A P2-type high-capacity manganese-based layered oxide cathode material doped with non-metallic interstitial sites, its preparation method, and its application in sodium-ion batteries.

Abstract

This invention belongs to the field of sodium-ion batteries, and relates to a P2-type high-capacity manganese-based layered oxide cathode material doped with non-metallic element interstitial sites, its preparation method, and its application in sodium-ion batteries. The molecular formula of the manganese-based layered oxide cathode material is Na. x M a B c Mn b O2; wherein M is one or more of Li, Mg, Zn, Ni, Fe, Cu, Nb, and Zr; wherein 0.5 < x ≤ 0.8, 0 < a ≤ 0.25, 0.5 ≤ b ≤ 0.8, 0.02 < c ≤ 0.04, and a+b=1, where M and Mn are located in the transition metal layer, and B in the material is in the form of BO3. 3‑ BO4 5‑ Both configurations exist in the interlayer gaps of the transition metal layers. This invention disrupts the ordered honeycomb superlattice structure of Li / Mn through boron interstitial doping, suppressing transition metal rearrangement and voltage decay, while simultaneously achieving high capacity and long-term cycling stability.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries, and relates to a P2-type high-capacity manganese-based substrate oxide cathode material doped with non-metallic element interstitial sites, its preparation method, and its application in sodium-ion batteries. Background Technology

[0002] With the rapid development of the global battery industry and the increasing awareness of environmental protection, rechargeable batteries have attracted much attention in the new round of energy transition. Among them, lithium-ion batteries, with their advantages of high energy density and long cycle life, have been widely used in various portable electronic devices and new energy vehicles. However, the limited and uneven distribution of lithium resources in the earth's crust has led to their high price, making it difficult to meet the core requirements of low cost and resource sustainability for large-scale energy storage systems (such as grid energy storage and renewable energy-supporting energy storage). Against this backdrop, sodium-ion batteries, due to the abundant and widely distributed sodium resources and their low cost, have become a highly promising alternative technology to lithium-ion batteries, gradually becoming a research hotspot in the field of large-scale energy storage and showing broad prospects for practical applications.

[0003] In sodium-ion batteries, the cathode material is a key component determining the battery's energy density, output voltage, and cycle stability, directly limiting the overall application level of sodium-ion batteries. Currently, reported cathode materials for sodium-ion batteries mainly fall into four categories: transition metal oxides, polyanionic compounds, Prussian blue analogs, and organic compounds. Among these, layered transition metal oxides (TLOs) possess significant development potential due to their combination of high energy density and good cycle stability, along with relatively simple synthesis processes and ease of large-scale preparation. Based on the coordination environment of sodium ions and the stacking pattern of oxygen atoms within the smallest repeating unit of the crystal, layered oxide cathode materials are mainly divided into two systems: P2-type and O3-type. Compared to O3-type materials, P2-type layered oxides have a larger interlayer spacing, providing a smoother transport channel for sodium ion insertion / extraction and achieving faster sodium ion diffusion kinetics. Simultaneously, their phase transition process during charge-discharge cycling is simpler, less prone to irreversible structural distortion, thus exhibiting superior rate performance and cycle stability, making it one of the key research directions for current layered oxide cathode materials.

[0004] Studies have shown that in sodium-ion batteries, P2-Na, a P2-type layered oxide material... xIn MnO2, the introduction of doping elements such as Li, Mg, and Zn can induce the generation of non-bonded oxygen 2p orbitals in the crystal lattice, activating the anion redox reaction under high voltage, providing an effective way to overcome the traditional capacity bottleneck. However, the activation mechanism of the anion redox reaction is not yet fully understood, and the irreversible loss of lattice oxygen and oxygen evolution during the reaction can lead to irreversible damage to the material's crystal structure, severely deteriorating its structural stability and electrochemical performance, becoming a key bottleneck restricting the practical application of such high-capacity cathode materials. Therefore, achieving a balance between specific capacity and structural stability, or even breaking this balance—that is, simultaneously achieving high capacity and long cycle life—is a huge challenge in sodium-ion battery cathode material technology.

[0005] Chinese patent CN116314739B achieves low cell volume change and high capacity by introducing Li dual-site substitution (Li simultaneously occupies transition metal sites and alkali metal sites) into the Na–Li–Mn–O system to activate anion redox reactions and using Mg doping to stabilize the lattice. However, its voltage decay problem remains unresolved, and no voltage retention rate data is provided. Similarly, Chinese patent CN120261524A employs a composite strategy of boron interstitial doping combined with surface B2O3 coating to improve cycle stability in a ternary Ni–Co–Mn matrix, but its capacity is only about 120 mAh / g, it does not activate anion redox reactions, and the complex multi-step process increases preparation costs.

[0006] In addition, metal ions (such as Mg) are commonly used in existing technologies. 2+ Zn 2+ Substitutional doping of transition metal sites (such as nitrogen, phosphorus, and nitrogen) can stabilize the structure or modulate electrochemical performance. However, such substitutional doping often occupies active sites, leading to capacity loss, and it is difficult to simultaneously suppress voltage decay. Although nonmetallic boron doping has been reported, it is mostly used for surface coating or co-doping with other elements. There are no reports of selectively doping boron in specific coordination forms into the tetrahedral interstices of the transition metal layer in a P2-type Na–Li–Mn–O matrix, and using it to disrupt the superlattice structure while simultaneously locking Li and Mn to achieve high capacity and no voltage decay.

[0007] Therefore, developing a cathode material that can simultaneously activate anion redox reactions, suppress voltage decay, and has a simple preparation process is of great significance for promoting the development of high-energy-density sodium-ion batteries. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a P2-type high-capacity manganese-based layered oxide cathode material doped with non-metallic element interstitial sites, aiming to solve the problems of severe voltage decay and difficulty in achieving both high capacity and high stability in existing anion redox cathode materials.

[0009] This invention is achieved through the following technical solution:

[0010] The first aspect of the present invention is to provide a high-capacity P2-type manganese-based layered oxide cathode material doped with non-metallic interstitial sites, characterized in that the molecular formula of the manganese-based layered oxide cathode material is Na. x M a B c Mn b O2; wherein M is one or more of Li, Mg, Zn, Ni, Fe, Cu, Nb, and Zr; wherein 0.5 < x ≤ 0.8, 0 < a ≤ 0.25, 0.5 ≤ b ≤ 0.8, 0.02 < c ≤ 0.04, and a+b =1. Where M and Mn are located in the transition metal layer, and the non-metallic boron (B) in the material is in the form of BO3. 3- BO4 5- Both configurations exist in the interlayer of the transition metal layer and do not replace the original lattice sites of M and Mn in the transition metal layer.

[0011] Na in this invention x M a B c Mn b The O2 cathode material is a P2 phase manganese-based layered oxide with a single-crystal structure. Its morphology is hexagonal plates with a particle size ranging from 2 µm to 4 µm. The prepared manganese-based layered oxide cathode material is a pure phase, belonging to the hexagonal crystal system, with space group [space group missing]. P6 3 / mmc In this system, M and Mn are located in the transition metal layer, while the doped non-metallic boron is located in the transition metal interstitial space. When M is Li, Mg, or Zn, Li in the transition metal layer forms a localized Na-O-Li (Mg, Zn) electronic configuration, thereby stimulating anionic redox reactions and increasing the specific capacity of the material. Due to its very small radius, boron preferentially occupies tetrahedral sites in the transition metal layer, mainly as BO4. 5- BO3 3-The two configurations exist in the tetrahedral interstitials within the transition metal layer, without occupying the original lattice sites of Li and Mn in the transition metal layer. This doping method does not cause a significant loss in the specific capacity of the material. Boron doping physically blocks the migration of cations in the transition metal layer through interstitial doping, thus achieving a balance between structural stabilization and capacity preservation. Furthermore, after boron doping, the material exhibits excellent stability against air and water, making it suitable for large-scale production.

[0012] More preferably, the P2-type high-capacity manganese-based substrate oxide cathode material doped with non-metallic interstitial sites is Na. 0.75 Li 0.22 B 0.03 Mn 0.78 O2. Na prepared in this invention 0.75 Li 0.22 B 0.03 Mn 0.78 O2 materials possess high specific capacity while maintaining structural stability during long-term cycling, thus achieving both high capacity and long cycling duration.

[0013] Interstitial boron doping disrupts the originally existing Li / Mn ordered honeycomb superlattice structure in the Na–Li–Mn–O material, thereby suppressing large-scale transition metal rearrangement during charge and discharge, thus reducing irreversible oxygen precipitation and lattice distortion. Simultaneously, boron interstitial doping achieves dual locking of Li migration and Mn over-reduction, effectively suppressing voltage decay. This material achieves a high specific capacity of >230 mAh / g and a voltage retention rate of >99% (150 cycles) simultaneously over a wide voltage window (1.5–4.5 V), and exhibits excellent air / water stability.

[0014] A second aspect of this invention provides a method for preparing a P2-type high-capacity manganese-based layered oxide cathode material doped with non-metallic interstitial sites, comprising the following steps: ball milling a sodium source, an M source, a boron source, and a manganese source to achieve uniform mixing; reacting at 700 ℃-900 ℃ for 12 h-24 h; and cooling to obtain the manganese-based layered oxide cathode material. Preferably, the ball milling conditions are: a rotation speed of 100 r / min-500 r / min and a time of 4 h-12 h. Under these ball milling speed and time conditions, the source materials can be thoroughly and uniformly mixed, which helps to avoid the generation of impurity phases during subsequent synthesis.

[0015] The heating temperature is 700 ℃-900 ℃ and the heating time is 12 h-24 h. Under these heating temperature and heating time conditions, the material is more likely to form a pure P2 phase structure.

[0016] Preferably, the sodium source used is one or more of sodium carbonate, sodium acetate, sodium nitrate, sodium fluoride, and sodium chloride; the manganese source is one or more of manganese monoxide, manganese trioxide, manganese dioxide, manganese carbonate, manganese acetate, manganese chloride, manganese sulfate, and manganese nitrate; and the boron source is a boron-containing oxide.

[0017] Preferably, the M source is a lithium source, and the lithium source used is one or more of lithium carbonate, lithium acetate, lithium nitrate, lithium fluoride, lithium chloride, and lithium hydroxide.

[0018] Preferably, when the M source is a magnesium source, the magnesium source used is one or more of magnesium carbonate, magnesium acetate, magnesium nitrate, magnesium chloride, magnesium hydroxide, and magnesium oxide. When the M source is a zinc source, the zinc source used is one or more of zinc carbonate, zinc acetate, zinc nitrate, zinc chloride, zinc hydroxide, and zinc oxide. When the M source is a nickel source, the nickel source used is one or more of nickel acetate, nickel nitrate, and nickel hydroxide. Preferably, when the M source is an iron source, the iron source used is one or more of ferric nitrate, ferric acetate, ferric chloride, and ferrous chloride. Preferably, when the M source is a copper source, the copper source used is one or more of copper acetate, copper nitrate, copper chloride, copper carbonate, and copper sulfate. When the M source is a niobium source, the niobium source used is one or more of niobium nitrate and niobium pentoxide. When the M source is a zirconium source, the zirconium source used is one or more of zirconium oxynitrate, zirconium acetate, zirconium chloride, zirconium oxychloride, zirconium ethoxide, and zirconium hydroxide.

[0019] A third aspect of the present invention is to provide a positive electrode sheet for a sodium-ion battery, comprising the aforementioned positive electrode material, as well as a conductive agent and a binder.

[0020] A fourth aspect of the present invention is to provide a sodium-ion battery comprising the aforementioned positive electrode, negative electrode, separator, and electrolyte.

[0021] Furthermore, the negative electrode material is a carbon material or metallic sodium, and the sodium salt in the electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium trifluoromethanesulfonate, and the solvent is one or more of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC).

[0022] The fifth aspect of the present invention is the application of the cathode material in the preparation of sodium-ion batteries.

[0023] Advantages and beneficial effects of the present invention:

[0024] 1. This invention proposes a mechanism for disrupting the superlattice by B interstitial doping: by selectively doping B into the tetrahedral interstices of the transition metal layer of a P2-type material, the original ordered honeycomb superlattice structure of Li / Mn is disrupted without replacing any lattice sites, thereby suppressing large-scale rearrangement of the transition metal and lattice oxygen evolution in the first cycle, providing a novel structural control method for achieving long cycles and suppressing voltage decay.

[0025] 2. Excellent overall electrochemical performance: It achieves a high specific capacity of >230 mAh / g and an ultra-high voltage retention rate of 99.2% (150 cycles) simultaneously within a wide voltage window (1.5–4.5 V), and has excellent air / water stability. Its overall performance far exceeds that of similar materials reported in the prior art.

[0026] 3. Simple preparation process: It adopts a one-step solid-phase method, which has low raw material cost, good process repeatability, and is easy to scale up production. Attached Figure Description

[0027] Figure 1 Na synthesized in Example 1 of the invention 0.75 Li 0.22 B 0.03 Mn 0.78 XRD pattern of O2 material;

[0028] Figure 2 The image shows the Na synthesized in Example 1. 0.75 Li 0.22 B 0.03 Mn 0.78 SEM and EDS images of O2;

[0029] Figure 3 Na synthesized in Example 1 0.75 Li 0.22 B 0.03 Mn 0.78 FTIR plot of O2;

[0030] Figure 4 The image shows the Na synthesized in Example 2. 0.72 Li 0.22 B 0.03 Mn 0.78 O2 and Na synthesized in Example 3 0.8 Li 0.22 B 0.03 Mn 0.78 XRD pattern of O2;

[0031] Figure 5 The image shows the Na synthesized in Comparative Example 1. 0.8 Li 0.22 Mn 0.78 XRD pattern of O2;

[0032] Figure 6 The image shows the Na synthesized in Comparative Example 1. 0.8 Li 0.22 Mn 0.78 SEM and EDS images of O2;

[0033] Figure 7 The image shows the Na synthesized in Example 1. 0.75 Li 0.22 B 0.03 Mn 0.78 O2 charge / discharge curves for the first two weeks (rate: 0.05C, voltage window: 1.5 V-4.5 V);

[0034] Figure 8 The image shows the Na synthesized in Comparative Example 1. 0.8 Li 0.22 Mn 0.78 O2 charge / discharge curves for the first two weeks (rate: 0.05 C, voltage window: 1.5 V-4.5 V);

[0035] Figure 9 The image shows the Na synthesized in Example 1. 0.75 Li 0.22 B 0.03 Mn 0.78 Na synthesized from O2 and Comparative Example 1 0.8 Li 0.22 Mn 0.78 O2 cycle performance diagram;

[0036] Figure 10 The image shows the Na synthesized in Example 1. 0.75 Li 0.22 B 0.03 Mn 0.78 Na synthesized from O2 and Comparative Example 1 0.8 Li 0.22 Mn 0.78 Average voltage diagram of O2;

[0037] Figure 11 The image shows the Na synthesized in Example 2. 0.72 Li 0.22 B 0.03 Mn 0.78 O2 and Na synthesized in Example 3 0.75 Li 0.22 B 0.03 Mn 0.78 O2 cycle performance diagram;

[0038] Figure 12 Na synthesized in Example 1 shown 0.75 Li 0.22 B 0.03 Mn0.78 XRD pattern of O2 after air exposure and water treatment.

[0039] Figure 13 The image shows the Na synthesized in Comparative Example 2. 0.7 Li 0.15 Mg 0.1 Mn 0.75 XRD pattern and average voltage plot of O2, (a) is the XRD pattern; (b) is the average voltage plot.

[0040] Figure 14 The image shows the Na synthesized using a boron-replaced source in Comparative Example 3. 0.75 Li 0.22 B 0.03 Mn 0.78 XRD pattern of O2.

[0041] Figure 15 The image shows 1% B-doped Na synthesized in Comparative Example 4. 0.75 Li 0.22 B 0.01 Mn 0.78 The XRD pattern, cycling performance plot and average voltage plot of O2 are shown, where (a) is the XRD pattern; (b) is the cycling performance plot; and (c) is the average voltage plot.

[0042] Figure 16 The image shows 5% B-doped Na synthesized in Comparative Example 5. 0.75 Li 0.22 B 0.05 Mn 0.78 Cyclic performance plot and average voltage plot of O2, where (a) is the cyclic performance plot and (b) is the average voltage plot.

[0043] Figure 17 The XRD patterns of the materials synthesized in Comparative Example 6 at 600 and 1000 °C are shown. Detailed Implementation

[0044] The following will provide a clear and complete description of the concept and technical effects of the present invention in conjunction with the embodiments and accompanying drawings, so as to fully understand the purpose, solution and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0045] Example 1

[0046] A non-metallic element-doped P2-type manganese-based layered oxide cathode material with the molecular formula Na 0.75 Li 0.22 B 0.03 Mn 0.78 O2, the synthesis method of which includes the following steps:

[0047] Weigh out 1.08 g sodium carbonate (2% excess), 0.24 g lithium carbonate (2% excess), 0.027 g boron oxide, and 1.76 g manganese dioxide according to the stoichiometric ratio in the molecular formula. Mix the raw materials evenly and place them in a ball mill at 400 r / min for 4 h. After further mixing, obtain the precursor. Take an appropriate amount of the precursor and press it into tablets under a pressure of 10 MPa. Then, calcine the precursor tablets at 800 ℃ for 12 h. After the material cools naturally, Na is obtained. 0.75 Li 0.22 B 0.03 Mn 0.78 O2.

[0048] Example 2

[0049] A non-metallic element-doped P2-type manganese-based layered oxide cathode material with the molecular formula Na 0.72 Li 0.22 B 0.03 Mn 0.78 O2, the synthesis method of which includes the following steps:

[0050] Weigh out 1.08 g sodium carbonate (2% excess), 0.25 g lithium carbonate (2% excess), 0.029 g boron oxide, and 1.83 g manganese dioxide according to the stoichiometric ratio in the molecular formula. Mix the raw materials evenly and place them in a ball mill at 400 r / min for 4 h. After further mixing, obtain the precursor. Take an appropriate amount of the precursor and press it into tablets under a pressure of 10 MPa. Then, calcine the precursor tablets at 800 ℃ for 12 h. After the material cools naturally, Na is obtained. 0.72 Li 0.22 B 0.03 Mn 0.78 O2

[0051] Example 3

[0052] A non-metallic element-doped P2-type manganese-based layered oxide cathode material with the molecular formula Na 0.8 Li 0.22 B 0.03 Mn 0.78 O2, the synthesis method of which includes the following steps:

[0053] Weigh out 1.08 g sodium carbonate (2% excess), 0.22 g lithium carbonate (2% excess), 0.026 g boron oxide, and 1.65 g manganese dioxide according to the stoichiometric ratio in the molecular formula. Mix the raw materials evenly and place them in a ball mill at 400 r / min for 4 h. After further mixing, obtain the precursor. Take an appropriate amount of the precursor and press it into tablets under a pressure of 10 MPa. Then, calcine the precursor tablets at 800 ℃ for 12 h. After the material cools naturally, Na is obtained. 0.8 Li 0.22 B 0.03 Mn 0.78 O2.

[0054] Comparative Example 1

[0055] A non-metallic element-doped P2-type manganese-based layered oxide cathode material with the molecular formula Na 0.8 Li 0.22 Mn 0.78 O2, the synthesis method of which includes the following steps:

[0056] Weigh out 1.08 g of sodium carbonate (2% excess), 0.22 g of lithium carbonate (2% excess), and 1.65 g of manganese dioxide according to the stoichiometric ratio in the molecular formula. Mix the raw materials evenly and place them in a ball mill at 400 r / min for 4 h. After further mixing, obtain the precursor. Take an appropriate amount of the precursor and press it into tablets under a pressure of 10 MPa. Then, calcine the precursor tablets at 800℃ for 12 h. After the material cools naturally, Na is obtained. 0.8 Li 0.22 Mn 0.78 O2.

[0057] Comparative Example 2:

[0058] The preparation method of Example 1 was followed, but boron oxide was replaced with MgO, and the ratio was adjusted so that the molecular formula was Na. 0.7 Li 0.15 Mg 0.1 Mn 0.75 O2.

[0059] Comparative Example 3

[0060] The preparation method of Example 1 was followed, but boron oxide was replaced with an equimolar amount of H3BO3.

[0061] Comparative Example 4

[0062] Following the preparation method of Example 1, the B doping amount was adjusted to 1 at%, and the synthesized molecular formula was Na. 0.75 Li 0.22 B 0.01 Mn 0.78O2 cathode material.

[0063] Comparative Example 5

[0064] Following the preparation method of Example 1, the B doping amount was adjusted to 5 at%, and the synthesized molecular formula was Na. 0.75 Li 0.22 B 0.05 Mn 0.78 O2 cathode material.

[0065] Comparative Example 6

[0066] Following the preparation method of Example 1, the calcination temperature was adjusted to 600℃ and 1000℃ respectively, while other conditions remained unchanged.

[0067] XRD, SEM, EDS, FTIR characterization

[0068] This embodiment characterizes the manganese-based morphological oxide cathode materials prepared in Examples 1-3 and Comparative Examples 1-6.

[0069] The material obtained in Example 1 is as follows Figure 1 The XRD pattern shows that the prepared Na 0.75 Li 0.22 B 0.03 Mn 0.78 O2 is the pure P2 phase, belonging to the hexagonal crystal system, with space group [space group number missing]. P6 3 / mmc Furthermore, the absence of superlattice peaks in the structure indicates that the introduction of boron disrupts the original superlattice structure, thereby mitigating voltage decay caused by structural rearrangement during charging and discharging. Figure 2 As shown in the SEM and EDS images, the sample has a single-crystal structure with hexagonal plate-like particles. Na, Li, and Mn elements are uniformly distributed in the material, and the particle size ranges from 2 µm to 4 µm. Figure 3 FTIR characterization of the material revealed a value at 1250 cm⁻¹. -1 and 700 cm -1 BO3 3- The vibration peak is BO4 at 1050 cm⁻¹. 5- The vibration peaks indicate that B exists in two configurations.

[0070] The materials obtained in Examples 2 and 3 are as follows Figure 4 As shown in the XRD pattern, both materials are P2 type materials.

[0071] The material Na prepared in Comparative Example 1 0.8 Li 0.22 B 0.03 Mn 0.78 O2 as Figure 5The XRD pattern shows that it is a pure P2 phase, belonging to the hexagonal crystal system, with space group 1. P6 3 / mmc .like Figure 6 As shown in the SEM and EDS images, the sample has a single-crystal structure with hexagonal plate-like particle morphology. Na, Li, and Mn elements are uniformly distributed in the material with a particle size range of 2 µm-4 µm.

[0072] The material Na prepared in Comparative Example 2 0.7 Li 0.15 Mg 0.1 Mn 0.75 XRD of O2, such as Figure 13 In (a), the peak at an angle of 20-30 degrees corresponds to the superlattice structure, proving that the introduction of Mg did not destroy the superlattice structure.

[0073] The material prepared in Comparative Example 3, after the boron source was replaced with boric acid, showed a distinct Li2MnO3 impurity peak at an 18-degree angle in its XRD pattern. Figure 14 Furthermore, the appearance of a sodium carbonate peak at approximately 2θ = 30° indicates that boric acid generates H₂O during calcination, which influences crystal structure growth. This demonstrates that B₂O₃ is a key boron source for achieving interstitial doping, superlattice disruption, and oxygen activation.

[0074] Na prepared in Comparative Example 4 0.75 Li 0.22 B 0.01 Mn 0.78 XRD patterns of O2 materials, such as Figure 15 A superlattice peak appeared at 22 degrees, proving that 1% boron doping did not completely destroy the superlattice structure.

[0075] Comparative Example 6: Materials Na annealed at different temperatures 0.75 Li 0.22 B 0.03 Mn 0.78 XRD of O2, such as Figure 17 It was found that the material obtained at 600℃ tends to form the P3 phase rather than the pure P2 phase, and the material obtained at 1000℃, due to the easy formation of the O3 phase at high temperature, also does not yield the pure P2 phase.

[0076] Electrode preparation and electrochemical performance testing

[0077] In this embodiment, the P2-type manganese-based basal oxide cathode materials prepared in Examples 1-3 and Comparative Examples 1-6 were assembled into sodium-ion batteries and their battery performance was tested according to the following method.

[0078] 1. Na prepared in Example 1 0.75 Li 0.22 B0.03 Mn 0.78 Testing of O2 cathode materials

[0079] (1) Preparation of positive electrode material electrode

[0080] Will Na 0.75 Li 0.22 B 0.03 Mn 0.78 O2 cathode material, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were ground in a mass ratio of 8:1:1 and uniformly dispersed in N-methylpyrrolidone (NMP) solvent to obtain a mixed slurry of cathode material. The mixed slurry was uniformly coated onto aluminum foil cathode current collector, vacuum dried overnight, and then cut into circular cathode sheets with a diameter of 10 mm.

[0081] (2) Assembly of sodium-ion batteries

[0082] Using the above-mentioned positive electrode as the positive electrode, sodium sheet as the negative electrode, and 1 M sodium hexafluorophosphate (NaPF6) + propylene carbonate (PC) + 2 wt% fluoroethylene carbonate (DEC) as the electrolyte, along with other necessary battery components (separator and casing, etc.), a button cell is assembled in a glove box filled with high-purity argon gas.

[0083] (3) Battery performance testing

[0084] The batteries assembled using the above method were subjected to charge-discharge performance tests in a battery testing system at a temperature of 25°C and a voltage window of 1.5 V-4.5 V.

[0085] Test results show that the Na provided in this embodiment 1 0.75 Li 0.22 B 0.03 Mn 0.78 The O2 cathode material exhibits an initial discharge capacity of 235 mAh g at a 0.05 C rate. -1 Furthermore, the charging curve exhibits a single voltage plateau around 4.2 V, which is the characteristic plateau of the oxygen anion reaction, indicating that the charging capacity is primarily contributed by oxygen oxidation. Figure 7 As shown. Figure 9 As shown, at a 0.5 C expansion rate, Na 0.75 Li 0.22 B 0.03 Mn 0.78 The O2 cathode material exhibits good cycle performance, with a capacity retention of 90.6% after 100 cycles and 84% after 150 cycles. Figure 10As shown, at a C rate of 0.5, the average voltage retention rate after 150 cycles is 99.2%. The excellent cycling performance and voltage retention rate demonstrate that boron doping enhances the structural stability.

[0086] (4) Stability test of cathode material to air and water

[0087] Na after 180 days of exposure to air 0.75 Li 0.22 B 0.03 Mn 0.78 O2 and Na after water treatment 0.75 Li 0.22 B 0.03 Mn 0.78 O2 was subjected to XRD testing, and the results are as follows: Figure 12 The test results show that the P2 phase can be well preserved, proving its good stability to air and water.

[0088] 2. Na prepared in Example 2 0.72 Li 0.22 B 0.03 Mn 0.78 The testing method for the O2 cathode material is the same as in Example 1.

[0089] Test results are as follows Figure 11 As shown, in Example 2, at a 0.5 C expansion rate, Na... 0.72 Li 0.22 B 0.03 Mn 0.78 The O2 cathode material maintained good capacity after 150 cycles, indicating that the doping of the non-metallic element boron significantly improved the cycle stability.

[0090] 3. Na prepared in Example 3 0.8 Li 0.22 B 0.03 Mn 0.78 The testing method for the O2 cathode material is the same as in Example 1.

[0091] Test Results Figure 11 This indicates that in Example 2, at a 0.5 C expansion rate, Na 0.72 Li 0.22 B 0.03 Mn 0.78 The O2 cathode material maintained good capacity after 150 cycles, indicating that the doping of the non-metallic element boron significantly improved the cycle stability.

[0092] 4. Na prepared in Comparative Example 1 0.8 Li 0.22 Mn 0.78 The testing method for the O2 cathode material is the same as in Example 1.

[0093] Test results show that the Na provided in this implementation 0.8 Li 0.22 Mn 0.78 The O2 cathode material exhibits an initial discharge capacity of 243 mAh g⁻¹ at a rate of 0.05 C. -1 Furthermore, the charging curve exhibits a single voltage plateau around 4.2 V, which is the characteristic plateau of the oxygen anion reaction, indicating that the charging capacity is primarily contributed by oxygen oxidation. Figure 8 As shown. Figure 9 As shown, at a 0.5 C expansion rate, Na 0.8 Li 0.22 Mn 0.78 The O2 cathode material exhibits good cycle performance, with a capacity retention of only 26% after 150 cycles. Furthermore, as... Figure 10 At a rate of 0.5 C, the average voltage retention rate after 150 cycles is 85.3%.

[0094] 5. Na prepared in Comparative Example 2 0.7 Li 0.15 Mg 0.1 Mn 0.75 The testing method for the O2 cathode material is the same as in Example 1.

[0095] The test results show that ( Figure 13 Since Mg doping replaces transition metal atoms, it does not destroy the superlattice structure, resulting in a strong superlattice peak. However, because the superlattice will be destroyed in subsequent cycles, the rearrangement of the transition metal will cause vacancy accumulation, leading to voltage decay. Figure 13 This is the average voltage of the material after 100 cycles at 0.5 C, with a voltage retention rate of 89%. This is lower than the material in Example 1. This demonstrates that the mechanism of interstitial doping in this application that disrupts the superlattice is fundamentally different from existing metal substitution doping, and is more effective.

[0096] 6. Na prepared in Comparative Example 4 0.75 Li 0.22 B 0.01 Mn 0.78 The testing method for the O2 cathode material is the same as in Example 1.

[0097] The test results show that ( Figure 15 Insufficient boron doping cannot completely destroy the superlattice structure and cannot fully mitigate the structural damage caused by the rearrangement of the transition metals in the first cycle. After 100 cycles at 0.5 C, the capacity is only about 100 mAh / g. It has some effect on suppressing voltage decay, but the effect is not as good as the material in Example 1. This demonstrates that 3% boron doping is the optimized value for achieving complete superlattice destruction and excellent voltage stability.

[0098] 7. Na prepared in Comparative Example 50.75 Li 0.22 B 0.05 Mn 0.78 The testing method for the O2 cathode material is the same as in Example 1.

[0099] The test results show that ( Figure 16 After 100 cycles at 0.5 C, the capacity was approximately 136 mAh / g, indicating that excessive boron (B) leads to a decrease in capacity. This is because more BO-Li is formed, and the strong covalent nature of B reduces the activity of the Na-O-Li configuration, resulting in a capacity decrease. The average voltage retention was 92%. This demonstrates that B doping can suppress irreversible redox reactions and significantly inhibit voltage decay. The overall performance of this material is inferior to that of the material in Example 1, proving that 3% B doping is the optimal value; excessively high or low doping levels negatively impact the performance.

[0100] Although the description of the invention has been quite detailed and particularly of several described embodiments, it is not intended to limit it to any of these details or embodiments or any particular embodiment, but should be considered as providing a broad possible interpretation of the claims by referring to the appended claims and taking into account the prior art, thereby effectively covering the intended scope of the invention. Furthermore, the invention has been described above with respect to embodiments foreseeable by the inventors in order to provide a useful description, and non-substantial modifications to the invention that have not yet been foreseen may still represent equivalent modifications.

Claims

1. A high-capacity P2-type manganese-based substrate oxide cathode material doped with non-metallic element interstitial sites, characterized in that, The molecular formula of the manganese-based oxide cathode material is Na. x M a B c Mn b O2; wherein M is one or more of Li, Mg, Zn, Ni, Fe, Cu, Nb, and Zr; wherein 0.5 < x ≤ 0.8, 0 < a ≤ 0.25, 0.5 ≤ b ≤ 0.8, 0.02 < c ≤ 0.04, and a+b =1, where M and Mn are located in the transition metal layer, and B in the material is in the form of BO3. 3- BO4 5- Both configurations exist in the interlayer of the transition metal layers and do not replace the original lattice sites of M and Mn in the transition metal layers.

2. The manganese-based layered oxide cathode material according to claim 1, characterized in that, M is Li, and the chemical formula of the cathode material is Na. 0.75 Li 0.22 B 0.03 Mn 0.78 O2 and B form B–O–Li and B–O–Mn bonds with adjacent Li and Mn respectively, achieving dual locking of Li migration and Mn over-reduction. This enables a high specific capacity of >230 mAh / g and a voltage retention rate of >99% at 1.5–4.5 V.

3. A method for preparing the cathode material according to any one of claims 1-2, characterized in that, Sodium source, M source, boron source and manganese source are ball-milled and mixed evenly; heated at 700 ℃-900 ℃ for 12 h-24 h, and then cooled to obtain the cathode material, wherein the boron source is a boron-containing oxide.

4. The preparation method according to claim 3, characterized in that, The ball milling conditions include: a rotation speed of 100 r / min-500 r / min and a time of 4 h-12 h.

5. The preparation method according to claim 3, characterized in that, The M source is a lithium source, which is one or more of lithium carbonate, lithium acetate, lithium nitrate, lithium fluoride, lithium chloride, and lithium hydroxide.

6. The preparation method according to claim 3, characterized in that, The sodium source is one or more of sodium hydroxide, sodium carbonate, sodium nitrate, sodium peroxide, sodium acetate, and sodium oxalate; the manganese source is one or more of manganese-containing metal oxides, metal carbonates, metal sulfates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides.

7. A positive electrode sheet for a sodium-ion battery, characterized in that, It comprises the positive electrode material according to any one of claims 1-2, as well as a conductive agent and a binder.

8. A sodium-ion battery, characterized in that, It includes the positive electrode, negative electrode, separator and electrolyte as described in claim 7.

9. The sodium-ion battery according to claim 8, characterized in that, The negative electrode material is carbon material or metallic sodium, and the sodium salt in the electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium trifluoromethanesulfonate, and the solvent is one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate.

10. The application of the cathode material according to any one of claims 1-2 in the preparation of sodium-ion batteries.

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