A method for improving the performance of cathode materials for sodium-ion batteries by utilizing the Jahn-Teller effect

Abstract

The present invention relates to a method for improving the performance of the cathode material of a sodium-ion battery by using the Jahn-Teller effect. The molecular formula of the cathode material is Na a Mn x Ni y Cu z O2, where 0.85 ≤ a ≤ 1, 0.45 ≤ x ≤ 0.55, 0.4 ≤ y ≤ 0.5, and 0.05 ≤ z ≤ 0.15. By controlling the timing of doping with the Cu element, adjusting its diffusion mechanism in the transition metal layer TMO6 octahedron during high-temperature sintering, changing the microstructure of the Cu-O octahedron, and activating the Cu 2+ Jahn-Teller distortion in the transition metal layer, promoting the rapid migration of Na ions in the transition metal layer, enabling the O3-type sodium-ion layered cathode material to exhibit a discharge capacity of 67.2 mAh / g at a charge-discharge rate of 10C (1C = 120 mA / g) in the 2-4V potential range, greatly improving the fast charge-discharge ability of ordinary O3 materials, and effectively improving the cycle stability of the cathode.

Description

Technical Field

[0001] The present invention belongs to the field of cathode materials for sodium-ion batteries, and particularly relates to a method for improving the performance of cathode materials for sodium-ion batteries by utilizing the Jahn-Teller effect. Background Art

[0002] The uneven distribution of global lithium resources and the widespread commercial application of lithium-ion batteries have pushed the price of Li sources to another peak. As a metal in the same main group, Na metal is widely and evenly distributed in the earth's crust, which makes sodium-ion batteries with the same energy storage mechanism a promising alternative to lithium-ion batteries. When not considering the volume and mass energy density, such as in large-scale stationary energy storage applications, the economic advantages of Na-ion batteries will surely enable them to occupy a place.

[0003] O3-type layered sodium-ion cathode materials are one of the most promising cathode materials for sodium-ion batteries due to their high energy density, low cost, high tap density, and easy industrialization. The transition metal layer elements of the O3-type layered oxide cathode generally include active metals Ni, Fe, Mn, Co, Cr that undergo redox reactions in the charge-discharge potential range to provide capacity, and inactive metals Li, Mg, Ti, Cu, Zn mainly play roles in stabilizing the structure of the transition metal layer and suppressing phase changes. Among these metals, high-spin configuration Mn 3+ (d 4 ), Cr 2+ (d 4 ), Fe 4+ (d 4 ) complexes and low-spin configuration Ni 3+ (d 7 ), Co 2+ (d 7 ) complexes exhibit strong Jahn-Teller distortion. The strong distortion will lead to serious structural deformation, poor cycling stability, and deterioration of the fast charge-discharge ability of the material. On the contrary, relatively mild Jahn-Teller distortion such as Cu 2+ (d 9 ) can not only maintain a stable structure but also regulate the electronic and ionic conductivities of the electrode material during cycling. This weakened JT effect can further assist the diffusion of Na ions in the alkali metal layer, improving the cycling stability and fast charge-discharge ability of the cathode material.

[0004] In previous work, Cu 2+Doping in the transition metal layer can stabilize the structure, inhibit phase change during charge and discharge, and improve air stability. When exploring the effect of Cu doping on material properties, the Cu-containing precursor is generally mixed with other transition metal sources and Na sources, and sintered once to obtain the target product, without exploring the order of adding the Cu source. Based on the above problems, the present invention proposes for the first time to add the product Na after sintering once. 0.9 Mn 0.5 Ni 0.5 O2 and CuO are used as precursors, uniformly mixed and sintered twice. 2+ The diffusion mechanism at high temperature further activates Cu 2+ The Jahn-Teller effect is achieved to simultaneously improve material stability and rate performance. Summary of the invention

[0005] In view of the problems pointed out in the above background technology, the present invention proposes a method and a preparation method thereof for improving the cycle stability and charge-discharge rate performance of the positive electrode material of a sodium ion battery by utilizing the Jahn-Teller effect. Specifically, the present invention provides the following technical solutions:

[0006] A method for improving the performance of a positive electrode material for a sodium ion battery by utilizing the Jahn-Teller effect, wherein the molecular formula of the positive electrode material for a sodium ion battery is Na a Mn x Ni y Cu z O2, where 0.85≤a≤1, 0.45≤x≤0.55, 0.4≤y≤0.5, 0.05≤z≤0.15, and Cu element is doped into Na by secondary annealing. a Mn x Ni y O2 matrix, XAS characterization results show that Cu element is doped into Na a Mn x Ni y The O2 matrix exhibits a wider edge front peak compared to the single sintering, and further EXAFS characterization results show that the bond length of Cu-O is distributed in two types: 1.41 Å and 1.71 Å.

[0007] Furthermore, the method of improving the performance of the positive electrode material of a sodium ion battery by utilizing the Jahn-Teller effect comprises the following steps:

[0008] 1) According to the chemical formula Na a Mn x Ni yWeigh the precursors of Na, Mn, and Ni in the proportion of the molar ratio of each element in O2: 0.85 ≤ a ≤ 1, 0.45 ≤ x ≤ 0.55, 0.4 ≤ y ≤ 0.5 and mix them evenly. Among them, the nickel source compound includes any one or more of nickel oxide, nickel hydroxide, nickel acetate, and nickel nitrate; the manganese source compound includes any one or more of manganese oxide, manganese hydroxide, manganese carbonate, manganese acetate, and manganese nitrate; the precursor of sodium is selected from any one or more of its oxides, hydroxides, carbonates, nitrates, and oxalates.

[0009] 2) Grind, dry, and tablet the premixed powder obtained in step 1) with a solvent dispersant, where the pressure is 1000 - 3000 Pa;

[0010] 3) Pre-sinter the sheet mixture obtained in step 2) in an air atmosphere to 400 - 600 °C and maintain the temperature for 3 - 5 hours;

[0011] 4) Continue to heat up to 850 - 1000 °C for sintering on the basis of step 3) and maintain the temperature for 10 - 14 hours, and then cool down to room temperature with the furnace to obtain the sintered NMNO;

[0012] 5) Grind the sintered NMNO in step 4) into particles smaller than 50 μm and uniformly mix it with CuO in a corresponding molar ratio of 5% - 15%;

[0013] 6) Re-tablet the mixed material in step 5) and pre-sinter the obtained sheet mixture in an air atmosphere to 400 - 600 °C and maintain the temperature for 1 - 3 hours;

[0014] 7) Continue to heat up to 900 - 950 °C for sintering on the basis of step 6) and maintain the temperature for 3 - 5 hours, and then cool down to room temperature with the furnace.

[0015] Further, in step 1), a = 0.9, x = 0.5, y = 0.5; the nickel source compound is nickel oxide; the manganese source compound is manganese oxide or manganese carbonate.

[0016] Further, in step 2), the pressure is 2000 Pa.

[0017] Further, the heating rate in step 3) is 2 - 10 °C / minute, and the pre-sintering temperature is 500 °C.

[0018] Further, the sintering temperature in step 4) is 900 °C; the holding temperature is 14 hours.

[0019] Further, the proportion of CuO in step 5) is 10% of the molar amount of NMNO.

[0020] Further, in step 6), the pre-sintering temperature is 500 °C and the holding time is 2 hours.

[0021] Further, in step 7), the sintering temperature is 950 °C and the holding time is 5 hours. On the other hand, the O3-type sodium layered cathode material prepared by the method of the present invention to activate the Jahn-Teller effect of Cu ions has a discharge capacity of 115 mAh / g in the range of 2-4 V, maintains 87.5% of the original capacity after 200 cycles at a 1C rate, maintains 70.3% of the original capacity after 1000 cycles at a 5C rate, and shows a high specific capacity of 67.2 mAh / g at a high rate of 10C.

[0022] The principle of the present invention includes: (1) Using Na a Mn x Ni y O2 and CuO as precursors, uniformly mixing and re-firing them. The presence of CuO makes the originally flaky Na a Mn x Ni y O2 orderly assemble into aggregates of about 60 μm. CuO plays a dual role of dopant and "sticky welding" in the subsequent annealing. This special structure can prevent the excessive contact between the cathode active material and the electrolyte, reduce the side reaction process of the electrolyte on the material surface. In addition, the interlaced flaky structure in the sphere may form an active channel more conducive to Na ion transport, promoting the insertion and extraction of Na ions.

[0023] (2) In the principle of the invention (1), the diffusion of Cu element into the Na a Mn x Ni y O2 matrix to form Na a Mn x Ni y Cu z O2 process involves the breaking and recombination of metal-oxygen bonds in the transition metal layer. Na a Mn x Ni y O2 is already a high-temperature stable phase. The incorporation of Cu element forms Mn x Ni y Cu z When forming the transition metal layer, more diffusion energy is required. Therefore, Cu 2+The diffusion of 2+ and the subsequent formation of Cu-O bonds involve the compression and stretching of Cu-O octahedrons in specific axial directions, and this process activates the Jahn-Teller effect of Cu-O octahedrons. In contrast, when metal oxides NiO, Mn2O3, and CuO are used as precursors and sintered together, the octahedral coordination structures formed by Ni-O, Mn-O, and Cu-O are closer to perfection and have almost no Jahn-Teller distortion. Therefore, the secondary addition of CuO is the key to activating the effective Jahn-Teller effect of Cu

[0024] (3) Different from high-spin configurations of Mn 3+ (d 4 ), Cr 2+ (d 4 ), Fe 4+ (d 4 ), complex compounds and low-spin configurations of Ni 3+ (d 7 ), Co 2+ (d 7 ) complex compounds exhibit strong Jahn-Teller distortion. The above strong distortion will lead to serious structural deformation and poor cycling stability, deteriorating the fast charge and discharge capabilities of the material. On the contrary, relatively mild Jahn-Teller distortion such as Cu 2+ (d 9 ), can not only maintain a stable structure, but also regulate the electronic and ionic conductivities of the electrode material during the cycling process, further assisting the diffusion of Na ions in the alkali metal layer and improving the cycling stability and fast charge and discharge capabilities of the cathode material.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The cathode material for sodium-ion batteries in the present invention has low cost, simple preparation process, and easy access to raw materials;

[0027] (2) The method adopted in the present invention has strong process controllability, and the special assembly structure can effectively improve the compaction density. It is suitable for

[0028] large-scale production of materials; and the invention principle is convenient in real time, only through secondary sintering.

[0029] (3) The cathode material prepared by the present invention has excellent cycling stability and rate performance. It can maintain 87.5% of the original capacity after 200 cycles at a 1 C rate, 70.3% of the original capacity after 1000 cycles at a 5 C rate, and shows a high specific capacity of 67.2 mAh / g at a high rate of 10 C. Description of the Drawings

[0030] The accompanying drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0031] Figure 1 In Example 1 of the present invention, using Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 5% molar ratio of CuO as the precursor, the 1C rate stability cycle diagram of the product sintered at 950°C for 5 hours.

[0032] Figure 2 In Example 1 of the present invention, using Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 5% molar ratio of CuO as the precursor, the rate performance diagram of the product sintered at 950°C for 5 hours.

[0033] Figure 3 In Example 2 of the present invention, using Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 10% molar ratio of CuO as the precursor, the XAS extended edge r space diagram of the product sintered at 950°C for 5 hours.

[0034] Figure 4 In Example 2 of the present invention, using Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 10% molar ratio of CuO as the precursor, the SEM diagram of the product sintered at 950°C for 5 hours.

[0035] Figure 5 In Example 2 of the present invention, using Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 10% molar ratio of CuO as the precursor, the XRD diagram of the product sintered at 950°C for 5 hours.

[0036] Figure 6 In Example 2 of the present invention, using Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 10% molar ratio of CuO as the precursor, the 1C rate stability cycle diagram of the product sintered at 950°C for 5 hours.

[0037] Figure 7 In Example 2 of the present invention, using Na 0.9 (Mn 0.5 Ni 0.5)Rate performance graph of the product sintered at 950 °C for 5 hours with O2 and 10% molar ratio of CuO as the precursor.

[0038] Figure 8 In Example 3 of the present invention, with Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 15% molar ratio of CuO as the precursor, 1C rate stability cycle graph of the product sintered at 950 °C for 5 hours.

[0039] Figure 9 In Example 3 of the present invention, with Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 15% molar ratio of CuO as the precursor, rate performance graph of the product sintered at 950 °C for 5 hours.

[0040] Figure 10 In Comparative Example 1 of the present invention, XRD graph of Na 0.9 (Mn 0.5 Ni 0.5 )O2.

[0041] Figure 11 In Comparative Example 1 of the present invention, Na 0.9 (Mn 0.5 Ni 0.5 )O2 SEM graph.

[0042] Figure 12 In Comparative Example 1 of the present invention, Na 0.9 (Mn 0.5 Ni 0.5 )O2 cycle stability graph at 1C rate.

[0043] Figure 13 In Comparative Example 1 of the present invention, Na 0.9 (Mn 0.5 Ni 0.5 )O2 rate performance graph.

[0044] Figure 14 XAS extended edge r-space graph of the primary sintered product with Mn2O3, NiO, and CuO as the precursors in Comparative Example 2 of the present invention.

[0045] Figure 15 XRD graph of the primary sintered product with Mn2O3, NiO, and CuO as the precursors in Comparative Example 2 of the present invention.

[0046] Figure 16 SEM graph of the primary sintered product with Mn2O3, NiO, and CuO as the precursors in Comparative Example 2 of the present invention.

[0047] Figure 17 It is the 1C rate stability cycle diagram of the primary sintering product with Mn2O3, NiO, and CuO as the precursors in Comparative Example 2 of the present invention.

[0048] Figure 18 It is the rate performance diagram of the primary sintering product with Mn2O3, NiO, and CuO as the precursors in Comparative Example 2 of the present invention.

[0049] Figure 19 It is the comparison of the XAS near-edge absorption edge front intensity between Example 2 and Comparative Example 2 of the present invention.

[0050] Figure 20 It is for Comparative Example 3 of the present invention with Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 5% molar ratio of ZnO as the precursors, and the 1C rate stability cycle diagram of the product sintered at 950°C for 5 hours.

[0051] Figure 21 It is for Comparative Example 3 of the present invention with Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 5% molar ratio of ZnO as the precursors, and the rate performance diagram of the product sintered at 950°C for 5 hours.

[0052] Figure 22 It is for Comparative Example 4 of the present invention with Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 10% molar ratio of ZnO as the precursors, and the XRD diagram of the product sintered at 950°C

[0053] for 5 hours.

[0054] Figure 23 It is for Comparative Example 4 of the present invention with Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 10% molar ratio of ZnO as the precursors, and the SEM diagram of the product sintered at 950°C for 5 hours.

[0055] Figure 24 It is for Comparative Example 4 of the present invention with Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 10% molar ratio of ZnO as the precursors, and the 1C rate stability cycle diagram of the product sintered at 950°C for 5 hours.

[0056] Figure 25 It is for Comparative Example 4 of the present invention with Na 0.9 (Mn 0.5 Ni0.5 )The rate performance graph of the product sintered at 950 °C for 5 hours with O2 and 10% molar ratio of ZnO as the precursor.

[0057] Figure 26 In Comparative Example 5 of the present invention, using Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 15% molar ratio of ZnO as the precursor, the 1C rate stability cycle graph of the product sintered at 950 °C for 5 hours.

[0058] Figure 27 In Comparative Example 5 of the present invention, using Na 0.9 (Mn 0.5 Ni 0.5 )O2 and 15% molar ratio of ZnO as the precursor, the rate performance graph of the product sintered at 950 °C for 5 hours.

[0059] Figure 28 XRD graph of the primary sintered product using Mn2O3, NiO, ZnO as the precursor in Comparative Example 6 of the present invention.

[0060] Figure 29 1C rate stability cycle graph of the primary sintered product using Mn2O3, NiO, ZnO as the precursor in Comparative Example 6 of the present invention.

[0061] Figure 30 Rate performance graph of the primary sintered product using Mn2O3, NiO, ZnO as the precursor in Comparative Example 6 of the present invention. Detailed implementation manners

[0062] 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.

[0063] Example 1

[0064] 1) According to the stoichiometry of Na 0.9 (Mn 0.5 Ni 0.5 )O2, weigh Na2CO3, Mn2O3, and NiO for premixing to obtain a premixed powder;

[0065] 2) Use ball milling to uniformly mix the premixed powder and the solvent dispersant obtained in step 1), where the rotation speed of the ball milling is 500 rpm and the time is 10 h;

[0066] 3) Press the mixed powder obtained in step 2), where the pressure is 2000 Pa;

[0067] 4) Pre-sinter the flaky mixture obtained in step 3) in an air atmosphere to 500 °C and maintain the temperature for 4 hours;

[0068] 5) Based on step 4), continue to heat up to 900 °C for sintering and maintain the temperature for 14 hours, then cool down to room temperature with the furnace.

[0069] 6) Grind the sintered Na 0.9 (Mn 0.5 Ni 0.5 )O2 in step 5) into particles with a size below 50 μm and uniformly mix it with CuO with a corresponding molar ratio of 5%;

[0070] 7) Repeat step 3) for the mixed material in step 6), and pre-sinter the obtained flaky mixture in an air atmosphere to 500 °C and maintain the temperature for 2 hours;

[0071] 8) Based on step 7), continue to heat up to 950 °C for sintering and maintain the temperature for 5 hours, then cool down to room temperature with the furnace;

[0072] Using the Na 0.9 Mn 0.5 Ni 0.5 Cu 0.05 O2 material prepared in this example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and 1M NaClO4 in PC / FEC (95:5 wt%) solution as the electrolyte, assemble a button battery. The voltage range is 2 - 4 V. Select the rate mode for charge and discharge tests. At a rate of 1 C, the capacity retention of the positive electrode material after 200 cycles is 76%, and the discharge capacity at a rate of 10 C is 58.7 mAh / g.

[0073] Example 2

[0074] The difference from Example 1 is only that the molar amount of CuO in step 6) of Example 1 is changed to 10%. According to the stoichiometry of Na 0.9 Mn 0.5 Ni 0.5 Cu 0.1 O2, weigh Na 0.9 Mn 0.5 Ni 0.5 O2 and CuO. Using the material prepared in this example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and 1M NaClO4 in PC / FEC (95:5 wt%) solution as the electrolyte, assemble a button battery and conduct charge and discharge tests. The voltage range is 2 - 4 V. Select the rate mode for charge and discharge tests. At a rate of 1 C, the capacity retention of the positive electrode material after 200 cycles is 87.5%, and the discharge capacity at a rate of 10 C is 67.2 mAh / g.

[0075] Example 3

[0076] The difference from Example 1 is only that the amount of CuO in step 6) of Example 1 is changed to 15%, and according to the stoichiometry of Na 0.9 Mn 0.5 Ni 0.5 Cu 0.15 O2, weigh Na 0.9 Mn 0.5 Ni 0.5 O2, CuO. Using the material prepared in this example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a 1M NaClO4 PC / FEC (95:5 wt%) solution as the electrolyte, assemble a button battery and perform charge-discharge tests. The voltage range is 2 - 4 V. Select the rate mode for charge-discharge tests. At a 1 C rate, the capacity retention of the positive electrode material after 200 cycles is 82.2%, and the discharge capacity at a 10 C rate is 62.4 mAh / g.

[0077] Comparative Example 1

[0078] Prepare the precursor Na 0.9 Mn 0.5 Ni 0.5 O2 in the manner of steps 1) - 5) of Example 1. Using the material prepared in this comparative example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a 1M NaClO4 PC / FEC (95:5 wt%) solution as the electrolyte, assemble a button battery and perform charge-discharge tests. The voltage range is 2 - 4 V. Select the rate mode for charge-discharge tests. At a 1 C rate, the capacity retention of the positive electrode material after 200 cycles is 64.2%, and the discharge capacity at a 10 C rate is 27.8 mAh / g.

[0079] Comparative Example 2

[0080] The difference from Example 1 is only that, according to the stoichiometry of Na 0.9 Mn 0.5 Ni 0.5 Cu 0.1 O2, weigh Na2CO3, Mn2O3, NiO, CuO, and perform steps 1) - 5) in Example 1. Using the material prepared in this comparative example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a 1M NaClO4 PC / FEC (95:5 wt%) solution as the electrolyte, assemble a button battery and perform charge-discharge tests. The voltage range is 2 - 4 V. Select the rate mode for charge-discharge tests. At a 1 C rate, the capacity retention of the positive electrode material after 200 cycles is 73%, and the discharge capacity at a 10 C rate is 51.3 mAh / g.

[0081] Comparative Example 3

[0082] The difference from Example 1 is only that, according to the stoichiometry of Na 0.9 Mn 0.5 Ni 0.5 Zn 0.05 O2, the precursor in step 6) of Example 1 was changed to Na 0.9 Mn 0.5 Ni 0.5 O2 and ZnO. Using the material prepared in this comparative example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a 1M NaClO4 PC / FEC (95:5 wt%) solution as the electrolyte, an assembled button cell was subjected to charge and discharge tests. The voltage range was 2 - 4 V. The rate mode was selected for the charge and discharge tests. At a 1 C rate, the capacity retention of the positive electrode material after 200 cycles was 65.6%, and the discharge capacity at a 10 C rate was 22.8 mAh / g.

[0083] Comparative Example 4

[0084] The difference from Example 1 is only that, according to the stoichiometry of Na 0.9 Mn 0.5 Ni 0.5 Zn 0.1 O2, the precursor in step 6) of Example 1 was changed to Na 0.9 Mn 0.5 Ni 0.5 O2 and ZnO. Using the material prepared in this comparative example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a 1M NaClO4 PC / FEC (95:5 wt%) solution as the electrolyte, an assembled button cell was subjected to charge and discharge tests. The voltage range was 2 - 4 V. The rate mode was selected for the charge and discharge tests. At a 1 C rate, the capacity retention of the positive electrode material after 200 cycles was 66.6%, and the discharge capacity at a 10 C rate was 19.1 mAh / g.

[0085] Comparative Example 5

[0086] The difference from Example 1 is only that, according to the stoichiometry of Na 0.9 Mn 0.5 Ni 0.5 Zn 0.15 O2, the precursor in step 6) of Example 1 was changed to Na 0.9 Mn 0.5 Ni 0.5O2 and ZnO. Using the material prepared in this comparative example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a 1M NaClO4 PC / FEC (95:5 wt%) solution as the electrolyte, an assembled button cell was subjected to charge and discharge tests. The voltage range was 2 - 4 V. The rate mode was selected for the charge and discharge tests. At a 1 C rate, the capacity retention of the positive electrode material after 200 cycles was 59.8%, and the discharge capacity at a 10 C rate was 15.4 mAh / g.

[0087] Comparative Example 6

[0088] The difference from Example 1 was only that, according to the stoichiometry of Na 0.9 Mn 0.5 Ni 0.5 Zn 0.1 O2, Na2CO3, Mn2O3, NiO, and ZnO were weighed. Steps 1) - 5) in Example 1 were carried out. Using the material prepared in this comparative example as the positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and a 1M NaClO4 PC / FEC (95:5 wt%) solution as the electrolyte, an assembled button cell was subjected to charge and discharge tests. The voltage range was 2 - 4 V. The rate mode was selected for the charge and discharge tests. At a 1 C rate, the capacity retention of the positive electrode material after 200 cycles was 61%, and the discharge capacity at a 10 C rate was 31.8 mAh / g.

[0089] Table 1 Performance Comparison between Examples 1 - 3 and Comparative Examples 1 - 6

[0090] Sample Component Calcination Conditions Capacity Retention Rate after 200 Cycles of 1C Charge and Discharge Discharge Capacity at 5C Rate Discharge Capacity at 10C Rate Example 1 <![CDATA[Sodium 0.9 Manganese 0.5 Nickel 0.5 Copper 0.05 Oxygen₂]]> Re - calcination 76% 84.9 mAh / g 58.7 mAh / g Example 2 <![CDATA[Sodium 0.9 Manganese 0.5 Nickel 0.5 Copper 0.1 Oxygen₂]]> Re - calcination 87.5% 92.3 mAh / g 67.2 mAh / g Example 3 <![CDATA[Sodium 0.9 Manganese 0.5 Nickel 0.5 Copper 0.15 Oxygen]]> Re - calcination 82.2% 87.1 mAh / g 62.4 mAh / g Comparative Example 1 <![CDATA[Sodium 0.9 Manganese 0.5 Nickel 0.5 Oxygen₂]]> Single Sintering 64.2% 47.3 mAh / g 27.8 mAh / g Comparative Example 2 <![CDATA[Sodium 0.9 Manganese 0.5 Nickel 0.5 Copper 0.1 Oxygen₂]]> Single Sintering 73% 75.2 mAh / g 51.3 mAh / g Comparative Example 3 <![CDATA[Sodium 0.9 Manganese 0.5 Nickel 0.5 Zinc 0.05 Oxygen]]> Re - calcination 65.6% 46.5 mAh / g 22.8 mAh / g Comparative Example 4 <![CDATA[Sodium 0.9 Manganese 0.5 Nickel 0.5 Zinc 0.1 Oxygen]]> Re - calcination 66.6% 44.5 mAh / g 19.1 mAh / g Comparative Example 5 <![CDATA[Sodium 0.9 Manganese 0.5 Nickel 0.5 Zinc 0.15 Oxygen]]> Re - calcination 59.8% 37.2 mAh / g 15.4 mAh / g Comparative Example 6 <![CDATA[Sodium 0.9 Manganese 0.5 Nickel 0.5 Zinc 0.1 Oxygen]]> Single Sintering 61% 62.5 mAh / g 31.8 mAh / g

[0091] As can be seen from Table 1, Examples 1 - 3 had obvious advantages in terms of the capacity retention rate after 200 cycles of 1C charge and discharge, and the specific capacities of 5 C and 10 C rapid charge and discharge compared with Comparative Examples 1 - 6. The comparison between Examples 1 - 3 showed that when the content of the secondary doping Cu was 10%, the best performance was exhibited. The comparison between Examples 1 - 3 and Comparative Example 2 indicated that the secondary sintering with Cu doping was the key to activating the Jahn - Teller effect of Cu ions, and its overall rate performance was better than that of the primary homogeneous sintering results. The comparison between Comparative Examples 3 - 5 and Comparative Example 6 showed that the secondary doping of ZnO sintering could not increase the rate performance of the material, and the 3d 10 electronic structure of Zn ions did not have the Jahn - Teller effect. The strategy of improving the rate performance of the positive electrode by secondary sintering and incorporating oxides was not applicable to all elements. The secondary addition of Zn elements deteriorated the rate performance, and in addition, its cycle stability was not significantly improved. Overall, the strategy we developed to activate the Jahn - Teller effect of the positive electrode material of the layered sodium - ion battery by secondary sintering greatly improved the cycle stability and rate performance of the positive electrode material, which was well verified in the case of Cu and Zn elements. Additionally, weFigure 3 Compared with Figure 14 Na sintered with secondary Cu doping, it is found that the XAS extended edge R-space map of Na 0.9 Mn 0.5 Ni 0.5 Cu 0.1 O2 has different Cu-O bond lengths, and the Cu element obtained in Figure 19 shows a wider pre-edge peak in the NaMn 0.5 Ni 0.5 O2 matrix after secondary annealing compared with primary sintering. All of the above indicate the distortion of the Cu-O octahedron. In summary, we confirm that the secondary annealing process is the key step to activate the Jahn-Teller effect.

[0092] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for improving the performance of the cathode material of a sodium-ion battery by utilizing the Jahn-Teller effect, characterized in that, It includes the following steps: 1) According to the chemical formula Na a Mn x Ni y Precursors of Na, Mn, and Ni are weighed according to the molar ratio of each element in O2 as 0.85 ≤ a ≤ 1, 0.45 ≤ x ≤ 0.55, and 0.4 ≤ y ≤ 0.5 and mixed evenly. Among them, the precursor of Ni includes any one or more of nickel oxide, nickel hydroxide, nickel acetate, and nickel nitrate; the precursor of Mn includes any one or more of manganese oxide, manganese hydroxide, manganese carbonate, manganese acetate, and manganese nitrate; the precursor of Na is selected from any one or more of its oxides, hydroxides, carbonates, nitrates, and oxalates; 2) Grind, dry and tablet the premixed powder and solvent dispersant obtained in step 1), where the pressure is 1000 - 3000 Pa; 3) Presinter the flaky mixture obtained in step 2) to 400 - 600 °C in an air atmosphere and maintain the temperature for 3 - 5 hours; 4) Based on step 3), continue to heat up to 850 - 1000 °C for sintering and maintain the temperature for 10 - 14 hours, and then cool down to room temperature with the furnace to obtain the sintered NMNO; 5) Grind the sintered NMNO in step 4) into particles below 50 μm and uniformly mix it with CuO in a molar ratio of 5% - 15%; 6) Re - tablet the mixed material in step 5), and presinter the obtained flaky mixture to 400 - 600 °C in an air atmosphere and maintain for 1 - 3 hours; 7) Based on step 6), continue to heat up to 900 - 950 °C for sintering and maintain for 3 - 5 hours, and then cool down to room temperature with the furnace; The molecular formula of the prepared cathode material for sodium-ion batteries is Na a Mn x Ni y Cu z O2, where 0.85 ≤ a ≤ 1, 0.45 ≤ x ≤ 0.55, 0.4 ≤ y ≤ 0.5, 0.05 ≤ z ≤ 0.

15.

2. A method for improving the performance of the cathode material of a sodium-ion battery by utilizing the Jahn-Teller effect, characterized in that, In step 1), a = 0.9, x = 0.5, y = 0.5; the precursor of Ni is nickel oxide; the precursor of Mn is manganese oxide or manganese carbonate.

3. A method for improving the performance of the cathode material of a sodium-ion battery by utilizing the Jahn-Teller effect, characterized in that, In step 2), the pressure is 2000 Pa.

4. A method for improving the performance of the cathode material of a sodium-ion battery by utilizing the Jahn-Teller effect, characterized in that, In step 3), the heating rate is 2 - 10 °C / minute, and the presintering temperature is 500 °C.

5. A method for improving the performance of the cathode material of a sodium-ion battery by utilizing the Jahn-Teller effect, characterized in that: In step 4), the sintering temperature is 900 °C; maintain the temperature for 14 hours.

6. A method for improving the performance of the cathode material of a sodium-ion battery by utilizing the Jahn-Teller effect, characterized in that: In step 5), the proportion of CuO is 10% of the molar amount of NMNO.

7. A method for improving the performance of the cathode material of a sodium-ion battery by utilizing the Jahn-Teller effect, characterized in that: In step 6), the presintering temperature is 500 °C, and the holding time is 2 hours.

8. A method for improving the performance of the cathode material of a sodium-ion battery by utilizing the Jahn-Teller effect according to claim 1, characterized in that: In step 7), the sintering temperature is 950 °C, and the holding time is 5 hours.

9. A method for improving the performance of the cathode material of a sodium-ion battery by utilizing the Jahn-Teller effect, characterized in that: The prepared cathode material for sodium - ion batteries has a discharge capacity of 67.2 mAh / g at a potential range of 2 - 4 V and a charge - discharge rate of 10C.

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