A layered oxide material, its preparation method and application

Abstract

The present invention provides a layered oxide material, a preparation method and an application thereof. The chemical structural formula of the oxide material is: Na 1‑x M 1‑x Ti x O2, wherein M is at least one of Ni, Cu, Zn, Co, Mn, Fe, Cr, V. The material has an O3-type layered structure, in which M and Ti respectively form octahedrons with the six nearest oxygen atoms, and the octahedrons are connected by sharing edges to form a layered distribution. Na is located at the octahedral interstitial position between the layers; and in the primary particles, the concentration of Ti decreases gradually from the surface to the inside; wherein, 0 < x ≤ 0.3. When used as an electrode active material, it can maintain the capacity of the electrochemical energy storage device while effectively improving the cycle stability of the electrochemical energy storage device.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode material preparation, and more specifically, to a layered oxide material, a preparation method thereof, and an application thereof. Background Art

[0002] Currently, developing high-performance, long-life, and low-cost cathode materials is a key task for the development of sodium-ion batteries. Among many candidate materials, layered oxides have the advantages of small molecular weight, high specific capacity, good electrochemical activity, and simple preparation process, and are one of the most promising cathode materials. Among many reported layered oxide cathode materials, classic ternary materials have shown outstanding advantages. Theoretically, such materials can provide an initial capacity of greater than 230 mAh / g, an actual reversible specific capacity of > 130 mAh / g (4.1 - 2.0 V), and at the same time have a relatively high working voltage (> 3.1), wide raw material distribution, and low cost, showing broad application prospects. However, although such materials exhibit a high initial reversible specific capacity, their cycle stability is not ideal. In addition, there are also problems such as strong hygroscopicity and instability in air, which limit their practical applications.

[0003] Through research, the capacity decay of such materials may stem from two aspects: one is the complex phase transformation accompanied by the charge and discharge process of the material, which induces internal stress, structural distortion, and even cracks, hindering the transmission and reversible insertion / extraction of sodium ions; the other is the side reaction between the surface of the electrode material and the electrolyte at high voltage, resulting in problems such as the dissolution of transition metal elements (such as Ni, Mn, etc.), structural decay, and negative electrode dendrites. These disadvantages are particularly prominent in high-nickel high-capacity layered materials and are problems that must be overcome on the road to achieving high energy density in sodium-ion batteries.

[0004] Existing reports show that using metal elements for bulk doping can, to a certain extent, improve the cycle stability of electrode materials, but it often requires sacrificing a certain amount of capacity as a price. In addition, surface coating is one of the common methods to inhibit surface side reactions and the dissolution of transition metal elements, and the problem is that there is an obvious phase interface between the coating layer and the bulk phase, and the uneven stress change during the sodium insertion / extraction process will lead to problems such as cracks and coating layer separation. Summary of the Invention

[0005] Based on the above technical problems existing in the prior art, one of the objectives of the present invention is to provide a layered oxide material, and the chemical structural formula of the oxide material is: Na 1-x M 1-x Ti xO2, where M is at least one of Ni, Cu, Zn, Co, Mn, Fe, Cr, V, and the material has an O3-type layered structure. In this structure, M and Ti respectively form octahedrons with the six nearest oxygen atoms, and these octahedrons are connected by sharing edges to form a layered distribution. Na is located at the octahedral interstitial position between the layers; moreover, in the primary particles, the concentration of Ti decreases in a gradient manner from the surface to the interior; where 0 < x ≤ 0.3.

[0006] In some embodiments, M is Ni, Fe, Mn. Among them, Ni is in the +2 valence state, Fe is in the +3 valence state, and Mn is in the +4 valence state; Ni, Fe, Mn, and Ti respectively form NO6 (N = Ni, Fe, Mn, Ti) octahedral structures with the six nearest oxygen atoms. The NO6 octahedrons are connected by sharing edges to form a transition metal layer, and the alkali metal Na+ is located in the octahedral interstitial positions between the transition metal layers to form an alkali metal layer, corresponding to the space group R-3m.

[0007] The second object of the present invention is to provide a preparation method of the layered oxide material in any of the above embodiments. This method includes the following steps:

[0008] Mix a NaMO2 layered oxide with an O3-phase structure and a titanium source evenly, and then calcine at a temperature of 700 - 1000 °C to obtain the layered oxide material; where the titanium source is rutile-type and / or anatase-type TiO2 particles; and M is at least one of Ni, Cu, Zn, Co, Mn, Fe, Cr, V.

[0009] In some embodiments, the particle size of the TiO2 particles is 20 - 50 nm.

[0010] In some embodiments, the molar ratio of the NaMO2 layered oxide to the titanium source is y:z, where 0.7 < y / z < 1.0, 0 < z ≤ 0.3, and y + z = 1.

[0011] In some embodiments, the calcination atmosphere is an air atmosphere or an oxygen atmosphere.

[0012] In some embodiments, the calcination time is 1 - 24 hours.

[0013] In some embodiments, this method includes the following steps:

[0014] Mix the NaMO2 layered oxide and the titanium source, add an organic solvent, stir evenly to form a slurry, then dry, and calcine at a temperature of 700 - 1000 °C to obtain the layered oxide material; where the organic solvent is at least one of ethanol, isopropanol, and N-methylpyrrolidone.

[0015] In some embodiments, after mixing the NaMO2 layered oxide and the titanium source, the organic solvent is added, and magnetic stirring is carried out for 5 - 10 h, and then it is evaporated to dryness at 80 - 120 °C to obtain a precursor powder; preferably, the organic solvent is N-methylpyrrolidone.

[0016] In some embodiments, the NaMO2 layered oxide can be directly commercially available or prepared by a solid-phase sintering method; the solid-phase sintering method includes the following steps:

[0017] The raw materials are proportioned according to the stoichiometric ratio, mixed, and ethanol or acetone is used as the ball-milling medium, and ball-milling is carried out for 4 - 12 h to prepare a mixed slurry, which is dried at 60 - 80 °C to obtain a precursor powder; then it is put into an alumina crucible, heated to 800 - 1000 °C in a muffle furnace, and held for 6 - 12 h. After sintering is completed, it is cooled naturally to obtain;

[0018] The raw materials are a mixture of an M source and a sodium source, the M source is at least one of an oxide, hydroxide, carbonate, acetate, sulfate, nitrate of M; the sodium source is at least one of an oxide, hydroxide, carbonate, acetate, sulfate, nitrate of sodium; wherein the sodium source is in excess by 5 - 10%.

[0019] A third object of the present invention is to provide a positive electrode active material, which includes the layered oxide material of any of the above embodiments and / or the layered oxide material obtained by the preparation method of any of the above embodiments.

[0020] A fourth object of the present invention is to provide a positive electrode material, which includes the above positive electrode active material.

[0021] A fifth object of the present invention is to provide a positive electrode, which includes the above positive electrode material.

[0022] A sixth object of the present invention is to provide an electrochemical energy storage device, which includes the above positive electrode.

[0023] In some embodiments, the electrochemical energy storage device includes, but is not limited to, sodium ion batteries, sodium ion capacitors, etc.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The layered oxide material provided by the present invention has an O3-type layered structure. M and Ti respectively form octahedrons with the six nearest oxygen atoms, and these octahedrons are connected by sharing edges to form a layered distribution. Na is located at the octahedral interstitial position between the layers. Moreover, in the primary particles, the concentration of Ti decreases in a gradient from the surface to the interior. The layered oxide material with this specific structure can utilize the highly stable Ti-O bond to enhance the surface structural stability of the particles, effectively inhibit the dissolution of transition metals, and does not affect the intercalation and deintercalation of Na ions; at the same time, it is beneficial to avoid the generation of heterogeneous interface stress, thereby inhibiting the attenuation of the material capacity and improving the cycle stability. When this material is applied to an electrochemical energy storage device, it can effectively improve the cycle stability of the electrochemical energy storage device while maintaining the capacity.

[0026] The preparation method of the layered oxide material provided by the present invention can achieve efficient gradient doping of Ti elements into the NaMO2 layered oxide, and the process is simple, the cost is low, and it is suitable for industrial applications. Description of the Drawings

[0027] Figure 1 XRD pattern of the material obtained in Example 1;

[0028] Figure 2 Charge-discharge curve of the material obtained in Example 1 in a sodium-ion battery;

[0029] Figure 3 Cycle performance graph of the material obtained in Example 1 in a sodium-ion battery;

[0030] Figure 4 XRD pattern of the material obtained in Example 2;

[0031] Figure 5 Charge-discharge curve of the material obtained in Example 2 in a sodium-ion battery;

[0032] Figure 6 Cycle performance graph of the material obtained in Example 2 in a sodium-ion battery;

[0033] Figure 7 XRD pattern of the material obtained in Comparative Example 1;

[0034] Figure 8 XRD pattern of the material obtained in Comparative Example 2;

[0035] Figure 9 XRD pattern of the material obtained in Comparative Example 3;

[0036] Figure 10 Charge-discharge curve of the material obtained in Comparative Example 3 in a sodium-ion battery;

[0037] Figure 11Cycling performance comparison chart of the materials obtained in Comparative Example 3 and Example 2 in a sodium-ion battery. Detailed implementation mode

[0038] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific implementations disclosed below.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention.

[0040] Example 1

[0041] This example provides a preparation method of O3-type NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, which specifically includes the following steps:

[0042] Using Na2CO3, NiO, Fe2O3, and MnO2 as raw materials, proportioned according to a molar ratio of 3:2:1:2, with Na2CO3 being 5% in excess, using an appropriate amount of ethanol as the ball-milling medium, ball-milling for 6 h to make a slurry, and then drying at 80 °C to obtain a precursor powder; subsequently, the precursor powder is stamped into a thin sheet under 20 MPa, placed in an alumina crucible, heated to 900 °C in a muffle furnace, kept warm in an air atmosphere for 10 h, and cooled naturally to obtain. The XRD pattern and SEM performance diagram of the obtained material are as Figure 1 shown, and the diffraction peaks indicate that the obtained material is a pure-phase O3-type material.

[0043] Using the above-prepared NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material as the positive electrode active material of a sodium-ion secondary battery to make a positive electrode plate, and the specific method is as follows: Mix the prepared NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 powder with acetylene black and polyvinylidene fluoride (PVDF, binder) according to a mass ratio of 8:1:1, drop an appropriate amount of N-methylpyrrolidone (NMP) solution as a dispersant, and grind for 30 minutes to make a slurry; subsequently, coat the slurry on an aluminum foil current collector, dry it in vacuum at 120 °C for 8 h, and transfer it to an Ar atmosphere glove box for standby.

[0044] Assemble the half-cell in an Ar atmosphere glove box: Use metallic sodium as the counter electrode and a solution of NaClO4 / ethylene carbonate (EC:DMC:DEC = 1:1:1) as the electrolyte to assemble a CR2016 type button cell.

[0045] Use the constant current charge-discharge mode to conduct charge-discharge tests at different current densities. Set the charge cut-off voltage to 4.1 V and the discharge cut-off voltage to 2.0 V. The charge-discharge curves at different rates are as Figure 2 shown. The discharge specific capacities at 0.1 C (1 C = 120 mA / g), 1 C, and 5 C are 133, 108, and 79 mAh / g respectively. The cycling performance at 1 C is as Figure 3 shown. The initial capacity is 100 mAh / g, and the capacity retention rate after 100 cycles is 80%.

[0046] Example 2

[0047] This example provides an O3-type Na 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Ti 0.1 O2, and its preparation method includes the following steps:

[0048] Disperse the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 powder prepared in Example 1 and nano-TiO2 in a molar ratio of 0.9:0.1 in N-methylpyrrolidone (NMP) (the solid-liquid ratio is 5 g:10 mL), stir for 6 h, then evaporate to dryness at 120 °C to obtain the precursor powder; then press the precursor powder into a thin sheet under 20 MPa and put it into an alumina crucible, heat it to 900 °C in a muffle furnace, keep it warm in an air atmosphere for 8 h, and cool it naturally to obtain the product. The XRD pattern of the obtained material is as Figure 4 shown. The diffraction peaks indicate that the obtained material is a pure-phase O3-type material.

[0049] Use the method of Example 1 to use the prepared Na 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Ti 0.1 O2 material as the positive electrode active material of a sodium-ion secondary battery, fabricate a positive electrode plate and assemble a sodium-ion half-cell.

[0050] Use the constant current charge-discharge mode to conduct charge-discharge tests at different current densities. Set the charge cut-off voltage to 4.1 V and the discharge cut-off voltage to 2.0 V. The charge-discharge curves at different rates are as Figure 6As shown, its discharge specific capacities at 0.1C, 1C, and 5C are 135, 122, and 100 mAh / g respectively. The cycling performance at 1C is as Figure 6 shown. The initial capacity is 124 mAh / g, and the capacity is 105 mAh / g after 100 cycles, with a capacity retention rate of 85%; the cycling performance at 2C is as Figure 11 shown. The initial capacity is 120 mAh / g, and the capacity is 106 mAh / g after 200 cycles, with a capacity retention rate of 88%.

[0051] Comparative Example 1

[0052] The specific preparation method and raw material ratio of this comparative example are basically the same as those of Example 2, except that the calcination condition is changed to heat preservation at 600 °C for 2 h. The XRD pattern of the obtained material is shown in Figure 7 . The diffraction peaks indicate that the main body of the material obtained in this example is the O3 phase, but there are a small number of weak TiO2 characteristic peaks, indicating that Ti can enter the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 surface lattice under this condition, but the reaction is not complete, and part of the TiO2 is coated on the surface of the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 particles, indicating that the calcination temperature and time have a key influence on the doping depth and concentration distribution of Ti elements.

[0053] Comparative Example 2

[0054] The specific preparation method and raw material ratio of this comparative example are basically the same as those of Example 2, except that the calcination condition is changed to heat preservation at 300 °C for 2 h. The XRD pattern of the obtained material is shown in Figure 8 . Its main body is the diffraction peak of the O3 phase, and there are relatively strong TiO2 phase characteristic peaks, indicating that TiO2 does not react with NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 under this condition, further indicating that the calcination temperature and time have a key influence on the doping depth and concentration distribution of Ti elements.

[0055] Comparative Example 3

[0056] The preparation method of this comparative example is basically the same as that of Example 2, except for the preparation process of the precursor. That is, using Na2CO3, NiO, Fe2O3, MnO2, and TiO2 as raw materials, proportioning according to a molar ratio of 9:6:3:6:2, with Na2CO3 being 5% in excess, using an appropriate amount of volatile organic solvents such as ethanol as the ball-milling medium, ball-milling for 6 h to make a slurry, and then drying at 80 °C to obtain the precursor powder. The chemical composition of the obtained material is also Na 0.9 Ni 0.3Fe 0.3 Mn 0.3 Ti 0.1 O2, and its XRD is as Figure 9 shown, being a pure-phase O3-type structure.

[0057] The prepared material is used as the positive electrode active material of a sodium-ion secondary battery, and a positive electrode plate is made and a sodium-ion half-cell is assembled.

[0058] Using the constant current charge-discharge mode, charge-discharge tests are carried out at different current densities. The charge cut-off voltage is set to 4.1 V, and the discharge cut-off voltage is set to 2.0 V. The charge-discharge curves at different rates are as Figure 10 shown, and its discharge specific capacities at 0.1C, 1C, and 5C are 132, 112, and 90 mAh / g respectively. The cycling performance at 2C is as Figure 11 shown, with an initial capacity of 113 mAh / g, a capacity of 92 mAh / g after 200 cycles, and a capacity retention rate of 81%.

[0059] It can be seen that the layered oxide material with a specific structure provided by the present invention has obvious advantages in terms of rate compared with the materials doped by other methods. In addition, from Figure 11 it can be known that the gradient doping achieved by the method of the present invention can improve the rate performance and cycling stability under high-rate conditions of the material by improving the surface stability of the electrode-electrolyte and reducing the surface residual alkali at the same time, fully demonstrating the advantages of the gradient doping method of the present invention.

[0060] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0061] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A method for preparing a layered oxide material, characterized in that, The chemical structural formula of the oxide material is: Na 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Ti 0.1 O2, where the material has an O3-type layered structure. Among them, Ni is +2 valence, Fe is +3 valence, Mn is +4 valence. Ni, Fe, Mn, and Ti respectively form octahedrons with the six nearest oxygen atoms. The octahedrons are connected by sharing edges to form a layered distribution. Na is located at the octahedral interstitial position between the layers; and in the primary particles, the concentration of Ti decreases in a gradient from the surface to the interior; The preparation of the layered oxide material comprises the following steps: Mix the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 layered oxide and a titanium source in a molar ratio of 0.9:0.1, ball-mill and mix them evenly, then dry them, and calcine them at a temperature of 700 - 1000 °C in an air atmosphere or an oxygen atmosphere for 8 - 24 h; after the calcination is completed, let it cool naturally to obtain the layered oxide material; wherein, the titanium source is rutile-type and / or anatase-type TiO2 particles.

2. The preparation method of the layered oxide material according to claim 1, characterized in that, Comprising the following steps: Mix the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 layered oxide with a titanium source, add an organic solvent, ball-mill evenly to form a slurry, then dry it, and calcine it at a temperature of 700-1000 °C to obtain the layered oxide material; wherein, the organic solvent is at least one of ethanol, isopropanol, and N-methylpyrrolidone.

3. A layered oxide material, characterized in that, Obtained by the preparation method according to any one of claims 1-2.

4. A cathode active material, characterized in that, Comprising the layered oxide material according to claim 3.

5. A cathode material, characterized in that, Comprising the cathode active material according to claim 4.

6. A cathode, characterized in that it comprises the cathode material according to claim 5.

7. An electrochemical energy storage device, characterized in that, Comprising the cathode according to claim 6.

Images