A modified layered oxide and its preparation method and application

Abstract

The present invention relates to a modified layered oxide and its preparation method and application. The chemical formula of the modified layered oxide is Na 2 / 3+a K b Cu 1 / 3+x Mn 2 / 3+y M c S d O 2+β , M is selected from one or more of Fe, Co, Ni, Mg, Ti, Al, Cr, Li, Ca, Zn, Sr, Y, Zr, La, F, Si, P, and B; wherein, ‑0.05≤a≤0.05, ‑0.05≤x≤0.05, ‑0.05≤y≤0.05, x+y+c=0, 0<b≤0.05, 0≤c≤0.05, 0<d≤0.025, 0≤β≤4d. The modified layered oxide according to one embodiment of the present invention can be used as a positive electrode material for sodium-ion secondary batteries. By doping with specific amounts of potassium and sulfur, the structural stability between layers of the material during the charge and discharge process can be effectively improved, thereby improving the long cycle and rate performance of the material. The material can also have better interfacial stability and reduce the occurrence of interfacial side reactions.

Description

Technical Field

[0001] The present invention relates to a modified layered oxide, in particular to a modified layered oxide suitable for a positive electrode material of a sodium ion battery. Background Art

[0002] Currently, the most widely studied sodium-ion cathode materials include layered oxides, polyanions, and Prussian blue. Among layered oxide cathode materials, O3-type and P2-type layered oxides are the most common.

[0003] Compared with the high-capacity O3 layered oxide positive electrode material, the sodium ratio of the P2 layered oxide positive electrode material is relatively low, which also leads to the low theoretical capacity of the P2 layered oxide. Although there is no advantage in capacity, the P2 material has greater potential in long cycle and rate.

[0004] Based on this, the main problem faced in the research on P2-type layered oxides is how to prepare high-rate and long-cycle modified materials under lower raw material costs and lower processing costs. Summary of the Invention

[0005] In order to overcome at least one of the defects of the above-mentioned prior art, in the first aspect, one embodiment of the present invention provides a modified layered oxide, the chemical formula of which is Na 2 / 3+a K b Cu 1 / 3+x Mn 2 / 3+y M c S d O 2+β , M is selected from one or more of Fe, Co, Ni, Mg, Ti, Al, Cr, Li, Ca, Zn, Sr, Y, Zr, La, F, Si, P and B;

[0006] Among them, -0.05≤a≤0.05, -0.05≤x≤0.05, -0.05≤y≤0.05, x+y+c=0, 0<b≤0.05, 0≤c≤0.05, 0<d≤0.025, 0≤β≤4d.

[0007] According to one embodiment of the present invention, 0.617≤2 / 3+a≤0.717, 0.001≤b≤0.01, 0.28≤1 / 3+x≤0.37, 0.617≤2 / 3+y≤0.717, 0.01≤c≤0.02, and 0.001≤d≤0.01.

[0008] According to one embodiment of the present invention, 0≤b / (2 / 3+a)≤0.082.

[0009] According to one embodiment of the present invention, the modified layered oxide is a P2-type layered oxide.

[0010] In a second aspect, an embodiment of the present invention provides a method for preparing the above-mentioned modified layered oxide, comprising treating the raw materials through a solid-phase sintering process to obtain the modified layered oxide; wherein the raw materials include a sodium source, a potassium source, a copper source, a manganese source, an M-containing compound and a sulfur source.

[0011] According to one embodiment of the present invention, the sintering temperature of the solid phase sintering process is 750-1000° C., and the sintering time is 5-20 hours.

[0012] According to one embodiment of the present invention, the sodium source includes one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, and sodium sulfide; the potassium source includes one or more of potassium carbonate, potassium hydroxide, potassium bicarbonate, potassium sulfate, and potassium sulfide; the copper source includes one or more of copper oxide, cuprous oxide, copper carbonate, and copper sulfate; the manganese source includes one or more of manganese dioxide, manganese trioxide, manganese tetraoxide, manganese sulfate, and manganese carbonate; the sulfur source includes one or more of sodium sulfide, potassium sulfide, copper sulfate, manganese sulfate, and sulfur powder; and the M-containing compound includes one or more of oxides, salts, and hydroxides of M.

[0013] In a third aspect, one embodiment of the present invention provides a positive electrode material for a sodium ion secondary battery, comprising the modified layered oxide described above or the modified layered oxide prepared by the method described above.

[0014] In a fourth aspect, an embodiment of the present invention provides a sodium ion secondary battery positive electrode plate, the material of which includes the above-mentioned sodium ion secondary battery positive electrode material.

[0015] In a fifth aspect, an embodiment of the present invention provides a sodium ion secondary battery, comprising the above-mentioned sodium ion secondary battery positive electrode sheet.

[0016] The modified layered oxide of one embodiment of the present invention can be used as a positive electrode material for sodium-ion secondary batteries. By doping with specific amounts of potassium and sulfur elements, the structural stability between layers of the material during the charge and discharge process can be effectively improved, thereby improving the long cycle and rate performance of the material; and it can also make the material have better interface stability and reduce the occurrence of interface side reactions.

[0017] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are only used to illustrate specific embodiments and are not to be considered as limiting the present invention.

[0019] Figure 1A This is a SEM image of the modified layered oxide prepared in Example 1 of the present invention;

[0020] Figure 1B for Figure 1A SEM image of the modified layered oxide after washing;

[0021] Figure 2 This is a SEM image of the modified layered oxide prepared in Example 2 of the present invention;

[0022] Figure 3 This is a SEM image of the modified layered oxide prepared in Example 3 of the present invention;

[0023] Figure 4 This is a SEM image of the modified layered oxide prepared in Example 4 of the present invention;

[0024] Figure 5 This is a SEM image of the modified layered oxide prepared in Example 5 of the present invention;

[0025] Figure 6 This is a SEM image of the layered oxide prepared in Comparative Example 1 of the present invention;

[0026] Figure 7 This is a SEM image of the layered oxide prepared in Comparative Example 2 of the present invention;

[0027] Figure 8 This is a SEM image of the layered oxide prepared in Comparative Example 3 of the present invention;

[0028] Figure 9 This is a SEM image of the layered oxide prepared in Comparative Example 4 of the present invention;

[0029] Figure 10 This is a SEM image of the layered oxide prepared in Comparative Example 5 of the present invention;

[0030] Figure 11 The XRD patterns of the layered oxides prepared in Example 1 and Comparative Example 4 of the present invention are shown;

[0031] Figure 12 This is a charge and discharge curve of a button battery made using the modified layered oxide of Example 3 of the present invention as an electrode material;

[0032] Figure 13 This is a charge and discharge curve of a button battery made using the layered oxide of Comparative Example 1 of the present invention as the electrode material;

[0033] Figure 14 This is a charge and discharge curve of a button battery prepared using the modified layered oxide of Example 6 of the present invention as an electrode material;

[0034] Figure 15 This is a charge and discharge curve of a button battery made with the layered oxide of Comparative Example 6 of the present invention as the electrode material. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention are described in detail below, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0036] One embodiment of the present invention provides a modified layered oxide having the chemical formula Na 2 / 3+a K b Cu 1 / 3+x Mn 2 / 3+ y M c S d O 2+β , M is selected from one or more of Fe, Co, Ni, Mg, Ti, Al, Cr, Li, Ca, Zn, Sr, Y, Zr, La, F, Si, P and B;

[0037] Wherein, -0.05≤a≤0.05, -0.05≤x≤0.05, -0.05≤y≤0.05, x+y+c=0, 0<b≤0.05, 0≤c≤0.05, 0<d≤0.025, 0≤β≤4d; the stoichiometric coefficients in the above chemical formula satisfy the balance of element valences, that is, the absolute value of the sum of the valences of all positive ions (or the sum of the charges) is equal to the absolute value of the sum of the valences of all negative ions.

[0038] In one embodiment, in the chemical formula of the modified layered oxide, the stoichiometric coefficient 2 / 3+a of Na is between 0.617 and 0.717, for example, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, and 0.71; the stoichiometric coefficient b of K is greater than 0 and less than or equal to 0.05, and further, the value of b is between 0.001 and 0.01, for example, 0.001, 0.002, 0.005, 0.006, 0.008, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, and 0.045; the stoichiometric coefficient 1 / 3+x of Cu is between 0.28 and 0.39, for example, 0.28, 0.2 9, 0.3, 0.32, 0.33, 0.35, 0.37, 0.38; the stoichiometric coefficient 2 / 3+y of Mn is between 0.617 and 0.717, such as 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71; the stoichiometric coefficient c of M is between 0 and 0.05 The stoichiometric coefficient d of S is greater than 0 and less than or equal to 0.025, such as 0.001, 0.002, 0.004, 0.005, 0.01, 0.02; the stoichiometric coefficient 2+β of O is between 2 and 2.1, such as 2.01, 2.02, 2.05, 2.06, 2.08.

[0039] In one embodiment, potassium ions have a larger atomic diameter than sodium ions. When potassium ions are incorporated into the sodium layer, a large amount of sodium ions are released during the battery's charge and discharge processes. The presence of potassium ions can further support and stabilize the layered structure of the de-sodiumized material, resulting in improved structural stability in the de-intercalated material. In the chemical formula of the modified layered oxide, the stoichiometric coefficient of potassium ions is 0 < b ≤ 0.05, preferably 0 < b < 0.01.

[0040] In one embodiment, sulfur is primarily present on the surface of the modified layered oxide material in the form of Na2SO4. This immobilizes excess sodium ions in the material phase, reduces residual alkali content, isolates the material from air, and enhances the material's air and water stability. In the chemical formula of the modified layered oxide, the stoichiometric coefficient of sulfur is 0 < d ≤ 0.025, preferably 0 < d < 0.01.

[0041] In the modified layered oxide of one embodiment of the present invention, 0≤b / (2 / 3+a)≤0.082, further, 0≤b / (2 / 3+a)≤0.0725, and still further, 0≤b / (2 / 3+a)≤0.069, and the ratio of the stoichiometric coefficients of potassium ions and sodium ions is maintained within the above range, which can enable a secondary battery using the modified layered oxide as the positive electrode material to have a higher capacity and rate.

[0042] In one embodiment, the doping element M can be one or more of Fe, Co, Ni, Mg, Ti, Al, Cr, Li, Ca, Zn, Sr, Y, Zr, La, F, Si, P, and B. M is doped into the bulk phase. Depending on the type of M, the overall performance of the material can be optimized to varying degrees. In the chemical formula of the modified layered oxide, the stoichiometric coefficient of the M ion is preferably 0 < c < 0.05.

[0043] The modified layered oxide according to one embodiment of the present invention is a P2-type layered oxide having a similar microstructure to the existing P2-type layered oxide, for example, belonging to the hexagonal crystal system and having a space group of P63 / mmc.

[0044] One embodiment of the present invention provides a method for preparing the above-mentioned modified layered oxide, comprising treating the raw materials through a solid-phase sintering process to obtain the modified layered oxide; wherein the raw materials include a sodium source, a potassium source, a copper source, a manganese source, a compound containing M and a sulfur source.

[0045] In one embodiment, by using a sulfur source as a component in the raw materials, the S element is doped into the material during the sintering process, so that compounds mainly composed of Na2SO4 are formed on the surface of the material when the material is sintered and cooled. The formation of these compounds fixes the excess sodium ions in the material phase on the one hand, and reduces the generation of Na2CO3 on the surface of the material on the other hand. The main difference between Na2SO4 and Na2CO3 is that Na2SO4 does not absorb water easily, while Na2CO3 is alkaline and easily absorbs water, which will cause the deterioration of the material. Therefore, the presence of the Na2SO4 layer can prevent the ionic material from directly contacting the air, play a certain role in storing sodium and protecting the material, thereby avoiding the excessive amount of residual alkali in the material caused by contact with air, and the decrease in capacity and cycle performance.

[0046] In one embodiment, the sintering temperature of the solid phase sintering process can be 750-1000°C, and can further be 750-950°C, for example, 760°C, 780°C, 800°C, 820°C, 840°C, 850°C, 860°C, 880°C, 900°C, 920°C, 950°C, 980°C; the sintering time can be 5-20h, and can further be 8-15h, for example, 6h, 8h, 10h, 12h, 14h, 16h, 18h.

[0047] In one embodiment, the sodium source can be one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, and sodium sulfide; the potassium source can be one or more of potassium carbonate, potassium hydroxide, potassium bicarbonate, potassium sulfate, and potassium sulfide; the copper source can be one or more of copper oxide, cuprous oxide, copper carbonate, and copper sulfate; the manganese source can be one or more of manganese dioxide, manganese trioxide, manganese tetraoxide, manganese sulfate, and manganese carbonate; the sulfur source can be one or more of sodium sulfide, potassium sulfide, copper sulfate, manganese sulfate, and sulfur powder; the compound containing M can be one or more of oxides, salts (such as carbonates, metal fluorides), and hydroxides of M, and the metal fluoride can be aluminum fluoride.

[0048] A method for preparing a modified layered oxide according to one embodiment of the present invention comprises:

[0049] The various raw material components are processed through a mixing process;

[0050] sintering the mixed raw materials in a high-temperature atmosphere; and

[0051] The sintered product is crushed.

[0052] In one embodiment, the mixing process may be one or more of a ball milling process and an oxide dry / wet mixing process.

[0053] One embodiment of the present invention provides a positive electrode material for a sodium ion secondary battery, comprising the modified layered oxide described above.

[0054] One embodiment of the present invention provides a sodium ion secondary battery positive electrode plate, the material of which includes the above-mentioned sodium ion secondary battery positive electrode material.

[0055] One embodiment of the present invention provides a sodium ion secondary battery, comprising the aforementioned sodium ion secondary battery positive electrode sheet. The sodium ion secondary battery can be used in 3C, electric vehicles, energy storage and other fields.

[0056] Compared with the prior art, the modified layered oxide of the present invention can achieve at least one of the following beneficial effects:

[0057] 1. The modified layered oxide according to one embodiment of the present invention can be used as a positive electrode material for sodium-ion secondary batteries. By doping with a specific amount of potassium, the structural stability between layers of the material during the charge and discharge process can be effectively improved, thereby improving the long-cycle and rate performance of the material. By doping with a specific amount of sulfur, an effective separator layer is formed between the material and the air or electrolyte, thereby giving the material better interface stability and reducing the occurrence of interfacial side reactions.

[0058] 2. The modified layered oxide of one embodiment of the present invention, through the doping of potassium and sulfur, can withstand a higher discharge voltage upper limit when used as a battery positive electrode material, effectively improving the material's resistance to high-voltage charge and discharge, and reducing the gas production problem caused by side reactions during the high-voltage cycle process (low residual alkali on the material surface).

[0059] 3. The modified layered oxide according to one embodiment of the present invention uses cheap and readily available raw materials, resulting in a relatively low raw material cost.

[0060] 4. The modified layered oxide according to one embodiment of the present invention has a simple preparation process and can be mass-produced using commonly used sintering and pulverizing equipment. Furthermore, the material is stable and can be produced without a dehumidified environment, so the processing and post-processing costs are low.

[0061] The following further describes the modified layered oxide and its preparation according to one embodiment of the present invention, with reference to the accompanying drawings and specific examples. In the raw materials used in the examples and comparative examples, the sodium content is 2% in excess of that in the designed chemical formula to compensate for sintering losses of the sodium salt.

[0062] Example 1

[0063] According to Na 0.69 K 0.005 Cu 0.32 Mn 0.66 Mg 0.02 S 0.01 The stoichiometric ratio of O2 was determined, and corresponding amounts of sodium carbonate as a sodium source, copper oxide as a copper source, manganese trioxide as a manganese source, potassium sulfide as a potassium source and a sulfur source, and magnesium hydroxide as a magnesium source were weighed respectively; the above components were fully mixed using a high-speed mixing device; thereafter, the mixed raw materials were kept warm in an atmosphere furnace at 750°C for 20 hours, and after being taken out of the furnace, the obtained materials were crushed using a jet mill. The particle size D50 value of the crushed material can be found in Table 1, and a modified layered oxide of the P2 phase was obtained.

[0064] The obtained product was tested for component content using an ICP element analyzer, and the results showed that the content of each element in the modified layered oxide was basically consistent with the above chemical formula.

[0065] Example 2

[0066] According to Na 0.68 K 0.005 Cu 0.33 Mn 0.62 Ti 0.04 Li 0.005 La 0.005 S 0.001The stoichiometric ratio of O2 was adjusted, and the corresponding amounts of sodium hydroxide as the sodium source, potassium carbonate as the potassium source, copper oxide as the first copper source, copper sulfate as the sulfur source and the second copper source, manganese dioxide as the manganese source, titanium dioxide as the titanium source, lithium carbonate as the lithium source, and lanthanum trioxide as the lanthanum source were weighed respectively; the above components were mixed by a ball milling mixing process, and were fully ground and mixed for at least 30 minutes (the particle size of the mixture was controlled to be D50 < 2 μm); thereafter, the mixed raw materials were kept warm in an atmosphere furnace at 800°C for 15 hours, and the obtained materials were crushed by a jet mill after being taken out of the furnace. The particle size D50 value of the crushed material was shown in Table 1, and a modified layered oxide of the P2 phase was obtained.

[0067] Example 3

[0068] According to Na 0.71 K 0.002 Cu 0.35 Mn 0.64 Ni 0.005 Zr 0.005 S 0.004 The stoichiometric ratio of O2 was adjusted, and corresponding amounts of sodium bicarbonate as a sodium source, potassium sulfate as a potassium source and a sulfur source, copper carbonate as a copper source, manganese carbonate as a manganese source, nickel hydroxide as a nickel source, and zirconium dioxide as a zirconium source were weighed respectively; the above components were mixed using a rotary evaporation device + ethanol wet method to obtain a fully mixed raw material; thereafter, the mixed raw material was kept warm in an atmosphere furnace at 850°C for 18 hours, and after being taken out of the furnace, the obtained material was crushed by a jet mill. The particle size D50 value of the crushed material can be found in Table 1, and a modified layered oxide of the P2 phase was obtained.

[0069] Among them, the mixing method of rotary evaporation equipment + ethanol wet method is as follows: all raw materials are added to the rotary evaporation equipment, and an appropriate amount of ethanol is added as a stirring dispersion liquid, wherein the mass ratio of ethanol to raw materials is 1:1, and the mixture is fully stirred and mixed in the rotary evaporation equipment for at least 5 minutes, and then heated to between 70 and 90°C under vacuum conditions, and rotary evaporation is performed to obtain raw materials that are evenly mixed after evaporation.

[0070] Example 4

[0071] According to Na 0.62 K 0.001 Cu 0.283 Mn 0.717 S 0.025 The stoichiometric ratio of O2 was adjusted, and corresponding amounts of sodium carbonate as a sodium source, copper oxide as a copper source, manganese trioxide as a manganese source, potassium carbonate as a potassium source, and sulfur powder as a sulfur source were weighed respectively; the above components were fully mixed using a high-speed mixing device; thereafter, the mixed raw materials were kept warm in an atmosphere furnace at 920°C for 10 hours, and after being taken out of the furnace, the obtained materials were crushed using a jet mill. The particle size D50 value of the crushed material can be found in Table 1, and a modified layered oxide of the P2 phase was obtained.

[0072] Example 5

[0073] According to Na 0.717 K 0.05 Cu 0.37 Mn 0.62 Al 0.005 Fe 0.01 F 0.015 S 0.01 The stoichiometric ratio of O2 was determined, and the corresponding amounts of sodium hydroxide as the sodium source, potassium carbonate as the first potassium source, potassium sulfide as the sulfur source and the second potassium source, copper oxide as the copper source, manganese tetraoxide as the manganese source, aluminum fluoride as the aluminum source and the fluorine source, and ferric oxide as the iron source were weighed respectively; the above components were mixed by a ball milling mixing process, and the mixture was fully ground and mixed for at least 30 minutes (the particle size of the mixture was controlled to be D50 < 2 μm); thereafter, the mixed raw materials were kept warm in an atmosphere furnace at 980°C for 5 hours, and the obtained materials were crushed by a jet mill after being taken out of the furnace. The particle size D50 value of the crushed material can be found in Table 1, and a modified layered oxide of the P2 phase was obtained.

[0074] Example 6

[0075] According to Na 0.65 K 0.05 Cu 0.32 Mn 0.66 Mg 0.02 S 0.01 The stoichiometric ratio of O2 was determined, and corresponding amounts of sodium carbonate as a sodium source, copper oxide as a copper source, manganese trioxide as a manganese source, potassium sulfide as a potassium source and a sulfur source, and magnesium hydroxide as a magnesium source were weighed respectively; the above components were fully mixed using a high-speed mixing device; thereafter, the mixed raw materials were kept warm in an atmosphere furnace at 750°C for 20 hours, and after being taken out of the furnace, the obtained materials were crushed using a jet mill. The particle size D50 value of the crushed material can be found in Table 1, and a modified layered oxide of the P2 phase was obtained.

[0076] Comparative Example 1

[0077] According to Na 0.70 Cu 0.35 Mn 0.65 The stoichiometric ratio of O2 was determined, and corresponding amounts of sodium carbonate as a sodium source, copper oxide as a copper source, and manganese dioxide as a manganese source were weighed respectively; the above components were fully mixed using a high-speed mixing device; thereafter, the mixed raw materials were kept warm in an atmosphere furnace at 750°C for 20 hours, and after being taken out of the furnace, the obtained materials were crushed using a jet mill. The particle size D50 value of the crushed materials can be found in Table 1, and a layered oxide of the P2 phase was obtained.

[0078] Comparative Example 2

[0079] According to Na 0.71 K 0.01 Cu 0.36 Mn0.63 Ti 0.01 The stoichiometric ratio of O2 was adjusted, and corresponding amounts of sodium hydroxide as a sodium source, potassium hydroxide as a potassium source, copper oxide as a copper source, manganese manganese tetroxide as a manganese source, and titanium dioxide as a titanium source were weighed respectively; the above components were mixed using a ball mill with zirconium oxide beads, and the mixture was fully ground and mixed for at least 30 minutes (the particle size of the mixture was controlled to be less than 2 μm); thereafter, the mixed raw materials were kept warm in an atmosphere furnace at 850°C for 10 hours, and the obtained materials were crushed by a jet mill after being taken out of the furnace. The particle size D50 value of the crushed material can be found in Table 1, and a layered oxide of the P2 phase was obtained.

[0080] Comparative Example 3

[0081] According to Na 0.62 Cu 0.30 Mn 0.70 S 0.01 The stoichiometric ratio of O2 was adjusted, and corresponding amounts of sodium carbonate as the first sodium source, sodium sulfide as the second sodium source and sulfur source, cuprous oxide as the copper source, and manganese tetraoxide as the manganese source were weighed respectively; the above components were mixed using the same rotary evaporation equipment + ethanol wet method as in Example 3 to obtain a fully mixed raw material; thereafter, the mixed raw material was kept warm in an atmosphere furnace at 1000°C for 5h, and after being taken out of the furnace, the obtained material was crushed by a jet mill. The particle size D50 value of the crushed material was shown in Table 1, and a layered oxide of the P2 phase was obtained.

[0082] Comparative Example 4

[0083] According to Na 0.64 K 0.06 Cu 0.32 Mn 0.66 Mg 0.02 S 0.01 The stoichiometric ratio of O2 was determined, and corresponding amounts of sodium carbonate as a sodium source, copper oxide as a copper source, manganese trioxide as a manganese source, potassium sulfide as a potassium source and a sulfur source, and magnesium hydroxide as a magnesium source were weighed respectively; the above components were fully mixed using a high-speed mixing device; thereafter, the mixed raw materials were kept warm in an atmosphere furnace at 750°C for 20 hours, and after being taken out of the furnace, the obtained materials were crushed using a jet mill. The particle size D50 value of the crushed material can be found in Table 1, and a modified layered oxide of the P2 phase was obtained.

[0084] Comparative Example 5

[0085] According to Na 0.77 K 0.002 Cu 0.35 Mn 0.64 Ni 0.005 Zr 0.005 S 0.03The stoichiometric ratio of O2 was adjusted, and corresponding amounts of sodium bicarbonate as a sodium source, potassium sulfate as a potassium source and a sulfur source, copper carbonate as a copper source, manganese carbonate as a manganese source, nickel hydroxide as a nickel source, and zirconium dioxide as a zirconium source were weighed respectively; the above components were mixed using the same rotary evaporation equipment + ethanol wet method as in Example 3 to obtain a fully mixed raw material; thereafter, the mixed raw material was kept warm in an atmosphere furnace at 850°C for 18 hours, and after being taken out of the furnace, the obtained material was crushed by a jet mill. The particle size D50 value of the crushed material was shown in Table 1, and a modified layered oxide of the P2 phase was obtained.

[0086] Comparative Example 6

[0087] According to Na 0.63 K 0.001 Cu 0.283 Mn 0.717 S 0.03 The stoichiometric ratio of O2 was adjusted, and corresponding amounts of sodium carbonate as a sodium source, copper oxide as a copper source, manganese trioxide as a manganese source, potassium carbonate as a potassium source, and sulfur powder as a sulfur source were weighed respectively; the above components were fully mixed using a high-speed mixing device; thereafter, the mixed raw materials were kept warm in an atmosphere furnace at 920°C for 10 hours, and after being taken out of the furnace, the obtained materials were crushed using a jet mill. The particle size D50 value of the crushed material can be found in Table 1, and a modified layered oxide of the P2 phase was obtained.

[0088] The layered oxides prepared in Examples 1 to 6 and Comparative Examples 1 to 6 were used as positive electrode materials to prepare button-type batteries according to the following method. The layered oxides prepared in Examples 1 to 6 and Comparative Examples 1 to 6 and the button-type batteries prepared therefrom were subjected to relevant tests. The test results are shown in Table 1.

[0089] Assembly and testing of button batteries

[0090] Layered oxide, conductive carbon black SP, and polyvinylidene fluoride (PVDF) are mixed and ground evenly in a mass ratio of 90:5:5, and NMP is added to the mixture to form a viscous glue. The glue is coated on aluminum foil and dried in a vacuum oven to serve as the positive electrode sheet, and the metal sodium sheet is used as the negative electrode sheet. A glass fiber film is used as a separator, and a 1 mol / L EC / DMC solution of sodium hexafluorophosphate is used as the electrolyte. A button half-cell is assembled in the order of positive electrode shell, positive electrode sheet, separator, negative electrode, and negative electrode shell.

[0091] The prepared button half-cell was subjected to electrical performance testing, with the gram capacity at 0.1C and 1C and the cycle retention rate at 1C rate being used as the evaluation basis.

[0092] H2O content test

[0093] After the layered oxide was sintered and crushed in a dry environment, the sample was exposed to room temperature for 24 hours and then the moisture content was tested using a Karl Fischer moisture tester under the same conditions.

[0094] pH Testing

[0095] After the layered oxide is crushed in a dry environment, it is immediately sent for testing. The test method is as follows: at room temperature, take 2g of layered oxide material, add 40mL of pure water, stir magnetically for 10 minutes, let it stand for 5 minutes, and measure the pH value to record it as the material pH.

[0096] Particle size testing

[0097] After the layered oxide is crushed in a dry environment, the sample is immediately sent for testing. The testing method is: using a Malvern particle size analyzer, take 1g of layered oxide material, use pure water as the dispersion liquid, and perform particle size volume distribution testing under ultrasonic conditions.

[0098] Table 1

[0099]

[0100] Figures 1A to 10 The SEM images of the layered oxides prepared in Examples 1 to 6 and Comparative Examples 1 to 6 are shown. According to the descriptions of Examples 1 to 6 and Comparative Examples 1 to 6, among all the layered oxides, only the layered oxides of Comparative Examples 1 and 2 are not doped with S element. Figures 1A to 10 It can be seen that, except for the layered oxides of Comparative Examples 1 and 2, the surfaces of the layered oxide materials of other comparative examples and Examples 1 to 5 all have coating layers to varying degrees, indicating that the doped S element is formed on the surface of the material in the form of a coating layer.

[0101] Figure 1A 、 1B The following are SEM images of the layered oxide material from Example 1 before and after water washing. Testing revealed a sulfur content of 0.27% before water washing, which is consistent with the sulfur content indicated by the stoichiometric coefficient in the chemical formula. After water washing, the sulfur content was 0.02%. This result indicates that water washing can remove sulfur, and therefore, sulfur should primarily exist on the surface of the material in the form of soluble sodium sulfate. Combined with the SEM characteristics of the material before and after water washing and the change in sulfur content, it can be further determined that the fuzzy coating on the surface before water washing is primarily composed of sodium sulfate.

[0102] Further reference to the physical and chemical performance data in Table 1 shows that the layered oxides of Comparative Examples 1 and 2, which do not contain sulfur, have high moisture content and high pH values, indicating that the materials easily absorb water and have poor air stability, further confirming the role of sulfur doping. Furthermore, higher pH values ​​indicate higher residual alkali content and poorer water stability in the materials, leading to adverse effects such as difficult back-end battery cell processing, poor cycling, and gas generation in the battery cells when used as positive electrode materials. Therefore, the poor air and water stability of layered oxide materials is not conducive to their industrial application.

[0103] As can be seen from the descriptions of Examples 1-6 and Comparative Examples 1 and 3, compared to Examples 1-6, the layered oxides of Comparative Examples 1 and 3 are not doped with the K element. However, according to the electrical performance results in Table 1, the capacity, rate, and cycle performance of batteries using the layered oxides of Comparative Examples 1 and 3 as positive electrode materials are generally worse than those of the batteries of Examples 1-6, fully demonstrating that doping the positive electrode layered oxide with an appropriate amount of potassium is more beneficial for improving the electrochemical performance of the battery.

[0104] According to the descriptions of Examples 1-6 and Comparative Examples 2 and 3, compared to Examples 1-6, the layered oxide of Comparative Example 2 is doped with K but not S; and the layered oxide of Comparative Example 3 is doped with S but not K. The electrical performance results in Table 1 show that the electrical performance of batteries using the layered oxides of Comparative Examples 2 and 3 as positive electrode materials is worse than that of the batteries of Examples 1-6, indicating that the dual-element K and S doping of the layered oxide has a synergistic effect in improving material performance.

[0105] According to the description of Example 1 and Comparative Example 4, the main difference between the layered oxides of Example 1 and Comparative Example 4 is that the molar ratio of potassium element to sodium element in Comparative Example 4 is 0.094, which is greater than the ratio of 0.082 specified in one embodiment of the present invention and also greater than the corresponding molar ratio of 0.007 in Example 1. Figure 11 The XRD patterns of the layered oxides prepared in Example 1 and Comparative Example 4 show that the characteristic peaks of the layered oxides in Comparative Example 4 are weakened (the portion marked with a dotted line in the figure), which is caused by excessive doping of potassium in Comparative Example 4.

[0106] Referring again to Table 1, when the stoichiometric coefficient b of embodiment 5 and embodiment 6 potassium elements increases to 0.05, the cycle retention rate of corresponding batteries is respectively 86% and 82%, which is at a relatively low level. On the basis of embodiment 6 materials, potassium content is continued to be increased, and its stoichiometric coefficient b is 0.06 (i.e. comparative example 4). As can be seen from Table 1, the capacity and rate of comparative example 4 batteries are significantly reduced, and the retention rate is significantly reduced to 62%. This is because the excessive doping of potassium element has caused the reduction of the amount of sodium, and the effective active substance is reduced, and the structural influence of the matrix material of the P2 phase by excessive potassium element doping is more serious, which further also causes the deterioration of material performance. Thus, in modified layered oxides, the value of the stoichiometric coefficient b of potassium should not exceed 0.05, and the ratio of the stoichiometric coefficients of potassium ion and sodium ion is preferably 0≤b / (2 / 3+a)≤0.082.

[0107] According to the description of Example 3, Example 4, Comparative Example 5, and Comparative Example 6, the main difference between the layered oxides of Example 3, Example 4, Comparative Example 5, and Comparative Example 6 is that the S element doped in Comparative Example 5 and Comparative Example 6 is higher, and the corresponding stoichiometric coefficient d value is greater than 0.025. Comparing the electrical performance data in Table 1, it can be seen that the comprehensive performance of the batteries of Example 3 and Example 4 is better than that of Comparative Example 5 and Comparative Example 6, mainly in terms of rate, cycle, and capacity. The battery of Example 4 is slightly worse than the battery of Example 3, and the performance of the batteries of Comparative Example 5 and Comparative Example 6, which further increase the S content of the positive electrode material, becomes even worse. This is because excessive doping of sulfur elements will cause a large amount of sodium sulfate to form on the surface of the material, and sodium sulfate itself has no electrochemical activity. Although excessive sodium sulfate can increase the air stability of the material (lower moisture), it will also cause its own electrochemical performance to deteriorate. Therefore, in the modified layered oxide, the value of the stoichiometric coefficient d of the sulfur ion should not exceed 0.025.

[0108] Overall, the positive electrode materials and batteries of Examples 1-6 outperformed those of Comparative Examples 1-6. For example, the retention rates of the batteries of Comparative Examples 1-6 were lower, while those of Examples 1-6 were higher, demonstrating that the positive electrode materials of the batteries of Examples possess high voltage resistance. These results clearly demonstrate that the overall performance of layered oxides as positive electrode materials can be improved by appropriately doping them with K and S.

[0109] Furthermore, the stoichiometric coefficient b of K in Examples 1 to 4 is within 0.005, and the b value of Examples 5 and 6 is 0.05, which is greater than the b value in Examples 1 to 4. Referring to the data in Table 1, it can be seen that compared with Examples 1 to 4, the 1C 100-cycle retention rate of the batteries in Examples 5 and 6 has decreased (86% and 82%, respectively), indicating that the potassium content in the material should not be too high, that is, the value of the stoichiometric coefficient b of K should be less than or equal to 0.05. In addition, the data of Comparative Example 4 can further prove that after the value of b exceeds 0.05, the corresponding physical and chemical properties deteriorate overall.

[0110] Similarly, the stoichiometric coefficients d of S in Examples 1-3, 5, and 6 were all within 0.01. The b value of Example 4 was 0.025, which was greater than the d values ​​in Examples 1-3, 5, and 6. Referring again to the data in Table 1, the capacity of the battery in Example 4 was significantly reduced compared to that in Examples 1-3, 5, and 6, indicating that the sulfur content in the sulfur-containing material should not be too high, that is, the stoichiometric coefficient d of S should be less than or equal to 0.025. Furthermore, the data from Comparative Examples 5 and 6 further demonstrate that when the value of d exceeds 0.025, the corresponding overall physical and chemical properties deteriorate.

[0111] in addition, Figure 12 This is a charge and discharge curve of a button battery prepared using the modified layered oxide of Example 3 of the present invention as the electrode material. As can be seen from the figure, the curve has a relatively obvious platform position and is highly symmetrical, indicating that the polarization of the material is smaller. Figure 14 This is a charge and discharge curve of a button battery made using the modified layered oxide of Example 6 of the present invention as an electrode material. Figure 14 The curve has Figure 12 The curves have the same characteristics.

[0112] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A modified layered oxide, characterized in that The chemical formula of the modified layered oxide is Na 2 / 3+a K b Cu 1 / 3+ x Mn 2 / 3+y M c S d O 2+β , M is selected from one or more of Fe, Co, Ni, Mg, Ti, Al, Cr, Li, Ca, Zn, Sr, Y, Zr, La, F, Si, P and B; Wherein, -0.05≤a≤0.05, -0.05≤x≤0.05, -0.05≤y≤0.05, x+y+c=0, 0<b≤0.05, 0≤c≤0.05, 0<d≤0.025, 0≤β≤4d, 0<b / (2 / 3+a)≤0.082; Potassium ions are doped in the sodium layer; sulfur elements mainly exist in the form of Na2SO4 on the surface of the modified layered oxide material.

2. The modified layered oxide according to claim 1, characterized in that 0.617≤2 / 3+a≤0.717, 0.001≤b≤0.01, 0.28≤1 / 3+x≤0.37, 0.617≤2 / 3+y≤0.717, 0.01≤c≤0.02, 0.001≤d≤0.

01.

3. The modified layered oxide according to claim 1, characterized in that 0<b / (2 / 3+a)≤0.0725.

4. The modified layered oxide according to any one of claims 1 to 3, characterized in that The modified layered oxide is a P2 type layered oxide.

5. A method for preparing the modified layered oxide according to any one of claims 1 to 4, characterized in that: The method comprises processing raw materials through a solid phase sintering process to obtain the modified layered oxide; wherein the raw materials include a sodium source, a potassium source, a copper source, a manganese source, a compound containing M and a sulfur source.

6. The method according to claim 5, characterized in that The sintering temperature of the solid phase sintering process is 750-1000° C., and the sintering time is 5-20 hours.

7. The method according to claim 5, characterized in that The sodium source includes one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, and sodium sulfide; the potassium source includes one or more of potassium carbonate, potassium hydroxide, potassium bicarbonate, potassium sulfate, and potassium sulfide; the copper source includes one or more of copper oxide, cuprous oxide, copper carbonate, and copper sulfate; the manganese source includes one or more of manganese dioxide, manganese trioxide, manganese tetraoxide, manganese sulfate, and manganese carbonate; the sulfur source includes one or more of sodium sulfide, potassium sulfide, copper sulfate, manganese sulfate, and sulfur powder; and the M-containing compound includes one or more of oxides, salts, and hydroxides of M.

8. A positive electrode material for a sodium ion secondary battery, characterized in that: The modified layered oxide comprises the modified layered oxide according to any one of claims 1 to 4 or the modified layered oxide prepared by the method according to any one of claims 5 to 7.

9. A positive electrode plate for a sodium ion secondary battery, characterized in that: The material of the sodium ion secondary battery positive electrode substrate includes the sodium ion secondary battery positive electrode material according to claim 8.

10. A sodium ion secondary battery, characterized in that: Including the sodium ion secondary battery positive electrode sheet according to claim 9.

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