A sodium-ion battery layered oxide cathode material and a preparation method and application thereof

Abstract

The application provides a sodium ion battery layered oxide positive electrode material and a preparation method and application thereof. The sodium ion battery layered oxide positive electrode material is a P-type structure material, and metal elements in the sodium ion positive electrode material, except sodium, include chromium and tantalum. The positive electrode material provided by the application has a P2 configuration, widens the interplanar spacing of a sodium dichromate layered oxide, effectively avoids the complex phase transition problem of sodium dichromate used as a positive electrode material of a sodium ion battery, the introduction of tantalum ions solves the low coulomb efficiency problem caused by the decrease of sodium ion content due to the configuration design, and helps electronic rearrangement, realizes the disordered arrangement of sodium / vacancies in the material, and improves the rate, capacity and cycle performance of the positive electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and relates to a layered oxide positive electrode material of a sodium ion battery and a preparation method and application thereof. BACKGROUND

[0002] Sodium ion batteries have developed rapidly in recent years and are expected to complement lithium ion batteries. Sodium resources are abundant and evenly distributed globally, which is of great significance to the realization of large-scale energy storage. However, the ionic radius of sodium ions is slightly larger than that of lithium ions, and the complex phase transition caused by the deintercalation of sodium ions in the positive electrode material will affect the battery performance. Therefore, it is still a challenge to develop suitable sodium ion battery positive electrode materials to realize high-stability sodium ion batteries.

[0003] Layered oxides have high specific capacity and good rate performance, and have become a widely studied positive electrode material for sodium ion batteries. Layered oxides can be divided into O-type and P-type, such as O3, P2, P3 and other structure materials.

[0004] In O-type layered oxide materials, sodium ions occupy octahedral sites, so the theoretical specific capacity performance of sodium ion battery positive electrodes using such materials is high. For example, CN113292113A discloses a kind of sodium ion battery O3 phase layered oxide positive electrode material and a preparation method thereof. The preparation method comprises: dissolving transition metal salt and soluble sodium salt in deionized water to obtain a mixed salt solution; the mixed salt solution is sprayed and pyrolyzed to obtain a sodium-containing oxide precursor; the sodium-containing oxide precursor is pressed into a sheet and then subjected to high-temperature solid-phase sintering to obtain an O3 phase layered oxide positive electrode material. However, due to the high ion migration barrier of O3 phase structure layered oxide material, the battery positive electrode produced faces the problem of rapid capacity decay during charging and discharging.

[0005] O3-type NaCrO2 layered oxide material has a high theoretical specific capacity, so it has attracted much attention from researchers. Studies have found that when NaCrO2 is used as a positive electrode for sodium ion batteries, the material collapses due to complex phase changes during charging and discharging, which is manifested in poor stability of the positive electrode, seriously affecting the practical application of such materials. Although surface coating, improving the microstructure and element substitution can modify NaCrO2, it is still impossible to improve the capacity of NaCrO2 layered oxide positive electrode material while maintaining the structural stability of the material.

[0006] The P-type structured layered oxide material has an open sodium ion transmission channel, which helps to maintain the stability of the material structure. Therefore, the P-type structured layered oxide material has significant application prospects in the field of sodium ion batteries. For example, CN111710855A discloses a P-phase aluminum-containing layered oxide positive electrode material, a preparation method, and a sodium ion battery. The P-phase aluminum-containing layered oxide positive electrode material is a P-phase layered structure with a general chemical formula of Na x Al y M 1-y O2, 0<x<1, 0.1<y<1; M is one or more transition metals selected from Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn. It is worth noting that in this material design, to maintain structural stability, the stoichiometric ratio of the material adopts a low sodium strategy, resulting in a low Coulombic efficiency for this type of material.

[0007] Therefore, how to provide a sodium ion battery layered oxide positive electrode material with high stability, high rate performance, and high coulombic efficiency is a technical problem that needs to be solved urgently. Summary of the Invention

[0008] The object of the present invention is to provide a sodium ion battery layered oxide positive electrode material and its preparation method and application. The preparation of the layered oxide positive electrode material provided by the present invention, the sodium ion positive electrode material has the characteristics of a P2 type structure, and the P2 configuration positive electrode material is obtained by rationally designing the stoichiometric ratio of sodium ions and transition metals, widening the interplanar spacing of sodium chromite layered oxide, and effectively avoiding the phase transition problem when sodium chromite is used as a sodium ion battery positive electrode material. At the same time, tantalum ions are introduced into the transition metal layer to reduce the impact of the reduced sodium ion content due to the configuration design. The Fermi energy difference between tantalum ions and chromium ions is utilized to promote the formation of disordered arrangement of sodium / vacancies in the material, thereby improving the coulombic efficiency and capacity of the positive electrode material.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a sodium ion battery layered oxide positive electrode material, wherein the sodium ion layered positive electrode material has a P-type structure, and the metal elements other than sodium in the sodium ion positive electrode material include chromium and tantalum.

[0011] The layered oxide positive electrode material provided by the application rationally designs the stoichiometric ratio of sodium ions and transition metals, regulates the material configuration by increasing the cation potential, and the increase in the cation potential means that the interaction between the transition metals and oxygen bonds is enhanced, thereby causing the decrease in the distance between transition metals and the increase in the distance between sodium layers, and finally obtaining a P-type structure positive electrode material. The optimized P-type structure has better stability and a wider sodium ion layer spacing, effectively avoiding the problem of complex phase transition of the sodium chromite positive electrode due to sodium ion deintercalation during charging and discharging, inhibiting the collapse of the structure, and improving the stability of the material. At the same time, the introduction of tantalum ions into the chromium layer replaces part of the chromium ions. Due to the large Fermi level difference between tantalum ions and chromium ions, the sodium / vacancies in the material will form a disordered arrangement, increase the free energy in the sodium ion deintercalation process, ensure a high sodium ion migration rate, further improve the rate performance of the material, and at the same time, enhance the reversibility of sodium ion deintercalation and improve the coulombic efficiency.

[0012] The sodium chromite-based sodium ion positive electrode material in the application has a P-type structure (P2 phase), and the rationally designed stoichiometric ratio of sodium ions and transition metals and the introduction of tantalum are crucial. The reason why the sodium chromite layered compound material as a positive electrode material for a sodium ion battery exhibits poor cycle stability is mainly related to the fact that the material belongs to an O3 phase. Since the ion migration barrier of the layered oxide material with an O3 phase structure is high, the rapid migration of ions is difficult, and therefore, the material faces the problem of rapid capacity decay during charging and discharging. By rationally designing the stoichiometric ratio, the O3 phase structure sodium chromite layered compound can be converted into a P-type material. The layered oxide material with a P-type structure has an open sodium ion transmission channel, can accelerate the transmission of sodium ions in the material, and has better structural stability, thereby effectively solving the problem of phase transition that easily occurs in the original positive electrode material during charging and discharging, and improving the stability of the positive electrode. If the tantalum element is not introduced, the problem of rearrangement of sodium / vacancies during the sodium ion deintercalation process of the sodium chromite layered compound as a positive electrode material for a sodium ion battery cannot be solved, which is specifically manifested in that the high-rate charging and discharging performance of the positive electrode material is low. At the same time, the capacity of the sodium chromite layered compound material without the use of tantalum elements decreases significantly with the increase of the discharge rate.

[0013] Preferably, the chemical formula of the sodium ion battery layered oxide positive electrode material is Na x Cr y Ta 1-y O2, wherein 0.6≤x≤0.75, 0.6≤x≤0.75.

[0014] In the present invention, the stoichiometric ratio of each element in the layered oxide cathode material for sodium-ion batteries directly affects the material's crystal structure and the product performance when used as a sodium-ion cathode. Different sodium contents, different transition metal element types, valence states, and compositions can all lead to layered materials with different structures, which in turn affect the electrochemical performance of the cathode material. Therefore, the x value is crucial to the formation of the P structure: if the x value is too large (x>0.75), too few sodium ions participate in charge and discharge, the cationic potential is reduced, and it is not conducive to the formation of the P2 configuration; if the x value is too small (x<0.6), the reversible capacity and initial coulombic efficiency will be too low. The y value controls the proportion of tantalum ions occupying the chromium ion layer: if the y value is too large (y>0.75, that is, 1-y is too small), the amount of tantalum ions replacing chromium ions is too small, and the interaction with chromium ions is not significant; if the y value is too small (y<0.6, that is, 1-y is too large), the amount of tantalum ions replacing chromium ions is too large, and the capacity will decrease sharply. Tantalum is introduced into the chromium ion layer as the second transition metal, replacing part of the chromium ions and playing an important role in adjusting the electron cloud arrangement. The disordered electron arrangement and the sodium / vacancy arrangement are coupled with each other to achieve a disordered sodium / vacancy arrangement, so that the material can obtain better rate performance and higher coulombic efficiency while maintaining the P2 configuration.

[0015] Preferably, the D50 of the sodium ion positive electrode material is 70 nm to 120 nm, for example, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm or 120 nm.

[0016] The particle size of the material itself affects the sodium ion intercalation and deintercalation process, thereby affecting the battery's ion migration rate and charge-discharge platform. The smaller the particle size, the shorter the intercalation and deintercalation channel, which is conducive to rapid charge and discharge. However, too small a particle size can lead to low compaction density and reduced safety.

[0017] Preferably, in the sodium ion battery layered oxide positive electrode material, sodium occupies the prismatic sites between the oxide layers.

[0018] In a second aspect, the present invention provides a method for preparing the layered oxide positive electrode material for sodium ion batteries as described in the first aspect, the preparation method comprising the following steps:

[0019] The sodium source, the chromium source and the tantalum source are wet ball-milled and sintered under a protective atmosphere to obtain the sodium ion battery layered oxide positive electrode material.

[0020] The preparation method provided by the present invention achieves uniform mixing of raw materials through simple wet ball milling, and then obtains a structurally stable layered oxide positive electrode material for sodium ion batteries through simple sintering. The preparation process is simple, operability is strong, and it is suitable for large-scale production.

[0021] Preferably, the D50 of the sodium source is 750 μm to 1000 μm, for example, 750 μm, 800 μm, 850 μm, 900 μm, 950 μm or 1000 μm.

[0022] Preferably, D50 of the chromium source is 500 μm to 800 μm, for example, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm or 800 μm.

[0023] Preferably, D50 of the tantalum source is 1000 μm to 1200 μm, for example, 1000 μm, 1050 μm, 1100 μm, 1150 μm or 1200 μm.

[0024] In the present invention, the D50 of the raw materials works synergistically to achieve uniform mixing between the particles, and then after wet ball milling and sintering, better fusion between the particles can be achieved, thereby obtaining a positive electrode material with uniform element distribution and stable phase structure.

[0025] Preferably, the sodium source comprises Na2CO3 or NaHCO3.

[0026] Preferably, the chromium source comprises Cr2O3.

[0027] Preferably, the tantalum source comprises Ta2O5.

[0028] Preferably, the dispersant in the wet ball milling process is a polar solvent.

[0029] Preferably, the dispersant comprises ethanol and / or isopropanol.

[0030] Preferably, during the wet ball milling process, the ball-to-material ratio is 10:1.

[0031] Preferably, during the wet ball milling process, the solid content of the slurry to be ball milled is 50% to 80%.

[0032] In the present invention, if the solid content of the slurry to be ball-milled is too low, it will be disadvantageous for the particles to fully contact with the ball milling beads during the milling process, while if it is too high, it will lead to uneven distribution of particles during the milling process.

[0033] Preferably, the wet ball-milled material is dried.

[0034] Preferably, the rotation speed of the wet ball milling is 200 rpm to 400 rpm, for example, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm or 400 rpm, etc.

[0035] In the present invention, too low a ball milling speed will result in uneven particle distribution and failure to obtain micron-sized particles. At too high a milling speed, the powder tends to agglomerate due to mutual collision, proximity, and attraction of molecules or particles, resulting in a "reverse milling" phenomenon, which in turn increases the particle size.

[0036] Preferably, the wet ball milling time is 5 h to 10 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

[0037] Preferably, the sintering temperature is 700°C to 1000°C, for example, 700°C, 730°C, 750°C, 780°C, 800°C, 830°C, 850°C, 880°C, 900°C, 930°C, 950°C, 980°C or 1000°C.

[0038] Preferably, the sintering time is 5 h to 10 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h.

[0039] In a third aspect, the present invention further provides a sodium ion battery, comprising the sodium ion battery layered oxide positive electrode material as described in the first aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The layered oxide positive electrode material provided by the present invention has the characteristics of high stability, high rate performance and high coulombic efficiency. The rational design of the stoichiometric ratio of sodium ions and transition metals enhances the interaction between transition metals and oxygen bonds, so that the material has a P2 configuration, broadens the interplanar spacing of sodium chromite layered oxides, and effectively avoids the complex phase transition problem when sodium chromite is used as a positive electrode material for sodium ion batteries. The introduction of tantalum ions into the transition metal layer (chromium layer) solves the problem of low coulombic efficiency caused by the reduction of sodium ion content due to the configuration design, and at the same time helps electron rearrangement, realizes the disordered arrangement of sodium / vacancies in the material, and improves the rate capacity and cycle performance. The battery adopts the positive electrode material provided by the present invention, and its general chemical formula is Na x Cr y Ta 1-yO2, 0.6≤x≤0.75, 0.6≤x≤0.75, and after controlling the rotation speed of wet ball milling in the preparation process, the specific discharge capacity of the battery at 1C can reach 120.0 mAh / g or more, and the capacity retention rate after 50 cycles at 1C can reach 90.55% or more.

[0042] (2) The preparation method provided by the application realizes uniform mixing of raw materials through simple wet ball milling, and a structure-stable sodium-ion battery layered oxide positive electrode material can be obtained through simple sintering, so that the preparation process is simple, the operability is strong, the cost is low, and the method is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The first charge-discharge curve of the battery provided for Examples 1-8 and Comparative Examples 1-3 is shown in the following figure.

[0044] Figure 2 The XRD pattern of the sodium-ion battery layered oxide positive electrode material provided for Example 1 is shown in the following figure.

[0045] Figure 3 The SEM pattern of the sodium-ion battery layered oxide positive electrode material provided for Example 1 is shown in the following figure. DETAILED DESCRIPTION

[0046] The technical solutions of the application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the application and should not be regarded as specific limitations on the application.

[0047] Example 1

[0048] This embodiment provides a sodium-ion battery layered oxide positive electrode material (D50 is 70 nm), and the chemical formula of the positive electrode material is Na 0.75 Cr 0.75 Ta 0.25 O2, the positive electrode material is P-type structure (P2 phase).

[0049] The preparation method of the positive electrode material is as follows:

[0050] Na2CO3(D50 is 750 μm), Cr2O3(D50 is 500 μm) and Ta2O5(D50 is 1000 μm) raw materials are weighed according to a molar ratio of Na:Cr:Ta = 0.75:0.75:0.25, and then are put into a ball mill tank, 10% (wt) of sodium carbonate is additionally added to prevent loss of sodium ions, a small amount of anhydrous ethanol is added to adjust the raw materials into a slurry (solid content is 70%), and the slurry is ball milled at a speed of 350 rpm for 8 h to obtain a mixed precursor, the obtained sample is vacuum dried at 60℃ for 12 h, and the dried precursor is heated to 900℃ at a heating rate of 5℃ / min in an argon atmosphere, and is kept for 5 h, and then is naturally cooled to obtain a product, i.e. the high-stability layered oxide positive electrode material.

[0051] Figure 2 An XRD pattern of the sodium-ion battery layered oxide positive electrode material provided in Example 1 is shown, from which it can be seen that the Na Figure 2 It can be seen that the Na 0.75 Cr 0.75 Ta 0.25 O2 is in a P2 configuration, rather than an O3 configuration same as NaCrO2.

[0052] Figure 3 An SEM pattern of the sodium-ion battery layered oxide positive electrode material provided in Example 1 is shown, from which it can be seen that the particle size is small (70 nm), the shape is regular, and the crystallinity is good. Figure 3 It can be seen that the particle size is small (70 nm), the shape is regular, and the crystallinity is good.

[0053] Example 2

[0054] This example provides a sodium-ion battery layered oxide positive electrode material (D50 is 100 nm), and the chemical formula of the positive electrode material is Na 0.7 Cr 0.7 Ta 0.3 O2, and the positive electrode material is in a P-type structure (P2 phase).

[0055] The preparation method of the positive electrode material is as follows:

[0056] Na2CO3(D50 of 850 μm), Cr2O3(D50 of 600 μm) and Ta2O5(D50 of 1100 μm) raw materials are weighed according to a molar ratio of Na:Cr:Ta=0.7:0.7:0.3, and then placed in a ball mill jar, 10%wt of sodium carbonate is additionally added to prevent sodium ion loss, a small amount of anhydrous ethanol is added to adjust the raw materials into a slurry (solid content of 70%), and the slurry is ball milled at a speed of 200 rpm for 10 h to obtain a uniformly mixed precursor. The obtained sample is vacuum dried at 60°C for 12 h, and then the dried precursor is heated to 700°C at a heating rate of 5°C / min in an argon atmosphere, and then kept for 10 h. After natural cooling, a product is obtained, which is the high-stability layered oxide positive electrode material.

[0057] Example 3

[0058] This example provides a sodium ion battery layered oxide positive electrode material (D50 of 120 nm), and the chemical formula of the positive electrode material is Na 0.6 Cr 0.6 Ta 0.4 O2, and the positive electrode material is a P-type structure (P2 phase).

[0059] The preparation method of the positive electrode material is as follows:

[0060] Na2CO3(D50 of 1000 μm), Cr2O3(D50 of 800 μm) and Ta2O5(D50 of 1200 μm) raw materials are weighed according to a molar ratio of Na:Cr:Ta=0.6:0.6:0.4, and then placed in a ball mill jar, 10%wt of sodium carbonate is additionally added to prevent sodium ion loss, a small amount of anhydrous ethanol is added to adjust the raw materials into a slurry (solid content of 70%), and the slurry is ball milled at a speed of 400 rpm for 5 h to obtain a uniformly mixed precursor. The obtained sample is vacuum dried at 60°C for 12 h, and then the dried precursor is heated to 1000°C at a heating rate of 5°C / min in an argon atmosphere, and then kept for 5 h. After natural cooling, a product is obtained, which is the high-stability layered oxide positive electrode material.

[0061] Example 4

[0062] The difference between this example and Example 1 is that the chemical formula of the positive electrode material in this example is Na 0.7 Cr 0.5 Ta 0.5 O2.

[0063] In the preparation method, the added amount of the raw material is adjusted adaptively according to the chemical formula.

[0064] The rest of the preparation method and parameters remain the same as those of Example 1.

[0065] Example 5

[0066] The difference between this embodiment and embodiment 1 is that the chemical formula of the positive electrode material in this embodiment is Na 0.7 Cr 0.8 Ta 0.2 O2.

[0067] In the preparation method, the addition amount of the raw materials in the raw materials is adjusted adaptively according to the chemical formula.

[0068] The rest of the preparation method and parameters remain the same as those in embodiment 1.

[0069] Embodiment 6

[0070] The difference between this embodiment and embodiment 1 is that the chemical formula of the positive electrode material in this embodiment is Na 0.5 Cr 0.7 Ta 0.3 O2.

[0071] In the preparation method, the addition amount of the raw materials in the raw materials is adjusted adaptively according to the chemical formula.

[0072] The rest of the preparation method and parameters remain the same as those in embodiment 1.

[0073] Embodiment 7

[0074] The difference between this embodiment and embodiment 1 is that the chemical formula of the positive electrode material in this embodiment is Na 0.8 Cr 0.7 Ta 0.3 O2.

[0075] In the preparation method, the addition amount of the raw materials in the raw materials is adjusted adaptively according to the chemical formula.

[0076] The rest of the preparation method and parameters remain the same as those in embodiment 1.

[0077] Embodiment 8

[0078] The difference between this embodiment and embodiment 1 is that the rotation speed of the ball milling in the preparation method of this embodiment is 150 rpm.

[0079] The rest of the preparation method and parameters remain the same as those in embodiment 1.

[0080] Embodiment 9

[0081] The difference between this embodiment and embodiment 1 is that the rotation speed of the ball milling in the preparation method of this embodiment is 450 rpm.

[0082] The rest of the preparation method and parameters remain the same as those in embodiment 1.

[0083] Comparative Example 1

[0084] The difference between the present comparative example and Example 1 is that the present comparative example provides a positive electrode material with a chemical formula of NaCrO2.

[0085] In the preparation method, no tantalum source is added, and the addition amount of the raw material is adjusted according to the chemical formula.

[0086] The remaining preparation method and parameters remain the same as those of Example 1.

[0087] Comparative Example 2

[0088] The difference between the present comparative example and Example 1 is that the positive electrode material in the present example has a chemical formula of Na 0.75 CrO2.

[0089] In the preparation method, no tantalum source is added, and the addition amount of the raw material is adjusted according to the chemical formula.

[0090] The remaining preparation method and parameters remain the same as those of Example 1.

[0091] Comparative Example 3

[0092] The difference between the present comparative example and Example 1 is that the present comparative example provides a positive electrode material with an O-type structure, and the chemical formula of the positive electrode material is NaCr 0.75 Ta 0.25 O2.

[0093] In the preparation method, the addition amount of the raw material is adjusted according to the chemical formula.

[0094] The remaining preparation method and parameters remain the same as those of Example 1.

[0095] Comparative Example 4

[0096] The difference between the present comparative example and Example 1 is that the present comparative example provides a positive electrode material with a chemical formula of Na 0.7 Cr 0.7 V 0.3 O2.

[0097] In the preparation method, a vanadium source is used instead of a tantalum source.

[0098] The remaining preparation method and parameters remain the same as those of Example 1.

[0099] Figure 1 The first charge-discharge curves of the batteries provided by Examples 1-8 and Comparative Examples 1-3 are shown in FIG. 1. Figure 1 It can be seen that the batteries obtained by using the positive electrode materials provided by Examples 1-3 all have high specific capacity and long cycle life.

[0100] The positive electrode material provided by Examples 1-9 and Comparative Examples 1-4, Super P and PVDF were ground uniformly in a mass ratio of 8:1:1, and then stirred uniformly in an appropriate amount of NMP to obtain an electrode slurry. The slurry was coated on an aluminum foil, dried, and then cut into electrode pieces. The electrode pieces were assembled into half-cells.

[0101] The half-cells provided by Examples 1-9 and Comparative Examples 1-4 were subjected to electrochemical performance testing. The discharge capacity and cycle performance were tested at 1C. The discharge capacity test conditions were: room temperature 25°C, and voltage range 2-3.6V. The cycle performance test conditions were: voltage range 2-3.6V, 1C cycle at 25°C for 50 cycles. The test results are shown in Table 1.

[0102] Table 1

[0103]

[0104] As can be seen from the data results of Examples 1, 2 and 3, by reasonably matching the stoichiometric ratios of sodium, chromium and tantalum, the positive electrode materials provided by Examples 1-3 have higher specific capacity and longer cycle life.

[0105] As can be seen from the data results of Example 1 and Examples 4 and 5, if the stoichiometric ratio of chromium (i.e. y) is too small, i.e. the amount of chromium added is too small (too much tantalum is added), it is not conducive to charge compensation, resulting in too small capacity, and if it is too large, i.e. the amount of chromium added is too large (too little tantalum is added), it will also result in poor coulombic efficiency.

[0106] As can be seen from the data results of Example 1 and Examples 6 and 7, if the stoichiometric ratio of sodium (i.e. x) is too small, it will affect the number of de-embeddable sodium ions, and the reversible capacity will be small, and if it is too large, it will also result in the inability to form the ideal P2 configuration, and the stability will be poor.

[0107] As can be seen from the data results of Example 1 and Examples 8 and 9, during the wet ball milling process, if the rotation speed of the ball mill is too slow, it will result in uneven mixing of the raw materials, and if the rotation speed is too fast, it will also cause agglomeration, the particles will become larger, and the performance will be reduced.

[0108] As can be seen from the data results of Example 1 and Comparative Example 1, compared to the original sodium chromite, Example 1 has greatly improved cycle performance while ensuring the initial capacity.

[0109] As can be seen from the data results of Example 1 and Comparative Example 2, if no tantalum is added (i.e. 1-y=0), even if a P2 configuration is formed, the specific capacity and cycle performance of the positive electrode material cannot be improved, i.e. the cycle performance cannot be improved on the basis of ensuring the specific capacity.

[0110] From the data results of Example 1 and Comparative Example 3, it can be seen that the stoichiometric ratio of sodium (i.e., x=1) is too large, which is not conducive to the formation of the P2 configuration. In other words, even if tantalum is incorporated under the O-type structure, its cycle performance cannot be improved while ensuring the specific capacity of the positive electrode material.

[0111] From the data results of Example 1 and Comparative Example 4, it can be seen that the addition of other elements into the chromium-based sodium ion oxide material will lead to lattice mismatch, causing the sodium / vacancy to form an ordered arrangement, thereby affecting the performance.

[0112] In summary, the layered oxide positive electrode material provided by the present invention has high specific capacity and high stability. By introducing Ta element into the layered oxide sodium chromite transition metal layer, Ta and Cr elements work together to form a disordered arrangement of sodium / vacancies, widen the interplanar spacing, avoid the complex phase transition process of the positive electrode material, and obtain a P-type structure positive electrode material. At the same time, its coulombic efficiency and capacity are also improved. The battery adopts the positive electrode material provided by the present invention, and its chemical formula is Na x Cr y Ta 1-y When O2, 0.6≤x≤0.75, 0.6≤x≤0.75, and the rotation speed of the wet ball milling is controlled during the preparation process, the discharge specific capacity of the battery at 1C can reach more than 120.0mAh / g, and the capacity retention rate after 50 cycles at 1C can reach more than 90.55%.

[0113] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A layered oxide positive electrode material for a sodium ion battery, characterized in that: The sodium ion battery layered oxide positive electrode material is a P-type structure material, and the metal elements other than sodium in the sodium ion battery positive electrode material include chromium and tantalum; The chemical formula of the sodium ion battery layered oxide positive electrode material is Na x Cr y Ta 1-y O2, where 0.6≤x≤0.75, 0.6≤y≤0.

75.

2. The sodium ion battery layered oxide positive electrode material according to claim 1, characterized in that The D50 of the sodium ion positive electrode material is 70nm to 120nm.

3. The sodium ion battery layered oxide positive electrode material according to claim 1, characterized in that In the sodium ion battery layered oxide positive electrode material, sodium occupies prismatic sites between oxide layers.

4. A method for preparing the layered oxide positive electrode material for sodium ion batteries according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: The sodium source, the chromium source and the tantalum source are wet ball-milled and sintered under a protective atmosphere to obtain the sodium ion battery layered oxide positive electrode material.

5. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The D50 of the sodium source is 750 μm to 1000 μm.

6. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The D50 of the chromium source is 500 μm to 800 μm.

7. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The D50 of the tantalum source is 1000 μm to 1200 μm.

8. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The sodium source includes Na2CO3 or NaHCO3.

9. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The chromium source includes Cr2O3.

10. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The tantalum source includes Ta2O5.

11. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The dispersant in the wet ball milling process is a polar solvent.

12. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 11, wherein: The dispersant includes ethanol and / or isopropyl alcohol.

13. The method for preparing a sodium ion battery layered oxide positive electrode material according to claim 4, characterized in that: During the wet ball milling process, the solid content of the slurry to be ball milled is 50% to 80%.

14. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The wet ball-milled material is dried.

15. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The rotation speed of the wet ball mill is 200 rpm to 400 rpm.

16. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, characterized in that: The wet ball milling time is 5 hours to 10 hours.

17. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, wherein: The sintering temperature is 700°C to 1000°C.

18. The method for preparing a layered oxide positive electrode material for sodium ion batteries according to claim 4, characterized in that: The sintering time is 5 hours to 10 hours.

19. A sodium ion battery, characterized in that: The sodium ion battery comprises the sodium ion battery layered oxide positive electrode material according to any one of claims 1 to 3.

Images