Negative electrode active materials and their preparation methods, negative electrodes for sodium-ion batteries, sodium-ion batteries and their electrical devices.

Abstract

This application provides an anode active material and its preparation method, an anode for sodium-ion batteries, a sodium-ion battery, and a power device. The anode active material comprises a nitrogen-doped carbon sphere matrix and manganese monoxide embedded within the nitrogen-doped carbon sphere matrix; the average particle size of the manganese monoxide is 1.5 nm to 2.5 nm. In the above-mentioned anode active material, embedding quantum dot-level MnO within the nitrogen-doped carbon sphere matrix achieves a tight intercalation structure (non-surface loading) between the quantum dot-level MnO and the nitrogen-doped carbon spheres, effectively mitigating the volume expansion during sodium ion insertion and extraction, and providing a highly efficient electron / ion transport channel. Simultaneously, the quantum dot-level MnO has a larger specific surface area, and the nitrogen-doped carbon provides more adsorption sites; therefore, the composite material exhibits pseudocapacitive-dominated sodium storage behavior, endowing it with ultra-high rate performance and ultra-long cycle life.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, specifically to a negative electrode active material and its preparation method, a negative electrode for sodium-ion batteries, a sodium-ion battery, and an electrical device thereof. Background Technology

[0002] Sodium-ion batteries (SIBs), as a potential alternative to lithium-ion batteries (LIBs), have attracted increasing attention in recent years for large-scale energy storage applications due to the low cost and abundant reserves of sodium resources, and the similar chemical and physical properties of sodium and lithium. However, graphite, as a commercial lithium-ion battery anode material, exhibits unsatisfactory capacity when used in sodium-ion batteries due to the large size of sodium ions. Therefore, there is an urgent need to explore suitable sodium-ion storage host materials to improve the electrochemical performance of sodium-ion batteries. To date, researchers have been dedicated to exploring various anode materials suitable for sodium-ion batteries, including various carbon materials, alloy materials (such as Sn and Sb), metal sulfides (such as MoS2, SnS2, and FeS), phosphides, and transition metal oxides (such as CuO, TiO2, Co3O4, and MnOx). Among these, MnO is considered an excellent choice due to its significant advantages, including high theoretical capacity based on conversion reaction mechanisms, abundant natural resources, low cost, and environmental friendliness. Despite this, the application of MnO as an anode material is still hindered by its low intrinsic conductivity and drastic volume and structural changes during charge and discharge, which leads to a sharp decline in capacity, deterioration in cycle performance, and rate performance. Combining MnO with carbon is a relatively effective method. However, most current carbon composite schemes still have the following limitations: in terms of structural design, only a carbon layer is coated on the surface of MnO. This structure suffers from problems such as easy interface delamination due to expansion stress and a sharp increase in capacity decay after a certain number of cycles. Summary of the Invention

[0003] Therefore, it is necessary to provide a negative electrode active material with high capacity retention, good cycle performance, and high rate performance, as well as a method for preparing the same. Furthermore, it is necessary to provide a negative electrode for sodium-ion batteries, a sodium-ion battery, and a power-consuming device.

[0004] The first aspect of this application provides a negative electrode active material, comprising: a nitrogen-doped carbon sphere matrix and manganese monoxide embedded within the nitrogen-doped carbon sphere matrix; the average particle size of the manganese monoxide is 1.5 nm to 2.5 nm.

[0005] In the aforementioned anode active material, embedding quantum dot-level MnO within a nitrogen-doped carbon sphere matrix achieves a tight-fitting structure (non-surface loading) between the quantum dot-level MnO and the nitrogen-doped carbon spheres. This effectively mitigates the volume expansion during sodium ion insertion and extraction and provides a highly efficient electron / ion transport channel. Simultaneously, the quantum dot-level MnO has a larger specific surface area, providing more adsorption sites; both the quantum dot-level MnO and nitrogen-doped carbon spheres also possess numerous adsorption sites. Therefore, this anode active material exhibits pseudocapacitive-dominated sodium storage behavior, endowing sodium-ion batteries with ultra-high rate performance and ultra-long cycle life.

[0006] Preferably, the average particle size of manganese monoxide is 1.8 nm to 2.2 nm.

[0007] In some embodiments, the mass ratio of nitrogen-doped carbon sphere matrix to manganese monoxide is 1:(0.5-2). Controlling the mass ratio of nitrogen-doped carbon sphere matrix to MnO can regulate the percentage of active material.

[0008] In some embodiments, the nitrogen content in the nitrogen-doped carbon sphere matrix is ​​5.5% to 7.5% by mass. Preferably, the nitrogen content in the nitrogen-doped carbon sphere matrix is ​​5.77% to 7.26% by mass.

[0009] In some embodiments, the diameter of the nitrogen-doped carbon sphere substrate is 50 nm to 5000 nm. Preferably, the diameter of the nitrogen-doped carbon sphere substrate is 50 nm to 200 nm, and more preferably, the diameter of the nitrogen-doped carbon sphere substrate is 80 nm to 150 nm.

[0010] A second aspect of this application provides a method for preparing a negative electrode active material, comprising the following steps:

[0011] (a) Prepare a mixed aqueous solution of dopamine hydrochloride and manganese source to obtain solution A; the mass ratio of dopamine hydrochloride to manganese source is 1:(2~5.7);

[0012] (b) Stir the ammonium bicarbonate solution at 50℃~80℃ for 0.5h~1.5h, and cool it to room temperature to obtain solution B;

[0013] (c) Mix solution A with solution B and react for 0.5 h to 1.5 h to obtain a precursor of manganese carbonate quantum dots embedded in polydopamine;

[0014] (d) The precursor is freeze-dried and then calcined in an inert gas atmosphere.

[0015] In the above preparation method, dopamine hydrochloride, manganese source and ammonium bicarbonate are used as raw material system. The ammonium bicarbonate solution is stirred at 50℃~80℃ for 0.5h~1.5h in advance. On the one hand, it accelerates the dehydration of bicarbonate to generate carbonate ions, and on the other hand, it promotes the volatilization of ammonia to reduce the pH value of the solution. This dynamic change creates a unique reaction microenvironment, under which dual reaction synergy is achieved: (1) Dopamine hydrochloride undergoes oxidative self-polymerization to form polydopamine (PDA) spheres; (2) Mn 2+ With HCO3 - Under the in-situ spatial confinement of PDA, manganese carbonate (MnCO3) quantum dots@PDA precursors with uniform particle size distribution were generated. Finally, after high-temperature heat treatment in an inert atmosphere, the PDA was pyrolyzed into a nitrogen-doped carbon matrix, while the MnCO3 quantum dots were thermally decomposed into 1.5nm~2.5nm MnO quantum dots while maintaining their in-situ embedded structure.

[0016] When dopamine hydrochloride, a manganese source, and a low-concentration ammonium bicarbonate solution are directly mixed and reacted in the traditional method, the nucleation process is entirely: Mn 2+ First, it chelates with the catechol group of dopamine, and then the slowly released carbonate ions lead to heterogeneous nucleation, forming a large-sized manganese carbonate-PDA complex. Therefore, traditional techniques are difficult to use to prepare quantum dot-sized MnO, and the resulting composite microspheres are also larger in size.

[0017] The above preparation method is simple and low-cost, and can produce MnO-based anode materials with quantum dot-level confined structure, strong interface coupling characteristics and pseudocapacitance-dominant mechanism, which is a key path to break through the performance bottleneck of sodium-ion batteries.

[0018] In some embodiments, the above preparation method satisfies at least one of the following conditions:

[0019] (1) The mass ratio of dopamine hydrochloride to the manganese source is 1:(2~5.7);

[0020] (2) The manganese source is selected from one or more of manganese sulfate monohydrate, manganese acetate tetrahydrate, manganese nitrate and manganese chloride;

[0021] (4) In the mixed aqueous solution, the concentration of dopamine hydrochloride is 1.9 mg / mL to 3.1 mg / mL;

[0022] (5) The concentration of ammonium bicarbonate in the ammonium bicarbonate solution is 5.0 mg / mL to 8.3 mg / mL.

[0023] In some embodiments, the above preparation method satisfies at least one of the following conditions:

[0024] (1) Freeze-drying conditions include: temperature of -70℃ to -50℃ and time of 12h to 24h;

[0025] (2) The calcination conditions include heating the dried precursor to 600℃~800℃ at a rate of 2℃ / min~10℃ / min and holding it at that temperature for 1h~3h;

[0026] (3) The protective gas is selected from argon and nitrogen.

[0027] The third aspect of this application provides a negative electrode for a sodium-ion battery, including the negative electrode active material provided in the first aspect of this application, or including a negative electrode active material prepared according to the method provided in the second aspect.

[0028] The fourth aspect of this application provides a sodium-ion battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode includes the negative electrode active material provided in the first aspect of this application, or the negative electrode includes the negative electrode active material prepared according to the method provided in the first aspect of this application.

[0029] The fourth aspect of this application provides an electrical device that includes the sodium-ion battery provided in the fourth aspect of this application.

[0030] Preferably, the electrical device includes mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, and energy storage systems. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0032] Figure 1 The XRD patterns of the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1 and the XRD patterns of the manganese monoxide standard sample are shown.

[0033] Figure 2 XPS spectrum of manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1.

[0034] Figure 3 SEM image of manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1.

[0035] Figure 4 TEM image of manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1; wherein Figure 4 a and Figure 4 b represents TEM images at different magnifications.

[0036] Figure 5 HRTEM image of manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1.

[0037] Figure 6 The TEM energy spectrum mapping diagram of the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1 is shown below; Figure 6 a is the TEM image. Figure 6 b is the energy spectrum mapping diagram for C, Mn, N, and O elements.

[0038] Figure 7 The image shows a TGA image of the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1.

[0039] Figure 8 The discharge specific capacity diagram of the sodium-ion battery corresponding to the composite electrode prepared in Example 1 at different cycle numbers.

[0040] Figure 9 The sodium-ion battery corresponding to the composite electrode prepared in Example 1 was tested at 0.2 Ag. -1 Ratio plot after 500 cycles at current density.

[0041] Figure 10 The sodium-ion battery corresponding to the composite electrode prepared in Example 1 was tested at 0.2 Ag. -1 Cycling for 500 cycles at a current density, then at 10.0 Ag -1 Long-cycle diagram of 4100 cycles at current density.

[0042] Figure 11 The sodium-ion battery corresponding to the composite electrode prepared in Example 1 operates at 0.2 mV·s. -1 ~1.0 mV·s -1 Cyclic voltammetry curves for different scan rate ranges.

[0043] Figure 12 The diagram shows the b-values ​​in the sodium-ion battery corresponding to the composite electrode prepared in Example 1.

[0044] Figure 13 This is a diagram showing the proportion of pseudocapacitance in the sodium-ion battery corresponding to the composite electrode prepared in Example 1; where, Figure 13 a is a bar chart showing the proportion of pseudocapacitance in sodium-ion batteries at different scan rates; Figure 13 b represents the sodium-ion battery at a scan rate of 0.8 mVs. -1 The following is a diagram showing the proportion of pseudocapacitance. Detailed Implementation

[0045] The embodiments described in this specification are merely for explaining this application and are not intended to limit this application.

[0046] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0047] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "multiple (items)" in "one or more" or "one or more" means two or more.

[0048] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0049] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0050] Example 1

[0051] 676 mg of MnSO4·H2O and 200 mg of dopamine hydrochloride were weighed and added to 80 mL of deionized water and stirred thoroughly to form solution A. Then, 400 mg of NH4HCO3 was dissolved in 60 mL of deionized water, and this solution was placed in a 70°C water bath and magnetically stirred for 1 hour to form solution B. After solution B cooled to room temperature, it was quickly added to solution A, and the reaction proceeded for 1 hour to form mixed solution C. Solution C was vacuum filtered, washed four times with water, and then freeze-dried for 12 hours. The dried precursor product was then annealed at 650°C for 2 hours in a tube furnace filled with argon gas. Finally, a composite material of MnO quantum dots uniformly embedded in nitrogen-doped carbon spheres (i.e., manganese monoxide quantum dots@nitrogen-doped carbon composite material) was obtained.

[0052] Preparation of the composite electrode: The prepared composite material, acetylene black, and polyvinylidene fluoride were uniformly mixed at a mass ratio of 80:10:10. Then, N-methylpyrrolidone solution was added, and a uniform slurry was formed under magnetic stirring. The slurry was coated onto copper foil, and finally dried in a vacuum oven at 100°C for 12 hours to obtain the composite electrode.

[0053] Characterization tests of manganese monoxide quantum dot@nitrogen-doped carbon composite materials:

[0054] The morphology, microstructure, and crystal phase of the samples were characterized by scanning electron microscopy (SEM, Hitachi SU8010), transmission electron microscopy (TEM, JEOL2100F), and X-ray diffraction (XRD, Rigaku UltimaIV), respectively. X-ray photoelectron spectroscopy (XPS, PHI-5000 VersaProbe spectrometer) and Raman spectroscopy (Invia Micro-Raman spectrometer) were also used for characterization. The mass fraction of MnO in the composite material was determined by thermogravimetric analysis (TGA, NETzsch TG 209F3) in air.

[0055] Figure 1 The XRD patterns of the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1 and the XRD pattern of the manganese monoxide standard sample (JCPDS no. 07-0230) are shown. Figure 1 As can be seen, the positions of the characteristic peaks of the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1 correspond one-to-one with the characteristic peaks of the manganese monoxide standard sample (JCPDS no. 07-0230), indicating that the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1 contains MnO.

[0056] Figure 2 XPS spectra of the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1. Figure 2As can be seen, the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1 contains Mn, O, C, and N elements.

[0057] Figure 3 SEM image of manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1. Figure 4 This is a TEM image of the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1, wherein... Figure 4 a and Figure 4 b represents TEM images at different magnifications. Figure 5 HRTEM image of the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1. Figure 3 It can be observed that the average size of the carbon spheres in the manganese monoxide quantum dot@nitrogen-doped carbon composite material is approximately 100 nm; from Figure 4 The TEM image shows that the size and shape of the carbon spheres are consistent with those in the SEM image; and from... Figure 4 As can be seen in b, there are many tiny nanoparticles inside the carbon spheres; Figure 5 The HRTEM image further showed that the nanoparticles had an average diameter of about 2 nm and were uniformly embedded in the carbon spheres, thus proving the nanostructure of quantum dots uniformly embedded in carbon spheres. Figure 6 The energy spectrum mapping diagram of the TEM image corresponding to the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1 is shown below. Figure 6 a is the TEM image. Figure 6 b is the energy spectrum mapping diagram for C, Mn, N and O elements, showing the uniform distribution of Mn, O, C and N elements, indicating the uniform doping of N element.

[0058] Figure 7 The image shows the TGA image of the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1. MnO, after high-temperature oxidation, ultimately forms Mn2O3 with a mass retention rate of 69.1%. The manganese monoxide content in the composite material is calculated to be 62.2% through conversion.

[0059] Electrochemical performance testing:

[0060] The composite electrode prepared in Example 1 was cut into discs with an active material loading of 0.7 mg to 1.1 mg and used directly as the working electrode, with a sodium metal disc as the counter electrode. A 1 M NaClO4 solution (PC and FEC mass ratio 95:5) was used as the electrolyte, and glass fiber was used as the separator. The cells were assembled into 2025 type coin cells (sodium-ion batteries) in a glove box under a high-purity argon atmosphere. Constant current charge-discharge tests were performed using a battery testing system (NEWARE BTS-610), with a voltage range of 0.01 V to 3.0 V. Cyclic voltammetry (CV) tests were performed on a CHI660E electrochemical workstation. The voltage range for CV tests was 0.01 V to 3.0 V.

[0061] Sodium-ion battery discharge specific capacity test: The sodium-ion battery corresponding to the composite electrode prepared in Example 1 was tested at 0.2 A g. -1 After 500 cycles at the current density, its discharge specific capacity was observed. The test results are as follows: Figure 8 As shown. Among them, Figure 8 The specific discharge capacity of the sodium-ion battery after different number of cycles is shown. Figure 8 As can be seen, sodium-ion batteries at 0.2Ag -1 After 500 cycles at the current density, it exhibits a high discharge specific capacity of 479.8 mAh / g and a capacity retention of up to 110% (compared to the second discharge specific capacity). This capacity increase may be attributed to the gradual activation of the material during cycling, demonstrating outstanding cycling performance.

[0062] Rate performance testing: The sodium-ion battery corresponding to the composite electrode prepared in Example 1 was tested at 0.2 A g. -1 The rate performance of the sodium-ion battery was observed after 500 cycles at the current density. The test results are as follows: Figure 9 As shown. Figure 9 The sodium-ion battery corresponding to the composite electrode prepared in Example 1 was tested at 0.2 A g. -1 The rate performance graph after 500 cycles at the current density shows that this sodium-ion battery achieves good performance at 0.2 A g. -1 0.4A g -1 0.5A g -1 1.0A g -1 2.0A g -1 4.0A g -1 5.0A g -1 and 10.0A g -1The specific capacities at the specified current densities were 481.1 mAh / g, 452.1 mAh / g, 443.9 mAh / g, 407.3 mAh / g, 364.7 mAh / g, 321.2 mAh / g, 302.9 mAh / g, and 258.3 mAh / g, respectively. At an ultra-high current density of 15.0 Ag... -1 Under these conditions, this sodium-ion battery still exhibits a high discharge specific capacity of 229.2 mAh / g, demonstrating good rate performance.

[0063] Cycle life performance test: The sodium-ion battery corresponding to the composite electrode prepared in Example 1 was subjected to a cycle life test at 0.2 A g. -1 Cycling at current density for 500 cycles, then at 10.0 A g. -1 Its discharge specific capacity was observed after 4100 cycles at a current density. The test results are as follows: Figure 10 As shown. From Figure 10 It can be seen that when the manganese monoxide quantum dot@nitrogen-doped carbon composite material prepared in Example 1 is used as the negative electrode in a sodium-ion battery, the sodium-ion battery achieves a performance of 0.2 A g. -1 Cycling for 500 cycles under current density conditions, then at 10.0 Ag -1 After 4100 cycles at the current density, the discharge specific capacity reached 258.4 mAh / g, with a specific capacity retention of 89% (compared to 10.0 A·g). -1 Compared to the second cycle at the current density, sodium-ion batteries exhibit longer cycle life and higher specific capacity.

[0064] Electrode kinetics test: The sodium-ion battery corresponding to the composite electrode prepared in Example 1 was tested at 0.2 mV·s. -1 ~1.0 mV·s -1 The sodium-ion battery was scanned within a certain scan rate range to obtain cyclic voltammetry (CV) curves at different scan rates. The results are as follows: Figure 11 As shown, this sodium-ion battery operates at 0.2 mV s. -1 ~1.0 mV s -1 The CV curves within the scan rate range exhibit highly similar morphologies, indicating that they possess significant electrode kinetic characteristics.

[0065] Figure 12 The graph shows the b-values ​​of the sodium-ion battery corresponding to the composite electrode prepared in Example 1 of this application. The horizontal axis represents the logarithm of the scan rate (Log), and the vertical axis represents the logarithm of the current (Log). As can be seen from the graph, the b-values ​​of the cathode peak and the anode peak are 0.91 and 0.86, respectively, confirming that the sodium storage behavior of the manganese monoxide quantum dot@nitrogen-doped carbon anode is jointly controlled by pseudocapacitance and diffusion process.

[0066] Pseudocapacitance contribution rate calculation: based on the formula i = k1v + k2v 1 / 2 Where k1v is the contribution of pseudocapacitive control, and k2v 1 / 2 This contributes to diffusion control. The results are as follows: Figure 13 As shown, Figure 13 b represents the sodium-ion battery corresponding to the composite electrode prepared in Example 1 at a scan rate of 0.8 mVs. -1 The percentage of pseudocapacitors is shown in the pink area. Figure 13 a is a bar chart showing the pseudocapacitance ratio of the sodium-ion battery corresponding to the composite electrode prepared in Example 1 of this application at different scan rates. Figure 13 a shows that the contribution rate of pseudocapacitance increases with increasing scan rate. Figure 13 b shows at 0.8 mV s -1 The pseudocapacitive contribution rate reached 73%, indicating that the pseudocapacitive mechanism plays a dominant role in the overall capacity of manganese monoxide quantum dots@nitrogen-doped carbon anodes in sodium-ion batteries.

[0067] Example 2

[0068] The preparation method in this embodiment is basically the same as that in Example 1, except that the water bath stirring temperature of the NH4HCO3 aqueous solution is 50°C.

[0069] Example 3

[0070] The preparation method in this embodiment is basically the same as that in Example 1, except that the water bath stirring temperature of the NH4HCO3 aqueous solution is 60°C.

[0071] Example 4

[0072] The preparation method in this embodiment is basically the same as that in Example 1, except that the water bath stirring temperature of the NH4HCO3 aqueous solution is 80℃.

[0073] Comparative Example 1

[0074] 676 mg of MnSO4·H2O was weighed and added to 80 mL of deionized water, and stirred thoroughly to form solution A. Then, 400 mg of NH4HCO3 was dissolved in 60 mL of deionized water, and this solution was placed in a 70°C water bath and magnetically stirred for 1 hour to form solution B. After solution B cooled to room temperature, it was quickly added to solution A, and the reaction proceeded for 1 hour to form a mixed solution C. Solution C was vacuum filtered, washed four times with water, and then freeze-dried for 12 hours. The dried precursor product was then annealed in an argon-filled tube furnace at 650°C for 2 hours to finally obtain the MnO material.

[0075] Comparative Example 2

[0076] The preparation method of this comparative example is basically the same as that of Example 1. The only difference is that the NH4HCO3 aqueous solution was not stirred in a water bath under high temperature conditions in this comparative example. Instead, the NH4HCO3 aqueous solution was directly mixed with solution A and reacted.

[0077] Performance testing:

[0078] The preparation parameters and average particle size of manganese monoxide quantum dots@nitrogen-doped carbon in each embodiment and comparative example were tested using scanning electron microscopy and transmission electron microscopy. The test results are shown in Table 1.

[0079] The manganese monoxide quantum dots@nitrogen-doped carbon prepared in the above embodiments and comparative examples were used to prepare corresponding sodium-ion batteries according to the sodium-ion battery preparation steps in Example 1, and the results were tested at a current density of 0.2 A g. -1 The discharge specific capacity after 500 cycles under certain conditions, and then at 10.0 A g. -1 Capacitance retention after 4100 cycles at current density compared to the second cycle.

[0080]

[0081] As shown in Table 1, the average particle size of MnO in the manganese monoxide quantum dot@nitrogen-doped carbon composite materials prepared by the method described in Examples 1-4 reaches 2 nm to 3 nm; the average particle size of the nitrogen-doped carbon sphere matrix reaches 100 nm to 2000 nm; and the discharge specific capacity of the sodium-ion battery corresponding to the negative electrode material prepared by this composite material reaches 210.5 mAh g. -1 ~479.8mAh g -1 The specific capacity retention rate reached 70%~89%, showing a significant advantage compared to Comparative Examples 1 and 2. Furthermore, in Examples 2 and 3, the NH4HCO3 aqueous solution was stirred in a water bath at 50℃ and 60℃ respectively, and the average particle size of the prepared nitrogen-doped carbon sphere matrix reached 1800nm~2000nm; this is because the ionic strength of the solution after low-temperature pretreatment is higher (NH4). + / HCO3 - This may reduce the repulsive force between carbon spheres through electrostatic shielding, promoting the fusion and growth of carbon spheres. Furthermore, high-temperature pretreatment results in lower ionic strength, better carbon sphere dispersion, and smaller size.

[0082] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator; the negative electrode includes a negative electrode active material. The negative electrode active material comprises: a nitrogen-doped carbon sphere matrix and manganese monoxide embedded within the nitrogen-doped carbon sphere matrix; the average particle size of the manganese monoxide is 1.5 nm to 2.5 nm; and the diameter of the nitrogen-doped carbon sphere matrix is ​​50 nm to 200 nm.

2. The sodium-ion battery according to claim 1, characterized in that, The mass ratio of the nitrogen-doped carbon sphere matrix to the manganese monoxide is 1:(0.5-2).

3. The sodium-ion battery according to claim 1, characterized in that, The nitrogen content in the nitrogen-doped carbon sphere matrix is ​​5.5% to 7.5% by mass.

4. The sodium-ion battery according to claim 1, characterized in that, The preparation method of the negative electrode active material includes the following steps: (a) Prepare a mixed aqueous solution of dopamine hydrochloride and manganese source to obtain solution A; (b) Stir the ammonium bicarbonate solution at 70℃~80℃ for 0.5h~1.5h, and cool it to room temperature to obtain solution B; (c) Mix the solution A with the solution B and react for 0.5 h to 1.5 h to obtain a precursor of manganese carbonate quantum dots embedded in polydopamine; (d) The precursor is freeze-dried and then calcined in a protective gas.

5. The sodium-ion battery according to claim 4, characterized in that, The mass ratio of dopamine hydrochloride to the manganese source is 1:(2~5.7).

6. The sodium-ion battery according to claim 4, characterized in that, The manganese source is selected from one or more of manganese sulfate monohydrate, manganese acetate tetrahydrate, manganese nitrate, and manganese chloride.

7. The sodium-ion battery according to any one of claims 4 to 6, characterized in that, The freeze-drying conditions include: a temperature of -70℃ to -50℃ and a time of 12h to 24h.

8. The sodium-ion battery according to any one of claims 4 to 6, characterized in that, The calcination conditions include heating the dried precursor to 600℃~800℃ at a rate of 2℃ / min~10℃ / min and holding it at that temperature for 1h~3h.

9. The sodium-ion battery according to any one of claims 4 to 6, characterized in that, The protective gas is selected from argon and nitrogen.

10. The sodium-ion battery according to any one of claims 4 to 6, characterized in that, In the mixed aqueous solution, the concentration of dopamine hydrochloride is 1.9 mg / mL to 3.1 mg / mL.

11. The sodium-ion battery according to any one of claims 4 to 6, characterized in that, The concentration of ammonium bicarbonate in the ammonium bicarbonate solution is 5.0 mg / mL to 8.3 mg / mL.

12. An electrical appliance, characterized in that, The electrical device includes a sodium-ion battery as described in any one of claims 1 to 11.

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