Preparation Method of Tunnel-Type Sodium-Ion Battery Cathode Material

Abstract

The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a preparation method of a tunnel-type sodium-ion battery cathode material. The preparation method described in the present invention consists of the following steps: (1) grinding and mixing a sodium source, a manganese source, and a doping source of a high-entropy anion in an agate mortar to obtain a mixture; (2) putting the mixture into a tablet press to press it into a cylindrical shape, then performing high-temperature treatment, and finally grinding after cooling to obtain the tunnel-type sodium-ion battery cathode material. The tunnel-type sodium-ion battery cathode material prepared by the preparation method described in the present invention has a stable product structure. The half-cell formed by using it as the sodium-ion battery cathode has a high discharge capacity and good cycle stability. Moreover, its preparation process is simple, the cost is low, and it is easy to realize large-scale batch production.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a preparation method of a tunnel-type sodium-ion battery cathode material. Background Art

[0002] Sodium-ion batteries are regarded as ideal alternatives to lithium-ion batteries due to their low cost and excellent safety performance. In recent years, with the continuous growth of the global demand for battery energy storage systems, sodium-ion batteries, with their economy and safety, can provide a more cost-effective alternative to existing lithium-based energy storage systems, especially suitable for large-scale energy storage applications that are sensitive to safety and cost. The cathode materials of sodium-ion batteries are mainly divided into three categories: layered metal oxides, polyanion compounds, and Prussian blue compounds. Among them, layered sodium-based manganese oxides have low cost and relatively reversible sodium ion insertion / extraction characteristics, and are a kind of sodium-ion battery cathode material with potential application prospects. However, the manganese redox reaction inevitably produces the Jahn-Teller effect, resulting in serious lattice distortion and obvious capacity decay. Compared with the limited two-dimensional sodium ion transmission path of layered cathodes, the tunnel-type sodium-ion battery cathode can achieve isotropic sodium ion diffusion through its three-dimensional interconnected S-type channel network. This feature can greatly inhibit the Jahn-Teller effect, significantly reduce the activation energy of sodium ion migration, and effectively alleviate the concentration polarization phenomenon during high-rate charge and discharge. In addition, the intrinsic rigid framework of the tunnel structure can significantly inhibit the initiation and expansion of microcracks caused by volume deformation during the deep sodiation / desodiation process. Therefore, the tunnel-type sodium-ion battery cathode has irreplaceable advantages in the new energy field, especially in scenarios such as fast charging and long-life applications.

[0003] Patent CN118908304A discloses a single-crystalline layered sodium-ion battery cathode material prepared by using organic amines as a structure template agent and initially forming crystal nuclei by a solvothermal method, and then performing high-temperature solid-phase synthesis by a step-by-step sodium supplementation method. This material has high energy density and cycle stability in terms of electrochemical performance, but its complex preparation process has great limitations under large-scale demand.

[0004] Therefore, exploring a preparation method for a new type of tunnel-type sodium-ion battery cathode material has become an urgent technical problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a tunnel-type sodium-ion battery cathode material. The tunnel-type sodium-ion battery cathode material prepared by using this method has the characteristics of good cycle stability and high half-cell discharge capacity.

[0006] The preparation method of the tunnel-type sodium-ion battery cathode material described in the present invention consists of the following steps:

[0007] (1) Using sodium carbonate as the sodium source, manganese(III) oxide as the manganese source, and a mixture of sodium fluoride, sodium chloride, sodium bromide, and boron oxide as the doping source for high-entropy anions, grind the sodium source, manganese source, and doping source of high-entropy anions in an agate mortar for 25 - 35 min to mix evenly and obtain a mixture.

[0008] (2) Put the mixture prepared in step (1) into a tablet press to press it into a cylindrical shape, then conduct high-temperature treatment, and finally grind it after cooling to obtain a tunnel-type sodium battery cathode material. The molecular formula of the tunnel-type sodium battery cathode material is Na 0.67 MnOF a Cl b Br c B d , where 0.005 ≤ a ≤ 0.035, 0.005 ≤ b ≤ 0.035, 0.005 ≤ c ≤ 0.035, 0.005 ≤ d ≤ 0.035.

[0009] Among them:

[0010] In the mixture in step (1), the molar ratio of sodium carbonate, manganese(III) oxide, sodium fluoride, sodium chloride, sodium bromide, and boron oxide is 0.67 : 1 : a : b : c : d, where 0.005 ≤ a ≤ 0.035, 0.005 ≤ b ≤ 0.035, 0.005 ≤ c ≤ 0.035, 0.005 ≤ d ≤ 0.035.

[0011] The pressure during tablet pressing in step (2) is 400 - 500 N.

[0012] In step (2), the high-temperature treatment is to heat up to 900 °C at a heating rate of 5 °C / min and sinter for 12 h.

[0013] In step (2), grinding after cooling is to cool to 150 °C at a rate of 5 °C / min, and then grind through a 400-mesh sieve.

[0014] The tunnel-type sodium battery cathode material prepared in step (2) needs to be stored in a dry environment at 60 - 80 °C to avoid being contaminated by water vapor.

[0015] Preferably, the molecular formula of the tunnel-type sodium battery cathode material prepared in step (2) is Na 0.67 MnOF a Cl b Br c B d , where a is 0.030, b is 0.005, c is 0.030, and d is 0.030.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The preparation method of the tunnel-type sodium battery cathode material of the present invention induces a layered sodium battery cathode material into a tunnel-type sodium battery cathode material by doping high-entropy anions, solving the technical problems of the inability to balance the electrochemical performance and stability and the complex preparation process in the layered oxide cathode material of sodium ion batteries.

[0018] (2) The preparation method of the tunnel-type sodium battery cathode material of the present invention constructs an irregular polyhedron composed of a manganese oxide 4 quadrilateral pyramid and two or three groups of manganese oxide 6 octahedrons through this preparation method. These octahedrons establish large tunnels and smaller inactive channels. These tunnels can withstand more lattice distortions caused by the reversible insertion / extraction of sodium ions, thereby avoiding capacity decay, which cannot be achieved by layered sodium battery cathode materials.

[0019] (3) The tunnel-type sodium battery cathode material prepared by using the preparation method of the present invention has a stable product structure. The half-cell formed by using it as the sodium battery cathode has a high discharge capacity, good cycle stability, and its simple preparation process, low cost, and is easy to realize large-scale batch production. Description of the Drawings

[0020] Figure 1 SEM image of the tunnel-type sodium battery cathode material prepared in Example 1;

[0021] Figure 2 X-ray diffraction pattern of the tunnel-type sodium battery cathode material prepared in Example 1;

[0022] Figure 3 X-ray diffraction pattern of the layered sodium battery cathode material prepared in Comparative Example 1;

[0023] Figure 4 Comparative diagram of the cycle performance of the sodium battery cathode materials prepared in Examples 1-5 and Comparative Examples 1-5. Detailed Embodiments

[0024] The present invention will be further described below in conjunction with embodiments.

[0025] Example 1

[0026] The preparation method of the tunnel-type sodium battery cathode material described in this Example 1 consists of the following steps:

[0027] (1) Using sodium carbonate as the sodium source, manganese dioxide as the manganese source, and a mixture of sodium fluoride, sodium chloride, sodium bromide, and boron oxide as the doping source of high-entropy anions, the sodium source, manganese source, and doping source of high-entropy anions are ground in an agate mortar for 30 minutes and mixed evenly to obtain a mixture;

[0028] (2) Put the mixture prepared in step (1) into a tablet press to press it into a cylindrical shape, then conduct high-temperature treatment, and finally grind it after cooling to prepare a tunnel-type sodium-ion battery cathode material. The molecular formula of the tunnel-type sodium-ion battery cathode material is Na 0.67 MnOF a Cl b Br c B d , where a is 0.030, b is 0.005, c is 0.030, and d is 0.030.

[0029] Wherein:

[0030] The molar ratio of sodium carbonate, manganese(III) oxide, sodium fluoride, sodium chloride, sodium bromide, and boron oxide in the mixture in step (1) is 0.67:1:a:b:c:d, where a is 0.030, b is 0.005, c is 0.030, and d is 0.030.

[0031] The pressure during tablet pressing in step (2) is 450 N.

[0032] In step (2), the high-temperature treatment is to heat up to 900 °C at a heating rate of 5 °C / min and sinter for 12 h.

[0033] In step (2), the grinding after cooling is to cool to 150 °C at a rate of 5 °C / min, and then grind through a 400-mesh sieve.

[0034] The tunnel-type sodium-ion battery cathode material prepared in step (2) needs to be stored in a dry environment at 70 °C to avoid being contaminated by water vapor.

[0035] Perform SEM testing on the tunnel-type sodium-ion battery cathode material prepared in Example 1, and its SEM image is as shown in the appendix Figure 1 shown; perform X-ray diffraction testing on it, and its X-ray diffraction pattern is as shown in the appendix Figure 2 shown.

[0036] Example 2

[0037] The preparation method of the tunnel-type sodium-ion battery cathode material described in this Example 2 consists of the following steps:

[0038] (1) Using sodium carbonate as the sodium source, manganese(III) oxide as the manganese source, and a mixture of sodium fluoride, sodium chloride, sodium bromide, and boron oxide as the doping source of high-entropy anions, grind the sodium source, manganese source, and doping source of high-entropy anions in an agate mortar for 25 min to mix them evenly to prepare a mixture;

[0039] (2) Put the mixture prepared in step (1) into a tablet press to press it into a cylindrical shape, then conduct high-temperature treatment, and finally grind it after cooling to prepare a tunnel-type sodium battery cathode material. The molecular formula of the tunnel-type sodium battery cathode material is Na 0.67 MnOF a Cl b Br c B d , where a is 0.030, b is 0.020, c is 0.030, and d is 0.030.

[0040] Among them:

[0041] In the mixture in step (1), the molar ratio of sodium carbonate, manganese(III) oxide, sodium fluoride, sodium chloride, sodium bromide, and boron oxide is 0.67 : 1 : a : b : c : d, where a is 0.030, b is 0.020, c is 0.030, and d is 0.030.

[0042] The pressure during tablet pressing in step (2) is 400 N.

[0043] In step (2), the high-temperature treatment is to heat up to 900 °C at a heating rate of 5 °C / min and sinter for 12 h.

[0044] In step (2), grinding after cooling is to cool to 150 °C at a rate of 5 °C / min, and then grind through a 400-mesh sieve.

[0045] The tunnel-type sodium battery cathode material prepared in step (2) needs to be stored in a dry environment at 60 °C to avoid being contaminated by water vapor.

[0046] Example 3

[0047] The preparation method of the tunnel-type sodium battery cathode material described in this Example 3 consists of the following steps:

[0048] (1) Using sodium carbonate as the sodium source, manganese(III) oxide as the manganese source, and a mixture of sodium fluoride, sodium chloride, sodium bromide, and boron oxide as the doping source of high-entropy anions, grind the sodium source, manganese source, and doping source of high-entropy anions in an agate mortar for 35 min to mix them evenly to prepare a mixture;

[0049] (2) Put the mixture prepared in step (1) into a tablet press to press it into a cylindrical shape, then conduct high-temperature treatment, and finally grind it after cooling to prepare a tunnel-type sodium battery cathode material. The molecular formula of the tunnel-type sodium battery cathode material is Na 0.67 MnOF a Cl b Br c B d, where a is 0.005, b is 0.005, c is 0.005, and d is 0.005.

[0050] Where:

[0051] In the mixture described in step (1), the molar ratio of sodium carbonate, manganese sesquioxide, sodium fluoride, sodium chloride, sodium bromide, and boron oxide is 0.67 : 1 : a : b : c : d, where a is 0.005, b is 0.005, c is 0.005, and d is 0.005.

[0052] The pressure during tablet pressing in step (2) is 500 N.

[0053] In step (2), the high-temperature treatment is to heat up to 900 °C at a heating rate of 5 °C / min and sinter for 12 h.

[0054] In step (2), the grinding after cooling is to cool to 150 °C at a rate of 5 °C / min, and then grind through a 400-mesh sieve.

[0055] The tunnel-type sodium battery cathode material prepared in step (2) needs to be stored in a dry environment at 80 °C to avoid being contaminated by water vapor.

[0056] Example 4

[0057] The preparation method of the tunnel-type sodium battery cathode material described in this Example 4 consists of the following steps:

[0058] (1) Using sodium carbonate as the sodium source, manganese sesquioxide as the manganese source, and a mixture of sodium fluoride, sodium chloride, sodium bromide, and boron oxide as the doping source of high-entropy anions, grind the sodium source, manganese source, and doping source of high-entropy anions in an agate mortar for 33 min to mix evenly, and prepare a mixture.

[0059] (2) Put the mixture prepared in step (1) into a tablet press to press it into a cylindrical shape, then carry out high-temperature treatment, and finally grind after cooling to prepare a tunnel-type sodium battery cathode material, and the molecular formula of the tunnel-type sodium battery cathode material is Na 0.67 MnOF a Cl b Br c B d , where a is 0.035, b is 0.035, c is 0.035, and d is 0.035.

[0060] Where:

[0061] In the mixture described in step (1), the molar ratio of sodium carbonate, manganese(III) oxide, sodium fluoride, sodium chloride, sodium bromide, and boron oxide is 0.67 : 1 : a : b : c : d, where a is 0.035, b is 0.035, c is 0.035, and d is 0.035.

[0062] In step (2), the pressure during tablet pressing by the tablet press is 480 N.

[0063] In step (2), the high-temperature treatment is to heat up to 900 °C at a heating rate of 5 °C / min and sinter for 12 h.

[0064] In step (2), the grinding after cooling is to cool down to 150 °C at a rate of 5 °C / min, and then grind through a 400-mesh sieve.

[0065] The tunnel-type sodium-ion battery cathode material prepared in step (2) needs to be stored in a dry environment at 75 °C to avoid being contaminated by water vapor.

[0066] Example 5

[0067] The preparation method of the tunnel-type sodium-ion battery cathode material described in this Example 5 consists of the following steps:

[0068] (1) Using sodium carbonate as the sodium source, manganese(III) oxide as the manganese source, and a mixture of sodium fluoride, sodium chloride, sodium bromide, and boron oxide as the doping source of high-entropy anions, grind the sodium source, manganese source, and doping source of high-entropy anions in an agate mortar for 30 min to mix evenly, and prepare a mixture.

[0069] (2) Put the mixture prepared in step (1) into a tablet press and press it into a cylindrical shape, then perform high-temperature treatment, and finally grind after cooling to prepare a tunnel-type sodium-ion battery cathode material. The molecular formula of the tunnel-type sodium-ion battery cathode material is Na 0.67 MnOF a Cl b Br c B d , where a is 0.030, b is 0.030, c is 0.030, and d is 0.030.

[0070] Among them:

[0071] In the mixture described in step (1), the molar ratio of sodium carbonate, manganese(III) oxide, sodium fluoride, sodium chloride, sodium bromide, and boron oxide is 0.67 : 1 : a : b : c : d, where a is 0.030, b is 0.030, c is 0.030, and d is 0.030.

[0072] In step (2), the pressure during tablet pressing by the tablet press is 450 N.

[0073] In step (2), the high-temperature treatment is to increase the temperature to 900 °C at a heating rate of 5 °C / min and sinter for 12 h.

[0074] In step (2), the grinding after cooling is to cool to 150 °C at a rate of 5 °C / min, and then grind through a 400-mesh sieve.

[0075] The tunnel-type sodium battery cathode material prepared in step (2) needs to be stored in a dry environment at 70 °C to avoid being contaminated by water vapor.

[0076] Comparative Example 1

[0077] The preparation method of the layered sodium battery cathode material described in this Comparative Example 1 consists of the following steps:

[0078] (1) Using sodium carbonate as the sodium source and manganese dioxide as the manganese source, grind the sodium source and manganese source in an agate mortar for 30 min to mix evenly, and obtain a mixture.

[0079] (2) Put the mixture prepared in step (1) into a tablet press to press it into a cylindrical shape, then carry out high-temperature treatment, and finally grind after cooling to obtain a layered sodium battery cathode material, and the molecular formula of the layered sodium battery cathode material is Na 0.67 MnO 2 .

[0080] Among them:

[0081] In the mixture described in step (1), the molar ratio of sodium carbonate to manganese dioxide is 0.67:1.

[0082] The pressure during tablet pressing in step (2) is 450 N.

[0083] In step (2), the high-temperature treatment is to increase the temperature to 900 °C at a heating rate of 5 °C / min and sinter for 12 h.

[0084] In step (2), the grinding after cooling is to cool to 150 °C at a rate of 5 °C / min, and then grind through a 400-mesh sieve.

[0085] The layered sodium battery cathode material prepared in step (2) needs to be stored in a dry environment at 70 °C to avoid being contaminated by water vapor.

[0086] Perform SEM testing on the layered sodium battery cathode material prepared in Comparative Example 1, and its SEM image is as shown in the appendix Figure 3 .

[0087] Comparative Example 2

[0088] The preparation method of the tunnel-type sodium battery cathode material described in this Comparative Example 2 consists of the following steps:

[0089] (1) Grind sodium carbonate, manganese(III) oxide, and sodium fluoride in an agate mortar for 30 min to mix them evenly, obtaining a mixture.

[0090] (2) Put the mixture obtained in step (1) into a tablet press to press it into a cylindrical shape, then conduct high-temperature treatment, and finally grind it after cooling to obtain a tunnel-type sodium-ion battery cathode material, and the molecular formula of the tunnel-type sodium-ion battery cathode material is Na 0.67 MnOF a , where a is 0.035.

[0091] Wherein:

[0092] In the mixture in step (1), the molar ratio of sodium carbonate, manganese(III) oxide, and sodium fluoride is 0.67:1:0.035.

[0093] The pressure during tablet pressing in step (2) is 450 N.

[0094] In step (2), the high-temperature treatment is to heat up to 900 °C at a heating rate of 5 °C / min and sinter for 12 h.

[0095] In step (2), the grinding after cooling is to cool down to 150 °C at a rate of 5 °C / min, and then grind and pass through a 400-mesh sieve.

[0096] The tunnel-type sodium-ion battery cathode material prepared in step (2) needs to be stored in a dry environment at 70 °C to avoid being contaminated by water vapor.

[0097] Comparative Example 3

[0098] The preparation method of the tunnel-type sodium-ion battery cathode material described in this Comparative Example 3 consists of the following steps:

[0099] (1) Grind sodium carbonate, manganese(III) oxide, sodium fluoride, sodium bromide, and boron oxide in an agate mortar for 30 min to mix them evenly, obtaining a mixture.

[0100] (2) Put the mixture obtained in step (1) into a tablet press to press it into a cylindrical shape, then conduct high-temperature treatment, and finally grind it after cooling to obtain a tunnel-type sodium-ion battery cathode material, and the molecular formula of the tunnel-type sodium-ion battery cathode material is Na 0.67 MnOF a Br c B d , where a is 0.030, c is 0.030, and d is 0.030.

[0101] Wherein:

[0102] In the mixture described in step (1), the molar ratio of sodium carbonate, manganese(III) oxide, sodium fluoride, sodium bromide, and boron oxide is 0.67 : 1 : 0.030 : 0.030 : 0.030.

[0103] In step (2), the pressure during tabletting by the tablet press is 450 N.

[0104] In step (2), the high-temperature treatment is carried out by heating at a rate of 5 °C / min to 900 °C and sintering for 12 h.

[0105] In step (2), the grinding after cooling is carried out by cooling at a rate of 5 °C / min to 150 °C, and then grinding through a 400-mesh sieve.

[0106] The tunnel-type sodium-ion battery cathode material prepared in step (2) needs to be stored in a dry environment at 70 °C to avoid being contaminated by water vapor.

[0107] Comparative Example 4

[0108] The preparation method of the tunnel-type sodium-ion battery cathode material described in this Comparative Example 4 consists of the following steps:

[0109] (1) Grind sodium carbonate, manganese(III) oxide, sodium fluoride, sodium chloride, and boron oxide in an agate mortar for 30 min to mix evenly to obtain a mixture.

[0110] (2) Put the mixture prepared in step (1) into a tablet press to press it into a cylindrical shape, then carry out high-temperature treatment, and finally grind after cooling to obtain a tunnel-type sodium-ion battery cathode material, and the molecular formula of the tunnel-type sodium-ion battery cathode material is Na 0.67 MnOF a Cl b B d , where a is 0.030, b is 0.030, and d is 0.030.

[0111] Where:

[0112] In the mixture described in step (1), the molar ratio of sodium carbonate, manganese(III) oxide, sodium fluoride, sodium chloride, and boron oxide is 0.67 : 1 : 0.030 : 0.030 : 0.030.

[0113] In step (2), the pressure during tabletting by the tablet press is 450 N.

[0114] In step (2), the high-temperature treatment is carried out by heating at a rate of 5 °C / min to 900 °C and sintering for 12 h.

[0115] In step (2), the grinding after cooling is carried out by cooling at a rate of 5 °C / min to 150 °C, and then grinding through a 400-mesh sieve.

[0116] The tunnel-type sodium battery cathode material prepared in step (2) needs to be stored in a dry environment at 70 °C to avoid being contaminated by water vapor.

[0117] Comparative Example 5

[0118] The preparation method of the tunnel-type sodium battery cathode material described in this Comparative Example 5 consists of the following steps:

[0119] (1) Grind sodium carbonate, manganese(III) oxide, sodium fluoride, sodium chloride, and sodium bromide in an agate mortar for 30 min to mix evenly and obtain a mixture.

[0120] (2) Put the mixture prepared in step (1) into a tablet press to press it into a cylindrical shape, then conduct high-temperature treatment, and finally grind it after cooling to obtain a tunnel-type sodium battery cathode material. The molecular formula of the tunnel-type sodium battery cathode material is Na 0.67 MnOF a Cl b Br c , where a is 0.030, b is 0.030, and c is 0.030.

[0121] Among them:

[0122] The molar ratio of sodium carbonate, manganese(III) oxide, sodium fluoride, sodium chloride, and sodium bromide in the mixture described in step (1) is 0.67 : 1 : 0.030 : 0.030 : 0.030.

[0123] The pressure during tablet pressing in step (2) is 450 N.

[0124] The high-temperature treatment in step (2) is to heat up to 900 °C at a heating rate of 5 °C / min and sinter for 12 h.

[0125] The grinding after cooling in step (2) is to cool to 150 °C at a rate of 5 °C / min, and then grind and pass through a 400-mesh sieve.

[0126] The tunnel-type sodium battery cathode material prepared in step (2) needs to be stored in a dry environment at 70 °C to avoid being contaminated by water vapor.

[0127] By analyzing the X-ray diffraction patterns of Example 1 and Comparative Example 1, Figure 2 the diffraction peaks show a typical tunnel structure. For example, the reflection (101) at about 2θ = 10°1 is a typical feature of this structure. However, the X-ray diffraction peaks show that there are still a small amount of P2-layered peak positions, but the signal intensity is extremely low. At the same time, Figure 1 is the SEM image of Example 1, showing that its microstructure is tunnel-type, which is consistent with the results of its X-ray diffraction. Figure 3It is the X-ray diffraction pattern of Comparative Example 1, corresponding to the diffraction peaks of the P2 phase, and the marked composition is Na0.67MnO 2 with a layered structure. It is not difficult to see that the doping of high-entropy anions has a huge impact on the structural properties of Na0.67MnO 2 . It successfully induces the layered structure into a tunnel-type structure. However, in this process, the doping of fluoride ions will affect the size of the tunnel and the layer / tunnel ratio. The synthesis with a higher fluoride dosage will cause a large amount of the layered structure to transform into a tunnel-like structure due to the preferred orientation of fluoride ions.

[0128] The cathode materials obtained in Examples 1-5 and Comparative Examples 1-5 were respectively uniformly dispersed in the solvent NMP (N-methylpyrrolidone) with Super P (super P conductive carbon black) and PVDF (polyvinylidene fluoride) according to a mass ratio of 8:1:1. Then, the mixed slurry was coated on the substrate aluminum foil, dried, and cut into circular pieces. Sodium metal was used as the counter electrode, and sodium perchlorate was used as the electrolyte to assemble a button battery for electrochemical performance testing. The test voltage range was 2.2V - 4.3V, and the change curve of the discharge specific capacity at a current density of 1C with the number of cycles was recorded (where a current of 0.1C was applied in the first two cycles for electrode activation), as Figure 4 shown.

[0129] From Figure 4It can be obtained that: in Example 1, the initial discharge specific capacity at 1C current is 157.43 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 126.57 mAh / g; in Example 2, the initial discharge specific capacity at 1C current is 141.25 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 96.70 mAh / g; in Example 3, the initial discharge specific capacity at 1C current is 112.58 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 97.22 mAh / g; in Example 4, the initial discharge specific capacity at 1C current is 154.48 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 102.34 mAh / g; in Example 5, the initial discharge specific capacity at 1C current is 153.42 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 120.11 mAh / g. In Comparative Example 1, the initial discharge specific capacity at 1C current is 88.49 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 75.91 mAh / g; in Comparative Example 2, the initial discharge specific capacity at 1C current is 109.02 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 92.23 mAh / g; in Comparative Example 3, the initial discharge specific capacity at 1C current is 112.45 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 75.28 mAh / g; in Comparative Example 4, the initial discharge specific capacity at 1C current is 82.75 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 76.93 mAh / g; in Comparative Example 5, the initial discharge specific capacity at 1C current is 135.95 mAh / g, and after 100 cycles, the discharge specific capacity at 1C is 82.44 mAh / g. By comparing the data of each example and each comparative example, it is not difficult to see that the scatter plot of the discharge specific capacity of the comparative examples shows a fluctuating curve, while the scatter plot of the examples is relatively much smoother, which is sufficient to illustrate that the stability of the examples is better than that of the comparative examples, demonstrating the improvement of the tunnel structure on the stability of sodium-ion batteries.

[0130] It is not difficult to see by comparison that the amount of different anions doped affects both the capacity and the cycle stability of the battery, but all the examples involved are better than the layered sodium cathode material (Comparative Example 1). Through screening, whether it is the reversible charge-discharge capacity or the cycle stability performance, Example 1 is currently an excellent high-entropy anion-doped tunnel-type sodium cathode material.

Claims

1. A method for preparing a tunnel-type sodium cathode material, characterized in that: It consists of the following steps: (1) using sodium carbonate as a sodium source, manganese trioxide as a manganese source, and a mixture of sodium fluoride, sodium chloride, sodium bromide, and boron oxide as a doping source of high entropy anions, grinding the sodium source, manganese source, and the doping source of high entropy anions in an agate mortar for 25-35 minutes to mix them evenly, thereby preparing a mixture; (2) The mixture prepared in step (1) is placed in a tablet press and pressed into a cylindrical shape, and then subjected to high temperature treatment, and finally ground after cooling to prepare a tunnel-type sodium positive electrode material. The molecular formula of the tunnel-type sodium positive electrode material is Na 0.67 MnOF a Cl b Br c B d , where 0.030≤a≤0.035, 0.005≤b≤0.035, 0.030≤c≤0.035, 0.030≤d≤0.

035.

2. The method for preparing a tunnel-type sodium positive electrode material according to claim 1, characterized in that: The molar ratio of sodium carbonate, manganese trioxide, sodium fluoride, sodium chloride, sodium bromide and boron oxide in the mixture of step (1) is 0.67:1: a: b: c: d, wherein 0.030≤a≤0.035, 0.005≤b≤0.035, 0.030≤c≤0.035, and 0.030≤d≤0.

035.

3. The method for preparing a tunnel-type sodium positive electrode material according to claim 1, characterized in that: The pressure of the tablet press in step (2) is 400-500N.

4. The method for preparing a tunnel-type sodium positive electrode material according to claim 1, characterized in that: The high temperature treatment in step (2) is to heat the temperature to 900°C at a heating rate of 5°C / min and sinter for 12 hours.

5. The method for preparing a tunnel-type sodium positive electrode material according to claim 1, characterized in that: The grinding after cooling in step (2) is to cool to 150°C at a rate of 5°C / min, and then grind through a 400-mesh sieve.

6. The method for preparing a tunnel-type sodium positive electrode material according to claim 1, characterized in that: The molecular formula of the tunnel-type sodium cathode material prepared in step (2) is Na 0.67 MnOF a Cl b Br c B d , where a is 0.030, b is 0.005, c is 0.030, and d is 0.030.

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