A copper-manganese-based sodium-ion battery cathode material and its preparation method

Abstract

This invention discloses a layered cathode material for copper-manganese-based sodium-ion batteries, wherein the cathode material has the chemical formula Na. x Cu 0.33‑0.5my M y+z Mn 0.67‑0.25mz O2, 0.67

Description

Technical Field

[0001] This invention belongs to the field of chemical power sources, specifically relating to a method for preparing a low-cost, long-cycle sodium-ion battery cathode based on copper and manganese, as well as a modified cathode. Background Technology

[0002] With the rapid development of renewable and environmentally friendly new energy sources over the past decade, the uneven global distribution and insufficient reserves of lithium resources have severely restricted the widespread application of lithium-ion batteries in large-scale energy storage. Conversely, sodium-ion batteries, due to the abundance and wide distribution of sodium resources, offer the advantage of low cost and are considered to have promising applications in large-scale energy storage. Compared to other types of sodium-ion cathode materials, layered cathode materials possess higher theoretical specific capacity and simpler, greener preparation methods, making them commercially promising and attracting widespread attention.

[0003] Driven by the demands of industrial production, copper-manganese-based substrate oxides, with prices far lower than those of elements such as nickel, cobalt, and vanadium, possess a significant cost advantage. However, they exhibit noticeable voltage decay, affecting their capacity retention and energy density. Furthermore, irreversible phase transitions, vacancy rearrangements, and transition metal dissolution occurring during charge and discharge affect cycle performance and high-current fast-charging capabilities, thus limiting their further development. Appropriate element doping to regulate the composition and crystal structure of cathode materials, thereby improving electrochemical performance, is a commonly used method.

[0004] Currently, commonly used preparation methods include solid-state methods and coprecipitation methods. Among them, the solid-state method is one of the main choices for industrialization due to its simple and controllable preparation process. However, the solid-state method cannot achieve atomic-level homogeneous mixing, thus limiting its application in elemental doping. The coprecipitation method requires complex processes and the introduction of other solvents, resulting in higher costs.

[0005] CN114368794A discloses a copper-based crystalline oxide material with the chemical formula Na. 1+x Cu y M h Mn k O 1+i Furthermore, by using solid-state methods to dope with elements such as Sc, Y, La, Nd, Ce, Ni, and Fe, the spatial structure and charge density were altered. After 100 cycles, the capacity retention of this material increased by approximately 15%, but the relatively low number of cycles could not achieve the goal of a low-cost, long-cycle cathode material. CN110165206A discloses a spherical sodium-ion battery cathode material and its preparation method, which utilizes a co-precipitation method to prepare a spherical Mn-based cathode with controllable composition of Cu and Ni doping, achieving long-cycle stability of 1000 cycles. However, the precursor and metal salt need to be ultrasonically mixed in water and dried, which is not conducive to large-scale production.

[0006] CN114171732A discloses a copper-manganese ordered high-voltage copper-based oxide material. Although such a honeycomb arrangement structure well alleviates the lattice distortion caused by divalent copper, the ordered structure is affected to a certain extent after doping with other elements or long-term cycling, so that the requirement for cycling stability cannot be guaranteed. Summary of the Invention

[0007] To address the problem that cathode materials for sodium-ion batteries cannot meet the electrochemical performance required for practical applications, especially the long-cycle performance of low-cost systems, the present invention regulates the crystal structure through an ion doping strategy to achieve a balance between low cost and long-cycle performance, and constructs a low-cost, long-cycle vacancy-disordered copper-manganese-based layered cathode material that has good air stability. The preparation method thereof is simple, easy to operate, and suitable for large-scale production.

[0008] To achieve the above-mentioned object of the invention, the present invention provides the following technical solution:

[0009] In a first aspect, the present invention discloses a copper-manganese-based low-cost long-cycle layered cathode material for a sodium-ion battery, the chemical formula of which is expressed as Na x Cu 0.33-0.5my M y+z Mn 0.67-0.25mz O2, 0.67<x<0.85, 0<y<0.1, 0<z<0.15, wherein M is an element doping Cu sites and Mn sites respectively, specifically comprising at least two selected from Li, K, Mg, Zn, V, Al, Ti, Sn and Fe; x, y and z are the mole percentages of corresponding elements; m is the valence state of doping element M, 1≤m≤5; the layered cathode is of a P2-phase structure or a P2 / P3-phase structure.

[0010] The metal element M consists of a low-valent metal M1 and a high-valent metal M2; M1 is preferably one of Mg and Zn, and M2 is preferably one of Ti, Sn, Fe and V.

[0011] M1 and M2 dope the Cu and Mn sites, and the synergistic co-doping of the two bimetallic elements at two different sites has a more obvious improvement effect on the long-cycle performance of the layered cathode material.

[0012] Preferably, the layered material has a P2-phase crystal structure, the morphology of the layered material is granular, and the particle size ranges from 0.5 μm to 10 μm.

[0013] When x is 0.67 or 0.78, the layered cathode has a P2-phase structure; when x is 0.85, the layered cathode has a P2 / P3-phase structure.

[0014] Further, x is 0.78, and 0<y<0.10, 0<z<0.15.

[0015] Excessive inert ion doping leads to a decrease in battery capacity, while insufficient doping results in insignificant improvement in capacity retention.

[0016] By adjusting the doping amount and proportion of each element within a suitable range, the optimal electrochemical performance of the cathode material can be achieved.

[0017] Furthermore, in a preferred embodiment, M is Mg, Ti, or Na. 0.67 Cu 0.33-y Mg y Mn 0.67-z Ti z O2, where 0 <y<0.10,0<z<0.15。

[0018] Further, in a preferred embodiment, the chemical formula is Na 0.67 Cu 0.28 Mg 0.05 Mn 0.62 Ti 0.05 O2.

[0019] In one embodiment of the present invention, M is Fe, Sn, and the chemical formula is Na. 0.67 Cu 0.255 Fe 0.05 Mn 0.62 Sn 0.05 O2.

[0020] In one embodiment of the present invention, M is Zn, V, and the chemical formula is Na. 0.67 Cu 0.28 Zn 0.05 Mn 0.6075 V 0.05 O2.

[0021] Furthermore, in the XRD spectrum of the copper-manganese base layer cathode material, the characteristic peak intensity of the vacancy-ordered structure is extremely weak and almost disappears.

[0022] In the past, sodium-ion battery layered metal oxide cathode materials have been improved by doping to induce an ordered structure to enhance structural stability. However, after a certain number of cycles, the stability of the unit structure decreases due to phase transition or dissolution of transition metals, resulting in the orderly rearrangement of vacancies, which affects cycle performance and ion diffusion and transport.

[0023] In one embodiment of the present invention, the vacancy-disordered copper-manganese-based cathode material with Mg and Ti co-doping control exhibits smaller volume deformation and structural stability during charge and discharge.

[0024] Secondly, the present invention provides a method for preparing the above-mentioned copper-manganese-based cathode material, comprising the following steps:

[0025] (S1) Source material mixing: Sodium source and doped metal source are added according to stoichiometric ratio, with sodium source added at 105%-120% of stoichiometric ratio. The mixture is ground thoroughly until homogeneous and then pressed into tablets to obtain intermediate material.

[0026] Further, the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium citrate, sodium propionate, and sodium pyruvate; the doping metal source is selected from at least two of metal oxides, sulfates, nitrates, carbonates, acetates, oxalates, and their hydrated compounds, specifically the metal element M is at least two of Li, K, Mg, Zn, V, Al, Ti, Sn, and Fe; preferably, the metal element M is a low-valence metal M1 and a high-valence metal M2; M1 is preferably one of Mg and Zn, and M2 is preferably one of Ti, Sn, Fe, and V.

[0027] Furthermore, the preferred sodium source is an organic sodium source of at least one of sodium citrate, sodium propionate, and sodium pyruvate. It is speculated that this may be because the electron cloud density of covalent bonds is relatively weak, which is conducive to the diffusion of sodium ions, optimizes the process of sodium ions entering the solid phase and the interface properties, thereby improving the discharge specific capacity and forming a stable doped layered cathode material.

[0028] The doping metal source is at least one selected from metal oxides, carbonates, acetates and their hydrated compounds.

[0029] The grinding method is ball milling, and then the powder is compressed into tablets using a tablet press.

[0030] Furthermore, the mass ratio of grinding balls to mixed raw materials is 10-20 times, the rotation speed is 300-500 rpm, and the ball milling time is 5-10 hours; preferably, the ball-to-material ratio is 15 times, 500 rpm, and 6 hours.

[0031] Furthermore, the pressure applied during tableting is 10-15 MPa; preferably 15 MPa.

[0032] Furthermore, after obtaining the intermediate material in step (S1), a cyclic freezing-thawing process is performed. The cyclic freezing-thawing process involves freezing the intermediate material at -40 to -20°C for 2-4 hours and then thawing it at 20-40°C for 3-6 hours. This cyclic freezing-thawing process is repeated 1-3 times before proceeding to step (S2) for sintering.

[0033] The inventors unexpectedly discovered that the freeze-thaw process can fully utilize the doped metal ions to form a more stable crystal framework structure and improve the uniformity of metal doping. At the same time, it can enable sodium ions to enter the bulk phase of the material better, thereby alleviating the problem of residual alkali on the surface and optimizing the structural stability of the cathode material. Furthermore, by adjusting the system temperature, the structure of the intermediate is optimized, which is conducive to improving the cycle stability of the cathode material and providing a foundation for improving the mechanical properties of the cathode material.

[0034] (S2) Cathode material sintering: The intermediate obtained in step (S1) is calcined at 650-950℃, held at that temperature for 12-24 hours, and then cooled to room temperature to obtain the layered cathode material Na. x Cu 0.33-0.5my M y+z Mn 0.67-0.25mz O2.

[0035] Furthermore, the roasting atmosphere is at least one of oxygen, air, argon, and nitrogen.

[0036] Furthermore, the heating rate is 1-10℃ / min during heating and the cooling rate is 1-10℃ / min during cooling.

[0037] After cooling to room temperature, the material is ground to obtain the layered cathode material of the copper-manganese-based sodium-ion battery.

[0038] Furthermore, the doping element M is preferably Mg, Ti; or Fe, Sn; or Zn, V.

[0039] The preparation method utilizes solid-state sintering to form a stable layered oxide material through interdiffusion of substances at high temperatures. The preparation method is simple in terms of conditions and process flow, and is easily scalable for mass production.

[0040] Thirdly, the present invention also provides a sodium-ion battery, wherein the cathode material is the layered cathode material of the low-cost, long-cycle sodium-ion battery based on copper-manganese as described in the first aspect.

[0041] Furthermore, the raw materials for preparing the positive electrode also include a conductive agent and a binder; the mass ratio of the positive electrode material, the conductive agent, and the binder is 6-9:0.5-2:0.5-2; preferably, the raw material ratio is 8-9:0.5-1:0.5-1.

[0042] The sodium-ion battery, due to the use of the copper-manganese-based low-cost long-cycle cathode material described in the first aspect, exhibits a smoother charge-discharge curve and a significantly reduced vacancy-ordered plateau (<4.0V), demonstrating its advantage in long-cycle stability. This indicates that appropriate element doping strategies have good application prospects in optimizing the performance of low-cost sodium-ion batteries.

[0043] The beneficial effects of this invention are as follows:

[0044] I. The cathode material of this invention is formed by doping Cu and Mn sites in the transition metal layer with metal ions to create a vacancy-disordered P2 phase copper-manganese base layer cathode material with good air stability. By utilizing the synergistic effect of multiple metal cations, the excellent structural stability of the copper-manganese base layer oxide cathode material during charge and discharge is effectively improved, thereby achieving a longer battery cycle life. The sodium-ion battery, after 500 long-cycle performance tests, still exhibits better capacity retention than other copper-manganese-based sodium-ion batteries under more stringent testing conditions, laying a good foundation for the subsequent realization of low-cost, long-cycle room temperature sodium-ion energy storage batteries.

[0045] Second, the cathode preparation method of this invention is a solid-state sintering method. Compared with the liquid-phase reaction environment and subsequent experimental steps such as drying and secondary calcination required by the sol-gel method and co-precipitation method, the preparation method of this invention only requires ball milling and mixing the raw materials in proportion, followed by high-temperature calcination to obtain the cathode material. No special atmosphere protection is required during the preparation process, the synthesis process is simple, and the production efficiency is high. Furthermore, all raw materials used in this invention are readily available, non-toxic, and inexpensive, especially copper and manganese, which are abundant and have a significant cost advantage, making them suitable for large-scale mass production.

[0046] Third, this invention addresses the voltage decay phenomenon and unsatisfactory long-cycle performance of low-cost copper-manganese-based materials by appropriately doping them with metal ions and utilizing the synergistic effect of multiple elements. This effectively improves the voltage decay phenomenon, structural damage, and transition metal dissolution of copper-manganese-based materials, thereby achieving a long cycle life for the battery.

[0047] IV. The cathode material prepared by this invention possesses the intrinsic property of good air stability, and its vacancy-disordered structural characteristics benefit from the regulation of crystal structure by ion doping. Unlike the decay of the ordered structure and the accompanying vacancy rearrangement during cycling of previous materials, this invention suppresses the structural distortion caused by rearrangement in the low-voltage region (<4V) by constructing a vacancy-disordered material.

[0048] Fifth, the small amount of inert ion doping strategy introduced in this invention significantly improves cycle stability while avoiding a significant reduction in the capacity of the cathode material, and at the same time maintains the high operating voltage of the material itself, thereby maintaining the energy density of the material.

[0049] VI. The present invention provides a low-cost copper-manganese-based layered cathode material for sodium-ion batteries. Through ion doping, a specific stable disordered structure is constructed, which exhibits excellent stability, especially under long-term cycling, providing a new research direction for the industrialization of sodium-ion batteries.

[0050] VII. This invention utilizes a freeze-thaw process to fully leverage the doped metal ions to form a more stable crystal framework structure and improve the uniformity of metal doping. Simultaneously, it enables sodium ions to better enter the bulk phase of the material, thereby alleviating the problem of residual alkali on the surface and optimizing the structural stability of the cathode material. Furthermore, by adjusting the system temperature, the structure of the intermediate is optimized, which is beneficial to improving the cycle stability of the cathode material and provides a foundation for improving the mechanical properties of the cathode material. Attached Figure Description

[0051] Figure 1 The XRD pattern of the cathode material prepared in Example 1;

[0052] Figure 2 SEM image of the cathode material prepared in Example 1;

[0053] Figure 3 The 0.1C charge-discharge curve of the sodium-ion battery prepared in Example 1;

[0054] Figure 4 The 1C cycle performance of the sodium-ion battery prepared in Example 1;

[0055] Figure 5 The 5C charge-discharge curve of the sodium-ion battery prepared in Example 1;

[0056] Figure 6 Comparison of X-ray powder diffraction patterns of the cathode material of Example 1 before and after one month of exposure to air;

[0057] Figure 7 SEM image of the cathode material prepared in Example 8;

[0058] Figure 8 This is a SEM image of the cathode material prepared in Example 9. Detailed Implementation

[0059] The following description, in conjunction with specific embodiments and accompanying drawings, further illustrates the method for preparing a low-cost, long-cycle sodium-ion battery cathode based on copper-manganese and the modified cathode according to the present invention. However, it should be understood that the scope of protection of the present invention is not limited to the following embodiments.

[0060] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0061] All materials and reagents used in this invention are commercially available products.

[0062] Example 1: Preparation of P2-Na 0.78 Mg 0.05 Cu0.28 Mn 0.62 Ti 0.05 O2 layered cathode material

[0063] (S1) Weigh 0.4095 mol Na2CO3, 0.05 mol MgO, 0.28 mol CuO, 0.62 mol MnO2, 0.05 mol TiO2 and ethanol of equal mass to the above materials, mix them and place them in a ball mill jar. Control the ball-to-material ratio to be 15:1, set the ball mill speed to 500 rpm, and use forward and reverse rotation mode. Ball mill for 6 hours, place it in an oven to dry and grind it finely, and then press it into small round discs with a diameter of 10 mm under 15 MPa to obtain the intermediate material.

[0064] (S2) The intermediate was calcined in a muffle furnace at a heating rate of 5°C / min until it reached 900°C. The temperature was then maintained for 15 hours, and the mixture was cooled to room temperature to obtain P2-Na. 0.78 Mg 0.05 Cu 0.28 Mn 0.62 Ti 0.05 O2 layered cathode material was transferred to the glove box for later use.

[0065] (S3) The obtained P2-Na 0.78 Mg 0.05 Cu 0.28 Mn 0.62 Ti 0.05 O2 layered positive electrode material, conductive additive SP, and binder PVDF are mixed in 80 parts, 10 parts, and 10 parts by weight, respectively, dissolved in solvent NMP, and stirred to obtain a uniform slurry. The slurry is then uniformly coated onto carbon-coated aluminum foil using a 200μm scraper, dried, and sliced ​​to obtain the positive electrode sheet.

[0066] Figure 4 This describes the cycling performance of the sodium-ion battery prepared in Example 1 at a current density of 100 mA / g, with a cycle retention rate as high as 87% after 500 cycles. Figure 1 , 3 It can be seen that the copper-manganese based cathode material exhibits excellent long-cycle performance due to stable vacancies. The absence of a structure-free environment avoids phase transitions and volume changes caused by vacancy rearrangement during charging and discharging, indicating that the ion doping strategy successfully modulates the material's crystal structure. Combined with... Figure 5 The material exhibits 75% of its high-current long-cycle performance at a current density of 500 mA / g, indicating good fast-charging capability. Combined with... Figure 6 This indicates that the cathode material of the present invention has good air stability.

[0067] Example 2

[0068] The operation steps are the same as in Example 1, except that the raw material feeding ratio in step (S1) is changed to 0.4095 mol Na2CO3, 0.08 mol MgO, 0.25 mol CuO, 0.62 mol MnO2, and 0.05 mol TiO2, resulting in the positive electrode material with the chemical formula: Na 0.78 Mg 0.08 Cu 0.25 Mn 0.62 Ti 0.05 O2.

[0069] Example 3

[0070] The operation steps are the same as in Example 1, except that the raw material feeding ratio in step (S1) is changed to 0.4095 mol Na2CO3, 0.03 mol MgO, 0.30 mol CuO, 0.62 mol MnO2, and 0.05 mol TiO2, resulting in the positive electrode material with the chemical formula: Na 0.78 Mg 0.03 Cu 0.30 Mn 0.62 Ti 0.05 O2.

[0071] Example 4

[0072] The operation steps are the same as in Example 1, except that the raw material feeding ratio in step (S1) is changed to 0.4095 mol Na2CO3, 0.05 mol MgO, 0.28 mol CuO, 0.64 mol MnO2, and 0.03 mol TiO2, resulting in the positive electrode material with the chemical formula: Na 0.78 Mg 0.05 Cu 0.28 Mn 0.64 Ti 0.03 O2.

[0073] Example 5

[0074] The operation steps are the same as in Example 1, except that the raw material input and ratio in step (S1) are changed to 0.4095 mol Na2CO3, 0.025 mol Fe2O3, 0.255 mol CuO, 0.62 mol MnO2, and 0.05 mol SnO2, resulting in the positive electrode material with the chemical formula: Na 0.67 Fe 0.05 Cu 0.255 Mn 0.62 Sn 0.05 O2.

[0075] Example 6

[0076] The operation steps are the same as in Example 1, except that the raw materials and proportions in step (S1) are changed to 0.4095 mol Na2CO3, 0.05 mol ZnO2, 0.28 mol CuO, 0.6075 mol MnO2, and 0.025 mol V2O3, resulting in the positive electrode material with the chemical formula: Na 0.67 Zn 0.05 Cu 0.28 Mn 0.6075 V 0.05 O2.

[0077] Example 7

[0078] The operation steps are the same as in Example 1, except that the sintering conditions in step (S2) are changed to be raised to 950°C and then kept at that temperature for 15 hours.

[0079] Example 8

[0080] The operation steps are the same as in Example 1, except that: the intermediate material obtained in step (S1) is first frozen at -30°C for 4 hours and then thawed at 40°C for 3 hours; then step (S2) is performed by placing it in a muffle furnace for roasting.

[0081] Example 9

[0082] The operation steps are the same as in Example 1, except that: the intermediate material obtained in step (S1) is first frozen at -40°C for 2 hours, then thawed at 30°C for 5 hours, and the freezing-thawing cycle is repeated twice; then step (S2) is performed and the material is placed in a muffle furnace for roasting.

[0083] Example 10

[0084] The operating steps are the same as in Example 1, except that: first, 0.273 mol sodium citrate, 0.05 mol MgO, 0.28 mol CuO, 0.62 mol MnO2, and 0.05 mol TiO2 are weighed in step (S1) to obtain the positive electrode material with the chemical formula: Na 0.78 Mg 0.05 Cu 0.28 Mn 0.62 Ti 0.05 O2.

[0085] Example 11

[0086] The operating steps are the same as in Example 1, except that: first, 0.819 mol sodium propionate, 0.05 mol MgO, 0.28 mol CuO, 0.62 mol MnO2, and 0.05 mol TiO2 are weighed in step (S1) to obtain the positive electrode material with the chemical formula: Na 0.78 Mg 0.05 Cu 0.28 Mn0.62 Ti 0.05 O2.

[0087] Example 12

[0088] First, weigh out 0.273 mol sodium citrate, 0.05 mol MgO, 0.28 mol CuO, 0.62 mol MnO2, 0.05 mol TiO2 and ethanol of equal mass as the above materials in step (S1), mix them and place them in a ball mill jar. Control the ball-to-material ratio to be 15:1, set the ball mill speed to 500 rpm, and use forward and reverse rotation mode. Ball mill for 6 hours, place it in an oven to dry and grind it finely, and then press it into small round discs with a diameter of 10 mm under 15 MPa to obtain the intermediate material.

[0089] The intermediate material obtained by (S2) was frozen at -40℃ for 3 hours and then thawed at 30℃ for 4 hours. It was then calcined in a muffle furnace at a heating rate of 5℃ / min until it reached 900℃, where it was held for 15 hours. After cooling to room temperature, the chemical formula Na was obtained. 0.78 Mg 0.05 Cu 0.28 Mn 0.62 Ti 0.05 O2 layered cathode material was transferred to the glove box for later use.

[0090] Step (S3) is the same as in Example 1.

[0091] Comparative Example 1

[0092] The operation steps are the same as in Example 1, except that the raw material feeding ratio in step (S1) is changed to 0.4095 mol Na2CO3, 0.33 mol CuO, and 0.67 mol MnO2, resulting in the positive electrode material with the chemical formula: Na 0.78 Cu 0.33 Mn 0.67 O2.

[0093] Comparative Example 2

[0094] The operation steps are the same as in Example 1, except that the raw material feeding ratio in step (S1) is changed to 0.4095 mol Na2CO3, 0.33 mol CuO, 0.62 mol MnO2, and 0.05 mol TiO2, resulting in the positive electrode material with the chemical formula: Na 0.78 Cu 0.33 Mn 0.62 Ti 0.05 O2.

[0095] Comparative Example 3

[0096] The operation steps are the same as in Example 1, except that the raw material feeding ratio in step (S1) is changed to 0.4095 mol Na2CO3, 0.05 mol MgO, 0.28 mol CuO, and 0.67 mol MnO2, resulting in the positive electrode material with the chemical formula: Na 0.78 Mg 0.05 Cu 0.28 Mn 0.67 O2.

[0097] Comparative Example 4

[0098] The operation steps are the same as in Example 1, except that the raw material feeding ratio in step (S1) is changed to 0.4095 mol Na2CO3, 0.1 mol MgO, 0.23 mol CuO, 0.52 mol MnO2, and 0.15 mol TiO2, resulting in the positive electrode material with the chemical formula: Na 0.78 Mg 0.1 Cu 0.23 Mn 0.52 Ti 0.15 O2 (x=0.78, y=0.1, z=0.15).

[0099] Application examples Electrochemical performance testing

[0100] Electrochemical performance testing: Coin cells were assembled using the electrodes obtained in Examples 1-12 and Comparative Examples 1-4 as positive electrodes, sodium metal sheets as negative electrodes, glass fiber as separators, and 1 mol / L NaClO4 (PC + 5% FEC) as electrolyte. The positive electrode was activated for 3 cycles at a current density of 10 mA / g within the voltage range of 2–4.15 V, followed by charge-discharge cycles at a current density of 100 mA / g. The pH of the materials in the examples and comparative examples of this invention and the corresponding electrochemical performance of the coin cells were tested, and the results are shown in Table 1.

[0101] Table 1

[0102]

[0103]

[0104] The discharge capacity in the first cycle* is the capacity in the fourth cycle. The capacity retention rate after 500 cycles is actually the capacity after 503 cycles compared to the fourth cycle. The first three cycles belong to the formation process.

[0105] from Figure 1 It can be seen that the layered structure of the copper-manganese base layer cathode material modified by ion doping does not change the layered structure of the P2 cathode, which can still be classified as the P63 / mmc type space group. At the same time, the stable vacancy disorder structure formed by regulation can hinder phase transition and volume expansion during charge and discharge, which is beneficial to long cycle performance. Figure 2The SEM images show that the doped cathode is in the form of stacked sheets with relatively uniform particle size. Figure 3 In the charge-discharge curves, the short plateaus attributed to vacancy rearrangement are relatively smooth, corresponding to Figure 1 The data results. Figure 4 , Figure 5 The electrochemical tests of the sodium-ion battery in this invention under different currents demonstrate its excellent long cycle life and fast charging capability.

[0106] The test results of the half-cells in Table 1 for each embodiment show that after elemental doping and ratio adjustment of the layered cathode material, the initial discharge specific capacity of the sodium battery remains almost unchanged, but the capacity retention rate after 500 cycles is significantly improved. For example, in Example 1, the reversible capacity retention rate after 500 cycles is still 87%, while that of the undoped Comparative Example 1 is only 35.6%. It is worth noting that the doping ion content and sintering conditions need to be appropriate. As shown in Table 1, the doping element and calcination temperature both have a certain impact on battery performance. In addition, compared with Comparative Examples 1-3, the synergistic co-doping of two elements has a more significant effect on the long-cycle performance of the layered cathode material than undoped or single-element modified copper-manganese-based oxides. Comparative Example 4 shows that when inert ions such as Mg and Ti are doped in excessive amounts (y = 0.1, z = 0.15), it leads to a significant reduction in battery capacity, which cannot meet the actual capacity requirements.

[0107] This invention achieves optimal electrochemical performance of cathode materials by adjusting the doping amount and proportion of each element within a suitable range.

[0108] Examples 8-9 employ a freeze-thaw process that fully utilizes doped metal ions to form a more stable crystal framework structure and improves the uniformity of bimetallic doping. At the same time, it allows sodium ions to better enter the bulk phase of the material, thereby alleviating the problem of residual alkali on the surface, optimizing the structural stability of the cathode material, and increasing the capacity retention rate by about 3% after 500 cycles. Figure 7 (Example 8) Figure 8 (Example 9) and Figure 1 Compared to Example 1, the SEM image of the cathode material is more regular and smooth, indicating that the freeze-thaw process is conducive to the formation of a more stable crystal framework structure by doped metal ions, and can optimize the intermediate structure and improve the uniformity of metal doping, thereby making the cathode material have higher cycle stability.

[0109] Examples 10-11 may be due to the use of an organic sodium source, which improves the discharge specific capacity of the cathode material.

[0110] Example 12 shows that the stability of the cathode material is significantly improved. It can be seen that the optimization and adjustment of the sodium source and precursor preparation method of the present invention effectively improves the problem of residual alkali on the surface and successfully adjusts the crystal framework structure, thereby improving the structural stability of the cathode material. This simultaneously enhances its cycle stability and discharge specific capacity, exhibiting excellent electrochemical performance.

[0111] This invention provides an application of a low-cost, long-cycle sodium-ion battery cathode based on copper-manganese in sodium batteries. Its contribution to existing technologies lies in utilizing ion-co-doping to regulate the crystal structure, obtaining a stable, vacancy-disordered layered cathode material, significantly improving the cycle stability of existing systems. The cathode material described in this invention can be prepared using a simple solid-state sintering method. This invention simultaneously meets the current demand for low-cost and long-cycle-life cathode materials and holds promise for large-scale production. It is understood that while the various embodiments of this invention describe the invention in detail with specific electrolytes, separators, current collectors, active materials, binders, conductive additives, etc., these descriptions are merely for legal purposes and to illustrate the composition of sodium-ion batteries; the invention is not limited to the given embodiments. Any modifications, equivalent substitutions, and improvements made using this specification within the spirit and principles of this invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this invention.

Claims

1. A copper-manganese based layered cathode material for sodium-ion batteries, having a chemical formula of Na x Cu 0.33-0.5my M y+z Mn 0.67-0.25mz O2, wherein 0.67 < x < 0.85, 0 < y < 0.1, 0 < z < 0.15, M is an element doped at Cu and Mn sites respectively, specifically comprising at least two of Li, K, Mg, Zn, V, Al, Ti, Sn and Fe; x, y and z are mole percentages of corresponding elements; m is the valence state of doped element M, 1 ≤ m ≤ 5; the layered cathode is of P2 phase structure or P2 / P3 phase structure; The copper-manganese-based sodium-ion battery layered cathode material is prepared by a method including the following steps: (S1) Source material mixing: Sodium source and doped metal source are added according to stoichiometric ratio, with sodium source added at 105%-120% of stoichiometric ratio. The mixture is ground thoroughly until homogeneous and then pressed into tablets to obtain intermediate material. The intermediate material is subjected to cyclic freezing-thawing, wherein the cyclic freezing-thawing is performed by freezing the intermediate material at -40~-20℃ for 2-4 hours and then thawing it at 20-40℃ for 3-6 hours, and repeating the cyclic freezing-thawing 1-3 times. (S2) Cathode material sintering: The intermediate material obtained in step (S1) is calcined at 650-950℃, held at that temperature for 12-24 hours, and then cooled to room temperature to obtain the layered cathode material Na. x Cu 0.33-0.5my M y+z Mn 0.67-0.25mz O2.

2. The cathode material according to claim 1, characterized in that, Metallic element M is a low-valence metal M1 and a high-valence metal M2; M1 is one of Mg and Zn, and M2 is one of Ti, Sn, Fe and V.

3. The cathode material according to claim 1 or 2, characterized in that, The layered material has a P2 phase crystal structure, a granular morphology, and a particle size range of 0.5-10 μm.

4. The cathode material according to claim 3, characterized in that, The sodium source in step (S1) is selected from sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium citrate, sodium propionate, and sodium pyruvate. The doping metal source is selected from metal oxides, sulfates, nitrates, carbonates, acetates, oxalates and their hydrated compounds.

5. The positive electrode material according to claim 4, characterized in that, In step (S1), the sodium source is selected from at least one of sodium citrate, sodium propionate, and sodium pyruvate; the grinding method is ball milling, and then the powder is compressed into tablets using a tableting machine.

6. The cathode material according to claim 4, characterized in that, In step (S1), the mass ratio of grinding balls to mixed raw materials is 10-20, the rotation speed is 300-500 rpm, and the ball milling time is 5-10 hours; the pressure applied during tableting is 10-15 MPa.

7. The cathode material according to claim 4, characterized in that, In step (S2), the roasting atmosphere is at least one of oxygen, air, argon, and nitrogen; the heating rate is 1-10℃ / min, and the cooling rate is 1-10℃ / min.

8. A sodium-ion battery, characterized in that, Includes the cathode material as described in any one of claims 1-7.

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