O3-type layered oxide positive electrode material and preparation method and application thereof

Abstract

This invention discloses an O3-type layered oxide cathode material, its preparation method, and its application, belonging to the field of sodium-ion battery technology; the general chemical formula of the cathode material is NaNi. x Fe 0.2 Mn 0.4 M y O2, wherein M is a dopant element, the bond energy of the chemical bond formed by the dopant element and oxygen is greater than the bond energy of the Mn-O bond, 0.35≤x<0.4, 0<y≤0.05, and x+y=0.4, and the ratio of each element satisfies charge conservation; this invention modifies the structure of O3-type layered oxide by introducing a high-valence dopant element that forms a strong chemical bond with oxygen, significantly enhancing the structural stability of the material, effectively suppressing irreversible phase transitions at low temperatures and high voltages, and improving low-temperature ion transport dynamics; the resulting cathode material shows no significant capacity decay after 90 cycles in an extreme low-temperature environment of -40℃, exhibiting excellent low-temperature cycling performance; the preparation process of this invention is simple and controllable, providing new ideas and technical support for the development of low-temperature O3-type sodium-ion battery cathode materials.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to an O3-type layered oxide cathode material, its preparation method, and its application. Background Technology

[0002] With the global energy structure transformation and the increasing demand for large-scale energy storage systems, sodium-ion batteries are considered an ideal supplement or alternative to lithium-ion batteries due to their abundant resources and low cost. Among various cathode materials, layered transition metal oxides (Na₂O₃) are... x Sodium-ion batteries (THMs) have attracted much attention due to their high theoretical specific capacity and scalable fabrication process. However, their performance in practical applications, especially over a wide temperature range, still faces significant challenges. Specifically, when the operating temperature drops below zero, the electrochemical performance of the material deteriorates sharply, which severely restricts the widespread application of sodium-ion batteries in extremely cold regions or special low-temperature scenarios.

[0003] Layered Na x TMO2 cathode materials are mainly classified into O3-type and P2-type based on differences in sodium ion coordination environment and oxygen layer stacking mode. Among them, O3-type cathode materials, due to their high initial sodium content (x≈1), can provide an ample source of active sodium and can be directly matched with sodium-free anodes such as hard carbon, giving them a significant advantage in full-cell design. However, the performance degradation of O3-type cathode materials is particularly pronounced at low temperatures. The fundamental reasons are as follows: Firstly, at low temperatures, the solid-phase diffusion coefficient of sodium ions inside the material decreases sharply, coupled with increased electrolyte viscosity and a significant increase in interfacial charge transfer impedance, resulting in severely limited ion transport kinetics. Secondly, during charge and discharge, O3-type materials are prone to complex irreversible phase transitions from the O3 phase to the O'3 phase or the P3 phase due to sodium ion intercalation and deintercalation. These phase transitions are accompanied by drastic changes in cell parameters, leading to the accumulation of lattice strain and the generation of microcracks, ultimately causing irreversible degradation of electrochemical performance. Low-temperature environments further exacerbate the irreversibility of these phase transitions, causing a rapid deterioration in the material's capacity and cycle life.

[0004] To improve the performance of O3-type cathode materials, researchers have explored various modification strategies, including elemental doping and surface coating. Among these, bulk doping with specific elements allows for fundamental control of the material at the lattice scale and is considered an effective way to improve structural stability and ion transport kinetics. Existing research indicates that doping with Ti... 4+ or Zr 4+ Elements such as Mg can utilize their strong electrostatic repulsion with the oxygen layer to widen the interlayer spacing, providing a more spacious channel for sodium ion migration; the addition of Mg 2+ or Cu 2+Electrochemically inert elements can serve as structural pillars, suppressing plate slippage during deep sodium removal. However, existing doping strategies still need improvement in comprehensively and synergistically addressing core challenges such as ion transport kinetic hysteresis at low temperatures, irreversible phase transitions at high voltages, and structural stability during long cycles. In particular, for applications in extreme low-temperature environments such as -40°C, a more efficient doping modification scheme urgently needs to be developed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an O3-type layered oxide cathode material, its preparation method and application.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This application provides an O3-type layered oxide cathode material with the general chemical formula NaNi. x Fe 0.2 Mn 0.4 M y O2; Wherein, M is a dopant element, and the bond energy of the chemical bond formed between the dopant element and oxygen is greater than the bond energy of the Mn-O bond; 0.35≤x<0.4, 0<y≤0.05, and x+y=0.4; The ratio of elements in the general chemical formula satisfies charge conservation.

[0007] Preferably, the dopant element M is a high-valence metal element with a valence state not lower than +4.

[0008] Preferably, the doping element M is selected from at least one of Nb, Ta, W, and Mo.

[0009] Preferably, the dopant element M is Nb.

[0010] Preferably, the positive electrode material retains more than 95% of its capacity after 90 charge-discharge cycles at a rate of 0.1C at an ambient temperature of -40°C.

[0011] A method for preparing the O3-type layered oxide cathode material as described above includes the following steps: S1. Weigh out sodium source, nickel source, iron source, manganese source and precursor containing doped element M or Nb according to the stoichiometric ratio of the general chemical formula or chemical formula, mix them evenly to obtain a precursor mixture; S2. The precursor mixture is sintered in an oxygen-containing atmosphere at a temperature of 900~1000℃ for 10~20 hours, and then cooled to obtain the O3-type layered oxide cathode material.

[0012] Preferably, the mixing in step S1 is ball milling, with a ball-to-material ratio of 3:1 to 5:1, a ball milling speed of 400 to 600 rpm, and a ball milling time of 6 to 18 hours.

[0013] Preferably, the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium acetate; The nickel source is selected from at least one of nickel oxide, nickel hydroxide, and nickel carbonate; The iron source is selected from at least one of ferric oxide, ferric oxide, and ferric hydroxide; The manganese source is selected from at least one of manganese dioxide, manganese trioxide, and manganese carbonate; The precursor is an oxide of the doping element or Nb.

[0014] Application of an O3-type layered oxide cathode material in a sodium-ion battery, the sodium-ion battery comprising: a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises the above-mentioned O3-type layered oxide cathode material, or comprises the O3-type layered oxide cathode material prepared by the above-mentioned preparation method.

[0015] Compared with the prior art, this application has the following beneficial effects: This invention proposes an O3-type layered oxide cathode material, its preparation method, and its applications. By introducing a high-valence dopant element M, which forms stronger chemical bonds with oxygen, and partially substituting Ni sites, this invention achieves a dual effect of anchoring and supporting the alkali metal interlayer structure of the O3-type layered oxide. On one hand, the high-bond-energy chemical bonds formed between the dopant element M and oxygen act like strong skeletal rivets implanted between the transition metal layers, significantly enhancing the structural integrity of the material during charge and discharge processes. This effectively suppresses the severe lattice slip and complex irreversible phase transitions caused by sodium ion insertion / extraction at low temperatures, thereby greatly improving the material's cycle reversibility and structural stability. On the other hand, the high-valence dopant element M generates stronger electrostatic repulsion between the oxygen layers, effectively expanding the interlayer spacing of sodium ion migration channels, reducing the solid-state diffusion barrier of sodium ions at low temperatures, and compensating for the insufficient ion kinetic energy at low temperatures, thus significantly improving the material's low-temperature ion transport kinetics. Furthermore, the enhanced bond energy also improves the overall thermodynamic stability of the material. The synergistic effect enables the cathode material provided by this invention to maintain excellent specific capacity and cycle stability even in extreme low-temperature environments such as -40℃. Attached Figure Description

[0016] Figure 1 The graph shows a comparison of the rate performance of the cathode materials prepared in each embodiment and comparative example at different rate ranges.

[0017] Figure 2The graph shows the long-cycle performance of the cathode material prepared in Example 1 at -20°C and 0.5°C.

[0018] Figure 3. Long-cycle performance and coulombic efficiency of the cathode material prepared in Example 1 at -40℃ and 0.1C.

[0019] Figure 4 The in-situ X-ray diffraction (XRD) pattern of Example 1 demonstrates the reversibility of its phase transition during the charge-discharge process. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Furthermore, in this invention, an element referred to as fixed to or disposed on another element may be directly disposed on the other element, or there may be an intermediate element. When an element is considered to be connected to another element, it may be directly connected to the other element, or there may be an intermediate element present simultaneously. The terms vertical, horizontal, left, right, and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0022] See Figures 1-4 This application provides an O3-type sodium-ion battery cathode material with excellent low-temperature performance, whose general chemical formula is NaNi. x Fe 0.2 Mn 0.4 M y O2; where M is a dopant element, the core feature of which is that the bond energy of the chemical bond formed between the dopant element and oxygen is greater than the bond energy of the Mn-O bond; by selecting high-valence elements (such as +4 valence and above) that meet this condition, the strong interaction between them and oxygen can be used to fundamentally strengthen the structural framework of the material.

[0023] In a preferred embodiment, the dopant element M is selected from at least one of Nb, Ta, W, and Mo; these elements not only have high valence states, but also their chemical bond energies with oxygen are significantly higher than those of the Mn-O bond (402 kJ·mol⁻¹). -1 ) and Ni-O bond (391.6 kJ·mol -1 Taking Nb as an example, the bond energy of the Nb-O bond reaches 753 kJ·mol⁻¹. -1 It can achieve the best structural stability and interlayer spacing control effect.

[0024] To balance capacity and stability, the doping amount y and nickel content x need to satisfy a specific proportional relationship; in the present invention, 0.35 ≤ x < 0.4, 0 < y ≤ 0.05, and x + y = 0.4; if the doping amount is too low, the modification effect is not obvious; if the doping amount is too high, the specific capacity of the material will be sacrificed due to the too low content of the electrochemically active element Ni. Therefore, this range is the interval with the optimal comprehensive performance.

[0025] For the further preferred solution of using Nb as the doping element, the chemical formula of this material can be directly expressed as NaNi x Fe 0.2 Mn 0.4 Nb y O2, where 0.35 ≤ x < 0.4, 0 < y ≤ 0.05, and x + y = 0.4, and x and y are the molar percentages of the corresponding elements respectively. Each component in the chemical formula satisfies charge conservation and stoichiometric ratio conservation; experiments have proved that this material has a capacity retention rate of 80% after 140 cycles at a current density of 16 mA g -1 within the voltage range of 2.0 - 4.2 V and at a temperature of -20 °C; in an extremely low temperature environment of -40 °C, when charged and discharged cyclically at a current density of 0.1 C (16 mA g -1 ), after 90 cycles, its capacity retention rate is greater than 95%, showing extremely excellent low-temperature cycle stability.

[0026] The present invention also provides a preparation method for the above O3-type layered oxide cathode material. This method is based on a simple and controllable high-temperature solid-phase reaction, and specifically includes the following steps: Step S1: Accurately weigh the sodium source, nickel source, iron source, manganese source, and the precursor containing the doping element M (or Nb) according to the stoichiometric ratio of the chemical general formula or chemical formula of the target product; in order to ensure that the elements can fully diffuse and react to form a homogeneous phase during the subsequent high-temperature sintering process, each raw material needs to be fully mixed evenly by mechanical means to obtain a precursor mixture.

[0027] To ensure the uniform mixing of each component at the microscale, the present invention preferably adopts a ball milling mixing process; place the weighed raw materials together in a ball milling tank and add agate balls as the grinding medium; to obtain the best mixing effect and particle size distribution, the ball-to-material ratio is controlled between 3:1 and 5:1, the ball milling speed is set at 400 to 600 revolutions per minute (rpm), and the ball milling time is 6 to 18 hours; for example, in a specific implementation, the ball-to-material ratio is set to 3:1, and ball milling is carried out at a speed of 500 rpm for 12 hours, and a precursor powder with a highly uniform component distribution can be obtained.

[0028] Step S2: Transfer the precursor mixture obtained in Step S1 to an alumina crucible, then place it in a muffle furnace for high-temperature solid-state sintering in an oxygen-containing atmosphere (such as air). The sintering regime is crucial in determining the crystal structure and properties of the material; the heating rate should not be too fast to facilitate the gradual regularization of the crystal form; the sintering temperature must be sufficient to drive long-range ion diffusion and form the target O3 phase layered structure; the holding time must ensure complete reaction and perfect crystallization; in this invention, it is preferable to heat to 900~1000℃ at a rate of 5℃ / min and hold at this temperature for 10~20 hours; after sintering, cool with the furnace to 100℃ or room temperature to obtain a black powdery O3-type layered oxide cathode material.

[0029] In the above preparation process, the raw materials used are widely available. The sodium source can be selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium acetate; the nickel source can be selected from at least one of nickel oxide, nickel hydroxide, and nickel carbonate; the iron source can be selected from at least one of ferric oxide, iron tetroxide, and ferric hydroxide; the manganese source can be selected from at least one of manganese dioxide, manganese trioxide, and manganese carbonate; the precursor containing the doping element M (or Nb) is preferably its corresponding oxide, such as niobium pentoxide (Nb2O5) as the niobium source when Nb doping is used; in a specific and preferred embodiment, to obtain the highest purity and best batch stability, sodium carbonate, nickel oxide, ferric oxide, manganese dioxide, and niobium pentoxide are used as starting materials respectively.

[0030] The technical solution of the present invention will be further described below through specific embodiments; unless otherwise explicitly stated, the methods used in each embodiment are conventional experimental methods in the art, and the reagents and raw materials used can be purchased through commercial channels.

[0031] Example 1 This embodiment prepares a chemical formula of NaNi x Fe 0.2 Mn 0.4 Nb y The positive electrode material of O2, where x=0.39 and y=0.01, is abbreviated as NFMNb-1.

[0032] Sodium carbonate (Na₂CO₃), nickel oxide (NiO), ferric oxide (Fe₂O₃), manganese dioxide (MnO₂), and niobium pentoxide (Nb₂O₅) powders were weighed according to the molar stoichiometric ratio of Na:Ni:Fe:Mn:Nb = 1:0.39:0.2:0.4:0.01. All raw materials were placed in a ball mill jar, and agate balls were added at a ball-to-material ratio of 3:1. The mixture was ball-milled at 500 rpm for 12 hours to obtain a homogeneous precursor mixture. The precursor powder was then placed in a corundum crucible and placed in a muffle furnace. The furnace was heated to 950°C at a rate of 5°C / min in air and held at that temperature for 15 hours. After cooling to 100°C in the furnace, the powder was removed and ground to obtain the target cathode material NFMNb-1.

[0033] Example 2 The only difference between this embodiment and Example 1 is that the stoichiometric ratio of Ni and Nb was adjusted to prepare a material with x=0.35 and y=0.05, which is abbreviated as NFMNb-5. Specifically, the same raw materials as in Example 1 were weighed according to the molar ratio of Na:Ni:Fe:Mn:Nb=1:0.35:0.2:0.4:0.05, and the subsequent ball milling and sintering processes were completely the same to obtain the target cathode material NFMNb-5.

[0034] Comparative Example For comparison, this comparative example prepared an undoped NaNi matrix material using the same process as in Example 1. x Fe 0.2 Mn 0.4 O2, where x=0.4, y=0, the product is abbreviated as NFM; raw materials other than niobium pentoxide are weighed according to the molar ratio of Na:Ni:Fe:Mn=1:0.4:0.2:0.4, and the same ball milling and sintering process is carried out to obtain the comparative material NFM.

[0035] Performance testing and characterization The positive electrode materials prepared in the above examples and comparative examples were used as active materials, mixed with conductive agents and binders in conventional proportions, and coated on aluminum foil to form positive electrode sheets; using a sodium metal sheet as the counter electrode, they were assembled into button batteries in a glove box for electrochemical performance testing.

[0036] Ratio Performance Test Figure 1The rate performance of batteries made from the cathode materials prepared in each embodiment and comparative example is shown in the graphs at 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, and 5C conditions. The test results show that NFMNb-1 prepared in Example 1 has faster sodium ion transport kinetics and stronger structural stability. At all rates, the discharge specific capacity of NFMNb-1 is significantly higher than that of the comparative example NFM, and when the current density recovers to 0.1C, the discharge capacity of the NFMNb-1 sample is close to its initial capacity, showing excellent reversibility. This fully demonstrates that the strong Nb-O bond introduced by Nb doping, as a key support for the structural framework, effectively resists the impact of rapid sodium ion insertion / extraction at high rates on the material structure, ensuring the integrity of the rapid ion transport channel.

[0037] Low temperature cycling performance test Figure 2 The battery made from the cathode material prepared in Example 1 exhibits long-cycle performance at -20°C and 0.5C. The results show that NFMNb-1 maintains high specific capacity and excellent stability during long-cycle operation at 0.5C, with a capacity retention of 80% after 140 cycles. This result is attributed to the fact that Nb doping increases the interlayer spacing, lowers the energy barrier for sodium ion diffusion at low temperatures, and thus significantly improves ion transport dynamics at low temperatures.

[0038] Figure 3 The image shows the long-cycle performance of a battery made from the cathode material prepared in Example 1 at -40°C and 0.1C. The results indicate that NFMNb-1, after 90 cycles of charge-discharge at a current density of 0.1C, showed no signs of capacity degradation, retaining more than 95% of its capacity. This strongly suggests that the presence of strong Nb-O bonds significantly stabilizes the material's crystal structure, effectively suppressing complex irreversible phase transitions such as O3→O'3 / P3 that are prone to occur under extreme low temperatures and large-scale sodium removal conditions. This results in a qualitative leap in the material's cycle stability and structural reversibility under extreme conditions.

[0039] Phase transition reversibility analysis Figure 4The in-situ XRD pattern of Example 1 is shown. The test results indicate that the phase transition of NFMNb-1 during charge and discharge processes exhibits good reversibility. The pattern shows that the peak positions and intensities of the diffraction peaks show regular and highly symmetrical reversible shifts with voltage changes, without the generation of irreversible new peaks or the disappearance of existing characteristic peaks. This indicates that during the entire process of sodium ion extraction and insertion, the material undergoes a highly reversible solid solution reaction and phase transition process, without any irreversible phase transitions leading to structural collapse. This directly confirms that the introduction of high-valence dopant elements with high MO bond energy in this invention effectively anchors the transition metal layers and suppresses severe lattice distortion, which is the fundamental reason for the material's excellent low-temperature performance and long cycle life.

[0040] The test results above show that the cathode material prepared by this invention can meet the requirements of fast charging, structural stability, and good cycle performance at low temperatures.

[0041] In summary, the O3-type layered oxide cathode material provided by this invention fundamentally and synergistically solves the common problems of low-temperature kinetic sluggishness and structural instability faced by O3-type cathode materials through an innovative doping strategy. Its preparation process is simple, the raw materials are readily available, and it is highly compatible with existing industrial production equipment, providing a practical material solution and technical support for developing high-performance, long-life sodium-ion batteries suitable for extreme environments such as high-altitude and cold regions.

[0042] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0043] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An O3-type layered oxide cathode material, characterized in that, Its general chemical formula is: Pretty x Feb 0.2 Mr 0.4 M y O2; Wherein, M is a dopant element, and the bond energy of the chemical bond formed between the dopant element and oxygen is greater than the bond energy of the Mn-O bond; 0.35≤x<0.4, 0<y≤0.05, and x+y=0.4; The ratio of elements in the general chemical formula satisfies charge conservation.

2. The O3-type layered oxide cathode material according to claim 1, characterized in that, The dopant element M is a high-valence metal element with a valence state not lower than +4.

3. The O3-type layered oxide cathode material according to claim 2, characterized in that, The doping element M is selected from at least one of Nb, Ta, W, and Mo.

4. The O3-type layered oxide cathode material according to claim 3, characterized in that, The doping element M is Nb.

5. The O3-type layered oxide cathode material according to claim 4, characterized in that, The positive electrode material retains more than 95% of its capacity after 90 charge-discharge cycles at a rate of 0.1C at an ambient temperature of -40°C.

6. A method for preparing an O3-type layered oxide cathode material as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Weigh out sodium source, nickel source, iron source, manganese source and precursor containing doped element M or Nb according to the stoichiometric ratio of the general chemical formula or chemical formula, mix them evenly to obtain a precursor mixture; S2. The precursor mixture is sintered in an oxygen-containing atmosphere at a temperature of 900~1000℃ for 10~20 hours, and then cooled to obtain the O3-type layered oxide cathode material.

7. The preparation method according to claim 6, characterized in that, The mixing described in step S1 is ball milling, with a ball-to-material ratio of 3:1 to 5:1, a ball milling speed of 400 to 600 rpm, and a ball milling time of 6 to 18 hours.

8. The preparation method according to claim 7, characterized in that, The sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium acetate; The nickel source is selected from at least one of nickel oxide, nickel hydroxide, and nickel carbonate; The iron source is selected from at least one of ferric oxide, ferric oxide, and ferric hydroxide; The manganese source is selected from at least one of manganese dioxide, manganese trioxide, and manganese carbonate; The precursor is an oxide of the doping element or Nb.

9. The application of an O3-type layered oxide cathode material in sodium-ion batteries, characterized in that, The sodium-ion battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises the O3-type layered oxide positive electrode material according to any one of claims 1-5, or comprises the O3-type layered oxide positive electrode material prepared by the preparation method according to any one of claims 6-8.

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