A p2-type sodium-ion layered positive electrode material stable in cycling at high voltage, and a preparation method and application thereof

Abstract

The application provides a P2 type sodium ion layered positive electrode material stable in circulation at high voltage and a preparation method and application thereof, and belongs to the technical field of sodium ion battery electrode materials.The chemical formula of the positive electrode material is (NaaMnxNiyXb)O2;0.6<=a<=0.85, 0.5<=x<=0.8, 0.1<=y<=0.4, 0<=b<=0.2, and x+y+b=1, and X includes Cu and / or Zn;in the XRD pattern of the positive electrode material, the ratio of the (002) peak height I1 to the (100) peak height I2, namely I1 / I2, is greater than 5.4.The positive electrode material is a spherical secondary particle with an electrochemically inert (002) crystal face, and can significantly improve the cycle stability of the P2 type material at high voltage.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery electrode material technology, and specifically relates to a P2-type sodium-ion layered cathode material that is stable under high voltage cycling, its preparation method, and its application. Background Technology

[0002] With the large-scale integration of renewable energy and the rapid transformation of the energy structure, the demand for safe, low-cost, and sustainable energy storage systems is becoming increasingly urgent. Sodium-ion batteries (SIBs) have attracted much attention due to their abundant sodium resources and similar working principle to lithium-ion batteries, and are considered one of the most promising candidate systems for large-scale grid energy storage. Among various cathode materials, layered transition metal oxides, especially P2-type structures, have advantages such as high operating voltage and favorable sodium content. + Diffusion channels, exhibiting advantages in balancing energy density and structural stability, are therefore highly valued in sodium ion storage applications. Coprecipitation methods, due to their good controllability and uniformity, are widely used in the preparation of P2-type materials.

[0003] However, P2 phase materials typically require a high voltage limit to achieve high energy density. At high voltages, the material surface undergoes extreme desodiumation and generates a large number of high-valence active ions. After multiple cycles, this leads to the formation of spinel and rock salt phases on the material surface. Surface phase transitions cause the accumulation of mismatch strain in the surface layer, further leading to material cracking and exacerbating electrolyte erosion, severely limiting the cycle life of P2 phase materials. Researchers have conducted extensive studies to address the material's interface problems. For example, non-uniform elemental distribution design of material particles (Angew Chem Int Ed., 2025, 64, e202517300), surface gradient doping (Angew Chem Int Ed., 2024, 63, e202410080), and surface coating (ACS Energy Lett., 2025, 11, 733-743) can all achieve good improvements in cycle stability. However, these modification methods undoubtedly complicate the preparation process and increase the material manufacturing cost. Summary of the Invention

[0004] To address the problem of poor cycle stability of P2-type cathode materials under high voltage, this invention provides a P2-type sodium ion layered cathode material that is stable under high voltage. This cathode material consists of spherical secondary particles with electrochemically inert (002) crystal planes mainly exposed, which can significantly improve the cycle stability of P2-type materials under high voltage.

[0005] This invention also provides a method for preparing and applying a P2-type sodium-ion layered cathode material that is stable under high voltage cycling.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a P2-type sodium-ion layered cathode material that is stable under high voltage cycling, wherein the chemical formula of the cathode material is (NaaMnxNiyXb)O2;

[0008] Wherein, 0.6≤a≤0.85, 0.5≤x≤0.8, 0.1≤y≤0.4, 0≤b≤0.2, and x+y+b=1, X includes Cu and / or Zn;

[0009] In the XRD pattern of the cathode material, the ratio of the peak height I1 of (002) to the peak height I2 of (100), i.e., I1 / I2, is greater than 5.4;

[0010] The space group to which the cathode material belongs is P63 / mmc.

[0011] Furthermore, the microstructure of the cathode material is a secondary particle with a spherical structure, which is formed by the aggregation of several primary particles, and the (002) crystal plane of the primary particles is exposed to the outside of the secondary particles.

[0012] The primary particle size distribution is 0.1–1 μm, and the secondary particle size distribution is 2–20 μm.

[0013] Furthermore, the P2-type sodium-ion layered cathode material has a 12 mA g / g capacitance in the range of 2–4.3V. -1 It has ≥110 mAh g at current density -1 The discharge capacity and average discharge voltage above 3.5 V, and 120mA g -1 The capacity retention rate is higher than 87% after 100 cycles.

[0014] Based on the same inventive concept, this invention provides a method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material, the preparation method comprising:

[0015] According to the molar ratio of each element in the chemical formula (NaaMnxNiyXb)O2, 0.6≤a≤0.85, 0.5≤x≤0.8, 0.1≤y≤0.4, 0≤b≤0.2, and x+y+b=1, the precursors of Na, Mn, Ni, and X are weighed and mixed evenly to obtain a mixture. The precursors of Mn, Ni, and X are selected from the co-precipitated carbonate compound Mn, Ni, and X. x Ni y X b CO3, the precursor of Na is selected from its carbonate, nitrate, oxalate, oxide or hydroxide;

[0016] The mixture is pre-sintered at 400–600 °C in an air atmosphere;

[0017] After the pre-sintering is completed, the temperature is raised to 825-1000℃ for secondary sintering, followed by cooling to obtain P2 type sodium ion layered cathode material.

[0018] Furthermore, the Mn x Ni y X b In CO3, X includes Cu and / or Zn.

[0019] Furthermore, the step of pre-sintering the mixture at 400–600 °C in an air atmosphere specifically includes:

[0020] In an air atmosphere, the mixture is heated to 400-600 °C at a rate of 2-10 °C / min for pre-sintering, and the holding time is 4±2 h.

[0021] Furthermore, after the pre-sintering is completed, the temperature is further increased to 825-1000℃ for secondary sintering, followed by cooling to obtain a P2 type sodium ion layered cathode material, specifically including:

[0022] After the pre-sintering is completed, the temperature is continued to rise to 825-1000℃ at a rate of 3-5℃ / min for secondary sintering, and the holding time is 14±2h.

[0023] After the secondary sintering is completed, the material is cooled to room temperature in the furnace to obtain P2 type sodium ion layered cathode material.

[0024] Preferably, the sintering temperature of the pre-sintering is 500°C.

[0025] Preferably, the sintering temperature of the secondary sintering is 950°C.

[0026] Based on the same inventive concept, this invention provides the application of a high-voltage, cycle-stable P2-type sodium-ion layered cathode material in the preparation of sodium-ion batteries or sodium-ion battery cathode sheets.

[0027] Based on the same inventive concept, the present invention provides a sodium-ion battery containing the above-mentioned P2-type sodium-ion layered cathode material that is stable under high voltage cycling.

[0028] Based on the same inventive concept, the present invention also provides a sodium-ion battery positive electrode sheet, wherein the sodium-ion battery positive electrode sheet contains the above-mentioned P2-type sodium-ion layered positive electrode material that is stable under high voltage cycling.

[0029] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0030] 1. The present invention provides a P2-type sodium-ion layered cathode material that is stable under high voltage cycling. The cathode material is a spherical secondary particle with electrochemically inert (002) crystal plane mainly exposed. The XRD pattern of this cathode material shows that the ratio of the (002) peak height I1 to the (100) peak height I2, i.e., I1 / I2, is greater than 5.4. The (002) crystal plane has no electrochemical activity and usually only produces a very thin phase transition layer. The present invention selectively exposes a more stable electrochemical crystal plane by utilizing the anisotropy of the primary particles, which can significantly improve the cycling stability of the P2-type material under high voltage.

[0031] 2. This invention provides a P2-type sodium-ion layered cathode material that is cycle-stable under high voltage. This cathode material exhibits a 12 mA g / g stability within the 2–4.3 V range. -1 It has ≥110 mAh g at current density -1 The discharge capacity and average discharge voltage above 3.5 V, and 120mA g -1 The capacity retention rate after 100 cycles is higher than 87%, which is significantly better than that of P2 type materials without crystal orientation control, achieving a comprehensive improvement in capacity, voltage and cycle stability.

[0032] 3. This invention discloses a method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material. By defining the composition of the carbonate precursor and designing the sintering process, the porous structure formed by the decomposition and gas generation of the carbonate precursor is used as a growth template, promoting grain growth along the circumferential direction of spherical particles. This achieves preferential exposure of the electrochemically inert (002) crystal plane in primary particles, making the surface crystal plane configuration highly controllable. This effectively reduces the accumulation of mismatch strain in the surface structure during cycling, improving the high-voltage cycling stability of the material. The material prepared by this method exhibits excellent structural stability and interface durability under high-voltage (2.0–4.3 V) cycling conditions, with a yield of 120 mA g. -1 After 100 cycles, the capacity retention rate was higher than 87%. Furthermore, this method utilizes a co-precipitated carbonate precursor, Mn. x Ni y X b The solid-state high-temperature sintering process of CO3 does not rely on complex surface coating or multi-step modification treatment. The process route is clear and highly controllable, which is conducive to large-scale production. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 In Embodiment 1 of the present invention, Mn 0.67 Ni 0.28 Cu 0.05 XRD pattern of the product sintered at 950 °C with CO3 as the precursor.

[0035] Figure 2 In Embodiment 1 of the present invention, Mn 0.67 Ni 0.28 Cu 0.05 SEM image of the product sintered at 950 °C with CO3 as the precursor.

[0036] Figure 3 In Embodiment 1 of the present invention, Mn 0.67 Ni 0.28 Cu 0.05 Charge-discharge curves of the sintered product at 950 °C using CO3 as a precursor.

[0037] Figure 4 In Embodiment 2 of the present invention, Mn 0.67 Ni 0.28 Zn 0.05 XRD pattern of the product sintered at 950 °C with CO3 as the precursor.

[0038] Figure 5 In Embodiment 2 of the present invention, Mn 0.67 Ni 0.28 Zn 0.05 SEM image of the product sintered at 950 °C with CO3 as the precursor.

[0039] Figure 6 In Embodiment 2 of the present invention, Mn 0.67 Ni 0.28 Zn 0.05 Charge-discharge curves of the sintered product at 950 °C using CO3 as a precursor.

[0040] Figure 7 The image shows the XRD pattern of the sintered product at 950 °C using oxide as a precursor in Comparative Example 1 of this invention.

[0041] Figure 8 This is a SEM image of the sintered product at 950 °C using oxide as a precursor in Comparative Example 1 of this invention.

[0042] Figure 9 In Comparative Example 2 of the present invention, Mn 0.67 Ni 0.28 Cu 0.05 XRD pattern of the product sintered at 950 °C using (OH)2 as a precursor.

[0043] Figure 10In Comparative Example 2 of the present invention, Mn 0.67 Ni 0.28 Cu 0.05 SEM image of the product sintered at 950 °C using (OH)2 as a precursor.

[0044] Figure 11 In Comparative Example 3 of the present invention, Mn 0.67 Ni 0.28 Cu 0.05 XRD pattern of the product sintered at 800 °C with CO3 as the precursor.

[0045] Figure 12 The diagram shows the cyclic performance of various embodiments and comparative examples of the present invention. Detailed Implementation

[0046] The present invention will be described in detail below with reference to specific embodiments and examples, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0047] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0048] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0049] The overall concept of this invention is as follows:

[0050] The applicant discovered that different crystal facets of primary particles typically exhibit different electrochemical activities. For example, the (002) crystal facet has no electrochemical activity and usually only produces a very thin phase transition layer, while thicker phase transition layers are mainly concentrated in the {010} electrochemically active crystal facet family. Therefore, exploring the electrochemical activity of different crystal facets can provide guidance for designing cycle-stable cathode materials. By leveraging the anisotropy of primary particles, selectively exposing more stable electrochemical crystal facets makes it possible to improve the electrochemical stability of the material.

[0051] In this invention, we achieved fundamental control over primary particle orientation and significantly improved electrochemical performance by limiting the composition of the carbonate precursor (Mn). x Ni y X bCO3) was used to prepare electrochemically inert secondary spherical particles with the (002) crystal plane mainly exposed by the corresponding sintering process. The XRD diffraction peaks of this morphology show that the ratio of the (002) peak height I1 to the (100) peak height I2, i.e., the I1 / I2 value, is greater than 5.4, which can significantly improve the cycling stability of P2 type materials under high voltage.

[0052] Specifically, the present invention provides a P2-type sodium-ion layered cathode material that is stable under high voltage cycling, wherein the chemical formula of the cathode material is (NaaMnxNiyXb)O2;

[0053] Wherein, 0.6≤a≤0.85, 0.5≤x≤0.8, 0.1≤y≤0.4, 0≤b≤0.2, and x+y+b=1, X includes Cu and / or Zn;

[0054] In the XRD pattern of the cathode material, the ratio of the peak height I1 of (002) to the peak height I2 of (100), i.e., I1 / I2, is greater than 5.4.

[0055] In this invention, the cathode material is a spherical secondary particle with an electrochemically inert (002) crystal plane mainly exposed. Its XRD pattern shows that the ratio of the (002) peak height I1 to the (100) peak height I2, i.e., I1 / I2, is greater than 5. The outward orientation of different crystal planes of the primary particles in the spherical secondary particles will significantly affect the change of XRD diffraction peaks. Usually, the intensity of the diffraction peaks of the crystal plane directly outward will be enhanced. Therefore, the ratio of the diffraction peak intensity of the (002) crystal plane to the diffraction peak intensity of the (100) crystal plane is used to measure the exposure ratio of the inert crystal plane (002), thereby indirectly judging the electrochemical stability of the material.

[0056] In this invention, the cathode material (NaaMnxNiyXb)O2 contains Zn and Cu. This type of material can stabilize lattice oxygen in the high voltage range and suppress irreversible phase transitions that occur under high voltage, thereby improving the electrochemical stability of the material.

[0057] Furthermore, the microstructure of the positive electrode material is a soccer ball-like structure, and the particle size distribution of the soccer ball-like structure is 2–20 μm.

[0058] In this invention, the cathode material is a spherical secondary particle. Compared with non-spherical single crystal particles, the mutual contact and connection between the primary particles in the secondary sphere will further reduce the exposure of the active crystal surface, thereby improving the cycle stability of the material.

[0059] This invention also provides a method for preparing a P2-type sodium-ion layered cathode material that is stable under high voltage cycling, the method comprising:

[0060] S1. According to the molar ratio of each element in the chemical formula (NaaMnxNiyXb)O2, 0.6≤a≤0.85, 0.5≤x≤0.8, 0.1≤y≤0.4, 0≤b≤0.2, and x+y+b=1, the precursors of Na, Mn, Ni, and X are weighed and mixed evenly to obtain a mixture. The precursors of Mn, Ni, and X are selected from the co-precipitated carbonate compound Mn, Ni, and X. x Ni y X b CO3, the precursor of Na is selected from its carbonate, nitrate, oxalate, oxide or hydroxide;

[0061] S2. Under air atmosphere, the mixture is heated to 400-600 °C for pre-sintering;

[0062] S3. After the pre-sintering is completed, the temperature is raised to 825-1000℃ for secondary sintering, and then cooled to obtain P2 type sodium ion layered cathode material.

[0063] In this invention, the carbonate precursor Mn is used. x Ni y X b Using CO3 as a raw material, the composition and structural basis of the carbonate precursor provide a natural template for the exposure of the (002) crystal face: First, the carbonate precursor is a spherical particle prepared by co-precipitation with a smooth surface. This spherical precursor lays the foundation for the spherical morphology of the subsequent secondary particles. The spherical structure can reduce the exposure of electrochemically active crystal faces through the mutual agglomeration between primary particles. Second, the carbonate precursor undergoes thermal decomposition during sintering to produce CO2. The escaped CO2 forms uniformly distributed small pores on the surface of the secondary spherical particles. Between each small pore, a hexagonal planar region is formed. These planar regions provide a template for the growth of the subsequent layered phase. The primary particles are generated along this direction. Therefore, the grown layered primary particles form a unique structure with the (002) crystal face facing outward. Furthermore, the (002) crystal face is electrochemically stable, reducing the exposure of the electrochemically active crystal face of the material, thereby improving cycle stability. Finally, the Cu / Zn doping (0≤b≤0.2) in the precursor can stabilize the layered lattice structure of the P2 type material, suppress lattice distortion under high voltage, and at the same time assist the directional growth of the (002) crystal plane, avoiding the disorder of crystal plane orientation caused by lattice distortion.

[0064] Step S2 specifically includes:

[0065] In an air atmosphere, the mixture is heated to 400-600 °C at a rate of 2-10 °C / min for pre-sintering, and the holding time is 4±2 h.

[0066] In this invention, the purpose of pre-sintering the mixture at a rate of 2-10 °C / min to 400-600 °C in an air atmosphere is to fully remove CO2, promote the formation of small pores, and thus promote the formation of the target layered phase, thereby constructing a complete (002) crystal growth template.

[0067] In this invention, the pre-sintering process employs an air atmosphere + heating rate of 2–10℃ / min + holding time of 4±2h. Its core function is to controllably decompose the carbonate precursor, fully release CO2, and form a uniform and complete hexagonal template.

[0068] 1. First, a slow heating rate avoids the rapid decomposition of carbonates, which generates a large number of bubbles and causes the template structure to break, ensuring uniform distribution of pores and thus forming a continuous hexagonal planar template. Second, the temperature range of 400-600℃ is the optimal decomposition temperature for carbonates, which achieves complete decomposition and avoids excessively high temperatures that could cause precursor particles to agglomerate and sinter, damaging the template morphology. Finally, sufficient CO2 escape allows the template structure to be fully formed, providing a stable guiding foundation for the directional growth of primary particles in the subsequent secondary sintering. If the pre-sintering is insufficient and the template structure is incomplete, it will lead to disordered orientation of the primary particle crystal planes, making it impossible to achieve preferential exposure of the (002) crystal plane.

[0069] Step S3 specifically includes:

[0070] After the pre-sintering is completed, the temperature is continued to rise to 825-1000℃ at a rate of 3-5℃ / min for secondary sintering, and the holding time is 14±2h.

[0071] After the secondary sintering is completed, the material is cooled to room temperature in the furnace to obtain P2 type sodium ion layered cathode material.

[0072] In this invention, the purpose of continuing to heat to 825-1000℃ for secondary sintering at a rate of 3-5℃ / min after pre-sintering is to promote the formation of the P2 phase and to allow for sufficient fusion and growth between primary particles, thereby reducing the exposure of active crystal faces and improving crystallinity.

[0073] In this invention, the secondary sintering process, employing a heating rate of 3–5 °C / min + holding time of 14 ± 2 h + furnace cooling, is the core control step for preferential exposure of the (002) crystal plane, primarily achieving three key functions:

[0074] 1.1) Promote the directional crystallization of P2 type layered phase: 825~1000℃ is the optimal crystallization temperature of P2 type NaaMnxNiyXbO2. The primary particles are grown in layers on the basis of the pre-sintered hexagonal template, and the (002) crystal plane is directly generated along the template direction to achieve the outward exposure of the crystal plane. If the temperature is too low, the degree of crystallization is insufficient, the template guiding effect fails and the (002) crystal plane cannot be preferentially exposed.

[0075] 2.2) Achieving full fusion and growth of primary particles: Long-term heat preservation for 14±2h allows primary particles (0.1~1μm) to fully fuse along the template direction. In the secondary particles (2~20μm) formed, the (002) crystal planes of the primary particles are aligned with each other, further enhancing the exposure ratio of inert crystal planes, while reducing grain boundary defects between primary particles and reducing the risk of electrolyte erosion.

[0076] 3.3) Slow cooling locks crystal orientation: furnace cooling avoids the thermal stress caused by rapid cooling, which leads to crystal orientation distortion, ensuring the integrity of the P2 type layered structure, so that the exposed orientation of the (002) crystal plane is stably preserved, and the ratio of the (002) peak height I1 to the (100) peak height I2 in the XRD pattern of the material is stable ≥5.4.

[0077] The following will provide a detailed description of a high-voltage, cycle-stable P2-type sodium-ion layered cathode material, its preparation method, and its application, in conjunction with embodiments and experimental data.

[0078] Example 1

[0079] This embodiment describes a method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material, specifically including:

[0080] (1) According to Na 0.67 Mn 0.67 Ni 0.28 Cu 0.05 O2 stoichiometry, weigh Mn 0.67 Ni 0.28 Cu 0.05 CO3 and Na2CO3 are mixed evenly to obtain a mixture.

[0081] In all embodiments of the present invention, Mn 0.67 Ni 0.28 Cu 0.05 The particle size of CO3 is 10 μm, and the particle size of Na2CO3 is less than 50 μm;

[0082] Mn 0.67 Ni 0.28 Cu 0.05CO3 was prepared by carbonate co-precipitation: Manganese sulfate, nickel sulfate, and copper sulfate were weighed according to stoichiometric ratio as raw materials and mixed with deionized water to prepare a mixed salt solution with a total metal ion concentration of 2 mol / L. A 60 g / L ammonia solution was used as a complexing agent and a 2 mol / L sodium carbonate solution was used as a precipitant solution. The mixed salt solution, complexing agent solution, and precipitant solution were flowed concurrently into a reactor containing 40% deionized water. The reaction temperature was 50℃, the pH value was 7.5, and the stirring speed was adjusted to 700 rpm. When the particle size grew to 10 μm, the reaction was stopped, and the material was washed and dried.

[0083] (2) In an air atmosphere, the mixture is heated to 500 °C at a rate of 5 °C / min and pre-sintered for 4 hours;

[0084] (3) After the pre-sintering is completed, the temperature is increased to 950 °C at a rate of 5 °C / min, and sintered in air atmosphere for 14 hours, and then naturally cooled to room temperature.

[0085] The obtained product, as determined by XRD analysis, exhibits a P2 phase. Figure 1 Its characteristic is that the ratio of the intensity of the (002) peak to the intensity of the (100) peak, I1 / I2, reaches 5.6. The SEM image of the product is shown below. Figure 2 Its characteristic is that the (002) crystal plane faces outward.

[0086] The material prepared in this embodiment was mixed with PVDF and NMP (mass ratio 8:1:1) to prepare the positive electrode. Sodium metal was used as the negative electrode, polypropylene as the separator, and a NaPF6 ethylene carbonate:propylene carbonate (1:1) solution as the electrolyte. A button cell was assembled and charge-discharge tests were conducted. The current density was 12 mA / g, and the voltage range was 2–4.3 V. The charge-discharge curves are shown below. Figure 3 As shown, the initial discharge capacity of the product can reach 110 mAh / g, the average discharge voltage is 3.62 V, and the capacity retention rate is 87% after 100 cycles at a current density of 120 mA / g (see...). Figure 12 ).

[0087] Example 2

[0088] This embodiment describes a method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material, specifically including:

[0089] (1) According to Na 0.67 Mn 0.67 Ni 0.28 Zn 0.05 O2 stoichiometry, weigh Mn 0.67 Ni 0.28 Zn 0.05 CO3 and Na2CO3 are mixed evenly to obtain a mixture.

[0090] (2) In an air atmosphere, the mixture is heated to 500 °C at a rate of 5 °C / min and pre-sintered for 4 hours;

[0091] (3) After the pre-sintering is completed, the temperature is increased to 950 °C at a rate of 5 °C / min, and sintered in air atmosphere for 14 hours, and then naturally cooled to room temperature.

[0092] The obtained product, as determined by XRD analysis, exhibits a P2 phase. Figure 4 Its characteristic is that the ratio of the intensity of the (002) peak to the intensity of the (100) peak, I1 / I2, reaches 5.8. The SEM image of the product is shown below. Figure 5 Its characteristic is that the (002) crystal plane faces outward, which is consistent with the characteristics of a high-intensity (002) peak.

[0093] The material prepared in this embodiment was mixed with PVDF and NMP (mass ratio 8:1:1) to prepare the positive electrode. Sodium metal was used as the negative electrode, polypropylene as the separator, and a NaPF6 ethylene carbonate:propylene carbonate (1:1) solution as the electrolyte. A button cell was assembled and charge-discharge tests were conducted. The current density was 12 mA / g, and the voltage range was 2–4.3 V. The charge-discharge curves are shown below. Figure 6 As shown, the initial discharge capacity of the product can reach 115 mAh / g, the average discharge voltage is 3.61 V, and the capacity retention rate is 92% after 100 cycles at a current density of 120 mA / g.

[0094] Example 3

[0095] This embodiment describes a method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material, specifically including:

[0096] (1) According to Na 0.6 Mn 0.5 Ni 0.4 Zn 0.1 O2 stoichiometry, weigh Mn 0.5 Ni 0.4 Zn 0.1 CO3 and Na2CO3 are mixed evenly to obtain a mixture.

[0097] (2) In an air atmosphere, the mixture is heated to 400 °C at a rate of 2 °C / min and pre-sintered for 4 hours;

[0098] (3) After the pre-sintering is completed, the temperature is increased to 825 °C at a rate of 2 °C / min, and sintered in air atmosphere for 14 hours, and then naturally cooled to room temperature.

[0099] The obtained product was analyzed by XRD and was characterized by a ratio of I1 / I2 of the intensity of the (002) peak to that of the (100) peak reaching 5.4.

[0100] The material prepared in this embodiment was mixed with PVDF and NMP (mass ratio 8:1:1) to prepare a positive electrode. Sodium metal was used as the negative electrode, polypropylene as the separator, and a NaPF6 ethylene carbonate:propylene carbonate (1:1) solution as the electrolyte. A button cell was assembled and charge-discharge tests were conducted at a current density of 12 mA / g and a voltage range of 2–4.3 V. The initial discharge capacity of the product reached 125 mAh / g, the average discharge voltage was 3.5 V, and at a current density of 120 mA / g, the capacity retention after 100 cycles was 90%.

[0101] Example 4

[0102] This embodiment describes a method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material, specifically including:

[0103] (1) According to Na 0.85 Mn 0.80 Ni 0.10 Zn 0.1 O2 stoichiometry, weigh Mn 0.80 Ni 0.10 Zn 0.1 CO3 and Na2CO3 are mixed evenly to obtain a mixture.

[0104] (2) In an air atmosphere, the mixture is heated to 600 °C at a rate of 10 °C / min and pre-sintered for 4 hours;

[0105] (3) After the pre-sintering is completed, the temperature is increased to 1000 °C at a rate of 10 °C / min, and sintered in air atmosphere for 14 hours, and then naturally cooled to room temperature.

[0106] XRD analysis of the obtained product showed that the ratio of the (002) peak intensity to the (100) peak intensity, I1 / I2, reached 6.0. The material prepared in this embodiment was mixed with PVDF and NMP (mass ratio 8:1:1) to prepare a positive electrode, with metallic sodium as the negative electrode, polypropylene as the separator, and a NaPF6 ethylene carbonate:propylene carbonate (1:1) solution as the electrolyte. A button cell was assembled and charge-discharge tests were conducted at a current density of 12 mA / g and a voltage range of 2–4.3 V. The initial discharge capacity of the product reached 105 mAh / g, the average discharge voltage was 3.52 V, and the capacity retention rate after 100 cycles at a current density of 120 mA / g was 95%.

[0107] Comparative Example 1

[0108] This comparative example provides a method for preparing a cathode material:

[0109] The preparation process of the positive electrode material is the same as in Example 1, except that the precursor is Mn2O3, NiO, CuO and Na2CO3, which are mixed evenly by ball milling, compacted into sheets and sintered. The sintering process is the same as in Example 1.

[0110] The obtained product, as determined by XRD analysis, exhibits a P2 phase. Figure 7 Its characteristic is that the ratio of the intensity of the (002) peak to the intensity of the (100) peak, I1 / I2, is 4.9. The SEM image of the product is shown below. Figure 8 Their characteristic is that they are all single-crystal primary particles.

[0111] Using the material prepared in this comparative example as the positive electrode, metallic sodium as the negative electrode, polypropylene as the separator, and a NaPF6 ethylene carbonate:propylene carbonate (1:1) solution as the electrolyte, a button cell was assembled and charged and discharged. The current density was 12 mA / g, the voltage range was 2–4.3 V, the initial discharge capacity of the product was 101 mAh / g, the average discharge voltage was 3.60 V, and the capacity retention rate was 78% after 100 cycles at a current density of 120 mA / g.

[0112] Comparative Example 2

[0113] This comparative example provides a method for preparing a cathode material:

[0114] The preparation process of the cathode material is the same as in Example 1, except that the precursor is Mn. 0.67 Ni 0.28 Cu 0.05 (OH)2 and Na2CO3 are mixed evenly, and the sintering process is the same as in Example 1.

[0115] The obtained product, as determined by XRD analysis, exhibits a P2 phase. Figure 9 Its characteristic is that the ratio of the intensity of the (002) peak to the intensity of the (100) peak, I1 / I2, is 3.8. The SEM image of the product is shown below. Figure 10 Its characteristic is that the electrochemically active crystal plane group faces outward, and only a small number of primary particles have the (002) crystal plane facing outward.

[0116] The material prepared in this comparative example was mixed with PVDF and NMP to prepare a positive electrode (same as in Example 1). Sodium metal was used as the negative electrode, polypropylene as the separator, and a NaPF6 ethylene carbonate:propylene carbonate (1:1) solution as the electrolyte. A button cell was assembled and a charge-discharge test was conducted. The current density was 12 mA / g, the voltage range was 2–4.3 V, the initial discharge capacity of the product was 119 mAh / g, the average discharge voltage was 3.64 V, and the capacity retention rate was 79% after 100 cycles at a current density of 120 mA / g.

[0117] Comparative Example 3

[0118] This comparative example provides a method for preparing a cathode material:

[0119] The preparation process of the cathode material is the same as in Example 1, except that the secondary sintering temperature is 800 ℃.

[0120] The obtained product, as determined by XRD analysis, exhibits a P2 phase. Figure 11 Its characteristic is that the ratio of the intensity of the (002) peak to the intensity of the (100) peak, I1 / I2, is 3.5.

[0121] The material prepared in this comparative example was mixed with PVDF and NMP to prepare a positive electrode (same as in Example 1). Sodium metal was used as the negative electrode, polypropylene as the separator, and a NaPF6 ethylene carbonate:propylene carbonate (1:1) solution as the electrolyte. A button cell was assembled and a charge-discharge test was conducted. The current density was 12 mA / g, the voltage range was 2 to 4.3 V, the initial discharge capacity of the product was 105 mAh / g, the average discharge voltage was 3.59 V, and the capacity retention rate was 64% after 100 cycles at a current density of 120 mA / g.

[0122] Table 1 Performance comparison of products from Examples 1-4 and Comparative Examples 1-3

[0123] Discharge capacity (mAh / g) Average discharge voltage (V) I1 / I2 value 100-cycle capacity retention Example 1 110 3.62 5.6 87% Example 2 115 3.61 5.8 92% Example 3 125 3.5 5.4 90 Example 4 105 3.52 6.0 95 Comparative Example 1 101 3.60 4.9 78% Comparative Example 2 119 3.64 3.8 79% Comparative Example 3 105 3.59 3.5 64%

[0124] Table 1 shows that Examples 1-4 have a higher I1 / I2 ratio than Comparative Examples 1-3. Figure 12 It can be concluded that Examples 1-4 exhibit higher capacity retention after 100 cycles. This indicates that the crystal orientation of primary particles can be fundamentally adjusted using carbonate precursors, ultimately achieving preferential exposure of the (002) crystal facet. In contrast, hydroxide precursors, due to the absence of CO2 generation during decomposition and the lack of a template effect, and the inheritance of morphology, result in a large exposure of the active facets of primary particles, leading to an I1 / I2 value of only 3.8 and consequently, poor cycle life. Therefore, the crystal orientation of primary particles has a significant impact on the cycling stability of the material.

[0125] In summary, this invention adopts a method based on Mn x Ni y X b The co-precipitation precursor of CO3 controls the sintering process and achieves one-time particle orientation regulation, preferentially exposing the electrochemically stable (002) crystal plane, enabling the P2 phase material to achieve a discharge specific capacity of more than 110 mAh / g and an average discharge voltage of more than 3.5V in the range of 2 to 4.3V. Compared with materials without specific crystal plane orientation, the present invention significantly improves the cycling stability of the material under high voltage.

[0126] Finally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0127] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0128] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A P2-type sodium-ion layered cathode material that is stable under high voltage cycling, characterized in that, The chemical formula of the positive electrode material is (NaaMnxNiyXb)O2; Wherein, 0.6≤a≤0.85, 0.5≤x≤0.8, 0.1≤y≤0.4, 0≤b≤0.2, and x+y+b=1, X includes Cu and / or Zn; In the XRD pattern of the cathode material, the ratio of the peak height I1 of (002) to the peak height I2 of (100), i.e., I1 / I2, is greater than 5.

4.

2. The P2-type sodium-ion layered cathode material that is cycle-stable under high voltage according to claim 1, characterized in that, The microstructure of the cathode material is a secondary particle with a spherical structure. The secondary particle is formed by the aggregation of several primary particles. The (002) crystal plane of the primary particle is exposed to the outside of the secondary particle. The primary particle size distribution is 0.1–1 μm, and the secondary particle size distribution is 2–20 μm.

3. The method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material as described in claim 1 or 2, characterized in that, The preparation method includes: According to the molar ratio of each element in the chemical formula (NaaMnxNiyXb)O2, 0.6≤a≤0.85, 0.5≤x≤0.8, 0.1≤y≤0.4, 0≤b≤0.2, and x+y+b=1, the precursors of Na, Mn, Ni, and X are weighed and mixed evenly to obtain a mixture. The precursors of Mn, Ni, and X are selected from the co-precipitated carbonate compound Mn, Ni, and X. x Ni y X b CO3, the precursor of Na is selected from its carbonate, nitrate, oxalate, oxide or hydroxide; The mixture is pre-sintered at 400–600 °C in an air atmosphere; After the pre-sintering is completed, the temperature is raised to 825-1000℃ for secondary sintering, followed by cooling to obtain P2 type sodium ion layered cathode material.

4. The method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material according to claim 3, characterized in that, The Mn x Ni y X b In CO3, X includes Cu and / or Zn.

5. The method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material according to claim 3, characterized in that, The process of pre-sintering the mixture at 400–600 °C in an air atmosphere specifically includes: In an air atmosphere, the mixture is heated to 400–600 °C at a rate of 2–10 °C / min for pre-sintering, and the holding time is 4 ± 2 h.

6. The method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material according to claim 3, characterized in that, After the pre-sintering is completed, the temperature is raised to 825-1000℃ for secondary sintering, followed by cooling to obtain a P2 type sodium ion layered cathode material, specifically including: After the pre-sintering is completed, the temperature is continued to rise to 825-1000℃ at a rate of 3-5℃ / min for secondary sintering, and the holding time is 14±2h. After the secondary sintering is completed, the material is cooled to room temperature in the furnace to obtain P2 type sodium ion layered cathode material.

7. A method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material according to claim 3 or 5, characterized in that, The sintering temperature of the pre-sintering is 500℃.

8. A method for preparing a high-voltage, cycle-stable P2-type sodium-ion layered cathode material according to claim 3 or 6, characterized in that, The sintering temperature for the secondary sintering is 950℃.

9. The application of the high-voltage, cycle-stable P2-type sodium-ion layered cathode material as described in claim 1 or 2 in the preparation of sodium-ion batteries or sodium-ion battery cathode sheets.

10. A sodium-ion battery, characterized in that, The sodium-ion battery contains a P2-type sodium-ion layered cathode material that is stable under high voltage cycling, as described in claim 1 or 2.

11. A positive electrode sheet for a sodium-ion battery, characterized in that, The positive electrode of the sodium-ion battery contains a P2-type sodium-ion layered positive electrode material that is stable under high voltage cycling, as described in claim 1 or 2.

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