Preparation and application of a beryllium-magnesium double-doped p2-type sodium-ion battery positive electrode material

Abstract

The application relates to a P2 type sodium ion battery positive electrode material, and the chemical formula of the positive electrode material is Na 0.85 Li 0.12 Ni 0.22‑ X M1 X M2 X Mn 0.66 O2, wherein M1 and M2 are respectively selected from one of alkaline earth metals Be, Mg, Ca, Sr and Ba, M1 is different from M2, and the value range of X is 0<=X<=0.022. In the sodium ion battery positive electrode material, the cycle stability under high rate is improved after the alkaline earth metals Be and Mg elements are doped, and the electrochemical performance of the battery is improved.

Description

Technical Field

[0001] This invention specifically relates to a P2-type sodium-ion battery cathode material doped with two metal elements, its preparation and application, belonging to the field of sodium-ion battery technology. Background Technology

[0002] Society cannot function without energy, but traditional fossil fuels like coal, oil, and natural gas will eventually be depleted as extraction continues. The escalating energy crisis and environmental problems caused by fossil fuels are drawing increasing attention. This has sparked a wave of research into renewable energy sources. However, the development of new energy sources like wind, solar, and tidal power is severely limited by external constraints. Meanwhile, electrochemical battery energy storage systems, due to their unique stability and usability, are attracting growing research attention. The 2019 Nobel Prize in Chemistry awarded to Goodenough, Whittalingham, and Akira Yoshino for their research on lithium-ion batteries further illustrates the growing importance placed on energy storage.

[0003] In the late 1970s, research on sodium-ion batteries began almost simultaneously with that on lithium-ion batteries. However, due to limitations in research conditions at the time and researchers' enthusiasm for lithium-ion batteries, sodium-ion battery research stagnated until around 2010, when it experienced a resurgence. It is well known that Earth's lithium resources are far less abundant than sodium resources, and lithium mines will eventually be depleted. In the long run, sodium-ion batteries have greater development potential. As a potential alternative to lithium-ion batteries, sodium-ion batteries have attracted researchers' attention due to their low cost, abundant resources, high operating voltage, and similar intercalation chemistry to lithium-ion batteries. Researchers have reported various types of potential cathode materials, the most common being transition metal oxides, Prussian blue analogs, and polyanionic compounds. Among these, sodium-based metal oxides with layered structures have remained a research hotspot due to their ease of synthesis, structural stability, and high energy density, and are currently the most widely used cathode materials in commercial products.

[0004] Layered transition metal oxides (Na) X TMO2 (TM represents transition metals such as Fe, Co, Mn, Ni, Cu, etc.) is a promising cathode due to its high theoretical specific capacity, low cost, and ease of synthesis. P2-type compounds exhibit better structural stability than O3-type compounds due to the open prismatic pathway of the P2 phase and direct diffusion of sodium ions between transition metal layers. During sodium ion insertion and extraction, the larger Na+ ions... The insertion / removal of Na+ in the crystal lattice usually causes large lattice strain and irreversible phase transitions, which leads to poor cycle stability and low cycle life of the battery under high current. This is one of the biggest challenges that needs to be solved to make it commercially viable.

[0005] Modification strategies involving elemental doping (Mg, Cu, Ti, Co, Al, etc.) and surface coatings (carbon, Al₂O₃, ZrO₂, MgO, etc.) have been widely reported. According to reports, doping modification can improve the electrochemical performance of materials in two ways. One is through doping with Ti... 4+ Cu 2+ To expand Na with other elements + Interlayer spacing to improve Na + One approach is to improve the diffusion coefficient and rate performance; another is to stabilize the layered structure and improve cycle stability through doping. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing and applying a sodium-ion battery cathode material simultaneously doped with two metal elements. The lack of sodium in P2-type cathodes easily leads to poor structural stability under deep radiation de-radiation conditions, and a portion of reversible capacity is lost during sodium ion extraction / insertion. These drawbacks result in poor rate performance and rapid capacity decay in most P2-type layered oxides. By doping with Be and Mg to stabilize the layered structure, the cycling performance of the cathode at high rates is effectively improved. This material shows great promise as a cathode material for sodium-ion batteries. Furthermore, the solid-state sintering method used to prepare this cathode material is simple, environmentally friendly, and easy to promote, yielding a P2-type sodium-ion battery cathode material with uniform elemental distribution.

[0007] The objective of this invention is achieved through the following technical solutions.

[0008] A P2 type sodium-ion battery cathode material, wherein the cathode material has the chemical formula Na 0.85 Li 0.12 Ni 0.22- X M1 X M2 X Mn 0.66 O2, M1, and M2 are selected from one of the alkaline earth metals Be, Mg, Ca, Sr, and Ba, respectively, and M1 and M2 are different. The value range of X is 0 ≤ X ≤ 0.022.

[0009] Preferably, M1 and M2 are selected from alkaline earth metals Mg and Be, respectively, and the positive electrode material has the chemical formula Na. 0.85 Li 0.12 Ni 0.22-2X Mg X Be XMn 0.66 The range of values ​​for O2 and X is 0 ≤ X ≤ 0.022.

[0010] Furthermore, X = 0.011 or 0.022.

[0011] This invention incorporates beryllium and magnesium elements, which shifts the characteristic peak of layered oxide (002) to the left, expands the interaxial spacing, provides a wider channel for the transport and movement of sodium ions, and enhances the electrochemical activity of the cathode material.

[0012] Doping with beryllium and magnesium, Mn 3+ The relative content of Mn decreased. 3+ / Mn 4+ The ratio decreases because of Mn 3+ The presence of this leads to the Jiang-Taylor distortion. After the effect is suppressed, the structure of the cathode material becomes more stable.

[0013] Meanwhile, the addition of beryllium and magnesium increases the ratio of active oxygen species (Lattice O:Surface O), which greatly improves the stability of the electrode structure during cycling.

[0014] A method for preparing the sodium-ion battery cathode material of the present invention employs a solid-state sintering method: sodium source, lithium source, nickel source, M1 metal source, M2 metal source and manganese source are uniformly mixed according to the stoichiometric ratio, and then ball-milled, calcined at high temperature and ground to obtain the P2 type sodium-ion battery cathode material.

[0015] In one embodiment of the present invention, the specific steps are as follows: Sodium source, lithium source, nickel source, magnesium source, beryllium source, and manganese source are uniformly mixed in a stoichiometric ratio (0.85:0.12:0.22-2X:X:X:0.66), and then ball-milled using a planetary ball mill. After ball milling, the mixture is removed and placed in a muffle furnace for sintering. The mixture is first heated to 800-1000°C and calcined for 20-25 hours. After calcination, the product is ground uniformly to obtain the desired P2 type sodium-ion battery cathode material.

[0016] Furthermore, the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, and sodium nitrate; the lithium source is selected from at least one of lithium carbonate, lithium perchlorate, lithium nitrate, lithium hydroxide, lithium hexafluorophosphate, and organic electrolyte lithium salts; the nickel source is selected from at least one of nickel oxide, nickel nitrate, and nickel hydroxide; the magnesium source is selected from at least one of magnesium carbonate, magnesium hydroxide, and magnesium nitrate; the beryllium source is selected from at least one of beryllium oxide, beryllium hydroxide, and beryllium chloride; and the manganese source is selected from manganese trioxide.

[0017] Furthermore, the mixture was mixed using ball milling at a rate of 400–500 r / min for 15–18 h.

[0018] Furthermore, the temperature is increased to 800-1000°C at a heating rate of 2-5°C / min, and then cooled at a rate of 2-5°C / min after sintering.

[0019] During beryllium and magnesium doping, the radius of Be ions is smaller than that of Ni ions, while the radius of Mg ions is similar to that of Ni ions. Therefore, Be and Mg ions can enter the nanocrystalline lattice of layered oxide materials and replace Ni. 2+ The doping of Be and Mg ions causes lattice mismatch in layered oxide nanocrystals, reducing the formation energy of defects (such as atomic vacancies) in the nanocrystals. The formation of these defects, in turn, provides more adsorption sites, further promoting the entry of Be and Mg ions into the lattice and improving elemental doping efficiency. This significantly improves the cycle stability of battery materials at high rates.

[0020] Currently, most doping methods employ a one-step process to dope oxide materials with multiple elements at different positions. In order to further optimize the doping process and understand the doping principle, the sodium-ion battery cathode material of this invention also adopts a step-by-step doping method for investigation.

[0021] The stepwise doping method includes: (1) uniformly mixing sodium source, lithium source, nickel source, M1 metal source and manganese source according to the stoichiometric ratio, ball milling, calcining and cooling; (2) adding M2 metal source, mixing and ball milling, calcining; (3) grinding to obtain the P2 type sodium-ion battery cathode material.

[0022] Preferably, the M1 metal source is a magnesium source; the M2 metal source is a beryllium source, and the calcination temperature is 800-1000℃.

[0023] In one embodiment of the present invention, the specific steps are as follows:

[0024] (1) Sodium source, lithium source, nickel source, magnesium source and manganese source are mixed evenly according to the stoichiometric ratio (0.85:0.12:0.22-2X:X:0.66), and then ball-milled using a planetary ball mill. After ball milling, the mixture is taken out and placed in a muffle furnace, heated to T1 for calcination, and then taken out after cooling.

[0025] (2) Add beryllium source and ball mill it using a planetary ball mill. After ball milling, take it out and place it in a muffle furnace to be heated to T2 for calcination.

[0026] (3) After calcination, grind the product evenly to obtain the P2 type sodium-ion battery cathode material.

[0027] The temperature ranges of T1 and T2 are 800 to 1000℃, and T2 > T1.

[0028] Preferably, T1 is 800-850℃; T is 900-1000℃.

[0029] The calcination time for steps (1) and (2) is 20-25 hours.

[0030] In the preparation of the cathode material in this invention, Mg is doped first, followed by Be, resulting in a sodium-ion cathode material with superior cycle stability. This is likely because Be ions have a smaller radius and are easily adsorbed randomly on the nanocrystal surface during doping, forming a passivation layer that hinders their entry into the crystal lattice. If Mg ions, with ions having a similar radius to Ni ions, are doped first, Mg ions can preferentially enter the nanocrystal lattice of the layered oxide material and replace Ni. 2+ The occupancy of these sites creates more active adsorption sites, which facilitates further doping of Be ions.

[0031] Furthermore, the applicant unexpectedly discovered that when Mg ions enter the nanolattice, some form a regular arrangement. By increasing the calcination temperature, it is easier for Be ions with smaller radii to enter the nanolattice, further increasing the interaxial spacing of the layered oxides. This provides a wider channel for the transport and movement of sodium ions, thereby improving the electrochemical performance of the cathode material.

[0032] The preparation and application of a P2 type sodium-ion battery positive electrode material are disclosed, wherein the aforementioned positive electrode material is used as the active material in the positive electrode of the sodium-ion battery. The positive electrode is generally coated with a current collector containing a conductive paste; commonly used current collectors include aluminum foil. The conductive paste is prepared by mixing the active material, conductive agent, and binder in a specific ratio.

[0033] Furthermore, in this invention, the ratio of active material, conductive agent, and binder in the conductive slurry is 8:1:1.

[0034] The beneficial effects achieved by this invention are as follows:

[0035] (1) In the sodium-ion battery cathode material of the present invention, the doping with Be and Mg elements improves the cycling stability of the original material at high rates, which is beneficial to improving the electrochemical performance of the battery. Therefore, when the sodium-ion battery cathode material of the present invention is used as a cathode in sodium-ion batteries, it is beneficial to improve the electrochemical performance of the battery:

[0036] a. By incorporating Be and magnesium elements, the (002) characteristic peak shifts to the left, expanding the interaxial spacing and providing a wider channel for the transport and movement of sodium ions, thereby enhancing the electrochemical activity of the cathode material.

[0037] b.Mn 3+ / Mn 4+ The ratio of Mn decreases with the incorporation of Be and Mg elements.3+ The relative content of Mn decreased because 3+ The presence of this leads to Jiang-Taylor distortion; once the effect is suppressed, the material structure becomes more stable.

[0038] c. An increased oxygen reactive species ratio (Lattice O:Surface O) significantly improves the stability of the electrode structure during cycling.

[0039] After substitution with Be and Mg, EIS tests showed that after 20 cycles at 1C, both the interfacial transfer resistance and diffusion resistance of the cathode material decreased. The interfacial transfer resistance decreased from 925.9 ohms to 537.8 ohms, and the diffusion resistance decreased from 2766 ohms to 323.8 ohms. This confirms that the incorporation of these two elements is beneficial to improving the electrochemical activity of the original material.

[0040] (2) This invention investigates the effects of one-step doping and step-by-step doping processes on the cathode material of sodium-ion batteries. Appropriate element doping sequence and ratio can improve electrochemical performance. At the same time, by controlling the calcination temperature in the secondary doping process, a wider channel can be provided for the transport and movement of sodium ions, further improving the electrochemical performance of the cathode material.

[0041] (3) The sodium-ion battery cathode material described in this invention can be prepared by solid-state sintering. The preparation process is simple and has good application prospects for promotion. Attached Figure Description

[0042] Figure 1 The image shows the XRD pattern of the NLNMMBO prepared in Example 1.

[0043] Figure 2 The graph shows the long-cycle test curve of NLNMMBO prepared in Example 1 at a 5C rate.

[0044] Figure 3 The rate performance curve of NLNMMBO prepared in Example 1.

[0045] Figure 4 The image shows the XRD pattern of NLNMMBO-2 prepared in Example 2.

[0046] Figure 5 Cyclic curve of NLNMMBO-2 prepared in Example 2 at 5C rate.

[0047] Figure 6 Rate performance curves of NLNMMBO-2 prepared for Comparative Example 1.

[0048] Figure 7 The image shows the XRD pattern of NLNMO prepared in Comparative Example 1.

[0049] Figure 8 The long-cycle test curve of NLNMO prepared for Comparative Example 1 at 5C rate.

[0050] Figure 9 The rate performance test chart of NLNMO prepared for Comparative Example 1.

[0051] Figure 10 The XRD curve of NLNMMO prepared for Comparative Example 2.

[0052] Figure 11 The long-cycle test curve of NLNMMO prepared for Comparative Example 2 at 5C.

[0053] Figure 12 The rate performance test chart for the NLNMMO prepared for Comparative Example 2.

[0054] Figure 13 The XRD pattern of NLNMBO prepared for Comparative Example 3.

[0055] Figure 14 The long-cycle test curve of NLNMBO prepared for Comparative Example 3 at 5C.

[0056] Figure 15 SEM image of NLNMMBO prepared in Example 1.

[0057] Figure 16 SEM image of NLNMO prepared for Comparative Example 1.

[0058] Figure 17 The EDS pattern of NLNMMBO prepared in Example 1.

[0059] Figure 18 The image shows a comparison of the XRD patterns of Example 1 and Comparative Example 1.

[0060] Figure 19 XPS diagram of NLNMMBO Mn 2p prepared in Example 1.

[0061] Figure 20 The XPS image of NLNMMBO O 1s prepared in Example 1.

[0062] Figure 21 XPS plot of NLNMO Mn 2p prepared for Comparative Example 1.

[0063] Figure 22 XPS plot of NLNMO O 1s prepared for Comparative Example 1.

[0064] Figure 23The image shows the EIS plots of the NLNMMBO prepared in Example 1 before and after cycling. Detailed Implementation

[0065] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0066] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0067] Example 1

[0068] (1) Anhydrous sodium carbonate, lithium carbonate, nickel oxide, manganese trioxide, magnesium carbonate, and beryllium oxide were ball-milled in a certain proportion at a milling rate of 500 r / min for 15 hours. The ball-milled sample was then taken out and calcined in a muffle furnace at 1000℃ for 20 hours.

[0069] (2) Grind the calcined sample to obtain the positive electrode material Na. 0.85 Li 0.12 Ni 0.198 Be 0.011 Mg 0.011 Mn 0.6 6O2, also known as NLNMMBO.

[0070] Figure 1 This is the XRD pattern of NLNMMBO.

[0071] CR 2032 half-cells were assembled using NLNMMBO as the positive and negative electrodes, and charge-discharge tests were performed (refer to Test Example 1).

[0072] Figure 2 The image shows the battery's long-cycle test curve at 5C. The initial discharge specific capacity was 75.2 mA h / g, and the discharge specific capacity after 500 cycles was 46.1 mA h / g, with a capacity retention of 61.3%. It can be seen that its coulombic efficiency remained almost entirely at 100%, indicating that the battery possesses excellent long-cycle performance at 5C.

[0073] Figure 3 The rate performance curve of the battery shows that the discharge specific capacity is approximately 110 mAh / g at 0.1C, and it maintains a high discharge specific capacity even at high rates. At 5C, it exhibits a discharge specific capacity of approximately 80 mAh / g, and at 10C, it displays 67.7 mAh / g. When the rate returns to 0.1C, the discharge specific capacity recovers to approximately 112 mAh / g, and the coulombic efficiency remains almost consistently around 100%. All of these indicators demonstrate the battery's excellent rate performance.

[0074] Example 2

[0075] (1) Anhydrous sodium carbonate, lithium carbonate, nickel oxide, manganese trioxide, magnesium carbonate, and beryllium oxide were ball-milled uniformly according to a certain stoichiometric ratio. The ball-milling rate was 500 r / min, and the ball-milling time was 15 hours. The ball-milled sample was taken out and calcined in a muffle furnace at 1000℃ for 20 hours.

[0076] (2) Grind the calcined sample to obtain the positive electrode material Na. 0.85 Li 0.12 Ni 0.176 Be 0.022 Mg 0.022 Mn 0.6 6O2, also known as NLNMMBO-2.

[0077] Figure 4 The image shows the XRD pattern of NLNMMBO-2.

[0078] NLNMMBO-2 was used as the positive and negative electrodes to assemble a CR 2032 half-cell for charge and discharge testing (refer to Test Example 1).

[0079] Figure 5 The graph shows the battery's long-cycle test at 5C. The initial discharge specific capacity was 60.1 mAh / g, and the discharge specific capacity after 500 cycles was 44.5 mAh / g, with a capacity retention of 74.2%. It can be seen that its coulombic efficiency remained almost 100% throughout. It can be seen that with the increase of the Be and Mg doping ratio, the cycle stability at 5C is significantly improved. However, its capacity also decreases slightly, but it still fully meets the requirements for battery use.

[0080] Figure 6 The rate performance curve of the battery shows that the discharge specific capacity is approximately 113 mAh / g at 0.1C, and as the rate increases, the discharge specific capacity at high rates is not as high as in Example 1. At 5C, it exhibits a discharge specific capacity of approximately 57 mAh / g, and at 10C, it shows 32 mAh / g. Furthermore, when the rate recovers to 0.1C, the discharge specific capacity recovers to approximately 116 mAh / g, and the coulombic efficiency remains almost consistently around 100%, demonstrating the battery's excellent rate performance.

[0081] Depending on the battery usage requirements and scenarios, the initial capacity and long-term stability of the battery can be controlled by adjusting the appropriate element doping ratio (X value). The following section further examines the impact of the doping sequence on the electrode material performance.

[0082] Example 3

[0083] (1) Anhydrous sodium carbonate, lithium carbonate, nickel oxide, manganese trioxide, and magnesium carbonate were ball-milled in a certain proportion at a speed of 500 r / min for 15 hours. The ball-milled sample was then taken out and calcined in a muffle furnace at 1000℃ for 20 hours, and then cooled to room temperature.

[0084] (2) Add beryllium oxide according to the proportion, ball mill at a rate of 500 r / min for 15 hours, take it out and place it in a muffle furnace at 1000℃ for 20 hours.

[0085] (3) Grind the calcined sample to obtain the positive electrode material Na. 0.85 Li 0.12 Ni 0.198 Be 0.011 Mg 0.011 Mn 0.6 6O2.

[0086] The Na 0.85 Li 0.12 Ni 0.198 Be 0.011 Mg 0.011 Mn 0.66 O2 was used as the positive and negative electrodes to assemble CR 2032 half-cells for charge and discharge testing (refer to Example 1). The test results are shown in Table 1.

[0087] Example 4

[0088] (1) Anhydrous sodium carbonate, lithium carbonate, nickel oxide, manganese trioxide, and beryllium oxide were ball-milled in a certain proportion at a speed of 500 r / min for 15 hours. The ball-milled sample was then taken out and calcined in a muffle furnace at 1000℃ for 20 hours, and then cooled to room temperature.

[0089] (2) Add magnesium carbonate according to the proportion, ball mill at 500 r / min for 15 hours, take it out and calcine it in a muffle furnace at 1000℃ for 20 hours.

[0090] (3) Grind the calcined sample to obtain the positive electrode material Na. 0.85 Li 0.12 Ni 0.198 Be 0.011 Mg 0.011 Mn 0.6 6O2.

[0091] The Na 0.85 Li 0.12 Ni 0.198 Be 0.011 Mg 0.011 Mn 0.66O2 was used as the positive and negative electrodes to assemble CR 2032 half-cells for charge and discharge testing (refer to Example 1). The test results are shown in Table 1.

[0092] Example 5

[0093] (1) Anhydrous sodium carbonate, lithium carbonate, nickel oxide, manganese trioxide, and magnesium carbonate were ball-milled in a certain proportion at a milling rate of 500 r / min for 15 hours. The ball-milled sample was then taken out and calcined in a muffle furnace at 850°C for 20 hours, and then cooled to room temperature.

[0094] (2) Add beryllium oxide according to the proportion, ball mill at a rate of 500 r / min for 15 hours, take it out and place it in a muffle furnace at 1000℃ for 20 hours.

[0095] (3) Grind the calcined sample to obtain the positive electrode material Na. 0.85 Li 0.12 Ni 0.198 Be 0.011 Mg 0.011 Mn 0.6 6O2.

[0096] The Na 0.85 Li 0.12 Ni 0.198 Be 0.011 Mg 0.011 Mn 0.66 O2 was used as the positive and negative electrodes to assemble CR 2032 half-cells for charge and discharge testing (refer to Example 1). The test results are shown in Table 1.

[0097] Comparative Example 1

[0098] (1) Anhydrous sodium carbonate, lithium carbonate, nickel oxide, and manganese trioxide were ball-milled and mixed evenly according to a certain electrochemical stoichiometric ratio. The ball milling rate was 500 r / min, and the ball milling time was 15 hours. The ball-milled sample was taken out and calcined in a muffle furnace at 1000℃ for 20 hours.

[0099] (2) Grind the calcined sample to obtain the positive electrode material Na. 0.85 Li 0.12 Ni 0.22 Mn 0.66 O2, also known as NLNMO.

[0100] Figure 7 for Na 0.85 Li 0.12 Ni 0.22 Mn 0.66 XRD pattern of O2.

[0101] The Na0.85 Li 0.12 Ni 0.22 Mn 0.66 O2 was used as the positive electrode to assemble a CR 2032 half-cell, and charge-discharge tests were conducted (refer to Example 1).

[0102] Figure 8 The battery's long-cycle test curve at 5C rate is shown. The initial discharge specific capacity is 68.2 mA h / g, and after 500 cycles, the discharge specific capacity is 38.1 mA h / g, with a capacity retention of 55.9%. After 1000 cycles, the discharge specific capacity is 20.3 mA h / g, with a capacity retention of 29.8%. It can be seen that the capacity gradually decreases with the increase of the number of cycles.

[0103] Figure 9 The rate performance curve of the battery shows that the discharge specific capacity at 0.1C is approximately 106.9 mAh / g, slightly lower than the experimental example. Furthermore, as the rate increases, the discharge specific capacity at 5C is approximately 71 mAh / g, and at 10C it exhibits 56 mAh / g.

[0104] Comparative Example 2

[0105] (1) Anhydrous sodium carbonate, lithium carbonate, nickel oxide, manganese trioxide, and magnesium carbonate were ball-milled uniformly in a certain proportion using a ball mill at a speed of 500 r / min for 15 hours. The ball-milled sample was then taken out and calcined in a muffle furnace at 1000℃ for 20 hours.

[0106] (2) Grind the calcined sample to obtain the positive electrode material Na. 0.85 Li 0.12 Ni 0.176 Mg 0.044 Mn 0.66 O2, also known as NLNMMO.

[0107] Figure 10 for Na 0.85 Li 0.12 Ni 0.176 Mg 0.044 Mn 0.66 XRD pattern of O2.

[0108] The Na 0.85 Li 0.12 Ni 0.176 Mg 0.044 Mn 0.66 O2 was used as the positive and negative electrodes to assemble a CR 2032 half-cell, and charge-discharge tests were conducted (refer to Example 1).

[0109] Figure 11The battery's long-cycle test curve at 5C rate is shown. The initial discharge specific capacity was 60.3 mA h / g, and after 500 cycles, the discharge specific capacity was 40.9 mA h / g, with a capacity retention rate of 67.8%. It can be seen that the capacity gradually decreases with increasing cycle count. Especially after 1000 cycles, both the discharge specific capacity and capacity retention rate decrease to undetectable levels, indicating poor long-term stability.

[0110] Figure 12 The rate performance curves of the battery show that the discharge specific capacity at 0.1C is approximately 102.6 mAh / g, slightly lower than that of Example 2. Furthermore, as the rate increases, the discharge specific capacity reaches approximately 63 mAh / g at 5C and 47 mAh / g at 10C. When the rate recovers to 0.1C, the discharge specific capacity returns to 102.2 mAh / g, and the coulombic efficiency remains almost entirely around 100%. Single Mg doping not only reduces capacity at low rates but also at 5C and 10C.

[0111] Comparative Example 3

[0112] (1) Anhydrous sodium carbonate, lithium carbonate, nickel oxide, manganese trioxide, and beryllium oxide were ball-milled uniformly in a certain proportion using a ball mill at a speed of 500 r / min for 15 hours. The ball-milled sample was then taken out and calcined in a muffle furnace at 1000℃ for 20 hours.

[0113] (2) Grind the calcined sample to obtain the positive electrode material Na. 0.85 Li 0.12 Ni 0.176 Be 0.044 Mn 0.66 O2, also known as NLNMBO.

[0114] Figure 13 for Na 0.85 Li 0.12 Ni 0.176 Be 0.044 Mn 0.66 XRD pattern of O2.

[0115] The Na 0.85 Li 0.12 Ni 0.176 Be 0.044 Mn 0.66 O2 was used as the positive and negative electrodes to assemble a CR 2032 half-cell, and charge-discharge tests were conducted (refer to Example 1).

[0116] Figure 14The specific capacity-voltage curve of the battery at a 5C rate shows that the initial discharge specific capacity is about 62.0 mA h / g, and the discharge specific capacity after 500 cycles is 43.1 mA h / g, with a capacity retention rate of 69.6%. Compared with Comparative Example 1, it can be seen that single doping with Be can improve the capacity retention rate, but it does not have the same high capacity stability as the electrode material of Example 2, which simultaneously incorporates both Be and Mg.

[0117] Performance testing:

[0118] Assembly of CR 2032 battery: The positive electrode material prepared in the examples and comparative examples was mixed with a conductive agent (Super P) and a binder (PVDF) to form a conductive slurry. The positive electrode was prepared by grinding the material in a mortar with N-methylproprololone (NMP) as a solvent. The conductive slurry was then uniformly coated onto an aluminum foil with a scraper. The coated aluminum foil was placed in a vacuum drying oven and dried at 80°C for 12 hours. The dried aluminum foil was cut into electrode sheets, which are the prepared positive electrode sheets. Sodium sheet was used as the negative electrode, glass fiber (Whatman GF-C) was used as the separator, the solute of the electrolyte was 1M sodium perchlorate (NaClO4), and the solvent was a PC:EC = 1:1 + 5% FEC solution. The battery was assembled in a glove box, and the electrochemical performance of the CR 2032 battery was tested using the Land system. The test temperature was maintained at 25℃, the test electrochemical window was 2-4.3V, and the test data was recorded using software, as shown in Table 1.

[0119] Table 1

[0120]

[0121]

[0122] from Figure 1 (Example 1 XRD) Figure 4 (Example 2 XRD) Figure 7 (Comparative Example 1 XRD) It can be seen that the present invention provides a novel idea of ​​simultaneously doping Be and Mg in layered oxides. The original phase structure was not destroyed after the two elements were incorporated into Examples 1-2.

[0123] Figure 15 (Comparative Example 1) Figure 16 The SEM images of (Example 1) show that the sample is a plate-like crystal with a diameter of 1–3 μm, and the addition of the two elements does not affect the original surface morphology; and through… Figure 17 EDS testing of (Example 1) showed that elements such as Na, Li, Ni, Mn, Be, Mg, and O were evenly distributed.

[0124] from Figure 18 As can be seen from the XRD comparison diagrams of Example 1 and Comparative Example 1, the addition of Be and Mg elements in Example 1 promotes each other, causing the (002) characteristic peak to shift to the left, expanding the interaxial spacing, providing a wider channel for the transport and movement of sodium ions, and improving the electrochemical activity of the cathode material.

[0125] from Figure 19 , Figure 21 It can be seen that the electrode material Mn in Example 1 3+ / Mn 4+ The ratio of Mn decreases with the incorporation of Be and Mg elements. 3+ The relative content of Mn decreased, inhibiting its activity. 3+ The presence of this leads to Jiang-Taylor distortion, making the material structure more stable, which in turn can improve the initial discharge capacity and cycle stability of the battery.

[0126] Furthermore, from Figure 20 , Figure 22 It can be seen that the oxygen active species ratio (Lattice O:Surface O) of the cathode material prepared in Example 1 is increased, from 2.49 to 4.97, which can greatly improve the stability of the electrode structure itself during battery cycling. Therefore, the battery of Example 1 is better than that of Comparative Example 1 in terms of initial discharge capacity and cycle stability.

[0127] pass Figure 23 As can be seen, in the electrode material of Example 1, after the substitution of Be and Mg elements, EIS test results show that after 20 cycles at 1C, both the interfacial transfer resistance and diffusion resistance of the cathode material decreased. The interfacial transfer resistance decreased from 925.9 ohms to 537.8 ohms, and the diffusion resistance decreased from 2766 ohms to 323.8 ohms. This also confirms that the incorporation of these two elements is beneficial to improving the electrochemical activity of the original material.

[0128] As can be seen from the data in Table 1, compared with Comparative Examples 1-3, the batteries prepared in Examples 1-5 all have higher cycle stability, especially the cycle stability at high rates, which can even improve the original capacity.

[0129] Compared with Comparative Examples 2 and 3, the battery with the dual-doped electrode material prepared in Example 2, although the initial specific capacity is not much different, can significantly improve its long-term stability: the battery of Example 2 can maintain a retention rate of 74.2% after 500 cycles and about 50% after 1000 cycles, which is significantly higher than that of Comparative Examples 2 and 3.

[0130] Furthermore, the data from Examples 1, 3, and 4 show that the one-step and stepwise doping methods have a certain impact on the performance of the electrode materials.

[0131] Example 3, which employed Mg doping followed by Be doping, exhibited superior initial specific capacity and cycle stability. This is likely because Mg ions, upon entering the nanolattice, can fully penetrate the nanocrystalline lattice of the layered oxide material and replace Ni ions, forming a regular arrangement. Simultaneously, adsorption sites are created, facilitating the entry of smaller Be ions into the nanolattice and improving the doping efficiency of Mg and Be elements within the nanolattice, thereby increasing the battery's initial specific capacity (76.3 mAh / g).

[0132] As can be seen from Examples 3 and 5, the initial specific capacity of the battery is improved by first doping with Mg and then increasing the calcination temperature of the second Be element. It is speculated that this may be because the interaxial spacing of the layered oxide is increased, providing a wider channel for the transport and movement of sodium ions; or it may be because the probability of Be ions forming a passivation layer on the nano-surface is reduced, thereby enabling effective dual doping of Mg and Be and improving the electrochemical performance of the battery material.

[0133] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A P2-type sodium-ion battery cathode material, characterized in that, The positive electrode material has the chemical formula Na. 0.85 Li 0.12 Ni 0.22-2X Mg X Be X Mn 0.66 O2, where X = 0.011 or X = 0.022; The method for preparing the positive electrode material includes the following steps: (1) Sodium source, lithium source, nickel source, magnesium source and manganese source are uniformly mixed according to the stoichiometric ratio, ball milled, heated to T1 for calcination, cooled and taken out; (2) Beryllium source is added, mixed and ball milled, heated to T2 for calcination; (3) Grinding, and the P2 type sodium-ion battery cathode material is obtained. T1 is 800-850℃; T2 is 900-1000℃.

2. The cathode material as described in claim 1, characterized in that, The sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, and sodium nitrate; the lithium source is selected from at least one of lithium carbonate, lithium perchlorate, lithium nitrate, lithium hydroxide, lithium hexafluorophosphate, and organic electrolyte lithium salts; the nickel source is selected from at least one of nickel oxide, nickel nitrate, and nickel hydroxide; the magnesium source is selected from at least one of magnesium carbonate, magnesium hydroxide, and magnesium nitrate; the beryllium source is selected from at least one of beryllium oxide, beryllium hydroxide, and beryllium chloride; and the manganese source is manganese trioxide.

3. The positive electrode material as described in claim 1, characterized in that, The ball milling rate is 400~500 r / min, and the ball milling time is 15~18 h.

4. The positive electrode material as described in claim 1, characterized in that, The calcination time for steps (1) and (2) is 20-25 h, respectively.

5. The application of the P2 type sodium-ion battery cathode material as described in any one of claims 1-4, characterized in that, The aforementioned cathode material is used as an active material in the cathode of a sodium-ion battery.

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