A core-shell structure sodium ion battery positive electrode material and an in-situ coating preparation method thereof

Abstract

The application discloses a core-shell structure sodium ion battery positive electrode material and an in-situ coating preparation method thereof, and belongs to the technical field of sodium ion batteries. x Fe y Mn 1‑x‑y O2@NaCrO2, the application first uniformly coats chromium hydroxide on the surface of a precursor through a coprecipitation method to obtain a chromium hydroxide coated precursor Ni x Fe y Mn 1‑x‑y (OH)2@Cr(OH)3; then, the chromium hydroxide coated precursor is mixed with a sodium source and sintered at high temperature to prepare the core-shell structure sodium ion battery positive electrode material NaNi x Fe y Mn 1‑x‑y O2@NaCrO2, the positive electrode material decomposes to provide active sodium during the first charging, effectively compensates for sodium loss caused by the formation of SEI / CEI films, significantly improves the specific capacity and cycle stability of the positive electrode material, and is suitable for industrialized production of sodium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a core-shell structured sodium-ion battery cathode material and its in-situ coating preparation method. Background Technology

[0002] Sodium-ion battery technology is now relatively mature, but its energy density is still lower than that of lithium-ion batteries. Furthermore, during the first charge and discharge cycle, the electrolyte forms CEI and SEI films at the positive and negative electrodes, respectively, causing irreversible loss of sodium ions and further reducing energy density. Pre-sodiuming technology, by introducing additional sodium sources at the positive and negative electrodes, can offset the sodium ion loss during the first charge and discharge cycle, effectively improving the battery's energy density and cycle performance.

[0003] Pre-sodiuming technology is divided into positive electrode pre-sodiuming technology and negative electrode pre-sodiuming technology. Negative electrode pre-sodiuming technology typically involves the use of a strongly reducing sodium source, requiring strict control over the atmosphere and humidity of the processing environment, thus increasing production costs. Positive electrode pre-sodiuming involves adding sodium-rich compounds during the electrode slurry preparation process to create sodium-rich electrode sheet materials, effectively increasing the sodium content of the positive electrode active material. Furthermore, this technology does not add an extra sodium battery process and is compatible with sodium battery production processes.

[0004] Patent CN202510217500.9 discloses "a sodium-supplementing additive, a positive electrode sheet, and a sodium-ion battery." The method involves vacuum mixing an organic sodium-supplementing agent and an inorganic additive with a positive electrode material, a conductive agent, and a binder, coating the mixture onto an aluminum foil current collector, and then vacuum drying to obtain the positive electrode sheet. While this method effectively adds the sodium-supplementing agent to the positive electrode sheet, its dispersibility is poor.

[0005] Patent CN202510103158.X discloses "positive electrode sodium supplement, positive electrode slurry and preparation method, positive electrode sheet and electrode assembly", which involves adding positive electrode material and positive electrode sodium supplement to a conductive adhesive solution, and then coating and drying to obtain a positive electrode sheet. This method can effectively stabilize the positive electrode interface and improve cycle stability, but it also suffers from the problem of uneven dispersion of the sodium supplement.

[0006] Patent CN202510215938.3 discloses "a sodium-ion battery double-layer coated composite sodium supplement agent and its preparation method and application". By constructing a double-layer coated composite sodium supplement agent, the core matrix is ​​beneficial to the growth of SEI film, and the outer shell can effectively isolate the sodium supplement agent and electrolyte, preventing the electrolyte from corroding and damaging the sodium supplement agent.

[0007] However, current sodium replenishing agents have drawbacks such as high decomposition voltage and low decomposition capacity. When the sodium replenishing agent has a high decomposition voltage, the battery's operating voltage range increases accordingly, requiring the electrolyte, positive electrode material, and negative electrode material to withstand high voltages, making them prone to damage. Conversely, when the sodium replenishing agent has a low decomposition capacity, it results in a lower amount of active positive electrode material per unit mass of electrode sheet, and a higher sodium replenishing agent content, further reducing the battery's energy density.

[0008] Therefore, there is a need to develop a cathode material for sodium-ion batteries that has high capacity and good cycle stability. Summary of the Invention

[0009] The first objective of this invention is to provide a core-shell structured sodium-ion battery cathode material with high capacity and good cycle stability.

[0010] The technical solution adopted in this invention is as follows:

[0011] A core-shell structured sodium-ion battery cathode material with the structural formula NaNi x Fe y Mn 1-x-y O2@NaCrO2, where: 0≤x≤0.9, 0≤y≤0.9.

[0012] This invention discloses a core-shell structured sodium-ion battery cathode material, wherein the cathode material has a core-shell structure and the core is NaNi. x Fe y Mn 1-x-y O2, NaCrO2 coated on NaNi x Fe y Mn 1-x-y On O2, NaCrO2 acts as NaNi x Fe y Mn 1-x-y The O2 coating not only releases Na during the first charge, preventing the loss of active sodium in the cathode material during the formation of SEI or CEI, but also has a low decomposition voltage, with a theoretical capacity of 250mAh / g.

[0013] The second aspect of this invention aims to provide an in-situ coating preparation method for a core-shell structured sodium-ion battery cathode material, comprising the following steps: preparing a chromium hydroxide coating precursor Ni using a co-precipitation method. x Fe y Mn 1-x-y (OH)2@Cr(OH)3, the above precursor is used to prepare core-shell structured sodium-ion battery cathode material by high-temperature calcination.

[0014] This invention uses a co-precipitation method to prepare the precursor and a simple and convenient high-temperature calcination method to prepare the cathode material, giving the material good electrochemical performance and cycle performance, and promoting the sustainable development of the sodium-ion battery industry.

[0015] Further settings are as follows:

[0016] A method for in-situ coating preparation of a core-shell structured sodium-ion battery cathode material includes the following steps:

[0017] (1) Preparation of Ni chromium hydroxide-coated precursor x Fe y Mn 1-x-y (OH)2@Cr(OH)3

[0018] Under certain pH conditions, aqueous solutions of Cr-containing compounds, NaOH solutions, and Ni... x Fe y Mn 1-x-y The (OH)₂ precursor was reacted under stirring to prepare the chromium hydroxide-coated precursor Ni. x Fe y Mn 1-x-y (OH)2@Cr(OH)3.

[0019] (2) Preparation of NaNi core-shell structured sodium-ion battery cathode material x Fe y Mn 1-x-y O2@NaCrO2

[0020] The chromium hydroxide precursor Ni prepared in step (1) is coated with the chromium hydroxide. x Fe y Mn 1-x-y (OH)₂@Cr(OH)₃ is blended with a sodium source in a certain molar ratio and sintered at high temperature under one or more atmospheres to obtain NaNi, a core-shell structured sodium-ion battery cathode material. x Fe y Mn 1-x-y O2@NaCrO2.

[0021] In step (1):

[0022] The Ni x Fe y Mn 1-x-y (OH)₂ precursor, 0≤x≤0.9, 0≤y≤0.9, preferably Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 precursor (i.e., NFM111 precursor).

[0023] The Ni x Fey Mn 1-x-y (OH)2 precursor, particle size D v 50 has a BET number of 10-30m in the 2-15μm range. 2 / g.

[0024] The Cr-containing compound is selected from one or a mixture of two or more of chromium trioxide, chromium nitrate, chromium sulfate, chromium chloride, and potassium chromium sulfate. The Cr-containing compound is combined with Ni... x Fe y Mn 1-x-y The amount of (OH)2 precursor is controlled so that the molar ratio of Cr / (Ni+Fe+Mn) is 0.05-0.1:1.

[0025] The pH value of the reaction is preferably controlled between 6 and 8, and particularly preferably pH = 7.

[0026] The stirring reaction is carried out at a speed of 400-600 rpm.

[0027] The reaction was carried out at room temperature for 1-3 hours.

[0028] In step (2):

[0029] The sodium source is selected from one or a mixture of two or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium citrate, sodium nitrate, and sodium oxalate, preferably sodium carbonate. Chromium hydroxide is used to coat the precursor Ni. x Fe y Mn 1-x-y The molar ratio of (OH)2@Cr(OH)3 to sodium source is 1:1.0-1.05.

[0030] The sintering atmosphere is selected from one or a mixture of two or more of nitrogen, hydrogen, argon and air.

[0031] The high-temperature sintering is preferably performed using gradient sintering, with the following stages: first stage: 400-600℃, holding for 1-3 hours; second stage: 600-800℃, holding for 9-11 hours; third stage: 800-900℃, holding for 1-3 hours. Particularly preferably, the first stage is performed in an air atmosphere, while the second and third stages are performed in a nitrogen and hydrogen mixture with a nitrogen to hydrogen volume ratio of 98:2.

[0032] The third objective of this invention is to provide an application of a core-shell structured sodium-ion battery cathode material in the preparation of sodium-ion batteries.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) Ni prepared by co-precipitation methodx Fe y Mn 1-x-y (OH)2@Cr(OH)3 allows Cr(OH)3 to better coat Ni. x Fe y Mn 1-x-y On (OH)2, an in-situ coating layer of NaCrO2 is formed during subsequent sintering, which greatly increases the cycling stability of the material.

[0035] (2) NaCrO2 as NaNi x Fe y Mn 1-x-y The coating layer of the O2 cathode material can not only release Na during the first charge, thus avoiding the loss of active sodium in the cathode material during the formation of SEI or CEI, but also has a low decomposition voltage and a theoretical capacity of 250mAh / g.

[0036] (3) Optimization of sintering process: gradient sintering is conducive to promoting NaCrO2 crystallization and forming a coating layer, effectively inhibiting Cr diffusion into the crystal structure of the cathode material.

[0037] (4) This method has a simple process flow and is suitable for continuous industrial production. Attached Figure Description

[0038] Figure 1 SEM images of the cathode materials prepared in Example 1 and Comparative Example 1.

[0039] Figure 2 The images show the XRD patterns of the cathode materials prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0040] The present invention will now be explained in more detail through specific embodiments. However, it should be understood that the specific functional details disclosed in this specification should not be construed as limiting, but rather as the basis for the claims and as a representative basis for teaching those skilled in the art to employ the invention in different ways in any suitable detailed embodiment. Unless otherwise specified, the raw materials and reagents used in the embodiments are prior art or commercially available products.

[0041] Example 1

[0042] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L aqueous solution A containing chromium chloride and a 2 mol / L aqueous solution B containing NaOH were prepared. Solutions A and B were added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was completed, the solution was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2@Cr(OH)3.

[0043] (2) Coating the Ni precursor with the aforementioned chromium hydroxide. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2 The reaction mixture was heated at 700℃ for 10 hours and then at 850℃ for 2 hours (98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 3Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0044] Example 2

[0045] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:20. A 0.3 mol / L chromium chloride aqueous solution A and a 2 mol / L NaOH aqueous solution B were prepared and added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2@Cr(OH)3.

[0046] (2) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2The reaction mixture was heated at 700℃ for 10 hours and at 850℃ for 2 hours (ratio 98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0047] Example 3

[0048] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L chromium chloride aqueous solution A and a 2 mol / L NaOH aqueous solution B were prepared and added dropwise using a flow pump to maintain the pH of the solution in the reactor at 8 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2@Cr(OH)3.

[0049] (2) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2 The reaction mixture was heated at 700℃ for 10 hours and at 850℃ for 2 hours (ratio 98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0050] Example 4

[0051] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L chromium chloride aqueous solution A and a 2 mol / L NaOH aqueous solution B were prepared and added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.05:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn1 / 3 (OH)2@Cr(OH)3.

[0052] (2) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2 The reaction mixture was heated at 700℃ for 10 hours and at 850℃ for 2 hours (ratio 98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0053] Example 5

[0054] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L chromium chloride aqueous solution A and a 2 mol / L NaOH aqueous solution B were prepared and added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.1:1. The reaction was carried out at 500 rpm for 2 hours at room temperature with continuous stirring. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2@Cr(OH)3.

[0055] (2) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2 The reaction mixture was heated at 700℃ for 10 hours and at 850℃ for 2 hours (ratio 98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0056] Example 6

[0057] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L chromium chloride aqueous solution A and a 2 mol / L NaOH aqueous solution B were prepared and added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 400 rpm for 3 hours at room temperature with continuous stirring. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2@Cr(OH)3.

[0058] (2) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2 The reaction mixture was heated at 700℃ for 10 hours and at 850℃ for 2 hours (ratio 98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0059] Example 7

[0060] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L chromium chloride aqueous solution A and a 2 mol / L NaOH aqueous solution B were prepared and added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2@Cr(OH)3.

[0061] (2) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.0. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2The reaction mixture was heated at 700℃ for 10 hours and at 850℃ for 2 hours (ratio 98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0062] Example 8

[0063] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L chromium chloride aqueous solution A and a 2 mol / L NaOH aqueous solution B were prepared and added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2@Cr(OH)3.

[0064] (2) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2 The reaction mixture was heated at 700℃ for 10 hours and at 900℃ for 3 hours (98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0065] Example 9

[0066] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L chromium chloride aqueous solution A and a 2 mol / L NaOH aqueous solution B were prepared and added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn1 / 3 (OH)2@Cr(OH)3.

[0067] (2) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours under a nitrogen atmosphere. The mixture was then subjected to a nitrogen and hydrogen mixture (V... N2 V H2 The reaction mixture was heated at 700℃ for 10 hours and at 850℃ for 2 hours (ratio 98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0068] Example 10

[0069] (1) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L chromium chloride aqueous solution A and a 2 mol / L NaOH aqueous solution B were prepared and added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2@Cr(OH)3.

[0070] (2) Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂@Cr(OH)₃ was mixed with sodium carbonate at a molar ratio of 1:1.03. The mixture was then heated at 500°C for 2 hours in air, followed by heating at 700°C for 10 hours and then at 850°C for 2 hours in air. After the reaction, the mixture was ground and sieved to obtain the cathode material NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2.

[0071] Example 11

[0072] (1) Ni 1 / 4 Fe 1 / 2 Mn 1 / 4The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L aqueous solution A containing chromium chloride and a 2 mol / L aqueous solution B containing NaOH were prepared. Solutions A and B were added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 4 Fe 1 / 2 Mn 1 / 4 (OH)2@Cr(OH)3.

[0073] (2) Ni 1 / 4 Fe 1 / 2 Mn 1 / 4 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2 The reaction mixture was heated at 700℃ for 10 hours and at 850℃ for 2 hours (ratio 98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 4 Fe 1 / 2 Mn 1 / 4 O2@NaCrO2.

[0074] Example 12

[0075] (1) Ni 1 / 5 Fe 2 / 5 Mn 2 / 5 The (OH)₂ precursor and water were added to a reactor at a mass ratio of 1:15. A 0.3 mol / L aqueous solution A containing chromium chloride and a 2 mol / L aqueous solution B containing NaOH were prepared. Solutions A and B were added dropwise using a flow pump to maintain the pH of the solution in the reactor at 7 and the molar ratio of Cr / (Ni+Fe+Mn) at 0.075:1. The reaction was carried out at 500 rpm for 2 hours at room temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain the chromium hydroxide-coated precursor Ni. 1 / 5 Fe 2 / 5 Mn 2 / 5 (OH)2@Cr(OH)3.

[0076] (2) Ni 1 / 5 Fe 2 / 5 Mn 2 / 5 (OH)₂@Cr(OH)₃ and sodium carbonate were mixed at a molar ratio of 1:1.03. The mixture was kept at 500°C for 2 hours in air atmosphere, and then subjected to a mixture of nitrogen and hydrogen gas (V). N2 V H2The reaction mixture was heated at 700℃ for 10 hours and at 850℃ for 2 hours (ratio 98:2). After the reaction was complete, the material was ground and sieved to obtain the cathode material NaNi. 1 / 5 Fe 2 / 5 Mn 2 / 5 O2@NaCrO2.

[0077] Comparative Example 1

[0078] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂ and sodium carbonate were blended at a molar ratio of 1:1.03 to obtain a mixture. The mixture was then subjected to sequential heating at 500℃ for 2 hours, 700℃ for 10 hours, and 850℃ for 2 hours in air atmosphere. After the reaction, the mixture was ground and sieved to obtain the positive electrode material NFM111.

[0079] Comparative Example 2

[0080] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂ and Cr(OH)₃ were blended at a molar ratio of Cr / (Ni+Fe+Mn) of 0.075:1 to obtain mixture A. Mixture A and sodium carbonate were then blended at a molar ratio of 1:1.03 to obtain mixture B. Mixture B was then heated at 500°C for 2 hours in air, followed by heating in a mixture of nitrogen and hydrogen gas (V... N2 V H2 =98:2) was heated at 700℃ for 10h and at 850℃ for 2h. After the reaction, the material was ground and sieved to obtain the positive electrode material.

[0081] Comparative Example 3

[0082] NFM111 and NaCrO2 were ball-milled and blended at a molar ratio of 1:0.075. The blend was then heated at 500°C for 2 hours in air and then heated in a mixture of nitrogen and hydrogen gas (V). N2 V H2 =98:2) was heated at 700℃ for 10h and at 850℃ for 2h after the reaction, and then ground and sieved to obtain the positive electrode material.

[0083] Product characteristics:

[0084] The positive electrode material NaNi prepared in Example 1 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaCrO2 and the positive electrode material NFM111 prepared in Comparative Example 1 were analyzed by SEM and XRD, respectively. Figure 1 , Figure 2 As shown.

[0085] Figure 1The images show SEM images of Example 1 and Comparative Example 1. As can be seen from the images, the NFM111 cathode material prepared in Comparative Example 1 has a relatively smooth and clean surface, clear secondary particle outlines, and sharp grain boundaries. In contrast, the cathode material prepared in Example 1 has a rougher surface and more rounded particle edges, proving that NaCrO2 is in situ coated on NFM111. Figure 2 The images show the XRD patterns of Example 1 and Comparative Example 1, both of which are of the O3 type. The presence of NaCrO2 on the material surface did not alter the crystal structure of the material. Thanks to the NaCrO2 coating on the surface of NFM111, during charge and discharge, NaCrO2 effectively blocks direct contact between the positive electrode material and the electrolyte, inhibits the continuous oxidative decomposition of the electrolyte in subsequent cycles, reduces excessive growth of the CEI film, lowers interfacial impedance, and suppresses changes in the material's crystal volume, enhancing the stability of the surface lattice structure, thereby improving the material's cycle performance. During charging, NaCrO2 releases Na ions onto the negative electrode material, effectively reducing Na ion loss in NFM111 and further improving the material's discharge specific capacity.

[0086] Performance testing:

[0087] The cathode materials prepared in Examples 1-12 and Comparative Examples 1-3 were applied to sodium-ion batteries according to the following methods, and their electrochemical performance was tested.

[0088] The testing method is as follows:

[0089] The positive electrode material powder is ground through a 200-mesh sieve, and then mixed with SP (conductive carbon black) and PVDF (polyvinylidene fluoride) in a mass ratio of 8:1:1. NMP (N-methylpyrrolidone) is added and stirred into a slurry, which is then coated onto aluminum foil. After drying, stamping and pressing, the positive electrode material of sodium-ion battery is produced.

[0090] Hard carbon is ground through a 200-mesh sieve and then mixed with SP (conductive carbon black) and CMC (sodium carboxymethyl cellulose) in a mass ratio of 95:2:3. Deionized water is added and stirred into a slurry, which is then coated onto carbon-coated aluminum foil. After drying, stamping and pressing, it is made into a sodium-ion battery negative electrode material.

[0091] Using glass fiber (Whatman GF / D brand) as the separator and a NaPF6 (sodium hexafluorophosphate) / PC (propylene carbonate) / EMC (ethyl methyl carbonate) solution as the electrolyte, CR2025 button batteries were assembled in an argon-filled glove box for charge-discharge testing. Under a voltage range of 1.5-3.9V, the batteries were first cycled twice at 0.2C, and then the capacity and cycle performance were tested at 1C / 1C. The test results are shown in Table 1.

[0092] Table 1

[0093] .

[0094] analyze:

[0095] As shown in Table 1, the cathode material prepared by this invention exhibits excellent electrochemical and cycling performance. Specifically, Example 1 achieved a discharge specific capacity of 138.4 mAh / g under conditions of 1.5-3.9V and 0.2C, with an initial efficiency improved to 92.7%. At 1C, the discharge specific capacity reached 134.7 mAh / g, and the capacity retention rate after 5000 cycles at 1C was 85.6%, demonstrating the best overall performance.

[0096] Compared with Example 1, the positive electrode material obtained by sintering in Comparative Example 1 is NFM111. In the button cell full-electric test, during the first charge and discharge process, the electrolyte forms CEI and SEI films on the positive and negative electrodes of the battery, respectively, causing some irreversible loss of sodium ions. As a result, the discharge specific capacity and first efficiency are relatively low compared with the Example.

[0097] Compared with Example 1, Comparative Examples 2 and 3 achieved uniform distribution of NFM111 and NaCrO2 through a blending method. However, compared with Example 1, the blending method could not uniformly coat NaCrO2 onto NFM111, resulting in relatively poor cycle stability of the material.

[0098] Compared with Example 1, Example 2 uses Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The mass ratio of (OH)2 precursor to water changed from 1:15 to 1:20. The increase in water content led to the reaction producing Cr(OH)3 and Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 The collision probability of the (OH)2 precursor decreases, causing Cr(OH)3 to self-aggregate and making it easier to form Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 The blend of (OH)2 and Cr(OH)3 cannot effectively form a NaCrO2 coating layer during subsequent sintering.

[0099] Compared to Example 1, Example 3 increased the pH value of the Cr(OH)3 synthesis reaction. The increased pH caused some Cr(OH)3 to dissolve, forming a soluble complex [Cr(OH)4]⁻, which reduced the thickness of the NaCrO2 coating layer on the surface of the final sintered cathode material, further decreasing the material's cycle performance. Furthermore, the reduced NaCrO2 content decreased the sodium replenishment effect of NaCrO2, thus lowering the material's discharge capacity. The increased pH accelerated the precipitation and aggregation of Cr(OH)3, forming large particles, which, in the Ni… 1 / 3 Fe 1 / 3 Mn 1 / 3A uniform and dense coating layer cannot be formed on the (OH)2 precursor.

[0100] Compared to Example 1, Example 4 reduced the Cr content, resulting in a thinner coating layer on the surface of the sintered cathode material. This makes the material more prone to cracking during cycling, thus reducing its cycle life. Furthermore, the reduced Cr content also leads to a decrease in the amount of NaCrO2 formed, further reducing the material's discharge capacity.

[0101] Compared to Example 1, Example 5 increased the Cr content. The increased Cr content facilitates the formation of more NaCrO2, reducing Na loss from the NFM111 core during the first charge-discharge cycle and improving the material's capacity. However, an excessively thick coating layer leads to Na... + The diffusion path is prolonged, leading to a decrease in the rate performance of the material. After multiple cycles, due to the different expansion coefficients of NaCrO2 and NFM111, stress concentration is easily generated, causing the coating layer to crack and peel off, further reducing the stability of the material.

[0102] Compared with Example 1, Example 6 reduced the stirring rate and increased the reaction aging time, resulting in larger chromium hydroxide particles generated by the reaction. As a result, a continuous coating layer could not be formed on the surface of the nickel-iron-manganese hydroxide precursor. After subsequent sintering to form the cathode material, the structural stability of the material was worse than that of Example 1.

[0103] Compared with Example 1, Example 7 reduced the Na content. The reduction in Na content significantly affected the material capacity, resulting in a decrease in the material's discharge specific capacity.

[0104] Compared to Example 1, Example 8 increased the sintering temperature and time in the third stage. Increasing the sintering temperature and time can effectively promote NaCrO2 crystallization, but excessively high temperature and excessively long sintering time cause Cr to diffuse into the NFM111 lattice, affecting the lattice arrangement and thus leading to a decrease in material properties.

[0105] Compared to Example 1, Example 9 changed the atmosphere of the first sintering process to nitrogen, but because Ni 1 / 3 Fe 1 / 3Mn 1 / 3 The reaction between the (OH)2 precursor and sodium carbonate requires oxygen, resulting in a lack of oxygen in the final sintered NFM111 lattice, which leads to poor electrochemical performance of the material.

[0106] Compared to Example 1, Example 10 replaced the mixed gas in the second and third sintering processes with air. Because air contains oxygen, the oxidation state of chromium increases from +3 to +6 during the reaction of chromium hydroxide and sodium carbonate. This not only forms environmentally harmful +6 chromium, but also Cr that can undergo redox reactions in the 1.5-3.9V operating range.3+ The reduced content further decreases the electrochemical performance of the material.

[0107] Compared with Example 1, Examples 11 and 12 respectively used Ni 1 / 4 Fe 1 / 2 Mn 1 / 4 (OH)2 and Ni 1 / 5 Fe 2 / 5Mn 2 / 5 (OH)2 serves as a precursor, which has a high Fe content and a low Ni content, resulting in a relatively low discharge specific capacity of the material. Furthermore, the increase in Fe content causes Fe to migrate from the transition metal layer to the Na layer, further reducing the material's cycle performance.

[0108] Those skilled in the art will readily understand that the above description is merely an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 core-shell structured sodium-ion battery cathode material, characterized in that, The structural formula is NaNi x Fe y Mn 1-x-y O2@NaCrO2, wherein: 0≤x≤0.9, 0≤y≤0.9; The core-shell structure sodium ion battery positive electrode material adopts an in-situ coating preparation method, including the following steps: adopting a coprecipitation method to prepare a chromium hydroxide coated precursor Ni x Fe y Mn 1-x-y (OH)2@Cr(OH)3, adopting a high-temperature sintering method to prepare a core-shell structure sodium ion battery positive electrode material NaNi x Fe y Mn 1-x-y (OH)2@Cr(OH)3, adopting a high-temperature sintering method to prepare a core-shell structure sodium ion battery positive electrode material NaNi x Fe y Mn 1-x-y O2@ NaCrO2, wherein 0≤x≤0.9 and 0≤y≤0.

9. The high-temperature sintering method adopts gradient sintering, the first stage: 400-600℃ for 1-3h; the second stage: 600-800℃ for 9-11h; the third stage: 800-900℃ for 1-3h, the first stage is carried out in air atmosphere, and the second stage and the third stage are carried out in mixed gas of nitrogen and hydrogen.

2. The core-shell structured sodium-ion battery cathode material according to claim 1, characterized in that: The positive electrode material is a core-shell structure, the inner core is NaNi x Fe y Mn 1-x-y O2, NaCrO2 is coated on NaNi x Fe y Mn 1-x-y O2.

3. An in-situ coating preparation method of the core-shell structure sodium ion battery positive electrode material of claim 1, characterized in that: (1) Preparation of chromium hydroxide coated precursor Ni x Fe y Mn 1-x-y (OH)2@Cr(OH)3 An aqueous solution of a compound containing the element Cr, a solution of NaOH and Ni x Fe y Mn 1-x-y (OH)2 precursor under stirring, to obtain a chromium hydroxide coated precursor Ni x Fe y Mn 1-x-y (OH)2@Cr(OH)3; (2) Preparation of core-shell structure sodium-ion battery cathode material NaNi x Fe y Mn 1-x-y O2@NaCrO2 The chromium hydroxide coated precursor Ni x Fe y Mn 1-x-y The core-shell structure sodium ion battery positive electrode material NaNi x Fe y Mn 1-x-y O2@NaCrO2. 4.The in-situ coating method of the core-shell structured sodium-ion battery cathode material of claim 3, characterized in that: In step (1), the Cr-containing compound is selected from one or more of chromium trioxide, chromium nitrate, chromium sulfate, chromium chloride, potassium chromium sulfate, and the like, and the Cr-containing compound is combined with Ni x Fe y Mn 1-x-y The amount of the (OH)2precursor is controlled to provide a molar ratio of Cr / (Ni+Fe+Mn) of 0.05-0.1:

1. 5.The in-situ coating method of the core-shell structured sodium-ion battery cathode material of claim 3, characterized in that: In step (1), the pH value of the reaction is controlled at 6-8, the stirring speed of the reaction is 400-600 rpm, the reaction temperature is room temperature, and the reaction time is 1-3 hours. 6.The in-situ coating method of the core-shell structured sodium-ion battery cathode material of claim 3, characterized in that: In step (2): the sodium source is selected from one or a mixture of two or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium citrate, sodium nitrate, sodium oxalate, chromium hydroxide coated precursor Ni x Fe y Mn 1-x-y Molar ratio of (OH)2@Cr(OH)3to sodium source is 1 : 1.0-1.

05.

7. The in-situ coating method of claim 3, wherein the coating is performed by a chemical vapor deposition method. In step (2), the high-temperature sintering adopts gradient sintering, the first stage: 400-600℃ for 1-3h; the second stage: 600-800℃ for 9-11h; the third stage: 800-900℃ for 1-3h, the first stage is carried out in air atmosphere, and the second stage and the third stage are carried out in mixed gas of nitrogen and hydrogen.

8. An application of the core-shell structure sodium ion battery positive electrode material of claim 1 in preparing a sodium ion battery. ​

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