Sodium-ion battery and preparation and application of in-situ coating gradient oxygen deficiency positive electrode active material of sodium-ion battery

Abstract

The invention belongs to the field of sodium ion battery positive electrode materials, and particularly provides an in-situ coating gradient oxygen deficiency positive electrode active material for a sodium ion battery and preparation and application of the in-situ coating gradient oxygen deficiency positive electrode active material for the sodium ion battery. And preparing the in-situ coated gradient oxygen deficiency positive electrode active material. X comprises at least one of Ca, Zr, Al, Mg, Sn, K, Nd, Sc, Y and Ce, and n is the valence of X; the micro-positive pressure two-stage gradient heat treatment stage comprises a first-stage heat preservation process at the temperature of 300-650 DEG C and a second-stage heat preservation process at the temperature of 700-900 DEG C. The material prepared by the preparation method disclosed by the invention can meet the application requirements of special conditions such as high pressure, low temperature, high magnification and long circulation of the sodium ion battery, and can effectively improve the problem of gas production caused by oxygen evolution under high pressure.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion secondary batteries, and in particular to the field of positive electrode active materials for sodium ion batteries. Background Art

[0002] Sodium-ion batteries have received widespread attention and developed rapidly due to their similar working principles and abundant resources to lithium-ion batteries. Among them, the layered oxide positive electrode material for sodium-ion batteries has the advantages of high energy density, high operating voltage, and simple preparation process. It is one of the key materials with the widest application range and the most promising prospects in the field of sodium-ion batteries. However, in order to promote the industrialization of sodium-ion batteries and improve their competitiveness with lithium batteries and lead-acid batteries, the low material capacity caused by the large atomic mass and ionic radius is still a key problem that needs to be solved urgently. For layered oxides, increasing the charging cutoff voltage of the material and allowing the anions to participate in the redox reaction can increase its specific capacity and energy density. However, as the voltage increases, the crystal structure undergoes a phase change, and a large number of anions participate in deep charge compensation, which can easily cause oxygen loss that is difficult to ignore. Excessive oxygen production will seriously affect the energy, life and safety performance of the battery. The above-mentioned adverse reactions will further lead to the dissolution of transition metals, resulting in the continuous occurrence of surface side reactions, and the cycle and rate performance of layered oxides will therefore decrease. Moreover, compared with lithium-ion layered oxides, Na + The ion size is larger, and the irreversible damage caused by the redox reaction of O ions participating in charge compensation under high voltage, such as oxygen release, cracks, structural collapse, metal ion migration and dissolution, is also more serious. Therefore, effective regulation of anion redox reactions is a key technology to achieve high voltage and develop environmentally sustainable, economical and efficient layered oxide cathode materials with high specific capacity, excellent rate, low temperature stability and long cycle life.

[0003] At present, in industrial production at home and abroad, in order to solve the problem of irreversible loss caused by high charging cut-off voltage of layered positive electrode materials, the doping coating method is usually simply adopted, using transition metal cations to stabilize the crystal structure, improving the interface side reactions through the coating layer, and further improving the material stability.

[0004] For example, the Chinese patent document with publication number CN118763209A discloses a sodium ion battery positive electrode material and its preparation method and application, the positive electrode material includes a layered oxide material and a coated lithium cobalt phosphate layer; the layered oxide material has a chemical formula of NawNixFeyMnzZnpTiqOmFn, wherein 0.2≤x≤0.4, 0.2≤y≤0.33, 0.3≤z≤0.4, 0≤p≤0.1, 0<q≤0.01, 1.8≤m≤2.2, 0<n≤0.4, 0.6≤w<1.2, and x+y+z+p+q=1. For another example, the Chinese patent document with publication number CN118969977A discloses a Ni-Fe-Mn-based layered oxide sodium ion positive electrode material and its preparation method and application, the general formula of which is NamNixFeyM11-xy-nMnnO2.

[0005] In summary, although conventional doping and coating processes can improve the performance of materials to a certain extent, this modification method requires a certain doping amount. Too high a doping amount will affect the capacity of the positive electrode material, and too low a doping amount will have no significant effect, and cannot effectively solve the irreversible problem caused by anion redox reactions under high voltage. Summary of the invention

[0006] In response to the problems faced by existing layered oxide positive electrode materials for sodium ion batteries, the first purpose of the present invention is to provide a method for preparing an in-situ coated gradient oxygen defect positive electrode active material, aiming to produce a positive electrode active material that can meet the requirements of high pressure, low temperature, high rate and long cycle applications.

[0007] The second object of the present invention is to provide an in-situ coated gradient oxygen defect positive electrode active material obtained by the preparation method and its application in sodium ion batteries.

[0008] The third object of the present invention is to provide a sodium ion battery comprising the in-situ coated gradient oxygen defect positive electrode active material, and its positive electrode and positive electrode material.

[0009] Unlike lithium-ion batteries, sodium batteries have low capacity. To improve competitiveness, it is necessary to increase the voltage to allow anions to participate in redox reactions to increase capacity. However, sodium battery anion redox reactions are more likely to occur than lithium batteries, but side reactions are also more numerous and more serious. Conventional doping and coating have poor improvement effects on them, and it is difficult to make them take into account good high-voltage, low-temperature, high-rate and long-cycle application requirements. In view of this problem, the present invention has been studied in depth and provides the following improvement scheme:

[0010] A method for preparing an in-situ coated gradient oxygen defect positive electrode active material for a sodium ion battery, comprising mixing a layered oxide positive electrode active material for a sodium ion battery with XHn and subjecting the mixture to a two-stage gradient heat treatment at a slight positive pressure to obtain the in-situ coated gradient oxygen defect positive electrode active material;

[0011] The X includes at least one of Ca, Zr, Al, Mg, Sn, K, Nd, Sc, Y, and Ce, and the n is the valence of X;

[0012] The two-stage gradient heat treatment stage under slight positive pressure includes a first stage heat preservation process at a temperature of 300-650°C and a second stage heat preservation process at a temperature of 700-900°C.

[0013] The present invention uses XHn to perform surface and bulk thermal modification on the positive electrode active material of the sodium ion battery, and further cooperates with the combination of XHn components and a two-stage gradient mechanism of micro-positive pressure, so that a gradient oxygen defect can be constructed. In addition, an in-situ coating layer can be formed on the surface. The material prepared by the preparation method of the present invention can adapt to the application requirements of special conditions such as high pressure, low temperature, high rate and long cycle of sodium ion batteries, and can effectively improve the gas production problem caused by oxygen precipitation under high pressure.

[0014] In the present invention, the layered oxide positive electrode active material can be any layered oxide active material used in sodium ion batteries. For example, in the present invention, the layered oxide positive electrode active material has the general formula of Na X TMO 2 , wherein the TM contains at least metal M; the M element includes at least one of Ni, Co, Fe, Mn, and Cr.

[0015] Furthermore, the TM also includes N element (also called doping element), and the N element includes at least one of Ca, La, W, Li, K, Sn, Sb, Mg, Ti, Al, Zn, and Zr.

[0016] Preferably, in TM, the metal N accounts for 1 to 20 mol% of the metal M; further, it may be 8 to 16 mol%.

[0017] In the present invention, the layered oxide positive electrode active material can be purchased from commercial products or prepared based on conventional means. For example, as an optional solution of the present invention, the layered oxide positive electrode active material is obtained by calcining a Na source and a TM source.

[0018] In the present invention, the Na source and TM source include at least one of oxides, carbonates, bicarbonates and hydroxides of the respective metal elements.

[0019] In the present invention, the molar ratio of Na / TM is 1.03-1.07:1.

[0020] In the present invention, the atmosphere in the calcination stage is an oxygen-containing atmosphere, such as air.

[0021] In the present invention, the roasting stage includes a first heat preservation process at a temperature of 400-800°C (or 600-750°C) and a second heat preservation process at a temperature of 900-1200°C (or 950-1100°C).

[0022] Preferably, the pressure in the calcination stage is +20 to +100 Pa, and may further be +30 to +50 Pa.

[0023] In the present invention, the temperature of the first heat preservation process is 2 to 10 hours (or 5 to 9 hours); the time of the second heat preservation process is 8 to 15 hours (or 10 to 14 hours).

[0024] In the present invention, XHn is preferably CaH 2 , YH 3 ScH 3 At least one of the following, preferably two or three of them. When three are selected, CaH 2 , YH 3 ScH 3 The molar ratio is 1:0.2-0.6:0.2-0.6. The present invention shows that under the two-stage positive pressure treatment process of the present invention, further combined with the combination of XHn, it is possible to further achieve synergy and enhance the fast charging and low temperature performance of the prepared material.

[0025] In the present invention, XHn accounts for 1 to 8% by mole of the layered oxide positive electrode active material, and may further be 2 to 5% by mole.

[0026] In the present invention, the heat treatment atmosphere is an inert atmosphere, such as argon.

[0027] In the present invention, the XHn is used to carry out the combined treatment, and further cooperates with the combination of the two-stage micro-positive pressure heat treatment mechanism, so that unexpected synergy can be achieved, the defects of the material and the gradient hybridization can be optimized, and the comprehensive performance of the prepared material such as high pressure, low temperature, high rate and long cycle can be further optimized.

[0028] The pressure of the two-stage gradient heat treatment with slight positive pressure is +15Pa~+100Pa; further, it can be +15Pa~+50Pa.

[0029] The temperature of the first stage of heat preservation treatment is 500-600°C. The temperature of the second stage of heat preservation treatment is 750-850°C.

[0030] Preferably, the first heat preservation process lasts for 2 to 5 hours, preferably 3 to 4 hours; the second heat preservation process lasts for 3 to 15 hours, preferably 5 to 10 hours.

[0031] The present invention also provides an in-situ coated gradient oxygen defect positive electrode active material prepared by the preparation method.

[0032] The preparation method described in the present invention can give the prepared material a special oxygen defect degree that decreases from the outside to the inside. In addition, an ultra-thin encapsulation layer can be formed in situ. The material prepared by the preparation method can effectively and significantly improve the electrochemical performance of sodium ion batteries, especially can significantly improve its cycle, rate and low temperature performance under high pressure.

[0033] The present invention also provides an application of an in-situ coated gradient oxygen defect positive electrode active material prepared by the preparation method, which is used as a positive electrode active material for preparing a sodium ion battery.

[0034] The present invention also provides a sodium ion battery comprising the in-situ coated gradient oxygen defect positive electrode active material, and a positive electrode and a positive electrode material thereof.

[0035] The sodium ion battery and its positive electrode and positive electrode material described in the present invention, except for the in-situ coated gradient oxygen defect positive electrode active material described in the present invention, other components and structural parts can be conventional.

[0036] Beneficial Effects

[0037] The present invention adopts XHn to perform surface and bulk thermal modification on the positive electrode active material of the sodium ion battery, and further cooperates with the combination of XHn components and a two-stage gradient mechanism of micro-positive pressure, so that oxygen defects with high surface concentration and gradient distribution to the bulk can be formed during the layered oxide coating process, which can effectively regulate the anion redox reaction, improve the structural stability, cycle performance and capacity of the battery, reduce the irreversible loss of lattice oxygen under the high voltage window, effectively inhibit the oxygen precipitation phenomenon of the material under high voltage, and further improve the gas production problem of the layered oxide.

[0038] The XHn-assisted micro-positive pressure gradient heat treatment process can also optimize the residual sodium on the surface of the positive electrode active material, and can inhibit the volume strain of the material under high voltage and the occurrence of interfacial side reactions. At the same time, it has excellent ionic conductivity, can improve the material's ionic conductivity, and improve the rate and low-temperature performance of the layered oxide positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is the XRD comparison diagram of Example 1 and Comparative Example 1;

[0040] Figures 2 to 6 They are SEM images of Example 1, Comparative Example 1, Comparative Example 4, Comparative Example 5 and Comparative Example 6 respectively;

[0041] Figure 7 The charge and discharge curves of Example 1, Comparative Example 1 and Comparative Example 2 are shown; DETAILED DESCRIPTION

[0042] Embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0044] Example 1

[0045] Step 1: Preparation of layered oxide cathode materials

[0046] Ni 0.33 Fe 0.33 Mn 0.33 (OH) 2 Precursor (M source, where M refers to the metal element in the precursor, such as Ni, Fe and Mn in this case), Na 2 CO 3 and a metal N source (in this case, Sb, Al, Ti, Zn, Sn, and Zr in a molar ratio of 2:2:2:2:2:2:2 2 O 3 、Al 2 O 3 、TiO 2 、ZnO、SnO 2 、ZrO 2 ) were added into a vertical mixer in sequence at a mixing speed of 2000 rpm for 10 min. The mixture was uniformly mixed without white spots to obtain a mixture (in the mixture, the N element in the metal N source was 12% of the molar amount of the M element in the precursor; the Na / (M+N) molar ratio was 1.05:1). The mixture was calcined at 700°C for 7h in an air box furnace at a positive pressure of +30Pa, then heated to 1070°C and calcined for 12h, and finally cooled to room temperature with the furnace. After air flow crushing, a layered oxide was obtained.

[0047] Step 2: Preparation of layered oxides for high-voltage sodium-ion batteries

[0048] According to the metal in the layered oxide in step 1 (M+N total metal molar amount): XHn (in this case CaH 2 ) molar ratio is 98:2, CaH 2The layered oxide obtained in step 1 is added into a vertical mixer for mixing. The mixer speed is 1000 rpm and the mixing time is 5 min. After mixing, the mixture is sintered at 600 ° C (T1) for 3 h in a positive pressure 15 Pa + argon protection box furnace, then heated to 800 ° C (T2) and calcined for 9 h. Finally, it is cooled to room temperature with the furnace to obtain a high-voltage sodium ion battery layered oxide.

[0049] Example 2

[0050] Compared with Example 1, the only difference is that the preparation of the layered oxide in step 1 is changed, and the other operations and parameters are the same as those in Example 1. The experimental groups are:

[0051] Group A: The metal N source was changed to SnO with a molar ratio of Sn, Al, Ti, Zn, La, and Zr of 2:2:3:3:2:2 2 、Al 2 O 3 、TiO 2 、ZnO、La 2 O 3 、ZrO 2 ; and the metal N is 14% of the molar amount of the metal M; other operations and parameters are the same as those in Example 1;

[0052] Group B: Only Ni 0.33 Fe 0.33 Mn 0.33 (OH) 2 Precursor and Na 2 CO 3 Mixed sintering without adding metal N source material; other operations and parameters are the same as those in Example 1;

[0053] Group C: Change the precursor (M source) to Ni 0.2 Fe 0.4 Mn 0.4 (OH) 2 Precursor; other operations and parameters are the same as in Example 1;

[0054] Group D: In the mixture, the molar ratio of Na / (M+N) is 1.06:1; the gas pressure in the sintering stage is a positive pressure of 50 Pa, the temperature of the first stage of insulation is 650°C, and the insulation time is 8 hours; the temperature of the second stage of calcination is 1000°C, and the time is 14 hours. Other operations and parameters are the same as those in Example 1.

[0055] Example 3

[0056] Compared with Example 1, the only difference is that the type and amount of XHn in step 2 are changed. The experimental groups are:

[0057] Group A: XHn to YH 3; The total molar amount is the same as in Example 1;

[0058] Group B: XHn to ScH 3 ; The total molar amount is the same as in Example 1;

[0059] Group C: XHn is CaH with a molar ratio of 1:0.5:0.5 2 :YH 3 ScH 3 The total molar amount is the same as in Example 1;

[0060] Group D: According to the metal in the layered oxide in step 1 (total molar amount of M+N): XHn (in this case, CaH 2 ) molar ratio is 96:4;

[0061] Other operations and parameters are the same as in Example 1.

[0062] Example 4

[0063] Compared with Example 1, the only difference is that the heat treatment conditions in step 2 are changed, specifically:

[0064] The gas pressure during the sintering process is a positive pressure of 50 Pa. The temperature of the first stage sintering is 500° C. and the time is 4 h. The temperature of the second stage sintering is 750° C. and the time is 10 h. Other operations and parameters are the same as in Example 1.

[0065] Comparative Example 1

[0066] Compared with Example 1, the only difference is that the treatment in step 2 is not performed, and the product in step 1 is directly used as the active material. Other operations and parameters are the same as in Example 1.

[0067] Comparative Example 2

[0068] Compared with Example 1, the only difference is that in step 2, an equimolar amount of CaO is used to replace the XHn, and other operations and parameters are the same as in Example 1.

[0069] Comparative Example 3

[0070] Compared with Example 1, the only difference is that in step 2, an equimolar amount of NaBH 4 Replace the CaH 2 , other operations and parameters are the same as in Example 1.

[0071] Comparative Example 4

[0072] Compared with Example 1, the only difference is that in step 2, the T1 / T2 insulation stage is not carried out under positive pressure, that is, it is carried out under atmospheric pressure, and other operations and parameters are the same as in Example 1.

[0073] Comparative Example 5

[0074] Compared with Example 1, the only difference is that the gradient sintering process is not selected in step 2, that is, the temperature T2 is set to be the same as the temperature T1, and the other operations and parameters are the same as in Example 1.

[0075] Comparative Example 6

[0076] Compared with Example 1, the only difference is that the gradient sintering process is not selected in step 2, that is, the temperature T1 is set to be the same as the temperature T2, and the other operations and parameters are the same as in Example 1.

[0077] Test Case

[0078] The positive electrode materials in the embodiments and comparative examples were assembled into half-cells, and the modified positive electrode materials finally obtained in the above cases were dispersed in nitrogen methyl pyrrolidone (NMP) solvent at a mass ratio of 8:1:1 with conductive agent acetylene black and binder polyvinylidene fluoride (PVDF), stirred evenly to obtain electrode slurry, coated the electrode slurry on the surface of aluminum foil, vacuum baked at 80°C for 12h, rolled, and cut to obtain positive electrode sheets; in combination with sodium sheet negative electrode, 1 mol / L NaPF6 and a two-component mixed solvent of EC:DMC=1:1 (v / v) were used to form an electrolyte, a polypropylene microporous membrane was used as a diaphragm, and a CR2032 button battery was assembled in an argon-filled glove box.

[0079] Perform the following test:

[0080] Rate: Constant current charge and discharge test at 2~4.2V / 0.1 / 1 / 5 / 10C at 25℃.

[0081] Low temperature performance: Constant current charge and discharge tests were performed at -20℃ and 25℃ at 2~4.2V / 0.1C.

[0082] Cycle: Perform constant current charge and discharge cycle test at 25℃, 2~4.2V / 1C for 200 cycles.

[0083] The results are shown in Table 1 and Figure 7 shown.

[0084] Table 1

[0085]

[0086] from Figure 1 It can be seen that the CaH 2 Compared with comparative example 1, the in-situ coated gradient oxygen defect positive electrode active material also maintains the crystal structure of O3 without change, and after secondary calcination, the material has higher peak strength and better crystallinity.

[0087] from Figures 2 to 6 From the SEM images, it can be seen that Example 1 has a uniform and dense coating layer on the surface of the particles compared with Comparative Example 1 which has not been treated in step 2; Example 1 has a thinner surface coating layer than Comparative Example 5 which has not been treated at high temperature in the second stage, but no coating layer is observed on the surface of the material directly treated at high temperature in Comparative Example 6; and the surface layer of the material of Comparative Example 4 which has not been treated at positive pressure is an uneven island-shaped coating. This shows that gradient heat treatment can regulate the surface structure so that part of the metal elements obtained by pyrolysis are incorporated into the bulk phase, making the coating layer thinner and denser, and having a higher degree of fit, while positive pressure heat treatment can make the coating layer more uniform.

[0088] Through Table 1 and Figure 7 It can be seen in the examples that the CaH selected in Example 1 2 The in-situ coated gradient oxygen defect positive electrode active material prepared under a specific process has excellent comprehensive electrochemical properties. Compared with the untreated positive electrode material in comparative example 1 and the positive electrode material coated with metal oxide, the material has greatly improved electrical properties such as capacity, rate, cycle and low temperature. By comparing with Example 3, it can be seen that the material performance can be further improved by optimizing the type of metal hydride.

[0089] Combining the SEM results of Example 1 and Comparative Examples 4, 5 and 6 and the electrical properties of the materials, we can find that positive pressure and two-stage gradient heat treatment not only affect the particle morphology but also more significantly affect the electrical properties of the materials. Positive pressure and two-stage gradient heat treatment can effectively improve the capacity, rate, cycle and low-temperature performance of the materials, and are key processes for improving material performance.

[0090] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0091] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing an in-situ coated gradient oxygen defect positive electrode active material for a sodium ion battery, characterized in that: The layered oxide positive electrode active material for sodium ion batteries and XHn are mixed and subjected to a two-stage gradient heat treatment at a slight positive pressure to obtain the in-situ coated gradient oxygen defect positive electrode active material; The X includes at least one of Ca, Zr, Al, Mg, Sn, K, Nd, Sc, Y, and Ce, and the n is the valence of X; The two-stage gradient heat treatment stage under slight positive pressure includes a first stage heat preservation process at a temperature of 300-650°C and a second stage heat preservation process at a temperature of 700-900°C.

2. The preparation method according to claim 1, characterized in that The general formula of layered oxide positive electrode active materials is Na X TMO2, wherein the TM contains at least a metal M; the M element includes at least one of Ni, Co, Fe, Mn, and Cr; Preferably, the TM further comprises N element, and the N element comprises at least one of Ca, La, W, Li, K, Sn, Sb, Mg, Ti, Al, Zn and Zr; Preferably, the metal N accounts for 1 to 20 mol% of the metal M in TM.

3. The preparation method according to claim 2, characterized in that: The layered oxide positive electrode active material is obtained by calcining a Na source and a TM source; Preferably, the Na source and TM source include at least one of oxides, carbonates, bicarbonates and hydroxides of the respective metal elements; Preferably, the molar ratio of Na / TM is 1.03 to 1.07:1; Preferably, the atmosphere during the calcination stage is an oxygen-containing atmosphere; Preferably, the roasting stage includes a first heat preservation process at a temperature of 400 to 800° C. and a second heat preservation process at a temperature of 900 to 1200° C.; Preferably, the pressure in the roasting stage is +20 to +100 Pa; Preferably, the temperature of the first insulation process is 2 to 10 hours; the time of the second insulation process is 8 to 15 hours.

4. The preparation method according to claim 1, characterized in that: XHn is 1 to 8% of the molar amount of the layered oxide positive electrode active material.

5. The preparation method according to claim 1, characterized in that: The heat treatment atmosphere is an inert atmosphere; the slightly positive pressure two-stage gradient heat treatment pressure is +15Pa to +100Pa.

6. The preparation method according to claim 1, characterized in that: The first heat preservation process lasts for 2 to 5 hours, preferably 3 to 4 hours; the second heat preservation process lasts for 3 to 15 hours.

7. An in-situ coated gradient oxygen defect positive electrode active material prepared by the preparation method according to any one of claims 1 to 6.

8. An application of an in-situ coated gradient oxygen defect positive electrode active material prepared by the preparation method according to any one of claims 1 to 6, characterized in that: It is used as positive electrode active material to prepare sodium ion batteries.

9. A positive electrode of a sodium ion battery, characterized in that: The invention comprises an in-situ coated gradient oxygen defect positive electrode active material prepared by the preparation method according to any one of claims 1 to 6.

10. A sodium ion battery, characterized in that: The positive electrode according to claim 9 is included.

Images