Sodium electric layered oxide positive electrode material and preparation method, positive electrode sheet, battery and electric device

Abstract

The application provides a sodium battery layered oxide positive electrode material and a preparation method, a positive electrode sheet, a battery and an electric device, and the sodium battery layered oxide positive electrode material comprises a uniform mixture of type I particles and type II particles, the phase structures of the type I particles and the type II particles are different; in an X-ray powder diffraction spectrum measured by using Cu-Ka rays, the uniform mixture at least exists: a diffraction peak P γ corresponding to a (003) crystal face and a diffraction peak P φ corresponding to a (002) crystal face, an diffraction angle of the diffraction peak P γ is gamma, a peak intensity is I γ , an diffraction angle of the diffraction peak P φ is phi, a peak intensity is I φ , and phi < gamma, the sodium battery layered oxide positive electrode material provided by the application improves the synergistic effect of the type I particles and the type II particles under different voltage conditions by adjusting the sodium manganese content in the type I particles and the type II particles and the ratio of the two types of particles, and the sodium battery layered oxide positive electrode material has the performances of high energy density, high discharge stability in a wide voltage range (1.5-4.2 V), long cycle life and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium-ion batteries, in particular to a sodium battery layered oxide positive electrode material, a preparation method thereof, a positive electrode sheet, a battery and an electric device. BACKGROUND

[0002] Sodium-ion batteries are considered to be another suitable large-scale commercializable rechargeable battery technology besides lithium-ion batteries due to their advantages in safety and cost. In sodium-ion batteries, layered oxide positive electrode materials are valued for their high energy density, fast sodium-ion movement speed, simple manufacturing process and low cost.

[0003] The commonly used layered oxide positive electrode materials for sodium-ion batteries mainly include O3 structure and P2 structure. Sodium battery layered oxide positive electrode materials with O3 structure can release more sodium ions and have a higher theoretical energy capacity, but during the charging and discharging process, the O3 structure material will undergo complex phase changes, especially irreversible phase changes at high voltage, which will seriously affect the cycle life and fast charging and discharging performance. In contrast, sodium battery layered oxide positive electrode materials with P2 structure have a larger sodium layer spacing, which is beneficial to the movement of sodium ions and has better high-voltage stability, but due to the lower sodium content, the theoretical capacity and actual capacity are significantly lower than those of sodium battery layered oxide positive electrode materials with O3 structure.

[0004] Some studies propose P, O mixed phase materials (P / O structure) to utilize the synergistic effect of the two phases to alleviate or inhibit the structural phase change at high voltage, thereby improving the electrochemical performance of the material. However, O3, P2 and P / O structures cannot solve the stability problem of high-depth discharge, and when the discharge cutoff voltage is <2V, a large amount of Mn 4+ is reduced to Mn 3+ , which makes the material structure stability worse, the metal dissolution more severe, and the cycle performance deteriorates, i.e., the discharge specific capacity and discharge voltage significantly decay. Therefore, the current sodium battery layered oxide positive electrode materials have not solved the key problems of high specific energy, high cycle stability and wide voltage range discharge stability. SUMMARY

[0005] The present application aims to provide a sodium battery layered oxide positive electrode material, a preparation method thereof, a positive electrode sheet, a battery and an electric device to solve the problems in the background art.

[0006] The technical scheme of the present application comprises: a sodium battery layered oxide positive electrode material, wherein the sodium battery layered oxide positive electrode material comprises a uniform mixture of type I particles and type II particles, the phase structures of the type I particles and the type II particles are different; in the X-ray powder diffraction pattern measured by using Cu-Kα rays, the uniform mixture at least exists: a diffraction peak P γ corresponding to a (003) crystal face and a diffraction peak P φ corresponding to a (002) crystal face at 15°-18° of 2θ, the diffraction angle of the diffraction peak P γ is γ, the peak intensity is I γ , the diffraction angle of the diffraction peak P φ is φ, the peak intensity is I φ , and φ<γ.

[0007] Further, in the respective X-ray powder diffraction patterns measured by using Cu-Kα rays, at 15°-18° of 2θ:

[0008] the type I particles exist a diffraction peak P δ corresponding to a (003) crystal face, the diffraction angle of the diffraction peak P δ is δ, and the peak intensity is I δ ;

[0009] the type II particles at least exist a diffraction peak P ε corresponding to a (002) crystal face, the diffraction angle of the diffraction peak P ε is ε, and the peak intensity is I ε ;

[0010] ε<δ, w is the mass ratio of the type I particles in the uniform mixture.

[0011] Further, the chemical general formula of the type I particles is Na x1 Ni a1 Mn b1 M y1 O2, and the chemical general formula of the type II particles is Na x2 Ni a2 Mn b2 M y2 O2, wherein:

[0012] 0.6<x2<0.9<x1<1.1, 0.3<b1<b2<1, and x1·w+x2·(1-w)>0.9.

[0013] Further, M in the chemical formula of the first type of particles and the chemical formula of the second type of particles is independently selected from one or more of Fe, Cu, Li, Mg, Al, Ca, Cu, Zn, Ti, Zr, Cr, Sr, Ba, Nb, Mo and W, a1+b1+y1=1, a2+b2+y2=1.

[0014] Further, when n moles of sodium ions are released from each mole of the first type of particles based on metallic sodium, the potential is U Ⅰ , and when n moles of sodium ions are released from each mole of the second type of particles based on metallic sodium, the potential is U Ⅱ , for any n≤0.5, U Ⅰ <U Ⅱ ;

[0015] In a sodium-ion battery containing the sodium electro-layered oxide positive electrode material, when the sodium-ion battery is discharged to U 放电截止 , the valence of Mn in the first type of particles is V Ⅰ , and the valence of Mn in the second type of particles is V Ⅱ , and when 1.5V≤U 放电截止 ≤2V, 3.5<V Ⅱ <V Ⅰ <4.0.

[0016] The technical solution of the present application also includes: a method for preparing the sodium electro-layered oxide positive electrode material as described above, comprising the steps of:

[0017] According to the molar ratio of elements in the first type of particles and the second type of particles, a sodium source, a nickel source, a manganese source and an M source are used to obtain the first type of raw material and the second type of raw material, respectively;

[0018] The first type of raw material and the second type of raw material are subjected to sectional sintering, crushing and sieving, respectively, to obtain the first type of particles and the second type of particles;

[0019] The first type of particles and the second type of particles are uniformly mixed according to the ratio to obtain the sodium electro-layered oxide positive electrode material.

[0020] Further, in the preparation method:

[0021] The sodium source includes at least one of sodium carbonate and sodium bicarbonate;

[0022] The nickel source, the manganese source and the M source each include at least one of oxides, hydroxides, chlorides and carbonates containing the corresponding metal elements;

[0023] The sectional sintering conditions are: first calcination at 500℃ for 1-10h, then calcination at 850-1100℃ for 6-30h, and finally cooling in the furnace, during which the relative humidity of the environment is ≤30%;

[0024] In the process of crushing, screening and mixing the type I particles and the type II particles, the relative humidity of the environment is less than or equal to 20%.

[0025] The technical solution of the present application further comprises: a positive pole piece containing the sodium-electric layered oxide positive pole material as described above.

[0026] The technical solution of the present application further comprises: a battery containing the positive pole piece as described above.

[0027] The technical solution of the present application further comprises: an electric device containing the battery as described above.

[0028] The sodium-electric layered oxide positive pole material provided by the present application realizes the adjustment and optimization of the structure and the electrochemical performance by adjusting the sodium-manganese content in the type I particles and the type II particles and the ratio of the two types of particles, improves the synergistic effect of the two under different voltage conditions, and thus guarantees that the sodium-electric layered oxide positive pole material with high energy density has high structural stability in the whole process of high-depth discharge, so that the sodium-electric layered oxide positive pole material has the performances of high energy density, high discharge stability in a wide voltage range (1.5-4.2V), and long cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is an XRD graph of the sodium-electric layered oxide positive pole material prepared in Example 1 of the present application;

[0030] Figure 2 is a charge-discharge curve of the type I particles, the type II particles and the sodium-electric layered oxide positive pole material prepared in Example 1;

[0031] Figure 3 is a comparison graph of the battery cycle performance of the sodium-electric layered oxide positive pole materials prepared in Examples 1-6 under 1.5V-4.2V;

[0032] Figure 4 is a comparison graph of the battery cycle performance of the sodium-electric positive pole materials prepared in Comparative Examples 1-6 under 1.5V-4.2V. DETAILED DESCRIPTION

[0033] The present application will be further described below in combination with examples and drawings:

[0034] Unless otherwise defined, all the professional terms used in the following have the same meaning as generally understood by those skilled in the art. The professional terms used in the present application are only for the purpose of describing the specific examples and the comparative examples, and are not intended to limit the protection scope of the present application. It should be specially noted that there can be multiple names for the same organic structure, as long as the structure is within the scope of the present patent, it belongs to the protection object of the present patent.

[0035] Unless otherwise defined, the starting materials, reagents, etc. in the following examples can be obtained from the market or prepared according to the reported methods.

[0036] In a first aspect of the present application, a sodium battery layered oxide positive electrode material is provided. According to an embodiment of the present application, the sodium battery layered oxide positive electrode material is a uniform mixture of type I particles and type II particles, the phase structures of the type I particles and the type II particles are different, the type I particles are in O3 phase, and the type II particles at least contain P2 phase and possibly contain part of P / O phase; in the sodium battery layered oxide positive electrode material, the mass percentage of the type I particles is w, and the mass percentage of the type II particles is 1-w; in the X-ray powder diffraction patterns of each of the type I particles and the type II particles measured using Cu-Ka rays, at 2θ of 15°-18°:

[0037] (1) the type I particles have a diffraction peak P corresponding to (003) crystal face δ , the diffraction angle of the diffraction peak P δ is δ, and the peak intensity is I δ ;

[0038] (2) the type II particles at least have a diffraction peak P corresponding to (002) crystal face ε , the diffraction angle of the diffraction peak P ε is ε, and the peak intensity is I ε , and possibly have a diffraction peak P' corresponding to (003) crystal face (the corresponding peak intensity is I');

[0039] (3) the sodium battery layered oxide positive electrode material has a diffraction peak P corresponding to (003) crystal face γ and a diffraction peak P corresponding to (002) crystal face φ , the diffraction angle of the diffraction peak P γ is γ, and the peak intensity is I γ , the diffraction angle of the diffraction peak P φ is φ, and the peak intensity is I φ ;

[0040] wherein ε < δ, and φ < γ,

[0041] In this embodiment, type I particles mainly contribute the O3 phase structure to the sodium-electric layered oxide cathode material, resulting in diffraction peaks corresponding to the (003) crystal plane in the XRD pattern. Furthermore, type I particles can release more sodium ions, leading to a higher theoretical capacity for the sodium-electric layered oxide cathode material. Type II particles mainly contribute the P2 phase structure to the sodium-electric layered oxide cathode material, and may contribute a small amount of P / O phase structure, resulting in diffraction peaks corresponding to the (002) crystal plane in the XRD pattern. This may also increase the peak intensity of the diffraction peaks corresponding to the (003) crystal plane in the XRD pattern. Furthermore, type II particles have more sodium ion vacancies and larger sodium interlayer spacing, which is conducive to the movement of sodium ions and improves the fast charge and discharge performance of sodium-ion layered oxide cathode materials.

[0042] Furthermore, the inventors of this technical solution also discovered in their research that during the charging and discharging process, the Type I particles, which mainly contribute to the O3 phase structure, undergo complex phase transitions, primarily including O3 phase → monoclinic O'3 phase → P3 phase → O phase. This occurs when the charging cutoff voltage > 4.0V (vs. Na / Na). + During the P3 phase → O phase evolution, the sodium interlayer spacing decreases sharply, resulting in extremely poor phase transition reversibility and severely impacting the material's cycle life and fast charge / discharge performance. In contrast, type II particles, which primarily contribute to the P2 phase structure, exhibit significant hysteresis during sodium removal at high voltages, thus demonstrating better high-voltage stability. The presence of type II particles can alleviate or suppress the irreversible phase transition tendency of type I particles at high voltages, improving the structural stability of the sodium-ion layered oxide cathode material under high voltages. When the discharge cutoff voltage is <2V, type II particles, which primarily contribute to the P2 phase structure (and may contain some P / O phase structures), have sodium ion vacancies. These vacancies allow sodium ions to re-embed into the sodium ion vacancies of type II particles, forming a sodium-rich phase, accompanied by Mn in the material. 4+ Reduced to Mn 3+ Mn 3+ The Ginger-Taylor effect degrades the structural stability of the material, intensifies metal dissolution, and worsens cycle performance. When present in type I particles, the presence of sodium ions can mitigate the over-intercalation of sodium ions in type II particles at low discharge voltages by accepting some sodium ions, thereby improving the structural stability of sodium-ion layered oxide cathode materials at low discharge voltages.

[0043] The inventors of this technical solution also discovered during their research: This effectively ensures a suitable sodium ion vacancy concentration in the sodium-ion layered oxide cathode material, enabling the achievement of a high plateau voltage and energy density retention during long-cycle operation; when At that time, the proportion of type II particles with high sodium ion vacancy concentration in sodium-ion layered oxide cathode materials is relatively small, which is not conducive to improving the plateau voltage of the material, and the high-voltage stability of the material deteriorates; when At that time, the proportion of type I particles with high sodium ion content in sodium-ion layered oxide cathode materials was relatively small, which suppressed the capacity of the material and made the material less stable during high-depth discharge.

[0044] The sodium-ion layered oxide cathode material provided in this embodiment, which meets the above conditions, utilizes the structural and electrochemical performance differences between type I and type II particles. By adjusting the mass ratio of type I and type II particles, the synergistic effect of the two under different voltage conditions is improved, thereby ensuring that the sodium-ion layered oxide cathode material with high energy density has high structural stability throughout the entire process of high-depth discharge. This gives it the properties of high energy density, high discharge stability over a wide voltage range (1.5–4.2V), and high cycle life.

[0045] According to the inventors' research findings, the sodium and manganese content in the material composition determines the number of sodium ions that can be inserted or removed and the sodium ion vacancy content in the material. The sodium ion vacancy content affects the spacing between the (003) and (002) crystal planes. At the same time, from the perspective of charge balance, the sodium ion vacancy concentration is also accompanied by the change in the valence state of manganese ions. Therefore, through experiments, exploration, and research, the chemical formula of the type I particles in this embodiment is determined to be Na. x1 Ni a1 Mn b1 M y1 O2, the general chemical formula for Class II particles is Na x2 Ni a2 Mn b2 M y2 O2, wherein M in the two general chemical formulas is independently taken from one or more of Fe, Cu, Li, Mg, Al, Ca, Cu, Zn, Ti, Zr, Cr, Sr, Ba, Nb, Mo, and W, a1+b1+y1=1, a2+b2+y2=1, 0.6 <x2<0.9<x1<1.1,0.3<b1<b2<1,x1·w+x2·(1-w)> 0.9.

[0046] Among them, x1·w+x2·(1-w)>0.9 can effectively ensure that there are enough sodium ions in the sodium-ion layered oxide cathode material, which can achieve high specific capacity; the appropriate addition of M element helps to further improve the structural stability of the material and improve the overall electrical performance of the material.

[0047] To further optimize the electrochemical performance of sodium-ion layered oxide cathode materials, the inventors of this technical solution conducted in-depth research and discovered that among Type I particles, Type II particles, and sodium-ion layered oxide cathode materials that meet the above conditions, when the following condition is met: n moles of sodium ions are released per mole of Type I particles based on metallic sodium, its potential is U Ⅰ When each mole of the aforementioned type II particle releases n moles of sodium ions based on metallic sodium, its potential is U. Ⅱ For any n ≤ 0.5, satisfying U Ⅰ <U Ⅱ This ensures that Type II particles exhibit significant hysteresis during sodium ion release compared to Type I particles, demonstrating excellent high-voltage stability. Thus, while providing effective capacity in the high-voltage range, it also mitigates the irreversible structural changes of Type I particles under high-voltage and high-SOC conditions.

[0048] To further optimize the electrochemical performance of sodium-ion battery layered oxide cathode materials, the inventors of this technical solution conducted in-depth research and discovered that among the Class I particles, Class II particles, and sodium-ion battery layered oxide cathode materials that meet the above conditions, when the following condition is met: in a sodium-ion battery containing this sodium-ion battery layered oxide cathode material, the sodium-ion battery discharges to U 放电截止 At that time, the valence state of Mn in type I particles is V. Ⅰ In type II particles, the valence state of Mn is V. Ⅱ 1.5V≤U 放电截止 When ≤2V, 3.5<V is satisfied. Ⅱ <V Ⅰ A value of <4.0 ensures that sodium ions do not over-intercalate into type II particles during high-depth discharge, reduces the content of +3 manganese ions in type II particles, improves the stability of the crystal structure, and ensures the stability of the plateau voltage during cycling.

[0049] It is worth noting that the above-mentioned I δ I ε I γ and I φ All values ​​are normalized diffraction peak intensities.

[0050] A second aspect of the present invention provides a method for preparing the sodium-ion layered oxide cathode material described in the first aspect. The preparation method provided in this embodiment includes the following steps:

[0051] (1) According to the molar ratio of elements in type I particles and type II particles, nano source, nickel source, manganese source and M source are used to obtain type I raw materials and type II raw materials respectively;

[0052] In this step, the sodium source includes at least one of sodium carbonate and sodium bicarbonate, and the nickel source, manganese source and M source each include at least one of oxides, hydroxides, chlorides and carbonates containing the corresponding metal elements.

[0053] (2) The raw materials of type I and type II are sintered, crushed and sieved in stages to obtain type I particles and type II particles respectively;

[0054] In this step, the conditions for segmented sintering are as follows: first, calcination at 500℃ for 1 to 10 hours, then calcination at 850 to 1100℃ for 6 to 30 hours, and finally cooling with the furnace. During the furnace cooling process, the relative humidity of the environment is ≤30%. During the crushing and sieving processes, the relative humidity of the environment is ≤20%.

[0055] (3) Mix type I particles and type II particles in a certain ratio to obtain sodium-electric layered oxide cathode material.

[0056] In this step, when mixing according to the ratio, a dry mixing method is used, and the relative humidity of the environment is ≤20%.

[0057] By controlling the relative humidity of the environment in steps (2) and (3) above, it is helpful to reduce the moisture content in Type I particles, Type II particles, and sodium-ion layered oxide cathode materials, and to prevent water molecules from embedding between the material layers and causing damage to the material structure. In addition, the dry mixing process is simple and fully compatible with existing cathode material production processes.

[0058] In a third aspect, the present invention provides a positive electrode sheet comprising the sodium-ion layered oxide positive electrode material described in the first aspect.

[0059] In a fourth aspect, the present invention provides a battery comprising the positive electrode sheet described in the third aspect.

[0060] In a fifth aspect, the present invention provides an electrical device comprising the battery described in the fourth aspect.

[0061] The present invention will now be described in detail through examples and comparative examples.

[0062] Example 1

[0063] (1) According to the molar ratio of elements in type I particles and type II particles, nano source, nickel source, manganese source and M source are used to obtain type I raw materials and type II raw materials respectively;

[0064] In this step, the sodium source in type I particles is Na2CO3, the nickel source is NiO, the manganese source is Mn2O3, and the M source is Fe2O3. The molar ratio of the elements in type I particles is: Na:Ni:Mn:Fe = 3:1:1:1. After use, the particles are mixed evenly in a high-speed mixer to obtain type I raw materials.

[0065] In this step, the sodium source in the type II particles is Na2CO3, the nickel source is NiO, the manganese source is Mn2O3, and the M source is Fe2O3. The molar ratio of the elements in the type II particles is: Na:Ni:Mn:Fe = 0.80:0.20:0.50:0.30. After use, the particles are mixed evenly in a high-speed mixer to obtain type II raw materials.

[0066] (2) The raw materials of type I and type II are sintered, crushed and sieved in stages to obtain type I particles and type II particles respectively;

[0067] In this step, the conditions for segmented sintering of the Type I raw material are as follows: first, calcination at 500℃ for 4 hours, then calcination at 950℃ for 24 hours, followed by furnace cooling with a relative humidity of 20% during the furnace cooling process; during the crushing and sieving processes, the relative humidity is 15%; the final product is NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3 Type I particles of O2;

[0068] In this step, the conditions for segmented sintering of the Class II raw material are as follows: first calcination at 500℃ for 4 hours, then calcination at 950℃ for 24 hours, and finally furnace cooling, with a relative humidity of 20% during the furnace cooling process; the relative humidity during crushing and sieving is 15%; the final product is Na 0.80 Ni 0.20 Mn 0.50 Fe 0.30 Type II particles of O2.

[0069] (3) Mix type I particles and type II particles in a certain ratio to obtain sodium-electric layered oxide cathode material.

[0070] In this step, the mass ratio of Class I particles to Class II particles is 750:250; when mixing according to the ratio, the particles are mixed evenly using a VC high-speed mixer, and the relative humidity of the environment is controlled at 20%.

[0071] Example 2

[0072] The only difference from Example 1 is that in step (3) of Example 2: the mass ratio of type I particles to type II particles is 600:400; when mixing according to the ratio, the particles are mixed evenly by a VC high-speed mixer, and the relative humidity of the environment is controlled at 15%.

[0073] Example 3

[0074] The only difference from Example 1 is that in step (3) of Example 3: the mass ratio of type I particles to type II particles is 900:100; when mixing according to the ratio, the particles are mixed evenly by a VC high-speed mixer, and the relative humidity of the environment is controlled at 15%.

[0075] Example 4

[0076] The only difference from Example 1 is that in steps (1) and (2) of Example 4, the raw materials used to prepare type I particles are Na2CO3 and Ni. 1 / 3 Mn 1 / 3 Fe 1 / 3 (OH)2, the raw materials used to prepare type II particles are Na2CO3 and Ni 0.2 Mn 0.5 Fe 0.3 (OH)2; the chemical formulas of Class I and Class II particles are the same as those in Example 1.

[0077] Example 5

[0078] The only difference from Example 1 is that in steps (1) and (2) of Example 5: the raw materials used to prepare type I particles are NaHCO3, Ni(OH)2, MnCO3, and FeCl3, and the raw materials used to prepare type II particles are NaHCO3, Ni(OH)2, MnCO3, and FeCl3; the chemical formulas of type I particles and type II particles are the same as those in Example 1.

[0079] Example 6

[0080] (1) According to the molar ratio of elements in type I particles and type II particles, nano source, nickel source, manganese source and M source are used to obtain type I raw materials and type II raw materials respectively;

[0081] In this step, the sodium source in type I particles is Na2CO3, the nickel source is NiO, the manganese source is Mn2O3, and the M source is CuO and TiO2. The molar ratio of the elements in type I particles is: Na:Ni:Mn:Cu:Ti = 0.95:0.40:0.40:0.10:0.10. After use, the particles are mixed evenly in a high-speed mixer to obtain type I raw materials.

[0082] In this step, the sodium source in the type II particles is Na2CO3, the nickel source is NiO, the manganese source is Mn2O3, the M source is LiOH, and MgCO3. The molar ratio of the elements in the type II particles is: Na:Ni:Mn:Li:Mg = 0.65:0.20:0.60:0.10:0.10. After use, the particles are mixed evenly in a high-speed mixer to obtain type II raw materials.

[0083] (2) The raw materials of type I and type II are sintered, crushed and sieved in stages to obtain type I particles and type II particles respectively;

[0084] In this step, the conditions for segmented sintering of the type I raw material are as follows: first calcination at 500℃ for 4 hours, then calcination at 1000℃ for 24 hours, and finally furnace cooling, with a relative humidity of 20% during the furnace cooling process; the relative humidity during crushing and sieving is 30%; the final product is Na 0.95 Ni 0.40 Mn 0.40 Cu 0.10 Ti 0.10 Type I particles of O2;

[0085] In this step, the conditions for segmented sintering of the Class II raw material are as follows: first calcination at 500℃ for 4 hours, then calcination at 950℃ for 24 hours, and finally furnace cooling, with a relative humidity of 20% during the furnace cooling process; the relative humidity during crushing and sieving is 15%; the final product is Na 0.65 Ni 0.20 Mn 0.60 Li 0.10 Mg 0.10 Type II particles of O2.

[0086] (3) Mix type I particles and type II particles in a certain ratio to obtain sodium-electric layered oxide cathode material.

[0087] In this step, the mass ratio of Class I particles to Class II particles is 750:250; when mixing according to the ratio, the particles are mixed evenly using a VC high-speed mixer, and the relative humidity of the environment is controlled at 20%.

[0088] Comparative Example 1

[0089] The sodium-ion cathode material of Comparative Example 1 contains only the type I particles prepared in Example 1.

[0090] Comparative Example 2

[0091] The sodium-ion cathode material of Comparative Example 2 contains only the type II particles prepared in Example 1.

[0092] Comparative Example 3

[0093] The only difference from Example 1 is that in step (3) of Comparative Example 3, the mass ratio of type I particles to type II particles is 950:50.

[0094] Comparative Example 4

[0095] The only difference from Example 1 is that the material selection principles followed in steps (1) and (2) of Comparative Example 4, and the materials obtained, both meet the following requirements: the chemical formula of type I particles is Na. 0.83 Ni 1 / 3 Mn 1 / 3 Fe 1 / 3 O2.

[0096] Comparative Example 5

[0097] The only difference from Example 1 is that the material selection principles followed in steps (1) and (2) of Comparative Example 5, and the materials obtained, both conform to the following: the chemical formula of the Class II particles is NaNi. 0.2 Mn 0.5 Fe 0.3 O2.

[0098] Comparative Example 6

[0099] The only difference from Example 1 is that the material selection principles followed in steps (1) and (2) of Comparative Example 6 and the materials obtained both meet the following requirements: the chemical formula of the type I particles is NaNi. 0.2 Mn 0.5 Fe 0.3 O2.

[0100] The present invention employs the following methods to perform physicochemical characterization tests on the sodium-electric layered oxide cathode materials, type I particles or type II particles prepared in Examples 1-6, and the sodium-electric cathode materials, type I particles or type II particles prepared in Comparative Examples 1-6 (hereinafter referred to as the test samples) and obtain the corresponding test results.

[0101] (1) ICP test: The sample was dissolved in hydrochloric acid and prepared into a solution of a certain concentration. The content and chemical composition of the metal elements in the sample were tested by inductively coupled plasma atomic emission spectrometry. The results are shown in Table 1.

[0102] Table 1 ICP Test Results

[0103] Source of test sample x1 x2 b1 b2 w Example 1 1.0 0.80 1 / 3 0.50 75％ Example 2 1.0 0.80 1 / 3 0.50 60％ Example 3 1.0 0.80 1 / 3 0.50 90％ Example 4 1.0 0.80 1 / 3 0.50 75％ Example 5 1.0 0.80 1 / 3 0.50 75％ Example 6 0.95 0.65 0.4 0.6 75％ Comparative Example 1 1.0 — 1 / 3 — 100％ Comparative Example 2 — 0.80 — 0.50 0％ Comparative Example 3 1.0 0.80 1 / 3 0.50 95％ Comparative Example 4 0.83 0.80 1 / 3 0.50 75％ Comparative Example 5 1.0 1.0 1 / 3 0.50 75％ Comparative Example 6 1.0 0.80 0.50 0.50 75％

[0104] (2) XRD testing: A Cu-Kα target was used, with an emission wavelength λ = 0.154 nm. The scanning voltage was 40 kV, and the current was 40 mA. A step-scan method was used, with a scanning range of 10° to 90°. The results are shown in Tables 2 and 3. The XRD pattern of the sodium-ion layered oxide cathode material prepared in Example 1 is shown below. Figure 1 As shown, it has excellent crystallinity, with two diffraction peaks in the range of 2θ = 15° to 18°, where γ and φ correspond to the (003) crystal plane of type I particles and the (002) crystal plane of type II particles, respectively.

[0105] Table 2 XRD Test Results - 1

[0106]

[0107] Table 3 XRD Test Results - 2

[0108]

[0109]

[0110] (3) Electrochemical performance testing and elemental valence state testing after discharge

[0111] The specific preparation method of sodium secondary batteries and their positive electrode sheets: The sample is mixed with acetylene black, carbon nanotubes, and polyvinylidene fluoride in a mass ratio of 90:5:1:4, and an appropriate amount of N-methylpyrrolidone is added as a dispersant. The mixture is then ground into a slurry. The slurry is then uniformly coated onto one side of an aluminum foil and vacuum dried at 120℃ for 10 hours. The dried electrode sheet is then rolled using a roller press, and the aluminum foil is cut into circular electrode sheets with a diameter of 1.3 cm using a slicing machine. The loading of the active material is controlled at 10 mg·cm³. -2 The half-cell was assembled in an argon atmosphere glove box, with a water partial pressure ≤0.1ppm and an oxygen partial pressure ≤0.1ppm. A CR2032 type coin cell was assembled using metallic sodium as the counter electrode and 1M NaPF6 (EC / DEC, volume ratio 1:1) solution as the electrolyte.

[0112] (3.1) Electrode potential test method under different sodium ion removal amounts: Coin cells containing type I or type II particles were charged at room temperature using a constant current charge-discharge mode. Based on the charge specific capacity C = n·26800 / Mr, where Mr is the molar mass of type I or type II particles, the C values ​​for different charge specific capacities were obtained using n = 0.1, 0.3, and 0.5 as examples. The cells were charged at a constant current density of 15 mA / g to the above different specific capacities, and the corresponding cutoff potentials U were recorded. The results are shown in Table 4.

[0113] Table 4 Electrode Potential Test Results

[0114]

[0115]

[0116] (3.2) Sodium-ion battery capacity and cycle testing method: The coin cells were charged and discharged at room temperature using a constant current charge-discharge mode. First, they were charged at a constant current density of 15 mA / g to 4.2V (vs. Na / Na). + Then, it was discharged at a constant current density of 15 mA / g to 1.5V (vs. Na / Na). + The specific capacity and first-cycle coulombic efficiency of the material were obtained. Cyclic testing involved 100 charge-discharge cycles at room temperature using a constant current charge-discharge mode, and the discharge specific energy of the material was recorded. The voltage range was 1.5V–4.2V, and the current density was 50 m³ / g. -1 The test results are shown in Table 5 and Appendix. Figures 2-4 .

[0117] Table 5. Battery capacity and cycle performance test results

[0118]

[0119] (3.3) XPS test: The elemental composition of the material surface after discharge (3.2) was analyzed by measuring the value and change of photoelectron kinetic energy / binding energy. The obtained data were fitted using Casa XPS software to analyze the chemical valence state of the material and the proportion of elements with different valence states. The results are shown in Table 6.

[0120] Table 6. Results of Mn element valence state test

[0121]

[0122]

[0123] Referring to the test results of Comparative Examples 4-6, when the sodium-manganese ratio in Type I and Type II particles changed, the diffraction peaks of the samples at 2θ of 15°–18° changed significantly (Table 1-3), indicating the appearance of impurity phases due to structural distortion in the material. Due to the change in the sample structure, the cutoff voltage changed significantly during charging for different sodium ion extraction amounts. At the same sodium ion extraction amount (n≤0.5), the potential U of Type II particles increased. Ⅱ <Potential U of Class I particles Ⅰ (Table 4), or the case where the valence state of Mn in the sample is lower than 3.5 at the end of the high-depth discharge (Table 6). The former shows that the hysteresis of type II particles compared with type I particles disappears when sodium ions are removed, making it difficult to achieve the synergistic effect of the two types of particles under high voltage. The latter shows that the material structure stability deteriorates significantly and exhibits obvious cycle energy decay during high-depth discharge (Table 5).

[0124] Referring to the test results of Comparative Examples 1-3, when the ratio of Type I particles and Type II particles in the sodium electrode material changes, When key control parameters exceed the specified range, the sodium electrode cathode material lacks the synergistic effect between the two types of particles, resulting in a significant decrease in the first-cycle coulombic efficiency and a sharp deterioration in long-cycle performance over a wide voltage range of 1.5V to 4.2V (Table 5).

[0125] The sodium-ion layered oxide cathode material provided by this invention achieves structural and electrochemical performance regulation and optimization by adjusting the sodium and manganese content in type I and type II particles and the ratio of the two types of particles, thereby improving the synergistic effect of the two under different voltage conditions. This ensures that the sodium-ion layered oxide cathode material with high energy density has high structural stability throughout the entire process of deep discharge, giving it high energy density, high discharge stability over a wide voltage range (1.5-4.2V), and long cycle life.

[0126] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A sodium-ion battery layered oxide cathode material, characterized in that, The sodium-electric layered oxide cathode material comprises a homogeneous mixture of type I particles and type II particles, wherein the phase structures of type I particles and type II particles are different; in the X-ray powder diffraction pattern obtained using Cu-Kα rays, the homogeneous mixture exhibits at least the following diffraction peak P corresponding to the (003) crystal plane at a 2θ of 15°~18°: γ and the diffraction peak P corresponding to the (002) crystal plane φ Diffraction peak P γ The diffraction angle is γ and the peak intensity is I. γ Diffraction peak P φ The diffraction angle is φ and the peak intensity is I. φ , φ<γ, ; In their respective X-ray powder diffraction patterns obtained using Cu-Kα rays, at 2θ of 15°–18°: The type I particles exhibit a diffraction peak P corresponding to the (003) crystal plane. δ Diffraction peak P δ The diffraction angle is δ and the peak intensity is I. δ ; The type II particles at least have a diffraction peak P corresponding to the (002) crystal plane. ε Diffraction peak P ε The diffraction angle is ε and the peak intensity is I. ε ; ε<δ, w is the mass percentage of type I particles in the homogeneous mixture; When each mole of the aforementioned type I particles releases n moles of sodium ions based on metallic sodium, its potential is U. Ⅰ When each mole of the aforementioned type II particle releases n moles of sodium ions based on metallic sodium, its potential is U. Ⅱ For any n ≤ 0.5, satisfying U Ⅰ <U Ⅱ ; In a sodium-ion battery containing the aforementioned sodium-ion layered oxide cathode material, the sodium-ion battery discharges to U 放电截止 At that time, the valence state of Mn in the type I particles is V. Ⅰ The valence state of Mn in the type II particles is V. Ⅱ 1.5V≤U 放电截止 When ≤2V, 3.5<V is satisfied. Ⅱ <V Ⅰ <4.0; The general chemical formula of the type I particles is Na. x1 Ni a1 Mn b1 M y1 O2, the general chemical formula of the type II particles is Na x2 Ni a2 Mn b2 M y2 O2, where: 0.6 <x2<0.9<x1<1.1,0.3<b1<b2<1,x1·w+x2·(1-w)> 0.9; The M in the general chemical formula of the Class I particles and the general chemical formula of the Class II particles are independently taken from one or more of Fe, Cu, Li, Mg, Al, Ca, Zn, Ti, Zr, Cr, Sr, Ba, Nb, Mo and W, respectively, and a1+b1+y1=1, a2+b2+y2=1.

2. The method for preparing the sodium-ion layered oxide cathode material according to claim 1, characterized in that, Including steps: Sodium source, nickel source, manganese source and M source are used according to the molar ratio of elements in type I particles and type II particles to obtain type I raw materials and type II raw materials respectively; The raw materials of type I and type II are sintered, crushed, and sieved in stages to obtain type I particles and type II particles respectively; Type I particles and Type II particles were mixed in a certain ratio to obtain sodium-ion layered oxide cathode material.

3. The method for preparing sodium-ion battery layered oxide cathode material according to claim 2, characterized in that, The sodium source includes at least one of sodium carbonate and sodium bicarbonate; The nickel source, manganese source, and M source each include at least one of oxides, hydroxides, chlorides, and carbonates containing the corresponding metal elements; The conditions for segmented sintering are as follows: first, calcination at 500℃ for 1~10h, then calcination at 850~1100℃ for 6~30h, and finally, cooling in the furnace, with the relative humidity of the environment ≤30% during the furnace cooling process; During the crushing, sieving, and mixing of Class I and Class II particles in proportion, the relative humidity of the environment is ≤20%.

4. A positive electrode sheet, characterized in that, The positive electrode sheet contains the sodium-electric layered oxide positive electrode material as described in claim 1.

5. A battery, characterized in that, The battery contains the positive electrode sheet as described in claim 4.

6. An electrical appliance, characterized in that, The electrical device contains the battery as described in claim 5.

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