later use;

[0112] Step (2): Weigh 15% of the total mass of surfactant (alkyl glucoside) from step (1), add it to a mixed solvent of ethanol and water (volume ratio of ethanol to water is 3:1) and stir. The ratio of mixed solvent to surfactant is 10 mL: 1 g.

[0113] Step (3): Transfer the solution obtained in step (2) to a ball mill jar and perform high-energy ball milling. Set the rotation speed to 2000 r / min and the ball milling time to 7 h.

[0114] Step (4): The ball-milled sample is dried in a forced-air drying oven at 90°C for 4 hours; then it is pressed into tablets at a pressure of 20 MPa for 5 minutes.

[0115] Step (5): Place the tableted sample in a muffle furnace and heat treat it in an oxygen atmosphere. The heating rate is 3℃ / min, the holding temperature is 1200℃, and the holding time is 24h. After cooling in the furnace, take it out and grind it.

[0116] Step (6): Place the powder sample from step (5) into a muffle furnace and heat treat it in an air atmosphere. The heating rate is 5℃ / min, the holding temperature is 950℃, and the holding time is 20h. At the same time, control the dew point of the environment to be no higher than -25℃.

[0117] The Zn-Ni-Fe-Mn sodium salt layered oxide prepared in this embodiment has a single-crystal structure, uniform particles, and a size of about 8 μm. 50 =4μm.

[0118] Example 4

[0119] This embodiment provides a layered oxide cathode material (Zn-Ni-Fe-Mn-Cu sodium salt layered oxide cathode material, with the molecular formula NaZn). 0.1 Ni 0.3 Mn 0.317 Fe 0.317 Cu 0.017 O2), which is prepared by the following method:

[0120] Step (1): Weigh and mix zinc oxide, nickel oxide, iron oxide, manganese dioxide, copper oxide and anhydrous sodium carbonate in a preset ratio (0.1:0.3:0.156:0.317:0.017:0.56) and put them into a ball mill jar for later use;

[0121] Step (2): Weigh 15% of the total mass of surfactant (alkyl glucoside) from step (1), add it to a mixed solvent of ethanol and water (volume ratio of ethanol to water is 1:1) and stir. The ratio of mixed solvent to surfactant is 10 mL: 1 g.

[0122] Step (3): Transfer the solution obtained in step (2) to a ball mill jar and perform high-energy ball milling. Set the rotation speed to 2000 r / min and the ball milling time to 7 h.

[0123] Step (4): The ball-milled sample is dried in a forced-air drying oven at 60°C for 8 hours; then it is pressed into tablets at a pressure of 20 MPa for 5 minutes.

[0124] Steps (5) and (6) are the same as in Example 3.

[0125] The Zn-Ni-Fe-Mn-Cu sodium salt layered oxide cathode material prepared in this embodiment has a single-crystal structure, uniform particles, and a size of about 10 μm. 50 =5μm.

[0126] Example 5

[0127] This embodiment provides a layered oxide cathode material (Zn-Ni-Fe-Mn sodium salt layered oxide cathode material, with the molecular formula NaZn). 0.05 Ni 0.317 Mn 0.317 Fe 0.317 O2), which is prepared by the following method:

[0128] Step (1): Weigh and mix zinc oxide, nickel oxide, ferrous oxide, manganese trioxide and anhydrous sodium carbonate in a preset ratio (0.05:0.317:0.317:0.156:0.56) and put them into a ball mill jar for later use;

[0129] Steps (2) to (6) are the same as in Example 4.

[0130] The Zn-Ni-Fe-Mn sodium salt layered oxide prepared in this embodiment has a single-crystal structure, uniform particles, and a size of about 8 μm. 50 =5μm.

[0131] Example 6

[0132] This embodiment provides a layered oxide cathode material (Zn-Ni-Fe-Mn sodium salt layered oxide cathode material, with the molecular formula NaZn). 0.05 Ni 0.317 Mn 0.317 Fe 0.317 O2), which is prepared by the following method:

[0133] Step (1): Weigh and mix zinc oxide, nickel oxide, iron oxide, manganese dioxide and anhydrous sodium carbonate according to the preset ratio (0.05:0.317:0.158:0.317:0.56), and put them into a ball mill jar for later use;

[0134] Step (2): Weigh 15% of the total mass of surfactant (sodium dodecylbenzenesulfonate) from step (1), add it to a mixed solvent of ethanol and water (volume ratio of ethanol to water is 1:1) and stir. The ratio of mixed solvent to surfactant is 10 mL: 1 g.

[0135] Steps (3) to (6) are the same as in Example 4.

[0136] The Zn-Ni-Fe-Mn sodium salt layered oxide prepared in this embodiment has a single-crystal structure, uniform particles, and a size of about 5 μm. 50 =3μm.

[0137] Comparative Example 1

[0138] The difference between this comparative example and Example 1 is that no surfactant was used during the ball milling process.

[0139] Comparative Example 2

[0140] The difference between this comparative example and Example 1 is that the ball milling speed is 800 r / min.

[0141] Comparative Example 3

[0142] The difference between this comparative example and Example 1 is that the ball milling speed is 2500 r / min.

[0143] Comparative Example 4

[0144] The difference between this comparative example and Example 1 is that only zirconium beads with diameters of 10mm and 4mm are used, and the mass ratio of the two diameters of zirconium beads is 1:1.

[0145] Comparative Example 5

[0146] The difference between this comparative example and Example 1 is that the heat treatment only includes the first heat treatment stage, without the second heat treatment stage.

[0147] Comparative Example 6

[0148] The difference between this comparative example and Example 1 is that there is no grinding process between the first heat treatment stage and the second heat treatment stage.

[0149] Comparative Example 7

[0150] The difference between this comparative example and Example 1 is that the temperature of the first heat treatment stage is 700°C.

[0151] Comparative Example 8

[0152] The difference between this comparative example and Example 1 is that the temperature of the first heat treatment stage is 1300°C.

[0153] Comparative Example 9

[0154] The difference between this comparative example and Example 1 is that the temperature of the second heat treatment stage is 900°C.

[0155] Comparative Example 10

[0156] The difference between this comparative example and Example 1 is that the temperature of the second heat treatment stage is 1300°C.

[0157] Comparative Example 11

[0158] The difference between this comparative example and Example 1 is that the heating rate in the first heat treatment stage is 8°C / min.

[0159] Comparative Example 12

[0160] The difference between this comparative example and Example 1 is that the heating rate in the first heat treatment stage is 3°C / min.

[0161] Comparative Example 13

[0162] The difference between this comparative example and Example 1 is that the dew point of the environment during the furnace cooling process after heat treatment is higher than -25°C.

[0163] Test case

[0164] The layered oxide cathode materials obtained in Examples 1-6 and Comparative Examples 1-13 were used to prepare sodium-ion batteries according to the following method, and the electrochemical performance of the obtained sodium-ion batteries was tested.

[0165] The battery is manufactured using the following method:

[0166] Electrode preparation stage:

[0167] a) Pulping: The original pulp is composed of active substances, conductive agents, binders and solvents, wherein the ratio of active substances, conductive agents and binders is 8:1:1.

[0168] Active material: The layered oxide cathode materials obtained in Examples 1-6 and Comparative Examples 1-13 were vacuum baked before slurry preparation at 120°C for 4 hours; Conductive agent: CNT; Binder: PVDF from Sigma-Aldrich, Mw~534000, CAS No. 24937-79-9; Solvent: NMP, purity ≥99%.

[0169] b) Slurry preparation stage:

[0170] Stirring to prepare the slurry: Add NMP and PVDF to the stirring container in sequence, and rotate the magnetic stirrer (speed ≤200r / min) to avoid PVDF adhering to the inner wall of the container during the process; then continue to add SP and active substances to the container and stir for 4 hours.

[0171] c) Electrode coating stage:

[0172] The current collector is made of double-sided smooth aluminum foil with a single-sided coating, with a thickness of 16μm and a width of 280mm; the scraper height is 200μm, and the dew point temperature of the low humidity chamber is controlled below -25℃.

[0173] Electrode drying, rolling, cutting and weighing:

[0174] a) Drying of electrode sheets:

[0175] The vacuum oven is designed to maintain a temperature of 80℃ for 2 hours, then re-vacuum and maintain a temperature of 120℃ for 12 hours.

[0176] b) Compressing and cutting:

[0177] After drying, the electrode sheets are pressed into sheets. The positive electrode sheet is rolled to a thickness of 18μm using a roller mill. Then, the prepared electrode sheets are clamped together with weighing paper and punched out into 14mm electrode sheets with no powder falling off the edges and no obvious burrs.

[0178] c) Weighing

[0179] Weighing was performed using a five-position balance with an accuracy of 0.0001 g; the active material loading of the electrode was not less than 2 mg / cm³. 2 .

[0180] Assembly of button cells:

[0181] The components for assembling a button cell include: a negative electrode shell, a sodium metal sheet, a separator, a spring sheet, a positive electrode shell, and an electrolyte. In addition, a pressing mold, a pipette, and insulated tweezers are also required.

[0182] Model: 2025;

[0183] Assembly environment: Inside the glove box, the environmental requirements are H2O < 0.01ppm; O2 < 0.01ppm; Diaphragm: Model Whatman.GF / D, d = 19mm;

[0184] Electrolyte: Model NP-202 (NaPF6), judged by wetting the separator; Sodium sheet: Size 15.6mm, thickness 0.45mm, purity >99.7% (standard type purchased), smooth surface; Encapsulation pressure: 55±5kg / cm 2 .

[0185] Electrochemical performance testing includes:

[0186] The button cell was placed in a constant temperature chamber, and the test environment temperature was 25℃.

[0187] 0.1C test procedure (nominal specific capacity of 130mAh / g):

[0188] Let stand for 12 hours; let stand for 3 minutes;

[0189] Charge at a constant current of 0.1C to 4.1V; let stand for 3 minutes;

[0190] Discharge at a constant current of 0.1C to 2.5V;

[0191] Repeat the above steps in a loop.

[0192] The results are shown in Table 1 and Figure 3 As shown. Among them, Figure 3 This is a charge-discharge curve of the sodium-ion battery corresponding to Example 3.

[0193] Table 1 Test Results

[0194]

[0195]

[0196] As can be seen from Table 1, the sodium-ion battery prepared from the layered oxide cathode material provided in this application has high voltage, high first-cycle coulombic efficiency and good cycle performance, and good safety.

[0197] In summary, the layered oxide cathode material provided in this application has a complete and uniform single-crystal particle structure with no aggregation between the single-crystal particles. Its preparation method is simple and inexpensive, using pollution-free green materials. The sodium-ion battery prepared from it exhibits high voltage, high first-cycle coulombic efficiency, good cycle performance, and good safety.

[0198] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a layered oxide cathode material, characterized in that, Includes the following steps: The mixture of sodium, zinc, nickel, iron and manganese sources in a preset ratio is subjected to high-energy ball milling with a solution containing surfactant; the ball-milled sample is dried, pressed into tablets, and then heat-treated. The zinc source is ZnO; the nickel source is NiO; the iron source is at least one of Fe2O3 and FeO; the manganese source is at least one of MnO2 and Mn2O3; and the amount of surfactant used is 0.1-15 wt% of the mixture. The high-energy ball mill has a rotation speed ≥1200 r / min; the zircon bead gradation ratio ≥3 grades; in the upper and lower gradations, the diameter of the smaller diameter zircon beads is 0.5-0.8 times the diameter of the larger diameter zircon beads; The heat treatment includes: first, a process at 750-1200 ℃ for 12-24 h, followed by a process at 950-1200 ℃ for 12-20 h; a grinding process is also included between the two heat treatment stages; the heating rate during the heat treatment process is 3-10 ℃ / min; the heat treatment is carried out in an air or oxygen atmosphere; after the heat treatment, furnace cooling is also included, and the dew point temperature of the environment during furnace cooling is not higher than -25 ℃; The surfactant includes at least one of anionic surfactants and nonionic surfactants; the anionic surfactant includes at least one of stearic acid and sodium dodecylbenzenesulfonate; the nonionic surfactant includes at least one of alkyl glucoside, fatty acid glycerides, fatty acid sorbitan, polysorbate and polyvinylpyrrolidone.

2. The preparation method according to claim 1, characterized in that, Drying is carried out at 60-120 ℃ for 1-5 hours; Tableting is performed at a pressure of 10-20 MPa for 1-5 minutes.

3. A layered oxide cathode material, characterized in that, It is prepared by the preparation method described in claim 1 or 2.

4. The layered oxide cathode material according to claim 3, characterized in that, The chemical formula of the layered oxide cathode material is Na. x Zn y Ni z Fe α Mn β C 1-y-z-α-β O2, 0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 1, 0 < α ≤ 1, 0 < β ≤ 1, 0 ≤ 1 - yz - α - β ≤ 1, C is any element other than Na, Zn, Ni, Fe, Mn and O; The layered oxide cathode material has a single-crystal particle structure; The single-crystal particles of the layered oxide cathode material are complete and uniform, without aggregation; The particle size of the layered oxide cathode material is 1-20 μm.

5. A sodium-ion battery, characterized in that, The sodium-ion battery has the layered oxide cathode material as described in claim 4.

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