Coherent dual-phase sodium-ion battery layered-oxide cathode material and method of making

Abstract

Coherent dual-phase sodium-ion battery layered-oxide cathode materials and methods of making. The cathode materials have a general structure of Na x M a O2@Na 0.8 M b O2, where 0.2

Description

Technical Field

[0001] The present invention relates to a cathode material for sodium-ion batteries. Background Art

[0002] As a key material determining battery performance and cell energy density, the cathode material accounts for up to 40% of the cost, which is a bottleneck restricting the development of high-performance sodium-ion batteries. Therefore, in order to reduce the market application cost of sodium-ion batteries, it is of great significance to design a layered cathode material with high energy density and high air stability. Summary of the Invention

[0003] The object of the present invention is to provide a layered cathode material for sodium-ion batteries, which can significantly improve the cyclic structural stability and / or material energy density.

[0004] According to one aspect of the present invention, there is provided a layered oxide cathode material for sodium-ion batteries, whose structural general formula is Na x M a O2@Na 0.8 M b O2, where 0.2 < x < 1; 0 < a ≤ 1; 0 < b ≤ 1; where M is selected from at least one of Ni, Mn, Fe, Co, Cu, Ti, V, Cr, Mg, Zn, K, Al, Ca, Mo, Ru, Nb, Ir and Zr.

[0005] For the cathode material according to the present invention, M can be selected from at least two of Ni, Mn, Fe, Mg and Ti, and more preferably from at least two of Ni, Mn and Fe.

[0006] According to another aspect of the present invention, there is provided a preparation method of the above cathode material, including:

[0007] Mixing a sodium source and an M source in a stoichiometric ratio and ball-milling them evenly in an inert atmosphere to obtain a mixed powder;

[0008] Pressing the obtained mixed powder into a mold and then performing a calcination treatment, and then performing a grinding treatment to obtain Na x M a O2 powder;

[0009] Dissolving a complexing agent, a sodium source and an M source in a stoichiometric ratio in a solvent to form a mixed solution;

[0010] Mixing the obtained Na x M a O2 powder and the obtained mixed solution evenly to form a biphasic mixed solution;

[0011] Heating the obtained biphasic mixed solution first to form a sol, and then continuing to heat it until it turns into a gel;

[0012] The gel obtained by vacuum drying was used to obtain a biphase powder material;

[0013] Na was obtained by calcining two-phase powder materials. x M a O2@Na 0.8 M b O2 cathode material.

[0014] This invention achieves the construction of a coherent dual-phase layered cathode material, wherein the coherent dual-phase structure constrains internal lattice expansion through coherent growth of the coherent structure, thereby suppressing irreversible phase transitions; and promotes internal Na+ through the synergistic effect of the two phases. + Migration kinetics, thereby improving Na + Transmission rate; simultaneously, the constructed Na 0.8 The MO2 functional surface layer acts as a protective layer to mitigate side reactions between the electrolyte and the internal materials, preserving the high reactivity of the internal materials and thus providing high reversible capacity. Therefore, the preparation method of this invention is simple and controllable, and the prepared cathode material exhibits long-term cycle stability and has broad application prospects.

[0015] According to the preparation method of the present invention, the sodium source may be selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium nitrate, sodium oxide, sodium peroxide, and sodium fluoride; the M source may be selected from at least one of oxides, carbonates, hydroxides, fluorides, nitrates and their hydrated compounds, and acetates and their hydrated compounds.

[0016] According to the preparation method of the present invention, the ball milling time can be 1 to 5 hours, and the ball mill speed can be 400 to 800 rpm.

[0017] According to the preparation method of the present invention, in the calcination treatment after the mixed powder is pressed and formed: the calcination temperature can be 600-1000℃, the holding time can be 2-24h, the calcination atmosphere can be selected from at least one of air, oxygen or nitrogen, and the heating rate can be 1-10℃ / min.

[0018] According to the preparation method of the present invention, the complexing agent may be selected from at least one of citric acid, sodium citrate, maleic acid and glycine, preferably citric acid and sodium citrate; the sodium source may be selected from at least one of sodium acetate, sodium oxalate, sodium nitrate, sodium sulfate and sodium carbonate and their hydrates, preferably sodium acetate, sodium oxalate and sodium carbonate; the M source may be selected from at least one of acetate, oxalate, nitrate, sulfate and carbonate and their hydrates, preferably acetate, oxalate and their hydrates; the solvent may be selected from at least one of water, methanol, ethanol, ethylene glycol, isopropanol, propanol, N-methylpyrrolidone, N,N-dimethylformamide, acetone, acetonitrile and diethyl ether, preferably methanol, ethanol and ethylene glycol.

[0019] According to the preparation method of the present invention, the heating temperature for forming the sol can be 50-80°C, and the heating temperature for transforming it into a gel can be 100-150°C.

[0020] According to the preparation method of the present invention, the vacuum drying temperature can be 100-130℃.

[0021] According to the preparation method of the present invention, in the calcination treatment of the two-phase powder material: the calcination temperature can be 900-1100℃, and the calcination time can be 12-36h, more preferably 15-20h. The heating rate is more preferably about 5℃ / min. The calcination atmosphere can be selected from air or oxygen.

[0022] The cathode material prepared according to the present invention is a coherent biphase layered cathode material for sodium-ion batteries, with a morphological structure of layered micron-sized particles and a particle size of approximately 1–5 μm. The present invention utilizes this unique localized coherent biphase structure to significantly improve cycle stability and material energy density.

[0023] According to another aspect of the present invention, a positive electrode for a sodium-ion battery is also provided, wherein the positive electrode is prepared by coating an aluminum foil current collector with a slurry formed from the above-mentioned layered positive electrode material, conductive carbon black, and polyvinylidene fluoride binder. The coating thickness of the positive electrode material can be 50-200 micrometers. The mass ratio of the layered positive electrode material, conductive carbon black, and binder can be 7:2:1. The loading of the positive electrode active material can be 70-90% by weight, the content of conductive carbon black can be 5-20% by weight, and the content of binder can be 5-20% by weight.

[0024] The sodium-ion battery assembled according to the present invention may include full cells and half cells. Half cells can be used to test the electrical performance of the battery electrode materials. The electrodes of the sodium-ion battery assembled according to the present invention have high energy density and excellent cycle stability, and can achieve rapid charge and discharge at high current densities.

[0025] The coherent biphase layered cathode material preparation process provided by this invention is simple and controllable, with low raw material costs, mild reaction conditions, and the ability to achieve large-scale production. Attached Figure Description

[0026] Figure 1 This is an X-ray powder diffraction test pattern according to Embodiment 1 of the present invention;

[0027] Figure 2 This is a scanning electron microscope image of the powder prepared according to Example 1 of the present invention;

[0028] Figure 3 This is an X-ray powder diffraction test pattern according to Embodiment 2 of the present invention; and

[0029] Figure 4This is a scanning electron microscope (SEM) image of the powder prepared according to Example 2 of the present invention. Detailed Implementation

[0030] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0031] Example 1

[0032] (1) Preparation of O3-NaNi 0.5 Mn 0.5 O2 layered cathode material: Take 10.5 mmol sodium carbonate, 10 mmol nickel oxide and 5 mmol manganese trioxide, mix them and put them in a ball mill jar. Transfer the ball mill jar to a glove box and fill it with Ar gas. The ball-to-material ratio is 20:1. The ball mill speed is 600 rpm and the running time is 180 min. The three materials are thoroughly mixed to obtain material A.

[0033] (2) After pressing the above mixed material into sheets, place them in a muffle furnace for calcination. The heating rate is 5℃ / min, the temperature is 800℃, the holding time is 10h, and after cooling to room temperature, grind the material into powder to obtain material B.

[0034] (3) Dissolve 2 mmol sodium citrate, 0.805 mmol sodium oxalate, 0.33 mmol nickel acetate and 0.67 mmol manganese acetate in ethanol to form a mixed solution C; then add material B to the mixed solution C and stir at 70°C for 24 h to form a sol, and then stir at 130°C until a gel is formed.

[0035] (4) The gel material was transferred to a vacuum oven and dried at 120°C for 24 hours to obtain a biphase powder material; subsequently, the biphase powder material was calcined at 1000°C for 24 hours at a heating rate of 5°C / min to obtain NaNi. 0.5 Mn 0.5 O2@Na 0.8 Ni 0.33 Mn 0.67 O2 cathode material (material D);

[0036] The prepared powder material D was subjected to XRD testing, such as... Figure 1 As shown, the material exhibits a coherent two-phase layered cathode material, with a microstructure consisting of layered micron-sized particles, such as... Figure 2 As shown. The prepared positive electrode material, binder, and conductive agent were mixed in a ratio of 7:2:1, coated onto aluminum foil with a coating thickness of 100 μm, dried in a vacuum oven at 80 °C for 24 h, and then cut into pieces.

[0037] The battery was assembled in a glove box under an argon atmosphere. The pre-cut electrode sheets were used as the working electrode, metallic sodium as the counter electrode, glass fiber as the separator, and 1M NaClO4 dissolved in EC / PC / 5% FEC solution as the electrolyte. The assembled battery was subjected to constant current charge-discharge testing in a Blue Electric testing system at a current density of 50 mA g. -1 The voltage range is 2-4.3V, and the reversible capacity of the material after 20 cycles is 130mAh g. -1 .

[0038] Examples 2-3

[0039] The amounts of raw materials added in step (3) of Example 1 were adjusted to: 4 mmol sodium citrate, 1.61 mmol sodium oxalate, 0.66 mmol nickel acetate and 1.34 mmol manganese acetate; and 8 mmol sodium citrate, 3.22 mmol sodium oxalate, 1.32 mmol nickel acetate and 2.68 mmol manganese acetate. All other preparation conditions remained unchanged, and the process was repeated for Examples 2 to 3. Table 1 shows the electrochemical performance of the layered cathode materials obtained in Examples 1 to 3.

[0040] Table 1: Electrochemical performance of Examples 1-3

[0041]

[0042]

[0043] Examples 4-7

[0044] In Example 1, step (1) involved replacing 10.5 mmol sodium carbonate, 10 mmol nickel oxide, and 5 mmol manganese oxide with the following: 10.5 mmol sodium carbonate, 8 mmol nickel oxide, 5 mmol manganese oxide, and 1 mmol ferric oxide; 10.5 mmol sodium carbonate, 6 mmol nickel oxide, 5 mmol manganese oxide, and 2 mmol ferric oxide; 10.5 mmol sodium carbonate, 4 mmol nickel oxide, 5 mmol manganese oxide, and 3 mmol ferric oxide; and 10.5 mmol sodium carbonate, 2 mmol nickel oxide, 5 mmol manganese oxide, and 4 mmol ferric oxide. All other preparation conditions remained unchanged, and the process was repeated for Examples 4 through 7. Table 2 shows the electrochemical performance of the layered cathode materials obtained in Examples 4 through 7.

[0045] Table 2: Electrochemical performance of Examples 4-7

[0046]

[0047] Examples 8-10

[0048] The amount of sodium oxalate added in step (3) of Example 1 was adjusted to 0.605 mmol, 0.705 mmol, and 0.905 mmol, respectively; other preparation conditions remained unchanged, and Examples 8 to 10 were carried out in sequence. Table 3 shows the electrochemical performance comparison of the layered cathode materials prepared in Examples 8 to 10.

[0049] Table 3: Electrochemical performance of Examples 8-10

[0050]

[0051]

[0052] Examples 11-13

[0053] In Example 1, step (3) involved replacing 2 mmol sodium citrate, 0.805 mmol sodium oxalate, 0.33 mmol nickel acetate, and 0.67 mmol manganese acetate with the following alternatives: 2 mmol sodium citrate, 0.805 mmol sodium oxalate, 0.22 mmol nickel acetate, 0.67 mmol manganese acetate, and 0.11 mmol ferric acetate; 2 mmol sodium citrate, 0.805 mmol sodium oxalate, 0.11 mmol nickel acetate, 0.67 mmol manganese acetate, and 0.22 mmol ferric acetate; and 2 mmol sodium citrate, 0.805 mmol sodium oxalate, 0.33 mmol nickel acetate, 0.33 mmol manganese acetate, and 0.33 mmol ferric acetate. These were then used to prepare Examples 11–13. Table 4 compares the electrochemical performance of the layered cathode materials prepared in Examples 11–13.

[0054] Table 4: Electrochemical performance of Examples 11-13

[0055]

[0056] Comparative Examples 1-2

[0057] Each example represents the construction of a coherent biphase layered cathode, while the comparative examples represent the construction of a single-phase layered cathode. Material B obtained after step (2) in Example 1 was used as Comparative Example 1. 2 mmol sodium citrate, 0.805 mmol sodium oxalate, 0.33 mmol nickel acetate, and 0.67 mmol manganese acetate were dissolved in ethanol to form a mixed solution C; the solution was stirred at 70°C for 24 h to form a sol, and then stirred at 130°C until a gel was formed; the gel material was transferred to a vacuum oven and dried at 120°C for 24 h to obtain a powder material; subsequently, the powder material was calcined at 1000°C for 24 h, and the resulting material was used as Comparative Example 2. Table 5 shows a comparison of the electrochemical performance of the layered cathode materials obtained in Comparative Examples 1 and 2.

[0058] Table 5: Electrochemical performance of Comparative Examples 1-2

[0059]

[0060] Comparing Example 1 with Comparative Examples 1 and 2, it can be found that Example 1, which has a coherent two-phase structure, has better structural stability and higher reversible capacity.

[0061] Comparing Example 1 with Examples 2-3 reveals that functional surface layers of different thicknesses have different effects on material properties. When the thickness is the same as in Example 2 (20%), the material properties are the best.

[0062] Comparing Examples 1-3 with Examples 4-7 and 11-13, it can be found that the formed heteroelement coherent two-phase materials have better structural stability and reversible capacity within a certain proportion;

[0063] Comparing Examples 1 and 8-10, it can be found that the reversible capacity of the coherent biphase material is related to the sodium content of the outer functional surface layer.

[0064] Furthermore, in each embodiment, the ratio of the actual content to the theoretical content of the sodium source is between 0.8 and 1.1, which is consistent with the component ratio of the prepared materials. In summary, this invention employs a method of constructing a functional surface layer to enhance the internal structural stability of layered cathode materials and improve the high activity of the internal materials, solving the problems of limited sodium storage capacity and poor cycle stability of layered cathode materials in practical applications of sodium-ion batteries. Specifically, the use of a highly active core and a highly stable shell formed by the sol-gel method as a dual-phase material has a synergistic effect on improving energy density and cycle life; the lattice coherent growth of the localized structure of the dual-phase material has a constraining effect on internal lattice expansion, thereby suppressing irreversible phase transitions and improving the material's cycle stability; the functional surface layer with fast ion channels is beneficial for Na… + Migration dynamics, thereby improving Na + The transmission rate increases the rate performance of the material.

Claims

1. A method for preparing a layered oxide cathode material for sodium-ion batteries, comprising: Sodium source and M source are ball-milled and mixed uniformly under an inert atmosphere according to stoichiometric ratio to obtain a mixed powder, wherein the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium nitrate, sodium oxide, sodium peroxide and sodium fluoride; and the M source is selected from at least one of oxides, carbonates, hydroxides, fluorides, nitrates and their hydrated compounds, acetates and their hydrated compounds. The resulting mixed powder was pressed into shape and then calcined, followed by grinding to obtain Na. x M a O2 powder; A complexing agent, a sodium source, and an M source are dissolved in a solvent in stoichiometric proportions to form a mixed solution. The complexing agent is selected from at least one of citric acid, sodium citrate, maleic acid, and glycine; the sodium source is selected from at least one of sodium acetate, sodium oxalate, sodium nitrate, sodium sulfate, and sodium carbonate and their hydrates; the M source is selected from at least one of acetate, oxalate, nitrate, sulfate, and carbonate and their hydrates; and the solvent is selected from at least one of water, methanol, ethanol, ethylene glycol, isopropanol, propanol, N-methylpyrrolidone, N,N dimethylformamide, acetone, acetonitrile, and diethyl ether. The obtained Na x M a O2 powder and the resulting mixed solution are mixed evenly to form a two-phase mixed solution; The resulting biphasic mixed solution was first heated to form a sol, and then heated further until it transformed into a gel; The gel obtained by vacuum drying was used to obtain a biphase powder material; Na was obtained by calcining two-phase powder materials. x M a O2@Na 0.8 M b O2 cathode material, of which 0.2 < x <1;0< a ≤1; 0< b ≤1; M is selected from at least two of Ni, Mn, Fe, Mg and Ti.

2. The preparation method according to claim 1, wherein the ball milling time is 1-5 h and the ball mill speed is 400-800 rpm.

3. The preparation method according to claim 1, wherein in the calcination treatment after the mixed powder is pressed and formed: the calcination temperature is 600~1000 ℃, the holding time is 2~24 h, the calcination atmosphere is selected from at least one of air, oxygen or nitrogen, and the heating rate is 1~10 ℃ / min.

4. The preparation method according to claim 1, wherein the heating temperature for forming the sol is 50~80 °C, and the heating temperature for transforming into a gel is 100~150 °C.

5. The preparation method according to claim 1, wherein the vacuum drying temperature is 100~130 ℃.

6. The preparation method according to claim 1, wherein in the calcination treatment of the biphase powder material: the calcination temperature is 900~1100 ℃, the calcination time is 12~36 h, and the heating rate is 1~10 ℃ / min.

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