A lithium-rich manganese-based cathode material, its preparation method and application

Abstract

This invention belongs to the field of lithium battery technology, specifically relating to a lithium-rich manganese-based cathode material, its preparation method, and its application. The invention involves mixing a metal salt solution, a precipitant, and a complexing agent, and then subjecting the resulting co-precipitation reaction precursor solution to a co-precipitation reaction to obtain a lithium-rich manganese-based precursor. The metal salt solution includes manganese, cobalt, and nickel. The lithium-rich manganese-based precursor, a lithium source, an additive, and a dispersant are mixed and calcined to obtain the lithium-rich manganese-based cathode material. The additive includes a nitrogen source, or a nitrogen source and a carbon source. This invention can improve the initial discharge specific capacity, rate performance, and cycle stability of the lithium-rich manganese-based cathode material, overcoming its problems of capacity decay, discharge voltage drop, and sluggish kinetics during electrochemical reactions.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a lithium-rich manganese-based cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of electronics and electric vehicles, higher requirements are being placed on the specific capacity, energy density, and cycle stability of lithium-ion batteries. Cathode materials, as a crucial component of lithium-ion batteries, significantly impact their energy density. Traditional cathode materials such as LiCoO2, LiMn4O2, and LiFePO4 cannot meet the high energy density requirements of electric and hybrid vehicles due to their relatively low discharge voltage and specific capacity. Therefore, there is an urgent need to develop novel cathode materials with high energy density. Layered lithium-rich manganese-based cathode materials, through the coupling effect of transition metal cations and oxygen anions in redox reactions, exhibit high discharge specific capacity (theoretical capacity at 0.1C > 250 mAh / g) and high energy density (900 Wh / kg), making them one of the most promising next-generation high-energy-density cathode materials.

[0003] However, the unique oxygen anion redox mechanism of lithium-rich manganese-based cathode materials causes irreversible loss of lattice oxygen and migration of transition metal ions, leading to structural instability, capacity decay, discharge voltage drop, and sluggish electrochemical reaction kinetics during cycling, which restricts their commercial application. Summary of the Invention

[0004] The present invention aims to provide a lithium-rich manganese-based cathode material, its preparation method and application. The present invention can improve the initial discharge specific capacity, rate performance and cycle stability of lithium-rich manganese-based cathode materials, and overcome the problems of capacity decay, discharge voltage drop and slow kinetics in electrochemical reaction.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a lithium-rich manganese-based cathode material, comprising the following steps:

[0007] A metal salt solution, a precipitant, and a complexing agent are mixed, and the resulting coprecipitation reaction precursor solution is subjected to a coprecipitation reaction to obtain a lithium-rich manganese-based precursor; the metal salt solution includes manganese, cobalt, and nickel.

[0008] The lithium-rich manganese-based precursor, lithium source, additives and dispersant are mixed and calcined to obtain a lithium-rich manganese-based cathode material; the additives include a nitrogen source, or a nitrogen source and a carbon source.

[0009] Preferably, the molar ratio of manganese, cobalt and nickel in the metal salt solution is x:y:z, 2 / 3≥x>0, 1 / 6≥y>0, 1 / 6≥z>0, and 1≥x+y+z>0.

[0010] Preferably, the nitrogen source is melamine and / or glutamic acid.

[0011] Preferably, the carbon source is glucose and / or sucrose.

[0012] Preferably, the nitrogen source accounts for 1 to 7 wt% of the mass of the lithium-rich manganese-based precursor.

[0013] Preferably, the carbon source accounts for 0.1 to 3 wt% of the lithium-rich manganese-based precursor.

[0014] Preferably, the calcination includes a first calcination and a second calcination in sequence; the temperature of the first calcination is 400~600℃ and the holding time is 4~8h; the temperature of the second calcination is 700~900℃ and the holding time is 8~14h.

[0015] Preferably, the precipitant is a sodium carbonate solution; the complexing agent is ammonia.

[0016] The present invention also provides lithium-rich manganese-based cathode materials prepared by the preparation method described above, including Li-Ni-Co-Mn-O materials doped with nitrogen in the crystal lattice, or Li-Ni-Co-Mn-O materials doped with nitrogen in the crystal lattice and coated with a carbon layer on the surface; wherein the carbon layer includes amorphous carbon.

[0017] The present invention also provides the application of the lithium-rich manganese-based cathode material described in the above technical solution in lithium batteries.

[0018] This invention provides a method for preparing a lithium-rich manganese-based cathode material, comprising the following steps: mixing a metal salt solution, a precipitant, and a complexing agent; subjecting the resulting coprecipitation reaction precursor solution to a coprecipitation reaction to obtain a lithium-rich manganese-based precursor; wherein the metal salt solution comprises manganese, cobalt, and nickel; mixing the lithium-rich manganese-based precursor, a lithium source, an additive, and a dispersant; and calcining the mixture to obtain the lithium-rich manganese-based cathode material; wherein the additive comprises a nitrogen source, or a nitrogen source and a carbon source.

[0019] Beneficial effects:

[0020] This invention successfully incorporates nitrogen (N) into the lattice of lithium-rich manganese-based cathode materials, achieving bulk doping. N doping optimizes the valence distribution of Mn, enhances the order of the [MnO6] octahedron, suppresses cation mixing, improves cation arrangement order, effectively inhibits lattice oxygen loss, enhances the structural stability and capacity retention of the material, improves the initial discharge specific capacity of the lithium-rich manganese-based cathode material, and suppresses voltage decay. Furthermore, this invention introduces a carbon source into the N-doped lithium-rich manganese-based cathode material. The carbonization of the carbon source forms an amorphous carbon coating layer with a highly conductive structure, reducing the direct contact between the electrode material and the electrolyte, improving the charge transport rate of the electrode, and increasing the discharge specific capacity of the cathode material. Modifying lithium-rich manganese-based cathode materials using the method of this invention can significantly improve the initial discharge specific capacity, rate performance, and cycle stability of the lithium-rich manganese-based cathode material, overcoming the problems of capacity decay, discharge voltage drop, and sluggish kinetics during electrochemical reactions. As can be seen from the results of the embodiments of the present invention, the lithium-rich manganese-based cathode material prepared by the preparation method of the present invention has a first discharge specific capacity of 255.31~316.39mAh / g at 0.1C. Attached Figure Description

[0021] Figure 1 The XRD spectra of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, 1, and 2 are shown below.

[0022] Figure 2 XPS spectra of lithium-rich manganese-based cathode materials prepared in Examples 1, 8, 1, and 2.

[0023] Figure 3 The first discharge specific capacity curves of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Example 1 and Comparative Example 2 at 0.1C;

[0024] Figure 4 The specific capacity / rate ratio of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, 1, and 2 are shown.

[0025] Figure 5 The long cycling curves at 1C are shown for the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Examples 1 and 2.

[0026] Figure 6 The electrochemical impedance and Z' vs ω of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Example 1, and Comparative Example 2 -1 / 2 relation. Detailed Implementation

[0027] This invention provides a method for preparing a lithium-rich manganese-based cathode material, comprising the following steps:

[0028] A metal salt solution, a precipitant, and a complexing agent are mixed, and the resulting coprecipitation reaction precursor solution is subjected to a coprecipitation reaction to obtain a lithium-rich manganese-based precursor; the metal salt solution includes manganese, cobalt, and nickel.

[0029] The lithium-rich manganese-based precursor, lithium source, additives and dispersant are mixed and calcined to obtain a lithium-rich manganese-based cathode material; the additives include a nitrogen source, or a nitrogen source and a carbon source.

[0030] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0031] This invention involves mixing a metal salt solution, a precipitant, and a complexing agent, and then subjecting the resulting coprecipitation reaction precursor solution to a coprecipitation reaction to obtain a lithium-rich manganese-based precursor.

[0032] In one embodiment, the metal salt solution includes manganese, cobalt, and nickel; the molar ratio of manganese, cobalt, and nickel in the metal salt solution is x:y:z, 2 / 3≥x>0, 1 / 6≥y>0, 1 / 6≥z>0, 1≥x+y+z>0, and in a specific embodiment, the molar ratio of manganese, cobalt, and nickel in the metal salt solution is 4:1:1; the metal salt solution is a metal sulfate solution; and the total concentration of metal ions in the metal salt solution is 0.1~2 mol / L, and in a specific embodiment, it is 2 mol / L.

[0033] In one embodiment, the precipitant is a sodium carbonate solution; the concentration of the sodium carbonate solution is 0.1~2 mol / L, specifically 2 mol / L in this embodiment; the complexing agent is ammonia water; the concentration of the ammonia water is 0.1~2 mol / L, specifically 2 mol / L in this embodiment; the volume ratio of the metal salt solution to the precipitant is (0.1~2):1, specifically 1:1 in this embodiment; the complexing agent makes the pH of the precursor solution for the co-precipitation reaction 7~9, specifically 8 in this embodiment.

[0034] In one embodiment, the metal salt solution, precipitant, and complexing agent are mixed by simultaneously adding the metal salt solution and precipitant dropwise to a coprecipitation reactor, and then adding the complexing agent to the resulting mixed solution to obtain a coprecipitation reaction precursor solution; the dropwise addition rate is 0.5~3 mL / min, and in a specific embodiment it is 3 mL / min.

[0035] In one embodiment, the pH value of the coprecipitation reaction is 7-9, specifically 8 in this embodiment; the temperature of the coprecipitation reaction is 50-70℃, specifically 60℃ in this embodiment; the coprecipitation reaction time is 8-12h, specifically 10h in this embodiment; the coprecipitation reaction is carried out under stirring conditions; the stirring speed is 400-700rpm, specifically 500rpm in this embodiment.

[0036] In one embodiment, after the coprecipitation reaction, the process further includes: aging, solid-liquid separation, and drying the product obtained from the coprecipitation reaction sequentially; the aging time is 2-10 hours, specifically 8 hours in this embodiment; the solid-liquid separation method is centrifugation; the centrifugation speed is 5000-10000 rpm, specifically 8000 rpm in this embodiment, and the centrifugation time is 1-5 minutes, specifically 3 minutes in this embodiment; the drying method is forced-air drying; the drying temperature is 60-100℃, specifically 80℃ in this embodiment; and the drying time is 8-12 hours, specifically 12 hours in this embodiment.

[0037] After obtaining the lithium-rich manganese-based precursor, the present invention mixes the lithium-rich manganese-based precursor, lithium source, additives and dispersant, and calcines them to obtain lithium-rich manganese-based material.

[0038] In one embodiment, the lithium source is lithium carbonate; the ratio of the amount of Li in the lithium source to the total amount of manganese, cobalt and nickel in the lithium-rich manganese-based precursor is (1~1.2):1, and in a specific embodiment it is 1.05:1.

[0039] In one embodiment, the additive includes a nitrogen source, or a nitrogen source and a carbon source; the nitrogen source is melamine and / or glutamic acid; the carbon source is glucose and / or sucrose, specifically glucose in this embodiment; the nitrogen source accounts for 1-7 wt% of the mass of the lithium-rich manganese-based precursor, specifically 1.05 wt%, 3 wt%, 3.5 wt%, 5 wt%, or 7 wt% in this embodiment. In this embodiment, the nitrogen source is melamine accounting for 5 wt% of the mass of the lithium-rich manganese-based precursor, or glutamic acid accounting for 3.5 wt% of the mass of the lithium-rich manganese-based precursor, or melamine and glutamic acid accounting for 3.5 wt% of the mass of the lithium-rich manganese-based precursor; the carbon source accounts for 0.1-3 wt% of the mass of the lithium-rich manganese-based precursor, specifically 2.5 wt% in this embodiment.

[0040] In one embodiment, the dispersant is isopropanol; the mass of the dispersant accounts for 1 to 10 wt% of the mass of the lithium-rich manganese-based precursor, and in a specific embodiment, it is 5 wt%.

[0041] In one embodiment, the calcination is carried out in an air atmosphere; the calcination includes a first calcination and a second calcination sequentially; the temperature of the first calcination is 400~600℃, specifically 500℃ in this embodiment, and the holding time is 4~8h, specifically 5h in this embodiment; the heating rate to the temperature of the first calcination is 3~10℃ / min, specifically 5℃ / min in this embodiment; the temperature of the second calcination is 700~900℃, specifically 850℃ in this embodiment, and the holding time is 8~14h, specifically 12h in this embodiment; the heating rate to the temperature of the second calcination is 3~10℃ / min, specifically 5℃ / min in this embodiment; after calcination, the product is further subjected to natural cooling to room temperature.

[0042] The present invention also provides lithium-rich manganese-based cathode materials prepared by the preparation method described above, including Li-Ni-Co-Mn-O materials doped with nitrogen in the crystal lattice, or Li-Ni-Co-Mn-O materials doped with nitrogen in the crystal lattice and coated with a carbon layer on the surface; wherein the carbon layer includes amorphous carbon.

[0043] The present invention also provides the application of the lithium-rich manganese-based cathode material described in the above technical solution in lithium batteries.

[0044] In one implementation, the lithium battery is a button cell, specifically a CR2032 button cell.

[0045] As one implementation method, the specific preparation method of the lithium battery is as follows: a lithium-rich manganese-based positive electrode material, a binder, a conductive agent and an organic solvent are mixed, the resulting slurry is coated on an aluminum foil, dried, made into a disc, and then pressed into an electrode sheet to obtain the positive electrode;

[0046] The positive electrode, negative electrode, separator, and electrolyte are assembled in an argon-filled glove box to obtain the lithium battery.

[0047] In one embodiment, the mass ratio of the lithium-rich manganese-based positive electrode material, binder, and conductive agent is 8:1:1; the organic solvent is N-methylpyrrolidone; the drying temperature is 80°C and the drying time is 12 hours; the drying equipment is a vacuum drying oven; the diameter of the disc is 13 mm; the pressing pressure is 8-10 MPa; the negative electrode is a lithium metal sheet; the separator is a Celgard 2500 polypropylene separator; the electrolyte is a 1 mol / L LiPF6 organic solution; the organic solvent in the electrolyte includes dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC); the volume ratio of dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate is 1:1:1; the water content in the argon glove box is <0.01 ppm and the oxygen content is <0.01 ppm.

[0048] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0049] Example 1

[0050] The preparation method of lithium-rich manganese-based cathode material is as follows:

[0051] (1) A metal sulfate solution with a total metal ion concentration of 2 mol / L was prepared according to the molar ratio of Mn:Co:Ni of 4:1:1. A sodium carbonate solution of the same concentration was used as a precipitant. The volume ratio of the metal sulfate solution to the precipitant was 1:1. The metal sulfate solution and the precipitant were added dropwise to the reaction vessel at a rate of 3 mL / min. Ammonia water was then added to make the pH value of the resulting mixed solution reach 8. The reaction temperature was maintained at 60℃, the stirring was turned on, the speed was 500 rpm, and the reaction was continued for 10 h. Then, it was aged for 8 h, centrifuged at 8000 rpm for 3 min, and dried in a forced-air condition at 80℃ for 12 h to obtain the lithium-rich manganese-based precursor Mn. 0.54 Ni 0.13 Co 0.13 (CO3) 0.8 ;

[0052] (2) The lithium-rich manganese-based precursor and lithium source are mixed at a molar ratio of Li:TM(Ni, Co, Mn) = 1.05:1, and melamine and glucose accounting for 5 wt% of the mass of the lithium-rich manganese-based precursor are added. Isopropanol is used as a dispersant, and the mass of the dispersant accounts for 5 wt% of the mass of the lithium-rich manganese-based precursor. The mixture is thoroughly ground and mixed in an agate mortar, placed in a corundum ceramic boat, and heated to 500℃ at 5℃ / min and held for 5h in a muffle furnace under air atmosphere. Then, the temperature is increased to 850℃ at 5℃ / min and held for 12h. After natural cooling to room temperature, the modified lithium-rich manganese-based cathode material is obtained.

[0053] Example 2

[0054] The only difference from Example 1 is that glutamic acid is used instead of melamine, and the mass of glutamic acid accounts for 3.5 wt% of the mass of the lithium-rich manganese-based precursor. All other conditions and parameters are exactly the same as in Example 1.

[0055] Example 3

[0056] The only difference from Example 1 is that melamine and glutamic acid are used instead of melamine. The mass of melamine accounts for 3.5 wt% of the mass of the lithium-rich manganese-based precursor, and the mass of glutamic acid accounts for 1.05 wt% of the mass of the lithium-rich manganese-based precursor. All other conditions and parameters are exactly the same as in Example 1.

[0057] Example 4

[0058] The only difference from Example 1 is that the mass of melamine accounts for 3 wt% of the mass of the lithium-rich manganese-based precursor; all other conditions and parameters are exactly the same as in Example 1.

[0059] Example 5

[0060] The only difference from Example 1 is that the mass of melamine accounts for 7 wt% of the mass of the lithium-rich manganese-based precursor; all other conditions and parameters are exactly the same as in Example 1.

[0061] Example 6

[0062] The only difference from Example 1 is that the mass of glucose accounts for 2 wt% of the mass of the lithium-rich manganese-based precursor; all other conditions and parameters are exactly the same as in Example 1.

[0063] Example 7

[0064] The only difference from Example 1 is that the mass of glucose accounts for 3 wt% of the mass of the lithium-rich manganese-based precursor; all other conditions and parameters are exactly the same as in Example 1.

[0065] Example 8

[0066] The difference from Example 1 is that no carbon source is added during the preparation of the cathode material, while the other conditions and parameters are exactly the same as in Example 1.

[0067] Comparative Example 1

[0068] The difference from Example 1 is that no nitrogen source is added during the preparation of the cathode material, while the other conditions and parameters are exactly the same as in Example 1.

[0069] Comparative Example 2

[0070] The difference from Example 1 is that no additional nitrogen source or carbon source is added during the preparation of the cathode material.

[0071] Performance testing

[0072] The positive electrode materials obtained in the examples and comparative examples were used to prepare coin cells. The specific preparation method was as follows: the positive electrode material, polyvinylidene fluoride (PVDF), and conductive agent acetylene black were dissolved in N-methylpyrrolidone at a mass ratio of 8:1:1, stirred to form a slurry, coated onto aluminum foil, and dried in a vacuum drying oven at 80°C for 12 hours to form a 13mm diameter disc. This disc was then pressed into an electrode sheet under 10MPa. The negative electrode material was a lithium metal sheet, the separator was a Celgard 2500 polypropylene separator, and the electrolyte was a 1mol / L LiPF6 organic solution (dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) in a volume ratio of 1:1:1). The cells were assembled into CR2032 coin cells in an argon glove box (water < 0.01ppm, oxygen < 0.01ppm), and finally placed in a Blue Electric testing system for electrochemical performance testing. Electrochemical performance testing conditions were as follows: charge / discharge voltage range of 2.0–4.8 V, test temperature of 30 °C, and material specific capacity using 1C = 250 mA / g as the standard. The initial charge / discharge capacity of the battery was tested after one cycle at 0.1C / 0.1C to calculate the first-cycle coulombic efficiency. Rate performance was tested at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 0.2C, and 0.1C. Cycle stability was tested after 200 cycles at 1C / 1C.

[0073] The lithium-rich manganese-based cathode materials prepared in Examples 1, 8, 1, and 2 were characterized by XRD and XPS.

[0074] Figure 1 The XRD patterns of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, 1, and 2 are shown below. Figure 1 As shown in (a), the XRD diffraction peak positions of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Examples 1 and 2 are consistent with those in the standard card (PDF No. 85-1983) for lithium-rich manganese-based cathode materials, corresponding to the R3m space group of the hexagonal α-NaFeO2 structure, with no impurity peaks. With the addition of nitrogen and carbon sources, the XRD diffraction peak intensities of all samples increased. However, the sample with added nitrogen source showed obvious splitting in the (108) / (110) peak, indicating that the N-doped lithium-rich manganese-based cathode material has a good layered structure. Furthermore, I(003) / I(104) > 1.2, indicating that the addition of N element suppressed cation mixing, which is beneficial to improving the electrochemical performance of the material. The XRD peak intensity of the sample prepared by further introducing glucose on the basis of fixed nitrogen source increased further without obvious peak shift, indicating that the addition of carbon source did not change the crystal structure of the material, but mainly promoted the further improvement of the crystallinity of the material and formed an amorphous carbon coating layer on the surface of the material. Figure 1 Image (b) is an enlarged view of the (003) crystal plane of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Examples 1 and 2. Figure 1 As shown in (b), after adding melamine, due to N 3- The ionic radius (1.46µm) is greater than that of O. 2- The ionic radius (1.40µm) and the (003) crystal plane shifting at a low angle indicate an increase in interlayer spacing, suggesting that N element has been successfully incorporated into the cathode material lattice.

[0075] Figure 2 The above are XPS spectra of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, 1, and 2. Figure 2 (a) shows the fine C1s spectra of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Examples 1 and 2. Figure 2 As shown in (a), the CC peak width at 284.8 eV is significantly increased, indicating that the residual carbon produced by the pyrolysis of melamine and glucose forms an amorphous carbon coating layer. The COC peak intensity decreases, indicating that the oxygen-containing functional groups on the surface of the cathode material with melamine added alone and with melamine and glucose added simultaneously are reduced, and some oxygen atoms are replaced. Figure 2 Image (b) shows the fine Mn 2p spectra of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Examples 1 and 2. Figure 2 As shown in (b), the positive electrode material Mn 2p modified with melamine has... 3 / 2 The peak shifts towards lower binding energy, and Mn 3+ / Mn 4+ The proportion is within a relatively optimal range, indicating that N doping optimizes the valence state distribution of Mn, which helps to enhance the structural stability and capacity retention of the cathode material. The modified sample contains Mn... 3+ Increase, with appropriate amounts of Mn 3+ It can provide more electrochemically active sites, but at the same time, it will reduce the initial coulombic efficiency of the material. The Mn content in the sample with only glucose added... 4+ Too little Mn may be due to excessive carbothermic reduction of glucose, leading to over-reduction of Mn. Figure 2 Image (c) shows the fine O 1s spectra of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Examples 1 and 2. Figure 2 As shown in (c), the peaks of the sample after adding the carbon source did not change significantly compared to the original sample. After adding the N source, the width of the lattice oxygen peak at around 529.5 eV of the cathode material decreased while the intensity increased, indicating that N doping improved the order of the [MnO6] octahedron. The area of ​​the oxygen vacancy peak at 531.3 eV decreased, indicating that the introduction of N improved the order of cation arrangement and effectively suppressed lattice oxygen loss. In the sample with both nitrogen and carbon sources added, the oxygen vacancy ratio increased while the lattice oxygen ratio decreased. This may be due to surface oxygen reconstruction caused by the carbon layer coating, but the main structure still remained ordered, consistent with the XRD characterization results. Figure 2Image (d) shows the fine N 1s spectrum of the lithium-rich manganese-based cathode material prepared in Example 1. Figure 2 As shown in (d), some of the nitrogen in calcined melamine is doped into the carbon layer on the surface of the material, forming a nitrogen-doped carbon layer, which improves the electrical conductivity of the material and thus improves the rate performance and cycle stability of the material.

[0076] Figure 3 The first discharge specific capacity curves of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Examples 1 and 2 at 0.1C are shown below. Figure 3 It can be seen that the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Examples 1 and 2 have initial discharge specific capacities of 316.39, 259.75, 236.94 and 221.64 mAg / h at 0.1C, respectively.

[0077] Figure 4 The specific capacity / rate ratio of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, 1, and 2 is given by... Figure 4 It can be seen that the discharge specific capacities of the lithium-rich manganese-based cathode material prepared in Example 1 at different rates are 316.39 (0.1C), 266.31 (0.2C), 233.56 (0.5C), 207.51 (1C), 181.48 (2C), and 170.93 (5C) mAg / h, respectively; and the discharge specific capacities of the lithium-rich manganese-based cathode material prepared in Example 8 at different rates are 266.80 (0.1C), 231.00 (0.2C), 196.50 (0.5C), 173.90 (1C), 162.7 (2C), and 151.50 (5C) mAg / h, respectively. The discharge specific capacities of the lithium-rich manganese-based cathode material prepared in Comparative Example 1 at different rates were 236.94 (0.1C), 200.25 (0.2C), 174.5 (0.5C), 159.97 (1C), 133.35 (2C), and 119.17 (5C) mAg / h, respectively; the discharge specific capacities of the lithium-rich manganese-based cathode material prepared in Comparative Example 2 at different rates were 221.64 (0.1C), 197.25 (0.2C), 169.84 (0.5C), 153.97 (1C), 143.35 (2C), and 109.17 (5C) mAg / h, respectively. This demonstrates that the preparation method of the present invention can significantly improve the rate performance of lithium-rich manganese-based cathode materials.

[0078] Figure 5 The long cycling curves at 1C are shown for the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Examples 1 and 2. Figure 5It can be seen that the capacity retention rate of the lithium-rich manganese-based cathode material prepared in Example 1 after 200 cycles at 1C is 90.4%, the capacity retention rate of the lithium-rich manganese-based cathode material prepared in Example 8 after 200 cycles at 1C is 83.7%, the capacity retention rate of the lithium-manganese-based cathode material prepared in Comparative Example 1 after 200 cycles at 1C is 71.9%, and the capacity retention rate of the lithium-rich manganese-based cathode material prepared in Comparative Example 2 after 200 cycles at 1C is 66.1%. This shows that the preparation method of the present invention can significantly improve the cycle stability of the lithium-rich manganese-based cathode material.

[0079] Figure 6 The electrochemical impedance and Z' vs ω of the lithium-rich manganese-based cathode materials prepared in Examples 1, 8, Comparative Example 1, and Comparative Example 2 -1 / 2 The relationship is given by (a) for electrochemical impedance and (b) for the relationship between Z' and ω. -1 / 2 Relationship. By Figure 6 As shown in Figure (a), the impedances of Examples 1, 8, Comparative Example 1, and Comparative Example 2 are 49.78 Ω, 53.06 Ω, 52.37 Ω, and 102.98 Ω, respectively. This indicates that nitrogen doping optimizes bulk electronic conduction, and the amorphous carbon layer effectively suppresses side reactions at the electrode-electrolyte interface, promoting rapid lithium-ion migration. Figure 6 (b) shows Z' and ω in Examples 1, 8, Comparative Example 1, and Comparative Example 2. -1 / 2 The slopes of the relationships are 352.5, 341.2, 291.3, and 215.2, respectively. Comparative Example 2 has the smallest slope, indicating that it has greater resistance to lithium-ion migration, which is consistent with the aforementioned cycle performance and rate performance results.

[0080] The initial discharge specific capacity and initial coulombic efficiency of the lithium-rich manganese-based cathode materials prepared in Examples 1-8 and Comparative Examples 1-2 at 0.1C are shown in Table 1.

[0081] Table 1. Lithium-rich manganese-based cathode materials prepared in Examples 1-8 and Comparative Examples 1-2

[0082] Results of initial discharge specific capacity and initial coulombic efficiency

[0083]

[0084] As can be seen from the comparison of Examples 1-8 and Comparative Examples 1-2 in Table 1, the addition of different nitrogen and carbon sources has a significant impact on the electrochemical performance of the lithium-rich manganese-based cathode material described in this invention. The sample with added melamine exhibits better electrochemical performance than the sample with added glutamic acid, glutamic acid, and melamine. This indicates that melamine, as a single nitrogen source, is more advantageous in promoting the formation of a stable crystal structure; its decomposition products can more effectively dope into the crystal lattice, optimizing the valence state distribution of manganese, thereby improving the reversibility of the electrochemical reaction and structural stability. The sample with added glucose as a carbon source, in addition to an appropriate amount of melamine as a nitrogen source, achieved the highest discharge specific capacity, but its initial coulombic efficiency was lower than that of the sample with only melamine added. This is mainly attributed to the conductive amorphous carbon coating layer formed after glucose carbonization, which undergoes a side reaction with the electrolyte during the first charge-discharge process, irreversibly consuming some lithium ions, leading to a decrease in initial efficiency. However, because the amorphous carbon coating layer inhibits the continuous erosion of the material by the electrolyte and the dissolution of transition metal ions during cycling, it ensures the structural integrity of the material during long-term cycling, resulting in better rate performance and long-cycle stability than the sample with only melamine added.

[0085] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: A metal salt solution, a precipitant, and a complexing agent are mixed, and the resulting coprecipitation reaction precursor solution is subjected to a coprecipitation reaction to obtain a lithium-rich manganese-based precursor; the metal salt solution includes manganese, cobalt, and nickel. The lithium-rich manganese-based precursor, lithium source, additives and dispersant are mixed and calcined to obtain a lithium-rich manganese-based cathode material. The additives include a nitrogen source and a carbon source; The nitrogen source is melamine and / or glutamic acid; The carbon source is glucose and / or sucrose; The nitrogen source accounts for 1-7 wt% of the mass of the lithium-rich manganese-based precursor; The carbon source accounts for 0.1~3 wt% of the lithium-rich manganese-based precursor. The dispersant is isopropanol; the mass of the dispersant accounts for 1 to 10 wt% of the mass of the lithium-rich manganese-based precursor.

2. The preparation method according to claim 1, characterized in that, The molar ratio of manganese, cobalt and nickel in the metal salt solution is x:y:z, 2 / 3≥x>0, 1 / 6≥y>0, 1 / 6≥z>0, and 1≥x+y+z>0.

3. The preparation method according to claim 1, characterized in that, The calcination includes a first calcination and a second calcination in sequence; the temperature of the first calcination is 400~600℃ and the holding time is 4~8h; the temperature of the second calcination is 700~900℃ and the holding time is 8~14h.

4. The preparation method according to claim 1, characterized in that, The precipitant is a sodium carbonate solution; the complexing agent is ammonia.

5. The lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 1 to 4, characterized in that, The material includes a Li-Ni-Co-Mn-O material with nitrogen doped in the crystal lattice and a nitrogen-doped carbon layer coated on the surface; the nitrogen-doped carbon layer includes amorphous carbon.

6. The application of the lithium-rich manganese-based cathode material according to claim 5 in lithium batteries.

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