A single-crystal cathode material for sodium-ion batteries, its preparation method and application

Abstract

This invention discloses a single-crystal cathode material for sodium-ion batteries, its preparation method, and its applications. This material achieves high operating voltage, excellent cycle stability, and rate performance through precise control of its chemical composition and microstructure. The preparation method of this invention solves the problem of partially doped metal ions being unable to be synthesized into the precursor via co-precipitation or in a high proportion. It effectively controls the microstructure and uniform elemental distribution of the material, and its performance is superior to conventional multi-component oxide mechanical solid-state synthesis methods. The addition of molten salt optimizes its single-crystal morphology and lowers the sintering temperature. M-element doping stabilizes the structure, improves its air stability and cycle stability under high voltage, and oxygen-containing compound coating reduces side reactions at the cathode material and electrolyte interface and enhances electrochemical performance under high voltage. The initial discharge specific capacity is 173.34 mAh / g, and after 100 charge-discharge cycles, it retains 91.5% of its capacity.

Description

Technical Field

[0001] This invention pertains to cathode material preparation technology, specifically relating to a sodium-ion battery single-crystal cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid growth of global demand for renewable energy and electric vehicles, the research and development of high-performance, low-cost energy storage materials has become particularly important. Sodium-ion batteries, as a potential alternative technology, have received widespread attention in recent years due to their abundant resources, low cost, and electrochemical properties similar to lithium-ion batteries. However, the commercialization of sodium-ion batteries still faces many challenges, among which improving the performance of cathode materials is crucial.

[0003] Currently, cathode materials for sodium-ion batteries mainly include layered oxides, polyanionic compounds, and Prussian blue compounds. Among them, layered oxides are considered one of the most promising cathode material candidates due to their high theoretical capacity and good ion transport performance. However, existing layered oxide cathode materials often suffer from poor cycle stability, insufficient rate performance, limited operating voltage, and high cost, which restricts their widespread application in sodium-ion batteries.

[0004] Specifically, traditional layered oxide cathode materials are often synthesized using a mechanical solid-state synthesis method. While this method is simple and easy to implement, it is difficult to precisely control the microstructure and elemental distribution of the material, leading to significant fluctuations in material performance. Furthermore, the synthesis of partially doped metal ions using co-precipitation methods is challenging, making it difficult to achieve high-proportion doping, which in turn affects the overall performance of the material.

[0005] To overcome the aforementioned technical challenges, researchers are constantly exploring new synthesis methods and material modification strategies. Among these, the molten salt method has gradually become a research hotspot due to its ability to optimize the single-crystal morphology of materials, reduce sintering temperatures, and decrease energy consumption. Meanwhile, through appropriate elemental doping and surface coating techniques, the structural stability and electrochemical performance of materials can be further improved.

[0006] For example, patent application CN114540934A discloses a method for preparing a single-crystal nickel-cobalt-manganese ternary cathode material. The preparation method includes the following steps: S1: First, a single-crystal precursor is prepared; S2: The single-crystal precursor, lithium compound, doped metal compound, additives, and deionized water are dry-mixed and granulated using a stirring granulator, calcined in an oxygen atmosphere, and then pulverized by air jet to obtain a large-particle-size single-crystal ternary material; S3: The obtained single-crystal ternary material is wet-coated with lithium carbonate and aluminum nitrate using a sol-gel method in a reactor to form a uniform coating layer on the surface; S4: Calcination in an air atmosphere yields a high-performance ternary cathode material. The preparation method provided by this invention is simple, easy to process, and the prepared material exhibits excellent charge-discharge efficiency, discharge specific capacity, rate performance, and cycle performance.

[0007] Patent application CN114695875A discloses a high-capacity single-crystal ternary cathode material and its preparation method. The cathode material is prepared by a first sintering of a high-nickel precursor, a lithium source, and an additive containing element M, followed by a second sintering with an additive containing element A. The ternary cathode material of this invention has a small and uniform particle size. The double-sintering doping method not only improves the structural stability of the cathode material and further enhances its electrochemical performance, particularly significantly improving discharge specific capacity and cycle stability, but also provides a simple and low-cost preparation method, facilitating industrial-scale production.

[0008] However, in order to solve the performance bottlenecks of traditional materials, improvements and innovations are still needed in existing sodium-ion battery cathode materials. Summary of the Invention

[0009] In view of this, the present invention proposes a single-crystal cathode material for sodium-ion batteries, its preparation method, and its applications. This material, through precise control of its chemical composition and microstructure, achieves high operating voltage, excellent cycle stability, and rate performance, while simultaneously reducing production costs, providing strong support for the commercial application of sodium-ion batteries.

[0010] The specific technical solution of the present invention is as follows:

[0011] This invention provides a method for preparing a single-crystal cathode material for sodium-ion batteries, comprising the following steps:

[0012] (1) Dissolve the nickel source and manganese source separately in water and mix them to obtain a mixed salt solution;

[0013] (2) Add alkali solution to the mixed salt solution to carry out a co-precipitation reaction, controlling the particle size of the precipitate within D. 50 =5-6μm (D is selected in the embodiments of the present invention) 50(5μm as an example), after reaction, the precursor powder is obtained by drying;

[0014] (3) After mixing the precursor powder with sodium source, copper source, titanium source and M compound, add molten salt and mix evenly, then perform the first calcination treatment to obtain the cathode material after the first calcination treatment.

[0015] Among them, M is a compound of calcium carbonate, calcium oxide, barium carbonate, barium oxide, potassium carbonate, or potassium oxide;

[0016] (4) The cathode material that has undergone the first calcination treatment is processed to obtain the single crystal cathode material that has undergone the first calcination treatment. The single crystal cathode material that has undergone the first calcination treatment is mixed evenly with an oxygen-containing compound and then subjected to a second calcination treatment to obtain the sodium-ion battery single crystal cathode material.

[0017] Specifically, in step (1), the nickel source is nickel sulfate, nickel chloride, nickel nitrate, or nickel acetate.

[0018] The manganese source is manganese sulfate, manganese chloride, manganese nitrate, or manganese acetate;

[0019] The concentration of the mixed salt solution is 1.0-2.0 mol / L, and the molar ratio of the metal elements is 1:1.

[0020] In some embodiments of the present invention, in step (2), the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkaline solution is 2.0-4.0 mol / L;

[0021] The co-precipitation temperature is 40-60℃.

[0022] The drying temperature is 90-120℃.

[0023] In some embodiments of the present invention, in step (3), the sodium source is sodium carbonate, sodium nitrate, or sodium hydroxide.

[0024] The copper source is copper oxide, copper acetate, copper nitrate, copper oxalate, copper sulfate, or copper chloride.

[0025] The titanium source is titanium dioxide, titanic acid, titanium tetrachloride, or barium metatitanate.

[0026] The molten salt is sodium sulfate, sodium chloride, or sodium phosphate.

[0027] The molar ratio of the metal element in the precursor powder to the sodium source in the sodium source is 1:0.9-1.1.

[0028] The molar ratio of metal elements to copper source in the precursor powder is 16:1-2.

[0029] The molar ratio of metal elements to titanium in the precursor powder is 16:1-4.

[0030] The ratio of metal elements in the precursor powder to metal elements in compound M is 1:0.01-0.03.

[0031] The amount of molten salt doping is 0.5-2 wt% of the precursor powder mass.

[0032] Preferably, in step (3), the conditions for the first calcination treatment are a calcination temperature of 800-1000℃ and a calcination time of 10-20 hours.

[0033] During mixing, a ball mill can be used to mix thoroughly. The ball mill speed is 200-450 r / min, the ball-to-material mass ratio is 1:1-2:1, and the ball milling time is 3-5 h.

[0034] In some embodiments of the present invention, in step (4), the cathode material that has undergone the first calcination treatment is subjected to airflow pulverization and sieving to obtain the single crystal cathode material that has undergone the first calcination treatment, wherein the sieve mesh number is 200-400 mesh.

[0035] In some embodiments of the present invention, in step (4), the oxygen-containing compound is boron oxide, boric acid, aluminum metaphosphate, tungsten oxide, zirconium oxide or titanium oxide; the coating amount of the oxygen-containing compound is 1000-3000 ppm of the sodium-ion battery single crystal cathode material.

[0036] Preferably, in step (4), the conditions for the second calcination treatment are a calcination temperature of 400-600℃ and a calcination time of 5-15 hours.

[0037] During mixing, a ball mill can be used to mix evenly. The ball mill speed is 200-450 r / r / min, the ball-to-material mass ratio is 1:1-2:1, and the ball milling time is 1-3 h.

[0038] This invention also provides a sodium-ion battery single-crystal cathode material prepared by the aforementioned method, with the chemical formula Na. b M a Ni 0.5-x Cu x Mn 0.5-y Ti y O2 (0.96≤b≤1, 0.01≤a≤0.03, 0<x<0.5, 0<y<0.5).

[0039] The present invention also provides a sodium-ion battery, comprising a positive electrode, a separator, and a negative electrode, wherein the positive electrode comprises the sodium-ion battery monocrystalline positive electrode material described above.

[0040] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0041] This invention provides a high-performance sodium-ion battery single-crystal cathode material with the chemical formula Na. b M a Ni 0.5-x Cu x Mn 0.5-y Ti y O2 (0.96≤b≤1, 0.01≤a≤0.03, 0<x<0.5, 0<y<0.5). The cathode material provided by this invention has high operating voltage, good cycle stability, high rate performance, and low cost, making it an ideal cathode material for sodium-ion batteries. This method can solve the problem that some doped metal ions cannot be synthesized into the precursor through co-precipitation or in a high proportion. It can effectively control the microstructure and uniform elemental distribution of the material, and its performance is superior to that of conventional multi-component oxide mechanical solid-state synthesis methods. The addition of molten salt can optimize its single crystal morphology and reduce the sintering temperature (saving energy consumption). M element doping can stabilize the structure and improve its air stability and cycle stability under high voltage. N element (oxygen-containing compound) coating can reduce side reactions at the cathode material and electrolyte interface and improve electrochemical performance under high voltage. This invention method is simple to operate, the raw materials are readily available, and it is suitable for industrial production. When used as a cathode material in sodium-ion batteries, it exhibits excellent specific capacity and cycle performance in electrochemical tests.

[0042] At a current density of 0.1C (voltage window 2-4.3V), the initial discharge specific capacity is 173.34 mAh / g. At a current density of 1C, after 100 charge-discharge cycles, it retains 91.5% of its capacity, demonstrating excellent cycle life and stability. This experimental method is simple, easy to implement, and inexpensive, and can be extended to the synthesis of other energy storage materials, thereby improving battery performance. Attached Figure Description

[0043] Figure 1 The Ni obtained in Example 2 of this invention 0.5 Mn 0.5 SEM image of (OH)2 precursor material;

[0044] Figure 2 This is a SEM image of the single-crystal cathode material obtained in Comparative Example 2 of this invention;

[0045] Figure 3 This is a SEM image of the single-crystal cathode material obtained in Example 2 of the present invention;

[0046] Figure 4 This is a charge-discharge curve of the single-crystal cathode material obtained in Example 2 of the present invention;

[0047] Table 1 shows the first-cycle discharge specific capacity of the examples and comparative samples at a current density of 0.1C and the capacity retention rate after 100 cycles at a current density of 1C. Detailed Implementation

[0048] Example 1

[0049] Precursor synthesis: A mixed salt solution of NiSO4·6H2O and MnSO4·H2O with a total concentration of 2.0 mol / L was pumped into a continuous stirred tank reactor. Simultaneously, a 2.5 mol / L NaOH solution was added to the reactor. Throughout the co-precipitation process, the solution temperature was maintained at 50℃, and the precipitate particle size D was controlled. 50 =5μm. The precipitate was washed with deionized water and dried in air at 120°C to obtain Ni. 0.5 Mn 0.5 (OH)2 precursor powder.

[0050] Synthesis of cathode material: Drying Ni 0.5 Mn 0.5 (OH)₂ powder and Na₂CO₃ were mixed in a molar ratio of M:Na = 1:0.98, and Na₂CO₃ was mixed in a molar ratio of M:Ca = 1:0.01, along with copper oxide and titanium dioxide in a molar ratio of 16:1. Sodium sulfate was added at 0.25 wt% of the precursor mass. The mixture was thoroughly mixed using a small ball mill (450 r / min, ball-to-powder mass ratio 2:1, milling time 3 h). The mixture was then calcined in air at 900 °C for 15 h at a heating rate of 5 °C / min, and naturally cooled to room temperature to obtain the cathode material Na. 0.98 Ca 0.01 Ni 0.45 Cu 0.05 Mn 0.45 Ti 0.05 O2 -0.25%.

[0051] The calcined cathode material was subjected to air jet milling and then passed through a 300-mesh vibrating sieve. The sieved cathode material was then ball-milled with boron oxide at a mass ratio of 1000 ppm (300 r / min, ball-to-material mass ratio 1:1, milling time 1 h). The mixture was then calcined in air at 500°C for 10 h at a heating rate of 5°C / min, and naturally cooled to room temperature to obtain the cathode material NaNi. 0.45 Cu 0.05 Mn 0.45 Ti 0.05 O2-0.25%@B2O3.

[0052] Example 2

[0053] Precursor synthesis: A mixed salt solution of NiSO4·6H2O and MnSO4·H2O with a total concentration of 2.0 mol / L was pumped into a continuous stirred tank reactor. Simultaneously, a 2.5 mol / L NaOH solution was added to the reactor. Throughout the co-precipitation process, the solution temperature was maintained at 50℃, and the precipitate particle size D was controlled. 50 =5μm. The precipitate was washed with deionized water and dried in air at 120°C to obtain Ni. 0.5 Mn 0.5 (OH)2 precursor powder, SEM image as follows: Figure 1 As shown.

[0054] Synthesis of cathode material: Drying Ni 0.5 Mn 0.5 (OH)₂ powder and Na₂CO₃ were mixed in a molar ratio of M:Na = 1:0.96, and Na₂CO₃ was mixed in a molar ratio of M:Ca = 1:0.02, along with copper oxide and titanium dioxide in a molar ratio of 8:1. Sodium sulfate was added at 0.5 wt% of the precursor mass. The mixture was thoroughly mixed using a small ball mill (450 r / min, ball-to-powder mass ratio 2:1, milling time 3 h). The mixture was then calcined in air at 900 °C for 18 h at a heating rate of 5 °C / min, and naturally cooled to room temperature to obtain the cathode material Na. 0.96 Ca 0.02 Ni 0.4 Cu 0.1 Mn 0.4 Ti 0.1 O2-0.5%.

[0055] The calcined cathode material was subjected to air jet milling and then passed through a 300-mesh vibrating sieve. The sieved cathode material was then ball-milled with boron oxide at a mass ratio of 1000 ppm (300 r / min, ball-to-material mass ratio 1:1, milling time 1 h). The mixture was then calcined in air at 500°C for 10 h at a heating rate of 5°C / min, and naturally cooled to room temperature to obtain the cathode material Na. 0.96 Ca 0.02 Ni 0.4 Cu 0.1 Mn 0.4 Ti 0.1 O2-0.5%@B2O3, SEM image as shown Figure 3 As shown.

[0056] Example 3

[0057] Precursor synthesis: A mixed salt solution of NiSO4·6H2O and MnSO4·H2O with a total concentration of 3.0 mol / L was pumped into a continuous stirred tank reactor. Simultaneously, a 3.0 mol / L NaOH solution was added to the reactor. Throughout the co-precipitation process, the solution temperature was maintained at 50℃, and the precipitate particle size D was controlled. 50 =5μm. The precipitate was washed with deionized water and dried in air at 120°C to obtain Ni. 0.5 Mn 0.5 (OH)2 precursor powder.

[0058] Synthesis of cathode material: Drying Ni 0.5 Mn 0.5 (OH)₂ powder was mixed with Na₂CO₃ at a molar ratio of M:Na = 1:0.96 and with calcium carbonate at a molar ratio of M:Ca = 1:0.02, with copper oxide and titanium dioxide at molar ratios of 16:1 and 4:1 respectively, and with 1.0 wt% sodium sulfate as a precursor. The mixture was thoroughly mixed using a small ball mill (450 r / min, ball-to-powder mass ratio of 2:1, milling time 3 h). The mixture was then calcined in air at 900 °C for 18 h at a heating rate of 5 °C / min, and naturally cooled to room temperature to obtain the cathode material Na. 0.96 Ca 0.02 Ni 0.45 Cu 0.05 Mn 0.2 Ti 0.2 O2-1.0%.

[0059] The calcined cathode material was subjected to air jet milling and then passed through a 300-mesh vibrating sieve. The sieved cathode material was then ball-milled with boron oxide at a mass ratio of 1000 ppm (400 r / min, ball-to-material mass ratio 1:1, milling time 1 h). The mixture was then calcined in air at 550°C for 10 h at a heating rate of 5°C / min, and naturally cooled to room temperature to obtain the cathode material Na. 0.96 Ca 0.02 Ni 0.45 Cu 0.05 Mn 0.2 Ti 0.2 O2-1.0%@B2O3.

[0060] Comparative Example 1

[0061] Precursor synthesis: A mixed salt solution of NiSO4·6H2O and MnSO4·H2O with a total concentration of 2.0 mol / L was pumped into a continuous stirred tank reactor. Simultaneously, a 2.0 mol / L NaOH solution was added to the reactor. Throughout the co-precipitation process, the solution temperature was maintained at 50℃, and the precipitate particle size D was controlled.50 =5μm. The precipitate was washed with deionized water and dried in air at 100°C to obtain Ni. 0.5 Mn 0.5 (OH)2 precursor powder.

[0062] Synthesis of cathode material: Drying Ni 0.5 Mn 0.5 (OH)2 powder and Na2CO3 were thoroughly mixed in a small ball mill at a molar ratio of 2:1. The mixture was then calcined in air at 900°C for 15 hours at a heating rate of 5°C / min, and then naturally cooled to room temperature to obtain the cathode material NaNi. 0.5 Mn 0.5 O2.

[0063] Comparative Example 2

[0064] Solid-state synthesis of cathode materials: according to Na 0.96 Ca 0.02 Ni 0.4 Cu 0.1 Mn 0.4 Ti 0.1 The molar ratio of metal elements in the O2 cathode material is as follows: nickel oxide, copper oxide, manganese oxide, titanium dioxide, sodium carbonate, and calcium carbonate are weighed out and thoroughly mixed using a small ball mill (mill speed 450 r / min, ball-to-material mass ratio 2:1, ball milling time 5 h). The mixture is then calcined in air at 900℃ with a heating rate of 5℃ / min for 18 h, and naturally cooled to room temperature to obtain the Na cathode material. 0.96 Ca 0.02 Ni 0.4 Cu 0.1 Mn 0.4 Ti 0.1 O2.

[0065] The calcined cathode material was subjected to air jet milling and then passed through a 200-mesh vibrating sieve. The sieved cathode material was then ball-milled with boron oxide at a mass ratio of 1000 ppm (400 r / min, ball-to-material mass ratio 1:1, milling time 1 h). The mixture was then calcined in air at 550°C for 10 h at a heating rate of 5°C / min, and naturally cooled to room temperature to obtain the cathode material Na. 0.96 Ca 0.02 Ni 0.4 Cu 0.1 Mn 0.4 Ti 0.1 O2@B2O3, SEM image as follows Figure 2 As shown.

[0066] Test Example 1

[0067] Preparation of battery electrode sheets: The active material, conductive agent (SP), and binder (PVDF) are weighed at a mass ratio of 90:5:5. First, 45 mg of the weighed active material is dissolved in a certain amount of NMP solvent, and the mixture is stirred continuously until the active material is completely dissolved. Then, PVDF is added to the active material solution. After the PVDF and active material are mixed evenly, the conductive agent is added, and the mixture is stirred continuously. After the active material, SP, and PVDF are mixed evenly, the slurry is evenly coated onto aluminum foil using a coating device. The coated aluminum foil is then transferred to a vacuum drying oven and dried at 120°C for 12 hours. Finally, the dried electrode sheets are cut into circular electrode sheets with a diameter of 14 mm using a cutting machine, and the mass of the cut electrode sheets is weighed.

[0068] Assembly of CR2032 button cells: In a glove box under an argon atmosphere, the cells are stacked in the following order: positive electrode shell, negative electrode plate, electrolyte, separator, electrolyte, sodium metal sheet, gasket, spring, and negative electrode shell. They are then pressed into button cells using a sealing machine and allowed to stand for 12 hours for activation before testing. The electrolyte is 1M NaPF6 / (PC+5% FEC); the separator is Whatman glass fiber; and the battery test voltage window is set to 2-4.3V.

[0069] The test results are shown in Table 1.

[0070] Table 1

[0071]

[0072] From Table 1 and Figure 4 The results show that, compared with the single-crystal cathode material obtained by conventional dry mixing in Examples 1 and 2 using this method, the 0.1C first-cycle discharge specific capacity and the 100-cycle retention rate are significantly improved. In Example 2, after using this method and doping coating, the first-cycle discharge specific capacity reached a maximum of 173.34 mAh / g at a voltage of 2-4.3V, and the retention rate after 100 cycles at 1C was 91.5%.

Claims

1. A method for preparing a single-crystal cathode material for sodium-ion batteries, characterized in that, Includes the following steps: (1) Dissolve the nickel source and manganese source separately in water and mix them to obtain a mixed salt solution; the concentration of the mixed salt solution is 1.0-2.0 mol / L and the molar ratio of the metal elements is 1:1; The nickel source is nickel sulfate, nickel chloride, nickel nitrate, or nickel acetate. The manganese source is manganese sulfate, manganese chloride, manganese nitrate, or manganese acetate; (2) Add alkali solution to the mixed salt solution to carry out a co-precipitation reaction, and control the particle size of the precipitate within D. 50 =5-6 μm, and after reaction and drying, a precursor powder is obtained; the co-precipitation temperature is 40-60℃, and the drying temperature is 90-120℃; The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkaline solution is 2.0-4.0 mol / L; (3) After mixing the precursor powder with sodium source, copper source, titanium source and M compound, molten salt is added and mixed evenly before the first calcination treatment is carried out to obtain the cathode material after the first calcination treatment; Wherein, compound M is calcium carbonate, calcium oxide, barium carbonate, barium oxide, potassium carbonate, or potassium oxide, and the sodium source is sodium carbonate, sodium nitrate, or sodium hydroxide. The copper source is copper oxide, copper acetate, copper nitrate, copper oxalate, copper sulfate, or copper chloride. The titanium source is titanium dioxide, titanic acid, titanium tetrachloride, or barium metatitanate. The molten salt is sodium sulfate, sodium chloride, or sodium phosphate. The molar ratio of the metal element in the precursor powder to the sodium in the sodium source is 1:0.9-1.

1. The molar ratio of the metal element in the precursor powder to the copper in the copper source is 16:1-2. The molar ratio of metal elements in the precursor powder to titanium in the titanium source is 16:1-4. The ratio of metal elements in the precursor powder to metal elements in compound M is 1:0.01-0.

03. The amount of molten salt doping is 0.5-2 wt% of the precursor powder mass; The conditions for the first calcination treatment are a calcination temperature of 800-1000℃ and a calcination time of 10-20 hours; (4) After the single-crystal cathode material that has undergone the first calcination treatment is mixed evenly with an oxygen-containing compound, a second calcination treatment is performed to obtain the sodium-ion battery single-crystal cathode material; The oxygen-containing compound is boron oxide, boric acid, aluminum metaphosphate, tungsten oxide, zirconium oxide, or titanium oxide; The amount of oxygen-containing compound coating is 1000-3000 ppm of the sodium-ion battery single-crystal cathode material; The conditions for the second calcination treatment are a calcination temperature of 400-600℃ and a calcination time of 5-15 hours; The cathode material that has undergone the first calcination treatment is subjected to airflow pulverization and sieving to obtain the single-crystal cathode material that has undergone the first calcination treatment, wherein the sieve mesh size is 200-400 mesh.

2. The sodium-ion battery single-crystal cathode material prepared by the preparation method according to claim 1.

3. A sodium-ion battery, comprising a positive electrode, a separator, and a negative electrode, characterized in that, The positive electrode sheet includes the sodium-ion battery single-crystal positive electrode material as described in claim 2.

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