Layered P2-phase sodium ion battery positive electrode material, preparation method and sodium ion battery

Abstract

The invention relates to the technical field of battery positive electrode materials, in particular to a layered P2-phase sodium-ion battery positive electrode material, a preparation method and a sodium-ion battery. The chemical general formula of the layered P2-phase sodium ion battery positive electrode material is Na < 0.8 > Li < 0.2 > Mg < 0.05 > Mn < 0.95-x > O < 2 >. The preparation method of the positive electrode material comprises the following steps: performing ball-milling compounding on sodium salt, lithium salt and metal oxide to prepare a precursor; the metal oxide is manganese dioxide; and tabletting the precursor, and calcining at the temperature of 900 DEG C + / -50 DEG C in an air atmosphere to prepare the layered P2-phase sodium-ion battery positive electrode material. According to the invention, through lithium doping, oxidation reduction of layered oxide positive electrode anions is excited, ultrahigh energy density is realized, the capacity retention ratio of the high-energy-density positive electrode can be improved, and the problem of voltage attenuation can be inhibited, so that the energy density of the high-energy-density positive electrode can be effectively maintained.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries and their cathode materials, and specifically relates to a layered P2-phase sodium-ion battery cathode material, a preparation method thereof, and a sodium-ion battery. Background Art

[0002] Sodium-ion batteries, compared with lithium-ion batteries, have the advantages of good fast-charging performance, high temperature tolerance, high safety, and the cost advantage of high sodium reserves, and have good development prospects in the future energy storage and power battery markets. However, the relatively low energy density of sodium-ion batteries restricts their further development and commercialization process. The cathode, as the most important component in the sodium-ion battery system, determines the energy density of the sodium-ion battery. Developing a sodium-ion battery cathode with high energy density and maintaining cycle stability is the current research focus and the direction to overcome.

[0003] The cathode materials of sodium-ion batteries include layered transition metal oxides, tunnel-type transition metal oxides, polyanion compounds, Prussian blue compounds, and organic cathode materials, etc. Among them, layered transition metal oxides have become one of the current research hotspots due to their advantages such as high theoretical specific capacity, simple material synthesis process, rich components, and controllable structure.

[0004] The structural general formula of layered transition metal oxides is Na x MO2, where 0 < x ≤ 1, and M represents one or more transition metal elements, such as Mn, Ni, Co, Fe, Ru, Gr, etc. The structure of layered Na x MO2 compounds can be regarded as composed of an MO6 octahedron layer formed by transition metal elements and six surrounding oxygen atoms and an alternating stacking of a NaO6 alkali metal layer. Oxygen atoms mainly play the role of a lattice framework in the structure of layered Na x MO2 compounds. The most common layered transition metal oxides are mainly composed of edge-sharing MO6 octahedrons. Among them, the edges of the MO6 octahedrons are connected, having a two-dimensional Na + insertion / extraction channel.

[0005] Sodium-based layered oxides are mainly divided into two major types: O3 type and P2 type, where O represents the coordination environment of Na + at the octahedral site, and P represents the coordination environment of Na + at the trigonal prism site. The numbers 2 or 3 represent the stacking layer number of the minimum repeating unit of oxygen. The P2 type has better rate performance and cycle stability compared with the O3 type. In the high-energy density layered P2-phase cathode of sodium-ion batteries, Na x [A y TM 1-y O2, where TM represents transition metal ions and A represents Li+ , Mg 2+ , Zn 2+ or layered oxides with anion redox activity such as vacancies can achieve a high discharge specific capacity. During the Na + insertion / extraction process, both transition metal cations and oxygen anions can participate in the charge compensation reaction, thereby obtaining a higher energy density.

[0006] However, the cathode material of this sodium-ion battery is still limited due to the defects of poor structural stability and rapid attenuation of the discharge specific capacity. In addition, the layered oxide cathode material that activates the anion redox activity also has a serious problem of voltage attenuation. During the cycling process of the sodium-ion battery, the gradual decrease of the average working voltage and the discharge specific capacity inevitably causes a large amount of energy loss, greatly reducing the energy density of the sodium-ion battery and hindering its practical utilization. Summary of the Invention

[0007] In order to solve the problems of rapid attenuation of the discharge specific capacity and serious voltage attenuation existing in the existing high-energy-density cathodes, the purpose of the present invention is to provide a layered P2-phase sodium-ion battery cathode material, a preparation method thereof, and a sodium-ion battery, so as to improve the capacity retention rate of the high-energy-density cathode and suppress the problem of voltage attenuation, thereby effectively maintaining its energy density.

[0008] To achieve the above object, the technical solution of the present invention is as follows.

[0009] In the first aspect of the present invention, a layered P2-phase sodium-ion battery cathode material is provided. The chemical general formula of the layered P2-phase sodium-ion battery cathode material is: Na y Li x Mg 0.05 Mn 0.95-x O2, where 0.2 ≤ x ≤ 0.21 and 0.78 < y ≤ 0.82.

[0010] Preferably, the chemical general formula of the layered P2-phase sodium-ion battery cathode material is: Na 0.8 Li 0.2 Mg 0.05 Mn0 .75 O2.

[0011] Through lithium doping, the present invention realizes the Na-O-Li configuration, and the unhybridized oxygen 2p orbitals are repositioned to a level higher than that of the Na-O-TM configuration, successfully activating the anion redox of the layered oxide cathode and achieving an ultra-high energy density. In addition, by adjusting the lithium doping amount within the range of 0.2 to 0.21, while improving the capacity retention rate of the high-energy density cathode and suppressing voltage decay, the energy density is effectively maintained, solving the problems of rapid discharge specific capacity decay and severe voltage decay existing in the existing high-energy density cathodes.

[0012] Compared with the P2-phase material Na 2 / 3 [Li 1 / 7 Mn 5 / 14 [Mg 1 / 7 Mn 5 / 14 O2, the capacity retention rate of the layered P2-phase sodium-ion battery cathode material of the present invention increased from 85.5% to 90.5% after 50 cycles at 1C. Moreover, after 200 cycles at a current density of 1C, the average discharge voltage retention rate of the layered P2-phase sodium-ion battery cathode material of the present invention can reach 98.49%.

[0013] The second aspect of the present invention provides a preparation method of a layered P2-phase sodium-ion battery cathode material, including the following steps: Ball-mill and compound a sodium salt, a lithium salt and a metal oxide to prepare a precursor; the metal oxide is magnesium oxide and manganese dioxide; press the precursor into tablets, and then calcine at a temperature of 900°C ± 50°C in an air atmosphere to prepare the layered P2-phase sodium-ion battery cathode material.

[0014] Subsequent test results show that as the calcination temperature increases, the specific capacity of the battery first increases and then decreases, and the specific capacity of the battery reaches the maximum at a calcination temperature of 900°C.

[0015] Preferably, the sodium salt is sodium carbonate; the lithium salt is lithium carbonate.

[0016] Preferably, before the ball-milling compounding, it further includes: weighing each raw material according to the molar ratio of Na, Li, Mg, and Mn of 0.83 to 0.86: 0.21 to 0.22: 0.05: 0.75. In the present invention, in order to offset the volatilization during the calcination process, the molar ratios of Na and Li are both increased by 5% on the basis of y:x.

[0017] Preferably, the calcination time is 9h to 15h. Subsequent test results show that as the calcination time increases, the specific capacity of the battery first increases and then decreases, and the specific capacity of the battery reaches the maximum at a calcination time of 12h. When the calcination time is 15h, the specific capacity of the battery is not much different from that at 12h. Therefore, the calcination time is preferably 12 to 15h.

[0018] Preferably, the conditions for tabletting are: the filling amount is 340 mg to 380 mg, the pressure is 14 Mpa to 16 Mpa, and the tabletting time is 8 min to 14 min.

[0019] Preferably, in the ball milling and compounding, ethanol is used as a dispersant, and sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide are ball milled and compounded.

[0020] Preferably, the rotation speed of the ball milling and compounding is 360 r / min to 400 r / min, and the time of the ball milling and compounding is 8 h to 10 h.

[0021] In the third aspect of the present invention, a sodium ion battery comprising a layered P2-phase sodium ion battery cathode material is provided. Compared with the existing P2-phase material Na 2 / 3 [Li 1 / 7 Mn 5 / 14 [Mg 1 / 7 Mn 5 / 14 O2, the capacity retention rate of the sodium ion battery of the present invention increases from 85.5% to 90.5% after 50 cycles at 1C.

[0022] Advantages of the present invention: 1. Through lithium doping, the present invention stimulates the anionic redox of the layered oxide cathode to achieve ultra-high energy density.

[0023] 2. The discharge specific capacity of the sodium ion battery of the present invention can reach 267.79 mAh / g, and the discharge voltage is 2.56 V vsNa / Na + , and the material energy density can reach 687.3 Wh / kg.

[0024] 3. Compared with the existing P2-phase material Na 2 / 3 [Li 1 / 7 Mn 5 / 14 [Mg 1 / 7 Mn 5 / 14 O2, the capacity retention rate of the sodium ion battery of the present invention increases from 85.5% to 90.5% after 50 cycles at 1C. Description of the Drawings

[0025] Figure 1 It is the XRD pattern of the layered P2-phase sodium ion battery cathode material prepared in Example 1 of the present invention.

[0026] Figure 2 It is the XRD refinement pattern of the layered P2-phase sodium ion battery cathode material prepared in Example 1 of the present invention. Among them, R wp is used to measure the fitting degree between the experimental data and the refinement model; R pis the unweighted fitting error between the experimental data and the refined model. Indicates that the corresponding diffraction peak is a superlattice structure peak. Yobs represents the observed intensity of the sample; Ycalc represents the theoretical diffraction intensity calculated by the Rietveld refinement model based on the known structural parameters; Bragg_position represents the Bragg peak position, which is used to indicate the diffraction peaks expected to appear at these 2θ angles; Diff represents the difference between Yobs and Ycalc, which is used to represent the deviation between the experimental data and the theoretical calculation. The Chinese name of the Rietveld refinement model is the Rietveld structure refinement model.

[0027] Figure 3 This is the SEM image of the layered P2-phase sodium-ion battery cathode material prepared in Example 1 of the present invention.

[0028] Figure 4 This is the charge-discharge curve of the coin-type half-cell prepared in Application Example 1. Among them, 1st represents the performance of the first cycle test.

[0029] Figure 5 This is the cycle test curve of the coin-type half-cell prepared in Application Example 1.

[0030] Figure 6 This is the discharge voltage cycle test curve of the coin-type half-cell prepared in Application Example 1. Detailed implementation manners

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0033] In the prior art, lithium-magnesium doping has poor stability on the basis of achieving a high discharge specific capacity, and the discharge voltage decays severely, making it difficult to maintain the energy density.

[0034] Based on the existing layered P2-phase sodium-ion battery cathode material doped with lithium and magnesium, by adjusting the sintering temperature, it is found that its stability is enhanced, but residual alkali impurities are generated. Then, by adjusting the lithium doping ratio, a pure-phase layered oxide is synthesized, and the discharge voltage decay is also inhibited.

[0035] The maximum lithium doping amount does not exceed 0.26. Literature research shows that if the lithium doping amount is too much, residual alkali is easily generated; if the lithium doping amount is less, the specific capacity improvement is less.

[0036] For example, the literature: Rong et al., Joule 3, 503–517. studies the cathode of a sodium-ion battery as Na 0.72 [Li 0.24 Mn 0.76 O 2 ， which records that the lithium doping amount reaches 0.24, stimulating anion redox to achieve a high discharge specific capacity of 271 mAh·g -1 , however, from the perspective of cycle stability, it only cycled stably for 30 cycles.

[0037] The lithium doping amount of the cathode material of high specific capacity type batteries is usually relatively large, generally in the range of 0.1 - 0.25, not exceeding 0.26. In addition, the difficulty of this type of cathode material for batteries lies in the formation of no impurities during the synthesis process and the performance stability.

[0038] The synthesis method of layered oxides is calcination, and the calcination temperature, holding time, etc. will all affect the performance of the final material.

[0039] It should be noted that the chemical general formula of the cathode material of sodium-ion batteries can be expressed as: Na y TM1O2, where TM represents transition metals, and the total molar amount of transition metals is generally 1; and lithium ions are doped at the transition metal sites. Thus, the lithium doping amount is the ratio of lithium ions to the total molar amount of transition metals.

[0040] The technical solution of the present invention will be further described below through specific embodiments. In the following embodiments, unless otherwise specified, the methods are all conventional methods; the reagents and materials, unless otherwise specified, can all be purchased on the market.

[0041] Example 1 A preparation method of a layered P2-phase sodium-ion battery cathode material, comprising the following steps: Step 1, preparation of the precursor: Using sodium carbonate, lithium carbonate, magnesium oxide, and manganese dioxide as the precursor, weighing each raw material according to the molar ratio of Na, Li, Mg, Mn of 0.84:0.21:0.05:0.75. Among them, in order to offset the volatilization during the calcination process, the molar ratios of Na and Li are both increased by 5% on the basis of 0.8:0.2.

[0042] Using absolute ethanol as a dispersant, adding it together with sodium carbonate, lithium carbonate, and manganese dioxide into a planetary ball mill, and performing ball milling at a speed of 400 r / min for 10 hours.

[0043] The ball-milled sample is placed in a blast drying oven and dried at 80°C for 12 hours to thoroughly dry the dispersant and obtain the precursor.

[0044] Step 2, Preparation of layered P2-phase sodium-ion battery cathode material: The precursor was pressed using a tablet press mold with an inner diameter of 15 mm. The filling amount for each pressing was 350 mg, the pressure was 16 Mpa, and the pressing time was 10 min. After pressing, it was calcined using a muffle furnace. Under an air atmosphere, it was heated to 900 °C at a heating rate of 5 °C / min and calcined at 900 °C for 12 hours.

[0045] After calcination, it was cooled to room temperature at a rate of 2 °C / min to obtain the layered P2-phase sodium-ion battery cathode material with the chemical formula Na 0.8 Li 0.2 Mg 0.05 Mn 0.75 O2.

[0046] The XRD and SEM analyses were performed on the layered P2-phase sodium-ion battery cathode material prepared in Example 1, and the results are as Figures 1 to 3 shown. The full English name of XRD is X-ray Diffraction, and the full Chinese name is X-ray diffraction. The full English name of SEM is Scanning Electron Microscope, and the full Chinese name is scanning electron microscope.

[0047] Figure 1 and Figure 2 The XRD results of show that the layered P2-phase sodium-ion battery cathode material in Example 1 is a pure-phase layered oxide, and there is no residual lithium compound. The presence of residual lithium compounds will cause the cathode material slurry to gel, resulting in difficult coating and reducing the electrochemical performance of the cathode material. Among them, R wp = 6.91%, R p = 5.39%. R wp is used to measure the degree of fit between experimental data and the refined model; R p is the unweighted fitting error between experimental data and the refined model. The generally acceptable range of R wp is 5% - 20%; when the R wp value is less than 10%, the refined result is usually considered very good. The generally acceptable range of R p is 5% - 15%, and R p is usually smaller than R wp . When the R p value is around 10%, the refined result is usually considered very good.

[0048] The morphology and size of the layered P2-phase sodium-ion battery cathode material in Example 1 were observed using a scanning electron microscope. From Figure 3In terms of appearance, the morphology of the layered P2-phase sodium-ion battery cathode material in Example 1 is irregular particle shape, and the particle size is between 2 μm and 5 μm.

[0049] In summary, the examples of the present invention achieve ultra-high energy density by lithium doping to stimulate the anion redox of the layered oxide cathode.

[0050] Example 2 A preparation method of a layered P2-phase sodium-ion battery cathode material includes the following steps: Step 1, preparation of the precursor: Using sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide as the precursor, weighing each raw material according to the molar ratio of Na, Li, Mg, Mn of 0.84:0.2625:0.05:0.7. Among them, in order to offset the volatilization during calcination, the molar ratios of Na and Li are both increased by 5% on the basis of 0.8:0.25. Using anhydrous ethanol as the dispersant, adding it together with sodium carbonate, lithium carbonate and manganese dioxide into a planetary ball mill, and ball milling at a speed of 400 r / min for 10 hours.

[0051] The ball-milled sample is placed in a blast drying oven and dried at 80 °C for 12 hours to thoroughly dry the dispersant and obtain the precursor.

[0052] Step 2, preparation of the layered P2-phase sodium-ion battery cathode material: The precursor is pressed using a tablet press mold with an inner diameter of 15 mm. The filling amount for each pressing is 350 mg, the pressure is 16 Mpa, and the pressing time is 10 min. After pressing, it is calcined using a muffle furnace. Under an air atmosphere, it is heated to 900 °C at a heating rate of 5 °C / min and calcined at 900 °C for 12 hours.

[0053] After the calcination is completed, it is cooled to room temperature at a rate of 2 °C / min to obtain the layered P2-phase sodium-ion battery cathode material with the chemical formula Na 0.8 Li 0.25 Mg 0.05 Mn 0.7 O2.

[0054] Example 3 A preparation method of a layered P2-phase sodium-ion battery cathode material includes the following steps: Step 1, preparation of the precursor: Sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide are used as precursors, and each raw material is weighed according to the molar ratio of Na, Li, Mg, and Mn of 0.84:0.1575:0.05:0.8. Among them, in order to offset the volatilization during the calcination process, the molar ratios of Na and Li are both increased by 5% on the basis of 0.8:0.15.

[0055] Anhydrous ethanol is used as a dispersant and is added to a planetary ball mill together with sodium carbonate, lithium carbonate and manganese dioxide, and ball milling is carried out at a speed of 400 r / min for 10 hours.

[0056] The ball-milled sample is placed in a forced-air drying oven and dried at 80 °C for 12 hours to thoroughly dry the dispersant, obtaining the precursor.

[0057] Step 2, preparation of the layered P2-phase sodium-ion battery cathode material: The precursor is pressed using a tablet press mold with an inner diameter of 15 mm. The filling amount for each pressing is 350 mg, the pressure is 16 Mpa, and the pressing time is 10 min. After pressing, it is calcined using a muffle furnace. Under an air atmosphere, it is heated to 900 °C at a heating rate of 5 °C / min and calcined at 900 °C for 12 hours.

[0058] After the calcination is completed, it is cooled to room temperature at a rate of 2 °C / min, obtaining the layered P2-phase sodium-ion battery cathode material with the chemical formula Na 0.8 Li 0.15 Mg 0.05 Mn 0.8 O2.

[0059] Application Example 1 A preparation method of a layered P2-phase sodium-ion battery includes the following steps: Using Na 0.8 Li 0.2 Mg 0.05 Mn 0.75 O2 prepared in Example 1 as the cathode, using a sodium sheet as the counter electrode, and assembling a coin-type half-cell with an electrolyte composed of sodium perchlorate as the solute, propylene carbonate as the solvent, and adding 5% fluorinated ethylene carbonate as an additive and a GF-D separator. The assembly of the coin-type half-cell is carried out in a glove box under argon protection.

[0060] As Figure 4 , the discharge specific capacity of the coin-type half-cell of Application Example 1 can reach 267.79 mAh / g, and the discharge voltage is 2.56 V vs Na / Na + , and the material energy density can reach 687.3 Wh / kg.

[0061] Compared with the P2-phase material Na 2 / 3 [Li 1 / 7 Mn 5 / 14 [Mg 1 / 7Mn 5 / 14 O2 that achieves the highest discharge specific capacity in the prior art 1, the capacity retention rate of the layered P2-phase sodium-ion battery cathode material in Example 1 of the present invention increased from 85.5% to 90.5% after 50 cycles at 1C, as shown in Figure 5 .

[0062] Moreover, after 200 cycles at a current density of 1C, the average discharge voltage retention rate of the layered P2-phase sodium-ion battery cathode material in Example 1 of the present invention can reach 98.49%, as shown in Figure 6 .

[0063] Prior art 1: Angew. Chem. Int. Ed. 2022, 61, e202206625. Application Example 2 A method for preparing a layered P2-phase sodium-ion battery, comprising the following steps: Using Na 0.8 Li 0.25 Mg 0.05 Mn 0.7 O2 prepared in Example 2 as the positive electrode, using a sodium sheet as the counter electrode, and assembling a coin-type half-cell with an electrolyte composed of sodium perchlorate as the solute, propylene carbonate as the solvent, and adding 5% fluoroethylene carbonate as an additive and a GF-D separator. The assembly of the coin-type half-cell is carried out in a glove box under argon protection.

[0064] Application Example 3 A method for preparing a layered P2-phase sodium-ion battery, comprising the following steps: Using Na 0.8 Li 0.15 Mg 0.05 Mn 0.8 O2 prepared in Example 3 as the positive electrode, using a sodium sheet as the counter electrode, and assembling a coin-type half-cell with an electrolyte composed of sodium perchlorate as the solute, propylene carbonate as the solvent, and adding 5% fluoroethylene carbonate as an additive and a GF-D separator. The assembly of the coin-type half-cell is carried out in a glove box under argon protection.

[0065] Coin-type half-cells were assembled for the layered P2-phase sodium-ion battery cathode materials with different lithium doping amounts according to the methods of Application Examples 1 to 3, and the specific capacity of the coin-type half-cells assembled from the layered P2-phase sodium-ion battery cathode materials with different lithium doping amounts was tested to explore the influence of different lithium doping amounts on the performance of the layered P2-phase sodium-ion battery cathode materials. The results are shown in Table 1.

[0066] Table 1 Influence of Different Lithium Doping Amounts on the Performance of Layered P2-Phase Sodium-Ion Battery Cathode Materials Note: The chemical formula is the chemical formula of the layered P2-phase sodium-ion battery cathode material prepared in the corresponding example.

[0067] As can be seen from the results in Table 1, with the increase of the lithium doping amount, the specific capacity of the battery first increases and then decreases, and when the lithium doping amount is 0.2%, the specific capacity of the battery reaches the maximum.

[0068] Example 4 A preparation method of a layered P2-phase sodium-ion battery cathode material, comprising the following steps: Step 1, preparation of the precursor: Using sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide as the precursor, weighing each raw material according to the ratio in Example 1, where the molar ratio of Na to Li is increased by 5% on the basis of 0.8:0.2 to offset the volatilization during calcination.

[0069] Using absolute ethanol as a dispersant, adding it together with sodium carbonate, lithium carbonate and manganese dioxide into a planetary ball mill, and carrying out ball milling at a speed of 400 r / min for 10 hours.

[0070] The ball-milled sample is placed in a forced-air drying oven and dried at 80 °C for 12 hours to thoroughly dry the dispersant, obtaining the precursor.

[0071] Step 2, preparation of the layered P2-phase sodium-ion battery cathode material: The precursor is pressed using a tablet press mold with an inner diameter of 15 mm, the filling amount for each pressing is 350 mg, the pressure is 16 Mpa, and the pressing time is 10 min. After pressing, it is calcined using a muffle furnace. Under an air atmosphere, it is heated to 1200 °C at a heating rate of 5 °C / min and calcined at 1200 °C for 12 hours. After the calcination is completed, it is cooled to room temperature at a rate of 2 °C / min, obtaining the layered P2-phase sodium-ion battery cathode material with the chemical formula Na 0.8 Li 0.2 Mg 0.05 Mn 0.75 O2.

[0072] Example 5 A preparation method of a layered P2-phase sodium-ion battery cathode material, comprising the following steps: Step 1, preparation of the precursor: Sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide are used as precursors, and each raw material is weighed according to the ratio of Example 1, wherein the molar ratio of Na to Li is increased by 5% on the basis of 0.8:0.2 to offset the volatilization during the calcination process.

[0073] Anhydrous ethanol is used as a dispersant and is added to a planetary ball mill together with sodium carbonate, lithium carbonate and manganese dioxide, and ball milling is carried out at a speed of 400 r / min for 10 hours.

[0074] The ball-milled sample is placed in a forced-air drying oven and dried at 80 °C for 12 hours to thoroughly dry the dispersant and obtain the precursor.

[0075] Step 2, Preparation of the layered P2-phase sodium-ion battery cathode material: The precursor is pressed using a tablet press mold with an inner diameter of 15 mm. The filling amount for each pressing is 350 mg, the pressure is 16 Mpa, and the pressing time is 10 min. After pressing, calcination is carried out using a muffle furnace. Under an air atmosphere, the temperature is raised to 1000 °C at a heating rate of 5 °C / min and calcined at 1000 °C for 12 hours. After the calcination is completed, the temperature is lowered to room temperature at a rate of 2 °C / min to obtain the layered P2-phase sodium-ion battery cathode material with the chemical formula Na 0.8 Li 0.2 Mg 0.05 Mn 0.75 O2.

[0076] Example 6 A method for preparing a layered P2-phase sodium-ion battery cathode material, comprising the following steps: Step 1, Preparation of the precursor: Sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide are used as precursors, and each raw material is weighed according to the ratio of Example 1, wherein the molar ratio of Na to Li is increased by 5% on the basis of 0.8:0.2 to offset the volatilization during the calcination process.

[0077] Anhydrous ethanol is used as a dispersant and is added to a planetary ball mill together with sodium carbonate, lithium carbonate and manganese dioxide, and ball milling is carried out at a speed of 400 r / min for 10 hours.

[0078] The ball-milled sample is placed in a forced-air drying oven and dried at 80 °C for 12 hours to thoroughly dry the dispersant and obtain the precursor.

[0079] Step 2, Preparation of the layered P2-phase sodium-ion battery cathode material: The precursor was tableted using a tablet press mold with an inner diameter of 15 mm. The filling amount for each tablet pressing was 350 mg, the pressure was 16 Mpa, and the tablet pressing time was 10 min. After tablet pressing, it was calcined using a muffle furnace. In an air atmosphere, it was heated to 800 °C at a heating rate of 5 °C / min and calcined at 800 °C for 12 hours. After the calcination was completed, it was cooled to room temperature at a rate of 2 °C / min to obtain a layered P2-phase sodium-ion battery cathode material with the chemical formula Na 0.8 Li 0.2 Mg 0.05 Mn 0.75 O2.

[0080] Example 7 A preparation method of a layered P2-phase sodium-ion battery cathode material, comprising the following steps: Step 1, preparation of the precursor: Sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide were used as the precursor, and each raw material was weighed according to the ratio of Example 1, wherein the molar ratio of Na to Li was increased by 5% on the basis of 0.8:0.2 to offset the volatilization during the calcination process.

[0081] Anhydrous ethanol was used as a dispersant and added to a planetary ball mill together with sodium carbonate, lithium carbonate and manganese dioxide, and ball milling was carried out at a speed of 400 r / min for 10 hours.

[0082] The ball-milled sample was placed in a blast drying oven and dried at 80 °C for 12 hours to thoroughly dry the dispersant and obtain the precursor.

[0083] Step 2, preparation of the layered P2-phase sodium-ion battery cathode material: The precursor was tableted using a tablet press mold with an inner diameter of 15 mm. The filling amount for each tablet pressing was 350 mg, the pressure was 16 Mpa, and the tablet pressing time was 10 min. After tablet pressing, it was calcined using a muffle furnace. In an air atmosphere, it was heated to 700 °C at a heating rate of 5 °C / min and calcined at 700 °C for 12 hours. After the calcination was completed, it was cooled to room temperature at a rate of 2 °C / min to obtain a layered P2-phase sodium-ion battery cathode material with the chemical formula Na 0.8 Li 0.2 Mg 0.05 Mn 0.75 O2.

[0084] The coin-type half-cells were assembled with the layered P2-phase sodium-ion battery cathode materials at different calcination temperatures according to the method of Application Example 1, and the specific capacity tests were carried out on the coin-type half-cells assembled with the layered P2-phase sodium-ion battery cathode materials at different calcination temperatures to explore the influence of different calcination temperatures on the performance of the layered P2-phase sodium-ion battery cathode materials. The results are shown in Table 2.

[0085] Table 2 Influence of Different Calcination Temperatures on the Performance of the Cathode Material for Layered P2-Phase Sodium-Ion Batteries As can be seen from the results in Table 2, with the increase of the calcination temperature, the specific capacity of the battery shows a trend of first increasing and then decreasing, and the specific capacity of the battery reaches the maximum at a calcination temperature of 900 °C.

[0086] Example 8 A preparation method of a cathode material for a layered P2-phase sodium-ion battery, comprising the following steps: Step 1, preparation of the precursor: Using sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide as the precursor, weighing each raw material according to the ratio of Example 1, wherein the molar ratio of Na to Li is increased by 5% on the basis of 0.8:0.2 to offset the volatilization during the calcination process.

[0087] Using anhydrous ethanol as a dispersant, adding it together with sodium carbonate, lithium carbonate and manganese dioxide into a planetary ball mill, and carrying out ball milling at a speed of 400 r / min for 10 hours.

[0088] The ball-milled sample is placed in a blast drying oven and dried at 80 °C for 12 hours to thoroughly dry the dispersant and obtain the precursor.

[0089] Step 2, preparation of the cathode material for the layered P2-phase sodium-ion battery: The precursor is pressed using a tablet press mold with an inner diameter of 15 mm, the filling amount for each pressing is 350 mg, the pressure is 16 Mpa, and the pressing time is 10 min. After pressing, it is calcined using a muffle furnace. Under an air atmosphere, it is heated to 900 °C at a heating rate of 5 °C / min and calcined at 900 °C for 15 hours. After the calcination is completed, it is cooled to room temperature at a rate of 2 °C / min to obtain the cathode material for the layered P2-phase sodium-ion battery, with the chemical formula of Na 0.8 Li 0.2 Mg 0.05 Mn 0.75 O2.

[0090] Example 9 A preparation method of a cathode material for a layered P2-phase sodium-ion battery, comprising the following steps: Step 1, preparation of the precursor: Using sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide as the precursor, weighing each raw material according to the ratio of Example 1, wherein the molar ratio of Na to Li is increased by 5% on the basis of 0.8:0.2 to offset the volatilization during the calcination process.

[0091] Use absolute ethanol as a dispersant and add it together with sodium carbonate, lithium carbonate and manganese dioxide into a planetary ball mill. Mill at a speed of 400 r / min for 10 hours.

[0092] Put the milled sample into a forced air drying oven and dry it at 80 °C for 12 hours to thoroughly dry the dispersant, obtaining a precursor.

[0093] Step 2, Preparation of layered P2-phase sodium-ion battery cathode material: Press the precursor using a tablet press mold with an inner diameter of 15 mm. The filling amount for each pressing is 350 mg, the pressure is 16 Mpa, and the pressing time is 10 min. After pressing, use a muffle furnace for calcination. Under an air atmosphere, heat it up to 900 °C at a heating rate of 5 °C / min and calcine at 900 °C for 9 hours. After the calcination is completed, cool it down to room temperature at a rate of 2 °C / min to obtain a layered P2-phase sodium-ion battery cathode material with the chemical formula Na 0.8 Li 0.2 Mg 0.05 Mn 0.75 O2.

[0094] Example 10 A preparation method of a layered P2-phase sodium-ion battery cathode material, comprising the following steps: Step 1, Preparation of precursor: Use sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide as precursors, weigh each raw material according to the ratio of Example 1, where the molar ratio of Na to Li is increased by 5% on the basis of 0.8:0.2 to offset the volatilization during the calcination process.

[0095] Use absolute ethanol as a dispersant and add it together with sodium carbonate, lithium carbonate and manganese dioxide into a planetary ball mill. Mill at a speed of 400 r / min for 10 hours.

[0096] Put the milled sample into a forced air drying oven and dry it at 80 °C for 12 hours to thoroughly dry the dispersant, obtaining a precursor.

[0097] Step 2, Preparation of layered P2-phase sodium-ion battery cathode material: Press the precursor using a tablet press mold with an inner diameter of 15 mm. The filling amount for each pressing is 350 mg, the pressure is 16 Mpa, and the pressing time is 10 min. After pressing, use a muffle furnace for calcination. Under an air atmosphere, heat it up to 900 °C at a heating rate of 5 °C / min and calcine at 900 °C for 5 hours. After the calcination is completed, cool it down to room temperature at a rate of 2 °C / min to obtain a layered P2-phase sodium-ion battery cathode material with the chemical formula Na 0.8 Li0.2 Mg 0.05 Mn 0.75 O2。

[0098] The coin-type half-cells assembled with the layered P2-phase sodium-ion battery cathode materials with different calcination times were assembled according to the method of Application Example 1, and the specific capacity tests were carried out on the coin-type half-cells assembled with the layered P2-phase sodium-ion battery cathode materials with different calcination times to explore the influence of different calcination times on the performance of the layered P2-phase sodium-ion battery cathode materials. The results are shown in Table 3.

[0099] Table 3 Influence of different calcination times on the performance of the layered P2-phase sodium-ion battery cathode materials It can be seen from the results in Table 3 that as the calcination time increases, the specific capacity of the battery shows a trend of first increasing and then decreasing, and when the calcination time is 12 h, the specific capacity of the battery reaches the maximum. When the calcination time is 15 h, the specific capacity of the battery is not much different from that at 12 h. Therefore, the preferred calcination time is 12 - 15 h.

[0100] In summary, through lithium doping in the embodiments of the present invention, the anion redox of the layered oxide cathode is excited, and ultra-high energy density is achieved. In addition, by adjusting the lithium doping amount, calcination temperature and calcination time, while improving the capacity retention rate of the high-energy density cathode and suppressing voltage decay, the energy density is effectively maintained.

[0101] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A layered P2-phase sodium-ion battery cathode material, characterized in that, The chemical general formula of the layered P2-phase sodium-ion battery cathode material is as follows: Na y Li x Mg 0.05 Mn 0.95-x O₂; where 0.2 ≤ x ≤ 0.21 and 0.78 < y ≤ 0.

82.

2. The layered P2-phase sodium-ion battery cathode material according to claim 1, wherein The chemical general formula of the layered P2-phase sodium-ion battery cathode material is as follows: Na 0.8 Li 0.2 Mg 0.05 Mn 0.75 O2。 3. A method for preparing the layered P2-phase sodium ion battery cathode material according to claim 1, characterized in that, It includes the following steps: Ball-mill and compound sodium salt, lithium salt and metal oxide to prepare a precursor; the metal oxide is magnesium oxide and manganese dioxide; Press the precursor into tablets, and then calcine it at a temperature of 900°C ± 50°C in an air atmosphere to prepare the layered P2-phase sodium-ion battery cathode material.

4. The preparation method of the layered P2-phase sodium ion battery cathode material according to claim 3, wherein, The sodium salt is sodium carbonate; the lithium salt is lithium carbonate.

5. The preparation method of the layered P2-phase sodium ion battery cathode material according to claim 4, wherein, Before the ball-milling compounding, it also includes: weighing each raw material according to the molar ratio of Na, Li, Mg, and Mn of 0.83 - 0.86:0.21 - 0.22:0.05:0.

75.

6. The preparation method of the layered P2-phase sodium-ion battery cathode material according to claim 3, characterized in that, The calcination time is 9h - 15h.

7. The preparation method of the layered P2-phase sodium ion battery cathode material according to claim 3, wherein, The conditions for pressing the tablets are as follows: The filling amount is 340mg - 380mg, the pressure is 14Mpa - 16Mpa, and the tablet pressing time is 8min - 14min.

8. The preparation method of the layered P2-phase sodium ion battery cathode material according to claim 3, wherein, The ball-milling compounding uses ethanol as a dispersant to ball-mill and compound sodium carbonate, lithium carbonate, magnesium oxide and manganese dioxide.

9. The preparation method of the layered P2-phase sodium ion battery cathode material according to claim 8, characterized in that, The rotation speed of the ball-milling compounding is 360r / min - 400r / min, and the time of the ball-milling compounding is 8h - 10h.

10. A sodium-ion battery comprising the layered P2-phase sodium-ion battery cathode material described in claim 1.

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