Sodium-ion battery positive electrode high-sodium state p2-type layered oxide material

Abstract

The application discloses a sodium-ion battery positive electrode high-sodium-state P2 type layered oxide material, and a chemical general formula of the high-sodium-state P2 type layered oxide material is Na x Mn 1‑y Cu y O 2+δ ; wherein Cu and Mn form an octahedral structure around six adjacent oxygen atoms, multiple octahedral structures are arranged in a common side to form a transition metal layer; sodium ions are located between every two transition metal layers to form a P2 phase layered oxide, and a space group is P63 / mmc; a relationship among x, y and z satisfies charge balance: x+3(1-y)+2y=2(2+delta), wherein 0.98 The sodium-ion battery positive electrode high-sodium-state P2 type layered oxide material has the characteristics of high pure phase degree, good safety and excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a P2 type layered oxide material with a high sodium state for a positive electrode of a sodium ion battery. BACKGROUND

[0002] With the increasing consumption of fossil fuels, it is generally recognized that it is urgent to develop energy storage technology with high energy efficiency and cost-effectiveness. In the past three decades, lithium ion batteries have been widely used in various fields due to their high energy density in existing rechargeable batteries. However, the high cost and limited resources of lithium limit its large-scale application. Under this background, sodium ion batteries (SIBs) are considered to be a viable energy storage system due to their low cost, widely distributed sodium resources and environmental friendliness. In particular, electrode materials have recently made rapid progress, such as carbon as a negative electrode material, Prussian blue compounds, polyanion compounds, layered metal oxides and organic compound materials as SIBs positive electrode materials. As a key part of SIBs, the cathode material plays a key role in determining the cost and performance. For sodium ion batteries, how to achieve high performance with low cost is the top priority of studying sodium ion batteries. Among the sodium ion battery cathode materials, layered oxide materials have become one of the main positive electrode materials for sodium ion batteries because of their periodic layered structure, simple preparation method, high specific capacity and high voltage.

[0003] Oxide positive electrode materials in sodium ion batteries are mainly divided into layered structure oxides and tunnel structure oxides. Layered structure is the most widely studied due to its high energy density and easy preparation. The layered structure is usually composed of MO6 octahedral structures of transition metal elements and surrounding six oxygen to form a transition metal layer, and sodium ions are interposed between the transition metal layers to form a structure of alternating MO6 and NaO6 arrangement. Delmas et al. divided the layered oxides into O3, O2, P3 and P2 structures according to the coordination configuration of sodium ions in the MO6 polyhedron and the stacking mode of oxygen. The capital letters represent the coordination configuration of sodium ions; O is the abbreviation of Octahedral, and P is the abbreviation of Prismatic, i.e. three-prismatic position, and the number represents the stacking number of the minimum repeating unit of oxygen (2-ABBA, 3-ABCABC). In the O3 structure, sodium ions only have one kind of occupation, which is connected with the transition metal MO6 to form a NaO6 octahedron; in the P3 structure, only one kind of NaO6 three-prismatic occupation is contained; and in the P2 structure, there are two kinds of three-prismatic and octahedral occupations, which are co-edge and co-plane Na e and Na f .

[0004] In the application of layered oxide cathode materials, the use of inexpensive metal ions to construct long cycle life, high rate charge-discharge, and high specific capacity cathode materials has become one of the important research topics. However, for transition metal oxide sodium battery layered cathode Na x For MO2 (M = Fe, Co, Ni, Mn, Cu, Mg, Cr, Ca, Ba, Ti, V), high specific capacity and long cycle are usually difficult to achieve, and in practice, due to the different ranges of sodium content x in the molecular formula, different configurations are caused, which mainly include the above P2, P3, O3, O2 structures. For O3 type structure, the phase transition is complex, with O3 - P3 - P3'- P3''- O1 and other complex phase transitions, and the structure stability is often insufficient during charge-discharge cycle. The advantage of P2 phase structure is that the phase transition process is simple and more reversible, and the structure life is more stable during charging, and P2 phase has Na f / Na e Two Na-extraction sites, more diffusion channels than O3 phase, better rate performance. For the generation mechanism of Na content, when the sodium content in the oxide is low (x < 0.5), the oxide with three-dimensional tunnel structure is mainly used. P2 phase is often generated in sodium-deficient state, i.e. (0.67 - 0.83), which is one of the problems of P2 phase. The sodium content of O3 phase is generally about 1.

[0005] Chinese invention patent application CN116259742A discloses a copper-manganese-based sodium ion battery cathode material and its preparation method, although a low-cost, long-cycle vacancy-disordered copper-manganese-based layered cathode material is constructed by ion doping strategy, but its sodium content can only be between 0.67~0.85, still in a serious sodium-deficient state, and still needs sodium supplement measures to be used normally as a positive electrode in a full battery, which limits its large-scale application.

[0006] Chinese invention patent application CN104617288A discloses a copper-based sodium-rich layered oxide material and its preparation method and use, which uses Cu to replace Ni and Co, and uses the earth-abundant and non-toxic element to obtain a P2 phase layered cathode material. But the selected Na ratio can only reach 0.67~0.9, still in a sodium-deficient state, and still needs sodium supplement measures in actual full battery application.

[0007] To solve the problem of insufficient sodium content of P2 type material, pre-sodium technology is often needed, but there are also some problems and disadvantages in cost. Through pre-sodium, a part of sodium ions can be stored in sodium ion battery in advance to compensate for the problem of insufficient sodium in full battery cycle.

[0008] Based on this, various pre-sodium methods including cathode and anode pre-sodium have been explored. Adding a self-sacrificing additive to the cathode electrode is a direct and effective method to provide additional sodium source. However, the additive will inevitably decompose and produce gas and solid by-products in subsequent cycles, which may affect the safety of the battery and adversely affect the cycle. In addition, the introduction of excess additives will significantly increase the mass of the battery, thereby reducing the energy density. SUMMARY

[0009] The purpose of the present application is to provide a sodium ion battery positive electrode high sodium state P2 type layered oxide material, which has the characteristics of high degree of pure phase, good safety and excellent electrochemical performance.

[0010] The present application can be realized by the following technical solutions:

[0011] The present application discloses a sodium ion battery positive electrode high sodium state P2 type layered oxide material, the chemical formula of the high sodium state P2 type layered oxide material is: Na x Mn 1-y Cu y O 2+δ ;

[0012] Among them, Cu and Mn form an octahedral structure with the surrounding six oxygen atoms, and multiple octahedral structures are arranged side by side to form a transition metal layer; sodium ions are located between every two layers of transition metal layers to form a P2 phase layered oxide, and the space group is P63 / mmc.

[0013] The relationship between x, y and z satisfies the charge balance: x+3(1-y)+2y=2(2+δ), and 0.98≤x≤1.4, 0.18≤y≤0.35; -0.05≤δ≤0.05.

[0014] In the protection scope of the element parameters in the above structural formula, by limiting the doping concentration range of Cu(II), the layered oxide material Na x Mn 1-y Cu y O 2+δ The P2 type thermodynamic stable phase under a certain temperature and time. Controlling the Cu(II) doping range of 0.18≤y≤0.35 will make Cu(II) in the above structural formula show a superstructure distribution, so as to facilitate more Na + Around Cu(II) to achieve charge balance, which makes it possible to generate P2 phase with high sodium content (0.98~1.4); and outside this doping range, it is easy to generate P3 and O3 phase oxides, because the change of doping ion content will change the ion potential, thereby affecting the Na +The distribution in the material body phase, combined with the influence of ion thermodynamics in the precursor under temperature and holding time, makes sodium ions with high sodium content tend to generate P2 phase as the final stable phase under certain conditions, rather than O3 phase.

[0015] In the present application, for P2 phase materials, in the feeding ratio of high sodium state, by controlling the specific copper ion valence state and the doping concentration range, the thermodynamic stable phase under certain temperature and time can be regulated, which makes it possible to generate P2 phase with high sodium content (0.98~1.4), and deviating from this condition will often generate P3, O3 phase oxides. This depends on the change of ion potential of doped ions, which affects the distribution of Na ions in the material body phase, and the ion thermodynamics in the precursor under different temperature holding time makes sodium ions tend to generate P2 phase as the final stable phase. At the same time, we combine the freeze-drying technology of precursor (to ensure uniform ion dispersion in the precursor), so that the ions are uniformly transported during sintering, which promotes the generation of pure P2 phase with high sodium state. The high sodium state has higher sodium content than ordinary P2 type oxide materials. Compared with the above pre-sodium technology, the high sodium state P2 type oxide material of the present application plays the role of self-sodium supplement material, which not only reduces the pre-sodium cost, but also solves the problems of gas production, safety and other problems caused by pre-sodium technology, and also solves the application problem of full battery, and the material can be produced on a large scale.

[0016] Further, the high sodium state P2 type layered oxide material is prepared by sol-gel method or solid phase method.

[0017] Further, the preparation process of sol-gel method includes the following steps:

[0018] S1, preparation of precursor solution: according to the molar ratio of sodium element to manganese element 0.98~1.512, sodium nitrate, manganese nitrate and copper nitrate are weighed and dissolved in deionized water, and then stirred to obtain a uniform precursor solution;

[0019] S2, preparation of citric acid solution: citric acid monohydrate is weighed and stirred to completely dissolve to obtain a citric acid solution with a mass percentage concentration range of 10%~30%;

[0020] S3, preparation of precursor dry gel: the precursor solution in step S1 is added to the citric acid solution in step S2, then continuously stirred under the control of temperature 40~60°C, so that a uniform wet gel is formed, the wet gel is dried to obtain a precursor dry gel;

[0021] S4, high temperature calcination: the precursor dry gel in step S3 is precalcined at 450~550°C in air atmosphere for 4~8h, then mixed after re-breaking, calcined at 750~900°C in air atmosphere for 8~15h, and then naturally cooled to obtain a high sodium state P2 type layered oxide positive electrode material.

[0022] Further, in the sol-gel method, the molar ratio of metal ions to monohydrated citric acid in the precursor solution is 0.5-1. Compared with uneven cooling or rapid cooling, natural cooling tends to generate a material that is a thermodynamically stable phase and can promote uniform growth of the material, and the generated material has good crystallinity.

[0023] Further, in step S3, the drying method is freeze drying and / or spray drying.

[0024] Further, the preparation process of the solid phase method comprises the following steps:

[0025] A1, preparation of the precursor powder: sodium carbonate, manganese source and copper oxide are weighed according to the stoichiometric ratio, and mixed to obtain the precursor powder;

[0026] A2, high-temperature calcination: the precursor powder in A1 is calcined at 750-900 °C in an air atmosphere for 8-15 h, and a high-sodium P2-type layered oxide positive electrode material is obtained after natural cooling. Compared with uneven cooling or rapid cooling, natural cooling tends to generate a material that is a thermodynamically stable phase and can promote uniform growth of the material, and the generated material has good crystallinity.

[0027] Further, in step A1, the molar ratio of sodium element to transition metal element is 0.98-1.512.

[0028] Further, in step A1, the manganese source is one or more of manganese sesquioxide, manganese dioxide and manganese carbonate.

[0029] Further, in step A1, the mixing method is ball milling and / or stirring.

[0030] The sodium ion battery positive electrode high-sodium P2-type layered oxide material has the following beneficial effects:

[0031] The new P2-type material Na x Mn 1-y Cu y O 2+δ , x+3(1-y)+2y=2(2+δ), wherein 0.98≤x≤1.4; 0.18≤y≤0.35; -0.05≤δ≤0.05. Within the protection range of each element parameter in the structural formula, by limiting the doping concentration range of Cu(II), the layered oxide material Na x Mn 1-y Cu y O 2+δP2 type thermodynamic stable phase at certain temperature and time. Controlling Cu(II) doping in the range of 0.18≤y≤0.35, Cu(II) will be distributed in the above structural formula in a superstructure, so as to accommodate more Na around Cu(II) + To achieve charge balance, which makes it possible to generate P2 phase with high sodium content (0.98~1.4); and out of this doping range, P3, O3 phase oxides are easily generated, because the change of doping ion content will change the ion potential, thereby affecting the Na + The distribution in the material body phase, combined with the influence of ion thermodynamics in the precursor under the temperature and holding time, makes the sodium ion with high sodium content tend to generate P2 phase as the final stable phase under certain conditions, rather than O3 phase.

[0032] Combined with the freeze-drying technology of the precursor, freeze-drying, also known as sublimation drying, is a drying method that freezes water-containing materials below the freezing point, changes water into ice, and then removes ice into vapor under high vacuum. The material can be frozen in the freezing device first, and then dried. Freeze-drying can reduce the phenomenon of uneven ion transmission caused by heating of the precursor, ensure uniform dispersion of ions in the precursor, make the ions uniformly transmit during sintering, and promote the generation of pure P2 phase.

[0033] The high-sodium state has higher sodium content than ordinary P2 type layered oxide materials, and compared with traditional pre-sodium technology, the high-sodium P2 type layered oxide material of the application is equivalent to self-sodium, which not only eliminates the additional cost of pre-sodium reagent, device or process, but also solves the problems of gas generation, safety and other problems caused by pre-sodium technology, and also solves the application bottleneck problem of P2 type layered oxide in full battery, which will promote the large-scale production and application of P2 type layered oxide materials. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 X-ray diffraction patterns of high-sodium layered oxide materials with different sodium contents;

[0035] Figure 2 The most suitable ratio P2 - Na x Mn 1-y Cu y O 2+δ Series of layered oxide materials 300 circle 1C long cycle diagram;

[0036] Figure 3 The different oxide materials 300 circle 1C long cycle comparison diagram generated under the conditions of example 4 and comparative example 1. DETAILED DESCRIPTION

[0037] In order to make the technical personnel in the art better understand the technical solutions of the present application, the product of the present application will be further described in detail below in conjunction with embodiments.

[0038] The application discloses a sodium-ion battery positive electrode high-sodium-state P2-type layered oxide material. x Mn 1-y Cu y O 2+δ ;

[0039] Among them, Cu and Mn form an octahedral structure with six adjacent oxygen atoms around them, and multiple octahedral structures are arranged side by side to form a transition metal layer; sodium ions are located between every two layers of transition metal layers to form a P2-phase layered oxide, and the space group is P63 / mmc.

[0040] The relationship between x, y and z satisfies charge balance: x+3(1-y)+2y=2(2+δ), wherein 0.98<x≤1.4, 0.18≤y≤0.35, and -0.05≤δ≤0.05.

[0041] Further, the high-sodium-state P2-type layered oxide material is prepared by a sol-gel method or a solid-phase method.

[0042] Further, the preparation process of the sol-gel method comprises the following steps:

[0043] S1, preparation of a precursor solution: sodium nitrate, manganese nitrate and copper nitrate are weighed according to a molar ratio of sodium element to manganese element of 0.98-1.512, and are dissolved in deionized water to obtain a uniform precursor solution;

[0044] S2, preparation of a citric acid solution: citric acid monohydrate is weighed, stirred and completely dissolved to obtain a citric acid solution with a mass percentage concentration range of 10%-30%;

[0045] S3, preparation of a precursor dry gel: the precursor solution in step S1 is added to the citric acid solution in step S2, then stirring is continuously performed under the control of a temperature of 40-60°C, so that a uniform wet gel is formed, the wet gel is dried to obtain a precursor dry gel;

[0046] S4, high-temperature calcination: the precursor dry gel in step S3 is pre-fired at 450-550°C in an air atmosphere for 4-8h, is mixed after being broken again, is calcined at 750-900°C in an air atmosphere for 8-15h, and is naturally cooled to obtain a high-sodium-state P2-type layered oxide positive electrode material.

[0047] Further, in the sol-gel method, the molar ratio of metal ions to citric acid monohydrate in the precursor solution is 0.5-1.

[0048] Further, in step S3, the drying method is freeze-drying and / or spray-drying.

[0049] Further, the preparation process of the solid phase method comprises the following steps:

[0050] A1, preparation of the precursor powder: sodium carbonate, manganese source, and copper oxide are weighed according to the stoichiometric ratio, and mixed to obtain the precursor powder;

[0051] A2, high-temperature calcination: the precursor powder in A1 is calcined at 750 ~ 900 °C in air atmosphere for 8 ~ 15 h, and the high-sodium P2-type layered oxide positive electrode material is obtained after natural cooling.

[0052] Further, in step A1, the molar ratio of sodium element to transition metal element is 0.98 ~ 1.512.

[0053] Further, in step A1, the manganese source is one or more of manganese sesquioxide, manganese dioxide, and manganese carbonate.

[0054] Example 1

[0055] The present embodiment provides a high-sodium P2-type layered oxide preparation method, specifically a solid phase method. The process flow is as follows:

[0056] Step S1, Na 1.00 Mn 0.8 Cu 0.2 O2 material: 0.021 mmol of sodium carbonate, 0.02 mmol of manganese carbonate, and copper oxide are weighed and mixed to obtain the precursor powder. The molar ratio of sodium element to transition metal element (the sum of manganese and copper) is 1.05:1.00.

[0057] Step S2, all the weighed sample powders are transferred into a 100 ml agate ball mill jar at one time, 10 ml of ethanol or acetone is added as a dispersant for the powder, and the sample powder is adjusted to a paste.

[0058] Step S3, the 100 ml agate ball mill jar of step S2 is placed in a QM-3C ball mill, the ball milling time is 12 h, and the ball milling speed is 400 rpm.

[0059] Step S4, after ball milling, the paste-like material obtained in step S3 is dried, ground, and pressed into a thin sheet using a tablet press and a tablet press, with a pressure of 15 MPa.

[0060] Step S5, then, the pressed wafer is placed in a crucible and put into a muffle furnace, and the calcination temperature is 800 °C. The sample is calcined in an air atmosphere for 12 h, and the muffle furnace has a heating rate of 3 °C min -1 .

[0061] Step S6, after the sample of step S5 is naturally cooled to room temperature, the sample is taken out and re-ground, and the ground final product is transferred into an anhydrous oxygen-free glove box for storage. The obtained final black powder is Na 1.00 Mn 0.8 Cu 0.2 O2material.

[0062] The embodiment provides a preparation method of a high-sodium layered oxide material, which can be used for preparing the high-sodium layered oxide material described in the above embodiment 1. The method provided in the embodiment is simple and easy to implement, low in cost, and suitable for large-scale manufacturing applications.

[0063] Embodiment 2

[0064] The embodiment provides a preparation method of a high-sodium P2-type layered oxide, specifically a sol-gel method, which comprises the following steps:

[0065] Step S1, a sol-gel method is used to prepare Na 1.00 Mn 0.8 Cu 0.2 O2material.

[0066] Step S2, the specific process is as follows: 0.021 mmol of sodium nitrate, 0.02 mmol of 50 wt% manganese nitrate tetrahydrate and copper nitrate trihydrate are weighed according to the proportion and dissolved in 50 ml of deionized water, wherein the molar ratio of sodium element to transition metal element (sum of manganese and copper) is 1.05:1.00. Heating and stirring at 40 degrees to obtain a uniform precursor solution.

[0067] Step S3, 0.04 mmol, 8.4048 g of citric acid monohydrate is weighed and then transferred to 25 ml of deionized water, and fully stirred to completely dissolve into a transparent and colorless citric acid solution. The mass percentage concentration of the citric acid solution ranges from 26%.

[0068] Step S4, select a pipette, and drop the solution of step S2 into the citric acid solution of step S3, and then continuously stir at 80 °C until a uniform wet gel is formed.

[0069] Step S5, the wet gel obtained in step S4 is placed in a freeze dryer for freeze drying to obtain a dry gel of the precursor.

[0070] Step S6, the xerogel obtained in step S5 was ground in a mortar to obtain fine and uniform powder.

[0071] Step S7, the powder obtained in step S6 was placed in a crucible and pre-fired at 450 °C for 6 h in a muffle furnace.

[0072] Step S8, the pre-fired product obtained in step S7 was pressed into thin sheets using a tablet press and a tablet presser, with a pressure of 15 MPa.

[0073] Step S9, the tablet product obtained in step S8 was placed in a corundum ceramic boat and calcined at 800 °C for 12 h in a muffle furnace under an air atmosphere, and naturally cooled,

[0074] Step S10, after the sample in step S9 was naturally cooled to room temperature, the sample was taken out and re-ground, and the ground final product was transferred into an anhydrous and anaerobic glove box for storage. The obtained final black powder was Na 1.00 Mn 0.8 Cu 0.2 O2 material.

[0075] The present embodiment provides a method for preparing a high-sodium layered oxide material, which can be used to prepare the high-sodium layered oxide material described in Embodiment 12 above. The method provided in the present embodiment is simple and easy to implement, low in cost, and suitable for large-scale manufacturing applications.

[0076] Embodiment 3

[0077] The present embodiment provides a method for preparing a high-sodium P2-type layered oxide, specifically a spray-drying method.

[0078] Step S1, a spray-drying method (sol-gel) was used to prepare Na 1.1 Mn 0.8 Cu 0.2 O2 material.

[0079] Step S2, the specific process is as follows: 0.0231 mmol of sodium nitrate, 0.02 mmol of 50 wt% manganese nitrate tetrahydrate, and 0.02 mmol of copper nitrate trihydrate were weighed according to the proportion and dissolved in 50 ml of deionized water, wherein the molar ratio of sodium element to transition metal element (sum of manganese and copper) was 1.05:1.00. Heating and stirring at 40 degrees to obtain a uniform precursor solution.

[0080] Step S3, 0.04 mmol, 8.4048 g of citric acid monohydrate was weighed and transferred to 25 ml of deionized water, and fully stirred to completely dissolve into a transparent and colorless citric acid solution. The mass percentage concentration of the citric acid solution was in the range of 26%.

[0081] Step S4, select a pipette, and add the solution of step S2 drop by drop into the citric acid solution of step S3, and then continue to stir at 40 °C until it forms a uniform complex solution.

[0082] Step S5, after spray freeze drying the precursor solution of step S4, a precursor powder is obtained.

[0083] Step S6, place the precursor powder of step S5 above into a crucible, and pre-sinter at 450 °C for 6 h in a muffle furnace to obtain a pre-sintered powder.

[0084] Step S7, re-mix the sample obtained in step S6.

[0085] Step S8, use a tablet press and a tablet presser to press the pre-sintered product of step S7 into a thin sheet, with a pressure of 15 MPa.

[0086] Step S9, place the tablet product of step S8 into a corundum ceramic boat, and calcine at 800 °C for 12 h in a muffle furnace under air atmosphere, and naturally cool down.

[0087] Step S10, after the sample of step S9 is naturally cooled to room temperature, take out the sample and re-mill, and transfer the milled final product into an anhydrous and anaerobic glove box for storage. The obtained final black powder is Na 1.1 Mn 0.8 Cu 0.2 O2material.

[0088] The present embodiment provides a method for preparing a high-sodium layered oxide material, which can be used to prepare the high-sodium layered oxide material described in the above-mentioned embodiment 13. The method provided in the present embodiment is simple and easy to implement, low in cost, and suitable for large-scale manufacturing applications.

[0089] Embodiment 4

[0090] In the present embodiment, the high-sodium layered oxide material is prepared by the sol-gel method described in the above-mentioned embodiment 2.

[0091] Step S1, the Na 1.00 Mn 0.8 Cu 0.2 O2material is prepared by a sol-gel method.

[0092] Step S2, the specific process is as follows: 0.021 mmol of sodium nitrate, 0.02 mmol of 50 wt% manganese nitrate tetrahydrate, and 0.02 mmol of copper nitrate trihydrate are weighed according to the proportion, and dissolved in 50 ml of deionized water, wherein the molar ratio of sodium element to transition metal element (the sum of manganese and copper) is 1.05:1.00. Heat and stir at 40 degrees to obtain a uniform precursor solution.

[0093] Step S3, after weighing 0.04 mmol, 8.4048 g of citric acid monohydrate, it was transferred to 25 ml of deionized water, and fully stirred to completely dissolve into a transparent colorless citric acid solution. The mass percentage concentration of the citric acid solution was in the range of 26%.

[0094] Step S4, select the pipette, and drop the solution of step S2 into the citric acid solution of step S3, and then continuously stir at 80 °C until it forms a uniform wet gel.

[0095] Step S5, the wet gel obtained in step S4 was placed in a freeze dryer for freeze drying to obtain a dry gel of the precursor.

[0096] Step S6, the dry gel obtained in step S5 was ground in a mortar to obtain a fine powder.

[0097] Step S7, the powder of step S6 was placed in a crucible and pre-fired at 450 °C for 6 h in a muffle furnace.

[0098] Step S8, the pre-fired product obtained in step S7 was pressed into a wafer using a tablet press and a tablet press, with a pressure of 15 MPa.

[0099] Step S9, the wafer product obtained in step S8 was placed in a corundum boat and calcined at 800 °C for 12 h in an air atmosphere in a muffle furnace, and naturally cooled,

[0100] Step S10, after the sample of step S9 was naturally cooled to room temperature, the sample was taken out and re-ground, and the ground final product was transferred into an anhydrous oxygen-free glove box for storage. The obtained final black powder was Na 1.00 Mn 0.8 Cu 0.2 O2material.

[0101] Step S11, the electrochemical performance of step S10 was characterized by constant current charge and discharge method. The mass ratio of active material, conductive agent (Super P) and binder (PVDF) in the electrode was 75:15:10. The battery was assembled with the electrode as the working electrode, sodium as the counter electrode, 1M NaPF6EC / DEC (vol 1:1) as the electrolyte, and a 2032 button cell was assembled in an anhydrous oxygen-free glove box.

[0102] Step S12, using constant current charge and discharge mode, 3 cycles of pre-cycling at 0.1C, and charge and discharge test at 1C current density, with a charge and discharge range of 2.0-4.5 V. The results are shown in Figure 2, with a 0.1C capacity of 100.6 mAh g -1The highest cycle retention at 1C was 280 cycles, 90% (calculated from the highest capacity).

[0103] Comparative Example 1

[0104] In this example, the sol-gel method described in Example 2 was used to prepare a high-sodium layered oxide material, but with different processes and proportions.

[0105] Step S1, Na 1.00 Mn 0.8 Cu 0.2 O2material was prepared using the sol-gel method.

[0106] Step S2, the specific process is as follows: 0.021 mmol of sodium nitrate, 0.02 mmol of 50 wt% manganese nitrate tetrahydrate, and 0.02 mmol of copper nitrate trihydrate were weighed according to the proportion and dissolved in 50 ml of deionized water, and the molar ratio of sodium element to transition metal element (sum of manganese and copper) was 1.05:1.00. Stirring at 40°C obtained a uniform precursor solution.

[0107] Step S3, 0.04 mmol, 8.4048 g of citric acid monohydrate was weighed and then transferred to 25 ml of deionized water, and stirred thoroughly to completely dissolve into a transparent colorless citric acid solution. The mass percentage concentration of the citric acid solution was in the range of 26%.

[0108] Step S4, select a pipette, and add the solution of step S2 dropwise to the citric acid solution of step S3, and then continue to stir at 80°C until a uniform wet gel is formed.

[0109] Step S5, the wet gel obtained in step S4 was placed in an oven and dried at 120°C.

[0110] Step S6, the dry gel obtained in step S5 was placed in a mortar and ground uniformly to obtain a fine powder.

[0111] Step S7, the powder of step S6 was placed in a crucible and pre-fired at 450°C for 6h in a muffle furnace.

[0112] Step S8, the pre-fired product obtained in step S7 was pressed into a thin sheet using a tablet press and a tablet press, with a pressure of 15 MPa.

[0113] Step S9, the tablet product obtained in step S8 was placed in a corundum ceramic boat and calcined at 750°C for 8h in an air atmosphere in a muffle furnace, and naturally cooled.

[0114] Step S10, after the sample of step S9 is naturally cooled to room temperature, the sample is taken out and re-ground, and the ground final product is transferred into anhydrous oxygen-free glove box for storage. The obtained final black powder is a non-P2 phase Na 1.00 Mn 0.8 Cu 0.2 O2material.

[0115] The electrochemical performance of the above material is characterized by constant current charge and discharge method. The mass ratio of active material, conductive agent (Super P) and binder (PVDF) in the electrode is 75:15:10. The battery is assembled with the electrode as the working electrode, sodium as the counter electrode, 1M NaPF6EC / DEC (vol 1:1) as the electrolyte, and a 2032 button cell is assembled in an anhydrous oxygen-free glove box.

[0116] The constant current charge and discharge mode is used, 3 cycles of pre-circulation at 0.1C, and charge and discharge test at 1C current density, with the charge and discharge range of 2.0-4.5V. The results are shown in Figure 2, and the 0.1C capacity in 2.0-4.5V is 100.6 mAh g -1 , the comparison diagram is shown in Figure Figure 3 , the cycle effect is obviously not as good as the black powder material Na 1.00 Mn 0.8 Cu 0.2 O2.

[0117] Table 1 Performance test results

[0118]

[0119] From Table 1, it can be seen that Examples 1 to 4 are pure phase high sodium P2 type materials synthesized by different methods, and it can be seen that under the condition of 1C charge and discharge, they have similar capacity. But there are slight differences in different methods, among which the capacity of Examples 2 to 4 is higher, which is 92.3, 92.3, 92.2 mAh / g respectively, showing excellent performance, which is due to the more uniform material synthesized by the synthesis method of Examples 2 to 4. The first week discharge of Comparative Example 1 is only 70.1 mAh / g, which is due to the non-P2 pure phase material synthesized by Comparative Example 1, and the cycle retention rate is 45% for 280 cycles, which is obviously lower than the above examples.

[0120] Figure 1 X-ray diffraction pattern of high sodium layered oxide material with different sodium content in Example 2; it can be seen that the synthesized Na content is in the interval of 0.98 to 1.3, and the material shows a pure phase structure of P2 phase, which verifies that the material synthesized under the protection condition of the present patent is a pure phase P2 type high sodium material.

[0121] Figure 2 P2 - Na x Mn 1-y Cu y O 2+δ Series of layered oxide material 300 circle 1C long cycle chart; it can be seen from the figure that the material synthesized by example 2 has good cycle stability, and the cycle retention rate is about 87% after 300 cycles at 2-4.5V and 1C rate.

[0122] Figure 3 The 300 circle 1C long cycle contrast chart of different oxide materials generated under the conditions of example 4 and comparative example 1. It can be seen that compared with the non-pure phase P2 type material synthesized by comparative example 1, the 300 cycle retention rate is 44.2 9%, and the material in example 4 has obviously higher capacity and better cycle retention rate, which is 89.64%, indicating the superiority of the synthesis method of the patent.

[0123] The above examples are only specific embodiments of the present application, which are described in detail, but cannot be construed as limiting the scope of the patent. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious alternative forms all belong to the protection scope of the present application.

Claims

1. A sodium-ion battery cathode high-sodium P2-type layered-oxide material, characterized in that: The high sodium P2-type layered oxide material has a general chemical formula of: Na x Mn 1-y Cu y O 2+δ ; The Cu and Mn form an octahedral structure with six adjacent oxygen atoms, and multiple octahedral structures are arranged side by side to form a transition metal layer; and the sodium ions are located between every two transition metal layers to form a P2 phase layered oxide with a space group of P63 / mmc. The relationship between x, y and z satisfies charge balance: x + 3(1-y) + 2y = 2(2+δ), wherein 0.98 < x < 1.4, 0.18 < y < 0.35, and -0.05 < δ < 0.

05.

2. The sodium-ion battery cathode high-sodium P2-type layered oxide material of claim 1, characterized in that: The high-sodium P2-type layered oxide material is prepared by a sol-gel method or a solid-phase method.

3. The sodium-ion battery cathode high-sodium P2-type layered oxide material of claim 2, wherein: The preparation process of the sol-gel method comprises the following steps: S1. Preparation of a precursor solution: sodium nitrate, manganese nitrate and copper nitrate are weighed according to a molar ratio of sodium element to manganese element of 0.98-1.512, and then dissolved in deionized water to obtain a uniform precursor solution; S2. Preparation of a citric acid solution: citric acid monohydrate is weighed and stirred to completely dissolve to obtain a citric acid solution with a mass percentage concentration in the range of 10%-30%; S3. Preparation of a precursor dry gel: the precursor solution in step S1 is added to the citric acid solution in step S2, and then continuously stirred at a controlled temperature of 40-60°C to form a uniform wet gel; the wet gel is dried to obtain a precursor dry gel; S4. High-temperature calcination: the precursor dry gel in step S3 is pre-fired at 450-550°C in an air atmosphere for 4-8h, and then calcined at 750-900°C in an air atmosphere for 8-15h after re-mixing and breaking, to obtain a high-sodium P2-type layered oxide positive electrode material after natural cooling.

4. The sodium-ion battery cathode high-sodium P2-type layered oxide material of claim 3, wherein: In the sol-gel method, the molar ratio of metal ions in the precursor solution to citric acid monohydrate is 0.5-1.

5. The sodium-ion battery cathode high-sodium P2-type layered oxide material of claim 4, wherein: In step S3, the drying method is freeze-drying and / or spray drying.

6. The sodium-ion battery cathode high-sodium P2-type layered oxide material of claim 2, wherein: The preparation process of the solid-phase method comprises the following steps: A1. Preparation of a precursor powder: sodium carbonate, a manganese source and copper oxide are weighed according to a stoichiometric ratio, and then mixed to obtain a precursor powder; A2. High-temperature calcination: the precursor powder in A1 is calcined at 750-900°C in an air atmosphere for 8-15h, and then naturally cooled to obtain a high-sodium P2-type layered oxide positive electrode material.

7. The sodium-ion battery cathode high-sodium P2-type layered oxide material of claim 6, wherein: 0.01 < x < 0.

05. In step A1, the molar ratio of sodium element to transition metal element is 0.98-1.

512.

8. The sodium-ion battery cathode high-sodium P2-type layered oxide material of claim 6, wherein: In step A1, the manganese source is one or two or more of manganese sesquioxide, manganese dioxide and manganese carbonate.

9. The sodium-ion battery cathode high-sodium P2-type layered oxide material of claim 6, wherein: In step A1, the mixing method is ball milling and / or stirring.

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